2017, 33(8):1-11. DOI: 10.11975/j.issn.1002-6819.2017.08.001
Abstract:Abstract: The meaning of agricultural machinery automation and intellectualization includes a wide range of content, involving a large number of engineering disciplines, such as navigation, images, models and strategies, actuators and data chain. The intellectualization of agricultural machinery is the symbol of a country's engineering and technical strength. How to co-ordinate the multidisciplinary technologies and reasonably integrate them into a system is the key to the success of intelligent agricultural machinery. According to the requirements of the development of land scale management in China, intelligent agricultural machinery should use advanced technology in the aeronautics, astronautics and ground to achieve high-speed computing and transmission of data information in a dynamic environment, and to command the actuator to complete the tasks efficiently and effectively. In recent years, the research on intelligent agricultural machinery has been mainly concentrated on vision measuring, image processing, trajectory tracking and vehicle navigation, pattern recognition and their application, and so on, which have focused on image information acquisition method, image processing and recognizing algorithm, intelligent navigation algorithm and system integration application, and so on. The technology of automatic steering control, obstacle detection and active obstacle avoidance, and multi machine cooperative navigation, and the technology of agricultural machinery will be the focus of the next generation of intelligent agricultural machinery. This paper studied the Beidou enhanced network and network RTK (real-time kinematic) method to improve the accuracy of positioning and navigation technology, accurately modeled and compensated aiming at the inertial navigation error of agricultural machinery, and prolonged the working time of positioning. The dynamic model of agricultural machinery was established, and the parameters of the model were identified on the basis of the actual situation. Based on the constraint conditions, the knowledge learning and decision control technology was introduced into the agricultural machinery. And then combined with machine vision, the perception of the working environment and operating objects was enhanced, and the image recognition algorithm was used to assist navigation and control. Finally, according to the requirements of remote monitoring, and navigation and positioning for data transmission, the realization of data transmission technology of three-dimensional topology was studied so as to ensure the real-time data fusion of various technical units. The invention disclosed a set of intelligent device with electromechanical integration. It was equipped with a multi-source fusion intelligent controller based on the dynamic model of agricultural machinery, and an inertial navigation system, which could effectively isolate the disturbance of agricultural machinery to achieve stable tracking and the combination of WIFI and the new generation of Internet of Things to complete the multi-link data communication. According to the dynamic analysis of agricultural machinery, the data model was obtained. The model structure was determined, but the parameters were uncertain. The model parameters could be obtained by on-line identification on the basis of the minimum value of the difference between the actual state and the model state. Then the control strategy was designed according to the model. Based on the navigation control error prediction, the control law parameters were optimized through minimizing the objective function of the future control deviation, and the trajectory tracking of agricultural machinery would be always controlled with the best control parameters. Agricultural navigation used the tight integrated navigation technology of Beidou plus IMU (inertial measurement unit), and machine vision was taken as an aid. Based on the enhanced technology of mobile network base station of Beidou Foundation and high precision standard inertial navigation system for precision agriculture applications, the continuity and reliability of navigation and positioning information were ensured, which laid the foundation for the use of intelligent agricultural machinery in remote sensing areas. Therefore, the agricultural machinery in the next period will be more intelligent and easy in operation. New farmers in the Farm Hall will command all kinds of agricultural machines to carry out operations in a variety of environmental conditions, and monitor agricultural machinery in a few kilometers or tens of kilometers away in real time, which greatly reduce the burden on farmers, and achieve high efficiency, standardization and hommization, and also provide some technical references for the development of other industries.
2017, 33(8):12-20. DOI: 10.11975/j.issn.1002-6819.2017.08.002
Abstract:Abstract: The collecting machinery of mulching plastic film offers an important technological means to curb the farmland residue pollution. The main method of residual film recycling in Xinjiang is the raking-film working. Due to the complex cotton field environment and the poor raking film effect of whole profiling of the used plastic film collector, the raking film tooth can not simultaneously carry out the monomer film collecting with copying with different cotton field terrain, which causes a low collecting rate during the process of residual film recycling. For the problem, this paper proposed a collecting-film mechanism of the profiling of the monomer. The theoretical design and mechanical analysis of the mechanism of collecting film were carried out. With the method of complex vector, the profiling-mechanism dynamics model was established, which involved the relationship between the reacting force of soil to land wheel of profiling and the spring-tooth resilience force. Based on the establishment and analysis of dynamics model, the collecting-film influencing factor could be initially determined. And the relevance of the spring-tooth stress states and the raking-film mechanism's operating condition was further explored. In order to confirm the operation parameters of the device of collecting film, the experiment of the response surface with 5 levels and 3 factors was accomplished on the soil bin trolley test-bed with the spring tooth of the raking film. Three test parameters, i.e. spring tooth number, test-car speed and spring tooth diameter, were chosen as the influence factors of the test-bed experiment. And collecting rate of residual film recycling was selected as the evaluation index of the test-bed experiment. Quadratic orthogonal rotation combination trial design was applied to build the quadratic polynomial regressive model, which interpreted the relationship between the experimental influence factors and evaluation index. Using the data analysis software of Design-Expert 8.0.6, the matching mathematical regression pattern was developed, the relation of salient factors with the evaluation index was analyzed, and the parameters of test were improved. The optimum combination of parameters could be reached when the number of spring teeth was 5, the diameter of spring tooth was 12 mm, and the speed of test car was 1.85 m/s. By using the soil bin trolley testing, the optimized results were verified on the basis of optimization parameters combination. The experimental consequences manifested that the collecting-film rate of the mechanism of monomer profiling raking-film was more than 88.5%, the optimization prediction model based on the quadratic multinomial fitting model was reliable, and the film recycling requirement could be met by the structure and working parameters combination. According to the standing cotton stalks standard field experiment in Changji, Xinjiang, the experimental cotton field was selected, which was pressed by the wheel of picking cotton locomotive and produced different fluctuation of pits and soil slope, and the results from the cotton field and the laboratory were basically consistent. The research provides an original theoretical reference for the design of raking film mechanism of single profiling, as well as the parameter optimization of remnant plastic film collector.
2017, 33(8):21-29. DOI: 10.11975/j.issn.1002-6819.2017.08.003
Abstract:Abstract: No-tillage seeder mainly uses the 2 ways of cutting and removing the straw to ensure seeding smoothly by now, and thus there are many problems: Higher power, environment pollution, twining and blocking of straw, and so on. To this end, a mechanism based on the special trajectory requirements was developed to enable the soil opener to penetrate into the surface without any treatment of the surface covering, which could lay substantial foundation for the implementation of injection-free no-tillage planting pattern. First of all, the analysis of mechanism aimed at the special trajectory was carried out and the five-bar mechanism was confirmed as the formation mechanism of trajectory. Moreover, the mathematical model of five-bar mechanism was set up, and the basic existence conditions and spatial constraints of double-crank and uniform five-bar mechanism were analyzed on the basis of the model. Given the feasible region of relative trajectory of the cavitation endpoint, and combined with the mechanical design module and knowledge engineering module of CATIA (computer aided three-dimensional interactive application) software, the parametric model was set up, the movement was simulated and the trajectory for five-bar mechanism was drawn. Subsequently, the distribution characteristics of region trajectory of cavitation endpoint were researched by the method of region localization of trajectory; the influence of the parameters on the trajectory was researched by the method of numerical cycle and comparison, and combined with the constrain conditions, the combination of structural parameters and operation parameters was obtained corresponding to different distance; on the above condition, the effective operation trajectory at the vertical direction changed from 251.2 to 344.7 mm. In May, 2016, the experiments were carried out with the prototype in the Soil Laboratory of the College of Engineering, Northeast Agricultural University. The conditions were set as follows: The length of mulching straw was 3 m and the average thickness of straw was 15 cm. In order to simulate the actual working condition in the field, the straw was scattered on the soil surface, and part of straw was stuck in the soil layer. The whole process that the soil opener device perforated through the straw until the straw was removed completely was shot by high-speed camera with the same planting spacing under different setting angle of soil opener of five-bar mechanism; the experiments were also conducted on different plant spacing respectively, and then the experimental images were observed and analyzed. Combined with the motion simulation of CATIA, the soil opener setting angle of five-bar cavitation mechanism was obtained, which could meet the requirement for the best hole-forming points. The angles were 128?, 128?, 134?, 134?, 134?, 128?, 128?, 128?, 128? and 122? respectively corresponding to the spacing of 60, 80, 100, 120, 140, 290, 310, 330, 350, and 370 mm. Research showed that the formation mechanism of trajectory in the process of no-tillage seeding based on the five-bar mechanism could drive cavitation device to complete the operation under the condition of straw returning drastically, and perforate through the straw effectively and form cavitation as required, with fewer scraping phenomena. It is confirmed that the region localization of trajectory can improve the solution efficiency of parameters combination of the five-bar mechanism, and also provide the effective method of solving the parameters of five-bar mechanism according to the ratio of long axis to short axis of similar ellipse trajectory.
2017, 33(8):30-36. DOI: 10.11975/j.issn.1002-6819.2017.08.004
Abstract:Abstract: Millet is the main crop in China. At present, due to the lower mechanization level of millet cultivation in China, it is easy to damage seeds and clog suction holes when sowing. In view of the problem of poor hole formation, precision sowing has become a modern technological means to improve grain yield. In order to realize precision sowing, the mechanical and physical properties of three domestic typical millets were firstly studied by measuring size, sphericity degree and the maximum coefficient of static friction between the millet and the steel plate. And to make our design of the suction hole have a good adaptability, the comparative analysis was performed in the Jingu 21 millet. According to the physical characteristics of the millet, air -sucking seeding disc was designed, and Q235 cold-rolled steel plate was selected as the material for making the seed plate. There were 18 holes evenly distributed in the circumferential direction of the seed plate, and the range of pore size was from 1.04 to 1.17 mm. Four kinds of structure of seed suction holes were designed, including cylindrical hole, chamfered truncated cone hole, truncated cone hole and four-prism hole. In order to test the seeding effect, the millet seeding experiment was carried out by using the JPS-12 seeding device performance test rig. The relevant national standard of the planter was cited and six test indices were selected: the average grains number per hill, the qualified rate of grains number per hole, the average hill distance, the qualified rate of hill distance, the single grain rate, and the average seed's quantity per hill. Three kinds of hole geometry on the seeding disc, such as cylindrical hole, chamfered truncated cone hole, truncated cone hole, were selected to test the seed selection efficiency, and the results showed that truncated cone hole was the best in the 3 kinds of adsorption pore structures, which could effectively reduce all kinds of plugging holes, so truncated cone hole was chosen to continue to compare. Two kinds of seed suction hole structures, such asthe truncated cone hole and four frustum pyramid, were selected to conduct the comparative experiment on the seeding efficiency. The results showed the optimal structure of seed suction hole was four-prism hole structure on the seeding disc, which had the best effect on seed sowing and solved the problems of serious seed damage, suction hole plugging, and cavitation. Through the millet seeding effect comparison test, the design scheme of the suction hole was ultimately determined as four-prism hole structure. The millet seeding performance test of this suction hole structure was carried out to determine the best seeding index. The seeding performance indices were the average number of seeds per hill of 3.3, the qualified rate of seeds per hill of 89%, and the qualified rate of hill space of 94%, and the average hole distance was 1.24 cm. Through the seeding performance test, the best working parameters of the seeder were determined: Vacuum degree was -2 kPa, and the rotation speed was 28 r/min. Precision hole sowing of millet seed was preliminarily realized by the use of air-suction seed-metering device in this study. The test results will provide a theoretical reference for the design and related research of millet precision seeding device.
2017, 33(8):37-46. DOI: 10.11975/j.issn.1002-6819.2017.08.005
Abstract:Abstract: Seed metering device as the core component of seeding machine, plays a vital role in seeding performance of a seeder. At present, most of the corn seeder in Northeast China use pneumatic seed metering device or finger-clamping metering device which is accurate but expensive, while horizontal disc seed metering device has the advantages of easy falling into the hole, simple structure and low price, but it's not suitable for high seeding speed. To meet the precision seeding requirements under high speed conditions, the working principle of the metering device was analyzed. As corn accurate seeding requires uni-grain, i.e. into each hole only a seed, the state of the seed falling into the hole can only be side lying or side standing. By studying the shape and size of flat corn seeds used in Northeast China, longitudinal rectangular holes adequate for flat seeds were determined with specific size of 11 mm length, 6 mm width and 6 mm depth. Combined with stress analysis and kinematic analysis, a seed metering disc with inclination hole and small fillet chamfer, which was suitable for high working speed, was designed. Small fillet on the rear edge was bound to accelerate the speed of seeds falling into holes, so as to improve the filling rate of the holes. Front chamfer and side chamfer of the holes on seeding disc could effectively improve the relative speed of seeds, and it made the nearby seeds more stable and more efficient to fall into the holes. Inclination hole was a type of hole which was opposite to the rotation direction of the seed metering disc. When the seeds fell from the filling hole, the force at the vertical direction it suffered not only contained its own gravity, but also the component of vertical downward force given by the reverse slope of the inclined holes. The vertical force could ensure the seed to drop from the holes to the guide tube effectively. It changed the way of the traditional horizontal disc metering device relying solely on seed gravity free falling movement, and ensured the seeding process could be completed successfully. In order to improve the working performance and get the best performance parameters of the seed metering device, a quadratic orthogonal rotary composite experiment was designed. The seed metering device's rotational speed, chamfer length and inclination angle of hole were taken as experimental factors, and the qualified index, the multiple index and the missing index were evaluated. The experiment was carried out on the JPS-12 seeding test bench. Using Design-expert 8.0.6 software, the mathematical models of experimental factors and test indices were established based on the experimental data obtained from the bench test. Response surface methodology (RSM) was used for multi-objective optimization of the regression equation. Test results showed that when the rotational speed of seed metering device was 33 r/min, the chamfer length was 7 mm and the inclination angle of hole was 61°, the qualified index was 92.47%, the multiple index was 3.56%, and the missing index was 3.97%. On this basis, field experiment was carried out to verify the working performance of the seed metering device and to test the adaptability of different corn seed varieties. Field validation test showed that when the seed metering device speed was 33 r/min, the line speed of seeding disc was 0.41 m/s, and the unit forward speed was 8.6 km/h, the seeding performance index could meet the agronomic requirements of precision seeding. It also proved that the seed metering device had a good adaptability for different corn varieties and a good seeding performance. The research provides a reference method for designing and analysis of mechanical precision seed metering device.
2017, 33(8):47-55. DOI: 10.11975/j.issn.1002-6819.2017.08.006
Abstract:Abstract: In order to improve the mechanical weeding efficiency and reduce the injury rate of seedling caused by frequent swerve at the end of the field, a wide-swath machine, named 3GY-1920 type wide-swath weeder, was designed for intertillage and weeding in paddy field. This weeding machine driven by the paddy tractor mounted relevant components including the wide-swath adjustable frame, the hydraulic control system, the weeding unit and profiling mechanisms. To match triple working widths of ride style high-speed rice transplanter, this weeder was equipped with 19 weeding rolls. The working width was designed to be 5.4 m according to line spacing of rice seeding, which was normally 0.3 m. As the transplanter could not follow one path line in 3 different processes, the whole frame was divided into 3 parts including the left-side frame, the right-side frame and the bearing frame. A hydraulic system, including oil pump, different types of electromagnetic valves, hand valve, 4 hydraulic cylinders, relief valve, throttle valves and so on, were equipped to control the 4 single-rod double-acting hydraulic cylinders, which could adjust the frames to fold or unfold for transportation or weeding, and the real-time motion of rolls on the side frames. The weeding roll was designed as the spiral cutter weeding roll referring to the existing rollers and the bearing capacity and shearing strength of paddy. And the different parameters for weeding rolls such as the working resistance and the capacity to damage soil were tested with the explicit finite element software ANSYS/LSDYNA. The weeding roll was composed of 6 cutters; every cutter was sharpened and rotated around the axis by 720° and welded into the reel. A spring type profiling mechanism was also designed and applied to ensure the stable working depth. The installation height and working depth of weeding machine were adjusted before weeding so as to avoid injuring the plants due to the difference of the size of the rice seedlings. When the weeding machine moved forward at a certain speed, the weeding rolls were rotated by the force of soil resistance, elastic force of spring, and forward stress of traction. And the spiral cutters on the roll moved downward into and out of the soil for shearing weeds and stirring soils to cover weeds at the same time. An all-factor experiment on the weeding rate and injury rate of seedlings was conducted to test the performance of this weeding machine. Depth of the weeding and travel speed were selected as 2 factors in this experiment. Results showed that the operating efficiency of this weeding machine was 0.6-1.8 hm2/h, the average weeding rate was 82%, and the average seedling injury rate was 4.8%. With the increment of travel velocity, the weeding rate rose and then fell, and the injury rate kept rising. With the increase of working depth, the weeding rate continued to rise, and the seedling injury rate went up at first and then declined. The weeder showed the optimal operation effect when the weeder's speed was 0.6 m/s, and the roll's working depth was maintained at 6 cm. Under the parameter combination, the average weeding rate was 87.2% and no seedlings were damaged. A yield test was also performed to compare the differences between 2 weeding methods (mechanical weeding and chemical weeding). Results were as follows: The average yield of rice under mechanical weeding was 686.56 g/m2 while that under chemical weeding was 659.83 g/m2. The average number of useful spikes per hole in the testing zone was 13.25 under the condition of mechanical weeding and 9.36 using chemical method of weed control. The average number of holes per square meter was 19.71 and 21.68 based on mechanical and chemical weeding respectively. The result suggests that the mechanical weeding may hurt the seedlings compared to chemical weeding method, however, its weeding and inter-cultivation function can promote the tilling of plants and improve the yield of rice.
2017, 33(8):56-61. DOI: 10.11975/j.issn.1002-6819.2017.08.007
Abstract:Abstract: In recent years, the traffic accidents occur frequently in winter and how to prevent frequent traffic accidents has become an urgent problem to be solved. Reindeer lives in frigid areas and possesses the superior walking ability on ice. Reindeer feet are the exclusive parts which contact with the ice directly. The sole characteristic morphology of foot bottom is the key factor to the excellent anti-skid performance of reindeer. The research of the reindeer feet bottom characteristics will help to apply the superior characteristics to snow tire tread and improve the trafficability property of tire on ice ground. Therefore, the mathematical models of the reindeer feet were studied. The feet were taken from 4 eighteen-year-old adult homebred reindeers, which were bought from the Ewenki nationality located in Genhe City, Inner Mongolia, China. In order to avoid impurity interference, the feet were cleared up before the experiments. The geometric point clouds of the reindeer feet were obtained by using a three-dimensional (3D) hand-held non-contact laser scanner. After that, the data were imported to Geomagic Studio software and we reconstructed the analytical model. With the cutting function of the software, the reconstructed model of reindeer foot was divided into 4 typical characteristic areas: The edge curves (inside edge and outside edge), the ridge groove surface and spherical cap surface. In addition, these point clouds were imported to CATIA (computer aided three-dimensional interactive application) to be filtered, which reduced the calculation amount of the fitting curves and surfaces. We filtered the dense point clouds through adopting the reasonable method and the retained characteristic points that reflected the edge and sole morphology of reindeer foot with the digitized shape editor module of CATIA. Through the above processes, the 3D coordinate data points of these characteristic areas were exported. The edge curves were fitted using curve fitting software 1stOpt (First Optimization), and then fitting the equation and the fitted parameters were acquired, respectively. We also used the surface fitting function of Matlab software to fit 2 surfaces: Ridge groove surface and spherical cap surface. Finally, 2 surface fitting models were achieved. The fitting results revealed that the R2 (coefficient of determination) values of 2 curves and 2 surfaces were 0.994, 0.992, 0.96, and 0.98, respectively, which were all close to 1. It showed that the characteristic areas of reindeer feet were successfully transformed from the biological model to the mathematical model. In order to verify the model's scientificity, the specimen of other reindeer foot was used. We acquired the 3D coordinate data of the same characteristic areas of other reindeer foot by adopting the same treatment. The values of x and y axis for 4 areas were imported into relevant mathematical models and the relevant values that were dependent variables were acquired. By comparing the differences between fitting values and actual values, the residual error range, relative error range and mean relative error were analyzed. The relative error range of 2 curves models was 0.16%-2.73% and 0.12%-1.66% respectively, and the mean relative error was 1.5% and 0.68%, respectively. The relative error range of surfaces models was 0.43%-10.28% and 1.25%-9.74%, respectively. The maximum was about 10%, due to the influence of air impurities. However, the mean relative errors of surfaces models were 4.83% and 4.27%, respectively. The mean relative errors of 4 models were within 5%, which proved the mathematical models' effectiveness in this paper. In addition, the elements of reindeer feet were examined with EDS (energy dispersive spectroscopy). It included such elements as S, Si, Fe, Al, K and Ca, besides C, O and N. Different chemical elements meant different compounds, and different surfaces with different skid-resistance were composed of different elements. This paper will provide research direction for studying tire on ice ground with engineering bionic technology.
2017, 33(8):62-68. DOI: 10.11975/j.issn.1002-6819.2017.08.008
Abstract:Abstract: Due to that the design aims for structural parameters of semi-trailer tractor are multivariate and the constricted boundary condition of this designing process is complicated, the utilizations of empirical approach and the single objective optimization can't always promote the comprehensive performance of semi-trailer tractor. Based on non-dominated sorting genetic algorithm II (NSGA-II), a new optimizing method about semi-trailer tractor's structure parameters was put forward. By analyzing structural and dynamic characteristics of semi-trailer tractor's 2-DoF (degree of freedom) model, optimizing principles were established. According to the tractor operation performance including the manipulative stability, negative weight addition, limitation of driving wheel's load, load rate of engine power and adhesive characteristic, the constricted boundary conditions were designed. The optimizing objective functions were formulated, which included fuel economy, power performance and force status of tractive point. YTO-150 tractor and the matched semi-trailer were collected as the investigative and optimized object. According to the theoretical analysis and mathematical modeling of the tractor and trailer dynamic performance, the 4 objective functions were divided into 2 groups which involved contradictory relation. After the multiple mathematic conversions of objective functions and constraint functions, the complicated and coupled relationship between the optimal objects could be simplified. Using NSGA-II two times , the semi-trailer tractor's structure parameters and the gear ratios of transportation work condition were calculated. And relevant program was redacted. Parameters including the gravity of the tractor and semi-trailer, and the position of each part's barycenter were optimized. And the transmission ratio of each transportation gear was modified. The figure describing the Pareto front end of each aimed function was plotted. As compared with the primitive semi-trailer tractor, the total weight was declined by 6.86%, the position of the tractor's barycenter moved forward by 0.074 m, and the position of the trailer's barycenter moved backward by 0.14 m. As compared with the single objective optimizing result with the way of developing the CAD (computer aided design) systems of Delphi, the total weight was declined by 3.26%, the position of the tractor's barycenter moved backward by 0.022 m, and the position of the trailer's barycenter moved backward by 0.3 m. On 5 different gradient test ramps, the climbing performance experiment was performed. And in the climbing tractor and trailer, the velocity and pull force on the traction axle were measured by the GPS (global position system) device and resistance strain pull and pressure sensor. When the tractor was driven under the transportation gearⅠ, the maximum climbing degree was improved by 1.35% and 1.68%, and the average force of the tractive point declined by 1 222 and 703 N, respectively, compared with the single objective optimizing scheme and primitive semi-trailer tractor. When the tractor was driven under the transportation gearⅡ, the maximum climbing degree was improved by 1.38% and 0.57%, and the average force of the tractive point declined by 2 792 and 2 125 N, respectively, compared with the single objective optimizing scheme and primitive semi-trailer tractor. The fuel economy of the tractor trailer systems was simulated by the simulator, which was developed upon the dynamic joint between AVL CRUISE and MATLAB. When the simulation adopted the marked working condition based on EUDC (extra urban driving cycle), the fuel consuming rate of the multi-objective optimized semi-trailer tractor declined by 12.9% and 15.8%, respectively, compared with the single objective optimizing scheme and primitive semi-trailer tractor. To sum up, this optimized method reaches the requirement of the objective functions, and provides the theoretical and technologic foundation for improving tractive vehicle systems.
2017, 33(8):69-75. DOI: 10.11975/j.issn.1002-6819.2017.08.009
Abstract:Abstract: Axial vortex is a kind of special relative flow within the adjacent blades of hydrodynamic coupler. The distribution of flow field structure and its evolution law are considered as the important foundation for the research on the internal energy losses of hydrodynamic coupler. Transparent square cavity hydrodynamic coupler model prototype made by plexiglass was taken as the experimental measurement object. Axial vortex flow images of hydrodynamic coupler under braking condition were collected based on particle image velocimetry. In order to improve the quality of flow images, image preprocessing was used to identify the flow characteristics of particles in flow images. In order to get a better image calibration result, a special geometric structure of hydrodynamic coupler was taken as an external calibration object. The calibration images were acquired with high-definition CCD (charge coupled device) camera, and then optical characteristics of the special geometry structure were identified and extracted by image processing technology. Dynamic calibration coefficient of flow images was obtained finally. The flow field of axial cross section in pump was identified and extracted based on straight line detection algorithm of Hough transform, and the linear characteristics of particle trajectories were identified and extracted successfully. The flow field of axial cross section in turbine was calculated based on cross-correlation algorithm between consecutive 2 frames of particle images, and the technology of interrogation window offset was used to extract the velocity field and vorticity field. In order to identify and eliminate the incorrect flow velocity vectors of the initial calculation results, a method of setting a threshold was used to check the difference between ambient velocity vector and the center velocity vector, and the consistency and coherence characteristics of flow velocity vectors on the flow area were detected by this method. Subsequently, calculation results of flow field were optimized, and a much smoother flow pattern was acquired finally. On the basis of the flow field measurement results, the unsteady viscous flow phenomena of hydrodynamic coupler under braking condition were researched, and the distribution law of axial cross section was analyzed in detail. Research results indicated that: Firstly, the flow of axial cross section in pump was a compound accelerated motion; secondly, there were a lot of multi-scale vortices in the main flow region of axial cross section in turbine, and the flow velocity in the mainstream area was 0.2-0.4 m/s. There were many small-scale vortices in the intersection area between outer ring and blades, and the flow velocity in these area was 0.6-1.1 m/s. In addition, some small-scale vortices which existed in the intersection area between upper blade and interface area were different from others; the flow direction of these vortices was the same as the mainstream circulation direction, the vorticity value of this area was -8 s?1, and these small-scale vortices would promote transmission and conversion of hydrodynamic energy. On the contrary, the flow direction of small-scale vortices in other areas was opposite to the mainstream circulation direction, and the vorticity value in these areas was 13, 15 and 20 s?1. The small-scale vortices in the local region were mixed with the main circulating vortex in the main region, and as the result, the internal flow became slow with a large amount of energy loss. The phenomena of irregular secondary flow and reverse flow came into view near the middle flow area of blade. According to the visualization results of axial vortex flow in hydrodynamic coupler under braking condition, the reasons to the generation about axial vortex in hydrodynamic coupler were explored, and the influences of flow energy transfer and dissipation were analyzed. The result will provide valuable reference for the study of axial vortex flow phenomenon.
2017, 33(8):76-81. DOI: 10.11975/j.issn.1002-6819.2017.08.010
Abstract:Abstract: Light weight and high power become the trend of the development of diesel engine. At the same time, the liner cavitation erosion of engine cylinder becomes one of the important restrictions of engine reliability and life. A lot of research has been made and the results show that cooling water jacket cavitation erosion theories widely accepted are: A high frequency vibration of cooling water jacket leads to the cavitation and the cavitation bubbles breaking produces a shock wave and micro-jet, which have the mechanical action to cooling water jacket and lead to the occurrence of cavitation erosion. Therefore, the study of the flow characteristics of the cooling water jacket near the vibrating wall is an effective way to understand the spatial and temporal distribution of cavitation. In this paper, the computational fluid dynamics (CFD) simulation method was used to investigate the forming mechanism of cavitation in engine cooling jacket. By analyzing the cooling water jacket of the diesel engine, taking the part of cooling water jacket in the minimum space of the flow channel near the vibration wall as the research object, a three-dimentional model of diesel cooling water jacket was built. Then according to the calculation and analysis of the vibration wall components' single knock experiment, the moving mesh was set. Then the characteristics of flow and cavitation under various inlet velocity and fluid temperature with and without wall vibration were simulated. The cavitation characteristics were compared and analyzed under the conditions of different inlet velocity and different flow field temperature with the influence of cylinder wall vibration, and the numerical theory of cooling water jacket cavitation erosion was improved, which also guided the cooling water jacket cavitation erosion experiment of the vibration. According to the simulation results, a wall vibration cavitation erosion visualization bench was designed and built, the related experimental verification was proceeded in the visual experiment platform, and the credibility of the simulation calculation was confirmed. The simulation results were validated by the experiments on this optical rig. The outcome of the study indicated that cavitation occurred in the minimum space of the flow channel, and grew up in the downstream. Higher velocity of inlet flow (from 2 000 to 3 000 liters per hour) caused stronger cavitation near the vibration wall of the cooling water flow field, but it was not significant, so the significant change was not observed in the cavitation images under the condition of different inlet flow velocity. On the contrary, higher temperature of inlet flow (above 50 ℃) caused weaker cavitation, and the strongest cavitation occurred at the temperature of 50 ℃. An obvious cavitation phenomenon appeared when the wall which fluid flowed by was vibrated in a very high frequency, and this change of cavitation was much stronger than those caused by various inlet flow velocity and fluid temperature. So the author thought that cooling water jacket vibration was the more important factor than cooling water flow velocity and temperature that caused cavitation. This study will be helpful in controlling the occurrence of cavitation in cooling water jacket and lowering the cavitation erosion risk of cooling water jacket.
2017, 33(8):82-89. DOI: 10.11975/j.issn.1002-6819.2017.08.011
Abstract:Abstract: Wind turbine is often exposed to dramatically different operational conditions, from icy environments to deserts with sand storms, and there are contaminants in these environments, like dust, dirt, ice, and even insects. These contaminants change the aerodynamic shape of blade and increase the surface roughness, which results in the lower utilization rate of wind energy. The aerodynamic performance of wind turbine blade can be improved through the airfoil modification, so the blunt trailing-edge structure is adopted during the design of an airfoil. Compared with the original airfoil, the blunt trailing-edge modification with bigger trailing-edge thickness and cross-section area not only has a great improvement in the maximum lift coefficient and the stall angle of attack, but also makes the maximum lift less sensitive to the leading-edge roughness. Therefore, it is of great significance to study the aerodynamic performance of blunt trailing-edge modification of the airfoil with rough surface for the improvement of the power utilization coefficient of wind turbine. The aerodynamic performance of the airfoil with rough surface and the blunt trailing-edge modification have been numerically and experimentally investigated in recent years. However, these 2 problems have been discussed separately, and the effects of the blunt trailing-edge modification on the aerodynamic performance improvement of wind turbine airfoil have been less investigated considering the roughness sensitivity position. In the present study, the aerodynamic performance of wind turbine airfoil and its blunt trailing-edge modification considering the roughness sensitivity position was numerically investigated to reveal the effect of the blunt trailing-edge modification on the lift enhancement of airfoil with rough surface. The dedicated wind turbine airfoil S822 from National Renewable Energy Laboratory (NREL) was used for the simulation. The lift and drag coefficients of S822 airfoil with smooth or rough surfaces were calculated by the k-ω SST turbulence model, and were compared with the aerodynamic data from wind tunnel tests, which offered a good opportunity to examine the capability of CFD (computational fluid dynamics) simulation. The mathematical expression of the blunt trailing-edge airfoil profile was established using the coordinates' rotation combined with the zoom coefficient of coordinates, and the airfoil S822 was modified to be symmetrical blunt trailing-edge airfoil. The lift enhancement of modified airfoils was analyzed to get the best trailing-edge thickness. In order to obtain the roughness sensitivity position of suction and pressure surfaces, the aerodynamic performance of the airfoil with rough surface was studied. The lift and drag coefficients and the lift-drag ratio were calculated for the airfoils with the roughness sensitivity position and their symmetrical modifications with the best trailing-edge thickness. And the roughness sensitivity of sharp and blunt trailing-edge airfoils was also analyzed. The results indicated that the best trailing-edge thickness was 2% of chord length for symmetrical blunt trailing-edge airfoil. The roughness sensitivity positions of suction and pressure surfaces were 1% and 5% of chord length away from the leading-edge, respectively. After the blunt trailing-edge modification, the lift coefficient and the maximum lift-drag ratio of the airfoil with the roughness sensitivity position significantly increased. The lift-drag ratio of the blunt trailing-edge airfoil was higher than that of the original airfoil for the angle of attack less than 11.19° when the suction surface of airfoil is rough, and so does the airfoil with rough suction and pressure surfaces. It is the same change ruler as above for the airfoil with rough pressure surface at different angles of attack ranging from 1° to 13.23°. The blunt trailing-edge modification makes the lift coefficient and the maximum lift-drag ratio significantly increase, which remarkably improves the aerodynamic performance of rough airfoil. The compositive index of the roughness sensitivity was 10.68% and 8.15% for sharp and blunt trailing-edge airfoils, respectively. The modification reduces the airfoil's sensitivity to the roughness position. The research provides a significant guidance for designing and optimizing the wind turbine airfoil under rough blade surface conditions.
2017, 33(8):90-96. DOI: 10.11975/j.issn.1002-6819.2017.08.012
Abstract:Abstract: The viscoelastic damping structure is widely used in the vibration and noise control of the agricultural engineering vehicle because of its high vibration dissipation capability, simple structure and lower maintenance cost. The mechanical behavior of the viscoelastic materials displays anelastic feature and temperature-frequency dependence, so the precise dynamic modeling is the key step in the viscoelastic structure design and its vibration damping analysis process. For anelasticity, the fractional derivative defined based on global definition can precisely represent the history dependence of the system function, and be extensively applied to the viscoelastic models with fewer parameters and better data fitting ability. For temperature-frequency dependence, the time-temperature superposition (TTS) principle was adopted, according to which the frequency spectrums at various temperatures can be collapsed into a master curve at the reference temperature by multiplying the conversion factors. The master curve covers a wide reduced frequency range up to many orders of magnitudes. In this research, the fractional time-temperature superposition model (FTTSM) for dynamic mechanical properties of viscoelastic materials was proposed based on the fractional order relationship, the Vogel-Fulcher-Tammann equation and the WLF (Williams-Landel-Ferry) equation. The frequency conversion factor from FTTSM was derived and its parameter identification process was developed based on tensile test and DMA (dynamic thermo mechanical analysis) test. In order to understand the parameter influence on the conversion factor, the variation of the conversion factor was studied under the material parameter of 0.2, 0.4, 0.6, 0.8 and 1 and the environment parameter of 0, 0.4, 0.6, 0.8 and 1. For the application and validation, the tensile test was conducted following GB/T 528-1998 on the M350-10 kN type precise elongation apparatus (Testometric, Britain), after preparing the I type dumbbell-shaped sample following GB/T 9865.1. In addition, the DMA test was also carried out according to ISO 6721-1 using the DMA 242C (Netzsch, Germany), in a 3-piont bending mode with a 40 mm span between the supports, in which the sample was supported on 2 supporting edges, while the probe edge applied load to the sample. On the base of the test data, the master curves at reference temperature of 5 ℃ from FTTSM and WLF equation, constructed through horizontally superposing the isothermals at various temperatures onto the isothermal at reference temperature, were comparatively studied. Furthermore, the theoretical prediction over the same frequency span was made through fractional Kelvin-Voigt constitutive model (KFVEO) to testify the master curves. The results indicated that the frequency conversion factors from FTTSM and WLF equation showed a good consistence with the maximum error of 0.984 4% within temperature scope (-80-80 ℃), and the master curves constructed by FTTSM and WLF equation greatly extended the frequency range up to 10 decades. The RMSE (root mean square error) between the master curves from FTTSM and WLF and the KFVEO prediction value was1.291 and 1.834 respectively, which manifested the FTTSM was more precise. Regarding the extended frequency, the minimum extended frequency by FTTSM was 2 orders of magnitudes less than that by WLF equation, while the maximum extended frequency stayed at the same level for these 2 models. This indicated a higher frequency extended capacity of FTTSM. This research can provide the theoretical reference for the investigation of viscoelastic material on dynamic behavior prediction, physical aging and mechanism of creep damage evolution, and so on.
2017, 33(8):97-103. DOI: 10.11975/j.issn.1002-6819.2017.08.013
Abstract:Abstract: Artificial reef (AR) is widely used to improve marine ecological environment. Some fisheries developed countries, such as America, Japan, Korea, Australia, New Zealand and some EU (European Union) states, have acquired a lot of achievements on the exploitation and protection of fishery resources by use of ARs. Flow field effect, bait effect and avoidance effect will be caused when the ARs are placed on the sea floor. Flow field effect is deemed to the main affecting mechanism of ARs, and the upwelling and back vortex are important indices to measure the flow field effect of ARs. So far, the study on the flow field effect of ARs has been limited to one or several reefs in China. However, no one has yet scientifically investigated the flow field effect of the Chinese general ARs. This study focused on the 18 types of general ARs, which were divided into 6 kinds, to investigate different flow field effects among them. And several representative reefs were selected for further study, which was the study on the effects of various flow velocity on the characteristics of upwelling and back vortex. Based on theory of computational fluid dynamics, numerical models of turbulent flow were built. Three-dimensional Navier-Stokes equations were solved by the finite volume method. The software CFX (computational fluid X) was used to study the performances of the flow field around reefs when flow passed through them. The 2 evaluation methods, the reef height ratio and the concrete volume ratio, were used to analyze the upwelling area, the back vortex area and the height of upwelling on the central plane. The reef height ratio is the ratio of the maximum upwelling height, upwelling area or back vortex area to reef height. And the concrete volume ratio is the ratio of the maximum upwelling height, upwelling area or back vortex area to concrete volume of reef. The paper was aimed to discuss the advantages and disadvantages of the 2 methods, and to analyze the different flow field effects among 18 types of ARs. Besides, the better reefs would be selected for diverse requirements. The results suggested the concrete volume ratio was a better criterion when studying the upwelling area and the back vortex area, and the height ratio was more appropriate when studying the height of upwelling. Regardless of the upwelling or the back vortex, triangle reefs had the largest relative area and complex reefs were the second, while frame reefs were the least. Then one reef was selected from each type to conduct the research to find out whether there were the effects of different flow velocity (0.2, 0.4, 0.6, 0.8 and 1.0 m/s) on upwelling area, back vortex area, the maximum upwelling velocity and maximum height of upwelling. The results demonstrated that the height of upwelling, the upwelling area, and the back vortex area fluctuated in an extremely narrow range under the 5 flow velocities. The maximum flow velocity of upwelling was linear with the flow velocity, and the slope showed the difference among different reefs. Moreover, reefs for different demands had been selected. AR11, AR10 and AR13 had a larger back vortex area with low cost. AR13, AR11 and AR18 should be chosen for the need of larger upwelling area. AR11 had not only the largest relative area of back vortex but also the largest relative influence area (sum of the upwelling area and the back vortex area). In addition, AR11 had the highest height of upwelling at the same reef height (followed by AR16 and AR02). The top 3 types of reefs with the maximum flow velocity were AR16, AR10 and AR13. The study provides the theoretical basis for the selection of AR, which can cater to various demands. Moreover, it also has certain reference value for the design of AR.
2017, 33(8):104-111. DOI: 10.11975/j.issn.1002-6819.2017.08.014
Abstract:Abstract: The red-green-blue (RGB) digital camera on unmanned aerial vehicle (UAV) with the relatively low cost and near real-time image acquisition renders a remote sensing platform, which is an ideal tool for crop monitoring in precision agriculture. Some successful applications have been made in biomass and yield estimation. However, retrieval of leaf area index (LAI) using plant height information extracted by crop surface models (CSMs) has been paid very limited attention to. Therefore, the objective of this study was to demonstrate the feasibility of estimating LAI with CSMs-based plant height. The study was conducted in warm and wet southern China where the sugarcane was planted widely. In this study, we acquired RGB imaging data of sugarcane in whole growing stage (8 flights) by this platform. Afterward, 42 ground control points (GCPs) were evenly distributed across the field due to the rugged terrain of the experimental area. The CSMs were built with the GCPs data and the UAV-based RGB image with very high resolution using the structure from motion (SfM) algorithm, and then the plant height information derived from CSMs was applied to estimate the LAI of sugarcane. The estimated LAI values were validated using the ground measurement data, which were collected simultaneously with the image acquisition. To assess the accuracy of plant height extracted from the CSMs without geo-referencing by GCPs data, we also constructed the ground elevation model by inverse distance weighted (IDW) interpolation to obtain plant height. In addition, we applied 6 visible band vegetation indices including green-red vegetation index (GRVI), normalized redness intensity (NRI), normalized greenness intensity (NGI), green leaf index (GLI), atmospherically resistant vegetation index (ARVI), and modified green-red vegetation index (MGRVI) from RGB image to predict the LAI, respectively. The performance of prediction models based on 6 vegetation indices was assessed by comparing with that based on plant height. The predicted plant heights based on GCPs geo-referenced CSMs matched well with the observations in the validation set, with the R2 value of 0.961 2 and the root mean square error (RMSE) of 0.215 2 at the 0.01 significance level. This result demonstrated that the UAV-based CSMs with geo-referencing by GCPs were more effective in monitoring the characteristics of sugarcane canopy over rugged terrain. In all the selected visible band vegetation indices, GRVI had the decent agreement with LAI prior to late elongation stage, with the R2 value of 0.779 0, the RMSE value of 0.556 1, and the mean relative error (MRE) of 0.168 0 in the validation set. In contrast, the plant height models showed a better performance than the visible band VIs over the same period, and the best estimate for LAI was obtained from CSMs-based plant height (R2=0.904 4, RMSE=0.366 2, and MRE=0.124 3). Unfortunately, due to that leaves turned to be withering since late elongation stage, all models in this study had relatively poor performance in estimating the LAI in the whole growing stage. NRI performed the best for the LAI estimation in the whole growing stage (R2=0.668 4, RMSE=0.636 0, and MRE=0.187 5), while its effect was poorer compared with the result before late elongation stage. Hence, it was unsuitable for LAI estimation from visible band VIs and plant height after late elongation stage. Furthermore, all above visible band VIs in this study were affected by the saturation phenomenon with varying degrees at high LAI levels. Conversely, the CSMs-based plant height model, which showed a linear trend without saturation at high LAI, proved to be the best predictor before late elongation stage. Because the key growing stage covered the period from seedling stage to late elongation stage, and the plant height models overcame the saturation limits of visible band VIs, it was better to estimate LAI with plant height. The results of this study indicate that using CSMs-based plant height to retrieve LAI of sugarcane in the important growth period is feasible. Moreover, since the excellent fitting of CSMs-based plant height to the ground observations, this technology is a powerful tool to obtain crop canopy features accurately and rapidly and provides a new approach to the crop condition monitoring in large areas.
2017, 33(8):112-118. DOI: 10.11975/j.issn.1002-6819.2017.08.015
Abstract:Abstract: In order to improve the mechanical property of negative pressure water seepage material polyvinyl formal (PVFM), 5 auxiliaries including silica, kaolin, silicone oil, silicone oil + silica, and silicone oil + kaolin, were added into PVFM, which were then moulded to water seepage tube using the mechanical foaming method. Their basic physical properties, mechanical properties, negative pressure water permeability and pore structure were characterized under negative pressure irrigation, and then, the results were compared with that of PVFM without adding auxiliaries (CK). The results showed that besides SiO2 powder, the 4 auxiliaries could improve the appearance quality of PVFM, and make the surface smooth and delicate. Adding auxiliaries could reduce the water absorbency of PVFM and increase the apparent density, true density and porosity, and the auxiliary of kaolin could significantly (P<0.05) improve the porosity and ensure a high water absorption at the same time. Compound auxiliaries could improve the mechanical properties of PVFM; the most great improvement of the hardness was 62.5% and that of tensile strength was 51.9%, which were caused by silicone oil + SiO2, and that of the elongation at break was 33.5%, which was caused by silicone oil + kaolin. Adding auxiliaries could significantly (P<0.05) improve the bubble point value of PVFM, and silicone oil + kaolin could make an increase of 70.7%. But adding these auxiliaries could not improve PVFM cumulative infiltration and infiltration rate. Only in lower negative pressure (?10 kPa), adding SiO2 into PVFM could maintain a slightly higher cumulative infiltration and infiltration rate. Adding auxiliaries could make the pore structure more uniform. Silicone oil + kaolin was the most obvious one to make pores uniform and small, and the bubbles few. In general, the 2 treatments with mixed auxiliaries simultaneously improved the appearance quality and bubble point value. The increase range was higher than that of single promoter in varying degree. SiO2 powder could improve PVFM cumulative infiltration and seepage rate under ?10 kPa. This study provides a promising direction for the improvement of polymer negative pressure water seepage material.
2017, 33(8):119-125. DOI: 10.11975/j.issn.1002-6819.2017.08.016
Abstract:Abstract: The vegetation filter strip is an effective land management practice to reduce the runoff and sediment yield in the sloping orchards in Loess Plateau, China. In the present paper, the feasibility of using vegetative filter strip model (VFSMOD) as a tool to predict the runoff coefficient and sediment yield of vegetative filter strip was evaluated. The experiment was carried out in Yangling, Shannxi. The loess soil was silt loam with bulk density of 1.35-1.40 g/cm3. Two kinds of plots included jujube-grass plots (each was 1.4 m in length, 0.8 m in width and 0.8 m in height) and jujube plots (each was 0.8 m in length, width and height). In 2011, a jujube (Ziziphus jujube Mill.) tree was planted in the center at 0.8 m away from the upper boundary of the plots and grass was planted at the seeding rate of 15 g/m2 in the center at 0.6 m away from the lower boundary of the plots. Grass species were white clover (Triolium repens L.) and birdfoot trefoil (Lotus corniculatus L.) conjoined to source areas. Each type of vegetative filter strip treatments had 3 replications. Simulated rainfalls were applied in 3 development periods (early, middle and late period) of the grass. In each period, 3 rainfall events with different intensities (1.0, 1.2 and 1.5 mm/min) and identical rainfall duration of 60 minutes were designed. The initial soil water content was 0.26-0.29 for all the rainfalls. Grass was cut to 10 cm in height before rainfall. Runoff from each plot was collected for runoff coefficient (the ratio of runoff to rainfall) calculation and sediment yield measurement. Meanwhile, the VFSMOD model was used to simulate the runoff coefficient and sediment yield. The results showed that the bias of runoff coefficient simulation was between -10% and 10%. The Nash coefficient (NE) was higher than 0.9 and the normalized root mean square (NRMSE) was 6.2%. It indicated that the simulation was reliable for runoff. For the sediment yield, the model had the NRMSE of 41.5%. The bias analysis showed that the large error occurred to the birdfoot trefoil at the rainfall intensity of 1.2 and 1.5 mm/min. The VFSMOD model underestimated the sediment yield of birdfoot trefoil filter strip in late September by 28.8% at 1.2 mm/min rainfall intensity and 40.6% at 1.5 mm/min rainfall intensity. The large bias might be attributed to the poor growth status of birdfoot trefoil vegetation filter strip in late September (the stem spacing of 3.07 cm) and poor coverage on the ground. Soil erosion occurred inside the vegetation filter strip in this condition, which was contradicted with the assumption of VFSMOD on soil erosion inside the vegetation filter strip. In the practice, the poor growth status at the storm season should be avoided since it would lead to great sediment yield. Removing these values of birdfoot trefoil, the model had a better simulation with NRMSE of 10.9% and NE of 0.98. Thus, the VFSMOD could well simulate the runoff and sediment yield of soil in the white clover filter strips and the filter strips of birdfoot trefoil at the early and middle development periods. The simulated results showed that the runoff coefficient increased during the development periods of the 2 grass species. The runoff coefficient was 9.2%-29.6%. The runoff coefficient increased with increasing the rainfall intensity, indicating the large rainfall may lead to big runoff. At the same rainfall intensity and development period, the white clover had the lower runoff coefficient (P<0.05) than the birdfoot trefoil. It suggested that the former grass had the better runoff reduction effect after rainfall. The sediment yield of the 2 species was different. At the early period, both were similar in sediment yield. At the late period, the sediment yield of birdfoot trefoil was significantly higher than the white clover (P<0.05). Since the plot with the white clover filter strip had the small runoff and sediment yield in September when rainfall occurs frequently in the loess plateau. Thus, it rather than the birdfoot trefoil was probably suitable to use for filter strip in the loess plateau especially in September.
2017, 33(8):126-133. DOI: 10.11975/j.issn.1002-6819.2017.08.017
Abstract:Abstract: Rill erosion is one of the main sediment sources. Rill erodibility and critical shear stress are essential parameters for soil erosion prediction for Water Erosion Prediction Project (WEEP) model. Soil subsurface hydraulic gradient on soil loss is important to an accurate prediction of soil erosion and channel initiation. The objectives of this study were 1) to quantitatively explore the response of parameters of WEPP to different subsurface hydraulic gradients; and 2) to investigate the relationship between measured and calculate values in WEPP of critical shear stress. Taking typical yellow soil as example, runoff scouring experiment and a method of measuring critical shear stress were conducted by using a V-shaped soil pan under a slope of 5%. The experiments were carried out in Jinyun Mountain of the upper and middle reaches of the Yangtze River, China (106°22′E, 29°45′N). A total of 5 hydraulic gradients were ?1.43, ?0.71, 0, 0.71 and 1.43 m/m and 3 discharges were 0.55, 1.58 and 2.51 L/min, respectively. Average runoff, average sediment, soil detachment rate and shear stress were determined by collecting runoff samples every 30 s intervals in 8 minutes for each experimental treatment. Rill erodibility and critical shear stress were calculated in WEPP model. The measured value of critical shear stress was determined by varying the flow rate until erosion began when soil particles were continuously detached. Results showed that the average runoff for all the experiments increased with the increase of hydraulic gradient. The average sediment increased with the increase of hydraulic gradient when discharges were 0.55 and 1.58 L/min, showing a change range of 2.55-5.77 and 14.58-28.74 g, respectively. However, when the hydraulic gradient was increased from ?1.43 to 0 m/m and then to 1.43 m/m for 2.51 L/min discharge, the average sediment exhibited a trend of first sharp decrease from 46.10 to 24.48 g and then slight increase from 24.48 to 29.21 g. When the discharge was increased from 0.55 to 1.58 L/min and then to 2.51 L/min under the drainage conditions (hydraulic gradient from ?1.43 to ?0.71 m/m), the average sediment increased by 217.40%-217.39% and 64.38%-66.20%, respectively. However, when the discharge was increased from 1.58 to 2.51 L/min under the saturation/seepage conditions (hydraulic gradient from 0 to 1.43 m/m), the average sediment only increased by 1.64%-17.41%. The average sediment under the drainage conditions was 42.24%-88.32% higher than that under saturation/seepage conditions for 2.51 L/min discharge. The soil detachment rate decreased firstly and then changed stably with the increase of scouring time under the saturation/ seepage conditions, and the similar trend of soil detachment rate was found under the drainage conditions for 0.55 L/min discharge. However, the change tread of soil detachment rate were fluctuated under the drainage conditions with the increase of discharge, and the fluctuation of soil detachment rate under 2.51 L/min discharge was stronger than that under 1.58 L/min discharge. The average value of rill erodibility for the 5 hydraulic gradients was 2.51×10?2 s/m. The value of rill erodibility under the saturation/seepage condition was 3.07×10?2 s/m, and was then 1.78 times higher than that under drainage conditions. When the hydraulic gradient was ?1.43 m/m, the critical shear stress was nearly equal between the calculated value in WEPP and the measured value. However, when hydraulic gradient ranged from ?0.71 to 1.43 m/m, the calculated value overestimated from 14.24% to 55.02% with an average overestimate of 36.85% compared to the measured value. Moreover, an exponential relationship was fitted between the calculated value in WEPP model and the measured value of critical shear stress (R2 was 0.77, Nash coefficient was 0.66, P value was smaller than 0.01). This study not only provides a guidance for controlling soil erosion on yellow soil region, but also offers an important database for correcting critical shear stress of rill erosion in WEPP.
2017, 33(8):134-140. DOI: 10.11975/j.issn.1002-6819.2017.08.018
Abstract:Abstract: Soil erosion with surface runoff in red soil hilly in tropical and subtropical zones of central China cause severe soil quality degradation and environmental issues. It is driven by both rainfall and runoff flow that usually take place simultaneously during an erosion event. The objectives of this study were to determine the main process of rill erosion evolution and explore the main erosion parameters that affected the erosion rate during the process. In order to simulate the erosion process, an indoor experiment including the experimental combination of 3 slopes (5?, 8?, 12?), 2 discharges (5, 7.5 L/min) and 2 rainfall conditions (no rain and 90 mm/h rainfall intensity) was carried out on a red soil flume (3-m length and 0.5-m wide and 0.4-m height). The slit clay soil passing through a 2-cm sieve was used for the experiment. Before the experiment, the bulk density and moisture for the soil sample was controlled at 1.35 g/cm3 and 30%, respectively. The staining method was utilized to measure the flow velocity; the runoff width could be measured through using a ruler at 3 positions; the sediment yield and flow rate were be deduced and calculated from the water bottle used for collecting the runoff samples at the bottom of the flume during a set time interval. A single trial persisted 50 min. The hydrodynamic parameters including shear stress, unit stream power and stream power were calculated. Results showed that: 1) The erosion of red soil slope had obvious periodic development. The initial phase of erosion processes was mainly based on the layer erosion before the first 3-min and then followed by rill erosion. Steep grade, high flow rate and rainfall condition could greatly accelerate the development of rill erosion process and largely increase the erosion rate. 2) The mean erosion rate of each erosion phase was followed by: initial phase> rill development phase> rill stabile phase. In general, the total sediment yield of each erosion phase was followed by: rill development phase> initial phase> rill stabile phase. The erosion in the rill development phase accounted for 38.43%-84.84% of the total sediment yield. The relationship between the hydraulic parameters and the erosion rate of initial phase was closer by stream power> slope> shear stress> unit stream power = flow velocity > flow rate. The mean erosion rate of rill development phase was extremely significant (P<0.01) with stream power, and was significant (P<0.05) with shear stress and slope, while the erosion rate of rill stable phase was just related to flow rate and slope. 3) Stream power was the optimal predictor to predict erosion rate for both layer erosion and rill erosion with a linear relationship. The critical stream power for the layer erosion, the rill erosion in the flow scouring test, and the rill erosion under the interaction of rainfall and scouring flow was 0.091, 0.121, ?1.691 N/(m·s), and their corresponding erodibility was 19.95×10-3, 2.64×10-3, 3.59×10?3 s2/m2, respectively. The results are valuable for agricultural water-soil engineering and controlling soil loss of red soil, and also play a significant role in improving soil erosion models.
2017, 33(8):141-146. DOI: 10.11975/j.issn.1002-6819.2017.08.019
Abstract:Abstract: Soil crust plays an important role in rainfall, runoff and erosion process. When it comes to the present situation, most studies analyze the impact mechanism of soil erosion on the existence of soil surface crust, through comparison analysis of sediment yield, runoff producing and characteristic of hydrodynamic under the crust and no crust slope. However, limited studies report on the characteristic of soil sediment yield, runoff produced and the rule of feature variation for hydrodynamic, also, no quantitative evaluation about the hydraulics parameter's influence on sediment yield. Therefore, in our research, according to crust strength variation and hydrodynamic characteristic under different crust strength, we conducted quantitative analysis on the impact of crust on slope erosion, and through comparison analysis for characteristic of slope sediment yield, under different crust intensities. We further analyzed the change features of hydraulics parameter under slope erosion, and described strength of effect quantitatively under influence factor, for providing important material to predicate accurately and effectively slope soil erosion. In this paper, the impact mechanism of soil crust on slope erosion was reported using quantitative analysis method. The strength of soil crust change of 4 soil types (Lou soil, Loess soil, Heilu soils and Huangshan soil) under 3 rainfall intensities (60, 90, 120 mm/h) was analyzed. Our results showed that the relationship between the crust strength and rainfall intensity was complex when soil water content was more than 30%. However, when soil water content was less than 30%, crust strength increased with the increase of rainfall intensity. Taking the 10° slope of Lou soil as an example, sediment yield, shear stress, resistance coefficient and flow velocity of different crust strength under artificial rainfall experiments were determined and analyzed. The existence of crust could reduce slope sediment yield effectively, and the sediment yield of no crust slope was 1.24-8.72 times more than crust slope's. The crust on slope effectively reduced the erosion and sediment yield. The greater the crust strength was, the stronger the reduction was. The flow shear stress, stream power, resistance coefficient of no crust slope were all larger than the crust slope, but for crust slope, flow shear stress of various crust strength was not significant different (P>0.05). Stream power and flow shear stress were enhanced with increase of crust strength. The larger crust strength was, the smoother surface was, the larger flow velocity was, the smaller resistance was, which improved the stream power. The stream power of high strength crust was larger than low strength crust, but with the smaller sediment yield, its resistance of slope was large. Therefore, the formation of soil erosion was synthetic result of erosion dynamic, slope resistance and soil anti-erodibility. The grey correlation analysis showed that with the increase of the soil crust strength, the influence of the stream power on the erosion of the soil was decreased, and the effect of the resistance coefficient was increased. Therefore, there was a positive effect of water flow on sediment reduction, and the soil erosion resistance of the soil was enhanced with the increase of crust strength, so the erosion amount of soil would decrease greatly.
2017, 33(8):147-152. DOI: 10.11975/j.issn.1002-6819.2017.08.020
Abstract:Abstract: The agricultural internet of things (Ag-IoT), which promotes deep integration of modern information and agricultural technology, has become the focus in precision agriculture research. However, it is inconvenient to replace the battery for sensor nodes in real applications due to the facts of complicated farmland environment, large monitoring area, numerous sensor nodes and long crop growth cycle, which brings a big challenge to the power supply of Ag-IoT sensor node. Fortunately, with the rapid development of the electronic technology, the power consumption for the wireless sensor node decreases quickly, which has reached the μW level, and the ambient energy harvesting technology makes it possible for Ag-IoT sensor nodes to have self-power supply and free maintenance. The traditional energy harvesting devices are always limited to only one sort of ambient energy and have big size with poor reliability. This paper proposed a novel hybrid ambient energy harvesting integration system, focusing on the RF (radio frequency) energy and vibration energy which are rich in the environment. A new type of integrated hybrid ambient energy harvesting device was designed, and the RF energy and vibration energy could be harvested at the same time by the combination of the RF antenna and the piezoelectric ceramic effectively. The system consisted of antenna, matching network, piezoelectric module and rectifier. The antenna received the RF(radio frequency) electromagnetic wave and the matching network improved the power transmission from the antenna to the rectifier, and 2 Schottky diodes and 2 capacitances were used to form the double-voltage rectifier. To reduce the size and improve the conversion efficiency, the rectifier was designed to rectify both the RF electromagnetic wave and the low frequency vibration signal. The converted DC (direct current) power was saved in a super capacitance which had high quality factor with very low leakage current. The energy harvesting antenna was designed in an array with 4 antenna elements in order to collect more RF energy. It was simulated and optimized at the frequency of 1.9 GHz (3G band) by using 3D (three-dimensional) electromagnetic simulation tool HFSS (high frequency structure simulator), and the matching network was designed and optimized by using the ADS (advanced design system). The antenna was implemented by the common FR4 printed circuit board which had low cost. The energy harvesting system was measured by the VNA(vector network analyzer) and oscilloscope, and the measured return loss of the antenna was ?20.5 dB, which agreed well with the simulation results. The maximum output power of the harvested RF energy could reach 38 mW, and meanwhile, considering the typical low vibration frequency in farmland enviroment, we used 10 Hz as the vibration frequency for the vibration energy converting measurement. The measured maximum output power of the harvested vibration energy could reach 25 mW, which met the power requirement of the low power consumption sensor node. This device not only improves the reliability for the system power supply and the adaptive capacity to the environment, but also reduces the size of the device obviously, providing a new way for solving the problem of sensor node power supply during the rapid development of Ag-IoT.
2017, 33(8):153-159. DOI: 10.11975/j.issn.1002-6819.2017.08.021
Abstract:Abstract: As a general definition, open field burning is the burning of living and dead vegetation. An annual average amount of 730 Tg biomass was burnt in Asia, out of which 250 Tg came from agricultural burning. Burning straw after harvest was common, and it was a significant seasonal source of air pollution, which should not be ignored in China. In recent years, straw combustion was serious in Henan Province in autumn, where mechanized farming was practiced, for the farmers were more inclined to burn the crop residues. At present, remote sense monitoring is a practical solution for detection and assessment of this burning. Many researchers used MODIS (moderate resolution imaging spectroradiometer) and FY data to monitor the straw combustion, but the spatial resolution of these data was low and cannot satisfy the requirement of high frequency and high precision monitoring. Especially, many mixed pixels exist in MODIS and FY remote sensing data, which aggrandized the difficulties to get the spatial distribution with high frequency and precision. So, effective and quick means were necessary to deal with this key problem. Generally, high frequency satellite observations could inverse the changing process of straw burned areas. In the present study, Landsat8, GF-1 and HJ-1A/B data were used comprehensively to improve the remote sensing spatial resolution, while the overlay analysis and the object-oriented image analysis (OOIA) methods were adopted to extract the straw burned areas in Taikang County. Based on the OOIA, the remote sensing interpretation sign was established through the ground investigation, and the straw burned area was extracted with a multi-term single-day form. Straw burned areas of 8 stages were extracted using the full-coverage remote sensing images. With the changing detection at the township scale, the temporal change trend of cumulative straw burned area, new added straw burned area and new added farmland plowing area after straw burned were calculated. The spatiotemporal spreading trend of straw burning showed that after the maize harvest, straw burned started at a certain point in time after a large area of crop was harvested, and spread from a number of fire points to a main direction with the time. The new added straw burned area changed with a wavy pattern, due to that intermittent large-scale plowing occurred subsequently in the added burned area. The rate of plowing was beyond the rate of straw burned, and the incineration activity tended to end. Compared with field observed data, the calculated area extraction accuracy was above 93.89%, and the calculated change trend of new straw burned area was basically consistent with the monitoring results of the Ministry of Environmental Protection. Experiment results have indicated that the method presented in this study is timely and accurate, which can reveal more details and regularities than traditional large-scale application of low spatial resolution satellite remote sensing data.
2017, 33(8):160-165. DOI: 10.11975/j.issn.1002-6819.2017.08.022
Abstract:Abstract: Xinjiang is the largest cotton producing area in China accounting for more than 50% of the total cotton production in China. So the accuracy of the prediction of cotton production in Xinjiang is particularly important. Based on calibration and validation of cotton growth model COSIM, in this paper, we used a dynamic prediction model for cotton yield forecast and focused on solving the problem of the unknown climatic data substitution during the prediction period. In the process of prediction, the model read the climatic data day by day. For predicting the growth, development and yield of cotton by the dynamic prediction model, in this study, we substituted the measured climatic data in the recent 50, 30, 20, 10, and 5 years for the unknown climatic data from forecasting day to harvest day, respectively. Meanwhile, the climatic data measured in the year was input into the model before forecasting day. In this way, the cotton yield and development could be predicted day by day. To test the reliability of the method, an experiment with 5 different sowing date (April 10th, April 20th, April 30th, May 10th, May 20th) was designed in 2011 at Wusu, Xinjiang (44°43′ N，84°67′ E). Each treatment was replicated 3 times. The cotton was harvested on September 10th, September 15th, September 21th, September 29th and October 5th, respectively. During the experiment, the growing stage of the cotton was recorded. The leaf area and biomass were determined. These parameter values were input into the COSIM model for cotton lint yield prediction. The model reliability was evaluated by comparing the simulated and measured values of lint yield and growing stages. For the simulation, the climatic data measured in 2011 was used. The results showed that the root mean square error (RMSE) of the cotton growing from emergence to flowering stage was 2.2-5.9 d. The determination coefficient was 0.99. For the lint yields simulations, the RMSE was 165.9 kg/hm2. It indicated that the model was reliable in simulating cotton development and lint yield. Based on experimental results of treatment 1 (sowing date was April 20th), we selected the best substitution one for the unknown climatic data from the 5 schemes (climatic data of the recent 50, 30, 20, 10, and 5 years) and then validated by the results from the other treatments. The results showed that the for the randomly selected 7 predicting time (April 1st, May 1st, June 1st, July 1st, August 1st, September 1st, October 1st), the standard deviation of the measured and predicted lint yield of the 5 schemes from 50 to 5 years' climatic data was 171, 123, 82, 86 and 106 kg/hm2, respectively. The predicting accuracy was above 87% compared with the measured values and above 83% compared with the simulated values for the lint yields. Among them, the accuracy in the predicting time after the sowing date was above 93%. Based on the predicting accuracy and the standard deviation, the best scheme was the 10 years' climatic data substation scheme. The validation of the best scheme using the results from the other treatments showed that predicting accuracy could reach 81.3%-99.6%, indicating the reliability of the best scheme for cotton lint yield prediction. Compared with a single station forecasting, the regional forecasting of cotton yield is more important to national macro-control. In a large region, cotton is not sowing on the same day but during a time period. Therefore, in predicting the regional cotton yield, the effect of sowing time should be taken into consideration. As a case, this study only does the forecast once a month. In practice, the daily dynamic forecast would be realized.
2017, 33(8):166-175. DOI: 10.11975/j.issn.1002-6819.2017.08.023
Abstract:Abstract: Knowledge of multi-scale evapotranspiration (ET) is the basis of increasing agricultural water use efficiency and realizing optimal water resources allocation. However, there is little information about the characteristics of multi-scale ET and the difference in the quantitative response of leaf and plant transpiration and farm-scale ET to the meteorological factors, especially for the solar greenhouse, which limits our understanding of agricultural water and energy cycles. In this study, theET at different scales was investigated in solar greenhouse tomato and their main influential factors were analyzed. Experiments were carried out in a typical solar greenhouse to investigate variation in leaf and plant transpiration and farmland ET of drip-irrigated tomato under different water conditions in 2 continuous seasons. Field trials were conducted during the growing season from March to June, 2015 and 2016 at Xinxiang Comprehensive Experimental Station, Chinese Academy of Agricultural Sciences (35°9′N, 113°47′E, and an altitude of 78.7 m), located in Xinxiang, Henan province. Tomato was used in the experiment on a plot of 8.8 m2 (8.0 m long by 1.1 m wide) with 2 rows and 50 plants. There are 4 replications for each treatment. Tomato seedlings were transplanted on March 8th, 2015 and March 9th, 2016 respectively and irrigated with a drip irrigation system. Irrigation amount was determined based on the accumulated evaporation in 20 cm pan, and 2 treatments were designed with full irrigation and deficit irrigation. Leaf transpiration was measured with a photosynthesis system, plant transpiration (expressed as sap flow rate) measured by a sap flow meter and farm-scale ET measured by a weighing lysimeter. Besides, solar radiation, net radiation, relative humidity and air temperature inside the solar greenhouse were constantly monitored with an automatic weather station at 2.0 m height above ground level. And then the difference of quantitative response of leaf transpiration, plant transpiration and farm-scale ET to the meteorological factors was performed using the path analysis method. Results showed that leaf transpiration rate and stomatal conductance gradually increased with the increase in solar radiation, and reached their maximum values at 10:00-14:00, and then rapidly decreased with solar radiation. Difference in leaf transpiration rate between full irrigation and deficit irrigation appeared at 54-58 days after transplanting. Daily average of leaf transpiration rate in the full irrigation was 10.8% and 14.7% higher than that in deficit irrigation, respectively. Tomato sap flow rate changed with weather conditions, and the difference in plant transpiration between the full irrigation and deficit irrigation was the largest in the sunny day, and the smallest in rainy days, and the plant transpiration was related to solar radiation but lagged behind 1 hour. Daily average of leaf transpiration rate in the full irrigation was 54.8% and 41.2% higher than that in deficit irrigation, respectively in the 2 years. The daily farm-scale ET in the full irrigation and deficit irrigation ranged between 0.32-6.65 mm/d and 0.15-5.91 mm/d, respectively, over the whole growth stage, and the farm-scale evapotranspiration reached the maximum in the full fruit period, accounting for 31.7%-34.7% of the total ET. The path analysis of evapotranspiration at different scales and its controlling meteorological factors indicated that leaf transpiration rate, plant transpiration and farm-scale evapotranspiration could be characterized by the net solar radiation, and the vapor pressure deficit also had significant influence on the scale of individual plant and farmland scale. The influence of wind speed should be considered in estimating plant transpiration rate and farm-scale evapotranspiration. Besides, adding leaf temperature could significantly improve the estimation accuracy of plant transpiration and farm-scale evapotranspiration under the condition of deficit irrigation. This paper provides valuable information for constructing conversion methods and theoretic model at various spatio-temporal scales.
2017, 33(8):176-182. DOI: 10.11975/j.issn.1002-6819.2017.08.024
Abstract:Abstract: Heat recovery ventilation, as a kind of energy saving ventilation, can alleviate the contradiction between heating energy consumption and ventilation. The application of heat recovery ventilation system for residential buildings has turned out that it has the problems of low ventilation efficiency and high cost when applied in the livestock house. A modified heat recovery ventilation system for livestock house was designed in this study, and the efficiency of heat recovery ventilation equipment under 3 different operating conditions was tested to find out the optimal operation conditions. In the first operating condition, the temperature difference inside and outside the livestock house was 12.08 ℃. The size of plate-fin heat exchanger was 500 mm ? 500 mm ? 250 mm. Fresh air supply adopted a positive pressure way and exhaust air used a negative pressure way. When the approach velocities were 1.05 and 0.86 m/s, the fresh air temperature through the heat exchanger increased by 1.93 and 2.79 ℃, the sensible heat recovery efficiency was 35.88% and 43.63%, the heat recovery load was 0.16 and 0.19 kW, and the coefficient of performance was 1.37 and 1.61, respectively. The sensible heat efficiency under both approach velocities was far below the energy saving standard in winter (≥65%). In the second operating condition, 2 plate-fin heat exchangers were in cascade connection, and the fresh air went through the 2 plate-fin heat exchangers in sequence. The size of heat exchanger, fan type and ventilation pattern were the same with the first condition. In this way, when the temperature difference between inside and outside was 10.49 ℃, the fresh air temperature passing through the first heat exchanger increased by 2.59 ℃. The sensible heat recovery efficiency was 52.11%, and meanwhile the heat recovery load and the coefficient of performance were respectively 0.39 kW and 3.26. The poor performance of the second heat exchanger showed that the two heat exchangers in series for livestock house were unnecessary. In the third configuration condition, both matching parameters and connection ways between heat exchanger and fans were optimized. The plate heat exchanger and the axial flow fan with low noise and large volume were used. The heat exchanger size was 600 mm ? 600 mm ? 600 mm. Both fresh air supply and exhaust air used a negative pressure way. When the temperature difference between inside and outside was 12.12 ℃ and the approach velocity was 4 m/s, the fresh air temperature increased by 8.23 ℃. The sensible heat recovery efficiency was 69.9%, and the coefficient of performance was 8.0, meeting the national energy-saving standard requirement. It is concluded that the heat recovery ventilation aimed to improve the balance between heat recovery efficiency and ventilation efficiency can meet the requirement of large volume ventilation and energy saving in the livestock house. So it is of great value to optimize the parameter and structure of heat recovery ventilation system for livestock house.
2017, 33(8):183-190. DOI: 10.11975/j.issn.1002-6819.2017.08.025
Abstract:Abstract: Pond aquaculture plays a very important role in China's aquaculture industry and is the main source of aquatic product supply. To improve the effect of pond aquaculture, a partitioned recirculating aquaculture pond system (PRAPS) was designed and built based on the characteristics of pond aquaculture in freshwater, which consisted of feeding fish culture zone (20% of water surface) and filter-feeding fish culture zone (80% of water surface). The structure of facilities and equipment of PRAPS was optimized by setting up the overflow weir, propeller flow device, paddlewheel device, and pollutant absorption and collecting device. Tests on the mechanical properties revealed that both propeller flow device and paddlewheel device could achieve the design demand; the energy efficiency of the propeller flow device was about 340 m3/(kW·h), the flow rate was around 204 m3/h, and the no-load running noise was 60 dB; the energy efficiency of the paddlewheel device was about 360 m3/(kW·h), the flow rate was around 180 m3/h, and the no-load running noise was 67 dB; the total flow rate of the overflow weir was about 331 m3/h. The exchange capacity was totally about 7 900 m3/day, accounting for about 50% of the pond water capacity. Additionally, the system could reduce the total energy consumption and farming pollution and effectively improve the pond aquaculture ecological effect, which met the production requirement of energy saving and environmental protection. It was conducive to improve the water quality of the pond though the impeller disturbed the water. The pollutant could be gathered into the middle of bottom by the collecting device, and removed out of system by the pollutant absorption device, in which way the transparency of water was improved, and the content of TN (total nitrogen) and TP (total phosphorus) in the system was decreased. The propeller flow device and paddlewheel impeller stirring water could realize water convection in large scale, so the water was exposed to sunshine and air, which could increase the dissolved oxygen in the water. Tests showed that the dissolved oxygen of the middle and lower layer in the test pond was 59.5% higher than the control pond; the content of TN in the test pond was 21.4% lower than the control pond; the content of TP was 53.1% lower than the control pond; the chlorophyll a concentration in the test pond was lower than the control pond. Because the breeding density in the test pond was higher than the control pond, the content of ammonia nitrogen and nitrite nitrogen in the system was increased. Overall the water quality in the test pond was better than the control pond. For the PRAPS, the one-time investment was big at the beginning and it needed professional and technical personnel to maintain, while the PRAPS had a high economic efficiency. The yield of bream in the test pond was 10 280 kg, and the food coefficient was 1.7; the yield of bream in the control pond was 8 488 kg, and the food coefficient was 2.1. The result showed that the yield of bream increased by 21.1% using the PRAPS, the feed coefficient decreased by more than 23.5%, and the annual output value increased by 6%. The result provides the reference for the model establishment of healthy breeding pond system, which is helpful to make PRAPS become a more mature and reliable novel pond aquaculture system.
2017, 33(8):191-196. DOI: 10.11975/j.issn.1002-6819.2017.08.026
Abstract:Abstract: Improper treatment of biogas slurry results in serious environmental pollution. Cultivating algae using the biogas slurry is a promising strategy. By doing this, we can realize the reuse of nutrients, the further treatment of wastewater and the biomass production. In this study, the produced Chlorella cultivated in the biogas slurry of chicken manure was used as feedstock for biocrude oil production through hydrothermal liquefaction (HTL). An orthogonal design was applied to investigate the effects of operational parameters on biocrude oil production, including the holding temperature (250, 290 and 330 ℃), the retention time (30, 60 and 90 min) and the total solid content (15%, 20% and 25%). The characteristics of products and element migration during HTL were analyzed. The highest biocrude oil yield reached up to 23.83% under a temperature of 330 ℃, a retention time of 60 min and a total solid content of 15%. The low yield of biocrude oil in this study may result from the low content of lipid (1.00%) and high content of ash (55.06%). The reaction conditions significantly affected the biocrude oil yields and chemical distribution of HTL products. The carbon recovery, hydrogen recovery and nitrogen recovery of the biocrude oil were 16.13%-31.14%, 19.18%-34.89% and 5.97%-14.32%, respectively. The highest carbon recovery was achieved under the condition of 330 ℃, 60 min and 15%, and the lowest nitrogen recovery was achieved at the condition of 250 ℃, 30 min and 15%. The increased carbon and hydrogen recovery of biocrude oil were mainly due to the increase of the biocrude oil yield. Carbon (48.74%-60.43%), hydrogen (46.81%-62.13%) and nitrogen (74.84%-82.67%) were effectively recovered in the aqueous phase. The high nitrogen recovery in the aqueous phase was mainly due to the promotion of the denitrification during the HTL process. The high nitrogen distribution in the aqueous phase had a harmful effect to biocrude oil, nitrogen content of which needed to be further decreased. Gas chromatograph-mass spectrometer (GC-MS) was chosen to analyze the organic groups in the biocrude oil. The hydrocarbons content in the biocrue oil was 16.14%-24.91%. The highest hydrocarbon content was obtained under the condition of 330 ℃, 30 min and 25%. However, the high content of oxygenates and nitrogen containing compounds in the biocrude oil decreased the quality of biocrude oil. Hence, the further deoxygenation and denitrogenation of the biocrude oil were maybe required before its application to the transport fuel. A thermogravimetric analyzer (TGA) was used to simulate the distribution of boiling points in the biocrude oil. The results indicated that the biocrude oil contained a lot of high molecular weight compounds. Based on the analysis, the biocrude oil seemed suitable for the production of lubricating oil. The concentration of total organic carbon, the total phosphorous and the ammonia nitrogen in the aqueous phase were 24 360-47 760, 107-270 and 1 218-3 629 mg/L, respectively, and the pH value was 8.53-9.15. The aqueous phase rich in nutrients could be recycled for algae cultivation. In addition, the main gas products CO2 (>93%) could be used as carbon asset for algae cultivation. This study provides a potential approach for the biofuel production from Chlorella cultivated in biogas slurry.
2017, 33(8):197-203. DOI: 10.11975/j.issn.1002-6819.2017.08.027
Abstract:Abstract: Reclaimed water has been widely used to restore rivers and lakes in water scarce areas as well as in Beijing City, China. However, refilling the rivers and lakes with reclaimed water may result in groundwater pollution. Purification is necessary prior to utilization in order to minimize the pollution and human-health risk. To study the long-term NO3-N removal efficiency during land filtration system under different water supply conditions, a long-term filtration system was built using soil columns supplied with reclaimed water from reclaimed wastewater treatment plant. Four sets of soil columns (100 cm in length, 20 cm in diameter) repacked with sandy loam soil were utilized to simulate the land filtration system. Four water supply conditions were considered including continuous wetting, alternating wetting/drying, constant flow rate and lateral injection. The results showed that NO3-N removal efficiency decreased with the increase of hydraulic loading rate when the hydraulic loading rate varied from 0.25 to 2.65 cm/d. Different NO3-N removal efficiencies were mainly attributed to the different hydraulic retention time under different water supply conditions. For the constant flow rate and lateral injection condition, longer hydraulic retention time was conducive to efficient denitrification. Removal efficiency of NO3-N reached higher than 90% in the constant flow rate and lateral injection column. The highest removal efficiency of NO3-N was obtained in the column recharged with lateral injection, with an average removal efficiency of 96.1%. NO3-N concentrations in the effluents in the alternating wetting/drying, constant flow rate and lateral injection columns were all lower than the drinkable water standard (<10 mg/L). The transport and removal of NO3-N varied with soil depth. The variation trend of NO3-N removal along soil depth was different under different water supply conditions. For the continuous wetting and lateral injection condition, NO3-N concentration decreased rapidly in the top 20 cm depth. Top 20 cm layer of the sandy loam columns (0-20 cm for the continuous wetting condition, 40-60 cm for the lateral injection condition) was the main zone for NO3-N removal. For the alternating wetting/drying and constant flow rate condition, NO3-N concentration decreased gradually along the soil depth. For the alternating wetting/drying condition, NO3-N removal efficiency increased from 23.2% in 20 cm to 76.2% in 100 cm. For the constant flow rate condition, NO3-N removal efficiency increased from 20.8% in 20 cm to 94.1% in 100 cm. The results indicated that the NO3-N removal efficiency in different soil depths was correlated to the number of denitrifying bacteria in 4 soil columns. The results also showed that the NO3-N removal efficiency presented an exponential relationship with the temperature ranging from 15 to 32 ℃ under the continuous wetting condition. For the alternating wetting/drying condition, NO3-N removal efficiency showed a power function relationship with the temperature, while temperature had no significant influences on NO3-N removal under low hydraulic loading rate condition, i.e., constant flow rate and lateral injection condition. The results confirmed that the NO3-N removal performance under constant flow rate and lateral injection condition could both be relatively stable during the land filtration system's long-term running. The land filtration system could be used for further purification for reclaimed water. The result can provide important information for the reuse of reclaimed water in refilling rivers and lakes.
2017, 33(8):204-210. DOI: 10.11975/j.issn.1002-6819.2017.08.028
Abstract:Abstract: Bioethanol has been indispensable in future due to the consumption of fossil fuels, greenhouse effect and environmental degradation. Thus acetone-butanol-ethanol (ABE) fermentation by Clostridium species has played a vital role in production of renewable energy used to relieve the energy crisis. Renewable biomass such as corn stover as a kind of low cost raw material has replaced molasses needed for fermentation. Butanol production from corn stover hydrolysates (CSH) has obvious advantages in the field of biomass conversion. The inhibitory compounds formed during the corn stover pretreatment. Therefore detoxification of hydrolysate can be used to increase butanol production by overcoming inhibitory effects of toxic by-products such as phenols, furfural and acid. All kinds of detoxification especially the physical and chemical methods have some disadvantages because of the damage of glucose and the pollution of the environment in the downstream process. Among the different detoxification methods, enzymatic detoxification has become a high efficient and environmental-friendly biological method. In order to relieve the influence of a variety of toxic substances in the CSH on microbial growth and fermentation production, the best strategy of detoxification with laccase and formate dehydrogenase (FDH) was studied. The optimum adding content of laccase and FDH was studied to eliminate phenols and formate in hydrolysates, respectively. The results showed that ABE and butanol production from CSH dealt with 5 U/mL laccase were respectively 0.78 and 1.03 g/L by fermentation with Clostridium acetobutylicum CICC 8016, which were increased by 56% and 77.59% compared to that from non-detoxified hydrolysate, respectively. However, ABE production was lower than control group when adding laccase greater than or equal to 15 U/mL. The production from P2 medium with 0.74 g/L formate when adding 1 U/mL FDH achieved the same effect with that without adding formate medium. And ABE and butanol production from CSH dealt with 1 U/mL FDH were 0.77 and 1.11 g/L, respectively, which were increased by 57.14% and 60.87% compared with that from non-detoxified hydrolysate, respectively. Through the fermentation results with P2 and corn straw hydrolysate as medium, FDH had an obvious effect for removing formic acid in the medium. In addition, butanol production and glucose consumption were increased by 165.78% and 27.16% respectively through adsorbing treatment with 1% activated carbon. Under this condition, an efficient enzymatic composite detoxification strategy was formed assisted with activated charcoal detoxification. The enzymatic composite detoxification strategy was feasible for the CSH treated by 5 U/mL laccase, 1 U/mL FDH and 1% activated carbon after steam explosion and pretreatment of corn straw. Butanol and ABE production from composite detoxified CSH were 2.90 and 4.4 g/L respectively, which were about 5 times higher than the control group. The utilization of reducing sugar reached 98%-100%, and the yield of ABE increased by 300% compared with the control group. This research provides a reliable detoxification method for butanol fermentation with the hydrolysate of steam exploded corn straw, and the enzymatic composite detoxification strategy is more efficient and environmental-friendly than the single physical or chemical detoxification method.
2017, 33(8):211-218. DOI: 10.11975/j.issn.1002-6819.2017.08.029
Abstract:Abstract: Phosphorus is one of the key nutrients that cause eutrophication of water bodies, and excessive phosphorus in water will cause water ecosystem structure and function change, deterioration of water quality and landscape, and biodiversity decrease. Therefore, preventive measure of phosphorus pollution in the aquatic environment and processing must be paid more attention. The processing methods of phosphorous water include biological phosphorus removal technology, chemical precipitation, adsorption, and so on. Adsorption technology is efficient and cheap, and has a good removal effect, which has come into notice of researchers. So far, some studies have been conducted on preparation of straw biochar for removal of phosphate radical from aqueous solutions. In this study, a porous nano biochar composite (nanoSiO2/AR-biochar) was prepared by nanoSiO2 doping, which was homogeneously cladded using amino starch resin, and kneading molding, then foaming coking technology were adopted in situ preparation as well as the carbonizing treatment. Transmission electron microscope (TEM), thermogravimetry, scanning electron microscope (SEM), specific surface area analysis, nitrogen adsorption-desorption isothermal and compression were used to characterize the pore structure, thermal stability, microstructure and compression performance of nanoSiO2/AR-biochar. Phosphate adsorption process of nanoSiO2/AR-biochar was studied by means of isothermal and adsorption kinetics. Results showed that the specific surface area, total pore volume, and micropore volume of nanoSiO2/AR-biochars increased monotonously. The nanoSiO2/AR-biochars prepared at 550℃ possessed the maximum single point adsorption total pore volume (0.177 5 cm3/g), and the pore diameter of the ultramicropores was mainly in the range from 1 to 50 nm. The t-plot micropore area, and Brunauer-Emmet-Teller surface area of this kind of nanoSiO2/AR-biochar were 302.86 and 352.70 m2/g, respectively, when the doping amount of nanoSiO2 was 6% of straw powder quality. SEM and TEM analysis showed that the surface of the porous granular biochar materials doped nanoSiO2 could form the similar sponge flocculent structure, which could provide more adsorption sites for removal of phosphate ions. More it was worth mentioning that the compressive strength of nanoSiO2/AR-biochars was increasing from 3.89 to 7.96 MPa, a growth of 104.6%, which could solve the problems such as short service life, difficulty in recycle and dust pollution of traditional biochar. Adsorption experiments showed that the adsorption capacity of the nanoSiO2/AR-biochar could be as high as 18.42 mg/g (within 5 min), higher than straw biochar, of which the process could be described with Ho's pseudo-second-order kinetic model. The result of the adsorption process of phosphate radical conformed to the pseudo-second-order dynamic model, which assumes that the adsorption process conforms to the chemical adsorption. The process after the rapid adsorption accorded with the chemical adsorption assumption, and the initial phase was mainly described by physical adsorption. Compared to the traditional straw biochar material, it has lots of advantages such as high adsorption capacity, high compressive strength, recycling, and environmental friendliness. What was more, according to the design in the work, there would be an excellent market prospect of nanoSiO2/AR-biochar. In a conclusion, the nanoSiO2/AR-biochar has the potential to replace the straw biochar for purifying the polluted water. These results will provide a feasible treatment approach and theoretical foundation to reaserch biochar materials on effectively removing phosphorus from eutrophication waters.
2017, 33(8):219-225. DOI: 10.11975/j.issn.1002-6819.2017.08.030
Abstract:Abstract: CA simulation system of cultivated land planning can be used for planning cultivated land scientifically and rationally, so as to provide a reference for managers to make the general land use planning. Indices constraining and partitions controlling, as the existing pattern of general land use planning, is to ensure the total amount stable of cultivated land. However, phenomenon such as the unreasonable index of land quantity, the inadequate index of building land occupation, and the decline of cultivated land quality from 'Dynamic Balance of Total Amount of Cultivated Land', leads to the relevant departments cannot but make adjustments to the planning. Previous research of cultivated land is mainly focused on its protection, evaluation as well as change. There is a little literature on cultivated land planning. CA simulation system is a user-defined tool of ArcGIS, which is easy to be invoked in Geographic Information System (GIS). In the CA simulation system, the land suitability and planning indicators are taken as the cell transformation rule and constraint condition respectively, and optimal probability is used to select strategy. The paper taking Lankao County in Henan Province as example, selected the natural factors which affect the distribution of cultivated land, including soil texture, soil organic matter, effective thickness of soil layer, irrigation guarantee rate, distance to roads, distance to villages and slope; the ecological limiting factors of river and forest land that restrict the spatial distribution of cultivated land; and competitive factors for the conversion of other land to cultivated land from the three aspects of suitability, limitation and competition. Delphi method and expert scoring method were applied to calculating the weights of those factors. The evaluation score of cultivated land suitability is 0.46-0.91, while that of land suitability is 0.49-0.90 combining with spatial neighborhood analysis. The research result shows that in 2020 the area of cultivated land in Lankao County will increase by 8 000.69 hm2 and reach to 76 411.32 hm2 by overlaying with the land use status map in 2009. Because the urban development made the area of cultivated land decreased by 226.44 hm2, while the utilization conversion of village, inland beach, orchard land and other land made the area of cultivated land increased by 8 227.13 hm2. The results show that the quality of cultivated land in 2020 is relatively higher than that of the cultivated land in current land use planning, and the space distribution is stable by avoiding the town development, ecological protection and other factors. The study has important guiding significance for the future land planning.
2017, 33(8):226-235. DOI: 10.11975/j.issn.1002-6819.2017.08.031
Abstract:Abstract: Rapid industrialization and urbanization have brought a series of environmental problems related to soil pollution in the Pearl River Delta region. A systematic and synthetic evaluation of the cultivated land quality is of great significance to guide the rational utilization and protection of cultivated land, as well as to realize the comprehensive balance and management of cultivated land. However, the soil pollution factors have seldom been considered in cultivated land quality evaluation system, which was also short of a sensitivity analysis of the index weight. Based on GIS (geographic information system) multi-objective decision analysis, the paper conducted a study on the evaluation of cultivated land quality and the sensitivity analysis of index weight by taking Zengcheng District of Pearl River Delta as an example. With soil fertility factor and environmental assessment index taken into consideration, the comprehensive evaluation index system of cultivated land quality was constructed from 4 aspects: Soil physical and chemical properties, agricultural production conditions, location conditions and soil environment, so as to analyze the general characteristics of cultivated land quality and the spatial layout rule in Zengcheng District, and the weight sensitivity analysis of OAT (one-at-a-time) method was adopted to evaluate the influence degree of each index weight's uncertainty on the evaluation results. In order to reflect the trend and regularity of the changon cultivated land quality and its spatial pattern, the weight value of only one factor changed at a time while the other factors remained unchanged. When the value of RPC (range of percent change) and IPC (increment of percent change) were at ±30% and ±2% respectively, and every criterion factor was applied to all the evaluation indicators as the main change factor, a total of 420 groups of weight values were generated, among which every group of weights were calculated to produce a new evaluation result of the comprehensive quality of cultivated land. The main results of the study were as follows: 1) The cultivated land in Zengcheng District had a good overall quality, but high quality cultivated land was lacked. The grades of cultivated land quality were mainly concentrated at the 2nd and 3rd grade, which accounted for 30.88% and 31.69%, respectively. The proportion of middle and low yield field was relatively large. 2) From the perspective of the spatial distribution, the cultivated land with better quality was mainly distributed in the southern plains, the basins with better irrigation conditions like Zengjiang River basin, East River basin and Xifu River basin, as well as North River valley. The comprehensive quality of most cultivated land in Zhengguo, Xiaolou and Paitan was not high, and the overall quality of cultivated land in Xintang Town was poor. 3) The changes of weights had a certain influence on the quality distribution of cultivated land. Seen from the spatial distribution of change rate of cultivated land quality generated from different weight distribution, the spatial differences of the calculated results were rather big. When the weight increased or decreased by the same value, the same factor showed the same sensitivity to the quality evaluation results of cultivated land. 4) The maximum MACR (mean absolute change rate) value of 3.558 2% was much lower than the corresponding weight change rate of 30%, showing that the evaluation results were relatively stable, and the quality of cultivated land in Zengcheng District was overall stable. In conclusion, in the comprehensive evaluation of cultivated land quality, the soil environmental factors should be taken into consideration, and a quantitative analysis of micro-data of the soil pollution situation should be conducted to make the evaluation system more comprehensive and more scientific. The sensitivity analysis of the index weight can verify the reliability of the evaluation results, which can help the relevant departments make better decisions, and reduce the uncertainty in the spatial multi-criterion decision-making.
2017, 33(8):236-244. DOI: 10.11975/j.issn.1002-6819.2017.08.032
Abstract:Abstract: Analysis of the spatial structure of rural residential area is important to optimize the spatial pattern of rural residential area. In previous studies, complex network analysis was rarely used to analyze the spatial structure of rural residential area, and studies about temporal and spatial characteristics of rural residential complex network were rare at the macro (provincial) spatial scale. This paper, utilizing complex networks constructed based on the interaction of rural residential areas with the gravity model, analyzed the changes of node network characteristics of typical rural residential areas in typical counties (Huanren, Tai'an and Jianping County) and the changes of spatial distribution pattern of rural residential network characteristics in various cities or counties in Liaoning Province. The statistical characteristics ofαindex,βindex,γindex, degree centrality, closeness centrality and betweenness centrality in complex networks were calculated and descripted. The results proved that: 1) Analysis of typical counties indicated that spatial pattern of rural settlement network had obvious regional differences, which was affected by the terrain strongly. For Tai'an County, the rural residential network in the eastern area had more rural residential settlement nodes and shorter network connection, and that in the central plain had a close contact network structure with higher degree centrality. Due to topographical constraints, the nodes of the rural residential network of Jianping County in the western hilly region and Huanren County in the eastern hilly region were scattered and separated, and the rural residential network in these 2 counties was relatively sparse and had more isolated nodes or isolated network groups. 2) Rural residential network structure of various cities or counties in Liaoning Province presented obvious regularity and spatial differences. The network complexity indices of rural residential networks were higher in the central plain region (that in Jinzhou was the highest). The network complexity indices were relatively lower in the eastern and western hilly regions (that in the municipal district of Dandong City located in the eastern hilly region was the lowest). The network centralization indices of rural residential networks in the central plain region and in the western hilly region were higher compared with the eastern hilly region, and the structures of rural residential networks in the central plain region became more complex. 3) The responses of different network indices to the change of spatial layout structure of rural residential areas were not the same. Graph theory indicators had significant differences in different periods, and the difference between centralization indices in different periods was not significant, but the rank of counties and basic statistics result of network indices had differences. There was a great difference between high and low value ofαindex,βindex andγindex and high and low value of centralization indices. The results have contributed to explore spatial differentiation characteristics of rural residential structure in Liaoning Province from the perspective of complex network structure, and to provide a scientific basis for regional urban system planning.
2017, 33(8):245-250. DOI: 10.11975/j.issn.1002-6819.2017.08.033
Abstract:Abstract: Determination of internal quality of fruit and vegetable with a suitable technique is crucial for processing detection and quality control. While substantial progress has recently been made in the miniaturization of near-infrared (NIR) spectrometers, there remains continued interest from end-users and product developers in pushing the technology envelope toward even smaller and lower cost analyzers. The potential of these instruments to revolutionize on-site applications can be realized only if the reduction in size does not compromise performance of the spectrometer beyond the practical need of a given application. In this paper, the working principle of a novel, extremely miniaturized NIR spectrometer is presented. The ultra-compact spectrometer relies on digital micromirror device (DMD) technology for the light dispersing element. DMD is a two-dimensional array of electro-mechanical mirror elements whose surface normal angles can be controlled. Digitally programmable DMD can set the spectral resolution and wavelength range according to user needs, adjust the integration time, and adapt the luminous flux. The system design with DMD and single-pixel InGaAs detector can significantly reduce the cost, and meanwhile ensure the detect precision. The DLP (digital light procession) NIRscan module is used as spectrometer optical engine in the miniaturized system. In the specific implementation, a sample is placed against the sapphire front window of the reflectance head. During a scan, the sample absorbs a specific amount of NIR light and diffusely reflects the non-absorbed light into the system. The illuminating lamps are designated as lens-end lamps because the front end of the glass bulb is formed into a lens that directs more lights from the filament to the sample test region. The collection lens gathers collimated light from a 2.5 mm diameter region at the sample window. The handheld system supports the following modes of operation: USB (Universal Serial Bus) connection and Bluetooth for 2 communication channels. Special analyzer software was developed for quality inspection based on multithread programming technology. The advantages of this software are presented by the process of modular design, including software system initialization, information communication, information interaction, spectral data acquisition and processing, spectral curve real-time display, quality index calculation, and statistics and save of detection results. Miniaturized handheld NIR spectrometer was developed and used to acquire reflectance spectra from fruit and vegetable samples in the wavelength range of 900-1 700 nm. In order to verify the design and performance, tomato was selected as research object. A total of 78 tomato samples were randomly divided into 2 subsets. The first subset was called the calibration set with 52 samples and used for building model, while the other one was called the prediction set with 26 samples and used for testing the robustness of the model. In the process of model establishment, a simplified strategy was proposed. Firstly, characteristic spectrum bands were selected to remove the uninformative variable and the low-correlation band. And then feature wavelengths were optimized to eliminate the collinearity relationship in the spectral data. Finally, simplified model was built, which had good robustness and stability. Synergy internal partial least square (siPLS) and successive projections algorithm (SPA) were sequentially applied to calibrate models. The siPLS was applied to select an optimized spectral interval and an optimized combination of spectral regions selected from informative regions in model calibration. The subsequent application of SPA to this reduced domain could lead to an efficient and refined model. The measurement results of the final model were achieved as follows: correlation coefficient (Rp) was 0.899 and root mean square error of prediction (RMSEP) was 0.133% for soluble solid content in tomato, and Rp was 0.886 and RMSEP was 2.508 mg/kg for lycopene content in tomato. The results will provide the method reference for rapid, non-destructive, and on-site detection technology and equipment of fruit internal quality.
2017, 33(8):251-258. DOI: 10.11975/j.issn.1002-6819.2017.08.034
Abstract:Abstract: In order to study the performance of bionic olfactory detection device, the bionic olfactory detection device was designed using purging method in this research This detection device consisted of the gas transmission and flow control pipes, the bionic olfactory control unit and the software of bionic olfactory detection analysis. The gas transmission and flow control pipes were the carrier of bionic olfactory gas transmission, and the bionic olfactory control unit completed the signal output and sensor signal acquisition, the software of bionic olfactory detection analysis could not only complete setting up parameters in the process of olfactory detection analysis and controlling working process, but also complete data preprocessing, feature extraction and pattern recognition. According to current documents, the heating voltage of sensor array, gas humidity and gas flow have an effect on the performance of this device. In order to study the effect of these control parameters on the performance of detection device, the ethylene and nitrogen gas were respectively selected as testing sample and carrier gas, and each of the control parameters was studied with single factor experiment. Then, according to the sensibility, response time, recovery time of sensor array, the optimal control parameters of this device were selected. Furthermore, the feasibility and performance of the bionic olfactory detection device were verified under optimized control parameters. The results of experiment showed that the sensitivity of the sensor array increased with the increase of heating voltage. When the heating voltage of sensor was 5.0 V, the sensibility of the sensor array was the maximum, which ranged from 2.260 to 4.823, and the response and recovery time of the sensor array were both the minimum, which ranged from 46 to 53 s and from 44 to 70 s, respectively. So when the heating voltage of sensor was 5.0 V, the detection device could get a better performance. When the humidity increased, the sensibility of the sensor array decreased, and the response time and recovery time of the sensor array were both lengthened. So, when the relative humidity of the gas was 30%, the detection device could get a better performance. The sensibility of the sensor array firstly increased and then decreased with the increment of the gas flow; the response time and recovery time of the sensor array firstly decreased and then increased with the increment of the flow. If the sensitivity, recovery time and recovery time of the sensor array were comprehensively considered, when the flow was 100 mL/min, the sensibility of the sensor array was the maximum, which ranged from 2.853 to 7.559, the response and the recovery time of the sensor array were the minimum, which ranged from 35 to 50 s and from 30 to 50 s, respectively. So, when the flow was 100 mL/min, the detection device could get a better performance. Therefore, when the heating voltage of sensor was 5.0 V, the relative humidity of the gas was 30%, and the flow was 100 mL/min, these control parameters were the optimal control parameters. The detection device adopted the optimized control parameters, and then the device was used to detect the ethylene gas with the volume fraction of 0.002%, 0.004%, 0.006%, 0.010%, 0.020%, 0.030%, 0.040% and 0.050%. The results showed that when the volume fraction was controlled in the range of 0.002%-0.020%, the sensibility of the device was higher, which ranged from 3 577.1 to 6 700.7, and the linearity and repeatability of the device were both better, whose coefficient of determination was from 0.901 to 0.997, and coefficient of variation ranged from 0.832% to 9.696%. So, the device can meet the requirements of odor detection, and also can provide data reference and technical support for the further research on the application of bionic olfaction.
2017, 33(8):259-266. DOI: 10.11975/j.issn.1002-6819.2017.08.035
Abstract:Abstract: With the development of information technologies and the improved consciousness of food safety, various agricultural product traceability systems have been developed and applied in China. Lack of data share between different systems has led to the decreasing of the credibility and analysis capacity. Therefore, establishing a collaborative traceability platform on the distributed environment is an urgent need to enhance the ability of unified traceability and collaborative analysis. Combining data from different business systems, a platform framework was constructed, which included 3 layers i.e. data integration, model analysis and application supply. Enterprise credit evaluation model was the important part in the model analysis layer. An evaluation index system with 4 factors and 14 sub-factors was designed. The index included enterprise qualification, quality inspection, product traceability, and consumer feedback. The evaluation factors' weight was confirmed using the AHP (analytic hierarchy process) method and the evaluation score was calculated with the weighted sum algorithm.. Multi-source heterogeneous data integration technology was researched based on ontology. It included 3 parts: Data format integration, semantic mapping and heterogeneous data analysis. Traceability information was described with five-factor knowledge ontology and expressed with OWL (Ontology Web Language). Layered dynamic tracing technology was implemented in order to trace different agro-food in a unified platform. In this part, there were 2 layers including basis information and extended information designed, and the dynamic mechanism of invoking the traceability data was developed according to the product features. Taking Tianjin City as an example, and using Microsoft Visual Studio 2010 as the system design and development tool, the united traceability platform of agro-food safety was developed. It provided traceability service for the consumer, which was production tracing, enterprise credit overview and production evaluation. The platform also provided data analysis function for the government, which was base registration statistics, farming process statistics, traceability barcodes print amount analysis, agro-food price analysis and enterprise credit evaluation. The ability of concurrent access and the retrospective effect were analyzed. The results showed that when the number of concurrent users reached 40, the average response time of a single transaction reached 19 s. The comparison of the platform and the other 4 traceability systems was performed. The results showed that this platform presented the features of multi-category tracing, tracing information diversity, and interactive features. In the future work, the platform performance will be optimized through the updated hardware and software. The decision support function will also be enhanced through developing the model on the accumulated data. The research achievements provide the beneficial support to improve the integration level of traceability information and analysis capacity of traceability results.
2017, 33(8):267-277. DOI: 10.11975/j.issn.1002-6819.2017.08.036
Abstract:Abstract: For the weak points of citrus huanglongbing (HLB) heat treatment by sunlight, such as long treatment period, low efficiency, serious dependence on natural condition, and large temperature difference in treatment enclosure, one citrus HLB hot air rapid treatment method was proposed. To solve the problem of large temperature difference in the heat treatment enclosure, an experimental platform was set up for analyzing the temperature field distribution characteristics of HLB hot air rapid treatment, which consisted of heat treatment enclosure, industrial hot air blower, paperless recorder and 12-channel temperature recorder. And the influence of air return duct existence or not, wind speed, hot air inlet position, outlet position, and inlet hot air temperature on the temperature field distribution of hot air treatment were investigated. The results showed that: (a) Return air duct had a significant impact on the cross section of middle and upper layer and the longitudinal section where the hot air inlet position existed in the enclosure, but had no significant effect on the cross section of lower layer and the longitudinal section where the hot air outlet position existed. When there was a air return duct, not only the uniformity was better in the enclosure, but also the energy consumption was lower than the condition without it. (b) Wind speed had a significant impact on each section in the heat treatment enclosure, and the average temperature of each section increased with the increase of wind speed. When the wind speed was 14.5 m/s, the uniformity of each section was better. (c) Hot air inlet position had a significant impact on each section in the heat treatment enclosure, and the uniformity of each section was better when the hot air inlet position was located at the lower layer of the enclosure. (d) Hot air outlet position had a significant impact on each section in the heat treatment enclosure, and the uniformity of each section was better when the hot air outlet position was located at the upper layer of the enclosure, which had a 90° angle with the inlet position. (e) Inlet hot air temperature had a significant impact on each section in the heat treatment enclosure, and the higher the inlet temperature, the faster the temperature rising in the heat treatment enclosure. When the uniformity and the rising speed of temperature in the enclosure were taken into consideration, 90 ℃ was the best temperature of inlet hot air. (f) The optimal parameters were that there was a return air duct, the wind speed was 14.5 m/s, the hot air inlet position was located at the lower layer of the enclosure, the hot air outlet position was located at the upper layer of the enclosure, which had a 90° angle with the inlet position, and the inlet hot air temperature was 90℃. Under the optimal parameters, the temperature in the treatment enclosure rising from 32 to 48 ℃ took about 9 min, and the temperature range of the whole enclosure was 3.9 ℃, which dropped by 14.1 ℃ compared to that under non-optimal parameters; and the temperature range of each section under the optimal parameters was also decreased. Under the optimal parameters, the effectiveness of rapid hot air treatment on the control of citrus HLB was proved, and the average reduction rate of bacteria concentration after treatment was 80.28%. The results provide a reference for the optimization design of large-scale HLB hot air treatment equipment.
2017, 33(8):278-285. DOI: 10.11975/j.issn.1002-6819.2017.08.037
Abstract:Abstract: To research the effect of low voltage electrostatic field (LVEF) assisted freezing-thawing on beef quality, using bovine longissimus dorsi as experimental materials, the beef quality of samples at the distance of 15, 30, 45 and 60 cm away from the electrostatic field generating plate (test group) and without LVEF treatment (control group) was studied during freezing-thawing process. The test group and the control group had the same freezing temperature of ?18 ℃ and thawing temperature of 4 ℃. The indices including freezing-thawing temperature curve, color, thawing loss, protein content of thawing drip, cooking loss, texture profiles were compared and analyzed. Scanning electron micrograph (SEM) and transmission electron microscope (TEM) were used to observe the microstructure of muscle, and the ice crystal morphology in muscle fiber tissue was observed under light microscope. During the process of freezing, the temperature curve showed that LVEF had accelerated the freezing process of beef samples, and the time used in the zone of the maximum ice crystal formation was shorter compared to the control group. Accordingly, the ice crystals in muscle fiber tissue were smaller and uniformly distributed under LVEF. From the thawing temperature curve, it was found that the thawing speed of treatment group was faster. After the process of thawing, several indices were determined. The result showed that LVEF could significantly increase lightness (L*) value, redness (a*) value, chroma (C) value, tenderness and chewiness (P<0.05). In addition, cooking loss, thawing loss and protein content of thawing drip were significantly decreased by LVEF (P<0.05). SEM and TEM showed that the muscle microstructures of control group and treatment group were both damaged after freezing-thawing process. The microstructure of muscle fiber bundles of control group was damaged more seriously, and more muscle fiber bundles were torn and a visibly larger gap was exhibited between muscle fibers, while the muscle microstructure of treatment sample was less damaged and the fiber bundles were relatively tight. Particularly, the samples at the distance of 30 cm away from the electrostatic field generating plate (LVEF30) required the shortest time to finish the process of freezing and thawing, and the time used in the zone of the maximum ice crystal formation was only 290 min, which was shortened by 66% compared with the control group. LVEF30 formed the smallest and most uniform ice crystals, and the muscle fiber tissue was less damaged by ice crystals. SEM showed that LVEF30 maintained the structure of muscle fibers and perimysium effectively, and the gap between muscle fibers had no obvious expansion. TEM showed that Z-disc and M-disc remained relatively intact and A-band and I-band were still clear and legible, which indicated that LVEF30 maintained the integrity of the myofibrillar structure effectively. The L* value, a* value and C value of LVEF30 were 39.47, 21.77 and 23.71 respectively, which were significantly higher than 31.74, 17.76 and 20.73 of the control group (P<0.05), and had no significant differences with the fresh meat (P>0.05). Thawing loss, protein content of thawing drip and cooking loss of LVEF30 were reduced 4.18, 8.28 and 0.7 percent points, respectively, compared to the control group, and the difference was also significant (P<0.05). The experimental results show that LVEF is able to alleviate the deterioration of beef quality during the freezing-thawing process and improve the quality of the thawed beef significantly, and the most suitable gauge for treatment group is 30 cm.
2017, 33(8):293-300. DOI: 10.11975/j.issn.1002-6819.2017.08.039
Abstract:Abstract: Flavor is an essential indicator to evaluate the quality of soymilk products, but the effects of heat treatment and β-cyclodextrin addition during soymilk processing on the entire flavor quality are not clear. In this study, the changes in the contents of critical soymilk flavor compounds during heat treatment (30-90 ℃) were investigated, and then the flavor profiles of soymilk with the addition of β-cyclodextrin (0.25%, 0.50%, 0.75%, 1.00%) at different heating periods (before heating, at 40℃, at 60 ℃, after heating) were analyzed. Results showed that, different flavor compounds varied in the sensitivity to temperature, and as the temperature increased during heat treatment, the intensity of beany flavor tended to decrease, whereas non-beany flavor was relatively enhanced. β-cyclodextrin addition could decrease the contents of critical soymilk flavor compounds, and a high concentration of β-cyclodextrin (≥0.50%) added at 60 ℃ led to the most significant decrease in the contents of critical beany flavor compounds including hexanal, hexanol, 1-octen-3-ol (P＜0.05), but trans-2-octenal, as the critical non-beany flavor compound, also suffered the greatest loss. Similar tendency was obtained according to the scores of beany odor, mushroom flavor, and sweet aroma by sensory evaluation, and the results of comprehensive scoring indicated that, the soymilk with the addition of 0.75% β-cyclodextrin at 60 ℃ during heat treatment had the best flavor quality. Since β-cyclodextrin is low-priced and safe, and the addition during soymilk processing is also easily practiced, it can be well applied in soymilk production for the improvement of flavor quality.
2017, 33(8):301-308. DOI: 10.11975/j.issn.1002-6819.2017.08.040
Abstract:Abstract: Blueberry has a very rich source of bioactive compounds, including vitamin C and E, and phenolic compounds (anthocyanins). Many studies indicated that anthocyanins are beneficial to human health by reducing the risk of cardiovascular disease and improving vision. However, anthocyanins have a poor stability. Microencapsulation is an effective and promising method to prevent the degradation of functional ingredients. In order to explore the effect of storage time and temperature on the quality of blueberry anthocyanin microcapsules, and find out the appropriate storage conditions, quality evolution of microcapsules stored for 6 months under ?18, 4 and 25 ℃ was investigated respectively. The results revealed that there were no significant differences in water activity, hygroscopicity and encapsulation efficiency of encapsulated powders during the storage (P>0.05), which meant that anthocyanins were coated successfully in microcapsules using protein-polysaccharide as wall material. However, with the increase of storage time, the caking degree showed a gradual increasing trend (P<0.05), although the differences under different temperatures were insignificant (P>0.05). It was also found that the glass transition temperature decreased during the storage. One of the most remarkable things was that there was a sharp decrease in the glass transition temperature of anthocyanins stored for more than 4 months. During the storage, the total anthocyanins and total phenolics of microcapsules showed a decreasing trend (P<0.05), while the latter declined less. Storage under ?18 ℃ could increase the stability of anthocyanins and total phenolics obviously (P<0.05). It needed to be emphasized that the presence of whey proteins may improve the stability of malvidin-3-glucoside. Scanning electron microscopic images of encapsulated powders showed that particle size increased gradually due to the glass transition temperature declining. This led to antioxidant capacities, measured by ABTS radical scavenging assay and ferric iron reducing antioxidant power, decreased significantly (P<0.05). The peak intensity at 1 637, 1 508 and 1 030 cm?1 was weakened, which was associated with the possible weakening of the interactions between core and wall materials as well as the interactions among wall materials. Moreover, with the extension of storage time, encapsulation productivity of encapsulated powder and its release rate in water decreased gradually (P<0.05), and the encapsulated powder stored under ?18 ℃ had a higher encapsulation productivity and release rate in water than others (P<0.05). It could be due to that low temperature inhibited the weakening of intermolecular force. In addition, there existed an interaction effect of storage time and temperature on glass transition temperature, encapsulation productivity, release rate in water, value of ABTS and content of monomeric anthocyanins including malvidin-3-glucoside, peonidin-3-glucoside together with cyaniding-3-O-glucoside. Compared with the storage time, storage temperature was a less important factor affecting the stability of blueberry anthocyanin microcapsules. In general, whey protein isolate, maltodextrin, β-cyclodextrin and gum arabic are combined as wall materials, for encapsulation can benefit blueberry anthocyanins through alleviating their quality decrease during the storage. Moreover, the weakened interaction force between the molecules possibly causes a decline in the quality of blueberry anthocyanins during the storage. The suitable storage time and temperature are 3 months and -18 oC, respectively. This research provides the theoretical basis for the application of blueberry anthocyanin encapsulates.
2017, 33(8):309-314. DOI: 10.11975/j.issn.1002-6819.2017.08.041
Abstract:Abstract: Lycium barbarum L., which is well known as one of the traditional Chinese medicines, is mainly cultivated in Northwest China. Due to its delicious taste and nutritional value, its consumption demands are increasing tremendously worldwide. It brings great economic benefit for the local community. But Lycium barbarum L. is highly perishable, which makes it have a short storage period. And dried Lycium barbarum L. becomes a core product of Lycium barbarum L.. However, single product is difficult to satisfy the demands of modern consumers. In order to increase the variety of Lycium barbarum L. products and further promote the profitability of Lycium barbarum L., a new processing technology of Lycium barbarum L. suitable for industrial production was developed and optimized in this study. The processing technology was mainly based on the Maillard reaction principle. High temperature and high humidity conditions were 2 key parameters of the processing technology. During the processing, fresh Lycium barbarum L. was processed into black cooked Lycium barbarum L. in high temperature and high humidity conditions. The processing technology was composed of 3 stages: The pre-dewatering treatment stage, the cooking treatment stage and the final forming treatment stage. First, Lycium barbarum L. was dried at 4 different temperatures (50, 55, 60 and 65 ℃) at the first stage. The effects of temperature and drying time on moisture content and damage rate of Lycium barbarum L. were evaluated comprehensively. Then, the Lycium barbarum L. after pre-dewatering treatment was cooked under constant temperature of 65, 70 and 80 ℃ and relative humidity of 65%. And the product quality was evaluated through reducing sugar content, amino acid nitrogen content and color of cooked Lycium barbarum L.. At last, the cooked Lycium barbarum L. was dried at 45 ℃ respectively for 4, 6 and 8 h in order to gain the product with the best sensory quality. Experimental results under the first stage showed that the drying temperature should not be too high. High drying temperature would lead to higher damage rate of Lycium barbarum L.. In contrast, the temperature should be higher at the cooking treatment stage. High temperature was benefit to Maillard reaction. Through researching, the three-phase-drying method for the cooked Lycium barbarum L. was found. The temperatures for the pre-dewatering treatment, the cooking treatment and the final forming treatment were 60, 80 and 45 ℃, respectively. The processing time was 12, 24 and 6 h, respectively. And the humidity of the cooking treatment stage should be held within 65%. The cooked Lycium barbarum L. had a color from red to black brown and a sweet and sour taste. And its antioxidant activity was better than the normal dried Lycium barbarum. The reducing power, and ·OH and DPPH (1,1-diphenyl-2-picryl-hydrazyl) radical scavenging activities of the cooked Lycium barbarum L. were about 1.87, 1.45 and 2.21 times that of the normal dried production. The study provides a valuable and useful method for the development and utilization of Lycium barbarum L..