Abstract:In order to satisfy the tractor speed and power requirements under various operation conditions, the control and interaction system of tractor hydro-mechanical CVT was studied. The principle of power split mechanism and infinite speed variation of a new kind of hydro-mechanical CVT were introduced. And the control method of infinite speed variation and load adaptive adjustment were analyzed. On the one hand, a point-to-point control method was studied through dividing the range of speed ratio into 96 work points, and building the mapping between work point and the actuators such as the exciting voltage of pump, the electromagnetic valve for pump flow direction control, and the electromagnetic valve for clutch control, the controller described the mapping as a control table to realize the infinite speed variation and power shift. On the other hand, based on the target of engine power control, an automatic speed ratio control strategy was proposed to follow the change of load and the corresponding fuzzy control table was acquired. The interaction system and control unit of tractor hydromechanical CVT were designed for further research. Finally, based on the presented control system, some key experiments such as tractor acceleration and load adaptive speed ratio adjustment were made. The test of acceleration showed that there was a stationary process for speed ratio adjustment with algorithm of point-to-point control under different work conditions due to the open loop control method. The test of load adaptive speed ratio adjustment showed that the speed ratio was quickly changed under different load levels to maintain the constant of engine power because of the closed loop control method. Results showed that the designed control system was reliable and the proposed algorithm was correct.

Abstract:Two-wheel drive electric tractor has several advantages, including simple structure and electrically differential and flexible manipulation in narrowly closed working environment, and it enables us to make full use of adhesion and improve adhesion utilization and dynamic performance. The overall structure program of two-wheel drive electric tractor was proposed which adopted two 5kW drive motors. Electric drag traction performance was analyzed from both electric tractor load stress and traction efficiency aspects. Matching analysis of transmission components was also put forward based on force balance equation of electric tractor cultivation operation. Tests on traction performance, load startup and transportation conditions were done in the built electric tractor driving test platform. According to the result, the proposed electric tractor torque reached 1800N·m, which can meet the need of deeper tillage operations. With load started, driving torque value was increased from 700N·m to 1600N·m and speed was increased from 0 to 7km/h, which spent about 1.1s. As for transport experiments, when transported goods were weighed 1710kg, the speed reached 6.5km/h.

Abstract:Aiming at the characteristics of parameter perturbations and the effect of disturbance outside in agricultural tracked robot control system, a self-adaptive fuzzy sliding mode control was proposed based on fuzzy logic theory to improve the control precision and stability, which combined sliding mode control with fuzzy theory. Firstly, the motion equation of agricultural tracked robot was derived and analyzed. Secondly, an integral sliding mode surface was proposed, and an adaptive fuzzy sliding mode control was designed based on equivalent efficiency control and switching control, which held the celerity and robustness of sliding mode control and also weakened the buffeting very well. The simulation and test results showed that compared with conventional sliding mode control method, the proposed control possessed the advantages of good adaptability and robustness to outside disturbances and parameter uncertainty, and also had fast dynamic response and well tracking performance, which was feasible for agricultural tracked robot controlling system.

Abstract:During the working process of press roller, the deficiencies in the soil adhesion and the large slip rate on the profiling elastic press roller are existed. Based on the flexible geometry features of the typical soil animal body surface, the reducing soil adhesion and anti-slip structure were designed to solve the problem. The structure consists of rubber bulges, which are fixed by the existing bionic rib structure. This structure has the advantages of less soil adhesion, lower slip rate, more uniform pressure distribution and better soil crushing effect. The movement process of the reducing soil adhesion and anti-slip structure was researched by using theoretical calculation and kinematics analysis, the characteristic equation of rubber bulges and the value ranges of bulge height and rib height were obtained. The orthogonal combination experiments of three factors and three levels were designed and performed. The results showed that the primacy sequence of the experiment factors influencing soil adhesion was: rubber bulge height (H), rib height (L), total loads (F) and the primacy sequence of the experiment factors influencing slip rate was: rib height, rubber bulge height and total loads. Optimal levels of the experiment factors influencing soil adhesion and slip rate were F of 450.0N, H of 13.9mm, L of 15.1mm. At the same time, verification tests and comparison tests were conducted in the field. The results showed the soil adhesion quality was 39.2g, the slip rate was 3.89%, compared with the roller without the reducing soil adhesion and anti-slip structure, the soil adhesion quality was reduced by 60.1% and the slip rate was reduced by 54.3%.

Abstract:Considering the deficiencies in uneven soil compaction and the too long vertical size that exists in the soybean tillage sowing machine during conservation tillage, the profiling elastic press roller which adopts the elastic spoke structure was designed. The main structure parameters of the press roller were determined through theoretical analysis, which means diameter D of 450mm, breadth B of 210mm and number of spokes n of 12. The work process of the roller was simulated by using the ADAMS software, at the same time, orthogonal tests of L9(34) were performed in an indoor soil bin with moisture content (dry basis) of 20%. The effects of spring stiffness coefficient (k), total loads (F), operation speed (v) and soil compactness (P) on pressure fluctuation were determined. The optimum ranges of each factor were determined through the ADAMS motion simulation. The results of orthogonal tests showed the primacy sequence of the experiment factors were total loads, spring stiffness coefficient, soil compactness, the operation speed, and optimal levels of the experiment factors were F of 800N,k of 5N/mm,P of 15kPa and v of 0.5m/s. The simulation results are in good agreement with the experimental results in the pressure fluctuations. Under the condition of a certain inclination angle on the ridge surface, the profiling elastic press roller can better ensure uniformity of soil compaction than that of conventional roller.

Abstract:A new kind of 2-DOF clamp-type manipulator was developed relying on the feature and principle of 2-DOF manipulator for automatically pulling up and transplanting multiple cell-tray potted-seedlings. The characteristics of operating targets, main structure and control circuit of the manipulator were described. The key component of seedling clamp mechanism was designed, and 3D structure model was established and virtually assembled by using Pro/E. Dynamics simulation to the seedling clamp mechanism ensured the reliability of its opening and closing process. Preliminary performance experiment was conducted on a program controlled prototype platform. Four related factors were considered, including the type of cell-tray, moisture of soil ball, extending force of clip’s spring and feeding mode of cell-tray. And the effect of above factors on the evaluate index of successful pulling up rate of the manipulator was analyzed. Results showed that type of cell-tray and moisture of soil ball both had very significant effects on successful pulling up rate (P<0.01), while no significant difference for both extending force of clip’s spring (15,22N) and feeding mode of cell-tray (P>0.05). When the extending force of clip’s spring and feeding mode of cell-tray were unchanged, cultivating the potted-seedlings by using red tray or maintaining moisture of soil ball of potted-seedling above 30% can increase successful pulling up rate. And the performance of seedlings automatic transporting and feeding mechanism can meet the requirements of transporting and feeding cell-tray potted-seedlings row-by-row. The results provide a useful reference for subsequent optimization on manipulator’s performance.

Abstract:The mechanical work such as weeding, spraying and fertilization requires the chassis should move along the crops’ row spacing. Since the row spacing of different crops is various and the row spacing of the same crop in different regions or by different planted methods are also not uniform, there are some problems such as poor flexibility, difficult passing ability, and tendency to destroy the crops when the existing agricultural vehicles running. So the agricultural chassis’ wheel track should be adjustable basing on the different crop spacings, during which the steering must be difficult. At present, steering has been solved by hydraulic drive, servo control the turning wheel, or servo motor control the turning wheel, which are more complicated. According to the demand for the chassis’ adjustable wheel track varying with different row spacings, the linkage principle of wheel track and steering was researched. Based on the Ackerman steering and parallelogram mechanism，the steering mechanism with adjustable wheel track was proposed in which the wheel track adjustment and steering can be completed independently and simultaneously, and the calculation method of key parameters and steering error were ascertained. A kind of agricultural chassis with adjustable wheel track was designed which included steering mechanism with adjustable wheel track on front bridge, adjustable wheel track mechanism and driving system on rear bridge. Basing on the characteristic of mechanism movement and the criterion of mechanical design, considering the present related chassis and the crop planting mode of China, the key parameters of the chassis has been determined. And the key parameters of steering mechanism with adjustable wheel track on front bridge were determined and optimized by taking minimum wheel track as basic wheel track. The steering error calculation results in different wheel tracks showed that the chassis’adjustable wheel track and steering performance could meet the agricultural needs.

Abstract:The low head pump system, mainly axial-flow pump system research and technological innovation in China are introduced. The research and development trend on hydraulic performance of the axial flow pump system are discussed. The applications of high speed axial-flow pump hydraulic model and development progress are presented. Through inductive characteristics of axial-flow pump system, the classification of the system is put forward according to the installation position of the motor，namely the shaft extension type axial-flow pump system and the tubular axial-flow pump system. The innovation applying of the different types of axial-flow pump systems in a quantity pumping station projects is introduced respectively. From the perspective of technological development, the development trends and application prospects of axial-flow pump system are analyzed. The limitations of the traditional pump selection method are discussed, and the applicable rationality of a new method of pump selection for the axial-flow pump system is introduced. The variable angle adjustment formula and applicability based on the test data of axial-flow pump system are introduced. The harmfulness to the pump units from the intake vortex and the safety policies are analyzed. The research results of the vortices in the pump sump and the measures of vortices prevention and elimination are described. As regarding the real and potential problems in research development on axial-flow pump system, the suggestions for further deepen researches are presented. Although the hydraulic performance of axial flow pump system research has reached a higher level, but possibility of partial breakthroughs still exists. The future research direction of pump system should be more to the structural optimization, the pump system reliability and adaptability, vibration and noise, and run quality promotion.

Abstract:In order to analyze the flow influence mechanism of axial-flow pump on the siphon outlet passage, the three-dimensional internal flow of an axial-flow pumping system with siphon outlet passage was simulated based on CFD method under different running conditions. The relationship between guide vane outlet velocity circulation and flow rate had obvious influence on hydraulic loss and internal flow field of siphon outlet passage. The flow field characteristics of siphon outlet passage were analyzed qualitatively, and the mathematical relationship between them was analyzed quantitatively. The research results indicated that there was great difference between internal flow field of siphon outlet passage under different running conditions, and the hydraulic loss of siphon outlet passage was mainly concentrated on flow passage before hump section. The average value of velocity-weighted average swirl angle was 52.34°, and it had small fluctuation in the flow coefficient range of 0.35~0.70 for hump section. With the increase of flow coefficient, the axial velocity distribution uniformity of hump section increased gradually, while the guide vane outlet velocity circulation decreased firstly and then increased, and the minimum velocity circulation was in the high efficiency area. Guide vane outlet velocity circulation made the relationship of hydraulic loss of siphon outlet passage and flow rate more complicated, and there was no quadratic regression relationship between hydraulic loss and flow rate. These study results were available reference for design optimization of siphon outlet passage.

Abstract:A series of pressure fluctuation and vibration acceleration were measured at the key monitoring points under the speeds of 1450, 1200, 1000r/min, and their correlations were discussed. The experimental results showed that the peak to peak values of the pressure fluctuation didn’t obey the pump similarity law. The pressure fluctuation patterns were different under different rotating speeds. The maximum peak-to-peak value moved from the impeller inlet to the guide vane outlet with the rotating speed increased. The main frequency at impeller inlet was the blade passing frequency (BPF) under different rotating speeds, and the main frequency in impeller outlet and guide vane outlet were slightly lower than the blade passing frequency with rotating speed increased. The amplitude at the impeller outlet was increased firstly, and then decreased, while it was always increased at the guide vane outlet with rotating speed increased. The vibrations at different positions in the model pump mainly included shaft frequency which was induced by mass unbalance of rotor system and the low frequency induced by the unsteady fluid in pump. In the frequency ranged from about 0 to 2 times，the pressure pulsation and vibration tendency was substantially the same, and the speed variations had a similar effect on both of them. There were main 1~4 times rotation frequencies in pressure fluctuation frequency domain at different monitoring points, which were changed under different rotating speeds, while only 1 and 2 times of shaft rotation frequency played the main role in the vibration frequency domain at different monitoring locations.

Abstract:Numerical simulations based on CFD had been performed by the IS150—125—315 singl-stage single-suction centrifugal pump. The numerical results showed a good agreement with the experimental measurements. The performance, i.e., head, efficiency and shaft power of pump were studied under five balance hole diameters. For each of the diameter, the spatial distribution law of balance cavity pressure was researched. The influence of holes diameter on shroud force was analyzed and the relation curve p-=f(k-) was further drew. The results showed that the head had no relation with balance hole diameter when the flow rate was larger than design flow condition. After balance hole diameter increased to a certain value, shaft power was obviously increased and the efficiency was reduced at the same flow condition. The differential pressure of centrifugal pump without balance holes is larger than that with balance holes at the same massflow. Balance cavity pressure of the holes with the same diameter increased along radial direction from pump shaft to seal ring, while the change of its value was negligible along axial and tangential directions. In the region where the radius was less than the vertical distance between balance holes center and pump shaft center, a smaller diameter of balance cavity made the pressure approach zero. Out of this radius, the pressure increased as the balance hole diameter increased. When k-≥2.645, the shroud force on the balance cavity almost achieved balance.

Abstract:To improve the efficiency of residual heat removal pump, 35 impellers, whose design variables are the radius of shroud arc, radius of hub arc, angle of shroud and angle of hub, were designed by Latin hypercube sampling method. 3D steady simulation was conducted to get the efficiency under designed flow rate by ANSYS CFX 14.5 software. A radial basis neural network was used to build the approximation model between efficiency and design variables. Finally, the best combination of the design variables was obtained by solving the approximation model with genetic algorithm. The results showed that performance curve simulated by CFD had a good agreement with that of experiment. The deviations of efficiency and head between numerical result and experimental result were -2.1% and -3.7%, respectively. Compared the efficiency predicted by CFD with that predicted by radial basis neural network, the deviation was only 0.02%, thus the radial basis neural network can predict the efficiency under design condition accurately. The efficiency of the optimal pump was 76.75% and the optimization made an increase in efficiency by a percentage of 6.18. The optimization improved the velocity and turbulence kinetic energy distributions in the impeller. The vortexes disappeared and the velocity became uniform at the shroud. Thus, the optimization process for the impeller meridional shape was practical.

Abstract:The pressure pulsation in double-suction centrifugal pump is one of the key factors affecting the stability of pump unit operation. In order to reduce the pressure pulsation, the main causes of pressure pulsations in double-suction centrifugal pump were analyzed. The effects of blade loading curves on flow patterns in pumps were investigated. The relations between blade loading, blade outlet obliquity, staggered angle and the flow features including secondary flow and pressure pulsation were established. A new impeller design method with alternate loading was proposed. In the new design method, the main loading point on shroud located at the front of blade loading curve, and the main loading point on hub located at the rear of its curve. The impeller designed by this method was in the type of staggered arrangement in circumferential direction. The blade outlet edge was tilted forward, and the wrap angle difference between shroud and hub was very small. The field test on a large irrigation pumping station showed that the dominant frequency of pressure pulsations in the double-suction centrifugal pump designed by using this method was reduced significantly. The optimum efficiency and high-efficiency-range of the pump were also improved. This method could be used as a new approach to design/redesign double-suction centrifugal pumps with large power.

Abstract:Pressure fluctuations inside centrifugal pump, especially those near the volute tongue, are the primary excitations to pump vibration and noise. The performance and pressure fluctuations of a centrifugal pump running at different flow rates and variable speeds were experimentally studied. The pump performance measurement showed that the pump worked at low flow rate condition, and the pump hydraulic performance varied with the rotational speed according to one-dimensional design theory. The pressure fluctuation measurement showed that discrete components were the main contributions in the pressure fluctuation spectra, especially the blade passing frequency (BPF) and its second harmonic. The overall strength of pressure fluctuation was approximately 1% of the reference dynamic pressure, and it varied in a quadratic function form with rotary speed. At a constant rotation speed, the pressure fluctuation magnitude at the outlet side of volute tongue had no obvious change with the decrease of flow rate, but places at the inner side and tongue tip experienced noticeable increase at sufficiently low flow rates owing to the pressure fluctuations below BPF. The study provided a basis for future study of flow-induced pump vibration and noise.

Abstract:A special testing apparatus was designed for measure and calculation of fluid leakage in flow passage of pump chamber. Gap-diameter ratio was changed by changing axial position of the impeller, i.e., changing the axial clearance of the pump chamber, when gap of wear-ring was 0.2mm and 0.3mm,respectively, and length of wearring was 15mm, the import and export liquid pressure and fluid leakage in flow passage of pump chamber (gap-diameter ratio was 0.127, 0.101, 0.076, 0.051, 0.025 and 0.006, respectively) were tested and analyzed. The curves of leakage coefficient and pressure coefficient were obtained under different gapdiameter ratios conditions. In addition, the curves of velocity coefficient and gapdiameter ratio with different pressure coefficients were provided by calculating the experimental data. Results showed that under different gap-diameter ratios, fluid leakage coefficient and pressure coefficient in flow passage of pump chamber varied regularly, their relation curves were almost oblique lines, but gapdiameter ratio and gap of wearring can significantly affect curves. When the structure of pump was constant, decrease of axial clearance of pump chamber can effectively reduce fluid leakage, thus the volume efficiency of pump can be increased, and the optimum value range of axial clearance of pump chamber was 1~5mm. Computational formula of fluid leakage in flow passage of pump chamber and determination method of velocity coefficient were presented. This study is of great significance to the volume efficiency of pump, wheel resistance loss, liquid pressure distribution in pump chamber and the calculation of axial thrust.

Abstract:The use of sewage effluent subjected to proper treatment for agricultural irrigation has been increasingly considered as a supplemental source of freshwater in many countries where a shortage of potable water is current reality. However, concern exists over the pollution risk due to the toxic accumulation from sewage effluent, which is the main restraint on the application of sewage effluent irrigation. Extensive researches on system stability, environmental sustainability, and efficient control are highly necessary to ensure the efficient and safe use of sewage effluent for agricultural irrigation. The effects of sewage effluent application on drip emitters, irrigation system, environments and agricultural products were reviewed. The behaviors and interaction between nutrients, salts, microorganisms and typical pollutants were summarized. Several theoretical and technical issues that need to be further studied, including the micro mechanism and macro behaviors of the influences of sewage application on irrigation system performance, the dynamics process of environmental changes imposed by sewage irrigation, the effects of sewage application on nutrient uptake and utilization, and efficiently safe control mechanisms of sewage irrigation, were prospected. Expected researches on these issues can add new knowledge to the regulation theory of water, nutrients and salts for irrigation and it will be a contribution to enhancing the efficiency and safty of use of sewage effluent for agricultural irrigation.

Abstract:The long-time excessive application of N fertilizer caused detrimental effects on soil and groundwater environment in North China Plain (NCP). Therefore, the reasonable water and N managements are essential for the sustainable agricultural production in this region. A two-year field experiment (2010—2011) was carried out in the wheat—maize rotation cropping field at Tongzhou Experimental Base for Water-saving Irrigation Research (TEB), Chinese Academy of Sciences, Tongzhou District, Beijing, China. The collected data in the experiment was used to calibrate and validate the hydrologic, nitrogen and crop growth components of the root zone water quality model (RZWQM). And the validated RZWQM was used to evaluate N fertilizer and water management practices in wheat—maize rotation cropping system under sprinkler irrigation system in NCP. The validation results showed that the RMSE (root mean square errors) and MRE(mean relative error) for soil water content ranged from 0.015cm3/cm3 to 0.026cm3/cm3 and from -6.66% to 5.83%, respectively. The simulated soil water storage was close to the measured ones. The relative errors (RE) of measured and predicted crops yields and N uptakes of winter wheat and maize were generally less than 25%. The RZWQM was used to simulate the dynamics of soil water and nitrogen in the wheat—maize rotation cropping system under different irrigation interval when N application was the same to local N management (330kg/hm2). Results showed that the crop yields were higher, however, NO3-N leaching and mean N losses were less at irrigation interval with accumulated pan evaporation of 30~70mm than those at irrigation interval with pan evaporation of 90~110mm. Therefore, sprinkler irrigation interval with pan evaporation of 30~70mm was recommended in wheat—maize rotation system in NCP.

Abstract:In order to improve the utilization rates of water and fertilizer and reduce the loss of nitrogen fertilizer and deep seepage under bubbled-root irrigation, the change features of soil wetted body as well as the water and nitrogen movement characteristics with different fertilizer solution concentrations were studied. The relation between the cumulative infiltration volume and transportation distance of wetting front with the change of solution concentration was presented. Besides, the empirical models for cumulative infiltration volume and wetting front transportation distance were established under bubbled-root irrigation; the impact of fertilizer solution concentration on the distribution laws of NO-3N and NH+4N content within the scope of infiltration depth was analyzed. The results of the experiment showed that when the liquid concentration was increased, the cumulative infiltration in unit area was increased with time, and both infiltration amount and wetting front transportation distance showed remarkable power function relationship with infiltration time. The determination coefficients were up to 0.98 and 0.96, respectively, which were greater than the critical correlation index (0.6055); in the redistribution of infiltration, the liquid concentration of 41.7g/L could guarantee better water absorption of jujube root, the influences of different concentrations of nitrogen on conversion rate of soil were different, the conversion rate of nitrate nitrogen was not significant, and the conversion rate of ammonium nitrogen of 33.3g/L was the highest.

Abstract:In order to explore the relationships between jujube tree transpiration and soil moisture in semi-arid loess hilly area, soil moisture and jujube tree sap flow were monitored for three consecutive years. Results showed that temporal and spatial variability of soil moisture were significant. Soil moisture increased with the increase of soil depth but its coefficient of variation decreased gradually in the vertical direction. According to the variation of soil moisture, soil depth was divided into three layers from top to bottom: soil moisture changing layer (0~2.6m), dried soil layer (2.6~6.0m) and soil moisture recovery layer (6.0~10.0m). Parameters of jujube tree sap flow were significantly different between growth period and dormant period, therefore, the growth period of jujube tree could be demarcated more accurately. The growth period divided based on sap flow characteristics lasted about 160d, which was similar to that determined by sprout and defoliation observation method, but it started and ended nearly 5d in advance. The increase of soil moisture led to forward of minimum values and delay of maximum values of jujube tree sap flow, the “lunch break” time was shortened, but the transpiration time was strongly prolonged, and vice versa. Jujube tree sap flow increased at the early growth stage, and the positive correlation between transpiration and soil moisture were significant at the middle and late growth stages.

Abstract:In order to analyze the effect of straw mulching on changing characteristics of soil moisture during seasonal freeze-thaw period, Harbin City was selected as the objective study area, and soil liquid volumetric moisture content at different soil depths (i.e. 20, 40, 60, 100, 140, 180cm) was measured in the field under straw mulching thicknesses of 5, 10 and 15cm in winter, and bare soil was taken as control. Meanwhile, the meteorological data was obtained from automatic meteorological station in the study area. The results showed that straw mulching thickness can retard the temporal inflection point of increasing or decreasing of soil volumetric moisture content between 0cm and 60cm soil depth, the retard effectiveness was more obvious with thicker straw mulching, and the retard effectiveness was more obvious in freezing period than that in thawing period. The snowmelt infiltration was prevented by the straw mulching at the beginning of thawing period, thus the liquid volumetric moisture content appeared temporary peak value at soil depth of 20, 40 and 60cm under the condition of bare soil. However, the liquid volumetric moisture content was lower in bare soil treatment than that in other three treatments due to straw mulching at the end of thawing period. The straw mulching could effectively adjust and remain the liquid volumetric moisture content at soil depth of 0~60cm during freeze-thaw period, meanwhile, the adjustment effectiveness was weakened with the increase of soil depth. Both snowmelt and straw mulching can effectively increase soil moisture, but the increasing capability of soil moisture decreased with increasing soil depth. The order of the increasing capability of soil moisture at soil depth of 0~60cm was 15, 10 and 5cm thickness of mulching straw.

Abstract:Irrigation uniformity is one of the most important indicators of drip irrigation system, and clogging is perhaps the most common factor which affects the uniformity. In order to evaluate the influence of clogged emitters on the irrigation uniformity and the growth of crops during the operational process of drip irrigation system, the concept and computational method of location distribution uniformity of clogged emitters were set up based on the Christiansen uniformity, and then a new computational method of drip irrigation uniformity was proposed by using the arithmetic mean of the location distribution uniformity of clogged emitters and the flux uniformity of emitters, finally a comparison between several types of computational method of uniformity in a lateral and a subunit was made. The results showed that both the drip irrigation uniformity which considered the location distribution of clogged emitters and the Christiansen uniformity can reflect the influence of the amount of clogged emitter and the level of clogging on irrigation uniformity. In the meanwhile, the proposed method can also reflect the influence of location distribution of clogged emitters on the irrigation uniformity and overcome the weakness of Christiansen uniformity which only considered the influence of flow deviation. 

Abstract:Soil shrinkage curves of different depths in slope disintegration profiles were measured using soil shrinkage tester (SS—1 type) to investigate the spatial variability of soil shrinkage characteristics. Results showed that in the process of dehydration, soil linear shrinkage ratio displayed increase firstly and then attained to steady level. The relationship between linear shrinkage ratio and water content can be fitted well by the Logistic model. Soil shrinkage curves of red soil layer and speckle soil layer could be apparently divided into three stages. The variation rate in soil linear shrinkage ratio showed an unimodal trend with the decreasing of soil water content, which was not suited to that of sandy soil layer. Linear shrinkage ratio increased when soil texture changed to heavy. Significant difference was found in shrinkage characteristic between different layers of slope disintegration body. Radial shrinkage strain was larger than axial shrinkage strain for red soil layer and speckle soil layer but it was opposite for sandy soil layer, which indicated that horizontal cracks mainly occurred in surface layer during the soil dryness dynamic process. Correlation analysis showed that radial shrinkage strain was positively correlated with sand content (r=-0.933); volume shrinkage strain and shrinkage limit were significantly correlated with clay content positively (r=0.891) and sand content negatively (r=-0.838), which indicated that soil shrinkage process was influenced by both soil texture and soil water state. Measures could be taken to reduce drastic variation of soil water content to prevent damage from shrinkage behavior in slope stability.

Abstract:A field experiment was conducted in order to evaluate the effects of soil amendments on soil air permeability under plastic mulching condition. The results showed that soil texture kept slight changes after applying soil amendments; however, it resulted in significant decrease of soil bulk density and increase of saturated water content and field capacity. Although plastic sheet mulch was helpful for soil water storage and heat preservation, it prevented air exchange at soil-atmosphere interface which led to decrease of soil air permeability. Meanwhile, soil structure and physical properties were improved through the application of soil amendments, resulting in clear air flow in soil pores, which led to increase of soil air permeability. Furthermore, the improvement of three types of soil amendment on soil air permeability were ranked in the order of phosphogypsum (PG) > polyacrylamide (PAM) > Handilong. As for PAM and Handilong treatments, high application rate had better effect on soil air permeability than that of low application rate. As for PG treatment, the value of soil air permeability under high application rate was 1.12 times as high as that under low application rate, and moderate and low application rates had similar effects on soil air permeability. The results indicated that soil amendments could obviously improve soil air permeability, which certainly provided new methods for improving soil air permeability during field crops growth.

Abstract:A real-time soil moisture measurement method on line scale was proposed and a real-time detection of plant root zone soil moisture information sensing system based on frequency domain oscillometry was designed. The system consisted of soil moisture sensor, PVC casing, electric traction system and controller. The sensor was reciprocated in the casing which was dragged by motors, and it can obtain 240cm real-time soil volumetric water content information. The dynamic response time of sensor was 32ms, standard deviation of stability test was 0.0061V, determination coefficient between measured results and TDR was 0.989, and the requirement of the soil moisture measurement was satisfied. The results of field tests showed that the mean squared error compared with that of BD-III soil moisture sensors based on SWR (accuracy of ±2%) which were buried 10cm apart and paralleled to the sensing system was less than 0.5% when the sensing system was buried under the ground of 30cm. The measured data can reflect the volumetric water content of plant root zone under different rainfall conditions and verify the effectiveness of the system. 

Abstract:Ephemeral gully is widespread on the hilly Loess Plateau of China. A better understanding of the spatial variability in soil cohesion across the ephemeral gully will improve understanding of ephemeral gully erosion. However, quantitative research about the spatial heterogeneity of soil cohesion is quite few. The study was conducted to investigate and predict the spatial variation of soil cohesion in an ephemeral gully of hilly Loess Plateau by using classical linear regression and state-space methodologies. The results showed that soil cohesion had a moderate variation, and it was considerably influenced by elevation, clay content, sand content and bulk density. The autocorrelation functions for above-mentioned five variables were sufficient to identify their spatial representatives. The cross-correlation functions showed a strong spatial dependence between soil cohesion and elevation, clay content, sand content and bulk density. All the derived state-space models described the spatial variation of soil cohesion better than that of the equivalent linear regression models. The best state-space models based on clay content can explain 97.2% of the soil cohesion variation. Thus, state-space model was recommended as a useful tool to predict soil cohesion in ephemeral gullies of the hilly Loess Plateau. Furthermore, the result can provide valuable data base for setting up soil erosion model.

Abstract:The aim of this study was to investigate the influence of pyrolysis temperature on the physic-chemical properties of biochar, and the effect of biochar addition on carbon contents of soil organic matter fractions and carbon mineralization characteristics. Biochars were produced by fast pyrolysis of apple tree twigs at 300, 400, 500 and 600℃, respectively. Characterizations of biochars were determined by elemental analysis, Brunauer—Emmett—Teller (BET) for surface area, scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy. Four kinds of biochar were added to soils at five application rates as soil only (control), soil+0.5% biochar, soil+1% biochar, soil+2% biochar and soil+3% biochar, which were incubated at 25℃ in lab. Carbon mineralization was analyzed by alkali absorption of CO2 released periodically over 180d. Soil samples were analyzed for microbial biomass carbon (MBC) and soil dissolved organic carbon (DOC). The results showed that the generated biochars contained 62.20%~80.01% of carbon (C), 2.72%~5.18% of hydrogen (H) and 15.99%~30.94% of oxygen (O). The BET surface area was 2.35~107.76m2/g, basic functional groups were 0.11~0.40mmol/g and acidic functional groups were 0.44~1.16mmol/g. The increasing temperature (from 300℃ to 600℃) increased biochar C content, BET surface area and basic functional groups, while decreased the content of O and H, H/C and O/C ratio, acidic functional groups and total functional groups. Soil respiration, MBC and DOC were increased by biochar application. As pyrolysis temperature increased and biochar application rate decreased, soil respiration, MBC and DOC decreased in all soils. The mineralization of biochar C decreased significantly (P＜005) from 7.86% to 0.60% when pyrolysis temperature increased from 300℃ to 600℃. A doubleexponential equation was used to describe C mineralization kinetics and curve fitting was performed to mathematically define the size and turnover rate of two C source pools (labile and stable). The size of labile pool (A1) varied from 0.31g/kg to 0.94g/kg, while the size of stable pool (A2) varied from 6.88g/kg to 30.82g/kg. The decreased mineralization rates of the labile and stable pools (k1 and k2) were resulted from the increased pyrolysis temperature and the decreased biochar application rates. Halflife of C in soil varied between 24.09a and 44.76a and increased with the increase of pyrolysis temperature and biochar application rates. Conclusively, pyrolysis temperature had important effect on the physico-chemical properties of biochar and therefore resulting in different stabilities of soil organic matter. Considering the carbon loss in the process of preparing biochar, 500℃ would be the optimal temperature for preparing apple-derived biochar due to the most significant promotion of soil organic carbon.

Abstract:To effectively improve the enzymatic digestibility of carbohydrates in lignocelluloses, the combined hydrogen peroxide and liquid ammonia treatment (H-LAT) was employed as pretreatment for corn cob. The effects of temperature and H2O2 loading on solid recovery, enzymatic digestibility and lignocellulosic structure of corn cob were investigated. The results showed that the H-LAT pretreatment could effectively remove lignin and retain the most of carbohydrate in the corn cob. Enzymatic hydrolysis using cocktail enzymes including cellulase, β-glucosidase and xylanase for 72h after pretreatment under optimal conditions, the H-LAT pretreatment achieved 85.0% of theoretical sugar yield, and it could produce 593.1g fermentable monosaccharide per kilogram of dry biomass. Compared with untreated substrates, it was about 3.53 fold in sugars yields for H-LAT treated substrates. X-ray diffraction analysis showed that the crystalline region and amorphous region of corn cob were synchronously decreased; the crystallinity changes were depended on the interaction of the two effects. Infrared spectrum analysis showed that the H-LAT pretreatment effectively broke down cellulose hydrogen bonds, and disrupted ester linkage in lignin-carbohydrate complexes. Meanwhile, lignin molecular structure was partly destructed, and the distribution of lignin produced certain changes. As a result, these changes effectively reduced the biomass recalcitrance of corn cob.

Abstract:A biological pretreatment with Trichoderma reesei culture was used to pretreat straw wastes (i.e. rice straw, wheat stalk and their mixture) at ambient temperature (30±1)℃ to improve their biodegradability and anaerobic biogas production. The initial Trichoderma reesei spores dose was 200μL, it had twice expanding training, and the pretreatment time of 72h was appropriate for biological pretreatment. These treatment conditions resulted in more total biogas yield, methane yield and shorter technical digestion time compared with the untreated sample. The total gas production from pretreated straw wastes reached the maximum of 14555, 15103 and 17130mL for rice straw, wheat straw and their mixture, respectively. The average methane concentration levels were at 48.2%, 45.4% and 47.8%, respectively. The highest methane concentrations were at 60.5%, 66.1% and 66.8%, respectively. The average methane concentrations were increased by 205.1%, 213.1% and 214.5% compared with the untreated sample. The values of pH, VFA were located in normal range. The average daily degradation values of COD reached 522.23, 542.50 and 668.72g/d and TS degradative rates were 172.84, 183.12 and 205.54mL/g, respectively. The digestion time DT90 for pretreated straw waste which contained a mixture of rice straw and wheat stalk was calculated. The significant reduction of digestion time indicated that the straw had become more accessible and readily biodegradable after biological pretreatment.

Abstract:Recent consumer trends towards healthier and low fat products have had a significant impact on the snack industry. Vacuum and atmospheric frying of lotus root slices were compared, in terms of oil uptake under same pretreatment conditions. The objective of this study was to examine the most important quality parameters of vacuum frying and atmospheric frying lotus root slices in order to identify the specific advantages of vacuum technology and to understand the relationship between key microstructural changes and oil absorption. Confocal laser scanning microscopy is a new technology that can be used to observe the microstructure of fried lotus root slices after vacuum frying and atmospheric frying. Vacuum frying was shown to be a promising technique that can be used to reduce oil content. when using a driving force of ΔT=60℃, vacuum frying slices absorbed less than 30% of the oil absorbed by atmospheric frying ones. In addition, the results showed that after frying, the cellular structures were well conserved in terms of shape and size. Oil was shown to be mainly located in the surface of the crust occupying. Oil remained in the cut cells emptied during the washing or the frying operation or in the damaged cells partially filled with starch. Cell detachment, because of starch swelling and dehydration, seemed to be the preferential connection between cell layers. The positive effect of vacuum frying toward oil uptake reduction could be the restriction of these connections. Overall, this study has an important significance for decreasing oil uptake in terms of microstructural changes. Besides, it provides reliable data and effective study means for the future.

Abstract:The objective of the study was to investigate the effects of lactoferrin-polyphenol conjugates on the stability of β-carotene emulsions. Conjugates of lactoferrin with polyphenol ((-)-epigallocatechin-3-gallate(EGCG), chlorogenic acid and gallic acid) were achieved by a free radical grafting procedure. The hydrophilic/hydrophobic characteristics of latoferrin and lactoferrin-polyphenol conjugates were studied by reverse-phase HPLC. Lactoferrin-polyphenol conjugates were used as emulsifiers to prepare β-carotene emulsions, and the stability of β-carotene emulsions was characterized by transmission profiles through using novel centrifugal sedimentation and β-carotene degradation in the emulsion during storage. The results implied that hydrophilicity of lactoferrin was increased after modified by polyphenol; compared with those stabilized by lactoferrin alone, the emulsions stabilized by lactoferrin-polyphenol conjugates were able to improve the stability of β-carotene emulsions and inhibit the deterioration of β-carotene in oil-in-water emulsions, and lactoferrin-chlorogenic acid conjugate was the best emulsifier among the lactoferrin-EGCG, lactoferrin-chlorogenic acid and lactoferrin-gallic acid conjugates. 

Abstract:The aim of this paper was to investigate the changes of protein, lipid oxidation and its impact on water holding capacity of Psoas major, Quadriceps femoris and Longissimus dorsi from yak during 140d of frozen storage (-18℃). Samples were analyzed at sampling times upon thawing (0, 28, 56, 84 and 140d) for lipid (TBARS, hexanal) and protein oxidation products (α-aminoadipic and γ-glutamic semialdehydes, α-aminoadipic acid, Schiff bases). During the frozen storage, heme-iron and superoxide dismutase played an important role in the lipid oxidation process of Longissimus dorsi. Owing to a lower content of heme-iron and a relatively higher content of superoxide dismutase, Longissimus dorsi had a lower content of TBARS and hexanal. Frozen storage significantly influenced the oxidative stability of proteins in Psoas major and Quadriceps femoris. The protein oxidation process of PM and QF was co-regulated by heme-iron, superoxide dismutase and catalase. Because of the promoting oxidation of heme-iron, the content of α-aminoadipic and γ-glutamic semialdehydes were also significantly improved. However, the content of heme-iron in Psoas major was significantly higher than Quadriceps femoris, the content of α-aminoadipic and γ-glutamic semialdehydes in Psoas major and Quadriceps femoris had no significant differences due to the higher content of superoxide dismutase and catalase. The content of α-aminoadipic acid was relatively higher because of the higher content of heme-iron in Psoas major, but the content of α-aminoadipic acid in Psoas major was significantly lower than Quadriceps femoris (P<0.05). Furthermore, the water holding capacity of yak meat was significantly affected by protein carbonylation reaction during the frozen storage. Owing to the lowest antioxidant enzyme activity and the highest heme-iron, the water holding capacity of Quadriceps femoris was the worst in three kinds of yak meat. The purge of Quadriceps femoris was higher than Longissimus dorsi for 3.55 times.

Abstract:The effect of low acyl gellan (LA)/sodium caseinate (SC) weight ratio, total polymer concentration, ion valence and cation concentration on the gelling properties of low acyl gellan-sodium caseinate mixtures were investigated by using compression tests. The results showed that ion valence and cation concentrations had a pronounced effect on the gel strength of low acyl gellan-sodium caseinate mixed gels. The failure strain of mixed gels decreased with the increase of cation concentrations. Moreover, the failure strain was less sensitive to LA/SC weight ratios and total polymer concentrations. The failure stress and Young’s modulus of mixed gels increased with the increase of total polymer concentrations and the proportion of low acyl gellan. Moreover, at each LA/SC weight ratio and total polymer concentration, the failure stress and Young’s modulus increased with the increase of cation until cation concentration reached a critical level, after which further increases in cation resulted in a reduction of failure stress and Young’s modulus. At optimum cation levels, mixed gels with Mg2+ were stronger than that with Na+. Water holding capacity of mixed gels decreased as cation concentrations increased. The higher the total polymer concentration and LA/SC weight ratio, the better the water holding capacity.

Abstract:Grilled mutton chops are traditional meat products, and the quality is greatly influenced by the final core temperature. However, the core temperature of mutton chops during grilling is difficult to monitor. To predict the core temperature of mutton chops during grilling accurately and conveniently, a mathematical model based on grilling time and shapes of mutton chops was established. Mutton chops with different cross-sectional areas of lean meat from 7cm2 to 15cm2 were grilled in an electric heat oven at 120℃ or 220℃. Fifteen samples were grilled independently at each temperature until the core temperature reached 75℃ and the temperature-time curves were recorded. Seven thermal probes were inserted into the different points of the mutton chops during grilling and the lowest temperature was taken as the core temperature. The model for predicting core temperature with grilling time and cross-sectional areas of lean meat was built with regression method, which was used to evaluate the quality of grilled mutton chops. The results showed that the established model could well predict the temperature changes of grilled mutton chops and the relative errors between simulated and measured results were lower than 6%. Different quality characteristics of mutton chops were formed under different grilling temperature based on the application of the model. The mathematical model could provide a convenient and timely method for predicting the core temperature of mutton chops during grilling. 

Abstract:There is an urgent need in the food and beverages industry for evaluation of the sweetness taste by using a rapid and objective method. An electronic tongue was used to evaluate sweetness taste and compare different steviol glycosides (different compositions of rebaudioside A: RA95, RA97, RA99, RA/RB(90/10), RA/RD(90/7)). Five RA samples and sucrose used as a reference were analyzed by the electronic tongue and sensory panels. Sensory analysis demonstrated that the RA samples (0.2~0.8g/L) were 90~220 times sweeter than that of sucrose (0.03~0.09g/mL). The data obtained by electronic tongue was analyzed by principal component analysis (PCA). The extinction time of all RA samples ranged from 10s to more than 60s, and RA at 1.2g/L exhibited intense bitter taste. Five RA samples were successfully discriminated on the PCA score plot. Compared with sucrose at different concentrations, the intensity of sweetness taste of RA samples was ranked as: RA/RD(90/7)＞RA95＞RA/RB(90/10) and RA99＞RA97＞RA95. Based on euclidean distance on the PCA score plot, RA99 was revealed more similar taste than that of RA95 and RA97. The results showed that the electronic tongue analysis might be a useful method to complement sensory panels in evaluation of sweetness.

Abstract:Traditional methods of obtaining nitrogen content of citrus leaves are time-consuming, and the process is cumbersome and harmful to citrus leaves, which need proficient experiment techniques and amounts of instruments, equipment and chemical reagents. According to the high dimensionality and redundancy of origin spectral reflectance, a nitrogen content obtaining method of citrus leaves was provided based on manifold learning algorithm which was applied to the high-dimensional spectral vectors for dimension reduction and feature extraction. During four different growth stages, corresponding to germination, stability, bloom and picking stages, spectral reflectance of citrus leaves were measured by the ASD FieldSpec 3 spectrometer, respectively, and at the same time, nitrogen content of citrus leaves was obtained by using Kjeldahl method. For data processing, firstly the parameter combination of wavelet denoising which was used to the high-frequency noise removal was optimized through orthogonal test, and then the principal component analysis (PCA), multidimensional scaling (MDS), locally-linear embedding (LLE), isometric mapping (Isomap) and laplacian eigenmaps (LE) manifold learning algorithms were applied to extract features of original spectrum and denoised spectrum. Finally, the five corresponding support vector regression (SVR) prediction models of nitrogen content for citrus leaves were established based on their features. Experiment results reveal that the five manifold learning algorithms can be effectively used to predict nitrogen content of citrus leaves, which provides theoretical basis for obtaining nitrogen content of citrus leaves rapidly and non-destructively, as well as in growth monitoring and variable-rate fertilization.

Abstract:A non-destructive testing method was studied to rapidly and accurately detect pesticide residues on mulberry leaves. Six groups of mulberry leaves were chosen as experimental samples, which contained pesticide residues of dichlorvos, chlorpyrifos, acephate, dimethoate and phoxim as the first to fifth groups, respectively, and the sixth group without pesticide residues was taken as control. Hyperspectral images of samples in 390~1.050nm were acquired by hyperspectral imaging devices. The region of interest from hyperspectral image was selected, and ten characteristic wavelengths, which were 452.51, 469.88, 517.28, 539.85, 578.92, 643.72, 727.24, 758.34, 785.67 and 819.67nm, were selected by the successive projections algorithm (SPA). Based on RBF kernel function of SVM and 10 fold crossvalidation methods, the detection models of pesticide residues on mulberry leaves were established. The impacts of three parameter optimization algorithms (grid search, genetic algorithm and particle swarm optimization) on the model performance were discussed. The results showed that performance of SVM model by using grid search was the optimal one, and its cross-validation accuracy was 63.89% and forecast accuracy was 78.33%. In order to further enhance the classification performance of the model, the adaptive algorithm (Adaboost) was introduced into the SVM model, and Ada—SVM algorithm was used to build classification model, which can detect pesticide residues on mulberry leaves and identify the kinds of pesticide residues. The results showed that the prediction accuracy of Ada—SVM model reached 97.78%, which was increased by 19.45% compared with the original SVM model. Therefore, hyperspectral imaging technology combined with Ada—SVM algorithm can accurately identify the pesticide residues on mulberry leaves. 

Abstract:Field weed is the big enemy of agricultural production, and also is one of the key problems that blocked the crop growth in Chinese agriculture. Accurate positioning weeds and realizing the variable precision applying pesticide or herbicide are particularly important. To solve various field weeds positioning difficult problems, a multi-feature based weed reverse positioning method was proposed. By taking the field crops as the research object, the multi-objective weed positioning issue was transformed into single objective crop recognition problem. Firstly, seven moment invariants and eight shape feature parameters were extracted from many of the individual soybean crop leaves, and the mean value of moment invariants and shape features were taken as standard soybean leave feature value. Secondly, after a series of image preprocessing such as image segmentation, regional separation feature match and connected component analysis, multi-feature recognition method with HU invariant moments and shape features of crops were utilized to accurately locate each crop plant. Finally, based on color feature, the green plants outside of the crops region were treated as weeds. Furthermore, a small weed positioning device was designed based on this method, which was applied to wide pesticide spraying machine. Field experiment results showed that weed recognition accuracy of this system for weed in soybean field was more than 90% when the spraying machine working speed was 5km/h, hence weed positioning and pesticide accurate spraying problems could be well settled.

Abstract:Study on light distribution of apple tree canopy is one of the important ways to optimize type of fruit trees and improve potential production. The reasonable and effective use of light energy and optimization of light distribution within fruit tree canopy have vital significance for the formation of fruit tree growth and fruit quality. Calculation method of light distribution of free spindle apple canopy was carried out. In recent years, there were several researches on light distribution of plant canopy on the basis of three dimensional morphology of plant canopy by using mathematical simulation methods which could not express the real light distribution. In order to reveal real light distribution rule of canopy intelligently and efficiently, apple trees of spindle shape were selected as research objects, and based on the correlation that the target image color changed with the light intensity. Firstly, 3D point cloud of apple tree canopy in leaf curtain stability period was captured by Trimble TX5 laser scanner; secondly, according to the actual canopy division method, color information of different areas in 3D canopy space was extracted; thirdly, aiming at the shortcomings of complexity, fuzziness and indescribability by precise and quantitative symbols under natural environment, the fuzzy neural network was constructed to predict light distribution with color characteristic as input and relative light intensity as output. The experimental results showed that the precision of the proposed method had good feasibility, the prediction accuracy was 80.57%. The result of this study will provide theoretical basis for scientific pruning to get the best light distribution.

Abstract:Premixed methanol diesel dual fuel (PMDDF) is a combustion mode in which methanol is injected from the intake port and then ignited by the direct injected diesel in the cylinder. Many studies have shown that PMDDF mode has the potential to reduce NOx and PM emissions simultaneously. In this study, investigation on realizing national phase Ⅳ emission standard by using PMDDF combustion mode coupling with diesel oxidation catalyst (DOC) and particulate oxidation catalyst (POC) was carried out on a 6-cylinder heavy-duty diesel engine. The effects of premixed methanol on engine combustion process and fuel economy were also investigated. The experimental results showed that with the engine power keeping unchanged, the emission level of the engine was improved from national phase Ⅲ to Ⅳ by using PMDDF combustion mode and the simple aftertreatment DOC+POC. And the specific fuel consumption almost remained unchanged. This technology provided a new route for the realization of national phase Ⅳ emission standard. In addition, it was also found that the ignition delay of PMDDF combustion mode was prolonged and the combustion duration was shortened with the increase of premixed methanol ratio. At high engine load, the brake specific fuel consumption of PMDDF combustion mode was lower than that of baseline engine, but it was slightly higher at low engine load. Therefore, the premixed methanol ratio can be a little higher at high engine load but can not be very high at low engine load. 

Abstract:The spray characteristics of gasoline, n-butanol and ethanol injected from an outward-opening gasoline piezoelectric injector were investigated with Schlieren and laser Mie scattering techniques in a constant volume vessel. Experimental results showed that the hollow conical spray was composed of numerous tiny jets. The macrostructures of spray were affected by the magnitude of back pressure. With the increase of back pressure, the gap between two adjacent jets was decreased and finally disappeared. In the meantime, the penetration and projected area of spray were sharply reduced. However, the spray cone angel was nearly unchanged with time regardless of the magnitude of back pressure and fuel types. Furthermore, the decline of spray penetration was always larger in horizontal direction than that in vertical direction. But the penetration in horizontal direction was longer than that in vertical direction. The spray penetration in vertical direction for ethanol and n-butanol with relatively higher viscosity was longer than that for gasoline, which was contributed to the vortex formed during injection. The larger the scale of the vortex, the longer the penetration in horizontal direction was.

Abstract:In order to perfect the work efficiency evaluation system of diesel SCR system and improve the work efficiency of SCR system, the theoretical urea decomposition efficiency calculation method of diesel engine SCR system was proposed. The urea decomposition efficiency, amount of leakage of NH3 and NOx conversion efficiency of SCR system for diesel engine were investigated on an engine test bench, the influence of space velocity, NH3/NO ratio and SCR temperatures were analyzed. Experiment results showed that the changing trend of NOx conversion efficiency and urea decomposition efficiency was basically the same. In the catalyst activation temperature range, the urea decomposition efficiency was above 90%; with the increase of space velocity, the urea decomposition efficiency was increased first and then decreased. NH3/NO ratio was 1 with high NOx conversion efficiency, but the amount of leakage of NH3 was exceeded the limit value. NH3/NO ratio had little effect on the urea decomposition efficiency, and it was increased with the amount of leakage of NH3 increasing. When the exhaust gas temperature was raised, the urea decomposition efficiency increased. The space velocity and exhaust gas temperature were the most important factors influencing the urea decomposition efficiency, the level of urea decomposition efficiency was the comprehensive effect of both. Through the study on the factors affecting the decomposition efficiency of urea, to reduce the deposition of urea in the exhaust pipe and improve the removal efficiency of NOx. The proposed calculation method can exhibit a trend of urea decomposition efficiency and provide a basis for improving the work efficiency of SCR system. 

Abstract:Research of existing automobiles of energy-saving and emission reduction is very important in the interim period before popularization of new energy automobiles. Some research results showed that about 50% frictional loss of engine was generated from friction pair of piston-cylinder liner system. Based on great usage amount of engines, frictional loss of engine was reduced within a narrow range; it could exert a large influence on energy consumption and environmental enhancement. The 1.6L engine of Jetta car was used as testing subject. The pits on the Cybister bengalensis’ surface, which could reduce drag and increase wearability, were applied to the main friction pair of engine—piston skirt for the first time. Firstly, the ranges of bionic apertures and separation distances were designated according to the configuration sizes of pits of cybister surface. Then the optimal bionic apertures and separation distances were determined by relative speed drag reduction rate on the basis of relative speed of bionic piston under the three calibration conditions. The ultimate speed of bionic piston was increased as drag reduction rate increased, and the anti-drag and wear-resisting were improved with smaller friction of bionic piston. Secondly, the stress arrangement of thermalstructure coupling analysis of standard piston skirt showed that the maximum stress was at the top and the maximum deformation was at the bottom. Variable aperture and variable line spacing of bionic holes was innovatively designed. Larger aperture and greater line spacing were located near the piston top. Three levels and three factors orthogonal test was made. Level one was holes distribution, which included uniform form, stagger form, line by line to increase; level two was bionic hole, including throughhole, pit, pit and through-hole alternating; level three was bionic aperture, including three bionic aperture sizes. Under the worst conditions, standard and nine bionic pistons were done by finite element thermalstructure coupling analysis. Three typical target variables were selected as test indexes, which were maximum stress of the top of piston, maximum deformation of piston skirt and maximum stress of spill port. The test indexes of nine kinds of bionic pistons were optimized by range analysis. Primary and secondary factors were bionic hole, holes distribution and bionic aperture, and optimal combination were stagger form, pit and through-hole alternating, and bionic aperture as 2.5, 2, 1.5, 1mm. Finally, three pistons as standard piston, the best optimal performance bionic piston and optimal combination piston were selected, and the durability tests were done on test bench of engine. The temperature of the top of piston in every air cylinder, gas pressure gradient, piston wear extent and piston skirt’s surface roughness were got, which could verify the superiorities of anti-drag and wear-resisting of bionic pistons. Results of simulation and bench test indicated that the former was better in deformation and its skirt bottom had less wear and better lubrication when comparing the variable aperture, variable line spacing and uniform distribution bionic holes; through-hole unloaded concentrated stress best; the best aperture range was 1~3.5mm; stagger form could avoid blind angle in oil gathering, configuration oil and storage chip; bionic piston abrasion loss was reduced by 90%, power of work gas was increased by 50% in the air cylinder and heat dissipation efficiency was increased by 0.5% compared with standard piston.

Abstract:In order to simulate and analyze the economy performance of the tracked hybrid electric bulldozer under whole operation cycle, a secondary development of ADVISOR was applied and straight and steering dynamics model, track model, oil pump model and transfer case model, etc., were established in Matlab/Simulink, then the models of hybrid electric bulldozer and its compared bulldozer were built. The real two compared bulldozers’ tests were conducted under straight cycle and steering cycle, respectively. And then the key operating parameters of powertrain source and powertrain terminal in simulations and tests, such as speed of engine, power of genset, voltage of super capacitors and traction and velocity of bulldozer, were compared to validate the accuracy of the models. The results showed that the established models had relatively high simulation accuracy. The economy performance was simulated under whole operation cycle by using the established models, which showed that the hybrid electric bulldozer had significant energy savings under both straight dozing and steering cycles, furthermore, the adoption of the enginegenerator set optimal efficiency curve control strategy can further enhance the energy saving effect.

Abstract:To improve the shift performance stability of the direct-drive automated manual transmission (AMT) gearshift system, inverse system method (ISM) was introduced according to the characteristics of 2-DOF electromagnetic actuator. The structure and working principle of the actuator were described, and the analysis of the mathematical model indicated that the parameters of the actuator affected each other. Static characteristics experiments proved that the output characteristics were nonlinear. The reversibility of the system was analyzed and ISM was adopted to build the pseudo-linear system, and the state feedback controller was designed according to the linear system theory. Extended state observer (ESO) was added to weaken the influence of time varying friction force to the stability of the output characteristics. The simulation and experiment results indicate that controlled by the ISM—ESO controller, the gearshift performance is robust to variable parameters. The precision of displacement control is better. The stability of the output characteristics is improved. Based on the inverse system method, the gearshift performance of the direct-drive automated manual transmission is relatively excellent, and it is conducive to improve the competitiveness of AMT.

Abstract:To compact the dynamic analysis and improve the computation efficiency, the advantages of Kanes equations and the product of exponential (POE) formulas were combined based on screw theory to propose a new effective dynamic modeling of robot manipulator with explicit geometric significance, and based on this dynamic model, a non-singular terminal sliding mode control was presented to achieve better performance. The velocity Jacobian matrix was addressed in the product of exponential form by introducing the screw theory, and the partial velocity of Kane’s equations was selected specifically from the suitable velocity Jacobian matrix. Then a dynamic modeling example based on Kane’s equations and screw theory was established, which led to be less complicated compared with other typically dynamic methods. With the proposed dynamic equations of serial robot manipulator, a fast non-singular terminal sliding mode (FNTSM) control was presented by introducing an improved fast non-singular terminal sliding mode surface, which was designed to ensure the fast convergence in global system state whether it was near to equilibrium or far away from the equilibrium. Then the stability analysis of the proposed method was performed by using Lyapunov stability theory. Finally, comparative experiments were implemented to demonstrate the effectiveness and robustness of the proposed approach.

Abstract:The thrust vectoring technology is becoming a research hotspot for underwater vehicle. Combination of spherical parallel mechanism with propeller makes an approach to the above technology. A new-type of decoupled 2-DOF spherical parallel mechanism was proposed for vectored thruster of underwater vehicle. Based on the screw theory, the degree of freedom was calculated, and the direct and inverse kinematics solutions were obtained by using analytic geometry. The first-order kinematic influence coefficient was employed to deduce the Jacobian matrix. The detailed dynamic model was got by the Newton—Euler equation and hydrodynamic of ship propulsors. Corresponding numerical examples were finally given to verify the effectiveness of all above methods. The proposed spherical parallel mechanism is simple in construction, convenient to control and has good decoupling performance. In conclusion, it shows superiority for vectored thruster in engineering application.

Abstract:With the popularity of high pressure hydraulic system and the increasing requirements for the efficient and automatic control, the measure of tiny flow under the high pressure condition is more and more important. And the relevant research also has great importance for the development of domestic flow meters industry. A bi-directional oval gear flowmeter used for the measurement of tiny flow under high pressure condition was presented, which used a pair of low eccentricity oval gears as the core components and used hall sensors for the non-contact signal-detection. The designed flowmeter was with a lower displacement in order to measure tiny flow. A fully closed measurement volume was built so that the flowmeter can endure high pressure. A complete CAD model was established for the CNC machining of oval gear in order to ensure the high accuracy, including the pitch curve equation of oval gear and the solution of tooth profile based on the converted method. In order to validate the design and research the flowmeters metrological characteristics, experiments on a prototype fabricated were performed. And a modification method of flow coefficient was proposed on the basis of least square method. The experiments results showed that the maximal pressure loss was 0.46MPa at flow rate of 3L/min, and the flowmeter was with a relative error less than 1% over a flow rate range of 0.03~3L/min, and 0.5% over a flow rate range of 0.05~3L/min.

Abstract:Taking granular materials composed of wood particles and clay particles as sample, the rolling motion and separation of density-type binary dispersed granular materials within a cylinder were simulated by using discrete element method. Mixing index of materials was defined by using contact-number between particles, and then transverse separation process was quantitatively investigated by using Hong’s theory—the mechanism of competition between percolation and condensation. The results showed that material bed was composed of active layer and passive layer in radial section, where separation between particles was occurred in the active layer. Condensation mechanism, which was caused by density differences between wood particles and clay particles, made the material bed form a moon-pattern separation form. Then wood particles dispersed to the drum wall and clay particles gathered to the center of bed. Percolation mechanism can be introduced by configuring the radios of wood particle and clay particle. The separation could be avoided when percolation effect and condensation effect were balanced each other. The addition of percolation mechanism was not affected by the size of cylinder drum.

Abstract:A new method of fast identifying temperature rise characteristics for machine tool spindle was developed. The nonlinear prediction technology based on support vector machine regression can predict the spindle temperature rise curve for a long time by only using a short period of measurement time. The steady-state temperature and thermal equilibrium time can be easily obtained from temperature prediction. The thermal balance test in the vertical machining center was done, and the method was applied under different working conditions. When spindle was running at 5000r/min with room temperature of 18℃, the temperature rise of the selected point was identified in 48min while the time for obtaining the temperature rise curve from start-up of machine tool to temperature steady-state machine tool in practice can reach 400min. The root mean square error (RMSE) between estimated and measured temperature was 0.1848℃, and the error between estimated and measured steady-state temperature was 0.0392℃. The method can greatly shorten thermal balance test duration. The experimental research illustrated that the method of identifying spindle temperature rise characteristics was fit for thermal balance test. It proved that the novel method was effective and feasible. 

Abstract:A novel design project of bi-direction thrust torsion coupling was put forward for 2D electro-hydraulic proportional directional valve by using spherical roller, the wedge’s linear motion could be translated into spools rotary motion, and the output torque and 2D spool’s torsion angle could be amplified. On the basis of the mathematical model, the dynamic characteristic of thrust torsion coupling and the hysteresis characteristics due to backlash were analyzed by using phase-plane analysis method. The backlash was overcome by using dither compensation technology and the effect for eliminating the backlash was achieved. Based on the mathematical model and the prototype, the relationship between linear motion of the wedge and rotation angular displacement of the spool was researched and simulated. Simulation and experimental results were consistent. Experimental results showed that the hysteresis of backlash could be reduced efficiently by using dither compensation technology, the hysteresis was about 3.7% as dither amplitude was half of backlash, and it could be controlled below 2%, as dither amplitude was beyond the backlash. Bi-direction thrust torsion coupling could be used in the 2D electro-hydraulic proportional directional valve and the amplification of the displacement could be realized. 

Abstract:In order to further increase the power density for axial-piston pump, the quantitative formulas were derived and the most important factors were studied. One factor was the amount of volumetric displacement of pump per revolution divided by the spatial volume of pump, and the analysis indicated that it was determined by swashplate angle and piston pitch-radius, and 60% increase of it could be obtained by using an inverted piston-slipper design. The other factor was the maximal speed which was determined by the self-priming ability (SPA) of pump. The analysis result showed that the SPA was affected by resistance caused by viscous resistance and forced vortex, and the ability dropped with the rotating speed increasing, which was the defect of current structure of cylinder block. In order to overcome the defect, a new structure of cylinder block with bidirectional inclined cylinder block hole was presented, and the results of simulation demonstrated that SPA of axial-piston pump was increased by 45.4%. Finally, to meet the requirement of large displacement pump, a symmetrical X shape axial-piston pump was proposed and its power density was verified theoretically. The analysis result showed that the power density was increased by 43% compared with a double-pump.

Abstract:Simulating the movement, deformation and break-up of immiscible two-phase flow interface was complex and difficult in the liquid—liquid dispersion atomization system. Based on the volume of fraction (VOF) with role of surface tension and interface reconstruction, a model of tracking the immiscible liquid—liquid interface was built with two modes of large and small jet flow rates. The change of oil—water interface was tracked in the process of liquid—liquid dispersion atomization, the micro characteristics of jet break-up and drop formation and growth were simulated, and the mechanism of influence of Re, Ca and Bo criterion numbers on jet break-up and drop formation was also discussed. The results showed that the process of liquid—liquid dispersion atomization can be simulated by the interface tracking model set-up under different jet flow rates, but the simulation capability was short of tracking the process of small scale vortex break-up. Under different modes of drop formation, jet break-up was characterized by randomness, and enhanced with increase of jet flow rate; small droplets were formatted by the volatility and instability of two phases' interface. Under the modes of drop formation of trickling and laminar jet, the shape of drop, jet surface and the section of jet break-up were mainly affected by the variation of Re, Ca and Bo criterion numbers, however, for the mode of drop formation of turbulent motion jet, these criterion numbers mainly influenced the extent of jet break-up and drop size. 

Abstract:The ultrasonic pulse echo method was adopted to test the localized void defects in thick section composites and the extracted ultrasonic backscattered signal was analyzed. The results showed that the resonance structure noise may appear in the near surface region of the material. The voids can result in frequency reduction and amplitude decrease of the structure noise. The backscattered signal was back to normal state in the far surface region and the voids can lead to the appearance of low amplitude echo. The localized void identification method based on the backscattered signal processing was proposed. The near surface signal was processed by a modified S-transform to generate time-frequency coefficient matrix. The minimum and gain of the signal main frequency can be calculated to identify the voids. For the far surface signal, the wavelet transform modulus maximum denoising method was applied firstly, and then the denoised signal was processed by the modified S-transform to generate time-frequency coefficient matrix. Finally, the maximum and gain of the signal main frequency could be calculated to identify the voids. The experiments were implemented for the thick section composite plate specimen and curved surface specimen, respectively. The results showed that the localized void defects in thick section composites could be effectively identified by this signal process method.