| As the main aquatic vegetable in China,lotus root is widely cultivated,whose production is rising year by year with promising developing foreground.However,its low automation,low efficiency,high crushing rate and low net recovery rate in harvesting process lead to a large amount of lotus roots rot in the field every year due to the failure of timely harvesting,causing a serious impact on the lotus root industry,restricting the development of the lotus root industry.Therefore,in order to optimize nozzle structural parameters and hydraulic parameters,discrete element simulation studies were carried out on the crushing mechanics of the main lotus root and the adhesion mechanics of the soil-main lotus root.Hydraulic scour process was analyzed based on EDEM-FLUENT coupling.At the same time,a double scour group lotus root harvester was designed and trial-produced.According to the simulation analysis results,the key components of the machine were designed and selected,the prototype was trial-produced,and the harvest effect was verified by field performance test.The main research contents are as follows:（1）Establishment of discrete element crushing mechanical model of main lotus root and calibration of simulation parametersTo optimize and improve the mechanized harvesting technology and equipment of lotus root,bending failure discrete element analysis of lotus root was carried out by simulation analysis.Taking Elian No.5 as test subject,the elastic modulus,shear modulus,Poisson’s ratio and other intrinsic parameters were obtained by uniaxial compression test,and the contact parameters such as the collision coefficient of restitution,static friction coefficient and rolling friction coefficient among lotus roots and between lotus roots and steel were obtained by friction and collision test.Geomagic studio 3D and Solid Works software were adopted to model the main lotus root.By using the Hertz Mindlin with bonding model in EDEM simulation software,the discrete element model of main lotus root was established.The bending failure test of the main lotus root was carried out on the texture analyzer.Referring to the test results,the single-factor and two-factor discrete element simulation tests of the bending failure of the main lotus root were carried out with normal stiffness per unit area,shear stiffness per unit area,critical normal stress and critical shear stress as the influencing factors.The results showed that the normal stiffness per unit area and the shear stiffness per unit area had significant effects on the displacement and the first peak value when the first bending failure occurs,while the critical normal stress and the critical shear stress had no obvious effects on them.When the critical normal stress was 3.80 MPa and the critical shear stress was 3.12 MPa,the optimal solutions of the normal stiffness per unit area and the shear stiffness per unit area were obtained to be 5.814×108N/m3and 3.450×108N/m3respectively by steepest descent method.Based on this,the simulation peak value of the first bending failure of the main lotus root was 269.72N and the displacement value was 7.14mm,and the relative errors of the simulation results and the measured results were 2.56%and 2.00%respectively.（2）Establishment of discrete element adhesion mechanical model of soil-main lotus root and calibration of simulation parametersIn order to provide a theoretical basis for the subsequent simulation research on the propelling resistance of furrow opener in the mechanical harvesting process and nozzle structure optimization.The intrinsic parameters of soil were determined by core cutter method,consolidation undrained shear test（CU）test,elastic modulus test and repeated loading and unloading test.The soil volume density was 1784.72kg/m3,soil particle size and its distribution,angle of inner friction of soil was 11.00°,and soil cohesion was 126.94KPa.Soil plastic、liquid limit、plastic index were 30.83%,25.52%,5.31%,and elastic modulus was17.88MPa,respectively.Combined with the calibrated discrete element crushing mechanical model of main lotus root,the Hysteretic Spring model and Liner Cohesion model in EDEM software were used to establish the soil-main lotus root adhesion discrete element model.The uniaxial compression test results were taken as the control,and the response surface test method was used.Relevant discrete element simulation parameters of the model were calibrated.Yield strength of soil-soil is 0.34MPa,energy density of soil-soil is 51.16J/m3,energy density of soil-main lotus root is 51.16J/m3,energy density of soil-steel is 18.84J/m3,corresponding particle density of soil is 2345kg/m3.At this time,the cumulative error of simulation is 9%,and the relative error is 4.20%compared with the measured value of soil-main lotus root pulling force test.（3）Simulation based on EDEM-FLUENT coupling of process of nozzle impacting soilIn order to optimize the structural parameters and hydraulic parameters of the nozzle,the process of the nozzle scour soil was simulated based on EDEM-FLUENT coupling.The parameters of the soil-main lotus root coupling discrete element adhesion model were used.The outlet flow rate x1and the nozzle installation Angle x2were taken as test factors,and the scour depth Htand scour width Dtwere taken as test indexes.The experiment was designed according to CCD test design method,The quadratic regression equation of scour depth and scour width with respect to outlet flow rate x1and nozzle installation Angle x2was obtained by variance analysis.The analysis shows that the nozzle outlet flow x1is positively correlated with the scour depth Ht,and the nozzle installation angle x2is negatively correlated with the scour depth Ht,that is,with the increase of nozzle oulet flow,the scour depth Htincreases,and with the increase of nozzle installation Angle,the scour depth Htdecreases;The nozzle installation Angle x2is positively correlated with the scour depth Dt,that is,the scour depth Dtincreases with the increase of the nozzle installation angle.Taking the maximum scour depth and both the maximum scour depth and the maximum scour width as the optimization objectives,the optimal nozzle installation Angle x2is 0°and 41°,respectively,under the condition that the nozzle flow x1is 30m3/h and the diameter is 21mm.In order to determine whether two sets of the nozzle will damage the lotus root,based on discrete element crushing mechanical model of main lotus root and parameters obtained above,discrete element-fluid coupling simulation is carried out,optimal nozzle parameters were determined whether will damage the main lotus root,and two optimal nozzle parameters did not damage the surface of the main lotus root,indicating that the nozzle parameters were reasonable.（4）Design of whole machine and key parts of double scour group lotus root harvesterCombined with hydraulic scour and mechanically assisted harvesting,a double scour group lotus root harvester was designed,which completed 3D drawing and 2D drawing design,power system selection,key parts processing and prototype trial production;Based on the simulation results of nozzle and furrow opener,the hydraulic system and electronic control system are designed and selected;frictional head loss and local head loss in the hydraulic system loop are calculated;two kinds of nozzle diameters are calculated and their installation and arrangement are designed;in order to solve the problem that the increase of nozzle target distance affects the harvesting effect,a depth adjustment structure is designed to adjust the depth between nozzle and furrow opener and soil surface.（5）Field performance test of double scour group lotus root harvesterA prototype of double scour group lotus root harvester was trial-produced,and the performance test of the scour effect of the nozzle of the prototype was carried out.The nozzle with diameter of 21mm was installed according to 0°、30°、60°respectively,and the scour depth and scour width were 160、140、90mm and 110、120、190mm respectively by fixed-point scour method;with the increase of installation angle,the scour depth decreases and the scour width increases.The problems of water pump and inlet clogging appear in the performance verification test,and solutions such as replacing water pump and installing furrow opener are put forward.Experiments were made on the scour depth of nozzle.After 3min of steady scouring at rated flow rate of 30m3/h,the maximum scour depth reached by the two groups of nozzles was tested,and the measured value was compared with the simulation value.The experimental results show that the scour depth of the nozzle with the installation angle of 0°and 41°is160mm and 110mm respectively,and the relative errors with the simulation value are 7.91%and 9.54%,respectively.the scour depth of the nozzle with the installation angle of 0°and 41°is 110mm and 160mm respectively,and the relative errors with the simulation value are5.90%and 10.08%,respectively. |
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