Simulation On Resistance Reduction In Vibration Digging Based On Discrete Element Method And Experimental Research

Rhizome harvesters are playing more and more significance role in China since the policy promoted about regarding the potato as one of the major staple food.However,there are many problems existed in fixed shovel rhizome harvester,such as high digging resistance,high energy consumption and poor adaptability.Since the vibration digging technology can improve these problems greatly,simulation on resistance reduction in vibration digging based on discrete element method and experimental research was carried out in this paper.The main research contents and conclusions are as follows:(1)Measurement of the basic parameters and discrete element method calibration of the micro-parameters of the field soil.In order to make the situations more close to the actual situation in the field when establishing the discrete element simulation model and preparing the soil in the soil bin,the basic parameters of the soil,which including soil texture,consistency,moisture content and wet density,were measured in the field.For micro soil parameters which are inconvenient to measure directly,the discrete element method was adopted to do the calibration.Box-Behnken response surface experimental method was used for soil accumulation angle to obtain the parameters consistent with soil physical accumulation angle corresponding to the microscopic parameters of the soil:the surface energy JKR,coefficient of restitution,coefficient of static friction and coefficient of rolling friction were 4.5 J/m~2,0.73,0.51 and 0.13,respectively.(2)Establishing the vibration excavation test bed.In order to be able to carry out indoor soil bin test,a soil bin was built.The cam mechanism with large and small eccentric wheel structure was designed.The oscillating vibration form of cam mechanism with front end fixed and back end connected was put forward,the vibration amplitude and frequency,therefore,can be adjusted by the eccentricity distance of cam mechanism and rotation speed respectively.Through the force analysis to the contact soil component,it was clear that the traction resistance included the resultant force of friction force,pressure and resistance in the horizontal direction.Through the kinematics analysis of the simplified four-bar mechanism of the vibration excavator,the adjustment relationship between the vibration amplitude and the eccentricity of the excavator was obtained.In addition,S-type sensors and high-speed photographic equipment were installed in the test bed for the measurement of traction resistance and the recording of soil disturbance respectively.The soil whose parameters were basically consistent with those of the field was prepared in the soil bin,and a preliminary test was carried out.The range of vibration amplitude,frequency and forward speed parameters suitable for the test were obtained,which were 7～11 mm,8～16Hz and 0.4～0.6 m/s,respectively.(3)Simulation of vibration mining process based on the discrete element method.The discrete element software EDEM was used to establish the contact soil component-soil model with the determined parameters.Through the translational motion test,it was verified that the discrete element model can be used to simulate the excavation process in the soil bin.On this basis,the operating process of the contact parts was simulated and analyzed,and the mechanical characteristic curves of the horizontal,lateral and vertical directions and the overall force changing with time were obtained.The analysis showed that the lateral force was almost zero and negligible,and the horizontal force was greater than the vertical one.In order to obtain the effect of stabilizing operation process,the effective operation time periods under different forward speeds were divided and determined.The contrastive simulation tests of excavation resistance with and without vibration were carried out,and it was confirmed that the vibration excavation has the effect on resistance reduction,and the resistance reduction was 8.4%,15.50%and 5.94%in the horizontal direction,the vertical direction and the overall force respectively.After that,the single-factor experiment of the influence of vibration amplitude,frequency and advancing speed on excavation resistance was carried out.The horizontal and vertical forces had a polynomial relationship with the vibration amplitude and frequency.However,the horizontal forces decreased first and then increased with the increase of the vibration amplitude.The vertical forces decreased first and then increased with the increase of the vibration frequency.However,the horizontal force on the contact soil component had a positive linear correlation with the forward speed,which increased with the increase of the forward speed while the vertical force had a negative polynomial correlation with the forward speed,which decreased with the increase of the forward speed.The results of soil disturbance analysis showed that the disturbance range of soil particles was the largest in the shallow layer,followed by the middle layer,and the deep layer was the smallest.And velocity change of the soil particles in forward domain was positively correlated with the velocity change of the digging shovel in vertical direction.(4)Comparative analysis of soil bin test and simulation test results.In the soil bin,the comparison test of vibration excavation with and without vibration showed that vibration excavation can reduce the traction resistance by 21.9%.After that,the single-factor experiment of vibration amplitude,frequency and forward speed on traction resistance were carried out,the comparison between the soil bin test and the simulation test showed that the trend of the traction resistance in the vibration digging test and the horizontal force in the simulation was consistent with the variation of the motion parameters.Within a certain range of parameters,with the increase of vibration amplitude,it decreased first and then increased,while decreased with the increase of vibration frequency,and increased with the increase of forward speed.And the accumulated angle of soil operation and the process of soil collapse were recorded by high-speed photography equipment.The analysis of soil disturbance showed that the change of accumulation angle of soil operation both in the experiment and simulation were very small,which basically kept at about 16°.The process of soil collapse was periodic as the velocity change of soil particle in forward domain.The above results showed that vibration excavation did have effect on resistance reduction,and its motion parameters such as vibration amplitude,frequency and forward speed had different effects on the excavation resistance.Discrete element method was an effective way to reflect the excavation resistance in digging shovel and soil disturbance in the process of vibration excavation.