滩涂土壤离散元接触模型优化与现场铲削试验

Optimization of the discrete element contact model for tidal flat soil and field shoveling experiment

为解决现有离散元接触模型对滩涂土壤特性表征准确性差的问题,该研究基于离散元仿真软件EDEM的API二次开发功能,以Hertz-Mindlin接触模型为基础,通过增加塑性、粘附特征并更改切向滑动摩擦力,得到优化后的高湿黏弹塑性(moist elasto-plastic adhesion,MEPA)模型。通过模拟活塞拔出试验,结合Plackett-Burman试验筛选出影响标定指标的显著参数,完成接触模型参数标定。搭建了铲削试验平台进行现场铲削试验,对比分析了MEPA模型、JKR模型、EEPA模型以及Bonding模型的土壤特性表征效果。试验结果表明,在铲削阻力方面,MEPA模型较JKR模型、EEPA模型和Bonding模型的仿真精度分别提升约65.957%、74.206%和59.326%;相较于现场试验结果,MEPA模型的堆积厚度与侧边距相对误差分别为5.598%和6.362%,两者均保持在10%以内,能够较好地模拟滩涂土壤,对滩涂工作装置的工况模拟和优化设计具有重要意义。

A contact model can be expected to accurately and rapidly characterize the tidal flat soil using the discrete element method(DEM).In this study,the contact model was optimized using the API secondary development function of the discrete element simulation software(EDEM).The target model was selected as the Hertz-Mindlin contact model.Firstly,the plasticity and adhesion were added to the normal contact force.Secondly,the sliding friction force with the relative tangential velocity was input into the tangential contact force.Then,the moist elasto-plastic adhesion(MEPA)model was obtained.The maximum normal pressure and normal adhesion force of the piston pull-out test were selected as the indexes of virtual calibration.Plackett-Burman test showed that there were significant effects of the correction coefficient of sliding friction,Young's modulus of soil,static friction coefficient between soil particles,rolling friction coefficient between particles,static friction coefficient between particles,and geometry on the maximum normal pressure of the probe.The maximum adhesion force of the probe depended mainly on the adhesion coefficient between particles and the geometry and their interaction.The piston pullout test showed that the combination of parameters was achieved in the comparison indexes for the virtual calibration of tidal flat soil under target working conditions,including the 0 h settling time,0 min contact time,and 210 mm/min separation velocity.The virtual calibration of DEM parameters was realized using non-significant and significant parameters.Among them,the non-significant parameters were referred to the existing data,while the significant parameters were continuously adjusted to make the simulated curve of piston pull-out force close to the actual.The MEPA,JKR,EEPA,and Bonding models were compared to characterize the tidal flat soil.The shoveling test platform was then built to verify the accuracy of the models.The tidal flat soil with a thickness of 11 cm was accumulated in the soil box.The digging shovel had a cutting depth of 5cm in the soil box.Two tests were set firstly,where the angle of the digging shovel was adjusted to 25°and 30°,respectively,and the forward speed was 0.08m/s.Then one test was that the digging shovel angle of 20°,and the forward speed of 0.16 m/s.The force was accurately obtained at the sensor of the shoveling device.The EDEM and the multi-dynamics(RecurDyn)software were also selected to simulate the shoveling.The test results showed that the average absolute error of the MEPA model was controlled within 50 N,compared with the actual shoveling resistance.The simulation accuracies of the MEPA model were about 65.957%,74.206%,and 59.326%higher than those of the JKR,EEPA,and the Bonding model,respectively.Compared with the field test,the relative errors of the MEPA model were 5.598%and 6.362%in the soil accumulation thickness and side margins,respectively.Both errors were remained within 10%.Therefore,the MEPA model can be used to better simulate the tidal flat soil.It is of great significance to simulate and optimize the tidal flat device.