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

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 pull-out 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.