Calibration and simulation of discrete element contact parameters for subtidal sediments aquaculture of Manila clams

Accurate contact parameters between sediment particles are often required during harvesting buried shellfish, like Manila clam (Ruditapes philippinarum). This study aims to calibrate the contact parameters for the Manila clam in the subtidal sediment aquaculture in the farming region of Dalu Island, Dandong, Liaoning Province, China. The discrete element model was established on the spherical subtidal sediments using EDEM software. Hertz Mindlin with the JKR was chosen as the particle-particle contact model for the sediments with high viscosity and plasticity, such as the subtidal sediments. The combination of simulation and physical tests was used to calibrate the particle-particle contact parameters of the subtidal sediments. Physical tests revealed that the subtidal sediments' moisture content, bulk density, accumulation angle, cohesion, and Poisson's ratio were in the order of 57.40%, 1.66 g/cm³, 38.87°, 6.28 kPa, and 0.27. According to the funnel method, the accumulation angle of the subtidal sediments was found to be 51.00°. The Generic EDEM material model database (GEMM) was used to measure the material properties of the subtidal sediments. The simulation size was chosen to be the small scale. The specific range of contact properties was required for calibration, including the JKR surface energy 4.50-18.00 J/m², coefficient of restitution 0.35-0.75, the coefficient of static friction 0.20-1.04, and coefficient of rolling friction 0.10～0.20. The three-level simulation was then carried out using the Box-Behnken principle. A regression model was developed for the accumulation angle, thus taking the response value from the simulation. The JKR surface energy, coefficient of restitution, coefficient of static friction, and coefficient of rolling friction were optimized to be 10.96 J/m², 0.37, 0.63, and 0.10, respectively, using Design-Expert software. There was a relative error of 2.29% in the accumulation angle between the simulated (49.83°) and the physical test (51.00°) under the optimal combination. The rotational tillage test was performed on the subtidal sediments after the indentation test while considering the strain surrounding the subtidal sediments. Six sets were compared on the subtidal sediments as part of the rotary tillage test. The results demonstrated that the smallest relative error was achieved in the torque of the blade shaft during rotary tillage, compared with the physical test. There was an error value of only 7.76% in the significant amount of experimental data under the set of multiple parameters. The high accuracy and dependability of the calibrated discrete element model were achieved for the subtidal sediment particles from the standpoint of error analysis. Therefore, the JKR surface energy, coefficient of restitution, coefficient of static friction, and coefficient of rolling friction between subtidal sediments were taken as 10.96 J/m², 0.37, 0.63, and 0.10, respectively, in the discrete element simulation. The accurate and dependable calibration was realized on the contact parameters between subtidal sediment particles. The finding can provide valuable references on the interaction among subtidal sediments, clams, and harvesting devices.