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Most of the tidal flat shellfish harvesting equipment predominantly employed tracked or wheeled walking devices, which encountered issues such as significant sinking of the driving components during operation, poor load-carrying capacity of the devices, and high maintenance costs in the later stage. Therefore, this paper designed a tidal flat walking device based on the principle of spiral propulsion, which could be used for transportation, and conducted structural design and experimental research on the walking device. The impact of the spiral blade structure on working performance was analyzed by using DEMMBD(discrete element method-multibody dynamics) coupling simulation technology. A single-factor test was carried out to identify the optimal range for height, thickness, and helix angle of spiral blade on the walking mechanism. Subsequently, a three-factor and three-level orthogonal test method was then used to determine the optimal design parameters of blade. Finally, no-load and load operating performance tests were carried out on an experimental prototype, which was constructed according to similar criteria to evaluate the working performance of the designed running gear. The results indicated the following: 1) When all factors were independent, the slip rate of the walking device increased with higher helix angles. Both the traction force and working efficiency of the walking device initially increased and then decreased with higher helix angles. The slip rate of the walking device increased with the thickness increased, while working efficiency and traction coefficient of the walking device followed an initial increase and then decrease pattern. On the other hand, increasing the height-to-diameter ratio resulted in a decrease followed in slip rate of the walking device. The traction coefficient, increased overall with higher height-to-diameter ratios, with working efficiency exhibiting a similar trend. 2) The walking device demonstrated optimal driving performance with a helix angle of 25°, a height of 150 mm, and a thickness of 7.5 mm as determined by orthogonal test. 3) The slip rate of the walking device was 46.92% with no load, 63.56% with a 10 kg load, and 58.34% with a 15 kg load. The slip rate displayed an overall upward trend with increasing load. The subsidence amount was directly proportional to the load, with values of 47.59, 60.09, and 70.22 mm for no load, 10, and 15 kg load respectively, with a proportional coefficient of 1.512. 4) The rated load of the walking device was approximately 8 kg while the ultimate load was around 21.61 kg, which demonstrated its robust carrying capacity in the tidal flat environment. 5) In comparison with the simulation experiments, the deviation rates of subsidence and slip rate were 10.191% and 3.176% with no load, 3.744% and 3.571% with a 10 kg load, and 24.614% and 4.061% with a 15 kg load respectively. This affirmed that the simulation results could offer reference for prediction and analysis of walking device performance. These research findings were valuable for the development of more efficient tidal flat harvesting equipment with stronger carrying capacity. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]