Based on the DEM-SPH Coupled Method for Analyzing the Dynamic Characteristics of a Spiral Sorting Device for Fish Grading

In the fish grading process, traditional mechanical sorting devices tend to cause fish stacking, collisions, and increased stress responses, seriously affecting fish health and commercial value. This paper designs a power-free fish pre-sorting device based on a spiral chute structure, achieving automatic and gentle separation and output driven by the fish’s own weight and water flow; it constructs a multi-stage dynamic model of fish in the spiral chute to analyze the forces and motion patterns; and it introduces an innovative DEM-SPH coupled numerical simulation technology to accurately simulate the complex interactions between fish and water, thereby revealing the self-sorting mechanism of fish inside the device. By setting different conditions such as fish length and water layer thickness, the sorting effect and stability of the device are systematically verified. The results show that this spiral power-free sorting device can effectively achieve automatic spacing separation of fish, reducing collisions and stress responses; fish of 130 mm length have better sorting stability under a water layer thickness of 3–5 cm, and the minimum initial release spacing for effective operation of the device is determined to be 0.11 m.