Design and experiment of spin-jet flow type lotus root digging machine based on EDEM-Fluent

Abstract: In order to solve the problems that the manually digging lotus roots was high in labor intensity, low in efficiency and easy to damage lotus roots, and that the existing digging equipment of lotus roots had the defects of high cost and the cumbersome operating process, which needed operator to have a certain experience in technology, a spin-jet flow type lotus root digging machine was designed. The structure and working principle of this machine were described in this paper. And the mechanism of interaction between soil and jet was analyzed by the coupling simulation of the enhanced discrete element method (EDEM) and the fluid dynamics. At the same time, the influence rules of the structural parameters of the key component nozzle were defined. The model of Hertz-Mindlin with JKR (Johnson Kendall Roberts), a cohesive contact model considering the influence of van der Waals force and the viscous contact, was used in the simulation. The EDEM parameters from field measurement and related literatures were as follows: The approximate value of the particle radius was 3 mm by considering computer power and simulation efficiency; the volume density was 1714 kg/m3; the JKR coefficient was 60 in GEMM (Generic EDEM Material Model) database with the repose angle of the soil; the coefficient of restitution was 0.15; the coefficient of static friction was 1.16; the coefficient of rolling friction was 0.2; the elastic modulus of the soil was 1143.2 kPa; and Poisson's ratio was 0.4. The simulation shows that the depth of digging decreases with the increasing of jet angle from 30° to 60°, while increases with the increasing of jet velocity from 10 to 20 m/s. Through the analysis of the simulation process, it can be found that when the angle is 30°, the soil backfill will happen. Based on the three-inch pump HONDA WB30XH, the bench test and field test were carried out, and the results showed that the spin-jet lotus roots digging machine with the 30° jet angle and 17 mm nozzle diameter can advance with the speed of 0.1 s, which can completely dig the lotus roots buried in mud depth of 400 mm without damage and dirt stuck on the surface. And the soil backfill does not affect the floating rate of lotus root. The digging depth can reach 420 mm, while digging width can reach about 1.2 m. It can be obtained from the bench test that the rotation speed of the rotating pipeline also has a certain effect on the digging effect. When the jet angle is larger, the rotation speed of the pipeline is faster, which conforms to the law of fluid mechanics. When the diameter of the nozzle is larger, the rotation speed of the pipeline is also larger. It is shown that larger diameter nozzle produces more reaction force to the pipeline. Comparing the relative floating rate with the pipeline speed, it can be seen that the smaller the rotation speed, the higher the floating rate. Due to the reason of pipeline structure, the rotation speed regulation test cannot be carried out. Furthermore, the average error of digging depth is 9.5% between simulation test and bench test, so the comparison results show that the application of the coupling of discrete element and finite element method of fluid dynamics is feasible in the research of soil-jet interaction. Because the digging process of lotus root below the water is not easy to observe, the application of EDEM-Fluent coupling simulation is beneficial to the study of the mechanism of the lotus root digging equipment, providing theoretical basis for the design and the optimization of the equipment. The method can also be applied to other areas of hydraulic research, such as river and lake dredging, and pipeline cleaning.