## 3 Results and discussion
### Discussion  
The burying weeding working mode was proposed, the weeding device with driving rake teeth was designed, and the structural parameters and working parameters were optimized to improve the comprehensive operation performance. In the actual operation process in the field, not only is the weeding device needed to effectively ensure the quality of weeding but its effect on paddy soil tillage also needs to be improved to increase the porosity of soil and effectively promote nutrient absorption in the field management period. Due to the complex working environment of paddy fields, the interaction mechanism between mechanical components, water and soil is very complex and cannot be completely determined through theoretical analysis. With the development of computer technology, virtual simulation provides a good technical method for this aspect of study. Many scholars have performed relevant simulation research on this topic. [PERSON] et al. [22] simulated the interaction between plows and soil through the finite element method and explored the best plow angle. [PERSON] et al. [23] established a soil model by using discrete element simulation software and explored the best parameter combination of the trencher of a direct seeding machine for rape. [PERSON] al. [24] used the discrete element method to simulate the infiltration of soil through the cone permeameter and effectively evaluated the mechanical properties of the soil. Most of the above studies focus on dry land with single soil characteristics and obvious particle properties, which is not suitable for complex paddy field environments. The weeding wheel blends the water and soil [25; 26]. However, the paddy field environment cannot be directly observed and analyzed through actual operation. Therefore, to simulate the soil plowing state of optimized weeding wheels, the explicit dynamics software LS-DYNA was used to establish the fluid-solid coupling model of weeding wheels and water soil. The weeding wheels were placed in a paddy field to analyze the soil disturbance and coupling stress. The model of the weeding wheels was simplified to reduce the simulation time and to reasonably and effectively perform simulations and calculations [27; 28]. All materials are defined as rigid bodies, and irrelevant parts are removed. The model of the weeding wheels was meshed by hexahedral grid cells, and the K-files were generated and imported into LS-Prepost of LS-DYNA. The material of the weeding wheels uses the MAT_RIGID keyword, and the parameters of the area were as follows: the density was 0.00786 g/mm\({}^{3}\), the elastic modulus was 2.12 \(\times\) 10\({}^{5}\) MPa, and the Poisson's ratio was 0.288 [29]. The water layer model and soil model were established by LS-Prepost of LS-DYNA. The water model is directly built on the soil model. The node coincidence command is used to overlap the nodes of the two cuboid models to form the coupling model of water and soil. According to the agronomic requirements, the size of the model of the water layer was set at 650 \(\times\) 300 \(\times\) 30 mm, and the size of the soil model was set at 650 \(\times\) 300 \(\times\) 60 mm. MAT_NULL in LS-DYNA was selected as the water layer material. The density was 0.001 g/mm\({}^{3}\), and the cutoff pressure was \(-\)1 \(\times\) 10\({}^{-5}\) MPa [30]. The EOS equation of state was defined to determine the material parameters of soil and air. MAT_FHWA_SOIL in LS-DYNA was selected as the soil layer material. The main parameters were as follows: the soil density was 0.00161 g/mm\({}^{3}\), soil particle density was 0.00273 g/mm\({}^{3}\), bulk modulus was 5.6 MPa, shear modulus was 1.9 MPa, cohesion was 0.0155 MPa, internal friction angle was 15\({}^{\circ}\), and water content was 40% [31]. The selection of other parameters was based on the previously determined value of MAT147. The solid grid cell of the multi-material ALE algorithm was used to define the type of water grid and soil grid cell.