Study On Fluid-solid Coupling Numerical Simulation In Rice Transplanting Process

The technology of machine-planting rice paddy seedlings originated from Japan and developed rapidly after localization and improvement.But our country has complex terrain and diverse planting systems.In multi-cultivation areas such as rice-wheat areas,rice-oil areas and double-cropping rice areas,the next crop is delayed because of short interval between crops for rotation.In areas with multiple one-time irrigation such as water scarce areas,high terrain areas and integrated farming of rice and aquatic animal areas,weed becomes a problem.These problems restrict the popularization and application of the technology of machine planting rice paddy seedlings.Due to large vegetative,strong resistance and strong rejuvenation of big seedling plant,machine planting rice big seedlings with long seedling age can effectively alleviate these problems with small seedling machine-planting.However,the current rice transplanter is difficult to meet the production needs of big seedlings.There are some problems such as leaves bridging,pushing seedlings,and hurting seedlings.The interaction mechanism between seedlings,seedling transplanters,and paddy soil in the mechanical transplanting process is still blank.Therefore,it is necessary to explore the causes of problems such as poor seedling growth and heavy seedling injury in big seedling machine planting.This paper first studies the physical and mechanical properties of rice seedlings,and carry out dynamic analysis of seedlings and transplanting mechanism.On this basis,the numerical simulation technology is used to clarify the interaction mechanism between seedlings,seedling transplanters and paddy soil.The main research contents and conclusions are as follows:(1)The microstructure,macrophysical properties and mechanical properties of rice seedlings were measured and tested,and the correlation between microstructure and macrophysical properties and mechanical properties was analyzed.The results showed that the cross-sectional microstructure of rice seedling stalks was oval-like wrapped by multi-layer mesh-like leaf tissues.Within 15-35 days of seedling age,the shear strength,shear modulus,and compression energy of various rice stems varied seedling age first increases and then decreases.The elastic modulus decreases first and then increases.The overall trend of shear work increases with seedling age.Except for shear strength,the mechanical properties of rice stalks of various varieties are significantly or extremely significantly related to the number of large and small vascular bundles.The correlation between mechanical properties and macroscopic physical properties is dominated by genetic properties,and varieties with similar genetic properties(plant type,genotype)perform more consistently.(2)Determine the type and trajectory parameters of the large seedling transplanting mechanism.Based on the physical characteristics of rice seedlings,the kinematics and dynamics theoretical analysis of the seedling-contacting components was carried out.The mechanical state of the seedlings in the three stages of transplanting,transporting and transplanting was analyzed during the mechanical transplantation operation.Various factors affecting the planting effect of rice plants were clearly defined.The results show that the difference between the initial installation angle of the crank and the cam affects the seedling standing.The factors affecting the mechanical transplanting effect of rice seedlings mainly include the cohesion between the matrix soil,the friction coefficient between the seedling and the seedling claw,the opening width of the seedling claw,the cam installation angle,the crank angle Speed,seedling height,seedling stalk cross-sectional area,paddy soil type,paddy field water depth,mud water density.(3)Simulated the interaction of rice plants,sub-transplantation mechanism and paddy soil in the process of machine transplanting based on ANSYS/LS-DYNA software.The stress and deformation of the rice plant during the mechanical transplanting process were obtained.On the basis of the orthogonal combination test method,the stress changes of rice plants in the process of transplanting rice and the posture after transplanting were analyzed to determine the optimal parameter combination.The results show that the order of the factors affecting the maximum stress of the seedlings are the width of the claw,the cam installation angle,the crank angular velocity,the water depth of the paddy field,and the plant height of the seedlings.The order of the factors affecting the inclination of the seedlings are the cam installation angle,Seedling height,paddy field water depth,crank angular velocity,seedling claw width.When the cam installation angle is 3 °,the width of the seedling claw is 8 mm,the crank angular velocity is 35 rad/s,the seedling height is 28 cm,and the water depth of the paddy field is 6 cm,the seedling damage is minimal.When the cam installation angle is 2 °,the width of the seedling claw is 4 mm When the crank angular velocity is 31 rad/s,the seedling height is 24 cm,and the water depth of the paddy field is 2 cm,the seedling stands best.(4)Based on the results of the simulation test,the three most significant factors are selected to carry out the three-factor three-level orthogonal test on the integrated test bench of the add-drop mechanism.verified the feasibility of the simulation test.Obtain best matching structure and working parameters in the deep water field environment and the state of long seedlings.