Dynamic Characteristics Analysis And Structural Optimization Design Of Multi-Stage Boom

The boom sprayer is a plant protection equipment which is most commonly used in field pest control.It needs good dynamic performance to ensure the stability and uniformity of spraying.At present,China's boom sprayer is easily affected by external excitation when traveling on the uneven field,resulting in the vibration of the sprayer's body,and even transmitting to the boom,which can cause the vibration of the boom,resulting in the decline of operation efficiency.Therefore,the key to improve the quality of spraying and the uniformity of droplet distribution is to improve the dynamic performance of the boom and reduce the vibration of the boom.In this paper,a five-stage boom sprayer was taken as the research object,and the dynamic characteristics of the boom under the deployment state of the boom were studied according to the initial design defect of the dynamic characteristics of the boom structure.Then the structure optimization of topology optimization and size optimization of spray rod were used to design a lightweight flexible truss boom to meet the requirements of stiffness.Then the test of random vibration simulation was taken and the vibration damping effect of the spray boom was verified,which provided a theoretical basis for the study on dynamic characteristics and structural optimization of multi-stage boom.The specific research work was as follows:(1)Research on the dynamic characteristics of initial model of the multi-stage boom.The 3D software was used to establish the initial geometric modeling of the five stage spray rod,and then the model was imported into ANSYS Workbench to calculate the first 6 natural frequencies and modal shapes of the boom using the finite modal analysis method.The results showed that the first order natural frequency of each boom was in the range of 1~7Hz and of the whole boom was 2.3Hz,which was close to the frequency range of the excitation source and the resonance was easy to occur.(2)Modal test of the multi-stage boom.After towing by a crane and suspending by a spring,the modal test of the spray rod was carried out by hammering method.Comparing the test results with the finite element modal test,it could be showed that the first 8 resonance frequency difference was less than 10% and the corresponding modal assurance criterion was greater than 0.8 and verified the reliability of theoretical analysis.(3)Topology optimization design of the initial multi-stage boom.The distortional strain energy density of the material was taken as the optimization objective,and the topology optimization design based on the variable density method was done in ABAQUS software,according to the initial structure of the spray bar and the actual working conditions.The initial design space of the spray rod was set up and the design domain was established,after which,topology optimization of the structure was done and the topology structure of the boom was obtained,which can meet the stiffness and the vibration frequency requirements simultaneously.Based on the structure,the boom structure was improved and the truss structure with a reasonable material distribution was obtained.(4)Dimension optimization design of multi-stage boom truss.After determining the internal material distribution of the boom structure,it was necessary to optimize the size of the boom truss structure.Defined the quality of spray rod structure as the objective function and the first-order natural frequency of structure was defined as the constraint function,under the premise of ensuring the little change of the stiffness,a flexible lightweight truss structure was obtained with each spray rod thickness decreasing and the overall quality reducing.On the basis,had a dynamic analysis on the optimal spray rod structure,whose results showed that when the quality of the five-stage spray bar decreased 16.3%,the first-order natural frequency of the spray bar was up to 7.39Hz(increased 4.93Hz),which can effectively avoid the frequency range of the excitation sources and reduce the vibration of the spray bar.(5)Stochastic vibration simulation analysis of the optimized boom truss.Based on the topology optimization and size optimization of the initial boom structure,a new nozzle structure with reasonable material distribution and truss size was obtained.On this basis,a new boom prototype was made,for which to have a vibration displacement test of the spray rod prototype.The result showed the maximum displacement response of the vibration response point in the direction of Y was within the range of 200 mm,and the response of the vibration displacement was in the 100 mm range after optimization.The vibration of the boom achieved good results,which proved the rationality of the simulation analysis and verified the optimization effect and dynamic performance of new spray boom.