Structural Dynamic Optimization Design Of Spray Boom

Boom sprayers are widely used in crop protection of large filed because of its high efficiency and low damage.During the boom sprayer spraying,the vibration of the boom excited by field ground roughness not only influences homogeneity of spray distribution,but also reduces the life of the sprayer.To improve the structure dynamic behavior of the original boom design,a multi-variable optimization approach by genetic algorithms was presented.The behavior of boom structure was researched by FEM(finite element method).According to the optimal design theory,the mathematic model of the optimization was set up.In the model,shape and section dimension of the boom were taken as design variables to find out a new structure which had better dynamic performance.Then a modal test was be done to verified the dynamic model.The main working and researches have been completed as follows:(1)Based on the trussing characteristic of the structure,the plans and methods of optimal design were be designed.(2)A piece of software for structural dynamic behavior of uniform and homogeneous rods was built by MATLAB.The curve of the relation between factors and first natural frequencies was got in ISIGHT to analyze the section parameters impact on the dynamic behavior.(3)A parametric finite element model of the 18 bar plane truss element was built by the finite element software ABAQUS.Then the mass of spray boom is taken as optimization goal.The element node coordinate and section dimension of spray boom are taken as design variables.All the design variables are transformed to dimensionless variables based on the unified design variable method to avoid optimization analysis failing to converge.(4)The design variables and the optimization goal of the model were set on the Isight multidisciplinary multi-objective optimization platform.Then the mass of spray boom is taken as optimization goal.The first mode frequency of spray boom is taken as constraint condition.The shape of the boom structure and bar section dimension were optimized by using Multi-Island Genetic Algorithm(MIGA)method to obtain a single lance structure with 10.87 Hz first mode frequency,35.82 kg mass and 5 m width.(5)According to technological requirements,the optimized structural dimensionwere adjusted to manufacture an actual sample.In order to ensure the reliability and accuracy of the finite element model,the modal test in impact method was done to validate the finite element model and its modal parameters.In the test,the boom was fixed on the concrete column to make the actual model consistent with the finite element model.Single-point excitation and multi-point acquisition method was used.The exciting signal was generated by an impulse hammer and the response signal was measured by acceleration sensors.Then the modal parameters were identified in the computer.After the test,a comparison between test and simulation was made.The result showed that the difference of first 6 modes frequency between finite element model and test modal model were all less than 10%,the modal assurance criterion(MAC)of the first 6 modes between finite element model and test modal model were all more than 0.85,which indicated that the finite element model and the modal parameters of the model met the requirement of engineering research.(6)A rigid-flexible coupling sprayer virtual prototyping is established in Abaqus to compare vibration displacement between the spray booms before and after optimization.Generally,hose laid was used in the pesticide transport,which has little impact on spray boom structure dynamic behavior.So the pipeline and nozzle was substituted by the uniform distribution mass in the sprayer model.Random vibration response was analyzed under the excitation of power spectrum density(PSD)of the class D road at the tractor speed of 12 km/h.The result showed that the maximal vibration deformations at the end point of the spray boom were about 7.9 mm and 9.5 mm relative to the static condition before and after optimization respectively.The deformations were all less than 10 mm.The maximal deformation after the optimization was not increased obviously with the mass of the optimized spray boom was decreased by 48.43%.