Research On Topology Optimization Design For Head Section Of Crane Lattice Boom

Topology optimization design for head section is one of the key issues in structural design of crane lattice boom. Because its reasonableness of material layout can directly influence the mechanical properties and the scale of overall anti-buckling capability of lattice boom, thereby affecting the overall lifting performance of the lattice boom crane.The structure of lattice boom head section is complex and has diverse working conditions, it is not easy to obtain optimal solution using conventional topology optimization way. A new approach of optimal design has been proposed to deal with such problem, the general ideas of which are as follows:Firstly, based on the elastic stability constraint method, the optimal distribution for joint point of boom head can be obtained which aims at minimizing buckling strain energy. Secondly, the topology optimization for boom head under multiple static loading cases can be solved using modified compromise programming approach based on grey method. Lastly, nonlinear filter technique is applied in topology optimization to prevent numerical instabilities and ensure manufacturability avoiding grey material boundary. The main works of the dissertation are as follows:(1) Elastic stability constraint-based method for joint point distribution optimization of the lattice boom head sectionBased on Timoshenko theory, the truss boom can be simplified into Timoshenko beam. The mathematic model based on such simplification has been set up and aims at minimizing buckling strain energy. The genetic algorithm has been adopted to optimize the joint point distribution of the truss boom head section.(2) SIMP-based method for continuum structural topology optimization under single load caseBased on the SIMP material interpolation schemes, the topology optimization mathematic model has been set up for lattice boom head under single static loading case. The optimality criterion has been set up for the single stiffness topology optimization design under single static loading case.(3) SIMP-based method for multi-objective topology optimization of the lattice boom head sectionBased on SIMP method, the multiple stiffness topology optimizations mathematic model has been set up for lattice boom head section under multiple static loading cases using compromise programming approach. An expert evaluation method of weights based on grey system is introduced to obtain reasonable objective weights eliminating subjective factors. The optimization model is solved in the OptiStruct software.(4) Nonlinear filter techniques in topology optimization avoiding grey material boundaryTo prevent numerical instabilities, such as checkerboard and mesh independency, and ensure manufacrurability, filter techniques should be applied in topology optimization. However, when conventional filters are used, some grey elements often emerge along the material boundary which causes difficulty in extracting structural boundary from the optimal topology result. Nonlinear filter techniques, such as Heaviside nonlinear density filter and modified Heaviside nonlinear density filter, can eliminate grey domain along material boundary, but they cannot maintain the material volume which causes oscillation during optimization iteration. Different from the two Heaviside nonlinear density filters, volume preserving density filter based on Heaviside function is volume preserving, which ensures efficiency and stability in optimization.A volume preserving density filter is presented in this paper. Through a compliance minimization problem in engineer practice, the filter has been verified to be efficiency and stability in optimization. Compared with the volume preserving density filter based on Heaviside function, this filter’s function is much simpler in expression and astringency in computing.