| Structure optimization is one of the most important methods in thelightweight design. Frame structures made of section bars are widely usedin the load-bearing structures of trucks. In the finite element analysis ofcomplex frame structures, if no simplification is made, brick or shellelements are usually used, but the aspect ratio of elements should belimited in a certain range. For this reason, the number of elements can behuge for the thin section bars. Moreover, the automatic meshing can behardly implemented due to the complicated structure and the large numberof connection points in the frame. As a result, there are two main problemsin the optimization design: on one hand, the structure can’t beautomatically meshed; on the other hand, huge computation might beunavoidable. Although there have already been some mature commercialsoftware in structural optimization, limitations still exist in theoptimization design of frame structures.There are two aspects in the optimization design of frame structures:the section size and the connection positions. Considering that thedeformation characteristics of beam can be found in every section bar ofthe structure, the paper proposed a method for simplifying the structurefrom solid frame to the linear beam model. Based on the simplified model,an optimization method is established for the complex frame structures toacquire the optimized section size and connection positions. Theconversion from the frame structure to the linear beam model was studied,and the automatic conversion software was developed. Meanwhile, thetechnologies in optimizations of the section size and the connectionpositions were also investigated in the frame structure. The methodsmentioned above were then applied in the optimization of a complex truck frame structure, which lead to a reasonable optimal result, and theeffectiveness of the methods was verified.According to the size and characteristics of the section, the method ingenerating section parameters of the linear beam model was built up,which make the conversion from entity structure to linear beam modelboth efficiency and accuracy. With the application of the seconddevelopment interface of HyperMesh software and the data format inABAUQS, a program was developed based on TCL and C#language,which was applied in a semi-automatic conversion from entity structure tolinear beam model. The program can not only enhance the speed of modelestablishment, but also effectively avoid unnecessary omissions and errors.A practically feasible and suitable optimization method for thecomplex frame structure was studied and explored. And the two-stepoptimization was proposed based on the search method thoughts andcompensation method thoughts. The connection positions of beams werefirstly optimized to reduce the maximum stress and homogenize the stressdistribution; the sizes of cross sections were then optimized to determinethe reasonable section size. When optimizing the positions of connectionpoints, the changing direction was defined on the axis of beam. Meshing ofbeam elements was automotive and parameterized as the connection pointsmoved. A section size exponent was defined in the optimization, whichwas optimized to bring out the potentials of the load capacity.A certain type of a truck cab frame from one domestic automobileenterprise was studied. Made up by more than440section bars, it has aframe structure of aluminum alloy profiles with hollow thin-walledcharacteristics. The program developed in this paper was applied to buildup a corresponding linear beam model, which was proved to be inagreement with the calculated result of non-simplified shell element model.Afterwards, the linear beam was set as the model to optimize theconnection points and section sizes, which lead to a light-weight of thestructure and a decrease of the maximum stress from378MPa to124MPa. It was proved that the deformation characteristics of entity beam modelcould be revealed by the linear beam one. And through the optimization,the frame structure is improved with lower weight and more homogenizedstress distribution which meets the requirement of the mechanical property. |
