Okuma M., Yoshida M., Nakahara T.

In this paper, the authors present a new structural optimization method based on FE modeling, modal analysis and an evolutionary optimization algorithm with respect to dynamic strength and rigidity of structure. This is then very strongly related to structural design of vibration characteristics. The method consists of two optimization processes in outline. The first process is to find the best topology by evolutionarily growth of structure. An structure having any shape can be used as initial structure to be optimized. In general, an initial structure having simple and slender shape will be appropriately available. So the method can make such an initial structure grow evolutionarily. The second process is to optimize the best size of the topologically optimized structure according to externally applied force and load. The method computes some number of natural frequencies and natural modes, and the deformation of the structure due to externally applied force. The algorithm of the proposed method is presented in detail first. A demonstration of a connecting-rod model optimization is presented next as an interesting example. Connecting-rods will be ones of interesting mechanical structural components that must be designed with light weight and enough strength against the inertia load and vibration generated by its kinetic motion and firing impact in piston-crank mechanism. The initial FE model is based on an actual connecting-rod for a kind of small Japanese passenger car. The optimization design of the example is obtained with evaluation of not only strength and deformation but also fatigue strength. The resultant connecting-rod model has lighter and stronger structural characteristics than the initial one.