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This paper describes a new method for engine design using dynamic optimization and substructure synthesis method. A very important theme in engine design is how to shift the peak of the natural frequency of the vibration mode that causes some noise and vibration problems. This must be resolved by effective modification of structural design. In order to carry out effectively vibration analysis of a large scaled structure like engine assembly and conduct dynamic optimization with many iterative calculations, we have used substructure synthesis method that devides a whole structure into a number of substructures and solves each substructure. Vibration analysis of engine assembly (cylinder block, crank shaft, bearing caps and flywheel systems) was carried out by using this substructure synthesis method.

A new method is introduced here to identify modal parameters by fitting curves with multiple degrees of freedom to experimental data in frequency domain. Unknown parameters in our method are natural frequencies and modal damping ratios, and, from these parameters natural modes and residual terms are determined. In comparing our method with the conventional Van Loon's method, fewer unknown parameters are dealt with, and thus computing time is shorter with better convergence of solution. Simulation results obtained show that our method is useful especially in refering to many data simultaneously.