It is a recent trend for advanced ships and submarines to apply composite structure with damped material. Many researches on optimization technique for vibration characteristics have carried out in order to reduce vibrations and noises.
There are two methods on vibration analysis for structural dynamic. One is a finite element analysis, the other is experimental vibration analysis.
First, the finite element analysis can accurately analyze vibration parameters but it has a defect, that is, the computational time rapidly increases when structures get bigger and bigger.
Second, the experimental vibration analysis is the process to identify structural dynamic characteristics such as natural frequencies, modal damping ratios and mode shapes.
In this study, optimum analysis for nonproportional damping system is conducted using the multi-level optimization technique, where finite element analysis and experimental vibration analysis are combined.
The results obtained in this research are accurate and computational time is decreased. The results show that this technique is useful for the optimum modification of vibration characteristics for nonproportional damping structures.