Research On The Mid-frequency Vibration Analysis Of Ship Structure

The frequency spectrum,where simulation methods can be utilized for vibration analysis,can be divided into three regions:low,mid and high frequency.In the low frequency region,FEA was widely used,and SEA was universal applied in the high frequency.The mid-frequency vibration analysis contained FEA which solved vibration for deterministic substructure and SEA which solved vibration for underminstic substructure at the same time.According to the hybrid FE/SEA theory,the mid-frequency vibration analysis was divided into three steps:(1)The whole structure was divided into FE substructure and SEA substructure.(2)According to effective impedance,FE substructure was solved.(3)Bring in the result of FE substructure vibration,FE substructure was solved.This paper concerned mid-frequency vibration problems and the hybrid methods were developed to solve such problems.A beam-plate system was involved as an example to show the mid-frequency problem and to study the influence of boundaryconditions on the effective impedance of flexible members.The numerical results were obtained and compared with the dense mesh,coarse mesh and the hybrid methods.The results were accurate obtainded with the dense mesh and the hybrid FE/SEA methods,errors obtained with coarse mesh method.The cost of the dense mesh method was enormous.A stiff beam-flexible plate system is employed to study the sensitivity of the effective impedance and the response variance induced by the uncertainty of the effective impedance.The numerical results show that the vibration mode and the static mode have the most significant influence on the effective impedance.The response variance induced by the uncertainty of the effective impedance is not significant.