The Practical Implementation of SEA

Abstract

For the past three decades, structural dynamics prediction models have been almost exclusively based on the Finite Element Method (FEM) together with its Experimental Modal Analysis (EMA) counterpart. Although this tool has proved highly successful for stress and low frequency vibration modelling, it has been found to have severe limitations for noise. This is because the accuracy of many finite element structural models becomes unacceptably poor by about the 10th to 20th mode, particularly if there are bolted or spotwelded joints. The important acoustic frequency range, however, often extends beyond the 100th mode. It is for this reason that there has recently been a renewed interest in the Statistical Energy Analysis (SEA) technique for high frequency vibration and noise prediction. The successful application of SEA in its standard form relies on high modal density, high modal overlap and short wavelengths, ie the very factors which render FEM inaccurate. This is because SEA works with the average response of a structure and it needs these factors to ensure that the average is a realistic and thus a useful quantity. SEA and FEM are therefore complimentary rather than competitive techniques - FEM for low frequency and SEA for high frequency.