Statistical Energy Analysis (SEA) is a powerful method for prediction of the response of complex coupled acoustic spaces
and structures. The method was originally developed in the sixties for prediction of the response of the Saturn launch vehicle.
The method has undergone continuously development and it has been applied successfully to most areas of engineering e.g.
aerospace & spacecraft structures, road & rail vehicles, civil engineering structures (buildings) and naval structures.
Statistical Energy Analysis is primarily intended for high frequency prediction. The term 'high frequency' depends on the
size of the structure. By high frequency is normally meant that the wavelength is relatively short compared to the dimensions
of the structure. For a car, high frequency might be above say 500Hz. In the high frequency range the dynamic response is
normally rather sensitive to exact dimensions, material properties, assembly etc. and this makes it difficult to predict
the response accurately. A deterministic approach such as e.g. the finite element method will normally not be
suited for high frequency predictions due to the uncertainties as well as the number of elements required.
The 'Statistical' in Statistical Energy Analysis refers to that SEA employs certain averaging procedures and that it aims
at predicting the response of an average structure so-called assembly average. Assuming that the conditions for SEA are fulfilled,
a good prediction will normally predict the response levels within ±3dB.
The 'Energy' in Statistical Energy Analysis refers to that the primary parameter for a SEA model is the energy level of
the various sub-systems: acoustic and structural. As there is a relation between energy of acoustic spaces and structural
systems it is possible from the energy levels to estimate the sound pressure levels for acoustic spaces and vibrations levels
for structural systems.
An important part of a Statistical Energy Analysis model is to predict accurately the energy exchange between various parts
of the SEA model. These SEA energy exchanges are found from coupling loss factors,ηij,
that normally are calculated from transmission coefficients, τ, and sound radiation
efficiencies, σ. These coefficients and efficiencies are either determined from analytical
calculations, measurements or finite element models. An example of transmission coefficients, τ,
for plate to plate coupling is shown in Fig. 3. The transmission coefficients shown in Fig. 3 are for an incident
bending wave on a 900 degree plate junction. The coefficients are a function of angle of incidence cos(φ). Three wave types are required to fulfil the boundary conditions at the coupling:
bending waves, shear waves and longitudinal waves. The sound radiation efficiencies, σ,
(Figs. 4 & 5) are used for calculation of the coupling loss factors between structures and acoustic fluids. For sound
transmission through partitions, transmission coefficients similar to those shown on the page are employed.
