8 Coupling Loss Factors
The first step in SEA modelling is to find a realistic description of the subsystems by a diffuse wave field. Wavenumber, group wave speed, and geometry provide the modal density. From the physics of wave motion the relationship of the wave physical quantities (pressure, displacement) to physical units is derived. The damping properties are measured or estimated.
Once the properties of the subsystems are fixed, the next step is the derivation of the coupling loss factors using equation (7.27). So, why do we spend a full chapter with coupling loss factor derivation?
First, it is a complicated task that it is often neglected in textbooks. Starting from expression (7.27) there is a clear and straightforward rule, but we need a certain set of matrices and at least the radiation stiffness matrices for two coupled subsystems. Depending on the choice of degrees of freedom, the expressions for the radiation stiffness and the total stiffness can be very complex.
Second, the understanding of the coupling phenomena is very important for noise control in general. When we thoroughly understand how waves are transmitted through junctions, we have the key in our hand to reduce the amount of transmitted acoustic or vibrational power.
Third, the value of the coupling loss factor determines if it makes sense to perform the SEA approach for the chosen subsystem configuration. Lyon and DeJong (#c8-bib-0008) quoted that for coupling loss factors higher than the damping ...
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