Energy density equations and power flow in structures

A potential alternative to Statistical Energy Analysis that is gaining increasing interest in recent years is the “thermal” energy flow approach. Its advantage is represented by the possibility of modelling the spatial distribution of energy density at high frequencies, thus yielding a more effective estimate of the system behaviour than the average constant value given by SEA. However, the thermal analogy proposed by the energy flow approach is questionable for any type of wave in any type of structure. To make the analysis more clear, exact equations for power balance in continuous structures are derived. The investigation confirms the questionability of the thermal approach and shows whether and when it is possible to determine exact equations for the energy density. Physical considerations are developed to explain some critical points. For one-dimensional systems a transmission potential is defined in analogy to the temperature in heat conduction problems.