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On fluid/structure boundary conditions for fluctuating total enthalpy as the generalized acoustic field

The general problem of acoustical fluid/structure interaction is considered when the usual concept that the interaction at the common surface of the fluid and the solid is one between traditional acoustic waves and the elastic waves in the solid is replaced by one in which the traditional acoustic waves in the fluid are considered instead to be total enthalpy waves - i.e., the basic generalized acoustic waves [1]. The inhomogeneous wave equation for these total enthalpy waves (completely general and exact for a mass-conserving fluid with an ideal gas equation of state) has recently been presented and discussed in detail in reference [1]. Since total enthalpy is defined as H(x k , t) ≡ h(x k , t) + {v i (x k , t)} 2 , where h is the enthalpy, with δh = c p δ T where cp is the specific heat at constant pressure, T is the temperature, x k is the Cartesian position vector and v i is the Cartesian fluid velocity vector, i, k = 1, 2, 3, H is a specific energy (energy per unit mass), a sum of an adiabatic thermal potential energy, h, and a macroscopic kinetic energy, v i 2 Therefore at an interface between a fluid and an elastic solid the boundary conditions involve both thermal and kinetic considerations. These are presented and discussed, for the general case, and an outline of how the necessary and sufficient boundary and initial conditions can be established is presented.