Mapped infinite wave envelope elements for acoustic radiation in a uniformly moving medium

Variable order mapped infinite wave envelope elements are developed for finite-element modelling (FEM) of acoustic radiation in a uniformly moving medium. These elements can be used as a non-reflecting boundary condition for computations on an infinite domain in which a radiating body is immersed in a moving medium which is essentially undisturbed outside of the near field. An additional result of this study shows that the mapped wave envelope elements provide a boundary condition equivalent to stiffness, mass, and damping matrices appended to the inner mesh. By choosing the transition between the standard FEM mesh and the mapped infinite wave envelope as a surface of constant phase the mass matrix is caused to vanish identically. This has implications for transient FEM modelling of acoustic radiation. A demonstration of the characteristics of mapped infinite wave envelope elements is given in the context of acoustic radiation from a turbofan inlet for which benchmark results are known. (C) 1999 Academic Press.