A COMPARISON OF APPROXIMATE BOUNDARY-CONDITIONS AND INFINITE ELEMENT METHODS FOR EXTERIOR HELMHOLTZ PROBLEMS

We compare the accuracy of a variety of approximate boundary condition s (ABCs) and two versions of an infinite element method (IEM) for appr oximating solutions of exterior Helmholtz problems. The infinite eleme nts are of variable order in the radial direction and differ only in w hether the test functions in the weak formulation are conjugated or no t. We find that the accuracy of the ABCs decreases with increasing fre quency, and that at higher frequencies their accuracy is several order s of magnitude lower than that obtained with the IEMs. We show that th e convergence rate of the conjugated element is slower than the rate f or the unconjugated element and that the latter element fails to conve rge in the far field. (C) 1998 Elsevier Science S.A. All rights reserv ed.