## 4pUW10. Acoustic radiation or scattering: A multifrequency analysis by boundary element method.

### Session: Thursday Afternoon, December 5

### Time: 3:37

**Author: Christian Vanhille**

**Location: Inst. d'Electronique et de Microelectronique du Nord, U.M.R. C.N.R.S. 9929, Dept. I.S.E.N., Lab. d'Acoustique, 41 Boulevard Vauban, 59046 Lille Cedex, France**

**Author: Antoine Lavie**

**Location: Inst. d'Electronique et de Microelectronique du Nord, U.M.R. C.N.R.S. 9929, Dept. I.S.E.N., Lab. d'Acoustique, 41 Boulevard Vauban, 59046 Lille Cedex, France**

**Abstract:**

In the field of underwater acoustics, the boundary element method is
usually used to model acoustic radiation or scattering from an immersed
structure impinged by an acoustic wave. The EQI boundary element code uses
Helmholtz integral equation. The Sommerfeld radiation condition is implicitly
included in the formulation, and the pressure field in the surrounding fluid is
evaluated from the mesh restricted to the surface of the body. At some
frequencies called irregular frequencies, this integral formulation presents an
infinite number of solutions. This problem is solved with the help of the Jones
method: The integral equations system is overdetermined by null-field equations.
For a multifrequency analysis, integral equations matrix assembling is very
computation time consuming. A new boundary element algorithm based upon a
frequency interpolation is proposed. It is adapted to quadratic isoparametric
discretization for any geometry. This technique is original for two reasons: the
automation of its utilization between 0 Hz and the top frequency of the
spectrum; its adaptation to axisymmetrical problems by decomposition of circular
integration surfaces. This algorithm allows an important saving of computation
time which increases with the size of the problem without loss of precision.

ASA 132nd meeting - Hawaii, December 1996