Finite-element modeling of acoustic scattering from 3-D elastic structures

David S. Burnett
Naval Surface Warfare Center
Panama City, USA

The author is integrating a suite of software tools for modeling the scattering of acoustic beams (sonar) from undersea targets (mines) that may be buried or partially buried in the sedimentary ocean bottom in littoral (shallow water) environments. This is a Multiphysics problem involving acoustic waves in the water, acoustic or poro-elastic waves in the sediment, and both elastic and acoustic waves in the targets. It is also a multiscale problem, both spatially and temporally. Spatially, dimensions range from O(10-2 m) for important target details to O(103 m) for the littoral ocean environment. Temporally, the acoustic sources are broadband, with frequencies ranging from O(103 Hz) to O(105 Hz), resulting in an even greater range of wavelengths due to the presence of “evanescent” waves next to the target.

These spatial and temporal multiscale features necessitate a variety of different computational strategies. The author is bringing together four major software systems, with COMSOL Multiphysics being the central one for modeling the complicated nearfield target scattering, with its mix of evanescent and propagating waves; the other three will be coupled to COMSOL Multiphysics’ input or output.

Verification (of the finite-element solution relative to the exact solution of the idealized mathematical model) and validation (of the idealized mathematical model relative to the real world) play a key role in this multiyear project; they are essential to the goal of producing reliable simulations of the real world.

The talk will explain physical phenomena that guide the modeling approach, present highlights of the other codes and how they will interface with COMSOL Multiphysics, and show progress to date with COMSOL Multiphysics and challenges lying ahead. A few examples from the author’s previous modeling experience will illustrate why it is expected that this suite of software, with COMSOL Multiphysics at the core, will provide the “next generation” in computer simulation of structural acoustic target scattering.

Keynote speaker's biography: Dave Burnett worked more than 28 years at Bell Laboratories (of Lucent Technologies; formerly part of AT&T), primarily in undersea R&D for the U.S. Navy, specializing in theoretical and computational mechanics (elasticity and acoustics). In the ‘80s and ‘90s he was a group technical leader for the development of 3-D finite-element structural acoustics codes for anti-submarine warfare applications. In 1983 he received the title of Distinguished Member of Technical Staff, and in 1996 the title of Fellow, Bell Labs’ highest honor. In 1998 he retired from Bell Labs to take up a position as Principal Scientist for the Supreme Allied Command Atlantic of NATO, at the Undersea Research Center in La Spezia, Italy, where he was project leader for the development of 3-D finite-element structural acoustics codes for modeling scattering from undersea mines. In 2004 he retired from NATO and began his next adventure at the Naval Surface Warfare Center in Florida, where he is currently bringing together a variety of computational technologies, including COMSOL Multiphysics, for modeling acoustic scattering of sonar signals from complex targets in realistic undersea environments, from low to high frequencies. Dr. Burnett received BS and M. Eng. degrees in Engineering Physics from Cornell University, an MS in Engineering Science from the California Institute of Technology, and a PhD in Applied Mechanics from the Univ. of California, Berkeley. He holds twenty-five U.S. and international patents in the fields of computational acoustics and electromagnetism and is the author of Finite Element Analysis: From Concepts to Applications.

David S. Burnett was one of the keynote speakers at the COMSOL User's Conference, fall 2005 in Boston