TECHNOLOGY AREAS: Information Systems, Battlespace, Human Systems

ACQUISITION PROGRAM: Effects of Sound on the Marine Environment (ACAT IV);

OBJECTIVE: Produce exact acoustic scattering solutions for complex natural (marine mammal) and man-made (submarines, mines) elastic objects embedded in shallow water using recent advances in finite element modeling. Reduce costs for at-sea training and environmental planning by providing a better set of synthetic training and modeling tools.

DESCRIPTION: Modeling acoustic propagation and boundary/target scattering in complex shallow water environments requires numerical modeling. To date, the models used make simplifying assumptions to handle the numerical complexities that arise. Recent advances in finite element modeling hold the promise of producing exact solutions that include the full elastic behavior of ocean seafloors, mammal skeletal structure and man-made objects. Incorporating these solutions into a modular design can improve the speed and versatility of the total model.

PHASE I: Demonstrate the capability to calculate the acoustic field propagated to, produced within, and scattered from a simple elastic object in shallow water. Finite element results must address water depths of 10 to100 meters and source to object ranges of at least 1000 acoustic wavelengths. Elasticity must be included for both the ocean seafloor and the object.

PHASE II: Couple the numerical solutions from Phase 1 to more approximate numerical codes so that scattering can be calculated for source to object ranges of at least 10000 acoustic wavelengths. This phase must include demonstration of front-end modules that allow the user to change the ocean environment and the object being examined without accessing the finite element code backend directly.

PHASE III: A successful development has the potential: to assess exposure levels within the body of a marine mammal or other objects, and to simulate active sonar for both ASW and long range mine countermeasures. SECRET clearance may be required for Phase III.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: The specific application would have primary application in the military or DHS. There is some potential for the technology to spin off to scientific and fisheries applications that involve detection of fish or marine mammals.

REFERENCES:
1. M. Zampolli, A. Tesei, F. B. Jensen, N. Malm, and J. B. Blottman, "A computationally efficient finite element model with perfectly matched layers applied to scattering from axially symmetric objects," J. Acoust. Soc. Am. 122, 1472�1485 (2007).

2. M. Zampolli, A. Tessi, G. Canepa, and O. A. Godin, J., "Computing the far field scattered or radiated by objects inside layered fluid media using approximate Green's functions," J. Acoust. Soc. Am. 123, 4051-4058 (2008).

KEYWORDS: acoustic; scattering; active; sonar; finite-element; modeling