Acoustic scattering from submerged and buried objects

• Two techniques are described for numerical prediction of transient scattering by 3D objects in the water column or buried in the bottom sediment. In the first method,b the scattering problem is formulated as a boundary integral equation (BIE) for a three-dimensional body inside a range-independent layered fluid-solid medium. The Green's function of the layered medium is computed by an accurate transform integral method employing exact finite elements and adaptive high-order numerical integration. A Burton-Miller formulation of the BIE is used, leading to a linear combination of weakly singular and 'hypersingular' BIE free from artificial singularities. The BIE is discretized using B-spline basis functions, global high-order integration and point collocation, and then solved iteratively with a preconditioned generalized minimum residual (GMRES) method. The second method is a fast approximative scattering model based on a combination of acoustic ray tracing and Kirchhoff's approximation of the scattered field. Both methods are formulated in the frequency domain, and Fourier synthesis is used for computing transient fields. Examples of scattered pulses predicted by the two techniques are presented. The predicted fields are compared with data from experiments in which a semi-buried object was probed by a ROV-mounted parametric sonar and the scattered field was registered by bistatically located receivers. A method for identification of parameters of the scattering objects, based on the fast scattering model combined with an algorithm for global nonlinear optimization is described. Both the optimization method and the fast scattering model are highly parallelizable, and are implemented on workstation clusters under MPICH, allowing for convenient handling of also computationally demanding broadband excitations. Some examples of parameter inversion results using experimental data from the EU project SITAR are presented. ©

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Maskinteknik -- Strömningsmekanik och akustik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Mechanical Engineering -- Fluid Mechanics and Acoustics (hsv//eng)

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