An algorithm for computing wavefront amplitudes and inverse problems (tsunami,electrodynamics, acoustics,and viscoelasticity)

An algorithm for computing the amplitude of the leading wavefront generated by an impulse source of oscillations is proposed. According to the algorithm, the fundamental solution is represented in the form of the sum of singular and regular components. As a result, the time required for the amplitude computation is reduced by one order of magnitude. Examples of wavefront amplitudes of tsunami, electromagnetic, acoustic, and viscoelastic waves are given.     

Numerical solution of the problem of computational time reversal in a quadrant

The problem of computational time reversal is posed as the inverse problem of the determination of an unknown initial condition with a finite support in a hyperbolic equation, given the Cauchy data at the lateral surface. Two such two-dimensional inverse problems are solved numerically in the case when the domain is a quadrant and the Cauchy data are given at finite parts of the coordinate axes. The previously obtained Lipschitz stability estimate implies refocusing of the time-reversed wave field in the case of a small amount of noise in the data. It also indicates the possibility of good performance of a proper numerical method. Such performance is demonstrated in this paper for a particular problem and a particular numerical method.     

A numerical method for solving an inverse thermoacoustic problem

In this paper, we consider an inverse problem of determining the initial condition of an initial boundary value problem for the wave equation with some additional information about solving a direct initial boundary value problem. The information is obtained from measurements at the boundary of the solution domain. The purpose of our paper is to construct a numerical algorithm for solving the inverse problem by an iterative method called a method of simple iteration (MSI) and to study the resolution quality of the inverse problem as a function of the number and location of measurement points. Three two-dimensional inverse problem formulations are considered. The results of our numerical calculations are presented. It is shown that the MSI decreases the objective functional at each iteration step. However, due to the ill-posedness of the inverse problem the difference between the exact and approximate solutions decreases up to some fixed number k _min, and then monotonically increases. This shows the regularizing properties of the MSI, and the iteration number can be considered a regularization parameter.     

Justification of the Steepest Descent Method for the Integral Statement of an Inverse Problem for a Hyperbolic Equation

Under consideration is the steepest descent method for solving the problem of determination of a coefficient in a hyperbolic equation in integral statement. The properties of solutions to the direct and inverse problems are studied. Estimates for the objective functional and its gradient are obtained. Convergence in the mean is proved for the steepest descent method for minimizing the residual functional.     

A numerical algorithm for computing tsunami wave amplitudes

A numerical multistep algorithm for computing tsunami wave front amplitudes is proposed. The first step consists in solving an appropriate eikonal equation. The eikonal equation is solved with Godunov’s approach and a bicharacteristic method. A qualitative comparison of the two methods is done. A change of variables is made with the eikonal equation solution at the second step. At the last step, using an expansion of the fundamental solution to the shallow water equations in the new variables, we obtain a Cauchy problem of lesser dimension for the leading edge wave amplitude. The results of numerical experiments are presented.     

A gradient descent method for solving an inverse coefficient heat conduction problem

An iterative gradient descent method is applied to solve an inverse coefficient heat conduction problem with overdetermined boundary conditions. Theoretical estimates are derived showing how the target functional varies with varying the coefficient. These estimates are used to construct an approximation for a target functional gradient. In numerical experiments, iteration convergence rates are compared for different descent parameters.     

Inverse acoustic problems: theory and numerical methods

We study the inverse problem for the acoustic equation. The several numerical methods are considered and investigated. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optimization Methods for Solving Inverse Immunology and Epidemiology Problems

Computational Mathematics and Mathematical Physics - Inverse problems for systems of nonlinear ordinary differential equations are studied. In these problems, the unknown coefficients and...