Determination of forcing functions in the wave equation. Part I: the space-dependent case

We consider the inverse problem for the wave equation which consists in determining an unknown space-dependent force function acting on a vibrating structure from Cauchy boundary data. Since only boundary data are used as measurements, the study has given importance and significance to non-intrusive and non-destructive testing of materials. This inverse force problem is linear, and the solution is unique, but the problem is still ill-posed since, in general, the solution does not exist and, even if it exists, it does not depend continuously on the input data. Numerically, the finite-difference method combined with Tikhonov regularization is employed in order to obtain a stable solution. Several orders of regularization are investigated. The choice of the regularization parameter is based on the L-curve method. Numerical results show that the solution is accurate for exact data and stable for noisy data. An extension to the case of multiple additive forces is also addressed. In a companion paper, in Part II [J Eng Math 2015, this volume], the time-dependent force identification will be undertaken.