In this paper, we present a shape identification of a cavity in a structure based on the finite element and the adjoint variable methods using the hammering testing data. The governing equation is employed the equation of motion in the three dimensions. A formulation of the problem based on the adjoint variable method is performed to find the optimal cavity shape so as to minimize the residual between the computed displacement and the observed displacement. The random tunneling algorithm is introduced to obtain the optimal cavity shape. Some numerical experiments are carried out to investigate the effects of several hammering force on the accuracy of the identified cavity shape.
