Identification of external excitations in self-adjoint distributed systems using modal filters

A method is presented for the identification of external excitations acting on distributed parameter systems and, for certain special cases, the parameters contained in the equations of motion. By extracting the modal co-ordinates from the system output, and using these modal co-ordinates to identify the modal excitations acting on a number of modes, the actual external disturbances are synthesized. The modal co-ordinates are extracted from the system output by interpolation of the sensors measurements and use of the expansion theorem, a process known as modal filtering. It is shown that the accuracy of the identification improves as the number of sensors is increased. The effects of factors such as measurement noise and interpolation error are analyzed.