THE GENERATION OF WAVES IN INFINITE STRUCTURES BY MOVING HARMONIC LOADS

The theory of convolution is extended to account for time-varying load s moving over infinite systems. Fourier transforms are used to simplif y the convolution, reducing it-to a multiplication of transforms of sy stem impulse response and load. Ifa harmonic load is moving over the s ystem it is found that the possible existence of travelling waves can be identified, for a given system, load frequency and velocity, withou t the need to perform the inverse Fourier transform, a task which is o ften difficult. The possible presence of travelling waves can be ident ified by a simple method involving straight line constructions on a pl ot of the system's frequency spectrum. The phase velocities, group vel ocities and frequencies of waves ahead of and behind the load can be i dentified along with any critical speeds and velocities that may exist .