Abstract
Estimation of the numerical errors on Fourier Transform method for a request of time series response of one dimensional wave function included viscoelastic term. This errors was guessed from the response of vibrational system of one degree of freedom. According to studies, especially important errors are discrete error and circulation error. 1) Discrete error This error is determined by relation of sampling ratio and natural period of system. Relative error is 0.28% in case that sampling time is one ten of natural period of system, and in case of one twenty, error is 0.034%. 2) Circulation error This phenomenon is that a part of free vibrational response of system turn to front of data. This quantity relate to natural period and damping factor of system, the more long of period and small of damping the more increasing of error. In case of multi-layerd structural ground, at the surface response to income wave, circulation error is most in comparison of other boundary response. But we can avoid this error by waste calculation about 15-20 seconds. When we assume viscosity in the layer, absolute value of circulation error decrease, but relative error not decrease because of whole amplitude too small. As above mentioned, practically, when we adopt that sampling time is 0.02 second and waste calculating time is 15-20 seconds, relative error is inner of 5%.
