Comments on: Covariance–Invariant Digital Filtering–A Better Digital Processing Technique for Ground Motion Studies; by J. E. Ehrenberg and E. N. Hernandez

摘要

Ehrenberg and Hernandez (1981) have presented a novel recursive digital algorithm for computing the relative displacement of a single degree-of-freedom linear udoscillator subjected to a digitized ground motion record. Their stated aim is to udachieve an accurate and numerically efficient algorithm which will allow the displacement response spectrum at several oscillator frequencies to be computed in udreal time by a microprocessor system. They compare their algorithm, the ud"covariance-invariant filter" with the "bilinear z filter" proposed by Stagner and udHart (1970), and show that the new algorithm gives better accuracy for a given ratio udfs/fn, where fs and fn are the sample and oscillator frequencies, respectively, and that udthe improvement in relative accuracy becomes greater as f~/fn is decreased. Alternatively, for a given accuracy and oscillator frequency, the ground motion can be udsampled at a lower rate for their algorithm, thereby ensuring it is more efficient udcomputationally than the bilinear z filter.