Evolutionary spectra-based time-varying coherence function and its engineering application

Priestley's evolutionary spectral theory, due to its physical meaning, is extensively employed in the characterization, modeling and simulation of multivariate nonstationary excitation processes and the structural dynamic analysis under these excitations. When the nonstation-ary processes are modeled as oscillatory processes, the evolutionary spectra-based coherence function becomes time-invariant. The sigma-oscillatory process theory and Wold-Cramer decomposition model can be used to account for the time-varying coherence function. The Wold-Cramer decomposition model is a special case of the general sigma-oscillatory process theory. Due to the simplicity of Wold-Cramer decomposition model, it is applied to model the nonstationary winds and the corresponding alongwind response analysis framework of tall buildings in engineering field. Taken the measured wind speed data as an numerical example, the time-varying coherence function models of a downburst event are developed. The influence of time-varying coherence of nonstationary winds on the alongwind tall building response is investigated. Results show that use of conventional time-invariant coherence function may underestimate the alongwind tall building response in comparison with the time-varying coherence function.