Numerical Simulation of Wind and Wave Fields for Coastal Slender Bridges

Fatigue damage of coastal slender bridges resulting from strong winds and high waves can accumulate during extreme hurricane or winter storm events and lead to possible catastrophic failures in a bridge's lifecycle. With the transient, nonstationary features of extreme winds and strong waves, the interactions of winds, waves, and coastal slender bridges can be complicated because of the nonlinear nature of the structural system and fluid-structure interactions. For accurate coupled dynamic analysis, simulation of wind and wave fields around the structures under extreme weather conditions is necessary. This paper presents a numerical scheme to simulate the nonstationary wind and wave fields around a coastal slender bridge during hurricane events that also can be used in bridge-wind-wave (BWW) system dynamic analyses. In the present study, the wind was modeled as a time-varying mean component plus nonstationary fluctuation components, and the associated wave was modeled as a nonstationary random process. The near-surface (i.e., 10 m in height) time-varying mean wind speed was treated as a deterministic function, which was simulated by utilizing a parametric hurricane wind model composed of the storm vortex and environmental background flow. To consider the correlations of mean wind speeds at the near-surface and gradient levels, the vertical mean wind profile was adopted. Both the wind fluctuation and wave were characterized in terms of their evolutionary power spectral density (EPSD) functions. The nonstationary wind fluctuation was modeled as a uniformly modulated evolutionary vector stochastic process, and the EPSD for the nonstationary wave was obtained by direct extension from the current stationary wave spectrum based on the assumption of slow change in the large-scale structure of the hurricane. Finally, the proposed scheme was used to generate wind and wave fields for a coastal slender bridge, and a wavelet transform (WT) method was applied to check the similarity of the time frequency of the energy distribution for the target and estimated EPSDs. (C) 2016 American Society of Civil Engineers.