Influence of Initial Conditions on Wind Characteristics at a Bridge Middle Span in a U-Shaped Valley by CFD and AHP

Abstract

The wind parameter distribution law at a bridge midspan in a U-shaped valley has important influence on the wind strength of this bridges. In this paper, the wind characteristics were researched by computational fluid dynamics (CFD). The surface roughness, the inlet wind speed, the wind speed profile, and the oncoming wind direction were selected as the initial conditions; the wind speed, the wind attack angle, and the wind azimuth angle were set as wind parameters; and the effect of the four initial conditions on the wind parameters was comprehensively analyzed. An innovative quantification model used to connect the coefficient of sensitivity factors with scale values was established, and the influence of initial conditions on wind parameters was studied by analytic hierarchy process (AHP) for the first time. The results show that the spatial distribution of wind characteristics in a U-shaped valley is complex and obviously affected by the initial conditions. The established quantification model has certain practicability. The AHP evaluation results showed that the influence of the oncoming wind direction on wind parameters was the most obvious. The influence degree of oncoming wind direction and wind speed profile on wind speed was just as important, accounting for 77.4%. The sensitivity of wind attack angle to oncoming wind direction was 60.8%, which was much higher than the surface roughness, inlet wind speed, and wind speed profile. The influence degree of oncoming wind direction on wind azimuth angle was the sum of the other three initial conditions.

CFD simulation of spatiotemporal distribution of residual chlorine in secondary water supply tanks

“…In addition to temperature, the initial condition of chlorine concentration distribution in the water tank is another factor that can the predictions of residual chlorine. Although CFD simulation undoubtedly relies on the initial condition, 35 initializing a non-uniform condition is a significant challenge for CFD modeling, especially when it is unobservable. The impact of the initial condition in the study was demonstrated by the larger uncertainty in chlorine concentration variation during the first 400 min for UGT, which was caused by the unrealistic initial condition of uniformly-distributed chlorine concentration.…”