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|Title:||Crosswind effects on road vehicles moving on ground and long-span bridges||Authors:||Wang, Bin||Degree:||Ph.D.||Issue Date:||2014||Abstract:||This thesis mainly focuses on the ride comfort and safety of road vehicles moving on either the ground or long-span bridges under crosswinds using advanced vehicle models and considering aerodynamic interferences among moving vehicles, bridge deck, bridge tower and the ground. The aerodynamic interferences between a moving vehicle and the ground are first explored using the Computational Fluid Dynamics (CFD) technique. A delicate numerical model simulating the flows around a stationary road vehicle on the ground is set up. The aerodynamic forces on the vehicle are computed in terms of the aerodynamic coefficients of the vehicle under different yaw angles. The computed aerodynamic coefficients are compared with wind tunnel test results, and the comparison is very good. The validated numerical model is then extended to simulate the flows around the moving vehicle by considering a moving ground simulation. The aerodynamic coefficients of the moving vehicle on the ground are accordingly determined and compared with those of the stationary vehicle on the ground. The comparative results show that the motion of the ground affects the flows around the vehicle only in the boundary layer of the ground and the flows around and the pressure distributions over the surfaces of the vehicle are slightly affected. The effects become even weak with the increase of yaw angle. The aerodynamic coefficients of the chosen moving vehicle show no obvious differences with these on the stationary vehicle if the relative motion between the vehicle and the ground is taken into account as currently adopted. An advanced vehicle model is then presented in order to demonstrate the progressive instability of the moving vehicle on the ground with emphasis in the lateral motions under the action of both crosswinds and drivers. The dynamic equations of the vehicle model are established in a local coordinate system fixed on the vehicle body. The small displacement assumption commonly used in the previous studies is no longer required. Some of the tires can be allowed to lose contact with the road. The traditional singe-variable random method to simulate the road surface roughness in a line is extended to model the surface roughness in a plane to consider the asynchronous road excitation to the wheels of the two sides of the vehicle. The wind loads on the vehicle are the function of not only wind speeds but also the attitude of the vehicle. Based on the advanced model and using the aerodynamic coefficients determined by CFD, the progressive instability of the moving vehicle is demonstrated. The safety and ride comfort of the moving vehicle on the ground are assessed against several criteria. The critical vehicle speeds are given as the function of the critical wind speed for practical use. The aerodynamic interferences between a moving vehicle and the deck of a real long span bridge are explored using the CFD.
A new numerical model simulating the flows around the stationary vehicle on the first lane of the bridge deck is generated. The aerodynamic coefficients of the stationary vehicle on the bridge deck are computed and compared with the results from wind tunnel tests, and the comparison is found satisfactory. The simulation of the relative motion between the vehicle and the deck is achieved by considering a moving deck simulation. The computer simulation shows that the movement of the vehicle on the first lane of the bridge deck does affect the aerodynamic coefficients of the bridge deck but has only slight effects on the aerodynamic coefficients of the vehicle if the relative motion between the vehicle and the deck is taken into account. A new framework of the coupled Road Vehicle-Bridge-Wind (RVBW) system is then formed by incorporating the advanced road vehicle model, the road roughness in plane, and the driver's model. The ride comfort of the moving vehicle on the bridge deck is investigated. The wind loads on both the vehicle and the bridge deck are updated with the computed aerodynamic coefficients considering the interference between the moving vehicle and the bridge deck. The computed results show that the slight differences exist if adopting the aerodynamic coefficients of a road vehicle on the ground and the aerodynamic coefficients of the pure bridge deck compared with the actual aerodynamic coefficients in the situation of the moving vehicle on the deck. The ride comfort of the moving vehicle over a long span cable-stayed bridge is evaluated in terms of ISO criteria and compared with that of the vehicle on the ground situation. Slight differences exist in the ride comfort of the single vehicle moving on the ground and the bridge deck. The variation of aerodynamic forces on the vehicle during its passage by the bridge tower and the shielding effects of the tower are also investigated using CFD. A lower-level numerical model is set up to simulate the flows around a stationary vehicle on the deck at different locations relative to the bridge tower. The computed aerodynamic forces on the vehicle are compared with the results from wind tunnel tests. It is found that the simulated aerodynamic coefficients are in general larger than those measured from the wind tunnel. Since the vehicle-deck-tower system is very complicated and there are uncertainties in both numerical simulation and wind tunnel test, it is difficult to judge the accuracy of the numerical simulation at this moment. The CFD simulation is then extended to simulate the motion of the vehicle using the dynamic mesh method. The computed results show that the shielding effects of the tower on the aerodynamic forces of the moving vehicle are very significant. The aerodynamic coefficients exhibit sharp changes. The framework of the RVBW system incorporated with the advanced road vehicle model is then employed to assess the safety of a road vehicle passing by a bridge tower. The computed varying aerodynamic coefficients of the moving vehicle passing by a bridge tower are formulized and incorporated into the RVBW system. The computation results show that neglecting the variation of aerodynamic coefficients induced by the tower would underestimate the overturning and course deviation risk of the vehicle passing by the bridge tower. It is also found that the dynamic responses of the bridge deck have slightly effects on the safety of the vehicle passing by the tower, and using the ground condition with the existence of the tower is feasible to assess the safety of a single vehicle passing by a bridge tower. Compared with the moving vehicle on the ground, the critical vehicle speed/critical wind speed of the vehicle passing by the tower is much lower.
|Subjects:||Motor vehicles -- Aerodynamics
Bridges, Long-span -- Aerodynamics
Hong Kong Polytechnic University -- Dissertations
|Pages:||xxiii, 287 p. : ill. (some col.) ; 30 cm.|
|Appears in Collections:||Thesis|
View full-text via https://theses.lib.polyu.edu.hk/handle/200/7491
Citations as of May 22, 2022
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