Numerical Simulation And Mechanism Study On Rain-Wind Induced Vibration Of Stay Cable

Rain-wind induced vibration (RWIV) is a large amplitude and low frequencyvibration of cables of cable-stayed bridges under wind and rain, which may cause thefatigue failure of stay cable and reduce its service life. As RWIV is a very complexproblem of coupling oscillation of gas, liquid and solid, its mechanism is still unclearso far. For this reason, in this paper RWIV of saty cable is simulated by combininglubrication theory with computational fluid dynamics (CFD) method and finiteelement method based on Volume of fluid method (VOF method), respectively. Onthis basis, the mutual influences of water film evolution, lift and vibration of cable areanalysed to reveal the mechanism of RWIV. The main research contents include:Considering the influence of wind pressure coefficient and friction coefficient onmorphology of water film around stay cable, a theoretical model for simulation ofmorphological change of water film around stay cable under wind and rain bycombining lubrication theory with CFD method is presented. And then2D coupledequations of water film evolution and cable vibration are presented for the first timebased on the combination of lubrication theory and vibration theory of single-modesystem.Negelcted the effect of cable vibration on the change of water-film morphology,the relations between the lift and the change of water-film morphology around staycable with different wind speeds and directions are investigated by theoretical model.The results show that only when wind speed is located in the certain region whenRWIV occurs and stay cable is down inclined along wind direction, the change ofwater-film morphology and the lift of stay cable have obvious periodicity with thesame frequency closed to cable natural frequency, which confirms the conclusion thatthe resonance between rivulets and cable may be one of the main reasons for RWIVThe two-way coupling between the change of water-film morphology aroundcable and cable vibration is studied by theoretical model considering the effect ofcable vibration on the change of water-film morphology. The results show that in thewind speed range when RWIV occurs, upper and lower rivulets are formed on cablesurface, and cable vibrates with large amplitude and the dominant frequency closed toits natural frequency. The variation of water film morphology and the lift of cable alsodisplay a significant periodicity with the similar frequency, which is similar to cable natural frequency. These further explain that the resonance between rivulets and cablemay leads to RWIV.A new method to simulate the evolution of rivulets on stay cable surface ispresented combining gas-liquid two-phase theory and volume of fluid method (VOFmethod). The initial time of rivulet formation, rivulet location and morphology underdifferent wind speeds and gravity are investigated by this method using CFX software.On this basis, the formation and oscilation of rivulets around cable are simulated bythe way of water supplement on point source, which can ensure the continuousdistribution and mass conservation of water film. The aerodynamic lift obtained byCFX is applied to a single degree of freedom model of stay cable to calculate cablevibration response. Similar to the numerical calculation results by lubrication theory,the conclusion that the resonance between upper rivulet and cable causes RWIV canbe drawn by study the influence of rivulet motion on aerodynamic lift change andvibration of stay cable.