Experimental Investigation And Numerical Simulation Of Rain-Windinduced Vibration Of Stay Cables

Cable-stayed bridges are one of main types of large-span bridges and stay cables are the most key components of cable-stayed bridges. The vortex-induced vibration and wind-rain-induced vibration of the stay cables easily occur under the wind or wind-rain, and will induce accumulating of damage, attenuating of bearing capacity and even an emergent accident for attachment structures of the stay cables. So far, mechanism vibration of the wind-rain–induced vibration (RWIV) of the stay cable is a complicated yet still not well solved technical problem and research focus; and it is worthy to investigate the vortex-induced vibration (VIV) of the stay cable under a wind speed profile. Firstly, the wind tunnel tests and CFD numerical simulations are carried out to investigate the RWIV of the stay cable; then, CFD numerical simulation is employed to study the 3-D vortex-induced vibration of a stay cable under a wind speed profile. The main contents are included as follows:Firstly, this paper develops an ultrasonic transmission thickness measurement system (UTTMS) capable of measuring time-dependent spatial distribution of water rivulets around the surface of the inclined stay cable when the RWIV reoccurs. The mechanism, layout, and measurement accuracy of UTTMS are illustrated in detail. The spatial resolution in the radial direction and circumferential direction are calculated for the water rivulets by UTTMS respectively. Measurement methods of water rivulets may be classified into two categories according to the rotation speed of the micro motor: moving-point measurement method (MPMM) and fixed-point measurement method (FPMM).Secondly, the wind tunnel tests of RWIV of the stay cables are carried out and the rivulet ultrasonic signals of the cable surface are monitored by UTTMS. The processing methods of the rivulet ultrasonic signals are investigated and the change law of the rivulets is revealed when the RWIV occur. The mean thickness, width and shape for rivulets are obtained by statistically analyzing the geometry characteristics through two methods of MPMM and FPMM. Furthermore, the oscillation equilibrium positions, amplitude and frequency are obtained by investigating the dynamical characteristics of upper rivulet.Thirdly, the upper rivulet states are analyzed under different wind speeds, and the relationship between of the upper rivulet states and RWIV of the cable is revealed. The correlation between the geometric characteristics of water rivulets and the RWIV of the stay cable is analyzed, and relationship between the oscillation equilibrium positions, amplitude, frequency and phase with the RWIV of the stay cable is revealed. A modified model of upper rivulet oscillation is proposed with consideration of the influences of turbulent velocity and the frictional damping force between the upper rivulet and the stay cable through boundary layer theory. The influences of turbulent velocity for the oscillation amplitude of the upper rivulets are investigated and compared with the experimental results to demonstrate the accuracy of modified model.Fourthly, a hybrid substructure method combined with CFD numerical simulation and physics experiment is presented and the basic principle of this method is analyzed. The validity and feasibility are by comparing the hybrid substructure method and a fluid-solid interaction method of CFD numerical simulation for vortex-indcued vibration of a circular cylinder. Based on the wind tunnel tests, the hybrid substructure method is employed to investigate the RWIV of the stay cables. The characteristics of flow around the cable and the influences of the upper rivulet for the flow field are analyzed (the change law of lift and drag coefficients, pressure distributions, wake vorticity structures and vortex patterns). The results of the hybrid substructure method are compared with the experimental results of the cable with a fixed artificial rivulet. The differences of aerodynamic coefficients between the hybrid substructure method and the experimental results are investigated.Lastly, VIV (Vortex-induced vibration) of a CFRP (Carbon Fiber Reinforced Polymer) cable subjected to a wind profile is numerically simulated through combining CFD (Computational Fluid Dynamics) code CFX and CSD (Computational Structural Dynamics) code ANSYS through a fluid-solid coupling method. Two regions of lift coefficient frequency lock-in and nonlock-in are formed along the axial direction of the stay cable. The change laws of lift coefficient, pressure distribution and vortex shedding are analyzed in the frequency lock-in and nonlock-in regions. Based on the results of the fluid-solid coupling method, the hybrid substructure method of CFD numerical simulation for the VIV of the cable is investigated. The differences of aerodynamic coefficients and computational efficiency between two methods are analyzed.