| Cables of cable-stayed bridge(hereinafter referred to as stay cable)are highly sensitive to wind loads.As tipycal wind-induced vibration modes,Vortex-induced vibration,dray-galloping and rain-wind induced vibration et al.may cause the fatigue damage or even immediate damage of structures,which impacted the safety and service life of structures.Flow control method is an important appraoch to improve the cables’ wind-resistant performance.Generally,traditional flow control methods are developed based on the investigation about the 2D flow mechanism of a stay cable,while the flow field with obvious 3D characteristics around the cable is neglected.As an efficient,simple and low-cost means for suppressing the wind-induced cable vibration,the 3D flow control method depends on the research about the flow regime in the 3D flow around a cble.Therefore,this paper aims at revealing the 3D flow characteristics around a cable and developing a flow control method for wind-induced cable vibration.Based on the approaches including theoretical analysis,numerical simulations and wind tunnel experiments,this paper proposed an identification method for the vortex structures in 3D flow around a circular cylinder,and revealed the wind-induced 3D flow effects around a cable.An efficient and simple control method for suppressing wind-induced cable vibration was proposed based on 3D flow control.Its effectiveness was verified and the control mechanism was revealed in the research.The main contents are included as follows:(1)Aiming at indentifying the vortex structures in 3D flow around a circular cylinder,the OPTICS cluster algorithm based on correlation distance is proposed by comparing OPTICS algorithm and k-means algorithm and analysing several common similarity indexes.The identification results of the OPTICS cluster algorithm based on correlation distance is studyed based on the vortex structure samples around a circular cylinder model calculated by a numerical simulation.Study results prove that the OPTICS algorithm based on correlation distance is effective for identifying 3D vortex structures.It has the advantages of the insensitivity to the initial parameters,good robustness under noise,and the stability of indentification results.(2)The flow around a cable is abstracted as the 3D flow around a yawed segmental circular cylinder model.A numerical simulation is implemented to systematically study the effects of the moedl’s inclination on the aerodynamic forces,the wake flow velocities,the wake vortex structures and axial flow structures.It is found that the increase of model’s inclination leads to the obvious change of the 3D flow structures,an then affects the fluctuation characteristics of aerodynamic forces and the spanwise correlation of wake flow.There are prominent coupling effects among the 3D flow structures.(3)A flow visualization measurement is performed to observe the 3D flow structures around a yawed cable model based on PIV wind tunnel test.The measurement results are used to verify the numerical results.The analysis ways including phase-averaging and OPTICS algorithm based on correlation distance are employed to capture the wake flow fluctuation features,the vortex structures and axial flow structures in model wake flow.The effects of model’s inlination and Reynolds number are analyzed,and the mechanism of the coupling effects among3 D flow strutures is revealed.The study confirms the numerical results.It is found that there are two ways of coupling effects: one is coupled axial vortex and turbulence kinetic energy and the other one is coupled axial vortex,secondary vortex and axial flow.It is verified that there are quasi-steady 3D flow structures.(4)Based on the coupling regime of 3D flow structures around cable,the vane-type vortex generator is proposed to be used to control the vortex-induced cable vibration.Its 3D flow control mechanism is analyzed.By a wind tunnel experiment,the 3D flow control effectiveness of the vane-type vortex generator is verified.The effects of control parameters are explored,and the flow mechanism is revealed.Study results indicate that the vane-type vortex generator is an effective device for controlling vortex-induced cable vibration.The parameters of vane-type vortex generator have “fade area” for control effects of suppressing the vortex-induced cable vibration,which can be eliminated by extending the length of vane-type vortex generator units.(5)According to the requierment of eliminating the parameters’ “fade area” for control effects,the helical vortex generator for suppressing vortex-induced cable vibration is proposed by extending the length of vane-type vortex generator units along a helical trajectory on cable surface.The double helical vortex generator is confirmed as the optimal mode by a wind tunnel test.A series of systematically wind tunnel tests are performed to verify the effectiveness of the double helical vortex generator for suppressing vortex-imduced cable vibration and perturbing the uniform distribution of axial flow.The effects of control parameters are explored,and the flow mechanism is revealed.The experimental results indicate that the method of double helical vortex generator is effective for controlling vortex-induced cable vibration,and has the potential of controlling dry-galloping of cables. |
