| Cable-stayed Bridges and Suspension Bridges are widely used in new bridges due to their graceful shapes and outstanding spanning capacity.And long-span bridges often undertake extremely important traffic tasks,thus the safety of bridges is very important.However,the stiffness and damping of long-span bridges are small,which can easily generate wind induced vibration under the action of wind loading,affecting the safety and durability of bridges.The stay cables and suspenders are flexible structures in long-span bridges,which are prone to occur vortex-induced vibration under the action of wind loading,resulting in the fatigue damage of the stay cables for a long time,having a direct impact on durability of the bridges and driving comfort.Harbor seals can hunt efficiently in the muddy waters and the dark deep sea by relying on their vibrissa.Harbor seal vibrissa have a unique shape,which improves their ability of detecting the wake of prey,so that they can hunt more efficiently.It is found that the shape of harbor seal vibrissa can suppress vortex-induced vibration.Based on the unique shape of harbor seal vibrissa,we presents two new bionic stay cables for passive flow control of the stay cables in this paper and carried on the following research:The aerodynamic characteristic of bionic stay cable model are investigated at first.The aerodynamic coefficients and surface pressure distribution of bionic stay cable under different wind attack angle are measured in wind tunnel to evaluate the control effects.Compared with the standard circular cylinder,the average drag coefficient and the root mean square of lift coefficient of the first kind of stay cable model can be reduced by 27% and 90%,respectively.Similar to harbor seal vibrissa,the first kind of bionic stay cable is also sensitive to the angle of incoming airflow.The control effect is better when the direction of incoming airflow parallel or perpendicular to the axis of typical cross-section.When the angle change by approximately 45° the control effect weakens or even disappears.Therefore,the second type of helical bionic stay cable is designed,which is not affected by the change of wind attack angle.The average drag coefficient and the root mean square of lift coefficient can be reduced by 35% and 95%,respectively.And then,the flow field of the bionic stay cable were measured by Particle image velocimetry(PIV)to investigate the characteristic of flow field.The results show that the bionic surface can push the region of the vortex formation of the wake further downstream and reduce the turbulence kinetic energy of the wake,and further weaken the aerodynamic force acting on the model.In addition,the bionicsurface changes the scale of the span-wise vortex.The length and size of vortex formation region at the rear of different sections show regular changes,which weakens the correlation of span-wise flow field and conducive to reduce the aerodynamic force.At last,the control mechanism of bionic stay cable was studied.A gap was formed between the surface of stay cable model and the wake vortex,which significantly reduce the fluctuation of wind speed in the near wake and reduce the aerodynamic forces loading on the model.In addition,the bionic surface changed the distribution of wake flow along the span-wise and weaken the correlation of span-wise flow.The flow field presented a three-dimensional flow posture,which is conducive to reducing aerodynamic force. |
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