Numerical Investigation On Vortex-induced Vibrations Of The Tandem Wavy Cylinders

As a new type of bridge independent from the girder bridge,arch bridge and suspension bridge,cable-stayed bridge has many advantages such as good structure performance,strong spanning ability etc.With the wide application of cable-stayed bridge in long-span bridges,the stay cable's multi-field coupling vibration under wind and rain load is now getting more and more concern by bridge designers.So finding out the vortex induced vibration mechanism of stay cable and seeking an effective method to control vibration is the research focus of designing the modern long span cable-stayed bridge nowadays.This paper did extensively numerical research on studied the vortex induced vibration of two tandem straight cylinders and two tandem wavy cylinders by using commercial CFD software and writing related program.Explored the vortex induced vibration's response characteristics of two tandem straight cylinders,which has different spacing ratio L/D(L/D=2.0,3.0,4.0,5.0)and different reduced velocity Ur(Ur=2.4 ~12);Analyzed the influence of the aerodynamic interference effect between upstream cylinder and downstream cylinder caused by the vortex induced vibration(single / double degree of freedom)of downstream cylinder when the different spacing ratio L/D is different and the Reynolds number Re=100,the mass ratio m*=10,damping ratio ?=0.001;Obtained the variation of the lift drag coefficient and the flow structure between two cylinders when the reduced velocity Ur is changing;Observed the phase change between lift and displacement of downstream cylinder and two different vortex shedding patterns(the 2S and 2P).The research results showed that when the space ratio L/D<4.0,the phase between downstream cylinder's lift and displacement is same with Ur<7.2,but inverse from Ur>7.2.When the space ratio L/D=5.0,the phase between downstream cylinder's lift and displacement is same with Ur<6.0,and inverse from Ur>9.6,but alternate appearance two kinds of phase at 6.0<Ur<9.6.Besides,with the reduced velocity Ur increasing,the amplitude of the downstream cylinders were first increased and then decreased,but reached the maximum value when reduced velocity Ur=7.2.As for the research on two tandem wavy cylinders' vortex induced vibration,this paper selected three different types of wavy cylinders(?/Dm=6,2;a/Dm=0.15,0.3)as research objects,observe the response characteristics of different wave type cylinder and the structure between cylinders with the reduced velocity Ur is varying.The research results showed that: for the ?/Dm=6,a/Dm=0.15 wavy cylinder,the downstream wavy cylinder shows good effect on drag reduction and vibration suppression when the downstream wavy cylinder is outside of the "lock-in" range(Ur<8.7 or Ur>10.8).Once the downstream wavy cylinder get into the "lock-in" range(8.7<Ur<10.8),the effect on drag reduction and vibration suppression of the downstream wavy cylinder will weaken.For ?/Dm=2,a/Dm=0.15 wavy cylinder and ?/Dm=2,a/Dm=0.3 wavy cylinder,when the reduced velocity Ur<6.0,the amplitude of a /Dm=2,a/Dm=0.15 wavy cylinder is more than that of straight cylinder,and the amplitude of ?/Dm=2,a/Dm=0.3 wavy cylinder is near to zero.When the reduced velocity Ur<6.0,the two wavy cylinders' vibration response characteristic is similar to straight cylinder's,which shows the two wavy cylinders have no ability on drag reduction and vibration suppression.