The Effect Of Current On Vortex-induced Vibration

In recent years,scientists have envisaged the use of vortex-induced vibration technology to obtain stable clean energy from the current,but because vortex-induced vibration is essentially a very complex nonlinear vibration,and the additional mass,stiffness and damping of vortex-induced vibration system are accompanied by the changes of current velocity,this paper takes vortex-induced vibration system as the research object.The main research work in this paper is as follows:1.Using the experimental data about vortex-induced vibration in the curve fitting reference,the functional relationship between damping ratio ?,natural frequency f_n,wand dimensionless flow velocity U* is obtained.A complex vortex-induced vibration equation is simplified into a linear vibration equation and a nonlinear vibration equation,and then the two simplified vibration equations are qualitatively analyzed according to the knowledge of vibration mechanics.2.for the simplified linear vortex-induced vibration equation,the complex eigenvalue is described mathematically using the Argand graph.At the same time,the linear vortex-induced vibration equation is solved numerically,and the variation of system amplitude is analyzed and discussed when current velocity changes.Finally,through theoretical analysis,we can get:when the current's dimensionless velocity is 0<U*<15,the vibration forms of vortex-induced vibration are all steady-state vibration.And when the value of the lift coefficient C_y corresponding to the dimensionless flow velocity U* is larger,the response amplitude of vortex-induced vibration system is also larger.Especially when the dimensionless velocity U*=4.4,and the corresponding lift coefficient C_y reach the maximum,so that the response amplitude of the vortex-induced vibration system reaches the maximum value.3.Based on the stability theory of nonlinear dynamic system,the simplified nonlinear vortex-induced vibration equation is investigated,and the phase trajectory map and bifurcation map corresponding to different flow rates are obtained.The singularity type in the phase trajectory map and the chaotic interval in the bifurcation map are discussed,so the vortex-induced vibration system with nonlinear vibration characteristics is deeplystudied.Finally,through theoretical analysis,we can get:when the current's dimensionless velocity U*the range is?2.37,2.67?,?3.1,3.55?,?7.5,8.1?,?9.1,10?,?10.1,10.2?,?10.6,11.2?,the vortex-induced vibration system is in chaotic state,which will bring harm to the structure of the system,so for practical application of vortex-induced vibration in marine engineering,the numerical value and interval range of dimensionless flow velocity U* should be avoided.And when the lift coefficientC_y corresponding to the non-dimensional flow velocity U* of the current is larger,the external excitation of the vortex-induced vibration system becomes larger,and the vortex-induced vibration system is relatively stable.Conversely,when the corresponding lift coefficient C_y the dimensionless flow velocity U* is smaller,it will make the external excitation of vortex-induced vibration system smaller,and the vortex-induced vibration system is relatively unstable.Therefore,in marine engineering,when we use the vortex-induced vibration technology for practical application,If the lift coefficient C_y corresponding to the dimensionless flow velocity U* of the current is larger,this will ensure better stability of the system and make its structure more secure.