INSTABILITY MECHANISM OF FLEXIBLE BEAM AXIALLY MOVING IN A CONSTRAINED REGION

利用多体动力学公式和实验，讨论了被拉入弹性壁面狭缝中的柔性梁的动力行为。这种行为被称为“意大利面问题”。在第一步中，通过狭缝的间隙大小来影响梁的侧向变形。对梁的动力特性进行了数值模拟，并以梁的间隙大小和拉拔速度为参数检验了所提公式的准确性。结果表明，间隙大小和拉拔速度对狭缝入口附近横向振动的增大有影响。在第二步，本文研究了具有剪切流体流动的充满流体的狭窄空间中运动的柔性腹板的流激振动的理论稳定性分析。在稳定性分析中，流体绕动腹板流动的基本方程是基于对动腹板表面与侧边间隙宽度积分的Navier-Sokes方程，更重要的是，假设间隙宽度相对于腹板长度足够小。横向运动腹板的结构振动方程基于Kirchhoff-Love薄板模型。从这些基本方程出发，利用动腹板表面的运动边界条件，得到了流固耦合运动方程。利用多模态展开法和伽辽金法对方程进行了线性化处理，得到了方程的解。导出了腹板轴向运动速度的特征方程。系统的稳定性和频率分别由特征方程复特征值的虚部和实部定义。分析结果表明，随着腹板轴向运动速度的增加，由于剪切流体的流动，在轴向运动腹板中出现颤振型失稳（行波型流激振动）和散度型失稳。分析结果明确了随流体附加质量参数的变化，这两种不稳定类型的范围。少

The dynamic behavior of the flexible beam, which is pulled into the slit of the elastic wall, is discussed with Multibody Dynamics formulation and experiments. This behavior is called "Spaghetti Problem".In the first step, the gap size of the slit is though to affect the lateral deformation of the beam. Dynamic behavior of the beam is simulated numerically and examined the accuracy of the presented formulation by the gap size and the pulling velocity of the beam as parameters. It is clarified that the gap size and the pulling velocity influence the increase of the lateral vibration near the inlet of the slit.In the second step, This study deals with a theoretical stability analysis of flow-induced vibration generated in a flexible web moving in a fluid-filled narrow space with shear fluid flow. In the stability analysis, the basic equations of fluid flow around the moving web are based on the Navier-Sokes equations integrated over the gap width between the moving web surface and side w … More all, assuming that the gap width is enough small compared with the length of the web. The structural vibration equation of the moving web in the transverse motion is based on the Kirchhoff-Love's thin-plate model. From these basic equations, the equations of the fluid-structure coupling motion are obtained, employing the moving boundary conditions of the surface of the moving web. And these equations are linearized around the equilibrium position, and the solution of these equations is obtained by using the muti-modal expansion method and applying the Galerkin's method. The characteristic equation of the system is derived as a function of the axially moving speed of the web. And the stability and frequency of the system are defined by the imaginary and real part of the complex eigen values of the characteristics equation respectively.As a result, the analytical results show that flutter type instability (traveling-wave type flow-induced vibration) and divergence type instability occur in the axially moving web due to the shear fluid flow with increasing the axially moving speed of the web. And the analytical results clarify the region of these two types of instability with varying the added mass parameter of the fluid. Less