| The flow-induced vibrations(FIVs) of structures widely exist in nature and engineering. FIV phenomenon can be treated as a double-edged sword: it may not only induce serious structural damages, but may also provide a new energy resource for human beings though vibration energy harvester. Therefore, study on FIV becomes a hot topic in the world. Undoubtedly, the mechanisms of complicated interactions between fluid and structure are far from clear currently. This dissertation aims to develop a computational program which can be applied for solving the fluid-structure interaction(FSI) problem, and then perform several numerical investigations on the FIVs of rigid and flexible structures. Using the in-house code, the effects of flow conditions, structural characteristics and flow interferences on the FIV responses are comprehensively analyzed, and the related internal physical mechanisms are clearly elucidated. Main work and achievements of this study are summarized as follows:1) Novel finite element methods(FEM) have been proposed for solving laminar flow and turbulent flow problems. To get the solution of Navier-Stokes equations, an semi-implicit four-step fractional scheme is adopted with the combination of Streamline Upwind/Petrov-Galerkin(SUPG) stabilization method. The validation tests show that this scheme is of good efficiency, accurate and stable to be implemented. Then, the four-step fractional SUPG formulation is introduced for solving Reynolds-averaged Navier-Stokes(RANS) equations with SST k-ω turbulent model.2) An improved dynamic mesh technique is proposed for the mesh moving problem based on the initial mesh deformation and the modified Laplace equation. It is indicated from the numerical tests that the improved mesh updating algorithm is more effective compared with the traditional one.3) A numerical scheme for FSI problem is established as an efficient computational tool for numerically simulating the FIVs of fundamental structures. Regarding to the fluid domain with moving boundaries, the proposed FEM schemes for flow governing equations are extended to the arbitrary Lagrangian-Eulerian(ALE) formulations. The explicit time integration algorithm is used to solve the dynamic equation of rigid structure, while the implicit Newmark and Newton-Laphson methods are applied to solve the dynamic FEM equation of flexible structure with large deformation in Total Lagrangian(T.L.) description. Then, a partitioned loose coupling algorithm is developed for the solution of FSI problem, which combines the fluid solver, solid solver and the improved dynamic mesh technique.4) Based on the new FSI solver, the FIVs of an elastically mounted triangular cylinder with two degrees of freedom are numerically investigated, and the impacts of the flow incidence angle on the dynamic response and wake mode are discussed. The characteristics of structural vibration amplitudes, frequencies, trajectories, and hydrodynamic parameters are revealed. The pressure and vorticity distributions on the cylinder surface are also depicted.5) Based on the new FSI solver, the wake-induced vibrations(WIVs) of an elastically mounted circular cylinder located downstream of a stationary larger circular cylinder are numerically studied. The effects of the Reynolds number, reduced velocity and degree of freedom on the wake pattern and dynamic response of the smaller cylinder are analyzed in details. With the help of instantaneous flow visualization, the mechanisms of the WIV under the effect of the flow interference are revealed.Finally, the WIVs of a flexible plate located downstream of a stationary circular cylinder are numerically investigated using the new FSI solver. The effects of the spacing ratio on the gap flow mode and the vibration characteristic of the flexible plate are comprehensively discussed. The internal relations between the pressure distribution and the structural dynamic response are also illustrated clearly. |
PDF Full Text Request