Numerical Study And Analysis On Flow Over Bluff Bodies And Vortex-induced Vibrations In Shear Flow

The oncoming flow stream is mostly the shear flow rather than uniform flow in the nature. The problems of flow around bluff bodies and flow-induced vibration are widely encountered in many engineering applications, such as high-rise buildings, cable structures, bridge structures, offshore structures, to name but a few.Taking wind engineering and ocean engineering as the backgrounds in the paper, numerical investigations are proposed and carried out on basic science issues of flow over bluff bodies and flow-induced vibration in the planar shear flow by using innovative stabilized finite element method. Meanwhile, the flow interference effects and wake characteristics between stationary multiple bluff bodies are studied; the flow-induced vibration of a rigid body and the fluid-structure coupling effect of rigid bodies are considered. Main innovations and contributions are reflected as follows:1. Four-step Semi-implicit Characteristic-Based Split(4-SICBS) stabilized finite element scheme is proposed, providing a powerful tool for the calculations of incompressible flow a past bluff body. Compared to the traditional Characteristic-based split finite element method, this algorithm allows a lager time step and a better computational stability solving the problem of incompressible viscous fluid flow in the laminar flow region.2. A new stabilized finite element scheme, namely 4-SICBS-ALE, is developed for the solution of the fluid-structure interaction issue, providing a powerful tool for the calculations of vortex-induced vibration(VIV). The 4-SICBS is extended to the framework of Arbitrary Lagrangian-Eulerian(ALE) description, establishing an efficient partitioned fluid-structure interaction algorithm by associating with a dynamic mesh method which is introduced a smooth technology. 4-SICBS-ALE can effectively avoid the grid failure after the large motion of rigid bodies, providing more accurate and stable numerical method for the rigid bodies’ VIV problems in the planar shear flow.3. Based on some application backgrounds of transmissions lines, cable structures and marine pipes, the flow around couple of circular cylinders in the tandem arrangement subjected to the planar shear flow is systematically investigated. The effects of shear ratio, spacing ratio and Reynolds number are revealed on the flow characteristics and aerodynamic parameters of the static structures, while the flow interference mechanisms around the bluff bodies are clarified. The study shows that compared with the uniform case, the interference effect between two circular cylinders in the planar shear flow are much more complicated, as well as the aerodynamic characteristics and wake patterns around bluff bodies have significant changes.4. Based on some application backgrounds of high-rise buildings with polygonal cross section, billboards and marine structures, the flow past a rotationally oscillating triangular cylinder in the uniform flow is studied. The influences of key parameters(incidence angle, Reynolds number, oscillating amplitude and oscillating frequency) on the flow around a triangular cylinder are analyzed. Lock-on region, aerodynamic parameters and wake characteristics of the system are revealed, while the intrinsic mechanisms of the flow over an oscillation triangle are elucidated. The study shows that the Reynolds number effect on the problem is significant at different incidence angles.5. Based on some application backgrounds of cable structures, marine risers and sea-bed pipelines, the flow-induced vibrations of an elastically mounted cylinder immersed in the planar shear flow with the 1-DOF(only transverse direction) and 2-DOF(in-line and cross-flow directions) are studied numerically by using the 4-SICBS-ALE algorithm proposed in this dissertation. At Re=150, the influences of key parameters(shear ratio, reduced velocity and frequency ratio) on the characteristics of VIV response and the vortex shedding patterns behind the cylinder are analyzed. Meanwhile, the dynamic responses, orbital trajectories, vortex shedding patterns and aerodynamic characteristics of the cylinder are revealed. The vortex dynamics mechanism of structures undergoing fluid-structure interaction in the planar shear flow is elucidated.6. Based on some application backgrounds of cable structures, transmission lines and marine risers, the vortex-induced vibrations of two elastically mounted cylinder in the tandem arrangement subjected to the planar shear flow with the 2-DOF are studied numerically. At Re=160, the influences of key parameters(shear ratio, space ratio and reduced velocity) on the characteristics of VIV response and the vortex shedding pattern behind the cylinder are analyzed. Meanwhile, the dynamic responses, orbital trajectories and vortex shedding patterns of the system are revealed. The interference mechanism of the interaction between fluid and multiple bluff bodies in the planar shear flow is illustrated.The 4-SICBS stabilized finite element method is developed in this dissertation, solving the flow past rigid bodies and VIV subjects in the planar shear flow efficiently and stably. The detailed results and conclusions of the specific research issues which are scientifically refined from practical engineering applications can be regarded as theoretical basis and design reference for the related problems in civil engineering and marine engineering. On the other hand, they also are of important academic significances to intensify knowledge of the intrinsic mechanisms of the issue.