Research On Novel Lattice Boltzmann Method For Fluid-structure Interaction And Its Application In Bridge Wind Engineering

The modern long-span bridges have become more flexible and slender, and thus are more susceptible to a variety of wind-induced vibrations. These wind-induced structural vibrations may result in catastrophic structural failure. Therefore, aeroelastic instability is a major concern in the design of modern long-span bridges.Nowadays, with advances and improvements in computational power and the area of computational fluid dynamics, the virtual wind tunnel technique has become a very attractive way to investigate bridge aeroelastic instability. Conventional numerical methods for the solution of fluid-structure interaction problems are based on the body-fitted grid such as finite element method and finite volume method, where the moving grid is achieved through the arbitrary Lagrangian–Eulerian method. In such methods, the grid is distributed to provide appropriate local resolution, but in order to avoid severe mesh distortion, grid re-generation is usually needed every few time steps. In contrast, lattice Boltzmann method(LBM) based on the non-body-conformal Cartesian grid has increasingly received much attention in recent years as they are essentially simpler in handling the complex and moving geometries. Thus lattice Boltzmann method was developed to simulate bridge aeroelasticity in this thesis. The content of this thesis mainly contains:1. The multi-block scheme of the single relaxation time lattice Boltzmann method was extended up to multiple relaxation time Lattice Boltzmann Method(MRT-LBM), and a multi-block approach for MRT-LBM was developed.2. Large-eddy simulation of turbulent flows using LBM and dynamic Smagorinsky sub-grid model. A new large-eddy simulation solver—MRT-LBM-DSM, was constructed through modifying the kinematic viscosity of MRT-LBM by incorporating dynamic Smagorinsky sub-grid model. The unsteady flows past square cylinder, rectangle cylinder and bridge decks were analyzed to verify MRT-LBM-DSM. Numerical tests confirmed that MRT-LBM-DSM was indeed a promising solution strategy for turbulent flows.3. Lattice Boltzmann model of fluid-structure interaction with move boundary. A fluid-structure interaction algorithm which was marked as MB-LBM,was developed based on MRT-LBM-DSM. In the present algorithm, the unsteady fluid field was solved by MRT-LBM-DSM, while the structure was modelled by an elastically suspended rigid body and its dynamic analysis was performed using a Runge–Kutta method. The fluid and structure solvers were coupled through move boundary of lattice Boltzmann method and a reconstruction strategy of the particle distribution function of the new fluid node. Vortex-induced vibrations and galloping of a rectangular section and flutter analysis of Great Belt east bridge and Guamá bridge were investigated using MB-LBM. The numerical results showed that MB-LBM has a good prediction for the flutter onset velocities of Great Belt east bridge and Guamá bridge.4. Lattice Boltzmann model of fluid-structure interaction with iterative immersed boundary method. Another fluid-structure interaction algorithm based on Immersed Boundary–Lattice Boltzmann method was presented and was marked as IIB-LBM. Vortex-induced vibrations and galloping of a rectangular section with length-to-width ratio 2:1 and flutter analysis of a rectangular section with length-to-width ratio 4:1 and Forth road bridge were investigated using IIB-LBM. Numerical tests confirmed that IIB-LBM was indeed a promising solution strategy for bridge aeroelasticity. Compared with MB-LBM, IIB-LBM has a higher calculation accuracy on the data transmission between structure solver and fluid solver.5. Research on the identification method of aerodynamic derivatives based on MRT-LBM-DSM. A new numerical procedure for estimating aerodynamic derivatives of the bridge deck was presented. The proposed method consists of two steps. In the first step, the aerodynamic forces were numerically evaluated by MRT-LBM-DSM with move boundary. In the second step, aerodynamic derivatives were evaluated based on the simulated unsteady aerodynamic forces. Aerodynamic derivatives of thin flat plate, box girder section and central-slotted box section were computed successfully. Then a double-parameter optimization model for searching critical flutter velocity and critical frequency was established. The critical flutter velocity of thin flat plate, box girder section and central-slotted box section were evaluated by the double-parameter optimization model based on the simulated aerodynamic derivatives. The results indicated that the optimization model can give much better prediction for the flutter onset velocities.6. Numerical study on suppression of wind-induced vibrations of bridge decks by aerodynamic countermeasures by means of MB-LBM and IIB-LBM. First the flutter instability of a box girder bridge section in the presence of central stabilizer was investigated using IIB-LBM, and influence of the central stabilizer on flutter instability was analyzed. Then the flutter instability of a twin-deck bridge section was investigated using IIB-LBM and effects of gap-width on flutter instability were analyzed. In addition, the mechanism of reduction in the amplitude of vortex-induced vibrations for a box girder bridge section in the presence of double flaps was investigated using MB-LBM and the mechanism was clarified.