Design of fluid-structure interaction using computational simulations

The first objective of the present study is to develop a computational methodology for high-fidelity predictions of both fluid and structural dynamics and their unsteady interaction. In order to accomplish this objective, the computational methodology of the present study combines an immersed-boundary method, which is capable of simulating flow over non-grid-conforming complex moving bodies and a structural dynamics solver, which is based on a finite-element method and is capable of predicting time-accurate dynamics of deforming solid structures. In the present methodology, pressure and velocity of fluid and geometric information of submerged structures are time-accurately coupled through an integration algorithm.;Discrete forcing immersed boundary methods are generally known to suffer from the generation of spurious force oscillations on the surface of a moving immersed body. To overcome the issue of spurious force oscillations, a new immersed boundary method, which provides a highly enhanced capability for controlling the generation of spurious force oscillations in moving-body simulations, is developed. In the present immersed boundary method, a sharp-interface ghost-cell immersed-boundary method is coupled with a mass source and sink algorithm to improve mass conservation across non-grid conforming immersed boundaries. To facilitate the control for temporal discontinuity in the flow field due to a motion of an immersed body, a fully-implicit time-integration scheme is employed. A novel backward time-integration scheme is developed to effectively treat multiple layers of fresh cells generated by a motion of an immersed body at high Courant-Friedrichs-Lewy (CFL) number condition.;The capability of the present computational methodology is assessed in a number of test cases. Simulation results using the present immersed boundary method are shown to agree well with other results from body-fitted grid methods and experiments. Also, the present immersed boundary method is found to effectively suppress spurious force oscillations during simulations of flow over moving bodies. The predictive capability as well as the computational efficiency of the present computational structural dynamics code is assessed in a simulation of a simply supported 3-ply plate subject to a cylindrical bending load. Comparison between the present numerical solution and an exact solution shows second-order spatial convergence with increasing number of finite-elements. The capability of the present computational fluid dynamics (CFD) - computational structural dynamics (CSD) integrated simulation technique has been verified and validated in simulations of flow over a square cylinder with a linear-elastic splitter plate and flow over a circular cylinder with a hyperelastic splitter plate. The results of both simulations are found to agree well with other simulation results from body-fitted grid methods.;The second objective of the present study is to design fluid-structure interaction in aero-/hydro-dynamic systems using computational simulations. Fluid-structure interaction in aero-/hydro-dynamic systems consists of active motion and passive deformation of a submerged body, unsteady fluid motions, and associated interaction between the submerged body and the fluid. To investigate the effect of passive body deformation on the unsteady fluid-structure interaction, vortex-shedding-induced vibration of a flexible splitter plate, which is attached at rear stagnation point a circular cylinder in freestream, is studied. The effect of a splitter plate's flexibility and geometry on manipulation of vortex shedding, structural vibration and their unsteady interaction has been examined by altering Young's moduli and length of the splitter plate.;The effectiveness of passive body deformation in a thrust-generating foil with active body motion is investigated to understand fluid-structure interactions taking place in energy-efficient propulsion of aquatic animals. For this purpose, computational analyses are utilized in simulations of flow over a two-or three-dimensional flapping foil with flexible or rigid material properties. To find the optimal body kinematics and flexibility of a flapping foil, the present CFD-CSD integrated technique is coupled with a surrogate management framework, which is a non-gradient-based optimization algorithm.