Perpustakaan Digital ITB

Fluid-structure interaction (FSI) is a phenomenon generally encountered in nature, such as in the cardiovascular system, swimming modes of fish-like organisms, and flapping of insects. Proper understanding of this phenomenon is also important in many engineering fields. The increasing trend of the use of thin flexible structures, such as in long-span bridges, tall buildings, and light aerial vehicles, requires accurate prediction of the FSI phenomenon since it can exhibit catastrophic failures to the structures. This phenomenon can also be used for beneficial purposes, such as for the flutter energy harvesting system. The interactions of the flow and the thin flexible structures, however, are yet to be fully understood due to complex behaviours governing the interactions and limitations in measuring and modeling the systems. In the present work, the fluid-structure interaction of flexible thin structures undergoing large displacements is investigated through numerical simulations. A new FSI algorithm is proposed to achieve this objective. This FSI algorithm is developed via a partitioned approach. In this context, the flow is resolved using the remeshed-Vortex Particle Method (R-VPM), whereas the response of the flexible structure is evaluated using a FEM-based elastodynamics solver. The Vortex Particle Method (VPM) has been considered an accurate and efficient computational fluid dynamics (CFD) tool to simulate flow around complex geometries. In this study, the existing remeshed-VPM is modified and extended with new developments to enhance its applicability for complex FSI simulations of thin flexible structures. In this context, the remeshed-VPM algorithm is combined with the iterative Brinkman penalization method and a multiresolution scheme to accurately enforce the boundary conditions on a thin immersed solid. A new force formulation is developed, applicable to generate accurate distributed body forces even though the iterative Brinkman penalization is employed. The flow solver is coupled with an elastodynamics solver that can accurately simulate the dynamic analysis of flexible thin structures undergoing large displacements. In the present work, the structural dynamics is evaluated using corotational beam formulation since it is simple, accurate, and efficient to solve geometrically nonlinear structures. A consistent and energy-preserving two dimensional (2D) corotational beam formulation is employed to maintain accuracy and stability for long-term FSI simulations. The novelty is the extension of this approach from the two-dimensional (2D) formulation to a three-dimensional (3D) formulation. Both the flow solver and the structural solver are validated using a number of popular benchmark problems available in the literature, both for 2D and 3D cases. Comparisons between the simulation results with some numerical data show very good agreement. The flow solver is more accurate and efficient than the pure Lagrangian and standard remeshed-VPM since accurate results with great efficiency can be achieved by the combination of the multiresolution scheme with the iterative Brinkman penalization method. Regarding the structural solver, it is concluded that it is more accurate and stable than the non-consistent and nonenergy- conserving corotational formulation and its efficiency can be improved by the use of the simplified version of the consistent corotational formulation. The flow and structural solvers are coupled using a loosely coupled scheme and the coupled FSI algorithm is validated on large-displacement FSI benchmark problems such as cantilever oscillation due to vortex shedding from a square cylinder and large amplitude flapping of an inverted flag in a uniform flow. The results are in excellent agreement with some numerical simulations and experimental measurements available in the literature. Due to the rich set of complex interactions of the generated wake dynamics with the flexible inverted flag, the FSI solver is further employed in a series of FSI simulations using this inverted flag model to understand the physics governing these complex interactions. The proposed FSI solver demonstrates its capability as a reliable means to study the physics of some main modes of the inverted flag systems. The original contributions of this work are: a new force formulation based on corrected penalization velocity that is capable to generate distributed body forces, applicable for both classical and iterative Brinkman penalization method; the extension of the multiresolution scheme using patches to 3D remeshed-VPM; the development and application of consistent and approximately energy-preserving 3D corotational beam formulation for nonlinear dynamics of highly flexible structures; the development and application of a multiresolution scheme combined with the iterative Brinkman penalization method for remeshed-VPM, both for 2D and 3D flow and FSI applications; the applications of fully 3D remeshed-VPM coupled with 3D consistent and energy-conserving corotational beam formulation for FSI simulations of the inverted flag system; and the exposition of the flapping mechanism of an inverted flag system.