All ETDs from UAB

Advisory Committee Chair

Roy P Koomullil

Advisory Committee Members

David R McDaniel

David L Littlefield

Haibin Ning

Amr A Hassan

Document Type

Dissertation

Date of Award

2016

Degree Name by School

Doctor of Philosophy (PhD) School of Engineering

Abstract

Fluid-Structure Interaction (FSI) is an important topic that needs to be addressed during the design and analysis of air vehicles. The main components of an FSI analysis framework include: 1) computational fluid dynamics (CFD) solver, 2) computational structural dynamics (CSD) solver, 3) mesh deformation module, and 4) module for data transfer between computational fluid and structural solvers. In this PhD research work a loosely-coupled FSI methodology with all of the above components in a single framework has been developed. An in-house CFD solver has been used for the solution of the fluid dynamics equations. A structural solver has been developed by discretizing the linear elasticity equations using the finite-volume method that is used in the in-house CFD solver. The developed finite volume based structural mechanics solver has been validated against analytical and finite element based numerical results. Results were found to be in a good agreement for bending and tensile deflections as well as for distributed and concentrated loads. Furthermore, the implemented CSD methodology was tested for the prediction of large deflection cases. Two different dimensionless load magnitudes have been applied. The error in the deflection amplitude for the lower load and higher load were 5.5% and 7.19%, respectively, with frequency shifts of 1.0% and 4.8%, respectively. In addition, an extensive survey of the existing mesh deformation techniques has been conducted. Per this survey, Radial Basis Functions (RBF) based mesh deformation technique has been adopted for further improvements. A novel concept to solve the RBF system of equations incrementally combined with a greedy algorithm has been introduced. This improvement decreased the computational complexity of solving the RBF’s system of equations from O(n3) to O(n2), where n is the total number of fluid mesh boundary nodes. Benchmark test cases with four different analytic deformations were used to evaluate the performance of the presented approach. Mesh deformation results were also presented for deflections of a cantilever beam and a rectangular supercritical wing. These simulations showed that the developed incremental approach saves up to 67% of CPU time as compared to the traditional RBF solvers. The developed FSI methodology is a general purpose one that can be applied to different types of problems and is capable of handling any mesh topology. The numerical compatibility between the CFD and CSD solvers implies same mesh requirements for both domains. Therefore, an identical surface meshes at the interface have been used for both fluid and structural domains. This eliminated the interpolation errors during the data transfer between the structural and fluid solvers. The developed FSI approach has been tested on the case of flow-induced cantilever beam vibration. Four different flow inlet speeds have been analyzed. The predicted beam vibration has preserved the natural frequency for all cases. Furthermore, increasing the flow velocity increases the magnitude of the beam deflection, as expected. Moreover, two different structural densities were simulated. The results were validated against the FSI results produced by coupling a finite element structural solver with a finite volume fluid solver. The predicted structural response was found to be in a good agreement for both density values. The proposed FV-FSI solver under-predicted the maximum deflection by 7% and over-predicted the vibration frequency by 0.16%.

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