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Title:	Adaptive mesh refinement for a thin body using a two-stage corrections immersed boundary method
Authors:	Mohammed Suleman Aldlemy (P72669)
Supervisor:	Mohammad Rasidi Rasani, Dr.
Keywords:	Fluid-structure interaction Immersion in liquids Universiti Kebangsaan Malaysia -- Dissertations Dissertations, Academic -- Malaysia
Issue Date:	3-Jun-2019
Description:	Fluid-structure interaction (FSI) problems commonly encountered in engineering and biological applications involve thin, complex, flexible or rigid bodies. Thin structures require sophisticated meshing to accurately represent their shape. The immersed boundary method (IBM) is widely used in FSI modelling because of its simplicity in using fixed grids without requiring uneconomical remeshing schemes. IBM accuracy is affected by the use of volumetric coupling in fluid-structure coupling, which leads to discontinuities in velocity derivatives and pressure. In addition, a fine mesh is required to precisely resolve and capture the flow physics in the thin boundary layer at the fluid-structure interface at the expense of increased computational cost. Hence, this thesis aims to develop an adaptive mesh refinement (AMR) algorithm combined with IBM using two-stage pressure-velocity corrections for thin-object FSI problems. The fluid is Newtonian; and the flow is laminar, single phase and two-dimensional. To achieve the objective of this study, the AMR-IBM algorithm discretises and solves the equations of motion for the flow that involves rigid thin structures. Then, the AMR-immersed boundary finite element method (IBFEM) algorithm is coupled with the finite element method to compute the equations of motion for the flow within the thin elastic boundary layer at the fluid-solid interface. The body forces are computed in proportion to the fraction of the solid volume in the IBM fluid cells to incorporate fluid and solid motions into the boundary. The fractional step method is applied to solve the pressure field, whilst the pressure retrieval method is used to allocate the pressure information from the nearest fluid cell to the Lagrangian points on the object surface. The momentum exchange procedure is adopted to solve the velocity field for the cells within the solid region. Pressure correction is also applied to this region.The simplified marker and cell method is implemented to determine the scalar values for the velocity and pressure corrections. The algorithm is applied to the flow around a thin object inclined at incidence angles of 15°, 30° and 45°. The algorithms are written in FORTRAN on an Ubuntu 16.04 LTS operating system. The simulation results are compared with those of previous studies and those produced using OpenFOAM to determine the errors of the AMR-IBM algorithm. The flow around a cylinder is selected as the benchmark case to validate the numerical model, and a few numerical examples are provided to demonstrate the performance and accuracy of the AMR-IBM algorithm. The percentage errors in the Strouhal number, drag coefficient and lift coefficient are 2.0%, 0.46% and 2.0%, respectively, relative to the published data. The normalised root-mean-square errors are determined to support the validation. Relatively small errors of 0.0270 and 0.0126 are obtained for the drag and lift coefficients, respectively. The results verify the accuracy and robustness of the developed algorithms in simulating flow characteristics in the boundary layers of thin structures. These algorithms can simulate uniform flows around various thin, rigid structures, including sharp-edged objects. In general, the AMR-IBM algorithm performs satisfactorily, providing fast, reliable results, in which computational time is reduced by 86.2% for the flow around a cylinder and 98.3% in the case of a thin rigid object compared with those for a non-adaptive fine grid. The proposed algorithms can be successfully applied to solve complex FSI problems.,Ph.D.
Pages:	136
Call Number:	TA357.5.F58A433 2019 3 tesis
Publisher:	UKM, Bangi
Appears in Collections:	Faculty of Engineering and Built Environment / Fakulti Kejuruteraan dan Alam Bina

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