Development of an octree based grid coarsening and multigrid flow solution

Download
index.pdf
2010
Mahmutyazıcıoğlu, Emel
Show full item record
108
views
79
downloads
The multigrid technique is one of the most effective techniques to achieve the reduction of the CPU cost for flow solvers. The multigrid strategy uses the multilevel grids which are the coarsening subsets of fine grid. An explicit solver rapidly reduces the high frequency errors on the computational grids. Since high frequency errors on coarse grids correspond to low frequency errors on fine grids, cycling through the coarse grid levels rapidly reduces the errors ranging from high-to-low frequency. The aim of this study is, therefore, to accelerate SENSE3D solver developed by TUBITAK-SAGE by implementating multigrid concept. In this work, a novel grid coarsening method suitable for cell-centered hybrid/unstructured grids is developed to provide the cells with high aspect ratio. This new grid coarsening technique relies on the agglomeration of cells based on their distribution on octree data structure. Then, the multigrid strategy is implemented to the baseline flow solver. During this implementation, the flux calculation along the face loops is modified without changing cell-centered scheme. The performance of the coarsening algorithm is investigated for all grid types in two and three dimension. The grid coarsening algorithm produces well defined, nested, body fitted coarser grids with aspect ratios of one and the coarse grids have similar characteristics of Cartesian grids. Then, the multigrid flow solutions are obtained at inviscid, laminar and turbulent flows. It is shown that, the convergence accelerations are up to 14 times for inviscid flows and in a range of 4 to 110 fold for turbulent flow solutions.
Electronic computers., Computational Fluid Dynamic.
http://etd.lib.metu.edu.tr/upload/12612549/index.pdf
https://hdl.handle.net/11511/20014
Graduate School of Natural and Applied Sciences, Thesis

Suggestions

Computation of multi-passage cascade flows with overset and deforming grids
Tuncer, İsmail Hakkı (null; 1997-12-01)
An overset grid method is applied to the solution of single and multi-passage cascade flows with a compressible Navier-Stokes solver. C-type grids around individual blades are overset onto a Cartesian background grid. Overset grids are allowed to move in time relative to each other as prescribed by the oscillatory plunging motion. The overset grid method uses a simple, robust numerical algorithm to localize moving boundary points and to interpolate solution variables across intergrid boundaries. Computation...
On efficient use of simulated annealing in complex structural optimization problems
Hasançebi, Oğuzhan (Springer Science and Business Media LLC, 2002-01-01)
The paper is concerned with the efficient use of simulated annealing (SA) in structural optimization problems of high complexity. A reformulation of the working mechanism of the Boltzmann parameter is introduced to accelerate and enhance the general productivity of SA in terms of convergence reliability. Two general and complementary parameters, referred as "weighted Boltzmann parameter" and "critical Boltzmann parameter," are proposed, Several alternative methodologies are suggested for these two parameter...
Application of fully implicit coupled method for 2D incompressible flows on unstructured grids
Zengin, Şeyda; Tarman, Işık Hakan; Department of Engineering Sciences (2012)
In the subject of Computational Fluid Dynamics (CFD), there seems to be small number of important progress in the pressure-based methods for several decades. Recent studies on the implicit coupled algorithms for pressure-based methods have brought a new insight. This method seems to provide a huge reduction in the solution times over segregated methods. Fully implicit coupled algorithm for pressure-based methods is very new subject with only few papers in literature. One of the most important work in this a...
Application of spring analogy mesh deformation technique in airfoil design optimization
Yang, Yosheph; Özgen, Serkan; Department of Aerospace Engineering (2015)
In this thesis, an airfoil design optimization with Computational Fluid Dynamics (CFD) analysis combined with mesh deformation method is elaborated in detail. The mesh deformation technique is conducted based on spring analogy method. Several improvements and modifications are addressed during the implementation of this method. These enhancements are made so that good quality of the mesh can still be maintained and robustness of the solution can be achieved. The capability of mesh deformation is verified by...
Advanced Design of Schottky Photodiodes in Bulk CMOS for High Speed Optical Receivers
Orsel, Ogulcan Emre; Erdil, Mertcan; Kocaman, Serdar (Institute of Electrical and Electronics Engineers (IEEE), 2020-02-01)
This paper provides theoretical insight on how circular Schottky photodiodes in bulk CMOS can be optimized for certain integrated receiver applications. An optimal photodiode size is analytically demonstrated and the effects of a metal plate reflector are simulated using a transfer-matrix method, both for frontside and backside illumination. Finally, a distributed circuit model is presented, which deviates from the classical lumped model for large photodiodes or sheet resistances. The presented methodologie...
Citation Formats
E. Mahmutyazıcıoğlu, “Development of an octree based grid coarsening and multigrid flow solution,” Ph.D. - Doctoral Program, Middle East Technical University, 2010.
METU IIS - Integrated Information Service open@metu.edu.tr