Browsing by Subject "r-refinement"

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    A ball-vertex approach to r-refinement for accuracy enhancements in CFD Calculations
    (2015) Jones, Bevan W S; Malan, Arnaud G; van Rooyen, Jacobus A
    Presented in this paper is an accuracy enhancing r-refinement scheme based on the ballvertex method [1, 2]. Due the success of the method in mesh movement, this work seeks to extend its use to error minimization for computational fluid dynamics calculations. To this end, element edges are loaded via error driven monitor functions. The latter are estimated from both field gradients and curvature. Boundary nodal movement is facilitated via the use of automated B`ezier surface reconstruction. The application study involves both analytical as well as industrial test-cases. The latter involves 2D and 3D transonic flow calculations. When compared with the mesh independence solution, an error reduction in the computed coefficient of lift and moment of 60% was achieved even on relatively coarse meshes and close to an order of magnitude on finer meshes. Finally, a mesh deformation, moving boundary, problem was completed to demonstrate duality as both a mesh optimisation and deformation tool.
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    Mesh adaptation through r-refinement using a truss network analogy
    (2015) Jones, Bevan W S; Malan, Arnaud G
    This project investigates the use of a truss network, a structural mechanics model, as a metaphor for adapting a computational fluid dynamics (CFD) mesh. The objective of such adaptation is to increase computational effi- ciency by reducing the numerical error. To drive the adaptation, or to give the scheme an understanding of accuracy, computational errors are translated into forces at mesh vertices via a so-called monitor function. The ball-vertex truss network method is employed as it offers robustness and is applicable to problems in both two and three dimensions. In support of establishing a state-of-the-art adaptive meshing tool, boundary vertices are allowed to slide along geometric boundaries in an automated manner. This is achieved via feature identification followed by the construction of 3rd order bezier surface patches over boundary faces. To investigate the ability of the scheme, three numerical test cases were investigated. The first comprised an analytical case, with the aim of qualitatively assessing the ability to cluster vertices according to gradient. The developed scheme proved successful in doing this. Next, compressible transonic flow cases were considered in 2D and 3D. In both cases, the computed coefficient of lift and moment were investigated on the unrefined and refined meshes and then compared for error reduction. Improvements in accuracy of at least 60% were guaranteed, even on coarse meshes. This is viewed as a marked achievement in the sphere of robust and industrially viable r-refinement schemes.