Discretization of multiply connected surfaces using submapping

Una de las técnicas más utilizadas para generar mallas estructuradas de cuadriláteros es el método de submapping. Este método descompone la geometría en piezas lógicamente equivalentes a un cuadrilátero y después malla cada una de ellas por separado manteniendo la compatibilidad de la malla mediante la resolución de un problema lineal entero. El algoritmo de submapping tiene dos limitaciones principales. La primera de ellas es que sólo se puede aplicar en geometrías tales que el ángulo entre dos aristas consecutivas es, aproximadamente, un múltiplo entero de π/2. La segunda limitación es que la geometría tiene que ser simplemente conexa. Con el objetivo de mitigar estas restricciones, en este artículo se presentan dos modificaciones originales que permiten reducir el efecto de dichas limitaciones. Finalmente, se presentan diversos ejemplos numéricos que ponen de manifiesto la robustez y la aplicabilidad de los algoritmos desarrollados.Peer Reviewe

Generation of curved high-order meshes with optimal quality and geometric accuracy

We present a novel methodology to generate curved high-order meshes featuring optimal mesh quality and geometric accuracy. The proposed technique combines a distortion measure and a geometric L2-disparity measure into a single objective function. While the element distortion term takes into account the mesh quality, the L2-disparity term takes into account the geometric error introduced by the mesh approximation to the target geometry. The proposed technique has several advantages. First, we are not restricted to interpolative meshes and therefore, the resulting mesh approximates the target domain in a non-interpolative way, further increasing the geometric accuracy. Second, we are able to generate a series of meshes that converge to the actual geometry with expected rate while obtaining high-quality elements. Third, we show that the proposed technique is robust enough to handle real-case geometries that contain gaps between adjacent entities.Peer ReviewedPostprint (published version

Visualization of pentatopic meshes

We propose a simple tool to visualize 4D unstructured pentatopic meshes. The method slices unstructured 4D pentatopic meshes (fields) with an arbitrary 3D hyperplane and obtains a conformal 3D unstructured tetrahedral representation of the mesh (field) slice ready to explore with standard 3D visualization tools. The results show that the method is suitable to visually explore 4D unstructured meshes. This capability has facilitated devising our 4D bisection method, and thus, we think it might be useful when devising new 4D meshing methods. Furthermore, it allows visualizing 4D scalar fields, which is a crucial feature for our space-time application

Size preserving mesh generation in adaptivity processes

It is well known that the variations of the element size have to be controlled in order to generate a high-quality mesh. Hence, several techniques have been developed to limit the gradient of the element size. Although these methods allow generating high-quality meshes, the obtained discretizations do not always reproduce the prescribed size function. Specifically, small elements may not be generated in a region where small element size is prescribed. This is critical for many practical simulations, where small elements are needed to reduce the error of the numerical simulation. To solve this issue, we present the novel size-preserving technique to control the mesh size function prescribed at the vertices of a background mesh. The result is a new size function that ensures a high-quality mesh with all the elements smaller or equal to the prescribed element size. That is, we ensure that the new mesh handles at least one element of the correct size at each local minima of the size function. In addition, the gradient of the size function is limited to obtain a high-quality mesh. Two direct applications are presented. First, we show that we can reduce the number of iterations to converge an adaptive process, since we do not need additional iterations to generate a valid mesh. Second, the size-preserving approach allows to generate quadri- lateral meshes that correctly preserves the prescribed element size.Peer ReviewedPostprint (published version

Discretización de superficies múltiplemente conexas mediante submapping

Una de las técnicas más utilizadas para generar mallas estructuradas de cuadriláteros es el método de submapping. Este método descompone la geometría en piezas lógicamente equivalentes a un cuadrilátero y después malla cada una de ellas por separado manteniendo la compatibilidad de la malla mediante la resolución de un problema lineal entero. El algoritmo de submapping tiene dos limitaciones principales. La primera de ellas es que sólo se puede aplicar en geometrías tales que el ángulo entre dos aristas consecutivas es, aproximadamente, un múltiplo entero de π/2. La segunda limitación es que la geometría tiene que ser simplemente conexa. Con el objetivo de mitigar estas restricciones, en este artículo se presentan dos modificaciones originales que permiten reducir el efecto de dichas limitaciones. Finalmente, se presentan diversos ejemplos numéricos que ponen de manifiesto la robustez y la aplicabilidad de los algoritmos desarrollados.Peer ReviewedPostprint (published version

Defining an2-disparity measure to check and improve the geometric accuracy of noninterpolating curved high-order meshes

We define an2-disparity measure between curved high-order meshes and parameterized manifolds in terms of an2norm. The main application of the proposed definition is to measure and improve the distance between a curved high-order mesh and a target parameterized curve or surface. The approach allows considering meshes with the nodes on top of the curve or surface (interpolative), or floating freely in the physical space (non-interpolative). To compute the disparity measure, the average of the squared point-wise differences is minimized in terms of the nodal coordinates of an auxiliary parametric high-order mesh. To improve the accuracy of approximating the target manifold with a noninterpolating curved high-order mesh, we minimize the square of the disparity measure expressed both in terms of the nodal coordinates of the physical and parametric curved high-order meshes. The proposed objective functions are continuously differentiable and thus, we are able to use minimization algorithms that require the first or the second derivatives of the objective function. Finally, we present several examples that show that the proposed methodology generates high-order approximations of the target manifold with optimal convergence rates for the geometric accuracy even when non-uniform parameterizations of the manifolds are prescribed. Accordingly, we can generate coarse curved high-order meshes significantly more accurate than finer low-order meshes that feature the same resolution.Peer ReviewedPostprint (author's final draft

Checking and improving the geometric accuracy of non-interpolating curved high-order meshes

Peer ReviewedPostprint (author's final draft

Unstructured and semi-structured hexahedral mesh generation methods

Discretization techniques such as the finite element method, the finite volume method or the discontinuous Galerkin method are the most used simulation techniques in ap- plied sciences and technology. These methods rely on a spatial discretization adapted to the geometry and to the prescribed distribution of element size. Several fast and robust algorithms have been developed to generate triangular and tetrahedral meshes. In these methods local connectivity modifications are a crucial step. Nevertheless, in hexahedral meshes the connectivity modifications propagate through the mesh. In this sense, hexahedral meshes are more constrained and therefore, more difficult to gener- ate. However, in many applications such as boundary layers in computational fluid dy- namics or composite material in structural analysis hexahedral meshes are preferred. In this work we present a survey of developed methods for generating structured and unstructured hexahedral meshes.Peer ReviewedPostprint (published version

A new procedure to compute imprints in multi-sweeping algorithms

One of the most widely used algorithms to generate hexahedral meshes in extrusion volumes with several source and target surfaces is the multi-sweeping method. However, the multi-sweeping method is highly dependent on the final location of the nodes created during the decomposition process. Moreover, inaccurate location of inner nodes may generate erroneous imprints of the geometry surfaces such that a final mesh could not be generated. In this work, we present a new procedure to decompose the geometry in many-to-one sweepable volumes. The decomposition is based on a least-squares approximation of affine mappings defined between the loops of nodes that bound the sweep levels. In addition, we introduce the concept of computational domain, in which every sweep level is planar. We use this planar representation for two purposes. On the one hand, we use it to perform all the imprints between surfaces. Since the computational domain is planar, the robustness of the imprinting process is increased. On the other hand, the computational domain is also used to compute the projection onto source surfaces. Finally, the location of the inner nodes created during the decomposition process is computed by averaging the locations computed projecting from target and source surfaces.Postprint (published version

Defining an L2-disparity Measure to Check and Improve the Geometric Accuracy of Non-interpolating Curved High-order Meshes

We define an Full-size image L2-disparity measure between curved high-order meshes and parameterized manifolds in terms of an Full-size image L2 norm. The main application of the proposed definition is to measure and improve the distance between a curved high-order mesh and a target parameterized curve or surface. The approach allows considering meshes with the nodes on top of the curve or surface (interpolative), or floating freely in the physical space (non-interpolative). To compute the disparity measure, the average of the squared point-wise differences is minimized in terms of the nodal coordinates of an auxiliary parametric high-order mesh. To improve the accuracy of approximating the target manifold with a non-interpolating curved high-order mesh, we minimize the square of the disparity measure expressed both in terms of the nodal coordinates of the physical and parametric curved high-order meshes. The proposed objective functions are continuously differentiable and thus, we are able to use minimization algorithms that require the first or the second derivatives of the objective function. Finally, we present several examples that show that the proposed methodology generates high-order approximations of the target manifold with optimal convergence rates for the geometric accuracy even when non-uniform parameterizations of the manifolds are prescribed. Accordingly, we can generate coarse curved high-order meshes significantly more accurate than finer low-order meshes that feature the same resolution.This research was partially supported by CONACYT-SENER ("Fondo Sectorial CONACYT SENER HIDROCARBUROS", gran contract 163723). The work of the corresponding author was partially supported by the Boeing CO. & US Air Force Office of Scientific Research & European Comission through the Boeing-MIT Alliance & Computational Math Program & Marie Sklodowska-Curie Actions (HiPerMeGaFlows project), respectively.Peer ReviewedPostprint (published version