William Roshan Quadros

Skeleton-based computational method for the generation of a 3D finite element mesh sizing function

This paper focuses on the generation of a three-dimensional (3D) mesh sizing function for geometry-adaptive finite element (FE) meshing. The mesh size at a point in the domain of a solid depends on the geometric complexity of the solid. This paper proposes a set of tools that are sufficient to measure the geometric complexity of a solid. Discrete skeletons of the input solid and its surfaces are generated, which are used as tools to measure the proximity between geometric entities and feature size. The discrete skeleton and other tools, which are used to measure the geometric complexity, generate source points that determine the size and local sizing function at certain points in the domain of the solid. An octree lattice is used to store the sizing function as it reduces the meshing time. The size at every lattice-node is calculated by interpolating the size of the source points. The algorithm has been tested on many industrial models, and it can be extended to consider other non-geometric factors that influence the mesh size, such as physics, boundary conditions, etc.

A computational framework for automating generation of sizing function in assembly meshing via disconnected skeletons

This paper proposes a framework for generating mesh sizing functions for assembly models. Size control is crucial in obtaining a high-quality mesh with a reduced number of elements. The reduction in the number of elements will decrease computation time and memory use during mesh generation and analysis. The framework consists of a background octree lattice for storing the sizing function, a set of source entities for providing sizing information based on geometric information, and an interpolation module for calculating the sizing on the background octree lattice using the source entities. Source entities are generated by performing a detailed systematic study to identify all the geometric factors of an assembly. Disconnected skeletons are extracted and used as tools to measure 3D proximity and 2D proximity, which are two of the geometric factors. The framework facilitates the generation of a variety of meshes with a low computational cost, to meet industry needs. The framework has been tested on many industrial parts, and sizing control on a few typical assemblies has been presented to demonstrate the effectiveness of the proposed framework.

Defeaturing CAD models using a geometry-based size field and facet-based reduction operators

We propose a method to automatically defeature a CAD model by detecting irrelevant features using a geometry-based size field and a method to remove the irrelevant features via facet-based operations on a discrete representation. A discrete B-Rep model is first created by obtaining a faceted representation of the CAD entities. The candidate facet entities are then marked for reduction using a geometry-based size field. This is accomplished by estimating local mesh sizes based on geometric criteria. If the field value at a facet entity goes below a user-specified threshold value then it is identified as an irrelevant feature and is marked for reduction. The reduction of marked facet entities is performed using various facet operators. Care is taken to retain a valid geometry and topology of the discrete model throughout the procedure. The original model is not altered as the defeaturing is performed on a separate discrete model. Associativity between the entities of the discrete model and that of original CAD model is maintained in order to decode the attributes and boundary conditions applied on the original CAD entities onto the mesh via the entities of the discrete model. Example models are presented to illustrate the effectiveness of the proposed approach.

Pen-Based User Interface for Geometric Decomposition for Hexahedral Mesh Generation

In this work, we present a pen-based user interface (UI) that makes manual geometry decomposition easier and helps reduce user time spent on geometry decomposition for hexahedralmeshing. This paper presents the first attempt to apply a pen-based UI for geometry preparation for mesh generation. The proposed UI is more natural, intuitive, and easier to use than existing interfaces such as Window-Icon-Mouse-Pointer and commandline interfaces. The pen-based UI contains the following features: (1) drawing freeform strokes, (2) fitting and aligning strokes to CAD geometry automatically, (3) creating cutting surfaces, and (4) performing various tasks including webcutting through gestures. The proposed pen-based UI has been tested on a few models to demonstrate its effectiveness in decomposition, defeaturing and controlling mesh orientation.

Geometric reasoning in sketch-based volumetric decomposition framework for hexahedral meshing

This paper presents a sketch-based volumetric decomposition framework using geometric reasoning to assist in hex meshing. The sketch-based user interface makes the framework user-friendly and intuitive, and the geometric reasoning engine makes the framework smarter and improves the usability. The system first generates a database that contains both the B-rep and 3D medial object to capture the exterior and interior of the input model, respectively. Next, the geometric reasoning process determines sweeping direction and two types of sweepable regions and provides visual aids to assist the user in developing decomposition solutions. The user conducts decomposition via the sketch-based user interface, which understands the user’s intent through freehand stroke inputs for smart decomposition. Imprint and merge operations are then performed on the decomposed model before passing it to the sweeping algorithm to create hex meshes. The proposed framework has been tested on industrial models.

Volumetric Decomposition via Medial Object and Pen-Based User Interface for Hexahedral Mesh Generation

This paper describes an approach that combines the volumetric decomposition suggestions and a pen-based user interface (UI) to assist in the geometry decomposition process for hexahedral mesh generation. To generate the suggestions for decomposition, a 3D medial object (MO) is first used to recognize and group sweepable regions. Second, each sweepable region of the original model is visualized using different colors. Third, the ideal cutting regions to create cutting surfaces are highlighted. Based on the visual suggestions, users then create cutting surfaces with the pen-based UI. The models are then decomposed into sweepable sub-volumes following the MO based suggestions. The pen-based UI offers three types of tools to create cutting surfaces: (1) Freeform based tool, (2) B-REP based tool, and (3) MO based tool. The pen-based UI also selects a suitable type of tool automatically based on users input. The proposed approach has been tested on industrial CAD models and hex meshing results are presented.

A Computational Framework for Generating Sizing Function in Assembly Meshing

This paper proposes a framework for generating sizing function in meshing assemblies. Size control is crucial in obtaining a high-quality mesh with a reduced number of elements, which decreases computational time and memory use during mesh generation and analysis. This proposed framework is capable of generating a sizing function based on geometric and non-geometric factors that influence mesh size. The framework consists of a background octree grid for storing the sizing function, a set of source entities for providing sizing information based on geometric and non-geometric factors, and an interpolation module for calculating the sizing on the background octree grid using the source entities. Source entities are generated by performing a detailed systematic study to identify all the geometric factors of an assembly. Disconnected skeletons are extracted and used as tools to measure 3D-proximity and 2D-proximity, which are two of the geometric factors. Non-geometric factors such as user-defined size and pre-meshed entities that influence size are also addressed. The framework is effective in generating a variety of meshes of industry models with less computational cost.

Guest editorial: 20th international meshing roundtable special issue

The 20th International Meshing Roundtable (IMR) committee is pleased to publish the special journal edition of the 20th IMR conference held on October 23–26, 2011 in Paris, France. Sandia National Laboratories started the IMR conference series in 1992 as a small meeting of likeminded companies and organizations striving to establish a common focus for research and development in the field of mesh and grid generation. Sandia National Laboratories continues to organize the IMR, which has become recognized as an international focal point annually attended by researchers and developers from dozens of countries around the world. The 20th IMR is the first time the conference was held outside the US territory, which resulted in a significant increase in participation from European countries. The 20th IMR included researchers and developers from academia, national labs and industry in a stimulating, open environment to share technical information related to mesh generation and general pre-processing techniques. The 20th IMR was one of the best attended with 54 papers submitted, among which 34 papers were accepted. The committee invited the top 10 papers with best reviews to submit their work for this special issue, and 9 papers eventually appeared in this special issue. The papers in this volume present theoretical and novel ideas and algorithms with practical potential in computational engineering, geometric modeling, and computer graphics. These papers highlight some of the latest advances in these areas in research and industrial settings. We would like to thank the authors, the reviewers, and the publishing staff for their efforts to make this special journal issue possible.