A case study in hexahedral mesh generation: Simulation of the human mandible

We provide a case study for the generation of pure hexahedral meshes for the numerical simulation of physiological stress scenarios of the human mandible. Due to its complex and very detailed free-form geometry, the mandible model is very demanding. This test case is used as a running example to demonstrate the applicability of a combinatorial approach for the generation of hexahedral meshes by means of successive dual cycle eliminations, which has been proposed by the second author in previous work. We report on the progress and recent advances of the cycle elimination scheme. The given input data, a surface triangulation obtained from computed tomography data, requires a substantial mesh reduction and a suitable conversion into a quadrilateral surface mesh as a first step, for which we use mesh clustering and b-matching techniques. Several strategies for improved cycle elimination orders are proposed. They lead to a significant reduction in the mesh size and a better structural quality. Based on the resulting combinatorial meshes, gradient-based optimized smoothing with the condition number of the Jacobian matrix as objective together with mesh untangling techniques yielded embeddings of a satisfactory quality. To test our hexahedral meshes for the mandible model within an FEM simulation we used the scenario of a bite on a ‘hard nut.’ Our simulation results are in good agreement with observations from biomechanical experiments

Etat de l'art de la segmentation de maillage 3D par patchs surfaciques

National audienceLa segmentation de maillage 3D est une composante essentielle de nombreuses applications. Elle se décline en deux familles : la segmentation en patchs surfaciques et la segmentation en parties significatives. Dans cet article, nous traitons principalement de la segmentation de maillages 3D en patchs surfaciques et en proposons un état de l'art. Nous positionnons le contexte de ce type de segmentation et discutons des contributions les plus pertinentes

Generalizing the advancing front method to composite surfaces in the context of meshing constraints topology

International audienceBeing able to automatically mesh composite geometry is an important issue in the context of CAD-FEA integration. In some specific contexts of this integration, such as using virtual topology or meshing constraints topology (MCT), it is even a key requirement. In this paper, we present a new approach to automatic mesh generation over composite geometry. The proposed mesh generation approach is based on a generalization of the advancing front method (AFM) over curved surfaces. The adaptation of the AFM to composite faces (composed of multiple boundary representation (B-Rep) faces) involves the computation of complex paths along these B-Rep faces, on which progression of the advancing front is based. Each mesh segment or mesh triangle generated through this progression on composite geometry is likely to lie on multiple B-Rep faces and consequently, it is likely to be associated with a composite definition across multiple parametric spaces. Collision tests between new front segments and existing mesh elements also require specific and significant adaptations of the AFM, since a given front segment is also likely to lie on multiple B-Rep faces. This new mesh generation approach is presented in the context of MCT, which requires being able to handle composite geometry along with non-manifold boundary configurations, such as edges and vertices lying in the interior domain of B-Rep faces

3D mesh segmentation of historic buildings for architectural surveys

[EN] Advances in three-dimensional (3D) acquisition systems have introduced this technology to more fields of study, such as archaeology or architecture. In the architectural field, scanning a building is one of the first possible steps from which a 3D model can be obtained and can be later used for visualisation and/or feature analysis, thanks to computer-based pattern recognition tools. The automation of these tools allows for temporal savings and has become a strong aid for professionals, so that more and more methods are developed with this objective. In this article, a method for 3D mesh segmentation focused on the representation of historic buildings is proposed. This type of buildings is characterised by having singularities and features in façades, such as doors or windows. The main objective is to recognise these features, understanding them as those parts of the model that differ from the main structure of the building. The idea is to use a recognition algorithm for planar faces that allows users to create a graph showing the connectivity between them, therefore allowing the reflection of the shape of the 3Dmodel. At a later step, this graph is matched against some pre-defined graphs that represent the patterns to look for. Each coincidence between both graphs indicate the position of one of the characteristics sought. The developed method has proved to be effective for feature detection and suitable for inclusion in architectural surveying applications.[ES] Los avances en los sistemas de adquisición tridimensionales (3D) han provocado que este tipo de tecnología se introduzca en cada vez más campos de estudio, como son la arqueología o la arquitectura. En el campo arquitectónico el escaneado de edificios constituye el primer paso con el que se obtienen modelos 3Dque más tarde, pueden ser utilizados para la visualización y/o análisis de las características de los mismos edificios, gracias a herramientas informáticas de reconocimiento de patrones. La automatización de estas herramientas permite un ahorro temporal y supone una ayuda a los profesionales, por lo que cada vez más métodos se desarrollan con este objetivo. En este artículo se propone un método de segmentación de mallas 3D enfocado a la representación de edificios históricos. Este tipo de edificios se caracterizan por tener singularidades y elementos característicos en las fachadas, tales como puertas o ventanas. El objetivo principal consiste en reconocer estas características en los edificios, entendiéndose como tales aquellas partes del modelo que difieren de la estructura principal del mismo. La idea es utilizar un algoritmo de reconocimiento de caras planas que permita crear un grafo que muestre la conectividad entre ellas y que por tanto refleje la forma del modelo tridimensional. En una etapa posterior, este grafo se compara con grafos predefinidos que conforman los patrones a buscar. Cada coincidencia entre ambos grafos indica la posición de una de las características buscadas. El método desarrollado ha resultado ser eficaz para la detección de características y adecuado para su inclusión en aplicaciones de levantamiento arquitectónico.Este trabajo se ha realizado parcialmente en el marco del proyecto de investigación “R4FA. Desarrollo de un Sistema Integrado de Restauracion, Recomposicion, Restitucion y Representacion de Fragmentos Arqueologicos” (HAR2015-69408-R), financiado por el Programa Estatal de Investigación, Desarrollo e Innovación Orientada a los Retos de la Sociedad, Convocatoria 2015, Modalidad 1: «Proyectos de I+D+I».Herráez, BJ.; Vendrell, E. (2018). Segmentación de mallas 3D de edificios históricos para levantamiento arquitectónico. Virtual Archaeology Review. 9(18):66-76. https://doi.org/10.4995/var.2018.5858SWORD667691

Fast global and partial reflective symmetry analyses using boundary surfaces of mechanical components

International audienceAxisymmetry and planar reflective symmetry properties of mechanical components can be used throughout a product development process to restructure the modeling process of a component, simplify the computation of tool path trajectories, assembly trajectories, etc. To this end, the restructured geometric model of such components must be at least as accurate as the manufacturing processes used to produce them, likewise their symmetry properties must be extracted with the same level of accuracy to preserve the accuracy of their geometric model. The proposed symmetry analysis is performed on a B-Rep CAD model through a divide-and-conquer approach over the boundary of a component with faces as atomic entities. As a result, it is possible to identify rapidly all global symmetry planes and axisymmetry as well as local symmetries. Also, the corresponding algorithm is fast enough to be inserted in CAD/CAM operators as part of interactive modeling processes, it performs at the same level of tolerance than geometric modelers and it is independent of the face and edge parameterizations

Camera-based Texture Mapping: An Approach for Creating Digital Environments with Foreground Forms Using 2d Paintings

This thesis develops the method of using textures projected from the perspective of a projection camera, in combination with two-dimensional paintings and threedimensional models, to create digital environments. Past uses have demonstrated effectiveness only for background and midground scene elements with limited camera movement. This work explores how camera animation can be maximized using the projected texture technique onto foreground environment forms. Through several case studies, general guidelines for artists are developed for using camera-based projected textures

AUTOMATIC PAPER SLICEFORM DESIGN FROM 3D SOLID MODELS

Master'sMASTER OF SCIENC

A priori evaluation of simulation models preparation processes using artificial intelligence techniques

Controlling the well-known triptych costs, quality and time during the different phases of the Product Development Process (PDP) is an everlasting challenge for the industry. Among the numerous issues that are to be addressed, the development of new methods and tools to adapt to the various needs the models used all along the PDP is certainly one of the most challenging and promising improvement area. This is particularly true for the adaptation of Computer-Aided Design (CAD) models to Computer-Aided Engineering (CAE) applications, and notably during the CAD models simplification steps. Today, even if methods and tools exist, such a preparation phase still requires a deep knowledge and a huge amount of time when considering Digital Mock-Up (DMU) composed of several hundreds of thousands of parts. Thus, being able to estimate a priori the impact of DMU adaptation scenarios on the simulation results would help identifying the best scenario right from the beginning. This paper addresses such a difficult problem and uses artificial intelligence (AI) techniques to learn and accurately predict behaviours from carefully selected examples. The main idea is to identify rules from these examples used as inputs of learning algorithms. Once those rules obtained, they can be used on a new case to a priori estimate the impact of a preparation process without having to perform it. To reach this objective, a method to build a representative database of examples has been developed, the right input (explanatory) and output (preparation process quality criteria) variables have been identified, then the learning model and its associated control parameters have been tuned. One challenge was to identify explanatory variables from geometrical key characteristics and data characterizing the preparation processes. A second challenge was to build a effective learning model despite a limited number of examples. The rules linking the output variables to the input ones are obtained using AI techniques such as well-known neural networks and decision trees. The proposed approach is illustrated and validated on industrial examples in the context of computational fluid dynamics simulations

Manufacturability Analysis of Thermally-Enhanced Polymer Composite Heat Exchangers

Thermally-enhanced polymer composite heat exchangers are an attractive alternative for applications such as the use of seawater as a cooling medium and other corrosive environments that traditionally use expensive exotic metallic alloys, but a number of manufacturing challenges exist. The goal of this thesis is to develop an understanding of the manufacturing feasibility, in particular mold filling and fiber orientation, of utilizing thermally-enhanced polymer composites and injection molding to manufacture polymer heat exchangers. To best predict mold filling feasibility, this thesis proposes developing an explicit construction of the boundary, represented as a surface based on the parameter space, which separates the feasible and infeasible design space. The feasibility boundary for injection molding in terms of the design parameters is quite complex due to the highly nonlinear process physics, which, consequently, makes molding simulation computationally intensive and time consuming. This thesis presents a new approach for the explicit construction of a moldability-based feasibility boundary based on intelligent Design of Experiments and adaptive control techniques to minimize the number or computation experiments needed to build an accurate model of the feasibility boundary. Additionally, to improve the flexibility of the mold filling prediction framework to changes in overall heat exchanger design, a model simplification approach is presented to predict mold filling for general finned-plate designs by determining an equivalent flat plate representation and utilizing a developed flat plate mold filling metamodel to estimate mold filling. Finally, a fiber orientation measurement methodology is presented for experimentally determining fiber orientation behavior for sample heat exchanger geometries that develops both a local and global understanding of the fiber orientation behavior and compares thesis findings to simulation predictions. The work presented in this thesis significantly advances the understanding of manufacturability considerations for utilizing thermally-enhanced polymer composites in heat exchanger applications and is useful in design exploration, optimization, and decision-making approaches

Capturing design process information and rationale to support knowledge-based design and analysis integration

Issued as final reportUnited States. Dept. of Commerc