Интерполяция триангулированной поверхности в задачах синтеза изображений методом обратного трассирования

Розглядається метод інтерполяції тріангульованої поверхні при синтезі зображення методом зворотнього трасування. Вхідними даними для інтерполяції є сітка трикутників з визначеними нормалями у вершинах сітки. Метод, що пропонується, дозволяє, з оного боку, використовувати існуючу базу програмних засобів створення полігональних моделей, а з іншого – використати можливість геометричної інтерполяції поверхні при синтезі зображення методом зворотнього трасування.The method for smooth interpolation of triangulated surfaces is considered. Input data for algorithm are triangle mesh with normal at each vertex. Purposed method make possible to use current modeling software for creation polygonal models, on the one hand, and use possibility of analytically interpolation of polygonal surfaces during visualization with ray-tracing, on the other hand

Интерполяция триангулированной поверхности в задачах синтеза изображений методом обратного трассирования

Розглядається метод інтерполяції тріангульованої поверхні при синтезі зображення методом зворотнього трасування. Вхідними даними для інтерполяції є сітка трикутників з визначеними нормалями у вершинах сітки. Метод, що пропонується, дозволяє, з оного боку, використовувати існуючу базу програмних засобів створення полігональних моделей, а з іншого – використати можливість геометричної інтерполяції поверхні при синтезі зображення методом зворотнього трасування.The method for smooth interpolation of triangulated surfaces is considered. Input data for algorithm are triangle mesh with normal at each vertex. Purposed method make possible to use current modeling software for creation polygonal models, on the one hand, and use possibility of analytically interpolation of polygonal surfaces during visualization with ray-tracing, on the other hand

Direct slicing of STEP based NURBS models for layered manufacturing

Abstract Direct slicing of CAD models to generate process planning instructions for solid freeform fabrication may overcome inherent disadvantages of using stereolithography format in terms of the process accuracy, ease of file management, and incorporation of multiple materials. This paper will present the results of our development of a direct slicing algorithm for layered freeform fabrication. The direct slicing algorithm was based on a neutral, international standard (ISO 10303) STEP-formatted non-uniform rational B-spline (NURBS) geometric representation and is intended to be independent of any commercial CAD software. The following aspects of the development effort will be presented: (1) determination of optimal build direction based upon STEP-based NURBS models; (2) adaptive subdivision of NURBS data for geometric refinement; and (3) ray-casting slice generation into sets of raster patterns. The development also provides for multi-material slicing and will provide an effective tool in heterogeneous slicing processes.

Robust h-adaptive meshing strategy considering exact arbitrary CAD geometries in a Cartesian grid framework

[EN] Geometry plays a key role in contact and shape optimization problems in which the accurate representation of the exact geometry and the use of adaptive analysis techniques are crucial to obtaining accurate computationally-efficient Finite Element (FE) simulations. We propose a novel algorithm to generate 3D h-adaptive meshes for an Immersed Boundary Method (IBM) based on Cartesian grids and the so-called NEFEM (NURBS-Enhanced FE Method) integration techniques. To increase the accuracy of the results at the minimum computational cost we seek to keep the efficient Cartesian structure of the mesh during the whole analysis process while considering the exact boundary representation of domains given by NURBS or T-Splines. Within the framework of Cartesian grids, the two significant contributions of this paper are: (a) the methodology used for the mesh-geometry intersection, which represents a considerable challenge due to their independence; and (b) the robust procedure used to generate the integration subdomains that exactly represent the CAD model. The numerical examples given show the proper convergence of the method, its capacity to mesh complex 3D geometries and that Cartesian grid-based IBM can be considered a robust and reliable tool in terms of accuracy and computational cost.The authors wish to thank the Spanish Ministerio de Economia y Competitividad for the financial support received through Project DPI2013-46317-R and the FPI program (BES-2011-044080), also the Generalitat Valenciana for the assistance received through Project PROMETEO/2016/007.Marco, O.; Ródenas, J.; Navarro-Jiménez, J.; Tur Valiente, M. (2017). Robust h-adaptive meshing strategy considering exact arbitrary CAD geometries in a Cartesian grid framework. Computers & Structures. 193:87-109. doi:10.1016/j.compstruc.2017.08.004S8710919

XML-basierte Sichtweise auf die einzelnen Phasen des Produktlebenszyklus von ambienten Beleuchtungssystemen

Ziel dieser Arbeit war es, eine XML-basierte Sichtweise auf die einzelnen Phasen des Produktlebenszyklus von ambienten Beleuchtungssystemen zu realisieren. Dies hat zu der Entwicklung des XML-Konverters geführt, der speziell für den Produktentwicklungsprozess von ambienten Beleuchtungssystemen entwickelt wurde. Ausgangspunkt waren die intelligente Datenbereitstellung, -aufbereitung, -weitergabe entlang des gesamten Produktlebenszyklus von ambienten Beleuchtungssystemen in einer gültigen XML-basierten Datenstruktur, die Organisation und Verwaltung der immensen Datenmengen, die in jeder Phase des Produktlebenszyklus von ambienten Beleuchtungssystemen auffallen, die Protokolle des Datenaustausches zwischen den Phasen des Produktlebenszyklus und für die verteilte Produktentwicklung, sowie die Automatisierung dieses Datenaustausches. Dieser Beitrag ist insbesondere wichtig, weil er der erste ist, der diese Thematik in ihrer Gesamtheit betrachtet, analysiert und behandelt. Er liefert eine konkrete Lösung der Problemstellung und somit stellt er die ersten Schritte in diese Thematik dar. Seit dem Anfang dieser Arbeit lag der Fokus immer auf der erweiterbaren Auszeichnungssprache XML, weil XML flexible Mechanismen für den Datenaustausch und die Aufbereitung von Inhalten für die unterschiedlichsten Zielmedien liefert und weil sie viele Potentiale zu versprechen scheint. Über die Trennung von Inhalt, Struktur und Erscheinungsbild gelingt es, im XML dies und mehr zu realisieren. Die Erweiterbarkeit von XML an bestehende Problemlösungen ist ein weiterer wichtiger Aspekt bei der Weiterentwicklung und Verbreitung von den XML-Dokumentenstrukturen. Im Laufe dieser Arbeit wird u.a. ganz klar, dass XML die Zukunft insbesondere im Bereich des Daten- und Dokumentenaustausch und der Präsentation von Daten nach aktuellem Stand der Technik gehört. Der hier vorgestellte XML-Konverter ist erst ein Einstieg in die Thematik und stellt somit die erste Lösung dieser Problematik dar. Für die weitere Entwicklung des XML-Konverters ist eine Verbesserung der inkrementellen Verarbeitung denkbar

Doctor of Philosophy

dissertationWhile boundary representations, such as nonuniform rational B-spline (NURBS) surfaces, have traditionally well served the needs of the modeling community, they have not seen widespread adoption among the wider engineering discipline. There is a common perception that NURBS are slow to evaluate and complex to implement. Whereas computer-aided design commonly deals with surfaces, the engineering community must deal with materials that have thickness. Traditional visualization techniques have avoided NURBS, and there has been little cross-talk between the rich spline approximation community and the larger engineering field. Recently there has been a strong desire to marry the modeling and analysis phases of the iterative design cycle, be it in car design, turbulent flow simulation around an airfoil, or lighting design. Research has demonstrated that employing a single representation throughout the cycle has key advantages. Furthermore, novel manufacturing techniques employing heterogeneous materials require the introduction of volumetric modeling representations. There is little question that fields such as scientific visualization and mechanical engineering could benefit from the powerful approximation properties of splines. In this dissertation, we remove several hurdles to the application of NURBS to problems in engineering and demonstrate how their unique properties can be leveraged to solve problems of interest

Biomimetic design and fabrication of tissue engineered scaffolds using computer aided tissue engineering

The field of tissue engineering brings together the multidisciplinary research of life sciences and engineering to seek man-made substitutes for the regeneration of damaged tissue or organs. A key component in tissue engineering is the use of porous scaffolds to guide cells for attachment, proliferation and differentiation in the tissue regenerative process. Upon satisfactory in-vitro culture, this engineered living scaffold is implanted into the regeneration site of the patient to function as the tissue substitute. Conventional processing techniques for the fabrication of scaffolds often encounter difficulties in the precise control of the internal architecture, interconnectivity and distribution of pores within the scaffold. These challenges, along with the advances in biology, medicine, and information technology for tissue engineering applications, have led to the development of a new field of Computer Aided Tissue Engineering (CATE).CATE enables a systematic application of computer-aided technologies, i.e., computer-aided design (CAD), image processing, computer-aided manufacturing (CAM), and solid freeform fabrication (SFF) for modeling, designing, simulation, and manufacturing of biological tissue and organ substitutes. Through the use of CATE, the design of intricate three dimensional architecture of scaffold can be realized and these scaffolds can be fabricated with reproducible accuracy to assist biologists in studying complex tissue engineering problems. This thesis reports a research addressing some of the challenges in applying the CATE approach for the biomimetic design and freeform fabrication of tissue scaffolds. The major research accomplishments reported in this thesis include: a) The development of a BioCAD modeling technique for the design and representation of patient specific 3D tissue models based on non-invasive medical image data. b) The development of a biomimetic design approach for design of load bearing tissue scaffold subject to multiple biophysical, geometrical and manufacturing requirements. This includes the design of the unit cell micro-architecture based on tissue morphologies, unit cell characterization and evaluation of the mechanical and transport properties, and the use of unit cells as building block to design anatomic tissue scaffold replacements. c) The development of a CAD based path planning procedure through a direct slicing algorithm which can convert a neutral ISO (International Standards Organization) standardized STEP (Standard for the Exchange of Product Data) formatted NURBS (Non-Uniform Rational B-Spline) geometric representation to a tool path instruction set for layered freeform fabrication. d) The development of a novel Internal Architecture Design (IAD) approach for the mapping of characteristic patterns of the unit cell micro-architectures designed within the 3D scaffold. This design approach is implemented into a process algorithm that converts these 2D patterns to tool path datasets for the 3DP™ (threedimensional printing) and extrusion based freeform fabrication.CATE enables many novel approaches in modeling, design, and fabrication of complex tissue substitutes with enhanced functionality for research in patient specific implant analysis and simulation, image guided surgical planning and scaffold guided tissue engineering. The research will also enable cell biologists and engineers to expand their scope of research and study in the field of tissue engineering and regenerative medicine.Ph.D., Mechanical Engineering -- Drexel University, 200

Structural shape optimization using Cartesian grids and automatic h-adaptive mesh projection

[EN] We present a novel approach to 3D structural shape optimization that leans on an Immersed Boundary Method. A boundary tracking strategy based on evaluating the intersections between a fixed Cartesian grid and the evolving geometry sorts elements as internal, external and intersected. The integration procedure used by the NURBS-Enhanced Finite Element Method accurately accounts for the nonconformity between the fixed embedding discretization and the evolving structural shape, avoiding the creation of a boundary-fitted mesh for each design iteration, yielding in very efficient mesh generation process. A Cartesian hierarchical data structure improves the efficiency of the analyzes, allowing for trivial data sharing between similar entities or for an optimal reordering of thematrices for the solution of the system of equations, among other benefits. Shape optimization requires the sufficiently accurate structural analysis of a large number of different designs, presenting the computational cost for each design as a critical issue. The information required to create 3D Cartesian h- adapted mesh for new geometries is projected from previously analyzed geometries using shape sensitivity results. Then, the refinement criterion permits one to directly build h-adapted mesh on the new designs with a specified and controlled error level. Several examples are presented to show how the techniques here proposed considerably improve the computational efficiency of the optimization process.The authors wish to thank the Spanish Ministerio de Economia y Competitividad for the financial support received through the project DPI2013-46317-R and the FPI program (BES-2011-044080), and the Generalitat Valenciana through the project PROMETEO/2016/007.Marco, O.; Ródenas, J.; Albelda Vitoria, J.; Nadal, E.; Tur Valiente, M. (2017). 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