Dissertations / Theses on the topic 'Geometrical constraints'
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1
Nestoras, Konstantinos Nav E. Massachusetts Institute of Technology. "A tool to create hydrodynamically optimized hull-forms with geometrical constraints from internal arrangements." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/81587.
Abstract:
Thesis (Nav. E.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering; and, (S.M.)--Massachusetts Institute of Technology, Engineering Systems Division, 2013.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 145-146).
Internal arrangements and bulky equipment like machinery have been treated for many years as a secondary aspect of the ship design. Traditionally, in the design process, the centerpiece of the effort is the hull and its hydrodynamic performance. Once the hull of a ship has been selected, all the other systems, like propulsion and electric plants, are selected and fitted in the ship. Due to the fact that the hull is considered as the most important system of the ship, any compromises and systems trade-offs that need to be done in the design process are focused mainly on all the systems apart from the hull-form. This inherent prioritization in the traditional design process, might lead to the selection of suboptimal solutions for the other systems like the propulsion and electric plants, which in turns might lead to a global suboptimal solution for the whole ship design. Unfortunately, these decisions bound the designed ship for lifetime and, down the road, might lead to excess operational costs. The tool developed in this thesis treats the internal arrangements and the hull-form of the ship as two systems that need to be optimized together and not on a decoupled manner. Thus, the selection of the propulsion and electric plants or even large weapon systems like VLCs becomes as important as the hull during the design process. Propulsion and electric systems can be preselected in the early stage design, based on their efficiency and then a hull can be wrapped around them. The optimization of the hull can be done either with the use of the Holtrop method or a potential flow panel method, which provides higher fidelity. The designer has the ability to utilize this tool in order to easily conduct trade-off studies between the internal arrangements and the hull-form or save time from their integration and allocate it in other important problems of the design. This could aid the decision-making process in the early stage of the design, where information is scarce, decisions are crucial and uncertainty is high.
by Konstantinos Nestoras.
S.M.
Nav.E.
2
Nesselroth, Susan Marian. "I Substituent effects on carbanion photophysics An application of the energy gap law : II Solvent and geometrical constraints on excited state proton transfer." Diss., Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/30331.
3
Wang, Bihao. "Geometrical and contextual scene analysis for object detection and tracking in intelligent vehicles." Thesis, Compiègne, 2015. http://www.theses.fr/2015COMP2197/document.
Abstract:
Pour les véhicules intelligents autonomes ou semi-autonomes, la perception constitue la première tâche fondamentale à accomplir avant la décision et l’action. Grâce à l’analyse des données vidéo, Lidar et radar, elle fournit une représentation spécifique de l’environnement et de son état, à travers l’extraction de propriétés clés issues des données des capteurs. Comparé à d’autres modalités de perception telles que le GPS, les capteurs inertiels ou les capteurs de distance (Lidar, radar, ultrasons), les caméras offrent la plus grande quantité d’informations. Grâce à leur polyvalence, les caméras permettent aux systèmes intelligents d’extraire à la fois des informations contextuelles de haut niveau et de reconstruire des informations géométriques de la scène observée et ce, à haute vitesse et à faible coût. De plus, la technologie de détection passive des caméras permet une faible consommation d’énergie et facilite leur miniaturisation. L’utilisation des caméras n’est toutefois pas triviale et pose un certain nombre de questions théoriques liées à la façon dont ce capteur perçoit son environnement. Dans cette thèse, nous proposons un système de détection d’objets mobiles basé seule- ment sur l’analyse d’images. En effet, dans les environnements observés par un véhicule intelligent, les objets en mouvement représentent des obstacles avec un risque de collision élevé, et ils doivent être détectés de manière fiable et robuste. Nous abordons le problème de la détection d’objets mobiles à partir de l’extraction du contexte local reposant sur une segmentation de la route. Après transformation de l’image couleur en une image invariante à l’illumination, les ombres peuvent alors être supprimées réduisant ainsi leur influence négative sur la détection d’obstacles. Ainsi, à partir d’une sélection automatique de pixels appartenant à la route, une région d’intérêt où les objets en mouvement peuvent apparaître avec un risque de collision élevé, est extraite. Dans cette zone, les pixels appartenant à des objets mobiles sont ensuite identifiés à l’aide d’une approche plan+parallaxe. À cette fin, les pixels potentiellement mobiles et liés à l’effet de parallaxe sont détectés par une méthode de soustraction du fond de l’image; puis trois contraintes géométriques différentes: la contrainte épipolaire, la contrainte de cohérence structurelle et le tenseur trifocal, sont appliquées à ces pixels pour filtrer ceux issus de l’effet de parallaxe. Des équations de vraisemblance sont aussi proposées afin de combiner les différents contraintes d’une manière complémentaire et efficace. Lorsque la stéréovision est disponible, la segmentation de la route et la détection d’obstacles peuvent être affinées en utilisant une segmentation spécifique de la carte de disparité. De plus, dans ce cas, un algorithme de suivi robuste combinant les informations de l’image et la profondeur des pixels a été proposé. Ainsi, si l’une des deux caméras ne fonctionne plus, le système peut donc revenir dans un mode de fonctionnement monoculaire ce qui constitue une propriété importante pour la fiabilité et l’intégrité du système de perception. Les différents algorithmes proposés ont été testés sur des bases de données d’images publiques en réalisant une évaluation par rapport aux approches de l’état de l’art et en se comparant à des données de vérité terrain. Les résultats obtenus sont prometteurs et montrent que les méthodes proposées sont efficaces et robustes pour différents scénarios routiers et les détections s’avèrent fiables notamment dans des situations ambiguësFor autonomous or semi-autonomous intelligent vehicles, perception constitutes the first fundamental task to be performed before decision and action/control. Through the analysis of video, Lidar and radar data, it provides a specific representation of the environment and of its state, by extracting key properties from sensor data with time integration of sensor information. Compared to other perception modalities such as GPS, inertial or range sensors (Lidar, radar, ultrasonic), the cameras offer the greatest amount of information. Thanks to their versatility, cameras allow intelligent systems to achieve both high-level contextual and low-level geometrical information about the observed scene, and this is at high speed and low cost. Furthermore, the passive sensing technology of cameras enables low energy consumption and facilitates small size system integration. The use of cameras is however, not trivial and poses a number of theoretical issues related to how this sensor perceives its environmen. In this thesis, we propose a vision-only system for moving object detection. Indeed,within natural and constrained environments observed by an intelligent vehicle, moving objects represent high risk collision obstacles, and have to be handled robustly. We approach the problem of detecting moving objects by first extracting the local contextusing a color-based road segmentation. After transforming the color image into illuminant invariant image, shadows as well as their negative influence on the detection process can be removed. Hence, according to the feature automatically selected onthe road, a region of interest (ROI), where the moving objects can appear with a high collision risk, is extracted. Within this area, the moving pixels are then identified usin ga plane+parallax approach. To this end, the potential moving and parallax pixels a redetected using a background subtraction method; then three different geometrical constraints : the epipolar constraint, the structural consistency constraint and the trifocaltensor are applied to such potential pixels to filter out parallax ones. Likelihood equations are also introduced to combine the constraints in a complementary and effectiveway. When stereo vision is available, the road segmentation and on-road obstacles detection can be refined by means of the disparity map with geometrical cues. Moreover, in this case, a robust tracking algorithm combining image and depth information has been proposed. If one of the two cameras fails, the system can therefore come back to a monocular operation mode, which is an important feature for perception system reliability and integrity. The different proposed algorithms have been tested on public images data set with anevaluation against state-of-the-art approaches and ground-truth data. The obtained results are promising and show that the proposed methods are effective and robust on the different traffic scenarios and can achieve reliable detections in ambiguous situations
4
Rohmer, Damien. "Géométrie active pour l'animation et la modélisation." Phd thesis, Université de Grenoble, 2011. http://tel.archives-ouvertes.fr/tel-00635079.
Abstract:
Engendrer en temps-réel des déformations visuellement réalistes d'objets 3D, comme par exemple le corps et les vêtements de personnages, est un point crucial en animation, que ce pour des applications au jeu vidéo ou à la production cinématographique. Les méthodes de déformations géométriques actuelles rapides telles que le "skinning" ou l'animation physique à basse résolution ne capturent cependant pas certains comportements naturels essentiels. En particulier les déformations à volume constant du corps, le gonflement des muscles pour un personnage, ou la génération de plis sur ses vêtements dus au fait que leurs surfaces doivent rester développable. Cette thèse présente une série de méthodes rendant les modèles géométriques "actifs", c'est à dire capables de maintenir un certain nombre de contraintes intrinsèques de la surface portant sur le volume englobé ou sur le caractère développable de celle-ci. Nous étudions trois exemples: - l'ajout de contraintes locales de volumes lors de l'animation d'une créature virtuelle par skinning. - l'ajout de plis de vêtements modélisant une surface quasi-inextensible à partir d'une animation à basse résolution donnée en entrée. - la génération d'une surface de type papier froissé, basée sur la préservation de l'isométrie vis-à-vis d'un patron planaire. Dans tous ces modèles, notre approche est procédurale. Elle se base sur la déformation progressive et, potentiellement, le raffinement dynamique de la géométrie juste avant l'étape de rendu.
5
Seth, Abhishek. "Combining physical constraints with geometric constraint-based modeling for virtual assembly." [Ames, Iowa : Iowa State University], 2007.
6
Lie, Chin Cheong Patrick. "Geometrically constrained matching schemes." Thesis, McGill University, 1992. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=39316.
Abstract:
We present an effective method for solving different types of noisy pattern matching problems in Euclidean space. The matching is performed in either a least-squares or a mixed-norm sense under the constraint that a transformation matrix $ Theta$ is restricted to belong to the orthogonal group. Matching problems of this type can be recast as function optimization problems which can be solved by representing the orthogonal group to which $ Theta$ belongs as a Lie group and then investigating the gradient vector field associated with the function to be optimized. The projection of the gradient field onto the tangent space of the Lie group at $ Theta$, i.e., the Lie algebra, results in a descent/ascent equation for the function. The descent/ascent equation so obtained is used in a classical steepest-descent/ascent algorithm and a singular value decomposition-based recursive method in order to determine the maximum or minimum point of the function under consideration. Since $ Theta$ belongs to the orthogonal group which includes the group of permutations as a subgroup, the proposed procedure works not only for patterns consisting of ordered feature points, but also for the combinatorial problem involving patterns having unordered feature points. Generalizations of the matching problem are also formulated and include the matching of patterns from Euclidean spaces of different dimensions and the matching of patterns having unequal numbers of feature points from the same Euclidean space. Simulations are performed which demonstrate the effectiveness and the efficiency of the proposed approach in solving some practical matching problems which arise in computer vision and pattern analysis.
7
Baltsavias, Emmanuel P. Baltsavias Emmanuel P. Baltsavias Emmanuel P. "Multiphoto geometrically constrained matching /." Zürich, 1991. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=9561.
8
Coulter, Stewart. "Representation of geometric constraints in parametric synthesis." Thesis, Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/17982.
9
Phipps, Richard L. "Some Geometric Constraints on Ring-Width Trend." Tree-Ring Society, 2005. http://hdl.handle.net/10150/262639.
Abstract:
Simulations of tree rings from trees of undisturbed forest sites are used to describe natural, long-term width trends. Ring-width trends of canopy-sized white oak are simulated from regressions of BAI (ring area) data of real trees. Examples are given of a tree from a typical re-growth forest in Illinois and of a more slowly growing tree from an old-growth forest in Kentucky. The long-term width trend was simulated as being toward constant ring width regardless of growth rate of the tree. Conditions by which either increasing or decreasing ring-width trends could be simulated from the same linear BAI trend are examined. I conclude that curvilinear width trends, either increasing or decreasing, represent width adjustments to changes in growth rate (BAI trend) after which the width trend stabilizes to a near-constant value. Interpretation of ring-width trends of trees from undisturbed stands may be useful in assessing stand disturbance history.
10
Ma'ani-Hessari, Nason J. "Design of quadruplex DNA through geometric constraints." Thesis, University of Ulster, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.551558.
Abstract:
This thesis is concerned with the rational design of a group of DNA higher order architectures known as quadruplex DNA. Quadruplex DNA is comprised of a stem of stacking guanine tetrads linked by loops comprised of single stranded DNA. Due to the different combinations of loop types possible, it has great structural diversity and has potential nanotechnological and biological applications. Currently, only a few loop combinations, or topologies are known. Those that have been determined experimentally were not explicitly designed. Using a geometric formalism, the sum of currently available knowledge on quadruplex folding was used to create a set of parameters for the design of novel quadruplex architectures. We present the proof of principle for rational design of said structures, through making the novel topology (-pd+l) and the (G:C:G:C) tetrad- containing topology -(Ppp). We apply this principle to interpret thermal difference spectra signatures of a number of designed quadruplexes. Finally, we show that such novel quadruplexes can be used as building blocks for nanowires. This thesis therefore describes the proof of principle of design, means to expediate design, and an example application of design, of quadruplex nucleic acids. Through achieving these three aims, we present the feasibility of designing novel quadruplexes to be used as nanotechnological or medical devices.
11
Wilczkowiak, Marta. "3D modelling from images using geometric constraints." Grenoble INPG, 2004. http://www.theses.fr/2004INPG0034.
12
Robson, Mark Andrew. "Geometric quantization of constrained systems." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.363252.
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Dodwell, Timothy J. "Multilayered folding with constraints." Thesis, University of Bath, 2011. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.549892.
Abstract:
In the deformation of layered materials such as geological strata, or stacks of paper, mechanical properties compete with the geometry of layering. Smooth, rounded corners lead to voids between layers, while close packing leads to geometrically induced curvature singularities. When creation of voids is penalized by external pressure, the system trades off these competing effects, leading to various accommodating formations. Three two dimensional energy based nonlinear models are presented to describe the formation of voids at areas of intense geological folding. For each model the layers are assumed to be flexible elastic beams under hard unilateral contact constraint; which are solved as quasi-static obstacle problems with a free boundary. In each case an application of Kuhn-Tucker theory leads to representation as a nonlinear fourth order differential equation. Firstly a single layered model for voiding is presented. An elastic layer is forced into a V-shaped singularity by a uniform overburden pressure, where the fourth order free boundary problem is shown to have a unique, convex, symmetric solution. Drawing parallels with the Kuhn-Tucker theory, virtual work and ideas of duality, the physical significance of this differential equation is emphasised. Finally, appropriate scaling of either the potential energy or the differential equation shows the solutions scale to a single parametric group, for which the size of the void scales inversely with the ratio of overburden pressure to bending stiffness of the layer. Common to structural geology, one or several especially thick layers can dominate the deformation process. As a result, the remaining weak layers must accommodate into the geometry imposed by these competent layers. The second model, extends the first by introducing a plastic hinge to replicate the geometry imposed by the competent layer, and also axial springs to resist the slip over the limbs. The equilibrium equations for the system are investigated using the mathematical techniques developed for the first model. Under rigid loading the system may snap from an initially flat state to a convex voiding solution, as seen in the first model. However, if resistance to slip is high, the slightest imperfection causes the system to jump to a convoluted up-buckled solution, following a de-stiffened path to a point of self contact. These solutions have similarities with the delamination of carbon fibre composites. Finally, we extend the two single layered models to a simple multilayered model, which describes the periodic formation of voids in a chevron fold. The model shows that in the limit of high overburden pressures solutions form voids every layer, producing straight limbs punctured by sharp corners. This analysis shows good agreement when compared with recent experiments. This work provides the basis for future work on the buckling of thin multilayer assemblies in which voids may develop, and emphasizes the importance of the intricate nonlinear constraints of layers fitting together in multilayered folds.
14
Tarrés, Puertas Marta Isabel. "Direct tree decomposition of geometric constraint graphs." Doctoral thesis, Universitat Politècnica de Catalunya, 2014. http://hdl.handle.net/10803/285011.
Abstract:
The evolution of constraint based geometric models is tightly tied to parametric and feature-based Computer-Aided Design (CAD) systems. Since the introduction of parametric design by Pro/Engineer in the 1980's, most major CAD systems adopted constraint based geometric models as a core technology. Constraint based geometric models allowed CAD systems to provide a more powerful data model while offering an intuitive user interface. Later on, the same models also found application to fields like linkage design, chemical modeling, computer vision and dynamic geometry.
Constraint based geometric models are unevaluated models. A key problem related to constraint based geometric models is the geometric constraint based solving problem which, roughly speaking, can be stated as the problem of evaluating a constraint based model. Among the different approaches to geometric constraint solving, we are interested in graph-based Decomposition-Recombination solvers. In the graph-based constructive approach, the geometric problem is first translated into a graph whose vertices represent the set of geometric elements and whose edges are the constraints. Then the constraint problem is solved by decomposing the graph into a set of sub-problems, each sub-problem is recursively divided until reaching basic problems which are solved by a dedicated equational solver. The solution to the initial problem is computed by merging the solutions to the sub-problems.
The approach used by DR-solvers has been particularly successful when the decomposition into subproblems and subsequent recombination of solutions to these subproblems can be described by a plan generated a priori, that is, a plan generated as a preprocessing step without actually solving the subsystems. The plan output by the DR-planner remains unchanged as numerical values of parameters change. Such a plan is known as a DR-plan and the unit in the solver that generates it is the DR-planner. In this setting, the DR-plan is then used to drive the actual solving process, that is, computing specific coordinates that properly place geometric objects with respect to each other.
In this thesis we develop a new DR-planner algorithm for graph-constructive two dimensional DR-solvers. This DR-planner is based on the tree-decomposition of a graph. The triangle- or tree-decomposition of a graph decomposes a graph into three subgraphs such that subgraphs pairwise share one vertex. Shared vertices are called hinges. The tree-decomposition of a geometric constraint graph is in some sense the construction plan that solves the corresponding problem. The DR-planner algorithm first transforms the input graph into a simpler, planar graph. After that, an specific planar embedding is computed for the transformed graph where hinges, if any, can be straightly found. In the work we proof the soundness of the new algorithm. We also show that the worst case time performance of the resthe number of vertices of the input graph. The resulting algorithm is easy to implement and is as efficient as other known solving algorithms.L'evolució de models geomètrics basats en restriccions està fortament lligada al sistemes de Disseny Assistit per Computador (CAD) paramètrics i als basats en el paradigma de disseny per mitjà de característiques. Des de la introducció del disseny paramètric per part de Pro/Engineer en els anys 80, la major part de sistemes CAD utilitzaren com a tecnologia de base els models geomètrics basats en restriccions. Els models geomètrics basats en restriccions permeteren als sistemes CAD proporcionar un model d'informació més ampli i alhora oferir una interfície d'usuari intuitiva. Posteriorment, els mateixos models s'aplicaren en camps com el disseny de mecanismes, el modelatge químic, la visió per computador i la geometria dinàmica. Els models geomètrics basats en restriccions són models no avaluats. Un problema clau relacionat amb el models de restriccions geomètriques és el problema de la resolució de restriccions geomètriques, que es resumeix com el problema d'avaluar un model basat en restriccions. Entre els diferents enfocs de resolució de restriccions geomètriques, tractem els solvers de Descomposició-Recombinació (DR-solvers) basats en graphs. En l'enfoc constructiu basat en grafs, el problema geomètric es trasllada en un pas inicial a un graf, on els vèrtexs del graf representen el conjunt d'elements geomètrics i on les arestes corresponen a les restriccions geomètriques entre els elements. A continuació el problema de restriccions es resol descomposant el graf en un conjunt de subproblemes, cadascun dels quals es divideix recursivament fins a obtenir problemes bàsics, que sovint són operacions geomètriques realitzables, per exemple, amb regle i compàs, i que es resolen per mitjà d'un solver numèric específic. Finalment, la solució del problema inicial s'obté recombinant les solucions dels subproblemes. L'enfoc utilitzat pels DR-solvers ha esdevingut especialment interessant quan la descomposició en subproblemes i la posterior recombinació de solucions d'aquests subproblemes es pot descriure com un pla de construcció generat a priori, és a dir, un pla generat com a pas de pre-procés sense necessitat de resoldre realment els subsistemes. El pla generat pel DR-planner esdevé inalterable encara que els valors numèrics dels paràmetres canviin. Aquest pla es coneix com a DR-plan i la unitat en el solver que el genera és l'anomenat DR-planner. En aquest context, el DR-plan s'utilitza com a eina del procés de resolució en curs, és a dir, permet calcular les coordenades específiques que correctament posicionen els elements geomètrics uns respecte els altres. En aquesta tesi desenvolupem un nou algoritme que és la base del DR-planner per a DR-solvers constructius basats en grafs en l'espai bidimensional. Aquest DR-planner es basa en la descomposició en arbre d'un graf. La descomposició en triangles o arbre de descomposició d'un graf es basa en descomposar un graf en tres subgrafs tals que comparteixen un vèrtex 2 a 2. El conjunt de vèrtexs compartits s'anomenen \emph{hinges}. La descomposició en arbre d'un graf de restriccions geomètriques equival, en cert sentit, a resoldre el problema de restriccions geomètriques. L'algoritme del DR-planner en primer lloc transforma el graf proporcionat en un graf més simple i planar. A continuació, es calcula el dibuix en el pla del graf transformat, on les hinges, si n'hi ha, es calculen de manera directa. En aquest treball demostrem la correctesa del nou algoritme. Finalment, proporcionem l'estudi de la complexitat temporal de l'algoritme en cas pitjor i demostrem que és quadràtica en el nombre de vèrtexs del graf proporcionat. L'algoritme resultant és senzill d'implementar i tan eficient com altres algoritmes de resolució concrets
15
Hidalgo, García Marta R. "Geometric constraint solving in a dynamic geometry framework." Doctoral thesis, Universitat Politècnica de Catalunya, 2013. http://hdl.handle.net/10803/134690.
Abstract:
Geometric constraint solving is a central topic in many fields such as parametric solid modeling, computer-aided design or chemical molecular docking. A geometric constraint problem consists of a set geometric objects on which a set of constraints is defined. Solving the geometric constraint problem means finding a placement for the geometric elements with respect to each other such that the set of constraints holds.
Clearly, the primary goal of geometric constraint solving is to define rigid shapes. However an interesting problem arises when we ask whether allowing parameter constraint values to change with time makes sense. The answer is in the positive. Assuming a continuous change in the variant parameters, the result of the geometric constraint solving with variant parameters would result in the generation of families of different shapes built on top of the same geometric elements but governed by a fixed set of constraints. Considering the problem where several parameters change simultaneously would be a great accomplishment. However the potential combinatorial complexity make us to consider problems with just one variant parameter. Elaborating on work from other authors, we develop a new algorithm based on a new tool we have called h-graphs that properly solves the geometric constraint solving problem with one variant parameter. We offer a complete proof for the soundness of the approach which was missing in the original work.
Dynamic geometry is a computer-based technology developed to teach geometry at secondary school, which provides the users with tools to define geometric constructions along with interaction tools such as drag-and-drop. The goal of the system is to show in the user's screen how the geometry changes in real time as the user interacts with the system. It is argued that this kind of interaction fosters students interest in experimenting and checking their ideas. The most important drawback of dynamic geometry is that it is the user who must know how the geometric problem is actually solved. Based on the fact that current user-computer interaction technology basically allows the user to drag just one geometric element at a time, we have developed a new dynamic geometry approach based on two ideas: 1) the underlying problem is just a geometric constraint problem with one variant parameter, which can be different for each drag-and-drop operation, and, 2) the burden of solving the geometric problem is left to the geometric constraint solver.
Two classic and interesting problems in many computational models are the reachability and the tracing problems. Reachability consists in deciding whether a certain state of the system can be reached from a given initial state following a set of allowed transformations. This problem is paramount in many fields such as robotics, path finding, path planing, Petri Nets, etc. When translated to dynamic geometry two specific problems arise: 1) when intersecting geometric elements were at least one of them has degree two or higher, the solution is not unique and, 2) for given values assigned to constraint parameters, it may well be the case that the geometric problem is not realizable. For example computing the intersection of two parallel lines. Within our geometric constraint-based dynamic geometry system we have developed an specific approach that solves both the reachability and the tracing problems by properly applying tools from dynamic systems theory.
Finally we consider Henneberg graphs, Laman graphs and tree-decomposable graphs which are fundamental tools in geometric constraint solving and its applications. We study which relationships can be established between them and show the conditions under which Henneberg constructions preserve graph tree-decomposability. Then we develop an algorithm to automatically generate tree-decomposable Laman graphs of a given order using Henneberg construction steps.
16
Lomonosov, Andrew. "Graph and combinatorial algorithms for geometric constraint solving." [Gainesville, Fla.] : University of Florida, 2004. http://purl.fcla.edu/fcla/etd/UFE0001060.
17
Latham, Richard Samuel. "Combinatorial algorithms for the analysis and satisfaction of geometric constraints." Thesis, Brunel University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.336642.
18
GRITAI, ALEXEI. "MULTI-VIEW GEOMETRIC CONSTRAINTS FOR HUMAN ACTION RECOGNITION AND TRACKING." Doctoral diss., University of Central Florida, 2007. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4032.
Abstract:
Human actions are the essence of a human life and a natural product of the human mind. Analysis of human activities by a machine has attracted the attention of many researchers. This analysis is very important in a variety of domains including surveillance, video retrieval, human-computer interaction, athlete performance investigation, etc. This dissertation makes three major contributions to automatic analysis of human actions. First, we conjecture that the relationship between body joints of two actors in the same posture can be described by a 3D rigid transformation. This transformation simultaneously captures different poses and various sizes and proportions. As a consequence of this conjecture, we show that there exists a fundamental matrix between the imaged positions of the body joints of two actors, if they are in the same posture. Second, we propose a novel projection model for cameras moving at a constant velocity in 3D space, \emph cameras, and derive the Galilean fundamental matrix and apply it to human action recognition. Third, we propose a novel use for the invariant ratio of areas under an affine transformation and utilizing the epipolar geometry between two cameras for 2D model-based tracking of human body joints. In the first part of the thesis, we propose an approach to match human actions using semantic correspondences between human bodies. These correspondences are used to provide geometric constraints between multiple anatomical landmarks ( e.g. hands, shoulders, and feet) to match actions observed from different viewpoints and performed at different rates by actors of differing anthropometric proportions. The fact that the human body has approximate anthropometric proportion allows for innovative use of the machinery of epipolar geometry to provide constraints for analyzing actions performed by people of different anthropometric sizes, while ensuring that changes in viewpoint do not affect matching. A novel measure in terms of rank of matrix constructed only from image measurements of the locations of anatomical landmarks is proposed to ensure that similar actions are accurately recognized. Finally, we describe how dynamic time warping can be used in conjunction with the proposed measure to match actions in the presence of nonlinear time warps. We demonstrate the versatility of our algorithm in a number of challenging sequences and applications including action synchronization , odd one out, following the leader, analyzing periodicity etc. Next, we extend the conventional model of image projection to video captured by a camera moving at constant velocity. We term such moving camera Galilean camera. To that end, we derive the spacetime projection and develop the corresponding epipolar geometry between two Galilean cameras. Both perspective imaging and linear pushbroom imaging form specializations of the proposed model and we show how six different ``fundamental" matrices including the classic fundamental matrix, the Linear Pushbroom (LP) fundamental matrix, and a fundamental matrix relating Epipolar Plane Images (EPIs) are related and can be directly recovered from a Galilean fundamental matrix. We provide linear algorithms for estimating the parameters of the the mapping between videos in the case of planar scenes. For applying fundamental matrix between Galilean cameras to human action recognition, we propose a measure that has two important properties. First property makes it possible to recognize similar actions, if their execution rates are linearly related. Second property allows recognizing actions in video captured by Galilean cameras. Thus, the proposed algorithm guarantees that actions can be correctly matched despite changes in view, execution rate, anthropometric proportions of the actor, and even if the camera moves with constant velocity. Finally, we also propose a novel 2D model based approach for tracking human body parts during articulated motion. The human body is modeled as a 2D stick figure of thirteen body joints and an action is considered as a sequence of these stick figures. Given the locations of these joints in every frame of a model video and the first frame of a test video, the joint locations are automatically estimated throughout the test video using two geometric constraints. First, invariance of the ratio of areas under an affine transformation is used for initial estimation of the joint locations in the test video. Second, the epipolar geometry between the two cameras is used to refine these estimates. Using these estimated joint locations, the tracking algorithm determines the exact location of each landmark in the test video using the foreground silhouettes. The novelty of the proposed approach lies in the geometric formulation of human action models, the combination of the two geometric constraints for body joints prediction, and the handling of deviations in anthropometry of individuals, viewpoints, execution rate, and style of performing action. The proposed approach does not require extensive training and can easily adapt to a wide variety of articulated actions.Ph.D.
School of Electrical Engineering and Computer Science
Engineering and Computer Science
Computer Science PhD
19
Stein, Gideon P. (Gideon Pascal). "Geometric and photometric constraints : motion and structure from three views." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/9959.
Abstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1998.Includes bibliographical references (p. 165-171).
by Gideon P. Stein.
Ph.D.
20
Lawver, Jordan D. "Robust Feature Tracking in Image Sequences Using View Geometric Constraints." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1365611706.
21
Fleming, Alan Duncan. "Analysis of uncertainties and geometric tolerances in assemblies of parts." Thesis, University of Edinburgh, 1988. http://hdl.handle.net/1842/6626.
Abstract:
Computer models of the geometry of the real world have a tendency to assume that the shapes and positions of objects can be described exactly. However, real surfaces are subject to irregularities such as bumps and undulations and so do not have perfect, mathematically definable forms. Engineers recognise this fact and so assign tolerance specifications to their designs. This thesis develops a representation of geometric tolerance and uncertainty in assemblies of rigid parts. Geometric tolerances are defined by tolerance zones which are regions in which the real surface must lie. Parts in an assembly can slop about and so their positions are uncertain. Toleranced parts and assemblies of toleranced parts are represented by networks of tolerance zones and datums. Each arc in the network represents a relationship implied by the tolerance specification or by a contact between the parts. It is shown how all geometric constraints can be converted to an algebraic form. Useful results can be obtained from the network of tolerance zones and datums. For example it is possible to determine whether the parts of an assembly can be guaranteed to fit together. It is also possible to determine the maximum slop that could occur in the assembly assuming that the parts satisfy the tolerance specification. Two applications of this work are (1) tolerance checking during design and (2) analysis of uncertainty build-up in a robot assembly plan. I n the former, a designer could check a proposed tolerance specification to make sure that certain design requirements are satisfied. In the latter, knowledge of manufacturing tolerances of parts being manipulated can be used to determine the constraints on the positions of the parts when they are in contact with other parts.
22
KAIMAL, VINOD GOPALKRISHNA. "A NEURAL METHOD OF COMPUTING OPTICAL FLOW BASED ON GEOMETRIC CONSTRAINTS." University of Cincinnati / OhioLINK, 2002. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1037632137.
23
Bonifas, Nicolas. "Geometric and Dual Approaches to Cumulative Scheduling." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLX119/document.
Abstract:
Ce travail s’inscrit dans le domaine de l’ordonnancement à base de programmation par contraintes. Dans ce cadre, la contrainte de ressource la plus fréquemment rencontrée est la cumulative, qui permet de modéliser des processus se déroulant de manière parallèle.Nous étudions dans cette thèse la contrainte cumulative en nous aidant d’outils rarement utilisés en programmation par contraintes (analyse polyédrale, dualité de la programmation linéaire, dualité de la géométrie projective) et proposons deux contributions pour le domaine.Le renforcement cumulatif est un moyen de générer des contraintes cumulatives redondantes plus serrées, de manière analogue à la génération de coupes en programmation linéaire entière. Il s'agit ici de l'un des premiers exemples de contrainte globale redondante.Le Raisonnement Énergétique est une propagation extrêmement puissante pour la contrainte cumulative, avec jusque-là une complexité élevée en O(n^{3}). Nous proposons un algorithme qui calcule cette propagation avec une complexité O(n^{2}log n), ce qui constitue une amélioration significative de cet algorithme connu depuis plus de 25 ansThis work falls in the scope of constraint-based scheduling. In this framework, the most frequently encountered resource constraint is the cumulative, which enables the modeling of parallel processes.In this thesis, we study the cumulative constraint with the help of tools rarely used in constraint programming (polyhedral analysis, linear programming duality, projective geometry duality) and propose two contributions for the domain.Cumulative strengthening is a means of generating tighter redundant cumulative constraints, analogous to the generation of cuts in integer linear programming. This is one of the first examples of a redundant global constraint.Energy Reasoning is an extremely powerful propagation for cumulative constraint, with hitherto a high complexity of O(n^{3}). We propose an algorithm that computes this propagation with a O(n^{2}log n) complexity, which is a significant improvement of this algorithm known for more than 25 years
24
Faulke, Darren Andrew. "The effect of geometric constraint on mixed mode crack paths." Thesis, University College London (University of London), 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.285148.
25
Oung, Jianjun. "Design and implementation of an object-oriented geometric constraint solver." [Gainesville, Fla.] : University of Florida, 2001. http://etd.fcla.edu/etd/uf/2001/ank7123/thesis.pdf.
Abstract:
Thesis (M.S.)--University of Florida, 2001.Title from first page of PDF file. Document formatted into pages; contains ix, 82 p.; also contains graphics. Vita. Includes bibliographical references (p. 78-81).
26
Chen, Jin. "The use of multiple cameras and geometric constraints for 3-D measurement." Thesis, City University London, 1995. http://openaccess.city.ac.uk/7542/.
Abstract:
This thesis addresses some of the problems involved in the automation of 3-D photogrammetric measurement using multiple camera viewpoints. The primary research discussed in this thesis concerns the automatic solution of the correspondence problem. This and associated research has led to the development of an automated photograrnmetric measuring system which combines the techniques from both machine vision and photogrammetry. Such a system is likely to contribute greatly to the accessibility of 3-D measurement to non-photogrammetrists who will generally have little knowledge and expertise of photogrammetry. A matching method, which is called the 3-D matching method, is developed in the thesis. This method is based on a 3-D intersection and "epipolar plane", as opposed to the 2-D intersection of the epipolar line method. The method is shown to provide a robust and flexible procedure,especially where camera orientation parameters are not well known. The theory of the method is derived and discussed. It is further developed by combination with a bundle adjustment process to iteratively improve the estimated camera orientations and to gradually introduce legitimate matched target images from multiple cameras. The 3-D target matching method is also optimised using a 3-D space constrained search technique. A globally consistent search is developed in which pseudo target images are defined to overcome problems due to occlusion. Hypothesis based heuristic algorithms are developed to optimise the matching process. This method of solving target correspondences is thoroughly tested and evaluated by simulation and by its use in practical applications. The characteristics of the components necessary for a photogrammetric measuring system are investigated. These include sources of illumination, targets, sensors, lenses, and framegrabbers. Methods are introduced for analysis of their characteristics. CCD cameras are calibrated using both plumb line and self calibration methods. These methods provide an estimation of some of the sources of error, which influence the performance of the system as a whole. The design of an automated photogrammetric measuring system with a number of novel features is discussed and a prototype system is developed for use in a constrained environment. The precision, accuracy, reliability, speed, and flexibility of the developed system are explored in a number of laboratory and experimental applications. Trials show that with further development the system could have commercial value and be used to provide a solution suitable for photogrammetrists and trained operators in a wide range of applications.
27
Shehadeh, Mhd Ali. "Geometrické řízení hadům podobných robotů." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2020. http://www.nusl.cz/ntk/nusl-417115.
Abstract:
This master’s thesis describes equations of motion for dynamic model of nonholonomic constrained system, namely the trident robotic snakes. The model is studied in the form of Lagrange's equations and D’Alembert’s principle is applied. Actually this thesis is a continuation of the study going at VUT about the simulations of non-holonomic mechanisms, specifically robotic snakes. The kinematics model was well-examined in the work of of Byrtus, Roman and Vechetová, Jana. So here we provide equations of motion and address the motion planning problem regarding dynamics of the trident snake equipped with active joints through basic examples and propose a feedback linearization algorithm.
28
Patel, Pritesh V. "Stepwise construction and spectroscopy of geometrically constrained bimetallic molecular triads." Thesis, University of Newcastle Upon Tyne, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.427410.
29
Bass, Henry Morgan. "Automatic modification of part geometries subject to manufacturing constraints using fuzzy logic." Thesis, Virginia Tech, 1996. http://hdl.handle.net/10919/45086.
Abstract:
There is frequently a need for algorithms capable of automatic modification of geometric models in response to manufacturing process constraints. Designers typically initiate product models using ideal, exact geometry; however, several non-traditional manufacturing processes frequently require slight modifications to the ideal model to accommodate various manufacturing process constraints. These modifications can be difficult, complex, and tedious to compute. For instance, metal-ceramic brazing requires adjustments to the part geometry
primarily to accommodate thermal expansion and to allow for the insertion of a narrow braze-filler gap. These adjustments depend on the particular geometry, material properties, and processing parameters. Any modification to these product model parameters necessitates extensive recomputation to reestablish a manufacturable part geometry.
This thesis demonstrates in part the integration of geometry into the overall product model by having the non-geometric parts of the product model provide feedback to the geometry by means of automatically modifying its shape. The methodology is demonstrated in a prototype model which introduces the concept of auxiliary geometric structures. In particular, the auxiliary geometric structures provide a mapping between the designer's intent and the part geometry
described in the solid model. The designer's intent is represented in a rule base for metal-ceramic brazing that is controlled by fuzzy logic. This rule base aids the user in quantifying and generating from the auxiliary geometric structures the geometric modifications needed to conform with a complex set of rules derived from both analytic and empirical work in metal-ceramic brazingMaster of Science
30
MEDEIROS, VIVIAN SUZANO. "DETERMINATION OF THE OPTIMAL TRAJECTORIES ON RACE TRACKS WITH DYNAMIC AND GEOMETRIC CONSTRAINTS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2015. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=25685@1.
Abstract:
PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
FUNDAÇÃO DE APOIO À PESQUISA DO ESTADO DO RIO DE JANEIRO
O presente projeto de pesquisa objetiva desenvolver um procedimento para determinação de trajetórias ótimas em pistas de corrida baseado em técnicas de otimização, considerando os limites geométricos da pista e as características dinâmicas do veículo. O veículo será representado por meio de um modelo simplificado de partícula orientada, mas que inclui as capacidades de tração, frenagem e aceleração normal típicas de um veículo terrestre de competição. Primeiramente, é determinada a trajetória de tempo mínimo para uma curva de 90 graus por meio da análise geométrica do problema e em seguida, é obtida a solução analítica geral para aplicação a qualquer ângulo. Em seguida, técnicas de otimização com restrição são empregadas de forma a obter a curva de menor tempo que concatena as trajetórias ótimas individuais de cada curva, previamente determinadas. São estudadas, ainda, as características dinâmicas de algumas curvas polinomiais para inferir aquela que melhor pode ser aplicada no processo de concatenação. A trajetória de menor tempo da pista de corrida obtida pelo procedimento de concatenação é apresentada e é feita uma análise das vantagens e desvantagens do método proposto. Como alternativa, é apresentada uma visão geral do problema de controle ótimo e é formulada a modelagem completa do problema de trajetória de mínimo tempo utilizando esta abordagem, incluindo as restrições dinâmicas do veículo e as restrições geométricas da pista. Algumas técnicas possíveis para solução do problema de controle ótimo são sugeridas.
This work proposes a new procedure to determine the optimal trajectory on race tracks based on constrained optimization techniques, where the constraints are defined by means of the dynamic characteristics of the vehicle and the geometrical limits of the track. The vehicle is represented by an oriented particle with the capabilities of traction, braking and normal acceleration, which are typical in a competition vehicle. First, the minimum-time trajectory for a 90-degree curve is obtained through a geometrical analysis of the problem. The solution is then expanded to be applied to all angles. Starting from the individual minimum-time trajectory for each curve of the track, constrained optimization techniques are employed in order to obtain the shorter curve that concatenates these individual optimal trajectories. The dynamic characteristics of some polynomial curves are analyzed to infer the one that can best be applied in the concatenation process. The minimum-time trajectory for the race track obtained by the concatenation procedure is presented and the advantages and disadvantages of the proposed method are discussed. Alternatively, an overview of the optimal control problem is presented and a complete model of the minimum-time trajectory problem is developed using this approach, including the dynamic constraints of the vehicle and the geometric constraints of the track. Some possible methods for the solution of the optimal control problem are suggested.
31
Kohareswaran, Naganandhini. "Design and implementation of Sketcher user interface for a geometric constraint solver /." [Gainesville, Fla.] : University of Florida, 2002. http://purl.fcla.edu/fcla/etd/UFE0000556.
32
Campher, Andre Herman. "A systematic approach to model predictive controller constraint handling : rigorous geometric methods." Diss., University of Pretoria, 2011. http://hdl.handle.net/2263/28378.
Abstract:
The models used by model predictive controllers (MPCs) to predict future outcomes are usually unconstrained forms like impulse or step responses and discrete state space models. Certain MPC algorithms allow constraints to be imposed on the inputs or outputs of a system; but they may be infeasible as they are not checked for consistency via the process model. Consistent constraint handling methods - which account for their interdependence and disambiguate the language used to specify constraints – would therefore be an attractive aid when using any MPC package. A rigorous and systematic approach to constraint management has been developed, building on the work of Vinson (2000), Lima (2007) and Georgakis et al. (2003) in interpreting constraint interactions. The method supports linear steady-state system models, and provides routines to obtain the following information: - effects of constraint changes on the corresponding input and output constraints,
- feasibility checks for constraints,
- specification of constraint-set size and
- optimal fitting of constraints within the desirable input and output space.
Dissertation (MEng)--University of Pretoria, 2011.
Chemical Engineering
unrestricted
33
Demenkov, Maxim. "Geometric algorithms for input constrained systems with application to flight control." Thesis, De Montfort University, 2007. http://hdl.handle.net/2086/4950.
Abstract:
In this thesis novel numerical algorithms are developed to solve some problems of analysis and control design for unstable linear dynamical systems having their input constrained by maximum amplitude and rate of the control signals. Although the results obtained are of a general nature, all the problems considered are induced by flight control applications. Moreover, all these problems are stated in terms of geometry, and because of this their solution in the thesis was effectively achieved by geometrically-oriented methods. The problems considered are mainly connected with the notions of the controllable and stability regions. The controllable region is defined as the set of states of an unstable dynamical system that can be stabilized by some realizable control action. This region is bounded due to input constraints and its size can serve as a controllability measure for the control design problem. A numerical algorithm for the computation of two-dimensional slices of the region is proposed. Moreover, the stability region design is also considered. The stability region of the closed-loop system is the set of states that can be stabilized by a particular controller. This region generally utilizes only a part of the controllable region. Therefore, the controller design objective may be formulated as maximizing this region. A controller that is optimal in this sense is proposed for the case of one and two exponentially unstable open-loop eigenvalues. In the final part of the thesis a linear control allocation problem is considered for overactuated systems and its real-time solution is suggested. Using the control allocation, the actuator selection task is separated from the regulation task in the control design. All fault detection and reconfiguration capabilities are concentrated in one special unit called the control allocator, while a general control algorithm, which produces 'virtual' input for the system, remains intact. In the case of an actuator fault, only the control allocation unit needs to be reconfigured and in many cases it can generate the same 'virtual' input using a different set of control effectors. A novel control allocation algorithm, which is proposed in the thesis, is based on multidimensional interval bisection techniques.
34
Diedrich, Florian [Verfasser]. "Approximation algorithms for linear programs and geometrically constrained packing roblems / Florian Diedrich." Kiel : Universitätsbibliothek Kiel, 2009. http://d-nb.info/1019865903/34.
35
Changizi, Navid. "FRAME TOPOLOGY OPTIMIZATION WITH STANDARD CROSS SECTIONS: ACCOUNTING FOR BUCKLING, STRESS CONSTRAINTS AND GEOMETRIC VARIABILITY." Cleveland State University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=csu1470847100.
36
Wong, Kok Cheong. "Representation, feature extraction and geometric constraints for recognising 3D objects from a single perspective view." Thesis, University of Surrey, 1992. http://epubs.surrey.ac.uk/843449/.
Abstract:
This dissertation considers the problem of modelling, feature extraction and recognizing 3D objects from a single perspective view. A solid modelling system based on generalized cylinder is presented. A new algorithm is proposed for grouping 2D line segments into intermediate token features to be used as geometric cues for indexing into the model database and for generating hypotheses for polyhedral objects. A polyhedral object recognition system using a hypothesis and verification paradigm has been proposed and developed. In the modelling system, generalized cylinders are used as geometric primitives for representing objects. The analysis of generalized cylinders is presented. A number of useful expressions and properties of the contour generators of straight homogeneous generalized cylinders are derived under perspective projection. Right and oblique straight homogeneous generalized cylinders with circular and abitrary cross-section are discussed. A novel algorithm for extracting geometric features such as triples of connected edges, triangle- pairings, image trihedral vertices and closed polygons is implemented. Both heuristic and physical rules are utilised to control the combinatorial explosion of the feature grouping process. Physical rules are used to reject closed polygons which are incompatible with a single planar surface hypothesis. Experiments are demonstrated on real data and many features which could reasonably be due to spatial physical properties of the objects are idenified. Only a few spurious features are accidently detected. These irrelevant features are then pruned away in the hypothesis generation and verification process modules of the proposed recognition system. A polyhedral object recognition system based on a single perspective image is developed. A hypothesis and verification paradigm based on the use of local geometric features of objects is presented. In the framework, two high-level geometric primitives, namely triangle-pair and quadrilateral are employed as key features for model invocation and hypothesis generation. Two geometric constraints, namely distance and angle constraints are proposed and integrated into the recognition system. Many model and scene correspondences are pruned away in the early stage of the matching process using the two geometric constraints. As a by-product of the hypothesis generation the relative pose of the 3D objects expressed in camera frame is recovered. A verification process for performing a detailed check on the model-to-scene correspondences is developed. Detailed experimental results are performed to confirm the feasibility and robustness of the recognition system. An intuitive mathematical formulation is proposed for the interpretation of the geometric relationships of a triple of spatial edges and their perspective projection forming image lines. No restriction is imposed on the configuration of the triple of spatial edges. An eighth-degree polynomial equation explicitly defined by the space angles between the corresponding three spatial edges measured with respect to an object centered coordinate system is derived. The crux of this representation is that the angular attributes of pairs of spatial edges are object-independent. An effective hypothesis generation scheme is proposed which can take advantage of the commonality of this novel representation. It avoids replicating the same recognition module for every occurrence of the same triple feature in the same generic triple group. The groups are distinguished by the angles between the constituent model edges and do not involve any length metric property. Generally, a relatively small number of defined generic triple groups are employed to describe a wide range of polyhedral object models. Particular closed form solutions are derived for specific but common configurations of edges such as rectangular bar end and orthogonal triple. The practical significance and generality of our result are multifold. Extensive experiments are performed to verify the plausibility of employing connected triple edges and trihedral vertices as key features in the paradigm of hypothesis-generation and Hough-clustering approaches to object recognition. It is demonstrated that the accuracy of the estimated pose of objects is adequate. Finally, outstanding problems identified and possible solutions to these problems are discussed. Future research directions are proposed.
37
Foster, Michael S. "Using Lidar to geometrically-constrain signature spaces for physics-based target detection /." Online version of thesis, 2007. http://hdl.handle.net/1850/5827.
38
Bole, Marcus. "A hull surface generation technique based on a form topology and geometric constraint approach." Thesis, University of Strathclyde, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.288605.
39
Salgado, Rebolledo Patricio. "Symplectic Structure of Constrained Systems: Gribov Ambiguity and Classical Duals for 3D Gravity." Doctoral thesis, Universite Libre de Bruxelles, 2015. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/220463.
Abstract:
The present thesis is divided into two parts. Part I is devoted to the study of Gribov ambiguity in gauge systems and its relation with the appearance of degeneracies in the symplectic structure of the corresponding reduced phase space after gauge fixation. Part II is concerned with classical dual field theories for three-dimensional Einstein gravity and the symplectic structure on coadjoint orbits of the corresponding asymptotic symmetry group.In Part I, the Gribov problem is studied in the context of finite temperature QCD and the structure of the gluon propagator is analyzed. The standard confined scenario is found for low temperatures, while for high enough temperatures deconfinement takes place and a free gluon propagator is obtained. Subsequently, the relation between Gribov ambiguity and degeneracies in the symplectic structure of gauge systems is analyzed. It is shown that, in finite-dimensional systems, the presence of Gribov ambiguities in regular constrained systems always leads to a degenerate symplectic form upon Dirac reduction. The implications for the Gribov-Zwanziger approach to QCD and the symplectic structure of the theory are discussed. In Part II, geometrical actions for three-dimensional Einstein gravity are constructed by studying the symplectic structure on coadjoint orbits of the asymptotic symmetry group. The geometrical action coming from the Kirillov-Kostant symplectic form on coadjoint orbits is analyzed thought Dirac's algorithm for constrained systems. By studying the case of centrally extended groups and semi-direct products, the symplectic structure on coadjoint orbits of the Virasoro and the BMS3 group are analyzed. This allows one to associate separate geometric actions to each coadjoint orbit of the solution space, leading to two-dimensional dual fiel theories for asymptotically AdS and asymptotically flat three-dimensional gravity respectively.Doctorat en Sciences
info:eu-repo/semantics/nonPublished
40
Kivelä, S. M. (Sami Mikael). "Evolution of insect life histories in relation to time constraints in seasonal environments:polymorphism and clinal variation." Doctoral thesis, Oulun yliopisto, 2011. http://urn.fi/urn:isbn:9789514293788.
Abstract:
Abstract Both the length of the season that is favourable for insect growth and reproduction and the number of generations emerging per season (voltinism) increase with decreasing latitude. Thus, time constraints on reproduction and juvenile development decrease with decreasing latitude, except where voltinism changes and time constraints suddenly increase as the season must be shared with one more generation. I studied the evolution of insect life histories in relation to time constraints from two perspectives: polymorphism and clinal variation. Life history polymorphism in seasonal environments was studied with the butterfly Pieris napi that has discrete life history strategies, and polymorphic natural populations. Experimental studies showed that asymmetric intraspecific larval competition and divergent timing of reproduction between the strategies may promote the maintenance of polymorphism. A simulation model showed that the divergent timing of reproduction between the strategies is sufficient to maintain polymorphism even in the absence of intraspecific competition. Clinal variation was studied empirically with four geometrid moths (Cabera exanthemata, Cabera pusaria, Chiasmia clathrata and Lomaspilis marginata) and generally in theory. Due to latitudinal saw-tooth variation in time constraints, traditional theory predicts a saw-tooth cline in body size and development time. A common garden experiment with the four geometrid moths did not support the traditional theory even when a saw-tooth cline in body size was found, suggesting that the theory is based on unrealistic assumptions. A theoretical analysis showed that reproductive effort should be high in populations under intense time constraints and low in populations experiencing no time constraints, resulting in a saw-tooth cline. In the four geometrid moths, support for these predictions was found, although the observed clinal variation deviated from the predicted pattern. The results imply that clinal variation is expected in almost any continuous life history trait, whereas polymorphism of different strategies may emerge when life histories fall into discrete categories. When inferring the evolution of a single trait, complex interdependencies among several traits should be considered, as well as the possibility that the time constraints are not similar for each generation in multivoltine populationsTiivistelmä Hyönteisten kasvu ja kehitys ovat pääsääntöisesti mahdollisia vain kesän aikana. Etelään päin mentäessä kesä pitenee, ja saman kesän aikana kehittyvien hyönteissukupolvien määrä kasvaa. Kesän pituus aiheuttaa lisääntymiseen ja toukkien kasvuun kohdistuvan aikarajoitteen, joka heikkenee etelään päin siirryttäessä. Aikarajoite kuitenkin tiukkenee siellä, missä yksi uusi sukupolvi ehtii juuri kehittymään saman kesän aikana, sillä kesä on nyt jaettava useamman sukupolven kesken. Väitöstyössä tarkastelin hyönteisten elinkierto-ominaisuuksien evoluutiota suhteessa aikarajoitteisiin sekä diskreetin että jatkuvan muuntelun näkökulmista. Diskreettiä muuntelua tutkin lanttuperhosella (Pieris napi), jolla esiintyy diskreettejä elinkiertostrategioita. Kokeellisesti osoitin, että toukkien välinen kilpailu on epäsymmetristä, mikä yhdessä eri elinkiertostrategioiden erilaisen lisääntymisen ajoittumisen kanssa voi ylläpitää diskreettiä muuntelua. Simulaatiomalli osoitti, että erilaiset elinkiertostrategiat voivat säilyä populaatiossa pelkästään niiden erilaisen lisääntymisen ajoittumisen ansiosta. Elinkierto-ominaisuuksien jatkuvaa muuntelua tutkin neljän mittariperhosen (Cabera exanthemata, Cabera pusaria, Chiasmia clathrata ja Lomaspilis marginata) avulla ja teoreettisesti yleisellä tasolla. Aikaisempi teoria ennustaa ruumiinkoon ja kehitysajan muuntelevan sahalaitakuvion mukaisesti siirryttäessä pohjoisesta etelään, koska aikarajoitteet muuntelevat samalla tavalla. Tämä teoria perustunee epärealistisiin oletuksiin, koska kokeelliset tulokset eivät tukeneet teoriaa silloinkaan, kun mittariperhosten ruumiinkoko muunteli ennustetulla tavalla. Teoreettinen tutkimus osoitti, että myös lisääntymispanostuksen tulisi muunnella sahalaitakuvion mukaisesti suhteessa kesän pituuteen siten, että se on korkeimmillaan siellä, missä aikarajoitteet ovat tiukat. Mittariperhosten tutkiminen antoi jossain määrin tukea tälle ennusteelle. Tulosten perusteella jatkuvaa maantieteellistä muuntelua ennustetaan elinkierto-ominaisuuksille, jotka muuntelevat jatkuvalla asteikolla. Erilaiset elinkiertostrategiat voivat sen sijaan säilyä populaatiossa, jos elinkierto-ominaisuuksien muuntelu on diskreettiä. Eri ominaisuuksien monimutkaiset vuorovaikutukset sekä eri sukupolvien mahdollisesti kokemat erilaiset aikarajoitteet olisi syytä tuntea, kun tarkastelun kohteena on yksittäisen ominaisuuden evoluutio
41
Keuthen, Moritz [Verfasser], Michael [Akademischer Betreuer] Ulbrich, Roland [Akademischer Betreuer] Herzog, and Wolfgang [Akademischer Betreuer] Ring. "Second Order Shape Optimization with Geometric Constraints / Moritz Keuthen. Betreuer: Michael Ulbrich. Gutachter: Roland Herzog ; Wolfgang Ring ; Michael Ulbrich." München : Universitätsbibliothek der TU München, 2015. http://d-nb.info/1082034258/34.
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Lindqvist, Björn. "Combined Control and Path Planning for a Micro Aerial Vehicle based on Non-linear MPC with Parametric Geometric Constraints." Thesis, Luleå tekniska universitet, Rymdteknik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-76212.
Abstract:
Using robots to navigate through un-mapped environments, specially man-made infrastructures, for the purpose of exploration or inspection is a topic that has gathered a lot of interest in the last years. Micro Aerial Vehicles (MAV's) have the mobility and agility to move quickly and access hard-to-reach areas where ground robots would fail, but using MAV's for that purpose comes with its own set of problems since any collision with the environment results in a crash. The control architecture used in a MAV for such a task needs to perform obstacle avoidance and on-line path-planning in an unknown environment with low computation times as to not lose stability. In this thesis a Non-linear Model Predictive Controller (NMPC) for obstacle avoidance and path-planning on an aerial platform will be established. Included are methods for constraining the available state-space, simulations of various obstacle avoidance scenarios for single and multiple MAVs and experimental validation of the proposed control architecture. The validity of the proposed approach is demonstrated through multiple experimental and simulation results. In these approaches, the positioning information of the obstacles and the MAV are provided by a motion-capture system. The thesis will conclude with the demonstration of an experimental validation of a centralized NMPC for collision avoidance of two MAV's.
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Keuthen, Moritz Verfasser], Michael [Akademischer Betreuer] [Ulbrich, Roland [Akademischer Betreuer] Herzog, and Wolfgang [Akademischer Betreuer] Ring. "Second Order Shape Optimization with Geometric Constraints / Moritz Keuthen. Betreuer: Michael Ulbrich. Gutachter: Roland Herzog ; Wolfgang Ring ; Michael Ulbrich." München : Universitätsbibliothek der TU München, 2015. http://nbn-resolving.de/urn:nbn:de:bvb:91-diss-20151221-1275877-1-5.
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Oyini, Mbouna Ralph. "Illumination Independent Head Pose and Pupil Center Estimation for Gaze Computation." Master's thesis, Temple University Libraries, 2011. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/208725.
Abstract:
Electrical EngineeringM.S.E.E.
Eyes allow us to see and gather information about the environment. Eyes mainly act as an input organ as they collect light, but they also can be considered an output organ as they indicate the subject's gaze direction. Using the orientation of the head and the position of the eyes, it is possible to estimate the gaze path of an individual. Gaze estimation is a fast growing technology that track a person's eyes and head movements to "pin point" where the subject is looking at on a computer screen. The gaze direction is described as a person's line of sight. The gaze point, also known as the focus point, is defined as the intersection of the line of sight with the screen. Gaze tracking has an infinite number of applications such as monitoring driver alertness or helping track a person's eyes with a psychological disorder that cannot communicate his/her issues. Gaze tracking is also used as a human-machine interface for disabled people that have lost total control of their limbs. Another application of gaze estimation is marketing. Companies use the information given by the gaze estimation system from their customers to design their advertisements and products.
Temple University--Theses
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Napolitano, Ralph E. Jr. "Finite differenc-cellular automation modeling of the evolution of interface morphology during alloy solidification under geometrical constraint : application to metal matrix composite solidification." Diss., Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/32810.
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De, Leon Daniel Milbrath. "Otimização topológica de mecanismos flexíveis com controle da tensão máxima considerando não linearidades geométrica e material." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2015. http://hdl.handle.net/10183/118880.
Abstract:
Mecanismos flexíveis, nos quais a deformação elástica é aproveitada na atuação cinemática, têm grande empregabilidade em dispositivos de mecânica de precisão, engenharia biomédica, e mais recentemente em microeletromecanismos (MEMS). Entre as diversas técnicas empregadas para o seu projeto, a otimização topológica tem se mostrado a mais genérica e sistemática. A grande dificuldade destes projetos é conciliar os requisitos cinemáticos com a resistência mecânica da estrutura. Neste trabalho, é implementado um critério de resistência dentro da formulação do problema de otimização, com o intuito de gerar mecanismos que cumpram a tarefa cinemática desejada mas ao mesmo tempo não ultrapassem limites de tensão predeterminados. Esta restrição adicional também visa aliviar o problema bastante conhecido do aparecimento de articulações. Não linearidade geométrica e de material (hiperelasticida de compressível) são implementadas na solução das equações através do método dos elementos finitos para levar em conta os grandes deslocamentos do mecanismo. O método das assíntotas móveis é usado para a atualização das variáveis de projeto. As derivadas do problema de otimização são calculadas analiticamente, pelo método adjunto. Técnicas de projeção são aplicadas para a garantia de topologias livres de instabilidades numéricas comuns em otimização topológica, e projetos otimizados mais próximos de um espaço 0/1 para as densidades físicas.Compliant me hanisms, in whi h the elasti strain is the basis for kinemati a tua- tion are widely used in pre ision me hani s devi es, biomedi al engineering, and re ently in mi roele trome hani al systems (MEMS). Among several te hniques applied in ompliant me hanisms design, topology optimization has been one of the most general and systemati . The great hallenge in these designs is to ouple both the kinemati s and the me hani al strength riteria requirements. In this work, a strength riteria for the optimization problem is applied, with the aim of generating ompliant me hanisms that ful ll the desired kine- mati tasks while omplying with a stress threshold. The addition of a stress onstraint to the formulation for ompliant me hanisms in topology optimization also aims to allevi- ate the appearan e of hinges in the optimized topology, a well known issue in the design of ompliant me hanisms. Geometri al and material ( ompressible hyperelasti ity) nonlin- earities are applied to the nite element equilibrium equations, to take into a ount large displa ements. The method of moving asymptotes is applied for design variables updating. The derivatives are al ulated analyti ally, by the adjoint method. Proje tion ltering te h- niques are applied, in order to guarantee topologies free of ommon numeri al instabilities in topology optimization, and optimized designs near the 0/1 solution for the physi al densities.
47
Olakoyejo, O. T. (Olabode Thomas). "Geometric optimisation of conjugate heat transfer in cooling channels with different cross-sectional shapes." Thesis, University of Pretoria, 2012. http://hdl.handle.net/2263/25484.
Abstract:
In modern heat transfer, shape and geometric optimisation are new considerations in the evaluation of thermal performance. In this research, we employed constructal theory and design to present three-dimensional theoretical and numerical solutions of conjugate forced convection heat transfer in heat generating devices with cooling channels of different cross-sectional shapes. In recent times, geometric configurations of cooling channel have been found to play an important role in thermal performance. Therefore, an efficient ways of optimally designing these cooling channels shapes is required. Experimentation has been extensively used in the past to understand the behaviour of heat removals from devices. In this research, the shapes of the cooling channels and the configurations of heat-generating devices were analytically and numerically studied to minimise thermal resistance and thus illustrate cooling performance under various design conditions. The cooling channels of five different cross-sectional shapes were studied: Circular, square, rectangular, isosceles right triangular and equilateral triangular. They were uniformly packed and arranged to form larger constructs. The theoretical analysis is presented and developed using the intersection of asymptotes method. This proves the existence of an optimal geometry of parallel channels of different cross-sectional shapes that penetrate and cool a volume with uniformly distributed internal heat generation and heat flux, thus minimising the global thermal resistance. A three-dimensional finite volume-based numerical model was used to analyse the heat transfer characteristics of the cross-sectional shapes of various cooling channels. The numerical computational fluid dynamics (CFD) package recently provided a more cost-effective and less time-consuming means of achieving the same objective. However, in order to achieve optimal design solutions using CFD, the thermal designers have to be well experienced and carry out a number of trial-and-error simulations. Unfortunately, this can not always guarantee an accurate optimal design solution. In this thesis a mathematical optimisation algorithm (a leapfrog optimisation program and DYNAMIC-Q algorithm) coupled with numerical CFD was employed and incorporated into the finite volume solver, –FLUENT, and grid (geometry and mesh) generation package, – GAMBIT to search and identify the optimal design variables at which the system would perform optimally for greater efficiency and better accuracy. The algorithm was also specifically designed to handle constraint problems where the objective and constraint functions were expensive to evaluate. The automated process was applied to different design cases of cooling channels shapes. These cooling channels were embedded in a highly conductive solid and the peak temperature was minimised. The trend and performance of all the cooling channel shapes cases studied were compared analytically and numerically. It was concluded that an optimal design can be achieved with a combination of CFD and mathematical optimisation. Furthermore, a geometric optimisation of cooling channels in the forced convection of a vascularised material (with a localised self-cooling property subjected to a heat flux) was also considered. A square configuration was studied with different porosities. Analytical and numerical solutions were provided. This gradient-based optimisation algorithm coupled with CFD was used to determine numerically the optimal geometry that gave the lowest thermal resistance. This optimiser adequately handled the numerical objective function obtained from numerical simulations of the fluid flow and heat transfer. The numerical results obtained were in good agreement with results obtained in the approximate solutions based on scale analyses at optimal geometry dimensions. The approximate dimensionless global thermal resistance predicted the trend obtained in the numerical results. This shows that there were unique optimal design variables (geometries) for a given applied dimensionless pressure number for fixed porosity. The results also showed that the material property had a significant influence on the performance of the cooling channel. Therefore, when designing the cooling structure of vascularised material, the internal and external geometries of the structure, material properties and pump power requirements would be very important parameters to be considered in achieving efficient and optimal designs for the best performance. Finally, this research investigated a three-dimensional geometric optimisation of conjugate cooling channels in forced convection with an internal heat generation within the solid for an array of cooling channels. Three different flow orientations based on constructal theory were studied numerically- firstly, an array of channels with parallel flow; secondly, an array of channels in which flow of every second row was in a counter direction and finally, an array of channels in which the flow direction in every channel was opposite to that of previous channel. The geometric configurations and flow orientations were optimised in such a way that the peak temperature was minimised subject to the constraint of fixed global volume of solid material. The optimisation algorithm coupled with CFD was also used to determine numerically the optimal geometry that gave the lowest thermal resistance. The use of the optimisation algorithm coupled with the computational fluid dynamics package; render the numerical results more robust with respect to the selection of optimal structure geometries, internal configurations of the flow channels and dimensionless pressure difference.Thesis (PhD(Eng))--University of Pretoria, 2012.
Mechanical and Aeronautical Engineering
unrestricted
48
Castanheiro, Letícia Ferrari. "Geometric model of a dual-fisheye system composed of hyper-hemispherical lenses /." Presidente Prudente, 2020. http://hdl.handle.net/11449/192117.
Abstract:
Orientador: Antonio Maria Garcia TommaselliResumo: A combinação de duas lentes com FOV hiper-hemisférico em posição opostas pode gerar um sistema omnidirecional (FOV 360°) leve, compacto e de baixo custo, como Ricoh Theta S e GoPro Fusion. Entretanto, apenas algumas técnicas e modelos matemáticos para a calibração um sistema com duas lentes hiper-hemisféricas são apresentadas na literatura. Nesta pesquisa, é avaliado e definido um modelo geométrico para calibração de sistemas omnidirecionais compostos por duas lentes hiper-hemisféricas e apresenta-se algumas aplicações com esse tipo de sistema. A calibração das câmaras foi realizada no programa CMC (calibração de múltiplas câmeras) utilizando imagens obtidas a partir de vídeos feitos com a câmara Ricoh Theta S no campo de calibração 360°. A câmara Ricoh Theta S é composto por duas lentes hiper-hemisféricas fisheye que cobrem 190° cada uma. Com o objetivo de avaliar as melhorias na utilização de pontos em comum entre as imagens, dois conjuntos de dados de pontos foram considerados: (1) apenas pontos no campo hemisférico, e (2) pontos em todo o campo de imagem (isto é, adicionar pontos no campo de imagem hiper-hemisférica). Primeiramente, os modelos ângulo equisólido, equidistante, estereográfico e ortogonal combinados com o modelo de distorção Conrady-Brown foram testados para a calibração de um sensor da câmara Ricoh Theta S. Os modelos de ângulo-equisólido e estereográfico apresentaram resultados melhores do que os outros modelos. Portanto, esses dois modelos de projeção for... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: The arrangement of two hyper-hemispherical fisheye lenses in opposite position can design a light weight, small and low-cost omnidirectional system (360° FOV), e.g. Ricoh Theta S and GoPro Fusion. However, only a few techniques are presented in the literature to calibrate a dual-fisheye system. In this research, a geometric model for dual-fisheye system calibration was evaluated, and some applications with this type of system are presented. The calibrating bundle adjustment was performed in CMC (calibration of multiple cameras) software by using the Ricoh Theta video frames of the 360° calibration field. The Ricoh Theta S system is composed of two hyper-hemispherical fisheye lenses with 190° FOV each one. In order to evaluate the improvement in applying points in the hyper-hemispherical image field, two data set of points were considered: (1) observations that are only in the hemispherical field, and (2) points in all image field, i.e. adding points in the hyper-hemispherical image field. First, one sensor of the Ricoh Theta S system was calibrated in a bundle adjustment based on the equidistant, equisolid-angle, stereographic and orthogonal models combined with Conrady-Brown distortion model. Results showed that the equisolid-angle and stereographic models can provide better solutions than those of the others projection models. Therefore, these two projection models were implemented in a simultaneous camera calibration, in which the both Ricoh Theta sensors were considered i... (Complete abstract click electronic access below)
Mestre
49
Imbach, Rémi. "Résolution de contraintes géométriques en guidant une méthode homotopique par la géométrie." Thesis, Strasbourg, 2013. http://www.theses.fr/2013STRAD033/document.
Abstract:
Suivant le domaine où on les sollicite, les solutions d’un système de contraintes géométriques (SCG) peuvent être : – formelles et exactes : elles prennent par exemple la forme d’un plan de construction produisant toutes les solutions, obtenu en appliquant des règles dérivées de lemmes de géométrie. Beaucoup de SCG, surtout en 3D, résistent à cette approche ; – numériques et approchées : elles sont les solutions d’un système d’équations construit à partir des contraintes et trouvées grâce à des méthodes numériques efficaces quand elles ne recherchent qu’une solution. De par la nature des problèmes traités, chercher toutes les solutions conduit à une complexité exponentielle. Les méthodes par continuation, ou homotopie, permettent d’obtenir toutes les solutions d’un système d’équations polynomiales. Leur application à des SCG est coûteuse et difficilement sujette aux raisonnements permis par l’origine géométrique du problème car elles opèrent hors de l’espace des figures géométriques. Notre travail a pour objet la spécialisation d’une méthode par continuation à des SCG. La géométrie simplifie et justifie sa mise en œuvre dans l’espace des figures, ou des raisonnements géométriques sont possibles. On aborde également les cas ou l’ensemble de solutions d’un problème contient des éléments isolés et des continuums. Des solutions proches d’une esquisse fournie par un utilisateur sont d’abord trouvées. La recherche d’autres solutions, malgré sa complexité exponentielle, est rendue envisageable par une approche itérative. Une nouvelle méthode de décomposition est proposée pour maîtriser le coût de la résolutionDepending on the required application field, the solutions of a geometric constraints system (GCS) are either : – symbolic and exact such as construction plans, providing all the solutions, obtained by applying geometric rules. Many problems, mostly in a 3D context, resist to this approach ; – or numerical and approximated : they are the solutions of a system of equations built from the constraints, provided by generical numerical methods that are efficient when only one solution is sought. However, searching all the solutions leads to an exponential computation cost, due to the nature of problems. Continuation methods, also called homotopic methods, find all the solutions of a polynomial system. Using them to solve systems of equations associated to systems of constraints is nevertheless costly. Moreover, combining them with geometric reasoning is a challenge, because they act in a projective complex space and not in the realizations space. The aim of this work is to specialize a continuation method to GCS. Geometry is exploited to simplify and justify its adaptation in the space of realizations, so allowing geometric reasoning. Cases where the connected components of the solution space of a problem have heterogeneous dimensions are addressed. The method discussed here provides in a first step solutions that are similar to a sketch drawn by the user. Then a procedure is proposed to search new solutions. Its iterative nature seems to make the exponential complexity of this task bearable. A new decomposition method is proposed, that restrains the resolution cost
50
Hu, Hao. "Detection and treatment of inconsistent or locally over-constrained configurations during the manipulation of 3D geometric models made of free-form surfaces." Thesis, Paris, ENSAM, 2018. http://www.theses.fr/2018ENAM0002/document.
Abstract:
Trois modules seront développés: Le module de détection a produit une analyse des problématiques figurations con, à savoir un ensemble de domaines où soit quelques nouveaux DDL ou des changements locaux dans les contraintes sont obligatoires. Le module de traitement permettra à la défi nition des mécanismes pour aider la décision sur modi cations. Le module de prédiction dire le degré de déformation en pré-analyser les caractéristiques des configurations de NURBSThree modules will be developed: The detection module has produced an analysis of problematic con figurations, i.e. a set of areas where either some new DOFs or some local changes in the constraints are mandatory. The treatment module will enable the defi nition of mechanisms to help the decision on modi cations. The prediction module will tell the degree of deformation by pre-analyzing the features of NURBS configurations