Geometric constraint subsets and subgraphs in the analysis of assemblies and mechanisms

Geometric Reasoning ability is central to many applications in CAD/CAM/CAPP environments. An increasing demand exists for Geometric Reasoning systems which evaluate the feasibility of virtual scenes specified by geometric relations. Thus, the Geometric Constraint Satisfaction or Scene Feasibility (GCS/SF) problem consists of a basic scenario containing geometric entities, whose context is used to propose constraining relations among still undefined entities. If the constraint specification is consistent, the answer of the problem is one of finitely or infinitely many solution scenarios satisfying the prescribed constraints. Otherwise, a diagnostic of inconsistency is expected. The three main approaches used for this problem are numerical, procedural or operational and mathematical. Numerical and procedural approaches answer only part of the problem, and are not complete in the sense that a failure to provide an answer does not preclude the existence of one. The mathematical approach previously presented by the authors describes the problem using a set of polynomial equations. The common roots to this set of polynomials characterizes the solution space for such a problem. That work presents the use of Groebner basis techniques for verifying the consistency of the constraints. It also integrates subgroups of the Special Euclidean Group of Displacements SE(3) in the problem formulation to exploit the structure implied by geometric relations. Although theoretically sound, these techniques require large amounts of computing resources. This work proposes Divide-and-Conquer techniques applied to local GCS/SF subproblems to identify strongly constrained clusters of geometric entities. The identification and preprocessing of these clusters generally reduces the effort required in solving the overall problem. Cluster identification can be related to identifying short cycles in the Spatial Constraint graph for the GCS/SF problem. Their preprocessing uses the aforementioned Algebraic Geometry and Group theoretical techniques on the local GCS/SF problems that correspond to these cycles. Besides improving the efficiency of the solution approach, the Divide-and-Conquer techniques capture the physical essence of the problem. This is illustrated by applying the discussed techniques to the analysis of the degrees of freedom of mechanisms.MSC: 68U07La habilidad del Razonamiento Geométrico es central a muchas aplicaciones de CAD/CAM/CAPP (Computer Aided Design, Manufacturing and Process Planning). Existe una demanda creciente de sistemas de Razonamiento Geométrico que evalúen la factibilidad de escenas virtuales, especificados por relaciones geométricas. Por lo tanto, el problema de Satisfacción de Restricciones Geométricas o de Factibilidad de Escena (GCS/SF) consta de un escenario básico conteniendo entidades geométricas, cuyo contexto es usado para proponer relaciones de restricción entre entidades aún indefinidas. Si la especificación de las restricciones es consistente, la respuesta al problema es uno del finito o infinito número de escenarios solución que satisfacen las restricciones propuestas. De otra forma, un diagnóstico de inconsistencia es esperado. Las tres principales estrategias usadas para este problema son: numérica, procedimental y matemática. Las soluciones numérica y procedimental resuelven solo parte del problema, y no son completas en el sentido de que una ausencia de respuesta no significa la ausencia de ella. La aproximación matemática previamente presentada por los autores describe el problema usando una serie de ecuaciones polinómicas. Las raíces comunes a este conjunto de polinomios caracterizan el espacio solución para el problema. Ese trabajo presenta el uso de técnicas con Bases de Groebner para verificar la consistencia de las restricciones. Ella también integra los subgrupos del grupo especial Euclídeo de desplazamientos SE(3) en la formulación del problema para explotar la estructura implicada por las relaciones geométricas. Aunque teóricamente sólidas, estas técnicas requieren grandes cantidades de recursos computacionales. Este trabajo propone técnicas de Dividir y Conquistar aplicadas a subproblemas GCS/SF locales para identificar conjuntos de entidades geométricas fuertemente restringidas entre sí. La identificación y pre-procesamiento de dichos conjuntos locales, generalmente reduce el esfuerzo requerido para resolver el problema completo. La identificación de dichos sub-problemas locales está relacionada con la identificación de ciclos cortos en el grafo de Restricciones Geométricas del problema GCS/SF. Su preprocesamiento usa las ya mencionadas técnicas de Geometría Algebraica y Grupos en los problemas locales que corresponden a dichos ciclos. Además de mejorar la eficiencia de la solución, las técnicas de Dividir y Conquistar capturan la esencia física del problema. Esto es ilustrado por medio de su aplicación al análisis de grados de libertad de mecanismos.MSC: 68U0

Modelado de Materiales Compuestos por Elementos Finitos usando Restricciones Cinemáticas

The purpose of this article is to present simulations of the behavior of composite materials based on kinematic restrictions between the same fibers and between the fibers and the surrounding resin. In the literature review, the authors have found that kinematic restrictions have not been fully exploited to model composite materials, probably due to their high computational cost. The purpose of this article is to expose the implementation and results of such a model, using Finite Element Analysis of prescribed geometric constraints to the resin and fiber nodes. Analytical descriptions of the behavior of composite materials rarely appear. Many approaches to describe composite materials in layers are based on the theory of functions C1Z and C0 Z, such as the Classical Layer Theory (CLT). These theories of functions contain significant simplifications of the material, especially for woven compounds. A hybrid approach to modeling composite materials with Finite Elements (FEA) was developed by Sidhu and Averill and adapted by Li and Sherwood for composite materials woven with glass polypropylene.El propósito de este artículo es presentar simulaciones del comportamiento de materiales compuestos basado en restricciones cinemáticas entre las mismas fibras y entre las fibras y la resina circundante. En la revisión de literatura, los autores han encontrado que las restricciones cinemáticas no han sido plenamente explotadas para modelar materiales compuestos, probablemente debido a su alto costo computacional. El propósito de este articulo es exponer la implementación y resultados de tal modelo, usando Análisis por Elementos Finitos de restricciones geométricas prescritas a los nodos de la resina y las fibras. Las descripciones analíticas del comportamiento de materiales compuestos raramente aparecen. Muchas aproximaciones para describir materiales compuestos en capas son basadas en la teoría de funciones C1Z y C0 Z, tal como la Teoría Clásica de Capas (CLT). Estas teorías de funciones contienen significativas simplificaciones del material, especialmente para compuestos tejidos. Una aproximación hibrida para modelar materiales compuestos con Elementos Finitos (FEA) fue desarrollada por Sidhu y Averill y adaptada por Li y Sherwood para materiales compuestos tejidos con polipropileno de vidrio

Triangular mesh parameterization with trimmed surfaces

Given a 2manifold triangular mesh $M \subset {\mathbb {R}}^3$, with border, a parameterization of $M$ is a FACE or trimmed surface $F=\{S,L_0,\ldots, L_m\}$ -- $F$ is a connected subset or region of a parametric surface $S$, bounded by a set of LOOPs $L_0,\ldots ,L_m$ such that each $L_i \subset S$ is a closed 1manifold having no intersection with the other $L_j$ LOOPs -- The parametric surface $S$ is a statistical fit of the mesh $M$ -- $L_0$ is the outermost LOOP bounding $F$ and $L_i$ is the LOOP of the ith hole in $F$ (if any) -- The problem of parameterizing triangular meshes is relevant for reverse engineering, tool path planning, feature detection, redesign, etc -- Stateofart mesh procedures parameterize a rectangular mesh $M$ -- To improve such procedures, we report here the implementation of an algorithm which parameterizes meshes $M$ presenting holes and concavities -- We synthesize a parametric surface $S \subset {\mathbb {R}}^3$ which approximates a superset of the mesh $M$ -- Then, we compute a set of LOOPs trimming $S$, and therefore completing the FACE F=\ {S,L_0,\ldots ,L_m\} -- Our algorithm gives satisfactory results for $M$ having low Gaussian curvature (i.e., $M$ being quasi-developable or developable) -- This assumption is a reasonable one, since $M$ is the product of manifold segmentation preprocessing -- Our algorithm computes: (1) a manifold learning mapping $\phi : M \rightarrow U \subset {\mathbb {R}}^2$, (2) an inverse mapping $S: W \subset {\mathbb {R}}^2 \rightarrow {\mathbb {R}}^3$, with \ (W\) being a rectangular grid containing and surpassing $U$ -- To compute $\phi$ we test IsoMap, Laplacian Eigenmaps and Hessian local linear embedding (best results with HLLE) -- For the back mapping (NURBS) $S$ the crucial step is to find a control polyhedron $P$, which is an extrapolation of $M$ -- We calculate $P$ by extrapolating radial basis functions that interpolate points inside $\phi (M)$ -- We successfully test our implementation with several datasets presenting concavities, holes, and are extremely nondevelopable -- Ongoing work is being devoted to manifold segmentation which facilitates mesh parameterizatio

Visualisation of flow fields in the web platform

Visualization of vector fields plays an important role in research activities nowadays. Web applications allow a fast, multi-platform and multi-device access to data, which results in the need of optimized applications to be implemented in both high and low-performance devices. The computation of trajectories usually repeats calculations due to the fact that several points might lie over the same trajectory. This paper presents a new methodology to calculate point trajectories over a highly-dense and uniformly-distributed grid of points in which the trajectories are forced to lie over the points in the grid. Its advantages rely on a highly parallel computing implementation and in the reduction of the computational effort to calculate the stream paths since unnecessary calculations are avoided by reusing data through iterations. As case study, the visualization of oceanic streams in the web platform is presented and analyzed, using WebGL as the parallel computing architecture and the rendering engine

Sensitivity analysis in optimized parametric curve fitting

Purpose – Curve fitting from unordered noisy point samples is needed for surface reconstruction in many applications -- In the literature, several approaches have been proposed to solve this problem -- However, previous works lack formal characterization of the curve fitting problem and assessment on the effect of several parameters (i.e. scalars that remain constant in the optimization problem), such as control points number (m), curve degree (b), knot vector composition (U), norm degree (k), and point sample size (r) on the optimized curve reconstruction measured by a penalty function (f) -- The paper aims to discuss these issues -- Design/methodology/approach - A numerical sensitivity analysis of the effect of m, b, k and r on f and a characterization of the fitting procedure from the mathematical viewpoint are performed -- Also, the spectral (frequency) analysis of the derivative of the angle of the fitted curve with respect to u as a means to detect spurious curls and peaks is explored -- Findings - It is more effective to find optimum values for m than k or b in order to obtain good results because the topological faithfulness of the resulting curve strongly depends on m -- Furthermore, when an exaggerate number of control points is used the resulting curve presents spurious curls and peaks -- The authors were able to detect the presence of such spurious features with spectral analysis -- Also, the authors found that the method for curve fitting is robust to significant decimation of the point sample -- Research limitations/implications - The authors have addressed important voids of previous works in this field -- The authors determined, among the curve fitting parameters m, b and k, which of them influenced the most the results and how -- Also, the authors performed a characterization of the curve fitting problem from the optimization perspective -- And finally, the authors devised a method to detect spurious features in the fitting curve -- Practical implications – This paper provides a methodology to select the important tuning parameters in a formal manner -- Originality/value - Up to the best of the knowledge, no previous work has been conducted in the formal mathematical evaluation of the sensitivity of the goodness of the curve fit with respect to different possible tuning parameters (curve degree, number of control points, norm degree, etc.

Agile and software engineering, an invisible bond

La relación entre metodologías ágiles y las mejores practices recomen-dadas por la Ingeniería de Software es clara y evidente para los profesionales experimentados en la operación de ambientes para desarrollo de alta madurez. Es sin embargo a menudo ignorada en la bibliografía del dominio donde se tartan como si fueran enfoques separados. Este artículo revisa una muestra significativa de la bibliografía y confirma esta tendencia desarrollando un mapa de cuales son las practicas establecidas de Ingeniería de Software y los conceptos subyacentes que operan en las metodologías ágiles. Se integran esfuerzos previos de investi-gación para reforzar que aspectos de la gestión de proyectos basados en metodo-logías ágiles necesitan ser abordados con prioridad de manera que el valor adi-cional que las mismas generan resulte protegido.The bond between agile practices and Software Engineering practices is clear and apparent for seasoned practitioners with experience in the operation of high maturity development environments, yet it is often ignored on the domain bibliography where mostly hybrid approaches are adopted. This article reviews a sensible sample of the bibliography to confirm that trend and develop a map be-tween long-established Software Engineering practices on the one hand, and con-cepts stated as agile foundation principles on the other. Previous research efforts are integrated into reinforcing those aspects of an agile-based project which need to be addressed with priority in order to protect the additional value yield by the usage of these methodologies.Sociedad Argentina de Informática e Investigación Operativ

Magnetic and elastic anisotropy in magnetorheological elastomers using nickel-based nanoparticles and nanochains

Nickel (Ni) based nanoparticles and nanochains were incorporated as fillers in polydimethylsiloxane (PDMS) elastomers and then these mixtures were thermally cured in the presence of a uniform magnetic field. In this way, macroscopically structured-anisotropic PDMS-Ni based magnetorheological composites were obtained with the formation of pseudo-chains-like structures (referred as needles) oriented in the direction of the applied magnetic field when curing. Nanoparticles were synthesized at room temperature, under air ambient atmosphere (open air, atmospheric pressure) and then calcined at 400 °C (in air atmosphere also). The size distribution was obtained by fitting SAXS experiments with a polydisperse hard spheres model and a Schulz-Zimm distribution, obtaining a size distribution centered at (10.0 - 0.6) nm with polydispersivity given by sigma= (8.0 ± 0.2) nm. The SAXS, XRD and TEM experiments are consistent with single crystal nanoparticles of spherical shape (average particle diameter obtained by TEM: (12 ± 1) nm). Nickel-based nanochains (average diameter: 360 nm; average length: 3 mm, obtained by SEM; aspect ratio=length/diameter ~10) were obtained at 85 ºC and ambient atmosphere (open air, atmospheric pressure). The magnetic properties of Ni-based nanoparticles and nanochains at room temperature are compared and discussed in terms of surface and size effects. Both Ni-based nanoparticles and nanochains were used as fillers for obtaining the PDMS structured magnetorheological composites, observing the presence of oriented needles. Magnetization curves, ferromagnetic resonance spectra (FMR) and strain-stress curves of low filler´s loading composites (2% w/w of fillers) were determined as functions of the relative orientation respect to the needles. The results indicate that even at low loadings it is possible to obtain magnetorheological composites with anisotropic properties, with larger anisotropy when using nanochains. For instance, the magnetic remanence, the FMR-resonance field and the elastic response to compression are higher when measured parallel to the needles (about 30% with nanochains as fillers). Analogously, the elastic response is also anisotropic, with larger anisotropy when using nanochains as fillers. Therefore, all experiments performed confirm the high potential of nickel nanochains to induce anisotropic effects in magnetorheological materials.Fil: Landa, Romina Ailín. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Instituto de Química Física de los Materiales del Medioambiente y Energía; Argentina;Fil: P Soledad Antonel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Instituto de Química Física de los Materiales del Medioambiente y Energía; Argentina;Fil: Mariano M. Ruiz. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Instituto de Química Física de los Materiales del Medioambiente y Energía; Argentina;Fil: Oscar E Pérez. Universidad de Buenos Aires. Facultad de Cs.exactas y Naturales. Departamento de Industrias;Fil: Alejandro Butera. Comisión Nacional de Energía Atómica;Fil: Guillermo Jorge. Universidad Nacional de General Sarmiento;Fil: Cristiano L. P. Oliveira. Instituto de Física, Universidade De São Paulo; Brasil;Fil: Martín Negri. Universidad de Buenos Aires. Facultad de Cs.exactas y Naturales. Departamento de Industrias

Factores de riesgo asociados a la aparición del linfedema en las pacientes mastectomizadas atendidas en el servicio de oncología del Hospital Julio C. Perrando entre los años 2011 y 2012

Se realizó una investigación cuantitativa, analítica de casos y controles, retrospectiva, transversal y observacional que tuvo como objetivo establecer la relación entre grupo etario, nivel de instrucción, tipo de cirugía, número de ganglios extirpados y la aparición del linfedema dentro del año posterior a la cirugía en pacientes mastectomizadas.Las unidades de análisis fueron pacientes mastectomizadas atendidas en el Servicio de Oncología del Hospital Julio C. Perrando de la Ciudad de Resistencia Chaco, entre 2011 y 2012.Los resultados mostraron que las pacientes mastectomizadas del grupo etario de 51 a 65 años tuvieron 1,22 veces más probabilidades de presentar linfedema; luego del año posterior a la cirugía.En cuanto al nivel de instrucción incompleto se asoció a la aparición del linfedema, presentándose como un factor de protección con un OR de 0,17 siendo estadísticamente significativo.Respecto al tipo de cirugía realizada, se constató que las pacientes que recibieron mastectomía radical obtuvieron un OR de 1,90 representó un factor de riesgo este tipo de cirugía; en cambio, las pacientes intervenidas quirúrgicamente con extirpación de más de 5 ganglios obtuvieron un OR de 2,5 presentándose como factor de riesgo para padecer linfedema