Low level direct interpolation for parametric curves

We present an algorithm for the direct interpolation of parametric curves with a CNC machine -- The algorithm expresses parametric planar curves as sequences of discrete axes movements of BLU size of the machining tool -- Therefore, the curve C(u) is directly approximated by the pulse trains, hence eliminating one source of the machining error

Las competencias del formador. Una visión desde la formación continua

Obra ressenyada: Antonio NAVÍO GÁMEZ; Fernando HERNÁNDEZ y Juana M. SANCHO (eds.), Las competencias del formador. Una visión desde la formación continua. Barcelona: Octaedro-EUB, 2005

Fitting of Analytic Surfaces to Noisy Point Clouds

Fitting -continuous or superior surfaces to a set of points sampled on a 2-manifold is central to reverse engi- neering, computer aided geometric modeling, entertaining, modeling of art heritage, etc -- This article addresses the fit- ting of analytic (ellipsoid, cones, cylinders) surfaces in general position in -- Currently, the state of the art presents limitations in 1) automatically finding an initial guess for the analytic surface F sought, and 2) economically estimat- ing the geometric distance between a point of and the analytic surface SF -- These issues are central in estimating an analytic surface which minimizes its accumulated distances to the point set -- In response to this situation, this article presents and tests novel user-independent strategies for addressing aspects 1) and 2) above, for cylinders, cones and ellipsoids -- A conjecture for the calculation of the distance point-ellipsoid is also proposed -- Our strategies produce good initial guesses for F and fast fitting error estimation for F, leading to an agile and robust optimization algorithm -- Ongoing work addresses the fitting of free-form parametric surfaces to

Bifurcations and Sequences of Elements in Non-Smooth Systems Cycles

This article describes the implementation of a novel method for detection and continuation of bifurcations in non- smooth complex dynamic systems -- The method is an alternative to existing ones for the follow-up of associated phe- nomena, precisely in the circumstances in which the traditional ones have limitations (simultaneous impact, Filippov and first derivative discontinuities and multiple discontinuous boundaries) -- The topology of cycles in non-smooth sys- tems is determined by a group of ordered segments and points of different regions and their boundaries -- In this article, we compare the limit cycles of non-smooth systems against the sequences of elements, in order to find patterns -- To achieve this goal, a method was used, which characterizes and records the elements comprising the cycles in the order that they appear during the integration process -- The characterization discriminates: a) types of points and segments; b) direction of sliding segments; and c) regions or discontinuity boundaries to which each element belongs -- When a change takes place in the value of a parameter of a system, our comparison method is an alternative to determine topo- logical changes and hence bifurcations and associated phenomena -- This comparison has been tested in systems with discontinuities of three types: 1) impact; 2) Filippov and 3) first derivative discontinuities -- By coding well-known cy- cles as sequences of elements, an initial comparison database was built -- Our comparison method offers a convenient approach for large systems with more than two regions and more than two sliding segment

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 Con straint 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 theefficiency 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 mechanism

EGCL: an extended G-Code Language with flow control, functions and mnemonic variables

In the context of computer numerical control (CNC) and computer aided manufacturing (CAM), the capabilities of programming languages such as symbolic and intuitive programming, program portability and geometrical portfolio have special importance -- They allow to save time and to avoid errors during part programming and permit code re-usage -- Our updated literature review indicates that the current state of art presents voids in parametric programming, program portability and programming flexibility -- In response to this situation, this article presents a compiler implementation for EGCL (Extended G-code Language), a new, enriched CNC programming language which allows the use of descriptive variable names, geometrical functions and flow-control statements (if-then-else, while) -- Our compiler produces low-level generic, elementary ISO-compliant Gcode, thus allowing for flexibility in the choice of the executing CNC machine and in portability -- Our results show that readable variable names and flow control statements allow a simplified and intuitive part programming and permit re-usage of the programs -- Future work includes allowing the programmer to define own functions in terms of EGCL, in contrast to the current status of having them as library built-in function

Análisis del sector del agua en España

Los objetivos del trabajo son analizar el sector del agua en España y Canarias, conocer los principales consumidores de este recurso natural, identificar los problemas del sector y discutir posibles soluciones. Para ello se ha seguido una metodología cuantitativa basada en el análisis de datos. Las conclusiones más importantes han sido que las aguas tratadas no se gestionan de la forma más eficientes posible y que el consumidor más importante es el sector primario, dando lugar a que la mayoría de soluciones más realistas sean por la vía de la demanda, mediante mejoras en la implantación de técnicas de riego más eficientes, al igual que una reducción de la producción de los alimentos con mayor huella hídrica azul y gris, lo cual supondría una reducción de la demanda de agua, siendo el uso del agua reutilizada el punto clave para atenuar los problemas de escasez de aguaThe aims of this dissertation are to analyse the water sector in Spain and the Canary Islands, to find out the main consumers of this natural resource, to identify the problems of the sector and to discuss possible solutions. To this end, a quantitative methodology based on data analysis has been applied. The most important conclusions were that treated wastewater is not managed in the most efficient way and that the most important consumer is the primary sector, logically, resulting in the most rational decision being demand-side solutions through improvements in the implementation of more efficient irrigation techniques, as well as a reduction in the production of foods with the largest blue and grey water footprint, which would lead to a reduction in the demand for water, being the reused of treated wastewater the key point to mitigate the problems of water scarcity

Fixed grid finite element analysis for 3D structural problems

Fixed Grid (FG) methodology was first introduced by García and Steven as an engine for numerical estimation of two-dimensional elasticity problems -- The advantages of using FG are simplicity and speed at a permissible level of accuracy -- Two dimensional FG has been proved effective in approximating the strain and stress field with low requirements of time and computational resources -- Moreover, FG has been used as the analytical kernel for different structural optimisation methods as Evolutionary Structural Optimisation, Genetic Algorithms (GA), and Evolutionary Strategies -- FG consists of dividing the bounding box of the topology of an object into a set of equally sized cubic elements -- Elements are assessed to be inside (I), outside (O) or neither inside nor outside (NIO) of the object -- Different material properties assigned to the inside and outside medium transform the problem into a multi-material elasticity problem -- As a result of the subdivision NIO elements have non-continuous properties -- They can be approximated in different ways which range from simple setting of NIO elements as O to complex noncontinuous domain integration -- If homogeneously averaged material properties are used to approximate the NIO element, the element stiffness matrix can be computed as a factor of a standard stiffness matrix thus reducing the computational cost of creating the global stiffness matrix. An additional advantage of FG is found when accomplishing re-analysis, since there is no need to recompute the whole stiffness matrix when the geometry changes -- This article presents CAD to FG conversion and the stiffness matrix computation based on non-continuous elements -- In addition inclusion/exclusion of O elements in the global stiffness matrix is studied -- Preliminary results shown that non-continuous NIO elements improve the accuracy of the results with considerable savings in time -- Numerical examples are presented to illustrate the possibilities of the metho

El uso de un entorno virtual en la enseñanza superior : una experiencia en los estudios de pedagogía de la Universitat Autònoma de Barcelona (UAB) y la Universitat Rovira i Virgili (URV)

La interacción educativa en la universidad está cambiando como consecuencia de la adaptación de nuestro sistema universitario a las directrices marcadas por el Espacio Europeo de Educación Superior (EEES). Esta nueva construcción del escenario europeo de educación conlleva importantes cambios: desde la revisión de la oferta de títulos que sea fácilmente comprensible y equiparable, la implantación de una estructura de estudios superiores basada, principalmente en dos ciclos, el establecimiento de un sistema armonizado de créditos europeos (ECTS), la búsqueda de sistemas de promoción de la movilidad, eliminando los obstáculos para un fluido y efectivo intercambio de alumnos y profesores, hasta el establecimiento de sistemas de acreditación y calidad. Todos estos elementos, que configuran el nuevo escenario de educación superior, imponen la reorganiza­ción y diseño de un nuevo planteamiento metodológico en la docencia, donde el aprendizaje permanente, la colaboración y el uso de las TIC como medios para el trabajo semipresencial y a distancia se convierten en los ejes principales de discusión y trabajo. El estudio trata de analizar el uso de la tecnología en la reestructuración de los procesos formativos en la enseñanza superior, es decir, en reflexionar sobre el papel del estudiante, del profesor y de los procesos de enseñanza-aprendizaje con el uso de entornos virtuales. En el artículo se presentan los resultados más relevantes del análisis del uso de un entorno virtual en cuatro asignaturas de pedagogía de la Universitat Autònoma de Barcelona (UAB) y la Universitat Rovira i Virgili de Tarragona (URV), ambas ubicadas en España, a partir de las valoraciones realizadas por los alumnos y profesores implicado