Scipedia: Documents published in 2009

Análisis de riesgo y confiabilidad de sistemas de retención para el manejo de la escorrentía pluvial

Scipedia content — Wed, 28 Jun 2017 11:14:03 +0200

El desarrollo urbanístico ha tenido como consecuencia el incremento en la frecuencia y magnitud de la ocurrencia de inundaciones locales, con el potencial de ocasionar graves daños a la infraestructura y rutas viales existentes. En este estudio se desarrolla un modelo probabilístico que permite evaluar la eficiencia operacional de un sistema de retención de escorrentía pluvial en términos del riesgo y la confiabilidad con respecto a desbordamientos de dicho sistema. Se evalúa la confiabilidad de un sistema de retención considerando la variabilidad del proceso de escorrentía y en función de sus variables de diseño. El modelo es de naturaleza analítica y sería de utilidad en la fase de planificación para el diseño de sistemas de manejo de escorrentía pluvial. Se han validado los resultados del modelo probabilístico con resultados de simulaciones con modelos numéricos.

Acerca del concepto de desastres naturales

Scipedia content — Wed, 28 Jun 2017 11:13:59 +0200

Editorial: Acerca del concepto de desastres naturales

Contacto intermitente y localizado entre dos superficies. Aplicación al caso de la interacción pastilla-vaina (PCI) en un combustible nuclear de potencia

Scipedia content — Wed, 14 Jun 2017 13:08:30 +0200

This work contains a study of an algorithm devised to analyze problems of contact between two materials separated by a gap, alternatively open and close. In the finite element scheme used the contact is expressed by restrictions. An approximation of incomplete field is employed; the domain is divided in two subdomains, in each of which an irreducible formulation in the displacements is used. Lagrange multipliers are used for the treatment of forces in the boundary between the subdomains. The calculation scheme derives from the virtual work principle, assuming continuity for the displacements at the boundary. The contact algorithm is tested in general problems with plane or axial symmetry, with well known analytical solution. Then it is applied to the simulation of the behavior of a nuclear fuel rod subjected to a postulated power history where the problem of pellet- cladding contact may arise. INTERMITENT AND LOCAL CONTACT BETWEEN TWO SURFACES. APPLICATION TO THE CASE OF PELLET-CLADDING INTERACTION (PCI) IN A NUCLEAR POWER FUEL ROD.

Diagrama geometrico y subdivision híbrida de triángulos

Scipedia content — Wed, 14 Jun 2017 13:08:26 +0200

In this work we introduce a geometrical diagram to study the geometric quality of triangles generated by iterative application of the four Triangles Longest Edge (4TLE) partition. The diagram provides a convenient graphic tool to visualize the evolution and migration of element shapes leading to a better understanding of the improvement process and the effect of recursive subdivision schemes. A complex variable mapping analysis supports the diagram and similarity class specifications. In addition, it is introduced a mesh subdivision method (hybrid 4TLE-SS) that combines the four Triangles Longest Edge (4TLE) subdivision pattern and the self-similar 4TSS. It is showed that the number of triangles of superior quality is greater than in the 4TLE method. The presented work is of interest in mesh generation and refinement for triangle meshes. A GEOMETRIC DIAGRAM AND HYBRID SCHEME FOR TRIANGLE SUBDIVISION.

Estudo teorico-experimental do comportamento dinamico de telhas de aço trapezoidais formadas a frio

Scipedia content — Wed, 14 Jun 2017 13:08:21 +0200

Cold-formed steel roofing sheets are applied over closings and coverings with several types of engineering structures. The connection between the structure and the sheets are often carried out through fixing purlins. The fixation between the sheets is normally done by using simple overlapping of the adjacent longitudinal edges, but it can also be done by means of rivets. Several times, it becomes dificult to evaluate the influence of the boundary conditions on the stiffness of these system types. For this reason, in the present work, the assessment of structural performance of trapezoidal steel roofing sheets regarding different boundary conditions has been carried out. In order to reach this aim, the natural frequencies and associated vibration modes for each studied case have been evaluated. A theoretical and experimental study has been developed to prove that the dynamical properties of the sheets can allow us to describe their structural behaviour. The theoretical model has been carried out by using the Finite Element Method. The comparison between theoretical and experimental results in terms of natural frequencies and eigenmodes associated with them has made it possible to calibrate the finite element models. A detailed analysis of different boundary conditions cases has permitted to arrive at some conclusions about the sheets characteristics, for example: the fixing of the sheets longitudinal edges does not affect its global stiffness, and the restriction level of the sheets edges directly determines the stiffness in some specific regions of the sheets. Discussion on the obtained results and conclusions are then presented. DYNAMIC BEHAVIOUR OF COLD-FORMED TRAPEZOIDAL STEEL ROOFING SHEETS: EXPERIMENTAL AND THEORETICAL ANALYSIS.

Diseño de una herramienta porosa para el pulido de superficies ópticas usando programación lineal

Scipedia content — Wed, 14 Jun 2017 13:08:16 +0200

In this work a new polishing tool of optical surfaces has been designed. We have called a porous tool, because it is formed by perforations and circular posts. The design of this new tool is based on the design of a previous petal tool which generates a desired wear. The proposed tool will be constructed in two parts; perforations are placed in the first part and posts in the second. As a first step, we obtain the function that describes the contour of the petal tool using cubic spline interpolation; from this information we determine the number of posts and perforations and their distribution on the porous tool. An iterative algorithm that solves a sequence of linear programs to find the solution of this problem is presented. Finally we show examples where we applied this method to design diferent porous tools that produce wear similar to that produced by the original petal tools, in order to make both concave and convex surfaces. DESIGN OF A POROUS TOOL FOR POLISHING OPTICAL SURFACES USING LINEAR PROGRAMMING.

Análisis de vigas tubulares de acero estructural sometidas a flexion biaxial mediante la teoría del daño concentrado

Scipedia content — Wed, 14 Jun 2017 13:08:11 +0200

In this work a mathematical model based on the lumped damage mechanics is developed. The model allows predicting the damage evolution on steel hollows structural beams subjected to biaxial bending. The most significant phenomenon in this case is the appearance and development of the local buckling. In order to describe this process, it is admitted that the inelastic phenomena can be concentrated in plastic hinges. It is introduced then a damage variable that can take values between zero and one that characterizes the level of local buckling in the structural member. The damage evolution is described by the introduction of local buckling domain that can be compared to the elastic domain used in the conventional theory of plasticity. The model is validated by numerical simulation of experimental tests carried out in the Structural Mechanics Laboratory at the Centroccidental Lisandro Alvarado University. ANALYSIS OF STEEL HOLLOW STRUCTURAL BEAMS SUBJECTED TO BIAXIAL BENDING BY LUMPED DAMAGE MECHANICS.

Uma abordagem unificada da formulaçao co-rotacional para elementos de treliça 2D, treliça 3D e viga 2D

Scipedia content — Wed, 14 Jun 2017 13:08:06 +0200

This article presents a unified corotational kinematics of deformable bar elements that can be represented as plane truss, spatial truss or 2D beam elements. The corotational kinematics is based on the separation of the motion on deformationaland rigid body components. For the case of translations and rotations, determined by a single angular parameter, the deformational motions are expressible in closed form. It is demonstrated that the determination of the deformational motions are based on a unique vectorial expression independent on the bar element used. In addition, the element internal force and consistent tangent stiffness matrix are derived by taking variations of the internal energy with respect to nodal freedoms.

Formación de patrones en sistemas de reacción-difusión en dominios crecientes

Scipedia content — Wed, 14 Jun 2017 13:08:03 +0200

Reaction-diffusion systems with Turing instabilities have been used to represent several biological phenomena, which may involve growth of organs or tissues. This article studies the influence of growth rate and the spatial scale in the evolution of spatial scale in the evolution of spatial -temporal patterns generated in this kind of systems. A computational study using the finite element method is performed in order to solve a reaction -diffusion system with turing instabilities using a square domain which grows at different rates. it was found that variations in the parameters related to the system and in the growth rate change the shape, heterogeneity and evolution of the generated patterns. The results confirm the robustness of the reaction-diffusion systems, in the terms of the independence regarding the initial conditions, and suggest the existence of a limit growth rate above which heterogeneous spatial-temporal patterns are not generated.

Simulaçao numérica do comportamento de vigas e pilares de concreto armado via mef usando o código CASTEM 2000

Scipedia content — Wed, 14 Jun 2017 13:07:59 +0200

The objective of this paper is the numerical sttudy of the behavior concrete beams and columns by non-linear numerical simulations. The numerical analysis is based on the finite element method implemented in CASTEM 2000. This program uses the constitutive elestoplastic perfect model for the stee, the Drucker-Prager model for the concrete and the Newton-Raphson for the solution of non-linear systems. This work concentrates on the determination of equilibrium curves to the beams and force-strain curves to the columns. The numeric responses are confronted with experimental results found in the literature in order to check the reliability of the numerical analyses.

Analísis de vibración libre de una viga Timoshenko escalonada, centrífugamente rigidizada, mediante el método de cuadratura diferencial

Scipedia content — Wed, 14 Jun 2017 13:07:55 +0200

This paper dels with the transverse vibration of non-uniform rotating beams, by means of the differential quadrature method (DQM). The formulation is based on the Timoshenko beam theory, wich takes into account the inertia forces due to the transverse translation together with the constributions of shear deformation and rotatory inertia. The application of the differential quadrature method is demostrated by investigating the natural frequencies. The results ara compared with published results given in the open literature and with values obtained by the authors using a finite element code. The proposed method offers a direct and efficient procedure to analyze the natural vibration of non-uniform rotating beams with very good accuracy.

Procedimiento de empaquetamiento de partículas genéricas para el método de elementos discretos

Scipedia content — Wed, 14 Jun 2017 13:07:51 +0200

There have been stated the mathematical foundations that allow to obtain packings of any type of particles, which will contribute to make simulations and modeling of physical problems through the Discrete Element Method. There is also described in detail the numerical method for solving the problem in 2D, for which is exposed in a completely general fashion a procedure for constructing a curve in outer contact with other two, being this formulation extended to 3D. There is analyzed in detail the case of the superquadric curves, due to its usefulness and degree of generality. In the formulation there are taken into account two ways of solution of the problem with an advancing fron algorithms: (1) making each particle be in contact with at least other two and (2) maing each particle be in contact with at least another one. These two alternatives can be used separately or at the same time during the generation of a packing.

Modelos continuos de sondas de perforación para la industria petrolera: Análisis de enfoques y su discretización

Scipedia content — Wed, 14 Jun 2017 13:07:47 +0200

In this paper a continuous model is presented that by finite element discretization is employed in the analysis of coupled extensional flexural and torsional vibrations of a drill-string. The drill-string is described as an axially rotating beam constrained to move inside a rigid cylinder that simulates the walls of the perforation hole. The beam is subjected to its own weight, reaction forces and perturbation bending moments acting in the drill-bit. The friction and the lateral impacts of the drill-string are considered by means of simplified schemes. Due to its inherent complexity, the dynamics of a drill-string is normally analyzed by means of models with lumped parameters, whose features are obtained by correlation with experimental data collected in the oil felds. However these lumped-parameter models do not include in a realistic way effects, such as geometric stiffening among others, that are quite important in flexible structures. There are some continuous models of drill-strings based on linear approaches and also accounting for geometric stiffening. Under this context, the objective of the present work is devoted to analyze, and compare with other approaches, the influence of geometric non-linearity together with patterns of vibro-impact in the dynamics of drill-strings. The continuous drill-string model is discretized by means of a beam-type finite element with 12 degrees of freedom per element. The results of this study show the in°uence of the considered effects in the dynamic response of drill-strings, especially when they are subjected to strong vibro-impact patterns with the walls and the bottom rock formation.

Cálculo directo de la carga crítica de pandeo de pórticos. Parte i

Scipedia content — Wed, 14 Jun 2017 13:07:44 +0200

Of all the design conditions for frames, in many cases the most critical one consists on ensuring that, under any possible combination of loads, flexural buckling should not take place, specially when the current trend is to design slender structures with high strength steels. Therefore, it is important to have a method to determine in a simple and clear way the maximum acceptable load level, usually known as the critical buckling load. With this purpose, we consider the equilibrium equations of each beam in its deformed configuration, under the hypothesis of infitesimal strains and displacements (First-Order Theory), resulting in a system of linear di®erential equations for each element. To obtain the nonlinear response of the frame, it is necessary to impose in each beam-end the compatibility of displacements and the equilibrium also in the deformed configuration. The objective of this work is to develop a systematic method to determine the critical buckling load and the buckling mode of any frame, without using the common simplifications usually assumed in matrix analysis or finite element approaches. This allow to obtain precise results regardless of the discretization done.

Modelado y simulación computacional de evacuación en edificios singulares

Scipedia content — Wed, 14 Jun 2017 13:07:41 +0200

To assess the adequacy of the safety aspects of people in the buildings, it is necessary to make an accurate estimate of time required for occupants to move a safe place. There are various ways of approaching the problem of evacuating a building. The analytical calculations, based on the standards regulations and requirements, pose a quick solution to the problem by calculating occupancy capacity, travel distance and dimensions of the means of egress. But when it comes to a complex building, these approaches may be insuficient. This paper examines the evacuation process of places and spaces of a passenger rail station consisting of diferent uses (assembly, entertainment, transport services, etc.) through Evacuation Modelling and Simulation. The results allowed to determine the impact of diferent geometry conditions of the building and physical and behavioral occupants characteristics in the calculation of the evacuation process and its impact on the required egress safe time in an emergency situation.

Determinación de parámetros modales a través del ajuste global de la respuesta

Scipedia content — Wed, 14 Jun 2017 13:07:37 +0200

The present study develops the application of optimization techniques via the use of Overall Adjustment of the Response to determine modal parameters for the identification method in the general case of hysteretic or structural damping. A new approach to solving the inverse problem in modal analysis is presented which enables the modal model to be determined from the system response. A decomposition method is proposed for working with complex magnitudes in product-matrix operations that allows the real and the imaginary parts to be dealt with separately. In addition, an example of this method is presented for its implementation in commercial optimization programmes. The proposed algorithm achieves a global estimation of parameters (natural frequencies, damping coficients and the modal matrix) by means of an iterative calculation process, creating a model of artificial frequency response functions related to the total degrees of freedom of the system under study. It is thus possible to obtain a set of unique, consistent solutions for these properties simultaneously processing all the information.

Análise da distribuiçao do carregamento transversal móvel em pontes mistas aço-concreto

Scipedia content — Wed, 14 Jun 2017 13:07:34 +0200

Sumário O presente trabalho apresenta os resultados de um estudo numérico - computacional para determinaçao da distribuiçao de carregamento transversais em pontes mistas a»co concreto, usando as seguintes metodologias: coeficiente de distribuiçao de carregamento transversal previsto pela AASHTO e o trem tipo definido pela NBR 7188/1982, linhas de influencia e Método dos Elementos Finitos. O estudo se fundamenta na análise numérica, via elementos finitos, de pontes vigas mistas, considerando a interaçao de todos os elementos que compoem a estrutura. Pontes de vários vaos (16, 20, 24 e 26 metros) foram estudados e seus resultados comparados aos obtidos por metodologias simplificadas. Os resultados mostram que o uso de linhas de influencia para a distribuiçao de carregamento transversal sobre as vigas é inseguro, ja para o uso do coeficiente de distribuiçao de carregamento preconizado pela AASHTO, os resultados sao menores que os obtidos pelo Método dos Elementos Finitos. Os resultados obtidos nos casos avaliados no presente estudo validam o uso do Método dos Elementos Finitos para o projeto de pontes mistas.

Modelo higro-termo-mecánico para el hormigón expuesto al fuego

Scipedia content — Wed, 14 Jun 2017 13:07:30 +0200

In this paper, a hygro-thermo-mechanical model for concrete exposed to fire, based in the mechanics of unsatured porous media of Coussy, is introduced. The model state variables are derived from a energetic potential which leads to thermodynamics consistency. The government equations of the problem are developed, including the balances equations of fluids phases mass of energy and linear momentum. Details of the FEM numerical solution of the proposed model are presented. A validation example for the developed model is presented. In this example an acceptable agreement between the numerical and experimental results is shown. Finally, as an application example the analysis of a concrete column exposed to fire is presented.

Estima de error residual explícita para cantidades de interés utilizando funciones burbuja

Scipedia content — Wed, 14 Jun 2017 13:07:25 +0200

A new goal-oriented residual a posteriori error estimator is introduced for elliptic problems. The proposed estimate is based on using bubble functions over both elements and edges. The error representation of the quantity of interest prescribed by the user is performed using an adjoint problem. These quantities of interest are either averaged values of the solution (mean temperature) or point values as, for instance, the displacement of a given point. The estimation procedure is organized in two phases. First, the error is approximated in the interior of the elements projecting it into a given bubble function. The first contribution to the overall error (interior estimate) is just the sum of all these projections. Second, a new family of bubble functions is considered, each associated with one edge of the finite element mesh. The remaining part of the error is projected into this new family of functions. This second error contribution (edge estimate) is added to the previous one to obtain the complete estimate. The present estimator is independent of the typical unknown constants appearing in explicit residual type estimates. Despite of its explicit character, the present estimator gets rid of these constants by properly combining the residuals in the adjoint and direct problems, although both are explicitly computed.

Aplicacao de um modelo numérico nao-linear tridimensional na análise de ondas sobre quebra-mares trapezoidais submersos

Scipedia content — Wed, 14 Jun 2017 13:07:21 +0200

The performance of the three-dimensional non-linear Navier-Stokes model, FLUINCO, in the simulation of wave propagation on variable depth is here analyzed. The numerical model is based on the integration of the Navier-Stokes equations (Teixeira46), which are discretized in time and space by two steps semi-implicit Taylor-Galerkin scheme that uses linear tetrahedra. An arbitrary lagrangean eulerian formulation that is compatible with the free surface movement is adopted. First, the code is tested for the case of a monochromatic wave propagation in a channel and the numerical results (pressure and velocity fields) are compared with the theoretical solutions. Then, the model is successively applied to problems involving the trapezoidal breakwaters. Diffeerent breakwater profiles were considered: all have the same slope of 1:20 on the sea side, but the breakwaters have slopes of 1:10 (breakwater profile was studied experimentally by Dingemans10), 45 degrees and 90 degrees on the lee side. In addition to the free surface elevation values at several points in the domain, pressure and velocity fields are also presented. Whereas in the first case, with downslope of 1:10, the flow shows no separation vortices formation, the same does not apply to the other two cases, where the presence of vortices near the junction of the platform with the downstream ramp is observed. The results show the ability of the model to deal with problems in which the vertical movement is significant, including phenomena such as flow separation and vortex formation.

Optimización de código para un simulador de estructuras aporticadas y su implementación como una herramienta productiva

Scipedia content — Wed, 14 Jun 2017 13:07:14 +0200

In this paper the optimization of the program "Processor" is presented. The "processor" is a finite element program used by the tool "Portal of Damage" (http://portaldeporticos.ula.ve), coded in Fortran-90, and based in the lumped damage mechanics. This program allows the simulation and modelling of the inelastic behaviour and damage in reinforced concrete structures under static or dynamic loads. To decrease the computing time of the structure analysis, the library UCSparceLib (University of Carabobo Sparse) was included, and to make even more efficient, to improve the performance of the Processor is implemented a queue manager in the cluster where the Portal is lodged. The queue manager is designed under discrete events simulation paradigm. The experimental results show a reduction in the computing time of more than 80% for the examples. Finally, an implementation using OpenMP is done in a shared memory computer.

Utilización de árboles de cubrimiento para interpolar usando funciones de base radial enfocado a la visualización cientíca de grandes volúmenes de datos

Scipedia content — Wed, 14 Jun 2017 13:07:10 +0200

In the following paper it is developed a new method to interpolate large volumes of scattered date, focused mainly on the results of the Mesh-free Methods, Points Methods and the Particles Methods application. Through this one, local radial basis functions are used as interpolating functions. Also, cover trees are used as the data structure that allows to accelerate the localization of the data that influences to interpolate the values at a new point, speeding up the application of scientific visualization techniques to generate images from large data volumes from the application of Mesh-free Methods, Points and Particles Methods, in the resolution of diverse models of physics-mathematics. As an example, the results obtained after applying this method using the local interpolation functions of Shepard are shown.

CIMNE Verification of the validation analysis of Xfinas elements database

Scipedia content — Fri, 09 Jun 2017 17:58:58 +0200

In order to validate the Xfinas code a very comprehensive series of test examples were solved by Prof Ki-Du Kim and his co-workers. A collection of the more representative benchmarks were chosen at CIMNE for testing the good behavior of every element implemented in the software.
The aim of the validation work carried out at CIMNE has been to asses the accuracy of the Xfinas program. This was done studying the whole validation process carried out by Prof Ki-Du Kim’s team in detail. For this purpose we have chosen at CIMNE randomly the different benchmarks to be reproduced between those of the validation manual (VM from now on). In every example we checked the agreement of the results with the Xfinas validation data.

Interfase GiD per a la generació paramètrica de geometries trenades per a l’apantallament de cables coaxials

María Jesús Samper — Thu, 26 Jan 2017 16:20:23 +0100

SIMPACT: Explicit Dynamic Code for non Linear Structural Analysis

María Jesús Samper — Thu, 26 Jan 2017 15:55:01 +0100

SIMPACT is a finite element computer system developed at the International Center for Numerical Methods in Engineering (CIMNE) in Barcelona, Spain, for analysis of structures subjected to dynamic and impact loading. Typical application of SIMPACT include among others the seismic analysis of structures, the study of structures subjected to internal of external vibrations, the prediction of ship motions originated by waves crashworthiness studies in automobiles, aerospace and maritime vehicles, analysis of structures subjected to blast pressure loading and a wide range of impact problems typical of defense applications.

Implementation of an Automated Benchmarking module for Kratos

María Jesús Samper — Thu, 26 Jan 2017 15:07:02 +0100

The steady and careful checking process of the test examples is almost impossible for developers and users of Kratos, and needs to be automated. This has been the inspiration of development of an Automated Benchmarking module. During the nightly builds of Kratos, which will be done on the upcoming Kratos server, this module automatically runs all test examples and verifies the results against a reference data set. It will send an email containing the status of each test example to a list of recipients. This can be useful in several ways. First, it will be clear when a conflict has occurred. This will help greatly to find the user committed the changes, ask him / her to correct / undo it. Also, it will let other users to be aware of a conflict in the latest code base, and avoid updating their own local code base, before it has been corrected. This can save them a lot of time and effort.

Calculation of shells by analytical methods

Scipedia content — Tue, 24 May 2016 19:11:01 +0200

The forms of revolution generated by shell structures are the simplest of classical art. Thus, the main motivation of this paper is present the basic tools for understanding shell behavior and the reader can design it without any problems.

The text will focus on analyzing the two most common shells. First the dome and second cylindrical wall. Having analyzed the two types we will look the union between these two types and see the ring edge necessary in many cases.