Scipedia: Documents published in 2012

Formulación de una regla de flujo no asociativa basada en la teoría de tensión-dilatancia de Rowe

Scipedia content — Wed, 28 Jun 2017 11:37:31 +0200

En este artículo se revisa la teoría de tensión-dilatancia de Rowe desde el punto de vista de su implementación como regla de flujo de la plasticidad convencional. Se deducen expresiones operativas, se analizan las consecuencias teóricas y numéricas de su forma matemática y se plantean elementos para su validación experimental.

Comportamiento y modelación de geo-materiales sometidos a cargas repetitivas

Scipedia content — Wed, 28 Jun 2017 11:37:27 +0200

Muchos sistemas geotécnicos están sometidos a solicitaciones repetitivas de pequeña magnitud que producen acumulación de deformaciones en el largo plazo. Este artículo propone un esquema de solución de problemas de borde mecánicos con elementos finitos utilizando un modelo basado en plasticidad para la carga estática y el primer ciclo de carga, complementado por un modelo híbrido con acumulación empírica para la carga repetitiva. El modelo híbrido considera el umbral de deformación elástico, la densidad terminal y "ratcheting". Los resultados del análisis de una fundación superficial sometida a una carga vertical repetitiva muestran la acumulación gradual de deformaciones y el cambio del estado de esfuerzos durante la carga repetitiva. Finalmente, se reconoce la necesidad de un esquema de modelación del comportamiento a largo plazo de suelos sometidos a ciclos térmicos, de congelamiento-deshielo, de humedecimiento-secado y de cambios químicos.

Aplicación y mejoras al método MPM para el análisis de deslizamientos y movimientos de tierra

Scipedia content — Wed, 28 Jun 2017 11:37:24 +0200

En este artículo se presentan dos extensiones al Método de Puntos Materiales (MPM) que mejoran la aptitud del método en la simulación de deslizamientos y movimientos de tierra. La primera consiste en el uso de una formulación de multi-fase que permite el análisis de mezclas sólido-fluido y su interacción a varias escalas. La segunda provee una técnica apropiada para mitigar el problema de "locking" que surge de usar, en el MPM estándar, funciones de interpolación lineales en una grilla Euleriana. Para este caso se propone una estrategia de relajación basada en el principio de Hu-Washizu y se demuestra su aplicabilidad en la modelación de flujos granulares.

Segundo encuentro de profesores e investigadores latinos de geotecnia (geolatina 2011)

Scipedia content — Wed, 28 Jun 2017 11:37:20 +0200

Editorial: Segundo encuentro de profesores e investigadores latinos de geotecnia (geolatina 2011)

La reparación de los daños catastróficos: Catástrofes naturales, administración y derecho público

Scipedia content — Wed, 28 Jun 2017 11:37:17 +0200

Revisión: La reparación de los daños catastróficos: Catástrofes naturales, administración y derecho público

Nuevos conglomerantes complementarios del cemento portland

Scipedia content — Wed, 28 Jun 2017 11:37:14 +0200

El desarrollo de nuevos conglomerantes complementarios al cemento portland se presenta como una alternativa que permitirá reciclar residuos, entre otros posibles beneficios. Estos nuevos materiales difícilmente podrán competir con el cemento portland ya que sus aplicaciones son limitadas y su coste, en general, más elevado.

Causas y consecuencias de accidentes químicos ocurridos entre la población civil. Caso: Ciudad de Tapachula, Chiapas, México (2002-2010)

Scipedia content — Wed, 28 Jun 2017 11:37:10 +0200

Con el objetivo de conocer el tipo de eventos, las causas, consecuencias, materiales involucrados y frecuencia de accidentes químicos en fuentes fijas y transporte para la zona Sur de México, se realizó un estudio preliminar en la ciudad de Tapachula, Chiapas, usando como fuente de información el registro de eventos registrados por el H. Cuerpo de Bomberos de Tapachula en el período correspondiente de 2002 a 2010. La información fue analizada aplicando el método de Análisis Histórico de Accidentes (AHA), encontrando que los accidentes químicos constituyen una problemática social y de salud en el área de estudio, ocasionando afectaciones a la salud humana, propiedades de la población, la infraestructura pública y al medio ambiente.

Patrones de carga reglamentarios para torres de transmisión de alta tensión sujetas a viento intenso

Scipedia content — Wed, 28 Jun 2017 11:37:07 +0200

Se analizan dos torres de celosía para transmisión eléctrica de alta tensión, aplicando 14 patrones de velocidad de viento, según diferentes normatividades internacionales, y describiendo las características generales de las torres y normas utilizadas. Se realiza un análisis no lineal ante carga estática monótona creciente para obtener las velocidades de viento regionales asociadas al colapso estructural. El estudio muestra la conveniencia de que el patrón de velocidades considere en forma explícita las diferencias entre vientos continentales y huracanados, así como ciertas inconsistencias en algunas normatividades.

Determinação das áreas de risco de óbitos provocados por deslizamentos e por inudações no estado de São Paulo - Brasil durante a operação verão de 2001 a 2007

Scipedia content — Wed, 28 Jun 2017 11:37:03 +0200

Este trabalho apresenta a aplicação do uso dos indicadores multivariados locais de corelação espacial (LISA) no mapeamento das ocorrências de deslizamentos de terra e inundações, no Estado de São Paulo - BRA, durante a Operação Verão de 2001 a 2007. Os resultados mostram que há uma correlação espacial entre a ocorrência de óbitos causados por deslizamentos e inundações. Através da aplicação desta técnica estatística foi possível identificar que as áreas de maior risco de deslizamento estão localizadas na Região Metropolitana de São Paulo, nos municípios localizados nos contrafortes nas encostas da Serra da Mantiqueira e do Planalto Atlântico e no vale do rio Paraíba do Sul. Por sua vez, as áreas de maior risco de inundação estão localizadas, na Região Metropolitana de São Paulo e nos municípios situados nos vales do rio Paraíba do Sul e Ribeira de Iguape.

Modelo analítico para turbinas eólicas sometidas a movimientos sísmicos

Scipedia content — Wed, 28 Jun 2017 11:36:59 +0200

La evaluación de la integridad estructural de las turbinas eólicas sometidas a terremotos es un tema poco estudiado debido en parte a la complejidad que conlleva modelar la dinámica rotacional del sistema en operación. Este estudio presenta el desarrollo de un modelo analítico de una turbina eólica de tres paletas con eje horizontal que gira a velocidad constante y es sometida a un movimiento de la base. El rotor se modela como un sistema compuesto de barras esbeltas conectadas al buje por medio de pasadores y resortes torsionales. La torre se modela por medio de tres elementos de vigas. Para evaluar la estabilidad del sistema y la extracción de los modos de vibración del sistema en operación se usó la teoría de Floquet para sistemas periódicos. Los resultados muestran que ante un terremoto los primeros dos modos de vibración de la torre en cada dirección (frontal y lateral) son los que se excitan predominantemente. Se encontró que la dirección lateral de la turbina es la más susceptible a sufrir desplazamientos mayores y a tener problemas de resonancia por carecer de suficiente amortiguamiento. Si bien la turbina en consideración resistió las cargas inducidas por los terremotos evaluados, se encontró que la parte más susceptible del sistema es la parte superior de la torre. Se encontró además que la combinación de las cargas de terremoto junto a las cargas de viento promedio controla el diseño de la sección superior de la torre en vez de las cargas de viento extremo.

Análisis y clasificación de los impactos en situaciones de crisis

Scipedia content — Wed, 28 Jun 2017 11:36:55 +0200

Las crisis son fenómenos complejos, de diversa naturaleza, la mayoría de las veces inevitables y cuya gestión resulta muy complicada. Por ello, para facilitar el proceso de gestión, es necesario realizar un profundo análisis de los posibles impactos que puedan ser consecuencia de una crisis.En el presente artículo se procede a analizar las diversas metodologías para la clasificación de impactos que se utilizan actualmente para, posteriormente, hacer una crítica constructiva sobre las dificultades que en dichas clasificaciones se encuentran. Finalmente se describen una serie de recomendaciones para mejorar el proceso de clasificación de impactos en situaciones de crisis.

Acerca de la importancia del trabajo colaborativo en el desarrollo de proyectos en riesgo de ser expuestos a desastres naturales

Scipedia content — Wed, 28 Jun 2017 11:36:52 +0200

Editorial: Acerca de la importancia del trabajo colaborativo en el desarrollo de proyectos en riesgo de ser expuestos a desastres naturales

Numerical simulation of turbulent air flow with dispersed droplets in cooling tower eliminators

Scipedia content — Fri, 31 Mar 2017 13:13:46 +0200

This work presents a numerical study on the turbulent flow of air with dispersed water droplets in separators of mechanical cooling towers. The averaged Navier-Stokes equations are discretised through a finite volume method, using the Fluent and Phoenics codes, and alternatively employing the turbulence models k − ϵ, k − ω and the Reynolds stress model, with low-Re version and wall enhanced treatment refinements. The results obtained are compared with numerical and experimental results taken from the literature. The degree of accuracy obtained with each of the considered models of turbulence is stated. The influence of considering whether or not the simulation of the turbulent dispersion of droplets is analyzed, as well as the effects of other relevant parameters on the collection efficiency and the coefficient of pressure drop. Focusing on four specific eliminators (‘Belgian wave’, ‘H1-V’, ‘L-shaped’ and ‘Zig-zag’), the following ranges of parameters are outlined: 1 ≤ Ue ≤ 5 m/s for the entrance velocity, 2 ≤ Dp ≤ 50 μm for the droplet diameter, 650 ≤ Re ≤ 8.500 for Reynolds number, and 0.05 ≤ Pi ≤ 5 for the inertial parameter. Results reached alternately with Fluent and Phoenics codes are compared. The best results correspond to the simulations performed with Fluent, using the SST k − ω turbulence model, with values of the dimensionless scaled distance to wall y+ in the range 0.2 to 0.5. Finally, correlations are presented to predict the conditions for maximum collection efficiency (100 %), depending on the geometric parameter of removal efficiency of each of the separators, which is introduced in this work.

Shape Optimization of 2D parametric models based on geometric weighting and evolutionary rules

Scipedia content — Fri, 31 Mar 2017 13:12:14 +0200

This paper presents a method for shape optimization of two-dimensional models subjected to simple or multiple load cases. The optimization is performed iteratively using evolutionary rules, based on the stress level. These rules determine regions on the boundary where the material is underused or overused, the objective is that the model evolves to a minimum weight model with a high and homogeneous stress level. The evolution is performed by modifying the boundary of the model slowly. Since the boundary is defined by parametric B-spline curves, generated changes result in a smooth boundary. The main proposal of the method is that boundary modifications are given by a set of displacements that, its magnitude and direction, take into account the geometrical information of the neighborhood, unlike other methods that simply generate displacement perpendicular to the boundary. Finally, the paper presents the design of a frame bike in order to show the good performance of the method.

Modeling flow through non linear coarse porous media by a finite difference scheme, with application to rockfill dams overtopping

Scipedia content — Fri, 31 Mar 2017 13:06:03 +0200

Flow through coarse porous media, as rockfill, gravel or sand of big size, exhibit a non linear relation between hydraulic gradient and seepage velocity. This behavior is observed when water flows over the crest of a rockfill dam, seeps into the downstream shoulder and moves through the rockfill voids. A finite difference scheme is used here to solve this problem through numerical modeling. It is implemented in the code MNLEE.RDS for solving dam overtopping problems. In addition, a procedure is provided to solve the coupled problem of flow over and through the rockfill dam. For that purpose, the concept of «law of flow exchange»is introduced.

Boundary conditions for gradient-enhanced models with smoothed displacements

Scipedia content — Fri, 31 Mar 2017 13:02:30 +0200

Gradient-enhanced models based on regularised displacements are an alternative to standard models in order to simulate material failure. In this alternative formulation, mechanical displacements u coexist with smoothed displacements u˜, which are the solution of a diffusion-reaction equation. Analogously to regularised standard models, prescribing boundary conditions in this alternative formulation is an open problem. Nevertheless, imposing these conditions for the displacement field (rather than the internal state variable) seems to be easier to interpret. The goal of this work is to study the influence of these conditions: neither Dirichlet conditions (prescribed at the beginning) nor homogeneous Neumann conditions (reminiscence of standard gradient models) allow to obtain realistic numerical results, on the other hand, by means of non-homogeneous Neumann boundary conditions, these results are physically admissible. However, these conditions do not ensure volume conservation, which is an interesting property in some constitutive models. Hence, new conditions (combined conditions) are proposed. These satisfy the necessary properties for regularisation: (a) reproducibility of order 1 (u=u˜ if u is a linear field), (b) displacement smoothing along the boundary and (c) volume preservation. In this work various two-dimensional numerical tests are carried out in order to illustrate the influence of the different boundary conditions.

Mandibular advancement devices in the treatment of obstructive sleep apnea syndrome

Scipedia content — Fri, 31 Mar 2017 13:02:10 +0200

Obstructive sleep apnea syndrome (OSAS) consists in the occurrence of recurrent episodes of airflow limitation during sleep, with undesirable consequences for the health. The phenomenon is well known from a medical point of view (prognosis, diagnosis and treatment), but there is not a methodology or analysis tools for the quantification of the clinical response using Mandibular Advancement Devices (MAD). This paper shows how combining image processing, fluid dynamics and engineering design criteria, imported from other fields, allow to establish a simple analysis method clinically useful to decide the more convenient positioning of the MAD based on the pressure or mechanical movement of the jaw. This methodology is applied to a patient suffering OSAS which the objective to evaluate the changes provoked in the upper-airways due to an innovative mandibular device.

Comparasion of unidimensional and bidimensional flow models for earthen dam failures

Scipedia content — Fri, 31 Mar 2017 13:01:38 +0200

The development of more and more potent computers and the recent research in the field of hidroinformatics makes possible the free surface flow modelling in two dimensions caused by earthen dam failures. In this paper, the results obtained by uni-dimensional model (HEC-RAS) and two-dimensional model (CARPA) are compared. The use of the HEC-RAS software assumes the hypothesis of unidimensionality to be true, no infiltration and existence of a minimal initial flow. The comparison is made by analyzing the effect of these hypothesis in the downstream flow hydrographs. The used models reproduce the water discharge generated by a possible failure of dam number 1 of the 5th District of the Segarra-Garrigues Irrigation Project in the Ebro river basin in Spain.

Numerical modelling of landslides in reservoirs via the Particle Finite Element Method (PFEM)

Scipedia content — Fri, 31 Mar 2017 12:59:33 +0200

The paper presents the results of the application of the Particle Finite Element Method (PFEM) to the analysis of landslides in reservoirs. This is a complex phenomenon, because of the interaction between the landslide, the still water in the reservoir and the dam. PFEM combines a Lagrangian approach with the solution of the governing equations of the problem using the FEM. A mesh connecting the initial set of particles (nodes) is re-generated in every time step. Some validation cases are presented, in which PFEM results are compared with experimental data. More complex calculations have been made over the actual geometry of reservoirs taken from the cartographic information of the sites. In these cases the wave generation, its propagation and dam overtopping are reproduced. Finally, Lituya bay rock slide in which 90 × 106 tons of rocks fell on the bay, generating a huge wave that caused a maximum run-up of 524 m on the opposite shore, has been simulated in 3D. The results show that PFEM is a useful tool in risk assessment related with landslides in reservoirs as it gives a good approximation to the potential affections, thus allowing the appropriate design of protection measures.

A minimum weight formulation with stress constraints in topology optimization of structures

Scipedia content — Fri, 31 Mar 2017 12:58:03 +0200

Optimum design of structures has been traditionally focused on the analysis of shape and dimensions optimization problems. However, more recently a new discipline has emerged: the topology optimization of the structures. This discipline states innovative models that allow to obtain optimal solutions without a previous definition of the type of structure being considered. These formulations obtain the optimal topology and the optimal shape and size of the resulting elements. The most usual formulations of the topology optimization problem try to obtain the structure of maximum stiffness. These approaches maximize the stiffness for a given amount of material to be used. These formulations have been widely analyzed and applied in engineering but they present considerable drawbacks from a numerical and from a practical point of view. In this paper the author propose a different formulation, as an alternative to maximum stiffness approaches, that minimizes the weight and includes stress constraints. The advantages of this kind of formulations are crucial since the cost of the structure is minimized, which is the most frequent objective in engineering, and they guarantee the structural feasibility since stresses are constrained. In addition, this approach allows to avoid some of the drawbacks and numerical instabilities related to maximum stiffness approaches. Finally, some practical examples have been solved in order to verify the validity of the results obtained and the advantages of the proposed formulation.

A predictive evolution model of rocky coasts

Scipedia content — Fri, 31 Mar 2017 12:57:46 +0200

The recession of coastal cliffs is a widespread phenomenon on the rocky shores that are exposed to the combined incidence of marine and meteorological processes that occur in the shoreline. This phenomenon is revealed violently and occasionally as gravitational movements of the ground and can cause material or human losses. Their prediction is difficult, however it is basic for the proper coastal management and the clear understanding of erosion risks. There are several models of the coastal cliff recession processes. From the stochastic type models based on historical erosion events, to the theoretical models as described by Eikonal or Boussinesq equations. In this work an intermediate solution is adopted (process-response model), such as models based on simplified balance of forces as trigger mechanisms involved in the erosion of the rocks. This model fits the marine dynamics: sea level changes, tidal range and wave transformation, along with the evolution of the land: the slope of the surf zone, erosion and rock falls. So far these models have been limited to small slope cliffs, since its numerical stability and the propagation of errors are unknowns. For these reasons, the development of a generic model that reproduces the spatial and temporal evolution of a cliff-2D profile (platform, beach and slope) consisting on semi-consolidated heterogeneous materials, is presented. In addition, the computational implementation, the study of different numerical resolution techniques and the produced errors, are also exposed and analysed.

Numerical-experimental study of the FRP-epoxy-concrete interface for reinforced structures under double shear

Scipedia content — Fri, 31 Mar 2017 12:55:40 +0200

The strengthening of concrete structures with laminates of carbon fibers CFRP (Carbon Fibers Reinforced Polymer) began in the 1980s. Nowdays, this technology is one of the most promising one because of the good mechanical properties of laminates and their easy hand-work. Laminates are bonded to the concrete structure by means of epoxy resins. The load-carrying capacity of the strengthening depends directly on the proper behavior of the interface laminate-concrete. While the concrete is capable of transferring stresses to the laminate, this one becomes in charge and collaborates to the strength mechanism of the structure. The safety factor of the reinforcement can be guaranteed if we can predict the behavior at the interface between both materials. In this work we present a pure shear test and a simulation three-dimensional to characterize the behavior of the interface between the laminate and the concrete.

On the need for the use of error-controlled finite element analyses in structural shape optimization processes with evolutionary algorithms

Scipedia content — Fri, 31 Mar 2017 12:53:47 +0200

This work analyzes the influence of the discretization error contained in the Finite Element (FE) analyses of each design configuration proposed by the structural shape optimization algorithms over the behavior of the algorithm. The paper clearly shows that if FE analyses are not accurate enough, the final solution provided by the optimization algorithm will neither be optimal nor satisfy the constraints. The need for the use of adaptive FE analysis techniques in shape optimum design will be shown. The paper proposes the combination of two strategies to reduce the computational cost related to the use of mesh adaptivity in evolutionary optimization algorithms: (a) the use of the algorithm described by Bugeda et al. [1] which reduces the computational cost associated to the adaptive FE analysis of each geometrical configuration and, (b) the successive increase of the required accuracy of the FE analyses in order to obtain a considerable reduction of the computational cost in the early stages of the optimization process.

Turing patterns formation on surfaces under deformation: A total lagrangian method approach

Scipedia content — Fri, 31 Mar 2017 12:51:44 +0200

In this work we have developed several numerical examples of reaction-diffusion equations with growing domain. For this purpose we have used the Schnakenberg reaction model with parameters in space Turing. Therefore numerical tests are performed on the appearance of Turing patterns on surfaces that have high deformation rate. For the solution of reaction diffusion equations is presented a solution method on surfaces in three dimensions using the finite element method under the use of the total Lagrangian formulation. The results show that the formation of Turing patterns depends on the features of surface deformation and the rate at which change in position of each point of the domain. These results can explain some phenomena of change of pattern on the surface of the skin of animals that exhibit characteristic spots.

Numeric validation of the cyclic behaviour of interior connections in waffle-flat-plate structures

Scipedia content — Fri, 31 Mar 2017 12:51:32 +0200

Several approaches are investigated to model interior reinforced concrete waffle-flat-plate-column connections. A model is proposed that provides very good results with reasonable low computational cost. The proposed model is validated with the experimental results obtained on a 3/5 scale specimen, subjected to quasi-static in cyclic loads up to collapse. To this end, the non-linear advanced theory of reinforced concrete is applied on a three-dimensional finite element model and non-linear analysis are conducted. Both fiber and layer elements are used for the one-dimensional and bi-dimensional components respectively. The main results of the simulation were: (i) the capacity curve obtained through out a push-over analysis with displacement control, (ii) the hysteretic curves of the slab, and (iii) the crack patterns. A very good agreement is found between numerical and experimental results.

A mortar contact algorithm for three-dimensional elasticity problems

Scipedia content — Fri, 31 Mar 2017 12:49:35 +0200

In this paper we propose a mortar algorithm for the study of contact mechanics in three dimensional elasticity problems. The projection surface used for integrating the equations is selected through a local cartesiana base defined in each contact element. In this way, some difficulties in the algorithm implementation as well as in the linearization of the equations are avoided. The proposed examples show that the algorithm satisfies the patch tests. Finally, we use the algorithm in an industrial application, the contact of an internal combustion engine valve with its seat.

A shock-capturing method based on shape functions for high order discontinuous Galerkin

Scipedia content — Fri, 31 Mar 2017 12:49:02 +0200

This article presents a high-order Discontinuous Galerkin method for compressible flow problems, in which is very frequent the formation of shocks. The stabilization is introduced by a new basis functions. This base has the flexibility to vary locally (within each element) between continuous polynomial functions space and a space of piecewise polynomial functions. Thus, the proposed method provides a bridge between the standard methods of high-order Discontinuous Galerkin and classical Finite Volume methods, maintaining the locality and compactness of the scheme. The variation of basis functions is automatically set according to the regularity of the solution and the stabilization is introduced by the jump operator, standard in Discontinuous Galerkin methods. Unlike the classical methods of slope limiting, the strategy here presented is very local, robust, and applies to any order of approximation. Moreover, the proposed method does not require adaptive mesh refinement techniques and it can be used with any temporal integration scheme. Several applications of the Euler equations are shown, demonstrating the validity and effectiveness of the method, especially for high orders of approximation.

Explicit time integration with large time steps for the heat flow equations

Scipedia content — Fri, 31 Mar 2017 12:47:26 +0200

We present a novel fully explicit time integration method that remains stable for large time steps, requires neither matrix inversions nor solving a system of equations and therefore allows for nearly effort-less parallelization. In this first paper the proposed approach is applied to solve conduction heat transfer problems, showing that it is stable for any time step as is the case with implicit methods but with a much lower computation time.

Optimum sizing of launching nose of prestressed concrete bridges

Scipedia content — Thu, 23 Mar 2017 15:56:39 +0100

The design of the launching nose of an incrementally launched bridge determines its constructive process and, therefore, also its dimensions. The optimization of the launching nose can raise as a first step to improve the design of a launched bridge. The conventional design process of a launching nose is based on trial and error method to reduce bending moment of prestressed concrete deck at the foremost support during launch. In this way, there is no guarantee that the obtained solution is the best among all the possible solutions since they all depend on the experience and intuition of a designer, and they are also restricted by a limited number of possible iterations. Given that launched bridges constitute an important constructive typology, all the available capacities of design innovation should be incorporated, among which it can be found numerical optimization. This research work proposes an objective and rigorous formulation to optimize a launching nose of launched bridge under real constraints that a bridge designer can encounter in practice. Comparing the results obtained by conventional process and that by optimization techniques, it can be verified that some of the assumptions, considered in classical design methods of a launching nose, are not based on any theoretical foundation. This fact demonstrates the utility of numerical optimization to improve a design.

Numerical simulation of sloshing in liquid storing tanks by an arbitrary Lagrangian-Eulerian strategy

Scipedia content — Tue, 28 Feb 2017 15:19:47 +0100

Sloshing of fluids with a free surface contained in liquid storage tanks is numerically simulated by an arbitrary Lagrangian-Eulerian formulation. The fluid is considered viscous and Newtonian, while the flow is assumed laminar and incompressible. A partitioned and distributed computational code is employed, which solves three instances each time step: (i) the determination of the fluid state, given by the Navier–Stokes equations, (ii) the displacement of the free surface, and (iii) the update of the position of the internal nodes of the mesh, that is deformed as a consequence of the free surface displacement. The purpose of the work is verifying the applicability of the method to sloshing problems with known solutions, as well as the resolution of some practical examples. Numerical examples include validations against analytical solutions, where the wave period and damping rate are well captured, comparisons with reference results from other authors and a sample of sloshing induced by seismic actions.

An empirical expression for loss factor

Scipedia content — Tue, 28 Feb 2017 15:17:56 +0100

Noise transmitted by the sidewalls of buildings is essential to study the overall airborne sound insulation. For the determination of the lateral transmissions we must determine a parameter known as vibration reduction index. To obtain the value of the vibration reduction index to know the acoustic behaviour of the whole constructive, it is necessary to know the velocity level difference and the structural reverberation time. The indeterminations in the velocity level difference, or in the structural reverberation time will add diversions in the global determination of the isolation of the whole constructive. In the Standard UNE EN 12354-1:2000 there are empirical expressions for obtained the structural reverberation time. In the Standard UNE-EN ISO 10848-1:2007 there is a detailed procedure to determine experimentally the velocity level difference and the structural reverberation time, and to know the sidewalls transmissions. In this work, it is compared the structural reverberation time obtained by empirical expression and the structural reverberation time obtained experimentally, applying the normalized procedure. Based on this comparison we readjusted the empirical equations with a fundamental parameter, the loss factor. It is observed that the estimates do not reflect reality if we consider the same loss factor for all the structural elements, as it is allowed in the predictions of UNE EN 12354.

Decomposition in circular pistons to obtain the acoustic radiation of a rectangular piston

Scipedia content — Tue, 28 Feb 2017 15:17:45 +0100

Obtaining pressure radiated by flat surfaces is not a new problem. This problem has studied by the complexity of the topic and its application to design flat speakers. These kind of speakers are the speakers that we use in televisions, ceilings, cinema screens, panels, etc. in this cases usually we have rectangular speakers. The single source model is the simplest model to convert the surface vibration to radiated pressure in a point. This is an easy model but it is very slow, especially when we want calculate at high frequencies. For rectangular surfaces there are models that use relatively complex auxiliary functions. In this case the calculation is accelerated but its implementation is more complicated and is necessary to particularize each situation. This paper presents the decomposition of a rectangular surface in several circular surfaces, by means of area associations, seeking a rapid method based on circular pistons whose behavior is known with an acceptable error in the allocation.

The use of CFD to study wind pressures on curve roofs without walls

Scipedia content — Tue, 28 Feb 2017 15:17:35 +0100

This work shows results of the application of computational fluid dynamics on studying the aerodynamics of isolated curved roof buildings, without cladding walls. This type of structures are widely used in Argentine Republic in cities and and country areas, and they could be seen in very different uses, such as parking areas, sport facilities, educational buildings and so on. Current Argentinean wind loads code tells nothing about them and the same situation is found in other countries codes. Finite element program and a computer cluster were used to obtain numerical results, and a wind tunnel study undertaken at the Universidad Nacional del Nordeste boundary layer wind tunnel, to measure wind pressures on a model was used to validate computational results. A good agreement between computational and experimental results was achieved and original results for this type of structures was also obtained.

Numerical simulation of the behaviour of musculoskeletal tissue

Scipedia content — Tue, 28 Feb 2017 15:16:56 +0100

This paper presents a three dimensional computational model to simulate the mechanical behavior of the muscle-tendon unit (MTU). The model has been formulated through a strain energy density function for hyperelastic materials incorporating both the passive and active behavior of the connective tissues, and taking into account preferential directions for both behaviours, not necessarily coincident. The initial stresses, usually present in soft tissues, have been considered when performing the MTU simulation. The geometry used corresponds to the rat tibialis anterior muscle reconstructed from «in-vivo » magnetic resonance images. This paper also studies the effect of the fascia on the MTU passive behaviour and the setting of a hyperelastic model for this tissue by means of experimental tests.

Short span bridges dynamic behaviour account for the vehicle-track-structure-soil dynamic interaction

Scipedia content — Tue, 28 Feb 2017 15:15:52 +0100

The dynamic vehicle-track-bridge-soil interaction is studied on high speed lines. The analysis is carried out using a general and fully three dimensional multi-body-finite element-boundary element model, formulated in the time domain to predict vibrations due to the train passage over the bridge. The vehicle is modelled as a multi-body system, the track and the bridge are modelled using finite elements and the soil is considered as a homogeneous half-space by the boundary element method. Usually, moving force model and moving mass model are employed to study the dynamic response of bridges. In this work, the multi-body system allows one to consider the quasi-static and dynamic excitation mechanisms. Soil-structure interaction is taken into account on the dynamic structure behaviour on simply-supported short span bridges. The influence of soil-structure interaction is analysed in both resonant and non-resonant regimes.

Robust Design Optimization applied to aeronautics combining stochastic calculus with evolutionary algoritms

Scipedia content — Tue, 28 Feb 2017 14:08:27 +0100

Uncertainties are a daily issue to deal with in aerospace engineering and applications. Robust optimization methods commonly use a random generation of the inputs and take advantage of multi-point criteria to look for robust solutions accounting with uncertainty definition. From the computational point of view, the application to coupled problems, like fluid-dynamics (CFD) or fluid-structure interaction (FSI), can be extremely expensive. This work presents a coupling between stochastic analysis techniques and evolutionary optimization algorithms for the definition of a stochastic robust optimization procedure. At first, a stochastic procedure is proposed to be applied into optimization problems. The proposed method has been applied to both CFD and FSI problems for the reduction of drag and flutter, respectively.

Comparative study of models of impedance boundary conditions in acoustic problems

Scipedia content — Tue, 28 Feb 2017 14:06:24 +0100

In this paper, different implementations of numerical locally reacting boundary conditions are studied for acoustic problems. In this comparative study we analyze two types of equations, the Euler equations and the wave equation. We also analyze both finite-differences time-domain (FDTD) algorithms, and pseudo-spectral time domain (PSTD) numerical schemes. We compare different numerical implementations existing in the literature by means of exhaustive numerical experiments. These numerical experiments allow for the study of the absorbing properties of the different schemes as a function of the frequency and the angle of the incident sound waves. This novel comparative study will help the acoustic engineer in order to choose the proper numerical scheme for his/her simulations.

Seismic assessment of the masonry buildings typical of Barcelona using the Risk-UE methodology

Scipedia content — Tue, 28 Feb 2017 14:05:28 +0100

In this work, a study about the vulnerability and seismic damage of unreinforced masonry buildings is carried out. Three models of buildings representatives of the Eixample district of Barcelona have been chosen. The seismic vulnerability is evaluated by means of the Risk-UE methodology. The seismic demand is described by elastic project spectrum, in this case, defined by the Eurocode 8. Fragility curves are obtained from a nonlinear analysis, considering the capacity spectra. Expected seismic damage is gotten with the damage probability matrices, which indicate the occurrence probability of a damage state for a seismic demand given. The analysis of the buildings has been performed by TreMuri program by means of a macroelements model, which represents of a whole masonry panel. The buildings, here, analyzed are real and detailed structural drawings and reports have been used to model them. The results shown a considerable vulnerability in this type of buildings, therefore, in spite of the seismic hazard the expected seismic risk is significant.

Evaluating manoeuvering and seakeeping performance of a surface effect ship

María Jesús Samper — Mon, 30 Jan 2017 16:39:58 +0100

Interfaces 3DShell y 3DSolid. GiD-Sap2000

María Jesús Samper — Mon, 30 Jan 2017 13:20:02 +0100

Este documento se ha diseñado a partir de la interfaz GiD-Sap90 y lo que pretende es hacer una actualización de esta metodología aplicada a las últimas versiones del GiD (Versión 10) y Sap2000 (versiones 12 y 14). Este trabajo se ha llevado a cabo entre investigadores del Instituto de Ingeniería de la UNAM y la Escuela Técnica Superior de Arquitectura del Valles y Barcelona de la U.P.C. Esta actualización incorpora una doble interfaz. Lo que se pretende es que el usuario continúe trabajando en GiD todo el preproceso para la generación de modelos numéricos de geometría compleja y pueda exportar a Sap2000 el archivo para su análisis. Una vez ahí, el usuario puede decidir si continua analizando el modelo dentro de Sap2000 o regresar a GiD mediante esta interfaz para visualizar los resultados en GiD. Estas interfaces son herramientas muy potentes para los usuarios que se dedican a analizar estructuras complejas como lo son los edificios históricos, ya que GiD y su preproceso ha sido creado para trabajar y estructurar mallas sofisticadas geométricamente. Además, esta interfaz le permite al usuario incorporar, dentro de GiD, todas las condiciones que Sap2000 requiere para el análisis numérico de una estructura. En resumen, estas interfaces permiten agilizar el análisis numérico de estructuras complejas como lo son los edificios históricos.

Simulador de voladura en macizos rocosos

María Jesús Samper — Fri, 27 Jan 2017 15:52:14 +0100

Se presenta la formulación básica para la modelación de voladura en macizos rocosos mediante el MED. El modelo presentado muestra las características esperadas para este tipo de simulaciones. La condición del explosivo debe ser estudiada con más detalle para asegurar la relación entre los valores característicos de la condición y un explosivo determinado. Se establecen las condiciones requeridas para el modelo 2D, pudiendo ser extendidas durante el proyecto a la versión 3D.

Se han desarrollado las interfaces de usuarios completamente funcionales tanto para 2D como 3D, denominando al software BLAST, con su respectivo manual de instrucciones

Se presenta además un estudio del efecto de las cargas explosivas en 2D, donde se aprecia el comportamiento del macizo rocoso para distintos niveles de carga, los cuales están directamente relacionados con el explosivo utilizado, además de todas las consideraciones operacionales que puedan ser consideradas por el operario, como el diámetro del barreno o posibles cámaras de aire para desacoplar el explosivo.

El reto de la transferencia de los resultados de la investigación a la industria

Scipedia content — Mon, 23 Jan 2017 12:40:02 +0100

En este trabajo se analizan algunas de las razones que dificultan y favorecen la transferencia de los resultados de la investigación que se desarrolla en entornos científicos al sector industrial.

En concreto se analiza el proceso de la innovación y sus factores de impulso e inhibición. También se describe el ciclo que siguen las ideas, desde que se originan en un entorno científico hasta que se transforman en productos de éxito comercial. Finalmente, se presentan algunas recomendaciones para favorecer el proceso de transferencia de los resultados de la investigación a la industria y se propone la creación de un nuevo modelo de centro de I+D+I.

Analysis of fluid-soil-structure interaction problems with the Particle Finite Element Method (PFEM)

María Jesús Samper — Wed, 26 Oct 2016 15:44:40 +0200

We present some developments in the Particle Finite Element Method (PFEM) for analysis of coupled problems in mechanics involving fluid-soil-structure interaction (FSSI). The PFEM uses an updated Lagrangian description to model the motion of material points in both the fluid and the solid domains (the later including soil/rocks and structures). A mesh connects the particles (nodes) defining the discretized domain where the governing equations for each of the constituent materials are solved as in the standard FEM. The procedure to model frictional contact conditions and material erosion at fluid-solid and solid-solid interfaces is described. We present several examples of application of the PFEM to solve FSSI problems such as the motion of rocks by water streams, the erosion of river beds, the stability of breakwaters and constructions under sea waves, the falling of landslides on houses and into a reservoir and the failure of rockfill dams in overspill situations.