Seleção de topologias ótimas de estruturas elásticas 2D com restrição de tensão – via Smooth Evolutionary Structural Optimization

This paper approaches the topology optimization problems in plane linear elasticity considering the minimization of the volume with restriction of the stress employing an index of performance for monitoring the meeting of the optimum region. It is used for this purpose the classical evolutionary structural optimization, or ESO ‐ evolutionary structural optimization. This procedure is based on systematic and gradual removal of the elements with lower stress compared with the maximum stress of the structure. This procedure also known as a process “hard‐kill”. It is proposed a variant of the ESO method, called SESO ‐ Smoothing ESO, which is based on the philosophy that if an element is not really necessary for the structure, its contribution to the structural stiffness will gradually diminish until it has no longer influence in the structure, so its removal is performed smoothly. That is, their removal is done smoothly, reducing the values of the constitutive matrix of the element as if it were in the process of damage. A new performance index for the monitoring of this evolutionary process smoothed is proposed herein. The applications of ESO and SESO are made with the finite element method, but considering a high order triangular element based on the free formulation. Finally, it is implemented a spatial filter in terms of stress control, which was associated with SESO technique proved to be very stable and efficient in eliminating the formation of the checkerboard.     

Análise de vigas laminadas utilizando o natural neighbour radial point interpolation method

In this work, a meshless method, “natural neighbour radial point interpolation method” (NNRPIM), is applied to the one‐dimensional analysis of laminated beams, considering the theory of Timoshenko.The NNRPIM combines the mathematical concept of natural neighbours with the radial point interpolation. Voronoï diagrams allows to impose the nodal connectivity and the construction of a background mesh for integration purposes, via influence cells. The construction of the NNRPIM interpolation functions is shown, and, for this, it is used the multiquadratic radial basis function. The generated interpolation functions possess infinite continuity and the delta Kronecker property, which facilitates the enforcement of boundary conditions, since these can be directly imposed, as in the finite element method (FEM).In order to obtain the displacements and the deformation fields, it is considered the Timoshenko theory for beams under transverse efforts. Several numerical examples of isotropic beams and laminated beams are presented in order to demonstrate the convergence and accuracy of the proposed application. The results obtained are compared with analytical solutions available in the literature.     

Implementación eficiente de una formulación semirrecursiva para la dinámica de sistemas multicuerpo de gran tamaño

This article shows an efficient implementation of a dynamic semi-recursive formulation for large and complex multibody system simulations, with interesting applications in the automotive field and especially with industrial vehicles. These systems tend to have a huge amount of kinematic constraints, becoming usual the presence of redundant but compatible systems of equations. The maths involved in the solution of these problems have a high computational cost, making very challenging to achieve real-time simulations.In this article, two implementations to increase the efficiency of these computations will be shown. The difference between them is the way they consider the Jacobian matrix of the constraint equations. The first one treats this matrix as a dense one, using the BLAS functions to solve the system of equations. The second one takes into account the sparse pattern of the Jacobian matrix, introducing the sparse function MA48 from Harwell.Both methodologies have been applied on two multibody system models with different sizes. The first model is a vehicle IVECO DAILY 35C15 with 17 degrees of freedom. The second one is a semi-trailer truck with 40 degrees of freedom. Taking as a reference the standard C/C + + implementation, the efficiency improvements that have been achieved using dense matrices (BLAS) have been of 15% and 50% respectively. The results in the first model have not improved significantly by using sparse matrices, but in the second one, the times with sparse matrices have been reduced 8% with respect to the BLAS ones.     

Predição de propagação de fissuras através de modelos constitutivos locais e técnica de construção progressiva da trajetória de descontinuidade

This paper addresses the study of the quality and objectivity of responses obtained with the distinct formulations (symmetric and non-symmetric) of the discontinuity embedded finite elements, as well as with the local continuum approach (smeared model), in which the softening law dependent on the element size is combined with a scheme to track the discontinuity path. The study is based on the concepts of kinematic and static consistency of the embedded discontinuity formulations.     

Desenvolvimento de uma ferramenta computacional para a análise de elementos de membrana em concreto estrutural

Reinforced concrete elements subjected to membrane forces, i.e., elements subjected to in-plane shear and axial stresses are very common for modeling complex structures such as aircraft hangars, nuclear power plants, offshore oil platforms and long-span bridges. While the design of reinforcement for membrane elements is well adressed the same can not be said regarding the analysis of performance of these elements. Into this context, the present paper aims at providing a numerical tool developed in the Matlab platform, taking into account the “Modified Compression Field Theory”. In order to certificate the performance of the proposed tool, extensive numerical results were compared with experimental results available in the literature. The obtained results revealed that the proposed tool is very confident for the analysis of reinforced concrete membrane elements.     

Diseño óptimo del pico de lanzamiento de puentes lanzados de hormigón pretensado

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.     

Existenc'a de máximo de funciones reales continuas en espacios casi numerablemente compactos

Summary By the concept of countable almost-compactness, here defined, a characterization of topological spaces on which each continuous real function has a maximum and minimum is given. Besides a careful study of the relations between several concepts of compactness and axioms of separation is performed.

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La redacción de este trabajo nos ha sido simplificada por las notas que tomó nuestra alumna Srta. Callaved de una exposición que hicimos de él en el Seminario Matemático de la Universidad de Zaragoza.     

Estimations explicites sur le taux de décroissance exponentielle pour le système de von Kármán de plaques thermoélastiques

On considère le système de von Kármán pour une plaque thermoélastique bornée et régulière. On suppose que la plaque est encastrée. On démontre des estimations explicites sur le taux de décroissance en temps des solutions, montrant que l'énergie des solutions d'énergie initiale égale à R décroit comme exp (−ωt/(1 + R²)) lorsque t → ∞, où ω > 0 est une constante indépendante de la donnée initiale.     

Formulação numérica de estruturas compósitas amortecidas utilizando as teorias da Deformação Cisalhante de Primeira Ordem e de Alta Ordem

Composite materials have been used in the design of the aircrafts structures because their low weight and high mechanical strength. However, structures made in composite material are exposed to dynamical and/or static loading environments. Therefore, a major research effort is undertaken in the development of tools numerical for analysis and design of composite structures. This paper presents a numerical formulation of the composite structures using the Finite Element Method (FEM). The damped composite structures, using inserted viscoelastic devices, and undamped composite structures are formulated by FEM. Viscoelastic materials are applied as continuous layers inserted on composite structures. The intrinsic damping of the composite material is included in the studies, too. The First‐order (FSDT) and Higher‐order Shear Deformation (HSDT) theories are formulated. They are distinguished by order of the approximation functions used in the mechanical displacements field. Both theories are computationally implemented using the Serendipity finite element. This is a rectangular finite element with 8 nodes, 5 or 11 degrees of freedom per node. The results are compared with papers predictions. The advantages and disadvantages of using each theory in the modeling of composite (thin or thick) and thick sandwiches structures, including the intrinsic and the viscoelastic damping, are discusses.     

Optimización robusta en aplicaciones aeronáuticas con la combinación de cálculo estocástico y algoritmos evolutivos

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.     

Modelado numérico del proceso de soldadura FSW incorporando una técnica de estimación de parámetros

Numerical models of heat transfer and fluid flow used in the simulation of the friction-stir welding (FSW) process have contributed to the understanding of the process. However, there are some input model parameters that cannot be easily determined from fundamental principles or the welding conditions. As a result, the model predictions are not always in agreement with experimental results. In this work, the Levenberg-Marquardt (LM) method is used in order to perform a non-linear estimation of the unknown parameters present in the heat transfer and fluid flow models, by adjusting the temperatures results obtained with the models to temperature experimental measurements. These models are implemented in a general-purpose software that uses a numerical formulation developed from the finite element method (FEM). The unknown parameters are: the friction coefficient and the amount of adhesion of material to the surface of the tool, the heat transfer coefficient on the bottom surface and the amount of viscous dissipation converted into heat. The obtained results show an improvement in the numerical model predictions from the incorporation of parameter estimation techniques.     

Respuesta dinámica de edificaciones producida por campos de ondas incidentes considerando la interacción suelo-estructura

This paper presents 2 methodologies based on the Boundary Element Method and the Finite Element Method to study soil-structure interaction effect on building behaviour. A 3-story building response induced by an incident wave field is studied using both methods. The results obtained show a good agreement. Then, a simplified model is validated from these methods and several buildings are analysed. Conclusions show that structural responses are due to floor deformation, and depend on their area, support conditions and coupling. A coupling between floors and columns when both elements have similar stiffness is also observed.     

Algoritmo compensador neuronal discreto de dinámica en robots móviles usando filtro de Kalman extendido

This paper presents the design of an algorithm based on neural networks in discrete time for its application in mobile robots. In addition, the system stability is analyzed and an evaluation of the experimental results is shown.The mobile robot has two controllers, one addressed for the kinematics and the other one designed for the dynamics. Both controllers are based on the feedback linearization. The controller of the dynamics only has information of the nominal dynamics (parameters). The neural algorithm of compensation adapts its behaviour to reduce the perturbations caused by the variations in the dynamics and the model uncertainties. Thus, the differences in the dynamics between the nominal model and the real one are learned by a neural network RBF (radial basis functions) where the output weights are set using the extended Kalman filter. The neural compensation algorithm is efficient, since the consumed processing time is lower than the one required to learning the totality of the dynamics. In addition, the proposed algorithm is robust with respect to failures of the dynamic controller. In this work, a stability analysis of the adaptable neural algorithm is shown and it is demonstrated that the control errors are bounded depending on the error of approximation of the neural network RBF. Finally, the results of experiments performed by using a mobile robot are shown to test the viability in practice and the performance for the control of robots.     

Evaluación probabilista de la capacidad,fragilidad y daño sísmico de edificios de hormigón armado

Currently, many structures existing in seismic areas are highly vulnerable because they have been built without the use of seismic design codes or by using outdated codes. Often, methods for assessing the vulnerability of the structures do not take into account that their seismic behavior is dynamic and highly nonlinear and, moreover, that the structural characteristics and action have large uncertainties. This article aims to assess the vulnerability of structures taking into account that the mechanical properties of materials and the seismic action are random variables, by using advanced techniques based on the Monte Carlo method and on the nonlinear stochastic dynamics. The results obtained with these techniques are compared with those corresponding to a standard vulnerability assessment, based on deterministic models, in order to highlight the differences between both approaches. The main conclusion of this work is the need to address the vulnerability assessment problem from a probabilistic perspective which, combined with advanced nonlinear static and dynamic structural analysis techniques, provides a powerful tool giving information impossible to be captured by means of deterministic models. Finally, detailed results obtained for a building with waffle slabs, which is a structural typology widely used in Spain, are included and discussed.     

Modelación del funcionamiento hidráulico de los dispositivos de aireación de desagües de fondo de presas mediante el método de partículas y elementos finitos

Dam bottom are key elements to control the water surface elevation below the spillway crest level. As a consequence, they are essential in reservoir management, and play a vital role in dam safety.The convenience of installing an aeration system in dam bottom outlets is well known nowadays. Otherwise, damages due to cavitation and vibration are frequently serious, as could be observed in several dams built in the beginning of the 20th century.The intrinsic features of the phenomenon make it hard to analyze either in situ or in full scaled experimental facilities. As a consequence, most of the previous studies have been carried out in small-scale physical models. The results of these works have been used to develop empirical formulas which provide an estimation of the maximum air demand of the aeration system.The progress in the development of numerical methods allows addressing this problem using numerical modeling. The Particle Finite Element Method (PFEM) had been previously applied and validated for the analysis of the performance of other hydraulic structures. In this work, it has been used to simulate air-water interaction in free-flowing gated conduits. The objective is to avoid the scale effects of physical modeling and to study in detail the key parameters. The results clarify the behaviour of the involved fluids (air and water) and provide information about the influence of the main variables that affect their circulation.     

Aplicación de métodos computacionales en la evaluación de la respuesta aeroelástica de puentes soportados por cables

The possibilities of computational methods for assessing the response of cable supported bridges under wind action are considered in this work. The main objective is to study the possibilities of substituting wind tunnel campaigns by computer based analyses, particularly at the early design stage. The preliminary proposed design for a continuous cable-stayed bridge with two main spans of 650 m and a single box girder deck has been considered as a case study. The force coefficients of the deck cross-section have been computed and the unsteady response associated to vortex-shedding has been simulated using CFD commercial software. Furthermore, an in-house piece of software has been employed to obtain the response for flutter and buffeting phenomena adopting the hybrid approach; with that purpose the experimental flutter functions of a similar box girder deck were adopted. The computational results have been validated by comparison with similar experimental results published by other researchers. It has been verified that the set of adopted methods offers reliable results with moderate costs; therefore, the proposed approach is very suitable at the early design stage of long span bridges or at conceptual design works.     

Diseño óptimo robusto utilizando modelos Kriging: aplicación al diseño óptimo robusto de estructuras articuladas

Conventional methods addressing the robust design optimization problem of structures usually require high computational requirements due to the nesting of uncertainty quantification within the optimization process. In order to address such a problem, this work proposes a methodology, based on Kriging models, to efficiently assess the uncertainty quantification in the optimization process. The Kriging model approximates the structural performance both in the design domain and in the stochastic domain, which allows to decouple the uncertainty quantification process and the optimization process. In addition, an infill criterion based on the variance of the Kriging prediction is included to update the Kriging model towards the global Pareto front. Three numerical examples show the applicability and the accuracy of the proposed methodology. The results show that the proposed method is appropriate to solve the robust design optimization problem with reasonable accuracy and a considerably lower number of function calls than required by conventional methods.     

Entiers friables : inégalité de Turán–Kubilius et applications

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