Documents published in Scipedia

• Finite Elements in mixed least-squares formulation for simulating transient convection-diffusion

  V. Ruas, R. Leal-Toledo, M. Kischinhevsky

  Revista Internacional de Métodos Numéricos para Cálculo y Diseño en Ingeniería (2017). Vol. 33, (1)

  
  

  Abstract

  A mixed least-squares finite element scheme designed for solving the transient convection-diffusion equations expressed in terms of both the primal unknown and its flux, incorporating or not a reaction term, is studied. Once a time discretization of the Crank-Nicholson type is performed, the resulting system of equations allows for a stable approximation of both fields, by means of classical Lagrange continuous piecewise polynomial functions of arbitrary degree, in both simplicial and non-simplicial geometry, in any space dimension. The scheme is also convergent in space in the mean-square sense as far as the primal unknown field, its gradient, the flux variable and its divergence are concerned, and in time in an appropriate sense for each one of these four fields. Numerical results certify that the scheme performs well for any Péclet number, thereby allowing to confirm theoretical predictions, at least in the case where there is no narrow boundary layer. In the latter case however the method fails to produce reliable results. The technique is also compared with three existing methods to solve the convection-diffusion equations in the transient case. These include two recent ones proposed by the first author and collaborators.

  Abstract
  A mixed least-squares finite element scheme designed for solving the transient convection-diffusion equations expressed in terms of both the primal unknown and its flux, incorporating [...]

  • 0
  •  read

• Discrete neural compensator algorithm of dynamic in mobile robots using extended Kalman filter

  F. Rossomando, C. Soria, R. Carelli

  Revista Internacional de Métodos Numéricos para Cálculo y Diseño en Ingeniería (2017). Vol. 33, (1)

  
  

  Abstract

  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.

  Abstract
  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 [...]

  • 0
  •  read

• Application of an evolutionary algorithm for optimizing the computational modeling of materials pyrolysis

  E. Puente, M. Lázaro, O. Abreu, J. Capote, D. Alvear

  Revista Internacional de Métodos Numéricos para Cálculo y Diseño en Ingeniería (2017). Vol. 33, (1)

  
  

  Abstract

  The pyrolysis models undergoes a fast development due to the enhancement of both the computational power and the new test used to characterize the behaviour of materials under thermal stresses, which were widely used in the field of the chemical engineering to obtain the reaction rates. Thus, these models allow us to characterize either the transient heat of material (thermal inertia) or the complete chemical scheme of mass loss processes (kinetic triplet). The pyrolysis model needs a several number of parameters what does the optimization of a suitable set of parameters a difficult task. Two kinds of materials have been investigated, the first one was a real material which mass loss process was characterized as “one-step” reaction and the second one as a “two-steps” process. Further, it has been analyzed the influence of some algorithm features (initial population number, parameter range, crossover influence) in the optimization time and also in the accuracy of results.

  Abstract
  The pyrolysis models undergoes a fast development due to the enhancement of both the computational power and the new test used to characterize the behaviour of materials under [...]

  • 0
  •  read

• Numerical modeling of FSW welding process incorporating a parameter estimation technique

  S. Pereyra, G. Lombera, S. Urquiza

  Revista Internacional de Métodos Numéricos para Cálculo y Diseño en Ingeniería (2014). Vol. 30, (1)

  
  

  Abstract

  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.

  Abstract
  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, [...]

  • 0
  •  read

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

  J. París, S. Martínez, X. Nogueira, I. Colominas, F. Navarrina, M. Casteleiro

  Revista Internacional de Métodos Numéricos para Cálculo y Diseño en Ingeniería (2015). Vol. 31, (1)

  
  

  Abstract

  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.

  Abstract
  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: [...]

  • 0
  •  read

• A predictive evolution model of rocky coasts

  C. Paredes, R. Castedo, M. Llorente, L. Laín

  Revista Internacional de Métodos Numéricos para Cálculo y Diseño en Ingeniería (2013). Vol. 29, (1)

  
  

  Abstract

  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.

  Abstract
  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 [...]

  • 0
  •  read

• Application of computational methods in the assessment of the aeroelastic response of cable supported bridges

  F. Nieto, J. Jurado, S. Hernández, I. Kusano

  Revista Internacional de Métodos Numéricos para Cálculo y Diseño en Ingeniería (2017).

  
  

  Abstract

  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.

  Abstract
  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 [...]

  • 0
  •  read

• On the use of Cartesian grid finite element code in structural optimization

  E. Nadal, J. Ródenas, E. Sánchez-Orgaz, S. López-Real, J. Martí-Pellicer

  Revista Internacional de Métodos Numéricos para Cálculo y Diseño en Ingeniería (2017).

  
  

  • 0
  •  read

• Analysis of laminated beams using the natural neighbour radial point interpolation method

  S. Moreira, J. Belinha, L. Dinis, R. Jorge

  Revista Internacional de Métodos Numéricos para Cálculo y Diseño en Ingeniería (2017).

  
  

  Abstract

  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.

  Abstract
  In this work, a meshless method, “natural neighbour radial point interpolation method” (NNRPIM), is applied to the one‐dimensional analysis of laminated beams, considering [...]

  • 0
  •  read

• The concept hyperbeam as generalization of 1-dimensional models in rod elastostatics

  S. Monleón, C. Lázaro

  Revista Internacional de Métodos Numéricos para Cálculo y Diseño en Ingeniería (2017).

  
  

  Abstract

  This paper is concerned with the general formulation of linear problems in rod elastostatics, and with the identification of their common formal and structural features, valid for every kinematical hypothesis. The generalized variables (section forces and generalized deformations) defining the 1-dimensional model are introduced in a consistent and natural way, through a convenient factorization of the density of complementary potential energy, for every kinematical constraint which can be expressed as a linear combination of the generalized displacements. The identification of this complementary energy function with the Hamiltonian functional of analytical mechanics allows a systematic procedure to construct the equations which rule this class of problems. In this frame, the main target is to establish the required conditions to write the rod equilibrium equations in a purely statical form (with no interplay of kinematical variables). We primarily conclude that this is possible when the kinematics of the cross-sections is constrained to a rigid body movement. As a consequence, the concept of hyperbeam is proposed in order to define those models with deformation modes beyond rigid body movements of the cross section: in them, section forces and generalized displacements are coupled in the equilibrium equations. This is related to the idea of local static indeterminacy (hyperstaticity ) and justifies the new name.

  Abstract
  This paper is concerned with the general formulation of linear problems in rod elastostatics, and with the identification of their common formal and structural features, valid [...]

  • 0
  •  read