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• Elastoplastic Analysis of Framed Structures with Interaction Surfaces Obtained for Multiple Linear Regression

  P. Vieira, W. Silva

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

  
  

  Abstract

  The ultimate limit state criteria (yielding surfaces) applied to structural designs are easier in stress resultants. There are many difficulties to generating interaction surfaces with six sectional efforts obtained through to numerical or experimental models of a space-frame analysis. The approach, in the literature, to nonlinear analysis of structures with 3D beams is use of interaction surfaces with only three combined efforts in the cross-section. Therefore, a better understanding of load types, of interactions between the six efforts and of local and global stability of structure are necessary. The interaction surfaces with three efforts are presented in planes, quadrics, more complex, or a mixture of them shapes, so that techniques which use analytical formulations with combined efforts and several section shapes are more or less complex. Multiple linear regression allows to treat the resultant efforts of several analyses for obtaining a yielding surface with the combined efforts. In this paper, the formulation to obtaining of the surfaces and their applications in the analysis of elasto-plastic frame structures are presented.

  Abstract
  The ultimate limit state criteria (yielding surfaces) applied to structural designs are easier in stress resultants. There are many difficulties to generating interaction [...]

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

  F. Villegas, S. Gutiérrez

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

  
  

  Abstract

  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.

  Abstract
  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 [...]

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• Stability and dispersion of the problem of seismic wave propagation in 2-D using the generalized finite difference method

  F. Prieto, J. Muñoz, L. Corvinos, E. Casino, Á. Acevedo

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

  
  

  Abstract

  This paper shows the solution to the problem of seismic wave propagation in 2-D using generalized finite difference (GFD) explicit schemes. Regular and irregular meshes can be used with this method. As we are using an explicit method, it is necessary to obtain the stability condition by using the von Neumann analysis. We also obtained the star dispersion formulas for the phase velocities for the P and S waves, as well as the ones for the group velocities. As the control over the irregularity in the mesh is very important in the application of this method, we have defined an index of irregularity for the star (IIS) and another for the cloud (IIC), analyzing its relationship with the dispersion and time step used in the calculations.

  Abstract
  This paper shows the solution to the problem of seismic wave propagation in 2-D using generalized finite difference (GFD) explicit schemes. Regular and irregular meshes can [...]

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

  M. Toledo, R. Morán, H. Campos

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

  
  

  Abstract

  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.

  Abstract
  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 [...]

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• Efficient calculation of formation energies of kink-pairs in BCC crystals

  E. Tellechea, O. Sabri, M. Ariza

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

  
  

  Abstract

  Motion of screw dislocations in BCC materials at low temperature is believed to be related to the formation of mobile kinks on the dislocation line. Therefore, the accurate prediction of kink nucleation energies is required to fully describe mobility of screw dislocations in these materials. Studies of fundamental dislocation processes at atomic length scale are numerically and computationally intensive problems. This work studies the calculation of zero-stress formation energies of kink-pair configurations for BCC crystals. Our model for stored energy associated to a dislocation line configuration is based on the theory of discrete dislocations of Ariza and Ortiz. Its value is computed efficiently using an algorithm developed on the NVIDIA Compute Unified Device Architecture (CUDA). Results confirm those obtained using atomistic potentials and first principles calculations, and those based on the continuum theory of dislocations.

  Abstract
  Motion of screw dislocations in BCC materials at low temperature is believed to be related to the formation of mobile kinks on the dislocation line. Therefore, the accurate [...]

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• Boundary conditions for gradient-enhanced models with smoothed displacements

  E. Tamayo-Mas, A. Rodríguez-Ferran

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

  
  

  Abstract

  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.

  Abstract
  Gradient-enhanced models based on regularised displacements are an alternative to standard models in order to simulate material failure. In this alternative formulation, mechanical [...]

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• Mandibular advancement devices in the treatment of obstructive sleep apnea syndrome

  E. Soudah, M. Bordone, A. Álvarez, J. Cobo, F. Carlos, B. Suarez

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

  
  

  Abstract

  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.

  Abstract
  Obstructive sleep apnea syndrome (OSAS) consists in the occurrence of recurrent episodes of airflow limitation during sleep, with undesirable consequences for the health. [...]

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• Comparasion of unidimensional and bidimensional flow models for earthen dam failures

  J. Soler, E. Bladé, M. Sánchez-Juny

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

  
  

  Abstract

  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.

  Abstract
  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 [...]

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• An algorithm for the design of a feedforward controller in canals

  J. Soler, M. Gómez, J. Rodellar

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

  
  

  Abstract

  When it is carried out any movement of a gate or another mechanism of control of a canal in free surface flow, an answer of the flow can take a lot of time in being noticed in the place of the canal takes place in which it was generated the necessity to increase or to reduce the irrigation demand, for example. Usually, the scheduled perturbations of the flow can be programmed for a future horizon. In this manner, the control action can also be programmed. This work, it shows a feedforward control algorithm that plans the gate trajectories when the demand at offtakes are programmed in a prediction horizon. The Hydraulic Influence Matrix (HIM) or matrix of sensibility of the hydrodynamic conditions in the canals to changes in the parameters of the gate trajectories is a tool that is shown very effective in the control of canals in open loop. The work defines the concept, it presents the form of to calculate and to compile the HIM starting from the complete equations of Saint-Venant in their characteristic form. Later on, it shows up an algorithm in that HIM is used: a feedforward controller algorithm so-called GoRoSo. Known the water demands at offtakes, the algorithm calculates the optimal gate trajectories in advance for a prediction horizon with the objective of keeping constant the water depth at gravity offtakes.

  Abstract
  When it is carried out any movement of a gate or another mechanism of control of a canal in free surface flow, an answer of the flow can take a lot of time in being noticed [...]

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

  F. Salazar, E. Oñate, R. Morán

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

  
  

  Abstract

  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.

  Abstract
  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 [...]

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