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• Cool steam method for desalinating seawater

  P. Arnau, N. Navarro, J. Soraluce, J. Martínez-Iglesias, J. Illas, E. Oñate

  Water (2019). Vol. 11 (11), 16 pp.

  
  

  Abstract

  Cool steam is an innovative distillation technology based on low-temperature thermal distillation (LTTD), which allows obtaining fresh water from non-safe water sources with substantially low energy consumption. LTTD consists of distilling at low temperatures by lowering the working pressure and making the most of low-grade heat sources (either natural or artificial) to evaporate water and then condensate it at a cooler heat sink. To perform the process, an external heat source is needed that provides the latent heat of evaporation and a temperature gradient to maintain the distillation cycle. Depending on the available temperature gradient, several stages can be implemented, leading to a multi-stage device. The cool steam device can thus be single or multi-stage, being raw water fed to every stage from the top and evaporated in contact with the warmer surface within the said stage. Acting as a heat carrier, the water vapor travels to the cooler surface and condensates in contact with it. The latent heat of condensation is then conducted through the conductive wall to the next stage. Net heat flux is then established from the heat source until the heat sink, allowing distilling water inside every parallel stage.

  Abstract
  Cool steam is an innovative distillation technology based on low-temperature thermal distillation (LTTD), which allows obtaining fresh water from non-safe water sources with [...]

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• PFEM formulation for thermo-coupled FSI analysis. Application to nuclear core melt accident

  A. Franci, E. Oñate, J. Carbonell, M. Chiumenti

  Comput. Methods Appl. Mech. Engrg., (2017). Vol. 325, pp. 711-732

  
  

  Abstract

  The aim of this paper is to present a Lagrangian formulation for thermo-coupled fluid–structure interaction (FSI) problems and to show its applicability to the simulation of hypothetical scenarios of a nuclear core melt accident. During this emergency situation, an extremely hot and radioactive lava-like material, the corium, is generated by the melting of the fuel assembly. The corium may induce collapse of the nuclear reactor devices and, in the worst case, breach the reactor containment and escape into the environment. This work shows the capabilities of the proposed formulation to reproduce the structural failure mechanisms induced by the corium that may occur during a meltdown scenario. For this purpose, a monolithic method for FSI problems, the so-called Unified formulation, is here enhanced in order to account for the thermal field and to model phase change phenomena with the Particle Finite Element Method (PFEM). Several numerical examples are presented. First, the convergence of the thermo-coupled method and phase change algorithm is shown for two academic problems. Then, two complex simulations of hypothetical nuclear meltdown situations are studied in 2D as in 3D.

  Abstract
  The aim of this paper is to present a Lagrangian formulation for thermo-coupled fluid–structure interaction (FSI) problems and to show its applicability [...]

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• A FIC-based stabilized finite element formulation for turbulent flows

  J. Cotela-Dalmau, R. Rossi, E. Oñate

  Comput. Methods Appl. Mech. Engrg., (2017). (preprint) Vol. 315, pp. 607-631

  
  

  Abstract

  We present a new stabilized finite element (FEM) formulation for incompressible flows based on the Finite Increment Calculus (FIC) framework (Oñate, 1998). In comparison to existing FIC approaches for fluids, this formulation involves a new term in the momentum equation, which introduces non-isotropic dissipation in the direction of velocity gradients. We also follow a new approach to the derivation of the stabilized mass equation, inspired by recent developments for quasi-incompressible flows (Oñate et al., 2014). The presented FIC-FEM formulation is used to simulate turbulent flows, using the dissipation introduced by the method to account for turbulent dissipation in the style of implicit large eddy simulation.

  Abstract
  We present a new stabilized finite element (FEM) formulation for incompressible flows based on the Finite Increment Calculus (FIC) framework (Oñate, [...]

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• A shallow water model by finite point method

  C. Bouchart, W. Kanok-Nukulschai, E. Ortega, E. Oñate

  International Journal of Computational Methods (2014). Vol. 11 (1), 27 pp., Paper N: 1350047

  
  

  Abstract

  In this paper, "finite point method" (FPM) is presented for modeling 2D shallow water flow problem. The method is based on the use of a weighted least-square approximation procedure, incorporating QR factorization and an iterative adjustment of local approximation parameters. The stabilization of the convective term in this present work is derived from the approximate Riemann solver proposed by Roe. The present method is shown to produce competitive accuracy in the comparisons with the analytical solutions and the well-known Galerkin characteristic-based split (CBS) algorithm.

  Abstract
  In this paper, "finite point method" (FPM) is presented for modeling 2D shallow water flow problem. The method is based on the use of a weighted least-square approximation [...]

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• Advances in the development of a FEM model for evaluation of a Surface-Effect Ship (SES) including skirt dynamics

  J. García-Espinosa, B. Camas, D. Di Capua, P. Ubach de Fuentes, E. Oñate

  Ingeniería Naval (2013). Vol. 1 (920), pp. 68-91

  
  

  Abstract

  El “Innovative Naval Prototype Transformable Craft” (T-Craft) es un nuevo concepto de buque desarrollado por la marina de los Estados Unidos de América para la conexión de una base en alta mar con tierra. El TCraft puede operar en múltiple modos, usándose para conectar una base intermedia de soporte con la principal, y luego ser utilizado como conexión de alta velocidad con la costa, transportando vehículos y otros equipos y carga pesada hasta la playa. El T-Craft se ha concebido como un buque de efecto superficie (Surface-Effect Ship, SES) con un colchón de aire activo entre dos cascos rígidos, que permite al buque operar a desplazamiento completo, con soporte parcial del colchón o con el colchón plenamente activo. Este artículo presenta el trabajo reciente de los autores en el desarrollo de un modelo de evaluación del comportamiento en la mar y la maniobrabilidad del T-Craft, incluyendo la interacción del faldón. Este modelo está basado en la resolución de las ecuaciones de flujo potencial en el dominio del tiempo, mediante el método de los elementos finitos, integrando la superficie libre a lo largo de las líneas de corriente. Este artículo revisa el algoritmo de interacción fluido estructura desarrollado para la simulación de la compleja dinámica de los sellos, en la interfaz entre el colchón de aire y el agua. El algoritmo se basa, por una parte, en un algoritmo explícito alternado que permite la comunicación entre los solvers fluido-dinámico y estructural mediante TCP-IP sockets, intercambiando fuerzas de presión y desplazamientos en los sellos durante la ejecución, y por otra parte, en un innovador esquema de secado-mojado que permite predecir la interacción del agua con los sellos. Se incluyen varios casos de aplicación de la metodología desarrollada sobre el modelo l XR-1B.

  Abstract
  El “Innovative Naval Prototype Transformable Craft” (T-Craft) es un nuevo concepto de buque desarrollado por la marina de los Estados Unidos de América [...]

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• Analysis of the melting, burning and flame spread of polymers with the particle finite element method

  E. Oñate, J. Marti, P. Ryzhakov, R. Rossi, S. Idelsohn

  Computer Assisted Methods in Engineering and Sciences (2013). Vol. 20 (3), pp. 165-184

  
  

  Abstract

  A computational procedure for analysis of the melting, burning and flame spread of polymers under fire conditions is presented. The method, termed particle finite element method (PFEM), combines concepts from particle-based techniques with those of the standard finite element method (FEM). The key feature of the PFEM is the use of an updated Lagrangian description to model the motion of nodes (particles) in the thermoplastic material. Nodes are viewed as material points which can freely move and even separate from the main analysis domain representing, for instance, the effect of melting and dripping of polymer particles. A mesh connects the nodes defining the discretized domain where the governing equations are solved using the FEM. An incremental iterative scheme for the solution of the nonlinear transient coupled thermal-flow problem, including radiation, loss of mass by gasification and combustion is used. Examples of the possibilities of the PFEM for the modelling and simulation of the melting, burning and flame spread of polymers under different fire conditions are described.

  Abstract
  A computational procedure for analysis of the melting, burning and flame spread of polymers under fire conditions is presented. The method, termed particle finite element [...]

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• Analysis of the discharge capacity of radial-gated spillways using CFD and ANN – Oliana Dam case study

  F. Salazar, R. Morán Moya, R. Rossi, E. Oñate

  Journal of Hydraulic Research (2013). (preprint) Vol. 51 (3), pp. 244-252

  
  

  Abstract

  The paper focuses on the analysis of radial-gated spillways, which is carried out by the solution of a numerical model based on the finite element method (FEM). The Oliana Dam is considered as a case study and the discharge capacity is predicted both by the application of a level-set-based free-surface solver and by the use of traditional empirical formulations. The results of the analysis are then used for training an artificial neural network to allow real-time predictions of the discharge in any situation of energy head and gate opening within the operation range of the reservoir. The comparison of the results obtained with the different methods shows that numerical models such as the FEM can be useful as a predictive tool for the analysis of the hydraulic performance of radial-gated spillways.

  Abstract
  The paper focuses on the analysis of radial-gated spillways, which is carried out by the solution of a numerical model based on the finite element method (FEM). The Oliana [...]

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• Olgierd Cecil Zienkiewicz obituary

  M. Kleiber, E. Oñate

  Archives of Comp. Meths. Engng. (2009). Vol. 16, pp. 465

  
  

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• Control of the finite element discretization error during the convergence of structural shape optimization algorithms

  G. Bugeda, J. Ródenas, J. Albelda, E. Oñate

  Int. J. Simul. Multidisci. Des. Optim. (2009). Vol. 3 (3), pp. 363-369

  
  

  Abstract

  This work analyzes the influence of the discretization error contained in the Finite Element (FE) analyses of each design configuration proposed by structural shape optimization algorithms over the behaviour of the algorithm. If the FE analyses are not accurate enough, the final solution 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 also proposes the use of the algorithm described in [1] in order to reduce the computational cost associated to the adaptive FE analysis of each geometrical configuration when evolutive optimization algorithms are used.

  Abstract
  This work analyzes the influence of the discretization error contained in the Finite Element (FE) analyses of each design configuration proposed by structural shape optimization [...]

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• Advances in the particle finite element method for fluid-structure interaction problems

  E. Oñate, S. Idelsohn, M. Celigueta, R. Rossi

  Computational Mechanics (2006). Vol. 6, pp. 41-62

  
  

  Abstract

  We present a general formulation for analysis of fluid-structure interaction problems using the particle finite element method (PFEM). The key feature of the PFEM is the use of a Lagrangian description to model the motion of nodes (particles) in both the fluid and the structure domains. Nodes are thus viewed as particles which can freely move and even separate from the main analysis domain representing, for instance, the effect of water drops. A mesh connects the nodes defining the discretized domain where the governing equations, expressed in an integral from, are solved as in the standard FEM. The necessary stabilization for dealing with the incompressibility of the fluid is introduced via the finite calculus (FIC) method. A fractional step scheme for the transient coupled fluid-structure solution is described. Examples of application of the PFEM to solve a number of fluid-structure interaction problems involving large motions of the free surface and splashing of waves are presented.

  Abstract
  We present a general formulation for analysis of fluid-structure interaction problems using the particle finite element method (PFEM). The key feature of the PFEM is the use [...]

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