Center Internacional Of Metodes Numerics En Enginyeria Cimne

Barcelona, Spain

Center Internacional Of Metodes Numerics En Enginyeria Cimne

Barcelona, Spain

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Avila M.,Center Internacional Of Metodes Numerics En Enginyeria Cimne | Principe J.,Polytechnic University of Catalonia | Codina R.,Polytechnic University of Catalonia
Journal of Computational Physics | Year: 2011

In this work we propose a variational multiscale finite element approximation of thermally coupled low speed flows. The physical model is described by the low Mach number equations, which are obtained as a limit of the compressible Navier-Stokes equations in the small Mach number regime. In contrast to the commonly used Boussinesq approximation, this model permits to take volumetric deformation into account. Although the former is more general than the latter, both systems have similar mathematical structure and their numerical approximation can suffer from the same type of instabilities.We propose a stabilized finite element approximation based on the variational multiscale method, in which a decomposition of the approximating space into a coarse scale resolvable part and a fine scale subgrid part is performed. Modeling the subscale and taking its effect on the coarse scale problem into account results in a stable formulation. The quality of the final approximation (accuracy, efficiency) depends on the particular model.The distinctive features of our approach are to consider the subscales as transient and to keep the scale splitting in all the nonlinear terms. The first ingredient permits to obtain an improved time discretization scheme (higher accuracy, better stability, no restrictions on the time step size). The second ingredient permits to prove global conservation properties. It also allows us to approach the problem of dealing with thermal turbulence from a strictly numerical point of view.Numerical tests show that nonlinear and dynamic subscales give more accurate solutions than classical stabilized methods. © 2011 Elsevier Inc.


Servan-Camas B.,Center Internacional Of Metodes Numerics En Enginyeria Cimne | Garcia-Espinosa J.,Center Internacional Of Metodes Numerics En Enginyeria Cimne | Garcia-Espinosa J.,Polytechnic University of Catalonia
Journal of Computational Physics | Year: 2013

Being capable of predicting seakeeping capabilities in the time domain is of great interest for the marine and offshore industries. However, most computer programs used work in the frequency domain, with the subsequent limitation in the accuracy of their model predictions. The main objective of this work is the development of a time domain solver based on the finite element method capable of solving multi-body seakeeping problems on unstructured meshes. In order to achieve this objective, several techniques are combined: the use of an efficient algorithm for the free surface boundary conditions, the use of deflated conjugate gradients, and the use of a graphic processing unit for speeding up the linear solver. The results obtained by the developed model showed good agreement with analytical solutions, experimental data for an actual offshore structure model, as well as numerical solutions obtained by other numerical method. Also, a simulation with sixteen floating bodies was carried out in an affordable CPU time, showing the potential of this approach for multi-body simulation. © 2013 Elsevier Inc.


Verdugo F.,Polytechnic University of Catalonia | Diez P.,Polytechnic University of Catalonia | Diez P.,Center Internacional Of Metodes Numerics En Enginyeria Cimne
Computer Methods in Applied Mechanics and Engineering | Year: 2012

This work presents a new technique yielding computable bounds of quantities of interest in the framework of linear visco-elastodynamics. A novel expression for the error representation is introduced, alternative to the previous ones using the Cauchy-Schwarz inequality. The proposed formulation utilizes symmetrized forms of the error equations to derive error bounds in terms of energy error measures. The practical implementation of the method is based on constructing admissible fields for both the original problem and the adjoint problem associated with the quantity of interest. Here, the flux-free technique is considered to compute the admissible stress fields. The proposed methodology yields estimates with better quality than the ones based on the Cauchy-Schwarz inequality. In the studied examples the bound gaps obtained are approximately halved, that is the estimated intervals of confidence are reduced. © 2012 Elsevier B.V..


Badia S.,Center Internacional Of Metodes Numerics En Enginyeria Cimne | Badia S.,Polytechnic University of Catalonia
Computer Methods in Applied Mechanics and Engineering | Year: 2012

In this work we propose a stabilized finite element method that permits us to circumvent discrete inf-sup conditions, e.g. allowing equal order interpolation. The type of method we propose belongs to the family of symmetric stabilization techniques, which are based on the introduction of additional terms that penalize the difference between some quantities, i.e. the pressure gradient in the Stokes problem, and their finite element projections. The key feature of the formulation we propose is the definition of the projection to be used, a non-standard Scott-Zhang projector that is well-defined for L 1(Ω) functions. The resulting method has some appealing features: the projector is local and nested meshes or enriched spaces are not required. © 2012 Elsevier B.V.


Verdugo F.,Polytechnic University of Catalonia | Pares N.,Polytechnic University of Catalonia | Diez P.,Polytechnic University of Catalonia | Diez P.,Center Internacional Of Metodes Numerics En Enginyeria Cimne
International Journal for Numerical Methods in Engineering | Year: 2013

This article presents a new approach to assess the error in specific quantities of interest in the framework of linear elastodynamics. In particular, a new type of quantities of interest (referred as timeline-dependent quantities) is proposed. These quantities are scalar time-dependent outputs of the transient solution, which are better suited to time-dependent problems than the standard scalar ones, frozen in time. The proposed methodology furnishes error estimates for both the standard scalar and the new timeline-dependent quantities of interest. The key ingredient is the modal-based approximation of the associated adjoint problems, which allows efficiently computing and storing the adjoint solution. The approximated adjoint solution is readily post-processed to produce an enhanced solution, requiring only one spatial post-process for each vibration mode and using the time-harmonic hypothesis to recover the time dependence. Thus, the proposed goal-oriented error estimate consists in injecting this enhanced adjoint solution into the residual of the direct problem. The resulting estimate is very well suited for transient dynamic simulations because the enhanced adjoint solution is computed before starting the forward time integration of the direct problem. Thus, the cost of the error estimate at each time step is very low. © 2013 John Wiley & Sons, Ltd.


Kouhi M.,Center Internacional Of Metodes Numerics En Enginyeria Cimne | Onate E.,Center Internacional Of Metodes Numerics En Enginyeria Cimne | Onate E.,Polytechnic University of Catalonia
Computational Mechanics | Year: 2015

A new implicit stabilized formulation for the numerical solution of the compressible Navier–Stokes equations is presented. The method is based on the finite calculus (FIC) scheme using the Galerkin finite element method (FEM) on triangular grids. Via the FIC formulation, two stabilization terms, called streamline term and transverse term, are added to the original conservation equations in the space-time domain. The non-linear system of equations resulting from the spatial discretization is solved implicitly using a damped Newton method benefiting from the exact Jacobian matrix. The matrix system is solved at each iteration with a preconditioned GMRES method. The efficiency of the proposed stabilization technique is checked out in the solution of 2D inviscid and laminar viscous flow problems where appropriate solutions are obtained especially near the boundary layer and shock waves. The work presented here can be considered as a follow up of a previous work of the authors Kouhi, Oñate (Int J Numer Methods Fluids 74:872–897, 2014). In that paper, the stabilized Galerkin FEM based on the FIC formulation was derived for the Euler equations together with an explicit scheme. In the present paper, the extension of this work to the Navier–Stokes equations using an implicit scheme is presented. © 2015, Springer-Verlag Berlin Heidelberg.


Perrigault T.,Center Internacional Of Metodes Numerics En Enginyeria Cimne | Weatherford V.,University of Colorado at Boulder | Marti-Herrero J.,Center Internacional Of Metodes Numerics En Enginyeria Cimne | Poggio D.,Instituto para una Alternativa Agraria IAA
Bioresource Technology | Year: 2012

A cold climate, low cost, tubular digester is monitored and temperatures from different parts of the slurry, greenhouse, and adobe walls are presented, discussing the thermal performance of the digester. The slurry exhibits a vertical gradient of 6. °C, with a mean value of 24.5. °C, while the ambient temperature varies from 10. °C to 30. °C, showing the efficiency of the system as a solar heat collector with thermal inertia. A simple time-dependent thermal model is developed using inputs of solar radiation, wind velocity, ambient temperature, and digester geometry. The model outputs include temperatures of the slurry, the biogas, its holding membrane and the greenhouse air, wall and cover. Radiative, convective and conductive heat transfer phenomena are considered between all system elements. The model has 0.47. °C (2%) standard error for the average slurry temperature. This model can be used to predict the influence of geometry and materials on the performance of the digester. © 2012 Elsevier Ltd.


Marti-Herrero J.,Center Internacional Of Metodes Numerics En Enginyeria Cimne | Cipriano J.,Center Internacional Of Metodes Numerics En Enginyeria Cimne
Bioresource Technology | Year: 2012

The aim of this paper is to present a novel, universal, methodology for the design of low cost tubular digesters. This method improves on the established methodology by avoiding assumptions that tend to reduce the final hydraulic retention time (HRT) of digesters once installed. This work recommends designing the digester using trench cross-sectional area and proposes an optimization of the trench dimensions with respect to the angle of the walls and the relationship between the length of the biogas bell and the top width of the trench. The influence of the biogas pressure is considered. A simple geometrical analysis is presented that, by parameterization, can be applied in a wide range of situations. © 2011 Elsevier Ltd.


Ryzhakov P.,Center Internacional Of Metodes Numerics En Enginyeria Cimne
Revista Internacional de Metodos Numericos para Calculo y Diseno en Ingenieria | Year: 2016

We propose a Lagrangian fluid formulation particularly suitable for fluid-structure interaction (FSI) simulation involving free-surface flows and light-weight structures. The technique combines the features of fractional step and quasi-incompressible approaches. The fractional momentum equation is modified so as to include an approximation for the current-step pressure using the assumption of quasi-incompressibility. The volumetric term in the tangent matrix is approximated allowing for the element-wise pressure condensation in the prediction step. The modified fractional momentum equation can be readily coupled with a structural code in a partitioned or monolithic fashion. The use of the quasi-incompressible prediction ensures convergent fluid-structure solution even for challenging cases when the densities of the fluid and the structure are similar. Once the prediction was obtained, the pressure Poisson equation and momentum correction equation are solved leading to a truly incompressible solution in the fluid domain except for the boundary where essential pressure boundary condition is prescribed. The paper concludes with two benchmark cases, highlighting the advantages of the method and comparing it with similar approaches proposed formerly. © 2015 CIMNE (Universitat Politècnica de Catalunya).


Danov S.,Center Internacional Of Metodes Numerics En Enginyeria Cimne | Carbonell J.,Center Internacional Of Metodes Numerics En Enginyeria Cimne | Cipriano J.,Center Internacional Of Metodes Numerics En Enginyeria Cimne | Marti-Herrero J.,Center Internacional Of Metodes Numerics En Enginyeria Cimne
Energy and Buildings | Year: 2013

A method for determining the total heat loss coefficient, the effective heat capacity and the net solar gain of a building is presented. The method uses a linear regressions approach based on daily energy consumption combined with readily available meteorological data. The effective heat capacity of the building is evaluated by correlating the energy consumption and outdoor temperature changes from the previous day. The net solar gain of the building is assessed by analysing the data separated into groups by amount of daily solar irradiation. Corrected total heat loss coefficient is determined by explicitly including in the building's energy balance the accumulated heat and the solar gain. The method has been applied to the analysis of nine public buildings in Spain. An improvement of the estimated heat loss coefficient due to the corrections is observed. The effective heat capacity normalised by the building area is shown to be a useful indicator of the building operation, detecting continuous or intermittent heating. The estimated parameters in this study can enable specific benchmarking, detecting opportunities for energy savings and evaluating their potential. With the increasing implementation of smart metering technologies, the method is promising for application to the analysis of large building stocks. © 2012 Elsevier B.V.

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