JOURNALS

Documents published in Scipedia

• Validation of the particle finite element method (PFEM) for simulation of rock slides in lakes and reservoirs

  J. Irazábal, F. Salazar, E. Oñate

  (2012). Research Report, Nº PI390

  
  

  Abstract

  The analysis of landslides in reservoirs is particularly interesting because the oscillation of the water surface elevation (especially rapid drawdowns) can foster their occurrence. The existence of the reservoir for a long enough time makes the material of the slopes turn saturated, thus its pore pressure raises and, as a consequence, its effective stress is reduced. This unstabilizing effect is partially compensated by the raise of total stress due to hydrostatic pressure generated by the water in the reservoir. A rapid drawdown eliminates the stabilization in a lapse which is frequently not enough for the pore pressure to be dissipated (this depends on the permeability of the material as well as on the velocity of the water level drop, but is quite frequent). In this situation, the probability of occurrence of a landslide is greater. In this report some validation cases are described, where the impact of sliding blocks against a mass of water is simulated, as well as the generation and propagation of the subsequent impulse wave. They are based on the experiments performed by Sælevik et al. [21].

  Abstract
  The analysis of landslides in reservoirs is particularly interesting because the oscillation of the water surface elevation (especially rapid drawdowns) can foster their occurrence. [...]

  • 40
  •  read

• On the arc length method: combining ideas and implementations aspects

  N. Lafontaine, X. Wang, K. Huang, M. Yuan, E. Oñate

  (2013). Research Report, Nº PI399

  
  

  Abstract

  In this work we introduced and implemented the AL method in NOLM program. Basically the actual implementation in NOLM is based in the work proposed by Lam and Morley (1992) and was coded with take into account the sign for no tracking back the solution. An ecient method was included for avoid complex roots and if the problem persist, two method is available to get the convergence. In case of no convergence is reached, we introduce a user factor, for reducing the arc-length, that should be taken betweens (0:5 - 0:75) per cent of the actual arc length. A linear truss-element, together to the isotropic smeared crack model was introduced for testing and benchmarking the AL method . During the work, we found several diculties to converge in the standard constitutive law implemented in NOLM when a softening parameter was introduced. It is caused by the no mechanical dissipation in the model. However, for a perfect plastic an hardening they get the corresponding results. All meshing process and post-processing was made with Gid[4], proving that it is possible to connect the developed owner software and this Pre-and post processing program.

  Abstract
  In this work we introduced and implemented the AL method in NOLM program. Basically the actual implementation in NOLM is based in the work proposed by Lam and Morley (1992) [...]

  • 2612
  •  read

• Updated Lagrangian mixed finite element formulation for quasi and fully incompressible fluids

  E. Oñate, J. Carbonell

  (2013). Research Report, Nº PI393

  
  

  Abstract

  We present a mixed velocity-pressure finite element formulation for solving the updated Lagrangian equations for quasi and fully incompressible fluids. Details of the governing equations for the conservation of momentum and mass are given in both differential and variational form. The finite element interpolation uses an equal order approximation for the velocity and pressure unknowns. The procedure for obtaining stabilized FEM solutions is outlined. The solution in time of the discretized governing conservation equations using an incremental iterative segregated scheme is described. The linearization of these equations and the derivation of the corresponding tangent stiffness matrices is detailed. Other iterative schemes for the direct computation of the nodal velocities and pressures at the updated configuration are presented. The advantages and disadvantages of choosing the current or the updated configuration as the reference configuration in the Lagrangian formulation are discussed.

  Abstract
  We present a mixed velocity-pressure finite element formulation for solving the updated Lagrangian equations for quasi and fully incompressible fluids. Details of the governing [...]

  • 217
  •  read

• Lagrangian formulation for finite element analysis of quasi-incompressible fluids with reduced mass losses

  E. Oñate, A. Franci, J. Puigbó

  Int. J. for Numerical Methods in Fluids (2014). Vol. 74 pp. 699-731 Vol. 74 pp. 699-731 (preprint)

  
  

  Abstract

  We present a Lagrangian formulation for finite element analysis of quasi-incompressible fluids that has excellent mass preservation features. The success of the formulation lays on a new residual-based stabilized expression of the mass balance equation obtained using the Finite Calculus (FIC) method. The governing equations are discretized with the FEM using simplicial elements with equal linear interpolation for the velocities and the pressure. The merits of the formulation in terms of reduced mass loss and overall accuracy are verified in the solution of 2D and 3D quasi-incompressible free-surface flow problems using the Particle Finite Element Method (PFEM, www.cimne.com/pfem). Examples include the sloshing of water in a tank, the collapse of one and two water columns in rectangular and prismatic tanks and the falling of a water sphere into a cylindrical tank containing water. Copyright c 0000 John Wiley & Sons, Ltd.

  Abstract
  We present a Lagrangian formulation for finite element analysis of quasi-incompressible fluids that has excellent mass preservation features. The success of the formulation [...]

  • 66
  •  read

• Computational fluid dynamics indicators to improve cardiovascular pathologies diagnosis

  E. Soudah, E. Oñate, M. Cervera

  Monograph CIMNE (2016). M167

  
  

  Abstract

  In recent years, the study of computational hemodynamics within anatomically complex vascular regions has generated great interest among clinicians. The progress in computational fluid dynamics, image processing and high-performance computing have allowed us to identify the candidate vascular regions for the appearance of cardiovascular diseases and to predict how this disease may evolve. In this monograph we attempt to introduce into medicine the computational predictive paradigm that has been used in engineering for many years. Several groups have tried to create predictive models for cardiovascular pathologies, but they have not yet begun to use them in clinical practice. Our final aim is to go further and obtain predictive variables to be used in the clinical field. We try to predict the evolution of aortic abdominal aneurysm, aortic coarctation and coronary artery disease in a personalized way for each patient. We propose diagnostic indicators that can improve the diagnosis and predict the evolution of the disease more efficiently than the methods used until now. In particular, a new methodology for computing diagnostic indicators based on computational hemodynamics and medical imaging is proposed. We have worked with data of anonymous patients to create real predictive technology that will allow us to continue advancing in personalized medicine and generate a more sustainable health systems. The objective of this monograph is therefore to develop predictive models for cardiovascular pathologies by merging medical imaging and computational techniques at a clinical level. It is expected in the near future that larger databases of patient-specific computational models will be available to doctors. These data can be used with predictive models to improve diagnosis and to define personalized therapies and treatments.

  Abstract
  In recent years, the study of computational hemodynamics within anatomically complex vascular regions has generated great interest among clinicians. The progress in computational [...]

  • 782
  •  read

• Development of new computational methods for fluid-structure interaction analysis of multi-fractured media

  I. Pouplana, E. Oñate

  Monograph CIMNE (2018). M177

  
  

  Abstract

  The objective of this monograph is the derivation and implementation of a robust Finite Element formulation for the solution of solid-pore fluid coupled problems in multi-fractured porous media. A coupled displacement-pore pressure FEM formulation for solving solid-pore fluid interaction problems is first introduced. The interaction between both components is governed by two equations: the balance of momentum for the mixture solid-fluid and the mass balance for the pore fluid. Under nearly undrained-incompressible conditions, such formulation suffers from instability problems because of the violation of Babuska-Brezzi conditions. In order to work with elements of equal order interpolation for the displacement and pore pressure, the formulation is stabilized by means of the Finite Increment Calculus method (FIC). The FIC-stabilized formulation is tested against stable elements with a higher order interpolation for the displacement field in 2D and 3D examples. Continuum damage mechanics is the basis of the crack growth strategy for the proposed fracture propagation technique. The strain softening models used for quasi-brittle materials favour spurious strain localization and ill-posedness of the boundary value problem if the damage variable only depends on the strain state at the point under consideration. An integral-type non-local damage model associated to a characteristic length parameter is presented as a method to control the size of the fracture process zone and fully regularize the problem. Two examples are solved assessing the robustness of the model in front of changes in the spatial discretization. Quasi-zero-thickness interface elements are formulated to represent discontinuities in the porous domain. A bilinear cohesive fracture model is used to describe its mechanical behaviour, and a formulation derived from the cubic law models the fluid flow through the crack. Finally, a new methodology for the simulation of fracture propagation processes in saturated porous media is presented. The non-local damage model is used in conjunction with the interface elements to predict the degradation pattern of the domain and insert new fractures followed by remeshing. Fluid-driven fracture propagation examples in 2D and 3D are presented to illustrate the accuracy of the proposed technique.  

  Abstract
  The objective of this monograph is the derivation and implementation of a robust Finite Element formulation for the solution of solid-pore fluid coupled problems in multi-fractured [...]

  • 110
  •  read

• Analysis of the discharge capacity of radial gated spillways using numerical modelling application to Oliana dam

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

  (2011). Research Report, Nº PI369

  
  

  Abstract

  Current paper focuses on the analysis of radial gated spillways, which are analyzed by the solution of a numerical model. The Oliana Dam study case is considered 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 in training an Artificial Neural Network so 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 can be useful as a predictive tool for the analysis of the hydraulic performance of radial-gated spillways, and highlights some drawbacks regarding the application of the empirical formulas.

  Abstract
  Current paper focuses on the analysis of radial gated spillways, which are analyzed by the solution of a numerical model. The Oliana Dam study case is considered and the discharge [...]

  • 30
  •  read

• Advances in the DEM and coupled DEM and FEM techniques in non linear solid mechanics

  E. Oñate, F. Zarate, M. Celigueta, J. González, J. Miquel, J. Puigbó, F. Arrufat, S. Latorre, M. Santasusana

  Eugenio Oñate's Research Reports (2019).

  
  

  Abstract

  In this chapter we present recent advances in the Discrete Element Method (DEM) and in the coupling of the DEM with the Finite Element Method (FEM) for solving a variety of problems in non linear solid mechanics involving damage, plasticity and multifracture situations.

  Abstract
  In this chapter we present recent advances in the Discrete Element Method (DEM) and in the coupling of the DEM with the Finite Element Method (FEM) for solving a variety of [...]

  • 51
  •  read

• A stabilized finite element formulation for high‐speed inviscid compressible flows using finite calculus

  M. Kouhi, E. Oñate

  Int. J. Numer. Meth. Engng. (2014). Vol. 74(2) pp. 872-897

  
  

  Abstract

  This paper aims at the development of a new stabilization formulation based on the Finite Calculus (FIC) scheme for solving the Euler equations using the Galerkin finite element method (FEM) on unstructured triangular grids. The FIC method is based on expressing the balance of fluxes in a space-time domain of finite size. It is used to prevent the creation of instabilities typically present in numerical solutions due to the high convective terms and sharp gradients. Two stabilization terms, respectively called streamline term and transverse term, are added via the FIC formulation to the original conservative equations in the spacetime domain. An explicit fourth order Runge-Kutta scheme is implemented to advance the solution in time. The presented numerical test examples for inviscid flows prove the ability of the proposed stabilization technique for providing appropriate solutions especially near shock waves. Although the derived methodology delivers precise results with a nearly coarse mesh, a mesh refinement technique is coupled to the solution process for obtaining a suitable mesh particularly in the high gradient zones.

  Abstract
  This paper aims at the development of a new stabilization formulation based on the Finite Calculus (FIC) scheme for solving the Euler equations using the Galerkin finite element [...]

  • 37
  •  read

• Simple and efficient numerical tools for the analysis of parachutes

  R. Flores, E. Ortega, E. Oñate

  Engineering Computations (2014). Vol. 31(5) pp. 957-985

  
  

  Abstract

  This work describes a set of simple yet effective, numerical method for the design and evaluation of parachute-payload system. The developments include a coupled fluidstructural solver for unsteady simulations of ram-air type parachutes. For an efficient solution of the aerodynamic problem, an unsteady panel method has been chosen exploiting the fact that large areas of separated flow are not expected under nominal flight conditions of ram-air parachutes. A dynamic explicit finite element solver is used for the structure. This approach yields a robust solution even when highly non-linear effects due to large displacements and material response are present. The numerical results show considerable accuracy and robustness. An added benefit of the proposed aerodynamic and structural techniques is that they can be easily vectored and thus suitable for use in parallel architectures. The main features of the computational tools are described and several numerical examples are provided to illustrate the performance and capabilities of the technique.

  Abstract
  This work describes a set of simple yet effective, numerical method for the design and evaluation of parachute-payload system. The developments include a coupled fluidstructural [...]

  • 76
  •  read