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• El laboratorio de ensayo de estructuras en modelo reducido de la Escuela de Ingenieros de Caminos de Barcelona

  J. Oliver, B. Suárez, E. Blanco, E. Oñate

  Acero y Hormigón (1982). Vol. 145, pp. 65-78

  
  

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• PFEM–DEM for particle-laden flows with free surface

  A. Franci, I. de-Pouplana, G. Casas, M. Celigueta, J. González-Usúa, E. Oñate

  Computational Particle Mechanics (2020). Vol. 7, pp. 101-120

  
  

  Abstract

  This work proposes a fully Lagrangian formulation for the numerical modeling of free-surface particle-laden flows. The fluid phase is solved using the particle finite element method (PFEM), while the solid particles embedded in the fluid are modeled with the discrete element method (DEM). The coupling between the implicit PFEM and the explicit DEM is performed through a sub-stepping staggered scheme. This work only considers suspended spherical particles that are assumed not to affect the fluid motion. Several tests are presented to validate the formulation. The PFEM–DEM results show very good agreement with analytical solutions, laboratory tests and numerical results from alternative numerical methods.

  Abstract
  This work proposes a fully Lagrangian formulation for the numerical modeling of free-surface particle-laden flows. The fluid phase is solved using the particle finite element [...]

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• A bonded discrete element method for modeling ship–ice interactions in broken and unbroken sea ice fields

  O. Jou Devesa, M. Celigueta, S. Latorre, F. Arrufat, E. Oñate

  Computational Particle Mechanics (2019). Vol. 6 (4), pp 739–765

  
  

  Abstract

  This work investigates the failure patterns of ice cakes and floe-icewhen loaded by amoving and sloping structure (ice-breaking ships and cones). In the paper, we introduce the most frequently encountered ice infested scenarios, the main characteristics of ice-breaking ships and the predicted failure modes of floe-ice depending on the loading conditions, the structure type and the ice feature dimensions and thickness. For the simulations, a local bonded discrete element method (DEM) is used to model sea ice and its fractures. The packing of bonded spherical particles which reproduce the ice continuum can break due to ship–ice interactions and the failure modes are studied. A set of validation simulations are first carried out. A level ice sheet breaking against an installed ice-breaking cone with different slope angles is studied, and the results are compared with other DEM simulations. Then, a group of bonded DEM simulations are performed to predict the different failure modes produced when an ice-breaking ship bow contacts with ice cakes and floe-ice of different dimensions and thickness, typical in broken ice fields. Finally, the study of breaking a continuous level ice sheet is carried out by modeling with the bonded DEM an “infinite” large domain of sea ice and loaded by a single-degree-of-freedom model of an ice-breaking ship.

  Abstract
  This work investigates the failure patterns of ice cakes and floe-icewhen loaded by amoving and sloping structure (ice-breaking ships and cones). In the paper, we introduce [...]

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• Shockwaves in spillways with the particle finite element method

  F. Salazar, J. San-Mauro, M. Celigueta, E. Oñate

  Comp. Part. Mech. (2020). Vol. 7 (1), pp. 87-99

  
  

  Abstract

  Changes in direction and cross section in supercritical hydraulic channels generate shockwaves which result in an increase in flow depth with regard to that for uniform regime. These disturbances are propagated downstream and need to be considered in the design of the chute walls. In dam spillways, where flow rates are often high, this phenomenon can have significant implications for the cost and complexity of the solution. It has been traditionally analysed by means of reduced-scale experimental tests, as it has a clear three-dimensional character and therefore cannot be approached with two-dimensional numerical models. In this work, the ability of the particle finite element method (PFEM) to reproduce this phenomenon is analysed. PFEM has been successfully applied in previous works to problems involving high irregularities in free surface. First, simple test cases available in the technical bibliography were selected to be reproduced with PFEM. Subsequently, the method was applied in two spillways of real dams. The results show that PFEM is capable of capturing the shockwave fronts generated both in the contractions and in the expansions that occur behind the spillway piers. This suggests that the method may be useful as a complement to laboratory test campaigns for the design and hydraulic analysis of dam spillways with complex geometries.

  Abstract
  Changes in direction and cross section in supercritical hydraulic channels generate shockwaves which result in an increase in flow depth with regard to that for uniform regime. [...]

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• An investigation on thermal performance of wollastonite and bentonite reinforced intumescent fire-retardant coating for steel structures

  F. Ahmad, S. Ullah, N. Merican, E. Oñate, A. Al-Sehemi, G. Yeoh

  Construction and Building Material (2019). Vol. 228, 116734

  
  

  Abstract

  This research emphases on the synthesis of new formulations of intumescent coating with improved thermal performance for steel structures. The coating formulations were based on the expandable graphite reinforced with wollastonite and bentonite. Ten samples of five formulations were synthesized by varying grinding time duration between 1 and 2 min. To analyse the substrate temperature of coated steel, fire test was performed according to ASTM-E119. The char morphology was observed by Field Emission Scanning Electron (FESEM) and Transmission Electron Microscopy (TEM). FTIR and X-ray Diffraction (XRD) test is conducted to analyse the composition of the residual char. The residual char mass was perceived by Thermogravimetric analysis (TGA) of the coating. X-ray Photo Electron Spectroscopy (XPS) was utilized for binding energy and elemental composition of the char. One-hour fire protection test showed 166 _C, the lowest substrate temperature of IFRC5-2 and 40.46% residual mass was obtained by TGA analysis. XRD analysis showed that residual char has aluminum borate and borophosphate and confirmed by functional group analysis using and FTIR. FESEM and TEM illustrated that char relates to hexagonal particles of wollastonite. XPS analysis of IFRC5-2 showed the carbon and oxygen contents were 41.40% and 51.20%. Pyrolysis-Gas Chromatography–Mass Spectrometry (Pyrolysis GC–MS) results showed IFRC-5 produced less concentration of the gaseous products compared to IFRC-C. The formulations developed by grinding solid ingredients for 2 min showed improved thermal performance compared with the formulation produced by grinding solid ingredients for 1 min. Longer grinding time and higher amount of filler improved the thermal properties of the intumescent coating.

  Abstract
  This research emphases on the synthesis of new formulations of intumescent coating with improved thermal performance for steel structures. The coating formulations were based [...]

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• Full-scale numerical calculation of ballasted tracks with the Discrete Element Method

  J. Irazábal, F. Salazar, E. Oñate, J. Irazábal González

  J. Irazábal's Conference proceedings (2019). 1

  
  

  Abstract

  Rail transport, both for people and goods, is becoming increasingly significant all over the world, which is reflected in the great growth of conventional and high-speed train lines. Most of these infrastructures are built with railway ballast, a granular material whose main functions are to resist vertical and horizontal loads and to face climatic actions. The growing popularity of these infrastructures has led to the development of numerical models to evaluate their performance. Among a wide range of numerical methods, the Discrete Element Method (DEM) was found to be effective for evaluating the performance of granular materials. This approach considers their discontinuous nature and has proven to be a useful tool to determine the dynamic behaviour of groups of particles. Moreover, the DEM is also used to compute the behaviour of continuum materials. In this work, rails and bearing plates are characterised in the calculations using this methodology, called the bonded DEM. It is a modification of the classical DEM which assumes that bonds exist between particles, resisting their separation. The code used is developed within DEMPack, a specific software tool for modelling physical problems using the DEM. Currently, DEMPack allows the use of two different types of geometry: spheres with rolling friction and clusters of spheres. A previous analysis showed that spheres are more effective for studying the macroscopic behaviour of the ballast layer, while clusters are necessary for small-scale tests involving highly compacted particles since their results are greatly influenced by particles and contacts distribution. After calibrating the code, full-scale tests were performed applying the load of a high-speed train on a railway track section in different situations. Considering the amount of material (about 260,000 particles) and that the aim is to evaluate the deflection of the rails, the calculations are carried out using spheres. The numerical results correctly capture the effect on the deflection of the rails. It can be concluded that the DEM increases the possibilities for analysing innovative solutions since real case-scenarios can be studied with enough accuracy and feasible time.

  Abstract
  Rail transport, both for people and goods, is becoming increasingly significant all over the world, which is reflected in the great growth of conventional and high-speed train [...]

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• A general methodology for deriving shear constrained Reissner-Mindlin plate elements

  E. Oñate, O. Zienkiewicz, B. Suarez

  (1990). Research Report, Nº PI5

  
  

  Abstract

  In this paper the necessary requirements for the good behaviour of shear constrained Reissner–Mindlin plate elements for thick and thin plate situations are re‐interpreted and a simple explicit form of the substitute shear strain matrix is obtained. This extends the previous work of the authors presented in References 18 and 31. The general methodology is applied to the re‐formulation of some well known quadrilateral plate elements and some new triangular and quadrilateral plate elements which show promising features. Some examples of the good behaviour of these elements are given.

  Abstract
  In this paper the necessary requirements for the good behaviour of shear constrained Reissner–Mindlin plate elements for thick and thin plate situations are re‐interpreted [...]

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• Finite volume VS finite element. Is there really a choice

  O. Zienkiewicz, E. Oñate

  (1990). Research Report, Nº PI8

  
  

  Abstract

  The finite volume method appears to be a particular case of finite elements with a non Galerkin weighting. It is course less accurate for self adjoint problems but has some computationally useful features for first order equations involving only surface integrals. For certain problems this is a substational economy and leads to computationally useful approximations.  

  Abstract
  The finite volume method appears to be a particular case of finite elements with a non Galerkin weighting. It is course less accurate for self adjoint problems but has some [...]

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• A finite element method for the solution of potencial flow in two dimensions

  T. Hughes, E. Oñate, J. Canet

  (1991). Research Report, Nº PI11

  
  

  Abstract

  This report presents a method for the solution of two dimensional, potential flow around an aerofoil base on a Finite Element Method for the solution of Laplace’s equation. Solutions to approximate the “real” flow are constructed from the observation that potential flow solutions are linear and thus, many potential flows may be superimposed to yield the desired flow. Indeed, in this way, one of the effects of viscosity, that of fixing the rear stagnation point to the trailing edge for up to moderate angle of attack cases, is modelled by the imposition of a potential flow due to a point vortex (located at the ¼ chord point) sufficient to fix the rear stagnation point at the trailing edge (Kutta condition). It must be remembered however, that potential flow solutions are inviscid and as such do not model correctly the flow separation point and further, the absence of viscosity falsely causes the model to predict zero drag caused by the aerofoil. However, the predictions made for the lift (derived from the calculated circulation to fix the Kutta condition via the Kutta-Joukowski theorem) are shown to be good for low Mach number cases at moderate angles of attack.    

  Abstract
  This report presents a method for the solution of two dimensional, potential flow around an aerofoil base on a Finite Element Method for the solution of Laplace’s equation. [...]

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• A penalty finite element method for non‐Newtonian creeping flows

  R. Codina, M. Cervera, E. Oñate

  (1991). Research Report, Nº PI13

  
  

  Abstract

  In this paper we present an iterative penalty finite element method for viscous non‐Newtonian creeping flows. The basic idea is solving the equations for the difference between the exact solution and the solution obtained in the last iteration by the penalty method. For the case of Newtonian flows, one can show that for sufficiently small penalty parameters the iterates converge to the incompressible solution. The objective of the present work is to show that the iterative penalization can be coupled with the iterative scheme used to deal with the non‐linearity arising from the constitutive law of non‐Newtonian fluids. Some numerical experiments are conducted in order to assess the performance of the approach for fluids whose viscosity obeys the power law.

  Abstract
  In this paper we present an iterative penalty finite element method for viscous non‐Newtonian creeping flows. The basic idea is solving the equations for the difference [...]

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