COLLECTIONS

Documents published in Scipedia

• Possibilities of the particle finite element method for fluid-structure interaction problems with free surface waves

  E. Oñate, S. Idelsohn, F. Del Pin, R. Aubry

  Revue Européenne des Éléments Finis (2004). Vol. 13, pp. 637-666

  
  

  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 condition in 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 method 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 [...]

  • 5
  •  read

• An Implicit Material Point Method Applied to Granular Flows

  I. Iaconeta, A. LARESE, R. Rossi, E. Oñate

  Procedia Engineering (2017). Vol. 175, pp. 226-232

  
  

  Abstract

  The main objective of this work lies in the development of a variational implicit Material Point Method (MPM), implemented in the open source Kratos Multiphysics framework. The ability of the MPM technique to solve large displacement and large deformation problems is widely recognised and its use ranges over many problems in industrial and civil engineering. In the current work the continuum based implicit MPM is applied to engineering applications, where granular material flow is involved. For the resolution of the length and time scale of these particular problems, both continuum and discrete models are typically used. Even if discrete techniques predict more feasible results, nowadays, their use is limited to the investigation of element tests of particles, or to the simulation of reduced systems, not allowing to make important decisions in the analysis and design of granular processes. Some advantages of MPM over discrete methods are tested, such as, the ability to simulate granular flow at the large scale with acceptable computational cost and the capability to get information of stress and strain state in a more straightforward way. The focus of this paper is a comparative study between an irreducible and a mixed formulation, both implemented in the MPM code, to assess the improvement in accuracy and reliability of the numerical results when the latter formulation is adopted.

  Abstract
  The main objective of this work lies in the development of a variational implicit Material Point Method (MPM), implemented in the open source Kratos Multiphysics framework. [...]

  • 17
  •  read

• Modelling and simulation of the sea-landing of aerial vehicles using the Particle Finite Element Method

  P. Ryzhakov, R. Rossi, A. Viña, E. Oñate

  Ocean Engng. (2013). Vol. 66, pp. 92-100

  
  

  Abstract

  In this paper the Particle Finite Element Method (PFEM) is applied to the simulation of the sea-landing of an unmanned aerial vehicle (UAV). The problem of interest consists in modelling the impact of the vehicle against the water surface, analyzing the main kinematic and dynamic quantities (such as loads exerted upon the capsule at the moment of the impact). The PFEM, a methodology well-suited for free-surface flow simulation is used for modelling the water while a rigid body model is chosen for the vehicle. The vehicle under consideration is characterized by low weight. This leads to difficulties in modelling the fluid–structure interaction using standard Dirichlet–Neumann coupling. We apply a modified partitioned strategy introducing the interface Laplacian into the pressure Poisson's equation for obtaining a convergent FSI solution. The paper concludes with an industrial example of a vehicle sea-landing modelled using PFEM.

  Abstract
  In this paper the Particle Finite Element Method (PFEM) is applied to the simulation of the sea-landing of an unmanned aerial vehicle (UAV). The problem of interest consists [...]

  • 28
  •  read

• An extended class of multilayer perceptron

  R. López, E. Oñate

  Neurocomputing (2008). Vol. 71 (13-15), pp. 2538-2543

  
  

  Abstract

  In this work an extended class of multilayer perceptron is presented. This includes independent parameters, boundary conditions and lower and upper bounds. In some cases, such extensions contain a priori information of the problem. On some other situations they are necessary in order to define a correct representation for the solution. The use of this augmented class of neural network is illustrated through a case study in the optimal control theory. The numerical results are compared against the analytical solution.

  Abstract
  In this work an extended class of multilayer perceptron is presented. This includes independent parameters, boundary conditions and lower and upper bounds. In some cases, [...]

  • 8
  •  read

• A co-rotational 8-node assumed strain shell element for postbuckling analysis of laminated composite plates and shells

  G. Lomboy, K. Kim, E. Oñate

  Mechanics of Advanced Materials and Structures (2007). Vol. 14 (2), pp. 89-105

  
  

  Abstract

  A nonlinear resultant shell element is developed for the solution of problems of composite plates and shells undergoing nonlinear static and nonlinear dynamic behavior with progressive layer failure. The formulation of the tangent stiffness is defined on the mid-surface and is efficient for analyzing thick laminated plates and shells by incorporating bending moments and transverse shear resultant forces in the geometric stiffness. The composite element is free of both membrane and shear locking behavior by using the assumed natural strain method, such that the element also performs very well as thin laminate shells. An equilibrium approach is used to derive the improved transverse shear stiffness, instead of using a shear correction factor. The proposed formulation is computationally efficient and the test results show good agreement with references. The composite shell element is extended to determine ply failures in laminated composite structures undergoing nonlinear static or dynamic behavior. The failure analysis is done by first, computing for the inter-laminar stresses at each gauss point in an element. Having obtained the stresses in each layer, checking for failure is performed based on a chosen failure criterion. Four failure criteria are available to enable the user to adopt the appropriate criterion for the type of problem parameters present.

  Abstract
  A nonlinear resultant shell element is developed for the solution of problems of composite plates and shells undergoing nonlinear static and nonlinear dynamic behavior with [...]

  • 16
  •  read

• Analysis of segmentally constructed prestressed concrete bridges using hexahedral elements with realistic tendon profiles

  P. Norachan, K. Kim, E. Oñate

  Journal of Structural Engineering (2014). Vol. 140 (6), pp. 04014028/1-17

  
  

  Abstract

  The paper presents a systematically numerical procedure based on the finite-element method for three-dimensional analysis of segmentally constructed prestressed concrete bridges using hexahedral elements including realistic tendon profiles. The enhanced assumed strain (EAS) is used in the formulation of the hexahedral element in order to improve the element performances. Both the geometric nonlinearity and time-dependent effects due to creep, shrinkage, and aging of the concrete and relaxation of the prestress are taken into account, while variations of the structural configuration due to changes of the structural geometry and boundary conditions during the construction process are also incorporated. To include realistic tendon profiles, the idealized prestressing tendon is represented by a system of piecewise linear prestressing segments. Several numerical examples in a wide range of prestressed concrete structures are presented to demonstrate the validity and efficiency of the proposed procedure. Finally, application to the erection of a segmentally erected prestressed concrete bridge is discussed at the end of the paper.

  Abstract
  The paper presents a systematically numerical procedure based on the finite-element method for three-dimensional analysis of segmentally constructed prestressed concrete bridges [...]

  • 7
  •  read

• Modeling of ground excavation with the particle finite-element method

  J. Puigbó, E. Oñate, B. Suarez

  Journal of Engineering Mechanics (2010). Vol. 136 (4), pp. 455-463

  
  

  Abstract

  An excavation process is a nonlinear dynamic problem that includes geometrical, material, and contact nonlinearities. The simulation of ground excavation has to face contact interaction in a changing geometry composed by several solid domains. The particle finite-element method (PFEM) is based on a Lagrangian description for modeling the motion of a continuum medium. The PFEM is particularly suitable for modeling a fluid motion with free surfaces. The application of the PFEM in ground excavation includes the use of the remeshing process, α-shape concepts for detecting the domain boundary, contact mechanics laws, material constitutive models, and surface wear models. Everything is correctly matched to quantify the excavation and the corresponding damage caused to the ground. The erosion and wear parameters of the soil/rock material govern the evolution of the excavation process. The preliminary results presented in this paper show that the PFEM it is a very suitable tool for the simulation of ground excavation processes.

  Abstract
  An excavation process is a nonlinear dynamic problem that includes geometrical, material, and contact nonlinearities. The simulation of ground excavation has to face contact [...]

  • 30
  •  read

• Approximating the Basset force by optimizing the method of van Hinsberg et al.

  G. Casas, A. Ferrer, E. Oñate

  Journal of Computational Physics (2018). Vol. 352, pp. 142-171

  
  

  Abstract

  In this work we put the method proposed by van Hinsberg et al. to the test, highlighting its accuracy and efficiency in a sequence of benchmarks of increasing complexity. Furthermore, we explore the possibility of systematizing the way in which the method's free parameters are determined by generalizing the optimization problem that was considered originally. Finally, we provide a list of worked-out values, ready for implementation in large-scale particle-laden flow simulations.

  Abstract
  In this work we put the method proposed by van Hinsberg et al. to the test, highlighting its accuracy and efficiency in a sequence of benchmarks of increasing complexity. [...]

  • 16
  •  read

• Volumetric constraint models for anisotropic elastic solids

  C. Felippa, E. Oñate

  Journal of Applied Mechanics (2004). Vol. 71 (5), pp. 731-734

  
  

  Abstract

  We study three “incompressibility flavors” of linearly-elastic anisotropic solids that exhibit volumetric constraints: isochoric, hydroisochoric and rigidtropic. An isochoric material deforms without volume change under any stress system. An hydroisochoric material does so under hydrostatic stress. A rigidtropic material undergoes zero deformations under a certain stress pattern. Whereas the three models coalesce for isotropic materials, important differences appear for anisotropic behavior. We find that isochoric and hydroisochoric models under certain conditions may be hampered by unstable physical behavior. Rigidtropic models can represent semistable physical materials of arbitrary anisotropy while including isochoric and hydroisochoric behavior as special cases.

  Abstract
  We study three “incompressibility flavors” of linearly-elastic anisotropic solids that exhibit volumetric constraints: isochoric, hydroisochoric and rigidtropic. [...]

  • 21
  •  read

• Active transonic aerofoil design optimization using robust multiobjective evolutionary algorithms

  D. Lee, J. Periaux, L. González, E. Oñate, N. Qin

  Journal of Aircraft (2011). Vol. 48 (3) pp. 1084-1094

  
  

  Abstract

  The use of adaptive wing/aerofoil designs is being considered, as they are promising techniques in aeronautic/ aerospace since they can reduce aircraft emissions and improve aerodynamic performance of manned or unmanned aircraft. This paper investigates the robust design and optimization for one type of adaptive techniques: active flow control bump at transonic flow conditions on a natural laminar flow aerofoil. The concept of using shock control bump is to control supersonic flow on the suction/pressure side of natural laminar flow aerofoil that leads to delaying shock occurrence (weakening its strength) or boundary-layer separation. Such an active flow control technique reduces total drag at transonic speeds due to reduction of wave drag. The location of boundary-layer transition can influence the position and structure of the supersonic shock on the suction/pressure side of aerofoil. The boundarylayer transition position is considered as an uncertainty design parameter in aerodynamic design due to the many factors, such as surface contamination or surface erosion. This paper studies the shock-control-bump shape design optimization using robust evolutionary algorithms with uncertainty in boundary-layer transition locations. The optimization method is based on a canonical evolution strategy and incorporates the concepts of hierarchical topology, parallel computing, and asynchronous evaluation. Two test cases are conducted: the first test assumes the boundary-layer transition position is at 45% of chord from the leading edge, and the second test considers robust design optimization for the shock control bump at the variability of boundary-layer transition positions. The numerical result shows that the optimization method coupled to uncertainty design techniques produces Pareto optimal shock-control-bump shapes, which have low sensitivity and high aerodynamic performance while having significant total drag reduction.

  Abstract
  The use of adaptive wing/aerofoil designs is being considered, as they are promising techniques in aeronautic/ aerospace since they can reduce aircraft emissions and improve [...]

  • 23
  •  read