Abstract

This paper investigates the possibility of using the material point method (MPM) to solve small strains quasi-static problems and dynamic problems related to large distortions. Traditional methods such as the finite element method (FEM) face difficulties when large strains are involved. Therefore, tools such as the MPM have become more important in recent years. As a new tool, the MPM needs to prove its functionality for geotechnical engineering problems. In first place the MPM mathematical formulation is shortly described. Next, numerical simulations of a shallow foundation, an unconfined compression test and a slope problem are performed in an open source MPM code. The results are compared with FEM simulations, analytical solutions and real laboratory tests. The study shows qualitative and quantitative agreement when compared; a better performance of MPM for solving stresses better than strains is detected. The set of simulations validates the MPM to solve geotechnical engineering problems when dealing with small and large strains. However, the traditional FEM showed a better performance for quasi-static cases.

Abstract

This paper extends the capabilities of previous BST and EBST rotation‐free thin shell elements to the analysis of kinked and branching surfaces. The computation of the curvature tensor is first redefined in terms of the angle change between the normals at the adjacent elements. This allows to deal with arbitrary large angles between adjacent elements and to treat kinked surfaces. A relative stiffness between elements is introduced to consider non‐homogeneous surfaces. This idea is latter generalized to deal with branching shells. Several linear and non‐linear examples are presented showing that the formulation leads to the correct results. Copyright © 2006 John Wiley & Sons, Ltd.

Abstract

This paper describes a computational framework for the numerical analysis of quasi-static soil-structure insertion problems in water saturated media. The Particle Finite Element Method is used to solve the linear momentum and mass balance equations at large strains. Solid-fluid interaction is described by a simplified Biot formulation using pore pressure and skeleton displacements as basic field variables. The robustness and accuracy of the proposal is numerically demonstrated presenting results from two benchmark examples. The first one addresses the consolidation of a circular footing on a poroelastic soil. The second one is a parametric analysis of the cone penetration test (CPTu) in a material described by a Cam-clay hyperelastic model, in which the influence of permeability and contact roughness on test results is assessed.

Abstract

The paper presents total-stress numerical analyses of large-displacement soil-structure interaction problems in geomechanics using the Particle Finite Element Method (PFEM). This method is characterized by frequent remeshing and the use of low order finite elements to evaluate the solution. Several important features of the method are: (i) a mixed formulation (displacement-mean pressure) stabilized numerically to alleviate the volumetric locking effects that are characteristic of low order elements when the medium is incompressible, (ii) a penalty method to prescribe the contact constraints between a rigid body and a deformable media combined with an implicit scheme to solve the tangential contact constraint, (iii) an explicit algorithm with adaptive substepping and correction of the yield surface drift to integrate the finite-strain multiplicative elasto-plastic constitutive relationship, and (iv) the mapping schemes to transfer information between successive discretizations. The performance of the method is demonstrated by several numerical examples, of increasing complexity, ranging from the insertion of a rigid strip footing to a rough cone penetration test. It is shown that the proposed method requires fewer computational resources than other numerical approaches addressing the same type of problems.

Abstract

A numerical model for the load transfer mechanism in mooring anchor systems, commonly used in offshore petroleum industry, is presented in this work. Special attention is paid to the mechanical modelling of the contact interaction of the two medium components, namely the soil and the embedded mooring line. Resorting to the 'embedded element concept' [1], a mixed 3D-1D finite element formulation is developed in the context of finite elastoplasticity. A Tresca-like model is used to describe the nonlinear material behaviour of the surrounding soil under undrained conditions, whereas the embedded mooring line regarded as curvilinear bar-like inclusion is assumed to behave elastically with account for geometric nonlinearities. The Mohr-Coulomb model is employed to define the bond-stress and bond-slip relationships at the interface. Nonlinear static and dynamic analyses are performed with a corotational kinematic description in order to include large deformation in the problem [2]. Preliminary results indicate that the main frequencies of the dynamic load applied to the mooring line-soil system are much lower than those of the system itself, thus the overall system may be evaluated disregarding inertial effects. Further simulations based on parametric studies by varying relevant problem parameters are needed to corroborate this result. Moreover, the average load attenuation induced by friction along the soil/mooring line interface for the studied cases is around 25%. Formulation of the interface constitutive behaviour in the context of large strain to address large relative movements between embedded inclusion and surrounding soil is an ongoing task [3]. Parallel implementation of the finite element model with specific data structure storage and iterative solver is currently addressed to handle large 3D computational models. 

Abstract

In this paper a finite element for the non-linear analysis of two dimensional beams and axisymmetric shells is presented. The element uses classical thin shell assumptions (no transverse shear strains). The main feature of the element is that it has no rotational degrees of freedom. Curvatures are computed using geometrical information from the patch of three elements formed by the main element and the two neighbour (adjacent) elements. Special attention is devoted to non-smooth geometries and branching shells. An elastic-plastic material law is considered. Large strains are treated using a logarithmic strain measure and a through-the-thickness numerical integration of the constitutive equations. Several examples are presented including linear problems to study convergence properties, and non-linear problems for both elastic and elastic-plastic materials and large strains.

Abstract