Antonio Munjiza

Coupled FEMDEM/Fluids for coastal engineers with special reference to armour stability and breakage

Sea-level rise and increased storminess present huge challenges to coastal engineers worldwide. The seaward slope of many breakwaters and shoreline defence structures consists of thousands of interlocking units of concrete or rock making up a massive granular defence against wave attack. The units are placed freely to form an armour layer which is intended to both dissipate wave energy and remain structurally stable. Design guidance on the mass and shape of these units is based on empirical equations derived from Froude scale physical model tests. The two main failure modes for concrete armour layers are displacement (hydraulic instability) and breakage (structural instability) which are strongly coupled. Breakage mechanisms cannot all be faithfully reproduced under scaled physical models. Fundamental understanding of the forces governing such wave-structure interaction remains poor and unit breakages continue to baffle the designers of concrete armour units. This paper illustrates a range of DEM and FEMDEM methods being developed to model the granular solid skeleton of freely packed brittle units. Such discrete element methods are increasingly being used by engineers for solids modelling. They are especially powerful when coupled with a CFD model which can resolve ocean wave dynamics. The aim is to describe a framework for coupled modelling technologies applicable to coastal engineering problems. Preliminary simulation test cases, still at proof of concept stage, but based on a wealth of validation studies are presented. Thus, we report a snap-shot of progress towards a future where designers combine multi-physics numerical technology with knowledge from scaled physical models for a better understanding of wave energy turbulence, block movement, and internal stresses within armour units.

A generalized anisotropic deformation formulation for geomaterials

In this paper, the combined finite-discrete element method (FDEM) has been applied to analyze the deformation of anisotropic geomaterials. In the most general case geomaterials are both non-homogeneous and non-isotropic. With the aim of addressing anisotropic material problems, improved 2D FDEM formulations have been developed. These formulations feature the unified hypo-hyper elastic approach combined with a multiplicative decomposition-based selective integration for volumetric and shear deformation modes. This approach is significantly different from the co-rotational formulations typically encountered in finite element codes. Unlike the co-rotational formulation, the multiplicative decomposition-based formulation naturally decomposes deformation into translation, rotation, plastic stretches, elastic stretches, volumetric stretches, shear stretches, etc. This approach can be implemented for a whole family of finite elements from solids to shells and membranes. This novel 2D FDEM based material formulation was designed in such a way that the anisotropic properties of the solid can be specified in a cell by cell basis, therefore enabling the user to seed these anisotropic properties following any type of spatial variation, for example, following a curvilinear path. In addition, due to the selective integration, there are no problems with volumetric or shear locking with any type of finite element employed.

Modelling fracture and fragmentation using open source FEM/DEM

ABSTRACT Fracture and fragmentation processes are an integral part of many industrial operations such as block caving, blasting, milling, impact, penetration, etc. Numerical capture of fracture is coupled with difficulties. In recent years a novel so called FEM/DEM approach has been developed. It combines discrete elements with finite elements and has been demonstrated to produce accurate fracture patterns for rock and rock-like materials. It is now available as Y2D C based code in open source format free of charge. In this paper FEM/DEM has been summarised and key aspects of Y2D open source code described.

Unstructured Computational Meshes for Subdivision Geometry of Scanned Geological Objects

This paper presents a generic approach to generation of surface and volume unstructured meshes for complex free-form objects, obtained by laser scanning. A four-stage automated procedure is proposed for discrete data sets: surface mesh extraction from Delaunay tetrahedrization of scanned points, surface mesh simplification, definition of triangular interpolating subdivision faces, Delaunay volumetric meshing of obtained geometry. The mesh simplification approach is based on the medial Hausdorff distance envelope between scanned and simplified geometric surface meshes. The simplified mesh is directly used as an unstructured control mesh for subdivision surface representation that precisely captures arbitrary shapes of faces, composing the boundary of scanned objects. CAD model in Boundary Representation retains sharp and smooth features of the geometry for further meshing. Volumetric meshes with the MezGen code are used in the combined Finite-Discrete element methods for simulation of complex phenomena within the integrated Virtual Geoscience Workbench environment (VGW).