Publications
112 results found
Su K, Latham J-P, Pavlidis D, et al., 2015, Multiphase flow simulation through porous media with explicitly resolved fractures, Geofluids, Vol: 15, Pages: 592-607, ISSN: 1468-8123
Accurate simulation of multiphase flow in fractured porous media remains a challenge. An important problem is the representation of the discontinuous or near discontinuous behaviour of saturation in real geological formations. In the classical continuum approach, a refined mesh is required at the interface between fracture and porous media to capture the steep gradients in saturation and saturation-dependent transport properties. This dramatically increases the computational load when large numbers of fractures are present in the numerical model. A discontinuous finite element method is reported here to model flow in fractured porous media. The governing multiphase porous media flow equations are solved in the adaptive mesh computational fluid dynamics code IC-FERST on unstructured meshes. The method is based on a mixed control volume – discontinuous finite element formulation. This is combined with the PN+1DG-PNDG element pair, which has discontinuous (order N+1) representation for velocity and discontinuous (order N) representation for pressure. A number of test cases are used to evaluate the method's ability to model fracture flow. The first is used to verify the performance of the element pair on structured and unstructured meshes of different resolution. Multiphase flow is then modelled in a range of idealised and simple fracture patterns. Solutions with sharp saturation fronts and computational economy in terms of mesh size are illustrated.
Guo L, Xiang J, Latham JP, et al., 2015, Numerical simulation of hydraulic fracturing using a three-dimensional fracture model coupled with an adaptive mesh fluid model, Pages: 2170-2179
A three-dimensional fracture model developed in the context of the combined finite-discrete element method is incorporated into a two-way fluid-solid coupling model. The fracture model is capable of simulating the whole fracturing process. It includes pre-peak hardening deformation, post-peak strain softening, transition from continuum to discontinuum, and the explicit interaction between discrete fracture surfaces, for both tensile and shear fracture initiation and propagation. The fluid-solid coupling model can simulate the interactions between moving fluids and multi-body solids. By incorporating the fracture model into the coupling model, a methodology of using the new coupling model to capture fracturing behaviour of solids in fluid-solid coupling simulations is proposed. To solve the problem in the coupling model of having adaptive continuous meshes being used by the fluid code and discontinuous meshes in the solid code, a scheme to convert different meshes is developed. A single fracture propagation driven by fluid pressures is simulated and the results show that the modelling obtains the correct critical load and propagation direction for fluid-driven fracturing. Several important phenomena, such as stress concentration ahead of the fracture tip, adaptive refinement of fluid mesh as a response to the fracture propagation and fluids flowing into fractures, are properly captured.
Latham JP, Xiang J, Higuera P, 2015, Numerical Modelling of the Stability of Breakwater Armour Systems, Pages: 687-698
Rubble-mound breakwaters using granular cover layers of rock or concrete units are mainly designed using empirical equations, scaled hydraulics laboratory test models and precedent practice. Multi-body solids numerical models can now represent the geometry and contact forces in such armour systems, when at rest or in a dynamic state of motion. The challenge tackled in this paper is to introduce oscillatory wave disturbance forces to such solids models with sufficient realism so that useful new numerical model information on armour stability can be used by designers. This is achieved using advanced 3D numerical wave tank simulations of wave-induced fluid flows inside the armour and under layers. Pressure-time histories of 2D sea states are also modelled enabling longer runs and entire storm sea states to be investigated for the equivalent rubble-mound structure. The correctly calibrated pressure-time storm history for the entire 3D domain heralds the introduction of a new 'wave proxy' method, based on the multi-body solids FEMDEM solver, Solidity. The integrated surface pressures acting on units yield the required oscillatory hydraulic and buoyancy forces. These drive the potential instability and movements and are superimposed on each unit in combination with the constantly updated contact, inertia and body forces. Results of this 'one-way' coupling method are briefly illustrated. We compare the effect of two different extreme storm conditions on the stability of a Core-Loc structure.
Guo L, Latham J-P, Xiang J, 2014, Numerical simulation of breakages of concrete armour units using a three-dimensional fracture model in the context of the combined finite-discrete element method, Computers and Structures, Vol: 146, Pages: 117-142, ISSN: 0045-7949
Lei Q, Latham J-P, Xiang J, et al., 2014, Effects of geomechanical changes on the validity of a discrete fracture network representation of a realistic two-dimensional fractured rock, International Journal of Rock Mechanics and Mining Sciences, Vol: 70, Pages: 507-523, ISSN: 0020-7624
This paper aims to examine the validity of the discrete fracture network (DFN) method in representing a realistic two-dimensional fractured rock in terms of their geomechanical response to in-situ stresses and hydraulic behaviour in a steady state fluid field. First, a real fracture network is extracted from the geological map of an actual rock outcrop, which is termed the analogue fracture network (AFN). Multiple DFN realisations are created using the statistics of the analogue pattern. A conductivity parameter that was found to have a linear relationship with the conductivity of 2D fracture networks is included to further enhance network similarity. A series of numerical experiments are designed with far-field stresses applied at a range of angles to the rock domains and their geomechanical response is modelled using the combined finite-discrete element method (FEMDEM). A geomechanical comparison between the AFN and its DFN equivalents is made based on phenomena such as heterogeneity of fracture-dependent stress contours, sliding between pre-existing fracture walls, coalescence of propagating fractures and variability of aperture distribution. Furthermore, an indirect hydro-mechanical (HM) coupling is applied and the hydraulic behaviour of the porous rock models is investigated using the hybrid finite element-finite volume method (FEFVM). A further comparison is conducted focusing on the hydraulic behaviour of the AFN and DFNs under the effects of geomechanical changes. The results show that although DFNs may represent an AFN quite well for fixed mechanical conditions, such a representation may not be dependable if mechanical changes occur.
Lei Q, Latham J-P, Xiang J, et al., 2014, Representation of large scale network geometry with realisticapertures determined by mesoscale geomechanical modelling of a natural fracture system, 48th US Rock Mechanics/Geomechanics Symposium
Sakai M, Abe M, Shigeto Y, et al., 2014, Verification and validation of a coarse grain model of the DEM in a bubbling fluidized bed, CHEMICAL ENGINEERING JOURNAL, Vol: 244, Pages: 33-43, ISSN: 1385-8947
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- Citations: 177
Latham JP, Xiang J, Anastasaki E, et al., 2014, Numerical modelling of forces, stresses and breakages of concrete armour units, ISSN: 0161-3782
Numerical modelling has the potential to probe the complexity of the interacting physics of rubble mound armour systems. Through forward modelling of armour unit packs, stochastic variables such as unit displacement and maximum contact force per unit during an external oscillatory disturbance can be predicted. The combined finite-discrete element method (FEMDEM) is a multi-body method ideally suited to model the behaviour of the armour layer system and the stresses generated within complex shape units. In this paper we highlight the latest developments made with the application of FEMDEM technology to breakwater modelling including realistic rock underlayer and concrete unit layer topologies, maximum contact force distributions, internal unit stresses, fracture and unit breakages. Finally, fully coupled wave and multi-body armour unit motion with internal dynamic stress generation is illustrated.
Vire A, Jiang J, Piggott MD, et al., 2014, Towards the Numerical Modelling of Floating Offshore Renewables, Fluid-Structure-Sound Interactions and Control, Editors: Zhou, Yang, Huang, Hodges, Publisher: Springer Berlin Heidelberg, Pages: 413-417, ISBN: 978-3-642-40370-5
Anastasaki E, Xiang J, Latham JP, 2014, BUILDING CONCRETE UNIT ARMOURED BREAKWATERS IN A NUMERICAL MODEL ENVIRONMENT - A NEW PLACEMENT TECHNIQUE, Coasts, Marine Structures and Breakwaters 2013: From Sea to Shore - Meeting the Challenges of the Sea
Guo L, Latham J-P, Xiang J, et al., 2013, A numerical investigation of fracture pattern and fracture aperturedevelopment in multi-layered rock using a combined finite-discrete element method, 47th US Rock Mechanics/Geomechanics Symposium
Lei Q, Latham J-P, Xiang J, et al., 2013, A geomechanical comparison between a naturally fractured rockmass and its DFN equivalent based on FEMDEM simulation, 3rd ISRM SINOROCK Symposium, Pages: 397-402
Lei Q, Latham JP, Xiang J, et al., 2013, A geomechanical comparison between a naturally fractured rock mass and its DFN equivalent based on FEMDEM simulation, Rock Characterisation, Modelling and Engineering Design Methods, Pages: 397-402, ISBN: 9781138000575
This paper presents a comparison between natural and stochastic fracture systems in terms of their geomechanical response to in-situ stresses. An analogue fracture network (AFN) is extracted from the geological map of a limestone outcrop. A corresponding discrete fracture network (DFN) is generated using the statistics obtained from the analogue pattern, to ensure the two networks share the same statistical characteristics. The geomechanical response is modelled using the combined finite-discrete element method (FEMDEM). A series of numerical experiments is designed with far-field stresses applied at a range of angles to the rock domain. A comparison between the natural fracture system and its DFN equivalent is made based on phenomena such as fracture-dependent stress heterogeneity, re-activation of pre-existing fractures, new crack propagation and variability of aperture distribution. This study addressed the validity of using the DFN approach for geomechanical modelling of fractured rock masses and also has implications for flow simulations.
Latham J-P, Anastasaki E, Xiang J, 2013, New modelling and analysis methods for concrete armour unit systems using FEMDEM, Coastal Engineering, Vol: 77, Pages: 151-166
Rubble mound breakwaters armoured with concrete units rely on collective behaviour between adjacent concrete armour units but existing largely empirical approaches have been unable to provide a detailed understanding of how these gigantic granular systems work. The problem has been that current methods cannot investigate the interdependence of hydraulic and structural stability at the scale of individual units. Numerical methods have the potential to provide such answers but there are many challenges to overcome. We present a solution to the first major bottleneck concerning the solids modelling: the numerical creation of a breakwater trunk section of single layer concrete units with geometrical and mechanical properties that conform to realistic prototype structure placements. Positioning of units is achieved with a new versatile software tool, POSITIT, which incorporates user-defined deposition variables and the initial positioning grid necessary to achieve the required design packing densities. The code Y3D, based on the combined finite-discrete element method, FEMDEM, solves the multi-body mechanics of the problem. First, we show numerically constructed breakwater sections with armour layers of 8 m3 CORE-LOC™ units placed on rock underlayers. The numerically-generated packs are deemed acceptable when examined according to a range of criteria indicative of acceptably placed armour layers, as set by concrete unit designers. Breakwater sections with packing densities ranging from 0.59 to 0.63 are then created. Using a set of analysis tools, local variation in packing density as an indicator of heterogeneity, centroid spacing, unit contacts and orientation of unit axes are presented, together with mechanical information showing the variation in contact forces. For these five packs examined, an increasingly tighter pack was associated with a steady increase in coordination number and a more steeply and accelerating increase in average maximum contact force per
Vire A, Xiang J, Piggott M, et al., 2013, Numerical Modelling of Fluid-structure Interactions for Floating Wind Turbine Foundations, Twenty-third International Offshore and Polar Engineering Conference, Pages: 377-382
The aim of this study is to model the interactions between fluids and solids using fully nonlinear models. Non-linearity is important in the context of floating wind turbines, for example, to model breaking waves impacting on the structure and the effect of the solid’s elasticity. In this work, the fluid- and solid-dynamics equations are solved using separate finite-element models, which are coupled at every time step. This enables the mutual interactions between fluids and moving solids to be modelled. Importantly, the coupling algorithm ensures that the action-reaction principle is satisfied at a discrete level, independently of the order of representation of the discrete fields in each model. To the authors’ knowledge, the present algorithm is novel in that it can simultaneously handle (i) non-matching fluid and solid meshes, (ii) different polynomial orders of the basis functions on each mesh, and (iii) different fluid and solid time steps. Results are shown for: (i) a bottom-mounted pile subjected to small-amplitude waves in a numerical wave tank, and (ii) a truncated pile floating at an interface between air and water.
Vire A, Xiang J, Piggott M, et al., 2013, Towards the fully-coupled numerical modelling of floating wind turbines, 10th Deep Sea Offshore Wind R and D Conference (DeepWind), Publisher: ELSEVIER SCIENCE BV, Pages: 43-51, ISSN: 1876-6102
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- Citations: 12
VirĂ© A, Xiang J, Milthaler F, et al., 2012, Modelling of fluid–solid interactions using an adaptive mesh fluid model coupled with a combined finite–discrete element model, Ocean Dynamics
Sakai M, Takahashi H, Pain CC, et al., 2012, Study on a large-scale discrete element model for fine particles in a fluidized bed, ADVANCED POWDER TECHNOLOGY, Vol: 23, Pages: 673-681, ISSN: 0921-8831
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- Citations: 106
Latham JP, Xiang J, Belayneh M, et al., 2012, Modelling stress-dependent permeability in fractured rock including effects of propagating and bending fractures, International Journal of Rock Mechanics and Mining Sciences, Vol: 57, Pages: 100-112
Latham J, Xiang J, Latham JP, et al., 2012, COUPLED FLUIDITY/Y3D TECHNOLOGY AND SIMULATION TOOLS FOR NUMERICAL BREAKWATER MODELLING., 33rd International Conference on Coastal Engineering
Latham JP, Anastasaki E, Xiang J, 2012, A FEMDEM NUMERICAL MODEL STUDY OF RUBBLE-MOUND STRUCTURES ARMOURED WITH CONCRETE ARMOUR UNITS
Latham JP, Guo L, Wang X, et al., 2011, Modelling the evolution of fractures using a combined FEM-DEM numerical method, Harmonising Rock Engineering and the Environment, Pages: 250-251, ISBN: 9780415804448
Latham J-P, Xiang J, Harrison JP, et al., 2011, Development of Virtual Geoscience Simulation Tools, VGeST for irregular blocky rock applications in rock engineering using the combined finite discrete element method, FEMDEM, 44th US Rock Mechanics Symposium and 5th U.S.-Canada Rock Mechanics Symposium, Publisher: Curran Associates, Pages: 965-976
Latham J-P, Guo L, Wang X, 2011, Modelling the Evolution of Fractures using a Combined FEMDEM Numerical Method, 12th International Congress on Rock Mechanics, Harmonising Rock Engineering and the Environment, Publisher: ISRM Digital Library, One Petro
Milthaler F, Xiang J, Pavlidis D, et al., 2011, The immersed body method combined with mesh adaptivity for solid-fluid coupling, 6th International Conference on Coastal Structures
Xiang J, Latham J-P, Zimmer D, et al., 2011, Modelling breakwater armour layers and the dynamic response of armour units., 6th International Conference on Coastal Structures
Latham J-P, Xiang J, 2011, A numerical investigation of the influence of friction and vibration on laboratory scale armour unit layers, 6th International Conference on Coastal Structures, Publisher: World Scientific Publishing Company Pte Ltd.
Harrison JP, Xiang J, Latham JP, 2011, Stress Heterogeneity in a Fractured Rock Mass Modelled with the Combined Finite-DiscreteElement Method, 44th US Rock Mechanics Symposium and 5th U.S.-Canada Rock Mechanics Symposium, Pages: 1051-1056
xiang J, Latham J-P, Harrison JP, 2011, A Numeric Simulation of Rock Avalanches Using the Combined Finite-Discrete Element Method,FEMDEM, 44th US Rock Mechanics Symposium and 5th U.S.-Canada Rock Mechanics Symposium, Pages: 921-927
Xiang J, 2009, The effect of air on the packing structure of fine particles, POWDER TECHNOLOGY, Vol: 191, Pages: 280-293, ISSN: 0032-5910
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- Citations: 7
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