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Modelling of massive particulates for breakwater engineering using coupled FEMDEM and CFD

Particuology 2008年第6期6卷 572-583页

作者： John-Paul Lathama Antonio Munjiza Julian Mindel Jiansheng Xiang Romain Guises Xavier Garcia Chris Pain Gerard Gorman Matthew Piggott Department of earth science and engineering Imperial College London UK Department of engineering Queen Mary London University London UK

The seaward slope of many breakwaters consists of thousands of interlocking units of rock or concrete comprising a massive granular system of large elements each weighing tens of tonnes. The dumped quarry materials in the core are protected by progressively coarser particulates. The outer armour layer of freely placed units is intended to both dissipate wave energy and remain structurally stable as strong flows are drawn in and out of the particulate core. Design guidance on the mass and shape of these units is based on empirical equations derived from scaled physical model tests. The main failure mode for armour layers exposed to severe storms is hydraulic instability where the armour units of concrete or rock are subjected to uplift and drag forces which can in turn lead to rocking, displacement and collisions sufficient to cause breakage of units. Recently invented armour unit designs making up such granular layered system owe much of their success to the desirable emergent properties of interlock and porosity and how these combine with individual unit structural strength and inertial mass. Fundamental understanding of the forces governing such wave-structure interaction remains poor. We use discrete element and combined finite-discrete element methods to model the granular solid skeleton of randomly packed units coupled to a CFD code which resolves the wave dynamics through an interface tracking technique. The CFD code exploits several methods including a compressive advection scheme, node movement, and general mesh optimization. We provide the engineering context and report progress towards the numerical modelling of instability in these massive granular systems.

关键词： Modelling DEM Wave-structure interaction Armour units Breakwater

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The Virtual Geoscience Workbench, VGW: Open Source tools for discontinuous systems

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Particuology 2010年第2期8卷 100-105页

作者： A. Munjiza J. Xiang X. Garcia J.P. Latham G.G. Schiava D'Albano N.W.M. John Department of engineering Queen Mary London University London UK Department of earth science and engineering Imperial College London UK

In 1989 work began on merging finite and discrete elements. During 1990 algorithmic solutions for the new combined method were developed, together with a C-based implementation known as the Y code. In 2004 these developments and implementations were published as a textbook. Queen Mary University of london ~QMUL） and imperial college are currently engaged in a research project to make Y codes in both 2D and 3D available in Open Source format and with mainly geoscience problems in mind. The result is a set of Open Source tools for Geoscience （VGW）, key components of which are summarised in this paper, together with illustrative range of simulation results. 2009 Chinese Society of Particuology and Institute of Process engineering, Chinese Academy of sciences. Published by Elsevier B.V. All rights reserved.

关键词： Combined finite-discrete elementWorkbenchModellingGeoscience

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Hydro-mechanical interaction effects and channelling in threedimensional fracture networks undergoing growth and nucleation

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Journal of Rock Mechanics and Geotechnical engineering 2020年第4期12卷 707-719页

作者： Adriana Paluszny Robin NThomas Maria CSaceanu Robert WZimmerman Department of earth science and engineering Imperial College LondonLondonSW72AZUK

The flow properties of geomechanically generated discrete fracture networks are examined in the context of *** networks are generated by growing fractures in tension,modelling the low permeability rock as a linear elastic *** are modelled as discrete surfaces which grow quasi-statically within a three-dimensional(3D)*** may have their locations specified as a simulation input,or be generated as a function of damage,quantified using the local variation in equivalent *** properties of the grown networks are shown to be a product of in situ stress,relative orientation of initial flaws,and competitive process of fracture interaction and *** grow preferentially in the direction perpendicular to the direction of maximum tension and may deviate from this path due to mechanical fracture *** is significantly channelled through a subset of the fractures in the full domain,consistent with observations of other real and simulated *** the fracture networks grow,small changes in the geometry of the fractures lead to large changes in the locations and scale of primary flow *** flow variability and formation of channels are examined for two growing networks,one with a fixed amount of fractures,and another with nucleating *** interaction between fractures is shown to modify the local stress field,and in turn the aperture of the *** for single-phase flow are the results of hydro-mechanical effects in fracture networks during *** are the results of changes to the topology of the network as well as the result of mechanical self-organisation which occurs during interaction leading to growth and intersection.

关键词： Fracture growth Fracture mechanics Stress intensity factor(SIF) Quasi-static growth Finite elements

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Influence of inter-grain cementation stiffness on the effective elastic properties of porous Bentheim sandstone

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Journal of Rock Mechanics and Geotechnical engineering 2023年第3期15卷 573-583页

作者： Bin Chen Jiansheng Xiang John-Paul Latham Department of earth science and engineering Faculty of EngineeringImperial College LondonLondonSW72BXUK

Effective elastic properties of porous media are known to be significantly influenced by *** this paper,we investigated the influence of another critical factor,the inter-grain cementation stiffness,on the effective elastic properties of a granular porous rock(Bentheim sandstone)using an advanced numerical workflow with realistic rock microstructure and a theoretical ***,the disparity between the experimentally tested elastic properties of Bentheim sandstone and the effective elastic properties predicted by empirical equations was ***,a micro-computed tomography(CT)-scan based approach was implemented with digital imaging software AVIZO to construct the 3D(three-dimensional)realistic microstructure of Bentheim *** microstructural model was imported to a mechanics solver based on the 3D finite element model with inter-grain boundaries modelled by cohesive *** simulations were run to test the effective elastic properties for different shear and normal intergrain cementation ***,a relation between the macroscale Young’s modulus and inter-grain cementation stiffness was derived with a theoretical model which can also account for porosity *** the numerical and theoretical results indicate the influence of the inter-grain cementation stiffness,on the effective elastic properties is significant for porous *** calibrated normal and shear stiffnesses at the inter-grain boundaries are 1.2×10^(5) and 4×10^(4) GPa/m,respectively.

关键词： Porous sandstone Cohesive finite element model Grain-based model Rock microstructure Micro-computed tomography(CT)

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Reflection full waveform inversion

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science China earth sciences 2017年第10期60卷 1783-1794页

作者： YAO Gang WU Di Department of earth science and engineering Imperial College London The Unconventional Natural Gas Institute China University of Petroleum

Because of the combination of optimization algorithms and full wave equations, full-waveform inversion(FWI) has become the frontier of the study of seismic exploration and is gradually becoming one of the essential tools for obtaining the earth interior information. However, the application of conventional FWI to pure reflection data in the absence of a highly accurate starting velocity model is difficult. Compared to other types of seismic waves, reflections carry the information of the deep part of the subsurface. Reflection FWI, therefore, is able to improve the accuracy of imaging the earth interior further. Here, we demonstrate a means of achieving this successfully by interleaving least-squares RTM with a version of reflection FWI in which the tomographic gradient that is required to update the background macro-model is separated from the reflectivity gradient using the Born approximation during forward modeling. This provides a good update to the macro-model. This approach is then followed by conventional FWI to obtain a final high-fidelity high-resolution result from a poor starting model using only reflection *** analysis reveals the high-resolution result is achieved due to a deconvolution imaging condition implicitly used by FWI.

关键词： Full-waveform inversion Reflection full-waveform inversion Least-squares reverse-time migration Tomographic gradient Reflectivity gradient Deconvolution imaging condition

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Least-squares reverse-time migration for reflectivity imaging

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science China earth sciences 2015年第11期58卷 1982-1992页

作者： YAO Gang WU Di Department of earth science and engineering Imperial College London The Unconventional Natural Gas Institute China University of Petroleum (Beijing)

A least-squares reverse-time migration scheme is presented for reflectivity imaging. Based on an accurate reflection modeling formula, this scheme produces amplitude-preserved stacked reflectivity images with zero phase. Spatial preconditioning, weighting and the Barzilai-Borwein method are applied to speed up the convergence of the least-squares inversion. In addition, this scheme compensates the effect of ghost waves to broaden the bandwidth of the reflectivity images. Furthermore, roughness penalty constraint is used to regularize the inversion, which in turn stabilizes inversion and removes high-wavenumber artifacts and mitigates spatial aliasing. The examples of synthetic and field datasets demonstrate the scheme can generate zerophase reflectivity images with broader bandwidth, higher resolution, fewer artifacts and more reliable amplitudes than conventional reverse-time migration.

关键词： adjoint migration least-squares reverse-time migration cross-correlation imaging condition deconvolution imagingcondition deghost

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Study on sedimentation distribution based on cooperative analysis of geologic-geophysical in less well area: A case study of Suweiyi sandstone in the DB area, Kuqa Depression in Tarim Basin

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Petroleum Research 2020年第4期5卷 339-346页

作者： Huiling Niu Lixia Liang Linbo Wang Chenchen Wang Juan Zhang Exploration and Development Research Intstitute Sinopec Northwest Oifield Company Urumqi 830011Xingfiang China college of earth sciences Yangtze University Wuhan430100HubeiChina departoment of earth science and engineering imperial college london LondonSW72AZ UK

The Kuqa Depression in Tarim Basin develops fan deltaic,braided river deltaic,and lacustrine sedi-mentation,espeially extensive braided river deltaic sedimentation,in the Cretaceous-Paleogene ***,fine sedimentary pattern of the Kuqa Depression and North Tarim Uplift belt since the Middle Cenozoic still needs to be *** a combination zone of the Kuqa Depression and North Tarim Uplift,the sedimentary characteristics of the DB area in the southern margin of the east of the Kuqa depression have been paid more *** better understand the sedimentary framework in the Kuqa Depression and North Tarim Uplift in the Mesozoic and Cenozoic,through joint geologic-geophysical study,sedime ntation of sandstone at the bottom of the Paleogene Suweiyi Formation in the DB area and its peripheral area is *** facies and sandstone distribution in the area are identified through core observation,component analysis,logging interpretation and seismic *** on seismic facies analysis,sedimentary facies distribution in the area is *** show that sandstone at the bottom of the Paleogene Suweiyi Fommation in the DB area and its peripheral area is developed in shore shallow lacustrine beach-bar *** beach-bar arenaceous sediments are mainly distnibuted in the southern DB area and the shallow lacustrine mudstone is developed in northern DB area,showing obvious north south di ferentiation charactenistics.

关键词： Suweiyi formation Sandstone Seismic inversion Seismic facies Logging facies Sedimentary facies Kuqa depression Tarim basin

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Pores for thought:generative adversarial networks for stochastic reconstruction of 3D multi-phase electrode microstructures with periodic boundaries

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npj Computational Materials 2020年第1期6卷 971-981页

作者： Andrea Gayon-Lombardo Lukas Mosser Nigel P.Brandon Samuel J.Cooper Department of earth science and engineering Imperial College LondonLondon SW72BPUK earth science Analytics ASA Professor Olav Hanssens vei 7AStavanger 4021Norge Dyson School of Design engineering Imperial College LondonLondon SW72DBUK

The generation of multiphase porous electrode microstructures is a critical step in the optimisation of electrochemical energy storage *** work implements a deep convolutional generative adversarial network(DC-GAN)for generating realistic nphase microstructural *** same network architecture is successfully applied to two very different three-phase microstructures:A lithium-ion battery cathode and a solid oxide fuel cell anode.A comparison between the real and synthetic data is performed in terms of the morphological properties(volume fraction,specific surface area,triple-phase boundary)and transport properties(relative diffusivity),as well as the two-point correlation *** results show excellent agreement between datasets and they are also visually *** modifying the input to the generator,we show that it is possible to generate microstructure with periodic boundaries in all three *** has the potential to significantly reduce the simulated volume required to be considered“representative”and therefore massively reduce the computational cost of the electrochemical simulations necessary to predict the performance of a particular microstructure during optimisation.

关键词： microstructure electrode phase

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Baseline distribution optimization and missing data completion in wavelet-based CS-Tomo SAR

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science China(Information sciences) 2018年第4期61卷 164-172页

作者： Hui BI Jianguo LIU Bingchen ZHANG Wen HONG science and Technology on Microwave Imaging Laboratory Institute of ElectronicsChinese Academy of Sciences University of Chinese Academy of sciences Department of earth science and engineering Imperial College London

In this paper, we propose a coherence of measurement matrix-based baseline distribution optimization criterion, together with an L1 regularization missing data completion method for unobserved baselines(not belonging to the actual baseline distribution), to facilitate wavelet-based compressive sensingtomographic synthetic aperture radar imaging(CS-Tomo SAR) in forested areas. Using M actual baselines,we first estimate the optimal baseline distribution with N baselines(N > M), including N-M unobserved baselines, via the proposed coherence criterion. We then use the geometric relationship between the actual and unobserved baseline distributions to reconstruct the transformation matrix by solving an L1 regularization problem, and calculate the unobserved baseline data using the measurements of actual baselines and the estimated transformation matrix. Finally, we exploit the wavelet-based CS technique to reconstruct the elevation via the completed data of N baselines. Compared to results obtained using only the data of actual baselines, the recovered image based on the dataset obtained by our proposed method shows higher elevation recovery accuracy and better super-resolution ability. Experimental results based on simulated and real data validated the effectiveness of the proposed method.

关键词： tomographic synthetic aperture radar imaging(Tomo SAR) compressive sensing(CS) baseline distribution optimization coherence of measurement matrix

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Effective Variational Data Assimilation in Air-Pollution Prediction

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Big Data Mining and Analytics 2018年第4期1卷 297-307页

作者： Rossella Arcucci Christopher Pain Yi-Ke Guo Data science Institute Department of ComputingImperial College LondonLondonSW72AZUnited Kingdom Department of earth science&engineering Imperial College LondonLondonSW72AZUnited Kingdom

Numerical simulations are widely used as a predictive tool to better understand complex air flows and pollution transport on the scale of individual buildings,city blocks,and entire *** improve prediction for air flows and pollution transport,we propose a Variational Data Assimilation(VarDA)model which assimilates data from sensors into the open-source,finite-element,fluid dynamics model *** is based on the minimization of a function which estimates the discrepancy between numerical results and observations assuming that the two sources of information,forecast and observations,have errors that are adequately described by error covariance *** conditioning of the numerical problem is dominated by the condition number of the background error covariance matrix which is *** this paper,a preconditioned VarDA model is presented,it is based on a reduced background error covariance *** Empirical Orthogonal Functions(EOFs)method is used to alleviate the computational cost and reduce the space *** results are provided assuming observed values provided by sensors from positions mainly located on roofs of buildings.

关键词： data assimilation reduced order space big data preconditioning

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