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Analysis of three-dimensional single stage and two-dimensional multistage models of flows in turbomolecular pumps

VACUUM 1997年第5期48卷 449-453页

作者： Schneider, TN Katsimichas, S deOliveira, CRE Goddard, AJH Applied Modelling and Computation Group Centre for Environmental Technology Imperial College of Science Technology and Medicine Prince Consort Road London SW7 2BP UK

At high blade speeds, the traditional two-dimensional (2D) infinite blade row model of a single turbomolecular pump (TMP) stage becomes inappropriate and a three-dimensional (3D) model should be used. The reasons for the improved compression performance predicted in 3D are investigated by comparing the velocity, angular and spatial probability distributions of particles obtained from Monte Carlo simulation. In addition, that direct multiple stages are better than the extrapolation of single stage results would suggest due to the modification of the angular probabilty distribution by adjacent stages. The flow is examined for a rotor-stator combination. (C) 1997 Elsevier Science Ltd.

关键词： Vacuum pumps

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Application of the finite-discrete element method to dynamic stress development in armour units and armour layers

Application of the finite-discrete element method to dynamic...

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9th International Conference on Coasts, Marine Structures and Breakwaters: Adapting to Change

作者： Latham, John-Paul Xiang, Jiansheng Applied Modelling and Computation Group Department of Earth Science and Engineering Imperial College London United Kingdom

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A surrogate-model assisted approach for optimising the size of tidal turbine arrays

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International Journal of Marine Energy 2017年 19卷 357-373页

作者： Culley, D.M. Funke, S.W. Kramer, S.C. Piggott, M.D. Applied Modelling and Computation Group Department of Earth Science and Engineering Imperial College London London United Kingdom Center for Biomedical Computing Simula Research Laboratory Oslo Norway Grantham Institute Imperial College London London United Kingdom

The new and costly nature of tidal stream energy extraction technologies can lead to narrow margins of success for a project. The design process is thus a delicate balancing act - to maximise the energy extracted, while minimising cost and risk. Scenario specific factors, such as site characteristics, technological constraints and practical engineering considerations greatly impact upon both the appropriate number of turbines to include within a tidal current turbine array (array size), and the individual locations of those turbines (turbine micro-siting). Both have been shown to significantly impact upon the energy yield and profitability of an array. The micro-siting arrangement for a given number of turbines can significantly influence the power extraction of a tidal farm. Until the layout has been optimised (a process which may incorporate turbine parameters, local bathymetry and a host of other practical, physical, legal, financial or environmental constraints) an accurate forecast of the yield of that array cannot be determined. This process can be thought of as 'tuning' an array to the proposed site to maximise desirable outcomes and mitigate undesirable effects. The influence of micro-siting on the farm performance means that determining the optimal array size needs to be coupled to the micro-siting process. In particular, the micro-siting needs to be repeated for any new trial array size in order to be able to compare the performance of the different farm sizes. Considering the large number of design variables in the micro-siting problem (which includes at least the positions of each turbine) it becomes clear that algorithmic optimisation is a key tool to rigorously determine the optimal array size and layout. This paper proposes a nested optimisation approach for solving the array size and layout problem. The core of this approach consists of two nested optimisation procedures. The 'outer' optimisation determines the array size. At each 'outer' iteration t

关键词： Turbines

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modelling of granular materials in the FETCH coupled criticality code

Modelling of granular materials in the FETCH coupled critica...

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2009 ANS Annual Meeting and Embedded Topical Meeting: Nuclear and Emerging Technologies for Space, NETS 2009

作者： Pain, Christopher C. Gomes, Jefferson L. M. A. Eaton, Matthew D. Goddard, Tony Tollit, Brendan Hadi, Justin Imperial College London Department of Earth Science and Engineering Applied Modelling and Computation Group SW7 2AZ London United Kingdom

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Generative network-based reduced-order model for prediction, data assimilation and uncertainty quantification

arXiv

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arXiv 2021年

作者： Silva, Vinicius L.S. Heaney, Claire E. Nenov, Nenko Pain, Christopher C. Applied Modelling and Computation Group Imperial College London United Kingdom

We propose a new method in which a generative network (GN) integrate into a reduced-order model (ROM) framework is used to solve inverse problems for partial differential equations (PDE). The aim is to match available measurements and estimate the corresponding uncertainties associated with the states and parameters of a numerical physical simulation. The GN is trained using only unconditional simulations of the discretized PDE model. We compare the proposed method with the golden standard Markov chain Monte Carlo. We apply the proposed approaches to a spatio-temporal compartmental model in epidemiology. The results show that the proposed GN-based ROM can efficiently quantify uncertainty and accurately match the measurements and the golden standard, using only a few unconditional simulations of the full-order numerical PDE model. Copyright © 2021, The Authors. All rights reserved.

关键词： Inverse problems

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modelling the evolution of a fracture network under excavation-induced unloading and seepage effects based on a fully coupled fluid-solid simulation 51

Modelling the evolution of a fracture network under excavati...

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51st US Rock Mechanics / Geomechanics Symposium 2017

作者： Obeysekara, A. Lei, Q. Salinas, P. Pavlidis, D. Xiang, J. Latham, J.-P. Pain, C. Applied Modelling and Computation Group Department of Earth Science and Engineering Imperial College London Prince Consort Road LondonSW7 2AZ United Kingdom

ISBN: (纸本)9781510857582

In order to assess the dynamic, coupled geomechanical and hydraulic response of a highly fractured rock during/after excavation, it is important to quantify the changes in the connectivity and conductivity of the fracture system. The objective of the work is to explore the seepage effect on fracture network evolution during a tunnel excavation in a highly fractured rock mass based on fully coupled hydro-geomechanical modelling. An empirical joint constitutive model (JCM) that can capture the normal and shear behavior of rough fractures has been implemented in the combined finite-discrete element method (FEMDEM) code 'Solidity'. Solidity can simulate the deformability of matrix blocks, the interaction of pre-existing fractures, and the propagation of new cracks driven by mode I, mode II or mixed mode brittle failure using nonlinear fracture mechanics in terms of a 'smeared crack model'. The 'JCM-Solidity' model is further coupled to the multiphase flow solver 'IC-FERST' which is based on a CV-FEM formulation. This is achieved using a conservative mesh-to-mesh interpolation between solids and fluids, while forces are balanced using the novel 'immersed body method' for full two-way coupling. Anisotropic adaptive mesh refinement is used in the coupled domain to capture the fracture characteristics throughout the simulation. Thus, geomechanically-constrained hydraulically equivalent fracture apertures inform the local permeability for often highly refined fluids mesh elements within fractured regions of the porous rock mass, leak-off being automatically accommodated. Fluid flow is solved over the entire domain which represents the fractured system, with underlying details from the solid model. Coupled deformation, fracturing and flow processes can thus be captured by such a fully coupled solution scheme. © 2017 ARMA, American Rock Mechanics Association.

关键词： Excavation

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Thermo-bioconvection transport of nanofluid over an inclined stretching cylinder with Cattaneo–Christov double-diffusion

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Communications in Theoretical Physics 2021年第7期73卷 47-58页

作者： Hassan Waqas Umair Manzoor Taseer Muhammad Sajjad Hussain Department of Mathematics Government College University FaisalabadLayyah Campus 31200Pakistan Department of Mathematics College of SciencesKing Khalid UniversityAbha 61413Saudi Arabia Mathematical Modelling and Applied Computation Research Group(MMAC) Department of MathematicsKing Abdulaziz UniversityPO Box 80203Jeddah 21589Saudi Arabia

In this paper,Newtonian nanofluid flow is observed under the effects of the magnetic field,activation energy and motile microorganisms over an inclined stretchable *** magnificent aspects of nanoliquid are demonstrated by enduring the Brownian motion and thermophoresis diffusion *** higher order partial differential equations are transformed into first-order ordinary differential equations with suitable similarity *** attained sets of governing equations are then cracked by bvp4 c procedure in MATLAB mathematical *** numerical and graphical outcomes of controlling parameters such as Prandtl number,mixed convection,activation energy,thermophoresis,Brownian parameter,Biot number,Lewis number,Peclet number and motile concentration parameter against the velocity,temperature,volumetric concentration and motile concentration of nanoparticles of the fluid are *** velocity is enhanced with the growth valuation in mixed convection and decay by rising variation of buoyancy ratio parameter,magnetic parameter and bio-convective Rayleigh *** evolution in motile microorganisms is due to the increasing values of microorganisms Biot *** presented data can be helpful in enhancement of manufacturing processes,biomolecules,extrusion systems applications and energy production improvement.

关键词： bio-convection magnetic-nanofluid Cattaneo–Christov theory motile microorganisms inclined stretching cylinder

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The Supertree Tool Kit

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BMC Research Notes 2010年第1期3卷 1-6页

作者： Davis, Katie E Hill, Jon Faculty of Biomedical and Life Sciences Graham Kerr Building University of Glasgow Glasgow G12 8QQ United Kingdom Applied Modelling and Computation Group Earth Science and Engineering Imperial College London London SW7 2AZ United Kingdom

Background. Large phylogenies are crucial for many areas of biological research. One method of creating such large phylogenies is the supertree method, but creating supertrees containing thousands of taxa, and hence providing a comprehensive phylogeny, requires hundred or even thousands of source input trees. Managing and processing these data in a systematic and error-free manner is challenging and will become even more so as supertrees contain ever increasing numbers of taxa. Protocols for processing input source phylogenies have been proposed to ensure data quality, but no robust software implementations of these protocols as yet exist. Findings. The aim of the Supertree Tool Kit (STK) is to aid in the collection, storage and processing of input source trees for use in supertree analysis. It is therefore invaluable when creating supertrees containing thousands of taxa and hundreds of source trees. The STK is a Perl module with executable scripts to carry out various steps in the processing protocols. In order to aid processing we have added meta-data, via XML, to each tree which contains information such as the bibliographic source information for the tree and how the data were derived, for instance the character data used to carry out the original analysis. These data are essential parts of previously proposed protocols. Conclusions. The STK is a bioinformatics tool designed to make it easier to process source phylogenies for inclusion in supertree analysis from hundreds or thousands of input source trees, whilst reducing potential errors and enabling easy sharing of such datasets. It has been successfully used to create the largest known supertree to date containing over 5000 taxa from over 700 source phylogenies. © 2010 Davis et al;licensee BioMed Central Ltd.

关键词： Source Tree Supertree Method Taxon List Perl Module Large Phylogeny

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An investigation into the accuracy of the depth-Averaging used in tidal turbine array optimisation

arXiv

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arXiv 2018年

作者： Abolghasemi, Mohammad Amin Piggott, Matthew D. Kramer, Stephan C. Department of Engineering Science University of Oxford Applied Modelling and Computation Group Department of Earth Science and Engineering Imperial College London

Depth-Averaged shallow water models are widely used for the large-scale sim-ulation of tidal turbine arrays. The relatively low computational complexity of this approach allows for layout optimisations aimed at improving the to-tal array power output as well as an assessment of large-scale environmental impacts. In order to assess the suitability of using depth-Averaged models to optimise array configurations, a comprehensive comparison between the wake profiles and power outputs predicted by a 2D shallow water model and a 3D actuator disc momentum (ADM) model is presented. Initially, a vis-cosity sensitivity analysis is presented to outline the limitations associated with using a constant eddy viscosity in the depth-Averaged model and to outline the importance of correctly calibrating this value in line with the freestream velocity magnitude. Thereafter, the depth-Averaged OpenTidal-Farm (OTF) tool is used to optimise the positions of an array of 32 turbines in an ideal channel and the 3D Fluidity ADM-RANS model is used to assess the accuracy of the OTF predictions for the first time. It is shown that with the help of corrected power calculations a good agreement between the two models can be achieved, thus demonstrating the value of the eddy viscosity calibration implemented in the depth-Averaged model. Copyright © 2018, The Authors. All rights reserved.

关键词： Sensitivity analysis

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Steps towards verification and validation of the Fetch code for Level 2 analysis, design, and optimization of aqueous homogeneous reactors

Steps towards verification and validation of the Fetch code ...

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International Conference on the Physics of Reactors 2012: Advances in Reactor Physics, PHYSOR 2012

作者： Nygaard, E.T. Pain, C.C. Eaton, M.D. Gomes, J.L.M.A. Goddard, A.J.H. Gorman, G. Tollit, B. Buchan, A.G. Cooling, C.M. Angelo, P.L. Babcock and Wilcox Technical Services Group 800 Main Street Lynchburg VA 24504 United States Applied Modelling and Computation Group Department of Earth Science and Engineering Imperial College London SW7 2AZ United Kingdom Y-12 National Security Complex Oak Ridge TN 37831 United States

ISBN: (纸本)9781622763894

Babcock and Wilcox Technical Services group (B&W) has identified aqueous homogeneous reactors (AHRs) as a technology well suited to produce the medical isotope molybdenum 99 (Mo99). AHRs have never been specifically designed or built for this specialized purpose. However, AHRs have a proven history of being safe research reactors. In fact, in 1958, AHRs had "a longer history of operation than any other type of research reactor using enriched fuel" and had "experimentally demonstrated to be among the safest of all various type of research reactor now in use [1]." While AHRs have been modeled effectively using simplified "Level 1" tools, the complex interactions between fluids, neutronics, and solid structures are important (but not necessarily safety significant). These interactions require a "Level 2" modeling tool. Imperial College London (ICL) has developed such a tool: Finite Element Transient Criticality (FETCH). FETCH couples the radiation transport code EVENT with the computational fluid dynamics code (Fluidity), the result is a code capable of modeling sub-critical, critical, and super-critical solutions in both two-and three-dimensions. Using FETCH, ICL researchers and B&W engineers have studied many fissioning solution systems include the Tokimura criticality accident, the Y12 accident, SILENE, TRACY, and SUPO. These modeling efforts will ultimately be incorporated into FETCH'S extensive automated verification and validation (V&V) test suite expanding FETCH'S area of applicability to include all relevant physics associated with AHRs. These efforts parallel B&W's engineering effort to design and optimize an AHR to produce Mo99.

关键词： Molybdenum

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