The Experts below are selected from a list of 90 Experts worldwide ranked by ideXlab platform
Odd M. Faltinsen - One of the best experts on this subject based on the ideXlab platform.
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A Numerical Study on Stratified Shear Layers With Relevance to Oil-Boom Failure
Journal of Offshore Mechanics and Arctic Engineering, 2015Co-Authors: David Kristiansen, Odd M. FaltinsenAbstract:Interface dynamics of two-phase flow, with relevance for leakage of oil retained by mechanical oil barriers, is studied by means of a two-dimensional (2D) lattice-Boltzmann method (LBM) combined with a phase-field model for interface capturing. A multirelaxation-time (MRT) model of the collision process is used to obtain a numerically stable model at high Reynolds number flow. In the phase-field model, the interface is given a finite but small thickness, where the fluid properties vary continuously across a thin interface layer. Surface tension is modeled as a volume force in the transition layer. The numerical model is implemented for simulations with the graphic processing unit (GPU) of a desktop personal computer. Verification tests of the model are presented. The model is then applied to simulate gravity currents (GCs) obtained from a lock-Exchange Configuration, using fluid parameters relevant for those of oil and water. Interface instability phenomena are observed, and obtained numerical results are in good agreement with theory. This work demonstrates that the numerical model presented can be used as a numerical tool for studies of stratified shear flows with relevance to oil-boom failure.
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A Numerical Study on Stratified Shear Layers With Relevance to Oil-Boom Failure
Volume 8B: Ocean Engineering, 2014Co-Authors: David Kristiansen, Odd M. FaltinsenAbstract:Interface dynamics of two-phase flow, with relevance for leakage of oil retained by mechanical oil barriers, is studied by means of a 2D lattice-Boltzmann method combined with a phase-field model for interface capturing. A Multi-Relaxation-Time (MRT) model of the collision process is used to obtain a numerically stable model at high Reynolds-number flow. In the phase-field model, the interface is given a finite but small thickness where the fluid properties vary continuosly across a thin interface layer. Surface tension is modelled as a volume force in the transition layer. The numerical model is implemented for simulations with the graphic processing unit (GPU) of a desktop PC. Verification tests of the model are presented. The model is then applied to simulate gravity currents (GC) obtained from a lock-Exchange Configuration, using fluid parameters relevant for those of oil and water. Interface instability phenomena are observed, and obtained numerical results are in good agreement with theory. This work demonstrates that the numerical model presented can be used as a numerical tool for studies of stratified shear flows with relevance to oil-boom failure.
Jean-michel Reneaume - One of the best experts on this subject based on the ideXlab platform.
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Modelling a Solar Absorption Chiller Using Positive Flash to Estimate the Physical State of Streams and Theoretical Plate Concept for the Generator
Renewable Energy, 2017Co-Authors: Sabine Sochard, Y. Vitupier, L. Castillo Garcia, Sylvain Serra, Jean-michel ReneaumeAbstract:In this paper a general model for the steady state simulation of a solar absorption chiller is proposed. The novelty of this model is to calculate the physical state of all the streams rather than fix them (especially at the outlet of the condenser and evaporator). The thermodynamic properties of the mixture can be calculated by suitable predictive thermodynamic models, hence the working pair can be changed easily. Using this thermodynamic model, a general Positive Flash model is able to describe all the possible states (sub-cooled, super-heated, biphasic) of the various streams which are all considered as multicomponent mixtures. In the positive flash the same set of governing equations is valid for all phase regions. Another originality of the present study is that the generator is modelled as a distillation column, using the theoretical plate concept: MESH equations (Mass balance, Equilibrium, Summation, Heat balance) were written for each stage. Despite the modular structure of the software, a global solution strategy was implemented, using a Newton-Raphson method. This model is successfully compared to an example in the literature which deals with a GAX (Generator-Absorber heat Exchange) Configuration absorption chiller using ammonia/water as the working pair. \textcopyright 2017 Elsevier Ltd
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Dynamic Modelling of Water- Ammonia Absorption Chiller in Gax Configuration
2015Co-Authors: L.c. Garcia, Sabine Sochard, Jean-michel Reneaume, Y. VitupierAbstract:In this paper a general model for the dynamic simulation of an absorption chiller is proposed. The softwe has been designed in a modul way allowing the simulation of vious absorption chiller Configurations (single or multi-stage). Thermodynamic Properties of the mixture of the working fluids can be calculated by suitable thermodynamic models. Hence the working pair can be changed easily. The model is based on mass and energy balances applied to the vious devices of the machine (evaporator, absorber, valves, etc.) and it includes mass storage. A general Positive Flash model enables the description of all the possible states (sub-cooled, super-heated, biphasic...) of the vious streams which e all considered as multicomponent mixtures. In the positive flash the same set of governing equations is valid for all phase regions so that this model can handle the formation of a new phase or the disappeance of an existing one because of composition, pressure or temperature changes due to the dynamic state. The generator is modeled using the concept of theoretical plates: MESH equations (Mass balance, Equilibrium, Summation, Heat balance) have been written for each stage. Finally a general procedure is developed for the modeling of heat Exchangers in order to take into account a local overall heat transfer coefficient according to the local states of the two fluids (sub-cooled, super-heated, evaporating, condensing). Despite the modul structure of the softwe, a global solution strategy has been implemented, using a Ge's method. This general model is then applied to an ammonia/water absorption chiller. The simulated cycle is a GAX (Generator-Absorber heat Exchange) Configuration.
David Kristiansen - One of the best experts on this subject based on the ideXlab platform.
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A Numerical Study on Stratified Shear Layers With Relevance to Oil-Boom Failure
Journal of Offshore Mechanics and Arctic Engineering, 2015Co-Authors: David Kristiansen, Odd M. FaltinsenAbstract:Interface dynamics of two-phase flow, with relevance for leakage of oil retained by mechanical oil barriers, is studied by means of a two-dimensional (2D) lattice-Boltzmann method (LBM) combined with a phase-field model for interface capturing. A multirelaxation-time (MRT) model of the collision process is used to obtain a numerically stable model at high Reynolds number flow. In the phase-field model, the interface is given a finite but small thickness, where the fluid properties vary continuously across a thin interface layer. Surface tension is modeled as a volume force in the transition layer. The numerical model is implemented for simulations with the graphic processing unit (GPU) of a desktop personal computer. Verification tests of the model are presented. The model is then applied to simulate gravity currents (GCs) obtained from a lock-Exchange Configuration, using fluid parameters relevant for those of oil and water. Interface instability phenomena are observed, and obtained numerical results are in good agreement with theory. This work demonstrates that the numerical model presented can be used as a numerical tool for studies of stratified shear flows with relevance to oil-boom failure.
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A Numerical Study on Stratified Shear Layers With Relevance to Oil-Boom Failure
Volume 8B: Ocean Engineering, 2014Co-Authors: David Kristiansen, Odd M. FaltinsenAbstract:Interface dynamics of two-phase flow, with relevance for leakage of oil retained by mechanical oil barriers, is studied by means of a 2D lattice-Boltzmann method combined with a phase-field model for interface capturing. A Multi-Relaxation-Time (MRT) model of the collision process is used to obtain a numerically stable model at high Reynolds-number flow. In the phase-field model, the interface is given a finite but small thickness where the fluid properties vary continuosly across a thin interface layer. Surface tension is modelled as a volume force in the transition layer. The numerical model is implemented for simulations with the graphic processing unit (GPU) of a desktop PC. Verification tests of the model are presented. The model is then applied to simulate gravity currents (GC) obtained from a lock-Exchange Configuration, using fluid parameters relevant for those of oil and water. Interface instability phenomena are observed, and obtained numerical results are in good agreement with theory. This work demonstrates that the numerical model presented can be used as a numerical tool for studies of stratified shear flows with relevance to oil-boom failure.
F Necker - One of the best experts on this subject based on the ideXlab platform.
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analysis and direct numerical simulation of the flow at a gravity current head part 1 flow topology and front speed for slip and no slip boundaries
Journal of Fluid Mechanics, 2000Co-Authors: Carlos Hartel, Eckart Meiburg, F NeckerAbstract:Direct numerical simulations are performed of gravity-current fronts in the lock-Exchange Configuration. The case of small density differences is considered, where the Boussinesq approximations can be adopted. The key objective of the investigation is a detailed analysis of the flow structure at the foremost part of the front, where no previous high-resolution data were available. For the simulations, high-order numerical methods are used, based on spectral and spectral-element discretizations and compact finite differences. A three-dimensional simulation is conducted of a front spreading along a no-slip boundary at a Reynolds number of about 750. The simulation exhibits all features typically observed in experimental flows near the gravity-current head, including the lobe-and-cleft structure at the leading edge. The results reveal that the flow topology at the head differs from what has been assumed previously, in that the foremost point is not a stagnation point in a translating system. Rather, the stagnation point is located below and slightly behind the foremost point in the vicinity of the wall. The relevance of this finding for the mechanism behind the lobe-and-cleft instability is discussed. In order to explore the high-Reynolds-number regime, and to assess potential Reynolds-number effects, two-dimensional simulations are conducted for Reynolds numbers up to about 30000, for both no-slip and slip (i.e. shear-stress free) boundaries. It is shown that although quantitative Reynolds-number effects persist over the whole range examined, no qualitative changes in the flow structure at the head can be observed. A comparison of the two-dimensional results with laboratory data and the three-dimensional simulation provides evidence that a two-dimensional model is able to capture essential features of the flow at the head. The simulations also show that for the free-slip case the shape of the head agrees closely with the classical inviscid theory of Benjamin.
Sabine Sochard - One of the best experts on this subject based on the ideXlab platform.
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Modelling a Solar Absorption Chiller Using Positive Flash to Estimate the Physical State of Streams and Theoretical Plate Concept for the Generator
Renewable Energy, 2017Co-Authors: Sabine Sochard, Y. Vitupier, L. Castillo Garcia, Sylvain Serra, Jean-michel ReneaumeAbstract:In this paper a general model for the steady state simulation of a solar absorption chiller is proposed. The novelty of this model is to calculate the physical state of all the streams rather than fix them (especially at the outlet of the condenser and evaporator). The thermodynamic properties of the mixture can be calculated by suitable predictive thermodynamic models, hence the working pair can be changed easily. Using this thermodynamic model, a general Positive Flash model is able to describe all the possible states (sub-cooled, super-heated, biphasic) of the various streams which are all considered as multicomponent mixtures. In the positive flash the same set of governing equations is valid for all phase regions. Another originality of the present study is that the generator is modelled as a distillation column, using the theoretical plate concept: MESH equations (Mass balance, Equilibrium, Summation, Heat balance) were written for each stage. Despite the modular structure of the software, a global solution strategy was implemented, using a Newton-Raphson method. This model is successfully compared to an example in the literature which deals with a GAX (Generator-Absorber heat Exchange) Configuration absorption chiller using ammonia/water as the working pair. \textcopyright 2017 Elsevier Ltd
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Dynamic Modelling of Water- Ammonia Absorption Chiller in Gax Configuration
2015Co-Authors: L.c. Garcia, Sabine Sochard, Jean-michel Reneaume, Y. VitupierAbstract:In this paper a general model for the dynamic simulation of an absorption chiller is proposed. The softwe has been designed in a modul way allowing the simulation of vious absorption chiller Configurations (single or multi-stage). Thermodynamic Properties of the mixture of the working fluids can be calculated by suitable thermodynamic models. Hence the working pair can be changed easily. The model is based on mass and energy balances applied to the vious devices of the machine (evaporator, absorber, valves, etc.) and it includes mass storage. A general Positive Flash model enables the description of all the possible states (sub-cooled, super-heated, biphasic...) of the vious streams which e all considered as multicomponent mixtures. In the positive flash the same set of governing equations is valid for all phase regions so that this model can handle the formation of a new phase or the disappeance of an existing one because of composition, pressure or temperature changes due to the dynamic state. The generator is modeled using the concept of theoretical plates: MESH equations (Mass balance, Equilibrium, Summation, Heat balance) have been written for each stage. Finally a general procedure is developed for the modeling of heat Exchangers in order to take into account a local overall heat transfer coefficient according to the local states of the two fluids (sub-cooled, super-heated, evaporating, condensing). Despite the modul structure of the softwe, a global solution strategy has been implemented, using a Ge's method. This general model is then applied to an ammonia/water absorption chiller. The simulated cycle is a GAX (Generator-Absorber heat Exchange) Configuration.
