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Transport Simulation (transport + simulation)
Selected AbstractsEvaluating MT3DMS for Heat Transport Simulation of Closed Geothermal SystemsGROUND WATER, Issue 5 2010Jozsef Hecht-Méndez Owing to the mathematical similarities between heat and mass transport, the multi-species transport model MT3DMS should be able to simulate heat transport if the effects of buoyancy and changes in viscosity are small. Although in several studies solute models have been successfully applied to simulate heat transport, these studies failed to provide any rigorous test of this approach. In the current study, we carefully evaluate simulations of a single borehole ground source heat pump (GSHP) system in three scenarios: a pure conduction situation, an intermediate case, and a convection-dominated case. Two evaluation approaches are employed: first, MT3DMS heat transport results are compared with analytical solutions. Second, simulations by MT3DMS, which is finite difference, are compared with those by the finite element code FEFLOW and the finite difference code SEAWAT. Both FEFLOW and SEAWAT are designed to simulate heat flow. For each comparison, the computed results are examined based on residual errors. MT3DMS and the analytical solutions compare satisfactorily. MT3DMS and SEAWAT results show very good agreement for all cases. MT3DMS and FEFLOW two-dimensional (2D) and three-dimensional (3D) results show good to very good agreement, except that in 3D there is somewhat deteriorated agreement close to the heat source where the difference in numerical methods is thought to influence the solution. The results suggest that MT3DMS can be successfully applied to simulate GSHP systems, and likely other systems with similar temperature ranges and gradients in saturated porous media. [source] Simulating short-circuiting flow in a constructed wetland: the implications of bathymetry and vegetation effectsHYDROLOGICAL PROCESSES, Issue 6 2009Joong-Hyuk Min Abstract Short-circuiting flow, commonly experienced in many constructed wetlands, reduces hydraulic retention times in unit wetland cells and decreases the treatment efficiency. A two-dimensional (2-D), physically based, distributed modelling approach was used to systematically address the effects of bathymetry and vegetation on short-circuiting flow, which previously have been neglected or lumped in one-dimensional wetland flow models. In this study, a 2-D transient hydrodynamics with advection-dispersion model was developed using MIKE 21 and calibrated with bromide tracer data collected at the Orlando Easterly Wetland Cell 7. The estimated topographic difference between short-circuiting flow zone and adjacent area ranged from 0·3 to 0·8 m. A range of the Manning roughness coefficient at the short-circuiting flow zone was estimated (0·022,0·045 s m,1/3). Sensitivity analysis of topographical and vegetative heterogeneity deduced during model calibration shows that relic ditches or other ditch-shaped landforms and the associated sparse vegetation along the main flow direction intensify the short-circuiting pattern, considerably affecting 2-D solute transport simulation. In terms of hydraulic efficiency, this study indicates that the bathymetry effect on short-circuiting flow is more important than the vegetation effect. Copyright © 2009 John Wiley & Sons, Ltd. [source] A new approach for numerical simulation of quantum transport in double-gate SOIINTERNATIONAL JOURNAL OF NUMERICAL MODELLING: ELECTRONIC NETWORKS, DEVICES AND FIELDS, Issue 6 2007Tarek M. Abdolkader Abstract Numerical simulation of nanoscale double-gate SOI (Silicon-on-Insulator) greatly depends on the accurate representation of quantum mechanical effects. These effects include, mainly, the quantum confinement of carriers by gate-oxides in the direction normal to the interfaces, and the quantum transport of carriers along the channel. In a previous work, the use of transfer matrix method (TMM) was proposed for the simulation of the first effect. In this work, TMM is proposed to be used for the solution of Schrodinger equation with open boundary conditions to simulate the second quantum-mechanical effect. Transport properties such as transmission probability, carrier concentration, and I,V characteristics resulting from quantum transport simulation using TMM are compared with that using the traditional tight-binding model (TBM). Comparison showed that, when the same mesh size is used in both methods, TMM gives more accurate results than TBM. Copyright © 2007 John Wiley & Sons, Ltd. [source] Effect of dynamic loading on solute transport in soft gels implication for drug deliveryAICHE JOURNAL, Issue 3 2008F. Urciuolo Abstract Solute transport through soft gels and tissues is intimately coupled to mechanical stress and deformation of the macromolecular network. The aim of this study was to investigate the effect of periodic mechanical stimuli upon solute transport through agarose gels at different concentrations. For this purpose it was experimentally evaluated the materials parameters that govern the coupling between elasto-dynamic and solute transport: hydraulic conductivity (K), elastic modulus (HA), and macromolecular diffusivity (Dg) along with their strain dependence behavior. Mechanical activated solute transport simulation was carried out in order to elucidate the role of amplitude and frequency of soliciting mechanical stimuli on mass kinetics release. Results show that mechanical loading affects the release of macromolecules from a gel in a frequency and strain dependent manner. These findings pave the way for novel strategies for the design and engineering of smart drug delivery devices with transport mechanisms triggered by mechanical stimuli. © 2008 American Institute of Chemical Engineers AIChE J, 2008 [source] Modelling the reciprocal water exchange between a river (Havel) and a lake (Tegeler See) during spring and autumn overturnsLAKES & RESERVOIRS: RESEARCH AND MANAGEMENT, Issue 3 2000Karl-Erich Lindenschmidt Abstract A finite volume computer model (current flow and transport) was used to simulate the reciprocal water exchange between a river (Havel) and a lake (Tegeler See) appendaged to the river in Berlin, Germany. The discretization of the model control volume is 2-D along the plane of the water surface, which restricts the modelling to time periods of complete overturn. The finite volume method does, however, allow a depth to be given for each volume cell. A k -, turbulence submodel was integrated into the model to calculate the distinct dispersion coefficients for each volume cell. As current flow measurements were unavailable, the model was verified indirectly by the transport simulation of dissolved chloride, a conservative substance. The results show that the Havel contributes up to 30% of the total inflow to Tegeler See when it is overturned. As the Havel is more heavily polluted with respect to phosphorus loading, this has negative implications to the water quality of Tegeler See. Suggestions are given for controlling the Havel inflow amount by increasing the output of the phosphate elimination facility, the second main inflow to Tegeler See. Its output has very low phosphorus concentrations and serves as a flushing function. [source] Performance assessment of hanging funnel-and-gate structures designed by reverse particle tracking for capturing polluted groundwaterREMEDIATION, Issue 3 2007Paul F. Hudak The objective of this study was to evaluate the capability of partially penetrating (hanging) funnel-and-gate structures, designed using reverse flow trajectories, for capturing plumes of contaminated groundwater. Linear capture structures, comprised of two slurry cutoff walls on either side of a permeable gate, were positioned perpendicular to regional groundwater flow in a hypothetical unconfined aquifer. A four-step approach was used for each of two simulated settings: (1) a numerical mass transport model generated a contaminant plume originating from a source area; (2) a particle-tracking model projected groundwater flow paths upstream from a treatment gate; (3) the structure was widened and deepened until bounding path lines contained the plume; and (4) mass transport simulation tested the ability of the structure to capture the plume. Results of this study suggest that designing funnel-and-gate structures using reverse particle tracking may result in too small a structure to capture a contaminant plume. This practice generally ignores effects of hydrodynamic dispersion, which may enlarge plumes such that contaminants move beneath or around a capture structure. This bypassing effect may be considerable even for low values of dispersivity. Particle-tracking approaches may also underestimate the amount of time required to reduce contaminant concentrations to acceptable levels. © 2007 Wiley Periodicals, Inc. [source] Supplementary oxygen and temperature management during live transportation of greenlip abalone, Haliotis laevigata (Donovan, 1808)AQUACULTURE RESEARCH, Issue 7 2009Erin J Bubner Abstract Live greenlip abalone, Haliotis laevigata, are highly valued in Australian export markets with demand increasingly being met with cultured stock. Live transportation of abalone requires the maintenance of favourable conditions within transport containers for periods exceeding 35 h. We examined the combined effects of temperature regulation (ice provision) and of supplemental oxygen (60% and 100% concentrations) on mortality rates of abalone over 7 days following a 35-h simulated live-transport experiment. We also examined the physiological condition of greenlip abalone (oxygen consumption rate, haemolymph pH and weight) during the simulation experiment. The provision of ice and supplementary oxygen reduced abalone mortalities. Omission of ice and supplementary oxygen during the transport simulation resulted in mortality rates ranging from 70% to 100%. The addition of ice to containers with ambient oxygen concentrations decreased average mortality rates by 50%. While supplementary oxygen further reduced these rates, the provision of both ice and 100% oxygen was by far the most effective combination, reducing mortalities to between 2% and 6%. Supplementary oxygen increased oxygen consumption rates of abalone above those transported at ambient oxygen concentrations. Live-transport decreased haemolymph pH in all treatments but was most pronounced in treatments without ice or supplementary oxygen. On average, abalone lost 7,13% of their weight during the simulation but this loss was independent of transport treatment. [source] Accuracy of Galerkin finite elements for groundwater flow simulations in two and three-dimensional triangulationsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 4 2001Christian Cordes Abstract In standard finite element simulations of groundwater flow the correspondence between hydraulic head gradients and groundwater fluxes is represented by the stiffness matrix. In two-dimensional problems the use of linear triangular elements on Delaunay triangulations guarantees a stiffness matrix of type M. This implies that the local numerical fluxes are physically consistent with Darcy's law. This condition is fundamental to avoid the occurrence of local maxima or minima, and is of crucial importance when the calculated flow field is used in contaminant transport simulations or pathline evaluation. In three spatial dimensions, the linear Galerkin approach on tetrahedra does not lead to M -matrices even on Delaunay meshes. By interpretation of the Galerkin approach as a subdomain collocation scheme, we develop a new approach (OSC, orthogonal subdomain collocation) that is shown to produce M -matrices in three-dimensional Delaunay triangulations. In case of heterogeneous and anisotropic coefficients, extra mesh properties required for M -stiffness matrices will also be discussed. Copyright © 2001 John Wiley & Sons, Ltd. [source] Light curves for off-centre ignition models of Type Ia supernovaeMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2007S. A. Sim ABSTRACT Motivated by recent models involving off-centre ignition of Type Ia supernova explosions, we undertake three-dimensional time-dependent radiation transport simulations to investigate the range of bolometric light-curve properties that could be observed from supernovae in which there is a lop-sided distribution of the products from nuclear burning. We consider both a grid of artificial toy models which illustrate the conceivable range of effects and a recent three-dimensional hydrodynamical explosion model. We find that observationally significant viewing angle effects are likely to arise in such supernovae and that these may have important ramifications for the interpretation of the observed diversity of Type Ia supernova and the systematic uncertainties which relate to their use as standard candles in contemporary cosmology. [source] LO Peg in 1998: star-spot patterns and differential rotationMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2005J. R. Barnes ABSTRACT We present Doppler images of the young K5V,K7V rapid rotator LO Peg from seven nights of continuous spectroscopy obtained in 1998 from July 04 to July 10. The images reveal the presence of a strong polar cap with appendages extending to mid-latitudes, but no star-spots are seen below 15°. We briefly discuss the distribution of spots in light of recent flux transport simulations, which are able to reproduce the observed latitude dependence. With the full time series of spectra, of which 314 are useful, many phases are observed three times over the seven nights of observations. Using star-spots as tracers of a solar-like latitudinal differential rotation in our image reconstructions, we find that the equatorial regions complete one more rotation than the polar regions every 181 ± 35 d. LO Peg is the second coolest star for which such a measurement has been made using indirect imaging methods. The degree of latitudinal shear is less than that seen in G and early K dwarfs, suggesting a trend in which differential rotation decreases with stellar mass in (pre-)main-sequence objects. [source] | |||||||||||||