An Axisymmetric, Hydrodynamical Model for the Torus Wind in Active Galactic Nuclei
NASA Technical Reports Server (NTRS)
Dorodnitsyn, A.; Kallman, T.; Proga, D.
2008-01-01
We report on time-dependent axisymmetric simulations of an X-ray-excited flow from a parsec-scale, rotating, cold torus around an active galactic nucleus. Our simulations account for radiative heating and cooling and radiation pressure force. The simulations follow the development of a broad biconical outflow induced mainly by X-ray heating. We compute synthetic spectra predicted by our simulations. The wind characteristics and the spectra support the hypothesis that a rotationally supported torus can serve as the source of a wind which is responsible for the warm absorber gas observed in the X-ray spectra of many Seyfert galaxies.
An Axisymmetric, Hydrodynamical Model for the Torus Wind in Active Galactic Nuclei
NASA Technical Reports Server (NTRS)
Dorodnitsyn, A.; Kallman, T.; Proga, D.
2008-01-01
We report on time-dependent axisymmetric simulations of an X-ray-excited flow from a parsec-scale, rotating, cold torus around an active galactic nucleus. Our simulations account for radiative heating and cooling and radiation pressure force. The simulations follow the development of a broad biconical outflow induced mainly by X-ray heating. We compute synthetic spectra predicted by our simulations. The wind characteristics and the spectra support the hypothesis that a rotationally supported torus can serve as the source of a wind which is responsible for the warm absorber gas observed in the X-ray spectra of many Seyfert galaxies.
An Axisymmetric Hydrodynamical Model for the Torus Wind in AGN. 2; X-ray Excited Funnel Flow
NASA Technical Reports Server (NTRS)
Dorodnitsyn, A.; Kallman, T.; Proga, D.
2008-01-01
We have calculated a series of models of outflows from the obscuring torus in active galactic nuclei (AGN). Our modeling assumes that the inner face of a rotationally supported torus is illuminated and heated by the intense X-rays from the inner accretion disk and black hole. As a result of such heating a strong biconical outflow is observed in our simulations. We calculate 3-dimensional hydrodynamical models, assuming axial symmetry, and including the effects of X-ray heating, ionization, and radiation pressure. We discuss the behavior of a large family of these models, their velocity fields, mass fluxes and temperature, as functions of the torus properties and X-ray flux. Synthetic warm absorber spectra are calculated, assuming pure absorption, for sample models at various inclination angles and observing times. We show that these models have mass fluxes and flow speeds which are comparable to those which have been inferred from observations of Seyfert 1 warm absorbers, and that they can produce rich absorption line spectra.
Modeling axisymmetric flow and transport.
Langevin, Christian D
2008-01-01
Unmodified versions of common computer programs such as MODFLOW, MT3DMS, and SEAWAT that use Cartesian geometry can accurately simulate axially symmetric ground water flow and solute transport. Axisymmetric flow and transport are simulated by adjusting several input parameters to account for the increase in flow area with radial distance from the injection or extraction well. Logarithmic weighting of interblock transmissivity, a standard option in MODFLOW, can be used for axisymmetric models to represent the linear change in hydraulic conductance within a single finite-difference cell. Results from three test problems (ground water extraction, an aquifer push-pull test, and upconing of saline water into an extraction well) show good agreement with analytical solutions or with results from other numerical models designed specifically to simulate the axisymmetric geometry. Axisymmetric models are not commonly used but can offer an efficient alternative to full three-dimensional models, provided the assumption of axial symmetry can be justified. For the upconing problem, the axisymmetric model was more than 1000 times faster than an equivalent three-dimensional model. Computational gains with the axisymmetric models may be useful for quickly determining appropriate levels of grid resolution for three-dimensional models and for estimating aquifer parameters from field tests.
Modeling axisymmetric flow and transport
Langevin, C.D.
2008-01-01
Unmodified versions of common computer programs such as MODFLOW, MT3DMS, and SEAWAT that use Cartesian geometry can accurately simulate axially symmetric ground water flow and solute transport. Axisymmetric flow and transport are simulated by adjusting several input parameters to account for the increase in flow area with radial distance from the injection or extraction well. Logarithmic weighting of interblock transmissivity, a standard option in MODFLOW, can be used for axisymmetric models to represent the linear change in hydraulic conductance within a single finite-difference cell. Results from three test problems (ground water extraction, an aquifer push-pull test, and upconing of saline water into an extraction well) show good agreement with analytical solutions or with results from other numerical models designed specifically to simulate the axisymmetric geometry. Axisymmetric models are not commonly used but can offer an efficient alternative to full three-dimensional models, provided the assumption of axial symmetry can be justified. For the upconing problem, the axisymmetric model was more than 1000 times faster than an equivalent three-dimensional model. Computational gains with the axisymmetric models may be useful for quickly determining appropriate levels of grid resolution for three-dimensional models and for estimating aquifer parameters from field tests.
A minimal axisymmetric hurricane model
NASA Astrophysics Data System (ADS)
Mai, Nguyen Chi; Smith, Roger K.; Zhu, Hongyan; Ulrich, Wolfgang
2002-10-01
Solutions of an axisymmetric version of the minimal three-dimensional numerical model of a tropical cyclone developed by Zhu et al. (2001) are described and compared with those of the three-dimensional model. Vortex evolution is similar in the two models during the early stages of intensification, but the period of rapid intensification occurs earlier in the axisymmetric model due to the higher effective resolution obtained using a staggered grid. There are marked differences at later times, when, in the three-dimensional model, asymmetric structures develop. The findings are compared with those of an earlier study by Anthes (1972). The axisymmetric model is used to investigate certain fundamental aspects of tropical-cyclone dynamics, including the emergence of a region of supergradient winds in the boundary layer and the evolution of regions satisfying necessary conditions for inertial and barotropic instability.Supergradient winds develop in the boundary layer within a radius of about 100 km of the vortex axis at an early stage of evolution and appear to be a natural feature of the vortex boundary layer. The development of flow regions satisfying necessary conditions for inertial and barotropic instability occur later, and may be attributed inter alia to the upward transfer of air with relatively high angular momentum, from the boundary layer to the middle and upper layers, by the secondary circulation of the vortex, and the downward transfer of air with relatively low angular momentum to the middle layer. A linear analysis of a two-layer slab-symmetric flow suggests why inertial instability does not occur in the axisymmetric model. Barotropic instability does not appear to be the mechanism responsible for the growth of asymmetries in the calculations using the three-dimensional version of the model.
Hydrodynamic analysis and shape optimization for vertical axisymmetric wave energy converters
NASA Astrophysics Data System (ADS)
Zhang, Wan-chao; Liu, Heng-xu; Zhang, Liang; Zhang, Xue-wei
2016-12-01
The absorber is known to be vertical axisymmetric for a single-point wave energy converter (WEC). The shape of the wetted surface usually has a great influence on the absorber's hydrodynamic characteristics which are closely linked with the wave power conversion ability. For complex wetted surface, the hydrodynamic coefficients have been predicted traditionally by hydrodynamic software based on the BEM. However, for a systematic study of various parameters and geometries, they are too multifarious to generate so many models and data grids. This paper examines a semi-analytical method of decomposing the complex axisymmetric boundary into several ring-shaped and stepped surfaces based on the boundary discretization method (BDM) which overcomes the previous difficulties. In such case, by using the linear wave theory based on eigenfunction expansion matching method, the expressions of velocity potential in each domain, the added mass, radiation damping and wave excitation forces of the oscillating absorbers are obtained. The good astringency of the hydrodynamic coefficients and wave forces are obtained for various geometries when the discrete number reaches a certain value. The captured wave power for a same given draught and displacement for various geometries are calculated and compared. Numerical results show that the geometrical shape has great effect on the wave conversion performance of the absorber. For absorbers with the same outer radius and draught or displacement, the cylindrical type shows fantastic wave energy conversion ability at some given frequencies, while in the random sea wave, the parabolic and conical ones have better stabilization and applicability in wave power conversion.
Dynamo Models for Saturn's Axisymmetric Magnetic Field
NASA Astrophysics Data System (ADS)
Stanley, S.; Tajdaran, K.
2012-12-01
Magnetic field measurements by the Cassini mission have confirmed the earlier Pioneer 11 and Voyager missions' results that Saturn's observed magnetic field is extremely axisymmetric . For example, Saturn's dipole tilt is less than 0.06 degrees (Cao et al., 2011) . The nearly-perfect axisymmetry of Saturn's dipole is troubling because of Cowling's Theorem which states that an axisymmetric magnetic field cannot be maintained by a dynamo. However, Cowling's Theorem applies to the magnetic field generated inside the dynamo source region and we can avert any contradiction with Cowling's Theorem if we can find reason for a non-axisymmetric field generated inside the dynamo region to have an axisymmetrized potential field observed at satellite altitude. Stevenson (1980) proposed a mechanism for this axisymmetrization. He suggested that differential rotation in a stably-stratified electrically conducting layer (i.e. the helium rain-out layer) surrounding the dynamo could act to shear out the non-axisymmetry and hence produce an axisymmetric observed magnetic field. In previous work, we used three-dimensional self-consistent numerical dynamo models to demonstrate that a thin helium rain-out layer can produce a more axisymmetrized field (Stanley, 2010). We also found that the direction of the zonal flows in the layer is a crucial factor for magnetic field axisymmetry. Here we investigate the influence of the thickness of the helium rain-out layer and the intensity of the thermal winds on the axisymmetrization of the field. We search for optimal regions in parameter space for producing axisymmetric magnetic fields with similar spectral properties to the observed Saturnian field.
NASA Astrophysics Data System (ADS)
Bazilevs, Y.; Long, C. C.; Akkerman, I.; Benson, D. J.; Shashkov, M. J.
2014-04-01
A recent Isogeometric Analysis (IGA) formulation of Lagrangian shock hydrodynamics [4] is extended to the 3D axisymmetric case. The Euler equations of compressible hydrodynamics are formulated using the rz-cylindrical coordinates, and are discretized in the weak form using NURBS-based IGA. Artificial shock viscosity and internal energy projection are added to stabilize the formulation. The resulting discretization exhibits good accuracy and robustness properties. It also gives exact symmetry preservation on the appropriately constructed meshes. Several benchmark examples are computed to examine the performance of the proposed formulation.
AXISYMMETRIC SIMULATIONS OF HOT JUPITER–STELLAR WIND HYDRODYNAMIC INTERACTION
Christie, Duncan; Arras, Phil; Li, Zhi-Yun
2016-03-20
Gas giant exoplanets orbiting at close distances to the parent star are subjected to large radiation and stellar wind fluxes. In this paper, hydrodynamic simulations of the planetary upper atmosphere and its interaction with the stellar wind are carried out to understand the possible flow regimes and how they affect the Lyα transmission spectrum. Following Tremblin and Chiang, charge exchange reactions are included to explore the role of energetic atoms as compared to thermal particles. In order to understand the role of the tail as compared to the leading edge of the planetary gas, the simulations were carried out under axisymmetry, and photoionization and stellar wind electron impact ionization reactions were included to limit the extent of the neutrals away from the planet. By varying the planetary gas temperature, two regimes are found. At high temperature, a supersonic planetary wind is found, which is turned around by the stellar wind and forms a tail behind the planet. At lower temperatures, the planetary wind is shut off when the stellar wind penetrates inside where the sonic point would have been. In this regime mass is lost by viscous interaction at the boundary between planetary and stellar wind gases. Absorption by cold hydrogen atoms is large near the planetary surface, and decreases away from the planet as expected. The hot hydrogen absorption is in an annulus and typically dominated by the tail, at large impact parameter, rather than by the thin leading edge of the mixing layer near the substellar point.
Superluminous Supernovae hydrodynamic models
NASA Astrophysics Data System (ADS)
Orellana, M.
2017-07-01
We use our radiation hydrodynamic code in order to simulate magnetar powered Superluminous Supernovae (SLSNe). It is assumed that a central rapidly rotating magnetar deposits all its rotational energy into the ejecta where is added to the usual power. The magnetar luminosity and spin-down timescale are adopted as the free parameters of the model. For the case of ASASSN-15lh, which has been claimed as the most luminous supernova ever discovered, we have found physically plausible magnetar parameters can reproduce the overall shape of the bolometric light curve (LC) provided the progenitor mass is ≍ 8M⊙. The ejecta dynamics of this event shows signs of the magnetar energy input which deviates the expansion from the usually assumed homologous behaviour. Our numerical experiments lead us to conclude that the hydrodynamical modeling is necessary in order to derive the properties of powerful magnetars driving SLSNe.
Lotic Water Hydrodynamic Model
Judi, David Ryan; Tasseff, Byron Alexander
2015-01-23
Water-related natural disasters, for example, floods and droughts, are among the most frequent and costly natural hazards, both socially and economically. Many of these floods are a result of excess rainfall collecting in streams and rivers, and subsequently overtopping banks and flowing overland into urban environments. Floods can cause physical damage to critical infrastructure and present health risks through the spread of waterborne diseases. Los Alamos National Laboratory (LANL) has developed Lotic, a state-of-the-art surface water hydrodynamic model, to simulate propagation of flood waves originating from a variety of events. Lotic is a two-dimensional (2D) flood model that has been used primarily for simulations in which overland water flows are characterized by movement in two dimensions, such as flood waves expected from rainfall-runoff events, storm surge, and tsunamis. In 2013, LANL developers enhanced Lotic through several development efforts. These developments included enhancements to the 2D simulation engine, including numerical formulation, computational efficiency developments, and visualization. Stakeholders can use simulation results to estimate infrastructure damage and cascading consequences within other sets of infrastructure, as well as to inform the development of flood mitigation strategies.
A solvable model of axisymmetric and non-axisymmetric droplet bouncing.
Andrew, Matthew; Yeomans, Julia M; Pushkin, Dmitri O
2017-02-07
We introduce a solvable Lagrangian model for droplet bouncing. The model predicts that, for an axisymmetric drop, the contact time decreases to a constant value with increasing Weber number, in qualitative agreement with experiments, because the system is well approximated as a simple harmonic oscillator. We introduce asymmetries in the velocity, initial droplet shape, and contact line drag acting on the droplet and show that asymmetry can often lead to a reduced contact time and lift-off in an elongated shape. The model allows us to explain the mechanisms behind non-axisymmetric bouncing in terms of surface tension forces. Once the drop has an elliptical footprint the surface tension force acting on the longer sides is greater. Therefore the shorter axis retracts faster and, due to the incompressibility constraints, pumps fluid along the more extended droplet axis. This leads to a positive feedback, allowing the drop to jump in an elongated configuration, and more quickly.
Recent development of hydrodynamic modeling
NASA Astrophysics Data System (ADS)
Hirano, Tetsufumi
2014-09-01
In this talk, I give an overview of recent development in hydrodynamic modeling of high-energy nuclear collisions. First, I briefly discuss about current situation of hydrodynamic modeling by showing results from the integrated dynamical approach in which Monte-Carlo calculation of initial conditions, quark-gluon fluid dynamics and hadronic cascading are combined. In particular, I focus on rescattering effects of strange hadrons on final observables. Next I highlight three topics in recent development in hydrodynamic modeling. These include (1) medium response to jet propagation in di-jet asymmetric events, (2) causal hydrodynamic fluctuation and its application to Bjorken expansion and (3) chiral magnetic wave from anomalous hydrodynamic simulations. (1) Recent CMS data suggest the existence of QGP response to propagation of jets. To investigate this phenomenon, we solve hydrodynamic equations with source term which exhibits deposition of energy and momentum from jets. We find a large number of low momentum particles are emitted at large angle from jet axis. This gives a novel interpretation of the CMS data. (2) It has been claimed that a matter created even in p-p/p-A collisions may behave like a fluid. However, fluctuation effects would be important in such a small system. We formulate relativistic fluctuating hydrodynamics and apply it to Bjorken expansion. We found the final multiplicity fluctuates around the mean value even if initial condition is fixed. This effect is relatively important in peripheral A-A collisions and p-p/p-A collisions. (3) Anomalous transport of the quark-gluon fluid is predicted when extremely high magnetic field is applied. We investigate this possibility by solving anomalous hydrodynamic equations. We found the difference of the elliptic flow parameter between positive and negative particles appears due to the chiral magnetic wave. Finally, I provide some personal perspective of hydrodynamic modeling of high energy nuclear collisions
Numerical models in hydrodynamics
NASA Astrophysics Data System (ADS)
Belotserkovskii, Oleg Mikhailovich
The use of numerical models in fluid mechanics is examined with emphasis on separated flows at high Reynolds numbers. Topics discussed include the splitting method, homogeneous difference schemes, calculation of the nonstationary motion of ordered and large-scale structures, and numerical modeling of the stochastic component of turbulent shear flow. Attention is also given to motion in wake flows, the problem of turbulent spot breakup, and stability problems.
Modeling the Orion nebula as an axisymmetric blister
NASA Technical Reports Server (NTRS)
Rubin, R. H.; Simpson, J. P.; Haas, M. R.; Erickson, E. F.
1991-01-01
The ionized gas in the Orion nebula is examined by means of axisymmetric modeling that is based on observational data from the ionized, neutral, and molecular regions. Nonsymmetrical features are omitted, radial dependence from the Trapezium is assumed, and azimuthal symmetry in the plane of the sky is used. Stellar properties and abundances of certain elements are described, and these data are used to compare the present axisymmetric-blister model to a previous spherical model. Strong singly-ionized emission that are visible near the Trapezium are found to originate in the ionization-bounded region in the dense Trapezium zone. The model can be more tightly constrained by adding near-IR data on noncentral zones for (Ar II), (AR III), (Ne II), and (S IV). The quadrant with the 'bar' creates an nonsymmetry that influences the observational data, and the model can therefore be improved with the additional data.
Modeling the Orion nebula as an axisymmetric blister
NASA Technical Reports Server (NTRS)
Rubin, R. H.; Simpson, J. P.; Haas, M. R.; Erickson, E. F.
1991-01-01
The ionized gas in the Orion nebula is examined by means of axisymmetric modeling that is based on observational data from the ionized, neutral, and molecular regions. Nonsymmetrical features are omitted, radial dependence from the Trapezium is assumed, and azimuthal symmetry in the plane of the sky is used. Stellar properties and abundances of certain elements are described, and these data are used to compare the present axisymmetric-blister model to a previous spherical model. Strong singly-ionized emission that are visible near the Trapezium are found to originate in the ionization-bounded region in the dense Trapezium zone. The model can be more tightly constrained by adding near-IR data on noncentral zones for (Ar II), (AR III), (Ne II), and (S IV). The quadrant with the 'bar' creates an nonsymmetry that influences the observational data, and the model can therefore be improved with the additional data.
A simple, analytical, axisymmetric microburst model for downdraft estimation
NASA Technical Reports Server (NTRS)
Vicroy, Dan D.
1991-01-01
A simple analytical microburst model was developed for use in estimating vertical winds from horizontal wind measurements. It is an axisymmetric, steady state model that uses shaping functions to satisfy the mass continuity equation and simulate boundary layer effects. The model is defined through four model variables: the radius and altitude of the maximum horizontal wind, a shaping function variable, and a scale factor. The model closely agrees with a high fidelity analytical model and measured data, particularily in the radial direction and at lower altitudes. At higher altitudes, the model tends to overestimate the wind magnitude relative to the measured data.
Application of the PTT model to axisymmetric free surface flows
NASA Astrophysics Data System (ADS)
Merejolli, R.; Paulo, G. S.; Tomé, M. F.
2013-10-01
This work is concerned with numerical simulation of axisymmetric viscoelastic free surface flows using the Phan-Thien-Tanner (PTT) constitutive equation. A finite difference technique for solving the governing equations for unsteady incompressible flows written in Cylindrical coordinates on a staggered grid is described. The fluid is modelled by a Marker-and-Cell type method and an accurate representation of the fluid surface is employed. The full free surface stress conditions are applied. The numerical method is verified by comparing numerical predictions of fully developed flow in a pipe with the corresponding analytic solutions. To demonstrate that the numerical method can simulate axisymmetric free surface flows governed by the PTT model, numerical results of the flow evolution of a drop impacting on a rigid dry plate are presented. In these simulations, the rheological effects of the parameters ɛ and ξ are investigated.
Hydrodynamic Synchronisation of Model Microswimmers
NASA Astrophysics Data System (ADS)
Putz, V. B.; Yeomans, J. M.
2009-12-01
We define a model microswimmer with a variable cycle time, thus allowing the possibility of phase locking driven by hydrodynamic interactions between swimmers. We find that, for extensile or contractile swimmers, phase locking does occur, with the relative phase of the two swimmers being, in general, close to 0 or π, depending on their relative position and orientation. We show that, as expected on grounds of symmetry, self T-dual swimmers, which are time-reversal covariant, do not phase-lock. We also discuss the phase behaviour of a line of tethered swimmers, or pumps. These show oscillations in their relative phases reminiscent of the metachronal waves of cilia.
Axisymmetric model of the ionized gas in the Orion Nebula
NASA Technical Reports Server (NTRS)
Rubin, R. H.; Simpson, J. P.; Haas, M. R.; Erickson, E. F.
1991-01-01
New ionization and thermal equilibrium models for the ionized gas in the Orion Nebula with an axisymmetric two-dimensional 'blister' geometry/density distribution are presented. The HII region is represented more realistically than in previous models, while the physical detail of the microphysics and radiative transfer of the earlier spherical modeling is maintained. The predicted surface brightnesses are compared with observations for a large set of lines at different positions to determine the best-fitting physical parameters. The model explains the strong singly ionized line emission along the lines of sight near the Trapezium.
Axisymmetric model of the ionized gas in the Orion Nebula
NASA Technical Reports Server (NTRS)
Rubin, R. H.; Simpson, J. P.; Haas, M. R.; Erickson, E. F.
1991-01-01
New ionization and thermal equilibrium models for the ionized gas in the Orion Nebula with an axisymmetric two-dimensional 'blister' geometry/density distribution are presented. The HII region is represented more realistically than in previous models, while the physical detail of the microphysics and radiative transfer of the earlier spherical modeling is maintained. The predicted surface brightnesses are compared with observations for a large set of lines at different positions to determine the best-fitting physical parameters. The model explains the strong singly ionized line emission along the lines of sight near the Trapezium.
Model reduction for axisymmetric tokamak control
Tinios, G.; Horne, S. F.; Hutchinson, I. H.; Wolfe, S. M.
1992-12-31
We deal with the problem of reducing a complicated electromagnetic passive structure model coupled to a linear plasma response model to a size that allows rapid calculations of gains for plasma position and shape control. We find that model reduction through eigenmode decomposition does not reproduce the input-to-output relationship of the system, unless one has a good idea of which eigenmodes are important. Hankel singular mode decomposition, on the other hand, provides an orthogonal basis for the system response, where the modes are ordered by their importance to the input-to-output relationship. A perturbed equilibrium plasma response model is used together with an electromagnetic model of the Alcator C-MOD passive structure to assess the performance of different model reduction schemes. We find that between 10 and 20 modes are required to give an adequate representation of the passive system. Emphasis is placed on keeping the reduction process independent of the parameters of the plasma we are trying to control.
The thermal modeling of large axisymmetric forgings
NASA Astrophysics Data System (ADS)
van Tyne, C. J.; Focht, R. B.; Nelson, T. D.; Reese, W.
1994-09-01
Three thermal models for simulating the heating cycles used for large forgings were developed. They were designed for accuracy, user friendliness, and rapid calculation on a personal computer. The results that are obtained from these models are the temperature profiles that occur within the ingot, forging or roll at various depths from the surface. The values for these temperature versus time curves can be used to examine several features about the heat treatment process. The example presented in this paper showed the effect of heating rate and hold at 704 °C on the surface-to-center temperature difference that occurs in a medium carbon steel ingot.
Accuracy Improvement in Magnetic Field Modeling for an Axisymmetric Electromagnet
NASA Technical Reports Server (NTRS)
Ilin, Andrew V.; Chang-Diaz, Franklin R.; Gurieva, Yana L.; Il,in, Valery P.
2000-01-01
This paper examines the accuracy and calculation speed for the magnetic field computation in an axisymmetric electromagnet. Different numerical techniques, based on an adaptive nonuniform grid, high order finite difference approximations, and semi-analitical calculation of boundary conditions are considered. These techniques are being applied to the modeling of the Variable Specific Impulse Magnetoplasma Rocket. For high-accuracy calculations, a fourth-order scheme offers dramatic advantages over a second order scheme. For complex physical configurations of interest in plasma propulsion, a second-order scheme with nonuniform mesh gives the best results. Also, the relative advantages of various methods are described when the speed of computation is an important consideration.
Hydrodynamic models of a Cepheid atmosphere
NASA Technical Reports Server (NTRS)
Karp, A. H.
1975-01-01
Instead of computing a large number of coarsely zoned hydrodynamic models covering the entire atmospheric instability strip, the author computed a single model as well as computer limitations allow. The implicit hydrodynamic code of Kutter and Sparks was modified to include radiative transfer effects in optically thin zones.
Acoustic intensity calculations for axisymmetrically modeled fluid regions
NASA Technical Reports Server (NTRS)
Hambric, Stephen A.; Everstine, Gordon C.
1992-01-01
An algorithm for calculating acoustic intensities from a time harmonic pressure field in an axisymmetric fluid region is presented. Acoustic pressures are computed in a mesh of NASTRAN triangular finite elements of revolution (TRIAAX) using an analogy between the scalar wave equation and elasticity equations. Acoustic intensities are then calculated from pressures and pressure derivatives taken over the mesh of TRIAAX elements. Intensities are displayed as vectors indicating the directions and magnitudes of energy flow at all mesh points in the acoustic field. A prolate spheroidal shell is modeled with axisymmetric shell elements (CONEAX) and submerged in a fluid region of TRIAAX elements. The model is analyzed to illustrate the acoustic intensity method and the usefulness of energy flow paths in the understanding of the response of fluid-structure interaction problems. The structural-acoustic analogy used is summarized for completeness. This study uncovered a NASTRAN limitation involving numerical precision issues in the CONEAX stiffness calculation causing large errors in the system matrices for nearly cylindrical cones.
Process modeling and development for three axisymmetric net shape forgings
El-Gizawy, A.S. . Dept. of Mechanical Aerospace Engineering)
1992-03-01
The results of dynamic material modeling experiments are reported on aluminum alloys 6061 and 7050, and steel alloy 4340. This information was used to accurately describe the variables in the various constitutive equations used in computer modeling programs. A description of the experimental equipment used to deform the specimens and gather data was given. Previously reported work regarding computer modeling of interface friction and the forging process was reviewed. Using dynamic flow models, three different axisymmetric parts were analyzed for their potential for being produced by net shape or near net shape forging processes. Two aluminum alloy parts were recommended as potential candidates while the steel part was not a potential candidate. Recommendations for processing conditions were also given. 18 refs.
Numerical modeling in induction heating for axisymmetric geometries
Chaboudez, C.; Glardon, R.; Mari, D.; Clain, S.; Rappaz, J.; Swierkosz, M.
1997-01-01
Induction heating is widely used in today`s industry, in operations such as metal hardening, preheating for forging operations, or brazing. It is a complex process, involving both electromagnetic and thermal phenomena. Since the design and the investigation of an induction heating system usually relies upon a series of tedious, expensive and long experiments, numerical simulation can be a valuable help in this field. This paper deals with numerical simulation of induction heating for axisymmetric geometries. A mathematical model is presented, together with a numerical scheme based on the Finite Element Method. A numerical simulation code was implemented using the model presented in this paper. A comparison between results given by the code and experimental measurements is provided.
NASA Technical Reports Server (NTRS)
Sohrab, Siavash H.
1999-01-01
Counterflow premixed flames play a significant role in the modeling of laminar flames. This is in part motivated by the fact that stretched premixed flames simulate local flamelet dynamics within turbulent premixed flames. In the present study, the modified form of the Navier-Stokes equation for reactive fields introduced earlier is employed to investigate the hydrodynamics of spherical flows embedded within counterflows. The geometry of premixed flames near the stagnation point is also determined. The predictions are in favorable agreement with the experimental observations and prior numerical studies.
Dynamo Models for Saturn's Axisymmetric Magnetic Field: Finding the Non-axisymmetry
NASA Astrophysics Data System (ADS)
Stanley, S.; Tajdaran, K.
2013-12-01
Magnetic field measurements by the Cassini mission have confirmed the earlier Pioneer 11 and Voyager missions' results that Saturn's observed magnetic field is extremely axisymmetric. For example, Saturn's dipole tilt is less than 0.06 degrees. The near-perfect axisymmetry of Saturn's dipole is troubling because of Cowling's Theorem which states that an axisymmetric magnetic field cannot be maintained by a dynamo. However, Cowling's Theorem applies to the magnetic field generated inside the dynamo source region and we can avert any contradiction with the theorem if we can find reason for a non-axisymmetric field generated inside the dynamo region to have an axisymmetric potential field observed at satellite altitude. Stevenson (1980) proposed that the Helium Insolubility Layer (HIL), which forms at the top of the metallic hydrogen layer in Saturn, could provide such a mechanism. This layer is stably stratified and electrically conducting. Differential rotation in this layer, which surrounds the dynamo source region, could act to attenuate the non-axisymmetric features and hence produce an axisymmetric observed magnetic field. In previous work, we used three-dimensional self-consistent numerical dynamo models to demonstrate that the HIL can produce a more axisymmetric field. We found that the morphology of the zonal flows in the layer is a crucial factor for magnetic field axisymmetry. Here we investigate the influence of the HIL's thickness, stability and thermal wind intensity on the axisymmetrization of the field. We find regions in parameter space for producing axisymmetric magnetic fields with similar spectral properties as Saturn's field. We also find that non-axisymmetric features exist at the surface at smaller wavelengths (i.e. higher multipoles) at high latitudes. This suggests that Cassini's final orbital passes of Saturn in 2017 may find non-axisymmetric features in Saturn's magnetic field for the first time.
Nonstationary model of an axisymmetric mirror trap with nonequilibrium plasma
Yurov, D. V. Prikhodko, V. V. Tsidulko, Yu. A.
2016-03-15
The DOL nonstationary model intended to describe plasma processes in axisymmetric magnetic mirror traps is considered. The model uses averaging over the bounce period in order to take into account the dependence of plasma parameters on the coordinate along the facility axis. Examples of calculations of trap parameters by means of the DOL code based on this model are presented. Among the features of the DOL model, one can single out two points: first, the capability of calculating the terms of the collision integral with the use of a non-Maxwellian scattering function while evaluating the distribution function of fast ions and, second, concerning the background plasma, the capability of calculating the longitudinal particle and energy fluxes in confinement modes with the particle mean free path being on the order of the trap length. The influence of the scattering function approximation used to calculate the collision integral on the solution to the kinetic equation is analyzed. The dependences of plasma parameters on the power of heating injectors and the length of the fast-ion turning zone are presented as calculation examples. The longitudinal profile of the fusion reaction rate in the case of a trap with a long fast-ion turning zone is shown to depend strongly on the input parameters of the model.
Nonstationary model of an axisymmetric mirror trap with nonequilibrium plasma
NASA Astrophysics Data System (ADS)
Yurov, D. V.; Prikhodko, V. V.; Tsidulko, Yu. A.
2016-03-01
The DOL nonstationary model intended to describe plasma processes in axisymmetric magnetic mirror traps is considered. The model uses averaging over the bounce period in order to take into account the dependence of plasma parameters on the coordinate along the facility axis. Examples of calculations of trap parameters by means of the DOL code based on this model are presented. Among the features of the DOL model, one can single out two points: first, the capability of calculating the terms of the collision integral with the use of a non-Maxwellian scattering function while evaluating the distribution function of fast ions and, second, concerning the background plasma, the capability of calculating the longitudinal particle and energy fluxes in confinement modes with the particle mean free path being on the order of the trap length. The influence of the scattering function approximation used to calculate the collision integral on the solution to the kinetic equation is analyzed. The dependences of plasma parameters on the power of heating injectors and the length of the fast-ion turning zone are presented as calculation examples. The longitudinal profile of the fusion reaction rate in the case of a trap with a long fast-ion turning zone is shown to depend strongly on the input parameters of the model.
Axisymmetric curvature-driven instability in a model divertor geometry
Farmer, W. A.; Ryutov, D. D.
2013-09-15
A model problem is presented which qualitatively describes a pressure-driven instability which can occur near the null-point in the divertor region of a tokamak where the poloidal field becomes small. The model problem is described by a horizontal slot with a vertical magnetic field which plays the role of the poloidal field. Line-tying boundary conditions are applied at the planes defining the slot. A toroidal field lying parallel to the planes is assumed to be very strong, thereby constraining the possible structure of the perturbations. Axisymmetric perturbations which leave the toroidal field unperturbed are analyzed. Ideal magnetohydrodynamics is used, and the instability threshold is determined by the energy principle. Because of the boundary conditions, the Euler equation is, in general, non-separable except at marginal stability. This problem may be useful in understanding the source of heat transport into the private flux region in a snowflake divertor which possesses a large region of small poloidal field, and for code benchmarking as it yields simple analytic results in an interesting geometry.
Hydrodynamics of bacterial colonies: A model
NASA Astrophysics Data System (ADS)
Lega, J.; Passot, T.
2003-03-01
We propose a hydrodynamic model for the evolution of bacterial colonies growing on soft agar plates. This model consists of reaction-diffusion equations for the concentrations of nutrients, water, and bacteria, coupled to a single hydrodynamic equation for the velocity field of the bacteria-water mixture. It captures the dynamics inside the colony as well as on its boundary and allows us to identify a mechanism for collective motion towards fresh nutrients, which, in its modeling aspects, is similar to classical chemotaxis. As shown in numerical simulations, our model reproduces both usual colony shapes and typical hydrodynamic motions, such as the whirls and jets recently observed in wet colonies of Bacillus subtilis. The approach presented here could be extended to different experimental situations and provides a general framework for the use of advection-reaction-diffusion equations in modeling bacterial colonies.
Hydrodynamic Modeling and Its Application in AUC.
Rocco, Mattia; Byron, Olwyn
2015-01-01
The hydrodynamic parameters measured in an AUC experiment, s(20,w) and D(t)(20,w)(0), can be used to gain information on the solution structure of (bio)macromolecules and their assemblies. This entails comparing the measured parameters with those that can be computed from usually "dry" structures by "hydrodynamic modeling." In this chapter, we will first briefly put hydrodynamic modeling in perspective and present the basic physics behind it as implemented in the most commonly used methods. The important "hydration" issue is also touched upon, and the distinction between rigid bodies versus those for which flexibility must be considered in the modeling process is then made. The available hydrodynamic modeling/computation programs, HYDROPRO, BEST, SoMo, AtoB, and Zeno, the latter four all implemented within the US-SOMO suite, are described and their performance evaluated. Finally, some literature examples are presented to illustrate the potential applications of hydrodynamics in the expanding field of multiresolution modeling. © 2015 Elsevier Inc. All rights reserved.
Axisymmetric Numerical Modeling of Pulse Detonation Rocket Engines
NASA Technical Reports Server (NTRS)
Morris, Christopher I.
2005-01-01
Pulse detonation rocket engines (PDREs) have generated research interest in recent years as a chemical propulsion system potentially offering improved performance and reduced complexity compared to conventional rocket engines. The detonative mode of combustion employed by these devices offers a thermodynamic advantage over the constant-pressure deflagrative combustion mode used in conventional rocket engines and gas turbines. However, while this theoretical advantage has spurred considerable interest in building PDRE devices, the unsteady blowdown process intrinsic to the PDRE has made realistic estimates of the actual propulsive performance problematic. The recent review article by Kailasanath highlights some of the progress that has been made in comparing the available experimental measurements with analytical and numerical models. In recent work by the author, a quasi-one-dimensional, finite rate chemistry CFD model was utilized to study the gasdynamics and performance characteristics of PDREs over a range of blowdown pressure ratios from 1-1000. Models of this type are computationally inexpensive, and enable first-order parametric studies of the effect of several nozzle and extension geometries on PDRE performance over a wide range of conditions. However, the quasi-one-dimensional approach is limited in that it cannot properly capture the multidimensional blast wave and flow expansion downstream of the PDRE, nor can it resolve nozzle flow separation if present. Moreover, the previous work was limited to single-pulse calculations. In this paper, an axisymmetric finite rate chemistry model is described and utilized to study these issues in greater detail. Example Mach number contour plots showing the multidimensional blast wave and nozzle exhaust plume are shown. The performance results are compared with the quasi-one-dimensional results from the previous paper. Both Euler and Navier-Stokes solutions are calculated in order to determine the effect of viscous
Comparison of an axisymmetric hurricane model with the corresponding slab-symmetric ITCZ model
NASA Astrophysics Data System (ADS)
Ulrich, Wolfgang; Smith, Roger K.; Mai, Nguyen Chi
2002-10-01
We examine the difference between the evolution of a hurricane-like vortex in an axisymmetric model and that of an intertropical convergence-zone-like disturbance in a slab-symmetric model, starting from an initial disturbance with the same lateral structure. The main calculations are carried out using a hurricane model similar to that formulated by DeMaria and Pickle (1988), supplemented by a few calculations using a recently developed model by Nguyen et al. (2002). We show that, although the two flow configurations have many similarities, the slab-symmetric model does not provide a dynamical surrogate for the hurricane. The main difference can be attributed to a geometrical factor in the formula for the conservation of absolute angular momentum in the axisymmetric model, which for an inward-moving air parcel permits much larger tangential wind speeds to be attained than in the slab-symmetric model. As a result, the sea-surface latent-heat flux, which is wind-speed dependent, is much larger in the axisymmetric model, providing a larger energy supply to the growing disturbance per unit area than in the slab-symmetric case. A further geometrical effect is that for the same inflow velocity profile in the boundary layer, there is larger convergence in the axisymmetric model. Because this convergence determines the deep cumulus mass flux in the DeMaria and Pickle model, the cumulus heating is larger in the axisymmetric configuration. The non-development of the slab-symmetric perturbation is a feature also of calculations using the Nguyen et al. (2002) model, even though two of the closures on the deep-cumulus mass flux used do not depend on the mass convergence in the boundary layer.A few numerical details of the main model are described, including the method of solution, which differs from that used by DeMaria and Pickle (1988).
Theoretical model of gravitational perturbation of current collector axisymmetric flow field
NASA Astrophysics Data System (ADS)
Walker, John S.; Brown, Samuel H.; Sondergaard, Neal A.
1989-03-01
Some designs of liquid metal collectors in homopolar motors and generators are essentially rotating liquid metal fluids in cylindrical channels with free surfaces and will, at critical rotational speeds, become unstable. The role of gravity in modifying this ejection instability is investigated. Some gravitational effects can be theoretically treated by perturbation techniques on the axisymmetric base flow of the liquid metal. This leads to a modification of previously calculated critical current collector ejection values neglecting gravity effects. The derivation of the mathematical model which determines the perturbation of the liquid metal base flow due to gravitational effects is documented. Since gravity is a small force compared with the centrifugal effects, the base flow solutions can be expanded in inverse powers of the Froude number and modified liquid flow profiles can be determined as a function of the azimuthal angle. This model will be used in later work to theoretically study the effects of gravity on the ejection point of the current collector. A rederivation of the hydrodynamic instability threshold of a liquid metal current collector is presented.
Magneto-hydrodynamical model for plasma
NASA Astrophysics Data System (ADS)
Liu, Ruikuan; Yang, Jiayan
2017-10-01
Based on the Newton's second law and the Maxwell equations for the electromagnetic field, we establish a new 3-D incompressible magneto-hydrodynamics model for the motion of plasma under the standard Coulomb gauge. By using the Galerkin method, we prove the existence of a global weak solution for this new 3-D model.
MODELING MID-INFRARED VARIABILITY OF CIRCUMSTELLAR DISKS WITH NON-AXISYMMETRIC STRUCTURE
Flaherty, K. M.; Muzerolle, J.
2010-08-20
Recent mid-infrared observations of young stellar objects have found significant variations possibly indicative of changes in the structure of the circumstellar disk. Previous models of this variability have been restricted to axisymmetric perturbations in the disk. We consider simple models of a non-axisymmetric variation in the inner disk, such as a warp or a spiral wave. We find that the precession of these non-axisymmetric structures produces negligible flux variations but a change in the height of these structures can lead to significant changes in the mid-infrared flux. Applying these models to observations of the young stellar object LRLL 31 suggests that the observed variability could be explained by a warped inner disk with variable scale height. This suggests that some of the variability observed in young stellar objects could be explained by non-axisymmetric disturbances in the inner disk and this variability would be easily observable in future studies.
Hydrodynamical comparison test of solar models
NASA Astrophysics Data System (ADS)
Bach, K.; Kim, Y.-C.
2012-12-01
We present three dimensional radiation-hydrodynamical (RHD) simulations for solar surface convection based on three most recent solar mixtures: Grevesse & Sauval (1998), Asplund, Grevesse & Sauval (2005), and Asplund, Grevesse, Sauval & Scott (2009). The outer convection zone of the Sun is an extremely turbulent region composed of partly ionized compressible gases at high temperature. The super-adiabatic layer (SAL) is the transition region where the transport of energy changes drastically from convection to radiation. In order to describe physical processes accurately, a realistic treatment of radiation should be considered as well as convection. However, newly updated solar mixtures that are established from radiation-hydrodynamics do not generate properly internal structures estimated by helioseismology. In order to address this fundamental problem, solar models are constructed consistently based on each mixture and used as initial configurations for radiation-hydrodynamical simulations. From our simulations, we find that the turbulent flows in each model are statistically similar in the SAL.
Anisotropic bead models for molecular hydrodynamics
NASA Astrophysics Data System (ADS)
Pastor, Richard W.; Zwanzig, Robert
1989-05-01
Some qualitative effects of slip hydrodynamic boundary conditions can be incorporated into bead models by replacing the scalar friction constant of a bead with a friction tensor. Translational and rotational diffusion coefficients are calculated analytically and exactly for polygons, analytically but approximately for spherical shells, and numerically by the method of Bloomfield and de la Torre. The calculated diffusion constants of benzene agree with experiment; such agreement is not possible using scalar friction constants. Some comments are made about the transition from overall slip to stick hydrodynamic behavior when tensor friction constants are used.
Radiation Hydrodynamical Models of the Inner Rim in Protoplanetary Disks
NASA Astrophysics Data System (ADS)
Flock, Mario
2016-06-01
Many stars host planets orbiting within one astronomical unit (AU). These close planets’ origins are a mystery that motivates investigating protoplanetary disks’ central regions. A key factor governing the conditions near the star is the silicate sublimation front, which largely determines where the starlight is absorbed, and which is often called the inner rim. We present the first radiation hydrodynamical modeling of the sublimation front in the disks around the young intermediate-mass stars called Herbig Ae stars. The models are axisymmetric, and include starlight heating, silicate grains sublimating and condensing to equilibrium at the local, timedependent temperature and density, and accretion stresses parametrizing the results of MHD magneto-rotational turbulence models. The results compare well with radiation hydrostatic solutions, and prove to be dynamically stable. Passing the model disks into Monte Carlo radiative transfer calculations, we show that the models satisfy observational constraints on the inner rims’s location. A small optically-thin halo of hot dust naturally arises between the inner rim and the star. The inner rim has a substantial radial extent, corresponding to several disk scale heights. While the front’s overall position varies with the stellar luminosity, its radial extent depends on the mass accretion rate. A pressure maximum develops at the position of thermal ionization at temperatures about 1000 K. The pressure maximum is capable of halting solid pebbles’ radial drift and concentrating them in a zone where temperatures are su ciently high for annealing to form crystalline silicates.
Dynamic coupling of three hydrodynamic models
NASA Astrophysics Data System (ADS)
Hartnack, J. N.; Philip, G. T.; Rungoe, M.; Smith, G.; Johann, G.; Larsen, O.; Gregersen, J.; Butts, M. B.
2008-12-01
The need for integrated modelling is evidently present within the field of flood management and flood forecasting. Engineers, modellers and managers are faced with flood problems which transcend the classical hydrodynamic fields of urban, river and coastal flooding. Historically the modeller has been faced with having to select one hydrodynamic model to cover all the aspects of the potentially complex dynamics occurring in a flooding situation. Such a single hydrodynamic model does not cover all dynamics of flood modelling equally well. Thus the ideal choice may in fact be a combination of models. Models combining two numerical/hydrodynamic models are becoming more standard, typically these models combine a 1D river model with a 2D overland flow model or alternatively a 1D sewer/collection system model with a 2D overland solver. In complex coastal/urban areas the flood dynamics may include rivers/streams, collection/storm water systems along with the overland flow. The dynamics within all three areas is of the same time scale and there is feedback in the system across the couplings. These two aspects dictate a fully dynamic three way coupling as opposed to running the models sequentially. It will be shown that the main challenges of the three way coupling are time step issues related to the difference in numerical schemes used in the three model components and numerical instabilities caused by the linking of the model components. MIKE FLOOD combines the models MIKE 11, MIKE 21 and MOUSE into one modelling framework which makes it possible to couple any combination of river, urban and overland flow fully dynamically. The MIKE FLOOD framework will be presented with an overview of the coupling possibilities. The flood modelling concept will be illustrated through real life cases in Australia and in Germany. The real life cases reflect dynamics and interactions across all three model components which are not possible to reproduce using a two-way coupling alone. The
Hydrodynamic Modeling of Oxidizer-Rich Staged Combustion Injector Flow
NASA Technical Reports Server (NTRS)
Harper, Brent (Technical Monitor); Canino, J. V.; Heister, S. D.; Garrison, L. A.
2004-01-01
The main objective of this work is to determine the unsteady hydrodynamic characteristics of coaxial swirl atomizers of interest in oxidizer-rich staged combustion (ORSC) liquid rocket engines. To this end, the pseudo-density (homogeneous flow) treatment combined with the Marker-and-Cell (MAC) numerical algorithm has been used to develop an axisymmetric with swirl, two-phase, unsteady model. The numerical model is capable of assessing the time-dependent orifice exit conditions and internal mixing for arbitrary fuel and oxidizer gas injection conditions. Parametric studies have been conducted to determine the effect of geometry, gas properties, and liquid properties on the exit massflow rate and velocity. It has been found that the frequency at which the liquid film oscillates increases as the density ratio and thickness increase, decreases as film thickness and liquid swirl velocity increase, and is unaffected by the mixing length. Additionally, it has been determined that the variation in the massflow rate increases as the liquid swirl velocity and liquid film thickness increase, and decreases as the density ratio, collar thickness, and mixing length increase.
Modeling multiphase flow using fluctuating hydrodynamics.
Chaudhri, Anuj; Bell, John B; Garcia, Alejandro L; Donev, Aleksandar
2014-09-01
Fluctuating hydrodynamics provides a model for fluids at mesoscopic scales where thermal fluctuations can have a significant impact on the behavior of the system. Here we investigate a model for fluctuating hydrodynamics of a single-component, multiphase flow in the neighborhood of the critical point. The system is modeled using a compressible flow formulation with a van der Waals equation of state, incorporating a Korteweg stress term to treat interfacial tension. We present a numerical algorithm for modeling this system based on an extension of algorithms developed for fluctuating hydrodynamics for ideal fluids. The scheme is validated by comparison of measured structure factors and capillary wave spectra with equilibrium theory. We also present several nonequilibrium examples to illustrate the capability of the algorithm to model multiphase fluid phenomena in a neighborhood of the critical point. These examples include a study of the impact of fluctuations on the spinodal decomposition following a rapid quench, as well as the piston effect in a cavity with supercooled walls. The conclusion in both cases is that thermal fluctuations affect the size and growth of the domains in off-critical quenches.
Brownsville Ship Channel Hydrodynamic Modeling
2012-01-01
31 Figure 31. Laguna Madre analysis locations...wave resuspension and circulation of sediment in Laguna Madre .2 The navigation impacts are assessed by performing model simulations of the...to better resolve the shallow-water habitats, including South Bay, Bahia Grande, and South Laguna Madre . These habitats are discussed further
Hydrodynamic Modeling of Diego Garcia Lagoon
2014-08-01
largest coral reef atoll of more than 60 islands that make up the Chagos Archipelago south of the equator in the central Indian Ocean. It is located at...quality and coral reef health. Hydrodynamic modeling of lagoon waters is one key component of the investigation to understand lagoon circulation...NAVFAC and other researchers will then use the flushing time information to assess water quality conditions and coral reef health. Researchers use
Nonparabolic Hydrodynamic Modeling of Submicron Semiconductor Devices
NASA Astrophysics Data System (ADS)
Guo, Liangying; Cheng, Ming-C.; Fithen, Robert; Luo, Yansheng
1997-08-01
Several important issues arising from closure of the first three moment equations with a nonparabolic energy band for electron transport in submicron semiconductor devices have been studied. The common assumptions are involved in the Fourier-law heat flux and the electron temperature. These have resulted in many inconsistencies due to the nonparabolic band and non-Maxwellian electron distribution function.(Ming-C. Cheng, Liangying Guo, Robert Fithen, and Yansheng Luo, J. Phys. D: Appl. Phys., accepted for publication.) These inconsistencies are illustrated in Silicon. A Fourier-law hydrodynamic transport model based on the above-mentioned assumptions is applied to Si submicron n^+nn^+ diodes, compared to the Monte Carlo simulation. A simple hydrodynamic model, which completely discards use of the Fourier-law heat flux to avoid these inconsistencies, is proposed to make a further comparison with the Fourier-law-based hydrodynamic model. Results indicates that the unrealistic electron transport phenomena in submicron n^+nn^+ devices near the anode junction are mainly caused by the inadequate description of the Fourier-law heat flux.
Impact modeling with Smooth Particle Hydrodynamics
Stellingwerf, R.F.; Wingate, C.A.
1993-07-01
Smooth Particle Hydrodynamics (SPH) can be used to model hypervelocity impact phenomena via the addition of a strength of materials treatment. SPH is the only technique that can model such problems efficiently due to the combination of 3-dimensional geometry, large translations of material, large deformations, and large void fractions for most problems of interest. This makes SPH an ideal candidate for modeling of asteroid impact, spacecraft shield modeling, and planetary accretion. In this paper we describe the derivation of the strength equations in SPH, show several basic code tests, and present several impact test cases with experimental comparisons.
An Axisymmetric, Numerical Model for a Non-Hydrostatic Boussinesq Ocean.
1982-12-09
AD-A122 365 AN AXISYMMETRIC NUMERICAL MODEL FOR A-NON-HYDROSTATIC I// BOUSSINESO OCEAN(U NAVAL RESEARCH LAB WASHINGTON DC S W CHANG ET AL 09 DEC 92...Memorandum Report 4957 J) z 4 TITLE (and Subtlt 5 TYPE OF REPORT A PERIOD COVERED AN AXISYMMETRIC, NUMERICAL MODEL FOR F report A NON-HYDROSTATIC...necessary ad identify by block number) Ocean modelling Gulf stream rings Ocean eddies 20. AGiTfACT (ContinMe on revere side It neceesiy and Identify by
Towards modeling hydrodynamic stress limitations on transpiration
NASA Astrophysics Data System (ADS)
Matheny, A. M.; Bohrer, G.; Ivanov, V. Y.; Stoy, P. C.
2011-12-01
Evapotranspiration is one of the major forcing functions of Earth's climate, providing the link for the soil-plant-water continuum. Current models for transpiration assume a coupling between stomatal conductance and soil moisture through empirical relationships that do not resolve the hydrodynamic process of water movement from the soil to the leaves. This approach does not take advantage of recent advances in our understanding of water flow and storage in the trees, or of tree and canopy structure. It has been suggested that stomata respond to water potential in the leaf and branch, and that this hydrodynamic response is a mechanism for hydraulic limitation of stomatal conductance. Hydraulic limitations in forest ecosystems are common and are known to control transpiration when the soil is drying or when vapor pressure deficit (VPD) is very large. Hydraulic limitation can also impact stomatal apertures under conditions of adequate soil moisture and lower evaporative demand. Hydrodynamic stresses at the tree level act at several time scales, including the fast, minute-hour scale. These dynamics are faster than the time scales of hours to days at which drying soil will affect stomata conductance. The lack of representation of the tree-hydrodynamic process should therefore lead to atypical intra-daily patterns of error in results of current models. We use a large-scale comparison between observations and land-surface models to characterize the patterns of intra-daily error in simulated water flux. Through the use of the North American Carbon Program (NACP) dataset, more than 10 years of water flux data for 35 Fluxnet sites in the US and Canada have been analyzed. The diurnal error for each of the 24 models represented in this dataset allows the models to be categorized and evaluated on their ability to accurately predict the fast temporal dynamics of transpiration in different ecosystems and atmospheric forcing. Among well calibrated models, two general error
The quantum hydrodynamic model for semiconductor devices
Gardner, C.L. )
1994-04-01
The classical hydrodynamic equations can be extended to include quantum effects by incorporating the first quantum corrections. The full three-dimensional quantum hydrodynamic (QHD) model is derived for the first time by a moment expansion of the Wigner-Boltzmann equations. The QHD conservation laws have the same form as the classical hydrodynamic equations, but the energy density and stress tensor have additional quantum terms. These quantum terms allow particles to tunnel through potential barriers and to build up in potential wells. The three-dimensional QHD transport equations are mathematically classified as having two Schroedinger modes, two hyperbolic modes, and one parabolic mode. The one-dimensional steady-state QHD equations are discretized in conservation form using the second upwind method. Simulations of a resonant tunneling diode are presented that show charge buildup in the quantum well and negative differential resistance (NDR) in the current-voltage curve. These are the first simulations of the full QHD equations to show NDR in the resonant tunneling diode. The computed current-voltage curve agrees quantitatively with experimental measurements. NDR interpreted in terms of the time spent by electrons in the quantum well.
Numerical Simulation of Interacting Stellar Winds Model Using Smoothed Particle Hydrodynamics (SPH)
NASA Astrophysics Data System (ADS)
Thronson, H. A., Jr.; Li, P. S.; Kwok, S.
1997-12-01
In the past decade, the Interacting Stellar Winds (ISW) model has been shown to be successful in explaining the formation of planetary nebulae, Wolf-Rayet nebulae, slow novae, and supernovae. Since analytical methods applied to the ISW model have been limited to the spherical symmetric (1D) geometry, numerical methods are necessary for axisymmetric (2D) or arbitrary (3D) geometries, such as the study of formation and evolution of planetary nebulae, and for symbiotic nova outbursts. The Smoothed Particle Hydrodynamics (SPH) algorithm has been developed to study hydrodynamics using the particle method. This algorithm has been applied in many different fields successfully. In this paper, we apply the SPH algorithm using the TREE code to the problem of interacting winds dynamics. We present three simulations: (1) the interaction of two winds in spherical symmetry to demonstrate the validity of the algorithm in dealing with ISW modeling, (2) the formation and evolution of an axisymmetric nebula in the first 500 years, and (3) the interacting-colliding winds caused by a slow nova outburst in a symbiotic system. It is the first time that the SPH algorithm has been applied to an ISW simulation. The SPH algorithm is proved to be an accurate and powerful tool in studying ISW model. This work is supported by NASA's US ISO program and the University of Calgary.
Numerical Simulation of Slinger Combustor Using 2-D Axisymmetric Computational Model
NASA Astrophysics Data System (ADS)
Lee, Semin; Park, Soo Hyung; Lee, Donghun
2010-06-01
Small-size turbojet engines have difficulties in maintaining the chemical reaction due to the limitation of chamber size. The combustion chamber is generally designed to improve the reaction efficiency by the generation of vortices in the chamber and to enhance air-fuel mixing characteristics. In the initial stage of designing the combustor, analysis of the 3-D full configuration is not practical due to the huge time consuming computation and grid generation followed by modifications of the geometry. In the present paper, an axisymmetric model maintaining geometric similarity and flow characteristic of 3-D configuration is developed. Based on numerical results from the full 3-D configuration, model reduction is achieved toward 2-D axisymmetric configuration. In the modeling process, the area and location of each hole in 3-D full configuration are considered reasonably and replaced to the 2-D axisymmetric model. By using the 2-D axisymmetric model, the factor that can affect the performance is investigated with the assumption that the flow is non-reacting and turbulent. Numerical results from the present model show a good agreement with numerical results from 3-D full configuration model such as existence of vortex pair in forward region and total pressure loss. By simplifying the complex 3-D model, computing time can be remarkably reduced and it makes easy to find effects of geometry modification.
Stabilized plane and axisymmetric Lobatto finite element models
NASA Astrophysics Data System (ADS)
Hu, Y. C.; Sze, K. Y.; Zhou, Y. X.
2015-11-01
High order elements are renowned for their high accuracy and convergence. Among them, Lobatto spectral finite elements are commonly used in explicit dynamic analyses as their mass matrices when evaluated by the Lobatto integration rule are diagonal. While there are numerous advanced first and second order elements, advanced high order elements are rarely seen. In this paper, generic stabilization schemes are devised for the reduced integrated plane and axisymmetric elements. Static and explicit dynamic tests are considered for evaluating the relatively merits of the stabilized and conventional elements. The displacement errors of the stabilized elements are less than those of the conventional Lobatto elements. When the material is nearly incompressible, the stabilized elements are also more accurate in terms of the energy error norm. This advantage is of practical importance for bio-tissue and hydrated soil analyses.
Kinetic and hydrodynamic models of chemotactic aggregation
NASA Astrophysics Data System (ADS)
Chavanis, Pierre-Henri; Sire, Clément
2007-10-01
We derive general kinetic and hydrodynamic models of chemotactic aggregation that describe certain features of the morphogenesis of biological colonies (like bacteria, amoebae, endothelial cells or social insects). Starting from a stochastic model defined in terms of N coupled Langevin equations, we derive a nonlinear mean-field Fokker-Planck equation governing the evolution of the distribution function of the system in phase space. By taking the successive moments of this kinetic equation and using a local thermodynamic equilibrium condition, we derive a set of hydrodynamic equations involving a damping term. In the limit of small frictions, we obtain a hyperbolic model describing the formation of network patterns (filaments) and in the limit of strong frictions we obtain a parabolic model which is a generalization of the standard Keller-Segel model describing the formation of clusters (clumps). Our approach connects and generalizes several models introduced in the chemotactic literature. We discuss the analogy between bacterial colonies and self-gravitating systems and between the chemotactic collapse and the gravitational collapse (Jeans instability). We also show that the basic equations of chemotaxis are similar to nonlinear mean-field Fokker-Planck equations so that a notion of effective generalized thermodynamics can be developed.
Radiation Hydrodynamics Models of the Inner Rim in Protoplanetary Disks
NASA Astrophysics Data System (ADS)
Flock, M.; Fromang, S.; Turner, N. J.; Benisty, M.
2016-08-01
Many stars host planets orbiting within a few astronomical units (AU). The occurrence rate and distributions of masses and orbits vary greatly with the host star’s mass. These close planets’ origins are a mystery that motivates investigating protoplanetary disks’ central regions. A key factor governing the conditions near the star is the silicate sublimation front, which largely determines where the starlight is absorbed, and which is often called the inner rim. We present the first radiation hydrodynamical modeling of the sublimation front in the disks around the young intermediate-mass stars called Herbig Ae stars. The models are axisymmetric and include starlight heating silicate grains sublimating and condensing to equilibrium at the local, time-dependent temperature and density and accretion stresses parameterizing the results of MHD magnetorotational turbulence models. The results compare well with radiation hydrostatic solutions and prove to be dynamically stable. Passing the model disks into Monte Carlo radiative transfer calculations, we show that the models satisfy observational constraints on the inner rim’s location. A small optically thin halo of hot dust naturally arises between the inner rim and the star. The inner rim has a substantial radial extent, corresponding to several disk scale heights. While the front’s overall position varies with the stellar luminosity, its radial extent depends on the mass accretion rate. A pressure maximum develops near the location of thermal ionization at temperatures of about 1000 K. The pressure maximum is capable of halting solid pebbles’ radial drift and concentrating them in a zone where temperatures are sufficiently high for annealing to form crystalline silicates.
3D Fokker-Planck modeling of axisymmetric collisional losses of fusion products in TFTR
Goloborod`ko, V.Ya.; Reznik, S.N.; Yavorskij, V.A.; Zweben, S.J.
1995-10-01
Results of a 3D (in constants of motion space) Fokker-Planck simulation of collisional losses of fusion products in axisymmetric DT and DD discharges on TFTR are presented. The distributions of escaped ions over poloidal angle, pitch angle, and their energy spectra are obtained. Axisymmetric collisional losses of fusion products are found to be less than (2--5)%. The distribution of confined fusion products is shown to be strongly anisotropic and nonuniform in the radial coordinate mainly for slowed-down fusion products with small longitudinal energy. Comparison of these results of modeling and experimental data is done.
Detailed simulation of morphodynamics: 1. Hydrodynamic model
NASA Astrophysics Data System (ADS)
Nabi, M.; de Vriend, H. J.; Mosselman, E.; Sloff, C. J.; Shimizu, Y.
2012-12-01
We present a three-dimensional high-resolution hydrodynamic model for unsteady incompressible flow over an evolving bed topography. This is achieved by using a multilevel Cartesian grid technique that allows the grid to be refined in high-gradient regions and in the vicinity of the river bed. The grid can be locally refined and adapted to the bed geometry, managing the Cartesian grid cells and faces using a hierarchical tree data approach. A ghost-cell immersed-boundary technique is applied to cells intersecting the bed topography. The governing equations have been discretized using a finite-volume method on a staggered grid, conserving second-order accuracy in time and space. The solution advances in time using the fractional step approach. Large-eddy simulation is used as turbulence closure. We validate the model against several experiments and other results from literature. Model results for Stokes flow around a cylinder in the vicinity of a moving wall agree well with Wannier's analytical solution. At higher Reynolds numbers, computed trailing bubble length, separation angle, and drag coefficient compare favorably with experimental and previous computational results. Results for the flow over two- and three-dimensional dunes agree well with published data, including a fair reproduction of recirculation zones, horse-shoe structures, and boiling effects. This shows that the model is suitable for being used as a hydrodynamic submodel in the high-resolution modeling of sediment transport and formation and evolution of subaqueous ripples and dunes.
Hydrodynamic models for slurry bubble column reactors
Gidaspow, D.
1995-12-31
The objective of this investigation is to convert a {open_quotes}learning gas-solid-liquid{close_quotes} fluidization model into a predictive design model. This model is capable of predicting local gas, liquid and solids hold-ups and the basic flow regimes: the uniform bubbling, the industrially practical churn-turbulent (bubble coalescence) and the slugging regimes. Current reactor models incorrectly assume that the gas and the particle hold-ups (volume fractions) are uniform in the reactor. They must be given in terms of empirical correlations determined under conditions that radically differ from reactor operation. In the proposed hydrodynamic approach these hold-ups are computed from separate phase momentum balances. Furthermore, the kinetic theory approach computes the high slurry viscosities from collisions of the catalyst particles. Thus particle rheology is not an input into the model.
Axisymmetric toroidal modes of general relativistic magnetized neutron star models
Asai, Hidetaka; Lee, Umin E-mail: lee@astr.tohoku.ac.jp
2014-07-20
We calculate axisymmetric toroidal modes of magnetized neutron stars with a solid crust in the general relativistic Cowling approximation. We assume that the interior of the star is threaded by a poloidal magnetic field, which is continuous at the surface with an outside dipole field. We examine the cases of the field strength B{sub S} ∼ 10{sup 16} G at the surface. Since separation of variables is not possible for the oscillations of magnetized stars, we employ finite series expansions for the perturbations using spherical harmonic functions. We find discrete normal toroidal modes of odd parity, but no toroidal modes of even parity are found. The frequencies of the toroidal modes form distinct mode sequences and the frequency in a given mode sequence gradually decreases as the number of radial nodes of the eigenfunction increases. From the frequency spectra computed for neutron stars of different masses, we find that the frequency is almost exactly proportional to B{sub S} and is well represented by a linear function of R/M for a given B{sub S}, where M and R are the mass and radius of the star. The toroidal mode frequencies for B{sub S} ∼ 10{sup 15} G are in the frequency range of the quasi-periodic oscillations (QPOs) detected in the soft-gamma-ray repeaters, but we find that the toroidal normal modes cannot explain all the detected QPO frequencies.
Hydrodynamic models of AGN feedback in cooling core clusters
NASA Astrophysics Data System (ADS)
Vernaleo, John C.
X-ray observations show that the Intra Cluster Medium (ICM) in many galaxy clusters is cooling at a rapid rate, often to the point that it should have radiated away all of its energy in less than the age of the cluster. There is however a very clear lack of enough cool end products of this gas in the centers of the clusters. Energetic arguments indicate that Active Galactic Nuclei (AGN) should be capable of heating the inner regions of clusters enough to offset the radiative cooling; truncating massive galaxy formation and solving the cooling flow problem. We present three sets of high resolution, ideal hydrodynamic simulations with the ZEUS code to test this AGN heating paradigm. For the first set of simulations, we study the dependence of the interaction between the AGN jets and the ICM on the parameters of the jets themselves. We present a parameter survey of two-dimensional (axisymmetric) models of back-to-back jets injected into a cluster atmosphere. We follow the passive evolution of the resulting structures. These simulations fall into roughly two classes, cocoon-bounded and non-cocoon bounded. We find that the cocoon-bounded sources inject significantly more entropy into the core regions of the ICM atmosphere, even though the efficiency with which the energy is thermalized is independent of the morphological class. In all cases, a large fraction of the energy injected by the jet ends up as gravitational potential energy due to the expansion of the atmosphere. For the second set, we present three-dimensional simulations of jetted AGN that act in response to cooling-mediated accretion of an ICM atmosphere. We find that our models are incapable of producing a long term balance of heating and cooling; catastrophic cooling can be delayed by the jet action but inevitably takes hold. At the heart of the failure of these models is the formation of a low density channel through which the jet can freely flow, carrying its energy out of the cooling core. Finally, we
Multithread Hydrodynamic Modeling of a Solar Flare
NASA Astrophysics Data System (ADS)
Warren, Harry P.
2006-01-01
Past hydrodynamic simulations have been able to reproduce the high temperatures and densities characteristic of solar flares. These simulations, however, have not been able to account for the slow decay of the observed flare emission or the absence of blueshifts in high spectral resolution line profiles. Recent work has suggested that modeling a flare as a sequence of independently heated threads instead of as a single loop may resolve the discrepancies between the simulations and observations. In this paper, we present a method for computing multithread, time-dependent hydrodynamic simulations of solar flares and apply it to observations of the Masuda flare of 1992 January 13. We show that it is possible to reproduce the temporal evolution of high temperature thermal flare plasma observed with the instruments on the GOES and Yohkoh satellites. The results from these simulations suggest that the heating timescale for a individual thread is on the order of 200 s. Significantly shorter heating timescales (20 s) lead to very high temperatures and are inconsistent with the emission observed by Yohkoh.
A modified double distribution lattice Boltzmann model for axisymmetric thermal flow
NASA Astrophysics Data System (ADS)
Wang, Zuo; Liu, Yan; Wang, Heng; Zhang, Jiazhong
2017-04-01
In this paper, a double distribution lattice Boltzmann model for axisymmetric thermal flow is proposed. In the model, the flow field is solved by a multi-relaxation-time lattice Boltzmann scheme while the temperature field by a newly proposed lattice-kinetic-based Boltzmann scheme. Chapman-Enskog analysis demonstrates that the axisymmetric energy equation in the cylindrical coordinate system can be recovered by the present lattice-kinetic-based Boltzmann scheme for temperature field. Numerical tests, including the thermal Hagen-Poiseuille flow and natural convection in a vertical annulus, have been carried out, and the results predicted by the present model agree well with the existing numerical data. Furthermore, the present model shows better numerical stability than the existing model.
RECENT ADVANCES IN MACROMOLECULAR HYDRODYNAMIC MODELING
Aragon, Sergio R.
2010-01-01
The modern implementation of the boundary element method (S.R. Aragon, J. Comput. Chem. 25(2004)1191–12055) has ushered unprecedented accuracy and precision for the solution of the Stokes equations of hydrodynamics with stick boundary conditions. This article begins by reviewing computations with the program BEST of smooth surface objects such as ellipsoids, the dumbbell, and cylinders that demonstrate that the numerical solution of the integral equation formulation of hydrodynamics yields very high precision and accuracy. When BEST is used for macromolecular computations, the limiting factor becomes the definition of the molecular hydrodynamic surface and the implied effective solvation of the molecular surface. Studies on 49 different proteins, ranging in molecular weight from 9 to over 400 kDa, have shown that a model using a 1.1 A thick hydration layer describes all protein transport properties very well for the overwhelming majority of them. In addition, this data implies that the crystal structure is an excellent representation of the average solution structure for most of them. In order to investigate the origin of a handful of significant discrepancies in some multimeric proteins (over −20% observed in the intrinsic viscosity), the technique of Molecular Dynamics simulation (MD) has been incorporated into the research program. A preliminary study of dimeric α-chymotrypsin using approximate implicit water MD is presented. In addition I describe the successful validation of modern protein force fields, ff03 and ff99SB, for the accurate computation of solution structure in explicit water simulation by comparison of trajectory ensemble average computed transport properties with experimental measurements. This work includes small proteins such as lysozyme, ribonuclease and ubiquitin using trajectories around 10 ns duration. We have also studied a 150 kDa flexible monoclonal IgG antibody, trastuzumab, with multiple independent trajectories encompassing over
Code Differentiation for Hydrodynamic Model Optimization
Henninger, R.J.; Maudlin, P.J.
1999-06-27
Use of a hydrodynamics code for experimental data fitting purposes (an optimization problem) requires information about how a computed result changes when the model parameters change. These so-called sensitivities provide the gradient that determines the search direction for modifying the parameters to find an optimal result. Here, the authors apply code-based automatic differentiation (AD) techniques applied in the forward and adjoint modes to two problems with 12 parameters to obtain these gradients and compare the computational efficiency and accuracy of the various methods. They fit the pressure trace from a one-dimensional flyer-plate experiment and examine the accuracy for a two-dimensional jet-formation problem. For the flyer-plate experiment, the adjoint mode requires similar or less computer time than the forward methods. Additional parameters will not change the adjoint mode run time appreciably, which is a distinct advantage for this method. Obtaining ''accurate'' sensitivities for the j et problem parameters remains problematic.
Hydrodynamic models for slurry bubble column reactors
Dimitri Gidaspow
1996-10-01
The objective of this investigation is to convert learning gas-solid-liquid fluidization model into a predictive design model. The IIT hydrodynamic model computers the phase velocities and the volume fi-actions of gas, liquid and particulate phases. Model verification involves a comparison of these computed velocities and volume fractions to experimental values. As promised in the SIXTH TECHNICAL PROGRESS REPORT, January 1996, this report presents measurements of radial distribution function for 450 micron glass particles in liquid-solid fluidized bed. The report is in the form of a preliminary paper. The authors need the radial distribution function to compute the viscosity and the equation of state for particles. The principal results are as follows: (1) The measured radial distribution function, g{sub 0}, is a monotonic function of the solid volume fraction. The values of the radial distribution function g{sub 0} are in the range of the predictions from Bagnold equation and Carnahan and Starling equation. (2) The position of the first peak of the radial distribution function does not lie at r = d at contact (d is particle diameter). This differs from the predications from the hard sphere model and the measurements in the gas-solid system (Gidaspow and Huilin, 1996). This is due to a liquid film lubrication effect in the liquid-solid system.
A skin friction model for axisymmetric turbulent boundary layers along long thin circular cylinders
NASA Astrophysics Data System (ADS)
Jordan, Stephen A.
2013-07-01
Only a few engineering design models are presently available that adequately depict the axisymmetric skin friction (Cf) maturity along long thin turbulent cylinders. This deficit rests essentially on the experimental and numerical difficulties of measuring (or computing) the spatial evolution of the thin cylinder turbulence. Consequently, the present axisymmetric Cf models have questionable accuracy. Herein, we attempt to formulate a more robust Cf model that owns acceptable error. The formulation is founded on triple integration of the governing equation system that represents a thin cylinder turbulent boundary layer (TBL) at statistical steady-state in appropriate dimensionless units. The final model requires only the radius-based Reynolds number (Rea) and transverse curvature (δ/a) as input parameters. We tuned the accompanying coefficients empirically via an expanded statistical database (over 60 data points) that house new Cf values from large-eddy simulations (LES). The LES computations employed a turbulence inflow generation procedure that permits spatial resolution of the TBL at low-high Reynolds numbers and transverse curvatures. Compared to the new skin friction database, the Cf model revealed averaged predictive errors under 5% with a 3.5% standard deviation. Apart from owning higher values than the flat plate TBL, the most distinguishing characteristic of the axisymmetric skin friction is its rising levels when the boundary layer thickness exceeds the cylinder radius. All Cf levels diminish with increasing Reynolds number. These unique features differentiate the axisymmetric TBL along thin cylinders as a separate canonical flow when compared to the turbulent wall shear-layers of channels, pipes, and planar-type geometries.
An analytical model of flagellate hydrodynamics
NASA Astrophysics Data System (ADS)
Dölger, Julia; Bohr, Tomas; Andersen, Anders
2017-04-01
Flagellates are unicellular microswimmers that propel themselves using one or several beating flagella. We consider a hydrodynamic model of flagellates and explore the effect of flagellar arrangement and beat pattern on swimming kinematics and near-cell flow. The model is based on the analytical solution by Oseen for the low Reynolds number flow due to a point force outside a no-slip sphere. The no-slip sphere represents the cell and the point force a single flagellum. By superposition we are able to model a freely swimming flagellate with several flagella. For biflagellates with left–right symmetric flagellar arrangements we determine the swimming velocity, and we show that transversal forces due to the periodic movements of the flagella can promote swimming. For a model flagellate with both a longitudinal and a transversal flagellum we determine radius and pitch of the helical swimming trajectory. We find that the longitudinal flagellum is responsible for the average translational motion whereas the transversal flagellum governs the rotational motion. Finally, we show that the transversal flagellum can lead to strong feeding currents to localized capture sites on the cell surface.
Chemical and Hydrodynamical Models of Cometary Comae
NASA Technical Reports Server (NTRS)
Charnley, Steven
2012-01-01
Multi-fluid modelling of the outflowing gases which sublimate from cometary nuclei as they approach the Sun is necessary for understanding the important physical and chemical processes occurring in this complex plasma. Coma chemistry models can be employed to interpret observational data and to ultimately determine chemical composition and structure of the nuclear ices and dust. We describe a combined chemical and hydrodynamical model [1] in which differential equations for the chemical abundances and the energy balance are solved as a function of distance from the cometary nucleus. The presence of negative ions (anions) in cometary comae is known from Giotto mass spectrometry of 1P/Halley. The anions O(-), OH(-), C(-), CH(-) and CN(-) have been detected, as well as unidentified anions with masses 22-65 and 85-110 amu [2]. Organic molecular anions such as C4H(-) and C6H(-) are known to have a significant impact on the charge balance of interstellar clouds and circumstellar envelopes and have been shown to act as catalysts for the gas-phase synthesis of larger hydrocarbon molecules in the ISM, but their importance in cometary comae has not yet been fully explored. We present details of new models for the chemistry of cometary comae that include atomic and molecular anions and calculate the impact of these anions on the coma physics and chemistry af the coma.
Lattice Boltzmann model for incompressible axisymmetric thermal flows through porous media
NASA Astrophysics Data System (ADS)
Grissa, Kods; Chaabane, Raoudha; Lataoui, Zied; Benselama, Adel; Bertin, Yves; Jemni, Abdelmajid
2016-10-01
The present work proposes a simple lattice Boltzmann model for incompressible axisymmetric thermal flows through porous media. By incorporating forces and source terms into the lattice Boltzmann equation, the incompressible Navier-Stokes equations are recovered through the Chapman-Enskog expansion. It is found that the added terms are just the extra terms in the governing equations for the axisymmetric thermal flows through porous media compared with the Navier-Stokes equations. Four numerical simulations are performed to validate this model. Good agreement is obtained between the present work and the analytic solutions and/or the results of previous studies. This proves its efficacy and simplicity regarding other methods. Also, this approach provides guidance for problems with more physical phenomena and complicated force forms.
Lattice Boltzmann model for incompressible axisymmetric thermal flows through porous media.
Grissa, Kods; Chaabane, Raoudha; Lataoui, Zied; Benselama, Adel; Bertin, Yves; Jemni, Abdelmajid
2016-10-01
The present work proposes a simple lattice Boltzmann model for incompressible axisymmetric thermal flows through porous media. By incorporating forces and source terms into the lattice Boltzmann equation, the incompressible Navier-Stokes equations are recovered through the Chapman-Enskog expansion. It is found that the added terms are just the extra terms in the governing equations for the axisymmetric thermal flows through porous media compared with the Navier-Stokes equations. Four numerical simulations are performed to validate this model. Good agreement is obtained between the present work and the analytic solutions and/or the results of previous studies. This proves its efficacy and simplicity regarding other methods. Also, this approach provides guidance for problems with more physical phenomena and complicated force forms.
A hydrodynamic model for cooperating solidary countries
NASA Astrophysics Data System (ADS)
De Luca, Roberto; Di Mauro, Marco; Falzarano, Angelo; Naddeo, Adele
2017-07-01
The goal of international trade theories is to explain the exchange of goods and services between different countries, aiming to benefit from it. Albeit the idea is very simple and known since ancient history, smart policy and business strategies need to be implemented by each subject, resulting in a complex as well as not obvious interplay. In order to understand such a complexity, different theories have been developed since the sixteenth century and today new ideas still continue to enter the game. Among them, the so called classical theories are country-based and range from Absolute and Comparative Advantage theories by A. Smith and D. Ricardo to Factor Proportions theory by E. Heckscher and B. Ohlin. In this work we build a simple hydrodynamic model, able to reproduce the main conclusions of Comparative Advantage theory in its simplest setup, i.e. a two-country world with country A and country B exchanging two goods within a genuine exchange-based economy and a trade flow ruled only by market forces. The model is further generalized by introducing money in order to discuss its role in shaping trade patterns. Advantages and drawbacks of the model are also discussed together with perspectives for its improvement.
NASA Astrophysics Data System (ADS)
Haya, Laura; Tavoularis, Stavros
2017-06-01
Flow characteristics past a bileaflet mechanical heart valve were measured under physiological flow conditions in a straight tube with an axisymmetric expansion, similar to vessels used in previous studies, and in an anatomical model of the aorta. We found that anatomical features, including the three-lobed sinus and the aorta's curvature affected significantly the flow characteristics. The turbulent and viscous stresses were presented and discussed as indicators for potential blood damage and thrombosis. Both types of stresses, averaged over the two axial measurement planes, were significantly lower in the anatomical model than in the axisymmetric one. This difference was attributed to the lower height-to-width ratio and more gradual contraction of the anatomical aortic sinus. The curvature of the aorta caused asymmetries in the velocity and stress distributions during forward flow. Secondary flows resulting from the aorta's curvature are thought to have redistributed the fluid stresses transversely, resulting in a more homogeneous stress distribution in the anatomical aortic root than in the axisymmetric root. The results of this study demonstrate the importance of modelling accurately the aortic geometry in experimental and computational studies of prosthetic devices. Moreover, our findings suggest that grafts used for aortic root replacement should approximate as closely as possible the shape of the natural sinuses.
Modeling the Hydrodynamics of Phloem Sieve Plates
Jensen, Kaare Hartvig; Mullendore, Daniel Leroy; Holbrook, Noel Michele; Bohr, Tomas; Knoblauch, Michael; Bruus, Henrik
2012-01-01
Sieve plates have an enormous impact on the efficiency of the phloem vascular system of plants, responsible for the distribution of photosynthetic products. These thin plates, which separate neighboring phloem cells, are perforated by a large number of tiny sieve pores and are believed to play a crucial role in protecting the phloem sap from intruding animals by blocking flow when the phloem cell is damaged. The resistance to the flow of viscous sap in the phloem vascular system is strongly affected by the presence of the sieve plates, but the hydrodynamics of the flow through them remains poorly understood. We propose a theoretical model for quantifying the effect of sieve plates on the phloem in the plant, thus unifying and improving previous work in the field. Numerical simulations of the flow in real and idealized phloem channels verify our model, and anatomical data from 19 plant species are investigated. We find that the sieve plate resistance is correlated to the cell lumen resistance, and that the sieve plate and the lumen contribute almost equally to the total hydraulic resistance of the phloem translocation pathway. PMID:22811681
Modeling the hydrodynamics of Phloem sieve plates.
Jensen, Kaare Hartvig; Mullendore, Daniel Leroy; Holbrook, Noel Michele; Bohr, Tomas; Knoblauch, Michael; Bruus, Henrik
2012-01-01
Sieve plates have an enormous impact on the efficiency of the phloem vascular system of plants, responsible for the distribution of photosynthetic products. These thin plates, which separate neighboring phloem cells, are perforated by a large number of tiny sieve pores and are believed to play a crucial role in protecting the phloem sap from intruding animals by blocking flow when the phloem cell is damaged. The resistance to the flow of viscous sap in the phloem vascular system is strongly affected by the presence of the sieve plates, but the hydrodynamics of the flow through them remains poorly understood. We propose a theoretical model for quantifying the effect of sieve plates on the phloem in the plant, thus unifying and improving previous work in the field. Numerical simulations of the flow in real and idealized phloem channels verify our model, and anatomical data from 19 plant species are investigated. We find that the sieve plate resistance is correlated to the cell lumen resistance, and that the sieve plate and the lumen contribute almost equally to the total hydraulic resistance of the phloem translocation pathway.
Influence of high-permeability discs in an axisymmetric model of the Cadarache dynamo experiment
NASA Astrophysics Data System (ADS)
Giesecke, A.; Nore, C.; Stefani, F.; Gerbeth, G.; Léorat, J.; Herreman, W.; Luddens, F.; Guermond, J.-L.
2012-05-01
Numerical simulations of the kinematic induction equation are performed on a model configuration of the Cadarache von-Kármán-sodium dynamo experiment. The effect of a localized axisymmetric distribution of relative permeability μr that represents soft iron material within the conducting fluid flow is investigated. The critical magnetic Reynolds number Rmc for dynamo action of the first non-axisymmetric mode roughly scales like Rmcμr - Rmc∞∝μ-1/2r, i.e. the threshold decreases as μr increases. This scaling law suggests a skin effect mechanism in the soft iron discs. More important with regard to the Cadarache dynamo experiment, we observe a purely toroidal axisymmetric mode localized in the high-permeability discs which becomes dominant for large μr. In this limit, the toroidal mode is close to the onset of dynamo action with a (negative) growth rate that is rather independent of the magnetic Reynolds number. We qualitatively explain this effect by paramagnetic pumping at the fluid/disc interface and propose a simplified model that quantitatively reproduces numerical results. The crucial role of the high-permeability discs in the mode selection in the Cadarache dynamo experiment cannot be inferred from computations using idealized pseudo-vacuum boundary conditions (H × n = 0).
Progress and Challenges in Coupled Hydrodynamic-Ecological Estuarine Modeling
Numerical modeling has emerged over the last several decades as a widely accepted tool for investigations in environmental sciences. In estuarine research, hydrodynamic and ecological models have moved along parallel tracks with regard to complexity, refinement, computational po...
Progress and Challenges in Coupled Hydrodynamic-Ecological Estuarine Modeling
Numerical modeling has emerged over the last several decades as a widely accepted tool for investigations in environmental sciences. In estuarine research, hydrodynamic and ecological models have moved along parallel tracks with regard to complexity, refinement, computational po...
Potential Singularity for a Family of Models of the Axisymmetric Incompressible Flow
NASA Astrophysics Data System (ADS)
Hou, Thomas Y.; Jin, Tianling; Liu, Pengfei
2017-03-01
We study a family of 3D models for the incompressible axisymmetric Euler and Navier-Stokes equations. The models are derived by changing the strength of the convection terms in the equations written using a set of transformed variables. The models share several regularity results with the Euler and Navier-Stokes equations, including an energy identity, the conservation of a modified circulation quantity, the BKM criterion and the Prodi-Serrin criterion. The inviscid models with weak convection are numerically observed to develop stable self-similar singularity with the singular region traveling along the symmetric axis, and such singularity scenario does not seem to persist for strong convection.
Modeling Early Galaxies Using Radiation Hydrodynamics
2011-01-01
This simulation uses a flux-limited diffusion solver to explore the radiation hydrodynamics of early galaxies, in particular, the ionizing radiation created by Population III stars. At the time of this rendering, the simulation has evolved to a redshift of 3.5. The simulation volume is 11.2 comoving megaparsecs, and has a uniform grid of 10243 cells, with over 1 billion dark matter and star particles. This animation shows a combined view of the baryon density, dark matter density, radiation energy and emissivity from this simulation. The multi-variate rendering is particularly useful because is shows both the baryonic matter ("normal") and dark matter, and the pressure and temperature variables are properties of only the baryonic matter. Visible in the gas density are "bubbles", or shells, created by the radiation feedback from young stars. Seeing the bubbles from feedback provides confirmation of the physics model implemented. Features such as these are difficult to identify algorithmically, but easily found when viewing the visualization. Simulation was performed on Kraken at the National Institute for Computational Sciences. Visualization was produced using resources of the Argonne Leadership Computing Facility at Argonne National Laboratory.
Hydrodynamical Modeling of the Local Interstellar Medium
NASA Astrophysics Data System (ADS)
Slavin, Jonathan David
2017-01-01
Studies of the Local Interstellar Medium (LISM) provide us with the opportunity to make progress in understanding a wide range of physical processes that operate in the diffuse insterstellar medium (ISM) of galaxies. The LISM includes a large bubble of hot, supernova created gas, known as the Local Bubble, and several low density, warm clouds close to the Sun, known as the Complex of Local Insterstellar Clouds (CLIC). The CLIC includes the Local Interstellar Cloud that surrounds and confines the heliosphere and is the source of neutral H and He that has been detected flowing into the Solar System. Several important questions remain unanswered about the LISM including how the Local Bubble formed, how the CLIC got to be inside the Local Bubble, and what are the ongoing interactions of the hot gas with the CLIC gas. We report on our progress in creating numerical hydrodynamical models of the LISM that aim to help us to understand the wide range of observations we have of the CLIC and the Local Bubble and the origins and evolution of the LISM.
NASA Astrophysics Data System (ADS)
Fernández-Trincado, J. G.; Robin, A. C.; Bienaymé, O.; Reylé, C.; Valenzuela, O.; Pichardo, B.
2014-07-01
In this contributed poster we present a preliminary attempt to compute a non-axisymmetric potential together with previous axisymmetric potential of the Besançon galaxy model. The contribution by non-axisymmetric components are modeled by the superposition of inhomogeneous ellipsoids to approximate the triaxial bar and superposition of homogeneous oblate spheroids for a stellar halo, possibly triaxial. Finally, we have computed the potential and force field for these non-axisymmetric components in order to constraint the total mass of the Milky Way. We present preliminary results for the rotation curve and the contribution of the bar to it. This approach will allow future studies of dynamical constraints from comparisons of kinematical simulations with upcoming surveys such as RAVE, BRAVA, APOGEE, and GAIA in the near future. More details, are presented in https://gaia.ub.edu/Twiki/pub/GREATITNFC/ProgramFinalconference/Poster_JG.Fern%e1ndez.pdf.
NASA Astrophysics Data System (ADS)
Méchi, Rachid; Farhat, Habib; Said, Rachid
2016-01-01
Nongray radiation calculations are carried out for a case problem available in the literature. The problem is a non-isothermal and inhomogeneous CO2-H2O- N2 gas mixture confined within an axisymmetric cylindrical furnace. The numerical procedure is based on the zonal method associated with the weighted sum of gray gases (WSGG) model. The effect of the wall emissivity on the heat flux losses is discussed. It is shown that this property affects strongly the furnace efficiency and that the most important heat fluxes are those leaving through the circumferential boundary. The numerical procedure adopted in this work is found to be effective and may be relied on to simulate coupled turbulent combustion-radiation in fired furnaces.
Impact of axisymmetric mass models for dwarf spheroidal galaxies on indirect dark matter searches
NASA Astrophysics Data System (ADS)
Klop, Niki; Zandanel, Fabio; Hayashi, Kohei; Ando, Shin'ichiro
2017-06-01
Dwarf spheroidals are low-luminosity satellite galaxies of the Milky Way highly dominated by dark matter (DM). Therefore, they are prime targets to search for signals from dark matter annihilation using gamma-ray observations. While the typical assumption is that the dark matter density profile of these satellite galaxies can be described by a spherical symmetric Navarro-Frenk-White (NFW) profile, recent observational data of stellar kinematics suggest that the DM halos around these galaxies are better described by axisymmetric profiles. Motivated by such evidence, we analyze about seven years of pass8 Fermi data for seven classical dwarf galaxies, including Draco, adopting both the widely used NFW profile and observationally motivated axisymmetric density profiles. For four of the selected dwarfs (Sextans, Carina, Sculptor and Fornax), axisymmetric mass models suggest a cored density profile rather than the commonly adopted cusped profile. We found that upper limits on the annihilation cross section for some of these dwarfs are significantly higher than the ones achieved using an NFW profile. Therefore, upper limits in the literature obtained using spherical symmetric cusped profiles, such as the NFW, might be overestimated. Our results show that it is extremely important to use observationally motivated density profiles going beyond the usually adopted NFW in order to obtain accurate constraints on the dark matter annihilation cross section.
An axisymmetric magnetohydrodynamic model for the Crab pulsar wind bubble
NASA Technical Reports Server (NTRS)
Begelman, Mitchell C.; Li, Zhi-Yun
1992-01-01
We extend Kennel and Coroniti's (1984) spherical magnetohydrodynamic models for the Crab Nebula to include the pinching effect of the toroidal magnetic field. Since the bulk nebular flow is likely to be very submagnetosonic, a quasi-static treatment is possible. We show that the pinching effect can be responsible for the observed elongation of the pulsar wind bubble, as indicated by the surface brightness contours of optical synchrotron radiation. From the observed elongation we estimate a value for sigma, the ratio of Poynting flux to plasma kinetic energy flux in the free pulsar wind, which is consistent with previous results from spherical models. Using the inferred magnetic field configuration inside the pulsar wind bubble, combined with the observed dimensions of the X-ray nebula, we are able to constrain the particle distribution function. We conclude that, for a power-law injection function, the maximum energy has to be much larger in the pulsar equatorial region than in the polar region.
An axisymmetric magnetohydrodynamic model for the Crab pulsar wind bubble
NASA Technical Reports Server (NTRS)
Begelman, Mitchell C.; Li, Zhi-Yun
1992-01-01
We extend Kennel and Coroniti's (1984) spherical magnetohydrodynamic models for the Crab Nebula to include the pinching effect of the toroidal magnetic field. Since the bulk nebular flow is likely to be very submagnetosonic, a quasi-static treatment is possible. We show that the pinching effect can be responsible for the observed elongation of the pulsar wind bubble, as indicated by the surface brightness contours of optical synchrotron radiation. From the observed elongation we estimate a value for sigma, the ratio of Poynting flux to plasma kinetic energy flux in the free pulsar wind, which is consistent with previous results from spherical models. Using the inferred magnetic field configuration inside the pulsar wind bubble, combined with the observed dimensions of the X-ray nebula, we are able to constrain the particle distribution function. We conclude that, for a power-law injection function, the maximum energy has to be much larger in the pulsar equatorial region than in the polar region.
SAMPLE AOR CALCULATION USING ANSYS AXISYMMETRIC PARAMETRIC MODEL FOR TANK SST-S
JULYK, L.J.; MACKEY, T.C.
2003-06-19
This document documents the ANSYS axisymmetric parametric model for single-shell tank S and provides sample calculation for analysis-of-record mechanical load conditions. The purpose of this calculation is to develop a parametric model for single shell tank (SST) S, and provide a sample analysis of SST-S tank based on analysis of record (AOR) loads. The SST-S model is based on buyer-supplied as-built drawings and information for the AOR for SSTs, encompassing the existing tank load conditions, and evaluates stresses and deformations throughout the tank and surrounding soil mass.
SAMPLE AOR CALCULATION USING ANSYS AXISYMMETRIC PARAMETRIC MODEL FOR TANK SST-SX
JULYK, L.J.; MACKEY, T.C.
2003-06-19
This document documents the ANSYS axisymmetric parametric model for single-shell tank SX and provides sample calculation for analysis-of-record mechanical load conditions. The purpose of this calculation is to develop a parametric model for single shell tank (SST) SX, and provide a sample analysis of the SST-SX tank based on analysis of record (AOR) loads. The SST-SX model is based on buyer-supplied as-built drawings and information for the AOR for SSTs, encompassing the existing tank load conditions, and evaluates stresses and deformations throughout the tank and surrounding soil mass.
SAMPLE AOR CALCULATION USING ANSYS AXISYMMETRIC PARAMETRIC MODEL FOR TANK SST-AX
JULYK, L.J.; MACKEY, T.C.
2003-06-19
This document documents the ANSYS axisymmetric parametric model for single-shell tank AX and provides sample calculation for analysis-of-record mechanical load conditions. The purpose of this calculation is to develop a parametric model for single shell tank (SST) AX, and provide a sample analysis of SST-AX tank based on analysis of record (AOR) loads. The SST-AX model is based on buyer-supplied as-built drawings and information for the AOR for SSTs, encompassing the existing tank load conditions, and evaluates stresses and deformations throughout the tank and surrounding soil mass.
SAMPLE AOR CALCULATION USING ANSYS AXISYMMETRIC PARAMETRIC MODEL FOR TANK SST-A
JULYK, L.J.; MACKEY, T.C.
2003-06-19
This document documents the ANSYS axisymmetric parametric model for single-shell tank A and provides sample calculation for analysis-of-record mechanical load conditions. The purpose of this calculation is to develop a parametric model for single shell tank (SST) A, and provide a sample analysis of SST-A tank based on analysis of record (AOR) loads. The SST-A model is based on buyer-supplied as-built drawings and information for the AOR for SSTs, encompassing the existing tank load conditions, and evaluates stresses and deformations throughout the tank and surrounding soil mass.
DETAILED DECOMPOSITION OF GALAXY IMAGES. II. BEYOND AXISYMMETRIC MODELS
Peng, Chien Y.; Ho, Luis C.; Impey, Chris D.; Rix, Hans-Walter E-mail: lho@obs.carnegiescience.ed E-mail: rix@mpia-hd.mpg.d
2010-06-15
We present a two-dimensional (2D) fitting algorithm (GALFIT, ver. 3) with new capabilities to study the structural components of galaxies and other astronomical objects in digital images. Our technique improves on previous 2D fitting algorithms by allowing for irregular, curved, logarithmic and power-law spirals, ring, and truncated shapes in otherwise traditional parametric functions like the Sersic, Moffat, King, Ferrer, etc., profiles. One can mix and match these new shape features freely, with or without constraints, and apply them to an arbitrary number of model components of numerous profile types, so as to produce realistic-looking galaxy model images. Yet, despite the potential for extreme complexity, the meaning of the key parameters like the Sersic index, effective radius, or luminosity remains intuitive and essentially unchanged. The new features have an interesting potential for use to quantify the degree of asymmetry of galaxies, to quantify low surface brightness tidal features beneath and beyond luminous galaxies, to allow more realistic decompositions of galaxy subcomponents in the presence of strong rings and spiral arms, and to enable ways to gauge the uncertainties when decomposing galaxy subcomponents. We illustrate these new features by way of several case studies that display various levels of complexity.
Turbulence Model Comparisons for Shear Layers and Axisymmetric Jets.
1979-10-01
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Axisymmetric model of drop spreading on a horizontal surface
NASA Astrophysics Data System (ADS)
Mistry, Aashutosh; Muralidhar, K.
2015-09-01
Spreading of an initially spherical liquid drop over a textured surface is analyzed by solving an integral form of the governing equations. The mathematical model extends Navier-Stokes equations by including surface tension at the gas-liquid boundary and a force distribution at the three phase contact line. While interfacial tension scales with drop curvature, the motion of the contact line depends on the departure of instantaneous contact angle from its equilibrium value. The numerical solution is obtained by discretizing the spreading drop into disk elements. The Bond number range considered is 0.01-1. Results obtained for sessile drops are in conformity with limiting cases reported in the literature [J. C. Bird et al., "Short-time dynamics of partial wetting," Phys. Rev. Lett. 100, 234501 (2008)]. They further reveal multiple time scales that are reported in experiments [K. G. Winkels et al., "Initial spreading of low-viscosity drops on partially wetting surfaces," Phys. Rev. E 85, 055301 (2012) and A. Eddi et al., "Short time dynamics of viscous drop spreading," Phys. Fluids 25, 013102 (2013)]. Spreading of water and glycerin drops over fully and partially wetting surfaces is studied in terms of excess pressure, wall shear stress, and the dimensions of the footprint. Contact line motion is seen to be correctly captured in the simulations. Water drops show oscillations during spreading while glycerin spreads uniformly over the surface.
Kinetic theory model predictions compared with low-thrust axisymmetric nozzle plume data
NASA Technical Reports Server (NTRS)
Riley, B. R.; Fuhrman, S. J.; Penko, P. F.
1993-01-01
A system of nonlinear integral equations equivalent to the steady-state Krook kinetic equation was used to model the flow from a low-thrust axisymmetric nozzle. The mathematical model was used to numerically calculate the number density, temperature, and velocity of a simple gas as it expands into a near vacuum. With these quantities the gas pressure and flow directions of the gas near the exit plane were calculated and compared with experimental values for a low-thrust nozzle of the same geometry and mass flow rate.
Impact modeling with Smooth Particle Hydrodynamics
Stellingwerf, R.F.; Wingate, C.A.
1992-09-01
Smooth Particle Hydrodynamics (SPH) is a new computational technique uniquely suited to computation of hypervelocity impact phenomena. This paper reviews the characteristics, philosophy, and a bit of the derivation of the method. As illustrations of the technique, several test case computations and several application computations are shown.
Impact modeling with Smooth Particle Hydrodynamics
Stellingwerf, R.F.; Wingate, C.A.
1992-01-01
Smooth Particle Hydrodynamics (SPH) is a new computational technique uniquely suited to computation of hypervelocity impact phenomena. This paper reviews the characteristics, philosophy, and a bit of the derivation of the method. As illustrations of the technique, several test case computations and several application computations are shown.
Revisiting Turbulence Model Validation for High-Mach Number Axisymmetric Compression Corner Flows
NASA Technical Reports Server (NTRS)
Georgiadis, Nicholas J.; Rumsey, Christopher L.; Huang, George P.
2015-01-01
Two axisymmetric shock-wave/boundary-layer interaction (SWBLI) cases are used to benchmark one- and two-equation Reynolds-averaged Navier-Stokes (RANS) turbulence models. This validation exercise was executed in the philosophy of the NASA Turbulence Modeling Resource and the AIAA Turbulence Model Benchmarking Working Group. Both SWBLI cases are from the experiments of Kussoy and Horstman for axisymmetric compression corner geometries with SWBLI inducing flares of 20 and 30 degrees, respectively. The freestream Mach number was approximately 7. The RANS closures examined are the Spalart-Allmaras one-equation model and the Menter family of kappa - omega two equation models including the Baseline and Shear Stress Transport formulations. The Wind-US and CFL3D RANS solvers are employed to simulate the SWBLI cases. Comparisons of RANS solutions to experimental data are made for a boundary layer survey plane just upstream of the SWBLI region. In the SWBLI region, comparisons of surface pressure and heat transfer are made. The effects of inflow modeling strategy, grid resolution, grid orthogonality, turbulent Prandtl number, and code-to-code variations are also addressed.
Hydrodynamic and Salinity Intrusion Model in Selangor River Estuary
NASA Astrophysics Data System (ADS)
Haron, N. F.; Tahir, W.
2016-07-01
A multi-dimensional hydrodynamic and transport model has been used to develop the hydrodynamic and salinity intrusion model for Selangor River Estuary. Delft3D-FLOW was applied to the study area using a curvilinear, boundary fitted grid. External boundary forces included ocean water level, salinity, and stream flow. The hydrodynamic and salinity transport used for the simulation was calibrated and confirmed using data on November 2005 and from May to June 2014. A 13-day period for November 2005 data and a 6-day period of May to June 2014 data were chosen as the calibration and confirmation period because of the availability of data from the field-monitoring program conducted. From the calibration results, it shows that the model was well suited to predict the hydrodynamic and salinity intrusion characteristics of the study area.
Bortolotti, Mauro; Brugnara, Marco; Della Volpe, Claudio; Siboni, Stefano
2009-08-01
Axisymmetric drop shape analysis (ADSA) is a well-established methodology for estimating the contact angle value and the surface tension of liquids starting from sessile drops images. It consists of an iterative procedure in which a best fit between a theoretical axisymmetric Laplacian curve and an experimental drop profile is performed. When only an evaluation of the geometric contact angle value is needed, a similar numerical approach can be adopted by using simpler algebraic models in place of a Laplace profile, thus allowing more straightforward implementations and shorter computation times. In this work the relative merits of the different methodologies are compared. Beside the standard ADSA procedure, four different mathematical models are examined, namely the circular and elliptical models, the first-order perturbative solution of the Laplace equation, and a cubic spline model. Their relative statistical performances are tested on both calculated and experimental drop profiles. For simulated drops, the actual capability of the models to predict the correct contact angle is also investigated.
NASA Technical Reports Server (NTRS)
Hou, A. Y.
1984-01-01
A simple mechanistic model of a zonally averaged circulation forced by heat and momentum sources is developed and applied to the Venus atmosphere in the light of recent data. Basic equations for a steady-state axisymmetric circulation are discussed, and the parametric dependence of a nearly inviscid Hadley circulation in the absence of eddy forcing is examined and extended to a wide range of thermal Rossby numbers. The effect of diffusion is considered and found to be small for the Venus cloud region. The zonally averaged eddy sources and sinks required to support the zonal superrotation on Venus are determined.
Antenna design for microwave hepatic ablation using an axisymmetric electromagnetic model.
Bertram, John M; Yang, Deshan; Converse, Mark C; Webster, John G; Mahvi, David M
2006-02-27
An axisymmetric finite element method (FEM) model was employed to demonstrate important techniques used in the design of antennas for hepatic microwave ablation (MWA). To effectively treat deep-seated hepatic tumors, these antennas should produce a highly localized specific absorption rate (SAR) pattern and be efficient radiators at approved generator frequencies. As an example, a double slot choked antenna for hepatic MWA was designed and implemented using FEMLABtrade mark 3.0. This paper emphasizes the importance of factors that can affect simulation accuracy, which include boundary conditions, the dielectric properties of liver tissue, and mesh resolution.
Antenna design for microwave hepatic ablation using an axisymmetric electromagnetic model
Bertram, John M; Yang, Deshan; Converse, Mark C; Webster, John G; Mahvi, David M
2006-01-01
Background An axisymmetric finite element method (FEM) model was employed to demonstrate important techniques used in the design of antennas for hepatic microwave ablation (MWA). To effectively treat deep-seated hepatic tumors, these antennas should produce a highly localized specific absorption rate (SAR) pattern and be efficient radiators at approved generator frequencies. Methods and results As an example, a double slot choked antenna for hepatic MWA was designed and implemented using FEMLAB™ 3.0. Discussion This paper emphasizes the importance of factors that can affect simulation accuracy, which include boundary conditions, the dielectric properties of liver tissue, and mesh resolution. PMID:16504153
Calculations of axisymmetric vortex sheet roll-up using a panel and a filament model
NASA Technical Reports Server (NTRS)
Kantelis, J. P.; Widnall, S. E.
1986-01-01
A method for calculating the self-induced motion of a vortex sheet using discrete vortex elements is presented. Vortex panels and vortex filaments are used to simulate two-dimensional and axisymmetric vortex sheet roll-up. A straight forward application using vortex elements to simulate the motion of a disk of vorticity with an elliptic circulation distribution yields unsatisfactroy results where the vortex elements move in a chaotic manner. The difficulty is assumed to be due to the inability of a finite number of discrete vortex elements to model the singularity at the sheet edge and due to large velocity calculation errors which result from uneven sheet stretching. A model of the inner portion of the spiral is introduced to eliminate the difficulty with the sheet edge singularity. The model replaces the outermost portion of the sheet with a single vortex of equivalent circulation and a number of higher order terms which account for the asymmetry of the spiral. The resulting discrete vortex model is applied to both two-dimensional and axisymmetric sheets. The two-dimensional roll-up is compared to the solution for a semi-infinite sheet with good results.
3-D HYDRODYNAMIC MODELING IN A GEOSPATIAL FRAMEWORK
Bollinger, J; Alfred Garrett, A; Larry Koffman, L; David Hayes, D
2006-08-24
3-D hydrodynamic models are used by the Savannah River National Laboratory (SRNL) to simulate the transport of thermal and radionuclide discharges in coastal estuary systems. Development of such models requires accurate bathymetry, coastline, and boundary condition data in conjunction with the ability to rapidly discretize model domains and interpolate the required geospatial data onto the domain. To facilitate rapid and accurate hydrodynamic model development, SRNL has developed a pre- and post-processor application in a geospatial framework to automate the creation of models using existing data. This automated capability allows development of very detailed models to maximize exploitation of available surface water radionuclide sample data and thermal imagery.
Modeling non-stationary, non-axisymmetric heat patterns in DIII-D tokamak
Ciro, D.; Evans, T. E.; Caldas, I. L.
2016-10-27
Non-axisymmetric stationary magnetic perturbations lead to the formation of homoclinic tangles near the divertor magnetic saddle in tokamak discharges. These tangles intersect the divertor plates in static helical structures that delimit the regions reached by open magnetic field lines reaching the plasma column and leading the charged particles to the strike surfaces by parallel transport. In this article we introduce a non-axisymmetric rotating magnetic perturbation to model the time evolution of the three-dimensional magnetic field of a singlenull DIII-D tokamak discharge developing a rotating tearing mode. The non-axiymmetric field is modeled using the magnetic signals to adjust the phases andmore » currents of a set of internal filamentary currents that approximate the magnetic field in the plasma edge region. The stable and unstable manifolds of the asymmetric magnetic saddle are obtained through an adaptive calculation providing the cuts at a given poloidal plane and the strike surfaces. Lastly, for the modeled shot, the experimental heat pattern and its time development are well described by the rotating unstable manifold, indicating the emergence of homoclinic lobes in a rotating frame due to the plasma instabilities.« less
Modeling non-stationary, non-axisymmetric heat patterns in DIII-D tokamak
Ciro, D.; Evans, T. E.; Caldas, I. L.
2016-10-27
Non-axisymmetric stationary magnetic perturbations lead to the formation of homoclinic tangles near the divertor magnetic saddle in tokamak discharges. These tangles intersect the divertor plates in static helical structures that delimit the regions reached by open magnetic field lines reaching the plasma column and leading the charged particles to the strike surfaces by parallel transport. In this article we introduce a non-axisymmetric rotating magnetic perturbation to model the time evolution of the three-dimensional magnetic field of a singlenull DIII-D tokamak discharge developing a rotating tearing mode. The non-axiymmetric field is modeled using the magnetic signals to adjust the phases and currents of a set of internal filamentary currents that approximate the magnetic field in the plasma edge region. The stable and unstable manifolds of the asymmetric magnetic saddle are obtained through an adaptive calculation providing the cuts at a given poloidal plane and the strike surfaces. Lastly, for the modeled shot, the experimental heat pattern and its time development are well described by the rotating unstable manifold, indicating the emergence of homoclinic lobes in a rotating frame due to the plasma instabilities.
Modeling non-stationary, non-axisymmetric heat patterns in DIII-D tokamak
NASA Astrophysics Data System (ADS)
Ciro, D.; Evans, T. E.; Caldas, I. L.
2017-01-01
Non-axisymmetric stationary magnetic perturbations lead to the formation of homoclinic tangles near the divertor magnetic saddle in tokamak discharges. These tangles intersect the divertor plates in static helical structures that delimit the regions reached by open magnetic field lines reaching the plasma column and leading the charged particles to the strike surfaces by parallel transport. In this article we introduce a non-axisymmetric rotating magnetic perturbation to model the time evolution of the three-dimensional magnetic field of a single-null DIII-D tokamak discharge developing a rotating tearing mode. The non-axiymmetric field is modeled using the magnetic signals to adjust the phases and currents of a set of internal filamentary currents that approximate the magnetic field in the plasma edge region. The stable and unstable manifolds of the asymmetric magnetic saddle are obtained through an adaptive calculation providing the cuts at a given poloidal plane and the strike surfaces. For the modeled shot, the experimental heat pattern and its time development are well described by the rotating unstable manifold, indicating the emergence of homoclinic lobes in a rotating frame due to the plasma instabilities.
Concurrent multiscale modelling of atomistic and hydrodynamic processes in liquids.
Markesteijn, Anton; Karabasov, Sergey; Scukins, Arturs; Nerukh, Dmitry; Glotov, Vyacheslav; Goloviznin, Vasily
2014-08-06
Fluctuations of liquids at the scales where the hydrodynamic and atomistic descriptions overlap are considered. The importance of these fluctuations for atomistic motions is discussed and examples of their accurate modelling with a multi-space-time-scale fluctuating hydrodynamics scheme are provided. To resolve microscopic details of liquid systems, including biomolecular solutions, together with macroscopic fluctuations in space-time, a novel hybrid atomistic-fluctuating hydrodynamics approach is introduced. For a smooth transition between the atomistic and continuum representations, an analogy with two-phase hydrodynamics is used that leads to a strict preservation of macroscopic mass and momentum conservation laws. Examples of numerical implementation of the new hybrid approach for the multiscale simulation of liquid argon in equilibrium conditions are provided.
Concurrent multiscale modelling of atomistic and hydrodynamic processes in liquids
Markesteijn, Anton; Karabasov, Sergey; Scukins, Arturs; Nerukh, Dmitry; Glotov, Vyacheslav; Goloviznin, Vasily
2014-01-01
Fluctuations of liquids at the scales where the hydrodynamic and atomistic descriptions overlap are considered. The importance of these fluctuations for atomistic motions is discussed and examples of their accurate modelling with a multi-space–time-scale fluctuating hydrodynamics scheme are provided. To resolve microscopic details of liquid systems, including biomolecular solutions, together with macroscopic fluctuations in space–time, a novel hybrid atomistic–fluctuating hydrodynamics approach is introduced. For a smooth transition between the atomistic and continuum representations, an analogy with two-phase hydrodynamics is used that leads to a strict preservation of macroscopic mass and momentum conservation laws. Examples of numerical implementation of the new hybrid approach for the multiscale simulation of liquid argon in equilibrium conditions are provided. PMID:24982246
Process modeling and development for three axisymmetric net shape forgings. Progress report 5
El-Gizawy, A.S.
1992-03-01
The results of dynamic material modeling experiments are reported on aluminum alloys 6061 and 7050, and steel alloy 4340. This information was used to accurately describe the variables in the various constitutive equations used in computer modeling programs. A description of the experimental equipment used to deform the specimens and gather data was given. Previously reported work regarding computer modeling of interface friction and the forging process was reviewed. Using dynamic flow models, three different axisymmetric parts were analyzed for their potential for being produced by net shape or near net shape forging processes. Two aluminum alloy parts were recommended as potential candidates while the steel part was not a potential candidate. Recommendations for processing conditions were also given. 18 refs.
Rotationally-driven axisymmetric oscillatory convection in a semitransparent Czochralski melt model
NASA Astrophysics Data System (ADS)
Faiez, Reza; Rezaei, Yazdan
2017-01-01
A numerical study was carried out to investigate the effect of surface tension-driven convection on the transition of flow modes in an axisymmetric Czochralski oxide melt model. Computational results were obtained over a reasonably wide range of the crystal dummy rotation rate for the cases with and without Marangoni effect. The transition of the flow from steady-state to an axisymmetric oscillatory one was found to be occurred at a threshold value of the ratio between buoyancy and the rotationally-driven forces, which is considerably smaller in the presence of the Marangoni flow. This was shown that, in the presence of thermocapillary forces, the descending cold plume has a larger impact on the thermal field if compared to the case in which the Marangoni effect was ignored. Depending on the circumstances, each of the two different mechanisms, i.e., the rotating Rayleigh-Benard instability and the baroclinic instability, may play a dominant role in the steady-oscillatory flow transition. Thermocapillary effect on the mechanism of instability giving rise to the transition of the convective flow was studied.
Nonlinear axisymmetric and three-dimensional vorticity dynamics in a swirling jet model
NASA Technical Reports Server (NTRS)
Martin, J. E.; Meiburg, E.
1996-01-01
The mechanisms of vorticity concentration, reorientation, and stretching are investigated in a simplified swirling jet model, consisting of a line vortex along the jet axis surrounded by a jet shear layer with both azimuthal and streamwise vorticity. Inviscid three-dimensional vortex dynamics simulations demonstrate the nonlinear interaction and competition between a centrifugal instability and Kelvin-Helmholtz instabilities feeding on both components of the base flow vorticity. Under axisymmetric flow conditions, it is found that the swirl leads to the emergence of counterrotating vortex rings, whose circulation, in the absence of viscosity, can grow without bounds. Scaling laws are provided for the growth of these rings, which trigger a pinch-off mechanism resulting in a strong decrease of the local jet diameter. In the presence of an azimuthal disturbance, the nonlinear evolution of the flow depends strongly on the initial ratio of the azimuthal and axisymmetric perturbation amplitudes. The long term dynamics of the jet can be dominated by counterrotating vortex rings connected by braid vortices, by like-signed rings and streamwise braid vortices, or by wavy streamwise vortices alone.
Constructing stable 3D hydrodynamical models of giant stars
NASA Astrophysics Data System (ADS)
Ohlmann, Sebastian T.; Röpke, Friedrich K.; Pakmor, Rüdiger; Springel, Volker
2017-02-01
Hydrodynamical simulations of stellar interactions require stable models of stars as initial conditions. Such initial models, however, are difficult to construct for giant stars because of the wide range in spatial scales of the hydrostatic equilibrium and in dynamical timescales between the core and the envelope of the giant. They are needed for, e.g., modeling the common envelope phase where a giant envelope encompasses both the giant core and a companion star. Here, we present a new method of approximating and reconstructing giant profiles from a stellar evolution code to produce stable models for multi-dimensional hydrodynamical simulations. We determine typical stellar stratification profiles with the one-dimensional stellar evolution code mesa. After an appropriate mapping, hydrodynamical simulations are conducted using the moving-mesh code arepo. The giant profiles are approximated by replacing the core of the giant with a point mass and by constructing a suitable continuation of the profile to the center. Different reconstruction methods are tested that can specifically control the convective behaviour of the model. After mapping to a grid, a relaxation procedure that includes damping of spurious velocities yields stable models in three-dimensional hydrodynamical simulations. Initially convectively stable configurations lead to stable hydrodynamical models while for stratifications that are convectively unstable in the stellar evolution code, simulations recover the convective behaviour of the initial model and show large convective plumes with Mach numbers up to 0.8. Examples are shown for a 2 M⊙ red giant and a 0.67 M⊙ asymptotic giant branch star. A detailed analysis shows that the improved method reliably provides stable models of giant envelopes that can be used as initial conditions for subsequent hydrodynamical simulations of stellar interactions involving giant stars.
Automatization of hydrodynamic modelling in a Floreon+ system
NASA Astrophysics Data System (ADS)
Ronovsky, Ales; Kuchar, Stepan; Podhoranyi, Michal; Vojtek, David
2017-07-01
The paper describes fully automatized hydrodynamic modelling as a part of the Floreon+ system. The main purpose of hydrodynamic modelling in the disaster management is to provide an accurate overview of the hydrological situation in a given river catchment. Automatization of the process as a web service could provide us with immediate data based on extreme weather conditions, such as heavy rainfall, without the intervention of an expert. Such a service can be used by non scientific users such as fire-fighter operators or representatives of a military service organizing evacuation during floods or river dam breaks. The paper describes the whole process beginning with a definition of a schematization necessary for hydrodynamic model, gathering of necessary data and its processing for a simulation, the model itself and post processing of a result and visualization on a web service. The process is demonstrated on a real data collected during floods in our Moravian-Silesian region in 2010.
NASA Technical Reports Server (NTRS)
Goldstein, M.; Rosenbaum, B.
1973-01-01
A model based on Lighthill's theory for predicting aerodynamic noise from a turbulent shear flow is developed. This model is a generalization of the one developed by Ribner. It does not require that the turbulent correlations factor into space and time-dependent parts. It replaces his assumption of isotropic turbulence by the more realistic one of axisymmetric turbulence. In the course of the analysis, a hierarchy of equations is developed wherein each succeeding equation involves more assumptions than the preceding equation but requires less experimental information for its use. The implications of the model for jet noise are discussed. It is shown that for the particular turbulence data considered anisotropy causes the high-frequency self-noise to be beamed downstream.
Progress and challenges in coupled hydrodynamic-ecological estuarine modeling
Ganju, Neil K.; Brush, Mark J.; Rashleigh, Brenda; Aretxabaleta, Alfredo L.; del Barrio, Pilar; Grear, Jason S.; Harris, Lora A.; Lake, Samuel J.; McCardell, Grant; O’Donnell, James; Ralston, David K.; Signell, Richard P.; Testa, Jeremy M.; Vaudrey, Jamie M.P.
2016-01-01
Numerical modeling has emerged over the last several decades as a widely accepted tool for investigations in environmental sciences. In estuarine research, hydrodynamic and ecological models have moved along parallel tracks with regard to complexity, refinement, computational power, and incorporation of uncertainty. Coupled hydrodynamic-ecological models have been used to assess ecosystem processes and interactions, simulate future scenarios, and evaluate remedial actions in response to eutrophication, habitat loss, and freshwater diversion. The need to couple hydrodynamic and ecological models to address research and management questions is clear, because dynamic feedbacks between biotic and physical processes are critical interactions within ecosystems. In this review we present historical and modern perspectives on estuarine hydrodynamic and ecological modeling, consider model limitations, and address aspects of model linkage, skill assessment, and complexity. We discuss the balance between spatial and temporal resolution and present examples using different spatiotemporal scales. Finally, we recommend future lines of inquiry, approaches to balance complexity and uncertainty, and model transparency and utility. It is idealistic to think we can pursue a “theory of everything” for estuarine models, but recent advances suggest that models for both scientific investigations and management applications will continue to improve in terms of realism, precision, and accuracy. PMID:27721675
Modeling of nanoscale liquid mixture transport by density functional hydrodynamics
NASA Astrophysics Data System (ADS)
Dinariev, Oleg Yu.; Evseev, Nikolay V.
2017-06-01
Modeling of multiphase compositional hydrodynamics at nanoscale is performed by means of density functional hydrodynamics (DFH). DFH is the method based on density functional theory and continuum mechanics. This method has been developed by the authors over 20 years and used for modeling in various multiphase hydrodynamic applications. In this paper, DFH was further extended to encompass phenomena inherent in liquids at nanoscale. The new DFH extension is based on the introduction of external potentials for chemical components. These potentials are localized in the vicinity of solid surfaces and take account of the van der Waals forces. A set of numerical examples, including disjoining pressure, film precursors, anomalous rheology, liquid in contact with heterogeneous surface, capillary condensation, and forward and reverse osmosis, is presented to demonstrate modeling capabilities.
Numerical simulations of blast wave characteristics with a two-dimensional axisymmetric room model
NASA Astrophysics Data System (ADS)
Sugiyama, Y.; Homae, T.; Wakabayashi, K.; Matsumura, T.; Nakayama, Y.
2017-07-01
This paper numerically visualizes explosion phenomena in order to discuss blast wave characteristics with a two-dimensional axisymmetric room model. After the shock wave exits via an opening, the blast wave propagates into open space. In the present study, a parametric study was conducted to determine the blast wave characteristics from the room exit by changing the room shape and the mass of the high explosive. Our results show that the blast wave characteristics can be correctly estimated using a scaling factor proposed in the present paper that includes the above parameters. We conducted normalization of the peak overpressure curve using the shock overpressure at the exit and the length scale of the room volume. In the case where the scaling factor has the same value, the normalized peak overpressure curve does not depend on the calculation conditions, and the scaling factor describes the blast wave characteristics emerging from the current room model.
Numerical simulations of blast wave characteristics with a two-dimensional axisymmetric room model
NASA Astrophysics Data System (ADS)
Sugiyama, Y.; Homae, T.; Wakabayashi, K.; Matsumura, T.; Nakayama, Y.
2017-01-01
This paper numerically visualizes explosion phenomena in order to discuss blast wave characteristics with a two-dimensional axisymmetric room model. After the shock wave exits via an opening, the blast wave propagates into open space. In the present study, a parametric study was conducted to determine the blast wave characteristics from the room exit by changing the room shape and the mass of the high explosive. Our results show that the blast wave characteristics can be correctly estimated using a scaling factor proposed in the present paper that includes the above parameters. We conducted normalization of the peak overpressure curve using the shock overpressure at the exit and the length scale of the room volume. In the case where the scaling factor has the same value, the normalized peak overpressure curve does not depend on the calculation conditions, and the scaling factor describes the blast wave characteristics emerging from the current room model.
Absorption of acoustic waves by sunspots. II - Resonance absorption in axisymmetric fibril models
NASA Technical Reports Server (NTRS)
Rosenthal, C. S.
1992-01-01
Analytical calculations of acoustic waves scattered by sunspots which concentrate on the absorption at the magnetohydrodynamic Alfven resonance are extended to the case of a flux-tube embedded in a uniform atmosphere. The model is based on a flux-tubes of varying radius that are highly structured, translationally invariant, and axisymmetric. The absorbed fractional energy is determined for different flux-densities and subphotospheric locations with attention given to the effects of twist. When the flux is highly concentrated into annuli efficient absorption is possible even when the mean magnetic flux density is low. The model demonstrates low absorption at low azimuthal orders even in the presence of twist which generally increases the range of wave numbers over which efficient absorption can occur. Resonance absorption is concluded to be an efficient mechanism in monolithic sunspots, fibril sunspots, and plage fields.
Modelling the dusty circumstellar envelopes of axisymmetric post-AGB stars
NASA Astrophysics Data System (ADS)
Pérez-Estrada, A. M.; Molina, C. A.; Pérez-Sánchez, A. F.
2017-07-01
We studied the dust component of the dense circumstellar envelope (CSE) of two post-AGB sources known as Water Fountain nebulae: IRAS 16342-3814 and IRAS 18113-2503. The goal was to derive some of their physical properties and determine the dust temperature distribution of the sources. It has been proposed that axisymmetric post-AGB stars could be the progenitors of non-spherical planetary nebulae. The study of the structure and physical properties of the dusty CSE of these sources allows the assessment of this hypothesis, and casts light on the processes that occur during the last stages of evolution of low- to intermediate-mass stars. We considered a model with a dust density distribution consisting of a spherical distribution in the external region of the CSE and a component with axial symmetry inside, as well as a set of physical parameters for each source. Then, we performed radiative transfer calculations using the RADMC-3D code, which is a software package that runs thermal Monte Carlo simulations to compute the dust temperature, images and spectra for a model in dust continuum. We compared synthetic infrared spectral energy distributions with those observed by telescopes such as Spitzer and ISO, in order to get the best fit possible. As a result, we found good fits for both sources and axisymmetric dust temperature distributions for each one. Therefore, we concluded that our model is a suitable approximation to describe the dusty CSE of these stars, and it might be proposed to model the other water fountain sources known to date.
A 2D Axisymmetric Mixture Multiphase Model for Bottom Stirring in a BOF Converter
NASA Astrophysics Data System (ADS)
Kruskopf, Ari
2017-02-01
A process model for basic oxygen furnace (BOF) steel converter is in development. The model will take into account all the essential physical and chemical phenomena, while achieving real-time calculation of the process. The complete model will include a 2D axisymmetric turbulent multiphase flow model for iron melt and argon gas mixture, a steel scrap melting model, and a chemical reaction model. A novel liquid mass conserving mixture multiphase model for bubbling gas jet is introduced in this paper. In-house implementation of the model is tested and validated in this article independently from the other parts of the full process model. Validation data comprise three different water models with different volume flow rates of air blown through a regular nozzle and a porous plug. The water models cover a wide range of dimensionless number R_{{p}} , which include values that are similar for industrial-scale steel converter. The k- ɛ turbulence model is used with wall functions so that a coarse grid can be utilized. The model calculates a steady-state flow field for gas/liquid mixture using control volume method with staggered SIMPLE algorithm.
Hydrodynamic models of a Cepheid atmosphere. I - Deep envelope models
NASA Technical Reports Server (NTRS)
Karp, A. H.
1975-01-01
The implicit hydrodynamic code of Kutter and Sparks has been modified to include radiative transfer effects. This modified code has been used to compute deep envelope models of a classical Cepheid with a period of 12 days. It is shown that in this particular model the hydrogen ionization region plays only a small role in producing the observed phase lag between the light and velocity curves. The cause of the bumps on the model's light curve is examined, and a mechanism is presented to explain those Cepheids with two secondary features on their light curves. This mechanism is shown to be consistent with the Hertzsprung sequence only if the evolutionary mass-luminosity law is used.
NASA Astrophysics Data System (ADS)
Gizon, Laurent; Barucq, Hélène; Duruflé, Marc; Hanson, Chris S.; Leguèbe, Michael; Birch, Aaron C.; Chabassier, Juliette; Fournier, Damien; Hohage, Thorsten; Papini, Emanuele
2017-04-01
Context. Local helioseismology has so far relied on semi-analytical methods to compute the spatial sensitivity of wave travel times to perturbations in the solar interior. These methods are cumbersome and lack flexibility. Aims: Here we propose a convenient framework for numerically solving the forward problem of time-distance helioseismology in the frequency domain. The fundamental quantity to be computed is the cross-covariance of the seismic wavefield. Methods: We choose sources of wave excitation that enable us to relate the cross-covariance of the oscillations to the Green's function in a straightforward manner. We illustrate the method by considering the 3D acoustic wave equation in an axisymmetric reference solar model, ignoring the effects of gravity on the waves. The symmetry of the background model around the rotation axis implies that the Green's function can be written as a sum of longitudinal Fourier modes, leading to a set of independent 2D problems. We use a high-order finite-element method to solve the 2D wave equation in frequency space. The computation is embarrassingly parallel, with each frequency and each azimuthal order solved independently on a computer cluster. Results: We compute travel-time sensitivity kernels in spherical geometry for flows, sound speed, and density perturbations under the first Born approximation. Convergence tests show that travel times can be computed with a numerical precision better than one millisecond, as required by the most precise travel-time measurements. Conclusions: The method presented here is computationally efficient and will be used to interpret travel-time measurements in order to infer, e.g., the large-scale meridional flow in the solar convection zone. It allows the implementation of (full-waveform) iterative inversions, whereby the axisymmetric background model is updated at each iteration.
Qayyum, Mubashir; Khan, Hamid; Rahim, M. Tariq; Ullah, Inayat
2015-01-01
The aim of this article is to model and analyze an unsteady axisymmetric flow of non-conducting, Newtonian fluid squeezed between two circular plates passing through porous medium channel with slip boundary condition. A single fourth order nonlinear ordinary differential equation is obtained using similarity transformation. The resulting boundary value problem is solved using Homotopy Perturbation Method (HPM) and fourth order Explicit Runge Kutta Method (RK4). Convergence of HPM solution is verified by obtaining various order approximate solutions along with absolute residuals. Validity of HPM solution is confirmed by comparing analytical and numerical solutions. Furthermore, the effects of various dimensionless parameters on the longitudinal and normal velocity profiles are studied graphically. PMID:25738864
Hydrodynamic Modeling of the Interstellar Medium
NASA Astrophysics Data System (ADS)
Rosen, A.; Bregman, J. N.; Norman, M. L.
1992-12-01
We have completed 2D hydrodynamical simulations in order to investigate the structure and kinematics of the interstellar medium. These simulations have been performed with a version of Zeus, an Eulerian finite-difference code, that has been modified to allow for two cospatial interacting fluids. One fluid represents the gas while the other represents a collection of mean Pop I stars. Star formation, stellar mass loss, and stellar wind heating couple the stars with the gas; radiative cooling in the gas is also included. In these simulations, one dimension is perpendicular to the plane (+/- 15 kpc) and the other is along the plane (2 kpc). Both the external gravitational potential and column density of gas used are appropriate for the Galaxy at the solar circle. The simulations generate a network of dense filaments of H I, which dominate the mass, extend up to 4--5 kpc above the midplane and surround large bubbles of warm and hot gas. These bubbles can reach sizes of up to many kpc's and are elongated perpendicular to the midplane. Dilute, hot (log T > 5.0) gas takes up most of the volume close to the midplane, with ~ 10% of the volume in each of the cold and warm gas phases. Also, we calculate scale heights of the three gas phases and the stars, velocity distributions of the cold gas, and compare these with observations. We wish to acknowedge the support of NASA Grant NAGW-2135.
Evaluation of Industry Standard Turbulence Models on an Axisymmetric Supersonic Compression Corner
NASA Technical Reports Server (NTRS)
DeBonis, James R.
2015-01-01
Reynolds-averaged Navier-Stokes computations of a shock-wave/boundary-layer interaction (SWBLI) created by a Mach 2.85 flow over an axisymmetric 30-degree compression corner were carried out. The objectives were to evaluate four turbulence models commonly used in industry, for SWBLIs, and to evaluate the suitability of this test case for use in further turbulence model benchmarking. The Spalart-Allmaras model, Menter's Baseline and Shear Stress Transport models, and a low-Reynolds number k- model were evaluated. Results indicate that the models do not accurately predict the separation location; with the SST model predicting the separation onset too early and the other models predicting the onset too late. Overall the Spalart-Allmaras model did the best job in matching the experimental data. However there is significant room for improvement, most notably in the prediction of the turbulent shear stress. Density data showed that the simulations did not accurately predict the thermal boundary layer upstream of the SWBLI. The effect of turbulent Prandtl number and wall temperature were studied in an attempt to improve this prediction and understand their effects on the interaction. The data showed that both parameters can significantly affect the separation size and location, but did not improve the agreement with the experiment. This case proved challenging to compute and should provide a good test for future turbulence modeling work.
Meyer, Valentin; Maxit, Laurent; Audoly, Christian
2016-09-01
The scattered pressure from a stiffened axisymmetric submerged shell impinged by acoustic plane waves has been investigated experimentally, analytically and through numerical models. In the case where the shell is periodically stiffened, it is shown that helical, Bragg, and Bloch-Floquet waves can propagate. The influence of non-axisymmetric internal frames on these scattering phenomena is nevertheless not well known, as it can considerably increase the computational cost. To overcome this issue, the condensed transfer function (CTF) method, which has been developed to couple subsystems along linear junctions in the case of a mechanical excitation, is extended to acoustical excitations. It consists in approximating transfer functions on the junctions and deducing the behavior of the coupled system using the superposition principle and the continuity equations at the junctions. In particular, the CTF method can be used to couple a dedicated model of an axisymmetric stiffened submerged shell with non-axisymmetric internal structures modeled by the finite element method. Incident plane waves are introduced in the formulation and far-field reradiated pressure is estimated. An application consisting of a stiffened shell with curved plates connecting the ribs is considered. Supplementary Bloch-Floquet trajectories are observed in the frequency-angle spectrum and are explained using a simplified interference model.
Comparisons of linear and nonlinear plasma response models for non-axisymmetric perturbations
Turnbull, A. D.; Ferraro, N. M.; Lao, L. L.; Lanctot, M. J.; Izzo, V. A.; Lazarus, E. A.; Hirshman, S. P.; Park, J.-K.; Lazerson, S.; Reiman, A.; Cooper, W. A.; Liu, Y. Q.; Turco, F.
2013-05-15
With the installation of non-axisymmetric coil systems on major tokamaks for the purpose of studying the prospects of ELM-free operation, understanding the plasma response to the applied fields is a crucial issue. Application of different response models, using standard tools, to DIII-D discharges with applied non-axisymmetric fields from internal coils, is shown to yield qualitatively different results. The plasma response can be treated as an initial value problem, following the system dynamically from an initial unperturbed state, or from a nearby perturbed equilibrium approach, and using both linear and nonlinear models [A. D. Turnbull, Nucl. Fusion 52, 054016 (2012)]. Criteria are discussed under which each of the approaches can yield a valid response. In the DIII-D cases studied, these criteria show a breakdown in the linear theory despite the small 10{sup −3} relative magnitude of the applied magnetic field perturbations in this case. For nonlinear dynamical evolution simulations to reach a saturated nonlinear steady state, appropriate damping mechanisms need to be provided for each normal mode comprising the response. Other issues arise in the technical construction of perturbed flux surfaces from a displacement and from the presence of near nullspace normal modes. For the nearby equilibrium approach, in the absence of a full 3D equilibrium reconstruction with a controlled comparison, constraints relating the 2D system profiles to the final profiles in the 3D system also need to be imposed to assure accessibility. The magnetic helicity profile has been proposed as an appropriate input to a 3D equilibrium calculation and tests of this show the anticipated qualitative behavior.
Hydrodynamic model for picosecond propagation of laser-created nanoplasmas
NASA Astrophysics Data System (ADS)
Saxena, Vikrant; Jurek, Zoltan; Ziaja, Beata; Santra, Robin
2015-06-01
The interaction of a free-electron-laser pulse with a moderate or large size cluster is known to create a quasi-neutral nanoplasma, which then expands on hydrodynamic timescale, i.e., > 1 ps. To have a better understanding of ion and electron data from experiments derived from laser-irradiated clusters, one needs to simulate cluster dynamics on such long timescales for which the molecular dynamics approach becomes inefficient. We therefore propose a two-step Molecular Dynamics-Hydrodynamic scheme. In the first step we use molecular dynamics code to follow the dynamics of an irradiated cluster until all the photo-excitation and corresponding relaxation processes are finished and a nanoplasma, consisting of ground-state ions and thermalized electrons, is formed. In the second step we perform long-timescale propagation of this nanoplasma with a computationally efficient hydrodynamic approach. In the present paper we examine the feasibility of a hydrodynamic two-fluid approach to follow the expansion of spherically symmetric nanoplasma, without accounting for the impact ionization and three-body recombination processes at this stage. We compare our results with the corresponding molecular dynamics simulations. We show that all relevant information about the nanoplasma propagation can be extracted from hydrodynamic simulations at a significantly lower computational cost when compared to a molecular dynamics approach. Finally, we comment on the accuracy and limitations of our present model and discuss possible future developments of the two-step strategy.
Integrated modeling and parallel computation of laser-induced axisymmetric rod growth
NASA Astrophysics Data System (ADS)
Lan, Hong
2005-07-01
To fully investigate a pyrolytic Laser-induced chemical vapor deposition (LCVD) system for growing an axisymmetric rod, a novel integrated three-dimensional mathematical model was developed not only to describe the heat transport in the deposit and substrate, but also to simulate the gas-phase in the heated reaction zone and its effect on growth rate. The integrated model consists of three components: the substrate, rod, and gas-phase domains. Each component is a separate model and the three components are dynamically integrated into one model for simulating the iterative and complex process of rod deposition. The gas-phase reaction is modeled by the gas-phase component, an adaptive domain attached on the top part of the rod. Its size and mesh decomposition is dynamically determined by the rod temperature distribution and the chosen threshold. The temperature and molar ratio are predicted and used to adjust the growth rate, by taking into account the diffusion limited growth regime, and to improve the simulation of entire deposition process. The substrate component describes the heat flow into the substrate, and the substrate surface temperature can be used to predict the initial rod growth which may affect the successive growth of the rod. The rod growth process is simulated using a layer-by-layer axisymmetric model. For each layer, the rod grows along the outward normal direction at each point on the rod surface. This simplified model makes the process more predictable and easier to control by specifying the height of the rod and the number of total iterations. Finite difference schemes, iterative numerical methods, and parallel algorithms were developed for solving the model. The numerical computation is stable, convergent, and efficient. The model and numerical methods are implemented sequentially and in parallel using a standard C++ code and Message Passing Interface (MPI). The program can be easily installed and executed on different platforms, such as Unix
Modeling High Resolution Flare Spectra Using Hydrodynamic Simulations
NASA Astrophysics Data System (ADS)
Warren, Harry; Doschek, G.
2006-06-01
Understanding the hydrodynamic response of the solar atmosphere to the release of energy during a flare has been a long standing problem in solar physics. Early time-dependent hydrodynamic simulations were able to reproduce the high temperatures and densities observed in solar flares, but were not able to model the observations in any detail. For example, these simulations could not account for the relatively slow decay of the observed emission or the absence of blueshifts in high spectral resolution line profiles at flare onset. We have found that by representing the flare as a succession of independently heated filaments it is possible to reproduce both the evolution of line intensity and the shape of the line profile using hydrodynamic simulations. Here we present detailed comparisons between our simulation results and several flares observed with the Yohkoh Bragg Crystal Spectrometer (BCS). Comparisons with 3D MHD simulations will also be discussed.
Including Nearshore Processes in Phase-Averaged Hydrodynamics Models
2006-08-01
physical modeling of hydrodynamics to the use of numerical models. A suitable set of equations conserving mass, momen- tum, and energy do not suffer...the high cost and scale effects of physical models. Numerical models, however, rely on a set of discritized and sim- plified equations , and nonphysical...used in the interest of brevity. The solution of Equation 24 along with Equation 26 constitutes a solution for the depth-dependent cross-shore
Stability of Blowup for a 1D Model of Axisymmetric 3D Euler Equation
NASA Astrophysics Data System (ADS)
Do, Tam; Kiselev, Alexander; Xu, Xiaoqian
2016-10-01
The question of the global regularity versus finite- time blowup in solutions of the 3D incompressible Euler equation is a major open problem of modern applied analysis. In this paper, we study a class of one-dimensional models of the axisymmetric hyperbolic boundary blow-up scenario for the 3D Euler equation proposed by Hou and Luo (Multiscale Model Simul 12:1722-1776, 2014) based on extensive numerical simulations. These models generalize the 1D Hou-Luo model suggested in Hou and Luo Luo and Hou (2014), for which finite-time blowup has been established in Choi et al. (arXiv preprint. arXiv:1407.4776, 2014). The main new aspects of this work are twofold. First, we establish finite-time blowup for a model that is a closer approximation of the three-dimensional case than the original Hou-Luo model, in the sense that it contains relevant lower-order terms in the Biot-Savart law that have been discarded in Hou and Luo Choi et al. (2014). Secondly, we show that the blow-up mechanism is quite robust, by considering a broader family of models with the same main term as in the Hou-Luo model. Such blow-up stability result may be useful in further work on understanding the 3D hyperbolic blow-up scenario.
HYDRODYNAMIC AND TRANSPORT MODELING STUDY IN A HIGHLY STRATIFIED ESTUARY
This paper presents the preliminary results of hydrodynamic and salinity predictions and the implications to an ongoing contaminated sediment transport and fate modeling effort in the Lower Duwamish Waterway (LDW), Seattle, Washington. The LDW is highly strati-fied when freshwate...
The Quantum Hydrodynamic Model for Semiconductor Devices: Theory and Computations
2007-11-02
Quantum transport effects including electron or hole tunneling through potential barriers and buildup in quantum wells are important in predicting...semiconductor device. A new extension of the classical hydrodynamic model to include quantum transport effects was derived. This "smooth" quantum
HYDRODYNAMIC AND TRANSPORT MODELING STUDY IN A HIGHLY STRATIFIED ESTUARY
This paper presents the preliminary results of hydrodynamic and salinity predictions and the implications to an ongoing contaminated sediment transport and fate modeling effort in the Lower Duwamish Waterway (LDW), Seattle, Washington. The LDW is highly strati-fied when freshwate...
Homoclinic chaos in axisymmetric Bianchi-IX cosmological models with an ad hoc quantum potential
Correa, G. C.; Stuchi, T. J.; Joras, S. E.
2010-04-15
In this work we study the dynamics of the axisymmetric Bianchi-IX cosmological model with a term of quantum potential added. As it is well known, this class of Bianchi-IX models is homogeneous and anisotropic with two scale factors, A(t) and B(t), derived from the solution of Einstein's equation for general relativity. The model we use in this work has a cosmological constant and the matter content is dust. To this model we add a quantum-inspired potential that is intended to represent short-range effects due to the general relativistic behavior of matter in small scales and play the role of a repulsive force near the singularity. We find that this potential restricts the dynamics of the model to positive values of A(t) and B(t) and alters some qualitative and quantitative characteristics of the dynamics studied previously by several authors. We make a complete analysis of the phase space of the model finding critical points, periodic orbits, stable/unstable manifolds using numerical techniques such as Poincare section, numerical continuation of orbits, and numerical globalization of invariant manifolds. We compare the classical and the quantum models. Our main result is the existence of homoclinic crossings of the stable and unstable manifolds in the physically meaningful region of the phase space [where both A(t) and B(t) are positive], indicating chaotic escape to inflation and bouncing near the singularity.
2d axisymmetric "beam-bulk" modelling of the generation of runaway electrons by streamers.
NASA Astrophysics Data System (ADS)
Chanrion, Olivier; Bonaventura, Zdenek; Bourdon, Anne; Neubert, Torsten
2017-04-01
We present results from a 2d axisymmetric numerical model of streamers based on a "beam-bulk" approach which describes cold electrons with a fluid model and high energy electrons with a particle model. The interest is motivated by the generation of runaway electrons by streamers which may participate in the recently observed TGFs and which challenge the modelling. Runaway electrons are known to be generated from streamers when the electric field in its negative tip is of sufficient magnitude. After overtaking the streamer tip, runaways can affect the streamer propagation ahead and may produce high energy photons through the bremsstrahlung process. In conventional model of streamers, the evolution of the streamer discharge is mostly governed by cold electrons. By including runaway electrons, we model their production, their impact on the discharge propagation and can address their role in TGFs. Results of streamer propagation in leader electric field show that the runaway electrons accelerate the streamers, reduce the electric field in its tip and enlarge its radius by pre-ionizing the gas ahead. We observed that if we increase the electric field, the discharge is getting more diffuse, with a pattern driven by the increase in runaway induced ionisation.
Nested contour-dynamic models for axisymmetric vortex rings and vortex wakes
NASA Astrophysics Data System (ADS)
O'Farrell, Clara; Dabiri, John O.
2013-11-01
Jetting swimmers, such as squid and jellyfish, propel themselves by forming vortex rings. It is known that vortex rings cannot grow indefinitely, but rather ``pinch off'' once they reach their physical limit, and that a decrease in efficiency of fluid transport is associated with pinch-off. Previously, the Norbury family of vortices has been used as a model for axisymmetric vortex rings, and the response of this family to shape perturbations has been characterized. We improve upon the Norbury models, using nested patches of vorticity to construct a family of models for vortex rings generated by a piston-cylinder apparatus at different stroke ratios. The perturbation response of this family is considered by the introduction of a small region of vorticity at the rear of the vortex, which mimics the addition of circulation to a growing vortex ring by a feeding shear layer. Model vortex rings are found to either accept the additional circulation or shed it into a tail, depending on the perturbation size. A change in the behavior of the model vortex rings is identified at a stroke ratio of three. We hypothesize that this change in response is analogous to pinch-off, and that pinch-off might be understood and predicted based on the perturbation responses of model vortex rings.
New Equation of State Models for Hydrodynamic Applications
NASA Astrophysics Data System (ADS)
Young, David A.; Barbee, Troy W., III; Rogers, Forrest J.
1997-07-01
Accurate models of the equation of state of matter at high pressures and temperatures are increasingly required for hydrodynamic simulations. We have developed two new approaches to accurate EOS modeling: 1) ab initio phonons from electron band structure theory for condensed matter and 2) the ACTEX dense plasma model for ultrahigh pressure shocks. We have studied the diamond and high pressure phases of carbon with the ab initio model and find good agreement between theory and experiment for shock Hugoniots, isotherms, and isobars. The theory also predicts a comprehensive phase diagram for carbon. For ultrahigh pressure shock states, we have studied the comparison of ACTEX theory with experiments for deuterium, beryllium, polystyrene, water, aluminum, and silicon dioxide. The agreement is good, showing that complex multispecies plasmas are treated adequately by the theory. These models will be useful in improving the numerical EOS tables used by hydrodynamic codes.
Numerical modeling of axi-symmetrical cold forging process by ``Pseudo Inverse Approach''
NASA Astrophysics Data System (ADS)
Halouani, A.; Li, Y. M.; Abbes, B.; Guo, Y. Q.
2011-05-01
The incremental approach is widely used for the forging process modeling, it gives good strain and stress estimation, but it is time consuming. A fast Inverse Approach (IA) has been developed for the axi-symmetric cold forging modeling [1-2]. This approach exploits maximum the knowledge of the final part's shape and the assumptions of proportional loading and simplified tool actions make the IA simulation very fast. The IA is proved very useful for the tool design and optimization because of its rapidity and good strain estimation. However, the assumptions mentioned above cannot provide good stress estimation because of neglecting the loading history. A new approach called "Pseudo Inverse Approach" (PIA) was proposed by Batoz, Guo et al.. [3] for the sheet forming modeling, which keeps the IA's advantages but gives good stress estimation by taking into consideration the loading history. Our aim is to adapt the PIA for the cold forging modeling in this paper. The main developments in PIA are resumed as follows: A few intermediate configurations are generated for the given tools' positions to consider the deformation history; the strain increment is calculated by the inverse method between the previous and actual configurations. An incremental algorithm of the plastic integration is used in PIA instead of the total constitutive law used in the IA. An example is used to show the effectiveness and limitations of the PIA for the cold forging process modeling.
A model for droplet condensational growth in a turbulent, axisymmetric jet
NASA Astrophysics Data System (ADS)
Keedy, Ryan; Aliseda, Alberto
2011-11-01
Droplet growth at the edge of clouds is strongly influenced by the non-linear saturation field produced by mixing of warm, wet air inside the cloud with cold, dry air outside. This, together with the high intermittency of the turbulent at these geological scales, leads to uncertainty in the modeling of this process. We use experiments in a turbulent, axisymmetric jet to study this problem and develop a model. Although the distribution of a passive scalar in a turbulent jet is a classic problem, with a well-established solution, little attention has been devoted to heterogeneous nucleation, condensational growth and evaporation within a turbulent mixing layer where local supersaturation values may exceed unity. By leveraging the well-characterized self-similar behavior of a scalar (temperature, humidity) within a turbulent jet, we use a stochastic model for the instantaneous values from the statistics of the distribution to determine the super-saturation profile. Taking into account the high intermittency of the supersaturation field allows us to predict the droplet size at various stages of the flow. A Phase Doppler Particle Analyzer (PDPA) is used to collect statistics of velocity statistics, droplet growth and frequency that are used to inform the development and validation of the model.
Global modelling of non-axisymmetric disruptions and halo currents in tokamaks
NASA Astrophysics Data System (ADS)
McCarrick, James F.
1997-12-01
As tokamak plasmas become more robust with the development of increasingly advanced operating regimes, the occurrence of plasma disruptions places a greater demand on the tokamak structure. In particular, the flow of halo currents, large currents which appear in tokamak vacuum vessels as a result of direct contact with bulk plasma, has become a matter of increasing concern. Experimental measurements have confirmed the existence of large, toroidally asymmetric currents which flow poloidally in the wall, exerting strong localized forces on the wall as they interact with the toroidal magnetic field. A new model has been developed to study this phenomenon, based on the use of nested sheet currents to represent a disrupting plasma. This model contains the minimum number of degrees of freedom which permit the flow of continuous, non-axisymmetric poloidal and toroidal currents; furthermore, the model can be put into a compact integral formulation which allows rapid numerical solution even in the presence of complicated tokamak geometries. A fast code called TSPS-3D has been written to solve the sheet current model; the code has been matched against experimental data and used to examine basic scaling relationships of halo currents and the resulting J x B loads with plasma parameters. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253- 1690.)
Modeling tidal hydrodynamics of San Diego Bay, California
Wang, P.-F.; Cheng, R.T.; Richter, K.; Gross, E.S.; Sutton, D.; Gartner, J.W.
1998-01-01
In 1983, current data were collected by the National Oceanic and Atmospheric Administration using mechanical current meters. During 1992 through 1996, acoustic Doppler current profilers as well as mechanical current meters and tide gauges were used. These measurements not only document tides and tidal currents in San Diego Bay, but also provide independent data sets for model calibration and verification. A high resolution (100-m grid), depth-averaged, numerical hydrodynamic model has been implemented for San Diego Bay to describe essential tidal hydrodynamic processes in the bay. The model is calibrated using the 1983 data set and verified using the more recent 1992-1996 data. Discrepancies between model predictions and field data in beth model calibration and verification are on the order of the magnitude of uncertainties in the field data. The calibrated and verified numerical model has been used to quantify residence time and dilution and flushing of contaminant effluent into San Diego Bay. Furthermore, the numerical model has become an important research tool in ongoing hydrodynamic and water quality studies and in guiding future field data collection programs.
Hydrodynamic modeling of semi-planing hulls with air cavities
NASA Astrophysics Data System (ADS)
Matveev, Konstantin I.
2015-09-01
High-speed heavy loaded monohull ships can benefit from application of drag-reducing air cavities under stepped hull bottoms. The subject of this paper is the steady hydrodynamic modeling of semi-planing air-cavity hulls. The current method is based on a linearized potential-flow theory for surface flows. The mathematical model description and parametric calculation results for a selected configuration with pressurized and open air cavities are presented.
Hydrodynamic modeling of semi-planing hulls with air cavities
NASA Astrophysics Data System (ADS)
Matveev, Konstantin I.
2015-05-01
High-speed heavy loaded monohull ships can benefit from application of drag-reducing air cavities under stepped hull bottoms. The subject of this paper is the steady hydrodynamic modeling of semi-planing air-cavity hulls. The current method is based on a linearized potential-flow theory for surface flows. The mathematical model description and parametric calculation results for a selected configuration with pressurized and open air cavities are presented.
Hydrodynamic Tests of Models of Seaplane Floats
NASA Technical Reports Server (NTRS)
Eula, Antonio
1935-01-01
This report contains the results of tank tests carried out at free trim on seventeen hulls and floats of various types. The data as to the weight on water, trim, and relative resistance for each model are plotted nondimensionally and are referenced both to the total weight and to the weight on water. Despite the fact that the experiments were not made systematically, a study of the models and of the test data permits nevertheless some general deductions regarding the forms of floats and their resistance. One specific conclusion is that the best models have a maximum relative resistance not exceeding 20 percent of the total weight.
Modeling the Hydrodynamical Properties of the QGP at RHIC
NASA Astrophysics Data System (ADS)
Garishvili, Irakli; Soltz, Ron; Pratt, Scott; Cheng, Micael; Glenn, Andrew; Newby, Jason; Linden-Levy, Loren; Abelev, Betty
2010-11-01
Comparisons of the RHIC data to various theoretical models suggest that the evolution of the QGP, a state of matter believed to be created in early stages of heavy ion collisions at RHIC, is qualitatively well described by hydrodynamics. However, the key properties of the QGP, such as initial temperature, Tinit, and the ratio of shear viscosity to entropy density of matter, η/s, are not precisely known. To constrain these properties we have developed a multi-stage hydrodynamics/hadron cascade model of heavy ion collisions which incorporates Glauber initial state conditions, pre-equilibrium flow, the UVH2+1 viscous hydro model, Cooper-Frye freezeout, and the UrQMD hadronic cascade model. To test the sensitivity of the observables to the equation of state (EoS), we use several different EoS in the hydrodynamic evolution, including those derived from the hadron resonance gas model and lattice QCD. This framework has an ability to predict key QGP observables, such as, elliptic flow, spectra, and HBT radii for various particle species. For each set of model's input parameters (Tinit, η/s and initial flow) we perform a simultaneous comparison to spectra, elliptic flow, and HBT measured at RHIC. Based on this analysis the determinations of Tinit and η/s will be presented.
Hydrodynamic modeling for river delta salt marshes using lidar topography
NASA Astrophysics Data System (ADS)
Hodges, Ben R.
2014-05-01
Topographic data from lidar and multi-beam sonar create new challenges for hydrodynamic models of estuaries, tidelands, and river deltas. We now can readily obtain detailed elevation data on 1 m scales and finer, but solving hydrodynamics with model grid cells at these small scales remains computationally prohibitive (primarily because of the small time step required for small grid cells). Practical estuarine models for the next decade or so will likely have grid scales in the range of 5 to 15 m. So how should we handle known subgrid-scale features? Simply throwing out known data does not seem like a good idea, but there is no consensus on how best to incorporate knowledge of subgrid topography into either hydrodynamic or turbulence models. This presentation discusses both the theoretical foundations for modeling subgrid-scale features and the challenges in applying these ideas in the salt marshes of a river delta. The subgrid problem highlights some important areas for field and laboratory research to provide calibration parameters for new models that upscale the effects of known subgrid features.
Hydrodynamical models of cometary H ii regions
NASA Astrophysics Data System (ADS)
Steggles, H. G.; Hoare, M. G.; Pittard, J. M.
2017-04-01
We have modelled the evolution of cometary H ii regions produced by zero-age main-sequence stars of O and B spectral types, which are driving strong winds and are born off-centre from spherically symmetric cores with power-law (α = 2) density slopes. A model parameter grid was produced that spans stellar mass, age and core density. Exploring this parameter space, we investigated limb-brightening, a feature commonly seen in cometary H ii regions. We found that stars with mass M⋆ ≥ 12 M⊙ produce this feature. Our models have a cavity bounded by a contact discontinuity separating hot shocked wind and ionized ambient gas that is similar in size to the surrounding H ii region. Because of early pressure confinement, we did not see shocks outside of the contact discontinuity for stars with M⋆ ≤ 40 M⊙, but the cavities were found to continue to grow. The cavity size in each model plateaus as the H ii region stagnates. The spectral energy distributions of our models are similar to those from identical stars evolving in uniform density fields. The turn-over frequency is slightly lower in our power-law models as a result of a higher proportion of low-density gas covered by the H ii regions.
A new model for blood flow through an artery with axisymmetric stenosis.
Tandon, P N; Rana, U V
1995-03-01
Presented herein are the studies on the flow behavior of a blood type suspension through a circular tube with an axisymmetric stenosis. The suspension of the cells in plasma is represented by a layered fluid model, with a marginal cell-free layer of the suspending medium near the wall, a central core region and an annular layer of a biviscous fluid layer. It is understood that the proposed model may contribute to the inbuilt mechanism for drag reduction and prevention of the further development of the stenosis. The concept of lubricating pipe lining for transporting various industrial fluids is well represented through three-layered core-annular flows. The governing equations are solved numerically by using finite element method. The velocity fields, including separation and reattachment points, and the distribution of pressure and wall shear stresses have been brought out and discussed. The results of the analysis show that the presence of the marginal cell-free layer reduces the wall shear stresses and the length of the flow reversal zone. The non-Newtonian character of the suspension is helpful in reducing the abnormal effects of the stenosis. The model thus establishes the inbuilt character of blood for decreasing the stresses and this, in turn, reduces the load on the heart in propelling the blood.
Development of Reduced-order Models for Feedback Control of Axisymmetric Jets
NASA Astrophysics Data System (ADS)
Sinha, Aniruddha; Serrani, Andrea; Samimy, Mo
2009-11-01
We present the preliminary steps toward development of reduced-order models (ROM) for feedback control of a high-speed and high Reynolds number axisymmetric jet. The control objective is two-fold: attenuation of far-field acoustic radiation, or, enhancement of bulk mixing, using a set of localized arc filament plasma actuators that perturb the initial shear layer of the jet through intense localized Joule heating. The proposed feedback sensing mechanism involves pressure information from the irrotational near-field of the jet. The proposed route for creating the ROM involves collecting PIV data of the jet simultaneously with the pressure measurements, performing Proper Orthogonal Decomposition and Stochastic Estimation to obtain a time- and space-resolved database, and using Galerkin Projection to derive the dynamical model. Here we evaluate the above strategy using a DNS database (Freund, J. B., J. Fluid Mech., 438, 2001, 277--305). The ROMs obtained using various modeling options are simulated and their comparative fidelity are adjudged based on the original simulation results.
Axisymmetric modeling of cometary mass loading on an adaptively refined grid: MHD results
NASA Technical Reports Server (NTRS)
Gombosi, Tamas I.; Powell, Kenneth G.; De Zeeuw, Darren L.
1994-01-01
The first results of an axisymmetric magnetohydrodynamic (MHD) model of the interaction of an expanding cometary atmosphere with the solar wind are presented. The model assumes that far upstream the plasma flow lines are parallel to the magnetic field vector. The effects of mass loading and ion-neutral friction are taken into account by the governing equations, whcih are solved on an adaptively refined unstructured grid using a Monotone Upstream Centered Schemes for Conservative Laws (MUSCL)-type numerical technique. The combination of the adaptive refinement with the MUSCL-scheme allows the entire cometary atmosphere to be modeled, while still resolving both the shock and the near nucleus of the comet. The main findingsare the following: (1) A shock is formed approximately = 0.45 Mkm upstream of the comet (its location is controlled by the sonic and Alfvenic Mach numbers of the ambient solar wind flow and by the cometary mass addition rate). (2) A contact surface is formed approximately = 5,600 km upstream of the nucleus separating an outward expanding cometary ionosphere from the nearly stagnating solar wind flow. The location of the contact surface is controlled by the upstream flow conditions, the mass loading rate and the ion-neutral drag. The contact surface is also the boundary of the diamagnetic cavity. (3) A closed inner shock terminates the supersonic expansion of the cometary ionosphere. This inner shock is closer to the nucleus on dayside than on the nightside.
Filoux, Erwan; Callé, Samuel; Lou-Moeller, Rasmus; Lethiecq, Marc; Levassort, Franck
2010-05-01
The transient analysis of piezoelectric transducers is often performed using finite-element or finite-difference time-domain methods, which efficiently calculate the vibration of the structure but whose numerical dispersion prevents the modeling of waves propagating over large distances. A second analytical or numerical simulation is therefore often required to calculate the pressure field in the propagating medium (typically water) to deduce many important characteristics of the transducer, such as spatial resolutions and side lobe levels. This is why a hybrid algorithm was developed, combining finite- difference and pseudo-spectral methods in the case of 2-D configurations to simulate accurately both the generation of acoustic waves by the piezoelectric transducer and their propagation in the surrounding media using a single model. The algorithm was redefined in this study to take all three dimensions into account and to model single-element transducers, which usually present axisymmetrical geometry. This method was validated through comparison of its results with those of finite-element software, and was used to simulate the behavior of planar and lens-focused transducers. A high-frequency (30 MHz) transducer based on a screen-printed piezoelectric thick film was fabricated and characterized. The numerical results of the hybrid algorithm were found to be in good agreement with the experimental measurements of displacements at the surface of the transducer and of pressure radiated in water in front of the transducer.
A three-dimensional Babcock-Leighton solar dynamo model: Initial results with axisymmetric flows
NASA Astrophysics Data System (ADS)
Miesch, Mark S.; Teweldebirhan, Kinfe
2016-10-01
The main objective of this paper is to introduce the STABLE (Surface flux Transport And Babcock-LEighton) solar dynamo model. STABLE is a 3D Babcock-Leighton/Flux Transport dynamo model in which the source of poloidal field is the explicit emergence, distortion, and dispersal of bipolar magnetic regions (BMRs). Here we describe the STABLE model in more detail than we have previously and we verify it by reproducing a 2D mean-field benchmark. We also present some representative dynamo simulations, focusing on the special case of kinematic magnetic induction and axisymmetric flow fields. Not all solutions are supercritical; it can be a challenge for the BL mechanism to sustain the dynamo when the turbulent diffusion near the surface is ⩾ 1012 cm2 s-1. However, if BMRs are sufficiently large, deep, and numerous, then sustained, cyclic, dynamo solutions can be found that exhibit solar-like features. Furthermore, we find that the shearing of radial magnetic flux by the surface differential rotation can account for most of the net toroidal flux generation in each hemisphere, as has been recently argued for the Sun by Cameron and Schüssler (2015).
Chipman, V D
2011-09-20
Two-dimensional axisymmetric hydrodynamic models were developed using GEODYN to simulate the propagation of air blasts resulting from a series of high explosive detonations conducted at Kirtland Air Force Base in August and September of 2007. Dubbed Humble Redwood I (HR-1), these near-surface chemical high explosive detonations consisted of seven shots of varying height or depth of burst. Each shot was simulated numerically using GEODYN. An adaptive mesh refinement scheme based on air pressure gradients was employed such that the mesh refinement tracked the advancing shock front where sharp discontinuities existed in the state variables, but allowed the mesh to sufficiently relax behind the shock front for runtime efficiency. Comparisons of overpressure, sound speed, and positive phase impulse from the GEODYN simulations were made to the recorded data taken from each HR-1 shot. Where the detonations occurred above ground or were shallowly buried (no deeper than 1 m), the GEODYN model was able to simulate the sound speeds, peak overpressures, and positive phase impulses to within approximately 1%, 23%, and 6%, respectively, of the actual recorded data, supporting the use of numerical simulation of the air blast as a forensic tool in determining the yield of an otherwise unknown explosion.
Radiation Hydrodynamics Modeling of Hohlraum Energetics
NASA Astrophysics Data System (ADS)
Patel, Mehul V.; Mauche, Christopher W.; Jones, Ogden S.; Scott, Howard A.
2015-11-01
Attempts to model the energetics in NIF Hohlraums have been made with varying degrees of success, with discrepancies of 0-25% being reported for the X-ray flux (10-25% for the NIC ignition platform hohlraums). To better understand the cause(s) of these discrepancies, the effects of uncertainties in modeling thermal conduction, laser-plasma interactions, atomic mixing at interfaces, and NLTE kinetics of the high-Z wall plasma must be quantified. In this work we begin by focusing on the NLTE kinetics component. We detail a simulation framework for developing an integrated HYDRA hohlraum model with predefined tolerances for energetics errors due to numerical discretization errors or statistical fluctuations. Within this framework we obtain a model for a converged 1D spherical hohlraum which is then extended to 2D. The new model is used to reexamine physics sensitivities and improve estimates of the energetics discrepancy. Prepared by LLNL under Contract DE-AC52-07NA27344.
Assimilation of measurement data in hydrodynamic modeling
NASA Astrophysics Data System (ADS)
Karamuz, Emilia; Romanowicz, Renata J.
2016-04-01
This study focuses on developing methods to combine ground-based data from operational monitoring with data from satellite imaging to obtain a more accurate evaluation of flood inundation extents. The distributed flow model MIKE 11 was used to determine the flooding areas for a flood event with available satellite data. Model conditioning was based on the integrated use of data from remote measurement techniques and traditional data from gauging stations. Such conditioning of the model improves the quality of fit of the model results. The use of high resolution satellite images (from IKONOS, QuickBird e.t.c) and LiDAR Digital Elevation Model (DEM) allows information on water levels to be extended to practically any chosen cross-section of the tested section of the river. This approach allows for a better assessment of inundation extent, particularly in areas with a scarce network of gauging stations. We apply approximate Bayesian analysis to integrate the information on flood extent originating from different sources. The approach described above was applied to the Middle River Vistula reach, from the Zawichost to Warsaw gauging stations. For this part of the river the detailed geometry of the river bed and floodplain data were available. Finally, three selected sub-sections were analyzed with the most suitable satellite images of inundation area. ACKNOWLEDGEMENTS This research was supported by the Institute of Geophysics Polish Academy of Sciences through the Young Scientist Grant no. 3b/IGF PAN/2015.
Hydrodynamic Model for Conductivity in Graphene
Mendoza, M.; Herrmann, H. J.; Succi, S.
2013-01-01
Based on the recently developed picture of an electronic ideal relativistic fluid at the Dirac point, we present an analytical model for the conductivity in graphene that is able to describe the linear dependence on the carrier density and the existence of a minimum conductivity. The model treats impurities as submerged rigid obstacles, forming a disordered medium through which graphene electrons flow, in close analogy with classical fluid dynamics. To describe the minimum conductivity, we take into account the additional carrier density induced by the impurities in the sample. The model, which predicts the conductivity as a function of the impurity fraction of the sample, is supported by extensive simulations for different values of ε, the dimensionless strength of the electric field, and provides excellent agreement with experimental data. PMID:23316277
Modeling hydrodynamic nonequilibrium in cavitating flows
Chen, Y.; Heister, S.D.
1996-03-01
A nonlinear numerical model has been developed to assess nonequilibrium effects in cavitating flows. The numerical implementation involves a two-phase treatment with the use of a pseudo-density which varies between the liquid and gas/vapor extremes. A new constitutive equation for the pseudo-density is derived based on the bubble response described by a modified form of the Rayleigh-Plesset equation. Use of this constitutive equation in a numerical procedure permits the assessment of nonequilibrium effects. This scheme provides a quantitative description of scaling effects in cavitated flows. With minimal modifications, the model can also be used for bubbly two-phase flows.
Current SPE Hydrodynamic Modeling and Path Forward
Knight, Earl E.; Rougier, Esteban
2012-08-14
Extensive work has been conducted on SPE analysis efforts: Fault effects Non-uniform weathered layer analysis MUNROU: material library incorporation, parallelization, and development of non-locking tets Development of a unique continuum-based-visco-plastic strain-rate-dependent material model With corrected SPE data path is now set for a multipronged approach to fully understand experimental series shot effects.
Theoretical model of gravitational perturbation of current collector axisymmetric flow field
NASA Astrophysics Data System (ADS)
Walker, John S.; Brown, Samuel H.; Sondergaard, Neal A.
1990-05-01
Some designs of liquid-metal current collectors in homopolar motors and generators are essentially rotating liquid-metal fluids in cylindrical channels with free surfaces and will, at critical rotational speeds, become unstable. An investigation at David Taylor Research Center is being performed to understand the role of gravity in modifying this ejection instability. Some gravitational effects can be theoretically treated by perturbation techniques on the axisymmetric base flow of the liquid metal. This leads to a modification of previously calculated critical-current-collector ejection values neglecting gravity effects. The purpose of this paper is to document the derivation of the mathematical model which determines the perturbation of the liquid-metal base flow due to gravitational effects. Since gravity is a small force compared with the centrifugal effects, the base flow solutions can be expanded in inverse powers of the Froude number and modified liquid-flow profiles can be determined as a function of the azimuthal angle. This model will be used in later work to theoretically study the effects of gravity on the ejection point of the current collector.
An analytic model of axisymmetric mantle plume due to thermal and chemical diffusion
NASA Technical Reports Server (NTRS)
Liu, Mian; Chase, Clement G.
1990-01-01
An analytic model of axisymmetric mantle plumes driven by either thermal diffusion or combined diffusion of both heat and chemical species from a point source is presented. The governing equations are solved numerically in cylindrical coordinates for a Newtonian fluid with constant viscosity. Instead of starting from an assumed plume source, constraints on the source parameters, such as the depth of the source regions and the total heat input from the plume sources, are deduced using the geophysical characteristics of mantle plumes inferred from modelling of hotspot swells. The Hawaiian hotspot and the Bermuda hotspot are used as examples. Narrow mantle plumes are expected for likely mantle viscosities. The temperature anomaly and the size of thermal plumes underneath the lithosphere can be sensitive indicators of plume depth. The Hawaiian plume is likely to originate at a much greater depth than the Bermuda plume. One suggestive result puts the Hawaiian plume source at a depth near the core-mantle boundary and the source of the Bermuda plume in the upper mantle, close to the 700 km discontinuity. The total thermal energy input by the source region to the Hawaiian plume is about 5 x 10(10) watts. The corresponding diameter of the source region is about 100 to 150 km. Chemical diffusion from the same source does not affect the thermal structure of the plume.
A New Axisymmetric MHD Model of the Interaction of the Solar Wind with Venus
NASA Technical Reports Server (NTRS)
DeZeeuw, Darren L.; Nagy, Andrew F.; Gombosi, Tamas I.; Powell, Kenneth G.; Luhmann, Janet G.
1996-01-01
A new two-dimensional axisymmetric MHD model is used to study the interaction of the solar wind with Venus under conditions where the interplanetary field is approximately aligned with the solar wind velocity. This numerical model solves the MHD transport equations for density, velocity, pressure, and magnetic field on an adaptively refined, unstructured grid system. This use of an adaptive grid allows high spatial resolution in regions of large density/velocity gradients and yet can be run on a workstation. The actual grid sizes vary from about 0.06 R(sub v) near the bowshock to 2 R(sub v) in the unperturbed solar wind. The results of the calculations are compared with observed magnetic field values obtained from the magnetometer on the Pioneer Venus Orbiter, at a time when the angle between the solar wind velocity vector and the interplanetary magnetic field (IMF) was only 7.6 deg. Good qualitative agreement between the observed and calculated field behavior is found. The overall results suggest that the induced magnetotail disappears when the IMF is radial for an extended time period and implies that it weakens when the field rotated through a near-radial orientation.
Hydrodynamic characterization of Corpus Christi Bay through modeling and observation.
Islam, Mohammad S; Bonner, James S; Edge, Billy L; Page, Cheryl A
2014-11-01
Christi Bay is a relatively flat, shallow, wind-driven system with an average depth of 3-4 m and a mean tidal range of 0.3 m. It is completely mixed most of the time, and as a result, depth-averaged models have, historically, been applied for hydrodynamic characterization supporting regulatory decisions on Texas coastal management. The bay is highly stratified during transitory periods of the summer with low wind conditions. This has important implications on sediment transport, nutrient cycling, and water quality-related issues, including hypoxia which is a key water quality concern for the bay. Detailed hydrodynamic characterization of the bay during the summer months included analysis of simulation results of 2-D hydrodynamic model and high-frequency (HF) in situ observations. The HF radar system resolved surface currents, whereas an acoustic Doppler current profiler (ADCP) measured current at different depths of the water column. The developed model successfully captured water surface elevation variation at the mouth of the bay (i.e., onshore boundary of the Gulf of Mexico) and at times within the bay. However, large discrepancies exist between model-computed depth-averaged water currents and observed surface currents. These discrepancies suggested the presence of a vertical gradient in the current structure which was further substantiated by the observed bi-directional current movement within the water column. In addition, observed vertical density gradients proved that the water column was stratified. Under this condition, the bottom layer became hypoxic due to inadequate mixing with the aerated surface water. Understanding the disparities between observations and model predictions provides critical insights about hydrodynamics and physical processes controlling water quality.
Modeling Water Waves with Smoothed Particle Hydrodynamics
2013-09-30
criterion (Jeong & Hussain, 1995), which uses the symmetric and antisymmetric components of the velocity gradient tensor to identify regions of low...surf zone or as a first approximation to a tsunami . Wave data was obtain from the laboratory experiments of Ting (2006). In Figure 4, the measured...R., Hérault, A., & Bilotta, G. SPH modeling of mean velocity transmission in a rip current system, International Conference on Coastal Engineering
Toward Hydrodynamics with Solvent Free Lipid Models: STRD Martini.
Zgorski, Andrew; Lyman, Edward
2016-12-20
Solvent hydrodynamics are incorporated into simulations of the solvent-free Dry Martini model. The solvent hydrodynamics are modeled with the stochastic rotation dynamics (SRD) algorithm, a particle-based method for resolving fluid hydrodynamics. SRD does not require calculation of particle-particle distances in the solvent, and so is scalable to arbitrary volumes of solvent with minimal additional computational overhead. The viscosity of the solvent is easily tuned via parameters of the algorithm to span an order of magnitude in viscosity around the viscosity of water at room temperature. The combination "Stochastic Thermostatted Rotation Dynamics (STRD) with Martini" was implemented in Gromacs v.5.01. Simulations of an SRD/palmitoyloleoylphosphatidylcholine membrane demonstrate that the solvent may be included without reparametrizing the lipid model, with minimal perturbation to the thermodynamics. A recent generalization of Saffman-Delbruck theory to periodic geometries by Camley and Brown indicates that lipid dynamics are contaminated by a finite-size effect in typical molecular dynamics (MD) simulations, and that very large systems are required for quantitative simulation of dynamics. Analysis of lipid translational diffusion in this work shows good agreement with the theory, and with explicitly solvated simulations. This indicates that STRD Martini is a viable approach for quantitative simulation of membrane dynamics and does not require massive computational overhead to model the solvent. Copyright © 2016 Biophysical Society. Published by Elsevier Inc. All rights reserved.
Modeling Spitsbergen fjords by hydrodynamic MIKE engine.
NASA Astrophysics Data System (ADS)
Kosecki, Szymon; Przyborska, Anna; Jakacki, Jaromir
2013-04-01
Two Svalbard's fjords - Hornsund (on the western side of the most southern part of Spitsbergen island) and Kongsfjorden (also on the western side of Spitsbergen island, but in the northern part) are quite different - the first one is "cold" and second one is "warm". It is obvious that both of them are under influence of West Spitsbergen Current (WSC), which curry out warm Atlantic water and cold East Spitsbergen Current detaches Hornsund. But there is also freshwater stored in Spitsbergen glaciers that have strong influence on local hydrology and physical fjord conditions. Both, local and shelf conditions have impact on state of the fjord and there is no answer which one is the most important in each fjord. Modeling could help to solve this problem - MIKE 3D model has been implemented for both fjords. Mesh-grid of the each fjord has been extended for covering shelf area. External forces like tides, velocities at the boundary and atmospheric forces together with sources of cold and dens fresh water in the fjords will give reliable representation of physical conditions in Hornsund and Kongsfjorden. Calculations of balances between cold fresh water and warm and salt will provide additional information that could help to answer the main question of the GAME (Growing of the Arctic Marine Ecosystem) project - what is the reaction of physically controlled Arctic marine ecosystem to temperature rise.
A 3D Hydrodynamic Model for Cytokinesis of Eukaryotic Cells
2014-08-01
goes wrong may lead to a catastrophe or failure, which may lead to an unwelcome outcome for instance cancer . Thus, a detailed understanding on... biofilm - drug interaction. Discrete and Continuous Dynamical Systems Series B, 15:417–456, March 2011. 13 [17] Brandon Lindley, Qi Wang, and Tianyu Zhang...Multicomponent hydrodynamic model for heterogeneous biofilms : Two-dimensional numerical simulations of growth and in- teraction with flows. Physical
Modeling of hydrodynamics of water-methane heterogeneous system
NASA Astrophysics Data System (ADS)
Tsvetova, Elena A.
2015-11-01
To study the behavior of heterogeneous methane-water system, a mathematical model describing the joint processes of hydrodynamics, transport, and transformation of methane in a deep freshwater body is used. There are three phases of methane in the system: solid (hydrate), gaseous (bubbles) and dissolved in water. We discuss the physical origin of phase transitions in the specific conditions of Lake Baikal and possible mathematical formulations of problems. Some preliminary results of calculations are presented.
Numerical modeling of hydrodynamic in southwestern Johor, Malaysia
NASA Astrophysics Data System (ADS)
Jusoh, Wan Hasliza Wan; Tangang, Fredolin; Juneng, Liew; Hamid, Mohd. Radzi Abdul
2014-09-01
Tanjung Piai located at the southwest of Johor, Malaysia faces severe erosion since a few decades ago. Considering the condition in this particular area, understanding of its hydrodynamic behaviour should be clearly explained. Thus, a numerical modelling has been applied in this study in order to investigate the hydrodynamic of current flow along the study area. Hydrodynamic study was carried out by applying a numerical modelling of MIKE 21 software based on flexible mesh grids. The model generally described the current flow pattern in the study area corresponding to the several flows from surrounding water regime which are Malacca Strait, Singapore Strait and Java Sea. The interaction of various water flows in the area of Tanjung Piai which is located in the middle part of the meeting of the currents to have a very complicated hydrodynamic conditions. The study area generally experienced two tidal phase in a day as the water flows is greatly influenced by the adjacent water flow from Malacca and Singapore Straits. During first tidal cycle, the most dominant flow is influenced by a single water flow which is Malacca Strait for both ebbing and flooding event. The current velocity was generally higher during this first tidal phase particularly at the tips of Tanjung Piai where severe erosion is spotted. However, the second tidal phase gives different stress to the study area as the flow is relatively dominated by both Malacca and Singapore Straits. During this phase, the meeting of current from both straits can be discovered near to the Tanjung Piai as this occurrence makes relatively slower current velocity around the study area. Basically, the numerical modelling result in this study can be considered as basic information in describing the condition of study area as it would be very useful for extensive study especially the study of sediment transport and morphological processes in the coastal area.
An integrated coastal model for aeolian and hydrodynamic sediment transport
NASA Astrophysics Data System (ADS)
Baart, F.; den Bieman, J.; van Koningsveld, M.; Luijendijk, A. P.; Parteli, E. J. R.; Plant, N. G.; Roelvink, J. A.; Storms, J. E. A.; de Vries, S.; van Thiel de Vries, J. S. M.; Ye, Q.
2012-04-01
Dunes are formed by aeolian and hydrodynamic processes. Over the last decades numerical models were developed that capture our knowledge of the hydrodynamic transport of sediment near the coast. At the same time others have worked on creating numerical models for aeolian-based transport. Here we show a coastal model that integrates three existing numerical models into one online-coupled system. The XBeach model simulates storm-induced erosion (Roelvink et al., 2009). The Delft3D model (Lesser et al., 2004) is used for long term morphology and the Dune model (Durán et al., 2010) is used to simulate the aeolian transport. These three models were adapted to be able to exchange bed updates in real time. The updated models were integrated using the ESMF framework (Hill et al., 2004), a system for composing coupled modeling systems. The goal of this integrated model is to capture the relevant coastal processes at different time and spatial scales. Aeolian transport can be relevant during storms when the strong winds are generating new dunes, but also under relative mild conditions when the dunes are strengthened by transporting sand from the intertidal area to the dunes. Hydrodynamic transport is also relevant during storms, when high water in combination with waves can cause dunes to avalanche and erode. While under normal conditions the hydrodynamic transport can result in an onshore transport of sediment up to the intertidal area. The exchange of sediment in the intertidal area is a dynamic interaction between the hydrodynamic transport and the aeolian transport. This dynamic interaction is particularly important for simulating dune evolution at timescales longer than individual storm events. The main contribution of the integrated model is that it simulates the dynamic exchange of sediment between aeolian and hydrodynamic models in the intertidal area. By integrating the numerical models, we hope to develop a model that has a broader scope and applicability than
Tan, F P P; Wood, N B; Tabor, G; Xu, X Y
2011-05-01
In this study, two different turbulence methodologies are investigated to predict transitional flow in a 75% stenosed axisymmetric experimental arterial model and in a slightly modified version of the model with an eccentric stenosis. Large eddy simulation (LES) and Reynolds-averaged Navier-Stokes (RANS) methods were applied; in the LES simulations eddy viscosity subgrid-scale models were employed (basic and dynamic Smagorinsky) while the RANS method involved the correlation-based transitional version of the hybrid k-ε/k-ω flow model. The RANS simulations used 410,000 and 820,000 element meshes for the axisymmetric and eccentric stenoses, respectively, with y(+) less than 2 viscous wall units for the boundary elements, while the LES used 1,200,000 elements with y(+) less than 1. Implicit filtering was used for LES, giving an overlap between the resolved and modeled eddies, ensuring accurate treatment of near wall turbulence structures. Flow analysis was carried out in terms of vorticity and eddy viscosity magnitudes, velocity, and turbulence intensity profiles and the results were compared both with established experimental data and with available direct numerical simulations (DNSs) from the literature. The simulation results demonstrated that the dynamic Smagorinsky LES and RANS transitional model predicted fairly comparable velocity and turbulence intensity profiles with the experimental data, although the dynamic Smagorinsky model gave the best overall agreement. The present study demonstrated the power of LES methods, although they were computationally more costly, and added further evidence of the promise of the RANS transition model used here, previously tested in pulsatile flow on a similar model. Both dynamic Smagorinsky LES and the RANS model captured the complex transition phenomena under physiological Reynolds numbers in steady flow, including separation and reattachment. In this respect, LES with dynamic Smagorinsky appeared more successful than DNS
Self-Consistent Hydrodynamical Models For Stellar Winds
NASA Astrophysics Data System (ADS)
Boulangier, Jels; Homan, Ward; van Marle, Allard Jan; Decin, Leen; de Koter, Alex
2016-07-01
The physical and chemical conditions in the atmosphere of pulsating AGB stars are not well understood. In order to properly model this region, which is packed with shocks arisen from the pulsational behaviour of the star, we aim to understand the interplay between spatial and temporal changes in both the chemical composition and the hydro/thermodynamical behaviour inside these regions. Ideal models require the coupling of hydrodynamics, chemistry and radiative transfer, in three dimensions. As this is computationally not yet feasible, we aim to model this zone via a bottom-up approach. At first, we build correct 3D hydrodynamical set-up without any cooling or heating. Omitting cooling hampers the mass-loss of the AGB star within the reasonable confines of a realistic parameter space. Introducing cooling will decrease the temperature gradients in the atmosphere, counteracting the mass-loss even more. However, cooling also ensures the existence of regions where the temperature is low enough for the formation of dust to take place. This dust will absorb the momentum of the impacting photons from the AGB photosphere, accelerate outward and collide with the obstructing gas, dragging it along. Moreover, since chemistry, nucleation and dust formation depend critically on the temperature structure of the circumstellar environment, it is of utmost importance to include all relevant heating/cooling sources. Efforts to include cooling have been undertaken in the last decades, making use of different radiative cooling mechanisms for several chemical species, with some simplified radiative transfer. However, often the chemical composition of these 1D atmosphere models is fixed, implying the very strong assumption of chemical equilibrium, which is not at all true for a pulsating AGB atmosphere. We wish to model these atmospheres making as few assumptions as possible on equilibrium conditions. Therefore, as a first step, we introduce H2 dissociative cooling to the hydrodynamical
Unsteady CFD modeling of micro-adaptive flow control for an axisymmetric body
NASA Astrophysics Data System (ADS)
Sahu, Jubaraj; Heavey, Karen R.
2006-06-01
This paper describes a computational study undertaken, as part of a grand challenge project, to consider the aerodynamic effect of micro-adaptive flow control as a means to provide the divert authority needed to maneuver a projectile at a low subsonic speed. A time-accurate Navier Stokes computational technique has been used to obtain numerical solutions for the unsteady micro-jet-interaction flow field for the axisymmetric projectile body at subsonic speeds, Mach=0.11 and 0.24 and angles of attack, 0 4°. Numerical solutions have been obtained using both Reynolds-Averaged Navier Stokes (RANS) and a hybrid RANS/Large Eddy Simulation (LES) turbulence models. Unsteady numerical results show the effect of the jet on the flow field and the aerodynamic coefficients, in particular the lift force. This research has provided an increased fundamental understanding of the complex, three-dimensional (3D), time-dependent, aerodynamic interactions associated with micro-jet control for yawing spin-stabilized munitions.
New York Bight Study. Report 1. Hydrodynamic modeling. Technical report
Scheffner, N.W.; Vemulakonda, S.R.; Mark, D.J.; Butler, H.L.; Kim, K.W.
1994-08-01
As a part of the New York (NY) Bight Feasibility Study, a three-dimensional hydrodynamic model of the NY Bight was developed and applied by the Coastal Engineering R h Center of the U.S. Army Engineer Waterways Experiment Station. The study used the three-dimensional hydrodynamic model CH3D-WES for this purpose. A 76 x 45 cell boundary-fitted curvilinear grid was employed in the horizontal and five to ten sigma layers were used in the vertical. Steady-state and diagnostic tests were initially performed, using M, and mixed tides, cross-shelf gradients, winds, and freshwater flows in the Hudson River. All of the tests were successful in reproducing known circulation patterns of the NY Bight system. The model was next successfully calibrated and verified against prototype tidal elevations and currents measured during April and May 1976. As a demonstration of the feasibility of long-term modeling, the hydrodynamics, including salinity and temperature, were simulated for the period April-October 1976. Model results compared favorably with available prototype temperature measurements. Model output was furnished to a water quality model of the NY Bight, which successfully reproduced the hypoxic event of 1976. Model results also were used successfully to run particle tracking and oil spill models of the NY Bight. Finally, the model was demonstrated for the Long Island Sound and East River areas, for the period of May-July 1990. Computed results for elevation, velocity, salinity, and temperature in the Sound as well as net flux in the East River matched measurements reasonably.
Experimental Investigation and Computational Modeling of Hydrodynamics in Bifurcating Microchannels
Janakiraman, Vijayakumar; Sastry, Sudeep; Kadambi, Jaikrishnan R.; Baskaran, Harihara
2008-01-01
Methods involving microfluidics have been used in several chemical, biological and medical applications. In particular, a network of bifurcating microchannels can be used to distribute flow in a large space. In this work, we carried out experiments to determine hydrodynamic characteristics of bifurcating microfluidic networks. We measured pressure drop across bifurcating networks of various complexities for various flow rates. We also measured planar velocity fields in these networks by using particle image velocimetry. We further analyzed hydrodynamics in these networks using mathematical and computational modeling. Our results show that the experimental frictional resistances of complex bifurcating microchannels are about 30% greater than that predicted by Navier-Stokes’ equations. Experimentally measured velocity profiles indicate that flow distributes equally at a bifurcation regardless of the complexity of the network. Flow division other than bifurcation such as trifurcation or quadruplication can lead to heterogeneities. These findings were verified by the results from the numerical simulations. PMID:18175219
Hydrodynamic behavior of tumor cells in a confined model microvessel
NASA Astrophysics Data System (ADS)
Khan, Zeina S.; Vanapalli, Siva A.
2012-02-01
An important step in cancer metastasis is the hydrodynamic transport of circulating tumor cells (CTCs) through microvasculature. In vivo imaging studies in mice models show episodes of confined motion and trapping of tumor cells at microvessel bifurcations, suggesting that hydrodynamic phenomena are important processes regulating CTC dissemination. Our goal is to use microfluidics to understand the interplay between tumor cell rheology, confinement and fluid forces that may help to identify physical factors determining CTC transport. We use leukemia cells as model CTCs and mimic the in vivo setting by investigating their motion in a confined microchannel with an integrated microfluidic manometer to measure time variations in the excess pressure drop during cell motion. Using image analysis, variations in excess pressure drop, cell shape and cell velocity are simultaneously quantified. We find that the throughput of the technique is high enough ( 100 cells/min) to assess tumor cell heterogeneity. Therefore, in addition to measuring the hydrodynamic response of tumor cells in confined channels, our results indicate that the microfluidic manometer device could be used for rapid mechanical phenotyping of tumor cells.
Hydrodynamic model of temperature change in open ionic channels.
Chen, D P; Eisenberg, R S; Jerome, J W; Shu, C W
1995-01-01
Most theories of open ionic channels ignore heat generated by current flow, but that heat is known to be significant when analogous currents flow in semiconductors, so a generalization of the Poisson-Nernst-Planck theory of channels, called the hydrodynamic model, is needed. The hydrodynamic theory is a combination of the Poisson and Euler field equations of electrostatics and fluid dynamics, conservation laws that describe diffusive and convective flow of mass, heat, and charge (i.e., current), and their coupling. That is to say, it is a kinetic theory of solute and solvent flow, allowing heat and current flow as well, taking into account density changes, temperature changes, and electrical potential gradients. We integrate the equations with an essentially nonoscillatory shock-capturing numerical scheme previously shown to be stable and accurate. Our calculations show that 1) a significant amount of electrical energy is exchanged with the permeating ions; 2) the local temperature of the ions rises some tens of degrees, and this temperature rise significantly alters for ionic flux in a channel 25 A long, such as gramicidin-A; and 3) a critical parameter, called the saturation velocity, determines whether ionic motion is overdamped (Poisson-Nernst-Planck theory), is an intermediate regime (called the adiabatic approximation in semiconductor theory), or is altogether unrestricted (requiring the full hydrodynamic model). It seems that significant temperature changes are likely to accompany current flow in the open ionic channel. PMID:8599638
Hydrodynamic multibead modeling: problems, pitfalls, and solutions. 2. Proteins.
Zipper, Peter; Durchschlag, Helmut
2010-02-01
Hydrodynamic models of proteins have been generated by recourse to crystallographic data and applying a filling model strategy in order to predict both hydrodynamic and scattering parameters. The design of accurate protein models retaining the majority of the molecule peculiarities requires usage of many beads and consideration of many serious problems. Applying the expertise obtained with ellipsoid models and pilot tests on proteins, we succeeded in constructing precise models for several anhydrous and hydrated proteins of different shape, size, and complexity. The models constructed consist of many beads (up to about 11,000) for the protein constituents (atoms, amino acid residues, groups) and preferentially bound water molecules. While in the case of small proteins, parameter predictions are straightforward, computations for giant proteins necessitate drastic reductions of the number of initially available beads. Among several auxiliary programs, our advanced hydration programs, HYDCRYST and HYDMODEL, and modified versions of García de la Torre's program HYDRO were successfully employed. This allowed the generation of realistic protein models by imaging details of their fine structure and enabled the prediction of reliable molecular parameters including intrinsic viscosities. The appearance of the models and the agreement of molecular properties and distance distribution functions p(r) of unreduced and reduced models can be used for a meticulous inspection of the data obtained.
Modelling the mechanics and hydrodynamics of swimming E. coli.
Hu, Jinglei; Yang, Mingcheng; Gompper, Gerhard; Winkler, Roland G
2015-10-28
The swimming properties of an E. coli-type model bacterium are investigated by mesoscale hydrodynamic simulations, combining molecular dynamics simulations of the bacterium with the multiparticle particle collision dynamics method for the embedding fluid. The bacterium is composed of a spherocylindrical body with attached helical flagella, built up from discrete particles for an efficient coupling with the fluid. We measure the hydrodynamic friction coefficients of the bacterium and find quantitative agreement with experimental results of swimming E. coli. The flow field of the bacterium shows a force-dipole-like pattern in the swimming plane and two vortices perpendicular to its swimming direction arising from counterrotation of the cell body and the flagella. By comparison with the flow field of a force dipole and rotlet dipole, we extract the force-dipole and rotlet-dipole strengths for the bacterium and find that counterrotation of the cell body and the flagella is essential for describing the near-field hydrodynamics of the bacterium.
Use of hydrologic and hydrodynamic modeling for ecosystem restoration
Obeysekera, J.; Kuebler, L.; Ahmed, S.; Chang, M.-L.; Engel, V.; Langevin, C.; Swain, E.; Wan, Y.
2011-01-01
Planning and implementation of unprecedented projects for restoring the greater Everglades ecosystem are underway and the hydrologic and hydrodynamic modeling of restoration alternatives has become essential for success of restoration efforts. In view of the complex nature of the South Florida water resources system, regional-scale (system-wide) hydrologic models have been developed and used extensively for the development of the Comprehensive Everglades Restoration Plan. In addition, numerous subregional-scale hydrologic and hydrodynamic models have been developed and are being used for evaluating project-scale water management plans associated with urban, agricultural, and inland costal ecosystems. The authors provide a comprehensive summary of models of all scales, as well as the next generation models under development to meet the future needs of ecosystem restoration efforts in South Florida. The multiagency efforts to develop and apply models have allowed the agencies to understand the complex hydrologic interactions, quantify appropriate performance measures, and use new technologies in simulation algorithms, software development, and GIS/database techniques to meet the future modeling needs of the ecosystem restoration programs. Copyright ?? 2011 Taylor & Francis Group, LLC.
Hydrodynamic model for particle size segregation in granular media
NASA Astrophysics Data System (ADS)
Trujillo, Leonardo; Herrmann, Hans J.
2003-12-01
We present a hydrodynamic theoretical model for “Brazil nut” size segregation in granular materials. We give analytical solutions for the rise velocity of a large intruder particle immersed in a medium of monodisperse fluidized small particles. We propose a new mechanism for this particle size-segregation due to buoyant forces caused by density variations which come from differences in the local “granular temperature”. The mobility of the particles is modified by the energy dissipation due to inelastic collisions and this leads to a different behavior from what one would expect for an elastic system. Using our model we can explain the size ratio dependence of the upward velocity.
Modeling electrokinetic flows by consistent implicit incompressible smoothed particle hydrodynamics
NASA Astrophysics Data System (ADS)
Pan, Wenxiao; Kim, Kyungjoo; Perego, Mauro; Tartakovsky, Alexandre M.; Parks, Michael L.
2017-04-01
We present a consistent implicit incompressible smoothed particle hydrodynamics (I2SPH) discretization of Navier-Stokes, Poisson-Boltzmann, and advection-diffusion equations subject to Dirichlet or Robin boundary conditions. It is applied to model various two and three dimensional electrokinetic flows in simple or complex geometries. The accuracy and convergence of the consistent I2SPH are examined via comparison with analytical solutions, grid-based numerical solutions, or empirical models. The new method provides a framework to explore broader applications of SPH in microfluidics and complex fluids with charged objects, such as colloids and biomolecules, in arbitrary complex geometries.
Modeling electrokinetic flows by consistent implicit incompressible smoothed particle hydrodynamics
Pan, Wenxiao; Kim, Kyungjoo; Perego, Mauro; ...
2017-01-03
In this paper, we present a consistent implicit incompressible smoothed particle hydrodynamics (I2SPH) discretization of Navier–Stokes, Poisson–Boltzmann, and advection–diffusion equations subject to Dirichlet or Robin boundary conditions. It is applied to model various two and three dimensional electrokinetic flows in simple or complex geometries. The accuracy and convergence of the consistent I2SPH are examined via comparison with analytical solutions, grid-based numerical solutions, or empirical models. Lastly, the new method provides a framework to explore broader applications of SPH in microfluidics and complex fluids with charged objects, such as colloids and biomolecules, in arbitrary complex geometries.
Minimal model for synchronization induced by hydrodynamic interactions
NASA Astrophysics Data System (ADS)
Qian, Bian; Jiang, Hongyuan; Gagnon, David A.; Breuer, Kenneth S.; Powers, Thomas R.
2009-12-01
Motivated by the observed coordination of nearby beating cilia, we use a scale model experiment to show that hydrodynamic interactions can cause synchronization between rotating paddles driven at constant torque in a very viscous fluid. Synchronization is only observed when the shafts supporting the paddles have some flexibility. The phase difference in the synchronized state depends on the symmetry of the paddles. We use the method of regularized Stokeslets to model the paddles and find excellent agreement with the experimental observations. We also use a simple analytic theory based on far-field approximations to derive scaling laws for the synchronization time as a function of paddle separation.
Haider, M A; Guilak, F
2000-06-01
The micropipette aspiration test has been used extensively in recent years as a means of quantifying cellular mechanics and molecular interactions at the microscopic scale. However, previous studies have generally modeled the cell as an infinite half-space in order to develop an analytical solution for a viscoelastic solid cell. In this study, an axisymmetric boundary integral formulation of the governing equations of incompressible linear viscoelasticity is presented and used to simulate the micropipette aspiration contact problem. The cell is idealized as a homogeneous and isotropic continuum with constitutive equation given by three-parameter (E, tau 1, tau 2) standard linear viscoelasticity. The formulation is used to develop a computational model via a "correspondence principle" in which the solution is written as the sum of a homogeneous (elastic) part and a nonhomogeneous part, which depends only on past values of the solution. Via a time-marching scheme, the solution of the viscoelastic problem is obtained by employing an elastic boundary element method with modified boundary conditions. The accuracy and convergence of the time-marching scheme are verified using an analytical solution. An incremental reformulation of the scheme is presented to facilitate the simulation of micropipette aspiration, a nonlinear contact problem. In contrast to the halfspace model (Sato et al., 1990), this computational model accounts for nonlinearities in the cell response that result from a consideration of geometric factors including the finite cell dimension (radius R), curvature of the cell boundary, evolution of the cell-micropipette contact region, and curvature of the edges of the micropipette (inner radius a, edge curvature radius epsilon). Using 60 quadratic boundary elements, a micropipette aspiration creep test with ramp time t* = 0.1 s and ramp pressure p*/E = 0.8 is simulated for the cases a/R = 0.3, 0.4, 0.5 using mean parameter values for primary chondrocytes
Models of Jupiter's Growth Incorporating Thermal and Hydrodynamics Constraints
NASA Astrophysics Data System (ADS)
D'Angelo, G.; Lissauer, J. J.; Hubickyj, O.; Bodenheimer, P.
2008-12-01
We have modeled the growth of Jupiter incorporating both thermal and hydrodynamical constraints on its accretion of gas from the circumsolar disk. We have used a planetary formation code, based on a Henyey- type stellar evolution code, to compute the planet's internal structure and a three-dimensional hydrodynamics code to calculate the planet's interactions with the protoplanetary disk. Our principal results are: (1) Three dimensional hydrodynamics calculations show that the flow of gas in the circumsolar disk limits the region occupied by the planet's tenuous gaseous envelope to within about 0.25 Rh (Hill sphere radii) of the planet's center, which is much smaller than the value of ~ 1 Rh that was assumed in previous studies. (2) This smaller size of the planet's envelope increases the planet's accretion time, but only by 5-- 10%. In general, in agreement with previous results of Hubickyj et al. [Hubickyj, O., Bodenheimer, P., Lissauer, J.J., 2005. Icarus, 179, 415-431], Jupiter formation times are in the range 2.5--3 Myr, assuming a protoplanetary disk with solid surface density of 10 g/cm2 and dust opacity in the protoplanet's envelope equal to 2% that of interstellar material. Thermal pressure limits the rate at which a planet less than a few dozen times as massive as Earth can accumulate gas from the protoplanetary disk, whereas hydrodynamics regulates the growth rate for more massive planets. (3) In a protoplanetary disk whose alpha-viscosity parameter is ~ 0.004, giant planets will grow to several times the mass of Jupiter unless the disk has a small local surface density when the planet begins to accrete gas hydrodynamically, or the disk is dispersed very soon thereafter. The large number of planets known with masses near Jupiter's compared with the smaller number of substantially more massive planets is more naturally explained by planetary growth within circumstellar disks whose alpha-viscosity parameter is ~ 0.0004. (4) Capture of Jupiter's irregular
Anticipating the Role of SWOT in Hydrologic and Hydrodynamic Modeling
NASA Astrophysics Data System (ADS)
Pavelsky, T.; Biancamaria, S.; Andreadis, K.; Durand, M. T.; Schumann, G.
2015-12-01
The Surface Water and Ocean Topography (SWOT) satellite mission is a joint project of NASA and CNES, the French space agency. It aims to provide the first simultaneous, space-based measurements of inundation extent and water surface elevation in rivers, lakes, and wetlands around the world. Although the orbit repeat time is approximately 21 days, many areas of the earth will be viewed multiple times during this window. SWOT will observe rivers as narrow as 50-100 m and lakes as small as 0.01-0.06 km2, with height accuracies of ~10 cm for water bodies 1 km2 in area. Because SWOT will measure temporal variations in the height, width, and slope of rivers, several algorithms have been developed to estimate river discharge solely from SWOT measurements. Additionally, measurements of lake height and area will allow estimation of variability in lake water storage. These new hydrologic measurements will provide important sources of information both hydrologic and hydrodynamic models at regional to global scales. SWOT-derived estimates of water storage change and discharge will help to constrain simulation of the water budget in hydrologic models. Measurements of water surface elevation will provide similar constraints on hydrodynamic models of river flow. SWOT data will be useful for model calibration and validation, but perhaps the most exciting applications involve assimilation of SWOT data into models to enhance model robustness and provide denser temporal sampling than available from SWOT observations alone.
Validation of a Global Hydrodynamic Flood Inundation Model
NASA Astrophysics Data System (ADS)
Bates, P. D.; Smith, A.; Sampson, C. C.; Alfieri, L.; Neal, J. C.
2014-12-01
In this work we present first validation results for a hyper-resolution global flood inundation model. We use a true hydrodynamic model (LISFLOOD-FP) to simulate flood inundation at 1km resolution globally and then use downscaling algorithms to determine flood extent and depth at 90m spatial resolution. Terrain data are taken from a custom version of the SRTM data set that has been processed specifically for hydrodynamic modelling. Return periods of flood flows along the entire global river network are determined using: (1) empirical relationships between catchment characteristics and index flood magnitude in different hydroclimatic zones derived from global runoff data; and (2) an index flood growth curve, also empirically derived. Bankful return period flow is then used to set channel width and depth, and flood defence impacts are modelled using empirical relationships between GDP, urbanization and defence standard of protection. The results of these simulations are global flood hazard maps for a number of different return period events from 1 in 5 to 1 in 1000 years. We compare these predictions to flood hazard maps developed by national government agencies in the UK and Germany using similar methods but employing detailed local data, and to observed flood extent at a number of sites including St. Louis, USA and Bangkok in Thailand. Results show that global flood hazard models can have considerable skill given careful treatment to overcome errors in the publicly available data that are used as their input.
Explicit 3D continuum fracture modeling with smooth particle hydrodynamics
NASA Technical Reports Server (NTRS)
Benz, W.; Asphaug, E.
1993-01-01
Impact phenomena shaped our solar system. As usual for most solar system processes, the scales are far different than we can address directly in the laboratory. Impact velocities are often much higher than we can achieve, sizes are often vastly larger, and most impacts take place in an environment where the only gravitational force is the mutual pull of the impactors. The Smooth Particle Hydrodynamics (SPH) technique has been applied in the past to the simulations of giant impacts. In these simulations, the colliding objects were so massive (at least a sizeable fraction of the Earth's mass) that material strength was negligible compared to gravity. This assumption can no longer be made when the bodies are much smaller. To this end, we have developed a 3D SPH code that includes a strength model to which we have added a von Mises yielding relation for stresses beyond the Hugoniot Elastic Limit. At the lower stresses associated with brittle failure, we use a rate-dependent strength based on the nucleation of incipient flaws whose number density is given by a Weibull distribution. Following Grady and Kipp and Melosh et al., we introduce a state variable D ('damage'), 0 less than D less than 1, which expresses the local reduction in strength due to crack growth under tensile loading. Unfortunately for the hydrodynamics, Grady and Kipp's model predicts which fragments are the most probable ones and not the ones that are really formed. This means, for example, that if a given laboratory experiment is modeled, the fragment distribution obtained from the Grady-Kipp theory would be equivalent to a ensemble average over many realizations of the experiment. On the other hand, the hydrodynamics itself is explicit and evolves not an ensemble average but very specific fragments. Hence, there is a clear incompatibility with the deterministic nature of the hydrodynamics equations and the statistical approach of the Grady-Kipp dynamical fracture model. We remedy these shortcomings
Explicit 3D continuum fracture modeling with smooth particle hydrodynamics
NASA Technical Reports Server (NTRS)
Benz, W.; Asphaug, E.
1993-01-01
Impact phenomena shaped our solar system. As usual for most solar system processes, the scales are far different than we can address directly in the laboratory. Impact velocities are often much higher than we can achieve, sizes are often vastly larger, and most impacts take place in an environment where the only gravitational force is the mutual pull of the impactors. The Smooth Particle Hydrodynamics (SPH) technique has been applied in the past to the simulations of giant impacts. In these simulations, the colliding objects were so massive (at least a sizeable fraction of the Earth's mass) that material strength was negligible compared to gravity. This assumption can no longer be made when the bodies are much smaller. To this end, we have developed a 3D SPH code that includes a strength model to which we have added a von Mises yielding relation for stresses beyond the Hugoniot Elastic Limit. At the lower stresses associated with brittle failure, we use a rate-dependent strength based on the nucleation of incipient flaws whose number density is given by a Weibull distribution. Following Grady and Kipp and Melosh et al., we introduce a state variable D ('damage'), 0 less than D less than 1, which expresses the local reduction in strength due to crack growth under tensile loading. Unfortunately for the hydrodynamics, Grady and Kipp's model predicts which fragments are the most probable ones and not the ones that are really formed. This means, for example, that if a given laboratory experiment is modeled, the fragment distribution obtained from the Grady-Kipp theory would be equivalent to a ensemble average over many realizations of the experiment. On the other hand, the hydrodynamics itself is explicit and evolves not an ensemble average but very specific fragments. Hence, there is a clear incompatibility with the deterministic nature of the hydrodynamics equations and the statistical approach of the Grady-Kipp dynamical fracture model. We remedy these shortcomings
Weatherby, J.R.
1987-09-01
Results of axisymmetric structural analyses of a 1:6 scale model of a reinforced concrete nuclear containment building are presented. Both a finite element shell analysis and a simplified membrane analysis were made to predict the structural response and ultimate pressure capacity of the model. Analytical results indicate that the model will fail at an internal pressure of 187 psig when the stress level in the hoop reinforcement at the midsection of the cylinder exceeds the ultimate strength of the bar splices. 5 refs., 34 figs., 6 tabs.
Hydrodynamic and Ecological Assessment of Nearshore Restoration: A Modeling Study
Yang, Zhaoqing; Sobocinski, Kathryn L.; Heatwole, Danelle W.; Khangaonkar, Tarang; Thom, Ronald M.; Fuller, Roger
2010-04-10
Along the Pacific Northwest coast, much of the estuarine habitat has been diked over the last century for agricultural land use, residential and commercial development, and transportation corridors. As a result, many of the ecological processes and functions have been disrupted. To protect coastal habitats that are vital to aquatic species, many restoration projects are currently underway to restore the estuarine and coastal ecosystems through dike breaches, setbacks, and removals. Information on physical processes and hydrodynamic conditions are critical for the assessment of the success of restoration actions. Restoration of a 160- acre property at the mouth of the Stillaguamish River in Puget Sound has been proposed. The goal is to restore native tidal habitats and estuary-scale ecological processes by removing the dike. In this study, a three-dimensional hydrodynamic model was developed for the Stillaguamish River estuary to simulate estuarine processes. The model was calibrated to observed tide, current, and salinity data for existing conditions and applied to simulate the hydrodynamic responses to two restoration alternatives. Responses were evaluated at the scale of the restoration footprint. Model data was combined with biophysical data to predict habitat responses at the site. Results showed that the proposed dike removal would result in desired tidal flushing and conditions that would support four habitat types on the restoration footprint. At the estuary scale, restoration would substantially increase the proportion of area flushed with freshwater (< 5 ppt) at flood tide. Potential implications of predicted changes in salinity and flow dynamics are discussed relative to the distribution of tidal marsh habitat.
Dynamic mesoscale model of dipolar fluids via fluctuating hydrodynamics.
Persson, Rasmus A X; Voulgarakis, Nikolaos K; Chu, Jhih-Wei
2014-11-07
Fluctuating hydrodynamics (FHD) is a general framework of mesoscopic modeling and simulation based on conservational laws and constitutive equations of linear and nonlinear responses. However, explicit representation of electrical forces in FHD has yet to appear. In this work, we devised an Ansatz for the dynamics of dipole moment densities that is linked with the Poisson equation of the electrical potential ϕ in coupling to the other equations of FHD. The resulting ϕ-FHD equations then serve as a platform for integrating the essential forces, including electrostatics in addition to hydrodynamics, pressure-volume equation of state, surface tension, and solvent-particle interactions that govern the emergent behaviors of molecular systems at an intermediate scale. This unique merit of ϕ-FHD is illustrated by showing that the water dielectric function and ion hydration free energies in homogeneous and heterogenous systems can be captured accurately via the mesoscopic simulation. Furthermore, we show that the field variables of ϕ-FHD can be mapped from the trajectory of an all-atom molecular dynamics simulation such that model development and parametrization can be based on the information obtained at a finer-grained scale. With the aforementioned multiscale capabilities and a spatial resolution as high as 5 Å, the ϕ-FHD equations represent a useful semi-explicit solvent model for the modeling and simulation of complex systems, such as biomolecular machines and nanofluidics.
Hydrodynamic description of spin Calogero-Sutherland model
NASA Astrophysics Data System (ADS)
Abanov, Alexander; Kulkarni, Manas; Franchini, Fabio
2009-03-01
We study a non-linear collective field theory for an integrable spin-Calogero-Sutherland model. The hydrodynamic description of this SU(2) model in terms of charge density, charge velocity and spin currents is used to study non-perturbative solutions (solitons) and examine their correspondence with known quantum numbers of elementary excitations [1]. A conventional linear bosonization or harmonic approximation is not sufficient to describe, for example, the physics of spin-charge (non)separation. Therefore, we need this new collective bosonic field description that captures the effects of the band curvature. In the strong coupling limit [2] this model reduces to integrable SU(2) Haldane-Shastry model. We study a non-linear coupling of left and right spin currents which form a Kac-Moody algebra. Our quantum hydrodynamic description for the spin case is an extension for the one found in the spinless version in [3].[3pt] [1] Y. Kato,T. Yamamoto, and M. Arikawa, J. Phys. Soc. Jpn. 66, 1954-1961 (1997).[0pt] [2] A. Polychronakos, Phys Rev Lett. 70,2329-2331(1993).[0pt] [3] A.G.Abanov and P.B. Wiegmann, Phys Rev Lett 95, 076402(2005)
Dynamic mesoscale model of dipolar fluids via fluctuating hydrodynamics
NASA Astrophysics Data System (ADS)
Persson, Rasmus A. X.; Voulgarakis, Nikolaos K.; Chu, Jhih-Wei
2014-11-01
Fluctuating hydrodynamics (FHD) is a general framework of mesoscopic modeling and simulation based on conservational laws and constitutive equations of linear and nonlinear responses. However, explicit representation of electrical forces in FHD has yet to appear. In this work, we devised an Ansatz for the dynamics of dipole moment densities that is linked with the Poisson equation of the electrical potential ϕ in coupling to the other equations of FHD. The resulting ϕ-FHD equations then serve as a platform for integrating the essential forces, including electrostatics in addition to hydrodynamics, pressure-volume equation of state, surface tension, and solvent-particle interactions that govern the emergent behaviors of molecular systems at an intermediate scale. This unique merit of ϕ-FHD is illustrated by showing that the water dielectric function and ion hydration free energies in homogeneous and heterogenous systems can be captured accurately via the mesoscopic simulation. Furthermore, we show that the field variables of ϕ-FHD can be mapped from the trajectory of an all-atom molecular dynamics simulation such that model development and parametrization can be based on the information obtained at a finer-grained scale. With the aforementioned multiscale capabilities and a spatial resolution as high as 5 Å, the ϕ-FHD equations represent a useful semi-explicit solvent model for the modeling and simulation of complex systems, such as biomolecular machines and nanofluidics.
Study of hydrodynamic instabilities with a multiphase lattice Boltzmann model
NASA Astrophysics Data System (ADS)
Velasco, Ali Mauricio; Muñoz, José Daniel
2015-10-01
Rayleigh-Taylor and Kelvin-Helmholtz hydrodynamic instabilities are frequent in many natural and industrial processes, but their numerical simulation is not an easy challenge. This work simulates both instabilities by using a lattice Boltzmann model on multiphase fluids at a liquid-vapour interface, instead of multicomponent systems like the oil-water one. The model, proposed by He, Chen and Zhang (1999) [1] was modified to increase the precision by computing the pressure gradients with a higher order, as proposed by McCracken and Abraham (2005) [2]. The resulting model correctly simulates both instabilities by using almost the same parameter set. It also reproduces the relation γ ∝√{ A} between the growing rate γ of the Rayleigh-Taylor instability and the relative density difference between the fluids (known as the Atwood number A), but including also deviations observed in experiments at low density differences. The results show that the implemented model is a useful tool for the study of hydrodynamic instabilities, drawing a sharp interface and exhibiting numerical stability for moderately high Reynolds numbers.
Dynamic mesoscale model of dipolar fluids via fluctuating hydrodynamics
Persson, Rasmus A. X.; Chu, Jhih-Wei; Voulgarakis, Nikolaos K.
2014-11-07
Fluctuating hydrodynamics (FHD) is a general framework of mesoscopic modeling and simulation based on conservational laws and constitutive equations of linear and nonlinear responses. However, explicit representation of electrical forces in FHD has yet to appear. In this work, we devised an Ansatz for the dynamics of dipole moment densities that is linked with the Poisson equation of the electrical potential ϕ in coupling to the other equations of FHD. The resulting ϕ-FHD equations then serve as a platform for integrating the essential forces, including electrostatics in addition to hydrodynamics, pressure-volume equation of state, surface tension, and solvent-particle interactions that govern the emergent behaviors of molecular systems at an intermediate scale. This unique merit of ϕ-FHD is illustrated by showing that the water dielectric function and ion hydration free energies in homogeneous and heterogenous systems can be captured accurately via the mesoscopic simulation. Furthermore, we show that the field variables of ϕ-FHD can be mapped from the trajectory of an all-atom molecular dynamics simulation such that model development and parametrization can be based on the information obtained at a finer-grained scale. With the aforementioned multiscale capabilities and a spatial resolution as high as 5 Å, the ϕ-FHD equations represent a useful semi-explicit solvent model for the modeling and simulation of complex systems, such as biomolecular machines and nanofluidics.
New equation of state models for hydrodynamic applications
NASA Astrophysics Data System (ADS)
Young, David A.; Barbee, Troy W.; Rogers, Forrest J.
1998-07-01
Two new theoretical methods for computing the equation of state of hot, dense matter are discussed. The ab initio phonon theory gives a first-principles calculation of lattice frequencies, which can be used to compare theory and experiment for isothermal and shock compression of solids. The ACTEX dense plasma theory has been improved to allow it to be compared directly with ultrahigh pressure shock data on low-Z materials. The comparisons with experiment are good, suggesting that these models will be useful in generating global EOS tables for hydrodynamic simulations.
Delayed-feedback control in a Lattice hydrodynamic model
NASA Astrophysics Data System (ADS)
Redhu, Poonam; Gupta, Arvind Kumar
2015-10-01
The delayed-feedback control (DFC) method for lattice hydrodynamic traffic flow model is investigated on a unidirectional road. By using the Hurwitz criteria and the condition for transfer function in term of H∞ -norm, we designed the feedback gain and delay time to stabilize the traffic flow and suppress the traffic jam. The Bode-plot of transfer function have been plotted and discussed that the stability region enhances with delayed-feedback control. It is shown that the delayed-feedback control method stabilizes the traffic flow and suppresses the traffic jam efficiently. The simulation results are in good agreement with the theoretical analysis.
Mesoscale modeling of molecular machines: cyclic dynamics and hydrodynamical fluctuations.
Cressman, Andrew; Togashi, Yuichi; Mikhailov, Alexander S; Kapral, Raymond
2008-05-01
Proteins acting as molecular machines can undergo cyclic internal conformational motions that are coupled to ligand binding and dissociation events. In contrast to their macroscopic counterparts, nanomachines operate in a highly fluctuating environment, which influences their operation. To bridge the gap between detailed microscopic and simple phenomenological descriptions, a mesoscale approach, which combines an elastic network model of a machine with a particle-based mesoscale description of the solvent, is employed. The time scale of the cyclic hinge motions of the machine prototype is strongly affected by hydrodynamical coupling to the solvent.
Quantum hydrodynamic modeling of edge modes in chiral Berry plasmons
NASA Astrophysics Data System (ADS)
Zhang, Ya; Zhai, Feng; Guo, Bin; Yi, Lin; Jiang, Wei
2017-07-01
A quantum hydrodynamic model is used to study the edge modes of chiral Berry plasmons in two-dimensional materials with nonzero Berry flux. A quantum effect of collective electron motions appears in systems with a high electron density. For the considered edge plasmon, the transcendental equation of the dispersion relation is solved nonlinearly and semianalytically. We predict a one-way chiral edge state in the presence of the quantum statistical effect and quantum diffraction effect. Indeed, the plasmon frequencies for counterpropagating edge modes exhibit different long-wavelength limits. The quantum effect can enhance the chirality of edge plasmons and their spatial confinement.
Radiation Hydrodynamical Models for Type I Superluminous Supernovae
NASA Astrophysics Data System (ADS)
Nomoto, Ken'ichi; Sorokina, Elena; Blinnikov, Sergei; Tolstov, Alexey; Bersten, Melina; Quimby, Robert
The physical origin of Type I superluminous supernovae (SLSNe-I), whose luminosities are 10 to 100 times brighter than normal core-collapse supernovae, remains still unknown. Radioactive-decays, magnetars, and circumstellar interactions have been proposed for the power source the light curves, although no definitive conclusions have been reached yet. Since most of light curve studies have been based on simplified semi-analytic models, we have constructed detailed light curve models for various mass of stars including very massive ones and large amount of mass loss with radiation hydrodynamical calculations. Here we focus on the magnetar and circumstellar interaction models and compare their rising time, peak luminosity, width, decline rate of the light curves with observations which show quite a large diversities. We then discuss how to discriminate these models, relevant models parameters, their evolutionary origins, possible roles of chemical enrichment of the early universe, and implications for the identifications of first stars.
Two dimensional hydrodynamic modeling of a high latitude braided river
NASA Astrophysics Data System (ADS)
Humphries, E.; Pavelsky, T.; Bates, P. D.
2014-12-01
Rivers are a fundamental resource to physical, ecologic and human systems, yet quantification of river flow in high-latitude environments remains limited due to the prevalence of complex morphologies, remote locations and sparse in situ monitoring equipment. Advances in hydrodynamic modeling and remote sensing technology allow us to address questions such as: How well can two-dimensional models simulate a flood wave in a highly 3-dimensional braided river environment, and how does the structure of such a flood wave differ from flow down a similar-sized single-channel river? Here, we use the raster-based hydrodynamic model LISFLOOD-FP to simulate flood waves, discharge, water surface height, and velocity measurements over a ~70 km reach of the Tanana River in Alaska. In order to use LISFLOOD-FP a digital elevation model (DEM) fused with detailed bathymetric data is required. During summer 2013, we surveyed 220,000 bathymetric points along the study reach using an echo sounder system connected to a high-precision GPS unit. The measurements are interpolated to a smooth bathymetric surface, using Topo to Raster interpolation, and combined with an existing five meter DEM (Alaska IfSAR) to create a seamless river terrain model. Flood waves are simulated using varying complexities in model solvers, then compared to gauge records and water logger data to assess major sources of model uncertainty. Velocity and flow direction maps are also assessed and quantified for detailed analysis of braided channel flow. The most accurate model output occurs with using the full two-dimensional model structure, and major inaccuracies appear to be related to DEM quality and roughness values. Future work will intercompare model outputs with extensive ground measurements and new data from AirSWOT, an airborne analog for the Surface Water and Ocean Topography (SWOT) mission, which aims to provide high-resolution measurements of terrestrial and ocean water surface elevations globally.
Implementation of a hydrodynamic model for the upper Potomac Estuary
Schaffranek, Raymond W.; Baltzer, Robert A.
1989-01-01
A vertically integrated, two-dimensional hydrodynamic/transport model has been implemented for the upper extent of the Potomac Estuary between Indian Head and Morgantown, Md. The model computes water-surface elevations, flow velocities, and time-varying constituent concentrations by numerically integrating finite-difference forms of the equations of mass and momentum conservation in conjunction with transport equations for heat, salt, and dissolved constituents. Previous, preliminary calibration efforts have been extended and validity of the model implementation improved. Field-measured and model-computed water levels compare within ?? 2 cm and maximum computed flood and ebb flow discharges are within 3% of measured values. Indications are that further improvements can be effected.
Hydrodynamical Modeling of Hydrogen Escape from Rocky Planets
NASA Astrophysics Data System (ADS)
Barringer, Daniel; Zugger, M.; Kasting, J.
2013-01-01
Hydrogen escape affects both the composition of primitive atmospheres of terrestrial planets and the planet’s state of oxidation. On Mars, hydrogen escape played a critical role in how long the planet remained in a warm wet state amenable to life. For both solar and extrasolar planets, hydrogen-rich atmospheres are better candidates for originating life by way of Miller-Urey-type prebiotic synthesis. However, calculating the rate of atmospheric hydrogen escape is difficult, for a number of reasons. First, the escape can be controlled either by diffusion through the homopause or by conditions in the upper atmosphere, whichever is slower. Second, both thermal and non-thermal escape mechanisms are typically important. Third, thermal escape itself can be subdivided into Jeans escape (thin upper atmosphere), and hydrodynamic escape, and hydrodynamic escape can be further subdivided into transonic escape and slower subsonic escape, depending on whether the exobase occurs above or below the sonic point. Additionally, the rate of escape for real terrestrial planet atmospheres, which are not 100% hydrogen, depends upon the concentration of infrared coolants, and upon heating and photochemistry driven largely by extreme ultraviolet (EUV) radiation. We have modified an existing 1-D model of hydrodynamic escape (F. Tian et al., JGR, 2008) to work in the high- hydrogen regime. Calculations are underway to determine hydrogen escape rates as a function of atmospheric H2 mixing ratio and the solar EUV flux. We will compare these rates with the estimated upper limit on the escape rate based on diffusion. Initial results for early Earth and Mars will later be extended to rocky exoplanets.
Deschutes estuary feasibility study: hydrodynamics and sediment transport modeling
George, Douglas A.; Gelfenbaum, Guy; Lesser, Giles; Stevens, Andrew W.
2006-01-01
- Provide the completed study to the CLAMP Steering Committee so that a recommendation about a long-term aquatic environment of the basin can be made. The hydrodynamic and sediment transport modeling task developed a number of different model simulations using a process-based morphological model, Delft3D, to help address these goals. Modeling results provide a qualitative assessment of estuarine behavior both prior to dam construction and after various post-dam removal scenarios. Quantitative data from the model is used in the companion biological assessment and engineering design components of the overall study. Overall, the modeling study found that after dam removal, tidal and estuarine processes are immediately restored, with marine water from Budd Inlet carried into North and Middle Basin on each rising tide and mud flats being exposed with each falling tide. Within the first year after dam removal, tidal processes, along with the occasional river floods, act to modify the estuary bed by redistributing sediment through erosion and deposition. The morphological response of the bed is rapid during the first couple of years, then slows as a dynamic equilibrium is reached within three to five years. By ten years after dam removal, the overall hydrodynamic and morphologic behavior of the estuary is similar to the pre-dam estuary, with the exception of South Basin, which has been permanently modified by human activities. In addition to a qualitative assessment of estuarine behavior, process-based modeling provides the ability address specific questions to help to inform decision-making. Considering that predicting future conditions of a complex estuarine environment is wrought with uncertainties, quantitative results in this report are often expressed in terms of ranges of possible outcomes.
A two-dimensional hydrodynamic model of a tidal estuary
Walters, Roy A.; Cheng, Ralph T.
1979-01-01
A finite element model is described which is used in the computation of tidal currents in an estuary. This numerical model is patterned after an existing algorithm and has been carefully tested in rectangular and curve-sided channels with constant and variable depth. One of the common uncertainties in this class of two-dimensional hydrodynamic models is the treatment of the lateral boundary conditions. Special attention is paid specifically to addressing this problem. To maintain continuity within the domain of interest, ‘smooth’ curve-sided elements must be used at all shoreline boundaries. The present model uses triangular, isoparametric elements with quadratic basis functions for the two velocity components and a linear basis function for water surface elevation. An implicit time integration is used and the model is unconditionally stable. The resultant governing equations are nonlinear owing to the advective and the bottom friction terms and are solved iteratively at each time step by the Newton-Raphson method. Model test runs have been made in the southern portion of San Francisco Bay, California (South Bay) as well as in the Bay west of Carquinez Strait. Owing to the complex bathymetry, the hydrodynamic characteristics of the Bay system are dictated by the generally shallow basins which contain deep, relict river channels. Great care must be exercised to ensure that the conservation equations remain locally as well as globally accurate. Simulations have been made over several representative tidal cycles using this finite element model, and the results compare favourably with existing data. In particular, the standing wave in South Bay and the progressive wave in the northern reach are well represented.
Modeling nanoscale hydrodynamics by smoothed dissipative particle dynamics
Lei, Huan; Mundy, Christopher J.; Schenter, Gregory K.; Voulgarakis, Nikolaos
2015-05-21
Thermal fluctuation and hydrophobicity are two hallmarks of fluid hydrodynamics on the nano-scale. It is a challenge to consistently couple the small length and time scale phenomena associated with molecular interaction with larger scale phenomena. The development of this consistency is the essence of mesoscale science. In this study, we develop a nanoscale fluid model based on smoothed dissipative particle dynamics that accounts for the phenomena of associated with density fluctuations and hydrophobicity. We show consistency in the fluctuation spectrum across scales. In doing so, it is necessary to account for finite fluid particle size. Furthermore, we demonstrate that the present model can capture of the void probability and solvation free energy of apolar particles of different sizes. The present fluid model is well suited for a understanding emergent phenomena in nano-scale fluid systems.
Modelling pulsar glitches with realistic pinning forces: a hydrodynamical approach
NASA Astrophysics Data System (ADS)
Haskell, B.; Pizzochero, P. M.; Sidery, T.
2012-02-01
Although pulsars are some of the most stable clocks in the Universe, many of them are observed to 'glitch', i.e. to suddenly increase their spin frequency ? with fractional increases that range from ? to ?. In this paper, we focus on the 'giant' glitches, i.e. glitches with fractional increases in the spin rate of the order of ?, that are observed in a subclass of pulsars including the Vela. We show that giant glitches can be modelled with a two-fluid hydrodynamical approach. The model is based on the formalism for superfluid neutron stars of Andersson & Comer and on the realistic pinning forces of Grill & Pizzochero. We show that all stages of Vela glitches, from the rise to the post-glitch relaxation, can be reproduced with a set of physically reasonable parameters and that the sizes and waiting times between giant glitches in other pulsars are also consistent with our model.
Towards the simplest hydrodynamic lattice-gas model.
Boghosian, Bruce M; Love, Peter J; Meyer, David A
2002-03-15
It has been known since 1986 that it is possible to construct simple lattice-gas cellular automata whose hydrodynamics are governed by the Navier-Stokes equations in two dimensions. The simplest such model heretofore known has six bits of state per site on a triangular lattice. In this work, we demonstrate that it is possible to construct a model with only five bits of state per site on a Kagome lattice. Moreover, the model has a simple, deterministic set of collision rules and is easily implemented on a computer. In this work, we derive the equilibrium distribution function for this lattice-gas automaton and carry out the Chapman-Enskog analysis to determine the form of the Navier-Stokes equations.
Correlation lengths in hydrodynamic models of active nematics.
Hemingway, Ewan J; Mishra, Prashant; Marchetti, M Cristina; Fielding, Suzanne M
2016-09-28
We examine the scaling with activity of the emergent length scales that control the nonequilibrium dynamics of an active nematic liquid crystal, using two popular hydrodynamic models that have been employed in previous studies. In both models we find that the chaotic spatio-temporal dynamics in the regime of fully developed active turbulence is controlled by a single active scale determined by the balance of active and elastic stresses, regardless of whether the active stress is extensile or contractile in nature. The observed scaling of the kinetic energy and enstrophy with activity is consistent with our single-length scale argument and simple dimensional analysis. Our results provide a unified understanding of apparent discrepancies in the previous literature and demonstrate that the essential physics is robust to the choice of model.
Hydrodynamic ram modeling with the immersed boundary method
Lewis, M.W.; Kashiwa, B.A.; Rauenzahn, R.M.
1998-03-01
The authors have modeled a hydrodynamic ram experiment conducted at Wright-Patterson Air Force Base. In the experiment, a projectile traveling at 200 ft/sec impacted and penetrated a simulated airplane wing containing water. The structure consisted of composite panels with stiffeners and rivets, and an aluminum panel. The test included instrumentation to measure strains, accelerations, and pressures. The technique used for modeling this experiment was a multifluid compressible finite volume approach. The solid fields, namely the projectile and the plates which comprised the structure, were represented by a set of discrete, Lagrangian-frame, mass points. These mass points were followed throughout the computation. The contribution of the stress state at each mass point was applied on the grid to determine the stress divergence contribution to the equations of motion and resulting grid based accelerations. This approach has been defined as the immersed boundary method. The immersed boundary method allows the modeling of fluid-structure interaction problems involving material failure. The authors implemented a plate theory to allow the representation of each plate by a surface of mass points. This theory includes bending terms and transverse shear. Arbitrary constitutive models may be used for each plate. Here they describe the immersed boundary method as they have implemented. They then describe the plate theory and its implementation. They discuss the hydrodynamic ram experiment and describe how they modeled it. They compare computed results with test data. They finally conclude with a discussion of benefits and difficulties associated with this modeling approach and possible improvement to it.
Kinetic theory model for the flow of a simple gas from a three-dimensional axisymmetric nozzle
NASA Technical Reports Server (NTRS)
Riley, B. R.
1991-01-01
A system of nonlinear integral equations equivalent to the Krook kinetic equations for the steady state is the mathematical basis used to develop a computer code to model the flowfields for low-thrust three-dimensional axisymmetric nozzles. The method of characteristics is used to solve numerically by an iteration process the approximated Boltzmann equation for the number density, temperature, and velocity profiles of a simple gas as it expands into a vacuum. Results predict backscatter and show the effect of the nozzle wall boundary layer on the external flowfields.
Hydrodynamic Equations for Flocking Models without Velocity Alignment
NASA Astrophysics Data System (ADS)
Peruani, Fernando
2017-10-01
The spontaneous emergence of collective motion patterns is usually associated with the presence of a velocity alignment mechanism that mediates the interactions among the moving individuals. Despite of this widespread view, it has been shown recently that several flocking behaviors can emerge in the absence of velocity alignment and as a result of short-range, position-based, attractive forces that act inside a vision cone. Here, we derive the corresponding hydrodynamic equations of a microscopic position-based flocking model, reviewing and extending previous reported results. In particular, we show that three distinct macroscopic collective behaviors can be observed: i) the coarsening of aggregates with no orientational order, ii) the emergence of static, elongated nematic bands, and iii) the formation of moving, locally polar structures, which we call worms. The derived hydrodynamic equations indicate that active particles interacting via position-based interactions belong to a distinct class of active systems fundamentally different from other active systems, including velocity-alignment-based flocking systems.
Sharp Eccentric Rings in Planetless Hydrodynamical Models of Debris Disks
NASA Technical Reports Server (NTRS)
Lyra, W.; Kuchner, M. J.
2013-01-01
Exoplanets are often associated with disks of dust and debris, analogs of the Kuiper Belt in our solar system. These "debris disks" show a variety of non-trivial structures attributed to planetary perturbations and utilized to constrain the properties of the planets. However, analyses of these systems have largely ignored the fact that, increasingly, debris disks are found to contain small quantities of gas, a component all debris disks should contain at some level. Several debris disks have been measured with a dust-to-gas ratio around unity where the effect of hydrodynamics on the structure of the disk cannot be ignored. Here we report that dust-gas interactions can produce some of the key patterns seen in debris disks that were previously attributed to planets. Through linear and nonlinear modeling of the hydrodynamical problem, we find that a robust clumping instability exists in this configuration, organizing the dust into narrow, eccentric rings, similar to the Fomalhaut debris disk. The hypothesis that these disks might contain planets, though thrilling, is not necessarily required to explain these systems.
Hydrodynamic Model of Desalination by "Overlimiting" Electrodialysis with Electroconvective Vortices
NASA Astrophysics Data System (ADS)
Kwak, Rhokyun; Pham, Van Sang; Han, Jongyoon
2016-11-01
In 1968, Sonin and Probstein developed a hydrodynamic theory of desalination by electrodialysis. Under a laminar flow between ion exchange membranes, linear ion concentration gradients are developed near the membranes by ion concentration polarization (ICP) in Ohmic-limiting current regimes. This linear ICP determines the relations between current, voltage, and desalting performance. Here, we revisit the hydrodynamic model with nonlinear ICP phenomenon at overlimiting currents. In this regime, electroconvective vortices on the membrane induce flat and extremely low concentration zones. Based on the previous prediction of the vortex height under shear flow, we verify that the height directly represents the amount of the removed salt because there is almost no ion in the vortices. Next, from the mass continuity of ions, the amount of the removed salts is equal to the ion flux through the membrane (i.e. current); as a result, we can develop the relations between current, voltage, and salt removal. Lastly, from these relations, power consumption and desalination cost can be calculated to find the optimal operating condition of overlimiting electrodialysis.
Challenges of citizen science contributions to modelling hydrodynamics of floods
NASA Astrophysics Data System (ADS)
Assumpção, Thaine Herman; Popescu, Ioana; Jonoski, Andreja; Solomatine, Dimitri P.
2017-04-01
Citizen science is an established mechanism in many fields of science, including ecology, biology and astronomy. Citizen participation ranges from collecting and interpreting data towards designing experiments with scientists and cooperating with water management authorities. In the environmental sciences, its potential has begun to be explored in the past decades and many studies on the applicability to water resources have emerged. Citizen Observatories are at the core of several EU-funded projects such as WeSenseIt, GroundTruth, GroundTruth 2.0 and SCENT (Smart Toolbox for Engaging Citizens into a People-Centric Observation Web) that already resulted in valuable contributions to the field. Buytaert et al. (2014) has already reviewed the role of citizen science in hydrology. The work presented here aims to complement it, reporting and discussing the use of citizen science for modelling the hydrodynamics of floods in a variety of studies. Additionally, it highlights the challenges that lie ahead to utilize more fully the citizen science potential contribution. In this work, focus is given to each component of hydrodynamic models: water level, velocity, flood extent, roughness and topography. It is addressed how citizens have been contributing to each aspect, mainly considering citizens as sensors and citizens as data interpreters. We consider to which kind of model (1D or 2D) the discussed approaches contribute and what their limitations and potential uses are. We found that although certain mechanisms are well established (e.g. the use of Volunteer Geographic Information for soft validation of land-cover and land-use maps), the applications in a modelling context are rather modest. Also, most studies involving models are limited to replacing traditional data with citizen data. We recommend that citizen science continue to be explored in modelling frameworks, in different case studies, taking advantage of the discussed mechanisms and of new sensor technologies
Study of hydrodynamic model in sluice controlled river networks
NASA Astrophysics Data System (ADS)
Li, Yan; Zeng, Fantang
2010-05-01
Shiqi river network ,is situated in the Zhongshan city of Guangdong province in the P.R.China. The river network covers approximately 702.55km2 ,with a total river length of over 500km and extending over 34km from north to south and over 46km from east to west. The river network overlaps with the most densely populated and economically developed region in the Pear River Delta Economic Zone. In 2008 the region had a population of 1 846.9 thousands And a GDP of more than 8 2500 million RMB. All branches of the river network are encircled by the main rivers of Pear River Delta(PRD) network. With the economic and social development, all natural connections with the external rivers are controlled by the sluices, water body exchanges between the Shiqi river network and external rivers are significantly changed by human activities. The overall objective the research is to develop a tool for the local Environmental Protection Bureau to Understand and quantify the impact of the artificial construction on the hydrological cycle. The developed model can accurate representation of the water levels and flows in the study area, to allow accurate representation of the transport of pollutants. The river network topography is derived directly from the available database. Only the "major" rivers were included in the model, because cross-section data for the "minor" rivers are currently not available. In general, the 1D hydrodynamic model is provided with flow boundary conditions ("Q") at its upstream boundaries and with water level boundary conditions ("z") at its downstream boundaries. For all boundaries of Shiqi river network, there are no flow records available, all records are water level. To reflect the hydrodynamic process accurately, the author developed a new methods to set the hydrodynamic model's boundary. For each boundary, the boundary condition is "Z" when the sluice is open, and the boundary condition is "Q" while it is closed. The open or close condition is identified
Modeling of Waves with Smoothed Particle Hydrodynamics on the GPU
NASA Astrophysics Data System (ADS)
Dalrymple, R. A.; Herault, A.
2008-12-01
Providing an accurate representation of breaking waves is extremely difficult due to the complexity of the free surface, splash-up, and the induced vortical flows in the water. Monaghan (1994) and Dalrymple and Rogers (2004) are examples of using the numerical method Smoothed Particle Hydrodynamics to model these breaking waves. Both of these studies accurately show the plunging jet and the splash-up of breaking plungers. However, full details of the flow requires highly resolved 3-D calculations. SPH is computational intensive, involving large numbers of computational particles and very small time steps. Recently Herault (2008) has shown that very high resolution and significant speed-ups in model calculation occurs by computing on the graphics card (GPU), rather than the CPU of computers. This use of the GPU is an on-going paradigm shift, which will be shown. Examples of breaking waves, along with a number of example free surface flows, will be shown.
Modeling hydrodynamic properties of open-cell metal foams
NASA Astrophysics Data System (ADS)
De Jaeger, P.; De Schampheleire, S.; Huisseune, H.; Ameel, B.; T'Joen, C.; De Paepe, M.
2012-11-01
Modeling the hydrodynamics of open-cell aluminum foam still is a challenging task because of the large range of length-scales, own to the physical phenomena which occur in the complex structure. Upscaling the classical conservation equations is a promising approach, but introduces the problem of modeling closure terms. This is dealt with via the well-known porous properties, i.e., permeability and inertial loss factor. Derivation of these properties is commonly done by linking pressure drop data to velocity via a second order interpolation. This, however, introduces significant deviation between the available data set, up to anorder of magnitude, which in turn results in difficulties to predict pressure drop during desing the desing phase of an applicaiton. As the closure terms have a well-defined physical meaning, it should be possible to compute them with better accuracy. This forms the topic of this paper.
NASA Astrophysics Data System (ADS)
Galland, O.; Scheibert, J.
2013-03-01
In this paper, we develop a new axisymmetric analytic model of surface uplift upon sills and laccoliths, based on the formulation of a thin bending plate lying on an elastic foundation. In contrast to most former models also based on thin bending plate formulation, our model accounts for (i) axi-symmetrical uplift, (ii) both upon and outside the intrusion. The model accounts for shallow intrusions, i.e. the ratio a/h > 5 where a and h are the radius and depth of the intrusion, respectively. The main parameter of the model is the elastic length l, which is a function of the elastic properties of the bending plate and of the elastic foundation. The model exhibits two regimes depending on the ratio a/l. When a/l < 5, the uplift spreads over a substantial domain compared to that of the intrusion. In contrast, when a/l > 5, the uplift is mostly restricted upon the intrusion. When the elastic foundation is very stiff, our model converges towards that of a clamped plate. We provide, as supplementary material, a Matlab function that calculates the surface uplift from the set of system and control parameters. We discuss three possible applications of our model: (i) The model can be used to describe sill propagation by introducing a propagation criterion. For realistic values, our model reproduces well the behavior of horizontal intrusions simulated in experiments; (ii) The model can also be used to compute the critical size of saucer-shaped sills. It shows, for instance, that a soft elastic foundation favors the horizontal spreading of sills before they form inclined sheets; (iii) We show that the classical Mogi point source model cannot be used to constrain sill properties from the surface uplift. We thus propose that our model can be used as a valuable alternative to both simple analytical models like Mogi's and more complex numerical models used to analyze ground deformation resulting from sill intrusions in active volcanoes.
A hydrodynamic model for granular material flows including segregation effects
NASA Astrophysics Data System (ADS)
Gilberg, Dominik; Klar, Axel; Steiner, Konrad
2017-06-01
The simulation of granular flows including segregation effects in large industrial processes using particle methods is accurate, but very time-consuming. To overcome the long computation times a macroscopic model is a natural choice. Therefore, we couple a mixture theory based segregation model to a hydrodynamic model of Navier-Stokes-type, describing the flow behavior of the granular material. The granular flow model is a hybrid model derived from kinetic theory and a soil mechanical approach to cover the regime of fast dilute flow, as well as slow dense flow, where the density of the granular material is close to the maximum packing density. Originally, the segregation model has been formulated by Thornton and Gray for idealized avalanches. It is modified and adapted to be in the preferred form for the coupling. In the final coupled model the segregation process depends on the local state of the granular system. On the other hand, the granular system changes as differently mixed regions of the granular material differ i.e. in the packing density. For the modeling process the focus lies on dry granular material flows of two particle types differing only in size but can be easily extended to arbitrary granular mixtures of different particle size and density. To solve the coupled system a finite volume approach is used. To test the model the rotational mixing of small and large particles in a tumbler is simulated.
Viallet, Guilhem; Sgard, Franck; Laville, Frédéric; Boutin, Jérôme
2013-12-01
The axisymmetric hypothesis of the earplug-ear canal system geometry is commonly used. The validity of this hypothesis is investigated numerically in the case of a simplified configuration where the system is embedded in a rigid baffle and for fixed boundary conditions on the earplug lateral walls. This investigation is discussed for both individual and averaged insertion loss predictions of molded silicon earplugs. The insertion losses of 15 earplug-ear canal systems with realistic geometries are calculated using three-dimensional (3D) finite element models and compared with the insertion losses provided by two-dimensional equivalent axisymmetric finite element models using 6 different geometry reconstruction methods [all the models are solved using COMSOL Multiphysics (COMSOL, Sweden)]. These methods are then compared in order to find the most reliable ones in terms of insertion loss predictions in this simplified configuration. Two methods have emerged: The usage of a variable cross section (with the same area values as the 3D case) or the usage of a constant cross section (with the same length and volume as the 3D case).
Self-consistent Modeling of Reionization in Cosmological Hydrodynamical Simulations
NASA Astrophysics Data System (ADS)
Oñorbe, Jose; Hennawi, Joseph F.; Lukić, Zarija
2017-03-01
The ultraviolet background (UVB) emitted by quasars and galaxies governs the ionization and thermal state of the intergalactic medium (IGM), regulates the formation of high-redshift galaxies, and is thus a key quantity for modeling cosmic reionization. The vast majority of cosmological hydrodynamical simulations implement the UVB via a set of spatially uniform photoionization and photoheating rates derived from UVB synthesis models. We show that simulations using canonical UVB rates reionize and, perhaps more importantly, spuriously heat the IGM, much earlier (z˜ 15) than they should. This problem arises because at z> 6, where observational constraints are nonexistent, the UVB amplitude is far too high. We introduce a new methodology to remedy this issue, and we generate self-consistent photoionization and photoheating rates to model any chosen reionization history. Following this approach, we run a suite of hydrodynamical simulations of different reionization scenarios and explore the impact of the timing of reionization and its concomitant heat injection on the thermal state of the IGM. We present a comprehensive study of the pressure smoothing scale of IGM gas, illustrating its dependence on the details of both hydrogen and helium reionization, and argue that it plays a fundamental role in interpreting Lyα forest statistics and the thermal evolution of the IGM. The premature IGM heating we have uncovered implies that previous work has likely dramatically overestimated the impact of photoionization feedback on galaxy formation, which sets the minimum halo mass able to form stars at high redshifts. We make our new UVB photoionization and photoheating rates publicly available for use in future simulations.
Self-consistent Modeling of Reionization in Cosmological Hydrodynamical Simulations
Oñorbe, Jose; Hennawi, Joseph F.; Lukić, Zarija
2017-03-08
The ultraviolet background (UVB) emitted by quasars and galaxies governs the ionization and thermal state of the intergalactic medium (IGM), regulates the formation of high-redshift galaxies, and is thus a key quantity for modeling cosmic reionization. The vast majority of cosmological hydrodynamical simulations implement the UVB via a set of spatially uniform photoionization and photoheating rates derived from UVB synthesis models. In this paper, we show that simulations using canonical UVB rates reionize and, perhaps more importantly, spuriously heat the IGM, much earlier (more » $$z\\sim 15$$) than they should. This problem arises because at $$z\\gt 6$$, where observational constraints are nonexistent, the UVB amplitude is far too high. We introduce a new methodology to remedy this issue, and we generate self-consistent photoionization and photoheating rates to model any chosen reionization history. Following this approach, we run a suite of hydrodynamical simulations of different reionization scenarios and explore the impact of the timing of reionization and its concomitant heat injection on the thermal state of the IGM. We present a comprehensive study of the pressure smoothing scale of IGM gas, illustrating its dependence on the details of both hydrogen and helium reionization, and argue that it plays a fundamental role in interpreting Lyα forest statistics and the thermal evolution of the IGM. The premature IGM heating we have uncovered implies that previous work has likely dramatically overestimated the impact of photoionization feedback on galaxy formation, which sets the minimum halo mass able to form stars at high redshifts. Finally, we make our new UVB photoionization and photoheating rates publicly available for use in future simulations.« less
Modeling shallow-water hydrodynamics: Rotations, rips, and rivers
NASA Astrophysics Data System (ADS)
Long, Joseph W.
Hydrodynamic models are used as a diagnostic tool to understand the temporal variability of shallow-water processes that are difficult to completely resolve with traditional field measurements. For all simulations, modeled quantities are qualitatively or quantitatively compared with available measurements to gain confidence in conclusions derived from the modeled results. In this work we consider both vorticity motions and rip currents, which arise from alongshore inhomogeneities in the wave momentum flux but occur at much different time scales (O(min) vs. O(hours-weeks)). They each have an effect on sediment transport processes and dispersion of sediments or pollutants in the surf zone, which makes understanding their structure and persistence essential. The vorticity motions of interest here are associated with spatial and temporal wave height variations caused by wave grouping and can exist with either normally or obliquely incident wave conditions. We find that these flows persist for O(1000s) but their lifespan is controlled by the sequence of wave forcing rather than bottom friction as previously hypothesized. These motions can also be observed in combination with either stable or unstable alongshore currents. Our results suggest that, at times, these alongshore propagating wave group forced vortices are misinterpreted as instabilities of the alongshore current. Alternately, the rip currents considered in this research are controlled by strong wave height gradients in the surf zone generated by the refraction of incident waves over variable offshore depth contours. Thus, this type of circulation is governed by timescales associated with changing offshore wave conditions (O(hours - days)). We consider a four- week time period when variable offshore wave spectra were observed during a large-scale field experiment. The model and data are in good agreement for all wave conditions during the month and estimated model errors are similar to those found previously
A hydrodynamic model of locomotion in the Basilisk Lizard
NASA Astrophysics Data System (ADS)
Glasheen, J. W.; McMahon, T. A.
1996-03-01
ORGANISMS with a body mass of more than one gram and which live at the air-water interface generally support their weight with their buoyant bodies. The maximum swimming speed these animals can attain is limited by wave-making resistance1-3. For high-speed progression across a body of water, shore birds and basilisk lizards (Basiliscus basiliscus) support their bodies above the water surface by repeatedly striking the surface with their feet. Here we investigate the mechanism of support in moderately sized basilisk lizards (about 90 g) by combining hydrodynamic measurements of a physical model of the lizards' feet with an analysis of video records of foot movements. We find basilisks of intermediate size obtain little support for their body weight by slapping the water surface; most of the support comes from stroking the foot downwards while expanding an air cavity underwater. The lizard minimizes downward forces by pulling its foot upward before the cavity collapses.
A future Outlook: Web based Simulation of Hydrodynamic models
NASA Astrophysics Data System (ADS)
Islam, A. S.; Piasecki, M.
2003-12-01
Despite recent advances to present simulation results as 3D graphs or animation contours, the modeling user community still faces some shortcomings when trying to move around and analyze data. Typical problems include the lack of common platforms with standard vocabulary to exchange simulation results from different numerical models, insufficient descriptions about data (metadata), lack of robust search and retrieval tools for data, and difficulties to reuse simulation domain knowledge. This research demonstrates how to create a shared simulation domain in the WWW and run a number of models through multi-user interfaces. Firstly, meta-datasets have been developed to describe hydrodynamic model data based on geographic metadata standard (ISO 19115) that has been extended to satisfy the need of the hydrodynamic modeling community. The Extended Markup Language (XML) is used to publish this metadata by the Resource Description Framework (RDF). Specific domain ontology for Web Based Simulation (WBS) has been developed to explicitly define vocabulary for the knowledge based simulation system. Subsequently, this knowledge based system is converted into an object model using Meta Object Family (MOF). The knowledge based system acts as a Meta model for the object oriented system, which aids in reusing the domain knowledge. Specific simulation software has been developed based on the object oriented model. Finally, all model data is stored in an object relational database. Database back-ends help store, retrieve and query information efficiently. This research uses open source software and technology such as Java Servlet and JSP, Apache web server, Tomcat Servlet Engine, PostgresSQL databases, Protégé ontology editor, RDQL and RQL for querying RDF in semantic level, Jena Java API for RDF. Also, we use international standards such as the ISO 19115 metadata standard, and specifications such as XML, RDF, OWL, XMI, and UML. The final web based simulation product is deployed as
Radiation-hydrodynamical modelling of underluminous Type II plateau supernovae
NASA Astrophysics Data System (ADS)
Pumo, M. L.; Zampieri, L.; Spiro, S.; Pastorello, A.; Benetti, S.; Cappellaro, E.; Manicò, G.; Turatto, M.
2017-01-01
With the aim of improving our knowledge about the nature of the progenitors of low-luminosity Type II plateau supernovae (LL SNe IIP), we made radiation-hydrodynamical models of the well-sampled LL SNe IIP 2003Z, 2008bk and 2009md. For these three SNe, we infer explosion energies of 0.16-0.18 foe, radii at explosion of 1.8-3.5 × 1013 cm and ejected masses of 10-11.3 M⊙. The estimated progenitor mass on the main sequence is in the range ˜13.2-15.1 M⊙ for SN 2003Z and ˜11.4-12.9 M⊙ for SNe 2008bk and 2009md, in agreement with estimates from observations of the progenitors. These results together with those for other LL SNe IIP modelled in the same way enable us also to conduct a comparative study on this SN sub-group. The results suggest that (a) the progenitors of faint SNe IIP are slightly less massive and have less energetic explosions than those of intermediate-luminosity SNe IIP; (b) both faint and intermediate-luminosity SNe IIP originate from low-energy explosions of red (or yellow) supergiant stars of low to intermediate mass; (c) some faint objects may also be explained as electron-capture SNe from massive super-asymptotic giant branch stars; and (d) LL SNe IIP form the underluminous tail of the SNe IIP family, where the main parameter `guiding' the distribution seems to be the ratio of the total explosion energy to the ejected mass. Further hydrodynamical studies should be performed and compared to a more extended sample of LL SNe IIP before drawing any conclusion on the relevance of fall-back to this class of events.
Modeling MHD Equilibrium and Dynamics with Non-Axisymmetric Resistive Walls in LTX and HBT-EP
NASA Astrophysics Data System (ADS)
Hansen, C.; Levesque, J.; Bialek, J.; Boyle, D. P.; Schmitt, J.
2016-10-01
In experimental magnetized plasmas, currents in the first wall, vacuum vessel, and other conducting structures can have a strong influence on plasma shape and dynamics. These effects are complicated by the 3D nature of these structures, which dictate available current paths. Results from simulations to study the effect of external currents on plasmas in two different experiments will be presented: 1) The arbitrary geometry, 3D extended MHD code PSI-Tet is applied to study linear and non-linear plasma dynamics in the High Beta Tokamak (HBT-EP) focusing on toroidal asymmetries in the adjustable conducting wall. 2) Equilibrium reconstructions of the Lithium Tokamak eXperiment (LTX) in the presence of non-axisymmetric eddy currents. An axisymmetric model is used to reconstruct the plasma equilibrium, using the PSI-Tri code, along with a set of fixed eddy current distributions. Current distributions are generated using 3D time-dependent, thin-wall, eddy current simulations using VALEN or PSI-Tet. Simulations of detailed experimental geometries are enabled by use of the PSI-Tet code, which employs a high order finite element method on unstructured tetrahedral grids that are generated directly from CAD models. Further development of PSI-Tet will also be presented. Work supported by US DOE.
Calculations of the stability of some axisymmetric flows proposed as a model of vortex breakdown
NASA Technical Reports Server (NTRS)
Mhuiris, N. M. G.
1986-01-01
The term vortex breakdown refers to the abrupt and drastic changes of structure that can sometimes occur in swirling flows. It was conjectured that the bubble type of breakdown can be viewed as an axisymmetric wave traveling upstream in a primarily columnar vortex flow. In this scenario the wave's upstream progress is impeded only when it reaches a critical amplitude and it loses stability to some nonaxisymmetric disturbance. The stability of some axisymmetric wavy flows to three dimensional disturbances, viewing the amplitude of the wave as a bifurcation parameter is examined. The stability of a set of related columnar vortex flows, constructed by taking the two dimensional flow at a single axial location and extending it throughout the domain without variation, is investigated. The method used will be to expand the perturbation velocity in a series of divergence free vectors which ensures that the continuity equation for the incompressible fluid is satisfied exactly by the computed velocity field. Projections of the stability equation onto the space of inviscid vector fields eliminated the pressure term from the equation and reduces the differential eigen problem to a generalized matrix eigen problem. Results are presented both for the one dimensional, columnar vortex flows and also for the wavy bubble flow.
Hydrocyclone separation hydrodynamics
Ivanov, A.A.; Ruzanov, S.R.; Lunyushkina, I.A.
1987-10-20
The lack of an adequate hydrodynamic model for a hydrocyclone has so far been the main obstacle to devising a general method for designing such apparatus. The authors present a method of calculating the liquid flow in the working zone. The results have been used to calculate the separating power in application to dilute suspensions. The Navier-Stokes equations and the equation of continuity are used in examining the behavior together with assumptions based on experiment: the conditions for stationary axisymmetric flow, constant turbulent viscosity, and a constant radial profile for the tangential low speed at all the heights. The boundary conditions are those for liquid slip at the side walls and absence of vortex drainage at the axis. The results enable one to choose the dimensions for particular separations.
NASA Astrophysics Data System (ADS)
Cowley, S. W. H.; Provan, G.; Bunce, E. J.; Nichols, J. D.
2017-05-01
We evaluate the expected effects of magnetosphere-ionosphere coupling at Jupiter along the Juno Perijove 1 (PJ1) trajectory using an axisymmetric physical model. As found at Saturn, the model predicts distributed downward field-aligned currents over polar regions mapping to the tail and outer magnetosphere, closed principally through a ring of upward current mapping to the middle magnetosphere, which requires downward acceleration of magnetospheric electrons generating Jupiter's main auroral emission. Auroral location, width, intensity, electron energy, and current density are in accord with values derived from previous ultraviolet imaging, such that the model forms an appropriate baseline for comparison with Juno data. We evaluate the azimuthal field perturbations during six anticipated near-planet encounters with middle magnetosphere field lines at radial distances between 1.6 and 16 Jovian radii, discuss the expected form of the accelerated electron distributions, and comment briefly on model expectations in relation to first results derived from Juno PJ1 data.
Predictive Models for Hydrodynamic Coupling Coefficients in Clay Media.
NASA Astrophysics Data System (ADS)
Gueutin, P.; Gonçalvès, J.; Violette, S.
2007-12-01
In charged and low permeability media (e.g. clay media) the classical Darcy's law does not describe accurately the water movement. A generalized Darcy's law, one of the coupled fluxes equations, has to be used. The identification of the coupling parameters, in clay-rocks, is crucial in order to estimate the water flow. Here, we will only focus on the electrochemical-hydraulic coupling coefficients : the intrinsic permeability k and the osmotic permeability kc. These hydrodynamic coupling coefficients can be estimated using two approaches: (i) theoretical models : • porosity/intrinsic permeability relationships, defined for a clay medium, are used to estimate the intrinsic permeability. • an electrochemical model is used to estimate the osmotic coupling coefficient. The electrical model, a triple layer model, is implemented to simulate the interactions between the charged surfaces of the clay minerals and the pore solution. (ii) experiments : • at the sample scale. • at the field scale. The measurement of these parameters is generally challenging either at the sample or at the field scale. For this reason, predictive models can be useful. The purpose of this study is to give reference values for the two coupling parameters under consideration here, using to the petrophysical properties of the medium. Different models to estimate these coupling coefficients are tested : (i) the intrinsic permeability is estimated with a pretrophysical model. In this model, the intrinsic permeability depends on the effective pore radius and the electrical formation factor. (ii) the osmotic coupling coefficient is estimated with the model developed by Revil and Leroy (2004). The comparison between three different models with the available data shows that these data are more closely reproduced using this model. Some reference values are provided for several type of clays as a fonction of some readily measurable or estimable parameters or variables, such as the porosity, the
Mid-Bay Islands Hydrodynamics and Sedimentation Modeling Study, Chesapeake Bay
2006-08-01
B3 Hydrodynamic and sediment transport modeling with M2D ................. B7 Hydrodynamics...maximum current field, normal tide ............................... B6 Figure B6. Alt JI-7 M2D model grid...B7 Figure B7. Alt JI-7 maximum current field, NE33 ........................................ B9 Figure B8. Alt JI-7 M2D
Simulations of Model Microswimmers with Fully Resolved Hydrodynamics
NASA Astrophysics Data System (ADS)
Oyama, Norihiro; Molina, John J.; Yamamoto, Ryoichi
2017-10-01
Swimming microorganisms, which include bacteria, algae, and spermatozoa, play a fundamental role in most biological processes. These swimmers are a special type of active particle, that continuously convert local energy into propulsive forces, thereby allowing them to move through their surrounding fluid medium. While the size, shape, and propulsion mechanism vary from one organism to the next, they share certain general characteristics: they exhibit force-free motion and they swim at a small Reynolds number. To study the dynamics of such systems, we use the squirmer model, which provides an ideal representation of swimmers as spheroidal particles that propel owing to a modified boundary condition at their surface. We have considered the single-particle and many-particle dynamics of swimmers in bulk and confined systems using the smoothed profile method, which allows us to efficiently solve the coupled particle-fluid problem. For the single-particle dynamics, we studied the diffusive behavior caused by the swimming of the particles. At short-time scales, the diffusion is caused by the hydrodynamic interactions, whereas at long-time scales, it is determined by the particle-particle collisions. Thus, the short-time diffusion will be the same for both swimmers and inert tracer particles. We then investigated the dynamics of confined microswimmers using cylindrical and parallel-plate confining walls. For the cylindrical confinement, we find evidence of an order/disorder phase transition which depends on the specific type of swimmers and the size of the cylinder. Under parallel-plane walls, some swimmers exhibit wavelike modes, which lead to traveling density waves that bounce back and forth between the walls. From an analysis of the bulk systems, we can show that this wavelike motion can be understood as a pseudoacoustic mode and is a consequence of the intrinsic swimming properties of the particles. The results presented here, together with the simulation method that
Modeling and Prediction of the Noise from Non-Axisymmetric Jets
NASA Technical Reports Server (NTRS)
Leib, Stewart J.
2014-01-01
mean flows which were meant to represent noise reduction concepts being considered by NASA. Testing (Ref. 5) showed that the method was feasible for the types of mean flows of interest in jet noise applications. Subsequently, this method was further developed to allow use of mean flow profiles obtained from a Reynolds-averaged Navier-Stokes (RANS) solution of the flow. Preliminary testing of the generalized code was among the last tasks completed under this contract. The stringent noise-reduction goals of NASA's Fundamental Aeronautics Program suggest that, in addition to potentially complex exhaust nozzle geometries, next generation aircraft will also involve tighter integration of the engine with the airframe. Therefore, noise generated and propagated by jet flows in the vicinity of solid surfaces is expected to be quite significant, and reduced-order noise prediction tools will be needed that can deal with such geometries. One important source of noise is that generated by the interaction of a turbulent jet with the edge of a solid surface (edge noise). Such noise is generated, for example, by the passing of the engine exhaust over a shielding surface, such as a wing. Work under this task supported an effort to develop a RANS-based prediction code for edge noise based on an extension of the classical Rapid Distortion Theory (RDT) to transversely sheared base flows (Refs. 6 and 7). The RDT-based theoretical analysis was applied to the generic problem of a turbulent jet interacting with the trailing edge of a flat plate. A code was written to evaluate the formula derived for the spectrum of the noise produced by this interaction and results were compared with data taken at NASA Glenn for a variety of jet/plate configurations and flow conditions (Ref. 8). A longer-term goal of this task was to work toward the development of a high-fidelity model of sound propagation in spatially developing non-axisymmetric jets using direct numerical methods for solving the relevant
Hydrodynamics beyond Navier-Stokes: the slip flow model.
Yudistiawan, Wahyu P; Ansumali, Santosh; Karlin, Iliya V
2008-07-01
Recently, analytical solutions for the nonlinear Couette flow demonstrated the relevance of the lattice Boltzmann (LB) models to hydrodynamics beyond the continuum limit [S. Ansumali, Phys. Rev. Lett. 98, 124502 (2007)]. In this paper, we present a systematic study of the simplest LB kinetic equation-the nine-bit model in two dimensions--in order to quantify it as a slip flow approximation. Details of the aforementioned analytical solution are presented, and results are extended to include a general shear- and force-driven unidirectional flow in confined geometry. Exact solutions for the velocity, as well as for pertinent higher-order moments of the distribution functions, are obtained in both Couette and Poiseuille steady-state flows for all values of rarefaction parameter (Knudsen number). Results are compared with the slip flow solution by Cercignani, and a good quantitative agreement is found for both flow situations. Thus, the standard nine-bit LB model is characterized as a valid and self-consistent slip flow model for simulations beyond the Navier-Stokes approximation.
A Nanoscale Hydrodynamical Model for Transport of Water
NASA Astrophysics Data System (ADS)
Bhadauria, Ravi; Sanghi, Tarun; Aluru, N. R.
2015-11-01
We present here a one-dimensional isothermal hydrodynamic transport model for SPC/E water. Two separate mechanisms of flow, viz. viscous and slip are incorporated in the present formulation. Spatially varying viscosity is modeled using the local average density method. Slip velocity is provided as a form of the boundary condition which in turn depends upon the macroscopic interfacial friction coefficient. The friction coefficient bridges the atomistic and continuum descriptions of the problem. The value of this friction coefficient is computed using particle-based wall-fluid force autocorrelations and wall-fluid force-velocity cross correlations, where the particle trajectory is generated using a Generalized Langevin Equation formulation. To test the accuracy of the model, gravity driven flow of SPC/E water confined between graphene and silicon slit shaped nanochannels are considered as examples for low and high friction cases. The proposed model yields good quantitative agreement with the velocity profiles obtained from non-equilibrium molecular dynamics simulations. Furthermore, we demonstrate that the slip length is constant for different channel widths for a fixed thermodynamic state under the linear response regime.
NASA Astrophysics Data System (ADS)
Kalyan, Anuroopa; Karabasov, Sergey A.
2017-04-01
Supersonic jets that are subject to off-design operating conditions are marked by three distinct regions in their far-field spectra: mixing noise, screech and Broadband Shock Associated Noise (BBSAN). BBSAN is conspicuous by the prominent multiple peaks. The Morris and Miller BBSAN model that is based on an acoustic analogy, offering a straightforward implementation for RANS, forms the foundation of the present work. The analogy model robustly captures the peak frequency noise, that occurs near Strouhal number of about 1, based on the nozzle exit diameter but leads to major sound under prediction for higher frequencies. In the jet mixing noise literature, it has been shown that an inclusion of frequency dependence into the characteristic length and temporal scales of the effective noise sources improves the far-field noise predictions. In the present paper, several modifications of the original Morris and Miller model are considered that incorporate the frequency dependent scales as recommended in the jet mixing noise literature. In addition to these, a new mixed scale model is proposed that incorporates a correlation scale that depends both on the mean-flow velocity gradient and the standard mixing noise-type scaling based on the dissipation of turbulent kinetic energy. In comparison with the original Morris and Miller model, the mixed scale model shows considerable improvements in the noise predictions for the benchmark axisymmetric convergent-divergent and convergent jets. Further to this validation, the new model has been applied for improved predictions for elliptic jets of various eccentricity. It has been shown that, for the same thrust conditions, the elliptical nozzles lead to noise reduction at the source in comparison with the baseline axisymmetric jets.
Hydrodynamic modeling of petroleum reservoirs using simulator MUFITS
NASA Astrophysics Data System (ADS)
Afanasyev, Andrey
2015-04-01
MUFITS is new noncommercial software for numerical modeling of subsurface processes in various applications (www.mufits.imec.msu.ru). To this point, the simulator was used for modeling nonisothermal flows in geothermal reservoirs and for modeling underground carbon dioxide storage. In this work, we present recent extension of the code to petroleum reservoirs. The simulator can be applied in conventional black oil modeling, but it also utilizes a more complicated models for volatile oil and gas condensate reservoirs as well as for oil rim fields. We give a brief overview of the code by providing the description of internal representation of reservoir models, which are constructed of grid blocks, interfaces, stock tanks as well as of pipe segments and pipe junctions for modeling wells and surface networks. For conventional black oil approach, we present the simulation results for SPE comparative tests. We propose an accelerated compositional modeling method for sub- and supercritical flows subjected to various phase equilibria, particularly to three-phase equilibria of vapour-liquid-liquid type. The method is based on the calculation of the thermodynamic potential of reservoir fluid as a function of pressure, total enthalpy and total composition and storing its values as a spline table, which is used in hydrodynamic simulation for accelerated PVT properties prediction. We provide the description of both the spline calculation procedure and the flashing algorithm. We evaluate the thermodynamic potential for a mixture of two pseudo-components modeling the heavy and light hydrocarbon fractions. We develop a technique for converting black oil PVT tables to the potential, which can be used for in-situ hydrocarbons multiphase equilibria prediction under sub- and supercritical conditions, particularly, in gas condensate and volatile oil reservoirs. We simulate recovery from a reservoir subject to near-critical initial conditions for hydrocarbon mixture. We acknowledge
NASA Astrophysics Data System (ADS)
Cédric, Croizet; Gatignol, Renée
2016-11-01
Sub-millimeter-sized channels are present in many medical and industrial tools such as micro-filters. In order to describe the gas flows in these micro-channels, the DSMC methods are frequently used but a large computation time is usually required to obtain the solutions [1, 2]. Consequently, it is of main interest to develop alternative methods to describe these flows. In this contribution, we are interested in flows at low Mach numbers and with low to moderate Knudsen numbers so that the flow is in the slip regime. We propose an asymptotic model for the axisymmetric flow of a mixture of two compressible gases in circular microchannels with a temperature gradient at the wall. The model is obtained from the Navier-Stokes-Fourier equations. The results of the model are compared to DSMC simulations and the influence of the temperature gradient which is present along the walls is investigated.
Hydrodynamic modeling of tsunamis from the Currituck landslide
Geist, E.L.; Lynett, P.J.; Chaytor, J.D.
2009-01-01
Tsunami generation from the Currituck landslide offshore North Carolina and propagation of waves toward the U.S. coastline are modeled based on recent geotechnical analysis of slide movement. A long and intermediate wave modeling package (COULWAVE) based on the non-linear Boussinesq equations are used to simulate the tsunami. This model includes procedures to incorporate bottom friction, wave breaking, and overland flow during runup. Potential tsunamis generated from the Currituck landslide are analyzed using four approaches: (1) tsunami wave history is calculated from several different scenarios indicated by geotechnical stability and mobility analyses; (2) a sensitivity analysis is conducted to determine the effects of both landslide failure duration during generation and bottom friction along the continental shelf during propagation; (3) wave history is calculated over a regional area to determine the propagation of energy oblique to the slide axis; and (4) a high-resolution 1D model is developed to accurately model wave breaking and the combined influence of nonlinearity and dispersion during nearshore propagation and runup. The primary source parameter that affects tsunami severity for this case study is landslide volume, with failure duration having a secondary influence. Bottom friction during propagation across the continental shelf has a strong influence on the attenuation of the tsunami during propagation. The high-resolution 1D model also indicates that the tsunami undergoes nonlinear fission prior to wave breaking, generating independent, short-period waves. Wave breaking occurs approximately 40-50??km offshore where a tsunami bore is formed that persists during runup. These analyses illustrate the complex nature of landslide tsunamis, necessitating the use of detailed landslide stability/mobility models and higher-order hydrodynamic models to determine their hazard.
Accuracy of an estuarine hydrodynamic model using smooth elements
Walters, Roy A.; Cheng, Ralph T.
1980-01-01
A finite element model which uses triangular, isoparametric elements with quadratic basis functions for the two velocity components and linear basis functions for water surface elevation is used in the computation of shallow water wave motions. Specifically addressed are two common uncertainties in this class of two-dimensional hydrodynamic models: the treatment of the boundary conditions at open boundaries and the treatment of lateral boundary conditions. The accuracy of the models is tested with a set of numerical experiments in rectangular and curvilinear channels with constant and variable depth. The results indicate that errors in velocity at the open boundary can be significant when boundary conditions for water surface elevation are specified. Methods are suggested for minimizing these errors. The results also show that continuity is better maintained within the spatial domain of interest when ‘smooth’ curve-sided elements are used at shoreline boundaries than when piecewise linear boundaries are used. Finally, a method for network development is described which is based upon a continuity criterion to gauge accuracy. A finite element network for San Francisco Bay, California, is used as an example.
Hydrodynamic model of advanced pressurized fluidized bed combustion
Horio, Masayuki; Lei, H.W.
1997-12-31
A hydrodynamic model was developed for the advanced pressurized fluidized bed combustion (A-PFBC) process. The particular system investigated here is composed of a pressurized circulating fluidized bed (PCFB) for coal gasification/desulfurization and a PCFB for combustion with the gas-solid counter-current flow through the two PCFBs. One of the most important parameters may be the material seal height (MSH) in the downcomer connecting the gasifier/desulfurizer and the combustor, which is thought to strongly influence the safe and stable operation of the process. In this mode, MSH was determined according to the pressure balance between the gasifier/desulfurizer and the combustor. The solid flux in the lower dense region of the two PCFBs was estimated by considering the clustering suspension and core-annulus flow. The mean cluster size and voidage in the cluster phase were predicted by the cluster size model of Horio-Ito (1996). Solid flux of the gasifier and combustor was calculated based on mass balances of limestone, char and ash in the system. Based on this model, the whole pressure profile loop in the system was predicted, and the effects of operating conditions on MSH between the gasifier and the combustor were investigated. The feasibility of the A-PCFB system with PCFBs both for the gasifier/desulfurizer and for the combustor was successfully confirmed.
NASA Astrophysics Data System (ADS)
Maouche, B.; Feliachi, M.; Khenfer, N.
2006-01-01
We present the calculation of the impedance variation using a half-analytical formulation based on coupled electromagnetic variables. Such a formulation concerns an axisymmetrical device constituted with a voltage supplied solenoïdal inductor and a conducting workpiece. In this field of modelling, authors have already developed a method [Maouche and Feliachi, J. Phys. III France 10, 1967 (1997)] that determines the current distribution inside inductor coil loops in the case of weak skin depth and a low number of these coil loops. In the proposed development, the number of loops is relatively large and the skin effect in these loops is negligible. This formulation uses a voltage excitation, which makes the source field depending on induced currents and permits to consider the real geometry of the inductor. The model is applied to study an eddy current non destructive testing (ECNDT) device. The variation of the system impedance is calculated in the case of an axisymmetrical device. The obtained modelling results are validated by comparison to measurements and finite element computations [Rémy, Ph.D. thesis, University of Compiègne, France, 1997; La et al., Rev. Prog. Quant. Non-Destructive Eval. 16A, 295 (1997)]. Once validated, the proposed model is applied to determine geometrical and physical characteristics of an ECNDT device. To assemble this interest, we visualise the evolution of the impedance variation according respectively to the air-gap, to the thickness of the workpiece and its electric conductivity. The model is implemented within a software tool (CECM: Coupling Electromagnetic Circuits Method) developed in Matlab environment.
Quantum chromodynamics and the statistical hydrodynamical model of hadron production
NASA Astrophysics Data System (ADS)
Carruthers, P.; Duong-van, Minh
1983-07-01
We analyze the Fermi-Landau statistical hydrodynamical model of hadron-hadron multiplicities in the framework of QCD, using the Pokorski-Van Hove model wherein the collision of preexisting glue dominates the multiplicity. It is noted that previous dismissal of the possibility of thermalization in the basis of nuclear "transparency" is circumvented in this picture because the valence quarks pass through, whereas the gluon clouds interact strongly. Assuming that the gluons equilibrate to a thermalized plasmoid within the Fermi-Landau (FL) Lorentz-contracted initial volume, we derive a simple formula for the multiplicity with the form Nch~2.5f14Whad12 (three flavors excited), where 1-f is the fraction of energy carried away by the leading particles and Whad=fW is the energy left behind. If f were fixed at a constant value of 1/2 , the formula would agree extremely well with data up to and including p¯p collider energies. (The widely held belief that collider multiplicities rule out the Fermi power law was based on the use of W rather than Whad.) However, using the data of Basile et al., in which multiplicities are broken down as a function of Whad for different W values, we find that the f14 dependence is ruled out. We conclude that thermalization of the colliding gluon clouds in the FL volume is also ruled out, although thermalization in the gluon fragmentation and central regions remains a possibility.
A hydrodynamic model of an outer hair cell
NASA Technical Reports Server (NTRS)
Jacobson, B. O.
1982-01-01
On the model it is possible to measure the force and the force direction for each individual hair as a function of the flow direction and velocity. Measurements were made at the man flow velocity .01 m/s, which is equivalent to a flow velocity in the real ear of about 1 micrometer/s. The kinematic viscosity of the liquid used in the model was 10,000 times higher than the viscosity of perilymph to attain hydrodynamic equality. Two different geometries for the sterocilia pattern were tested. First the force distribution for a W-shaped sterocilia pattern was recorded. This is the sterocilia pattern found in all real ears. It is found that the forces acting on the hairs are very regular and perpendicular to the legs of the W when the flow is directed from the outside of the W. When the flow is reversed, the forces are not reversed, but are much more irregular. This can eventually explain the half wave rectification of the nerve signals. As a second experiment, the force distribution for a V-shaped sterocilia pattern was recorded. Here the forces were irregular both when the flow was directed into the V and when it was directed against the edge of the V.
Discussion of Stokes' hypothesis through the smoothed particle hydrodynamics model
NASA Astrophysics Data System (ADS)
Colagrossi, Andrea; Durante, Danilo; Bonet Avalos, Josep; Souto-Iglesias, Antonio
2017-08-01
Stokes' hypothesis, the zeroing of the bulk viscosity in a Newtonian fluid, is discussed in this paper. To this aim, a continuum macroscopic fluid domain is initially modeled as a Hamiltonian system of discrete particles, for which the interparticle dissipative forces are required to be radial in order to conserve the angular momentum. The resulting system of particles is then reconverted to the continuum domain via the framework of the smoothed particle hydrodynamics (SPH) model. Since an SPH-consistent approximation of the Newtonian viscous term in the momentum equation incorporates interparticle radial as well as nonradial terms, it is postulated that the latter must be null. In the present work it is shown that this constraint implies that first and second viscosities are equal, resulting in a positive value for the bulk viscosity, in contradiction to the cited Stokes' hypothesis. Moreover, it is found that this postulate leads to bulk viscosity coefficients close to values found in the experimental literature for monoatomic gases and common liquids such as water.
Computational modeling and analysis of the hydrodynamics of human swimming
NASA Astrophysics Data System (ADS)
von Loebbecke, Alfred
Computational modeling and simulations are used to investigate the hydrodynamics of competitive human swimming. The simulations employ an immersed boundary (IB) solver that allows us to simulate viscous, incompressible, unsteady flow past complex, moving/deforming three-dimensional bodies on stationary Cartesian grids. This study focuses on the hydrodynamics of the "dolphin kick". Three female and two male Olympic level swimmers are used to develop kinematically accurate models of this stroke for the simulations. A simulation of a dolphin undergoing its natural swimming motion is also presented for comparison. CFD enables the calculation of flow variables throughout the domain and over the swimmer's body surface during the entire kick cycle. The feet are responsible for all thrust generation in the dolphin kick. Moreover, it is found that the down-kick (ventral position) produces more thrust than the up-kick. A quantity of interest to the swimming community is the drag of a swimmer in motion (active drag). Accurate estimates of this quantity have been difficult to obtain in experiments but are easily calculated with CFD simulations. Propulsive efficiencies of the human swimmers are found to be in the range of 11% to 30%. The dolphin simulation case has a much higher efficiency of 55%. Investigation of vortex structures in the wake indicate that the down-kick can produce a vortex ring with a jet of accelerated fluid flowing through its center. This vortex ring and the accompanying jet are the primary thrust generating mechanisms in the human dolphin kick. In an attempt to understand the propulsive mechanisms of surface strokes, we have also conducted a computational analysis of two different styles of arm-pulls in the backstroke and the front crawl. These simulations involve only the arm and no air-water interface is included. Two of the four strokes are specifically designed to take advantage of lift-based propulsion by undergoing lateral motions of the hand
Analytical models for hydrodynamics of the steam superheating surfaces of a TGMP-344A boiler
NASA Astrophysics Data System (ADS)
Pikina, G. A.; Remeeva, A. R.
2009-10-01
A model with distributed parameters for describing the hydrodynamic processes in the convective steam superheater of a TGMP-344A boiler, which reflects the possibility that hydraulic pulsations will occur, is considered. A computer program is proposed that allows the frequency characteristics of hydrodynamic processes in complex systems to be estimated using recurrence relations.
Axisymmetric multiwormholes revisited
NASA Astrophysics Data System (ADS)
Clément, Gérard
2016-06-01
The construction of stationary axisymmetric multiwormhole solutions to gravitating field theories admitting toroidal reductions to three-dimensional gravitating sigma models is reviewed. We show that, as in the multi-black hole case, strut singularities always appear in this construction, except for very special configurations with an odd number of centers. We also review the analytical continuation of the multicenter solution across the n cuts associated with the wormhole mouths. The resulting Riemann manifold has 2^n sheets interconnected by 2^{n-1}n wormholes. We find that the maximally extended multicenter solution can never be asymptotically locally flat in all the Riemann sheets.
Gold-standard performance for 2D hydrodynamic modeling
NASA Astrophysics Data System (ADS)
Pasternack, G. B.; MacVicar, B. J.
2013-12-01
Two-dimensional, depth-averaged hydrodynamic (2D) models are emerging as an increasingly useful tool for environmental water resources engineering. One of the remaining technical hurdles to the wider adoption and acceptance of 2D modeling is the lack of standards for 2D model performance evaluation when the riverbed undulates, causing lateral flow divergence and convergence. The goal of this study was to establish a gold-standard that quantifies the upper limit of model performance for 2D models of undulating riverbeds when topography is perfectly known and surface roughness is well constrained. A review was conducted of published model performance metrics and the value ranges exhibited by models thus far for each one. Typically predicted velocity differs from observed by 20 to 30 % and the coefficient of determination between the two ranges from 0.5 to 0.8, though there tends to be a bias toward overpredicting low velocity and underpredicting high velocity. To establish a gold standard as to the best performance possible for a 2D model of an undulating bed, two straight, rectangular-walled flume experiments were done with no bed slope and only different bed undulations and water surface slopes. One flume tested model performance in the presence of a porous, homogenous gravel bed with a long flat section, then a linear slope down to a flat pool bottom, and then the same linear slope back up to the flat bed. The other flume had a PVC plastic solid bed with a long flat section followed by a sequence of five identical riffle-pool pairs in close proximity, so it tested model performance given frequent undulations. Detailed water surface elevation and velocity measurements were made for both flumes. Comparing predicted versus observed velocity magnitude for 3 discharges with the gravel-bed flume and 1 discharge for the PVC-bed flume, the coefficient of determination ranged from 0.952 to 0.987 and the slope for the regression line was 0.957 to 1.02. Unsigned velocity
Lattice hydrodynamic model based traffic control: A transportation cyber-physical system approach
NASA Astrophysics Data System (ADS)
Liu, Hui; Sun, Dihua; Liu, Weining
2016-11-01
Lattice hydrodynamic model is a typical continuum traffic flow model, which describes the jamming transition of traffic flow properly. Previous studies in lattice hydrodynamic model have shown that the use of control method has the potential to improve traffic conditions. In this paper, a new control method is applied in lattice hydrodynamic model from a transportation cyber-physical system approach, in which only one lattice site needs to be controlled in this control scheme. The simulation verifies the feasibility and validity of this method, which can ensure the efficient and smooth operation of the traffic flow.
NASA Astrophysics Data System (ADS)
Fita, L.; Romero, R.; Luque, A.; Emanuel, K.; Ramis, C.
2007-01-01
Tropical-like storms on the Mediterranean Sea are occasionally observed on satellite images, often with a clear eye surrounded by an axysimmetric cloud structure. These storms sometimes attain hurricane intensity and can severely affect coastal lands. A deep, cut-off, cold-core low is usually observed at mid-upper tropospheric levels in association with the development of these tropical-like systems. In this study we attempt to apply some tools previously used in studies of tropical hurricanes to characterise the environments in which seven known Mediterranean events developed. In particular, an axisymmetric, nonhydrostatic, cloud resolving model is applied to simulate the tropical-like storm genesis and evolution. Results are compared to surface observations when landfall occurred and with satellite microwave derived wind speed measurements over the sea. Finally, sensitivities of the numerical simulations to different factors (e.g. sea surface temperature, vertical humidity profile and size of the initial precursor of the storm) are examined.
Update on PHELIX Pulsed-Power Hydrodynamics Experiments and Modeling
NASA Astrophysics Data System (ADS)
Rousculp, Christopher; Reass, William; Oro, David; Griego, Jeffery; Turchi, Peter; Reinovsky, Robert; Devolder, Barbara
2013-10-01
The PHELIX pulsed-power driver is a 300 kJ, portable, transformer-coupled, capacitor bank capable of delivering 3-5 MA, 10 μs pulse into a low inductance load. Here we describe further testing and hydrodynamics experiments. First, a 4 nH static inductive load has been constructed. This allows for repetitive high-voltage, high-current testing of the system. Results are used in the calibration of simple circuit models and numerical simulations across a range of bank charges (+/-20 < V0 < +/-40 kV). Furthermore, a dynamic liner-on-target load experiment has been conducted to explore the shock-launched transport of particulates (diam. ~ 1 μm) from a surface. The trajectories of the particulates are diagnosed with radiography. Results are compared to 2D hydro-code simulations. Finally, initial studies are underway to assess the feasibility of using the PHELIX driver as an electromagnetic launcher for planer shock-physics experiments. Work supported by United States-DOE under contract DE-AC52-06NA25396.
Film rupture in the diffuse interface model coupled to hydrodynamics.
Thiele, U; Velarde, M G; Neuffer, K; Pomeau, Y
2001-09-01
The process of dewetting of a thin liquid film is usually described using a long-wave approximation yielding a single evolution equation for the film thickness. This equation incorporates an additional pressure term-the disjoining pressure-accounting for the molecular forces. Recently a disjoining pressure was derived coupling hydrodynamics to the diffuse interface model [L. M. Pismen and Y. Pomeau, Phys. Rev. E 62, 2480 (2000)]. Using the resulting evolution equation as a generic example for the evolution of unstable thin films, we examine the thickness ranges for linear instability and metastability for flat films, the families of stationary periodic and localized solutions, and their linear stability. The results are compared to simulations of the nonlinear time evolution. From this we conclude that, within the linearly unstable thickness range, there exists a well defined subrange where finite perturbations are crucial for the time evolution and the resulting structures. In the remainder of the linearly unstable thickness range the resulting structures are controlled by the fastest flat film mode assumed up to now for the entire linearly unstable thickness range. Finally, the implications for other forms of disjoining pressure in dewetting and for spinodal decomposition are discussed.
Lattice Models for Granular-Like Velocity Fields: Hydrodynamic Description
NASA Astrophysics Data System (ADS)
Manacorda, Alessandro; Plata, Carlos A.; Lasanta, Antonio; Puglisi, Andrea; Prados, Antonio
2016-08-01
A recently introduced model describing—on a 1d lattice—the velocity field of a granular fluid is discussed in detail. The dynamics of the velocity field occurs through next-neighbours inelastic collisions which conserve momentum but dissipate energy. The dynamics is described through the corresponding Master Equation for the time evolution of the probability distribution. In the continuum limit, equations for the average velocity and temperature fields with fluctuating currents are derived, which are analogous to hydrodynamic equations of granular fluids when restricted to the shear modes. Therefore, the homogeneous cooling state, with its linear instability, and other relevant regimes such as the uniform shear flow and the Couette flow states are described. The evolution in time and space of the single particle probability distribution, in all those regimes, is also discussed, showing that the local equilibrium is not valid in general. The noise for the momentum and energy currents, which are correlated, are white and Gaussian. The same is true for the noise of the energy sink, which is usually negligible.
Wang, Xu; Ding, Jie; Guo, Wan-Qian; Ren, Nan-Qi
2010-12-01
Investigating how a bioreactor functions is a necessary precursor for successful reactor design and operation. Traditional methods used to investigate flow-field cannot meet this challenge accurately and economically. Hydrodynamics model can solve this problem, but to understand a bioreactor in sufficient depth, it is often insufficient. In this paper, a coupled hydrodynamics-reaction kinetics model was formulated from computational fluid dynamics (CFD) code to simulate a gas-liquid-solid three-phase biotreatment system for the first time. The hydrodynamics model is used to formulate prediction of the flow field and the reaction kinetics model then portrays the reaction conversion process. The coupled model is verified and used to simulate the behavior of an expanded granular sludge bed (EGSB) reactor for biohydrogen production. The flow patterns were visualized and analyzed. The coupled model also demonstrates a qualitative relationship between hydrodynamics and biohydrogen production. The advantages and limitations of applying this coupled model are discussed.
Hydrodynamic modeling of Singapore's coastal waters: Nesting and model accuracy
NASA Astrophysics Data System (ADS)
Hasan, G. M. Jahid; van Maren, Dirk Sebastiaan; Ooi, Seng Keat
2016-01-01
The tidal variation in Singapore's coastal waters is influenced by large-scale, complex tidal dynamics (by interaction of the Indian Ocean and the South China Sea) as well as monsoon-driven low frequency variations, requiring a model with large spatial coverage. Close to the shores, the complex topography, influenced by headlands and small islands, requires a high resolution model to simulate tidal dynamics. This can be achieved through direct nesting or multi-scale nesting, involving multiple model grids. In this paper, we investigate the effect of grid resolution and multi-scale nesting on the tidal dynamics in Singapore's coastal waters, by comparing model results with observations using different statistical techniques. The results reveal that the intermediate-scale model is generally sufficiently accurate (equal to or better than the most refined model), but also that the most refined model is only more accurate when nested in the intermediate scale model (requiring multi-scale nesting). This latter is the result of the complex tidal dynamics around Singapore, where the dominantly diurnal tidal currents are decoupled from the semi-diurnal water level variations. Furthermore, different techniques to quantify model accuracy (harmonic analysis, basic statistics and more complex statistics) are inconsistent in determining which model is more accurate.
Stochastic Downscaling for Hydrodynamic and Ecological Modeling of Lakes
NASA Astrophysics Data System (ADS)
Schlabing, D.; Eder, M.; Frassl, M.; Rinke, K.; Bárdossy, A.
2012-04-01
with the help of QQ-downscaled time series. Results of water-quality and ecological modeling using data from VG is contributed by Marieke Anna Frassl under the title "Simulating the effect of meteorological variability on a lake ecosystem". Maria Magdalena Eder contributes three dimensional hydrodynamic lake simulations using VG data in a poster entitled "Advances in estimating the climate sensibility of a large lake using scenario simulations". Both posters can be found in the Session "Lakes and Inland Seas" (HS10.1).
Monitoring Mediterranean marine pollution using remote sensing and hydrodynamic modelling
NASA Astrophysics Data System (ADS)
La Loggia, Goffredo; Capodici, Fulvio; Ciraolo, Giuseppe; Drago, Aldo; Maltese, Antonino
2011-11-01
Human activities contaminate both coastal areas and open seas, even though impacts are different in terms of pollutants, ecosystems and recovery time. In particular, Mediterranean offshore pollution is mainly related to maritime transport of oil, accounting for 25% of the global maritime traffic and, during the last 25 years, for nearly 7% of the world oil accidents, thus causing serious biological impacts on both open sea and coastal zone habitats. This paper provides a general review of maritime pollution monitoring using integrated approaches of remote sensing and hydrodynamic modeling; focusing on the main results of the MAPRES (Marine pollution monitoring and detection by aerial surveillance and satellite images) research project on the synergistic use of remote sensing, forecasting, cleanup measures and environmental consequences. The paper also investigates techniques of oil spill detection using SAR images, presenting the first results of "Monitoring of marine pollution due to oil slick", a COSMO-SkyMed funded research project where X-band SAR constellation images provided by the Italian Space Agency are used. Finally, the prospect of using real time observations of marine surface conditions is presented through CALYPSO project (CALYPSO-HF Radar Monitoring System and Response against Marine Oil Spills in the Malta Channel), partly financed by the EU under the Operational Programme Italia-Malta 2007-2013. The project concerns the setting up of a permanent and fully operational HF radar observing system, capable of recording surface currents (in real-time with hourly updates) in the stretch of sea between Malta and Sicily. A combined use of collected data and numerical models, aims to optimize intervention and response in the case of marine oil spills.
2008-06-16
kinetic effects related to electron transport in the framework on hydrodynamic model of the plasma flow inside the Hall thruster channel. In...particular, kinetics of the near wall conductivity (NWC) is analyzed and analytical expression is derived that takes into account the sheath effects . The...NWC model is incorporated into the hydrodynamic model. In addition we consider an effect of SEE electron thermalization. It is found that current
NASA Astrophysics Data System (ADS)
Clark, Timothy; Rubinstein, Robert; Kurien, Susan
2016-11-01
The fluctuating-pressure-strain correlations present a significant challenge for engineering turbulence models. For incompressible flow, the pressure is an intrinsically two-point quantity (represented as Green's function, integrated over the field), and therefore representing the implied scale-dependence in a one-point model is difficult. The pioneering work of Launder, Reece and Rodi (1975) presented a model that satisfied the tensor symmetries and dimensional consistency with the underlying Green's function solution, and described the assumptions embedded in their one-point model. Among the constraints of such a model is its inability to capture scale-dependent anisotropic flow development. Restricting our attention to the case of axisymmetric mean-field strains, we present a one-point model of the mean-flow couplings, including the pressure-strain terms, starting from a directional (tensorially isotropic) and polarization (tensorially anisotropic and trace-free) representation of the two-point correlation equations, truncated to the lowest order terms. The model results are then compared to simulations performed using arbitrary orders of spherical harmonic functions from which the exact solution may be obtained to desired accuracy.
NASA Astrophysics Data System (ADS)
Challa, V.; Issen, K. A.
2003-12-01
Strain localization in porous granular rock occurs in field and laboratory settings. Compaction bands and dilation bands are of particular interest since localized deformation may increase (or decrease) porosity/permeability, possibly affecting fluid flow within geological formations and impacting drilling and extraction applications. Mollema and Antonellini (1996) first identified compaction bands as "thin planar zones of pure compressional deformation," oriented perpendicular to maximum compression. Bésuelle (2001), and Du Bernard, Eichhubl and Aydin (2002) recently reported dilation bands (oriented perpendicular to minimum compression) in laboratory and field settings, respectively. Rudnicki and Rice (1975) modeled strain localization as a bifurcation from homogeneous deformation using a single yield surface model to describe shear localization in low porosity rock. However, recent reexaminations of this model reveal that predicted band orientations do not agree with experimental observations of compaction bands in high porosity sandstone. Microstructural observations by Menéndez, Zhu and Wong suggest multiple active damage processes, prompting development of a two yield surface model by Issen to describe strain localization in high porosity sandstone. The first yield surface corresponds to a dilatant, frictional mechanism, while the cap corresponds to a compactant mechanism. This model successfully predicts the experimentally observed compaction bands under axisymmetric compression (ASC) when the slope of effective mean stress-inelastic volume strain curve is zero or slightly positive, corresponding to the stress plateau characteristic of compaction band formation. Determining conditions for dilation band formation under axisymmetric extension (ASE) using the two yield surface model is facilitated by certain mathematical symmetries with compaction band conditions for ASC. The conditions for dilation band formation though complex, depend largely on the
NASA Astrophysics Data System (ADS)
Wang, Lei; Sun, Jianglong
2017-08-01
An axisymmetric two-phase lattice Boltzmann method is applied to simulate the dewetting dynamics of a thin liquid film on a substrate. Initially, a circular dry spot exists in the center of the liquid film. A contact line forms around the dry spot and expands outwards. The liquid films dewetting on smooth and rough substrates are investigated. For a smooth substrate, the effects of the contact angle (θeq), Ohnesorge number (Oh), and viscosity ratio (λμ) are studied. It is observed that the contact line recedes with a constant velocity V and that if θeq > 45°, V has a linear relationship with θeq, which has never been mentioned in previous literatures. For a rough substrate, well-distributed pillars are set up to represent the roughness. There are two states for the liquid film dewetting on a rough substrate: Cassie and Wenzel states. By comparison, it is found that the speed of the liquid film dewetting on the rough substrate of the Cassie state is slightly faster than that on the smooth substrate but much faster than that on the rough substrate of the Wenzel state, i.e., Wenzel state can obviously hold back the movement of the receding contact line. The corresponding mechanism is analyzed. The effect of the geometric factors of the pillars on the dewetting speed is discussed in detail. It is indicated that both the width and the depth of the grooves in roughness can significantly affect the dewetting speed. The results are helpful to design structured substrates for controlling the dewetting process of the liquid film.
Two-dimensional hydrodynamic and transport models were used to simulate tidal and subtidal circulation, residence times, and the longitudinal distributions of conservative constituents in New Bedford Harbor, Massachusetts, before and after a hurricane barrier was constructed. The...
NASA Astrophysics Data System (ADS)
Savant, G.; Trahan, C. J.
2016-02-01
Next generation finite element method (FEM)hydrodynamic and transport code are expected to be at the fore front of Ocean modeling, of particular importance are the FEM codes that conserve hydrodynamic and transport mass (locally and globally). This talk will introduce the new U.S. Army Corps of Engineers enterprise implicit time stepping and multi-dimensional FEM model, this model is characterized by adaptive meshing to resolve the fine detail required to capture baroclinic effects on hydrodynamics as well as on transported quantities such as salt/heat/tracers etc. The FEM developmental theory that guarantees local and global mass conservation, and results from simulations will be presented, also presented will be the aspects of the Eulerian-Lagrangian meshing that removes certain limitations of sigma and z-gridding in hydrodynamic models.
Puget Sound Dissolved Oxygen Modeling Study: Development of an Intermediate-Scale Hydrodynamic Model
Yang, Zhaoqing; Khangaonkar, Tarang; Labiosa, Rochelle G.; Kim, Taeyun
2010-11-30
The Washington State Department of Ecology contracted with Pacific Northwest National Laboratory to develop an intermediate-scale hydrodynamic and water quality model to study dissolved oxygen and nutrient dynamics in Puget Sound and to help define potential Puget Sound-wide nutrient management strategies and decisions. Specifically, the project is expected to help determine 1) if current and potential future nitrogen loadings from point and non-point sources are significantly impairing water quality at a large scale and 2) what level of nutrient reductions are necessary to reduce or dominate human impacts to dissolved oxygen levels in the sensitive areas. In this study, an intermediate-scale hydrodynamic model of Puget Sound was developed to simulate the hydrodynamics of Puget Sound and the Northwest Straits for the year 2006. The model was constructed using the unstructured Finite Volume Coastal Ocean Model. The overall model grid resolution within Puget Sound in its present configuration is about 880 m. The model was driven by tides, river inflows, and meteorological forcing (wind and net heat flux) and simulated tidal circulations, temperature, and salinity distributions in Puget Sound. The model was validated against observed data of water surface elevation, velocity, temperature, and salinity at various stations within the study domain. Model validation indicated that the model simulates tidal elevations and currents in Puget Sound well and reproduces the general patterns of the temperature and salinity distributions.
Toward Developing a Hydrodynamic Flow & Inundation Model of the Lower Pearl River
2010-01-20
Hydrodynamic Flow & Inundation Model of the Lower Pearl River 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 0602782N 6...release, distribution is unlimited. 13. SUPPLEMENTARY NOTES 20100126157 14. ABSTRACT The lower Pearl River in Mississippi and Louisiana flows through...In order to improve flow and flood prediction capabilities, a hydrodynamic flow and inundation model for the lower Pearl River is being developed
Axisymmetric and non-axisymmetric modulated MHD waves in magnetic flux tubes
NASA Astrophysics Data System (ADS)
Chargeishvili, B. B.; Japaridze, D. R.
2016-02-01
Nonlinear modulated both axisymmetric and non-axisymmetric MHD wave propagation in magnetic flux tubes is studied. In the cylindrical coordinates, ordinary differential equation with cubic nonlinearity is derived. In both cases of symmetry, the equation has solitary solutions. Modulation stability of the solutions is studied. The results of the study show that the propagation of axisymmetric soliton causes rising of plasma temperature in peripheral regions of a magnetic flux tube. In the non-axisymmetric case, it gives also temperature rising effect. Results of theoretical study are examined on idealized model of chromospheric spicule.
Coupling hydrodynamic and wave propagation modeling for waveform modeling of SPE.
NASA Astrophysics Data System (ADS)
Larmat, C. S.; Steedman, D. W.; Rougier, E.; Delorey, A.; Bradley, C. R.
2015-12-01
The goal of the Source Physics Experiment (SPE) is to bring empirical and theoretical advances to the problem of detection and identification of underground nuclear explosions. This paper presents effort to improve knowledge of the processes that affect seismic wave propagation from the hydrodynamic/plastic source region to the elastic/anelastic far field thanks to numerical modeling. The challenge is to couple the prompt processes that take place in the near source region to the ones taking place later in time due to wave propagation in complex 3D geologic environments. In this paper, we report on results of first-principles simulations coupling hydrodynamic simulation codes (Abaqus and CASH), with a 3D full waveform propagation code, SPECFEM3D. Abaqus and CASH model the shocked, hydrodynamic region via equations of state for the explosive, borehole stemming and jointed/weathered granite. LANL has been recently employing a Coupled Euler-Lagrange (CEL) modeling capability. This has allowed the testing of a new phenomenological model for modeling stored shear energy in jointed material. This unique modeling capability has enabled highfidelity modeling of the explosive, the weak grout-filled borehole, as well as the surrounding jointed rock. SPECFEM3D is based on the Spectral Element Method, a direct numerical method for full waveform modeling with mathematical accuracy (e.g. Komatitsch, 1998, 2002) thanks to its use of the weak formulation of the wave equation and of high-order polynomial functions. The coupling interface is a series of grid points of the SEM mesh situated at the edge of the hydrodynamic code domain. Displacement time series at these points are computed from output of CASH or Abaqus (by interpolation if needed) and fed into the time marching scheme of SPECFEM3D. We will present validation tests and waveforms modeled for several SPE tests conducted so far, with a special focus on effect of the local topography.
Hydrodynamic Simulations of Planetary Rings
NASA Astrophysics Data System (ADS)
Miller, Jacob; Stewart, G. R.; Esposito, L. W.
2013-10-01
Simulations of rings have traditionally been done using N-body methods, granting insight into the interactions of individual ring particles on varying scales. However, due to the scale of a typical ring system and the sheer number of particles involved, a global N-body simulation is too computationally expensive, unless particle collisions are replaced by stochastic forces (Bromley & Kenyon, 2013). Rings are extraordinarily flat systems and therefore are well-suited to existing geophysical shallow-water hydrodynamics models with well-established non-linear advection methods. By adopting a general relationship between pressure and surface density such as a polytropic equation of state, we can modify the shallow-water formula to treat a thin, compressible, self-gravitating, shearing fluid. Previous hydrodynamic simulations of planetary rings have been restricted to axisymmetric flows and therefore have not treated the response to nonaxisymmetric perturbations by moons (Schmidt & Tscharnuter 1999, Latter & Ogilvie 2010). We seek to expand on existing hydrodynamic methods and, by comparing our work with complementary N-body simulations and Cassini observations, confirm the veracity of our results at small scales before eventually moving to a global domain size. We will use non-Newtonian, dynamically variable viscosity to model the viscous transport caused by unresolved self-gravity wakes. Self-gravity will be added to model the dynamics of large-scale structures, such as density waves and edge waves. Support from NASA Outer Planets and Planetary Geology and Geophysics programs is gratefully acknowledged.
Critical review of membrane bioreactor models--part 2: hydrodynamic and integrated models.
Naessens, W; Maere, T; Ratkovich, N; Vedantam, S; Nopens, I
2012-10-01
Membrane bioreactor technology exists for a couple of decades, but has not yet overwhelmed the market due to some serious drawbacks of which operational cost due to fouling is the major contributor. Knowledge buildup and optimisation for such complex systems can heavily benefit from mathematical modelling. In this paper, the vast literature on hydrodynamic and integrated MBR modelling is critically reviewed. Hydrodynamic models are used at different scales and focus mainly on fouling and only little on system design/optimisation. Integrated models also focus on fouling although the ones including costs are leaning towards optimisation. Trends are discussed, knowledge gaps identified and interesting routes for further research suggested. Copyright © 2012 Elsevier Ltd. All rights reserved.
A lattice Boltzmann study of non-hydrodynamic effects in shell models of turbulence
NASA Astrophysics Data System (ADS)
Benzi, R.; Biferale, L.; Sbragaglia, M.; Succi, S.; Toschi, F.
2004-10-01
A lattice Boltzmann scheme simulating the dynamics of shell models of turbulence is developed. The influence of high-order kinetic modes (ghosts) on the dissipative properties of turbulence dynamics is studied. It is analytically found that when ghost fields relax on the same timescale as the hydrodynamic ones, their major effect is a net enhancement of the fluid viscosity. The bare fluid viscosity is recovered by letting ghost fields evolve on a much longer timescale. Analytical results are borne out by high-resolution numerical simulations. These simulations indicate that the hydrodynamic manifold is very robust towards large fluctuations of non-hydrodynamic fields.
Simulation of Tailrace Hydrodynamics Using Computational Fluid Dynamics Models
Cook, Christopher B.; Richmond, Marshall C.
2001-05-01
This report investigates the feasibility of using computational fluid dynamics (CFD) tools to investigate hydrodynamic flow fields surrounding the tailrace zone below large hydraulic structures. Previous and ongoing studies using CFD tools to simulate gradually varied flow with multiple constituents and forebay/intake hydrodynamics have shown that CFD tools can provide valuable information for hydraulic and biological evaluation of fish passage near hydraulic structures. These studies however are incapable of simulating the rapidly varying flow fields that involving breakup of the free-surface, such as those through and below high flow outfalls and spillways. Although the use of CFD tools for these types of flow are still an active area of research, initial applications discussed in this report show that these tools are capable of simulating the primary features of these highly transient flow fields.
NASA Technical Reports Server (NTRS)
Khavaran, Abbas; Krejsa, Eugene A.; Kim, Chan M.
1991-01-01
The turbulent mixing noise of a supersonic jet is calculated for a round convergent-divergent nozzle at the design pressure ratio. Aerodynamic computations are performed using the PARC code with a k-epsilon turbulence model. Lighthill's acoustic analogy combined with Ribner's assumption is adopted. The acoustics solution is based upon the methodology followed by GE in the MGB code. The source correlation function is expressed as a linear combination of second-order tensors. Assuming separable second-order correlations and incorporating Batchelor's isotropic turbulence model, the source term was calculated from the kinetic energy of turbulence. A Gaussian distribution for the time-delay of correlation was introduced. The computational fluid dynamics (CFD) solution was used to obtain the source strength as well as the characteristic time-delay of correlation. The effect of sound/flow interaction was incorporated using the high frequency asymptotic solution to Lilley's equation for axisymmetric geometries. Acoustic results include sound pressure level directivity and spectra at different polar angles. The aerodynamic and acoustic results demonstrate favorable agreement with experimental data.
Zhuang, Jinda; Ju, Y Sungtaek
2015-09-22
The deformation and rupture of axisymmetric liquid bridges being stretched between two fully wetted coaxial disks are studied experimentally and theoretically. We numerically solve the time-dependent Navier-Stokes equations while tracking the deformation of the liquid-air interface using the arbitrary Lagrangian-Eulerian (ALE) moving mesh method to fully account for the effects of inertia and viscous forces on bridge dynamics. The effects of the stretching velocity, liquid properties, and liquid volume on the dynamics of liquid bridges are systematically investigated to provide direct experimental validation of our numerical model for stretching velocities as high as 3 m/s. The Ohnesorge number (Oh) of liquid bridges is a primary factor governing the dynamics of liquid bridge rupture, especially the dependence of the rupture distance on the stretching velocity. The rupture distance generally increases with the stretching velocity, far in excess of the static stability limit. For bridges with low Ohnesorge numbers, however, the rupture distance stay nearly constant or decreases with the stretching velocity within certain velocity windows due to the relative rupture position switching and the thread shape change. Our work provides an experimentally validated modeling approach and experimental data to help establish foundation for systematic further studies and applications of liquid bridges.
NASA Astrophysics Data System (ADS)
Khavaran, A.; Krejsa, E. A.; Kim, C. M.
1992-01-01
The turbulent mixing noise of a supersonic jet is calculated for a round convergent-divergent nozzle at the design pressure ratio. Aerodynamic computations are performed using the PARC code with a k-epsilon turbulence model. Lighthill's acoustic analogy combined with Ribner's assumption is adopted. The acoustics solution is based upon the methodology followed by GE in the MGB code. The source correlation function is expressed as a linear combination of second-order tensors. Assuming separable second-order correlations and incorporating Batchelor's isotropic turbulence model, the source term was calculated from the kinetic energy of turbulence. A Gaussian distribution for the time-delay of correlation was introduced. The computational fluid dynamics (CFD) solution was used to obtain the source strength as well as the characteristic time-delay of correlation. The effect of sound/flow interaction was incorporated using the high frequency asymptotic solution to Lilley's equation for axisymmetric geometries. Acoustic results include sound pressure level directivity and spectra at different polar angles. The aerodynamic and acoustic results demonstrate favorable agreement with experimental data.
Activity-induced clustering in model dumbbell swimmers: the role of hydrodynamic interactions.
Furukawa, Akira; Marenduzzo, Davide; Cates, Michael E
2014-08-01
Using a fluid-particle dynamics approach, we numerically study the effects of hydrodynamic interactions on the collective dynamics of active suspensions within a simple model for bacterial motility: each microorganism is modeled as a stroke-averaged dumbbell swimmer with prescribed dipolar force pairs. Using both simulations and qualitative arguments, we show that, when the separation between swimmers is comparable to their size, the swimmers' motions are strongly affected by activity-induced hydrodynamic forces. To further understand these effects, we investigate semidilute suspensions of swimmers in the presence of thermal fluctuations. A direct comparison between simulations with and without hydrodynamic interactions shows these to enhance the dynamic clustering at a relatively small volume fraction; with our chosen model the key ingredient for this clustering behavior is hydrodynamic trapping of one swimmer by another, induced by the active forces. Furthermore, the density dependence of the motility (of both the translational and rotational motions) exhibits distinctly different behaviors with and without hydrodynamic interactions; we argue that this is linked to the clustering tendency. Our study illustrates the fact that hydrodynamic interactions not only affect kinetic pathways in active suspensions, but also cause major changes in their steady state properties.
NASA Astrophysics Data System (ADS)
Wang, WeiZong; Yan, Joseph D.; Rong, MingZhe; Murphy, Anthony B.; Spencer, Joseph W.
2013-02-01
The behaviour of a decaying SF6 arc, which is representative of the approach to the final current-zero state of switching arcs in a high-voltage circuit breaker, is theoretically investigated by a two-temperature hydrodynamic model, taking into account the possible departure of the plasma state from local thermodynamic equilibrium (LTE). The model couples the plasma flow with electromagnetic fields in a self-consistent manner. The electrons and heavy species are assumed to have different temperatures. The species composition, thermodynamic properties and transport coefficients of the plasma under non-LTE conditions are calculated from fundamental theory. The model is then applied to a two-dimensional axisymmetric SF6 arc burning in a supersonic nozzle under well-controlled conditions; for this configuration, experimental results are available for comparison. The effect of turbulence is considered using the Prandtl mixing-length model. The edge absorption of the radiation emitted by the arc core is taken into account by a modified net emission coefficient approach. The complete set of conservation equations is discretized and solved using the finite volume method. The evolution of electron and heavy-particle temperatures and the total arc resistance, along with other physical quantities, is carefully analysed and compared with those of the LTE case. It is demonstrated that the electron and heavy-particle temperature diverge at all times in the plasma-cold-flow interaction region, in which strong gas flow exists, and further in the transient current-zero period, in which case the collision energy exchange is ineffective. This study quantitatively analyses the energy exchange mechanisms between electrons and heavy particles in the high-pressure supersonic SF6 arcs and provides the foundation for further theoretical investigation of transient SF6 arc behaviour as the current ramps down to zero in gas-blast circuit breakers.
Hydrodynamic models for slurry bubble column reactors. Fifth technical progress report
Gidaspow, D.
1995-10-01
The objective of this work is to convert our `learning gas-solid-liquid` fluidization model into a predictive design model. The IIT hydrodynamic model computes the phase velocities and the volume fractions of gas, liquid, and particulate phases. Model verification involves a comparison of these computed velocities and volume fractions to experimental values.
Hydrodynamic properties of San Quintin Bay, Baja California: Merging models and observations.
Melaku Canu, Donata; Aveytua-Alcázar, Leslie; Camacho-Ibar, Victor F; Querin, Stefano; Solidoro, Cosimo
2016-07-15
We investigated the physical dynamics of San Quintin Bay, a coastal lagoon located on the Pacific coast of northern Baja California, Mexico. We implemented, validated and used a finite element 2-D hydrodynamic model to characterize the spatial and temporal variability of the hydrodynamic of the bay in response to variability in the tidal regime and in meteorological forcing patterns. Our analysis of general circulation, residual currents, residence times, and tidal propagation delays allowed us to characterize spatial variability in the hydrodynamic basin features. The eulerian water residence time is -on average and under reference conditions- approximately 7days, although this can change significantly by region and season and under different tidal and meteorological conditions. Ocean upwelling events that bring colder waters into the bay mouth affect hydrodynamic properties in all areas of the lagoon and may affect ecological dynamics. A return to pre-upwelling conditions would take approximately 10days. Copyright © 2016 Elsevier Ltd. All rights reserved.
Filling the temporal gap in remote sensing observations by hydrodynamic modelling
NASA Astrophysics Data System (ADS)
Kawka, Marcin; Pitarch, Jaime; Odermatt, Daniel; Heege, Thomas; Schenk, Karin; Hartman, Knut; Bogner, Anke; Wuest, Alfred
2013-04-01
Remote sensing has recently become a powerful tool for water quality monitoring. Satellite-borne remote sensing information about water quality indicators of inland water bodies has limited availability. Due to cloudy weather or satellite instrument unavailability, time periods without remote sensing scenes may vary from several hours to several weeks. This is often unacceptable for operational end users. To overcome this problem we propose an idea of assimilating satellite observations into hydrodynamic model. In our study, we use MODIS-retrieved total suspended matter (TSM) distribution across the lake, processed with the Modular Inversion and Processing System (MIP). This scalar value is a vertically integrated quantity and has to be converted to information about TSM distribution in modeled water column. Besides TSM concentration, also optical penetration depth (z90) can be derived from MODIS satellite images. This quantity sets the lower integration boundary for integrated TSM concentration from the whole water column. Based on field studies with CTD profiler, satellite borne integrated TSM and z90, we reconstruct a TSM profile structure. Reconstructed TSM profiles are systematically (as far as MODIS acquisition is possible) assimilated to hydrodynamic model. Assimilation is based on weighted average between modeled (from Delft3d) and reconstructed (from satellite observation) TSM profiles. Averaging weights come from pixel quality information which is retrieved from satellite image during atmospheric correction. As a study site, Lake Constance has been chosen. Thanks to its large dimensions, it was possible to monitor it using the Moderate Resolution Imaging Spectroradiometer (MODIS). Another advantage of this study site is that in spring Lake Constance experiences also the mixing of inflowing, highly turbid, cold Alpine Rhine water and transparent warmer lake water. This phenomenon is highly related to hydrodynamic (wind induced and density-driven) currents
New York Bight Study. Report 1. Hydrodynamic Modeling
1994-08-01
Study. Report 1, Hydrodynamic mdeling / by Norman W. Scheff ner... Cet alo ] ; prepared for U.S. Army Engineer District, New York. 228 p. iV. ; 28 cm. -H...specify the river boundary condi- tion in this manner, because the head of tide is generally tens of miles up- stream of the river mouth and therefore...including the time for 0MB Nintrcto.s 0704-0188t.r] at .¢rc• .= IR buideriorlh te to verae I our r repons.ewingd instructions, searching existing data
NASA Astrophysics Data System (ADS)
Yamazaki, D.
2015-12-01
Global river routine models have been developed for representing freshwater discharge from land to ocean in Earth System Models. At the beginning, global river models had simulated river discharge along a prescribed river network map by using a linear-reservoir assumption. Recently, in parallel with advancement of remote sensing and computational powers, many advanced global river models have started to represent floodplain inundation assuming sub-grid floodplain topography. Some of them further pursue physically-appropriate representation of river and floodplain dynamics, and succeeded to utilize "hydrodynamic flow equations" to realistically simulate channel/floodplain and upstream/downstream interactions. State-of-the-art global river hydrodynamic models can well reproduce flood stage (e.g. inundated areas and water levels) in addition to river discharge. Flood stage simulation by global river models can be potentially coupled with land surface processes in Earth System Models. For example, evaporation from inundated water area is not negligible for land-atmosphere interactions in arid areas (such as the Niger River). Surface water level and ground water level are correlated each other in flat topography, and this interaction could dominate wetting and drying of many small lakes in flatland and could also affect biogeochemical processes in these lakes. These land/surface water interactions had not been implemented in Earth System Models but they have potential impact on the global climate and carbon cycle. In the AGU presentation, recent advancements of global river hydrodynamic modelling, including super-high resolution river topography datasets, will be introduces. The potential applications of river and surface water modules within Earth System Models will be also discussed.
NASA Astrophysics Data System (ADS)
Chu, Huaqiang; Consalvi, Jean-Louis; Gu, Mingyan; Liu, Fengshan
2017-08-01
Radiation heat transfer in axisymmetric jet diffusion flames under conditions relevant to oxygen-enriched combustion at total pressures of 1, 10, 20, and 30 atm was calculated using several gas radiation models: line-by-line (LBL), narrow-band correlated-k (NBCK), wide-band correlated-k (WBCK), full-spectrum correlated-k (FSCK), spectral-line based weight-sum-of-gray-gases (SLW), and weight-sum-of-gray-gases (WSGG). An optimized NBCK model, an optimized FSCK model, and a WBCK model were proposed and evaluated. The LBL results are used as the benchmark solution in the evaluation of other gas radiation models. The optimized NBCK model and the optimized FSCK model are much more computationally efficient than the standard implementation of these models with very little loss in accuracy. The NBCK, WBCK, and FSCK models are accurate and their normalized errors in both the radiative source term and radiative flux remain less than about 7% and display essentially no dependence on the total pressure. Whatever the pressure considered, the FSCK is found to provide accurate predictions by considering only 10 Gauss points. For the same number of gray gases, the SLW is less accurate than the FSCK, especially at pressures higher than the atmospheric pressure. However, its accuracy can be significantly improved to reach that of the FSCKby increasing the number of gray gases. The accuracy of WSGG models deteriorates somewhat with increasing the total pressure in the prediction of radiative heat flux, though it displays no significant dependence on the total pressure in the calculation of the radiative source term. The spectral line broadening has a non-negligible influence on radiative heat transfer in the jet diffusion flame. The somewhat increased inaccuracy of the WSGG model with increasing the total pressure is at least partially due to the application of the model parameters derived at 1 atm to high pressures. The normalized errors of WSGG are about 10 to 20%. The optimized
Interface-tracking electro-hydrodynamic model for droplet coalescence
NASA Astrophysics Data System (ADS)
Crowl Erickson, Lindsay; Noble, David
2012-11-01
Many fluid-based technologies rely on electrical fields to control the motion of droplets, e.g. micro-fluidic devices for high-speed droplet sorting, solution separation for chemical detectors, and purification of biodiesel fuel. Precise control over droplets is crucial to these applications. However, electric fields can induce complex and unpredictable fluid dynamics. Recent experiments (Ristenpart et al. 2009) have demonstrated that oppositely charged droplets bounce rather than coalesce in the presence of strong electric fields. Analytic hydrodynamic approximations for interfaces become invalid near coalescence, and therefore detailed numerical simulations are necessary. We present a conformal decomposition finite element (CDFEM) interface-tracking method for two-phase flow to demonstrate electro-coalescence. CDFEM is a sharp interface method that decomposes elements along fluid-fluid boundaries and uses a level set function to represent the interface. The electro-hydrodynamic equations solved allow for convection of charge and charge accumulation at the interface, both of which may be important factors for the pinch-off dynamics in this parameter regime.
Hydrodynamical Simulations of Colliding Jets: Modeling 3C 75
NASA Astrophysics Data System (ADS)
Molnar, S. M.; Schive, H.-Y.; Birkinshaw, M.; Chiueh, T.; Musoke, G.; Young, A. J.
2017-01-01
Radio observations suggest that 3C 75, located in the dumbbell shaped galaxy NGC 1128 at the center of Abell 400, hosts two colliding jets. Motivated by this source, we perform three-dimensional hydrodynamical simulations using a modified version of the GPU-accelerated Adaptive-MEsh-Refinement hydrodynamical parallel code (GAMER) to study colliding extragalactic jets. We find that colliding jets can be cast into two categories: (1) bouncing jets, in which case the jets bounce off each other keeping their identities, and (2) merging jets, when only one jet emerges from the collision. Under some conditions the interaction causes the jets to break up into oscillating filaments of opposite helicity, with consequences for their downstream stability. When one jet is significantly faster than the other and the impact parameter is small, the jets merge; the faster jet takes over the slower one. In the case of merging jets, the oscillations of the filaments, in projection, may show a feature that resembles a double helix, similar to the radio image of 3C 75. Thus we interpret the morphology of 3C 75 as a consequence of the collision of two jets with distinctly different speeds at a small impact parameter, with the faster jet breaking up into two oscillating filaments.
Topics in two-dimensional and axisymmetric vortex dynamics
NASA Astrophysics Data System (ADS)
Luithardt, Harry Hermann
1997-09-01
This work is composed of two independent parts whose common theme is the analysis of complex hydrodynamic phenomenon through the development of discrete vortex models. The first part investigates a new chaotic scattering phenomenon in two dimensions arising from the interaction of a thin vortex tube with a moving bluff body. Possible relevance to real hydrodynamic systems is established through development and implementation of a mixed finite difference-spectral algorithm applied to the direct simulation of Navier-Stokes equation around a cylindrical body for both inviscid and viscous boundary conditions. Small scale near boundary dynamics are resolved through employment of a radial stretching induced by a logarithmic coordinate transformation. Resulting simulations yielded an unexpectedly strong agreement between a point vortex model and the evolution of an initially Gaussian vortex patch. Completely new dynamics resulted only from initial conditions for large vortex patches which exhibit complex spatiotemporal dynamics. A new point vortex model was developed to explain this robustness of vortex patches. Pairs of point vortices were chosen. The guiding center of a pair corresponds to the previous single vortex, and the relative dynamics models internal degrees of freedom of a vortex patch. Resulting perturbation analysis and numerics reveals probable theoretical explanations of behavior observed in the CFD study. Further important parameters related to initial distribution of vorticity in patches are identified. Additional work done pertains to coherent structure formation in axisymmetric starting jets. A vortex sheet model for an impulsively started jet was decomposed into discrete, singular ideal vortex rings whose dynamical equations were derived from a Hamiltonian formalism. This motivated introduction of a novel symplectic integration scheme to avoid numerical stiffness. Detailed numerical studies show that simulations do not require artificial smoothing
Jean, Ronald P; Chen, Christopher S; Spector, Alexander A
2005-08-01
Endothelial cells possess a mechanical network connecting adhesions on the basal surface, the cytoskeleton, and the nucleus. Transmission of force at adhesions via this pathway can deform the nucleus, ultimately resulting in an alteration of gene expression and other cellular changes (mechanotransduction). Previously, we measured cell adhesion area and apparent nuclear stretch during endothelial cell rounding. Here, we reconstruct the stress map of the nucleus from the observed strains using finite-element modeling. To simulate the disruption of adhesions, we prescribe displacement boundary conditions at the basal surface of the axisymmetric model cell. We consider different scenarios of the cytoskeletal arrangement, and represent the cytoskeleton as either discrete fibers or as an effective homogeneous layer When the nucleus is in the initial (spread) state, cytoskeletal tension holds the nucleus in an elongated, ellipsoidal configuration. Loss of cytoskeletal tension during cell rounding is represented by reactive forces acting on the nucleus in the model. In our simulations of cell rounding, we found that, for both representations of the cytoskeleton, the loss of cytoskeletal tension contributed more to the observed nuclear deformation than passive properties. Since the simulations make no assumption about the heterogeneity of the nucleus, the stress components both within and on the surface of the nucleus were calculated. The nuclear stress map showed that the nucleus experiences stress on the order of magnitude that can be significant for the function of DNA molecules and chromatin fibers. This study of endothelial cell mechanobiology suggests the possibility that mechanotransduction could result, in part, from nuclear deformation, and may be relevant to angiogenesis, wound healing, and endothelial barrier dysfunction.
Jonkman, J. M.; Sclavounos, P. D.
2006-01-01
Aeroelastic simulation tools are routinely used to design and analyze onshore wind turbines, in order to obtain cost effective machines that achieve favorable performance while maintaining structural integrity. These tools employ sophisticated models of wind-inflow; aerodynamic, gravitational, and inertial loading of the rotor, nacelle, and tower; elastic effects within and between components; and mechanical actuation and electrical responses of the generator and of control and protection systems. For offshore wind turbines, additional models of the hydrodynamic loading in regular and irregular seas, the dynamic coupling between the support platform motions and wind turbine motions, and the dynamic characterization of mooring systems for compliant floating platforms are also important. Hydrodynamic loading includes contributions from hydrostatics, wave radiation, and wave scattering, including free surface memory effects. The integration of all of these models into comprehensive simulation tools, capable of modeling the fully coupled aeroelastic and hydrodynamic responses of floating offshore wind turbines, is presented.
Jin, Chao; Ren, Carolyn L; Emelko, Monica B
2016-04-19
It is widely believed that media surface roughness enhances particle deposition-numerous, but inconsistent, examples of this effect have been reported. Here, a new mathematical framework describing the effects of hydrodynamics and interaction forces on particle deposition on rough spherical collectors in absence of an energy barrier was developed and validated. In addition to quantifying DLVO force, the model includes improved descriptions of flow field profiles and hydrodynamic retardation functions. This work demonstrates that hydrodynamic effects can significantly alter particle deposition relative to expectations when only the DLVO force is considered. Moreover, the combined effects of hydrodynamics and interaction forces on particle deposition on rough, spherical media are not additive, but synergistic. Notably, the developed model's particle deposition predictions are in closer agreement with experimental observations than those from current models, demonstrating the importance of inclusion of roughness impacts in particle deposition description/simulation. Consideration of hydrodynamic contributions to particle deposition may help to explain discrepancies between model-based expectations and experimental outcomes and improve descriptions of particle deposition during physicochemical filtration in systems with nonsmooth collector surfaces.
Status of hydrodynamic technology as related to model tests of high speed marine vehicles
NASA Astrophysics Data System (ADS)
Wilson, R. A.; Savitsky, D.; Stevens, M. J.; Balquet, R. J.; Muller-Graf, B.; Murakami, T.; Prokohorov, S. D.; Vanoossanen, P.
1981-07-01
The High Speed Marine Vehicle Panel of the 16th International Towing Tank Conference prepared hydrodynamic technology status reports related to model tank tests of SWATH, semidisplacement round bilge hulls, planing hulls, semisubmerged hydrofoils, surface effect ships, and air cushion vehicles. Each status report, plus the results of an initial survey of worldwide towing tanks conducting model experiments of high speed vessels, are contained herein. Hydrodynamic problems related to model testing and the full-scale extrapolation of the data for these vehicle types are also presented.
Numerical modeling of ocean hydrodynamics with variational assimilation of observational data
NASA Astrophysics Data System (ADS)
Zalesny, V. B.; Agoshkov, V. I.; Shutyaev, V. P.; Le Dimet, F.; Ivchenko, B. O.
2016-07-01
Models and methods of the numerical modeling of ocean hydrodynamics dating back to the pioneering works of A.S. Sarkisyan are considered, with emphasis on the formulation of problems and algorithms of mathematical modeling and the four-dimensional variational assimilation of observational data. An algorithm is proposed for studying the sensitivity of the optimal solution to observational data errors in a seasurface temperature assimilation problem in order to retrieve heat fluxes on the surface. An example of a solution of the optimal problem of the World Ocean hydrodynamics with the assimilation of climatic temperature and salinity observations is offered.
Honarpour, M. M.; Schatzinger, R. A.; Szpakiewicz, M. J.; Jackson, S. R.; Sharma, B.; Tomutsa, L.; Chang, M. M.
1990-01-01
A comprehensive, multidisciplinary, stepwise methodology is developed for constructing and integration geological and engineering information for predicting petroleum reservoir performance. This methodology is based on our experience in characterizing shallow marine reservoirs, but it should also apply to other deposystems. The methodology is presented as Part 1 of this report. Three major tasks that must be studied to facilitate a systematic approach for constructing a predictive hydrodynamic model for petroleum reservoirs are addressed: (1) data collection, organization, evaluation, and integration; (2) hydrodynamic model construction and verification; and (3) prediction and ranking of reservoir parameters by numerical simulation using data derived from the model. 39 refs., 62 figs., 13 tabs.
NASA Technical Reports Server (NTRS)
Moore, W.; Schubert, Gerald; Sandwell, David T.
1992-01-01
Magellan altimetry has revealed that many coronae on Venus have trenches or moats around their peripheries and rises outboard of the trenches. This trench/outer rise topographic signature is generally associated with the tectonic annulus of the corona. Sandwell and Schubert have interpreted the trench/outer rise topography and the associated tectonic annulus around coronae to be the result of elastic bending of the Venus lithosphere (though the tectonic structures are consequences of inelastic deformation of the lithosphere). They used two-dimensional elastic plate flexure theory to fit topographic profiles across a number of large coronae and inferred elastic lithosphere thicknesses between about 15 and 40 km, similar to inferred values of elastic thickness for the Earth's lithosphere at subduction zones around the Pacific Ocean. Here, we report the results of using axisymmetric elastic flexure theory for the deformation of thin spherical shell plates to interpret the trench/outer rise topography of the large coronae modeled by Sandwell and Schubert and of coronae as small as 250 km in diameter. In the case of a corona only a few hundred kilometers in diameter, the model accounts for the small planform radius of the moat and the nonradial orientation of altimetric traces across the corona. By fitting the flexural topography of coronae we determine the elastic thickness and loading necessary to account for the observed flexure. We calculate the associated bending moment and determine whether the corona interior topographic load can provide the required moment. We also calculate surface stresses and compare the stress distribution with the location of annular tectonic features.
Slow hydrodynamic regime to model B supergiant winds
NASA Astrophysics Data System (ADS)
Venero, R. O. J.; Cidale, L. S.; Cure, M.; Haucke, M.
2017-10-01
Current hydrodynamic solutions for the winds of early-type stars are obtained from the theory of rotating stars with radiation-driven winds. These solutions are separated into two main branches: the fast solution and the slow solutions. The first set is the standard CAK solution, while the second set corresponds to a group of solutions with still poorly known properties. In this work we study the properties of the slow wind regime derived for different values of the line force parameters, and compute the resulting line profiles. Then we fit our synthetic line profiles with observed ones, in order to evaluate the ability of the slow solution to represent the variety of features observed in line profiles originated along the winds. We find that the winds of B supergiants can be well-represented by the slow regime, a result that could give new insights into the true nature of the outflows in early-type stars.
On the Possibility of a Hydrodynamic Model of the Electron
Pekeris, C. L.
1975-01-01
We explore the possibility that the mutual repulsive forces of a uniformly charged sphere could be kept in balance dynamically by a steady circulation of the material, which is assumed to be a nonconducting perfect fluid of uniform density. An exact solution is obtained of Maxwell's equations and of the hydrodynamic equations in the nonrelativistic approximation, which satisfies the boundary conditions on the surface of the sphere. In this solution all the components of the velocity and of the magnetic field are found to vanish on the surface, but not the electric field. The pressure can also be made to vanish on the surface, but in the interior it turns out to be negative, which makes the present solution unacceptable. PMID:16592245
Wuchterl, G. )
1991-05-01
A spherically symmetric protoplanetary model with a growing rigid core and a gaseous envelope of solar composition is used to investigate the character and evolution of the nucleated instability; the model equations formulated are used to follow the static evolution of a protogiant planet in the 'Kyoto' solar nebula, lying at Jupiter's solar distance, to its critical core mass. Convective energy transfer has been formulated for inclusion in implicit radiation hydrodynamical computations. It is established that collapse need not occur at the critical mass, which in agreement with earlier investigations is found to be of the order of 13.1 earth masses. This model is then used as an initial condition for a radiation hydrodynamical calculation of the nucleated instability. It is found that nonlinear hydrodynamic waves are excited by a kappa mechanism, and that an outflow is driven. 56 refs.
Survey of Multi-Material Closure Models in 1D Lagrangian Hydrodynamics
Maeng, Jungyeoul Brad; Hyde, David Andrew Bulloch
2015-07-28
Accurately treating the coupled sub-cell thermodynamics of computational cells containing multiple materials is an inevitable problem in hydrodynamics simulations, whether due to initial configurations or evolutions of the materials and computational mesh. When solving the hydrodynamics equations within a multi-material cell, we make the assumption of a single velocity field for the entire computational domain, which necessitates the addition of a closure model to attempt to resolve the behavior of the multi-material cells’ constituents. In conjunction with a 1D Lagrangian hydrodynamics code, we present a variety of both the popular as well as more recently proposed multi-material closure models and survey their performances across a spectrum of examples. We consider standard verification tests as well as practical examples using combinations of fluid, solid, and composite constituents within multi-material mixtures. Our survey provides insights into the advantages and disadvantages of various multi-material closure models in different problem configurations.
Bypassing Cowling's Theorem in Axisymmetric Fluid Dynamos
Gissinger, Christophe; Fauve, Stephan; Dormy, Emmanuel
2008-10-03
We present a numerical study of the magnetic field generated by an axisymmetrically forced flow in a spherical domain. We show that, even in the absence of nonaxisymmetric velocity fluctuations, a mean magnetic field with a dominant axisymmetric dipolar component can be generated via a secondary bifurcation from an equatorial dipole. We understand the dynamical behaviors that result from the interaction of equatorial and axial dipolar modes using simple model equations for their amplitudes derived from symmetry arguments.
Numerical modeling of hydrodynamic changes due to coastal reclamation projects in Xiamen Bay, China
NASA Astrophysics Data System (ADS)
Wang, Jia; Hong, Huasheng; Zhou, Lumin; Hu, Jianyu; Jiang, Yuwu
2013-03-01
Xiamen Bay in South China has experienced extensive coastal exploitation since the 1950s, resulting in some severe environmental problems. Local authorities now have completed or are implementing many environmental restoration projects. Evaluating the cumulative impact of exploitation and restoration activities on the environment is a complicated multi-disciplinary problem. However, hydrodynamic changes in the bay caused by such coastal projects can be characterized directly and definitively through numerical modeling. This paper assesses the cumulative effect of coastal projects on the hydrodynamic setting using a high-resolution numerical modeling method that makes use of tidal current speeds and the tidal prism as two hydrodynamic indices. Changes in tidal velocity and the characteristics of the tidal prism show that hydrodynamic conditions have declined from 1938 to 2007 in the full-tide area. The tidal current speed and tidal prism have decreased by 40% in the western part of the bay and 20% in the eastern part of the bay. Because of the linear relationship between tidal prism and area, the degraded hydrodynamic conditions are anticipated to be restored to 1972 levels following the completion of current and proposed restoration projects, i.e. 33% and 15% decrease in the hydrodynamic conditions of 1938 for the western and eastern parts of the bay, respectively. The results indicate that hydrodynamic conditions can be restored to some extent with the implementation of a sustainable coastal development plan, although a full reversal of conditions is not possible. To fully assess the environmental changes in a region, more indices, e.g., water quality and ecosystem parameters, should be considered in future evaluations.
NASA Astrophysics Data System (ADS)
Humphreys, D. A.; Ferron, J. R.; Leuer, J. A.; Walker, M. L.; Welander, A. S.
2003-10-01
Linear, perturbed equilibrium plasma response models can accurately represent the experimental response of tokamak plasmas to applied fields [A. Coutlis, et al., Nucl. Fusion 39, 663 (1999)]. However, agreement between experiment and model is much better when average flux over the plasma, rather than at each fluid element, is conserved [P. Vyas, et al., Nucl. Fusion 38, 1043 (1998)]. The close experimental agreement of average flux-conserving models is consistent with approximating field penetration effects produced by finite plasma resistivity, particularly in the edge region. We report on the development of nonrigid linear plasma response models which include finite local plasma resistivity in order to more accurately represent the dynamic response due to this field penetration. Such response models are expected to be important for designing profile control algorithms in advanced tokamaks. Accounting for finite plasma resistivity is also important in designing multivariable integrated controllers which must simultaneously regulate plasma shape and plasma current. Consequences of including resisitivity will be illustrated and comparisons with DIII-D experimental plasma responses will be made.
NASA Astrophysics Data System (ADS)
Ali, Farhad; Sheikh, Nadeem Ahmad; Khan, Ilyas; Saqib, Muhammad
2017-02-01
The effects of magnetohydrodynamics on the blood flow when blood is represented as a Casson fluid, along with magnetic particles in a horizontal cylinder is studied. The flow is due to an oscillating pressure gradient. The Laplace and finite Hankel transforms are used to obtain the closed form solutions of the fractional partial differential equations. Effects of various parameters on the flow of both blood and magnetic particles are shown graphically. The analysis shows that, the model with fractional order derivatives bring a remarkable changes as compared to the ordinary model. The study highlights that applied magnetic field reduces the velocities of both the blood and magnetic particles.
Honzík, Petr; Podkovskiy, Alexey; Durand, Stéphane; Joly, Nicolas; Bruneau, Michel
2013-11-01
The main purpose of the paper is to contribute at presenting an analytical and a numerical modeling which would be relevant for interpreting the couplings between a circular membrane, a peripheral cavity having the same external radius as the membrane, and a thin air gap (with a geometrical discontinuity between them), and then to characterize small scale electrostatic receivers and to propose procedures that could be suitable for fitting adjustable parameters to achieve optimal behavior in terms of sensitivity and bandwidth expected. Therefore, comparison between these theoretical methods and characterization of several shapes is dealt with, which show that the models would be appropriate to address the design of such transducers.
USING TWO-DIMENSIONAL HYDRODYNAMIC MODELS AT SCALES OF ECOLOGICAL IMPORTANCE. (R825760)
Modeling of flow features that are important in assessing stream habitat conditions has been a long-standing interest of stream biologists. Recently, they have begun examining the usefulness of two-dimensional (2-D) hydrodynamic models in attaining this objective. Current modelin...
An Evaluation of Boundary Condition Specification for a Littoral Hydrodynamic Model
2011-09-01
hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and...information, including suggestions for reducing the burden, to the Department of Defense, Executive Services and Communications Directorate (0704-0188...hydrodynamic models provide data to the littoral model boundaries as time series. The information can be interpolated in time and horizontal and
Blow-up of solutions to quantum hydrodynamic models in half space
NASA Astrophysics Data System (ADS)
Guo, Boling; Wang, Guangwu
2017-03-01
In this paper, we prove that any smooth solutions of quantum hydrodynamic model which satisfies suitable conditions will blow up in finite time in half space. This model can be considered as the compressible Euler equation with quantum potential. The main ideal is based on the construction of energy inequality.
USING TWO-DIMENSIONAL HYDRODYNAMIC MODELS AT SCALES OF ECOLOGICAL IMPORTANCE. (R825760)
Modeling of flow features that are important in assessing stream habitat conditions has been a long-standing interest of stream biologists. Recently, they have begun examining the usefulness of two-dimensional (2-D) hydrodynamic models in attaining this objective. Current modelin...
Hydrodynamic Modeling Analysis of Union Slough Restoration Project in Snohomish River, Washington
Yang, Zhaoqing; Wang, Taiping
2010-12-20
A modeling study was conducted to evaluate additional project design scenarios at the Union Slough restoration/mitigation site during low tide and to provide recommendations for finish-grade elevations to achieve desired drainage. This was accomplished using the Snohomish River hydrodynamic model developed previously by PNNL.
NASA Astrophysics Data System (ADS)
Kulikov, Igor; Chernykh, Igor; Tutukov, Alexander
2016-05-01
This paper presents a new hydrodynamic model of interacting galaxies based on the joint solution of multicomponent hydrodynamic equations, first moments of the collisionless Boltzmann equation and the Poisson equation for gravity. Using this model, it is possible to formulate a unified numerical method for solving hyperbolic equations. This numerical method has been implemented for hybrid supercomputers with Intel Xeon Phi accelerators. The collision of spiral and disk galaxies considering the star formation process, supernova feedback and molecular hydrogen formation is shown as a simulation result.
Hydrodynamics of rapidly rotating superfluid neutron stars with mutual friction
NASA Astrophysics Data System (ADS)
Passamonti, A.; Andersson, N.
2011-05-01
We study the hydrodynamics of superfluid neutron stars, focusing on the nature of the oscillation spectrum, the effect of mutual friction force on the oscillations and the spin-up phase of pulsar glitches. We linearize the dynamical equations of a Newtonian two-fluid model for rapidly rotating backgrounds. In the axisymmetric equilibrium configurations, the two-fluid components corotate and are in β-equilibrium. We use analytical equations of state that generate stratified and non-stratified stellar models, which enable us to study the coupling between the dynamical degrees of freedom of the system. By means of time-evolutions of the linearized dynamical equations, we determine the spectrum of axisymmetric and non-axisymmetric oscillation modes, accounting for the contribution of the gravitational potential perturbations, that is, without adopting the Cowling approximation. We study the mutual friction damping of the superfluid oscillations and consider the effects of the non-dissipative part of the mutual friction force on the mode frequencies. We also provide technical details and relevant tests for the hydrodynamical model of pulsar glitches discussed by Sidery, Passamonti & Andersson. In particular, we describe the method used to generate the initial data that mimic the pre-glitch state and derive the equations that are used to extract the gravitational-wave signal.
WASP4, a hydrodynamic and water-quality model - model theory, user's manual, and programmer's guide
Ambrose, R.B.; Wool, T.A.; Connolly, J.P.; Schanz, R.W.
1988-01-01
The Water Quality Analysis Simulation Program Version 4 (WASP4) is a dynamic compartment-modeling system that can be used to analyze a variety of water-quality problems in a diverse set of water bodies. WASP4 simulates the transport and transformation of conventional and toxic pollutants in the water column and benthos of ponds, streams, lakes, reservoirs, rivers, estuaries, and coastal waters. The WASP4 modeling system covers four major subjects--hydrodynamics, conservative mass transport, eutrophication-dissolved oxygen kinetics, and toxic chemical-sediment dynamics. The WASP4 modeling system consists of two stand-alone computer programs, DYNHYD4 and WASP4, that can be run in conjunction or separately. The hydrodynamic program, DYNHYD4, simulates the movement of water and the water quality program, WASP4, simulates the movement and interaction of pollutants within the water. The latter program is supplied with two kinetic submodels to simulate two of the major classes of water-quality problems--conventional pollution (dissolved oxygen, biochemical oxygen demand, nutrients, and eutrophication) and toxic pollution (organic chemicals, heavy metals, and sediment). The substitution of either sub-model constitutes the models EUTRO4 and TOXI4, respectively.
Adiabatic model of field reversal by fast ions in an axisymmetric open trap
Tsidulko, Yu. A.
2016-06-15
A model of field reversal by fast ions has been developed under the assumption of preservation of fast-ion adiabatic invariants. Analytical solutions obtained in the approximation of a narrow fast-ion layer and numerical solutions to the evolutionary problem are presented. The solutions demonstrate the process of formation of a field reversed configuration with parameters close to those of the planned experiment.
NASA Astrophysics Data System (ADS)
Steffen, W.; Koning, N.
2017-07-01
We demonstrate the potential for research and outreach of mixed polygon and hydrodynamic modeling and multi-waveband rendering in the interactive 3-D astrophysical virtual laboratory Shape. In 3-D special effects and animation software for the mass media, computer graphics techniques that mix polygon and numerical hydrodynamics have become common place. In astrophysics, however, interactive modeling with polygon structures has only become available with the software Shape. Numerical hydrodynamic simulations and their visualization are usually separate, while in Shape it is integrated with the polygon modeling approach that requires no programming by the user. With two generic examples, we demonstrate that research and outreach modeling can be achieved with techniques similar to those used in the media industry with the added capability for physical rendering at any wavelength band, yielding more realistic radiation modeling. Furthermore, we show how the hydrodynamics and the polygon mesh modeling can be mixed to achieve results that are superior to those obtained using either one of these modeling techniques alone.
A first computational framework for integrated hydrologic-hydrodynamic inundation modelling
NASA Astrophysics Data System (ADS)
Hoch, Jannis; Baart, Fedor; Neal, Jeffrey; van Beek, Rens; Winsemius, Hessel; Bates, Paul; Bierkens, Marc
2017-04-01
To provide detailed flood hazard and risk estimates for current and future conditions, advanced modelling approaches are required. Currently, many approaches are however built upon specific hydrologic or hydrodynamic model routines. By applying these routines in stand-alone mode important processes cannot accurately be described. For instance, global hydrologic models (GHM) run at coarse spatial resolution which does not identify locally relevant flood hazard information. Moreover, hydrologic models generally focus on correct computations of water balances, but employ less sophisticated routing schemes such as the kinematic wave approximation. Hydrodynamic models, on the other side, excel in the computations of open water flow dynamics, but are highly dependent on specific runoff or observed discharge for their input. In most cases hydrodynamic models are forced by applying discharge at the boundaries and thus cannot account for water sources within the model domain. Thus, discharge and inundation dynamics at reaches not fed by upstream boundaries cannot be modelled. In a recent study, Hoch et al. (HESS, 2017) coupled the GHM PCR-GLOBWB with the hydrodynamic model Delft3D Flexible Mesh. A core element of this study was that both models were connected on a cell-by-cell basis which allows for direct hydrologic forcing within the hydrodynamic model domain. The means for such model coupling is the Basic Model Interface (BMI) which provides a set of functions to directly access model variables. Model results showed that discharge simulations can profit from model coupling as their accuracy is higher compared to stand-alone runs. Model results of a coupled simulation clearly depend on the quality of the individual models. Depending on purpose, location or simply the models at hand, it would be worthwhile to allow a wider range of models to be coupled. As a first step, we present a framework which allows coupling of PCR-GLOBWB to both Delft3D Flexible Mesh and LISFLOOD
Two-fluid model of the pulsar magnetosphere represented as an axisymmetric force-free dipole
NASA Astrophysics Data System (ADS)
Petrova, S. A.
2017-05-01
Based on the exact dipolar solution of the pulsar equation the self-consistent two-fluid model of the pulsar magnetosphere is developed. We concentrate on the low-mass limit of the model, taking into account the radiation damping. As a result, we obtain the particle distributions sustaining the dipolar force-free configuration of the pulsar magnetosphere in case of a slight velocity shear of the electron and positron components. Over most part of the force-free region, the particles follow the poloidal magnetic field lines, with the azimuthal velocities being small. Close to the Y-point, however, the particle motion is chiefly azimuthal and the Lorentz-factor grows unrestrictedly. This may result in the very-high-energy emission from the vicinity of the Y-point and may also imply the magnetocentrifugal formation of a jet. As for the first-order quantities, the longitudinal accelerating electric field is found to change the sign, hinting at coexistence of the polar and outer gaps. Besides that, the components of the plasma conductivity tensor are derived and the low-mass analogue of the pulsar equation is formulated as well.
NASA Astrophysics Data System (ADS)
Hooper, Russell; Toose, Matthijs; Macosko, Christopher W.; Derby, Jeffrey J.
2001-12-01
A modified boundary element method (BEM) and the DEVSS-G finite element method (FEM) are applied to model the deformation of a polymeric drop suspended in another fluid subjected to start-up uniaxial extensional flow. The effects of viscoelasticity, via the Oldroyd-B differential model, are considered for the drop phase using both FEM and BEM and for both the drop and matrix phases using FEM. Where possible, results are compared with the linear deformation theory. Consistent predictions are obtained among the BEM, FEM, and linear theory for purely Newtonian systems and between FEM and linear theory for fully viscoelastic systems. FEM and BEM predictions for viscoelastic drops in a Newtonian matrix agree very well at short times but differ at longer times, with worst agreement occurring as critical flow strength is approached. This suggests that the dominant computational advantages held by the BEM over the FEM for this and similar problems may diminish or even disappear when the issue of accuracy is appropriately considered. Fully viscoelastic problems, which are only feasible using the FEM formulation, shed new insight on the role of viscoelasticity of the matrix fluid in drop deformation. Copyright
NASA Astrophysics Data System (ADS)
Tian, Feng; Solomon, Stanley C.; Qian, Liying; Lei, Jiuhou; Roble, Raymond G.
2008-07-01
An electron transport/energy deposition model is expanded to include atomic nitrogen and is coupled with a 1-D hydrodynamic thermosphere model. The coupled model is used to investigate the response of the Earth's thermosphere under extreme solar EUV conditions and is compared with previous studies. It is found that (1) the parameterization of Swartz and Nisbet (1972) underestimates the ambient electron heating by photoelectrons significantly in the upper thermosphere of the Earth under conditions with greater than 3 times the present solar EUV irradiance; (2) the transition of the Earth's thermosphere from a hydrostatic equilibrium regime to a hydrodynamic regime occurs at a smaller solar EUV flux condition when enhanced, more realistic, and self-consistent, ambient electron heating by photoelectrons is accounted for; (3) atomic nitrogen becomes the dominant neutral species in the upper thermosphere (competing against atomic oxygen) under extreme solar EUV conditions, and the electron impact processes of atomic nitrogen are important for both the chemistry and energetics in the corresponding thermosphere/ionosphere; (4) N+ remains a minor ion compared to O+, even when atomic nitrogen dominates the exobase; and (5) adiabatic cooling does not play an important role in electron gas energy budget. These findings highlight the importance of an electron transport/energy deposition model when investigating the thermosphere and ionosphere of terrestrial planets in their early evolutionary stages.
Hydrodynamic interaction between two trapped swimming model micro-organisms.
Matas Navarro, R; Pagonabarraga, I
2010-09-01
We present a theoretical study of the behaviour of two active particles under the action of harmonic traps kept at a fixed distance away from each other. We classify the steady configurations the squirmers develop as a function of their self-propelling velocity and the active stresses the swimmers induce around them. We have further analyzed the stability of such configurations, and have found that the ratio between their self-propelling velocity and the apolar flow generated through active stresses determines whether collinear parallel squirmers or perpendicularly swimming particles moving away from each other are stable. Therefore, there is a close connection between the stable configurations and the active mechanisms leading to the particle self-propulsion. The trap potential does not affect the stability of the configurations; it only modifies some of their relevant time scales. We have also observed the development of characteristic frequencies which should be observable. Finally, we show that the development of the hydrodynamic flows induced by the active particles may be relevant even when its time scale orders of magnitude smaller than the other present characteristic time scales and may destabilize the stable configurations.
Kurihara, Eru; Hay, Todd A.; Ilinskii, Yurii A.; Zabolotskaya, Evgenia A.; Hamilton, Mark F.
2011-01-01
Interaction between acoustically driven or laser-generated bubbles causes the bubble surfaces to deform. Dynamical equations describing the motion of two translating, nominally spherical bubbles undergoing small shape oscillations in a viscous liquid are derived using Lagrangian mechanics. Deformation of the bubble surfaces is taken into account by including quadrupole and octupole perturbations in the spherical-harmonic expansion of the boundary conditions on the bubbles. Quadratic terms in the quadrupole and octupole amplitudes are retained, and surface tension and shear viscosity are included in a consistent manner. A set of eight coupled second-order ordinary differential equations is obtained. Simulation results, obtained by numerical integration of the model equations, exhibit qualitative agreement with experimental observations by predicting the formation of liquid jets. Simulations also suggest that bubble-bubble interactions act to enhance surface mode instability. PMID:22088009
NASA Astrophysics Data System (ADS)
Kraatz, S.; Shields, G. M.; Tang, H.
2011-12-01
In the United States, more than half of bridge failures are attributed to hydraulic factors. Under climate change conditions, in particular sea level rise and stronger hurricanes, coastal bridges could be at risk of damage and destruction due to severe hydrodynamic impacts. In this work, hydrodynamic forces are simulated at a coastal bridge of New York City, and effects of the projected climate change conditions are investigated. In order to investigate the impacts on the bridge, a coupled geophysical fluid dynamic (GFD) and computational fluid dynamics (CFD) approach is employed. The former is used to capture large-scale background currents and the latter is employed to compute the local flow motions. The hybrid approach is realized by a two-way coupling of CFD and GFD models and domain decomposition method implemented with Chimera grids, and FVCOM is used as the GFD model and an unsteady, 3D incompressible flow solver is used as the CFD model. The coupled model approach allows for accurate small-scale simulations of hydrodynamic loads that are not possible by FVCOM alone, and permits for reduced computational effort associated with the CFD model only approach. Illustration will be made on how the hydrodynamics loads change with sea level and storm surge conditions.
Acoustic source model input parameter simulation via hydrodynamic modeling of breaking waves
NASA Astrophysics Data System (ADS)
Means, Steven L.; Szymczak, William G.
2003-10-01
Low-frequency source models for sound generation from breaking waves based on the collective oscillation of an entrained bubble cloud require a number of input parameters, e.g., void fraction, cloud size, etc. The present effort seeks to obtain simulations of these parameters using a volume of fluid type hydrodynamic model (BUB) to simulate the air entrainment processes occurring within a breaking wave. The constraint that mass is conserved and energy is nonincreasing is a unique feature of the BUB code that allows it to handle liquid collisions and violent free surface motions appropriately. Simulations of breakers of both spilling and plunging type will be presented along with their simulated acoustic source model input parameters. The simulations, in the waves reference frame, will be compared against video of breaking waves obtained in a wave tank at the University of Maryland with a high-speed, wave-following digital camera. Relationships between the simulated acoustically relevant hydrodynamic parameters and characteristics of breaker-generated acoustic signatures measured concurrently within the wave tank will be identified. [Work supported by ONR base funding at NRL.
Jashnsaz, Hossein; Al Juboori, Mohammed; Weistuch, Corey; Miller, Nicholas; Nguyen, Tyler; Meyerhoff, Viktoria; McCoy, Bryan; Perkins, Stephanie; Wallgren, Ross; Ray, Bruce D; Tsekouras, Konstantinos; Anderson, Gregory G; Pressé, Steve
2017-03-28
The Gram-negative Bdellovibrio bacteriovorus (BV) is a model bacterial predator that hunts other bacteria and may serve as a living antibiotic. Despite over 50 years since its discovery, it is suggested that BV probably collides into its prey at random. It remains unclear to what degree, if any, BV uses chemical cues to target its prey. The targeted search problem by the predator for its prey in three dimensions is a difficult problem: it requires the predator to sensitively detect prey and forecast its mobile prey's future position on the basis of previously detected signal. Here instead we find that rather than chemically detecting prey, hydrodynamics forces BV into regions high in prey density, thereby improving its odds of a chance collision with prey and ultimately reducing BV's search space for prey. We do so by showing that BV's dynamics are strongly influenced by self-generated hydrodynamic flow fields forcing BV onto surfaces and, for large enough defects on surfaces, forcing BV in orbital motion around these defects. Key experimental controls and calculations recapitulate the hydrodynamic origin of these behaviors. While BV's prey (Escherichia coli) are too small to trap BV in hydrodynamic orbit, the prey are also susceptible to their own hydrodynamic fields, substantially confining them to surfaces and defects where mobile predator and prey density is now dramatically enhanced. Colocalization, driven by hydrodynamics, ultimately reduces BV's search space for prey from three to two dimensions (on surfaces) even down to a single dimension (around defects). We conclude that BV's search for individual prey remains random, as suggested in the literature, but confined, however-by generic hydrodynamic forces-to reduced dimensionality.
A coning motion apparatus for hydrodynamic model testing in a non-planar cross-flow
NASA Astrophysics Data System (ADS)
Johnson, David C.
1989-06-01
As part of continuing research into the flow about slender bodies of revolution, a coning motion apparatus for hydrodynamic model testing was built and demonstrated. This is the first known use of a rotary balance apparatus for external flow hydrodynamic applications. The vorticity shed by the hull and appendages creates a wake field that interacts with the velocity distribution over the vehicle's surface. This in turn effects the surface pressure distribution and thus, when integrated over the body's surface, the total force on the hull/appendage combination. It is this interaction that prevents a closed-form analytic solution to the problem.
Environmental and Water Quality Operational Studies. Physical Modeling of Reservoir Hydrodynamics.
1985-12-01
reservoir flume (re- ferred to as the General Reservoir Hydrodynamic ( GRH ) Facility) located in the Hydraulics Laboratory of WES. In this case, the GRH was...their study. 49. GRH simulation. Data from the WES Generalized Reservoir Hydrodynamic ( GRH ) Facility was used as the prototype to make the second model...prototype comparison. The GRH is 80.0 ft long and 2.85 ft wide with a maximum depth of 3.0 ft. Details of the GRH are provided in Figure 6. 44 2.85 FT
Multi-phase SPH modelling of violent hydrodynamics on GPUs
NASA Astrophysics Data System (ADS)
Mokos, Athanasios; Rogers, Benedict D.; Stansby, Peter K.; Domínguez, José M.
2015-11-01
This paper presents the acceleration of multi-phase smoothed particle hydrodynamics (SPH) using a graphics processing unit (GPU) enabling large numbers of particles (10-20 million) to be simulated on just a single GPU card. With novel hardware architectures such as a GPU, the optimum approach to implement a multi-phase scheme presents some new challenges. Many more particles must be included in the calculation and there are very different speeds of sound in each phase with the largest speed of sound determining the time step. This requires efficient computation. To take full advantage of the hardware acceleration provided by a single GPU for a multi-phase simulation, four different algorithms are investigated: conditional statements, binary operators, separate particle lists and an intermediate global function. Runtime results show that the optimum approach needs to employ separate cell and neighbour lists for each phase. The profiler shows that this approach leads to a reduction in both memory transactions and arithmetic operations giving significant runtime gains. The four different algorithms are compared to the efficiency of the optimised single-phase GPU code, DualSPHysics, for 2-D and 3-D simulations which indicate that the multi-phase functionality has a significant computational overhead. A comparison with an optimised CPU code shows a speed up of an order of magnitude over an OpenMP simulation with 8 threads and two orders of magnitude over a single thread simulation. A demonstration of the multi-phase SPH GPU code is provided by a 3-D dam break case impacting an obstacle. This shows better agreement with experimental results than an equivalent single-phase code. The multi-phase GPU code enables a convergence study to be undertaken on a single GPU with a large number of particles that otherwise would have required large high performance computing resources.
NASA Astrophysics Data System (ADS)
Pahar, Gourabananda; Dhar, Anirban
2017-04-01
A coupled solenoidal Incompressible Smoothed Particle Hydrodynamics (ISPH) model is presented for simulation of sediment displacement in erodible bed. The coupled framework consists of two separate incompressible modules: (a) granular module, (b) fluid module. The granular module considers a friction based rheology model to calculate deviatoric stress components from pressure. The module is validated for Bagnold flow profile and two standardized test cases of sediment avalanching. The fluid module resolves fluid flow inside and outside porous domain. An interaction force pair containing fluid pressure, viscous term and drag force acts as a bridge between two different flow modules. The coupled model is validated against three dambreak flow cases with different initial conditions of movable bed. The simulated results are in good agreement with experimental data. A demonstrative case considering effect of granular column failure under full/partial submergence highlights the capability of the coupled model for application in generalized scenario.
NASA Astrophysics Data System (ADS)
Matheny, A. M.; Bohrer, G.
2013-12-01
Hydraulic limitations are known to control transpiration in forest ecosystems when the soil is drying or when the vapor pressure deficit between the air and stomata is very large, but they can also impact stomatal apertures under conditions of adequate soil moisture and lower evaporative demand. We use the NACP dataset of latent heat flux (LE) measurements and model observations for multiple site/model intercomparisons to evaluate the degree to which currently un-resolved high-frequency (sub-daily) hydrodynamic stresses affect the error in model prediction of latent heat flux. Particularly, we see that models have difficulty resolving the dynamics of intra-daily hysteresis. We hypothesize that this is a result of un-resolved afternoon stomata closure due to hydrodynamic stresses. We find that although no model or stomata parameterization was consistently best or worst in terms of ability to predict LE, errors in model-simulated LE were consistently largest and most variable when soil moisture and VPD were moderate to limiting. This suggests that models have trouble simulating the dynamics that cause stomata to close due to high VPD and moderate to low soil-water availability. Errors in LE occur most frequently when vegetative dynamics dominate. The majority of models tend to underestimate LE in the pre-noon hours and overestimate in the late evening. These diurnal error patterns are consistent with models' diminished ability to accurately simulate the natural hysteresis of transpiration. Nearly all models demonstrate a marked tendency to underestimate the degree of maximum hysteresis which, across all sites studied, is most pronounced during moisture limited conditions. The assumed empirical or semi-empirical coupling between stomatal conductance and soil moisture used by these current models does not resolve the hydrodynamic process of water movement from the soil to the leaves. This approach does not take advantage of advances in our understanding of water flow
ONE-DIMENSIONAL HYDRODYNAMIC/SEDIMENT TRANSPORT MODEL FOR STREAM NETWORKS: TECHNICAL REPORT
This technical report describes a new sediment transport model and the supporting post-processor, and sampling procedures for sediments in streams. Specifically, the following items are described herein:
EFDC1D - This is a new one-dimensional hydrodynamic and sediment tr...
Understanding impacts of climate change on hydrodynamic processes and ecosystem response within the Great Lakes is an important and challenging task. Variability in future climate conditions, uncertainty in rainfall-runoff model forecasts, the potential for land use change, and t...
Ballistic transport in the one-dimensional Hubbard model: The hydrodynamic approach
NASA Astrophysics Data System (ADS)
Ilievski, Enej; De Nardis, Jacopo
2017-08-01
We outline a general formalism of hydrodynamics for quantum systems with multiple particle species which undergo completely elastic scattering. In the thermodynamic limit, the complete kinematic data of the problem consist of the particle content, the dispersion relations, and a universal dressing transformation which accounts for interparticle interactions. We consider quantum integrable models and we focus on the one-dimensional fermionic Hubbard model. By linearizing hydrodynamic equations, we provide exact closed-form expressions for Drude weights, generalized static charge susceptibilities, and charge-current correlators valid on the hydrodynamic scale, represented as integral kernels operating diagonally in the space of mode numbers of thermodynamic excitations. We find that, on hydrodynamic scales, Drude weights manifestly display Onsager reciprocal relations even for generic (i.e., noncanonical) equilibrium states, and establish a generalized detailed balance condition for a general quantum integrable model. We present exact analytic expressions for the general Drude weights in the Hubbard model, and explain how to reconcile different approaches for computing Drude weights from the previous literature.
HOW TO MODEL HYDRODYNAMICS AND RESIDENCE TIMES OF 27 ESTUARIES IN 4 MONTHS
The hydrodynamics and residence times of 27 embayments were modeled during the first year of a project whose goal is to define the relation between nitrogen loadings and ecological responses of 44 systems that range from small to the size of Narragansett Bay and Buzzards Bay. The...
ONE-DIMENSIONAL HYDRODYNAMIC/SEDIMENT TRANSPORT MODEL FOR STREAM NETWORKS: TECHNICAL REPORT
This technical report describes a new sediment transport model and the supporting post-processor, and sampling procedures for sediments in streams. Specifically, the following items are described herein:
EFDC1D - This is a new one-dimensional hydrodynamic and sediment tr...
HOW TO MODEL HYDRODYNAMICS AND RESIDENCE TIMES OF 27 ESTUARIES IN 4 MONTHS
The hydrodynamics and residence times of 27 embayments were modeled during the first year of a project whose goal is to define the relation between nitrogen loadings and ecological responses of 44 systems that range from small to the size of Narragansett Bay and Buzzards Bay. The...
Hydrodynamic models of a Cepheid atmosphere. III - Line spectrum and radius determinations
NASA Technical Reports Server (NTRS)
Karp, A. H.
1975-01-01
Line profiles are computed on the basis of the moving atmospheres from the hydrodynamic models investigated by Karp (1975). It is found that the velocity gradients in the atmosphere can be used to explain the apparent, slightly supersonic microturbulence. The total observed microturbulence is seen to be consistent with the linear sum of the classical microturbulence and that caused by the velocity gradients.
The effect of coupling hydrologic and hydrodynamic models on probable maximum flood estimation
NASA Astrophysics Data System (ADS)
Felder, Guido; Zischg, Andreas; Weingartner, Rolf
2017-07-01
Deterministic rainfall-runoff modelling usually assumes stationary hydrological system, as model parameters are calibrated with and therefore dependant on observed data. However, runoff processes are probably not stationary in the case of a probable maximum flood (PMF) where discharge greatly exceeds observed flood peaks. Developing hydrodynamic models and using them to build coupled hydrologic-hydrodynamic models can potentially improve the plausibility of PMF estimations. This study aims to assess the potential benefits and constraints of coupled modelling compared to standard deterministic hydrologic modelling when it comes to PMF estimation. The two modelling approaches are applied using a set of 100 spatio-temporal probable maximum precipitation (PMP) distribution scenarios. The resulting hydrographs, the resulting peak discharges as well as the reliability and the plausibility of the estimates are evaluated. The discussion of the results shows that coupling hydrologic and hydrodynamic models substantially improves the physical plausibility of PMF modelling, although both modelling approaches lead to PMF estimations for the catchment outlet that fall within a similar range. Using a coupled model is particularly suggested in cases where considerable flood-prone areas are situated within a catchment.
Application of CFD modelling to study the hydrodynamics of various anaerobic pond configurations.
Vega, G P; Peña, M R; Ramírez, C; Mara, D D
2003-01-01
The simulation of hydrodynamics and transport phenomena in waste stabilization ponds is a developing tool worth studying in order to understand their internal processes and interactions. Pond design involves several physical, hydrological, geometric and dynamic variables so as to provide high hydrodynamic efficiency and maximum substrate utilization rates. CFD modelling allows the combination of these factors to predict the behaviour of ponds having different configurations. The two-dimensional depth-integrated model MIKE 21 was used in this study to simulate hydrodynamic and advection-dispersion processes in a full-scale anaerobic pond (AP) located in southwest Colombia. A set of 12 configurations including sludge contents, inlet-outlet positioning, baffling and pond geometry were modelled. Results showed that a crosswise (diagonally opposite) inlet-outlet layout, a length-to-breadth ratio of 2:1, plus provision of two cross baffles at 1/3 L and 2/3 L were the most effective measures to improve overall AP hydrodynamics and dispersion patterns.
Scaling tree-level hydrodynamics to plot-level hydrology using novel model and measurements
NASA Astrophysics Data System (ADS)
Bohrer, Gil; Matheny, Ashley; Mirfendersgi, Golnaz; Morin, Timothy; Fatichi, Simone
2016-04-01
Hydrodynamic limitations are driven by the water availability to leave of the individual tree crowns, and are known to control transpiration in forest ecosystems under both wet and dry conditions. Current land-surface models do not represent tree-level processes, nor do they represent the above-ground storage in trees. As the intra-daily dynamics of soil moisture are slower and very different than the faster dynamics of water storage in the tree xylem, the current approach that do not incorporate tree-water storage leads to deviations from the observed dynamics of transpiration. We propose a framework to resolve such tree hydrodynamics. The FETCH2 model resolves the water flow, water potential, and water storage in the tree stem and realistically links stomatal conductance to the water potential in the xylem, while water availability in the soil provides a bottom boundary condition for the hydrodynamic system. We use data from a large scale ecological disturbance experiment at a forest in Michigan to validate this approach. We use a very large array of sap-flow sensors in a plot with eddy-covariance measurements to parameterize the model at both tree-scale and plot scale. We demonstrate novel approaches to continuously measure tree water storage, and to evaluate tree-level hydrodynamic traits that control the ecohydrological response of the plot to water stress and disturbance.
CFD modelling of flow field and particle tracking in a hydrodynamic stormwater separator.
Lee, J H; Bang, K W; Choi, C S; Lim, H S
2010-01-01
The best management practices (BMPs) for control of urban stormwater pollution are evaluated to remove solid particles containing various pollutants. Currently, most storm runoff treatment devices using primary pollutant removal mechanism are applied to storm water since most pollutants in runoff are associated with the solid particulates. A hydrodynamic separator is a storm water treatment device using centrifugal motion which separates solids pollution from runoff. In this study, the velocity flow field and particle tracking of hydrodynamic separator were investigated using anthracite as a computational fluid dynamics (CFD) model particle. The Fluent 6.3.26 CFD program was used to predict the solid particles removal efficiency for various parameters such as particle size, surface loading rate, and the ratio of underflow to overflow. The velocity flow field in a hydrodynamic stormwater separator (HDS) has been simulated using CFD RNG κ-ε model. Modeling results for the removal efficiency of HDS were similar with the results obtained from experimental measurements of laboratory scale HDS. These results showed that the simulated velocity field was useful to interpret the behavior of flow in the hydrodynamic separator. The results obtained from particle tracking can be applied to predict the separation efficiency.
Blow-up of the smooth solution to quantum hydrodynamic models in Rd
NASA Astrophysics Data System (ADS)
Guo, Boling; Wang, Guangwu
2016-10-01
In this paper we firstly investigate the local-in-time existence of smooth solution for the quantum hydrodynamic models (QHD) in Rd. Then we prove that any smooth solution of the QHD model which satisfies suitable conditions will blow up in finite time. The model can be derived from nonlinear Schrödinger equation by a Madelung transformation. The main idea is based on the construction of approximate solution and energy inequality.
Thieulot, Cedric; Janssen, L P B M; Español, Pep
2005-07-01
A previously formulated smoothed particle hydrodynamics model for a phase separating mixture is tested for the case when viscous processes are negligible and only mass and energy diffusive processes take place. We restrict ourselves to the case of a binary mixture that can exhibit liquid-liquid phase separation. The thermodynamic consistency of the model is assessed and the potential of the model to study complex pattern formation in the presence of various thermal boundaries is illustrated.
2011-03-01
couples different models to each other, and the domain decomposition method ( DDM ) divides a flow domain into many subdomains, each of which is...assigned to an individual model. Combining HM and DDM is one of the most promising currently available techniques to bridge the scales and overcome...recent work in modeling of multiscale and multiphysics hydrodynamics phenomena using HM and DDM . We also discuss related sediment transport, with
A comparison of two finite element models of tidal hydrodynamics using a North Sea data set
Walters, R.A.; Werner, F.E.
1989-01-01
Using the region of the English Channel and the southern bight of the North Sea, we systematically compare the results of two independent finite element models of tidal hydrodynamics. The model intercomparison provides a means for increasing our understanding of the relevant physical processes in the region in question as well as a means for the evaluation of certain algorithmic procedures of the two models. ?? 1989.
A Parallel 2D Depth-averaged Hydrodynamic, Sediment Transport and River Morphological Model
NASA Astrophysics Data System (ADS)
Zhu, Z.
2016-12-01
Numerical models of river morphodynamics have become important tools for understanding process-form relationships in river channels through the computation of hydrodynamics, sediment transport and an evolving river bed morphology. While 2D depth-averaged models do not include vertical variation in velocities, they can provide appropriate hydrodynamic results in shallow water environments. Although 2D models are less computationally expensive than 3D models, computation speed is still a concern in many applications, especially in river morphological applications. This paper presents a new parallel 2D hydrodynamic, sediment transport and bed morphology model, developed using Open source Field Operation And Manipulation (OpenFOAM). The model uses the Message Passing Interface (MPI) for parallel computing. Further development and modification of the model are relatively straightforward to accomplish with the OpenFOAM framework. Thus, developers can focus on scientific questions rather than having to write their own code for numerical schemes or learn the intricacies of a particular coding language. The open source platform also allows others to add on to and improve the base model so that it becomes an evolving, community-based computational resource. Model validation and parallel efficiency evaluation will be presented and discussed.
A Novel Method for Modeling Neumann and Robin Boundary Conditions in Smoothed Particle Hydrodynamics
Ryan, Emily M.; Tartakovsky, Alexandre M.; Amon, Cristina
2010-08-26
In this paper we present an improved method for handling Neumann or Robin boundary conditions in smoothed particle hydrodynamics. The Neumann and Robin boundary conditions are common to many physical problems (such as heat/mass transfer), and can prove challenging to model in volumetric modeling techniques such as smoothed particle hydrodynamics (SPH). A new SPH method for diffusion type equations subject to Neumann or Robin boundary conditions is proposed. The new method is based on the continuum surface force model [1] and allows an efficient implementation of the Neumann and Robin boundary conditions in the SPH method for geometrically complex boundaries. The paper discusses the details of the method and the criteria needed to apply the model. The model is used to simulate diffusion and surface reactions and its accuracy is demonstrated through test cases for boundary conditions describing different surface reactions.
The hydrodynamics of off-vertical flow for corrosion modeling
Zhang, X.; Rajagopalan, S.; Wagner, J.; Tree, D.A.; High, M.S.
1998-12-31
A study has been conducted on pressure drop modeling in horizontal two-phase flow in order to extend the corrosion prediction software package, DREAM, into off-vertical wells and collection lines. Thermodynamic pressure has a significant influence on the amount of liquid present in gas wells which, in turn, influences the flow regime and mass transfer. Thus an accurate pressure drop model is essential to the prediction of corrosion rate. Four pressure drop models were evaluated for stratified flow, and three pressure drop models were evaluated for annular flow. The results from the pressure drop models were compared with experimental data. Based on the comparison with the experimental data, the best available pressure drop models are the model of Spedding and Hand for stratified flow and the Olujic model for annular flow.
Numerical modelling of spallation in 2D hydrodynamics codes
NASA Astrophysics Data System (ADS)
Maw, J. R.; Giles, A. R.
1996-05-01
A model for spallation based on the void growth model of Johnson has been implemented in 2D Lagrangian and Eulerian hydrocodes. The model has been extended to treat complete separation of material when voids coalesce and to describe the effects of elevated temperatures and melting. The capabilities of the model are illustrated by comparison with data from explosively generated spall experiments. Particular emphasis is placed on the prediction of multiple spall effects in weak, low melting point, materials such as lead. The correlation between the model predictions and observations on the strain rate dependence of spall strength is discussed.
A linked hydrodynamic and water quality model for the Salton Sea
Chung, E.G.; Schladow, S.G.; Perez-Losada, J.; Robertson, D.M.
2008-01-01
A linked hydrodynamic and water quality model was developed and applied to the Salton Sea. The hydrodynamic component is based on the one-dimensional numerical model, DLM. The water quality model is based on a new conceptual model for nutrient cycling in the Sea, and simulates temperature, total suspended sediment concentration, nutrient concentrations, including PO4-3, NO3-1 and NH4+1, DO concentration and chlorophyll a concentration as functions of depth and time. Existing water temperature data from 1997 were used to verify that the model could accurately represent the onset and breakup of thermal stratification. 1999 is the only year with a near-complete dataset for water quality variables for the Salton Sea. The linked hydrodynamic and water quality model was run for 1999, and by adjustment of rate coefficients and other water quality parameters, a good match with the data was obtained. In this article, the model is fully described and the model results for reductions in external phosphorus load on chlorophyll a distribution are presented. ?? 2008 Springer Science+Business Media B.V.
NASA Technical Reports Server (NTRS)
Bui, Trong T.
1992-01-01
The implementation and validation of the Chien low Reynolds number k-epsilon turbulence model in the two dimensional axisymmetric version Proteus, a compressible Navier-Stokes computer code, are presented. The set of k-epsilon equations are solved by marching in time using a coupled alternating direction implicit (ADI) solution procedure with generalized first or second order time differencing. To validate Proteus and the k-epsilon turbulence model, laminar and turbulent computations were done for several benchmark test cases: incompressible fully developed 2-D channel flow; fully developed axisymmetric pipe flow; boundary layer flow over a flat plate; and turbulent Sajben subsonic transonic diffuser flows. Proteus results from these test cases showed good agreement with analytical results and experimental data. Detailed comparisons of both mean flow and turbulent quantities showed that the Chien k-epsilon turbulence model given good results over a wider range of turbulent flow than the Baldwin-Lomax turbulence model in the Proteus code with no significant CPU time penalty for more complicated flow cases.
Tartakovsky, Alexandre M.; Panchenko, Alexander
2016-01-01
We present a novel formulation of the Pairwise Force Smoothed Particle Hydrodynamics Model (PF-SPH) and use it to simulate two- and three-phase flows in bounded domains. In the PF-SPH model, the Navier-Stokes equations are discretized with the Smoothed Particle Hydrodynamics (SPH) method and the Young-Laplace boundary condition at the fluid-fluid interface and the Young boundary condition at the fluid-fluid-solid interface are replaced with pairwise forces added into the Navier-Stokes equations. We derive a relationship between the parameters in the pairwise forces and the surface tension and static contact angle. Next, we demonstrate the accuracy of the model under static and dynamic conditions. Finally, to demonstrate the capabilities and robustness of the model we use it to simulate flow of three fluids in a porous material.
Hydrodynamic model for plasmonics: a macroscopic approach to a microscopic problem.
Ciracì, Cristian; Pendry, John B; Smith, David R
2013-04-15
In this concept, we present the basic assumptions and techniques underlying the hydrodynamic model of electron response in metals and demonstrate that the model can be easily incorporated into computational models. We discuss the role of the additional boundary conditions that arise due to nonlocal terms in the modified equation of motion and the ultimate impact on nanoplasmonic systems. The hydrodynamic model captures much of the microscopic dynamics relating to the fundamental quantum mechanical nature of the electrons and reveals intrinsic limitations to the confinement and enhancement of light around nanoscale features. The presence of such limits is investigated numerically for different configurations of plasmonic nanostructures. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
NASA Astrophysics Data System (ADS)
Tartakovsky, Alexandre M.; Panchenko, Alexander
2016-01-01
We present a novel formulation of the Pairwise Force Smoothed Particle Hydrodynamics (PF-SPH) model and use it to simulate two- and three-phase flows in bounded domains. In the PF-SPH model, the Navier-Stokes equations are discretized with the Smoothed Particle Hydrodynamics (SPH) method, and the Young-Laplace boundary condition at the fluid-fluid interface and the Young boundary condition at the fluid-fluid-solid interface are replaced with pairwise forces added into the Navier-Stokes equations. We derive a relationship between the parameters in the pairwise forces and the surface tension and static contact angle. Next, we demonstrate the model's accuracy under static and dynamic conditions. Finally, we use the Pf-SPH model to simulate three phase flow in a porous medium.
Modeling partially coupled objects with smooth particle hydrodynamics
Wingate, C.A.
1996-10-01
A very simple phenomenological model is presented to model objects that are partially coupled (i.e. welded or bonded) where usually the coupled interface is weaker than the bulk material. The model works by letting objects fully interact in compression and having the objects only partially interact in tension. A disconnect factor is provided to adjust the tensile interaction to simulate coupling strengths. Three cases of an example impact calculation are shown-no coupling, full coupling and partial coupling.
Dynamically Coupled Food-web and Hydrodynamic Modeling with ADH-CASM
NASA Astrophysics Data System (ADS)
Piercy, C.; Swannack, T. M.
2012-12-01
Oysters and freshwater mussels are "ecological engineers," modifying the local water quality by filtering zooplankton and other suspended particulate matter from the water column and flow hydraulics by impinging on the near-bed flow environment. The success of sessile, benthic invertebrates such as oysters depends on environmental factors including but not limited to temperature, salinity, and flow regime. Typically food-web and other types of ecological models use flow and water quality data as direct input without regard to the feedback between the ecosystem and the physical environment. The USACE-ERDC has developed a coupled hydrodynamic-ecological modeling approach that dynamically couples a 2-D hydrodynamic and constituent transport model, Adaptive Hydraulics (ADH), with a bioenergetics food-web model, the Comprehensive Aquatics Systems Model (CASM), which captures the dynamic feedback between aquatic ecological systems and the environment. We present modeling results from restored oyster reefs in the Great Wicomico River on the western shore of the Chesapeake Bay, which quantify ecosystem services such as the influence of the benthic ecosystem on water quality. Preliminary results indicate that while the influence of oyster reefs on bulk flow dynamics is limited due to the localized influence of oyster reefs, large reefs and the associated benthic ecosystem can create measurable changes in the concentrations of nitrogen, phosphorus, and carbon in the areas around reefs. We also present a sensitivity analysis to quantify the relative sensitivity of the coupled ADH-CASM model to both hydrodynamic and ecological parameter choice.
Uncertainty Analysis and Parameter Estimation For Nearshore Hydrodynamic Models
NASA Astrophysics Data System (ADS)
Ardani, S.; Kaihatu, J. M.
2012-12-01
Numerical models represent deterministic approaches used for the relevant physical processes in the nearshore. Complexity of the physics of the model and uncertainty involved in the model inputs compel us to apply a stochastic approach to analyze the robustness of the model. The Bayesian inverse problem is one powerful way to estimate the important input model parameters (determined by apriori sensitivity analysis) and can be used for uncertainty analysis of the outputs. Bayesian techniques can be used to find the range of most probable parameters based on the probability of the observed data and the residual errors. In this study, the effect of input data involving lateral (Neumann) boundary conditions, bathymetry and off-shore wave conditions on nearshore numerical models are considered. Monte Carlo simulation is applied to a deterministic numerical model (the Delft3D modeling suite for coupled waves and flow) for the resulting uncertainty analysis of the outputs (wave height, flow velocity, mean sea level and etc.). Uncertainty analysis of outputs is performed by random sampling from the input probability distribution functions and running the model as required until convergence to the consistent results is achieved. The case study used in this analysis is the Duck94 experiment, which was conducted at the U.S. Army Field Research Facility at Duck, North Carolina, USA in the fall of 1994. The joint probability of model parameters relevant for the Duck94 experiments will be found using the Bayesian approach. We will further show that, by using Bayesian techniques to estimate the optimized model parameters as inputs and applying them for uncertainty analysis, we can obtain more consistent results than using the prior information for input data which means that the variation of the uncertain parameter will be decreased and the probability of the observed data will improve as well. Keywords: Monte Carlo Simulation, Delft3D, uncertainty analysis, Bayesian techniques
A Hydrodynamic Model of The Human Leg Circulation.
ERIC Educational Resources Information Center
Klabunde, Richard E.; McDowell, Donald E.
1984-01-01
Describes the construction and use of a life-size model which shows blood flow under normal and pathological conditions. Four experimental procedures (single vessel occlusion, dilation of distal vascular bed, single artery stenosis, and multiple artery stenoses) typical of those demonstrated by the model are discussed and diagrammed. (DH)
A Hydrodynamic Model of The Human Leg Circulation.
ERIC Educational Resources Information Center
Klabunde, Richard E.; McDowell, Donald E.
1984-01-01
Describes the construction and use of a life-size model which shows blood flow under normal and pathological conditions. Four experimental procedures (single vessel occlusion, dilation of distal vascular bed, single artery stenosis, and multiple artery stenoses) typical of those demonstrated by the model are discussed and diagrammed. (DH)
Gidaspow, D.
1996-04-01
The objective of this investigation is to convert our ``learning gas solid-liquid`` fluidization model into a predictive design model. The IIT hydrodynamic model computes the phase velocities and the volume fractions of gas, liquid and particulate phase. Model verification involves a comparison of these computed velocities and volume fractions to experimental values. A hydrodynamic model for multiphase flows, based on the principles of mass, momentum and energy conservation for each phase, was developed and applied to model gas-liquid, gas-liquid-solid fluidization and gas-solid-solid separation. To simulate the industrial slurry bubble column reactors, a computer program based on the hydrodynamic model was written with modules for chemical reactions (e.g. the synthesis of methanol), phase changes and heat exchangers. In the simulations of gas-liquid two phases flow system, the gas hold-ups, computed with a variety of operating conditions such as temperature, pressure, gas and liquid velocities, agree well with the measurements obtained at Air Products` pilot plant. The hydrodynamic model has more flexible features than the previous empirical correlations in predicting the gas hold-up of gas-liquid two-phase flow systems. In the simulations of gas-liquid-solid bubble column reactors with and without slurry circulation, the code computes volume fractions, temperatures and velocity distributions for the gas, the liquid and the solid phases, as well as concentration distributions for the species (CO, H{sub 2}, CH{sub 3}0H, ... ), after startup from a certain initial state. A kinetic theory approach is used to compute a solid viscosity due to particle collisions. Solid motion and gas-liquid-solid mixing are observed on a color PCSHOW movie made from computed time series data. The steady state and time average catalyst concentration profiles, the slurry height and the rates of methanol production agree well with the measurements obtained at an Air Products` pilot plant.
Fractal hydrodynamic model of high-fluence laser ablation plasma expansion
Agop, M.; Nica, P.; Gurlui, S.; Focsa, C.
2010-10-08
Optical/electrical characterization of transient plasmas generated by high-fluence (up to 1 kJ/cm{sup 2}) laser ablation of various targets revealed as a general feature the splitting of the plume in two structures. In order to account for this behavior, a new fractal hydrodynamic model has been developed in a non-differentiable space-time. The model successfully retrieves the kinetics of the two structures.
Development and evaluation of a coupled hydrodynamic (FVCOM) and water quality model (CE-QUAL-ICM)
Kim, Taeyun; Labiosa, Rochelle G.; Khangaonkar, Tarang; Yang, Zhaoqing; Chen, Changsheng; Qi, Jianhua; Cerco, Carl
2010-01-08
Recent and frequent fish-kills in waters otherwise known for their pristine high quality, created increased awareness and urgent concern regarding potential for degradation of water quality in Puget Sound through coastal eutrophication caused by increased nutrient loading. Following a detailed review of leading models and tools available in public domain, FVCOM and CE-QUAL-ICM models were selected to conduct hydrodynamic and water quality simulations for the fjordal waters of Puget Sound.
A Modeling Study of Hydrodynamic Circulation in a Fjord of the Pacific Northwest
Wang, Taiping; Yang, Zhaoqing
2012-10-01
Increased eutrophication and degraded water quality in estuarine and coastal waters have been a worldwide environmental concern. While it is commonly accepted that anthropogenic impact plays a major role in many emerging water quality issues, natural conditions such as restricted water circulations controlled by geometry may also substantially contribute to unfavorable water quality in certain ecosystems. To elucidate the contributions from different factors, a hydrodynamic-water quality model that integrates both physical transport and pollutant loadings is particularly warranted. A preliminary modeling study using the Environmental Fluid Dynamic Code (EFDC) is conducted to investigate hydrodynamic circulation and low dissolved oxygen (DO) in Hood Canal, a representative fjord in the U.S. Pacific Northwest. Because the water quality modeling work is still ongoing, this paper focuses on the progress in hydrodynamic modeling component. The hydrodynamic model has been set up using the publicly available forcing data and was calibrated against field observations or NOAA predictions for tidal elevation, current, salinity and temperature. The calibrated model was also used to estimate physical transport timescales such as residence time in the estuary. The preliminary model results demonstrate that the EFDC Hood Canal model is capable of capturing the general circulation patterns in Hood Canal, including weak tidal current and strong vertical stratification. The long residence time (i.e., on the order of 100 days for the entire estuary) also indicates that restricted water circulation could contribute to low DO in the estuary and also makes the system especially susceptible to anthropogenic disturbance, such as excess nutrient input.
THE HYDRODYNAMICAL MODELS OF THE COMETARY COMPACT H ii REGION
Zhu, Feng-Yao; Zhu, Qing-Feng; Li, Juan; Wang, Jun-Zhi; Zhang, Jiang-Shui E-mail: zhuqf@ustc.edu.cn E-mail: jzwang@shao.ac.cn
2015-10-10
We have developed a full numerical method to study the gas dynamics of cometary ultracompact H ii regions, and associated photodissociation regions (PDRs). The bow-shock and champagne-flow models with a 40.9/21.9 M{sub ⊙} star are simulated. In the bow-shock models, the massive star is assumed to move through dense (n = 8000 cm{sup −3}) molecular material with a stellar velocity of 15 km s{sup −1}. In the champagne-flow models, an exponential distribution of density with a scale height of 0.2 pc is assumed. The profiles of the [Ne ii] 12.81 μm and H{sub 2} S(2) lines from the ionized regions and PDRs are compared for two sets of models. In champagne-flow models, emission lines from the ionized gas clearly show the effect of acceleration along the direction toward the tail due to the density gradient. The kinematics of the molecular gas inside the dense shell are mainly due to the expansion of the H ii region. However, in bow-shock models the ionized gas mainly moves in the same direction as the stellar motion. The kinematics of the molecular gas inside the dense shell simply reflects the motion of the dense shell with respect to the star. These differences can be used to distinguish two sets of models.
Modeling the three-dimensional river antidunes using a depth-integrated hydrodynamic model
NASA Astrophysics Data System (ADS)
Iwasaki, T.; Inoue, T.; Yabe, H.
2016-12-01
Dynamics of bedforms in rivers have been extensively studied in the last decades, however, the three-dimensionality of the river bedforms have been poorly understood because of the lack of experimental, theoretical and numerical works. Understanding the three-dimensional river bedorms is therefore one of challenging research topic in the engineering and the geomorphological research communities. Here, we propose a modeling of the three-dimensional river antidunes using a reduced horizontal two-dimensional morphodynamic model, which consists of a horizontal two-dimensional depth-integrated hydrodynamic model and a non-equilibrium bedload transport model. We use a simple submodel, which describes a phase lag of bed shear stress, into a depth-integrated shallow water flow model. First, a linear stability analysis is performed to understand the linear response of the morphodynamic model to a three-dimensional wavy bed perturbation. The analysis shows that the model could explain both the three-dimensional antidune instability and free bar instability. The dominant streamwise wavelength and spanwise mode of the antidunes obtained by the linear analysis are consistent with the results of experimental flumes. We then carried out numerical simulations to replicate the nonlinear dynamics of the three-dimensional antidunes and associated water surface deformation in straight channels. The numerical simulations show that the model is able to capture the formation and development of upstream-migrating antidunes and a co-evolution of the antidunes and alternate bars.
Hydrodynamic modeling of laser interaction with micro-structured targets
Velechovsky, Jan; Limpouch, Jiri; Liska, Richard; Tikhonchuk, Vladimir
2016-08-03
A model is developed for numerical simulations of laser absorption in plasmas made of porous materials, with particular interest in low-density foams. Laser absorption is treated on two spatial scales simultaneously. At the microscale, the expansion of a thin solid pore wall is modeled in one dimension and the information obtained is used in the macroscale fluid simulations for the description of the plasma homogenization behind the ionization front. This two-scale laser absorption model is implemented in the arbitrary Lagrangian–Eulerian hydrocode PALE. In conclusion, the numerical simulations of laser penetration into low-density foams compare favorably with published experimental data.
Hydrodynamic modeling of laser interaction with micro-structured targets
Velechovsky, Jan; Limpouch, Jiri; Liska, Richard; ...
2016-08-03
A model is developed for numerical simulations of laser absorption in plasmas made of porous materials, with particular interest in low-density foams. Laser absorption is treated on two spatial scales simultaneously. At the microscale, the expansion of a thin solid pore wall is modeled in one dimension and the information obtained is used in the macroscale fluid simulations for the description of the plasma homogenization behind the ionization front. This two-scale laser absorption model is implemented in the arbitrary Lagrangian–Eulerian hydrocode PALE. In conclusion, the numerical simulations of laser penetration into low-density foams compare favorably with published experimental data.
One-dimensional hydrodynamic model generating a turbulent cascade
NASA Astrophysics Data System (ADS)
Matsumoto, Takeshi; Sakajo, Takashi
2016-05-01
As a minimal mathematical model generating cascade analogous to that of the Navier-Stokes turbulence in the inertial range, we propose a one-dimensional partial-differential-equation model that conserves the integral of the squared vorticity analog (enstrophy) in the inviscid case. With a large-scale random forcing and small viscosity, we find numerically that the model exhibits the enstrophy cascade, the broad energy spectrum with a sizable correction to the dimensional-analysis prediction, peculiar intermittency, and self-similarity in the dynamical system structure.
Hydrodynamic modeling of granular flows in a modified Couette cell.
Jop, Pierre
2008-03-01
We present simulations of granular flows in a modified Couette cell, using a continuum model recently proposed for dense granular flows. Based on a friction coefficient, which depends on an inertial number, the model captures the positions of the wide shear bands. We show that a smooth transition in velocity-profile shape occurs when the height of the granular material is increased, leading to a differential rotation of the central part close to the surface. The numerical predictions are in qualitative agreement with previous experimental results. The model provides predictions for the increase of the shear band width when the rotation rate is increased.
Use Of Earth Observation Data For Hydrodynamic Modelling In The Mara Wetlands
NASA Astrophysics Data System (ADS)
Mtamba, Joseph O. D.; van der Velde, Rogier; Ndomba, Preksedis M.; Zoltan, Verkedy; Mtalo, Felix W.; Crosato, Alessandra
2013-12-01
Vegetation characteristics can not only be used to derive spatial hydrodynamic roughness parameters but also to correct vegetation artefacts in freely downloadable Digital Elevation Models for hydrodynamic modelling. An exponential backscattering model for vegetation canopy height model was developed using standard deviation of cross polarization backscatter coefficient of Radarsat-2 SAR wide swath mode and in situ vegetation height data. The retrieved spatial vegetation height was used to correct vegetation artefacts in freely downloadable Advanced Spaceborne Thermal Emission and Reflectance Radiometer Global Digital Elevation Model (ASTERDEM) released in 2011. The relative spatial hydrodynamic roughness within a vegetation class was derived from cross polarization ratio. Preliminary results show that the accuracy of ASTERDEM improved the elevation estimates by root mean square error from 5.1 m to 3.0m. Simulation results using Earth Observation (EO) data for calibration and validation using an internal gauging station yielded promising Nash - Sutcliffe efficiency criterion of 0.38 and 0.45. The results shows that if high resolution DEM is available, spatial roughness parametrization using cross-polarization ratio of Synthetic Aperture Radar (SAR) imagery may be useful in modelling extensive floodplains where optimization of roughness parameter is not necessary due to computational limitations.
Hydrodynamic Modeling of Circulation and Sediment Transport in Lake Hartwell, SC
NASA Astrophysics Data System (ADS)
Seker - Elci, S.
2001-12-01
This paper describes the application of a numerical model describing three-dimensional hydrodynamics of a large reservoir in the Piedmont region of South Carolina, USA. Emphasis is placed on long-term hydrodynamics, accounting for wind forcing, inflows, outflows, storage changes, and thermal stratification in Lake Hartwell. Lake Hartwell is a man-made reservoir on the Savannah River, bordering both Georgia and South Carolina. At the chosen site Environmental Protection Agency and the South Carolina Department of Health and Environmental Control detected large amounts of polychlorinated biphenyls (PCBs). Motivation is related to the fate of eroded sediments deposited in the reservoir. The EFDC model is used to describe lake hydrodynamics and sediment fate. Model inputs include basin geometry, inflow locations and strengths, wind forcing, and sediment and water properties. The model has been verified by comparison to analytical tests, where possible, and sensitivity of model results to input parameters have been assessed. Model results for cases with realistic long-term forcing indicate likely zones of sediment erosion and deposition, useful for mitigation of pollution problems as well as predictions of reservoir lifetime and development of maintenance schemes.
Hydrodynamic Instability in an Extended Landau/Levich Model of Liquid-Propellant Combustion
NASA Technical Reports Server (NTRS)
Margolis, Stephen B.; Sackesteder, Kurt (Technical Monitor)
1998-01-01
The classical Landau/Levich models of liquid propellant combustion, which serve as seminal examples of hydrodynamic instability in reactive systems, have been combined and extended to account for a dynamic dependence, absent in the original formulations, of the local burning rate on the local pressure and/or temperature fields. The resulting model admits an extremely rich variety of both hydrodynamic and reactive/diffusive instabilities that can be analyzed in various limiting parameter regimes. In the present work, a formal asymptotic analysis, based on the realistic smallness of the gas-to-liquid density ratio, is developed to investigate the combined effects of gravity, surface tension and viscosity on the hydrodynamic instability of the propagating liquid/gas interface. In particular, a composite asymptotic expression, spanning three distinguished wavenumber regimes, is derived for both cellular and pulsating hydrodynamic neutral stability boundaries A(sub p)(k), where A(sub p) is the pressure sensitivity of the burning rate and k is the disturbance wavenumber. For the case of cellular (Landau) instability, the results demonstrate explicitly the stabilizing effect of gravity on long-wave disturbances, the stabilizing effect of viscosity and surface tension on short-wave perturbations, and the instability associated with intermediate wavenumbers for critical negative values of A(sub p). In the limiting case of weak gravity, it is shown that cellular hydrodynamic instability in this context is a long-wave instability phenomenon, whereas at normal gravity, this instability is first manifested through O(l) wavenumber disturbances. It is also demonstrated that, in the large wavenumber regime, surface tension and both liquid and gas viscosity all produce comparable stabilizing effects in the large-wavenumber regime, thereby providing significant modifications to previous analyses of Landau instability in which one or more of these effects were neglected. In contrast
Hydrodynamic Models of the Accretion Stream in Magnetic Cataclysmic Variables
NASA Astrophysics Data System (ADS)
Belle, K. E.
2004-07-01
Here I use the MHD code, FLASH, from the University of Chicago ASCI Center for Astrophysical Thermonuclear Flashes, to simulate initial two-dimensional simple models of accretion streams in magnetic CVs. These models explore the evolution of inflowing material for two white dwarf masses; 0.5M⊙and 0.9M⊙. It is seen that a discontinuity forms at a height of 6.1×108 cm above the white dwarf 'surface' for M[WD] = 0.5M⊙and at 1.6×109 cm for M[WD] = 0.9M⊙. These models will be developed further with the ultimate goal of completing a three-dimensional model of magnetic accretion onto a WD surface.
Smoothed particle hydrodynamic model for viscoelastic fluids with thermal fluctuations.
Vázquez-Quesada, Adolfo; Ellero, Marco; Español, Pep
2009-05-01
We present a fluid-particle model for a polymer solution in nonisothermal situations. The state of the fluid particles is characterized by the thermodynamic variables and a configuration tensor that describes the underlying molecular orientation of the polymer molecules. The specification of very simple physical mechanisms inspired by the dynamics of single polymer molecules allows one, with the help of the general equation for nonequilibrium reversible-irreversible coupling (GENERIC) formalism, to derive the equations of motion for a set of fluid particles carrying polymer molecules in suspension. In the simplest case of Hookean dumbbells we recover a fluid-particle version of the Oldroyd-B model in which thermal fluctuations are included consistently. Generalization to more complex viscoelastic models, such as finitely extensible nonlinear elastic Peterlin (FENE-P) model, with the proper introduction of thermal fluctuations is straightforward.
Modeling the coupling of reaction kinetics and hydrodynamics in a collapsing cavity
Mishra, Sudib; Deymier, Pierre; Muralidharan, Krishna; Frantziskonis, G.; Pannala, Sreekanth; Simunovic, Srdjan
2010-01-01
We introduce a model of cavitation based on the multiphase Lattice Boltzmann method (LBM) that allows for coupling between the hydrodynamics of a collapsing cavity and supported solute chemical species. We demonstrate that this model can also be coupled to deterministic or stochastic chemical reactions. In a two-species model of chemical reactions (with a major and a minor specie), the major difference observed between the deterministic and stochastic reactions takes the form of random fluctuations in concentration of the minor species. We demonstrate that advection associated with the hydrodynamics of a collapsing cavity leads to highly inhomogeneous concentration of solutes. In turn these inhomogeneities in concentration may lead to significant increase in concentration-dependent reaction rates and can result in a local enhancement in the production of minor species.
Smoothed particle hydrodynamics model for phase separating fluid mixtures. I. General equations.
Thieulot, Cedric; Janssen, L P B M; Español, Pep
2005-07-01
We present a thermodynamically consistent discrete fluid particle model for the simulation of a recently proposed set of hydrodynamic equations for a phase separating van der Waals fluid mixture [P. Español and C.A.P. Thieulot, J. Chem. Phys. 118, 9109 (2003)]. The discrete model is formulated by following a discretization procedure given by the smoothed particle hydrodynamics (SPH) method within the thermodynamically consistent general equation for the nonequilibrium reversible-irreversible coupling (GENERIC) framework. Each fluid particle carries information on the mass, momentum, energy, and the mass fraction of the different components. The discrete model allows one to simulate nonisothermal dynamic evolution of phase separating fluids with surface tension effects while respecting the first and second laws of thermodynamics exactly.
Smoothed particle hydrodynamics model for phase separating fluid mixtures. I. General equations
NASA Astrophysics Data System (ADS)
Thieulot, Cedric; Janssen, L. P. B. M.; Español, Pep
2005-07-01
We present a thermodynamically consistent discrete fluid particle model for the simulation of a recently proposed set of hydrodynamic equations for a phase separating van der Waals fluid mixture [P. Español and C.A.P. Thieulot, J. Chem. Phys. 118, 9109 (2003)]. The discrete model is formulated by following a discretization procedure given by the smoothed particle hydrodynamics (SPH) method within the thermodynamically consistent general equation for the nonequilibrium reversible-irreversible coupling (GENERIC) framework. Each fluid particle carries information on the mass, momentum, energy, and the mass fraction of the different components. The discrete model allows one to simulate nonisothermal dynamic evolution of phase separating fluids with surface tension effects while respecting the first and second laws of thermodynamics exactly.
Hydrodynamics for a model of a confined quasi-two-dimensional granular gas.
Brey, J Javier; Buzón, V; Maynar, P; García de Soria, M I
2015-05-01
The hydrodynamic equations for a model of a confined quasi-two-dimensional gas of smooth inelastic hard spheres are derived from the Boltzmann equation for the model, using a generalization of the Chapman-Enskog method. The heat and momentum fluxes are calculated to Navier-Stokes order, and the associated transport coefficients are explicitly determined as functions of the coefficient of normal restitution and the velocity parameter involved in the definition of the model. Also an Euler transport term contributing to the energy transport equation is considered. This term arises from the gradient expansion of the rate of change of the temperature due to the inelasticity of collisions, and it vanishes for elastic systems. The hydrodynamic equations are particularized for the relevant case of a system in the homogeneous steady state. The relationship with previous works is analyzed.
NASA Astrophysics Data System (ADS)
Seppäläinen, Timo; Krug, Joachim
1999-05-01
We consider a one-dimensional totally asymmetric exclusion model with quenched random jump rates associated with the particles, and an equivalent interface growth process on the square lattice. We obtain rigorous limit theorems for the shape of the interface, the motion of a tagged particle, and the macroscopic density profile on the hydrodynamic scale. The theorems are valid under almost every realization of the disordered rates. Under suitable conditions on the distribution of jump rates the model displays a disorder-dominated low-density phase where spatial inhomogeneities develop below the hydrodynamic resolution. The macroscopic signature of the phase transition is a density discontinuity at the front of the rarefaction wave moving out of an initial step-function profile. Numerical simulations of the density fluctuations ahead of the front suggest slow convergence to the predictions of a deterministic particle model on the real line, which contains only random velocities but no temporal noise.
Hydrodynamic and morphodynamic modelling of the surf zone
NASA Astrophysics Data System (ADS)
Roelvink, J. A.
2002-12-01
Surf zones of sandy beaches are generally very dynamic systems showing complex behaviour over a range of time- and length scales. Modelling of this behaviour has evolved from two extremes of the spectrum: on the one hand, practical engineers who have to predict things on a timescale of months to years are trying to do this in an ever more detailed way, whereas research scientists (a.k.a. 'field guys') have typically tried to understand basic processes first. As long as predictive models are surf-zone averaged (as in many longshore transport predictors) or longshore-averaged (as in coastal profile models) many of the basic processes do not show up in the predictive models or are gathered in lump coefficients with a large scatter. This leads to a frustrating gap between the approaches, where it is often difficult to explain why large sums of money should be spent on either process research that does not improve predictions, or on development of models that do not represent many important processes. This presentation will focus on the challenge of bringing the process research and the development of predictive models together, in such a way that increased knowledge, for instance on the behaviour of rip currents or sand ripples, actually makes a difference in morphological predictions on practically relevant timescales. A very important step in meeting this challenge is to improve the efficiency of the process-based models that we can use both for integrating process knowledge and for making practical predictions. Some examples are: - reducing the domain by improving boundary conditions. A well-known example is the use of cyclic boundary conditions, but these are difficult to implement in implicit schemes and cannot be combined with tidal currents. A Neumann-type boundary condition where the longshore water level gradient is imposed at lateral boundaries provides a solution for surf zone models. - improving the smoothness of transport patterns by taking into account
NASA Astrophysics Data System (ADS)
Centeno, Felipe Roman; Brittes, Rogério; França, Francis. H. R.; Ezekoye, Ofodike A.
2015-05-01
The weighted-sum-of-gray-gases (WSGG) model is widely used in engineering computations of radiative heat transfer due to its relative simplicity, robustness and flexibility. This paper presents the computation of radiative heat transfer in a 2D axisymmetric chamber using two WSGG models to compute radiation in H2O and CO2 mixtures. The first model considers a fixed ratio between the molar concentrations of H2O and CO2, while the second allows the solution for arbitrary ratios. The correlations for both models are based on the HITEMP2010 database. The test case considers typical conditions found in turbulent methane flames, with steep variations in the temperature field as well as in the molar concentrations of the participating species. To assess the accuracy of the WSGG model, the results are compared with a solution obtained by line-by-line integration (LBL) of the spectrum.
Thermal and hydrodynamic modelling of active catheters for interventional radiology.
Marchandise, Emilie; Flaud, Patrice; Royon, Laurent; Blanc, Raphaël; Szewczyk, Jérome
2011-07-01
Interventional radiologists desire to improve their operating tools such as catheters. Active catheters in which the tip is moved using shape memory alloy actuators activated using the Joule effect present a promising approach for easier navigation in the small vessels. However, the increase in temperature caused by this Joule effect must be controlled in order to prevent damage to blood cells and tissues. This paper is devoted to the simulation and experimental validation of a fluid-thermal model of an active catheter prototype. Comparisons between computer-predicted and experimentally measured temperatures are presented for both experiments in air and water at 37°C. Good agreement between the computational and experimental results is found, demonstrating the validity of the developed computer model. These comparisons enable us to highlight some important issues in the modelling process and to determine the optimal current for the activation of the catheter.
Samadi-Dooki, Aref; Shodja, Hossein M; Malekmotiei, Leila
2015-05-14
In this paper an analytical approach to study the effect of the substrate physical properties on the kinetics of adhesion and motility behavior of cells is presented. Cell adhesion is mediated by the binding of cell wall receptors and substrate's complementary ligands, and tight adhesion is accomplished by the recruitment of the cell wall binders to the adhesion zone. The binders' movement is modeled as their axisymmetric diffusion in the fluid-like cell membrane. In order to preserve the thermodynamic consistency, the energy balance for the cell-substrate interaction is imposed on the diffusion equation. Solving the axisymmetric diffusion-energy balance coupled equations, it turns out that the physical properties of the substrate (substrate's ligand spacing and stiffness) have considerable effects on the cell adhesion and motility kinetics. For a rigid substrate with uniform distribution of immobile ligands, the maximum ligand spacing which does not interrupt adhesion growth is found to be about 57 nm. It is also found that as a consequence of the reduction in the energy dissipation in the isolated adhesion system, cell adhesion is facilitated by increasing substrate's stiffness. Moreover, the directional movement of cells on a substrate with gradients in mechanical compliance is explored with an extension of the adhesion formulation. It is shown that cells tend to move from soft to stiff regions of the substrate, but their movement is decelerated as the stiffness of the substrate increases. These findings based on the proposed theoretical model are in excellent agreement with the previous experimental observations.
Numerical study on pollutant transport in Dalian bay based on hydrodynamic model
NASA Astrophysics Data System (ADS)
Qiao, Huiting; Li, Jin; Zhang, Hongxing; Zhao, Kaibin; Zhang, Mingliang
2017-01-01
Based on the depth-averaged two-dimensional shallow water and pollutant transport equation, the coupling model of water flow and water quality with explicit scheme is developed in this study. The unstructured triangular grid is adopted to locally refine the mesh around sewage outlet or in high-gradient regions of terrain change for the coupling model. The finite volume method is applied to ensure the conservation of mass for each element. This hydrodynamic model applies the Roe solver approximate Riemann solution with second-order accuracy to compute the water momentum flux on the grid interface. Taking Dalian Bay as the research object, the numerical model established is used to simulate the hydrodynamic characteristics and pollutant transport process. The computed results of the tide level, flow current and flow direction agree well with the measured data in Dalian Bay. The spatial and temporal distribution of pollutant in water are analyzed and discussed in this study. Simulated results show that the two-dimensional hydrodynamic and pollutant transport model can accurately simulate the mass transport in coastal waters, and it can provide a scientific basis on coastal water environment protection for the research water.
NASA Astrophysics Data System (ADS)
Vogel, Ronald L.; Brown, Christopher W.
2016-07-01
Improving forecasts of salinity from coastal hydrodynamic models would further our predictive capacity of physical, chemical, and biological processes in the coastal ocean. However, salinity is difficult to estimate in coastal and estuarine waters at the temporal and spatial resolution required. Retrieving sea surface salinity (SSS) using satellite ocean color radiometry may provide estimates with reasonable accuracy and resolution for coastal waters that could be assimilated into hydrodynamic models to improve SSS forecasts. We evaluated the applicability of satellite SSS retrievals from two algorithms for potential assimilation into National Oceanic and Atmospheric Administration's Chesapeake Bay Operational Forecast System (CBOFS) hydrodynamic model. Of the two satellite algorithms, a generalized additive model (GAM) outperformed that of an artificial neural network (ANN), with mean bias and root-mean-square error (RMSE) of 1.27 and 3.71 for the GAM and 3.44 and 5.01 for the ANN. However, the RMSE for the SSS predicted by CBOFS (2.47) was lower than that of both satellite algorithms. Given the better precision of the CBOFS model, assimilation of satellite ocean color SSS retrievals will not improve CBOFS forecasts of SSS in Chesapeake Bay. The bias in the GAM SSS retrievals suggests that adding a variable related to precipitation may improve its performance.
Viscous Overstability in the B-ring: Hydrodynamic Modeling and Local Simulation
NASA Astrophysics Data System (ADS)
Schmidt, J.; Salo, H.; Spahn, F.
2000-10-01
Viscous overstability was suggested to cause radial structure in an opaque planetary ring (Schmit and Tscharnuter, Icarus, 1995, 115, p304). We extended that model by the hydrodynamic heat flow equation (Spahn et al., Icarus, 2000, 145, p657) and used expressions for the transport coefficients determined in direct N-particle simulations of a dense ring (see the accompanying poster by Salo et al.). The overstable modes of the extended model are in good quantitative agreement with the overstability observed in simulations where the disk's self-gravity is included via an enhancement of the frequency of vertical oscillations. In the model ring (meter sized smooth spherical particles, Bridges' velocity dependent inelasticity law for ice spheres) overstability sets in for optical depths larger than about one. In particular, the growth rates in the linear regime are predicted correctly by the hydrodynamic model, as well as the critical wavelength (wavelengths larger than about 100m are unstable), and the phase--shifts between the perturbations of density and radial and tangential velocities. A weakly nonlinear stability analysis of the isothermal hydrodynamic model yields a nonlinear saturation of the growth of the overstable modes and predicts standing waves to be unstable with respect to traveling waves. This is also observed in our simulations.
Reshocks, rarefactions, and the generalized Layzer model for hydrodynamic instabilities
Mikaelian, K O
2008-06-10
We report numerical simulations and analytic modeling of shock tube experiments on Rayleigh-Taylor and Richtmyer-Meshkov instabilities. We examine single interfaces of the type A/B where the incident shock is initiated in A and the transmitted shock proceeds into B. Examples are He/air and air/He. In addition, we study finite-thickness or double-interface A/B/A configurations like air/SF{sub 6}/air gas-curtain experiments. We first consider conventional shock tubes that have a 'fixed' boundary: A solid endwall which reflects the transmitted shock and reshocks the interface(s). Then we focus on new experiments with a 'free' boundary--a membrane disrupted mechanically or by the transmitted shock, sending back a rarefaction towards the interface(s). Complex acceleration histories are achieved, relevant for Inertial Confinement Fusion implosions. We compare our simulation results with a generalized Layzer model for two fluids with time-dependent densities, and derive a new freeze-out condition whereby accelerating and compressive forces cancel each other out. Except for the recently reported failures of the Layzer model, the generalized Layzer model and hydrocode simulations for reshocks and rarefactions agree well with each other, and remain to be verified experimentally.
Hydrodynamic Forces on Reverse Tainter Valves; Hydraulic Model Investigation
2013-12-01
FACILITY: Completion of a physical model study of the culvert valves of the Eisenhower and Snell Locks, St. Lawrence Seaway (Stockstill et al., in...evaluation of culvert valves at Eisenhower and Snell Locks, St. Lawrence Seaway. Vicksburg, MS: US Army Engineer Research and Development Center
Yang, Zhaoqing; Khangaonkar, Tarang; Wang, Taiping
2010-08-01
In this report we describe the 1) the expansion of the PNNL hydrodynamic model domain to include the continental shelf along the coasts of Washington, Oregon, and Vancouver Island; and 2) the approach and progress in developing the online/Internet disseminations of model results and outreach efforts in support of the Puget Sound Operational Forecast System (PS-OPF). Submittal of this report completes the work on Task 2.1.2, Effects of Physical Systems, Subtask 2.1.2.1, Hydrodynamics, for fiscal year 2010 of the Environmental Effects of Marine and Hydrokinetic Energy project.
The application of single particle hydrodynamics in continuum models of multiphase flow
NASA Technical Reports Server (NTRS)
Decker, Rand
1988-01-01
A review of the application of single particle hydrodynamics in models for the exchange of interphase momentum in continuum models of multiphase flow is presented. Considered are the equations of motion for a laminar, mechanical two phase flow. Inherent to this theory is a model for the interphase exchange of momentum due to drag between the dispersed particulate and continuous fluid phases. In addition, applications of two phase flow theory to de-mixing flows require the modeling of interphase momentum exchange due to lift forces. The applications of single particle analysis in deriving models for drag and lift are examined.
Flood hazard maps from SAR data and global hydrodynamic models
NASA Astrophysics Data System (ADS)
Giustarini, Laura; Chini, Marci; Hostache, Renaud; Matgen, Patrick; Pappenberger, Florian; Bally, Phillippe
2015-04-01
With flood consequences likely to amplify because of growing population and ongoing accumulation of assets in flood-prone areas, global flood hazard and risk maps are greatly needed for improving flood preparedness at large scale. At the same time, with the rapidly growing archives of SAR images of floods, there is a high potential of making use of these images for global and regional flood management. In this framework, an original method is presented to integrate global flood inundation modeling and microwave remote sensing. It takes advantage of the combination of the time and space continuity of a global inundation model with the high spatial resolution of satellite observations. The availability of model simulations over a long time period offers the opportunity to estimate flood non-exceedance probabilities in a robust way. The probabilities can later be attributed to historical satellite observations. SAR-derived flood extent maps with their associated non-exceedance probabilities are then combined to generate flood hazard maps with a spatial resolution equal to that of the satellite images, which is most of the time higher than that of a global inundation model. The method can be applied to any area of interest in the world, provided that a sufficient number of relevant remote sensing images are available. We applied the method on the Severn River (UK) and on the Zambezi River (Mozambique), where large archives of Envisat flood images can be exploited. The global ECMWF flood inundation model is considered for computing the statistics of extreme events. A comparison with flood hazard maps estimated with in situ measured discharge is carried out. An additional analysis has been performed on the Severn River, using high resolution SAR data from the COSMO-SkyMed SAR constellation, acquired for a single flood event (one flood map per day between 27/11/2012 and 4/12/2012). The results showed that it is vital to observe the peak of the flood. However, a single
Boussinesq modeling of wave-induced hydrodynamics in coastal wetlands
NASA Astrophysics Data System (ADS)
Chakrabarti, Agnimitro; Brandt, Steven R.; Chen, Qin; Shi, Fengyan
2017-05-01
In this paper, an improved formulation of the vegetation drag force, applicable for the fully nonlinear Boussinesq equations and based on the use of the depth-varying, higher-order expansion of the horizontal velocity, in the quadratic vegetation drag law has been presented. The model uses the same numerical schemes as FUNWAVE TVD but is based on the CACTUS framework. The model is validated for wave height and setup, against laboratory experiments with and without vegetation cover. The wave attenuation results using the improved formulation were compared with those using the first-order reference velocity as well as with analytical solutions using linear wave theory. The analytical solution using the depth-varying velocity, predicted by the linear wave theory, was shown to match the model results with the fully expanded velocity approach very well for all wave cases, except under near-emergent and emergent conditions (when the ratio of stem height to water depth is greater than 0.75) and when the Ursell (Ur) number is less than 5. Simulations during peak storm waves, during Hurricane Isaac, showed that vegetation is very effective in reducing setup on platforms and in reducing the wave energy within the first few hundred meters.
NASA Astrophysics Data System (ADS)
Atzberger, Paul J.
2006-03-01
A new derivation of the velocity correlations of a thermally fluctuating Brownian particle is shown by direct calculation from a stochastic hydrodynamic model in which the fluid-particle coupling is treated in a simple manner. The model significantly simplifies the calculation of statistics of a particle and has the virtue of being readily amenable to numerical simulation. To show that the model correctly captures physical features of a Brownian particle the diffusion coefficient in three dimensions is computed and shown to have the correct scaling in the physical parameters. The velocity correlation function for both short and long times scales is then discussed. It is found for short times that the velocity correlation of a particle satisfies an equipartition principle. For long times the autocorrelation function is shown to have non-exponential decay of algebraic order τ capturing well-known hydrodynamic effects [B.J. Alder, T.E. Wainwright, Phys. Rev. A 1 (1) (1970) 18 21]. The results are then compared with numerical simulations of the hydrodynamic model using the computational method proposed in [P.J. Atzberger, P.R. Kramer, C.S. Peskin, A stochastic immersed boundary method for microscopic biological fluid dynamics, (2005), submitted for publication].
Thermal equilibrium solution to new model of bipolar hybrid quantum hydrodynamics
NASA Astrophysics Data System (ADS)
Di Michele, Federica; Mei, Ming; Rubino, Bruno; Sampalmieri, Rosella
2017-08-01
In this paper we study the hybrid quantum hydrodynamic model for nano-sized bipolar semiconductor devices in thermal equilibrium. By introducing a hybrid version of the Bhom potential, we derive a bipolar hybrid quantum hydrodynamic model, which is able to account for quantum effects in a localized region of the device for both electrons and holes. Coupled with Poisson equation for the electric potential, the steady-state system is regionally degenerate in its ellipticity, due to the quantum effect only in part of the device. This regional degeneracy of ellipticity makes the study more challenging. The main purpose of the paper is to investigate the existence and uniqueness of the weak solutions to this new type of equations. We first establish the uniform boundedness of the smooth solutions to the modified bipolar quantum hydrodynamic model by the variational method, then we use the compactness technique to prove the existence of weak solutions to the original hybrid system by taking hybrid limit. In particular, we account for two different kinds of hybrid behaviour. We perform the first hybrid limit when both electrons and holes behave quantum in a given region of the device, and the second one when only one carrier exhibits hybrid behaviour, whereas the other one is presented classically in the whole domain. The semi-classical limit results are also obtained. Finally, the theoretical results are tested numerically on a simple toy model.
Buchanan, Cara; Rylander, Marissa Nichole
2013-08-01
The integration of tissue engineering strategies with microfluidic technologies has enabled the design of in vitro microfluidic culture models that better adapt to morphological changes in tissue structure and function over time. These biomimetic microfluidic scaffolds accurately mimic native 3D microenvironments, as well as permit precise and simultaneous control of chemical gradients, hydrodynamic stresses, and cellular niches within the system. The recent application of microfluidic in vitro culture models to cancer research offers enormous potential to aid in the development of improved therapeutic strategies by supporting the investigation of tumor angiogenesis and metastasis under physiologically relevant flow conditions. The intrinsic material properties and fluid mechanics of microfluidic culture models enable high-throughput anti-cancer drug screening, permit well-defined and controllable input parameters to monitor tumor cell response to various hydrodynamic conditions or treatment modalities, as well as provide a platform for elucidating fundamental mechanisms of tumor physiology. This review highlights recent developments and future applications of microfluidic culture models to study tumor progression and therapeutic targeting under conditions of hydrodynamic stress relevant to the complex tumor microenvironment.
NASA Astrophysics Data System (ADS)
Chen, Chi-Yin; Chuang, Jen-Chen; Tu, Jia-Ying
2016-09-01
This paper proposes modified coefficients for the dynamic model of hydraulic journal bearing system that integrates the hydrodynamic and hydrostatic properties. In recent years, design of hydraulic bearing for machine tool attracts worldwide attention, because hydraulic bearings are able to provide higher capacity and accuracy with lower friction, compared to conventional bearing systems. In order to achieve active control of the flow pressure and enhance the operation accuracy, the dynamic model of hydraulic bearings need to be developed. Modified coefficients of hydrostatic stiffness, hydrodynamic stiffness, and squeeze damping of the dynamic model are presented in this work, which are derived referring to small displacement analysis from literature. The proposed modified coefficients and model, which consider the pressure variations, relevant geometry size, and fluid properties of the journal bearings, are able to characterise the hydrodynamic and hydrostatic properties with better precision, thus offering the following pragmatic contribution: (1) on-line prediction of the eccentricity and the position of the shaft in the face of external force that results in vibration; (2) development of active control system to regulate the supply flow pressure and to minimize the eccentricity of the shaft. Theoretical derivation and simulation results with different vibration cases are discussed to verify the proposed techniques.
A general method for generating bathymetric data for hydrodynamic computer models
Burau, J.R.; Cheng, R.T.
1989-01-01
To generate water depth data from randomly distributed bathymetric data for numerical hydrodymamic models, raw input data from field surveys, water depth data digitized from nautical charts, or a combination of the two are sorted to given an ordered data set on which a search algorithm is used to isolate data for interpolation. Water depths at locations required by hydrodynamic models are interpolated from the bathymetric data base using linear or cubic shape functions used in the finite-element method. The bathymetric database organization and preprocessing, the search algorithm used in finding the bounding points for interpolation, the mathematics of the interpolation formulae, and the features of the automatic generation of water depths at hydrodynamic model grid points are included in the analysis. This report includes documentation of two computer programs which are used to: (1) organize the input bathymetric data; and (2) to interpolate depths for hydrodynamic models. An example of computer program operation is drawn from a realistic application to the San Francisco Bay estuarine system. (Author 's abstract)
Validation of Hydrodynamic Load Models Using CFD for the OC4-DeepCwind Semisubmersible: Preprint
Benitz, M. A.; Schmidt, D. P.; Lackner, M. A.; Stewart, G. M.; Jonkman, J.; Robertson, A.
2015-03-01
Computational fluid dynamics (CFD) simulations were carried out on the OC4-DeepCwind semi-submersible to obtain a better understanding of how to set hydrodynamic coefficients for the structure when using an engineering tool such as FAST to model the system. The focus here was on the drag behavior and the effects of the free-surface, free-ends and multi-member arrangement of the semi-submersible structure. These effects are investigated through code-to-code comparisons and flow visualizations. The implications on mean load predictions from engineering tools are addressed. The work presented here suggests that selection of drag coefficients should take into consideration a variety of geometric factors. Furthermore, CFD simulations demonstrate large time-varying loads due to vortex shedding, which FAST's hydrodynamic module, HydroDyn, does not model. The implications of these oscillatory loads on the fatigue life needs to be addressed.
A simple hydrodynamic model of tornado-like vortices
NASA Astrophysics Data System (ADS)
Kurgansky, M. V.
2015-05-01
Based on similarity arguments, a simple fluid dynamic model of tornado-like vortices is offered that, with account for "vortex breakdown" at a certain height above the ground, relates the maximal azimuthal velocity in the vortex, reachable near the ground surface, to the convective available potential energy (CAPE) stored in the environmental atmosphere under pre-tornado conditions. The relative proportion of the helicity (kinetic energy) destruction (dissipation) in the "vortex breakdown" zone and, accordingly, within the surface boundary layer beneath the vortex is evaluated. These considerations form the basis of the dynamic-statistical analysis of the relationship between the tornado intensity and the CAPE budget in the surrounding atmosphere.
Analysis of single point moored tanker using maneuvering hydrodynamic model
Nishimoto, K.; Brinati, H.L.; Fucatu, C.H.
1995-12-31
The Single Point Mooring Systems (SPM) are widely used as a tanker terminal in Brazilian south coast by Petrobras, Brazilian oil company. Although different authors (Wichers, 1987, Obokata, 1987, and Jiang et al., 1988) had analyzed the dynamic stability of SPM system, the down time of these systems due to large oscillatory ship motion in the horizontal plane is significant until now. The main source of the instability of these systems is considered to be the use of inadequate hawser length and bad weather. This paper deals with the dynamic behavior of SPM moored vessels considering the influence of the environmental forces as well as shallow water effects. In a first step, a nonlinear mathematical model developed for the simulation of low speed ship maneuvers (Takashina, 1986) is extended to study the behavior of a tanker moored to a single buoy in comparison with the Obokata`s SPM model, 1987. A large number of tanker motion simulations were carried out both for deep and shallow water and different environmental conditions. The influence of the system parameters shown by the study is, in general, in a good agreement with those obtained by the traditional SPM system analysis.
Ejecting basaltic achondrites from Vesta: Hydrodynamical impact models
NASA Technical Reports Server (NTRS)
Asphaug, E.; Melosh, H. J.; Ryan, E.
1993-01-01
Vesta is a large asteroid whose crust is mostly basaltic. Spectral heterogeneity suggests a sizable olivine feature which may be explained as impact excavation. The spectral data probably show a localized feature approximately 200 km in diameter or a diffuse feature approximately 400 km in diameter. Lightcurve irregularities suggest heterogeneity on a similar scale. This heterogeneity may represent the crater bowl, the extent of its ejecta deposit, or indeed something unrelated to cratering. In any case, drawing direct inferences about the state of Vesta's surface on the basis of these observations involves substantial speculation. We are still far from understanding the boundary between cratering and catastrophic disruption, particularly on targets for which strength and self-gravity both matter. But we are now able to model the underlying physical process -- dynamic fragmentation -- accurately with fragmentation hydrocodes such as SALE 2D and SPH3D. We present several impact scenarios for Vesta; our study is similar to a previous impact model for the formation of Stickney crater on Phobos. We illustrate the effects of impactors of different sizes and velocities, and the effect of gravity and structural inhomogeneity.
Explicit 2-D Hydrodynamic FEM Program
Lin, Jerry
1996-08-07
DYNA2D* is a vectorized, explicit, two-dimensional, axisymmetric and plane strain finite element program for analyzing the large deformation dynamic and hydrodynamic response of inelastic solids. DYNA2D* contains 13 material models and 9 equations of state (EOS) to cover a wide range of material behavior. The material models implemented in all machine versions are: elastic, orthotropic elastic, kinematic/isotropic elastic plasticity, thermoelastoplastic, soil and crushable foam, linear viscoelastic, rubber, high explosive burn, isotropic elastic-plastic, temperature-dependent elastic-plastic. The isotropic and temperature-dependent elastic-plastic models determine only the deviatoric stresses. Pressure is determined by one of 9 equations of state including linear polynomial, JWL high explosive, Sack Tuesday high explosive, Gruneisen, ratio of polynomials, linear polynomial with energy deposition, ignition and growth of reaction in HE, tabulated compaction, and tabulated.
Modeling hydrodynamics of large lagoons: Insights from the Albemarle-Pamlico Estuarine System
NASA Astrophysics Data System (ADS)
Clunies, Gregory J.; Mulligan, Ryan P.; Mallinson, David J.; Walsh, J. P.
2017-04-01
Large estuaries are influenced by winds over adjacent coastal ocean and land areas causing significant spatial variations in water levels, currents and surface waves. In this study we apply a numerical model to simulate hydrodynamics and waves in the Albemarle-Pamlico Estuarine System, a large and shallow back-barrier basin in eastern North Carolina, over a one-month study period (September 2008) with observations from several storm wind events of differing time scales and directions. Model performance is evaluated for a spatially varying wind field from the North American Regional Reanalysis (NARR) dataset in comparison to spatially uniform forcing from wind observations at offshore, coastal and land-based sites across the region. A spatially uniform wind field from offshore winds observations results in statistically better hydrodynamic simulations of water levels (R = 0.88) in the estuaries than NARR (R = 0.48) after comparison with measurements and indicates the importance of strong marine winds over most of the estuary surface area. The influence of a prominent bathymetric feature on hydrodynamics in Pamlico Sound is also investigated by numerically removing a 30 km long and 2-3 m deep shoal from the model grid and replacing it with an idealized depth of 6 m. The removal of the shoal increases water level setup by 14% at the estuarine shoreline, decreases current magnitudes by up to 40% in the shoal region and increases significant wave heights locally by up to 25% in the sound, indicating the importance of this relict geomorphic feature as a major control on the hydrodynamic response of the system during wind events. The results suggest that increasing the water depth over the shoal can lead to higher storm surges and wave heights with the possibility of increased inundation and erosion of the back-barrier and mainland coastal regions. The complex bathymetry and marine wind influence are critical input conditions for modeling large and shallow lagoonal
The use of hydro-dynamic models in the practice-oriented education of engineering students
NASA Astrophysics Data System (ADS)
Sziebert, J.; Zellei, L.; Tamás, E. A.
2009-04-01
Management tasks related to open channel flows became rather comprehensive and multi-disciplinary, particularly with the predominancy of nature management aspects. The water regime of our rivers has proven to reach extremities more and more frequently in the past decades. In order to develop and analyse alternative solutions and to handle and resolve conflicts of interests, we apply 1D hydro-dynamic models in education for the explanation of processes and to improve practical skills of our students.
Nguyen, Nam-Trung; Huang, Xiaoyang
2005-11-01
This paper theoretically and experimentally investigates a micromixer based on combined hydrodynamic focusing and time-interleaved segmentation. Both hydrodynamic focusing and time-interleaved segmentation are used in the present study to reduce mixing path, to shorten mixing time, and to enhance mixing quality. While hydrodynamic focusing reduces the transversal mixing path, time-interleaved sequential segmentation shortens the axial mixing path. With the same viscosity in the different streams, the focused width can be adjusted by the flow rate ratio. The axial mixing path or the segment length can be controlled by the switching frequency and the mean velocity of the flow. Mixing ratio can be controlled by both flow rate ratio and pulse width modulation of the switching signal. This paper first presents a time-dependent two-dimensional analytical model for the mixing concept. The model considers an arbitrary mixing ratio between solute and solvent as well as the axial Taylor-Aris dispersion. A micromixer was designed and fabricated based on lamination of four polymer layers. The layers were machined using a CO2 laser. Time-interleaved segmentation was realized by two piezoelectric valves. The sheath streams for hydrodynamic focusing are introduced through the other two inlets. A special measurement set-up was designed with synchronization of the mixer's switching signal and the camera's trigger signal. The set-up allows a relatively slow and low-resolution CCD camera to freeze and to capture a large transient concentration field. The concentration profile along the mixing channel agrees qualitatively well with the analytical model. The analytical model and the device promise to be suitable tools for studying Taylor-Aris dispersion near the entrance of a flat microchannel.
Hydrodynamic prevention of eutrophication in the Bay of Brest (France), a modelling approach
NASA Astrophysics Data System (ADS)
Le Pape, Olivier; Menesguen, Alain
1997-08-01
The Bay of Brest is a semi-enclosed coastal ecosystem where primary production is nutrient-limited, even if huge nutrients loading from tributaries are present. The most striking feature of the bay is the semi-diurnal tidal influence, resulting in large water exchange with the continental shelf. A historical study of the available data has shown the steadiness of this ecosystem during the two last decades in spite of increasing eutrophic conditions. This study has focused on hydrodynamic exchange which is one of the factors supposed to explain the resistance of this ecosystem to eutrophication: this stirring hinders the formation of a persistent upper mixed layer where phytoplankton would be in contact with nutrient-rich brackish waters and available light. Moreover, horizontal tidal currents lead to huge exchanges with the Iroise Sea and, then, to big losses of nutrients and living matter. To study this hydrodynamic influence thoroughly, a physical/biological model of this bay has been developed. This box model, based on the horizontal tidal circulation, has been developed thanks to "ELISE", an ecological modelling software and, then, tuned and validated on two data sets corresponding with the years 1977 and 1993. The model has allowed us to quantify the influence of hydrodynamics, climatic conditions and biological factors on biogeochemical processes in this ecosystem. It contributes to explain the good resistance of the Bay of Brest ecosystem to eutrophic conditions; both the hydrodynamic properties of this bay and the grazing pressure have prevented it from disturbances caused by high nitrogen loading from the watersheds and explain the steadiness of phytoplankton stocks in spite of increased loading. So, these results allow us to say that, even if nitrogen inputs increase continues, phytoplankton stocks will not increase in significant proportions. Nevertheless, changes in the phytoplanktonic populations may occur if such an enrichment continues.
Study of the hydrodynamical processes in the Boka Kotorska Bay with a finite element model
NASA Astrophysics Data System (ADS)
Bellafiore, Debora; Guarnieri, Antonio; Grilli, Federica; Penna, Pierluigi; Bortoluzzi, Giovanni; Giglio, Federico; Pinardi, Nadia
2011-09-01
Boka Kotorska Bay, located in the southeastern Adriatic Sea along the Montenegro coastline, is a complex morphological structure, consisting of three embayments. They are connected and interact with the sea through narrow straits and the bay can be considered one of the main freshwater inputs into the southern Adriatic Sea. In the framework of the ADRICOSM-STAR project, a hydrodynamical model of this region provided results that are compared with CTD data and hydrodynamic scenarios are discussed for the bay. A finite element coastal model nested in a finite difference model that runs on the Adriatic Sea has been used to reproduce the complex morphology of the bay. Hydrodynamic modeling allows studying the main characteristics of this bay, identifying it as a Region of Freshwater Influence (ROFI). The freshwater input coming from the numerous sources present in the bays can strongly modify temperature, salinity and current patterns. The computation of the buoyancy ratio of the thermal and haline buoyancy flux showed that the Kotor and Morinj Bays experience a major effect of surface heating in summer, while the rest of the bay seems to be mostly affected by freshwater influence from precipitation and river discharge. An average estuarine situation is seen, presenting a surface outflow and a bottom inflow of water. Specific hydrodynamic processes can be detected in the channels that connect the different sub-basins of the Boka Kotorska Bay. Moreover, the computation of the Kelvin number in correspondence of the internal straits suggests classifying the Kotor and Morinj Bays differently from the outermost areas. The innermost Kotor and Morinj Bays, generally exchange little water with the sea and they have high values of residence times. However, their fresh water springs and rivers have the highest discharges that can change abruptly the picture with increase of the total water exchange between the bay and the sea.
Tunneling with a hydrodynamic pilot-wave model
NASA Astrophysics Data System (ADS)
Nachbin, André; Milewski, Paul A.; Bush, John W. M.
2017-03-01
Eddi et al. [Phys. Rev Lett. 102, 240401 (2009), 10.1103/PhysRevLett.102.240401] presented experimental results demonstrating the unpredictable tunneling of a classical wave-particle association as may arise when a droplet walking across the surface of a vibrating fluid bath approaches a submerged barrier. We here present a theoretical model that captures the influence of bottom topography on this wave-particle association and so enables us to investigate its interaction with barriers. The coupled wave-droplet dynamics results in unpredictable tunneling events. As reported in the experiments by Eddi et al. and as is the case in quantum tunneling [Gamow, Nature (London) 122, 805 (1928), 10.1038/122805b0], the predicted tunneling probability decreases exponentially with increasing barrier width. In the parameter regimes examined, tunneling between two cavities suggests an underlying stationary ergodic process for the droplet's position.
A model of hydrodynamic interaction between swimming bacteria.
Gyrya, V.; Aranson, I. G.; Berlyand, L. V.; Karpeev, D.; Penn State Univ.
2010-01-01
We study the dynamics and interaction of two swimming bacteria, modeled by self-propelled dumbbell-type structures. We focus on alignment dynamics of a coplanar pair of elongated swimmers, which propel themselves either by 'pushing' or 'pulling' both in three- and quasi-two-dimensional geometries of space. We derive asymptotic expressions for the dynamics of the pair, which complemented by numerical experiments, indicate that the tendency of bacteria to swim in or swim off depends strongly on the position of the propulsion force. In particular, we observe that positioning of the effective propulsion force inside the dumbbell results in qualitative agreement with the dynamics observed in experiments, such as mutual alignment of converging bacteria.
Modeling the tidal and sub-tidal hydrodynamics in a shallow, micro-tidal estuary
NASA Astrophysics Data System (ADS)
Rayson, Matthew D.; Gross, Edward S.; Fringer, Oliver B.
2015-05-01
The three-dimensional hydrodynamics of Galveston Bay were simulated in two periods of several month duration. The physical setting of Galveston Bay is described by synthesis of long-term observations. Several processes in addition to tidal hydrodynamics and baroclinic circulation processes contribute substantially to the observed variability of currents, water level and salinity. The model was therefore forced with realistic water levels, river discharges, winds, coastal buoyancy currents (due to the Mississippi River plume) and surface heat fluxes. Quantitative metrics were used to evaluate model performance against observations and both spatial and temporal variability in tidal and sub-tidal hydrodynamics were generally well represented by the model. Three different unstructured meshes were tested, a triangular mesh that under-resolved the shipping channel, a triangular mesh that resolved it, and a mixed quadrilateral-triangular grid with approximately equivalent resolution. It is shown that salinity and sub-tidal velocity are better predicted when the important topographic features, such as the shipping channel, are resolved. It was necessary to increase the seabed drag roughness in the mixed quadrilateral-triangular grid simulation to attain similar performance to the equivalent triangular mesh.
Reduction of Waste Water in Erhai Lake Based on MIKE21 Hydrodynamic and Water Quality Model
Zhu, Changjun; Liang, Qinag; Yan, Feng; Hao, Wenlong
2013-01-01
In order to study the ecological water environment in Erhai Lake, different monitoring sections were set to research the change of hydrodynamics and water quality. According to the measured data, MIKE21 Ecolab, the water quality simulation software developed by DHI, is applied to simulate the water quality in Erhai Lake. The hydrodynamics model coupled with water quality is established by MIKE21FM software to simulate the current situation of Erhai Lake. Then through the comparison with the monitoring data, the model parameters are calibrated and the simulation results are verified. Based on this, water quality is simulated by the two-dimensional hydrodynamics and water quality coupled model. The results indicate that the level of water quality in the north and south of lake is level III, while in the center of lake, the water quality is level II. Finally, the water environment capacity and total emmision reduction of pollutants are filtered to give some guidance for the water resources management and effective utilization in the Erhai Lake. PMID:23997684
Greiner, N.R.; Blais, N.
1989-01-01
Laboratory-scale (25-50 mg) detonations of PETN, RDX, HNS, and TNT have been carried out in a high-vacuum chamber, and collisionless molecular beams of the freely expanding detonation products have been analyzed as a function of time with a mass spectrometer. Concurrently, time-sequenced schlieren and shadowgraph images of the initial expansion of the product plume are recorded using a pulsed laser for illumination. These data tie the chemistry and hydrodynamics of the detonation event together. The results, interpreted with the aid of a computer model, suggest that this experiment freezes the chemical reactions of detonation by rapid adiabatic cooling and provides a continuum of samples in the molecular beam, representing the sequence of reactions in the detonating charge. With a suitable model of the expansion hydrodynamics, the hydrodynamic histories of a sequence of volume elements can be associated with their frozen chemistries. We expect experiments like this to provide a test for molecular models of detonation. 10 refs., 5 figs.
Reduction of waste water in Erhai Lake based on MIKE21 hydrodynamic and water quality model.
Zhu, Changjun; Liang, Qinag; Yan, Feng; Hao, Wenlong
2013-01-01
In order to study the ecological water environment in Erhai Lake, different monitoring sections were set to research the change of hydrodynamics and water quality. According to the measured data, MIKE21 Ecolab, the water quality simulation software developed by DHI, is applied to simulate the water quality in Erhai Lake. The hydrodynamics model coupled with water quality is established by MIKE21FM software to simulate the current situation of Erhai Lake. Then through the comparison with the monitoring data, the model parameters are calibrated and the simulation results are verified. Based on this, water quality is simulated by the two-dimensional hydrodynamics and water quality coupled model. The results indicate that the level of water quality in the north and south of lake is level III, while in the center of lake, the water quality is level II. Finally, the water environment capacity and total emmision reduction of pollutants are filtered to give some guidance for the water resources management and effective utilization in the Erhai Lake.
NASA Astrophysics Data System (ADS)
Puchwein, Ewald; Baldi, Marco; Springel, Volker
2013-11-01
We present a new massively parallel code for N-body and cosmological hydrodynamical simulations of modified gravity models. The code employs a multigrid-accelerated Newton-Gauss-Seidel relaxation solver on an adaptive mesh to efficiently solve for perturbations in the scalar degree of freedom of the modified gravity model. As this new algorithm is implemented as a module for the P-GADGET3 code, it can at the same time follow the baryonic physics included in P-GADGET3, such as hydrodynamics, radiative cooling and star formation. We demonstrate that the code works reliably by applying it to simple test problems that can be solved analytically, as well as by comparing cosmological simulations to results from the literature. Using the new code, we perform the first non-radiative and radiative cosmological hydrodynamical simulations of an f (R)-gravity model. We also discuss the impact of active galactic nucleus feedback on the matter power spectrum, as well as degeneracies between the influence of baryonic processes and modifications of gravity.
García de la Torre, J
2001-11-28
The effect of hydration on hydrodynamic properties of globular proteins can be expressed in terms of two quantities: the delta (g/g) parameter and the thickness of the hydration layer. The two paradigms on hydration that originate these alternative measures are described and compared. For the numerical calculation of hydrodynamic properties, from which estimates of hydration can be made, we employ the bead modelling with atomic resolution implemented in programs HYDROPRO and HYDRONMR. As typical, average values, we find 0.3 g/g and a thickness of only approximately 1.2 A. However, noticeable differences in this parameter are found from one protein to another. We have made a numerical analysis, which leaves apart marginal influences of modelling imperfections by simulating properties of a spherical protein. This analysis confirms that the errors that one can attribute to the experimental quantities suffice to explain the observed fluctuations in the hydration parameters. However, for the main purpose of predicting protein solution properties, the above mentioned typical values may be safely used. Particularly for atomic bead modelling, a hydrodynamic radius of approximately 3.2 A yields predictions in very good agreement with experiments.
NASA Astrophysics Data System (ADS)
Adams, T. E.
2016-12-01
Accurate and timely predictions of the lateral exent of floodwaters and water level depth in floodplain areas are critical globally. This paper demonstrates the coupling of hydrologic ensembles, derived from the use of numerical weather prediction (NWP) model forcings as input to a fully distributed hydrologic model. Resulting ensemble output from the distributed hydrologic model are used as upstream flow boundaries and lateral inflows to a 1-D hydrodynamic model. An example is presented for the Potomac River in the vicinity of Washington, DC (USA). The approach taken falls within the broader goals of the Hydrologic Ensemble Prediction EXperiment (HEPEX).
Detonation initiation in a model of explosive: Comparative atomistic and hydrodynamics simulations
NASA Astrophysics Data System (ADS)
Murzov, S. A.; Sergeev, O. V.; Dyachkov, S. A.; Egorova, M. S.; Parshikov, A. N.; Zhakhovsky, V. V.
2016-11-01
Here we extend consistent simulations to reactive materials by the example of AB model explosive. The kinetic model of chemical reactions observed in a molecular dynamics (MD) simulation of self-sustained detonation wave can be used in hydrodynamic simulation of detonation initiation. Kinetic coefficients are obtained by minimization of difference between profiles of species calculated from the kinetic model and observed in MD simulations of isochoric thermal decomposition with a help of downhill simplex method combined with random walk in multidimensional space of fitting kinetic model parameters.
Hydrodynamic models for slurry bubble column reactors. Fourth technical progress report
Gidaspow, D.
1995-07-01
The objective of this investigation is to convert our ``learning gas-solid-liquid`` fluidization model into a predictive design model. The IIT hydrodynamic model computes the phase velocities and volume fractions of gas, liquid and particulate phases. Model verification involves a comparison of these computed velocities and volume fractions to experimental values. The simulation of Air Product methanol reactors described in this paper are continuing. Granular temperatures and viscosities have been computed. Preliminary measurements of granular temperatures using the Air Product catalysts were obtained using our CCD camera.
Development of a Hydrodynamic Model of Puget Sound and Northwest Straits
Yang, Zhaoqing; Khangaonkar, Tarang P.
2007-12-10
The hydrodynamic model used in this study is the Finite Volume Coastal Ocean Model (FVCOM) developed by the University of Massachusetts at Dartmouth. The unstructured grid and finite volume framework, as well as the capability of wetting/drying simulation and baroclinic simulation, makes FVCOM a good fit to the modeling needs for nearshore restoration in Puget Sound. The model domain covers the entire Puget Sound, Strait of Juan de Fuca, San Juan Passages, and Georgia Strait at the United States-Canada Border. The model is driven by tide, freshwater discharge, and surface wind. Preliminary model validation was conducted for tides at various locations in the straits and Puget Sound using National Oceanic and Atmospheric Administration (NOAA) tide data. The hydrodynamic model was successfully linked to the NOAA oil spill model General NOAA Operational Modeling Environment model (GNOME) to predict particle trajectories at various locations in Puget Sound. Model results demonstrated that the Puget Sound GNOME model is a useful tool to obtain first-hand information for emergency response such as oil spill and fish migration pathways.
The hydrodynamic model testing for closed loop DP assisted mooring
Aalbers, A.B.; Merchant, A.A.
1996-12-31
Far East Levingston Shipbuilding (FELS) is presently completing the construction of the Smedvig Production Unit SPU 380, which will be operated as FPSO for Esso Balder Field Offshore Norway. In good cooperation with FELS and ND and A Inc. of Houston an extensive model test program was carried out for approval and optimization of the DP assisted mooring system. The main aspects were: investigate the performance of the mooring in two water depths, i.e. 250 m and 70 m; optimization of DP control for the three azimuthing thrusters; measurement of motions and wave induced loads at e.g., the bilge keels, keel and deckhouse front; and determination of limit sea state for turning the vessel around against the weather. The tests were carried out in the Wave and Current Basin of MARIN, using a closed loop DP control system to steer the thrusters. The paper presents the findings with respect to the effect of DP control strategy on mooring loads and presents selected results of wave induced loads on bilge keels and deck house.
Hydrodynamic interaction of two swimming model micro-organisms
NASA Astrophysics Data System (ADS)
Ishikawa, Takuji; Simmonds, M. P.; Pedley, T. J.
2006-12-01
In order to understand the rheological and transport properties of a suspension of swimming micro-organisms, it is necessary to analyse the fluid-dynamical interaction of pairs of such swimming cells. In this paper, a swimming micro-organism is modelled as a squirming sphere with prescribed tangential surface velocity, referred to as a squirmer. The centre of mass of the sphere may be displaced from the geometric centre (bottom-heaviness). The effects of inertia and Brownian motion are neglected, because real micro-organisms swim at very low Reynolds numbers but are too large for Brownian effects to be important. The interaction of two squirmers is calculated analytically for the limits of small and large separations and is also calculated numerically using a boundary-element method. The analytical and the numerical results for the translational rotational velocities and for the stresslet of two squirmers correspond very well. We sought to generate a database for an interacting pair of squirmers from which one can easily predict the motion of a collection of squirmers. The behaviour of two interacting squirmers is discussed phenomenologically, too. The results for the trajectories of two squirmers show that first the squirmers attract each other, then they change their orientation dramatically when they are in near contact and finally they separate from each other. The effect of bottom-heaviness is considerable. Restricting the trajectories to two dimensions is shown to give misleading results. Some movies of interacting squirmers are available with the online version of the paper.
Applying downscaled global climate model data to a hydrodynamic surface-water and groundwater model
Swain, Eric; Stefanova, Lydia; Smith, Thomas
2014-01-01
Precipitation data from Global Climate Models have been downscaled to smaller regions. Adapting this downscaled precipitation data to a coupled hydrodynamic surface-water/groundwater model of southern Florida allows an examination of future conditions and their effect on groundwater levels, inundation patterns, surface-water stage and flows, and salinity. The downscaled rainfall data include the 1996-2001 time series from the European Center for Medium-Range Weather Forecasting ERA-40 simulation and both the 1996-1999 and 2038-2057 time series from two global climate models: the Community Climate System Model (CCSM) and the Geophysical Fluid Dynamic Laboratory (GFDL). Synthesized surface-water inflow datasets were developed for the 2038-2057 simulations. The resulting hydrologic simulations, with and without a 30-cm sea-level rise, were compared with each other and field data to analyze a range of projected conditions. Simulations predicted generally higher future stage and groundwater levels and surface-water flows, with sea-level rise inducing higher coastal salinities. A coincident rise in sea level, precipitation and surface-water flows resulted in a narrower inland saline/fresh transition zone. The inland areas were affected more by the rainfall difference than the sea-level rise, and the rainfall differences make little difference in coastal inundation, but a larger difference in coastal salinities.
Two-phase electro-hydrodynamic flow modeling by a conservative level set model.
Lin, Yuan
2013-03-01
The principles of electro-hydrodynamic (EHD) flow have been known for more than a century and have been adopted for various industrial applications, for example, fluid mixing and demixing. Analytical solutions of such EHD flow only exist in a limited number of scenarios, for example, predicting a small deformation of a single droplet in a uniform electric field. Numerical modeling of such phenomena can provide significant insights about EHDs multiphase flows. During the last decade, many numerical results have been reported to provide novel and useful tools of studying the multiphase EHD flow. Based on a conservative level set method, the proposed model is able to simulate large deformations of a droplet by a steady electric field, which is beyond the region of theoretic prediction. The model is validated for both leaky dielectrics and perfect dielectrics, and is found to be in excellent agreement with existing analytical solutions and numerical studies in the literature. Furthermore, simulations of the deformation of a water droplet in decyl alcohol in a steady electric field match better with published experimental data than the theoretical prediction for large deformations. Therefore the proposed model can serve as a practical and accurate tool for simulating two-phase EHD flow.
NASA Astrophysics Data System (ADS)
Albano, Raffaele; Sole, Aurelia; Mirauda, Domenica; Adamowski, Jan
2016-10-01
Large debris, including vehicles parked along floodplains, can cause severe damage and significant loss of life during urban area flash-floods. In this study, the authors validated and applied the Smoothed Particle Hydrodynamics (SPH) model, developed in Amicarelli et al. (2015), which reproduces in 3D the dynamics of rigid bodies driven by free surface flows, to the design of flood mitigation measures. To validate the model, the authors compared the model's predictions to the results of an experimental setup, involving a dam breach that strikes two fixed obstacles and three transportable floating bodies. Given the accuracy of the results, in terms of water depth over time and the time history of the bodies' movements, the SPH model explored in this study was used to analyse the mitigation efficiency of a proposed structural intervention - the use of small barriers (groynes) to prevent the transport of floating bodies. Different groynes configurations were examined to identify the most appropriate design and layout for urban area flash-flood damage mitigation. The authors found that groynes positioned upstream and downstream of each floating body can be effective as a risk mitigation measure for damage resulting from their movement.
Torak, L.J.
1993-01-01
A MODular, Finite-Element digital-computer program (MODFE) was developed to simulate steady or unsteady-state, two-dimensional or axisymmetric ground-water flow. Geometric- and hydrologic-aquifer characteristics in two spatial dimensions are represented by triangular finite elements and linear basis functions; one-dimensional finite elements and linear basis functions represent time. Finite-element matrix equations are solved by the direct symmetric-Doolittle method or the iterative modified, incomplete-Cholesky, conjugate-gradient method. Physical processes that can be represented by the model include (1) confined flow, unconfined flow (using the Dupuit approximation), or a combination of both; (2) leakage through either rigid or elastic confining beds; (3) specified recharge or discharge at points, along lines, and over areas; (4) flow across specified-flow, specified-head, or bead-dependent boundaries; (5) decrease of aquifer thickness to zero under extreme water-table decline and increase of aquifer thickness from zero as the water table rises; and (6) head-dependent fluxes from springs, drainage wells, leakage across riverbeds or confining beds combined with aquifer dewatering, and evapotranspiration. The report describes procedures for applying MODFE to ground-water-flow problems, simulation capabilities, and data preparation. Guidelines for designing the finite-element mesh and for node numbering and determining band widths are given. Tables are given that reference simulation capabilities to specific versions of MODFE. Examples of data input and model output for different versions of MODFE are provided.
Hydrodynamic Instability and Thermal Coupling in a Dynamic Model of Liquid-Propellant Combustion
NASA Technical Reports Server (NTRS)
Margolis, S. B.
1999-01-01
For liquid-propellant combustion, the Landau/Levich hydrodynamic models have been combined and extended to account for a dynamic dependence of the burning rate on the local pressure and temperature fields. Analysis of these extended models is greatly facilitated by exploiting the realistic smallness of the gas-to-liquid density ratio rho. Neglecting thermal coupling effects, an asymptotic expression was then derived for the cellular stability boundary A(sub p)(k) where A(sub p) is the pressure sensitivity of the burning rate and k is the disturbance wavenumber. The results explicitly indicate the stabilizing effects of gravity on long-wave disturbances, and those of viscosity and surface tension on short-wave perturbations, and the instability associated with intermediate wavenumbers for critical negative values of A(sub p). In the limit of weak gravity, hydrodynamic instability in liquid-propellant combustion becomes a long-wave, instability phenomenon, whereas at normal gravity, this instability is first manifested through O(1) wavenumbers. In addition, surface tension and viscosity (both liquid and gas) each produce comparable effects in the large-wavenumber regime, thereby providing important modifications to the previous analyses in which one or more of these effects was neglected. For A(sub p)= O, the Landau/Levich results are recovered in appropriate limiting cases, although this typically corresponds to a hydrodynamically unstable parameter regime for p << 1. In addition to the classical cellular form of hydrodynamic stability, there exists a pulsating form corresponding to the loss of stability of steady, planar burning to time-dependent perturbations. This occurs for negative values of the parameter A(sub p), and is thus absent from the original Landau/Levich models. In the extended model, however, there exists a stable band of negative pressure sensitivities bounded above by the Landau type of instability, and below by this pulsating form of hydrodynamic
Hydrodynamic Instability and Thermal Coupling in a Dynamic Model of Liquid-Propellant Combustion
NASA Technical Reports Server (NTRS)
Margolis, S. B.
1999-01-01
For liquid-propellant combustion, the Landau/Levich hydrodynamic models have been combined and extended to account for a dynamic dependence of the burning rate on the local pressure and temperature fields. Analysis of these extended models is greatly facilitated by exploiting the realistic smallness of the gas-to-liquid density ratio rho. Neglecting thermal coupling effects, an asymptotic expression was then derived for the cellular stability boundary A(sub p)(k) where A(sub p) is the pressure sensitivity of the burning rate and k is the disturbance wavenumber. The results explicitly indicate the stabilizing effects of gravity on long-wave disturbances, and those of viscosity and surface tension on short-wave perturbations, and the instability associated with intermediate wavenumbers for critical negative values of A(sub p). In the limit of weak gravity, hydrodynamic instability in liquid-propellant combustion becomes a long-wave, instability phenomenon, whereas at normal gravity, this instability is first manifested through O(1) wavenumbers. In addition, surface tension and viscosity (both liquid and gas) each produce comparable effects in the large-wavenumber regime, thereby providing important modifications to the previous analyses in which one or more of these effects was neglected. For A(sub p)= O, the Landau/Levich results are recovered in appropriate limiting cases, although this typically corresponds to a hydrodynamically unstable parameter regime for p << 1. In addition to the classical cellular form of hydrodynamic stability, there exists a pulsating form corresponding to the loss of stability of steady, planar burning to time-dependent perturbations. This occurs for negative values of the parameter A(sub p), and is thus absent from the original Landau/Levich models. In the extended model, however, there exists a stable band of negative pressure sensitivities bounded above by the Landau type of instability, and below by this pulsating form of hydrodynamic
Hydrodynamic models of a cepheid atmosphere. Ph.D. Thesis - Maryland Univ., College Park
NASA Technical Reports Server (NTRS)
Karp, A. H.
1974-01-01
A method for including the solution of the transfer equation in a standard Henyey type hydrodynamic code was developed. This modified Henyey method was used in an implicit hydrodynamic code to compute deep envelope models of a classical Cepheid with a period of 12(d) including radiative transfer effects in the optically thin zones. It was found that the velocity gradients in the atmosphere are not responsible for the large microturbulent velocities observed in Cepheids but may be responsible for the occurrence of supersonic microturbulence. It was found that the splitting of the cores of the strong lines is due to shock induced temperature inversions in the line forming region. The adopted light, color, and velocity curves were used to study three methods frequently used to determine the mean radii of Cepheids. It is concluded that an accuracy of 10% is possible only if high quality observations are used.
Montaño-Ley, Y; Peraza-Vizcarra, R; Páez-Osuna, F
2007-05-01
The tidal hydrodynamics of the Topolobampo coastal lagoon system (Mexico) has been investigated through a modified two dimensional non-linear hydrodynamic finite difference model. The advective and diffusive process acting over a hypothetical pollutant released into the coastal lagoon have also been simulated. Maxima tidal currents (0.85 m/s) were predicted within the main channel, in agree with direct measurements. The direction of the observed fastest currents (SW), also agree quite well with the direction of the strongest tidal current predicted in this investigation, which occur during the ebb when the water of the coastal lagoon is discharged into the Gulf of California. Residual currents (0.01-0.05 m/s) were also predicted. The hypothetical pollutant released within the Topolobampo Harbor would spread to both Ohuira and Topolobampo sections, reaching the inlet after approximately 12 days.
Calibration of HEC-Ras hydrodynamic model using gauged discharge data and flood inundation maps
NASA Astrophysics Data System (ADS)
Tong, Rui; Komma, Jürgen
2017-04-01
The estimation of flood is essential for disaster alleviation. Hydrodynamic models are implemented to predict the occurrence and variance of flood in different scales. In practice, the calibration of hydrodynamic models aims to search the best possible parameters for the representation the natural flow resistance. Recent years have seen the calibration of hydrodynamic models being more actual and faster following the advance of earth observation products and computer based optimization techniques. In this study, the Hydrologic Engineering River Analysis System (HEC-Ras) model was set up with high-resolution digital elevation model from Laser scanner for the river Inn in Tyrol, Austria. 10 largest flood events from 19 hourly discharge gauges and flood inundation maps were selected to calibrate the HEC-Ras model. Manning roughness values and lateral inflow factors as parameters were automatically optimized with the Shuffled complex with Principal component analysis (SP-UCI) algorithm developed from the Shuffled Complex Evolution (SCE-UA). Different objective functions (Nash-Sutcliffe model efficiency coefficient, the timing of peak, peak value and Root-mean-square deviation) were used in single or multiple way. It was found that the lateral inflow factor was the most sensitive parameter. SP-UCI algorithm could avoid the local optimal and achieve efficient and effective parameters in the calibration of HEC-Ras model using flood extension images. As results showed, calibration by means of gauged discharge data and flood inundation maps, together with objective function of Nash-Sutcliffe model efficiency coefficient, was very robust to obtain more reliable flood simulation, and also to catch up with the peak value and the timing of peak.
Using a coupled eco-hydrodynamic model to predict habitat for target species following dam removal
Tomsic, C.A.; Granata, T.C.; Murphy, R.P.; Livchak, C.J.
2007-01-01
A habitat suitability index (HSI) model was developed for a water quality sensitive fish (Greater Redhorse) and macroinvertebrate (Plecoptera) species to determine the restoration success of the St. John Dam removal for the Sandusky River (Ohio). An ArcGIS?? model was created for pre- and post-dam removal scenarios. Inputs to the HSI model consist of substrate distributions from river surveys, and water level and velocity time series, outputs from a hydrodynamic model. The ArcGIS?? model predicted habitat suitability indices at 45 river cross-sections in the hydrodynamic model. The model was programmed to produce polygon layers, using graphical user interfaces that were displayed in the ArcGIS?? environment. The results of the model clearly show an increase of habitat suitability from pre- to post-dam removal periods and in the former reservoir. The change in suitability of the model is attributed mostly to the change in depth in the river following the dam removal for both the fish and invertebrate species. The results of the invertebrate model followed the same positive trend as species enumerations from the river basin. ?? 2007 Elsevier B.V. All rights reserved.
Effect of longitudinal ridges on the hydrodynamic performance of a leatherback turtle model
NASA Astrophysics Data System (ADS)
Bang, Kyeongtae; Kim, Jooha; Lee, Sang-Im; Choi, Haecheon
2014-11-01
Leatherback sea turtles (Dermochelys coriacea) known as the fastest swimmer and the deepest diver among marine turtles have five longitudinal ridges on their carapace, and these ridges are the most remarkable morphological features distinguished from other marine turtles. To investigate the effect of these ridges on the hydrodynamic performance of the leatherback turtle, we model a carapace with and without ridges using a stuffed leatherback turtle in the National Science Museum, Korea. We measure the drag and lift forces on the ridged model in the ranges of real leatherback turtles' Reynolds number (Re) and angle of attack (α), and compare them with those of non-ridged model. At α < 6°, longitudinal ridges decrease drag on the ridged model by up to 32% compared to non-ridged model. On the other hand, at α > 6°, the drag and lift coefficients of the ridged model are higher than those of the non-ridged model, and the lift-to-drag ratio of the ridged model is higher by about 7% than that of the non-ridged model. We also measure the velocity field around both models using a particle image velocimetry and explain the hydrodynamic role of ridges in relation to diving behaviors of leatherback sea turtles. Supported by the NRF Program (2011-0028032).
Dadzie, S Kokou; Reese, Jason M
2012-04-01
There are some hydrodynamic equations that, while their parent kinetic equation satisfies fundamental mechanical properties, appear themselves to violate mechanical or thermodynamic properties. This paper aims to shed some light on the source of this problem. Starting with diffusive volume hydrodynamic models, the microscopic temporal and spatial scales are first separated at the kinetic level from the macroscopic scales at the hydrodynamic level. Then, we consider Klimontovich's spatial stochastic version of the Boltzmann kinetic equation and show that, for small local Knudsen numbers, the stochastic term vanishes and the kinetic equation becomes the Boltzmann equation. The collision integral dominates in the small local Knudsen number regime, which is associated with the exact traditional continuum limit. We find a subdomain of the continuum range, which the conventional Knudsen number classification does not account for appropriately. In this subdomain, it is possible to obtain a fully mechanically consistent volume (or mass) diffusion model that satisfies the second law of thermodynamics on the grounds of extended non-local-equilibrium thermodynamics.
Comparison of two methods of mathematical modeling in hydrodynamic sealing gap
NASA Astrophysics Data System (ADS)
Krutil, Jaroslav; Fojtášek, Kamil; Dvořák, Lukáš
2015-05-01
The aim of work is to compare two possible methods of mathematical modeling of hydrodynamic instabilities. This comparison is performed by monitoring the formation and evolution of Taylor vortices in hydrodynamic sealing gap. Sealing gaps are a part of the hydraulic machines with the impeller, such as turbines and pumps, and they have an effect on the volumetric efficiency of these devices. This work presents two examples of sealing gaps. These examples are closed sealing gap and modified sealing gap with expansion chamber. On these two examples are applied procedures of solution contained in CFD software (ANSYS Fluent 14.5). In ANSYS Fluent is two possible basic approaches of solution this task: the moving wall method and the sliding mesh method. The result of work is monitoring the impact of the expansion chamber on the formation of hydrodynamic instabilities in the sealing gap. Another result is comparison of two used methods of mathematical modeling, which shows that both methods can be used for similar tasks.
High-energy Particle Transport in Three-dimensional Hydrodynamic Models of Colliding-wind Binaries
NASA Astrophysics Data System (ADS)
Reitberger, K.; Kissmann, R.; Reimer, A.; Reimer, O.; Dubus, G.
2014-02-01
Massive stars in binary systems (such as WR 140, WR 147, or η Carinae) have long been regarded as potential sources of high-energy γ-rays. The emission is thought to arise in the region where the stellar winds collide and produce relativistic particles that subsequently might be able to emit γ-rays. Detailed numerical hydrodynamic simulations have already offered insight into the complex dynamics of the wind collision region (WCR), while independent analytical studies, albeit with simplified descriptions of the WCR, have shed light on the spectra of charged particles. In this paper, we describe a combination of these two approaches. We present a three-dimensional hydrodynamical model for colliding stellar winds and compute spectral energy distributions of relativistic particles for the resulting structure of the WCR. The hydrodynamic part of our model incorporates the line-driven acceleration of the winds, gravity, orbital motion, and the radiative cooling of the shocked plasma. In our treatment of charged particles, we consider diffusive shock acceleration in the WCR and the subsequent cooling via inverse Compton losses (including Klein-Nishina effects), bremsstrahlung, collisions, and other energy loss mechanisms.
Validating a hydrodynamic framework for long-term modelling of the German Bight
NASA Astrophysics Data System (ADS)
Koesters, Frank; Pluess, Andreas; Heyer, Harro; Kastens, Marko; Sehili, Aissa
2010-05-01
The intention of the "AufMod" project is to set up a modelling framework for questions concerning the large-scale, long-term morphodynamic evolution of the German Bight. First a hydrodynamic model has been set up which includes the entire North Sea and a sophisticated representation of the German Bight. In a second step, simulations of sediment transport and morphodynamic changes will be processed. This paper deals with the calibration and validation process for the hydrodynamic model in detail. The starting point for "AufMod" was the aim to better understand the morphodynamic processes in the German Bight. Changes in bottom topography need to be predicted to ensure a safe and easy transport through the German waterways leading to ports at the German coast such as Hamburg and Bremerhaven. Within "AufMod" this question is addressed through a combined effort of gaining a comprehensive sedimentological and bathymetric data set as well as running different numerical models. The model is based on the numerical method UnTRIM (Casulli and Zanolli, 2002). The model uses an unstructured grid in the horizontal to provide a good representation of the complex topography. The spatial resolution increases from about 20 km in the North Sea to 20 m within the estuaries. The model forcing represents conditions for the year 2006 and consists of wind stress at the surface, water level elevation and salinity at the open boundaries as well as freshwater inflows. Temperature is not taken into account. For the model validation, there exists a large number of over 40 hydrodynamic monitoring stations which are used to compare modelled and measured data. The calibration process consists of adapting the tidal components at the open boundaries following the approach of Pluess (2003). The validation process includes the analysis of tidal components of water level elevation and current values as well as an analysis of tidal characteristic values, e.g. tidal low and high water. Based on these
Coupling Kinetic and Hydrodynamic Models for Simulations of Gas Flows and Weakly Ionized Plasmas
NASA Astrophysics Data System (ADS)
Kolobov, V. I.; Arslanbekov, R. R.
2011-10-01
This paper presents adaptive kinetic/fluid models for simulations of gases and weakly ionized plasmas. We first describe a Unified Flow Solver (UFS), which combines Adaptive Mesh Refinement with automatic selection of kinetic or hydrodynamic models for different parts of flows. This Adaptive Mesh and Algorithm Refinement (AMAR) technique limits expensive atomistic-scale solutions only to the regions where they are needed. We present examples of plasma simulations with fluid models and describe kinetic solvers for electrons which are currently being incorporated into AMAR techniques for plasma simulations.
NASA Astrophysics Data System (ADS)
Wang, Yunong; Cheng, Rongjun; Ge, Hongxia
2017-08-01
In this paper, a lattice hydrodynamic model is derived considering not only the effect of flow rate difference but also the delayed feedback control signal which including more comprehensive information. The control method is used to analyze the stability of the model. Furthermore, the critical condition for the linear steady traffic flow is deduced and the numerical simulation is carried out to investigate the advantage of the proposed model with and without the effect of flow rate difference and the control signal. The results are consistent with the theoretical analysis correspondingly.
Assimilation of CryoSat-2 altimetry to a hydrodynamic model of the Brahmaputra river
NASA Astrophysics Data System (ADS)
Schneider, Raphael; Nygaard Godiksen, Peter; Ridler, Marc-Etienne; Madsen, Henrik; Bauer-Gottwein, Peter
2016-04-01
Remote sensing provides valuable data for parameterization and updating of hydrological models, for example water level measurements of inland water bodies from satellite radar altimeters. Satellite altimetry data from repeat-orbit missions such as Envisat, ERS or Jason has been used in many studies, also synthetic wide-swath altimetry data as expected from the SWOT mission. This study is one of the first hydrologic applications of altimetry data from a drifting orbit satellite mission, namely CryoSat-2. CryoSat-2 is equipped with the SIRAL instrument, a new type of radar altimeter similar to SRAL on Sentinel-3. CryoSat-2 SARIn level 2 data is used to improve a 1D hydrodynamic model of the Brahmaputra river basin in South Asia set up in the DHI MIKE 11 software. CryoSat-2 water levels were extracted over river masks derived from Landsat imagery. After discharge calibration, simulated water levels were fitted to the CryoSat-2 data along the Assam valley by adapting cross section shapes and datums. The resulting hydrodynamic model shows accurate spatio-temporal representation of water levels, which is a prerequisite for real-time model updating by assimilation of CryoSat-2 altimetry or multi-mission data in general. For this task, a data assimilation framework has been developed and linked with the MIKE 11 model. It is a flexible framework that can assimilate water level data which are arbitrarily distributed in time and space. Different types of error models, data assimilation methods, etc. can easily be used and tested. Furthermore, it is not only possible to update the water level of the hydrodynamic model, but also the states of the rainfall-runoff models providing the forcing of the hydrodynamic model. The setup has been used to assimilate CryoSat-2 observations over the Assam valley for the years 2010 to 2013. Different data assimilation methods and localizations were tested, together with different model error representations. Furthermore, the impact of
NASA Astrophysics Data System (ADS)
Ashton, A. D.; Ortiz, A. C.; Lorenzo-Trueba, J.; Donnelly, J. P.
2016-02-01
Between the deep open ocean and backing lagoon, atolls and barrier reefs are comprised of a series of linked environments, from the coral-dominated and carbonate-producing fore-reef, the shallow reef flat typically consisting of sediment and/or concreted carbonate, to, in some cases, detrital reef islands. Using the hydrodynamic components of the XBeach model, we have developed a consistent conceptual model that can be used to explain the development of a constant-depth reef flat that subsequently extends lagoonward as sediment is produced at the reef edge. As reef flats widen, shear stresses are minimized mid-flat, which could lead to the development of incipient islands that form at a distance from the ocean. Emergent islands block across-reef flow, and subsequently are expected to prograde seawards until reaching a steady-state distance from the shore. To quantify this conceptual model, and to better understand how interconnected reef systems may respond to climate change effects, including sea-level rise, change in storminess, and different carbonate production rates, we use XBeach model results spanning a variety of forcing conditions (offshore wave height) and reef geometries (reef flat width and depth, presence of reef island) to parameterize a numerical model of coupled reef flat and reef island dynamics. Model results demonstrate that during rising sea levels, the reef flat can serve as a sediment trap, starving reef islands of detrital sediment that would otherwise fortify the shore against sea-level-rise-driven erosion. On the other hand, if reef flats are currently shallow (likely due to geologic inheritance), such that sea-level rise does not result in sediment accumulation on the flat, sea-level rise will have less of an effect of reef island shorelines. Overall, the model allows a parameterized framework that can be applied to understand the interconnected response of coupled reef environments to climate change, with potential application to atolls
NASA Technical Reports Server (NTRS)
Hunter, Craig A.
1995-01-01
An analytical/numerical method has been developed to predict the static thrust performance of non-axisymmetric, two-dimensional convergent-divergent exhaust nozzles. Thermodynamic nozzle performance effects due to over- and underexpansion are modeled using one-dimensional compressible flow theory. Boundary layer development and skin friction losses are calculated using an approximate integral momentum method based on the classic karman-Polhausen solution. Angularity effects are included with these two models in a computational Nozzle Performance Analysis Code, NPAC. In four different case studies, results from NPAC are compared to experimental data obtained from subscale nozzle testing to demonstrate the capabilities and limitations of the NPAC method. In several cases, the NPAC prediction matched experimental gross thrust efficiency data to within 0.1 percent at a design NPR, and to within 0.5 percent at off-design conditions.
NASA Technical Reports Server (NTRS)
Sislian, J. P.
1978-01-01
The full Navier-Stokes time-dependent, compressible, turbulent, mean-flow equations in mass-averaged variables for plane or axisymmetric flow are presented. The equations are derived in a body-oriented, orthogonal, curvilinear coordinate system. Turbulence is modelled by a system of two equations for mass-averaged turbulent kinetic energy and dissipation rate proposed. These equations are rederived and some new features are discussed. A system of second order boundary layer equations is then derived which includes the effects of longitudinal curvature and the normal pressure gradient. The Wilcox and Chambers approach is used in considering effects of streamline curvature on turbulence phenomena in turbulent boundary layer type flows. Their two-equation turbulence model with curvature terms are rederived for the cases considered in the present report. The derived system equations serves as a basis for an investigation of problems where streamline curvature is of the order of the characteristic length in the longitudinal direction.
Numerical modeling of the hydrodynamics of the Northeastern Corridor Reserve in Puerto Rico
NASA Astrophysics Data System (ADS)
Salgado-Domínguez, G.; Canals, M.
2016-02-01
To develop an appropriate management plan for the marine section of the Northeast Corridor Reserve (NECR) of Puerto Rico it is necessary to understand the hydrodynamic connectivity between the different regions within the NECR. The USACE CMS Flow model has been implemented for the NECR using very high resolution telescoping grids, with a special focus on the complex coral reef areas of the La Cordillera Reefs Natural Reserve, established by the Department of Natural and Environmental Resources of Puerto Rico. To ensure correct application of boundary conditions and realistic representation of the tidal elevation within the NECR, water elevation model output data was compared with the Fajardo tide gauge; while the ocean current model output was compared with the depth-integrated observed currents at the CariCOOS Vieques Sound buoy. Comparison of model performance with buoy and tide gauge data has shown good agreement, however, further model tuning is necessary to optimize model performance. Further improvement of our models depends largely on obtaining more accurate boundary conditions as well as better wind forcing. We are currently implementing the USACE Particle Tracking Model (PTM) to characterize particle dispersion within the NECR. In the long-term, full 3D hydrodynamic models including riverine forcing hold the key to a complete understanding of larvae and sediment dispersion within the NECR.
NASA Astrophysics Data System (ADS)
Moreno Navas, Juan; Telfer, Trevor C.; Ross, Lindsay G.
2011-04-01
Hydrographic conditions, and particularly current speeds, have a strong influence on the management of fish cage culture. These hydrodynamic conditions can be used to predict particle movement within the water column and the results used to optimise environmental conditions for effective site selection, setting of environmental quality standards, waste dispersion, and potential disease transfer. To this end, a 3D hydrodynamic model, MOHID, has been coupled to a particle tracking model to study the effects of mean current speed, quiescent water periods and bulk water circulation in Mulroy Bay, Co. Donegal Ireland, an Irish fjard (shallow fjordic system) important to the aquaculture industry. A Lagangrian method simulated the instantaneous release of "particles" emulating discharge from finfish cages to show the behaviour of waste in terms of water circulation and water exchange. The 3D spatial models were used to identify areas of mixed and stratified water using a version of the Simpson-Hunter criteria, and to use this in conjunction with models of current flow for appropriate site selection for salmon aquaculture. The modelled outcomes for stratification were in good agreement with the direct measurements of water column stratification based on observed density profiles. Calculations of the Simpson-Hunter tidal parameter indicated that most of Mulroy Bay was potentially stratified with a well mixed region over the shallow channels where the water is faster flowing. The fjard was characterised by areas of both very low and high mean current speeds, with some areas having long periods of quiescent water. The residual current and the particle tracking animations created through the models revealed an anticlockwise eddy that may influence waste dispersion and potential for disease transfer, among salmon cages and which ensures that the retention time of waste substances from cages is extended. The hydrodynamic model results were incorporated into the ArcView TM GIS
NASA Astrophysics Data System (ADS)
Dascalescu, A. E.; Lazaroiu, G.; Scupi, A. A.; Oanta, E.
2016-08-01
The rotating half-bridge of a settling tank is employed to sweep the sludge from the wastewater and to vacuum and sent it to the central collector. It has a complex geometry but the main beam may be considered a slender bar loaded by the following category of forces: concentrated forces produced by the weight of the scrapping system of blades, suction pipes, local sludge collecting chamber, plus the sludge in the horizontal sludge transporting pipes; forces produced by the access bridge; buoyant forces produced by the floating barrels according to Archimedes’ principle; distributed forces produced by the weight of the main bridge; hydrodynamic forces. In order to evaluate the hydrodynamic loads we have conceived a numerical model based on the finite volume method, using the ANSYS-Fluent software. To model the flow we used the equations of Reynolds Averaged Navier-Stokes (RANS) for liquids together with Volume of Fluid model (VOF) for multiphase flows. For turbulent model k-epsilon we used the equation for turbulent kinetic energy k and dissipation epsilon. These results will be used to increase the accuracy of the loads’ sub-model in the theoretical models, e. the finite element model and the analytical model.
NASA Astrophysics Data System (ADS)
Ferrarin, Christian; Bergamasco, Alessandro; Umgiesser, Georg; Cucco, Andrea
2013-05-01
Since advection and diffusion are the main physical processes that influence the cleaning capacity of coastal transitional waters, the 3-D spatial distribution of the water renewal times was used to delineate a physically-based zonation scheme. The temporal and spatial variations of the hydrodynamics are assessed using a validated three dimensional hydrodynamic finite element model. The developed methodology was applied to the Cape Peloro system, a coastal protected area located in the Messina Strait (Italy) consisting of two connected small brackish basins: the shallow Lake Ganzirri and the deep meromictic Lake Faro. The hydrodynamics of the two coastal lakes shows strong seasonal and spatial variation. The 3-D distribution of the water renewal times suggests a horizontal partition of the Lake Ganzirri into two sub-basins and a vertical zonation of the Lake Faro, with the mixolimnion extending till 10 m depth and the presence of a persistent bottom stagnant layer. The derived physically-based zonation scheme helps in explaining the highly heterogeneous spatial distribution of many biogeochemical variables in the Cape Peloro coastal system.
Bailly-Bechet, Marc; Kerszberg, Michel; Gaill, Françoise; Pradillon, Florence
2008-12-07
Deep-sea hydrothermal vent animal communities along oceanic ridges are both patchy and transient. Larval dispersal is a key factor in understanding how these communities function and are maintained over generations. To date, numerical approaches simulating larval dispersal considered the effect of oceanic currents on larval transportation over hundreds of kilometers but very seldom looked at the effect of local conditions within meters around chimneys. However, small scale significant variations in the hydrodynamics may influence larval fate in its early stages after release, and hence have a knock-on effect on both dispersal and colonization processes. Here we present a new numerical approach to the study of larval dispersal, considering small scales within the range of the biological communities, called "bio-hydrodynamical" scale, and ranging from a few centimeters to a few meters around hydrothermal sources. We use a physical model for the vent based on jet theory and compute the turbulent velocity field around the smoker. Larvae are considered as passive particles whose trajectories are affected by hydrodynamics, topography of the vent chimney and larval biological properties. Our model predicts that bottom currents often dominate all other factors either by entraining all larvae away from the vent or enforcing strong colonization rates. When bottom currents are very slow (<1 mms(-1)), general larvae motion is upwards due to entrainment by the main smoker jet. In this context, smokers with vertical slopes favor retention of larvae because larval initial trajectory is nearly parallel to the smoker wall, which increases the chances to settle. This retention phenomenon is intensified with increasing velocity of the main smoker jet because entrainment in the high velocity plume is preceded by a phase when larvae are attracted towards the smoker wall, which occurs earlier with higher velocity of the main jet. Finally, the buoyancy rate of the larvae, measured to be
Castor, J I
2003-10-16
The discipline of radiation hydrodynamics is the branch of hydrodynamics in which the moving fluid absorbs and emits electromagnetic radiation, and in so doing modifies its dynamical behavior. That is, the net gain or loss of energy by parcels of the fluid material through absorption or emission of radiation are sufficient to change the pressure of the material, and therefore change its motion; alternatively, the net momentum exchange between radiation and matter may alter the motion of the matter directly. Ignoring the radiation contributions to energy and momentum will give a wrong prediction of the hydrodynamic motion when the correct description is radiation hydrodynamics. Of course, there are circumstances when a large quantity of radiation is present, yet can be ignored without causing the model to be in error. This happens when radiation from an exterior source streams through the problem, but the latter is so transparent that the energy and momentum coupling is negligible. Everything we say about radiation hydrodynamics applies equally well to neutrinos and photons (apart from the Einstein relations, specific to bosons), but in almost every area of astrophysics neutrino hydrodynamics is ignored, simply because the systems are exceedingly transparent to neutrinos, even though the energy flux in neutrinos may be substantial. Another place where we can do ''radiation hydrodynamics'' without using any sophisticated theory is deep within stars or other bodies, where the material is so opaque to the radiation that the mean free path of photons is entirely negligible compared with the size of the system, the distance over which any fluid quantity varies, and so on. In this case we can suppose that the radiation is in equilibrium with the matter locally, and its energy, pressure and momentum can be lumped in with those of the rest of the fluid. That is, it is no more necessary to distinguish photons from atoms, nuclei and electrons, than it is to distinguish
NASA Astrophysics Data System (ADS)
Premaratne, Pavithra Dhanuka
Disruption and fragmentation of an asteroid using nuclear explosive devices (NEDs) is a highly complex yet a practical solution to mitigating the impact threat of asteroids with short warning time. A Hypervelocity Asteroid Intercept Vehicle (HAIV) concept, developed at the Asteroid Deflection Research Center (ADRC), consists of a primary vehicle that acts as kinetic impactor and a secondary vehicle that houses NEDs. The kinetic impactor (lead vehicle) strikes the asteroid creating a crater. The secondary vehicle will immediately enter the crater and detonate its nuclear payload creating a blast wave powerful enough to fragment the asteroid. The nuclear subsurface explosion modeling and hydrodynamic simulation has been a challenging research goal that paves the way an array of mission critical information. A mesh-free hydrodynamic simulation method, Smoothed Particle Hydrodynamics (SPH) was utilized to obtain both qualitative and quantitative solutions for explosion efficiency. Commercial fluid dynamics packages such as AUTODYN along with the in-house GPU accelerated SPH algorithms were used to validate and optimize high-energy explosion dynamics for a variety of test cases. Energy coupling from the NED to the target body was also examined to determine the effectiveness of nuclear subsurface explosions. Success of a disruption mission also depends on the survivability of the nuclear payload when the secondary vehicle approaches the newly formed crater at a velocity of 10 km/s or higher. The vehicle may come into contact with debris ejecting the crater which required the conceptual development of a Whipple shield. As the vehicle closes on the crater, its skin may also experience extreme temperatures due to heat radiated from the crater bottom. In order to address this thermal problem, a simple metallic thermal shield design was implemented utilizing a radiative heat transfer algorithm and nodal solutions obtained from hydrodynamic simulations.
NASA Astrophysics Data System (ADS)
Donmez, Orhan
We present a general procedure to solve the General Relativistic Hydrodynamical (GRH) equations with Adaptive-Mesh Refinement (AMR) and model of an accretion disk around a black hole. To do this, the GRH equations are written in a conservative form to exploit their hyperbolic character. The numerical solutions of the general relativistic hydrodynamic equations is done by High Resolution Shock Capturing schemes (HRSC), specifically designed to solve non-linear hyperbolic systems of conservation laws. These schemes depend on the characteristic information of the system. We use Marquina fluxes with MUSCL left and right states to solve GRH equations. First, we carry out different test problems with uniform and AMR grids on the special relativistic hydrodynamics equations to verify the second order convergence of the code in 1D, 2 D and 3D. Second, we solve the GRH equations and use the general relativistic test problems to compare the numerical solutions with analytic ones. In order to this, we couple the flux part of general relativistic hydrodynamic equation with a source part using Strang splitting. The coupling of the GRH equations is carried out in a treatment which gives second order accurate solutions in space and time. The test problems examined include shock tubes, geodesic flows, and circular motion of particle around the black hole. Finally, we apply this code to the accretion disk problems around the black hole using the Schwarzschild metric at the background of the computational domain. We find spiral shocks on the accretion disk. They are observationally expected results. We also examine the star-disk interaction near a massive black hole. We find that when stars are grounded down or a hole is punched on the accretion disk, they create shock waves which destroy the accretion disk.
NASA Technical Reports Server (NTRS)
Chick, Kenneth M.; Gombosi, Tamas I.
1993-01-01
A numerical solution for the multiple light scattering in spherical axisymmetric geometry is applied to the simulation of images of a coma as it would appear to a near-flying satellite such as Giotto. The appearance of symmetric comas and dust jets is examined in detail; the nucleus visibility is studied; the effect of forward scattering is considered; and single and multiple scattering effects are quantified. Attention is given to simulated images of a coma with a hollow cone of dust, as predicted by dust-gas hydrodynamic modeling. The cone's appearance is very similar to the northern area of activity on Comet Halley, observed by the Giotto HMC.
NASA Technical Reports Server (NTRS)
Chick, Kenneth M.; Gombosi, Tamas I.
1993-01-01
A numerical solution for the multiple light scattering in spherical axisymmetric geometry is applied to the simulation of images of a coma as it would appear to a near-flying satellite such as Giotto. The appearance of symmetric comas and dust jets is examined in detail; the nucleus visibility is studied; the effect of forward scattering is considered; and single and multiple scattering effects are quantified. Attention is given to simulated images of a coma with a hollow cone of dust, as predicted by dust-gas hydrodynamic modeling. The cone's appearance is very similar to the northern area of activity on Comet Halley, observed by the Giotto HMC.
Analytic Modeling of the Hydrodynamic, Thermal, and Structural Behavior of Foil Thrust Bearings
NASA Technical Reports Server (NTRS)
Bruckner, Robert J.; DellaCorte, Christopher; Prahl, Joseph M.
2005-01-01
A simulation and modeling effort is conducted on gas foil thrust bearings. A foil bearing is a self acting hydrodynamic device capable of separating stationary and rotating components of rotating machinery by a film of air or other gaseous lubricant. Although simple in appearance these bearings have proven to be complicated devices in analysis. They are sensitive to fluid structure interaction, use a compressible gas as a lubricant, may not be in the fully continuum range of fluid mechanics, and operate in the range where viscous heat generation is significant. These factors provide a challenge to the simulation and modeling task. The Reynolds equation with the addition of Knudsen number effects due to thin film thicknesses is used to simulate the hydrodynamics. The energy equation is manipulated to simulate the temperature field of the lubricant film and combined with the ideal gas relationship, provides density field input to the Reynolds equation. Heat transfer between the lubricant and the surroundings is also modeled. The structural deformations of the bearing are modeled with a single partial differential equation. The equation models the top foil as a thin, bending dominated membrane whose deflections are governed by the biharmonic equation. A linear superposition of hydrodynamic load and compliant foundation reaction is included. The stiffness of the compliant foundation is modeled as a distributed stiffness that supports the top foil. The system of governing equations is solved numerically by a computer program written in the Mathematica computing environment. Representative calculations and comparisons with experimental results are included for a generation I gas foil thrust bearing.
Synthesis of Hydrodynamic and Wave Models with Sediment Data in a Shallow Tidal Embayment.
NASA Astrophysics Data System (ADS)
Jakobsen, N. G.; Kaergaard, K.; Jensen, J. H.
2006-12-01
Hydrodynamic and wave models have been established for Tampa Bay in Florida and the approaches to the Bay on the west Florida Shelf of the Gulf of Mexico. It uses an unstructured, bathymetry-following flexible mesh (bffm) which adapts to the complex coastline and inter-connected navigation channels. The model packages came from DHI Water & Environment. The hydrodynamics were calibrated against tidal currents in the main navigation channel supplied by the NOAA/NOS PORTS system operated by the University of South Florida. The model was validated for a period in September 2004 (including the passing of the hurricane Frances) using data from six tidal gauges in the Bay. Wave data were collected at several stations around the Bay in 2004 and from June 2005 to December 2006. These data were compared with both a full spectrum and parametric wave model. Production runs of all models were made for a 9 month period using measured surface elevation as boundary conditions extending from spring 2004 to winter 2005 and measured wind data at a station within the Bay. The results were used to derive exchange times and local wave climates around the Bay. The hydrodynamic and wave models were then used to determine sediment mobility. It is found that current is the most important influence on sediments in the deeper parts of the Bay but waves dominate sediment dynamics in the shallow regions of the Bay. Swell waves penetrate only a limited distance into the Bay. Comparisons are made with maps of bottom sediment and coastal habitat obtained from various data sources.
NASA Technical Reports Server (NTRS)
Liu, Wei; Petrosian, Vahe; Mariska, John T.
2009-01-01
Acceleration and transport of high-energy particles and fluid dynamics of atmospheric plasma are interrelated aspects of solar flares, but for convenience and simplicity they were artificially separated in the past. We present here self consistently combined Fokker-Planck modeling of particles and hydrodynamic simulation of flare plasma. Energetic electrons are modeled with the Stanford unified code of acceleration, transport, and radiation, while plasma is modeled with the Naval Research Laboratory flux tube code. We calculated the collisional heating rate directly from the particle transport code, which is more accurate than those in previous studies based on approximate analytical solutions. We repeated the simulation of Mariska et al. with an injection of power law, downward-beamed electrons using the new heating rate. For this case, a -10% difference was found from their old result. We also used a more realistic spectrum of injected electrons provided by the stochastic acceleration model, which has a smooth transition from a quasi-thermal background at low energies to a non thermal tail at high energies. The inclusion of low-energy electrons results in relatively more heating in the corona (versus chromosphere) and thus a larger downward heat conduction flux. The interplay of electron heating, conduction, and radiative loss leads to stronger chromospheric evaporation than obtained in previous studies, which had a deficit in low-energy electrons due to an arbitrarily assumed low-energy cutoff. The energy and spatial distributions of energetic electrons and bremsstrahlung photons bear signatures of the changing density distribution caused by chromospheric evaporation. In particular, the density jump at the evaporation front gives rise to enhanced emission, which, in principle, can be imaged by X-ray telescopes. This model can be applied to investigate a variety of high-energy processes in solar, space, and astrophysical plasmas.
NASA Technical Reports Server (NTRS)
Liu, Wei; Petrosian, Vahe; Mariska, John T.
2009-01-01
Acceleration and transport of high-energy particles and fluid dynamics of atmospheric plasma are interrelated aspects of solar flares, but for convenience and simplicity they were artificially separated in the past. We present here self consistently combined Fokker-Planck modeling of particles and hydrodynamic simulation of flare plasma. Energetic electrons are modeled with the Stanford unified code of acceleration, transport, and radiation, while plasma is modeled with the Naval Research Laboratory flux tube code. We calculated the collisional heating rate directly from the particle transport code, which is more accurate than those in previous studies based on approximate analytical solutions. We repeated the simulation of Mariska et al. with an injection of power law, downward-beamed electrons using the new heating rate. For this case, a -10% difference was found from their old result. We also used a more realistic spectrum of injected electrons provided by the stochastic acceleration model, which has a smooth transition from a quasi-thermal background at low energies to a non thermal tail at high energies. The inclusion of low-energy electrons results in relatively more heating in the corona (versus chromosphere) and thus a larger downward heat conduction flux. The interplay of electron heating, conduction, and radiative loss leads to stronger chromospheric evaporation than obtained in previous studies, which had a deficit in low-energy electrons due to an arbitrarily assumed low-energy cutoff. The energy and spatial distributions of energetic electrons and bremsstrahlung photons bear signatures of the changing density distribution caused by chromospheric evaporation. In particular, the density jump at the evaporation front gives rise to enhanced emission, which, in principle, can be imaged by X-ray telescopes. This model can be applied to investigate a variety of high-energy processes in solar, space, and astrophysical plasmas.
Optimization of a Two-Fluid Hydrodynamic Model of Churn-Turbulent Flow
Donna Post Guillen
2009-07-01
A hydrodynamic model of two-phase, churn-turbulent flows is being developed using the computational multiphase fluid dynamics (CMFD) code, NPHASE-CMFD. The numerical solutions obtained by this model are compared with experimental data obtained at the TOPFLOW facility of the Institute of Safety Research at the Forschungszentrum Dresden-Rossendorf. The TOPFLOW data is a high quality experimental database of upward, co-current air-water flows in a vertical pipe suitable for validation of computational fluid dynamics (CFD) codes. A five-field CMFD model was developed for the continuous liquid phase and four bubble size groups using mechanistic closure models for the ensemble-averaged Navier-Stokes equations. Mechanistic models for the drag and non-drag interfacial forces are implemented to include the governing physics to describe the hydrodynamic forces controlling the gas distribution. The closure models provide the functional form of the interfacial forces, with user defined coefficients to adjust the force magnitude. An optimization strategy was devised for these coefficients using commercial design optimization software. This paper demonstrates an approach to optimizing CMFD model parameters using a design optimization approach. Computed radial void fraction profiles predicted by the NPHASE-CMFD code are compared to experimental data for four bubble size groups.
On the sensitivity of urban hydrodynamic modelling to rainfall spatial and temporal resolution
NASA Astrophysics Data System (ADS)
Bruni, G.; Reinoso, R.; van de Giesen, N. C.; Clemens, F. H. L. R.; ten Veldhuis, J. A. E.
2015-02-01
Cities are increasingly vulnerable to floods generated by intense rainfall, because of urbanisation of flood-prone areas and ongoing urban densification. Accurate information of convective storm characteristics at high spatial and temporal resolution is a crucial input for urban hydrological models to be able to simulate fast runoff processes and enhance flood prediction in cities. In this paper, a detailed study of the sensitivity of urban hydrodynamic response to high resolution radar rainfall was conducted. Rainfall rates derived from X-band dual polarimetric weather radar were used as input into a detailed hydrodynamic sewer model for an urban catchment in the city of Rotterdam, the Netherlands. The aim was to characterise how the effect of space and time aggregation on rainfall structure affects hydrodynamic modelling of urban catchments, for resolutions ranging from 100 to 2000 m and from 1 to 10 min. Dimensionless parameters were derived to compare results between different storm conditions and to describe the effect of rainfall spatial resolution in relation to storm characteristics and hydrodynamic model properties: rainfall sampling number (rainfall resolution vs. storm size), catchment sampling number (rainfall resolution vs. catchment size), runoff and sewer sampling number (rainfall resolution vs. runoff and sewer model resolution respectively). Results show that for rainfall resolution lower than half the catchment size, rainfall volumes mean and standard deviations decrease as a result of smoothing of rainfall gradients. Moreover, deviations in maximum water depths, from 10 to 30% depending on the storm, occurred for rainfall resolution close to storm size, as a result of rainfall aggregation. Model results also showed that modelled runoff peaks are more sensitive to rainfall resolution than maximum in-sewer water depths as flow routing has a damping effect on in-sewer water level variations. Temporal resolution aggregation of rainfall inputs led to
Hydrodynamic modelling and global datasets: Flow connectivity and SRTM data, a Bangkok case study.
NASA Astrophysics Data System (ADS)
Trigg, M. A.; Bates, P. B.; Michaelides, K.
2012-04-01
The rise in the global interconnected manufacturing supply chains requires an understanding and consistent quantification of flood risk at a global scale. Flood risk is often better quantified (or at least more precisely defined) in regions where there has been an investment in comprehensive topographical data collection such as LiDAR coupled with detailed hydrodynamic modelling. Yet in regions where these data and modelling are unavailable, the implications of flooding and the knock on effects for global industries can be dramatic, as evidenced by the recent floods in Bangkok, Thailand. There is a growing momentum in terms of global modelling initiatives to address this lack of a consistent understanding of flood risk and they will rely heavily on the application of available global datasets relevant to hydrodynamic modelling, such as Shuttle Radar Topography Mission (SRTM) data and its derivatives. These global datasets bring opportunities to apply consistent methodologies on an automated basis in all regions, while the use of coarser scale datasets also brings many challenges such as sub-grid process representation and downscaled hydrology data from global climate models. There are significant opportunities for hydrological science in helping define new, realistic and physically based methodologies that can be applied globally as well as the possibility of gaining new insights into flood risk through analysis of the many large datasets that will be derived from this work. We use Bangkok as a case study to explore some of the issues related to using these available global datasets for hydrodynamic modelling, with particular focus on using SRTM data to represent topography. Research has shown that flow connectivity on the floodplain is an important component in the dynamics of flood flows on to and off the floodplain, and indeed within different areas of the floodplain. A lack of representation of flow connectivity, often due to data resolution limitations, means
MODELING OF FRICTION STIR WELDING (FSW) PROCESS USING SMOOTH PARTICLE HYDRODYNAMICS (SPH)
Tartakovsky, Alexandre M.; Grant, Glenn J.; Sun, Xin; Khaleel, Mohammad A.
2006-06-14
We present a novel modeling approach to simulate FSW process that may have significant advantages over current traditional finite element or finite difference based methods. The proposed model is based on Smoothed Particle Hydrodynamics (SPH) method, a fully Lagrangian particle method that can simulate the dynamics of interfaces, large material deformations, void formations and material's strain and temperature history without employing complex tracking schemes. Two- and three-dimensional simulations for different tool designs are presented. Preliminary numerical results are in good qualitative agreement with experimental observations.
NASA Astrophysics Data System (ADS)
Volkov, A. N.
2016-06-01
Parkers' model of thermal escape implies the search of solutions of one-dimensional hydrodynamic equations for an inviscid but thermally conducting gas with a critical point and vanishing temperature far from the source. The properties of solutions of this model are studied for neutral mon- and diatomic gases with the viscosity index varying from 1/2 to 1. The domains of existence and uniqueness of solutions in terms of the source Jeans escape parameter and Knudsen number are established. The solutions are found to exist only in a narrow range of the critical point Jeans parameter. The lower and upper limits of this range correspond to solutions that are dominated by either heat conduction or adiabatic expansion. Thermal escape described by Parker's model occurs in two asymptotic regimes: the low-density (LD) regime, when escape is dominated by heat conduction, and the high-density (HD) regime, when escape is dominated by adiabatic expansion. Expressions for the mass and energy escape rates in these regimes are found theoretically. The comparison of results of hydrodynamic and kinetic simulations performed in identical conditions shows that Parker's model is capable of describing thermal escape only in the HD regime, providing decent agreement with the kinetic model in terms of the atmospheric structure below the exobase and the mass and energy escape rates. In the LD regime, Parker's model predicts a much faster drop in atmospheric temperature and less extended atmospheres, and can both over- and underestimate the escape rates in orders of magnitude.
Stewart, Hannah Louise
2006-06-01
An upright posture in the water column may expose benthic marine organisms to faster flow higher in the water column than near the substratum, potentially increasing rates of mass exchange while also exposing the organisms to higher hydrodynamic forces. Benthic organisms maintain upright postures in the water column by one of two mechanisms, stiffness or buoyancy. Turbinaria ornata is a tropical macroalga that uses either buoyancy or flexural stiffness (EI), depending on its flow habitat. This study used physical models of T. ornata to compare the effect of different magnitudes of these two mechanisms on relative water velocity and hydrodynamic forces in both unidirectional and wavy flow. Models of the alga were constructed to span and exceed natural levels of T. ornata's EI and buoyancy. Models with high EI and high buoyancy maintained upright postures in both unidirectional flow and waves, and experienced higher forces than models with low EI and moderate or low buoyancy that deflected in the direction of water motion. In waves, buoyant models that were deflected by high velocity rebounded back into upright positions when the flow slowed. Non-buoyant, flexible models were also pushed over by flow but lacked the ability to rebound upright, which led to decreased force in unidirectional flow, but high force in waves.
Better Insight Into Water Resources Management With Integrated Hydrodynamic And Water Quality Models
NASA Astrophysics Data System (ADS)
Debele, B.; Srinivasan, R.; Parlange, J.
2004-12-01
Models have long been used in water resources management to guide decision making and improve understanding of the system. Numerous models of different scales -spatial and temporal - are available. Yet, very few models manage to bridge simulations of hydrological and water quality parameters from both upland watershed and riverine system. Most water quality models, such as QUAL2E and EPD-RIV1 concentrate on the riverine system while CE-QUAL-W2 and WASP models focus on larger waterbodies, such as lakes and reservoirs. On the other hand, the original SWAT model, HSPF and other upland watershed hydrological models simulate agricultural (diffuse) pollution sources with limited number of processes incorporated to handle point source pollutions that emanate from industrial sectors. Such limitations, which are common in most hydrodynamic and water quality models undermine better understanding that otherwise could be uncovered by employing integrated hydrological and water quality models for both upland watershed and riverine system. The SWAT model is a well documented and verified hydrological and water quality model that has been developed to simulate the effects of various management scenarios on the health of the environment in terms of water quantity and quality. Recently, the SWAT model has been extended to include the simulation of hydrodynamic and water quality parameters in the river system. The extended SWAT model (ESWAT) has been further extended to run using diurnally varying (hourly) weather data and produce outputs at hourly timescales. This and other improvements in the ESWAT model have been documented in the current work. Besides, the results from two case studies in Texas will be reported.
Ferrer, M L; Duchowicz, R; Carrasco, B; de la Torre, J G; Acuña, A U
2001-01-01
There is a striking disparity between the heart-shaped structure of human serum albumin (HSA) observed in single crystals and the elongated ellipsoid model used for decades to interpret the protein solution hydrodynamics at neutral pH. These two contrasting views could be reconciled if the protein were flexible enough to change its conformation in solution from that found in the crystal. To investigate this possibility we recorded the rotational motions in real time of an erythrosin-bovine serum albumin complex (Er-BSA) over an extended time range, using phosphorescence depolarization techniques. These measurements are consistent with the absence of independent motions of large protein segments in solution, in the time range from nanoseconds to fractions of milliseconds, and give a single rotational correlation time phi(BSA, 1 cP, 20 degrees C) = 40 +/- 2 ns. In addition, we report a detailed analysis of the protein hydrodynamics based on two bead-modeling methods. In the first, BSA was modeled as a triangular prismatic shell with optimized dimensions of 84 x 84 x 84 x 31.5 A, whereas in the second, the atomic-level structure of HSA obtained from crystallographic data was used to build a much more refined rough-shell model. In both cases, the predicted and experimental rotational diffusion rate and other hydrodynamic parameters were in good agreement. Therefore, the overall conformation in neutral solution of BSA, as of HSA, should be rigid, in the sense indicated above, and very similar to the heart-shaped structure observed in HSA crystals. PMID:11325741
NASA Astrophysics Data System (ADS)
Quinn, Niall; Freer, Jim; Coxon, Gemma; Dunne, Toby; Neal, Jeff; Bates, Paul; Sampson, Chris; Smith, Andy; Parkin, Geoff
2017-04-01
Computationally efficient flood inundation modelling systems capable of representing important hydrological and hydrodynamic flood generating processes over relatively large regions are vital for those interested in flood preparation, response, and real time forecasting. However, such systems are currently not readily available. This can be particularly important where flood predictions from intense rainfall are considered as the processes leading to flooding often involve localised, non-linear spatially connected hillslope-catchment responses. Therefore, this research introduces a novel hydrological-hydraulic modelling framework for the provision of probabilistic flood inundation predictions across catchment to regional scales that explicitly account for spatial variability in rainfall-runoff and routing processes. Approaches have been developed to automate the provision of required input datasets and estimate essential catchment characteristics from freely available, national datasets. This is an essential component of the framework as when making predictions over multiple catchments or at relatively large scales, and where data is often scarce, obtaining local information and manually incorporating it into the model quickly becomes infeasible. An extreme flooding event in the town of Morpeth, NE England, in 2008 was used as a first case study evaluation of the modelling framework introduced. The results demonstrated a high degree of prediction accuracy when comparing modelled and reconstructed event characteristics for the event, while the efficiency of the modelling approach used enabled the generation of relatively large ensembles of realisations from which uncertainty within the prediction may be represented. This research supports previous literature highlighting the importance of probabilistic forecasting, particularly during extreme events, which can be often be poorly characterised or even missed by deterministic predictions due to the inherent
Battaglia, N.; Trac, H.; Cen, R.; Loeb, A.
2013-10-20
We present a new method for modeling inhomogeneous cosmic reionization on large scales. Utilizing high-resolution radiation-hydrodynamic simulations with 2048{sup 3} dark matter particles, 2048{sup 3} gas cells, and 17 billion adaptive rays in a L = 100 Mpc h {sup –1} box, we show that the density and reionization redshift fields are highly correlated on large scales (∼> 1 Mpc h {sup –1}). This correlation can be statistically represented by a scale-dependent linear bias. We construct a parametric function for the bias, which is then used to filter any large-scale density field to derive the corresponding spatially varying reionization redshift field. The parametric model has three free parameters that can be reduced to one free parameter when we fit the two bias parameters to simulation results. We can differentiate degenerate combinations of the bias parameters by combining results for the global ionization histories and correlation length between ionized regions. Unlike previous semi-analytic models, the evolution of the reionization redshift field in our model is directly compared cell by cell against simulations and performs well in all tests. Our model maps the high-resolution, intermediate-volume radiation-hydrodynamic simulations onto lower-resolution, larger-volume N-body simulations (∼> 2 Gpc h {sup –1}) in order to make mock observations and theoretical predictions.
Observations and 3D hydrodynamical models of planetary nebulae with Wolf-Rayet type central stars
NASA Astrophysics Data System (ADS)
Rechy-García, J. S.; Velázquez, P. F.; Peña, M.; Raga, A. C.
2017-01-01
We present high-resolution, long-slit spectroscopic observations of two planetary nebulae, M 1-32 and M 3-15, with [WC] central stars located near the Galactic bulge. The observations were obtained with the 2.1-m telescope of the Observatorio Astronómico Nacional, San Pedro Mártir. M 1-32 shows wide wings on the base of its emission lines and M 3-15 has two very faint high-velocity knots. In order to model both planetary nebulae, we built a three-dimensional model consisting of a jet interacting with an equatorially concentrated slow wind, emulating the presence of a dense torus, using the Yguazú hydrodynamical code. From our hydrodynamical models, we obtained position-velocity diagrams in the [N II]λ6583 line for comparison with the observations. We find that the spectral characteristics of M 1-32 and M 3-15 can be explained with the same physical model - a jet moving inside an asymptotic giant branch wind - using different parameters (physical conditions and position angles of the jet). In agreement with our model and observations, these objects contain a dense torus seeing pole-on and a bipolar jet escaping through the poles. Then, we propose to classify this kind of objects as spectroscopic bipolar nebulae, although they have been classified morphologically as compact, round, or elliptical nebulae or with `close collimated lobes'.
Smoothed Particle Hydrodynamics Stochastic Model for Flow and Transport in Porous Media
Tartakovsky, Alexandre M.; Tartakovsky, Daniel M.; Meakin, Paul
2008-11-03
A meso-scale stochastic Lagrangian particle model was developed and used to simulate conservative and reactive transport in porous media. In the stochastic model, the fluid flow in a porous continuum is governed by a combination of a Langevin equation and continuity equation. Pore-scale velocity fluctuations, the source of hydrodynamic dispersion, are represented by the white noise. A smoothed particle hydrodynamics method was used to solve the governing equations. Changes in the properties of the fluid particles (e.g., the solute concentration) are governed by the advection-diffusion equation. The separate treatment of advective and diffusive mixing in the stochastic transport model is more realistic than the classical advection-dispersion theory, which uses a single effective diffusion coefficient (the dispersion coefficient) to describe both types of mixing leading to over-prediction of mixing induced effective reaction rates. The stochastic model predicts much lower reaction product concentrations in mixing induced reactions. In addition, the dispersion theory predicts more stable fronts (with a higher effective fractal dimension) than the stochastic model during the growth of Rayleigh-Taylor instabilities.
NASA Astrophysics Data System (ADS)
Fischer, Lukas P.; Peter, Toni; Holm, Christian; de Graaf, Joost
2015-08-01
The so-called "raspberry" model refers to the hybrid lattice-Boltzmann and Langevin molecular dynamics scheme for simulating the dynamics of suspensions of colloidal particles, originally developed by Lobaskin and Dünweg [New J. Phys. 6, 54 (2004)], wherein discrete surface points are used to achieve fluid-particle coupling. This technique has been used in many simulation studies on the behavior of colloids. However, there are fundamental questions with regards to the use of this model. In this paper, we examine the accuracy with which the raspberry method is able to reproduce Stokes-level hydrodynamic interactions when compared to analytic expressions for solid spheres in simple-cubic crystals. To this end, we consider the quality of numerical experiments that are traditionally used to establish these properties and we discuss their shortcomings. We show that there is a discrepancy between the translational and rotational mobility reproduced by the simple raspberry model and present a way to numerically remedy this problem by adding internal coupling points. Finally, we examine a non-convex shape, namely, a colloidal dumbbell, and show that the filled raspberry model replicates the desired hydrodynamic behavior in bulk for this more complicated shape. Our investigation is continued in de Graaf et al. [J. Chem. Phys. 143, 084108 (2015)], wherein we consider the raspberry model in the confining geometry of two parallel plates.
Radiative hydrodynamics in the highly super adiabatic layer of stellar evolution models
NASA Astrophysics Data System (ADS)
Robinson, F. J.; Demarque, P.; Sofia, S.; Chan, K. L.; Kim, Y.-C.; Guenther, D. B.
2001-01-01
We present results of three dimensional simulations of the uppermost part of the sun, at 3 stages of its evolution. Each model includes physically realistic radiative-hydrodynamics (the Eddington approximation is used in the optically thin region), varying opacities and a realistic equation of state (full treatment of the ionization of H and He). In each evolution model, we investigate a domain, which starts at the top of the photosphere and ends just inside the convection zone (about 2400 km in the sun model). This includes all of the super-adiabatic layer (SAL). Due to the different positions of the three models in the log(g) vs logTeff plane, the more evolved models haved lower density atmospheres. The reduction in density causes the extent of overshoot into the radiation layer, to be greater in the more evolved models.
Stellar hydrodynamical modeling of dwarf galaxies: simulation methodology, tests, and first results
NASA Astrophysics Data System (ADS)
Vorobyov, Eduard I.; Recchi, Simone; Hensler, Gerhard
2015-07-01
Context. In spite of enormous progress and brilliant achievements in cosmological simulations, they still lack numerical resolution or physical processes to simulate dwarf galaxies in sufficient detail. Accurate numerical simulations of individual dwarf galaxies are thus still in demand. Aims: We aim to improve available numerical techniques to simulate individual dwarf galaxies. In particular, we aim to (i) study in detail the coupling between stars and gas in a galaxy, exploiting the so-called stellar hydrodynamical approach; and (ii) study for the first time the chemodynamical evolution of individual galaxies starting from self-consistently calculated initial gas distributions. Methods: We present a novel chemodynamical code for studying the evolution of individual dwarf galaxies. In this code, the dynamics of gas is computed using the usual hydrodynamics equations, while the dynamics of stars is described by the stellar hydrodynamics approach, which solves for the first three moments of the collisionless Boltzmann equation. The feedback from stellar winds and dying stars is followed in detail. In particular, a novel and detailed approach has been developed to trace the aging of various stellar populations, which facilitates an accurate calculation of the stellar feedback depending on the stellar age. The code has been accurately benchmarked, allowing us to provide a recipe for improving the code performance on the Sedov test problem. Results: We build initial equilibrium models of dwarf galaxies that take gas self-gravity into account and present different levels of rotational support. Models with high rotational support (and hence high degrees of flattening) develop prominent bipolar outflows; a newly-born stellar population in these models is preferentially concentrated to the galactic midplane. Models with little rotational support blow away a large fraction of the gas and the resulting stellar distribution is extended and diffuse. Models that start from non
NASA Astrophysics Data System (ADS)
Novbari, E.; Oron, A.
2011-01-01
The nonlinear dynamics of an axisymmetric liquid film falling on the outer surface of a vertical cylinder is investigated in the framework of the set of two coupled evolution equations derived recently using the energy integral method (EIM). This set of EIM evolution equations is solved numerically and its solutions are compared with the traveling wave solutions derived from it using AUTO. We find that traveling wave solutions of EIM equations can bifurcate either supercritically or subcritically from the base state. The type of bifurcation depends on the parameter set of the problem. The set of EIM equations studied here admits both traveling wave and nonstationary wave flows. We demonstrate that in the case of subcritical primary bifurcation the film dynamics is sensitive to the choice of the initial condition and coexistence of up to five different flows is possible for the same parameter set in the domain of a given periodicity. The case of supercritical primary bifurcation exhibits much lesser dependence on the initial condition, though coexistence of two different flows for the same parameter set is possible. The synergetic approach based on both direct numerical solution of the governing evolution equations and search of traveling wave solutions using AUTO facilitate a discovery of a large variety of flows and help to conclude about stability of the traveling wave flows found using AUTO.
Modeling the hydrodynamic interactions of deep anoxic lagoons with their source basins
NASA Astrophysics Data System (ADS)
Gianni, Areti; Zacharias, Ierotheos
2012-09-01
This study investigates the management of an extension of the anoxic water layers, from deeper to shallower environments, and aims to control the consequences in lagoon environments with great economic and ecological value. The physicochemical status in a deep anoxic lagoon (Aitoliko, Greece) was monitored and the spatial distribution of anoxic conditions in the bottom waters was the focal point. The study investigated the management of an extension of the anoxic water layers, from deeper to shallower environments, and aims to control the consequences in lagoon environments with great economic and ecological value. A three-dimensional numerical model was used in order to describe the hydrodynamic conditions in the lagoon. The model was calibrated and validated with field measurements and it was used as a tool to examine how morphological modifications in lagoon's sill and changes of the lagoon's salt/fresh water budget can affect water column hydrodynamics. The model reliably reproduced the hydrodynamic changes in the lagoon caused by morphological and/or hydraulic modification, demonstrating an ideal management plan for the control of deep anoxic hypolimnia. It is concluded that by decreasing fresh water discharges into a deep lagoon, epilimnetic density values increase while the metalimnion extends. By extending the sill's cross section, water fluxes with the source basin are increased, affecting the surface layer density. Even under these conditions fresh water discharges control the characteristics of a thin surface water layer. If the sill's cross section expansion is followed by a decrease of fresh water discharge, turbulence conditions in the water column of a deep basin are substantially affected.
Linked Hydrologic-Hydrodynamic Model Framework to Forecast Impacts of Rivers on Beach Water Quality
NASA Astrophysics Data System (ADS)
Anderson, E. J.; Fry, L. M.; Kramer, E.; Ritzenthaler, A.
2014-12-01
The goal of NOAA's beach quality forecasting program is to use a multi-faceted approach to aid in detection and prediction of bacteria in recreational waters. In particular, our focus has been on the connection between tributary loads and bacteria concentrations at nearby beaches. While there is a clear link between stormwater runoff and beach water quality, quantifying the contribution of river loadings to nearshore bacterial concentrations is complicated due to multiple processes that drive bacterial concentrations in rivers as well as those processes affecting the fate and transport of bacteria upon exiting the rivers. In order to forecast potential impacts of rivers on beach water quality, we developed a linked hydrologic-hydrodynamic water quality framework that simulates accumulation and washoff of bacteria from the landscape, and then predicts the fate and transport of washed off bacteria from the watershed to the coastal zone. The framework includes a watershed model (IHACRES) to predict fecal indicator bacteria (FIB) loadings to the coastal environment (accumulation, wash-off, die-off) as a function of effective rainfall. These loadings are input into a coastal hydrodynamic model (FVCOM), including a bacteria transport model (Lagrangian particle), to simulate 3D bacteria transport within the coastal environment. This modeling system provides predictive tools to assist local managers in decision-making to reduce human health threats.
Modeling hydrodynamics, temperature and water quality in Henry Hagg Lake, Oregon, 2000-2003
Sullivan, Annette B.; Rounds, Stewart A.
2004-01-01
The two-dimensional model CE-QUAL-W2 was used to simulate hydrodynamics, temperature, and water quality in Henry Hagg Lake, Oregon, for the years 2000 through 2003. Input data included lake bathymetry, meteorologic conditions, tributary inflows, tributary temperature and water quality, and lake outflows. Calibrated constituents included lake hydrodynamics, water temperature, orthophosphate, total phosphorus, ammonia, algae, chlorophyll a, zooplankton, and dissolved oxygen. Other simulated constituents included nitrate, dissolved and particulate organic matter, dissolved solids, and suspended sediment. Two algal groups (blue-green algae, and all other algae) were included in the model to simulate the lakes algal communities. Measured lake stage data were used to calibrate the lakes water balance; calibration of water temperature and water quality relied upon vertical profile data taken in the deepest part of the lake near the dam. The model initially was calibrated with data from 200001 and tested with data from 200203. Sensitivity tests were performed to examine the response of the model to specific parameters and coefficients, including the light-extinction coefficient, wind speed, tributary inflows of phosphorus, nitrogen and organic matter, sediment oxygen demand, algal growth rates, and zooplankton feeding preference factors.
NASA Astrophysics Data System (ADS)
Coppex, François; Droz, Michel; Trizac, Emmanuel
2005-08-01
The hydrodynamic description of probabilistic ballistic annihilation, for which no conservation laws hold, is an intricate problem with hard spherelike dynamics for which no exact solution exists. We consequently focus on simplified approaches, the Maxwell and very-hard-particle (VHP) models, which allows us to compute analytically upper and lower bounds for several quantities. The purpose is to test the possibility of describing such a far from equilibrium dynamics with simplified kinetic models. The motivation is also in turn to assess the relevance of some singular features appearing within the original model and the approximations invoked to study it. The scaling exponents are first obtained from the (simplified) Boltzmann equation, and are confronted against direct Monte Carlo simulations. Then, the Chapman-Enskog method is used to obtain constitutive relations and transport coefficients. The corresponding Navier-Stokes equations for the hydrodynamic fields are derived for both Maxwell and VHP models. We finally perform a linear stability analysis around the homogeneous solution, which illustrates the importance of dissipation in the possible development of spatial inhomogeneities.
Models of hydrodynamic flow in the bowhead whale filter feeding apparatus.
Werth, Alexander J
2004-09-01
Anatomical and behavioral analyses suggest that the filtration mechanism of bowhead and right whales (Balaenidae) is driven by hydrodynamic as well as ram hydraulic pressures. Complementary models were devised to investigate biomechanical aspects of water flow in the buccal cavity of the bowhead whale Balaena mysticetus during continuous filter feeding. A mathematical model was created to test and quantify water flow predictions with steady state hydromechanical equations; a physical model of the bowhead mouth (approximately 1/15 scale) was constructed to visualize flow processes. Both models rely on morphometric data obtained from whales harvested by Inupiat Eskimos for subsistence purposes along with information on foraging ecology (locomotor velocity, gape, etc.). Results indicate that unique features of balaenid oral construction and function (e.g. subrostral gap, orolabial sulcus, curvature of baleen, extensive mandibular rotation and lingual mobility) not only permit steady, unidirectional flow of water through the mouth, but also establish Bernoulli and Venturi effects during feeding. These hydrodynamic conditions allow balaenids to improve filtering efficiency and avoid creation of an anterior compressive wave (by increasing flow velocity and thereby reducing pressure) so that they may capture elusive prey even at slow swimming speeds.
The moreau-evans hydrodynamic model applied to actual hall-héroult cells
NASA Astrophysics Data System (ADS)
Moreau, René J.; Ziegler, Donald
1988-10-01
An extension of the Moreau-Evans[1] model for Hall-Héroult cells hydrodynamics is presented. Numerical techniques are used to solve the Moreau-Evans model equations with realistic electromagnetic force fields; the predicted results are compared with those of another model which is the property of Kaiser Aluminum Company and whose results are considered as in fairly good agreement with available measurements (velocity in aluminum, for instance). The main input in this hydrodynamic model, i.e., the electromagnetic force field throughout the two liquids, was previously computed. For a given cell design these data were calculated using the electromagnetic program of Lympany and Evans.[2] For actual cells the forces were deduced from measurements of the magnetic field provided by Kaiser Aluminum Company. As expected, the cryolite flow is found to be governed by the large channels, and to be strongly dependent on the presence of such a channel between the two files of anodes. The use of numerical solution has made possible the analysis of new effects as the interfacial drag and the influence of small channels between anode blocks.
The Raspberry model for hydrodynamic interactions revisited. II. The effect of confinement
NASA Astrophysics Data System (ADS)
de Graaf, Joost; Peter, Toni; Fischer, Lukas P.; Holm, Christian
2015-08-01
The so-called "raspberry" model refers to the hybrid lattice-Boltzmann (LB) and Langevin molecular dynamics schemes for simulating the dynamics of suspensions of colloidal particles, originally developed by Lobaskin and Dünweg [New J. Phys. 6, 54 (2004)], wherein discrete surface points are used to achieve fluid-particle coupling. In this paper, we present a follow up to our study of the effectiveness of the raspberry model in reproducing hydrodynamic interactions in the Stokes regime for spheres arranged in a simple-cubic crystal [Fischer et al., J. Chem. Phys. 143, 084107 (2015)]. Here, we consider the accuracy with which the raspberry model is able to reproduce such interactions for particles confined between two parallel plates. To this end, we compare our LB simulation results to established theoretical expressions and finite-element calculations. We show that there is a discrepancy between the translational and rotational mobilities when only surface coupling points are used, as also found in Part I of our joint publication. We demonstrate that adding internal coupling points to the raspberry can be used to correct said discrepancy in confining geometries as well. Finally, we show that the raspberry model accurately reproduces hydrodynamic interactions between a spherical colloid and planar walls up to roughly one LB lattice spacing.
New control strategy for the lattice hydrodynamic model of traffic flow
NASA Astrophysics Data System (ADS)
Zhu, Chenqiang; Zhong, Shiquan; Li, Guangyu; Ma, Shoufeng
2017-02-01
The new delayed-feedback control strategy is applied for lattice hydrodynamic model of traffic flow by considering the control signal of the variation rate of the optimal velocity. The linear stability condition is derived in the frequency-domain with control theory. Then, different feedback gains under the periodic boundary scenery and on-ramp scenery are simulated. The periodic boundary scenery provides an initial small disturbance situation on the circle road, while the on-ramp scenery reproduces the disturbance triggered by the on-ramp on the open road. Both the theoretical analysis and simulations show that this new control signal has a positive effect to suppress traffic jams.
Well-posedness on a new hydrodynamic model of the fluid with the dilute charged particles
NASA Astrophysics Data System (ADS)
Wang, Yong; Liu, Chun; Tan, Zhong
2017-01-01
We use an energetic variational approach to derive a new hydrodynamic model, which could be called a generalized Poisson-Nernst-Planck-Navier-Stokes system. Such the system could describe the dynamics of the compressible conductive fluid with the dilute charged particles and be used to analyze the interactions between the macroscopic fluid motion and the microscopic charge transportation. Then, we develop a general method to obtain the unique local classical solution, the unique global solution under small perturbations and the optimal decay rates of the solution and its derivatives of any order.
Global well-posedness of the hydrodynamic model for two-carrier plasmas
NASA Astrophysics Data System (ADS)
Peng, Yue-Jun; Xu, Jiang
We prove results on the global well-posedness of the hydrodynamic model for two-carrier plasmas in whole space and periodic domain. We remove a technical condition which was first introduced by Alì and Jüngel [2] and developed in [14,18] to deal with the difficulty mainly arising from complicated coupling and cancellation between two carriers. The proofs depend on a result on continuity for compositions in Chemin-Lerner spaces and an elementary fact which indicates the connection between homogeneous and inhomogeneous Chemin-Lerner spaces.
NASA Astrophysics Data System (ADS)
Larmat, C. S.; Rougier, E.; Delorey, A.; Steedman, D. W.; Bradley, C. R.
2016-12-01
The goal of the Source Physics Experiment (SPE) is to bring empirical and theoretical advances to the problem of detection and identification of underground nuclear explosions. For this, the SPE program includes a strong modeling effort based on first principles calculations with the challenge to capture both the source and near-source processes and those taking place later in time as seismic waves propagate within complex 3D geologic environments. In this paper, we report on results of modeling that uses hydrodynamic simulation codes (Abaqus and CASH) coupled with a 3D full waveform propagation code, SPECFEM3D. For modeling the near source region, we employ a fully-coupled Euler-Lagrange (CEL) modeling capability with a new continuum-based visco-plastic fracture model for simulation of damage processes, called AZ_Frac. These capabilities produce high-fidelity models of various factors believed to be key in the generation of seismic waves: the explosion dynamics, a weak grout-filled borehole, the surrounding jointed rock, and damage creation and deformations happening around the source and the free surface. SPECFEM3D, based on the Spectral Element Method (SEM) is a direct numerical method for full wave modeling with mathematical accuracy. The coupling interface consists of a series of grid points of the SEM mesh situated inside of the hydrodynamic code's domain. Displacement time series at these points are computed using output data from CASH or Abaqus (by interpolation if needed) and fed into the time marching scheme of SPECFEM3D. We will present validation tests with the Sharpe's model and comparisons of waveforms modeled with Rg waves (2-8Hz) that were recorded up to 2 km for SPE. We especially show effects of the local topography, velocity structure and spallation. Our models predict smaller amplitudes of Rg waves for the first five SPE shots compared to pure elastic models such as Denny &Johnson (1991).
Wang, Taiping; Yang, Zhaoqing; Khangaonkar, Tarang
2010-04-22
In this study, a hydrodynamic model based on the unstructured-grid finite volume coastal ocean model (FVCOM) was developed for Bellingham Bay, Washington. The model simulates water surface elevation, velocity, temperature, and salinity in a three-dimensional domain that covers the entire Bellingham Bay and adjacent water bodies, including Lummi Bay, Samish Bay, Padilla Bay, and Rosario Strait. The model was developed using Pacific Northwest National Laboratory’s high-resolution Puget Sound and Northwest Straits circulation and transport model. A sub-model grid for Bellingham Bay and adjacent coastal waters was extracted from the Puget Sound model and refined in Bellingham Bay using bathymetric light detection and ranging (LIDAR) and river channel cross-section data. The model uses tides, river inflows, and meteorological inputs to predict water surface elevations, currents, salinity, and temperature. A tidal open boundary condition was specified using standard National Oceanic and Atmospheric Administration (NOAA) predictions. Temperature and salinity open boundary conditions were specified based on observed data. Meteorological forcing (wind, solar radiation, and net surface heat flux) was obtained from NOAA real observations and National Center for Environmental Prediction North American Regional Analysis outputs. The model was run in parallel with 48 cores using a time step of 2.5 seconds. It took 18 hours of cpu time to complete 26 days of simulation. The model was calibrated with oceanographic field data for the period of 6/1/2009 to 6/26/2009. These data were collected specifically for the purpose of model development and calibration. They include time series of water-surface elevation, currents, temperature, and salinity as well as temperature and salinity profiles during instrument deployment and retrieval. Comparisons between model predictions and field observations show an overall reasonable agreement in both temporal and spatial scales. Comparisons of
Combining Envisat type and CryoSat-2 altimetry to inform hydrodynamic models
NASA Astrophysics Data System (ADS)
Schneider, Raphael; Nygaard Godiksen, Peter; Villadsen, Heidi; Madsen, Henrik; Bauer-Gottwein, Peter
2015-04-01
Hydrological models are developed and used for flood forecasting and water resources management. Such models rely on a variety of input and calibration data. In general, and especially in data scarce areas, remote sensing provides valuable data for the parameterization and updating of such models. Satellite radar altimeters provide water level measurements of inland water bodies. So far, many studies making use of satellite altimeters have been based on data from repeat-orbit missions such as Envisat, ERS or Jason or on synthetic wide-swath altimetry data as expected from the SWOT mission. This work represents one of the first hydrologic applications of altimetry data from a drifting orbit satellite mission, using data from CryoSat-2. We present an application where CryoSat-2 data is used to improve a hydrodynamic model of the Ganges and Brahmaputra river basins in South Asia set up in the DHI MIKE 11 software. The model's parameterization and forcing is mainly based on remote sensing data, for example the TRMM 3B42 precipitation product and the SRTM DEM for river and subcatchment delineation. CryoSat-2 water levels were extracted over a river mask derived from Landsat 7 and 8 imagery. After calibrating the hydrological-hydrodynamic model against observed discharge, simulated water levels were fitted to the CryoSat-2 data, with a focus on the Brahmaputra river in the Assam valley: The average simulated water level in the hydrodynamic model was fitted to the average water level along the river's course as observed by CryoSat-2 over the years 2011-2013 by adjusting the river bed elevation. In a second step, the cross section shapes were adjusted so that the simulated water level dynamics matched those obtained from Envisat virtual station time series. The discharge calibration resulted in Nash-Sutcliffe coefficients of 0.86 and 0.94 for the Ganges and Brahmaputra. Using the Landsat river mask, the CryoSat-2 water levels show consistency along the river and are in
Can hydrodynamic models be implemented and calibrated on the basis of remotely sensed data only?
NASA Astrophysics Data System (ADS)
Domeneghetti, Alessio
2015-04-01
The implementation and calibration of hydrodynamic models are often constrained by the amount of available data (such as topographic and hydraulic data) which may be absent (e.g. in remote areas) or not sufficient to build accurate and trustable models. Nevertheless, the greater availability of remote sensing data (e.g. altimetry data, radar imageries, etc.) stimulates the scientific community to resort to these new data sources for overcoming these limits. The present study analyzes the potential of remotely sensed data, i.e. (i) Shuttle Radar Topography Mission (SRTM; a freely available global Digital Elevation Model with a resolution of 90 m) and (ii) satellite altimetry data (i.e. ERS and ENVISAT data), for a complete implementation and calibration of a one-dimensional (1D) hydrodynamic model. The test site is represented by ~140 km stretch of the Po river (the longest Italian river) where both traditional and remotely sensed topographical and hydrometric data are available. Adopting the SRTM data for representing the riverbed and floodplain morphology, the study investigates the performances of different 1D models in which the geometry of the main channel, which is generally submerged and cannot be remotely surveyed, is reconstructed on the basis of different approaches. The model calibrations are performed referring to long satellite altimetry timeseries (~16 years of observations), while the simulation results are compared with those obtained by means of a quasi-2D model implemented with detailed topographical data (i.e. airborne LiDAR available on the study area). The results of the study are encouraging and show the possibility to implement and calibrate a reliable 1D model referring exclusively to low-resolution DEM (e.g. SRTM) and remotely sensed water surface data (i.e. ERS and ENVISAT). The 1D model is particularly accurate for describing high-flow and flood events (i.e. root mean square error equal to 0.11 m) and comparable with traditionally
McCarthy, D T; Jovanovic, D; Lintern, A; Teakle, I; Barnes, M; Deletic, A; Coleman, R; Rooney, G; Prosser, T; Coutts, S; Hipsey, M R; Bruce, L C; Henry, R
2017-02-01
Urban estuaries around the world are experiencing contamination from diffuse and point sources, which increases risks to public health. To mitigate and manage risks posed by elevated levels of contamination in urban waterways, it is critical to identify the primary water sources of contamination within catchments. Source tracking using microbial community fingerprints is one tool that can be used to identify sources. However, results derived from this approach have not yet been evaluated using independent datasets. As such, the key objectives of this investigation were: (1) to identify the major sources of water responsible for bacterial loadings within an urban estuary using microbial source tracking (MST) using microbial communities; and (2) to evaluate this method using a 3-dimensional hydrodynamic model. The Yarra River estuary, which flows through the city of Melbourne in South-East Australia was the focus of this study. We found that the water sources contributing to the bacterial community in the Yarra River estuary varied temporally depending on the estuary's hydrodynamic conditions. The water source apportionment determined using microbial community MST correlated to those determined using a 3-dimensional hydrodynamic model of the transport and mixing of a tracer in the estuary. While there were some discrepancies between the two methods, this investigation demonstrated that MST using bacterial community fingerprints can identify the primary water sources of microorganisms in an estuarine environment. As such, with further optimization and improvements, microbial community MST has the potential to become a powerful tool that could be practically applied in the mitigation of contaminated aquatic systems.
Poblete, Simón; Wysocki, Adam; Gompper, Gerhard; Winkler, Roland G
2014-09-01
We investigate the hydrodynamic properties of a spherical colloid model, which is composed of a shell of point particles by hybrid mesoscale simulations, which combine molecular dynamics simulations for the sphere with the multiparticle collision dynamics approach for the fluid. Results are presented for the center-of-mass and angular velocity correlation functions. The simulation results are compared with theoretical results for a rigid colloid obtained as a solution of the Stokes equation with no-slip boundary conditions. Similarly, analytical results of a point-particle model are presented, which account for the finite size of the simulated system. The simulation results agree well with both approaches on appropriative time scales; specifically, the long-time correlations are quantitatively reproduced. Moreover, a procedure is proposed to obtain the infinite-system-size diffusion coefficient based on a combination of simulation results and analytical predictions. In addition, we present the velocity field in the vicinity of the colloid and demonstrate its close agreement with the theoretical prediction. Our studies show that a point-particle model of a sphere is very well suited to describe the hydrodynamic properties of spherical colloids, with a significantly reduced numerical effort.
The optimization of high resolution topographic data for 1D hydrodynamic models
NASA Astrophysics Data System (ADS)
Ales, Ronovsky; Michal, Podhoranyi
2016-06-01
The main focus of our research presented in this paper is to optimize and use high resolution topographical data (HRTD) for hydrological modelling. Optimization of HRTD is done by generating adaptive mesh by measuring distance of coarse mesh and the surface of the dataset and adapting the mesh from the perspective of keeping the geometry as close to initial resolution as possible. Technique described in this paper enables computation of very accurate 1-D hydrodynamic models. In the paper, we use HEC-RAS software as a solver. For comparison, we have chosen the amount of generated cells/grid elements (in whole discretization domain and selected cross sections) with respect to preservation of the accuracy of the computational domain. Generation of the mesh for hydrodynamic modelling is strongly reliant on domain size and domain resolution. Topographical dataset used in this paper was created using LiDAR method and it captures 5.9km long section of a catchment of the river Olše. We studied crucial changes in topography for generated mesh. Assessment was done by commonly used statistical and visualization methods.
A quasi-continuum hydrodynamic model for slit shaped nanochannel flow
NASA Astrophysics Data System (ADS)
Bhadauria, Ravi; Aluru, N. R.
2013-08-01
We propose a quasi-continuum hydrodynamic model for isothermal transport of Lennard-Jones fluid confined in slit shaped nanochannels. In this work, we compute slip and viscous contributions independently and superimpose them to obtain the total velocity profile. Layering of fluid near the interface plays an important role in viscous contribution to the flow, by apparent viscosity change along the confining dimension. This relationship necessitates computing density profiles, which is done using the recently proposed empirical-potential based quasi-continuum theory [A. V. Raghunathan, J. H. Park, and N. R. Aluru, J. Chem. Phys. 127, 174701 (2007)], 10.1063/1.2793070. Existing correlations for density dependent viscosity provided by Woodcock [AIChE J. 52, 438 (2006)], 10.1002/aic.10676 are used to compute viscosity profile in the nanopores. A Dirichlet type slip boundary condition based on a static Langevin friction model describing center-of-mass motion of fluid particles is used, the parameters of which are dependent on the fluctuations of total wall-fluid force from an equilibrium molecular dynamics simulation. Different types of corrugated surfaces are considered to study wall-fluid friction effects on boundary conditions. Proposed hydrodynamic model yields good agreement of velocity profiles obtained from non-equilibrium molecular dynamics simulations for gravity driven flow.
NASA Astrophysics Data System (ADS)
Colosqui, Carlos E.; Kavousanakis, Michail E.; Papathanasiou, Athanasios G.; Kevrekidis, Ioannis G.
2013-01-01
We present a model based on the lattice Boltzmann equation that is suitable for the simulation of dynamic wetting. The model is capable of exhibiting fundamental interfacial phenomena such as weak adsorption of fluid on the solid substrate and the presence of a thin surface film within which a disjoining pressure acts. Dynamics in this surface film, tightly coupled with hydrodynamics in the fluid bulk, determine macroscopic properties of primary interest: the hydrodynamic slip; the equilibrium contact angle; and the static and dynamic hysteresis of the contact angles. The p