For comprehensive and current results, perform a real-time search at Science.gov.

1

Two-dimensional simulations of magnetically-driven instabilities

A two-dimensional Eulerian MHD code is used to study the evolution of magnetically-driven instabilities in cylindrical geometry. The code incorporates an equation of state, resistivity, and radiative cooling model appropriate for an aluminum plasma. The simulations explore the effects of initial perturbations, electrical resistivity, and radiative cooling on the growth and saturation of the instabilities. Comparisons are made between the 2-D simulations, previous 1-D simulations, and results from the Pioneer experiments of the Los Alamos foil implosion program.

Peterson, D.; Bowers, R.; Greene, A.E.; Brownell, J.

1986-01-01

2

Resistive MHD reconstruction of two-dimensional coherent structures in space

NASA Astrophysics Data System (ADS)

We present a reconstruction technique to solve the steady resistive MHD equations in two dimensions with initial inputs of field and plasma data from a single spacecraft as it passes through a coherent structure in space. At least two components of directly measured electric fields (the spacecraft spin-plane components) are required for the reconstruction, to produce two-dimensional (2-D) field and plasma maps of the cross section of the structure. For convenience, the resistivity tensor ? is assumed diagonal in the reconstruction coordinates, which allows its values to be estimated from Ohm's law, E+v×B=?·j. In the present paper, all three components of the electric field are used. We benchmark our numerical code by use of an exact, axi-symmetric solution of the resistive MHD equations and then apply it to synthetic data from a 3-D, resistive, MHD numerical simulation of reconnection in the geomagnetic tail, in a phase of the event where time dependence and deviations from 2-D are both weak. The resistivity used in the simulation is time-independent and localized around the reconnection site in an ellipsoidal region. For the magnetic field, plasma density, and pressure, we find very good agreement between the reconstruction results and the simulation, but the electric field and plasma velocity are not predicted with the same high accuracy.

Teh, W.-L.; Sonnerup, B. U. Ö.; Birn, J.; Denton, R. E.

2010-11-01

3

Hall MHD Modeling of Two-dimensional Reconnection: Application to MRX Experiment

Two-dimensional resistive Hall magnetohydrodynamics (MHD) code is used to investigate the dynamical evolution of driven reconnection in the Magnetic Reconnection Experiment (MRX). The initial conditions and dimensionless parameters of the simulation are set to be similar to the experimental values. We successfully reproduce many features of the time evolution of magnetic configurations for both co- and counter-helicity reconnection in MRX. The Hall effect is shown to be important during the early dynamic X-phase of MRX reconnection, while effectively negligible during the late ''steady-state'' Y-phase, when plasma heating takes place. Based on simple symmetry considerations, an experiment to directly measure the Hall effect in MRX configuration is proposed and numerical evidence for the expected outcome is given.

V.S. Lukin; S.C. Jardin

2003-01-09

4

Merging of Coronal and Heliospheric Numerical Two-dimensional MHD Models

NASA Technical Reports Server (NTRS)

Space weather research requires investigation of a complex chain of coupled dynamic phenomena occurring simultaneously on various spatial and temporal scales between the Sun and Earth. Specialized physically based numerical models have been developed to address particular aspects of the entire system. However, an integrated modeling approach is necessary to provide a complete picture suitable for interpretation of various remote and in situ observations and for development of forecasting capabilities. In this paper we demonstrate merging of coronal and heliospheric MHD models for a two-dimensional hypothetical case involving a magnetic cloud, shock, streamer belt, and current sheet. The disruption of a sheared helmet streamer launches a coronal mass ejection (CME) (simulated by the coronal model), which evolves during its propagation through interplanetary space (simulated by the heliospheric model). These models employ different physical approximations and numerical grids to simulate physical phenomena over their respective spatial and temporal domains. The merging of the models enables accurate tracking of a CME from its origin in the solar atmosphere to its arrival at Earth.

Odstrcil, D.; Linker, J. A.; Lionello, R.; Mikic, Zoran; Riley, P.; Pizzo, V. J.; Luhmann, J. G.

2002-01-01

5

TWO DIMENSIONAL COMPUTER SIMULATION OF PLASMA IMMERSION

particles (B=0 T and =0) #12;Ion trajectories #12;Axial distribution of implantation current #12;Energy;Objectives Â· Development of realistic, particle-in-cell (PIC), computer simulation of plasma immersion ion confinement of the secondary electrons #12;2.5D computer simulation with code KARAT Spatial variables

6

On the Transition from Two-Dimensional to Three-Dimensional MHD Turbulence

NASA Technical Reports Server (NTRS)

We report a theoretical investigation of the robustness of two-dimensional inviscid MHD flows at low magnetic Reynolds numbers with respect to three-dimensional perturbations. We analyze three model problems, namely flow in the interior of a triaxial ellipsoid, an unbounded vortex with elliptical streamlines, and a vortex sheet parallel to the magnetic field. We demonstrate that motion perpendicular to the magnetic field with elliptical streamlines becomes unstable with respect to the elliptical instability once the velocity has reached a critical magnitude whose value tends to zero as the eccentricity of the streamlines becomes large. Furthermore, vortex sheets parallel to the magnetic field, which are unstable for any velocity and any magnetic field, are found to emit eddies with vorticity perpendicular to the magnetic field and with an aspect ratio proportional to N(sup 1/2). The results suggest that purely two-dimensional motion without Joule energy dissipation is a singular type of flow which does not represent the asymptotic behaviour of three-dimensional MHD turbulence in the limit of infinitely strong magnetic fields.

Thess, A.; Zikanov, Oleg

2004-01-01

7

Lattice Boltzmann simulation for forced two-dimensional turbulence

NASA Astrophysics Data System (ADS)

The direct numerical simulations of forced two-dimensional turbulent flow are presented by using the lattice Boltzmann method. The development of an energy-enstrophy double cascade is investigated in the two cases of external force of two-dimensional turbulence, Gaussian force and Kolmogorov force. It is found that the friction force is a necessary condition of the occurrence of a double cascade. The energy spectrum k-3 in the enstrophy inertial range is in accord with the classical Kraichnan theory for both external forces. The energy spectrum of the Gaussian force case in an inverse cascade is k-2; however, the Kolmogorov force drives the k-5/3 energy in a backscatter cascade. The result agrees with Scott's standpoint, which describes nonrobustness of the two-dimensional turbulent inverse cascade. Also, intermittency is found for the enstrophy cascade in two cases of the external force form. Intermittency refers to the nonuniform distribution of saddle points in the two-dimensional turbulent flow.

Xia, YuXian; Qian, YueHong

2014-08-01

8

Augmented Reality Simulator for Training in Two-Dimensional Echocardiography

In two-dimensional echocardiography the sonographer must synthesize multiple tomographic slices into a mental three-dimensional (3D) model of the heart. Computer graphics and virtual reality environments are ideal to visualize complex 3D spatial relationships. In augmented reality (AR) applications, real and virtual image data are linked, to increase the information content. In the presented AR simulator a 3D surface model of

M. Weidenbach; C. Wick; S. Pieper; K. J. Quast; T. Fox; G. Grunst; D. A. Redel

2000-01-01

9

Spectral effects simulation with two-dimensional magnetohydrodynamic models of the solar photosphere

To study the structure of spatially unresolved features of the solar photosphere, we calculated the Stokes profiles of seven photospheric iron lines using two-dimensional nonstationary MHD models of solar granulation for various amounts of magnetic flux (0, 10, 20, 30 mT). We investigate variations in the absolute wavelength shifts and bisectors of the I profiles, as well as variations in the zero-crossing wavelength shifts, amplitude and area asymmetry of the V profiles as functions of magnetic field strength and time. The center-to-limb variations of the Stokes profiles are analyzed. The iron abundance is found to be 7.57, with the photosphere inhomogeneities taken into account. Although most of the spectral effects simulated within the scope of the two-dimensional MHD models are in satisfactory agreement with observational data, these models cannot always give a quantitative agreement. The absolute wavelength shifts of the Stokes profiles of Fe II lines calculated with the MHD models are substantially smal...

Atroshchenko, I N; 10.3103/50884591305030022

2012-01-01

10

Two-dimensional Lagrangian simulation of suspended sediment

A two-dimensional laterally averaged model for suspended sediment transport in steady gradually varied flow that is based on the Lagrangian reference frame is presented. The layered Lagrangian transport model (LLTM) for suspended sediment performs laterally averaged concentration. The elevations of nearly horizontal streamlines and the simulation time step are selected to optimize model stability and efficiency. The computational elements are parcels of water that are moved along the streamlines in the Lagrangian sense and are mixed with neighboring parcels. Three applications show that the LLTM can accurately simulate theoretical and empirical nonequilibrium suspended sediment distributions and slug injections of suspended sediment in a laboratory flume.

Schoellhamer, David H.

1988-01-01

11

High order hybrid numerical simulations of two dimensional detonation waves

NASA Technical Reports Server (NTRS)

In order to study multi-dimensional unstable detonation waves, a high order numerical scheme suitable for calculating the detailed transverse wave structures of multidimensional detonation waves was developed. The numerical algorithm uses a multi-domain approach so different numerical techniques can be applied for different components of detonation waves. The detonation waves are assumed to undergo an irreversible, unimolecular reaction A yields B. Several cases of unstable two dimensional detonation waves are simulated and detailed transverse wave interactions are documented. The numerical results show the importance of resolving the detonation front without excessive numerical viscosity in order to obtain the correct cellular patterns.

Cai, Wei

1993-01-01

12

Two dimensional simulation of high power laser-surface interaction

For laser intensities in the range of 10{sup 8}--10{sup 9} W/cm{sup 2}, and pulse lengths of order 10 {micro}sec or longer, the authors have modified the inertial confinement fusion code Lasnex to simulate gaseous and some dense material aspects of the laser-matter interaction. The unique aspect of their treatment consists of an ablation model which defines a dense material-vapor interface and then calculates the mass flow across this interface. The model treats the dense material as a rigid two-dimensional mass and heat reservoir suppressing all hydrodynamic motion in the dense material. The computer simulations and additional post-processors provide predictions for measurements including impulse given to the target, pressures at the target interface, electron temperatures and densities in the vapor-plasma plume region, and emission of radiation from the target. The authors will present an analysis of some relatively well diagnosed experiments which have been useful in developing their modeling. The simulations match experimentally obtained target impulses, pressures at the target surface inside the laser spot, and radiation emission from the target to within about 20%. Hence their simulational technique appears to form a useful basis for further investigation of laser-surface interaction in this intensity, pulse-width range. This work is useful in many technical areas such as materials processing.

Goldman, S.R.; Wilke, M.D.; Green, R.E.L.; Johnson, R.P. [Los Alamos National Lab., NM (United States); Busch, G.E. [KMS Fusion, Inc., Ann Arbor, MI (United States)

1998-08-01

13

A Two-dimensional HLLC Riemann Solver for Conservation Laws : Application to Euler and MHD Flows

In this paper we present a genuinely two-dimensional HLLC Riemann solver. On logically rectangular meshes, it accepts four input states that come together at an edge and outputs the multi-dimensionally upwinded fluxes in both directions. This work builds on, and improves, our prior work on two-dimensional HLL Riemann solvers. The HLL Riemann solver presented here achieves its stabilization by introducing

Dinshaw S. Balsara

2011-01-01

14

Two-Dimensional Dynamic Simulation of a Continuous Foil Bearing

NASA Technical Reports Server (NTRS)

In this paper, the two dimensional(radial and circumferential) transient Navier-Stokes equations are used to solve the hydrodynamic problem in conjunction with the time dependent motion of the journal, and the deformable, spring supported foil. The elastic deformation of the foil and its supports are simulated by a finite element model. The time-dependent Navier-Stokes formulation is used to solve for the interaction between the fluid lubricant, the motion of the journal and the deformable foil boundary. The steady state, the quasi-transient and the full transient dynamic simulation of the foil-fluid journal interaction are examined on a comparative basis. For the steady state simulation, the fluid lubricant pressures are evaluated for a particular journal position, by means of an iterative scheme until convergence is achieved in both the fluid pressures and the corresponding foil deformation. For the quasi-transient case, the transient motion of the journal is calculated using a numerical integration scheme for the velocity and displacement of the journal. The deformation of the foil is evaluated through numerical iteration in feedback mode with the fluid film pressure generated by the journal motion until convergence at every time step is achieved. For the full transient simulation, a parallel real-time integration scheme is used to evaluate simultaneously the new journal position and the new deformed shape of the foil at each time step. The pressure of the fluid lubricant is iterated jointly with the corresponding journal position and the deformed foil geometry until convergence is achieved. A variable time-stepping Newmark-Beta integration procedure is used to evaluate the transient dynamics at each time step of the bearing.

Braun, M. Jack; Choy, F. K.; Dzodzo, Milorad; Hsu, J.

1996-01-01

15

Shear-Flow Driven Current Filamentation: Two-Dimensional Magnetohydrodynamic Simulations

The process of current filamentation in permanently externally driven, initially globally ideal plasmas is investigated by means of two-dimensional Magnetohydrodynamic (MHD)-simulations. This situation is typical for astrophysical systems like jets, the interstellar and intergalactic medium where the dynamics is dominated by external forces. Two different cases are studied. In one case, the system is ideal permanently and dissipative processes are excluded. In the second case, a system with a current density dependent resistivity is considered. This resistivity is switched on self-consistently in current filaments and allows for local dissipation due to magnetic reconnection. Thus one finds tearing of current filaments and, besides, merging of filaments due to coalescence instabilities. Energy input and dissipation finally balance each other and the system reaches a state of constant magnetic energy in time.

C. Konz; H. Wiechen; H. Lesch

2000-10-09

16

A Two-dimensional HLLC Riemann Solver for Conservation Laws : Application to Euler and MHD Flows

In this paper we present a genuinely two-dimensional HLLC Riemann solver. On logically rectangular meshes, it accepts four input states that come together at an edge and outputs the multi-dimensionally upwinded fluxes in both directions. This work builds on, and improves, our prior work on two-dimensional HLL Riemann solvers. The HLL Riemann solver presented here achieves its stabilization by introducing a constant state in the region of strong interaction, where four one-dimensional Riemann problems interact vigorously with one another. A robust version of the HLL Riemann solver is presented here along with a strategy for introducing sub-structure in the strongly-interacting state. Introducing sub-structure turns the two-dimensional HLL Riemann solver into a two-dimensional HLLC Riemann solver. The sub-structure that we introduce represents a contact discontinuity which can be oriented in any direction relative to the mesh. The Riemann solver presented here is general and can work with any system of conserva...

Balsara, Dinshaw S

2011-01-01

17

Two-Dimensional Inlet Simulation Using a Diagonal Implicit Algorithm.

National Technical Information Service (NTIS)

A modification of an implicit approximate-factorization finite-difference algorithm applied to the two-dimensional Euler and Navier-Stokes equations in general curvilinear coordinates is presented for supersonic freestream flow about and through inlets. T...

D. S. Chaussee, T. H. Pulliam

1981-01-01

18

Two-Dimensional Inlet Simulation Using a Diagonal Implicit Algorithm

NASA Technical Reports Server (NTRS)

A modification of an implicit approximate-factorization finite-difference algorithm applied to the two-dimensional Euler and Navier-Stokes equations in general curvilinear coordinates is presented for supersonic freestream flow about and through inlets. The modification transforms the coupled system of equations Into an uncoupled diagonal form which requires less computation work. For steady-state applications the resulting diagonal algorithm retains the stability and accuracy characteristics of the original algorithm. Solutions are given for inviscid and laminar flow about a two-dimensional wedge inlet configuration. Comparisons are made between computed results and exact theory.

Chaussee, D.S.; Pulliam, T. H.

1981-01-01

19

Numerical simulation of two-dimensional nonlinear standing acoustic waves

NASA Astrophysics Data System (ADS)

In this paper the behavior of strongly nonlinear waves in two-dimensional resonators filled with thermoviscous fluid is studied. For this purpose a set of differential equations, written in Lagrangian coordinates, is proposed and a time-domain numerical scheme is developed for solving them. Full nonlinear equations are derived from the conservation laws and state equation by assuming an irrotational fluid. Auxiliary conditions are written by considering a rigid-walled cavity, excitation at some points of the boundary, and rest at the outset. Finite differences are applied in the space and time domains, and lead to an implicit scheme. The numerical model solves the problem in terms of displacement vector field. The pressure field is then obtained from the displacement values. The algorithm allows us to analyze the evolution of the behavior of complex standing waves. The nonlinear characteristics of standing waves, well known in one-dimensional chambers, are now apparent in two-dimensional resonators by means of this new computational model. Some numerical experiments are carried out, a validation of the model is achieved, and results are given at a complex mode for which plane wave approximation is not appropriate. Several aspects of the nonlinear pressure field inside two-dimensional resonators are presented, such as harmonic distortion and nonlinear attenuation effects. In particular the quasi-standing character of such waves is detected and described. The effect of redistribution of rms pressure inside a two-dimensional cavity is commented.

Vanhille, Christian; Campos-Pozuelo, Cleofé

2004-07-01

20

An MHD Gadget for cosmological simulations

Various radio observations have showed that the hot atmospheres of galaxy clusters are magnetized. However, our understanding of the origin of these magnetic fields, their implications on structure formation and their interplay with the dynamics of the cluster atmosphere, especially in the centers of galaxy clusters is still very limited. In preparation to the upcoming new generation of radio telescopes (like EVLA, LWA, LOFAR and SKA), a huge effort is being made to learn more about cosmological magnetic fields from the observational perspective. Here we present the implementation of magneto hydrodynamics in the cosmological SPH code GADGET. We discuss the details of the implementation and various schemes to suppress numerical instabilities as well as regularization schemes, in the context of cosmological simulations. The performance of the SPH MHD code is demonstrated in various one and two dimensional test problems, which we performed if a fully, three dimensional setup to test the code under realistic circumstances. Comparing with solutions obtained with ATHENA, we find excellent agreement with our SPH MHD implementation. Finally we apply our SPH MHD implementation to forming galaxy clusters within a large, cosmological box. Performing a resolution study we demonstrate the robustness of the predicted shape of the magnetic field profiles in galaxy clusters, which is in good agreement with previous studies.

K. Dolag; F. A. Stasyszyn

2008-07-22

21

MHD wave propagation in the neighbourhood of a two-dimensional null point

The nature of fast magnetoacoustic and Alfv\\'en waves is investigated in a zero $\\beta$ plasma. This gives an indication of wave propagation in the low $\\beta$ solar corona. It is found that for a two-dimensional null point, the fast wave is attracted to that point and the front of the wave slows down as it approaches the null point, causing the current density to accumulate there and rise rapidly. Ohmic dissipation will extract the energy in the wave at this point. This illustrates that null points play an important role in the rapid dissipation of fast magnetoacoustic waves and suggests the location where wave heating will occur in the corona. The Alfv\\'en wave behaves in a different manner in that the wave energy is dissipated along the separatrices. For Alfv\\'en waves that are decoupled from fast waves, the value of the plasma $\\beta$ is unimportant. However, the phenomenon of dissipating the majority of the wave energy at a specific place is a feature of both wave types.

J. A. McLaughlin; A. W. Hood

2007-12-11

22

Resistive MHD and particle trajectory simulations on SSX

Formation, relaxation and reconnection of spheromaks in the Swarthmore Spheromak Experiment (SSX) are modeled by a 2-D axisymmetric resistive MHD simulation (TRIM) applied to the SSX boundary and initial conditions. Results are compared to corresponding one- and two-dimensional measurements of magnetic field in the experiment. Both global equilibrium and reconnection zone B-field configurations are reproduced. Several different resistivity implementation schemes

V. S. Lukin; M. R. Brown; G. Qui; W. H. Matthaeus

2000-01-01

23

Two-dimensional simulations of the inertial electrostatic confinement device

We discuss the application of the CELESTE simulation package to the simulation of the experiments conducted at the Los Alamos Inertial Electrostatic Confinement (IEC) device. Recently considerable experimental advances have been made in understanding of the stability of the virtual cathode and in the physics of POPS. This momentous experimental advance requires a new simulation effort for explaining the new

Alberto Marocchino; Giovanni Lapenta; Evstati Evstatiev; Richard Nebel; Jaeyoung Park

2006-01-01

24

Experiments being conducted at the Los Alamos National Laboratory Pegasus facility are examining stability issues for driving an aluminum liner with a pulsed magnetic field. The Pegasus facility provides a current of 5 to 8 Megamperes to compress a cylindrical liner. Liners of various size and thickness are used, depending on the specific experimental objectives. In several of these experiments, the outer surface clearly develops perturbations in the mass distribution. These perturbations are strongest when the aluminum is suspected to have melted and in some cases partially vaporized. A series of specific experiments was designed to examine the growth rate of these instabilities. These experiments involved machining a sine wave onto the outer surface of the liner to seed a given wavelength. Two-dimensional MHD calculations, using the measured current profile, were performed to model the behavior of the liner under magnetic field compression. These predictions were made with a 2D Eulerian code complete with a Steinburg-Guinan strength model. The results of these calculations will be discussed in this paper. The density contours at specific times will be compared with the processed radiography.

Atchison, W.L.; Faehl, R.J.; Morgan, D.V.; Reinovsky, R.E.

1997-10-01

25

TWO DIMENSIONAL IMMERSED BOUNDARY SIMULATIONS OF SWIMMING JELLYFISH

Simulations Of Swim- ming Jellyfish Examining Committee: Dr. Weiran Sun, Assistant Professor Chair Dr. John #12;"A journey of a thousand miles must begin with a single step." -- Lao-tzu vi #12;Acknowledgments

Stockie, John

26

Simulation of deep one- and two-dimensional redshift surveys

NASA Technical Reports Server (NTRS)

It is shown that slice or pencil-beam redshift surveys of galaxies can be simulated in a box with nonequal sides. This method saves a lot of computer time and memory while providing essentially the same results as from whole-cube simulations. A 2457.6/h Mpc-long rod (out to a redshift z = 0.58 in two opposite directions) is simulated using the standard biased cold dark matter model as an example to mimic the recent deep pencil-beam surveys by Broadhurst et al. (1990). The structures (spikes) seen in these simulated samples occur when the narrow pencil-beam pierces walls, filaments, and clusters appearing randomly along the line-of-sight. A statistical test for goodness of fit to a periodic lattice has been applied to the observations and the simulations. It is found that the statistical significance level (P = 15.4 percent) is not strong enough to reject the null hypothesis that the observations and the simulations were drawn at random from the same set.

Park, Changbom; Gott, J. Richard, III

1991-01-01

27

Two-dimensional simulations of the inertial electrostatic confinement device

NASA Astrophysics Data System (ADS)

We discuss the application of the CELESTE simulation package to the simulation of the experiments conducted at the Los Alamos Inertial Electrostatic Confinement (IEC) device. Recently considerable experimental advances have been made in understanding of the stability of the virtual cathode and in the physics of POPS. This momentous experimental advance requires a new simulation effort for explaining the new experimental findings, particularly in the area of stability of the configurations obtained experimentally. We have conducted a 2D stability study of the virtual cathode in the IEC device using the DEMOCRITUS package. DEMOCRITUS is a 2D general geometry electrostatic PIC code. In the present study we have done complete stability study and investigate the two-stream instability occuring in the IEC device.

Marocchino, Alberto; Lapenta, Giovanni; Evstatiev, Evstati; Nebel, Richard; Park, Jaeyoung

2006-04-01

28

Two-dimensional SPH simulations of wedge water entries

This paper presents a study based on the smoothed particles hydrodynamics (SPH) method, aiming at an accurate numerical simulation of solid–fluid coupling in a free surface flow context. The SPH scheme is first described and discussed through its formulations. Then a new technic based on a particle sampling method, and designed to evaluate fluid pressure on solid boundaries is introduced.

G. Oger; M. Doring; B. Alessandrini; P. Ferrant

2006-01-01

29

Pores in a two-dimensional network of DNA strands - computer simulations

Formation of random network of DNA strands is simulated on a two-dimensional triangular lattice. We investigate the size distribution of pores in the network. The results are interpreted within theory of percolation on Bethe lattice.

M. J. Krawczyk; K. Kulakowski

2006-09-23

30

Computational Fluid Dynamics Simulation of Green Water Around a Two-dimensional Platform

COMPUTATIONAL FLUID DYNAMICS SIMULATION OF GREEN WATER AROUND A TWO-DIMENSIONAL PLATFORM A Thesis by YUCHENG ZHAO Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment... of the requirements for the degree of MASTER OF SCIENCE December 2009 Major Subject: Ocean Engineering COMPUTATIONAL FLUID DYNAMICS SIMULATION OF GREEN WATER AROUND A TWO-DIMENSIONAL PLATFORM A Thesis by YUCHENG ZHAO Submitted...

Zhao, Yucheng

2010-07-14

31

Indiana University Southeast Physics Applets: Two Dimensional Diatomic Model Simulation

NSDL National Science Digital Library

This item is a simulation on the movement and energy of a diatomic molecule made up of two atoms with a mass ratio of 1:4. Users can observe the kinetic energy in both atoms, as well as the energy stored in the spring connecting them. Context-rich questions are included on the average kinetic energy of the atoms, their thermal equilibrium with each other, and how their speed changes as the spring gains energy. This page is part of a collection of Java applets with tutorial questions developed for students of undergraduate physics.

Forinash, Kyle

2008-08-31

32

Two-dimensional SPH simulations of wedge water entries

NASA Astrophysics Data System (ADS)

This paper presents a study based on the smoothed particles hydrodynamics (SPH) method, aiming at an accurate numerical simulation of solid-fluid coupling in a free surface flow context. The SPH scheme is first described and discussed through its formulations. Then a new technic based on a particle sampling method, and designed to evaluate fluid pressure on solid boundaries is introduced. This method is then extended to the capture of freely moving body dynamics in a fluid/solid coupling approach. This study involves a spatially varying resolution, based on the so-called variable smoothing length technique, for which a new formulation of the equations is proposed. Two distinct test cases of wedge water entry are presented in order to validate this new method. Pressure prediction is first compared with analytical and experimental results, evolution in time of the body dynamics is compared with experimental results in both cases, and the pressure field on the solid boundaries is studied and discussed on the first impact case.

Oger, G.; Doring, M.; Alessandrini, B.; Ferrant, P.

2006-04-01

33

MHD simulations: Corotating Interaction Regions

NASA Astrophysics Data System (ADS)

Corotating Interaction Regions (CIRs) form in the solar wind when parcels of fast-speed wind interact with slow-speed wind due to the rotation of the Sun. The resulting buildup of pressure generates disturbances that, with increasing time (or distance from the Sun), may develop into a so-called forward-reverse shock-pair. During solar-quiet times CIRs can be the dominant force shaping large-scale structures in the heliosphere. Studying CIRs is therefore important because the associated shocks are capable of e.g. accelerating energetic particles or deflecting cosmic rays. The global structure of CIRs can be modeled with an MHD approach that gives the plasma quantities needed to model the transport of particles in the heliosphere (with e.g. stochastic differential equations (SDEs)). Our MHD code CRONOS employs a semi-discrete finite volume scheme with adaptive time-stepping Runge-Kutta integration. The solenoidality of the magnetic field is ensured via constrained transport and the code supports Cartesian, Cylindrical and Spherical coordinates (including coordinate singularities) with the option for non-equidistant grids. The code runs in parallel (MPI) and supports the HDF5 output data format. Here, we show results from 3D-MHD simulations with our code CRONOS for a) analytic boundary conditions where results can be compared to those obtained with a different code and b) boundary conditions derived with the Wang-Sheeley-Arge model from observational data (WSO), which are compared to spacecraft observations. Comparison with Pizzo (1982) for analytic boundary conditions Comparison with STEREO A for Carrington Rotation 2060

Wiengarten, T.; Kleimann, J.; Fichtner, H.; Kühl, P.; Heber, B.; Kissmann, R.

2013-12-01

34

MHD Simulations: Corotating Interaction Regions

NASA Astrophysics Data System (ADS)

Corotating Interaction Regions (CIRs) form in the solar wind when parcels of fast-speed wind interact with slow-speed wind due to the rotation of the Sun. The resulting buildup of pressure generates disturbances that, with increasing time (or distance from the Sun), may develop into a so-called forward-reverse shock pair. During solar-quiet times CIRs can be the dominant force shaping large-scale structures in the heliosphere. Studying CIRs is therefore important because the associated shocks are capable of e.g. accelerating energetic particles or deflecting cosmic rays. The global structure of CIRs can be modeled with an MHD approach that gives the plasma quantities needed to model the transport of particles in the heliosphere with e.g. stochastic differential equations. Here, we show results from 3D-MHD simulations with our code CRONOS for a) analytic boundary conditions where results can be compared to those obtained with a different code and b) boundary conditions derived with the Wang-Sheeley-Arge model from observational data (WSO), which are compared to spacecraft observations.

Wiengarten, T.; Kleimann, J.; Fichtner, H.; Kissmann, R.

2014-09-01

35

Two-dimensional simulation of a miniaturized inductively coupled plasma reactor

Two-dimensional simulation of a miniaturized inductively coupled plasma reactor Sang Ki Nam-consistent simulation of a miniaturized inductively coupled plasma mICP reactor was developed. The coupled equations discharges,3 ac plasma displays,4 microwave,5 and rf inductively coupled plasmas.1,2 Miniatur- ized

Economou, Demetre J.

36

Lekner summation of dipolar interaction in quasi-two-dimensional simulations

The Lekner method for calculation of electrostatic interactions in periodically replicated simulation cells is extended to quasi-two-dimensional systems of particles with dipolar interactions. The electric field, potential energy, forces and torques are expressed through rapidly converging series of modified Bessel functions. The method contains no arbitrary parameters, and has no limitations on the simulation box width.

Sergey V. Lishchuk

2002-01-01

37

NASA Astrophysics Data System (ADS)

The propagation of a (1 + 1)-dimensional corrosion front into a quasi-two-dimensional aluminum foil confined in an electrochemically inert thin cell was studied experimentally. The corrosion experiments were carried out under controlled electrochemical and flow conditions leading to corrosion fronts consisting of isolated and coalesced pits. The geometry of digitized images of these disorderly corrosion fronts was analyzed quantitatively. A two-dimensional computer model these disorderly corrosion fronts was analyzed quantitatively. A two-dimensional computer model that includes passivation and depassivation processes was used to simulate the corrosion fronts and the simulated fronts were compared quantitatively and qualitatively with the experimental results. Unlike earlier passivation/depassivation models, this model includes the increasing electrolyte concentration in corrosion pits during the corrosion process, leading to the development of a more corrosive environment in the pits.

Johnsen, T.; Jøssang, A.; Jøssang, T.; Meakin, P.

1997-02-01

38

Hybrid simulation of whistler excitation by electron beams in two-dimensional non-periodic domains

NASA Astrophysics Data System (ADS)

We present a two-dimensional hybrid fluid-PIC scheme for the simulation of whistler wave excitation by relativistic electron beams. This scheme includes a number of features which are novel to simulations of this type, including non-periodic boundary conditions and fresh particle injection. Results from our model suggest that non-periodicity of the simulation domain results in the development of fundamentally different wave characteristics than are observed in periodic domains.

Woodroffe, J. R.; Streltsov, A. V.

2014-11-01

39

Two-dimensional Markov Chain Simulation of Soil Type Spatial Distribution

environmental research, especially for accurately assessing the water and solute transport processes in watershed scales. This study de- dicator geostatistics and transition probability matrices scribes an efficient Markov chain model for two-dimensional modeling (TPMs) provided by Markov chains. Currently, indica- and simulation of spatial distribution of soil types (or classes). The tor geostatistics (Journel, 1983), especially the sequen- model is

Weidong Li; Chuanrong Zhang; James E. Burt; A.-Xing Zhu; Jan Feyen

2004-01-01

40

Transient two-dimensional simulation of a cosmic event on a CMOS SRAM cell

Two-dimensional transient simulations of cosmic ion strikes on sensitive junctions of a CMOS SRAM have been carried out. The calculations determine time responses for transport variables of the four cross-coupled transistors and reveal the conditions for change of state or upset. 6 refs., 6 figs., 1 tab.

Fu, J.S.; Axness, C.L.; Weaver, H.T.

1985-01-01

41

Transient two-dimensional simulation of SEU in a CMOS SRAM cell

Two-dimensional transient simulations of cosmic ion strikes on sensitive junctions of a CMOS SRAM have been carried out. The calculations determine time responses for transport variables of the four cross-coupled transistors and reveal the conditions for change of state or upset. 4 refs., 5 figs.

Fu, J.S.; Axness, C.L.; Weaver, H.T.

1985-01-01

42

Tracking the Mechanism of Fibril Assembly by Simulated Two-Dimensional Ultraviolet Spectroscopy

14853-1301, United States *S Supporting Information ABSTRACT: Alzheimer's disease (AD) is a neurodegener in the early time-scale formation and growth of amyloid fibrils, simulated two-dimensional ultraviolet, a dock/lock pathway. 1. INTRODUCTION Alzheimer's disease (AD) is a neurodegenerative disorder whose

Mukamel, Shaul

43

Two-dimensional direct numerical simulation of nanoparticle precursor evolution in turbulent flames alter the particle size distribution. By control- ling the turbulent flow and the flame structure, a fundamental understanding of the role of turbulent combustion in the nucleation and particle evolution process

Raman, Venkat

44

A two-dimensional model simulation of the El Chichon volcanic eruption cloud

Using a two-dimensional model of sulfate photochemistry, transport, and aerosol microphysics, we have simulated a 2-year period following the eruptions of El Chichon. Our calculations suggest that the residence time of the cloud in the stratosphere exceeds 2 years. The model reproduces the observed optical depth, lidar backscatter, and infrared extinction coefficients if about 10 megatonnes of SO2 are injected.

Louis A. Capone; Owen B. Toon; Robert C. Whitten; Richard P. Turco; Christopher A. Riegel; Krishnamurthy Santhanam

1983-01-01

45

1 American Institute of Aeronautics and Astronautics Two-dimensional Simulation of Horseshoe-713 Copyright Â© 2010 by Authors. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. #12;2 American Institute of Aeronautics and Astronautics I. Introduction lasma that has been used

Roy, Subrata

46

NASA Astrophysics Data System (ADS)

A thermally assisted laser-induced fluorescence (LIF) detection system is developed to measure two-dimensional spatial profiles of number density of alkali atoms seeded in an open-cycle MHD generator, especially in the boundary layer on channel electrodes. The spatial resolution of this system is evaluated to be 1.3 mm. To assess the system, the LIF intensity from Na atoms used as a seed tracer is measured in a laminar air-acetylene flame. The detected spatial profiles of the intensity show good agreement with those of the number density of sodium atoms measured by the spectral line absorption method. The LIF intensity near the surface of a cooled metal piece placed in the acetylene flame is also measured with this system as a preliminary experiment for applying it to the boundary layer on MHD channel electrodes.

Watanabe, Y.; Ikegami, T.; Ueno, T.; Masuda, M.; Akazaki, M.

1987-09-01

47

Turbulence modeling for two-dimensional water hammer simulations in the low Reynolds number range

Modeling turbulence in two-dimensional water hammer simulations is considered in the present study. The Baldwin–Lomax turbulence model is implemented, both in quasi-steady and frozen forms. Numerical simulations using both forms agree well with experimental data for lower Reynolds numbers (Re=5600) and the attenuation of the transient is adequately captured. However, for higher Reynolds numbers (Re=15,800), the frozen form overpredicts the

E. M. Wahba

2009-01-01

48

Simulations of the Two-Dimensional Electronic Spectroscopy of the Photosystem II Reaction Center

We report simulations of the two-dimensional electronic spectroscopy of the Qy band of the D1-D2-Cyt b559 photosystem II reaction center at 77 K. We base the simulations on an existing Hamiltonian that was derived by simultaneous fitting to a wide range of linear spectroscopic measurements and described within modified Redfield theory. The model obtains reasonable agreement with most aspects of the two-dimensional spectra, including the overall peak shapes and excited state absorption features. It does not reproduce the rapid equilibration from high energy to low energy excitonic states evident by a strong cross-peak below the diagonal. We explore modifications to the model to incorporate new structural data and improve agreement with the two-dimensional spectra. We find that strengthening the system–bath coupling and lowering the degree of disorder significantly improves agreement with the cross-peak feature, while lessening agreement with the relative diagonal/antidiagonal width of the 2D spectra. We conclude that two-dimensional electronic spectroscopy provides a sensitive test of excitonic models of the photosystem II reaction center and discuss avenues for further refinement of such models. PMID:23210463

Lewis, K. L. M.; Fuller, F. D.; Myers, J. A.; Yocum, C. F.; Mukamel, S.; Abramavicius, D.; Ogilvie, J. P.

2013-01-01

49

MHD simulations with the FLASH code

NASA Astrophysics Data System (ADS)

The FLASH code developed at the University of Chicago Flash Center is a modular, general-purpose, adaptive, parallel simulation code capable of handling compressible flow problems in various physical, in particular astrophysical, environments. Starting with version release 2.0, the FLASH code supports the equations of magnetohydrodynamics (MHD). In this paper, we will describe the present state of the code and the integration of the MHD module into the code framework. We will further describe specific implementation details of the FLASH MHD module. Finally, we will provide examples of simulations of ideal and resistive MHD fluids and of self-gravitating magnetized plasmas. The FLASH code is available for public distribution. Both information regarding code licensing and code distribution can be found at the Flash Center web site: http://flash.uchicago.edu.

Linde, Timur

2002-03-01

50

Historical perspective on astrophysical MHD simulations

This contribution contains the introductory remarks that I presented at IAU Symposium 270 on ``Computational Star Formation" held in Barcelona, Spain, May 31 -- June 4, 2010. I discuss the historical development of numerical MHD methods in astrophysics from a personal perspective. The recent advent of robust, higher order-accurate MHD algorithms and adaptive mesh refinement numerical simulations promises to greatly improve our understanding of the role of magnetic fields in star formation.

Norman, Michael L

2010-01-01

51

Exploding solutions of the complex two-dimensional Burgers equations: Computer simulations

NASA Astrophysics Data System (ADS)

We study by computer simulations the complex solutions of the two-dimensional Burgers equations in the whole plane in absence of external forces. For such model the existence of singularities, corresponding to a divergence of the total energy at a finite time, is proved by Li and Sinai ["Singularities of complex-valued solutions of the two-dimensional Burgers system," J. Math. Phys. 51, 015205 (2010)], 10.1063/1.3276099 for a large class of initial data. The simulations show that the blow-up takes place in a very short time, of the order of 10-5 time units. Moreover near the blow-up time the support of the solution in Fourier space moves out to infinity along a straight line. In x-space the solutions are concentrated in a finite region, with large space derivatives, as one would expect for physical phenomena such as tornadoes.

Boldrighini, C.; Frigio, S.; Maponi, P.

2012-08-01

52

Simulation of wave interactions with MHD

The broad scientific objectives of the SWIM (Simulation of Wave Interaction with MHD) project are twofold: (1) improve our understanding of interactions that both radio frequency (RF) wave and particle sources have on extended-MHD phenomena, and to substantially improve our capability for predicting and optimizing the performance of burning plasmas in devices such as ITER: and (2) develop an integrated computational system for treating multiphysics phenomena with the required flexibility and extensibility to serve as a prototype for the Fusion Simulation Project. The Integrated Plasma Simulator (IPS) has been implemented. Presented here are initial physics results on RF effects on MHD instabilities in tokamaks as well as simulation results for tokamak discharge evolution using the IPS.

Batchelor, Donald B [ORNL; Abla, G [General Atomics, San Diego; Bateman, Glenn [Lehigh University, Bethlehem, PA; Bernholdt, David E [ORNL; Berry, Lee A [ORNL; Bonoli, P. [Massachusetts Institute of Technology (MIT); Bramley, R [Indiana University; Breslau, J. [Princeton Plasma Physics Laboratory (PPPL); Chance, M. [Princeton Plasma Physics Laboratory (PPPL); Chen, J. [Princeton Plasma Physics Laboratory (PPPL); Choi, M. [General Atomics; Elwasif, Wael R [ORNL; Fu, GuoYong [Princeton Plasma Physics Laboratory (PPPL); Harvey, R. W. [CompX, Del Mar, CA; Jaeger, Erwin Frederick [ORNL; Jardin, S. C. [Princeton Plasma Physics Laboratory (PPPL); Jenkins, T [University of Wisconsin; Keyes, David E [Columbia University; Klasky, Scott A [ORNL; Kruger, Scott [Tech-X Corporation; Ku, Long-Poe [Princeton Plasma Physics Laboratory (PPPL); Lynch, Vickie E [ORNL; McCune, Douglas [Princeton Plasma Physics Laboratory (PPPL); Ramos, J. [Massachusetts Institute of Technology (MIT); Schissel, D. [General Atomics; Schnack, [University of Wisconsin; Wright, J. [Massachusetts Institute of Technology (MIT)

2008-07-01

53

Accurate simulations of a two-dimensional photon scanning tunneling microscope (2D-PSTM) for incident p-polarized waves (TM-mode) have been performed by the boundary integral equations called guided-mode extracted integral equations. The method used in this paper is a global method and the case of uncoated dielectric probe is treated. Complete and rigorous integral equations for a given configuration of 2D-PSTM have been

Kazuo Tanaka; Masahiro Tanaka; Kiyofumi Katayama

1999-01-01

54

Two-Dimensional Dam-Break Flood Simulation on Unstructured Meshes

A two-dimensional dam-break flood simulation model using unstructured meshes has been developed to study the hydrodynamics of flooding processes. The model employs the finite volume method to solve the conservation form of the shallow water equations. The HLLC approximate Riemann solver is used for computing the fluxes at cell interfaces because of its easiness to implement and suitability to wet\\/dry

Lixiang Song; Jianzhong Zhou; Qiang Zou; Jun Guo; Yi Liu

2010-01-01

55

Simulation of upper troposphere CO2 from two-dimensional and three-dimensional models

The Caltech\\/JPL two-dimensional (2-D) chemistry and transport model (CTM) and three-dimensional (3-D) GEOS-CHEM model have been used to simulate the CO2 in the upper troposphere from 2000 to 2004. Model results agree well with the aircraft observations between 9 km and 13 km [Matsueda et al., Tellus 2002] in the tropics. However, in the mid-latitudes there are some discrepancies between

X. Jiang; R. Shia; Q. Li; M. T. Chahine; E. T. Olsen; L. L. Chen; Y. L. Yung

2006-01-01

56

Two-dimensional simulations of nonlinear beam-plasma interaction in isotropic and magnetized plasmas

Nonlinear interaction of a low density electron beam with a uniform plasma is studied using two-dimensional particle-in-cell (PIC) simulations. We focus on formation of coherent phase space structures in the case, when a wide two-dimensional wave spectrum is driven unstable, and we also study how nonlinear evolution of these structures is affected by the external magnetic field. In the case of isotropic plasma, nonlinear buildup of filamentation modes due to the combined effects of two-stream and oblique instabilities is found to exist and growth mechanisms of secondary instabilities destroying the BGK--type nonlinear wave are identified. In the weak magnetic field, the energy of beam-excited plasma waves at the nonlinear stage of beam-plasma interaction goes predominantly to the short-wavelength upper-hybrid waves propagating parallel to the magnetic field, whereas in the strong magnetic field the spectral energy is transferred to the electrostatic whistlers with oblique propagation.

Timofeev, I V

2012-01-01

57

Simulation of two-dimensional Kerr photonic crystals via fast Fourier factorization.

We present an adaptation of the fast Fourier factorization method to the simulation of two-dimensional (2D) photonic crystals with a third-order nonlinearity. The algorithm and its performance are detailed and illustrated via the simulation of a Kerr 2D photonic crystal. A change in the transmission spectrum at high intensity is observed. We explain why the change does not reduce to a translation (redshift) but rather consists in a deformation and why one side of the bandgap is more suited to a switching application than the other one. PMID:16604765

Bonnefois, J J; Guida, Géraldine; Priou, Alain; Nevière, Michel; Popov, Evgeny

2006-04-01

58

Nonlinear kinetic modeling and simulations of Raman scattering in a two-dimensional geometry

NASA Astrophysics Data System (ADS)

In this paper, we present our nonlinear kinetic modeling of stimulated Raman scattering (SRS) by the means of envelope equations, whose coefficients have been derived using a mixture of perturbative and adiabatic calculations. First examples of the numerical resolution of these envelope equations in a two-dimensional homogeneous plasma are given, and the results are compared against those of particle-in-cell (PIC) simulations. These preliminary comparisons are encouraging since our envelope code provides threshold intensities consistent with those of PIC simulations while requiring computational resources reduced by 4 to 5 orders of magnitude compared to full-kinetic codes.

Bénisti, Didier; Morice, Olivier; Gremillet, Laurent; Friou, Alexandre; Lefebvre, Erik

2013-11-01

59

Cell-dynamical simulation of magnetic hysteresis in the two-dimensional Ising system

NASA Astrophysics Data System (ADS)

We present results from numerical simulations using a ``cell-dynamical system'' to obtain solutions to the time-dependent Ginzburg-Landau equation for a scalar, two-dimensional (2D), (?2)2 model in the presence of a sinusoidal external magnetic field. Our results confirm a recent scaling law proposed by Rao, Krishnamurthy, and Pandit [Phys. Rev. B 42, 856 (1990)], and are also in excellent agreement with recent Monte Carlo simulations of hysteretic behavior of 2D Ising spins by Lo and Pelcovits [Phys. Rev. A 42, 7471 (1990)].

Sengupta, Surajit; Marathe, Yatin; Puri, S.

1992-04-01

60

Preliminary results for a two-dimensional simulation of the working process of a Stirling engine

Stirling engines have several potential advantages over existing types of engines, in particular they can use renewable energy sources for power production and their performance meets the demands on the environmental security. In order to design Stirling Engines properly, and to put into effect their potential performance, it is important to more accurately mathematically simulate its working process. At present, a series of very important mathematical models are used for describing the working process of Stirling Engines and these are, in general, classified as models of three levels. All the models consider one-dimensional schemes for the engine and assume a uniform fluid velocity, temperature and pressure profiles at each plane of the internal gas circuit of the engine. The use of two-dimensional CFD models can significantly extend the capabilities for the detailed analysis of the complex heat transfer and gas dynamic processes which occur in the internal gas circuit, as well as in the external circuit of the engine. In this paper a two-dimensional simplified frame (no construction walls) calculation scheme for the Stirling Engine has been assumed and the standard {kappa}-{var{underscore}epsilon} turbulence model has been used for the analysis of the engine working process. The results obtained show that the use of two-dimensional CFD models gives the possibility of gaining a much greater insight into the fluid flow and heat transfer processes which occur in Stirling Engines.

Makhkamov, K.K.; Ingham, D.B.

1998-07-01

61

MHD simulation of wire ablation and implosion in wire-array Z-pinch

We present magnetohydrodynamic (MHD) simulation of ablated tungsten wire in the wire-array Z-pinch on MAGPIE using the GORGON code. The simulation is incorporated with theoretical models of equation-of-state and electrical conductivities for nonideal plasmas in addition to an astrophysical model for radiation cooling effects. The dynamic behaviors of exploding wire plasma are demonstrated in a two-dimensional domain during the early

Deok-Kyu Kim; Jeremy P. Chittenden; Sergey V. Lebedev; A. Marocchino; F. Suzuki-Vidal

2010-01-01

62

MHD simulations with the FLASH code

The FLASH code developed at the University of Chicago Flash Center is a modular, general-purpose, adaptive, parallel simulation code capable of handling compressible flow problems in various physical, in particular astrophysical, environments. Starting with version release 2.0, the FLASH code supports the equations of magnetohydrodynamics (MHD). In this paper, we will describe the present state of the code and the

Timur Linde

2002-01-01

63

Numerical simulation of compressible flow around complex two-dimensional cavities

NASA Technical Reports Server (NTRS)

Compressible viscous flow around two-dimensional cavities, that model the midplane flow in and around an airborne telescope cavity, are obtained through numerical simulation. Numerical solutions using the patched grid CSCM scheme for compressible, unsteady flow are presented for the cavities, with and without blowing. The time evolving solutions show interesting flow features. Relevant results for a limited number of problems presented here show the unsteady nature of the flow and its dependence on various parameters such as Reynolds number, the wall conditions, etc. The voluminous data of time evolving flow field solutions are analyzed through movies of the velocity vectors, and contours of other flow variables.

Venkatapathy, Ethiraj; Lombard, C. K.; Nagaraj, N.

1987-01-01

64

Comparative study of three methods for the simulation of two-dimensional photonic crystals.

Three methods for the efficient simulation of two-dimensional photonic crystal structures are compared, namely, a semianalytical multiple-scattering technique; a vectorial eigenmode expansion technique; and a FDTD-ROM technique. The basic principles of each method are presented. For the semianalytical technique and for the vectorial eigenmode expansion technique, we show how reflections coming from abruptly terminated waveguides can be avoided. The main advantages and disadvantages of each method are discussed. Results from use of the three methods are compared for several photonic crystal structures. PMID:15535377

Pissoort, Davy; Denecker, Bart; Bienstman, Peter; Olyslager, Frank; De Zutter, Daniël

2004-11-01

65

Simulation of two-dimensional electronic spectra of phycoerythrin 545 at ambient temperature.

By using a hierarchical equations-of-motion approach, we reproduce the two-dimensional electronic spectra of phycoerythrin 545 from Rhodomonas CS24 at ambient temperature (294 K). The simulated spectra are in agreement with the experimental results reported in Wong et al. (Nat. Chem. 2012, 4, 396). The evolutions of cross peaks for rephasing spectra and diagonal peaks for nonrephasing spectra have also been plotted. The peaks oscillate with the population times, with frequencies, phases, and amplitudes of the oscillating curves also being qualitatively consistent with the experimental results. PMID:25299464

Leng, Xuan; Liang, Xian-Ting

2014-10-30

66

The two-dimensional, transient numerical model of heat and water vapor convection and diffusion during air exfiltration within fiberglass insulation, presented in Part I, is validated in Part II, with experimental data for temperature, moisture and frost accumulation, and heat flux. With a few exceptions, the simulation results and experimental data agree within the experimental uncertainty. Exfiltration airflow in the two-dimensional

Hong Chen; Robert W. Besant; Yong-Xin Tao

1997-01-01

67

MHD simulation studies of z-pinch shear flow stabilization

NASA Astrophysics Data System (ADS)

The development of the m=0 instability in a z-pinch in the presence of sheared plasma flows is investigated with the aid of a two-dimensional magnetohydrodynamic (MHD) simulation code (MHRDR). The linear growth rates are compared to the results obtained by solving the ideal MHD linearized equations [1] and to the results obtained using a 3D hybrid simulation code [2]. The instability development is followed into the nonlinear regime where its growth and saturation are examined. [1] V.I. Sotnikov, I. Paraschiv, V. Makhin, B.S. Bauer, J.-N. Leboeuf, and J.M. Dawson, "Linear analysis of sheared flow stabilization of global magnetohydrodynamic instabilities based on the Hall fluid mode", Phys. Plasmas 9, 913 (2002). [2] V.I. Sotnikov, V. Makhin, B.S. Bauer, P. Hellinger, P. Travnicek, V. Fiala, J.-N. Leboeuf, "Hybrid Simulations of Current-Carrying Instabilities in Z-pinch Plasmas with Sheared Axial Flow", AIP Conference Proceedings, Volume 651, Dense Z-Pinches: 5th International Conference on Dense Z-Pinches, edited by J. Davis et al., page 396, June 2002.

Paraschiv, I.; Bauer, B. S.; Sotnikov, V. I.; Makhin, V.; Siemon, R. E.

2003-10-01

68

A sheet-shaped thermal lithium beam probe has been developed for two-dimensional density measurements in the edge region of the torus plasma. A numerical simulation was carried out to confirm the validity of the diagnostics for fast and transient phenomena such as edge localized modes or blobs, etc., where the velocity of blobs is faster than that of the probe beam. It was found in the simulation that the density of the blob itself is reconstructed to be low and unexpected ghosts appear in the reconstructed density profile near the blob, if the conventional reconstruction method is employed. These results invite our attention to the numerical errors in the density reconstruction process. On the other hand, the errors can be corrected by using the simulation results.

Tsuchiya, H.; Morisaki, T.; Komori, A.; Motojima, O. [Graduate University for Advanced Studies, Toki 509-5292 (Japan); National Institute for Fusion Science, Toki 509-5292 (Japan)

2006-10-15

69

Two-dimensional simulation of a miniaturized inductively coupled plasma reactor

NASA Astrophysics Data System (ADS)

A two-dimensional self-consistent simulation of a miniaturized inductively coupled plasma (mICP) reactor was developed. The coupled equations for plasma power deposition, electron temperature, and charged and neutral species densities, were solved to obtain the spatial distribution of an argon discharge. The effect of control parameters, such as power and pressure, on the evolution of plasma density and electron temperature was investigated. Strong ion density gradients were observed which can make spatially resolved Langmuir probe measurements particularly challenging. Simulation results were in reasonable agreement with available experimental data. The neutral gas temperature was predicted to be close to the wall temperature, due to the small length scale of the mICP, allowing for efficient heat transfer.

Nam, Sang Ki; Economou, Demetre J.

2004-03-01

70

Two-dimensional simulation of holographic data storage medium for multiplexed recording.

In this paper, we propose a new analysis model for photopolymer recording processes that calculate the two-dimensional refractive index distribution of multiplexed holograms. For the simulation of the photopolymer medium, time evolution of monomer diffusion and polymerization need to be calculated simultaneously. The distribution of the refractive index inside the medium is induced by these processes. By evaluating the refractive index pattern on each layer, the diffraction beams from the multiplexed hologram can be read out by beam propagation method (BPM). This is the first paper to determine the diffraction beam from a multiplexed hologram in a simulated photopolymer medium process. We analyze the time response of the multiplexed hologram recording processes in the photopolymer, and estimate the degradation of diffraction efficiency with multiplexed recording. This work can greatly contribute to understanding the process of hologram recording. PMID:18542367

Toishi, Mitsuru; Takeda, Takahiro; Tanaka, Kenji; Tanaka, Tomiji; Fukumoto, Atsushi; Watanabe, Kenjiro

2008-02-18

71

Mesoscopic simulations of two-dimensional grain growth with anisotropic grain-boundary properties.

Grain-boundary (GB) properties in a polycrystalline system are generally anisotropic; in particular, both the GB energy and the mobility depend on the GB misorientation. Here the effect of anisotropic GB properties on two- dimensional grain growth is investigated by computer simulation. A stochastic velocity Monte Carlo algorithm based on a variational formulation for the dissipated power is implemented. The simulations show that grain growth leads to an increase in the fraction of small-angle GBs during the growth process. The average grain area is found to grow with a smaller exponent than in a system with isotropic GB properties. An extended von Neumann-Mullins relation based on averaged GB properties is proposed.

Moldovan, D.; Wolf, D.; Phillpot, S. R.; Haslam, A. J.; Materials Science Division

2002-05-10

72

The bulk of the solar chromosphere is weakly ionized and interactions between ionized particles and neutral particles likely have significant consequences for the thermodynamics of the chromospheric plasma. We investigate the importance of introducing neutral particles into the MHD equations using numerical 2.5D radiative MHD simulations obtained with the Bifrost code. The models span the solar atmosphere from the upper layers of the convection zone to the low corona, and solve the full MHD equations with non-gray and non-LTE radiative transfer, and thermal conduction along the magnetic field. The effects of partial ionization are implemented using the generalized Ohm's law, i.e., we consider the effects of the Hall term and ambipolar diffusion in the induction equation. The approximations required in going from three fluids to the generalized Ohm's law are tested in our simulations. The Ohmic diffusion, Hall term, and ambipolar diffusion show strong variations in the chromosphere. These strong variations of the various magnetic diffusivities are absent or significantly underestimated when, as has been common for these types of studies, using the semi-empirical VAL-C model as a basis for estimates. In addition, we find that differences in estimating the magnitude of ambipolar diffusion arise depending on which method is used to calculate the ion-neutral collision frequency. These differences cause uncertainties in the different magnetic diffusivity terms. In the chromosphere, we find that the ambipolar diffusion is of the same order of magnitude or even larger than the numerical diffusion used to stabilize our code. As a consequence, ambipolar diffusion produces a strong impact on the modeled atmosphere. Perhaps more importantly, it suggests that at least in the chromospheric domain, self-consistent simulations of the solar atmosphere driven by magnetoconvection can accurately describe the impact of the dominant form of resistivity, i.e., ambipolar diffusion. This suggests that such simulations may be more realistic in their approach to the lower solar atmosphere (which directly drives the coronal volume) than previously assumed.

Martinez-Sykora, Juan; De Pontieu, Bart; Hansteen, Viggo, E-mail: j.m.sykora@astro.uio.no [Lockheed Martin Solar and Astrophysics Laboratory, Palo Alto, CA 94304 (United States)

2012-07-10

73

NASA Technical Reports Server (NTRS)

Investigations of one- and two-dimensional (1- or 2-D) simulations of Stirling machines centered around experimental data generated by the U. of Minnesota Mechanical Engineering Test Rig (METR) are covered. This rig was used to investigate oscillating flows about a zero mean with emphasis on laminar/turbulent flow transitions in tubes. The Space Power Demonstrator Engine (SPDE) and in particular, its heater, were the subjects of the simulations. The heater was treated as a 1- or 2-D entity in an otherwise 1-D system. The 2-D flow effects impacted the transient flow predictions in the heater itself but did not have a major impact on overall system performance. Information propagation effects may be a significant issue in the simulation (if not the performance) of high-frequency, high-pressure Stirling machines. This was investigated further by comparing a simulation against an experimentally validated analytic solution for the fluid dynamics of a transmission line. The applicability of the pressure-linking algorithm for compressible flows may be limited by characteristic number (defined as flow path information traverses per cycle); this warrants further study. Lastly the METR was simulated in 1- and 2-D. A two-parameter k-w foldback function turbulence model was developed and tested against a limited set of METR experimental data.

Goldberg, Louis F.

1990-01-01

74

We report the results of a 2-step two-dimensional (2D) diffusion study by Scanning Capacitance Microscopy (SCM) and 2D TSUPREM IV process simulation. A quantitative 2D dopant profile of gate-like structures consisting heavily implanted n+ regions separated by a lighter doped n-type region underneath 0.56 {mu}m gates is measured with the SCM. The SCM is operated in the constant-change-in-capacitance mode. The 2-D SCM data is converted to dopant density through a physical model of the SCM/silicon interaction. This profile has been directly compared with 2D TSUPREM IV process simulation and used to calibrate the simulation parameters. The sample is then further subjected to an additional diffusion in a furnace for 80 minutes at 1000C. The SCM measurement is repeated on the diffused sample. This final 2D dopant profile is compared with a TSUPREM IV process simulation tuned to fit the earlier profile with no change in the parameters except the temperature and time for the additional diffusion. Our results indicate that there is still a significant disagreement between the two profiles in the lateral direction. TSUPREM IV simulation considerably underestimates the diffusion under the gate region.

Kim, J.; McMurray, J. S.; Williams, C. C.; Slinkman, J. [Department of Physics, University of Utah, Salt Lake City, Utah 84112 (United States); IBM Microelectronics, Essex Jct., Vermont 05452 (United States)

1998-11-24

75

NASA Astrophysics Data System (ADS)

Using atomistic computer simulations based on analytical potential and density-functional theory models, we study effects of ion irradiation on graphene. We identify the types and concentrations of defects which appear in graphene under impacts of various ions with energies ranging from tens of electron volts to mega-electron volts. For two-dimensional targets, defects beyond single and double vacancies are formed via in-plane recoils. We demonstrate that the conventional approach based on binary-collision approximation and stochastic algorithms developed for bulk solids cannot be applied to graphene and other low-dimensional systems. Finally, taking into account the gas-holding capacity of graphene, we suggest the use of graphene as the ultimate membrane for ion-beam analysis of gases and other volatile systems which cannot be put in the high vacuum required for the operation of ion beams.

Lehtinen, O.; Kotakoski, J.; Krasheninnikov, A. V.; Tolvanen, A.; Nordlund, K.; Keinonen, J.

2010-04-01

76

NASA Astrophysics Data System (ADS)

Magneto-optical phenomena in quasi two-dimensional magnetophotonic crystals (Q-2D MPCs) have been investigated experimentally and numerically. Multiple Bragg diffraction was shown to be responsible for enhancement of the Faraday rotation and for alteration of its sign in spectra of experimental samples fabricated from bismuth-substituted yttrium iron garnet. It was shown that, for the magnetic superprism effect-control of the light propagation direction by the external magnetic, materials with much larger magneto-optical activity than that of experimental samples are necessary. Spectra obtained by numerical simulations were in a good agreement with experimental ones. Magnetic superprism effect was demonstrated for model samples and parameters necessary for alteration flow of light in quasi-2D MPCs were obtained.

Baek, Seungmin; Baryshev, Alexander V.; Inoue, Mitsuteru

2012-04-01

77

An efficient numerical algorithm for simulating a two-dimensional glow discharge

NASA Astrophysics Data System (ADS)

A numerical algorithm of the second approximation order with respect to the space variables for simulating a two-dimensional elevated pressure glow discharge in the framework of the drift-diffusion approximation is presented. A specific feature of this algorithm is the use of the Laplace resolving operator for the solution of the system of grid equations. This makes it possible to ensure the convergence of the solution in strong grid norms. Mathematical aspects of the statement of the differential-difference and finite difference problems (solvability, nonnegativity, approximation, stability, and convergence) are discussed, and bounds on the norms of the corresponding differential and difference operators that are required for constructing an optimal iterative process are obtained.

Islamov, R. Sh.

2006-11-01

78

Melting in two-dimensional Yukawa systems: A Brownian dynamics simulation

NASA Astrophysics Data System (ADS)

We studied the melting behavior of two-dimensional colloidal crystals with a Yukawa pair potential by Brownian dynamics simulations. The melting follows the Kosterlitz-Thouless-Halperin-Nelson-Young (KTHNY) scenario with two continuous phase transitions and a middle hexatic phase. The two phase-transition points were accurately identified from the divergence of the translational and orientational susceptibilities. Configurational temperatures were employed to monitor the equilibrium of the overdamped system and the strongest temperature fluctuation was observed in the hexatic phase. The inherent structure obtained by rapid quenching exhibits three different behaviors in the solid, hexatic, and liquid phases. The measured core energy of the free dislocations, Ec = 7.81 +/- 0.91 kBT, is larger than the critical value of 2.84 kBT, which consistently supports the KTHNY melting scenario.

Qi, Wei-Kai; Wang, Ziren; Han, Yilong; Chen, Yong

2010-12-01

79

NASA Astrophysics Data System (ADS)

Global observation of the GPS satellite constellation for ionospheric diagnostics is now a worldwide activity driven by both practical and scientific objectives. Diagnostic methods exploit an induced frequency-dependent phase change, which is proportional to the path-integrated electron density (TEC). However, intermediate-scale structure causes a stochastic modulation of the GPS signals (scintillation), which is a nuisance for data assimilation. Indeed, sufficiently strong propagation disturbances degrade TEC and ultimately disrupt GPS operations altogether. However, the physical processes that generate intermediate-scale structure are intimately part of ionospheric physics. In the best of all possible worlds irregularity identification and classification would be an integral part of ionospheric diagnostics. A two-dimensional propagation model has been used to explore the ramifications of intermediate scale structure on TEC data assimilation and, particularly tomographic reconstruction. Although two-dimensional models confine structure to a planar region, the results are relevant, with caveats, to propagation through highly anisotropic ionospheric structures. In-plane propagation from a source to an array of receivers is amenable to reconstruction with tomographic filtered back-projection algorithms. The angle-dependent Fourier decomposition of the array signal phase identifies a spectral slice. The signals from which the phase is derived are generated with an oblique forward propagation procedure developed by Costa and Basu Costa:02. Under weak-scatter conditions the signal phase is proportional to the ray path integral. The primary challenge for simulation is realistic simulation of the structure environment. Large scale ESF structure can be constructed with physics-based models, but populating the intermediate scale requires untested structure hypotheses. In particular, there is no clear demarcation between quasi-deterministic variation and definitive stochastic variation. Fractional Brownian motion admits trend-like structure variation at large scales that overlaps physics-based realizations. The two-dimensional constraint makes it feasible to explore a broad range of configurations, including meridional field-aligned structure. The results demonstrate the ramifications of diffractive distortion of path-integrated phase as well as unresolved stochastic structure. Anisotropic structure that subtends the distrubed region complicates the reconstruction procedures, particularly under strong scatter conditions. The utility of backpropagation to mitigate propagation disturbances will also be explored.

Rino, C. L.

2013-12-01

80

In this paper, two-dimensional (2D) simulation of interdigitated back contact silicon heterojunction (IBC-SHJ) solar cells is presented using Sentaurus Device, a software package of Synopsys TCAD. A model is established incorporating a distribution of trap states of amorphous-silicon material and thermionic emission across the amorphous-silicon / crystalline-silicon heterointerface. The 2D nature of IBC-SHJ device is evaluated and current density-voltage (J-V) curves are generated. Optimization of IBC-SHJ solar cells is then discussed through simulation. It is shown that the open circuit voltage (VOC) and short circuit current density (JSC) of IBC-SHJ solar cells increase with decreasing front surface recombination velocity. The JSC improves further with the increase of relative coverage of p-type emitter contacts, which is explained by the simulated and measured position dependent laser beam induced current (LBIC) line scan. The S-shaped J-V curves with low fill factor (FF) observed in experiments are also simulated, and three methods to improve FF by modifying the intrinsic a-Si buffer layer are suggested: (i) decreased thickness, (ii) increased conductivity, and (iii) reduced band gap. With all these optimizations, an efficiency of 26% for IBC-SHJ solar cells is potentially achievable.

Lu, Meijun; Das, Ujjwal; Bowden, Stuart; Hegedus, Steven; Birmire, Robert

2009-06-09

81

NASA Astrophysics Data System (ADS)

A new idea to calculate ultracold neutron (UCN) production by using Monte Carlo simulation method to calculate the cold neutron (CN) flux and an analytical approach to calculate the UCN production from the simulated CN flux was given. A super-thermal source (UCN source) was modeled based on an arrangement of D2O and solid D2 (sD2). The D2O was investigated as the neutron moderator, and sD2 as the converter. In order to determine the required parameters, a two-dimensional (2D) neutron balance equation written in Matlab was combined with the MCNPX simulation code. The 2D neutron-transport equation in cylindrical (? - z) geometry was considered for 330 neutron energy groups in the sD2. The 2D balance equation for UCN and CN was solved using simulated CN flux as boundary value. The UCN source dimensions were calculated for the development of the next UCN source. In the optimal condition, the UCN flux and the UCN production rate (averaged over the sD2 volume) equal to 6.79 × 106 cm-2s-1 and 2.20 ×105 cm-3s-1, respectively.

Gheisari, R.; Firoozabadi, M. M.; Mohammadi, H.

2014-01-01

82

Numerical simulation of two-dimensional spatially-developing mixing layers

NASA Technical Reports Server (NTRS)

Two-dimensional, incompressible, spatially developing mixing layer simulations are performed at Re = 10(exp 2) and 10(exp 4) with two classes of perturbations applied at the inlet boundary; combinations of discrete modes from linear stability theory, and a broad spectrum of modes derived from experimentally measured velocity spectra. The effect of the type and strength of inlet perturbations on vortex dynamics and time-averaged properties are explored. Two-point spatial velocity and autocorrelations are used to estimate the size and lifetime of the resulting coherent structures and to explore possible feedback effects. The computed time-averaged properties such as mean velocity profiles, turbulent statistics, and spread rates show good agreement with experimentally measured values. It is shown that by forcing with a broad spectrum of modes derived from an experimental energy spectrum many experimentally observed phenomena can be reproduced by a 2-D simulation. The strength of the forcing merely affected the length required for the dominant coherent structures to become fully-developed. Thus intensities comparable to those of the background turbulence in many wind tunnel experiments produced the same results, given sufficient simulation length.

Wilson, R. V.; Demuren, A. O.

1994-01-01

83

Two-dimensional viscous flow simulation of a shock accelerated heavy gas cylinder

NASA Astrophysics Data System (ADS)

Numerical simulation of Richtmyer-Meshkov instability (RMI) is conducted using an improved localized artificial diffusivity (LAD) method, which is used to treat discontinuities in the form of material interfaces and shocks in the flow-field. The RMI occurs on a cylindrical interface between air and SF6 accelerated by a Mach 1.2 shock initially in air. Navier-Stokes simulation is conducted to accurately predict the mixing between the two fluids. The initial conditions for the two-dimensional simulations are matched to previous experimental work by C. Tomkins et al. ["An experimental investigation of mixing mechanisms in shock-accelerated flow," J. Fluid Mech. 611, 131 (2008)] and good agreement is found between the experimental data and numerical results. The study on initial condition sensitivity indicates that the initial pressure and density gradient are critical parameters that determine the primary vortex generation responsible for the flow development. A grid convergence study is carried out and the relative contribution of the artificial properties introduced by the LAD method is characterized. Novel to this study is the exploration of the effect of the third species (acetone used as a tracer particle in the experiments to obtain contour fields using planar laser induced florescence). The effect of the presence of the third species on the evolution of the RMI and mixing is shown to be non-negligible and an estimate of the amount of the tracer species that was present in the initial experimental set-up is given.

Shankar, Santhosh K.; Kawai, Soshi; Lele, Sanjiva K.

2011-02-01

84

Tracking the Mechanism of Fibril Assembly by Simulated Two-Dimensional Ultraviolet Spectroscopy

Alzheimer’s disease (AD) is a neurodegenerative disorder characterized by the accumulation of plaque deposits in the human brain. The main component of these plaques consists of highly ordered structures called amyloid fibrils, formed by the amyloid ?-peptide (A?). The mechanism connecting A? and AD is yet undetermined. In a previous study, a coarse-grained united-residue model and molecular dynamics simulations were used to model the growth mechanism of A ? amyloid fibrils. Based on these simulations, a dock/lock mechanism was proposed, in which A? fibrils grow by adding monomers at either end of an amyloid fibril template. To examine the structures in the early time-scale formation and growth of amyloid fibrils, simulated two-dimensional ultraviolet spectroscopy is used. These early structures are monitored in the far ultraviolet regime (? = 190–250 nm) in which the computed signals originate from the backbone n?* and ??* transitions. These signals show distinct cross-peak patterns that can be used, in combination with molecular dynamics, to monitor local dynamics and conformational changes in the secondary structure of A?-peptides. The protein geometry-correlated chiral xxxy signal and the non-chiral combined signal xyxy- xyyx were found to be sensitive to, and in agreement with, a dock/lock pathway. PMID:23214934

Lam, A. R.; Rodriguez, J. J.; Rojas, A.; Scheraga, H.A; Mukamel, S.

2013-01-01

85

MACH2: A two-dimensional magnetohydrodynamic simulation code for complex experimental configurations

NASA Astrophysics Data System (ADS)

MACH2 is a flexible and powerful two-dimensional magnetohydrodynamic simulation code designed specifically to handle complex experimental configurations. The code's capabilities include a numerically generated solution-adaptive grid which permits it to be used for either Eulerian or Lagrangian flow problems, use of real equations of state and transport properties from the Los Alamos National Laboratory SESAME package, and a multigrid implicit magnetic field diffusion solver which can be used to simulate problems with vacuum. The descriptive power of the namelist-based problem input language is sufficient that no code modifications are required to set up any of a broad class of problems. Almost no knowledge of the internal data structures and numerical techniques is required to do simulations that realistically model complex experiments. This is made possible by the code's multiblock architecture and table-driven control structure. Code reliability and flexibility are ensured and enhanced by a structured and modular implementation of boundary conditions and block coupling. This report details the physical model, including boundary conditions; permissible problem geometries; time differencing; and spatial discretization, centering, and differencing of MACH2.

Frese, Michael H.

1987-09-01

86

Two-dimensional simulations of the neutron yield in cryogenic deuterium-tritium implosions on OMEGA

Maximizing the neutron yield to obtain energy gain is the ultimate goal for inertial confinement fusion. Nonuniformities seeded by target and laser perturbations can disrupt neutron production via the Rayleigh-Taylor instability growth. To understand the effects of perturbations on the neutron yield of cryogenic DT implosions on the Omega Laser Facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)], two-dimensional DRACO[P. B. Radha et al., Phys. Plasmas 12, 056307 (2005)] simulations have been performed to systematically investigate each perturbation source and their combined effects on the neutron-yield performance. Two sources of nonuniformity accounted for the neutron-yield reduction in DRACO simulations: target offset from the target chamber center and laser imprinting. The integrated simulations for individual shots reproduce the experimental yield-over-clean (YOC) ratio within a factor of 2 or better. The simulated neutron-averaged ion temperatures

Hu, S. X.; Goncharov, V. N.; Radha, P. B.; Marozas, J. A.; Skupsky, S.; Boehly, T. R.; Sangster, T. C.; Meyerhofer, D. D.; McCrory, R. L. [Laboratory for Laser Energetics, University of Rochester, 250 E. River Road, Rochester, New York 14623 (United States)

2010-10-15

87

Two-dimensional numerical simulation of trapped ion mode turbulence in a tokamak

A two-dimensional [ital k]-space simulation of long-wavelength trapped ion mode turbulence is used to investigate Bohm (macroscopic) versus gyro-Bohm (microscopic) scaling behavior in tokamaks. A nonlinear two-field model of dissipative trapped ion turbulence evolving trapped ion and trapped electron density fluctuations shows gyro-Bohm-like scaling in contrast to earlier simulation work by Saison [ital et] [ital al]. [Plasma Phys. [bold 20], 1 (1978)]. In fact, nearly all features of trapped ion mode turbulence and transport originally posited by Kadomtsev and Pogutse [[ital Reviews] [ital of] [ital Plasma] [ital Physics] (Consultants Bureau, New York, 1970), Vol. 5, p. 379] are recovered. However, the widely used Kadomtsev--Pogutse one-field approximation to the two-field dissipative trapped ion model is unexpectedly found to be unrepresentative with much different fluctuation levels and diffusion. Transformation to a new field basis diagonalizing the linear part of the two-field equations clarifies the importance of the damped branch not contained in the one-field equation. The two-field collisionless trapped ion mode equations are transformed into a parameterless single equation for a complex field providing a perfect scaling relation for the dependence on the driving curvature drifts.

Kingsbury, O.T.; Waltz, R.E. (General Atomics, San Diego, California 92186-9784 (United States))

1993-03-01

88

High-volume fraction simulations of two-dimensional vesicle suspensions

NASA Astrophysics Data System (ADS)

We consider numerical algorithms for the simulation of the rheology of two-dimensional vesicles suspended in a viscous Stokesian fluid. The vesicle evolution dynamics is governed by hydrodynamic and elastic forces. The elastic forces are due to local inextensibility of the vesicle membrane and resistance to bending. Numerically resolving vesicle flows poses several challenges. For example, we need to resolve moving interfaces, address stiffness due to bending, enforce the inextensibility constraint, and efficiently compute the (non-negligible) long-range hydrodynamic interactions. Our method is based on the work of Rahimian et al. (2010) [33]. It is a boundary integral formulation of the Stokes equations coupled to the interface mass continuity and force balance. We extend the algorithms presented in that paper to increase the robustness of the method and enable simulations with concentrated suspensions. In particular, we propose a scheme in which both intra-vesicle and inter-vesicle interactions are treated semi-implicitly. In addition we use special integration for near-singular integrals and we introduce a spectrally accurate collision detection scheme. We test the proposed methodologies on both unconfined and confined flows for vesicles whose internal fluid may have a viscosity contrast with the bulk medium. Our experiments demonstrate the importance of treating both intra-vesicle and inter-vesicle interactions accurately.

Quaife, Bryan; Biros, George

2014-10-01

89

Two-dimensional nonsteady viscous flow simulation on the Navier-Stokes computer miniNode

NASA Technical Reports Server (NTRS)

The needs of large-scale scientific computation are outpacing the growth in performance of mainframe supercomputers. In particular, problems in fluid mechanics involving complex flow simulations require far more speed and capacity than that provided by current and proposed Class VI supercomputers. To address this concern, the Navier-Stokes Computer (NSC) was developed. The NSC is a parallel-processing machine, comprised of individual Nodes, each comparable in performance to current supercomputers. The global architecture is that of a hypercube, and a 128-Node NSC has been designed. New architectural features, such as a reconfigurable many-function ALU pipeline and a multifunction memory-ALU switch, have provided the capability to efficiently implement a wide range of algorithms. Efficient algorithms typically involve numerically intensive tasks, which often include conditional operations. These operations may be efficiently implemented on the NSC without, in general, sacrificing vector-processing speed. To illustrate the architecture, programming, and several of the capabilities of the NSC, the simulation of two-dimensional, nonsteady viscous flows on a prototype Node, called the miniNode, is presented.

Nosenchuck, Daniel M.; Littman, Michael G.; Flannery, William

1986-01-01

90

Two-dimensional nonsteady viscous flow simulation on the Navier-Stokes computer miniNode

The needs of large-scale scientific computation are outpacing the growth in performance of mainframe supercomputers. In particular, problems in fluid mechanics involving complex flow simulations require far more speed and capacity than that provided by current and proposed Class VI supercomputers. To address this concern, the Navier-Stokes Computer (NSC) was developed. The NSC is a parallel-processing machine, comprised of individual Nodes, each comparable in performance to current supercomputers. The global architecture is that of a hypercube, and a 128-Node NSC has been designed. New architectural features, such as a reconfigurable many-function ALU pipeline and a multifunction memory-ALU switch, have provided the capability to efficiently implement a wide range of algorithms. Efficient algorithms typically involve numerically intensive tasks, which often include conditional operations. These operations may be efficiently implemented on the NSC without, in general, sacrificing vector-processing speed. To illustrate the architecture, programming, and several of the capabilities of the NSC, the simulation of two-dimensional, nonsteady viscous flows on a prototype Node, called the miniNode, is presented. 8 references.

Nosenchuck, D.M.; Littman, M.G.; Flannery, W.

1986-01-01

91

We have constructed a lattice Wigner-Weyl code to expand the Buot-Jensen algorithm to calculation of electron transport in two-dimensional cylindrically symmetric structures. Almost all of the numerical simulations to date have dealt with the restricted problem of one-dimensional transport. In real devices, electrons are not confined to a single transport dimension and the coulombic potential is fully present and felt in three dimensions. We show the derivation of the 2D equation in cylindrical coordinates as well as approximations employed in the calculation of the four-dimensional convolution integral of the Wigner function and the potential. We work under the assumption that longitudinal transport is more dominant than radial transport and employ parallel processing techniques. The total transport is calculated in two steps: (1) transport the particles in the longitudinal direction in each shell separately, then (2) each shell exchanges particles with its nearest neighbor. Most of this work is concerned with the former step: A 1D space and 2D momentum transport problem. Time evolution simulations based on these method are presented for three different cases. Each case lead to numerical results consistent with expectations. Discussions of future improvements are discussed.

Recine, Greg [Applied Electronics Laboratory, Department of Physics and Engineering Physics, Stevens Institute of Technology, Hoboken, NJ 07030 (United States)]. E-mail: gjr5y@virginia.edu; Rosen, Bernard [Applied Electronics Laboratory, Department of Physics and Engineering Physics, Stevens Institute of Technology, Hoboken, NJ 07030 (United States); Cui, H.-L. [Applied Electronics Laboratory, Department of Physics and Engineering Physics, Stevens Institute of Technology, Hoboken, NJ 07030 (United States)

2005-11-01

92

Rapid two-dimensional self-consistent simulation of inductively coupled plasma and comparison-dimensional self-consistent simulation of plasma transport and reaction in an inductively coupled source for meeting the demands of gigascale integrated circuits.1 Inductively coupled plasma ICP sources are par

Economou, Demetre J.

93

General Relativistic MHD Simulations of Jet Formation

NASA Technical Reports Server (NTRS)

We have performed 3-dimensional general relativistic magnetohydrodynamic (GRMHD) simulations of jet formation from an accretion disk with/without initial perturbation around a rotating black hole. We input a sinusoidal perturbation (m = 5 mode) in the rotation velocity of the accretion disk. The simulation results show the formation of a relativistic jet from the accretion disk. Although the initial perturbation becomes weakened by the coupling among different modes, it survives and triggers lower modes. As a result, complex non-axisymmetric density structure develops in the disk and the jet. Newtonian MHD simulations of jet formation with a non-axisymmetric mode show the growth of the m = 2 mode but GRMHD simulations cannot see the clear growth of the m = 2 mode.

Mizuno, Y.; Nishikawa, K.-I.; Hardee, P.; Koide, S.; Fishman, G. J.

2005-01-01

94

Movement, deformation, and partitioning of mammalian red blood cells (RBCs) in diverging microvessel bifurcations are simulated using a two-dimensional, flexible-particle model. A set of viscoelastic elements represents the RBC membrane and the cytoplasm. Motion of isolated cells is considered, neglecting cell-to-cell interactions. Center-of-mass trajectories deviate from background flow streamlines due to migration of flexible cells towards the mother vessel centerline upstream of the bifurcation and due to flow perturbations caused by cell obstruction in the neighborhood of the bifurcation. RBC partitioning in the bifurcation is predicted by determining the RBC fraction entering each branch, for a given partition of total flow and for a given upstream distribution of RBCs. Typically, RBCs preferentially enter the higher-flow branch, leading to unequal discharge hematocrits in the downstream branches. This effect is increased by migration toward the centerline but decreased by the effects of obstruction. It is stronger for flexible cells than for rigid circular particles of corresponding size, and decreases with increasing parent vessel diameter. For unequally-sized daughter vessels, partitioning is asymmetric, with RBCs tending to enter the smaller vessel. Partitioning is not significantly affected by branching angles. Model predictions are consistent with previous experimental results. PMID:18686035

Barber, Jared O.; Alberding, Jonathan P.; Restrepo, Juan M.; Secomb, Timothy W.

2008-01-01

95

Two-Dimensional Blast-Wave-Driven Rayleigh-Taylor Instability: Experiment and Simulation

NASA Astrophysics Data System (ADS)

This paper shows results from experiments diagnosing the development of the Rayleigh-Taylor instability with two-dimensional initial conditions at an embedded, decelerating interface. Experiments are performed at the Omega Laser and use ~5 kJ of energy to create a planar blast wave in a dense, plastic layer that is followed by a lower density foam layer. The single-mode interface has a wavelength of 50 ?m and amplitude of 2.5 ?m. Some targets are supplemented with additional modes. The interface is shocked then decelerated by the foam layer. This initially produces the Richtmyer-Meshkov instability followed and then dominated by Rayleigh-Taylor growth that quickly evolves into the nonlinear regime. The experimental conditions are scaled to be hydrodynamically similar to SN1987A in order to study the instabilities that are believed to occur at the He/H interface during the blast-wave-driven explosion phase of the star. Simulations of the experiment were performed using the FLASH hydrodynamics code.

Kuranz, C. C.; Drake, R. P.; Harding, E. C.; Grosskopf, M. J.; Robey, H. F.; Remington, B. A.; Edwards, M. J.; Miles, A. R.; Perry, T. S.; Blue, B. E.; Plewa, T.; Hearn, N. C.; Knauer, J. P.; Arnett, D.; Leibrandt, D. R.

2009-05-01

96

Platelet Motion near a Vessel Wall or Thrombus Surface in Two-Dimensional Whole Blood Simulations

Computational simulations using a two-dimensional lattice-Boltzmann immersed boundary method were conducted to investigate the motion of platelets near a vessel wall and close to an intravascular thrombus. Physiological volume fractions of deformable red blood cells and rigid platelet-size elliptic particles were studied under arteriolar flow conditions. Tumbling of platelets in the red-blood-cell depleted zone near the vessel walls was strongly influenced by nearby red blood cells. The thickness of the red-blood-cell depleted zone was greatly reduced near a thrombus, and platelets in this zone were pushed close to the surface of the thrombus to distances that would facilitate their cohesion to it. The distance, nature, and duration of close platelet-thrombus encounters were influenced by the porosity of the thrombus. The strong influence on platelet-thrombus encounters of red-blood-cell motion and thrombus porosity must be taken into account to understand the dynamics of platelet attachment to a growing thrombus. PMID:23601323

Skorczewski, Tyler; Erickson, Lindsay Crowl; Fogelson, Aaron L.

2013-01-01

97

Two-dimensional model simulations of the QBO in ozone and tracers in the tropical stratosphere

, Maryland, USA David B. Considine NASA Langley Research Center, Hampton, Virginia, USA Received 24 July 2001 Citation: Fleming, E. L., C. H. Jackman, J. E. Rosenfield, and D. B. Considine, Two-dimensional model

Jackman, Charles H.

98

MHD simulations of penumbra fine structure

We present results of numerical 3D MHD simulations with radiative energy transfer of fine structure in a small sunspot of about 4 Mm width. The simulations show the development of filamentary structures and flow patterns that are, except for the lengths of the filaments, very similar to those observed. The filamentary structures consist of gaps with reduced field strength relative to their surroundings. Calculated synthetic images show dark cores like those seen in the observations; the dark cores are the result of a locally elevated $\\tau=1$ surface. The magnetic field in these cores is weaker and more horizontal than for adjacent brighter structures, and the core support a systematic outflow. Movies show migration of the dark-cored structures towards the umbra, and fragments of magnetic flux that are carried away from the spot by a large scale `moat flow'. We conclude that the simulations are in qualitative agreement with observed penumbra filamentary structures, Evershed flows and moving magnetic features.

T. Heinemann; A. Nordlund; G. B. Scharmer; H. C. Spruit

2006-12-21

99

Two-dimensional FSI simulation of closing dynamics of a tilting disc mechanical heart valve

The fluid dynamics during valve closure resulting in high shear flows and large residence times of particles has been implicated in platelet activation and thrombus formation in mechanical heart valves. Our previous studies with bi-leaflet valves have shown that large shear stresses induced in the gap between the leaflet edge and the valve housing results in relatively high platelet activation levels whereas flow between the leaflets results in shed vortices not conducive to platelet damage. In this study we compare the result of closing dynamics of a tilting disc valve with that of a bi-leaflet valve. The two-dimensional fluid-structure interaction analysis of a tilting disc valve closure mechanics is performed with a fixed grid Cartesian mesh flow solver with local mesh refinement, and a Lagrangian particle dynamic analysis for computation of potential for platelet activation. Throughout the simulation the flow remains in the laminar regime and the flow through the gap width is marked by the development of a shear layer which separates from the leaflet downstream of the valve. Zones of re-circulation are observed in the gap between the leaflet edge and the valve housing on the major orifice region of the tilting disc valve and are seen to be migrating towards the minor orifice region. Jet flow is observed at the minor orifice region and a vortex is formed which sheds in the direction of fluid motion as observed in experiments using PIV measurements. The activation parameter computed for the tilting disc valve, at the time of closure was found to be 2.7 times greater than that of the bi-leaflet mechanical valve and was found to be in the vicinity of the minor orifice region mainly due to the migration of vortical structures from the major to the minor orifice region during the leaflet rebound of the closing phase. PMID:20209095

Govindarajan, V.; Udaykumar, H.S.; Herbertson, L. H.; Deutsch, S.; Manning, K. B.; Chandran, K.B.

2010-01-01

100

Numerical simulation of two-dimensional single- and multiple-material flow fields

NASA Astrophysics Data System (ADS)

Over the last several years, Sandia National Laboratories has had an interest in developing capabilities to predict the flow fields around vehicles entering or exiting the water at a wide range of speeds. Such prediction schemes have numerous engineering applications in the design of weapon systems. For example, such a scheme could be used to predict the forces and moments experienced by an air launched antisubmarine weapon on water entry. Furthermore, a water exit prediction capability could be used to model the complicated surface closure jet resulting from a missile being shot out of the water. The CCICE (Cell-Centered Implicit Continuous-fluid Eulerian) code developed at Los Alamos National Laboratory (LANL) was chosen to provide the fluid dynamics solver for high speed water entry and water exit problems. This implicit time marching, two dimensional, conservative, finite volume code solves the multi-material, compressible, inviscid fluid dynamics equations. The incompressible version of the CCICE code, CCMAC (Cell-Centered Marker and Cell), was chosen for low speed water entry and water exit problems in order to reduce the computational expense. These codes were chosen to take advantage of certain advances in numerical methods for computational fluid dynamics (CFD) that have taken place at LANL. Notable among these advances is the ability to perform implicit, multi-material, compressible flow simulations, with a fully cell-centered data structure. This means that a single set of control volumes are used, on which a discrete form of the conservation laws is satisfied. This is in control to the more classical staggered mesh methods, in which separate control volumes are defined for mass and momentum.

Lopez, A. R.; Baty, R. S.; Kashiwa, B. A.

101

Two-dimensional simulation of Pinatubo aerosol and its effect on stratospheric ozone

This paper presents time-dependent simulations of the response of the stratosphere to the injection into the atmosphere of massive amounts of sulfur during the eruption of Mt. Pinatubo (The Philippines) in June 1991. The study is based on a coupled two-dimensional chemical-dynamical-radiative model to which a microphysical model for sulfate aerosol formation and fate has been added. The study suggests that, during the first year (July 1991 to June 1992) following the volcanic eruption, the observed changes in the ozone amount integrated between 65 deg S and 65 deg N were caused primarily by changes in the meridional circulation (associated with heating by the volcanic cloud in the tropics) and in the photolysis rate of molecules such as ozone (associated with backscattering of light by the cloud). During the second year after the eruption, as the aerosol was dispersed at all latitudes and, in particular, reached the polar region, the largest contribution to ozone reduction resulted from the heterogeneous chemical conversion of N2O5 and ClONO2 on the surface of the aerosol particles. The conversion of the latter compound, and hence the magnitude of the calculated ozone depletion, is highly dependent on the temperature in the lower stratosphere. Despite the fact that the surface area provided by aerosol particles decreased during the second year following the eruption, the calculated ozone depletion remained significant because the conversion of N2O5 is insensitive to the aerosol surface area density for values larger than 1-10 sq microns/cu cm (depending on latitude). The predicted reduction in ozone at 20 km in March during the third year (July 1993 to June 1994) of the model integration is smaller by a factor of 2 than it was during the second year.

Tie, X.; Brasseur, G.P.; Briegleb, B.; Granier, C. [National Center for Atmospheric Research, Boulder, CO (United States)

1994-10-01

102

Two-dimensional network simulation of diffusion-driven coarsening of foam inside a porous medium

In order to use foams in subsurface applications, it is necessary to understand their stability in porous media. Diffusion-driven coarsening of a stationary or nonflowing foam in a porous medium results in changing gas pressures and a coarsening of the foam texture. A two-dimensional network simulation has been created that predicts the behavior of foam in a porous medium by physically specifying the locations of all the lamellae in the system and by solving the complete set of Young-Laplace and diffusion equations. An hourglass approximates the shape of the pores, and the pore walls are considered to be highly water wet. A singularity arises in the system of differential algebraic equations due to the curvature of the pore walls. This singularity is a signal that the system must undergo oscillations or sudden lamellar rearrangements before the diffusion process can continue. Newton-Raphson iteration is used along with Keller`s method of arc-length continuation and a new jump resolution technique to locate and resolve bifurcations in the system of coupled lamellae. Gas bubbles in pore throats are regions of encapsulated pressure. As gas is released from these bubbles during diffusion, the pressure of the bubbles in the pore bodies increases. When the pressure increase is scaled by the characteristic Young-Laplace pressure, the equilibrium time for the diffusion process is scaled by the ratio of the square of the characteristic length to the gas diffusivity and two dimensionless groups. One describes the ease with which gas can diffuse through a lamella, and the second represents the amount of gas encapsulated within the pore throats initially. Given this scaling, the resulting plots of pressure versus time and normalized lamellae positions versus time are universal for all system sizes and characteristics. This is true as long as the initial lamella distribution is the same in each case.

Cohen, D.; Radke, C.J. [Lawrence Berkeley National Lab., CA (United States)] [Lawrence Berkeley National Lab., CA (United States); Patzek, T.W. [Univ. of California, Berkeley, CA (United States)] [Univ. of California, Berkeley, CA (United States)

1996-05-10

103

Two-dimensional network simulation of diffusion driven coarsening of foam inside a porous medium

In order to use foams in subsurface applications, it is necessary to understand their stability in porous media. Diffusion driven coarsening of a stationary or nonflowing foam in a porous medium results in changing gas pressures and a coarsening of the foam texture. A two-dimensional network simulation has been created that predicts the behavior of foam in a porous medium by physically specifying the locations of all the lamellae in the system and by solving the complete set of Young-Laplace and diffusion equations. An hourglass approximates the shape of the pores, and the pore walls are considered to be highly water wet. A singularity arises in the system of differential algebraic equations due to the curvature of the pore walls. This singularity is a signal that the system must undergo oscillations or sudden lamellar rearrangements before the diffusion process can continue. Newton-Raphson iteration is used along with Keller`s method of arc-length continuation and a new jump resolution technique to locate and resolve bifurcations in the system of coupled lamellae. Gas bubbles in pore throats are regions of encapsulated pressure. As gas is released from these bubbles during diffusion, the pressure of the bubbles in the pore bodies increases. When the pressure increase is scaled by the characteristic Young-Laplace pressure, the equilibrium time for the diffusion process is scaled by the ratio of the square of the characteristic length to the gas diffusivity and two dimensionless groups. One describes the ease with which gas can diffuse through a lamella, the second represents the amount of gas encapsulated within the pore throats initially. Given this scaling, the resulting plots of pressure versus time and normalized lamellae positions versus time are universal for all system sizes and characteristics. This is true as long as the initial lamella distribution is the same in each case.

Cohen, D.; Patzek, T.W.; Radke, C.J.

1996-04-01

104

Two-dimensional dynamic simulation of platelet activation during mechanical heart valve closure.

A major drawback in the operation of mechanical heart valve prostheses is thrombus formation in the near valve region. Detailed flow analysis in this region during the valve closure phase is of interest in understanding the relationship between shear stress and platelet activation. A fixed-grid Cartesian mesh flow solver is used to simulate the blood flow through a bi-leaflet mechanical valve employing a two-dimensional geometry of the leaflet with a pivot point representing the hinge region. A local mesh refinement algorithm allows efficient and fast flow computations with mesh adaptation based on the gradients of the flow field in the leaflet-housing gap at the instant of valve closure. Leaflet motion is calculated dynamically based on the fluid forces acting on it employing a fluid-structure interaction algorithm. Platelets are modeled and tracked as point particles by a Lagrangian particle tracking method which incorporates the hemodynamic forces on the particles. A platelet activation model is included to predict regions which are prone to platelet activation. Closure time of the leaflet is validated against experimental studies. Results show that the orientation of the jet flow through the gap between the housing and the leaflet causes the boundary layer from the valve housing to be drawn in by the shear layer separating from the leaflet. The interaction between the separating shear layers is seen to cause a region of intensely rotating flow with high shear stress and high residence time of particles leading to high likelihood of platelet activation in that region. PMID:17013660

Krishnan, S; Udaykumar, H S; Marshall, J S; Chandran, K B

2006-10-01

105

Numerical Simulation of Two-Dimensional Flow over Three Cylinders by Lattice Boltzmann Method

NASA Astrophysics Data System (ADS)

The numerical simulation using the multiple relaxation time lattice Boltzmann method (MRT-LBM) is carried out for the purpose of investigating the two-dimensional flow around three circular cylinders. Among these three circular cylinders, one of the three cylinders on which a forced in-line vibrating is used to do this research and attempt to find out the effects of the moving cylinder and the other two rigid cylinders on the wake characteristics and vortex formation. As a benchmark problem to discuss the problem of lift coefficient r.m.s for these cylinders with spacing ratios T/D between other rigid side-by-side cylinders, and the calculation is carried out with two compared cases at Reynolds number of 100, two of the cylinders are rigid and the other one is an in-line vibrated cylinder lying downstream, in addition, forced vibrating amplitude and frequency are A/D = 0.5 and fv = 0.4 (where A is the forced amplitude, D is the cylinder diameter, and fv stands for the vibrating frequency, respectively). The calculated results not only indicate that the spacing ratios T/D (T is the center-to-center spacing between the two upstream cylinders) have influence on the wake patterns and the formation of vortex shedding, but also analyze the lift coefficient r.m.s for the three cylinders with the spacing ratios S/D (where S is the center-to-center spacing between the center of upstream two side-by-side cylinders and downstream cylinder).

Yang, Hong-Bing; Liu, Yang; Xu, You-Sheng; Kou, Jian-Long

2010-11-01

106

MHD Simulation of Plasma Flow through the VASIMR Magnetic Nozzle

NASA Astrophysics Data System (ADS)

The VASIMR (Variable Specific Impulse Magnetoplasma Rocket, [1]) concept is currently in the experimental development phase at the Advanced Space Propulsion Laboratory, NASA Johnson Space Center. The current experimental effort is mainly focused on the demonstration of the efficient plasma production (light ion helicon source, [2]) and energy boosting (ion cyclotron resonance heating section). Two other critical issues, the plasma detachment process and the collimation of the plasma plume in the magnetic nozzle, are essential for the near term experimental development and are being addressed through an MHD simulation modeling effort with the NIMROD code [3,4]. The model follows the plasma flow up to few meters from the nozzle throat: at that distance the plasma exhaust parameters reach values comparable with the ionospheric plasma background [5]. Results from two-dimensional simulation runs (cylindrical geometry, assuming azimuthal symmetry) aimed in particular at testing the effectiveness of different open-end boundary condition schemes are presented. [1] F. R. Chang-Diaz, Scientific American, p. 90, Nov. 2000 [2] M. D. Carter, et al., Phys. Plasmas 9, 5097-5110, 2002 [3] http://www.nimrodteam.org [4] A. Tarditi et al., 28th Int. Electric Propulsion Conf., IEPC 2003, Toulouse, France, March 2003 [5] A. V. Ilin et al., Proc. 40th AIAA Aerospace Sciences Meeting, Reno, NV, Jan. 2002

Tarditi, A. G.; Shebalin, J. V.

2003-10-01

107

A multiple type-II burst associated with a coronal transient and its MHD simulation

NASA Astrophysics Data System (ADS)

A large coronal transient took place on May 8, 1981. The transient was related to an M7.7/2B flare and was associated with at least two coronal type-II bursts. The velocities of the type-II bursts were in the range 1100-1800 km/s, in excess of the transient velocity of 1000 km/s. Two dimensional positions of the type-II radio sources are available from both the Clark Lake and the Culgoora Radio Observatories. Two dimensional MHD simulations of the event are carried out, taking into account the observed velocity, position, and size of the type-II bursts. The multiple shocks observed during the event and their interaction are simulated, and results of the simulation are discussed.

Gergely, T. E.; Kundu, M. R.; Wu, S. T.; Dryer, M.; Smith, Z.; Stewart, R. T.

108

NASA Astrophysics Data System (ADS)

SummaryRiver-training structures, such as spur dikes, are effective engineered methods used to protect banks and improve aquatic habitat. This paper reports the development and application of a two-dimensional depth-averaged hydrodynamic model to simulate suspended sediment concentration distribution in a groyne field. The governing equations of flow hydrodynamic model are depth-averaged two-dimensional Reynold's averaged momentum equations and continuity equation in which the density of sediment laden-flow varies with the concentration of suspended sediment. The depth-averaged two-dimensional convection and diffusion equation was solved to obtain the depth-averaged suspended sediment concentration. The source term is the difference between suspended sediment entrainment and deposition from bed surface. One laboratory experiment was chosen to verify the simulated flow field around a groyne, and the other to verify the suspended sediment concentration distribution in a meandering channel. Then, the model utility was demonstrated in a field case study focusing on the confluence of the Kankakee and Iroquois Rivers in Illinois, United States, to simulate the distribution of suspended sediment concentration around spur dikes. Results demonstrated that the depth-averaged, two-dimensional model can approximately simulate the flow hydrodynamic field and concentration of suspended sediment. Spur dikes can be used to effectively relocate suspended sediment in alluvial channels.

Duan, Jennifer G.; Nanda, S. K.

2006-08-01

109

We applied a genetic algorithm and a simulated annealing approach to the two-dimensional non-guillotine cutting stock problem and carried out experimentation on several test cases. The performance and efficiency of these two heuristic algorithms on this problem were compared.

T. W Leung; C. H Yung; Marvin D Troutt

2001-01-01

110

Geological and geochemical data from six wells, and several seismic profiles from strata in a Cenozoic accretion belt, which occurs between the Aleutian volcanic arc and the Aleutian trench in the Kodiak Shelf, Alaska, have been used in quantitative basin analysis studies. Applying both one-dimensional and two-dimensional fluid flow/compaction models to the basin has enabled a simulation to be made of the history of sedimentation, together with evolutionary behaviors for porosity, permeability, basement subsidence, fluid movement in the strata, formation pressure, paleoheat flux, maturation of organic carbon, and hydrocarbon generation and migration in specific locations and in a two-dimensional cross section of the basin.

Jianchang, Liu; Lerche, I. (Univ. of South Carolina, Columbia (United States))

1991-03-01

111

The two-dimensional, transient numerical model of heat and water vapor convection and diffusion during air exfiltration within fiberglass insulation, presented in Part 1 is validated in Part 2, with experimental data for temperature, moisture and frost accumulation, and heat flux. With a few exceptions, the simulation results and experimental data agree within the experimental uncertainty. Exfiltration airflow in the two-dimensional space showed strong entrance and exit effects for temperature, moisture and frost accumulation, and heat flux on the cold side. Between the entrance and exit, the temperature, mass accumulation, and heat flux showed characteristics similar to a boundary layer.

Chen, H.; Besant, R.W. [Univ. of Saskatchewan, Saskatoon, Saskatchewan (Canada). Dept. of Mechanical Engineering; Tao, Y.T. [Tennessee State Univ., Nashville, TN (United States). Mechanical Engineering Dept.

1998-10-01

112

Dynamics of the Solar Magnetic Network: Two-dimensional MHD Simulations

The aim of this work is to identify the physical processes that occur in the network and contribute to its dynamics and heating. We model the network as consisting of individual flux tubes with a non-potential field structure that are located in intergranular lanes. With a typical horizontal size of 200 km at the base of the photosphere, they expand upward and merge with their neighbors at a height of about 600 km. Above a height of approximately 1000 km the magnetic field starts to become uniform. Waves are generated in this medium by means of motions at the lower boundary. We focus on transverse driving, which generates both fast and slow waves within a flux tube and acoustic waves at the interface of the tube and the field-free medium. The acoustic waves at the interface are due to compression of the gas on one side of the flux tube and expansion on the other. These waves travel upward along the two sides of the (2D) flux tube and enter it, where they become longitudinal waves. For impulsive excitation with a time constant of 120 s, we find that a dominant feature is the creation of vortical motions that propagate upward. We have identified an efficient mechanism for the generation of longitudinal waves and shock formation in the chromospheric part of the flux concentration. We examine some broad implications of our results.

S. S. Hasan; A. A. van Ballegoiijen; W. Kalkofen; O. Steiner

2005-03-24

113

Monte Carlo simulation of a two dimensional anisotropic plane rotator model

We have studied a classical system, consisting of two-component unit vectors (plane rotators) associated with a two dimensional square lattice, and interacting via the nearest neighbour pair potential(s)where m is a positive integer and {?k} are the angles defining the orientation of the plane rotators in an arbitary reference frame. The two potential models Wm and – Wm possess essentially

S. Romano

1989-01-01

114

Numerical Simulation of Two-Dimensional Bubbles Initially Flattened Along a Flat Plate

Several researchers have reported the detachment of vapor bubbles from a vertical heated wall in upward flow boiling of water. In these experiments, the bubble shape was frequently flattened along the wall at inception but became more rounded before the onset of detachment. In this study, the motion of two-dimensional bubbles is investigated numerically to elucidate the mechanism of bubble

Tomio Okawa; Isao Kataoka; Michitsugu Mori

2006-01-01

115

We have developed a coupled two-dimensional dynamical\\/chemical\\/microphysical model to study the global distribution of stratospheric sulfate aerosols. In particular, we use this model to simulate the global distribution of volcanic aerosols after the eruption of El Chichón in Mexico in April 1982. The simulated background aerosol distributions are highly dispersed, while a slight latitudinal gradient is also noticed. The calculated

XueXi Tie; Xing Lin; Guy Brasseur

1994-01-01

116

It can be demonstrated analytically that under certain geometries used in numerical simulations of collisionless shocks in which there is at least one ignorable spatial coordinate, the transport of particles across the magnetic field is essentially zero. This notion is tested using one- and two-dimensional hybrid simulations (kinetic ions/fluid electrons). We find, as the theorem predicts, the particles treated kinetically are tied to the same field line on which they start.

Giacalone, J. [Univ. of Arizona, Tucson, AZ (United States)] [Univ. of Arizona, Tucson, AZ (United States)

1994-11-01

117

MHD Simulation Heliospheric Magnetic Fields and Turbulence

NASA Technical Reports Server (NTRS)

This talk will present a summary of our results on simulations of heliospheric structure and dynamics. We use a three-dimensional MHD code in spherical coordinates to produce a solar wind containing a rotating, tilted heliospheric current sheet, fast-slow stream and microstream shear layers, waves, 2-D turbulence, and pressure balanced structures that are input to the inner (superAlfvenic) boundary. The evolution of various combinations of these has led to a deeper understanding of sector structure, magnetic holes, fluctuation anisotropies, and general turbulent evolution. We show how the sectors are likely to be connected, how spiral fields can arise, and how field line diffusion can be caused by waves with transverse structure and microstream shears.

Roberts, D. Aaron

2005-01-01

118

Two-Dimensional Simulation of Left-Handed Metamaterial Flat Lens Using Remcon XFDTD

NASA Technical Reports Server (NTRS)

Remcom's XFDTD software was used to model the properties of a two-dimensional left-handed metamaterial (LHM) flat lens. The focusing capability and attenuation of the material were examined. The results showed strong agreement with experimental results and theoretical predictions of focusing effects and focal length. The inherent attenuation in the model corresponds well with the experimental results and implies that the code does a reasonably accurate job of modeling the actual metamaterial.

Wilson, Jeffrey D.; Reinert, Jason M.

2006-01-01

119

Two-dimensional dynamic simulation of a direct internal reforming solid oxide fuel cell

This study presents a two-dimensional mathematical model of a direct internal reforming solid oxide fuel cell (DIR-SOFC) stack which is based on the reforming reaction kinetics, electrochemical model and principles of mass and heat transfer. To stimulate the model and investigate the steady and dynamic performances of the DIR-SOFC stack, we employ a computational approach and several cases are used

Jun Li; Guang-Yi Cao; Xin-Jian Zhu; Heng-Yong Tu

2007-01-01

120

A two-dimensional theoretical and numerical model of biomass pyrolysis has been developed to determine the kinetic of wood particles pyrolysis in a fixed bed reactor. The adopted chemical model is coupled with a global transport bi-dimensional, and two temperatures model. The three modes of heat transfer (conduction, convection and\\/or radiation) between the solid and gas phases, and the wall are

Chekib Ghabi; Hmaied Benticha; Mohamed Sassi

2008-01-01

121

Comparison of spectral method and lattice Boltzmann simulations of two-dimensional hydrodynamics

Numerical solutions of the two-dimensional Navier–Stokes equations are presented by two methods; spectral and the novel lattice Boltzmann equation (LBE) scheme. Very good agreement is found for global quantities as well as energy spectra. The LBE scheme is, indeed, providing reasonably accurate solutions of the Navier–Stokes equations with an isothermal equation of state, in the nearly incompressible limit. Relaxation to

D. O. Marti´nez; S. Chen; D. C. Montgomery

1994-01-01

122

A two-dimensional sheet model was used to study the dynamics of reentry around a zone of functional block. The sheet is a\\u000a set of parallel, continuous, and uniform cables, transversely interconnected by a brick-wall arrangement of fixed resistors.\\u000a In accord with experimental observations on cardiac tissue, longitudinal propagation is continuous, whereas transverse propagation\\u000a exhibits discontinuous features. The width and length

L. J. Leon; F. A. Roberge; A. Vinet

1994-01-01

123

Computer simulation of the hydrodynamics of a two-dimensional gas-fluidized bed

A first principles model of a gas-fluidized bed has been applied to calculate the hydrodynamics of a two-dimensional (2-D) bed with an orifice in the middle of a porous plate distributor. The advanced hydrodynamic model is based on a two fluid model approach in which both phases are considered to be continuous and fully interpenetrating. Conservation equations for mass, momentum

J. A. M. Kuipers; Duin van KJ; F. P. H. van Beckum; W. P. M. van Swaaij

1993-01-01

124

Two-dimensional tsunami-dynamo simulations using the finite element method in the time domain

NASA Astrophysics Data System (ADS)

Conductive seawater moving in the ocean generates an electromotive force. This effect is called 'Oceanic dynamo effect' and transient tsunamis are also involved in this effect. Toh et al. (2011) reported that the 2006 and 2007 Krill earthquake tsunami induced electromagnetic (EM) variations in the northwest Pacific. Manoj et al. (2011) and Suetsugu et al. (2012) also reported that seafloor EM observations detected tsunami passages. Motional induction due to tsunamis, hereafter called 'Tsunami Dynamo Effect', has been studied mainly in the frequency domain. For example, Larsen (1971) derived an analytical solution considering the conductivity structures and the self-induction term, while Sanford (1971) included effects of bathymetry. Recently, Tyler (2005) analytically expected that the vertical component of the tsunami-induced magnetic field has the same waveform and phase as those of the sea level change in deep oceans. Although these works in the frequency domain are very powerful and useful, they are not able to focus on transient properties of the Tsunami Dynamo Effect. For mitigation of tsunami disasters, it is very important to investigate effects due to the first arrival of tsunamis. We, therefore, developed a two-dimensional finite element (FEM) tsunami dynamo simulation code in the time domain to reproduce magnetic tsunami signals observed in the northwest Pacific at the time of the 2011 off the Tohoku earthquake. We adopted FEM with triangular mesh in order to include realistic bathymetry and arbitrary conductivity structures beneath the seafloor. For the time evolution, the Crank Nikolson method was adopted. As a result, our simulation succeeded in reproducing the magnetic tsunami signals, especially in terms of the first wave. It is noticeable that an initial rise in the horizontal magnetic component as large as 1 nT, parallel to the tsunami propagation direction and observed 5 minutes prior to the tsunami arrival, was also induced by the tsunami. We conducted additional numerical experiments to investigate the initial rise. We laid half-space homogeneous conductor beneath the flat seafloor with a depth of 5km and let a Gaussian waveform soliton propagate with a wave height of 1m and a horizontal extent of 100km. As we assigned 0, 0.01, 0.1, and 1S/m to the conductivity beneath the seafloor, the peak of the initial rise became approximately 3, 2, <1, and ~0 nT, respectively. The initial rise, hence, vanished with the conductivity of 1S/m beneath the seafloor, because an induced current beneath the seafloor generated a horizontal magnetic field opposite to the initial rise. Our numerical results imply that this initial rise may enable us to detect the tsunami passage prior to the tsunami arrival itself under suitable conditions. In the presentation, we will report the initial rise in the horizontal magnetic component observed prior to the tsunami arrival and discuss its applicability to tsunami early warnings.

Minami, T.; Toh, H.

2013-12-01

125

Two-dimensional device simulation of AlGaN/GaN heterojunction FET side-gating effect

NASA Astrophysics Data System (ADS)

Side-gating effects on AlGaN/GaN heterojunction FETs (HFETs) are simulated using a two-dimensional device simulator incorporating the Shockley–Read–Hall (SRH) model for deep traps. With the trap parameters obtained from experiments, the simulation results are in agreement with the experimental results including the “half-recovery” from the side-gating effect and the current reduction in the recovery process from positive side-gate bias application. The simulation indicated that the finite thickness of semi-insulating i-GaN layers suppresses side-gating effects on AlGaN/GaN HFETs with thin i-GaN layers.

Ikawa, Yusuke; Lee, Keunsam; Ao, Jin-Ping; Ohno, Yasuo

2014-11-01

126

NASA Astrophysics Data System (ADS)

Gas heating in an atmospheric-pressure streamer discharge was analysed by a two-dimensional streamer discharge simulation model describing internal molecular energy transfer. Our two-dimensional streamer simulation model incorporates concepts from the fast gas heating mechanism proposed by Popov (2011 J. Phys. D: Appl. Phys. 44 285201) and our self-developed state-to-state vibrational kinetics. In dry air, gas heating occurs mainly from electron-impact dissociation reactions of O2 molecules and from quenching processes of electronically excited N2(B 3?g, C 3?u) molecules and O(1D) atoms. In humid air, rapid vibration-to-translation transitions of H2O and the exothermicity of the OH formation reactions additionally increase the gas temperature. It is shown that gas heating during the discharge pulse increases with humidity.

Komuro, Atsushi; Ono, Ryo

2014-04-01

127

Simulating the early stage of high-shear granulation using a two-dimensional Monte-Carlo approach

A two-dimensional (2-D) model of a granulation process is presented in this paper. It aims to simulate an entire granulation batch without the use of an initial experimental or fictitious 2-D density function, by taking the experimental operating conditions into account. The mass of liquid and solid in the granules are the two predicted internal variables. The 2-D population balance

M. Oullion; G. K. Reynolds; M. J. Hounslow

2009-01-01

128

. Surface Evolver simulations of flowing two-dimensional foams are described. These are used for two purposes. Firstly, to extract\\u000a the location of the T\\u000a 1 s, the changes in bubble topology that occur during plastic flow. It is shown that in linear Couette flow the T\\u000a 1 s are localized in space, becoming more so as the polydispersity of the foam

A. Wyn; I. T. Davies; S. J. Cox

2008-01-01

129

Numerical simulations of thermal conductivity in dissipative two-dimensional Yukawa systems

NASA Astrophysics Data System (ADS)

Numerical data on the heat transfer constants in two-dimensional Yukawa systems were obtained. Numerical study of the thermal conductivity and diffusivity was carried out for the equilibrium systems with parameters close to conditions of laboratory experiments with dusty plasma. For calculations of heat transfer constants the Green-Kubo formulas were used. The influence of dissipation (friction) on the heat transfer processes in nonideal systems was investigated. The approximation of the coefficient of thermal conductivity is proposed. Comparison of the obtained results to the existing experimental and numerical data is discussed.

Khrustalyov, Yu. V.; Vaulina, O. S.

2012-04-01

130

Heat transfer coefficients in two-dimensional Yukawa systems (numerical simulations)

New data on heat transfer in two-dimensional Yukawa systems have been obtained. The results of a numerical study of the thermal conductivity for equilibrium systems with parameters close to the conditions of laboratory experiments in dusty plasma are presented. The Green-Kubo relations are used to calculate the heat transfer coefficients. The influence of dissipation (internal friction) on the heat transfer processes in nonideal systems is studied. New approximations are proposed for the thermal conductivity and diffusivity for nonideal dissipative systems. The results obtained are compared with the existing experimental and numerical data.

Khrustalyov, Yu. V., E-mail: yuri.khrustalyov@gmail.com; Vaulina, O. S. [Russian Academy of Sciences, Joint Institute for High Temperatures (Russian Federation)

2013-05-15

131

Numerical simulations of thermal conductivity in dissipative two-dimensional Yukawa systems.

Numerical data on the heat transfer constants in two-dimensional Yukawa systems were obtained. Numerical study of the thermal conductivity and diffusivity was carried out for the equilibrium systems with parameters close to conditions of laboratory experiments with dusty plasma. For calculations of heat transfer constants the Green-Kubo formulas were used. The influence of dissipation (friction) on the heat transfer processes in nonideal systems was investigated. The approximation of the coefficient of thermal conductivity is proposed. Comparison of the obtained results to the existing experimental and numerical data is discussed. PMID:22680584

Khrustalyov, Yu V; Vaulina, O S

2012-04-01

132

Numerical simulation of the flow around two-dimensional partially cavitating hydrofoils

NASA Astrophysics Data System (ADS)

In the present study, a new approach is applied to the cavity prediction for two-dimensional (2D) hydrofoils by the potential based boundary element method (BEM). The boundary element method is treated with the source and doublet distributions on the panel surface and cavity surface by the use of the Dirichlet type boundary conditions. An iterative solution approach is used to determine the cavity shape on partially cavitating hydrofoils. In the case of a specified cavitation number and cavity length, the iterative solution method proceeds by addition or subtraction of a displacement thickness on the cavity surface of the hydrofoil. The appropriate cavity shape is obtained by the dynamic boundary condition of the cavity surface and the kinematic boundary condition of the whole foil surface including the cavity. For a given cavitation number the cavity length of the 2D hydrofoil is determined according to the minimum error criterion among different cavity lengths, which satisfies the dynamic boundary condition on the cavity surface. The NACA 16006, NACA 16012 and NACA 16015 hydrofoil sections are investigated for two angles of attack. The results are compared with other potential based boundary element codes, the PCPAN and a commercial CFD code (FLUENT). Consequently, it has been shown that the results obtained from the two dimensional approach are consistent with those obtained from the others.

Celik, Fahri; Ozden, Yasemin Arikan; Bal, Sakir

2014-09-01

133

Radiative MHD simulation of sunspot structure

Results of a 3D MHD simulation of a sunspot with a photospheric size of about 20 Mm are presented. The simulation has been carried out with the MURaM code, which includes a realistic equation of state with partial ionization and radiative transfer along many ray directions. The largely relaxed state of the sunspot shows a division in a central dark umbral region with bright dots and a penumbra showing bright filaments of about 2 to 3 Mm length with central dark lanes. By a process similar to the formation of umbral dots, the penumbral filaments result from magneto-convection in the form of upflow plumes, which become elongated by the presence of an inclined magnetic field: the upflow is deflected in the outward direction while the magnetic field is weakened and becomes almost horizontal in the upper part of the plume near the level of optical depth unity. A dark lane forms owing to the piling up of matter near the cusp-shaped top of the rising plume that leads to an upward bulging of the surfaces of constant optical depth. The simulated penumbral structure corresponds well to the observationally inferred interlocking-comb structure of the magnetic field with Evershed outflows along dark-laned filaments with nearly horizontal magnetic field and overturning perpendicular (`twisting') motion, which are embedded in a background of stronger and less inclined field. Photospheric spectral lines are formed at the very top and somewhat above the upflow plumes, so that they do not fully sense the strong flow as well as the large field inclination and significant field strength reduction in the upper part of the plume structures.

M. Rempel; M. Schuessler; M. Knoelker

2008-08-25

134

The SIMSYS2D two-dimensional water-quality simulation system is a large-scale digital modeling software system used to simulate flow and transport of solutes in freshwater and estuarine environments. Due to the size, processing requirements, and complexity of the system, there is a need to easily move the system and its associated files between computer sites when required. A series of job control language (JCL) procedures was written to allow transferability between IBM and IBM-compatible computers. (USGS)

Karavitis, G.A.

1984-01-01

135

Numerical simulations for MHD coronal seismology

NASA Astrophysics Data System (ADS)

Magnetohydrodynamic (MHD) processes are important for the transfer of energy over large scales in plasmas and so are essential to understanding most forms of dynamical activity in the solar atmosphere. The introduction of transverse structuring into models for the corona modifies the behavior of MHD waves through processes such as dispersion and mode coupling. Exploiting our understanding of MHD waves with the diagnostic tool of coronal seismology relies upon the development of sufficiently detailed models to account for all the features in observations. The development of realistic models appropriate for highly structured and dynamical plasmas is often beyond the domain of simple mathematical analysis and so numerical methods are employed. This paper reviews recent numerical results for seismology of the solar corona using MHD.

Pascoe, David James

2014-07-01

136

A new model for two-dimensional numerical simulation of pseudo-2D gas-solids fluidized beds

Pseudo-two dimensional (pseudo-2D) fluidized beds, for which the thickness of the system is much smaller than the other two dimensions, is widely used to perform fundamental studies on bubble behavior, solids mixing, or clustering phenomenon in different gas-solids fluidization systems. The abundant data from such experimental systems are very useful for numerical model development and validation. However, it has been reported that two-dimensional (2D) computational fluid dynamic (CFD) simulations of pseudo-2D gas-solids fluidized beds usually predict poor quantitative agreement with the experimental data, especially for the solids velocity field. In this paper, a new model is proposed to improve the 2D numerical simulations of pseudo-2D gas-solids fluidized beds by properly accounting for the frictional effect of the front and back walls. Two previously reported pseudo-2D experimental systems were simulated with this model. Compared to the traditional 2D simulations, significant improvements in the numerical predictions have been observed and the predicted results are in better agreement with the available experimental data.

Li, Tingwen; Zhang, Yongmin

2013-10-11

137

MHD Simulation of Periodic Plasmoid Ejections in Saturn

We study large-scale mass loading and plasma loss phenomena in Saturn's magnetosphere by means of global single-fluid MHD simulations (BATS-R-US). The major internal plasma sources, the rings, the icy satellites and Titan are incorporated as mass loading source terms in the MHD equations. We find that even under steady solar wind conditions, large plasmoids are pinched off quasi-periodically along a

B. Zieger; K. C. Hansen; T. I. Gombosi

2009-01-01

138

3D Hall MHD Simulation Studies (NRLHALL3D)

A 3D Hall MHD simulation code (NRLHALL3D) has recently been developed at the Naval Research Laboratory. The 3D Hall MHD equations are solved in conservative form using a finite-volume scheme. The hydrodynamic variables in a cell are updated by calculating fluxes across the cell interfaces. The fluxes of mass, momentum, and energy across cell interfaces are calculated by integrating a

J. D. Huba

2001-01-01

139

Two-dimensional simulations of the population inversion in recombining laser-produced plasma

Simulations of gain in recombining laser-produced plasma of Li-like ions of aluminum were performed using the 2-D code GIDRA-2. Symmetrical 4-beam scheme of fiber irradiation was modeled in accordance with experimental arrangement described in Ref. (1). These simulations show good agreement with earlier 1-D simulations for optically thin plasma. Maximal angle-averaged value of gain on 3d{sub 5/2}-4f{sub 7/2} transition in Li-like aluminum calculated using Sobolev approximation for photon escape probability and the Doppler line profile was 0.95 cm{sup -1}. These 2-D simulations also show more realistic laser energy absorption (25-30% in 2-D simulations compared to nearly 90% in 1-D simulations and 6% in experiments)

Roerich, V. C.; Starostin, A. N.; Stepanov, A. E. [Troitsk Institute for Innovation and Fusion Research, Troitsk, Moscow region, 142092 (Russian Federation)

1997-04-15

140

Two-dimensional simulations of the population inversion in recombining laser-produced plasma

Simulations of gain in recombining laser-produced plasma of Li-like ions of aluminum were performed using the 2-D code GIDRA-2. Symmetrical 4-beam scheme of fiber irradiation was modeled in accordance with experimental arrangement described in Ref. (1). These simulations show good agreement with earlier 1-D simulations for optically thin plasma. Maximal angle-averaged value of gain on 3d5\\/2?4f7\\/2 transition in Li-like aluminum

V. C. Roerich; A. N. Starostin; A. E. Stepanov

1997-01-01

141

Two-dimensional simulations of the population inversion in recombining laser-produced plasma

Simulations of gain in recombining laser-produced plasma of Li-like ions of aluminum were performed using the 2-D code GIDRA-2. Symmetrical 4-beam scheme of fiber irradiation was modeled in accordance with experimental arrangement described in Ref. (1). These simulations show good agreement with earlier 1-D simulations for optically thin plasma. Maximal angle-averaged value of gain on 3d5\\/2-4f7\\/2 transition in Li-like aluminum

V. C. Roerich; A. N. Starostin; A. E. Stepanov

1997-01-01

142

An automated reliable method for two-dimensional Reynolds-Averaged Navier-Stokes simulations

The development of computational fluid dynamics algorithms and increased computational resources have led to the ability to perform complex aerodynamic simulations. Obstacles remain which prevent autonomous and reliable ...

Modisette, James M

2011-01-01

143

Numerical simulation of two-dimensional fluid flow with strong shocks

Results of an extensive comparison of numerical methods for simulating hydrodynamics are presented and discussed. This study focuses on the simulation of fluid flows with strong shocks in two dimensions. By ''strong shocks,'' we here refer to shocks in which there is substantial entropy production. For the case of shocks in air, we therefore refer to Mach numbers of three

P. Woodward; P. Colella

1984-01-01

144

Embedding a Hall MHD plasma sheet simulation inside the Lyon-Fedder-Mobarry global MHD model

NASA Astrophysics Data System (ADS)

We have developed a 3D Hall magnetohydrodynamic (MHD) model with the goal of embedding this high-resolution module into the plasma sheet region of the Lyon-Fedder-Mobarry global MHD model. We intend to investigate the effect of the Hall term on the size and structure of fast flow channels observed in the plasma sheet. Owing to insufficient spatial spacecraft coverage of plasma sheet flow bursts, we appeal to global simulations possessing similar tail flow channels to assess the relative importance of the Hall term in plasma sheet transport. Current global ideal MHD models, however, contain features that are highly resolution dependent. The Hall term imposes a physical size scale on the equations in the plasma sheet, and we plan to quantify the effect of that term on the characteristics of fast flow channels.

Guild, T.; Spence, H.; Lyon, J.; Goodrich, C.; Merkin, V.; Kepko, L.

2005-12-01

145

NASA Astrophysics Data System (ADS)

Aqueous chemistries have recently been shown to be useful for the deposition of hydrophobic films of nonionic and cationic silanes on hydrophilic substrates for the prevention of stiction in MEMS. The Monte Carlo method is used to simulate in two dimensions the self-assembly of silane films on a hydrophilic surface. We investigate the impact of charged group in cationic silane on the overall structure of the films. We characterize the film structure with spatial pair correlations at each molecular layer of the deposited films. The simulations reveal long-range correlations for the film of cationic silanes. Based on our two-dimensional simulations, we report an average "most probable" structure for the films of nonionic and cationic silanes.

Kapila, Vivek; Almanza-Workman, A. Marcia; Deymier, Pierre A.; Raghavan, Srini

2004-05-01

146

Three Dimensional Simulations of Compressible Hall MHD Plasmas

NASA Astrophysics Data System (ADS)

We have developed three dimensional, time dependent, compressible, non-adiabatic, driven and massively parallelized Hall magnetohydrodynamic (MHD) simulations to investigate turbulent spectral cascades in a regime where characteristic lengthscales associated with plasma fluctuations are smaller than ion gyro radii. Such regime is ubiquitously present in solar wind and many other collisionless space plasmas. Particularly in the solar wind, the high time resolution databases identify a spectral break at the end of MHD inertial range spectrum that corresponds to a high frequency regime. In the regime, turbulent cascades cannot be explained by the usual MHD models. With the help of our 3D Hall MHD code, we find that characteristic turbulent interactions in the high frequency regime evolve typically on kinetic Alfven time scales. The turbulent fluctuation associated with kinetic Alfven interactions are compressive and anisotropic and possess equipartition of kinetic and magnetic energies.

Shaikh, Dastgeer; Shukla, P. K.

2008-10-01

147

Three Dimensional Simulations of Compressible Hall MHD Plasmas

We have developed three dimensional, time dependent, compressible, non-adiabatic, driven and massively parallelized Hall magnetohydrodynamic (MHD) simulations to investigate turbulent spectral cascades in a regime where characteristic lengthscales associated with plasma fluctuations are smaller than ion gyro radii. Such regime is ubiquitously present in solar wind and many other collisionless space plasmas. Particularly in the solar wind, the high time resolution databases identify a spectral break at the end of MHD inertial range spectrum that corresponds to a high frequency regime. In the regime, turbulent cascades cannot be explained by the usual MHD models. With the help of our 3D Hall MHD code, we find that characteristic turbulent interactions in the high frequency regime evolve typically on kinetic Alfven time scales. The turbulent fluctuation associated with kinetic Alfven interactions are compressive and anisotropic and possess equipartition of kinetic and magnetic energies.

Shaikh, Dastgeer; Shukla, P. K. [Center for Space Plasma and Aeronomy Research, University of Alabama in Huntsville, Huntsville, AL-35899 (United States) and Institut fuer Theoretische Physik IV and Centre for Plasma Science and Astrophysics, Fakultaet fuer Physik und Astronomie, Ruhr-Universitaet Bochum, D-44780 Bochum (Germany)

2008-10-15

148

Monte Carlo-molecular dynamics simulations for two-dimensional magnets

A combined Monte Carlo-molecular dynamics simulation technique is used to study the dynamic structure factor on a square lattice for isotropic Heisenberg and planar classical ferromagnetic spin Hamiltonians.

Kawabata, C.; takeuchi, M.; Bishop, A.R.

1985-01-01

149

the convection effects and to use either view-factors or ray- tracing techniques to determine the radiation effects inside the cavities. However, these types of simulations and techniques are rarely undertaken

150

We present new 3D magnetohydrodynamic (MHD) simulations of a supernova-driven, stratified interstellar medium. These simulations were run using the Waagan (2009) positivity preserving scheme for ideal MHD implemented in the Flash code. The scheme is stable even for the Mach numbers approaching 100 found in this problem. We have previously shown that the density distribution arising from hydrodynamical versions of

Mordecai-Mark Mac Low; Alex S. Hill; M. Ryan Joung; Knut Waagan; Christian Klingenberg; Kenneth Wood; Robert A. Benjamin; Christoph Federrath; L. Matthew Haffner

2011-01-01

151

Simulation of Two Dimensional Electrophoresis and Tandem Mass Spectrometry for Teaching Proteomics

ERIC Educational Resources Information Center

In proteomics, complex mixtures of proteins are separated (usually by chromatography or electrophoresis) and identified by mass spectrometry. We have created 2DE Tandem MS, a computer program designed for use in the biochemistry, proteomics, or bioinformatics classroom. It contains two simulations--2D electrophoresis and tandem mass spectrometry.…

Fisher, Amanda; Sekera, Emily; Payne, Jill; Craig, Paul

2012-01-01

152

Purpose – The purpose of this paper is to investigate the formation process of linear-shaped charge jet using the smoothed particle hydrodynamics (SPH). Different material yield models are embed to test the performance of SPH method in the simulation of explosive driven metal liner. The effects of different ignition model to the formation of metal jet have also been studied.

Yang Gang; Han Xu; Hu Dean

2011-01-01

153

Diffuse interface method is becoming a more and more popular approach for simulation of multiphase flows. As compared to other solvers, it is easy to implement and can keep conservation of mass and momentum. In the diffuse interface method, the interface is not considered as a sharp discontinuity. Instead, it treats the interface as a diffuse layer with a small

L. Ding; C. Shu; H. Ding; N. Zhao

2010-01-01

154

The core helium flash revisited: I. One and two-dimensional hydrodynamic simulations

We investigate the hydrodynamics of the core helium flash near its peak. Past research concerned with the dynamics of this event is inconclusive. However, the most recent multidimensional hydrodynamic studies suggest a quiescent behavior and seem to rule out an explosive scenario. Previous work indicated, that depending on initial conditions, employed turbulence models, grid resolution, and dimensionality of the simulation, the core helium flash leads either to the disruption of a low-mass star or to a quiescent quasi-hydrostatic evolution. We try to clarify this issue by simulating the evolution with advanced numerical methods and detailed microphysics. Assuming spherical or axial symmetry, we simulate the evolution of the helium core of a $1.25 M_{\\odot}$ star with a metallicity Z=0.02 during the core helium flash at its peak with a grid-based hydrodynamics code. We find that the core helium flash neither rips the star apart, nor that it significantly alters its structure, as convection plays a crucial role in keeping the star in hydrostatic equilibrium. In addition, our simulations show the presence of overshooting, which implies new predictions concerning mixing of chemical species in red giants.

M. Mocak; E. Mueller; A. Weiss; K. Kifonidis

2008-05-09

155

The Post Arc (PA) phase of Vacuum Interrupters (Vis) and the effects of dominant physical parameters of vacuum arc investigated in this paper. 2-D movement of PA plasma in the presence of Transient Recovery Voltage (TRV) is simulated in a proper Finite Element Method (FEM). The residual plasma at Current Zero (CZ) crossing is assumed in the inter-electrode space. Due

Amir Hayati Soloot; Jouya Jadidian; Edris Agheb; Hans Kristian Hoidalen

2010-01-01

156

NASA Astrophysics Data System (ADS)

In this work, phonon transport in two-dimensional (2D) porous silicon structures with aligned pores is investigated by Monte Carlo simulations considering the frequency-dependent phonon mean free paths (MFPs). A boundary condition based on the periodic heat flux with constant virtual wall temperature is developed for the studied periodic structures. Such periodic boundary conditions enable the simulation of the lattice thermal conductivities with a minimum computational domain. For the 2D case, it is found that phonon size effects caused by the periodically arranged pores can be remarkable even when the pore size and spacing are much larger than the averaged phonon MFPs. Our results show the importance of considering the frequency dependence of phonon MFPs in the analysis of micro- and nanostructured materials.

Hao, Qing; Chen, Gang; Jeng, Ming-Shan

2009-12-01

157

Monte Carlo simulations and finite-size scaling analysis have been carried out to study the critical behavior in a two-dimensional system of particles with two bonding sites that, by decreasing temperature or increasing density, polymerize reversibly into chains with discrete orientational degrees of freedom and, at the same time, undergo a continuous isotropic-nematic (IN) transition. A complete phase diagram was obtained as a function of temperature and density. The numerical results were compared with mean field (MF) and real space renormalization group (RSRG) analytical predictions about the IN transformation. While the RSRG approach supports the continuous nature of the transition, the MF solution predicts a first-order transition line and a tricritical point, at variance with the simulation results. PMID:20942554

López, L G; Linares, D H; Ramirez-Pastor, A J; Cannas, S A

2010-10-01

158

Two Dimensional Schrodinger Equation

NSDL National Science Digital Library

The Two Dimensional Schrodinger Equation model simulates the time evolution of a two-dimensional wave packet as it moves towards a slit with an obstacle in it, both with variable widths. By changing three parameters via sliders provided, slit width, obstacle width, and initial position of the wave packet, different behaviors can be explored. These phenomena include interference, diffraction produced by a slit, a corner, and an obstacle, and bouncing of the wave packet. In addition, the angle of propagation for the diffracted part of the wave packet can be measured. This simulation is described by a paper in the European Journal of Physics, "A versatile applet to explore the wave behaviour of particles, " J I FernÃ¡ndez Palop, 2009 Eur. J. Phys. 30 771, which outlines the simulation and how the usefulness of the simulation has been tested in the subject of quantum physics. The Two Dimensional Schrodinger Equation model was created using the Easy Java Simulations (EJS) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the ejs_qm_schrodinger2d.jar file will run the program if Java is installed.

Palop, Jose I.

2010-07-16

159

Two-dimensional simulations of the tsunami dynamo effect using the finite element method

NASA Astrophysics Data System (ADS)

Conductive seawater moving in the geomagnetic main field generates electromotive force in the ocean. This effect is well known as the "oceanic dynamo effect." Recently, it has been reported that tsunamis are also associated with the oceanic dynamo effect, and tsunami-induced electromagnetic field variations were actually observed on the seafloor. For instance, our research group succeeded in observing tsunami-induced magnetic variations on the seafloor in the northwest Pacific at the time of the 2011 Tohoku earthquake. In this study, we developed a time domain tsunami dynamo simulation code using the finite element method to explain the tsunami-induced electromagnetic variations observed on the seafloor. Our simulations successfully reproduced the observed seafloor magnetic variations as large as 3 nT. It was also revealed that an initial rise in the horizontal magnetic component prior to the tsunami arrival as large as 1 nT was induced by the tsunami.

Minami, Takuto; Toh, Hiroaki

2013-09-01

160

Massively parallel molecular dynamics simulations of two-dimensional materials at high strain rates

NASA Astrophysics Data System (ADS)

Large scale molecular dynamics simulations on a massively parallel computer are performed to investigate the mechanical behavior of 2-dimensional materials. A pair potential and a model embedded atom many-body potential are examined, corresponding to 'brittle' and 'ductile' materials, respectively. A parallel molecular dynamics (MD) algorithm is developed to exploit the architecture of the Connection Machine, enabling simulations of greater than 10(exp 6) atoms. A model spallation experiment is performed on a 2-D triagonal crystal with a well-defined nanocrystalline defect on the spall plane. The process of spallation is modeled as a uniform adiabatic expansion. The spall strength is shown to be proportional to the logarithm of the applied strain rate and a dislocation dynamics model is used to explain the results. Good predictions for the onset of spallation in the computer experiments is found from the simple model. The nanocrystal defect affects the propagation of the shock front and failure is enhanced along the grain boundary.

Wagner, N. J.; Holian, B. L.

1992-11-01

161

A computational fluid dynamics (CFD) approach was applied to simulate the air-coal two-phase flow and combustion characteristics in a 50kW circulating fluidized bed (CFB) combustor. Eulerian–Granular multiphase model with a drag coefficient correction based on the extended energy-minimization multi-scale (EMMS\\/matrix) model was used to study the gas–solid hydrodynamics. One energy conservation equation was applied to the mixture of gases and

W. Zhou; C. S. Zhao; L. B. Duan; C. R. Qu; X. P. Chen

2011-01-01

162

Two-dimensional PIC simulations of ion-beam instabilities in Supernova-driven plasma flows

Supernova remnant (SNR) blast shells can reach the flow speed $v_s = 0.1 c$ and shocks form at its front. Instabilities driven by shock-reflected ion beams heat the plasma in the foreshock, which may inject particles into diffusive acceleration. The ion beams can have the speed $v_b \\approx v_s$. For $v_b \\ll v_s$ the Buneman or upper-hybrid instabilities dominate, while for $v_b \\gg v_s$ the filamentation and mixed modes grow faster. Here the relevant waves for $v_b \\approx v_s$ are examined and how they interact nonlinearly with the particles. The collision of two plasma clouds at the speed $v_s$ is modelled with particle-in-cell (PIC) simulations, which convect with them magnetic fields oriented perpendicular to their flow velocity vector. One simulation models equally dense clouds and the other one uses a density ratio of 2. Both simulations show upper-hybrid waves that are planar over large spatial intervals and that accelerate electrons to $\\sim$ 10 keV. The symmetric collision yields only short oscillatory wave pulses, while the asymmetric collision also produces large-scale electric fields, probably through a magnetic pressure gradient. The large-scale fields destroy the electron phase space holes and they accelerate the ions, which facilitates the formation of a precursor shock.

M. E. Dieckmann; A. Meli; P. K. Shukla; L. O. C. Drury; A. Mastichiadis

2008-04-16

163

Two-Dimensional Distribution of Volatiles in the Lunar Regolith from Space Weathering Simulations

NASA Technical Reports Server (NTRS)

We present simulations of space weathering effects on ice deposits in regions of permanent shadow on the Moon. These Monte Carlo simulations follow the effects of space weathering processes on the distribution of the volatiles over time. The model output constrains the coherence of volatile deposits with depth, lateral separation, and time. The results suggest that ice sheets become broken and buried with time. As impacts begin to puncture an initially coherent surficial ice sheet, small areas with a deficit of ice compared to surrounding areas are formed first. As time progresses, holes become prevalent and the anomalous regions are local enhancements of ice concentration in a volume. The 3-D distribution is also heterogeneous because the ice is buried to varying depths in different locations. Analysis of the coherence of ice on 10 cm scales predicts that putative ice sheets in anomalous radar craters are < 100 Myr old. Surface frost becomes homogenized within 20 Myr. The simulations show the data from the LCROSS impact and surrounding region are consistent with the ice deposit in Cabeus being >1000 Myr old. For future in situ analysis of cold trap volatiles, a horizontal range of 10 m is sufficient to acquire surface-based measurements of heterogeneously distributed ice. These results also support previous analyses that Mercury's cold traps are young.

Hurley, Dana M.; Lawrence, David J.; Bussey, D. Benjamin J.; Vondrak, Richard R.; Elphic, Richard C.; Gladstone, G. Randall

2012-01-01

164

Advances in Simulation of Wave Interaction with Extended MHD Phenomena

The Integrated Plasma Simulator (IPS) provides a framework within which some of the most advanced, massively-parallel fusion modeling codes can be interoperated to provide a detailed picture of the multi-physics processes involved in fusion experiments. The presentation will cover four topics: 1) recent improvements to the IPS, 2) application of the IPS for very high resolution simulations of ITER scenarios, 3) studies of resistive and ideal MHD stability in tokamk discharges using IPS facilities, and 4) the application of RF power in the electron cyclotron range of frequencies to control slowly growing MHD modes in tokamaks and initial evaluations of optimized location for RF power deposition.

Batchelor, Donald B [ORNL; Abla, Gheni [ORNL; D'Azevedo, Ed F [ORNL; Bateman, Glenn [Lehigh University, Bethlehem, PA; Bernholdt, David E [ORNL; Berry, Lee A [ORNL; Bonoli, P. [Massachusetts Institute of Technology (MIT); Bramley, R [Indiana University; Breslau, Joshua [ORNL; Chance, M. [Princeton Plasma Physics Laboratory (PPPL); Chen, J. [Princeton Plasma Physics Laboratory (PPPL); Choi, M. [General Atomics; Elwasif, Wael R [ORNL; Foley, S. [Indiana University; Fu, GuoYong [Princeton Plasma Physics Laboratory (PPPL); Harvey, R. W. [CompX, Del Mar, CA; Jaeger, Erwin Frederick [ORNL; Jardin, S. C. [Princeton Plasma Physics Laboratory (PPPL); Jenkins, T [University of Wisconsin; Keyes, David E [Columbia University; Klasky, Scott A [ORNL; Kruger, Scott [Tech-X Corporation; Ku, Long-Poe [Princeton Plasma Physics Laboratory (PPPL); Lynch, Vickie E [ORNL; McCune, Douglas [Princeton Plasma Physics Laboratory (PPPL); Ramos, J. [Massachusetts Institute of Technology (MIT); Schissel, D. [General Atomics; Schnack, [University of Wisconsin; Wright, J. [Massachusetts Institute of Technology (MIT)

2009-01-01

165

Advances in Simulation of Wave Interactions with Extended MHD Phenomena

The Integrated Plasma Simulator (IPS) provides a framework within which some of the most advanced, massively-parallel fusion modeling codes can be interoperated to provide a detailed picture of the multi-physics processes involved in fusion experiments. The presentation will cover four topics: (1) recent improvements to the IPS, (2) application of the IPS for very high resolution simulations of ITER scenarios, (3) studies of resistive and ideal MHD stability in tokamak discharges using IPS facilities, and (4) the application of RF power in the electron cyclotron range of frequencies to control slowly growing MHD modes in tokamaks and initial evaluations of optimized location for RF power deposition.

Batchelor, Donald B [ORNL] [ORNL; D'Azevedo, Eduardo [ORNL] [ORNL; Bateman, Glenn [ORNL] [ORNL; Bernholdt, David E [ORNL] [ORNL; Bonoli, P. [Massachusetts Institute of Technology (MIT)] [Massachusetts Institute of Technology (MIT); Bramley, Randall B [ORNL] [ORNL; Breslau, Joshua [ORNL] [ORNL; Elwasif, Wael R [ORNL] [ORNL; Foley, S. [Indiana University] [Indiana University; Jaeger, Erwin Frederick [ORNL] [ORNL; Jardin, S. C. [Princeton Plasma Physics Laboratory (PPPL)] [Princeton Plasma Physics Laboratory (PPPL); Klasky, Scott A [ORNL] [ORNL; Kruger, Scott E [ORNL] [ORNL; Ku, Long-Poe [ORNL] [ORNL; McCune, Douglas [Princeton Plasma Physics Laboratory (PPPL)] [Princeton Plasma Physics Laboratory (PPPL); Ramos, J. [Massachusetts Institute of Technology (MIT)] [Massachusetts Institute of Technology (MIT); Schissel, David P [ORNL] [ORNL; Schnack, Dalton D [ORNL] [ORNL

2009-01-01

166

A FORTRAN-77 computer program code that helps solve a variety of aquifer management problems involving the control of groundwater hydraulics. It is intended for use with any standard mathematical programming package that uses Mathematical Programming System input format. The computer program creates the input files to be used by the optimization program. These files contain all the hydrologic information and management objectives needed to solve the management problem. Used in conjunction with a mathematical programming code, the computer program identifies the pumping or recharge strategy that achieves a user 's management objective while maintaining groundwater hydraulic conditions within desired limits. The objective may be linear or quadratic, and may involve the minimization of pumping and recharge rates or of variable pumping costs. The problem may contain constraints on groundwater heads, gradients, and velocities for a complex, transient hydrologic system. Linear superposition of solutions to the transient, two-dimensional groundwater flow equation is used by the computer program in conjunction with the response matrix optimization method. A unit stress is applied at each decision well and transient responses at all control locations are computed using a modified version of the U.S. Geological Survey two dimensional aquifer simulation model. The program also computes discounted cost coefficients for the objective function and accounts for transient aquifer conditions. (Author 's abstract)

Lefkoff, L.J.; Gorelick, S.M.

1987-01-01

167

A new composite two-dimensional process\\/two-dimensional device simulation system (TOPMODE) (FOOTNOTE: Standing for TOshiba Simulation Program for MOS DEvice.) has been developed to provide a straightforward means of predicting small-geometry device characteristics using the fabrication process sequence. Using TOP-MODE, an analysis of the anomalous subthreshold drain current peculiar to buried oxide isolation (BOX) structure device has been conducted and the physical

S. Onga; M. Konaka; A. Ohmichi; K. Kanaka; R. Dang

1986-01-01

168

Two-dimensional streamflow simulations of the Jordan River, Midvale and West Jordan, Utah

The Jordan River in Midvale and West Jordan, Utah, flows adjacent to two U.S. Environmental Protection Agency Superfund sites: Midvale Slag and Sharon Steel. At both sites, geotechnical caps extend to the east bank of the river. The final remediation tasks for these sites included the replacement of a historic sheet-pile dam and the stabilization of the river banks adjacent to the Superfund sites. To assist with these tasks, two hydraulic modeling codes contained in the U.S. Geological Survey (USGS) Multi-Dimensional Surface-Water Modeling System (MD_SWMS), System for Transport and River Modeling (SToRM) and Flow and Sediment Transport and Morphological Evolution of Channels (FaSTMECH), were used to provide predicted water-surface elevations, velocities, and boundary shear-stress values throughout the study reach of the Jordan River. A SToRM model of a 0.7 mile subreach containing the sheet-pile dam was used to compare water-surface elevations and velocities associated with the sheet-pile dam and a proposed replacement structure. Maps showing water-surface elevation and velocity differences computed from simulations of the historic sheet-pile dam and the proposed replacement structure topographies for streamflows of 500 and 1,000 cubic feet per second (ft3/s) were created. These difference maps indicated that the velocities associated with the proposed replacement structure topographies were less than or equal to those associated with the historic sheet-pile dam. Similarly, water-surface elevations associated with the proposed replacement structure topographies were all either greater than or equal to water-surface elevations associated with the sheet-pile dam. A FaSTMECH model was developed for the 2.5-mile study reach to aid engineers in bank stabilization designs. Predicted water-surface elevations, velocities and shear-stress values were mapped on an aerial photograph of the study reach to place these parameters in a spatial context. Profile plots of predicted cross-stream average water-surface elevations and cross-stream maximum and average velocities showed how these parameters change along the study reach for two simulated discharges of 1,040 ft3/s and 2,790 ft3/s. The profile plots for the simulated streamflow of 1,040 ft3/s show that the highest velocities are associated with the constructed sheet-pile replacement structure. Results for the simulated streamflow of 2,790 ft3/s indicate that the geometry of the 7800 South Bridge causes more backwater and higher velocities than the constructed sheet-pile replacement structure.

Kenney, Terry A.; Freeman, Michael L.

2011-01-01

169

Two Dimensional Simulations of Plastic-Shell, Direct-Drive Implosions on OMEGA

Multidimensional hydrodynamic properties of high-adiabat direct-drive plastic-shell implosions on the OMEGA laser system [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] are investigated using the multidimensional hydrodynamic code, DRACO. Multimode simulations including the effects of nonuniform illumination and target roughness indicate that shell stability during the acceleration phase plays a critical role in determining target performance. For thick shells that remain integral during the acceleration phase, target yields are significantly reduced by the combination of the long-wavelength ({ell} < 10) modes due to surface roughness and beam imbalance and the intermediate modes (20 {le} {ell} {le} 50) due to single-beam nonuniformities. The neutron-production rate for these thick shells truncates relative to one-dimensional (1-D) predictions. The yield degradation in the thin shells is mainly due to shell breakup at short wavelengths ({lambda} {approx} {Delta}, where {Delta} is the in-flight shell thickness). The neutron-rate curves for the thinner shells have significantly lower amplitudes and a fall-off that is less steep than 1-D rates. DRACO simulation results are consistent with experimental observations.

Radha, P B; Goncharov, V N; Collins, T B; Delettrez, J A; Elbaz, Y; Glebov, V Y; Keck, R L; Keller, D E; Knauer, J P; Marozas, J A; Marshall, F J; McKenty, P W; Meyerhofer, D D; Regan, S P; Sangster, T C; Shvarts, D; Skupsky, S; Srebro, Y; Town, R J; Stoeckl, C

2004-09-27

170

Parametric decay of oblique Alfvén waves in two-dimensional hybrid simulations.

Certain types of plasma waves are known to become parametrically unstable under specific plasma conditions, in which the pump wave will decay into several daughter waves with different wavenumbers and frequencies. In the past, the related plasma instabilities have been treated analytically for various parameter regimes and by use of various numerical methods, yet the oblique propagation with respect to the background magnetic field has rarely been dealt with in two dimensions, mainly because of the high computational demand. Here we present a hybrid-simulation study of the parametric decay of a moderately oblique Alfvén wave having elliptical polarization. It is found that such a compressive wave can decay into waves with higher and lower wavenumbers than the pump. PMID:23005891

Verscharen, D; Marsch, E; Motschmann, U; Müller, J

2012-08-01

171

FRANC2D: A two-dimensional crack propagation simulator. Version 2.7: User's guide

NASA Technical Reports Server (NTRS)

FRANC 2D (FRacture ANalysis Code, 2 Dimensions) is a menu driven, interactive finite element computer code that performs fracture mechanics analyses of 2-D structures. The code has an automatic mesh generator for triangular and quadrilateral elements. FRANC2D calculates the stress intensity factor using linear elastic fracture mechanics and evaluates crack extension using several methods that may be selected by the user. The code features a mesh refinement and adaptive mesh generation capability that is automatically developed according to the predicted crack extension direction and length. The code also has unique features that permit the analysis of layered structure with load transfer through simulated mechanical fasteners or bonded joints. The code was written for UNIX workstations with X-windows graphics and may be executed on the following computers: DEC DecStation 3000 and 5000 series, IBM RS/6000 series, Hewlitt-Packard 9000/700 series, SUN Sparc stations, and most Silicon Graphics models.

Wawrzynek, Paul; Ingraffea, Anthony

1994-01-01

172

Two-Dimensional Simulations of X-Ray Absorption Spectra from Nonuniformly Driven Planar Targets

NASA Astrophysics Data System (ADS)

The effects of the ablative Rayleigh-Taylor instability on simulated absorption spectra in planar targets are examined. Spectra from embedded layers have been used as diagnostics of thermal transport, shock preheat, and other effects. Obtaining consistent temperature values from conventional analysis requires that the signature material remain within bounds that do not exceed a narrow range of conditions. We consider modifications of the spectrum due to, for example, dilution and bias by higher transmission through thin spots in the absorbing layer. We also examine the applicability of one-dimensional turbulent mix modeling to short-scale, multidimensional structure. In this work, the spectral analysis post-processor SPECT3D(Prism Computational Sciences, Inc.) is used in conjunction with the one-dimensional hydrocode LILAC and the multidimensional hydrocode DRACO. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC03-92SF19460.

Epstein, R.; Ling, B.; Delettrez, J. A.; Radha, P. B.; Boehly, T. R.; Yaakobi, B.; Macfarlane, J. J.

2000-10-01

173

Two dimensional hydrological simulation in elastic swelling/shrinking peat soils

NASA Astrophysics Data System (ADS)

Peatlands respond to natural hydrologic cycles of precipitation and evapotranspiration with reversible deformations due to variations of water content in both the unsaturated and saturated zone. This phenomenon results in short-term vertical displacements of the soil surface that superimpose to the irreversible long-term subsidence naturally occurring in drained cropped peatlands because of bio-oxidation of the organic matter. The yearly sinking rates due to the irreversible process are usually comparable with the short-term deformation (swelling/shrinkage) and the latter must be evaluated to achieve a thorough understanding of the whole phenomenon. A mathematical model describing swelling/shrinkage dynamics in peat soils under unsaturated conditions has been derived from simple physical considerations, and validated by comparison with laboratory shrinkage data. The two-parameter model relates together the void and moisture ratios of the soil. This approach is implemented in a subsurface flow model describing variably saturated porous media flow (Richards' equation), by means of an appropriate modification of the general storage term. The contribution of the saturated zone to total deformation is considered by using information from the elastic storage coefficient. Simulations have been carried out for a drained cropped peatland south of the Venice Lagoon (Italy), for which a large data set of hydrological and deformation measurements has been collected since the end of 2001. The considered domain is representative of a field section bounded by ditches, subject to rainfall and evapotranspiration. The comparison between simulated and measured quantities demonstrates the capability of the model to accurately reproduce both the hydrological and deformation dynamics of peat, with values of the relevant parameters that are in good agreement with the literature.

Camporese, M.; Ferraris, S.; Paniconi, C.; Putti, M.; Salandin, P.; Teatini, P.

2005-12-01

174

The role of condensation and heat conduction in the formation of prominences - An MHD simulation

NASA Technical Reports Server (NTRS)

The effects of condensation and thermal conduction on the formation of Kippenhahn-Schlueter (K-S) type prominences in quiet regions (QP) due to symmetric mass injection are investigated. To implement this investigation a self-consistent, two-dimensional, nonplanar, time-dependent MHD simulation model is developed. In the model, various values of the injection velocity, density, and magnetic field strength are used to determine the most favorable conditions for the QP formation. Based on these simulation results, it is found that the formation of a K-S type field configuration should be considered as a dynamic process which needs both condensation amd mass injection to supply enough mass to maintain such a configuration to complete the quiescent prominence formation process.

Wu, S. T.; Bao, J. J.; An, C. H.; Tandberg-Hanssen, E.

1990-01-01

175

Two-dimensional Euler and Navier-Stokes Time accurate simulations of fan rotor flows

NASA Technical Reports Server (NTRS)

Two numerical methods are presented which describe the unsteady flow field in the blade-to-blade plane of an axial fan rotor. These methods solve the compressible, time-dependent, Euler and the compressible, turbulent, time-dependent, Navier-Stokes conservation equations for mass, momentum, and energy. The Navier-Stokes equations are written in Favre-averaged form and are closed with an approximate two-equation turbulence model with low Reynolds number and compressibility effects included. The unsteady aerodynamic component is obtained by superposing inflow or outflow unsteadiness to the steady conditions through time-dependent boundary conditions. The integration in space is performed by using a finite volume scheme, and the integration in time is performed by using k-stage Runge-Kutta schemes, k = 2,5. The numerical integration algorithm allows the reduction of the computational cost of an unsteady simulation involving high frequency disturbances in both CPU time and memory requirements. Less than 200 sec of CPU time are required to advance the Euler equations in a computational grid made up of about 2000 grid during 10,000 time steps on a CRAY Y-MP computer, with a required memory of less than 0.3 megawords.

Boretti, A. A.

1990-01-01

176

The effect of parametric wave phase conjugation (WPC) in application to ultrasound or acoustic waves in magnetostrictive solids has been addressed numerically by Ben Khelil et al. [J. Acoust. Soc. Am. 109, 75-83 (2001)] using 1-D unsteady formulation. Here the numerical method presented by Voinovich et al. [Shock waves 13(3), 221-230 (2003)] extends the analysis to the 2-D effects. The employed model describes universally elastic solids and liquids. A source term similar to Ben Khelil et al.'s accounts for the coupling between deformation and magnetostriction due to external periodic magnetic field. The compatibility between the isotropic constitutive law of the medium and the model of magnetostriction has been considered. Supplementary to the 1-D simulations, the present model involves longitudinal/transversal mode conversion at the sample boundaries and separate magnetic field coupling with dilatation and shear stress. The influence of those factors in a 2-D geometry on the potential output of a magneto-elastic wave phase conjugator is analyzed in this paper. The process under study includes propagation of a wave burst of a given frequency from a point source in a liquid into the active solid, amplification of the waves due to parametric resonance, and formation of time-reversed waves, their radiation into liquid, and focusing. The considered subject is particularly important for ultrasonic applications in acoustic imaging, nondestructive testing, or medical diagnostics and therapy. PMID:16419796

Voinovich, Peter; Merlen, Alain

2005-12-01

177

Static field simulation of two-dimensional negative-U Hubbard model

NASA Astrophysics Data System (ADS)

As a simplest model which yields high-Tc superconductivity, the negative-U Hubbard model on a 2-D square lattice is investigated in this thesis by using a newly developed static field analysis. The static field approximation is an action saddle-point algorithm, which is used to find partially classical solutions of strongly correlated electron systems. With the introduction of Stratonovich-Hubbard (S-H) fields, the electron-electron interaction is decoupled. The Stratonovich-Hubbard fields are purely static (i.e., classical) and handled by Monte Carlo simulation. For each S-H field configuration (each Monte Carlo step), the "free"-electron subsystem can be diagonalized exactly. This algorithm overcomes the difficulty of pure perturbation theories for handling the strong coupling limit, which exhibits a ground state energy gap in the half-filled spectral density. The single-electron spectral density and the static response functions for charge density and superconducting order are given. The Kosterlitz-Thouless phase transition temperatures are estimated by finite-size scaling. Phase diagrams for different interaction strengths are plotted. At optimal interaction strength, U = -4t, and optimal doping,

Zhang, Bo

178

Two-Dimensional Optical Measurement of Waves on Liquid Lithium Jet Simulating IFMIF Target Flow

Waves on a liquid-lithium jet flow, simulating a proposed high-energy beam target design, have been measured using an optical technique based on specular reflection of a single laser beam on the jet surface. The stream-wise and spanwise fluctuations of the local free-surface slope were least-square fitted with a sinusoidal curve to makeup the signals lost due to the constriction in the optical arrangement. The waveform was estimated with an assumption that wave phase speed can be calculated using the dispersion relation for linear capillary-gravity waves. The direction of propagation on the jet surface was also evaluated so that the wave amplitudes, calculated by integral of slope angle signal, agree consistently in stream-wise and spanwise direction. These measurements and analyses show that the waves at the measurement location for a jet velocity of 1.2 m/s can best be represented by oblique waves with an inclination of 1.23 rad, a wavelength of 3.8 mm and a wave amplitude of about 0.05 mm. (authors)

Kazuhiro Itoh; Hiroyuki Koterazawa [University of Hyogo, 1-3-3, Higashikawasaki-cho, Chuo-ku, Kobe-shi, Hyogo (Japan); Taro Itoh; Yutaka Kukita [Nagoya University, Furo-cho, Chikusa-ku, Nagoya-shi, Aichi, 464-8603 (Japan); Hiroo Kondo; Nobuo Yamaoka; Hiroshi Horiike [Osaka University, 1-8 Yamadaoka, Suita, Osaka 565-0871 (Japan); Mizuho Ida; Hideo Nakamura; Hiroo Nakamura [Japan Atomic Energy Agency (Japan); Takeo Muroga [National Institute for Fusion Science, 322-6, Oroshi-cho, Toki, GIFU, 509-5292 (Japan)

2006-07-01

179

A two-dimensional model of water: Theory and computer simulations

NASA Astrophysics Data System (ADS)

We develop an analytical theory for a simple model of liquid water. We apply Wertheim's thermodynamic perturbation theory (TPT) and integral equation theory (IET) for associative liquids to the MB model, which is among the simplest models of water. Water molecules are modeled as 2-dimensional Lennard-Jones disks with three hydrogen bonding arms arranged symmetrically, resembling the Mercedes-Benz (MB) logo. The MB model qualitatively predicts both the anomalous properties of pure water and the anomalous solvation thermodynamics of nonpolar molecules. IET is based on the orientationally averaged version of the Ornstein-Zernike equation. This is one of the main approximations in the present work. IET correctly predicts the pair correlation function of the model water at high temperatures. Both TPT and IET are in semi-quantitative agreement with the Monte Carlo values of the molar volume, isothermal compressibility, thermal expansion coefficient, and heat capacity. A major advantage of these theories is that they require orders of magnitude less computer time than the Monte Carlo simulations.

Urbi?, T.; Vlachy, V.; Kalyuzhnyi, Yu. V.; Southall, N. T.; Dill, K. A.

2000-02-01

180

A two-dimensional simulation of tritium transport in the vadose zone at the Nevada Test site

The site of a 0.75-kiloton underground nuclear explosion, the Cambric event, was selected for the study of radionuclide transport in the hydrologic environment. Water samples from RNM-2S, a well located 91 m from Cambric, have been analyzed for tritium and other radionuclides since the initiation of pumping. Water from RNM-2S flows to Frenchman Lake via an unlined canal. Flume data indicate canal transmission losses of approximately 2m{sup 3}/day/meter of canal. To determine if infiltrating canal water might be recirculated by RNM-2S, and therefore provide an additional radionuclide input to water samples collected at RNM-2S, a two-dimensional variably saturated solute transport computer model (SATURN, Huyakorn et al., 1983) was used to simulate the movement of tritium from the canal to the water table. Results indicate that recirculated canal water has not had a significant effect on the breakthrough of tritium at RNM-2S.

Ross, W.C.; Wheatcraft, S.W.

1994-09-01

181

NASA Astrophysics Data System (ADS)

We analyzed, based on the theoretical spectroscopic modeling, how the differences in the folding landscapes of two ?-hairpin peptides trpzip2 and trpzip4 are reflected in their thermal unfolding infrared measurements. The isotope-edited equilibrium FTIR and two dimensional infrared spectra of the two peptides were calculated, using the nonlinear exciton propagation method, at a series of temperatures. The spectra calculations were based on the configuration distributions generated using the GBOBC implicit solvent MD simulation and the integrated tempering sampling technique. Conformational analysis revealed the different local thermal stabilities for these two peptides, which suggested the different folding landscapes. Our study further suggested that the ellipticities of the isotope peaks in the coherent IR signals are more sensitive to these local stability differences compared with other spectral features such as the peak intensities. Our technique can thus be combined with the relevant experimental measurements to achieve a better understanding of the peptide folding behaviors.

Wu, Tianmin; Zhang, Ruiting; Li, Huanhuan; Yang, Lijiang; Zhuang, Wei

2014-02-01

182

We use a two-dimensional volatility basis set (2D-VBS) box model to simulate secondary organic aerosol (SOA) mass yields of linear oxygenated molecules: n-tridecanal, 2- and 7-tridecanone, 2- and 7-tridecanol, and n-pentadecane. A hybrid model with explicit, a priori treatment of the first-generation products for each precursor molecule, followed by a generic 2D-VBS mechanism for later-generation chemistry, results in excellent model-measurement agreement. This strongly confirms that the 2D-VBS mechanism is a predictive tool for SOA modeling but also suggests that certain important first-generation products for major primary SOA precursors should be treated explicitly for optimal SOA predictions. PMID:22970932

Chacon-Madrid, Heber J; Murphy, Benjamin N; Pandis, Spyros N; Donahue, Neil M

2012-10-16

183

Two-Dimensional Model Simulations of Interannual Variability in the Tropical Stratosphere

NASA Technical Reports Server (NTRS)

Meteorological data from the United Kingdom Meteorological Office (UKMO) and constituent data from the Upper Atmospheric Research Satellite (UARS) are used to construct yearly zonal mean dynamical fields for the 1990s for use in the GSFC 2-D chemistry and transport model. This allows for interannual dynamical variability to be included in the model constituent simulations. In this study, we focus on the tropical stratosphere. We find that the phase of quasi-biennial oscillation (QBO) signals in equatorial CH4, and profile and total column 03 data is resolved quite well using this empirically- based 2-D model transport framework. However. the QBO amplitudes in the model constituents are systematically underestimated relative to the observations at most levels. This deficiency is probably due in part to the limited vertical resolutions of the 2-D model and the UKMO and UARS input data sets. We find that using different heating rate calculations in the model affects the interannual and QBO amplitudes in the constituent fields, but has little impact on the phase. Sensitivity tests reveal that the QBO in transport dominates the ozone interannual variability in the lower stratosphere. with the effect of the temperature QBO being dominant in the tipper stratosphere via the strong temperature dependence of the ozone loss reaction rates. We also find that the QBO in odd nitrogen radicals, which is caused by the QBO modulated transport of NOy, plays a significant but not dominant role in determining the ozone QBO variability in the middle stratosphere. The model mean age of air is in good overall agreement with that determined from tropical lower,middle stratospheric OMS balloon observations of SF6 and CO2. The interannual variability of tile equatorial mean age in the model increases with altitude and maximizes near 40 km, with a range, of 4-5 years over the 1993-2000 time period.

Fleming, Eric L.; Jackman, Charles H.; Considine, David B.; Rosenfeld, Joan; Bhartia, P. K. (Technical Monitor)

2001-01-01

184

NASA Astrophysics Data System (ADS)

Aquatic habitat models utilize flow variables which may be predicted with one-dimensional (1D) or two-dimensional (2D) hydrodynamic models to simulate aquatic habitat quality. Studies focusing on the effects of hydrodynamic model dimensionality on predicted aquatic habitat quality are limited. Here we present the analysis of the impact of flow variables predicted with 1D and 2D hydrodynamic models on simulated spatial distribution of habitat quality and Weighted Usable Area (WUA) for fall-spawning Chinook salmon. Our study focuses on three river systems located in central Idaho (USA), which are a straight and pool-riffle reach (South Fork Boise River), small pool-riffle sinuous streams in a large meadow (Bear Valley Creek) and a steep-confined plane-bed stream with occasional deep forced pools (Deadwood River). We consider low and high flows in simple and complex morphologic reaches. Results show that 1D and 2D modeling approaches have effects on both the spatial distribution of the habitat and WUA for both discharge scenarios, but we did not find noticeable differences between complex and simple reaches. In general, the differences in WUA were small, but depended on stream type. Nevertheless, spatially distributed habitat quality difference is considerable in all streams. The steep-confined plane bed stream had larger differences between aquatic habitat quality defined with 1D and 2D flow models compared to results for streams with well defined macro-topographies, such as pool-riffle bed forms. KEY WORDS: one- and two-dimensional hydrodynamic models, habitat modeling, weighted usable area (WUA), hydraulic habitat suitability, high and low discharges, simple and complex reaches

Benjankar, R. M.; Sohrabi, M.; Tonina, D.; McKean, J. A.

2013-12-01

185

CENTRAL REGIONS OF BARRED GALAXIES: TWO-DIMENSIONAL NON-SELF-GRAVITATING HYDRODYNAMIC SIMULATIONS

The inner regions of barred galaxies contain substructures such as off-axis shocks, nuclear rings, and nuclear spirals. These substructures may affect star formation, and control the activity of a central black hole (BH) by determining the mass inflow rate. We investigate the formation and properties of such substructures using high-resolution, grid-based hydrodynamic simulations. The gaseous medium is assumed to be infinitesimally thin, isothermal, and non-self-gravitating. The stars and dark matter are represented by a static gravitational potential with four components: a stellar disk, a bulge, a central BH, and a bar. To investigate various galactic environments, we vary the gas sound speed, c{sub s} , as well as the mass of the central BH, M{sub BH}. Once the flow has reached a quasi-steady state, off-axis shocks tend to move closer to the bar major axis as c{sub s} increases. Nuclear rings shrink in size with increasing c{sub s} , but are independent of M{sub BH}, suggesting that the ring position is not determined by the Lindblad resonances. Rings in low-c{sub s} models are narrow since they are occupied largely by gas on x{sub 2}-orbits and well decoupled from nuclear spirals, while they become broad because of large thermal perturbations in high-c{sub s} models. Nuclear spirals persist only when either c{sub s} is small or M{sub BH} is large; they would otherwise be destroyed completely by the ring material on eccentric orbits. The shape and strength of nuclear spirals depend sensitively on c{sub s} and M{sub BH} such that they are leading if both c{sub s} and M{sub BH} are small, weak trailing if c{sub s} is small and M{sub BH} is large, and strong trailing if both c{sub s} and M{sub BH} are large. While the mass inflow rate toward the nucleus is quite small in low-c{sub s} models because of the presence of a narrow nuclear ring, it becomes larger than 0.01 M{sub Sun} yr{sup -1} when c{sub s} is large, providing a potential explanation of nuclear activity in Seyfert galaxies.

Kim, Woong-Tae; Seo, Woo-Young [Center for the Exploration of the Origin of the Universe (CEOU), Astronomy Program, Department of Physics and Astronomy, Seoul National University, Seoul 151-742 (Korea, Republic of); Stone, James M. [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States); Yoon, Doosoo [FPRD, Department of Physics and Astronomy, Seoul National University, Seoul 151-742 (Korea, Republic of); Teuben, Peter J., E-mail: wkim@astro.snu.ac.kr [Department of Astronomy, University of Maryland, College Park, MD 20742 (United States)

2012-03-01

186

NASA Astrophysics Data System (ADS)

There are a number of modeling challenges posed by space weather simulations. Most of them arise from the multiscale and multiphysics aspects of the problem. The multiple scales dramatically increase the requirements, in terms of computational resources, because of the need of performing large scale simulations with the proper small-scales resolution. Lately, several suggestions have been made to overcome this difficulty by using various refinement methods which consist in splitting the domain into regions of different resolutions separated by well defined interfaces. The multiphysics issues are generally treated in a similar way: interfaces separate the regions where different equations are solved. This paper presents an innovative approach based on the coexistence of several levels of description, which differ by their resolutions or, potentially, by their physics. Instead of interacting through interfaces, these levels are entirely simulated and are interlocked over the complete extension of the overlap area. This scheme has been applied to a parallelized, two-dimensional, Implicit Moment Method Particle in Cell code in order to investigate its multiscale description capabilities. Simulations of magnetic reconnection and plasma expansion in vacuum are presented and possible implementation options for this scheme on very large systems are also discussed.

Beck, A.; Innocenti, M. E.; Lapenta, G.; Markidis, S.

2014-08-01

187

The dynamic response of two-dimensional granular matter subjected to the impact of a spherical projectile is investigated experimentally and also numerically using discrete element method (DEM). The granular matter is modeled by the mono-disperse aggregation of nylon spheres arranged regularly and two-dimensionally in a rectangular container. The numerical simulations are compared with the experiments using high-speed video camera for the

K Tanaka; M Nishida; T Kunimochi; T Takagi

2002-01-01

188

Electron acceleration mechanism at high Mach number collisionless shocks propagating in a weakly magnetized medium is investigated by a self-consistent two-dimensional particle-in-cell simulation. Simulation results show that strong electrostatic waves are excited via the electron-ion electrostatic two-stream instability at the leading edge of the shock transition region as in the case of earlier one-dimensional simulations. We observe strong electron acceleration that is associated with the turbulent electrostatic waves in the shock transition region. The electron energy spectrum in the shock transition region exhibits a clear power-law distribution with spectral index of $2.0 {\\rm -} 2.5$. By analyzing the trajectories of accelerated electrons, we find that the acceleration mechanism is very similar to shock surfing acceleration of ions. In contrast to the ion shock surfing, however, the energetic electrons are reflected by electron-scale electrostatic fluctuations in the shock transition region, but not by the ion-scale cross-shock electrostatic potential. The reflected electrons are then accelerated by the convective electric field in front of the shock. We conclude that the multidimensional effects as well as the self-consistent shock structure are essential for the strong electron acceleration at high Mach number shocks.

Takanobu Amano; Masahiro Hoshino

2008-05-08

189

NASA Astrophysics Data System (ADS)

With the rapid increase of GPS/GNSS receivers being deployed and operated in China, real-time GPS data from nearly a thousand sites are available at the National Center for Space Weather, China Meteorology Administration. However, it is challenging to generate a high-quality regional total electron content (TEC) map with the traditional two-dimensional (2-D) retrieval scheme because a large horizontal gradient has been reported over east-south Asia due to the northern equatorial ionization anomaly. We developed an Ionosphere Data Assimilation Analysis System (IDAAS), which is described in this study, using an International Reference Ionosphere (IRI) model as the background and applying a Kalman filter for updated observations. The IDAAS can reconstruct a three-dimensional ionosphere with the GPS slant TEC. The inverse slant TEC correlates well with observations both for GPS sites involved in the reconstruction and sites that are not involved. Based on the IDAAS, simulations were performed to investigate the deviation relative to the slant-to-vertical conversion (STV). The results indicate that the relative deviation induced by slant-to-vertical conversion may be significant in certain instances, and the deviation varies from 0% to 40% when the elevation decreases from 90° to 15°, while the relative IDAAS deviation is much smaller and varies from -5% to 15% without an elevation dependence. Compared with ‘true TEC’ map derived from the model, there is large difference in STV TEC map but no obvious discrepancy in IDAAS map. Generally, the IDAAS TEC map is much closer to the “true TEC” than is STV TEC map is. It is suggested that three-dimensional inversion technique is necessary for GPS observations of low elevation at an equatorial anomaly region, wherein the high horizontal electron density gradient may produce significant slant-to-vertical deviations using the two-dimensional STV inversion method.

Yu, Tao; Mao, Tian; Wang, Yungang; Zeng, Zhongcao; Xia, Chunliang; Wu, Fenglei; Wang, Le

2014-08-01

190

Radiative Models of Sagittarius A* and M87 from Relativistic MHD Simulations

Radiative Models of Sagittarius A* and M87 from Relativistic MHD Simulations Jason Dexter;#12;University of Washington Abstract Radiative Models of Sagittarius A* and M87 from Relativistic MHD relativistic MHD (GRMHD) simulations currently provide the most realistic physical description of black hole

Militzer, Burkhard

191

Two-dimensional numerical simulations of an accretion flow in a close binary system are performed by solving the Euler equations with radiative transfer. In the present study, the specific heat ratio is assumed to be constant while radiative cooling effect is included as a non-adiabatic process. The cooling effect of the disc is considered by discharging energy in the vertical directions from the top and bottom surfaces of the disc. We use the flux-limited diffusion approximation to calculate the radiative heat flux values. Our calculations show that a disc structure appears and the spiral shocks are formed on the disc. These features are similar to that observed in the case of an adiabatic gas with a lower specific heat ratio, $\\gamma=1.01$. It is found that when radiative cooling effect is accounted for, the mass of the disc becomes larger than that assuming $\\gamma=5/3$, and smaller than that assuming $\\gamma=1.01$. It is concluded that employing an adiabatic gas with a lower specific heat ratio is almost a valid assumption for simulating accretion disc with radiative cooling effect.

Jun'ichi Sato; Keisuke Sawada; Naofumi Ohnishi

2003-04-14

192

Two-dimensional axisymmetric particle-in-cell simulations with Monte Carlo collision calculations (PIC-MCC) have been conducted to investigate argon microplasma characteristics of a miniature inductively coupled plasma source with a 5-mm-diameter planar coil, where the radius and length are 5 mm and 6 mm, respectively. Coupling the rf-electromagnetic fields to the plasma is carried out based on a collisional model and a kinetic model. The former employs the cold-electron approximation and the latter incorporates warm-electron effects. The numerical analysis has been performed for pressures in the range 370-770 mTorr and at 450 MHz rf powers below 3.5 W, and then the PIC-MCC results are compared with available experimental data and fluid simulation results. The results show that a considerably thick sheath structure can be seen compared with the plasma reactor size and the electron energy distribution is non-Maxwellian over the entire plasma region. As a result, the distribution of the electron temperature is quite different from that obtained in the fluid model. The electron temperature as a function of rf power is in a reasonable agreement with experimental data. The pressure dependence of the plasma density shows different tendency between the collisional and kinetic model, implying noncollisional effects even at high pressures due to the high rf frequency, where the electron collision frequency is less than the rf driving frequency.

Takao, Yoshinori; Kusaba, Naoki; Eriguchi, Koji; Ono, Kouichi [Department of Aeronautics and Astronautics, Graduate School of Engineering, Kyoto University, Yoshida-Honmachi, Sakyo-ku, Kyoto 606-8501 (Japan)

2010-11-15

193

NASA Technical Reports Server (NTRS)

Spatial and seasonal distribution of ozone and other trace gases are simulated using a interactive two-dimensional model of the stratosphere updated to include full gas phase chemistry. The model consists of a primitive equation dynamics module, a full radiative transfer scheme, and a comprehensive gas phase chemistry module. The circulation is derived from heating rates in the stratosphere that are calculated using model-generated ozone. In the troposphere, parameterized heating rates are adopted. The eddy momentum flux divergence in the zonal mean momentum equation is given by the eddy fluxes of potential vorticity. Eddy fluxes of potential vorticity and tracers are parameterized using a set of predetermined diffusion coefficients. The adopted values for K(sub yy), show a hemispherical asymmetry in that the values in the lower stratosphere are consistently smaller in the southern hemisphere. The asymmetry in K(sub yy) and in the parameterization of the tropospheric heating rate results in an asymmetry in the circulation giving rise to unique signatures in the trace gas distributions. The model successfully simulates the observed asymmetry in the column abundance of the springtime ozone maxima between northern and southern hemisphere. Results for other trace gases are in agreement with the gross observed features although specific differences exist.

Ko, Malcolm K. W.; Schneider, Hans R.; Shia, Run-Lie; Weisenstein, Debra K.; Sze, Nien-Dak

1993-01-01

194

Starting as highly relativistic collimated jets, gamma-ray burst outflows gradually slow down and become nonrelativistic spherical blast waves. Although detailed analytical solutions describing the afterglow emission received by an on-axis observer during both the early and late phases of the outflow evolution exist, a calculation of the received flux during the intermediate phase and for an off-axis observer requires either a more simplified analytical model or direct numerical simulations of the outflow dynamics. In this paper, we present light curves for off-axis observers covering the long-term evolution of the blast wave, calculated from a high-resolution two-dimensional relativistic hydrodynamics simulation using a synchrotron radiation model. We compare our results to earlier analytical work and calculate the consequence of the observer angle with respect to the jet axis both for the detection of orphan afterglows and for jet break fits to the observational data. We confirm earlier results in the literature finding that only a very small number of local type Ibc supernovae can harbor an orphan afterglow. For off-axis observers, the observable jet break can be delayed up to several weeks, potentially leading to overestimation of the beaming-corrected total energy. In addition we find that, when using our off-axis light curves to create synthetic Swift X-ray data, jet breaks are likely to remain hidden in the data.

Van Eerten, Hendrik; Zhang Weiqun; MacFadyen, Andrew [Center for Cosmology and Particle Physics, Physics Department, New York University, New York, NY 10003 (United States)

2010-10-10

195

Electron accelerations at high Mach number collisionless shocks are investigated by means of two-dimensional electromagnetic particle-in-cell simulations with various Alfven Mach numbers, ion-to-electron mass ratios, and the upstream electron {beta}{sub e} (the ratio of the thermal pressure to the magnetic pressure). We find electrons are effectively accelerated at a super-high Mach number shock (M{sub A} {approx} 30) with a mass ratio of M/m = 100 and {beta}{sub e} = 0.5. The electron shock surfing acceleration is an effective mechanism for accelerating the particles toward the relativistic regime even in two dimensions with a large mass ratio. Buneman instability excited at the leading edge of the foot in the super-high Mach number shock results in a coherent electrostatic potential structure. While multi-dimensionality allows the electrons to escape from the trapping region, they can interact with the strong electrostatic field several times. Simulation runs in various parameter regimes indicate that the electron shock surfing acceleration is an effective mechanism for producing relativistic particles in extremely high Mach number shocks in supernova remnants, provided that the upstream electron temperature is reasonably low.

Matsumoto, Yosuke [Department of Physics, Chiba University, Yayoi-cho 1-33, Inage-ku, Chiba 263-8522 (Japan); Amano, Takanobu; Hoshino, Masahiro, E-mail: ymatumot@astro.s.chiba-u.ac.jp [Department of Earth and Planetary Science, University of Tokyo, Hongo 1-33, Bunkyo-ku, Tokyo 113-0033 (Japan)

2012-08-20

196

NASA Astrophysics Data System (ADS)

We present computer simulation study of two-dimensional infrared spectroscopy (2D-IR) of water confined in reverse micelles (RMs) of various sizes. The present study is motivated by the need to understand the altered dynamics of confined water by performing layerwise decomposition of water, with an aim to quantify the relative contributions of different layers water molecules to the calculated 2D-IR spectrum. The 0-1 transition spectra clearly show substantial elongation, due to inhomogeneous broadening and incomplete spectral diffusion, along the diagonal in the surface water layer of different sized RMs. Fitting of the frequency fluctuation correlation functions reveal that the motion of the surface water molecules is sub-diffusive and indicate the constrained nature of their dynamics. This is further supported by two peak nature of the angular analogue of van Hove correlation function. With increasing system size, the water molecules become more diffusive in nature and spectral diffusion almost completes in the central layer of the larger size RMs. Comparisons between experiments and simulations establish the correspondence between the spectral decomposition available in experiments with the spatial decomposition available in simulations. Simulations also allow a quantitative exploration of the relative role of water, sodium ions, and sulfonate head groups in vibrational dephasing. Interestingly, the negative cross correlation between force on oxygen and hydrogen of O-H bond in bulk water significantly decreases in the surface layer of each RM. This negative cross correlation gradually increases in the central water pool with increasing RMs size and this is found to be partly responsible for the faster relaxation rate of water in the central pool.

Biswas, Rajib; Furtado, Jonathan; Bagchi, Biman

2013-10-01

197

The presence of long-range quantum spin correlations underlies a variety of physical phenomena in condensed-matter systems, potentially including high-temperature superconductivity. However, many properties of exotic, strongly correlated spin systems, such as spin liquids, have proved difficult to study, in part because calculations involving N-body entanglement become intractable for as few as N???30 particles. Feynman predicted that a quantum simulator--a special-purpose 'analogue' processor built using quantum bits (qubits)--would be inherently suited to solving such problems. In the context of quantum magnetism, a number of experiments have demonstrated the feasibility of this approach, but simulations allowing controlled, tunable interactions between spins localized on two- or three-dimensional lattices of more than a few tens of qubits have yet to be demonstrated, in part because of the technical challenge of realizing large-scale qubit arrays. Here we demonstrate a variable-range Ising-type spin-spin interaction, J(i,j), on a naturally occurring, two-dimensional triangular crystal lattice of hundreds of spin-half particles (beryllium ions stored in a Penning trap). This is a computationally relevant scale more than an order of magnitude larger than previous experiments. We show that a spin-dependent optical dipole force can produce an antiferromagnetic interaction J(i,j) proportional variant d(-a)(i,j), where 0???a???3 and d(i,j) is the distance between spin pairs. These power laws correspond physically to infinite-range (a = 0), Coulomb-like (a = 1), monopole-dipole (a = 2) and dipole-dipole (a = 3) couplings. Experimentally, we demonstrate excellent agreement with a theory for 0.05???a???1.4. This demonstration, coupled with the high spin count, excellent quantum control and low technical complexity of the Penning trap, brings within reach the simulation of otherwise computationally intractable problems in quantum magnetism. PMID:22538611

Britton, Joseph W; Sawyer, Brian C; Keith, Adam C; Wang, C-C Joseph; Freericks, James K; Uys, Hermann; Biercuk, Michael J; Bollinger, John J

2012-04-26

198

We have developed a coupled two-dimensional dynamical/chemical/microphysical model to study the global distribution of stratospheric sulfate aerosols. We use this model to simulate the global distribution of volcanic aerosols after the eruption of El Chichon in Mexico in April 1982. The simulated background aerosol distribution are highly dispersed, while a slight latitudinal gradient is also noticed. The calculated background aerosol surface area and mass are about 0.7 to 1.0 sq microns/cu cm and 0.3 to 0.5 parts per billion by mass, respectively, at midlatitude in the northern hemisphere, in fair agreement with available observations. After the eruption of El Chichon in April 1982, the stratospheric aerosol load rapidly increases in the tropics at an altitude of 20 to 25 km. The aerosol area in the tropics reaches a maximum 50 sq microns/ cu cm in the lower stratosphere, which is about 70-100 times the background aerosol area. Six months after the eruption, volcanic aerosols spread out globally but are still centered in the tropics. One year after the eruption the enhanced aerosol begins to decrease and tends to become uniformly distributed in the lower stratosphere. Two years after the eruption the global aerosol is about 5 times the background aerosol load in the lower stratosphere. The e-folding time of the aerosol load is about 10 months in the tropics during the postvolcanic period. Compared to observations (in terms of spatial, temporal, and size distributions), the model quantitatively simulates the evolution of volcanic aerosol clouds. Thus this model could be a useful tool for studying the impacts of volcanic eruptions on stratospheric ozone and climate.

Tie, X.; Lin, X.; Brasseur, G. [National Center for Atmospheric Research, Boulder, CO (United States)]|[Environmental Research Laboratory, NOAA, Boulder, CO (United States)

1994-08-01

199

FireStem2D - A Two-Dimensional Heat Transfer Model for Simulating Tree Stem Injury in Fires

FireStem2D, a software tool for predicting tree stem heating and injury in forest fires, is a physically-based, two-dimensional model of stem thermodynamics that results from heating at the bark surface. It builds on an earlier one-dimensional model (FireStem) and provides improved capabilities for predicting fire-induced mortality and injury before a fire occurs by resolving stem moisture loss, temperatures through the stem, degree of bark charring, and necrotic depth around the stem. We present the results of numerical parameterization and model evaluation experiments for FireStem2D that simulate laboratory stem-heating experiments of 52 tree sections from 25 trees. We also conducted a set of virtual sensitivity analysis experiments to test the effects of unevenness of heating around the stem and with aboveground height using data from two studies: a low-intensity surface fire and a more intense crown fire. The model allows for improved understanding and prediction of the effects of wildland fire on injury and mortality of trees of different species and sizes. PMID:23894599

Chatziefstratiou, Efthalia K.; Bohrer, Gil; Bova, Anthony S.; Subramanian, Ravishankar; Frasson, Renato P. M.; Scherzer, Amy; Butler, Bret W.; Dickinson, Matthew B.

2013-01-01

200

Human Papillomavirus (HPV) has been known as one of the cause of virus-induced cancer such as cervical cancer and carcinoma. Among other types of cancer, this type has higher chance in being prevented earlier. The main idea is to eradicate the virus as soon as it enters the body by marking it with antibodies; signaling the immune system to dispose of it. However, the antibodies must be trained to recognize the virus. They can be trained by inserting an object similar to the virus allowing them to learn to recognize and surround the inserted object. In response to this, molecular dynamics simulation was chosen to study the antibody-virus interaction. In this work, two-dimensional case that involves HPV and immunoglobulin (Ig) was studied and observed. Two types of objects will be defined; one stands for HPV while another stands for antibodies. The interaction between the two objects will be governed by two forces; Coulomb force and repulsive contact force. Through the definition of some rules and condition, th...

Haris, Luman; Khotimah, Siti Nurul; Haryanto, Freddy; Viridi, Sparisoma

2013-01-01

201

of the Gyrokinetic PIC Code for MHD Simulation* Hiroshi Naitou1 , Kenichi Kobayashi1 , Hiroki Hashimoto1 , Takehisa, a new algorithm is proposed1 for the gyrokinetic PIC (Particle-In-Cell) code for MHD simulation (GpicMHD2 ). GpicMHD was developed to study global and kinetic MHD phenomena in tokamaks. In the new

Ito, Atsushi

202

NASA Technical Reports Server (NTRS)

Over the southern California coastal region, observations of the vertical distributions of pollutants show that maximum concentrations can occur within temperature inversion layers well above the surface. A mesoscale model is used to study the dynamical phenomena that cause such layers, including sea breezes and mountain flows, and to study the characteristics of air pollutant transport in a coastal environment capped by a temperature inversion. The mathematical and physical structure of the model is described. Two-dimensional simulations corresponding to four configurations of coastal plains and mountains are discussed. The simulations reveal that pollutant transport over a coastal plain is strongly influenced by the topographic configuration, including the height of coastal mountains and their distance from the coastline. Sea breezes induced by land-sea thermal contrasts, as well as upslope winds induced along mountain flanks, both create vertical transport that can lead to the formation of elevated pollution layers. The sea-breeze circulation generates pollution layers by undercutting the mixed layer and lofting pollutants into the stable layer. Heating of mountain slopes acts to vent pollutants above the mountain ridge during the day; during the evening, pollutants can be injected directly into the inversion layer from the decaying upslope flows. In a land-sea configuration with mountains close to the coastline, the sea breeze and heated-mountain flow are strongly coupled. In the afternoon, this interaction can produce upslope flow from which polluted air is detrained into the inversion layer as a return circulation. When the mountains lie farther inland, however, pollutants may be trapped aloft when the mixed layer stabilizes in the late afternoon. As the nocturnal boundary layer forms over the coast in the evening, polluted mixed-layer air is effectively left behind in the inversion layer. In the Los Angeles Basin, the formation mechanism for elevated polluted layers is most similar to our cases with inland mountains.

Lu, Rong; Turco, Richard P.

1994-01-01

203

NASA Technical Reports Server (NTRS)

We have developed a new empirically-based transport algorithm for use in our GSFC two-dimensional transport and chemistry assessment model. The new algorithm contains planetary wave statistics, and parameterizations to account for the effects due to gravity waves and equatorial Kelvin waves. We will present an overview of the new algorithm, and show various model-data comparisons of long-lived tracers as part of the model validation. We will also show how the new algorithm gives substantially better agreement with observations compared to our previous model transport. The new model captures much of the qualitative structure and seasonal variability observed methane, water vapor, and total ozone. These include: isolation of the tropics and winter polar vortex, the well mixed surf-zone region of the winter sub-tropics and mid-latitudes, and the propagation of seasonal signals in the tropical lower stratosphere. Model simulations of carbon-14 and strontium-90 compare fairly well with observations in reproducing the peak in mixing ratio at 20-25 km, and the decrease with altitude in mixing ratio above 25 km. We also ran time dependent simulations of SF6 from which the model mean age of air values were derived. The oldest air (5.5 to 6 years) occurred in the high latitude upper stratosphere during fall and early winter of both hemispheres, and in the southern hemisphere lower stratosphere during late winter and early spring. The latitudinal gradient of the mean ages also compare well with ER-2 aircraft observations in the lower stratosphere.

Fleming, Eric L.; Jackman, Charles H.; Stolarski, Richard S.; Considine, David B.

1998-01-01

204

Kinetic MHD simulation of large &'circ; tearing mode instability

NASA Astrophysics Data System (ADS)

We have developed a second-order accurate semi-implicit ?f method for kinetic MHD simulation with Lorentz force ion and fluid electron. The model has been implemented in GEM code and benchmarked on Alfvén waves, ion sound waves and whistler waves against analytical dispersion relation in a uniform plasma. We have also studied the resistive tearing mode instability by adding a resistive term in the generalized Ohm's law using the Harris sheet equilibrium. For small &'circ;, the linear growth rate and eigenmode structure are comparable with resistive MHD analysis. The Rutherford stage and saturation are demonstrated, though the simulation exhibits different behaviors than previous MHD simulations. For large &'circ;, the tearing mode develops multiple islands in the nonlinear regime and the islands start to coalesce later on. The competition between the two processes strongly influences the reconnection rates and eventually leads the reconnection to a steady state. We will identify the role played by particle ions in the process using detailed ion diagnostics.

Cheng, Jianhua; Chen, Yang; Parker, Scott; Uzdensky, Dmitri

2011-11-01

205

On the possibility of using an electromagnetic ionosphere in global MHD simulations

On the possibility of using an electromagnetic ionosphere in global MHD simulations P. Janhunen magnetohydrodynamic (MHD) simu- lations of the Earth's magnetosphere must be coupled with a dynamical ionospheric) from the magnetospheric MHD variables at the ionospheric boundary. The ionospheric potential is solved

Paris-Sud XI, UniversitÃ© de

206

We present the detailed global structure of black hole accretion flows and outflows through newly performed two-dimensional radiation-magnetohydrodynamic simulations. By starting from a torus threaded with weak toroidal magnetic fields and by controlling the central density of the initial torus, {rho}{sub 0}, we can reproduce three distinct modes of accretion flow. In model A, which has the highest central density, an optically and geometrically thick supercritical accretion disk is created. The radiation force greatly exceeds the gravity above the disk surface, thereby driving a strong outflow (or jet). Because of mild beaming, the apparent (isotropic) photon luminosity is {approx}22L{sub E} (where L{sub E} is the Eddington luminosity) in the face-on view. Even higher apparent luminosity is feasible if we increase the flow density. In model B, which has moderate density, radiative cooling of the accretion flow is so efficient that a standard-type, cold, and geometrically thin disk is formed at radii greater than {approx}7 R{sub S} (where R{sub S} is the Schwarzschild radius), while the flow is radiatively inefficient otherwise. The magnetic-pressure-driven disk wind appears in this model. In model C, the density is too low for the flow to be radiatively efficient. The flow thus becomes radiatively inefficient accretion flow, which is geometrically thick and optically thin. The magnetic-pressure force, together with the gas-pressure force, drives outflows from the disk surface, and the flow releases its energy via jets rather than via radiation. Observational implications are briefly discussed.

Ohsuga, Ken [National Astronomical Observatory of Japan, Osawa, Mitaka, Tokyo 181-8588 (Japan); Mineshige, Shin [Department of Astronomy, Graduate School of Science, Kyoto University, Kyoto 606-8502 (Japan)

2011-07-20

207

Experimental investigations indicate that colloidal particles are transported more rapidly than soluble tracers through porous and fractured media. The prevailing in- terpretation is that colloids are confined to larger pores, larger channels or regions within channels where flow is more rapid. A lattice-Boltzmann modeling approach was used to analyze how size-dependent exclusion from low velocity fields in chan- nels can lead to accelerated transport of an inert non-Brownian colloidal particle in low-Reynolds number flows in two-dimensional smooth-walled and rough-walled channels. The simulations were based on pore-scale particle-fluid hydrodynamics without direct interactions between the particle surface and the channel surface. For the smooth-walled channel, the particle consistently drifted towards the center- line and traveled faster than the average fluid velocity. In rough-walled channels, differences between the velocity of the particle and the average velocity of the fluid displayed stronger variations than in the smooth-walled channel. Surface roughness increased the residence time of the particle in the flow channel and modified its trajectories differently in each flow regime. The final position (at the channel exit) and the average velocity of the particle in the rough-walled flow channel were sen- sitive to the release location of the particle, the flow strength, and the magnitude of the surface roughness in the channel. Under all flow conditions investigated, a large particle had a longer residence time in rough-walled flow channels, but drifted Preprint submitted to Elsevier Science 19 September 2006 toward the centerline more strongly than a smaller particle as it approached the channel walls.

H. Basagaoglu; Meakin, P.; S. Succi; Redden, George D; T.R. Ginn

2008-05-01

208

A grid resolution sensitivity analysis using a two-dimensional flood inundation model has been presented in this paper. Simulations for 6 dam breaches located randomly in the United States were run at 10,30,60,90, and 120 meter resolutions. The dams represent a range of topographic conditions, ranging from 0% slope to 1.5% downstream of the dam. Using 10 meter digital elevation model (DEM) simulation results as the baseline, the coarser simulation results were compared in terms of flood inundation area, peak depths, flood wave travel time, daytime and nighttime population in flooded area, and economic impacts. The results of the study were consistent with previous grid resolution studies in terms of inundated area, depths, and velocity impacts. The results showed that as grid resolution is decreased, the relative fit of inundated area between the baseline and coarser resolution decreased slightly. This is further characterized by increasing over prediction as well as increasing under prediction with decreasing resolution. Comparison of average peak depths showed that depths generally decreased as resolution decreased, as well as the velocity. It is, however, noted that the trends in depth and velocity showed less consistency than the inundation area metrics. This may indicate that for studies in which velocity and depths must be resolved more accurately (urban environments when flow around buildings is important in the calculation of drag effects), higher resolution DEM data should be used. Perhaps the most significant finding from this study is the perceived insensitivity of socio-economic impacts to grid resolution. The difference in population at risk (PAR) and economic cost generally remained within 10% of the estimated impacts using the high resolution DEM. This insensitivity has been attributed to over estimated flood area and associated socio-economic impacts compensating for under estimated flooded area and associated socio-economic impacts. The United States has many dams that are classified as high-hazard potential that need an emergency action plan (EAP). It has been found that the development of EAPs for all high-hazard dams is handicapped due to funding limitations. The majority of the cost associated with developing an EAP is determining the flooded area. The results of this study have shown that coarse resolution dam breach studies can be used to provide an acceptable estimate of the inundated area and economic impacts, with very little computational cost. Therefore, the solution to limited funding may be to perform coarse resolution dam breach studies on high-hazard potential dams and use the results to help prioritize the order in which detailed EAPs should be developed.

Judi, David R [Los Alamos National Laboratory; Mcpherson, Timothy N [Los Alamos National Laboratory; Burian, Steven J [UNIV OF UTAH

2009-01-01

209

Simulations of MHD flows with moving interfaces

We report on the numerical simulation of a two-fluid magnetohydrodynamics problem arising in the industrial production of aluminium. The motion of the two non-miscible fluids is modeled through the incompressible Navier–Stokes equations coupled with the Maxwell equations. Stabilized finite elements techniques and an arbitrary Lagrangian–Eulerian formulation (for the motion of the interface separating the two fluids) are used in the

J.-F. Gerbeau; T. Lelièvre; C. Le Bris

2003-01-01

210

MHD simulations of Earth`s bow shock at low Mach numbers: Standoff distances

Global, three-dimensional, ideal MHD simulations of Earth`s bow shock are reported for low Alfven Mach numbers M{sub A} and quasi-perpendicular magnetic field orientations. The simulations use a hard, infinitely conducting magnetopause obstacle, with axisymmetric three-dimensional location given be a scaled standard model, to directly address previous gasdynamic (GD) and field-aligned MHD (FA-MHD) work. Tests of the simulated shocks` density jumps

Iver H. Cairns; J. G. Lyon

1995-01-01

211

NASA Astrophysics Data System (ADS)

A generalized energy transport (G-ET) model is introduced. This model incorporates the effects of non -analytic carrier distribution functions and the dominant scattering process on the formulation of the energy transport model, also includes effects of the electron transfer between the lower valley occurs in multivalley semi-conductors. A path-integration and slope-weighting Monte Carlo (PSMC) method is introduced to speed up the conventional MC method, and to improve its accuracy and smoothness. A stable extended S-G discretization algorithm was developed for the G-ET model. Further, many numerical techniques, including methods of mesh auto generation, updating and scaling, trial solution with 2D extrapolation, a global convergence test, a convergence refining, a forced -damping and residual-current filtering, were developed to improve the convergence and the computation efficiency. UMDFET2, a general submicron device simulator, was implemented with G-ET model, an efficient hot electron injection model, a Fowler-Nordheim tunneling model, an impact ionization model, and a model for band-to-band tunneling have also been added. A discretized gate capacitor (DGC) EPROM model and post-processing quasi-transient (PPQT) method has been introduced to efficiently and accurately simulate EPROM devices. Deep submicron NMOS devices have been simulated to study velocity overshoot and hot electron effects. UMDFET2 has been successfully used to predict the V_{t}, I_{ds}, I_{sub}, I_{g}, the programming and erasing characteristics V_ {t}(t) of submicron EPROM/Flash devices. A "Virtual Fab", which consists of statistics analysis tool for experimental design and data analysis, SUPREM3/4 for process simulation, and UMDFET2 for device simulation, has been used successfully for EPROM device design and optimization, and has demonstrated a good predicting ability with excellent overall accuracy. The correlation of the ET models and MC models has been studied, and it has been found that the Soret effect (dT_{e}/dx) causes a fundamental discrepancy between the ET model which includes this term, and the Monte Carlo model which uses only electrical field as a driving force, does not include the carrier -carrier scattering. Consistency between the generalized ET model and the MC model can be assumed by including the Soret effect as an additional driving force in the MC calculation.

Peng, Zezhong

1992-01-01

212

MHD simulations of boundary layer formation along the dayside Venus ionopause due to mass loading

NASA Astrophysics Data System (ADS)

A two-dimensional magnetohydrodynamic (MHD) simulation of mass-loaded solar wind flow around the dayside of Venus is presented. For conditions appropriate to a low-altitude ionopause the simulations show that mass loading from the pickup of oxygen ions produces a boundary layer of finite thickness along the ionopause. Within this layer the temperatures exhibit strong gradients normal to and away from the ionopause. Furthermore, there is a shear in the bulk flow velocity across the boundary layer, such that the (predominantly tangential) flow decreases in speed as the ionopause is approached and remains small along the ionopause, consistent with Pioneer Venus observations. The total mass density increases significantly as the flow approaches the ionopause, where the contribution of O(+) to the total number density is a few percent. Numerical simulations are carried out for various mass addition rates and demonstrate that the boundary layer develops when oxygen ion production exceeds approximately 2 x 105/cu m/s. For the upstream solar wind parameters and mass loading rates chosen for these simulations, the results are consistent with observations made on the dayside of Venus for average ionopause conditions near 300 km.

McGary, J. E.; Pontius, D. H.

1994-02-01

213

A nite volume ideal Numerical simulations of MHD ows with shocks have been performed

Chapter 4 A #12;nite volume ideal MHD code Numerical simulations of MHD ows with shocks have been for Computational Fluid Dynamics (CFD) simulations. Only since a decade or so, these new numerical methods have been of the basic concepts of numerical simulation of ow problems with shocks, we give a brief but complete

De Sterck, Hans

214

Plasmoid dynamics in 3D resistive MHD simulations of magnetic reconnection

NASA Astrophysics Data System (ADS)

Magnetic reconnection is a well known plasma process believed to lie at the heart of a variety of phenomena such as sub-storms in the Earth's magnetosphere, solar/stellar and accretion-disk flares, sawteeth activity in fusion devices, etc. During reconnection, the global magnetic field topology changes rapidly, leading to the violent release of magnetic energy. Over the past few years, the basic understanding of this fundamental process has undergone profound changes. The validity of the most basic, and widely accepted, reconnection paradigm - the famous Sweet-Parker (SP) model, which predicts that, in MHD, reconnection is extremely slow, its rate scaling as S-1/2, where S is the Lundquist number of the system - has been called into question as it was analytically demonstrated that, for S ? 1, SP-like current sheets are violently unstable to the formation of a large number of secondary islands, or plasmoids. Subsequent numerical simulations in 2D have confirmed the validity of the linear theory, and shown that plasmoids quickly grow to become wider than the thickness of the original SP current sheet, thus effectively changing the underlying reconnection geometry. Ensuing numerical work has revealed that the process of plasmoid formation, coalescence and ejection from the sheet drastically modifies the steady state picture assumed by Sweet and Parker, and leads to the unexpected result that MHD reconnection is independent of S. In this talk, we review these recent developments and present results from three-dimensional simulations of high-Lundquist number reconnection in the presence of a guide field. A parametric study varying the strength of the guide field is presented. Plasmoid flux and width distribution functions are quantified and compared with corresponding two dimensional simulations.

Samtaney, R.; Loureiro, N. F.; Uzdensky, D. A.; Schekochihin, A. A.

2012-04-01

215

3D Solar Null Point Reconnection MHD Simulations

Numerical MHD simulations of 3D reconnection events in the solar corona have improved enormously over the last few years, not only in resolution, but also in their complexity, enabling more and more realistic modeling. Various ways to obtain the initial magnetic field, different forms of solar atmospheric models as well as diverse driving speeds and patterns have been employed. This study considers differences between simulations with stratified and non-stratified solar atmospheres, addresses the influence of the driving speed on the plasma flow and energetics, and provides quantitative formulae for mapping electric fields and dissipation levels obtained in numerical simulations to the corresponding solar quantities. The simulations start out from a potential magnetic field containing a null-point, obtained from a Solar and Heliospheric Observatory (SOHO) magnetogram extrapolation approximately 8 hours before a C-class flare was observed. The magnetic field is stressed with a boundary motion pattern similar t...

Baumann, G; Nordlund, Å

2012-01-01

216

Relativistic MHD simulations of stellar core collapse and magnetars

NASA Astrophysics Data System (ADS)

We present results from simulations of magneto-rotational stellar core collapse along with Alfvén oscillations in magnetars. These simulations are performed with the CoCoA/CoCoNuT code, which is able to handle ideal MHD flows in dynamical spacetimes in general relativity. Our core collapse simulations highlight the importance of genuine magnetic effects, like the magneto-rotational instability, for the dynamics of the flow. For the modelling of magnetars we use the anelastic approximation to general relativistic MHD, which allows for an effective suppression of fluid modes and an accurate description of Alfvén waves. We further compute Alfvén oscillation frequencies along individual magnetic field lines with a semi-analytic approach. Our work confirms previous results based on perturbative approaches regarding the existence of two families of quasi-periodic oscillations (QPOs), with harmonics at integer multiples of the fundamental frequency. Additional material is presented in the accompanying contribution by Gabler et al (2010b) in these proceedings.

Font, José A.; Cerdá-Durán, Pablo; Gabler, Michael; Müller, Ewald; Stergioulas, Nikolaos

2011-02-01

217

NASA Technical Reports Server (NTRS)

Finite element modeling alternatives as well as the utility and limitations of the two dimensional structural response computer code CIVM-JET 4B for predicting the transient, large deflection, elastic plastic, structural responses of two dimensional beam and/or ring structures which are subjected to rigid fragment impact were investigated. The applicability of the CIVM-JET 4B analysis and code for the prediction of steel containment ring response to impact by complex deformable fragments from a trihub burst of a T58 turbine rotor was studied. Dimensional analysis considerations were used in a parametric examination of data from engine rotor burst containment experiments and data from sphere beam impact experiments. The use of the CIVM-JET 4B computer code for making parametric structural response studies on both fragment-containment structure and fragment-deflector structure was illustrated. Modifications to the analysis/computation procedure were developed to alleviate restrictions.

Stagliano, T. R.; Witmer, E. A.; Rodal, J. J. A.

1979-01-01

218

In cooperation with the Missouri Department of Transportation, the U.S. Geological Survey determined hydrologic and hydraulic parameters for the Gasconade River at the site of a proposed bridge replacement and highway realignment of State Highway 17 near Waynesville, Missouri. Information from a discontinued streamflow-gaging station on the Gasconade River near Waynesville was used to determine streamflow statistics for analysis of the 25-, 50-, 100-, and 500-year floods at the site. Analysis of the streamflow-gaging stations on the Gasconade River upstream and downstream from Waynesville indicate that flood peaks attenuate between the upstream gaging station near Hazelgreen and the Waynesville gaging station, such that the peak discharge observed on the Gasconade River near Waynesville will be equal to or only slightly greater (7 percent or less) than that observed near Hazelgreen. A flood event occurred on the Gasconade River in March 2008, and a flood measurement was obtained near the peak at State Highway 17. The elevation of high-water marks from that event indicated it was the highest measured flood on record with a measured discharge of 95,400 cubic feet per second, and a water-surface elevation of 766.18 feet near the location of the Waynesville gaging station. The measurements obtained for the March flood resulted in a shift of the original stage-discharge relation for the Waynesville gaging station, and the streamflow statistics were modified based on the new data. A two-dimensional hydrodynamic flow model was used to simulate flow conditions on the Gasconade River in the vicinity of State Highway 17. A model was developed that represents existing (2008) conditions on State Highway 17 (the 'model of existing conditions'), and was calibrated to the floods of March 20, 2008, December 4, 1982, and April 14, 1945. Modifications were made to the model of existing conditions to create a model that represents conditions along the same reach of the Gasconade River with preliminary proposed replacement bridges and realignment of State Highway 17 (the 'model of proposed conditions'). The models of existing and proposed conditions were used to simulate the 25-, 50-, 100-, and 500-year recurrence floods, as well as the March 20, 2008 flood. Results from the model of proposed conditions show that the proposed replacement structures and realignment of State Highway 17 will result in additional backwater upstream from State Highway 17 ranging from approximately 0.18 foot for the 25-year flood to 0.32 foot for the 500-year flood. Velocity magnitudes in the proposed overflow structures were greater than in the existing structures [by as much as 4.9 feet per second in the left (west) overflow structure for the 500-year flood], and shallow, high-velocity flow occurs at the upstream edges of the abutments of the proposed overflow structures in the 100- and 500-year floods where flow overtops parts of the existing road embankment that will be left in place in the proposed scenario. Velocity magnitude in the main channel of the model of proposed conditions increased by a maximum of 1.2 feet per second over the model of existing conditions, with the maximum occurring approximately 1,500 feet downstream from existing main channel structure J-802.

Huizinga, Richard J.

2008-01-01

219

Global MHD Simulation of Mesoscale Structures at the Magnetospheric Boundary

NASA Technical Reports Server (NTRS)

The research carried out for this protocol was focused on the study of mesoscales structures at the magnetospheric boundary. We investigated three areas: (1) the structure of the magnetospheric boundary for steady solar wind conditions; (2) the dynamics of the dayside magnetospheric boundary and (3) the dynamics of the distant tail magnetospheric boundary. Our approach was to use high resolution three-dimensional global magnetohydrodynamic (MHD) simulations of the interaction of the solar wind with the Earth's magnetosphere. We first considered simple variations of the interplanetary conditions to obtain generic cases that helped us in establishing the basic cause and effect relationships for steady solar wind conditions. Subsequently, we used actual solar wind plasma and magnetic field parameters measured by an upstream spacecraft as input to the simulations and compared the simulation results with sequences of events observed by another or several other spacecraft located downstream the bow shock. In particular we compared results with observations made when spacecraft crossed the magnetospheric boundary.

Berchem, Jean

1998-01-01

220

Understanding Accretion Disks through Three Dimensional Radiation MHD Simulations

NASA Astrophysics Data System (ADS)

I study the structures and thermal properties of black hole accretion disks in the radiation pressure dominated regime. Angular momentum transfer in the disk is provided by the turbulence generated by the magneto-rotational instability (MRI), which is calculated self-consistently with a recently developed 3D radiation magneto-hydrodynamics (MHD) code based on Athena. This code, developed by my collaborators and myself, couples both the radiation momentum and energy source terms with the ideal MHD equations by modifying the standard Godunov method to handle the stiff radiation source terms. We solve the two momentum equations of the radiation transfer equations with a variable Eddington tensor (VET), which is calculated with a time independent short characteristic module. This code is well tested and accurate in both optically thin and optically thick regimes. It is also accurate for both radiation pressure and gas pressure dominated flows. With this code, I find that when photon viscosity becomes significant, the ratio between Maxwell stress and Reynolds stress from the MRI turbulence can increase significantly with radiation pressure. The thermal instability of the radiation pressure dominated disk is then studied with vertically stratified shearing box simulations. Unlike the previous results claiming that the radiation pressure dominated disk with MRI turbulence can reach a steady state without showing any unstable behavior, I find that the radiation pressure dominated disks always either collapse or expand until we have to stop the simulations. During the thermal runaway, the heating and cooling rates from the simulations are consistent with the general criterion of thermal instability. However, details of the thermal runaway are different from the predictions of the standard alpha disk model, as many assumptions in that model are not satisfied in the simulations. We also identify the key reasons why previous simulations do not find the instability. The thermal instability has many important implications for understanding the observations of both X-ray binaries and Active Galactic Nuclei (AGNs). However, direct comparisons between observations and the simulations require global radiation MHD simulations, which will be the main focus of my future work.

Jiang, Yan-Fei

221

Thermodynamic MHD Simulation of the Bastille Day Event

NASA Astrophysics Data System (ADS)

The "Bastille Day" event on July 14, 2000 is one of the most extensively studied solar eruptions. It originated in a complex active region close to disk center and produced an X5.7 flare, a fast halo CME, and an intense geomagnetic storm. We have recently begun to model this challenging event, with the final goal to simulate its whole evolution, from the pre-eruptive state to the CME's arrival at 1 AU. To this end, we first produce a steady-state MHD solution of the background corona that incorporates realistic energy transport ("thermodynamic MHD"), photospheric magnetic field measurements, and the solar wind. In order to model the pre-eruptive magnetic field, we then insert into this solution a stable, elongated flux rope that resides above the highly curved polarity inversion line of the active region. Finally, we produce an eruption by imposing photospheric flows that slowly converge towards the polarity inversion line. In this presentation we describe our method, compare the simulation results with the observations, and discuss the challenges and limitations involved in modeling such complex and powerful eruptions.

Torok, Tibor; Downs, Cooper; Lionello, Roberto; Linker, Jon A.; Mikic, Zoran; Titov, Viacheslav S.; Riley, Pete

2014-05-01

222

Multi-dimensional computer simulation of MHD combustor hydrodynamics

NASA Astrophysics Data System (ADS)

Argonne National Laboratory is investigating the nonreacting jet gas mixing patterns in an MHD second stage combustor by using a 2-D multiphase hydrodynamics computer program and a 3-D single phase hydrodynamics computer program. The computer simulations are intended to enhance the understanding of flow and mixing patterns in the combustor, which in turn may lead to improvement of the downstream MHD channel performance. A 2-D steady state computer model, based on mass and momentum conservation laws for multiple gas species, is used to simulate the hydrodynamics of the combustor in which a jet of oxidizer is injected into an unconfined cross stream gas flow. A 3-D code is used to examine the effects of the side walls and the distributed jet flows on the non-reacting jet gas mixing patterns. The code solves the conservation equations of mass, momentum, and energy, and a transport equation of a turbulence parameter and allows permeable surfaces to be specified for any computational cell.

Berry, G. F.; Chang, S. L.; Lottes, S. A.; Rimkus, W. A.

1991-04-01

223

Numerical simulations exhibiting backscattering enhancement of electromagnetic waves from two-dimensional dielectric random rough surfaces (three-dimensional scattering problem) are presented. The StrattonChu surface integral equation formulation is used with the method of moments to solve for the tangential and normal components of surface fields. The solution of the matrix equation is calculated efficiently by using the sparse-matrix canonical grid (SMCG) method.

Kyung Pak; Leung Tsang; Joel Johnson

1997-01-01

224

An Eulerian\\/Lagrangian-type numerical simulation was performed on a two-dimensional fluidized bed in which the particle motion is restricted by parallel front and rear walls. Particle motion was calculated using Newton's equation of motion, and the contact forces were modeled by the discrete element method. The locally averaged equations were solved to calculate the fluid motion, taking into account the interaction

T. Kawaguchi; T. Tanaka; Y. Tsuji

1998-01-01

225

Two-dimensional simulation of large-area InGaAs/InP p-i-n photodiodes

A stationary physical model of the p-i-n photodiode based on a two-dimensional drift-diffusion scheme of charge transport in multilayer In{sub x}Ga{sub 1-x}As{sub y}P{sub 1-y}/InP heterostructures is developed. The model takes into account the Fermi statistics for electrons and holes, charge carrier mobility dependence on the electric field and impurity concentration, as well as thermionic emission and tunneling at the heterointerfaces. The effect of design parameters on the characteristics of large area p-i-n photodiodes is analyzed and methods for increasing their dynamic range are suggested.

Malyshev, S. A., E-mail: malyshev@ieee.org; Chizh, A. L., E-mail: chizh@ieee.org; Vasileuski, Yu. G. [National Academy of Sciences of Belarus, Institute of Electronics (Belarus)], E-mail: vasileuski@ieee.org

2006-09-15

226

A self-consistent approach is proposed to determine the temperature dependent thermal conductivity k(T) of fused silica, for a range of temperatures up to material evaporation using a CO{sub 2} laser irradiation. Calculation of the temperature of silica using a two-dimensional axi-symmetric code was linked step by step as the laser power was increased with experimental measurements using infrared thermography. We show that previously reported k(T) does not reproduce the temporal profile as well as our adaptive fit which shows that k(T) evolves with slope discontinuities at the annealing temperature and the softening temperature.

Combis, Patrick [CEA DAM Ile-de-France, F-91297 ARPAJON (France); Cormont, Philippe; Hebert, David; Robin, Lucile; Rullier, Jean-Luc [CEA CESTA, F-33114 LE BARP (France); Gallais, Laurent [Institut Fresnel, CNRS, Aix-Marseille Universite, Ecole Centrale Marseille, 13013 Marseille (France)

2012-11-19

227

NASA Technical Reports Server (NTRS)

When analyzing data from an array of spacecraft (such as Cluster or MMS) crossing a site of magnetic reconnection, it is desirable to be able to accurately determine the orientation of the reconnection site. If the reconnection is quasi-two dimensional, there are three key directions, the direction of maximum inhomogeneity (the direction across the reconnection site), the direction of the reconnecting component of the magnetic field, and the direction of rough invariance (the "out of plane" direction). Using simulated spacecraft observations of magnetic reconnection in the geomagnetic tail, we extend our previous tests of the direction-finding method developed by Shi et al. (2005) and the method to determine the structure velocity relative to the spacecraft Vstr. These methods require data from four proximate spacecraft. We add artificial noise and calibration errors to the simulation fields, and then use the perturbed gradient of the magnetic field B and perturbed time derivative dB/dt, as described by Denton et al. (2010). Three new simulations are examined: a weakly three-dimensional, i.e., quasi-two-dimensional, MHD simulation without a guide field, a quasi-two-dimensional MHD simulation with a guide field, and a two-dimensional full dynamics kinetic simulation with inherent noise so that the apparent minimum gradient was not exactly zero, even without added artificial errors. We also examined variations of the spacecraft trajectory for the kinetic simulation. The accuracy of the directions found varied depending on the simulation and spacecraft trajectory, but all the directions could be found within about 10 for all cases. Various aspects of the method were examined, including how to choose averaging intervals and the best intervals for determining the directions and velocity. For the kinetic simulation, we also investigated in detail how the errors in the inferred gradient directions from the unmodified Shi et al. method (using the unperturbed gradient) depended on the amplitude of the calibration errors. For an accuracy of 3 for the maximum gradient direction, the calibration errors could be as large as 3% of reconnection magnetic field, while for the same accuracy for the minimum gradient direction, the calibration errors could only be as large as 0.03% of the reconnection magnetic field. These results suggest that the maximum gradient direction can normally be determined by the unmodified Shi et al. method, while the modified method or some other method must be used to accurately determine the minimum gradient direction. The structure velocity was found with magnitude accurate to 2% and direction accurate to within 5%.

Denton, R.; Sonnerup, B. U. O.; Swisdak, M.; Birn, J.; Drake, J. F.; Heese, M.

2012-01-01

228

MHD simulations of ELMs using the BOUT++ code

NASA Astrophysics Data System (ADS)

The new BOUT++ code [1] is an extensible tool for studying non- linear plasma phenomena such as ELMs. It is capable of solving an arbitrary number of scalar and vector fluid equations in curvilinear geometry, and has been benchmarked against analytically solvable problems, and other codes in X-point geometry. Here we present linear simulations of 3-field reduced MHD for plasmas with circular cross-section, and compare with the ELITE linear MHD code [2,3]. These show good agreement in both the mode structure and growth rates, giving confidence that BOUT++ can reproduce the ideal ballooning mode. Suppression of ballooning modes by diamagnetic and flow-shear effects is demonstrated. Non-linear development of ballooning modes has been studied, showing eruption of filaments from the plasma edge, which are observed to accelerate outwards. Finally, the effect of non-asymmetric perturbations will be studied, in both the linear and non-linear regimes to understand the effect of resonant magnetic perturbations on ELMs. [1] B.D.Dudson et. al. Pre-print arXiv.org:0810.5757 [2] P.B.Snyder et. al. Phys. Plas. 9 (2002) 2037 [3] H.R.Wilson et. al. Phys. Plas. 9 (2002) 1277

Dudson, B. D.; Umansky, M. V.; Xu, X. Q.; Snyder, P. B.; Wilson, H. R.

2009-05-01

229

Final Report: "Large-Eddy Simulation of Anisotropic MHD Turbulence"

To acquire better understanding of turbulence in flows of liquid metals and other electrically conducting fluids in the presence of steady magnetic fields and to develop an accurate and physically adequate LES (large-eddy simulation) model for such flows. The scientific objectives formulated in the project proposal have been fully completed. Several new directions were initiated and advanced in the course of work. Particular achievements include a detailed study of transformation of turbulence caused by the imposed magnetic field, development of an LES model that accurately reproduces this transformation, and solution of several fundamental questions of the interaction between the magnetic field and fluid flows. Eight papers have been published in respected peer-reviewed journals, with two more papers currently undergoing review, and one in preparation for submission. A post-doctoral researcher and a graduate student have been trained in the areas of MHD, turbulence research, and computational methods. Close collaboration ties have been established with the MHD research centers in Germany and Belgium.

Zikanov, Oleg

2008-06-23

230

NASA Astrophysics Data System (ADS)

We demonstrate results of a numerical analysis on functionality of waveguide circulators working in the spectral range of optical communication. Studied circulators were silicon-based three-port waveguide splitters where working elements were slabs of two-dimensional magnetophotonic crystals (2D MPCs) with different structural parameters. An optimized circulator had a 2D MPC slab-hexagonal array of cylindrical air holes in silicon with a magneto-optical defect made of bismuth-substituted yttrium iron garnet and demonstrated an insertion loss of 9 dB and an isolation of 16 dB. If compared to circulators reported in Z. Wan and S. Fan [Appl. Phys. B 81, 369 (2005)], the studied circulators are attractive for realization due to the relative simplicity of their designs.

Yayoi, Kazuo; Tobinaga, Kazuma; Kaneko, Yusuke; Baryshev, Alexander V.; Inoue, Mitsuteru

2011-04-01

231

NASA Technical Reports Server (NTRS)

Numerous studies have been concerned with the possibility of a reduction of the stratospheric ozone layer. Such a reduction could lead to an enhanced penetration of ultraviolet (UV) radiation to the ground, and, as a result, to damage in the case of several biological processes. It is pointed out that the distributions of many trace gases, such as ozone, are governed in part by transport processes. The present investigation presents a two-dimensional photochemistry-transport model using the residual circulation. The global distribution of both ozone and components with ground sources computed in this model is in good agreement with the observations even though slow diffusion is adopted. The agreement is particularly good in the Northern Hemisphere. The results provide additional support for the idea that tracer transport in the stratosphere is mainly of advective nature.

Stordal, F.; Isaksen, I. S. A.; Horntveth, K.

1985-01-01

232

We present new 3D magnetohydrodynamic (MHD) simulations of a supernova-driven, stratified interstellar medium. These simulations were run using the Waagan (2009) positivity preserving scheme for ideal MHD implemented in the Flash code. The scheme is stable even for the Mach numbers approaching 100 found in this problem. We have previously shown that the density distribution arising from hydrodynamical versions of these simulations creates low-density pathways through which Lyman continuum photons can travel to heights |z| > 1 kpc. This naturally produces the warm ionized medium through photoionization due primarily to O stars near the plane. However, our earlier models reproduce the peak but not the width of the observed emission measure distribution. Here, we examine whether inclusion of magnetic fields and a greater vertical extent to the simulation domain produce a gas distribution that better matches the observations. We further study the change of magnetic energy over time in our models, showing that it ...

Mac Low, Mordecai-Mark; Joung, M Ryan; Waagan, Knut; Klingenberg, Christian; Wood, Kenneth; Benjamin, Robert A; Federrath, Christoph; Haffner, L Matthew

2011-01-01

233

Relative timing of substorm features in MHD simulations

NASA Technical Reports Server (NTRS)

An investigation of the temporal sequence of substorm phenomena based on three dimensional MHD (magnetohydrodynamic) simulations of magnetic reconnection and plasmoid formation is presented. The investigation utilizes a spatially localized resistivity model which leads to a significantly faster evolution than found in previous investigations. The analysis of the results concentrates on substorm features that have received considerable attention in the past. The formation of magnetic neutral lines, the occurrence of fast flows directed both earthward and tailward, and the magnetic field changes leading to the formation of the substorm current wedge, and to the depolarization of the magnetic field earthward of the reconnection region and its dependence on the spatial distribution of resistivity, are discussed. These phenomena are seen as an integral part of the nonlinear evolution of the three dimensional tearing instability.

Hesse, Michael; Birn, Joachim

1992-01-01

234

Embedding a Hall MHD plasma sheet simulation inside the Lyon-Fedder-Mobarry global MHD model

We have developed a 3D Hall magnetohydrodynamic (MHD) model with the goal of embedding this high-resolution module into the plasma sheet region of the Lyon-Fedder-Mobarry global MHD model. We intend to investigate the effect of the Hall term on the size and structure of fast flow channels observed in the plasma sheet. Owing to insufficient spatial spacecraft coverage of plasma

T. Guild; H. Spence; J. Lyon; C. Goodrich; V. Merkin; L. Kepko

2005-01-01

235

MHD Simulations of Relic Radio Bubbles in Clusters

In order to better understand the origin and evolution of relic radio bubbles in clusters of galaxies, we report on an extensive set of 2D MHD simulations of hot buoyant bubbles evolving in a realistic intracluster medium. Our bubbles are inflated near the base of the ICM over a finite time interval from a region whose magnetic field is isolated from the ICM. We confirm both the early conjecture from linear analysis and the later results based on preformed MHD bubbles; namely, that very modest ICM magnetic fields can stabilize the rising bubbles against disruption by Rayleigh-Taylor and Kelvin-Helmholtz instabilities. We find in addition that amplification of the ambient fields as they stretch around the bubbles can be sufficient to protect the bubbles or their initial fragments even if the fields are initially much too weak to play a significant role early in the evolution of the bubbles. Indeed, even with initial fields less than a micro-Gauss and values of $\\beta = P_g/P_b$ approaching $10^5$, magnetic stresses in our simulations eventually became large enough to influence the bubble evolution. Magnetic field influence also depends significantly on the geometry of the ICM field and on the topology of the field at the bubble/ICM interface. For example, reconnection of anti-parallel fields across the bubble top greatly reduced the ability of the magnetic field to inhibit disruptive instabilities. Our results confirm earlier estimates of $10^8$ yr for relic radio bubble lifetimes and show that magnetic fields can account for the long term stability of these objects against disruption by surface instabilities. In addition these calculations show that lifting and mixing of the ambient ICM may be a critical function of field geometries in both the ICM and in the bubble interior.

T. W. Jones; D. S. DeYoung

2005-02-07

236

Comparison of Iridium Determined Field-Aligned Current Patterns with MHD Simulations

The engineering magnetometers aboard the 70+ Iridium satellites arranged in six equally spaced polar orbital planes provide a unique database for determination of global field-aligned currents [Waters et al., 2001]. In this study we compare these field-aligned currents with MHD simulation results to quantitatively evaluate the MHD results in a global way. We report analysis for three events of steady

H. Korth; B. J. Anderson; C. C. Goodrich; C. L. Waters; V. G. Merkine

2002-01-01

237

MHD Simulations of the Initiation of Coronal Mass Ejections

NASA Astrophysics Data System (ADS)

Using three-dimensional MHD simulations, we model the quasi-static evolution and the onset of eruption of twisted magnetic flux ropes in the solar corona. We present simulations where the eruption is triggered by either the onset of the torus instability or the helical kink instability of the line-tied coronal flux rope. The simulations show that S (or inverse S) shaped current sheets develop along topological structures identified as Quasi Separatrix Layers (QSLs), during the quasi-static phase before the eruption. Reconnections in the current sheets effectively add twisted flux to the flux rope and thus allow it to rise quasi-statically to the critical height for the onset of the torus instability. We examine the thermal features produced by the current sheet formation and the associated reconnections and found that they can explain some of the observed features in coronal prominence cavities as well as in pre-eruption active regions. We also present simulations of the development of a homologous sequence of CMEs caused by the repeated formation and partial eruption of kink unstable flux ropes as a result of continued flux emergence. It is found that such homologous CMEs tend to be cannibalistic, leading to the formation of more energetic, highly twisted ejecta.

Fan, Yuhong; Chatterjee, Piyali

238

NASA Astrophysics Data System (ADS)

This work is part of an attempt to quantify the relationship between the permeability tensor ( K) and the micro-structure of natural porous media. A brief account is first provided of popular theories used to relate the micro-structure to K. Reasons for the lack of predictive power and restricted generality of current models are discussed. An alternative is an empirically based implicit model wherein K is expressed as a consequence of a few “pore-types” arising from the dynamics of depositional processes. The analytical form of that implicit model arises from evidence of universal association between pore-type and throat size in sandstones and carbonates. An explicit model, relying on the local change of scale technique is then addressed. That explicit model allows, from knowledge of the three-dimensional micro-geometry to calculate K explicitly without having recourse to any constitutive assumptions. The predictive and general character of the explicit model is underlined. The relevance of the change of scale technique is recalled to be contingent on the availability of rock-like three-dimensional synthetic media. A random stationary ergodic process is developed, that allows us to generate three-dimensional synthetic media from a two-dimensional autocorrelation function r(? x ,? y ) and associated probability density function ? ? measured on a single binary image. The focus of this work is to ensure the rock-like character of those synthetic media. This is done first through a direct approach: n two-dimensional synthetic media, derived from single set ( ? ? , r(? x ,? y )) yield n permeability tensors K {/i-1,n i} (calculated by the local change of scale) of the same order. This is a necessary condition to ensure that r(? x ,? y ) and ? ? carry all structural information relevant to K. The limits of this direct approach, in terms of required Central Process Unit time and Memory is underlined, raising the need for an alternative. This is done by comparing the pore-type content of a sandstone sample and n synthetic media derived from r(? x ,? y ) and ? ? measured on that sandstone-sample. Achievement of a good match ensures that the synthetic media comprise the fundamental structural level of all natural sandstones, that is a domainal structure of well-packed clusters of grains bounded by loose-packed pores.

Anguy, Yannick; Bernard, Dominique; Ehrlich, Robert

1996-05-01

239

The kinetic processes accompanying plasma column formation in an inhomogeneous discharge in a Ne/Xe/HCl gas mixture at a pressure of 4 atm were investigated by using a two-dimensional model. Two cathode spots spaced by 0.7 cm were initiated by distorting the cathode surface at local points, which resulted in an increase in the field strength in the cathode region. Three regimes differing in the charging voltage, electric circuit inductance, and electric field strength at the local cathode points were considered. The spatiotemporal distributions of the discharge current; the electron density; and the densities of excited xenon atoms, HCl(v = 0) molecules in the ground state, and HCl(v > 0) molecules in vibrational levels were calculated. The development of the discharge with increasing the electron density from 10{sup 4} to 10{sup 16} cm{sup -3} was analyzed, and three characteristic stages in the evolution of the current distribution were demonstrated. The width of the plasma column was found to depend on the energy deposited in the discharge. The width of the plasma column was found to decrease in inverse proportion to the deposited energy due to spatiotemporal variations in the rates of electron production and loss. The calculated dependences of the cross-sectional area of the plasma column on the energy deposited in the discharge agree with the experimental results.

Bychkov, Yu. I., E-mail: bych-yu@yandex.ru; Yampolskaya, S. A.; Yastremskii, A. G. [Russian Academy of Sciences, Institute of High Current Electronics, Siberian Branch (Russian Federation)

2013-05-15

240

NASA Astrophysics Data System (ADS)

The kinetic processes accompanying plasma column formation in an inhomogeneous discharge in a Ne/Xe/HCl gas mixture at a pressure of 4 atm were investigated by using a two-dimensional model. Two cathode spots spaced by 0.7 cm were initiated by distorting the cathode surface at local points, which resulted in an increase in the field strength in the cathode region. Three regimes differing in the charging voltage, electric circuit inductance, and electric field strength at the local cathode points were considered. The spatiotemporal distributions of the discharge current; the electron density; and the densities of excited xenon atoms, HCl( v = 0) molecules in the ground state, and HCl( v > 0) molecules in vibrational levels were calculated. The development of the discharge with increasing the electron density from 104 to 1016 cm-3 was analyzed, and three characteristic stages in the evolution of the current distribution were demonstrated. The width of the plasma column was found to depend on the energy deposited in the discharge. The width of the plasma column was found to decrease in inverse proportion to the deposited energy due to spatiotemporal variations in the rates of electron production and loss. The calculated dependences of the cross-sectional area of the plasma column on the energy deposited in the discharge agree with the experimental results.

Bychkov, Yu. I.; Yampolskaya, S. A.; Yastremskii, A. G.

2013-05-01

241

Electronic excitations and the optical properties of the photosynthetic complex PSI are analyzed using an effective exciton model developed by Vaitekonis et al. [Photosynth. Res. 2005, 86, 185]. States of the reaction center, the linker states, the highly delocalized antenna states and the red states are identified and assigned in absorption and circular dichroism spectra by taking into account the spectral distribution of density of exciton states, exciton delocalization length, and participation ratio in the reaction center. Signatures of exciton cooperative dynamics in nonchiral and chirality-induced two-dimensional (2D) photon-echo signals are identified. Nonchiral signals show resonances associated with the red, the reaction center, and the bulk antenna states as well as transport between them. Spectrally overlapping contributions of the linker and the delocalized antenna states are clearly resolved in the chirality-induced signals. Strong correlations are observed between the delocalized antenna states, the linker states, and the RC states. The active space of the complex covering the RC, the linker, and the delocalized antenna states is common to PSI complexes in bacteria and plants. PMID:19351124

Abramavicius, Darius; Mukamel, Shaul

2010-01-01

242

MHD Simulations of the Plasma Flow in the Magnetic Nozzle

NASA Technical Reports Server (NTRS)

The magnetohydrodynamic (MHD) flow of plasma through a magnetic nozzle is simulated by solving the governing equations for the plasma flow in the presence of an static magnetic field representing the applied nozzle. This work will numerically investigate the flow and behavior of the plasma as the inlet plasma conditions and magnetic nozzle field strength are varied. The MHD simulations are useful for addressing issues such as plasma detachment and to can be used to gain insight into the physical processes present in plasma flows found in thrusters that use magnetic nozzles. In the model, the MHD equations for a plasma, with separate temperatures calculated for the electrons and ions, are integrated over a finite cell volume with flux through each face computed for each of the conserved variables (mass, momentum, magnetic flux, energy) [1]. Stokes theorem is used to convert the area integrals over the faces of each cell into line integrals around the boundaries of each face. The state of the plasma is described using models of the ionization level, ratio of specific heats, thermal conductivity, and plasma resistivity. Anisotropies in current conduction due to Hall effect are included, and the system is closed using a real-gas equation of state to describe the relationship between the plasma density, temperature, and pressure.A separate magnetostatic solver is used to calculate the applied magnetic field, which is assumed constant for these calculations. The total magnetic field is obtained through superposition of the solution for the applied magnetic field and the self-consistently computed induced magnetic fields that arise as the flowing plasma reacts to the presence of the applied field. A solution for the applied magnetic field is represented in Fig. 1 (from Ref. [2]), exhibiting the classic converging-diverging field pattern. Previous research was able to demonstrate effects such as back-emf at a super-Alfvenic flow, which significantly alters the shape of the magnetic field in both the near- and far-field regions. However, in that work the downstream domain was constrained to a channel of constant cross-sectional area. In the present work we seek to address this issue by modeling the downstream region with a domain that permits free expansion of the plasma, permitting a better evaluation of the downstream effects the applied field has on the plasma. The inlet boundary conditions and applied magnetic field values will also be varied to determine the effect the initial plasma energy content and applied magnetic field energy density have on the near- and far-field plasma properties on the MHD code. This will determine the effect of inlet boundary conditions on the results downstream and address issues related to the restrictive numerical domain previously used.

Smith, T. E. R.; Keidar, M.; Sankaran, K.; olzin, K. A.

2013-01-01

243

Real-time Earth's magnetosphere simulator with 3-dimensional MHD code

Adopting the three-dimensional (3D) magneto-hydrodynamical (MHD) simulation code developed by Tanaka, we have constructed the real-time numerical simulator of interplanetary space-magnetosphere-ionosphere coupling system. By using the real-time one-minute solar wind data of a density, a flow speed and interplanetary magnetic field (IMF) from the ACE spacecraft as boundary conditions, this MHD simulation system reproduced numerically the global structure of magnetosphere

M. den; T. Tanaka; T. Obara; H. Shimazu; H. Amo; Y. Hayashi; Y. Seo; K. Suehiro; H. Takahara; T. Takei

2004-01-01

244

Nonlinear MHD simulation of DC helicity injection in spherical tokamaks

NASA Astrophysics Data System (ADS)

3-D nonlinear MHD computations using the NIMROD code have been performed to study DC helicity injection in the HIT-II and Pegasus spherical tokamaks. Current drive via DC helicity injection has been successfully employed with either a poloidal-gap voltage known as coaxial helicity injection (CHI) [used in HIT-II and NSTX] or a biased miniature plasma gun [used in CDX and Pegasus]. Numerical studies of CHI in a simplified geometry with ?=0 reproduce the ``bubble-burst" formation and the subsequent excitation and saturation (characterized in HIT-II by amplification of poloidal flux) of a line-tied internal kink-mode. The computed strength of saturated fluctuations and poloidal flux are in quantitative agreement with data obtained in the HIT-II experiment. Results from ?!=0 simulations with an experimentally accurate geometry will also be presented. Cases driven by a numerical representation of miniature plasma gun self-consistently evolve pressure and anisotropic thermal transport and simulate the formation, merger, and relaxation of the current filaments to a tokamak-like plasma. The results are compared to experimental data from the Pegasus ST. In both injection scenarios the simulations permit a detailed description of the 3-D equilibria exhibited by the helicity-injected driven plasma and reproduce the observations made in the Pegasus ST and HIT-II of amplified poloidal flux and generation of toroidal current.

Bayliss, R. A.; Sovinec, C. R.

2007-11-01

245

Relativistic mhd simulations of pulsar winds and inner nebulae

NASA Astrophysics Data System (ADS)

In this talk we review the results of recent relativistic MHD simulations of plerionic nebulae created by anisotropic pulsar winds. These simulations reveal complex dynamics of the post-shock flow, very different from the steady quasi-radial outflow assumed in earlier analytical models for plerions. The termination shock has the shape of a distorted torus and most of the downstream flow is initially confined to the equatorial plane. Provided the wind magnetization is higher than a certain value, the magnetic hoop stress stops the outflow in the surface layers of the equatorial disc and redirects it into magnetically confined polar jets. The outflow in the inner layers of the equatorial disc continues until it reaches the slowly expanding outer shell and then turns back and forms the vortex flow filling the nebular volume at intermediate latitudes. We simulated the synchrotron images of the nebula taking into account the relativistic beaming effect and the particle energy losses. These images are strikingly similar to the well-known images of the Crab and other pulsar wind nebulae obtained by Chandra and HST. They exhibit both a system of rings, which makes an impression of an equatorial disc-like or even a toroidal structure, and well collimated polar jets, which appear to originate from the pulsar. A number of fine details of the inner Crab nebula find natural explanation including the bright knot discovered by Hester et al.(1995) very close to the Crab pulsar.

Komissarov, S. S.

246

High Resolution Simulations of Relativistic Hydrodynamic and MHD Turbulence

NASA Astrophysics Data System (ADS)

We present a program of simulations designed to investigate the basic properties of relativistic hydrodynamic and magnetohydrodynamic (MHD) turbulence. We employ a well-tested 5th-order accurate numerical scheme at resolutions of up to 2048^3 zones for hydrodynamic turbulence, and a minimally diffusive 2nd-order scheme at resolutions of up to 1024^3 in the case of relativistic MHD. For the hydrodynamic case, we simulate a relativistically hot gas in a cubic periodic domain continuously driven at large scales with Lorentz factor of about 3. We find that relativistic turbulent velocity fluctuations with ? ? > 1 persist from the driving scale down to scales an order of magnitude smaller, demonstrating the existence of a sustained relativistic turbulent cascade. The power spectrum of the fluid 4-velocity is broadly Kolmogorov-like, roughly obeying a power law with 5/3 index between scales 1/10 and 1/100 of the domain. Departures from 5/3 scaling are larger for the power spectrum of 3-velocity. We find that throughout the inertial interval, 25% of power is in dilatational modes, which obey strict power law scaling between 1/2 and 1/100 of the domain with an index of 1.88. Our program also explores turbulent amplification of magnetic fields in the conditions of merging neutron stars, using a realistic equation of state for dense nuclear matter (? ˜ 10^13 g/cm^3). We find that very robustly, seed fields are amplified to magnetar strength (? 4 * 10^16 Gauss) within ˜1 micro-second for fluid volumes near the size of the NS crust thickness <10 meters. We present power spectra of the kinetic and magnetic energy taken long into the fully stationary evolution of the highest resolution models, finding the magnetic energy to be in super-equipartition (4 times larger) with the kinetic energy through the inertial range. We believe that current global simulations of merging NS binaries are insufficiently resolved for studying field amplification via turbulent processes. Larger magnetic fields, as found in our high resolution local simulations, may have consequences for gravitational wave signals, GRB precursor events, radio afterglows, and optical afterglows due to emission from ejected radioactive r-process material.

Zrake, Jonathan; MacFadyen, A.

2013-01-01

247

Using dynamic cluster quantum Monte Carlo simulations, we study the superconducting behavior of a 1/8 doped two-dimensional Hubbard model with imposed unidirectional stripelike charge-density-wave modulation. We find a significant increase of the pairing correlations and critical temperature relative to the homogeneous system when the modulation length scale is sufficiently large. With a separable form of the irreducible particle-particle vertex, we show that optimized superconductivity is obtained for a moderate modulation strength due to a delicate balance between the modulation enhanced pairing interaction, and a concomitant suppression of the bare particle-particle excitations by a modulation reduction of the quasiparticle weight. PMID:20867327

Maier, T A; Alvarez, G; Summers, M; Schulthess, T C

2010-06-18

248

NASA Astrophysics Data System (ADS)

Results of a new relativistic two-dimensional particle-in-cell code for simulation of laser-driven ion acceleration are presented. It is shown that a complex electric field structure arose during the laser-target interaction as well as the evolution of the ion and electron concentration for the laser-induced cavity pressure acceleration scheme took place. During computation the influence of parameters such as target thickness and width, target starting position inside cavity and its atomic composition, as well as laser pulse length and beam width are examined. Values adopted for the calculation reflect the experimental conditions.

Jab?o?ski, S?awomir

2014-05-01

249

NASA Astrophysics Data System (ADS)

Large scale molecular dynamics simulations of two-dimensional melting have been carried out on massively parallel supercomputers. (Kun Chen, Theodore Kaplan, and Mark Mostoller, Phys. Rev. Lett. 74, 4019 (1995).) A recently revised Parrinello-Rahman scheme is employed. A metastable state is observed between the solid and liquid phases in Lennard-Jones systems of 36864 and 102400 atoms. This intermediate state shows the characteristics of the hexatic phase predicted by the theory of Kosterlitz, Thouless, Halperin, Nelson, and Young. In addition, the relationship between the interaction potential and the stability of this intermediate `hexatic' phase is examined.

Chen, Kun; Kaplan, Theodore; Mostoller, Mark

1996-03-01

250

NASA Astrophysics Data System (ADS)

Microdischarges have gained much attention in the plasma process community for a variety of applications. Recently, microdischarges have been proposed in applications that incorporate bulk fluid flow. For example, in one recent study, microhollow electrode plasma devices have been proposed for use as microflow reactors. Our motivation for this study comes from our proposed application in microthrusters for small satellite propulsion. The phenomena of intense, localized, controllable gas heating in microdischarges enables the development of an electrothermal class device capable of thrust levels in the mN range. While some estimates of properties of microdischarges are available, a detailed understanding of the plasma dynamics, chemistry and coupling with bulk flow is lacking. The focus of this talk is to explore the fundamental characteristics of microdischarges, and investigate interactions between plasma dynamics and bulk fluid flow using two-dimensional computational modelling. In view of our proposed microthruster application, the gas-heating aspect of microdischarges is explored in detail. The model incorporates a self-consistent representation of the plasma that includes a description of multi-species transport and chemistry, electric field, electron and heavy species energy distributions in the microdischarge. The Poisson's equation is solved for the electric field and species conservation equations for generation and transport of species in the discharge. The electron energy equation is solved to determine the electron temperature distribution and the heavy species energy equation is used to determine the gas temperature. Our studies indicate that the structure of the microdischarge is highly inhomogeneous, and electron temperatures of order several tens of electron volts are possible. Significant gas heating is predicted, with typical gas temperatures in the range 600-1000 K. The gas temperature is found to vary strongly with discharge current, but shows a relatively weaker dependence on the operating pressure. It is observed that the plasma dynamics are relatively insensitive to bulk fluid flow, confirming that these two phenomena are decoupled.

Kothnur, Prashanth; Raja, Laxminarayan

2004-09-01

251

A conic-section simulation analysis to determine the stress intensity factors for fracture mechanics problems of practical interest using the finite element method is presented. The method makes use of elliptic displacement functions which are satisfied by the introduction of an “equivalent ellipse” obtained through first simulating the actual crack surface displacements as a part of a parabola or a hyperbola.

C. L. Chow; K. J. Lau

1976-01-01

252

MHD Simulations of Jet Acceleration:. the Role of Disk Resistivity

NASA Astrophysics Data System (ADS)

Accretion disks and astrophysical jets are used to model many active astrophysical objects, viz., young stars, relativistic stars, and active galactic nuclei.The problem of jet acceleration and collimation is central for understanding the physics of these objects. There is now a general consensus that jet acceleration is the result of an interplay between rotation and magnetic field. Global numerical simulations that include both the disk and jet physics have so far been limited to relatively short time scales and small ranges of viscosity and resistivity parameters that may be crucial to define the coupling of the inflow/outflow dynamics. Along these lines, we present in this paper self-consistent time-dependent simulations of supersonic jets launched from magnetized accretion disks, using high resolution numerical techniques. In particular we study the effects of the disk magnetic resistivity, parametrized through an ?-presctiption, in determining the properties of the inflow/outflow system .We use the MHD FLASH code with adaptive mesh refinement, allowing us to follow the evolution of the structure for a time scale long enough to reach steady state.

Bodo, G.; Zanni, C.; Ferrari, A.; Massaglia, S.

2007-08-01

253

Preliminary analysis of the dynamic heliosphere by MHD simulations

A preliminary analysis of the dynamic heliosphere to estimate the termination shock (TS) distance from the sun around the time when Voyager 1 passed the termination shock at December 16, 2004 is performed by using MHD simulations. For input to this simulation, we use the Voyager 2 solar-wind data. We first find a stationary solution of the 3-D outer heliosphere by assigning a set of LISM parameters as our outer boundary conditions and then the dynamical analysis is performed. The model TS crossing is within 6 months of the observed date. The TS is pushed outward every time a high ram-pressure solar wind pulse arrives. After the end of the high ram-pressure wind, the TS shock shrinks inward. When the last Halloween event passed through the TS at DOY 250, 2004, the TS began to shrink inward very quickly and the TS crossed V1. The highest inward speed of the TS is over 400 km/s. The high ram-pressure solar wind transmitted through the TS becomes a high thermal-pressure plasma in the heliosheath, acting to push the TS inward. This suggests that the position of the TS is determined not only by the steady-state pressure balance condition between the solar wind ram-pressure and the LISM pressure, but by the dynamical ram pressure too. The period when the high ram-pressure solar wind arrives at the TS shock seems to correspond to the period of the TS particle event (Stone et al, 2005, Decker et al., 2005). The TS crossing date will be revised in future simulations using a more appropriate set of parameters for the LISM. This will enable us to undertake a detailed comparison of the simulation results with the TS particle events.

Washimi, H.; Zank, G. P. [Institute of Geophysics and Planetary Physics (IGPP), University of California, Riverside, CA 92521 (United States); Tanaka, T. [Faculty of Science, Kyushu University, Hakozaki, Fukuoka 812-8581 (Japan)

2006-09-26

254

This paper assesses the accuracy of the simplified frame cavity conduction/convection and radiation models presented in ISO 15099 and used in software for rating and labeling window products. Temperatures and U-factors for typical horizontal window frames with internal cavities are compared; results from Computational Fluid Dynamics (CFD) simulations with detailed radiation modeling are used as a reference. Four different frames were studied. Two were made of polyvinyl chloride (PVC) and two of aluminum. For each frame, six different simulations were performed, two with a CFD code and four with a building-component thermal-simulation tool using the Finite Element Method (FEM). This FEM tool addresses convection using correlations from ISO 15099; it addressed radiation with either correlations from ISO 15099 or with a detailed, view-factor-based radiation model. Calculations were performed using the CFD code with and without fluid flow in the window frame cavities; the calculations without fluid flow were performed to verify that the CFD code and the building-component thermal-simulation tool produced consistent results. With the FEM-code, the practice of subdividing small frame cavities was examined, in some cases not subdividing, in some cases subdividing cavities with interconnections smaller than five millimeters (mm) (ISO 15099) and in some cases subdividing cavities with interconnections smaller than seven mm (a breakpoint that has been suggested in other studies). For the various frames, the calculated U-factors were found to be quite comparable (the maximum difference between the reference CFD simulation and the other simulations was found to be 13.2 percent). A maximum difference of 8.5 percent was found between the CFD simulation and the FEM simulation using ISO 15099 procedures. The ISO 15099 correlation works best for frames with high U-factors. For more efficient frames, the relative differences among various simulations are larger. Temperature was also compared, at selected locations on the frames. Small differences was found in the results from model to model. Finally, the effectiveness of the ISO cavity radiation algorithms was examined by comparing results from these algorithms to detailed radiation calculations (from both programs). Our results suggest that improvements in cavity heat transfer calculations can be obtained by using detailed radiation modeling (i.e. view-factor or ray-tracing models), and that incorporation of these strategies may be more important for improving the accuracy of results than the use of CFD modeling for horizontal cavities.

Gustavsen, Arlid; Kohler, Christian; Dalehaug, Arvid; Arasteh, Dariush

2008-12-01

255

The present study addresses the capability of a large set of shock-capturing schemes to recover the basic interactions between acoustic, vorticity and entropy in a direct numerical simulation (DNS) framework. The basic dispersive and dissipative errors are first evaluated by considering the advection of a Taylor vortex in a uniform flow. Two transonic cases are also considered. The first one

C. Tenaud; E. Garnier; P. Sagaut

2000-01-01

256

Dayside reconnection in 3D global Hall MHD numerical simulations

NASA Astrophysics Data System (ADS)

We investigate magnetic reconnection at the dayside magnetopause using three dimensional global resistive Hall MHD numerical simulations with the new code, Hall OpenGGCM. Runs are performed with constant spatially uniform resistivity and steady southward IMF conditions at various values of Lundquist number and ion-skin depth to determine scaling. Our results show that in the high Lundquist number limit, Hall physics can allow magnetic flux-pileup to be locally suppressed. The pileup scalings obtained are compared with the stagnation point flow solutions of Sonnerup and Priest [J. Plasma Phys., 14, 1975], and the Hall mediated flux pileup analysis of Dorelli [Phys. Plasmas, 10, 2003]. We also investigate how asymmetric reconnection manifests itself in 3D Hall simulations with particular attention to the 2D analysis of Cassak and Shay [Phys. Plasmas, 14, 2007]. While the theory appears to give reasonable predictions for the offset locations of the x-point and stagnation points, the expressions given for the reconnection electric field and outflow velocities do not agree with what we observe and likely require remediation to account for realistic global geometry. Much like what is observed in 2D collisionless reconnection studies, Hall physics in these global simulations gives rise to more compact dissipation regions with bifurcations in current density extending polewards (when viewed in the GSEx-GSEz plane) which bulge outwards into the magnetosheath. We note also that at larger Lundquist numbers, macroscopic dissipation region structures appear to filament along the flanks of the magnetopause due to the development of Kelvin-Helmholtz instability. The bearing of Hall physics on the relative frequency and character of poleward propagating flux transfer events is also discussed.

Lin, L.; Germaschewski, K.; Bhattacharjee, A.; Maynard, K.; Sullivan, B. P.; Raeder, J.

2012-12-01

257

Development of MHD-SDE Methods for Radiation Belt Simulations

NASA Astrophysics Data System (ADS)

In this paper we report on the development of methods to simulate both radial transport and local acceleration/loss in the radiation belts. The new model will use bounce-averaged relativistic equations of motion to follow marker particles in the Lyon-Fedder-Mobarry global MHD code. The marker particles would be subjected to energy and pitch-angle diffusion by a variety of high-frequency waves, including whistler waves, EMIC waves, and other ELF/VLF waves, by using stochastic differential equation (SDE) methods to diffusively adjust the marker-particle phase-space coordinates. The marker trajectories would then be used to construct phase-space densities and particle fluxes using Liouville-theorem weighting techniques similar to particle-in-cell methods. The model would calculate effects of (i) local acceleration and loss due to interactions with chorus waves, hiss waves, EMIC waves, and magnetosonic equatorial noise, and (ii) radial transport, including (but not restricted to) radial diffusion caused by magnetohydrodynamic waves, all in a dynamic global magnetosphere.

Chan, Anthony; Elkington, Scot; Albert, Jay

258

NASA Astrophysics Data System (ADS)

Several studies have demonstrated that the success of natural and engineered in situ remediation of groundwater pollutants relies on the transverse mixing of reactive chemicals or nutrients along plume margins. Efforts to predict reactions in groundwater generally rely on dispersion coefficients obtained from nonreactive tracer experiments to determine the amount of mixing, but these coefficients may be affected by spreading, which does not contribute to reaction. Mixing is controlled only by molecular diffusion in pore spaces, and the length scale of transverse mixing zones can be small, often on the order of millimeters to centimeters. We use 2D pore-scale simulation to investigate whether classical transverse dispersion coefficients can be applied to model mixing-controlled reactive transport in three different porous media geometries: periodic, random, and macroscopically trending. The lattice-Boltzmann method is used to solve the steady flow field; a finite volume code is used to solve for reactive transport. Nonreactive dispersion coefficients are determined from the transverse spreading of a conservative tracer. Reactive dispersion coefficients are determined by fitting a continuum model which calculates the total product formation as a function of distance to the results from our pore scale simulation. Nonreactive and reactive dispersion coefficients from these simulations are compared. Results indicate that, regardless of the geometrical properties of the media, product formation can be predicted using transverse dispersion coefficients determined from a conservative tracer, provided dispersion coefficients are determined beyond some critical distance downgradient where the plume has spread over a sufficiently large transverse distance compared to the mean grain diameter. This result contrasts with other studies where reactant mixing was controlled by longitudinal hydrodynamic dispersion; in those studies longitudinal dispersion coefficients determined from nonreactive tracer experiments over-estimated the extent of reaction and product formation. Additional work is called for in order to confirm that these findings hold for a wider variety of grain sizes and geometries.

Acharya, Ram C.; Valocchi, Albert J.; Werth, Charles J.; Willingham, Thomas W.

2007-10-01

259

NASA Technical Reports Server (NTRS)

In this study, we examine the sensitivity of long lived tracers to changes in the base transport components in our 2-D model. Changes to the strength of the residual circulation in the upper troposphere and stratosphere and changes to the lower stratospheric K(sub zz) had similar effects in that increasing the transport rates decreased the overall stratospheric mean age, and increased the rate of removal of material from the stratosphere. Increasing the stratospheric K(sub yy) increased the mean age due to the greater recycling of air parcels through the middle atmosphere, via the residual circulation, before returning to the troposphere. However, increasing K(sub yy) along with self-consistent increases in the corresponding planetary wave drive, which leads to a stronger residual circulation, more than compensates for the K(sub yy)-effect, and produces significantly younger ages throughout the stratosphere. Simulations with very small tropical stratospheric K(sub yy) decreased the globally averaged age of air by as much as 25% in the middle and upper stratosphere, and resulted in substantially weaker vertical age gradients above 20 km in the extratropics. We found only very small stratospheric tracer sensitivity to the magnitude of the horizontal mixing across the tropopause, and to the strength of the mesospheric gravity wave drag and diffusion used in the model. We also investigated the transport influence on chemically active tracers and found a strong age-tracer correlation, both in concentration and calculated lifetimes. The base model transport gives the most favorable overall comparison with a variety of inert tracer observations, and provides a significant improvement over our previous 1995 model transport. Moderate changes to the base transport were found to provide modest agreement with some of the measurements. Transport scenarios with residence times ranging from moderately shorter to slightly longer relative to the base case simulated N2O lifetimes that were within the observational estimates of Volk et al. [1997]. However, only scenarios with rather fast transport rates were comparable with the Volk et al. estimates of CFCl3 lifetimes. This is inconsistent with model-measurement comparisons of mean age in which the base model or slightly slower transport rates compared the most favorably with balloon SF6 data. For all comparisons shown, large transport changes away from the base case resulted in simulations that were outside the range of measurements, and in many cases, far outside this range.

Fleming, Eric L.; Jackman, Charles H.; Considine, David B.; Stolarski, Richard S.

1999-01-01

260

NASA Astrophysics Data System (ADS)

Under concentration conditions, it is important to optimize the design of electrodes and cell structures, because high-density energy is emitted to the cell and photocurrent with high density is generated by each subcell of a multijunction solar cell. The in-plane distributions of power consumption by the each resistance component were calculated using a total three-dimensional (3D) simulator. In the case of optical design without a homogenizer, high power consumption at the electrode and top layer was observed in part of the cell. In the middle and bottom layers, power consumption was also observed, though it was slight in comparison with the upper layers. On the other hand, in the case of the optical design with a homogenizer, the power consumption was considerably reduced. This technique can be applied to the structural optimization of solar cells for concentration.

Ota, Yasuyuki; Nishioka, Kensuke

2012-02-01

261

NASA Astrophysics Data System (ADS)

We report for the first time on full 2-D radiation-hydrodynamic implosion simulations that explore the impact of highly compressed imposed magnetic fields on the ignition and burn of perturbed spherical implosions of ignition-scale cryogenic capsules. Using perturbations that highly convolute the cold fuel boundary of the hotspot and prevent ignition without applied fields, we impose initial axial seed fields of 20-100 T (potentially attainable using present experimental methods) that compress to greater than 4 × 104 T (400 MG) under implosion, thereby relaxing hotspot areal densities and pressures required for ignition and propagating burn by ˜50%. The compressed field is high enough to suppress transverse electron heat conduction, and to allow alphas to couple energy into the hotspot even when highly deformed by large low-mode amplitudes. This might permit the recovery of ignition, or at least significant alpha particle heating, in submarginal capsules that would otherwise fail because of adverse hydrodynamic instabilities.

Perkins, L. J.; Logan, B. G.; Zimmerman, G. B.; Werner, C. J.

2013-07-01

262

NASA Astrophysics Data System (ADS)

The biodegradation of oxidizable hydrocarbon contaminants in the subsurface requires the presence of compatible microbial communities as well as sufficient amounts of electron acceptors and nutrients. In this context, transverse mixing, driven by dispersion and diffusion, is one of the main mechanisms governing the availability of dissolved electron acceptors at a hydrocarbon plume fringe. Aerobic and anaerobic biodegradation of hydrocarbons limited by transverse mixing has been studied experimentally in 2D bench-scale flow-through tanks, filled with a saturated porous medium. Flow of groundwater through the tanks was induced by pumping water at one side through injection ports, and simultaneously extracting water at the other side of the tank. An ethylbenzene plume was established by injection through the central inlet port. A mixture of unlabeled and fully deuterium-labeled isotopomers was used in order to investigate the spatial distribution of degradation processes via monitoring of compound-specific stable isotope fractionation. In the first phase of the experiment, aerobic biodegradation was studied. For this purpose, the tank was recharged with water containing oxygen as a dissolved electron acceptor and the aerobic strain Pseudomonas putida F1 was inoculated. Later, nitrate was added to the recharge water as an additional electron acceptor and the denitrifying strain Aromatoleum aromaticum EbN1 was amended to study competitive aerobic/anaerobic biodegradation. A numerical reactive transport model of the experiment was set up for a model based interpretation of the observed degradation patterns. In a sensitivity analysis, the influence of the relevant hydrodynamic parameters on the observable distributions of ethylbenzene isotopomers, oxygen and nitrate was studied. Subsequent model calibration allowed for a good agreement with ethylbenzene concentrations measured at the tank outlet ports as well as oxygen concentrations, which were measured at several profiles perpendicular to the flow direction along the plume. Simulated microbial growth was strongest near the central tank inlet, where both, oxygen and ethylbenzene were available at high concentrations, and along the transverse mixing zone at the fringe of the developed ethylbenzene plume. Model based interpretation of the aerobic/anaerobic phase with competitive biodegradation proved to be ambiguous due to uncertainties regarding the actual stoichiometry of the specific denitrification reaction. Also, the simulated isotopic patterns were very sensitive to the assumed initial distribution of the A. aromaticum EbN1 biomass. Ethylbenzene concentrations and isotopic patterns predicted by the numerical model match the measurements quite well for the first half of the aerobic/anaerobic phase. A distinct increase in biodegradation dynamics later on hints at a change in biodegradation dynamics during the course of the experiment.

Beyer, C.; Ballarini, E.; Bauer, R.; Griebler, C.; Bauer, S.

2011-12-01

263

NASA Astrophysics Data System (ADS)

The magnetic network is one of the most characteristic horizontal structures observed in the lower-atmospheric (UV and IR) emission of the sun. The horizontal advection by the horizontal flow of supergranulation is often perceived to form the magnetic network. However, the origin of supergranulation itself remains unsolved for over 50 years. We newly develop a radiative magneto-hydrodynamic simulation code for the realistic calculation of the solar surface magneto-convection to show the formation process of the magnetic network and supergranulation. When the magnetic field strength is moderate, no supergranular peak is found in the kinetic energy spectrum. However, the magnetic energy spectrum has an clear peak at the scale of the magnetic network. The horizontal structure of this magnetic network has a correlation with the horizontal flow at a depth of about 3 Mm. When the magnetic field becomes sufficiently strong, the back reaction from the magnetic network to the supergranular convection occurs and the supergranular spectral peak appears in the kinetic energy spectrum.

Iijima, H.; Yokoyama, T.

2013-12-01

264

NASA Astrophysics Data System (ADS)

Gravel-bed braided rivers are characterized by shallow, branching flow across low relief, complex, and mobile bed topography. These conditions present a major challenge for the application of higher dimensional hydraulic models, the predictions of which are nevertheless vital to inform flood risk and ecosystem management. This paper demonstrates how high-resolution topographic survey and hydraulic monitoring at a density commensurate with model discretization can be used to advance hydrodynamic simulations in braided rivers. Specifically, we detail applications of the shallow water model, Delft3d, to the Rees River, New Zealand, at two nested scales: a 300 m braid bar unit and a 2.5 km reach. In each case, terrestrial laser scanning was used to parameterize the topographic boundary condition at hitherto unprecedented resolution and accuracy. Dense observations of depth and velocity acquired from a mobile acoustic Doppler current profiler (aDcp), along with low-altitude aerial photography, were then used to create a data-rich framework for model calibration and testing at a range of discharges. Calibration focused on the estimation of spatially uniform roughness and horizontal eddy viscosity, ?H, through comparison of predictions with distributed hydraulic data. Results revealed strong sensitivity to ?H, which influenced cross-channel velocity and localization of high shear zones. The high-resolution bed topography partially accounts for form resistance, and the recovered roughness was found to scale by 1.2-1.4 D84 grain diameter. Model performance was good for a range of flows, with minimal bias and tight error distributions, suggesting that acceptable predictions can be achieved with spatially uniform roughness and ?H.

Williams, R. D.; Brasington, J.; Hicks, M.; Measures, R.; Rennie, C. D.; Vericat, D.

2013-09-01

265

Complexities of a 3-D plasmoid flux rope as shown by an MHD simulation

The results of a global magnetohydrodynamic (MHD) simulation of a pair of magnetospheric substorms on 11 August 2002 are presented. Comparisons of data with simulation results reveal a good agreement regarding the sequence of events during substorm development. We give particular emphasis to results in the simulation of a flux rope formed during the second substorm. Unlike standard 2-D depictions

N. L. Farr; D. N. Baker; M. Wiltberger

2008-01-01

266

Ionospheric energy input as a function of solar wind parameters: global MHD simulation results

. We examine the global energetics of the solar wind magnetosphere-ionosphere system by using the global MHD simulation code GUMICS-4. We show simulation results for a major magnetospheric storm (6 April 2000) and a moderate substorm (15 August 2001). The ionospheric dissipation is investigated by determining the Joule heating and precipitation powers in the simulation during the two events. The

M. Palmroth; P. Janhunen; T. I. Pulkkinen; H. E. J. Koskinen

2004-01-01

267

NASA Astrophysics Data System (ADS)

We present new 3D magnetohydrodynamic (MHD) simulations of a supernova-driven, stratified interstellar medium. These simulations were run using the Waagan (2009) positivity preserving scheme for ideal MHD implemented in the Flash code. The scheme is stable even for the Mach numbers approaching 100 found in this problem. We have previously shown that the density distribution arising from hydrodynamical versions of these simulations creates low-density pathways through which Lyman continuum photons can travel to heights |z| > 1 kpc. This naturally produces the warm ionized medium through photoionization due primarily to O stars near the plane. However, our earlier models reproduce the peak but not the width of the observed emission measure distribution. Here, we examine whether inclusion of magnetic fields and a greater vertical extent to the simulation domain produce a gas distribution that better matches the observations. We further study the change of magnetic energy over time in our models, showing that it appears to reach a steady state after a few hundred megayears, presumably supported by a turbulent dynamo driven by the supernova explosions.

Low, M.-M. M.; Hill, A. S.; Joung, M. R.; Waagan, K.; Klingenberg, C.; Wood, K.; Benjamin, R. A.; Federrath, C.; Haffner, L. M.

2012-07-01

268

Relativistic MHD Simulations of Poynting Flux-driven Jets

NASA Astrophysics Data System (ADS)

Relativistic, magnetized jets are observed to propagate to very large distances in many active galactic nuclei (AGNs). We use three-dimensional relativistic MHD simulations to study the propagation of Poynting flux-driven jets in AGNs. These jets are already assumed to be being launched from the vicinity (~103 gravitational radii) of supermassive black holes. Jet injections are characterized by a model described in Li et al., and we follow the propagation of these jets to ~parsec scales. We find that these current-carrying jets are always collimated and mildly relativistic. When ?, the ratio of toroidal-to-poloidal magnetic flux injection, is large the jet is subject to nonaxisymmetric current-driven instabilities (CDI) which lead to substantial dissipation and reduced jet speed. However, even with the presence of instabilities, the jet is not disrupted and will continue to propagate to large distances. We suggest that the relatively weak impact by the instability is due to the nature of the instability being convective and the fact that the jet magnetic fields are rapidly evolving on Alfvénic time scales. We present the detailed jet properties and show that far from the jet launching region, a substantial amount of magnetic energy has been transformed into kinetic energy and thermal energy, producing a jet magnetization number ? < 1. In addition, we have also studied the effects of a gas pressure supported "disk" surrounding the injection region, and qualitatively similar global jet behaviors were observed. We stress that jet collimation, CDIs, and the subsequent energy transitions are intrinsic features of current-carrying jets.

Guan, Xiaoyue; Li, Hui; Li, Shengtai

2014-01-01

269

The signal loss that occurs in regions of disturbed flow significantly decreases the clinical usefulness of MR angiography in the imaging of diseased arteries. This signal loss is most often attributed to turbulent flow; but on a typical MR angiogram, the signal is lost in the nonturbulent upstream region of the stenosis as well as in the turbulent downstream region. In the current study we used a flow phantom with a forward-facing step geometry to model the upstream region. The flow upstream of the step was convergent, which created high levels of convective acceleration. This region of the flow field contributes to signal loss at the constriction, leading to overestimation of the area of stenosis reduction. A computer program was designed to simulate the image artifacts that would be caused by this geometry in two-dimensional time-of-flight MR angiography. Simulated images were compared with actual phantom images and the flow artifacts were highly correlated. The computer simulation was then used to test the effects of different orders of motion compensation and of fewer pixels per diameter, as would be present in MR angiograms of small arteries. The results indicated that the computational simulation of flow artifacts upstream of the stenosis provides an important tool in the design of optimal imaging sequences for the reduction of signal loss. PMID:8748485

Siegel, J M; Oshinski, J N; Pettigrew, R I; Ku, D N

1995-01-01

270

Theory and Simulations of Interaction of Radiation Belt Electrons with MHD Waves

NASA Astrophysics Data System (ADS)

Radiation belt dynamics is often modeled using a Fokker-Planck equation for phase-space density as a function of one, two, or three adiabatic invariants (or some equivalent set of phase-space variables, plus corresponding Jacobian factors). In such equations the particle motion is assumed to be diffusive and the diffusion coefficients are derived using quasilinear theory. In this paper we describe two approaches to calculating MHD-wave induced radial transport of radiation belt electrons: (1) We use a simple but general model of a spectrum of MHD waves to analytically and numerically examine the validity of quasilinear theory. This includes new calculations of single-wave drift-resonance island widths, and examination of the Chirikov overlap criterion, the transition to global chaos, the conditions under which the chaotic motion becomes diffusive, the scaling of the autocorrelation time, and the accuracy of the analytic quasilinear diffusion coefficient formula. (2) We compare measurements of phase-space density at equatorial GPS locations during the January 1995 high-speed-stream storm to results from (a) an MHD-particle simulation, and (b) a radial diffusion simulation that uses quasilinear diffusion coefficients calculated from power spectral densities of the MHD waves of the MHD simulation. Overall, our results indicate that quasilinear theory is a useful tool for describing interactions of radiation belt electrons with MHD waves.

Chan, A. A.; Elkington, S. R.; Tao, X.; Yu, B.; Keenan, B.

2009-12-01

271

The two-dimensional finite-difference model for simulation of groundwater flow was modified to enable simulation of surface-water/groundwater interactions during periods of low streamflow. Changes were made to the program code in order to calculate surface-water heads for, and flow either to or from, contiguous surface-water bodies; and to allow for more convenient data input. Methods of data input and output were modified and entries (RSORT and HDRIVER) were added to the COEF and CHECKI subroutines to calculate surface-water heads. A new subroutine CALC was added to the program which initiates surface-water calculations. If CALC is not specified as a simulation option, the program runs the original version. The subroutines which solve the ground-water flow equations were not changed. Recharge, evapotranspiration, surface-water inflow, number of wells, pumping rate, and pumping duration can be varied for any time period. The Manning formula was used to relate stream depth and discharge in surface-water streams. Interactions between surface water and ground water are represented by the leakage term in the ground-water flow and surface-water mass balance equations. Documentation includes a flow chart, data deck instructions, input data, output summary, and program listing. Numerical results from the modified program are in good agreement with published analytical results. (USGS)

Ozbilgin, M.M.; Dickerman, D.C.

1984-01-01

272

In this paper, we describe a cell-centered Lagrangian scheme devoted to the numerical simulation of solid dynamics on two-dimensional unstructured grids in planar geometry. This numerical method, utilizes the classical elastic-perfectly plastic material model initially proposed by Wilkins [M.L. Wilkins, Calculation of elastic–plastic flow, Meth. Comput. Phys. (1964)]. In this model, the Cauchy stress tensor is decomposed into the sum of its deviatoric part and the thermodynamic pressure which is defined by means of an equation of state. Regarding the deviatoric stress, its time evolution is governed by a classical constitutive law for isotropic material. The plasticity model employs the von Mises yield criterion and is implemented by means of the radial return algorithm. The numerical scheme relies on a finite volume cell-centered method wherein numerical fluxes are expressed in terms of sub-cell force. The generic form of the sub-cell force is obtained by requiring the scheme to satisfy a semi-discrete dissipation inequality. Sub-cell force and nodal velocity to move the grid are computed consistently with cell volume variation by means of a node-centered solver, which results from total energy conservation. The nominally second-order extension is achieved by developing a two-dimensional extension in the Lagrangian framework of the Generalized Riemann Problem methodology, introduced by Ben-Artzi and Falcovitz [M. Ben-Artzi, J. Falcovitz, Generalized Riemann Problems in Computational Fluid Dynamics, Cambridge Monogr. Appl. Comput. Math. (2003)]. Finally, the robustness and the accuracy of the numerical scheme are assessed through the computation of several test cases.

Maire, Pierre-Henri, E-mail: maire@celia.u-bordeaux1.fr [CEA/CESTA, 15 Avenue des Sablières, CS 60001 33116 Le Barp cedex (France)] [CEA/CESTA, 15 Avenue des Sablières, CS 60001 33116 Le Barp cedex (France); Abgrall, Rémi, E-mail: remi.abgrall@math.u-bordeau1.fr [INRIA and Univ. Bordeaux, F-33405 Talence (France)] [INRIA and Univ. Bordeaux, F-33405 Talence (France); Breil, Jérôme, E-mail: breil@celia.u-bordeaux1.fr [Univ. Bordeaux, CEA, CNRS, CELIA, UMR5107, F-33400 Talence (France)] [Univ. Bordeaux, CEA, CNRS, CELIA, UMR5107, F-33400 Talence (France); Loubère, Raphaël, E-mail: raphael.loubere@math.univ-toulouse.fr [CNRS Institut de Mathématiques de Toulouse, 31062 Toulouse (France)] [CNRS Institut de Mathématiques de Toulouse, 31062 Toulouse (France); Rebourcet, Bernard, E-mail: bernard.rebourcet@cea.fr [CEA/DAM Ile de France, 91 297 Arpajon cedex (France)] [CEA/DAM Ile de France, 91 297 Arpajon cedex (France)

2013-02-15

273

NASA Astrophysics Data System (ADS)

In this paper, we describe a cell-centered Lagrangian scheme devoted to the numerical simulation of solid dynamics on two-dimensional unstructured grids in planar geometry. This numerical method, utilizes the classical elastic-perfectly plastic material model initially proposed by Wilkins [M.L. Wilkins, Calculation of elastic-plastic flow, Meth. Comput. Phys. (1964)]. In this model, the Cauchy stress tensor is decomposed into the sum of its deviatoric part and the thermodynamic pressure which is defined by means of an equation of state. Regarding the deviatoric stress, its time evolution is governed by a classical constitutive law for isotropic material. The plasticity model employs the von Mises yield criterion and is implemented by means of the radial return algorithm. The numerical scheme relies on a finite volume cell-centered method wherein numerical fluxes are expressed in terms of sub-cell force. The generic form of the sub-cell force is obtained by requiring the scheme to satisfy a semi-discrete dissipation inequality. Sub-cell force and nodal velocity to move the grid are computed consistently with cell volume variation by means of a node-centered solver, which results from total energy conservation. The nominally second-order extension is achieved by developing a two-dimensional extension in the Lagrangian framework of the Generalized Riemann Problem methodology, introduced by Ben-Artzi and Falcovitz [M. Ben-Artzi, J. Falcovitz, Generalized Riemann Problems in Computational Fluid Dynamics, Cambridge Monogr. Appl. Comput. Math. (2003)]. Finally, the robustness and the accuracy of the numerical scheme are assessed through the computation of several test cases.

Maire, Pierre-Henri; Abgrall, Rémi; Breil, Jérôme; Loubère, Raphaël; Rebourcet, Bernard

2013-02-01

274

Multidimensional MHD Simulations of Waves in Solar Magnetic Flux Tubes

Results of the propagation of non-linear MHD waves in multi-dimensional magnetic flux tubes will be presented. Starting with a potential magnetic field whose strength decreases with height, and which spreads out to give the familiar ``canopy'' shape, the evolution of a photospheric impulse is examined. It will be shown that the wave fronts propagate upward with both speeds and degrees

P. J. Cargill; J. Chen; J. Krall; D. S. Spicer; S. T. Zalesak

1996-01-01

275

This study is devoted to investigating the heat and mass transfer phenomena that occur during the convective drying of wood at high temperatures. A comparison will be made between an existing two-dimensional computer code known as Transpore. which was developed by Perre in France, and another two-dimensional code which was developed independently by Turner in Australia. Both numerical codes use

I. W. Tumer; P. Perre

1995-01-01

276

Two-Dimensional Velocimetry Instrumentation.

National Technical Information Service (NTIS)

This a brief report on the acquisition and implementation of instrumentation which will be used to make two-dimensional velocimetry measurements in a study of premixed turbulent flames. Two-dimensional velocimetry. (eg)

D. A. Santavicca

1990-01-01

277

3D MHD free surface fluid flow simulation based on magnetic-field induction equations

3D MHD free surface fluid flow simulation based on magnetic-field induction equations H.L. Huang 1 in order to force the local divergence free condition of the magnetic fields. The second is that we extend. These simulation results for lithium film free surface flows under NSTX outboard mid-plane magnetic field

Abdou, Mohamed

278

3D MHD Free Surface Fluid Flow Simulation Based on Magnetic-Field Induction Equations

1 3D MHD Free Surface Fluid Flow Simulation Based on Magnetic-Field Induction Equations H.L. HUANG, a penalty factor is introduced in order to force the local divergence free condition of the magnetic fields boundaries is null. These simulation results for lithium film free surface flows under NSTX outboard mid

California at Los Angeles, University of

279

MHD Simulations of a Supernova-driven ISM and the Warm Ionized Medium

We present new 3D MHD simulations of a supernova-driven, stratified interstellar medium. We have previously shown that the density distribution arising from hydrodynamical versions of these simulations creates low-density pathways through which Lyman continuum photons can travel to heights |z| > 1 kpc. This naturally produces the warm ionized medium through photoionization due primarily to O stars near the plane.

Alex S. Hill; M. R. Joung; R. A. Benjamin; L. M. Haffner; C. Klingenberg; M. M. Mac Low; K. Waagan; K. A. Wood

2011-01-01

280

Some slides on UCLA LM-MHD capabilities Preliminary Incompressible LM Jet Simulations in

Some slides on UCLA LM-MHD capabilities and Preliminary Incompressible LM Jet Simulations in Muon example pictured: both numerical & experimental results show that the free surface height variation Muon Collider Simulation Jet Parameters Horizontal solenoid with center at 0,0,0 Field approximated

McDonald, Kirk

281

We present the implementation of a radiative transfer solver with coherent scattering in the new BIFROST code for radiative magneto-hydrodynamical (MHD) simulations of stellar surface convection. The code is fully parallelized using MPI domain decomposition, which allows for large grid sizes and improved resolution of hydrodynamical structures. We apply the code to simulate the surface granulation in a solar-type star,

W. Hayek; M. Asplund; M. Carlsson; R. Trampedach; R. Collet; B. V. Gudiksen; V. H. Hansteen; J. Leenaarts

2010-01-01

282

NASA Astrophysics Data System (ADS)

Two-dimensional (2D) photon-echo spectra of a single subunit of the Fenna-Matthews-Olson (FMO) bacteriochlorophyll trimer of Chlorobium tepidum are simulated, employing the equation-of-motion phase-matching approach (EOM-PMA). We consider a slightly extended version of the previously proposed Frenkel exciton model, which explicitly accounts for exciton coherences in the secular approximation. The study is motivated by a recent experiment reporting long-lived coherent oscillations in 2D transients [Engel et al., Nature 446, 782 (2007)] and aims primarily at accurate simulations of the spectroscopic signals, with the focus on oscillations of 2D peak intensities with population time. The EOM-PMA accurately accounts for finite pulse durations as well as pulse-overlap effects and does not invoke approximations apart from the weak-field limit for a given material system. The population relaxation parameters of the exciton model are taken from the literature. The effects of various dephasing mechanisms on coherence lifetimes are thoroughly studied. It is found that the experimentally detected multiple frequencies in peak oscillations cannot be reproduced by the employed FMO model, which calls for the development of a more sophisticated exciton model of the FMO complex.

Sharp, Leah Z.; Egorova, Dassia; Domcke, Wolfgang

2010-01-01

283

Large-scale two-dimensional (2D) full particle-in-cell simulations are carried out for studying the relationship between the dynamics of a perpendicular shock and microinstabilities generated at the shock foot. The structure and dynamics of collisionless shocks are generally determined by Alfven Mach number and plasma beta, while microinstabilities at the shock foot are controlled by the ratio of the upstream bulk velocity to the electron thermal velocity and the ratio of the plasma-to-cyclotron frequency. With a fixed Alfven Mach number and plasma beta, the ratio of the upstream bulk velocity to the electron thermal velocity is given as a function of the ion-to-electron mass ratio. The present 2D full PIC simulations with a relatively low Alfven Mach number (M_A ~ 6) show that the modified two-stream instability is dominant with higher ion-to-electron mass ratios. It is also confirmed that waves propagating downstream are more enhanced at the shock foot near the shock ramp as the mass ratio becomes higher. T...

Umeda, Takayuki; Matsukiyo, Shuichi; Yamazaki, Ryo

2014-01-01

284

Two-dimensional (2D) photon-echo spectra of a single subunit of the Fenna-Matthews-Olson (FMO) bacteriochlorophyll trimer of Chlorobium tepidum are simulated, employing the equation-of-motion phase-matching approach (EOM-PMA). We consider a slightly extended version of the previously proposed Frenkel exciton model, which explicitly accounts for exciton coherences in the secular approximation. The study is motivated by a recent experiment reporting long-lived coherent oscillations in 2D transients [Engel et al., Nature 446, 782 (2007)] and aims primarily at accurate simulations of the spectroscopic signals, with the focus on oscillations of 2D peak intensities with population time. The EOM-PMA accurately accounts for finite pulse durations as well as pulse-overlap effects and does not invoke approximations apart from the weak-field limit for a given material system. The population relaxation parameters of the exciton model are taken from the literature. The effects of various dephasing mechanisms on coherence lifetimes are thoroughly studied. It is found that the experimentally detected multiple frequencies in peak oscillations cannot be reproduced by the employed FMO model, which calls for the development of a more sophisticated exciton model of the FMO complex.

Sharp, Leah Z.; Egorova, Dassia; Domcke, Wolfgang [Department of Chemistry, Technische Universitaet Muenchen, D-85747 Garching (Germany)

2010-01-07

285

We present a detailed two-dimensional stellar dynamical analysis of a sample of 44 cosmological hydrodynamical simulations of individual central galaxies and their satellites. Kinematic maps of the stellar line-of-sight velocity, velocity dispersion, and higher-order Gauss-Hermite moments $h_3$ and $h_4$ are constructed for each central galaxy and for the most massive satellites. The amount of rotation is quantified using the $\\lambda_{\\mathrm{R}}$-parameter. The velocity, velocity dispersion, $h_3$, and $h_4$ fields of the simulated galaxies show a diversity similar to observed kinematic maps of early-type galaxies in the ATLAS$^{\\rm{3D}}$ survey. This includes fast (regular), slow, and misaligned rotation, hot spheroids with embedded cold disk components as well as galaxies with counter-rotating cores or central depressions in the velocity dispersion. We link the present day kinematic properties to the individual cosmological formation histories of the galaxies. In general, major galaxy mergers have a signi...

Naab, T; Emsellem, E; Cappellari, M; Krajnovic, D; McDermid, R M; Alatalo, K; Bayet, E; Blitz, L; Bois, M; Bournaud, F; Bureau, M; Crocker, A; Davies, R L; Davis, T A; de Zeeuw, P T; Duc, P -A; Hirschmann, M; Johansson, P H; Khochfar, S; Kuntschner, H; Morganti, R; Oosterloo, T; Sarzi, M; Scott, N; Serra, P; van de Ven, G; Weijmans, A; Young, L M

2013-01-01

286

2D MHD test-particle simulations in modeling geomagnetic storms

NASA Astrophysics Data System (ADS)

The effects of magnetic storms on the evolution of the electron radiation belts are studied using MHD test-particle simulations. The 2D guiding center code developed by Elkington et al. (2002) has been used to simulate particle motion in the Solar Magnetic equatorial plane in the MHD fields calculated from the Lyon-Fedder-Mobarry global MHD code. However, our study shows that the B-minimum plane is well off the SM equatorial plane during solstice events. Since 3D test-particle simulation is computationally expensive, we improve the 2D model by pushing particles in the B-minimum surface instead of the SM equatorial plane. Paraview software is used to visualize the LFM data file and to find the B-minimum surface. Magnetic and electric fields on B-minimum surface are projected to the equatorial plane for particle pushing.

Li, Z.; Elkington, S. R.; Hudson, M. K.; Murphy, J. J.; Schmitt, P.; Wiltberger, M. J.

2012-12-01

287

Comparison of solar photospheric bright points between SUNRISE observations and MHD simulations

Bright points (BPs) in the solar photosphere are radiative signatures of magnetic elements described by slender flux tubes located in the darker intergranular lanes. They contribute to the ultraviolet (UV) flux variations over the solar cycle and hence may influence the Earth's climate. Here we combine high-resolution UV and spectro-polarimetric observations of BPs by the SUNRISE observatory with 3D radiation MHD simulations. Full spectral line syntheses are performed with the MHD data and a careful degradation is applied to take into account all relevant instrumental effects of the observations. It is demonstrated that the MHD simulations reproduce the measured distributions of intensity at multiple wavelengths, line-of-sight velocity, spectral line width, and polarization degree rather well. Furthermore, the properties of observed BPs are compared with synthetic ones. These match also relatively well, except that the observations display a tail of large and strongly polarized BPs not found in the simulation...

Riethmüller, T L; Berdyugina, S V; Schüssler, M; Pillet, V Mart\\'\\inez; Feller, A; Gandorfer, A; Hirzberger, J

2014-01-01

288

NASA Astrophysics Data System (ADS)

We use the two-dimensional (2D) version of our Storm Electrification Model to test its potential for studying lightning-produced NOx. We assume that NO production is a function of energy dissipation and calculate this value from the electric field before and after each lightning flash. We use a production rate of 9.2 × 1016 molecules joule-1 to generate the NO. Using a limited set of chemical reactions involving NO, NO2, and O3, we simulated a small storm with 10 intracloud lightning flashes produced over a 2-min span. Their energy dissipation ranged between 0.024 and 0.28 GJ. The simulation was run an additional 18 min after the cessation of lightning. Our results show that the parameterization produced NO mixing ratios internal to the cloud of the order of 10 ppbv after the most energetic flashes and 1-2 ppbv in the upwind portion of the anvil toward the end of the simulation. These mixing ratios are shown to be comparable to observations in a generic sense. Comparison with the C-shaped profiles developed by [1998], also using a 2D model, show similarities, but our results are more weighted toward larger values at higher altitudes than those of Pickering et al. This may be due to differences in the length of the simulation, a lack of cloud-to-ground lightning in our work, a lack of reactive chemistry in Pickering et al., or the use by Pickering et al. of the assumption of [1997] that intracloud flashes dissipate one tenth the energy of cloud-to-ground flashes. We show, using recent observational data and an analysis of the assumptions of Price et al., that this one tenth energy dissipation assumption is not appropriate. We conclude that our use of an explicit lightning scheme to study NO production at the process level is a viable methodology.

Zhang, Xingjun; Helsdon, John H.; Farley, Richard D.

2003-09-01

289

Integrated Physics Advances in Simulation of Wave Interactions with Extended MHD Phenomena

The broad scientific objectives of the SWIM (Simulation of Wave Interaction with MHD) project are: (A) To improve our understanding of interactions that both RF wave and particle sources have on extended-MHD phenomena, and to substantially improve our capability for predicting and optimizing the performance of burning plasmas in devices such as ITER: and (B) To develop an integrated computational system for treating multi-physics phenomena with the required flexibility and extensibility to serve as a prototype for the Fusion Simulation Project (FSP).

Batchelor, Donald B [ORNL; D'Azevedo, Eduardo [ORNL; Bateman, Glenn [Lehigh University, Bethlehem, PA; Bernholdt, David E [ORNL; Berry, Lee A [ORNL; Bonoli, P. [Massachusetts Institute of Technology (MIT); Bramley, R [Indiana University; Breslau, J. [Princeton Plasma Physics Laboratory (PPPL); Chance, M. [Princeton Plasma Physics Laboratory (PPPL); Chen, J. [Princeton Plasma Physics Laboratory (PPPL); Choi, M. [General Atomics; Elwasif, Wael R [ORNL; Fu, GuoYong [Princeton Plasma Physics Laboratory (PPPL); Harvey, R. W. [CompX, Del Mar, CA; Houlberg, Wayne A [ORNL; Jaeger, Erwin Frederick [ORNL; Jardin, S. C. [Princeton Plasma Physics Laboratory (PPPL); Keyes, David E [Columbia University; Klasky, Scott A [ORNL; Kruger, Scott [Tech-X Corporation; Ku, Long-Poe [Princeton Plasma Physics Laboratory (PPPL); McCune, Douglas [Princeton Plasma Physics Laboratory (PPPL); Schissel, D. [General Atomics; Schnack, D. [University of Wisconsin; Wright, J. C. [Massachusetts Institute of Technology (MIT)

2007-06-01

290

Two-dimensional unsteady flows of homogeneous density in estuaries and embayments can be described by hyperbolic, quasi-linear partial differential equations involving three dependent and three independent variables. A linear combination of these equations leads to a parametric equation of characteristic form, which consists of two parts: total differentiation along the bicharacteristics and partial differentiation in space. For its numerical solution, the specified-time-interval scheme has been used. The unknown, partial space-derivative terms can be eliminated first by suitable combinations of difference equations, converted from the corresponding differential forms and written along four selected bicharacteristics and a streamline. Other unknowns are thus made solvable from the known variables on the current time plane. The computation is carried to the second-order accuracy by using trapezoidal rule of integration. Means to handle complex boundary conditions are developed for practical application. Computer programs have been written and a mathematical model has been constructed for flow simulation. The favorable computer outputs suggest further exploration and development of model worthwhile. (Woodard-USGS)

Lai, Chintu

1977-01-01

291

Monte Carlo methods have been used to simulate internal motions of aromatic protons of an oligonucleotide at the nanosecond time scale. Each proton is allowed to fluctuate about its equilibrium position. The longitudinal cross-relaxation rates of such a system of spins have been determined by computing the appropriate correlation functions. Then the interproton distances have been deduced according to the procedure generally used in two-dimensional nmr techniques (nuclear Overhauser effect spectroscopy--NOESY) and compared to the true values. The influence of the amplitude A and of the internal rotational diffusion constant Dint characterizing the dynamics of the system has been checked for in-phase and for uncorrelated motions. It is shown that for the investigated models the distances deduced from NOESY experiments may be under- or overestimated, depending strongly on the values of A and Dint. Furthermore, the cross-relaxation rate of a couple of protons is very sensitive to the correlation level of the motions of both protons. PMID:2597738

Genest, D

1989-11-01

292

Atmospheric sensible and latent heat fluxes constitute an important component of the total poleward energy transport in the climate system. The authors investigate the relative role of these heat fluxes in normal and enhanced CO{sub 2} warming scenarios, using a two-dimensional latitude-height multilayer energy balance climate model. The model uses a diffusive scheme to parameterize the heat transports, where the diffusion coefficients are calculated as a function of the temperature gradient. Results of various numerical experiments show that changes in the diffusion coefficients of both the latent and sensible heat fluxes can significantly affect the present (1 x CO{sub 2}) equilibrium climate. The difference between the 2 x CO{sub 2} and 1 x CO{sub 2} climate, however, as measured by the simulated difference temperature field, is much more sensitive to changes in the latent heat rather than the sensible heat diffusion coefficients, particularly in the Tropics. The parameterization scheme with temperature-dependent diffusion coefficients is able to resolve the water vapor feedback in the 2 x CO{sub 2} warming, thus enabling simple energy balance climate models to produce results comparable to those obtained by more complex climate models such as general circulation models. 22 refs., 11 figs., 1 tab.

Chan, D.; Higuchi, K. [Climate and Atmospheric Research Directorate, Ontario (Canada); Lin, C.A. [Centre for Climate and Global Change Research, Montreal, Quebec (Canada)

1995-04-01

293

NASA Astrophysics Data System (ADS)

We employ an efficient list-based kinetic Monte Carlo (KMC) method to study traffic flow models on one-dimensional (1D) and two-dimensional (2D) lattices based on the exclusion principle and Arrhenius microscopic dynamics. This model implements stochastic rules for cars' movements based on the configuration of the traffic ahead of each car. In particular, we compare two different look-ahead rules: one is based on the distance from the car under consideration to the car in front of it, and the other one is based on the density of cars ahead. The 1D numerical results of these two rules suggest different coarse-grained macroscopic limits in the form of integro-differential Burgers equations. The 2D results of both rules exhibit a sharp phase transition from freely flowing to fully jammed, as a function of the initial density of cars. However, the look-ahead rule based on the density of the traffic produces more realistic results. The KMC simulations reported in this paper are compared with those from other well-known traffic flow models and the corresponding empirical results from real traffic.

Sun, Yi; Timofeyev, Ilya

2014-05-01

294

NASA Astrophysics Data System (ADS)

A two-dimensional computational model of a single red blood cell (RBC) floating in a plasma-alcohol solution through a microchannel with stenosis was created using the Arbitrary Lagrangian-Eulerian (ALE) method with moving mesh for a fluid structure interaction problem. Cell deformability and stability were studied in a plasma-alcohol solution at different fluid flow conditions during movement through the channel with stenosis. Different results were obtained for different input parameters. Motion through 45% and 70% stenoses with the high and law velocities of the RBC and different viscosities was analyzed and successfully simulated. Results show that changes in RBC deformability were due to the effects of alcohol. Changes in behavior during motion were also observed. At low shear rate and high surrounding fluid viscosity the RBC showed a tendency to rotate during movement. The proposed model with its coupling of structural and fluid analysis techniques could be useful to understand the effect of alcohol on the RBC passing through stenosis.

Ni, Aleksey; Cheema, Taqi Ahmad; Kwak, Moon Kyu; Park, Cheol Woo

2014-08-01

295

Resistive MHD and kinetic simulations of 2D magnetotail equilibria leading to reconnection onset

NASA Astrophysics Data System (ADS)

Recent progress in theory and fully kinetic particle-in-cell simulations of 2D magnetotail-like configurations has revealed an important class of equilibria, which can be unstable to ion tearing instability and eventually result in explosive dissipation of energy, fast plasma sheet flows, dipolarizations and changes in initial magnetic topology (reconnection). Such configurations are characterized by an increase of magnetic flux at the tailward end of the equilibrium state. While the instability and subsequent reconfiguration of the initial state exhibit kinetic signatures, the question remains, which parts of the process can be reproduced using reduced plasma models, e.g., resistive and Hall MHD. In this presentation we explore the stability of the new class of magnetotail equilibria to the resistive tearing mode and investigate its properties as a function of equilibrium parameters, e.g., the current sheet thickness and the amount of flux accumulation at the tailward end of the equilibrium, as well as other system parameters, e.g., resistivity and Lundquist number. We discuss comparative aspects of the system behavior in kinetic and resistive MHD simulations, in particular, what, if any, parameters of the MHD system lead to similar growth rates of the instability. Since the theoretical onset condition of the kinetic tearing mode can be expressed fully in MHD terms, we also investigate the effects of including this criterion as an additional constraint on the tearing onset in our resistive MHD simulations. This work is a first step toward inclusion of a kinetically-motivated description of reconnection onset in global MHD simulations of the magnetosphere.

Merkin, V. G.; Sitnov, M. I.; Lyon, J.; Cassak, P.

2013-12-01

296

Four different probabilistic risk assessment methods were compared using the data from the Sangamo Weston\\/Lake Hartwell Superfund site. These were one-dimensional Monte Carlo, two-dimensional Monte Carlo considering uncertainty in the concentration term, two-dimensional Monte Carlo considering uncertainty in ingestion rate, and microexposure event analysis. Estimated high-end risks ranged from 2.0×10 to 3.3×10. Microexposure event analysis produced a lower risk estimate

Ted W. Simon

1999-01-01

297

NASA Astrophysics Data System (ADS)

Ag/AgX sheathed Bi2Sr2CaCu2Ox (Bi2212) is the only superconducting round wire (RW) with high critical current density (Jc) at high magnetic (>25 T) and is thus a strong candidate for high field magnets for nuclear magnetic resonance and high energy physics. A significant remaining challenge, however, is the relatively poor electromechanical behavior of Bi2212 RW, yet there is little understanding of the relationships between the internal Bi2212 microstructure and the mechanical behavior. This is in part due to the complex microstructures within the Bi2212 filaments and the uncertain role of interfilamentary bridges. Here, two-dimensional peridynamic simulations are used to study the stress distribution of the Bi2212 RWs under an axial tensile load. The simulations use scanning electron micrographs obtained from high Jc wires as a starting point to study the impact of various defects on the distribution of stress concentration within the Bi2212 microstructure and Ag. The flexibility of the peridynamic approach allows various defects, including those captured from SEM micrographs and artificially created defects, to be inserted into the microstructure for systematic study. Furthermore, this approach allows the mechanical properties of the defects to be varied, so the effects of porosity and both soft and hard secondary phases are evaluated. The results show significant stress concentration around defects, interfilamentary bridges and the rough Bi2212/Ag interface. In general, the stress concentration resulting from porosity is greater than that of solid-phase inclusions. A clear role of the defect geometry is observed. Results indicate that crack growth is likely to initiate at the Ag/Bi2212 interface or at voids, but that voids may also arrest crack growth in certain circumstances. These results are consistent with experimental studies of Bi2212 electromechanical behavior and magneto-optical imaging of crack growth.

Le, Q. V.; Chan, W. K.; Schwartz, J.

2014-11-01

298

NASA Astrophysics Data System (ADS)

Global scale magnetohydrodynamic simulations have been used to successfully study the evolution of the magnetosphere-ionosphere system under a variety of solar wind conditions. Early studies with the Lyon-Fedder-Mobarry (LFM) model show the presence of flow channels in substorm simulations that had characteristics similar to those seen in observations of bursty bulk flows (BBFs) observed by numerous spacecraft, such as AMPTE and Geotail. More recently the THEMIS constellation has provided a unique opportunity to track the evolution of dipolarization fronts (DFs) from the mid-tail into the inner magnetosphere. Additionally, advances in high performance computing capability make it possible to conduct ultra-high resolution global simulations. In this paper we present comparisons between these ultra-high resolution simulations and the observations of THEMIS. The comparisons include a case study for a DF that was well observed on February 27, 2009 and statistical properties of the flow and electromagnetic field signatures seen in observations and MHD simulations with idealized solar wind conditions. In addition to these comparisons we will present results of using test-particle simulations of electrons driven by the simulated fields to study particle energization in regions around DFs.

Wiltberger, M. J.; Lyon, J.; Elkington, S. R.; Merkin, V. G.

2013-12-01

299

MHD simulations of jet formation - protostellar jets & applications to AGN jets

Jet formation MHD simulations are presented considering a variety of model setups. The first approach investigates the interrelation between the disk magnetisation profile and jet collimation. Our results suggest (and quantify) that outflows launched from a very concentrated region at the inner disk tend to be weakly collimated. In the second approach, jet formation is investigated from a magnetic field

Christian Fendt; Bhargav Vaidya; Oliver Porth; Somayeh Sheikh Nezami

2011-01-01

300

Bursty bulk flows and dipolarization in MHD simulations of magnetotail reconnection

Using three-dimensional MHD simulations of magnetic reconnection in the magnetotail, we investigate the fate of earthward bursty bulk flows (BBFs). The flow bursts are identified as entropy-depleted magnetic flux tubes (“bubbles”) generated by the severance of a plasmoid via magnetic reconnection. The onset of fast reconnection coincides closely with a drastic entropy reduction at the onset of lobe reconnection. The

J. Birn; R. Nakamura; E. V. Panov; M. Hesse

2011-01-01

301

Large eddy simulations in MHD: The rise of counter-rotating vortices at the magnetopause

A study of the magnetohydrodinamic (MHD) development of coherent structures in compressible, inhomogeneous, mixing layers due to the velocity shear instability is reported. The non-linear evolution of the original vorticity sheet is computed with 3-D large eddy simulations (LES) of temporal mixing layers tailored to represent distinctive conditions at the terrestrial magnetopause. We find that the boundary layer is characterized

F. T. Gratton; L. E. Bilbao; C. J. Farrugia; G. Gnavi

2009-01-01

302

Nonlinear MHD Simulations of Inductive Transients in Spheromaks and Spherical Tori

NASA Astrophysics Data System (ADS)

The improved magnetic topology during decay from electrostatic drive shown previously in zero-plasma-beta nonlinear resistive MHD simulations [C. R. Sovinec, J. M. Finn, and D. del-Castillo-Negrete, PoP 8, 475 (2001).] is studied at finite beta and subject to a range of voltage decay rates. New results obtained with the NIMROD code indicate that MHD fluctuations are also reduced in finite-beta conditions, and transient confinement improvement is examined quantitatively in the context of anisotropic thermal conduction. The same type of modeling is also being applied to study MHD activity during Ohmic startup of spherical tori. Simulations with applied loop voltage, Ohmic heating, anisotropic conduction, temperature-dependent resistivity, and time-dependent vertical field reproduce the growth of shaped equilibria in the Pegasus experiment [http://plasma.ep.wisc.edu/pegasus]. Self-consistent 3D simulations show MHD instabilities during startup that affect confinement and Ohmic-drive efficiency. We also describe recent improvements for modeling two-fluid effects in these and other NIMROD simulations.

Cone, G. A.; Sovinec, C. R.; Tian, H.; Cohen, B. I.

2002-11-01

303

MECHANISMS FOR MHD POYNTING FLUX GENERATION IN SIMULATIONS OF SOLAR PHOTOSPHERIC MAGNETOCONVECTION

We investigate the generation mechanisms of MHD Poynting flux in the magnetized solar photosphere. Using radiative MHD modeling of the solar photosphere with initial magnetic configurations that differ in their field strength and geometry, we show the presence of two different mechanisms for MHD Poynting flux generation in simulations of solar photospheric magnetoconvection. The weaker mechanism is connected to vertical transport of weak horizontal magnetic fields in the convectively stable layers of the upper photosphere, while the stronger is the production of Poynting flux in strongly magnetized intergranular lanes experiencing horizontal vortex motions. These mechanisms may be responsible for the energy transport from the solar convection zone to the higher layers of the solar atmosphere.

Shelyag, S.; Mathioudakis, M.; Keenan, F. P. [Astrophysics Research Centre, School of Mathematics and Physics, Queen's University, Belfast BT7 1NN (United Kingdom)

2012-07-01

304

NASA Astrophysics Data System (ADS)

We have performed an analysis of fluid instabilities below the neutrinospheres of the collapsed cores of supernova progenitors using a methodology introduced by Bruenn and Dineva [28, 29, 31]. In an extensive survey we found that the rate of lepton diffusion always exceeds the rate of thermal diffusion and as a result we do not anywhere see the neutron finger instability as described by the Livermore group [16, 17]. A new instability, lepto-entropy fingers, extending from a radius of 10 15 km out to the vicinity of the neutrinosphere, driven by the cross-response functions (i.e. the dependence of lepton transport on entropy perturbations and vice versa) was discovered. This instability has a maximum growth rate of the order of 100 s-1 with a scale of approximately 1/20 the distance of a perturbed fluid element from the core center [18]. This instability has probably already been seen in some multi-dimensional core collapse calculations. To test our results predicting the presence of doubly diffusive instabilities below the neutrinosphere of a proto-supernova, we have performed two dimensional hydrodynamic simulations with radial ray neutrino transport. This entailed rewriting RadHyd, which is the merger of EVH-1 hydrodynamics and MGFLD neutrino transport developed by Bruenn and DiNisco [43], for two dimensions. In particular, hydrodynamic evolution along angular arrays was included, as was MPI message passing capabilities, in order to utilize massively parallel computer platform such as FAU's BOCA4 Beowulf cluster. This work was partially funded by a grant from the DOE Office of Science, Scientific Discovery through Advanced Computing Program.

Raley, Elizabeth

2004-12-01

305

The evaluation of scour at bridges throughout the State of Missouri has been ongoing since 1991, and most of these evaluations have used one-dimensional hydraulic analysis and application of conventional scour depth prediction equations. Occasionally, the complex conditions of a site dictate a more thorough assessment of the stream hydraulics beyond a one-dimensional model. This was the case for structure A-1700, the Interstate 155 bridge crossing the Mississippi River near Caruthersville, Missouri. To assess the complex hydraulics at this site, a two-dimensional hydrodynamic flow model was used to simulate flow conditions on the Mississippi River in the vicinity of the Interstate 155 structure A-1700. The model was used to simulate flow conditions for three discharges: a flood that occurred on April 4, 1975 (the calibration flood), which had a discharge of 1,658,000 cubic feet per second; the 100-year flood, which has a discharge of 1,960,000 cubic feet per second; and the project design flood, which has a discharge of 1,974,000 cubic feet per second. The project design flood was essentially equivalent to the flood that would cause impending overtopping of the mainline levees along the Mississippi River in the vicinity of structure A-1700. Discharge and river-stage readings from the flood of April 4, 1975, were used to calibrate the flow model. The model was then used to simulate the 100-year and project design floods. Hydraulic flow parameters obtained from the three flow simulations were applied to scour depth prediction equations to determine contraction, local pier, and abutment scour depths at structure A-1700. Contraction scour and local pier scour depths computed for the project design discharge generally were the greatest, whereas the depths computed for the calibration flood were the least. The maximum predicted total scour depth (contraction and local pier scour) for the calibration flood was 66.1 feet; for the 100-year flood, the maximum predicted total scour depth was 74.6 feet; for the project design flood, the maximum predicted total scour depth was 93.0 feet. If scour protection did not exist, bent 14 and piers 15 through 21 would be substantially exposed or undermined by the predicted total scour depths in all of the flood simulations. However, piers 18 through 21 have a riprap blanket around the base of each, and the riprap blanket observed on the right bank around bent 14 is thought to extend around the base of pier 15, which would limit the amount of scour that would occur at these piers. Furthermore, the footings and caissons that are not exposed by computed contraction scour may arrest local pier scour, which will limit local pier scour at several bents and piers. Nevertheless, main-channel piers 16 and 17 and all of the bents on the left (as viewed facing downstream) overbank are moderately to substantially exposed by the predicted scour depths from the three flood simulations, and there is no known scour protection at these piers or bents. Abutment scour depths were computed for structure A-1700, but abutment scour is expected to be mitigated by the presence of guidebanks upstream from the bridge abutments, as well as riprap revetment on the abutment and guidebank faces.

Huizinga, Richard J.

2007-01-01

306

Global MHD simulations of disk-magnetosphere interactions: accretion and outflows

We outline recent progress in understanding the accretion of plasma to rotating magnetized stars obtained from global axisymmetric (2D) and 3D magnetohydrodynamic (MHD) simulations in three main areas: (1.) Formation of jets from disk accretion onto rotating magnetized stars: From simulations where the viscosity and magnetic diffusivity within the disk are described by alpha models, we find long-lasting conical outflows\\/jets

M. M. Romanova; R. V. E. Lovelace; G. V. Ustyugova; A. V. Koldoba

2011-01-01

307

3D Simulations of Fluctuation Spectra in the Hall-MHD Plasma

Turbulent spectral cascades are investigated by means of fully three-dimensional (3D) simulations of a compressible Hall-magnetohydrodynamic (H-MHD) plasma in order to understand the observed spectral break in the solar wind turbulence spectra in the regime where the characteristic length scales associated with electromagnetic fluctuations are smaller than the ion gyroradius. In this regime, the results of our 3D simulations exhibit

Dastgeer Shaikh; P. K. Shukla

2009-01-01

308

2-D MHD numerical simulations of EML plasma armatures with ablation

NASA Astrophysics Data System (ADS)

We use a 2-D) resistive MHD code to simulate an EML plasma armature. The energy equation includes Ohmic heating, radiation heat transport and the ideal gas equation of state, allowing for variable ionization using the Saha equations. We calculate rail ablation taking into account the flow of heat into the interior of the rails. Our simulations show the development of internal convective flows and secondary arcs. We use an explicit Flux Corrected Transport algorithm to advance all quantities in time.

Boynton, G. C.; Huerta, M. A.; Thio, Y. C.

1993-01-01

309

NASA Astrophysics Data System (ADS)

We present a detailed two-dimensional stellar dynamical analysis of a sample of 44 cosmological hydrodynamical simulations of individual central galaxies with stellar masses of 2 × 1010 M? ? M* ? 6 × 1011 M?. Kinematic maps of the stellar line-of-sight velocity, velocity dispersion and higher order Gauss-Hermite moments h3 and h4 are constructed for each central galaxy and for the most massive satellites. The amount of rotation is quantified using the ?R-parameter. The velocity, velocity dispersion, h3 and h4 fields of the simulated galaxies show a diversity similar to observed kinematic maps of early-type galaxies in the ATLAS3D survey. This includes fast (regular), slow and misaligned rotation, hot spheroids with embedded cold disc components as well as galaxies with counter-rotating cores or central depressions in the velocity dispersion. We link the present-day kinematic properties to the individual cosmological formation histories of the galaxies. In general, major galaxy mergers have a significant influence on the rotation properties resulting in both a spin-down as well as a spin-up of the merger remnant. Lower mass galaxies with significant (?18 per cent) in situ formation of stars since z ? 2, or with additional gas-rich major mergers - resulting in a spin-up - in their formation history, form elongated (? ˜ 0.45) fast rotators (?R ˜ 0.46) with a clear anticorrelation of h3 and v/?. An additional formation path for fast rotators includes gas-poor major mergers leading to a spin-up of the remnants (?R ˜ 0.43). This formation path does not result in anticorrelated h3 and v/?. The formation histories of slow rotators can include late major mergers. If the merger is gas rich, the remnant typically is a less flattened slow rotator with a central dip in the velocity dispersion. If the merger is gas poor, the remnant is very elongated (? ˜ 0.43) and slowly rotating (?R ˜ 0.11). The galaxies most consistent with the rare class of non-rotating round early-type galaxies grow by gas-poor minor mergers alone. In general, more massive galaxies have less in situ star formation since z ˜ 2, rotate slower and have older stellar populations. We discuss general implications for the formation of fast and slowly rotating galaxies as well as the weaknesses and strengths of the underlying models.

Naab, Thorsten; Oser, L.; Emsellem, E.; Cappellari, Michele; Krajnovi?, D.; McDermid, R. M.; Alatalo, K.; Bayet, E.; Blitz, L.; Bois, M.; Bournaud, F.; Bureau, M.; Crocker, A.; Davies, R. L.; Davis, T. A.; de Zeeuw, P. T.; Duc, P.-A.; Hirschmann, M.; Johansson, P. H.; Khochfar, S.; Kuntschner, H.; Morganti, R.; Oosterloo, T.; Sarzi, M.; Scott, N.; Serra, P.; Ven, G. van de; Weijmans, A.; Young, L. M.

2014-11-01

310

The intensity contrast of solar granulation: comparing Hinode SP results with MHD simulations

The contrast of granulation is an important quantity characterizing solar surface convection. We compare the intensity contrast at 630 nm, observed using the Spectro-Polarimeter (SP) aboard the Hinode satellite, with the 3D radiative MHD simulations of V{\\"o}gler & Sch{\\"u}ssler (2007). A synthetic image from the simulation is degraded using a theoretical point-spread function of the optical system, and by considering other important effects. The telescope aperture and the obscuration by the secondary mirror and its attachment spider, reduce the simulated contrast from 14.4 % to 8.5 %. A slight effective defocus of the instrument brings the simulated contrast down to 7.5 %, close to the observed value of 7.0 %. A proper consideration of the effects of the optical system and a slight defocus, lead to sufficient degradation of the synthetic image from the MHD simulation, such that the contrast reaches almost the observed value. The remaining small discrepancy can be ascribed to straylight and slight imperfections of the instrument, which are difficult to model. Hence, Hinode SP data are consistent with a granulation contrast which is predicted by 3D radiation MHD simulations.

S. Danilovic; A. Gandorfer; A. Lagg; M. Schüssler; S. K. Solanki; A. Vögler; Y. Katsukawa; S. Tsuneta

2008-04-26

311

In the early morning hours of June 11, 2010, substantial flooding occurred at Albert Pike Recreation Area in the Ouachita National Forest of west-central Arkansas, killing 20 campers. The U.S. Forest Service needed information concerning the extent and depth of flood inundation, the water velocity, and flow paths throughout Albert Pike Recreation Area for the flood and for streamflows corresponding to annual exceedence probabilities of 1 and 2 percent. The two-dimensional flow model Fst2DH, part of the Federal Highway Administration’s Finite Element Surface-water Modeling System, and the graphical user interface Surface-water Modeling System (SMS) were used to perform a steady-state simulation of the flood in a 1.5-mile reach of the Little Missouri River at Albert Pike Recreation Area. Peak streamflows of the Little Missouri River and tributary Brier Creek served as inputs to the simulation, which was calibrated to the surveyed elevations of high-water marks left by the flood and then used to predict flooding that would result from streamflows corresponding to annual exceedence probabilities of 1 and 2 percent. The simulated extent of the June 11, 2010, flood matched the observed extent of flooding at Albert Pike Recreation Area. The mean depth of inundation in the camp areas was 8.5 feet in Area D, 7.4 feet in Area C, 3.8 feet in Areas A, B, and the Day Use Area, and 12.5 feet in Lowry’s Camp Albert Pike. The mean water velocity was 7.2 feet per second in Area D, 7.6 feet per second in Area C, 7.2 feet per second in Areas A, B, and the Day Use Area, and 7.6 feet per second in Lowry’s Camp Albert Pike. A sensitivity analysis indicated that varying the streamflow of the Little Missouri River had the greatest effect on simulated water-surface elevation, while varying the streamflow of tributary Brier Creek had the least effect. Simulated water-surface elevations were lower than those modeled by the U.S. Forest Service using the standard-step method, but the comparison between the two was favorable with a mean absolute difference of 0.58 feet in Area C and 0.32 feet in Area D. Results of a HEC-RAS model of the Little Missouri River watershed upstream from the U.S. Geological Survey streamflow-gaging station near Langley showed no difference in mean depth in the areas in common between the models, and a difference in mean velocity of only 0.5 foot per second. Predictions of flooding that would result from streamflows corresponding to annual exceedence probabilities of 1 and 2 percent indicated that the extent of inundation of the June 11, 2010, flood exceeded that of the 1 percent flood, and that for both the 1 and 2 percent floods, all of Areas C and D, and parts of Areas A, B, and the Day Use Area were inundated. Predicted water-surface elevations for the 1 and 2 percent floods were approximately 1 foot lower than those predicted by the U.S. Forest Service using a standard-step model.

Wagner, Daniel M.

2013-01-01

312

NASA Astrophysics Data System (ADS)

Radial diffusion is one of the most important acceleration mechanisms for radiation belt electrons, which can be enhanced from drift-resonant interactions with large-scale fluctuations of the magnetosphere's magnetic and electric fields (Pc5 range of ULF waves). In order to physically quantify the radial diffusion coefficient, DLL, we run the global Lyon-Fedder-Mobarry (LFM) MHD simulations to obtain the mode structure and power spectrum of the ULF waves and validate the simulation results with available satellite measurements. The calculated diffusion coefficients, directly from the MHD fields over a Corotating Interaction Region (CIR) storm in March 2008, are generally higher when solar wind dynamic pressure is enhanced or AE index is high. In contrary to the conventional understanding, our results show that inside geosynchronous orbit the total diffusion coefficient from MHD fields is dominated by the contribution from electric field perturbations, rather than the magnetic field perturbations. The calculated diffusion coefficient has a physical dependence on ? (or electron energy) and L, which is missing in the empirical diffusion coefficient, DLLKp as a function of Kp index, and DLLKp are generally greater than our calculated DLL during the storm event. Validation of the MHD ULF waves by spacecraft field data shows that for this event the LFM code reasonably well-reproduces the Bz wave power observed by GOES and THEMIS satellites, while the E? power observed by THEMIS probes are generally underestimated by LFM fields, on average by about a factor of ten.

Tu, Weichao; Elkington, Scot R.; Li, Xinlin; Liu, Wenlong; Bonnell, J.

2012-10-01

313

Global Hall-MHD simulations of magnetorotational instability in a plasma Couette flow experiment

Global MHD and Hall-MHD numerical simulations relevant to the Madison plasma Couette flow experiment (MPCX) have been performed using the extended MHD code NIMROD. The MPCX has been constructed to study the magnetorotational instability (MRI) in a plasma. The two-fluid Hall effect, which is relevant to some astrophysical situations such as protostellar disks, is also expected to be important in the MPCX. Here, we first derive the local Hall dispersion relation including viscosity, extending earlier work by Balbus and Terquem [Astrophys. J. 552, 235 (2001)]. The predictions of the local analysis are then compared with nonlocal calculations of linear stability of the MRI for a parameter range relevant to the MPCX. It is found that the MHD stability limit and mode structure are altered by the Hall term, and nonlocal analysis is necessary to obtain quantitatively reliable predictions for MPCX. Two-fluid physics also significantly changes the nonlinear evolution and saturation of the axisymmetric MRI. Both the Reynolds and Maxwell stresses contribute significantly to momentum transport. In the Hall regime, when the magnetic field is parallel to the rotation axis, the Maxwell stress is larger than the Reynolds stress (similar to the MHD regime). However, when the magnetic field is antiparallel to the rotation axis in the Hall regime, the Reynolds stress is much larger than the Maxwell stress. To further study the role of non-axisymmetric modes, we have also carried out fully nonlinear MHD computations. Non-axisymmetric modes play an increasingly important role as the magnetic Reynolds number increases and grow to large amplitudes in a saturated turbulent state.

Ebrahimi, F.; Lefebvre, B.; Bhattacharjee, A. [Center for Magnetic Self-Organization in Laboratory and Astrophysical Plasmas, University of New Hampshire, 8 College Road, Durham, New Hampshire 03824 (United States); Forest, C. B. [University of Wisconsin, 1150 University Avenue, Madison, Wisconsin 53706 (United States)

2011-06-15

314

Stochastic models of two-dimensional fracture

Two statistical models of (strictly two-dimensional) layer destruction are presented. The first is built as a strict percolation model with an added ``conservation law'' (conservation of mass) as physical constraint. The second allows for damped or limited fracture. Two successive fracture crack thresholds are considered. Percolation (i.e., fracture) probability and cluster distributions are studied by use of numerical simulations. Different

M. Ausloos; J. M. Kowalski

1992-01-01

315

NASA Astrophysics Data System (ADS)

Physical models of the radiation belt seek to simulate and predict variations in the space radiation environment based on first-principles views of the particle dynamics, making necessary approximations to turn complex field and particle interactions into computationally tractable problems. For example, global magnetohydrodynamic (MHD) models of the magnetosphere provide large-scale views of the interactions of the solar wind with the geomagnetic environment; coupling these global models with test particle simulations provides one means of examining aspects of the evolution of the radiation belts under complex driving conditions. In this work we discuss how global MHD/particle models may be extended to predict the spatiotemporal and frequency characteristics of plasma waves precluded by the MHD approximation, (e.g. magnetospheric EMIC and chorus waves), and examine ways in which the impact of these non-MHD waves may be included in the MHD/particle approach.

Elkington, Scot; Chan, Anthony; McCollough, James

2012-07-01

316

NASA Astrophysics Data System (ADS)

Interest in utilizing liquid metal film flows to protect the plasma-facing solid structures places increasing demand on understanding the magnetohydrodynamics (MHD) of such flows in a magnetic field with spatial variation. The field gradient effect is studied by a two-dimensional (2D) model in Cartesian coordinates. The thin film flow down an inclined plane in spanwise (z-direction) magnetic field with constant streamwise gradient and applied current is analyzed. The solution to the equilibrium flow shows forcefully the M-shaped velocity profile and dependence of side layer thickness on Ha-1/2 whose definition is based on field gradient. The major part of the dissertation is the numerical simulation of free surface film flows and understanding the results. The VOF method is employed to track the free surface, and the CSF model is combined with VOF method to account for surface dynamics condition. The code is validated with respect to Navier-Stokes solver and MHD implementation by computations of ordinary wavy films, MHD flat films and a colleague proposed film flow. The comparisons are performed against respective experimental, theoretical or numerical solutions, and the results are well matched with them. It is found for the ordinary water falling films, at low frequency and high flowrate, the small forcing disturbance at inlet flowrate develops into big roll waves preceded by small capillary bow waves; at high frequency and low Re, it develops into nearly sinusoidal waves with small amplitude and without fore-running capillary waves. The MHD surface instability is investigated for two kinds of film flows in constant streamwise field gradient: one with spatial disturbance and without surface tension, the other with inlet forcing disturbance and with surface tension. At no surface tension condition, the finite amplitude disturbance is rapidly amplified and degrades to irregular shape. With surface tension to maintain smooth interface, finite amplitude regular waves can be established only on near inlet region and they decay to nearly zero amplitude ripple on the far downstream region. At both film conditions, the wave traveling velocity is reduced by the MHD drag from field gradient. The code is also used to explore the exit-pipe and first wall conceptual designs for fusion reactor being proposed in the APEX program. It is seen that the field gradient restrains and lifts up the flow to the whole channel in the exit-pipe high field gradient condition, but an applied streamwise current can propel the flow through the gradient region. The Sn jet flow with high inertia is able to overcome the inverted gravity and MHD induction to form the desired protection liquid layer on top of the first wall.

Gao, Donghong

317

NASA Astrophysics Data System (ADS)

Water flowing through the Sacramento-San Joaquin River Delta supplies drinking water to more than 20 million people in California. Delta water contains elevated concentrations of dissolved organic carbon (DOC) from drainage through the delta peat soils, forming trihalomethanes when the water is chlorinated for drinking. Land subsidence caused by oxidation of the peat soils has led to increased pumping of drainage water from delta islands to maintain arable land. An agricultural field on Twitchell Island was flooded in 1997 to evaluate continuous flooding as a technique to mitigate subsidence. The effects of shallow flooding on DOC loads to the drain water must be determined to evaluate the feasibility of this technique. In this study, heat is used as a nonconservative tracer to determine shallow ground-water flux and calculate DOC loads to an adjacent drainage ditch. Temperature profiles and water levels were measured in 12 wells installed beneath the pond, in the pond, and in an adjacent drainage ditch from May 2000 to June 2001. The range in seasonal temperatures decreased with depth, but seasonal temperature variation was evident in wells screened as deep as 10 to 12 feet below land surface. A constant temperature of 17 degrees C was measured in wells 25 feet beneath the pond. Ground-water flux beneath the pond was quantified in a two-dimensional simulation of water and heat exchange using the SUTRA flow and transport model. The effective vertical hydraulic conductivity of the peat soils underlying the pond was estimated through model calibration. Calibrated hydraulic conductivity is higher (1E-5 m/sec) than estimates from slug tests (2E-6 m/sec). Modeled pond seepage is similar to that estimated from a water budget, although the total seepage determined from the water budget is within the range of error of the instrumentation. Overall, model results indicate that recharge from the pond flows along shallow flow paths and that travel times through the peat to the drainage ditch may be on the order of decades.

Burow, K. R.; Gamble, J. M.; Fujii, R.; Constantz, J.

2001-12-01

318

The use of one-dimensional hydraulic models currently is the standard method for estimating velocity fields through a bridge opening for scour computations and habitat assessment. Flood-flow contraction through bridge openings, however, is hydrodynamically two dimensional and often three dimensional. Although there is awareness of the utility of two-dimensional models to predict the complex hydraulic conditions at bridge structures, little guidance is available to indicate whether a one- or two-dimensional model will accurately estimate the hydraulic conditions at a bridge site. The U.S. Geological Survey, in cooperation with the North Carolina Department of Transportation, initiated a study in 2004 to compare one- and two-dimensional model results with field measurements at complex riverine and tidal bridges in North Carolina to evaluate the ability of each model to represent field conditions. The field data consisted of discharge and depth-averaged velocity profiles measured with an acoustic Doppler current profiler and surveyed water-surface profiles for two high-flow conditions. For the initial study site (U.S. Highway 13 over the Tar River at Greenville, North Carolina), the water-surface elevations and velocity distributions simulated by the one- and two-dimensional models showed appreciable disparity in the highly sinuous reach upstream from the U.S. Highway 13 bridge. Based on the available data from U.S. Geological Survey streamgaging stations and acoustic Doppler current profiler velocity data, the two-dimensional model more accurately simulated the water-surface elevations and the velocity distributions in the study reach, and contracted-flow magnitudes and direction through the bridge opening. To further compare the results of the one- and two-dimensional models, estimated hydraulic parameters (flow depths, velocities, attack angles, blocked flow width) for measured high-flow conditions were used to predict scour depths at the U.S. Highway 13 bridge by using established methods. Comparisons of pier-scour estimates from both models indicated that the scour estimates from the two-dimensional model were as much as twice the depth of the estimates from the one-dimensional model. These results can be attributed to higher approach velocities and the appreciable flow angles at the piers simulated by the two-dimensional model and verified in the field. Computed flood-frequency estimates of the 10-, 50-, 100-, and 500-year return-period floods on the Tar River at Greenville were also simulated with both the one- and two-dimensional models. The simulated water-surface profiles and velocity fields of the various return-period floods were used to compare the modeling approaches and provide information on what return-period discharges would result in road over-topping and(or) pressure flow. This information is essential in the design of new and replacement structures. The ability to accurately simulate water-surface elevations and velocity magnitudes and distributions at bridge crossings is essential in assuring that bridge plans balance public safety with the most cost-effective design. By compiling pertinent bridge-site characteristics and relating them to the results of several model-comparison studies, the framework for developing guidelines for selecting the most appropriate model for a given bridge site can be accomplished.

Wagner, Chad R.

2007-01-01

319

Five model flows of increasing complexity belonging to the class of stationary two-dimensional planar field-aligned magnetohydrodynamic (MHD) flows are presented which are well suited to the quantitative evaluation of MHD codes. The physical properties of these five flows are investigated using characteristic theory. Grid convergence criteria for flows belonging to this class are derived from characteristic theory, and grid convergence

H. De Sterck; A. Cs??k; D. Vanden Abeele; S. Poedts; H. Deconinck

2001-01-01

320

3D Simulations of Fluctuation Spectra in the Hall-MHD Plasma

Turbulent spectral cascades are investigated by means of fully three-dimensional (3D) simulations of a compressible Hall-magnetohydrodynamic (H-MHD) plasma in order to understand the observed spectral break in the solar wind turbulence spectra in the regime where the characteristic length scales associated with electromagnetic fluctuations are smaller than the ion gyroradius. In this regime, the results of our 3D simulations exhibit that turbulent spectral cascades in the presence of a mean magnetic field follow an omnidirectional anisotropic inertial-range spectrum close to k{sup -7/3}. The latter is associated with the Hall current arising from nonequal electron and ion fluid velocities in our 3D H-MHD plasma model.

Shaikh, Dastgeer; Shukla, P. K. [Center for Space Plasma and Aeronomic Research, University of Alabama in Huntsville, Huntsville. Alabama, 35899 (United States); Institut fuer Theoretische Physik IV, Ruhr-Universitaet Bochum, D-44780 Bochum, Germany, and School of Physics, University of KwaZulu-Natal, Durban (South Africa)

2009-01-30

321

3D MHD simulations of planet migration in turbulent stratified disks

We performed 3D MHD numerical simulations of planet migration in stratified disks using the Godunov code PLUTO (Mignone et al. 2007). The disk is invaded by turbulence generated by the magnetorotational instability (MRI). We study the migration for planets with different mass to primary mass ratio. The migration of the low-mass planet (q=Mp\\/Ms=10-5) is dominated by random fluctuations in the

Ana Uribe; Hubert Klahr; Mario Flock; Thomas Henning

2011-01-01

322

2D MHD Simulation of the Emergence and Merging of Coherent Structures

NASA Technical Reports Server (NTRS)

A model of sporadic localized merging of coherent structures has recently been proposed by Chang to describe the dynamics of the Earth's magnetotail. Here we report the results of MHD simulations regarding the development and merging of 2D coherent structures. With a magnetic shear. such coherent structures are generated in alignment with the imposed current sheet. The calculated fluctuation spectra suggest long-ranged correlations with power-law characteristics.

Wu, Cheng-Chin; Chang, Tom

2002-01-01

323

Investigation of transient redox electrochemical MHD using numerical simulations

To advance numerical simulation capabilities of electrochemical magnetohydrodynamics (ECMHD), we employed potential step and potential sweep voltammetry in simulations of the ECMHD of a redox couple. Using time-varying boundary conditions based on the Butler–Volmer electrode kinetics model, we studied the interplay of Lorentz force, convection and redox species concentration distribution. Parametric studies of potential sweep rate, standard rate constant, solution

D. Sen; K. M. Isaac; N. Leventis; I. Fritsch

2011-01-01

324

MHD simulations of substorms: Energy flow through the magnetotail

Substorms have been a continued matter of discussion over several decades. Magnetometers and other instruments on ground and on satellites have made it possible to quantify the changes that Earth's magnetic field goes through over the course of such an event. Realistic simulations add large scale results to micro scale observations. This dissertation will therefore use both measurements and simulations

Sandra Brogl

2008-01-01

325

Global magnetospheric simulation results of the field-aligned current (FAC) density at low altitudes are compared with global two-dimensional distributions of Birkeland currents at the topside ionosphere derived from magnetic field data of the Iridium satellite constellation. We present two events with opposite direction of the interplanetary magnetic field By, 23 November 1999 1400–1700 UT, By > 0, and 31 March

H. Korth; B. J. Anderson; M. J. Wiltberger; J. G. Lyon; P. C. Anderson

2004-01-01

326

On March 24, 1995, the Geotail spacecraft observed large fluctuations of the magnetic field and plasma properties in the low-latitude boundary layer about 15RE tailward of the dusk meridian. Although the magnetospheric and magnetosheath magnetic fields were strongly northward, the Bz component showed strong short-duration fluctuations in which Bz could even reach negative values. We have used two-dimensional magnetohydrodynamic simulations

A. Otto; D. H. Fairfield

2000-01-01

327

Beaver Lake is considered a primary watershed of concern in the State of Arkansas. As such, information is needed to assess water quality, especially nutrient enrichment, nutrient-algal relations, turbidity, and sediment issues within the system. A previously calibrated two-dimensional, laterally averaged model of hydrodynamics and water quality was used for the evaluation of changes in input nutrient and sediment concentrations on the water quality of the reservoir for the period of April 2001 to April 2003. Nitrogen and phosphorus concentrations were increased and decreased and tested independently and simultaneously to examine the nutrient concentrations and algal response in the reservoir. Suspended-solids concentrations were increased and decreased to identify how solids are distributed in the reservoir, which can contribute to decreased water clarity. The Beaver Lake model also was evaluated using a conservative tracer. A conservative tracer was applied at various locations in the reservoir model to observe the fate and transport and how the reservoir might react to the introduction of a conservative substance, or a worst-case spill scenario. In particular, tracer concentrations were evaluated at the locations of the four public water-supply intakes in Beaver Lake. Nutrient concentrations in Beaver Lake increased proportionally with increases in loads from the three main tributaries. An increase of 10 times the calibrated daily input nitrogen and phosphorus in the three main tributaries resulted in daily mean total nitrogen concentrations in the epilimnion that were nearly 4 times greater than the calibration concentrations at site L2 and more than 2 times greater than the calibrated concentrations at site L5. Increases in daily input nitrogen in the three main tributaries independently did not correspond in substantial increases in concentrations of nitrogen in Beaver Lake. The greatest proportional increase in phosphorus occurred in the epilimnion at sites L3 and L4 and the least increase occurred at sites L2 and L5 when calibrated daily input phosphorus concentrations were increased. When orthophosphorus was increased in all three tributaries simultaneously by a factor of 10, daily mean orthophosphorus concentrations in the epilimnion of the reservoir were almost 11 times greater than the calibrated concentrations at sites L2 and L5, and 15 times greater in the epilimnion of the reservoir at sites L3 and L4. Phosphorus concentrations in Beaver Lake increased less when nitrogen and phosphorus were increased simultaneously than when phosphorus was increased independently. The greatest simulated increase in algal biomass (represented as chlorophyll a) occurred when nitrogen and phosphorus were increased simultaneously in the three main tributaries. On average, the chlorophyll a values only increased less than 1 microgram per liter when concentrations of nitrogen or phosphorous were increased independently by a factor of 10 at all three tributaries. In comparison, when nitrogen and phosphorus were increased simultaneously by a factor of 10 for all three tributaries, the chlorophyll a concentration increased by about 10 micrograms per liter on average, with a maximum increase of about 57 micrograms per liter in the epilimnion at site L3 in Beaver Lake. Changes in algal biomass with changes in input nitrogen and phosphorus were variable through time in the Beaver Lake model from April 2001 to April 2003. When calibrated daily input nitrogen and phosphorus concentrations were increased simultaneously for the three main tributaries, the increase in chlorophyll a concentration was the greatest in late spring and summer of 2002. Changes in calibrated daily input inorganic suspended solids concentrations were examined because of the effect they may have on water clarity in Beaver Lake. The increase in total suspended solids was greatest in the hypolimnion at the upstream end of Beaver Lake, and negligible changes

Galloway, Joel M.; Green, W. Reed

2007-01-01

328

NASA Astrophysics Data System (ADS)

This dissertation describes the details of the development of a general, stable and efficient computer code for simulating transient, three-dimensional fluid flows with properly chosen computational boundaries as well as physical boundaries. The topics in the description include: (1) the numerical techniques used in the computer code, which includes a refined version of an existing algorithm for solving the Navier-Stokes and the magnetohydrodynamic (MHD) equations, (2) extensive usage of a fast solver for linear systems of equations, (3) application of the method of characteristics to solving multi-dimensional MHD time -dependent boundary conditions, and (4) a series of numerical experiments to validate the numerical techniques and the computer coding. And finally, a simulation case is done on a shear motion induced phenomena in the solar corona that serves as an example application to demonstrate the usefulness of the computer code. The algorithm developed in this study for solving the difference equations of the Navier-Stokes and MHD equations is called the Nimble Implicit Continuous-fluid Eulerian (NICE), algorithm which is a refined version of the FICE algorithm (Hu and Wu, Journal of Computational Physics 55 (1984), 33). The NICE algorithm is a pressure-based algorithm that solves the equations through a single-loop iteration in which the velocity field is solved within a predictor step and corrected by the corrector that results from a Poisson-type pressure correction equation which simultaneously satisfies the continuity equation, the momentum equation, and the equation of state. All of the formulated difference equations are expressed in linear systems of equations and solved by the solver that incorporates an incomplete pre-condition technique called the Dupont-Kendall -Rachford (DKR) partial factorization and the ORTHOMIN accelerator procedure in an iterative manner. The time-dependent boundary conditions are formulated in such a way that through boundary treatments the characteristic method can apply to any kind of time-dependent boundary conditions for multi-dimensional MHD problems. Among them are the non-reflecting and coupled boundary conditions which are developed and applied in this study. The numerical experiments to verify this code include a time-dependent compressible flow, a steady incompressible Hartmann flow, and a time-dependent plasma critical shear flow. In the numerical experiment for plasma critical shear flow, the results suggest a mechanism which could be used to explain the observed non-thermal line broadening in solar active regions during quiescent periods by a transition to MHD 'non-equilibrium' with the generation of MHD waves from the lower solar atmosphere.

Sun, Ming-Tsung

329

Simulation of Radiation Belt Wave-Particle Interactions Using MHD-SDE Methods

NASA Astrophysics Data System (ADS)

Interactions with a variety of plasma waves, including whistler-mode waves, EMIC waves and MHD waves, can cause significant local acceleration and loss, and/or radial transport of radiation belt particles, especially relativistic electrons. In this paper we report on the development of a new computational model designed to comprehensively simulate local acceleration/loss and radial transport in the radiation belts. The model uses bounce-averaged relativistic equations of motion to follow marker particles in the Lyon-Fedder-Mobarry global MHD code. The marker particles are subjected to energy and pitch-angle diffusion by a variety of high-frequency waves, including whistler waves and other ELF/VLF waves, by using stochastic differential equation (SDE) methods to diffusively adjust the marker-particle phase-space coordinates. The marker trajectories are used to construct phase-space densities and particle fluxes using Liouville-theorem weighting techniques similar to particle-in-cell methods. The new simulation model will calculate effects of (i) local acceleration and loss due to interactions with chorus, hiss, and EMIC waves, and magnetosonic equatorial noise, including quasilinear and non-quasilinear nonlinear interactions, and (ii) radial transport, including (but not restricted to) radial diffusion caused by MHD waves, all in a dynamic global magnetosphere.

Chan, A. A.; Elkington, S. R.; Albert, J. M.

2010-12-01

330

Three-Dimensional MHD Simulation of Caltech Plasma Jet Experiment: First Results

Magnetic fields are believed to play an essential role in astrophysical jets with observations suggesting the presence of helical magnetic fields. Here, we present three-dimensional (3D) ideal MHD simulationsof the Caltech plasma jet experiment using a magnetic tower scenario as the baseline model. Magnetic fields consist of an initially localized dipole-like poloidal component and a toroidal component that is continuously being injected into the domain. This flux injection mimics the poloidal currents driven by the anode-cathode voltage drop in the experiment. The injected toroidal field stretches the poloidal fields to large distances, while forming a collimated jet along with several other key features. Detailed comparisons between 3D MHD simulations and experimental measurements provide a comprehensive description of the interplay among magnetic force, pressure and flow effects. In particular, we delineate both the jet structure and the transition process that converts the injected magnetic energy to othe...

Zhai, Xiang; Bellan, Paul M; Li, Shengtai

2014-01-01

331

Explosive Turbulent Magnetic Reconnection: A New Approach of MHD-Turbulent Simulation

NASA Astrophysics Data System (ADS)

Turbulent flows are often observed in association with magnetic reconnection in space and astrophysical plasmas, and it is often hypothesized that the turbulence can contribute to the fast magnetic reconnection through the enhancement of magnetic dissipation. In this presentation, we demonstrate that an explosive turbulent reconnection can happen by using a new turbulent MHD simulation, in which the evolution of the turbulent transport coefficients are self-consistently solved together with the standard MHD equations. In our model, the turbulent electromotive force defined by the correlation of turbulent fluctuations between v and B is added to the Ohm's law. We discuss that the level of turbulent can control the topology of reconnection, namely the transition from the Sweet-Parker reconnection to the Petscheck reconnection occurs when the level of fluctuations becomes of order of the ambient physical quantities, and show that the growth of the turbulent Petscheck reconnection becomes much faster than the conventional one.

Hoshino, Masahiro; Yokoi, Nobumitsu; Higashimori, Katsuaki

2013-04-01

332

Global magnetosphere simulations using constrained-transport Hall-MHD with CWENO reconstruction

NASA Astrophysics Data System (ADS)

We present a new CWENO (Centrally-Weighted Essentially Non-Oscillatory) reconstruction based MHD solver for the OpenGGCM global magnetosphere code. The solver was built using libMRC, a library for creating efficient parallel PDE solvers on structured grids. The use of libMRC gives us access to its core functionality of providing an automated code generation framework which takes a user provided PDE right hand side in symbolic form to generate an efficient, computer architecture specific, parallel code. libMRC also supports block-structured adaptive mesh refinement and implicit-time stepping through integration with the PETSc library. We validate the new CWENO Hall-MHD solver against existing solvers both in standard test problems as well as in global magnetosphere simulations.

Lin, L.; Germaschewski, K.; Maynard, K. M.; Abbott, S.; Bhattacharjee, A.; Raeder, J.

2013-12-01

333

MHD Simulations of Jet Acceleration:. the Role of Disk Resistivity

Accretion disks and astrophysical jets are used to model many active astrophysical objects, viz., young stars, relativistic stars, and active galactic nuclei.The problem of jet acceleration and collimation is central for understanding the physics of these objects. There is now a general consensus that jet acceleration is the result of an interplay between rotation and magnetic field. Global numerical simulations

G. Bodo; C. Zanni; A. Ferrari; S. Massaglia

2007-01-01

334

MHD Simulations of Interstellar Turbulence 1 Alexei Kritsuk

Kritsuk #12;MassÂradius relation for a sample of 580 MCs 6 The fractal dimension of the ISM is around 2 Â December 20, 2010 Alexei Kritsuk #12;Magnetic field direction in Taurus 7 The 13 CO antenna temperature MIST LANL Astro Seminar Â December 20, 2010 Alexei Kritsuk #12;Simulations reproduce the fractal

Kritsuk, Alexei

335

Broken Ergodicity in Two-Dimensional Homogeneous Magnetohydrodynamic Turbulence

NASA Technical Reports Server (NTRS)

Two-dimensional (2-D) homogeneous magnetohydrodynamic (MHD) turbulence has many of the same qualitative features as three-dimensional (3-D) homogeneous MHD turbulence.The se features include several ideal invariants, along with the phenomenon of broken ergodicity. Broken ergodicity appears when certain modes act like random variables with mean values that are large compared to their standard deviations, indicating a coherent structure or dynamo.Recently, the origin of broken ergodicity in 3-D MHD turbulence that is manifest in the lowest wavenumbers was explained. Here, a detailed description of the origins of broken ergodicity in 2-D MHD turbulence is presented. It will be seen that broken ergodicity in ideal 2-D MHD turbulence can be manifest in the lowest wavenumbers of a finite numerical model for certain initial conditions or in the highest wavenumbers for another set of initial conditions.T he origins of broken ergodicity in ideal 2-D homogeneous MHD turbulence are found through an eigen analysis of the covariance matrices of the modal probability density functions.It will also be shown that when the lowest wavenumber magnetic field becomes quasi-stationary, the higher wavenumber modes can propagate as Alfven waves on these almost static large-scale magnetic structures

Shebalin, John V.

2010-01-01

336

Broken ergodicity in two-dimensional homogeneous magnetohydrodynamic turbulence

Two-dimensional (2D) homogeneous magnetohydrodynamic (MHD) turbulence has many of the same qualitative features as three-dimensional (3D) homogeneous MHD turbulence. These features include several ideal (i.e., nondissipative) invariants along with the phenomenon of broken ergodicity (defined as nonergodic behavior over a very long time). Broken ergodicity appears when certain modes act like random variables with mean values that are large compared to their standard deviations, indicating a coherent structure or dynamo. Recently, the origin of broken ergodicity in 3D MHD turbulence that is manifest in the lowest wavenumbers was found. Here, we study the origin of broken ergodicity in 2D MHD turbulence. It will be seen that broken ergodicity in ideal 2D MHD turbulence can be manifest in the lowest wavenumbers of a finite numerical model for certain initial conditions or in the highest wavenumbers for another set of initial conditions. The origins of broken ergodicity in an ideal 2D homogeneous MHD turbulence are found through an eigenanalysis of the covariance matrices of the probability density function and by an examination of the associated entropy functional. When the values of ideal invariants are kept fixed and grid size increases, it will be shown that the energy in a few large modes remains constant, while the energy in any other mode is inversely proportional to grid size. Also, as grid size increases, we find that broken ergodicity becomes manifest at more and more wavenumbers.

Shebalin, John V. [Astromaterials Research and Exploration Science Office, NASA Johnson Space Center, Houston, Texas 77058-3696 (United States)

2010-09-15

337

NASA Technical Reports Server (NTRS)

A two dimensional (altitude and latitude) model of the atmosphere is used to investigate problems relating to the variability of the dynamics and temperature of the atmosphere on the ozone distribution, solar cycle variations of atmospheric constituents, the sensitivity of model results to tropospheric trace gas sources, and assessment computations of changes in ozone related to manmade influences. In a comparison between two dimensional model results in which the odd nitrogen family was transported together and model results in which the odd nitrogen species was transported separately, it was found that the family approximations are adequate for perturbation scenario calculations.

Jackman, Charles H.; Douglass, Anne R.; Stolarski, Richard S.; Guthrie, Paul D.; Thompson, A. M.

1990-01-01

338

General relativistic MHD simulations of monopole magnetospheres of black holes

In this paper we report the results of the first ever time-dependent general relativistic magnetohydrodynamic simulations of the magnetically dominated monopole magnetospheres of black holes. It is found that the numerical solution evolves towards a stable steady-state solution which is very close to the corresponding force-free solution found by Blandford and Znajek. Contrary to the recent claims, the particle inertia does not become dynamically important near the event horizon and the force-free approximation provides a proper framework for magnetically dominated magnetospheres of black holes. For the first time, our numerical simulations show the development of an ultra-relativistic particle wind from a rotating black hole. However, the flow remains Poynting dominated all the way up to the fast critical point. This suggests that the details of the so-called ``astrophysical load'', where the electromagnetic energy is transferred to particles, may have no effect on the efficiency of the Blandford-Znajek mechanism.

S. S. Komissarov

2004-02-18

339

A fully three-dimensional (3D), time-dependent, MHD interplanetary global model (3D IGM) has been used, for the first time, to study the relationship between different forms of solar activity and transient variations of the north-south component, Bz, of the interplanetary magnetic field (IMF) at 1 AU. One form of solar activity, the flare, is simulated by using a pressure pulse at

C.-C. Wu; M. Dryer; S. T. Wu

1996-01-01

340

Magnetically dominated MHD bow shock ows

Chapter 6 Magnetically dominated MHD bow shock ows: symmetrical two-dimensional ow around-aligned MHD bow shock ows with top-bottom symmetry around perfectly conducting rigid cylinders. Fig. 6.1a e#11;ects dominate, MHD bow shock ows have the same topology as hydrodynamic bow shock ows

De Sterck, Hans

341

Superdiffusion in two-dimensional Yukawa liquids.

Superdiffusion of two-dimensional (2D) liquids was studied using an equilibrium molecular dynamics simulation. At intermediate temperatures, the mean-squared displacement, probability distribution function (PDF), and velocity autocorrelation function (VACF) all indicate superdiffusion; the VACF has a long-time tail; and the PDF indicates no Lévy flights. These effects are predicted to occur in 2D dusty plasmas and other 2D liquids that can be modeled with a long-range repulsive potential. PMID:17358266

Liu, Bin; Goree, J

2007-01-01

342

THE SUBMILLIMETER BUMP IN Sgr A* FROM RELATIVISTIC MHD SIMULATIONS

Recent high resolution observations of the Galactic center black hole allow for direct comparison with accretion disk simulations. We compare two-temperature synchrotron emission models from three-dimensional, general relativistic magnetohydrodynamic simulations to millimeter observations of Sgr A*. Fits to very long baseline interferometry and spectral index measurements disfavor the monochromatic face-on black hole shadow models from our previous work. Inclination angles {<=}20{sup 0} are ruled out to 3{sigma}. We estimate the inclination and position angles of the black hole, as well as the electron temperature of the accretion flow and the accretion rate, to be i=50{sup o+35o}{sub -15}{sup o}, {xi}=-23{sup o+97o}{sub -22}{sup o}, T{sub e} = (5.4 {+-} 3.0) x 10{sup 10} K, and M-dot =5{sup +15}{sub -2}x10{sup -9} M{sub sun} yr{sup -1}, respectively, with 90% confidence. The black hole shadow is unobscured in all best-fit models, and may be detected by observations on baselines between Chile and California, Arizona, or Mexico at 1.3 mm or .87 mm either through direct sampling of the visibility amplitude or using closure phase information. Millimeter flaring behavior consistent with the observations is present in all viable models and is caused by magnetic turbulence in the inner radii of the accretion flow. The variability at optically thin frequencies is strongly correlated with that in the accretion rate. The simulations provide a universal picture of the 1.3 mm emission region as a small region near the midplane in the inner radii of the accretion flow, which is roughly isothermal and has {nu}/{nu} {sub c} {approx} 1-20, where {nu} {sub c} is the critical frequency for thermal synchrotron emission.

Dexter, Jason [Department of Physics, University of Washington, Seattle, WA 98195-1560 (United States); Agol, Eric [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195 (United States); Fragile, P. Chris [Department of Physics and Astronomy, College of Charleston, Charleston, SC 29424 (United States); McKinney, Jonathan C., E-mail: jdexter@u.washington.ed [Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, Stanford, CA 94305-4060 (United States)

2010-07-10

343

MHD simulations of homologous and cannibalistic coronal mass ejections

NASA Astrophysics Data System (ADS)

We present magneto-hydrodynamic simulations of the development of a homologous sequence of coronal mass ejections (CMEs) and demonstrate their so-called cannibalistic behavior. These CMEs originate from the repeated formations and partial eruptions of kink unstable flux ropes as a result of the continued emergence of a twisted flux rope across the lower boundary into a pre-existing coronal potential arcade field. The simulations show that a CME erupting into the open magnetic field created by a preceding CME has a higher speed, and therefore tends to be cannibalistic, catching up and merging with the preceding one into a single fast CME. All the CMEs attained speeds of about 1000 km/s as they exit the domain. The reformation of a twisted flux rope after each CME eruption during the sustained flux emergence can naturally explain the X-ray observations of repeated reformations of sigmoids and “sigmoid-under-cusp” configurations at a low-coronal source of homologous CMEs.

Fan, Yuhong; Chatterjee, Piyali

2014-06-01

344

NASA Astrophysics Data System (ADS)

Dynamic models of the coronal magnetic field show promise as space weather forecasting tools. Such models should be driven by electric fields derived from sequences of photospheric vector magnetograms, the only routine measurements of the solar magnetic field currently available. Previous studies derived flows --- or, equivalently, ideal electric fields --- consistent with evolution of the normal photospheric field, which could be used in "component driving" of an MHD model, i.e., enforcing consistent evolution of the observed and modeled normal magnetic fields. In this extension of the component-driving approach, we demonstrate how to derive ideal electric fields consistent with the observed evolution of both the normal and horizontal magnetic field, useful for "vector driving," i.e., enforcing consistency between all three components of the observed and model photospheric magnetic vectors. To drive an MHD model, this "ideal vector driving" (IVD) approach amount to specification of both the velocity (perpendicular the magnetic field) and its vertical derivative at the model's bottom boundary. The IVD method can incorporate results from local/ tracking methods (e.g., LCT or DAVE) and/or results from global methods (e.g., MEF or poloidal-toroidal decomposition [PTD]). We have applied this new approach to "synthetic magnetograms" extracted from MHD simulations (where the magnetic and electric fields are exactly known), as well as to a four-hour sequence of vector magnetograms from NOAA AR 8210, on 01 May 1998, just prior to an M-class flare and geoeffective CME.

Welsch, B. T.; Fisher, G. H.; Abbett, W. P.; Bercik, D. J.

2008-05-01

345

NASA Technical Reports Server (NTRS)

Loading and consequent unloading of magnetic flux is an essential element of the substorm cycle in Earth's magnetotail. We are unaware of an available global MHD magnetospheric simulation model that includes a loading- unloading cycle in its behavior. Given the central role that MHD models presently play in the development of our understanding of magnetospheric dynamics, and given the present plans for the central role that these models will play in ongoing space weather prediction programs, it is clear that this failure must be corrected. A 2-dimensional numerical driven current-sheet model has been developed that incorporates an idealized current- driven instability with a resistive MHD system. Under steady loading, the model exhibits a global loading- unloading cycle. The specific mechanism for producing the loading-unloading cycle will be discussed. It will be shown that scale-free avalanching of electromagnetic energy through the model, from loading to unloading, is carried by repetitive bursts of localized reconnection. Each burst leads, somewhat later, to a field configuration that is capable of exciting a reconnection burst again. This process repeats itself in an intermittent manner while the total field energy in the system falls. At the end of an unloading interval, the total field energy is reduced to well below that necessary to initiate the next unloading event and, thus, a loading-unloading cycle results. It will be shown that, in this model, it is the topology of bursty localized reconnection that is responsible for the appearance of the loading-unloading cycle.

Klimas, A. J.; Uritsky, V.; Vassiliadis, D.; Baker, D. N.

2005-01-01

346

MHD Turbulence Simulation in a Cosmic Structure Context

The gaseous media of galaxy clusters and cosmic filaments, which constitute most of the baryonic matter in the universe, is highly dynamic. It is also probably turbulent, although the turbulence properties are poorly known. The gas is highly rarefied, essentially fully ionized plasma. Observational evidence suggests intracluster media (ICMs) are magnetized at some level. There are several possible origins for ICM seed fields; the observed fields are likely the result of turbulence in the ICM. We are engaged in a simulation study designed to understand in this context how very weak initial magnetic fields evolve in driven turbulence. We find that the magnetic fields eventually evolve towards equipartition levels with the vortical, solenoidal kinetic energy in the turbulence. As they do so the topology of the field structures transition from filamentary forms into ribbon-like structures in which the field orientations are laminated with vorticity structures.

Jones, T W; Ryu, D; Cho, J

2011-01-01

347

NASA Astrophysics Data System (ADS)

At NICT (National Institute of Information and Communications Technology) we have been developing a new research environment named "OneSpaceNet". The OneSpaceNet is a cloud-computing environment to provide the researchers rich resources for research studies, such as super-computers, large-scale disk area, licensed applications, database and communication devices. The large-scale disk area is rovided via Gfarm, which is one of the distributed file systems. This paper first proposes a distributed data-type and/or data-intensive processing system that are provided via Gfarm as a solution to large-scale data processing in the context of distributed data management and data processing environments in the field of solar-terrestrial physics. The usefulness of a system composed of many file system nodes was examined using large-scale computer simulation data. In the parallel 3D visualization of computer simulation data varying in terms of data processing granularity, optimized load balancing through FIFO scheduling or pipe-line scheduling yielded parallelization efficacy. Using the large-scale data processing system, we have developed a magnetic flux tracing system of global MHD simulations. Under the assumption of magnetic field frozen-in theory of ideal MHD plasma, we trace an element (or elements) of plasma at all steps of global MHD simulation, and visualize magnetic flux (magnetic field lines) penetrating the element(s). Since this system depends on the frozen-in theory, we need to examine when and where this assumption breaks before we apply it for physical data analyses. Figure (a) and Figure (b) show magnetic field lines in the vicinity of the Earth's magnetopause visualized via present system. Both figures show that the magnetic field lines are scattered as they advance downward. In the present talk we discuss the error in the tracings and the restrictions to apply for this technique.

Murata, K. T.; Watari, S.; Kubota, Y.; Fukazawa, K.; Tsubouchi, K.; Fujita, S.; Tanaka, T.; Den, M.; Murayama, Y.

2011-12-01

348

Numerical Simulations of Driven Supersonic Relativistic MHD Turbulence

NASA Astrophysics Data System (ADS)

Models for GRB outflows invoke turbulence in relativistically hot magnetized fluids. In order to investigate these conditions we have performed high-resolution three-dimensional numerical simulations of relativistic magneto-hydrodynamical (RMHD) turbulence. We find that magnetic energy is amplified to several percent of the total energy density by turbulent twisting and folding of magnetic field lines. Values of ?B>~0.01 are thus naturally expected. We study the dependence of saturated magnetic field energy fraction as a function of Mach number and relativistic temperature. We then present power spectra of the turbulent kinetic and magnetic energies. We also present solenoidal (curl-like) and dilatational (divergence-like) power spectra of kinetic energy. We propose that relativistic effects introduce novel couplings between these spectral components. The case we explore in most detail is for equal amounts of thermal and rest mass energy, corresponding to conditions after collisions of shells with relative Lorentz factors of several. These conditions are relevant in models for internal shocks, for the late afterglow phase, for cocoon material along the edge of a relativistic jet as it propagates through a star, as well neutron stars merging with each other and with black hole companions. We find that relativistic turbulence decays extremely quickly, on a sound crossing time of an eddy. Models invoking sustained relativistic turbulence to explain variability in GRB prompt emission are thus strongly disfavored unless a persistant driving of the turbulence is maintained for the duration of the prompt emission.

Zrake, Jonathan; MacFadyen, Andrew

2011-08-01

349

Extended MHD Simulations of Tearing Instabilities and the Dynamo Effect in the Reversed-Field Pinch

NASA Astrophysics Data System (ADS)

Observations on MST indicate the importance of the Hall current in sawtooth crashes and the dynamo effect in a RFP. We employ our Magnetic Reconnection Code (MRC) to perform fully 3D extended MHD simulations in the RFP, including the Hall current and electron pressure gradient in a generalized Ohm's law. The MRC is an MPI-parallelized finite-volume based simulation code that integrates the extended MHD equations. It supports arbitrary curvilinear coordinate mappings, allowing it to be adapted to cylindrical and toroidal geometries. In order to overcome restrictive time-step limits, it uses implicit time integration. We have benchmarked the code for linear tearing instabilities, and performed fully nonlinear simulations. Due to the presence of the Hall current, novel vortical flows are seen in the vicinity of rational surfaces, akin to those seen in recent sawtooth studies in tokamaks, when the peak of the current density separates from the stagnation point of the flow. We calculate the dynamo field by averaging, and compare simulations with observations.

Germaschewski, K.; Dearborn, J.; Bhattacharjee, A.

2009-11-01

350

NASA Astrophysics Data System (ADS)

In an MHD particle simulation of the September 1998 magnetic storm the evolution of the radiation belt electron radial flux profile appears to be diffusive, and diffusion caused by ULF waves has been invoked as the probable mechanism. In order to separate adiabatic and nonadiabatic effects and to investigate the radial diffusion mechanism during this storm, in this work we solve a radial diffusion equation with ULF wave diffusion coefficients and a time-dependent outer boundary condition, and the results are compared with the phase space density of the MHD particle simulation. The diffusion coefficients include contributions from both symmetric resonance modes (? ? m?d, where ? is the wave frequency, m is the azimuthal wave number, and ?d is the bounce-averaged drift frequency) and asymmetric resonance modes (? ? (m ± 1)?d). ULF wave power spectral densities are obtained from a Fourier analysis of the electric and magnetic fields of the MHD simulation and are used in calculating the radial diffusion coefficients. The asymmetric diffusion coefficients are proportional to the magnetic field asymmetry, which is also calculated from the MHD field. The resulting diffusion coefficients vary with the radial coordinate L (the Roederer L-value) and with time during different phases of the storm. The last closed drift shell defines the location of the outer boundary. Both the location of the outer boundary and the value of the phase space density at the outer boundary are time-varying. The diffusion calculation simulates a 42-hour period during the 24-26 September 1998 magnetic storm, starting just before the storm sudden commencement and ending in the late recovery phase. The differential flux calculated in the MHD particle simulation is converted to phase space density. Phase space densities in both simulations (diffusion and MHD particle) are functions of Roederer L-value for fixed first and second adiabatic invariants. The Roederer L-value is calculated using drift shell tracing in the MHD magnetic field, and particles have zero second invariant. The radial diffusion calculation reproduces the main features of the MHD particle simulation quite well. The symmetric resonance modes dominate the radial diffusion, especially in the inner and middle L region, while the asymmetric resonances are more important in the outer region. Using both symmetric and asymmetric terms gives a better result than using only one or the other and is better than using a simple power law diffusion coefficient. We find that it is important to specify the value of the phase space density on the outer boundary dynamically in order to get better agreement between the radial diffusion simulation and the MHD particle simulation.

Fei, Yue; Chan, Anthony A.; Elkington, Scot R.; Wiltberger, Michael J.

2006-12-01

351

A two-dimensional, steady-state ground-water-flow model of the shallow ground-water-flow system near the community of New Post, Sawyer County, Wis., was refined from an existing model of the area. Hydraulic-conductivity and recharge values were not changed from the existing model for the scenario simulations described in this report. Rather, the model was refined by adding detail along the Chippewa Flowage and then was used to simulate contributing areas for three potential replacement wells pumping 30,000 gallons per day. The model also was used to simulate potential surface-water leakage out of the Chippewa Flowage captured by replacement-well pumping. A range in resistance to vertical ground-water flow was simulated along the Chippewa Flowage for each potential replacement-well location to bound the potential effects of representing three-dimensional flow with a two-dimensional model. Results indicate that pumping from a replacement well sited about 130 feet from the Chippewa Flowage could capture as much as 39 percent of the total pumping from the flowage. Pumping from either of two potential replacement wells sited at least 400 feet from the Chippewa Flowage did not induce surface-water leakage out of the flowage regardless of the resistance applied along the flowage for simulations described in this report.

Juckem, Paul F.; Hunt, Randall J.

2008-01-01

352

Thermodynamic MHD Simulation of the July 14, 2000, "Bastille Day" Solar Eruption

NASA Astrophysics Data System (ADS)

The "Bastille Day" event on July 14, 2000, is one of the most extensively studied solar eruptions. It originated in a strong and complex active region close to disk center and produced an X5.7 flare, a fast halo CME, and an intense geomagnetic storm. We have recently begun to model this challenging event, with the final goal to simulate its whole evolution, from the pre-eruption state up to the CME's arrival at 1 AU. To this end, we first produce a steady-state MHD solution of the background corona that incorporates realistic energy transport ("thermodynamic MHD"), photospheric magnetic field measurements, and the solar wind. In order to model the pre-eruption core magnetic field, we then insert a chain of flux ropes along the polarity inversion line (PIL) of the active region. The ropes merge during the subsequent numerical relaxation to form one stable, elongated flux rope that resides above the highly curved PIL, mimicking the morphology of the observed pre-eruption filaments. Next, we impose photospheric flows that converge toward the PIL and successively expand the magnetic field overlying the flux rope, until equilibrium cannot be longer maintained and the rope erupts and produces a CME. Finally, we couple the coronal simulation with our recently developed heliospheric MHD code to model the propagation of the CME to 1 AU. In this presentation we briefly describe our method, compare the simulation results with the observations, and discuss the challenges and limitations involved in modeling such complex and powerful eruptions.

Torok, T.; Downs, C.; Lionello, R.; Linker, J.; Mikic, Z.; Titov, V. S.; Riley, P.

2013-12-01

353

Two-dimensional NMR spectrometry

This article is the second in a two-part series. In part one (ANALYTICAL CHEMISTRY, May 15) the authors discussed one-dimensional nuclear magnetic resonance (NMR) spectra and some relatively advanced nuclear spin gymnastics experiments that provide a capability for selective sensitivity enhancements. In this article and overview and some applications of two-dimensional NMR experiments are presented. These powerful experiments are important complements to the one-dimensional experiments. As in the more sophisticated one-dimensional experiments, the two-dimensional experiments involve three distinct time periods: a preparation period, t/sub 0/; an evolution period, t/sub 1/; and a detection period, t/sub 2/.

Farrar, T.C.

1987-06-01

354

Two dimensional unstable scar statistics.

This report examines the localization of time harmonic high frequency modal fields in two dimensional cavities along periodic paths between opposing sides of the cavity. The cases where these orbits lead to unstable localized modes are known as scars. This paper examines the enhancements for these unstable orbits when the opposing mirrors are both convex and concave. In the latter case the construction includes the treatment of interior foci.

Warne, Larry Kevin; Jorgenson, Roy Eberhardt; Kotulski, Joseph Daniel; Lee, Kelvin S. H. (ITT Industries/AES Los Angeles, CA)

2006-12-01

355

Particle escape in the interplanetary medium: Link between CME observations and MHD simulations

NASA Astrophysics Data System (ADS)

Among the more hazardous forms of space weather at Earth and in the heliosphere are the intense solar energetic particle (SEP) bursts associated with fast coronal mass ejections (CMEs) and eruptive flares. A fundamental question to understand the origin and the evolution of solar energetic particles is: How do solar energetic particles escape the Sun? Answering this question is critical for understanding how the corona couples dynamically to the heliosphere during explosive events, and is fundamental to developing any future forecasting capability for SEP events. The release onto open field lines of energetic particles originating in the low corona is the bridge connecting the acceleration site to the interplanetary propagation and is, therefore, the key to reconciling remote and in-situ observations of energetic particles. Recent multi-instrument studies showed that CMEs are important factors that determine whether the energetic particles escape into the heliosphere and partly define the spatial distribution of particle flux. In order to understand how and why CMEs play a crucial role in the particle escape, we must understand the dynamics of the corona disturbed by a CME ejection. The details of the dynamics can be studied through MHD simulations. To advance understanding, it is pertinent to combine observations and simulations to develop models that respect the observational constraints. Thus, first we will describe the observational results, then discuss how MHD simulations help demonstrate why CMEs are important for particle release.

Masson, Sophie; Antiochos, Spiro; DeVore, C. Richard

356

MHD Simulations of a Supernova-driven ISM and the Warm Ionized Medium

NASA Astrophysics Data System (ADS)

We present new 3D MHD simulations of a supernova-driven, stratified interstellar medium. We have previously shown that the density distribution arising from hydrodynamical versions of these simulations creates low-density pathways through which Lyman continuum photons can travel to heights |z| > 1 kpc. This naturally produces the warm ionized medium through photoionization due primarily to O stars near the plane. However, the hydrodynamical models reproduce the peak but not the width of the emission measure distribution observed in Wisconsin H-Alpha Mapper (WHAM) data. Here, we discuss the role of magnetic fields in the structure of gas away from the plane. We compare emission measure distributions from models with varying magnetic field strengths to the WHAM observations. The simulations were performed using the adaptive mesh refinement grid code FLASH with the new MHD solver developed by Waagan et al. This work was partly supported by NASA/SAO grant TM0-11008X and by NSF grant AST-0607512.

Hill, Alex S.; Joung, M. R.; Benjamin, R. A.; Haffner, L. M.; Klingenberg, C.; Mac Low, M. M.; Waagan, K.; Wood, K. A.

2011-01-01

357

Impurity Mixing Due to MHD in MGI Simulations of DIII-D

NASA Astrophysics Data System (ADS)

Simulations of massive gas injection (MGI) into DIII-D are performed with the NIMROD code. An impurity source that is strongly localized to the edge is used to initiate the simulated MGI shutdown, based on observations that gas jets do not penetrate deeply into the plasma. When the neutral impurity source is poloidally symmetric, it is found that the distribution of impurity ions does not remain poloidally symmetric as the ions diffuse toward the core; instead 2D flows tend to concentrate the impurities on the low-field-side (LFS). Later, 3D flows associated with an m=1/n=1 MHD instability, efficiently mix the impurities into the core, causing a rapid increase in the central electron density simultaneous with a rapid decrease in the central temperature. Further simulations are carried out in which the impurity source is concentrated only on the LFS or the high-field-side (HFS). The effects of varying the poloidal impurity distribution on the efficiency of the MHD mixing are investigated.

Izzo, V. A.

2012-03-01

358

Three-dimensional MHD simulation study of the structure at the leading part of a reconnection jet

We have performed three-dimensional MHD simulations of magnetic reconnection to investigate the structure of a reconnection jet. Our simulation results show that the leading edge of a reconnection jet deforms to put on a significantly complicated structure. In a randomly perturbed environment, smaller scale structure develops rapidly and finally the front of the reconnection jet becomes turbulent. In contrast when

Ryoji TanDokoro; Masaki Fujimoto

2005-01-01

359

NASA Technical Reports Server (NTRS)

The poloidal mode field line resonance in the Earth's dipole magnetic field is investigated using cold plasma ideal MHD simulations in dipole geometry. In order to excite the poloidal mode resonance, we use either an initial or a continuous velocity perturbation to drive the system. The perturbation is localized at magnetic shell L = 7 with plasma flow in the radial direction (electric field component in the azimuthal direction). It is found that with the initial perturbation alone, no polodial mode resonance can be obtained and the initially localized perturbation spreads out across all magnetic L shells. With the continuous perturbation, oscillating near the poloidal resonance frequency, a global-scale poloidal cavity mode can be obtained. For the first time, a localized guided poloidal mode resonance is obtained when a radial component of electric field is added to the initial perturbation such that the curl of the electric field is everywhere perpendicular to the background dipole magnetic field. During the localized poloidal resonance, plasma vortices parallel/antiparallel to the background dipole magnetic field B(sub 0). This circular flow, elongated radially, results in twisting of magnetic field flux tubes, which, in turn, leads to the slowdown of the circular plasma flow and reversal of the plasma vortices. The energy associated with the localized poloidal resonance is conserved as it shifts back and forth between the oscillating plasma vortices and the alternately twisted magnetic flux tubes. In the simulations the eigenfunctions associated with the localized poloidal resonance are grid-scale singular functions. This result indicates that ideal MHD is inadequate to describe the underlying problem and nonideal MHD effects are needed for mode broadening.

Ding, D. Q.; Denton, . E.; Hudson, M. K.; Lysak, R. L.

1995-01-01

360

Milne-Eddington (M-E) inversion codes for the radiative transfer equation are the most widely used tools to infer the magnetic field from observations of the polarization signals in photospheric and chromospheric spectral lines. Unfortunately, a comprehensive comparison between the different M-E codes available to the solar physics community is still missing, and so is a physical interpretation of their inferences. In this contribution we offer a comparison between three of those codes (VFISV, ASP/HAO, and HeLIx$^+$). These codes are used to invert synthetic Stokes profiles that were previously obtained from realistic non-grey three-dimensional magnetohydrodynamical (3D MHD) simulations. The results of the inversion are compared with each other and with those from the MHD simulations. In the first case, the M-E codes retrieve values for the magnetic field strength, inclination and line-of-sight velocity that agree with each other within $\\sigma_B \\leq 35$ (Gauss), $\\sigma_\\gamma \\leq 1.2\\deg$, and $\\sigma_{\\r...

Borrero, J M; Lagg, A; Rezaei, R; Rempel, M

2014-01-01

361

Nonlinear MHD simulation of DC helicity injection in the Pegasus spherical tokamak

NASA Astrophysics Data System (ADS)

DC helicity injection has been successfully employed in spherical tokamaks (ST's) to produce a tokamak-like plasma with either a poloidal-gap voltage known as coaxial helicity injection [HIT-II, NSTX] or a biased cathode gun configuration [CDX, PEGASUS]. In PEGASUS, the tokamak-like plasma which is subsequently ohmically driven is the product of a reversal of vacuum poloidal flux and a merger of gun-injected current filaments. A 3D nonlinear MHD computation using the NIMROD code [Sovinec et al. JCP 195, 355 (2004)] simulates the formation, merger, and relaxation of the gun-injected current filaments to the tokamak-like plasma. The reversal of poloidal flux due to the field induced by the helicity drive is reproduced and the MHD processes leading to the merger and relaxation of the current filaments are described. Over the lifetime of a helically-driven experimental shot (approximately 10ms), the extent to which the merged plasma exhibits amplication of poloidal flux and the injected current in the relaxed state, reported in PEGASUS, is explored. The results are compared with simulations of current drive in NSTX via coaxial helicity injection which exhibit an n=1 open field-line kink [Tang and Boozer, Phys. Plasmas 11, 2679 (2004)].

Bayliss, Adam; Sovinec, Carl

2006-10-01

362

NASA Technical Reports Server (NTRS)

Flow matching has been successfully achieved for an MHD energy bypass system on a supersonic turbojet engine. The Numerical Propulsion System Simulation (NPSS) environment helped perform a thermodynamic cycle analysis to properly match the flows from an inlet employing a MHD energy bypass system (consisting of an MHD generator and MHD accelerator) on a supersonic turbojet engine. Working with various operating conditions (such as the applied magnetic field, MHD generator length and flow conductivity), interfacing studies were conducted between the MHD generator, the turbojet engine, and the MHD accelerator. This paper briefly describes the NPSS environment used in this analysis. This paper further describes the analysis of a supersonic turbojet engine with an MHD generator/accelerator energy bypass system. Results from this study have shown that using MHD energy bypass in the flow path of a supersonic turbojet engine increases the useful Mach number operating range from 0 to 3.0 Mach (not using MHD) to a range of 0 to 7.0 Mach with specific net thrust range of 740 N-s/kg (at ambient Mach = 3.25) to 70 N-s/kg (at ambient Mach = 7). These results were achieved with an applied magnetic field of 2.5 Tesla and conductivity levels in a range from 2 mhos/m (ambient Mach = 7) to 5.5 mhos/m (ambient Mach = 3.5) for an MHD generator length of 3 m.

Benyo, Theresa L.

2011-01-01

363

The Evolution and Efficiency of Oblique MHD Cosmic-Ray Shocks: Two-Fluid Simulations

Using a new, second-order accurate numerical method we present dynamical simulations of oblique MHD cosmic ray (CR) modified plane shock evolution using the two-fluid model for diffusive particle acceleration. The numerical shocks evolve to published analytical steady state properties. In order to probe the dynamical role of magnetic fields we have explored for these time asymptotic states the parameter space of upstream fast mode Mach number, $M_f$, and plasma $\\beta$, compiling the results into maps of dynamical steady state CR acceleration efficiency, $\\epsilon_c$. These maps, along with additional numerical experiments, show that $\\epsilon_c$ is reduced through the action of compressive work on tangential magnetic fields in CR-MHD shocks. Thus $\\epsilon_c$ in low $\\beta$, moderate $M_f$ shocks tends to be smaller in quasi perpendicular shocks than it would be high $\\beta$ shocks of the same $M_f$. This result supports earlier conclusions that strong, oblique magnetic fields inhibit diffusive shock acceleration. For quasi parallel shocks with $\\beta < 1$, on the other hand, $\\epsilon_c$ seems to be increased at a given $M_f$ when compared to high $\\beta$ shocks. The apparent contradiction to the first conclusion results, however, from the fact that for small $\\beta$ quasi parallel shocks, the fast mode Mach number is not a good measure of compression through the shock. That is better reflected in the sonic Mach number, which is greater. Acceleration efficiencies for high and low $\\beta$ having comparable sonic Mach numbers are more similar. Time evolution of CR-MHD shocks is qualitatively similar to CR-gasdynamical shocks. However, several potentially interesting differences are apparent.

Adam Frank; T. W. Jones; Dongsu Ryu

1994-04-29

364

Two-dimensional Hubbard-Holstein model

NASA Astrophysics Data System (ADS)

The interplay of electron-phonon coupling and strong electronic correlations is studied in the frame of the two-dimensional Hubbard-Holstein model. Static and dynamic properties are determined by quantum Monte Carlo simulations and by Migdal-Eliashberg theory. The comparison allows us to assess the diagrammatic approach. The competition between the phonon-mediated electron-electron attraction and the local Coulomb repulsion leads to a rich phase diagram, which we study in detail for a wide range of parameters. We address the question, to which extent the systems can be described by an effective negative-U Hubbard model.

Berger, E.; Valášek, P.; von der Linden, W.

1995-08-01

365

NASA Astrophysics Data System (ADS)

Due to the existence of the magnetic field strength minimum in the outer cusp region, energetic particles (a few hundred keV protons and MeV electrons) approaching the dayside magnetic field lines with a minimum field off-equator will experience large scale transport toward high latitude, being trapped at high latitude, and then being scattered back through Shabansky orbit [Shabansky, 1971]. The particle trajectories inside the magnetosphere can be grouped into three classes: (a) bouncing around the Equator (trapped); (b) going through Shabansky Orbit or being elevated at dayside (pseudo-trapped); (c) lost. Characterizing these three regions of particles and understanding their dependence on the solar wind condition can help understand the energization and loss of energetic particles in the radiation belt. Recently, we developed a 3D particle tracing code to simulate particle transport in transient global MHD (LFM model) simulation output. The protons are traced with full-motion and electrons are traced with guiding-center approximation. By launching energetic electrons and protons with different pitch angle and from various location along the tail in the model magnetosphere, recording and averaging the latitude the particle experiences at the dayside, we derive the Shabansky Orbit Accessibility Map (SOAMap) to visualize the three regions (trapped, pseudo-trapped, and lost) and their dependence on the initial launching position and pitch angle. We derived the SOAMaps for both electrons and protons inside steady state magnetosphere under different solar wind conditions. We also studied the evolution of the SOAMaps during a simulated magnetospheric substorm triggered by the turning of the solar wind IMF from northward to southward. Combining 3D particle tracing and global MHD simulation provides an integrated view of 3D energetic particle transport inside the Earth's magnetosphere. Shabansky, V. P., Some processes in the magnetosphere, Space Sci. Rev., 12, 299, 1971.

Shao, X.; Fung, S. F.; Tan, L. C.; Papadopoulos, K.; Wiltberger, M.; Lyon, J. G.

2003-12-01

366

Interaction of Cometary Material With the Solar Corona: EUV Observations and MHD Simulations

NASA Astrophysics Data System (ADS)

Extreme ultraviolet (EUV) emission from two recent sun-grazing comets, C/2011 N3 and C/2011 W3 (Lovejoy), has been observed in the solar corona for the first time by the SDO/AIA and STEREO/EUVI instruments (Schrijver et al. 2011). These observations provided a unique opportunity to investigate the interaction of the cometary material with the solar corona and probe their physical conditions. We present here EUV observations and MHD simulations on this subject, focusing on the deceleration of the cometary tail material within the corona. We found that despite their different local coronal environments, the two comets exhibited quite similar characteristics. The initial EUV emitting tail had a projected velocity of 100-200 km/s, which was much lower than the orbital velocity of 500-600 km/s in the plane-of-sky. This indicates that significant deceleration had taken place while the tail material was heated to coronal temperatures on the order of 1 MK before it started to emit in EUV (Bryans & Pesnell 2012). After its initial appearance, the tail further experienced a projected deceleration of ~1 km/s^2 (or 4 g_Sun). In particular, in the Lovejoy case, the tail appeared as clusters of bright parallel striations roughly at right angles to the orbit direction, suggestive of magnetic field lines illuminated by the plasma frozen onto them. These striations came to a stop and then accelerated in an opposite direction (seen in projection), approaching a constant velocity of ~50 km/s. These observations suggest that a Lorentz force from the coronal magnetic field was operating on the newly ionized cometary plasma. To test this hypothesis and understand tail deceleration mechanisms, we adopted a multi-fluid MHD model (Jia et al. 2012) to simulate the interaction between charged particles and the magnetized coronal plasma. We used potential extrapolation (Schrijver & DeRosa 2003) and a more sophisticated global MHD model (Lionello et al. 2009) to infer the magnetic field and plasma conditions of the corona along the comet's orbit as inputs to the simulations. We will compare the observations and simulation results, and discuss the implications for using sun-grazing comets as probes to the solar corona in the context of NASA's future Solar Probe Plus mission.

Liu, W.; Jia, Y.; Downs, C.; Schrijver, C.; Saint-Hilaire, P.; Battams, K.; Tarbell, T. D.; Shine, R. A.

2012-12-01

367

3D MHD simulations of the flapping instability - magnetic reconnection interaction.

NASA Astrophysics Data System (ADS)

Earth's magnetotail is susceptible to MHD-scale kink-like oscillations that bend the current sheet in the equatorial plane. An analytical theory developed recently suggests that the oscillations can exist if normal and tangential magnetic field gradients are non-zero, hence the name (double-gradient mode). The mode is stable if the product of these two gradients is positive, and unstable if the product is negative. The latter case was successfully reproduced recently by large-scale MHD simulations. In the present report we investigate the interaction of localised magnetic reconnection pulse and the flapping instability. Grad-Shafranov equation solution provides for the initial tail-like condition, and reconnection is started by adding anomalous resistivity at the current sheet center. Plasma flows significantly increase the local gradients at the jet front, leading to much faster flapping mode development. Notably, if the initial configuration is flapping unstable, then the reconnection jet shows evidences of a kink-like bending in the equatorial plane. In the nonlinear stage the front extent in the vertical ("Z" GSM) direction increases due to instability, hence local generation of the mode can lead to structuring of magnetotail dipolarization fronts and is of potential importance for tail dynamics.

Divin, Andrey; Erkaev, Nikolay; Lapenta, Giovanni; Markidis, Stefano; Korovinskiy, Daniil; Semenov, Vladimir; Kubyshkina, Daria

368

Sub-Alfvenic Non-Ideal MHD Turbulence Simulations with Ambipolar Diffusion: I. Turbulence Statistics

Most numerical investigations on the role of magnetic fields in turbulent molecular clouds (MCs) are based on ideal magneto-hydrodynamics (MHD). However, MCs are weakly ionized, so that the time scale required for the magnetic field to diffuse through the neutral component of the plasma by ambipolar diffusion (AD) can be comparable to the dynamical time scale. We have performed a series of 256^3 and 512^3 simulations on supersonic but sub-Alfvenic turbulent systems with AD using the Heavy-Ion Approximation developed in Li, McKee, & Klein (2006). Our calculations are based on the assumption that the number of ions is conserved, but we show that these results approximately apply to the case of time-dependent ionization in molecular clouds as well. Convergence studies allow us to determine the optimal value of the ionization mass fraction when using the heavy-ion approximation for low Mach number, sub-Alfvenic turbulent systems. We find that ambipolar diffusion steepens the velocity and magnetic power spectra compared to the ideal MHD case. Changes in the density PDF, total magnetic energy, and ionization fraction are determined as a function of the AD Reynolds number. The power spectra for the neutral gas properties of a strongly magnetized medium with a low AD Reynolds number are similar to those for a weakly magnetized medium; in particular, the power spectrum of the neutral velocity is close to that for Burgers turbulence.

Pak Shing Li; Christopher F. McKee; Richard I. Klein; Robert T. Fisher

2008-05-05

369

Sub-Alfvenic Non-Ideal MHD Turbulence Simulations with Ambipolar Diffusion: I. Turbulence Statistics

Most numerical investigations on the role of magnetic fields in turbulent molecular clouds (MCs) are based on ideal magneto-hydrodynamics (MHD). However, MCs are weakly ionized, so that the time scale required for the magnetic field to diffuse through the neutral component of the plasma by ambipolar diffusion (AD) can be comparable to the dynamical time scale. We have performed a series of 256{sup 3} and 512{sup 3} simulations on supersonic but sub-Alfvenic turbulent systems with AD using the Heavy-Ion Approximation developed in Li et al. (2006). Our calculations are based on the assumption that the number of ions is conserved, but we show that these results approximately apply to the case of time-dependent ionization in molecular clouds as well. Convergence studies allow us to determine the optimal value of the ionization mass fraction when using the heavy-ion approximation for low Mach number, sub-Alfvenic turbulent systems. We find that ambipolar diffusion steepens the velocity and magnetic power spectra compared to the ideal MHD case. Changes in the density PDF, total magnetic energy, and ionization fraction are determined as a function of the AD Reynolds number. The power spectra for the neutral gas properties of a strongly magnetized medium with a low AD Reynolds number are similar to those for a weakly magnetized medium; in particular, the power spectrum of the neutral velocity is close to that for Burgers turbulence.

Klein, R I; Li, P S; McKee, C F; Fisher, R

2008-04-10

370

Characteristics of magnetic solar-like cycles in a 3D MHD simulation of solar convection

NASA Astrophysics Data System (ADS)

We analyse the statistical properties of the stable magnetic cycle unfolding in an extended 3D magnetohydrodynamic simulation of solar convection produced with the EULAG-MHD code. The millennium simulation spans over 1650 years, in the course of which forty polarity reversals take place on a regular ~40 yr cadence, remaining well-synchronized across solar hemispheres. In order to characterize this cycle and facilitate its comparison with measures typically used to represent solar activity, we build two proxies for the magnetic field in the simulation mimicking the solar toroidal field and the polar radial field. Several quantities that characterize the cycle are measured (period, amplitudes, etc.) and correlations between them are computed. These are then compared with their observational analogs. From the typical Gnevyshev-Ohl pattern, to hints of Gleissberg modulation, the simulated cycles share many of the characteristics of their observational analogs even though the simulation lacks poloidal field regeneration through active region decay, a mechanism nowadays often considered an essential component of the solar dynamo. Some significant discrepancies are also identified, most notably the in-phase variation of the simulated poloidal and toroidal large-scale magnetic components, and the low degree of hemispheric coupling at the level of hemispheric cycle amplitudes. Possible causes underlying these discrepancies are discussed. Appendix is available in electronic form at http://www.aanda.org

Passos, D.; Charbonneau, P.

2014-08-01

371

NASA Technical Reports Server (NTRS)

The NASA-Cornell Univ.-Worcester Polytechnic Institute Fast Fourier Transform (FFT) chip based on the architecture of the systolic FFT computation as presented by Boriakoff is implemented into an operating device design. The kernel of the system, a systolic inner product floating point processor, was designed to be assembled into a systolic network that would take incoming data streams in pipeline fashion and provide an FFT output at the same rate, word by word. It was thoroughly simulated for proper operation, and it has passed a comprehensive set of tests showing no operational errors. The black box specifications of the chip, which conform to the initial requirements of the design as specified by NASA, are given. The five subcells are described and their high level function description, logic diagrams, and simulation results are presented. Some modification of the Read Only Memory (ROM) design were made, since some errors were found in it. Because a four stage pipeline structure was used, simulating such a structure is more difficult than an ordinary structure. Simulation methods are discussed. Chip signal protocols and chip pinout are explained.

Boriakoff, Valentin; Chen, Wei

1990-01-01

372

1 Simulating the thermo-chemical magmatic and tectonic evolution of1 Venus' mantle and lithosphere Numerical convection models of the thermo-chemical evolution of Venus are compared to present-8 day overturn interspersed by periods of quiescence13 effectively loses Venus' heat while giving lower rates

Tackley, Paul J.

373

Predictions of an exact numerical model for scattering from a surface randomly rough in two directions are compared with experimental data. The numerical model is based on Monte Carlo simulation using an iterative version of the method of moments known as the sparse-matrix flat-surface iterative approach (SMFSIA). Experimental data is obtained from millimeter wave laboratory experiments in which the bistatic

Joel T. Johnson; Leung Tsang; Robert T. Shin; K. Pak; Chi H. Chan; Akira Ishimaru; Yasuo Kuga

1996-01-01

374

Numerical flow simulation in the slagging stage of an MHD coal combustor

NASA Astrophysics Data System (ADS)

MHD is a process for efficiently converting the energy in coal into electricity. The MHD process imposes some unique conditions on the coal combustor. First, the MHD process requires an electrically conductive gas stream. This is accomplished by burning the coal at a very high temperature, approaching 3000 K, by means of oxygen enrichment, and by seeding the combustion products with an easily ionized compound such as potassium carbonate. Second, it is desirable to prevent most of the coal slag from reaching the MHD channel. This is done by separating most of the slag from the gas stream in the combustor. A design criterion for MHD coal combustors in 90 percent slag rejection. The design of magnetohydrodynamics (MHD) combustors can be greatly enhanced by examining the flow patterns in existing MHD combustors. This article presents the present results of an effort to examine these flow patterns using numerical techniques.

Norton, O. P.; Skaggs, A.; Bouchillon, C. W.

375

Dayside Proton Aurora: Comparisons between Global MHD Simulations and Image Observations

NASA Technical Reports Server (NTRS)

The IMAGE mission provides a unique opportunity to evaluate the accuracy of current global models of the solar wind interaction with the Earth's magnetosphere. In particular, images of proton auroras from the Far Ultraviolet Instrument (FUV) onboard the IMAGE spacecraft are well suited to support investigations of the response of the Earth's magnetosphere to interplanetary disturbances. Accordingly, we have modeled two events that occurred on June 8 and July 28, 2000, using plasma and magnetic field parameters measured upstream of the bow shock as input to three-dimensional magnetohydrodynamic (MHD) simulations. This paper begins with a discussion of images of proton auroras from the FUV SI-12 instrument in comparison with the simulation results. The comparison showed a very good agreement between intensifications in the auroral emissions measured by FUV SI-12 and the enhancement of plasma flows into the dayside ionosphere predicted by the global simulations. Subsequently, the IMAGE observations are analyzed in the context of the dayside magnetosphere's topological changes in magnetic field and plasma flows inferred from the simulation results. Finding include that the global dynamics of the auroral proton precipitation patterns observed by IMAGE are consistent with magnetic field reconnection occurring as a continuous process while the iMF changes in direction and the solar wind dynamic pressure varies. The global simulations also indicate that some of the transient patterns observed by IMAGE are consistent with sporadic reconnection processes. Global merging patterns found in the simulations agree with the antiparallel merging model. though locally component merging might broaden the merging region, especially in the region where shocked solar wind discontinuities first reach the magnetopause. Finally, the simulations predict the accretion of plasma near the bow shock in the regions threaded by newly open field lines on which plasma flows into the dayside ionosphere are enhanced. Overall the results of these initial comparisons between global MHD simulation results and IMAGE observations emphasize the interplay between reconnection and dynamic pressure processes at the dayside magnetopause. as well as the intricate connection between the bow shock and the auroral region.

Berchem, J.; Fuselier, S. A.; Petrinec, S.; Frey, H. U.; Burch, J. L.

2003-01-01

376

NASA Astrophysics Data System (ADS)

A 2-D multi-stage simulation model incorporating realistic laser conditions and a fully resolved electron distribution handoff has been developed and compared to angularly and spectrally resolved Bremsstrahlung measurements from high-Z planar targets. For near-normal incidence and 0.5-1 × 1020 W/cm2 intensity, particle-in-cell (PIC) simulations predict the existence of a high energy electron component consistently directed away from the laser axis, in contrast with previous expectations for oblique irradiation. Measurements of the angular distribution are consistent with a high energy component when directed along the PIC predicted direction, as opposed to between the target normal and laser axis as previously measured.

Chen, C. D.; Kemp, A. J.; Pérez, F.; Link, A.; Beg, F. N.; Chawla, S.; Key, M. H.; McLean, H.; Morace, A.; Ping, Y.; Sorokovikova, A.; Stephens, R. B.; Streeter, M.; Westover, B.; Patel, P. K.

2013-05-01

377

NASA Astrophysics Data System (ADS)

We apply the Bammann inelastic internal state variable model (BIISV) to a mantle convection code TERRA2D to investigate the influence of a history dependent solid mechanics model on mantle convection. We compare and contrast the general purpose BIISV model to the commonly used power-law model. We implemented the BIISV model using a radial return algorithm and tested it against previously published mantle convection simulation results for verification. Model constants for the BIISV are used based on experimental stress-strain behaviour found in the literature. After implementation we give illustrative simulation examples were the BIISV produces hardened areas on the cold thermal boundary layer that the power-law model cannot produce. The hardened boundary layers divert material downward giving a plausible reason for the current subduction zones that are present on the Earth.

Sherburn, J. A.; Horstemeyer, M. F.; Bammann, D. J.; Baumgardner, J. R.

2011-09-01

378

NASA Technical Reports Server (NTRS)

We use the global magnetohydrodynamic (MHD) code BATS-R-US to model multipoint observations of Flux Transfer Event (FTE) signatures. Simulations with high spatial and temporal resolution predict that cavities of weak magnetic field strength protruding into the magnetosphere trail FTEs. These predictions are consistent with recently reported multi-point Cluster observations of traveling magnetopause erosion regions (TMERs).

Kuznetsova, M. M.; Sibeck, D. G.; Hesse, M.; Wang, Y.; Rastaetter, L.; Toth, G.; Ridley, A.

2009-01-01

379

We present three-dimensional magnetohydrodynamic (MHD) simulations of superbubbles, to study the importance of MHD effects in the interpretation of images from recent surveys of the Galactic plane. These simulations focus mainly on atmospheres defined by an exponential density distribution and the Dickey and Lockman density distribution. In each case, the magnetic field is parallel to the Galactic plane and we investigate cases with either infinite scale height (constant magnetic field) or a constant ratio of gas pressure to magnetic pressure. The three-dimensional structure of superbubbles in these simulations is discussed with emphasis on the axial ratio of the cavity as a function of magnetic field strength and the age of the bubble. We investigate systematic errors in the age of the bubble and scale height of the surrounding medium that may be introduced by modeling the data with purely hydrodynamic models. Age estimates derived with symmetric hydrodynamic models fitted to an asymmetric magnetized superbubble can differ by up to a factor of 4, depending on the direction of the line of sight. The scale height of the surrounding medium based on the Kompaneets model may be up to 50% lower than the actual scale height. We also present the first ever predictions of Faraday rotation by a magnetized superbubble based on three-dimensional MHD simulations. We emphasize the importance of MHD effects in the interpretation of observations of superbubbles.

Stil, Jeroen; Wityk, Nicole; Ouyed, Rachid; Taylor, A. R. [Department of Physics and Astronomy, University of Calgary, 2500 University Drive NW, Calgary, Alberta, T2N 1N4 (Canada)

2009-08-10

380

Successful restoration of the southern Florida ecosystem requires extensive knowledge of the physical characteristics and hydrologic processes controlling water flow and transport of constituents through extremely low-gradient freshwater marshes, shallow mangrove-fringed coastal creeks and tidal embayments, and near-shore marine waters. A sound, physically based numerical model can provide simulations of the differing hydrologic conditions that might result from various ecosystem restoration scenarios. Because hydrology and ecology are closely linked in southern Florida, hydrologic model results also can be used by ecologists to evaluate the degree of ecosystem restoration that could be achieved for various hydrologic conditions. A robust proven model, SWIFT2D, (Surface-Water Integrated Flow and Transport in Two Dimensions), was modified to simulate Southern Inland and Coastal Systems (SICS) hydrodynamics and transport conditions. Modifications include improvements to evapotranspiration and rainfall calculation and to the algorithms that describe flow through coastal creeks. Techniques used in this model should be applicable to other similar low-gradient marsh settings in southern Florida and elsewhere. Numerous investigations were conducted within the SICS area of southeastern Everglades National Park and northeastern Florida Bay to provide data and parameter values for model development and testing. The U.S. Geological Survey and the National Park Service supported investigations for quantification of evapotranspiration, vegetative resistance to flow, wind-induced flow, land elevations, vegetation classifications, salinity conditions, exchange of ground and surface waters, and flow and transport in coastal creeks and embayments. The good agreement that was achieved between measured and simulated water levels, flows, and salinities through minimal adjustment of empirical coefficients indicates that hydrologic processes within the SICS area are represented properly in the SWIFT2D model, and that the spatial and temporal resolution of these processes in the model is adequate. Sensitivity analyses were conducted to determine the effect of changes in boundary conditions and parameter values on simulation results, which aided in identifying areas of greatest uncertainty in the model. The parameter having the most uncertainty (most in need of further field study) was the flow coefficient for coastal creeks. Smaller uncertainties existed for wetlands frictional resistance and wind. Evapotranspiration and boundary inflows indicated the least uncertainty as determined by varying parameters used in their formulation and definition. Model results indicated that wind was important in reversing coastal creek flows. At Trout Creek (the major tributary connecting Taylor Slough wetlands with Florida Bay), flow in the landward direction was not simulated properly unless wind forcing was included in the simulation. Simulations also provided insight into the major influence that wind has on salinity mixing along the coast, the varying distribution of wetland flows at differing water levels, and the importance of topography in controlling flows to the coast. Slight topographic variations were shown to highly influence the routing of water. A multiple regression analysis was performed to relate inflows at the northern boundary of Taylor Slough bridge to a major pump station (S-332) north of the SICS model area. This analysis allows Taylor Slough bridge boundary conditions to be defined for the model from operating scenarios at S-332, which should facilitate use of the SICS model as an operational tool.

Swain, Eric D.; Wolfert, Melinda A.; Bales, Jerad D.; Goodwin, Carl R.

2004-01-01

381

MHD simulations of jet acceleration from Keplerian accretion disks: the effects of disk resistivity

Accretion disks and astrophysical jets are used to model many active astrophysical objects, viz., young stars, relativistic stars, and active galactic nuclei. In this paper we present self-consistent time-dependent simulations of supersonic jets launched from magnetized accretion disks, using high resolution numerical techniques. In particular we study the effects of the disk magnetic resistivity, parametrized through an alpha-prescription, in determining the properties of the inflow-outflow system. Moreover we analyze under which conditions steady state solutions of the type proposed in the self similar models of Blandford and Payne can be reached and maintained in a self consistent nonlinear stage. We use the resistive MHD FLASH code with adaptive mesh refinement, allowing us to follow the evolution of the structure for a time scale long enough to reach steady state. A detailed analysis of the initial configuration state is given. We obtain the expected solutions in the axisymmetric (2.5D) limit. Assuming a...

Zanni, C; Rosner, R; Bodo, G; Massaglia, S

2007-01-01

382

The magnetic topology of the plasmoid flux rope in a MHD-simulation of magnetotail reconnection

NASA Technical Reports Server (NTRS)

On the basis of a 3D MHD simulation, the magnetic topology of a plasmoid that forms by a localized reconnection process in a magnetotail configuration (including a net dawn-dusk magnetic field component B sub y N is discussed. As a consequence of B sub y N not equalling 0, the plasmoid assumes a helical flux rope structure rather than an isolated island or bubble structure. Initially all field lines of the plasmoid flux rope remain connected with the earth, while at later times a gradually increasing amount of flux tubes becomes separated, connecting to either the distant boundary or to the flank boundaries. In this stage, topologically different flux tubes become tangled and wrapped around each other, consistent with predictions on the basis of an ad hoc plasmoid model.

Birn, J.; Hesse, M.

1990-01-01

383

The magnetic topology of the plasmoid flux rope in a MHD simulation of magnetotail reconnection

On the basis of a three-dimensional MHD simulation we discuss the magnetic topology of a plasmoid that forms by a localized reconnection process in a magnetotail configuration including a net dawn-dusk magnetic field component B/sub yN/. As a consequence of b/sub yN/ /ne/ 0 the plasmid gets a helical flux rope structure rather than an isolated island or bubble structure. Initially all field lines of the plasmid flux rope remain connected with the Earth, while at later times a gradually increasing amount of flux tubes becomes separated, connecting to either the distant boundary or to the flank boundaries. In this stage topologically different flux tubes become tangled and wrapped around each other, consistent with predictions on the basis of ad-hoc plasmid models. 10 refs., 8 figs.

Birn, J.; Hesse, M.

1989-01-01

384

2009 US-Japan Workshop on Advanced Simulation Methods in Plasma Physics MHD Simulations of the Solar Astmosphere: Effects of Weak Ionization and Radiation Hiroaki Isobe1 1 Unit of Synergetic Studies subject in solar physics is to understand the variety of dynamics and structure formation

Ito, Atsushi

385

Towards a two dimensional lattice gas with dynamical geometry

We report on simulations using a lattice gas automaton in which the lattice is replaced by a triangulation of an arbitrary two-dimensional manifold. If the manifold is 2D Euclidean space the particles move on the Kagome lattice. We report results of simulations of channel flow for the flat space model and of simulations in which the particle state can change

Anna Klales; Donato Cianci; Zachary Needell; Peter Love

2009-01-01

386

Two-dimensional impurity profiling with emission computed tomography techniques

A technique for the determination of two-dimensional impurity profiles in silicon using methods for emission computed tomography is presented. Several one-dimensional impurity profiles obtained for different directions through the sample are used to reconstruct the two-dimensional profile. A simulation study of the experiment is described, and effects of various experimental and reconstruction parameters are discussed. Reconstructions of an area of

Scott H. Goodwin-johansson; Ravi Subrahmanyan; Carey E. Floyd; Hisham Z. Massoud

1989-01-01

387

Dynamics of Vortices in Two-Dimensional Magnets

Theories, simulations and experiments on vortex dynamics in quasi-two-dimensional magnetic materials are reviewed. These materials can be modelled by the classical two-dimensional anisotropic Heisenberg model with XY (easy-plane) symmetry. There are two types of vortices, characterized by their polarization (a second topological charge in addition to the vorticity): Planar vortices have Newtonian dynamics (even-order equations of motion) and exhibit strong

Franz G. Mertens; Alan R. Bishop

2000-01-01

388

Dynamics of Vortices in Two-Dimensional Magnets

Theories, simulations and experiments on vortex dynamics in quasi-two-dimensional magnetic materials are reviewed. These materials\\u000a can be modelled by the classical two-dimensional anisotropic Heisenberg model with XY (easy-plane) symmetry. There are two types of vortices, characterized by their polarization (a second topological charge\\u000a in addition to the vorticity): Planar vortices have Newtonian dynamics (evenorder equations of motion) and exhibit strong

Franz G. Mertens; Alan R. Bishop

389

Statistical Mechanics of Two-Dimensional Vortices and Stellar Systems

The formation of large-scale vortices is an intriguing phenomenon in two-dimensional turbulence. Such organization is observed\\u000a in large-scale oceanic or atmospheric flows, and can be reproduced in laboratory experiments and numerical simulations. A\\u000a general explanation of this organization was first proposed by Onsager (1949) by considering the statistical mechanics for\\u000a a set of point vortices in two-dimensional hydrodynamics. Similarly, the

Pierre-Henri Chavanis

2002-01-01

390

NASA Technical Reports Server (NTRS)

The goal of this project was the feasibility study of a particular architecture of a digital signal processing machine operating in real time which could do in a pipeline fashion the computation of the fast Fourier transform (FFT) of a time-domain sampled complex digital data stream. The particular architecture makes use of simple identical processors (called inner product processors) in a linear organization called a systolic array. Through computer simulation the new architecture to compute the FFT with systolic arrays was proved to be viable, and computed the FFT correctly and with the predicted particulars of operation. Integrated circuits to compute the operations expected of the vital node of the systolic architecture were proven feasible, and even with a 2 micron VLSI technology can execute the required operations in the required time. Actual construction of the integrated circuits was successful in one variant (fixed point) and unsuccessful in the other (floating point).

Boriakoff, Valentin

1994-01-01

391

NASA Astrophysics Data System (ADS)

A novel methodology for the simulation of 2D thermohaline double diffusive processes, driven by heterogeneous temperature and concentration fields in variable-density saturated porous media, is presented. The stream function is used to describe the flow field and it is defined in terms of mass flux. The partial differential equations governing system is given by the mass conservation equation of the fluid phase written in terms of the mass-based stream function, as well as by the advection-diffusion transport equations of the contaminant concentration and of the heat. The unknown variables are the stream function, the contaminant concentration and the temperature. The governing equations system is solved using a fractional time step procedure, splitting the convective components from the diffusive ones. In the case of existing scalar potential of the flow field, the convective components are solved using a finite volume marching in space and time (MAST) procedure; this solves a sequence of small systems of ordinary differential equations, one for each computational cell, according to the decreasing value of the scalar potential. In the case of variable-density groundwater transport problem, where a scalar potential of the flow field does not exist, a second MAST procedure has to be applied to solve again the ODEs according to the increasing value of a new function, called approximated potential. The diffusive components are solved using a standard Galerkin finite element method. The numerical scheme is validated using literature tests.

Aricò, Costanza; Tucciarelli, Tullio

2009-03-01

392

MHD simulations of disruption mitigation on DIII-D and Alcator C-Mod

NASA Astrophysics Data System (ADS)

The three potential threats posed by disruptions---halo currents, heat fluxes and runaway electrons---scale unfavorably from present tokamaks to ITER. Disruption mitigation experiments on several tokamaks have shown massive gas injection (MGI) to be an effective means of reducing poloidal halo current and heat flux. However, both theory and measurements support the conclusion the penetration of the neutral jet is weak. Thus the core thermal quench relies on MHD, both to mix impurities into the core, and to conduct heat to the impurity-dense edge. NIMROD simulations of C-Mod have shown that enhanced transport alone---due to large 1/1 and 2/1 modes triggered by edge cooling---can quench the core plasma [1]. These simulations show similarity to C-Mod temperature measurements [2], and the role of the 1/1 and 2/1 modes is supported by observations in DIII-D [3]. However, to determine the relative importance of thermal transport versus impurity mixing simulations that include both mechanisms are needed. An extension of the NIMROD code has been developed which includes both accurate atomic physics from the 0D KPRAD code and separate continuity equations for each species. C-Mod simulations for both helium and argon impurities are compared with earlier simulations and experimental data to assess the extent of impurity mixing and evaluate MGI as a mitigation technique for ITER. DIII-D simulations are carried out with different radial neutral fueling profiles to understand the thermal quench when impurity injection is more uniform, or centrally peaked, as would be the case for designer pellets or liquid jets. [1] V.A. Izzo, Nucl. Fusion 46 (2006) 541. [2] R.S. Granetz, et al., Nucl. Fusion 46 (2006) 1001. [3] E.M. Hollmann, et al., Nucl. Fusion 45 (2005) 1046.

Izzo, V. A.

2007-11-01

393

Time-dependent simulation of oblique MHD cosmic-ray shocks using the two-fluid model

NASA Technical Reports Server (NTRS)

Using a new, second-order accurate numerical method we present dynamical simulations of oblique MHD cosmic-ray (CR)-modified plane shock evolution. Most of the calculations are done with a two-fluid model for diffusive shock acceleration, but we provide also comparisons between a typical shock computed that way against calculations carried out using the more complete, momentum-dependent, diffusion-advection equation. We also illustrate a test showing that these simulations evolve to dynamical equilibria consistent with previously published steady state analytic calculations for such shocks. In order to improve understanding of the dynamical role of magnetic fields in shocks modified by CR pressure we have explored for time asymptotic states the parameter space of upstream fast mode Mach number, M(sub f), and plasma beta. We compile the results into maps of dynamical steady state CR acceleration efficiency, epsilon(sub c). We have run simulations using constant, and nonisotropic, obliquity (and hence spatially) dependent forms of the diffusion coefficient kappa. Comparison of the results shows that while the final steady states achieved are the same in each case, the history of CR-MHD shocks can be strongly modified by variations in kappa and, therefore, in the acceleration timescale. Also, the coupling of CR and MHD in low beta, oblique shocks substantially influences the transient density spike that forms in strongly CR-modified shocks. We find that inside the density spike a MHD slow mode wave can be generated that eventually steepens into a shock. A strong layer develops within the density spike, driven by MHD stresses. We conjecture that currents in the shear layer could, in nonplanar flows, results in enhanced particle accretion through drift acceleration.

Frank, Adam; Jones, T. W.; Ryu, Dongsu

1995-01-01

394

Center for Simulation of Wave Interactions with MHD (SWIM) PASCI PAC meeting, May, 2007

Driver component that uses framework services, to set up the working directory structure, initialize and other driving sources to study and control fast time-scale MHD phenomena such as optimizing burning plasma scenarios and improving the understanding of how RF can be employed to achieve long-time MHD

395

condmat/9801215 Crossovers in the Two Dimensional Ising Spin Glass

numerical evidence for a spin glass transition at finite temperature simulating intermediate lattice sizescondÂmat/9801215 v2 26 Jan 1998 Crossovers in the Two Dimensional Ising Spin Glass of extensive computer simulations we analyze in detail the two dimenÂ sional \\SigmaJ Ising spin glass

Roma "La Sapienza", UniversitÃ di

396

NASA Technical Reports Server (NTRS)

Magnetohydrodynamics (MHD) provides an approximate description of a great variety of processes in space physics. Accurate numerical solutions of the MHD equations are still a challenge, but in the past decade a number of robust methods have appeared. Once these techniques made the direct solution of MHD equations feasible, a number of global three-dimensional models were designed and applied to many space physics objects. The range of these objects is truly astonishing, including active galactic nuclei, the heliosphere, the solar corona, and the solar wind interaction with planets, satellites, and comets. Outside the realm of space physics, MHD theory has been applied to such diverse problems as laboratory plasmas and electromagnetic casting of liquid metals. In this paper we present a broad spectrum of models of different phenomena in space science developed in the recent years at the University of Michigan. Although the physical systems addressed by these models are different, they all use the MHD equations as a unifying basis.

Kabin, K.; Hansen, K. C.; Gombosi, T. I.; Combi, M. R.; Linde, T. J.; DeZeeuw, D. L.; Groth, C. P. T.; Powell, K. G.; Nagy, A. F.

2000-01-01

397

Computer simulations of two dimensional quasicrystals

:nn:::N:: Hrr H ~:pi u lH' n Hn'. . . 'H Figure 14. Fourier transform (trapped system). 0. 004 vs rn ? glass 0. 003 0. 002 0. 001 0. 000 0 10 Figure 15. Bond orientational order (trapped system). 0 0 0 0 0 0 0 og o p p 0 ~ p 0 p o op 0...:nn:::N:: Hrr H ~:pi u lH' n Hn'. . . 'H Figure 14. Fourier transform (trapped system). 0. 004 vs rn ? glass 0. 003 0. 002 0. 001 0. 000 0 10 Figure 15. Bond orientational order (trapped system). 0 0 0 0 0 0 0 og o p p 0 ~ p 0 p o op 0...

Johnson, Steven Lee

2012-06-07

398

We find and investigate via numerical simulations self-sustained two-dimensional turbulence in a magnetohydrodynamic flow with a maximally simple configuration: plane, noninflectional (with a constant shear of velocity), and threaded by a parallel uniform background magnetic field. This flow is spectrally stable, so the turbulence is subcritical by nature and hence it can be energetically supported just by a transient growth mechanism due to shear flow non-normality. This mechanism appears to be essentially anisotropic in the spectral (wave-number) plane and operates mainly for spatial Fourier harmonics with streamwise wave numbers less than the ratio of flow shear to Alfvén speed, ky~~MHD) turbulence research. We find similarity of the nonlinear dynamics to the related dynamics in hydrodynamic flows: to the bypass concept of subcritical turbulence. The essence of the analyzed nonlinear MHD processes appears to be a transverse redistribution of kinetic and magnetic spectral energies in the wave-number plane [as occurs in the related hydrodynamic flow; see Horton et al., Phys. Rev. E 81, 066304 (2010)] and differs fundamentally from the existing concepts of (anisotropic direct and inverse) cascade processes in MHD shear flows. PMID:24827349~~

Mamatsashvili, G R; Gogichaishvili, D Z; Chagelishvili, G D; Horton, W

2014-04-01

399

We put forward a new type of spectral method for the direct numerical simulation of flows where anisotropy or very fine boundary layers are present. The mean idea is to take advantage of the fact that such structures are dissipative and that their presence should reduce the number of degrees of freedom of the flow, when paradoxically, their fine resolution incurs extra computational cost in most current methods. The principle of this method is to use a functional basis with elements that already include these fine structure so as to avoid these extra costs. This leads us to develop an algorithm to implement a spectral method for arbitrary functional bases, and in particular, non-orthogonal ones. We construct a basic implementation of this algorithm to simulate Magnetohydrodynamic (MHD) channel flows with an externally imposed, transverse magnetic field, where very thin boundary layers are known to develop along the channel walls. In this case, the sought functional basis can be built out of the eigenfunctions...

Kornet, Kacper

2014-01-01

400

Attempts to Simulate Anisotropies of Solar Wind Fluctuations Using MHD with a Turning Magnetic Field

NASA Technical Reports Server (NTRS)

We examine a "two-component" model of the solar wind to see if any of the observed anisotropies of the fields can be explained in light of the need for various quantities, such as the magnetic minimum variance direction, to turn along with the Parker spiral. Previous results used a 3-D MHD spectral code to show that neither Q2D nor slab-wave components will turn their wave vectors in a turning Parker-like field, and that nonlinear interactions between the components are required to reproduce observations. In these new simulations we use higher resolution in both decaying and driven cases, and with and without a turning background field, to see what, if any, conditions lead to variance anisotropies similar to observations. We focus especially on the middle spectral range, and not the energy-containing scales, of the simulation for comparison with the solar wind. Preliminary results have shown that it is very difficult to produce the required variances with a turbulent cascade.

Ghosh, Sanjoy; Roberts, D. Aaron

2010-01-01

401

The Biermann Battery In Cosmological Mhd Simulations Of Population III Star Formation

We report the results of the first self-consistent three-dimensional adaptive mesh refinement magnetohydrodynamical simulations of Population III star formation including the Biermann battery effect. We find that the Population III stellar cores formed including this effect are both qualitatively and quantitatively similar to those from hydrodynamics-only (non-MHD) cosmological simulations. We observe peak magnetic fields of {approx_equal} 10{sup -9} G in the center of our star-forming halo at z {approx_equal} 17.55 at a baryon density of n{sub B} {approx} 10{sup 10} cm{sup -3}. The magnetic fields created by the Biermann battery effect are predominantly formed early in the evolution of the primordial halo at low density and large spatial scales, and then grow through compression and by shear flows. The fields seen in this calculation are never large enough to be dynamically important (with {beta} {ge} 10{sup 15} at all times before the termination of our calculation), and should be considered the minimum possible fields in existence during Population III star formation. The lack of magnetic support lends credibility to assumptions made in previous calculations regarding the lack of importance of magnetic fields in Population III star formation. In addition, these magnetic fields may be seed fields for the stellar dynamo or the magnetorotational instability at higher densities and smaller spatial scales.

Xu, Hao [Los Alamos National Laboratory; O' Shea, Brian W [Los Alamos National Laboratory; Li, Hui [Los Alamos National Laboratory; Li, Shengtai [Los Alamos National Laboratory; Norman, Michael L [UCSD; Collins, David C [UCSD

2008-01-01

402

NASA Astrophysics Data System (ADS)

We investigate the magnetopause energy conversion and transfer using Cluster spacecraft observations combined with large scale modeling results from GUMICS-4 global MHD simulation. We carry out both event studies observed by Cluster as well as perform a small statistical study to investigate energy transfer spatial dependence utilizing Cluster observations of flux transfer events (FTE's). In particular, we focus on the effect of the interplanetary magnetic field (IMF) y-component that has earlier been found to control the spatial dependence of energy transfer. In both the event studies as well as in the small statistical data set, we find that the GUMICS-4 energy transfer agrees with the Cluster observations spatially and is about 30% lower in magnitude. According to the simulation, most of the the energy transfer takes place in the plane of the IMF (as previous modeling results have suggested), and the locations of the load and generator regions on the magnetopause are controlled by the IMF orientation. Assuming that the model results are as well in accordance with the in situ observations also on other parts of the magnetopause, we are able to pin down the total energy transfer during the two events. Here, we estimate that the instantaneous total power transferring through the magnetopause during the two events is at least 1500-2000 GW, agreeing with epsilon parameter scaled using the mean magnetopause area in the simulation. Hence the combination of the simulation results and the Cluster observations indicate that the epsilon parameter is probably underestimated by a factor of 2-3.

Palmroth, M. M.; Fear, R.; Laitinen, T. V.; Anekallu, C. R.; Honkonen, I. J.; Dunlop, M. W.; Lucek, E. A.; Dandouras, I. S.

2012-12-01

403

Formation and Eruption of an Active Region Sigmoid: NLFFF Modeling and MHD Simulation

NASA Astrophysics Data System (ADS)

We present a magnetic analysis of the formation and eruption of an active region sigmoid in AR 11283 from 2011 September 4 to 6, which is jointly based on observations, static nonlinear force-free field (NLFFF) extrapolation and dynamic MHD simulation. A time sequence of NLFFF model's outputs are used to reproduce the evolution of the magnetic field of the region over three days leading to a X-class flare near the end of 2011 September 6. In the first day, a new bipolar emerges into the negative polarity of a pre-existing mature bipolar, forming a magnetic topology with a coronal null on the magnetic separatrix surface between the two flux system, while the field is still near potential at the end of the day. After then photospheric shearing and twisting build up non-potentiality in the embedded core region, with a flux rope (FR) formed there above the polarity inversion line by tether-cutting reconnection between the strongly sheared field lines. Within this duration, the core field has gained a magnetic free energy of ˜ 1032 erg. In this core a sigmoid is observed distinctly at 22:00 UT on September 6, closely before its eruption at 22:12 UT. Comparison of the SDO/AIA observations with coronal magnetic field suggests that the sigmoid is formed by emission due to enhanced current sheet along the BPSS (bald-patch separatrix surface, in which the field lines graze the line-tied photosphere at the neutral line) that separates the FR from the ambient flux. Quantitative inspection of the pre-eruption field on 22:00 UT suggests a mechanism for the eruption: tether cutting at the null triggers a torus instability of the FR--overlying field system. This pre-eruption NLFFF is then input into a time-dependent MHD model to simulate the fast magnetic evolution during eruption, which successfully reproduces the observations. The highly asymmetric magnetic environment along with the lateral location of the null leads to a strongly inclined non-radial direction of the eruption. The study of this kind provides important insights in a quantitative way to many open issues on the formation and eruption of sigmoidal FR.

Jiang, C.; Wu, S.; Feng, X.; Hu, Q.

2013-12-01

404

NASA Astrophysics Data System (ADS)

A parallel implementation of a nonlinear pseudo-spectral MHD code for the simulation of turbulent dynamos in spherical geometry is reported. It employs a dual domain decomposition technique in both real and spectral space. It is shown that this method shows nearly ideal scaling going up to 128 CPUs on Beowulf-type clusters with fast interconnect. Furthermore, the potential of exploiting single precision arithmetic on standard x86 processors is examined. It is pointed out that the MHD code thereby achieves a maximum speedup of 1.7, whereas the validity of the computations is still granted. The combination of both measures will allow for the direct numerical simulation of highly turbulent cases ( 1500

Reuter, K.; Jenko, F.; Forest, C. B.; Bayliss, R. A.

2008-08-01