Two-dimensional hybrid MHD-kinetic electron simulations of an Alfven wave pulse
Wright, Andrew N.
Two-dimensional hybrid MHD-kinetic electron simulations of an Alfve´n wave pulse P. A. Damiano hybrid MHD-kinetic model incorporating kinetic electrons is used to simulate a shear Alfve´n wave pulse field accurately. Citation: Damiano, P. A., and A. N. Wright (2005), Two-dimensional hybrid MHD-kinetic
Two-dimensional MHD simulation of isothermal plasma armatures
NASA Astrophysics Data System (ADS)
Boynton, G. C.; Huerta, M. A.
1989-06-01
The authors report results on the use of a two-dimensional resistive MHD code to simulate the internal dynamics in a railgun plasma armature, starting from a slightly perturbed equilibrium initial state. The plasma temperature, conductivity, and ionization fractions are treated as uniform in space and constant in time. The rear of the plasma is in contact with a low-pressure nonconducting gas. A finite-difference, explicit, Eulerian, flux-corrected transport code is used to advance all quantities in time. The computation grid has 200 cells parallel to the rails, and 20 across the rails. The results show the growth and subsequent shedding of the plasma mass toward the nonconducting region at the rear. The mass lost is not replenished and the armature becomes shorter, with steeper pressure and magnetic field profiles. The bulk of the profiles is not thoroughly disrupted, but behaves rather sturdily and seems to maintain a shape fairly close to the equilibrium profiles.
Two-dimensional MHD simulations of a neon Z pinch on Hawk
Joseph W. Schumer; David Mosher; Bryan Moosman; Bruce V. Weber; Robert J. Commisso; Niansheng Qi; Jochen Schein; Mahadevan Krishnan
2002-01-01
Two-dimensional magnetohydrodynamic (MHD) simulations using MACH2 are benchmarked against laser shearing interferometer (LSI) images of the evolving electron-density sheath during 250-ns neon gas-puff Z pinch implosions on the Naval Research Laboratory Hawk generator. The initial density distribution for the MHD simulations is calculated using a ballistic-flow-model fit to the measured initial gas-density distributions. The implosion is modeled using an applied
Two-dimensional heat conducting simulation of plasma armatures
Huerta, M.A.; Boynton, G. . Dept. of Physics)
1991-01-01
This paper reports on our development of a two-dimensional MHD code to simulate internal motions in a railgun plasma armature. The authors use the equations of resistive MHD, with Ohmic heating, and radiation heat transport. The authors use a Flux Corrected Transport code to advance all quantities in time. Our runs show the development of complex flows, subsequent shedding of secondary arcs, and a drop in the acceleration of the armature.
Matsumoto, Takuma
2011-01-01
We report the results of the first two-dimensional self-consistent simulations directly covering from the photosphere to the interplanetary space. We carefully set up grid points with spherical coordinate to treat Alfv\\'enic waves in the atmosphere with the huge density contrast, and successfully simulate hot coronal wind streaming out as a result of surface convective motion. Footpoint motion excites upwardly propagating Alfv\\'enic waves along an open magnetic flux tube. These waves, traveling in non-uniform medium, suffer reflection, nonlinear mode conversion to compressive modes, and turbulent cascade. Combination of these mechanisms, the Alfv\\'enic waves eventually dissipate to accelerate the solar wind. While the shock heating by the dissipation of the compressive wave plays a primary role in the coronal heating, both turbulent cascade and shock heating contribute to drive the solar wind.
Simulation of two-dimensional vortex dynamics
NASA Astrophysics Data System (ADS)
Minnhagen, Petter; Westman, Olof
1994-02-01
The two-dimensional XY model is simulated with a time-dependent Ginzburg-Landau type dynamics. The data are, in the limit of small driving force, well described by the Minnhagen phenomenology for vortex dynamics of a two-dimensional superfluid. This phenomenology is different and distinguishable from the conventional AHNS phenomenology. The Minnhagen phenomenology has been observed in recent experiments on Josephson-junction arrays and high- Tc BSCCO films. The present simulations suggest that this reflects an intrinsic property of the vortex dynamics for a two-dimensional superfluid.
Hall MHD Modeling of Two-dimensional Reconnection: Application to MRX Experiment
V.S. Lukin; S.C. Jardin
2003-01-09
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.
Two-dimensional MHD model of the Jovian magnetodisk
NASA Astrophysics Data System (ADS)
Kislov, R. A.; Malova, H. V.; Vasko, I. Y.
2015-09-01
A self-consistent stationary axially symmetric MHD model of the Jovian magnetodisk is constructed. This model is a generalization of the models of plane current sheets that have been proposed earlier in order to describe the structure of the current sheet in the magnetotail of the Earth [1, 2]. The model takes centrifugal force, which is induced by the corotation electric field, and the azimuthal magnetic field into account. The configurations of the magnetic field lines for the isothermic (plasma temperature assumed to be constant) and the isentropic (plasma entropy assumed to be constant) models of the magnetodisk are determined. The dependence of the thickness of the magnetodisk on the distance to Jupiter is obtained. The thickness of the magnetodisk and the magnetic field distribution in the isothermic and isentropic models are similar. The inclusion of a low background plasma pressure results in a considerable reduction in the thickness of the magnetodisk. This effect may be attributed to the fact that centrifugal force prevails over the pressure gradient at large distances from the planet. The mechanism of unipolar induction and the related large-scale current system are analyzed. The direct and return Birkeland currents are determined in the approximation of a weak azimuthal magnetic field. The modeling results agree with theoretical estimates from other studies and experimental data.
A Two Dimensional Car Crash Victim Simulation
M. Batman; R. Seliktar
1990-01-01
The purpose of this study was to develop a two dimensional mathematical model of an unrestrained, right, front seat, passenger car occupant, subjected to frontal collision. A 10 degrees of freedom linkage system made of 8 rigid segments connected with revolute joints was used as occupant model. Relative rotation between links were constrained by torsional springs, dampers, Coulomb frictions and
Two-dimensional Magnetohydrodynamic Simulations of Barred Galaxies
NASA Astrophysics Data System (ADS)
Kim, Woong-Tae; Stone, James M.
2012-06-01
Barred galaxies are known to possess magnetic fields that may affect the properties of bar substructures such as dust lanes and nuclear rings. We use two-dimensional high-resolution magnetohydrodynamic (MHD) simulations to investigate the effects of magnetic fields on the formation and evolution of such substructures, as well as on the mass inflow rates to the galaxy center. The gaseous medium is assumed to be infinitesimally thin, isothermal, non-self-gravitating, and threaded by initially uniform, azimuthal magnetic fields. We find that there exists an outermost x 1-orbit relative to which gaseous responses to an imposed stellar bar potential are completely different between inside and outside. Inside this orbit, gas is shocked into dust lanes and infalls to form a nuclear ring. Magnetic fields are compressed in dust lanes, reducing their peak density. Magnetic stress removes further angular momentum of the gas at the shocks, temporarily causing the dust lanes to bend into an "L" shape and eventually leading to a smaller and more centrally distributed ring than in unmagnetized models. The mass inflow rates in magnetized models correspondingly become larger, by more than two orders of magnitude when the initial fields have an equipartition value with thermal energy, than in the unmagnetized counterparts. Outside the outermost x 1-orbit, on the other hand, an MHD dynamo due to the combined action of the bar potential and background shear operates near the corotation and bar-end regions, efficiently amplifying magnetic fields. The amplified fields shape into trailing magnetic arms with strong fields and low density. The base of the magnetic arms has a thin layer in which magnetic fields with opposite polarity reconnect via a tearing-mode instability. This produces numerous magnetic islands with large density that propagate along the arms to turn the outer disk into a highly chaotic state.
TWO-DIMENSIONAL MAGNETOHYDRODYNAMIC SIMULATIONS OF BARRED GALAXIES
Kim, Woong-Tae; Stone, James M. E-mail: jstone@astro.princeton.edu
2012-06-01
Barred galaxies are known to possess magnetic fields that may affect the properties of bar substructures such as dust lanes and nuclear rings. We use two-dimensional high-resolution magnetohydrodynamic (MHD) simulations to investigate the effects of magnetic fields on the formation and evolution of such substructures, as well as on the mass inflow rates to the galaxy center. The gaseous medium is assumed to be infinitesimally thin, isothermal, non-self-gravitating, and threaded by initially uniform, azimuthal magnetic fields. We find that there exists an outermost x{sub 1}-orbit relative to which gaseous responses to an imposed stellar bar potential are completely different between inside and outside. Inside this orbit, gas is shocked into dust lanes and infalls to form a nuclear ring. Magnetic fields are compressed in dust lanes, reducing their peak density. Magnetic stress removes further angular momentum of the gas at the shocks, temporarily causing the dust lanes to bend into an 'L' shape and eventually leading to a smaller and more centrally distributed ring than in unmagnetized models. The mass inflow rates in magnetized models correspondingly become larger, by more than two orders of magnitude when the initial fields have an equipartition value with thermal energy, than in the unmagnetized counterparts. Outside the outermost x{sub 1}-orbit, on the other hand, an MHD dynamo due to the combined action of the bar potential and background shear operates near the corotation and bar-end regions, efficiently amplifying magnetic fields. The amplified fields shape into trailing magnetic arms with strong fields and low density. The base of the magnetic arms has a thin layer in which magnetic fields with opposite polarity reconnect via a tearing-mode instability. This produces numerous magnetic islands with large density that propagate along the arms to turn the outer disk into a highly chaotic state.
Numerical analysis of real gas MHD flow on two-dimensional self-field MPD thrusters
NASA Astrophysics Data System (ADS)
Xisto, Carlos M.; Páscoa, José C.; Oliveira, Paulo J.
2015-07-01
A self-field magnetoplasmadynamic (MPD) thruster is a low-thrust electric propulsion space-system that enables the usage of magnetohydrodynamic (MHD) principles for accelerating a plasma flow towards high speed exhaust velocities. It can produce an high specific impulse, making it suitable for long duration interplanetary space missions. In this paper numerical results obtained with a new code, which is being developed at C-MAST (Centre for Mechanical and Aerospace Technologies), for a two-dimensional self-field MPD thruster are presented. The numerical model is based on the macroscopic MHD equations for compressible and electrically resistive flow and is able to predict the two most important thrust mechanisms that are associated with this kind of propulsion system, namely the thermal thrust and the electromagnetic thrust. Moreover, due to the range of very high temperatures that could occur during the operation of the MPD, it also includes a real gas model for argon.
On the Transition from Two-Dimensional to Three-Dimensional MHD Turbulence
NASA Technical Reports Server (NTRS)
Thess, A.; Zikanov, Oleg
2004-01-01
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.
Stochastic simulation of chemical exchange in two dimensional infrared spectroscopy
Mukamel, Shaul
equations are employed to investigate the combined signatures of chemical exchange two-state jumpStochastic simulation of chemical exchange in two dimensional infrared spectroscopy Frantisek. INTRODUCTION Chemical exchange processes cause time-dependent spectral jumps between stable configurations
Dissipative MHD solutions for resonant Alfvén waves in two-dimensional poloidal magnetoplasmas
NASA Astrophysics Data System (ADS)
Tirry, W. J.; Goossens, M.
1995-12-01
The resonant excitation of Alfvén waves is considered in a resistive warm plasma embedded in a purely poloidal field. The magnetostatic equilibrium is invariant in the y direction. The driven problem is studied in the asymptotic state, so we can assume that all wave fields vary as exp[i(?y-?t)]. Resistive solutions are derived in the vicinity of the resonance with the aid of an asymptotic expansion procedure. We find that the zeroth-order functions of the flux coordinate have to satisfy differential equations analogous to those obtained by Goossens et al. [1995] for the resistive one-dimensional systems. Applied to the two-dimensional box model for the Earth's magnetosphere, we recover the results found by Thompson and Wright [1993] in ideal MHD, but in addition, we obtain the behavior in the dissipative layer in the asymptotic state.
MHD simulation studies of z-pinch shear flow stabilization
I. Paraschiv; B. S. Bauer; V. I. Sotnikov; V. Makhin; R. E. Siemon
2003-01-01
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
TreePM Method for Two-Dimensional Cosmological Simulations
Suryadeep Ray
2004-06-01
We describe the two-dimensional TreePM method in this paper. The 2d TreePM code is an accurate and efficient technique to carry out large two-dimensional N-body simulations in cosmology. This hybrid code combines the 2d Barnes and Hut Tree method and the 2d Particle-Mesh method. We describe the splitting of force between the PM and the Tree parts. We also estimate error in force for a realistic configuration. Finally, we discuss some tests of the code.
Two-dimensional Simulations of Correlation Reflectometry in Fusion Plasmas
E.J. Valeo; G.J. Kramer; R. Nazikian
2001-07-05
A two-dimensional wave propagation code, developed specifically to simulate correlation reflectometry in large-scale fusion plasmas is described. The code makes use of separate computational methods in the vacuum, underdense and reflection regions of the plasma in order to obtain the high computational efficiency necessary for correlation analysis. Simulations of Tokamak Fusion Test Reactor (TFTR) plasma with internal transport barriers are presented and compared with one-dimensional full-wave simulations. It is shown that the two-dimensional simulations are remarkably similar to the results of the one-dimensional full-wave analysis for a wide range of turbulent correlation lengths. Implications for the interpretation of correlation reflectometer measurements in fusion plasma are discussed.
Two dimensional particle simulations of Raman backward amplifier
NASA Astrophysics Data System (ADS)
Hur, Min; Lindberg, Ryan; Wurtele, Jonathan
2005-10-01
We carried out two-dimensional particle simulations of the Raman backward amplifier. The particle code is based on the one-dimensional averaged-PIC (aPIC) code [1]. From the speculation that the longitudinal ponderomotive driving by the two counter-propagating lasers is quite dominant over the transverse one, the two-dimensional version of the aPIC can be easily built up by putting many one-dimensional aPIC solvers in parallel. The solvers are coupled by the diffraction terms of the lasers, which enables one to simulate the transverse effects in the Raman backward amplifier. One of the most important issues regarding the transverse effects is the focusability of the amplified pulse. Previous simulations [2-3], which are based on the fluid model, show that the focusing phase of the seed laser is preserved well during the amplification process. However, there has scarcely been kinetic studies on the same problem. Various simulations from the fully kinetic two-dimensional aPIC are presented. We discuss the kinetic effects (electron trapping) on the focusablity of the amplified seed. [1] M.S. Hur, G. Penn, J.S. Wurtele, and R. Lindberg, Phys. Plasmas vol. 11, p. 5204 (2004). [2] A.A. Solodov, V.M. Malkin, and N.J. Fisch, Phys. Plasmas vol. 10, p. 2540 (2003). [3] G.M. Fraiman, N.A. Yampolsky, V.M. Malkin, and N.J. Fisch, Phys. Plasmas vol. 9, p.3617 (2002).
Two dimensional liquid crystal devices and their computer simulations
NASA Astrophysics Data System (ADS)
Wang, Bin
The main focus of the dissertation is design and optimization two dimensional liquid crystal devices, which means the liquid crystal director configurations vary in two dimensions. Several optimized and designed devices are discussed in the dissertation. They include long-term bistable twisted nematic liquid crystal display (BTN LCD), which is very low power consumption LCD and suitable for E-book application; wavelength tunable liquid crystal Fabry-Perot etalon filter, which is one of the key components in fiber optic telecommunications; high speed refractive index variable devices, which can be used in infrared beam steering and telecommunications; high density polymer wall diffractive liquid crystal on silicon (PWD-LCoS) light valve, which is a promising candidate for larger screen projection display and also can be used in other display applications. Two dimensional liquid crystal director simulation program (relaxation method) and two dimensional optical propagation simulation program (finite-difference time-domain, FDTD method) are developed. The algorithms of these programs are provided. It has been proved that they are the very efficient tools that used in design and optimization the devices described above.
Augmented reality simulator for training in two-dimensional echocardiography.
Weidenbach, M; Wick, C; Pieper, S; Quast, K J; Fox, T; Grunst, G; Redel, D A
2000-02-01
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 the human heart is linked with echocardiographic volume data sets. The 3D echocardiographic data sets are registered with the heart model to establish spatial and temporal congruence. The heart model, together with an animated ultrasound sector represents a reference scenario, which displays the currently selected two-dimensional echocardiographic cutting plane calculated from the volume data set. Modifications of the cutting plane within the echocardiographic data are transferred and visualized simultaneously and in real time within the reference scenario. The trainee can interactively explore the 3D heart model and the registered 3D echocardiographic data sets by an animated ultrasound probe, whose position is controlled by an electromagnetic tracking system. The tracking system is attached to a dummy transducer and placed on a plastic puppet to give a realistic impression of a two-dimensional echocardiographic examination. PMID:10772781
Two dimensional many particle simulation of trapped ions
NASA Astrophysics Data System (ADS)
Mitchell, Dale W.; Smith, Richard D.
1997-11-01
This work describes the implementation of the particle-in-cell simulation method with Monte-Carlo Langevin and hard sphere ion-neutral collisions in our two dimensional Cartesian and cylindrical coordinate system codes. The particle-in-cell method efficiently and accurately solves complex dynamics involving many interacting particles. In our case [`]many' means simulation runs with thousands to tens of thousands of Coulombically interacting particles on a workstation. In addition, the image charge induced on the device electrodes, which is required for self-consistency in order to make the electrodes equipotentials, is incorporated with this method. For an azimuthally symmetric confinement geometry and charge distribution, results using the two dimensional cylindrical (rz) particle simulator are identical to full three-dimensional simulations, by symmetry. These codes are applied to a number of examples which are relevant to trapped ion mass spectrometry in order to demonstrate their utility. Computer experiments are carried out to study the maximum number of ions which can be confined and equilibrium cloud shapes in cylindrical ICR traps, ion cloud collisional cooling in a combined trap, merger of two off-axis charge columns, Kelvin-Helmholtz instability in ring-shaped initial distributions, vortex crystallization, and image charge detection of coherent cyclotron motion.
Monte Carlo Simulations of the two-dimensional dipolar fluid
Jean-Michel Caillol; Jean-Jacques Weis
2015-02-12
We study a two-dimensional fluid of dipolar hard disks by Monte Carlo simulations in a square with periodic boundary conditions and on the surface of a sphere. The theory of the dielectric constant and the asymptotic behaviour of the equilibrium pair correlation function in the fluid phase is derived for both geometries. After having established the equivalence of the two methods we study the stability of the liquid phase in the canonical ensemble. We give evidence of a phase made of living polymers at low temperatures and provide a tentative phase diagram.
High order hybrid numerical simulations of two dimensional detonation waves
NASA Technical Reports Server (NTRS)
Cai, Wei
1993-01-01
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.
Simulations of Incompressible MHD Turbulence
Jason Maron; Peter Goldreich
2001-03-07
We simulate incompressible MHD turbulence in the presence of a strong background magnetic field. Our major conclusions are: 1) MHD turbulence is most conveniently described in terms of counter propagating shear Alfven and slow waves. Shear Alfven waves control the cascade dynamics. Slow waves play a passive role and adopt the spectrum set by the shear Alfven waves, as does a passive scalar. 2) MHD turbulence is anisotropic with energy cascading more rapidly along k_perp than along k_parallel, where k_perp and k_parallel refer to wavevector components perpendicular and parallel to the local magnetic field. Anisotropy increases with increasing k_perp. 3) MHD turbulence is generically strong in the sense that the waves which comprise it suffer order unity distortions on timescales comparable to their periods. Nevertheless, turbulent fluctuations are small deep inside the inertial range compared to the background field. 4) Decaying MHD turbulence is unstable to an increase of the imbalance between the flux of waves propagating in opposite directions along the magnetic field. 5) Items 1-4 lend support to the model of strong MHD turbulence by Goldreich & Sridhar (GS). Results from our simulations are also consistent with the GS prediction gamma=2/3. The sole notable discrepancy is that 1D power law spectra, E(k_perp) ~ k_perp^{-alpha}, determined from our simulations exhibit alpha ~ 3/2, whereas the GS model predicts alpha = 5/3.
Algebraic limitations on two-dimensional hydrodynamics simulations
Whalen, P.P. [Los Alamos National Lab., NM (United States)] [Los Alamos National Lab., NM (United States)
1996-03-01
Algebraic limitations imposed by the use of connected straightline segments to define meshes for hydrodynamics simulations in two-dimensional cylindrical geometries are shown. It is shown that in the simplest smooth isentropic flow of the spherical expansion of a gas with point symmetry, commonly, and currently, used finite difference, finite volume, or finite element staggered grid hydrodynamics equations cannot simultaneously preserve energy, entropy, and sphericity on an equal-angle R - {Theta} mesh. It is further shown why finite difference codes tend to preserve sphericity and entropy, while finite element codes tend to preserve sphericity and energy. Exact difference representations of interface (cell face) pressures and work terms and of the elements of the strain rate tensor in a cell are shown. 16 refs., 5 figs.
Granular dynamics simulations of two-dimensional heap formation
NASA Astrophysics Data System (ADS)
Baxter, J.; Tüautzüautn, U.; Burnell, J.; Heyes, D. M.
1997-03-01
Granular dynamics simulations have been carried out of vertical feed two-dimensional heap formation by a freefall method using a more realistic granule interaction law than has been employed in previous studies to permit prolonged contacts between adjacent granules. Stable heaps are found to form only on a geometrically rough base comprised of discrete particles, and heap formation is only weakly sensitive to the value of the contact friction coefficient. The appearance of avalanches, the pressure distribution on the base, and the voidage distribution are sensitive to the analytic form of the elastic component of the normal interaction, with a soft-sphere r-36 potential giving more realistic behavior than an equivalent Hooke law interaction with the same apparent spring constant. The r-36 interaction gives more realistic assembly dynamics as it introduces medium range collective motion caused by particle roughness and shape found in typical granular materials, without having to model anisotropic particles.
Two dimensional simulation of high power laser-surface interaction
Goldman, S.R.; Wilke, M.D.; Green, R.E.L.; Johnson, R.P.; Busch, G.E.
1998-08-01
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.
Shear-Flow Driven Current Filamentation: Two-Dimensional Magnetohydrodynamic Simulations
C. Konz; H. Wiechen; H. Lesch
2000-10-09
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.
Large-scale Simulation of the Two-dimensional Kinetic Ising Model
Heermann, Dieter W.
Large-scale Simulation of the Two-dimensional Kinetic Ising Model Andreas Linke, Dieter W. Heermann-scale Simulation of the Two-dimensional Kinetic Ising Model 3 Mt t, =z : 4 For the two-dimensional Ising model kinetic Ising model using a lattice of size 106 106 spins. We used Glauber as well as Metropolis dynamics
Simulation of two-dimensional flows in micropores
Din, X.; Michaelides, E.E. [Tulane Univ., New Orleans, LA (United States). Dept. of Mechanical Engineering
1994-12-31
An approach based on the Molecular Dynamics is used to simulate liquid flows in two-dimensional micropores and to obtain the steady-state characteristics of the flow. The mass flux of the liquid is taken as a constraint condition. Therefore, the driving force is introduced according to the Gauss least-constraint principle. The liquid molecules are considered as spheres with the same mass and density as water molecules. The interaction between the liquid molecules is of the Lennard-Jones type. Pure liquid flows and solid-liquid flows are simulated numerically. It is found that the velocity profile of the pure liquid flow matches very well the analytical solution of the plane Poiseuille flows. It was observed that larger particles will tend to flow closer to the walls. Also that the existence of the large particle makes the liquid flow somewhat faster in the center of the pore. Significant velocity slip was observed between the larger particle and the liquid.
Two dimensional numerical simulations of Supercritical Accretion Flows revisited
Yang, Xiao-Hong; Ohsuga, Ken; Bu, De-Fu
2013-01-01
We study the dynamics of super-Eddington accretion flows by performing two-dimensional radiation-hydrodynamic simulations. Compared to previous works, in this paper we include the $T_{\\theta\\phi}$ component of the viscous stress and consider various values of viscous parameter $\\alpha$. We find that when $T_{\\theta\\phi}$ is included, the rotational speed of the high-latitude flow decreases; while the density increases and decreases at the high- and low-latitudes, respectively. We calculate the radial profiles of inflow and outflow rates. We find that the inflow rate decreases inward, following a power-law form of $\\dot{M}_{\\rm in}\\propto r^s$. The value of $s$ depends on the magnitude of $\\alpha$ and is within the range of $\\sim 0.4-1.0$. Correspondingly, the radial profile of density becomes flatter compared to the case of a constant $\\dot{M}(r)$. We find that the density profile can be described by $\\rho(r)\\propto r^{-p}$, and the value of $p$ is almost same for a wide range of $\\alpha$ ranging from $\\alpha...
Two-dimensional numerical simulations of supercritical accretion flows revisited
Yang, Xiao-Hong; Yuan, Feng; Bu, De-Fu [Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030 (China); Ohsuga, Ken, E-mail: yangxh@cqu.ac.cn, E-mail: fyuan@shao.ac.cn [National Astronomical Observatory of Japan, Osawa, Mitaka, Tokyo 181-8588 (Japan)
2014-01-01
We study the dynamics of super-Eddington accretion flows by performing two-dimensional radiation-hydrodynamic simulations. Compared with previous works, in this paper we include the T {sub ??} component of the viscous stress and consider various values of the viscous parameter ?. We find that when T {sub ??} is included, the rotational speed of the high-latitude flow decreases, while the density increases and decreases at the high and low latitudes, respectively. We calculate the radial profiles of inflow and outflow rates. We find that the inflow rate decreases inward, following a power law form of M-dot {sub in}?r{sup s}. The value of s depends on the magnitude of ? and is within the range of ?0.4-1.0. Correspondingly, the radial profile of density becomes flatter compared with the case of a constant M-dot (r). We find that the density profile can be described by ?(r)?r {sup –p} and the value of p is almost same for a wide range of ? ranging from ? = 0.1 to 0.005. The inward decrease of inflow accretion rate is very similar to hot accretion flows, which is attributed to the mass loss in outflows. To study the origin of outflow, we analyze the convective stability of the slim disk. We find that depending on the value of ?, the flow is marginally stable (when ? is small) or unstable (when ? is large). This is different from the case of hydrodynamical hot accretion flow, where radiation is dynamically unimportant and the flow is always convectively unstable. We speculate that the reason for the difference is because radiation can stabilize convection. The origin of outflow is thus likely because of the joint function of convection and radiation, but further investigation is required.
Two-dimensional Numerical Simulations of Supercritical Accretion Flows Revisited
NASA Astrophysics Data System (ADS)
Yang, Xiao-Hong; Yuan, Feng; Ohsuga, Ken; Bu, De-Fu
2014-01-01
We study the dynamics of super-Eddington accretion flows by performing two-dimensional radiation-hydrodynamic simulations. Compared with previous works, in this paper we include the T ?phi component of the viscous stress and consider various values of the viscous parameter ?. We find that when T ?phi is included, the rotational speed of the high-latitude flow decreases, while the density increases and decreases at the high and low latitudes, respectively. We calculate the radial profiles of inflow and outflow rates. We find that the inflow rate decreases inward, following a power law form of \\dot{M}_in\\propto r^s. The value of s depends on the magnitude of ? and is within the range of ~0.4-1.0. Correspondingly, the radial profile of density becomes flatter compared with the case of a constant \\dot{M}(r). We find that the density profile can be described by ?(r)vpropr -p and the value of p is almost same for a wide range of ? ranging from ? = 0.1 to 0.005. The inward decrease of inflow accretion rate is very similar to hot accretion flows, which is attributed to the mass loss in outflows. To study the origin of outflow, we analyze the convective stability of the slim disk. We find that depending on the value of ?, the flow is marginally stable (when ? is small) or unstable (when ? is large). This is different from the case of hydrodynamical hot accretion flow, where radiation is dynamically unimportant and the flow is always convectively unstable. We speculate that the reason for the difference is because radiation can stabilize convection. The origin of outflow is thus likely because of the joint function of convection and radiation, but further investigation is required.
Two-dimensional simulation of optical wave propagation through atmospheric turbulence.
Hyde, Milo W; Basu, Santasri; Schmidt, Jason D
2015-01-15
A methodology for the two-dimensional simulation of optical wave propagation through atmospheric turbulence is presented. The derivations of common statistical field moments in two dimensions, required for performing and validating simulations, are presented and compared with their traditional three-dimensional counterparts. Wave optics simulations are performed to validate the two-dimensional moments and to demonstrate the utility of performing two-dimensional wave optics simulations so that the results may be scaled to those of computationally prohibitive 3D scenarios. Discussions of the benefits and limitations of two-dimensional atmospheric turbulence simulations are provided throughout. PMID:25679852
Exact solution of two-dimensional MHD boundary layer flow over a semi-infinite flat plate
NASA Astrophysics Data System (ADS)
Kudenatti, Ramesh B.; Kirsur, Shreenivas R.; Achala, L. N.; Bujurke, N. M.
2013-05-01
In the present paper, an exact solution for the two-dimensional boundary layer viscous flow over a semi-infinite flat plate in the presence of magnetic field is given. Generalized similarity transformations are used to convert the governing boundary layer equations into a third order nonlinear differential equation which is the famous MHD Falkner-Skan equation. This equation contains three flow parameters: the stream-wise pressure gradient (?), the magnetic parameter (M), and the boundary stretch parameter (?). Closed-form analytical solution is obtained for ?=-1 and M=0 in terms of error and exponential functions which is modified to obtain an exact solution for general values of ? and M. We also obtain asymptotic analyses of the MHD Falkner-Skan equation in the limit of large ? and ?. The results obtained are compared with the direct numerical solution of the full boundary layer equation, and found that results are remarkably in good agreement between the solutions. The derived quantities such as velocity profiles and skin friction coefficient are presented. The physical significance of the flow parameters are also discussed in detail.
Numerical simulation of two?dimensional tsunami runup
Z. Kowalik; T. S. Murty
1993-01-01
The hydrodynamic and mathematical problems connected with discontinuity between wet and dry domains, nonlinearity, friction, and computational instability are the main problems that have to be sorted out in the runup computation. A variety of runup models are analyzed, including the boundary conditions used to move the shoreline. Based on the initial experiments one?dimensional and two?dimensional algorithms are constructed. These
Extended MHD Simulations of Spheromaks
NASA Astrophysics Data System (ADS)
Howell, E. C.; Sovinec, C. R.
2012-10-01
Nonlinear extended MHD simulations of a spheromak in a cylindrical flux conserver are performed using the NIMROD code (JCP 195, 2004). An idealized series of simulations starting from a Grad-Shafranov equilibrium and small non-axisymmetric perturbations are performed to model the sustained decay phase. The resulting confinement leads to steep resistivity gradients. Strong current gradients develop, driving tearing modes that dominate the evolution of the spheromak. Absent in these simulations are the remains of n=1 fluctuations created during the formation process. A second series of simulations start from vacuum fields and model the full spheromak evolution, including the formation process where the n=1 fluctuations dominate. To understand the role of pressure driven instabilities in the evolution of the spheromak, a numerical diagnostic is developed to calculate the Mercier stability criterion from the axisymmetric fields.
Stability Studies of Two-dimensional Magnetic Bernstein-Greene-Kruskal Modes using PIC Simulations
Ng, Chung-Sang
Stability Studies of Two-dimensional Magnetic Bernstein- Greene-Kruskal Modes using PIC Simulations of these solutions, as well as Particle-in-Cell (PIC) simulations, we will present further studies of the stability
Atchison, W.L.; Faehl, R.J.; Morgan, D.V.; Reinovsky, R.E.
1997-10-01
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.
NASA Astrophysics Data System (ADS)
Riquelme, Mario A.; Quataert, Eliot; Sharma, Prateek; Spitkovsky, Anatoly
2012-08-01
The magnetorotational instability (MRI) is a crucial mechanism of angular momentum transport in a variety of astrophysical accretion disks. In systems accreting at well below the Eddington rate, such as the central black hole in the Milky Way (Sgr A*), the plasma in the disk is essentially collisionless. We present a nonlinear study of the collisionless MRI using first-principles particle-in-cell plasma simulations. We focus on local two-dimensional (axisymmetric) simulations, deferring more realistic three-dimensional simulations to future work. For simulations with net vertical magnetic flux, the MRI continuously amplifies the magnetic field, B, until the Alfvén velocity, vA , is comparable to the speed of light, c (independent of the initial value of vA /c). This is consistent with the lack of saturation of MRI channel modes in analogous axisymmetric MHD simulations. The amplification of the magnetic field by the MRI generates a significant pressure anisotropy in the plasma (with the pressure perpendicular to B being larger than the parallel pressure). We find that this pressure anisotropy in turn excites mirror modes and that the volume-averaged pressure anisotropy remains near the threshold for mirror mode excitation. Particle energization is due to both reconnection and viscous heating associated with the pressure anisotropy. Reconnection produces a distinctive power-law component in the energy distribution function of the particles, indicating the likelihood of non-thermal ion and electron acceleration in collisionless accretion disks. This has important implications for interpreting the observed emission—from the radio to the gamma-rays—of systems such as Sgr A*.
Nagai, Tetsuro; Okamoto, Yuko
2012-11-01
We have performed two-dimensional simulated tempering (ST) simulations of the two-dimensional Ising model with different lattice sizes in order to investigate the two-dimensional ST's applicability to dealing with phase transitions and study the crossover of critical scaling behavior. The external field, as well as the temperature, was treated as a dynamical variable updated during the simulations. Thus this simulation can be referred to as simulated tempering and magnetizing (STM). We also performed simulated magnetizing (SM) simulations, in which the external field was considered as a dynamical variable and temperature was not. As discussed in previous studies, the ST method is not always compatible with first-order phase transitions. This is also true in the magnetizing process. Flipping of the entire magnetization did not occur in the SM simulations under the critical temperature T{c} in large-lattice-size simulations; however, the phase changed through the high-temperature region in the STM simulations. Thus the dimensional extension let us eliminate the difficulty of the first-order phase transitions and study a wide area of the phase space. We discuss how frequently parameter-updating attempts should be made for optimal convergence. The results favor frequent attempts. We finally study the crossover behavior of the phase transitions with respect to the temperature and external field. The crossover behavior is clearly observed in the simulations, in agreement with the theoretical implications. PMID:23214904
Two-DIMENSIONAL WATER FLOOD AND MUDFLOW SIMULATION
Julien, Pierre Y.
by the Federal Emergency Management Agency (FEMA) (FAN, 1990). Since the FEMA method doesn't simulate flood must be filed with the ASCE Manager of Journals. The manuscript for this paper was submitted for review
Simulation of deep one- and two-dimensional redshift surveys
NASA Technical Reports Server (NTRS)
Park, Changbom; Gott, J. Richard, III
1991-01-01
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.
Two-dimensional simulations of the inertial electrostatic confinement device
NASA Astrophysics Data System (ADS)
Marocchino, Alberto; Lapenta, Giovanni; Evstatiev, Evstati; Nebel, Richard; Park, Jaeyoung
2006-04-01
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.
Evidence of active MHD instability in EULAG-MHD simulations of solar convection
Lawson, N; Charbonneau, P
2015-01-01
We investigate the possible development of magnetohydrodynamical instabilities in the EULAG-MHD "millenium simulation" of Passos & Charbonneau (2014). This simulation sustains a large-scale magnetic cycle characterized by solar-like polarity reversals taking place on a regular multidecadal cadence, and in which zonally-oriented bands of strong magnetic field accumulate below the convective layers, in response to turbulent pumping from above in successive magnetic half-cycles. Key aspects of this simulation include low numerical dissipation and a strongly subadiabatic fluid layer underlying the convectively unstable layers corresponding to the modeled solar convection zone. These properties are conducive to the growth and development of two-dimensional instabilities otherwise suppressed by stronger dissipation. We find evidence for the action of a non-axisymmetric magnetoshear instability operating in the upper portions of the stably stratified fluid layers. We also investigate the possibility that the Tay...
MHD simulation of mass injection - A mechanism for the formation of active region loops
NASA Technical Reports Server (NTRS)
Cheng, Chung-Chieh; Wu, S. T.
1988-01-01
A two-dimensional nonlinear MHD numerical code is used to simulate the formation and dynamic evolution of active regions loops subjected to mass injections at the footpoints. The UV and X-ray signatures of the plasmas are also calculated. It is found that it is possible to form loops in a low beta plasma that occurs in the solar active regions.
Two-dimensional SPH simulations of wedge water entries
NASA Astrophysics Data System (ADS)
Oger, G.; Doring, M.; Alessandrini, B.; Ferrant, P.
2006-04-01
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.
Two-dimensional simulations of pulsational pair-instability supernovae
Chen, Ke-Jung; Woosley, Stan [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Heger, Alexander [Monash Centre for Astrophysics, Monash University, Melbourne, Victoria 3800 (Australia); Almgren, Ann [Center for Computational Sciences and Engineering, Lawrence Berkeley National Lab, Berkeley, CA 94720 (United States); Whalen, Daniel J., E-mail: kchen@ucolick.org [T-2, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)
2014-09-01
Massive stars that end their lives with helium cores in the range of 35-65 M {sub ?} are known to produce repeated thermonuclear outbursts due to a recurring pair-instability. In some of these events, solar masses of material are ejected in repeated outbursts of several × 10{sup 50} erg each. Collisions between these shells can sometimes produce very luminous transients that are visible from the edge of the observable universe. Previous one-dimensional (1D) studies of these events produce thin, high-density shells as one ejection plows into another. Here, in the first multi-dimensional simulations of these collisions, we show that the development of a Rayleigh-Taylor instability truncates the growth of the high-density spike and drives mixing between the shells. The progenitor is a 110 M {sub ?} solar-metallicity star that was shown in earlier work to produce a superluminous supernova. The light curve of this more realistic model has a peak luminosity and duration that are similar to those of 1D models but a structure that is smoother.
Simulation of infrared backgrounds using two-dimensional models
NASA Astrophysics Data System (ADS)
Cadzow, James A.; Wilkes, Don M.; Peters, R. Alan, II; Li, Xingkang; Patel, Jamshed N.
1991-07-01
Analysis and simulation of smart munitions requires imagery for the munition's sensor to view. The imagery is usually infrared and depicts a target embedded in a background. Mathematical models of such imagery are useful to munitions researchers. A mathematical model can synthesize a test scenario at a cost much less than that of actual data acquisition. To date, most research has focused on the modeling targets. It is essential, however, to test a munition's target acquisition algorithms on images containing targets superimposed on a wide variety of backgrounds. Consequently, there is a need for accurate models of infrared backgrounds. Useful models are difficult to create because of the complexity and diversity of imagery viewed by smart munition sensors. A model of IR backgrounds is presented that will, given a textured image, generate another image. The synthetic image, although distinctly different from the original, has the general visual characteristics and the first and second-order statistics of the original image. In effect, the synthetic image looks like a continuation of the original scene, as if another picture of the scene were taken adjacent to the original. The model is an FIR kernel convolved with an excitation function, noise added to the result, and followed by histogram modification. The paper describes a procedure for deriving the correct FIR kernel using a signal enhancement algorithm, and reports a demonstration of the model in which it is used to mimic several diverse textured images.
Two-dimensional ion trap lattice on a microchip for quantum simulation
Sterling, R C; Weidt, S; Lake, K; Srinivasan, P; Webster, S C; Kraft, M; Hensinger, W K
2013-01-01
Using a controllable quantum system it is possible to simulate other highly complex quantum systems efficiently overcoming an in-principle limitation of classical computing. Trapped ions constitute such a highly controllable quantum system. So far, no dedicated architectures for the simulation of two-dimensional spin lattices using trapped ions in radio-frequency ion traps have been produced, limiting the possibility of carrying out such quantum simulations on a large scale. We report the operation of a two-dimensional ion trap lattice integrated in a microchip capable of implementing quantum simulations of two-dimensional spin lattices. Our device provides a scalable microfabricated architecture for trapping such ion lattices with coupling strengths between neighbouring ions sufficient to provide a powerful platform for the implementation of quantum simulations. In order to realize this device we developed a specialist fabrication process that allows for the application of very large voltages. We fabricated ...
Absence of Electron Surfing Acceleration in a Two-Dimensional Simulation
Yutaka Ohira; Fumio Takahara
2007-05-16
Electron acceleration in high Mach number perpendicular shocks is investigated through two-dimensional electrostatic particle-in-cell (PIC) simulation. We simulate the shock foot region by modeling particles that consist of three components such as incident protons and electrons and reflected protons in the initial state which satisfies the Buneman instability condition. In contrast to previous one-dimensional simulations in which strong surfing acceleration is realized, we find that surfing acceleration does not occur in two-dimensional simulation. This is because excited electrostatic potentials have a two-dimensional structure that makes electron trapping impossible. Thus, the surfing acceleration does not work either in itself or as an injection mechanism for the diffusive shock acceleration. We briefly discuss implications of the present results on the electron heating and acceleration by shocks in supernova remnants.
One- and two-dimensional STEALTH simulations of fuel-pin transient response. Final report. [BWR; PWR
Wahi, K.K.
1980-08-01
This report presents an assessment of the adaptability of EPRI's one- and two-dimensional STEALTH computer codes to perform transient fuel rod analysis. The ability of the STEALTH code to simulate transient mechanical or thermomechanical loss-of-coolant accident is described. Analytic models of one- and two-dimensional formulations and features included in the two-dimensional simulation are discussed.
Simulation of Two-Dimensional Ultraviolet Spectroscopy of Amyloid Fibrils Darius Abramavicius,
Mukamel, Shaul
Simulation of Two-Dimensional Ultraviolet Spectroscopy of Amyloid Fibrils Jun Jiang, Darius into the ultraviolet (UV) region, and this opens up new opportunities for probing fibrils. In a simulation study, we with Alzheimer's disease and two intermediate prefibrillar structures carry characteristic signatures of fibril
Simulation of wave interactions with MHD
Batchelor, Donald B; Abla, G; Bateman, Glenn; Bernholdt, David E; Berry, Lee A; Bonoli, P.; Bramley, R; Breslau, J.; Chance, M.; Chen, J.; Choi, M.; Elwasif, Wael R; Fu, GuoYong; Harvey, R. W.; Jaeger, Erwin Frederick; Jardin, S. C.; Jenkins, T; Keyes, David E; Klasky, Scott A; Kruger, Scott; Ku, Long-Poe; Lynch, Vickie E; McCune, Douglas; Ramos, J.; Schissel, D.; Schnack,; Wright, J.
2008-07-01
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.
Hybrid simulation of whistler excitation by electron beams in two-dimensional non-periodic domains
Woodroffe, J.R. Streltsov, A.V.
2014-11-01
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.
Theory and simulations of two-dimensional vortex motion driven by a background vorticity gradient
California at San Diego, University of
Theory and simulations of two-dimensional vortex motion driven by a background vorticity gradient-dimensional vortex motion in a shear-flow with nonuniform vorticity. Typically, a vortex travels to an extremum, above which the transverse vortex motion is suppressed. A brief account of some of these results has
Structure of the lunar wake: Two-dimensional global hybrid simulations
California at Berkeley, University of
Structure of the lunar wake: Two-dimensional global hybrid simulations Pavel Tra´vni´cek and Petr; accepted 21 February 2005; published 22 March 2005. [1] We study the structure and properties of the lunar with in situ observations the lunar wake is formed by two counterstreaming beams which fill the wake
Energy and enstrophy transfer in numerical simulations of two-dimensional' turbulence
Vallis, Geoff
Energy and enstrophy transfer in numerical simulations of two-dimensional' turbulence Mathew E that transfer energy and enstrophy in the both the energy and enstrophy inertial ranges. In the enstrophy these triads is directed from the intermediate to the largest wave-number mode (i.e., downscale transfer
Economou, Demetre J.
Fluid simulations of radio frequency glow discharges: Two-dimensional argon discharge including discharge models reported to date are one di- mensional and do not include neutral transport and reac- tion. It was "Author to whom correspondence should be addressed. shown that metastablesplay an important role
Simulation of the formation of two-dimensional Coulomb liquids and solids in dusty plasmas
Kushner, Mark
Simulation of the formation of two-dimensional Coulomb liquids and solids in dusty plasmas Helen H have motivated experimental studies of the Coulomb liquid and solid properties of these systems and solids. These predictions are based both on values of 2 liquid and 170 solid , where is the ratio
Two-dimensional simulations of extreme floods on a large watershed
Julien, Pierre Y.
September 2007; accepted 14 September 2007 KEYWORDS Flash floods; Flood design; Rainfall runoff; ExtremeTwo-dimensional simulations of extreme floods on a large watershed John F. England Jr. a,*, Mark L. Velleux b , Pierre Y. Julien c a Bureau of Reclamation, Flood Hydrology, 86-68530, Denver Federal Center
Derivation and simulation of an improved two-dimensional constitutive law for shape memory alloys
NASA Astrophysics Data System (ADS)
Wang, Wei; Yan, Shi; Song, Gangbing; Gu, Haichang
2007-04-01
An improved two-dimensional constitutive model for Shape memory alloys (SMAs), which can describe both the shape memory effect (SME) and super elasticity effect (SE) of the SMAs, is developed based on the previous work of Boyd and Lagoudas, who used the thermodynamics theories of free energy and dissipation energy to derive the constitutive law of SMAs. The improved model, which will combine the ideas of Brinsion's one-dimensional constitutive law and the concepts of Boyd and Lagoudas' two-dimensional one, has a simple but accurate expression. The results of the simulations show that the developed constitutive model can qualitatively describe the thermo-mechanical behaviors of two-dimensional SMAs and can be used in the analysis of structures actuated by SMAs.
Exploding solutions of the complex two-dimensional Burgers equations: Computer simulations
NASA Astrophysics Data System (ADS)
Boldrighini, C.; Frigio, S.; Maponi, P.
2012-08-01
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.
Quantitative analysis of voids in percolating structures in two-dimensional N-body simulations
NASA Technical Reports Server (NTRS)
Harrington, Patrick M.; Melott, Adrian L.; Shandarin, Sergei F.
1993-01-01
We present in this paper a quantitative method for defining void size in large-scale structure based on percolation threshold density. Beginning with two-dimensional gravitational clustering simulations smoothed to the threshold of nonlinearity, we perform percolation analysis to determine the large scale structure. The resulting objective definition of voids has a natural scaling property, is topologically interesting, and can be applied immediately to redshift surveys.
Paarmann, A; Hayashi, T; Mukamel, S; Miller, R J D
2009-05-28
A simulation formalism for the nonlinear response of vibrational excitons is presented and applied to the OH stretching vibrations of neat liquid H(2)O. The method employs numerical integration of the Schrodinger equation and allows explicit treatment of fluctuating transition frequencies, vibrational couplings, dipole moments, and the anharmonicities of all these quantities, as well as nonadiabatic effects. The split operator technique greatly increases computational feasibility and performance. The electrostatic map for the OH stretching vibrations in liquid water employed in our previous study [A. Paarmann et al., J. Chem. Phys. 128, 191103 (2008)] is presented. The two-dimensional spectra are in close agreement with experiment. The fast 100 fs dynamics are primarily attributed to intramolecular mixing between states in the two-dimensional OH stretching potential. Small intermolecular couplings are sufficient to reproduce the experimental energy transfer time scales. Interference effects between Liouville pathways in excitonic systems and their impact on the analysis of the nonlinear response are discussed. PMID:19485440
Paarmann, A.; Hayashi, T.; Mukamel, S.; Miller, R. J. D.
2009-01-01
A simulation formalism for the nonlinear response of vibrational excitons is presented and applied to the OH stretching vibrations of neat liquid H2O. The method employs numerical integration of the Schrödinger equation and allows explicit treatment of fluctuating transition frequencies, vibrational couplings, dipole moments, and the anharmonicities of all these quantities, as well as nonadiabatic effects. The split operator technique greatly increases computational feasibility and performance. The electrostatic map for the OH stretching vibrations in liquid water employed in our previous study [A. Paarmann et al., J. Chem. Phys. 128, 191103 (2008)] is presented. The two-dimensional spectra are in close agreement with experiment. The fast 100 fs dynamics are primarily attributed to intramolecular mixing between states in the two-dimensional OH stretching potential. Small intermolecular couplings are sufficient to reproduce the experimental energy transfer time scales. Interference effects between Liouville pathways in excitonic systems and their impact on the analysis of the nonlinear response are discussed. PMID:19485440
Entropic Lattice Boltzmann Simulations of MHD Turbulence
NASA Astrophysics Data System (ADS)
Vahala, George; Yepez, Jeffrey; Soe, Min; Vahala, Linda; Oganesov, Armen
2012-10-01
Lattice Boltzmann (LB) codes are ideal to study MHD turbulence since it is a mesoscopic algorithm in a higher dimensional space but whose solution in that space is far simpler to achieve that direct CFD algorithms. In particular, one is no longer hand-cuffed by fast magnetoacoustic waves which are sometimes filtered out by an anelastic approximation. Moreover, these LB simulations can enforce div B = 0 automatically since this arises as the trace of an asymmetric tensor. However the achievable Reynolds and magnetic Reynolds numbers are restricted by numerical instabilities. Here we consider entropic formulations of LB for MHD. For Navier-Stokes turbulence, an entropic scheme has permitted fully resolved simulations on 1600 x 1600 x 1600 spatial grid at a Reynolds number of 25 000.
D. Sydorenko; R. Rankin; K. Kabin
2009-01-01
This paper presents initial results based on kinetic extensions of a nonlinear two-dimensional (2D) multi-fluid (three ion species and fluid electrons) MHD model that is designed to study propagation of shear Alfven waves in low-altitude auroral flux tubes. It is intended to use the model for scientific support of the ``enhanced polar outflow probe'' e-POP\\/CASSIOPE spacecraft mission (launch scheduled in
A bounded two dimensional PIC-MCC code for simulating processing plasmas
Vahedi, V.; Birdsall, C.K.; Lieberman, M.A.
1992-12-01
The authors have developed a bounded two dimensional particle-in-cell simulation code with a Monte Carlo Collision (MCC) handler to study processing discharges. The MCC package models the collisions, between charged and neutral particles, which are needed to obtain a self sustained plasma and the proper electron and ion energy loss mechanisms. The simulations are aimed at determining uniformity of particle fluxes (magnitude and angle) across a typical target. Some early results are obtained from an x-y model with electrode area ratio of 6:1; a similar r-z model is in progress which can be used to study cylindrical chambers.
Nonlinear kinetic modeling and simulations of Raman scattering in a two-dimensional geometry
NASA Astrophysics Data System (ADS)
Bénisti, Didier; Morice, Olivier; Gremillet, Laurent; Friou, Alexandre; Lefebvre, Erik
2013-11-01
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.
Two-dimensional full-wave simulation of microwave reflectometry on Alcator C-Mod
Lin, Y.; Irby, J. H.; Nazikian, R.; Marmar, E. S.; Mazurenko, A.
2001-01-01
A new two-dimensional full-wave code has been developed to simulate ordinary (O) mode reflectometry signals caused by plasma density fluctuations. The code uses the finite-difference time-domain method with a perfectly matched layer absorption boundary to solve Maxwell's equations. Huygens wave sources are incorporated to generate Gaussian beams. The code has been used to simulate the reflectometer measurement of the quasicoherent mode (60--250 kHz) associated with enhanced D{sub {alpha}} (EDA) H modes in the Alcator C-Mod tokamak. It is found that an analysis of the realistic experimental layout is essential for the quantitative interpretation of the mode amplitude.
Global MHD Simulations of Cylindrical Keplerian Disks
John F. Hawley
2000-11-27
This paper presents a series of global three dimensional accretion disk simulations carried out in the cylindrical limit in which the vertical component of the gravitational field is neglected. The simulations use a cylindrical pseudo-Newtonian potential to model the main dynamical properties of the Schwarzschild metric. The disks are initially constant density with a Keplerian angular momentum distribution and contain a weak toroidal or vertical field. These simulations reaffirm many of the conclusions of previous local simulations. The magnetorotational instability grows rapidly and produces MHD turbulence with a significant Maxwell stress which drives accretion. Tightly-wrapped low-$m$ spiral waves are prominent. In some simulations radial variations in Maxwell stress concentrate gas into rings, creating substantial spatial inhomogeneities. There is a nonzero stress at the marginally stable orbit which produces a small decline in specific angular momentum inside the last stable orbit. Detailed comparisons between simulations are used to examine the effects of computational domain and equation of state. Simulations that begin with vertical fields have greater field amplification and higher ratios of stress to magnetic pressure compared with those beginning with toroidal fields. In contrast to MHD, hydrodynamics alone neither creates nor sustains turbulence.
Computer simulations of a two-dimensional system with competing interactions.
Stoycheva, Antitsa D; Singer, Sherwin J
2002-03-01
The results and methodology of large scale computer simulations of the two-dimensional dipolar Ising model with long-range interactions are reported. Systems as large as 117,649 particles were studied to elucidate the elementary excitations and phase diagram of two-dimensional systems, such as Langmuir monolayers, thin garnet films, and adsorbed films on solid surfaces, which spontaneously form patterns of stripes, bubbles, and intermediately shaped domains. The challenging numerical investigations of large scale systems with long-range interactions at low temperatures were made possible by combining the fast multipole method and a non-Metropolis Monte Carlo sampling technique. Our simulations provide evidence that, at sufficiently high ratios of the repulsive to the attractive coupling constant for the model, twofold stripe order in the systems of interest is lost through a defect-mediated mechanism. Heat capacity data and the excitations observed in our simulations as the system disorders indicate that it is most likely an instance of a Kosterlitz-Thouless phase transition. The results from simulations with and without external field are in excellent agreement with the predictions of an analytic scaling theory [A. D. Stoycheva and S. J. Singer, Phys. Rev. E 64, 016118 (2001)], confirming the phase diagram furnished by the analytic model. The scaling theory suggests that, under certain conditions, defect-mediated stripe melting may be supplanted by Ising like disordering within stripes for small repulsion strength. A qualitative discussion of a model that supports both disordering mechanisms is presented. PMID:11909306
Two-dimensional simulations of stimulated Brillouin scattering in laser produced plasmas
Amin, M.R.; Capjack, C.E. ); Frycz, P.; Rozmus, W.; Tikhonchuk, V.T. )
1993-07-05
A system of electromagnetic and ion acoustic wave equations coupled via the ponderomotive force are solved numerically in a two-dimensional planar geometry. The competition between forward, side, and backward Brillouin scattering of the finite size laser beam is studied for the first time without the standard paraxial optics approximation. Simulations reveal a strong dependence of the scattered light characteristics on the geometry of the interaction region, the shape of the pump beam, and the ion acoustic wave damping. The main effects include side and forward scattering enhancement and a stimulation of collimated backward scattered radiation.
Re-forming supercritical quasi-parallel shocks. I - One- and two-dimensional simulations
NASA Technical Reports Server (NTRS)
Thomas, V. A.; Winske, D.; Omidi, N.
1990-01-01
The process of reforming supercritical quasi-parallel shocks is investigated using one-dimensional and two-dimensional hybrid (particle ion, massless fluid electron) simulations both of shocks and of simpler two-stream interactions. It is found that the supercritical quasi-parallel shock is not steady. Instread of a well-defined shock ramp between upstream and downstream states that remains at a fixed position in the flow, the ramp periodically steepens, broadens, and then reforms upstream of its former position. It is concluded that the wave generation process is localized at the shock ramp and that the reformation process proceeds in the absence of upstream perturbations intersecting the shock.
Suppressing sampling noise in linear and two-dimensional spectral simulations
NASA Astrophysics Data System (ADS)
Kruiger, Johannes F.; van der Vegte, Cornelis P.; Jansen, Thomas L. C.
2015-02-01
We examine the problem of sampling noise encountered in time-domain simulations of linear and two-dimensional spectroscopies. A new adaptive apodization scheme based on physical arguments is devised for suppressing the noise in order to allow reducing the number of used disorder realisations, but introducing only a minimum of spectral aberrations and thus allowing a potential speed-up of these types of simulations. First, the method is demonstrated on an artificial dimer system, where the effect on slope analysis, typically used to study spectral dynamics, is analysed. It is, furthermore, tested on the simulated two-dimensional infrared spectra in the amide I region of the protein lysozyme. The cross polarisation component is investigated, particularly sensitive to sampling noise, because it relies on cancelling of the dominant diagonal spectral contributions. In all these cases, the adaptive apodization scheme is found to give more accurate results than the commonly used lifetime apodization scheme and in most cases better than the gaussian apodization scheme.
Suppressing sampling noise in linear and two-dimensional spectral simulations.
Kruiger, Johannes F; van der Vegte, Cornelis P; Jansen, Thomas L C
2015-02-01
We examine the problem of sampling noise encountered in time-domain simulations of linear and two-dimensional spectroscopies. A new adaptive apodization scheme based on physical arguments is devised for suppressing the noise in order to allow reducing the number of used disorder realisations, but introducing only a minimum of spectral aberrations and thus allowing a potential speed-up of these types of simulations. First, the method is demonstrated on an artificial dimer system, where the effect on slope analysis, typically used to study spectral dynamics, is analysed. It is, furthermore, tested on the simulated two-dimensional infrared spectra in the amide I region of the protein lysozyme. The cross polarisation component is investigated, particularly sensitive to sampling noise, because it relies on cancelling of the dominant diagonal spectral contributions. In all these cases, the adaptive apodization scheme is found to give more accurate results than the commonly used lifetime apodization scheme and in most cases better than the gaussian apodization scheme. PMID:25662638
Two-Dimensional Hybrid Particle-In-Cell Simulation of Solar Wind Plasma Flow around Magnetic Sail
NASA Astrophysics Data System (ADS)
Matsumoto, Masaharu; Kajimura, Yoshihiro; Hideyuki Usui; Ikkoh Funaki; Iku Sinohara, And
Solar wind plasma flow with interplanetary magnetic field (IMF) and the thrust of the magnetic sail are examined by time-dependent, two-dimensional, X-Y Cartesian, hybrid particle-in-cell (PIC) simulations. The hybrid-PIC simulation model is that the ions are treated kinetically as particles and the electrons are modeled as an inertia-less (mass-less) fluid. In this simulation, the real solar wind parameters around a near-earth orbit are used. The direction and strength of IMF are set to +Y direction which is perpendicular to the solar wind flow (+X direction) and 3 nT. Expressed in rL/L (the ratio of an ion Larmor radius rL of the solar wind at the magnetopause to a representative length of magnetic field L), when rL/L = 0.1 (in the case of MHD scale), magnetopause is formed accompanied by a fast magnetosonic bow shock. When rL/L = 2.0 (in the case of ion inertial scale), the electromagnetic interaction results in the formation of a magnetosphere with standing whistler waves. The drag coefficients, which is the thrust normalized by the solar wind inertial force, of both scales with IMF tend to increase compared with the cases without IMF because the incoming IMF accompanied by the solar wind piles up at upstream of the spacecraft. Also, on the ion inertial scale, the generation mechanism of Whistler wave and the influence of that on the thrust performance are revealed.
Nonlinear evolution of tidally distorted accretion disks: Two-dimensional simulations
NASA Technical Reports Server (NTRS)
Ryu, Dongsu; Goodman, Jeremy
1994-01-01
According to a previously published linear analysis, the tidal distortion of accretion disks in binary star systems produces a local hydrodynamic instability to m = 1 internal waves, which may have arbitrarily small wavelengths in the absence of viscosity. The instability is three-dimensional and approximately incrompressible. To explore the nonlinear outcome of this instability, we develop a shearing-sheet approximation on scales comparable to the disk thickness. The large-scale azimuthal variation of the disk is represented by varying the local metric with time (local orbital phase). The hydrodynamic equations can then be posed two-dimensionally on local meridional planes. We solve these equations with a second-order gasdynamical code based on the Total-Variation-Diminishing scheme. Our simulations confirm the predicted linear growth rate. The modes saturate chaotically at velocities scaling as the product of the linear growth rate and the wavelength. If the wavelength is small compared with the disk thickness, the modes remain nearly incompressible even when nonlinear. The two-dimensional power spectrum of velocities after saturation is roughly isotropic and extends over a broad range of scales in an approximately power-law fashion. We measure the heating rate associated with the nonlinear dissipation of the modes. The dissipation implies a secular torque on the disk and a return of angular momentum to the secondary star via the tidal potential. The estimated torque is somewhat larger than the tidal torque produced by maximal disk viscosity (alpha approximately 1). At least in these two-dimensional simulations, however, there is no significant angular momentum flux within the disk.
Two-dimensional fluid simulation of plasma reactors for the immobilization of krypton
NASA Astrophysics Data System (ADS)
Suetomi, E.; Tanaka, M.; Kamiya, S.; Hayashi, S.; Ikeda, S.; Sugawara, H.; Sakai, Y.
2000-03-01
Direct current glow discharge plasma sources are being developed as reactors for immobilization of radioactive krypton gas recovered from the off-gas stream of a nuclear fuel reprocessing plant. In order to design these reactors, two-dimensional simulations have been performed using a fluid model coupled with Poisson's equation. Nonlinear governing equations were expressed by a fully implicit scheme and the equations were solved using the Newton-Krylov method. We investigated algorithm performance of two methods from the Krylov projection techniques, namely the Bi-CGSTAB method and the transpose-free quasi-minimal residual (TFQMR) method. The results showed that the Bi-CGSTAB method converged considerably faster than the TFQMR method. Direct current glow discharge plasmas in three types of krypton immobilization apparatus were simulated to study the differences in electrode geometry. Simulation results agreed qualitatively with measurements of electron density.
General Relativistic MHD Simulations of Jet Formation
NASA Technical Reports Server (NTRS)
Mizuno, Y.; Nishikawa, K.-I.; Hardee, P.; Koide, S.; Fishman, G. J.
2005-01-01
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.
Ng, Chung-Sang
Stability Studies of Two-dimensional Magnetic Bernstein-Greene-Kruskal Modes using Particle-in-Cell form of these solutions, as well as Particle-in-Cell (PIC) simulations, we will present further studies
Simulation of alluvial channel migration processes with a two-dimensional numerical model
NASA Astrophysics Data System (ADS)
Duan, Guohong
An improved two dimensional numerical model for simulating the complicated meandering initiation, migration and widening processes of alluvial channels is presented in this research. The flow field simulation is obtained initially by the CCHE2D hydrodynamic model, which is obviously inadequate to predict the three-dimensional flow field in a channel bend. A set of empirical functions is proposed to convert the depth-averaged, two-dimensional flow field into an approximated three-dimensional one. As a result, a more realistic bed shear stress is predicted. Applying this enhanced model, the simulations of morphological processes in a channel bend are found to be more realistic than those produced by a traditional two-dimensional model. Due to the limitation of existing physical data, the CCHE3D after having been verified by physical models is employed as a computational experimentation flume to generate sufficient amount of data for establishing the empirical functions, so that the improved two-dimensional model can be nearly as accurate as three-dimensional models without having to solve three-dimensional numerical equations. In this study, the flow field of a meander channel is initially predicted by CCHE2D hydrodynamic model. By applying empirical functions to the flow field and bed shear stress field, the results of CCHE2D model are very close to those of CCHE3D. The predicted bed shear stress and velocity profiles of this enhanced CCHE2D are also in good agreements with the experimental data. Therefore, the hypothesis that an improved two-dimensional computational model can be applied to simulate three-dimensional physical processes adequately and cost-effectively is proved. In the sediment transport model, both bed load and suspended load are considered. The sediment incipient motion is affected by both the longitudinal and the transversal bed slope. In addition to the bed load transport due to bed shear stress, bed load transport in the transversal direction due to the transversal component of gravitational force is also calculated in this model. Suspended sediment transport rate is obtained by the integration of the product of velocity and concentration profiles. A general bank erosion equation is presented which indicates that bank erosion rate is related to the sediment transport rate as well as the erodibility of the bank. Even though bank erosion happens when shear stress acting on the bank is larger than the critical shear stress, the rate of bank retreat and advance depends on the balance of sediment transport, erosion and deposition. The enhanced CCHE2D is capable of predicting the alluvial channel bed degradation/aggradation, meandering channel initiation, migration and widening processes. Since bank erosion is assumed to be caused primarily by hydraulic erosion in the present study, geotechnical bank failure processes, which can also cause channel meandering, need to be included in future research. Non-equilibrium, non-uniform rather than equilibrium and uniform sediment transport models should also be implemented in the near future to further enhance the CCHE2D's capability. (Abstract shortened by UMI.)
A two-dimensional simulation of plasma leakage due to dengue infection
NASA Astrophysics Data System (ADS)
Nuraini, N.; Windarto, Jayanti, Swarna; Soewono, Edy
2014-03-01
Dengue Hemorrhagic Fever (DHF) is a disease caused by Dengue virus infection. One major characteristic in a patient with DHF is the occurrence of plasma leakage. Plasma leakage is a consequence of the immune system mechanism which activates cytokine. As a result, permeability of vascular will increase. Another characteristic in a DHF patient is hypoalbuminea (decreasing of albumin concentration). Plasma leakage can be modelled by constructing mathematical model of albumin concentration in plasma blood due to increasing of cytokine. In this paper, decreasing of albumin concentration in blood plasma is modelled using diffusion equation. In addition, two-dimensional numerical simulations of albumin concentration are also presented. From the simulation, it is found that the greater leakage rate or the wider leakage area, the greater decreasing albumin concentration will be. Furthermore, when time t increases, the albumin concentration decreases to zero.
NASA Astrophysics Data System (ADS)
Camporeale, Enrico; Burgess, David
2008-07-01
The kinetic electron firehose instability (EFI) is thought to be a crucial mechanism for constraining the observed electron anisotropy in expanding astrophysical plasmas, such as the solar wind. The EFI arises in a bi-Maxwellian plasma when the parallel temperature is greater than the perpendicular one, and its effect is to reduce anisotropy. We study this mechanism via kinetic linear theory, extending and refining previous results, and by new two-dimensional particle-in-cell (PIC) simulations with physical mass ratio. The results of PIC simulations show under which conditions the EFI can indeed be regarded as a constraint for electron distribution function. The detailed electron physics near marginal stability condition is discussed, with emphasis on the competition between growing and damping modes and on wave patterns formed at the nonlinear stage. The results also suggest an observational signature that the EFI has operated, namely the appearance of low-frequency, quasiperpendicular whistler/electron-cyclotron waves.
Vahedi, V.; Birdsall, C.K.; Lieberman, M.A. ); DiPeso, G.; Rognlien, T.D. )
1993-07-01
Weakly ionized processing plasmas are studied in two dimensions using a bounded particle-in-cell (PIC) simulation code with a Monte Carlo collision (MCC) package. The MCC package models the collisions between charged and neutral particles, which are needed to obtain a self-sustained plasma and the proper electron and ion energy loss mechanisms. A two-dimensional capacitive radio-frequency (rf) discharge is investigated in detail. Simple frequency scaling laws for predicting the behavior of some plasma parameters are derived and then compared with simulation results, finding good agreements. It is found that as the drive frequency increases, the sheath width decreases, and the bulk plasma becomes more uniform, leading to a reduction of the ion angular spread at the target and an improvement of ion dose uniformity at the driven electrode.
Two-dimensional full-wave code for reflectometry simulations in TJ-II
Blanco, E.; Heuraux, S.; Estrada, T.; Sanchez, J.; Cupido, L.
2004-10-01
A two-dimensional full-wave code in the extraordinary mode has been developed to simulate reflectometry in TJ-II. The code allows us to study the measurement capabilities of the future correlation reflectometer that is being installed in TJ-II. The code uses the finite-difference-time-domain technique to solve Maxwell's equations in the presence of density fluctuations. Boundary conditions are implemented by a perfectly matched layer to simulate free propagation. To assure the stability of the code, the current equations are solved by a fourth-order Runge-Kutta method. Density fluctuation parameters such as fluctuation level, wave numbers, and correlation lengths are extrapolated from those measured at the plasma edge using Langmuir probes. In addition, realistic plasma shape, density profile, magnetic configuration, and experimental setup of TJ-II are included to determine the plasma regimes in which accurate information may be obtained.
Shocked Magnetotail: ARTEMIS Observations and MHD Simulations
NASA Astrophysics Data System (ADS)
Zhou, Xiaoyan
2015-04-01
Interplanetary shocks can cause magnetospheric disturbances on various scales including kinetic and MHD processes. In this paper we study a shock event using ARTEMIS in situ observations and OpenGGCM MHD simulations, which shows how significant effect of interplanetary shocks could be on the magnetotail. The two ARTEMIS spacecraft were located near the tail current sheet and lobe center at (-60, 1, -5Re_GSM) when the shock arrived and recorded an abrupt tail compression leading to significant enhancements in the plasma density, temperature, magnetic field strength, and cross-tail current density, as well as to tailward flows and current sheet crossings. About 10 min later, the spacecraft entered the sheath solar wind unexpectedly. Two hypotheses are considered: either the tail was cut off by the high solar wind ram pressure (~25-30 nPa), or the compressed tail was pushed aside by the appreciable dawnward solar wind flow imposed by the shock. OpenGGMC simulation results confirmed the second hypothesis and revealed that during this 10 min interval, the lobe center moved dawnward by ~12 Re and the tail width in Y was reduced from ~40 to 26 Re, which eventually exposed ARTEMIS to the sheath solar wind. Comparisons of plasma and magnetic parameters between ARTEMIS in situ observations and simulations showed a satisfied consistence.
Martinez-Sykora, Juan; De Pontieu, Bart; Hansteen, Viggo
2012-07-10
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.
One- and two-dimensional simulations of whistler mode waves in an anisotropic plasma
Devine, P.E.; Chapman, S.C. [Univ. of Sussex, Brighton (United Kingdom)] [Univ. of Sussex, Brighton (United Kingdom); Eastwood, J.W. [Culham Lab., Oxfordshire (United Kingdom)] [Culham Lab., Oxfordshire (United Kingdom)
1995-09-01
We present results from self-consistent, one- and two-dimensional, electromagnetic simulations of the electron whistler mode instability relevant to the near-Earth nightside plasma sheet region during geomagnetically disturbed times. Specifically, we study the evolution of energetic, anisotropic electron distributions that are injected into the nightside ring current region at geomagnetically disturbed times, the resulting growth of electron whistler mode waves, and subsequent electron pitch angle diffusion via electron whistler wave-particle interactions. Growth of whistler mode waves from an initial pitch angle anisotropy (T{perpendicular} {approx} 4T{parallel}) is studied in the strong pitch angle diffusion regime (defined as having scattering times much shorter than a typical electron bounce time in the near Earth`s dipolar field). The quasi-linear and subsequent nonlinear evolution of waves and the corresponding migration of electrons in velocity space is followed over timescales such that ion motion may be neglected. Our simulations contain wave frequencies and growth rates that are a significant fraction of the electron gyrofrequency and the simultaneous evolution of waves propagating both parallel and nonparallel to the ambient magnetic field direction. Effects due to these are not usually accounted for in applications of quasi-linear theory to the problem of electron whistler wave-particle interactions, so that our self-consistent simulations of the electron whistler instability provide an important insight into the applicability of quasi-linear theory to the velocity space diffusion of electrons due to electron whistler wave-particle interactions. We examine the dependence of whistler mode wave growth rates, nonlinear wave mode saturation, and pitch angle diffusion rates on the {beta} value of the hot electron species which contains the resonant population, and we compare the differences between results of one- and two-dimensional simulations.
Topological events in two-dimensional grain growth: Experiments and simulations
Fradkov, V.E.; Glicksman, M.E.; Palmer, M.; Rajan, K. (Rensselaer Polytechnic Inst., Troy, NY (United States). Materials Engineering Dept.)
1994-08-01
Grain growth in polycrystals is a process that occurs as a result of the vanishing of small grains. The mean topological class of vanishing two-dimensional (2-D) grains was found experimentally to be about 4.5. This result suggests that most vanishing grains are either 4- or 5-sided. A recent theory of 2-D grain growth is explicitly based on this fact, treating the switching as random events. The process of shrinking of 4- and 5-sided two-dimensional grains was observed experimentally on polycrystalline films of transparent, pure succinonitrile (SCN). Grain shrinking was studied theoretically and simulated by computer (both dynamic and Monte Carlo). It was found that most shrinking grains are topologically stable and remain within their topological class until they are much smaller than their neighbors. They discuss differences which were found with respect to the behavior of 2-D polycrystals, a 2-D ideal soap froth, and a 2-D section of a 3-D grain structure.
Numerical simulation of discharge structures in Ar/Cs nonequilibrium plasma MHD generator
Okubo, M.; Kabashima, S.; Okuno, Y.; Yamasaki, H.
1998-07-01
As reported in previous papers, the quasi-one-dimensional simulation code has come to predict almost satisfactorily the performance of the shock tube driven disk MHD generator using cesium seeded argon plasma as working fluid. However, the agreement between experimental and predicted performances was not so good on the conditions that the external load resistance was small, the seed fraction was high or the stagnation pressure was low. On these conditions, it was observed that ionization instabilities occur in the MHD channel. On the other hand, high-speed photographs of the nonequilibrium plasma discharge in the MHD generator were taken on several working conditions during the experiment. From these photographs, discharges were classified into almost three kinds of patterns. (a) A single strong luminous ring-type discharge near the nozzle exit for low seed fraction, (b) an almost uniform discharge inside the MHD channel for medium seed fraction, (c) multiple ring-type or spiral discharges in the MHD channel for high seed fraction. The structures of the discharge were sometimes two-dimensional especially for high seed fraction. Therefore, it may be impossible in this case to simulate them and to predict the performance precisely with one-dimensional simulation code. In the present study, two-dimensional (r-q) numerical simulations were made on the disk MHD power generation experiment (thermal input is about 1.5MW). The objectives were to develop a numerical simulator with high accuracy for the disk MHD generator and to explain some interesting phenomena concerned with nonequilibrium plasma discharges. The system of basic equations was solved mainly using CIP method. The calculation region was taken as that located between the throat to the inlet of the second (final) cathode. The main results are summarized as follows; (A) On the condition that the seed fraction was lower than the optimum value, it was succeeded to simulate numerically the single strong luminous ring-type discharge. The ring-type discharge was caused by the partial ionization of argon due to the rapid increase in the electron temperature in the nozzle. The pressure increase like a shock wave was also induced there. (B) On the condition that the seed fraction was near the optimum value, an almost uniform plasma was obtained in the simulation and in the experiment. (C) On the condition that seed fraction was higher than the optimum value, A similar structure of discharge to experimental one was obtained in the calculation due to an ionization instability (streamer) caused by the partial ionization of seeded cesium. (D) The performances of the generator such as enthalpy extraction can be predicted well with this simulation code.
Simulation of femtosecond two-dimensional electronic spectra of conical intersections.
Kr?má?, Jind?ich; Gelin, Maxim F; Domcke, Wolfgang
2015-08-21
We have simulated femtosecond two-dimensional (2D) electronic spectra for an excited-state conical intersection using the wave-function version of the equation-of-motion phase-matching approach. We show that 2D spectra at fixed values of the waiting time provide information on the structure of the vibronic eigenstates of the conical intersection, while the evolution of the spectra with the waiting time reveals predominantly ground-state wave-packet dynamics. The results show that 2D spectra of conical intersection systems differ significantly from those obtained for chromophores with well separated excited-state potential-energy surfaces. The spectral signatures which can be attributed to conical intersections are discussed. PMID:26298135
NASA Astrophysics Data System (ADS)
Chua, Victor; Vissers, Michael; Law, Stephanie A.; Vishveshwara, Smitha; Eckstein, James N.
2015-03-01
We simulate the consequences of the superconducting proximity effect on the DC current response of a semiconductor-superconductor proximity device within the quasiclassical formalism in the diffusively disordered limit. The device is modeled on in-situ fabricated NS junctions of superconducting Nb films on metallic doped InAs films, with electrical terminals placed in an N-S-N T-junction configuration. Due to the non-collinear configuration of this three terminal device, a theoretical model based on coupled two dimensional spectral and distributional Usadel equations was constructed and numerically solved using Finite-Elements methods. In the regime of high junction conductance, our numerical results demonstrate strong temperature and spatial dependencies of the proximity induced modifications to spectral and transport properties. Such characteristics deviate strongly from usual tunnel junction behavior and aspects of this have been observed in prior experiments[arXiv:1402.6055].
Simulating and exploring Weyl semimetal physics with cold atoms in a two-dimensional optical lattice
NASA Astrophysics Data System (ADS)
Zhang, Dan-Wei; Zhu, Shi-Liang; Wang, Z. D.
2015-07-01
We propose a scheme to simulate and explore Weyl semimetal physics with ultracold fermionic atoms in a two-dimensional square optical lattice subjected to experimentally realizable spin-orbit coupling and an artificial dimension from an external parameter space, which may increase experimental feasibility compared with the cases in three-dimensional optical lattices. It is shown that this system with a tight-binding model is able to describe essentially three-dimensional Weyl semimetals with tunable Weyl points. The relevant topological properties are also addressed by means of the Chern number and the gapless edge states. Furthermore, we illustrate that the mimicked Weyl points can be experimentally detected by measuring the atomic transfer fractions in a Bloch-Zener oscillation, and the characteristic topological invariant can be measured with the particle pumping approach.
Simulating and exploring Weyl semimetal physics with cold atoms in a two-dimensional optical lattice
Dan-Wei Zhang; Shi-Liang Zhu; Z. D. Wang
2015-07-07
We propose a scheme to simulate and explore Weyl semimetal physics with ultracold fermionic atoms in a two-dimensional square optical lattice subjected to experimentally realizable spin-orbit coupling and an artificial dimension from an external parameter space, which may increase experimental feasibility compared with the cases in three dimensional optical lattices. It is shown that this system with a tight-binding model is able to describe essentially three-dimensional Weyl semimetals with tunable Weyl points. The relevant topological properties are also addressed by means of the Chern number and the gapless edge states. Furthermore, we illustrate that the mimicked Weyl points can be experimentally detected by measuring the atomic transfer fractions in a Bloch-Zener oscillation, and the characteristic topological invariant can be measured with the particle pumping approach.
Simulations of one- and two-dimensional complex plasmas using a modular, object-oriented code
Jefferson, R. A.; Cianciosa, M.; Thomas, E. Jr.
2010-11-15
In a complex plasma, charged microparticles ('dust') are added to a background of ions, electrons, and neutral particles. This dust fully interacts with the surrounding plasma and self-consistently alters the plasma environment leading to the emergence of new plasma behavior. Numerical tools that complement experimental investigations can provide important insights into the properties of complex plasmas. This paper discusses a newly developed code, named DEMON (dynamic exploration of microparticle clouds optimized numerically), for simulating a complex plasma. The DEMON code models the behavior of the charged particle component of a complex plasma in a uniform plasma background. The key feature of the DEMON code is the use of a modular force model that allows a wide variety of experimental configurations to be studied without varying the core code infrastructure. Examples of the flexibility of this modular approach are presented using examples of one- and two-dimensional complex plasmas.
Riley, M.E.
1998-03-01
This report describes the numerical procedure used to implement the Green`s function method for solving the Poisson equation in two-dimensional Cartesian coordinates. The procedure can determine the solution to a problem with any or all of applied voltage boundary conditions, dielectric media, floating (insulated) conducting media, dielectric surface charging, periodic (reflective) boundary conditions, and volumetric space charge. The numerical solution is reasonably fast, and the dimension of the linear problem to be solved is that of the number of elements needed to represent the surfaces, not the whole computational volume. The method of solution is useful in the simulation of plasma particle motion in the vicinity of complex surface structures as found in microelectronics plasma processing applications. A FORTRAN implementation of this procedure is available from the author.
Two-dimensional dynamic stall as simulated in a varying freestream
NASA Technical Reports Server (NTRS)
Pierce, G. A.; Kunz, D. L.; Malone, J. B.
1978-01-01
A low speed wind tunnel equipped with a axial gust generator to simulate the aerodynamic environment of a helicopter rotor was used to study the dynamic stall of a pitching blade in an effort to ascertain to what extent harmonic velocity perturbations in the freestream affect dynamic stall. The aerodynamic moment on a two dimensional, pitching blade model in both constant and pulsating airstream was measured. An operational analog computer was used to perform on-line data reduction and plots of moment versus angle of attack and work done by the moment were obtained. The data taken in the varying freestream were then compared to constant freestream data and to the results of two analytical methods. These comparisons show that the velocity perturbations have a significant effect on the pitching moment which can not be consistently predicted by the analytical methods, but had no drastic effect on the blade stability.
NASA Astrophysics Data System (ADS)
Rino, C. L.
2013-12-01
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.
Two-dimensional and three-dimensional direct numerical simulation of co-rotating vortices
NASA Astrophysics Data System (ADS)
Orlandi, P.
2007-01-01
Two-dimensional (2D) and three-dimensional (3D) simulations are presented for co-rotating vortices with distributed vorticity at different values of the separation distance b0. The ratio between the vortices' radius a0 and b0 is smaller than the critical value a0/b0?0.30 for merging in inviscid conditions of blobs of constant vorticity. The dependence of merging on Reynolds number and on a0/b0 has been investigated in 2D simulations. In 2D the resolution can be increased to perform simulations at Re =30000 when very long filaments are generated. These simulations confirm the findings of Brandt and Nomura [L. K. Brandt and K. K. Nomura, Phys. Fluids 18, 51701 (2006)] that the filaments play a minor role in merging. It has been found that a large increase of ?P?max (P is the pressure) indicates merging. Time evolving 3D simulations at Re =3000, are similar to the laboratory experiments by Meunier and Leweke [P. Meunier and T. Leweke, J. Fluid Mech. 533, 125 (2005)]. At the same values of a0/b0 as used in 2D, 3D simulations demonstrate that the merging is more complex than in 2D, and that it largely depends on the kind of axial disturbances imposed, at t =0, on the two vortices. 3D simulations of vortices evolving in space and time, without disturbances at x1=0, have shown that at Re =3000 the results, in a convective frame, do not differ from those in 2D simulations. This assumption, attempting to reproduce the evolution of the vortices behind aircrafts, demonstrates that, with the present computational resources, DNS at practical Reynolds numbers are not feasible.
Lu, Meijun; Das, Ujjwal; Bowden, Stuart; Hegedus, Steven; Birmire, Robert
2009-06-09
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.
NASA Astrophysics Data System (ADS)
Gheisari, R.; Firoozabadi, M. M.; Mohammadi, H.
2014-01-01
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.
2014-01-15
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 D{sub 2}O and solid D{sub 2} (sD{sub 2}). The D{sub 2}O was investigated as the neutron moderator, and sD{sub 2} 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 sD{sub 2}. 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 sD{sub 2} volume) equal to 6.79?×?10{sup 6} cm{sup ?2}s{sup ?1} and 2.20 ×10{sup 5} cm{sup ?3}s{sup ?1}, respectively.
Interstellar clouds in high-speed, supersonic flows: Two-dimensional simulations
NASA Technical Reports Server (NTRS)
Schiano, A. V. R.; Christiansen, Wayne A.; Knerr, Jeffrey M.
1995-01-01
We present a series of gasdynamical simulations of the interaction of a dense, cool interstellar cloud with a high-speed, supersonic wind that confines and accelerates the embedded cloud. Our goal is to attempt to determine if such clouds can survive various potentially disruptive instabilities, that occur at their peripheries, long enough to be accelerated to speeds which are comparable to the wind velocity. These simulations are performed using two-dimensional, Eulerian gas dynamics on both an axisymmetric (about the cloud axis) and 'slab' geometric grid. The spatial and temporal resolutions of the simulations are varied over a wide range to investigate the effects of small-scale instabilities on the overall acceleration of clouds and the development of large-scale, disruptive instabilities. Also, we study the effects of wind/cloud Mach number variations by changing the wind speed constant at about 12 km/s (which corresponds to a cloud temperature of 10,000 K). The current simulations track the evolution of clouds as they are accelerated to speeds approximately 4-5 times greater than their internal sound speeds. Furthermore, the models with the highest resolution were extended far beyond quasi-linear Rayleigh-Taylor growth times reaching 6-7 Rayleigh-Taylor growth times for the largest scale instabilities before being terminated because of the accumulation of errors at the rear grid boundary.
Simulation of Ozone and Long Lived Tracers in the GSFC Two-Dimensional Model
NASA Technical Reports Server (NTRS)
Fleming, Eric L.; Jackman, Charles H.; Considine, David B.; Stolarski, Richard S.
1999-01-01
The GSFC two-dimensional transport and chemistry model has been used for a wide variety of scientific and assessment studies of stratospheric ozone. Transport is a key element in the ozone simulations, and we have recently upgraded our model transport formulation to include much of the information about atmospheric transport processes available from existing data sets. To properly evaluate the model transport, it is desirable to examine the effects of transport and photochemistry separately. Recently, high quality observations of several long lived stratospheric tracers have become available from aircraft, balloon, and satellite measurement systems. This data provides a means to do a detailed model transport evaluation, as has been done in the recent Models and Measurements Intercomparison Project II. In this paper, we will discuss the GSFC 2D model simulations of ozone together with model-data comparisons of long lived tracers such as methane and the age of air transport diagnostic. We will show that the model can reproduce many of the transport-sensitive features observed in the stratosphere, and can compare reasonably well with measurements of both total ozone and long lived tracers simultaneously. We will also discuss the model deficiencies in simulating some of the detailed aspects of the observations.
Numerical simulation of two-dimensional spatially-developing mixing layers
NASA Technical Reports Server (NTRS)
Wilson, R. V.; Demuren, A. O.
1994-01-01
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.
Numerical simulation of steady flow in a two-dimensional total artificial heart model.
Kim, S H; Chandran, K B; Chen, C J
1992-11-01
In this paper, a numerical simulation of steady laminar and turbulent flow in a two-dimensional model for the total artificial heart is presented. A trileaflet polyurethane valve was simulated at the outflow orifice while the inflow orifice had a trileaflet or a flap valve. The finite analytic numerical method was employed to obtain solutions to the governing equations in the Cartesian coordinates. The closure for turbulence model was achieved by employing the k-epsilon-E model. The SIMPLER algorithm was used to solve the problem in primitive variables. The numerical solutions of the simulated model show that regions of relative stasis and trapped vortices were smaller within the ventricular chamber with the flap valve at the inflow orifice than that with the trileaflet valve. The predicted Reynolds stresses distal to the inflow valve within the ventricular chamber were also found to be smaller with the flap valve than with the trileaflet valve. These results also suggest a correlation between high turbulent stresses and the presence of thrombus in the vicinity of the valves in the total artificial hearts. The computed velocity vectors and turbulent stresses were comparable with previously reported in vitro measurements in artificial heart chambers. Analysis of the numerical solutions suggests that geometries similar to the flap valve (or a tilting disk valve) results in a better flow dynamics within the total artificial heart chamber compared to a trileaflet valve. PMID:1487902
Two-Dimensional Hybrid-PIC Simulation of Magnetic Sail Including Interplanetary Magnetic Field
NASA Astrophysics Data System (ADS)
Matsumoto, Masaharu; Kajimura, Yoshihiro; Usui, Hideyuki; Funaki, Ikkoh; Shinohara, Iku
Solar wind plasma behavior and thrust of a magnetic sail under the condition with interplanetary magnetic field (IMF) are examined by time-dependent, two-dimensional, X-Y Cartesian, hybrid particle-in-cell (PIC) simulations. Magnetic sail is a propellant less propulsion system proposed for an interplanetary space flight. The thrust force is produced by the interaction between magnetic dipole field artificially generated by superconducting coils in a spacecraft and a solar wind. In the present simulations, the ratio of ion Larmor radius at the magnetopause to characteristic length of the magnetosphere is set to 0.1, and IMF strength is set to 0 and 10nT. As simulation results, magnetic reconnection occurs due to superposition of IMF and dipole field in the solar wind flow field. The reconnection points depend on the direction of IMF and those have an important role in the formation of shock wave. When IMF is perpendicular to the solar wind flow direction, the thrust acting on the spacecraft increases compared to the case without IMF. When IMF is parallel to the solar wind flow direction, lift force is generated on the spacecraft. These phenomena are attributed to the difference in location of magnetic reconnection point depending on the direction of IMF.
Computer-based training in two-dimensional echocardiography using an echocardiography simulator.
Weidenbach, Michael; Wild, Florentine; Scheer, Kathrin; Muth, Gerhard; Kreutter, Stefan; Grunst, Gernoth; Berlage, Thomas; Schneider, Peter
2005-04-01
Two-dimensional (2D) echocardiography is a user-dependent technique that poses some inherent problems to the beginner. The first problem for beginners is spatial orientation, especially the orientation of the scan plane in reference to the 3-dimensional (3D) geometry of the heart. The second problem for beginners is steering of the ultrasound probe. We have designed a simulator to teach these skills. On a computer screen a side-by-side presentation of a 3D virtual reality scene on the right side and a 2D echocardiographic view on the left side is given. The virtual scene consists of a 3D heart and an ultrasound probe with scan plane. The 2D echocardiographic image is calculated from 3D echocardiographic data sets that are registered with the heart model to achieve spatial and temporal congruency. The displayed 2D echocardiographic image is defined and controlled by the orientation of the virtual scan plane. To teach hand-eye coordination we equipped a dummy transducer with a 3D tracking system and placed it on a dummy torso. We have evaluated the usability of the simulator in an introductory course for final-year medical students. The simulator was graded realistic and easy to use. According to a subjective self-assessment by a standardized questionnaire the aforementioned skills were imparted effectively. PMID:15846165
MHD simulations for cool star winds
NASA Astrophysics Data System (ADS)
Suzuki, Takeru K.
2015-08-01
In this talk I present some results of MHD simulations for the atmosphere and wind of cool stars.First, I introduce structured red giant winds with strong intermittency. In the atmosphere of stars near the Linsky & Haisch dividing line, magnetic-pressure supported hot (~10^6 K) and warm (>~10^5 K) bubbles are formed in cool (T<~2×10^4 K) chromospheric winds because of thermal instability. The mass loss rate largely varies in time and the X-ray radiation is also quite intermittent.Next, I briefly discuss the wind structure of cool main sequence stars. A small change of the energy input from the surface affect the atmospheric structure because of the reflection and nonlinear dissipation of Alfven waves. In active stars, the chromosphere is extended to a higher altitude than the typical solar condition, and the mass loss rate could be considerably (100-1000 times) larger than the solar mass loss rate.
Two-dimensional simulations of the neutron yield in cryogenic deuterium-tritium implosions on OMEGA
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.
2010-10-15
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
Solar wind turbulence from MHD to sub-ion scales: high-resolution hybrid simulations
Franci, Luca; Matteini, Lorenzo; Landi, Simone; Hellinger, Petr
2015-01-01
We present results from a high-resolution and large-scale hybrid (fluid electrons and particle-in-cell protons) two-dimensional numerical simulation of decaying turbulence. Two distinct spectral regions (separated by a smooth break at proton scales) develop with clear power-law scaling, each one occupying about a decade in wave numbers. The simulation results exhibit simultaneously several properties of the observed solar wind fluctuations: spectral indices of the magnetic, kinetic, and residual energy spectra in the magneto-hydrodynamic (MHD) inertial range along with a flattening of the electric field spectrum, an increase in magnetic compressibility, and a strong coupling of the cascade with the density and the parallel component of the magnetic fluctuations at sub-proton scales. Our findings support the interpretation that in the solar wind large-scale MHD fluctuations naturally evolve beyond proton scales into a turbulent regime that is governed by the generalized Ohm's law.
Solar Wind Turbulence from MHD to Sub-ion Scales: High-resolution Hybrid Simulations
NASA Astrophysics Data System (ADS)
Franci, Luca; Verdini, Andrea; Matteini, Lorenzo; Landi, Simone; Hellinger, Petr
2015-05-01
We present results from a high-resolution and large-scale hybrid (fluid electrons and particle-in-cell protons) two-dimensional numerical simulation of decaying turbulence. Two distinct spectral regions (separated by a smooth break at proton scales) develop with clear power-law scaling, each one occupying about a decade in wavenumbers. The simulation results simultaneously exhibit several properties of the observed solar wind fluctuations: spectral indices of the magnetic, kinetic, and residual energy spectra in the magnetohydrodynamic (MHD) inertial range along with a flattening of the electric field spectrum, an increase in magnetic compressibility, and a strong coupling of the cascade with the density and the parallel component of the magnetic fluctuations at sub-proton scales. Our findings support the interpretation that in the solar wind, large-scale MHD fluctuations naturally evolve beyond proton scales into a turbulent regime that is governed by the generalized Ohm’s law.
NASA Astrophysics Data System (ADS)
Ghasemi, Amirmahdi; Pathak, Ashish; Chiodi, Robert; Raessi, Mehdi
2013-11-01
Ocean waves represent a vast renewable energy resource, which is mostly untapped. We present a computational tool for simulation of the interactions between waves and two-dimensional oscillating solid bodies representing simple wave energy converters (WECs). The computational tool includes a multiphase flow solver, in which the two-step projection method with GPU acceleration is used to solve the Navier-Stokes equations. The fictitious domain method is used to capture the interactions of a moving rigid solid body with the two-fluid flow. The solid and liquid volumes are tracked using the volume-of-fluid (VOF) method, while the triple points and phase interfaces in three-phase cells are resolved. A consistent mass and momentum transport scheme is used to handle the large density ratio. We present results of two wave generation mechanisms with a piston or flap wave maker, where the theoretical and experimental results were used for validation. Then, simulation results of several simple devices representative of distinct WECs, including a bottom-hinged flap device as well as cylindrical or rectangular terminators are presented. The results are in good agreement with the available experimental data.
Direct two-dimensional electrochemical impedance spectra simulation for solid oxide fuel cell
NASA Astrophysics Data System (ADS)
Shi, Yixiang; Wang, Hongjian; Cai, Ningsheng
2012-06-01
A two-dimensional (2D) EIS simulation approach is developed by solving a SOFC unit cell model with imposed sinusoidal voltage perturbations at different frequencies. The transient SOFC unit cell model describes the intricate interdependency among the ionic/electronic conduction, multi-component species transport, electrochemical reaction processes and electrode microstructure as well as the coupling processes of mass, energy, momentum transport within flow channels. The model calculates the local transient response and impedance spectra as a function of channel position. The effects of the reaction depletion, product accumulation as well as the temperature variation along the flow channels on the EIS spectra are numerically simulated with a counter-flow mode. The results show that the convection-diffusion process along the flow channel has significant effects on the low frequency half circle of the impedance spectra. The temperature oscillations accumulate along the flow channels, and then affect the current responses which probably lead to an electro-thermal impedance effects.
Deymier, Pierre
Two-dimensional Monte Carlo simulations of ionic and nonionic silane self-assembly on hydrophilic 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
Two-dimensional simulations of explosive eruptions of Kick-em Jenny and other submarine volcanos
Gisler, Galen R.; Weaver, R. P.; Mader, Charles L.; Gittings, M. L.
2004-01-01
Kick-em Jenny, in the Eastern Caribbean, is a submerged volcanic cone that has erupted a dozen or more times since its discovery in 1939. The most likely hazard posed by this volcano is to shipping in the immediate vicinity (through volcanic missiles or loss-of-buoyancy), but it is of interest to estimate upper limits on tsunamis that might be produced by a catastrophic explosive eruption. To this end, we have performed two-dimensional simulations of such an event in a geometry resembling that of Kick-em Jenny with our SAGE adaptive mesh Eulerian multifluid compressible hydrocode. We use realistic equations of state for air, water, and basalt, and follow the event from the initial explosive eruption, through the generation of a transient water cavity and the propagation of waves away from the site. We find that even for extremely catastrophic explosive eruptions, tsunamis from Kick-em Jenny are unlikely to pose significant danger to nearby islands. For comparison, we have also performed simulations of explosive eruptions at the much larger shield volcano Vailuluu in the Samoan chain, where the greater energy available can produce a more impressive wave. In general, however, we conclude that explosive eruptions do not couple well to water waves. The waves that are produced from such events are turbulent and highly dissipative, and don't propagate well. This is consistent with what we have found previously in simulations of asteroid-impact generated tsunamis. Non-explosive events, however, such as landslides or gas hydrate releases, do couple well to waves, and our simulations of tsunamis generated by subaerial and sub-aqueous landslides demonstrate this.
NASA Astrophysics Data System (ADS)
Liu, Z.-S.; Sechovský, V.; Diviš, M.
2015-02-01
A new quantum simulation approach has been applied in the present work to the two-dimensional (2D) ferromagnetic and antiferromagnetic Ising lattices to calculate their magnetic structures, magnetizations, free energies and specific heats in the absence of an external magnetic field. Surprisingly, no size effects could be observed in our simulations performed for the Ising lattices of different sizes. Most importantly, our calculated spontaneous thermally averaged spins for the two kinds of systems are exactly same as those evaluated with quantum mean field theory, and the magnetic structures simulated at all chosen temperatures are perfectly ferromagnetic or antiferromagnetic, verifying the correctness and applicability of our quantum model and computational algorithm. On the other hand, if the classical Monte Carlo (CMC) method is applied to the ferromagnetic 2D Ising lattice with S=1, it is able to generate correct magnetization well consistent with Onsager's theory; but in the case of S=1/2, the computational results of CMC are incomparable to those predicted with the quantum mean field theory, giving rise to very much reduced magnetization and considerably underestimated Curie temperature. The difficulty met by the CMC method is mainly caused by its improperly calculated exchange energy of the randomly selected spin in every simulation step, especially immediately below the transition temperature, where the thermal averages of spins are much less than 1/2, however they are assigned to ±1/2 by CMC to evaluate the exchange energies of the spins, such improper manipulation is obviously impossible to lead the code to converge to the right equilibrium states of the spin systems.
NASA Astrophysics Data System (ADS)
Sydorenko, D.; Rankin, R.; Kabin, K.
2009-12-01
This paper presents initial results based on kinetic extensions of a nonlinear two-dimensional (2D) multi-fluid (three ion species and fluid electrons) MHD model that is designed to study propagation of shear Alfven waves in low-altitude auroral flux tubes. It is intended to use the model for scientific support of the “enhanced polar outflow probe” e-POP/CASSIOPE spacecraft mission (launch scheduled in 2010). Effects of gravity, thermal pressure, and geomagnetic field curvature are included, while the parallel electric field along geomagnetic field lines is calculated under the assumption of plasma quasineutrality. The model has been used successfully to study excitation of eigenmodes of the ionospheric Alfven resonator (IAR) by an Alfven wave packet injected from the magnetospheric end of the simulated plasma region. The formation of density cavities due to the ponderomotive force of standing oscillations in the IAR [Sydorenko, Rankin, and Kabin, 2008], and excitation of double layers and ion-acoustic wave packets, has been demonstrated. The kinetic extension of the multi-fluid code involves replacing the fluid electron model with a kinetic module that solves the simplified drift-kinetic Vlasov equation for the electron velocity distribution function (EVDF). To avoid undue complexity, it is assumed that (i) the electrons move only along geomagnetic field lines and (ii) the electron magnetic moment is conserved. As a result, the evolution of the EVDF is reduced to the problem of advection in 2D phase space “distance along the field line - velocity along the field line”. This problem is solved using a semi-Lagrangian algorithm [Staniforth and Cote, 1991]. The kinetic simulation starts from the initial equilibrium state similar to [Ergun et al., 2000]. The equilibrium assumes that the plasma consists of two electron populations: cold electrons with isotropic EVDF originating from the ionosphere, and hot anisotropic electrons with a loss-cone EVDF coming from the high-altitude end. The loss-cone distribution is prone to strong numerical dispersion, which is compensated by tracing the interface of the EVDF in the coordinate-velocity phase space. Ergun R. E., C. W. Carlson, J. P. McFadden, F. S. Mozer, and R. J. Strangeway (2000), Geophys. Res. Lett., 27, 4053-4056. Staniforth A. and J. Cote (1991), Mon. Wea. Rev., 119, 2206-2223 Sydorenko, D., R. Rankin, and K. Kabin (2008), J. Geophys. Res., 113, A10206, doi:10.1029/2008JA013579.
Simulations of super-structure domain walls in two dimensional assemblies of magnetic nanoparticles
NASA Astrophysics Data System (ADS)
Jordanovic, J.; Beleggia, M.; Schiøtz, J.; Frandsen, C.
2015-07-01
We simulate the formation of domain walls in two-dimensional assemblies of magnetic nanoparticles. Particle parameters are chosen to match recent electron holography and Lorentz microscopy studies of almost monodisperse cobalt nanoparticles assembled into regular, elongated lattices. As the particles are small enough to consist of a single magnetic domain each, their magnetic interactions can be described by a spin model in which each particle is assigned a macroscopic "superspin." Thus, the magnetic behaviour of these lattices may be compared to magnetic crystals with nanoparticle superspins taking the role of the atomic spins. The coupling is, however, different. The superspins interact only by dipolar interactions as exchange coupling between individual nanoparticles may be neglected due to interparticle spacing. We observe that it is energetically favorable to introduce domain walls oriented along the long dimension of nanoparticle assemblies rather than along the short dimension. This is unlike what is typically observed in continuous magnetic materials, where the exchange interaction introduces an energetic cost proportional to the area of the domain walls. Structural disorder, which will always be present in realistic assemblies, pins longitudinal domain walls when the external field is reversed, and makes a gradual reversal of the magnetization by migration of longitudinal domain walls possible, in agreement with previous experimental results.
Simulation of a two-dimensional model for colloids in a uniaxial electric field
Ahmad M. Almudallal; Ivan Saika-Voivod
2011-06-26
We perform Monte Carlo simulations of a simplified two-dimensional model for colloidal hard spheres in an external uniaxial AC electric field. Experimentally, the external field induces dipole moments in the colloidal particles, which in turn form chains. We therefore approximate the system as composed of well formed chains of dipolar hard spheres of a uniform length. The dipolar interaction between colloidal spheres gives rise to an effective interaction between the chains, which we treat as disks in a plane, that includes a short range attraction and long range repulsion. Hence, the system favors finite clustering over bulk phase separation and indeed we observe at low temperature and density that the system does form a cluster phase. As density increases, percolation is accompanied by a pressure anomaly. The percolated phase, despite being composed of connected, locally crystalline domains, does not bear the typical signatures of a hexatic phase. At very low densities, we find no indication of a "void phase" with a cellular structure seen recently in experiments.
NASA Astrophysics Data System (ADS)
Reith, Daniel; Bucior, Katarzyna; Yelash, Leonid; Virnau, Peter; Binder, Kurt
2012-03-01
As a generic model system for phase separation in polymer solutions, a coarse-grained model for hexadecane/carbon dioxide mixtures has been studied in two-dimensional geometry. Both the phase diagram in equilibrium (obtained from a finite size scaling analysis of Monte Carlo data) and the kinetics of state changes caused by pressure jumps (studied by large scale molecular dynamics simulations) are presented. The results are compared to previous work where the same model was studied in three-dimensional geometry and under confinement in slit geometry. For deep quenches the characteristic length scale ?(t) of the formed domains grows with time t according to a power law close to \\ell (t)\\propto \\sqrt{t}. Since in this problem both the polymer density ?p and the solvent density ?s matter, the time evolution of the density distribution PL(?p,?s,t) in L × L subboxes of the system is also analyzed. It is found that in the first stage of phase separation the system separates locally into low density carbon dioxide regions that contain no polymers and regions of high density polymer melt that are supersaturated with this solvent. The further coarsening proceeds via the growth of domains of rather irregular shapes. A brief comparison of our findings with results of other models is given.
Two-dimensional simulation of organic bulk heterojunction solar cell: influence of the morphology.
Raba, Adam; Cordan, Anne-Sophie; Leroy, Yann
2013-07-01
Recent developments in organic solar cells show interesting power conversion efficiencies. However, with the use of organic semiconductors and bulk heterojunction cells, many new concepts have to be introduced to understand their characteristics. Only few models investigate these new concepts, and most of them are one-dimensional only. In this work, we present a two-dimensional model based on solving the drift-diffusion equations. The model describes the generation of excitons in the donor phase of the active layer and their diffusion towards an interface between the two separate acceptor and donor domains. Then, when the exciton reaches the interface, it forms a charge transfer state which can split into free charges due to the internal potential. Finally, these free charges are transported toward the electrodes within their respective domains (electrons in acceptor domain, holes in donor domain) before being extracted. In this model, we can follow the distribution of each species and link it to the physical processes taken into account. Using the finite element method to solve the equations of the model, we simulate the effect of the bulk heterojunction morphology on photocurrent curves. We concentrate on the morphology parameters such as the mean acceptor/donor domain sizes and the roughness of,the interface between the donor and acceptor domains. Results are discussed in relation with experimental observations. PMID:23901547
Simulated two-dimensional electronic spectroscopy of the eight-bacteriochlorophyll FMO complex
NASA Astrophysics Data System (ADS)
Yeh, Shu-Hao; Kais, Sabre
2014-12-01
The Fenna-Matthews-Olson (FMO) protein-pigment complex acts as a molecular wire conducting energy between the outer antenna system and the reaction center; it is an important photosynthetic system to study the transfer of excitonic energy. Recent crystallographic studies report the existence of an additional (eighth) bacteriochlorophyll a (BChl a) in some of the FMO monomers. To understand the functionality of this eighth BChl, we simulated the two-dimensional electronic spectra of both the 7-site (apo form) and the 8-site (holo form) variant of the FMO complex from green sulfur bacteria, Prosthecochloris aestuarii. By comparing the spectrum, it was found that the eighth BChl can affect two different excitonic energy transfer pathways: (1) it is directly involved in the first apo form pathway (6 ? 3 ? 1) by passing the excitonic energy to exciton 6; and (2) it facilitates an increase in the excitonic wave function overlap between excitons 4 and 5 in the second pathway (7 ? 4,5 ? 2 ? 1) and thus increases the possible downward sampling routes across the BChls.
Lagrangian particle simulation of tracer dispersion in the lee of a schematic two-dimensional hill
Tinarelli, G.; Anfossi, D.; Brusasca, G.; Ferrero, E.; Giostra, U.; Morselli, M.G.; Moussafir, J.; Tampieri, F.; Trombetti, F. CNR, Turin Universita di Alessandria CNR, Bologna ARIA, Paris )
1994-06-01
Spray, a 3D Langrangian particle model for the simulation of complex flow dispersion, is presented. Its performance is tested against the Environmental Protection Agency wind tunnel concentration distribution of passive tracer released from elevated point sources, located in the lee region of a two-dimensional schematic hill, in a neutrally stratified boundary layer. Based on the measured values of the first two moments of the turbulent flow velocity, the mean fields are computed over a regular grid using a mass-consistent model, whereas the turbulence structure is simply interpolated. From these fields, trajectories of tracer particles are computed using a linear formulation of the Langevin equation, with a correlated, skewed forcing. The self-consistence test (well-mixed condition), aimed at maintaining an initially well-mixed particle distribution uniform in time, has shown satisfactory results in the region under study. The computed concentration field turns out to be in good agreement with the observed one. In detail, ground-level profiles and vertical cross sections of concentration are compared showing the important effects resulting from the topographic influence on the flow structure.
NASA Astrophysics Data System (ADS)
Watanabe, Go; Saito, Jun-ichi; Fujita, Yusuke; Tabe, Yuka
2013-08-01
We have carried out molecular dynamics (MD) simulations for monolayers of smectic A and C liquid crystal (LC) phases in order to investigate the in-plane molecular diffusion from the microscopic point of view. In contrast to similar complex two-dimensional systems (e.g., biomembranes) whose molecular diffusion is anomalous, in-plane mean square displacements (MSDs) for both phases increase linearly with passing time similar to typical fluids on the nanosecond time scale. By following the relation between the diffusion and the viscosity in the fluids, we estimated the viscosity coefficients for both LC monolayers, and the obtained values indicate that the smectic A monolayer has a higher viscosity than the smectic C one. Moreover, we investigate the in-plane self-diffusion anisotropy D\\|/D\\bot for smectic C and found that the diffusion parallel to the molecular tilt is 1.5 times larger than that in the perpendicular direction. This anisotropic diffusion property in the smectic C monolayer has not been clearly confirmed thus far.
Simulated two-dimensional electronic spectroscopy of the eight-bacteriochlorophyll FMO complex.
Yeh, Shu-Hao; Kais, Sabre
2014-12-21
The Fenna-Matthews-Olson (FMO) protein-pigment complex acts as a molecular wire conducting energy between the outer antenna system and the reaction center; it is an important photosynthetic system to study the transfer of excitonic energy. Recent crystallographic studies report the existence of an additional (eighth) bacteriochlorophyll a (BChl a) in some of the FMO monomers. To understand the functionality of this eighth BChl, we simulated the two-dimensional electronic spectra of both the 7-site (apo form) and the 8-site (holo form) variant of the FMO complex from green sulfur bacteria, Prosthecochloris aestuarii. By comparing the spectrum, it was found that the eighth BChl can affect two different excitonic energy transfer pathways: (1) it is directly involved in the first apo form pathway (6 ? 3 ? 1) by passing the excitonic energy to exciton 6; and (2) it facilitates an increase in the excitonic wave function overlap between excitons 4 and 5 in the second pathway (7 ? 4,5 ? 2 ? 1) and thus increases the possible downward sampling routes across the BChls. PMID:25527917
Monte Carlo simulations of two-dimensional hard core lattice gases
NASA Astrophysics Data System (ADS)
Fernandes, Heitor C. Marques; Arenzon, Jeferson J.; Levin, Yan
2007-03-01
Monte Carlo simulations are used to study lattice gases of particles with extended hard cores on a two-dimensional square lattice. Exclusions of one and up to five nearest neighbors (NN) are considered. These can be mapped onto hard squares of varying side length, ? (in lattice units), tilted by some angle with respect to the original lattice. In agreement with earlier studies, the 1NN exclusion undergoes a continuous order-disorder transition in the Ising universality class. Surprisingly, we find that the lattice gas with exclusions of up to second nearest neighbors (2NN) also undergoes a continuous phase transition in the Ising universality class, while the Landau-Lifshitz theory predicts that this transition should be in the universality class of the XY model with cubic anisotropy. The lattice gas of 3NN exclusions is found to undergo a discontinuous order-disorder transition, in agreement with the earlier transfer matrix calculations and the Landau-Lifshitz theory. On the other hand, the gas of 4NN exclusions once again exhibits a continuous phase transition in the Ising universality class—contradicting the predictions of the Landau-Lifshitz theory. Finally, the lattice gas of 5NN exclusions is found to undergo a discontinuous phase transition.
Simulation of Anderson localization in two-dimensional ultracold gases for pointlike disorder
NASA Astrophysics Data System (ADS)
Morong, W.; DeMarco, B.
2015-08-01
Anderson localization has been observed for a variety of media, including ultracold atomic gases with speckle disorder in one and three dimensions. However, observation of Anderson localization in a two-dimensional geometry for ultracold gases has been elusive. We show that a cause of this difficulty is the relatively high percolation threshold of a speckle potential in two dimensions, resulting in strong classical localization. We propose a realistic pointlike disorder potential that circumvents this percolation limit with localization lengths that are experimentally observable. The percolation threshold is evaluated for experimentally realistic parameters, and a regime of negligible classical trapping is identified. Localization lengths are determined via scaling theory, using both exact scattering cross sections and the Born approximation, and by direct simulation of the time-dependent Schrödinger equation. We show that the Born approximation can underestimate the localization length by four orders of magnitude at low energies, while exact cross sections and scaling theory provide an upper bound. Achievable experimental parameters for observing localization in this system are proposed.
TWO-DIMENSIONAL BLAST-WAVE-DRIVEN RAYLEIGH-TAYLOR INSTABILITY: EXPERIMENT AND SIMULATION
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.; Arnett, D.; Leibrandt, D. R.
2009-05-01
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 {approx}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 {mu}m and amplitude of 2.5 {mu}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.
Masson-Laborde, P. E.; Casanova, M.; Loiseau, P. [CEA, DAM, DIF, F-91297 Arpajon (France); Rozmus, W.; Peng, Z. [Department of Physics, Theoretical Physics Institute, University of Alberta, Edmonton, Alberta T6G 2G7 (Canada); Pesme, D.; Hueller, S.; Chapman, T. [Centre de Physique Theorique, CNRS, Ecole Polytechnique, 91128 Palaiseau Cedex (France); Bychenkov, V. Yu. [P. N. Lebedev Physics Institute, Russian Academy of Science, Leninskii pr. 53, 11991 Moscow (Russian Federation)
2010-09-15
In the following work, we analyze one-dimensional (1D) and two-dimensional (2D) full particle-in-cell simulations of stimulated Raman scattering (SRS) and study the evolution of Langmuir waves (LWs) in the kinetic regime. It is found that SRS reflectivity becomes random due to a nonlinear frequency shift and that the transverse modulations of LWs are induced by (i) the Weibel instability due to the current of trapped particles and (ii) the trapped particle modulational instability (TPMI) [H. Rose, Phys. Plasmas 12, 12318 (2005)]. Comparisons between 1D and 2D cases indicate that the nonlinear frequency shift is responsible for the first saturation of SRS. After this transient interval of first saturation, 2D effects become important: a strong side-scattering of the light, caused by these transverse modulations of the LW and the presence of a nonlinear frequency shift, is observed together with a strong transverse diffusion. This leads to an increase of the Landau damping rate of the LW, contributing to the limiting of Raman backscattering. A model is developed that reproduces the transverse evolution of the magnetic field due to trapped particles. Based on a simple 1D hydrodynamic model, the growth rate for the Weibel instability of the transverse electrostatic mode and magnetic field is estimated and found to be close to the TPMI growth rate [H. Rose et al., Phys. Plasmas 15, 042311 (2008)].
Jean-Michel Caillol
2015-01-22
We present two methods for solving the electrostatics of point charges and multipoles on the surface of a sphere, \\textit{i.e.} in the space $\\mathcal{S}_{2}$, with applications to numerical simulations of two-dimensional polar fluids. In the first approach, point charges are associated with uniform neutralizing backgrounds to form neutral pseudo-charges, while, in the second, one instead considers bi-charges, \\textit{i.e.} dumbells of antipodal point charges of opposite signs. We establish the expressions of the electric potentials of pseudo- and bi-charges as isotropic solutions of the Laplace-Beltrami equation in $\\mathcal{S}_{2}$. A multipolar expansion of pseudo- and bi-charge potentials leads to the electric potentials of mono- and bi-multipoles respectively. These potentials constitute non-isotropic solutions of the Laplace-Beltrami equation the general solution of which in spherical coordinates is recast under a new appealing form. We then focus on the case of mono- and bi-dipoles and build the theory of dielectric media in $\\mathcal{S}_{2}$. We notably obtain the expression of the static dielectric constant of a uniform isotropic polar fluid living in $\\mathcal{S}_{2}$ in term of the polarization fluctuations of subdomains of $\\mathcal{S}_{2}$. We also derive the long range behavior of the equilibrium pair correlation function under the assumption that it is governed by macroscopic electrostatics. These theoretical developments find their application in Monte Carlo simulations of the $2D$ fluid of dipolar hard spheres. Some preliminary numerical experiments are discussed with a special emphasis on finite size effects, a careful study of the thermodynamic limit, and a check of the theoretical predictions for the asymptotic behavior of the pair correlation function.
Caillol, Jean-Michel
2015-04-21
We present two methods for solving the electrostatics of point charges and multipoles on the surface of a sphere, i.e., in the space S2, with applications to numerical simulations of two-dimensional (2D) polar fluids. In the first approach, point charges are associated with uniform neutralizing backgrounds to form neutral pseudo-charges, while in the second, one instead considers bi-charges, i.e., dumbells of antipodal point charges of opposite signs. We establish the expressions of the electric potentials of pseudo- and bi-charges as isotropic solutions of the Laplace-Beltrami equation in S2. A multipolar expansion of pseudo- and bi-charge potentials leads to the electric potentials of mono- and bi-multipoles, respectively. These potentials constitute non-isotropic solutions of the Laplace-Beltrami equation, the general solution of which in spherical coordinates is recast under a new appealing form. We then focus on the case of mono- and bi-dipoles and build the theory of dielectric media in S2. We notably obtain the expression of the static dielectric constant of a uniform isotropic polar fluid living in S2 in terms of the polarization fluctuations of subdomains of S2. We also derive the long range behavior of the equilibrium pair correlation function under the assumption that it is governed by macroscopic electrostatics. These theoretical developments find their application in Monte Carlo simulations of the 2D fluid of dipolar hard spheres. Some preliminary numerical experiments are discussed with a special emphasis on finite size effects, a careful study of the thermodynamic limit, and a check of the theoretical predictions for the asymptotic behavior of the pair correlation function. PMID:25903895
Two-dimensional simulations of possible mesoscale effects of nuclear war fires 2. Model results
Giorgi, F.; Visconti, G.
1989-01-20
The two-dimensional mesoscale meteorological model and the aerosol model described in the companion papaer by Giorgi (this issue) are used to investigate mesoscale effects induced by atmospheric injections of purely absorbing smoke from nuclear war fires. Simulations are carried out for different fire types (city center, suburban, and forest fires), aerosol loadings, particle properties, and atmospheric conditions. We analyze three effects which develop on spatial scales of 10--500 km and time scales of 1--2 days and can be important for assessments of environmental impacts of nuclear war: (1) smoke-induced formation of clouds and precipitation and efficiency of smoke removal; (2) smoke vertical transport; and (3) surface cooling induced by the smoke absorption. In convectively unstable and moist environments the low-level uplifting induced by the smoke heating can initiate convective precipitation. In the absence of substantial moisture sources from the fires, precipitation develops mostly at the edges of the smoke plumes and is associated with the inhomogeneities in the smoke distribution, since these allow low-level smoke heating. When the smoke is dispersed by the atmospheric winds and attains a more homogeneous distribution, most of the heating takes place at more stable higher altitudes, the smoke shielding stabilizes the lower troposhere and precipitation formation is hindered. Wet removal dominates dry removal processes and its efficiency depends on the properties and vertical distribution of the injected aerosol. In a wide variety of experiments, the fraction of the total injected smoke mass removed during 48 hour simulations varied from 3 to 20% for injections from suburban fires, from 10 to 20% for forest fires, and 1% for city center fires.
NASA Technical Reports Server (NTRS)
Fleming, E. L.; Jackman, C. H.; Stolarski, R. S.; Considine, D. B.
1998-01-01
We have developed a new empirically-based transport algorithm for use in our GSFC two-dimensional transport and chemistry model. The new algorithm contains planetary wave statistics, and parameterizations to account for the effects due to gravity waves and equatorial Kelvin waves. As such, this scheme utilizes significantly more information compared to our previous algorithm which was based only on zonal mean temperatures and heating rates. The new model transport captures much of the qualitative structure and seasonal variability observed in long lived tracers, such as: isolation of the tropics and the southern hemisphere winter polar vortex; the well mixed surf-zone region of the winter sub-tropics and mid-latitudes; the latitudinal and seasonal variations of total ozone; and the seasonal variations of mesospheric H2O. The model also indicates a double peaked structure in methane associated with the semiannual oscillation in the tropical upper stratosphere. This feature is similar in phase but is significantly weaker in amplitude compared to the observations. The model simulations of carbon-14 and strontium-90 are in good agreement with observations, both in simulating the peak in mixing ratio at 20-25 km, and the decrease with altitude in mixing ratio above 25 km. We also find mostly good agreement between modeled and observed age of air determined from SF6 outside of the northern hemisphere polar vortex. However, observations inside the vortex reveal significantly older air compared to the model. This is consistent with the model deficiencies in simulating CH4 in the northern hemisphere winter high latitudes and illustrates the limitations of the current climatological zonal mean model formulation. The propagation of seasonal signals in water vapor and CO2 in the lower stratosphere showed general agreement in phase, and the model qualitatively captured the observed amplitude decrease in CO2 from the tropics to midlatitudes. However, the simulated seasonal amplitudes were attenuated too rapidly with altitude in the tropics. Overall, the simulations with the new transport formulation are in substantially better agreement with observations compared with our previous model transport.
Two-dimensional fully dynamic SEM simulations of the 2011 Tohoku earthquake cycle
NASA Astrophysics Data System (ADS)
Shimizu, H.; Hirahara, K.
2014-12-01
Earthquake cycle simulations have been performed to successfully reproduce the historical earthquake occurrences. Most of them are quasi-dynamic, where inertial effects are approximated using the radiation damping proposed by Rice [1993]. Lapusta et al. [2000, 2009] developed a methodology capable of the detailed description of seismic and aseismic slip and gradual process of earthquake nucleation in the entire earthquake cycle. Their fully dynamic simulations have produced earthquake cycles considerably different from quasi-dynamic ones. Those simulations have, however, never been performed for interplate earthquakes at subduction zones. Many studies showed that on dipping faults such as interplate earthquakes at subduction zones, normal stress is changed during faulting due to the interaction with Earth's free surface. This change in normal stress not only affects the earthquake rupture process, but also causes the residual stress variation that might affect the long-term histories of earthquake cycle. Accounting for such effects, we perform two-dimensional simulations of the 2011 Tohoku earthquake cycle. Our model is in-plane and a laboratory derived rate and state friction acts on a dipping fault embedded on an elastic half-space that reaches the free surface. We extended the spectral element method (SEM) code [Ampuero, 2002] to incorporate a conforming mesh of triangles and quadrangles introduced in Komatitsch et al. [2001], which enables us to analyze the complex geometry with ease. The problem is solved by the methodology almost the same as Kaneko et al. [2011], which is the combined scheme switching in turn a fully dynamic SEM and a quasi-static SEM. The difference is the dip-slip thrust fault in our study in contrast to the vertical strike slip fault. With this method, we can analyze how the dynamic rupture with surface breakout interacting with the free surface affects the long-term earthquake cycle. We discuss the fully dynamic earthquake cycle results focusing on the differences from previous quasi-dynamic studies such as Kato and Yoshida [2011]. They proposed a shallow strong patch model to explain the observed huge coseismic slip at the shallow portion close to the Japan Trench and the long recurrence time of several hundreds.
NASA Astrophysics Data System (ADS)
Duan, Jennifer G.; Nanda, S. K.
2006-08-01
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.
Martin Ridal; David E. Siskind
2002-01-01
A chemical oxidation scheme where CH3D produces HDO has been incorporated into a two-dimensional model to simulate the transport and isotopic composition chemistry of stratospheric methane and water. The model results show that deuterium ratios in water and methane are good tracers of stratospheric dynamics. Comparisons with measurements by the ATMOS instrument suggest that the modeled methane isotopic ratio is
Economou, Demetre J.
Two-dimensional pulsed-plasma simulation of a chlorine discharge Badri Ramamurthi and Demetre J chlorine discharge sustained in an inductively coupled plasma ICP reactor with a planar coil. The self of a pulsed chlorine discharge to achieve significant reduction in charging damage notching compared
Formation of relativistic MHD jets: stationary state solutions & numerical simulations
Fendt, Christian
2008-01-01
We discuss numerical results of relativistic magnetohydrodynamic (MHD) jet formation models. We first review some examples of stationary state solutions treating the collimation and acceleration process of relativistic MHD jets. We provide an a posteriori check for the MHD condition in highly magnetized flows, namely the comparison of particle density to Goldreich-Julian density. Using the jet dynamical parameters calculated from the MHD model we show the rest-frame thermal X-ray spectra of the jet, from which we derive the overall spectrum taking into account a variation of Doppler boosting and Doppler shift of emission lines along the outflow. Finally, we present preliminary results of relativistic MHD simulations of jet formation demonstrating the acceleration of a low velocity (0.01c) disk wind to a collimated high velocity (0.8c).
Formation of relativistic MHD jets: stationary state solutions & numerical simulations
Christian Fendt; Elisabetta Memola
2008-11-20
We discuss numerical results of relativistic magnetohydrodynamic (MHD) jet formation models. We first review some examples of stationary state solutions treating the collimation and acceleration process of relativistic MHD jets. We provide an a posteriori check for the MHD condition in highly magnetized flows, namely the comparison of particle density to Goldreich-Julian density. Using the jet dynamical parameters calculated from the MHD model we show the rest-frame thermal X-ray spectra of the jet, from which we derive the overall spectrum taking into account a variation of Doppler boosting and Doppler shift of emission lines along the outflow. Finally, we present preliminary results of relativistic MHD simulations of jet formation demonstrating the acceleration of a low velocity (0.01c) disk wind to a collimated high velocity (0.8c).
Two-dimensional simulation of red blood cell motion near a wall under a lateral force
NASA Astrophysics Data System (ADS)
Hariprasad, Daniel S.; Secomb, Timothy W.
2014-11-01
The motion of a red blood cell suspended in a linear shear flow adjacent to a fixed boundary subject to an applied lateral force directed toward the boundary is simulated. A two-dimensional model is used that represents the viscous and elastic properties of normal red blood cells. Shear rates in the range of 100 to 600 s-1 are considered, and the suspending medium viscosity is 1 cP. In the absence of a lateral force, the cell executes a tumbling motion. With increasing lateral force, a transition from tumbling to tank-treading is predicted. The minimum force required to ensure tank-treading increases nonlinearly with the shear rate. Transient swinging motions occur when the force is slightly larger than the transition value. The applied lateral force is balanced by a hydrodynamic lift force resulting from the positive orientation of the long axis of the cell with respect to the wall. In the case of cyclic tumbling motions, the orientation angle takes positive values through most of the cycle, resulting in lift generation. These results are used to predict the motion of a cell close to the outer edge of the cell-rich core region that is generated when blood flows in a narrow tube. In this case, the lateral force is generated by shear-induced dispersion, resulting from cell-cell interactions in a region with a concentration gradient. This force is estimated using previous data on shear-induced dispersion. The cell is predicted to execute tank-treading motions at normal physiological hematocrit levels, with the possibility of tumbling at lower hematocrit levels.
Po, Hoi Chun; Zhou, Qi
2015-01-01
Bosons have a natural instinct to condense at zero temperature. It is a long-standing challenge to create a high-dimensional quantum liquid that does not exhibit long-range order at the ground state, as either extreme experimental parameters or sophisticated designs of microscopic Hamiltonians are required for suppressing the condensation. Here we show that synthetic gauge fields for ultracold atoms, using either the Raman scheme or shaken lattices, provide physicists a simple and practical scheme to produce a two-dimensional algebraic quantum liquid at the ground state. This quantum liquid arises at a critical Lifshitz point, where a two-dimensional quartic dispersion emerges in the momentum space, and many fundamental properties of two-dimensional bosons are changed in its proximity. Such an ideal simulator of the quantum Lifshitz model allows experimentalists to directly visualize and explore the deconfinement transition of topological excitations, an intriguing phenomenon that is difficult to access in other systems. PMID:26268154
Po, Hoi Chun; Zhou, Qi
2015-01-01
Bosons have a natural instinct to condense at zero temperature. It is a long-standing challenge to create a high-dimensional quantum liquid that does not exhibit long-range order at the ground state, as either extreme experimental parameters or sophisticated designs of microscopic Hamiltonians are required for suppressing the condensation. Here we show that synthetic gauge fields for ultracold atoms, using either the Raman scheme or shaken lattices, provide physicists a simple and practical scheme to produce a two-dimensional algebraic quantum liquid at the ground state. This quantum liquid arises at a critical Lifshitz point, where a two-dimensional quartic dispersion emerges in the momentum space, and many fundamental properties of two-dimensional bosons are changed in its proximity. Such an ideal simulator of the quantum Lifshitz model allows experimentalists to directly visualize and explore the deconfinement transition of topological excitations, an intriguing phenomenon that is difficult to access in other systems. PMID:26268154
NASA Astrophysics Data System (ADS)
Po, Hoi Chun; Zhou, Qi
2015-08-01
Bosons have a natural instinct to condense at zero temperature. It is a long-standing challenge to create a high-dimensional quantum liquid that does not exhibit long-range order at the ground state, as either extreme experimental parameters or sophisticated designs of microscopic Hamiltonians are required for suppressing the condensation. Here we show that synthetic gauge fields for ultracold atoms, using either the Raman scheme or shaken lattices, provide physicists a simple and practical scheme to produce a two-dimensional algebraic quantum liquid at the ground state. This quantum liquid arises at a critical Lifshitz point, where a two-dimensional quartic dispersion emerges in the momentum space, and many fundamental properties of two-dimensional bosons are changed in its proximity. Such an ideal simulator of the quantum Lifshitz model allows experimentalists to directly visualize and explore the deconfinement transition of topological excitations, an intriguing phenomenon that is difficult to access in other systems.
Numerical simulations for MHD coronal seismology
NASA Astrophysics Data System (ADS)
Pascoe, David James
2014-07-01
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.
Mukamel, Shaul
for the study of dynamics in complex systems. As the optical equivalent of two- dimensional 2D nuclear magnetic statistics for transition frequency fluc- tuations of spatially localized vibrational or electronic modes.g., electric fields, onto the tran- sition frequencies.16,3234 This method was extended to in- clude bath
Two-Dimensional Simulation of Left-Handed Metamaterial Flat Lens Using Remcon XFDTD
NASA Technical Reports Server (NTRS)
Wilson, Jeffrey D.; Reinert, Jason M.
2006-01-01
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.
Spatial correlation of high-energy grain boundaries in two-dimensional simulated polycrystals
Clinton DeW. Van Siclen
2007-02-01
A polycrystal undergoes microstructural changes to reach a lower energy state. In particular, the system evolves so as to reduce the total grain boundary energy. A simple two-dimensional model of a polycrystal comprised of randomly oriented crystalline grains suggests that energy minimization reduces or eliminates any spatial correlation among high-energy grain boundaries. Thus grain boundary engineering not only reduces the density of high-energy boundaries, but it prevents their organization into a coarse, albeit discontinuous, network.
Nonlinear two-dimensional modeling of a McPherson suspension for kinematics and dynamics simulation
Jorge Hurel; Anthony Mandow; Alfonso Garcia-Cerezo
2012-01-01
This paper proposes a systematic and comprehensive development of a nonlinear two-dimensional mathematical quarter-car model of the McPherson suspension. The model considers not only vertical motion of the sprung mass (chassis) but also rotation and translation for the unsprung mass (wheel assembly). Furthermore, this model includes the wheel mass and its inertia moment about the longitudinal axis. This work improves
Three Dimensional Simulations of Compressible Hall MHD Plasmas
Shaikh, Dastgeer; Shukla, P. K.
2008-10-15
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.
Heat transfer coefficients in two-dimensional Yukawa systems (numerical simulations)
Khrustalyov, Yu. V. Vaulina, O. S.
2013-05-15
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.
MHD simulation of the planetary magnetospheres by using various scalar type supercomputer systems
NASA Astrophysics Data System (ADS)
Fukazawa, Keiichiro; Umeda, Takayuki; Ogino, Tatsuki; Walker, Raymond; Yumoto, Kiyohumi
Currently more than 85% of the "top 500" supercomputer systems in the world have adopted the "64-bit x86" processor architecture. However it is often mentioned that the performance of electromagnetic fluid codes is not as good on the scalar type computers (often less than 10% of peak performance efficiency) as compared to vector type computers. For instance our planetary magnetospheric magnetohydrodynamic code reached over 50% of performance efficiency on vector supercomputers. In this study we have carried out performance tuning and other measurements on massively parallel supercomputer systems with various types of scalar processors. We use the T2K open supercomputer at University of Tokyo (AMD Opteron processors), SR16000 at Kyushu University (IBM POWER6 processors), and FX1 (Fujitsu SPARC64VI processors) and HX600 (AMD Opteron processors) at Nagoya University. In this presentation, as a tuning technique, the MHD simulation model was run by using three decomposition methods for parallelization and one cache tuning method to find out which method is best for the MHD code. As a result we have obtained over 10% of peak performance efficiency using the T2K open supercomputer and we obtained much better performances with SR16000 and FX1, HX600 (over 20%). In particular we found that the two-dimensional decom-position of the MHD model is suitable for the T2K system and while for the SR16000 and FX1 cache tuned three-dimensional decomposition achieved the best performance. In this study we will show and compare the results of performance measurements and tuning techniques for MHD simulation codes of the planetary magnetospheres with scalar type supercomputers in detail. Finally we will present the latest simulation results of global planetary magnetosphere with high spatial resolution (three times the resolution of our current Saturn's model) using the result of performance tuning.
Advances in Simulation of Wave Interactions with Extended MHD Phenomena
Batchelor, Donald B; D'Azevedo, Eduardo; Bateman, Glenn; Bernholdt, David E; Bonoli, P.; Bramley, Randall B; Breslau, Joshua; Elwasif, Wael R; Foley, S.; Jaeger, Erwin Frederick; Jardin, S. C.; Klasky, Scott A; Kruger, Scott E; Ku, Long-Poe; McCune, Douglas; Ramos, J.; Schissel, David P; Schnack, Dalton D
2009-01-01
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.
Advances in Simulation of Wave Interaction with Extended MHD Phenomena
Batchelor, Donald B; Abla, Gheni; D'Azevedo, Ed F; Bateman, Glenn; Bernholdt, David E; Berry, Lee A; Bonoli, P.; Bramley, R; Breslau, Joshua; Chance, M.; Chen, J.; Choi, M.; Elwasif, Wael R; Foley, S.; Fu, GuoYong; Harvey, R. W.; Jaeger, Erwin Frederick; Jardin, S. C.; Jenkins, T; Keyes, David E; Klasky, Scott A; Kruger, Scott; Ku, Long-Poe; Lynch, Vickie E; McCune, Douglas; Ramos, J.; Schissel, D.; Schnack,; Wright, J.
2009-01-01
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.
NASA Astrophysics Data System (ADS)
Herring, J. R.; McWilliams, J. C.
1985-04-01
Several studies suggest that high-Reynolds-number two-dimensional turbulence may evolve in such a manner that there is little enstrophy flux to small scales. In these cases, the flow departs substantially from Gaussianity. It is pointed out that this condition is inhospitable to moment closures. The present study has the objective to gain inslight into the magnitude of this problem. A comparison is conducted of direct numerical simulations (DNS) with equivalent closure (TFM) for a variety of forcing functions, including spin-down (i.e. no forcing). The results obtained for forced cases are that the closure may be quantitatively accurate only if the disruptive effects of random stirring are sufficiently strong to prevent the formation of coherent structures natural to two-dimensional turbulence.
Two-dimensional self-consistent microwave argon plasma simulations with experimental verification
NASA Astrophysics Data System (ADS)
Li, Y.; Gordon, M. H.; Roe, L. A.; Hassouni, K.; Grotjohn, T.
2003-07-01
Optical emission spectroscopy (OES), absorption measurements, and thermal energy rate analysis were used in tandem with numerical models to characterize microwave argon plasmas. A WAVEMAT (model MPDR-3135) microwave diamond deposition system was used to generate argon plasmas at 5 Torr. Three excited state number densities (4p, 5p, and 5d) were obtained from the OES measurements, and a fourth excited state number density (4s) was obtained from the absorption measurements. Further, power absorbed in the substrate was monitored. A self-consistent two-dimensional argon model coupled with an electromagnetic field model and a 25-level two-dimensional (2D)-collisional-radiative model (CRM) was developed and validated with the experimental measurements. The 2D model provides the gas and electron temperature distributions, and the electron, ion, and 4s state number densities, which are then iteratively fed into the electromagnetic and CRM models. Both the numerically predicted thermal energy rates and excited state densities agreed, within the experimental and numerical uncertainties, with the experimental results.
Spectral dynamics of computer simulated two-dimensional fewtube fluidized beds
Chang, S.L.; Lyczkowski, R.W.; Berry, G.F.
1989-01-01
Fluidized bed combustion technology attracts intense commercial interest for its capability of burning high-sulfur coal in a more economic and environmentally acceptable manner, despite the unsolved erosion problem. Detailed knowledge of the complex phenomena of solids circulation and bubble motion in the bed could enhance the understanding of the problem and find solutions. Argonne National Laboratories (ANL) has been developing a methodology to investigate local erosion phenomenon in bubbling fluidized bed combustor (FBC) systems: (1) use of state-of-the-art two-phase two-dimensional hydrodynamic computer model (FLUFIX) to compute temporal and spatial distributions of the flow properties in an FBC and (2) use spectral analysis and several separated erosion models to evaluate flow dynamics and local erosion patterns and rates. In this paper, the spectral analysis uses the computational hydrodynamic results of a two-dimensional generic fewtube FBC system to correlate flow properties, porosity, pressure and velocities, as well as to determine oscillation modes and bubble propagation speeds. Several findings from this analysis are: flow properties have major oscillation modes of frequencies ranging from 0.7 to 4 Hz; porosity and pressure oscillations propagate from the bottom of the bed up with propagation speeds ranging from 0.4 to 1 m/s; pressure is well correlated with the lagging porosity at a location; phase diagrams show the randomness of oscillations but the attractor leading to chaotic motion is not found. 14 refs., 11 figs.
Karavitis, G.A.
1984-01-01
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)
The role of condensation and heat conduction in the formation of prominences - An MHD simulation
NASA Technical Reports Server (NTRS)
Wu, S. T.; Bao, J. J.; An, C. H.; Tandberg-Hanssen, E.
1990-01-01
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.
Critical Behavior in Global MHD Simulations of Substorms
NASA Astrophysics Data System (ADS)
Merkine, V. G.; Papadopoulos, K.; Sitnov, M.; Shao, X.; Sharma, A. S.; Goodrich, C.
2002-05-01
Global MHD simulations of substorms have shown features of global transitions and magnetic reconnection in the magnetotail is the underlying process for these sudden changes. The LFM global MHD code is used to study the nature of this phenomenon by making use of the extensive data available in the simulations. Reconnection is a non-MHD process and to study the dynamical behavior in the magnetosphere using the MHD code, we construct a parameter marking the non-MHD regions or sites of reconnection. The parallel electric field or parallel resistivity is a parameter suitable for monitoring the development toward magnetic reconnection and global transition in the simulations. The goal is to characterize the spatio-temporal developemnt of the chosen parameter and study its underlying features. The large scale dynamics during substorms reflect self-organization in the magnetosphere and the accompanying multiscale properties are indicative of critical behavior. We study the spatio-temporal structure of the parallel resistivity in a global MHD simulation of an idealized case driven by the solar wind with a sudden change of the magnetic field direction from northward to southward. It turns out that the color map of the parallel resistivity in the equatorial plane has the distinct patchy structure which can be considered as a first sign of multiscale behavior. It is also found that the spatio-temporal structure of the parallel resistivity or diffusion coefficient is very similar to that observed in simplified one-dimensional field reversal models. Both spatial and temporal spectra reveal power law dependence characteristic of criticality.
NASA Astrophysics Data System (ADS)
Prybytak, Dzmitry
2014-12-01
The paper presents the application of an indirect variant of the boundary element method (BEM) to solve the two-dimensional steady flow of a Stokes liquid. In the BEM, a system of differential equations is transformed into integral equations. This makes it possible to limit discretization to the border of the solution. Numerical discretization of the computational domain was performed with linear boundary elements, for which a constant value of unknown functions was assumed. The verification was carried out for the case of flow in a square cavity with one moving wall. The results obtained show that the use of approximations by simple linear functions is relatively easy for different shapes of the area, but the result may be affected by significant errors.
Hybrid Kinetic-MHD Simulations in General Geometry
NASA Astrophysics Data System (ADS)
Kim, Charlson C.; Parker, Scott E.; Sovinec, Carl R.
2003-10-01
We present a hybrid kinetic MHD model that is applicable to fusion relevent simulations. Previous research(Hsu ST, Sigmar DJ, PFB 4) 1492-1505, 1992 and simulation results suggest that the hot particle momentum contribution is not negligable and prompts reexamination of the hybrid kinetic MHD model equations(Cheng CZ, Johnson JR,JGR-S A-104) 413-427, 1999 typically used. The model equations have been applied to the NIMROD simulation(Sovinec CR, Gianakon TA, Held ED, et al., PoP 10) 1727-1732, 2003, a finite element, three dimensional, massively parallel, extended MHD simulation, capable of handling general geometries. A ? f PIC module has been incorporated into the NIMROD simulation to model the effects of a minority hot particle species on MHD instabilities. The details of the PIC implementation will be presented. As an example of the hybrid physics, a benchmark case of kinetic effects on the internal kink mode and the excitation of the fishbone mode will be presented. We also present performance results on various architectures.
NASA Technical Reports Server (NTRS)
Tsang, L.; Lou, S. H.; Chan, C. H.
1991-01-01
The extended boundary condition method is applied to Monte Carlo simulations of two-dimensional random rough surface scattering. The numerical results are compared with one-dimensional random rough surfaces obtained from the finite-element method. It is found that the mean scattered intensity from two-dimensional rough surfaces differs from that of one dimension for rough surfaces with large slopes.
Economou, Demetre J.
Simulation of a two-dimensional sheath over a flat insulatorconductor interface on a radio-frequency the two-dimensional 2D sheath over a flat insulator/conductor interface on a radio-frequency rf biased is exposed to plasma. The backing electrode is biased with a radio- frequency rf voltage source
MHD Pedestal Formation in Time-Dependent Simulations
NASA Astrophysics Data System (ADS)
Guazzotto, Luca; Betti, Riccardo; Jardin, Steve
2014-10-01
Finite toroidal and poloidal flows are routinely observed in the edge plasma region of tokamak experiments. MHD theory predicts that when the poloidal velocity is transonic with respect to the poloidal sound speed (csp ?csBp / B , where Bp is the poloidal field) a transient will develop. After the end of the transient, a steady-state MHD pedestal in plasma density and pressure is left, with the height of the pedestal depending on the poloidal location. The formation of the MHD pedestal was demonstrated with time-dependent simulations with the resistive-MHD code SIM2D. In the present work, we explore the effect of additional physics on the formation of the pedestal. The advanced model implemented in M3DC1 is used to validate and extend SIM2D calculations. Since M3DC1, contrary to SIM2D, was not developed to study transonic transients, this also gives a strong independent verification of the correctness of the MHD pedestal model. Special focus is given to poloidal viscosity, which is already implemented in M3DC1 and is being implemented in SIM2D. Analytic calculations complement and support numerical results. Work supported by US Department of Energy Contract No. DE-FG02-93ER54215.
Bezier surfaces and finite elements for MHD simulations
Czarny, Olivier
2008-08-10
A finite element method based on bicubic Bezier surfaces is applied to the simulation of MHD instabilities relevant to magnetically confined fusion. The major advantage of the new technique is that it allows a natural way to implement mesh refinement strategy, which is not supported by a pure Hermite formulation. Compared to a Lagrangian formulation the number of degrees of freedom is significantly reduced. The use of an isoparametric representation of the space coordinates allows an accurate alignment of the finite elements to the magnetic field line geometry in a tokamak plasma. The Bezier finite elements have been implemented in a MHD code using the non-linear reduced MHD model in toroidal geometry. As an illustration, results for Soloviev equilibrium and time-dependent current-hole computations are presented and discussed.
Hui SHEN; Yi-Jun HE
2006-01-01
Based on the research of Lynett and Liu, a new horizontal fully two-dimensional internal wave propagation model with rotation effect was deduced, which can be used to simulate the characteristics of internal waves in a horizontal fully two-dimensional plane. By combining the imaging mechanism of Synthetic Aperture Radar(SAR), a simulation procedure was fatherly acquired, which can simulate the propagation characteristics
Two-Dimensional Numerical Simulations of a Solid State Maxwell Demon
NASA Astrophysics Data System (ADS)
Putnam, Andrew R.
2002-11-01
Numerical simulations of the solid-state Maxwell demon proposed by Sheehan, Putnam, and Wright (2002) are presented. These verify the results of the original 1-D analytical model. A detailed description of the 2-D device simulator is given.
Two dimensional self-consistent fluid simulation of rf inductive sources
DiPeso, G.; Vahedi, V.; Hewett, D.W.; Rognlien, T.D.
1993-11-17
The two-dimensional (R - Z) electromagnetic code FMRZ has been written to model inductive sources self-consistently in time. The code models an argon plasma with momentum-transfer, excitation and ionization as electron-neutral reactions and scattering and charge-exchange for the ion-neutral reactions. The electrons and ions are treated as Maxwellian fluid species and a reduced set of Maxwell`s equations is used to advance the electromagnetic fields. The set of equations used in FMRZ is not subject to typical numerical constraints present in many time dynamic codes allowing one to choose appropriate the and space scales to resolve only the frequencies and scale lengths of interest. The model retains nonlinear driving terms which give rise to a pondermotive force that distorts the density profile. Density and power profiles will be used to illustrate the physical effects of various terms in the equations. Trends in average density and temperature compare well with an analytic model.
Hybrid Vlasov-Maxwell simulations of two-dimensional turbulence in plasmas
Valentini, F.; Servidio, S.; Veltri, P.; Perrone, D.; Califano, F.; Matthaeus, W. H.
2014-08-15
Turbulence in plasmas is a very challenging problem since it involves wave-particle interactions, which are responsible for phenomena such as plasma dissipation, acceleration mechanisms, heating, temperature anisotropy, and so on. In this work, a hybrid Vlasov-Maxwell numerical code is employed to study local kinetic processes in a two-dimensional turbulent regime. In the present model, ions are treated as a kinetic species, while electrons are considered as a fluid. As recently reported in [S. Servidio, Phys. Rev. Lett. 108, 045001 (2012)], nearby regions of strong magnetic activity, kinetic effects manifest through a deformation of the ion velocity distribution function that consequently departs from the equilibrium Maxwellian configuration. Here, the structure of turbulence is investigated in detail in phase space, by evaluating the high-order moments of the particle velocity distribution, i.e., temperature, skewness, and kurtosis. This analysis provides quantitative information about the non-Maxwellian character of the system dynamics. This departure from local thermodynamic equilibrium triggers several processes commonly observed in many astrophysical and laboratory plasmas.
Two-dimensional particle-in-cell simulations of transport in a magnetized electronegative plasma
Kawamura, E.; Lichtenberg, A. J.; Lieberman, M. A. [Department of Electrical Engineering, University of California, Berkeley, California 94720-1770 (United States)
2010-11-15
Particle transport in a uniformly magnetized electronegative plasma is studied in two-dimensional (2D) geometry with insulating (dielectric) boundaries. A 2D particle-in-cell (PIC) code is employed, with the results compared to analytic one-dimensional models that approximate the end losses as volume losses. A modified oxygen reaction set is used to scale to the low densities used in PIC codes and also to approximately model other gases. The principal study is the limiting of the transverse electron flow due to strong electron magnetization. The plasma in the PIC calculation is maintained by axial currents that vary across the transverse dimension. For a cosine current profile nearly uniform electron temperature is obtained, which at the B-fields studied (600-1200 G) give a small but significant fraction (0.25 or less) of electron to negative ion transverse loss. For a more transverse-confined current, and approximating the higher mass and attachment reaction rate of iodine, the fraction of electron to negative ion transverse loss can be made very small. The models which have been constructed reasonably approximate the PIC results and indicate that the cross-field transport is nearly classical.
NASA Astrophysics Data System (ADS)
Strandburg, Katherine J.
1988-01-01
For a decade now the subject of the nature of the two-dimensional melting transition has remained controversial. An elegant theory based on the unbinding of pairs of crystal defects suggested that two-dimensional solids might melt by a transition sequence involving two continuous transitions separated by a novel, nearest-neighbor-bond-orientationally ordered fluid-the hexatic phase. Competing theories predict that the transition is of the usual first-order type observed in three-dimensional systems. This paper is a critical review of the current status of research into the problem of two-dimensional melting, with an emphasis on computer simulations. An attempt is made to point out unresolved issues pertaining to this fascinating and still open question.
Kim, Kyungmok; Géringer, Jean; 10.1177/0954411911422843
2012-01-01
This paper describes a two-dimensional (2D) finite element simulation for fracture and fatigue behaviours of pure alumina microstructures such as those found at hip prostheses. Finite element models are developed using actual Al2O3 microstructures and a bilinear cohesive zone law. Simulation conditions are similar to those found at a slip zone in a dry contact between a femoral head and an acetabular cup of hip prosthesis. Contact stresses are imposed to generate cracks in the models. Magnitudes of imposed stresses are higher than those found at the microscopic scale. Effects of microstructures and contact stresses are investigated in terms of crack formation. In addition, fatigue behaviour of the microstructure is determined by performing simulations under cyclic loading conditions. It is shown that crack density observed in a microstructure increases with increasing magnitude of applied contact stress. Moreover, crack density increases linearly with respect to the number of fatigue cycles within a given con...
Labuhn, Henning; Ravets, Sylvain; de Léséleuc, Sylvain; Macrì, Tommaso; Lahaye, Thierry; Browaeys, Antoine
2015-01-01
Quantum simulation of spin Hamiltonians is currently a very active field of research, using different implementations such as trapped ions, superconducting qubits, or ultracold atoms in optical lattices. All of these approaches have their own assets and limitations. Here, we report on a novel platform for quantum simulation of spin systems, using individual atoms trapped in highly-tunable two-dimensional arrays of optical microtraps, that interact via strong, anisotropic interactions when excited to Rydberg $D$-states. We illustrate the versatility of our system by studying the dynamics of an Ising-like spin-$1/2$ system in a transverse field with up to thirty spins, for a variety of geometries in one and two dimensions, and for a wide range of interaction strengths. Our data agree well with numerical simulations of the spin-$1/2$ model except at long times, where we observe deviations that we attribute to the multilevel structure of Rydberg $D$-states.
An automated reliable method for two-dimensional Reynolds-Averaged Navier-Stokes simulations
Modisette, James M
2011-01-01
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 ...
One- and two-dimensional hybrid simulations of whistler mode waves in a dipole field
NASA Astrophysics Data System (ADS)
Wu, S.; Denton, R. E.; Liu, K.; Hudson, M. K.
2015-03-01
We simulate whistler mode waves using a hybrid code. There are four species in the simulations, hot electrons initialized with a bi-Maxwellian distribution with temperature in the direction perpendicular to background magnetic field greater than that in the parallel direction, warm isotropic electrons, cold inertialess fluid electrons, and protons as an immobile background. The density of the hot population is a small fraction of the total plasma density. Comparison between the dispersion relation of our model and other dispersion relations shows that our model is more accurate for lower frequency whistlers than for higher frequency whistlers. Simulations in 2-D Cartesian coordinates agree very well with those using a full dynamics code. In the 1-D simulations along the dipole magnetic field, the predicted frequency and wave number are observed. Rising tones are observed in the one-fourteenth scale simulations that have larger than realistic magnetic field spatial inhomogeneity. However, in the full-scale 1-D simulation in a dipole field, the waves are more broadband and do not exhibit rising tones. In the 2-D simulations in a meridional plane, the waves are generated with propagation approximately parallel to the background magnetic field. However, the wavefronts become oblique as they propagate to higher latitudes. Simulations with different plasma density profiles across L shell are performed to study the effect of the background density on whistler propagation.
Monte Carlo simulations of a model two-dimensional, two-patch colloidal particles
NASA Astrophysics Data System (ADS)
R?ysko, W.; Soko?owski, S.; Staszewski, T.
2015-08-01
We carried out Monte Carlo simulations of the two-patch colloids in two-dimensions. Similar model investigated theoretically in three-dimensions exhibited a re-entrant phase transition. Our simulations indicate that no re-entrant transition exists and the phase diagram for the system is of a swan-neck type and corresponds solely to the fluid-solid transition.
K. H. COATS; J. R. DEMPSEY; J. H. HENDERSON
1971-01-01
The use of the Vertical Equilibrium (VE) concept in simulating heterogeneous reservoirs is discussed. Where VE criteria are met, this technique allows 2-dimensional simulation of 3-dimensional problems with equivalent accuracy, and with attendant substantial savings in data preparation and machine time. The study presents the VE concept itself and a new dimensionless group as a possible criterion for the validity
Falvo, Cyril; Daniault, Louis; Vieille, Thibault; Kemlin, Vincent; Lambry, Jean-Christophe; Meier, Christoph; Vos, Marten H; Bonvalet, Adeline; Joffre, Manuel
2015-06-18
This Letter presents a comparison between experimental and simulated 2D mid-infrared spectra of carboxy-hemoglobin in the spectral region of the carbon monoxide stretching mode. The simulations rely on a fluctuating potential energy surface that includes both the effect of heme and the protein surroundings computed from molecular dynamics simulations. A very good agreement between theory and experiment is obtained with no adjustable parameters. The simulations show that the effect of the distal histidine through the hydrogen bond is strong and is directly responsible for the slow decay of the frequency-frequency correlation function on a 10 ps time scale. This study confirms that fluctuations in carboxy-hemoglobin are more inhomogeneous than those in the more frequently studied carboxy-myoglobin. The comparison between simulations and experiments brings valuable information on the complex relation between protein structure and spectral diffusion. PMID:26266594
Parallel kinetic Monte Carlo simulations of two-dimensional island coarsening.
Shi, Feng; Shim, Yunsic; Amar, Jacques G
2007-09-01
The results of parallel kinetic Monte Carlo (KMC) simulations of island coarsening based on a bond-counting model are presented. Our simulations were carried out both as a test of and as an application of the recently developed semirigorous synchronous sublattice (SL) algorithm. By carrying out simulations over long times and for large system sizes the asymptotic coarsening behavior and scaled island-size distribution (ISD) were determined. Our results indicate that while cluster diffusion and coalescence play a role at early and intermediate times, at late times the coarsening proceeds via Ostwald ripening. In addition, we find that the asymptotic scaled ISD is significantly narrower and more sharply peaked than the mean-field theory prediction. The dependence of the scaled ISD on coverage is also studied. Our results demonstrate that parallel KMC simulations can be used to effectively extend the time scale over which realistic coarsening simulations can be carried out. In particular, for simulations of the late stages of coarsening with system size L=1600 and eight processors, a parallel efficiency larger than 80% was obtained. These results suggest that the SL algorithm is likely to be useful in the future in parallel KMC simulations of more complicated models of coarsening. PMID:17930256
Parallel kinetic Monte Carlo simulations of two-dimensional island coarsening
NASA Astrophysics Data System (ADS)
Shi, Feng; Shim, Yunsic; Amar, Jacques G.
2007-09-01
The results of parallel kinetic Monte Carlo (KMC) simulations of island coarsening based on a bond-counting model are presented. Our simulations were carried out both as a test of and as an application of the recently developed semirigorous synchronous sublattice (SL) algorithm. By carrying out simulations over long times and for large system sizes the asymptotic coarsening behavior and scaled island-size distribution (ISD) were determined. Our results indicate that while cluster diffusion and coalescence play a role at early and intermediate times, at late times the coarsening proceeds via Ostwald ripening. In addition, we find that the asymptotic scaled ISD is significantly narrower and more sharply peaked than the mean-field theory prediction. The dependence of the scaled ISD on coverage is also studied. Our results demonstrate that parallel KMC simulations can be used to effectively extend the time scale over which realistic coarsening simulations can be carried out. In particular, for simulations of the late stages of coarsening with system size L=1600 and eight processors, a parallel efficiency larger than 80% was obtained. These results suggest that the SL algorithm is likely to be useful in the future in parallel KMC simulations of more complicated models of coarsening.
Monte Carlo-molecular dynamics simulations for two-dimensional magnets
Kawabata, C.; takeuchi, M.; Bishop, A.R.
1985-01-01
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.
Integrated Two-Dimensional DRACO Simulations of Cryogenic DT Target Performance on OMEGA
NASA Astrophysics Data System (ADS)
Hu, S. X.; Radha, P. B.; Goncharov, V. N.; Betti, R.; Epstein, R.; Marshall, F. J.; McCrory, R. L.; Meyerhofer, D. D.; Sangster, T. C.; Skupsky, S.
2013-10-01
Integrated simulations of cryogenic deuterium-tritium (DT) target implosions on OMEGA have been performed using the radiation-hydrodynamic code DRACO. Taking into account the known nonuniformities of target and laser irradiation, 2-D simulations examine the target performance of a variety of ignition-relevant implosions. The effects of cross-beam energy transfer and nonlocal heat transport are mimicked by a time-dependent flux limiter. DRACO simulations show good agreement with experiments in ?R , neutron yield, Ti, neutron rate, and x-ray images for the mid-adiabat (? ~ 4 ) implosions. For low-adiabat (? ~ 2) and high in-flight aspect ratio (IFAR > 24) implosions, the integrated simulations with the known nonuniformity sources cannot fully explain the reduction in target performance. Examinations of other possible nonuniformity sources and the thermal conductivity model will be presented. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.
Ohira, Yutaka; Takahara, Fumio; Reville, Brian; Kirk, John G.
2009-06-10
In supernova remnants, the nonlinear amplification of magnetic fields upstream of collisionless shocks is essential for the acceleration of cosmic rays to the energy of the 'knee' at 10{sup 15.5} eV. A nonresonant instability driven by the cosmic ray current is thought to be responsible for this effect. We perform two-dimensional, particle-in-cell simulations of this instability. We observe an initial growth of circularly polarized nonpropagating magnetic waves as predicted in linear theory. It is demonstrated that in some cases the magnetic energy density in the growing waves can grow to at least 10 times its initial value. We find no evidence of competing modes, nor of significant modification by thermal effects. At late times, we observe saturation of the instability in the simulation, but the mechanism responsible is an artifact of the periodic boundary conditions and has no counterpart in the supernova-shock scenario.
Cohen, B.I.; Divol, L.; Langdon, A.B.; Williams, E.A. [University of California, Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94551 (United States)
2006-02-15
Two-dimensional simulations with the BZOHAR [B. I. Cohen, B. F. Lasinski, A. B. Langdon, and E. A. Williams, Phys. Plasmas 4, 956 (1997)] hybrid code (kinetic particle ions and Boltzmann fluid electrons) have been used to investigate the saturation of stimulated Brillouin backscatter (SBBS) instability, including the effects of ion-ion collisions and inhomogeneity. Two types of Langevin-operator, ion-ion collision models were implemented in the simulations. In both models the collisions are functions of the local ion temperature and density, but the collisions have no velocity dependence in the first model. In the second model the collisions are also functions of the energy of the ion that is being scattered so as to represent a more physical Fokker-Planck collision operator. Collisions decorrelate the ions from the acoustic waves in SBS, which disrupts ion trapping in the acoustic wave. Nevertheless, ion trapping leading to a hot ion tail and two-dimensional physics that allows the SBS ion waves to nonlinearly scatter, remain important saturation mechanisms for SBBS in a high-gain limit over a range of ion collisionality. Ion-ion collisions tend to increase ion-wave dissipation, which decreases the gain exponent for stimulated Brillouin backscattering; and the peak Brillouin backscatter reflectivities decrease with increasing collisionality in the simulations for velocity-independent collisions and very weakly decrease for the range of Fokker-Planck collisionality considered. SBS backscatter in the presence of a spatially nonuniform plasma flow is also investigated. Simulations show that, depending on the sign of the spatial gradient of the flow relative to the backscatter, ion trapping effects that produce a nonlinear frequency shift can enhance (autoresonance) reflectivities relative to anti-autoresonant configurations, in agreement with theoretical arguments.
Cohen, B I; Divol, L; Langdon, A B; Williams, E A
2005-10-17
Two-dimensional simulations with the BZOHAR [B.I. Cohen, B.F. Lasinski, A.B. Langdon, and E.A. Williams, Phys. Plasmas 4, 956 (1997)] hybrid code (kinetic particle ions and Boltzmann fluid electrons) have been used to investigate the saturation of stimulated Brillouin backscatter (SBBS) instability including the effects of ion-ion collisions and inhomogeneity. Ion-ion collisions tend to increase ion-wave dissipation, which decreases the gain exponent for stimulated Brillouin backscattering; and the peak Brillouin backscatter reflectivities tend to decrease with increasing collisionality in the simulations. Two types of Langevin-operator, ion-ion collision models were implemented in the simulations. In both models used the collisions are functions of the local ion temperature and density, but the collisions have no velocity dependence in the first model. In the second model, the collisions are also functions of the energy of the ion that is being scattered so as to represent a Fokker-Planck collision operator. Collisions decorrelate the ions from the acoustic waves in SBS, which disrupts ion trapping in the acoustic wave. Nevertheless, ion trapping leading to a hot ion tail and two-dimensional physics that allows the SBS ion waves to nonlinearly scatter remain robust saturation mechanisms for SBBS in a high-gain limit over a range of ion collisionality. SBS backscatter in the presence of a spatially nonuniform plasma flow is also investigated. Simulations show that depending on the sign of the spatial gradient of the flow relative to the backscatter, ion trapping effects that produce a nonlinear frequency shift can enhance (auto-resonance) or decrease (anti-auto-resonance) reflectivities in agreement with theoretical arguments.
NASA Astrophysics Data System (ADS)
Cai, Libing; Wang, Jianguo; Zhu, Xiangqin; Wang, Yue; Zhang, Dianhui
2015-01-01
Based on the secondary electron emission avalanche (SEEA) model, the SEEA discharge on the vacuum insulator surface is simulated by using a 2D PIC-MCC code developed by ourselves. The evolutions of the number of discharge electrons, insulator surface charge, current, and 2D particle distribution are obtained. The effects of the strength of the applied electric field, secondary electron yield coefficient, rise time of the pulse, length of the insulator on the discharge are investigated. The results show that the number of the SEEA electrons presents a quadratic dependence upon the applied field strength. The SEEA current, which is on the order of Ampere, is directly proportional to the field strength and secondary electron yield coefficient. Finally, the electron-stimulated outgassing is included in the simulation code, and a three-phase discharge curve is presented by the simulation, which agrees with the experimental data.
NASA Astrophysics Data System (ADS)
Rollin, Bertrand; Denissen, Nicholas A.; Reisner, Jon M.; Andrews, Malcolm J.
2012-11-01
The tilted rig experiment is a derivative of the rocket rig experiment designed to investigate turbulent mixing induced by the Rayleigh-Taylor (RT) instability. A tank containing two fluids of different densities is accelerated downwards between two parallel guiding rods by rocket motors. The acceleration is such that the pressure and density gradients face opposite directions at the fluids interface, creating a Rayleigh-Taylor unstable configuration. The rig is tilted such that the tank is initially at an angle and the acceleration is not perpendicular to the fluids interface when the rockets fire. This results in a two dimensional Rayleigh-Taylor instability case where the fluids experience RT mixing and a bulk overturning motion. The tilted rig is therefore a valuable experiment to help calibrating two-dimensional mixing models. Large Eddy Simulations of the tilted rig experiments will be compared to available experimental results. A study of the behavior of turbulence variables relevant to turbulence modeling will be presented. LA-UR 12-23829. This work was performed for the U.S. Department of Energy by Los Alamos National Laboratory under Contract No.DEAC52- 06NA2-5396.
Lefkoff, L.J.; Gorelick, S.M.
1987-01-01
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)
Two-Dimensional Simulations of Plastic-Shell, Direct-Drive Implosions on OMEGA
Radha, P.B.; Goncharov, V.N.; Collins, T.J.B.; Delettrez, J.A.; Elbaz, Y.; Glebov, V.Yu.; 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.P.J.; Stoeckl, C.
2005-02-18
Multidimensional hydrodynamic properties of high-adiabat direct-drive plastic-shell implosions on the OMEGA laser system 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.
Amir Hayati Soloot; Jouya Jadidian; Edris Agheb; Hans Kristian Hoidalen
2010-01-01
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
Robust Numerical Simulation of Porosity Evolution in Chemical Vapor In ltration II: Two Dimensional
Jin, Shi
Robust Numerical Simulation of Porosity Evolution in Chemical Vapor In#12;ltration II: Two volume of the solid phase and diminishing porosity of the porous medium, due to the formation of a solid#11;. Decreas- ing porosity makes it possible to form inaccessible pores for gas transport
Simulation of Two Dimensional Electrophoresis and Tandem Mass Spectrometry for Teaching Proteomics
ERIC Educational Resources Information Center
Fisher, Amanda; Sekera, Emily; Payne, Jill; Craig, Paul
2012-01-01
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.…
A. M. Anile; S. F. Liotta; G. Mascali; S. Rinaudo
2000-01-01
One of the earlier and more widely known hydrodynamical models for simulation of semiconductor devices was put forward by Blotekjaer and subsequently investigated by Baccarani and Wordeman and by other authors (BBW model). In this paper we compare this model for a MESFET with a new hydrodynamical model recently proposed by Anile, Liotta and Mascali (ALM model). The variables are
Computational Fluid Dynamics Simulation of Green Water Around a Two-dimensional Platform
Zhao, Yucheng
2010-07-14
An interface-preserving level set method is incorporated into the Reynolds-Averaged Navier-Stokes (RANS) numerical method to simulate the application of the green water phenomena around a platform and the breaking wave above the deck. In the present...
Two-dimensional simulation of a miniaturized inductively coupled plasma reactor
Economou, Demetre J.
-turn planar coil powered at UHF 450 MHz . The rf current in the coil produces a time-varying magnetic field for the azi- muthal electric field powering the plasma was solved simul- taneously with the continuity, which in turn induces an azimuthal electric field heating the plasma electrons. The model consisted
Large eddy simulations of MHD Turbulence
NASA Astrophysics Data System (ADS)
Chhiber, R.; Wan, M.; Usmanov, A. V.; Matthaeus, W. H.; Goldstein, M. L.
2014-12-01
Increases in computer power, while important, are not likely to have a large impact on the problem of simulating turbulence at high Reynolds number. The energy and anisotropy are contained predominantly in the larger scales of motion, but most of the computational effort in a direct numerical simulation (DNS) is expended on the smallest dissipative motions. We present preliminary results from a large eddy simulation (LES) with periodic cubic geometry, where we do not attempt to simulate all the wavenumber modes up to the viscous cut-off. Only the large scales are explicitly resolved, while the interaction of the large scales with the smaller scales is modeled. The model is localized by dynamical calculation of the closure parameters. The performance of different models is evaluated by comparison of LES results with data from a higher resolution DNS. We intend this study to form a basis for the implementation of the large eddy simulation technique in a global simulation of the solar wind.
One and two dimensional electromagnetic gyrokinetic PIC simulation by ?f method
NASA Astrophysics Data System (ADS)
Chen, C. M.; Nishimura, Y.; Cheng, C. Z.
2014-10-01
An electromagnetic gyrokinetic Particle-in-Cell simulation is studied aiming at long-wave-length magnetohydrodynamic instabilities. A fully nonlinear characteristic method (?f method) of electrostatic gyrokinetic theory is employed. For a one dimensional geometry, ``0.5 dimension'' is taken in `` y-direction'' of the configuration space and another ``0.5 dimension'' is taken in the ``vz-direction'' of the velocity space. Recent electromagnetic ?f simulation shows optimistic results. We revisit the importance of the conservation properties in the low dimensional geometries. This work is supported by National Science Council of Taiwan, NSC 100-2112-M-006-021-MY3 and NSC 103-2112-M-006-021-MY3.
Numerical simulation of two-dimensional wave propagation in functionally graded materials
Arkadi Berezovski; Juri Engelbrecht; G. A Maugin
2003-01-01
The propagation of stress waves in functionally graded materials (FGMs) is studied numerically by means of the composite wave-propagation algorithm. Two distinct models of FGMs are considered: (i) a multilayered metal–ceramic composite with averaged properties within layers; (ii) randomly embedded ceramic particles in a metal matrix with prescribed volume fraction. The numerical simulation demonstrates the applicability of that algorithm to the modelling
Simulating the collapse transition of a two-dimensional semiflexible lattice polymer
Jie Zhou; Zhong-Can Ou-Yang; Haijun Zhou
2008-01-07
It has been revealed by mean-field theories and computer simulations that the nature of the collapse transition of a polymer is influenced by its bending stiffness $\\epsilon_{\\rm b}$. In two dimensions, a recent analytical work demonstrated that the collapse transition of a partially directed lattice polymer is always first-order as long as $\\epsilon_{\\rm b}$ is positive [H. Zhou {\\em et al.}, Phys. Rev. Lett. {\\bf 97}, 158302 (2006)]. Here we employ Monte Carlo simulation to investigate systematically the effect of bending stiffness on the static properties of a 2D lattice polymer. The system's phase-diagram at zero force is obtained. Depending on $\\epsilon_{\\rm b}$ and the temperature $T$, the polymer can be in one of three phases: crystal, disordered globule, or swollen coil. The crystal-globule transition is discontinuous, the globule-coil transition is continuous. At moderate or high values of $\\epsilon_{\\rm b}$ the intermediate globular phase disappears and the polymer has only a discontinuous crystal-coil transition. When an external force is applied, the force-induced collapse transition will either be continuous or discontinuous, depending on whether the polymer is originally in the globular or the crystal phase at zero force. The simulation results also demonstrate an interesting scaling behavior of the polymer at the force-induced globule-coil transition.
Simulation of two dimensional electrophoresis and tandem mass spectrometry for teaching proteomics.
Fisher, Amanda; Sekera, Emily; Payne, Jill; Craig, Paul
2012-01-01
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. The two simulations are integrated together and are designed to teach the concept of proteome analysis of prokaryotic and eukaryotic organisms. 2DE-Tandem MS can be used as a freestanding simulation, or in conjunction with a wet lab, to introduce proteomics in the undergraduate classroom. 2DE Tandem MS is a free program available on Sourceforge at https://sourceforge.net/projects/jbf/. It was developed using Java Swing and functions in Mac OSX, Windows, and Linux, ensuring that every student sees a consistent and informative graphical user interface no matter the computer platform they choose. Java must be installed on the host computer to run 2DE Tandem MS. Example classroom exercises are provided in the Supporting Information. PMID:23166029
Numerical Simulations of MHD Turbulence in Accretion Disks
Steven A. Balbus; John F. Hawley
2002-03-20
We review numerical simulations of MHD turbulence. The last decade has witnessed fundamental advances both in the technical capabilities of direct numerical simulation, and in our understanding of key physical processes. Magnetic fields tap directly into the free energy sources in a sufficiently ionized gas. The result is that adverse angular velocity and adverse temperature gradients, not the classical angular momentum and entropy gradients, destabilize laminar and stratified flow. This has profound consequences for astrophysical accretion flows, and has opened the door to a new era of numerical simulation experiments.}
NASA Astrophysics Data System (ADS)
Matteini, L.; Hellinger, P.; Landi, S.; Franci, L.; Verdini, A.; Travnicek, P. M.
2014-12-01
Couplings between large and small scales in solar wind turbulence are further complicated by the expansion, which acts at all scales and directly influences the particle thermodynamics. We present 2-D hybrid simulations of kinetic turbulence, including the effects of radial expansion by means of the hybrid expanding model (HEB). We investigate properties of the cascade first in standard hybrid simulations and then we analyze the effects of a slow expansion on the turbulent spectrum (spectral break, residual energy, cross-helicity). Incoherent spectra of balanced and inbalanced counter-propagating Alfvén waves are taken as initial conditions and the dependence on the plasma beta and the amplitude of fluctuations is investigated. We focus on the properties of the ion parallel and perpendicular heating driven by the turbulence, and on how this is modulated by the expansion. Turbulence shapes the properties of the plasma, generating local temperature anisotropy in the distribution functions, however the associated perpendicular heating and parallel cooling are not strong enough to counteract the expansion-driven anisotropic cooling. As a consequence, the plasma is driven towards the fire hose instability threshold with increasing heliocentric distance, in agreement with solar wind observations. Once the plasma enters into the fire hose unstable region, electromagnetic fluctuations driven by the ion temperature anisotropy are generated on top of the background turbulence. Despite the configuration of our simulations - out-of-plane mean magnetic field - which allows for the growth of only a subset of fire hose fluctuations, these waves are able to locally scatter the protons and partially reduce their unstable temperature anisotropy. Our findings show that kinetic instabilities driven by anisotropic distributions, like fire hose, can play a role also in turbulent and inhomogeneous plasmas, and suggest that these mechanisms are at work in the solar wind expansion.
Two-dimensional streamflow simulations of the Jordan River, Midvale and West Jordan, Utah
Kenney, Terry A.; Freeman, Michael L.
2011-01-01
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.
Two-dimensional simulations of plastic-shell, direct-drive implosions on OMEGA
Radha, P.B.; Goncharov, V.N.; Collins, T.J.B.; Delettrez, J.A.; Elbaz, Y.; Glebov, V.Yu.; 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.P.J.; Stoeckl, C.
2005-03-01
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 [D. Keller et al., Bull. Am. Phys. Soc. 44, 37 (1999)]. 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 (l<10) modes due to surface roughness and beam imbalance and the intermediate modes (20{<=}l{<=}50) due to single-beam nonuniformities. The neutron-production rate for these thick shells truncates relative to one-dimensional (1D) 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 1D rates. DRACO simulation results are consistent with experimental observations.
Two Dimensional Simulations of Plastic-Shell, Direct-Drive Implosions on OMEGA
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
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.
NASA Astrophysics Data System (ADS)
Cao, Duc; Moses, Gregory; Delettrez, Jacques
2015-08-01
An implicit, non-local thermal conduction algorithm based on the algorithm developed by Schurtz, Nicolai, and Busquet (SNB) [Schurtz et al., Phys. Plasmas 7, 4238 (2000)] for non-local electron transport is presented and has been implemented in the radiation-hydrodynamics code DRACO. To study the model's effect on DRACO's predictive capability, simulations of shot 60 303 from OMEGA are completed using the iSNB model, and the computed shock speed vs. time is compared to experiment. Temperature outputs from the iSNB model are compared with the non-local transport model of Goncharov et al. [Phys. Plasmas 13, 012702 (2006)]. Effects on adiabat are also examined in a polar drive surrogate simulation. Results show that the iSNB model is not only capable of flux-limitation but also preheat prediction while remaining numerically robust and sacrificing little computational speed. Additionally, the results provide strong incentive to further modify key parameters within the SNB theory, namely, the newly introduced non-local mean free path. This research was supported by the Laboratory for Laser Energetics of the University of Rochester.
Wu, Tianmin; Zhang, Ruiting; Li, Huanhuan; Zhuang, Wei E-mail: lijiangy@pku.edu.cn; Yang, Lijiang E-mail: lijiangy@pku.edu.cn
2014-02-07
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 GB{sup OBC} 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.
NASA Astrophysics Data System (ADS)
Luo, Liang; Yu, Boming; Cai, Jianchao; Zeng, Xiangfeng
2014-07-01
The tortuosity is a very important parameter for description of fluid flow in porous media, and it has been shown that porous media in nature have the fractal characteristics. The Sierpinski carpet is an exactly self-similar fractal model, which is often used to simulate fractal porous media. In this work, the tortuosity of different generations of Sierpinski carpet is calculated and analyzed by the finite volume method. A simple linear relation between the generations and tortuosity in pore fractal model of porous media is obtained. The results are compared with the available conclusions and show a more realistic tortuosity predication for fluid flow in the two-dimensional pore fractal models of porous media.
A nite volume ideal Numerical simulations of MHD ows with shocks have been performed
De Sterck, Hans
Chapter 4 A #12;nite volume ideal MHD code Numerical simulations of MHD ows with shocks have been to #12;nite volume discretizations. 4.1.1 Scalar conservation laws A scalar conservation law is described by @u @t + @f(u) @x = 0; (4.1) #12; 92 Chapter 4. A #12;nite volume ideal MHD code in terms of scalar u
Center for Simulation of Wave Interactions with MHD (SWIM) PASCI PAC meeting, May, 2007
Center for Simulation of Wave Interactions with MHD (SWIM) PASCI PAC meeting, May, 2007 E. D and particle sources have on extended-MHD phenomena thereby improving our capability for predicting discharge evolution in the presence of sporadic fast MHD events. This involves interfacing the IPS to both
FRANC2D: A two-dimensional crack propagation simulator. Version 2.7: User's guide
NASA Technical Reports Server (NTRS)
Wawrzynek, Paul; Ingraffea, Anthony
1994-01-01
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.
Attosecond double-ionization dynamics of aligned H2: Two-dimensional quantum simulations
NASA Astrophysics Data System (ADS)
Wang, Shang; Chen, Yanjun
2015-08-01
A fully quantum procedure, based on the numerical solution of the time-dependent Schrödinger equation (TDSE) with two spatial dimensions for every electron, is developed to study the attosecond double-ionization (DI) dynamics from aligned H2 molecules in strong laser fields. Our simulations are able to reproduce the orientation dependence of DI, as observed for N2 in experiments [D. Zeidler et al., Phys. Rev. Lett. 95, 203003 (2005)], 10.1103/PhysRevLett.95.203003. Our TDSE analyses reveal the important roles of the lateral motion of the electron and two-center interference in the orientation-dependent DI. Our results give suggestions on the ultrafast probing of the dynamics of DI from aligned molecules.
Nenov, Artur; Segarra-Martí, Javier; Giussani, Angelo; Conti, Irene; Rivalta, Ivan; Dumont, Elise; Jaiswal, Vishal K; Altavilla, Salvatore Flavio; Mukamel, Shaul; Garavelli, Marco
2015-01-01
The SOS//QM/MM [Rivalta et al., Int. J. Quant. Chem., 2014, 114, 85] method consists of an arsenal of computational tools allowing accurate simulation of one-dimensional (1D) and bi-dimensional (2D) electronic spectra of monomeric and dimeric systems with unprecedented details and accuracy. Prominent features like doubly excited local and excimer states, accessible in multi-photon processes, as well as charge-transfer states arise naturally through the fully quantum-mechanical description of the aggregates. In this contribution the SOS//QM/MM approach is extended to simulate time-resolved 2D spectra that can be used to characterize ultrafast excited state relaxation dynamics with atomistic details. We demonstrate how critical structures on the excited state potential energy surface, obtained through state-of-the-art quantum chemical computations, can be used as snapshots of the excited state relaxation dynamics to generate spectral fingerprints for different de-excitation channels. The approach is based on high-level multi-configurational wavefunction methods combined with non-linear response theory and incorporates the effects of the solvent/environment through hybrid quantum mechanics/molecular mechanics (QM/MM) techniques. Specifically, the protocol makes use of the second-order Perturbation Theory (CASPT2) on top of Complete Active Space Self Consistent Field (CASSCF) strategy to compute the high-lying excited states that can be accessed in different 2D experimental setups. As an example, the photophysics of the stacked adenine-adenine dimer in a double-stranded DNA is modeled through 2D near-ultraviolet (NUV) spectroscopy. PMID:25607949
Two dimensional hydrological simulation in elastic swelling/shrinking peat soils
NASA Astrophysics Data System (ADS)
Camporese, M.; Ferraris, S.; Paniconi, C.; Putti, M.; Salandin, P.; Teatini, P.
2005-12-01
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.
Two-dimensional hybrid simulations of Alfvénic fluctuations in the expanding solar wind
NASA Astrophysics Data System (ADS)
Landi, Simone; Matteini, Lorenzo; Hellinger, Petr; Verdini, Andrea; Travnicek, Pavel M.; Burgess, David
2014-05-01
The supersonic expansion of the solar wind and wave particle interactions which characterize the ion evolution are investigated using a hybrid expanding box model. We present 2D simulations of the interaction between Alfvénic like fluctuations using two different geometries: an in-plane mean magnetic field and an out-of-plane mean magnetic field. The initial conditions for the Alfvénic spectrum are a) a mixed parallel and oblique propagating modes (in-plane) and b) purely perpendicular wavevectors (out-of-plane). For both geometries we consider 2 kinds of initial conditions. 1) the imbalanced case with Alfvén waves propagating in one direction along the guide field, that is an initial condition with maximal correlation between u and b (maximal cross helicity and null residual energy) 2) the balanced case with counter-propagating Alfvén waves and with an initial magnetic energy dominating over kinetic energy (null cross helicity and maximal residual energy). Such characteristics are the most frequently observed in the solar wind. We investigate parallel and perpendicular proton heating properties of the turbulent spectra in the simulations and the influence of the expansion on the evolution of turbulence and its decay. As suggested by solar wind observations, the perpendicular heating and parallel cooling is not strong enough to overcome the expansion-driven anisotropic cooling. Once the expansion drives the system unstable with respect to the fire-hose instability driven by the proton temperature anisotropy, electromagnetic fluctuations are generated. These waves scatter protons and reduce their temperature anisotropy. Consequently, this mechanism constrains the temperature anisotropy and the system evolves along a marginal instability path.
Matsui, H.; Koike, Makoto; Kondo, Yutaka; Fast, Jerome D.; Takigawa, M.
2014-09-30
Number concentrations, size distributions, and mixing states of aerosols are essential parameters for accurate estimation of aerosol direct and indirect effects. In this study, we developed an aerosol module, designated Aerosol Two-dimensional bin module for foRmation and Aging Simulation (ATRAS), that can represent these parameters explicitly by considering new particle formation (NPF), black carbon (BC) aging, and secondary organic aerosol (SOA) processes. A two-dimensional bin representation is used for particles with dry diameters from 40 nm to 10 µm to resolve both aerosol size (12 bins) and BC mixing state (10 bins) for a total of 120 bins. The particles with diameters from 1 to 40 nm are resolved using an additional 8 size bins to calculate NPF. The ATRAS module was implemented in the WRF-chem model and applied to examine the sensitivity of simulated mass, number, size distributions, and optical and radiative parameters of aerosols to NPF, BC aging and SOA processes over East Asia during the spring of 2009. BC absorption enhancement by coating materials was about 50% over East Asia during the spring, and the contribution of SOA processes to the absorption enhancement was estimated to be 10 – 20% over northern East Asia and 20 – 35% over southern East Asia. A clear north-south contrast was also found between the impacts of NPF and SOA processes on cloud condensation nuclei (CCN) concentrations: NPF increased CCN concentrations at higher supersaturations (smaller particles) over northern East Asia, whereas SOA increased CCN concentrations at lower supersaturations (larger particles) over southern East Asia. Application of ATRAS to East Asia also showed that the impact of each process on each optical and radiative parameter depended strongly on the process and the parameter in question. The module can be used in the future as a benchmark model to evaluate the accuracy of simpler aerosol models and examine interactions between NPF, BC aging, and SOA processes under different meteorological conditions and emissions.
Lattice Boltzmann simulation of the rise and dissolution of two-dimensional immiscible droplets
NASA Astrophysics Data System (ADS)
Chen, Cheng; Zhang, Dongxiao
2009-10-01
We used a coupled multiphase lattice Boltzmann (LB) model to simulate the dissolution of immiscible liquid droplets in another liquid during the rising process resulting from buoyancy. It was found that there existed a terminal rise velocity for each droplet, and there was a power law relationship between the Eötvös (Eo) number and the terminal Reynolds (Re) number. Our simulation results were in agreement with the empirical correlation derived for predicting bubble rise. When more than two identical droplets rose simultaneously in a close proximity, the average terminal rise velocity was lower than that of a single droplet with the same size because of the mutual resistant interactions. The droplet trajectories at the noncentral positions were not straight because of the nonzero net horizontal forces acting on the droplets. The Damkohler (Da) and Peclet (Pe) numbers were varied to investigate the coupling between droplet size, flow field, dissolution at the interface, and solute transport. For a given Pe, increasing Da led to a higher dissolution rate. For a given Da, increasing Pe led to a higher dissolution rate. For a large Da and a small Pe, the process near the interface was diffusion limited, and the advective flow relative to the droplet resulting from droplet rise was unable to move the accumulated solute away from the interface quickly. In this case, it was favorable to split the single droplet into as many small ones as possible in order to increase the interface area per unit mass and consequently enhance the whole dissolution process. For a small Da and a large Pe, the process was dissolution limited near the interface. The mass of accumulated solute near the interface was little, so the advective flow at the top side of the droplet was able to clean the solute quickly. In this case it was favorable to keep the droplet as a single one in order to obtain a high rise velocity and consequently enhance the whole dissolution process. By studying the coupling between Da and Pe, we qualitatively proposed to construct a Da-Pe phase plane and found the interface dividing the plane into regions 1 and 2. Region 1 was the collection of points where it was favorable to break down the droplet into as many small ones as possible in order to accelerate dissolution, while region 2 was the collection of points where it was favorable to keep the droplet in a single one for the same purpose. Based on our LB simulations, we found that the interface was an increasing function of Pe. Region 1 was the portion above the interface, while region 2 was the portion below it. In real applications, if both Pe and Da are obtained, it will be easy to judge whether it is favorable to break down the droplet or not in order to accelerate dissolution by checking whether (Pe, Da) falls in region 1 or 2.
NASA Astrophysics Data System (ADS)
Roggan, Andre; Mueller, Gerhard J.
1994-12-01
A computer model is presented enabling the determination of optimized laser parameters in advance of a LITT treatment. Besides, a real-time simulation of the spatial temperature- and damage distribution can be performed during the treatment. Input parameters for the simulation are the specific optical and thermal properties of the tissue. The optical properties of human liver and human prostate were measured at 850 nm and 1064 nm using a double- integrating sphere technique and inverse Monte-Carlo simulations. The thermal tissue properties were calculated from the individual water contents. The calculation of the spatial intensity distribution is carried out by performing a fast three-dimensional Monte-Carlo simulation in small time steps. The change of the optical tissue properties during the process of coagulation is taken into account. The corresponding temperature distribution is calculated by a numerical solution of the two-dimensional bio-heat transport equation in cylindrical geometry. Finally the degree of tissue damage is determined by solving the Arrhenius formulas numerically. Blood perfusion of the tissue can be considered as an internal cooling effect. Comparison of the calculated temperature behavior with experimental data shows good agreement.
Two-Dimensional Optical Measurement of Waves on Liquid Lithium Jet Simulating IFMIF Target Flow
Kazuhiro Itoh; Hiroyuki Koterazawa; Taro Itoh; Yutaka Kukita; Hiroo Kondo; Nobuo Yamaoka; Hiroshi Horiike; Mizuho Ida; Hideo Nakamura; Hiroo Nakamura; Takeo Muroga
2006-07-01
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)
Central Regions of Barred Galaxies: Two-Dimensional Non-self-gravitating Hydrodynamic Simulations
Kim, Woong-Tae; Stone, James M; Yoon, Doosoo; Teuben, Peter J
2011-01-01
The inner regions of barred galaxies contain substructures such as off-axis shocks, nuclear rings, and nuclear spirals. These substructure 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, the bulge, a central BH, and the bar. To investigate various galactic environments, we vary the gas sound speed c_s as well as the mass of the central BH M_BH. Once the flow has reached a quasi-steady state, off-axis shocks tend to move closer to the bar major axis as c_s increases. Nuclear rings shrink in size with increasing c_s, but are independent of M_BH, suggesting that ring position is not determined by the Lindblad re...
Postcollapse hydrodynamics of SN 1987A - Two-dimensional simulations of the early evolution
NASA Technical Reports Server (NTRS)
Herant, Marc; Benz, Willy; Colgate, Stirling
1992-01-01
The first few seconds of the explosion of SN 1987A are modeled here using a 2D cylindrical geometry smooth particle hydrodynamics code. The success of the explosion is determined to be sensitive to the duration of the infall, the timing of the bounce, and the subsequent neutrino heating. A semianalytical model for the initial structure of the collapsed object is used to present two simulations that differ by the mass that has been allowed to collapse into a neutron star prior to the bounce. In the case of a short initial infall, the explosion fails due to excessive cooling. For a longer initial infall, the cooling is less and the explosion is successful although relatively weak. It is shown that in this case, a successful explosion is brought about by the presence of an entropy gradient which, combined with the gravitational pull of the neutron star, leads to extremely strong instabilities. The critical importance of the global circulation for the success of the explosion is demonstrated.
A two-dimensional model of water: Theory and computer simulations
NASA Astrophysics Data System (ADS)
Urbi?, T.; Vlachy, V.; Kalyuzhnyi, Yu. V.; Southall, N. T.; Dill, K. A.
2000-02-01
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.
Experimental apparatus for quantum simulation with two-dimensional 9Be + Coulomb crystals
NASA Astrophysics Data System (ADS)
Pyka, Karsten; Ball, Harrison; McRae, Terry; Edmunds, Claire; Lee, Michael W.; Henderson, Samuel; Biercuk, Michael J.; Quantum Control Lab Team
2015-03-01
We report on the development of a new experimental setup designed for Quantum Simulation studies at a computationally relevant scale using laser-cooled 9Be + ion-crystals in a Penning trap. The trap geometry is optimized using numerical calculations for trapping large ion crystals with enhanced optical access and reduced anharmonic perturbations. Separate loading and spectroscopy zones prevent long term drifts of the trapping parameters due to contamination of the trap electrodes with Be deposits. Our customized superconducting magnet provides a homogenous (dB/B <10-6) magnetic field at 3T required for ion trapping. Laser frequencies required for cooling/detection and spin-motion entanglement are generated from telecom wavelength fiber laser systems in the IR via nonlinear conversion. Our new approach employs high-efficiency telecom modulators and mode-selecting cavities to generate multiple beamlines from a single Sum-frequency-Generation step. Ultimately, this newly developed setup will allow for studies of many-body spin systems with tuneable interaction strength from infinite-range to nearest-neighbour type interaction.
NASA Astrophysics Data System (ADS)
Bandaru, Vinodh; Pracht, Julian; Boeck, Thomas; Schumacher, Jörg
2015-08-01
We consider a plane channel flow of an electrically conducting fluid which is driven by a mean pressure gradient in the presence of an applied magnetic field that is streamwise periodic with zero mean. Magnetic flux expulsion and the associated bifurcation in such a configuration are explored using direct numerical simulations (DNS). The structure of the flow and magnetic fields in the Hartmann regime (where the dominant balance is through Lorentz forces) and the Poiseuille regime (where viscous effects play a significant role) are studied, and detailed comparisons to the existing one-dimensional model of Kamkar and Moffatt (J Fluid Mech 90:107-122, 1982) are drawn to evaluate the validity of the model. Comparisons show good agreement of the model with DNS in the Hartmann regime, but significant differences arising in the Poiseuille regime when nonlinear effects become important. The effects of various parameters like the magnetic Reynolds number, imposed field wavenumber etc. on the bifurcation of the flow are studied. Magnetic field line reconnections occurring during the dynamic runaway reveal a specific two-step pattern that leads to the gradual expulsion of flux in the core region.
Two-dimensional Euler and Navier-Stokes Time accurate simulations of fan rotor flows
NASA Technical Reports Server (NTRS)
Boretti, A. A.
1990-01-01
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.
NASA Astrophysics Data System (ADS)
Voinovich, Peter; Merlen, Alain
2005-12-01
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.
Voinovich, Peter; Merlen, Alain
2005-12-01
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
NASA Astrophysics Data System (ADS)
Bandaru, Vinodh; Pracht, Julian; Boeck, Thomas; Schumacher, Jörg
2015-05-01
We consider a plane channel flow of an electrically conducting fluid which is driven by a mean pressure gradient in the presence of an applied magnetic field that is streamwise periodic with zero mean. Magnetic flux expulsion and the associated bifurcation in such a configuration are explored using direct numerical simulations (DNS). The structure of the flow and magnetic fields in the Hartmann regime (where the dominant balance is through Lorentz forces) and the Poiseuille regime (where viscous effects play a significant role) are studied, and detailed comparisons to the existing one-dimensional model of Kamkar and Moffatt (J Fluid Mech 90:107-122, 1982) are drawn to evaluate the validity of the model. Comparisons show good agreement of the model with DNS in the Hartmann regime, but significant differences arising in the Poiseuille regime when nonlinear effects become important. The effects of various parameters like the magnetic Reynolds number, imposed field wavenumber etc. on the bifurcation of the flow are studied. Magnetic field line reconnections occurring during the dynamic runaway reveal a specific two-step pattern that leads to the gradual expulsion of flux in the core region.
Bandaru, Vinodh; Boeck, Thomas; Schumacher, Jörg
2015-01-01
We consider a plane channel flow of an electrically conducting fluid which is driven by a mean pressure gradient in the presence of an applied magnetic field that is streamwise periodic with zero mean. Magnetic flux expulsion and the associated bifurcation in such a configuration is explored using direct numerical simulations (DNS). The structure of the flow and magnetic fields in the Hartmann regime (where the dominant balance is through Lorentz forces) and the Poiseuille regime (where viscous effects play a significant role) are studied and detailed comparisons to the existing one-dimensional model of Kamkar and Moffatt (J. Fluid. Mech., Vol.90, pp 107-122, 1982) are drawn to evaluate the validity of the model. Comparisons show good agreement of the model with DNS in the Hartmann regime, but significant diferences arising in the Poiseuille regime when non-linear effects become important. The effects of various parameters like the magnetic Reynolds number, imposed field wavenumber etc. on the bifurcation of ...
Two-Dimensional Model Simulations of Interannual Variability in the Tropical Stratosphere
NASA Technical Reports Server (NTRS)
Fleming, Eric L.; Jackman, Charles H.; Considine, David B.; Rosenfeld, Joan; Bhartia, P. K. (Technical Monitor)
2001-01-01
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.
A hybrid model for simulating diffused first reflections in two-dimensional acoustic environments
NASA Astrophysics Data System (ADS)
Martin, Geoffrey Glen
2001-07-01
Although it is widely accepted that the diffusion of early reflections in acoustic spaces intended for music performance greatly improves the perceived quality of sound, current manufacturers of synthetic reverberation engines continue to model reflecting surfaces as having almost perfectly specular characteristics. This dissertation describes a hybrid method of simulating diffusion based on both physical and phenomenological modeling components. In 1979, Manfred Schroeder described a method of designing and constructing diffusing surfaces based on a rather simple mathematical algorithm which provides diffused reflections in predictable frequency bands. This structural device, now known as a "Schroeder diffuser," has become a standard geometry used in constructing diffusive surfaces for spaces intended for music rehearsal, recording and performance. While it is possible to use DSP to model the characteristics of reflections off such a surface, a reflection model based exclusively on a surface constructed of a Schroeder diffuser has proven in informal tests to be as aesthetically inadequate as a perfectly specular model. Control of both the spatial and temporal envelopes of the diffusive reflection are required by an end user in order to tailor the reflection characteristics to the desired impression. In 1974 an empirical model for computing light reflections off objects in a three-dimensional environment was developed by Phong Bui-Toung. This algorithm incorporated both a specular and diffuse component with relationships controlled by an end user. This dissertation describes the adaptation and implementation of the Phong shading algorithm in conjunction with a physical model of components of the Schroeder diffuser for the modeling of diffuse reflections in synthetic acoustic environments. The inclusion of the Phong algorithm provides precise control over the balance between the spectral and diffusive components of the reflection. In addition, directivity functions for sound sources and receivers in the virtual space are described. Analysis and evaluation of the model using mathematical and empirical methodologies are discussed and stereo and multichannel audio examples produced by the system are included.
High-beta extended MHD simulations of toroidal stellarators
NASA Astrophysics Data System (ADS)
Bechtel, T. A.; Hegna, C. C.; Schlutt, M. G.; Hebert, J. D.
2014-10-01
The nonlinear, extended MHD code NIMROD is used to study high-beta, 3D magnetic topology evolution of a toroidal stellarator. The configurations under investigation derive from the geometry of the Compact Toroidal Hybrid (CTH) experiment. However, the vacuum rotational transform profile is artificially raised in an effort to examine the sensitivity of low order rational surfaces and/or magnetic islands. Finite beta plasmas are created using a heating source and anisotropic heat conduction in a manner similar to previous calculations of CTH where the effects of Ohmic current drive were simulated. The onset of MHD instabilities and nonlinear consequences are monitored as a function of beta as well as the fragility of the magnetic surfaces. Research supported by US DOE under Grant No. DE-FG02-99ER54546.
Quick Time-dependent Ionization Calculations Depending on MHD Simulations
NASA Astrophysics Data System (ADS)
Shen, Chengcai; Raymond, John C.; Murphy, Nicholas Arnold
2014-06-01
Time-dependent ionization is important in astrophysical environments where the thermodynamic time scale is shorter than ionization time scale. In this work, we report a FORTRAN program that performs fast non-equilibrium ionization calculations based on parallel computing. Using MHD simulation results, we trace the movements of plasma in a Lagrangian framework, and obtain evolutionary history of temperature and electron density. Then the time-dependent ionization equations are solved using the eigenvalue method. For any complex temperature and density histories, we introduce a advanced time-step strategy to improve the computational efficiency. Our tests show that this program has advantages of high numerical stability and high accuracy. In addition, it is also easy to integrate this solver with the other MHD routines.
CENTRAL REGIONS OF BARRED GALAXIES: TWO-DIMENSIONAL NON-SELF-GRAVITATING HYDRODYNAMIC SIMULATIONS
Kim, Woong-Tae; Seo, Woo-Young; Stone, James M.; Yoon, Doosoo; Teuben, Peter J.
2012-03-01
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.
NASA Astrophysics Data System (ADS)
Yu, Tao; Mao, Tian; Wang, Yungang; Zeng, Zhongcao; Xia, Chunliang; Wu, Fenglei; Wang, Le
2014-08-01
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.
Magnetic reconnection in Hall MHD simulations including electron inertia
NASA Astrophysics Data System (ADS)
Gomez, D. O.; Andres, N.; Martin, L. N.; Dmitruk, P.
2012-12-01
Magnetic reconnection is an important physical mechanism of energy conversion in various space plasma physics environments, such as the solar corona or planetary magnetospheres. Theoretical models of magnetic reconnection were first developed within the framework of one-fluid magnetohydrodynamics (MHD), where the Sweet-Parker regime leads to exceedingly low reconnection rates for most space physics problems. Kinetic plasma effects introduce new spatial and temporal scales into the theoretical description, which might significantly increase the reconnection rates. We work within the framework of two-fluid MHD for a fully ionized hydrogen plasma, retaining the effects of the Hall current and electron inertia. The corresponding equations of motion display three ideal invariants: total energy, electron helicity and ion helicity. We performed 2.5 D Hall MHD simulations including electron inertia using a pseudo-spectral code, which yield exponentially fast numerical convergence. Our results show that reconnection takes place in an electron-dominated region, whose spatial scale is given by the electron skin depth. This region is surrounded by a much larger ion-dominated region, with a spatial scale of the order of the ion skin depth. The computed reconnection rates remain a fair fraction of the Alfven velocity, which is much larger than the Sweet-Parker reconnection rate.
NASA Astrophysics Data System (ADS)
Yu, Zhicong; Noo, Frédéric; Dennerlein, Frank; Wunderlich, Adam; Lauritsch, Günter; Hornegger, Joachim
2012-07-01
Mathematical phantoms are essential for the development and early stage evaluation of image reconstruction algorithms in x-ray computed tomography (CT). This note offers tools for computer simulations using a two-dimensional (2D) phantom that models the central axial slice through the FORBILD head phantom. Introduced in 1999, in response to a need for a more robust test, the FORBILD head phantom is now seen by many as the gold standard. However, the simple Shepp-Logan phantom is still heavily used by researchers working on 2D image reconstruction. Universal acceptance of the FORBILD head phantom may have been prevented by its significantly higher complexity: software that allows computer simulations with the Shepp-Logan phantom is not readily applicable to the FORBILD head phantom. The tools offered here address this problem. They are designed for use with Matlab®, as well as open-source variants, such as FreeMat and Octave, which are all widely used in both academia and industry. To get started, the interested user can simply copy and paste the codes from this PDF document into Matlab® M-files.
Two-dimensional Maxwell-Bloch simulation of quasi-?-pulse amplification in a seeded XUV laser
NASA Astrophysics Data System (ADS)
Larroche, O.; Klisnick, A.
2013-09-01
The amplification of high-order-harmonics (HOH) seed pulses in a swept-gain XUV laser is investigated through numerical simulations of the full set of Bloch and two-dimensional paraxial propagation equations with our code colax. The needed atomic data are taken from a hydrodynamics and collisional-radiative simulation in the case of a Ni-like Ag plasma created from the interaction of an infrared laser with a solid target and pumped in the transient regime. We show that the interplay of strong population inversion and diffraction or refraction due to the short transverse dimensions and steep density gradient of the active plasma can lead to the amplification of an intense, ultrashort, quasi-“?” pulse triggered by the incoming seed. By properly tuning the system geometry and HOH pulse parameters, we show that an ?10 fs, 8×1012 W/cm2 amplified pulse can be achieved in a 3-mm-long Ni-like Ag plasma, with a factor of ?10 intensity contrast with respect to the longer-lasting wake radiation and amplified spontaneous emission.
Takao, Yoshinori; Kusaba, Naoki; Eriguchi, Koji; Ono, Kouichi
2010-11-15
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.
Yu, Zhicong; Noo, Frédéric; Dennerlein, Frank; Wunderlich, Adam; Lauritsch, Günter; Hornegger, Joachim
2012-07-01
Mathematical phantoms are essential for the development and early stage evaluation of image reconstruction algorithms in x-ray computed tomography (CT). This note offers tools for computer simulations using a two-dimensional (2D) phantom that models the central axial slice through the FORBILD head phantom. Introduced in 1999, in response to a need for a more robust test, the FORBILD head phantom is now seen by many as the gold standard. However, the simple Shepp-Logan phantom is still heavily used by researchers working on 2D image reconstruction. Universal acceptance of the FORBILD head phantom may have been prevented by its significantly higher complexity: software that allows computer simulations with the Shepp-Logan phantom is not readily applicable to the FORBILD head phantom. The tools offered here address this problem. They are designed for use with Matlab®, as well as open-source variants, such as FreeMat and Octave, which are all widely used in both academia and industry. To get started, the interested user can simply copy and paste the codes from this PDF document into Matlab® M-files. PMID:22713335
NASA Astrophysics Data System (ADS)
Matsumoto, Yosuke; Amano, Takanobu; Hoshino, Masahiro
2012-08-01
Electron accelerations at high Mach number collisionless shocks are investigated by means of two-dimensional electromagnetic particle-in-cell simulations with various Alfvén Mach numbers, ion-to-electron mass ratios, and the upstream electron ? e (the ratio of the thermal pressure to the magnetic pressure). We find electrons are effectively accelerated at a super-high Mach number shock (MA ~ 30) with a mass ratio of M/m = 100 and ? 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.
NASA Astrophysics Data System (ADS)
Matsumoto, Y.; Amano, T.; Hoshino, M.
2012-12-01
Electron accelerations at high Mach number collision-less 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 ?e (the ratio of the thermal pressure to the magnetic pressure). We found electrons are effectively accelerated at a super-high Mach number shock (MA ~ 30) with a mass ratio of M/m=100 and ?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 the 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 et al., Astrophys. J., 755, 109, 2012.
MHD simulations of boundary layer formation along the dayside Venus ionopause due to mass loading
NASA Technical Reports Server (NTRS)
Mcgary, J. E.; Pontius, D. H., Jr.
1994-01-01
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 10(exp 5)/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.
MHD simulations of boundary layer formation along the dayside Venus ionopause due to mass loading
NASA Astrophysics Data System (ADS)
McGary, J. E.; Pontius, D. H.
1994-02-01
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.
Analysis and gyrokinetic simulation of MHD Alfven wave interactions
NASA Astrophysics Data System (ADS)
Nielson, Kevin Derek
The study of low-frequency turbulence in magnetized plasmas is a difficult problem due to both the enormous range of scales involved and the variety of physics encompassed over this range. Much of the progress that has been made in turbulence theory is based upon a result from incompressible magnetohydrodynamics (MHD), in which energy is only transferred from large scales to small via the collision of Alfven waves propagating oppositely along the mean magnetic field. Improvements in laboratory devices and satellite measurements have demonstrated that, while theories based on this premise are useful over inertial ranges, describing turbulence at scales that approach particle gyroscales requires new theory. In this thesis, we examine the limits of incompressible MHD theory in describing collisions between pairs of Alfven waves. This interaction represents the fundamental unit of plasma turbulence. To study this interaction, we develop an analytic theory describing the nonlinear evolution of interacting Alfven waves and compare this theory to simulations performed using the gyrokinetic code AstroGK. Gyrokinetics captures a much richer set of physics than that described by incompressible MHD, and is well-suited to describing Alfvenic turbulence around the ion gyroscale. We demonstrate that AstroGK is well suited to the study of physical Alfven waves by reproducing laboratory Alfven dispersion data collected using the LAPD. Additionally, we have developed an initialization alogrithm for use with AstroGK that allows exact Alfven eigenmodes to be initialized with user specified amplitudes and phases. We demonstrate that our analytic theory based upon incompressible MHD gives excellent agreement with gyrokinetic simulations for weakly turbulent collisions in the limit that k?rho i << 1. In this limit, agreement is observed in the time evolution of nonlinear products, and in the strength of nonlinear interaction with respect to polarization and scale. We also examine the effect of wave amplitude upon the validity of our analytic solution, exploring the nature of strong turbulence. In the kinetic limit where k? rhoi ? 1 where incompressible MHD is no longer a valid description, we illustrate how the nonlinear evolution departs from our analytic expression. The analytic theory we develop provides a framework from which more sophisticated of weak and strong inertial-range turbulence theories may be developed. Characterization of the limits of this theory may provide guidance in the development of kinetic Alfven wave turbulence.
A. Kercek; W. Hillebrandt; J. Truran
1998-01-08
We present the results of two-dimensional calculations of turbulent nuclear burning of hydrogen-rich material accreted onto a white dwarf of 1 solar mass. The main aim of the present paper is to investigate the question as to whether and how the general properties of the burning are affected by numerical resolution effects. In particular, we want to see whether or not convective overshooting into the surface layers of the C+O white dwarf can lead to self-enrichment of the initially solar composition of the hydrogen-rich envelope with carbon and oxygen from the underlying white dwarf core. Our explicit hydrodynamic code is based on the PPM-method and computes the onset of the thermonuclear runaway on a Cartesian grid. In contrast to previous works we do not observe fast mixing of carbon and oxygen from the white dwarf's surface into the envelope by violent overshooting of large eddies. The main features of the flow fields in our simulations are the appearance of small persistent coherent structures of very high vorticity (and velocity) compared to the background flow. Their typical linear scales are about 10 to 20 grid zones and thus their physical size depends on the numerical resolution, i.e, their size decreases with increasing resolution. The two simulations (low and high resolution) which are presented here show only moderate differences in spatially integrated quantities such as laterally averaged temperature, energy generation rate, and chemical composition. We have not expanded both simulations equally long, but for the physical time under consideration the major difference seems to be that the highly resolved simulation is a bit less violent. In conclusion, we do find some self-enrichment, but on time-scales much longer than in previous calculations.
Plasmoid dynamics in 3D resistive MHD simulations of magnetic reconnection
NASA Astrophysics Data System (ADS)
Samtaney, R.; Loureiro, N. F.; Uzdensky, D. A.; Schekochihin, A. A.
2012-04-01
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.
Magnetic flux ropes in 3-dimensional MHD simulations
NASA Technical Reports Server (NTRS)
Ogino, Tatsuki; Walker, Raymond J.; Ashour-Abdalla, Maha
1990-01-01
The interaction of the solar wind and the earth's magnetosphere is presently simulated by a 3D, time-dependent, global MHD method in order to model the magnetopause and magnetotail generation of magnetic flux ropes. It is noted that strongly twisted and localized magnetic flux tubes simular to magnetic flux ropes appear at the subpolar magnetopause when the IMF has a large azimuthal component, as well as a southward component. Plasmoids are generated in the magnetotail after the formation of a near-earth magnetic neutral line; the magnetic field lines have a helical structure that is connected from dawn to dusk.
FireStem2D – A Two-Dimensional Heat Transfer Model for Simulating Tree Stem Injury in Fires
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
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
NASA Technical Reports Server (NTRS)
Herant, Marc; Benz, Willy
1991-01-01
Results are presented from numerical simulations of the early stages of the explosion of SN 1987A. Using a two-dimensional cylindrical geometry version of a smooth particle hydrodynamics code, the explosion is followed for three months to investigate both the early hydrodynamical instabilities and the effect of the subsequent radioactive decay of Ni-56 and Co-56 with half-lives of 6.1 and 77.8 days, respectively. It is shown that the mixing induced by hydrodynamical instabilities occurring during the first few hours is substantially modified at later time by the radioactive decay of Ni-56 and Co-56. The inner cavity of the expanding supernova remnant fills up with nickel, its decay products thus forming a giant 'nickel bubble'. The peak velocity of the nickel increases by approximately 30 percent after the decays. While these results adequately model the core of the observed Fe line profiles, they fail to reproduce the high velocity wings of the spectra.
Haris, Luman; Khotimah, Siti Nurul; Haryanto, Freddy; Viridi, Sparisoma
2013-01-01
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...
Global MHD Simulation of Mesoscale Structures at the Magnetospheric Boundary
NASA Technical Reports Server (NTRS)
Berchem, Jean
1998-01-01
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.
Florida, University of
IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 50, NO. 5, MAY 2003 1353 Two-Dimensional Semiconductor]. In addition, the con- tribution of such noise sources is dependent on its spatial loca- tion and the unknown
NASA Astrophysics Data System (ADS)
Savoini, P.; Lembége, B.; Stienlet, J.
2010-09-01
The foreshock region is populated by energetic backstreaming particles (electrons and ions) issued from the shock after having interacted with it. Several aspects concerning the origin of these high-energy particles and their corresponding acceleration mechanisms are still unresolved. The present study is focused on a quasi-perpendicular curved shock and associated electron foreshock region (i.e., for 90° ? $\\theta$Bn ? 45°, where $\\theta$Bn is the angle between the shock normal and the upstream magnetostatic field). Two-dimensional full-particle simulation is used in order to include self-consistently the electron and ion dynamics, the full dynamics of the shock, the curvature effects and the time-of-flight effects. All expected salient features of the bow shock are recovered both for particles and for electromagnetic fields. Present simulations evidence that the fast-Fermi acceleration (magnetic mirror) mechanism, which is commonly accepted, is certainly not the unique process responsible for the formation of energetic backstreaming electrons. Other mechanisms also contribute. More precisely, three different classes of backstreaming electrons are identified according to their individual penetration depth within the shock front: (i) “magnetic mirrored” electrons which only suffer a specular reflection at the front, (ii) “trapped” electrons which succeed to penetrate the overshoot region and suffer a local trapping within the parallel electrostatic potential at the overshoot, and (iii) “leaked” electrons which penetrate even much deeper into the downstream region. “Trapped” and “leaked” electrons succeed to find appropriate conditions to escape from the shock and to be reinjected back upstream. All these different types of electrons contribute together to the formation of energetic field-aligned beam. The acceleration mechanisms associated to each electron class and/or escape conditions are analyzed and discussed.
NASA Technical Reports Server (NTRS)
Fleming, Eric L.; Jackman, Charles H.; Stolarski, Richard S.; Considine, David B.
1998-01-01
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.
MHD Simulations of Earth's Bow Shock at low Mach Numbers: Standoff Distances
NASA Technical Reports Server (NTRS)
Cairns, Iver H.; Lyon, J. G.
1995-01-01
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 magnetopauause obstacle, with axisymmetric three-dimensional location given by scaled standard model, to directly address previous gasdynamic (GD) and field-aligned MHD (FA-MHD) work. Tests of the simulated shocks' density jumps X for 1.4 approx. less than MA approx. less than 10 and the high M(sub A) shock location, and reproduction of the GD relation between magnetosheath thickness and X for quasi-gasdynamic MHD runs with M(sub A) much greater than M(sub s), confirm that the MHD code is working correctly. The MHD simulations show the standoff distance a(sub s), increasing monotonically with decreasing M(sub A). Significantly larger a(sub s), are found at low M(sub A) than predicted by GD and phenomenological MHD models and FA-MHD simulations, as required qualitatively by observations. The GD and FA-MHD predictions err qualitatively, predicting either constant or decreasing a(sub s), with decreasing M(sub A). This qualitative difference between quasi- perpendicular MHD and FA-MHD simulations is direct evidence for a(sub s), depending on the magnetic field orientation Theta. The enhancement factor over the phenomenological MHD predictions at MA approx. 2.4 agrees quantitatively with one observatiorial estimate. A linear relationship is found between the magnetosheath thickness and X, modified both quantitatively and intrinsically by MHD effects from the GD result. The MHD and GD results agree in the high M(sub A) limit. An MHD theory is developed for a(sub s), restricted to sufficiently perpendicular Theta and high sonic Mach numbers M(sub s). It explains the simulation results with excellent accuracy. Observational and further simulation testing of this MHD theory, and of its predicted M(sub A), Theta, and M(sub s) effects, is desirable.
NASA Astrophysics Data System (ADS)
Weisberg, Robert H.; Zheng, Lianyuan
2008-12-01
We provide a dynamics-based comparison on the results from three-dimensional and two-dimensional simulations of hurricane storm surge. We begin with the question, What may have occurred in the Tampa Bay, Florida vicinity had Hurricane Ivan made landfall there instead of at the border between Alabama and Florida? This question is explored using a three-dimensional, primitive equation, finite volume coastal ocean model. The results show that storm surges are potentially disastrous for the Tampa Bay area, especially for landfalls located to the north of the bay mouth. The worst case among the simulations considered is for landfall at Tarpon Springs, such that the maximum wind is positioned at the bay mouth. Along with such regional aspects of storm surge, we then consider the dynamical balances to assess the importance of using a three-dimensional model instead of the usual, vertically integrated, two-dimensional approach to hurricane storm surge simulation. With hurricane storm surge deriving from the vertically integrated pressure gradient force tending to balance the difference between the surface and bottom stresses, we show that three-dimensional structure is intrinsically important. Two-dimensional models may overestimate (or underestimate) bottom stress, necessitating physically unrealistic parameterizations of surface stress or other techniques for model calibration. Our examination of the dynamical balances inherent to storm surges over complex coastal topography suggests that three-dimensional models are preferable over two-dimensional models for simulating storm surges.
MHD simulations of ram pressure stripping of a disk galaxy
NASA Astrophysics Data System (ADS)
Ramos, Mariana; Gomez, Gilberto
2015-08-01
The removal of the ISM of disk galaxies through ram pressure stripping (RPS) has been extensively studied in numerous simulations. These models show that this process has a significant impact on galaxy evolution (the truncation of the ISM will lead to a decrease in the star formation and the galaxy will become redder).Nevertheless, the role of the magnetic fields (MFs) on the dynamics of the gas in this process has been hardly studied, although the influence of magnetic fields on the large scale disk structure is well established. The presence of MFs produce a less compressible gas, thus increasing the scale height of the gas in the galaxy, that is, gas can be found farther away from the galactic potential well, which may lead to an easier removal of gas. We test this idea by performing a 3D MHD simulation of a disk galaxy that experiences RPS under the wind-tunnel approximation.
NASA Technical Reports Server (NTRS)
Gann, R. C.; Chakravarty, S.; Chester, G. V.
1978-01-01
Monte Carlo simulation, lattice dynamics in the harmonic approximation, and solution of the hypernetted chain equation were used to study the classical two-dimensional one component plasma. The system consists of a single species of charged particles immersed in a uniform neutralizing background. The particles interact via a l/r potential, where r is the two dimensional separation. Equations of state were calculated for both the liquid and solid phases. Results of calculation of the thermodynamic functions and one and two particle correlation functions are presented.
NASA Technical Reports Server (NTRS)
Denton, R.; Sonnerup, B. U. O.; Swisdak, M.; Birn, J.; Drake, J. F.; Heese, M.
2012-01-01
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%.
Ohsuga, Ken; Mineshige, Shin
2011-07-20
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.
H. Basagaoglu; Meakin, P.; S. Succi; Redden, George D; T.R. Ginn
2008-05-01
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.
NASA Astrophysics Data System (ADS)
Chung, Tracy N. H.; Liu, Chun-Ho
2013-07-01
Flow resistance, ventilation, and pollutant removal for idealized two-dimensional (2D) street canyons of different building-height to street-width (aspect) ratios AR are examined using the friction factor f, air exchange rate (ACH), and pollutant exchange rate (PCH), respectively, calculated by large-eddy simulation (LES). The flows are basically classified into three characteristic regimes, namely isolated roughness, wake interference, and skimming flow, as functions of the aspect ratios. The LES results are validated by various experimental and numerical datasets available in the literature. The friction factor increases with decreasing aspect ratio and reaches a peak at AR = 0.1 in the isolated roughness regime and decreases thereafter. As with the friction factor, the ACH increases with decreasing aspect ratio in the wake interference and skimming flow regimes, signifying the improved aged air removal for a wider street canyon. The PCH exhibits a behaviour different from its ACH counterpart in the range of aspect ratios tested. Pollutants are most effectively removed from the street canyon with AR = 0.5. However, a minimum of PCH is found nearby at AR = 0.3, at which the pollutant removal is sharply weakened. Besides, the ACH and PCH are partitioned into the mean and turbulent components to compare their relative contributions. In line with our earlier Reynolds-averaged Navier-Stokes calculations (Liu et al., Atmos Environ 45:4763-4769, 2011), the current LES shows that the turbulent components contribute more to both ACH and PCH, consistently demonstrating the importance of atmospheric turbulence in the ventilation and pollutant removal for urban areas.
Judi, David R; Mcpherson, Timothy N; Burian, Steven J
2009-01-01
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.
Final Report: "Large-Eddy Simulation of Anisotropic MHD Turbulence"
Zikanov, Oleg
2008-06-23
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.
NASA Astrophysics Data System (ADS)
Passos, D. M. D. C.; Charbonneau, P.
2014-12-01
The steady advance in computer power has finally enabled us to explore the solar dynamo problem by means of 3D global magnetohydrodynamical (MHD) simulations of the convection zone.Using the EULAG-MHD code, we have succeeded in producing simulations of the Sun's magnetic activity cycles that resemble the observed evolutionary patterns of the large-scale solar magnetic field. In these simulations the anelastic ideal MHD equations are solved in a thick, rotating shell of electrically conducting fluid, under solar-like stratification and thermal forcing. Since these simulations are fully dynamical in all time and spatial resolved scales, they achieve highly turbulent regimes and naturally produce variable amplitude solutions.We have recently been able to produce a simulation that spans for 1650 years and that produced 40 complete sunspot like cycles, the longest of its kind so far.This allows to perform statistical studies and establish direct comparisons with the observed solar cycle. Some of the main similarities and differences between the statistical properties of simulated and observed cycles are presented here (e.g. evidence for Gnevyshev-Ohl patterns, Gleissberg modulation or hemispheric coupling). Additionally, by studying the behaviour of the large scale flows in the simulation (differential rotation and meridional circulation) we also find evidence for solar cycle modulation of the deep equatorward flow in the meridional circulation. This result is briefly discussed as well as its implications for current helioseismic measurement methodologies and for classical kinematic mean-field flux transport dynamo simulations.
NASA Astrophysics Data System (ADS)
Forjan, Gary F.
2009-06-01
Explaining the nature of the million degree solar corona is a question that has been challenging astrophysicists for over 60 years. While many theories have been proposed to explain the nature of the heating mechanism, there is as yet no single answer to this question. An important step toward finding a solution would be to first determine where in the atmosphere the heating is occurring, for this would narrow the different theoretical possibilities for its cause. >From an observational standpoint, recent measurements by instruments on the Solar and Heliospheric Observatory (SOHO) and Transition Region and Coronal Explorer (TRACE) spacecraft revealed that many coronal loops in active regions on the sun are nearly isothermal in their coronal parts. Loop modeling using pseudo-stereoscopic methods applied to SOHO EIT data indicated that temperature gradients were much smaller than predicted from scaling laws. From these and other observations, some authors conclude that the heating results from processes operating in the chromospheric and transition regions. On the other hand, many observed loop properties may be explained by assuming that the heating mechanism is due to the idea of tangled magnetic fields combined with a growing instability that becomes turbulent and releases impulsive energy through magnetic reconnection. Some authors claim that these energy releases occur at higher altitudes in the corona and are responsible for supplying the majority of coronal heating. Clearly, current observations along with numerical modeling results are interpreted differently depending on the researcher and vigorous debate continues over the nature of the heating process and whether it is located near the chromosphere/lower transition region or in the corona. In this work we attempt to determine if there are observational discriminators derived through computer modeling that can distinguish where the heating occurs. To accomplish this we first use an astrophysical magneto-hydrodynamics computer code to model a solar flux tube having the physical conditions of a one million degree quiet sun corona. A series of experiments is then performed in which energy of various durations and peak intensities is injected at different locations along the flux tube. These experiments are evolved over time and the differences in the temperature, density and velocity profiles are observed. In performing the simulations, the details of the energy transport processes including thermal conduction, convection, radiative cooling, and the nature of the heating sources are studied. The purpose in examining these processes is that they give insight into the validity of various assumptions used by other authors in their analytical models of the corona. It is expected that the determination of the positional and temporal characteristics of the heating will lead to an understanding of the exact physical process responsible for the heating. Most work currently being done in coronal modeling is accomplished with limited one-dimensional codes that do not include a magnetic field. The primary justification for using such codes is that thermal conduction is constrained to operate only along the magnetic field lines. Our work uses a two-dimensional code and includes a magnetic field. This is more physically realistic and allows for the examination of any interaction between the plasma and the magnetic field. In the course of performing these experiments, a major computational goal was to develop the computer code needed to correctly model conduction only along the field lines and quantitatively compare the effects of isotropic vs. magnetic field-aligned thermal conduction on the evolution of the plasma in the flux tube. The results indicate that assuming all conduction is along the loop axis in one-dimensional loop models is more accurate than assuming isotropic conduction in multi-dimensional models. However, there are differences between the one-dimensional and two-dimensional models. Our work has produced three main results. First, we developed the techniques
F. Robin; H. Jacobs; O. Homan; A. Stemmer; W. Bächtold
2000-01-01
We have investigated the cross-sectional electric field and potential distribution of a cleaved n+-InP\\/InGaAsP\\/p+-InP p-i-n laser diode using Kelvin probe force microscopy (KFM) with a lateral resolution reaching 50 nm. The powerful characterization capabilities of KFM were compared with two-dimensional (2D) physics-based simulations. The agreement between simulations and KFM measurements regarding the main features of the electric field and potential
MHD Simulations of the Initiation of Coronal Mass Ejections
NASA Astrophysics Data System (ADS)
Fan, Yuhong; Chatterjee, Piyali
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.
NASA Technical Reports Server (NTRS)
Stagliano, T. R.; Witmer, E. A.; Rodal, J. J. A.
1979-01-01
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.
High Resolution Simulations of Relativistic Hydrodynamic and MHD Turbulence
NASA Astrophysics Data System (ADS)
Zrake, Jonathan; MacFadyen, A.
2013-01-01
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.
Mingyu Lu; Meng Lv; Arif A. Ergin; Balasubramaniam Shanker; Eric Michielssen
2004-01-01
Time domain boundary integrals are used to impose global transparent boundary conditions in two-dimensional finite difference time domain solvers. Augmenting classical methods for imposing these conditions with the multilevel plane wave time domain scheme reduces the computational cost of enforcing a global transparent boundary condition from O($\\\\tilde Ns^{2 $\\\\tilde Nt^{2) to O($\\\\tilde N$s $\\\\tilde N$t log $\\\\tilde N$s log $\\\\tilde
Mingyu Lu; Meng Lv; Arif A. Ergin; Balasubramaniam Shanker; Eric Michielssen
2004-01-01
Time domain boundary integrals are used to impose global transparent boundary conditions in two-dimensional finite difference time domain solvers. Augmenting classical methods for imposing these conditions with the multilevel plane wave time domain scheme reduces the computational cost of enforcing a global transparent boundary condition from O($\\\\tilde N^{s^{2}}$$\\\\tilde N^{t^{2}}$) to O($\\\\tilde N$s$\\\\tilde N$t log $\\\\tilde N$s log $\\\\tilde N$t); here
NASA Astrophysics Data System (ADS)
Hur, Min Sup; Wurtele, Jonathan S.
2009-04-01
Focusing of an intense laser pulse produced by backward Raman pulse amplification (BRA) has been numerically studied using a two-dimensional, axisymmetric kinetic model. The two-dimensional averaged particle-in-cell (aPIC) simulation assumes slowly varying field envelopes and is comprised of one-dimensional sub-models that are coupled radially through laser diffraction. A converging 33 TW seed pulse was amplified up to 1 PW. The focusing of the seed pulse, even when particle trapping was important, was maintained. It was also found that the focusing properties of the pulse tail can lead to some rewidening of the longitudinal pulse duration and some ideas for eliminating this effect were suggested. Simulations performed for various plasma densities and temperatures exhibited robust amplification and pulse shortening.
Pete Riley; J. T. Gosling; V. J. Pizzo
1997-01-01
Using a hydrodynamic simulation, we have studied the two-dimensional (symmetry in the azimuthal direction) evolution of a fast, high-pressure coronal mass ejection (CME) ejected into a solar wind with latitudinal variations similar to those observed by Ulysses. The latitudinal structure of the ambient solar wind in the meridional plane is approximated by two zones: At low latitudes (>20Â°) the solar
R. Matsumoto; T. Tajima; M. Kaisig; K. Shibata; Y. Ishido; S. Tsuneta; G Kawai; H. Kurokawa; M. Akioka; L. Acton; K. Strong; N. Nitta
1992-01-01
The soft X-ray telescope on the Yohkoh mission enabled us to observe the evolution of emerging flux regions (EFR) in coronal X-rays with high spatial and temportal resolution. Futhermore, we now have enough computing capability to perform three-dimensional MHD simulation of EFRs with sufficient spacial resolution to study details of the flux emergence process. These new tools provide the opportunity
Three-dimensional MHD Simulations of Radiatively Inefficient Accretion Flows
Igor V. Igumenshchev; Ramesh Narayan; Marek A. Abramowicz
2003-04-09
We present three-dimensional MHD simulations of rotating radiatively inefficient accretion flows onto black holes. In the simulations, we continuously inject magnetized matter into the computational domain near the outer boundary, and we run the calculations long enough for the resulting accretion flow to reach a quasi-steady state. We have studied two limiting cases for the geometry of the injected magnetic field: pure toroidal field and pure poloidal field. In the case of toroidal field injection, the accreting matter forms a nearly axisymmetric, geometrically-thick, turbulent accretion disk. The disk resembles in many respects the convection-dominated accretion flows found in previous numerical and analytical investigations of viscous hydrodynamic flows. Models with poloidal field injection evolve through two distinct phases. In an initial transient phase, the flow forms a relatively flattened, quasi-Keplerian disk with a hot corona and a bipolar outflow. However, when the flow later achieves steady state, it changes in character completely. The magnetized accreting gas becomes two-phase, with most of the volume being dominated by a strong dipolar magnetic field from which a thermal low-density wind flows out. Accretion occurs mainly via narrow slowly-rotating radial streams which `diffuse' through the magnetic field with the help of magnetic reconnection events.
Preliminary analysis of the dynamic heliosphere by MHD simulations
Washimi, H.; Zank, G. P.; Tanaka, T.
2006-09-26
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.
Combis, Patrick; Cormont, Philippe; Hebert, David; Robin, Lucile; Rullier, Jean-Luc; Gallais, Laurent
2012-11-19
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.
NASA Astrophysics Data System (ADS)
Lei, Jie; Zhu, Da-Peng; Xu, Ming-Chun; Hu, Shu-Jun
2015-10-01
By applying the on-site Coulomb interaction corrections on the anion:2p and the cation:3d electrons, we find that the GGA + U approach can completely compensate the underestimation of band gap of ZnO and GaN, two wide band gap semiconductors. Based on such approach, we investigate the electronic structure of ZnO/GaN (0001) heterostructure, particularly for the two dimensional electron gas formed near the polar interface. The polarization difference between ZnO and GaN induces the surface charge, resulting in the accumulation of band electrons on the N-polar interface.
Two-dimensional simulation of large-area InGaAs/InP p-i-n photodiodes
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
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.
MHD simulation of RF current drive in MST
Hendries, E. R.; Anderson, J. K.; Forest, C. B.; Reusch, J. A.; Seltzman, A. H.; Sovinec, C. R. [University of Wisconsin, Madison WI (United States); Diem, S. [Oak Ridge National Laboratory, Oak Ridge TN (United States); Harvey, R. W. [CompX, Del Mar, CA (United States)
2014-02-12
Auxiliary heating and current drive using RF waves such as the electron Bernstein wave (EBW) promises to advance the performance of the reversed field pinch (RFP). In previous computational work [1], a hypothetical edge-localized current drive is shown to suppress the tearing activity which governs the macroscopic transport properties of the RFP. The ideal conditions for tearing stabilization include a reduced toroidal induction, and precise width and radial position of the Gaussian-shaped external current drive. In support of the EBW experiment on the Madison Symmetric Torus, an integrated modeling scheme now incorporates ray tracing and Fokker-Plank predictions of auxiliary current into single fluid MHD. Simulations at low Lundquist number (S ? 10{sup 4}) generally agree with the previous work; significantly more burdensome simulations at MST-like Lundquist number (S ? 3×10{sup 6}) show unexpected results. The effect on nonlinearly saturated current profile by a particular RF-driven external force decreases in magnitude and widens considerably as the Lundquist number increases toward experimental values. Simulations reproduce the periodic current profile relaxation events observed in experiment (sawteeth) in the absence of current profile control. Reduction of the tearing mode amplitudes is still observable; however, reduction is limited to periods between the large bursts of magnetic activity at each sawtooth. The sawtoothing pattern persists with up to 10 MW of externally applied RF power. Periods with prolonged low tearing amplitude are predicted with a combination of external current drive and a reduced toroidal loop voltage, consistent with previous conclusions. Finally, the resistivity profile is observed to have a strong effect on the optimal externally driven current profile for mode stabilization.
Dayside reconnection in 3D global Hall MHD numerical simulations
NASA Astrophysics Data System (ADS)
Lin, L.; Germaschewski, K.; Bhattacharjee, A.; Maynard, K.; Sullivan, B. P.; Raeder, J.
2012-12-01
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.
Observations and MHD Simulations for a Shocked Magnetotail
NASA Astrophysics Data System (ADS)
Zhou, X.; Zhou, X. Z.; Angelopoulos, V.; Raeder, J.; Oliveira, D.; Shi, Q.
2014-12-01
Recent studies disclosed that interplanetary shocks not only raise global auroral activity, but also cause significant tail disturbances, ranging from ULF wave excitation to abrupt cross-tail current sheet thinning and current density increase, generation of burst bulk flows and dipolarization fronts, and to magnetic reconnection enhancement. In addition, shocks can also cause significant deformation of the magnetotail at ~60 Re and beyond. In this paper we study a shock event using ARTEMIS in situ observations and OpenGGCM MHD simulations. The two ARTEMIS spacecraft were located near the tail current sheet and lobe center at (-60, 1, -5Re_GSM) when the shock arrived and recorded an abrupt tail compression leading to significant enhancements in the plasma density, temperature, magnetic field strength, and cross-tail current density, as well as to tailward flows. However, ~10 min later, the spacecraft entered the sheath solar wind unexpectedly. Two hypotheses are considered: either the tail was cut off by the high solar wind ram pressure (~25-30 nPa), or the compressed tail was pushed aside by the appreciable Vy solar wind flow component imposed by the shock. OpenGGMC simulation results confirmed the second hypothesis and disclosed that for this event the magnetic pressure played a dominant role at X=-60 Re for the compression. In addition to the shock normal direction and shock compression, the anisotropic (transverse) magnetic pressure also contributed to the significant reduction of the lobe Y dimension. Therefore, during this 10 min interval, the lobe center moved dawnward by ~12 Re and the tail width in Y was reduced from 40 to 26 Re, which eventually exposed ARTEMIS to the sheath solar wind. Comparisons of plasma and magnetic parameters between ARTEMIS in situ observations and simulations showed a satisfied consistence.
NASA Technical Reports Server (NTRS)
Stordal, F.; Isaksen, I. S. A.; Horntveth, K.
1985-01-01
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.
Sandvik, Anders W.
2008-09-19
A two-dimensional lattice hard-core boson system with a small fraction of bosonic or fermionic impurities is studied. The impurity hopping and interactions are identical to those of the dominant bosons, so that effects due to quantum statistics can be isolated. A quantum Monte Carlo scheme is developed in which bosonic paths are sampled and the impurities are introduced at the level of summing over permutation cycles. For both types of impurities, an anomaly in the effective impurity interaction energy is found at the Kosterlitz-Thouless temperature; it changes from attractive for T>T{sub KT} to repulsive for T
Relativistic MHD simulations of poynting flux-driven jets
Guan, Xiaoyue; Li, Hui; Li, Shengtai
2014-01-20
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 (?10{sup 3} 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.
NASA Astrophysics Data System (ADS)
Ambrose, M. C.; Stamps, R. L.
2013-05-01
The strength of perpendicular anisotropy is known to drive the spin reorientation in thin magnetic films. Here, we consider the effect different order anisotropies have on two phase transitions: the spin reorientation and the orientational order transitions. We find that the relative magnitude of different order anisotropies can significantly enhance or suppress the degree to which the system reorients. Specifically, Monte Carlo simulations reveal significant changes in the cone angle and planar magnetization. In order to facilitate rapid computation, we have developed a stream processing technique, suitable for use on graphics processing unit (GPU) systems, for computing the transition probabilities in two-dimensional systems with dipole interactions.
Giannakis, Georgios
be modeled as a sum of sinu- soids (SOS), and has been widely used to simulate Rayleigh-fading communication the shadowing process. Three methods to fit the PSD of the simulated process to the true channel's PSD
Abramavicius, Darius; Mukamel, Shaul
2010-01-01
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
Maglaveras, N; Offner, F; van Capelle, F J; Allessie, M A; Sahakian, A V
1995-01-01
A two-dimensional anisotropic model of cardiac ventricular muscle was used to study the effects of discontinuities (barriers), such as dead cells or high-resistance areas, on longitudinal plane-wave propagation. Problems in propagation appear when long barriers become thicker and their spacing closer. Short barriers with large widths and small spacing also cause propagation disturbances and significant delays in their vicinity. If the plane wave front propagates through the barriers, the velocity returns to near normal within one-length constant away from the end of the barrier region. For a funnel-like structure, an opening of 13 cells should exist for longitudinal plane wave propagation. For smaller openings, the ratio of openings required for propagation to occur when traveling from a narrow to a wider area of tissue is proportional to the anisotropy ratio, which can cause unidirectional block. Tortuosity, created by spatial distribution of dead cell barriers, can facilitate propagation by changing the effective impedance the wave front sees, and can create multiple local delays, which may result in discrepancies when measuring propagation velocity. PMID:7897334
Bychkov, Yu. I. Yampolskaya, S. A.; Yastremskii, A. G.
2013-05-15
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.
NASA Astrophysics Data System (ADS)
Yeh, Shu-Hao; Kais, Sabre
2014-03-01
The Fenna-Matthews-Olson (FMO) complex in green sulfur bacteria funnels the excitation energy from the outer antenna system to the reaction center. FMO is an important system for studying the excitonic energy transfer in biological system including photosynthesis. Recently crystallographic studies have confirmed the existence of an `extra' bacteriochlorophyll (8-BChls), this additional BChl has been suggested to act as a linker to the baseplate. To investigate the role of this eighth BChl, we have simulated the two-dimensional electronic spectrum of theholo-form (8 BChls) of the FMO complex and compared it to its apo-form (7-BChls). Due to the comparable energy scale of the transition dipole coupling and the bath reorganization energy we have applied the hierarchy equation of motion (HEOM) to calculate the third order optical response functions, which are the crucial components to simulate the two-dimensional electronic spectra. Our simulated spectra show good agreement with previously published experimental studies; we have extracted dynamic details for the determination of energy transfer pathway in both forms.
Szabó-Plánka, Terézia; Nagy, Nóra Veronika; Rockenbauer, Antal; Korecz, László
2002-07-01
Twelve ESR-active (and one inactive) copper(II) complexes of L-histidylglycine (HL) were characterized via their formation (micro)constants and ESR parameters obtained by two-dimensional ESR spectroscopic evaluation in aqueous solution. In strongly acidic media, the ligand is coordinated through its N-terminal donor groups: the complex [CuLH(2)](3+) involves monodentate imidazole binding, whereas [CuLH](2+) involves bidentate ligation through the amino and imidazole N atoms. This histamine-like bonding mode also predominates in the isomers of [CuL(2)], formed at ligand excess near pH 7: in the major 4N isomer, both ligands occupy two equatorial sites, while in the 3N isomer, the second dipeptide is coordinated equatorially by the amino and axially by the imidazole groups. At above pH 3-4, deprotonation of the peptide group also starts: in approximately 60% of the molecules of [CuL](+), the peptide group is deprotonated, while in the minor isomer histamine-like coordination occurs. At higher pH, the active dimer [Cu(2)L(2)H(-2)], the mixed hydroxo complexes (the inactive [Cu(2)L(2)H(-3)](-) and the active [CuLH(-2)](-)), and the bis complexes [CuL(2)H](+) and [CuL(2)H(-1)](-) all involve tridentate equatorial ligation of the backbone by the amino and deprotonated peptide N and the carboxylate O atoms. In the active dimer, the neutral imidazole groups form bridges between CuLH(-1) units. In [CuL(2)H](+), the second ligand is bound equatorially via its imidazole group; in [CuL(2)H(-1)](-), the L ligand occupies the fourth equatorial site and an axial site through its amino and imidazole N atoms, respectively. PMID:12079468
NASA Astrophysics Data System (ADS)
Toth, G.; Daldorff, L. K. S.; Jia, X.; Gombosi, T. I.; Lapenta, G.
2014-12-01
We have recently developed a new modeling capability to embed theimplicit Particle-in-Cell (PIC) model iPIC3D into the BATS-R-USmagnetohydrodynamic model. The PIC domain can cover the regions wherekinetic effects are most important, such as reconnection sites. TheBATS-R-US code, on the other hand, can efficiently handle the rest ofthe computational domain where the MHD or Hall MHD description issufficient. As one of the very first applications of the MHD-EPICalgorithm (Daldorff et al. 2014, JCP, 268, 236) we simulate theinteraction between Jupiter's magnetospheric plasma with Ganymede'smagnetosphere, where the separation of kinetic and global scalesappears less severe than for the Earth's magnetosphere. Because theexternal Jovian magnetic field remains in an anti-parallel orientationwith respect to Ganymede's intrinsic magnetic field, magneticreconnection is believed to be the major process that couples the twomagnetospheres. As the PIC model is able to describe self-consistentlythe electron behavior, our coupled MHD-EPIC model is well suited forinvestigating the nature of magnetic reconnection in thisreconnection-driven mini-magnetosphere. We will compare the MHD-EPICsimulations with pure Hall MHD simulations and compare both modelresults with Galileo plasma and magnetic field measurements to assess therelative importance of ion and electron kinetics in controlling theconfiguration and dynamics of Ganymede's magnetosphere.
Transparent Boundary Conditions for MHD Simulations in Stratified Atmospheres
A. Dedner; D. Kröner; I. L Sofronov; M. Wesenberg
2001-01-01
In this paper we discuss a method of deriving artificial nonreflecting boundary conditions for systems of conservation laws. We focus on an application from solar physics. The governing equations are the equations of ideal compressible magnetohydrodynamics (MHD), which are solved in a gravitationally stratified atmosphere. We derive the necessary equations, discuss implementational aspects, and show the effectiveness and efficiency of
A 3D Global MHD Simulation of the Saturnian Magnetosphere
K. C. Hansen; D. L. Dezeeuw; T. I. Gombosi; C. P. T. Groth; K. G. Powell
1998-01-01
The recent launch of the Cassini spacecraft and the continued planning of its tour of the Saturnian system makes the development of predictive models and analysis tools very important. We present the results of a 3D global magnetohydrodynamic (MHD) model of the magnetosphere of Saturn as a first step in developing a detailed model which can be used for both
Extragalactic jets with helical magnetic fields: relativistic MHD simulations
NASA Astrophysics Data System (ADS)
Keppens, R.; Meliani, Z.; van der Holst, B.; Casse, F.
2008-08-01
Context: Extragalactic jets are judged to harbor dynamically important, organized magnetic fields that presumably aid in the collimation of the relativistic jet flows. Aims: We here explore the morphology of AGN jets pervaded by helical field and flow topologies by means of grid-adaptive, high-resolution numerical simulations. We concentrate on morphological features of the bow shock and the jet beam behind the Mach disk, for various jet Lorentz factors and magnetic field helicities. We investigate the influence of helical magnetic fields on jet beam propagation in an overdense external medium. We adopt a special relativistic magnetohydrodynamic (MHD) viewpoint on the shock-dominated AGN jet evolution. Due to the adaptive mesh refinement (AMR), we can concentrate on the long-term evolution of kinetic energy-dominated jets, with beam-averaged Lorentz factor ? ? 7, as they penetrate denser clouds. These jets have near-equipartition magnetic fields (with the thermal energy) and radially varying ?(R) profiles within the jet radius R
RANS Simulations of the Tilted Rig Experiment:A Two-dimensional Rayleigh-Taylor Instability Case
NASA Astrophysics Data System (ADS)
Denissen, Nicholas; Rollin, Bertran; Reisner, Jon; Andrews, Malcolm
2012-11-01
Modeling turbulent mixing due to unstable density stratification is of fundamental interest in many multiphysics applications. RANS models remain the tool of choice for efficient estimates of the effects of turbulence on complex problems. While many RANS models have been validated for canonical Rayleigh-Taylor turbulence, applications of interest often have non-planar/dynamic interfaces. This presentation will address the ability of a multispecies, compressible, turbulence model to compute RT mixing on a moving interface. The simulations are based on the tilted rocket-rig experiments designed to study mixing of fluids by the Rayleigh-Taylor instability. In this experiment, a tank containing two fluids of different densities is accelerated downward with the rig inclined by a few degrees off vertical. The RANS simulations are be compared to experiments, direct numerical simulations and large eddy simulations to analyze the model's ability to capture 2D flow features.
3D MHD Free Surface Fluid Flow Simulation Based on Magnetic-Field Induction Equations
California at Los Angeles, University of
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
3D MHD free surface fluid flow simulation based on magnetic-field induction equations
Abdou, Mohamed
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
Chacon-Golcher, Edwin; Bowers, Kevin J.
2006-03-15
A two-dimensional, three-velocity particle-in-cell with Monte Carlo collisions (MCC) gun code is under development at LANSCE to study surface conversion H{sup -} ion source physics from a first-principles approach. The code is electromagnetostatic and is based on a sine transform/tridiagonal matrix Poisson solver implemented in axisymmetric geometry. A filament discharge is simulated by the injection of seed electrons at a biased filament surface. These electrons drive the discharge through a collection of (presently 22) reactions implemented as a MCC package. The simulation region is rectangular with internal electrodes of arbitrary shape. Given the nature of the code, no ad hoc models are necessary to model sheath physics, diffusion across magnetic-field lines, ion extraction, or other plasma phenomena.
Gustavsen, Arlid; Kohler, Christian; Dalehaug, Arvid; Arasteh, Dariush
2008-12-01
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.
NASA Astrophysics Data System (ADS)
Gonzalez-Melchor, Minerva; Mendez, Arlette; Alejandre, Jose
2015-03-01
When the movement of particles is performed predominantly in two dimensions, the systems can be considered at a good extent as two-dimensional. For instance the lipids in a bilayer, micrometric particles in a quasi-two-dimensional colloidal suspension, colloids in a monolayer deposited on the air-water interface, and DNA complexes trapped at the water surface can be described at a first approach as bidimensional fluids. These systems are important for many applications in surface and colloidal science. In simulations where the explicit interface between liquid and vapor is present, the line tension can be directly computed. In this work we present molecular dynamics results obtained for the liquid/vapor coexistence curve of 2D Yukawa fluids and for the line tension. A comparison with the three-dimensional case is also presented.
NASA Astrophysics Data System (ADS)
Viridi, Sparisoma; Fauzi, Umar; Adelia
2010-12-01
Simulation of three grains investigating system stability using molecular dynamics method implementing Gear predictor-corrector algorithm of 5th order has been conducted. Linear spring-dashpot model and short range cohesive Coulomb-like force model are used as repeal and attractive force, respectively. Theoretical prediction, multiplied by a constant 0.02, agrees with the simulation results for lower layer consists of equal mass grains. Variations of mass of each grain in the lower layer and the results are also reported.
Yoon, E. S.; Chang, C. S., E-mail: cschang@pppl.gov [Princeton Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08543 (United States); Korea Advanced Institute of Science and Technology, Yuseong-gu, DaeJeon 305-701 (Korea, Republic of)
2014-03-15
An approximate two-dimensional solver of the nonlinear Fokker-Planck-Landau collision operator has been developed using the assumption that the particle probability distribution function is independent of gyroangle in the limit of strong magnetic field. The isotropic one-dimensional scheme developed for nonlinear Fokker-Planck-Landau equation by Buet and Cordier [J. Comput. Phys. 179, 43 (2002)] and for linear Fokker-Planck-Landau equation by Chang and Cooper [J. Comput. Phys. 6, 1 (1970)] have been modified and extended to two-dimensional nonlinear equation. In addition, a method is suggested to apply the new velocity-grid based collision solver to Lagrangian particle-in-cell simulation by adjusting the weights of marker particles and is applied to a five dimensional particle-in-cell code to calculate the neoclassical ion thermal conductivity in a tokamak plasma. Error verifications show practical aspects of the present scheme for both grid-based and particle-based kinetic codes.
Multidimensional MHD Simulations Of DSA Using AstroBEAR
NASA Astrophysics Data System (ADS)
Edmon, Paul; Jones, T.; Mitran, S.; Cunningham, A.; Frank, A.
2009-05-01
We present a modification to the AstroBEAR (Astronomical Boundary Embedded Adaptive Refinement) MHD code (Cunningham et. al. 2007) that allows it to treat time dependent Diffusive Shock Acceleration (DSA) of cosmic rays in multiple dimensions including dynamical feedback from the cosmic rays. Utilizing the power of Adaptive Mesh Refinement (AMR) in tandem with efficient methods for cosmic ray diffusion and advection, this allows us for the first time to explore the evolution of modified MHD shocks in more than one spatial dimension. Among the early applications of the code will be investigations of colliding and clumpy stellar winds, type II supernova remnants and cosmic ray driven instabilities. This work is supported at the University of Minnesota by NSF, NASA and the Minnesota Supercomputing Institute.
Modeling extreme (Carrington-type) space weather events using three-dimensional MHD code simulations
NASA Astrophysics Data System (ADS)
Ngwira, C. M.; Pulkkinen, A. A.; Kuznetsova, M. M.; Glocer, A.
2013-12-01
There is growing concern over possible severe societal consequences related to adverse space weather impacts on man-made technological infrastructure and systems. In the last two decades, significant progress has been made towards the modeling of space weather events. Three-dimensional (3-D) global magnetohydrodynamics (MHD) models have been at the forefront of this transition, and have played a critical role in advancing our understanding of space weather. However, the modeling of extreme space weather events is still a major challenge even for existing global MHD models. In this study, we introduce a specially adapted University of Michigan 3-D global MHD model for simulating extreme space weather events that have a ground footprint comparable (or larger) to the Carrington superstorm. Results are presented for an initial simulation run with ``very extreme'' constructed/idealized solar wind boundary conditions driving the magnetosphere. In particular, we describe the reaction of the magnetosphere-ionosphere system and the associated ground induced geoelectric field to such extreme driving conditions. We also discuss the results and what they might mean for the accuracy of the simulations. The model is further tested using input data for an observed space weather event to verify the MHD model consistence and to draw guidance for future work. This extreme space weather MHD model is designed specifically for practical application to the modeling of extreme geomagnetically induced electric fields, which can drive large currents in earth conductors such as power transmission grids.
Cosmic-ray pitch-angle scattering in imbalanced MHD turbulence simulations
Weidl, Martin S; Teaca, Bogdan; Schlickeiser, Reinhard
2015-01-01
Pitch-angle scattering rates for cosmic-ray particles in magnetohydrodynamic (MHD) simulations with imbalanced turbulence are calculated for fully evolving electromagnetic turbulence. We compare with theoretical predictions derived from the quasilinear theory of cosmic-ray diffusion for an idealized slab spectrum and demonstrate how cross helicity affects the shape of the pitch-angle diffusion coefficient. Additional simulations in evolving magnetic fields or static field configurations provide evidence that the scattering anisotropy in imbalanced turbulence is not primarily due to coherence with propagating Alfven waves, but an effect of the spatial structure of electric fields in cross-helical MHD turbulence.
Cosmic-Ray Pitch-Angle Scattering in Imbalanced MHD Turbulence Simulations
NASA Astrophysics Data System (ADS)
Weidl, Martin S.; Jenko, Frank; Teaca, Bogdan; Schlickeiser, Reinhard
2015-09-01
Pitch-angle scattering rates for cosmic-ray particles in MHD simulations with imbalanced turbulence are calculated for fully evolving electromagnetic turbulence. We compare with theoretical predictions derived from the quasilinear theory of cosmic-ray diffusion for an idealized slab spectrum and demonstrate how cross helicity affects the shape of the pitch-angle diffusion coefficient. Additional simulations in evolving magnetic fields or static field configurations provide evidence that the scattering anisotropy in imbalanced turbulence is not primarily due to coherence with propagating Alfvén waves, but an effect of the spatial structure of electric fields in cross-helical MHD turbulence.
Integrated Physics Advances in Simulation of Wave Interactions with Extended MHD Phenomena
Batchelor, Donald B; D'Azevedo, Eduardo; Bateman, Glenn; Bernholdt, David E; Berry, Lee A; Bonoli, P.; Bramley, R; Breslau, J.; Chance, M.; Chen, J.; Choi, M.; Elwasif, Wael R; Fu, GuoYong; Harvey, R. W.; Houlberg, Wayne A; Jaeger, Erwin Frederick; Jardin, S. C.; Keyes, David E; Klasky, Scott A; Kruger, Scott; Ku, Long-Poe; McCune, Douglas; Schissel, D.; Schnack, D.; Wright, J. C.
2007-06-01
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).
NASA Technical Reports Server (NTRS)
Fleming, Eric L.; Jackman, Charles H.; Considine, David B.
1999-01-01
We have adopted the transport scenarios used in Part 1 to examine the sensitivity of stratospheric aircraft perturbations to transport changes 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 residence time and reduced the magnitude of the negative perturbation response in total ozone. Increasing the stratospheric K(sub yy) increased the residence time and enhanced the global scale negative total ozone response. 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 results in a significantly weaker perturbation response, relative to the base case, throughout the stratosphere. We found a relatively minor model perturbation response sensitivity to the magnitude of K(sub yy) in the tropical stratosphere, and only a very small sensitivity to the magnitude of the horizontal mixing across the tropopause and to the strength of the mesospheric gravity wave drag and diffusion. These transport simulations also revealed a generally strong correlation between passive NO(sub y) accumulation and age of air throughout the stratosphere, such that faster transport rates resulted in a younger mean age and a smaller NO(y) mass accumulation. However, specific variations in K(sub yy) and mesospheric gravity wave strength exhibited very little NO(sub y)-age correlation in the lower stratosphere, similar to 3-D model simulations performed in the recent NASA "Models and Measurements" II analysis. The base model transport, which gives the most favorable overall comparison with inert tracer observations, simulated a global/annual mean total ozone response of -0.59%, with only a slightly larger response in the northern compared to the southern hemisphere. For transport scenarios which gave tracer simulations within some agreement with measurements, the annual/globally averaged total ozone response ranged from -0.45% to -0.70%. Our previous 1995 model exhibited overly fast transport rates, resulting in a global/annually averaged perturbation total ozone response of -0.25%, which is significantly weaker compared to the 1999 model. This illustrates how transport deficiencies can bias model simulations of stratospheric aircraft.
NASA Astrophysics Data System (ADS)
Acharya, Ram C.; Valocchi, Albert J.; Werth, Charles J.; Willingham, Thomas W.
2007-10-01
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.
Almarza, N. G. [Instituto de Química Física Rocasolano, CSIC, Serrano 119, E-28006 Madrid (Spain)] [Instituto de Química Física Rocasolano, CSIC, Serrano 119, E-28006 Madrid (Spain); Pekalski, J.; Ciach, A. [Institute of Physical Chemistry, Polish Academy of Sciences, 01-224 Warszawa (Poland)] [Institute of Physical Chemistry, Polish Academy of Sciences, 01-224 Warszawa (Poland)
2014-04-28
The triangular lattice model with nearest-neighbor attraction and third-neighbor repulsion, introduced by Pekalski, Ciach, and Almarza [J. Chem. Phys. 140, 114701 (2014)] is studied by Monte Carlo simulation. Introduction of appropriate order parameters allowed us to construct a phase diagram, where different phases with patterns made of clusters, bubbles or stripes are thermodynamically stable. We observe, in particular, two distinct lamellar phases—the less ordered one with global orientational order and the more ordered one with both orientational and translational order. Our results concern spontaneous pattern formation on solid surfaces, fluid interfaces or membranes that is driven by competing interactions between adsorbing particles or molecules.
NASA Astrophysics Data System (ADS)
Rhee, Hyop S.; Begg, Lester L.; Wetch, Joseph R.; Jang, Jong H.; Juhasz, Albert J.
An innovative pumped loop concept for 600 K space power system radiators utilizing direct contact heat transfer, which facilitates repeated startup/shutdown of the power system without complex and time-consuming coolant thawing during power startup, is under development. The heat transfer process with melting/freezing of Li in an NaK flow was studied through two-dimensional time-dependent numerical simulations to characterize and predict the Li/NaK radiator performance during startup (thawing) and shutdown (cold-trapping). Effects of system parameters and the criteria for the plugging domain are presented together with temperature distribution patterns in solid Li and subsequent melting surface profile variations in time.
NASA Astrophysics Data System (ADS)
Tahir, N. A.; Kim, V.; Lamour, E.; Lomonosov, I. V.; Piriz, A. R.; Rozet, J. P.; Stöhlker, Th.; Sultanov, V.; Vernhet, D.
2012-11-01
In this paper we report on two-dimensional numerical simulations of heating of a rotating, wheel shaped target impacted by the full intensity of the ion beam that will be delivered by the SPIRAL2 facility at Caen, France. The purpose of this work is to study heating of solid targets that will be used to strip the fast ions of SPIRAL2 to the required high charge state for the FISIC (Fast Ion-Slow Ion Collision) experiments. Strippers of aluminum with different emissivities and of carbon are exposed to high beam current of different ion species as oxygen, neon and argon. These studies show that carbon, due to its much higher sublimation temperature and much higher emissivity, is more favorable compared to aluminum. For the highest beam intensities, an aluminum stripper does not survive. However, problem of the induced thermal stresses and long term material fatigue needs to be investigated before a final conclusion can be drawn.
NASA Astrophysics Data System (ADS)
Noge, Hiroshi; Saito, Kimihiko; Sato, Aiko; Kaneko, Tetsuya; Kondo, Michio
2015-08-01
The performance of interdigitated back contact silicon heterojunction solar cells having overlapped p/i and n/i a-Si:H layers on the back has been investigated by two-dimensional simulation in comparison with the conventional cell structure having a gap between p/i and n/i layers. The results show that narrower overlap width leads to higher short circuit current and conversion efficiency, especially for poor heterojunction interface and thinner silicon substrate of the cells in addition to narrower uncovered width of p/i layer by a metal electrode. This is similar to the gap width dependence in the conventional cells, since both overlap and gap act as dead area for diffused excess carriers in the back contacts.
Nagata, Yuki; Mukamel, Shaul
2011-01-01
Using a classical simulation protocol for nonlinear optical signals, we predict the two-dimensional (2D) spectra of water near a monolayer of [1,2-dimytristoyl-sn-glycero-3-phosphatidylcholine] (DMPC) generated by three infrared and one visible probe pulses. Sum frequency generation 1D spectra show two peaks of the OH stretch representing two environments of near-bulk water non-adjacent to DMPC and top-layer water adjacent to DMPC. These peaks create a 2D pattern in the fourth-order signal. The asymmetric cross-peak pattern with respect to the diagonal line suggests coherence transfer from the higher to the lower frequency modes. The nodal lines in the imaginary part of the 2D spectrum show that the near-bulk water has fast spectral diffusion, resembling bulk water despite the orientation by the strong electrostatic field of DMPC. The top-layer water has slower spectral diffusion. PMID:21329386
NASA Astrophysics Data System (ADS)
Li, Hua-Bing; Jin, Li; Qiu, Bing
2008-11-01
To study two-dimensional red blood cells deforming in a shear Bow with the membrane nonuniform on the rigidity and mass, the membrane is discretized into equilength segments. The fluid inside and outside the red blood cell is simulated by the D2Q9 lattice Boltzmann model and the hydrodynamic forces exerted on the membrane from the inner and outer of the red blood cell are calculated by a stress-integration method. Through the global deviation from the curvature of uniform-membrane, we find that when the membrane is nonuniform on the rigidity, the deviation first decreases with the time increases and implies that the terminal profile of the red blood cell is static. To a red blood cell with the mass nonuniform on the membrane, the deviation becomes more large, and the mass distribution affects the profile of the two sides of the flattened red blood cell in a shear flow.
Resistive MHD and kinetic simulations of 2D magnetotail equilibria leading to reconnection onset
NASA Astrophysics Data System (ADS)
Merkin, V. G.; Sitnov, M. I.; Lyon, J.; Cassak, P.
2013-12-01
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.
NASA Astrophysics Data System (ADS)
Lisjak, A.; Liu, Q.; Zhao, Q.; Mahabadi, O. K.; Grasselli, G.
2013-10-01
Stress waves, known as acoustic emissions (AEs), are released by localized inelastic deformation events during the progressive failure of brittle rocks. Although several numerical models have been developed to simulate the deformation and damage processes of rocks, such as non-linear stress-strain behaviour and localization of failure, only a limited number have been capable of providing quantitative information regarding the associated seismicity. Moreover, the majority of these studies have adopted a pseudo-static approach based on elastic strain energy dissipation that completely disregards elastodynamic effects. This paper describes a new AE modelling technique based on the combined finite-discrete element method (FEM/DEM), a numerical tool that simulates material failure by explicitly considering fracture nucleation and propagation in the modelling domain. Given the explicit time integration scheme of the solver, stress wave propagation and the effect of radiated seismic energy can be directly captured. Quasi-dynamic seismic information is extracted from a FEM/DEM model with a newly developed algorithm based on the monitoring of internal variables (e.g. relative displacements and kinetic energy) in proximity to propagating cracks. The AE of a wing crack propagation model based on this algorithm are cross-analysed by traveltime inversion and energy estimation from seismic recordings. Results indicate a good correlation of AE initiation times and locations, and scaling of energies, independently calculated with the two methods. Finally, the modelling technique is validated by simulating a laboratory compression test on a granite sample. The micromechanical parameters of the heterogeneous model are first calibrated to reproduce the macroscopic stress-strain response measured during standard laboratory tests. Subsequently, AE frequency-magnitude statistics, spatial clustering of source locations and the evolution of AE rate are investigated. The distribution of event magnitude tends to decay as power law while the spatial distribution of sources exhibits a fractal character, in agreement with experimental observations. Moreover, the model can capture the decrease of seismic b value associated with the macrorupture of the rock sample and the transition of AE spatial distribution from diffuse, in the pre-peak stage, to strongly localized at the peak and post-peak stages, as reported in a number of published laboratory studies. In future studies, the validated FEM/DEM-AE modelling technique will be used to obtain further insights into the micromechanics of rock failure with potential applications ranging from laboratory-scale microcracking to engineering-scale processes (e.g. excavations within mines, tunnels and caverns, petroleum and geothermal reservoirs) to tectonic earthquakes triggering.
NASA Technical Reports Server (NTRS)
Fleming, Eric L.; Jackman, Charles H.; Considine, David B.; Stolarski, Richard S.
1999-01-01
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.
Perkins, L. J.; Logan, B. G.; Zimmerman, G. B.; Werner, C. J. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)] [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)
2013-07-15
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 × 10{sup 4} 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.
NASA Astrophysics Data System (ADS)
Elkaim, D.; Reggio, M.; Camarero, R.
1992-04-01
A numerical procedure to solve turbulent flow which makes use of the k-epsilon model is developed. The method is based on a control-volume finite-element method and an unstructured triangular domain discretization. The velocity-pressure coupling is addressed via the vorticity-streamfunction and special attention is given to the boundary conditions for vorticity. Wall effects are taken into account via wall functions or a low-Reynolds-number model. The latter is found to perform better in recirculation regions. Source terms of the k and epsilon transport equations are linearized in a particular way to avoid nonrealistic solutions. The vorticity and streamfunction discretized equations are solved in a coupled way to produce a faster and more stable computational procedure. Comparison between the numerical predictions and experimental data shows that the physics of the flow is correctly simulated.
Zhao, Bin; Wang, Shuxiao; Donahue, Neil M; Chuang, Wayne; Hildebrandt Ruiz, Lea; Ng, Nga L; Wang, Yangjun; Hao, Jiming
2015-02-17
We evaluate the one-dimensional volatility basis set (1D-VBS) and two-dimensional volatility basis set (2D-VBS) in simulating the aging of SOA derived from toluene and ?-pinene against smog-chamber experiments. If we simulate the first-generation products with empirical chamber fits and the subsequent aging chemistry with a 1D-VBS or a 2D-VBS, the models mostly overestimate the SOA concentrations in the toluene oxidation experiments. This is because the empirical chamber fits include both first-generation oxidation and aging; simulating aging in addition to this results in double counting of the initial aging effects. If the first-generation oxidation is treated explicitly, the base-case 2D-VBS underestimates the SOA concentrations and O:C increase of the toluene oxidation experiments; it generally underestimates the SOA concentrations and overestimates the O:C increase of the ?-pinene experiments. With the first-generation oxidation treated explicitly, we could modify the 2D-VBS configuration individually for toluene and ?-pinene to achieve good model-measurement agreement. However, we are unable to simulate the oxidation of both toluene and ?-pinene with the same 2D-VBS configuration. We suggest that future models should implement parallel layers for anthropogenic (aromatic) and biogenic precursors, and that more modeling studies and laboratory research be done to optimize the "best-guess" parameters for each layer. PMID:25581402
R. L. Fermo; J. F. Drake; M. Swisdak; K.-J. Hwang
2011-01-01
Island growth in Hall MHD simulations is consistent with our modelMerging plays an important role both in our simulations and in observationsStatistics of Cluster FTEs suggest the presence of many small FTEs
Two-Dimensional Colloidal Alloys
NASA Astrophysics Data System (ADS)
Law, Adam D.; Buzza, D. Martin A.; Horozov, Tommy S.
2011-03-01
We study the structure of mixed monolayers of large (3?m diameter) and small (1?m diameter) very hydrophobic silica particles at an octane-water interface as a function of the number fraction of small particles ?. We find that a rich variety of two-dimensional hexagonal super-lattices of large (A) and small (B) particles can be obtained in this system due to strong and long-range electrostatic repulsions through the nonpolar octane phase. The structures obtained for the different compositions are in good agreement with zero temperature calculations and finite temperature computer simulations.
MHD Simulation of Flare Experiment Jeffrey Kollasch, Prof. James F. Drake, Dr. Marc Swisdak
Anlage, Steven
MHD Simulation of Flare Experiment Jeffrey Kollasch, Prof. James F. Drake, Dr. Marc Swisdak-Universität Bochum, Germany [2] and PPPL [3] · Used massively parallel two-fluid code F3D [4] running on Franklin] Continuity Momentum Faraday's Law Acknowledgments: Jeffrey Kollasch gratefully acknowledges the advising
THE TURBULENT WARM IONIZED MEDIUM: EMISSION MEASURE DISTRIBUTION AND MHD SIMULATIONS
Wisconsin at Madison, University of
that sample the diffuse WIM. The distribution of EM sin jbj for the diffuse WIM sample is poorly characterized by a single normal distribution, but is extraordinarily well fit by a lognormal distribution, with hlog EM sinTHE TURBULENT WARM IONIZED MEDIUM: EMISSION MEASURE DISTRIBUTION AND MHD SIMULATIONS Alex S. Hill
DAYSIDE PROTON AURORA: COMPARISONS BETWEEN GLOBAL MHD SIMULATIONS AND IMAGE OBSERVATIONS
California at Berkeley, University of
DAYSIDE PROTON AURORA: COMPARISONS BETWEEN GLOBAL MHD SIMULATIONS AND IMAGE OBSERVATIONS J. BERCHEM Physics, University of California, Los Angeles, CA, USA 2Lockheed Martin Advanced Technology Center, Palo Alto, CA, USA 3 Space Sciences Laboratory, University of California, Berkeley, CA, USA 4 Southwest
Kato, Tsunehiko N.; Takabe, Hideaki, E-mail: kato-t@ile.osaka-u.ac.j [Institute of Laser Engineering, Osaka University, 2-6 Yamada-oka, Suita, Osaka 565-0871 (Japan)
2010-09-20
A two-dimensional particle-in-cell simulation is performed to investigate weakly magnetized perpendicular shocks with a magnetization parameter of {sigma} = 6 x 10{sup -5}, which is equivalent to a high Alfven Mach number M{sub A} of {approx}130. It is shown that current filaments form in the foot region of the shock due to the ion-beam-Weibel instability (or the ion filamentation instability) and that they generate a strong magnetic field there. In the downstream region, these current filaments also generate a tangled magnetic field that is typically 15 times stronger than the upstream magnetic field. The thermal energies of electrons and ions in the downstream region are not in equipartition and their temperature ratio is T{sub e}/T{sub i} {approx} 0.3-0.4. Efficient electron acceleration was not observed in our simulation, although a fraction of the ions are accelerated slightly on reflection at the shock. The simulation results agree very well with the Rankine-Hugoniot relations. It is also shown that electrons and ions are heated in the foot region by the Buneman instability (for electrons) and the ion-acoustic instability (for both electrons and ions). However, the growth rate of the Buneman instability is significantly reduced due to the relatively high temperature of the reflected ions. For the same reason, ion-ion streaming instability does not grow in the foot region.
Ozbilgin, M.M.; Dickerman, D.C.
1984-01-01
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)
NASA Astrophysics Data System (ADS)
Kato, Tsunehiko N.; Takabe, Hideaki
2010-09-01
A two-dimensional particle-in-cell simulation is performed to investigate weakly magnetized perpendicular shocks with a magnetization parameter of ? = 6 × 10-5, which is equivalent to a high Alfvén Mach number M A of ~130. It is shown that current filaments form in the foot region of the shock due to the ion-beam-Weibel instability (or the ion filamentation instability) and that they generate a strong magnetic field there. In the downstream region, these current filaments also generate a tangled magnetic field that is typically 15 times stronger than the upstream magnetic field. The thermal energies of electrons and ions in the downstream region are not in equipartition and their temperature ratio is T e/T i ~ 0.3-0.4. Efficient electron acceleration was not observed in our simulation, although a fraction of the ions are accelerated slightly on reflection at the shock. The simulation results agree very well with the Rankine-Hugoniot relations. It is also shown that electrons and ions are heated in the foot region by the Buneman instability (for electrons) and the ion-acoustic instability (for both electrons and ions). However, the growth rate of the Buneman instability is significantly reduced due to the relatively high temperature of the reflected ions. For the same reason, ion-ion streaming instability does not grow in the foot region.
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
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.
NASA Astrophysics Data System (ADS)
Maire, Pierre-Henri; Abgrall, Rémi; Breil, Jérôme; Loubère, Raphaël; Rebourcet, Bernard
2013-02-01
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.
MECHANISMS FOR MHD POYNTING FLUX GENERATION IN SIMULATIONS OF SOLAR PHOTOSPHERIC MAGNETOCONVECTION
Shelyag, S.; Mathioudakis, M.; Keenan, F. P.
2012-07-01
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.
Oblique MHD cosmic-ray modified shocks: Two-fluid numerical simulations
NASA Technical Reports Server (NTRS)
Frank, Adam; Jones, T. W.; Ryu, Dongsu
1991-01-01
We present the first results of time dependent, two-fluid, cosmic-ray (CR) modified, MHD shock simulations. The calculations were carried out with a new numerical code for 1-D ideal MHD. By coupling this code with the CR energy transport equation we can simulate the time-dependent evolution of MHD shocks including the acceleration of the CR and their feedback on the shock structures. We report tests of the combined numerical method including comparisons with analytical steady state results published earlier by Webb, as well as internal consistency checks for more general MHD CR shock structures after they appear to have converged to dynamical steady states. We also present results from an initial time dependent simulation which extend the parameter space domain of previous analytical models. These new results support Webb's suggestion that equilibrium oblique shocks are less effective than parallel shocks in the acceleration of CR. However, for realistic models of anisotropic CR diffusion, oblique shocks may achieve dynamical equilibrium on shorter timescale than parallel shocks.
Two-dimensional magnetohydrodynamic studies of implosion modes of nested wire array z-pinches
Huang, Jun; Ding, Ning, E-mail: ding-ning@iapcm.ac.cn; Xue, Chuang; Sun, Shunkai [Institute of Applied Physics and Computational Mathematics, Beijing 100088 (China)
2014-07-15
Implosion dynamics of nested wire arrays in (r, ?) geometry was studied with two-dimensional magnetohydrodynamic (2D MHD) simulations. Three different implosion modes are obtained by just changing the wire number of the outer array, when the other conditions, such as the initial radius, length, mass of each array, the wire number of the inner array, and the discharge voltage waveform, are fixed. Simulation results show that the effect of discrete wires, which cannot be described by the thin shell inductive model, will influence the distribution of current between the outer and inner arrays at the early stage, and the discrepancy between results from MHD and thin shell model increases with the interwire gap of the outer array.
NASA Astrophysics Data System (ADS)
Huang, Z.; Jia, X.; Rubin, M.; Fougere, N.; Gombosi, T. I.; Tenishev, V.; Combi, M. R.; Bieler, A. M.; Toth, G.; Hansen, K. C.; Shou, Y.
2014-12-01
We study the plasma environment of the comet Churyumov-Gerasimenko, which is the target of the Rosetta mission, by performing large scale numerical simulations. Our model is based on BATS-R-US within the Space Weather Modeling Framework that solves the governing multifluid MHD equations, which describe the behavior of the cometary heavy ions, the solar wind protons, and electrons. The model includes various mass loading processes, including ionization, charge exchange, dissociative ion-electron recombination, as well as collisional interactions between different fluids. The neutral background used in our MHD simulations is provided by a kinetic Direct Simulation Monte Carlo (DSMC) model. We will simulate how the cometary plasma environment changes at different heliocentric distances.
NASA Astrophysics Data System (ADS)
Marocchino, A.; Atzeni, S.; Schiavi, A.
2014-01-01
In some regions of a laser driven inertial fusion target, the electron mean-free path can become comparable to or even longer than the electron temperature gradient scale-length. This can be particularly important in shock-ignited (SI) targets, where the laser-spike heated corona reaches temperatures of several keV. In this case, thermal conduction cannot be described by a simple local conductivity model and a Fick's law. Fluid codes usually employ flux-limited conduction models, which preserve causality, but lose important features of the thermal flow. A more accurate thermal flow modeling requires convolution-like non-local operators. In order to improve the simulation of SI targets, the non-local electron transport operator proposed by Schurtz-Nicolaï-Busquet [G. P. Schurtz et al., Phys. Plasmas 7, 4238 (2000)] has been implemented in the DUED fluid code. Both one-dimensional (1D) and two-dimensional (2D) simulations of SI targets have been performed. 1D simulations of the ablation phase highlight that while the shock profile and timing might be mocked up with a flux-limiter; the electron temperature profiles exhibit a relatively different behavior with no major effects on the final gain. The spike, instead, can only roughly be reproduced with a fixed flux-limiter value. 1D target gain is however unaffected, provided some minor tuning of laser pulses. 2D simulations show that the use of a non-local thermal conduction model does not affect the robustness to mispositioning of targets driven by quasi-uniform laser irradiation. 2D simulations performed with only two final polar intense spikes yield encouraging results and support further studies.
NASA Astrophysics Data System (ADS)
Kanevce, Ana; Kuciauskas, Darius; Levi, Dean H.; Allende Motz, Alyssa M.; Johnston, Steven W.
2015-07-01
We use two-dimensional numerical simulations to analyze high spatial resolution time-resolved spectroscopy data. This analysis is applied to two-photon excitation time-resolved photoluminescence (2PE-TRPL) but is broadly applicable to all microscopic time-resolved techniques. By solving time-dependent drift-diffusion equations, we gain insight into carrier dynamics and transport characteristics. Accurate understanding of measurement results establishes the limits and potential of the measurement and enhances its value as a characterization method. Diffusion of carriers outside of the collection volume can have a significant impact on the measured decay but can also provide an estimate of carrier mobility as well as lifetime. In addition to material parameters, the experimental conditions, such as spot size and injection level, can impact the measurement results. Although small spot size provides better resolution, it also increases the impact of diffusion on the decay; if the spot size is much smaller than the diffusion length, it impacts the entire decay. By reproducing experimental 2PE-TRPL decays, the simulations determine the bulk carrier lifetime from the data. The analysis is applied to single-crystal and heteroepitaxial CdTe, material important for solar cells, but it is also applicable to other semiconductors where carrier diffusion from the excitation volume could affect experimental measurements.
Umeda, Takayuki Kidani, Yoshitaka; Matsukiyo, Shuichi; Yamazaki, Ryo
2014-02-15
Large-scale two-dimensional (2D) full particle-in-cell (PIC) 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{sub 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. The result suggests that these waves play a role in the modification of the dynamics of collisionless shocks through the interaction with shock front ripples.
Pak, K.; Tsang, L. [Department of Electrical Engineering, University of Washington, Box 352500, Seattle, Washington 98195-2500 (United States); Johnson, J. [The Ohio State University, 2015 Neil Avenue, Columbus, Ohio 43210 (United States)
1997-07-01
Numerical simulations exhibiting backscattering enhancement of electromagnetic waves from two-dimensional dielectric random rough surfaces (three-dimensional scattering problem) are presented. The Stratton{endash}Chu 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. The accuracy of the solution is assessed by comparing the bistatic scattering coefficients obtained from the SMCG and the matrix inversion method. Also, a sufficient sampling rate is established with respect to the dielectric constant below the rough-surface boundary. Numerical simulations are illustrated for moderate rms heights of 0.2 and 0.5 electromagnetic wavelengths with rms slopes of 0.5 and 0.7. The magnitude of the relative permittivity ranges from 3 to 7. With use of the SMCG method, scattered fields from a surface area of 256 square wavelengths (98,304 surface unknowns) are found. For a rms height of 0.5 wavelength and a correlation length of 1.0 wavelength, backscattering enhancement is observed in both co-polarization and cross polarization. However, in the case in which the rms height is 0.2 wavelength and the correlation length is 0.6 wavelength, backscattering enhancement is observed in cross polarization only. {copyright} 1997 Optical Society of America
NASA Astrophysics Data System (ADS)
Seki, Yusuke; Kandori, Akihiko
2007-06-01
We developed a two-dimensional gradiometer that detects the gradient of a magnetic field in two orthogonal directions to measure the biomagnetic signal in an unshielded environment. We based the gradiometer on a low-Tc superconducting quantum interference device (SQUID) and wire-wound pickup coil. The gradiometer we developed detects both the axial-second-order and planar-first-order gradient of a magnetic field. The experimental results revealed that its noise-reduction ratio (NRR) was 54 dB from 0.5 to 49 Hz and 14 dB (5 times) larger than that of the axial-second-order gradiometer. Moreover, by using the new gradiometer, we obtained a clear magnetocardiography (MCG) waveform in real time without averaging under an unshielded environment (noise level: 3.8 nT/\\sqrt{Hz} at 1 Hz; 150 pT/\\sqrt{Hz} at 10 Hz).
NASA Astrophysics Data System (ADS)
Liu, Hao-Ran; Ding, Hang
2015-08-01
We propose an approach to simulate flows with moving contact lines (MCLs) on curved substrates on a Cartesian mesh. The approach combines an immersed boundary method with a three-component diffuse-interface model and a characteristic MCL model. The immersed boundary method is able to accurately enforce the no-slip boundary condition at the solid surface, thereby circumventing the penetration of the gas and the liquid into the solid by convection. On the other hand, using the three-component diffuse-interface model can prevent the gas and liquid from infiltrating into the solid substrate through the diffusive fluxes during the interface evolution. A combination of these two methods appears to effectively conserve the mass of the phases in the computation. The characteristic MCL model not only allows the contact lines to move on the curved boundaries, but makes the gas-liquid interface to intersect the solid object at an angle in consistence with the prescribed contact angle, even with the variation of surface tangent at the solid substrate. We examine the performance of the approach through a variety of numerical experiments. The mass conservation and interface shapes at equilibrium were tested through the simulation of drop spreading on a circular cylinder. The dynamic behaviors of moving contact lines were validated by simulating the droplet spreading on a flat substrate, and we compared the numerical results against theoretical predictions and previous experimental observations. The method was also applied to the simulations of flows with curved boundaries and moving contact lines, such as drop impact on a sphere and water entry of a sphere. Finally, we studied the penetration process of a two-dimensional drop into a porous substrate that consists of a cluster of circular cylinders.
Second Core Formation and High Speed Jets: Resistive MHD Nested Grid Simulations
Masahiro N. Machida; Shu-ichiro Inutsuka; Tomoaki Matsumoto
2006-03-17
The stellar core formation and high speed jets driven by the formed core are studied by using three-dimensional resistive MHD nested grid simulations. Starting with a Bonnor-Ebert isothermal cloud rotating in a uniform magnetic field, we calculate the cloud evolution from the molecular cloud core (n = 10^6 cm^-3, r_c = 4.6 times 10^4 AU) to the stellar core (n \\simeq 10^23 cm^-3, r_c \\simeq 1 solar radius). We resolve cloud structure over 7 orders of magnitude in spatial extent and over 17 orders of magnitude in density contrast. For comparison, we calculate two models: resistive and ideal MHD models. Both models have the same initial condition, but the former includes dissipation process of magnetic field while the latter does not. The magnetic fluxes in resistive MHD model are extracted from the first core during 10^12 cm^-3 core (n \\simeq 10^20 cm^-3) in resistive MHD model is two orders of magnitude smaller than that in ideal MHD model. Since magnetic braking is less effective in resistive MHD model, rapidly rotating stellar core (the second core) is formed. After stellar core formation, the magnetic field of the core is largely amplified both by magneto-rotational instability and the shearing motion between the stellar core and ambient medium. As a consequence, high speed (simeq 45 km,s^-1) jets are driven by the second core, which results in strong mass ejection. A cocoon-like structure around the second core also forms with clear bow shocks.
Lai, Chintu
1977-01-01
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)
NASA Astrophysics Data System (ADS)
Sun, Yi; Timofeyev, Ilya
2014-05-01
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.
NASA Astrophysics Data System (ADS)
Nakagawa, Tomoko
2013-05-01
The ion entry into the wake behind an obstacle in the solar wind is studied using two-dimensional, electromagnetic full-particle simulations. A significant difference is found between the number of ions and electrons in the near wake, mainly due to the negative electric charge on the nightside surface of the obstacle. The ion acceleration toward the void is observed far from the position of the rarefaction wave expected in the self-similar solution. The velocity profile of the ions in the wake approaches the self-similar solution with finite ion temperature asymptotically until they reach the distance where the ions from both sides of the wake meet. The ions that entered from both sides are accelerated in the opposite directions. They raise the ion temperature and the pressure in the center of the wake, although each component remains cool when treated separately. The electron temperature appears nearly constant, except for the edge of the complete void of electrons. The large-scale obstacle and a slow solar wind are favorable conditions for a detection of well-accelerated ions near the nightside surface of the obstacle, because they have enough time to accelerate. The direction of the electric field in the wake seems consistent with the gradient of the electron pressure.
Liu Xiangmei; Song Yuanhong; Xu Xiang; Wang Younian
2011-08-15
A two-dimensional (2D) self-consistent fluid model is developed to describe the formation, subsequent growth, transport, and charging mechanisms of nanoparticles in a capacitively coupled silane discharge applied by two very high frequency (VHF) sources with phase shift. In this discharge process, large anions are produced by a series of chemical reactions of anions with silane molecules, while the lower limit of the initial nanoparticles are taken as large anions (Si{sub 12}H{sub 25}{sup -} and Si{sub 12}H{sub 24}{sup -}) to directly link the coagulation module with the nucleation module. And then, by using the coagulation module, the particle number density quickly decreases over several orders of magnitude, whereas the particle size strongly increases. We investigate in particular the growth of the nanoparticles ranging in size from {approx}1 to 50 nm in coagulation processes. The influences of controlled phase shifts between VHF (50 MHz) voltages on the electron density, electron temperature, nanoparticle uniformity, and deposition rate, are carefully studied. It is found from our simulation that the plasma density and nanoparticle density become center high and more uniform as the phase shift increases from 0 to 180 deg. Moreover, the role of phase-shift control in the silane discharge diluted with hydrogen gas is also discussed.
Bloch, Edward; Uddin, Nabil; Gannon, Laura; Rantell, Khadija; Jain, Saurabh
2015-01-01
Background Stereopsis is believed to be advantageous for surgical tasks that require precise hand-eye coordination. We investigated the effects of short-term and long-term absence of stereopsis on motor task performance in three-dimensional (3D) and two-dimensional (2D) viewing conditions. Methods 30 participants with normal stereopsis and 15 participants with absent stereopsis performed a simulated surgical task both in free space under direct vision (3D) and via a monitor (2D), with both eyes open and one eye covered in each condition. Results The stereo-normal group scored higher, on average, than the stereo-absent group with both eyes open under direct vision (p<0.001). Both groups performed comparably in monocular and binocular monitor viewing conditions (p=0.579). Conclusions High-grade stereopsis confers an advantage when performing a fine motor task under direct vision. However, stereopsis does not appear advantageous to task performance under 2D viewing conditions, such as in video-assisted surgery. PMID:25185439
NASA Astrophysics Data System (ADS)
Fan, Yu; Zou, Ying; Sun, Jizhong; Stirner, Thomas; Wang, Dezhen
2013-10-01
The influence of an applied magnetic field on plasma-related devices has a wide range of applications. Its effects on a plasma have been studied for years; however, there are still many issues that are not understood well. This paper reports a detailed kinetic study with the two-dimension-in-space and three-dimension-in-velocity particle-in-cell plus Monte Carlo collision method on the role of E ×B drift in a capacitive argon discharge, similar to the experiment of You et al. [Thin Solid Films 519, 6981 (2011)]. The parameters chosen in the present study for the external magnetic field are in a range common to many applications. Two basic configurations of the magnetic field are analyzed in detail: the magnetic field direction parallel to the electrode with or without a gradient. With an extensive parametric study, we give detailed influences of the drift on the collective behaviors of the plasma along a two-dimensional domain, which cannot be represented by a 1 spatial and 3 velocity dimensions model. By analyzing the results of the simulations, the occurring collisionless heating mechanism is explained well.
Chaudhuri, Saptarishi; Roy, Sanjukta; Unnikrishnan, C. S. [Fundamental Interactions Laboratory, Gravitation Group, Tata Institute of Fundamental Research, Mumbai-400005 (India)
2006-08-15
We discuss the implementation and characterization of the source of a slow, intense, and collimated beam of rubidium atoms. The cold atomic beam is produced by two-dimensional magneto-optical trapping in directions transverse to the atomic beam axis and unbalanced Doppler cooling in the axial direction. The vacuum design allows use of relatively low laser power and a considerably simplified assembly. The atomic beam has a high flux of about 2x10{sup 10} atoms/s at a total cooling laser power of 55 mW. It has a narrow longitudinal velocity distribution with mean velocity 15 m/s with full width at half maximum 3.5 m/s and has a low divergence of 26 mrad. The high flux enables ultrafast loading of about 10{sup 10} atoms into a three-dimensional (3D) magneto-optical trap within 500 ms. The variation of the atomic beam flux was studied as a function of the rubidium vapor pressure, cooling laser power, transverse cooling laser beam length, detuning of the cooling laser, and relative intensities of the cooling beams along the atomic beam axis. We also discuss a detailed comparison of our measurements of the cold atomic beam with a 3D numerical simulation.
Fan, Yu; Zou, Ying; Sun, Jizhong; Wang, Dezhen; Stirner, Thomas
2013-10-15
The influence of an applied magnetic field on plasma-related devices has a wide range of applications. Its effects on a plasma have been studied for years; however, there are still many issues that are not understood well. This paper reports a detailed kinetic study with the two-dimension-in-space and three-dimension-in-velocity particle-in-cell plus Monte Carlo collision method on the role of E×B drift in a capacitive argon discharge, similar to the experiment of You et al.[Thin Solid Films 519, 6981 (2011)]. The parameters chosen in the present study for the external magnetic field are in a range common to many applications. Two basic configurations of the magnetic field are analyzed in detail: the magnetic field direction parallel to the electrode with or without a gradient. With an extensive parametric study, we give detailed influences of the drift on the collective behaviors of the plasma along a two-dimensional domain, which cannot be represented by a 1 spatial and 3 velocity dimensions model. By analyzing the results of the simulations, the occurring collisionless heating mechanism is explained well.
NASA Technical Reports Server (NTRS)
Ngwira, Chigomezyo M.; Pulkkinen, Antti; Kuznetsova, Maria M.; Glocer, Alex
2014-01-01
There is a growing concern over possible severe societal consequences related to adverse space weather impacts on man-made technological infrastructure. In the last two decades, significant progress has been made toward the first-principles modeling of space weather events, and three-dimensional (3-D) global magnetohydrodynamics (MHD) models have been at the forefront of this transition, thereby playing a critical role in advancing our understanding of space weather. However, the modeling of extreme space weather events is still a major challenge even for the modern global MHD models. In this study, we introduce a specially adapted University of Michigan 3-D global MHD model for simulating extreme space weather events with a Dst footprint comparable to the Carrington superstorm of September 1859 based on the estimate by Tsurutani et. al., (2003). Results are presented for a simulation run with "very extreme" constructed/idealized solar wind boundary conditions driving the magnetosphere. In particular, we describe the reaction of the magnetosphere-ionosphere system and the associated induced geoelectric field on the ground to such extreme driving conditions. The model setup is further tested using input data for an observed space weather event of Halloween storm October 2003 to verify the MHD model consistence and to draw additional guidance for future work. This extreme space weather MHD model setup is designed specifically for practical application to the modeling of extreme geomagnetically induced electric fields, which can drive large currents in ground-based conductor systems such as power transmission grids. Therefore, our ultimate goal is to explore the level of geoelectric fields that can be induced from an assumed storm of the reported magnitude, i.e., Dst approx. = -1600 nT.
NASA Astrophysics Data System (ADS)
Ngwira, Chigomezyo M.; Pulkkinen, Antti; Kuznetsova, Maria M.; Glocer, Alex
2014-06-01
There is a growing concern over possible severe societal consequences related to adverse space weather impacts on man-made technological infrastructure. In the last two decades, significant progress has been made toward the first-principles modeling of space weather events, and three-dimensional (3-D) global magnetohydrodynamics (MHD) models have been at the forefront of this transition, thereby playing a critical role in advancing our understanding of space weather. However, the modeling of extreme space weather events is still a major challenge even for the modern global MHD models. In this study, we introduce a specially adapted University of Michigan 3-D global MHD model for simulating extreme space weather events with a Dst footprint comparable to the Carrington superstorm of September 1859 based on the estimate by Tsurutani et. al. (2003). Results are presented for a simulation run with "very extreme" constructed/idealized solar wind boundary conditions driving the magnetosphere. In particular, we describe the reaction of the magnetosphere-ionosphere system and the associated induced geoelectric field on the ground to such extreme driving conditions. The model setup is further tested using input data for an observed space weather event of Halloween storm October 2003 to verify the MHD model consistence and to draw additional guidance for future work. This extreme space weather MHD model setup is designed specifically for practical application to the modeling of extreme geomagnetically induced electric fields, which can drive large currents in ground-based conductor systems such as power transmission grids. Therefore, our ultimate goal is to explore the level of geoelectric fields that can be induced from an assumed storm of the reported magnitude, i.e., Dst˜=-1600 nT.
Modeling of substorm development with a kinematic effect by the global MHD simulations
NASA Astrophysics Data System (ADS)
den, Mitsue; Fujita, Shigeru; Tanaka, Takashi; Horiuchi, Ritoku
Magnetic reconnection is considered to play an important role in space phenomena such as substorm in the Earth's magnetosphere. Recently, Tanaka and Fujita reproduced substorm evoution process by numerical simulation with the global MHD code. In the MHD framework, the dissipation model is used for modeling of the kinetic effects. They found that the normalized reconnection viscosity, one of the dessipation model employed there, gave a large effect for the substorm development though that viscosity was assumed to be a constant parameter. It is well known that magnetric reconnection is controlled by microscopic kinetic mechanism. Horiuchi et al. investigated the roles of microscopic plasma instabilities on the violation of the frozen-in condition by examining the force balance equation based on explicit electromagnetic particle simulation for an ion-scale current sheet, and concluded that the growth of drift kink instability can create anomalous resistivity leading to the excitation of collisionless reconnection. They estimated the effective resistivity based on the particle simulation data. In this paper, we perform substorm simulation by using the global MHD code with this anomalous resistivity obtained in their microscopic approach istead of the emprical resistivity model, and investigate the relationship between the substorm development and the anomalous resistivity model.
Stability Analysis of Two-Dimensional Models of Quiescent Prominences
NASA Astrophysics Data System (ADS)
Trejo, J. Galindo
1987-09-01
Using the MHD energy principle of Bernstein et al. (1958) we develop a formalism in order to analyze the stability properties of two-dimensional magnetostatic plasma equilibria. We apply this to four models of quiescent prominences, namely those of Menzel (1951), Dungey (1953), Kippenhahn and Schlüter (1957), and finally Lerche and Low (1980). For the observed parameter range, all models are stable and they explain reasonably well the reported flare-initiated oscillations in quiescent prominences. We also investigate other parameters regions, which may be relevant in some stellar atmospheres. It is found that, with the exception of the Kippenhahn and Schlüter model, all models become unstable. The instabilities that occur show simultaneously several features of well-known MHD-instabilities. However, an unequivocal assignment of the instabilities to specific instability prototypes is not possible. Our formalism allows one to investigate not only more realistic prominence equilibria, but also arbitrary one- and two-dimensional static ideal MHD-equilibria.
Numerical Simulation of 3-D Supersonic Viscous Flow in an Experimental MHD Channel
NASA Technical Reports Server (NTRS)
Kato, Hiromasa; Tannehill, John C.; Gupta, Sumeet; Mehta, Unmeel B.
2004-01-01
The 3-D supersonic viscous flow in an experimental MHD channel has been numerically simulated. The experimental MHD channel is currently in operation at NASA Ames Research Center. The channel contains a nozzle section, a center section, and an accelerator section where magnetic and electric fields can be imposed on the flow. In recent tests, velocity increases of up to 40% have been achieved in the accelerator section. The flow in the channel is numerically computed using a new 3-D parabolized Navier-Stokes (PNS) algorithm that has been developed to efficiently compute MHD flows in the low magnetic Reynolds number regime. The MHD effects are modeled by introducing source terms into the PNS equations which can then be solved in a very e5uent manner. To account for upstream (elliptic) effects, the flowfield can be computed using multiple streamwise sweeps with an iterated PNS algorithm. The new algorithm has been used to compute two test cases that match the experimental conditions. In both cases, magnetic and electric fields are applied to the flow. The computed results are in good agreement with the available experimental data.
The scaling properties of two-dimensional compressible magnetohydrodynamic turbulence
Merrifield, J.A.; Arber, T.D.; Chapman, S.C.; Dendy, R.O.
2006-01-15
Understanding the phenomenology captured in direct numerical simulation (DNS) of magnetohydrodynamic (MHD) turbulence rests upon models and assumptions concerning the scaling of field variables and dissipation. Here compressible MHD turbulence is simulated in two spatial dimensions by solving the isothermal equations of resistive MHD on a periodic square grid. In these simulations it is found that the energy spectrum decreases more slowly with k, and the viscous cutoff length is larger, than would be expected from the 1941 phenomenology of Kolmogorov (K41). Both these effects suggest that the cascade time is modified by the presence of Alfven waves as in the phenomenology of Iroshnikov and Kraichnan (IK). Motivated by this, these scaling exponents are compared with those of the IK-based model of Politano and Pouquet [Phys. Rev. E 52, 636 (1995)], which is an extension of the model of She and Leveque [Phys. Rev. Lett. 72, 336 (1994)]. However, the scaling exponents from these simulations are not consistent with the model of Politano and Pouquet, so that neither IK nor K41 models would appear to describe the simulations. The spatial intermittency of turbulent activity in such simulations is central to the observed phenomenology and relates to the geometry of structures that dissipate most intensely via the scaling of the local rate of dissipation. The framework of She and Leveque implies a scaling relation that links the scaling of the local rate of dissipation to the scaling exponents of the pure Elsaesser field variables (z{sup {+-}}=v{+-}B/{radical}({mu}{sub o}{rho})). This scaling relation is conditioned by the distinct phenomenology of K41 and IK. These distinct scaling relations are directly tested using these simulations and it is found that neither holds. This deviation suggests that additional measures of the character of the dissipation may be required to fully capture the turbulent scaling, for example, pointing towards a refinement of the phenomenological models. It may also explain why previous attempts to predict the scaling exponents of the pure Elsaesser fields in two-dimensional magnetohydrodynamic turbulence by extending the theory of She and Leveque have proved unsuccessful.
Direct simulation of multi-phase MHD flows on an unstructured Cartesian adaptive system
NASA Astrophysics Data System (ADS)
Zhang, Jie; Ni, Ming-Jiu
2014-08-01
An approach for direct simulation of the multi-phase magnetohydrodynamics (MHD) flows has been developed in the present study on an unstructured Cartesian adaptive system. The approach is based on the volume-of-fluid (VOF) method for capturing the interface with the adaptive mesh refinement (AMR) technique used to well resolve the interface and the boundary layer. The Lorentz force is calculated using the consistent and conservative scheme, which is specially designed on a Cartesian adaptive mesh to conserve the physical conservation laws. The continuous-surface-tension (CSF) formulation is adopted for surface tension calculation. Moreover, the interfacial flows driven by thermal Marangoni effects at multifluid interfaces are also studied with a special numerical treatment presented. The method is able to simulate bubble motion in liquid metal under magnetic field irrespective of high density ratio and electric conductivity ratio. The proposed scheme for multi-phase MHD flows is validated by experimental results as well as analytical solutions.
Direct Numerical Simulations of Nonlinear Evolution of MHD Instability in LHD
Miura, H.; Nakajima, N.; Hayashi, T.; Okamoto, M.
2006-11-30
Nonlinear evolutions of MHD instabilities in the large helical device are studied by means of direct numerical simulations under the vacuum configuration with the magnetic axis position R = 3.6m, including effects of its full three-dimensional geometry, flows parallel to the magnetic field lines and the fluid compressibility. The linear growth of the pressure-driven modes and their nonlinear saturations are observed. The linear growth brings about the flows parallel to the magnetic field lines as strong as the perpendicular flows. The fluid compressibility reduces the linear growth rate significantly. In the nonlinear saturation process, a qualitative difference is found in the behaviors of the parallel and perpendicular flows. The plasma appears to approach to a near-equilibrium state, keeping finite amplitudes of the parallel flow. Our numerical results highlight important roles of the parallel flow and compressibility in nonlinear MHD simulations in the large helical device.
Gas Core Reactor Numerical Simulation Using a Coupled MHD-MCNP Model
NASA Technical Reports Server (NTRS)
Kazeminezhad, F.; Anghaie, S.
2008-01-01
Analysis is provided in this report of using two head-on magnetohydrodynamic (MHD) shocks to achieve supercritical nuclear fission in an axially elongated cylinder filled with UF4 gas as an energy source for deep space missions. The motivation for each aspect of the design is explained and supported by theory and numerical simulations. A subsequent report will provide detail on relevant experimental work to validate the concept. Here the focus is on the theory of and simulations for the proposed gas core reactor conceptual design from the onset of shock generations to the supercritical state achieved when the shocks collide. The MHD model is coupled to a standard nuclear code (MCNP) to observe the neutron flux and fission power attributed to the supercritical state brought about by the shock collisions. Throughout the modeling, realistic parameters are used for the initial ambient gaseous state and currents to ensure a resulting supercritical state upon shock collisions.
NASA Astrophysics Data System (ADS)
Zhang, Ya; Wang, Hong-yu; Jiang, Wei; Bogaerts, Annemie
2015-08-01
The plasma behavior in a parallel-plate dielectric barrier discharge (DBD) is simulated by a two-dimensional particle-in-cell/Monte Carlo collision model, comparing for the first time an unpacked (empty) DBD with a packed bed DBD, i.e., a DBD filled with dielectric spheres in the gas gap. The calculations are performed in air, at atmospheric pressure. The discharge is powered by a pulse with a voltage amplitude of ?20 kV. When comparing the packed and unpacked DBD reactors with the same dielectric barriers, it is clear that the presence of the dielectric packing leads to a transition in discharge behavior from a combination of negative streamers and unlimited surface streamers on the bottom dielectric surface to a combination of predominant positive streamers and limited surface discharges on the dielectric surfaces of the beads and plates. Furthermore, in the packed bed DBD, the electric field is locally enhanced inside the dielectric material, near the contact points between the beads and the plates, and therefore also in the plasma between the packing beads and between a bead and the dielectric wall, leading to values of 4× {10}8 V m?1, which is much higher than the electric field in the empty DBD reactor, i.e., in the order of 2× {10}7 V m?1, thus resulting in stronger and faster development of the plasma, and also in a higher electron density. The locally enhanced electric field and the electron density in the case of a packed bed DBD are also examined and discussed for three different dielectric constants, i.e., {? }r=22 (ZrO2), {? }r=9 (Al2O3) and {? }r=4 (SiO2). The enhanced electric field is stronger and the electron density is higher for a larger dielectric constant, because the dielectric material is more effectively polarized. These simulations are very important, because of the increasing interest in packed bed DBDs for environmental applications.
NASA Astrophysics Data System (ADS)
Bitzer, Klaus
1999-05-01
Geological processes that create sedimentary basins or act during their formation can be simulated using the public domain computer code `BASIN'. For a given set of geological initial and boundary conditions the sedimentary basin evolution is calculated in a forward modeling approach. The basin is represented in a two-dimensional vertical cross section with individual layers. The stratigraphic, tectonic, hydrodynamic and thermal evolution is calculated beginning at an initial state, and subsequent changes of basin geometry are calculated from sedimentation rates, compaction and pore fluid mobilization, isostatic compensation, fault movement and subsidence. The sedimentologic, hydraulic and thermal parameters are stored at discrete time steps allowing the temporal evolution of the basin to be analyzed. A maximum flexibility in terms of geological conditions is achieved by using individual program modules representing geological processes which can be switched on and off depending on the data available for a specific simulation experiment. The code incorporates a module for clastic and carbonate sedimentation, taking into account the impact of clastic sediment supply on carbonate production. A maximum of four different sediment types, which may be mixed during sedimentation, can be defined. Compaction and fluid flow are coupled through the consolidation equation and the nonlinear form of the equation of state for porosity, allowing nonequilibrium compaction and overpressuring to be calculated. Instead of empirical porosity-effective stress equations, a physically consistent consolidation model is applied which incorporates a porosity dependent sediment compressibility. Transient solute transport and heat flow are calculated as well, applying calculated fluid flow rates from the hydraulic model. As a measure for hydrocarbon generation, the Time-Temperature Index (TTI) is calculated. Three postprocessing programs are available to provide graphic output in PostScript format: BASINVIEW is used to display the distribution of parameters in the simulated cross-section of the basin for defined time steps. It is used in conjunction with the Ghostview software, which is freeware and available on most computer systems. AIBASIN provides PostScript output for Adobe Illustrator®, taking advantage of the layer-concept which facilitates further graphic manipulation. BASELINE is used to display parameter distribution at a defined well or to visualize the temporal evolution of individual elements located in the simulated sedimentary basin. The modular structure of the BASIN code allows additional processes to be included. A module to simulate reactive transport and diagenetic reactions is planned for future versions. The program has been applied to existing sedimentary basins, and it has also shown a high potential for classroom instruction, giving the possibility to create hypothetical basins and to interpret basin evolution in terms of sequence stratigraphy or petroleum potential.
MHD Simulation of Laboratory-Based Expanding Magnetic Flux Tubes
Anlage, Steven
Conditions Some Plasma Physics Simulations Summary and Future Work #12;Background and Motivation Existing BC's Hall term Initial Magnetic Field + = Electromagnet Current Discharge Superposition y #12;Some (Wikipedia) #12;Simulations |J| |J| x y z #12;Summary and Future Work What was accomplished: F3D code
Thermodynamic MHD Simulation of the 2000 July 14 "Bastille Day" Eruption
NASA Astrophysics Data System (ADS)
Torok, Tibor; Downs, Cooper; Lionello, Roberto; Linker, Jon A.; Titov, Viacheslav S.; Mikic, Zoran; Riley, Pete
2015-04-01
The "Bastille Day" event that occurred on 2000 July 14 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. Accurate numerical simulations of such events, in particular the matching of parameters relevant for space weather such as the CME velocity and magnetic orientation, require a realistic model of the large-scale magnetic field and plasma environment into which the eruption propagates and interacts, as well as a modeling of the pre-eruptive configuration and eruption initiation that are as realistic as possible. Here we present an MHD simulation of the Bastille Day event that complies with these requirements. 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 a stable, elongated flux rope that resides above the highly curved polarity inversion line of the active region. Finally, we produce the 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.
NASA Astrophysics Data System (ADS)
Ebrahimi, Fatima; Lefebvre, B.; Forest, C.; Bhattacharjee, A.
2010-05-01
We have performed numerical simulations of the Madison Plasma Couette Flow Experiment (MPCX) using the extended MHD code NIMROD (nimrodteam.org). The plasma Couette flow experiment has recently been constructed at UW-Madison to study magnetorotational instability (MRI) in a hot, unmagnetized and fast flowing plasma. Plasma is confined by a strong multipole magnetic field at the plasma surface, and it rotates through the generated toroidal ExB flow at the boundaries. As proof of principle we first numerically obtain an experimentally relevant flow, a Taylor-Couette flow generated by tangential electric field using the boundary condition ExB. Two-fluid Hall effect which is relevant to some astrophysical situations such as protostellar disks is also expected to be important in the MPCX. We extend the MHD model by including the Hall term both in linear and nonlinear MRI computations. Global linear stability analysis of MRI is numerically investigated both in MHD and Hall-MHD regimes for a range of magnetic Prandtl and magnetic Reynolds numbers. We find that in all cases the MHD stability limit is affected by the Hall term depending on the sign of the product of the components of the angular velocity and magnetic field along the perturbation wavenumber, as predicted by the earlier local linear studies. Global modal structure of MRI with Hall term is investigated and compared with the local approximations. Preliminary results of possible self-generation of the magnetic field by MRI-driven turbulence in the MPCX configuration will also be presented. This work is supported by NSF.
NASA Astrophysics Data System (ADS)
Raley, Elizabeth
2004-12-01
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.
PROPERTIES OF UMBRAL DOTS AS MEASURED FROM THE NEW SOLAR TELESCOPE DATA AND MHD SIMULATIONS
Kilcik, A.; Yurchyshyn, V. B.; Abramenko, V.; Goode, P. R.; Cao, W. [Big Bear Solar Observatory, Big Bear City, CA 92314 (United States); Rempel, M. [High Altitude Observatory, NCAR, Boulder, CO 80307-3000 (United States); Kitai, R.; Watanabe, H. [Kwasan and Hida Observatories, Kyoto University, Kyoto 607-8417 (Japan)
2012-02-01
We studied bright umbral dots (UDs) detected in a moderate size sunspot and compared their statistical properties to recent MHD models. The study is based on high-resolution data recorded by the New Solar Telescope at the Big Bear Solar Observatory and three-dimensional (3D) MHD simulations of sunspots. Observed UDs, living longer than 150 s, were detected and tracked in a 46 minute long data set, using an automatic detection code. A total of 1553 (620) UDs were detected in the photospheric (low chromospheric) data. Our main findings are (1) none of the analyzed UDs is precisely circular, (2) the diameter-intensity relationship only holds in bright umbral areas, and (3) UD velocities are inversely related to their lifetime. While nearly all photospheric UDs can be identified in the low chromospheric images, some small closely spaced UDs appear in the low chromosphere as a single cluster. Slow-moving and long-living UDs seem to exist in both the low chromosphere and photosphere, while fast-moving and short-living UDs are mainly detected in the photospheric images. Comparison to the 3D MHD simulations showed that both types of UDs display, on average, very similar statistical characteristics. However, (1) the average number of observed UDs per unit area is smaller than that of the model UDs, and (2) on average, the diameter of model UDs is slightly larger than that of observed ones.
Simulations of Stellar Magnetoconvection using the Radiative MHD Code `StellarBox'
Wray, Alan A; Kitiashvili, Irina N; Mansour, Nagi N; Kosovichev, Alexander G
2015-01-01
Realistic numerical simulations, i.e., those that make minimal use of ad hoc modeling, are essential for understanding the complex turbulent dynamics of the interiors and atmospheres of the Sun and other stars and the basic mechanisms of their magnetic activity and variability. The goal of this paper is to present a detailed description and test results of a compressible radiative MHD code, `StellarBox', specifically developed for simulating the convection zones, surface, and atmospheres of the Sun and moderate-mass stars. The code solves the three-dimensional, fully coupled compressible MHD equations using a fourth-order Pad\\'e spatial differentiation scheme and a fourth-order Runge-Kutta scheme for time integration. The radiative transfer equation is solved using the Feautrier method for bi-directional ray tracing and an opacity-binning technique. A specific feature of the code is the implementation of subgrid-scale MHD turbulence models. The data structures are automatically configured, depending on the co...
Solenoidal Discrete Initialization for Locally Divergence-free MHD Simulations
the results of a simulation of a shock interaction with a magnetized cloud. 1 Introduction The field for magnetohydrodynam- ics is the control of the divergence errors. Certainly, in the limit of finer grids any with a magnetized cloud. The solution at different times is discussed and provides insight into the special behavior
3-D Simulations of MHD Jets - The Stability Problem
Masanori Nakamura; David L. Meier
2003-12-02
Non-relativistic three-dimensional magnetohydrodynamic simulations of Poynting-flux-dominated (PFD) jets are presented. Our study focuses on the propagation of strongly magnetized hypersonic but sub-Alfv\\'enic flow ($C_{\\rm s}^2 1$), driven in large part by the radial component of the Lorentz force.
Hybrid MHD-kinetic electron simulations of global standing modes (Invited)
NASA Astrophysics Data System (ADS)
Damiano, P. A.; Johnson, J.; Kim, E.
2010-12-01
Geomagnetic Field Line Resonances (FLRs) are an example of large scale global structures that can directly couple energy from large perpendicular scale lengths to small scale kinetic Alfven wave (KAW) and inertial Alfven wave (IAW) scale lengths and ultimately in to the acceleration of particles to carry the field aligned currents. In this presentation, we will summarize the methodology and results of a hybrid MHD-kinetic electron model of FLRs which self consistently couples the cold plasma MHD equations to a system of kinetic guiding center electrons in a dipolar geometry. Results will highlight the cascade of energy evident in these simulations from large to small scale and will demonstrate that the deposition of this wave energy into electron acceleration is a significant sink of wave energy. The calculated wave spectra evident in this cascade will also be compared with observations and advances to the model using a gyrokinetic description of ion dynamics will be discussed.
Explosive Turbulent Magnetic Reconnection: A New Approach of MHD-Turbulent Simulation
NASA Astrophysics Data System (ADS)
Hoshino, Masahiro; Yokoi, Nobumitsu; Higashimori, Katsuaki
2013-04-01
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.
Global magnetosphere simulations using constrained-transport Hall-MHD with CWENO reconstruction
NASA Astrophysics Data System (ADS)
Lin, L.; Germaschewski, K.; Maynard, K. M.; Abbott, S.; Bhattacharjee, A.; Raeder, J.
2013-12-01
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.
An Object-Oriented Kinetic MHD Simulation Code using the POOMA C++ Class Library
NASA Astrophysics Data System (ADS)
Cummings, Julian; Zheng, Linjin; Chen, Liu
2000-04-01
A kinetic MHD simulation code has been developed for the study of trapped energetic particle effects on Alfvén-ballooning modes in a dipole magnetic configuration with anisotropic equilibria. The simulation code treats the core plasma as an MHD fluid, while the energetic particles are modeled using a gyrokinetic delta-f scheme, with finite-orbit-width effects taken into account. This simulation has been applied to both Alfvén instabilities in the MIT LDX dipole configuration and to the effects of ring current protons on disturbances in the Earth's magnetosphere. Currently, we are reconstructing this simulation code in a generic, object-oriented style and making use of physics-oriented classes and functions from the POOMA C++ class library. POOMA allows us to construct our model in terms of physical field quantities, particle populations with specified properties, and standard numerical algorithms such as interpolation schemes. Here we discuss this new code design and its benefits for exploring new magnetic equilibria, new simulation geometries, and new particle or fluid models within the same basic simulation framework.
Voronine, Dmitri V.; Abramavicius, Darius; Mukamel, Shaul
2008-01-01
Two-dimensional electronic chirality-induced signals of excitons in the photosynthetic Fenna-Matthews-Olson complex from two species of green sulfur bacteria (Chlorobium tepidum and Prosthecochloris aestuarii) are compared. The spectra are predicted to provide sensitive probes of local protein environment of the constituent bacteriochlorophyll a chromophores and reflect electronic structure variations (site energies and couplings) of the two complexes. Pulse polarization configurations are designed that can separate the coherent and incoherent exciton dynamics contributions to the two-dimensional spectra. PMID:18676650
A three-dimensional MHD simulation of the interaction of the solar wind with Comet Halley
NASA Technical Reports Server (NTRS)
Ogino, Tatsuki; Walker, Raymond J.; Ashour-Abdalla, Maha
1988-01-01
The interaction between the solar wind and cometary plasmas is simulated using a three-dimensional time-dependent MHD simulation model, and the results are compared with the recent satellite observations of Comet Halley. The model, which includes cometary mass loading, reproduces many of the features observed by the Suisei probe and the Giottot, including the weak bow shock, the enhancement of the magnetic field in front of the contact surface, and the plasma temperature increase across the bow shock (while it decreased near the comet).
NASA Astrophysics Data System (ADS)
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
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.
K. Ohsuga
2007-03-06
The supercritical disk accretion flow with radiatively driven outflows is studied based on two-dimensional radiation-hydrodynamic simulations for a wide range of the mass input rate, $\\dot{M}_{\\rm input}$, which is the mass supplied from the outer region to the disk per unit time. The $\\alpha$-prescription is adopted for the viscosity. We employ $\\alpha=0.5$, as well as $\\alpha=0.1$ for $\\dot{M}_{\\rm input}\\ge 3\\times 10^2L_{\\rm E}/c^2$ and only $\\alpha=0.5$ for $\\dot{M}_{\\rm input}\\le 10^2L_{\\rm E}/c^2$, where $L_{\\rm E}$ is the Eddington luminosity and $c$ is the speed of light. The quasi-steady disk and radiately driven outflows form in the case in which the mass input rate highly exceeds the critical rate, $\\dot{M}_{\\rm input}>3\\times 10^2 L_{\\rm E}/c^2$. Then, the disk luminosity as well as the kinetic energy output rate by the outflow exceeds the Eddington luminosity. The moderately supercritical disk, $\\dot{M}_{\\rm input}\\sim 10-10^2 L_{\\rm E}/c^2$, exhibits limit-cycle oscillations. The disk luminosity goes up and down across the Eddington luminosity, and the radiatively driven outflows intermittently appear. The time averaged mass, momentum, and kinetic energy output rates by the outflow as well as the disk luminosity increase with increase of the mass input rate, $\\propto \\dot{M}_{\\rm input}^{0.7-1.0}$ for $\\alpha=0.5$ and $\\propto \\dot{M}_{\\rm input}^{0.4-0.6}$ for $\\alpha=0.1$. Our numerical simulations show that the radiatively driven outflow model for the correlation between black hole mass and bulge velocity dispersion proposed by \\citeauthor{SR98} and \\citeauthor{King03} is successful if $\\dot{M}_{\\rm input}c^2/L_{\\rm E} \\sim$ a few 10 ($\\alpha=0.5$) or $\\gsim$ a few ($\\alpha=0.1$).
The Submillimeter Bump in Sgr A* from Relativistic MHD Simulations
NASA Astrophysics Data System (ADS)
Dexter, Jason; Agol, Eric; Fragile, P. Chris; McKinney, Jonathan C.
2010-07-01
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° are ruled out to 3?. 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°}^{+35°}_{-15°}, ? ={-23°}^{+97°}_{-22°}, Te = (5.4 ± 3.0) × 1010 K, and \\dot{M}=5^{+15}_{-2}× 10^{-9} M_? yr^{-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 ?/? c ~ 1-20, where ? c is the critical frequency for thermal synchrotron emission.
3D MHD simulation of polarized emission in SN 1006
NASA Astrophysics Data System (ADS)
Schneiter, E. M.; Velázquez, P. F.; Reynoso, E. M.; Esquivel, A.; De Colle, F.
2015-05-01
We use three-dimensional magnetohydrodynamic simulations to model the supernova remnant SN 1006. From our numerical results, we have carried out a polarization study, obtaining synthetic maps of the polarized intensity, the Stokes parameter Q, and the polar-referenced angle, which can be compared with observational results. Synthetic maps were computed considering two possible particle acceleration mechanisms: quasi-parallel and quasi-perpendicular. The comparison of synthetic maps of the Stokes parameter Q maps with observations proves to be a valuable tool to discern unambiguously which mechanism is taking place in the remnant of SN 1006, giving strong support to the quasi-parallel model.
Three-dimensional MHD simulation of the Caltech plasma jet experiment: first results
Zhai, Xiang; Bellan, Paul M. [Applied Physics, California Institute of Technology, Pasadena, CA 91125 (United States); Li, Hui [Theoretical Division, Los Alamos National Laboratory, Mail Stop B227, Los Alamos, NM 87545 (United States); Li, Shengtai, E-mail: xzhai@caltech.edu, E-mail: pbellan@caltech.edu, E-mail: hli@lanl.gov, E-mail: sli@lanl.gov [Mathematical Modeling and Analysis, Los Alamos National Laboratory, Mail Stop B284, Los Alamos, NM 87545 (United States)
2014-08-10
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 simulations of 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 other forms. With suitably chosen parameters that are derived from experiments, the jet in the simulation agrees quantitatively with the experimental jet in terms of magnetic/kinetic/inertial energy, total poloidal current, voltage, jet radius, and jet propagation velocity. Specifically, the jet velocity in the simulation is proportional to the poloidal current divided by the square root of the jet density, in agreement with both the experiment and analytical theory. This work provides a new and quantitative method for relating experiments, numerical simulations, and astrophysical observation, and demonstrates the possibility of using terrestrial laboratory experiments to study astrophysical jets.
Energy storage and dissipation in the magnetotail during substorms. 2. MHD simulations
Steinolfson, R.S. ); Winglee, R.M. )
1993-05-01
The authors present a global MHD simulation of the magnetotail in an effort to study magnetic storm development. They address the question of energy storage in the current sheet in the early phases of storm growth, which previous simulations have not shown. They address this problem by dealing with the variation of the resistivity throughout the magnetosphere. They argue that MHD theory should provide a suitable representation to this problem on a global scale, even if it does not handle all details adequately. For their simulation they use three different forms for the resistivity. First is a uniform and constant resistivity. Second is a resistivity proportional to the current density, which is related to argument that resistivity is driven by wave-particle interactions which should be strongest in regions where the current is the greatest. Thirdly is a model where the resistivity varies with the magnetic field strength, which was suggested by previous results from particle simulations of the same problem. The simulation then gives approximately the same response of the magnetosphere for all three of the models. Each results in the formation and ejection of plasmoids, but the energy stored in the magnetotail, the timing of substorm onset in relation to the appearance of a southward interplanetary magnetic field, and the speed of ejection of the plasmoids formed differ with the resistivity models.
MHD simulations of homologous and cannibalistic coronal mass ejections
NASA Astrophysics Data System (ADS)
Fan, Yuhong; Chatterjee, Piyali
2014-06-01
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.
The Submillimeter Bump in Sgr A* from Relativistic MHD Simulations
Dexter, Jason; Fragile, P Chris; McKinney, Jonathan C
2010-01-01
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 \\le 20 degrees 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+35-15 degrees, \\xi=-23+97-22 degrees, T_e=(5.4 +/- 3.0)x10^10 K and Mdot=(5+15-2)x10^-9 M_sun / yr 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 1.3mm or .87mm either through direct sampling of t...
Wagner, Chad R.
2007-01-01
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.
Numerical simulation of MHD shock waves in the solar wind
NASA Technical Reports Server (NTRS)
Steinolfson, R. S.; Dryer, M.
1978-01-01
The effects of the interplanetary magnetic field on the propagation speed of shock waves through an ambient solar wind are examined by numerical solutions of the time-dependent nonlinear equations of motion. The magnetic field always increases the velocity of strong shocks. Although the field may temporarily slow down weak shocks inside 1 AU, it eventually also causes weak shocks to travel faster than they would without the magnetic field at larger distances. Consistent with the increase in the shock velocity, the gas pressure ratio across a shock is reduced considerably in the presence of the magnetic field. The numerical method is used to simulate (starting at 0.3 AU) the large deceleration of a shock observed in the lower corona by ground-based radio instrumentation and the more gradual deceleration of the shock in the solar wind observed by the Pioneer 9 and Pioneer 10 spacecraft.
Extended MHD Simulation of Kelvin-Helmholtz Instability in a 2D Slab
NASA Astrophysics Data System (ADS)
Hatori, Tomoharu; Miura, Hideaki; Ito, Atsushi; Sato, Masahiko; Goto, Ryosuke
2013-10-01
Shear flow of plasma in magnetic confinement fusion devices can play important roles to achieve high-performance plasma.On one hand, it can improve plasma confinement.On the other hand, it can cause magnetohydrodynamic (MHD) instabilities such as Kelvin-Helmholtz (KH) instability.Although KH instability has been researched intensively in a (single-fluid) MHD theory, the effects of the ion inertia length (two-fluid effect) or finite Larmor radius (FLR effect) to KH modes have not yet been well investigated, especially for parameters suitable for magnetically confined plasmas.These small scale effects are important when the shear is strong, e.g. in the edge region of H-mode tokamaks.In this study, numerical simulations of the KH instability in a 2D slab are carried out by our nonlinear extended MHD code.Evolution of KH modes due to sheared-flow perpendicular to an equilibrium magnetic field is concerned.Two-fluid terms show stabilizing effect, while FLR terms destabilizing. Wave numbers that growth rates are affected by those effects vary by beta, which correspond to the ratio of the Larmor radius to the ion inertia length. Discussion about nonlinear evolution and saturation will be presented.
Simulation of 3-D Nonequilibrium Seeded Air Flow in the NASA-Ames MHD Channel
NASA Technical Reports Server (NTRS)
Gupta, Sumeet; Tannehill, John C.; Mehta, Unmeel B.
2004-01-01
The 3-D nonequilibrium seeded air flow in the NASA-Ames experimental MHD channel has been numerically simulated. The channel contains a nozzle section, a center section, and an accelerator section where magnetic and electric fields can be imposed on the flow. In recent tests, velocity increases of up to 40% have been achieved in the accelerator section. The flow in the channel is numerically computed us ing a 3-D parabolized Navier-Stokes (PNS) algorithm that has been developed to efficiently compute MHD flows in the low magnetic Reynolds number regime: The MHD effects are modeled by introducing source terms into the PNS equations which can then be solved in a very efficient manner. The algorithm has been extended in the present study to account for nonequilibrium seeded air flows. The electrical conductivity of the flow is determined using the program of Park. The new algorithm has been used to compute two test cases that match the experimental conditions. In both cases, magnetic and electric fields are applied to the seeded flow. The computed results are in good agreement with the experimental data.
Two dimensional topology of cosmological reionization
Wang, Yougang; Xu, Yidong; Chen, Xuelei; Kim, Juhan
2015-01-01
We study the two-dimensional topology of the 21-cm differential brightness temperature for two hydrodynamic radiative transfer simulations and two semi-numerical models. In each model, we calculate the two dimensional genus curve for the early, middle and late epochs of reionization. It is found that the genus curve depends strongly on the ionized fraction of hydrogen in each model. The genus curves are significantly different for different reionization scenarios even when the ionized faction is the same. We find that the two-dimensional topology analysis method is a useful tool to constrain the reionization models. Our method can be applied to the future observations such as those of the Square Kilometer Array.
NASA Astrophysics Data System (ADS)
Murata, K. T.; Watari, S.; Kubota, Y.; Fukazawa, K.; Tsubouchi, K.; Fujita, S.; Tanaka, T.; Den, M.; Murayama, Y.
2011-12-01
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.
NASA Astrophysics Data System (ADS)
Burow, K. R.; Gamble, J. M.; Fujii, R.; Constantz, J.
2001-12-01
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.
MRI-driven Accretion onto Magnetized stars: Axisymmetric MHD Simulations
Romanova, Marina M; Koldoba, Alexander V; Lovelace, Richard V E
2011-01-01
We present the first results of a global axisymmetric simulation of accretion onto rotating magnetized stars from a turbulent, MRI-driven disk. The angular momentum is transported outward by the magnetic stress of the turbulent flow with a rate corresponding to a Shakura-Sunyaev viscosity parameter alpha\\approx 0.01-0.04. The result of the disk-magnetosphere interaction depends on the orientation of the poloidal field in the disk relative to that of the star at the disk-magnetosphere boundary. If fields have the same polarity, then the magnetic flux is accumulated at the boundary and blocks the accretion which leads to the accumulation of matter at the boundary. Subsequently, this matter accretes to the star in outburst before accumulating again. Hence, the cycling, `bursty' accretion is observed. If the disc and stellar fields have opposite polarity, then the field reconnection enhances the penetration of the disk matter towards the deeper field lines of the magnetosphere. However, the magnetic stress at the...
Extragalactic jets with helical magnetic fields: relativistic MHD simulations
R. Keppens; Z. Meliani; B. van der Holst; F. Casse
2008-02-14
Extragalactic jets are inferred to harbor dynamically important, organized magnetic fields which presumably aid in the collimation of the relativistic jet flows. We here explore by means of grid-adaptive, high resolution numerical simulations the morphology of AGN jets pervaded by helical field and flow topologies. We concentrate on morphological features of the bow shock and the jet beam behind the Mach disk, for various jet Lorentz factors and magnetic field helicities. We investigate the influence of helical magnetic fields on jet beam propagation in overdense external medium. We use the AMRVAC code, employing a novel hybrid block-based AMR strategy, to compute ideal plasma dynamics in special relativity. The helicity of the beam magnetic field is effectively transported down the beam, with compression zones in between diagonal internal cross-shocks showing stronger toroidal field regions. In comparison with equivalent low-relativistic jets which get surrounded by cocoons with vortical backflows filled by mainly toroidal field, the high speed jets demonstrate only localized, strong toroidal field zones within the backflow vortical structures. We find evidence for a more poloidal, straight field layer, compressed between jet beam and backflows. This layer decreases the destabilizing influence of the backflow on the jet beam. In all cases, the jet beam contains rich cross-shock patterns, across which part of the kinetic energy gets transferred. For the high speed reference jet considered here, significant jet deceleration only occurs beyond distances exceeding ${\\cal O}(100 R_j)$, as the axial flow can reaccelerate downstream to the internal cross-shocks. This reacceleration is magnetically aided, due to field compression across the internal shocks which pinch the flow.
The Substorm Current Wedge: Further Insights from MHD Simulations
NASA Technical Reports Server (NTRS)
Birn, J.; Hesse, M.
2015-01-01
Using a recent magnetohydrodynamic simulation of magnetotail dynamics, we further investigate the buildup and evolution of the substorm current wedge (SCW), resulting from flow bursts generated by near-tail reconnection. Each flow burst generates an individual current wedge, which includes the reduction of cross-tail current and the diversion to region 1 (R1)-type field-aligned currents (earthward on the dawn and tailward on the duskside), connecting the tail with the ionosphere. Multiple flow bursts generate initially multiple SCW patterns, which at later times combine to a wider single SCW pattern. The standard SCWmodel is modified by the addition of several current loops, related to particular magnetic field changes: the increase of Bz in a local equatorial region (dipolarization), the decrease of |Bx| away from the equator (current disruption), and increases in |By| resulting from azimuthally deflected flows. The associated loop currents are found to be of similar magnitude, 0.1-0.3 MA. The combined effect requires the addition of region 2 (R2)-type currents closing in the near tail through dawnward currents but also connecting radially with the R1 currents. The current closure at the inner boundary, taken as a crude proxy of an idealized ionosphere, demonstrates westward currents as postulated in the original SCW picture as well as North-South currents connecting R1- and R2-type currents, which were larger than the westward currents by a factor of almost 2. However, this result should be applied with caution to the ionosphere because of our neglect of finite resistance and Hall effects.
Relativistic modeling capabilities in PERSEUS extended MHD simulation code for HED plasmas
NASA Astrophysics Data System (ADS)
Hamlin, Nathaniel D.; Seyler, Charles E.
2014-12-01
We discuss the incorporation of relativistic modeling capabilities into the PERSEUS extended MHD simulation code for high-energy-density (HED) plasmas, and present the latest hybrid X-pinch simulation results. The use of fully relativistic equations enables the model to remain self-consistent in simulations of such relativistic phenomena as X-pinches and laser-plasma interactions. By suitable formulation of the relativistic generalized Ohm's law as an evolution equation, we have reduced the recovery of primitive variables, a major technical challenge in relativistic codes, to a straightforward algebraic computation. Our code recovers expected results in the non-relativistic limit, and reveals new physics in the modeling of electron beam acceleration following an X-pinch. Through the use of a relaxation scheme, relativistic PERSEUS is able to handle nine orders of magnitude in density variation, making it the first fluid code, to our knowledge, that can simulate relativistic HED plasmas.
NASA Astrophysics Data System (ADS)
Den, M.; Horiuchi, R.; Fujita, S.; Tanaka, T.
2011-12-01
Magnetic reconnection is considered to play an important role in space phenomena such as substorm in the Earth's magnetosphere. Tanaka and Fujita reproduced substorm evolution process by numerical simulation with the global MHD code [1]. In the MHD framework, the dissipation model is introduced for modeling of the kinetic effects. They found that the normalized reconnection viscosity, one of the dissipation model employed there, gave a large effect for the dipolarization, central phenomenon in the substorm development process, though that viscosity was assumed to be a constant parameter. It is well known that magnetic reconnection is controlled by microscopic kinetic mechanism. Frozen-in condition is broken due to particle kinetic effects and collisionless reconnection is triggered when current sheet is compressed as thin as ion kinetic scales under the influence of external driving flow [2, 3]. Horiuchi and his collaborators showed that reconnection electric field generated by microscopic physics evolves inside ion meandering scale so as to balance the flux inflow rate at the inflow boundary, which is controlled by macroscopic physics [2]. That is, effective resistivity generated through this process can be expressed by balance equation between micro and macro physics. In this paper, we perform substorm simulation by using the global MHD code developed by Tanaka [3] with this effective resistivity instead of the empirical resistivity model. We obtain the AE indices from simulation data, in which substorm onset can be seen clearly, and investigate the relationship between the substorm development and the effective resistivity model. [1] T. Tanaka, A, Nakamizo, A. Yoshikawa, S. Fujita, H. Shinagawa, H. Shimazu, T. Kikuchi, and K. K. Hashimoto, J. Geophys. Res. 115 (2010) A05220,doi:10.1029/2009JA014676. [2] W. Pei, R. Horiuchi, and T. Sato, Physics of Plasmas,Vol. 8 (2001), pp. 3251-3257. [3] A. Ishizawa, and R. Horiuchi, Phys. Rev. Lett., Vol. 95, 045003 (2005). [4] T. Tanaka, J. Comp. Phys. 111 (1994) 381.
NASA Astrophysics Data System (ADS)
Ghomi, H.; Sharifian, M.; Niknam, A. R.; Shokri, B.
2006-12-01
In this paper, the temporal evolution of the ion-matrix sheath near a target with a rectangular groove as a function of time and potential is investigated numerically. A two-dimensional model with a single groove is adopted. The profiles of potential, ion density, and the normalized ion flux over the sidewall and the floor of the groove are obtained. These profiles are provided for insight regarding the uniformity and efficiency of ion implantation on the sidewall.
NIMROD Extended MHD Simulations of Reversed-Field Pinch Relaxation Dynamics
NASA Astrophysics Data System (ADS)
Sauppe, Joshua; Sovinec, Carl; Sarff, John; Triana, Joseph
2014-10-01
The nonlinear evolution and relaxation dynamics of an initially non-reversed two-fluid plasma in cylindrical geometry is investigated using the NIMROD code. The initial relaxation event brings the plasma to the characteristic reversed-field state. There is significant magnetic activity with MHD and Hall dynamos working together to relax the parallel current profile while the fluctuation-induced Lorentz force drives plasma flows. Subsequent events have considerably less magnetic activity and often have opposing MHD and Hall dynamos. The direction of the driven flows in these events differs from the initial event, and is consistent with experimental observations on the MST RFP. The nonlinear mode coupling during relaxation events is investigated, and the presence of the Hall dynamo is found to significantly alter the spectral power flow. Synthetic diagnostics are used to compare simulation results to experimental measurements of Hall dynamo mode structure with laser Faraday rotation and magnetic probes. At modest Lundquist number the time-scales of relaxation and drive are well-separated and the simulations are compared to two-fluid relaxation theories. Generalized two-fluid helicities are well-conserved relative to magnetic energy over the simulated relaxation events. Work supported by U.S. DoE and NSF.
2--D Resistive MHD Simulations of Merging Co-- and Counter--Helicity Spheromaks
NASA Astrophysics Data System (ADS)
Carter, T. A.; Jardin, S. C.
1997-11-01
Studies of the global equilibrium properties of merging spheromaks as well as of the local properties of the reconnection boundary layer in the MHD limit will be presented. The Princeton Tokamak Simulation Code (TSC)(S.C. Jardin, et. al., J. Comp. Phys. 66) (1986) 481, a free--boundary, axisymmetric resistive MHD code, is modified to resolve the two spatial scales of the merging spheromak problem, the equilibrium scale and the boundary layer, and to include convective terms in the coded set of scalar momentum equations. The simulations reported here are performed with parameters T ~ 15 eV, ne ~ 10^14 cm-3, Bz ~ 2 kG. We present comparisons of our simulation results with results from recent analytic(R. Kulsrud, D. Uzdensky, personal communication) and experimental work(M. Yamada, et. al., Phys. Rev. Lett. 78) (1997) 3117 and Y. Ono, et. al., Phys. Rev. Lett. 76 (1996) 3328. In particular we emphasize merging rates for co-- and counter--helicity merging, boundary layer geometry, scaling of merging rate with dimensionless parameters, and formation of spheromak and Field Reversed Configuration (FRC) plasmas as a result of co-- and counter--helicity merging.
Two-dimensional exciton revisited
NASA Astrophysics Data System (ADS)
Parfitt, D. G. W.; Portnoi, M. E.
2003-04-01
We present some interesting mathematical results arising from a consideration of two-dimensional excitons, screened and unscreened. These include bound-state wave functions in the momentum representation and a new integral relation in terms of special functions.
Co-existence of Discrete Modes and Turbulence in Direct MHD Simulations
NASA Astrophysics Data System (ADS)
Ghosh, S.; Thomson, D. J.; Dmitruk, P.; Matthaeus, W. H.; Lanzerotti, L. J.
2006-12-01
Motivated by measurements of discrete, reproducible modes in the solar wind and energetic particle fluxes that are in the frequency ranges that correspond to solar internal pressure (p) and gravity (g) modes, a controversy persists in the magnetohydrodynamic (MHD) turbulence community whether discrete modes (independent of their source) can persist in the presence of a turbulent cascade. We perform direct numerical simulations of a compressible 3-D MHD system to find evidence for such coexistence. We find two scenarios: First, in the presence of a DC magnetic field, turbulent cascades are known to be suppressed in the field-parallel direction. In this case, a discrete mode can persist for several nonlinear times without interacting strongly with the turbulence if its wavevector component parallel to the DC magnetic field is significantly larger than the turbulent cascade's k-space variation in the field-parallel direction. Second, for sufficiently weak forcing a driven mode can persist as a discrete mode despite being deeply embedded inside a turbulence cascade. In this case, the mode does not display spectral broadening, nor does the spectrum of the adjacent turbulence depart from a Kolmogorov-like cascade. Projection effects of the entire k-space onto a 1-D reduced spectrum direction, as typical of single-spacecraft observations, suggest the discrete mode is more likely to be observed when the angle between solar-wind flow direction and the DC magnetic-field direction is small. This study complements driven reduced MHD simulations of the solar corona [1] that support similar conclusions based on time-domain (frequency) analysis. [1] P. Dmitruk et al., GRL, 31, 21805 (2004).
NASA Technical Reports Server (NTRS)
Ding, D. Q.; Denton, . E.; Hudson, M. K.; Lysak, R. L.
1995-01-01
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.
NASA Astrophysics Data System (ADS)
Pietarila, A.; Cameron, R.; Solanki, S.
2009-12-01
The Hinode SOT (Tsuneta et al. 2008) NFI Na I D1 and SP Fe I data sampled at different positions on the solar disk provide a unique diagnostic for studying the expansion of magnetic flux concentrations with height. We make a comparative study of SOT observations and 2-dimensional (2D) radiative MHD-simulations to see how well the simulations capture the expansion properties. The expansion of flux concentrations is clearly seen in the SOT Na I D1 data, where most of the magnetic features appear unipolar at disk center while close to the limb bipolar appearance strongly dominates. This trend, albeit not as strong, is seen in the SP data as well. Some aspects of the observations are qualitatively reproduced by simulations with a potential (as opposed to vertical) upper boundary condition for the magnetic field.
Standard 1D solar atmosphere as initial condition for MHD simulations and switch-on effects
Bourdin, Philippe-A
2015-01-01
Many applications in Solar physics need a 1D atmospheric model as initial condition or as reference for inversions of observational data. The VAL atmospheric models are based on observations and are widely used since decades. Complementary to that, the FAL models implement radiative hydrodynamics and showed the shortcomings of the VAL models since almost equally long time. In this work, we present a new 1D layered atmosphere that spans not only from the photosphere to the transition region, but from the solar interior up to far in the corona. We also discuss typical mistakes that are done when switching on simulations based on such an initial condition and show how the initial condition can be equilibrated so that a simulation can start smoothly. The 1D atmosphere we present here served well as initial condition for HD and MHD simulations and should also be considered as reference data for solving inverse problems.
Shi, Ji-Ming; Lubow, Stephen H; Hawley, John F
2011-01-01
We present the first three-dimensional magnetohydrodynamic (MHD) simulations of a circumbinary disk surrounding an equal mass binary (off the computational grid, but assumed to have a fixed circular orbit of separation a). As in previous hydrodynamical simulations with a phenomenological (alpha-model) stress, strong torques by the binary clear a gap of radius 2a. Streams curve inward from r~2a toward the binary; some of their mass passes through the inner boundary, while the remainder swings back out to the disk, conveying angular momentum to it. However, we also find that near its inner edge the disk develops both a strong m = 1 asymmetry and growing orbital eccentricity. Moreover, the MHD stresses introduce more matter into the gap. As a result, the total torque per unit disk mass is 14 times larger than found previously. The inner boundary accretion rate per unit disk mass is 40 times greater than found from hydrodynamical {\\alpha}-model calculations and is ~ 1/3 the rate in the disk body. However, this fr...
Broken Ergodicity in Two-Dimensional Homogeneous Magnetohydrodynamic Turbulence
NASA Technical Reports Server (NTRS)
Shebalin, John V.
2010-01-01
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
Bifurcation analysis of magnetic reconnection in Hall-MHD-systems
NASA Astrophysics Data System (ADS)
Homann, Holger; Grauer, Rainer
2005-08-01
The influence of the Hall-term on the width of the magnetic islands of the tearing-mode is examined. We applied the center manifold (CMF) theory to a magnetohydrodynamic (MHD)-system. The MHD-system was chosen to be incompressible and includes in addition to viscosity the Hall-term in Ohm’s law. For certain values of physical parameters the corresponding center manifold is two-dimensional and therefore the original partial differential equations could be reduced to a two-dimensional system of ordinary ones. This amplitude equations exhibit a pitchfork-bifurcation which corresponds to the occurrence of the tearing-mode. Eigenvalue-problems and linear equations due to the center manifold reduction were solved numerically with the Arpack++-library. An important result of this analysis is the growth of the tearing mode island width by increasing the Hall-parameter, a feature which has been observed in recent numerical simulations of collisionless reconnection.
Nonlinear MHD simulations of Quiescent H-mode plasmas in DIII-D
NASA Astrophysics Data System (ADS)
Liu, F.; Huijsmans, G. T. A.; Loarte, A.; Garofalo, A. M.; Solomon, W. M.; Snyder, P. B.; Hoelzl, M.; Zeng, L.
2015-09-01
In the Quiescent H-mode (QH-mode) regime, the edge harmonic oscillation (EHO), thought to be a saturated kink-peeling mode (KPM) driven unstable by current and rotation, is found in experiment to provide sufficient stationary edge particle transport to avoid the periodic expulsion of particles and energy by edge localized modes (ELMs). In this paper, both linear and nonlinear MHD modelling of QH-mode plasmas from the DIII-D tokamak have been investigated to understand the mechanism leading to the appearance of the EHO in QH-mode plasmas. For the first time nonlinear MHD simulations with low-n modes both with ideal wall and resistive wall boundary conditions have been carried out with the 3D non-linear MHD code JOREK. The results show, in agreement with the original conjectures, that in the non-linear phase, kink peeling modes are the main unstable modes in QH-mode plasmas of DIII-D and that the kink-peeling modes saturate non-linearly leading to a 3D stationary state. The characteristics of the kink-peeling modes, in terms of mode structure and associated decrease of the edge plasma density associated with them, are in good agreement with experimental measurements of the EHO in DIII-D. The effect of plasma resistivity, the role of plasma parallel rotation as well as the effect of the conductivity of the vacuum vessel wall on the destabilization and saturation of kink-peeling modes have been evaluated for experimental QH-mode plasma conditions in DIII-D.
Three-dimensional MHD Simulation of Circumbinary Accretion Disks. II. Net Accretion Rate
NASA Astrophysics Data System (ADS)
Shi, Ji-Ming; Krolik, Julian H.
2015-07-01
When an accretion disk surrounds a binary rotating in the same sense, the binary exerts strong torques on the gas. Analytic work in the 1D approximation indicated that these torques sharply diminish or even eliminate accretion from the disk onto the binary. However, recent 2D and 3D simulational work has shown at most modest diminution. We present new MHD simulations demonstrating that for binaries with mass ratios of 1 and 0.1 there is essentially no difference between the accretion rate at large radius in the disk and the accretion rate onto the binary. To resolve the discrepancy with earlier analytic estimates, we identify the small subset of gas trajectories traveling from the inner edge of the disk to the binary and show how the full accretion rate is concentrated onto them as a result of stream–disk shocks driven by the binary torques.
Relativistic Modeling Capabilities in PERSEUS Extended MHD Simulation Code for HED Plasmas
NASA Astrophysics Data System (ADS)
Hamlin, Nathaniel; Seyler, Charles
2014-10-01
We discuss the incorporation of relativistic modeling capabilities into the PERSEUS extended MHD simulation code for high-energy-density (HED) plasmas, and present the latest simulation results. The use of fully relativistic equations enables the model to remain self-consistent in simulations of such relativistic phenomena as hybrid X-pinches and laser-plasma interactions. A major challenge of a relativistic fluid implementation is the recovery of primitive variables (density, velocity, pressure) from conserved quantities at each time step of a simulation. This recovery, which reduces to straightforward algebra in non-relativistic simulations, becomes more complicated when the equations are made relativistic, and has thus far been a major impediment to two-fluid simulations of relativistic HED plasmas. By suitable formulation of the relativistic generalized Ohm's law as an evolution equation, we have reduced the central part of the primitive variable recovery problem to a straightforward algebraic computation, which enables efficient and accurate relativistic two-fluid simulations. Our code recovers expected non-relativistic results and reveals new physics in the relativistic regime. Work supported by the National Nuclear Security Administration stewardship sciences academic program under Department of Energy cooperative Agreement DE-NA0001836.
3D Dynamics of Magnetopause Reconnection Using Hall-MHD Global Simulations
NASA Astrophysics Data System (ADS)
Maynard, K.; Germaschewski, K.; Raeder, J.; Bhattacharjee, A.
2011-12-01
Magnetic reconnection at Earth's magnetopause and in the magnetotail is of crucial importance for the dynamics of the global magnetosphere and space weather. Even though the plasma conditions in the magnetosphere are largely in the collisionless regime, most of the existing research using global computational models employ single-fluid magnetohydrodynamics (MHD) with artificial resistivity. Studies of reconnection in simplified, two-dimensional geometries have established that two-fluid and kinetic effects can dramatically alter dynamics and reconnection rates when compared with single-fluid models. These enhanced models also introduce particular signatures, for example a quadrupolar out-of-plane magnetic field component that has already been observed in space by satellite measurements. However, results from simplified geometries cannot be translated directly to the dynamics of three-dimensional magnetospheric reconnection. For instance, magnetic flux originating from the solar wind and arriving at the magnetopause can either reconnect or be advected around the magnetosphere. In this study, we use a new version of the OpenGGCM code that incorporates the Hall term in a Generalized Ohm's Law to study magnetopause reconnection under synthetic solar wind conditions and investigate how reconnection rates and dynamics of flux transfer events depend on the strength of the Hall term. The OpenGGCM, a global model of Earth's magnetosphere, has recently been ported to exploit modern computing architectures like the Cell processor and SIMD capabilities of conventional processors using an automatic code generator. These enhancements provide us with the performance needed to include the computationally expensive Hall physics.
Screening in two-dimensional foams
Simon Cox; François Graner; M. F. Vaz
2008-03-10
Using the Surface Evolver software, we perform numerical simulations of point-like deformations in a two-dimensional foam. We study perturbations which are infinitesimal or finite, isotropic or anisotropic, and we either conserve or do not conserve the number of bubbles. We measure the displacement fields around the perturbation. Changes in pressure decrease exponentially with the distance to perturbation, indicating a screening over a few bubble diameters.
Two-dimensional discrete Ginzburg-Landau solitons
Efremidis, Nikolaos K. [Department of Applied Mathematics, University of Crete, 71409 Heraklion, Crete (Greece); Christodoulides, Demetrios N. [College of Optics and Photonics, University of Central Florida, Orlando, Florida 32813 (United States); Hizanidis, Kyriakos [School of Electrical and Computer Engineering, National Technical University of Athens, Athens 15773 (Greece)
2007-10-15
We study the two-dimensional discrete Ginzburg-Landau equation. In the linear limit, the dispersion and gain curves as well as the diffraction pattern are determined analytically. In the nonlinear case, families of two-dimensional discrete solitons are found numerically as well as approximately in the high-confinement limit. The instability dynamics are analyzed by direct simulations.
NASA Technical Reports Server (NTRS)
Jackman, Charles H.; Douglass, Anne R.; Stolarski, Richard S.; Guthrie, Paul D.; Thompson, A. M.
1990-01-01
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.
MHD Simulation of a Disk Subjected to Lense-Thirring Precession
Sorathia, Kareem A; Hawley, John F
2013-01-01
When matter orbits around a central mass obliquely with respect to the mass's spin axis, the Lense-Thirring effect causes it to precess at a rate declining sharply with radius. Ever since the work of Bardeen & Petterson (1975), it has been expected that when a fluid fills an orbiting disk, the orbital angular momentum at small radii should then align with the mass's spin. Nearly all previous work has studied this alignment under the assumption that a phenomenological "viscosity" isotropically degrades fluid shears in accretion disks, even though it is now understood that internal stress in flat disks is due to anisotropic MHD turbulence. In this paper we report a pair of matched simulations, one in MHD and one in pure (non-viscous) HD in order to clarify the specific mechanisms of alignment. As in the previous work, we find that disk warps induce radial flows that mix angular momentum of different orientation; however, we also show that the speeds of these flows are generically transonic and are only very...
Global MHD Simulation of the Inner Accretion Disk in a Pseudo-Newtonian Potential
John F. Hawley; Julian H. Krolik
2000-09-28
We present a detailed three dimensional magnetohydrodynamic (MHD) simulation describing the inner region of a disk accreting onto a black hole. To avoid the technical complications of general relativity, the dynamics are treated in Newtonian fashion using the pseudo-Newtonian Pacz\\'ynski-Wiita potential. The disk evolves due to angular momentum transport which is produced naturally from MHD turbulence generated by the magnetorotational instability. We find that the resulting stress is continuous across the marginally stable orbit, in contradiction with the widely-held assumption that the stress should go to zero there. As a consequence, the specific angular momentum of the matter accreted into the hole is smaller than the specific angular momentum at the marginally stable orbit. The disk exhibits large fluctuations in almost every quantity, both spatially and temporally. In particular, the ratio of stress to pressure (the local analog of the Shakura-Sunyaev $\\alpha$ parameter) exhibits both systematic gradients and large fluctuations; from $\\sim 10^{-2}$ in the disk midplane at large radius, it rises to $\\sim 10$ both at a few gas density scaleheights above the plane at large radius, and near the midplane well inside the plunging region. Driven in part by large-amplitude waves excited near the marginally stable orbit, both the mass accretion rate and the integrated stress exhibit large fluctuations whose Fourier power spectra are smooth "red" power-laws stretching over several orders of magnitude in timescale.
Sub-Alfvenic Non-Ideal MHD Turbulence Simulations with Ambipolar Diffusion: I. Turbulence Statistics
Pak Shing Li; Christopher F. McKee; Richard I. Klein; Robert T. Fisher
2008-05-05
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.
On Europa's Magnetospheric Interaction: A MHD Simulation of the E4 Flyby
NASA Technical Reports Server (NTRS)
Kabin, K.; Combi, M. R.; Gombosi, T. I.; Nagy, A. F.; DeZeeuw, D. L.; Powell, K. G.
1999-01-01
The global three-dimensional interaction of Europa with the Jovian magnetosphere is modeled by using a complete set of ideal magnetohydrodynamic (MHD) equations. The model accounts for exospheric mass loading, ion-neutral charge exchange, recombination, and a possible intrinsic dipole magnetic field of Europa. The single-fluid MHD equations are solved by using a modem, finite volume, higher-order, Godunov-type method on an adoptively refined unstructured grid, which allows detailed modeling of the region near Europa while still resolving both the upstream region and the satellite's wake. The magnetic field and plasma density measured during Galileo's EGA flyby of December 19, 1996, are reproduced reasonably well in the simulation. We find the agreement between the data and our model particularly convincing if we assume that the plasma velocity during the EGA flyby deviated from the nominal corotation direction by approximately 20 deg. Evidence from the Galileo energetic particle detector also supports this assumption. In this case, we can fit the data using a dipole with orientation close to that of an induced dipole arising from the interaction of a hypothetical conducting subsurface layer on Europa with the periodically changing magnetic field of Jupiter. However, the magnitude of the dipole in our model is somewhat smaller (70%) than that suggested by Khurana et al. The total mass loading and ion-neutral charge exchange rates are consistent with the estimates of Europa's atmosphere and ionosphere.
Sub-Alfvenic Non-Ideal MHD Turbulence Simulations with Ambipolar Diffusion: I. Turbulence Statistics
Klein, R I; Li, P S; McKee, C F; Fisher, R
2008-04-10
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.
Characteristics of magnetic solar-like cycles in a 3D MHD simulation of solar convection
NASA Astrophysics Data System (ADS)
Passos, D.; Charbonneau, P.
2014-08-01
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
Intermittency, dissipation, and scaling in two-dimensional magnetohydrodynamic turbulence
Merrifield, J. A.; Chapman, S. C.; Dendy, R. O.
2007-01-15
Direct numerical simulations (DNS) provide a means to test phenomenological models for the scaling properties of intermittent MHD turbulence. The well-known model of She and Leveque, when generalized to MHD, is in good agreement with the DNS in three dimensions, however, it does not coincide with DNS in two dimensions (2D). This is resolved here using the results of recent DNS of driven MHD turbulence in 2D which directly determine the scaling of the rate of dissipation. Specifically, a simple modification to generalized refined similarity is proposed that captures the results of the 2D MHD simulations. This leads to a new generalization of She and Leveque in MHD that is coincident with the DNS results in 2D. A key feature of this model is that the most intensely dissipating structures, which are responsible for the intermittency, are thread-like in 2D, independent of whether the underlying phenomenology of the cascade is Kolmogorov or Iroshnikov Kraichnan.
A Real-time 3D Visualization of Global MHD Simulation for Space Weather Forecasting
NASA Astrophysics Data System (ADS)
Murata, K.; Matsuoka, D.; Kubo, T.; Shimazu, H.; Tanaka, T.; Fujita, S.; Watari, S.; Miyachi, H.; Yamamoto, K.; Kimura, E.; Ishikura, S.
2006-12-01
Recently, many satellites for communication networks and scientific observation are launched in the vicinity of the Earth (geo-space). The electromagnetic (EM) environments around the spacecraft are always influenced by the solar wind blowing from the Sun and induced electromagnetic fields. They occasionally cause various troubles or damages, such as electrification and interference, to the spacecraft. It is important to forecast the geo-space EM environment as well as the ground weather forecasting. Owing to the recent remarkable progresses of super-computer technologies, numerical simulations have become powerful research methods in the solar-terrestrial physics. For the necessity of space weather forecasting, NICT (National Institute of Information and Communications Technology) has developed a real-time global MHD simulation system of solar wind-magnetosphere-ionosphere couplings, which has been performed on a super-computer SX-6. The real-time solar wind parameters from the ACE spacecraft at every one minute are adopted as boundary conditions for the simulation. Simulation results (2-D plots) are updated every 1 minute on a NICT website. However, 3D visualization of simulation results is indispensable to forecast space weather more accurately. In the present study, we develop a real-time 3D webcite for the global MHD simulations. The 3-D visualization results of simulation results are updated every 20 minutes in the following three formats: (1)Streamlines of magnetic field lines, (2)Isosurface of temperature in the magnetosphere and (3)Isoline of conductivity and orthogonal plane of potential in the ionosphere. For the present study, we developed a 3-D viewer application working on Internet Explorer browser (ActiveX) is implemented, which was developed on the AVS/Express. Numerical data are saved in the HDF5 format data files every 1 minute. Users can easily search, retrieve and plot past simulation results (3D visualization data and numerical data) by using the STARS (Solar-terrestrial data Analysis and Reference System). The STARS is a data analysis system for satellite and ground-based observation data for solar-terrestrial physics.
Dayside Proton Aurora: Comparisons between Global MHD Simulations and Image Observations
NASA Technical Reports Server (NTRS)
Berchem, J.; Fuselier, S. A.; Petrinec, S.; Frey, H. U.; Burch, J. L.
2003-01-01
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.
J. Berchem; A. Marchaudon; M. Dunlop; C. P. Escoubet; J. M. Bosqued; H. Reme; I. Dandouras; A. Balogh; E. Lucek; C. Carr; Z. Pu
2008-01-01
This study uses two conjunctions between Cluster and Double Star TC-1 spacecraft together with global magnetohydrodynamic (MHD) simulations to investigate the large-scale configuration of magnetic reconnection at the dayside magnetopause. Both events involve southward interplanetary magnetic fields with significant By components. The first event occurred on 8 May 2004, while both spacecraft were exploring the dawn flank of the magnetosphere;
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
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.
NASA Technical Reports Server (NTRS)
Benyo, Theresa L.
2010-01-01
Preliminary flow matching has been demonstrated for a MHD energy bypass system on a supersonic turbojet engine. The Numerical Propulsion System Simulation (NPSS) environment was used to perform a thermodynamic cycle analysis to properly match the flows from an inlet to a MHD generator and from the exit of a supersonic turbojet to a MHD accelerator. Working with various operating conditions such as the enthalpy extraction ratio and isentropic efficiency of the MHD generator and MHD accelerator, interfacing studies were conducted between the pre-ionizers, the MHD generator, the turbojet engine, and the MHD accelerator. This paper briefly describes the NPSS environment used in this analysis and describes the NPSS analysis of a supersonic turbojet engine with a 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 an explored and desired range of 0 to 7.0 Mach.
Modeling CME-shock-driven storms in 2012-2013: MHD test particle simulations
NASA Astrophysics Data System (ADS)
Hudson, M. K.; Paral, J.; Kress, B. T.; Wiltberger, M.; Baker, D. N.; Foster, J. C.; Turner, D. L.; Wygant, J. R.
2015-02-01
The Van Allen Probes spacecraft have provided detailed observations of the energetic particles and fields environment for coronal mass ejection (CME)-shock-driven storms in 2012 to 2013 which have now been modeled with MHD test particle simulations. The Van Allen Probes orbital plane longitude moved from the dawn sector in 2012 to near midnight and prenoon for equinoctial storms of 2013, providing particularly good measurements of the inductive electric field response to magnetopause compression for the 8 October 2013 CME-shock-driven storm. An abrupt decrease in the outer boundary of outer zone electrons coincided with inward motion of the magnetopause for both 17 March and 8 October 2013 storms, as was the case for storms shortly after launch. Modeling magnetopause dropout events in 2013 with electric field diagnostics that were not available for storms immediately following launch have improved our understanding of the complex role that ULF waves play in radial transport during such events.
NASA Astrophysics Data System (ADS)
Gorby, M.; Schwadron, N.; Torok, T.; Downs, C.; Lionello, R.; Linker, J.; Titov, V. S.; Mikic, Z.; Riley, P.; Desai, M. I.; Dayeh, M. A.
2014-12-01
Recent work on the coupling between the Energetic Particle Radiation Environment Module (EPREM, a 3D energetic particle model) and Magnetohydrodynamics Around a Sphere (MAS, an MHD code developed at Predictive Science, Inc.) has demonstrated the efficacy of compression regions around fast coronal mass ejections (CMEs) for particle acceleration low in the corona (˜ 3 ? 6 solar radii). These couplings show rapid particle acceleration over a broad longitudinal extent (˜ 80 degrees) resulting from the pile-up of magnetic flux in the compression regions and their subsequent expansion. The challenge for forming large SEP events in such compression-acceleration scenarios is to have enhanced scattering within the acceleration region while also allowing for efficient escape of accelerated particles downstream (away from the Sun) from the compression region. We present here the most recent simulation results including energetic particle and CME plasma profiles, the subsequent flux and dosages at 1AU, and an analysis of the compressional regions as efficient accelerators.
The magnetic topology of the plasmoid flux rope in a MHD simulation of magnetotail reconnection
Birn, J.; Hesse, M.
1989-01-01
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.
MHD simulations of upflows in the Kippenhahn-Schlueter prominence model
NASA Astrophysics Data System (ADS)
Hillier, Andrew; Shibata, Kazunari; Isobe, Hiroaki; Berger, Thomas
The launch of SOT on the Hinode satellite, with it's previously unprecedented high resolution, high cadence images of solar prominences, led to the discovery of small scale, highly dynamic flows in quiescent prominences. Berger et al. (2008) reported dark upflows that propagated from the base of the prominence through a height of approximately 10 Mm before ballooning into the familiar mushroom shape often associated with the Rayleigh-Taylor instability. Whether such phenomena can be driven by instabilities and, if so, how the instability evolve is yet to be fully investigated. In this study, we use the Kippenhahn-Schlueter (K-S) prominence model as the base for 3D numerical MHD simulations. The K-S prominence model is linearly stable for ideal MHD perturbationss, but can be made unstable through nonlinear perturbations, which we impose through inserting a low density (high temperature) tube through the centre of the prominence. Our simulations follow the linear and nonlinear evolution of upflows propagating from the hot tube through the K-S prominence model. We excited Rayleigh-Taylor like modes inside the K-S model with a wave along the contact discontinuity created between the hot tube and the K-S prominence, and solved the pertur-bations of this system. For such a complex setting, the linear evolution of the instability has 0.7 not been studied, and we found the growth rate to be ˜ ( ?+ -?- - 0.05)k 0.22 . The most ?+ +?- unstable wavelength was ˜ 100 km which, through the inverse cascade process, created upflows of ˜ 300 km. The rising plumes obtained a constant rise velocity in the nonlinear stage due to the creation of adverse magnetic and gas pressure gradients at the top of the plume.
NASA Astrophysics Data System (ADS)
Kivelson, M.; Jia, X.
2013-12-01
In previous work we demonstrated that a magnetohydrodynamic (MHD) simulation of Saturn's magnetosphere in which periodicity is imposed by rotating vortical flows in the ionosphere reproduces many reported periodically varying properties of the system. Here we shall show that previously unreported features of the MHD simulation of Saturn's magnetosphere illuminate additional measured properties of the system. By averaging over a rotation period, we identify a global electric field whose magnitude is a few tenths of a mV/m (see Figure 1). The electric field intensity decreases with radial distance in the middle magnetosphere, consistent with drift speeds v=E/B of a few km/s towards the morning side and relatively independent of radial distance. The electric field within 10 RS in the equatorial plane is oriented from post-noon to post-midnight, in excellent agreement with observations [e.g., Thomsen et al., 2012; Andriopoulou et al., 2012, 2013; Wilson et al., 2013]. By following the electric field over a full rotation phase we identify oscillatory behavior whose magnitude is consistent with the reported fluctuations of measured electric fields. Of particular interest is the nature of the fast mode perturbations that produce periodic displacement of the magnetopause and flapping of the current sheet. Figure (2) shows the total perturbation pressure (the sum of magnetic and thermal pressure) in the equatorial plane at a rotation phase for which the ionospheric flow near noon is equatorward. By following the perturbations over a full rotation period, we demonstrate properties of the fast mode wave launched by the rotating flow structures and thereby characterize the 'cam' signal originally proposed by Espinosa et al. [2003].
NASA Technical Reports Server (NTRS)
Birn, J.; Hones, E. W., Jr.; Schindler, K.
1986-01-01
The outflow from a reconnection region in a realistic magnetotail geometry is studied using a two-dimensional time-dependent, compressible, resistive MHD code. Two cases are emphasized: (1) the evolution of near-earth reconnection, which grows in the form of an internal unstable mode after gradual externally forced changes have initiated an anomalous dissipation process, and (2) the evolution of more distant reconnection under influence of a nonuniform inflow that forces reconnection to occur at a given location in the distant tail. In both cases, it is demonstrated that plasma flow is primarily parallel to the magnetic field in regions away from the localized area of reconnection and outside a narrow central layer.
Groth, Clinton P. T.
three-dimensional MHD simulation of a space weather event: CME formation, interplanetary propagation the potential, as well as current limitations, of the MHD-based space weather model for enhancing the understanding of coronal physics, solar wind plasma processes, magnetospheric physics, and space weather
Two-dimensional NMR spectrometry
Farrar, T.C.
1987-06-01
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/.
Two-dimensional thermofield bosonization
Amaral, R.L.P.G.
2005-12-15
The main objective of this paper was to obtain an operator realization for the bosonization of fermions in 1 + 1 dimensions, at finite, non-zero temperature T. This is achieved in the framework of the real-time formalism of Thermofield Dynamics. Formally, the results parallel those of the T = 0 case. The well-known two-dimensional Fermion-Boson correspondences at zero temperature are shown to hold also at finite temperature. To emphasize the usefulness of the operator realization for handling a large class of two-dimensional quantum field-theoretic problems, we contrast this global approach with the cumbersome calculation of the fermion-current two-point function in the imaginary-time formalism and real-time formalisms. The calculations also illustrate the very different ways in which the transmutation from Fermi-Dirac to Bose-Einstein statistics is realized.
Two dimensional hyperbolic grid generation
Zuheyr Alsalihi
1987-01-01
A two dimensional body-fitted coordinate system was generated for use in solving the turbulent or laminar, (thin-layer) Navier-Stokes equations for transonic flow fields about airfoils. The technique employed is hyperbolic grid generation with the condition of orthogonality and cell area (inverse of the metric Jacobian) specification. Addition of fourth-order numerical dissipation terms in the streamwise direction has no detrimental effect
Two dimensional unstable scar statistics.
Warne, Larry Kevin; Jorgenson, Roy Eberhardt; Kotulski, Joseph Daniel; Lee, Kelvin S. H. (ITT Industries/AES Los Angeles, CA)
2006-12-01
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.
Global MHD simulations of Flux Transfer Events under generic southward IMF conditions
NASA Astrophysics Data System (ADS)
Dorelli, J.; Raeder, J.; Bhattacharjee, A.
2006-12-01
Recently, Raeder [Annales Geophys., 24, 2006] proposed a FTE generation mechanism in which Earth's dipole tilt, and the associated movement of the stagnation flow line away from the magnetic separator, results in the formation of a new dayside X line. As a result, a magnetic flux rope forms at the dayside magnetopause, eventually propagating toward one of the polar cusps. In Raeder's simulations, new flux ropes were observed to form periodically at the subsolar magnetopause via this mechanism. Fedder et al. [Journal of Geophys. Res., 107, 2002] proposed an alternative mechanism in which a dayside separator line becomes twisted as intense parallel currents develop along it, eventually undergoing a topological change in which one of the separator's dayside magnetic nulls becomes detached from the separator. As the nulls then move tailward, the flux rope propagates poleward, and the process begins anew. While the Fedder mechanism seems interesting and plausible, the idea has not been quantiatively tested (via a calculation of the time- dependent "magnetic skeleton" -- the system of nulls, separatrices and separators which characterizes the magnetic field topology) with simulations. In this presentation, we use global MHD simulations (the UNH OpenGGCM code) to test the Fedder mechanism by computing the time-dependent magnetic skeleton during time intervals where FTEs are observed under generic southward IMF conditions.
Time-dependent simulation of oblique MHD cosmic-ray shocks using the two-fluid model
NASA Technical Reports Server (NTRS)
Frank, Adam; Jones, T. W.; Ryu, Dongsu
1995-01-01
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.
Mukamel, Shaul
Pro-3 Pro-4 Ala-5 Phe-6 Phe-7 Pro- 8 Pro-9 Phe-10 Pro-) in chloroform is calculated using an explicit solvent molecular dynamics (MD) simulation combined with a density functional theory (DFT) map long time (nanosecond) molecular dynamics (MD) simulation. We had developed an electrostatic density
Magnetically dominated MHD bow shock ows
De Sterck, Hans
Chapter 6 Magnetically dominated MHD bow shock ows: symmetrical two-dimensional ow around (Fig. 2.3). As long as the upstream magnetic #12;eld strength is small and thermal or dynamic pressure in this dissertation is that MHD bow shock ows exhibit an entirely di#11;erent topology when the upstream magnetic #12
Transport in two-dimensional paper networks
Fu, Elain; Ramsey, Stephen A.; Kauffman, Peter; Lutz, Barry; Yager, Paul
2011-01-01
Two-dimensional paper networks (2DPNs) hold great potential for transcending the capabilities and performance of today's paper-based analytical devices. Specifically, 2DPNs enable sophisticated multi-step chemical processing sequences for sample pretreatment and analysis at a cost and ease-of-use that make them appropriate for use in settings with low resources. A quantitative understanding of flow in paper networks is essential to realizing the potential of these networks. In this report, we provide a framework for understanding flow in simple 2DPNs using experiments, analytical expressions, and computational simulations. PMID:22140373
Gerstein, Mark
-helix in solution is investigated by molecular simulation. A marked contrast is seen between the hydration atoms point their hydrogens outward and adopt the clathrate arrangement found in the hydration of small
NASA Technical Reports Server (NTRS)
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
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.
Numerical Simulation of Turbulent MHD Flows Using an Iterative PNS Algorithm
NASA Technical Reports Server (NTRS)
Kato, Hiromasa; Tannehill, John C.; Mehta, Unmeel B.
2003-01-01
A new parabolized Navier-Stokes (PNS) algorithm has been developed to efficiently compute magnetohydrodynamic (MHD) flows in the low magnetic Reynolds number regime. In this regime, the electrical conductivity is low and the induced magnetic field is negligible compared to the applied magnetic field. The MHD effects are modeled by introducing source terms into the PNS equation which can then be solved in a very efficient manner. To account for upstream (elliptic) effects, the flowfields are computed using multiple streamwise sweeps with an iterated PNS algorithm. Turbulence has been included by modifying the Baldwin-Lomax turbulence model to account for MHD effects. The new algorithm has been used to compute both laminar and turbulent, supersonic, MHD flows over flat plates and supersonic viscous flows in a rectangular MHD accelerator. The present results are in excellent agreement with previous complete Navier-Stokes calculations.
Three Fluid Hall MHD Simulations of a High Density Plasma Opening Switch
NASA Astrophysics Data System (ADS)
Sethuraman, P.; Strauss, H.; Doron, R.; Maron, Y.; Arad, R.
2004-11-01
Two ion species plasma opening switch (POS) simulations are studied computationally and compared with experiment [1]. The Hall parameter H, the ratio of ion skin depth to system size, is of order unity. The ion species are protons and carbon, with electrons maintaining quasineutality. The velocities of the ion species are combined into average and difference velocities. The average velocity satisfies the usual MHD equation with a modified inertial term. In the low H limit, the difference velocity is a drift in the direction of the current, in which light and heavy ions move in different directions. The simulations account for the two main experimental observations. First, the experimental evolution is not strongly dependent on the polarity of the magnetic field, as in a low density, high H POS. Second, light and heavy ions tend to move apart. Three fluid Hall equations are being developed with a three dimensional magnetic field, depending on two spatial directions. The 2 1/2D equations will be applied to reconnection studies. [1] A. Arad et al. Phys. Plasmas 10, 112 (2003)
Radiative 3D MHD simulations of the spontaneous small-scale eruptions in the solar atmosphere
NASA Astrophysics Data System (ADS)
Kitiashvili, Irina N.
2015-08-01
Studying non-linear turbulent dynamics of the solar atmosphere is important for understanding mechanism of the solar and stellar brightness variations. High-resolution observations of the quiet Sun reveal ubiquitous distributions of high-speed jets, which are transport mass and energy into the solar corona and feeding the solar wind. However, the origin of these eruption events is still unknown. Using 3D realistic MHD numerical simulations we find that small-scale eruptions are produced by ubiquitous magnetized vortex tubes generated by the Sun's turbulent convection in subsurface layers. The swirling vortex tubes (resembling tornadoes) penetrate into the solar atmosphere, capture and stretch background magnetic field, and push the surrounding material up, generating shocks. Our simulations reveal complicated high-speed flow patterns and thermodynamic and magnetic structure in the erupting vortex tubes and shows that the eruptions are initiated in the subsurface layers and are driven by high-pressure gradients in the subphotosphere and photosphere and by the Lorentz force in the higher atmosphere layers. I will discuss about properties of these eruptions, their effects on brightness and spectral variations and comparison with observations.
A three-dimensional high Mach number asymmetric magnetopause model from global MHD simulation
NASA Astrophysics Data System (ADS)
Liu, Z.-Q.; Lu, J. Y.; Wang, C.; Kabin, K.; Zhao, J. S.; Wang, M.; Han, J. P.; Wang, J. Y.; Zhao, M. X.
2015-07-01
The numerical results from a physics-based global magnetohydrodynamic (MHD) model are used to examine the effect of the interplanetary magnetic field (IMF), solar wind dynamic pressure, and dipole tilt angle on the size and shape of the magnetopause. The subsolar magnetopause is identified using the plasma velocity and density, the cusps are identified using the thermal pressure, and the whole shape of the magnetopause is determined with the three-dimensional streamlines traced through the simulation domain. The magnetopause surface obtained from the simulations is fitted with a three-dimensional surface function controlled by ten configuration parameters, which provide a description of the subsolar magnetopause, the cusp geometry, the flaring angle, the azimuthal asymmetry, the north-south asymmetry, and the twisting angle of the magnetopause. Effects of the IMF, solar wind dynamic pressure, and dipole tilt angle on the configuration parameters are analyzed and fitted by relatively simple functions. It is found that the solar wind dynamic pressure mainly affects the magnetopause size; the IMF mainly controls the magnetopause flaring angle, azimuthal asymmetry, and twisting angle; and the dipole tilt angle mainly affects the magnetopause north-south asymmetry and the cusp geometry. The model is validated by comparing with available empirical models and observational results, and it is demonstrated that the new model can describe the magnetopause for typical solar wind conditions.
Mini-magnetosphere: Laboratory experiment, physical model and Hall MHD simulation
NASA Astrophysics Data System (ADS)
Shaikhislamov, I. F.; Antonov, V. M.; Zakharov, Yu. P.; Boyarintsev, E. L.; Melekhov, A. V.; Posukh, V. G.; Ponomarenko, A. G.
2013-08-01
Magnetosphere with a size comparable to the ion kinetic scales is investigated by means of laboratory experiment, analytical analysis and Hall MHD simulation. In experiment a specific magnetic field was observed which is non-coplanar to dipole field, does not change sign at dipole moment inversion and could be generated only via the quadratic Hall term. Magnetopause position and plasma stand off distance were found to be profoundly different between the experimental regimes with small and large ion inertia length. In the previous studies of a mini-magnetosphere by kinetic codes such novel features were observed as absence of the bow shock and plasma stopping at the Stoermer particle limit instead of the pressure balance distance. Proposed analytical model explains these features by Hall currents which tend to cancel magnetic field convection by ions. Performed numerical simulation shows a good agreement with experiment and analytical model. It gives detailed spatial structure of the Hall field and reveals that while ions penetrate deep inside mini-magnetosphere electrons overflow around it along magnetopause boundary.
Extended MHD simulations of Rayleigh-Taylor instability with real frequency in a 2D slab
NASA Astrophysics Data System (ADS)
Goto, Ryosuke; Miura, Hideaki; Ito, Atsushi; Sato, Masahiko; Hatori, Tomoharu
2014-10-01
Small scale effects such as the Finite Larmor Radius (FLR) effect and the Hall term can change the linear and non-linear growth of the high wave number unstable modes of the pressure driven instability considerably. Here we consider a simple Rayleigh-Taylor (R-T) instability in a 2D slab, and study the effect of the Hall term and the FLR effect to the R-T instability by means of numerical simulations of the Braginskii-type extended MHD equations. As we have reported earlier, the linear growth rates of the high wave number modes are highly reduced when the Hall term and the FLR effect are added simultaneously. However, there appears little real frequency in the previous work. Since the diamagnetic drift associated with the real frequency is considered to affect the growth of the linear and nonlinear evolutions, we provide a new equilibrium in which appearance of the real frequency is expected and carry out numerical simulations. Influences of the real frequency on the growth rates as well as on the nonlinear mixing width for some combinations of the Hall and the FLR parameters are going to be presented.
The Biermann Battery In Cosmological Mhd Simulations Of Population III Star Formation
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
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.
G. C. Murphy; Rachid Ouyed; Guy Pelletier
2008-06-01
Magnetic reconnection plays a critical role in many astrophysical processes where high energy emission is observed, e.g. particle acceleration, relativistic accretion powered outflows, pulsar winds and probably in dissipation of Poynting flux in GRBs. The magnetic field acts as a reservoir of energy and can dissipate its energy to thermal and kinetic energy via the tearing mode instability. We have performed 3d nonlinear MHD simulations of the tearing mode instability in a current sheet. Results from a temporal stability analysis in both the linear regime and weakly nonlinear (Rutherford) regime are compared to the numerical simulations. We observe magnetic island formation, island merging and oscillation once the instability has saturated. The growth in the linear regime is exponential in agreement with linear theory. In the second, Rutherford regime the island width grows linearly with time. We find that thermal energy produced in the current sheet strongly dominates the kinetic energy. Finally preliminary analysis indicates a P(k) 4.8 power law for the power spectral density which suggests that the tearing mode vortices play a role in setting up an energy cascade.
3D MHD Simulations of Laser Plasma Guiding in Curved Magnetic Field
NASA Astrophysics Data System (ADS)
Roupassov, S.; Rankin, R.; Tsui, Y.; Capjack, C.; Fedosejevs, R.
1999-11-01
The guiding and confinement of laser produced plasma in a curved magnetic field has been investigated numerically. These studies were motivated by experiments on pulsed laser deposition of diamond-like films [1] in which a 1kG magnetic field in a curved solenoid geometry was utilized to steer a carbon plasma around a curved trajectory and thus to separate it from unwanted macroparticles produced by the laser ablation. The purpose of the modeling was to characterize the plasma dynamics during the propagation through the magnetic guide field and to investigate the effect of different magnetic field configurations. A 3D curvilinear ADI code developed on the basis of an existing Cartesian code [2] was employed to simulate the underlying resistive one-fluid MHD model. Issues such as large regions of low background density and nonreflective boundary conditions were addressed. Results of the simulations in a curved guide field will be presented and compared to experimental results. [1] Y.Y. Tsui, D. Vick and R. Fedosejevs, Appl. Phys. Lett. 70 (15), pp. 1953-57, 1997. [2] R. Rankin, and I. Voronkov, in "High Performance Computing Systems and Applications", pp. 59-69, Kluwer AP, 1998.
NASA Astrophysics Data System (ADS)
Lynch, Ben; Edmondson, Justin K.; Kazachenko, Maria D.; Guidoni, Silvina E.
2015-04-01
We present a detailed analysis of the properties of magnetic reconnection at large-scale current sheets in a very high cadence 2.5D MHD simulation of sympathetic magnetic breakout coronal mass ejections (CMEs) from a pseudostreamer source region. We examine the resistive tearing and breakup of the three main current sheets into chains of X- and O-type null points and follow the dynamics of magnetic island growth, their merging, transit, and ejection with the reconnection exhaust. For each current sheet, we quantify the evolution of the length-to-width aspect ratio (up to ~100:1), Lundquist number (~10^4), and reconnection rate (inflow-to-outflow ratios reaching ~0.15). We examine the statistical and spectral properties of the fluctuations in the current sheets resulting from the plasmoid instability, including the distribution of magnetic island width, mass, and flux content. We show that the temporal evolution of the spectral index of the reconnection-generated magnetic energy density fluctuations appear to reflect global properties of the current sheet evolution. Our results are in excellent agreement with recent, high resolution reconnection-in-a-box simulations even though our current sheets' formation, growth, and dynamics are intrinsically coupled to the global evolution of sequential sympathetic CME eruptions.
Collisionless magnetic reconnection under anisotropic MHD approximation
NASA Astrophysics Data System (ADS)
Hirabayashi, Kota; Hoshino, Masahiro
We study the formation of slow-mode shocks in collisionless magnetic reconnection by using one- and two-dimensional collisionless magneto-hydro-dynamic (MHD) simulations based on the double adiabatic approximation, which is an important step to bridge the gap between the Petschek-type MHD reconnection model accompanied by a pair of slow shocks and the observational evidence of the rare occasion of in-situ slow shock observation. According to our results, a pair of slow shocks does form in the reconnection layer. The resultant shock waves, however, are quite weak compared with those in an isotropic MHD from the point of view of the plasma compression and the amount of the magnetic energy released across the shock. Once the slow shock forms, the downstream plasma are heated in highly anisotropic manner and a firehose-sense (P_{||}>P_{?}) pressure anisotropy arises. The maximum anisotropy is limited by the marginal firehose criterion, 1-(P_{||}-P_{?})/B(2) =0. In spite of the weakness of the shocks, the resultant reconnection rate is kept at the same level compared with that in the corresponding ordinary MHD simulations. It is also revealed that the sequential order of propagation of the slow shock and the rotational discontinuity, which appears when the guide field component exists, changes depending on the magnitude of the guide field. Especially, when no guide field exists, the rotational discontinuity degenerates with the contact discontinuity remaining at the position of the initial current sheet, while with the slow shock in the isotropic MHD. Our result implies that the slow shock does not necessarily play an important role in the energy conversion in the reconnection system and is consistent with the satellite observation in the Earth's magnetosphere.
Two-dimensional kinetic field-reversed equilibria
Webster, R.B.; Schwarzmeier, J.L.; Lewis, H.R. (Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (US)); Choi, C.K.; Terry, W.K. (School of Nuclear Engineering, Purdue University, West Lafayette, Indiana 47907 (USA))
1991-04-01
A two-dimensional kinetic description of field-reversed equilibria has been developed. Three equilibrium models are presented: a kinetic model, a rigidly rotating model, and a magnetohydrodynamics (MHD) model. The kinetic model of equilibrium provides spatial distributions of the macroscopic moments, including velocity shear, that are in good agreement with experimental observations. The rigidly rotating and MHD models allow more general pressure profiles than previous studies. These models, which allow the computation of a wide range of equilibria, suggest that for parameters typical of the current experiments kinetic modifications of the equilibrium are small; however, they may be important if the field-reversed configuration is interacting strongly with a magnetic mirror. Also, the ability to compute kinetic equilibria makes possible a self-consistent examination of the stability of field-reversed configurations, which is believed to be strongly influenced by kinetic effects.
Alfvén waves and ideal two-dimensional Galerkin truncated magnetohydrodynamics
Giorgio Krstulovic; Marc-Etienne Brachet; Annick Pouquet
2011-01-05
We investigate numerically the dynamics of two-dimensional Euler and ideal magnetohydrodynamics (MHD) flows in systems with a finite number of modes, up to $4096^2$, for which several quadratic invariants are preserved by the truncation and the statistical equilibria are known. Initial conditions are the Orszag-Tang vortex with a neutral X-point centered on a stagnation point of the velocity field in the large scales. In MHD, we observe that the total energy spectra at intermediate times and intermediate scales correspond to the interactions of eddies and waves, $E_T(k)\\sim k^{-3/2}$. Moreover, no dissipative range is visible neither for Euler nor for MHD in two dimensions; in the former case, this may be linked to the existence of a vanishing turbulent viscosity whereas in MHD, the numerical resolution employed may be insufficient. When imposing a uniform magnetic field to the flow, we observe a lack of saturation of the formation of small scales together with a significant slowing-down of their equilibration, with however a cut-off independent partial thermalization being reached at intermediate scales.
Two-dimensional magnetization characteristics
Enokizono, M.; Todaka, T.; Kanao, S.
1994-07-01
Appeals for improved energy efficiency in recent years have been attended by increased emphasis on the magnetic characteristics of the magnetic materials used in transformer cores and other components, as a means of improving the efficiency of electrical equipment. In conventional magnetic measurements, only the same components of the magnetic flux intensity B and the magnetic field intensity H in the excited direction are measured. In short, the measured values are treated as scalar quantities. Since it is well known that B and H have a phase difference in space, these quantities should be dealt with as vectors. The authors have used a two-dimensional magnetic measurement apparatus to obtain a precise understanding of the behavior of B and H in magnetization processes. In conventional measurements, when the excited direction does not correspond to the rolling direction, the locus of the vectors of B is not an alternating flux; that is, it becomes a loop. Therefore, the iron loss obtained by the conventional method is different from that for two-dimensional measurements.
NASA Astrophysics Data System (ADS)
Roberts, D. A.; Goldstein, M. L.; Deane, A. E.
2002-12-01
Solar wind fluctuations are known to be anisotropic, both in wave vector and in field fluctuation directions. Various sets of two-spacecraft observations, in addition to ensembles of correlations from a single spacecraft, show there is some preference for wave vector directions nearly perpendicular to the mean magnetic field. Many studies have also shown that magnetic field (and to a lesser extent the velocity field) has a minimum variance direction typically along the mean magnetic field direction, and that this persists even as the mean field turns to nearly perpendicular to the radial in the outer heliosphere. The requirement that the wave vectors and fluctuations must turn with the mean field eliminates simple views of planar Alfvén waves or quasi-two-dimensional fluctuations or superpositions of these. In previously reported simulation work, we have shown that inhomogeneity transverse to the radial flow direction as well as nonlinear interactions are required to explain the observations. We now have added to our simulation code non-radial wave vectors to the inflow population of waves, as well as three-dimensional microstreams (radial flows that depend on both transverse directions). This paper will explore the extent to which these additions aid in solving the anisotropy and minimum variance problems. Preliminary results are similar to those found with 2-D simulations which showed some turning of wave vectors due to shear, but as yet no clear minimum variance signature. We will use higher resolution simulations to determine if part of the problem is that the scale of our assumed population of fluctuations is too large.
NASA Astrophysics Data System (ADS)
Reuter, K.; Jenko, F.; Forest, C. B.; Bayliss, R. A.
2008-08-01
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
Matsuda, K.; Terada, N.; Katoh, Y. [Space and Terrestrial Plasma Physics Laboratory, Department of Geophysics, Graduate School of Science, Tohoku University, Sendai, Miyagi 980-8578 (Japan); Misawa, H. [Planetary Plasma and Atmospheric Research Center, Graduate School of Science, Tohoku University, Sendai, Miyagi 980-8578 (Japan)
2011-08-15
There has been a great concern about the origin of the parallel electric field in the frame of fluid equations in the auroral acceleration region. This paper proposes a new method to simulate magnetohydrodynamic (MHD) equations that include the electron convection term and shows its efficiency with simulation results in one dimension. We apply a third-order semi-discrete central scheme to investigate the characteristics of the electron convection term including its nonlinearity. At a steady state discontinuity, the sum of the ion and electron convection terms balances with the ion pressure gradient. We find that the electron convection term works like the gradient of the negative pressure and reduces the ion sound speed or amplifies the sound mode when parallel current flows. The electron convection term enables us to describe a situation in which a parallel electric field and parallel electron acceleration coexist, which is impossible for ideal or resistive MHD.
NASA Astrophysics Data System (ADS)
Hong, Sung-Min; Jungemann, Christoph
2009-04-01
Noise simulation of a 2D semiconductor device by employing a deterministic BE solver has been reported. The fully coupled scheme enables small-signal analysis. As an example, the RF and noise performance of a SiGe HBT, including cutoff frequency, minimum noise figure, noise resistance, and electron noise current transit time, is investigated.
Llacer, J.; Chatterjee, A.; Batho, E.K.; Poskanzer, J.A.
1982-05-01
The characteristics and design of a high-accuracy and high-sensitivity 2-dimensional camera for the measurement of the end-point of the trajectory of accelerated heavy ion beams of positron emitter isotopes are described. Computer simulation methods have been used in order to insure that the design would meet the demanding criteria of ability to obtain the location of the centroid of a point source in the X-Y plane with errors smaller than 1 mm, with an activity of 100 nanoCi, in a counting time of 5 sec or less. A computer program which can be developed into a general purpose analysis tool for a large number of positron emitter camera configurations is described in its essential parts. The validation of basic simulation results with simple measurements is reported, and the use of the program to generate simulated images which include important second order effects due to detector material, geometry, septa, etc. is demonstrated. Comparison between simulated images and initial results with the completed instrument shows that the desired specifications have been met.
Comparison between YOHKOH Soft X-ray Images and 3D MHD Simulations of Solar Emerging Flux Regions
R. Matsumoto; T. Tajima; M. Kaisig; K. Shibata; Y. Ishido; S. Tsuneta; T. Shimizu; G. Kawai; H. Kurokawa; M. Akioka; L. Acton; K. Strong; N. Nitta
1992-01-01
The soft X-ray telescope on the Yohkoh mission enabled us to observe the evolution of emerging flux regions (EFR) in coronal X-rays with high spatial and temporal resolution. Furthermore, we now have enough computing capability to perform three-dimensional MHD simulation of EFRs with sufficient spacial resolution to study details of the flux emergence process. These new tools provide the opportunity
Analysis of Voyager observed high-energy electron fluxes in the heliosheath using MHD simulations
NASA Astrophysics Data System (ADS)
Washimi, H.; Webber, W. R.; Zank, G. P.; Hu, Q.; Florinski, V. A.; Adams, J. H.; Kubo, Y.
2011-12-01
The Voyager spacecraft (V1 and V2) observed electrons of 6-14 MeV in the heliosheath which showed several incidences of flux variation relative to a background of gradually increasing flux with distance from the Sun. The increasing flux of background electrons is thought to result from inward radial diffusion. We compare the temporal electron flux variation with dynamical phenomena in the heliosheath that are obtained from our MHD simulations. Because our simulation is based on V2 observed solar-wind data before V2 crossed the termination shock, this analysis is effective up to late 2008, i.e., about a year after the V2-crossing, during which disturbances, driven prior to the crossing time, survived in the heliosheath. Several electron flux variations correspond to times directly associated with interplanetary shock events. One noteworthy example corresponds to various times associated with the March 2006 interplanetary shock, these being the collision with the termination shock, the passage past the V1 spacecraft, and the collision with the region near the heliopause, as identified by W.R. Webber et al. (JGR, 114, A07108, 2009) for proton/helium of 7-200 MeV. Our simulations indicate that all other electron flux variations, except one, correspond well to the times when a shock-driven magneto-sonic pulse and its reflection in the heliosheath either passed across V1/V2, or collided with the termination shock or with the plasma sheet near the heliopause. This result suggests that these variations in the electron flux should be due to either direct or indirect effects of magnetosonic pulses in the heliosheath driven by interplanetary shocks.
NASA Astrophysics Data System (ADS)
Jia, Xianzhe; Hansen, Kenneth; Gombosi, Tamas; Ridley, Aaron; de Zeeuw, Darren
As revealed by the remote observations from the Hubble Space Telescope and in-situ observa-tions from Cassini, Saturn's magnetosphere responds strongly to the solar wind driving. We have used global MHD simulations to investigate in details the global configuration and dy-namics of Saturn's magnetosphere in response to changes in the solar wind. Our model uses a high-resolution, non-uniform spherical grid, which is crucial for capturing fine structures of the large-scale magnetospheric currents responsible for the coupling between the magnetosphere and the ionosphere. In order to distinguish effects due to different types of variations in the solar wind, we use an idealized solar wind input with features typical of those of Corotating Interaction Regions seen at Saturn's orbit. In particular, we divide our simulation into four stages during each of which (spans about one week) the strength of the IMF remains fixed but its orientation is set southward, dawnward, northward and duskward, respectively. A forward shock is then introduced in the solar wind during each of the four intervals. In this talk, we will compare the global configuration of Saturn's magnetosphere before and after the shock compression under different IMF conditions. We will also show the ionospheric response to the solar wind driving, in particular the field-aligned currents and convection pattern, and discuss their relationship with dynamics in the magnetosphere. Our simulation results show that pe-riodic plasmoid formation occurs in Saturn's magnetotail, independent of the IMF conditions. However, the periodicity of plasmoid formation in the tail appears to be affected by the solar wind conditions. We find that when a forward shock impinged on the magnetosphere, the magnetosphere significantly shrinks and periodic reconnection events in the magnetotail take place with a periodicity very close to the planet rotation period.
Chen, C. D.; Kemp, A. J.; Pérez, F.; Link, A.; Key, M. H.; McLean, H.; Ping, Y.; Patel, P. K. [Lawrence Livermore National Laboratory (United States)] [Lawrence Livermore National Laboratory (United States); Beg, F. N.; Chawla, S.; Sorokovikova, A.; Westover, B. [University of California, San Diego (United States)] [University of California, San Diego (United States); Morace, A. [University of Milan (Italy)] [University of Milan (Italy); Stephens, R. B. [General Atomics (United States)] [General Atomics (United States); Streeter, M. [Imperial College London (United Kingdom)] [Imperial College London (United Kingdom)
2013-05-15
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 × 10{sup 20} W/cm{sup 2} 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.
Studying Solar MHD Wave Propagation in Two Dimensions
NASA Astrophysics Data System (ADS)
McIntosh, S. W.; Bogdan, T. J.
1999-05-01
We present preliminary results on simulations of Magnetohydrodynamic (MHD) wave propagation in a two dimensional stratified model of the upper solar atmosphere. The simulations presented are obtained using the High-Order Godunov scheme of Zachary, Malagoli & Colella (1994). These simulations allow us to analyze quantitatively the coupling, resonances and absorption of MHD waves in a stratified plasma such as that of the Sun. In particular, we are able to observe the dynamic evolution of energy and momentum balances of the model atmosphere in response the wave propagation. In addition, we are able to study the phenomenology of MHD wave passage through particular regions of interest. We will concentrate mostly upon the physical manifestation of MHD waves propagating in ``network'' and ``internetwork'' regions and study the effect on physical parameters and the basic field structure imposed at outset. We believe that such simulations are important in that they compliment the high quality/temporal resolution data currently being acquired by the SOHO and TRACE spacecraft.
Two-Dimensional Phase Unwrapping
Evans, Brian L.
Aperture Radar Mountains Magnetic Resonance Imaging Knee Optical Doppler Tomography Blood Vessel #12 simulated ODT images with conjugate-gradient method Validate with 10 simulated ODT images Simulated images have variety of vessel sizes and shapes · Tested on 100 simulated ODT images #12;Simulated Image
Constraints on particle acceleration sites in the Crab Nebula from relativistic MHD simulations
Olmi, Barbara; Amato, Elena; Bucciantini, Niccolò
2015-01-01
The Crab Nebula is one of the most efficient accelerators in the Galaxy and the only galactic source showing direct evidence of PeV particles. In spite of this, the physical process behind such effective acceleration is still a deep mystery. While particle acceleration, at least at the highest energies, is commonly thought to occur at the pulsar wind termination shock, the properties of the upstream flow are thought to be non-uniform along the shock surface, and important constraints on the mechanism at work come from exact knowledge of where along this surface particles are being accelerated. Here we use axisymmetric relativistic MHD simulations to obtain constraints on the acceleration site(s) of particles of different energies in the Crab Nebula. Various scenarios are considered for the injection of particles responsible for synchrotron radiation in the different frequency bands, radio, optical and X-rays. The resulting emission properties are compared with available data on the multi wavelength time varia...
NASA Astrophysics Data System (ADS)
Rubin, M.; Jia, X.; Altwegg, K.; Combi, M. R.; Daldorff, L. K. S.; Gombosi, T. I.; Khurana, K.; Kivelson, M. G.; Tenishev, V. M.; Tóth, G.; Holst, B.; Wurz, P.
2015-05-01
The Jovian moon, Europa, hosts a thin neutral gas atmosphere, which is tightly coupled to Jupiter's magnetosphere. Magnetospheric ions impacting the surface sputter off neutral atoms, which, upon ionization, carry currents that modify the magnetic field around the moon. The magnetic field in the plasma is also affected by Europa's induced magnetic field. In this paper we investigate the environment of Europa using our multifluid MHD model and focus on the effects introduced by both the magnetospheric and the pickup ion populations. The model self-consistently derives the electron temperature that governs the electron impact ionization process, which is the major source of ionization in this environment. The resulting magnetic field is compared to measurements performed by the Galileo magnetometer, the bulk properties of the modeled thermal plasma population is compared to the Galileo Plasma Subsystem observations, and the modeled surface precipitation fluxes are compared to Galileo Ultraviolet Spectrometer observations. The model shows good agreement with the measured magnetic field and reproduces the basic features of the plasma interaction observed at the moon for both the E4 and the E26 flybys of the Galileo spacecraft. The simulation also produces perturbations asymmetric about the flow direction that account for observed asymmetries.
3D-MHD Simulation of the Dynamics of the Plasma Flow through a Magnetic Nozzle
NASA Astrophysics Data System (ADS)
Tarditi, Alfonso
2011-10-01
The present study focuses on the characterization of the plasma flow as it transitions through a diverging, axisymmetric, dipolar magnetic field that, performing the function of a `magnetic nozzle'. For sufficiently large plasma densities, the nozzle magnetic field (externally imposed) is perturbed as the plasma transitions along the axial direction. This scenario was modeled with the 3D-MHD NIMROD code for the purpose of analyzing the details of the resulting nonlinear interaction of the plasma with the magnetic field. The simulations show the formation of regions with reconnecting closed field lines: in the plasma parameter range that has been considered, these patterns occur on a faster time scale than the one characterizing the plasma convective motion, but on the same time scale as the thermal energy confinement time. The 3D results are analyzed to show quantitatively the role of the diamagnetic current that is generated in the plasma along the azimuthal direction. The relevance of this analysis for the establishment of flow conditions that lead to an effective detachment of the plasma from the magnetic field is discussed. Further developments are also considered in relation to the application of Rotating Magnetic Fields to FRC plasmas, as described in.
Counter equatorial electrojet and overshielding after substorm onset: Global MHD simulation study
NASA Astrophysics Data System (ADS)
Ebihara, Y.; Tanaka, T.; Kikuchi, T.
2014-09-01
By performing a global magnetohydrodynamic (MHD) simulation, we have demonstrated for the first time that an electrojet at the dayside magnetic equator can be reversed and an overshielding condition can be established in the inner magnetosphere after substorm onset without northward turning of the interplanetary magnetic field. Near the substorm onset, the plasma pressure is highly enhanced in the inner magnetosphere on the nightside. The Region 2 field-aligned current diverges from the diamagnetic current on the surface of the dayside extension of the high-pressure region, which is connected to the ionosphere in the relatively low-conductivity region a few degrees equatorward of the main auroral oval that is formed as the projection of the plasma sheet. The separation of the equatorward boundary of the auroral region and the equatorward boundary of the Region 2 current results in dusk-dawn electric fields that generate a counter electrojet (CEJ) at the dayside magnetic equator. Poleward electric fields in a narrow latitudinal width, which may be regarded as subauroral ion drift and subauroral polarization stream, are simultaneously intensified. The dusk-dawn electric fields may propagate to the inner magnetosphere along a field line as shear Alfvén waves. Then, the inner magnetosphere is completely constrained by the overshielding condition. The intensity and polarity of the CEJ depend largely on at least the ionospheric conductivity that is related to the plasma pressure (probably associated with diffuse aurora). This may explain the observational fact that overshielding does not always occur after onset.
3D MHD Simulations of Planet Migration in Turbulent Stratified Disks
Uribe, Ana; Flock, Mario; Henning, Thomas
2011-01-01
We performed 3D MHD simulations of planet migration in stratified disks using the Godunov code PLUTO, where the disk is turbulent due to the magnetorotational instability. We study the migration for planets with different planet-star mass ratios $q=M_{p}/M_{s}$. In agreement with previous studies, for the low-mass planet cases ($q=5\\times10^{-6}$ and $10^{-5}$), migration is dominated by random fluctuations in the torque. For a Jupiter-mass planet $(q=M_{p}/M_{s}=10^{-3}$ for $M_{s}=1M_{\\odot})$, we find a reduction of the magnetic stress inside the orbit of the planet and around the gap region. After an initial stage where the torque on the planet is positive, it reverses and we recover migration rates similar to those found in disks where the turbulent viscosity is modelled by an $\\alpha$ viscosity. For the intermediate-mass planets ($q=5\\times10^{-5}, 10^{-4}$ and $2\\times10^{-4}$) we find a new and so far unexpected behavior. In some cases they experience sustained and systematic outwards migration for th...
Swain, Eric D.; Wolfert, Melinda A.; Bales, Jerad D.; Goodwin, Carl R.
2004-01-01
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.
Magnetohydrodynamic Numerical Simulations of Magnetic Reconnection in Interstellar Medium
Syuniti Tanuma
2000-01-01
In this thesis, we perform two-dimensional (2D) resistive magnetohydrodynamic (MHD) numerical simulations of the magnetic reconnection in interstellar medium. Part I is introduction. The motivation of the study is to investigate the origin of hot gas in interstellar medium. A scenario for generating X-ray gas in Galaxy is proposed, and examined by performing 2D MHD simulations with simple assumptions (Part
Two-dimensional NMR spectroscopy
Croasmun, W.R.; Carlson, R.M.K.
1987-01-01
Written for chemists and biochemists who are not NMR spectroscopists, but who wish to use the new techniques of two-dimensional NMR spectroscopy, this book brings together for the first time much of the practical and experimental data needed. It also serves as information source for industrial, academic, and graduate student researchers who already use NMR spectroscopy, but not yet in two dimensions. The authors describe the use of 2-D NMR in a wide variety of chemical and biochemical fields, among them peptides, steroids, oligo- and poly-saccharides, nucleic acids, natural products (including terpenoids, alkaloids, and coal-derived heterocyclics), and organic synthetic intermediates. They consider throughout the book both the advantages and limitations of using 2-D NMR.
Coherent Two-Dimensional Nanoscopy
NASA Astrophysics Data System (ADS)
Aeschlimann, Martin; Brixner, Tobias; Fischer, Alexander; Kramer, Christian; Melchior, Pascal; Pfeiffer, Walter; Schneider, Christian; Strüber, Christian; Tuchscherer, Philip; Voronine, Dmitri V.
2011-09-01
We introduce a spectroscopic method that determines nonlinear quantum mechanical response functions beyond the optical diffraction limit and allows direct imaging of nanoscale coherence. In established coherent two-dimensional (2D) spectroscopy, four-wave-mixing responses are measured using three ingoing waves and one outgoing wave; thus, the method is diffraction-limited in spatial resolution. In coherent 2D nanoscopy, we use four ingoing waves and detect the final state via photoemission electron microscopy, which has 50-nanometer spatial resolution. We recorded local nanospectra from a corrugated silver surface and observed subwavelength 2D line shape variations. Plasmonic phase coherence of localized excitations persisted for about 100 femtoseconds and exhibited coherent beats. The observations are best explained by a model in which coupled oscillators lead to Fano-like resonances in the hybridized dark- and bright-mode response.
Coherent two-dimensional nanoscopy.
Aeschlimann, Martin; Brixner, Tobias; Fischer, Alexander; Kramer, Christian; Melchior, Pascal; Pfeiffer, Walter; Schneider, Christian; Strüber, Christian; Tuchscherer, Philip; Voronine, Dmitri V
2011-09-23
We introduce a spectroscopic method that determines nonlinear quantum mechanical response functions beyond the optical diffraction limit and allows direct imaging of nanoscale coherence. In established coherent two-dimensional (2D) spectroscopy, four-wave-mixing responses are measured using three ingoing waves and one outgoing wave; thus, the method is diffraction-limited in spatial resolution. In coherent 2D nanoscopy, we use four ingoing waves and detect the final state via photoemission electron microscopy, which has 50-nanometer spatial resolution. We recorded local nanospectra from a corrugated silver surface and observed subwavelength 2D line shape variations. Plasmonic phase coherence of localized excitations persisted for about 100 femtoseconds and exhibited coherent beats. The observations are best explained by a model in which coupled oscillators lead to Fano-like resonances in the hybridized dark- and bright-mode response. PMID:21835982
Solar wind-magnetosphere interaction as determined by observations and a global MHD simulation
NASA Astrophysics Data System (ADS)
Palmroth, Minna Maria Emilia
The behavior of the Earth's magnetosphere as affected by the solar wind is examined utilizing both observational data as well as a computer simulation (GUMICS-4), developed in the Geophysical Research Department of the Finnish Meteorological Institute. The total energy transferred from the solar wind to the magnetosphere is quantified both temporally and spatially. The energy flux to the ionosphere is estimated. The fundamental processes within the magnetosphere that are directly fueled by the solar wind are summarized. Satellite observations and simulation results are further used to examine the influence of the solar wind magnetic field and ram pressure on the shape and structure of the magnetosphere. A computer simulation based on magnetohydrodynamic (MHD) theory describes the physical conditions in the simulation domain using a solar wind point measurement. Considering the large size of the magnetosphere and the strong spatial dependence of the energy transfer process, the amount of transferred energy cannot be directly measured on the magnetopause. Therefore, a simulation provides a unique opportunity to calculate quantitatively how much solar wind energy transfers to the magnetosphere and where the energy transfer process takes place. This thesis presents the first calculation of this kind. In particular it is shown that the focusing of the solar wind Poynting flux towards the magnetopause governs both the temporal and spatial variation of the total transferred energy. A small amount of transferred energy is consumed in the ionosphere, where there are two main energy sinks: Part of the energy is converted to Joule heat, whereas part of the energy is left in the ionosphere as magnetospheric electrons precipitate into the ionosphere producing auroral light. The energy related to these processes was quantified using the GUMICS-4 simulation. The amount and time variation of the total energy in the ionosphere was correlated with solar wind parameters to obtain a relationship that can be used to predict the total ionospheric energy from a point measurement in the solar wind. The developed relationship can have practical significance in situations where the total ionospheric energy is needed to be estimated quickly.
Physical Mechanisms of Two-Dimensional Turbulence
NASA Astrophysics Data System (ADS)
Ecke, Robert
2004-03-01
Turbulence has slowly yielded its mysteries through over 100 years of persistent effort. Recently experimental techniques and computation power have reached the stage where significant progress has been made on this very challenging problem. Two dimensional turbulence offers some real advantages in terms of reduced degrees of freedom such that the problem can now be thoroughly explored from many perspectives. Further, two-dimensional turbulence exhibits the basic phenomena of direct-enstrophy and inverse-energy cascades thought to apply to oceanic and atmospheric systems. We have investigated the properties of turbulence in two spatial dimensions using experimental measurements of the grid turbulence in a flowing soap film^1 and of the electromagnetically-forced turbulence in a thin salt layer floating on a dense immiscible fluid underlayer. We have also explored 2D turbulence using several different direct numerical simulations of homogeneous, isotropic turbulence in a periodic box^2. The data for both consist of high resolution fields of velocity; some are statistically independent sets and others are temporally resolved for dynamics. From this data we construct conventional Eulerian statistics, directly measure energy and enstrophy transfer^1, identify coherent structures in the flow, determine Lagrangian quantities, and calculate stretching fields. This comprehensive experimental and numerical characterization elucidates the physical mechanisms of two-dimensional turbulence. ^1 M.K. Rivera, W.B. Daniel and R.E. Ecke, Phys. Rev. Lett. 90, 104502 (2003). ^2 S. Chen, R.E. Ecke, G. Eyink, X. Wang, and Z. Xiao, Phys. Rev. Lett. 91, 214501 (2003).
Resistive MHD Simulations of Laminar Round Jets with Application to Magnetic Nozzle Flows
Araya, Daniel
2012-02-14
This thesis investigates fundamental flows of resistive magnetohydrodynamics (MHD) by a new numerical tool based on the gas-kinetic method. The motivation for this work stems from the need to analyze the mechanisms of plasma detachment...
Two dimensional QCD is a string theory
Gross, David J
1993-01-01
The partition function of two dimensional QCD on a Riemann surface of area $A$ is expanded as a power series in $1/N$ and $A$. It is shown that the coefficients of this expansion are precisely determined by a sum over maps from a two dimensional surface onto the two dimensional target space. Thus two dimensional QCD has a simple interpretation as a closed string theory.
NASA Technical Reports Server (NTRS)
Jackman, Charles H.; Douglas, Anne R.; Brueske, Kurt F.; Klein, Stephen A.
1991-01-01
The influence of dynamics on model results is investigated via a 2D photochemical model. Three representations of atmospheric transport are tested in order to simulate total ozone and C-14 amounts after nuclear tests in the early 1960s. Three scenarios of NO(x) injections from a proposed fleet of stratospheric aircraft and their effects on ozone are simulated. The three dynamical formulations used are Dynamics A, a base dynamics used in previous work with this model; Dynamics B, a strong circulation dynamics discussed by Jackman et al. (1989); and Dynamics C, the dynamics used by Shia et al. (1989). The advective component of the stratosphere to the troposphere mass exchange rate is largest for Dynamics B (5.8 x 10 exp 17 kg/yr) and smallest for Dynamics C (1.4 x 10 exp 17 kg/yr), with the advective strat/trop exchange rate for Dynamics A (2.4 x 10 exp 17 kg/yr) being these two extremes. Ozone depletion from NO(x) injections of stratospheric aircraft showed a strong sensitivity to dynamics.
Correspondence Quantification in Comprehensive Two-Dimensional
Reichenbach, Stephen E.
in Comprehensive Two- Dimensional Liquid Chromatography",1 proposed a method for integrating peaks. In discussingCorrespondence Quantification in Comprehensive Two-Dimensional Liquid Chromatography Stephen E., "Quantification in Comprehen- sive Two-Dimensional Liquid Chromatography" [Mon- dello, L.; Herrero, M.; Kumm, T
NASA Technical Reports Server (NTRS)
Boriakoff, Valentin
1994-01-01
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).
NASA Astrophysics Data System (ADS)
Hale, J. M.; Paty, C. S.
2014-12-01
Charon's mass, orbital parameters, and distinct surface composition relative to Pluto suggest that it plays a significant role in Pluto's dynamic interaction with the solar wind. Its high mass ( ~ 10% of total system mass ) and close orbit ( < 20 Pluto Radii ) are thought to result in regionally enhanced atmospheric escape from Pluto as well as ionospheric deformation. Additionally, there are multiple mechanisms through which Charon could possess a tenuous atmosphere—and therefore ionosphere. Firstly, spectral observations of short-lived hydrated ammonia on Charon's surface could be caused by semi-regular cryovolcanism, which would also source a water group atmosphere (Cook et al., 2007). Secondly, recent work indicates that Charon could have a nightside parasitic atmosphere that is captured from material escaping from Pluto (Tucker et al., 2014). Either possibility would result in Charon presenting a sizable obstacle to the incoming solar wind. This work studies Charon's effects on the Pluto-solar wind interaction using a 3-dimensional multifluid MHD model which has been modified to include a second body within the system. This second body (Charon) represents not only an additional gravitational perturbation to the system, but can also provide a local and distinct plasma source, a sink for plasma sourced from Pluto or the solar wind, and cause an obstruction and perturbation to the solar wind. Specifically, we investigate the possibility of enhanced ionospheric loss from Pluto due to Charon's gravitational attraction, as well as the overall dynamics of a two-body system interacting with the solar wind in which each body has an ionosphere and periodically passes through the bow shock of the other body. The former objective is made possible by tracking the flux of plasma sourced from Pluto. The latter objective is accomplished by performing simulations in which Charon is upstream of Pluto as well as simulations in which Charon is placed downstream, within Pluto's wake.
Global Structure of Idealized Stream Interaction Regions Using 3D MHD Simulations
NASA Astrophysics Data System (ADS)
Pahud, D. M.; Hughes, W. J.; Merkin, V. G.
2014-12-01
The global structure of the heliosphere during solar cycles (SC) 23 and 24 differed significantly in many ways, for example in terms of global magnetic field strength, velocity structure and the observed properties of Stream Interaction Region (SIR) and associated shocks. The differences considered in this study focus primarily on the effects of the three-dimensional (3D) structure of SIRs. During the minimum of SC 24, equatorial coronal holes were prevalent as sources of low-latitude high-speed solar wind. In contrast, the canonical depiction of SC 23's minimum wind configuration is of a band of slow wind undulating about the heliographic equator. Using the heliospheric adaptation of the Lyon-Fedder-Mobarry magnetohydrodynamic (MHD) model (LFM-helio), we have run simulations for two idealized global solar wind conditions. The first simulation approximates the classical tilted dipole, with fast solar wind at high latitudes and a band of slow wind tilted with respect to the heliographic equator, and the second consists of global slow solar wind with equatorial circular sources of high-speed streams. The evolution of the SIRs from 0.1 AU to 2.0 AU is characterized using the amplitude and location of the maximum compressions of the plasma and the magnetic field as well as the largest deflection of solar wind flow. The relation between plasma and magnetic field compressions differs between the two cases considered. The SIRs produced by the equatorial coronal holes have similar maximum densities to those of the tilted dipole case, but the magnetic field magnitude is larger and the plasma is hotter. This suggests that evolution depends on the 3D structure of the SIR and its effects on the competitive roles of the growth of the structure, driven by compression from dynamic pressure, and and relaxation from the plasma flow and magnetic field deflections occurring in the region. Magnetic field threading SIRs and tracing plasma parcels are examined.
NASA Astrophysics Data System (ADS)
Merkin, V. G.; Lyon, J.; Claudepierre, S. G.
2013-12-01
The Kelvin-Helmholtz Instability (KHI) has long been suggested to operate on the magnetospheric boundary, where the magnetosheath plasma streams past the magnetosphere. The instability is thought to be responsible for inducing various wave populations in the magnetosphere and for mass, momentum and energy transport across the magnetospheric boundary. Waves attributed to the KHI have been observed at the Earth's magnetosphere flanks as well as at Saturn and Mercury during spacecraft crossings, and remotely at boundaries of Coronal Mass Ejections (CMEs). Recent high-resolution global 3D magnetohydrodynamic (MHD) simulations of the magnetosphere confirm the existence of pronounced perturbations of the magnetospheric boundary, which are thought to be due to KHI. Such global simulations had been challenging in the past because of the need to encompass the entire magnetosphere, while sufficiently resolving the boundary layer. Here we present results of such a high-resolution simulation of the magnetosphere, using the Lyon-Fedder-Mobarry (LFM) model, under steady northward Interplanetary Magnetic Field (IMF) conditions. We find the magnetospheric boundary to be globally unstable, including the high-latitude boundary layer (meridional plane), where magnetic tension is apparently not sufficient to stabilize the growth of oscillations. Roughly beyond the terminator, global modes, coupled into the surface modes, become apparent, so that the entire body of the magnetosphere is engaged in an oscillatory motion. The wave vector of the surface oscillations has a component perpendicular to the background flow and tangential to the shear layer (in the equatorial plane, k_z component of the wave vector), which is consistent with the generation of field-aligned currents that flow on closed field lines between the inner portion of the boundary layer and the ionosphere. We calculate the distribution of wave power in the equatorial plane and find it consistent with the existence of a double-vortex sheet, with vortex trains propagating along the inner and outer edges of the boundary layer. The double-vortex sheet is most apparent in the simulation past the terminator plane, but is transient and appears to be unstable, and is most likely a consequence of non-linear development of the velocity shear layer with a finite width. We compute the salient characteristics of the KH waves, including phase speeds, spectra and growth rates. The latter are compared with linear theory and found to be in excellent agreement. Finally, we find that the plasma compressibility is a key factor in controlling the growth rate of the KHI at the magnetosphere flanks in our simulations.
NASA Technical Reports Server (NTRS)
Fairfield, Donald H.; Otto, A.
1999-01-01
On March 24, 1995 the Geotail spacecraft observed large fluctuations of the magnetic field and plasma properties in the Low Latitude Boundary Layer (LLBL) about 15 R(sub E) tailward of the dusk meridian. Although the magnetospheric and the magnetosheath field were strongly northward, the B(sub z) component showed strong short duration fluctuations in which B(sub z) could even reach negative values. We have used two-dimensional magnetohydrodynamic simulations with magnetospheric and magnetosheath input parameters specifically chosen for this. Geotail event to identify the processes which cause the observed boundary properties. It is shown that these fluctuations can be explained by the Kelvin-Helmholtz instability if the k vector of the instability has a component along the magnetic field direction. The simulation results show many of the characteristic properties of the Geotail observations. In particular, the quasi-periodic strong fluctuations are well explained by satellite crossings through the Kelvin-Helmholtz vortices. It is illustrated how the interior structure of the Kelvin-Helmholtz vortices leads to the rapid fluctuations in the Geotail observations. Our results suggest an average Kelvin-Helmholtz wavelength of about 5 R(sub E) with a vortex size of close to 2 R(sub E) for an average repetition time of 2.5 minutes. The growth time for these waves implies a source region of about 10 to 16 R(sub E) upstream from the location of the Geotail spacecraft (i.e., near the dusk meridian). The results also indicate a considerable mass transport of magnetosheath material into the magnetosphere by magnetic reconnection in the Kelvin-Helmholtz vortices.
Reconnection events in two-dimensional Hall magnetohydrodynamic S. Donato,1
2012) The statistical study of magnetic reconnection events in two-dimensional turbulence has been bifurcated current sheets and quadrupolar magnetic field structures in analogy to laminar studies, leading is locally enhanced by both MHD turbulence and by the Hall effect, investigating the statistics of magnetic
MHD Simulation of Dynamic Heliosphere Around the Time When Voyager 1 Crossed the Termination Shock
NASA Astrophysics Data System (ADS)
Washimi, H.; Zank, G. P.; Hu, Q.; Tanaka, T.
2006-12-01
An analysis of the dynamic heliosphere around the time when Voyager 1 (V-1 passed the termination shock (TS) on December 16, 2004 is performed using ideal MHD simulations. For input to this simulation, we use the Voyager 2 (V-2) solar wind data from September 10, 2002. We first provide a stationary solution of the 3-D outer heliosphere by assigning a set of LISM parameters as our outer boundary conditions so that V-1 crosses the TS at the end of 2004, and then the dynamical analysis is performed. We find that the TS position was always very near Voyager 1 from September 2002, when the TS-particle events became evident, to the time of the TS-crossing. During this period, the TS was pushed outward each time a high ram-pressure solar wind pulse arrived, but the maximum distance from V-1 was never greater than 15 AU. When the ram pressure was relatively low, the TS approached Voyager 1 to within 3 AU. At the end of the high ram-pressure wind associated with the Halloween events, the TS began to move inward very quickly and the TS crossed V1. The modeled TS crossing time is within 12 days of the observed date based on our LISM parameters. 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. Hence in our simulation, 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 also by the highly variable dynamical ram pressure of the solar wind. The periods when the high ram-pressure solar wind pulses arrive at the TS shock seem to correspond to the period of the TS particle events observed at V-1. We plan to estimate the solar-wind deceleration between the positions of V-1 and V-2 by using V-2 magnetic data in our simulations and comparing time-correlations between the calculated magnetic field at the V-1 position with the observed V-1 magnetic field.
The Delta x B = 0 Constraint Versus Minimization of Numerical Errors in MHD Simulations
NASA Technical Reports Server (NTRS)
Yee, H. C.; Sjoegreen, Bjoern; Mansour, Nagi (Technical Monitor)
2002-01-01
The MHD equations are a system of non-strictly hyperbolic conservation laws. The non-convexity of the inviscid flux vector resulted in corresponding Jacobian matrices with undesirable properties. It has previously been shown by Powell et al. (1995) that an 'almost' equivalent MHD system in non-conservative form can be derived. This non-conservative system has a better conditioned eigensystem. Aside from Powell et al., the MHD equations can be derived from basic principles in either conservative or non-conservative form. The Delta x B = 0 constraint of the MHD equations is only an initial condition constraint, it is very different from the incompressible Navier-Stokes equations in which the divergence condition is needed to close the system (i.e., to have the same number of equations and the same number of unknown). In the MHD formulations, if Delta x B = 0 initially, all one needs is to construct appropriate numerical schemes that preserve this constraint at later time evolutions. In other words, one does not need the Delta x B condition to close the MHD system. We formulate our new scheme together with the Cargo & Gallice (1997) form of the MHD approximate Riemann solver in curvilinear grids for both versions of the MHD equations. A novel feature of our new method is that the well-conditioned eigen-decomposition of the non-conservative MHD equations is used to solve the conservative equations. This new feature of the method provides well-conditioned eigenvectors for the conservative formulation, so that correct wave speeds for discontinuities are assured. The justification for using the non-conservative eigen-decomposition to solve the conservative equations is that our scheme has a better control of the numerical error associated with the divergence of the magnetic condition. Consequently, computing both forms of the equations with the same eigen-decomposition is almost equivalent. It will be shown that this approach, using the non-conservative eigensystem when solving the conservative equations, also works well in the context of standard shock-capturing schemes.