Evolution of generalized two-dimensional magnetotail equilibria in ideal and resistive MHD
NASA Astrophysics Data System (ADS)
Merkin, V. G.; Sitnov, M. I.; Lyon, J. G.
2015-03-01
We present results of two-dimensional (2-D) magnetohydrodynamic (MHD) simulations of the terrestrial magnetotail. A regional adaptation of the Lyon-Fedder-Mobarry global MHD model is used. As initial conditions, we employ a class of asymptotic magnetotail equilibria with and without an accumulation of magnetic flux at the tailward end (a Bz hump). The former have been recently shown by full particle simulations to be unstable to a kinetic mode with formal properties of ion tearing. Thus, our goal here is to investigate the evolution of the same equilibria in the MHD approximation and assist in the physical interpretation of the kinetic simulations. This is additionally motivated by the energy principle considerations which suggest that if the system is unstable kinetically, it may also be unstable ideally. To seek dynamical MHD regimes similar to those observed in kinetic simulations, we implement two sets of boundary conditions (velocity balanced, VB, and momentum balanced, MB), one allowing plasma flows through the boundaries and the other inhibiting such flows. The use of more reflecting MB boundary conditions results in suppression of any significant dynamics, and we see no substantial changes beyond initial equilibrium relaxation. On the other hand, VB boundary conditions allow a more efficient relaxation of initial equilibrium and absorb subsequently generated plasma flows. With these boundary conditions we find the equilibrium without a flux accumulation (i.e., with constant magnetic field component normal to the current sheet) to develop an apparently resistive mode accompanied by tailward plasma flows. At the same time, the equilibria with a Bz hump of sufficiently large amplitude develop a different, ideal, mode characterized by spontaneous generation of earthward plasma flows and an exponential growth of the corresponding electric field. This growth is qualitatively similar to the corresponding fully kinetic simulations although no explosive growth of the earthward moving Bz peak is evident in the MHD calculations, just an earthward shift of a part of the initial flux accumulation. We discuss implications of our results for the possibility of existence and impact of such equilibria in the Earth's magnetotail and in global MHD simulations.
Two-dimensional non-reacting jet-gas mixing in an MHD (magnetohydrodynamic) second stage combustor
S. L. Chang; S. A. Lottes; G. F. Berry
1990-01-01
Computer simulation is used to aid in the design of a magnetohydrodynamic (MHD) second stage combustor. A two-dimensional steady state computer model, based on mass and momentum conservation laws for multiple gas species, is used to simulate the hydrodynamics of the combustor in which a jet of oxidizer is injected into a confined cross-stream gas flow. The model predicts jet-gas
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.
Global magnetohydrodynamic simulation of the two-dimensional magnetosphere
NASA Technical Reports Server (NTRS)
Leboeuf, J. N.; Tajima, T.; Kennel, C. F.; Dawson, J. M.
1979-01-01
The time-dependent magnetohydrodynamic interaction of the solar wind with a two-dimensional dipole magnetic field has been simulated using a novel Lagrangian particle type of MHD code that can treat local low density or vacuum regions without numerical instability. This enables one to simulate the time-dependent magnetic tail. When the solar wind field is southward, a magnetic field line topology consistent with Dungey's model emerges in steady state. The tail, however, is short, and the x-points are only slightly shifted from their vacuum locations, because of strong numerical resistivity. Different configurations resulting from different relative orientations of the solar wind magnetic field and dipole axis are also presented. While the magnetic field is relatively steady, the density and flow in the magnetosheath are turbulent, as are the bow shock and magnetopause; the Kelvin-Helmholtz instability may account for these phenomena. We also model a 'substorm' as the passage of a rotational discontinuity in the solar wind over the dipole. Both 90 and 180 deg shifts to a southward solar wind field cause a violent readjustment of the magnetic tail which eventually settles down to the Dungey configuration.
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.
Two-Dimensional Cure Simulation of Thick Thermosetting Composites
Travis A. Bogetti; John W. Gillespie
1991-01-01
An investigation into the two-dimensional cure simulation of thick thermosetting composites is presented. Temperature and degree of cure distributions within arbitrary cross-sectional geometries are predicted as a function of the autoclave temperature history. The heat conduction equation for two-dimensional, transient anisotropic heat transfer is coupled to the cure kinetics of the thermosetting composite material. A heat generation term, expressed as
Finite Element Simulation of Two-Dimensional Incompressible Magnetohydrodynamic Flows
NASA Astrophysics Data System (ADS)
Ip, Justin Tsz Ching
A new finite element code has been developed for simulation of the dynamics of two-dimensional incompressible magnetohydrodynamic flows. The solution scheme used in spatial discretization is the Galerkin weighted-residual finite-element method, incorporating the mixed interpolation technique, and a combination of the penalty and pseudocompressibility methods for implementing the incompressibility constraint. An implicit and stable theta-weighting finite difference scheme is used for integration in time, and a non-iterative time-level averaging method is employed for treatment of nonlinear terms. The code has been extensively benchmarked against known analytical solutions in magnetohydrodynamics and has been found to produce highly accurate results. The tearing-mode instability of a magnetic-field-reversing current sheet in the presence of coplanar stagnation-point flow, in which the unperturbed equilibrium state is an exact solution of the steady-state dissipative MHD equations, has been examined by use of the code. Simulation results indicate stability for sufficiently small values of the viscous Lundquist number, S_nu, or the resistive Lundquist number, S_eta : a curve in the S_nu -S_eta plane separating the stable and unstable regions has been found. In the unstable regime, the results show occurrence of multiple x-line reconnection along the center of the current sheet at x = 0. Small-scale structures of vorticity and current density near the x-point reconnection sites are observed and are found to be consistent with results obtained by Matthaeus (1982). Average linear growth rates are estimated for modest values of S_eta. In the range S_eta<=500, the number of magnetic islands is found to be independent of Seta, which implies that there exists a single dominant wavelength of the tearing-mode in this range. The stretching of magnetic islands which is present in this configuration but not in the perpendicular flow and field configuration examined by Phan and Sonnerup (1991), caused a substantial decrease in linear growth rate relative to that obtained by those authors. It is of particular interest that, unlike most simulations of the tearing-mode, no symmetry conditions are imposed on the perturbations; nevertheless they develop in an anti -symmetric manner.
TWO DIMENSIONAL IMMERSED BOUNDARY SIMULATIONS OF SWIMMING JELLYFISH
Stockie, John
TWO DIMENSIONAL IMMERSED BOUNDARY SIMULATIONS OF SWIMMING JELLYFISH by Haowen Fang B.Eng., Nanjing Simulations Of Swim- ming Jellyfish Examining Committee: Dr. Weiran Sun, Assistant Professor Chair Dr. John iii #12;Abstract The swimming behavior of jellyfish, driven by the periodic contraction of body
Two-dimensional simulation of an electron cyclotron resonance discharge
J. H. Shiau; J. H. Tsai; S. H. Chen; J. Y. Yang; C. J. Chiou
1999-01-01
Summary form only given, as follows. A two-dimensional three-moment simulation code was developed and performed for the study of the electron cyclotron resonance (ECR) plasma sources based on the self-consistent fluid model which determines the dynamics of the plasma as well as its interactions with the microwave. In particular, the ECR discharges can be characterized by two major parameters, one
An MHD GADGET for cosmological simulations
NASA Astrophysics Data System (ADS)
Dolag, K.; Stasyszyn, F.
2009-10-01
Various radio observations have shown that the hot atmospheres of galaxy clusters are magnetized. However, our understanding of the origin of these magnetic fields, their implications on structure formation and their interplay with the dynamics of the cluster atmosphere, especially in the centres of galaxy clusters, is still very limited. In preparation for the upcoming new generation of radio telescopes (like Expanded Very Large Array, Low Wavelength Array, Low Frequency Array and Square Kilometer Array), a huge effort is being made to learn more about cosmological magnetic fields from the observational perspective. Here we present the implementation of magnetohydrodynamics (MHD) in the cosmological smoothed particle hydrodynamics (SPH) code GADGET. We discuss the details of the implementation and various schemes to suppress numerical instabilities as well as regularization schemes, in the context of cosmological simulations. The performance of the SPH-MHD code is demonstrated in various one- and two-dimensional test problems, which we performed with a fully, three-dimensional set-up to test the code under realistic circumstances. Comparing solutions obtained using ATHENA, we find excellent agreement with our SPH-MHD implementation. Finally, we apply our SPH-MHD implementation to galaxy cluster formation within a large, cosmological box. Performing a resolution study we demonstrate the robustness of the predicted shape of the magnetic field profiles in galaxy clusters, which is in good agreement with previous studies.
Monte Carlo Simulations of the two-dimensional dipolar fluid
Caillol, Jean-Michel
2015-01-01
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.
Two-dimensional theory and simulation of free electron lasers
Kwan, T.J.T.; Cary, J.R.
1981-01-01
Two-dimensional homogeneous theory of free-electron lasers with a wiggler magnetic field of constant wavelength is formulated. It has been found from the theory that waves propagating obliquely with respect to the electron beam are always unstable with appreciable growth rates; therefore, mode competition among the on-axis and off-axis modes is an important consideration in the design of the free-electron laser. Furthermore, electromagnetic waves with group velocities opposite to the direction of electron beam propagation are absolutely unstable if k/sub o/v/sub o/ > ..omega../sub pe/(1/..gamma../sup 3/2/ + 1/..gamma../sup 1/2/). Due to strong nonlinear saturation levels of the low-frequency absolute instability, the dynamics of the electron beam and the generation of the high-frequency electromagnetic radiation can be severely affected. Two-dimensional particle simulations show that the efficiency of generation of the on-axis high-frequency electromagnetic wave decreases significantly due to instability of the off-axis modes. In addition, complete disruption of the electron beam and laser oscillation due to the onset of the absolute instability have been observed in simulations.
An MHD Gadget for cosmological simulations
K. Dolag; F. A. Stasyszyn
2009-05-19
Various radio observations have showed that the hot atmospheres of galaxy clusters are magnetized. However, our understanding of the origin of these magnetic fields, their implications on structure formation and their interplay with the dynamics of the cluster atmosphere, especially in the centers of galaxy clusters is still very limited. In preparation to the upcoming new generation of radio telescopes (like EVLA, LWA, LOFAR and SKA), a huge effort is being made to learn more about cosmological magnetic fields from the observational perspective. Here we present the implementation of magneto hydrodynamics in the cosmological SPH code GADGET. We discuss the details of the implementation and various schemes to suppress numerical instabilities as well as regularization schemes, in the context of cosmological simulations. The performance of the SPH MHD code is demonstrated in various one and two dimensional test problems, which we performed if a fully, three dimensional setup to test the code under realistic circumstances. Comparing with solutions obtained with ATHENA, we find excellent agreement with our SPH MHD implementation. Finally we apply our SPH MHD implementation to forming galaxy clusters within a large, cosmological box. Performing a resolution study we demonstrate the robustness of the predicted shape of the magnetic field profiles in galaxy clusters, which is in good agreement with previous studies.
Gradient Drift Instabilities in Two Dimensional Hybrid Hall Thruster Simulations
NASA Astrophysics Data System (ADS)
Aley, Jacob; Dowdy, Caleb; Fernandez, Eduardo
2014-10-01
Instabilities triggered by a variety of mechanisms have been theoretically predicted for Hall thruster plasmas. Experimentally, fluctuations spanning a wide range of frequencies and wave numbers have been observed. Perhaps more importantly, fluctuations have been postulated to play a role in regulating cross-field electron transport in Hall thrusters. However, a clear understanding of what instabilities are responsible for such transport is presently lacking. In this work we focus on analysis of long wavelength gradient drift instability in the Hall thruster via two dimensional hybrid fluid-PIC simulations that resolve azimuthal dynamics. Recent theoretical analysis by Frias et al. shows that previous stability criteria for drift instabilities are modified due to compressibility of the electron flow. In our simulations, we test this improved criterion by examining the transient waves that emerge in the simulation from a smooth initial condition. The simulations give good agreement with the theory, both in the frequency/growth rate characteristics of the waves as well as the region of the thruster where such disturbances are predicted to emerge. These results suggest that gradient drift instabilities play a significant role in Hall thruster plasmas. Jacob Aley, Caleb Dowdy, and Eduardo Fernandez are supported by a grant from the II-VI Foundation.
Two dimensional simulation of high power laser-surface interaction
Goldman, S.R.; Wilke, M.D.; Green, R.E.L.; Johnson, R.P. [Los Alamos National Lab., NM (United States); Busch, G.E. [KMS Fusion, Inc., Ann Arbor, MI (United States)
1998-08-01
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.
Two-dimensional simulations of displacement accumulation incorporating shear strain
Bayer, Matthew; Hall, Timothy J.; Neves, Lucio P.; Carneiro, A. A. O.
2015-01-01
Using ultrasound images to track large tissue deformations usually requires breaking up the deformation into steps and then summing the resulting displacement estimates. The accumulated displacement estimation error therefore depends on the error in each step, but also on the statistical relationships between estimation steps. These relationships have not been thoroughly studied. Building on previous work with one-dimensional simulations, the work reported here measured error variance for single-step and accumulated displacement estimates using two-dimensional numerical simulations of ultrasound echo signals, subjected to both normal and axial shear strain as well as electronic noise. Previous results were confirmed, showing that errors due to electronic noise are negatively correlated between steps and accumulate slowly, while errors due to strain are positively correlated and accumulate quickly. These properties hold for both normal and axial shear strain. A general comparison of tracking performance for tissue under normal and axial shear strain was also performed. Under axial shear strain error variance tends to increase with larger lateral kernel sizes but decrease for larger axial kernel sizes; the opposite relationship holds under normal strain. A combination of these two types of strain limits the practical kernel size in both dimensions. PMID:24275539
Dynamics of coronal transients - Two-dimensional non-plane MHD models
NASA Technical Reports Server (NTRS)
Nakagawa, Y.; Wu, S. T.; Han, S. M.
1980-01-01
Numerical results are obtained for non-plane MHD responses to a sudden energy release in a stratified model atmosphere. In agreement with observations, it is shown that after the energy release, the magnetic field affected by the energy release relaxes toward the potential configuration while the outer atmospheric fields increase its shear. Additional results suggest a new way of interpreting the energy storage and release in repeated flares.
An MHD Gadget for cosmological simulations
Dolag, K
2008-01-01
Various observations have showed that the hot atmospheres of galaxy clusters are magnetized. However, our understanding of the origin of these magnetic fields, their implications on structure formation and their interplay with the dynamics of the cluster atmosphere, especially in the centers of galaxy clusters is still very limited. In preparation to the upcoming new generation of radio telescopes (like EVLA, LWA, LOFAR and SKA), a huge effort is being made to learn more about cosmological magnetic fields from the observational perspective. Here we present the implementation of magneto hydrodynamics in the cosmological SPH code GADGET. We discuss the details of the implementation and various schemes to suppress numerical instabilities as well as regularization schemes, in the context of cosmological simulations. The performance of the SPH MHD code is demonstrated in various one and two dimensional test problems, which we performed if a fully, three dimensional setup to test the code under realistic circumstan...
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.
NASA Astrophysics Data System (ADS)
Takasao, Shinsuke; Matsumoto, Takuma; Nakamura, Naoki; Shibata, Kazunari
2015-06-01
Solar flares are an explosive phenomenon where super-sonic flows and shocks are expected in and above the post-flare loops. To understand the dynamics of post-flare loops, a two-dimensional magnetohydrodynamic (2D MHD) simulation of a solar flare has been carried out. We found new shock structures in and above the post-flare loops, which were not resolved in the previous work by Yokoyama & Shibata. To study the dynamics of flows along the reconnected magnetic field, the kinematics and energetics of the plasma are investigated along selected field lines. It is found that shocks are crucial to determine the thermal and flow structures in the post-flare loops. On the basis of the 2D MHD simulation, we developed a new post-flare loop model, which we defined as the pseudo-2D MHD model. The model is based on the one-dimensional (1D) MHD equations, where all variables depend on one space dimension, and all the three components of the magnetic and velocity fields are considered. Our pseudo-2D model includes many features of the multi-dimensional MHD processes related to magnetic reconnection (particularly MHD shocks), which the previous 1D hydrodynamic models are not able to include. We compared the shock formation and energetics of a specific field line in the 2D calculation with those in our pseudo-2D MHD model, and found that they give similar results. This model will allow us to study the evolution of the post-flare loops in a wide parameter space without expensive computational cost or neglecting important physics associated with magnetic reconnection.
Simulation of two-dimensional infrared spectroscopy of amyloid fibrils
Zhuang, Wei; Abramavicius, Darius; Voronine, Dimitrii V.; Mukamel, Shaul
2007-01-01
We propose to use infrared coherent two-dimensional correlation spectroscopy (2DCS) to characterize the fibril structure of Ab42, the dominant composition of Ab deposit, which is crucial for investigating its toxicity and aggregation mechanism. By optimizing the pulse polarization configurations with a genetic algorithm combined with sensitivity analysis, we obtained signals with well resolved cross-peak features attributed to the couplings within and between different structural motifs. These signals may provide new constraints for refining of the currently available NMR structure. Two-dimensional correlation spectroscopy also can differentiate the turn structure of Ab42 and other Ab derivatives. PMID:17675411
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
Multigrid ADI method for two-dimensional electromagnetic simulations
Shumin Wang; J. Chen
2006-01-01
We propose a multigrid alternating-direction implicit (ADI) method for solving two-dimensional Maxwell's equations. This method is based on interpreting the ADI method as an iterative solver for the Crank-Nicolson (CN) scheme. By introducing a special procedure to solve the residual equation within the ADI framework, multigrid methods are incorporated into the iterative ADI method. The accuracy and efficiency of the
Seabed disposal project two-dimensional axisymmetric penetrometer simulations
Chavez, P.F.; Dawson, P.R.; Schuler, K.W.
1980-03-01
Preliminary two-dimensional, one-constituent hole closure analyses of an experimental apparatus and the flow of in situ ocean sediments following a penetrometer explacement have been performed. Boundary conditions associated with the experimental apparatus were found to greatly affect cavity response. Difficulties were encountered in modelling penetrometer-sediment interfaces and in obtaining smooth stress histories. The use of a different computer code in later analyses led to more realistic penetrometer-sediment interface models and to improved success in obtaining stress histories. These results along with some recommendations for future work are presented.
Riquelme, Mario A.; Quataert, Eliot [Astronomy Department and Theoretical Astrophysics Center, University of California, Berkeley, CA 94720 (United States); Sharma, Prateek [Department of Physics, Indian Institute of Science, Banglore 560012 (India); Spitkovsky, Anatoly, E-mail: marh@astro.berkeley.edu, E-mail: eliot@astro.berkeley.edu, E-mail: prateek@physics.iisc.ernet.in, E-mail: anatoly@astro.princeton.edu [Department of Astrophysical Sciences, Princeton University, Princeton, NJ (United States)
2012-08-10
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 Alfven velocity, v{sub A} , is comparable to the speed of light, c (independent of the initial value of v{sub A} /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*.
MHD Simulations: Corotating Interaction Regions
NASA Astrophysics Data System (ADS)
Wiengarten, T.; Kleimann, J.; Fichtner, H.; Kissmann, R.
2014-09-01
Corotating Interaction Regions (CIRs) form in the solar wind when parcels of fast-speed wind interact with slow-speed wind due to the rotation of the Sun. The resulting buildup of pressure generates disturbances that, with increasing time (or distance from the Sun), may develop into a so-called forward-reverse shock pair. During solar-quiet times CIRs can be the dominant force shaping large-scale structures in the heliosphere. Studying CIRs is therefore important because the associated shocks are capable of e.g. accelerating energetic particles or deflecting cosmic rays. The global structure of CIRs can be modeled with an MHD approach that gives the plasma quantities needed to model the transport of particles in the heliosphere with e.g. stochastic differential equations. Here, we show results from 3D-MHD simulations with our code CRONOS for a) analytic boundary conditions where results can be compared to those obtained with a different code and b) boundary conditions derived with the Wang-Sheeley-Arge model from observational data (WSO), which are compared to spacecraft observations.
Simulation Study of Chiral Two-Dimensional Ultraviolet Spectroscopy of the Protein Backbone
Mukamel, Shaul
of proteins derives from the variety of stable and flexible three-dimensional geometrical structures.1 structure using optical methods. Two-dimensional (2D) resonance laser spectroscopy in the infraredSimulation Study of Chiral Two-Dimensional Ultraviolet Spectroscopy of the Protein Backbone Darius
Two-dimensional simulations of the inertial electrostatic confinement device
Alberto Marocchino; Giovanni Lapenta; Evstati Evstatiev; Richard Nebel; Jaeyoung Park
2006-01-01
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
Grand-canonical simulation of two-dimensional simplicial gravity
S. Oda; N. Tsuda; T. Yukawa
1997-09-21
The string susceptibility exponents of dynamically triangulated 2-dimensional surfaces with various topologies, such as a sphere, torus and double-torus, were calculated by the grand-canonical Monte Carlo method. These simulations were made for surfaces coupled to $d$-Ising spins ($d$=0,1,2,3,5). In each simulation the area of surface was constrained to within 1000 to 3000 of triangles, while maintaining the detailed-balance condition. The numerical results show excellent agreement with theoretical predictions as long as $d \\leq 2$.
Simulation of two-dimensional waterflooding using mixed finite elements
Chavent, G.; Jaffre, J.; Cohen, G.; Dupuy, M.; Dieste, I.
1982-01-01
A new method for the simulation of incompressible diphasic flows in two dimensions is presented, the distinctive features of which are: (1) reformation of the basic equation and specific choices of the finite element approximation of the same; (11) use of a mixed finite elements method, approximating both scalar and vector functions. Several test examples are shown, including gravity and capillary effects. The use of discontinuous basis functions proved successful for an accurate representation of sharp fronts. 16 refs.
Nonparametric Estimation and Simulation of Two--Dimensional Gaussian Image Textures \\Lambda
Lee, Chun Man "Thomas"
Nonparametric Estimation and Simulation of Two--Dimensional Gaussian Image Textures \\Lambda Thomas Textures Estimation and Simulation Corresponding author: Thomas C. M. Lee Fax: +61 2 93253200 Phone: +61 2 by the need to simulate a variety of real--world image textures, all of which can be well approximated
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.
Lekner summation of dipolar interaction in quasi-two-dimensional simulations
Sergey V. Lishchuk
2002-01-01
The Lekner method for calculation of electrostatic interactions in periodically replicated simulation cells is extended to quasi-two-dimensional systems of particles with dipolar interactions. The electric field, potential energy, forces and torques are expressed through rapidly converging series of modified Bessel functions. The method contains no arbitrary parameters, and has no limitations on the simulation box width.
Simulation of switched reluctance motor drives using two-dimensional bicubic spline
Xiang-Dang Xue; K. W. E. Cheng; S. L. Ho
2002-01-01
In this paper, a novel simulation algorithm of switched reluctance motor drives is presented. With the proposed algorithm the two-dimensional (2-D) bicubic spline interpolation is used to describe the nonlinear magnetic characteristics in switched reluctance motors. The corresponding computational method of 2-D bicubic spline function is described in detail. The simulation results are also compared with and validated by experimental
Robert R. Arslanbekov; Vladimir I. Kolobov
2003-01-01
The transition from Townsend to glow discharge is studied via two-dimensional simulations of discharges with moderate pd values corresponding to the right branch of the Paschen curve (p is the gas pressure and d the electrode spacing). The discharge model is coupled to the external circuit model enabling simulations of subnormal oscillations during the discharge transition from the Townsend to
Simulation of wave interactions with MHD
Batchelor, Donald B [ORNL; Abla, G [General Atomics, San Diego; Bateman, Glenn [Lehigh University, Bethlehem, PA; Bernholdt, David E [ORNL; Berry, Lee A [ORNL; Bonoli, P. [Massachusetts Institute of Technology (MIT); Bramley, R [Indiana University; Breslau, J. [Princeton Plasma Physics Laboratory (PPPL); Chance, M. [Princeton Plasma Physics Laboratory (PPPL); Chen, J. [Princeton Plasma Physics Laboratory (PPPL); Choi, M. [General Atomics; Elwasif, Wael R [ORNL; Fu, GuoYong [Princeton Plasma Physics Laboratory (PPPL); Harvey, R. W. [CompX, Del Mar, CA; Jaeger, Erwin Frederick [ORNL; Jardin, S. C. [Princeton Plasma Physics Laboratory (PPPL); Jenkins, T [University of Wisconsin; Keyes, David E [Columbia University; Klasky, Scott A [ORNL; Kruger, Scott [Tech-X Corporation; Ku, Long-Poe [Princeton Plasma Physics Laboratory (PPPL); Lynch, Vickie E [ORNL; McCune, Douglas [Princeton Plasma Physics Laboratory (PPPL); Ramos, J. [Massachusetts Institute of Technology (MIT); Schissel, D. [General Atomics; Schnack, [University of Wisconsin; Wright, J. [Massachusetts Institute of Technology (MIT)
2008-07-01
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.
Implicit Predictor-Corrector finite difference scheme for the ideal MHD simulations
NASA Astrophysics Data System (ADS)
Tsai, T.; Yu, H.; Lai, S.
2012-12-01
A innovative simulation code for ideal magnetohydrodynamics (MHD) is developed. We present a multiple-dimensional MHD code based on high-order implicit predictor-corrector finite difference scheme (high-order IPCFD scheme). High-order IPCFD scheme adopts high-order predictor-corrector scheme for the time integration and high-order central difference method as the spatial derivative solver. We use Elimination-of-the-Runoff-Errors (ERE) technology to avoid the numerical oscillations and numerical instability in the simulation results. In one-dimensional MHD problem, our simulation results show good agreement with the Brio & Wu MHD shock tube problem. The divergent B constraint remains fully satisfied, that is the divergent B equals to zero throughout the simulation. When solving the two-dimensional (2D) linear wave in MHD plasma, we clearly obtain the group-velocity Friedrichs diagrams of the MHD waves. Here we demonstrate 2D simulation results of rotor problem, Orszag-Tang vortex system, vortex type K-H instability, and kink type K-H instability by using our IPCFD MHD code and discuss the advantage of our simulation code.
Two-dimensional simulations of possible mesoscale effects of nuclear war fires 2. Model results
Filippo Giorgi; Guido Visconti
1989-01-01
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
Dynamic simulation of the flow of suspensions of two-dimensional particles with arbitrary shapes
C. Pozrikidis
2001-01-01
A boundary-element method is implemented for simulating the motion of two-dimensional rigid particles with arbitrary shapes suspended in a viscous fluid in Stokes flow. The numerical implementation results in a system of linear equations for the components of the hydrodynamic traction over boundary elements distributed over the particle surfaces, and for the velocity of translation and angular velocity of rotation
Two-dimensional RANS simulations of the flow through a compressor cascade with jet flaps
S. Fischer; H. Saathoff; R. Radespiel
2008-01-01
With the aim to reduce the blade count in a stator row, in this paper the application of active blowing is discussed. Based on a high-speed compressor stage blade geometries for a stator cascade with jet flap implementation are developed. Two-dimensional numerical simulations of the cascade flow clarify that a reasonable appliance of the jet is particularly possible at high
Roy, Subrata
1 American Institute of Aeronautics and Astronautics Two-dimensional Simulation of Horseshoe-713 Copyright © 2010 by Authors. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. #12;2 American Institute of Aeronautics and Astronautics I. Introduction lasma that has been used
Li, Zhenyu; Abramavicius, Darius; Zhuang, Wei; Mukamel, Shaul
2007-01-01
The two dimensional (2D) photon echo spectrum of the amide ultraviolet (UV) bands of proteins are simulated. Two effective exciton Hamiltonian parameter sets developed by Woody and Hirst, which predict similar CD spectra, may be distinguished by their very different 2DUV spectra. These differences are enhanced in specific configurations of pulse polarizations which provide chirality-induced signals. PMID:19011677
Two-dimensional model simulations of the QBO in ozone and tracers in the tropical stratosphere
Jackman, Charles H.
variation in ozone and long-lived trace species [e.g., Hasebe, 1994; Eluszkiewicz et al., 1996; Cordero etTwo-dimensional model simulations of the QBO in ozone and tracers in the tropical stratosphere Eric impact on the phase. Sensitivity tests reveal that the QBO in transport dominates the ozone interannual
Two-dimensional gravity simulation of the tectonosphere under the American-Antarctic Ridge
A. A. Bulychev; D. A. Gilod
2009-01-01
This paper discusses the results of a two-dimensional gravity simulation along a number of transects across the American-Antarctic\\u000a Spreading System. Bathymetric data, as well as the data of gravity anomalies from satellite altimetry and data on the age\\u000a of the ocean floor, were used as data. The results of a preliminary three-dimensional simulation were applied for constructing\\u000a the model and
Kaijun Liu; S. Peter Gary; Dan Winske
2010-01-01
The two-dimensional Los Alamos hybrid simulation code is used to study the excitation of fluctuations and the associated ion dynamics at the high Alfvén-Mach heliospheric termination shock and in the near-shock heliosheath. This simulation represents the electrons as a zero-mass fluid, addresses only a perpendicular shock, and considers the upstream ions to consist of a cool solar wind component and
Kijeong Kwac; Chewook Lee; Yousung Jung; Jaebeom Han; Kyungwon Kwak; Junrong Zheng; M. D. Fayer; Minhaeng Cho
2006-01-01
Molecular dynamics (MD) simulations and quantum mechanical electronic structure calculations are used to investigate the nature and dynamics of the phenol-benzene complex in the mixed solvent, benzene?CCl4. Under thermal equilibrium conditions, the complexes are continuously dissociating and forming. The MD simulations are used to calculate the experimental observables related to the phenol hydroxyl stretching mode, i.e., the two dimensional infrared
Simulations of the Two-Dimensional Electronic Spectroscopy of the Photosystem II Reaction Center
Lewis, K. L. M.; Fuller, F. D.; Myers, J. A.; Yocum, C. F.; Mukamel, S.; Abramavicius, D.; Ogilvie, J. P.
2013-01-01
We report simulations of the two-dimensional electronic spectroscopy of the Qy band of the D1-D2-Cyt b559 photosystem II reaction center at 77 K. We base the simulations on an existing Hamiltonian that was derived by simultaneous fitting to a wide range of linear spectroscopic measurements and described within modified Redfield theory. The model obtains reasonable agreement with most aspects of the two-dimensional spectra, including the overall peak shapes and excited state absorption features. It does not reproduce the rapid equilibration from high energy to low energy excitonic states evident by a strong cross-peak below the diagonal. We explore modifications to the model to incorporate new structural data and improve agreement with the two-dimensional spectra. We find that strengthening the system–bath coupling and lowering the degree of disorder significantly improves agreement with the cross-peak feature, while lessening agreement with the relative diagonal/antidiagonal width of the 2D spectra. We conclude that two-dimensional electronic spectroscopy provides a sensitive test of excitonic models of the photosystem II reaction center and discuss avenues for further refinement of such models. PMID:23210463
Global Mhd Simulations: Comparisons With Cluster Observations
NASA Astrophysics Data System (ADS)
Berchem, J.
Three-dimensional magnetohydrodynamic (MHD) simulation has become a power tool to investigate the global interaction of the solar wind with the Earth magne- tosphere and to link multispacecraft measurements. Although Cluster's multi-point measurements provide most of the time information on a finer scale than that resolv- able by MHD models, global simulations can be used to establish causal relationships between local measurements and the large-scale dynamics of the magnetosphere. We present the results of several studies based on recent Cluster passes through the day- side magnetopause and the cusp. These case studies use magnetic field and plasma parameters measured upstream of the bow shock as input to the simulations and in- clude both typical and extreme solar wind conditions. We demonstrate how comparing local data streams and ionospheric activity deduced from the simulations with Cluster measurements provides information that can be used to reconstruct the global topol- ogy and dynamics of the dayside magnetosphere extant during the events.
MHD Simulation of the Inverse Pinch Plasma Discharge
Esaulov, A; Bauer, B; Lindemuth, I; Makhin, V; Presura, R; Ryutov, D
2004-07-01
A wall confined plasma in an inverse pinch configuration holds potential as a plasma target for Magnetized Target Fusion (MTF) as well as the simple geometry to study wall-confined plasma. An experiment is planned to study the inverse pinch configuration using the Nevada Terawatt Facility (NTF) at the University of Nevada, Reno (UNR). The dynamics of the discharge formation have been analyzed using analytic models and numerical methods. Strong heating occurs by thermalization of directed energy when an outward moving current sheet (the inverse pinch effect) collides with the outer wall of the experimental chamber. Two dimensional MHD simulations show Rayleigh-Taylor and Richtmyer-Meshkov -like modes of instability, as expected because of the shock acceleration during plasma formation phase. The instabilities are not disruptive, but give rise to a mild level of turbulence. The conclusion from this work is that an interesting experiment relevant to wall confinement for MTF could be done using existing equipment at UNR.
C. Scheurer; A. Piryatinski; S. Mukamel
2001-01-01
An ensemble of exciton Hamiltonians for the amide-I band of the folded and unfolded states of a helical ‚-heptapeptide is generated using a molecular dynamics (MD) simulation. The correlated fluctuations of its parameters and their signatures in two-dimensional (2D) vibrational echo spectroscopy are computed. This technique uses infrared pulse sequences to provide ultrafast snapshots of molecular structural fluctuations, in analogy
MINBU Distribution of Two-Dimensional Quantum Gravity:. Simulation Result and Semiclassical Analysis
S. Ichinose; N. Tsuda; T. Yukawa
1997-01-01
We analyze the MINBU distribution of two-dimensional quantum gravity. New data of R2-gravity by the Monte Carlo simulation and its theoretical analysis by the semiclassical approach are presented. In the distribution, the cross-over phenomenon takes place at some size of the baby universe where the randomness competes with the smoothing (or roughening) force of R2-term. The dependence on the central
Two-dimensional simulation of polysilicon etching with chlorine in a high density plasma reactor
Dimitris P. Lymberopoulos; Demetre J. Economou
1995-01-01
A two-dimensional fluid simulation of polysilicon etching with chlorine in an inductively-coupled high density plasma source is presented. A modular approach was used to couple in a self-consistent manner the disparate time scales of plasma and neutral species transport. This way, complex plasma chemical reactions (involving electrons, ions and neutrals) as well as surface chemistry can be included in the
Two-dimensional simulation of a miniaturized inductively coupled plasma reactor
Sang Ki Nam; Demetre J. Economou
2004-01-01
A two-dimensional self-consistent simulation of a miniaturized inductively coupled plasma (mICP) reactor was developed. The coupled equations for plasma power deposition, electron temperature, and charged and neutral species densities, were solved to obtain the spatial distribution of an argon discharge. The effect of control parameters, such as power and pressure, on the evolution of plasma density and electron temperature was
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.
Two-dimensional simulation of unsteady heat transfer from a circular cylinder in crossflow
Salem Bouhairie; Vincent H. Chu
2007-01-01
The heat transfer from the surface of a circular cylinder into a crossflow has been computed using a two-dimensional model, for a range of Reynolds numbers from Re=200 to 15550. The boundary-layer separation, the local and overall heat-transfer rates, the eddy- and flare-detachment frequencies and the width of the flares were determined from the numerical simulations. In this range of
A one-fluid, two-dimensional flow simulation model for a kettle reboiler
David A. McNeil; Khalid Bamardouf; Bryce M. Burnside
2010-01-01
A one-fluid, or algebraic slip, model has been developed to simulate two-dimensional, two-phase flow in a kettle reboiler. The model uses boundary conditions that allow for a change in flow pattern from bubbly to intermittent flow at a critical superficial gas velocity, as has been observed experimentally. The model is based on established correlations for void fraction and for the
Long range antiferromagnetic order in Ising model simulations in a two-dimensional Penrose lattice
Susumu Matsuo; Shoji Fujiwara; Hiroshi Nakano; Tsutmu Ishimasa
2004-01-01
Long-range antiferromagnetic order was found in simulated annealing calculations for an Ising spin system on a two-dimensional Penrose lattice under Ruderman–Kittel–Kasuya–Yosida-like alternating exchange interactions at low temperatures. Two models of magnetic interactions resulted in the long-range antiferromagnetic order; a model of an antiferromagnetic interaction for the shortest distance and ferromagnetic interaction for the second and the third shortest distances, and
Two-dimensional simulations of steady perforated-plate stabilized premixed flames
H. Murat Altay; Kushal S. Kedia; Raymond L. Speth; Ahmed F. Ghoniem
2010-01-01
The objective of this work is to examine the impact of the operating conditions and the perforated-plate design on the steady, lean premixed flame characteristics. We perform two-dimensional simulations of laminar flames using a reduced chemical kinetics mechanism for methane–air combustion, consisting of 20 species and 79 reactions. We solve the heat conduction problem within the plate, allowing heat exchange
Thermal relaxation of a two dimensional plasma in a dc magnetic field. Part 2: Numerical simulation
NASA Technical Reports Server (NTRS)
Hsu, J. Y.; Joyce, G.; Montgomery, D.
1974-01-01
The thermal relaxation process for a spatially uniform two dimensional plasma in a uniform dc magnetic field is simulated numerically. Thermal relaxation times are defined in terms of the time necessary for the numerically computer Boltzman H-function to decrease through a given part of the distance to its minimum value. Dependence of relaxation time on two parameters is studied: number of particles per Debye square and ratio of gyrofrequency to plasma frequency.
Computer simulations of domain growth in off-critical quenches of two-dimensional binary mixtures
A. Lamura; G. Gonnella
2002-10-08
The phase separation of two-dimensional binary mixtures has been studied through numerical Langevin simulations based on a Ginzburg-Landau free energy. We have considered not symmetric mixtures with and without imposed shear flow. In the sheared case our main results are as follows: (1) domains are distorted by the flow; (2) the structure factor has four peaks; (3) excess viscosity shows a peak whose position is independent of shear rate but its height decreases increasing shear rate.
NASA Astrophysics Data System (ADS)
Krishnamachari, Badrinarayan
This thesis describes Monte Carlo simulations of two systems; the first part of the thesis describes studies of two dimensional (2D) He using variational wave functions, while the second half of the thesis describes Monte Carlo simulations of a 2D lattice gas. Monte Carlo simulations of the two dimensional phases of sp4He, using a "shadow" wave function are described in chapter 1. This wave function provides a unified description of the solid and liquid phases, with spontaneous crystallization occurring in the solid phase without recourse to a lattice. It provides a particularly effective description of the solid phase where it yields energies lower than existing trial wave functions. We have investigated the properties of the solid phase in detail and have found that it lacks long range translational order, has a high density of defects, and less angular order relative to classical systems. These results are similar to results obtained for simulations of a quantum hard disc system. We have also computed these properties for the liquid phase. These properties vary rapidly in the transition region and serve as a good signal for the transition itself. We proceed to study the simplest inhomogeneous phase of He in 2D viz. a puddle, in chapter 2. We use the same trial wave function modified by a one body form factor to simulate these 2D puddles. We extract the line tension of the puddles and the energy in the bulk from our simulations. The bulk energy matches well with the values obtained from our studies of the homogeneous phase. We also study the surface profile and width of the surface region of the puddles as a function of system size. We find that the width increases with system size in a manner similar to classical 2D drops viz., W˜sqrt{L}. The same wave functions are used to study the binding of bosonic sp3He. We find that mass 3 bosons are very weakly self bound in two dimensions and fermions of the same mass are unlikely to bind. Further we believe that a monolayer film of sp3He on graphite will not bind into a liquid puddle; it would be a gas at low densities and a solid at very high densities. In the second half of the thesis we report simulation studies of equilibrium features viz., circular islands on model surfaces. In particular we are interested in studying the relationship between the density of vapour around a curved island and its curvature. This is given by the Gibbs-Thomson formula, which assumes that the vapour surrounding the island is an ideal gas. Results from numerical simulations of a lattice gas model reported in chapter 3, do not fit very well to the Gibbs-Thomson formula. By exploiting a mapping to the Ising model we show how we can calculate an accurate equation of state for the lattice gas, using high field series expansions. This improves upon the ideal gas equation of state, and is used to derive a corrected Gibbs-Thomson formula for the lattice gas. This formula agrees very well with the data from our simulation. We also investigate the effects of finite size on the stability of the islands both theoretically and through simulations.
Two-dimensional Green`s function Poisson solution appropriate for cylindrical-symmetry simulations
Riley, M.E.
1998-04-01
This report describes the numerical procedure used to implement the Green`s function method for solving the Poisson equation in two-dimensional (r,z) cylindrical coordinates. The procedure can determine the solution to a problem with any or all of the applied voltage boundary conditions, dielectric media, floating (insulated) conducting media, dielectric surface charging, 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. This report is a stand-alone supplement to the previous Sandia Technical Report SAND98-0537 presenting the two-dimensional Cartesian Poisson solver.
Two-dimensional simulation of temperature distributions inside pressurized fluidized bed combustors
Artlich, S.; Mackens, W.; Werther, J. [Technical Univ. Hamburg-Harburg, Hamburg (Germany)
1997-12-31
A particular characteristic of Pressurized Fluidized Bed Combustors with stationary fluidized beds (PFBC) is the high rate of heat release in the vicinity of he coal feed points. This may cause local overheating of the bed. Thus a two-dimensional model is presented which describes the temperature distribution inside a PFBC as a function of coal characteristics, operating parameters and geometry. The model is composed of two mass balances describing the carbon and the oxygen concentration inside the stationary bed as well as of an enthalpy balance. Furthermore, a submodel takes into account the feed of coal into the reactor as a coal-water mixture. The numerical calculations yield two-dimensional profiles of the carbon and the oxygen concentration and the temperature distribution, respectively. The simulation results point at and quantify critical parameters which have to be considered when dealing with the scale-up of boilers from the pilot-scale to large-scale size.
Two-dimensional numerical simulation of boron diffusion for pyramidally textured silicon
NASA Astrophysics Data System (ADS)
Ma, Fa-Jun; Duttagupta, Shubham; Shetty, Kishan Devappa; Meng, Lei; Samudra, Ganesh S.; Hoex, Bram; Peters, Ian Marius
2014-11-01
Multidimensional numerical simulation of boron diffusion is of great relevance for the improvement of industrial n-type crystalline silicon wafer solar cells. However, surface passivation of boron diffused area is typically studied in one dimension on planar lifetime samples. This approach neglects the effects of the solar cell pyramidal texture on the boron doping process and resulting doping profile. In this work, we present a theoretical study using a two-dimensional surface morphology for pyramidally textured samples. The boron diffusivity and segregation coefficient between oxide and silicon in simulation are determined by reproducing measured one-dimensional boron depth profiles prepared using different boron diffusion recipes on planar samples. The established parameters are subsequently used to simulate the boron diffusion process on textured samples. The simulated junction depth is found to agree quantitatively well with electron beam induced current measurements. Finally, chemical passivation on planar and textured samples is compared in device simulation. Particularly, a two-dimensional approach is adopted for textured samples to evaluate chemical passivation. The intrinsic emitter saturation current density, which is only related to Auger and radiative recombination, is also simulated for both planar and textured samples. The differences between planar and textured samples are discussed.
Numerical Simulation of Flow Induced Vibration of a Two-Dimensional Airfoil
NASA Astrophysics Data System (ADS)
Gharedaghi Mollahajloo, Samad; Hassan Rahimian, Mohammad
2009-09-01
The aim of this paper is to simulate the interaction between a two-dimensional incompressible viscous flow and a rigid airfoil with two degrees of freedom. The airfoil can rotate around its elastic axis while oscillating in the vertical direction. The numerical simulation consists of a coupled system of below mentioned equations: 1- Governing equations of flow field which are solved by SIMPLE algorithm. 2- A system of nonlinear ordinary differential equations which describes the airfoil motions. To determine the location of airfoil in each time step an algorithm based on VOF method for a system of fixed mesh is developed. Results are compared well with references.
Goldberg, L.F. [Univ. of Minnesota, Minneapolis, MN (United States)
1990-08-01
The activities described in this report do not constitute a continuum but rather a series of linked smaller investigations in the general area of one- and two-dimensional Stirling machine simulation. The initial impetus for these investigations was the development and construction of the Mechanical Engineering Test Rig (METR) under a grant awarded by NASA to Dr. Terry Simon at the Department of Mechanical Engineering, University of Minnesota. The purpose of the METR is to provide experimental data on oscillating turbulent flows in Stirling machine working fluid flow path components (heater, cooler, regenerator, etc.) with particular emphasis on laminar/turbulent flow transitions. Hence, the initial goals for the grant awarded by NASA were, broadly, to provide computer simulation backup for the design of the METR and to analyze the results produced. This was envisaged in two phases: First, to apply an existing one-dimensional Stirling machine simulation code to the METR and second, to adapt a two-dimensional fluid mechanics code which had been developed for simulating high Rayleigh number buoyant cavity flows to the METR. The key aspect of this latter component was the development of an appropriate turbulence model suitable for generalized application to Stirling simulation. A final-step was then to apply the two-dimensional code to an existing Stirling machine for which adequate experimental data exist. The work described herein was carried out over a period of three years on a part-time basis. Forty percent of the first year`s funding was provided as a match to the NASA funds by the Underground Space Center, University of Minnesota, which also made its computing facilities available to the project at no charge.
Modeling open boundaries in dissipative MHD simulation
NASA Astrophysics Data System (ADS)
Meier, E. T.; Glasser, A. H.; Lukin, V. S.; Shumlak, U.
2012-04-01
The truncation of large physical domains to concentrate computational resources is necessary or desirable in simulating many natural and man-made plasma phenomena. Three open boundary condition (BC) methods for such domain truncation of dissipative magnetohydrodynamics (MHD) problems are described and compared here. A novel technique, lacuna-based open boundary conditions (LOBC), is presented for applying open BC to dissipative MHD and other hyperbolic and mixed hyperbolic-parabolic systems of partial differential equations. LOBC, based on manipulating Calderon-type near-boundary sources, essentially damp hyperbolic effects in an exterior region attached to the simulation domain and apply BC appropriate for the remaining parabolic effects (if present) at the exterior region boundary. Another technique, approximate Riemann BC (ARBC), is adapted from finite volume and discontinuous Galerkin methods. In ARBC, the value of incoming flux is specified using a local, characteristic-based method. A third commonly-used open BC, zero-normal derivative BC (ZND BC), is presented for comparison. These open BC are tested in several gas dynamics and dissipative MHD problems. LOBC are found to give stable, low-reflection solutions even in the presence of strong parabolic behavior, while ARBC are stable only when hyperbolic behavior is dominant. Pros and cons of the techniques are discussed and put into context within the body of open BC research to date.
Reconnection events in two-dimensional Hall magnetohydrodynamic S. Donato,1
Reconnection events in two-dimensional Hall magnetohydrodynamic turbulence S. Donato,1 S. Servidio performed by comparing numerical simulations of magnetohydrodynamics (MHD) and Hall magnetohydrodynamics reconnection in 2D Hall magnetohydrodynamic (HMHD) tur- bulence. Using high resolution pseudo
Thermal structure of the ionosphere of Mars - Simulations with one- and two-dimensional models
NASA Technical Reports Server (NTRS)
Singhal, R. P.; Whitten, R. C.
1988-01-01
Heat flux saturation effects are included in the present one- and two-dimensional models of the Martian upper ionosphere's thermal structure. The inclusion of small upper boundary and volume heat sources is found to yield satisfactory simulations of the dayside ion temperature observation results obtained by Viking 1's retarding potential analyzers. It is noted that the plasma flow-transport of heat from the dayside to the nightside makes no contribution to the ion and electron temperatures that have been calculated for the nightside.
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.
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.
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.
Simulation study of chiral two dimensional ultraviolet (2DUV) spectroscopy of the protein backbone
Abramavicius, Darius; Jiang, Jun; Bulheller, Benjamin M.; Hirst, Jonathan D.; Mukamel, Shaul
2010-01-01
Amide n –?* and ?-?* excitations around 200 nm are prominent spectroscopic signatures of the protein backbone, which are routinely used in ultraviolet (UV) circular dichroism for structure characterization. Recently developed ultrafast laser sources may be used to extend these studies to two dimensions (2D). We apply a new algorithm for modelling protein electronic transitions to simulate two-dimensional ultraviolet (2DUV) photon echo signals in this regime and to identify signatures of protein backbone secondary (and tertiary) structure. Simulated signals for a set of globular and fibrillar proteins and their specific regions reveal characteristic patterns of helical and sheet secondary structures. We investigate how these patterns vary and converge with the size of the structural motif. Specific chiral polarization configurations of the UV pulses are found to be sensitive to aspects of the protein structure. This information significantly augments that available from linear circular dichroism. PMID:20481498
Vahedi, V.; Birdsall, C.K.; Lieberman, M.A.; DiPeso, G.; Rognlien, T.D.
1992-12-15
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 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. We find 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.
Creation of two-dimensional coulomb crystals of ions in oblate Paul traps for quantum simulations
Bryce Yoshimura; Marybeth Stork; Danilo Dadic; W. C. Campbell; J. K. Freericks
2014-06-20
We develop the theory to describe the equilibrium ion positions and phonon modes for a trapped ion quantum simulator in an oblate Paul trap that creates two-dimensional Coulomb crystals in a triangular lattice. By coupling the internal states of the ions to laser beams propagating along the symmetry axis, we study the effective Ising spin-spin interactions that are mediated via the axial phonons and are less sensitive to ion micromotion. We find that the axial mode frequencies permit the programming of Ising interactions with inverse power law spin-spin couplings that can be tuned from uniform to $r^{-3}$ with DC voltages. Such a trap could allow for interesting new geometrical configurations for quantum simulations on moderately sized systems including frustrated magnetism on triangular lattices or Aharonov-Bohm effects on ion tunneling. The trap also incorporates periodic boundary conditions around loops which could be employed to examine time crystals.
Martinez-Sykora, Juan; De Pontieu, Bart; Hansteen, Viggo, E-mail: j.m.sykora@astro.uio.no [Lockheed Martin Solar and Astrophysics Laboratory, Palo Alto, CA 94304 (United States)
2012-07-10
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.
Numerical simulations of two-dimensional foam by the immersed boundary method
NASA Astrophysics Data System (ADS)
Kim, Yongsam; Lai, Ming-Chih; Peskin, Charles S.
2010-07-01
In this paper, we present an immersed boundary (IB) method to simulate a dry foam, i.e., a foam in which most of the volume is attributed to its gas phase. Dry foam dynamics involves the interaction between a gas and a collection of thin liquid-film internal boundaries that partition the gas into discrete cells or bubbles. The liquid-film boundaries are flexible, contract under the influence of surface tension, and are permeable to the gas, which moves across them by diffusion at a rate proportional to the local pressure difference across the boundary. Such problems are conventionally studied by assuming that the pressure is uniform within each bubble. Here, we introduce instead an IB method that takes into account the non-equilibrium fluid mechanics of the gas. To model gas diffusion across the internal liquid-film boundaries, we allow normal slip between the boundary and the gas at a velocity proportional to the (normal) force generated by the boundary surface tension. We implement this method in the two-dimensional case, and test it by verifying the von Neumann relation, which governs the coarsening of a two-dimensional dry foam. The method is further validated by a convergence study, which confirms its first-order accuracy.
Kim, J.; McMurray, J. S.; Williams, C. C.; Slinkman, J. [Department of Physics, University of Utah, Salt Lake City, Utah 84112 (United States); IBM Microelectronics, Essex Jct., Vermont 05452 (United States)
1998-11-24
We report the results of a 2-step two-dimensional (2D) diffusion study by Scanning Capacitance Microscopy (SCM) and 2D TSUPREM IV process simulation. A quantitative 2D dopant profile of gate-like structures consisting heavily implanted n+ regions separated by a lighter doped n-type region underneath 0.56 {mu}m gates is measured with the SCM. The SCM is operated in the constant-change-in-capacitance mode. The 2-D SCM data is converted to dopant density through a physical model of the SCM/silicon interaction. This profile has been directly compared with 2D TSUPREM IV process simulation and used to calibrate the simulation parameters. The sample is then further subjected to an additional diffusion in a furnace for 80 minutes at 1000C. The SCM measurement is repeated on the diffused sample. This final 2D dopant profile is compared with a TSUPREM IV process simulation tuned to fit the earlier profile with no change in the parameters except the temperature and time for the additional diffusion. Our results indicate that there is still a significant disagreement between the two profiles in the lateral direction. TSUPREM IV simulation considerably underestimates the diffusion under the gate region.
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.
The void spectrum in two-dimensional numerical simulations of gravitational clustering
NASA Technical Reports Server (NTRS)
Kauffmann, Guinevere; Melott, Adrian L.
1992-01-01
An algorithm for deriving a spectrum of void sizes from two-dimensional high-resolution numerical simulations of gravitational clustering is tested, and it is verified that it produces the correct results where those results can be anticipated. The method is used to study the growth of voids as clustering proceeds. It is found that the most stable indicator of the characteristic void 'size' in the simulations is the mean fractional area covered by voids of diameter d, in a density field smoothed at its correlation length. Very accurate scaling behavior is found in power-law numerical models as they evolve. Eventually, this scaling breaks down as the nonlinearity reaches larger scales. It is shown that this breakdown is a manifestation of the undesirable effect of boundary conditions on simulations, even with the very large dynamic range possible here. A simple criterion is suggested for deciding when simulations with modest large-scale power may systematically underestimate the frequency of larger voids.
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.
Gheisari, R., E-mail: gheisari@pgu.ac.ir [Physics Department, Persian Gulf University, Bushehr 75169 (Iran, Islamic Republic of); Nuclear Energy Research Center, Persian Gulf University, Bushehr 75169 (Iran, Islamic Republic of); Firoozabadi, M. M.; Mohammadi, H. [Department of Physics, University of Birjand, Birjand 97175 (Iran, Islamic Republic of)] [Department of Physics, University of Birjand, Birjand 97175 (Iran, Islamic Republic of)
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.
An Integrated One-Dimensional and Two-Dimensional Urban Stormwater Flood Simulation Model
NASA Astrophysics Data System (ADS)
Fang, Xing; Su, Dehui
2006-06-01
Flash flooding is the rapid flooding of low lying areas caused by the stormwater of intense rainfall associated with thunderstorms. Flash flooding occurs in many urban areas with relatively flat terrain and can result in severe property damage as well as the loss of lives. In this paper, an integrated one-dimensional (1-D) and two-dimensional (2-D) hydraulic simulation model has been established to simulate stormwater flooding processes in urban areas. With rainfall input, the model simulates 2-D overland flow and 1-D flow in underground stormwater pipes and drainage channels. Drainage channels are treated as special flow paths and arranged along one or more sides of a 2-D computational grid. By using irregular computation grids, the model simulates unsteady flooding and drying processes over urban areas with complex drainage systems. The model results can provide spatial flood risk information (e.g., water depth, inundation time and flow velocity during flooding). The model was applied to the City of Beaumont, Texas, and validated with the recorded rainfall and runoff data from Tropical Storm Allison with good agreement.
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.
Tracking the Mechanism of Fibril Assembly by Simulated Two-Dimensional Ultraviolet Spectroscopy
Lam, A. R.; Rodriguez, J. J.; Rojas, A.; Scheraga, H.A; Mukamel, S.
2013-01-01
Alzheimer’s disease (AD) is a neurodegenerative disorder characterized by the accumulation of plaque deposits in the human brain. The main component of these plaques consists of highly ordered structures called amyloid fibrils, formed by the amyloid ?-peptide (A?). The mechanism connecting A? and AD is yet undetermined. In a previous study, a coarse-grained united-residue model and molecular dynamics simulations were used to model the growth mechanism of A ? amyloid fibrils. Based on these simulations, a dock/lock mechanism was proposed, in which A? fibrils grow by adding monomers at either end of an amyloid fibril template. To examine the structures in the early time-scale formation and growth of amyloid fibrils, simulated two-dimensional ultraviolet spectroscopy is used. These early structures are monitored in the far ultraviolet regime (? = 190–250 nm) in which the computed signals originate from the backbone n?* and ??* transitions. These signals show distinct cross-peak patterns that can be used, in combination with molecular dynamics, to monitor local dynamics and conformational changes in the secondary structure of A?-peptides. The protein geometry-correlated chiral xxxy signal and the non-chiral combined signal xyxy- xyyx were found to be sensitive to, and in agreement with, a dock/lock pathway. PMID:23214934
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.
Laser-shock-wave simulation of two-dimensional nuclear shock waves
Wilke, M.D.; Stone, S.N.; Barasch, G.E.
1982-01-01
Results from experiments that used shock waves generated by a high-power laser to simulate multi-dimensional nuclear shocks are described. The shocks were produced in 50 torr air by irradiating hollow plastic shell targets with 30J, 300 ps Nd-glass laser pulses. The individual near-spherical shocks were investigated to determine over what range the shock radius, R/sub s/, obeyed the Taylor-von-Neumann-Sedov expansion law, R/sub s/..cap alpha..t/sup 2/5/. The relationship was found to hold for 0.9 cm less than or equal to R/sub s/ less than or equal to 2.0 cm. Also, the shocks were modeled with the nuclear effects code RADFLO and good agreement was found between calculation and data for R/sub s/ vs t and also gas and electron densities determined from two-wavelength interferograms of the shock waves. Based on the understanding of the individual shocks, two experiments were designed to investigate two-dimensional shock waves. The first experiment consisted of reflecting a spherical shock off a plastic block suspended 0.9 cm above the target. In the second experiment, two identical spherical shocks were simultaneously generated approx. 1.8 cm apart and allowed to collide. The reflected shocks were compared through scaling laws to the Teapot/Met shock wave generated from a 22 KT nuclear explosion 122 M above the ground. The Mach structures were found to be similar. Then the reflecting and interacting shocks were modeled with a two-dimensional effects code using the one-dimensional RADFLO output to start the problem. Calculation and data for Mach angles and triple point propagation were found to be in good agreement.
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.
NASA Astrophysics Data System (ADS)
Thornhill, J. W.; Giuliani, J. L.; Chong, Y. K.; Velikovich, A. L.; Dasgupta, A.; Apruzese, J. P.; Jones, B.; Ampleford, D. J.; Coverdale, C. A.; Jennings, C. A.; Waisman, E. M.; Lamppa, D. C.; McKenney, J. L.; Cuneo, M. E.; Krishnan, M.; Coleman, P. L.; Madden, R. E.; Elliott, K. W.
2012-09-01
Argon Z-pinch experiments are to be performed on the refurbished Z machine (which we will refer to as ZR here in order to distinguish between pre-refurbishment Z) at Sandia National Laboratories with a new 8 cm diameter double-annulus gas puff nozzle constructed by Alameda Applied Sciences Corporation (AASC). The gas exits the nozzle from an outer and inner annulus and a central jet. The amount of gas present in each region can be varied. Here a two-dimensional radiation MHD (2DRMHD) model, MACH2-TCRE, with tabular collisional radiative equilibrium atomic kinetics is used to theoretically investigate stability and K-shell emission properties of several measured (interferometry) initial gas distributions emanating from this new nozzle. Of particular interest is to facilitate that the distributions employed in future experiments have stability and K-shell emission properties that are at least as good as the Titan nozzle generated distribution that was successfully fielded in earlier experiments on the Z machine before it underwent refurbishment. The model incorporates a self-consistent calculation for non-local thermodynamic equilibrium kinetics and ray-trace based radiation transport. This level of detail is necessary in order to model opacity effects, non-local radiation effects, and the high temperature state of K-shell emitting Z-pinch loads. Comparisons of radiation properties and stability of measured AASC gas profiles are made with that of the distribution used in the pre-refurbished Z experiments. Based on these comparisons, an optimal K-shell emission producing initial gas distribution is determined from among the AASC nozzle measured distributions and predictions are made for K-shell yields attainable from future ZR experiments.
Demetxe J. Economou; Timothy J. Bartel; Richard S. Wise; Dimitris P. Lymberopoulos
1995-01-01
We present a two dimensional direct simulation Monte Carlo (DSMC) study of the rarefied reactive flow of neutrals and ions in a low pressure inductively coupled plasma reactor. The spatially-dependent rate coefficients of electron impact reactions and the electrostatic field were obtained from a fluid plasma simulation. Neutral and ion etching of polysilicon with chlorine gas was studied with emphasis
Economou, Demetre J.
simulation the reactor was divided into bulk plasma and sheath. The bulk plasma was assumed quasineutralRapid two-dimensional self-consistent simulation of inductively coupled plasma and comparison with experimental data Richard S. Wise, Dimitris P. Lymberopoulos, and Demetre J. Economoua) Plasma Processing
Florida, University of
device simulator is presented. Using the impedance-field method with cyclostationary noise sources-assisted GR noise sources. The drift-diffusion simulation of semiconductor devices re- quires the solutionIEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 50, NO. 5, MAY 2003 1353 Two-Dimensional Semiconductor
1987-01-01
The Tar Sand Reservoir Simulator (TSRS) is expanded in order to simulate the multidimensional nature of the thermal recovery of oil from a tar sand block in Western Research Institute's block reactor. TSRS now rigorously accounts for many of the phenomena associated with the thermal processing of tar sand in one or two dimensions. In the two-dimensional mode, fundamental differential
Two-dimensional simulations of explosive eruptions of Kick-em Jenny and other submarine volcanos
Gisler, Galen R.; Weaver, R. P. (Robert P.); Mader, Charles L.; Gittings, M. L. (Michael 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)
Piontek, Robert A.; Ostriker, Eve C.
2004-02-01
The structure and dynamics of diffuse gas in the Milky Way and other disk galaxies may be strongly influenced by thermal and magnetorotational instabilities (TI and MRI, respectively) on scales ~1-100 pc. We initiate a study of these processes, using two-dimensional numerical hydrodynamic and magnetohydrodynamic simulations with conditions appropriate for the atomic interstellar medium (ISM). Our simulations incorporate thermal conduction and adopt local ``shearing-periodic'' equations of motion and boundary conditions to study dynamics of a (100 pc) 2 radial-vertical section of the disk. We demonstrate, consistent with previous work, that nonlinear development of ``pure TI'' produces a network of filaments that condense into cold clouds at their intersections, yielding a distinct two-phase warm/cold medium within ~20 Myr. TI-driven turbulent motions of the clouds and warm intercloud medium are present but saturate at quite subsonic amplitudes for uniform initial P/k=2000 K cm -3. MRI has previously been studied in near-uniform media; our simulations include both TI+MRI models, which begin from uniform-density conditions, and cloud+MRI models, which begin with a two-phase cloudy medium. Both the TI+MRI and cloud+MRI models show that MRI develops within a few galactic orbital times, just as for a uniform medium. The mean separation between clouds can affect which MRI mode dominates the evolution. Provided intercloud separations do not exceed half the MRI wavelength, we find the MRI growth rates are similar to those for the corresponding uniform medium. This opens the possibility that if low cloud volume filling factors increase MRI dissipation times compared to those in a uniform medium, then MRI-driven motions in the ISM could reach amplitudes comparable to observed H I turbulent line widths.
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.
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.
Two-dimensional simulation of a low-current dielectric barrier discharge in atmospheric helium
Zhang Yuantao; Wang Dezhen; Kong, Michael G. [State Key Laboratory of Materials Modification by Laser, Ion and Electron Beams, Department of Physics, Dalian University of Technology, Dalian (China); Department of Electronic and Electrical Engineering, Loughborough University, Leicestershire LE11 3TU (United Kingdom)
2005-12-01
A two-dimensional computational study is presented to unravel radial structure of a dielectric barrier discharge in atmospheric helium when the gas voltage exceeds slightly the breakdown voltage and the discharge current is low to retain a repetitive dynamic pattern of one discharge event every half cycle of the applied voltage. Simulation results reveal that during each half cycle of the applied voltage gas breakdown occurs first in a central region around the electrode axis. After it is extinguished, a second breakdown is triggered in the boundary region near the radial edge of the two electrodes as confirmed by the dynamic evolution of the radial profile of the electric field, the current density and the charged particles. These predictions are consistent with relevant experimental observations in literature. It is also shown that an increase in the applied voltage or in the excitation frequency reduces the time delay between the two breakdown events and the difference between their corresponding current densities. This offers a route to improve the uniformity of atmospheric dielectric barrier discharges for their intended applications.
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
Large Eddy Simulation of a turbulent flow in two dimensional dunes using an immersed boundary method
NASA Astrophysics Data System (ADS)
Agegnehu, Getnet; Smith, Heather D.
2013-11-01
The flow over dunes separates at the crest, generating a shear layer which has a big role for energy dissipation and formation of coherent structures. Large Eddy Simulations using bodyfitted and immersed boundary grids are performed to study the detailed flow dynamics that occurs in a fixed two dimensional dunes. We used a three-dimensional, non-hydrostatic solver; OpenFOAM for this study. The immersed boundary method was implemented using a discrete forcing approach with direct imposition of the boundary conditions. A periodic boundary condition is imposed in both the streamwise and spanwise directions. No-slip and free slip conditions are applied for the bottom and top walls respectively. The flow is forced with a pressure gradient which yields the mean velocity. The numerical results have been quantitatively compared with an experimental data for the mean flow and turbulence profiles. Resolved streamwise velocity profiles from both the immersed boundary and bodyfitted grids are in a good agreement with the experimental data. A good correlation of turbulent intensities and instantaneous flow fields are also observed between the two methods. It is also shown that the numerical model overestimates the vertical velocity profiles in the leeward side of the dune.
TWO-DIMENSIONAL BLAST-WAVE-DRIVEN RAYLEIGH-TAYLOR INSTABILITY: EXPERIMENT AND SIMULATION
Kuranz, C. C.; Drake, R. P.; Harding, E. C.; Grosskopf, M. J. [University of Michigan, MI (United States); Robey, H. F.; Remington, B. A.; Edwards, M. J.; Miles, A. R.; Perry, T. S. [Lawrence Livermore National Laboratory, University of California, P.O. Box 5508, L-487, Livermore, CA 94550 (United States); Blue, B. E. [General Atomics, San Diego, CA (United States); Plewa, T. [Department of Scientific Computing, Florida State University, Dirac Science Library Tallahassee, FL 32306-4120 (United States); Hearn, N. C. [ASC/Alliances Center for Astrophysical Thermonuclear Flashes, University of Chicago, IL (United States); Knauer, J. P. [Laboratory of Laser Energetics, University of Rochester, Rochester, NY (United States); Arnett, D. [Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States); Leibrandt, D. R. [Massachusetts Institute of Technology, Cambridge, MA 02139 (United States)
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.
NASA Astrophysics Data System (ADS)
Murillo, J.; García-Navarro, P.; Burguete, J.
2009-08-01
An explicit finite volume model to simulate two-dimensional shallow water flow with multi-component transport is presented. The governing system of coupled conservation laws demands numerical techniques to avoid unrealistic values of the transported scalars that cannot be avoided by decreasing the size of the time step. The presence of non conservative products such as bed slope and friction terms, and other source terms like diffusion and reaction, can make necessary the reduction of the time step given by the Courant number. A suitable flux difference redistribution that prevents instability and ensures conservation at all times is used to deal with the non-conservative terms and becomes necessary in cases of transient boundaries over dry bed. The resulting method belongs to the category of well-balanced Roe schemes and is able to handle steady cases with flow in motion. Test cases with exact solution, including transient boundaries, bed slope, friction, and reaction terms are used to validate the numerical scheme. Laboratory experiments are used to validate the techniques when dealing with complex systems as the ?-? model. The results of the proposed numerical schemes are compared with the ones obtained when using uncoupled formulations.
TWO-DIMENSIONAL BLAST-WAVE-DRIVEN RAYLEIGH-TAYLOR INSTABILITY: EXPERIMENT AND SIMULATION
Kuranz, C. C.
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 ...
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.
NASA Astrophysics Data System (ADS)
Caillol, Jean-Michel
2015-04-01
We present two methods for solving the electrostatics of point charges and multipoles on the surface of a sphere, i.e., in the space S 2 , 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 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 S 2 . We notably obtain the expression of the static dielectric constant of a uniform isotropic polar fluid living in S 2 in terms of the polarization fluctuations of subdomains of 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 magnetic pulsations upstream of the Earth's bow shock
NASA Astrophysics Data System (ADS)
Dubouloz, N.; Scholer, M.
1995-06-01
The development of turbulence upstream of the quasi-parallel portion of the Earth's bow shock is investigated usng two-dimensional hybrid simulations involving the injection of a very hot ion beam against a cold incident ion flow. Initially, waves are produced in the right-hand resonant ion beam mode and with wave vectors mainly parallel to the ambient magnetic field B0 as expected in linear theory. The waves attempt to propagate upstream but are convected back toward the shock by the incident flow and strongly grow in amplitude as they encounter larger beam densities. Wave growth is associated with reduction of both incident and beam ion bulk velocities. Differential slowing of the incident flow between the different wave fronts and, when the angle ?Bn between B0 and the shock normal n is non zero, along the fronts themselves, leads to wave front refraction parallel to the shock and fragmentation into smaller structures. Simultaneously, strong scattering by the waves generates beam ion clumps containing a significant fraction of ions with velocities antiparallel to the beam bulk velocity, which enables the destabilization of the left-hand resonant ion beam mode. The beam ions ultimately form a diffuse distribution whose density ratio relative to the solar wind is a few percents in average, but increases up to about 20% in the immediate vicinity of the shock. These processes result in the formation of magnetic pulsations whose extension parallel and perpendicular to n is typically 15 and a few tens of ion inertial lengths, respectively. These structures can reach total amplitudes ?B of 3 to 4 B0, and exhibit most of the time a left-handed polarization in the rest frame, in agreement with spacecraft observations upstream of the Earth's bow shock. The simulations show that pulsations induced slowing and moderate heating of the incident flow and play an active role in the quasi-parallel shock transition.
Dimitris P. Lymberopoulos; Demetre J. Economou
1995-01-01
Over the pst few years multidimensional self-consistent plasma simulations including complex chemistry have been developed which are promising tools for furthering the understanding of reactive gas plasmas and for reactor design and optimization. These simulations must be benchmarked against experimental data obtained in well-characterized systems such as the Gaseous Electronics Conference (GEC) reference cell. Two-dimensional simulations relevant to the GEC
Dynamics of the Solar Magnetic Network: Two-dimensional MHD Simulations
S. S. Hasan; A. A. van Ballegoiijen; W. Kalkofen; O. Steiner
2005-03-24
The aim of this work is to identify the physical processes that occur in the network and contribute to its dynamics and heating. We model the network as consisting of individual flux tubes with a non-potential field structure that are located in intergranular lanes. With a typical horizontal size of 200 km at the base of the photosphere, they expand upward and merge with their neighbors at a height of about 600 km. Above a height of approximately 1000 km the magnetic field starts to become uniform. Waves are generated in this medium by means of motions at the lower boundary. We focus on transverse driving, which generates both fast and slow waves within a flux tube and acoustic waves at the interface of the tube and the field-free medium. The acoustic waves at the interface are due to compression of the gas on one side of the flux tube and expansion on the other. These waves travel upward along the two sides of the (2D) flux tube and enter it, where they become longitudinal waves. For impulsive excitation with a time constant of 120 s, we find that a dominant feature is the creation of vortical motions that propagate upward. We have identified an efficient mechanism for the generation of longitudinal waves and shock formation in the chromospheric part of the flux concentration. We examine some broad implications of our results.
L. M. Martiouchev; V. D. Seleznev; S. A. Skopinov
1998-01-01
Two-dimensional nonequilibrium growth of crystals (quasistable faceted and dendritic) in the presence of a phase separating impurity is studied by computer simulation. It is shown that there is a gradual modification in this system from quasistable faceted growth to the formation of dendrites when the impurity concentration increases. If there is dendritic growth in the presence of a phase-separating impurity,
Numerical simulation of two-dimensional single- and multiple-material flow fields
Lopez, A.R.; Baty, R.S. [Sandia National Labs., Albuquerque, NM (United States); Kashiwa, B.A. [Los Alamos National Lab., NM (United States)
1992-03-01
Over the last several years, Sandia National Laboratories has had an interest in developing capabilities to predict the flow fields around vehicles entering or exiting the water at a wide range of speeds. Such prediction schemes have numerous engineering applications in the design of weapon systems. For example, such a scheme could be used to predict the forces and moments experienced by an air-launched anti-submarine weapon on water-entry. Furthermore, a water-exit prediction capability could be used to model the complicated surface closure jet resulting from a missile being shot out of the water. The CCICE (Cell-Centered Implicit Continuous-fluid Eulerian) code developed at Los Alamos National Laboratory (LANL) was chosen to provide the fluid dynamics solver for high speed water-entry and water-exit problems. This implicit time-marching, two-dimensional, conservative, finite-volume code solves the multi-material, compressible, inviscid fluid dynamics equations. The incompressible version of the CCICE code, CCMAC (cell-Centered Marker and Cell), was chosen for low speed water- entry and water-exit problems in order to reduce the computational expense. These codes were chosen to take advantage of certain advances in numerical methods for computational fluid dynamics (CFD) that have taken place at LANL. Notable among these advances is the ability to perform implicit, multi-material, compressible flow simulations, with a fully cell-centered data structure. This means that a single set of control volumes are used, on which a discrete form of the conservation laws is satisfied. This is in control to the more classical staggered mesh methods, in which separate control volumes are defined for mass and momentum. 12 refs.
Numerical simulation of two-dimensional single- and multiple-material flow fields
Lopez, A.R.; Baty, R.S. (Sandia National Labs., Albuquerque, NM (United States)); Kashiwa, B.A. (Los Alamos National Lab., NM (United States))
1992-01-01
Over the last several years, Sandia National Laboratories has had an interest in developing capabilities to predict the flow fields around vehicles entering or exiting the water at a wide range of speeds. Such prediction schemes have numerous engineering applications in the design of weapon systems. For example, such a scheme could be used to predict the forces and moments experienced by an air-launched anti-submarine weapon on water-entry. Furthermore, a water-exit prediction capability could be used to model the complicated surface closure jet resulting from a missile being shot out of the water. The CCICE (Cell-Centered Implicit Continuous-fluid Eulerian) code developed at Los Alamos National Laboratory (LANL) was chosen to provide the fluid dynamics solver for high speed water-entry and water-exit problems. This implicit time-marching, two-dimensional, conservative, finite-volume code solves the multi-material, compressible, inviscid fluid dynamics equations. The incompressible version of the CCICE code, CCMAC (cell-Centered Marker and Cell), was chosen for low speed water- entry and water-exit problems in order to reduce the computational expense. These codes were chosen to take advantage of certain advances in numerical methods for computational fluid dynamics (CFD) that have taken place at LANL. Notable among these advances is the ability to perform implicit, multi-material, compressible flow simulations, with a fully cell-centered data structure. This means that a single set of control volumes are used, on which a discrete form of the conservation laws is satisfied. This is in control to the more classical staggered mesh methods, in which separate control volumes are defined for mass and momentum. 12 refs.
Monte Carlo simulations of two-dimensional fermion systems with string-bond states
NASA Astrophysics Data System (ADS)
Song, J.-P.; Clay, R. T.
2014-02-01
We describe an application of variational Monte Carlo to two-dimensional fermionic systems within the recently developed tensor-network string-bond state ansatz. We use a combination of variational Monte Carlo and stochastic optimization to optimize the matrix-product state matrices representing the ground state. We present results for a two-dimensional spinless fermion model including nearest-neighbor Coulomb interactions and determine using finite-size scaling the phase boundary between charge-ordered insulating and metallic phases. This approach can treat frustrated systems and be easily extended to fermion models with spin.
NUMERICAL SIMULATION OF A TWO DIMENSIONAL FLOOD WAVE PROPAGATION DUE TO DAM FAILURE
Th. Xanthopoulos; Ch. Koutitas
1976-01-01
The propagation of a flood wave on a two dimensional dry plain is investigated by the aid of a numerically solved mathematical model.The velocity components, the water depth and the position of the water front for each time step are computed through an explicit finite difference scheme in Eulerian space. The forcing function consists of the charge by a discharge
Two-dimensional tsunami-dynamo simulations using the finite element method in the time domain
NASA Astrophysics Data System (ADS)
Minami, T.; Toh, H.
2013-12-01
Conductive seawater moving in the ocean generates an electromotive force. This effect is called 'Oceanic dynamo effect' and transient tsunamis are also involved in this effect. Toh et al. (2011) reported that the 2006 and 2007 Krill earthquake tsunami induced electromagnetic (EM) variations in the northwest Pacific. Manoj et al. (2011) and Suetsugu et al. (2012) also reported that seafloor EM observations detected tsunami passages. Motional induction due to tsunamis, hereafter called 'Tsunami Dynamo Effect', has been studied mainly in the frequency domain. For example, Larsen (1971) derived an analytical solution considering the conductivity structures and the self-induction term, while Sanford (1971) included effects of bathymetry. Recently, Tyler (2005) analytically expected that the vertical component of the tsunami-induced magnetic field has the same waveform and phase as those of the sea level change in deep oceans. Although these works in the frequency domain are very powerful and useful, they are not able to focus on transient properties of the Tsunami Dynamo Effect. For mitigation of tsunami disasters, it is very important to investigate effects due to the first arrival of tsunamis. We, therefore, developed a two-dimensional finite element (FEM) tsunami dynamo simulation code in the time domain to reproduce magnetic tsunami signals observed in the northwest Pacific at the time of the 2011 off the Tohoku earthquake. We adopted FEM with triangular mesh in order to include realistic bathymetry and arbitrary conductivity structures beneath the seafloor. For the time evolution, the Crank Nikolson method was adopted. As a result, our simulation succeeded in reproducing the magnetic tsunami signals, especially in terms of the first wave. It is noticeable that an initial rise in the horizontal magnetic component as large as 1 nT, parallel to the tsunami propagation direction and observed 5 minutes prior to the tsunami arrival, was also induced by the tsunami. We conducted additional numerical experiments to investigate the initial rise. We laid half-space homogeneous conductor beneath the flat seafloor with a depth of 5km and let a Gaussian waveform soliton propagate with a wave height of 1m and a horizontal extent of 100km. As we assigned 0, 0.01, 0.1, and 1S/m to the conductivity beneath the seafloor, the peak of the initial rise became approximately 3, 2, <1, and ~0 nT, respectively. The initial rise, hence, vanished with the conductivity of 1S/m beneath the seafloor, because an induced current beneath the seafloor generated a horizontal magnetic field opposite to the initial rise. Our numerical results imply that this initial rise may enable us to detect the tsunami passage prior to the tsunami arrival itself under suitable conditions. In the presentation, we will report the initial rise in the horizontal magnetic component observed prior to the tsunami arrival and discuss its applicability to tsunami early warnings.
Masahiro Nishida; Yusuke Tanaka
2010-01-01
The dynamic response of a two-dimensional ordered particle packing composed of nylon-66 spheres 6.35 mm in diameter impacted\\u000a by a spherical projectile was investigated both experimentally and numerically using the discrete element method (DEM). First,\\u000a the influence of the number of layers in the particle packing on wave propagation and post-impact movement were examined.\\u000a As the number of layers increased, the
Two-dimensional simulations of droplet evaporation and deformation at high pressure
Zheng-Tao Deng; Ron Litchford; Shenghun Jeng; San-Mou Jeng
1992-01-01
A two-dimensional analysis of n-Heptane droplet vaporization in a high-pressure nitrogen gas is made with special attention devoted to droplet deformation and breakup. The considered theoretical model can solve two-phase fluid flows separated by a material interface where surface tension forces and interfacial heat, mass, and momentum exchanges exist. The computational model, which includes free-surface (droplet surface) tracking and complex
Two-Dimensional Numerical Simulation of Boiling Two-Phase Flow of Liquid Nitrogen
Jun Ishimoto; Mamoru Oike; Kenjiro Kamijo
2001-01-01
Two-dimensional characteristics of the boiling two-phase flow of liquid nitrogen in a duct flow are numerically investigated to contribute to the further development of new high-performance cryogenic engineering applications. First, the governing equations of the boiling two-phase flow of liquid nitrogen based on the unsteady drift-flux model are presented and several flow characteristics are numerically calculated taking account the effect
Maze energetics revealed by a large-scale two-dimensional Ginzburg-Landau type simulation
NASA Astrophysics Data System (ADS)
Iwano, Kaoru; Mitsumata, Chiharu; Ono, Kanta
2014-05-01
To understand the magnetization process of permanent magnets, the structural analysis of a so-called maze pattern plays a key role, because demagnetized states consist of maze domains. Motivated by this viewpoint, we explore the phase space of a magnetic order parameter in a thin film and clarify the energetics of various nonlinear states including the mazes, based on a two-dimensional Ginzburg-Landau model augmented by long-range dipole-dipole interaction
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.
Henrike Heise; Sorin Luca; Bert L. de Groot; Helmut Grubmüller; Marc Baldus
2005-01-01
An approach is introduced to characterize conformational ensembles of intrinsically unstructured peptides on the atomic level using two-dimensional solid-state NMR data and their combination with molecular dynamics simulations. For neurotensin, a peptide that binds with high affinity to a G-protein coupled receptor, this method permits the investigation of the changes in conformational preferences of a neurotransmitter transferred from a frozen
Understanding the cause of IV kink in GaAs MESFETs with two-dimensional numerical simulations
M. R. Wilson; I. Zdebel; P. Wennekers; R. Anholt
1995-01-01
High performance GaAs MESFETs have been observed to exhibit kinks in their IV characteristics, particularly when high drain-source voltages are applied, Such characteristics make the design of circuits with high operating voltages difficult since this type of IV anomaly is typically not modeled by circuit simulators. This work has identified the cause of these kinks through the use of two-dimensional
Gan Mo; Franz Rosenberger
1991-01-01
Binary diffusive-convective gas flows in a two-dimensional channel with atomically rough walls were studied by molecular-dynamics simulations. It was found that, similar to the behavior of monocomponent flows investigated earlier, the no-slip condition arises when the mean free path in the gas mixture is of the same order of magnitude as or smaller than the atomic-wall-roughness amplitude. However, if there
NASA Astrophysics Data System (ADS)
Daldorff, L. K. S.; Toth, G.; Borovikov, D.; Gombosi, T. I.; Lapenta, G.
2014-12-01
With the new modeling capability in the Space Weather Modeling Framework (SWMF) of embedding an implicit Particle-in-Cell (PIC) model iPIC3D into the BATS-R-US magnetohydrodynamics model (Daldorff et al. 2014, JCP, 268, 236) we are ready to locally handle the full physics of the reconnection and its implications on the full system where globally, away from the reconnection region, a magnetohydrodynamic description is satisfactory. As magnetic reconnection is one of the main drivers in magnetospheric and heliospheric plasma dynamics, the self-consistent description of the electron dynamics in the coupled MHD-EPIC model is well suited for investigating the nature of these systems. We will compare the new embedded MHD-EPIC model with pure MHD and Hall MHD simulations of the Earth's magnetosphere.
Heat transfer coefficients in two-dimensional Yukawa systems (numerical simulations)
NASA Astrophysics Data System (ADS)
Khrustalyov, Yu. V.; Vaulina, O. S.
2013-05-01
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.
Numerical simulations of thermal conductivity in dissipative two-dimensional Yukawa systems.
Khrustalyov, Yu V; Vaulina, O S
2012-04-01
Numerical data on the heat transfer constants in two-dimensional Yukawa systems were obtained. Numerical study of the thermal conductivity and diffusivity was carried out for the equilibrium systems with parameters close to conditions of laboratory experiments with dusty plasma. For calculations of heat transfer constants the Green-Kubo formulas were used. The influence of dissipation (friction) on the heat transfer processes in nonideal systems was investigated. The approximation of the coefficient of thermal conductivity is proposed. Comparison of the obtained results to the existing experimental and numerical data is discussed. PMID:22680584
Advances in Simulation of Wave Interaction with Extended MHD Phenomena
Batchelor, Donald B [ORNL; Abla, Gheni [ORNL; D'Azevedo, Ed F [ORNL; Bateman, Glenn [Lehigh University, Bethlehem, PA; Bernholdt, David E [ORNL; Berry, Lee A [ORNL; Bonoli, P. [Massachusetts Institute of Technology (MIT); Bramley, R [Indiana University; Breslau, Joshua [ORNL; Chance, M. [Princeton Plasma Physics Laboratory (PPPL); Chen, J. [Princeton Plasma Physics Laboratory (PPPL); Choi, M. [General Atomics; Elwasif, Wael R [ORNL; Foley, S. [Indiana University; Fu, GuoYong [Princeton Plasma Physics Laboratory (PPPL); Harvey, R. W. [CompX, Del Mar, CA; Jaeger, Erwin Frederick [ORNL; Jardin, S. C. [Princeton Plasma Physics Laboratory (PPPL); Jenkins, T [University of Wisconsin; Keyes, David E [Columbia University; Klasky, Scott A [ORNL; Kruger, Scott [Tech-X Corporation; Ku, Long-Poe [Princeton Plasma Physics Laboratory (PPPL); Lynch, Vickie E [ORNL; McCune, Douglas [Princeton Plasma Physics Laboratory (PPPL); Ramos, J. [Massachusetts Institute of Technology (MIT); Schissel, D. [General Atomics; Schnack, [University of Wisconsin; Wright, J. [Massachusetts Institute of Technology (MIT)
2009-01-01
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.
Advances in Simulation of Wave Interactions with Extended MHD Phenomena
Batchelor, Donald B [ORNL] [ORNL; D'Azevedo, Eduardo [ORNL] [ORNL; Bateman, Glenn [ORNL] [ORNL; Bernholdt, David E [ORNL] [ORNL; Bonoli, P. [Massachusetts Institute of Technology (MIT)] [Massachusetts Institute of Technology (MIT); Bramley, Randall B [ORNL] [ORNL; Breslau, Joshua [ORNL] [ORNL; Elwasif, Wael R [ORNL] [ORNL; Foley, S. [Indiana University] [Indiana University; Jaeger, Erwin Frederick [ORNL] [ORNL; Jardin, S. C. [Princeton Plasma Physics Laboratory (PPPL)] [Princeton Plasma Physics Laboratory (PPPL); Klasky, Scott A [ORNL] [ORNL; Kruger, Scott E [ORNL] [ORNL; Ku, Long-Poe [ORNL] [ORNL; McCune, Douglas [Princeton Plasma Physics Laboratory (PPPL)] [Princeton Plasma Physics Laboratory (PPPL); Ramos, J. [Massachusetts Institute of Technology (MIT)] [Massachusetts Institute of Technology (MIT); Schissel, David P [ORNL] [ORNL; Schnack, Dalton D [ORNL] [ORNL
2009-01-01
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.
Numerical simulation of the flow around two-dimensional partially cavitating hydrofoils
NASA Astrophysics Data System (ADS)
Celik, Fahri; Ozden, Yasemin Arikan; Bal, Sakir
2014-09-01
In the present study, a new approach is applied to the cavity prediction for two-dimensional (2D) hydrofoils by the potential based boundary element method (BEM). The boundary element method is treated with the source and doublet distributions on the panel surface and cavity surface by the use of the Dirichlet type boundary conditions. An iterative solution approach is used to determine the cavity shape on partially cavitating hydrofoils. In the case of a specified cavitation number and cavity length, the iterative solution method proceeds by addition or subtraction of a displacement thickness on the cavity surface of the hydrofoil. The appropriate cavity shape is obtained by the dynamic boundary condition of the cavity surface and the kinematic boundary condition of the whole foil surface including the cavity. For a given cavitation number the cavity length of the 2D hydrofoil is determined according to the minimum error criterion among different cavity lengths, which satisfies the dynamic boundary condition on the cavity surface. The NACA 16006, NACA 16012 and NACA 16015 hydrofoil sections are investigated for two angles of attack. The results are compared with other potential based boundary element codes, the PCPAN and a commercial CFD code (FLUENT). Consequently, it has been shown that the results obtained from the two dimensional approach are consistent with those obtained from the others.
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)
NASA Astrophysics Data System (ADS)
Bond, Robert E.
The National Aero-Space Plane (NASP) was conceptually designed for flight at hypersonic speeds. Because its airframe configuration was determined by the need for good high-speed flight performance, its low-speed and ground effect characteristics were poor. The purpose of this investigation was to characterize the ground effect aerodynamic performance of a two-dimensional model of the NASP with thrust simulation. This study included a comparison between experimental and numerical results. The experiments were conducted in the WVU subsonic wind tunnel, while numerical results were obtained using FLUENT, a commercial finite volume CFD code. The aerodynamic characteristics of the two-dimensional NASP model were reported as functions of various parameters such as: model configuration, angle of attack, ground plane proximity and thrust coefficient. In this research program, it was found that the characteristic ground effect lift loss, associated with previously studied three-dimensional hypersonic models operating at low, subsonic speed was related to that measured with a two-dimensional model. In an attempt to improve low-speed take-off and landing performance, the simulated engine exhaust was ducted to the upper aft surface and to the trailing edge of the model in two different configurations. Those two in addition to the base configuration were modeled using CFD to compare with experimental data. The test results demonstrated that exhaust ducting can be used to achieve dramatically enhanced lift coefficient characteristics while in ground effect. Of these configurations, the use of external ducting yielded the most favorable ground effect characteristics for the two-dimensional geometry. Additionally, this was the only configuration which produced positive lift in the take-off configuration. The computational fluid dynamic code used for this research failed to produce accurate coefficient data; however, it was found to estimate the lift curve slopes of each of the configurations with reasonable accuracy. Additionally, trends in the lift, drag and pressure coefficients were also predicted with reasonable accuracy.
FEM-simulation of laminar flame propagation. I: Two-dimensional flames
NASA Astrophysics Data System (ADS)
Michaelis, B.; Rogg, B.
2004-05-01
In this paper, we present a numerical model for two-dimensional low-Mach-number flows of reactive ideal-gas mixtures based on the fundamental conservation equations in primitive variables. Chemical reaction is described by a detailed mechanism of elementary reactions, and detailed models for molecular transport and thermodynamics are taken into account. The equations are discretized by a finite-element method on unstructured grids using the well known Taylor-Hood element. A streamline-diffusion upwinding technique is used to avoid instabilities in convection-dominated regions of the flowfield. A fully operative local adaptive mesh-refinement procedure is used. As numerical examples we consider steadily propagating laminar flames in flat channels, which appear in a variety of shapes depending on the boundary conditions.
A numerical study of the alpha model for two-dimensional magnetohydrodynamic turbulent flows
Pouquet, Annick
A numerical study of the alpha model for two-dimensional magnetohydrodynamic turbulent flows Pablo the "Lagrangian-averaged" model, for two-dimensional incompressible magnetohydrodynamic (MHD) turbulence
MHD Simulations of Plasma Thruster in application to VASIMR project
S. V. Novakowski; R. Z. Sagdeev; F. R. Chang-Diaz; A. Ilin
1998-01-01
The results of the computer simulation of the MHD processes occuring in the plasma of the thruster in VASIMR rocket (F. R. Chang-Diaz, Research Status of the Variable Specific Impulse Magnetoplasma Rocket, in Bull. of the APS, Vol. 42, No. 10, p. 2057 ) are presented. The geometry of the thruster chamber and the exaust region is considered and a
A new model for two-dimensional numerical simulation of pseudo-2D gas-solids fluidized beds
Li, Tingwen; Zhang, Yongmin
2013-10-11
Pseudo-two dimensional (pseudo-2D) fluidized beds, for which the thickness of the system is much smaller than the other two dimensions, is widely used to perform fundamental studies on bubble behavior, solids mixing, or clustering phenomenon in different gas-solids fluidization systems. The abundant data from such experimental systems are very useful for numerical model development and validation. However, it has been reported that two-dimensional (2D) computational fluid dynamic (CFD) simulations of pseudo-2D gas-solids fluidized beds usually predict poor quantitative agreement with the experimental data, especially for the solids velocity field. In this paper, a new model is proposed to improve the 2D numerical simulations of pseudo-2D gas-solids fluidized beds by properly accounting for the frictional effect of the front and back walls. Two previously reported pseudo-2D experimental systems were simulated with this model. Compared to the traditional 2D simulations, significant improvements in the numerical predictions have been observed and the predicted results are in better agreement with the available experimental data.
Criteria for Scaled Laboratory Simulations of Astrophysical MHD Phenomena
Ryutov, D. D.; Drake, R. P.; Remington, B. A.
2000-04-01
We demonstrate that two systems described by the equations of the ideal magnetohydrodynamics (MHD) evolve similarly, if the initial conditions are geometrically similar and certain scaling relations hold. The thermodynamic properties of the gas must be such that the internal energy density is proportional to the pressure. The presence of the shocks is allowed. We discuss the applicability conditions of the ideal MHD and demonstrate that they are satisfied with a large margin both in a number of astrophysical objects, and in properly designed simulation experiments with high-power lasers. This allows one to perform laboratory experiments whose results can be used for quantitative interpretation of various effects of astrophysical MHD. (c) 2000 The American Astronomical Society.
NASA Astrophysics Data System (ADS)
Snyder, K. A.; Garboczi, E. J.; Day, A. R.
1992-12-01
An algorithm, combining digital-image with spring network techniques, has been developed that enables computation of the elastic moduli of random two-dimensional multiphase composites. This algorithm is used to study the case of isotropic, randomly centered, overlapping circular inclusions in an isotropic elastic matrix. The results of the algorithm for the few-inclusion limit, as well as the case where both phases have the same shear moduli, agree well with the exact results for these two problems. The case where the two phases have the same Poisson's ratio, but different Young's moduli, is also studied, and it is shown that the effective medium theory developed by Thorpe and Sen agrees well with the numerical results. A surprising result is that the effective moduli of systems with nonoverlapping circular inclusions are almost identical with the overlapping inclusion case, up to an inclusion area fraction of 50%. Using the validated effective medium theory, we illustrate how the effective Poisson's ratio ? behaves as a function of ?0, the pure phase Poisson's ratio, and the stiffness ratio between the two components. Two distinct regions of behavior are found, defined by ?0??* and ?0
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.
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...
Akira Miura
1997-01-01
For a two-dimensional (2-D) transverse configuration, where the plasma motion occurs in a 2-D plane transverse to the magnetic field, the nonlinear evolution of the magnetohydrodynamic (MHD) Kelvin–Helmholtz (K–H) instability is investigated by means of a 2-D MHD simulation for a convective fast magnetosonic Mach number 0.35, which is defined for the total jump of the flow velocity. The compressibility
A general Cluster data and global MHD simulation comparison
NASA Astrophysics Data System (ADS)
Daum, P.; Denton, M. H.; Wild, J. A.; Taylor, M. G. G. T.; Afránková, J. Å.; Hayosh, M.
2008-11-01
Among the many challenges facing the space weather modelling community today, is the need for validation and verification methods of the numerical models available describing the complex nonlinear Sun-Earth system. Magnetohydrodynamic (MHD) models represent the latest numerical models of this environment and have the unique ability to span the enormous distances present in the magnetosphere, from several hundred kilometres to several thousand kilometres above the Earth's surface. This makes it especially difficult to develop verification and validation methods which posses the same range spans as the models. In this paper we present a first general large-scale comparison between four years (2001 2004) worth of in situ Cluster plasma observations and the corresponding simulated predictions from the coupled Block-Adaptive-Tree-Solarwind-Roe-Upwind-Scheme (BATS-R-US) MHD code. The comparison between the in situ measurements and the model predictions reveals that by systematically constraining the MHD model inflow boundary conditions a good correlation between the in situ observations and the modeled data can be found. These results have an implication for modelling studies addressing also smaller scale features of the magnetosphere. The global MHD simulation can therefore be used to place localised satellite and/or ground-based observations into a global context and fill the gaps left by measurements.
NASA Astrophysics Data System (ADS)
Lee, Kuang Wu; Buechner, Joerg
Two-dimensional particle-in-cell simulation of Weibel instability in a current-free return beam plasma system Lee, Kuang Wu and Joerg Buechner In the collisionless plasmas of stellar coro-nae and planetary magnetospheres return beams are generated in order to compensate strong flows of accelerated electrons. In this process return beams help to maintain charge neutrality in the electron downflow channels. In laser plasma experiments return beams beams are also observed to compensate injected electrons. In return-beam two-stream systems plasma insta-bilities are excited that cause an electron temperature anisotropy. The latter, in turn, can cause Weibel instability. Weibel instability leads to the excitation of electromagnetic and transverse waves which play a vital role in plasma transport in collisionless plasmas. While, according to previous investigations, electrostatic waves dominate during the initial stage of the instability evolution later strong anomalous (collisionless) transport converts kinetic energy into thermal energy. Finally, during a highly nonlinear stage, obliquely propagating electromagnetic waves are generated which, again, isotropize the system and drive it toward a new equilibrium. By means of solving the corrsponding linear dispersion analysis we obtained the stability conditions in a higher-dimensional return-beam system. Then we used a two-dimensional electromagnetic particle-in-cell (2D EM PIC) simulation code to study the nonlnear evolution of the instabilities and the waves, generated in the course of these processes.
Chung-Yueh Wang; Jyh-tong Teng; George P. G. Huang
2011-01-01
Purpose – The purpose of this paper is to develop the numerical simulated methodology for sloshing motion of fluid inside a two dimension rectangular tank, and parametric studies were performed for three parameters – excitation frequency, excitation amplitude, and liquid depth. Design\\/methodology\\/approach – A numerically simulated methodology by using the cell-centered pressure-based SIMPLE scheme and level set method for the
Understanding of GRB-SN Connection by General Relativistic MHD Simulations
Nagataki, S
2009-01-01
I have developed two numerical codes to investigate the dynamics of collapsars. One is two-dimensional MHD code that are performed using the Newtonian (ZEUS-2D) code where realistic equation of state, neutrino cooling and heating processes are taken into account. The other one is two-dimensional general relativistic magnetohydrodynamic (GRMHD) code. I have performed numerical simulations of collapsars using these codes and realistic progenitor models. In the Newtonian code, it is found that neutrino heating processes are not efficient enough to launch a jet in this study. It is also found that a jet is launched mainly by toroidal fields that are amplified by the winding-up effect. However, since the ratio of total energy relative to the rest-mass energy in the jet is not as high as several hundred, we conclude that the jets seen in this study are not GRB jets. In the GRMHD simulation, it is shown that a jet is launched from the center of the progenitor. We also find that the mass accretion rate after the laun...
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.
NASA Astrophysics Data System (ADS)
Takagi, S.; Og˜uz, H. N.; Zhang, Z.; Prosperetti, A.
2003-05-01
This paper presents a new approach to the direct numerical simulation of particle flows. The basic idea is to use a local analytic representation valid near the particle to "transfer" the no-slip condition from the particle surface to the adjacent grid nodes. In this way the geometric complexity arising from the irregular relation between the particle boundary and the underlying mesh is avoided and fast solvers can be used. The results suggest that the computational effort increases very slowly with the number of particles so that the method is efficient for large-scale simulations. The focus here is on the two-dimensional case (cylindrical particles), but the same procedure, to be developed in forthcoming papers, applies to three dimensions (spherical particles). Several extensions are briefly discussed.
NASA Astrophysics Data System (ADS)
Ng, C. S.; Soundararajan, S. J.
2010-11-01
We present here a new analysis in constructing two-dimensional Bernstein-Greene-Kruskal (BGK) modes in a magnetized plasma with finite magnetic field strength. The original method of constructing these modes [Ng, Bhattacharjee, and Skiff, Phys. Plasmas 13, 055903 (2006)], which satisfy the exact electromagnetic Vlasov-Poisson-Ampere system, requires solving them iteratively. An interesting property of these modes is that they can have a strong magnetic component for large electron thermal velocity. Exact solutions are presented using a new method that solves more directly without this iterative step for any electron thermal velocity. We will also present preliminary results on simulating these modes using Particle-in-Cell (PIC) simulations, which is important in studying the stability of these modes.
NASA Astrophysics Data System (ADS)
Ng, C.; Soundararajan, S.; Yasin, E. S.
2011-12-01
Electrostatic structures have been observed in many regions of space plasmas, including the solar wind, the magnetosphere, and the auroral acceleration region. One possible theoretical description of some of these structures is the concept of Bernstein-Greene-Kruskal (BGK) modes, which are exact nonlinear steady-state solutions of the Vlasov-Poisson system of equations in collisionless kinetic theory. We will present latest Particle-in-Cell (PIC) simulations using exact solutions of two-dimensional (2D) BGK modes in a magnetized plasma with finite magnetic field strength [Ng, Bhattacharjee, and Skiff, Phys. Plasmas 13, 055903 (2006)] as initial conditions to study their stability. We will also present simulations using more general initial conditions, which shows that while these are not steady-state solutions, they still keep their overall structures with modulations having frequency of the order of electron cyclotron frequency. This work is supported by a National Science Foundation grant PHY-1004357.
NASA Astrophysics Data System (ADS)
Shukla, H. S.; Tamsir, Mohammad; Srivastava, Vineet K.
2015-01-01
In this paper, a modified cubic B-spline differential quadrature method (MCB-DQM) is employed for the numerical simulation of two-space dimensional nonlinear sine-Gordon equation with appropriate initial and boundary conditions. The modified cubic B-spline works as a basis function in the differential quadrature method to compute the weighting coefficients. Accordingly, two dimensional sine-Gordon equation is transformed into a system of second order ordinary differential equations (ODEs). The resultant system of ODEs is solved by employing an optimal five stage and fourth-order strong stability preserving Runge-Kutta scheme (SSP-RK54). Numerical simulation is discussed for both damped and undamped cases. Computational results are found to be in good agreement with the exact solution and other numerical results available in the literature.
Yavuzturk, C.; Spitler, J.D.; Rees, S.J.
1999-07-01
The ability to predict both the long-term and short-term behavior of ground loop heat exchangers is critical to the design and energy analysis of ground source heat pump systems. A numerical model for the simulation of transient heat transfer in vertical ground loop heat exchangers is presented. The model is based on a two-dimensional fully implicit finite volume formulation. Numerical grids have been generated for different pipe sizes, shank spacing and borehole sizes using an automated parametric grid generation algorithm. The numerical method and grid generation techniques have been validated against an analytical model. The model has been developed with two main purposes in mind. The first application is used in a parameter estimation technique used to find the borehole thermal properties from short time scale test data. The second application is the calculation of nondimensional temperature response factors for short time scales that can be used in annual energy simulation.
Integrated two-dimensional simulations of dynamic hohlraum driven inertial fusion capsule implosions
NASA Astrophysics Data System (ADS)
Slutz, S. A.; Peterson, K. J.; Vesey, R. A.; Lemke, R. W.; Bailey, J. E.; Varnum, W.; Ruiz, C. L.; Cooper, G. W.; Chandler, G. A.; Rochau, G. A.; Mehlhorn, T. A.
2006-10-01
Simulations have been useful for improving the design of dynamic hohlraums for the purpose of imploding inertial fusion capsules [S. A. Slutz, J. E. Bailey, G. A. Chandler et al., Phys. Plasmas 10, 1875 (2003)]. These design changes, which have resulted in capsule implosions with hot dense cores [J. E. Bailey, G. A. Chandler, S. A. Slutz et al., Phys. Rev. Lett. 92, 085002 (2004)] and the production of thermonuclear neutrons [C. L. Ruiz, G. Cooper, S. A. Slutz et al., Phys. Rev. Lett. 93, 015001 (2005)], were based primarily on a series of one-dimensional numerical simulations, which treated the dynamic hohlraum and the capsule implosion separately. In this paper we present simulations which are fully integrated to include the implosion of wire arrays onto foam convertors, the implosion of the capsule imbedded in the foam, and the absorption of radiation into the electrodes. These simulations yield predictions that are in remarkably good agreement with measured values considering the complexity of the problem, which spans more than 100ns of wire implosion with the subsequent capsule implosion on a few ns timescale. For example, the predicted neutron yields are less than a factor of 2 higher than the measured values, while the predicted shock velocity is about 30% higher than the measured value. The spectroscopically inferred imploded capsule gas core temperatures are somewhat lower than predicted by the simulations, while the gas densities are about a factor of 2 higher. Simulations indicate that a more slowly rising radiation drive temperature yields higher core densities and lower temperatures and thus better agreement with experimental measurements. Possible reasons for a more slowly rising radiation drive are discussed.
2010-01-01
We propose to use infrared coherent two-dimensional correlation spectroscopy (2DCS) to characterize the folding mechanism of the mini-protein Beta3s. In this study Beta3s was folded by molecular dynamics (MD) simulation and intermediate conformational ensembles were identified. The one and two-dimensional correlation spectrum was calculated for the intermediate and native states of the mini-protein. A direct structure-spectra relationship was determined by analysis of conformational properties and specific residue contributions. We identified the structural origin of diagonal and off-diagonal peaks in the 2DCS spectra for the native and intermediate conformational ensembles in the folding mechanism. This work supports the implementation of computational techniques in conjunction with experimental 2DCS to study the folding mechanism of proteins. In addition to exploring the folding mechanism the work presented here can be applied in combination with experiment to refine and validate current molecular dynamics force fields. PACS Codes: 87.15.Cc, 87.15.hm, 87.15.hp PMID:20302645
Two-dimensional segmentation of small convective patterns in radiation hydrodynamics simulations
NASA Astrophysics Data System (ADS)
Lemmerer, B.; Utz, D.; Hanslmeier, A.; Veronig, A.; Thonhofer, S.; Grimm-Strele, H.; Kariyappa, R.
2014-03-01
Context. Recent results from high-resolution solar granulation observations indicate the existence of a population of small granular cells that are smaller than 600 km in diameter. These small convective cells strongly contribute to the total area of granules and are located in the intergranular lanes, where they form clusters and chains. Aims: We study high-resolution radiation hydrodynamics simulations of the upper convection zone and photosphere to detect small granular cells, define their spatial alignment, and analyze their physical properties. Methods: We developed an automated image-segmentation algorithm specifically adapted to high-resolution simulations to identify granules. The resulting segmentation masks were applied to physical quantities, such as intensity and vertical velocity profiles, provided by the simulation. A new clustering algorithm was developed to study the alignment of small granular cells. Results: Small granules make a distinct contribution to the total area of granules and form clusters of chain-like alignments. The simulation profiles demonstrate a different nature for small granular cells because they exhibit on average lower intensities, lower horizontal velocities, and are located deeper inside of convective layers than regular granules. Their intensity distribution deviates from a normal distribution as known for larger granules, and follows a Weibull distribution.
Two-dimensional simulation of a miniaturized inductively coupled plasma reactor
Economou, Demetre J.
-consistent simulation of a miniaturized inductively coupled plasma mICP reactor was developed. The coupled equations temperature was predicted to be close to the wall temperature, due to the small length scale of the mICP inductively coupled plasmas mICP are a scaled down version of the ICPs used for large scale manufacturing
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
Yang Gang; Han Xu; Hu Dean
2011-01-01
Purpose – The purpose of this paper is to investigate the formation process of linear-shaped charge jet using the smoothed particle hydrodynamics (SPH). Different material yield models are embed to test the performance of SPH method in the simulation of explosive driven metal liner. The effects of different ignition model to the formation of metal jet have also been studied.
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...
The core helium flash revisited: I. One and two-dimensional hydrodynamic simulations
M. Mocak; E. Mueller; A. Weiss; K. Kifonidis
2008-05-09
We investigate the hydrodynamics of the core helium flash near its peak. Past research concerned with the dynamics of this event is inconclusive. However, the most recent multidimensional hydrodynamic studies suggest a quiescent behavior and seem to rule out an explosive scenario. Previous work indicated, that depending on initial conditions, employed turbulence models, grid resolution, and dimensionality of the simulation, the core helium flash leads either to the disruption of a low-mass star or to a quiescent quasi-hydrostatic evolution. We try to clarify this issue by simulating the evolution with advanced numerical methods and detailed microphysics. Assuming spherical or axial symmetry, we simulate the evolution of the helium core of a $1.25 M_{\\odot}$ star with a metallicity Z=0.02 during the core helium flash at its peak with a grid-based hydrodynamics code. We find that the core helium flash neither rips the star apart, nor that it significantly alters its structure, as convection plays a crucial role in keeping the star in hydrostatic equilibrium. In addition, our simulations show the presence of overshooting, which implies new predictions concerning mixing of chemical species in red giants.
Two-dimensional compressible flow simulation on emulated digital CNN-UM
S. Kocsardi; Z. Nagy; A. Csik; P. Szolgay
2008-01-01
In the area of mechanical, aerospace, chemical and civil engineering the solution of partial differential equations (PDEs) has been one of the most important problems of mathematics for a long time. In this field, one of the most exciting areas is the simulation of fluid flow, which involves for example problems of air, sea and land vehicle motion. In this
NUMERICAL SIMULATION OF SCREECH NOISE IN A TWO-DIMENSIONAL SUPERSONIC JET
Joseph D. Berry
A model of a free supersonic jet has been produced using FLUENT. The shock cell structure agrees very well with available experimental data. Evidence of the instability waves required to generate the screech noise has been found. The introduction of random perturbations into the flow allowed these instability waves to form, negating the need to run the simulation for an
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...
MINBU Distribution of Two Dimensional Quantum Gravity: Simulation Result and Semiclassical Analysis
S. Ichinose; N. Tsuda; T. Yukawa
1995-01-01
We analyse MINBU distribution of 2 dimensional quantum gravity. New data of\\u000aR$^2$-gravity by the Monte Carlo simulation and its theoretical analysis by the\\u000asemiclassical approach are presented. The cross-over phenomenon takes place at\\u000asome size of the baby universe where the randomness competes with the smoothing\\u000aforce of $R^2$-term. The dependence on the central charge $c_m$\\\\ and on the
Two dimensional modeling and simulation of mass transport in microfabricated preconcentrators.
Manginell, Ronald Paul; Robinson, Alex Lockwood; Sheriati, Maryam (ESI US R& D, Inc., Huntsville, AL); Radhakrishnan, Sekhar (ESI US R& D, Inc., Huntsville, AL)
2005-07-01
The adsorption and desorption behavior of a planar microfabricated preconcentrator (PC) has been modeled and simulated using the computational fluid dynamics (CFD) package CFDRC-ACE+trade. By comparison with the results of a designed experiment, model parameters were determined. Assuming a first-order reaction for the adsorption of a light hydrocarbon chemical analyte onto the PC adsorbent and a unity-value sticking coefficient, a rate constant of 36,500 s{sup -1} was obtained. This compares favorably with the value of 25,300 s{sup -1} obtained by application of the Modified-Wheeler equation. The modeled rate constant depends on the concentration of adsorbent sites, estimated to be 6.94 ldr 10{sup -8} kmol/m{sup 2} for the Carboxen 1000 adsorbent used. Using the integral method, desorption was found to be first order with an Arrhenius temperature dependence and an activation energy of 30.1 kj/mol. Validation of this model is reported herein, including the use of Aris-Taylor dispersion to predict the influence of fluidics surrounding the PC. A maximum in desorption peak area with flow rate, predicted from a quadratic fit to the results of the designed experiment, was not observed in the 2-D simulation. Either approximations in the simulated model or the nonphysical nature of the quadratic fit are responsible. Despite the apparent simplicity of the model, the simulation is internally self consistent and capable of predicting performance of new device designs. To apply the method to other analytes and other adsorbent materials, only a limited number of comparisons to experiment are required to obtain the necessary rate constants.
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
Two-Dimensional Simulations of Drainage Winds and Diffusion Compared to Observations.
NASA Astrophysics Data System (ADS)
Garrett, Alfred J.; Smith, Frank G., III
1984-04-01
A vertically integrated dynamical drainage flow model is developed from conservation equations for momentum and mass in a terrain-following coordinate system. Wind fields from the dynamical model drive a Monte Carlo transport and diffusion model. The model needs only topographic data, an Eulerian or Lagrangian time scale and a surface drag coefficient for input data, and can be started with a motionless atmosphere. Model wind and diffusion predictions are compared to observations from the rugged Geysers, California area. Model winds generally agree with observed surface winds, and in some cases may give better estimates of area-averaged flow than point observations. Tracer gas concentration contours agree qualitatively with observed contours, and point predictions of maximum concentrations were correctly predicted to within factors of 2 to 10. Standard statistical tests of model skill showed that the accuracy of the predictions varied significantly from canyon to canyon in the Geysers area. Model wind predictions are also compared to observations from the South Carolina Savannah River Plant, which has gently rolling terrain. The model correctly simulated the slower development of drainage winds and slower deepening of the drainage layer in the Savannah River Valley, relative to the Geysers, California simulations. The South Carolina simulations and observations suggest that drainage winds are more frequent in the southeastern United States than is generally recognized. They may be responsible for some of the errors in air pollution concentration predictions made by Gaussian models, which assume homogeneous winds and turbulence.
Forward and inverse cascades in decaying two-dimensional electron magnetohydrodynamic turbulence
Haase, Markus
Forward and inverse cascades in decaying two-dimensional electron magnetohydrodynamic turbulence C magnetohydrodynamic EMHD turbulence in two dimensions is studied via high-resolution numerical simulations's magnetosphere. Turbulence governed by Eq. 1 is known as electron magnetohydrodynamic EMHD , Hall MHD
On the possibility of using an electromagnetic ionosphere in global MHD simulations
Paris-Sud XI, Université de
On the possibility of using an electromagnetic ionosphere in global MHD simulations P. Janhunen magnetohydrodynamic (MHD) simu- lations of the Earth's magnetosphere must be coupled with a dynamical ionospheric) from the magnetospheric MHD variables at the ionospheric boundary. The ionospheric potential is solved
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.
A Two-Dimensional Simulation of Pulsed Discharge for a Color DC-Type Plasma Display Panel
NASA Astrophysics Data System (ADS)
Murakami, Yukio; Matsuzaki, Hideomi; Murakami, Hiroshi; Tachibana, Kunihide
2000-02-01
Two-dimensional spatio-temporal behaviors of particle densities were investigated in a pulsed microdischarge cell of a DC-type plasma display panel (PDP) filled with a mixture of He and Xe gases. In the computer simulation, a fluid model was employed under local field approximation (LFA) for electrons, four kinds of ions, and seven kinds of excited species. Twelve simultaneous continuity equations were solved together with Poisson’s equation with consideration of the absorption and reemission of imprisoned resonant radiations, and also the secondary electron emission at the cathode due to incidences of ions, metastable atoms and vacuum ultraviolet (VUV) photons. The results on the density of the resonance state Xe*(1s_4) atoms, metastable state Xe*(1s_5) atoms as well as the discharge current waveform, showed good agreement with the corresponding experimental results. The effects of electrode size and gap length were also investigated.
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 two-dimensional simulation of tritium transport in the vadose zone at the Nevada Test site
Ross, W.C.; Wheatcraft, S.W.
1994-09-01
The site of a 0.75-kiloton underground nuclear explosion, the Cambric event, was selected for the study of radionuclide transport in the hydrologic environment. Water samples from RNM-2S, a well located 91 m from Cambric, have been analyzed for tritium and other radionuclides since the initiation of pumping. Water from RNM-2S flows to Frenchman Lake via an unlined canal. Flume data indicate canal transmission losses of approximately 2m{sup 3}/day/meter of canal. To determine if infiltrating canal water might be recirculated by RNM-2S, and therefore provide an additional radionuclide input to water samples collected at RNM-2S, a two-dimensional variably saturated solute transport computer model (SATURN, Huyakorn et al., 1983) was used to simulate the movement of tritium from the canal to the water table. Results indicate that recirculated canal water has not had a significant effect on the breakthrough of tritium at RNM-2S.
MINBU Distribution of Two Dimensional Quantum Gravity: Simulation Result and Semiclassical Analysis
S. Ichinose; N. Tsuda; T. Yukawa
1995-08-14
We analyse MINBU distribution of 2 dimensional quantum gravity. New data of R$^2$-gravity by the Monte Carlo simulation and its theoretical analysis by the semiclassical approach are presented. The cross-over phenomenon takes place at some size of the baby universe where the randomness competes with the smoothing force of $R^2$-term. The dependence on the central charge $c_m$\\ and on the $R^2$-coupling are explained for the ordinary 2d quantum gravity and for $R^2$-gravity. The $R^2$-Liouville solution plays the central role in the semiclassical analysis. A total derivative term (surface term) and the infrared regularization play important roles . The surface topology is that of a sphere.
Simulation of two-dimensional waterflooding by using mixed finite elements
Chavent, G.; Cohen, G.; Dieste, I.; Dupuy, M.; Jaffre, J.
1984-08-01
A new method to simulate incompressible diphasic flow in two dimensions (2D) is presented. Its distinctive features include (1) a reformulation of the basic equation using the premise of a global pressure and (2) approximation of convective terms by an upwind scheme for discontinuous finite elements. A mixed finite-element method approximates both the scalar functions (pressure and saturation) and the vector functions (total velocity field and capillary diffusion vector). The pressure (resp. the saturation) is approximated by a discontinuous function piecewise constant (resp. linear) on the elements of the mesh. A basis of divergence-free vectors is used in the pressure equation, which accelerates computation. Several test examples, which include gravity and capillary effects, are presented.
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.
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.
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.
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.
Postcollapse hydrodynamics of SN 1987A - Two-dimensional simulations of the early evolution
Herant, M.; Benz, W.; Colgate, S. (Harvard-Smithsonian Center for Astrophysics, Cambridge, MA (United States) Steward Observatory, Tucson, AZ (United States) Los Alamos National Laboratory, NM (United States))
1992-08-01
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. 43 refs.
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.
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.
Simulating a two-dimensional frustrated spin system with fermionic resonating-valence-bond states
NASA Astrophysics Data System (ADS)
Chou, Chung-Pin; Chen, Hong-Yi
2014-07-01
The frustrated Heisenberg J1-J2 model on a square lattice is numerically investigated by variational Monte Carlo simulations. We propose an antiferromagnetic fermion resonating-valence-bond (AF-fRVB) state that has the ability to examine the entire phase diagram in the J1-J2 model. Two phase transition points, the second order around J2/J1=0.45 and the first order around J2/J1=0.6, can be extracted more clearly than the conventional bosonic RVB state. At the maximally frustrated point (J2/J1=0.5), the AF-fRVB state shows the variational ground-state energy in the thermodynamic limit very close to the one estimated by the projected entangled pair state at the largest bond dimension available. On the other hand, in the frustrated regime 0.4?J2/J1?0.5, AF-fRVB states with exts2 (using the terminology in the field of iron-based superconductors) and dxy pairing symmetries are degenerate in the thermodynamic limit, implying the existence of gapless Dirac excitations in the spinon spectrum.
NASA Technical Reports Server (NTRS)
Montgomery, David
1988-01-01
Three areas of study in MHD turbulence are considered. These are the turbulent relaxation of the toroidal Z pinch, density fluctuations in MHD fluids, and MHD cellular automata. A Boolean computer game that updates a cellular representation in parallel and that has macroscopic averages converging to solutions of the two-dimensional MHD equations is discussed.
Riconda, C.; Weber, S.; Tikhonchuk, V. T.; Adam, J.-C.; Heron, A. [Centre Lasers Intenses et Applications (CELIA), UMR 5107 CNRS Universite Bordeaux 1 CEA, Universite Bordeaux 1, 33405 Talence, France and Centre de Physique Theorique (CPHT), UMR 7644 CNRS Ecole Polytechnique, Ecole Polytechnique, 91128 Palaiseau Cedex (France); Centre Lasers Intenses et Applications (CELIA), UMR 5107 CNRS Universite Bordeaux 1 CEA, Universite Bordeaux 1, 33405 Talence (France); Centre de Physique Theorique (CPHT), UMR 7644 CNRS Ecole Polytechnique, Ecole Polytechnique, 91128 Palaiseau Cedex (France)
2006-08-15
Two-dimensional particle-in-cell simulations of laser-plasma interaction using a plane-wave geometry show strong bursty stimulated Brillouin backscattering, rapid filamentation, and subsequent plasma cavitation. It is shown that the cavitation is not induced by self-focusing. The electromagnetic fields below the plasma frequency that are excited are related to transient soliton-like structures. At the origin of these solitons is a three-wave decay process exciting new modes in the plasma. The cavitation is responsible for a strong local reduction of the reflectivity and goes along with an efficient but transient heating of the electrons. Once heating ceases, transmission starts to increase. Local as well as global average reflectivities attain a very low value due to strong plasma density variations brought about by the cavitation process. On the one hand, the simulations confirm the existence of a new mechanism of cavity and soliton formation in nonrelativistic laser-plasma interaction in two dimensions, which was shown to exist in one-dimensional simulations [S. Weber, C. Riconda, and V. T. Tikhonchuk, Phys. Rev. Lett. 94, 055005 (2005)]. On the other hand, new aspects are introduced inherently related to the additional degree of freedom.
Takanobu Amano; Masahiro Hoshino
2008-09-02
Electron acceleration mechanism at high Mach number collisionless shocks propagating in a weakly magnetized medium is investigated by a self-consistent two-dimensional particle-in-cell simulation. Simulation results show that strong electrostatic waves are excited via the electron-ion electrostatic two-stream instability at the leading edge of the shock transition region as in the case of earlier one-dimensional simulations. We observe strong electron acceleration that is associated with the turbulent electrostatic waves in the shock transition region. The electron energy spectrum in the shock transition region exhibits a clear power-law distribution with spectral index of $2.0 {\\rm -} 2.5$. By analyzing the trajectories of accelerated electrons, we find that the acceleration mechanism is very similar to shock surfing acceleration of ions. In contrast to the ion shock surfing, however, the energetic electrons are reflected by electron-scale electrostatic fluctuations in the shock transition region, but not by the ion-scale cross-shock electrostatic potential. The reflected electrons are then accelerated by the convective electric field in front of the shock. We conclude that the multidimensional effects as well as the self-consistent shock structure are essential for the strong electron acceleration at high Mach number shocks.
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.
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.
Matsumoto, Yosuke [Department of Physics, Chiba University, Yayoi-cho 1-33, Inage-ku, Chiba 263-8522 (Japan); Amano, Takanobu; Hoshino, Masahiro, E-mail: ymatumot@astro.s.chiba-u.ac.jp [Department of Earth and Planetary Science, University of Tokyo, Hongo 1-33, Bunkyo-ku, Tokyo 113-0033 (Japan)
2012-08-20
Electron accelerations at high Mach number collisionless shocks are investigated by means of two-dimensional electromagnetic particle-in-cell simulations with various Alfven Mach numbers, ion-to-electron mass ratios, and the upstream electron {beta}{sub e} (the ratio of the thermal pressure to the magnetic pressure). We find electrons are effectively accelerated at a super-high Mach number shock (M{sub A} {approx} 30) with a mass ratio of M/m = 100 and {beta}{sub e} = 0.5. The electron shock surfing acceleration is an effective mechanism for accelerating the particles toward the relativistic regime even in two dimensions with a large mass ratio. Buneman instability excited at the leading edge of the foot in the super-high Mach number shock results in a coherent electrostatic potential structure. While multi-dimensionality allows the electrons to escape from the trapping region, they can interact with the strong electrostatic field several times. Simulation runs in various parameter regimes indicate that the electron shock surfing acceleration is an effective mechanism for producing relativistic particles in extremely high Mach number shocks in supernova remnants, provided that the upstream electron temperature is reasonably low.
Evaluation of subgrid-scale models in large eddy simulation of flow past a two-dimensional block
NASA Astrophysics Data System (ADS)
Cheng, W. C.; Porté-Agel, F.
2012-04-01
Large eddy simulations (LES) are performed to study flow past a two-dimensional (2D) block. An immersed boundary method (IBM) is developed and implemented to model the block in the simulation. The accuracy of the IBM method and the performance of four subgrid-scale (SGS) models are examined by comparing the results with wind tunnel experimental data from the literature. The SGS models that are tested include (a) the Smagorinsky model, (b) the Lagrangian dynamc model, (c) the scale-dependent Largrangian dynamic model, and (d) the modulated gradient model. Good agreement is observed between the experiments and the results from the scale-dependent Lagrangian dynamic model and the modulated gradient model. These models are able to reproduce the mean wind and turbulence statistics around the block. Moreover, the values of the eddy viscosity coefficient and scale-dependence coefficient obtained with the Lagrangian scale-dependent dynamic model are found to have strong spatial variability. Lower values of the eddy viscosity coefficient are found in regions of the flow with higher shear in order to account for the reduced length scales of the turbulence.
NASA Technical Reports Server (NTRS)
Ko, Malcolm K. W.; Schneider, Hans R.; Shia, Run-Lie; Weisenstein, Debra K.; Sze, Nien-Dak
1993-01-01
Spatial and seasonal distribution of ozone and other trace gases are simulated using a interactive two-dimensional model of the stratosphere updated to include full gas phase chemistry. The model consists of a primitive equation dynamics module, a full radiative transfer scheme, and a comprehensive gas phase chemistry module. The circulation is derived from heating rates in the stratosphere that are calculated using model-generated ozone. In the troposphere, parameterized heating rates are adopted. The eddy momentum flux divergence in the zonal mean momentum equation is given by the eddy fluxes of potential vorticity. Eddy fluxes of potential vorticity and tracers are parameterized using a set of predetermined diffusion coefficients. The adopted values for K(sub yy), show a hemispherical asymmetry in that the values in the lower stratosphere are consistently smaller in the southern hemisphere. The asymmetry in K(sub yy) and in the parameterization of the tropospheric heating rate results in an asymmetry in the circulation giving rise to unique signatures in the trace gas distributions. The model successfully simulates the observed asymmetry in the column abundance of the springtime ozone maxima between northern and southern hemisphere. Results for other trace gases are in agreement with the gross observed features although specific differences exist.
Multifluid MHD Simulation of Saturn's Interchange Fingers
NASA Astrophysics Data System (ADS)
Lucas, N.; Rajendar, A.; Paty, C. S.
2014-12-01
Saturn's magnetosphere exhibits rich dynamics that have only become apparent through recent missions such as the Cassini mission currently in progress. Examining local time variations in the magnetosphere has shown some interesting phenomena. One of the primary expressions of the dynamics we observe in Saturn's magnetosphere are plasma interchange fingers. These fingers carry hot plasma from the outer magnetosphere to the inner magnetosphere to balance magnetic flux lost due to outward radial transport of cold dense plasma sourced from the neutral cloud. This process leads to a mixing of hot and cold plasma throughout the magnetosphere. Understanding how mass interchange fingers form and quantifying how the plasma they contain is heated and transported will be important for understanding other dynamic processes occurring in the magnetosphere. In this study, we will be using our existing multifluid simulation of Saturn's magnetosphere in combination with data from the Cassini mission in order to investigate the formation of plasma interchange fingers and their dynamics. Our results will be compared with observations as well as previous modeling studies of Saturn's interchange fingers.
Three-dimensional time-dependent MHD simulation model of the solar corona and solar wind
K. Hayashi
2006-01-01
We will present the MHD simulation model for the solar corona and solar wind. The simulation utilizes the solar photospheric magnetic field measurement data as the boundary condition, and the obtained MHD solution is fully matching the given solar surface magnetic field distribution. In order that the simulated situation will be more realistic, the boundary treatment in our code is
NASA Astrophysics Data System (ADS)
Biswas, Rajib; Furtado, Jonathan; Bagchi, Biman
2013-10-01
We present computer simulation study of two-dimensional infrared spectroscopy (2D-IR) of water confined in reverse micelles (RMs) of various sizes. The present study is motivated by the need to understand the altered dynamics of confined water by performing layerwise decomposition of water, with an aim to quantify the relative contributions of different layers water molecules to the calculated 2D-IR spectrum. The 0-1 transition spectra clearly show substantial elongation, due to inhomogeneous broadening and incomplete spectral diffusion, along the diagonal in the surface water layer of different sized RMs. Fitting of the frequency fluctuation correlation functions reveal that the motion of the surface water molecules is sub-diffusive and indicate the constrained nature of their dynamics. This is further supported by two peak nature of the angular analogue of van Hove correlation function. With increasing system size, the water molecules become more diffusive in nature and spectral diffusion almost completes in the central layer of the larger size RMs. Comparisons between experiments and simulations establish the correspondence between the spectral decomposition available in experiments with the spatial decomposition available in simulations. Simulations also allow a quantitative exploration of the relative role of water, sodium ions, and sulfonate head groups in vibrational dephasing. Interestingly, the negative cross correlation between force on oxygen and hydrogen of O-H bond in bulk water significantly decreases in the surface layer of each RM. This negative cross correlation gradually increases in the central water pool with increasing RMs size and this is found to be partly responsible for the faster relaxation rate of water in the central pool.
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.
Banks, J. W.; Berger, R. L.; Cohen, B. I.; Hittinger, J. A. F. [Lawrence Livermore National Laboratory, Livermore, California 94551 (United States); Brunner, S. [Centre de Recherches en Physique des Plasmas, Ecole Polytechnique Federale de Lausanne, Lausanne (Switzerland)
2011-05-15
Two-dimensional Vlasov simulations of nonlinear electron plasma waves are presented, in which the interplay of linear and nonlinear kinetic effects is evident. The plasma wave is created with an external traveling wave potential with a transverse envelope of width {Delta}y such that thermal electrons transit the wave in a ''sideloss'' time, t{sub sl{approx}{Delta}}y/v{sub e}. Here, v{sub e} is the electron thermal velocity. The quasisteady distribution of trapped electrons and its self-consistent plasma wave are studied after the external field is turned off. In cases of particular interest, the bounce frequency, {omega}{sub be}=k{radical}(e{phi}/m{sub e}), satisfies the trapping condition {omega}{sub be}t{sub sl}>2{pi} such that the wave frequency is nonlinearly downshifted by an amount proportional to the number of trapped electrons. Here, k is the wavenumber of the plasma wave and {phi} is its electric potential. For sufficiently short times, the magnitude of the negative frequency shift is a local function of {phi}. Because the trapping frequency shift is negative, the phase of the wave on axis lags the off-axis phase if the trapping nonlinearity dominates linear wave diffraction. In this case, the phasefronts are curved in a focusing sense. In the opposite limit, the phasefronts are curved in a defocusing sense. Analysis and simulations in which the wave amplitude and transverse width are varied establish criteria for the development of each type of wavefront. The damping and trapped-electron-induced focusing of the finite-amplitude electron plasma wave are also simulated. The damping rate of the field energy of the wave is found to be about the sideloss rate, {nu}{sub e{approx}}t{sub sl}{sup -1}. For large wave amplitudes or widths {Delta}y, a trapping-induced self-focusing of the wave is demonstrated.
Govindarajan, V; Udaykumar, H S; Chandran, K B
2009-03-01
The hinge region of a mechanical bileaflet valve is implicated in blood damage and initiation of thrombus formation. Detailed fluid dynamic analysis in the complex geometry of the hinge region during the closing phase of the bileaflet valve is the focus of this study to understand the effect of fluid-induced stresses on the activation of platelets. A fixed-grid Cartesian mesh flow solver is used to simulate the blood flow through a two-dimensional geometry of the hinge region of a bileaflet mechanical valve. Use of local mesh refinement algorithm provides mesh adaptation based on the gradients of flow in the constricted geometry of the hinge. Leaflet motion is specified from the fluid-structure interaction analysis of the leaflet dynamics during the closing phase from a previous study, which focused on the fluid mechanics at the gap between the leaflet edges and the valve housing. A Lagrangian particle tracking method is used to model and track the platelets and to compute the magnitude of the shear stress on the platelets as they pass through the hinge region. Results show that there is a boundary layer separation in the gaps between the leaflet ear and the constricted hinge geometry. Separated shear layers roll up into vortical structures that lead to high residence times combined with exposure to high-shear stresses for particles in the hinge region. Particles are preferentially entrained into this recirculation zone, presenting the possibility of platelet activation, aggregation, and initiation of thrombi. PMID:19154061
Govindarajan, V.; Udaykumar, H.S.; Chandran, K.B.
2009-01-01
The hinge region of a mechanical bileaflet valve is implicated in blood damage and initiation of thrombus formation. Detailed fluid dynamic analysis in the complex geometry of the hinge region during the closing phase of the bileaflet valve is the focus of this study to understand the effect of fluid-induced stresses on the activation of platelets. A fixed-grid Cartesian mesh flow solver is used to simulate the blood flow through a two-dimensional geometry of the hinge region of a bi-leaflet mechanical valve. Use of local mesh refinement algorithm provides mesh adaptation based on the gradients of flow in the constricted geometry of the hinge. Leaflet motion is specified from the fluid-structure interaction analysis of the leaflet dynamics during the closing phase from a previous study which focused on the fluid mechanics at the gap between the leaflet edges and the valve housing. A Lagrangian particle tracking method is used to model and track the platelets and to compute the magnitude of the shear stress on the platelets as they pass through the hinge region. Results show that there is a boundary layer separation in the gaps between the leaflet ear and the constricted hinge geometry. Separated shear layers roll up into vortical structures that lead to high residence times combined with exposure to high shear stresses for particles in the hinge region. Particles are preferentially entrained into this re-circulation zone, presenting the possibility of platelet activation, aggregation, and initiation of thrombi. PMID:19154061
NASA Astrophysics Data System (ADS)
Arcones, A.; Janka, H.-Th.
2011-02-01
After the initiation of the explosion of core-collapse supernovae, neutrinos emitted from the nascent neutron star drive a supersonic baryonic outflow. This neutrino-driven wind interacts with the more slowly moving, earlier supernova ejecta forming a wind termination shock (or reverse shock), which changes the local wind conditions and their evolution. Important nucleosynthesis processes (alpha-process, charged-particle reactions, r-process, and ?p-process) occur or might occur in this environment. The nucleosynthesis depends on the long-time evolution of density, temperature, and expansion velocity. Here we present two-dimensional hydrodynamical simulations with an approximate description of neutrino-transport effects, which for the first time follow the post-bounce accretion, onset of the explosion, wind formation, and the wind expansion through the collision with the preceding supernova ejecta. Our results demonstrate that the anisotropic ejecta distribution has a great impact on the position of the reverse shock, the wind profile, and the long-time evolution. This suggests that hydrodynamic instabilities after core bounce and the consequential asymmetries may have important effects on the nucleosynthesis-relevant conditions in the neutrino-heated baryonic mass flow from proto-neutron stars.
On two-dimensional magnetohydrodynamic turbulence
A. Pouquet
1978-01-01
The reported investigation shows that two-dimensional MHD turbulence differs basically from two-dimensional nonmagnetic turbulence. Because of the relaxation of the vorticity constraint, the appearance of singularities at a finite time, as in three-dimensional turbulence, cannot be ruled out (at zero viscosity and zero magnetic diffusivity). Upon injection of kinetic and magnetic energy, a quasi-stationary state is obtained with a direct
Understanding Accretion Disks through Three Dimensional Radiation MHD Simulations
NASA Astrophysics Data System (ADS)
Jiang, Yan-Fei
I study the structures and thermal properties of black hole accretion disks in the radiation pressure dominated regime. Angular momentum transfer in the disk is provided by the turbulence generated by the magneto-rotational instability (MRI), which is calculated self-consistently with a recently developed 3D radiation magneto-hydrodynamics (MHD) code based on Athena. This code, developed by my collaborators and myself, couples both the radiation momentum and energy source terms with the ideal MHD equations by modifying the standard Godunov method to handle the stiff radiation source terms. We solve the two momentum equations of the radiation transfer equations with a variable Eddington tensor (VET), which is calculated with a time independent short characteristic module. This code is well tested and accurate in both optically thin and optically thick regimes. It is also accurate for both radiation pressure and gas pressure dominated flows. With this code, I find that when photon viscosity becomes significant, the ratio between Maxwell stress and Reynolds stress from the MRI turbulence can increase significantly with radiation pressure. The thermal instability of the radiation pressure dominated disk is then studied with vertically stratified shearing box simulations. Unlike the previous results claiming that the radiation pressure dominated disk with MRI turbulence can reach a steady state without showing any unstable behavior, I find that the radiation pressure dominated disks always either collapse or expand until we have to stop the simulations. During the thermal runaway, the heating and cooling rates from the simulations are consistent with the general criterion of thermal instability. However, details of the thermal runaway are different from the predictions of the standard alpha disk model, as many assumptions in that model are not satisfied in the simulations. We also identify the key reasons why previous simulations do not find the instability. The thermal instability has many important implications for understanding the observations of both X-ray binaries and Active Galactic Nuclei (AGNs). However, direct comparisons between observations and the simulations require global radiation MHD simulations, which will be the main focus of my future work.
NASA Technical Reports Server (NTRS)
Lu, Rong; Turco, Richard P.
1994-01-01
Over the southern California coastal region, observations of the vertical distributions of pollutants show that maximum concentrations can occur within temperature inversion layers well above the surface. A mesoscale model is used to study the dynamical phenomena that cause such layers, including sea breezes and mountain flows, and to study the characteristics of air pollutant transport in a coastal environment capped by a temperature inversion. The mathematical and physical structure of the model is described. Two-dimensional simulations corresponding to four configurations of coastal plains and mountains are discussed. The simulations reveal that pollutant transport over a coastal plain is strongly influenced by the topographic configuration, including the height of coastal mountains and their distance from the coastline. Sea breezes induced by land-sea thermal contrasts, as well as upslope winds induced along mountain flanks, both create vertical transport that can lead to the formation of elevated pollution layers. The sea-breeze circulation generates pollution layers by undercutting the mixed layer and lofting pollutants into the stable layer. Heating of mountain slopes acts to vent pollutants above the mountain ridge during the day; during the evening, pollutants can be injected directly into the inversion layer from the decaying upslope flows. In a land-sea configuration with mountains close to the coastline, the sea breeze and heated-mountain flow are strongly coupled. In the afternoon, this interaction can produce upslope flow from which polluted air is detrained into the inversion layer as a return circulation. When the mountains lie farther inland, however, pollutants may be trapped aloft when the mixed layer stabilizes in the late afternoon. As the nocturnal boundary layer forms over the coast in the evening, polluted mixed-layer air is effectively left behind in the inversion layer. In the Los Angeles Basin, the formation mechanism for elevated polluted layers is most similar to our cases with inland mountains.
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.
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. Specifically, the latitudinal structure of the ambient solar wind in the meridional plane is approximated by two zones: At low latitudes (<20°) the
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%.
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.
NASA Astrophysics Data System (ADS)
Richert, Alexander J. W.; Lyra, Wladimir; Boley, Aaron; Mac Low, Mordecai-Mark; Turner, Neal
2015-05-01
Recent observations of gaps and non-axisymmetric features in the dust distributions of transition disks have been interpreted as evidence of embedded massive protoplanets. However, comparing the predictions of planet–disk interaction models to the observed features has shown far from perfect agreement. This may be due to the strong approximations used for the predictions. For example, spiral arm fitting typically uses results that are based on low-mass planets in an isothermal gas. In this work, we describe two-dimensional, global, hydrodynamical simulations of disks with embedded protoplanets, with and without the assumption of local isothermality, for a range of planet-to-star mass ratios 1–10 {{M}J} for a 1 {{M}? } star. We use the Pencil Code in polar coordinates for our models. We find that the inner and outer spiral wakes of massive protoplanets (M? 5 {{M}J}) produce significant shock heating that can trigger buoyant instabilities. These drive sustained turbulence throughout the disk when they occur. The strength of this effect depends strongly on the mass of the planet and the thermal relaxation timescale; for a 10 {{M}J} planet embedded in a thin, purely adiabatic disk, the spirals, gaps, and vortices typically associated with planet–disk interactions are disrupted. We find that the effect is only weakly dependent on the initial radial temperature profile. The spirals that form in disks heated by the effects we have described may fit the spiral structures observed in transition disks better than the spirals predicted by linear isothermal theory.
NASA Astrophysics Data System (ADS)
Jeon, Jonggu; Cho, Minhaeng
2010-06-01
Multidimensional infrared (IR) spectroscopy has emerged as a viable tool to study molecular structure and dynamics in condensed phases, and the third-order vibrational response function is the central quantity underlying various nonlinear IR spectroscopic techniques, such as pump-probe, photon echo and two-dimensional (2D) IR spectroscopy. In this paper, a new computational method is presented that calculates this nonlinear response function in the classical limit from a series of classical molecular dynamics (MD) simulations, employing a quantum mechanical/molecular mechanical (QM/MM) force field. The method relies on the stability matrix formalism where the dipole-dipole quantum mechanical commutators appearing in the exact quantum response function are replaced by the corresponding Poisson brackets. We present the formulation and computational algorithm of the method for both the classical and the QM/MM force fields and apply it to the 2D IR spectroscopy of carbon monoxide (CO) and N-methylacetamide (NMA), each solvated in a water cluster. The conventional classical force field with harmonic bond potentials is shown to be incapable of producing a reliable 2D IR signal because intramolecular vibrational anharmonicity, essential to the production of the nonlinear signal, is absent in such a model. The QM/MM force field, on the other hand, produces distinct 2D spectra for the NMA and CO systems with clear vertical splitting and cross peaks, reflecting the vibrational anharmonicities and the vibrational couplings between the underlying vibrational modes, respectively. In the NMA spectrum, the coupling between the amide I and II modes is also well reproduced. While attaining the converged spectrum is found to be challenging with this method, with an adequate amount of computing it can be straightforwardly applied to new systems containing multiple chromophores with little modeling effort, and therefore it would be useful in understanding the multimode 2D IR spectrum of complex molecular systems.
Judi, David R [Los Alamos National Laboratory; Mcpherson, Timothy N [Los Alamos National Laboratory; Burian, Steven J [UNIV OF UTAH
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.
MHD Simulations of Relic Radio Bubbles in Clusters
Jones, T W
2005-01-01
In order to better understand the origin and evolution of relic radio bubbles in clusters of galaxies, we report on an extensive set of 2D MHD simulations of hot buoyant bubbles evolving in a realistic intracluster medium. Our bubbles are inflated near the base of the ICM over a finite time interval from a region whose magnetic field is isolated from the ICM. We confirm both the early conjecture from linear analysis and the later results based on preformed MHD bubbles; namely, that very modest ICM magnetic fields can stabilize the rising bubbles against disruption by Rayleigh-Taylor and Kelvin-Helmholtz instabilities. We find in addition that amplification of the ambient fields as they stretch around the bubbles can be sufficient to protect the bubbles or their initial fragments even if the fields are initially much too weak to play a significant role early in the evolution of the bubbles. Indeed, even with initial fields less than a micro-Gauss and values of $\\beta = P_g/P_b$ approaching $10^5$, magnetic str...
Gravitational waves from 3D MHD core collapse simulations
NASA Astrophysics Data System (ADS)
Scheidegger, S.; Fischer, T.; Whitehouse, S. C.; Liebendörfer, M.
2008-10-01
We present the gravitational wave analyses from rotating (model s15g) and nearly non-rotating (model s15h) 3D MHD core collapse supernova simulations at bounce and during the first couple of ten milliseconds afterwards. The simulations are launched from 15 M? progenitor models stemming from stellar-evolution calculations. Gravity is implemented by a spherically symmetric effective general relativistic potential. The input physics uses the Lattimer-Swesty equation of state for hot, dense matter and a neutrino parametrisation scheme that is accurate until the first few ms after bounce. The 3D simulations allow us to study features already known from 2D simulations, as well as nonaxisymmetric effects. In agreement with recent results, we find only type I gravitational wave signals at core bounce. In the later stage of the simulations, one of our models (s15g) shows nonaxisymmetric gravitational wave emission caused by a low T/|W| dynamical instability, while the other model radiates gravitational waves due to a convective instability in the protoneutron star. The total energy released in gravitational waves within the considered time intervals is 1.52×10-7~M? (s15g) and 4.72×10-10~M? (s15h). Both core collapse simulations indicate that corresponding events in our Galaxy would be detectable either by the LIGO or Advanced LIGO detector.
Nonlinear evolution of the MHD Kelvin-Helmholtz instability in a compressible plasma
S. H. Lai; L. H. Lyu
2006-01-01
Kelvin-Helmholtz (K-H) instability at a magnetohydrodynamic (MHD) tangential discontinuity (TD) is studied by means of two-dimensional MHD simulation. The TD is of finite thickness with both magnetic shear and velocity shear across the TD. Our simulation results indicate that the nonlinear evolution of MHD surface waves at the TD depends on the fast-mode Mach numbers of the plasma flows on
MHD simulation of deuterium-fiber-initiated Z-pinches with two-fluid effects
Sheehey, P. [California Univ., Los Angeles, CA (United States). Dept. of Physics; Lindemuth, I.R. [Los Alamos National Lab., NM (United States)
1993-05-01
Two-dimensional ``cold-start`` resistive MHD computations of formation and evolution of deuterium-fiber-initiated Z-pinches have been extended to include separate ion and electron energy equations and finite-Larmor-radius ordered terms. In the Ohm`s Law (magnetic field evolution) equation, Hall and diamagnetic pressure terms have been added, and corresponding terms have been added to the energy equations. Comparison is made of the results of these computations with previous computations and with experiments.
MHD simulation of deuterium-fiber-initiated Z-pinches with two-fluid effects
Sheehey, P. (California Univ., Los Angeles, CA (United States). Dept. of Physics); Lindemuth, I.R. (Los Alamos National Lab., NM (United States))
1993-01-01
Two-dimensional cold-start'' resistive MHD computations of formation and evolution of deuterium-fiber-initiated Z-pinches have been extended to include separate ion and electron energy equations and finite-Larmor-radius ordered terms. In the Ohm's Law (magnetic field evolution) equation, Hall and diamagnetic pressure terms have been added, and corresponding terms have been added to the energy equations. Comparison is made of the results of these computations with previous computations and with experiments.
Reconnection events in two-dimensional Hall magnetohydrodynamic turbulence
Donato, S.; Servidio, S.; Carbone, V. [Dipartimento di Fisica, Universita della Calabria, I-87036 Cosenza (Italy); Dmitruk, P. [Departamento de Fisica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires and Instituto de Fisica de Buenos Aires, CONICET, Buenos Aires (Argentina); Shay, M. A.; Matthaeus, W. H. [Bartol Research Institute and Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716 (United States); Cassak, P. A. [Department of Physics, West Virginia University, Morgantown, West Virginia 26506 (United States)
2012-09-15
The statistical study of magnetic reconnection events in two-dimensional turbulence has been performed by comparing numerical simulations of magnetohydrodynamics (MHD) and Hall magnetohydrodynamics (HMHD). The analysis reveals that the Hall term plays an important role in turbulence, in which magnetic islands simultaneously reconnect in a complex way. In particular, an increase of the Hall parameter, the ratio of ion skin depth to system size, broadens the distribution of reconnection rates relative to the MHD case. Moreover, in HMHD the local geometry of the reconnection region changes, manifesting bifurcated current sheets and quadrupolar magnetic field structures in analogy to laminar studies, leading locally to faster reconnection processes in this case of reconnection embedded in turbulence. This study supports the idea that the global rate of energy dissipation is controlled by the large scale turbulence, but suggests that the distribution of the reconnection rates within the turbulent system is sensitive to the microphysics at the reconnection sites.
MHD Simulations of the Plasma Flow in the Magnetic Nozzle
NASA Technical Reports Server (NTRS)
Smith, T. E. R.; Keidar, M.; Sankaran, K.; olzin, K. A.
2013-01-01
The magnetohydrodynamic (MHD) flow of plasma through a magnetic nozzle is simulated by solving the governing equations for the plasma flow in the presence of an static magnetic field representing the applied nozzle. This work will numerically investigate the flow and behavior of the plasma as the inlet plasma conditions and magnetic nozzle field strength are varied. The MHD simulations are useful for addressing issues such as plasma detachment and to can be used to gain insight into the physical processes present in plasma flows found in thrusters that use magnetic nozzles. In the model, the MHD equations for a plasma, with separate temperatures calculated for the electrons and ions, are integrated over a finite cell volume with flux through each face computed for each of the conserved variables (mass, momentum, magnetic flux, energy) [1]. Stokes theorem is used to convert the area integrals over the faces of each cell into line integrals around the boundaries of each face. The state of the plasma is described using models of the ionization level, ratio of specific heats, thermal conductivity, and plasma resistivity. Anisotropies in current conduction due to Hall effect are included, and the system is closed using a real-gas equation of state to describe the relationship between the plasma density, temperature, and pressure.A separate magnetostatic solver is used to calculate the applied magnetic field, which is assumed constant for these calculations. The total magnetic field is obtained through superposition of the solution for the applied magnetic field and the self-consistently computed induced magnetic fields that arise as the flowing plasma reacts to the presence of the applied field. A solution for the applied magnetic field is represented in Fig. 1 (from Ref. [2]), exhibiting the classic converging-diverging field pattern. Previous research was able to demonstrate effects such as back-emf at a super-Alfvenic flow, which significantly alters the shape of the magnetic field in both the near- and far-field regions. However, in that work the downstream domain was constrained to a channel of constant cross-sectional area. In the present work we seek to address this issue by modeling the downstream region with a domain that permits free expansion of the plasma, permitting a better evaluation of the downstream effects the applied field has on the plasma. The inlet boundary conditions and applied magnetic field values will also be varied to determine the effect the initial plasma energy content and applied magnetic field energy density have on the near- and far-field plasma properties on the MHD code. This will determine the effect of inlet boundary conditions on the results downstream and address issues related to the restrictive numerical domain previously used.
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.
Chewook Lee; Kwang-Hee Park; Jin-A. Kim; Seungsoo Hahn; Minhaeng Cho
2006-01-01
A theoretical description of the vibrational excitons in DNA is presented by using the vibrational basis mode theory developed in Papers I and II. The parameters obtained from the density functional theory calculations, such as vibrational coupling constants and basis mode frequencies, are used to numerically simulate two-dimensional (2D) IR spectra of dGn:dCn and dAn:dTn double helices with n varying
NASA Technical Reports Server (NTRS)
Chao, D. F. K.
1983-01-01
Transient, numerical simulations of the de-icing of composite aircraft components by electrothermal heating were performed for a two dimensional rectangular geometry. The implicit Crank-Nicolson formulation was used to insure stability of the finite-difference heat conduction equations and the phase change in the ice layer was simulated using the Enthalpy method. The Gauss-Seidel point iterative method was used to solve the system of difference equations. Numerical solutions illustrating de-icer performance for various composite aircraft structures and environmental conditions are presented. Comparisons are made with previous studies. The simulation can also be used to solve a variety of other heat conduction problems involving composite bodies.
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.
MHD simulation of RF current drive in MST
NASA Astrophysics Data System (ADS)
Hendries, E. R.; Anderson, J. K.; Diem, S.; Forest, C. B.; Harvey, R. W.; Reusch, J. A.; Seltzman, A. H.; Sovinec, C. R.
2014-02-01
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 ˜ 104) generally agree with the previous work; significantly more burdensome simulations at MST-like Lundquist number (S ˜ 3×106) 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.
Wu, Benxin; Shin, Yung C. [Center for Laser-based Manufacturing, Purdue University, West Lafayette, Indiana 47907 (United States)
2007-05-15
In laser shock peening (LSP) under a water-confinement regime, laser-matter interaction near the coating-water interface can induce very high pressures in the order of gigapascals, which can impart compressive residual stresses into metal workpieces to improve fatigue and corrosion properties. For axisymmetric laser spots with finite size, the pressure generation near the water-coating interface is a two dimensional process in nature. This is in particular the case for microscale LSP performed with very small laser spots, which is a very promising technique to improve the reliability performance of microdevices. However, models capable of predicting two dimensional (2D) spatial distributions of the induced pressures near the coating-water interface in LSP have rarely been reported in literature. In this paper, a predictive 2D axisymmetric model is developed by numerically solving the hydrodynamic equations, supplemented with appropriate equations of state of water and the coating material. The model can produce 2D spatial distributions of material responses near the water-coating interface in LSP, and is verified through comparisons with experimental measurements. The model calculation shows that the effect of radial release wave on pressure spatial distributions becomes more significant as the laser spot size decreases, indicating the importance of a 2D model, particularly for microscale LSP.
Parallel, AMR MHD for Global Space Weather Simulations
Kenneth G. Powell; Darren L. De Zeeuw; Igor V. Sokolov; Gábor Tóth; Tamas Gombosi; Quentin Stout
This paper presents the methodology behind and results of adaptive mesh refinement in global magnetohydrodynamic models of the space environment. Techniques used in solving the governing equations of semi-relativistic magnetohydrodynamics (MHD) are presented. These techniques include high-resolution upwind schemes, block-based solution-adaptive grids, explicit, implicit and partial-implicit time-stepping, and domain decomposition for parallelization. Recent work done in coupling the MHD model
An adaptive MHD method for global space weather simulations
Darren L. De Zeeuw; Tamas I. Gombosi; Clinto P. T. Groth; Kenneth G. Powell; Quentin F. Stout
2000-01-01
A 3D parallel adaptive mesh refinement (AMR) scheme is described for solving the partial-differential equations governing ideal magnetohydrodynamic (MHD) flows. This new algorithm adopts a cell-centered upwind finite-volume discretization procedure and uses limited solution reconstruction, approximate Riemann solvers, and explicit multi-stage time stepping to solve the MHD equations in divergence form, providing a combination of high solution accuracy and computational
NASA Astrophysics Data System (ADS)
Huang, Huaxiong; Takagi, Shu
2003-08-01
In this paper, we study the convergence property of PHYSALIS when it is applied to incompressible particle flows in two-dimensional space. PHYSALIS is a recently proposed iterative method which computes the solution without imposing the boundary conditions on the particle surfaces directly. Instead, a consistency equation based on the local (near particle) representation of the solution is used as the boundary conditions. One of the important issues needs to be addressed is the convergence properties of the iterative procedure. In this paper, we present the convergence analysis using Laplace and biharmonic equations as two model problems. It is shown that convergence of the method can be achieved but the rate of convergence depends on the relative locations of the cages. The results are directly related to potential and Stokes flows. However, they are also relevant to Navier-Stokes flows, heat conduction in composite media, and other problems.
NASA Astrophysics Data System (ADS)
Zhang, Ya; Jiang, Wei; Song, Yuan-Hong; Wang, You-Nian
2015-02-01
Isochoric heating of an aluminum target by proton beams has been studied with a two-dimensional self-consistent electromagnetic quantum-hydrodynamic model, including the nonlinear quantum effects. It is shown that most protons deposit their energy within several micrometers near the surface, and the aluminum metal target is heated up to several electron volts in tens of Mbar pressure regime within one picosecond. Comparison between electrostatic and electromagnetic cases shows that the strength of electromagnetic field is much smaller than that of the electrostatic field at initial stage but increases more rapidly and becomes larger at later time. The results show that the time evolution of electric field has a significant influence on the interaction of intense beams with a solid target, while the effect of the self-magnetic field is small for non-relativistic beams considered here.
Moran, S. D.; Preketes, N. K.; Zhang, T. O.; Zanni, M. T.; Mukamel, S.
2013-01-01
Cataracts is a misfolding protein disease in which one of its major components is the ?D-crystallin protein. The conformational structure of the aggregated ?D-crystallin and the interactions that cause aggregation are largely unknown. A recent experimental two-dimensional infrared (2DIR) spectroscopy study determined that the C-terminal domain has a high propensity to form ?-sheets whereas the N-terminal domain forms a disordered structure in the fiber state. We present a combined computational molecular dynamics (MD) and infrared spectroscopy study of the local dynamics of these domains. The computed 2DIR signals agree remarkably well with experiment. We show that both domains having a Greek key structural fold experience different electrostatic environments, which may be related to the fact that the C-terminal domain is more structurally stable than the N-terminal domain. We correlate the vibrational couplings to known energy dissipation mechanisms and reveal their origin. PMID:23972032
Ionospheric power consumption in global MHD Simulation predicted from solar wind measurements
Minna Palmroth; Hannu E. J. Koskinen; Tuija I. Pulkkinen; Pekka Janhunen
2004-01-01
Ionospheric power consumption in a global magnetohydrodynamic (MHD) simulation is investigated. The sum of Joule heating and precipitation power integrated over both hemispheres is calculated in four simulation runs. The simulation results of the total ionospheric dissipation are correlated with solar wind density, velocity, and magnetic field using a linear multi-variable fit and a power law. The fitting procedure yields
Relativistic MHD simulations of poynting flux-driven jets
Guan, Xiaoyue; Li, Hui; Li, Shengtai, E-mail: guan@lanl.gov [Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)
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.
Maier, Thomas A [ORNL; Alvarez, Gonzalo [ORNL; Summers, Michael Stuart [ORNL; Schulthess, Thomas C [ORNL
2010-01-01
Using dynamic cluster quantum Monte Carlo simulations, we study the superconducting behavior of a 1=8 doped two-dimensional Hubbard model with imposed unidirectional stripelike charge-density-wave modulation. We find a significant increase of the pairing correlations and critical temperature relative to the homogeneous system when the modulation length scale is sufficiently large. With a separable form of the irreducible particle-particle vertex, we show that optimized superconductivity is obtained for a moderate modulation strength due to a delicate balance between the modulation enhanced pairing interaction, and a concomitant suppression of the bare particle-particle excitations by a modulation reduction of the quasiparticle weight.
NASA Astrophysics Data System (ADS)
Kasaba, Y.; Matsumoto, H.; Omura, Y.
2001-09-01
We have performed computer simulations of the self-consistent nonlinear evolution of electrostatic and electromagnetic 2fp waves excited by electron beams with electromagnetic particle code. In both one- and two-dimensional periodic systems an electrostatic 2fp wave is generated at twice the wave number of forward propagating Langmuir waves by wave-wave coupling. This wave grows with the forward propagating Langmuir wave in the nonlinear stage of the simulations. The electrostatic 2fp wave in the simulations is saturated at about -20~-30dB of that of the Langmuir waves. It is larger than the value expected from observations in the terrestrial electron foreshock. The electromagnetic 2fp wave is only excited in two-dimensional systems. The magnitude of the electromagnetic 2fp wave is correlated with the backward propagating Langmuir wave, not with the electrostatic 2fp wave. This result suggests that the electromagnetic 2fp wave is excited by the wave-wave coupling of forward and backward propagating Langmuir waves. The typical power density estimated from a reasonable amplitude of Langmuir wave is of the same order or much weaker than the value typically observed around the electron foreshock.
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
Hofschen, S.; Wolff, I. [Gerhard Mercator Univ. of Duisburg (Germany). Dept. of Electrical Engineering] [Gerhard Mercator Univ. of Duisburg (Germany). Dept. of Electrical Engineering
1996-08-01
Time-domain simulation results of two-dimensional (2-D) planar waveguide finite-difference time-domain (FDTD) analysis are normally analyzed using Fourier transform. The introduced method of time series analysis to extract propagation and attenuation constants reduces the desired computation time drastically. Additionally, a nonequidistant discretization together with an adequate excitation technique is used to reduce the number of spatial grid points. Therefore, it is possible to reduce the number of spatial grid points. Therefore, it is possible to simulate normal- and superconducting planar waveguide structures with very thin conductors and small dimensions, as they are used in MMIC technology. The simulation results are compared with measurements and show good agreement.
NASA Astrophysics Data System (ADS)
Hur, Min Young; Lee, Ho-Jun; Lee, Hae June; Choe, Won Ho; Seon, Jong Ho
2013-09-01
Oscillations of the plasma potential have been observed in many Hall thruster experiments. It was estimated that the oscillations are triggered by the interaction between the plasma and the dielectric materials such as secondary electron emission, but detailed mechanism has not been proven. In this paper, the effects of the interaction between the plasma and dielectric material are simulated with a two-dimensional particle-in-cell (PIC) code for the acceleration channel of the hall thruster. Especially, the simulation code is parallelized using graphic processing units (GPUs). To analyze the effect, the simulation is confirmed to change following two parameters, magnetic flux density and secondary electron emission coefficient (SEEC). The particle trajectory is presented with the variation of the SEEC and magnetic flux density as well as its curvature. Oscillations of the plasma potential have been observed in many Hall thruster experiments. It was estimated that the oscillations are triggered by the interaction between the plasma and the dielectric materials such as secondary electron emission, but detailed mechanism has not been proven. In this paper, the effects of the interaction between the plasma and dielectric material are simulated with a two-dimensional particle-in-cell (PIC) code for the acceleration channel of the hall thruster. Especially, the simulation code is parallelized using graphic processing units (GPUs). To analyze the effect, the simulation is confirmed to change following two parameters, magnetic flux density and secondary electron emission coefficient (SEEC). The particle trajectory is presented with the variation of the SEEC and magnetic flux density as well as its curvature. This research is supported by a ``Core technology development of high Isp electric propulsion system for space exploration'' from National Space Lab. sponsored by the National Reshearch Foundation of korea (NRF).
NASA Astrophysics Data System (ADS)
Tran, Diana X.; Yang, Ming-Jim; Weiss, James N.; Garfinkel, Alan; Qu, Zhilin
2007-12-01
Ventricular fibrillation is a lethal arrhythmia characterized by multiple wavelets usually starting from a single or figure-of-eight re-entrant circuit. Understanding the factors regulating vulnerability to the re-entry is essential for developing effective therapeutic strategies to prevent ventricular fibrillation. In this study, we investigated how pre-existing tissue heterogeneities and electrical restitution properties affect the initiation of re-entry by premature extrastimuli in two-dimensional cardiac tissue models. We studied two pacing protocols for inducing re-entry following the "sinus" rhythm (S1) beat: (1) a single premature (S2) extrastimulus in heterogeneous tissue; (2) two premature extrastimuli (S2 and S3) in homogeneous tissue. In the first case, the vulnerable window of re-entry is determined by the spatial dimension and extent of the heterogeneity, and is also affected by electrical restitution properties and the location of the premature stimulus. The vulnerable window first increases as the action potential duration (APD) difference between the inside and outside of the heterogeneous region increases, but then decreases as this difference increases further. Steeper APD restitution reduces the vulnerable window of re-entry. In the second case, electrical restitution plays an essential role. When APD restitution is flat, no re-entry can be induced. When APD restitution is steep, re-entry can be induced by an S3 over a range of S1S2 intervals, which is also affected by conduction velocity restitution. When APD restitution is even steeper, the vulnerable window is reduced due to collision of the spiral tips.
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.
Criteria for Scaled Laboratory Simulations of Astrophysical MHD Phenomena
D. D. Ryutov; R. P. Drake; B. A. Remington
2000-01-01
We demonstrate that two systems described by the equations of the ideal magnetohydrodynamics (MHD) evolve similarly, if the initial conditions are geometrically similar and certain scaling relations hold. The thermodynamic properties of the gas must be such that the internal energy density is proportional to the pressure. The presence of the shocks is allowed. We discuss the applicability conditions of
Andre Roggan; Gerhard J. Mueller
1994-01-01
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
3D Global MHD Simulation of the Saturn Magnetospheric Plasma Interaction with Titan's Ionosphere
Yingjuan Ma; A. F. Nagy; T. E. Cravens; G. Toth; F. J. Crary; A. J. Coates; M. K. Dougherty
2006-01-01
The interaction between Titan's ionosphere and its surrounding plasma is simulated using our 3D multi-species MHD model.We compare the simulation results with the observations obtained during the T9 flyby, using the upstream plasma parameters measured during the flyby. The Hall term (JXB) is also included in the model to investigate the ion gyro-radii effect.
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
Cold dense magnetopause boundary layer under northward IMF: Results from THEMIS and MHD simulations
California at Berkeley, University of
Cold dense magnetopause boundary layer under northward IMF: Results from THEMIS and MHD simulations 2008; accepted 8 December 2008; published 3 February 2009. [1] A layer of nearly stagnant cold dense numerical model, we successfully reproduce this observed cold dense plasma layer in the simulation
NASA Astrophysics Data System (ADS)
Liu, Xiang-Mei; Song, Yuan-Hong; Jiang, Wei; Yi, Lin
2013-04-01
A two-dimensional (2D) fluid model is presented to study the behavior of silicon plasma mixed with SiH4, N2, and NH3 in a radio-frequency capacitively coupled plasma (CCP) reactor. The plasma-wall interaction (including the deposition) is modeled by using surface reaction coefficients. In the present paper we try to identify, by numerical simulations, the effect of variations of the process parameters on the plasma properties. It is found from our simulations that by increasing the gas pressure and the discharge gap, the electron density profile shape changes continuously from an edge-high to a center-high, thus the thin films become more uniform. Moreover, as the N2/NH3 ratio increases from 6/13 to 10/9, the hydrogen content can be significantly decreased, without decreasing the electron density significantly.
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.
Integrated Physics Advances in Simulation of Wave Interactions with Extended MHD Phenomena
Batchelor, Donald B [ORNL; D'Azevedo, Eduardo [ORNL; Bateman, Glenn [Lehigh University, Bethlehem, PA; Bernholdt, David E [ORNL; Berry, Lee A [ORNL; Bonoli, P. [Massachusetts Institute of Technology (MIT); Bramley, R [Indiana University; Breslau, J. [Princeton Plasma Physics Laboratory (PPPL); Chance, M. [Princeton Plasma Physics Laboratory (PPPL); Chen, J. [Princeton Plasma Physics Laboratory (PPPL); Choi, M. [General Atomics; Elwasif, Wael R [ORNL; Fu, GuoYong [Princeton Plasma Physics Laboratory (PPPL); Harvey, R. W. [CompX, Del Mar, CA; Houlberg, Wayne A [ORNL; Jaeger, Erwin Frederick [ORNL; Jardin, S. C. [Princeton Plasma Physics Laboratory (PPPL); Keyes, David E [Columbia University; Klasky, Scott A [ORNL; Kruger, Scott [Tech-X Corporation; Ku, Long-Poe [Princeton Plasma Physics Laboratory (PPPL); McCune, Douglas [Princeton Plasma Physics Laboratory (PPPL); Schissel, D. [General Atomics; Schnack, D. [University of Wisconsin; Wright, J. C. [Massachusetts Institute of Technology (MIT)
2007-06-01
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).
Elzubier A. Salih; Thomas S. Y. Choong; S. Y. Sergie; N. L. Chin; O. M. Ibrahim
2009-01-01
Problem statement: Earlier work on ohmic heating technique focused on viscous food and foods containing solid particles. In this stud y, the use of ohmic heating on sterilization of gua va juice is carried out. Computational fluid dynamics is used to model and simulate the system. Approach: Investigate the buoyancy effect on the CFD simulati on of continuous ohmic heating
nanoMOS 2.5: A two-dimensional simulator for quantum transport in double-gate MOSFETs
Zhibin Ren; Ramesh Venugopal; Sebastien Goasguen; Supriyo Datta; Mark S. Lundstrom
2003-01-01
A program to numerically simulate quantum transport in double gate metal oxide semiconductor field effect transistors (MOSFETs) is described. The program uses a Green's function approach and a simple treatment of scattering based on the idea of so-called Buttiker probes. The double gate device geometry permits an efficient mode space approach that dramatically lowers the computational burden and permits use
NASA Astrophysics Data System (ADS)
Chiang, Yun-Wei; Freed, Jack H.
2011-01-01
The Lanczos algorithm (LA) is a useful iterative method for the reduction of a large matrix to tridiagonal form. It is a storage efficient procedure requiring only the preceding two Lanczos vectors to compute the next. The quasi-minimal residual (QMR) method is a powerful method for the solution of linear equation systems, Ax = b. In this report we provide another application of the QMR method: we incorporate QMR into the LA to monitor the convergence of the Lanczos projections in the reduction of large sparse matrices. We demonstrate that the combined approach of the LA and QMR can be utilized efficiently for the orthogonal transformation of large, but sparse, complex, symmetric matrices, such as are encountered in the simulation of slow-motional 1D- and 2D-electron spin resonance (ESR) spectra. Especially in the 2D-ESR simulations, it is essential that we store all of the Lanczos vectors obtained in the course of the LA recursions and maintain their orthogonality. In the LA-QMR application, the QMR weight matrix mitigates the problem that the Lanczos vectors lose orthogonality after many LA projections. This enables substantially more Lanczos projections, as required to achieve convergence for the more challenging ESR simulations. It, therefore, provides better accuracy for the eigenvectors and the eigenvalues of the large sparse matrices originating in 2D-ESR simulations than does the previously employed method, which is a combined approach of the LA and the conjugate-gradient (CG) methods, as evidenced by the quality and convergence of the 2D-ESR simulations. Our results show that very slow-motional 2D-ESR spectra at W-band (95 GHz) can be reliably simulated using the LA-QMR method, whereas the LA-CG consistently fails. The improvements due to the LA-QMR are of critical importance in enabling the simulation of high-frequency 2D-ESR spectra, which are characterized by their very high resolution to molecular orientation.
NASA Astrophysics Data System (ADS)
Parashar, R.; Reeves, D. M.
2009-12-01
The role of fracture networks in providing preferential pathways for fluid flow and solute transport in geologic media is well known. Predictions of flow and transport in fractured media typically rely on the discrete fracture network (DFN) modeling approach, which assumes flow and transport exclusively occurs through fracture networks, to explicitly model complex patterns of interconnected fractures as linear or planar discontinuities within a two- or three-dimensional domain. While the DFN approach excels in providing fluid flow and solute transport predictions for saturated, low-permeability rock masses, limitations of this method arise from computational constraints in both processing speed and memory, and difficulties in simulating variably-saturated flow and diffusional mass transfer between matrix and fracture continua. Hybrid methods, including fracture continuum methods which map discrete fracture networks onto a continuum grid, provide an attractive alternative to simulating fracture flow and transport by reducing computational constraints and allowing for the simulation of processes not presently achievable using DFN methods. We present an improved fracture continuum (FC) methodology, based on fracture mapping and upscaling rules and particle tracking methods, to model both fluid flow and solute transport through complex fracture networks. Comparisons with DFN simulations demonstrate the accuracy of the improved FC method in simulating both fluid flow and solute breakthrough curve characteristics, including early- and late-time tails, for a wide range of fracture density values and grid cell sizes. For network types and grid combinations that lead to multiple fractures intersecting single cells, we introduce a novel time-domain particle tracking method to better describe sub-grid heterogeneity. This time-domain particle tracking approach only adds minimal expense to the computational effort.
Teresa Castán; Per-Anker Lindgård
1989-01-01
By means of Monte Carlo computer simulation and scaling theory, we study the domain growth kinetics associated with a weak first-order transition between two non-symmetry-related ordered phases, exemplified by martensitic transformations, surface reconstructions, or magnetic transitions. The model studied has two kinds of domain walls: sharp, straight stacking faults, and broad, curved solitonlike walls. The domain wall motion after a
Jakov V. Toporkov; Mark A. Sletten
2007-01-01
Statistical properties of the X-band sea clutter are studied using 2-D direct numerical simulations. Surfaces are modeled as realizations of a Gaussian random process with the Pierson-Moskowitz or Elfouhaily spectrum. The Creamer transform is further applied to account for the lowest-order surface nonlinearities. Backscattered field at a given frequency is found using the first-principles boundary integral equation (BIE) technique. Calculations
Nonlinear evolution of the MHD Kelvin-Helmholtz instability in a compressible plasma
S. H. Lai; L. H. Lyu
2006-01-01
Received 6 August 2004; revised 3 November 2005; accepted 9 November 2005; published 14 January 2006. (1) Kelvin-Helmholtz (K-H) instability at a magnetohydrodynamic (MHD) tangential discontinuity (TD) is studied by means of two-dimensional MHD simulation. The TD is of finite thickness with both magnetic shear and velocity shear across the TD. Our simulation results indicate that the nonlinear evolution of
NASA Astrophysics Data System (ADS)
Li, Hong; Zhang, Wei; Zhang, Zhenguo; Chen, Xiaofei
2015-07-01
A discontinuous grid finite-difference (FD) method with non-uniform time step Runge-Kutta scheme on curvilinear collocated-grid is developed for seismic wave simulation. We introduce two transition zones: a spatial transition zone and a temporal transition zone, to exchange wavefield across the spatial and temporal discontinuous interfaces. A Gaussian filter is applied to suppress artificial numerical noise caused by down-sampling the wavefield from the finer grid to the coarser grid. We adapt the non-uniform time step Runge-Kutta scheme to a discontinuous grid FD method for further increasing the computational efficiency without losing the accuracy of time marching through the whole simulation region. When the topography is included in the modelling, we carry out the discontinuous grid method on a curvilinear collocated-grid to obtain a sufficiently accurate free-surface boundary condition implementation. Numerical tests show that the proposed method can sufficiently accurately simulate the seismic wave propagation on such grids and significantly reduce the computational resources consumption with respect to regular grids.
Two-Fluid 2.5D MHD-Code for Simulations in the Solar Atmosphere
NASA Astrophysics Data System (ADS)
Piantschitsch, I.; Amerstorfer, U.; Thalmann, J.; Utz, D.; Hanslmeier, A.; Bárta, M.; Thonhofer, S.; Lemmerer, B.
We investigate magnetic reconnection due to the evolution of magnetic flux tubes in the solar chromosphere. We developed a new numerical two-fluid magnetohydrodynamic (MHD) code which will perform a 2.5D simulation of the dynamics from the upper convection zone up to the transition region. Our code is based on the Total Variation Diminishing Lax-Friedrichs scheme and makes use of an alternating-direction implicit method, in order to accommodate the two spatial dimensions. Since we apply a two-fluid model for our simulations, the effects of ion-neutral collisions, ionization/recombination, thermal/resistive diffusivity and collisional/resistive heating are included in the code. As initial conditions for the code we use analytically constructed vertically open magnetic flux tubes within a realistic stratified atmosphere. Initial MHD tests have already shown good agreement with known results of numerical MHD test problems like e.g. the Orszag-Tang vortex test.
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.
Two dimensional NMR spectroscopy
Schram, J.; Bellama, J.M.
1988-01-01
Two dimensional NMR represents a significant achievement in the continuing effort to increase solution in NMR spectroscopy. This book explains the fundamentals of this new technique and its analytical applications. It presents the necessary information, in pictorial form, for reading the ''2D NMR,'' and enables the practicing chemist to solve problems and run experiments on a commercial spectrometer by using the software provided by the manufacturer.
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)
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.
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.
Almarza, N G; P?kalski, J; Ciach, A
2014-04-28
The triangular lattice model with nearest-neighbor attraction and third-neighbor repulsion, introduced by P?kalski, 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. PMID:24784300
Davis, F.J. Jr.; Hassan, Y.A. (Texas A and M Univ., College Station, TX (United States). Coll. of Engineering)
1994-04-01
A major concern in the nuclear power industry is failure of the steam generator tubes. Failure of the tubes necessitates the plugging of the failed tubes with the result that nuclear plants are forced to operate at lower, or derated, power levels after expensive repairs. Turbulence-induced vibration is a primary cause of premature and accelerated fretting and wear of the steam generator tubes. An alternative unsteady analysis method for incompressible fluid flow problems is demonstrated. The approach employs large eddy simulation (LES) in conjunction with the finite element method (FEM). A segregated solution technique, solving for each field variable at all nodes, diminishes storage requirements by eliminating the need to solve the globally assembled finite element matrix. A direct benefit is that finer nodalizations can be employed. Equal-order quadrilateral elements are used to facilitate the segregated solution algorithm. The solution scheme is accurate to higher order to mitigate the effects of numerical diffusion in the advection terms. The Smagorinsky-type closure model for the sub-grid scale turbulence is used. The model is easily implemented into this algorithm. This combination of FEM and LES is unique. The time-dependent terms are explicitly treated. The time history of a steam generator tube bundle experiment is studied. The results show the applicability of FEM/LES and determine the prospects for further development of this methodology.
MHD simulation of an interaction of a shock wave with a magnetic cloud
M. Vandas; S. Fischer; M. Dryer; Z. Smith; T. Detman; A. Geranios
1997-01-01
Interplanetary shock waves, propagating in the heliosphere faster than earlier-emitted coronal ejecta, penetrate them and modify their parameters during this interaction. Using two and one half dimensional MHD simulations, we show how a magnetic cloud (flux rope) propagating with a speed 3 times higher than the ambient solar wind is affected by an even faster traveling shock wave overtaking the
Two-dimensional modeling of the formation of spheromak configurations
Jardin, S.C.; Park, W.
1980-09-01
A reduced set of two-dimensional MHD equations have been derived describing the axisymmetric time evolution of a MHD stable plasma evolving slowly due to resistive diffusion and changing boundary conditions. The equations are restricted to low ..beta.. but allow changing topology. They are integrated in time to demonstrate a possible spheromak formation method. External circuit equations are integrated simultaneously with the plasma equations to determine the electromagnetic boundary conditions self consistently. The effects of a finite conductivity vacuum chamber are included.
NASA Technical Reports Server (NTRS)
Wu, S. T.; Song, M. T.; Martens, P. C. H.; Dryer, M.
1991-01-01
A situation wherein a bipolar magnetic field embedded in a stratified solar atmosphere undergoes symmetrical shear motion at the footpoints is investigated via a 2D (nonplanar) MHD simulation. It was found that the vertical plasma flow velocities grow exponentially, leading to a new type of global MHD instability. The growth rate increases almost linearly until it reaches the same order of magnitude as the Alfven speed. Then a nonlinear MHD instability occurs beyond this point. It was found that the central loops are pinched by opposing Lorentz forces, and the outer closed loops stretch upward with the vertically-rising mass flow. The nonlinear dynamical shearing instability is illustrated by a numerical example that is given for three different values of the plasma beta that span several orders of magnitude.
NASA Astrophysics Data System (ADS)
Bankura, Arindam; Chandra, Amalendu
2015-01-01
The dynamics of proton transfer (PT) through hydrogen bonds in a two-dimensional water layer confined between two graphene sheets at room temperature are investigated through ab initio and quantum-classical simulations. The excess proton is found to be mostly solvated as an Eigen cation where the hydronium ion donates three hydrogen bonds to the neighboring water molecules. In the solvation shell of the hydronium ion, the three coordinated water molecules with two donor hydrogen bonds are found to be properly presolvated to accept a proton. Although no hydrogen bond needs to be broken for transfer of a proton to such presolvated water molecules from the hydronium ion, the PT rate is still found to be not as fast as it is for one-dimensional chains. Here, the PT is slowed down as the probability of finding a water with two donor hydrogen bonds in the solvation shell of the hydronium ion is found to be only 25%-30%. The hydroxide ion is found to be solvated mainly as a complex anion where it accepts four H-bonds through its oxygen atom and the hydrogen atom of the hydroxide ion remains free all the time. Here, the presolvation of the hydroxide ion to accept a proton requires that one of its hydrogen bonds is broken and the proton comes from a neighboring water molecule with two acceptor and one donor hydrogen bonds. The coordination number reduction by breaking of a hydrogen bond is a slow process, and also the population of water molecules with two acceptor and one donor hydrogen bonds is only 20%-25% of the total number of water molecules. All these factors together tend to slow down the hydroxide ion migration rate in two-dimensional water layers compared to that in three-dimensional bulk water.
Marocchino, A.; Atzeni, S.; Schiavi, A. [Dipartimento SBAI, Università di Roma “La Sapienza” and CNISM, Roma 00161 (Italy)] [Dipartimento SBAI, Università di Roma “La Sapienza” and CNISM, Roma 00161 (Italy)
2014-01-15
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.
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
Umeda, Takayuki, E-mail: umeda@stelab.nagoya-u.ac.jp; Kidani, Yoshitaka [Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya 464-8601 (Japan)] [Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya 464-8601 (Japan); Matsukiyo, Shuichi, E-mail: matsukiy@esst.kyushu-u.ac.jp [Earth System Science and Technology, Kyushu University, Kasuga 816-8580 (Japan)] [Earth System Science and Technology, Kyushu University, Kasuga 816-8580 (Japan); Yamazaki, Ryo, E-mail: ryo@phys.aoyama.ac.jp [Department of Physics and Mathematics, Aoyama Gakuin University, Sagamihara 252-5258 (Japan)] [Department of Physics and Mathematics, Aoyama Gakuin University, Sagamihara 252-5258 (Japan)
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.
Sharp, Leah Z.; Egorova, Dassia; Domcke, Wolfgang [Department of Chemistry, Technische Universitaet Muenchen, D-85747 Garching (Germany)
2010-01-07
Two-dimensional (2D) photon-echo spectra of a single subunit of the Fenna-Matthews-Olson (FMO) bacteriochlorophyll trimer of Chlorobium tepidum are simulated, employing the equation-of-motion phase-matching approach (EOM-PMA). We consider a slightly extended version of the previously proposed Frenkel exciton model, which explicitly accounts for exciton coherences in the secular approximation. The study is motivated by a recent experiment reporting long-lived coherent oscillations in 2D transients [Engel et al., Nature 446, 782 (2007)] and aims primarily at accurate simulations of the spectroscopic signals, with the focus on oscillations of 2D peak intensities with population time. The EOM-PMA accurately accounts for finite pulse durations as well as pulse-overlap effects and does not invoke approximations apart from the weak-field limit for a given material system. The population relaxation parameters of the exciton model are taken from the literature. The effects of various dephasing mechanisms on coherence lifetimes are thoroughly studied. It is found that the experimentally detected multiple frequencies in peak oscillations cannot be reproduced by the employed FMO model, which calls for the development of a more sophisticated exciton model of the FMO complex.
Subhash, P. V.; Madhavan, S.; Chaturvedi, S. [Institute for Plasma Research, Bhat, Gandhinagar-382 428, Gujarat (India)
2006-07-15
This article reports, for the first time, two-dimensional magnetohydrodynamic liner-on-plasma simulations for the compression phase of a magnetized target fusion (MTF) system with an inverse Z-pinch target. These simulations evolve the complete liner-plasma system along with the driving pulsed-power source. First, it has been demonstrated that closely coupled liner-on-plasma simulations produce results that are significantly different from loosely coupled simulations that have been reported in the literature. Second, it has been found that an initially stable plasma, satisfying the Kadomtsev criteria, and with a small initial pressure perturbation in the axial direction, remains stable all through the compression phase, even though there are large changes in the pressure and magnetic field levels. Third, a plasma that violates the Kadomtsev criteria, even by a small amount, turns out to be unstable, as predicted by theory. In practical terms, this means that it is preferable to stay well away from the stability limit, even at the cost of some reduction of initial plasma pressure. Fourth, even during the burn phase, when there is a large and rapid increase in plasma pressure due to fusion energy deposition, an initially stable plasma generally tends to remain stable, and even improves its stability margin. This observation shows that the inverse Z pinch is fairly benign as a MTF target, as an initially stable plasma remains stable during both the compression and burn phases. Fifth, certain unusual features are observed in the temperature profile--these depend upon the time scale for implosion. This has implications for plasma-surface interactions at the liner and central conductor.
MHD simulation of the solar wind interaction with the magnetosphere of Mercury
NASA Astrophysics Data System (ADS)
Varela, Jacobo; Pantellini, Filippo; Moncuquet, Michel
2014-05-01
We show MHD simulations of the solar wind interaction with the magnetosphere of Mercury. We use the open source codes Pluto and MPI-AMRVAC in 3 dimensional spherical geometry. In order to appreciate the limits of the MHD approach in the context of Mercury's environment we do first compare our simulations with hybrid simulation (e.g. Trávní?ek et al, Icarus, 209, pp 11-22, 2010). We do also compare magnetic field profiles from the magnetometer on Messenger with profiles sampled along the corresponding spacecraft trajectory in the simulations. These comparisons show that despite the lack of kinetic effects, MHD simulation provide a more than fair description of the interaction of the solar wind with Mercury at low computational cost making it a useful tool to help decrypt data from current and future exploratory missions in the hermean magnetosphere (e.g. Bepi Colombo-MMO). The research leading to these results has received funding from the European Commission's Seventh Framework Programme (FP7/2007-2013) under the grant agreement SHOCK (project number 284515).
NASA Astrophysics Data System (ADS)
Gao, Donghong
Interest in utilizing liquid metal film flows to protect the plasma-facing solid structures places increasing demand on understanding the magnetohydrodynamics (MHD) of such flows in a magnetic field with spatial variation. The field gradient effect is studied by a two-dimensional (2D) model in Cartesian coordinates. The thin film flow down an inclined plane in spanwise (z-direction) magnetic field with constant streamwise gradient and applied current is analyzed. The solution to the equilibrium flow shows forcefully the M-shaped velocity profile and dependence of side layer thickness on Ha-1/2 whose definition is based on field gradient. The major part of the dissertation is the numerical simulation of free surface film flows and understanding the results. The VOF method is employed to track the free surface, and the CSF model is combined with VOF method to account for surface dynamics condition. The code is validated with respect to Navier-Stokes solver and MHD implementation by computations of ordinary wavy films, MHD flat films and a colleague proposed film flow. The comparisons are performed against respective experimental, theoretical or numerical solutions, and the results are well matched with them. It is found for the ordinary water falling films, at low frequency and high flowrate, the small forcing disturbance at inlet flowrate develops into big roll waves preceded by small capillary bow waves; at high frequency and low Re, it develops into nearly sinusoidal waves with small amplitude and without fore-running capillary waves. The MHD surface instability is investigated for two kinds of film flows in constant streamwise field gradient: one with spatial disturbance and without surface tension, the other with inlet forcing disturbance and with surface tension. At no surface tension condition, the finite amplitude disturbance is rapidly amplified and degrades to irregular shape. With surface tension to maintain smooth interface, finite amplitude regular waves can be established only on near inlet region and they decay to nearly zero amplitude ripple on the far downstream region. At both film conditions, the wave traveling velocity is reduced by the MHD drag from field gradient. The code is also used to explore the exit-pipe and first wall conceptual designs for fusion reactor being proposed in the APEX program. It is seen that the field gradient restrains and lifts up the flow to the whole channel in the exit-pipe high field gradient condition, but an applied streamwise current can propel the flow through the gradient region. The Sn jet flow with high inertia is able to overcome the inverted gravity and MHD induction to form the desired protection liquid layer on top of the first wall.
Liu Xiangmei; Song Yuanhong; Xu Xiang; Wang Younian [School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian 116024 (China)
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.
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.
NASA Astrophysics Data System (ADS)
Amrani, M.; Benamara, Z.; Menezla, R.; Boudissa, A.; Chellali, M.; Brahim, T. Mohammed; Raoult, F.
2005-02-01
A two-dimensional numerical code is developed to model the effect of grains boundaries (g.b.) on the capacitance-voltage (C-V) characteristics of polysilicon diodes. The test structures are lateral polysilicon P+N diodes where the thickness of the film tf deposited by the low-pressure chemical vapour deposition method is 700 or 450 nm. The P+ and N dopings were performed by ion implantation using, respectively, boron in a dose of 2 × 1015 cm-2 and phosphorus in two doses of 1014 cm-2 for tf = 700 nm and 5 × 1014 cm-2 for tf = 450 nm. Using scanning electron microscopy, the presence of one grain boundary (g.b.) perpendicular to the metallurgic junction and localized at 100 nm of the interface deposition has been observed. In this work, we particularly investigate the effect of this g.b. on the C-V characteristics. The measured C-V characteristics at 100 kHz and 1 MHz show that the frequency effect is more important in the case of the weakly doped film (tf = 700 nm). A determination of the series resistance gives the profile doping concentration: abrupt (ND = 5.5 × 1018 cm-3) for tf = 700 nm and gradual (slope = 5 × 1025 cm-4) for tf = 450 nm. Using the previous experimental parameters in the two-dimensional simulation, we show that the presence of the perpendicular g.b. can reduce by up to 25% the capacitance of the diode and decreases considerably the VRP voltage that corresponds to the realizing-pinning of the electrostatic potential at the first parallel g.b. This effect is more important when the doping is gradual. The fit of the experimental curves gives, in the weak doping case (tf = 700 nm), the position of the first parallel g.b. (LG1 = 37.5 nm) and the density of the inter-granular trap states (NT = 3.2 × 1012 cm-2). On the other hand, when the doping is relatively strong (tf = 450 nm), the fit shows that the C-V characteristic is dominated much more by the doping profile than by the position of the first grain boundary and the density of the inter-granular trap states.
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.
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.
3D Simulations of Fluctuation Spectra in the Hall-MHD Plasma
Shaikh, Dastgeer; Shukla, P. K. [Center for Space Plasma and Aeronomic Research, University of Alabama in Huntsville, Huntsville. Alabama, 35899 (United States); Institut fuer Theoretische Physik IV, Ruhr-Universitaet Bochum, D-44780 Bochum, Germany, and School of Physics, University of KwaZulu-Natal, Durban (South Africa)
2009-01-30
Turbulent spectral cascades are investigated by means of fully three-dimensional (3D) simulations of a compressible Hall-magnetohydrodynamic (H-MHD) plasma in order to understand the observed spectral break in the solar wind turbulence spectra in the regime where the characteristic length scales associated with electromagnetic fluctuations are smaller than the ion gyroradius. In this regime, the results of our 3D simulations exhibit that turbulent spectral cascades in the presence of a mean magnetic field follow an omnidirectional anisotropic inertial-range spectrum close to k{sup -7/3}. The latter is associated with the Hall current arising from nonequal electron and ion fluid velocities in our 3D H-MHD plasma model.
NASA Astrophysics Data System (ADS)
Le, Q. V.; Chan, W. K.; Schwartz, J.
2014-11-01
Ag/AgX sheathed Bi2Sr2CaCu2Ox (Bi2212) is the only superconducting round wire (RW) with high critical current density (Jc) at high magnetic (>25 T) and is thus a strong candidate for high field magnets for nuclear magnetic resonance and high energy physics. A significant remaining challenge, however, is the relatively poor electromechanical behavior of Bi2212 RW, yet there is little understanding of the relationships between the internal Bi2212 microstructure and the mechanical behavior. This is in part due to the complex microstructures within the Bi2212 filaments and the uncertain role of interfilamentary bridges. Here, two-dimensional peridynamic simulations are used to study the stress distribution of the Bi2212 RWs under an axial tensile load. The simulations use scanning electron micrographs obtained from high Jc wires as a starting point to study the impact of various defects on the distribution of stress concentration within the Bi2212 microstructure and Ag. The flexibility of the peridynamic approach allows various defects, including those captured from SEM micrographs and artificially created defects, to be inserted into the microstructure for systematic study. Furthermore, this approach allows the mechanical properties of the defects to be varied, so the effects of porosity and both soft and hard secondary phases are evaluated. The results show significant stress concentration around defects, interfilamentary bridges and the rough Bi2212/Ag interface. In general, the stress concentration resulting from porosity is greater than that of solid-phase inclusions. A clear role of the defect geometry is observed. Results indicate that crack growth is likely to initiate at the Ag/Bi2212 interface or at voids, but that voids may also arrest crack growth in certain circumstances. These results are consistent with experimental studies of Bi2212 electromechanical behavior and magneto-optical imaging of crack growth.
Y. Ma; A. F. Nagy; T. Cravens; I. Sokolov
2004-01-01
We present our simulation results of the interaction between Saturn's magnetospheric plasma flow and Titan's atmosphere\\/ionosphere by using a multi-species global MHD model. A chemical model is used to describe Titan's atmosphere\\/ionosphere, which is based on 10 neutral and 7 ion spieces. This new model uses spherical coordinates (similar to our Mars model) leading to very good(~28km) altitude resolution. The
2D MHD Simulation of the Emergence and Merging of Coherent Structures
NASA Technical Reports Server (NTRS)
Wu, Cheng-Chin; Chang, Tom
2002-01-01
A model of sporadic localized merging of coherent structures has recently been proposed by Chang to describe the dynamics of the Earth's magnetotail. Here we report the results of MHD simulations regarding the development and merging of 2D coherent structures. With a magnetic shear. such coherent structures are generated in alignment with the imposed current sheet. The calculated fluctuation spectra suggest long-ranged correlations with power-law characteristics.
Nonthermal Emission in Radio Galaxies from Simulated Relativistic Electron Transport in 3D MHD Flows
I. L. Tregillis; T. W. Jones; Dongsu Ryu
2000-12-04
We perform a series of so-called ``synthetic observations'' on a set of 3D MHD jet simulations which explicitly include energy-dependent transport of relativistic electrons, as described in the companion paper by Jones, Tregillis, & Ryu. Analyzing them in light of the complex source dynamics and energetic particle distributions described in that paper, we find that the standard model for radiative aging in radio galaxies does not always adequately reflect the detailed source structure.
Bow shock and magnetopause contributions to the cross-tail current from global MHD simulations
B. B. Tang; X. C. Guo; C. Wang; Y. Q. Hu; J. R. Kan
2009-01-01
We performed a series of global MHD simulations to study the closure of the cross-tail current in the magnetotail under different solar wind conditions. The cross-tail current closes totally within the magnetopause, forming the classical $\\\\theta$ structure when IMF is set to be zero. The situation changes for southward IMF cases: part of the cross-tail current passes through the magnetosheath
Comparison of solar photospheric bright points between Sunrise observations and MHD simulations
NASA Astrophysics Data System (ADS)
Riethmüller, T. L.; Solanki, S. K.; Berdyugina, S. V.; Schüssler, M.; Martínez Pillet, V.; Feller, A.; Gandorfer, A.; Hirzberger, J.
2014-08-01
Bright points (BPs) in the solar photosphere are thought to be the radiative signatures (small-scale brightness enhancements) of magnetic elements described by slender flux tubes or sheets located in the darker intergranular lanes in the solar photosphere. They contribute to the ultraviolet (UV) flux variations over the solar cycle and hence may play a role in influencing the Earth's climate. Here we aim to obtain a better insight into their properties by combining high-resolution UV and spectro-polarimetric observations of BPs by the Sunrise Observatory with 3D compressible radiation magnetohydrodynamical (MHD) simulations. To this end, full spectral line syntheses are performed with the MHD data and a careful degradation is applied to take into account all relevant instrumental effects of the observations. In a first step it is demonstrated that the selected MHD simulations reproduce the measured distributions of intensity at multiple wavelengths, line-of-sight velocity, spectral line width, and polarization degree rather well. The simulated line width also displays the correct mean, but a scatter that is too small. In the second step, the properties of observed BPs are compared with synthetic ones. Again, these are found to match relatively well, except that the observations display a tail of large BPs with strong polarization signals (most likely network elements) not found in the simulations, possibly due to the small size of the simulation box. The higher spatial resolution of the simulations has a significant effect, leading to smaller and more numerous BPs. The observation that most BPs are weakly polarized is explained mainly by the spatial degradation, the stray light contamination, and the temperature sensitivity of the Fe i line at 5250.2 Å. Finally, given that the MHD simulations are highly consistent with the observations, we used the simulations to explore the properties of BPs further. The Stokes V asymmetries increase with the distance to the center of the mean BP in both observations and simulations, consistent with the classical picture of a production of the asymmetry in the canopy. This is the first time that this has been found also in the internetwork. More or less vertical kilogauss magnetic fields are found for 98% of the synthetic BPs underlining that basically every BP is associated with kilogauss fields. At the continuum formation height, the simulated BPs are on average 190 K hotter than the mean quiet Sun, the mean BP field strength is found to be 1750 G, and the mean inclination is 17°, supporting the physical flux-tube paradigm to describe BPs. On average, the synthetic BPs harbor downflows increasing with depth. The origin of these downflows is not yet understood very well and needs further investigation.
NASA Astrophysics Data System (ADS)
Huang, Can; Lu, Quanming; Lu, San; Wang, Peiran; Wang, Shui
2014-02-01
A magnetic island plays an important role in magnetic reconnection. In this paper, using a series of two-dimensional particle-in-cell simulations, we investigate the magnetic structures of a magnetic island formed during multiple X line magnetic reconnections, considering the effects of the guide field in symmetric and asymmetric current sheets. In a symmetric current sheet, the current in the x direction forms a tripolar structure inside a magnetic island during antiparallel reconnection, which results in a quadrupole structure of the out-of-plane magnetic field. With the increase of the guide field, the symmetry of both the current system and out-of-plane magnetic field inside the magnetic island is distorted. When the guide field is sufficiently strong, the current forms a ring along the magnetic field lines inside a magnetic island. At the same time, the current carried by the energetic electrons accelerated in the vicinity of the X lines forms another ring at the edge of the magnetic island. Such a dual-ring current system enhances the out-of-plane magnetic field inside the magnetic island with a dip in the center of the magnetic island. In an asymmetric current sheet, when there is no guide field, electrons flow toward the X lines along the separatrices from the side with a higher density and are then directed away from the X lines along the separatrices to the side with a lower density. The formed current results in the enhancement of the out-of-plane magnetic field at one end of the magnetic island and the attenuation at the other end. With the increase of the guide field, the structures of both the current system and the out-of-plane magnetic field are distorted.
Simulation of Radiation Belt Wave-Particle Interactions Using MHD-SDE Methods
NASA Astrophysics Data System (ADS)
Chan, A. A.; Elkington, S. R.; Albert, J. M.
2010-12-01
Interactions with a variety of plasma waves, including whistler-mode waves, EMIC waves and MHD waves, can cause significant local acceleration and loss, and/or radial transport of radiation belt particles, especially relativistic electrons. In this paper we report on the development of a new computational model designed to comprehensively simulate local acceleration/loss and radial transport in the radiation belts. The model uses bounce-averaged relativistic equations of motion to follow marker particles in the Lyon-Fedder-Mobarry global MHD code. The marker particles are subjected to energy and pitch-angle diffusion by a variety of high-frequency waves, including whistler waves and other ELF/VLF waves, by using stochastic differential equation (SDE) methods to diffusively adjust the marker-particle phase-space coordinates. The marker trajectories are used to construct phase-space densities and particle fluxes using Liouville-theorem weighting techniques similar to particle-in-cell methods. The new simulation model will calculate effects of (i) local acceleration and loss due to interactions with chorus, hiss, and EMIC waves, and magnetosonic equatorial noise, including quasilinear and non-quasilinear nonlinear interactions, and (ii) radial transport, including (but not restricted to) radial diffusion caused by MHD waves, all in a dynamic global magnetosphere.
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.
Radiation-MHD Simulations of Black Hole Accretion Flows and Outflows
NASA Astrophysics Data System (ADS)
Ohsuga, K.
2012-08-01
We perform two-dimensional radiation-magnetohydrodynamic simulations of the accretion disks, jets, and disk outflows around black holes. We can reproduce the three distinct inflow-outflow modes, which corresponds to the two-dimensional version of the slim disk model, the standard disk model, and the radiatively inefficient accretion flow, with one numerical code. In the case of the super-Eddington accretion flow, we find that a radiatively driven, magnetically collimated jet is produced around the rotation axis and that a time-dependent, clumpy outflow with larger opening angle forms. Such jet and outflow might resolve the relativistic powerful jets of the luminous compact objects and the ultra fast outflows of active galactic nuclei.
Energy storage and dissipation in the magnetotail during substorms. 2. MHD simulations
Steinolfson, R.S. (Southwest Research Inst., San Antonio, TX (United States)); Winglee, R.M. (Univ. of Washington, Seattle (United States))
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.
Gravity waves in magnetized solar atmospheres from MHD simulations.
NASA Astrophysics Data System (ADS)
Jackiewicz, Jason; Gangadharan, Vigeesh
2014-06-01
The solar atmosphere is believed to be a region where gravity waves are generated and propagate, but a variety of effects makes observations of them rather difficult. Measurements of gravity wave properties could, however, show how they play an important role in the upper photosphere and chromosphere and even deposit energy there. Here we show how analysis of gravity waves from detailed numerical simulations can be used to study magnetic fields and energy deposition in the atmosphere, and how mode conversion to slow magneto-acoustic waves changes their observable properties.
Wagner, Daniel M.
2013-01-01
In the early morning hours of June 11, 2010, substantial flooding occurred at Albert Pike Recreation Area in the Ouachita National Forest of west-central Arkansas, killing 20 campers. The U.S. Forest Service needed information concerning the extent and depth of flood inundation, the water velocity, and flow paths throughout Albert Pike Recreation Area for the flood and for streamflows corresponding to annual exceedence probabilities of 1 and 2 percent. The two-dimensional flow model Fst2DH, part of the Federal Highway Administration’s Finite Element Surface-water Modeling System, and the graphical user interface Surface-water Modeling System (SMS) were used to perform a steady-state simulation of the flood in a 1.5-mile reach of the Little Missouri River at Albert Pike Recreation Area. Peak streamflows of the Little Missouri River and tributary Brier Creek served as inputs to the simulation, which was calibrated to the surveyed elevations of high-water marks left by the flood and then used to predict flooding that would result from streamflows corresponding to annual exceedence probabilities of 1 and 2 percent. The simulated extent of the June 11, 2010, flood matched the observed extent of flooding at Albert Pike Recreation Area. The mean depth of inundation in the camp areas was 8.5 feet in Area D, 7.4 feet in Area C, 3.8 feet in Areas A, B, and the Day Use Area, and 12.5 feet in Lowry’s Camp Albert Pike. The mean water velocity was 7.2 feet per second in Area D, 7.6 feet per second in Area C, 7.2 feet per second in Areas A, B, and the Day Use Area, and 7.6 feet per second in Lowry’s Camp Albert Pike. A sensitivity analysis indicated that varying the streamflow of the Little Missouri River had the greatest effect on simulated water-surface elevation, while varying the streamflow of tributary Brier Creek had the least effect. Simulated water-surface elevations were lower than those modeled by the U.S. Forest Service using the standard-step method, but the comparison between the two was favorable with a mean absolute difference of 0.58 feet in Area C and 0.32 feet in Area D. Results of a HEC-RAS model of the Little Missouri River watershed upstream from the U.S. Geological Survey streamflow-gaging station near Langley showed no difference in mean depth in the areas in common between the models, and a difference in mean velocity of only 0.5 foot per second. Predictions of flooding that would result from streamflows corresponding to annual exceedence probabilities of 1 and 2 percent indicated that the extent of inundation of the June 11, 2010, flood exceeded that of the 1 percent flood, and that for both the 1 and 2 percent floods, all of Areas C and D, and parts of Areas A, B, and the Day Use Area were inundated. Predicted water-surface elevations for the 1 and 2 percent floods were approximately 1 foot lower than those predicted by the U.S. Forest Service using a standard-step model.
Two-dimensional river modeling
Thompson, James Cameron
1988-01-01
as to the best use of two-dimensional river models, and recommendations are made for the application and further development of two-dimensional river models. This thesis contains four sample applications using the finite Element hzurface-Water godeling ~S...
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.
NASA Technical Reports Server (NTRS)
Klimas, A. J.; Uritsky, V.; Vassiliadis, D.; Baker, D. N.
2005-01-01
Loading and consequent unloading of magnetic flux is an essential element of the substorm cycle in Earth's magnetotail. We are unaware of an available global MHD magnetospheric simulation model that includes a loading- unloading cycle in its behavior. Given the central role that MHD models presently play in the development of our understanding of magnetospheric dynamics, and given the present plans for the central role that these models will play in ongoing space weather prediction programs, it is clear that this failure must be corrected. A 2-dimensional numerical driven current-sheet model has been developed that incorporates an idealized current- driven instability with a resistive MHD system. Under steady loading, the model exhibits a global loading- unloading cycle. The specific mechanism for producing the loading-unloading cycle will be discussed. It will be shown that scale-free avalanching of electromagnetic energy through the model, from loading to unloading, is carried by repetitive bursts of localized reconnection. Each burst leads, somewhat later, to a field configuration that is capable of exciting a reconnection burst again. This process repeats itself in an intermittent manner while the total field energy in the system falls. At the end of an unloading interval, the total field energy is reduced to well below that necessary to initiate the next unloading event and, thus, a loading-unloading cycle results. It will be shown that, in this model, it is the topology of bursty localized reconnection that is responsible for the appearance of the loading-unloading cycle.
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.
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.
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.
Numerical Simulations of Driven Supersonic Relativistic MHD Turbulence
NASA Astrophysics Data System (ADS)
Zrake, Jonathan; MacFadyen, Andrew
2011-08-01
Models for GRB outflows invoke turbulence in relativistically hot magnetized fluids. In order to investigate these conditions we have performed high-resolution three-dimensional numerical simulations of relativistic magneto-hydrodynamical (RMHD) turbulence. We find that magnetic energy is amplified to several percent of the total energy density by turbulent twisting and folding of magnetic field lines. Values of ?B>~0.01 are thus naturally expected. We study the dependence of saturated magnetic field energy fraction as a function of Mach number and relativistic temperature. We then present power spectra of the turbulent kinetic and magnetic energies. We also present solenoidal (curl-like) and dilatational (divergence-like) power spectra of kinetic energy. We propose that relativistic effects introduce novel couplings between these spectral components. The case we explore in most detail is for equal amounts of thermal and rest mass energy, corresponding to conditions after collisions of shells with relative Lorentz factors of several. These conditions are relevant in models for internal shocks, for the late afterglow phase, for cocoon material along the edge of a relativistic jet as it propagates through a star, as well neutron stars merging with each other and with black hole companions. We find that relativistic turbulence decays extremely quickly, on a sound crossing time of an eddy. Models invoking sustained relativistic turbulence to explain variability in GRB prompt emission are thus strongly disfavored unless a persistant driving of the turbulence is maintained for the duration of the prompt emission.
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...
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.
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.
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.
Comparison of resistive MHD simulations and experimental CHI discharges in NSTX
NASA Astrophysics Data System (ADS)
Hooper, E. B.; Sovinec, C. R.; Raman, R.; Fatima, F.
2013-10-01
Resistive MHD simulations using NIMROD simulate CHI discharges for NSTX startup plasmas. Quantitative comparison with experiment ensures that the simulation physics includes a minimal physics set needed to extend the simulations to new experiments, e.g. NSTX-U. Important are time-varying vacuum magnetic field, ohmic heating, thermal transport, impurity radiation, and spatially-varying plasma parameters including density. Equilibria are compared with experimental injector currents, voltages and parameters including toroidal current, photographs of emitted light and measurements of midplane temperature profiles, radiation and surface heating. Initial results demonstrate that adjusting impurity radiation and cross-field transport yields temperatures and injected-current channel widths similar to experiment. These determine the plasma resistance, feeding back to the impedance on the injector power supply. Resistive MHD simulations using NIMROD simulate CHI discharges for NSTX startup plasmas. Quantitative comparison with experiment ensures that the simulation physics includes a minimal physics set needed to extend the simulations to new experiments, e.g. NSTX-U. Important are time-varying vacuum magnetic field, ohmic heating, thermal transport, impurity radiation, and spatially-varying plasma parameters including density. Equilibria are compared with experimental injector currents, voltages and parameters including toroidal current, photographs of emitted light and measurements of midplane temperature profiles, radiation and surface heating. Initial results demonstrate that adjusting impurity radiation and cross-field transport yields temperatures and injected-current channel widths similar to experiment. These determine the plasma resistance, feeding back to the impedance on the injector power supply. Work performed under the auspices of the U.S. Department of Energy under contracts DE-AC52-07NA27344 at LLNL and DE-AC02-09CH11466 at PPPL, and grants DE-FC02-05ER54813 at PSI Center (U. Wisc.) and DOE-FG02-12ER55115 (at Princeton U.).
Inertial Current Generators of Poynting Flux in MHD Simulations of Black Hole Ergospheres
Brian Punsly
2005-05-04
This Letter investigates the physics that is responsible for creating the current system that supports the outgoing Poynting flux emanating from the ergosphere of a rotating black hole in the limit that the magnetic energy density greatly exceeds the plasma rest mass density (magnetically dominated limit). The underlying physics is derived from published three-dimensional simulations that obey the general relativistic equations of perfect magnetohydrodynamics (MHD). It is found that the majority of the Poynting flux emitted from the magnetically dominated regions of the ergosphere has a source associated with inertial effects outside of the event horizon.
Testing the Connection Between Radio Mini-Halos and Core Gas Sloshing with MHD Simulations
ZuHone, John; Brunetti, Gianfranco
2011-01-01
Radio mini-halos are diffuse, steep-spectrum synchrotron sources associated with relaxed clusters of galaxies. Observations of some mini-halo sources indicate a correlation between the radio emission and the X-ray signature of gas sloshing, ``cold fronts.'' Some authors have suggested turbulence associated with the sloshing motions reaccelerate relativistic electrons, resulting in emission associated with the fronts. We present MHD simulations of core gas sloshing in a galaxy cluster, where we measure the turbulence created by these motions and employ passive tracer particles to act as relativistic electrons that may be accelerated by such turbulence. Our preliminary results support such a link between sloshing motions and particle reacceleration.
MHD Simulations of the Solar Corona in Early August 2010 Using the HMI Magnetic Field Data
NASA Astrophysics Data System (ADS)
Hayashi, Keiji; Zhao, X.; Liu, Y.; Sun, X.; Hoeksema, J.; HMI Team
2011-05-01
The HMI is observing the line-of-sight magnetic field, vector field and the Doppler plasma velocity. The full-disk magnetogram observation with high temporal and spatial resolution provides better global solar magnetic field map, in that the data gap is minimized and the noise level is quite low. To utilize the benefit of the HMI's magnetogram observation, we conducted the MHD simulation of the global solar corona using the HMI data. We chose a period around August 1st, 2010, to see how the magnetic field connectivity in the global scale had changed around the period: In early August period, the changes of the global coronal magnetic field seen at the entire Earth-side hemisphere seem to be well related with the emergence of the sunspot at the north-east part of the full disk images, though the dynamics involving both magnetic field and plasma will be retrieved by means of the MHD simulation models. We used the synchronic frame format to make the global solar surface magnetic field maps so that the magnetic field distribution at the time of interest will be better specified thus the simulated situation will be more realistic. In addition, we used the daily-updated global maps that are made by regularly replacing the portion of the global map with the meridional slip of the full-disk data on regular (daily) basis as well as the standard ones that are well low-nose dataset made with better-calibrated data.
NASA Technical Reports Server (NTRS)
1982-01-01
Information on the Japanese National Aerospace Laboratory two dimensional transonic wind tunnel, completed at the end of 1979 is presented. Its construction is discussed in detail, and the wind tunnel structure, operation, test results, and future plans are presented.
Galloway, Joel M.; Green, W. Reed
2007-01-01
Beaver Lake is considered a primary watershed of concern in the State of Arkansas. As such, information is needed to assess water quality, especially nutrient enrichment, nutrient-algal relations, turbidity, and sediment issues within the system. A previously calibrated two-dimensional, laterally averaged model of hydrodynamics and water quality was used for the evaluation of changes in input nutrient and sediment concentrations on the water quality of the reservoir for the period of April 2001 to April 2003. Nitrogen and phosphorus concentrations were increased and decreased and tested independently and simultaneously to examine the nutrient concentrations and algal response in the reservoir. Suspended-solids concentrations were increased and decreased to identify how solids are distributed in the reservoir, which can contribute to decreased water clarity. The Beaver Lake model also was evaluated using a conservative tracer. A conservative tracer was applied at various locations in the reservoir model to observe the fate and transport and how the reservoir might react to the introduction of a conservative substance, or a worst-case spill scenario. In particular, tracer concentrations were evaluated at the locations of the four public water-supply intakes in Beaver Lake. Nutrient concentrations in Beaver Lake increased proportionally with increases in loads from the three main tributaries. An increase of 10 times the calibrated daily input nitrogen and phosphorus in the three main tributaries resulted in daily mean total nitrogen concentrations in the epilimnion that were nearly 4 times greater than the calibration concentrations at site L2 and more than 2 times greater than the calibrated concentrations at site L5. Increases in daily input nitrogen in the three main tributaries independently did not correspond in substantial increases in concentrations of nitrogen in Beaver Lake. The greatest proportional increase in phosphorus occurred in the epilimnion at sites L3 and L4 and the least increase occurred at sites L2 and L5 when calibrated daily input phosphorus concentrations were increased. When orthophosphorus was increased in all three tributaries simultaneously by a factor of 10, daily mean orthophosphorus concentrations in the epilimnion of the reservoir were almost 11 times greater than the calibrated concentrations at sites L2 and L5, and 15 times greater in the epilimnion of the reservoir at sites L3 and L4. Phosphorus concentrations in Beaver Lake increased less when nitrogen and phosphorus were increased simultaneously than when phosphorus was increased independently. The greatest simulated increase in algal biomass (represented as chlorophyll a) occurred when nitrogen and phosphorus were increased simultaneously in the three main tributaries. On average, the chlorophyll a values only increased less than 1 microgram per liter when concentrations of nitrogen or phosphorous were increased independently by a factor of 10 at all three tributaries. In comparison, when nitrogen and phosphorus were increased simultaneously by a factor of 10 for all three tributaries, the chlorophyll a concentration increased by about 10 micrograms per liter on average, with a maximum increase of about 57 micrograms per liter in the epilimnion at site L3 in Beaver Lake. Changes in algal biomass with changes in input nitrogen and phosphorus were variable through time in the Beaver Lake model from April 2001 to April 2003. When calibrated daily input nitrogen and phosphorus concentrations were increased simultaneously for the three main tributaries, the increase in chlorophyll a concentration was the greatest in late spring and summer of 2002. Changes in calibrated daily input inorganic suspended solids concentrations were examined because of the effect they may have on water clarity in Beaver Lake. The increase in total suspended solids was greatest in the hypolimnion at the upstream end of Beaver Lake, and negligible changes
Chatterjee, Dipankar; Amiroudine, Sakir
2011-02-01
A comprehensive non-isothermal Lattice Boltzmann (LB) algorithm is proposed in this article to simulate the thermofluidic transport phenomena encountered in a direct-current (DC) magnetohydrodynamic (MHD) micropump. Inside the pump, an electrically conducting fluid is transported through the microchannel by the action of an electromagnetic Lorentz force evolved out as a consequence of the interaction between applied electric and magnetic fields. The fluid flow and thermal characteristics of the MHD micropump depend on several factors such as the channel geometry, electromagnetic field strength and electrical property of the conducting fluid. An involved analysis is carried out following the LB technique to understand the significant influences of the aforementioned controlling parameters on the overall transport phenomena. In the LB framework, the hydrodynamics is simulated by a distribution function, which obeys a single scalar kinetic equation associated with an externally imposed electromagnetic force field. The thermal history is monitored by a separate temperature distribution function through another scalar kinetic equation incorporating the Joule heating effect. Agreement with analytical, experimental and other available numerical results is found to be quantitative. PMID:21053082
Tail Current Sheet Under Strong Driving: MHD Simulations and in-situ Observations Compared
NASA Astrophysics Data System (ADS)
Pulkkinen, T. I.; Goodrich, C. C.; Lyon, J.; Baker, D. N.; Wiltberger, M.
2006-05-01
We use in-situ multipoint measurements and global MHD simulations to examine the large-scale structure of the tail current sheet and its response to the variable solar wind driving. The Lyon - Fedder - Mobarry code was run for three events: A substorm on Aug 11, 2002, a steady convection event on Feb 4, 1998, and a sawtooth event on Apr 18, 2002. For each of the events, multispacecraft observations in the inner and mid-magnetotail reveal the timing, location, and structure of an intense current sheet that developed in the tail. Each of the events was driven by an extended period of southward IMF, but the dynamics were quite different: During the substorm, gradual intensification and thinning of the current sheet led to the substorm onset after about 1 hour of growth phase. The SMC period was characterized by a relatively intense current sheet that remained stable over a period of almost 9 hours. The sawtooth events show repeated injections, which disrupt part, but not all, of the current in the inner magnetosphere. We use the MHD simulations to quantify the magnetospheric response to the solar wind driving and to seek for dynamic elements in the global system that control the large-scale response of the magnetotail.
MHD simulation for the interaction of an interplanetary shock with the Earth's magnetosphere
NASA Astrophysics Data System (ADS)
Samsonov, A. A.; Sibeck, D. G.; Imber, J.
2007-12-01
The global BATS-R-US MHD code is used to simulate the interaction of a moderately strong interplanetary shock with the Earth's magnetosphere. The model predicts the propagation of a transmitted fast shock through the magnetosheath and magnetosphere and the reflection of this shock from the inner numerical boundary. The reflected fast shock propagates sunward through the dayside magnetosphere and magnetosheath. The passage of the transmitted shock causes the bow shock and magnetopause to move inward, while the passage of the reflected fast shock causes these boundaries to move outward, consistent with previously reported in situ observations. A supplementary study employing a one-dimensional MHD model addresses the interaction of the forward fast shock with the plasmapause. This study demonstrates that most of the energy associated with the fast shock energy penetrates into the plasmasphere. Consequently, the transmitted fast wave must reach the ionosphere, produce the well known sudden impulse signatures, and then be reflected due to the shielding effects of ionospheric currents. The predictions of the numerical simulations are consistent with observations of the dayside geosynchronous magnetic field.
Broken ergodicity in two-dimensional homogeneous magnetohydrodynamic turbulence
Shebalin, John V. [Astromaterials Research and Exploration Science Office, NASA Johnson Space Center, Houston, Texas 77058-3696 (United States)
2010-09-15
Two-dimensional (2D) homogeneous magnetohydrodynamic (MHD) turbulence has many of the same qualitative features as three-dimensional (3D) homogeneous MHD turbulence. These features include several ideal (i.e., nondissipative) invariants along with the phenomenon of broken ergodicity (defined as nonergodic behavior over a very long time). Broken ergodicity appears when certain modes act like random variables with mean values that are large compared to their standard deviations, indicating a coherent structure or dynamo. Recently, the origin of broken ergodicity in 3D MHD turbulence that is manifest in the lowest wavenumbers was found. Here, we study the origin of broken ergodicity in 2D MHD turbulence. It will be seen that broken ergodicity in ideal 2D MHD turbulence can be manifest in the lowest wavenumbers of a finite numerical model for certain initial conditions or in the highest wavenumbers for another set of initial conditions. The origins of broken ergodicity in an ideal 2D homogeneous MHD turbulence are found through an eigenanalysis of the covariance matrices of the probability density function and by an examination of the associated entropy functional. When the values of ideal invariants are kept fixed and grid size increases, it will be shown that the energy in a few large modes remains constant, while the energy in any other mode is inversely proportional to grid size. Also, as grid size increases, we find that broken ergodicity becomes manifest at more and more wavenumbers.
3D MHD simulation of Caltech Plasma Jet Experiment and Implications for Astrophysical Jets
NASA Astrophysics Data System (ADS)
Zhai, Xiang
2014-10-01
Magnetic fields are believed to play an essential role in astrophysical jets with observations suggesting the presence of helical magnetic fields. In this talk we present 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, poloidal current, 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. The work has been done under the collaboration between Caltech Bellan group and LANL Li group.
NASA Technical Reports Server (NTRS)
Benyo, Theresa L.
2011-01-01
Flow matching has been successfully achieved for an MHD energy bypass system on a supersonic turbojet engine. The Numerical Propulsion System Simulation (NPSS) environment helped perform a thermodynamic cycle analysis to properly match the flows from an inlet employing a MHD energy bypass system (consisting of an MHD generator and MHD accelerator) on a supersonic turbojet engine. Working with various operating conditions (such as the applied magnetic field, MHD generator length and flow conductivity), interfacing studies were conducted between the MHD generator, the turbojet engine, and the MHD accelerator. This paper briefly describes the NPSS environment used in this analysis. This paper further describes the analysis of a supersonic turbojet engine with an MHD generator/accelerator energy bypass system. Results from this study have shown that using MHD energy bypass in the flow path of a supersonic turbojet engine increases the useful Mach number operating range from 0 to 3.0 Mach (not using MHD) to a range of 0 to 7.0 Mach with specific net thrust range of 740 N-s/kg (at ambient Mach = 3.25) to 70 N-s/kg (at ambient Mach = 7). These results were achieved with an applied magnetic field of 2.5 Tesla and conductivity levels in a range from 2 mhos/m (ambient Mach = 7) to 5.5 mhos/m (ambient Mach = 3.5) for an MHD generator length of 3 m.
3D MHD Simulations of Spontaneous Flow Ejections by Turbulent Convection into the Chromosphere
NASA Astrophysics Data System (ADS)
Kitiashvili, I.; Kosovichev, A. G.; Mansour, N.; Wray, A.
2012-12-01
Dynamical interaction of the highly turbulent subsurface and the low atmosphere layers is a source of many observed phenomena on various scales in the solar chromosphere. We investigate the energetic and dynamical links between the turbulent convection and the chromosphere by using 3D radiative MHD simulations. Our simulations of quiet-Sun regions reveal ubiquitous formation of small-scale vortex tubes which can drive flow ejections into the chromosphere. The vortex tubes are formed through two basic mechanisms: convective instability inside the granules and the Kelvin-Helmholtz instability in the intergranular lanes. During their formation the vortex tubes become mostly vertical and usually can be detected in the intergranular lanes. Dispute their small scale the vortex tubes represent highly dynamical structures, which can capture surrounding magnetic field and easily penetrate into the atmosphere layers, producing quasi-periodic flow ejections, shocks and Alfven waves, and contribute to the chromosphere heating.
GPU Particle Tracking and MHD Simulations with Greatly Enhanced Computational Speed
NASA Astrophysics Data System (ADS)
Ziemba, T.; O'Donnell, D.; Carscadden, J.; Cash, M.; Winglee, R.; Harnett, E.
2008-12-01
GPUs are intrinsically highly parallelized systems that provide more than an order of magnitude computing speed over a CPU based systems, for less cost than a high end-workstation. Recent advancements in GPU technologies allow for full IEEE float specifications with performance up to several hundred GFLOPs per GPU, and new software architectures have recently become available to ease the transition from graphics based to scientific applications. This allows for a cheap alternative to standard supercomputing methods and should increase the time to discovery. 3-D particle tracking and MHD codes have been developed using NVIDIA's CUDA and have demonstrated speed up of nearly a factor of 20 over equivalent CPU versions of the codes. Such a speed up enables new applications to develop, including real time running of radiation belt simulations and real time running of global magnetospheric simulations, both of which could provide important space weather prediction tools.
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.
Acoustics 2000 1 The Two Dimensional Numerical Modeling
account for wave propagation in the seabed but an acoustic wave approximation is often used for seabedAcoustics 2000 1 The Two Dimensional Numerical Modeling Of Acoustic Wave Propagation in Shallow on a two dimensional numerical simulation of acoustic wave propagation that has been developed to visualize
Numerical model of a two-dimensional, non-plane transient magnetohydrodynamic flow
NASA Technical Reports Server (NTRS)
Han, S. M.; Wu, S. T.; Nakagawa, Y.
1982-01-01
The equations describing two-dimensional three-component magnetohydrodynamic (MHD) transient flows are formulated for a system of spherical coordinates. With the numerical code based on Implicit Continuous Fluid Eulerian (ICE) scheme, MHD flows resulting from a sudden energy release in a stratified medium are examined. Because of the inclusion of out-of-plane components of velocity and magnetic fields, MHD transverse waves are observed in addition to fast, slow and entropy waves. Numerical results for compressible MHD shocks are found in satisfactory agreement with the theoretical predictions.
NASA Astrophysics Data System (ADS)
Kanki, Takashi; Nagata, Masayoshi; Kagei, Yasuhiro
2011-10-01
The dynamics of structures of magnetic field, current density, and plasma flow generated during multi-pulsed coaxial helicity injection in spherical torus is investigated by 3-D nonlinear MHD simulations. During the driven phase, the flux and current amplifications occur due to the merging and magnetic reconnection between the preexisting plasma in the confinement region and the ejected plasma from the gun region involving the n = 1 helical kink distortion of the central open flux column (COFC). Interestingly, the diamagnetic poloidal flow which tends toward the gun region is then observed due to the steep pressure gradients of the COFC generated by ohmic heating through an injection current winding around the inboard field lines, resulting in the formation of the strong poloidal flow shear at the interface between the COFC and the core region. This result is consistent with the flow shear observed in the HIST. During the decay phase, the configuration approaches the axisymmetric MHD equilibrium state without flow because of the dissipation of magnetic fluctuation energy to increase the closed flux surfaces, suggesting the generation of ordered magnetic field structure. The parallel current density ? concentrated in the COFC then diffuses to the core region so as to reduce the gradient in ?, relaxing in the direction of the Taylor state.
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.
NASA Astrophysics Data System (ADS)
Pantellini, Filippo; Griton, Léa; Varela, Jacobo
2015-07-01
We show that slow mode compressional fronts form upstream of the day side magnetopause in MHD simulations of Mercury's magnetosphere. The strongest compressional fronts are located upstream of the magnetopause with strong magnetic shear. Compressional fronts are crossed by magnetic field lines connecting the interplanetary magnetic field and the planet's intrinsic field, their role is to bend the magnetic field in the magnetosheath towards the magnetopause. Besides these compressional fronts, already observed in space and theoretically discussed by various authors for the case of the Earth, we observe the formation of a slow mode standing rarefaction wave spatially growing over a substantial fraction of the distance between the bow shock and the magnetopause. The slow mode source region for the rarefaction waves is located in the magnetosheath, near the bow shock's nose. The generated standing rarefaction waves, however, form even at large distances from the source region along the magnetospheric flanks. They fine-tune the magnetic field line draping and plasma flow around the magnetopause. In ideal MHD the magnetospheres of Mercury, the Earth and the giant planets do closely resemble each other, we therefore expect the mentioned slow mode structures not to be specific to Mercury.
Cloaking two-dimensional fermions
Lin, De-Hone [Department of Physics, National Sun Yat-sen University, Kaohsiung, Taiwan (China)
2011-09-15
A cloaking theory for a two-dimensional spin-(1/2) fermion is proposed. It is shown that the spinor of the two-dimensional fermion can be cloaked perfectly through controlling the fermion's energy and mass in a specific manner moving in an effective vector potential inside a cloaking shell. Different from the cloaking of three-dimensional fermions, the scaling function that determines the invisible region is uniquely determined by a nonlinear equation. It is also shown that the efficiency of the cloaking shell is unaltered under the Aharonov-Bohm effect.
Juckem, Paul F.; Hunt, Randall J.
2008-01-01
A two-dimensional, steady-state ground-water-flow model of the shallow ground-water-flow system near the community of New Post, Sawyer County, Wis., was refined from an existing model of the area. Hydraulic-conductivity and recharge values were not changed from the existing model for the scenario simulations described in this report. Rather, the model was refined by adding detail along the Chippewa Flowage and then was used to simulate contributing areas for three potential replacement wells pumping 30,000 gallons per day. The model also was used to simulate potential surface-water leakage out of the Chippewa Flowage captured by replacement-well pumping. A range in resistance to vertical ground-water flow was simulated along the Chippewa Flowage for each potential replacement-well location to bound the potential effects of representing three-dimensional flow with a two-dimensional model. Results indicate that pumping from a replacement well sited about 130 feet from the Chippewa Flowage could capture as much as 39 percent of the total pumping from the flowage. Pumping from either of two potential replacement wells sited at least 400 feet from the Chippewa Flowage did not induce surface-water leakage out of the flowage regardless of the resistance applied along the flowage for simulations described in this report.
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.
M. Palmroth; P. Janhunen; G. Germany; D. Lummerzheim; K. Liou; D. N. Baker; C. Barth; A. T. Weatherwax; J. Watermann
2006-01-01
We compare the ionospheric electron precipitation morphology and power from a global MHD simulation (GUMICS-4) with direct measurements of auroral energy flux during a pair of substorms on 28-29 March 1998. The electron precipitation power is computed directly from global images of auroral light observed by the Polar satellite ultraviolet imager (UVI). Independent of the Polar UVI measurements, the electron
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 B y components. The first event occurred on 8 May 2004, while both spacecraft were exploring the dawn flank of the
Bow shock contributions to region 1 field-aligned current: A new result from global MHD simulations
X. C. Guo; C. Wang; Y. Q. Hu; J. R. Kan
2008-01-01
We present a new result, based on a global MHD simulation model, that the bow shock contributes significantly to the region 1 field-aligned current (FAC) under strong southward interplanetary magnetic field conditions. More than 50 percent of the total region 1 FAC may originate from the bow shock in certain circumstances. Stronger southward interplanetary magnetic field, higher solar wind speed,
3D HD and MHD Adaptive Mesh Refinement Simulations of the Global and Local ISM
Miguel A. de Avillez; Dieter Breitschwerdt
2004-02-18
We have performed high resolution 3D simulations with adaptive mesh refinement, following the ISM evolution in a star forming galaxy both on small (10 kpc) scales, enabling us to track structures in cooling shock compressed regions as well as the entire Galactic fountain flow. It is shown in an MHD run that the latter one is not inhibited by a large scale disk parallel magnetic field. The fountain plays a vital role in limiting the volume filling factor of the hot gas. Contrary to classical models most of the gas between 100K and 8000 K is found to be thermally unstable. On scales of superbubbles we find that the internal temperature structure is rather inhomogeneous for an old object like our Local Bubble, leading to low OVI column densities, consistent with observations.
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.
External Sources of Poynting Flux in MHD Simulations of Black Hole Ergospheres
Brian Punsly
2005-10-31
This article investigates the physics that is responsible for creating the outgoing Poynting flux emanating from the ergosphere of a rotating black hole in the limit that the magnetic energy density greatly exceeds the plasma rest mass density (magnetically dominated limit). The underlying physics is derived from published 3-D simulations that obey the general relativistic equations of perfect magnetohydrodynamics (MHD). It is found that the majority of the outgoing radial Poynting flux emitted from the magnetically dominated regions of the ergosphere is injected into the magnetosphere by a source outside of the event horizon. It is concluded that the primary source of the Poynting flux is associated with inertial forces in the magnetically dominated region proper or in the lateral boundaries of the region. However, the existing numerical data does not rule out the possibility that large computational errors are actually the primary source of the Poynting flux.
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.
Numerical flow simulation in the slagging stage of an MHD coal combustor
Norton, O.P.; Skaggs, A.; Bouchillon, C.W. [Mississippi State Univ., MS (United States)
1994-01-01
A numerical model has been developed to simulate the flow in a swirling flow MHD coal combustor. This model was developed using a commercial computational fluid dynamics package, PHOENICS, distributed by CHAM of North America. PHOENICS uses a finite volume formulation to solve the discretized equations of continuity and momentum. The SIMPLE algorithm is used to correct the pressure field in such a way that the velocity field solves the continuity equation. Both a standard k - {epsilon} model and a modified k - {epsilon} model were used to model the turbulence in the combustor. When the model results are compared with experimental velocity measurements, both models seem to have difficulties predicting the swirling flow in this combustor. It is concluded that other types of turbulence models should be investigated, such as nonisotropic Reynolds stress models.
3D MHD Simulation of Flare Supra-Arcade Downflows in a Turbulent Current Sheet Medium
NASA Astrophysics Data System (ADS)
Cécere, M.; Zurbriggen, E.; Costa, A.; Schneiter, M.
2015-07-01
Supra-arcade downflows (SADs) are sunward, generally dark, plasma density depletions originated above posteruption flare arcades. In this paper, using 3D MHD simulations we investigate whether the SAD cavities can be produced by a direct combination of the tearing mode and Kelvin–Helmholtz instabilities leading to a turbulent current sheet (CS) medium or if the current sheet is merely the background where SADs are produced, triggered by an impulsive deposition of energy. We find that to give an account of the observational dark lane structures an addition of local energy, provided by a reconnection event, is required. We suggest that there may be a closed relation between characteristic SAD sizes and CS widths that must be satisfied to obtain an observable SAD.
Ito, Atsushi
subject in solar physics is to understand the variety of dynamics and structure formation2009 US-Japan Workshop on Advanced Simulation Methods in Plasma Physics MHD Simulations of the Solar Astmosphere: Effects of Weak Ionization and Radiation Hiroaki Isobe1 1 Unit of Synergetic Studies
MHD Simulations of Near-Surface Convection in Cool Main-Sequence Stars
NASA Astrophysics Data System (ADS)
Beeck, Benjamin; Schussler, Manfred; Reiners, Ansgar
2015-01-01
The solar photospheric magnetic field is highly structured owing to its interaction with the convective flows. Its local structure has a strong influence on the profiles of spectral lines not only by virtue of the Zeeman effect, but also through the modification of the thermodynamical structure (e.g. line weakening in hot small-scale magnetic structures). Many stars harbor surface magnetic fields comparable to or larger than the Sun at solar maximum. Therefore, a strong influence of the field on the surface convection and on spectral line profiles can be expected. We carried out 3D local-box MHD simulations of unipolar magnetized regions (average fields of 20, 100, and 500G) with parameters corresponding to six main-sequence stars (spectral types F3V to M2V). The influence of the magnetic field on the convection and the local thermodynamical structure were analyzed in detail. For three spectral lines, we determined the impact of the magnetic field on the disc-integrated Stokes-I profiles. Line weakening has in many cases a stronger impact on the spectral line profiles than the Zeeman effect. Moreover, for some stars, the correlation between the magnetic field and the vertical velocity strongly influences the line shapes. These effects can impair determinations of stellar magnetic fields since currently used methods neglect the local structure of the magnetic field and its interaction with the convective flows. The MHD simulations presented can be used to quantify these effects and thus help to improve magnetic field measurements of cool main-sequence stars.
A. G. Wehr; R. Tang
1981-01-01
The MHD Energy Center has constructed a test stand that will simulate the conditions that are present at any point in a coal-fired magnetohydrodynamic (MHD) power plant. This test stand was used to examine the effect of primary combustion stoichiometry and various secondary combustion parameters on the generation of nitrogen oxides. The secondary combustion air was injected at eight different
NASA Astrophysics Data System (ADS)
Vlasyuka, A. P.; Zhukovskaya, N. A.
2015-03-01
This paper considers the problem of mathematical simulation of the stressed-strained state of the foundation of the earth dam with account for the heat and mass transfer in the presence of a free surface of ground waters. We have obtained a numerical solution of the corresponding boundary-value problem in the two-dimensional case in the inverse formulation with the use of a computational algorithm based on numerical conformal mapping of the composition domain with a curved boundary and the finite difference method.
Two-dimensional thermofield bosonization
Amaral, R.L.P.G. [Instituto de Fisica, Universidade Federal Fluminense, Av. Litoranea S/N, Boa Viagem, Niteroi, CEP, 24210-340 Rio de Janeiro (Brazil)]. E-mail: rubens@if.uff.br; Belvedere, L.V. [Instituto de Fisica, Universidade Federal Fluminense, Av. Litoranea S/N, Boa Viagem, Niteroi, CEP, 24210-340 Rio de Janeiro (Brazil); Rothe, K.D. [Institut fuer Theoretische Physik, Universitaet Heidelberg, Philosophenweg 16, D-69120 Heidelberg (Germany)
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 flexible nanoelectronics
NASA Astrophysics Data System (ADS)
Akinwande, Deji; Petrone, Nicholas; Hone, James
2014-12-01
2014/2015 represents the tenth anniversary of modern graphene research. Over this decade, graphene has proven to be attractive for thin-film transistors owing to its remarkable electronic, optical, mechanical and thermal properties. Even its major drawback--zero bandgap--has resulted in something positive: a resurgence of interest in two-dimensional semiconductors, such as dichalcogenides and buckled nanomaterials with sizeable bandgaps. With the discovery of hexagonal boron nitride as an ideal dielectric, the materials are now in place to advance integrated flexible nanoelectronics, which uniquely take advantage of the unmatched portfolio of properties of two-dimensional crystals, beyond the capability of conventional thin films for ubiquitous flexible systems.
Two-dimensional river modeling
Thompson, James Cameron
1988-01-01
The three dimensional flow structure is not required for most river applications. Neglecting vertical velocities and vertical accelerations, the depth-averaged velocity may obtained by integrating the horizontal velocity components from the bed elevation...TWO-DIMENSIONAL RIVER MODELING A Thesis by JAMES CAMERON THOMPSON Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE December 1988 Major Subject...
Steven A. Moszkowski
1979-01-01
We discuss the spatially symmetric configurations for four particles in the two-dimensional version of the p shell and (s,d) shell with a surface delta interaction and show how these configurations can be described as a system of two interacting bosons. The boson-boson interaction is shown to be predominantly quadrupole with a somewhat weaker hexadecupole component. With increasing numbers of bosons,
Simulation of a particle-laden combustion flow in an MHD second stage combustor
Chang, S.L.; Lottes, S.A.
1992-01-01
An Argonne two-phase combustion flow computer code is used to simulate reacting flows to aid the development of an advanced combustor for magnetohydrodynamic power generation. The combustion code is a general hydrodynamics computer code for two-phase two-dimensional, steady state, turbulent, and reacting flows, based on mass, momentum, and energy conservation laws for multiple gas species. The combustion code includes turbulence, integral combustion, and particle evaporation submodels. The newly developed integral combustion submodel makes calculations more efficient and more stable while still preserving major physical effects of the complex combustion processes. The combustor under investigation is a magnetohydrodynamic second stage combustor in which opposed jets of oxidizer are injected into a confined cross-stream of hot coal gas flow following a first stage swirl combustor. The simulation is intended to enhance the understanding of seed particle evolution in the combustor and evaluate the effects of combustor operation conditions on seed particle evolution and vapor dispersion, which directly affect overall magnetohydrodynamic power generation. Simulation results show that oxidizer jet angle and particle size have great effect on the particle evolution and vapor dispersion. At a jet angle about 130 degrees, particle evaporation rate is the highest because of the highest average gas temperature. For particles having a smaller mean diameter, particle evaporation is more complete and vapor dispersion is more uniform.
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.
Time-dependent simulation of oblique MHD cosmic-ray shocks using the two-fluid model
NASA Astrophysics Data System (ADS)
Frank, Adam; Jones, T. W.; Ryu, Dongsu
1995-03-01
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, Mf, and plasma beta. We compile the results into maps of dynamical steady state CR acceleration efficiency, epsilonc. 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.
NASA Astrophysics Data System (ADS)
Kitiashvili, I.; Abramenko, V.; Goode, P. R.; Kosovichev, A.; Mansour, N.; Wray, A.; Yurchyshyn, V.
2012-12-01
Recent progress in observational capabilities and numerical modeling have provided unique high-resolution information demonstrating complicated dynamics and structures of turbulent flows and magnetic field on the Sun. The realistic approach to numerical simulations is based on physical first principles and takes into account compressible fluid flow in a highly stratified magnetized medium, 3D multi-bin radiative energy transfer between fluid elements, a real-gas equation of state, ionization, and excitation of all abundant species, magnetic effects and sub-grid turbulence. We present new results of 3D radiative MHD simulations of the upper solar convection zone and chromosphere that reveal a fundamental role of small-scale vortex dynamics, and compare the numerical results and predictions with observational results from the 1.6 m clear aperture New Solar Telescope (NST) at Big Bear Observatory. In particular, we investigate formation and dynamics of ubiquitous small-scale vortex tubes mostly concentrated in the intergranular lanes and their role in magnetic structuring and acoustic emission of the Sun. These whirlpool-like flows are characterized by very strong horizontal shear velocities (7 - 11 km/s) and downflows (~7 km/s), and are accompanied by sharp decreases in temperature, density and pressure at the surface. High-speed whirlpool flows can attract and capture other vortices, penetrate into the low chromosphere, and form stable magnetic flux tubes. The simulations also reveal a strong connection between acoustic wave excitation events and the dynamics of vortex tubes. In this talk, we will discuss different aspects of small-scale turbulent dynamics of the low atmosphere from the high-resolution simulations in comparison with recent NST observations, and the strategy for future synergies of numerical simulations and observations with large aperture solar telescopes.
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.
Attempts to Simulate Anisotropies of Solar Wind Fluctuations Using MHD with a Turning Magnetic Field
NASA Technical Reports Server (NTRS)
Ghosh, Sanjoy; Roberts, D. Aaron
2010-01-01
We examine a "two-component" model of the solar wind to see if any of the observed anisotropies of the fields can be explained in light of the need for various quantities, such as the magnetic minimum variance direction, to turn along with the Parker spiral. Previous results used a 3-D MHD spectral code to show that neither Q2D nor slab-wave components will turn their wave vectors in a turning Parker-like field, and that nonlinear interactions between the components are required to reproduce observations. In these new simulations we use higher resolution in both decaying and driven cases, and with and without a turning background field, to see what, if any, conditions lead to variance anisotropies similar to observations. We focus especially on the middle spectral range, and not the energy-containing scales, of the simulation for comparison with the solar wind. Preliminary results have shown that it is very difficult to produce the required variances with a turbulent cascade.
The Biermann Battery in Cosmological MHD Simulations of Population III Star Formation
Hao Xu; Brian W. O'Shea; David C. Collins; Michael L. Norman; Hui Li; Shengtai Li
2008-07-18
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 stars 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 ~10^-9 G in the center of our star-forming halo at z ~ 17.55. 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 >= 10^{15} at all times), and should be considered the minimum possible fields in existence during Population III star formation, and may be seed fields for the stellar dynamo or the magnetorotational instability at higher densities and smaller spatial scales.
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.
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 MHD Simulation of Flux-Rope Formed Ejecta Interaction with Bi-modal Solar Wind
NASA Astrophysics Data System (ADS)
Wu, S. T.; Wang, A. H.; Tsurutani, B.; Tan, A.
2001-12-01
Recent SOHO and WIND observations have shown that CMEs could be accelerated or decelerated due to their interactions with the solar wind. These interactions will result in different solar wind signatures. In order to understand the physics of CME interaction with non-uniform solar wind during propagation, we combined our previously developed two-dimensional planar bi-modal solar wind model (Wang et al. 1996) and streamer and flux-rope model (Wu et al. 1995) to study the fast and slow wind interactions with the propagating CME. This simulation is carried out up to the inner heliosphere ( ~30 Rs (solar radii)). The results will show the effect of CME propagation speed by the fast and slow speed solar wind, and the shock formation and their comparison with the uniform solar wind. Also the features of the deflection of CME propagation due to streamer will be discussed. STW and AHW acknowledge AFOSR, NSF, JPL, and AAMU subcontract of NASA prime contract. Wang, A. H., S. T. Wu, S. T. Suess, and G. Poletto, Global Model of Corona with Heat and Momentum Addition, J. Geophys. Res., 103, A2, 1413-1922, 1996. Wu, S. T., W. P. Guo, and J. F. Wang, Dynamical Evolution of Coronal Streamer Bubble System: I. A Self-consistent Planar Magnetohydrodynamic Simulation, Solar Physics, 157, 325-348, 1995.
Two dimensional bulge disk decomposition
Yogesh Wadadekar; Braxton Robbason; Ajit Kembhavi
1997-05-27
We propose a two dimensional galaxy fitting algorithm to extract parameters of the bulge, disk, and a central point source from broad band images of galaxies. We use a set of realistic galaxy parameters to construct a large number of model galaxy images which we then use as input to our galaxy fitting program to test it. We find that our approach recovers all structural parameters to a fair degree of accuracy. We elucidate our procedures by extracting parameters for 3 real galaxies -- NGC 661, NGC 1381, and NGC 1427.
A renormalization group analysis of two-dimensional magnetohydrodynamic turbulence
NASA Technical Reports Server (NTRS)
Liang, Wenli Z.; Diamond, P. H.
1993-01-01
The renormalization group (RNG) method is used to study the physics of two-dimensional (2D) magnetohydrodynamic (MHD) turbulence. It is shown that, for a turbulent magnetofluid in two dimensions, no RNG transformation fixed point exists on account of the coexistence of energy transfer to small scales and mean-square magnetic flux transfer to large scales. The absence of a fixed point renders the RNG method incapable of describing the 2D MHD system. A similar conclusion is reached for 2D hydrodynamics, where enstrophy flows to small scales and energy to large scales. These analyses suggest that the applicability of the RNG method to turbulent systems is intrinsically limited, especially in the case of systems with dual-direction transfer.
Formation and Eruption of an Active Region Sigmoid: NLFFF Modeling and MHD Simulation
NASA Astrophysics Data System (ADS)
Jiang, C.; Wu, S.; Feng, X.; Hu, Q.
2013-12-01
We present a magnetic analysis of the formation and eruption of an active region sigmoid in AR 11283 from 2011 September 4 to 6, which is jointly based on observations, static nonlinear force-free field (NLFFF) extrapolation and dynamic MHD simulation. A time sequence of NLFFF model's outputs are used to reproduce the evolution of the magnetic field of the region over three days leading to a X-class flare near the end of 2011 September 6. In the first day, a new bipolar emerges into the negative polarity of a pre-existing mature bipolar, forming a magnetic topology with a coronal null on the magnetic separatrix surface between the two flux system, while the field is still near potential at the end of the day. After then photospheric shearing and twisting build up non-potentiality in the embedded core region, with a flux rope (FR) formed there above the polarity inversion line by tether-cutting reconnection between the strongly sheared field lines. Within this duration, the core field has gained a magnetic free energy of ˜ 1032 erg. In this core a sigmoid is observed distinctly at 22:00 UT on September 6, closely before its eruption at 22:12 UT. Comparison of the SDO/AIA observations with coronal magnetic field suggests that the sigmoid is formed by emission due to enhanced current sheet along the BPSS (bald-patch separatrix surface, in which the field lines graze the line-tied photosphere at the neutral line) that separates the FR from the ambient flux. Quantitative inspection of the pre-eruption field on 22:00 UT suggests a mechanism for the eruption: tether cutting at the null triggers a torus instability of the FR--overlying field system. This pre-eruption NLFFF is then input into a time-dependent MHD model to simulate the fast magnetic evolution during eruption, which successfully reproduces the observations. The highly asymmetric magnetic environment along with the lateral location of the null leads to a strongly inclined non-radial direction of the eruption. The study of this kind provides important insights in a quantitative way to many open issues on the formation and eruption of sigmoidal FR.
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)
Khodin, Aliaksandr
2002-05-01
Quasi-two-dimensional space-time configuration is presented as a photon model in the frames of a topological approach. The photon configuration is considered in the model as the simplest stable disturbance of non-linear (in relativistic sence) space-time medium. The configuration is governed by the ultimate relativistic condition [1] in its central point for every external time moment as a prerequisite for the configuration' stability under Lorentz transformations. A photon is represented as a localized quasi-two-dimensional spatio-temporal object possessing the Doppler effect behaviour in the case it propagates with the ultimate light velocity only. Characteristic transversal size of a photon is of its wavelength order. Photon spin is ascribed to the configuration's "rotation" around the propagation direction; the only permissible rotation period corresponding to the photon wavelength. It is shown that the ordered one-dimensional superposition of single-photon configurations along the propagation direction composes a restricted stable coherent harmonic-type packet. Two- and three-dimensional coherent superposition of single-photon configurations leads to some types of transversal photons ordering inside the coherent packet. 1. A.Khodin. Hierarchical model of elementary symmetries in configurational approach. EPS-11: Trends in Physics. 11th Gen. Conf. of Eur. Phys. Soc. London, UK, 6-10 Sept.1999.
Miura, A. [Department of Earth and Planetary Physics, University of Tokyo, Bunkyo-ku, Tokyo 113 (Japan)] [Department of Earth and Planetary Physics, University of Tokyo, Bunkyo-ku, Tokyo 113 (Japan)
1997-08-01
For a two-dimensional (2-D) transverse configuration, where the plasma motion occurs in a 2-D plane transverse to the magnetic field, the nonlinear evolution of the magnetohydrodynamic (MHD) Kelvin{endash}Helmholtz (K{endash}H) instability is investigated by means of a 2-D MHD simulation for a convective fast magnetosonic Mach number 0.35, which is defined for the total jump of the flow velocity. The compressibility and the nonzero baroclinic vector are shown to violate the conservation of the enstrophy for the 2-D MHD transverse configuration and for the 2-D fluid motion. After the nonlinear saturation of the linearly fastest growing vortices, the vortices continue to coalesce until no more vortex pairing is allowed, owing to a finite length of the simulation system. The plasma inside the vortex is rarefied strongly by the fast magnetosonic rarefaction and each vortex is associated with an eddy current, which is inertia current in nature. The plasma flow velocity is enhanced at the periphery of the vortex and the net momentum transport and shear relaxation by the instability occur as long as the vortex pairing continues. Anomalous viscosity by the K{endash}H instability increases with the vortex pairing and its increase is due to the growth of subharmonic modes. {copyright} {ital 1997 American Institute of Physics.}
NASA Technical Reports Server (NTRS)
Boriakoff, Valentin; Chen, Wei
1990-01-01
The NASA-Cornell Univ.-Worcester Polytechnic Institute Fast Fourier Transform (FFT) chip based on the architecture of the systolic FFT computation as presented by Boriakoff is implemented into an operating device design. The kernel of the system, a systolic inner product floating point processor, was designed to be assembled into a systolic network that would take incoming data streams in pipeline fashion and provide an FFT output at the same rate, word by word. It was thoroughly simulated for proper operation, and it has passed a comprehensive set of tests showing no operational errors. The black box specifications of the chip, which conform to the initial requirements of the design as specified by NASA, are given. The five subcells are described and their high level function description, logic diagrams, and simulation results are presented. Some modification of the Read Only Memory (ROM) design were made, since some errors were found in it. Because a four stage pipeline structure was used, simulating such a structure is more difficult than an ordinary structure. Simulation methods are discussed. Chip signal protocols and chip pinout are explained.
Delrue, Steven; Van Den Abeele, Koen; Blomme, Erik; Deveugele, Jurgen; Lust, Pieter; Matar, Olivier Bou
2010-02-01
Non-contact air-coupled ultrasonic inspection of materials using single-sided access offers interesting possibilities for the development of in-line non-destructive testing (NDT) systems. This contribution reports observations and simulations obtained from a single-sided air-coupled pitch-catch configuration. The pitch-catch technique involves a set-up in which transmitter and receiver are located at the same side of the test object. Sound waves, reflected once or multiple times from the back-wall of the object or refracted by a discontinuity, are recorded and analyzed for visualization. The feasibility of the technique is demonstrated, experimentally, in the case of artificial defects in aluminium samples. Depending on the configuration one or more ultrasonic images of the defect can be observed, their number and relative position containing information about the location of the defect. The experiments are simulated using two distinctive methods. The first simulation is based on a ray tracing (shadow) approach, the second method uses a spectral solution implemented within COMSOL. Both simulation methods allow simple prediction of the response images in experimental conditions with supplementary levels of complexity, which will assist the development and optimization of online inspection techniques. PMID:19732929
Tackley, Paul J.
1 Simulating the thermo-chemical magmatic and tectonic evolution of1 Venus' mantle and lithosphere Numerical convection models of the thermo-chemical evolution of Venus are compared to present-8 day overturn interspersed by periods of quiescence13 effectively loses Venus' heat while giving lower rates
Zhibao Dong; Guangqiang Qian; Wanyin Luo; Hongtao Wang
2007-01-01
Secondary airflow plays an important role in dune formation and development. The lee airflow pattern over transverse dunes is important in determining the shape, alignment, and spacing of dunes and is influenced significantly by the lee slope angle. In this paper we present the results of scaled wind tunnel simulations of the effects of stoss slope on the mean lee
NASA Astrophysics Data System (ADS)
Knizhnik, K.; Sitnov, M. I.; Swisdak, M. M.
2012-12-01
Unsteady magnetic reconnection in the magnetosphere and in the solar corona involves the formation of localized ejecta, such as the magnetotail dipolarization fronts (DFs) and coronal supra-arcade downflowing loops (SADLs). Both DFs and SADLs move in the direction opposite to the initial magnetic field stretching with a speed comparable to the Alfven speed. However, the DF scales are comparable to the ion gyro radius and therefore their analysis requires kinetic theory and simulations. Recent kinetic theory and PIC simulations of 2D magnetotail equilibria revealed two possible mechanisms of the DF formation, namely mutual attraction of parallel current filaments in thin current sheets causing magnetic reconnection via the tearing instability and magnetic buoyancy resulting in the ballooning-interchange instability. Both mechanisms are most efficient in the geometries with accumulation of magnetic flux at the tailward end of a thin current sheet. To understand the roles of magnetic reconnection and buoyancy in the formation and evolution of DFs we perform 3D PIC simulations of 2D current sheets, where two magnetotails are separated by an equilibrium X-line. To justify modeling the long terrestrial magnetotail in a relatively small simulation box: Lx x Ly x Lz= 40d x 20d x 5d (d is the ion inertial length; GSM coordinate system is used) open boundary conditions are employed in the x-direction. The magnetotail parts of the 2D equilibrium include regions of accumulated magnetic flux, consistent with the Geotail observations of similar signatures prior to substorm onset. We investigate which of the mechanisms is responsible for the formation of DF-like structures in 3D configurations and discuss their subsequent motion and structure. Simulations are compared with recent THEMIS observations of DFs and ballooning-interchange oscillations in the magnetotail, as well as SDO observations of solar flares.
An MHD simulation study of the dynamics of the 8-9 March 2008 CIR-/HSS-driven geomagnetic storm
NASA Astrophysics Data System (ADS)
Peroomian, Vahé; Garg, Shobhit; El-Alaoui, Mostafa
2014-04-01
We have carried out a global magnetohydrodynamic (MHD) simulation of a geomagnetic storm initiated by a corotating interaction region followed by a high-speed solar wind (HSS) stream that occurred on 8-9 March 2008. The event began with the arrival of a corotating interaction region (CIR) at ~0720 UT on 8 March. The stream interface arrived at Earth at ~1830 UT on 8 March, and the arrival of a second density enhancement (a second CIR) at ~0140 UT on 9 March resulted in the main phase of the storm, with a peak Dst of -97 nT at 0600 UT on 9 March. Our MHD simulation of the event, spanning the interval of 0400 UT on 8 March to 0800 UT on 9 March, shows that the arrival of the first CIR changes the configuration of the magnetotail, and that after a strong substorm at ~1230 UT on 8 March, the tail evolves into a churning state in which the magnetic topology and flow structure of the magnetotail are never steady. In addition, we find that increases in ring current energy density show a nearly one-to-one correspondence to periods of VxBz > 0 (southward interplanetary magnetic field (IMF)). More importantly, we find that the ring current energy density in the MHD simulation shows a nearly linear response to increases in solar wind dynamic pressure, but only for the northward IMF intervals during the initial phase of the event, from 0400 UT to 1800 UT on 8 March.
Properties of Ganymede's magnetosphere inferred from improved three-dimensional MHD simulations
NASA Astrophysics Data System (ADS)
Jia, Xianzhe; Walker, Raymond J.; Kivelson, Margaret G.; Khurana, Krishan K.; Linker, Jon A.
2009-09-01
We describe a three-dimensional single-fluid MHD simulation of Ganymede's magnetosphere that accords extremely well with the Galileo particles and fields measurements. Major improvements to our previously published model involve the modification of the inner boundary condition and the implementation of an anomalous resistivity model. The improved model couples the moon's ionosphere (with finite Pedersen conductance) with the magnetosphere self-consistently. The previous model applied only in the limit of unreasonably high ionospheric conductivity. We illustrate in detail the global convection pattern inferred from the new model and demonstrate some features of the convection that differ from that of the Earth's magnetosphere because Ganymede lacks a corotation electric field. Our new model does a better job of reproducing magnetic field and plasma observations from multiple Galileo passes, which sampled different external conditions and different regions of the magnetosphere. In particular, for a critical upstream pass (G8) during which the Galileo spacecraft entered onto closed field lines, the simulated magnetosphere provides an excellent fit to the measurements without the need for tuning the spacecraft trajectory. In comparison with the plasma measurements of the G2 flyby, our model also yields good agreement with the Galileo PLS observations and supports the conclusion reached by Vasyli?nas and Eviatar (2000) that the observed ionospheric outflow consists of oxygen ions. For constant external conditions, dynamic variations associated with magnetic reconnection on timescales of the order of tens of seconds are found over a large region near the magnetopause in the simulations. Future applications of our model, such as test particle tracing and investigating the behavior of the cross polar cap potential under different external and ionospheric conditions, will provide a more comprehensive understanding of Ganymede's magnetospheric environment.
3D Simulations of MHD Jet Propagation Through Uniform and Stratified External Environments
S. M. O'Neill; I. L. Tregillis; T. W. Jones; Dongsu Ryu
2005-07-26
We present a set of high-resolution 3D MHD simulations of steady light, supersonic jets, exploring the influence of jet Mach number and the ambient medium on jet propagation and energy deposition over long distances. The results are compared to simple self-similar scaling relations for the morphological evolution of jet-driven structures and to previously published 2D simulations. For this study we simulated the propagation of light jets with internal Mach numbers 3 and 12 to lengths exceeding 100 initial jet radii in both uniform and stratified atmospheres. The propagating jets asymptotically deposit approximately half of their energy flux as thermal energy in the ambient atmosphere, almost independent of jet Mach number or the external density gradient. Nearly one-quarter of the jet total energy flux goes directly into dissipative heating of the ICM, supporting arguments for effective feedback from AGNs to cluster media. The remaining energy resides primarily in the jet and cocoon structures. Despite having different shock distributions and magnetic field features, global trends in energy flow are similar among the different models. As expected the jets advance more rapidly through stratified atmospheres than uniform environments. The asymptotic head velocity in King-type atmospheres shows little or no deceleration. This contrasts with jets in uniform media with heads that are slowed as they propagate. This suggests that the energy deposited by jets of a given length and power depends strongly on the structure of the ambient medium. While our low-Mach jets are more easily disrupted, their cocoons obey evolutionary scaling relations similar to the high-Mach jets.
First MHD simulation of collapse and fragmentation of magnetized molecular cloud cores
NASA Astrophysics Data System (ADS)
Machida, Masahiro N.; Tomisaka, Kohji; Matsumoto, Tomoaki
2004-02-01
This is the first paper about fragmentation and mass outflow in molecular clouds by using three-dimensional magnetohydrodynamical (MHD) nested-grid simulations. The binary star formation process is studied, paying particular attention to the fragmentation of a rotating magnetized molecular cloud. We assume an isothermal rotating and magnetized cylindrical cloud in hydrostatic balance. Non-axisymmetric as well as axisymmetric perturbations are added to the initial state and the subsequent evolutions are studied. The evolution is characterized by three parameters: the amplitude of the non-axisymmetric perturbations, the rotation speed and the magnetic field strength. As a result, it is found that non-axisymmetry hardly evolves in the early phase, but begins to grow after the gas contracts and forms a thin disc. Disc formation is strongly promoted by the rotation speed and the magnetic field strength. There are two types of fragmentation: that from a ring and that from a bar. Thin adiabatic cores fragment if their thickness is less than 1/4 of the radius. For the fragments to survive, they should be formed in a heavily elongated barred core or a flat round disc. In the models showing fragmentation, outflows from respective fragments are found as well as those driven by the rotating bar or the disc.
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.
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.
Chen, Bo; Tycko, Robert
2011-06-22
We report Monte Carlo simulations of the initial stages of self-assembly of the HIV-1 capsid protein (CA), using a coarse-grained representation that mimics the CA backbone structure and intermolecular contacts observed experimentally. A simple representation of N-terminal domain/N-terminal domain and N-terminal domain/C-terminal domain interactions, coupled with the correct protein shape, is sufficient to drive formation of an ordered lattice with the correct hexagonal symmetry in two dimensions. We derive an approximate concentration/temperature phase diagram for lattice formation, and we investigate the pathway by which the lattice develops from initially separated CA dimers. Within this model, lattice formation occurs in two stages: 1), condensation of CA dimers into disordered clusters; and 2), nucleation of the lattice by the appearance of one hexamer unit within a cluster. Trimers of CA dimers are important early intermediates, and pentamers are metastable within clusters. Introduction of a preformed hexamer at the beginning of a Monte Carlo run does not directly seed lattice formation, but does facilitate the formation of large clusters. We discuss possible connections between these simulations and experimental observations concerning CA assembly within HIV-1 and in vitro. PMID:21689538
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 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.
Large plasmoids in global MHD simulations: Solar wind dependence and ionospheric mapping
NASA Astrophysics Data System (ADS)
Honkonen, Ilja; Palmroth, Minna; Pulkkinen, T.; Janhunen, Pekka
The energy from the solar wind drives magnetospheric dynamics. An important, but the most difficult to measure, factor is the energy released in plasmoids. Plasmoids are large magnetic structures that form in the Earth's magnetotail during substorms, which are the main mecha-nism of extracting and releasing solar wind energy from the magnetosphere. During plasmoid formation the 3-d structure of the magnetotail becomes complicated, with spatially alternating closed and open magnetic topologies. While the formation and the release of plasmoids are unresolved, they are classically thought to detach from the magnetotail at the substorm onset. Using our global magnetohydrodynamic (MHD) simulation GUMICS-4, we investigate how different parameters of the solar wind affect the formation of plasmoids. Specifically we con-centrate on the role of the solar wind magnetic field parameters. We also investigate the solar wind dependence of plasmoid foot points, which are the end points of the plasmoid magnetic field in the ionosphere. Preliminary results suggest that plasmoid formation and plasmoid foot point location in the ionosphere strongly depend on the solar wind magnetic field param-eters. Our work may be of importance when interpreting some observed, but unexplained, ionospheric phenomena. We also present an operational definition of plasmoids, which enables their automatic detection in simulations. The project has received funding from the European Research Council under the European Community's Seventh Framework Programme (FP7/2007-2013) / ERC Starting Grant agree-ment number 200141-QuESpace. The work of IH and MP is supported by the Academy of Finland.
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.
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).
Magnetic Reconnection in Two-Dimensional Magnetohydrodynamic Turbulence S. Servidio,1
Shay, Michael
Magnetic Reconnection in Two-Dimensional Magnetohydrodynamic Turbulence S. Servidio,1 W. H-dimensional magnetohydrodynamic turbulence reveals the presence of a large number of X-type neutral points where magnetic be expected to be of importance in more general circumstances, including magnetohydrodynamic (MHD) turbulence
Mamatsashvili, G R; Gogichaishvili, D Z; Chagelishvili, G D; Horton, W
2014-04-01
We find and investigate via numerical simulations self-sustained two-dimensional turbulence in a magnetohydrodynamic flow with a maximally simple configuration: plane, noninflectional (with a constant shear of velocity), and threaded by a parallel uniform background magnetic field. This flow is spectrally stable, so the turbulence is subcritical by nature and hence it can be energetically supported just by a transient growth mechanism due to shear flow non-normality. This mechanism appears to be essentially anisotropic in the spectral (wave-number) plane and operates mainly for spatial Fourier harmonics with streamwise wave numbers less than the ratio of flow shear to Alfvén speed, kyMHD) turbulence research. We find similarity of the nonlinear dynamics to the related dynamics in hydrodynamic flows: to the bypass concept of subcritical turbulence. The essence of the analyzed nonlinear MHD processes appears to be a transverse redistribution of kinetic and magnetic spectral energies in the wave-number plane [as occurs in the related hydrodynamic flow; see Horton et al., Phys. Rev. E 81, 066304 (2010)] and differs fundamentally from the existing concepts of (anisotropic direct and inverse) cascade processes in MHD shear flows. PMID:24827349
T. Tanaka
1994-01-01
A three-dimensional (3D) high-resolution magnetohydrodynamic (MHD) simulation scheme on an unstructured grid system is developed for inhomogeneous systems, including strong background potential fields. The scheme is based on the finite volume method (FVM) with an upwinding numerical flux by the linearized Riemann solver. Upwindings on an unstructured grid system are realized from the fact that the MHD equations are symmetric
Two-dimensional melting under quenched disorder
Sven Deutschländer; Tobias Kruppa; Hartmut Löwen; Georg Maret; Peter Keim
2013-05-16
We study the influence of quenched disorder on the two-dimensional melting behavior by using both video-microscopy of superparamagnetic colloidal particles and computer simulations of repulsive parallel dipoles. Quenched disorder is provided by pinning a fraction of the particles. We confirm the occurrence of the Kosterlitz-Thouless-Halperin-Nelson-Young scenario with an intermediate hexatic phase. While the fluid-hexatic transition remains largely unaffected by disorder, the hexatic-solid transition shifts towards lower temperatures for increasing disorder resulting in a significantly broadened stability range of the hexatic phase. In addition, we observe spatio-temporal critical(-like) fluctuations consistent with the continuous character of the phase transitions.
Malapaka, Shiva Kumar; Mueller, Wolf-Christian [Max-Planck Institute for Plasma Physics, Boltzmannstrasse 2, D-85748 Garching bei Muenchen (Germany)
2013-09-01
Statistical properties of the Sun's photospheric turbulent magnetic field, especially those of the active regions (ARs), have been studied using the line-of-sight data from magnetograms taken by the Solar and Heliospheric Observatory and several other instruments. This includes structure functions and their exponents, flatness curves, and correlation functions. In these works, the dependence of structure function exponents ({zeta}{sub p}) of the order of the structure functions (p) was modeled using a non-intermittent K41 model. It is now well known that the ARs are highly turbulent and are associated with strong intermittent events. In this paper, we compare some of the observations from Abramenko et al. with the log-Poisson model used for modeling intermittent MHD turbulent flows. Next, we analyze the structure function data obtained from the direct numerical simulations (DNS) of homogeneous, incompressible 3D-MHD turbulence in three cases: sustained by forcing, freely decaying, and a flow initially driven and later allowed to decay (case 3). The respective DNS replicate the properties seen in the plots of {zeta}{sub p} against p of ARs. We also reproduce the trends and changes observed in intermittency in flatness and correlation functions of ARs. It is suggested from this analysis that an AR in the onset phase of a flare can be treated as a forced 3D-MHD turbulent system in its simplest form and that the flaring stage is representative of decaying 3D-MHD turbulence. It is also inferred that significant changes in intermittency from the initial onset phase of a flare to its final peak flaring phase are related to the time taken by the system to reach the initial onset phase.
Two dimensional hydrodynamic and evolution sequences of rotating stars
Deupree, R. G. (Robert G.); Guzik, J. A. (Joyce Ann); Neuforge, C. M. (Corinne M.)
2001-01-01
Two dimensional hydrodynamic simulations were calculated for ZAMS models with Z=0.02, and masses of 3,5, 8,12, and 20 Ma. For each mass five models were calculated - one nonrotating and four with progressively higher rotation rates. The rotating models were categorized by the ratio of the polar to the equatorial radius, with values of 0.985, 0.92, 0.84, and 0.72. The simulations were performed with the fully two dimensional implicit code ROTORC (actually what is known as 2.5 dimensions, with azimuthal symmetry, but with a conservation law for the rotational velocity in the azimuthal direction.)
Yang, Zhongwei; Richardson, John D; Lu, Quanming; Huang, Can; Wang, Rui
2015-01-01
The transition between the supersonic solar wind and the subsonic heliosheath, the termination shock (TS), was observed by Voyager 2 (V2) on 2007 August 31-September 1 at a distance of 84 AU from the Sun. The data reveal multiple crossings of a complex, quasi-perpendicular supercritical shock. These experimental data are the starting point for a more sophisticated analysis that includes computer modeling of a shock in the presence of pickup ions (PUIs). here, we present two-dimensional (2-D) particle-in-cell (PIC) simulations of the TS including PUIs self-consistently. We also report the ion velocity distribution across the TS using the Faraday cup data from V2. A relatively complete plasma and magnetic field data set from V2 gives us the opportunity to do a full comparison between the experimental data and PIC simulation results. Our results show that: (1) The nonstationarity of the shock front is mainly caused by the ripples along the shock front and these ripples from even if the percentage of PUIs is high...
Khan, Najeeb Alam; Aziz, Shahnila; Khan, Nadeem Alam
2014-01-01
The present work is devoted to study the numerical simulation for unsteady MHD flow and heat transfer of a couple stress fluid over a rotating disk. A similarity transformation is employed to reduce the time dependent system of nonlinear partial differential equations (PDEs) to ordinary differential equations (ODEs). The Runge-Kutta method and shooting technique are employed for finding the numerical solution of the governing system. The influences of governing parameters viz. unsteadiness parameter, couple stress and various physical parameters on velocity, temperature and pressure profiles are analyzed graphically and discussed in detail. PMID:24835274
Resistive MHD Simulations of Laminar Round Jets with Application to Magnetic Nozzle Flows
Araya, Daniel
2012-02-14
this large-scale device can fully function only in a vacuum. This difficulty makes computational analysis and modeling an important part of the design and testing process. A parallelized Boltzmann-BGK continuum flow solver is expanded to include resistive MHD...
Parallel, Adaptive-Mesh-Refinement MHD for Global Space-Weather Simulations
Kenneth G. Powell; Tamas I. Gombosi; Darren L. De Zeeuw; Aaron J. Ridley; Igor V. Sokolov; Quentin F. Stout; Ga´bor To´th
2003-01-01
The first part of this paper reviews some issues representing major computational challenges for global MHD models of the space environment. These issues include mathematical formulation and discretization of the governing equations that ensure the proper jump conditions and propagation speeds, regions of relativistic Alfve´n speed, and controlling the divergence of the magnetic field. The second part of the paper
K. Hayashi; M. Tokumaru; M. Kojima; K. Fujiki
2008-01-01
We present our new boundary treatment to introduce the temporal variation of the observation-based magnetic field and plasma parameters on the inner boundary sphere (at 30 to 50 Rs) to the MHD simulation of the interplanetary space and the simulation results. The boundary treatment to induce the time-variation of the magnetic field including the radial component is essentially same as
Magnetohydrodynamic waves in two-dimensional prominences embedded in coronal arcades
Terradas, J.; Soler, R.; Díaz, A. J.; Oliver, R.; Ballester, J. L., E-mail: jaume.terradas@uib.es [Departament de Física, Universitat de les Illes Balears, E-07122 Palma de Mallorca (Spain)
2013-11-20
Solar prominence models used so far in the analysis of MHD waves in two-dimensional structures are quite elementary. In this work, we calculate numerically magnetohydrostatic models in two-dimensional configurations under the presence of gravity. Our interest is in models that connect the magnetic field to the photosphere and include an overlying arcade. The method used here is based on a relaxation process and requires solving the time-dependent nonlinear ideal MHD equations. Once a prominence model is obtained, we investigate the properties of MHD waves superimposed on the structure. We concentrate on motions purely two-dimensional, neglecting propagation in the ignorable direction. We demonstrate how, by using different numerical tools, we can determine the period of oscillation of stable waves. We find that vertical oscillations, linked to fast MHD waves, are always stable and have periods in the 4-10 minute range. Longitudinal oscillations, related to slow magnetoacoustic-gravity waves, have longer periods in the range of 28-40 minutes. These longitudinal oscillations are strongly influenced by the gravity force and become unstable for short magnetic arcades.
Two Dimensional Air Drop Model
NSDL National Science Digital Library
2010-04-16
This interactive simulation shows an airplane flying at constant horizontal velocity preparing to drop relief supplies to a small island. Download Simulation Below As captain of the plane, you must determine when to release the package and activate the release button. The trajectory of the falling package is traced onscreen. If you were too far off, the package will drop in the ocean. The motion can be viewed from the perspective of a person standing on the island or an airplane flying nearby. Extend the learning by activating air friction to see how this variable affects the motion of the projectile. Editor's Note: Students may insist that there is a horizontal force acting upon the package since it has a horizontal motion. See Annotation for an editor-recommended tutorial that will explain what is happening (the horizontal motion of the package results from its inertia). This item was created with Easy Java Simulations (EJS), a modeling tool that allows users without formal programming experience to generate computer models and simulations.
Ahlers, M; Grainger, D W; Herron, J N; Lim, K; Ringsdorf, H; Salesse, C
1992-01-01
Three model biomembrane systems, monolayers, micelles, and vesicles, have been used to study the influence of chemical and physical variables of hapten presentation at membrane interfaces on antibody binding. Hapten recognition and binding were monitored for the anti-fluorescein monoclonal antibody 4-4-20 generated against the hapten, fluorescein, in these membrane models as a function of fluorescein-conjugated lipid architecture. Specific recognition and binding in this system are conveniently monitored by quenching of fluorescein emission upon penetration of fluorescein into the antibody's active site. Lipid structure was shown to play a large role in affecting antibody quenching. Interestingly, the observed degrees of quenching were nearly independent of the lipid membrane model studied, but directly correlated with the chemical structure of the lipids. In all cases, the antibody recognized and quenched most efficiently a lipid based on dioctadecylamine where fluorescein is attached to the headgroup via a long, flexible hydrophilic spacer. Dipalmitoyl phosphatidylethanolamine containing a fluorescein headgroup demonstrated only partial binding/quenching. Egg phosphatidylethanolamine with a fluorescein headgroup showed no susceptibility to antibody recognition, binding, or quenching. Formation of two-dimensional protein domains upon antibody binding to the fluorescein-lipids in monolayers is also presented. Chemical and physical requirements for these antibody-hapten complexes at membrane surfaces have been discussed in terms of molecular dynamics simulations based on recent crystallographic models for this antibody-hapten complex (Herron et al., 1989. Proteins Struct. Funct. Genet. 5:271-280). Images FIGURE 7 FIGURE 8 PMID:1420916
Agapiou, A; Zorba, E; Mikedi, K; McGregor, L; Spiliopoulou, C; Statheropoulos, M
2015-07-01
Field experiments were devised to mimic the entrapment conditions under the rubble of collapsed buildings aiming to investigate the evolution of volatile organic compounds (VOCs) during the early dead body decomposition stage. Three pig carcasses were placed inside concrete tunnels of a search and rescue (SAR) operational field terrain for simulating the entrapment environment after a building collapse. The experimental campaign employed both laboratory and on-site analytical methods running in parallel. The current work focuses only on the results of the laboratory method using thermal desorption coupled to comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry (TD-GC×GC-TOF MS). The flow-modulated TD-GC×GC-TOF MS provided enhanced separation of the VOC profile and served as a reference method for the evaluation of the on-site analytical methods in the current experimental campaign. Bespoke software was used to deconvolve the VOC profile to extract as much information as possible into peak lists. In total, 288 unique VOCs were identified (i.e., not found in blank samples). The majority were aliphatics (172), aromatics (25) and nitrogen compounds (19), followed by ketones (17), esters (13), alcohols (12), aldehydes (11), sulfur (9), miscellaneous (8) and acid compounds (2). The TD-GC×GC-TOF MS proved to be a sensitive and powerful system for resolving the chemical puzzle of above-ground "scent of death". PMID:26088782
Two dimensional computational fluid dynamic models for waste stabilisation ponds
M. G Wood; T Howes; J Keller; M. R Johns
1998-01-01
Traditional waste stabilisation pond (WSP) models encounter problems predicting pond performance because they cannot account for the influence of pond features, such as inlet structure or pond geometry, on fluid hydrodynamics. In this study, two dimensional (2-D) computational fluid dynamics (CFD) models were compared to experimental residence time distributions (RTD) from literature. In one of the three geometries simulated, the
Two dimensional echocardiographic diagnosis of situs
J C Huhta; J F Smallhorn; F J Macartney
1982-01-01
At present there is no reliable method of recognising atrial isomerism by two dimensional echocardiography. We therefore used two dimensional echocardiography to examine 158 patients including 25 with atrial isomerism and four with situs inversus. Particular attention was paid to the short and long axis subcostal scans of the abdomen. Using the position of the inferior vena cava and the
NASA Technical Reports Server (NTRS)
Berchem, J.; Raeder, J.; Ashour-Abdalla, M.; Frank, L. A.; Paterson, W. R.; Ackerson, K. L.; Kokubun, S.; Yamamoto, T.; Lepping, R. P.
1998-01-01
Understanding the large-scale dynamics of the magnetospheric boundary is an important step towards achieving the ISTP mission's broad objective of assessing the global transport of plasma and energy through the geospace environment. Our approach is based on three-dimensional global magnetohydrodynamic (MHD) simulations of the solar wind-magnetosphere- ionosphere system, and consists of using interplanetary magnetic field (IMF) and plasma parameters measured by solar wind monitors upstream of the bow shock as input to the simulations for predicting the large-scale dynamics of the magnetospheric boundary. The validity of these predictions is tested by comparing local data streams with time series measured by downstream spacecraft crossing the magnetospheric boundary. In this paper, we review results from several case studies which confirm that our MHD model reproduces very well the large-scale motion of the magnetospheric boundary. The first case illustrates the complexity of the magnetic field topology that can occur at the dayside magnetospheric boundary for periods of northward IMF with strong Bx and By components. The second comparison reviewed combines dynamic and topological aspects in an investigation of the evolution of the distant tail at 200 R(sub E) from the Earth.
3D Global MHD Simulation of Titan's interaction with its surrounding plasma
Y. Ma; A. F. Nagy; G. Toth; D. Najib; T. E. Cravens; F. Crary; A. J. Coates; C. Bertucci; F. M. Neubauer
2006-01-01
The interaction of Titan's ionosphere with its surrounding plasma flow is more complex than analogous solar wind-planet interactions, because of Titan's varying relative location in the Sun-Saturn system. We have studied the role of the angle between the direction of the solar radiation and the corotating plasma flow using our 3D multi-species MHD model. We also present results from a
Three-dimensional MHD simulation of a flux rope driven CME
Ward B. Manchester; Tamas I. Gombosi; Ilia Roussev; Darren L. De Zeeuw; I. V. Sokolov; Kenneth G. Powell; Gábor Tóth; Merav Opher
2004-01-01
We present a three-dimensional (3-D) numerical ideal magnetohydrodynamics (MHD) model, describing the time-dependent expulsion of plasma and magnetic flux from the solar corona that resembles a coronal mass ejection (CME). We begin by developing a global steady-state model of the corona and solar wind that gives a reasonable description of the solar wind conditions near solar minimum. The model magnetic
A two-dimensional spin liquid in quantum kagome ice.
Carrasquilla, Juan; Hao, Zhihao; Melko, Roger G
2015-01-01
Actively sought since the turn of the century, two-dimensional quantum spin liquids (QSLs) are exotic phases of matter where magnetic moments remain disordered even at zero temperature. Despite ongoing searches, QSLs remain elusive, due to a lack of concrete knowledge of the microscopic mechanisms that inhibit magnetic order in materials. Here we study a model for a broad class of frustrated magnetic rare-earth pyrochlore materials called quantum spin ices. When subject to an external magnetic field along the [111] crystallographic direction, the resulting interactions contain a mix of geometric frustration and quantum fluctuations in decoupled two-dimensional kagome planes. Using quantum Monte Carlo simulations, we identify a set of interactions sufficient to promote a groundstate with no magnetic long-range order, and a gap to excitations, consistent with a Z2 spin liquid phase. This suggests an experimental procedure to search for two-dimensional QSLs within a class of pyrochlore quantum spin ice materials. PMID:26096331
NASA Astrophysics Data System (ADS)
Li, S.; Karimabadi, H.; Krauss-Varban, D.; Huba, J.; Daughton, W.
2004-12-01
Two commonly used techniques for performing reconnection simulations have been to either localize the resistivity (in simulations where electron kinetic effects are not included) or impose an external perturbation on the system. In MHD, it has been shown that depending on the spatial extent of resistivity, the nature of the solution changes. When resistivity region occupies a large fraction of simulation domain, one obtains a Sweet-Parker solution whereas in a localized resistivity case, the solution is Petschek-like. We demonstrate that this is due to the fact that in MHD the size of the diffusion region coincides with the region of localized resistivity. In non-MHD limit, this is no longer the case. In order to gain a better understanding of the effect of initialization on the physics of reconnection, we compare and contrast different initialization schemes, including new initialization procedure. We examine the reconnection details and the size of the diffusion region in four types of simulations codes: Hall MHD, hybrid (electron fluid, kinetic ions), Hall-less hybrid, and full particle simulations.
Two-dimensional dense gas dynamics
NASA Astrophysics Data System (ADS)
Brown, Brady Polk
Certain polyatomic fluids with large molecular weights referred to as dense gases exhibit unusual thermodynamic and flow properties in the region of the thermodynamic critical point. A computer program developed to solve two-dimensional flow fields is used to analyze non- classical dense gas phenomena in the single-phase gas region. A two-step, flux-limited, total variation diminishing scheme solves the time-dependent Euler equations for supersonic steady flow fields and mixed subsonic and supersonic transient flow fields. Two non- ideal gas models are incorporated into the numerical scheme in order to simulate dense gas effects. The van der Waals model, which is the simplest gas model that will show dense gas behavior, is employed to economically demonstrate qualitative trends in dense gas flows. The more complex Martin-Hou model is incorporated for cases where quantitative accuracy becomes more important. Simulated flows over simple geometries such as wedges, arcs, ramps, and steps using both the van der Waals gas model and the perfect gas model demonstrate significant differences in wave field configurations between dense gases and ideal gases. Results are also computed using the Martin-Hou equation of state which is more conservative in predicting dense gas effects than the van der Waals model. In addition to exploring the basic nature of dense gas flows for simple geometries, the utilization of dense gas properties to improve the efficiency of organic Rankine- cycle engines is investigated. Simulations of supersonic dense gas flows through impulse turbine cascades demonstrate improvements in flow quality through the cascades by reducing losses due to shock waves.
Two-dimensional vortices and accretion disks
NASA Astrophysics Data System (ADS)
Nauta, Michiel Doede
2000-01-01
Observations show that there are disks around certain stars that slowly rain down on the central (compact) object: accretion disks. The rate of depletion of the disk might be slow but is still larger than was expected on theoretical grounds. That is why it has been suggested that the disks are turbulent. Because the disk is thin and rotating this turbulence might be related to two-dimensional (2D) turbulence which is characterized by energy transfers towards small wave numbers and the formation of 2D-vortices. This hypothesis is investigated in this thesis by numerical simulations. After an introduction, the numerical algorithm that was inplemented is discussed together with its relation to an accretion disk. It performs well under the absence of discontinuities. The code is used to study 2D-turbulence under the influence of background rotation with compressibility and a shearing background flow. The first is found to be of little consequence but the shear flow alters 2D-turbulence siginificantly. Only prograde vortices of enough strength are able to withstand the shear flow. The size of the vortices in the cross stream direction is also found to be smaller than the equivalent of the thickness of an accretion disk. These circulstances imply that the assumption of two-dimensionality is questionable so that 2D-vortices might not abound in accretion disks. However, the existence of such vortices is not ruled out and one such a cortex is studied in detail in chapter 4. The internal structure of the vortex is well described by a balance between Coriolis, centrifugal and pressure forces. The vortex is also accompanied by two spiral compressible waves. These are not responsible for the azimuthal drift of the vortex, which results from secondary vortices, but they might be related to the small radial drift that is observed. Radial drift leads to accretion but it is not very efficient. Multiple vortex interactions are the topic of tha last chapter and though interesting the increase in accretion grows only linearly with the number of vortices.
NASA Astrophysics Data System (ADS)
Shen, F.; Feng, X. S.; Wang, Yuming; Wu, S. T.; Song, W. B.; Guo, J. P.; Zhou, Y. F.
2011-09-01
A three-dimensional (3-D), time-dependent, numerical magnetohydrodynamic (MHD) model is used to investigate the evolution and interaction of two coronal mass ejections (CMEs) in the nonhomogeneous ambient solar wind. The background solar wind is constructed on the basis of the self-consistent source surface with observed line of sight of magnetic field and density from the source surface of 2.5 Rs to Earth's orbit (215 Rs) and beyond. The two successive CMEs occurring on 28 March 2001 and forming a multiple magnetic cloud in interplanetary space are chosen as a test case, in which they are simulated by means of a two high-density, high-velocity, and high-temperature magnetized plasma blobs model, and are successively ejected into the nonhomogeneous background solar wind medium along different initial launch directions. The dynamical propagation and interaction of the two CMEs between 2.5 and 220 Rs are investigated. Our simulation results show that, although the two CMEs are separated by 10 h, the second CME is able to overtake the first one and cause compound interactions and an obvious acceleration of the shock. At the L1 point near Earth the two resultant magnetic clouds in our simulation are consistent with the observations by ACE. In this validation study we find that this 3-D MHD model, with the self-consistent source surface as the initial boundary condition and the magnetized plasma blob as the CME model, is able to reproduce and explain some of the general characters of the multiple magnetic clouds observed by satellite.
Relativity on two-dimensional spacetimes
Do-Hyung Kim
2013-07-26
Lorentz transformation on two-dimensional spacetime is obtained without assumption of linearity. To obtain this, we use the invariance of wave equations, which is recently proved to be equivalent to the causality preservation.
Mars Pathfinder Two-Dimensional Model
NSDL National Science Digital Library
2012-08-03
This activity is about the Mars Pathfinder spacecraft. Using cardboard and other materials, learners will create a two dimensional model of the spacecraft. A diagram with approximate measures of each component is provided.
Two-dimensional order and disorder thermofields
Belvedere, L. V. [Instituto de Fisica - Universidade Federal Fluminense, Av. Litora circumflex nea S/N, Boa Viagem Niteroi, CEP 24210-340 Rio de Janeiro (Brazil)
2006-11-15
The main objective of this paper was to obtain the two-dimensional order and disorder thermal operators using the Thermofield Bosonization formalism. We show that the general property of the two-dimensional world according with the bosonized Fermi field at zero temperature can be constructed as a product of an order and a disorder variables which satisfy a dual field algebra holds at finite temperature. The general correlation functions of the order and disorder thermofields are obtained.
Two-dimensional photonic band gap crystals
Cheryl Marie Anderson
1999-01-01
A photonic crystal is a periodic dielectric structure that possesses a band of frequencies in which propagating electromagnetic waves are forbidden. Two-dimensional photonic crystals exhibit a band gap for waves traveling in the crystal plane, a property that offers promise for improved operation of optoelectronic devices including semiconductor lasers, light-emitting diodes, and frequency filters. A theoretical investigation of two-dimensional photonic
MHD simulations of the flapping instability in tail-like magnetic configurations with guide field
NASA Astrophysics Data System (ADS)
Korovinskiy, Daniil; Divin, Andrey; Ivanov, Ivan; Semenov, Vladimir; Erkaev, Nikolay; Artemiev, Anton; Markidis, Stefano; Lapenta, Giovanni; Ivanova, Viktoria; Kubyshkina, Darya
2014-05-01
The flapping (kink) mode developing in the magnetotail-like magnetic configuration with tailward growing normal magnetic component and finite guide field is studied by means of linearized 2-dimensional and non-linear 3-dimensional MHD modeling. We consider a particular case of a weak normal magnetic component (that is, small radius of the magnetic field line curvature), which makes the configuration unstable to a special branch of ballooning instability known as "double-gradient" mode, introduced recently to describe the magnetotail flapping oscillations. The initial tail-like equilibrium is provided by conventional Grad-Shafranov equation. The results of the 2D linearized MHD code are in agreement with the analytical predictions, and the growth rate is found to be close to the peak value provided by an analytical estimate. Both 2D and 3D calculations confirm that the double-gradient mode is excited in a region of large curvature of the magnetic field lines. In agreement with the analytical predictions, non-zero guide field reduces the growth rate significantly for large (compare to the current sheet width L) wave numbers k, hence the modes kL ~ 1 are the fastest growing. Thus, the non-zero guide field introduces a characteristic wavelength corresponding to the dispersion curve peak. For the guide field of ~ 0.5 (in the lobe magnetic field units), the mode decays totally.
NASA Astrophysics Data System (ADS)
Fukazawa, K.; Walker, R. J.; Eriksson, S.
2014-12-01
In a series of simulation studies we have reported that vortices formed at Saturn's dawn magnetopause in simulations when IMF was northward. We interpreted these vortices as resulting from the Kelvin Helmholtz (K-H) instability. Thanks to recent advances in computer performance, we have been able to perform high resolution global MHD simulations of the Kronian magnetosphere with 0.1 Rs grid spacing. In these simulations we obtained the signature of the field-aligned currents from the K-H vortices in Saturn's auroral ionosphere and found small patchy regions of upward field-aligned current which may be related to auroral emissions. These patchy aurorae resembling our results have been reported from Cassini observations. In our previous simulations we have used the constant and simple solar wind conditions to understand the basic behavior of Kronian magnetosphere. In this study we have used Cassini observations of the solar wind upstream of Saturn to drive a massively parallel simulation. Using these solar wind data we simulated the Kronian magnetosphere from 2008-02-12/14:00:31 to 2008-02-13/01:59:31 when the Hubble Space Telescope (HST) observed Kronian UV auroral emissions. For these solar wind conditions there are several enhancements of the solar wind dynamic pressure (shocks) and a polarity reversal in the IMF components. From these simulations we obtained the dynamically changing shape and convection pattern of the Kronian magnetosphere in response to the variation of solar wind dynamic pressure and IMF direction. In particular, a layered convection pattern formed between the corotation region and magnetopause. The layers in this convection system interacted with each other, forming large vortices. We calculated the configuration of field aligned currents from the simulation and found layered and patchy distributions in the ionosphere. The pattern of these upward field aligned currents in the dawn side ionosphere resembles the configuration of auroral emission observed by HST well.
Juan E. Sanchez; Gijs Bosman; Mark E. Law
2003-01-01
The simulation of generation-recombination (GR) noise under periodic large-signal conditions in a partial differential equation-based silicon device simulator is presented. Using the impedance-field method with cyclostationary noise sources, it is possible to simulate the self- and cross-spectral densities between sidebands of a periodic large-signal stimulus. Such information is needed to develop noise correlation matrices for use with a circuit simulator.
NASA Astrophysics Data System (ADS)
Deng (??, Wei; Li (??, Hui; Zhang (??, Bing; Li (???, Shengtai
2015-06-01
We perform 3D relativistic ideal magnetohydrodynamics (MHD) simulations to study the collisions between high-? (Poynting-flux-dominated (PFD)) blobs which contain both poloidal and toroidal magnetic field components. This is meant to mimic the interactions inside a highly variable PFD jet. We discover a significant electromagnetic field (EMF) energy dissipation with an Alfvénic rate with the efficiency around 35%. Detailed analyses show that this dissipation is mostly facilitated by the collision-induced magnetic reconnection. Additional resolution and parameter studies show a robust result that the relative EMF energy dissipation efficiency is nearly independent of the numerical resolution or most physical parameters in the relevant parameter range. The reconnection outflows in our simulation can potentially form the multi-orientation relativistic mini jets as needed for several analytical models. We also find a linear relationship between the ? values before and after the major EMF energy dissipation process. Our results give support to the proposed astrophysical models that invoke significant magnetic energy dissipation in PFD jets, such as the internal collision-induced magnetic reconnection and turbulence model for gamma-ray bursts, and reconnection triggered mini jets model for active galactic nuclei. The simulation movies are shown in http://www.physics.unlv.edu/?deng/simulation1.html.
NASA Astrophysics Data System (ADS)
Karimabadi, H.; Krauss-Varban, D.; Huba, J. D.; Vu, H. X.
2004-09-01
Magnetic reconnection in a plane current sheet is investigated in both two and three dimensions, using three different types of simulation codes, Hall MHD, hybrid (electron fluid, kinetic ions), and a new code called Hall-less hybrid. The latter code, which is similar to the hybrid code but has the Hall term removed, enables us to clarify the differences between kinetic ion and Hall MHD approaches. The major findings of this research are (1) Sweet-Parker regime of reconnection cannot be maintained and does not reach a steady state in a kinetic plasma for physically interesting parameter regimes. (2) Fast asymptotic reconnection rate of 0.15VA0B0 is obtained both in the hybrid and Hall-less hybrid simulations with outflow boundaries. VA0 and B0 are the Alfvén velocity and magnetic field strength in the upstream region. This finding has two immediate implications. First, ion kinetics are sufficient to lead to fast reconnection even in the absence of the Hall term, and second, explanation of fast reconnection in terms of quadratic disperion of whistlers needs to be reconsidered, as whistlers are dispersionless in Hall-less hybrid limit. (3) Unlike in MHD, diffusion region is different in size that the region of localized resistivity. (4) While both Hall and hybrid codes show that reconnection is inherently asymmetric in three dimensions, there are differences in the nature of the asymmetry. In Hall MHD we show that the X-line grows in the direction of the electron drift, propagating as a (reconnection) wave because the current is carried by electrons, although the wave direction can change in the presence of a substantial ion flow. However, in the hybrid simulations here, as is the case for typical conditions at the magnetopause and magnetotail, ions carry the bulk of the current, and the observed asymmetry is found to be due to ion flow and not a wave motion unless the extent of finite resistivity in the third dimension is very thin, comparable to the current sheet thickness. Thus aside from scenarios where electrons are the dominant current carriers, such as very thin current sheets that are on electron scales, we do not expect the reconnection wave to form. This result is relevant to the magnetotail where dawn-dusk asymmetries are observed in the motions of auroral brightenings and surges, as well as in the statistical location of pressure decreases, flows, and magnetic signatures associated with the near-Earth neutral line and early plasmoids. We attribute the observed dawn-dusk asymmetries to ion flows. One interesting question left for future work is the possibility that reconnection waves may form in thin electron-scale current layers that are sometimes observed embedded within a thicker sheet in the magnetotail.
Statistics of the inverse-cascade regime in two-dimensional magnetohydrodynamic turbulence
Debarghya Banerjee; Rahul Pandit
2014-03-26
We present a detailed direct numerical simulation of statistically steady, homogeneous, isotropic, two-dimensional magnetohydrodynamic (2D MHD) turbulence. Our study concentrates on the inverse cascade of the magnetic vector potential. We examine the dependence of the statistical properties of such turbulence on dissipation and friction coefficients. We extend earlier work sig- nificantly by calculating fluid and magnetic spectra, probability distribution functions (PDFs) of the velocity, magnetic, vorticity, current, stream-function, and magnetic-vector-potential fields and their increments. We quantify the deviations of these PDFs from Gaussian ones by computing their flatnesses and hyperflatnesses. We also present PDFs of the Okubo-Weiss parameter, which distin- guishes between vortical and extensional flow regions, and its magnetic analog. We show that the hyperflatnesses of PDFs of the increments of the stream-function and the magnetic vector potential exhibit significant scale dependence and we examine the implication of this for the multiscaling of structure functions. We compare our results with those of earlier studies.
NASA Astrophysics Data System (ADS)
Hayashi, Keiji; Hoeksema, J. T.; Liu, Y.; Sun, X.; Bobra, M.; Norton, A. A.
2013-07-01
We investigate the dynamics of the solar active regions by means of our data-driven time-dependent three-dimensional MHD simulation model using the HMI vector magnetic field data. The simulations start with pre-emergence phase, or very early phase of the active region so that the development of the loop structures and other signatures of the active regions will be traced. We tested several cases, mainly for AR 11158 of Feb. 2011. Either of the plasma motion or electric field, inferred from the DAVE4VM (Schuck, 2008) is given to the solar-surface boundary surface of the simulation box to which the method of projected normal characteristics (Nakagawa et al. 1987; Wu and Wang, 1987) is applied to ensure the numerical stability and consistency in physics. As our first attempt, we choose the ideal MHD equations without any additional terms except gravity. The results of the simulation show that the method can trace some signatures of the solar active regions, such as development of the magnetic-field loop and (nonlinear) twist. Not having all information at the simulation initial time, nor all physics processes on the photosphere, at transition region, and in the solar corona, agreements in plasma quantities with the other observation such as AIA image data are limited. No flare-like eruptions were obtained under a simulation setting we currently test. The temporal sequences of three-component vector data can give good constraints on the MHD simulation studies of the sub-Alfvenic region, though, we will need more observations, and probably assumptions, to fulfill the physics system. The MHD simulation can be a powerful tool to bridge the measurements and observation, helping interpretation and giving requirement.
Jones, Joseph L.; Fulford, Janice M.; Voss, Frank D.
2002-01-01
A system of numerical hydraulic modeling, geographic information system processing, and Internet map serving, supported by new data sources and application automation, was developed that generates inundation maps for forecast floods in near real time and makes them available through the Internet. Forecasts for flooding are generated by the National Weather Service (NWS) River Forecast Center (RFC); these forecasts are retrieved automatically by the system and prepared for input to a hydraulic model. The model, TrimR2D, is a new, robust, two-dimensional model capable of simulating wide varieties of discharge hydrographs and relatively long stream reaches. TrimR2D was calibrated for a 28-kilometer reach of the Snoqualmie River in Washington State, and is used to estimate flood extent, depth, arrival time, and peak time for the RFC forecast. The results of the model are processed automatically by a Geographic Information System (GIS) into maps of flood extent, depth, and arrival and peak times. These maps subsequently are processed into formats acceptable by an Internet map server (IMS). The IMS application is a user-friendly interface to access the maps over the Internet; it allows users to select what information they wish to see presented and allows the authors to define scale-dependent availability of map layers and their symbology (appearance of map features). For example, the IMS presents a background of a digital USGS 1:100,000-scale quadrangle at smaller scales, and automatically switches to an ortho-rectified aerial photograph (a digital photograph that has camera angle and tilt distortions removed) at larger scales so viewers can see ground features that help them identify their area of interest more effectively. For the user, the option exists to select either background at any scale. Similar options are provided for both the map creator and the viewer for the various flood maps. This combination of a robust model, emerging IMS software, and application interface programming should allow the technology developed in the pilot study to be applied to other river systems where NWS forecasts are provided routinely.
Two-dimensional Lennard-Jones liquid-vapour interphase
NASA Astrophysics Data System (ADS)
Mederos, L.; Chacón, E.; Navascués, G.; Lombardero, M.
A functional perturbation theory is used to study the properties of a two-dimensional Lennard-Jones liquid-vapour interphase. The coexistence curve, density profile, line tension, structure factor and isothermal compressibility are obtained and discussed. Comparison with computer simulations is also included. The effects of the dimensionality are also studied. The product of the line tension by the isothermal compressibility is discussed. Several critical exponents are estimated by this theory and compared with the classical and exact values.
Teaching Sequence for Two Dimensional Motion R. A. Morse, St. Albans School, Washington, DC
Steinberg, Richard N.
_morse@cathedral.org PER Conference Guelph 2000 Teaching tools for two dimensional motion Dynaturtle Simulation: rocket ship in friction free two-dimensional space. impulse engine gives "kick" when button pressed. can, multiple kicks, rotations and starting and stopping the rocket b) try to find highest speed obtained going
Shear viscosity and shear thinning in two-dimensional Yukawa , J. Goree2
Goree, John
Shear viscosity and shear thinning in two-dimensional Yukawa liquids Z. Donk´o1 , J. Goree2 , P using two different nonequi- librium molecular dynamics simulation methods. Shear viscosity values.e., the viscosity diminishes with increasing shear rate. It is expected that two-dimensional dusty plasmas
Information-Theoretic Limits of Two-Dimensional Optical Recording Channels
Paul H. Siegel
2006-01-01
Two-dimensional intersymbol interference channels are models for two-dimensional optical storage and holographic recording systems. We describe analytical bounds and simulation-output estimates for achievable rates of such channels, as well as signal processing and coding algorithms that approach these information-theoretic limits
Two-dimensional nonlinear beam shaping.
Shapira, Asia; Shiloh, Roy; Juwiler, Irit; Arie, Ady
2012-06-01
We develop a technique for two-dimensional arbitrary wavefront shaping in quadratic nonlinear crystals by using binary nonlinear computer generated holograms. The method is based on transverse illumination of a binary modulated nonlinear photonic crystal, where the phase matching is partially satisfied through the nonlinear Raman-Nath process. We demonstrate the method experimentally showing a conversion of a fundamental Gaussian beam pump light into three Hermite-Gaussian and three Laguerre-Gaussian beams in the second harmonic. Two-dimensional binary nonlinear computer generated holograms open wide possibilities in the field of nonlinear beam shaping and mode conversion. PMID:22660146
Entanglement entropy in two dimensional string theory
Hartnoll, Sean A
2015-01-01
To understand an emergent spacetime is to understand the emergence of locality. Entanglement entropy is a powerful diagnostic of locality, because locality leads to a large amount of short distance entanglement. Two dimensional string theory is among the very simplest instances of an emergent spatial dimension. We compute the entanglement entropy in the large $N$ matrix quantum mechanics dual to two dimensional string theory, in the semiclassical limit of weak string coupling. We isolate a logarithmically large, but finite, contribution that corresponds to the short distance entanglement of the tachyon field in the emergent spacetime. From the spacetime point of view, the entanglement is regulated by a nonperturbative `graininess' of space.
NASA Technical Reports Server (NTRS)
Whitten, R. C.; Borucki, W. J.; Watson, V. R.; Shimazaki, T.; Woodward, H. T.; Riegel, C. A.; Capone, L. A.; Becker, T.
1977-01-01
The two-dimensional model of stratospheric constituents is presented in detail. The derivation of pertinent transport parameters and the numerical solution of the species continuity equations, including a technique for treating the stiff differential equations that represent the chemical kinetic terms, and appropriate methods for simulating the diurnal variations of the solar zenith angle and species concentrations are discussed. Predicted distributions of tracer constituents (ozone, carbon 14, nitric acid) are compared with observed distributions.
Extended MHD Simulations of the Formation, Merging, and Heating of Compact Tori
NASA Astrophysics Data System (ADS)
Macnab, Angus; Woodruff, Simon
2008-11-01
We examine the formation, compression, merging, and stability of compact tori (CT) for magnetic field generation and heating by use of the 3D extended MHD code, NIMROD [C.R. Sovinec et al. J. Comp. Phys. 355, 195, (2004)]. Recent advances in the NIMROD code allow us to study plasmas, including the effects of Hall physics and highly anisotropic and field dependent transport. The physics of CT formation and acceleration requires numerical models that can effectively treat plasma flows in systems that are often far from equilibrium. The formation of plasmas with strong magnetic fields by use of a low power source still remains a critical issue. Recently, a novel means for generating strong B from a low current source was developed, and relies on the repetitive injection of plasma from a coaxial gun, leading to the step-wise increase in both total circulating current and core plasma temperature. A natural limit is encountered much as in CT injection for fueling into tokamaks, namely the injected plasma must penetrate the target plasma. To reach high fields, this then will require compression before injection. Stability of the configuration to fluid (e.g. Rayleigh-Taylor) and ideal modes (e.g. tilt/shift) are examined.
The Effects of Differential Rotation on the Magnetic Structure of the Solar Corona: MHD Simulations
NASA Technical Reports Server (NTRS)
Lionello, Roberto; Riley, Pete; Linker, Jon A.; Mikic, Zoran
2004-01-01
Coronal holes are magnetically open regions from which the solar wind streams. Magnetic reconnection has been invoked to reconcile the apparently rigid rotation of coronal holes with the differential rotation of magnetic flux in the photosphere. This mechanism might also be relevant to the formation of the slow solar wind, the properties of which seem to indicate an origin from the opening of closed magnetic field lines. We have developed a global MHD model to study the effect of differential rotation on the coronal magnetic field. Starting from a magnetic flux distribution similar to that of Wang et al., which consists of a bipolar magnetic region added to a background dipole field, we applied differential rotation over a period of 5 solar rotations. The evolution of the magnetic field and of the boundaries of coronal holes are in substantial agreement with the findings of Wang et al.. We identified examples of interchange reconnection and other changes of topology of the magnetic field. Possible consequences for the origin of the slow solar wind are also discussed.
Particle simulation algorithms with short-range forces in MHD and fluid flow
Cable, S.; Tajima, T.; Umegaki, K.
1992-07-01
Attempts are made to develop numerical algorithms for handling fluid flows involving liquids and liquid-gas mixtures. In these types of systems, the short-range intermolecular interactions are important enough to significantly alter behavior predicted on the basis of standard fluid mechanics and magnetohydrodynamics alone. We have constructed a particle-in-cell (PIC) code for the purpose of studying the effects of these interactions. Of the algorithms considered, the one which has been successfully implemented is based on a MHD particle code developed by Brunel et al. In the version presented here, short range forces are included in particle motion by, first, calculating the forces between individual particles and then, to prevent aliasing, interpolating these forces to the computational grid points, then interpolating the forces back to the particles. The code has been used to model a simple two-fluid Rayleigh-Taylor instability. Limitations to the accuracy of the code exist at short wavelengths, where the effects of the short-range forces would be expected to be most pronounced.
Detecting disparity in two-dimensional patterns
Bart Farell
One can measure the disparities between two retinal images in several different ways. Experiments were conducted to identify the measure that is invariant at the threshold for detecting the disparity of two-dimensional patterns. The patterns used were stereo plaids, which permit a partial dissociation between the disparity of the pattern and the disparities of its one-dimensional compo- nents. For plaids
Numerical Modelling of the Two-Dimensional
potential, and the numerical scheme is formulated so that the continuity equation for the currents that the divergences of the electromagnetic fields are fulfilled up to the local truncation error of the numerical 1Numerical Modelling of the Two-Dimensional Vlasov-Maxwell System Bengt Eliasson Department
NASA Astrophysics Data System (ADS)
Daw, Harold A.
1987-08-01
A two-dimensional flame table was constructed for visually demonstrating acoustical modes in a cavity. This flame table is an extension of the one-dimensional flame tube or Rubens flame tube apparatus. Photographs of some of the lower-order modes on rectangular box and cylindrical box flame table cavities are included.
Two Dimensional Quantum Gravity Coupled to Matter
R. B. Mann
1992-06-25
A classical two dimensional theory of gravity which has a number of interesting features (including a Newtonian limit, black holes and gravitational collapse) is quantized using conformal field theoretic techniques. The critical dimension depends upon Newton's constant, permitting models with $d=4$. The constraint algebra and scaling properties of the model are computed.
Two-Dimensional Turbulence in Magnetized Plasmas
ERIC Educational Resources Information Center
Kendl, A.
2008-01-01
In an inhomogeneous magnetized plasma the transport of energy and particles perpendicular to the magnetic field is in general mainly caused by quasi two-dimensional turbulent fluid mixing. The physics of turbulence and structure formation is of ubiquitous importance to every magnetically confined laboratory plasma for experimental or industrial…
On the two-dimensional sloshing problem
Kozlov, Vladimir; Kuznetsov, Nikolay; Motygin, Oleg
2011-01-01
A correct proof is given for the following assertions about the two-dimensional sloshing problem. The fundamental eigenvalue is simple and the corresponding stream function may be chosen to be non-negative in the closure of the water domain. New proof is based on stricter assumptions about the water domain; namely, it must satisfy John’s condition. PMID:24959097
Canonical quantization of two-dimensional gravity
S. N. Vergeles
2001-02-01
A canonical quantization of two-dimensional gravity minimally coupled to real scalar and spinor Majorana fields is presented. The physical state space of the theory is completely described and calculations are also made of the average value of the metric tensor relative to states close to the ground state
NASA Astrophysics Data System (ADS)
Shao, X.; Tan, L. C.; Fung, S. F.; Vassiliadis, D.; Sharma, A. S.
2011-12-01
Recent work of Tan et al. [2011] found evidence of relativistic electron acceleration by the compressional-mode ULF waves during a storm sudden commencement event on September 25, 2001 from the observations by four Cluster spacecraft measuring ULF waves and low-energy electron flux, and five LANL spacecraft measuring energetic electron fluxes over a wide energy range. We perform global MHD simulation through NASA/CCMC to investigate the excitation and distribution of compressional ULF waves during the event. Comparison with satellite and ground observations are given. In this event, the energetic electron flux measured by LANL shows modulation of low-energy electrons and acceleration of high-energy electrons by the compressional poloidal-mode electric field oscillations within 2-3 hours. Implication of simulated ULF wave distribution for relativistic electron acceleration will be discussed. Tan, L. C., X. Shao, A. S. Sharma, and S. F. Fung (2011), Relativistic electron acceleration by compressional-mode ULF waves: Evidence from correlated Cluster, Los Alamos National Laboratory spacecraft, and ground-based magnetometer measurements, J. Geophys. Res., 116, A07226, doi:10.1029/2010JA016226.
Ward Manchester IV; Angelos Vourlidas; Gabor Toth; Noe Lugaz; Ilia Roussev; Tamas Gombosi; Igor Sokolov; Darren De Zeeuw; Merav Opher
2008-05-23
We numerically model the coronal mass ejection (CME) event of October 28, 2003 that erupted from active region 10486 and propagated to Earth in less than 20 hours causing severe geomagnetic storms. The magnetohydrodynamic (MHD) model is formulated by first arriving at a steady state corona and solar wind employing synoptic magnetograms. We initiate two CMEs from the same active region, one approximately a day earlier that preconditions the solar wind for the much faster CME on the 28th. This second CME travels through the corona at a rate of over 2500 km s$^{-1}$ driving a strong forward shock. We clearly identify this shock in an image produced by the Large Angle Spectrometric Coronagraph (LASCO) C3, and reproduce the shock and its appearance in synthetic white light images from the simulation. We find excellent agreement with both the general morphology and the quantitative brightness of the model CME with LASCO observations. These results demonstrate that the CME shape is largely determined by its interaction with the ambient solar wind and may not be sensitive to the initiation process. We then show how the CME would appear as observed by wide-angle coronagraphs onboard the Solar Terrestrial Relations Observatory (STEREO) spacecraft. We find complex time evolution of the white-light images as a result of the way in which the density structures pass through the Thomson sphere. The simulation is performed with the Space Weather Modeling Framework (SWMF).
NASA Astrophysics Data System (ADS)
Wang, C.; Li, W. Y.; Lin, D.; Guo, X. C.
2014-12-01
Using the PPMLR-MHD global simulation model, we examined the Kelvin-Helmholtz (K-H) instability at the magnetopause for northward interplanetary magnetic field (IMF) conditions with various solar wind speed (400, 600, and 800 km/s). The spatial distribution of the K-H wave power in the equatorial plane shows two distinct power populations, referring to the two modes of K-H surface waves. The K-H instability starts at about 30o longitude, and grows exponentially with a spatial growth rate of 0.28 ~ 0.87 RE-1until ~45o longitude where the vortices fully develop. The wave frequency, wavelength, and phase speed are also given. The KH wavelength grows spatially with increasing distance from the sub-solar point tail-ward along the flank magnetopause. Model results show that the higher solar wind speed generates K-H waves with higher frequency under the northward IMF, and the wavelengths and the phase speeds increase with the increase of the longitude. Statistically study of the 56 KHI events observed by THEMIS,Geotail, TC-1, Cluster support our simulation predictions.
Two-dimensional behavior of Megagauss-field-confined solid fiber Z-pinches
Lindemuth, I.R.
1989-01-01
At Los Alamos, we have performed one-dimensional and two-dimensional magnetohydrodynamic (MHD) computations of the formation and evolution of fiber-formed plasmas. Our one-dimensional computations show that current in the existing Los Alamos and Naval Research Laboratory experiments is carried by hot plasma which has been ablated from the solid fiber. Our two-dimensional computations exhibit m = 0 unstable behavior in the hot, exterior plasma prior to complete ablation of the solid fiber; the m = 0 behavior enhances the fiber ablation rate. The MHD model used in our computations accesses the Los Alamos SESAME tabulated atomic data base computer library to determine material properties. The MHD partial differential equations are solved numerically using an alternating-direction implicit finite difference method which does not resort to fractional time steps, or operator splitting.'' The computations use cold start'' initial conditions in an attempt to compute the behavior of the pinches from t = 0. The two-dimensional computations begin with a 2% random variation superimposed upon the density profile of the solid core to provide perturbations for instability growth. In this paper, the two-dimensional computations are further examined. In the computations reported here, two-different axial lengths, l, are considered, l = 5 mm and l = 300 {mu}m, to study long- and short-wavelength behavior. The long-wavelength computations show the formation and evolution of hot spots in the hot corona surrounding the cold, solid core of the plasma channel; subsequently, hot spots form on the axis of the discharge. The short-wavelength computations exhibit a periodic re-establishment of a quasi-one-dimensional configuration. 5 refs., 5 figs.
Transport behavior of water molecules through two-dimensional nanopores
Zhu, Chongqin; Li, Hui; Meng, Sheng, E-mail: smeng@iphy.ac.cn [Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China)
2014-11-14
Water transport through a two-dimensional nanoporous membrane has attracted increasing attention in recent years thanks to great demands in water purification and desalination applications. However, few studies have been reported on the microscopic mechanisms of water transport through structured nanopores, especially at the atomistic scale. Here we investigate the microstructure of water flow through two-dimensional model graphene membrane containing a variety of nanopores of different size by using molecular dynamics simulations. Our results clearly indicate that the continuum flow transits to discrete molecular flow patterns with decreasing pore sizes. While for pores with a diameter ?15 Å water flux exhibits a linear dependence on the pore area, a nonlinear relationship between water flux and pore area has been identified for smaller pores. We attribute this deviation from linear behavior to the presence of discrete water flow, which is strongly influenced by the water-membrane interaction and hydrogen bonding between water molecules.
Two-Dimensional Mathematical Modeling of the Pack Carburizing Process
NASA Astrophysics Data System (ADS)
Sarkar, S.; Gupta, G. S.
2008-10-01
Pack carburization is the oldest method among the case-hardening treatments, and sufficient attempts have not been made to understand this process in terms of heat and mass transfer, effect of alloying elements, dimensions of the sample, etc. Thus, a two-dimensional mathematical model in cylindrical coordinate is developed for simulating the pack carburization process for chromium-bearing steel in this study. Heat and mass balance equations are solved simultaneously, where the surface temperature of the sample varies with time, but the carbon potential at the surface during the process remains constant. The fully implicit finite volume technique is used to solve the governing equations. Good agreement has been found between the predicted and published data. The effect of temperature, carburizing time, dimensions of the sample, etc. on the pack carburizing process shows some interesting results. It is found that the two-dimensional model gives better insight into understanding the carburizing process.
Two-Dimensional Computational Model for Wave Rotor Flow Dynamics
NASA Technical Reports Server (NTRS)
Welch, Gerard E.
1996-01-01
A two-dimensional (theta,z) Navier-Stokes solver for multi-port wave rotor flow simulation is described. The finite-volume form of the unsteady thin-layer Navier-Stokes equations are integrated in time on multi-block grids that represent the stationary inlet and outlet ports and the moving rotor passages of the wave rotor. Computed results are compared with three-port wave rotor experimental data. The model is applied to predict the performance of a planned four-port wave rotor experiment. Two-dimensional flow features that reduce machine performance and influence rotor blade and duct wall thermal loads are identified. The performance impact of rounding the inlet port wall, to inhibit separation during passage gradual opening, is assessed.
Vortex annihilation and inverse cascades in two dimensional superfluid turbulence
NASA Astrophysics Data System (ADS)
Lucas, Andrew; Chesler, Paul M.
2015-03-01
The dynamics of a dilute mixture of vortices and antivortices in a turbulent two-dimensional superfluid at finite temperature is well described by first order Hall-Vinen-Iordanskii equations, or dissipative point vortex dynamics. These equations are governed by a single dimensionless parameter: the ratio of the strength of drag forces to Magnus forces on vortices. When this parameter is small, we demonstrate using numerical simulations that the resulting superfluid enjoys an inverse energy cascade where small scale stirring leads to large scale vortex clustering. We argue analytically and numerically that the vortex annihilation rate in a laminar flow may be parametrically smaller than the rate in a turbulent flow with an inverse cascade. This suggests a new way to detect inverse cascades in experiments on two-dimensional superfluid turbulence using cold atomic gases, where traditional probes of turbulence such as the energy spectrum are not currently accessible.
SOLVING THE TWO-DIMENSIONAL DIFFUSION FLOW MODEL.
Hromadka, T.V., II; Lai, Chintu
1985-01-01
A simplification of the two-dimensional (2-D) continuity and momentum equations is the diffusion equation. To investigate its capability, the numerical model using the diffusion approach is applied to a hypothetical failure problem of a regional water reservoir. The model is based on an explicit, integrated finite-difference scheme, and the floodplain is simulated by a popular home computer which supports 64K FORTRAN. Though simple, the 2-D model can simulate some interesting flooding effects that a 1-D full dynamic model cannot.
Magnetization study of two dimensional helium three
NASA Astrophysics Data System (ADS)
Guo, Lei
This dissertation discusses a magnetization study of a two dimensional Fermi system. Our group developed a SQUID NMR system to study the magnetization of two dimensional 3He on both GTA grafoil and ZYX Graphite substrates. Benefiting from SQUID technology, our NMR experiments were performed at very low applied magnetic field thus avoid the masking of ordering by strong external field. Monolayer 3He films adsorbed on crystalline graphite are considered a nearly ideal example of a two dimensional system of highly correlated fermions. By controlling the 3He areal density, adsorbed films exhibit a wide range of structures with different temperature- dependent magnetic properties and heat capacities. Our recent experiments on two dimensional 3He adsorbed on ZYX graphite focused on the anti-ferromagnetic 4/7 phase and the ferromagnetic incommensurate solid state of a second 3He monolayer. Ferromagnetic order was observed in two dimensional 3He films on both Grafoil and highly oriented ZYX grade exfoliated graphite. The dipolar field plays an important role in magnetic ordering in two dimensional spin systems. The dipole-dipole interaction leads to a frequency shift of the NMR absorption line. The resulting 3He NMR lineshape on Grafoil was a broad peak shifted towards lower frequency with a background from the randomly oriented regions extending to positive frequencies. Compared to Grafoil, ZYX graphite has a much greater structural coherence and is more highly oriented. When studying magnetism of 3He films on ZYX substrate we found that the features we observed in our original Grafoil experiment were much more pronounced on ZYX graphite. In addition, we observed some multi-peak structure on the 3He NMR lineshape, which suggest a series of spin wave resonances. We also studied the magnetic properties of the second layer of 3He films on ZYX substrate at density around 4/7 phase. To eliminate the paramagnetic signal of the first layer solid, we pre-plated a 4He layer on the ZYX that serves as a substrate for the 3He layer. In this region of density, the 3He film acts as a quantum antiferromagnet with disordered ground state (Quantum Spin Liquid). Our experimental results are reported and similar work is reviewed.
Large Eddy - Lattice Boltzmann (LES-LB) Simulations of Fluid and MHD Turbulence
Brian Keating; Min Soe; George Vahala; Linda Vahala; Jeffrey Yepez; Jonathan Carter
2007-01-01
For high Reynolds number turbulence, the resource requirements for a full space-time DNS simulation scales as Re^3 -- which is far beyond any foreseeable computational resources. For problems that require instantaneous fields, one is forced into an LES in which one filters out the unresolvable small scales in the simulation but must then deal with the effects of the subgrid
Shen, Fang; Zhang, Jie; Hess, Phillip; Wang, Yuming; Feng, Xueshang; Cheng, Hongze; Yang, Yi
2015-01-01
The dynamic process of coronal mass ejections (CMEs) in the heliosphere provides us the key information for evaluating CMEs' geo-effectiveness and improving the accurate prediction of CME induced Shock Arrival Time (SAT) at the Earth. We present a data constrained three dimensional (3D) magnetohydrodynamic (MHD) simulation of the evolution of the CME in a realistic ambient solar wind for the July 12-16, 2012 event by using the 3D COIN-TVD MHD code. A detailed comparison of the kinematic evolution of the CME between the observations and the simulation is carried out, including the usage of the time-elongation maps from the perspectives of both Stereo A and Stereo B. In this case study, we find that our 3D COIN-TVD MHD model, with the magnetized plasma blob as the driver, is able to re-produce relatively well the real 3D nature of the CME in morphology and their evolution from the Sun to Earth. The simulation also provides a relatively satisfactory comparison with the in-situ plasma data from the Wind spacecraf...
NASA Technical Reports Server (NTRS)
Le Texier, H.; Solomon, S.; Thomas, R. J.; Garcia, R. R.
1989-01-01
Seasonal variations of the OH-asterisk (7-5) mesospheric hydroxyl emission at 1.89 microns observed by the SME near-IR spectrometer are compared with the theoretical predictions of a two-dimensional dynamical/chemical model. The good agreement found at low latitudes for both dayglow and nightglow provides support for the model assumption that breaking gravity waves induce seasonal and latitudinal variations in diffusion. The seasonal behavior of atomic hydrogen in the upper mesosphere (related to vertical transport) and/or uncertainties in the OH Meinel band parameters are proposed as possible explanations for the discrepancy noted between model and observational data for the middle latitudes.
Plasmonics with two-dimensional conductors.
Yoon, Hosang; Yeung, Kitty Y M; Kim, Philip; Ham, Donhee
2014-03-28
A wealth of effort in photonics has been dedicated to the study and engineering of surface plasmonic waves in the skin of three-dimensional bulk metals, owing largely to their trait of subwavelength confinement. Plasmonic waves in two-dimensional conductors, such as semiconductor heterojunction and graphene, contrast the surface plasmonic waves on bulk metals, as the former emerge at gigahertz to terahertz and infrared frequencies well below the photonics regime and can exhibit far stronger subwavelength confinement. This review elucidates the machinery behind the unique behaviours of the two-dimensional plasmonic waves and discusses how they can be engineered to create ultra-subwavelength plasmonic circuits and metamaterials for infrared and gigahertz to terahertz integrated electronics. PMID:24567472
Symmetry in two-dimensional gravity
Xu, K.W. (Center for Theoretical Physics, Physics Dept., Texas A and M Univ., TX (US)); Zhu, C.J. (International Center for Theoretical Physics, I-34100 Trieste (IT))
1991-05-30
The authors study the symmetry of two-dimensional gravity by choosing a generic gauge. A local action is derived which reduces to either the Liouville action or the Polyakov one by reducing to the conformal or light-cone gauge respectively. The theory is also solved classically. This paper shows that an SL(2,R) covariant gauge can be chosen so that the two-dimensional gravity has a manifest Virasoro and the s1(2,R)-current symmetry discovered by Polyakov. The symmetry algebra of the light-cone gauge is shown to be isomorphic to the Beltrami algebra. By using the contour integration method the authors construct the BRST charge Q{sub B} corresponding to this algebra following the Fradkin-Vilkovisky procedure and prove that the nilpotence of Q{sub B} requires c = 28 and {alpha}{sub 0} = 1.
Tsiklauri, D
2014-01-01
Previous studies [Malara et al ApJ, 533, 523 (2000)] considered small-amplitude Alfven wave (AW) packets in Arnold-Beltrami-Childress (ABC) magnetic field using WKB approximation. In this work linearly polarised Alfven wave dynamics in ABC magnetic field via direct 3D MHD numerical simulation is studied for the first time. Gaussian AW pulse with length-scale much shorter than ABC domain length and harmonic AW with wavelength equal to ABC domain length are studied for four different resistivities. While it is found that AWs dissipate quickly in the ABC field, surprisingly, AW perturbation energy increases in time. In the case of the harmonic AW perturbation energy growth is transient in time, attaining peaks in both velocity and magnetic perturbation energies within timescales much smaller than resistive time. In the case of the Gaussian AW pulse velocity perturbation energy growth is still transient in time, attaining a peak within few resistive times, while magnetic perturbation energy continues to grow. It ...
Manchester, Ward; Toth, Gabor; Lugaz, Noe; Roussev, Ilia; Gombosi, Tamas; Sokolov, Igor; De Zeeuw, Darren; Opher, Merav
2008-01-01
We numerically model the coronal mass ejection (CME) event of October 28, 2003 that erupted from active region 10486 and propagated to Earth in less than 20 hours causing severe geomagnetic storms. The magnetohydrodynamic (MHD) model is formulated by first arriving at a steady state corona and solar wind employing synoptic magnetograms. We initiate two CMEs from the same active region, one approximately a day earlier that preconditions the solar wind for the much faster CME on the 28th. This second CME travels through the corona at a rate of over 2500 km s$^{-1}$ driving a strong forward shock. We clearly identify this shock in an image produced by the Large Angle Spectrometric Coronagraph (LASCO) C3, and reproduce the shock and its appearance in synthetic white light images from the simulation. We find excellent agreement with both the general morphology and the quantitative brightness of the model CME with LASCO observations. These results demonstrate that the CME shape is largely determined by its interact...
Deeply subrecoil two-dimensional Raman cooling
Boyer, V.; Phillips, W.D. [National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States); Clarendon Laboratory, University of Oxford, Oxford OX1 3PU (United Kingdom); Lising, L.J.; Rolston, S.L. [National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States)
2004-10-01
We report the implementation of a two-dimensional Raman cooling scheme using sequential excitations along the orthogonal axes. Using square pulses, we have cooled a cloud of ultracold cesium atoms down to an rms velocity spread of 0.39(5) recoil velocities, corresponding to an effective transverse temperature of 30 nK (0.15T{sub rec}). This technique can be useful to improve cold-atom atomic clocks and is particularly relevant for clocks in microgravity.
Two Dimensional Electronic Spectroscopy of Molecular Complexes
Minhaeng Cho; Tobias Brixner; Igor Stiopkin; Harsha Vaswanib; Graham R. Flemingb
Two dimensional (2D) heterodyne-detected electronic photon echo spectroscopy is introduced and described. We give an intuitive description of the origin and information content of 2D electronic spectra, focusing on molecular complexes. We identify two important quantities—the transition dipole term, and the transition frequency cross correlation function that controls the appearance of 2D electronic spectra. We also show how the transition
Performance prediction of straight two dimensional diffusers
NASA Technical Reports Server (NTRS)
Greywall, M. S.
1980-01-01
A method, based on full viscous calculations, is presented to predict performance of straight two dimensional diffusers. The method predicts adequately the experimental pressure recovery data, up to the point of maximum pressure recovery, for small and large inlet boundary layer thicknesses. It is shown that at the point of maximum pressure recovery the streamwise velocity in the very near wall region varies as Z to the 0.22 power, where Z is the distance from the diffuser wall.
Two-dimensional microwave tomographic system
S. Y. Semenov; A. E. Bulyshev; A. E. Souvorov; R. H. Svenson; Y. E. Sizov; V. Y. Borisov; I. M. Kozlov; V. G. Poskuh; G. P. Tatsis
1996-01-01
The results of experiments on the two-dimensional (2D) quasi real-time microwave tomographic system are reported. Reconstruction possibilities of this system are demonstrated on the phantoms and the heart, including canine beating heart. The analysis of the quality of 2D images of the physical and mathematical phantoms is reported. The accurate solution of the inverse problem of the scalar Helmholtz equation
Two-dimensional arrays for medical ultrasound
S. W. Smith; G. E. Trahey; O. T. von Ramm
1991-01-01
The design, fabrication and evaluation of two-dimensional transducer arrays are described for medical ultrasound imaging. A 4×32, 2.8-MHz array was developed to use new signal processing techniques for improved B-scan imaging including elevation focusing, phase correction and synthetic aperture imaging. Laboratory measurements from typical array elements showed 50 ? insertion loss of -56 dB, -6 dB fractional bandwidth of 43%,
Two Dimensional Knapsack with Unloading Constraints
Jefferson L. M. da Silveira; Eduardo C. Xavier; Flávio K. Miyazawa
2011-01-01
n this paper we present approximation algorithms for the two dimensional knapsack problem with unloading constraints. In this problem, we have a bin B of width and height 1, and a list L with n items of C different classes, each item ai with height h(ai), width w(ai), profit p(ai) and class c(ai). We have to pack a subset of
Statistical Mechanics of Two-dimensional Foams
Marc Durand
2010-09-07
The methods of statistical mechanics are applied to two-dimensional foams under macroscopic agitation. A new variable -- the total cell curvature -- is introduced, which plays the role of energy in conventional statistical thermodynamics. The probability distribution of the number of sides for a cell of given area is derived. This expression allows to correlate the distribution of sides ("topological disorder") to the distribution of sizes ("geometrical disorder") in a foam. The model predictions agree well with available experimental data.
Two-dimensional photonic crystal lasers
Mitsuru Yokoyama; Masahiro Imada; Susumu Noda
2002-01-01
In this article, we report on a two-dimensional (2D) photonic crystal (PhC) laser with a surface-emitting function. First of all, 2D PhC laser with triangular-lattice structure is described. A uniform 2D coherent lasing oscillation based on coupling of lightwaves propagating to six equivalent Gamma-X directions is successfully demonstrated. A large area 2D lasing oscillation over 300 micrometers in diameter and
A Two-Dimensional Photonic Crystal Laser
Kuon Inoue; Michihide Sasada; Jun Kawamata; Kazuaki Sakoda; Joseph W. Haus
1999-01-01
We report on observation of laser action unique to a two-dimensional (2D) photonic lattice.When dye-solution filled in air-holes of a 2D lattice was optically-pumped, laser action withoutexternal mirrors is found to occur at a specific wavelength corresponding to a flat band-dispersionin a high-symmetry direction of the 2D lattice plane; a small group-velocity is responsible for thelasing. On further increasing the
3D Relativistic MHD Simulations of Magnetized Spine-Sheath Relativistic Jets
NASA Astrophysics Data System (ADS)
Mizuno, Yosuke; Hardee, P.; Nishikawa, K.-I.
We have performed numerical simulations of weakly and strongly magnetized relativistic jets em- bedded in a weakly and strongly magnetized stationary or mildly relativistic (0.5c) sheath using the RAISHIN code. In the numerical simulations a jet with Lorentz factor ? = 2.5 is precessed to break the initial equilibrium configuration. Results of the numerical simulations are compared to theoretical predictions from a normal mode analysis of the linearized RMHD equations de- scribing a uniform axially magnetized cylindrical relativistic jet embedded in a uniform axially magnetized moving sheath. The prediction of increased stability of a weakly-magnetized sys- tem with mildly relativistic sheath flow to Kelvin-Helmholtz instabilities and the stabilization of a strongly-magnetized system with mildly relativistic sheath flow is confirmed by the numerical simulations.
3D Relativistic MHD Simulations of Magnetized Spine-Sheath Relativistic Jets
Y. Mizuno; P. Hardee; K. -I. Nishikawa
2006-11-06
We have performed numerical simulations of weakly and strongly magnetized relativistic jets embedded in a weakly and strongly magnetized stationary or mildly relativistic (0.5c) sheath using the RAISHIN code. In the numerical simulations a jet with Lorentz factor \\gamma=2.5 is precessed to break the initial equilibrium configuration. Results of the numerical simulations are compared to theoretical predictions from a normal mode analysis of the linearized RMHD equations describing a uniform axially magnetized cylindrical relativistic jet embedded in a uniform axially magnetized moving sheath. The prediction of increased stability of a weakly-magnetized system with mildly relativistic sheath flow to Kelvin-Helmholtz instabilities and the stabilization of a strongly-magnetized system with mildly relativistic sheath flow is confirmed by the numerical simulations.
Meridional circulation dynamics from 3D MHD global simulations of solar convection
Passos, Dario; Miesch, Mark
2015-01-01
The form of the solar meridional circulation is a very important ingredient for mean field flux transport dynamo models. Yet a shroud of mystery still surrounds this large-scale flow, given that its measurement using current helioseismic techniques is challenging. In this work we use results from 3D global simulations of solar convection to infer the dynamical behavior of the established meridional circulation. We make a direct comparison between the meridional circulation that arises in these simulations and the latest observations. Based on our results we argue that there should be an equatorward flow at the base of the convection zone at mid latitudes, below the current maximum depth helioseismic measures can probe (0.75 R). We also provide physical arguments to justify this behaviour. The simulations indicate that the meridional circulation undergoes substantial changes in morphology as the magnetic cycle unfolds. We close by discussing the importance of these dynamical changes for current methods of obse...
A Global 3D Radiation MHD Simulation of Super-Eddington Accretion Disks
NASA Astrophysics Data System (ADS)
Jiang, Yanfei
2014-10-01
We study how black holes can accrete above the Eddington limit using a global three dimensional radiation magneto-hydrodynamic simulation without ad-hoc assumptions. The simulation reaches an accretion rate ~ 220L_Edd/c^2 and forms a radiation driven outflow along the rotation axis. The radiative luminosity of this flow is ~ 10L_Edd. This yields a radiative efficiency ~ 4.5%, which is comparable to the value in a standard thin disk model. In our simulation, vertical advection of radiation caused by magnetic buoyancy transports energy faster than photon diffusion, allowing a significant fraction of the photons to escape from the surface of the disk before being advected into the black hole. We contrast our results with the lower radiative efficiencies inferred in slim disk model, which neglect vertical advection. The results have important implications for the growth of supermassive black holes in the early universe, tidal disruption events and ultra-luminous X-ray sources.
Secondary Models for Radio Mini-Halos in Galaxy Clusters with MHD Simulations of Gas Sloshing
ZuHone, John; Giacintucci, Simona; Markevitch, Maxim
2014-01-01
We present simulations of a radio minihalo in a galaxy cluster core with sloshing cold fronts, under the assumption that the source of the synchrotron-emitting electrons is hadronic interactions between cosmic-ray protons with the thermal intracluster gas. This is an alternative to the hypothesis where the cosmic ray electrons are reaccelerated by the intracluster turbulence, which we have discussed in an earlier work. We follow the evolution of cosmic-ray electron spectra associated with passive tracer particles, taking into account the time-dependent injection of new electrons from the hadronic interactions and energy losses along each particle's trajectory. We then simulate the radio emission from these particles. The drop in radio emission at the cold front surfaces is less prominent than that in our previous simulations, based on electron reacceleration from sloshing-induced turbulence, where the emission is definitively confined to the regions within cold fronts. The result is that the emission is overa...
3D MHD Simulations of accreting neutron stars: evidence of QPO emission from the surface
Bachetti, Matteo; Burderi, Luciano [Universita degli Studi di Cagliari (Italy); Romanova, Marina M.; Kulkarni, Akshay [Cornell University (United States); Salvo, Tiziana di [Universita degli Studi di Palermo (Italy)
2010-07-15
3D Magnetohydrodynamic simulations show that when matter accretes onto neutron stars, in particular if the misalignment angle is small, it does not constantly fall at a fixed spot. Instead, the location at which matter reaches the star moves. These moving hot spots can be produced both during stable accretion, where matter falls near the magnetic poles of the star, and unstable accretion, characterized by the presence of several tongues of matter which fall on the star near the equator, due to Rayleigh-Taylor instabilities. Precise modeling with Monte Carlo simulations shows that those movements could be observed as high frequency Quasi Periodic Oscillations. We performed a number of new simulation runs with a much wider set of parameters, focusing on neutron stars with a small misalignment angle. In most cases we observe oscillations whose frequency is correlated with the mass accretion rate M. Moreover, in some cases double QPOs appear, each of them showing the same correlation with M.
A nite volume ideal Numerical simulations of MHD ows with shocks have been performed
De Sterck, Hans
for Computational Fluid Dynamics (CFD) simulations. Only since a decade or so, these new numerical methods have been and accurate shock-capturing numerical techniques of the so-called high- resolution type have been developed report on our development of the PAR-MA (PAR- allel MAgnetohydrodynamics) code, which is a massively
FTE Structures and Dynamics from Global MHD Simulations and Cluster Multi-Spacecraft Observations
Y. Wang; J. Birn; R. C. Elphic; J. Raeder; B. Lavraud; X. Zhang
2005-01-01
Flux transfer events (FTEs) are patchy, transient reconnection process on the magnetopause, which play an important role for the transfer of mass, momentum, and energy from the solar wind into the Earth's magnetosphere. The structures and dynamics of FTEs carry important information about the effectiveness and influence of such coupling. However, conventional observations with single satellites and simulations with restricted
Novel Colloidal Crystalline States on Two Dimensional Periodic Substrates
C. Reichhardt; C. J. Olson
2002-01-15
We show using numerical simulations that a rich variety of novel colloidal crystalline states are realized on square and triangular two dimensional periodic substrates which can be experimentally created using crossed laser arrays. When there are more colloids than potential substrate minima, multiple colloids are trapped at each substrate minima and act as a single particle with a rotational degree of freedom, giving rise to a new type of orientational order. We call these states colloidal molecular crystals. A two-step melting can also occur in which individual colloidal molecules initially rotate, destroying the overall orientational order, followed by the onset of inter-well colloidal hopping.
Universality of Probability Distributions Among Two-Dimensional Turbulent Flows
Norbert Schorghofer
1999-07-09
We study statistical properties of two-dimensional turbulent flows. Three systems are considered: the Navier-Stokes equation, surface quasi-geostrophic flow, and a model equation for thermal convection in the Earth's mantle. Direct numerical simulations are used to determine 1-point fluctuation properties. Comparative study shows universality of probability density functions (PDFs) across different types of flow. Especially for the derivatives of the ``advected'' quantity, the shapes of the PDFs are the same for the three flows, once normalized by the average size of fluctuations. Theoretical models for the shape of PDFs are briefly discussed.
Fringe demodulation using the two-dimensional phase differencing operator.
Rajshekhar, Gannavarpu; Rastogi, Pramod
2012-10-15
The Letter proposes a method for phase estimation from a fringe pattern. The proposed method relies on a parametric approach where the phase is locally approximated as a two-dimensional (2D) polynomial, with the ensuing polynomial coefficients as the respective parameters. These coefficients are then estimated using the phase differencing operator. Because of the 2D formulation, the proposed method simultaneously analyzes signal samples along the horizontal and vertical dimensions, which enables robust estimation in the presence of noise. In addition, the method directly provides the desired phase without the requirement of complex unwrapping algorithms. Simulation and experimental results are presented to validate the method's potential. PMID:23073436
Percolation and epidemics in a two-dimensional small world
NASA Astrophysics Data System (ADS)
Newman, M. E.; Jensen, I.; Ziff, R. M.
2002-02-01
Percolation on two-dimensional small-world networks has been proposed as a model for the spread of plant diseases. In this paper we give an analytic solution of this model using a combination of generating function methods and high-order series expansion. Our solution gives accurate predictions for quantities such as the position of the percolation threshold and the typical size of disease outbreaks as a function of the density of ``shortcuts'' in the small-world network. Our results agree with scaling hypotheses and numerical simulations for the same model.
Double Dirac cones in two-dimensional dielectric photonic crystals.
Li, Yan; Mei, Jun
2015-05-01
By exploiting the accidental degeneracy of the doubly-degenerate dipolar and quadrupolar modes, we show that a two-dimensional dielectric photonic crystal (PC) can exhibit the double Dirac cone dispersion relation at the ? point. Using a perturbation method and group theory, we demonstrate that the double cone is composed of two identical and overlapping Dirac cones with predictable linear slopes, and the linearity of the dispersion is guaranteed by the spatial symmetry of the Bloch eigenstates. Numerical simulations including wave-front shaping, unidirectional transmission and perfect tunneling show that the corresponding PC structure can be characterized by a zero effective refractive index. PMID:25969297
Thermodynamics and phase transitions in two-dimensional Yukawa systems
NASA Astrophysics Data System (ADS)
Vaulina, O. S.; Koss, X. G.
2014-10-01
The results of numerical simulations of strongly-coupled two-dimensional dissipative Yukawa systems are presented. The thermodynamic characteristics of these systems were studied, namely the internal energy, the specific heat and the entropy. For the first time, it is discovered that the considered characteristics have two singular points on the melting line; one of these points corresponds to the first-order phase transition from crystal to the hexatic phase, and another point corresponds to the second-order phase transition from the hexatic phase to the isotropic liquid. The obtained results are compared to the existing numerical and analytical data.
Nonlinear Cascades in Two-Dimensional Turbulent Magnetoconvection
Skandera, Dan; Mueller, Wolf-Christian [Max-Planck-Institut fuer Plasmaphysik, 85748 Garching (Germany)
2009-06-05
The dynamics of spectral transport in two-dimensional turbulent convection of electrically conducting fluids is studied by means of direct numerical simulations in the frame of the magnetohydrodynamic Boussinesq approximation. The system performs quasioscillations between two different regimes of small-scale turbulence: one dominated by nonlinear magnetohydrodynamic interactions; the other governed by buoyancy forces. The self-excited change of turbulent states is reported here for the first time. The process is controlled by the ideal invariant cross helicity, H{sup C}=SdSv{center_dot}b. The observations are explained by the interplay of convective driving with the nonlinear spectral transfer of total magnetohydrodynamic energy and cross helicity.
Longitudinal viscosity of two-dimensional Yukawa liquids
NASA Astrophysics Data System (ADS)
Feng, Yan; Goree, J.; Liu, Bin
2013-01-01
The longitudinal viscosity ?l is obtained for a two-dimensional (2D) liquid using a Green-Kubo method with a molecular dynamics simulation. The interparticle potential used has the Debye-Hückel or Yukawa form, which models a 2D dusty plasma. The longitudinal ?l and shear ?s viscosities are found to have values that match very closely, with only negligible differences for the entire range of temperatures that is considered. For a 2D Yukawa liquid, the bulk viscosity ?b is determined to be either negligibly small or not a meaningful transport coefficient.
Longitudinal viscosity of two-dimensional Yukawa liquids.
Feng, Yan; Goree, J; Liu, Bin
2013-01-01
The longitudinal viscosity ?(l) is obtained for a two-dimensional (2D) liquid using a Green-Kubo method with a molecular dynamics simulation. The interparticle potential used has the Debye-Hückel or Yukawa form, which models a 2D dusty plasma. The longitudinal ?(l) and shear ?(s) viscosities are found to have values that match very closely, with only negligible differences for the entire range of temperatures that is considered. For a 2D Yukawa liquid, the bulk viscosity ?(b) is determined to be either negligibly small or not a meaningful transport coefficient. PMID:23410445
Fractional-step method for two-dimensional estuarine transport
Bales, Jerad D.; Holley, Edward R.
1988-01-01
The fractional-step method was used in this study to split the longitudinal advective transport term from the other terms in the two-dimensional, laterally-averaged equation for estuarine mass transport. The method of characteristics with spline interpolations was used to approximate the longitudinal advective transport. A general discussion of the fractional-step method, the specific algorithm developed in this investigation, and results of numerical tests are presented. Application of the fractional-step method in conjunction with the characteristic-spline scheme offers the potential for improved simulations of transport for situations in which concentration gradients are steep.
A fractal transition in the two dimensional shear layer
NASA Technical Reports Server (NTRS)
Jimenez, Javier; Martel, Carlos
1990-01-01
The dependence of product generation with the Peclet and Reynolds number in a numerically simulated, reacting, two dimensional, temporally growing mixing layer is used to compute the fractal dimension of passive scalar interfaces. A transition from a low dimension of 4/3 to a higher one of 5/3 is identified and shown to be associated to the kinematic distortion on the flow field during the first pairing interaction. It is suggested that the structures responsible for this transition are non-deterministic, non-random, inhomogeneous fractals. Only the large scales are involved. No further transition is found for Reynolds numbers up to 20,000.
NASA Astrophysics Data System (ADS)
Merkin, V. G.; Lyon, J. G.; Claudepierre, S. G.
2013-09-01
We present results of a global, fully three-dimensional, high-resolution magnetohydrodynamic (MHD) simulation of the magnetosphere during steady northward interplanetary magnetic field (IMF) conditions. We investigate the stability of the magnetospheric boundary with respect to the growth of the Kelvin-Helmholtz instability (KHI) driven by the velocity shear between the nearly stagnant magnetospheric plasma and the magnetosheath flow past it. We find the magnetospheric boundary to be globally unstable, including the high-latitude boundary layer (meridional plane), where magnetic tension is not sufficient to stabilize the growth of oscillations. Roughly beyond the terminator, global modes coupled into the surface modes become most 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, kz 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. The distribution of wave power in the equatorial plane is 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 nonlinear development of the velocity shear layer with a finite width. For the simulation with the solar wind velocity of 600 km/s, we find the width of the layer to be ??1 RE at the terminator and the phase speed there to be similar to half of the total velocity drop across the layer (˜440 km/s), which is expected for a shear layer with uniform background density. We calculate the spatial growth rate for the dominant frequency mode in this region (˜4.4 mHz) to be ˜0.19RE-1, which is in excellent agreement with linear theory. For this mode, we find k??0.9, where k is the wave number, which corresponds to the fastest growing mode predicted by the linear theory. 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 simulation.
Numerical simulation of MHD for electromagnetic edge dam in continuous casting.
Chang, F. C.
1999-03-30
A computer model was developed to predict eddy currents and fluid flows in molten steel. The model was verified by comparing predictions with experimental results of liquid-metal containment and fluid flow in electromagnetic (EM) edge dams (EMDs) designed at Inland Steel for twin-roll casting. The model can optimize the EMD design so it is suitable for application, and minimize expensive, time-consuming full-scale testing. Numerical simulation was performed by coupling a three-dimensional (3-D) finite-element EM code (ELEKTRA) and a 3-D finite-difference fluids code (CaPS-EM) to solve heat transfer, fluid flow, and turbulence transport in a casting process that involves EM fields. ELEKTRA is able to predict the eddy-current distribution and the electromagnetic forces in complex geometries. CaPS-EM is capable of modeling fluid flows with free surfaces. Results of the numerical simulation compared measurements obtained from a static test.
3-D mesoscale MHD simulations of a cusp-like magnetic configuration: method and first results
NASA Astrophysics Data System (ADS)
Adamson, E.; Nykyri, K.
2011-05-01
We present a local mesoscale model of the magnetospheric cusp region with high resolution (up to 300 km). We discuss the construction and implementation of the initial configuration and give a detailed description of the numerical simulation. An overview of simulation results for the case of strongly northward interplanetary magnetic field (IMF) is then presented and compared with data from Cluster 2 spacecraft from 14 February 2003. Results show a cusp diamagnetic cavity (CDC) with depth normal to the magnetospheric boundary on the order of 1-2 RE and a much larger extent of ~5-9 RE tangential to the boundary, bounded by a gradual inner boundary with the magnetospheric lobe and a more distinct exterior boundary with the magnetosheath. These results are qualitatively consistent with observational data.
Observational evidence of CMEs interacting in the inner heliosphere as inferred from MHD simulations
Lugaz, N; Roussev, I I; Gombosi, T I
2008-01-01
The interaction of multiple Coronal Mass Ejections (CMEs) has been observed by LASCO coronagraphs and by near-Earth spacecraft, and it is thought to be an important cause of geo-effective storms, large Solar Energetic Particles events and intense Type II radio bursts. New and future missions such as STEREO, the LWS Sentinels, and the Solar Orbiter will provide additional observations of the interaction of multiple CMEs between the Sun and the Earth. We present the results of simulations of two and more CMEs interacting in the inner heliosphere performed with the Space Weather Modeling Framework (SWMF). Based on those simulations, we discuss the observational evidence of the interaction of multiple CMEs, both in situ and from coronagraphs. The clearest evidence of the interaction of the CMEs are the large temperature in the sheath, due to the shocks merging, and the brightness increase in coronagraphic images, associated with the interaction of the leading edges. The importance of having multiple satellites at...
Mark Chun Ming Cheung; Manfred Schuessler; Fernando Moreno-Insertis
2007-02-25
We study the emergence of magnetic flux from the near-surface layers of the solar convection zone into the photosphere. To model magnetic flux emergence, we carried out a set of numerical radiative magnetohydrodynamics simulations. Our simulations take into account the effects of compressibility, energy exchange via radiative transfer, and partial ionization in the equation of state. All these physical ingredients are essential for a proper treatment of the problem. Furthermore, the inclusion of radiative transfer allows us to directly compare the simulation results with actual observations of emerging flux. We find that the interaction between the magnetic flux tube and the external flow field has an important influence on the emergent morphology of the magnetic field. Depending on the initial properties of the flux tube (e.g. field strength, twist, entropy etc.), the emergence process can also modify the local granulation pattern. The emergence of magnetic flux tubes with a flux of $10^{19}$ Mx disturbs the granulation and leads to the transient appearance of a dark lane, which is coincident with upflowing material. These results are consistent with observed properties of emerging magnetic flux.
Stability of Two-Dimensional Soft Quasicrystals
Kai Jiang; Jiajun Tong; Pingwen Zhang; An-Chang Shi
2015-05-26
The relative stability of two-dimensional soft quasicrystals is examined using a recently developed projection method which provides a unified numerical framework to compute the free energy of periodic crystal and quasicrystals. Accurate free energies of numerous ordered phases, including dodecagonal, decagonal and octagonal quasicrystals, are obtained for a simple model, i.e. the Lifshitz-Petrich free energy functional, of soft quasicrystals with two length-scales. The availability of the free energy allows us to construct phase diagrams of the system, demonstrating that, for the Lifshitz-Petrich model, the dodecagonal and decagonal quasicrystals can become stable phases, whereas the octagonal quasicrystal stays as a metastable phase.
Intermittency in forced two-dimensional turbulence
W. Brent Daniel; Maarten A. Rutgers
2000-05-03
We find strong evidence for intermittency in forced two dimensional (2D) turbulence in a flowing soap film experiment. In the forward enstrophy cascade the structure function scaling exponents are nearly indistinguishable from 3D studies. Intermittency corrections are present in the inverse energy cascade as well, but weaker. Stretched exponential tails of the velocity difference probability distribution functions and shock like events at large velocity differences also resemble 3D studies. For decaying turbulence, where only the forward enstrophy cascade remains, all signs of intermittency disappear.
Gauge equivalence in two-dimensional gravity
Fujiwara, T. (Department of Physics, Ibaraki University, Mito 310 (Japan)); Igarashi, Y. (Faculty of Education, Niigata University, Niigata 950-21 (Japan)); Kubo, J. (College of Liberal Arts, Kanazawa University, Kanazawa 920 (Japan)); Tabei, T. (Department of Physics, Ibaraki University, Mito 310 (Japan))
1993-08-15
Two-dimensional quantum gravity is identified as a second-class system which we convert into a first-class system via the Batalin-Fradkin (BF) procedure. Using the extended phase space method, we then formulate the theory in the most general class of gauges. The conformal gauge action suggested by David, Distler, and Kawai is derived from first principles. We find a local, light-cone gauge action whose Becchi-Rouet-Stora-Tyutin invariance implies Polyakov's curvature equation [partial derivative][sub [minus
Two-dimensional signatures for molecular identification
NASA Astrophysics Data System (ADS)
Qazi, Muhammad; Vogt, Thomas; Koley, Goutam
2008-03-01
Simultaneous measurements of the conductance and surface work function (SWF) changes on nanostructured graphite layers have been performed to detect several gaseous analyte molecules. It has been observed that the gradient of the SWF versus conductance response plotted for specific analyte molecules is constant irrespective of their concentration or fractional occupancy of surface adsorption sites. The SWF and conductance changes have been found to be uncorrelated for different analyte molecules, resulting in unique gradients that can be used as two-dimensional signatures for molecular identification.
A Simple GPU-Accelerated Two-Dimensional MUSCL-Hancock Solver for Ideal Magnetohydrodynamics
NASA Technical Reports Server (NTRS)
Bard, Christopher; Dorelli, John C.
2013-01-01
We describe our experience using NVIDIA's CUDA (Compute Unified Device Architecture) C programming environment to implement a two-dimensional second-order MUSCL-Hancock ideal magnetohydrodynamics (MHD) solver on a GTX 480 Graphics Processing Unit (GPU). Taking a simple approach in which the MHD variables are stored exclusively in the global memory of the GTX 480 and accessed in a cache-friendly manner (without further optimizing memory access by, for example, staging data in the GPU's faster shared memory), we achieved a maximum speed-up of approx. = 126 for a sq 1024 grid relative to the sequential C code running on a single Intel Nehalem (2.8 GHz) core. This speedup is consistent with simple estimates based on the known floating point performance, memory throughput and parallel processing capacity of the GTX 480.
The physics of twisted magnetic tubes rising in a stratified medium: two dimensional results
T. Emonet; F. Moreno-Insertis
1997-11-06
The physics of a twisted magnetic flux tube rising in a stratified medium is studied using a numerical MHD code. The problem considered is fully compressible (no Boussinesq approximation), includes ohmic resistivity, and is two dimensional, i.e., there is no variation of the variables in the direction of the tube axis. We study a high plasma beta case with small ratio of radius to external pressure scaleheight. The results obtained can therefore be of relevance to understand the transport of magnetic flux across the solar convection zone.
3D MHD simulation and the role of null points in coronal reconnection
NASA Astrophysics Data System (ADS)
Finn, J.; Lapenta, G.
2004-12-01
STEREO represents a quantum leap from the perspective of the simulations. By providing a 2-satellite view it will be able to determine the true 3D stereoscopic view of the structure of the magnetic field lines and to investigate the motions of the field lines. A crucial issue among the key mission objectives is the study of reconnection and coronal mass ejections. The theory of 3D magnetic reconnection is still far from being fully developed. But a pivotal aspect is the role played by null points in the topology changes induced by reconnection [1]. STEREO will provide a unique opportunity to look directly at this issue. We will investigate the role of null points using our simulation tool, FLIP-3D [2], and our diagnostic tools to pick up null points and to study Poincare plots. We will provide evidence of the type of theoretical predictions [3] that will be best compared with STEREO observations. [1] Y. Lau, J. Finn, ApJ, 350, 672 (1990) [2] J.U. Brackbill, JCP, 96, 163 (1991) [3] G. Lapenta, D.A. Knoll, Solar Physics, 214, 107-129 (2003); ApJ, submitted.
Reproducibility of two-dimensional exercise echocardiography.
Oberman, A; Fan, P H; Nanda, N C; Lee, J Y; Huster, W J; Sulentic, J A; Storey, O F
1989-10-01
To determine the reproducibility of two-dimensional exercise echocardiography, duplicate studies were performed on the same patients a median of 14 days apart. Because measurements are operator-dependent, interobserver variability was calculated for two experienced readers who interpreted the findings independently in a blinded manner. A high degree of interobserver agreement was found in evaluation of both ejection fraction measurements and wall motion abnormalities. Readings for ejection fraction immediately after exercise taken on different days could be estimated within 4% of the values measured in the first test; similarly measured wall motion score index was within 6% of that in the first test. Ejection fractions and wall motion scores were highly correlated between tests 1 and 2. The correlation coefficients between tests 1 and 2 were 0.92 for both the pre- and postexercise ejection fractions and 0.98 for both the pre- and postexercise wall motion scores. Quantitative two-dimensional echocardiography immediately after exercise is highly reproducible, providing a valuable tool for assessing serial changes in left ventricular function. PMID:2794280
Two-dimensional phonon transport in graphene.
Nika, Denis L; Balandin, Alexander A
2012-06-13
Properties of phonons-quanta of the crystal lattice vibrations-in graphene have recently attracted significant attention from the physics and engineering communities. Acoustic phonons are the main heat carriers in graphene near room temperature, while optical phonons are used for counting the number of atomic planes in Raman experiments with few-layer graphene. It was shown both theoretically and experimentally that transport properties of phonons, i.e. energy dispersion and scattering rates, are substantially different in a quasi-two-dimensional system such as graphene compared to the basal planes in graphite or three-dimensional bulk crystals. The unique nature of two-dimensional phonon transport translates into unusual heat conduction in graphene and related materials. In this review, we outline different theoretical approaches developed for phonon transport in graphene, discuss contributions of the in-plane and cross-plane phonon modes, and provide comparison with available experimental thermal conductivity data. Particular attention is given to analysis of recent results for the phonon thermal conductivity of single-layer graphene and few-layer graphene, and the effects of the strain, defects, and isotopes on phonon transport in these systems. PMID:22562955
X-Ray Spectra from MHD Simulations of Accreting Black Holes
NASA Technical Reports Server (NTRS)
Schnittman, Jeremy D.; Noble, Scott C.; Krolik, Julian H.
2011-01-01
We present new global calculations of X-ray spectra from fully relativistic magneto-hydrodynamic (MHO) simulations of black hole (BH) accretion disks. With a self consistent radiative transfer code including Compton scattering and returning radiation, we can reproduce the predominant spectral features seen in decades of X-ray observations of stellar-mass BHs: a broad thermal peak around 1 keV, power-law continuum up to >100 keV, and a relativistically broadened iron fluorescent line. By varying the mass accretion rate, different spectral states naturally emerge: thermal-dominant, steep power-law, and low/hard. In addition to the spectral features, we briefly discuss applications to X-ray timing and polarization.
MHD Simulations of Bondi Accretion to a Star in the "Propeller" Regime
M. M. Romanova; O. D. Toropina; Yu. M. Toropin; R. V. E. Lovelace
2002-09-25
This work investigates Bondi accretion to a rotating magnetized star in the "propeller" regime using axisymmetric resistive, magnetohydrodynamic simulations. In this regime accreting matter tends to be expelled from the equatorial region of the magnetosphere where the centrifugal force on matter rotating with the star exceeds the gravitational force. The regime is predicted to occur if the magnetospheric radius larger than the corotation radius and less than the light cylinder radius. The simulations show that accreting matters is expelled from the equatorial region of the magnetosphere and that it moves away from the star in a supersonic, disk-shaped outflow. At larger radial distances the outflow slows down and becomes subsonic. The equatorial matter outflow is initially driven by the centrifugal force, but at larger distances the pressure gradient becomes significant. We find that the star is spun-down mainly by the magnetic torques at its surface with the rate of loss of angular momentum $\\dot{L}$ proportional to $-\\Omega_*^{1.3}\\mu^{0.8}$, where $\\Omega_*$ is the star's rotation rate and $\\mu$ is its magnetic moment. Further, we find that $\\dot{L}$ is approximately independent of the magnetic diffusivity of the plasma $\\eta_m$. The fraction of the Bondi accretion rate which accretes to the surface of the star is found to be $\\propto\\Omega_*^{-1.0}\\mu^{-1.7}\\eta_m^{0.4}$. Predictions of this work are important for the observability of isolated old neutron stars and for wind fed pulsars in X-ray binaries.
Interpretation of solar irradiance monitor measurements through analysis of 3D MHD simulations
Criscuoli, S.; Uitenbroek, H. [National Solar Observatory, Sacramento Peak, P.O. Box 62, Sunpsot, NM 88349 (United States)
2014-06-20
Measurements from the Spectral Irradiance Monitor (SIM) on board the Solar Radiation and Climate Experiment mission indicate that solar spectral irradiance at visible and IR wavelengths varies in counter phase with the solar activity cycle. The sign of these variations is not reproduced by most of the irradiance reconstruction techniques based on variations of surface magnetism employed so far, and it is not yet clear whether SIM calibration procedures need to be improved or if instead new physical mechanisms must be invoked to explain such variations. We employ three-dimensional magnetohydrodynamic simulations of the solar photosphere to investigate the dependence of solar radiance in SIM visible and IR spectral ranges on variations of the filling factor of surface magnetic fields. We find that the contribution of magnetic features to solar radiance is strongly dependent on the location on the disk of the features, which are negative close to disk center and positive toward the limb. If features are homogeneously distributed over a region around the equator (activity belt), then their contribution to irradiance is positive with respect to the contribution of HD snapshots, but decreases with the increase of their magnetic flux for average magnetic flux larger than 50 G in at least two of the visible and IR spectral bands monitored by SIM. Under the assumption that the 50 G snapshots are representative of quiet-Sun regions, we thus find that the Spectral Irradiance can be in counter-phase with the solar magnetic activity cycle.
NASA Astrophysics Data System (ADS)
Jia, X.; Slavin, J. A.; Gombosi, T. I.; Daldorff, L.; Toth, G.
2013-12-01
Mercury's comparatively weak intrinsic magnetic field and its close proximity to the Sun lead to a mini-magnetosphere that undergoes more direct space-weathering interactions than other planets. A unique aspect of the Mercury interaction system relates to the large ratio of the scale of the planet to the scale of the tiny magnetosphere and the presence of a large-size core (with radius ~ 80% of the planetary radius) composed of highly conducting material, implying that there is potentially strong feedback between the planet's interior and the magnetosphere, especially under conditions of strong solar wind driving. Understanding the solar wind-magnetosphere-exosphere-interior interaction at Mercury as a highly coupled system requires not only analysis of spacecraft data but also a modeling framework that is both comprehensive and inclusive. To this end, we have developed a new global MHD model of Mercury's interaction with the solar wind based on the BATSRUS code in which the interior of the planet (modeled as layers of different electric conductivities) is electrodynamically coupled to the surrounding space plasma environment. The new modeling capability allows for self-consistently characterizing the dynamical response of the Mercury system to time-varying external conditions. In particular, we have applied the coupled model to assess quantitatively the effect of induction arising from the planet's conducting core on the global magnetosphere. A set of idealized simulations have been carried out in which Mercury's magnetosphere is impacted by solar wind disturbances with different levels of pressure enhancement. Our results show that due to the induction effect, Mercury's core can impose strong global influences on the way Mercury responds to changes in the external environment, including modifying the global magnetospheric structure and affecting the extent to which the solar wind directly impacts the planetary surface. By applying the model to simulate extreme events, such as those observed by MESSENGER during impact of Coronal Mass Ejections (Slavin et al., 2013), we aim to obtain a deeper understanding of the tightly coupled Mercury system, and thereby to develop further constraints on the properties of the planet's interior.
Applications of two-dimensional infrared spectroscopy.
Le Sueur, Amanda L; Horness, Rachel E; Thielges, Megan C
2015-06-15
Two-dimensional infrared (2D IR) spectroscopy has recently emerged as a powerful tool with applications in many areas of scientific research. The inherent high time resolution coupled with bond-specific spatial resolution of IR spectroscopy enable direct characterization of rapidly interconverting species and fast processes, even in complex systems found in chemistry and biology. In this minireview, we briefly outline the fundamental principles and experimental procedures of 2D IR spectroscopy. Using illustrative example studies, we explain the important features of 2D IR spectra and their capability to elucidate molecular structure and dynamics. Primarily, this minireview aims to convey the scope and potential of 2D IR spectroscopy by highlighting select examples of recent applications including the use of innate or introduced vibrational probes for the study of nucleic acids, peptides/proteins, and materials. PMID:26007625
Two-dimensional fourier transform spectrometer
DeFlores, Lauren; Tokmakoff, Andrei
2013-09-03
The present invention relates to a system and methods for acquiring two-dimensional Fourier transform (2D FT) spectra. Overlap of a collinear pulse pair and probe induce a molecular response which is collected by spectral dispersion of the signal modulated probe beam. Simultaneous collection of the molecular response, pulse timing and characteristics permit real time phasing and rapid acquisition of spectra. Full spectra are acquired as a function of pulse pair timings and numerically transformed to achieve the full frequency-frequency spectrum. This method demonstrates the ability to acquire information on molecular dynamics, couplings and structure in a simple apparatus. Multi-dimensional methods can be used for diagnostic and analytical measurements in the biological, biomedical, and chemical fields.
Phonon hydrodynamics in two-dimensional materials.
Cepellotti, Andrea; Fugallo, Giorgia; Paulatto, Lorenzo; Lazzeri, Michele; Mauri, Francesco; Marzari, Nicola
2015-01-01
The conduction of heat in two dimensions displays a wealth of fascinating phenomena of key relevance to the scientific understanding and technological applications of graphene and related materials. Here, we use density-functional perturbation theory and an exact, variational solution of the Boltzmann transport equation to study fully from first-principles phonon transport and heat conductivity in graphene, boron nitride, molybdenum disulphide and the functionalized derivatives graphane and fluorographene. In all these materials, and at variance with typical three-dimensional solids, normal processes keep dominating over Umklapp scattering well-above cryogenic conditions, extending to room temperature and more. As a result, novel regimes emerge, with Poiseuille and Ziman hydrodynamics, hitherto typically confined to ultra-low temperatures, characterizing transport at ordinary conditions. Most remarkably, several of these two-dimensional materials admit wave-like heat diffusion, with second sound present at room temperature and above in graphene, boron nitride and graphane. PMID:25744932
New Two-Dimensional Ice Models
NASA Astrophysics Data System (ADS)
Kirov, Mikhail V.
2012-11-01
This paper presents a new approach for enumerating all hydrogen bond arrangements of ice-like systems with periodic boundary conditions. It is founded on a topological procedure for the dimensional reduction and a new variant of the transfer matrix method based on small conditional transfer matrices. We consider a couple of new two-dimensional ice models on very unusual lattices. One of them is the twisted square ice model with crossing H-bonds. The other is the digonal-hexagonal model with double H-bonds. In spite of their uncommonness, these models are quite realistic, because from the standpoint of combinatorics and topology they are equivalent to the layers of usual hexagonal ice Ih under periodic boundary conditions in one of the directions. The exact proton configuration statistics for a number of 2D-expanded unit cells of hexagonal ice Ih and the residual entropy of the new ice models in the large system limit are presented.
Internal tide generation by arbitrary two-dimensional topography
Peacock, Thomas
To date, analytical models of internal tide generation by two-dimensional ridges have considered only idealized shapes. Here, we advance the Green function approach to address the generation of internal tides by two-dimensional ...