Two-dimensional MHD simulations of tokamak plasmas with poloidal flow
NASA Astrophysics Data System (ADS)
Hu, Bo; Betti, R.
2006-10-01
It has been shown [1] that, according to the ideal MHD equilibrium theory, poloidal flow in a tokamak can give rise to a pedestal structure with the pressure, density and velocity developing sharp discontinuities in their radial profiles. Such a pedestal arises when the poloidal velocity exceeds the poloidal sound speed. Since the poloidal sound speed vanishes at the separatrix, it is conceivable that evena rather slow poloidal flow can become transonic near the plasma edge, thus inducing a pedestal in the hydrodynamic profiles. While equilibrium calculations [1-4] of such a pedestal are well established, only a few two-dimensional time-dependent simulations have been carried out [5]. Here, we show the preliminary results from a two dimensional MHD code that simulates the formation of the pedestal starting from a poloidal velocity profile that becomes supersonic at the plasma edge. This work was supported by US-DOE under Contract DE-FG02-93ER54215. [1] Betti and Freidberg, Phys. Plasmas 7, 2439 (2000). [2] Guazzotto, Betti, Manickam and Kaye, Phys. Plasmas 11, 604 (2004). [3] Guazzotto and Betti, Phys. Plasmas 12, 056107 (2005). [4] Thyagaraja and McClements, Phys. Plasmas 13, 062502 (2006). [5] Gardiner, Betti and Guazzotto, Bull. Am. Phys. Soc. 46, No. 8, 166 (2001).
Two-dimensional magnetohydrodynamic simulations of poloidal flows in tokamaks and MHD pedestal
NASA Astrophysics Data System (ADS)
Guazzotto, L.; Betti, R.
2011-09-01
Poloidal rotation is routinely observed in present-day tokamak experiments, in particular near the plasma edge and in the high-confinement mode of operation. According to the magnetohydrodynamic (MHD) equilibrium theory [R. Betti and J. P. Freidberg, Phys. Plasmas 7, 2439 (2000)], radial discontinuities form when the poloidal velocity exceeds the poloidal sound speed (or rather, more correctly, the poloidal magneto-slow speed). Two-dimensional compressible magnetohydrodynamic simulations show that the transonic discontinuities develop on a time scale of a plasma poloidal revolution to form an edge density pedestal and a localized velocity shear layer at the pedestal location. While such an MHD pedestal surrounds the entire core, the outboard side of the pedestal is driven by the transonic discontinuity while the inboard side is caused by a poloidal redistribution of the mass. The MHD simulations use a smooth momentum source to drive the poloidal flow. Soon after the flow exceeds the poloidal sound speed, the density pedestal and the velocity shear layer form and persist into a quasi steady state. These results may be relevant to the L-H transition, the early stages of the pedestal and edge transport barrier formation.
Two-dimensional magnetohydrodynamic simulations of poloidal flows in tokamaks and MHD pedestal
Guazzotto, L.; Betti, R.
2011-09-15
Poloidal rotation is routinely observed in present-day tokamak experiments, in particular near the plasma edge and in the high-confinement mode of operation. According to the magnetohydrodynamic (MHD) equilibrium theory [R. Betti and J. P. Freidberg, Phys. Plasmas 7, 2439 (2000)], radial discontinuities form when the poloidal velocity exceeds the poloidal sound speed (or rather, more correctly, the poloidal magneto-slow speed). Two-dimensional compressible magnetohydrodynamic simulations show that the transonic discontinuities develop on a time scale of a plasma poloidal revolution to form an edge density pedestal and a localized velocity shear layer at the pedestal location. While such an MHD pedestal surrounds the entire core, the outboard side of the pedestal is driven by the transonic discontinuity while the inboard side is caused by a poloidal redistribution of the mass. The MHD simulations use a smooth momentum source to drive the poloidal flow. Soon after the flow exceeds the poloidal sound speed, the density pedestal and the velocity shear layer form and persist into a quasi steady state. These results may be relevant to the L-H transition, the early stages of the pedestal and edge transport barrier formation.
Two-Dimensional MHD Simulations of Tokamak Plasmas with Poloidal Flow
NASA Astrophysics Data System (ADS)
Guazzotto, L.; Betti, R.
2002-11-01
A two- dimensional MHD code has been developed to simulate the temporal evolution of Tokamak plasmas with an imposed poloidal flow. The code is fully compressible and can resolve the shock structures arising when the poloidal velocity is of the order of the poloidal sound speed (V_θ ˜ Cs B_θ/B) near the plasma edge, where the plasma is cold and the sound speed is low. The poloidal flow is assigned as an initial condition with a velocity profile ranging from subsonic to supersonic near the edge. It is found that a continuous band of shocks is formed near the edge. Such shocks travel poloidally, leaving behind a pedestal structure similar to the one predicted in Ref. 1 [R. Betti and J. P. Freidberg, Phys. Plasmas 7, 2439 (2000)]. Here, the pedestal is defined as a sharp discontinuity in the pressure, temperature, and density profiles. The pedestal height is modulated in the poloidal angle; it is maximum on the outboard side (θ = 0) and minimum on the inboard (θ = π). Furthermore, both poloidal and toroidal flows develop a shear layer at the location of the pedestal. The large velocity shear (both poloidal and toroidal) occurring in the pedestal region is likely to suppress turbulent eddies and reduce anomalous transport. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC03-92SF19460.
Simulation of two-dimensional fully developed laminar flow for a magneto-hydrodynamic (MHD) pump.
Wang, Pei-Jen; Chang, Chia-Yuan; Chang, Ming-Lang
2004-07-30
MHD micro-pumps circumvent the wear and fatigue caused by high pressure-drop across the check valves of mechanical micro-pumps in micro-fluidic systems. Early analyses of the fluid flow for MHD micro-pumps were mostly made possible by the Poiseuille flow theory; however, this conventional laminar approach cannot illustrate the effects of various channel sizes and shapes. This paper, therefore, presents a simplified MHD flow model based upon steady state, incompressible and fully developed laminar flow theory to investigate the characteristics of a MHD pump. Inside the pump, flowing along the channel is the electrically conducting fluid flowing driven by the Lorentz forces in the direction perpendicular to both dc magnetic field and applied electric currents. The Lorentz forces were converted into a hydrostatic pressure gradient in the momentum equations of the MHD channel flow model. The numerical simulations conducted with the explicit finite difference method show that the channel dimensions and the induced Lorentz forces have significant influences on the flow velocity profile. Furthermore, the simulation results agree well with the experimental results published by other researchers.
NASA Astrophysics Data System (ADS)
Kaminou, Yasuhiro; Guo, Xuehan; Inomoto, Michiaki; Ono, Yasushi; Horiuchi, Ritoku
2017-03-01
Hall effects on counter-helicity spheromak merging were investigated by two-dimensional MHD and Hall-MHD simulations of merging two axisymmetric toroidal flux tubes. In Hall-MHD cases, the structure of the reconnection current sheet and reconnection outflow are modified from the MHD case due to the Hall effect. We compared two cases (called "case-O" and "case-I") of counter-helicity merging, which are distinguished by the polarity of toroidal magnetic fluxes. Radial motion of the reconnection X-point is controlled by poloidal electron flow accompanying the toroidal flux of the merging two spheromaks, and this creates a large difference in the current sheet and flow structure between the two cases of the Hall-MHD regime. The radial shift of the reconnection X-point depending on the polarity of toroidal magnetic flux of the spheromaks breaks the symmetry between the two cases. It was also found that there widely exists separation of ion and electron flow which are affected by the modification of the current sheet structure due to the radial shift of the X-point in the downstream side of the merging, and its spatial scale of the distribution of the Hall electric field is larger than the ion skin depth.
Structure and computation of two-dimensional incompressible extended MHD
NASA Astrophysics Data System (ADS)
Grasso, D.; Tassi, E.; Abdelhamid, H. M.; Morrison, P. J.
2017-01-01
A comprehensive study of the extended magnetohydrodynamic model obtained from the two-fluid theory for electrons and ions with the enforcement of quasineutrality is given. Starting from the Hamiltonian structure of the fully three-dimensional theory, a Hamiltonian two-dimensional incompressible four-field model is derived. In this way, the energy conservation along with four families of Casimir invariants is naturally obtained. The construction facilitates various limits leading to the Hamiltonian forms of Hall, inertial, and ideal MHD, with their conserved energies and Casimir invariants. Basic linear theory of the four-field model is treated, and the growth rate for collisionless reconnection is obtained. Results from nonlinear simulations of collisionless tearing are presented and interpreted using, in particular, normal fields, a product of the Hamiltonian theory that gives rise to simplified equations of motion.
Two-dimensional MHD generator model. [GEN code
Geyer, H. K.; Ahluwalia, R. K.; Doss, E. D.
1980-09-01
A steady state, two-dimensional MHD generator code, GEN, is presented. The code solves the equations of conservation of mass, momentum, and energy, using a Von Mises transformation and a local linearization of the equations. By splitting the source terms into a part proportional to the axial pressure gradient and a part independent of the gradient, the pressure distribution along the channel is easily obtained to satisfy various criteria. Thus, the code can run effectively in both design modes, where the channel geometry is determined, and analysis modes, where the geometry is previously known. The code also employs a mixing length concept for turbulent flows, Cebeci and Chang's wall roughness model, and an extension of that model to the effective thermal diffusities. Results on code validation, as well as comparisons of skin friction and Stanton number calculations with experimental results, are presented.
Two-dimensional MHD model of the Jovian magnetodisk
NASA Astrophysics Data System (ADS)
Kislov, R. A.; Malova, H. V.; Vasko, I. Y.
2015-09-01
A self-consistent stationary axially symmetric MHD model of the Jovian magnetodisk is constructed. This model is a generalization of the models of plane current sheets that have been proposed earlier in order to describe the structure of the current sheet in the magnetotail of the Earth [1, 2]. The model takes centrifugal force, which is induced by the corotation electric field, and the azimuthal magnetic field into account. The configurations of the magnetic field lines for the isothermic (plasma temperature assumed to be constant) and the isentropic (plasma entropy assumed to be constant) models of the magnetodisk are determined. The dependence of the thickness of the magnetodisk on the distance to Jupiter is obtained. The thickness of the magnetodisk and the magnetic field distribution in the isothermic and isentropic models are similar. The inclusion of a low background plasma pressure results in a considerable reduction in the thickness of the magnetodisk. This effect may be attributed to the fact that centrifugal force prevails over the pressure gradient at large distances from the planet. The mechanism of unipolar induction and the related large-scale current system are analyzed. The direct and return Birkeland currents are determined in the approximation of a weak azimuthal magnetic field. The modeling results agree with theoretical estimates from other studies and experimental data.
Hall MHD Modeling of Two-dimensional Reconnection: Application to MRX Experiment
V.S. Lukin; S.C. Jardin
2003-01-09
Two-dimensional resistive Hall magnetohydrodynamics (MHD) code is used to investigate the dynamical evolution of driven reconnection in the Magnetic Reconnection Experiment (MRX). The initial conditions and dimensionless parameters of the simulation are set to be similar to the experimental values. We successfully reproduce many features of the time evolution of magnetic configurations for both co- and counter-helicity reconnection in MRX. The Hall effect is shown to be important during the early dynamic X-phase of MRX reconnection, while effectively negligible during the late ''steady-state'' Y-phase, when plasma heating takes place. Based on simple symmetry considerations, an experiment to directly measure the Hall effect in MRX configuration is proposed and numerical evidence for the expected outcome is given.
Two-dimensional Magnetohydrodynamic Simulations of Barred Galaxies
NASA Astrophysics Data System (ADS)
Kim, Woong-Tae; Stone, James M.
2012-06-01
Barred galaxies are known to possess magnetic fields that may affect the properties of bar substructures such as dust lanes and nuclear rings. We use two-dimensional high-resolution magnetohydrodynamic (MHD) simulations to investigate the effects of magnetic fields on the formation and evolution of such substructures, as well as on the mass inflow rates to the galaxy center. The gaseous medium is assumed to be infinitesimally thin, isothermal, non-self-gravitating, and threaded by initially uniform, azimuthal magnetic fields. We find that there exists an outermost x 1-orbit relative to which gaseous responses to an imposed stellar bar potential are completely different between inside and outside. Inside this orbit, gas is shocked into dust lanes and infalls to form a nuclear ring. Magnetic fields are compressed in dust lanes, reducing their peak density. Magnetic stress removes further angular momentum of the gas at the shocks, temporarily causing the dust lanes to bend into an "L" shape and eventually leading to a smaller and more centrally distributed ring than in unmagnetized models. The mass inflow rates in magnetized models correspondingly become larger, by more than two orders of magnitude when the initial fields have an equipartition value with thermal energy, than in the unmagnetized counterparts. Outside the outermost x 1-orbit, on the other hand, an MHD dynamo due to the combined action of the bar potential and background shear operates near the corotation and bar-end regions, efficiently amplifying magnetic fields. The amplified fields shape into trailing magnetic arms with strong fields and low density. The base of the magnetic arms has a thin layer in which magnetic fields with opposite polarity reconnect via a tearing-mode instability. This produces numerous magnetic islands with large density that propagate along the arms to turn the outer disk into a highly chaotic state.
On the Transition from Two-Dimensional to Three-Dimensional MHD Turbulence
NASA Technical Reports Server (NTRS)
Thess, A.; Zikanov, Oleg
2004-01-01
We report a theoretical investigation of the robustness of two-dimensional inviscid MHD flows at low magnetic Reynolds numbers with respect to three-dimensional perturbations. We analyze three model problems, namely flow in the interior of a triaxial ellipsoid, an unbounded vortex with elliptical streamlines, and a vortex sheet parallel to the magnetic field. We demonstrate that motion perpendicular to the magnetic field with elliptical streamlines becomes unstable with respect to the elliptical instability once the velocity has reached a critical magnitude whose value tends to zero as the eccentricity of the streamlines becomes large. Furthermore, vortex sheets parallel to the magnetic field, which are unstable for any velocity and any magnetic field, are found to emit eddies with vorticity perpendicular to the magnetic field and with an aspect ratio proportional to N(sup 1/2). The results suggest that purely two-dimensional motion without Joule energy dissipation is a singular type of flow which does not represent the asymptotic behaviour of three-dimensional MHD turbulence in the limit of infinitely strong magnetic fields.
Two-dimensional coupled fluid and electrodynamic calculations for a MHD DCW channel with slag layers
NASA Astrophysics Data System (ADS)
Liu, B. L.
1982-01-01
A fully coupled, two dimensional numerical method of modeling linear, coal-fired MHD generators is developed for the case of a plasma flow bounded by a slag layer on the channel walls. The governing partial differential equations for the plasma flow, slag layer and electrodynamics are presented and their coupling discussed. An iterative, numerical procedure employing non-uniform computational meshes and appropriate tridiagonal matrix solution schemes for the equations is presented. The method permits the investigation of the mutual plasma flow-slag layer development for prescribed wall temperatures, electrode geometry, slag properties and channel loading. In particular, the slag layer-plasma interface properties which require prior specification in an uncoupled analysis comprise part of the solution in the present approach. Results are presented for a short diagonally connected generator channel and include contour plots of the electric potential and current stream function as well as transverse and axial profiles of pertinent plasma properties. The results indicate that a thin electrode slag layer can be maintained in the presence of reasonable current density levels.
A two-dimensional MHD global coronal model - Steady-state streamers
NASA Technical Reports Server (NTRS)
Wang, A.-H.; Wu, S. T.; Suess, S. T.; Poletto, G.
1993-01-01
We describe a two-dimensional time-dependent, numerical, magnetohydrodynamic model for the determination of the physical properties of coronal streamers from the top of the transition zone (solar radius = 1) to 15 solar radii. Four examples are given: for dipole, quadrupole, and hexapole initial field topologies. The computed parameters are density, temperature, velocity, and magnetic field. In addition to the properties of the solutions, their accuracy is discussed. We use the model as the basis for a general discussion of the way boundary conditions are specified in this and similar simulations.
A two-dimensional MHD global coronal model - Steady-state streamers
NASA Technical Reports Server (NTRS)
Wang, A.-H.; Wu, S. T.; Suess, S. T.; Poletto, G.
1992-01-01
A 2D, time-dependent, numerical, MHD model for the simulation of coronal streamers from the solar surface to 15 solar is presented. Three examples are given; for dipole, quadrupole and hexapole (Legendre polynomials P1, P2, and P3) initial field topologies. The computed properties are density, temperature, velocity, and magnetic field. The calculation is set up as an initial-boundary value problem wherein a relaxation in time produces the steady state solution. In addition to the properties of the solutions, their accuracy is discussed. Besides solutions for dipole, quadrupole, and hexapole geometries, the model use of realistic values for the density and Alfven speed while still meeting the requirement that the flow speed be super-Alfvenic at the outer boundary by extending the outer boundary to 15 solar radii.
Toward the Accurate Simulation of Two-Dimensional Electronic Spectra
NASA Astrophysics Data System (ADS)
Giussani, Angelo; Nenov, Artur; Segarra-Martí, Javier; Jaiswal, Vishal K.; Rivalta, Ivan; Dumont, Elise; Mukamel, Shaul; Garavelli, Marco
2015-06-01
Two-dimensional pump-probe electronic spectroscopy is a powerful technique able to provide both high spectral and temporal resolution, allowing the analysis of ultrafast complex reactions occurring via complementary pathways by the identification of decay-specific fingerprints. [1-2] The understanding of the origin of the experimentally recorded signals in a two-dimensional electronic spectrum requires the characterization of the electronic states involved in the electronic transitions photoinduced by the pump/probe pulses in the experiment. Such a goal constitutes a considerable computational challenge, since up to 100 states need to be described, for which state-of-the-art methods as RASSCF and RASPT2 have to be wisely employed. [3] With the present contribution, the main features and potentialities of two-dimensional electronic spectroscopy are presented, together with the machinery in continuous development in our groups in order to compute two-dimensional electronic spectra. The results obtained using different level of theory and simulations are shown, bringing as examples the computed two-dimensional electronic spectra for some specific cases studied. [2-4] [1] Rivalta I, Nenov A, Cerullo G, Mukamel S, Garavelli M, Int. J. Quantum Chem., 2014, 114, 85 [2] Nenov A, Segarra-Martí J, Giussani A, Conti I, Rivalta I, Dumont E, Jaiswal V K, Altavilla S, Mukamel S, Garavelli M, Faraday Discuss. 2015, DOI: 10.1039/C4FD00175C [3] Nenov A, Giussani A, Segarra-Martí J, Jaiswal V K, Rivalta I, Cerullo G, Mukamel S, Garavelli M, J. Chem. Phys. submitted [4] Nenov A, Giussani A, Fingerhut B P, Rivalta I, Dumont E, Mukamel S, Garavelli M, Phys. Chem. Chem. Phys. Submitted [5] Krebs N, Pugliesi I, Hauer J, Riedle E, New J. Phys., 2013,15, 08501
Augmented reality simulator for training in two-dimensional echocardiography.
Weidenbach, M; Wick, C; Pieper, S; Quast, K J; Fox, T; Grunst, G; Redel, D A
2000-02-01
In two-dimensional echocardiography the sonographer must synthesize multiple tomographic slices into a mental three-dimensional (3D) model of the heart. Computer graphics and virtual reality environments are ideal to visualize complex 3D spatial relationships. In augmented reality (AR) applications, real and virtual image data are linked, to increase the information content. In the presented AR simulator a 3D surface model of the human heart is linked with echocardiographic volume data sets. The 3D echocardiographic data sets are registered with the heart model to establish spatial and temporal congruence. The heart model, together with an animated ultrasound sector represents a reference scenario, which displays the currently selected two-dimensional echocardiographic cutting plane calculated from the volume data set. Modifications of the cutting plane within the echocardiographic data are transferred and visualized simultaneously and in real time within the reference scenario. The trainee can interactively explore the 3D heart model and the registered 3D echocardiographic data sets by an animated ultrasound probe, whose position is controlled by an electromagnetic tracking system. The tracking system is attached to a dummy transducer and placed on a plastic puppet to give a realistic impression of a two-dimensional echocardiographic examination.
High order hybrid numerical simulations of two dimensional detonation waves
NASA Technical Reports Server (NTRS)
Cai, Wei
1993-01-01
In order to study multi-dimensional unstable detonation waves, a high order numerical scheme suitable for calculating the detailed transverse wave structures of multidimensional detonation waves was developed. The numerical algorithm uses a multi-domain approach so different numerical techniques can be applied for different components of detonation waves. The detonation waves are assumed to undergo an irreversible, unimolecular reaction A yields B. Several cases of unstable two dimensional detonation waves are simulated and detailed transverse wave interactions are documented. The numerical results show the importance of resolving the detonation front without excessive numerical viscosity in order to obtain the correct cellular patterns.
Onset of solar flares as predicted by two-dimensional MHD-models of quiescent prominences
NASA Technical Reports Server (NTRS)
Galindotrejo, J.
1985-01-01
The close connection between the sudden disapperance (disparition brusque) of the quiescent prominences and the two-ribbon flares are well known. During this dynamic phase the prominence ascends rapidly (typically with a velocity about 100 Km/sec) and disappears. In another later stage is observed material falling back into the chromosphere. The impact of this downfalling matter on the chromosphere produces the H brightening, which shows the symmetric double pattern. The occurence of the disparition brusque is thought to be a consequence of a plasma instability of magnetohydrostatic (MHD) structures. By means of the MHD-energy principle, the stability properties of four prominence models are analyzed. It is shown that all considered models undergo instabilities for parameters outside of the observed range at quiescent prominences. The possibility that such instabilities in the flare parameter range may indicate just the onset of a flare is considered.
Molecular-dynamics simulation of two-dimensional thermophoresis
Paredes; Idler; Hasmy; Castells; Botet
2000-11-01
A numerical technique is presented for the thermal force exerted on a solid particle by a gaseous medium between two flat plates at different temperatures, in the free molecular or transition flow. This is a two-dimensional molecular-dynamics simulation of hard disks in a inhomogeneous thermal environment. All steady-state features exhibited by the compressible hard-disk gas are shown to be consistent with the expected behaviors. Moreover the thermal force experienced by a large solid disk is investigated, and compared to the analytical case of cylinders moving perpendicularly to the constant temperature gradient for an infinite Knudsen number and in an infinite medium. We show precise examples of how this technique can be used simply to investigate more difficult practical problems, in particluar the influence of nonlinear gradients for large applied differences of temperature, of proximity of the walls, and of smaller Knudsen numbers.
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.
A two-dimensional global simulation study of inductive-dynamic magnetosphere-ionosphere coupling
NASA Astrophysics Data System (ADS)
Tu, Jiannan; Song, Paul
2016-12-01
We present the numerical methods and results of a global two-dimensional multifluid-collisional-Hall magnetohydrodynamic (MHD) simulation model of the ionosphere-thermosphere system, an extension of our one-dimensional three-fluid MHD model. The model solves, self-consistently, Maxwell's equations, continuity, momentum, and energy equations for multiple ion and neutral species incorporating photochemistry, collisions among the electron, ion and neutral species, and various heating sources in the energy equations. The inductive-dynamic approach (solving self-consistently Faraday's law and retaining inertia terms in the plasma momentum equations) used in the model retains all possible MHD waves, thus providing faithful physical explanation (not merely description) of the magnetosphere-ionosphere/thermosphere (M-IT) coupling. In the present study, we simulate the dawn-dusk cross-polar cap dynamic responses of the ionosphere to imposed magnetospheric convection. It is shown that the convection velocity at the top boundary launches velocity, magnetic, and electric perturbations propagating with the Alfvén speed toward the bottom of the ionosphere. Within the system, the waves experience reflection, penetration, and rereflection because of the inhomogeneity of the plasma conditions. The reflection of the Alfvén waves may cause overshoot (stronger than the imposed magnetospheric convection) of the plasma velocity in some regions. The simulation demonstrates dynamic propagation of the field-aligned currents and ionospheric electric field carried by the Alfvén waves, as well as formation of closure horizontal currents (Pedersen currents in the E region), indicating that in the dynamic stage the M-I coupling is via the Alfvén waves instead of field-aligned currents or electric field mapping as described in convectional M-I coupling models.
Simulation of two-dimensional flows in micropores
Din, X.; Michaelides, E.E.
1994-12-31
An approach based on the Molecular Dynamics is used to simulate liquid flows in two-dimensional micropores and to obtain the steady-state characteristics of the flow. The mass flux of the liquid is taken as a constraint condition. Therefore, the driving force is introduced according to the Gauss least-constraint principle. The liquid molecules are considered as spheres with the same mass and density as water molecules. The interaction between the liquid molecules is of the Lennard-Jones type. Pure liquid flows and solid-liquid flows are simulated numerically. It is found that the velocity profile of the pure liquid flow matches very well the analytical solution of the plane Poiseuille flows. It was observed that larger particles will tend to flow closer to the walls. Also that the existence of the large particle makes the liquid flow somewhat faster in the center of the pore. Significant velocity slip was observed between the larger particle and the liquid.
Hysteresis and avalanches in two-dimensional foam rheology simulations
NASA Astrophysics Data System (ADS)
Jiang, Yi; Swart, Pieter J.; Saxena, Avadh; Asipauskas, Marius; Glazier, James A.
1999-05-01
Foams have unique rheological properties that range from solidlike to fluidlike. We study two-dimensional noncoarsening foams of different disorder under shear in a Monte Carlo simulation, using a driven large-Q Potts model. Simulations of periodic shear on an ordered foam show several different response regimes. At small strain amplitudes, bubbles deform and recover their shapes elastically, and the macroscopic response is that of a linear elastic cellular material. For increasing strain amplitude, the energy-strain curve starts to exhibit hysteresis before any topological rearrangements occur, indicating a macroscopic viscoelastic response. When the applied strain amplitude exceeds a critical value, the yield strain, topological rearrangements occur, the foam starts to flow, and we observe macroscopic irreversibility. We find that the dynamics of topological rearrangements depend sensitively on the structural disorder. Structural disorder decreases the yield strain; sufficiently high disorder changes the macroscopic response of a foam from a viscoelastic solid to a viscoelastic fluid. This wide-ranging dynamical response and the associated history effects of foams result from avalanchelike rearrangement events. The spatiotemporal statistics of rearrangement events do not display long-range correlations for ordered foams or at low shear rates, consistent with experimental observations. As the shear rate or structural disorder increases, the topological events become more correlated and their power spectra change from that of white noise toward 1/f noise. Intriguingly, the power spectra of the total stored energy also exhibit this 1/f trend.
Takasao, Shinsuke; Nakamura, Naoki; Shibata, Kazunari; Matsumoto, Takuma
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 and 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.
Two-dimensional numerical simulations of supercritical accretion flows revisited
Yang, Xiao-Hong; Yuan, Feng; Bu, De-Fu; Ohsuga, Ken E-mail: fyuan@shao.ac.cn
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 θφ} component of the viscous stress and consider various values of the viscous parameter α. We find that when T {sub θφ} 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 α 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 ρ(r)∝r {sup –p} and the value of p is almost same for a wide range of α ranging from α = 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 α, the flow is marginally stable (when α is small) or unstable (when α is large). This is different from the case of hydrodynamical hot accretion flow, where radiation is dynamically unimportant and the flow is always convectively unstable. We speculate that the reason for the difference is because radiation can stabilize convection. The origin of outflow is thus likely because of the joint function of convection and radiation, but further investigation is required.
Two-Dimensional Inlet Simulation Using a Diagonal Implicit Algorithm
NASA Technical Reports Server (NTRS)
Chaussee, D.S.; Pulliam, T. H.
1981-01-01
A modification of an implicit approximate-factorization finite-difference algorithm applied to the two-dimensional Euler and Navier-Stokes equations in general curvilinear coordinates is presented for supersonic freestream flow about and through inlets. The modification transforms the coupled system of equations Into an uncoupled diagonal form which requires less computation work. For steady-state applications the resulting diagonal algorithm retains the stability and accuracy characteristics of the original algorithm. Solutions are given for inviscid and laminar flow about a two-dimensional wedge inlet configuration. Comparisons are made between computed results and exact theory.
NASA Astrophysics Data System (ADS)
Lepping, R. P.; Wu, C.-C.; McClernan, K.
2003-07-01
This study examines the degree of two-dimensional curvature of solar wind directional discontinuity (DD) surfaces at 1 AU using magnetic field, density, and velocity data from the WIND and IMP-8 spacecraft for a large number (N = 134) of carefully selected events having large "discontinuity angles" of 90° or greater. The discontinuity angle (ω) is measured in the DD's current sheet, the normal (n) to which is estimated by field variance analysis. The fundamental analysis depends on estimates of these DD surface normals at the two spacecraft and the DD's center-times and positions. On average, the transit time from one DD sighting to the other was 36 minutes, and the associated distance along the normal direction was 137 RE. The transition-interval lengths across the DDs are translated into thicknesses and examined for the amount of change between the two spacecraft observing points. The average thickness is relatively large, 14 RE.; the most probable thickness is ≈6 RE. All relevant quantities are examined statistically to establish their distributions, average, and degree of change. A weighted average of the radius of curvature is estimated to be 380 RE, but its most probable value is 290 RE. The average ω is 140° with a relatively large spread (σ = 28°). The average direction of propagation is: longitude (ϕn) = 194° and latitude (θn) = 7° (but <∣θn∣> = 27°), where ϕn = 0° is sunward and θn = 0° is the ecliptic plane. Various parameters are studied with respect to DD type, i.e., rotational or tangential discontinuity (RD or TD), defined in terms of the "ratio" (in percent) of speed of propagation to net speed of the DD surface, where the net speed is the sum of the convection velocity (along n) plus the propagation speed. The RD %-ratio is moderately small, but the TD ratio is very small or zero. The results by this definition of type are favorably compared to those from the more conventional method, which depends on the absolute strength of
MHD simulations: Corotating Interaction Regions
NASA Astrophysics Data System (ADS)
Wiengarten, T.; Kleimann, J.; Fichtner, H.; Kühl, P.; Heber, B.; Kissmann, R.
2013-12-01
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 (SDEs)). Our MHD code CRONOS employs a semi-discrete finite volume scheme with adaptive time-stepping Runge-Kutta integration. The solenoidality of the magnetic field is ensured via constrained transport and the code supports Cartesian, Cylindrical and Spherical coordinates (including coordinate singularities) with the option for non-equidistant grids. The code runs in parallel (MPI) and supports the HDF5 output data format. Here, we show results from 3D-MHD simulations with our code CRONOS for a) analytic boundary conditions where results can be compared to those obtained with a different code and b) boundary conditions derived with the Wang-Sheeley-Arge model from observational data (WSO), which are compared to spacecraft observations. Comparison with Pizzo (1982) for analytic boundary conditions Comparison with STEREO A for Carrington Rotation 2060
Atchison, W.L.; Faehl, R.J.; Morgan, D.V.; Reinovsky, R.E.
1997-10-01
Experiments being conducted at the Los Alamos National Laboratory Pegasus facility are examining stability issues for driving an aluminum liner with a pulsed magnetic field. The Pegasus facility provides a current of 5 to 8 Megamperes to compress a cylindrical liner. Liners of various size and thickness are used, depending on the specific experimental objectives. In several of these experiments, the outer surface clearly develops perturbations in the mass distribution. These perturbations are strongest when the aluminum is suspected to have melted and in some cases partially vaporized. A series of specific experiments was designed to examine the growth rate of these instabilities. These experiments involved machining a sine wave onto the outer surface of the liner to seed a given wavelength. Two-dimensional MHD calculations, using the measured current profile, were performed to model the behavior of the liner under magnetic field compression. These predictions were made with a 2D Eulerian code complete with a Steinburg-Guinan strength model. The results of these calculations will be discussed in this paper. The density contours at specific times will be compared with the processed radiography.
Two-Dimensional Simulation of Truckee River Hydrodynamics
2006-09-01
ANALYSIS: The Truckee River originates from Lake Tahoe , flowing 140 miles (225 km) through Reno, NV, to Pyramid Lake . The downstream boundary of the...riverine restoration design. A two-dimensional (2-D) hydrodynamic model was applied to the McCarran Ranch reach of the Truckee River to evaluate...existing condition and future restoration plan condition hydraulics. The impact of the restoration design is presented in terms of the difference in the
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.
Two-dimensional particle simulation of a perpendicular shock with a shock rest frame model
NASA Astrophysics Data System (ADS)
Yamao, M.; Umeda, T.; Yamazaki, R.; Ogino, T.
2009-12-01
A two-dimensional shock-rest-frame model for particle simulations is developed. This model does not need a huge simulation domain in the propagation direction of the shock wave as previous simulation models do. We performed a two-dimensional full particle simulation of a perpendicular collisionless shock and compared with one-dimensional simulation results. In both simulations, the excited shock waves show almost the same time evolution, periodically reforming at the timescale of the downstream ion gyro-period. In the two-dimensional simulation, electrons are thermalized along the transverse magnetic field, and electromagnetic whistler mode waves are excited in the shock front region. The amplitude of the exited whistler mode waves is not so strong and the shock magnetic field keeps almost one-dimensional structure. The two-dimensional simulation also shows the absence of electrostatic solitary structures in the shock foot region, which is necessary for electron shock surfing acceleration.
Two-dimensional simulations of pulsational pair-instability supernovae
Chen, Ke-Jung; Woosley, Stan; Heger, Alexander; Almgren, Ann; Whalen, Daniel J.
2014-09-01
Massive stars that end their lives with helium cores in the range of 35-65 M {sub ☉} are known to produce repeated thermonuclear outbursts due to a recurring pair-instability. In some of these events, solar masses of material are ejected in repeated outbursts of several × 10{sup 50} erg each. Collisions between these shells can sometimes produce very luminous transients that are visible from the edge of the observable universe. Previous one-dimensional (1D) studies of these events produce thin, high-density shells as one ejection plows into another. Here, in the first multi-dimensional simulations of these collisions, we show that the development of a Rayleigh-Taylor instability truncates the growth of the high-density spike and drives mixing between the shells. The progenitor is a 110 M {sub ☉} solar-metallicity star that was shown in earlier work to produce a superluminous supernova. The light curve of this more realistic model has a peak luminosity and duration that are similar to those of 1D models but a structure that is smoother.
Simulation of wave interactions with MHD
Batchelor, Donald B; Abla, G; Bateman, Glenn; Bernholdt, David E; Berry, Lee A; Bonoli, P.; Bramley, R; Breslau, J.; Chance, M.; Chen, J.; Choi, M.; Elwasif, Wael R; Fu, GuoYong; Harvey, R. W.; Jaeger, Erwin Frederick; Jardin, S. C.; Jenkins, T; Keyes, David E; Klasky, Scott A; Kruger, Scott; Ku, Long-Poe; Lynch, Vickie E; McCune, Douglas; Ramos, J.; Schissel, D.; Schnack,; Wright, J.
2008-07-01
The broad scientific objectives of the SWIM (Simulation of Wave Interaction with MHD) project are twofold: (1) improve our understanding of interactions that both radio frequency (RF) wave and particle sources have on extended-MHD phenomena, and to substantially improve our capability for predicting and optimizing the performance of burning plasmas in devices such as ITER: and (2) develop an integrated computational system for treating multiphysics phenomena with the required flexibility and extensibility to serve as a prototype for the Fusion Simulation Project. The Integrated Plasma Simulator (IPS) has been implemented. Presented here are initial physics results on RF effects on MHD instabilities in tokamaks as well as simulation results for tokamak discharge evolution using the IPS.
EVIDENCE OF ACTIVE MHD INSTABILITY IN EULAG-MHD SIMULATIONS OF SOLAR CONVECTION
Lawson, Nicolas; Strugarek, Antoine; Charbonneau, Paul E-mail: strugarek@astro.umontreal.ca
2015-11-10
We investigate the possible development of magnetohydrodynamical instabilities in the EULAG-MHD “millennium simulation” of Passos and Charbonneau. This simulation sustains a large-scale magnetic cycle characterized by solar-like polarity reversals taking place on a regular multidecadal cadence, and in which zonally oriented bands of strong magnetic fields accumulate below the convective layers, in response to turbulent pumping from above in successive magnetic half-cycles. Key aspects of this simulation include low numerical dissipation and a strongly sub-adiabatic fluid layer underlying the convectively unstable layers corresponding to the modeled solar convection zone. These properties are conducive to the growth and development of two-dimensional instabilities that are otherwise suppressed by stronger dissipation. We find evidence for the action of a non-axisymmetric magnetoshear instability operating in the upper portions of the stably stratified fluid layers. We also investigate the possibility that the Tayler instability may be contributing to the destabilization of the large-scale axisymmetric magnetic component at high latitudes. On the basis of our analyses, we propose a global dynamo scenario whereby the magnetic cycle is driven primarily by turbulent dynamo action in the convecting layers, but MHD instabilities accelerate the dissipation of the magnetic field pumped down into the overshoot and stable layers, thus perhaps significantly influencing the magnetic cycle period. Support for this scenario is found in the distinct global dynamo behaviors observed in an otherwise identical EULAG-MHD simulations, using a different degree of sub-adiabaticity in the stable fluid layers underlying the convection zone.
Simulation of laser bistatic two-dimensional scattering imaging about lambertian cylinders
NASA Astrophysics Data System (ADS)
Gong, Yanjun; Li, Lang; Wang, Mingjun; Gong, Lei
2016-10-01
This paper deals with the simulation of laser bi-static scattering imaging about lambertian cylinders. Two-dimensional imaging of a target can reflect the shape of the target and material property on the surface of the target. Two-dimensional imaging has important significance for target recognition. Simulations results of laser bi-static two-dimensional scattering imaging of some cylinders are given. The laser bi-static scattering imaging of cylinder, whose surface material with diffuse lambertian reflectance, is given in this paper. The scattering direction of laser bi-static scattering imaging is arbitrary direction. The scattering direction of backward two-dimensional scattering imaging is at opposite direction of the incident direction of laser. The backward two-dimensional scattering imaging is special case of bi-static two dimensional scattering imaging. The scattering intensity of a micro-element on the target could be obtained based on the laser radar equation. The intensity is related to local angle of incidence, local angle of scattering and the infinitesimal area on the surface of cylinder. According to the incident direction of incident laser and normal of infinitesimal area, the local incidence angle can be calculated. According to the scattering direction and normal of infinitesimal area, the local angle of scattering can be calculated. Through surface integration and the introduction of the rectangular function, we can get the intensity of imaging unit on the imaging surface, and then get mathematical model of bi-static laser two dimensional scattering imaging about lambert cylinder. From the results given, one can see that the simulation results of laser bi-static scattering about lambert cylinder is correct.
Arrays of individually controlled ions suitable for two-dimensional quantum simulations
Mielenz, Manuel; Kalis, Henning; Wittemer, Matthias; Hakelberg, Frederick; Warring, Ulrich; Schmied, Roman; Blain, Matthew; Maunz, Peter; Moehring, David L.; Leibfried, Dietrich; Schaetz, Tobias
2016-01-01
A precisely controlled quantum system may reveal a fundamental understanding of another, less accessible system of interest. A universal quantum computer is currently out of reach, but an analogue quantum simulator that makes relevant observables, interactions and states of a quantum model accessible could permit insight into complex dynamics. Several platforms have been suggested and proof-of-principle experiments have been conducted. Here, we operate two-dimensional arrays of three trapped ions in individually controlled harmonic wells forming equilateral triangles with side lengths 40 and 80 μm. In our approach, which is scalable to arbitrary two-dimensional lattices, we demonstrate individual control of the electronic and motional degrees of freedom, preparation of a fiducial initial state with ion motion close to the ground state, as well as a tuning of couplings between ions within experimental sequences. Our work paves the way towards a quantum simulator of two-dimensional systems designed at will. PMID:27291425
Two dimensional PIC simulations of plasma heating by the dissipation of Alfven waves
NASA Technical Reports Server (NTRS)
Liewer, P. C.; Kruecken, T. J.; Ferraro, R. D.; Decyk, V. K.; Goldstein, B. E.
1992-01-01
Two dimensional plasma particle simulations of the evolution of large amplitude circularly polarized Alfven waves propagating parallel to the magnetic field show that the waves decay via both one- and two- dimensional parametric decay instabilities. For parameters studied, one-dimensional processes dominate the simulations, but two-dimensional decay processes, including the recently predicted filamentation instability are also observed. The daughter waves generated by the parametric decay are primarily damped by the ions, leading to ion heating. The parametric decay processes efficiently convert the ordered fluid ion motion in the Alfven wave into ion thermal energy. These processes may be important for the dissipation of Alfven waves in the solar wind, the corona and other space plasma environments. The computations were performed on the Intel Touchstone parallel supercomputer.
Li, Zhenyu; Abramavicius, Darius; Zhuang, Wei; Mukamel, Shaul
2007-11-15
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.
Laser bistatic two-dimensional scattering imaging simulation of lambert cone
NASA Astrophysics Data System (ADS)
Gong, Yanjun; Zhu, Chongyue; Wang, Mingjun; Gong, Lei
2015-11-01
This paper deals with the laser bistatic two-dimensional scattering imaging simulation of lambert cone. Two-dimensional imaging is called as planar imaging. It can reflect the shape of the target and material properties. Two-dimensional imaging has important significance for target recognition. The expression of bistatic laser scattering intensity of lambert cone is obtained based on laser radar eauqtion. The scattering intensity of a micro-element on the target could be obtained. The intensity is related to local angle of incidence, local angle of scattering and the infinitesimal area on the cone. According to the incident direction of laser, scattering direction and normal of infinitesimal area, the local incidence angle and scattering angle can be calculated. Through surface integration and the introduction of the rectangular function, we can get the intensity of imaging unit on the imaging surface, and then get Lambert cone bistatic laser two-dimensional scattering imaging simulation model. We analyze the effect of distinguishability, incident direction, observed direction and target size on the imaging. From the results, we can see that the scattering imaging simulation results of the lambert cone bistatic laser is correct.
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.
Inductive ionospheric solver for magnetospheric MHD simulations
NASA Astrophysics Data System (ADS)
Vanhamäki, H.
2011-01-01
We present a new scheme for solving the ionospheric boundary conditions required in magnetospheric MHD simulations. In contrast to the electrostatic ionospheric solvers currently in use, the new solver takes ionospheric induction into account by solving Faraday's law simultaneously with Ohm's law and current continuity. From the viewpoint of an MHD simulation, the new inductive solver is similar to the electrostatic solvers, as the same input data is used (field-aligned current [FAC] and ionospheric conductances) and similar output is produced (ionospheric electric field). The inductive solver is tested using realistic, databased models of an omega-band and westward traveling surge. Although the tests were performed with local models and MHD simulations require a global ionospheric solution, we may nevertheless conclude that the new solution scheme is feasible also in practice. In the test cases the difference between static and electrodynamic solutions is up to ~10 V km-1 in certain locations, or up to 20-40% of the total electric field. This is in agreement with previous estimates. It should also be noted that if FAC is replaced by the ground magnetic field (or ionospheric equivalent current) in the input data set, exactly the same formalism can be used to construct an inductive version of the KRM method originally developed by Kamide et al. (1981).
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.
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.
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.
NASA Technical Reports Server (NTRS)
Deluca, E. E.; Werne, J.; Rosner, R.; Cattaneo, F.
1990-01-01
Results on the transition from soft to hard turbulence in simulations of two-dimensional Boussinesq convection are reported. The computed probability densities for temperature fluctuations are exponential in form in both soft and hard turbulence, unlike what is observed in experiments. In contrast, a change is obtained in the Nusselt number scaling on Rayleigh number in good agreement with the three-dimensional experiments.
Octavio, M. ); Free, J.U. Physics Department, Harvard University, Cambridge, Massachusetts ); Benz, S.P. ); Newrock, R.S.; Mast, D.B. ); Lobb, C.J. )
1991-09-01
We present simulations of two-dimensional Josephson-junction arrays to study giant Shapiro steps in these arrays. The amplitude and frequency dependence of the step widths is found to be more complex than in single junctions. The fractional step widths are found to decrease more rapidly with increasing frequency or rf current than conventional steps in single junctions. The washboard model of single junctions is extended to arrays to explain these differences between arrays and single junctions.
Simulation of two-dimensional gratings for SERS-active substrate
NASA Astrophysics Data System (ADS)
Zou, Wenlong; Wu, Jianhong
2016-11-01
Raman spectroscopy provides intrinsic vibrational and rotational mode of molecules in materials, which is widely used in chemical, medical and environmental domains. As known, the magnitude of surface enhanced Raman scattering can be amplified several orders. Nowadays, common Raman scattering has been gradually replaced by surface enhanced Raman scattering in low concentration detection domain. Generally speaking, the signal of surface enhanced Raman scattering on periodic nanostructures is more reliable and reproducible than on irregular nanostructures. In this paper, two-dimensional gratings coated by noble metal are used as SERS-active substrate. The surface plasmon resonance can be obtained by tuning the period of two-dimensional grating when the excitation laser interacts on the grating. The local electric field distribution is simulated by finite-difference-time-domain (FDTD). The wavelength of 632.8nm and 785nm are usually assembled on commercial Raman spectrometer. The optimization procedure of two-dimensional grating period is simulated by FDTD for above two wavelengths. The relation between the grating period and surface plasmon resonance is obtained in theory. The parameters such as depth of photoresist and thickness of coated metal are systematic discussed. The simulation results will greatly guide our post manufacture, which can be served for the commercial Raman spectrometer in SERS detection.
MHD simulation of the Bastille day event
NASA Astrophysics Data System (ADS)
Linker, Jon; Torok, Tibor; Downs, Cooper; Lionello, Roberto; Titov, Viacheslav; Caplan, Ronald M.; Mikić, Zoran; Riley, Pete
2016-03-01
We describe a time-dependent, thermodynamic, three-dimensional MHD simulation of the July 14, 2000 coronal mass ejection (CME) and flare. The simulation starts with a background corona developed using an MDI-derived magnetic map for the boundary condition. Flux ropes using the modified Titov-Demoulin (TDm) model are used to energize the pre-event active region, which is then destabilized by photospheric flows that cancel flux near the polarity inversion line. More than 1033 ergs are impulsively released in the simulated eruption, driving a CME at 1500 km/s, close to the observed speed of 1700km/s. The post-flare emission in the simulation is morphologically similar to the observed post-flare loops. The resulting flux rope that propagates to 1 AU is similar in character to the flux rope observed at 1 AU, but the simulated ICME center passes 15° north of Earth.
HYBRID AND HALL-MHD SIMULATIONS OF COLLISIONLESS RECONNECTION: EFFECTS OF PLASMA PRESSURE TENSOR
L. YIN; D. WINSKE; ET AL
2001-05-01
In this study we performed two-dimensional hybrid (particle ions, massless fluid electrons) and Hall-MHD simulations of collisionless reconnection in a thin current sheet. Both calculations include the full electron pressure tensor (instead of a localized resistivity) in the generalized Ohm's law to initiate reconnection, and in both an initial perturbation to the Harris equilibrium is applied. First, electron dynamics from the two calculations are compared, and we find overall agreement between the two calculations in both the reconnection rate and the global configuration. To address the issue of how kinetic treatment for the ions affects the reconnection dynamics, we compared the fluid-ion dynamics from the Hall-MHD calculation to the particle-ion dynamics obtained from the hybrid simulation. The comparison demonstrates that off-diagonal elements of the ion pressure tensor are important in correctly modeling the ion out-of-plane momentum transport from the X point. It is that these effects can be modeled efficiently using a particle Hall-MHD simulation method in which particle ions used in a predictor/corrector to implement the ion gyro-radius corrections. We also investigate the micro- macro-scale coupling in the magnetotail dynamics by using a new integrated approach in which particle Hall-MHD calculations are embedded inside a MHD simulation. Initial results of the simulation concerning current sheet thinning and reconnection dynamics are discussed.
NASA Astrophysics Data System (ADS)
Fang, WenXiao; En, YunFei; Zhou, Bin; Huang, QinWen; Liu, Xin; Chen, YiQiang
2012-12-01
The magnetization recovery of a two-dimensional ferromagnetic system after excitation by intensive ultrafast pump pulses is investigated by a Monte Carlo method with a focus on the evolution of domain structure and the magnetization in the equilibrium state. Our simulations can explain the effect of the pumping fluence on the recovery process. In particular, they reveal the importance of domain formation in the recently reported accumulation effect already found by the pump-probe magnetization hysteresis loop measurement of a metallic ferromagnetic film. In the framework of the model, it is predicted that by repeating pump pulses a sufficient number of times, the magnetization of the two-dimensional ferromagnetic system can be eliminated when the pump fluence is above a critical value.
Two-dimensional numerical simulation of boron diffusion for pyramidally textured silicon
Ma, Fa-Jun Duttagupta, Shubham; Shetty, Kishan Devappa; Meng, Lei; Hoex, Bram; Peters, Ian Marius; Samudra, Ganesh S.
2014-11-14
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.
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.
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.
Goldberg, L.F.
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.
Preliminary results for a two-dimensional simulation of the working process of a Stirling engine
Makhkamov, K.K.; Ingham, D.B.
1998-07-01
Stirling engines have several potential advantages over existing types of engines, in particular they can use renewable energy sources for power production and their performance meets the demands on the environmental security. In order to design Stirling Engines properly, and to put into effect their potential performance, it is important to more accurately mathematically simulate its working process. At present, a series of very important mathematical models are used for describing the working process of Stirling Engines and these are, in general, classified as models of three levels. All the models consider one-dimensional schemes for the engine and assume a uniform fluid velocity, temperature and pressure profiles at each plane of the internal gas circuit of the engine. The use of two-dimensional CFD models can significantly extend the capabilities for the detailed analysis of the complex heat transfer and gas dynamic processes which occur in the internal gas circuit, as well as in the external circuit of the engine. In this paper a two-dimensional simplified frame (no construction walls) calculation scheme for the Stirling Engine has been assumed and the standard {kappa}-{var{underscore}epsilon} turbulence model has been used for the analysis of the engine working process. The results obtained show that the use of two-dimensional CFD models gives the possibility of gaining a much greater insight into the fluid flow and heat transfer processes which occur in Stirling Engines.
Computer simulations of a two-dimensional system with competing interactions.
Stoycheva, Antitsa D; Singer, Sherwin J
2002-03-01
The results and methodology of large scale computer simulations of the two-dimensional dipolar Ising model with long-range interactions are reported. Systems as large as 117,649 particles were studied to elucidate the elementary excitations and phase diagram of two-dimensional systems, such as Langmuir monolayers, thin garnet films, and adsorbed films on solid surfaces, which spontaneously form patterns of stripes, bubbles, and intermediately shaped domains. The challenging numerical investigations of large scale systems with long-range interactions at low temperatures were made possible by combining the fast multipole method and a non-Metropolis Monte Carlo sampling technique. Our simulations provide evidence that, at sufficiently high ratios of the repulsive to the attractive coupling constant for the model, twofold stripe order in the systems of interest is lost through a defect-mediated mechanism. Heat capacity data and the excitations observed in our simulations as the system disorders indicate that it is most likely an instance of a Kosterlitz-Thouless phase transition. The results from simulations with and without external field are in excellent agreement with the predictions of an analytic scaling theory [A. D. Stoycheva and S. J. Singer, Phys. Rev. E 64, 016118 (2001)], confirming the phase diagram furnished by the analytic model. The scaling theory suggests that, under certain conditions, defect-mediated stripe melting may be supplanted by Ising like disordering within stripes for small repulsion strength. A qualitative discussion of a model that supports both disordering mechanisms is presented.
Two-dimensional numerical simulation of flow around three-stranded rope
NASA Astrophysics Data System (ADS)
Wang, Xinxin; Wan, Rong; Huang, Liuyi; Zhao, Fenfang; Sun, Peng
2016-08-01
Three-stranded rope is widely used in fishing gear and mooring system. Results of numerical simulation are presented for flow around a three-stranded rope in uniform flow. The simulation was carried out to study the hydrodynamic characteristics of pressure and velocity fields of steady incompressible laminar and turbulent wakes behind a three-stranded rope. A three-cylinder configuration and single circular cylinder configuration are used to model the three-stranded rope in the two-dimensional simulation. The governing equations, Navier-Stokes equations, are solved by using two-dimensional finite volume method. The turbulence flow is simulated using Standard κ-ɛ model and Shear-Stress Transport κ-ω (SST) model. The drag of the three-cylinder model and single cylinder model is calculated for different Reynolds numbers by using control volume analysis method. The pressure coefficient is also calculated for the turbulent model and laminar model based on the control surface method. From the comparison of the drag coefficient and the pressure of the single cylinder and three-cylinder models, it is found that the drag coefficients of the three-cylinder model are generally 1.3-1.5 times those of the single circular cylinder for different Reynolds numbers. Comparing the numerical results with water tank test data, the results of the three-cylinder model are closer to the experiment results than the single cylinder model results.
Simulation of two-dimensional target motion based on a liquid crystal beam steering method
NASA Astrophysics Data System (ADS)
Lin, Yixiang; Ai, Yong; Shan, Xin; Liu, Min
2015-05-01
A simulation platform is established for target motion using a liquid crystal (LC) spatial light modulator as a nonmechanical beam steering control device. By controlling the period and orientation of the phase grating generated by the spatial light modulator, the platform realizes two-dimensional (2-D) beam steering using a single LC device. The zenith and azimuth angle range from 0 deg to 2.89 deg and from 0 deg to 360 deg, respectively, with control resolution of 0.0226 deg and 0.0300 deg, respectively. The response time of the beam steering is always less than 0.04 s, irrespective of steering angle. Three typical aircraft tracks are imitated to evaluate the performance of the simulation platform. The correlation coefficients between the theoretical and simulated motions are larger than 0.9822. Results show that it is highly feasible to realize 2-D target motion simulation using the LC spatial light modulator.
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.
Thermal structure of the ionosphere of Mars - simulations with one- and two-dimensional models
Singhal, R.P.; Whitten, R.C.
1988-05-01
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. 22 references.
Palanichamy, Jegathambal; Schüttrumpf, Holger; Palani, Sundarambal
2008-01-01
In recent years evolutionary computing algorithms have been proposed to solve many engineering problems. Genetic algorithms, Neural Networks, and Cellular Automata are the branches of evolutionary computing techniques. In this study, it is proposed to simulate the contaminant transport in porous media using a Cellular Automaton. The physical processes and chemical reactions occurring in the ground water system are intricately connected at various scales of space, time, transport coefficients and molecular concentration. The validity of continuous approach for the simulation of chemical systems with low concentration of species and intracellular environments has become subtle. Due to the difference in scales of various processes that occur in the ground water system, the description of the system can be well defined in the intermediate scale called mesoscopic scale, which is in between microscopic and macroscopic description. Mesoscopic models provide the relationship between various parameters and their evolvement in time, thus establishing the contact between modeling at various scales at the interface. In this paper, a Probabilistic Cellular Automaton (PCA) model has been developed based on the transport and reaction probability values. The developed model was verified and validated for one, two dimensional transport systems and also for the simulation of BTEX transport in two dimensional system in ground water.
Suppressing sampling noise in linear and two-dimensional spectral simulations
NASA Astrophysics Data System (ADS)
Kruiger, Johannes F.; van der Vegte, Cornelis P.; Jansen, Thomas L. C.
2015-02-01
We examine the problem of sampling noise encountered in time-domain simulations of linear and two-dimensional spectroscopies. A new adaptive apodization scheme based on physical arguments is devised for suppressing the noise in order to allow reducing the number of used disorder realisations, but introducing only a minimum of spectral aberrations and thus allowing a potential speed-up of these types of simulations. First, the method is demonstrated on an artificial dimer system, where the effect on slope analysis, typically used to study spectral dynamics, is analysed. It is, furthermore, tested on the simulated two-dimensional infrared spectra in the amide I region of the protein lysozyme. The cross polarisation component is investigated, particularly sensitive to sampling noise, because it relies on cancelling of the dominant diagonal spectral contributions. In all these cases, the adaptive apodization scheme is found to give more accurate results than the commonly used lifetime apodization scheme and in most cases better than the gaussian apodization scheme.
Theory and simulation of two-dimensional nematic and tetratic phases.
Geng, Jun; Selinger, Jonathan V
2009-07-01
Recent experiments and simulations have shown that two-dimensional systems can form tetratic phases with fourfold rotational symmetry, even if they are composed of particles with only twofold symmetry. To understand this effect, we propose a model for the statistical mechanics of particles with almost fourfold symmetry, which is weakly broken down to twofold. We introduce a coefficient kappa to characterize the symmetry breaking, and find that the tetratic phase can still exist even up to a substantial value of kappa. Through a Landau expansion of the free energy, we calculate the mean-field phase diagram, which is similar to the result of a previous hard-particle excluded-volume model. To verify our mean-field calculation, we develop a Monte Carlo simulation of spins on a triangular lattice. The results of the simulation agree very well with the Landau theory.
Martinez-Sykora, Juan; De Pontieu, Bart; Hansteen, Viggo
2012-07-10
The bulk of the solar chromosphere is weakly ionized and interactions between ionized particles and neutral particles likely have significant consequences for the thermodynamics of the chromospheric plasma. We investigate the importance of introducing neutral particles into the MHD equations using numerical 2.5D radiative MHD simulations obtained with the Bifrost code. The models span the solar atmosphere from the upper layers of the convection zone to the low corona, and solve the full MHD equations with non-gray and non-LTE radiative transfer, and thermal conduction along the magnetic field. The effects of partial ionization are implemented using the generalized Ohm's law, i.e., we consider the effects of the Hall term and ambipolar diffusion in the induction equation. The approximations required in going from three fluids to the generalized Ohm's law are tested in our simulations. The Ohmic diffusion, Hall term, and ambipolar diffusion show strong variations in the chromosphere. These strong variations of the various magnetic diffusivities are absent or significantly underestimated when, as has been common for these types of studies, using the semi-empirical VAL-C model as a basis for estimates. In addition, we find that differences in estimating the magnitude of ambipolar diffusion arise depending on which method is used to calculate the ion-neutral collision frequency. These differences cause uncertainties in the different magnetic diffusivity terms. In the chromosphere, we find that the ambipolar diffusion is of the same order of magnitude or even larger than the numerical diffusion used to stabilize our code. As a consequence, ambipolar diffusion produces a strong impact on the modeled atmosphere. Perhaps more importantly, it suggests that at least in the chromospheric domain, self-consistent simulations of the solar atmosphere driven by magnetoconvection can accurately describe the impact of the dominant form of resistivity, i.e., ambipolar diffusion. This
Forced Reconnection in the Near Magnetotail: Onset and Energy Conversion in PIC and MHD Simulations
NASA Technical Reports Server (NTRS)
Birn, J.; Hesse, Michael
2014-01-01
Using two-dimensional particle-in-cell (PIC) together with magnetohydrodynamic (MHD) Q1 simulations of magnetotail dynamics, we investigate the evolution toward onset of reconnection and the subsequent energy transfer and conversion. In either case, reconnection onset is preceded by a driven phase, during which magnetic flux is added to the tail at the high-latitude boundaries, followed by a relaxation phase, during which the configuration continues to respond to the driving. The boundary deformation leads to the formation of thin embedded current sheets, which are bifurcated in the near tail, converging to a single sheet farther out in the MHD simulations. The thin current sheets in the PIC simulation are carried by electrons and are associated with a strong perpendicular electrostatic field, which may provide a connection to parallel potentials and auroral arcs and an ionospheric signal even prior to the onset of reconnection. The PIC simulation very well satisfies integral entropy conservation (intrinsic to ideal MHD) during this phase, supporting ideal ballooning stability. Eventually, the current intensification leads to the onset of reconnection, the formation and ejection of a plasmoid, and a collapse of the inner tail. The earthward flow shows the characteristics of a dipolarization front: enhancement of Bz, associated with a thin vertical electron current sheet in the PIC simulation. Both MHD and PIC simulations show a dominance of energy conversion from incoming Poynting flux to outgoing enthalpy flux, resulting in heating of the inner tail. Localized Joule dissipation plays only a minor role.
MHD Simulation of Plasma Flow through the VASIMR Magnetic Nozzle
NASA Astrophysics Data System (ADS)
Tarditi, A. G.; Shebalin, J. V.
2003-10-01
The VASIMR (Variable Specific Impulse Magnetoplasma Rocket, [1]) concept is currently in the experimental development phase at the Advanced Space Propulsion Laboratory, NASA Johnson Space Center. The current experimental effort is mainly focused on the demonstration of the efficient plasma production (light ion helicon source, [2]) and energy boosting (ion cyclotron resonance heating section). Two other critical issues, the plasma detachment process and the collimation of the plasma plume in the magnetic nozzle, are essential for the near term experimental development and are being addressed through an MHD simulation modeling effort with the NIMROD code [3,4]. The model follows the plasma flow up to few meters from the nozzle throat: at that distance the plasma exhaust parameters reach values comparable with the ionospheric plasma background [5]. Results from two-dimensional simulation runs (cylindrical geometry, assuming azimuthal symmetry) aimed in particular at testing the effectiveness of different open-end boundary condition schemes are presented. [1] F. R. Chang-Diaz, Scientific American, p. 90, Nov. 2000 [2] M. D. Carter, et al., Phys. Plasmas 9, 5097-5110, 2002 [3] http://www.nimrodteam.org [4] A. Tarditi et al., 28th Int. Electric Propulsion Conf., IEPC 2003, Toulouse, France, March 2003 [5] A. V. Ilin et al., Proc. 40th AIAA Aerospace Sciences Meeting, Reno, NV, Jan. 2002
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.
Reformation at a low-Mach-number perpendicular shock: Two-dimensional full particle simulations
NASA Astrophysics Data System (ADS)
Umeda, T.; Kidani, Y.; Matsukiyo, S.; Yamazaki, R.
2012-12-01
Large-scale two-dimensional full particle-in-cell simulations are carried out for studying periodic self-reformation of supercritical perpendicular shocks. It is confirmed that the shock reformation becomes absent with specific parameters. When electromagnetic whistler mode waves are strongly excited by the modified two-stream instability, both incoming and reflected ions are strongly scattered and the shock reformation becomes absent. On the other hand, when electrostatic waves are weakly excited or there is no microinstabilities, reflected ions show a coherent behavior and the shock reformation is persistent. In this case, however, the reformation period is modified essentially due to the shock-front ripples. The present simulation result suggests that the persistence and absence of the shock reformation are controlled by the cross-scale coupling between electron-scale microinstabilities and ion-scale shock-front ripples.
Aerodynamic effects of simulated ice shapes on two-dimensional airfoils and a swept finite tail
NASA Astrophysics Data System (ADS)
Alansatan, Sait
An experimental study was conducted to investigate the effect of simulated glaze ice shapes on the aerodynamic performance characteristics of two-dimensional airfoils and a swept finite tail. The two dimensional tests involved two NACA 0011 airfoils with chords of 24 and 12 inches. Glaze ice shapes computed with the LEWICE code that were representative of 22.5-min and 45-min ice accretions were simulated with spoilers, which were sized to approximate the horn heights of the LEWICE ice shapes. Lift, drag, pitching moment, and surface pressure coefficients were obtained for a range of test conditions. Test variables included Reynolds number, geometric scaling, control deflection and the key glaze ice features, which were horn height, horn angle, and horn location. For the three-dimensional tests, a 25%-scale business jet empennage (BJE) with a T-tail configuration was used to study the effect of ice shapes on the aerodynamic performance of a swept horizontal tail. Simulated glaze ice shapes included the LEWICE and spoiler ice shapes to represent 9-min and 22.5-min ice accretions. Additional test variables included Reynolds number and elevator deflection. Lift, drag, hinge moment coefficients as well as boundary layer velocity profiles were obtained. The experimental results showed substantial degradation in aerodynamic performance of the airfoils and the swept horizontal tail due to the simulated ice shapes. For the two-dimensional airfoils, the largest aerodynamic penalties were obtained when the 3-in spoiler-ice, which was representative of 45-min glaze ice accretions, was set normal to the chord. Scale and Reynolds effects were not significant for lift and drag. However, pitching moments and pressure distributions showed great sensitivity to Reynolds number and geometric scaling. For the threedimensional study with the swept finite tail, the 22.5-min ice shapes resulted in greater aerodynamic performance degradation than the 9-min ice shapes. The addition of 24
NASA Astrophysics Data System (ADS)
Hou, Lujing; Wang, Younian; Z, L. Miskvic
2004-08-01
The characteristics of collisional radio-frequency (rf) sheath dynamics over an electrode with a cylindrical hole is simulated by means of a self-consistent model which consists of two-dimensional time-dependent fluid equations coupled with Poisson equation. In addition, an equivalent-circuit model is coupled to the fluid equations in order to self-consistently determine relationship between the instantaneous potential at the rf-biased electrode and the sheath thickness. Two-dimensional profiles of the potential, the ion fluid velocity, and the distributions of the ion and electron densities within the sheath are computed under various discharge conditions, such as the discharge powers and the gas pressures. The results show that the existence of the cylindrical hole on the electrode significantly affects the sheath structure and generates a potential trap in the horizontal direction, which is particularly strong when the sheath thickness is comparable to the depth of the hole. Moreover, it is found that the collisional effects have a significant influence on the sheath characteristics.
Topological events in two-dimensional grain growth: Experiments and simulations
Fradkov, V.E.; Glicksman, M.E.; Palmer, M.; Rajan, K. . Materials Engineering Dept.)
1994-08-01
Grain growth in polycrystals is a process that occurs as a result of the vanishing of small grains. The mean topological class of vanishing two-dimensional (2-D) grains was found experimentally to be about 4.5. This result suggests that most vanishing grains are either 4- or 5-sided. A recent theory of 2-D grain growth is explicitly based on this fact, treating the switching as random events. The process of shrinking of 4- and 5-sided two-dimensional grains was observed experimentally on polycrystalline films of transparent, pure succinonitrile (SCN). Grain shrinking was studied theoretically and simulated by computer (both dynamic and Monte Carlo). It was found that most shrinking grains are topologically stable and remain within their topological class until they are much smaller than their neighbors. They discuss differences which were found with respect to the behavior of 2-D polycrystals, a 2-D ideal soap froth, and a 2-D section of a 3-D grain structure.
NASA Astrophysics Data System (ADS)
Heilman, Warren Emanuel
A two-dimensional second-order turbulence-closure model based on level three of the Mellor-Yamada turbulence hierarchy has been developed and used to examine the nocturnal and early morning turbulence characteristics over Rattlesnake Mountain in Washington. The model includes radiation, soil, canopy, and slope parameterizations for calculating mean and turbulence variables over two-dimensional terrain features. Simulations of mean horizontal velocities and potential temperatures show good agreement with data obtained over Rattlesnake Mountain during nocturnal drainage-flow conditions. Qualitative analysis of simulated turbulence fields during these conditions indicates significant variations over the windward and leeward slopes. Turbulence anisotropy develops in the drainage-flow region where vertical wind shears and atmospheric stability are large. The buoyant portion of the turbulent heat flux enhances the vertical component of turbulent kinetic energy, especially over the leeward slope. Derived turbulent diffusivities reflect the developed anisotropic turbulence conditions. Simulations of the atmospheric conditions over Rattlesnake Mountain during the early morning hours indicate significant growth of the convective boundary layer when the initial stability over the entire depth of the modeled region is very weak. Upslope flow develops when no ambient wind is present. The buoyancy-generated turbulence inhibits the formation of large upslope velocity maxima when ambient winds are present. Spatial variations in the turbulent kinetic energy develop over the mountain, but they are less than the variations during nocturnal drainage-flow conditions. Turbulence anisotropy is significant in the convective boundary layer. However, the developed anisotropy plays a minor role in affecting turbulent diffusivity magnitudes. The transition from nocturnal drainage-flow conditions to convective conditions is characterized by a redistribution of energy among the turbulent
NASA Technical Reports Server (NTRS)
Goldberg, Louis F.
1990-01-01
Investigations of one- and two-dimensional (1- or 2-D) simulations of Stirling machines centered around experimental data generated by the U. of Minnesota Mechanical Engineering Test Rig (METR) are covered. This rig was used to investigate oscillating flows about a zero mean with emphasis on laminar/turbulent flow transitions in tubes. The Space Power Demonstrator Engine (SPDE) and in particular, its heater, were the subjects of the simulations. The heater was treated as a 1- or 2-D entity in an otherwise 1-D system. The 2-D flow effects impacted the transient flow predictions in the heater itself but did not have a major impact on overall system performance. Information propagation effects may be a significant issue in the simulation (if not the performance) of high-frequency, high-pressure Stirling machines. This was investigated further by comparing a simulation against an experimentally validated analytic solution for the fluid dynamics of a transmission line. The applicability of the pressure-linking algorithm for compressible flows may be limited by characteristic number (defined as flow path information traverses per cycle); this warrants further study. Lastly the METR was simulated in 1- and 2-D. A two-parameter k-w foldback function turbulence model was developed and tested against a limited set of METR experimental data.
Simulations of one- and two-dimensional complex plasmas using a modular, object-oriented code
NASA Astrophysics Data System (ADS)
Jefferson, R. A.; Cianciosa, M.; Thomas, E.
2010-11-01
In a complex plasma, charged microparticles ("dust") are added to a background of ions, electrons, and neutral particles. This dust fully interacts with the surrounding plasma and self-consistently alters the plasma environment leading to the emergence of new plasma behavior. Numerical tools that complement experimental investigations can provide important insights into the properties of complex plasmas. This paper discusses a newly developed code, named DEMON (dynamic exploration of microparticle clouds optimized numerically), for simulating a complex plasma. The DEMON code models the behavior of the charged particle component of a complex plasma in a uniform plasma background. The key feature of the DEMON code is the use of a modular force model that allows a wide variety of experimental configurations to be studied without varying the core code infrastructure. Examples of the flexibility of this modular approach are presented using examples of one- and two-dimensional complex plasmas.
Zhang, Jiao; Wang, Yanhui Wang, Dezhen
2015-11-15
A two-dimensional fluid model is developed to study the filaments (or discharge channels) in atmospheric-pressure discharge with one plate electrode covered by a dielectric layer. Under certain discharge parameters, one or more stable filaments with wide radii could be regularly arranged in the discharge space. Different from the short-lived randomly distributed microdischarges, this stable and thick filament can carry more current and have longer lifetime. Because only one electrode is covered by a dielectric layer in the simulation, the formed discharge channel extends outwards near the dielectric layer and shrinks inwards near the naked electrode, agreeing with the experimental results. In this paper, the evolution of channel is studied, and its behavior is like a streamer or an ionization wave, but the propagation distance is short. The discharge parameters such as voltage amplitude, electrode width, and N{sub 2} impurities content could significantly influence the number of discharge channel, which is discussed in the paper.
NASA Astrophysics Data System (ADS)
Chua, Victor; Vissers, Michael; Law, Stephanie A.; Vishveshwara, Smitha; Eckstein, James N.
2015-03-01
We simulate the consequences of the superconducting proximity effect on the DC current response of a semiconductor-superconductor proximity device within the quasiclassical formalism in the diffusively disordered limit. The device is modeled on in-situ fabricated NS junctions of superconducting Nb films on metallic doped InAs films, with electrical terminals placed in an N-S-N T-junction configuration. Due to the non-collinear configuration of this three terminal device, a theoretical model based on coupled two dimensional spectral and distributional Usadel equations was constructed and numerically solved using Finite-Elements methods. In the regime of high junction conductance, our numerical results demonstrate strong temperature and spatial dependencies of the proximity induced modifications to spectral and transport properties. Such characteristics deviate strongly from usual tunnel junction behavior and aspects of this have been observed in prior experiments[arXiv:1402.6055].
NASA Astrophysics Data System (ADS)
Renouf, M.; Bonamy, D.; Dubois, F.; Alart, P.
2005-10-01
The rheology of two-dimensional steady surface flow of cohesionless cylinders in a rotating drum is investigated through nonsmooth contact dynamics simulations. Profiles of volume fraction, translational and angular velocity, rms velocity, strain rate, and stress tensor are measured at the midpoint along the length of the surface-flowing layer, where the flow is generally considered as steady and homogeneous. Analysis of these data and their interrelations suggest the local inertial number—defined as the ratio between local inertial forces and local confinement forces—to be the relevant dimensionless parameter to describe the transition from the quasistatic part of the packing to the flowing part at the surface of the heap. Variations of the components of the stress tensor as well as the ones of rms velocity as a function of the inertial number are analyzed within both the quasistatic and the flowing phases. Their implications are discussed.
NASA Astrophysics Data System (ADS)
Rino, C. L.
2013-12-01
Global observation of the GPS satellite constellation for ionospheric diagnostics is now a worldwide activity driven by both practical and scientific objectives. Diagnostic methods exploit an induced frequency-dependent phase change, which is proportional to the path-integrated electron density (TEC). However, intermediate-scale structure causes a stochastic modulation of the GPS signals (scintillation), which is a nuisance for data assimilation. Indeed, sufficiently strong propagation disturbances degrade TEC and ultimately disrupt GPS operations altogether. However, the physical processes that generate intermediate-scale structure are intimately part of ionospheric physics. In the best of all possible worlds irregularity identification and classification would be an integral part of ionospheric diagnostics. A two-dimensional propagation model has been used to explore the ramifications of intermediate scale structure on TEC data assimilation and, particularly tomographic reconstruction. Although two-dimensional models confine structure to a planar region, the results are relevant, with caveats, to propagation through highly anisotropic ionospheric structures. In-plane propagation from a source to an array of receivers is amenable to reconstruction with tomographic filtered back-projection algorithms. The angle-dependent Fourier decomposition of the array signal phase identifies a spectral slice. The signals from which the phase is derived are generated with an oblique forward propagation procedure developed by Costa and Basu Costa:02. Under weak-scatter conditions the signal phase is proportional to the ray path integral. The primary challenge for simulation is realistic simulation of the structure environment. Large scale ESF structure can be constructed with physics-based models, but populating the intermediate scale requires untested structure hypotheses. In particular, there is no clear demarcation between quasi-deterministic variation and
SOLAR WIND TURBULENCE FROM MHD TO SUB-ION SCALES: HIGH-RESOLUTION HYBRID SIMULATIONS
Franci, Luca; Verdini, Andrea; Landi, Simone; Matteini, Lorenzo; Hellinger, Petr
2015-05-10
We present results from a high-resolution and large-scale hybrid (fluid electrons and particle-in-cell protons) two-dimensional numerical simulation of decaying turbulence. Two distinct spectral regions (separated by a smooth break at proton scales) develop with clear power-law scaling, each one occupying about a decade in wavenumbers. The simulation results simultaneously exhibit several properties of the observed solar wind fluctuations: spectral indices of the magnetic, kinetic, and residual energy spectra in the magnetohydrodynamic (MHD) inertial range along with a flattening of the electric field spectrum, an increase in magnetic compressibility, and a strong coupling of the cascade with the density and the parallel component of the magnetic fluctuations at sub-proton scales. Our findings support the interpretation that in the solar wind, large-scale MHD fluctuations naturally evolve beyond proton scales into a turbulent regime that is governed by the generalized Ohm’s law.
Lu, Meijun; Das, Ujjwal; Bowden, Stuart; Hegedus, Steven; Birmire, Robert
2009-06-09
In this paper, two-dimensional (2D) simulation of interdigitated back contact silicon heterojunction (IBC-SHJ) solar cells is presented using Sentaurus Device, a software package of Synopsys TCAD. A model is established incorporating a distribution of trap states of amorphous-silicon material and thermionic emission across the amorphous-silicon / crystalline-silicon heterointerface. The 2D nature of IBC-SHJ device is evaluated and current density-voltage (J-V) curves are generated. Optimization of IBC-SHJ solar cells is then discussed through simulation. It is shown that the open circuit voltage (VOC) and short circuit current density (JSC) of IBC-SHJ solar cells increase with decreasing front surface recombination velocity. The JSC improves further with the increase of relative coverage of p-type emitter contacts, which is explained by the simulated and measured position dependent laser beam induced current (LBIC) line scan. The S-shaped J-V curves with low fill factor (FF) observed in experiments are also simulated, and three methods to improve FF by modifying the intrinsic a-Si buffer layer are suggested: (i) decreased thickness, (ii) increased conductivity, and (iii) reduced band gap. With all these optimizations, an efficiency of 26% for IBC-SHJ solar cells is potentially achievable.
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.
Modeling power flow in the induction cavity with a two dimensional circuit simulation
NASA Astrophysics Data System (ADS)
Guo, Fan; Zou, Wenkang; Gong, Boyi; Jiang, Jihao; Chen, Lin; Wang, Meng; Xie, Weiping
2017-02-01
We have proposed a two dimensional (2D) circuit model of induction cavity. The oil elbow and azimuthal transmission line are modeled with one dimensional transmission line elements, while 2D transmission line elements are employed to represent the regions inward the azimuthal transmission line. The voltage waveforms obtained by 2D circuit simulation and transient electromagnetic simulation are compared, which shows satisfactory agreement. The influence of impedance mismatch on the power flow condition in the induction cavity is investigated with this 2D circuit model. The simulation results indicate that the peak value of load voltage approaches the maximum if the azimuthal transmission line roughly matches the pulse forming section. The amplitude of output transmission line voltage is strongly influenced by its impedance, but the peak value of load voltage is insensitive to the actual output transmission line impedance. When the load impedance raises, the voltage across the dummy load increases, and the pulse duration at the oil elbow inlet and insulator stack regions also slightly increase.
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
2013-01-17
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 β-peptide (Aβ). The mechanism connecting Aβ 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 Aβ amyloid fibrils. On the basis of these simulations, a dock/lock mechanism was proposed, in which Aβ 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 (λ = 190-250 nm) in which the computed signals originate from the backbone nπ* and ππ* 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 Aβ-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.
Postek, Michael T; Vladár, András E; Lowney, Jeremiah R; Keery, William J
2002-01-01
Traditional Monte Carlo modeling of the electron beam-specimen interactions in a scanning electron microscope (SEM) produces information about electron beam penetration and output signal generation at either a single beam-landing location, or multiple landing positions. If the multiple landings lie on a line, the results can be graphed in a line scan-like format. Monte Carlo results formatted as line scans have proven useful in providing one-dimensional information about the sample (e.g., linewidth). When used this way, this process is called forward line scan modeling. In the present work, the concept of image simulation (or the first step in the inverse modeling of images) is introduced where the forward-modeled line scan data are carried one step further to construct theoretical two-dimensional (2-D) micrographs (i.e., theoretical SEM images) for comparison with similar experimentally obtained micrographs. This provides an ability to mimic and closely match theory and experiment using SEM images. Calculated and/or measured libraries of simulated images can be developed with this technique. The library concept will prove to be very useful in the determination of dimensional and other properties of simple structures, such as integrated circuit parts, where the shape of the features is preferably measured from a single top-down image or a line scan. This paper presents one approach to the generation of 2-D simulated images and presents some suggestions as to their application to critical dimension metrology.
Tong, Mingming; Cole, Katie; Brito-Parada, Pablo R; Neethling, Stephen; Cilliers, Jan J
2017-04-05
Pseudo-two-dimensional (2D) foams are commonly used in foam studies as it is experimentally easier to measure the bubble size distribution and other geometric and topological properties of these foams than it is for a 3D foam. Despite the widespread use of 2D foams in both simulation and experimental studies, many important geometric and topological relationships are still not well understood. Film size, for example, is a key parameter in the stability of bubbles and the overall structure of foams. The relationship between the size distribution of the films in a foam and that of the bubbles themselves is thus a key relationship in the modeling and simulation of unstable foams. This work uses structural simulation from Surface Evolver to statistically analyze this relationship and to ultimately formulate a relationship for the film size in 2D foams that is shown to be valid across a wide range of different bubble polydispersities. These results and other topological features are then validated using digital image analysis of experimental pseudo-2D foams produced in a vertical Hele-Shaw cell, which contains a monolayer of bubbles between two plates. From both the experimental and computational results, it is shown that there is a distribution of sizes that a film can adopt and that this distribution is very strongly dependent on the sizes of the two bubbles to which the film is attached, especially the smaller one, but that it is virtually independent of the underlying polydispersity of the foam.
GIS-based two-dimensional numerical simulation of rainfall-induced debris flow
NASA Astrophysics Data System (ADS)
Wang, C.; Li, S.; Esaki, T.
2008-02-01
This paper aims to present a useful numerical method to simulate the propagation and deposition of debris flow across the three dimensional complex terrain. A depth-averaged two-dimensional numerical model is developed, in which the debris and water mixture is assumed to be continuous, incompressible, unsteady flow. The model is based on the continuity equations and Navier-Stokes equations. Raster grid networks of digital elevation model in GIS provide a uniform grid system to describe complex topography. As the raster grid can be used as the finite difference mesh, the continuity and momentum equations are solved numerically using the finite difference method. The numerical model is applied to simulate the rainfall-induced debris flow occurred in 20 July 2003, in Minamata City of southern Kyushu, Japan. The simulation reproduces the propagation and deposition and the results are in good agreement with the field investigation. The synthesis of numerical method and GIS makes possible the solution of debris flow over a realistic terrain, and can be used to estimate the flow range, and to define potentially hazardous areas for homes and road section.
Computer-based training in two-dimensional echocardiography using an echocardiography simulator.
Weidenbach, Michael; Wild, Florentine; Scheer, Kathrin; Muth, Gerhard; Kreutter, Stefan; Grunst, Gernoth; Berlage, Thomas; Schneider, Peter
2005-04-01
Two-dimensional (2D) echocardiography is a user-dependent technique that poses some inherent problems to the beginner. The first problem for beginners is spatial orientation, especially the orientation of the scan plane in reference to the 3-dimensional (3D) geometry of the heart. The second problem for beginners is steering of the ultrasound probe. We have designed a simulator to teach these skills. On a computer screen a side-by-side presentation of a 3D virtual reality scene on the right side and a 2D echocardiographic view on the left side is given. The virtual scene consists of a 3D heart and an ultrasound probe with scan plane. The 2D echocardiographic image is calculated from 3D echocardiographic data sets that are registered with the heart model to achieve spatial and temporal congruency. The displayed 2D echocardiographic image is defined and controlled by the orientation of the virtual scan plane. To teach hand-eye coordination we equipped a dummy transducer with a 3D tracking system and placed it on a dummy torso. We have evaluated the usability of the simulator in an introductory course for final-year medical students. The simulator was graded realistic and easy to use. According to a subjective self-assessment by a standardized questionnaire the aforementioned skills were imparted effectively.
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 β-peptide (Aβ). The mechanism connecting Aβ 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 β amyloid fibrils. Based on these simulations, a dock/lock mechanism was proposed, in which Aβ 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 (λ = 190–250 nm) in which the computed signals originate from the backbone nπ* and ππ* 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 Aβ-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
1985-08-01
id This report should be cited as follows: -0 Thompson , J . F ., and Bernard, R. S. 1985. "WESSEL: Code for Numerical Simulation of Two-Dimensional Time...Bodies," Ph. D. Dissertation, Mississippi State University, Mississippi State, Miss. Thompson , J . F . 1983. "A Boundary-Fitted Coordinate Code for General...Vicksburg, Miss. Thompson , J . F ., and Bernard, R. S. 1985. "Numerical Modeling of Two-Dimensional Width-Averaged Flows Using Boundary-Fitted Coordinate
GPU-based simulation of the two-dimensional unstable structure of gaseous oblique detonations
Teng, H.H.; Kiyanda, C.B.; Ng, H.D.; Morgan, G.H.; Nikiforakis, N.
2015-03-10
In this paper, the two-dimensional structure of unstable oblique detonations induced by the wedge from a supersonic combustible gas flow is simulated using the reactive Euler equations with a one-step Arrhenius chemistry model. A wide range of activation energy of the combustible mixture is considered. Computations are performed on the Graphical Processing Unit (GPU) to reduce the simulation runtimes. A large computational domain covered by a uniform mesh with high grid resolution is used to properly capture the development of instabilities and the formation of different transverse wave structures. After the initiation point, where the oblique shock transits into a detonation, an instability begins to manifest and in all cases, the left-running transverse waves first appear, followed by the subsequent emergence of right-running transverse waves forming the dual-head triple point structure. This study shows that for low activation energies, a long computational length must be carefully considered to reveal the unstable surface due to the slow growth rate of the instability. For high activation energies, the flow behind the unstable oblique detonation features the formation of unburnt gas pockets and strong vortex-pressure wave interaction resulting in a chaotic-like vortical structure.
Langevin dynamics simulations of a two-dimensional colloidal crystal under confinement and shear.
Wilms, D; Virnau, P; Sengupta, S; Binder, K
2012-06-01
Langevin dynamics simulations are used to study the effect of shear on a two-dimensional colloidal crystal (with implicit solvent) confined by structured parallel walls. When walls are sheared very slowly, only two or three crystalline layers next to the walls move along with them, while the inner layers of the crystal are only slightly tilted. At higher shear velocities, this inner part of the crystal breaks into several pieces with different orientations. The velocity profile across the slit is reminiscent of shear banding in flowing soft materials, where liquid and solid regions coexist; the difference, however, is that in the latter case the solid regions are glassy while here they are crystalline. At even higher shear velocities, the effect of the shearing becomes smaller again. Also the effective temperature near the walls (deduced from the velocity distributions of the particles) decreases again when the wall velocity gets very large. When the walls are placed closer together, thereby introducing an incommensurability between the periodicity of the confined crystal and the walls, a structure containing a soliton staircase arises in simulations without shear. Introducing shear increases the disorder in these systems until no solitons are visible anymore. Instead, similar structures like in the case without mismatch result. At high shear rates, configurations where the incommensurability of the crystalline structure is compensated by the creation of holes become relevant.
Two-dimensional simulation of polysilicon etching with chlorine in a high density plasma reactor
Lymberopoulos, D.P.; Economou, D.J.
1995-08-01
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 simulation. The power deposited into the plasma was calculated by an electromagnetics module which solves Maxwell`s equations. The power deposition was used in the electron energy module to find the electron temperature and the rate coefficients of electron-impact reactions. These were in turn used as source terms in separate neutral and charged species transport modules. By iterating among the modules, a self-consistent solution was obtained. Quantities of interest, such as power deposition, species density and flux, and etch rate and uniformity were thus calculated. As power deposition was increased, the electron density increased linearly, the plasma became less electronegative, the degree of gas dissociation increased, and the plasma potential remained constant. The radial uniformity of the Cl atom flux was better than that of the ion flux. The reactivity of the wafer as compared to that of the surrounding electrode surface significantly affected the etch uniformity, despite the low pressure of 10 mTorr.
Ito, Hironobu; Jo, Ju-Yeon; Tanimura, Yoshitaka
2015-01-01
Recent developments in two-dimensional (2D) THz-Raman and 2D Raman spectroscopies have created the possibility for quantitatively investigating the role of many dynamic and structural aspects of the molecular system. We explain the significant points for properly simulating 2D vibrational spectroscopic studies of intermolecular modes using the full molecular dynamics approach, in particular, regarding the system size, the treatment of the thermostat, and inclusion of an Ewald summation for the induced polarizability. Moreover, using the simulation results for water employing various polarization functions, we elucidate the roles of permanent and induced optical properties in determining the 2D profiles of the signal. PMID:26798823
Two-dimensional simulations of explosive eruptions of Kick-em Jenny and other submarine volcanos
Gisler, Galen R.; Weaver, R. P.; Mader, Charles L.; Gittings, M. L.
2004-01-01
Kick-em Jenny, in the Eastern Caribbean, is a submerged volcanic cone that has erupted a dozen or more times since its discovery in 1939. The most likely hazard posed by this volcano is to shipping in the immediate vicinity (through volcanic missiles or loss-of-buoyancy), but it is of interest to estimate upper limits on tsunamis that might be produced by a catastrophic explosive eruption. To this end, we have performed two-dimensional simulations of such an event in a geometry resembling that of Kick-em Jenny with our SAGE adaptive mesh Eulerian multifluid compressible hydrocode. We use realistic equations of state for air, water, and basalt, and follow the event from the initial explosive eruption, through the generation of a transient water cavity and the propagation of waves away from the site. We find that even for extremely catastrophic explosive eruptions, tsunamis from Kick-em Jenny are unlikely to pose significant danger to nearby islands. For comparison, we have also performed simulations of explosive eruptions at the much larger shield volcano Vailuluu in the Samoan chain, where the greater energy available can produce a more impressive wave. In general, however, we conclude that explosive eruptions do not couple well to water waves. The waves that are produced from such events are turbulent and highly dissipative, and don't propagate well. This is consistent with what we have found previously in simulations of asteroid-impact generated tsunamis. Non-explosive events, however, such as landslides or gas hydrate releases, do couple well to waves, and our simulations of tsunamis generated by subaerial and sub-aqueous landslides demonstrate this.
Simulations of super-structure domain walls in two dimensional assemblies of magnetic nanoparticles
NASA Astrophysics Data System (ADS)
Jordanovic, J.; Beleggia, M.; Schiøtz, J.; Frandsen, C.
2015-07-01
We simulate the formation of domain walls in two-dimensional assemblies of magnetic nanoparticles. Particle parameters are chosen to match recent electron holography and Lorentz microscopy studies of almost monodisperse cobalt nanoparticles assembled into regular, elongated lattices. As the particles are small enough to consist of a single magnetic domain each, their magnetic interactions can be described by a spin model in which each particle is assigned a macroscopic "superspin." Thus, the magnetic behaviour of these lattices may be compared to magnetic crystals with nanoparticle superspins taking the role of the atomic spins. The coupling is, however, different. The superspins interact only by dipolar interactions as exchange coupling between individual nanoparticles may be neglected due to interparticle spacing. We observe that it is energetically favorable to introduce domain walls oriented along the long dimension of nanoparticle assemblies rather than along the short dimension. This is unlike what is typically observed in continuous magnetic materials, where the exchange interaction introduces an energetic cost proportional to the area of the domain walls. Structural disorder, which will always be present in realistic assemblies, pins longitudinal domain walls when the external field is reversed, and makes a gradual reversal of the magnetization by migration of longitudinal domain walls possible, in agreement with previous experimental results.
Huang, Zhiming; Hao, Yanpeng; Yang, Lin; Han, Yongxia; Li, Licheng
2015-12-15
A two-dimensional (2D) fluid model is presented to investigate the spatiotemporal generation and dynamic mechanics of dielectric barrier columnar discharges in atmospheric helium. The model was examined with discharge currents measured in experiments and images taken by an intensified charge couple device camera. Based on the model, a columnar discharge was simulated for several cycles after being ignited. The discharge could be regarded as an initial unstable stage for the first three and a half cycles, then a steady state for the following cycles. In the initial stage, the discharge evolves from a uniform pattern into a columnar one. The calculated equipotential lines, 2D radial electric field, and electron density distributions at the edge of uniform discharges show the radial electric field accounts for the shrinking discharge area and the formation of discharge columns in the end. The columnar glow discharges and the Townsend discharges beyond the columns could coexist in the initial stage, and a Townsend discharge might develop into a new glow column in the next half-cycle. The radial electric field surrounding a glow discharge column has an inhibiting effect on the ionization in the peripheral area.
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 κ-ɛ model. The results of the proposed numerical schemes are compared with the ones obtained when using uncoupled formulations.
NASA Astrophysics Data System (ADS)
Ota, Keigo; Suzuki, Kosuke; Inamuro, Takaji
2012-08-01
Two-dimensional (2D) symmetric flapping flight is investigated by an immersed boundary-lattice Boltzmann method (IB-LBM). In this method, we can treat the moving boundary problem efficiently on the Cartesian grid. We consider a model consisting of 2D symmetric flapping wings without mass connected by a hinge with mass. Firstly, we investigate the effect of the Reynolds number in the range of 40-200 on flows around symmetric flapping wings under no gravity field and find that for high Reynolds numbers (Re ⩾ 55), asymmetric vortices with respect to the horizontal line appear and the time-averaged lift force is induced on the wings, whereas for low Reynolds numbers (Re ⩽ 50), only symmetric vortices appear around the wings and no lift force is induced. Secondly, the effect of the initial position of the wings is investigated, and the range of the initial phases where the upward flight is possible is found. The effects of the mass and flapping amplitude are also studied. Finally, we carry out free flight simulations under gravity field for various Reynolds numbers in the range 60 ⩽ Re ⩽ 300 and Froude numbers in the range 3 ⩽ Fr ⩽ 60 and identify the region where upward flight is possible.
Barber, Jared O.; Alberding, Jonathan P.; Restrepo, Juan M.; Secomb, Timothy W.
2008-01-01
Movement, deformation, and partitioning of mammalian red blood cells (RBCs) in diverging microvessel bifurcations are simulated using a two-dimensional, flexible-particle model. A set of viscoelastic elements represents the RBC membrane and the cytoplasm. Motion of isolated cells is considered, neglecting cell-to-cell interactions. Center-of-mass trajectories deviate from background flow streamlines due to migration of flexible cells towards the mother vessel centerline upstream of the bifurcation and due to flow perturbations caused by cell obstruction in the neighborhood of the bifurcation. RBC partitioning in the bifurcation is predicted by determining the RBC fraction entering each branch, for a given partition of total flow and for a given upstream distribution of RBCs. Typically, RBCs preferentially enter the higher-flow branch, leading to unequal discharge hematocrits in the downstream branches. This effect is increased by migration toward the centerline but decreased by the effects of obstruction. It is stronger for flexible cells than for rigid circular particles of corresponding size, and decreases with increasing parent vessel diameter. For unequally-sized daughter vessels, partitioning is asymmetric, with RBCs tending to enter the smaller vessel. Partitioning is not significantly affected by branching angles. Model predictions are consistent with previous experimental results. PMID:18686035
Simulations of super-structure domain walls in two dimensional assemblies of magnetic nanoparticles
Jordanovic, J.; Frandsen, C.; Beleggia, M.; Schiøtz, J.
2015-07-28
We simulate the formation of domain walls in two-dimensional assemblies of magnetic nanoparticles. Particle parameters are chosen to match recent electron holography and Lorentz microscopy studies of almost monodisperse cobalt nanoparticles assembled into regular, elongated lattices. As the particles are small enough to consist of a single magnetic domain each, their magnetic interactions can be described by a spin model in which each particle is assigned a macroscopic “superspin.” Thus, the magnetic behaviour of these lattices may be compared to magnetic crystals with nanoparticle superspins taking the role of the atomic spins. The coupling is, however, different. The superspins interact only by dipolar interactions as exchange coupling between individual nanoparticles may be neglected due to interparticle spacing. We observe that it is energetically favorable to introduce domain walls oriented along the long dimension of nanoparticle assemblies rather than along the short dimension. This is unlike what is typically observed in continuous magnetic materials, where the exchange interaction introduces an energetic cost proportional to the area of the domain walls. Structural disorder, which will always be present in realistic assemblies, pins longitudinal domain walls when the external field is reversed, and makes a gradual reversal of the magnetization by migration of longitudinal domain walls possible, in agreement with previous experimental results.
Simulation of Anderson localization in two-dimensional ultracold gases for pointlike disorder
NASA Astrophysics Data System (ADS)
Morong, W.; DeMarco, B.
2015-08-01
Anderson localization has been observed for a variety of media, including ultracold atomic gases with speckle disorder in one and three dimensions. However, observation of Anderson localization in a two-dimensional geometry for ultracold gases has been elusive. We show that a cause of this difficulty is the relatively high percolation threshold of a speckle potential in two dimensions, resulting in strong classical localization. We propose a realistic pointlike disorder potential that circumvents this percolation limit with localization lengths that are experimentally observable. The percolation threshold is evaluated for experimentally realistic parameters, and a regime of negligible classical trapping is identified. Localization lengths are determined via scaling theory, using both exact scattering cross sections and the Born approximation, and by direct simulation of the time-dependent Schrödinger equation. We show that the Born approximation can underestimate the localization length by four orders of magnitude at low energies, while exact cross sections and scaling theory provide an upper bound. Achievable experimental parameters for observing localization in this system are proposed.
Simulated two-dimensional electronic spectroscopy of the eight-bacteriochlorophyll FMO complex
Yeh, Shu-Hao; Kais, Sabre
2014-12-21
The Fenna-Matthews-Olson (FMO) protein-pigment complex acts as a molecular wire conducting energy between the outer antenna system and the reaction center; it is an important photosynthetic system to study the transfer of excitonic energy. Recent crystallographic studies report the existence of an additional (eighth) bacteriochlorophyll a (BChl a) in some of the FMO monomers. To understand the functionality of this eighth BChl, we simulated the two-dimensional electronic spectra of both the 7-site (apo form) and the 8-site (holo form) variant of the FMO complex from green sulfur bacteria, Prosthecochloris aestuarii. By comparing the spectrum, it was found that the eighth BChl can affect two different excitonic energy transfer pathways: (1) it is directly involved in the first apo form pathway (6 → 3 → 1) by passing the excitonic energy to exciton 6; and (2) it facilitates an increase in the excitonic wave function overlap between excitons 4 and 5 in the second pathway (7 → 4,5 → 2 → 1) and thus increases the possible downward sampling routes across the BChls.
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 mesoscale simulations of projectile instability during penetration in dry sand
NASA Astrophysics Data System (ADS)
Dwivedi, S. K.; Teeter, R. D.; Felice, C. W.; Gupta, Y. M.
2008-10-01
To gain insight into the instability and trajectory change in projectiles penetrating dry sand at high velocities, two dimensional plane strain mesoscale simulations were carried out using representative models of a particulate system and of a small projectile. A program, ISP-SAND, was developed and used to generate the representative particulate system with mean grain sizes of 60 and 120 μm as well as ±30% uniform size distribution from the mean. Target porosities ranged from 30% to 40%. The penetration of ogive nose steel projectiles with caliber radius head of 3.5 and length-to-diameter (l /d) ratio of 3.85 was simulated using the updated Lagrangian explicit parallel finite element code ISP-TROTP. Deformation of the projectile and individual sand grains was analyzed using a nonlinear elastic-inelastic model for these materials. Grain-grain and grain-projectile interactions were analyzed using a contact algorithm with and without friction. Projectile instability was quantified and compared using the lateral displacement of the center of mass, lateral force acting on the projectile, and its rotational momentum about the center of mass. The main source of projectile instability and the ensuing trajectory change in the penetration simulations was found to be the inhomogeneous loading of the projectile due to the heterogeneities and randomness inherent in a particulate media like sand. The granularity of the media has not been considered explicitly in previous work. Projectile instability increased with impact velocity, as expected. However, it also increased for the case of elastic impactor that preserved the nose shape, with an increase in grain size, and for uniform grain sizes. Moreover, friction, inherently present in geologic materials, was found to be a major contributor to instability. Conclusions derived from one projectile depth simulations were confirmed by two deeper penetration simulations considering up to three full lengths of penetration (requiring
MHD simulations of supernova driven ISM turbulence
NASA Astrophysics Data System (ADS)
Gressel, Oliver; Ziegler, Udo
The dynamic evolution of the (stratified) turbulent interstellar medium (ISM) is simulated utilizing a three-dimensional MHD model including various physical effects. The computational domain covers a box of 0.5x0.5x2.0 kpc at a resolution of typically 128x128x1024 grid cells. The model includes (constant kinematic) viscosity and magnetic diffusivity. The adiabatic equation of state is supplemented by a parameterized heating- and cooling-function allowing for thermal instability (TI). The update due to heating and cooling is implemented implicitly using a Patankar-type discretization. Turbulence is driven by supernova explosions which are modelled as local injections of thermal energy, smeared over three standard-deviations of a Gaussian support with FWHM of 20pc. Supernova rates are adopted for typical cited values. Within our model we make a distinction between Type I and Type II SNe. Latter are statistically clustered by the (artificial) constraint that the density at the explosion site be above average (with respect to a horizontal slab) - former are spatially uncorrelated. The dual-energy feature of the conservative NIRVANA-code is used to tackle the extreme ratio of kinetic to internal energy that arises from the violent energy input. We stress the importance of using a conservative scheme to properly transfer the injected energy to kinetic motion. The model also includes a differentially rotating background (with shearing boundary conditions in radial direction) as well as vertical stratification. The initial density and pressure profiles are in hydrostatic equilibrium with respect to the equation of state given by the radiative equilibrium. Including z-dependent heating rates this leads to a considerable deviation from usual isothermal initial models. The primary focus of this work is on the galactic dynamo and the generation of large-scale magnetic fields. As a secondary target we are also interested in general properties of the ISM that are of importance
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 S{sub 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{sub 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{sub 2}. We notably obtain the expression of the static dielectric constant of a uniform isotropic polar fluid living in S{sub 2} in terms of the polarization fluctuations of subdomains of S{sub 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.
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
Two-dimensional fully dynamic SEM simulations of the 2011 Tohoku earthquake cycle
NASA Astrophysics Data System (ADS)
Shimizu, H.; Hirahara, K.
2014-12-01
Earthquake cycle simulations have been performed to successfully reproduce the historical earthquake occurrences. Most of them are quasi-dynamic, where inertial effects are approximated using the radiation damping proposed by Rice [1993]. Lapusta et al. [2000, 2009] developed a methodology capable of the detailed description of seismic and aseismic slip and gradual process of earthquake nucleation in the entire earthquake cycle. Their fully dynamic simulations have produced earthquake cycles considerably different from quasi-dynamic ones. Those simulations have, however, never been performed for interplate earthquakes at subduction zones. Many studies showed that on dipping faults such as interplate earthquakes at subduction zones, normal stress is changed during faulting due to the interaction with Earth's free surface. This change in normal stress not only affects the earthquake rupture process, but also causes the residual stress variation that might affect the long-term histories of earthquake cycle. Accounting for such effects, we perform two-dimensional simulations of the 2011 Tohoku earthquake cycle. Our model is in-plane and a laboratory derived rate and state friction acts on a dipping fault embedded on an elastic half-space that reaches the free surface. We extended the spectral element method (SEM) code [Ampuero, 2002] to incorporate a conforming mesh of triangles and quadrangles introduced in Komatitsch et al. [2001], which enables us to analyze the complex geometry with ease. The problem is solved by the methodology almost the same as Kaneko et al. [2011], which is the combined scheme switching in turn a fully dynamic SEM and a quasi-static SEM. The difference is the dip-slip thrust fault in our study in contrast to the vertical strike slip fault. With this method, we can analyze how the dynamic rupture with surface breakout interacting with the free surface affects the long-term earthquake cycle. We discuss the fully dynamic earthquake cycle results
NASA Astrophysics Data System (ADS)
Lu, Q.; Wu, M.; Huang, C.; Wang, S.
2011-12-01
A multi-dimensional electron phase-space hole (electron hole) is considered to be unstable to the transverse instability. We perform two-dimensional (2D) particle-in-cell (PIC) simulations to study the evolution of electron holes at different plasma conditions; we find that the evolution is determined by combined actions between the transverse instability and the stabilization by the ackground magnetic field. In very weakly magnetized plasma, the transverse instability dominates the evolution of the electron holes. The parallel cut of the perpendicular electric field has bipolar structures, accompanied by the kinking of the electron holes. Such structures last for only tens of electron plasma periods. With the increase of the background magnetic field, the evolution of the electron holes becomes slower. The bipolar structures of the parallel cut of the perpendicular electric field in the electron holes can evolve into unipolar structures. In very strongly magnetized plasma, the unipolar structures of the parallel cut of the perpendicular electric field can last for thousands of electron plasma periods. At the same time, the perpendicular electric field in the electron holes can also influence electron trajectories passing through the electron holes, which results in variations of charge density along the direction perpendicular to the background magnetic field outside of the electron holes. When the amplitude of the electron hole is sufficiently strong, streaked structures of the perpendicular electric field can be formed outside of the electron holes, which then emit electrostatic whistler waves because of the interactions between the streaked structures of the perpendicular electric field and vibrations of the kinked electron holes.
Two-dimensional simulation of red blood cell motion near a wall under a lateral force.
Hariprasad, Daniel S; Secomb, Timothy W
2014-11-01
The motion of a red blood cell suspended in a linear shear flow adjacent to a fixed boundary subject to an applied lateral force directed toward the boundary is simulated. A two-dimensional model is used that represents the viscous and elastic properties of normal red blood cells. Shear rates in the range of 100 to 600 s^{-1} are considered, and the suspending medium viscosity is 1 cP. In the absence of a lateral force, the cell executes a tumbling motion. With increasing lateral force, a transition from tumbling to tank-treading is predicted. The minimum force required to ensure tank-treading increases nonlinearly with the shear rate. Transient swinging motions occur when the force is slightly larger than the transition value. The applied lateral force is balanced by a hydrodynamic lift force resulting from the positive orientation of the long axis of the cell with respect to the wall. In the case of cyclic tumbling motions, the orientation angle takes positive values through most of the cycle, resulting in lift generation. These results are used to predict the motion of a cell close to the outer edge of the cell-rich core region that is generated when blood flows in a narrow tube. In this case, the lateral force is generated by shear-induced dispersion, resulting from cell-cell interactions in a region with a concentration gradient. This force is estimated using previous data on shear-induced dispersion. The cell is predicted to execute tank-treading motions at normal physiological hematocrit levels, with the possibility of tumbling at lower hematocrit levels.
Two-dimensional FSI simulation of closing dynamics of a tilting disc mechanical heart valve
Govindarajan, V.; Udaykumar, H.S.; Herbertson, L. H.; Deutsch, S.; Manning, K. B.; Chandran, K.B.
2010-01-01
The fluid dynamics during valve closure resulting in high shear flows and large residence times of particles has been implicated in platelet activation and thrombus formation in mechanical heart valves. Our previous studies with bi-leaflet valves have shown that large shear stresses induced in the gap between the leaflet edge and the valve housing results in relatively high platelet activation levels whereas flow between the leaflets results in shed vortices not conducive to platelet damage. In this study we compare the result of closing dynamics of a tilting disc valve with that of a bi-leaflet valve. The two-dimensional fluid-structure interaction analysis of a tilting disc valve closure mechanics is performed with a fixed grid Cartesian mesh flow solver with local mesh refinement, and a Lagrangian particle dynamic analysis for computation of potential for platelet activation. Throughout the simulation the flow remains in the laminar regime and the flow through the gap width is marked by the development of a shear layer which separates from the leaflet downstream of the valve. Zones of re-circulation are observed in the gap between the leaflet edge and the valve housing on the major orifice region of the tilting disc valve and are seen to be migrating towards the minor orifice region. Jet flow is observed at the minor orifice region and a vortex is formed which sheds in the direction of fluid motion as observed in experiments using PIV measurements. The activation parameter computed for the tilting disc valve, at the time of closure was found to be 2.7 times greater than that of the bi-leaflet mechanical valve and was found to be in the vicinity of the minor orifice region mainly due to the migration of vortical structures from the major to the minor orifice region during the leaflet rebound of the closing phase. PMID:20209095
Two-dimensional simulation of red blood cell motion near a wall under a lateral force
Hariprasad, Daniel S.; Secomb, Timothy W.
2015-01-01
The motion of a red blood cell suspended in a linear shear flow adjacent to a fixed boundary subject to an applied lateral force directed towards the boundary is simulated. A two-dimensional model is used that represents the viscous and elastic properties of normal red blood cells. Shear rates in the range of 100 s−1 to 600 s−1 are considered, and the suspending medium viscosity is 1 cP. In the absence of a lateral force, the cell executes a tumbling motion. With increasing lateral force, a transition from tumbling to tank-treading is predicted. The minimum force required to ensure tank-treading increases non-linearly with the shear rate. Transient swinging motions occur when the force is slightly larger than the transition value. The applied lateral force is balanced by a hydrodynamic lift force resulting from the positive orientation of the long axis of the cell with respect to the wall. In the case of cyclic tumbling motions, the orientation angle takes positive values through most of the cycle, resulting in lift generation. These results are used to predict the motion of a cell close to the outer edge of the cell-rich core region that is generated when blood flows in a narrow tube. In this case, the lateral force is generated by shear-induced dispersion, resulting from cell-cell interactions in a region with a concentration gradient. This force is estimated using previous data on shear-induced dispersion. The cell is predicted to execute tank-treading motions at normal physiological hematocrit levels, with the possibility of tumbling at lower hematocrit levels. PMID:25493888
Computation and validation of two-dimensional PSF simulation based on physical optics
NASA Astrophysics Data System (ADS)
Tayabaly, K.; Spiga, D.; Sironi, G.; Canestrari, R.; Lavagna, M.; Pareschi, G.
2015-09-01
The Point Spread Function (PSF) is a key figure of merit for specifying the angular resolution of optical systems and, as the demand for higher and higher angular resolution increases, the problem of surface finishing must be taken seriously even in optical telescopes. From the optical design of the instrument, reliable ray-tracing routines allow computing and display of the PSF based on geometrical optics. However, such an approach does not directly account for the scattering caused by surface micro-roughness, which is interferential in nature. Although the scattering effect can be separately modeled, its inclusion in the ray-tracing routine requires assumptions that are difficult to verify. In that context, a purely physical optics approach is more appropriate as it remains valid regardless of the shape and size of the defects appearing on the optical surface. Such a computation, when performed in two-dimensional consideration, is memory and time consuming because it requires one to process a surface map with a few micron resolution, and the situation becomes even more complicated in case of optical systems characterized by more than one reflection. Fortunately, the computation is significantly simplified in far-field configuration, since the computation involves only a sequence of Fourier Transforms. In this paper, we provide validation of the PSF simulation with Physical Optics approach through comparison with real PSF measurement data in the case of ASTRI-SST M1 hexagonal segments. These results represent a first foundation stone for future development in a more advanced computation taking into account micro-roughness and multiple reflection in optical systems.
Numerical simulation of two-dimensional single- and multiple-material flow fields
Lopez, A.R.; Baty, R.S. ); Kashiwa, B.A. )
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.
Numerical simulation of two-dimensional single- and multiple-material flow fields
Lopez, A.R.; Baty, R.S.; Kashiwa, B.A.
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.
Two-dimensional network simulation of diffusion driven coarsening of foam inside a porous medium
Cohen, D.; Patzek, T.W.; Radke, C.J.
1996-04-01
In order to use foams in subsurface applications, it is necessary to understand their stability in porous media. Diffusion driven coarsening of a stationary or nonflowing foam in a porous medium results in changing gas pressures and a coarsening of the foam texture. A two-dimensional network simulation has been created that predicts the behavior of foam in a porous medium by physically specifying the locations of all the lamellae in the system and by solving the complete set of Young-Laplace and diffusion equations. An hourglass approximates the shape of the pores, and the pore walls are considered to be highly water wet. A singularity arises in the system of differential algebraic equations due to the curvature of the pore walls. This singularity is a signal that the system must undergo oscillations or sudden lamellar rearrangements before the diffusion process can continue. Newton-Raphson iteration is used along with Keller`s method of arc-length continuation and a new jump resolution technique to locate and resolve bifurcations in the system of coupled lamellae. Gas bubbles in pore throats are regions of encapsulated pressure. As gas is released from these bubbles during diffusion, the pressure of the bubbles in the pore bodies increases. When the pressure increase is scaled by the characteristic Young-Laplace pressure, the equilibrium time for the diffusion process is scaled by the ratio of the square of the characteristic length to the gas diffusivity and two dimensionless groups. One describes the ease with which gas can diffuse through a lamella, the second represents the amount of gas encapsulated within the pore throats initially. Given this scaling, the resulting plots of pressure versus time and normalized lamellae positions versus time are universal for all system sizes and characteristics. This is true as long as the initial lamella distribution is the same in each case.
Transport and MHD simulations of intrinsic and pellet induced ELMs
NASA Astrophysics Data System (ADS)
Kim, Ki Min; Na, Yong-Su; Yi, Sumin; Kim, Hyunseok; Kim, Jin Yong
2010-11-01
Verification of ELM mechanism and demonstration of ELM control are important issues in current fusion researches targeting ITER and DEMO. This work investigates the physics and operational characteristics of intrinsic and pellet induced ELMs throughout transport simulations using 1.5 D transport codes (C1.5/ASTRA) and MHD simulations using M3D code. Transport simulations are focused on prediction of the global parameters such as ELM energy loss in the type-I ELMy H-mode discharges with and without pellet pace making to examine an applicability of pellet injection for ELM mitigation in KSTAR and ITER. On the other hand, MHD simulations are conducted to explore the physics of intrinsic and pellet induced ELMs by applying the artificial free energy sources of velocity stream and density perturbations on the marginally stable equilibrium, respectively. Similarities and differences of triggering phenomena between intrinsic and pellet induced ELMs are discussed from the MHD approach.
Po, Hoi Chun; Zhou, Qi
2015-01-01
Bosons have a natural instinct to condense at zero temperature. It is a long-standing challenge to create a high-dimensional quantum liquid that does not exhibit long-range order at the ground state, as either extreme experimental parameters or sophisticated designs of microscopic Hamiltonians are required for suppressing the condensation. Here we show that synthetic gauge fields for ultracold atoms, using either the Raman scheme or shaken lattices, provide physicists a simple and practical scheme to produce a two-dimensional algebraic quantum liquid at the ground state. This quantum liquid arises at a critical Lifshitz point, where a two-dimensional quartic dispersion emerges in the momentum space, and many fundamental properties of two-dimensional bosons are changed in its proximity. Such an ideal simulator of the quantum Lifshitz model allows experimentalists to directly visualize and explore the deconfinement transition of topological excitations, an intriguing phenomenon that is difficult to access in other systems. PMID:26268154
Po, Hoi Chun; Zhou, Qi
2015-08-13
Bosons have a natural instinct to condense at zero temperature. It is a long-standing challenge to create a high-dimensional quantum liquid that does not exhibit long-range order at the ground state, as either extreme experimental parameters or sophisticated designs of microscopic Hamiltonians are required for suppressing the condensation. Here we show that synthetic gauge fields for ultracold atoms, using either the Raman scheme or shaken lattices, provide physicists a simple and practical scheme to produce a two-dimensional algebraic quantum liquid at the ground state. This quantum liquid arises at a critical Lifshitz point, where a two-dimensional quartic dispersion emerges in the momentum space, and many fundamental properties of two-dimensional bosons are changed in its proximity. Such an ideal simulator of the quantum Lifshitz model allows experimentalists to directly visualize and explore the deconfinement transition of topological excitations, an intriguing phenomenon that is difficult to access in other systems.
Simulation of Viscous Steady Flow Past An Arbitrary Two-Dimensional Body.
1980-02-01
34 J. Computational Phys., Vol. 15 (1974) p. 299. 7. J. F. Thompson, F. C. Thames and C. W. Mastin, "TOMCAT - A Code for Numerical Generation of Boundary Fitted Curvilinear Coordinate Systems on Fields Containing Any Number of Arbitrary Two - Dimensional Bodies ," J
Classical MHD shocks: theory and numerical simulation
Pogorelov, Nikolai V.
2005-08-01
Recent results are surveyed in the investigation of the behavior of shocks in ideal magnetohydrodynamics (MHD) and corresponding structures in dissipative/resistive plasma flows. In contrast to evolutionary shocks, a solution of the problem of the nonevolutionary shock interaction with small perturbations is either nonunique or does not exist. The peculiarity of non-ideal MHD is in that some nonevolutionary shocks have dissipative structures. Since this structure is always non-plane, it can reveal itself in problems where transverse perturbations do not exist due to symmetries restrictions. We discuss the numerical behavior of nonevolutionary shocks and argue that they necessarily disappear once the problem is solved in a genuinely three-dimensional statement.
MHD simulations on an unstructured mesh
Strauss, H.R.; Park, W.; Belova, E.; Fu, G.Y.; Longcope, D.W.; Sugiyama, L.E.
1998-12-31
Two reasons for using an unstructured computational mesh are adaptivity, and alignment with arbitrarily shaped boundaries. Two codes which use finite element discretization on an unstructured mesh are described. FEM3D solves 2D and 3D RMHD using an adaptive grid. MH3D++, which incorporates methods of FEM3D into the MH3D generalized MHD code, can be used with shaped boundaries, which might be 3D.
Advances in Simulation of Wave Interaction with Extended MHD Phenomena
Batchelor, Donald B; Abla, Gheni; D'Azevedo, Ed F; Bateman, Glenn; Bernholdt, David E; Berry, Lee A; Bonoli, P.; Bramley, R; Breslau, Joshua; Chance, M.; Chen, J.; Choi, M.; Elwasif, Wael R; Foley, S.; Fu, GuoYong; Harvey, R. W.; Jaeger, Erwin Frederick; Jardin, S. C.; Jenkins, T; Keyes, David E; Klasky, Scott A; Kruger, Scott; Ku, Long-Poe; Lynch, Vickie E; McCune, Douglas; Ramos, J.; Schissel, D.; Schnack,; Wright, J.
2009-01-01
The Integrated Plasma Simulator (IPS) provides a framework within which some of the most advanced, massively-parallel fusion modeling codes can be interoperated to provide a detailed picture of the multi-physics processes involved in fusion experiments. The presentation will cover four topics: 1) recent improvements to the IPS, 2) application of the IPS for very high resolution simulations of ITER scenarios, 3) studies of resistive and ideal MHD stability in tokamk discharges using IPS facilities, and 4) the application of RF power in the electron cyclotron range of frequencies to control slowly growing MHD modes in tokamaks and initial evaluations of optimized location for RF power deposition.
Advances in Simulation of Wave Interactions with Extended MHD Phenomena
Batchelor, Donald B; D'Azevedo, Eduardo; Bateman, Glenn; Bernholdt, David E; Bonoli, P.; Bramley, Randall B; Breslau, Joshua; Elwasif, Wael R; Foley, S.; Jaeger, Erwin Frederick; Jardin, S. C.; Klasky, Scott A; Kruger, Scott E; Ku, Long-Poe; McCune, Douglas; Ramos, J.; Schissel, David P; Schnack, Dalton D
2009-01-01
The Integrated Plasma Simulator (IPS) provides a framework within which some of the most advanced, massively-parallel fusion modeling codes can be interoperated to provide a detailed picture of the multi-physics processes involved in fusion experiments. The presentation will cover four topics: (1) recent improvements to the IPS, (2) application of the IPS for very high resolution simulations of ITER scenarios, (3) studies of resistive and ideal MHD stability in tokamak discharges using IPS facilities, and (4) the application of RF power in the electron cyclotron range of frequencies to control slowly growing MHD modes in tokamaks and initial evaluations of optimized location for RF power deposition.
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.
NASA Astrophysics Data System (ADS)
Jo, Ju-Yeon; Ito, Hironobu; Tanimura, Yoshitaka
2016-12-01
Frequency-domain two-dimensional (2D) Raman signals, which are equivalent to coherent two-dimensional Raman scattering (COTRAS) signals, for liquid water and carbon tetrachloride were calculated using an equilibrium-nonequilibrium hybrid molecular dynamics (MD) simulation algorithm. An appropriate representation of the 2D Raman spectrum obtained from MD simulations provides an easy-to-understand depiction of structural and dynamical properties. We elucidate mechanisms governing the 2D signal profiles involving anharmonic mode-mode coupling and the nonlinearities of the polarizability for the intermolecular and intramolecular vibrational modes. The predicted signal profiles and intensities can be utilized to analyze recently developed single-beam 2D spectra, whose signals are generated from a coherently controlled pulse, allowing the single-beam measurement to be carried out more efficiently. Moreover, the MD simulation results allow us to visualize the molecular structure and dynamics by comparing the accurately calculated spectrum with experimental result.
Kato, Takaumi; Sone, Shusaku; Funamoto, Kenichi; Hayase, Toshiyuki; Kadowaki, Hiroko; Taniguchi, Nobuyuki
2016-09-01
Two-dimensional ultrasonic-measurement-integrated (2D-UMI) simulation correctly reproduces hemodynamics even with an inexact inflow velocity distribution. This study aimed to investigate which is superior, a two-dimensional ordinary (2D-O) simulation with an accurate inflow velocity distribution or a 2D-UMI simulation with an inaccurate one. 2D-O and 2D-UMI simulations were performed for blood flow in a carotid artery with four upstream velocity boundary conditions: a velocity profile with backprojected measured Doppler velocities (condition A), and velocity profiles with a measured Doppler velocity distribution, a parabolic one, and a uniform one, magnitude being obtained by inflow velocity estimation (conditions B, C, and D, respectively). The error of Doppler velocity against the measurement data was sensitive to the inflow velocity distribution in the 2D-O simulation, but not in the 2D-UMI simulation with the inflow velocity estimation. Among the results in conditions B, C, and D, the error in the worst 2D-UMI simulation with condition D was 31 % of that in the best 2D-O simulation with condition B, implying the superiority of the 2D-UMI simulation with an inaccurate inflow velocity distribution over the 2D-O simulation with an exact one. Condition A resulted in a larger error than the other conditions in both the 2D-O and 2D-UMI simulations.
NASA Astrophysics Data System (ADS)
Yang, H.; Bhattacharjee, A.; Forbes, T. G.
2008-12-01
It has long been suggested that eruptive phenomena such as coronal mass ejections, prominence eruptions, and large flares might be caused by a loss of equilibrium in a coronal flux rope (Van Tend and Kuperus, 1978). Forbes et al. (1994) developed an analytical two-dimensional model in which eruptions occur due to a catastrophic loss of equilibrium and relaxation to a lower-energy state containing a thin current sheet. Magnetic reconnection then intervenes dynamically, leading to the release of magnetic energy and expulsion of a plasmoid. We have carried out high-Lundquist-number simulations to test the loss-of equilibrium mechanism, and demonstrated that it does indeed occur in the quasi-ideal limit. We have studied the subsequent dynamical evolution of the system in resistive and Hall MHD models for single as well as multiple arcades. The typical parallel electric fields are super-Dreicer, which makes it necessary to include collisionless effects via a generalized Ohm's law. It is shown that the nature of the local dissipation mechanism has a significant effect on the global geometry and dynamics of the magnetic configuration. The presence of Hall currents is shown to alter the length of the current sheet and the jets emerging from the reconnection site, directed towards the chromosphere. Furthermore, Hall MHD effects break certain symmetries of resistive MHD dynamics, and we explore their observational consequences.
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.
Simulation and study of Fresnel diffraction for arbitrary two-dimensional apertures
Dauger, D.E.
1996-11-01
A stable, efficient algorithm to calculate numerically a Fresnel diffraction image, given any two-dimensional aperture or obstacle, is introduced. The algorithm predicts both the intensity and relative phase of the image. An alternate faster algorithm is presented for a limited class of apertures. Also examined are images formed from a variety of aperture shapes. Using this computational technique, plots on the complex plane are shown to give insight into Fresnel diffraction. With additional modifications to accept parameters from an experimental apparatus, the algorithms model Fresnel diffraction for laboratory situations. In addition, the algorithms are suitable for numerical implementation on personal computers. {copyright} {ital 1996 American Institute of Physics.}
NASA Astrophysics Data System (ADS)
Chao, D. F. K.
1983-11-01
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.
The role of condensation and heat conduction in the formation of prominences - An MHD simulation
NASA Technical Reports Server (NTRS)
Wu, S. T.; Bao, J. J.; An, C. H.; Tandberg-Hanssen, E.
1990-01-01
The effects of condensation and thermal conduction on the formation of Kippenhahn-Schlueter (K-S) type prominences in quiet regions (QP) due to symmetric mass injection are investigated. To implement this investigation a self-consistent, two-dimensional, nonplanar, time-dependent MHD simulation model is developed. In the model, various values of the injection velocity, density, and magnetic field strength are used to determine the most favorable conditions for the QP formation. Based on these simulation results, it is found that the formation of a K-S type field configuration should be considered as a dynamic process which needs both condensation amd mass injection to supply enough mass to maintain such a configuration to complete the quiescent prominence formation process.
Numerical simulations of blast wave characteristics with a two-dimensional axisymmetric room model
NASA Astrophysics Data System (ADS)
Sugiyama, Y.; Homae, T.; Wakabayashi, K.; Matsumura, T.; Nakayama, Y.
2017-01-01
This paper numerically visualizes explosion phenomena in order to discuss blast wave characteristics with a two-dimensional axisymmetric room model. After the shock wave exits via an opening, the blast wave propagates into open space. In the present study, a parametric study was conducted to determine the blast wave characteristics from the room exit by changing the room shape and the mass of the high explosive. Our results show that the blast wave characteristics can be correctly estimated using a scaling factor proposed in the present paper that includes the above parameters. We conducted normalization of the peak overpressure curve using the shock overpressure at the exit and the length scale of the room volume. In the case where the scaling factor has the same value, the normalized peak overpressure curve does not depend on the calculation conditions, and the scaling factor describes the blast wave characteristics emerging from the current room model.
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.
Guo, Xun; Zhang, Xitong; Zhao, Shijun; Huang, Qing; Xue, Jianming
2016-01-07
Density functional theory (DFT) calculation is employed to study the adsorption properties of Pb and Cu on recently synthesized two-dimensional materials MXenes, including Ti3C2, V2C1 and Ti2C1. The influence of surface decoration with functional groups such as H, OH and F have also been investigated. Most of these studied MXenes exhibit excellent capability to adsorb Pb and Cu, especially the adsorption capacity of Pb on Ti2C1 is as high as 2560 mg g(-1). Both the binding energies and the adsorption capacities are sensitive to the functional groups attached to the MXenes' surface. Ab initio molecular dynamics (ab-init MD) simulation confirms that Ti2C1 remains stable at room temperature after adsorbing Pb atoms. Our calculations imply that these newly emerging two-dimensional MXenes are promising candidates for wastewater treatment and ion separation.
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)
MHD simulations of three-dimensional resistive reconnection in a cylindrical plasma column
NASA Astrophysics Data System (ADS)
Striani, E.; Mignone, A.; Vaidya, B.; Bodo, G.; Ferrari, A.
2016-11-01
Magnetic reconnection is a plasma phenomenon where a topological rearrangement of magnetic field lines with opposite polarity results in dissipation of magnetic energy into heat, kinetic energy and particle acceleration. Such a phenomenon is considered as an efficient mechanism for energy release in laboratory and astrophysical plasmas. An important question is how to make the process fast enough to account for observed explosive energy releases. The classical model for steady state magnetic reconnection predicts reconnection times scaling as S1/2 (where S is the Lundquist number) and yields time-scales several order of magnitude larger than the observed ones. Earlier two-dimensional MHD simulations showed that for large Lundquist number the reconnection time becomes independent of S (`fast reconnection' regime) due to the presence of the secondary tearing instability that takes place for S ≳ 1 × 104. We report on our 3D MHD simulations of magnetic reconnection in a magnetically confined cylindrical plasma column under either a pressure balanced or a force-free equilibrium and compare the results with 2D simulations of a circular current sheet. We find that the 3D instabilities acting on these configurations result in a fragmentation of the initial current sheet in small filaments, leading to enhanced dissipation rate that becomes independent of the Lundquist number already at S ≃ 1 × 103.
NASA Astrophysics Data System (ADS)
Wen, Bing-Hai; Liu, Hai-Yan; Zhang, Chao-Ying; Wang, Qiang
2009-10-01
Boundary conditions (BCs) play an essential role in lattice Boltzmann (LB) simulations. This paper investigates several most commonly applied BCs by evaluating the relative L2-norm errors of the LB simulations for two-dimensional (2-D) Poiseuille flow. It is found that the relative L2-norm error resulting from FHML's BC is smaller than that from other BCs as a whole. Then, based on the FHML's BC, it formulates an LB model for simulating fluid flows in 2-D channel with complex geometries. Afterwards, the flows between two inclined plates, in a pulmonary blood vessel and in a blood vessel with local expansion region, are simulated. The numerical results are in good agreement with the analytical predictions and clearly show that the model is effective. It is expected that the model can be extended to simulate some real biologic flows, such as blood flows in arteries, vessels with stenosises, aneurysms and bifurcations, etc.
Trobo, Marta L; Albano, Ezequiel V; Binder, Kurt
2016-05-01
As a simplified model of a liquid nanostripe adsorbed on a chemically structured substrate surface, a two-dimensional Ising system with two boundaries at which surface fields act is studied. At the upper boundary, the surface field is uniformly negative, while at the lower boundary (a distance L apart), the surface field is negative only outside a range of extension b, where a positive surface stabilizes a droplet of the phase with positive magnetization for temperatures T exceeding the critical temperature T_{w} of the wetting transition of this model. We investigate the local order parameter profiles across the droplet, both in the directions parallel and perpendicular to the substrate, varying both b and T. Also, precursor effects to droplet formation as T approaches T_{w} from below are studied. In accord with theoretical predictions, for T>T_{w} the droplet is found to have the shape of a semiellipse, where the width (distance of the interface from the substrate) scale is proportional to b (b^{1/2}). So, the area of the droplet is proportional to b^{3/2}, and the temperature dependence of the corresponding prefactor, which also involves the interfacial stiffness, is studied.
Monte Carlo simulation of diffusion and reaction in two-dimensional cell structures.
Riley, M R; Buettner, H M; Muzzio, F J; Reyes, S C
1995-01-01
Diffusion and reaction processes control the dynamics of many different biological systems. For example, tissue respiration can be limited by the delivery of oxygen to the cells and to the mitochondria. In this case, oxygen is small and travels quickly compared with the mitochondria, which can be considered as immobile reactive traps in the cell cytoplasm. A Monte Carlo theoretical investigation quantifying the interplay of diffusion, reaction, and structure on the reaction rate constant is reported here for diffusible particles in two-dimensional, reactive traps. The placement of traps in overlapping, nonoverlapping, and clustered spatial arrangements can have a large effect on the rate constant when the process is diffusion limited. However, under reaction-limited conditions the structure has little effect on the rate constant. For the same trap fractions and reactivities, nonoverlapping traps have the highest rate constants, overlapping traps yield intermediate rate constants, and clustered traps have the lowest rate constants. An increase in the particle diffusivity in the traps can increase the rate constant by reducing the time required by the particles to reach reactive sites. Various diffusive, reactive, and structural conditions are evaluated here, exemplifying the versatility of the Monte Carlo technique. Images FIGURE 3 PMID:7612815
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.
Domel, N.D.; Thompson, D.S. )
1991-01-01
The effect of shock impingement on the mixing and combustion of a reacting shear-layer is numerically simulated. Hydrogen fuel is injected at sonic velocity behind a backward facing step in a direction parallel to a supersonic freestream vitiated with H{sub 2}O. The two-dimensional Navier-Stokes equations are solved and explicitly coupled to a chemistry package employing a global, two-step combustion model. The results show that shock impingement enhances the mixing and combustion. 17 refs.
NASA Technical Reports Server (NTRS)
Tsang, L.; Lou, S. H.; Chan, C. H.
1991-01-01
The extended boundary condition method is applied to Monte Carlo simulations of two-dimensional random rough surface scattering. The numerical results are compared with one-dimensional random rough surfaces obtained from the finite-element method. It is found that the mean scattered intensity from two-dimensional rough surfaces differs from that of one dimension for rough surfaces with large slopes.
Neural field simulator: two-dimensional spatio-temporal dynamics involving finite transmission speed
Nichols, Eric J.; Hutt, Axel
2015-01-01
Neural Field models (NFM) play an important role in the understanding of neural population dynamics on a mesoscopic spatial and temporal scale. Their numerical simulation is an essential element in the analysis of their spatio-temporal dynamics. The simulation tool described in this work considers scalar spatially homogeneous neural fields taking into account a finite axonal transmission speed and synaptic temporal derivatives of first and second order. A text-based interface offers complete control of field parameters and several approaches are used to accelerate simulations. A graphical output utilizes video hardware acceleration to display running output with reduced computational hindrance compared to simulators that are exclusively software-based. Diverse applications of the tool demonstrate breather oscillations, static and dynamic Turing patterns and activity spreading with finite propagation speed. The simulator is open source to allow tailoring of code and this is presented with an extension use case. PMID:26539105
Two Dimensional Numerical Simulator for Modeling NDC Region in SNDC Devices
NASA Astrophysics Data System (ADS)
Sinha, Dheeraj Kumar; Chatterjee, Amitabh; Trivedi, Gaurav
2016-10-01
This paper deals about making a numerical simulator for observing the self-organization phenomenon like current filament formation in the negative differential conductivity (NDC) region of operation in a device using MATLAB environment. Emphasis is laid on choosing the appropriate boundary conditions in simulator to observe the NDC part of the device Current-Voltage (I — V) characteristics along with the appropriate isothermal physical models are included for mobility and the recombination-generation. The simulator used in this paper is designed to observe NDC region in S-shaped NDC (SNDC) devices like BJT and similar conditions can be used to observe the field domains in the N-shaped NDC (NNDC) devices with appropriate changes. Dirichlet and Neumann boundary conditions are applied to BJT and I — V characteristics of the developed device simulator are compared with the commercial available TCAD device simulator (i.e., Sentaurus).
NASA Technical Reports Server (NTRS)
Lin, Zhenyi; Li, Wei; Gatebe, Charles; Poudyal, Rajesh; Stamnes, Knut
2016-01-01
An optimized discrete-ordinate radiative transfer model (DISORT3) with a pseudo-two-dimensional bidirectional reflectance distribution function (BRDF) is used to simulate and validate ocean glint reflectances at an infrared wavelength (1036 nm) by matching model results with a complete set of BRDF measurements obtained from the NASA cloud absorption radiometer (CAR) deployed on an aircraft. The surface roughness is then obtained through a retrieval algorithm and is used to extend the simulation into the visible spectral range where diffuse reflectance becomes important. In general, the simulated reflectances and surface roughness information are in good agreement with the measurements, and the diffuse reflectance in the visible, ignored in current glint algorithms, is shown to be important. The successful implementation of this new treatment of ocean glint reflectance and surface roughness in DISORT3 will help improve glint correction algorithms in current and future ocean color remote sensing applications.
Dynamical simulations of fractional giant Shapiro steps in two-dimensional Josephson arrays
Free, J.U.; Benz, S.P.; Rzchowski, M.S.; Tinkham, M.; Lobb, C.J. Division of Applied Sciences, Harvard University, Cambridge, Massachusetts 02138 ); Octavio, M. )
1990-04-01
We have performed computer simulations of arrays of resistively shunted Josephson junctions in the presence of commensurate magnetic fields and alternating and direct currents. We have found {ital fractional} giant Shapiro steps in the simulated current-voltage characteristics in agreement with recent experimental measurements. The detailed motion of the magnetic-field-induced vortices is shown to be in agreement with a previously proposed phenomenological model of Benz {ital et} {ital al}. (Phys. Rev. Lett. 64, 693 (1990)).
High-beta extended MHD simulations of stellarators
NASA Astrophysics Data System (ADS)
Bechtel, T. A.; Hegna, C. C.; Sovinec, C. R.; Roberds, N. A.
2016-10-01
The high beta properties of stellarator plasmas are studied using the nonlinear, extended MHD code NIMROD. In this work, we describe recent developments to the semi-implicit operator which allow the code to model 3D plasma evolution with better accuracy and efficiency. The configurations under investigation are an l=2, M=5 torsatron with geometry modeled after the Compact Toroidal Hybrid (CTH) experiment and an l=2, M=10 torsatron capable of having vacuum rotational transform profiles near unity. High-beta plasmas are created using a volumetric heating source and temperature dependent anisotropic thermal conduction and resistivity. To reduce computation expenses, simulations are initialized from stellarator symmetric pseudo-equilibria by turning on symmetry breaking modes at finite beta. The onset of MHD instabilities and nonlinear consequences are monitored as a function of beta as well as the fragility of the magnetic surfaces. Research supported by US DOE under Grant No. DE-FG02-99ER54546.
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.
Cai, Libing; Wang, Jianguo; Zhu, Xiangqin; Wang, Yue; Zhang, Dianhui
2015-01-15
Based on the secondary electron emission avalanche (SEEA) model, the SEEA discharge on the vacuum insulator surface is simulated by using a 2D PIC-MCC code developed by ourselves. The evolutions of the number of discharge electrons, insulator surface charge, current, and 2D particle distribution are obtained. The effects of the strength of the applied electric field, secondary electron yield coefficient, rise time of the pulse, length of the insulator on the discharge are investigated. The results show that the number of the SEEA electrons presents a quadratic dependence upon the applied field strength. The SEEA current, which is on the order of Ampere, is directly proportional to the field strength and secondary electron yield coefficient. Finally, the electron-stimulated outgassing is included in the simulation code, and a three-phase discharge curve is presented by the simulation, which agrees with the experimental data.
NASA Astrophysics Data System (ADS)
Cai, Libing; Wang, Jianguo; Zhu, Xiangqin; Wang, Yue; Zhang, Dianhui
2015-01-01
Based on the secondary electron emission avalanche (SEEA) model, the SEEA discharge on the vacuum insulator surface is simulated by using a 2D PIC-MCC code developed by ourselves. The evolutions of the number of discharge electrons, insulator surface charge, current, and 2D particle distribution are obtained. The effects of the strength of the applied electric field, secondary electron yield coefficient, rise time of the pulse, length of the insulator on the discharge are investigated. The results show that the number of the SEEA electrons presents a quadratic dependence upon the applied field strength. The SEEA current, which is on the order of Ampere, is directly proportional to the field strength and secondary electron yield coefficient. Finally, the electron-stimulated outgassing is included in the simulation code, and a three-phase discharge curve is presented by the simulation, which agrees with the experimental data.
Stable low-resolution simulations of two-dimensional vesicle suspensions
NASA Astrophysics Data System (ADS)
Kabacaoglu, Gokberk; Quaife, Bryan; Biros, George
2016-11-01
Vesicles, which resist bending and are locally inextensible, serve as experimental and numerical proxies for red blood cells. Vesicle flows, which are governed by hydrodynamic and elastic forces, refer to flow of vesicles that are filled with and suspended in a Stokesian fluid. In this work we present algorithms for stable and accurate low-resolution simulations of the vesicle flows in two-dimensions. We use an integral equation formulation of the Stokes equation coupled to the interface mass continuity and force balance. The problem poses numerical difficulties such as long-range hydrodynamic interactions, strong nonlinearities and stiff governing equations. These difficulties make simulations with long time horizons challenging, especially at low resolutions. We develop algorithms to control aliasing errors, correct errors in vesicle's area and arc-length, and avoid collision of vesicles. Additionally, we discuss several error measures to study the accuracy of the simulations. Then we closely look at how accurate the low-resolution simulations can capture true physics of the vesicle flows.
Simulation of Two Dimensional Electrophoresis and Tandem Mass Spectrometry for Teaching Proteomics
ERIC Educational Resources Information Center
Fisher, Amanda; Sekera, Emily; Payne, Jill; Craig, Paul
2012-01-01
In proteomics, complex mixtures of proteins are separated (usually by chromatography or electrophoresis) and identified by mass spectrometry. We have created 2DE Tandem MS, a computer program designed for use in the biochemistry, proteomics, or bioinformatics classroom. It contains two simulations--2D electrophoresis and tandem mass spectrometry.…
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 ρR , neutron yield, Ti, neutron rate, and x-ray images for the mid-adiabat (α ~ 4 ) implosions. For low-adiabat (α ~ 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.
Spectral Methods in General Relativistic MHD Simulations
NASA Astrophysics Data System (ADS)
Garrison, David
2012-03-01
In this talk I discuss the use of spectral methods in improving the accuracy of a General Relativistic Magnetohydrodynamic (GRMHD) computer code. I introduce SpecCosmo, a GRMHD code developed as a Cactus arrangement at UHCL, and show simulation results using both Fourier spectral methods and finite differencing. This work demonstrates the use of spectral methods with the FFTW 3.3 Fast Fourier Transform package integrated with the Cactus Framework to perform spectral differencing using MPI.
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.
Ohira, Yutaka; Takahara, Fumio; Reville, Brian; Kirk, John G.
2009-06-10
In supernova remnants, the nonlinear amplification of magnetic fields upstream of collisionless shocks is essential for the acceleration of cosmic rays to the energy of the 'knee' at 10{sup 15.5} eV. A nonresonant instability driven by the cosmic ray current is thought to be responsible for this effect. We perform two-dimensional, particle-in-cell simulations of this instability. We observe an initial growth of circularly polarized nonpropagating magnetic waves as predicted in linear theory. It is demonstrated that in some cases the magnetic energy density in the growing waves can grow to at least 10 times its initial value. We find no evidence of competing modes, nor of significant modification by thermal effects. At late times, we observe saturation of the instability in the simulation, but the mechanism responsible is an artifact of the periodic boundary conditions and has no counterpart in the supernova-shock scenario.
Horowitz, A; Sheinman, I; Lanir, Y; Perl, M; Sideman, S
1988-02-01
A two-dimensional incompressible plane-stress finite element is formulated for the simulation of the passive-state mechanics of thin myocardial strips. The formulation employs a total Lagrangian and materially nonlinear approach, being based on a recently proposed structural material law, which is derived from the histological composition of the tissue. The ensuing finite element allows to demonstrate the mechanical properties of a single myocardial layer containing uniformly directed fibers by simulating various loading cases such as tension, compression and shear. The results of these cases show that the fiber direction is considerably stiffer than the cross-fiber direction, that there is significant coupling between these two directions, and that the shear stiffness of the tissue is lower than its tensile and compressive stiffness.
A zero-equation turbulence model for two-dimensional hybrid Hall thruster simulations
Cappelli, Mark A. Young, Christopher V.; Cha, Eunsun; Fernandez, Eduardo
2015-11-15
We present a model for electron transport across the magnetic field of a Hall thruster and integrate this model into 2-D hybrid particle-in-cell simulations. The model is based on a simple scaling of the turbulent electron energy dissipation rate and the assumption that this dissipation results in Ohmic heating. Implementing the model into 2-D hybrid simulations is straightforward and leverages the existing framework for solving the electron fluid equations. The model recovers the axial variation in the mobility seen in experiments, predicting the generation of a transport barrier which anchors the region of plasma acceleration. The predicted xenon neutral and ion velocities are found to be in good agreement with laser-induced fluorescence measurements.
Two-Dimensional Distribution of Volatiles in the Lunar Regolith from Space Weathering Simulations
NASA Technical Reports Server (NTRS)
Hurley, Dana M.; Lawrence, David J.; Bussey, D. Benjamin J.; Vondrak, Richard R.; Elphic, Richard C.; Gladstone, G. Randall
2012-01-01
We present simulations of space weathering effects on ice deposits in regions of permanent shadow on the Moon. These Monte Carlo simulations follow the effects of space weathering processes on the distribution of the volatiles over time. The model output constrains the coherence of volatile deposits with depth, lateral separation, and time. The results suggest that ice sheets become broken and buried with time. As impacts begin to puncture an initially coherent surficial ice sheet, small areas with a deficit of ice compared to surrounding areas are formed first. As time progresses, holes become prevalent and the anomalous regions are local enhancements of ice concentration in a volume. The 3-D distribution is also heterogeneous because the ice is buried to varying depths in different locations. Analysis of the coherence of ice on 10 cm scales predicts that putative ice sheets in anomalous radar craters are < 100 Myr old. Surface frost becomes homogenized within 20 Myr. The simulations show the data from the LCROSS impact and surrounding region are consistent with the ice deposit in Cabeus being >1000 Myr old. For future in situ analysis of cold trap volatiles, a horizontal range of 10 m is sufficient to acquire surface-based measurements of heterogeneously distributed ice. These results also support previous analyses that Mercury's cold traps are young.
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.
Feng, Yuan; Huang, Jing; Kim, Seongheun; Shim, Ji Hyun; MacKerell, Alexander D; Ge, Nien-Hui
2016-06-23
We have studied the structure of (Ala)5, a model unfolded peptide, using a combination of 2D IR spectroscopy and molecular dynamics (MD) simulation. Two different isotopomers, each bis-labeled with (13)C═O and (13)C═(18)O, were strategically designed to shift individual site frequencies and uncouple neighboring amide-I' modes. 2D IR spectra taken under the double-crossed ⟨π/4, -π/4, Y, Z⟩ polarization show that the labeled four-oscillator systems can be approximated by three two-oscillator systems. By utilizing the different polarization dependence of diagonal and cross peaks, we extracted the coupling constants and angles between three pairs of amide-I' transition dipoles through spectral fitting. These parameters were related to the peptide backbone dihedral angles through DFT calculated maps. The derived dihedral angles are all located in the polyproline-II (ppII) region of the Ramachandran plot. These results were compared to the conformations sampled by Hamiltonian replica-exchange MD simulations with three different CHARMM force fields. The C36 force field predicted that ppII is the dominant conformation, consistent with the experimental findings, whereas C22/CMAP predicted similar population for α+, β, and ppII, and the polarizable Drude-2013 predicted dominating β structure. Spectral simulation based on MD representative conformations and structure ensembles demonstrated the need to include multiple 2D spectral features, especially the cross-peak intensity ratio and shape, in structure determination. Using 2D reference spectra defined by the C36 structure ensemble, the best spectral simulation is achieved with nearly 100% ppII population, although the agreement with the experimental cross-peak intensity ratio is still insufficient. The dependence of population determination on the choice of reference structures/spectra and the current limitations on theoretical modeling relating peptide structures to spectral parameters are discussed. Compared
Cohen, B I; Divol, L; Langdon, A B; Williams, E A
2005-10-17
Two-dimensional simulations with the BZOHAR [B.I. Cohen, B.F. Lasinski, A.B. Langdon, and E.A. Williams, Phys. Plasmas 4, 956 (1997)] hybrid code (kinetic particle ions and Boltzmann fluid electrons) have been used to investigate the saturation of stimulated Brillouin backscatter (SBBS) instability including the effects of ion-ion collisions and inhomogeneity. Ion-ion collisions tend to increase ion-wave dissipation, which decreases the gain exponent for stimulated Brillouin backscattering; and the peak Brillouin backscatter reflectivities tend to decrease with increasing collisionality in the simulations. Two types of Langevin-operator, ion-ion collision models were implemented in the simulations. In both models used the collisions are functions of the local ion temperature and density, but the collisions have no velocity dependence in the first model. In the second model, the collisions are also functions of the energy of the ion that is being scattered so as to represent a Fokker-Planck collision operator. Collisions decorrelate the ions from the acoustic waves in SBS, which disrupts ion trapping in the acoustic wave. Nevertheless, ion trapping leading to a hot ion tail and two-dimensional physics that allows the SBS ion waves to nonlinearly scatter remain robust saturation mechanisms for SBBS in a high-gain limit over a range of ion collisionality. SBS backscatter in the presence of a spatially nonuniform plasma flow is also investigated. Simulations show that depending on the sign of the spatial gradient of the flow relative to the backscatter, ion trapping effects that produce a nonlinear frequency shift can enhance (auto-resonance) or decrease (anti-auto-resonance) reflectivities in agreement with theoretical arguments.
Lin, Yi-Chung; Haftka, Raphael T; Queipo, Nestor V; Fregly, Benjamin J
2009-04-01
Computational speed is a major limiting factor for performing design sensitivity and optimization studies of total knee replacements. Much of this limitation arises from extensive geometry calculations required by contact analyses. This study presents a novel surrogate contact modeling approach to address this limitation. The approach involves fitting contact forces from a computationally expensive contact model (e.g., a finite element model) as a function of the relative pose between the contacting bodies. Because contact forces are much more sensitive to displacements in some directions than others, standard surrogate sampling and modeling techniques do not work well, necessitating the development of special techniques for contact problems. We present a computational evaluation and practical application of the approach using dynamic wear simulation of a total knee replacement constrained to planar motion in a Stanmore machine. The sample points needed for surrogate model fitting were generated by an elastic foundation (EF) contact model. For the computational evaluation, we performed nine different dynamic wear simulations with both the surrogate contact model and the EF contact model. In all cases, the surrogate contact model accurately reproduced the contact force, motion, and wear volume results from the EF model, with computation time being reduced from 13 min to 13 s. For the practical application, we performed a series of Monte Carlo analyses to determine the sensitivity of predicted wear volume to Stanmore machine setup issues. Wear volume was highly sensitive to small variations in motion and load inputs, especially femoral flexion angle, but not to small variations in component placements. Computational speed was reduced from an estimated 230 h to 4 h per analysis. Surrogate contact modeling can significantly improve the computational speed of dynamic contact and wear simulations of total knee replacements and is appropriate for use in design sensitivity
Two-dimensional streamflow simulations of the Jordan River, Midvale and West Jordan, Utah
Kenney, Terry A.; Freeman, Michael L.
2011-01-01
The Jordan River in Midvale and West Jordan, Utah, flows adjacent to two U.S. Environmental Protection Agency Superfund sites: Midvale Slag and Sharon Steel. At both sites, geotechnical caps extend to the east bank of the river. The final remediation tasks for these sites included the replacement of a historic sheet-pile dam and the stabilization of the river banks adjacent to the Superfund sites. To assist with these tasks, two hydraulic modeling codes contained in the U.S. Geological Survey (USGS) Multi-Dimensional Surface-Water Modeling System (MD_SWMS), System for Transport and River Modeling (SToRM) and Flow and Sediment Transport and Morphological Evolution of Channels (FaSTMECH), were used to provide predicted water-surface elevations, velocities, and boundary shear-stress values throughout the study reach of the Jordan River. A SToRM model of a 0.7 mile subreach containing the sheet-pile dam was used to compare water-surface elevations and velocities associated with the sheet-pile dam and a proposed replacement structure. Maps showing water-surface elevation and velocity differences computed from simulations of the historic sheet-pile dam and the proposed replacement structure topographies for streamflows of 500 and 1,000 cubic feet per second (ft3/s) were created. These difference maps indicated that the velocities associated with the proposed replacement structure topographies were less than or equal to those associated with the historic sheet-pile dam. Similarly, water-surface elevations associated with the proposed replacement structure topographies were all either greater than or equal to water-surface elevations associated with the sheet-pile dam. A FaSTMECH model was developed for the 2.5-mile study reach to aid engineers in bank stabilization designs. Predicted water-surface elevations, velocities and shear-stress values were mapped on an aerial photograph of the study reach to place these parameters in a spatial context. Profile plots of predicted
Lefkoff, L.J.; Gorelick, S.M.
1987-01-01
A FORTRAN-77 computer program code that helps solve a variety of aquifer management problems involving the control of groundwater hydraulics. It is intended for use with any standard mathematical programming package that uses Mathematical Programming System input format. The computer program creates the input files to be used by the optimization program. These files contain all the hydrologic information and management objectives needed to solve the management problem. Used in conjunction with a mathematical programming code, the computer program identifies the pumping or recharge strategy that achieves a user 's management objective while maintaining groundwater hydraulic conditions within desired limits. The objective may be linear or quadratic, and may involve the minimization of pumping and recharge rates or of variable pumping costs. The problem may contain constraints on groundwater heads, gradients, and velocities for a complex, transient hydrologic system. Linear superposition of solutions to the transient, two-dimensional groundwater flow equation is used by the computer program in conjunction with the response matrix optimization method. A unit stress is applied at each decision well and transient responses at all control locations are computed using a modified version of the U.S. Geological Survey two dimensional aquifer simulation model. The program also computes discounted cost coefficients for the objective function and accounts for transient aquifer conditions. (Author 's abstract)
Cao, Duc; Moses, Gregory; Delettrez, Jacques
2015-08-15
An implicit, non-local thermal conduction algorithm based on the algorithm developed by Schurtz, Nicolai, and Busquet (SNB) [Schurtz et al., Phys. Plasmas 7, 4238 (2000)] for non-local electron transport is presented and has been implemented in the radiation-hydrodynamics code DRACO. To study the model's effect on DRACO's predictive capability, simulations of shot 60 303 from OMEGA are completed using the iSNB model, and the computed shock speed vs. time is compared to experiment. Temperature outputs from the iSNB model are compared with the non-local transport model of Goncharov et al. [Phys. Plasmas 13, 012702 (2006)]. Effects on adiabat are also examined in a polar drive surrogate simulation. Results show that the iSNB model is not only capable of flux-limitation but also preheat prediction while remaining numerically robust and sacrificing little computational speed. Additionally, the results provide strong incentive to further modify key parameters within the SNB theory, namely, the newly introduced non-local mean free path. This research was supported by the Laboratory for Laser Energetics of the University of Rochester.
Two Dimensional Wake Vortex Simulations in the Atmosphere: Preliminary Sensitivity Studies
NASA Technical Reports Server (NTRS)
Proctor, F. H.; Hinton, D. A.; Han, J.; Schowalter, D. G.; Lin, Y.-L.
1998-01-01
A numerical large-eddy simulation model is currently being used to quantify aircraft wake vortex behavior with meteorological observables. The model, having a meteorological framework, permits the interaction of wake vortices with environments characterized by crosswind shear, stratification, and humidity. The addition of grid-scale turbulence as an initial condition appeared to have little consequence. Results show that conventional nondimensionalizations work very well for vortex pairs embedded in stably stratified flows. However, this result is based on simple environments with constant Brunt-Vaisala frequency. Results presented here also show that crosswind profiles exert important and complex interactions on the trajectories of wake vortices. Nonlinear crosswind profiles tended to arrest the descent of wake vortex pairs. The member of the vortex pair with vorticity of same sign as the vertical change in the ambient along-track vorticity may be deflected upwards.
FRANC2D: A two-dimensional crack propagation simulator. Version 2.7: User's guide
NASA Technical Reports Server (NTRS)
Wawrzynek, Paul; Ingraffea, Anthony
1994-01-01
FRANC 2D (FRacture ANalysis Code, 2 Dimensions) is a menu driven, interactive finite element computer code that performs fracture mechanics analyses of 2-D structures. The code has an automatic mesh generator for triangular and quadrilateral elements. FRANC2D calculates the stress intensity factor using linear elastic fracture mechanics and evaluates crack extension using several methods that may be selected by the user. The code features a mesh refinement and adaptive mesh generation capability that is automatically developed according to the predicted crack extension direction and length. The code also has unique features that permit the analysis of layered structure with load transfer through simulated mechanical fasteners or bonded joints. The code was written for UNIX workstations with X-windows graphics and may be executed on the following computers: DEC DecStation 3000 and 5000 series, IBM RS/6000 series, Hewlitt-Packard 9000/700 series, SUN Sparc stations, and most Silicon Graphics models.
Attosecond double-ionization dynamics of aligned H2: Two-dimensional quantum simulations
NASA Astrophysics Data System (ADS)
Wang, Shang; Chen, Yanjun
2015-08-01
A fully quantum procedure, based on the numerical solution of the time-dependent Schrödinger equation (TDSE) with two spatial dimensions for every electron, is developed to study the attosecond double-ionization (DI) dynamics from aligned H2 molecules in strong laser fields. Our simulations are able to reproduce the orientation dependence of DI, as observed for N2 in experiments [D. Zeidler et al., Phys. Rev. Lett. 95, 203003 (2005)], 10.1103/PhysRevLett.95.203003. Our TDSE analyses reveal the important roles of the lateral motion of the electron and two-center interference in the orientation-dependent DI. Our results give suggestions on the ultrafast probing of the dynamics of DI from aligned molecules.
Nenov, Artur; Segarra-Martí, Javier; Giussani, Angelo; Conti, Irene; Rivalta, Ivan; Dumont, Elise; Jaiswal, Vishal K; Altavilla, Salvatore Flavio; Mukamel, Shaul; Garavelli, Marco
2015-01-01
The SOS//QM/MM [Rivalta et al., Int. J. Quant. Chem., 2014, 114, 85] method consists of an arsenal of computational tools allowing accurate simulation of one-dimensional (1D) and bi-dimensional (2D) electronic spectra of monomeric and dimeric systems with unprecedented details and accuracy. Prominent features like doubly excited local and excimer states, accessible in multi-photon processes, as well as charge-transfer states arise naturally through the fully quantum-mechanical description of the aggregates. In this contribution the SOS//QM/MM approach is extended to simulate time-resolved 2D spectra that can be used to characterize ultrafast excited state relaxation dynamics with atomistic details. We demonstrate how critical structures on the excited state potential energy surface, obtained through state-of-the-art quantum chemical computations, can be used as snapshots of the excited state relaxation dynamics to generate spectral fingerprints for different de-excitation channels. The approach is based on high-level multi-configurational wavefunction methods combined with non-linear response theory and incorporates the effects of the solvent/environment through hybrid quantum mechanics/molecular mechanics (QM/MM) techniques. Specifically, the protocol makes use of the second-order Perturbation Theory (CASPT2) on top of Complete Active Space Self Consistent Field (CASSCF) strategy to compute the high-lying excited states that can be accessed in different 2D experimental setups. As an example, the photophysics of the stacked adenine-adenine dimer in a double-stranded DNA is modeled through 2D near-ultraviolet (NUV) spectroscopy.
Relativistic MHD simulations of extragalactic jets
NASA Astrophysics Data System (ADS)
Leismann, T.; Antón, L.; Aloy, M. A.; Müller, E.; Martí, J. M.; Miralles, J. A.; Ibáñez, J. M.
2005-06-01
We have performed a comprehensive parameter study of the morphology and dynamics of axisymmetric, magnetized, relativistic jets by means of numerical simulations. The simulations have been performed with an upgraded version of the GENESIS code which is based on a second-order accurate finite volume method involving an approximate Riemann solver suitable for relativistic ideal magnetohydrodynamic flows, and a method of lines. Starting from pure hydrodynamic models we consider the effect of a magnetic field of increasing strength (up to β ≡ |b|2/2p ≈ 3.3 times the equipartition value) and different topology (purely toroidal or poloidal). We computed several series of models investigating the dependence of the dynamics on the magnetic field in jets of different beam Lorentz factor and adiabatic index. We find that the inclusion of the magnetic field leads to diverse effects which contrary to Newtonian magnetohydrodynamics models do not always scale linearly with the (relative) strength of the magnetic field. The relativistic models show, however, some clear trends. Axisymmetric jets with toroidal magnetic fields produce a cavity which consists of two parts: an inner one surrounding the beam which is compressed by magnetic forces, and an adjacent outer part which is inflated due to the action of the magnetic field. The outer border of the outer part of the cavity is given by the bow-shock where its interaction with the external medium takes place. Toroidal magnetic fields well below equipartition (β = 0.05) combined with a value of the adiabatic index of 4/3 yield extremely smooth jet cavities and stable beams. Prominent nose cones form when jets are confined by toroidal fields and carry a high Poynting flux (σ≡ |b|2/ρ>0.01 and β≥ 1). In contrast, none of our models possessing a poloidal field develops such a nose cone. The size of the nose cone is correlated with the propagation speed of the Mach disc (the smaller the speed the larger is the size). If two
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.
Two-Dimensional Optical Measurement of Waves on Liquid Lithium Jet Simulating IFMIF Target Flow
Kazuhiro Itoh; Hiroyuki Koterazawa; Taro Itoh; Yutaka Kukita; Hiroo Kondo; Nobuo Yamaoka; Hiroshi Horiike; Mizuho Ida; Hideo Nakamura; Hiroo Nakamura; Takeo Muroga
2006-07-01
Waves on a liquid-lithium jet flow, simulating a proposed high-energy beam target design, have been measured using an optical technique based on specular reflection of a single laser beam on the jet surface. The stream-wise and spanwise fluctuations of the local free-surface slope were least-square fitted with a sinusoidal curve to makeup the signals lost due to the constriction in the optical arrangement. The waveform was estimated with an assumption that wave phase speed can be calculated using the dispersion relation for linear capillary-gravity waves. The direction of propagation on the jet surface was also evaluated so that the wave amplitudes, calculated by integral of slope angle signal, agree consistently in stream-wise and spanwise direction. These measurements and analyses show that the waves at the measurement location for a jet velocity of 1.2 m/s can best be represented by oblique waves with an inclination of 1.23 rad, a wavelength of 3.8 mm and a wave amplitude of about 0.05 mm. (authors)
NASA Astrophysics Data System (ADS)
Bandaru, Vinodh; Pracht, Julian; Boeck, Thomas; Schumacher, Jörg
2015-08-01
We consider a plane channel flow of an electrically conducting fluid which is driven by a mean pressure gradient in the presence of an applied magnetic field that is streamwise periodic with zero mean. Magnetic flux expulsion and the associated bifurcation in such a configuration are explored using direct numerical simulations (DNS). The structure of the flow and magnetic fields in the Hartmann regime (where the dominant balance is through Lorentz forces) and the Poiseuille regime (where viscous effects play a significant role) are studied, and detailed comparisons to the existing one-dimensional model of Kamkar and Moffatt (J Fluid Mech 90:107-122, 1982) are drawn to evaluate the validity of the model. Comparisons show good agreement of the model with DNS in the Hartmann regime, but significant differences arising in the Poiseuille regime when nonlinear effects become important. The effects of various parameters like the magnetic Reynolds number, imposed field wavenumber etc. on the bifurcation of the flow are studied. Magnetic field line reconnections occurring during the dynamic runaway reveal a specific two-step pattern that leads to the gradual expulsion of flux in the core region.
Two-dimensional plastic flow of foams and emulsions in a channel: experiments and simulations
NASA Astrophysics Data System (ADS)
Sbragaglia, Mauro; Andrea Scagliarini Collaboration; Benjamin Dollet Collaboration
2015-11-01
In order to understand the flow profiles of complex fluids, a crucial issue concerns the emergence of spatial correlations among plastic rearrangements exhibiting cooperativity flow behaviour at the macroscopic level. In this paper, the rate of plastic events in a Poiseuille flow is experimentally measured on a confined foam in a Hele-Shaw geometry. The correlation with independently measured velocity profiles is quantified by looking at the relationship between the localisation length of the velocity profiles and the localisation length of the spatial distribution of plastic events. To complement the cooperativity mechanisms studied in foam with those of other soft glassy systems, we compare the experiments with simulations of dense emulsions based on the lattice Boltzmann method, which are performed both with and without wall friction. Finally, unprecedented results on the distribution of the orientation of plastic events show that there is a non-trivial correlation with the underlying local shear strain. These features, not previously reported for a confined foam, lend further support to the idea that cooperativity mechanisms, originally invoked for concentrated emulsions (Goyon et al., Nature, vol. 454, 2008, pp. 84-87), have parallels in the behaviour of other soft glassy ma ERC Grant n.279004-DROEMU
Two-dimensional Vlasov Simulation of Driven, Nonlinear Electron Plasma Waves
NASA Astrophysics Data System (ADS)
Hittinger, J. A.; Banks, J. W.; Berger, R. L.; Cohen, B. I.; Brunner, S.
2010-11-01
In the VALHALLA project at LLNL, we are developing advanced, scalable algorithms for the continuum solution of Vlasov-Maxwell that differ from traditional approaches to continuum Vlasov methods.ootnotetextJ. Banks and J.Hittinger, sub. to IEEE Trans. Plas. Sci. (Dec 2009), LLNL-JRNL-420843. Here, continuum solution of the Vlasov-Maxwell system using these techniques is extended to two spatial dimensions and two velocity dimensions. We report Vlasov simulation studies of ponderomotively driven electron plasma waves (EPW) with fixed ions. Motivated plasma waves driven by SRS in light speckles, we consider a driving potential with a finite transverse width. This localization introduces losses as the waves propagate transversely out of the driven region and the particles are only transiently trapped. Linearly, the transverse localization leads to constant phase surfaces that defocus the EPW while nonlinearly, the constant phase surfaces from trapping-induced frequency shifts focus the EPW. We show how these processes are affected by the system length and the boundary conditions.
Two-Dimensional Model Simulations of Interannual Variability in the Tropical Stratosphere
NASA Technical Reports Server (NTRS)
Fleming, Eric L.; Jackman, Charles H.; Considine, David B.; Rosenfeld, Joan; Bhartia, P. K. (Technical Monitor)
2001-01-01
Meteorological data from the United Kingdom Meteorological Office (UKMO) and constituent data from the Upper Atmospheric Research Satellite (UARS) are used to construct yearly zonal mean dynamical fields for the 1990s for use in the GSFC 2-D chemistry and transport model. This allows for interannual dynamical variability to be included in the model constituent simulations. In this study, we focus on the tropical stratosphere. We find that the phase of quasi-biennial oscillation (QBO) signals in equatorial CH4, and profile and total column 03 data is resolved quite well using this empirically- based 2-D model transport framework. However. the QBO amplitudes in the model constituents are systematically underestimated relative to the observations at most levels. This deficiency is probably due in part to the limited vertical resolutions of the 2-D model and the UKMO and UARS input data sets. We find that using different heating rate calculations in the model affects the interannual and QBO amplitudes in the constituent fields, but has little impact on the phase. Sensitivity tests reveal that the QBO in transport dominates the ozone interannual variability in the lower stratosphere. with the effect of the temperature QBO being dominant in the tipper stratosphere via the strong temperature dependence of the ozone loss reaction rates. We also find that the QBO in odd nitrogen radicals, which is caused by the QBO modulated transport of NOy, plays a significant but not dominant role in determining the ozone QBO variability in the middle stratosphere. The model mean age of air is in good overall agreement with that determined from tropical lower,middle stratospheric OMS balloon observations of SF6 and CO2. The interannual variability of tile equatorial mean age in the model increases with altitude and maximizes near 40 km, with a range, of 4-5 years over the 1993-2000 time period.
Chacon-Madrid, Heber J; Murphy, Benjamin N; Pandis, Spyros N; Donahue, Neil M
2012-10-16
We use a two-dimensional volatility basis set (2D-VBS) box model to simulate secondary organic aerosol (SOA) mass yields of linear oxygenated molecules: n-tridecanal, 2- and 7-tridecanone, 2- and 7-tridecanol, and n-pentadecane. A hybrid model with explicit, a priori treatment of the first-generation products for each precursor molecule, followed by a generic 2D-VBS mechanism for later-generation chemistry, results in excellent model-measurement agreement. This strongly confirms that the 2D-VBS mechanism is a predictive tool for SOA modeling but also suggests that certain important first-generation products for major primary SOA precursors should be treated explicitly for optimal SOA predictions.
Boriskina, Svetlana V; Sewell, Phillip; Benson, Trevor M; Nosich, Alexander I
2004-03-01
A fast and accurate method is developed to compute the natural frequencies and scattering characteristics of arbitrary-shape two-dimensional dielectric resonators. The problem is formulated in terms of a uniquely solvable set of second-kind boundary integral equations and discretized by the Galerkin method with angular exponents as global test and trial functions. The log-singular term is extracted from one of the kernels, and closed-form expressions are derived for the main parts of all the integral operators. The resulting discrete scheme has a very high convergence rate. The method is used in the simulation of several optical microcavities for modern dense wavelength-division-multiplexed systems.
NASA Astrophysics Data System (ADS)
Kong, Wei; Yang, Fang; Liu, Songfen; Shi, Feng
2016-10-01
A Langevin dynamics simulation method is used to study the two-dimensional (2D) equilibrium structure of complex plasmas while considering an external magnetic field. The traditional Yukawa potential and a modified Yukawa potential according to Shukla et al. [Phys. Lett. A 291, 413 (2001); Shukla and Mendonca, Phys. Scr. T113 82 (2004)] and Salimullah et al. [Phys. Plasmas 10, 3047 (2003)] respectively, are employed to account for the interaction of the charged dust particles. It is found that the collisions between neutral gas and charged dust particles have minor effects on the 2D equilibrium structure of the system. Based on the modified Yukawa potential, studies on the 2D equilibrium structure show that the traditional Yukawa potential is still suitable for describing the magnetized complex plasmas, even if the shielding distance of charged dust particles is affected by the strong external magnetic field.
Matsui, H.; Koike, Makoto; Kondo, Yutaka; Fast, Jerome D.; Takigawa, M.
2014-09-30
Number concentrations, size distributions, and mixing states of aerosols are essential parameters for accurate estimation of aerosol direct and indirect effects. In this study, we developed an aerosol module, designated Aerosol Two-dimensional bin module for foRmation and Aging Simulation (ATRAS), that can represent these parameters explicitly by considering new particle formation (NPF), black carbon (BC) aging, and secondary organic aerosol (SOA) processes. A two-dimensional bin representation is used for particles with dry diameters from 40 nm to 10 µm to resolve both aerosol size (12 bins) and BC mixing state (10 bins) for a total of 120 bins. The particles with diameters from 1 to 40 nm are resolved using an additional 8 size bins to calculate NPF. The ATRAS module was implemented in the WRF-chem model and applied to examine the sensitivity of simulated mass, number, size distributions, and optical and radiative parameters of aerosols to NPF, BC aging and SOA processes over East Asia during the spring of 2009. BC absorption enhancement by coating materials was about 50% over East Asia during the spring, and the contribution of SOA processes to the absorption enhancement was estimated to be 10 – 20% over northern East Asia and 20 – 35% over southern East Asia. A clear north-south contrast was also found between the impacts of NPF and SOA processes on cloud condensation nuclei (CCN) concentrations: NPF increased CCN concentrations at higher supersaturations (smaller particles) over northern East Asia, whereas SOA increased CCN concentrations at lower supersaturations (larger particles) over southern East Asia. Application of ATRAS to East Asia also showed that the impact of each process on each optical and radiative parameter depended strongly on the process and the parameter in question. The module can be used in the future as a benchmark model to evaluate the accuracy of simpler aerosol models and examine interactions between NPF, BC aging, and SOA
NASA Astrophysics Data System (ADS)
Matsui, H.; Koike, M.; Kondo, Y.; Fast, J. D.; Takigawa, M.
2014-09-01
Number concentrations, size distributions, and mixing states of aerosols are essential parameters for accurate estimations of aerosol direct and indirect effects. In this study, we develop an aerosol module, designated the Aerosol Two-dimensional bin module for foRmation and Aging Simulation (ATRAS), that can explicitly represent these parameters by considering new particle formation (NPF), black carbon (BC) aging, and secondary organic aerosol (SOA) processes. A two-dimensional bin representation is used for particles with dry diameters from 40 nm to 10 μm to resolve both aerosol sizes (12 bins) and BC mixing states (10 bins) for a total of 120 bins. The particles with diameters between 1 and 40 nm are resolved using additional eight size bins to calculate NPF. The ATRAS module is implemented in the WRF-Chem model and applied to examine the sensitivity of simulated mass, number, size distributions, and optical and radiative parameters of aerosols to NPF, BC aging, and SOA processes over East Asia during the spring of 2009. The BC absorption enhancement by coating materials is about 50% over East Asia during the spring, and the contribution of SOA processes to the absorption enhancement is estimated to be 10-20% over northern East Asia and 20-35% over southern East Asia. A clear north-south contrast is also found between the impacts of NPF and SOA processes on cloud condensation nuclei (CCN) concentrations: NPF increases CCN concentrations at higher supersaturations (smaller particles) over northern East Asia, whereas SOA increases CCN concentrations at lower supersaturations (larger particles) over southern East Asia. The application of ATRAS in East Asia also shows that the impact of each process on each optical and radiative parameter depends strongly on the process and the parameter in question. The module can be used in the future as a benchmark model to evaluate the accuracy of simpler aerosol models and examine interactions between NPF, BC aging, and SOA
NASA Astrophysics Data System (ADS)
Matsui, H.; Koike, M.; Kondo, Y.; Fast, J. D.; Takigawa, M.
2014-04-01
Number concentrations, size distributions, and mixing states of aerosols are essential parameters for accurate estimation of aerosol direct and indirect effects. In this study, we develop an aerosol module, designated Aerosol Two-dimensional bin module for foRmation and Aging Simulation (ATRAS), that can represent these parameters explicitly by considering new particle formation (NPF), black carbon (BC) aging, and secondary organic aerosol (SOA) processes. A two-dimensional bin representation is used for particles with dry diameters from 40 nm to 10 μm to resolve both aerosol size (12 bins) and BC mixing state (10 bins) for a total of 120 bins. The particles with diameters from 1 to 40 nm are resolved using an additional 8 size bins to calculate NPF. The ATRAS module is implemented in the WRF-chem model and applied to examine the sensitivity of simulated mass, number, size distributions, and optical and radiative parameters of aerosols to NPF, BC aging and SOA processes over East Asia during the spring of 2009. BC absorption enhancement by coating materials is about 50% over East Asia during the spring, and the contribution of SOA processes to the absorption enhancement is estimated to be 10-20% over northern East Asia and 20-35% over southern East Asia. A clear north-south contrast is also found between the impacts of NPF and SOA processes on cloud condensation nuclei (CCN) concentrations: NPF increases CCN concentrations at higher supersaturations (smaller particles) over northern East Asia, whereas SOA increases CCN concentrations at lower supersaturations (larger particles) over southern East Asia. Application of ATRAS to East Asia also shows that the impact of each process on each optical and radiative parameter depends strongly on the process and the parameter in question. The module can be used in the future as a benchmark model to evaluate the accuracy of simpler aerosol models and examine interactions between NPF, BC aging, and SOA processes under
Magnetic flux ropes in 3-dimensional MHD simulations
NASA Technical Reports Server (NTRS)
Ogino, Tatsuki; Walker, Raymond J.; Ashour-Abdalla, Maha
1990-01-01
The interaction of the solar wind and the earth's magnetosphere is presently simulated by a 3D, time-dependent, global MHD method in order to model the magnetopause and magnetotail generation of magnetic flux ropes. It is noted that strongly twisted and localized magnetic flux tubes simular to magnetic flux ropes appear at the subpolar magnetopause when the IMF has a large azimuthal component, as well as a southward component. Plasmoids are generated in the magnetotail after the formation of a near-earth magnetic neutral line; the magnetic field lines have a helical structure that is connected from dawn to dusk.
Kim, K; Forest, B; Geringer, J
2011-12-01
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 contact stress range. Meanwhile, as applied contact stress increases, number of cycles to failure decreases gradually. Finally, this proposed finite element simulation offers an effective method for identifying fracture and fatigue behaviours of a microstructure provided that microstructure images are available.
NASA Astrophysics Data System (ADS)
Baran, Adam J.
This dissertation presents original research into the melting process of a downward facing cryogenic solid hydrogen surface subject to a two dimensional axisymmetric jet impingement flow of superheated hydrogen vapor. The motivation for the study is to investigate concepts of storing rocket propellants as a solid and rapidly melting the solid for liquid propellant delivery to a rocket engine. The present study considers a more favorable liquid removal arrangement than prior (1970s) experiments which melted solid hydrogen at the bottom of a cryostat. This is a numerical study that involves computation fluid dynamic (CFD) simulation of four distinct physical phenomena: (1) melting, (2) jet impingement heat transfer (JIHT), (3) multiphase transport, and (4) film breakup/droplet formation. The volume of fluid (VOF) method is used with the V2F turbulence model in a commercial CFD Navier-Stokes solver (FLUENT) to investigate the multiphase nature of melt transport and its interaction with the vapor stream; i.e., the phenomena relevant to effective heat transfer between the vapor and the melting interface. The goal of the research is: (1) to develop a numerical method to study the problem and (2) evaluate several simple configurations to begin investigating relevant phenomena for the purpose of enhancing melting rate. Many options exist for the vapor to interact with the solid surface. The scope of this initial research is limited to a steady jet of single phase superheated hydrogen vapor at fixed jet exit conditions (T = 525 R and Re = 11,000) at a fixed jet standoff ( H/D = 1.0). Condensation/vaporization are not considered. Although film breakup/droplet formation is a phenomenon where two dimensional features evolve into three dimensional events, this phenomenon is approximated as two dimensional to allow a computationally tractable problem for this initial study. Calculations are performed validating the numerical method for melting and JIHT against known results
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
Global MHD Simulation of Mesoscale Structures at the Magnetospheric Boundary
NASA Technical Reports Server (NTRS)
Berchem, Jean
1998-01-01
The research carried out for this protocol was focused on the study of mesoscales structures at the magnetospheric boundary. We investigated three areas: (1) the structure of the magnetospheric boundary for steady solar wind conditions; (2) the dynamics of the dayside magnetospheric boundary and (3) the dynamics of the distant tail magnetospheric boundary. Our approach was to use high resolution three-dimensional global magnetohydrodynamic (MHD) simulations of the interaction of the solar wind with the Earth's magnetosphere. We first considered simple variations of the interplanetary conditions to obtain generic cases that helped us in establishing the basic cause and effect relationships for steady solar wind conditions. Subsequently, we used actual solar wind plasma and magnetic field parameters measured by an upstream spacecraft as input to the simulations and compared the simulation results with sequences of events observed by another or several other spacecraft located downstream the bow shock. In particular we compared results with observations made when spacecraft crossed the magnetospheric boundary.
NASA Astrophysics Data System (ADS)
Agarwal, Sumit; Briant, Clyde L.; Krajewski, Paul E.; Bower, Allan F.; Taleff, Eric M.
2007-04-01
A finite element method was recently designed to model the mechanisms that cause superplastic deformation (A.F. Bower and E. Wininger, A Two-Dimensional Finite Element Method for Simulating the Constitutive Response and Microstructure of Polycrystals during High-Temperature Plastic Deformation, J. Mech. Phys. Solids, 2004, 52, p 1289-1317). The computations idealize the solid as a collection of two-dimensional grains, separated by sharp grain boundaries. The grains may deform plastically by thermally activated dislocation motion, which is modeled using a conventional crystal plasticity law. The solid may also deform by sliding on the grain boundaries, or by stress-driven diffusion of atoms along grain boundaries. The governing equations are solved using a finite element method, which includes a front-tracking procedure to monitor the evolution of the grain boundaries and surfaces in the solid. The goal of this article is to validate these computations by systematically comparing numerical predictions to experimental measurements of the elevated-temperature response of aluminum alloy AA5083 (M.-A. Kulas, W.P. Green, E.M. Taleff, P.E. Krajewski, and T.R. McNelley, Deformation Mechanisms in Superplastic AA5083 materials. Metall. Mater. Trans. A, 2005, 36(5), p 1249-1261). The experimental work revealed that a transition occurs from grain-boundary sliding to dislocation (solute-drag) creep at approximately 0.001/s for temperatures between 425 and 500 °C. In addition, increasing the grain size from 7 to 10 μm decreased the transition to significantly lower strain rates. Predictions from the finite element method accurately predict the effect of grain size on the transition in deformation mechanisms.
Riconda, C.; Weber, S.; Tikhonchuk, V. T.; Adam, J.-C.; Heron, A.
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.
NASA Astrophysics Data System (ADS)
Shonnard, D. R.; Taylor, R. T.; Hanna, M. L.; Boro, C. O.; Duba, A. G.
1994-01-01
For some potentially useful and emerging in situ bioremediation technologies it is important to control bacterial attachment to subsurface materials during the injection of microbial cell suspensions. In this study the attachment patterns of Methylosinus trichosporium OB3b were measured after horizontal injections into a two-dimensional miniature aquifer simulator containing a wet homogeneous sand. In preliminary sand column assays, bacterial attachment to the sand was increased nearly 2 orders of magnitude compared to attachment in the presence of distilled water by raising the concentration of a pH 7.0 sodium-potassium phosphate buffer to 10 mM. The maximal concentration of attached cells was ˜4×108 cells/g dry sand with both sand minicolumns and the wet sand aquifer simulator. For the latter this occurred on streamlines directly between the horizontal injector and withdrawal ports, where injection-withdrawal velocities were the highest. The effects of a simulated groundwater cross flow during suspension injection on bacterial attachment to the aquifer simulator sands were also studied, and a peristaltic pumping method to counteract these groundwater flow effects resulted in a more localized pattern, i.e., without extensive downstream skewing of the bacterial attachment zone. Phenol red was utilized as a nonbinding, red-colored tracer compound. It proved to be very convenient for quantitatively measuring the earlier breakthroughs of cells versus an inert tracer during the aquifer simulator and subsequent capillary tube cell injection experiments and also for visualizing the anticipated boundaries of cell attachment in the aquifer simulator. The effect of injection velocity on the observed bacterial attachment patterns in these experiments appears to be accounted for by colloid filtration theory.
Kadowaki, Hiroko; Hayase, Toshiyuki; Funamoto, Kenichi; Taniguchi, Nobuyuki
2016-02-01
Information on hemodynamics is essential for elucidation of mechanisms and development of novel diagnostic methods for circulatory diseases. Two-dimensional ultrasonic-measurement-integrated (2D-UMI) simulation can correctly reproduce an intravascular blood flow field and hemodynamics by feeding back an ultrasonic measurement to the numerical blood flow simulation. In this method, it is critically important to give the correct cross-sectional average inflow velocity (inflow velocity) as the boundary condition. However, systematic study has not been done on the relative validity and effectiveness of existing inflow velocity estimation methods for various target flow fields. The aim of this study was to examine the existing methods systematically and to establish a method to accurately estimate inflow velocities for various vessel geometries and flow conditions in 2D-UMI simulations. A numerical experiment was performed for 2D-UMI simulation of blood flow models in a straight vessel with inflow velocity profiles symmetric and asymmetric to the vessel axis using existing evaluation functions based on Doppler velocity error for the inflow velocity estimation. As a result, it was clarified that a significantly large estimation error occurs in the asymmetric flow due to a nonfeedback domain near the downstream end of the calculation domain. Hence, a new inflow velocity estimation method of 2D-UMI simulation is proposed in which the feedback and evaluation domains are extended to the downstream end. Further numerical experiments of 2D-UMI simulation for two realistic vessel geometries of a healthy blood vessel and a stenosed one confirmed the effectiveness of the proposed method.
Thermodynamic MHD Simulation of the Bastille Day Event
NASA Astrophysics Data System (ADS)
Torok, Tibor; Downs, Cooper; Lionello, Roberto; Linker, Jon A.; Mikic, Zoran; Titov, Viacheslav S.; Riley, Pete
2014-05-01
The "Bastille Day" event on July 14, 2000 is one of the most extensively studied solar eruptions. It originated in a complex active region close to disk center and produced an X5.7 flare, a fast halo CME, and an intense geomagnetic storm. We have recently begun to model this challenging event, with the final goal to simulate its whole evolution, from the pre-eruptive state to the CME's arrival at 1 AU. To this end, we first produce a steady-state MHD solution of the background corona that incorporates realistic energy transport ("thermodynamic MHD"), photospheric magnetic field measurements, and the solar wind. In order to model the pre-eruptive magnetic field, we then insert into this solution a stable, elongated flux rope that resides above the highly curved polarity inversion line of the active region. Finally, we produce an eruption by imposing photospheric flows that slowly converge towards the polarity inversion line. In this presentation we describe our method, compare the simulation results with the observations, and discuss the challenges and limitations involved in modeling such complex and powerful eruptions.
Lee, J H; Lim, S K; Huh, S H; Lee, D; Lee, W
1998-10-01
Melanocortins, which are involved in melanocyte pigmentation control and glucocorticoid stimulation, have functional roles in various physiological mechanisms and have been shown to participate in higher cortical functions. Recently, it has also been reported that melanocyte-stimulating hormone (MSH) and melanocortin 4 receptor (MC4R) are the key components of the hypothalamic response to obesity. The solution structures of both melanocyte-stimulating hormone alpha-MSH (Ac-Ser-Tyr-Ser-Met-Glu-His-Phe-Arg-Trp-Gly-Lys-Pro-Val-NH2) and its analog alpha-MSH-ND (Ac-Ahx-Asp-His-DPhe-Arg-Trp-Lys-NH2) (Ahx, 2-aminohexanoic acid) have been determined by two-dimensional NMR spectroscopy and simulated-annealing calculations. The NMR data revealed that alpha-MSH forms a hairpin loop conformation which includes conserved message sequences, whereas alpha-MSH-ND prefers a type I beta-turn comprising residues of Asp2-His3-DPhe4-Arg5. Final simulated-annealing structures of both alpha-MSH-ND and alpha-MSH peptides converged with rmsd of 0.07 nm for alpha-MSH-ND and 0.1 nm for alpha-MSH between backbone atoms, respectively. This result will provide the structural bases of melanocortin functions as well as valuable information for structure-based drug design involving the regulation of obesity and feeding.
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.
NASA Astrophysics Data System (ADS)
Matsumoto, Yosuke; Amano, Takanobu; Hoshino, Masahiro
2012-08-01
Electron accelerations at high Mach number collisionless shocks are investigated by means of two-dimensional electromagnetic particle-in-cell simulations with various Alfvén Mach numbers, ion-to-electron mass ratios, and the upstream electron β e (the ratio of the thermal pressure to the magnetic pressure). We find electrons are effectively accelerated at a super-high Mach number shock (MA ~ 30) with a mass ratio of M/m = 100 and β e = 0.5. The electron shock surfing acceleration is an effective mechanism for accelerating the particles toward the relativistic regime even in two dimensions with a large mass ratio. Buneman instability excited at the leading edge of the foot in the super-high Mach number shock results in a coherent electrostatic potential structure. While multi-dimensionality allows the electrons to escape from the trapping region, they can interact with the strong electrostatic field several times. Simulation runs in various parameter regimes indicate that the electron shock surfing acceleration is an effective mechanism for producing relativistic particles in extremely high Mach number shocks in supernova remnants, provided that the upstream electron temperature is reasonably low.
NASA Astrophysics Data System (ADS)
Matsumoto, Y.; Amano, T.; Hoshino, M.
2012-12-01
Electron accelerations at high Mach number collision-less shocks are investigated by means of two-dimensional electromagnetic Particle-in-Cell simulations with various Alfven Mach numbers, ion-to-electron mass ratios, and the upstream electron βe (the ratio of the thermal pressure to the magnetic pressure). We found electrons are effectively accelerated at a super-high Mach number shock (MA ~ 30) with a mass ratio of M/m=100 and βe=0.5. The electron shock surfing acceleration is an effective mechanism for accelerating the particles toward the relativistic regime even in two dimensions with the large mass ratio. Buneman instability excited at the leading edge of the foot in the super-high Mach number shock results in a coherent electrostatic potential structure. While multi-dimensionality allows the electrons to escape from the trapping region, they can interact with the strong electrostatic field several times. Simulation runs in various parameter regimes indicate that the electron shock surfing acceleration is an effective mechanism for producing relativistic particles in extremely-high Mach number shocks in supernova remnants, provided that the upstream electron temperature is reasonably low. Matsumoto et al., Astrophys. J., 755, 109, 2012.
Yu, Zhicong; Noo, Frédéric; Dennerlein, Frank; Wunderlich, Adam; Lauritsch, Günter; Hornegger, Joachim
2012-07-07
Mathematical phantoms are essential for the development and early stage evaluation of image reconstruction algorithms in x-ray computed tomography (CT). This note offers tools for computer simulations using a two-dimensional (2D) phantom that models the central axial slice through the FORBILD head phantom. Introduced in 1999, in response to a need for a more robust test, the FORBILD head phantom is now seen by many as the gold standard. However, the simple Shepp-Logan phantom is still heavily used by researchers working on 2D image reconstruction. Universal acceptance of the FORBILD head phantom may have been prevented by its significantly higher complexity: software that allows computer simulations with the Shepp-Logan phantom is not readily applicable to the FORBILD head phantom. The tools offered here address this problem. They are designed for use with Matlab®, as well as open-source variants, such as FreeMat and Octave, which are all widely used in both academia and industry. To get started, the interested user can simply copy and paste the codes from this PDF document into Matlab® M-files.
Matsumoto, Yosuke; Amano, Takanobu; Hoshino, Masahiro
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.
Two-dimensional Maxwell-Bloch simulation of quasi-π-pulse amplification in a seeded XUV laser
NASA Astrophysics Data System (ADS)
Larroche, O.; Klisnick, A.
2013-09-01
The amplification of high-order-harmonics (HOH) seed pulses in a swept-gain XUV laser is investigated through numerical simulations of the full set of Bloch and two-dimensional paraxial propagation equations with our code colax. The needed atomic data are taken from a hydrodynamics and collisional-radiative simulation in the case of a Ni-like Ag plasma created from the interaction of an infrared laser with a solid target and pumped in the transient regime. We show that the interplay of strong population inversion and diffraction or refraction due to the short transverse dimensions and steep density gradient of the active plasma can lead to the amplification of an intense, ultrashort, quasi-“π” pulse triggered by the incoming seed. By properly tuning the system geometry and HOH pulse parameters, we show that an ≃10 fs, 8×1012 W/cm2 amplified pulse can be achieved in a 3-mm-long Ni-like Ag plasma, with a factor of ≳10 intensity contrast with respect to the longer-lasting wake radiation and amplified spontaneous emission.
NASA Astrophysics Data System (ADS)
Hosseinzadeh-Nik, Zahra; Regele, Jonathan D.
2015-11-01
Dense compressible particle-laden flow, which has a complex nature, exists in various engineering applications. Shock waves impacting a particle cloud is a canonical problem to investigate this type of flow. It has been demonstrated that large flow unsteadiness is generated inside the particle cloud from the flow induced by the shock passage. It is desirable to develop models for the Reynolds stress to capture the energy contained in vortical structures so that volume-averaged models with point particles can be simulated accurately. However, the previous work used Euler equations, which makes the prediction of vorticity generation and propagation innacurate. In this work, a fully resolved two dimensional (2D) simulation using the compressible Navier-Stokes equations with a volume penalization method to model the particles has been performed with the parallel adaptive wavelet-collocation method. The results still show large unsteadiness inside and downstream of the particle cloud. A 1D model is created for the unclosed terms based upon these 2D results. The 1D model uses a two-phase simple low dissipation AUSM scheme (TSLAU) developed by coupled with the compressible two phase kinetic energy equation.
Nenov, Artur; Mukamel, Shaul; Garavelli, Marco; Rivalta, Ivan
2015-08-11
First-principles simulations of two-dimensional electronic spectroscopy in the ultraviolet region (2DUV) require computationally demanding multiconfigurational approaches that can resolve doubly excited and charge transfer states, the spectroscopic fingerprints of coupled UV-active chromophores. Here, we propose an efficient approach to reduce the computational cost of accurate simulations of 2DUV spectra of benzene, phenol, and their dimer (i.e., the minimal models for studying electronic coupling of UV-chromophores in proteins). We first establish the multiconfigurational recipe with the highest accuracy by comparison with experimental data, providing reference gas-phase transition energies and dipole moments that can be used to construct exciton Hamiltonians involving high-lying excited states. We show that by reducing the active spaces and the number of configuration state functions within restricted active space schemes, the computational cost can be significantly decreased without loss of accuracy in predicting 2DUV spectra. The proposed recipe has been successfully tested on a realistic model proteic system in water. Accounting for line broadening due to thermal and solvent-induced fluctuations allows for direct comparison with experiments.
3-D MHD Simulation of Oscillating Field Current Drive
NASA Astrophysics Data System (ADS)
Ebrahimi, F.; Prager, S. C.; Wright, J. C.
2000-10-01
Oscillating Field Current Drive (OFCD) is a proposed low frequency steady-state current drive technique for the Reversed Field Pinch (RFP). In OFCD toroidal and poloidal oscillating electric fields are applied with 90^circ phase difference to inject magnetic helicity. In the present work, the 3-D nonlinear, resistive MHD code DEBS is used to simulate OFCD in relaxed RFP plasmas. The present simulations are at high Lundquist number S=10^5 and low spect ratio R/a=1.5. The physics issues investigated are the response of background magnetic fluctuations to the oscillating fields, the relative contributions of the tearing mode dynamo and the oscillating fields to the current profile, and the sustainment and control of the steady-state current profile. Initial results with low amplitude oscillating fields show the expected increase in magnetic helicity and current. Results with higher amplitude will also be presented.
MHD simulation of the inner-heliospheric magnetic field
NASA Astrophysics Data System (ADS)
Wiengarten, T.; Kleimann, J.; Fichtner, H.; Cameron, R.; Jiang, J.; Kissmann, R.; Scherer, K.
2013-01-01
Maps of the radial magnetic field at a heliocentric distance of 10 solar radii are used as boundary conditions in the MHD code CRONOS to simulate a three-dimensional inner-heliospheric solar wind emanating from the rotating Sun out to 1 AU. The input data for the magnetic field are the result of solar surface flux transport modeling using observational data of sunspot groups coupled with a current-sheet source surface model. Among several advancements, this allows for higher angular resolution than that of comparable observational data from synoptic magnetograms. The required initial conditions for the other MHD quantities are obtained following an empirical approach using an inverse relation between flux tube expansion and radial solar wind speed. The computations are performed for representative solar minimum and maximum conditions, and the corresponding state of the solar wind up to the Earth's orbit is obtained. After a successful comparison of the latter with observational data, they can be used to drive outer-heliospheric models.
Pan, Kuo-Chuan; Liebendörfer, Matthias; Hempel, Matthias; Thielemann, Friedrich-Karl
2016-01-20
The neutrino mechanism of core-collapse supernova is investigated via non-relativistic, two-dimensional (2D), neutrino radiation–hydrodynamic simulations. For the transport of electron flavor neutrinos, we use the interaction rates defined by Bruenn and the isotropic diffusion source approximation (IDSA) scheme, which decomposes the transported particles into trapped-particle and streaming-particle components. Heavy neutrinos are described by a leakage scheme. Unlike the “ray-by-ray” approach in some other multidimensional supernova models, we use cylindrical coordinates and solve the trapped-particle component in multiple dimensions, improving the proto-neutron star resolution and the neutrino transport in angular and temporal directions. We provide an IDSA verification by performing one-dimensional (1D) and 2D simulations with 15 and 20 M{sub ⊙} progenitors from Woosley et al. and discuss the difference between our IDSA results and those existing in the literature. Additionally, we perform Newtonian 1D and 2D simulations from prebounce core collapse to several hundred milliseconds postbounce with 11, 15, 21, and 27 M{sub ⊙} progenitors from Woosley et al. with the HS(DD2) equation of state. General-relativistic effects are neglected. We obtain robust explosions with diagnostic energies E{sub dia} ≳ 0.1–0.5 B (1 B ≡ 10{sup 51} erg) for all considered 2D models within approximately 100–300 ms after bounce and find that explosions are mostly dominated by the neutrino-driven convection, although standing accretion shock instabilities are observed as well. We also find that the level of electron deleptonization during collapse dramatically affects the postbounce evolution, e.g., the neglect of neutrino–electron scattering during collapse will lead to a stronger explosion.
NASA Astrophysics Data System (ADS)
Cohen, B. I.
2005-10-01
Two-dimensional simulations of stimulated Brillouin backscattering (SBBS) with the BZOHAR^1 code have been extended to include ion-ion collisions and spatial nonuniformity in the mean ion flow. BZOHAR hybrid simulations (particle-in-cell kinetic ions and Boltzmann fluid electrons) have shown^2 that SBBS saturation is dominated by ion trapping effects and secondary instability of the primary ion wave (decay into subharmonic ion waves and ion quasi-modes). Here we address the effects of ion collisions^3 on SBBS saturation and employ the efficient Langevin ion collision algorithm of Ref. 4 and the Fokker-Planck collision operator of Ref. 5. We also report simulations of SBBS with a linear gradient in the mean ion drift, which in conjunction with the nonlinear frequency shift due to ion trapping can introduce auto-resonance effects that may enhance reflectivities.^6 For SBBS in a high-gain limit with ion collisions or inhomogeneity, we find that ion trapping and secondary ion wave instabilities are robust saturation mechanisms. *Work performed for US DOE by UC LLNL under Contr. W-7405-ENG-48. ^1B.I. Cohen, et al., Phys. Plasmas 4, 956 (1997). ^2B.I. Cohen, et al., Phys. Plasmas, 12, 052703 (2005),. ^ 3P.W. Rambo, et al., Phys. Rev. Lett. 79, 83 (1997). ^ 4M.E. Jones, et al., J. Comp. Phys. 123, 169, (1996). ^ 5W. M. Manheimer, et al., J. Comp. Phys. 138, 563 (1997). ^ 6E.A. Williams, et al., Phys. Plasmas 11, 231 (2004).
NASA Astrophysics Data System (ADS)
Pan, Kuo-Chuan; Liebendörfer, Matthias; Hempel, Matthias; Thielemann, Friedrich-Karl
2016-01-01
The neutrino mechanism of core-collapse supernova is investigated via non-relativistic, two-dimensional (2D), neutrino radiation-hydrodynamic simulations. For the transport of electron flavor neutrinos, we use the interaction rates defined by Bruenn and the isotropic diffusion source approximation (IDSA) scheme, which decomposes the transported particles into trapped-particle and streaming-particle components. Heavy neutrinos are described by a leakage scheme. Unlike the “ray-by-ray” approach in some other multidimensional supernova models, we use cylindrical coordinates and solve the trapped-particle component in multiple dimensions, improving the proto-neutron star resolution and the neutrino transport in angular and temporal directions. We provide an IDSA verification by performing one-dimensional (1D) and 2D simulations with 15 and 20 M⊙ progenitors from Woosley et al. and discuss the difference between our IDSA results and those existing in the literature. Additionally, we perform Newtonian 1D and 2D simulations from prebounce core collapse to several hundred milliseconds postbounce with 11, 15, 21, and 27 M⊙ progenitors from Woosley et al. with the HS(DD2) equation of state. General-relativistic effects are neglected. We obtain robust explosions with diagnostic energies Edia ≳ 0.1-0.5 B (1 B ≡ 1051 erg) for all considered 2D models within approximately 100-300 ms after bounce and find that explosions are mostly dominated by the neutrino-driven convection, although standing accretion shock instabilities are observed as well. We also find that the level of electron deleptonization during collapse dramatically affects the postbounce evolution, e.g., the neglect of neutrino-electron scattering during collapse will lead to a stronger explosion.
FireStem2D--a two-dimensional heat transfer model for simulating tree stem injury in fires.
Chatziefstratiou, Efthalia K; Bohrer, Gil; Bova, Anthony S; Subramanian, Ravishankar; Frasson, Renato P M; Scherzer, Amy; Butler, Bret W; Dickinson, Matthew B
2013-01-01
FireStem2D, a software tool for predicting tree stem heating and injury in forest fires, is a physically-based, two-dimensional model of stem thermodynamics that results from heating at the bark surface. It builds on an earlier one-dimensional model (FireStem) and provides improved capabilities for predicting fire-induced mortality and injury before a fire occurs by resolving stem moisture loss, temperatures through the stem, degree of bark charring, and necrotic depth around the stem. We present the results of numerical parameterization and model evaluation experiments for FireStem2D that simulate laboratory stem-heating experiments of 52 tree sections from 25 trees. We also conducted a set of virtual sensitivity analysis experiments to test the effects of unevenness of heating around the stem and with aboveground height using data from two studies: a low-intensity surface fire and a more intense crown fire. The model allows for improved understanding and prediction of the effects of wildland fire on injury and mortality of trees of different species and sizes.
FireStem2D – A Two-Dimensional Heat Transfer Model for Simulating Tree Stem Injury in Fires
Chatziefstratiou, Efthalia K.; Bohrer, Gil; Bova, Anthony S.; Subramanian, Ravishankar; Frasson, Renato P. M.; Scherzer, Amy; Butler, Bret W.; Dickinson, Matthew B.
2013-01-01
FireStem2D, a software tool for predicting tree stem heating and injury in forest fires, is a physically-based, two-dimensional model of stem thermodynamics that results from heating at the bark surface. It builds on an earlier one-dimensional model (FireStem) and provides improved capabilities for predicting fire-induced mortality and injury before a fire occurs by resolving stem moisture loss, temperatures through the stem, degree of bark charring, and necrotic depth around the stem. We present the results of numerical parameterization and model evaluation experiments for FireStem2D that simulate laboratory stem-heating experiments of 52 tree sections from 25 trees. We also conducted a set of virtual sensitivity analysis experiments to test the effects of unevenness of heating around the stem and with aboveground height using data from two studies: a low-intensity surface fire and a more intense crown fire. The model allows for improved understanding and prediction of the effects of wildland fire on injury and mortality of trees of different species and sizes. PMID:23894599
NASA Astrophysics Data System (ADS)
Wang, Xin; Zhang, Yanqi; Zhang, Limin; Li, Jiao; Zhou, Zhongxing; Zhao, Huijuan; Gao, Feng
2016-04-01
We present a generalized strategy for direct reconstruction in pharmacokinetic diffuse fluorescence tomography (DFT) with CT-analogous scanning mode, which can accomplish one-step reconstruction of the indocyanine-green pharmacokinetic-rate images within in vivo small animals by incorporating the compartmental kinetic model into an adaptive extended Kalman filtering scheme and using an instantaneous sampling dataset. This scheme, compared with the established indirect and direct methods, eliminates the interim error of the DFT inversion and relaxes the expensive requirement of the instrument for obtaining highly time-resolved date-sets of complete 360 deg projections. The scheme is validated by two-dimensional simulations for the two-compartment model and pilot phantom experiments for the one-compartment model, suggesting that the proposed method can estimate the compartmental concentrations and the pharmacokinetic-rates simultaneously with a fair quantitative and localization accuracy, and is well suitable for cost-effective and dense-sampling instrumentation based on the highly-sensitive photon counting technique.
One-dimensional GIS-based model compared with a two-dimensional model in urban floods simulation.
Lhomme, J; Bouvier, C; Mignot, E; Paquier, A
2006-01-01
A GIS-based one-dimensional flood simulation model is presented and applied to the centre of the city of Nîmes (Gard, France), for mapping flow depths or velocities in the streets network. The geometry of the one-dimensional elements is derived from the Digital Elevation Model (DEM). The flow is routed from one element to the next using the kinematic wave approximation. At the crossroads, the flows in the downstream branches are computed using a conceptual scheme. This scheme was previously designed to fit Y-shaped pipes junctions, and has been modified here to fit X-shaped crossroads. The results were compared with the results of a two-dimensional hydrodynamic model based on the full shallow water equations. The comparison shows that good agreements can be found in the steepest streets of the study zone, but differences may be important in the other streets. Some reasons that can explain the differences between the two models are given and some research possibilities are proposed.
Large-Eddy Simulation for the Mechanism of Pollutant Removal from a Two-Dimensional Street Canyon
NASA Astrophysics Data System (ADS)
Michioka, Takenobu; Sato, Ayumu; Takimoto, Hiroshi; Kanda, Manabu
2011-02-01
Large-eddy simulation (LES) is conducted to investigate the mechanism of pollutant removal from a two-dimensional street canyon with a building-height to street-width (aspect) ratio of 1. A pollutant is released as a ground-level line source at the centre of the canyon floor. The mean velocities, turbulent fluctuations, and mean pollutant concentration estimated by LES are in good agreement with those obtained by wind-tunnel experiments. Pollutant removal from the canyon is mainly determined by turbulent motions, except in the adjacent area to the windward wall. The turbulent motions are composed of small vortices and small-scale coherent structures of low-momentum fluid generated close to the plane of the roof. Although both small vortices and small-scale coherent structures affect pollutant removal, the pollutant is largely emitted from the canyon by ejection of low-momentum fluid when the small-scale coherent structures appear just above the canyon where the pollutant is retained. Large-scale coherent structures also develop above the canyon, but they do not always affect pollutant removal.
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
MHD Simulations of the Initiation of Coronal Mass Ejections
NASA Astrophysics Data System (ADS)
Fan, Yuhong; Chatterjee, Piyali
Using three-dimensional MHD simulations, we model the quasi-static evolution and the onset of eruption of twisted magnetic flux ropes in the solar corona. We present simulations where the eruption is triggered by either the onset of the torus instability or the helical kink instability of the line-tied coronal flux rope. The simulations show that S (or inverse S) shaped current sheets develop along topological structures identified as Quasi Separatrix Layers (QSLs), during the quasi-static phase before the eruption. Reconnections in the current sheets effectively add twisted flux to the flux rope and thus allow it to rise quasi-statically to the critical height for the onset of the torus instability. We examine the thermal features produced by the current sheet formation and the associated reconnections and found that they can explain some of the observed features in coronal prominence cavities as well as in pre-eruption active regions. We also present simulations of the development of a homologous sequence of CMEs caused by the repeated formation and partial eruption of kink unstable flux ropes as a result of continued flux emergence. It is found that such homologous CMEs tend to be cannibalistic, leading to the formation of more energetic, highly twisted ejecta.
Comparing MHD simulations of RFP plasmas to RELAX experiments
NASA Astrophysics Data System (ADS)
McCollam, K. J.; den Hartog, D. J.; Jacobson, C. M.; Sauppe, J. P.; Masamune, S.; Sanpei, A.
2015-11-01
Standard reversed-field pinch (RFP) plasmas provide a nonlinear dynamical system as a validation domain for numerical MHD simulation codes, which can be applied to general toroidal confinement scenarios including tokamaks. Using the NIMROD code, we calculate linear stability and simulate the nonlinear evolution of plasmas similar to those in the RELAX RFP experiment, whose relatively modest Lundquist numbers of order 104 make the simulations tractable given present computing resources. The chosen RELAX cases cover a broad range of RFP reversal parameters and have also been previously simulated with the MIPS code (N. Mizuguchi et al., TH/P3-26, IAEA FEC, 2012). Experimental diagnostics that can be used for validation purposes include Thomson scattering for electron temperature, interferometry for electron density, SXR imaging, and external and internal magnetic probes. RELAX's small aspect ratio (~ 2) motivates a comparison study using toroidal and cylindrical geometries in NIMROD. This work is supported by the U.S. DOE and NSF and by the Japan Society for the Promotion of Science.
NASA Astrophysics Data System (ADS)
Lamb, K. G.; Warn-Varnas, A.
2015-05-01
The interaction of barotropic tides with Luzon Strait topography generates some of the world's largest internal solitary waves which eventually shoal and dissipate on the western side of the northern South China Sea. Two-dimensional numerical simulations of the shoaling of a single internal solitary wave at the site of the Asian Seas International Acoustic Experiment (ASIAEX) have been undertaken in order to investigate the sensitivity of the shoaling process to the stratification and the underlying bathymetry and to explore the influence of rotation. The bulk of the simulations are inviscid; however, exploratory simulations using a vertical eddy-viscosity confined to a near bottom layer, along with a no-slip boundary condition, suggest that viscous effects may become important in water shallower than about 200 m. A shoaling solitary wave fissions into several waves. At depths of 200-300 m the front of the leading waves become nearly parallel to the bottom and develop a very steep back as has been observed. The leading waves are followed by waves of elevation (pedestals) that are conjugate to the waves of depression ahead and behind them. Horizontal resolutions of at least 50 m are required to simulate these well. Wave breaking was found to occur behind the second or third of the leading solitary waves, never at the back of the leading wave. Comparisons of the shoaling of waves started at depths of 1000 and 3000 m show significant differences and the shoaling waves can be significantly non-adiabatic even at depths greater than 2000 m. When waves reach a depth of 200 m, their amplitudes can be more than 50% larger than the largest possible solitary wave at that depth. The shoaling behaviour is sensitive to the presence of small-scale features in the bathymetry: a 200 m high bump at 700 m depth can result in the generation of many mode-two waves and of higher mode waves. Sensitivity to the stratification is considered by using three stratifications based on summer
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
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
Jin, Wang; Penington, Catherine J; McCue, Scott W; Simpson, Matthew J
2016-10-07
Two-dimensional collective cell migration assays are used to study cancer and tissue repair. These assays involve combined cell migration and cell proliferation processes, both of which are modulated by cell-to-cell crowding. Previous discrete models of collective cell migration assays involve a nearest-neighbour proliferation mechanism where crowding effects are incorporated by aborting potential proliferation events if the randomly chosen target site is occupied. There are two limitations of this traditional approach: (i) it seems unreasonable to abort a potential proliferation event based on the occupancy of a single, randomly chosen target site; and, (ii) the continuum limit description of this mechanism leads to the standard logistic growth function, but some experimental evidence suggests that cells do not always proliferate logistically. Motivated by these observations, we introduce a generalised proliferation mechanism which allows non-nearest neighbour proliferation events to take place over a template of [Formula: see text] concentric rings of lattice sites. Further, the decision to abort potential proliferation events is made using a crowding function, f(C), which accounts for the density of agents within a group of sites rather than dealing with the occupancy of a single randomly chosen site. Analysing the continuum limit description of the stochastic model shows that the standard logistic source term, [Formula: see text], where λ is the proliferation rate, is generalised to a universal growth function, [Formula: see text]. Comparing the solution of the continuum description with averaged simulation data indicates that the continuum model performs well for many choices of f(C) and r. For nonlinear f(C), the quality of the continuum-discrete match increases with r.
NASA Astrophysics Data System (ADS)
Jin, Wang; Penington, Catherine J.; McCue, Scott W.; Simpson, Matthew J.
2016-10-01
Two-dimensional collective cell migration assays are used to study cancer and tissue repair. These assays involve combined cell migration and cell proliferation processes, both of which are modulated by cell-to-cell crowding. Previous discrete models of collective cell migration assays involve a nearest-neighbour proliferation mechanism where crowding effects are incorporated by aborting potential proliferation events if the randomly chosen target site is occupied. There are two limitations of this traditional approach: (i) it seems unreasonable to abort a potential proliferation event based on the occupancy of a single, randomly chosen target site; and, (ii) the continuum limit description of this mechanism leads to the standard logistic growth function, but some experimental evidence suggests that cells do not always proliferate logistically. Motivated by these observations, we introduce a generalised proliferation mechanism which allows non-nearest neighbour proliferation events to take place over a template of r≥slant 1 concentric rings of lattice sites. Further, the decision to abort potential proliferation events is made using a crowding function, f(C), which accounts for the density of agents within a group of sites rather than dealing with the occupancy of a single randomly chosen site. Analysing the continuum limit description of the stochastic model shows that the standard logistic source term, λ C(1-C), where λ is the proliferation rate, is generalised to a universal growth function, λ C f(C). Comparing the solution of the continuum description with averaged simulation data indicates that the continuum model performs well for many choices of f(C) and r. For nonlinear f(C), the quality of the continuum-discrete match increases with r.
Driving Coronal MHD Simulations with Flux Evolution Models
NASA Astrophysics Data System (ADS)
Linker, J.; Lionello, R.; Mikic, Z.; Riley, P.; Downs, C.; Arge, C. N.; Henney, C. J.
2013-12-01
The solar corona and solar wind strongly influences space weather at Earth. While coronal mass ejections (CMEs) are the most obvious source of this influence, the structure and dynamics of the ambient solar corona and solar wind also play an important role. Coronal structure leads to the partitioning of the solar wind into fast and slow streams, which are the source of recurrent geomagnetic activity. The geo-effectiveness of CMEs is in part determined by their interaction with the ambient wind, and the connection of the ambient interplanetary magnetic field to CME-related shocks and impulsive solar flares determines where solar energetic particles propagate. MHD simulations of the solar corona based on maps of the solar magnetic field have been demonstrated to describe many aspects of coronal structure. However, these models are typically integrated to steady state, using synoptic or daily-updated magnetic maps to derive the boundary conditions. The Sun's magnetic flux is always evolving, and these changes in the flux affect the structure and dynamics of the corona and heliosphere. In this presentation, we describe an approach to evolutionary models of the corona and so wind, using time-dependent boundary conditions. A key aspect of our approach is the use of the Air Force Data Assimilative Photospheric flux Transport (ADAPT) model to develop time-evolving boundary conditions for the magnetic field. ADAPT incorporates data assimilation techniques into the Worden and Harvey (2000) flux evolution model, making it an especially suitable candidate for providing boundary conditions to MHD models. We describe initial results and compare them with more traditional approaches. Research supported by AFOSR, NASA, and NSF.
Garcia, A.L.; Baras, F.; Mansour, M.M.
1994-06-30
In a recent paper, Watanabe, {ital et. al.} used direct simulation Monte Carlo to study Rayleigh-B{acute e}nard convection. They reported that, using stress-free boundary conditions, the onset of convection in the simulation occurred at a Rayleigh number much larger than the critical Rayleigh number predicted by linear stability analysis. We show that the source of their discrepancy is their failure to include the temperature jump effect in the calculation of Rayleigh number.
Britton, Joseph W; Sawyer, Brian C; Keith, Adam C; Wang, C-C Joseph; Freericks, James K; Uys, Hermann; Biercuk, Michael J; Bollinger, John J
2012-04-25
The presence of long-range quantum spin correlations underlies a variety of physical phenomena in condensed-matter systems, potentially including high-temperature superconductivity. However, many properties of exotic, strongly correlated spin systems, such as spin liquids, have proved difficult to study, in part because calculations involving N-body entanglement become intractable for as few as N ≈ 30 particles. Feynman predicted that a quantum simulator--a special-purpose 'analogue' processor built using quantum bits (qubits)--would be inherently suited to solving such problems. In the context of quantum magnetism, a number of experiments have demonstrated the feasibility of this approach, but simulations allowing controlled, tunable interactions between spins localized on two- or three-dimensional lattices of more than a few tens of qubits have yet to be demonstrated, in part because of the technical challenge of realizing large-scale qubit arrays. Here we demonstrate a variable-range Ising-type spin-spin interaction, J(i,j), on a naturally occurring, two-dimensional triangular crystal lattice of hundreds of spin-half particles (beryllium ions stored in a Penning trap). This is a computationally relevant scale more than an order of magnitude larger than previous experiments. We show that a spin-dependent optical dipole force can produce an antiferromagnetic interaction J(i,j) proportional variant d(-a)(i,j), where 0 ≤ a ≤ 3 and d(i,j) is the distance between spin pairs. These power laws correspond physically to infinite-range (a = 0), Coulomb-like (a = 1), monopole-dipole (a = 2) and dipole-dipole (a = 3) couplings. Experimentally, we demonstrate excellent agreement with a theory for 0.05 ≲ a ≲ 1.4. This demonstration, coupled with the high spin count, excellent quantum control and low technical complexity of the Penning trap, brings within reach the simulation of otherwise computationally intractable problems in quantum magnetism.
Judi, David R; Mcpherson, Timothy N; Burian, Steven J
2009-01-01
A grid resolution sensitivity analysis using a two-dimensional flood inundation model has been presented in this paper. Simulations for 6 dam breaches located randomly in the United States were run at 10,30,60,90, and 120 meter resolutions. The dams represent a range of topographic conditions, ranging from 0% slope to 1.5% downstream of the dam. Using 10 meter digital elevation model (DEM) simulation results as the baseline, the coarser simulation results were compared in terms of flood inundation area, peak depths, flood wave travel time, daytime and nighttime population in flooded area, and economic impacts. The results of the study were consistent with previous grid resolution studies in terms of inundated area, depths, and velocity impacts. The results showed that as grid resolution is decreased, the relative fit of inundated area between the baseline and coarser resolution decreased slightly. This is further characterized by increasing over prediction as well as increasing under prediction with decreasing resolution. Comparison of average peak depths showed that depths generally decreased as resolution decreased, as well as the velocity. It is, however, noted that the trends in depth and velocity showed less consistency than the inundation area metrics. This may indicate that for studies in which velocity and depths must be resolved more accurately (urban environments when flow around buildings is important in the calculation of drag effects), higher resolution DEM data should be used. Perhaps the most significant finding from this study is the perceived insensitivity of socio-economic impacts to grid resolution. The difference in population at risk (PAR) and economic cost generally remained within 10% of the estimated impacts using the high resolution DEM. This insensitivity has been attributed to over estimated flood area and associated socio-economic impacts compensating for under estimated flooded area and associated socio-economic impacts. The United
NASA Technical Reports Server (NTRS)
Gann, R. C.; Chakravarty, S.; Chester, G. V.
1978-01-01
Monte Carlo simulation, lattice dynamics in the harmonic approximation, and solution of the hypernetted chain equation were used to study the classical two-dimensional one component plasma. The system consists of a single species of charged particles immersed in a uniform neutralizing background. The particles interact via a l/r potential, where r is the two dimensional separation. Equations of state were calculated for both the liquid and solid phases. Results of calculation of the thermodynamic functions and one and two particle correlation functions are presented.
NASA Astrophysics Data System (ADS)
Pétri, J.
2009-08-01
Context: The physics of the pulsar magnetosphere near the neutron star surface remains poorly constrained by observations. Indeed, little is known about its emission mechanism, from radio to high-energy X-ray and gamma-rays. Nevertheless, it is believed that large vacuum gaps exist in this magnetosphere, and a non-neutral plasma partially fills the neutron star surroundings to form an electrosphere in differential rotation. Aims: According to several of our previous works, the equatorial disk in this electrosphere is diocotron and magnetron unstable, at least in the linear regime. To better assess the long term evolution of these instabilities, we study the behavior of the non-neutral plasma using particle simulations. Methods: We designed a two-dimensional electrostatic particle-in-cell (PIC) code in cylindrical coordinates, solving Poisson equation for the electric potential. In the diocotron regime, the equation of motion for particles obeys the electric drift approximation. As in the linear study, the plasma is confined between two conducting walls. Moreover, in order to simulate a pair cascade in the gaps, we add a source term feeding the plasma with charged particles having the same sign as those already present in the electrosphere. Results: First we checked our code by looking for the linear development of the diocotron instability in the same regime as the one used in our previous work, for a plasma annulus and for a typical electrosphere with differential rotation. To very good accuracy, we retrieve the same growth rates, supporting the correctness of our PIC code. Next, we consider the long term non-linear evolution of the diocotron instability. We found that particles tend to cluster together to form a small vortex of high charge density rotating around the axis of the cylinder with only little radial excursion of the particles. This grouping of particles generates new low density or even vacuum gaps in the plasma column. Finally, in more general
Reconnection events in two-dimensional Hall magnetohydrodynamic turbulence
Donato, S.; Servidio, S.; Carbone, V.; Dmitruk, P.; Shay, M. A.; Matthaeus, W. H.; Cassak, P. A.
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.
An MHD simulation of the interaction of the solar wind with the outflowing plasma from a comet
NASA Technical Reports Server (NTRS)
Ogino, T.; Walker, R. J.; Ashour-Abdalla, M.
1986-01-01
The interaction between the solar wind and the outflowing plasmas from a comet has been studied by using a two-dimensional time-dependent magnetohydrodynamic (MHD) simulation. The model reproduced several features of the comet-solar wind interaction predicted by earlier theories and observed on the recent cometary probes. These include the formation of the contact surface and the cometary magnetotail. For a constant interplanetary magnetic field (IMF) the cometary plasma captures field lines which drape over the comet to form an antiparallel magnetic field configuration in the tail and a thin plasma sheet. Eventually, tail magnetic reconnection begins to occur at several points. When the IMF orientation is reversed dayside magnetic reconnection occurs at the subsolar point and a large disturbance propagation down the tail.
MHD simulation of RF current drive in MST
Hendries, E. R.; Anderson, J. K.; Forest, C. B.; Reusch, J. A.; Seltzman, A. H.; Sovinec, C. R.; Diem, S.; Harvey, R. W.
2014-02-12
Auxiliary heating and current drive using RF waves such as the electron Bernstein wave (EBW) promises to advance the performance of the reversed field pinch (RFP). In previous computational work [1], a hypothetical edge-localized current drive is shown to suppress the tearing activity which governs the macroscopic transport properties of the RFP. The ideal conditions for tearing stabilization include a reduced toroidal induction, and precise width and radial position of the Gaussian-shaped external current drive. In support of the EBW experiment on the Madison Symmetric Torus, an integrated modeling scheme now incorporates ray tracing and Fokker-Plank predictions of auxiliary current into single fluid MHD. Simulations at low Lundquist number (S ∼ 10{sup 4}) generally agree with the previous work; significantly more burdensome simulations at MST-like Lundquist number (S ∼ 3×10{sup 6}) show unexpected results. The effect on nonlinearly saturated current profile by a particular RF-driven external force decreases in magnitude and widens considerably as the Lundquist number increases toward experimental values. Simulations reproduce the periodic current profile relaxation events observed in experiment (sawteeth) in the absence of current profile control. Reduction of the tearing mode amplitudes is still observable; however, reduction is limited to periods between the large bursts of magnetic activity at each sawtooth. The sawtoothing pattern persists with up to 10 MW of externally applied RF power. Periods with prolonged low tearing amplitude are predicted with a combination of external current drive and a reduced toroidal loop voltage, consistent with previous conclusions. Finally, the resistivity profile is observed to have a strong effect on the optimal externally driven current profile for mode stabilization.
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.
Numerical simulation of propagation of the MHD waves in sunspots
NASA Astrophysics Data System (ADS)
Parchevsky, K.; Kosovichev, A.; Khomenko, E.; Olshevsky, V.; Collados, M.
2010-11-01
We present results of numerical 3D simulation of propagation of MHD waves in sunspots. We used two self consistent magnetohydrostatic background models of sunspots. There are two main differences between these models: (i) the topology of the magnetic field and (ii) dependence of the horizontal profile of the sound speed on depth. The model with convex shape of the magnetic field lines near the photosphere has non-zero horizorntal perturbations of the sound speed up to the depth of 7.5 Mm (deep model). In the model with concave shape of the magnetic field lines near the photosphere Δ c/c is close to zero everywhere below 2 Mm (shallow model). Strong Alfven wave is generated at the wave source location in the deep model. This wave is almost unnoticeable in the shallow model. Using filtering technique we separated magnetoacoustic and magnetogravity waves. It is shown, that inside the sunspot magnetoacoustic and magnetogravity waves are not spatially separated unlike the case of the horizontally uniform background model. The sunspot causes anisotropy of the amplitude distribution along the wavefront and changes the shape of the wavefront. The amplitude of the waves is reduced inside the sunspot. This effect is stronger for the magnetogravity waves than for magnetoacoustic waves. The shape of the wavefront of the magnetogravity waves is distorted stronger as well. The deep model causes bigger anisotropy for both mgnetoacoustic and magneto gravity waves than the shallow model.
NASA Technical Reports Server (NTRS)
Stagliano, T. R.; Witmer, E. A.; Rodal, J. J. A.
1979-01-01
Finite element modeling alternatives as well as the utility and limitations of the two dimensional structural response computer code CIVM-JET 4B for predicting the transient, large deflection, elastic plastic, structural responses of two dimensional beam and/or ring structures which are subjected to rigid fragment impact were investigated. The applicability of the CIVM-JET 4B analysis and code for the prediction of steel containment ring response to impact by complex deformable fragments from a trihub burst of a T58 turbine rotor was studied. Dimensional analysis considerations were used in a parametric examination of data from engine rotor burst containment experiments and data from sphere beam impact experiments. The use of the CIVM-JET 4B computer code for making parametric structural response studies on both fragment-containment structure and fragment-deflector structure was illustrated. Modifications to the analysis/computation procedure were developed to alleviate restrictions.
Huizinga, Richard J.
2008-01-01
In cooperation with the Missouri Department of Transportation, the U.S. Geological Survey determined hydrologic and hydraulic parameters for the Gasconade River at the site of a proposed bridge replacement and highway realignment of State Highway 17 near Waynesville, Missouri. Information from a discontinued streamflow-gaging station on the Gasconade River near Waynesville was used to determine streamflow statistics for analysis of the 25-, 50-, 100-, and 500-year floods at the site. Analysis of the streamflow-gaging stations on the Gasconade River upstream and downstream from Waynesville indicate that flood peaks attenuate between the upstream gaging station near Hazelgreen and the Waynesville gaging station, such that the peak discharge observed on the Gasconade River near Waynesville will be equal to or only slightly greater (7 percent or less) than that observed near Hazelgreen. A flood event occurred on the Gasconade River in March 2008, and a flood measurement was obtained near the peak at State Highway 17. The elevation of high-water marks from that event indicated it was the highest measured flood on record with a measured discharge of 95,400 cubic feet per second, and a water-surface elevation of 766.18 feet near the location of the Waynesville gaging station. The measurements obtained for the March flood resulted in a shift of the original stage-discharge relation for the Waynesville gaging station, and the streamflow statistics were modified based on the new data. A two-dimensional hydrodynamic flow model was used to simulate flow conditions on the Gasconade River in the vicinity of State Highway 17. A model was developed that represents existing (2008) conditions on State Highway 17 (the 'model of existing conditions'), and was calibrated to the floods of March 20, 2008, December 4, 1982, and April 14, 1945. Modifications were made to the model of existing conditions to create a model that represents conditions along the same reach of the Gasconade
NASA Astrophysics Data System (ADS)
Komura, Yukihiro; Okabe, Yutaka
2013-01-01
We present multiple GPU computing with the common unified device architecture (CUDA) for the Swendsen-Wang multi-cluster algorithm of two-dimensional (2D) q-state Potts model. Extending our algorithm for single GPU computing [Y. Komura, Y. Okabe, GPU-based Swendsen-Wang multi-cluster algorithm for the simulation of two-dimensional classical spin systems, Comput. Phys. Comm. 183 (2012) 1155-1161], we realize the GPU computation of the Swendsen-Wang multi-cluster algorithm for multiple GPUs. We implement our code on the large-scale open science supercomputer TSUBAME 2.0, and test the performance and the scalability of the simulation of the 2D Potts model. The performance on Tesla M2050 using 256 GPUs is obtained as 37.3 spin flips per a nano second for the q=2 Potts model (Ising model) at the critical temperature with the linear system size L=65536.
NASA Astrophysics Data System (ADS)
Benna, M.; Piot, A.; Barriot, J.-P.; Kofman, W.
2002-11-01
To prepare the Comet Nucleus Sounding Experiment using Radio wave Transmission during the Rosetta mission, we study the electromagnetic wave propagation through a comet nucleus model and tomographic inversion in a two-dimensional setting. For the propagation, the Ray Tracing Method (RTM) is validated with respect to the Pseudo-Spectral Time Domain (PSTD) method. For the inverse problem, a Tikhonov-like inverse RTM method based on weak permittivity assumptions is used, with synthetic data derived from the PSTD algorithm. Reconstruction results show that the Consert data will permit a reliable tomography of the comet nucleus. Surface data will enhance the quality of the imaging.
Combis, Patrick; Cormont, Philippe; Hebert, David; Robin, Lucile; Rullier, Jean-Luc; Gallais, Laurent
2012-11-19
A self-consistent approach is proposed to determine the temperature dependent thermal conductivity k(T) of fused silica, for a range of temperatures up to material evaporation using a CO{sub 2} laser irradiation. Calculation of the temperature of silica using a two-dimensional axi-symmetric code was linked step by step as the laser power was increased with experimental measurements using infrared thermography. We show that previously reported k(T) does not reproduce the temporal profile as well as our adaptive fit which shows that k(T) evolves with slope discontinuities at the annealing temperature and the softening temperature.
Wang, Ping; Zhou, Ye; MacLaren, Stephan A.; Huntington, Channing M.; Raman, Kumar S.; Doss, Forrest W.; Flippo, Kirk A.
2015-11-06
Three- and two-dimensional numerical studies have been carried out to simulate recent counter-propagating shear flow experiments on the National Ignition Facility. A multi-physics three-dimensional, time-dependent radiation hydrodynamics simulation code is used. Using a Reynolds Averaging Navier-Stokes model, we show that the evolution of the mixing layer width obtained from the simulations agrees well with that measured from the experiments. A sensitivity study is conducted to illustrate a 3D geometrical effect that could confuse the measurement at late times, if the energy drives from the two ends of the shock tube are asymmetric. Implications for future experiments are discussed.
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.
Wang, Ping; Zhou, Ye MacLaren, Stephan A.; Huntington, Channing M.; Raman, Kumar S.; Doss, Forrest W.; Flippo, Kirk A.
2015-11-15
Three- and two-dimensional numerical studies have been carried out to simulate recent counter-propagating shear flow experiments on the National Ignition Facility. A multi-physics three-dimensional, time-dependent radiation hydrodynamics simulation code is used. Using a Reynolds Averaging Navier-Stokes model, we show that the evolution of the mixing layer width obtained from the simulations agrees well with that measured from the experiments. A sensitivity study is conducted to illustrate a 3D geometrical effect that could confuse the measurement at late times, if the energy drives from the two ends of the shock tube are asymmetric. Implications for future experiments are discussed.
Two-dimensional structure of the solar wind near the sun
Washimi, H.; Ogino, T.; Yoshino, Y.
1987-05-01
The two-dimensional structure of the solar wind near the sun is analyzed by the method of MHD simulation. The helmet-streamer configuration with a sharp boundary between the closed and open field regions has been reproduced. Due to the pressure-driven current in the sheet, the magnetic field, which has a dipole configuration at the photosphere, is found to behave like R/sup -2/ at a large distance, R, from the sun. copyrightAmerican Geophysical Union 1987
Zhang, Ya; Jiang, Wei; Song, Yuan-Hong; Wang, You-Nian
2015-02-15
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.
NASA Technical Reports Server (NTRS)
Stordal, F.; Isaksen, I. S. A.; Horntveth, K.
1985-01-01
Numerous studies have been concerned with the possibility of a reduction of the stratospheric ozone layer. Such a reduction could lead to an enhanced penetration of ultraviolet (UV) radiation to the ground, and, as a result, to damage in the case of several biological processes. It is pointed out that the distributions of many trace gases, such as ozone, are governed in part by transport processes. The present investigation presents a two-dimensional photochemistry-transport model using the residual circulation. The global distribution of both ozone and components with ground sources computed in this model is in good agreement with the observations even though slow diffusion is adopted. The agreement is particularly good in the Northern Hemisphere. The results provide additional support for the idea that tracer transport in the stratosphere is mainly of advective nature.
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)
Leggate, Huw; Turner, Miles
2016-09-01
We discuss a two-dimensional implementation of the particle-in-cell algorithm with Monte Carlo collisions. This implementation is designed for multiprocessor environments in which each processor is assumed to offer vector capabilities and multiple execution threads. An appropriate implementation therefore combines OpenMP to exploit multithreading with MPI to coupled computing nodes. This approach promises to achieve accelerations of a least a factor of several hundred, relative to to a simple serial implementation. However, the complexity involved also offers many opportunities for error, and makes correctness demonstrations especially desirable. In this presentation we discuss the characteristics of this parallel implementation, and we describe a suite of verification tests that collectively create a strong presumption that the code is correct. Work supported by the EUROfusion consortium.
Bychkov, Yu. I. Yampolskaya, S. A.; Yastremskii, A. G.
2013-05-15
The kinetic processes accompanying plasma column formation in an inhomogeneous discharge in a Ne/Xe/HCl gas mixture at a pressure of 4 atm were investigated by using a two-dimensional model. Two cathode spots spaced by 0.7 cm were initiated by distorting the cathode surface at local points, which resulted in an increase in the field strength in the cathode region. Three regimes differing in the charging voltage, electric circuit inductance, and electric field strength at the local cathode points were considered. The spatiotemporal distributions of the discharge current; the electron density; and the densities of excited xenon atoms, HCl(v = 0) molecules in the ground state, and HCl(v > 0) molecules in vibrational levels were calculated. The development of the discharge with increasing the electron density from 10{sup 4} to 10{sup 16} cm{sup -3} was analyzed, and three characteristic stages in the evolution of the current distribution were demonstrated. The width of the plasma column was found to depend on the energy deposited in the discharge. The width of the plasma column was found to decrease in inverse proportion to the deposited energy due to spatiotemporal variations in the rates of electron production and loss. The calculated dependences of the cross-sectional area of the plasma column on the energy deposited in the discharge agree with the experimental results.
Mallari, K J B; Kim, H; Pak, G; Aksoy, H; Yoon, J
2015-01-01
At the hillslope scale, where the rill-interrill configuration plays a significant role, infiltration is one of the major hydrologic processes affecting the generation of overland flow. As such, it is important to achieve a good understanding and accurate modelling of this process. Horton's infiltration has been widely used in many hydrologic models, though it has been occasionally found limited in handling adequately the antecedent moisture conditions (AMC) of soil. Holtan's model, conversely, is thought to be able to provide better estimation of infiltration rates as it can directly account for initial soil water content in its formulation. In this study, the Holtan model is coupled to an existing overland flow model, originally using Horton's model to account for infiltration, in an attempt to improve the prediction of runoff. For calibration and validation, experimental data from a two-dimensional flume which is incorporated with hillslope configuration have been used. Calibration and validation results showed that Holtan's model was able to improve the modelling results with better performance statistics than the Horton-coupled model. Holtan's infiltration equation, which allows accounting for AMC, provided an advantage and resulted in better runoff prediction of the model.
NASA Astrophysics Data System (ADS)
Kim, Jeongmin; Sung, Bong June
2015-03-01
Near the glass transition, translation is often faster than expected from the viscosity of liquids unlike rotation. It is the well-known translation-rotation decoupling phenomenon. In this poster, we present the dependence of the decoupling on tracer shape in two-dimensional (2D) colloids using three representative tracer shapes (diamond, distorted diamond and square). We find that near the freezing (liquid-hexatic) transition, the translation-rotation decoupling occurs for all tracers regardless of shapes, but trends are different for different shape. In 2D, there exists an orientationally ordered liquid phase called a hexatic phase between isotropic liquid and solid phases. Entering the hexatic phase, 2D colloids exhibit the heterogeneous dynamics with several dynamic regions of different mobility like glass-forming liquids. We find that the observed decoupling of tracer diffusion is attributed to the dynamic heterogeneity of 2D colloids. To our surprise, the shape-dependence of decoupling trend relate closely to the rotational diffusion of tracers. Square shape tracer disturbs the hexagonal ordering of 2D colloids, thus resulting in faster rotation of square tracers, which is not observed for diamond shape tracers.
MHD simulations for investigating interaction processes between a CME and ambient solar wind
NASA Astrophysics Data System (ADS)
An, Junmo; Magara, Tetsuya
2016-05-01
The interaction between coronal mass ejections (CMEs) and ambient solar winds is one of the important issues of space weather because it affects the trajectory of a flying CME, which determines whether the CME hits the Earth and produces geomagnetic disturbances or not. In this study, two-step 3D magnetohydrodynamic (MHD) simulations including a spheromak-type CME and an ambient solar wind are performed to investigate their interaction processes such as deflection and rotation of a CME. We perform the 1st-step MHD simulation using averaged surface magnetic field data to construct a steady state with an ambient solar wind. A spheromak-type CME is then injected through the solar surface, and subsequent evolution is reproduced by performing the 2nd-step MHD simulation. We discuss key parameters that characterize interaction processes between a CME and ambient solar wind.
Accuracy of MHD simulations: Effects of simulation initialization in GUMICS-4
NASA Astrophysics Data System (ADS)
Lakka, Antti; Pulkkinen, Tuija; Dimmock, Andrew; Osmane, Adnane; Palmroth, Minna; Honkonen, Ilja
2016-04-01
We conducted a study aimed at revealing how different global magnetohydrodynamic (MHD) simulation initialization methods affect the dynamics in different parts of the Earth's magnetosphere-ionosphere system. While such magnetosphere-ionosphere coupling codes have been used for more than two decades, their testing still requires significant work to identify the optimal numerical representation of the physical processes. We used the Grand Unified Magnetosphere-Ionosphere Coupling Simulation (GUMICS-4), the only European global MHD simulation being developed by the Finnish Meteorological Institute. GUMICS-4 was put to a test that included two stages: 1) a 10 day Omni data interval was simulated and the results were validated by comparing both the bow shock and the magnetopause spatial positions predicted by the simulation to actual measurements and 2) the validated 10 day simulation run was used as a reference in a comparison of five 3 + 12 hour (3 hour synthetic initialisation + 12 hour actual simulation) simulation runs. The 12 hour input was not only identical in each simulation case but it also represented a subset of the 10 day input thus enabling quantifying the effects of different synthetic initialisations on the magnetosphere-ionosphere system. The used synthetic initialisation data sets were created using stepwise, linear and sinusoidal functions. Switching the used input from the synthetic to real Omni data was immediate. The results show that the magnetosphere forms in each case within an hour after the switch to real data. However, local dissimilarities are found in the magnetospheric dynamics after formation depending on the used initialisation method. This is evident especially in the inner parts of the lobe.
Integrated Physics Advances in Simulation of Wave Interactions with Extended MHD Phenomena
Batchelor, Donald B; D'Azevedo, Eduardo; Bateman, Glenn; Bernholdt, David E; Berry, Lee A; Bonoli, P.; Bramley, R; Breslau, J.; Chance, M.; Chen, J.; Choi, M.; Elwasif, Wael R; Fu, GuoYong; Harvey, R. W.; Houlberg, Wayne A; Jaeger, Erwin Frederick; Jardin, S. C.; Keyes, David E; Klasky, Scott A; Kruger, Scott; Ku, Long-Poe; McCune, Douglas; Schissel, D.; Schnack, D.; Wright, J. C.
2007-06-01
The broad scientific objectives of the SWIM (Simulation of Wave Interaction with MHD) project are: (A) To improve our understanding of interactions that both RF wave and particle sources have on extended-MHD phenomena, and to substantially improve our capability for predicting and optimizing the performance of burning plasmas in devices such as ITER: and (B) To develop an integrated computational system for treating multi-physics phenomena with the required flexibility and extensibility to serve as a prototype for the Fusion Simulation Project (FSP).
Maier, Thomas A; Alvarez, Gonzalo; Summers, Michael Stuart; Schulthess, Thomas C
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)
Liu, Yue; Booth, Jean-Paul; Chabert, Pascal; cold plasma Team, LPP Team
2016-09-01
The majority of previous two dimensional (usually fluid) simulations of radio frequency capacitively coupled plasmas have focused on geometrically-asymmetric reactors (with a much larger grounded electrode than power electrode), which produces a strong dc self-bias. However, a commonly-used geometry comprises electrodes of equal area surrounded by a dielectric side wall, but this has not been widely simulated. We have developed a two dimensional (Cartesian) PIC/MC code based on the work of Hongyu Wang, Wei Jiang and Younian Wang, to simulate argon plasmas in this kind of chamber. Even using a thick dielectric, a peak in plasma density and electron power deposition is adjacent to the dielectric. The profiles of the electron and ion fluxes show that the period-averaged currents to the powered electrode are not locally balanced; the electron flux peaks closer to the dielectric edge, before dropping sharply. Finally, the effect of the dielectric thickness on the surface charge distribution and the angular distributions of ions arriving at boundaries is examined. This work is supported by China Scholarship Council.
Davis, Joe M
2004-04-01
The correlation of retention times in comprehensive two-dimensional gas chromatography caused by correlation of enthalpy and entropy changes between two stationary phases, methylsilicone and poly(ethylene glycol), was examined using commercial GC software and in-house Monte Carlo simulation. The enthalpy change, deltaH0, and entropy change, deltaS0, of 93 compounds were predicted from isothermal one-dimensional gas chromatograms predicted by the software. These values then were mimicked by Monte Carlo simulation, which removed the strong correlation of deltaH0 and modest correlation of deltaS0 between the two phases. Retention times in a comprehensive two-dimensional gas chromatogram (GC x GC) and in simulations of it were predicted for typical dual-capillary temperature-programmed conditions using the actual, correlated values of deltaH0 and deltaS0 and their uncorrelated Monte Carlo counterparts, respectively. The uncorrelated deltaH0 and deltaS0 values caused the retention-time range of the simulations' second dimension to expand substantially beyond that in the GC x GC. Other simulations were developed using a restricted range of uncorrelated deltaH0 and deltaS0 values to mimic more closely the retention-time range of the GC x GC's second dimension. The intervals between nearest neighbor retention-time coordinates were calculated in both the latter simulations and the GC x GC. The intervals were larger in the simulations than in the GC x GC because the former contained uncorrelated coordinates and the latter contained correlated ones, which clustered along or near the diagonal. The retention times in the first dimension of the GC x GC were Poisson distributed, as assessed by statistical-overlap theory. In contrast, the two-dimensional reduced retention-time coordinates in the GC x GC were not Poisson distributed, because retention times were correlated. However, the reduced retention-time coordinates in the simulations were Poisson distributed.
Gustavsen, Arlid; Kohler, Christian; Dalehaug, Arvid; Arasteh, Dariush
2008-12-01
This paper assesses the accuracy of the simplified frame cavity conduction/convection and radiation models presented in ISO 15099 and used in software for rating and labeling window products. Temperatures and U-factors for typical horizontal window frames with internal cavities are compared; results from Computational Fluid Dynamics (CFD) simulations with detailed radiation modeling are used as a reference. Four different frames were studied. Two were made of polyvinyl chloride (PVC) and two of aluminum. For each frame, six different simulations were performed, two with a CFD code and four with a building-component thermal-simulation tool using the Finite Element Method (FEM). This FEM tool addresses convection using correlations from ISO 15099; it addressed radiation with either correlations from ISO 15099 or with a detailed, view-factor-based radiation model. Calculations were performed using the CFD code with and without fluid flow in the window frame cavities; the calculations without fluid flow were performed to verify that the CFD code and the building-component thermal-simulation tool produced consistent results. With the FEM-code, the practice of subdividing small frame cavities was examined, in some cases not subdividing, in some cases subdividing cavities with interconnections smaller than five millimeters (mm) (ISO 15099) and in some cases subdividing cavities with interconnections smaller than seven mm (a breakpoint that has been suggested in other studies). For the various frames, the calculated U-factors were found to be quite comparable (the maximum difference between the reference CFD simulation and the other simulations was found to be 13.2 percent). A maximum difference of 8.5 percent was found between the CFD simulation and the FEM simulation using ISO 15099 procedures. The ISO 15099 correlation works best for frames with high U-factors. For more efficient frames, the relative differences among various simulations are larger. Temperature was also
NASA Astrophysics Data System (ADS)
Mayer, M.; Malinský, P.; Schiettekatte, F.; Zolnai, Z.
2016-10-01
The codes RBS-MAST, STRUCTNRA, F95-Rough and CORTEO are simulation codes for ion beam analysis spectra from two- or three-dimensional sample structures. The codes were intercompared in a code-code comparison using an idealized grating structure and by comparison to experimental data from a silicon grating on tantalum interlayer. All codes are in excellent agreement at higher incident energies and not too large energy losses. At lower incident energies, grazing angles of incidence and/or larger energy losses plural scattering effects play an increasing role. Simulation codes with plural scattering capabilities offer higher accuracy and better agreement to experimental results in this regime.
NASA Astrophysics Data System (ADS)
Christ, John A.; Lemke, Lawrence D.; Abriola, Linda M.
2005-01-01
The influence of reduced dimensionality (two-dimensional (2-D) versus 3-D) on predictions of dense nonaqueous phase liquid (DNAPL) infiltration and entrapment in statistically homogeneous, nonuniform permeability fields was investigated using the University of Texas Chemical Compositional Simulator (UTCHEM), a 3-D numerical multiphase simulator. Hysteretic capillary pressure-saturation and relative permeability relationships implemented in UTCHEM were benchmarked against those of another lab-tested simulator, the Michigan-Vertical and Lateral Organic Redistribution (M-VALOR). Simulation of a tetrachloroethene spill in 16 field-scale aquifer realizations generated DNAPL saturation distributions with approximately equivalent distribution metrics in two and three dimensions, with 2-D simulations generally resulting in slightly higher maximum saturations and increased vertical spreading. Variability in 2-D and 3-D distribution metrics across the set of realizations was shown to be correlated at a significance level of 95-99%. Neither spill volume nor release rate appeared to affect these conclusions. Variability in the permeability field did affect spreading metrics by increasing the horizontal spreading in 3-D more than in 2-D in more heterogeneous media simulations. The assumption of isotropic horizontal spatial statistics resulted, on average, in symmetric 3-D saturation distribution metrics in the horizontal directions. The practical implication of this study is that for statistically homogeneous, nonuniform aquifers, 2-D simulations of saturation distributions are good approximations to those obtained in 3-D. However, additional work will be needed to explore the influence of dimensionality on simulated DNAPL dissolution.
NASA Astrophysics Data System (ADS)
Wang, Ping; Raman, Kumar; MacLaren, Stephan; Huntington, Channing; Nagel, Sabrina
2016-10-01
We present simulations of recent high-energy-density (HED) re-shock experiments on the National Ignition Facility (NIF). The experiments study the Rayleigh-Taylor (RT) and Richtmyer-Meshkov (RM) instability growth that occurs after successive shocks transit a sinusoidally-perturbed interface between materials of different densities. The shock tube is driven at one or both ends using indirect-drive laser cavities or hohlraums. X-ray area-backlit imaging is used to visualize the growth at different times. Our simulations are done with the three-dimensional, radiation hydrodynamics code ARES, developed at LLNL. We show the instabilitygrowth rate, inferred from the experimental radiographs, agrees well with our 2D and 3D simulations. We also discuss some 3D geometrical effects, suggested by our simulations, which could deteriorate the images at late times, unless properly accounted for in the experiment design. Work supported by U.S. Department of Energy under Contract DE- AC52-06NA27279. LLNL-ABS-680789.
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. PMID:21261335
Chiang, Yun-Wei; Freed, Jack H
2011-01-21
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)
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.
Plasma wave signatures in the magnetotail reconnection region - MHD simulation and ray tracing
NASA Technical Reports Server (NTRS)
Omura, Yoshiharu; Green, James L.
1993-01-01
An MHD simulation was performed to obtain a self-consistent model of magnetic field and plasma density near the X point reconnection region. The MHD model was used to perform extensive ray tracing calculations in order to clarify the propagation characteristics of the plasma waves near the X point reconnection region. The dynamic wave spectra possibly observed by the Geotail spacecraft during a typical cross-tail trajectory are reconstructed. By comparing the extensive ray tracing calculations with the plasma wave data from Geotail, it is possible to perform a kind of 'remote sensing' to identify the location and structure of potential X point reconnection regions.
AMPEL experiments: nitric-oxide concentration measurements in a simulated MHD combustion gas
Dunn, P. F.; Johnson, T. R.; Reed, C. B.
1980-12-01
Results are presented of recent investigations of the effect of secondary combustion on nitric oxide (NO) concentrations in an simulated magnetohydrodynamic (MHD) combustion gas. Forty-one experiments, in which NO concentration measurements were made, were conducted at the Argonne MHD Process Engineering Laboratory (AMPEL). In sixteen of those experiments, secondary air mixed with the primary combustion gas was combusted over two temperature ranges (1500-1800/sup 0/K and 1700-2000/sup 0/K). For all clean-fuel experiments conducted, the measured changes in NO concentration that resulted from secondary combustion were predicted to within 10%, using an Argonne modification of the NASA chemical kinetics code. This predictive code was extended to estimate changes in NO concentrations that would occur during secondary combustion in a larger MHD facility. It is concluded that, in addition to mixing and several other factors, the heat loss from the secondary combustion zone strongly influences the amount of NO formed during secondary combustion.
2014-09-26
linear electronic specific heat disappears in strong magnetic fields if Landau levels are not broadened. Thus, the amplitude of the magnetothermal...Molec. Crys. Liq. Crys. 121, 169 (1984). In consideration of mixing of low-lying Landau levels, the magneto- conductance of two-dimensional electrons...and narrowing can be explained when the Landau level filling factor v is larger than 1. Actually, we have shown that the resonance phenomena are
Two-dimensional numerical simulation of O-mode to Z-mode conversion in the ionosphere
NASA Astrophysics Data System (ADS)
Cannon, P. D.; Honary, F.; Borisov, N.
2016-03-01
Experiments in the illumination of the F region of the ionosphere via radio frequency waves polarized in the ordinary mode (O-mode) have revealed that the magnitude of artificial heating-induced effects depends strongly on the inclination angle of the pump beam, with a greater modification to the plasma observed when the heating beam is directed close to or along the magnetic zenith direction. Numerical simulations performed using a recently developed finite-difference time-domain (FDTD) code are used to investigate the contribution of the O-mode to Z-mode conversion process to this effect. The aspect angle dependence and angular size of the radio window for which conversion of an O-mode pump wave to the Z-mode occurs is simulated for a variety of plasma density profiles including 2-D linear gradients representative of large-scale plasma depletions, density-depleted plasma ducts, and periodic field-aligned irregularities. The angular shape of the conversion window is found to be strongly influenced by the background plasma profile. If the Z-mode wave is reflected, it can propagate back toward the O-mode reflection region leading to resonant enhancement of the electric field in this region. Simulation results presented in this paper demonstrate that this process can make a significant contribution to the magnitude of electron density depletion and temperature enhancement around the resonance height and contributes to a strong dependence of the magnitude of plasma perturbation with the direction of the pump wave.
High fidelity studies of exploding foil initiator bridges, Part 3: ALEGRA MHD simulations
NASA Astrophysics Data System (ADS)
Neal, William; Garasi, Christopher
2017-01-01
Simulations of high voltage detonators, such as Exploding Bridgewire (EBW) and Exploding Foil Initiators (EFI), have historically been simple, often empirical, one-dimensional models capable of predicting parameters such as current, voltage, and in the case of EFIs, flyer velocity. Experimental methods have correspondingly generally been limited to the same parameters. With the advent of complex, first principles magnetohydrodynamic codes such as ALEGRA and ALE-MHD, it is now possible to simulate these components in three dimensions, and predict a much greater range of parameters than before. A significant improvement in experimental capability was therefore required to ensure these simulations could be adequately verified. In this third paper of a three part study, the experimental results presented in part 2 are compared against 3-dimensional MHD simulations. This improved experimental capability, along with advanced simulations, offer an opportunity to gain a greater understanding of the processes behind the functioning of EBW and EFI detonators.
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
NASA Astrophysics Data System (ADS)
Wiltberger, M. J.; Lyon, J.; Elkington, S. R.; Merkin, V. G.
2013-12-01
Global scale magnetohydrodynamic simulations have been used to successfully study the evolution of the magnetosphere-ionosphere system under a variety of solar wind conditions. Early studies with the Lyon-Fedder-Mobarry (LFM) model show the presence of flow channels in substorm simulations that had characteristics similar to those seen in observations of bursty bulk flows (BBFs) observed by numerous spacecraft, such as AMPTE and Geotail. More recently the THEMIS constellation has provided a unique opportunity to track the evolution of dipolarization fronts (DFs) from the mid-tail into the inner magnetosphere. Additionally, advances in high performance computing capability make it possible to conduct ultra-high resolution global simulations. In this paper we present comparisons between these ultra-high resolution simulations and the observations of THEMIS. The comparisons include a case study for a DF that was well observed on February 27, 2009 and statistical properties of the flow and electromagnetic field signatures seen in observations and MHD simulations with idealized solar wind conditions. In addition to these comparisons we will present results of using test-particle simulations of electrons driven by the simulated fields to study particle energization in regions around DFs.
NASA Astrophysics Data System (ADS)
Almarza, N. G.; PÈ©kalski, J.; Ciach, A.
2014-04-01
The triangular lattice model with nearest-neighbor attraction and third-neighbor repulsion, introduced by Pȩkalski, 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.
Yoon, E. S.; Chang, C. S.
2014-03-15
An approximate two-dimensional solver of the nonlinear Fokker-Planck-Landau collision operator has been developed using the assumption that the particle probability distribution function is independent of gyroangle in the limit of strong magnetic field. The isotropic one-dimensional scheme developed for nonlinear Fokker-Planck-Landau equation by Buet and Cordier [J. Comput. Phys. 179, 43 (2002)] and for linear Fokker-Planck-Landau equation by Chang and Cooper [J. Comput. Phys. 6, 1 (1970)] have been modified and extended to two-dimensional nonlinear equation. In addition, a method is suggested to apply the new velocity-grid based collision solver to Lagrangian particle-in-cell simulation by adjusting the weights of marker particles and is applied to a five dimensional particle-in-cell code to calculate the neoclassical ion thermal conductivity in a tokamak plasma. Error verifications show practical aspects of the present scheme for both grid-based and particle-based kinetic codes.
Halliday, I; Lishchuk, S V; Spencer, T J; Pontrelli, G; Evans, P C
2016-08-01
We present a method for applying a class of velocity-dependent forces within a multicomponent lattice Boltzmann equation simulation that is designed to recover continuum regime incompressible hydrodynamics. This method is applied to the problem, in two dimensions, of constraining to uniformity the tangential velocity of a vesicle membrane implemented within a recent multicomponent lattice Boltzmann simulation method, which avoids the use of Lagrangian boundary tracers. The constraint of uniform tangential velocity is carried by an additional contribution to an immersed boundary force, which we derive here from physical arguments. The result of this enhanced immersed boundary force is to apply a physically appropriate boundary condition at the interface between separated lattice fluids, defined as that region over which the phase-field varies most rapidly. Data from this enhanced vesicle boundary method are in agreement with other data obtained using related methods [e.g., T. Krüger, S. Frijters, F. Günther, B. Kaoui, and J. Harting, Eur. Phys. J. 222, 177 (2013)10.1140/epjst/e2013-01834-y] and underscore the importance of a correct vesicle membrane condition.
NASA Astrophysics Data System (ADS)
Halliday, I.; Lishchuk, S. V.; Spencer, T. J.; Pontrelli, G.; Evans, P. C.
2016-08-01
We present a method for applying a class of velocity-dependent forces within a multicomponent lattice Boltzmann equation simulation that is designed to recover continuum regime incompressible hydrodynamics. This method is applied to the problem, in two dimensions, of constraining to uniformity the tangential velocity of a vesicle membrane implemented within a recent multicomponent lattice Boltzmann simulation method, which avoids the use of Lagrangian boundary tracers. The constraint of uniform tangential velocity is carried by an additional contribution to an immersed boundary force, which we derive here from physical arguments. The result of this enhanced immersed boundary force is to apply a physically appropriate boundary condition at the interface between separated lattice fluids, defined as that region over which the phase-field varies most rapidly. Data from this enhanced vesicle boundary method are in agreement with other data obtained using related methods [e.g., T. Krüger, S. Frijters, F. Günther, B. Kaoui, and J. Harting, Eur. Phys. J. 222, 177 (2013), 10.1140/epjst/e2013-01834-y] and underscore the importance of a correct vesicle membrane condition.
NASA Technical Reports Server (NTRS)
Fleming, Eric L.; Jackman, Charles H.; Considine, David B.; Stolarski, Richard S.
1999-01-01
In this study, we examine the sensitivity of long lived tracers to changes in the base transport components in our 2-D model. Changes to the strength of the residual circulation in the upper troposphere and stratosphere and changes to the lower stratospheric K(sub zz) had similar effects in that increasing the transport rates decreased the overall stratospheric mean age, and increased the rate of removal of material from the stratosphere. Increasing the stratospheric K(sub yy) increased the mean age due to the greater recycling of air parcels through the middle atmosphere, via the residual circulation, before returning to the troposphere. However, increasing K(sub yy) along with self-consistent increases in the corresponding planetary wave drive, which leads to a stronger residual circulation, more than compensates for the K(sub yy)-effect, and produces significantly younger ages throughout the stratosphere. Simulations with very small tropical stratospheric K(sub yy) decreased the globally averaged age of air by as much as 25% in the middle and upper stratosphere, and resulted in substantially weaker vertical age gradients above 20 km in the extratropics. We found only very small stratospheric tracer sensitivity to the magnitude of the horizontal mixing across the tropopause, and to the strength of the mesospheric gravity wave drag and diffusion used in the model. We also investigated the transport influence on chemically active tracers and found a strong age-tracer correlation, both in concentration and calculated lifetimes. The base model transport gives the most favorable overall comparison with a variety of inert tracer observations, and provides a significant improvement over our previous 1995 model transport. Moderate changes to the base transport were found to provide modest agreement with some of the measurements. Transport scenarios with residence times ranging from moderately shorter to slightly longer relative to the base case simulated N2O lifetimes
NASA Astrophysics Data System (ADS)
Shukla, Chandrasekhar; Das, Amita; Patel, Kartik
2016-08-01
We carry out particle-in-cell simulations to study the instabilities associated with a 2-D sheared electron flow configuration against a neutralizing background of ions. Both weak and strong relativistic flow velocities are considered. In the weakly relativistic case, we observe the development of electromagnetic Kelvin-Helmholtz instability with similar characteristics as that predicted by the electron Magnetohydrodynamic (EMHD) model. On the contrary, in a strong relativistic case, the compressibility effects of electron fluid dominate and introduce upper hybrid electrostatic oscillations transverse to the flow which are very distinct from EMHD fluid behavior. In the nonlinear regime, both weak and strong relativistic cases lead to turbulence with broad power law spectrum.
Djouder, M. Kermoun, F.; Mitiche, M. D.; Lamrous, O.
2016-01-15
Dust particles observed in universe as well as in laboratory and technological plasma devices are still under investigation. At low temperature, these particles are strongly negatively charged and are able to form a 2D or 3D coulomb crystal. In this work, our aim was to check the ideal gas law validity for a 2D single-layer dust crystal recently reported in the literature. For this purpose, we have simulated, using the molecular dynamics method, its thermodynamic properties for different values of dust particles number and confinement parameters. The obtained results have allowed us to invalidate the ideal gas behaviour and to propose an effective equation of state which assumes a near zero dust temperature. Furthermore, the value of the calculated sound velocity was found to be in a good agreement with experimental data published elsewhere.
Northrop, Paul W. C.; Pathak, Manan; Rife, Derek; ...
2015-03-09
Lithium-ion batteries are an important technology to facilitate efficient energy storage and enable a shift from petroleum based energy to more environmentally benign sources. Such systems can be utilized most efficiently if good understanding of performance can be achieved for a range of operating conditions. Mathematical models can be useful to predict battery behavior to allow for optimization of design and control. An analytical solution is ideally preferred to solve the equations of a mathematical model, as it eliminates the error that arises when using numerical techniques and is usually computationally cheap. An analytical solution provides insight into the behaviormore » of the system and also explicitly shows the effects of different parameters on the behavior. However, most engineering models, including the majority of battery models, cannot be solved analytically due to non-linearities in the equations and state dependent transport and kinetic parameters. The numerical method used to solve the system of equations describing a battery operation can have a significant impact on the computational cost of the simulation. In this paper, a model reformulation of the porous electrode pseudo three dimensional (P3D) which significantly reduces the computational cost of lithium ion battery simulation, while maintaining high accuracy, is discussed. This reformulation enables the use of the P3D model into applications that would otherwise be too computationally expensive to justify its use, such as online control, optimization, and parameter estimation. Furthermore, the P3D model has proven to be robust enough to allow for the inclusion of additional physical phenomena as understanding improves. In this study, the reformulated model is used to allow for more complicated physical phenomena to be considered for study, including thermal effects.« less
Northrop, Paul W. C.; Pathak, Manan; Rife, Derek; De, Sumitava; Santhanagopalan, Shriram; Subramanian, Venkat R.
2015-03-09
Lithium-ion batteries are an important technology to facilitate efficient energy storage and enable a shift from petroleum based energy to more environmentally benign sources. Such systems can be utilized most efficiently if good understanding of performance can be achieved for a range of operating conditions. Mathematical models can be useful to predict battery behavior to allow for optimization of design and control. An analytical solution is ideally preferred to solve the equations of a mathematical model, as it eliminates the error that arises when using numerical techniques and is usually computationally cheap. An analytical solution provides insight into the behavior of the system and also explicitly shows the effects of different parameters on the behavior. However, most engineering models, including the majority of battery models, cannot be solved analytically due to non-linearities in the equations and state dependent transport and kinetic parameters. The numerical method used to solve the system of equations describing a battery operation can have a significant impact on the computational cost of the simulation. In this paper, a model reformulation of the porous electrode pseudo three dimensional (P3D) which significantly reduces the computational cost of lithium ion battery simulation, while maintaining high accuracy, is discussed. This reformulation enables the use of the P3D model into applications that would otherwise be too computationally expensive to justify its use, such as online control, optimization, and parameter estimation. Furthermore, the P3D model has proven to be robust enough to allow for the inclusion of additional physical phenomena as understanding improves. In this study, the reformulated model is used to allow for more complicated physical phenomena to be considered for study, including thermal effects.
Comparison of empirical magnetic field models and global MHD simulations: The near-tail currents
NASA Technical Reports Server (NTRS)
Pulkkinen, T. I.; Baker, D. N.; Walker, R. J.; Raeder, J.; Ashour-Abdalla, M.
1995-01-01
The tail currents predicted by empirical magnetic field models and global MHD simulations are compared. It is shown that the near-Earth currents obtained from the MHD simulations are much weaker than the currents predicted by the Tsyganenko models, primarily because the ring current is not properly represented in the simulations. On the other hand, in the mid-tail and distant tail the lobe field strength predicted by the simulations is comparable to what is observed at about 50 R(sub E) distance, significantly larger than the very low lobe field values predicted by the Tsyganenko models at that distance. Ways to improve these complementary approaches to model the actual magnetospheric configuration are discussed.
Magnetic fields in protoplanetary discs: from MHD simulations to ALMA observations
NASA Astrophysics Data System (ADS)
Bertrang, G. H.-M.; Flock, M.; Wolf, S.
2017-01-01
Magnetic fields significantly influence the evolution of protoplanetary discs and the formation of planets, following the predictions of numerous magnetohydrodynamic (MHD) simulations. However, these predictions are yet observationally unconstrained. To validate the predictions on the influence of magnetic fields on protoplanetary discs, we apply 3D radiative transfer simulations of the polarized emission of aligned aspherical dust grains that directly link 3D global non-ideal MHD simulations to Atacama Large Millimeter/submillimeter Array (ALMA) observations. Our simulations show that it is feasible to observe the predicted toroidal large-scale magnetic field structures, not only in the ideal observations but also with high-angular resolution ALMA observations. Our results show further that high-angular resolution observations by ALMA are able to identify vortices embedded in outer magnetized disc regions.
2-D MHD numerical simulations of EML plasma armatures with ablation
NASA Astrophysics Data System (ADS)
Boynton, G. C.; Huerta, M. A.; Thio, Y. C.
1993-01-01
We use a 2-D) resistive MHD code to simulate an EML plasma armature. The energy equation includes Ohmic heating, radiation heat transport and the ideal gas equation of state, allowing for variable ionization using the Saha equations. We calculate rail ablation taking into account the flow of heat into the interior of the rails. Our simulations show the development of internal convective flows and secondary arcs. We use an explicit Flux Corrected Transport algorithm to advance all quantities in time.
NASA Technical Reports Server (NTRS)
Juday, Richard D. (Inventor)
1992-01-01
A two-dimensional vernier scale is disclosed utilizing a cartesian grid on one plate member with a polar grid on an overlying transparent plate member. The polar grid has multiple concentric circles at a fractional spacing of the spacing of the cartesian grid lines. By locating the center of the polar grid on a location on the cartesian grid, interpolation can be made of both the X and Y fractional relationship to the cartesian grid by noting which circles coincide with a cartesian grid line for the X and Y direction.
NASA Astrophysics Data System (ADS)
Rhee, Hyop S.; Begg, Lester L.; Wetch, Joseph R.; Jang, Jong H.; Juhasz, Albert J.
An innovative pumped loop concept for 600 K space power system radiators utilizing direct contact heat transfer, which facilitates repeated startup/shutdown of the power system without complex and time-consuming coolant thawing during power startup, is under development. The heat transfer process with melting/freezing of Li in an NaK flow was studied through two-dimensional time-dependent numerical simulations to characterize and predict the Li/NaK radiator performance during startup (thawing) and shutdown (cold-trapping). Effects of system parameters and the criteria for the plugging domain are presented together with temperature distribution patterns in solid Li and subsequent melting surface profile variations in time.
NASA Astrophysics Data System (ADS)
Noge, Hiroshi; Saito, Kimihiko; Sato, Aiko; Kaneko, Tetsuya; Kondo, Michio
2015-08-01
The performance of interdigitated back contact silicon heterojunction solar cells having overlapped p/i and n/i a-Si:H layers on the back has been investigated by two-dimensional simulation in comparison with the conventional cell structure having a gap between p/i and n/i layers. The results show that narrower overlap width leads to higher short circuit current and conversion efficiency, especially for poor heterojunction interface and thinner silicon substrate of the cells in addition to narrower uncovered width of p/i layer by a metal electrode. This is similar to the gap width dependence in the conventional cells, since both overlap and gap act as dead area for diffused excess carriers in the back contacts.
NASA Astrophysics Data System (ADS)
Tahir, N. A.; Kim, V.; Lamour, E.; Lomonosov, I. V.; Piriz, A. R.; Rozet, J. P.; Stöhlker, Th.; Sultanov, V.; Vernhet, D.
2012-11-01
In this paper we report on two-dimensional numerical simulations of heating of a rotating, wheel shaped target impacted by the full intensity of the ion beam that will be delivered by the SPIRAL2 facility at Caen, France. The purpose of this work is to study heating of solid targets that will be used to strip the fast ions of SPIRAL2 to the required high charge state for the FISIC (Fast Ion-Slow Ion Collision) experiments. Strippers of aluminum with different emissivities and of carbon are exposed to high beam current of different ion species as oxygen, neon and argon. These studies show that carbon, due to its much higher sublimation temperature and much higher emissivity, is more favorable compared to aluminum. For the highest beam intensities, an aluminum stripper does not survive. However, problem of the induced thermal stresses and long term material fatigue needs to be investigated before a final conclusion can be drawn.
NASA Astrophysics Data System (ADS)
Suryavanshi, Saurabh V.; Pop, Eric
2016-12-01
We present a physics-based compact model for two-dimensional (2D) field-effect transistors (FETs) based on monolayer semiconductors such as MoS2. A semi-classical transport approach is appropriate for the 2D channel, enabling simplified analytical expressions for the drain current. In addition to intrinsic FET behavior, the model includes contact resistance, traps and impurities, quantum capacitance, fringing fields, high-field velocity saturation, and self-heating, the latter being found to play an important role. The model is calibrated with state-of-the-art experimental data for n- and p-type 2D-FETs, and it can be used to analyze device properties for sub-100 nm gate lengths. Using the experimental fit, we demonstrate the feasibility of circuit simulations using properly scaled devices. The complete model is implemented in SPICE-compatible Verilog-A, and a downloadable version is freely available at the nanoHUB.org.
Statistical properties of two-dimensional magnetohydrodynamic turbulence
NASA Astrophysics Data System (ADS)
Biskamp, D.; Welter, H.; Walter, M.
1990-12-01
The statistical properties of two-dimensional (2-D) magnetohydrodynamic (MHD) turbulence are studied by means of high-resolution numerical simulations. As a theoretical point of reference, the β model of intermittent turbulence is adapted to the MHD case. Comparison of simulation results for energy spectra with the β-model predictions shows intermittency corrections to be small, δ<0.2, while fourth-order correlation functions exhibit a stronger effect δ≂0.35, consistent with the numerically observed Reynolds-number dependence of the flatness factor F∝R1/2λ. An argument is given that this scaling valid for Rλ˜102 is, however, not characteristic of the asymptotic regime Rλ→∞, where a constant value of F is to be expected. The probability distributions of the field difference δv(x,t), δB(x,t) are Gaussian for large separation x or t, approaching an approximately exponential distribution for x, t→0. This behavior can be understood by a simple probabilistic argument. The probability distribution of the local energy dissipation rate ɛ is roughly consistent with a log-normal distribution at larger ɛ but shows a different behavior at small ɛ.
NASA Astrophysics Data System (ADS)
Westerhof, E.; de Blank, H. J.; Pratt, J.
2016-03-01
Two dimensional reduced MHD simulations of neoclassical tearing mode growth and suppression by ECCD are performed. The perturbation of the bootstrap current density and the EC drive current density perturbation are assumed to be functions of the perturbed flux surfaces. In the case of ECCD, this implies that the applied power is flux surface averaged to obtain the EC driven current density distribution. The results are consistent with predictions from the generalized Rutherford equation using common expressions for Δ \\text{bs}\\prime and Δ \\text{ECCD}\\prime . These expressions are commonly perceived to describe only the effect on the tearing mode growth of the helical component of the respective current perturbation acting through the modification of Ohm’s law. Our results show that they describe in addition the effect of the poloidally averaged current density perturbation which acts through modification of the tearing mode stability index. Except for modulated ECCD, the largest contribution to the mode growth comes from this poloidally averaged current density perturbation.
Zhao, Bin; Wang, Shuxiao; Donahue, Neil M; Chuang, Wayne; Hildebrandt Ruiz, Lea; Ng, Nga L; Wang, Yangjun; Hao, Jiming
2015-02-17
We evaluate the one-dimensional volatility basis set (1D-VBS) and two-dimensional volatility basis set (2D-VBS) in simulating the aging of SOA derived from toluene and α-pinene against smog-chamber experiments. If we simulate the first-generation products with empirical chamber fits and the subsequent aging chemistry with a 1D-VBS or a 2D-VBS, the models mostly overestimate the SOA concentrations in the toluene oxidation experiments. This is because the empirical chamber fits include both first-generation oxidation and aging; simulating aging in addition to this results in double counting of the initial aging effects. If the first-generation oxidation is treated explicitly, the base-case 2D-VBS underestimates the SOA concentrations and O:C increase of the toluene oxidation experiments; it generally underestimates the SOA concentrations and overestimates the O:C increase of the α-pinene experiments. With the first-generation oxidation treated explicitly, we could modify the 2D-VBS configuration individually for toluene and α-pinene to achieve good model-measurement agreement. However, we are unable to simulate the oxidation of both toluene and α-pinene with the same 2D-VBS configuration. We suggest that future models should implement parallel layers for anthropogenic (aromatic) and biogenic precursors, and that more modeling studies and laboratory research be done to optimize the "best-guess" parameters for each layer.
Two-Dimensional Colloidal Alloys
NASA Astrophysics Data System (ADS)
Law, Adam D.; Buzza, D. Martin A.; Horozov, Tommy S.
2011-03-01
We study the structure of mixed monolayers of large (3μm diameter) and small (1μm diameter) very hydrophobic silica particles at an octane-water interface as a function of the number fraction of small particles ξ. We find that a rich variety of two-dimensional hexagonal super-lattices of large (A) and small (B) particles can be obtained in this system due to strong and long-range electrostatic repulsions through the nonpolar octane phase. The structures obtained for the different compositions are in good agreement with zero temperature calculations and finite temperature computer simulations.
Two-dimensional colloidal alloys.
Law, Adam D; Buzza, D Martin A; Horozov, Tommy S
2011-03-25
We study the structure of mixed monolayers of large (3 μm diameter) and small (1 μm diameter) very hydrophobic silica particles at an octane-water interface as a function of the number fraction of small particles ξ. We find that a rich variety of two-dimensional hexagonal super-lattices of large (A) and small (B) particles can be obtained in this system due to strong and long-range electrostatic repulsions through the nonpolar octane phase. The structures obtained for the different compositions are in good agreement with zero temperature calculations and finite temperature computer simulations.
NASA Astrophysics Data System (ADS)
Ngwira, Chigomezyo M.; Pulkkinen, Antti; Kuznetsova, Maria M.; Glocer, Alex
2014-06-01
There is a growing concern over possible severe societal consequences related to adverse space weather impacts on man-made technological infrastructure. In the last two decades, significant progress has been made toward the first-principles modeling of space weather events, and three-dimensional (3-D) global magnetohydrodynamics (MHD) models have been at the forefront of this transition, thereby playing a critical role in advancing our understanding of space weather. However, the modeling of extreme space weather events is still a major challenge even for the modern global MHD models. In this study, we introduce a specially adapted University of Michigan 3-D global MHD model for simulating extreme space weather events with a Dst footprint comparable to the Carrington superstorm of September 1859 based on the estimate by Tsurutani et. al. (2003). Results are presented for a simulation run with "very extreme" constructed/idealized solar wind boundary conditions driving the magnetosphere. In particular, we describe the reaction of the magnetosphere-ionosphere system and the associated induced geoelectric field on the ground to such extreme driving conditions. The model setup is further tested using input data for an observed space weather event of Halloween storm October 2003 to verify the MHD model consistence and to draw additional guidance for future work. This extreme space weather MHD model setup is designed specifically for practical application to the modeling of extreme geomagnetically induced electric fields, which can drive large currents in ground-based conductor systems such as power transmission grids. Therefore, our ultimate goal is to explore the level of geoelectric fields that can be induced from an assumed storm of the reported magnitude, i.e., Dst˜=-1600 nT.
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
NASA Astrophysics Data System (ADS)
Maire, Pierre-Henri; Abgrall, Rémi; Breil, Jérôme; Loubère, Raphaël; Rebourcet, Bernard
2013-02-01
In this paper, we describe a cell-centered Lagrangian scheme devoted to the numerical simulation of solid dynamics on two-dimensional unstructured grids in planar geometry. This numerical method, utilizes the classical elastic-perfectly plastic material model initially proposed by Wilkins [M.L. Wilkins, Calculation of elastic-plastic flow, Meth. Comput. Phys. (1964)]. In this model, the Cauchy stress tensor is decomposed into the sum of its deviatoric part and the thermodynamic pressure which is defined by means of an equation of state. Regarding the deviatoric stress, its time evolution is governed by a classical constitutive law for isotropic material. The plasticity model employs the von Mises yield criterion and is implemented by means of the radial return algorithm. The numerical scheme relies on a finite volume cell-centered method wherein numerical fluxes are expressed in terms of sub-cell force. The generic form of the sub-cell force is obtained by requiring the scheme to satisfy a semi-discrete dissipation inequality. Sub-cell force and nodal velocity to move the grid are computed consistently with cell volume variation by means of a node-centered solver, which results from total energy conservation. The nominally second-order extension is achieved by developing a two-dimensional extension in the Lagrangian framework of the Generalized Riemann Problem methodology, introduced by Ben-Artzi and Falcovitz [M. Ben-Artzi, J. Falcovitz, Generalized Riemann Problems in Computational Fluid Dynamics, Cambridge Monogr. Appl. Comput. Math. (2003)]. Finally, the robustness and the accuracy of the numerical scheme are assessed through the computation of several test cases.
Maire, Pierre-Henri; Breil, Jérôme; Loubère, Raphaël; Rebourcet, Bernard
2013-02-15
In this paper, we describe a cell-centered Lagrangian scheme devoted to the numerical simulation of solid dynamics on two-dimensional unstructured grids in planar geometry. This numerical method, utilizes the classical elastic-perfectly plastic material model initially proposed by Wilkins [M.L. Wilkins, Calculation of elastic–plastic flow, Meth. Comput. Phys. (1964)]. In this model, the Cauchy stress tensor is decomposed into the sum of its deviatoric part and the thermodynamic pressure which is defined by means of an equation of state. Regarding the deviatoric stress, its time evolution is governed by a classical constitutive law for isotropic material. The plasticity model employs the von Mises yield criterion and is implemented by means of the radial return algorithm. The numerical scheme relies on a finite volume cell-centered method wherein numerical fluxes are expressed in terms of sub-cell force. The generic form of the sub-cell force is obtained by requiring the scheme to satisfy a semi-discrete dissipation inequality. Sub-cell force and nodal velocity to move the grid are computed consistently with cell volume variation by means of a node-centered solver, which results from total energy conservation. The nominally second-order extension is achieved by developing a two-dimensional extension in the Lagrangian framework of the Generalized Riemann Problem methodology, introduced by Ben-Artzi and Falcovitz [M. Ben-Artzi, J. Falcovitz, Generalized Riemann Problems in Computational Fluid Dynamics, Cambridge Monogr. Appl. Comput. Math. (2003)]. Finally, the robustness and the accuracy of the numerical scheme are assessed through the computation of several test cases.
Bankura, Arindam; Chandra, Amalendu
2015-01-28
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.
Bankura, Arindam; Chandra, Amalendu
2015-01-28
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.
Kuniansky, E.L.
1990-01-01
A computer program based on the Galerkin finite-element method was developed to simulate two-dimensional steady-state ground-water flow in either isotropic or anisotropic confined aquifers. The program may also be used for unconfined aquifers of constant saturated thickness. Constant head, constant flux, and head-dependent flux boundary conditions can be specified in order to approximate a variety of natural conditions, such as a river or lake boundary, and pumping well. The computer program was developed for the preliminary simulation of ground-water flow in the Edwards-Trinity Regional aquifer system as part of the Regional Aquifer-Systems Analysis Program. Results of the program compare well to analytical solutions and simulations .from published finite-difference models. A concise discussion of the Galerkin method is presented along with a description of the program. Provided in the Supplemental Data section are a listing of the computer program, definitions of selected program variables, and several examples of data input and output used in verifying the accuracy of the program.
Two-dimensional magnetohydrodynamic studies of implosion modes of nested wire array z-pinches
Huang, Jun; Ding, Ning Xue, Chuang; Sun, Shunkai
2014-07-15
Implosion dynamics of nested wire arrays in (r, θ) geometry was studied with two-dimensional magnetohydrodynamic (2D MHD) simulations. Three different implosion modes are obtained by just changing the wire number of the outer array, when the other conditions, such as the initial radius, length, mass of each array, the wire number of the inner array, and the discharge voltage waveform, are fixed. Simulation results show that the effect of discrete wires, which cannot be described by the thin shell inductive model, will influence the distribution of current between the outer and inner arrays at the early stage, and the discrepancy between results from MHD and thin shell model increases with the interwire gap of the outer array.
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.
3D simulations of fluctuation spectra in the hall-MHD plasma.
Shaikh, Dastgeer; Shukla, P K
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(-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.
Gas Core Reactor Numerical Simulation Using a Coupled MHD-MCNP Model
NASA Technical Reports Server (NTRS)
Kazeminezhad, F.; Anghaie, S.
2008-01-01
Analysis is provided in this report of using two head-on magnetohydrodynamic (MHD) shocks to achieve supercritical nuclear fission in an axially elongated cylinder filled with UF4 gas as an energy source for deep space missions. The motivation for each aspect of the design is explained and supported by theory and numerical simulations. A subsequent report will provide detail on relevant experimental work to validate the concept. Here the focus is on the theory of and simulations for the proposed gas core reactor conceptual design from the onset of shock generations to the supercritical state achieved when the shocks collide. The MHD model is coupled to a standard nuclear code (MCNP) to observe the neutron flux and fission power attributed to the supercritical state brought about by the shock collisions. Throughout the modeling, realistic parameters are used for the initial ambient gaseous state and currents to ensure a resulting supercritical state upon shock collisions.
Substorm effects in MHD and test particle simulations of magnetotail dynamics
Birn, J.; Hesse, M.
1998-12-31
Recent magnetohydrodynamic simulations demonstrate that a global tail instability, initiated by localized breakdown of MHD, can cause plasmoid formation and ejection as well as dipolarization and the current diversion of the substorm current wedge. The connection between the reconnection process and the current wedge signatures is provided by earthward flow from the reconnection site. Its braking and diversion in the inner magnetosphere causes dipolarization and the magnetic field distortions of the current wedge. The authors demonstrate the characteristic properties of this process and the current systems involved. The strong localized electric field associated with the flow burst and the dipolarization is also the cause of particle acceleration and energetic particle injections. Test particle simulations of orbits in the MHD fields yield results that are quite consistent with observed injection signatures.
Thermodynamic MHD Simulation of the 2000 July 14 "Bastille Day" Eruption
NASA Astrophysics Data System (ADS)
Torok, Tibor; Downs, Cooper; Lionello, Roberto; Linker, Jon A.; Titov, Viacheslav S.; Mikic, Zoran; Riley, Pete
2015-04-01
The "Bastille Day" event that occurred on 2000 July 14 is one of the most extensively studied solar eruptions. It originated in a complex active region close to disk center and produced an X5.7 flare, a fast halo CME, and an intense geomagnetic storm. Accurate numerical simulations of such events, in particular the matching of parameters relevant for space weather such as the CME velocity and magnetic orientation, require a realistic model of the large-scale magnetic field and plasma environment into which the eruption propagates and interacts, as well as a modeling of the pre-eruptive configuration and eruption initiation that are as realistic as possible. Here we present an MHD simulation of the Bastille Day event that complies with these requirements. We first produce a steady-state MHD solution of the background corona that incorporates realistic energy transport ("thermodynamic MHD"), photospheric magnetic field measurements, and the solar wind. In order to model the pre-eruptive magnetic field, we then insert a stable, elongated flux rope that resides above the highly curved polarity inversion line of the active region. Finally, we produce the eruption by imposing photospheric flows that slowly converge towards the polarity inversion line. In this presentation we describe our method, compare the simulation results with the observations, and discuss the challenges and limitations involved in modeling such complex and powerful eruptions.
Kanevce, Ana; Kuciauskas, Darius; Levi, Dean H.; Johnston, Steven W.; Allende Motz, Alyssa M.
2015-07-28
We use two-dimensional numerical simulations to analyze high spatial resolution time-resolved spectroscopy data. This analysis is applied to two-photon excitation time-resolved photoluminescence (2PE-TRPL) but is broadly applicable to all microscopic time-resolved techniques. By solving time-dependent drift-diffusion equations, we gain insight into carrier dynamics and transport characteristics. Accurate understanding of measurement results establishes the limits and potential of the measurement and enhances its value as a characterization method. Diffusion of carriers outside of the collection volume can have a significant impact on the measured decay but can also provide an estimate of carrier mobility as well as lifetime. In addition to material parameters, the experimental conditions, such as spot size and injection level, can impact the measurement results. Although small spot size provides better resolution, it also increases the impact of diffusion on the decay; if the spot size is much smaller than the diffusion length, it impacts the entire decay. By reproducing experimental 2PE-TRPL decays, the simulations determine the bulk carrier lifetime from the data. The analysis is applied to single-crystal and heteroepitaxial CdTe, material important for solar cells, but it is also applicable to other semiconductors where carrier diffusion from the excitation volume could affect experimental measurements.
Umeda, Takayuki Kidani, Yoshitaka; Matsukiyo, Shuichi; Yamazaki, Ryo
2014-02-15
Large-scale two-dimensional (2D) full particle-in-cell (PIC) simulations are carried out for studying the relationship between the dynamics of a perpendicular shock and microinstabilities generated at the shock foot. The structure and dynamics of collisionless shocks are generally determined by Alfven Mach number and plasma beta, while microinstabilities at the shock foot are controlled by the ratio of the upstream bulk velocity to the electron thermal velocity and the ratio of the plasma-to-cyclotron frequency. With a fixed Alfven Mach number and plasma beta, the ratio of the upstream bulk velocity to the electron thermal velocity is given as a function of the ion-to-electron mass ratio. The present 2D full PIC simulations with a relatively low Alfven Mach number (M{sub A} ∼ 6) show that the modified two-stream instability is dominant with higher ion-to-electron mass ratios. It is also confirmed that waves propagating downstream are more enhanced at the shock foot near the shock ramp as the mass ratio becomes higher. The result suggests that these waves play a role in the modification of the dynamics of collisionless shocks through the interaction with shock front ripples.
Extended MHD simulations for application to ITER disruption mitigation techniques
NASA Astrophysics Data System (ADS)
Woodruff, Simon; Stuber, James; Schetterer, Sam; ITER Disruption Mitigation Collaboration
2013-10-01
Various disruption scenarios are modeled computationally by use of the CORSICA and NIMROD codes, following the work of Kruger and Strauss with the aim of providing starting-points for investigation of tokamak disruption mitigation techniques. It is found that pressure-driven instabilities previously observed in simulations of DIII-D are verified, and that halo currents from vertical displacements are observed in simulations with implementation of resistive walls for ITER. We discuss implications and plans for simulations of disruption mitigation techniques. We outline validation activities for existing facilities. Work performed for USITER under DE-AC05-00OR22725 subcontract # 4000118643.
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
3D MHD Simulations of Injector Coupling and Current Drive in HIT-SI
NASA Astrophysics Data System (ADS)
Hansen, Chris; Marklin, George; Jarboe, Thomas
2013-10-01
A new non-linear reduced MHD code has been developed using the PSI-TET framework, which is capable of modeling the full HIT-SI geometry with consistent boundary conditions for the insulator coated flux conserver. The PSI-TET framework provides general mechanics supporting the development of multi-physics simulation using high order finite methods with a tetrahedral spatial discretization. Using these capabilities an implementation of reduced Hall-MHD was developed where temperature and density are assumed to be uniform and constant, reducing the full MHD equations to the momentum and induction equations. A Nedelec vector basis set is used for the magnetic field, which preserves the divergence free property of the induction equation, and a scalar Lagrange basis is used for each component of the velocity. The equation system is advanced using a time centered implicit scheme, which is solved using a multi-grid preconditioned Newton-Krylov method. Results will be presented focusing on internal injector dynamics and coupling to the Spheromak region. Comparison between this code and experimental data as well as existing NIMROD simulations of HIT-SI, which model the injector operation with boundary conditions on an axisymmetric grid, will also be shown. Work supported by DOE.
Explosive Turbulent Magnetic Reconnection: A New Approach of MHD-Turbulent Simulation
NASA Astrophysics Data System (ADS)
Hoshino, Masahiro; Yokoi, Nobumitsu; Higashimori, Katsuaki
2013-04-01
Turbulent flows are often observed in association with magnetic reconnection in space and astrophysical plasmas, and it is often hypothesized that the turbulence can contribute to the fast magnetic reconnection through the enhancement of magnetic dissipation. In this presentation, we demonstrate that an explosive turbulent reconnection can happen by using a new turbulent MHD simulation, in which the evolution of the turbulent transport coefficients are self-consistently solved together with the standard MHD equations. In our model, the turbulent electromotive force defined by the correlation of turbulent fluctuations between v and B is added to the Ohm's law. We discuss that the level of turbulent can control the topology of reconnection, namely the transition from the Sweet-Parker reconnection to the Petscheck reconnection occurs when the level of fluctuations becomes of order of the ambient physical quantities, and show that the growth of the turbulent Petscheck reconnection becomes much faster than the conventional one.
FTE Dependence on IMF Orientation and Presence of Hall Physics in Global MHD Simulations
NASA Astrophysics Data System (ADS)
Maynard, K. M.; Germaschewski, K.; Lin, L.; Raeder, J.
2013-12-01
Flux Transfer Events (FTEs) are poleward traveling flux ropes that form in the dayside magnetopause and represent significant coupling of the solar wind to the magnetosphere during times of southward IMF. In the 35 years since their discovery, FTEs have been extensively observed and modeled; however, there is still no consensus on their generation mechanism. Previous modeling efforts have shown that FTE occurrence and size depend on the resistivity model that is used in simulations and the structure of X-lines in the magnetopause. We use Hall OpenGGCM, a global Hall-MHD code, to study the formation and propagation of FTEs in the dayside magnetopause using synthetic solar wind conditions. We examine large scale FTE structure and nearby magnetic separators for a range of IMF clock angles and dipole tilts. In addition, we investigate how FTE formation and recurrence rate depends on the presence of the Hall term in the generalized Ohm's law compared with resistive MHD.
3-D MHD disk wind simulations of protostellar jets
NASA Astrophysics Data System (ADS)
Staff, Jan E.; Koning, Nico; Ouyed, Rachid; Tanaka, Kei; Tan, Jonathan C.
2016-01-01
We present the results of large scale, three-dimensional magnetohydrodynamics simulations of disk winds for different initial magnetic field configurations. The jets are followed from the source to distances, which are resolvable by HST and ALMA observations. Our simulations show that jets are heated along their length by many shocks. The mass of the protostar is a free parameter that can be inserted in the post processing of the data, and we apply the simulations to both low mass and high mass protostars. For the latter we also compute the expected diagnostics when the outflow is photoionized by the protostar. We compute the emission lines that are produced, and find excellent agreement with observations. For a one solar mass protostar, we find the jet width to be between 20 and 30 au while the maximum velocities perpendicular to the jet are found to be 100 km s-1. The initially less open magnetic field configuration simulations result in a wider, two-component jet; a cylindrically shaped outer jet surrounding a narrow and much faster, inner jet. For the initially most open magnetic field configuration the kink mode creates a narrow corkscrew-like jet without a clear Keplerian rotation profile and even regions where we observe rotation opposite to the disk (counter-rotating). This is not seen in the less open field configurations.
NASA Astrophysics Data System (ADS)
Yamamoto, Y.; Watanabe, S.; Tsuda, S. I.
2015-01-01
In this paper, a simple cavitation model is developed under the framework of homogeneousone-fluid model, in which the perfect mixture of liquid and vapor phases is assumed. In most of conventional models, the vapor phase is considered as a dispersed phase against the liquid phase as a continuous phase, while in the present model, two extreme conditions are considered: for low void fraction, dispersed vapor bubbles in continuous liquid phase, while for high void fraction, dispersed droplets in continuous vapor phase. The growth of bubbles and droplets are taken into account in the mass transfer between vapor and liquid phases, and are switched according to the local void fraction. The model is applied for the simulation of cavitating flow in a two-dimensional convergent-divergent nozzle, and the result is compared with that using a conventional model. To enhance the unsteadiness of cavitation due to the instability at the cavity interphase, the turbulent shear stress is modified depending upon the continuous phases in combination with the proposed cavitation model, which drastically reduces the turbulent viscosity for high void fraction region. As a result, the unsteadiness of cavitation observed in experiments is well reproduced.
Sun, Yi; Timofeyev, Ilya
2014-05-01
We employ an efficient list-based kinetic Monte Carlo (KMC) method to study traffic flow models on one-dimensional (1D) and two-dimensional (2D) lattices based on the exclusion principle and Arrhenius microscopic dynamics. This model implements stochastic rules for cars' movements based on the configuration of the traffic ahead of each car. In particular, we compare two different look-ahead rules: one is based on the distance from the car under consideration to the car in front of it, and the other one is based on the density of cars ahead. The 1D numerical results of these two rules suggest different coarse-grained macroscopic limits in the form of integro-differential Burgers equations. The 2D results of both rules exhibit a sharp phase transition from freely flowing to fully jammed, as a function of the initial density of cars. However, the look-ahead rule based on the density of the traffic produces more realistic results. The KMC simulations reported in this paper are compared with those from other well-known traffic flow models and the corresponding empirical results from real traffic.
NASA Astrophysics Data System (ADS)
Ni, Aleksey; Cheema, Taqi Ahmad; Kwak, Moon Kyu; Park, Cheol Woo
2014-08-01
A two-dimensional computational model of a single red blood cell (RBC) floating in a plasma-alcohol solution through a microchannel with stenosis was created using the Arbitrary Lagrangian-Eulerian (ALE) method with moving mesh for a fluid structure interaction problem. Cell deformability and stability were studied in a plasma-alcohol solution at different fluid flow conditions during movement through the channel with stenosis. Different results were obtained for different input parameters. Motion through 45% and 70% stenoses with the high and law velocities of the RBC and different viscosities was analyzed and successfully simulated. Results show that changes in RBC deformability were due to the effects of alcohol. Changes in behavior during motion were also observed. At low shear rate and high surrounding fluid viscosity the RBC showed a tendency to rotate during movement. The proposed model with its coupling of structural and fluid analysis techniques could be useful to understand the effect of alcohol on the RBC passing through stenosis.
Lai, Chintu
1977-01-01
Two-dimensional unsteady flows of homogeneous density in estuaries and embayments can be described by hyperbolic, quasi-linear partial differential equations involving three dependent and three independent variables. A linear combination of these equations leads to a parametric equation of characteristic form, which consists of two parts: total differentiation along the bicharacteristics and partial differentiation in space. For its numerical solution, the specified-time-interval scheme has been used. The unknown, partial space-derivative terms can be eliminated first by suitable combinations of difference equations, converted from the corresponding differential forms and written along four selected bicharacteristics and a streamline. Other unknowns are thus made solvable from the known variables on the current time plane. The computation is carried to the second-order accuracy by using trapezoidal rule of integration. Means to handle complex boundary conditions are developed for practical application. Computer programs have been written and a mathematical model has been constructed for flow simulation. The favorable computer outputs suggest further exploration and development of model worthwhile. (Woodard-USGS)
NASA Astrophysics Data System (ADS)
Sun, Yi; Timofeyev, Ilya
2014-05-01
We employ an efficient list-based kinetic Monte Carlo (KMC) method to study traffic flow models on one-dimensional (1D) and two-dimensional (2D) lattices based on the exclusion principle and Arrhenius microscopic dynamics. This model implements stochastic rules for cars' movements based on the configuration of the traffic ahead of each car. In particular, we compare two different look-ahead rules: one is based on the distance from the car under consideration to the car in front of it, and the other one is based on the density of cars ahead. The 1D numerical results of these two rules suggest different coarse-grained macroscopic limits in the form of integro-differential Burgers equations. The 2D results of both rules exhibit a sharp phase transition from freely flowing to fully jammed, as a function of the initial density of cars. However, the look-ahead rule based on the density of the traffic produces more realistic results. The KMC simulations reported in this paper are compared with those from other well-known traffic flow models and the corresponding empirical results from real traffic.
A three-dimensional MHD simulation of the interaction of the solar wind with Comet Halley
NASA Technical Reports Server (NTRS)
Ogino, Tatsuki; Walker, Raymond J.; Ashour-Abdalla, Maha
1988-01-01
The interaction between the solar wind and cometary plasmas is simulated using a three-dimensional time-dependent MHD simulation model, and the results are compared with the recent satellite observations of Comet Halley. The model, which includes cometary mass loading, reproduces many of the features observed by the Suisei probe and the Giottot, including the weak bow shock, the enhancement of the magnetic field in front of the contact surface, and the plasma temperature increase across the bow shock (while it decreased near the comet).
Disturbances of three cometary magnetospheres as explained by an MHD simulation
NASA Technical Reports Server (NTRS)
Kozuka, Y.; Saito, T.; Konno, Ichishiro; Oki, T.
1990-01-01
Outstanding disturbances of the plasma tails were observed in 1989 in three comets, Brorsen-Metcalf, Okazaki-Levy-Rudenko, and Aarseth-Brewington. Time variations of the tails were obtained from photographs provided by many astronomers. A 2-D MHD simulation was performed varying the speed and the direction of the solar wind flow. The simulation agreed quite well with the observations. Solar flares were identified as the sources of these disturbances. It was found that the sudden change in direction of the plasma tail axis occurs when the comet crosses a discontinuity surface of the solar wind structure accompanied by solar flares.
Global MHD modeling of resonant ULF waves: Simulations with and without a plasmasphere.
Claudepierre, S G; Toffoletto, F R; Wiltberger, M
2016-01-01
We investigate the plasmaspheric influence on the resonant mode coupling of magnetospheric ultralow frequency (ULF) waves using the Lyon-Fedder-Mobarry (LFM) global magnetohydrodynamic (MHD) model. We present results from two different versions of the model, both driven by the same solar wind conditions: one version that contains a plasmasphere (the LFM coupled to the Rice Convection Model, where the Gallagher plasmasphere model is also included) and another that does not (the stand-alone LFM). We find that the inclusion of a cold, dense plasmasphere has a significant impact on the nature of the simulated ULF waves. For example, the inclusion of a plasmasphere leads to a deeper (more earthward) penetration of the compressional (azimuthal) electric field fluctuations, due to a shift in the location of the wave turning points. Consequently, the locations where the compressional electric field oscillations resonantly couple their energy into local toroidal mode field line resonances also shift earthward. We also find, in both simulations, that higher-frequency compressional (azimuthal) electric field oscillations penetrate deeper than lower frequency oscillations. In addition, the compressional wave mode structure in the simulations is consistent with a radial standing wave oscillation pattern, characteristic of a resonant waveguide. The incorporation of a plasmasphere into the LFM global MHD model represents an advance in the state of the art in regard to ULF wave modeling with such simulations. We offer a brief discussion of the implications for radiation belt modeling techniques that use the electric and magnetic field outputs from global MHD simulations to drive particle dynamics.
Global MHD modeling of resonant ULF waves: Simulations with and without a plasmasphere
NASA Astrophysics Data System (ADS)
Claudepierre, S. G.; Toffoletto, F. R.; Wiltberger, M.
2016-01-01
We investigate the plasmaspheric influence on the resonant mode coupling of magnetospheric ultralow frequency (ULF) waves using the Lyon-Fedder-Mobarry (LFM) global magnetohydrodynamic (MHD) model. We present results from two different versions of the model, both driven by the same solar wind conditions: one version that contains a plasmasphere (the LFM coupled to the Rice Convection Model, where the Gallagher plasmasphere model is also included) and another that does not (the stand-alone LFM). We find that the inclusion of a cold, dense plasmasphere has a significant impact on the nature of the simulated ULF waves. For example, the inclusion of a plasmasphere leads to a deeper (more earthward) penetration of the compressional (azimuthal) electric field fluctuations, due to a shift in the location of the wave turning points. Consequently, the locations where the compressional electric field oscillations resonantly couple their energy into local toroidal mode field line resonances also shift earthward. We also find, in both simulations, that higher-frequency compressional (azimuthal) electric field oscillations penetrate deeper than lower frequency oscillations. In addition, the compressional wave mode structure in the simulations is consistent with a radial standing wave oscillation pattern, characteristic of a resonant waveguide. The incorporation of a plasmasphere into the LFM global MHD model represents an advance in the state of the art in regard to ULF wave modeling with such simulations. We offer a brief discussion of the implications for radiation belt modeling techniques that use the electric and magnetic field outputs from global MHD simulations to drive particle dynamics.
THE SUBMILLIMETER BUMP IN Sgr A* FROM RELATIVISTIC MHD SIMULATIONS
Dexter, Jason; Agol, Eric; Fragile, P. Chris; McKinney, Jonathan C.
2010-07-10
Recent high resolution observations of the Galactic center black hole allow for direct comparison with accretion disk simulations. We compare two-temperature synchrotron emission models from three-dimensional, general relativistic magnetohydrodynamic simulations to millimeter observations of Sgr A*. Fits to very long baseline interferometry and spectral index measurements disfavor the monochromatic face-on black hole shadow models from our previous work. Inclination angles {<=}20{sup 0} are ruled out to 3{sigma}. We estimate the inclination and position angles of the black hole, as well as the electron temperature of the accretion flow and the accretion rate, to be i=50{sup o+35o}{sub -15}{sup o}, {xi}=-23{sup o+97o}{sub -22}{sup o}, T{sub e} = (5.4 {+-} 3.0) x 10{sup 10} K, and M-dot =5{sup +15}{sub -2}x10{sup -9} M{sub sun} yr{sup -1}, respectively, with 90% confidence. The black hole shadow is unobscured in all best-fit models, and may be detected by observations on baselines between Chile and California, Arizona, or Mexico at 1.3 mm or .87 mm either through direct sampling of the visibility amplitude or using closure phase information. Millimeter flaring behavior consistent with the observations is present in all viable models and is caused by magnetic turbulence in the inner radii of the accretion flow. The variability at optically thin frequencies is strongly correlated with that in the accretion rate. The simulations provide a universal picture of the 1.3 mm emission region as a small region near the midplane in the inner radii of the accretion flow, which is roughly isothermal and has {nu}/{nu} {sub c} {approx} 1-20, where {nu} {sub c} is the critical frequency for thermal synchrotron emission.
Fanchi, J.R.
1985-04-01
Under the sponsorship of the US Department of Energy, a publicly available chemical simulator has been evaluated and substantially enhanced to serve as a useful tool for projecting polymer or chemical flood performance. The program, CHEM2D, is a two-dimensional, three-phase, nine-component finite-difference numerical simulator. It can model primary depletion, waterfloods, polymer floods, and micellar/polymer floods using heterogeneous linear, areal, or cross-sectional reservoir descriptions. The user may specify well performance as either pressure or rate constrained. Both a constant time step size and a variable time step size based on extrapolation of concentration changes are available as options. A solution technique which is implicit in pressure and explicit in saturations and concentrations is used. The major physical mechanisms that are modeled include adsorption, capillary trapping, cation exchange, dilution, dispersion, interfacial tension, binary or ternary phase behavior, non-Newtonian polymer rheology, and two-phase or three-phase relative permeability. Typical components include water, oil, surfactant, polymer, and three ions (chloride, calcium, and sodium). Components may partition amongst the aqueous, oleic, and microemulsion phases. Volume I of this report provides a discussion of the formulation and algorithms used within CHEM2D. Included in Volume I are a number of validation and illustrative examples, as well as the FORTRAN code. The CHEM2D user's manual, Volume II, contains both the input data sets for the examples presented in Volume I and an example output. All appendices and a phase behavior calculation program are collected in Volume III. 20 references.
MHD simulations of homologous and cannibalistic coronal mass ejections
NASA Astrophysics Data System (ADS)
Fan, Yuhong; Chatterjee, Piyali
2014-06-01
We present magneto-hydrodynamic simulations of the development of a homologous sequence of coronal mass ejections (CMEs) and demonstrate their so-called cannibalistic behavior. These CMEs originate from the repeated formations and partial eruptions of kink unstable flux ropes as a result of the continued emergence of a twisted flux rope across the lower boundary into a pre-existing coronal potential arcade field. The simulations show that a CME erupting into the open magnetic field created by a preceding CME has a higher speed, and therefore tends to be cannibalistic, catching up and merging with the preceding one into a single fast CME. All the CMEs attained speeds of about 1000 km/s as they exit the domain. The reformation of a twisted flux rope after each CME eruption during the sustained flux emergence can naturally explain the X-ray observations of repeated reformations of sigmoids and “sigmoid-under-cusp” configurations at a low-coronal source of homologous CMEs.
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.
Laser-Plasma Modeling Using PERSEUS Extended-MHD Simulation Code for HED Plasmas
NASA Astrophysics Data System (ADS)
Hamlin, Nathaniel; Seyler, Charles
2016-10-01
We discuss the use of the PERSEUS extended-MHD simulation code for high-energy-density (HED) plasmas in modeling laser-plasma interactions in relativistic and nonrelativistic regimes. By formulating the fluid equations as a relaxation system in which the current is semi-implicitly time-advanced using the Generalized Ohm's Law, PERSEUS enables modeling of two-fluid phenomena in dense plasmas without the need to resolve the smallest electron length and time scales. For relativistic and nonrelativistic laser-target interactions, we have validated a cycle-averaged absorption (CAA) laser driver model against the direct approach of driving the electromagnetic fields. The CAA model refers to driving the radiation energy and flux rather than the fields, and using hyperbolic radiative transport, coupled to the plasma equations via energy source terms, to model absorption and propagation of the radiation. CAA has the advantage of not requiring adequate grid resolution of each laser wavelength, so that the system can span many wavelengths without requiring prohibitive CPU time. For several laser-target problems, we compare existing MHD results to extended-MHD results generated using PERSEUS with the CAA model, and examine effects arising from Hall physics. This work is supported by the National Nuclear Security Administration stewardship sciences academic program under Department of Energy cooperative agreements DE-FOA-0001153 and DE-NA0001836.
You’re Cut Off: HD and MHD Simulations of Truncated Accretion Disks
NASA Astrophysics Data System (ADS)
Hogg, J. Drew; Reynolds, Christopher S.
2017-01-01
Truncated accretion disks are commonly invoked to explain the spectro-temporal variability from accreting black holes in both small systems, i.e. state transitions in galactic black hole binaries (GBHBs), and large systems, i.e. low-luminosity active galactic nuclei (LLAGNs). In the canonical truncated disk model of moderately low accretion rate systems, gas in the inner region of the accretion disk occupies a hot, radiatively inefficient phase, which leads to a geometrically thick disk, while the gas in the outer region occupies a cooler, radiatively efficient phase that resides in the standard geometrically thin disk. Observationally, there is strong empirical evidence to support this phenomenological model, but a detailed understanding of the disk behavior is lacking. We present well-resolved hydrodynamic (HD) and magnetohydrodynamic (MHD) numerical models that use a toy cooling prescription to produce the first sustained truncated accretion disks. Using these simulations, we study the dynamics, angular momentum transport, and energetics of a truncated disk in the two different regimes. We compare the behaviors of the HD and MHD disks and emphasize the need to incorporate a full MHD treatment in any discussion of truncated accretion disk evolution.
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.
Three-dimensional MHD simulation of the Caltech plasma jet experiment: first results
Zhai, Xiang; Bellan, Paul M.; Li, Hui; Li, Shengtai E-mail: pbellan@caltech.edu E-mail: sli@lanl.gov
2014-08-10
Magnetic fields are believed to play an essential role in astrophysical jets with observations suggesting the presence of helical magnetic fields. Here, we present three-dimensional (3D) ideal MHD simulations of the Caltech plasma jet experiment using a magnetic tower scenario as the baseline model. Magnetic fields consist of an initially localized dipole-like poloidal component and a toroidal component that is continuously being injected into the domain. This flux injection mimics the poloidal currents driven by the anode-cathode voltage drop in the experiment. The injected toroidal field stretches the poloidal fields to large distances, while forming a collimated jet along with several other key features. Detailed comparisons between 3D MHD simulations and experimental measurements provide a comprehensive description of the interplay among magnetic force, pressure, and flow effects. In particular, we delineate both the jet structure and the transition process that converts the injected magnetic energy to other forms. With suitably chosen parameters that are derived from experiments, the jet in the simulation agrees quantitatively with the experimental jet in terms of magnetic/kinetic/inertial energy, total poloidal current, voltage, jet radius, and jet propagation velocity. Specifically, the jet velocity in the simulation is proportional to the poloidal current divided by the square root of the jet density, in agreement with both the experiment and analytical theory. This work provides a new and quantitative method for relating experiments, numerical simulations, and astrophysical observation, and demonstrates the possibility of using terrestrial laboratory experiments to study astrophysical jets.
Energy storage and dissipation in the magnetotail during substorms. 2. MHD simulations
Steinolfson, R.S. ); Winglee, R.M. )
1993-05-01
The authors present a global MHD simulation of the magnetotail in an effort to study magnetic storm development. They address the question of energy storage in the current sheet in the early phases of storm growth, which previous simulations have not shown. They address this problem by dealing with the variation of the resistivity throughout the magnetosphere. They argue that MHD theory should provide a suitable representation to this problem on a global scale, even if it does not handle all details adequately. For their simulation they use three different forms for the resistivity. First is a uniform and constant resistivity. Second is a resistivity proportional to the current density, which is related to argument that resistivity is driven by wave-particle interactions which should be strongest in regions where the current is the greatest. Thirdly is a model where the resistivity varies with the magnetic field strength, which was suggested by previous results from particle simulations of the same problem. The simulation then gives approximately the same response of the magnetosphere for all three of the models. Each results in the formation and ejection of plasmoids, but the energy stored in the magnetotail, the timing of substorm onset in relation to the appearance of a southward interplanetary magnetic field, and the speed of ejection of the plasmoids formed differ with the resistivity models.
3-D General Relativistic MHD Simulations of Generating Jets
NASA Astrophysics Data System (ADS)
Nishikawa, K.-I.; Koide, S.; Shibata, K.; Kudoh, T.; Sol, H.; Hughes, J. P.
2001-12-01
We have investigated the dynamics of an accretion disk around Schwarzschild black holes initially threaded by a uniform poloidal magnetic field in a non-rotating corona (either in a steady-state infalling state) around a non-rotating black hole using a 3-D GRMHD with the ``axisymmetry'' along the z-direction. Magnetic field is tightly twisted by the rotation of the disk, and plasmas in the shocked region of the disk are accelerated by J x B force to form bipolar relativistic jets. In order to investigate variabilities of generated relativistic jets and magnetic field structure inside jets, we have performed calculations using the 3-D GRMHD code with a full 3-dimensional system without the axisymmetry. We have investigated how the third dimension affects the global disk dynamics and jet generation. We will perform simulations with various incoming flows from an accompanying star.
3-D General Relativistic MHD Simulations of Generating Jets
NASA Astrophysics Data System (ADS)
Nishikawa, K.-I.; Koide, S.; Shibata, K.; Kudoh, T.; Frank, J.; Sol, H.
1999-05-01
Koide et al have investigated the dynamics of an accretion disk initially threaded by a uniform poloidal magnetic field in a non-rotating corona (either in a steady-state infalling state or in hydrostatic equilibrium) around a non-rotating black hole using a 3-D GRMHD with the ``axisymmetry'' along the z-direction. Magnetic field is tightly twisted by the rotation of the disk, and plasmas in the shocked region of the disk are accelerated by J x B force to form bipolar relativistic jets. In order to investigate variabilities of generated relativistic jets and magnetic field structure inside jets, we have performed calculations using the 3-D GRMHD code on a full 3-dimensional system. We will investigate how the third dimension affects the global disk dynamics. 3-D RMHD simulations wil be also performed to investigate the dynamics of a jet with a helical mangetic field in it.
Jet Formation with 3-D General Relativistic MHD Simulations
NASA Astrophysics Data System (ADS)
Richardson, G. A.; Nishikawa, K.-I.; Preece, R.; Hardee, P.; Koide, S.; Shibata, K.; Kudoh, T.; Sol, H.; Hughes, J. P.; Fishman, J.
2002-12-01
We have investigated the dynamics of an accretion disk around Schwarzschild black holes initially threaded by a uniform poloidal magnetic field in a non-rotating corona (in a steady-state infalling state) around a non-rotating black hole using 3-D GRMHD with the ``axisymmetry'' along the z-direction. The magnetic field is tightly twisted by the rotation of the accretion disk, and plasmas in the shocked region of the disk are accelerated by the J x B force to form bipolar relativistic jets. In order to investigate variabilities of generated relativistic jets and the magnetic field structure inside jets, we have performed calculations using the 3-D GRMHD code with a full 3-dimensional system without the axisymmetry. We have investigated how the third dimension affects the global disk dynamics and jet generation. We will perform simulations with various incoming flows from an accompanying star.
3-D General Relativistic MHD Simulations of Generating Jets
NASA Astrophysics Data System (ADS)
Nishikawa, Ken-Ichi; Koide, Shinji; Shibata, Kazunari; Kudoh, Takashiro; Sol, Helene; Hughes, John
2002-04-01
We have investigated the dynamics of an accretion disk around Schwarzschild black holes initially threaded by a uniform poloidal magnetic field in a non-rotating corona (either in a steady-state infalling state) around a non-rotating black hole using a 3-D GRMHD with the ``axisymmetry'' along the z-direction. Magnetic field is tightly twisted by the rotation of the disk, and plasmas in the shocked region of the disk are accelerated by J × B force to form bipolar relativistic jets. In order to investigate variabilities of generated relativistic jets and magnetic field structure inside jets, we have performed calculations using the 3-D GRMHD code with a full 3-dimensional system without the axisymmetry. We have investigated how the third dimension affects the global disk dynamics and jet generation. We will perform simulations with various incoming flows from an accompanying star.
Photon Scattering in 3D Radiative MHD Simulations
NASA Astrophysics Data System (ADS)
Hayek, Wolfgang
2009-09-01
Recent results from 3D time-dependent radiative hydrodynamic simulations of stellar atmospheres are presented, which include the effects of coherent scattering in the radiative transfer treatment. Rayleigh scattering and electron scattering are accounted for in the source function, requiring an iterative solution of the transfer equation. Opacities and scattering coefficients are treated in the multigroup opacity approximation. The impact of scattering on the horizontal mean temperature structure is investigated, which is an important diagnostic for model atmospheres, with implications for line formation and stellar abundance measurements. We find that continuum scattering is not important for the atmosphere of a metal-poor Sun with metailicity [Fe/H] = -3.0, similar to the previously investigated photosphere at solar metallicity.
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.
Coronal extension of the MURaM radiative MHD code: From quiet sun to flare simulations
NASA Astrophysics Data System (ADS)
Rempel, Matthias D.; Cheung, Mark
2016-05-01
We present a new version of the MURaM radiative MHD code, which includes a treatment of the solar corona in terms of MHD, optically thin radiative loss and field-aligned heat conduction. In order to relax the severe time-step constraints imposed by large Alfven velocities and heat conduction we use a combination of semi-relativistic MHD with reduced speed of light ("Boris correction") and a hyperbolic formulation of heat conduction. We apply the numerical setup to 4 different setups including a mixed polarity quiet sun, an open flux region, an arcade solution and an active region setup and find all cases an amount of coronal heating sufficient to maintain a corona with temperatures from 1 MK (quiet sun) to 2 MK (active region, arcade). In all our setups the Poynting flux is self-consistently created by photospheric and sub-photospheric magneto-convection in the lower part of our simulation domain. Varying the maximum allowed Alfven velocity ("reduced speed of light") leads to only minor changes in the coronal structure as long as the limited Alfven velocity remains larger than the speed of sound and about 1.5-3 times larger than the peak advection velocity. We also found that varying details of the numerical diffusivities that govern the resistive and viscous energy dissipation do not strongly affect the overall coronal heating, but the ratio of resistive and viscous energy dependence is strongly dependent on the effective numerical magnetic Prandtl number. We use our active region setup in order to simulate a flare triggered by the emergence of a twisted flux rope into a pre-existing bipolar active region. Our simulation yields a series of flares, with the strongest one reaching GOES M1 class. The simulation reproduces many observed properties of eruptions such as flare ribbons, post flare loops and a sunquake.
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.
Comparing nonlinear MHD simulations of low-aspect-ratio RFPs to RELAX experiments
NASA Astrophysics Data System (ADS)
McCollam, K. J.; den Hartog, D. J.; Jacobson, C. M.; Sovinec, C. R.; Masamune, S.; Sanpei, A.
2016-10-01
Standard reversed-field pinch (RFP) plasmas provide a nonlinear dynamical system as a validation domain for numerical MHD simulation codes, with applications in general toroidal confinement scenarios including tokamaks. Using the NIMROD code, we simulate the nonlinear evolution of RFP plasmas similar to those in the RELAX experiment. The experiment's modest Lundquist numbers S (as low as a few times 104) make closely matching MHD simulations tractable given present computing resources. Its low aspect ratio ( 2) motivates a comparison study using cylindrical and toroidal geometries in NIMROD. We present initial results from nonlinear single-fluid runs at S =104 for both geometries and a range of equilibrium parameters, which preliminarily show that the magnetic fluctuations are roughly similar between the two geometries and between simulation and experiment, though there appear to be some qualitative differences in their temporal evolution. Runs at higher S are planned. This work is supported by the U.S. DOE and by the Japan Society for the Promotion of Science.
NASA Astrophysics Data System (ADS)
Raley, Elizabeth
2004-12-01
We have performed an analysis of fluid instabilities below the neutrinospheres of the collapsed cores of supernova progenitors using a methodology introduced by Bruenn and Dineva [28, 29, 31]. In an extensive survey we found that the rate of lepton diffusion always exceeds the rate of thermal diffusion and as a result we do not anywhere see the neutron finger instability as described by the Livermore group [16, 17]. A new instability, lepto-entropy fingers, extending from a radius of 10 15 km out to the vicinity of the neutrinosphere, driven by the cross-response functions (i.e. the dependence of lepton transport on entropy perturbations and vice versa) was discovered. This instability has a maximum growth rate of the order of 100 s-1 with a scale of approximately 1/20 the distance of a perturbed fluid element from the core center [18]. This instability has probably already been seen in some multi-dimensional core collapse calculations. To test our results predicting the presence of doubly diffusive instabilities below the neutrinosphere of a proto-supernova, we have performed two dimensional hydrodynamic simulations with radial ray neutrino transport. This entailed rewriting RadHyd, which is the merger of EVH-1 hydrodynamics and MGFLD neutrino transport developed by Bruenn and DiNisco [43], for two dimensions. In particular, hydrodynamic evolution along angular arrays was included, as was MPI message passing capabilities, in order to utilize massively parallel computer platform such as FAU's BOCA4 Beowulf cluster. This work was partially funded by a grant from the DOE Office of Science, Scientific Discovery through Advanced Computing Program.
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
Thermodynamic MHD Simulation of the July 14, 2000, "Bastille Day" Solar Eruption
NASA Astrophysics Data System (ADS)
Torok, T.; Downs, C.; Lionello, R.; Linker, J.; Mikic, Z.; Titov, V. S.; Riley, P.
2013-12-01
The "Bastille Day" event on July 14, 2000, is one of the most extensively studied solar eruptions. It originated in a strong and complex active region close to disk center and produced an X5.7 flare, a fast halo CME, and an intense geomagnetic storm. We have recently begun to model this challenging event, with the final goal to simulate its whole evolution, from the pre-eruption state up to the CME's arrival at 1 AU. To this end, we first produce a steady-state MHD solution of the background corona that incorporates realistic energy transport ("thermodynamic MHD"), photospheric magnetic field measurements, and the solar wind. In order to model the pre-eruption core magnetic field, we then insert a chain of flux ropes along the polarity inversion line (PIL) of the active region. The ropes merge during the subsequent numerical relaxation to form one stable, elongated flux rope that resides above the highly curved PIL, mimicking the morphology of the observed pre-eruption filaments. Next, we impose photospheric flows that converge toward the PIL and successively expand the magnetic field overlying the flux rope, until equilibrium cannot be longer maintained and the rope erupts and produces a CME. Finally, we couple the coronal simulation with our recently developed heliospheric MHD code to model the propagation of the CME to 1 AU. In this presentation we briefly describe our method, compare the simulation results with the observations, and discuss the challenges and limitations involved in modeling such complex and powerful eruptions.
Dynamics of heavy impurities in non-linear MHD simulations of sawtoothing tokamak plasmas
NASA Astrophysics Data System (ADS)
Ahn, Jae-H.; Garbet, X.; Lütjens, H.; Guirlet, R.
2016-12-01
The effect of sawteeth on impurity dynamics is studied with the XTOR-2F code. Non-linear full 3D MHD simulations including appropriate fluid equations for impurities in the high collisional regime show that the presence of regular sawtooth crashes affects the impurity behaviour. A spatial non-uniformity of 5 % in post-crash impurity density profiles persists due to 2D structures of impurity density which appear during sawtooth crashes. They are shown to be mainly driven by the \\mathbf{E}× \\mathbf{B} velocity, and are responsible for the sudden impurity transport in the core plasmas.
Voronine, Dmitri V.; Abramavicius, Darius; Mukamel, Shaul
2008-01-01
Two-dimensional electronic chirality-induced signals of excitons in the photosynthetic Fenna-Matthews-Olson complex from two species of green sulfur bacteria (Chlorobium tepidum and Prosthecochloris aestuarii) are compared. The spectra are predicted to provide sensitive probes of local protein environment of the constituent bacteriochlorophyll a chromophores and reflect electronic structure variations (site energies and couplings) of the two complexes. Pulse polarization configurations are designed that can separate the coherent and incoherent exciton dynamics contributions to the two-dimensional spectra. PMID:18676650
Huizinga, Richard J.
2007-01-01
The evaluation of scour at bridges throughout the State of Missouri has been ongoing since 1991, and most of these evaluations have used one-dimensional hydraulic analysis and application of conventional scour depth prediction equations. Occasionally, the complex conditions of a site dictate a more thorough assessment of the stream hydraulics beyond a one-dimensional model. This was the case for structure A-1700, the Interstate 155 bridge crossing the Mississippi River near Caruthersville, Missouri. To assess the complex hydraulics at this site, a two-dimensional hydrodynamic flow model was used to simulate flow conditions on the Mississippi River in the vicinity of the Interstate 155 structure A-1700. The model was used to simulate flow conditions for three discharges: a flood that occurred on April 4, 1975 (the calibration flood), which had a discharge of 1,658,000 cubic feet per second; the 100-year flood, which has a discharge of 1,960,000 cubic feet per second; and the project design flood, which has a discharge of 1,974,000 cubic feet per second. The project design flood was essentially equivalent to the flood that would cause impending overtopping of the mainline levees along the Mississippi River in the vicinity of structure A-1700. Discharge and river-stage readings from the flood of April 4, 1975, were used to calibrate the flow model. The model was then used to simulate the 100-year and project design floods. Hydraulic flow parameters obtained from the three flow simulations were applied to scour depth prediction equations to determine contraction, local pier, and abutment scour depths at structure A-1700. Contraction scour and local pier scour depths computed for the project design discharge generally were the greatest, whereas the depths computed for the calibration flood were the least. The maximum predicted total scour depth (contraction and local pier scour) for the calibration flood was 66.1 feet; for the 100-year flood, the maximum predicted total
Overview of the Simulation of Wave Interactions with MHD Project (SWIM)
NASA Astrophysics Data System (ADS)
Batchelor, Donald
2010-11-01
The SWIM center has the scientific objectives of: improving our understanding of interactions that both RF wave and particle sources have on extended-MHD phenomena, improving our capability for predicting and optimizing the performance of burning plasmas, developing 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, addressing mathematics issues related to the multi-scale, coupled physics of RF waves and extended MHD, and optimizing the integrated system on high performance computers. Our Center has now built an end-to-end computational system that allows existing physics codes to be able to function together in a parallel environment and connects them to utility software components and data management systems. We have used this framework to couple together state-of-the-art fusion energy codes to produce a unique and world-class simulation capability. A physicist's overview of the Integrated Plasma Simulator (IPS) will be given and applications described. For example the IPS is being employed to support ITER with operational scenario studies.
NASA Astrophysics Data System (ADS)
Kawasaki, Akira; Kubota, Kenichi; Funaki, Ikkoh; Okuno, Yoshihiro
2016-09-01
Steady-state and self-field magnetoplasmadynamic (MPD) thruster, which utilizes high-intensity direct-current (DC) discharge, is one of the prospective candidates of future high-power electric propulsion devices. In order to accurately assess the thrust performance and the electrode temperature, input electric power and wall heat flux must correctly be evaluated where electrostatic sheaths formed in close proximity of the electrodes affect these quantities. Conventional model simulates only plasma flows occurring in MPD thrusters with the absence of electrostatic sheath consideration. Therefore, this study extends the conventional model to a coupled magnetohydrodynamic (MHD) and thermal model by incorporating the phenomena relevant to the electrostatic sheaths. The sheaths are implemented as boundary condition of the MHD model on the walls. This model simulated the operation of the 100-kW-class thruster at discharge current ranging from 6 to 10 kA with argon propellant. The extended model reproduced the discharge voltages and wall heat load which are consistent with past experimental results. In addition, the simulation results indicated that cathode sheath voltages account for approximately 5-7 V subject to approximately 20 V of discharge voltages applied between the electrodes. This work was supported by JSPS KAKENHI Grant Numbers 26289328 and 15J10821.
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
FLASH MHD simulations of experiments that study shock-generated magnetic fields
NASA Astrophysics Data System (ADS)
Tzeferacos, P.; Fatenejad, M.; Flocke, N.; Graziani, C.; Gregori, G.; Lamb, D. Q.; Lee, D.; Meinecke, J.; Scopatz, A.; Weide, K.
2015-12-01
We summarize recent additions and improvements to the high energy density physics capabilities in FLASH, highlighting new non-ideal magneto-hydrodynamic (MHD) capabilities. We then describe 3D Cartesian and 2D cylindrical FLASH MHD simulations that have helped to design and analyze experiments conducted at the Vulcan laser facility. In these experiments, a laser illuminates a carbon rod target placed in a gas-filled chamber. A magnetic field diagnostic (called a Bdot) employing three very small induction coils is used to measure all three components of the magnetic field at a chosen point in space. The simulations have revealed that many fascinating physical processes occur in the experiments. These include megagauss magnetic fields generated by the interaction of the laser with the target via the Biermann battery mechanism, which are advected outward by the vaporized target material but decrease in strength due to expansion and resistivity; magnetic fields generated by an outward expanding shock via the Biermann battery mechanism; and a breakout shock that overtakes the first wave, the contact discontinuity between the target material and the gas, and then the initial expanding shock. Finally, we discuss the validation and predictive science we have done for this experiment with FLASH.
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.
Extension of the MURaM Radiative MHD Code for Coronal Simulations
NASA Astrophysics Data System (ADS)
Rempel, M.
2017-01-01
We present a new version of the MURaM radiative magnetohydrodynamics (MHD) code that allows for simulations spanning from the upper convection zone into the solar corona. We implement the relevant coronal physics in terms of optically thin radiative loss, field aligned heat conduction, and an equilibrium ionization equation of state. We artificially limit the coronal Alfvén and heat conduction speeds to computationally manageable values using an approximation to semi-relativistic MHD with an artificially reduced speed of light (Boris correction). We present example solutions ranging from quiet to active Sun in order to verify the validity of our approach. We quantify the role of numerical diffusivity for the effective coronal heating. We find that the (numerical) magnetic Prandtl number determines the ratio of resistive to viscous heating and that owing to the very large magnetic Prandtl number of the solar corona, heating is expected to happen predominantly through viscous dissipation. We find that reasonable solutions can be obtained with values of the reduced speed of light just marginally larger than the maximum sound speed. Overall this leads to a fully explicit code that can compute the time evolution of the solar corona in response to photospheric driving using numerical time steps not much smaller than 0.1 s. Numerical simulations of the coronal response to flux emergence covering a time span of a few days are well within reach using this approach.
Alignment of Velocity and Magnetic Fluctuations in Simulations of Anisotropic MHD Turbulence
NASA Astrophysics Data System (ADS)
Ng, C. S.; Bhattacharjee, A.
2007-11-01
There has been recent theoretical interest in the effect of the alignment of velocity and magnetic fluctuations in three-dimensional (3D) MHD turbulence with a large-scale magnetic field [Boldyrev 2005, 2006]. This theory predicts that the angle θ between the velocity and magnetic fluctuation vectors has a scaling of θ&1/4circ;, where λ is the spatial scale of the fluctuations. There have also been simulations on 3D forced MHD turbulence that supports this prediction [Mason et al. 2006, 2007]. The scaling has also been tested against observations of solar wind turbulence [Podesta et al. 2007]. We report here simulation results based on decaying 2D turbulence. The scaling of θ&1/4circ; and Iroshnikov-Kraichnan scaling has also been observed within a range of time interval and spatial scales, despite the fact that Boldyrev's theory was developed for fully 3D turbulence in the presence of a strong external field. As the external field is reduced in magnitude and becomes comparable to the magnitude of magnetic fluctuations or lower, the scale-dependent alignment is weakened. Implications for observations of solar wind turbulence will be discussed.
A global MHD simulation of an event with a quasi-steady northward IMF
NASA Astrophysics Data System (ADS)
Merkin, V. G.; Papadopoulos, D.; Lyon, J.; Anderson, B.
2005-12-01
We show results of a global MHD simulation, using the Lyon-Fedder-Mobarry (LFM) model, of an event previously examined using data from Iridium spacecraft observations as well as DMSP and IMAGE FUV data. The event is chosen because of the steady northward IMF sustained over a three-hour period during 16 July 2000. The Iridium observations showed very weak or absent Region 2 currents in the ionosphere, which makes the event favorable for global MHD modeling, despite the fact that it occured on the day after the "Bastille Day" storm, and there was a significant remnant ring current in the magnetosphere as indicated by a relatively high Dst index. Here, we compare the ionospheric field-aligned current and electric potential patterns with those recovered from Iridium observations. Particular attention is paid to a comparative analysis of the Pointing flux and the energy flux of precipitating particles, and the verification of the simulated particle flux against IMAGE FUV observations, that is used to validate the LFM precipitation model during weak driving.
Study of reconnection events through Global MHD simulation and observational data
NASA Astrophysics Data System (ADS)
Cardoso, F. R.; Gonzalez, W. D.; Sibeck, D. G.; Kuznetsova, M. M.; Alves, M. V.
2011-12-01
Magnetic reconnection is the dominant mechanism for solar wind energy and momentum transfer to the magnetosphere. It can be a continuous or a transient process. Time-varying reconnection produces flux transfer events (FTEs) which can be identified by bipolar signatures in the component of the magnetic field normal to the magnetopause, deflections in the component tangential, and variations in the magnetic field magnitude. Some events exhibit the mixed magnetospheric and magnetosheath plasma populations expected for reconnection. Global magnetohydrodynamics (MHD) simulations are important tools to understand the relevant magnetic reconnection mechanisms. We have identified magnetic reconnection events, especially FTEs, in global MHD simulations and observations. We study their spatial and temporal characteristics as a function of solar wind parameters, in particular the interplanetary magnetic field orientation. We determine the origin of FTEs as well as the properties that describe them such as their dimension, extent and motion as a function of time. In particular, we track the motion of FTEs in an attempt to determine their point of origin, their destination, and how fast they move.
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.
TWO-DIMENSIONAL TOPOLOGY OF COSMOLOGICAL REIONIZATION
Wang, Yougang; Xu, Yidong; Chen, Xuelei; Park, Changbom; Kim, Juhan E-mail: cbp@kias.re.kr
2015-11-20
We study the two-dimensional topology of the 21-cm differential brightness temperature for two hydrodynamic radiative transfer simulations and two semi-numerical models. In each model, we calculate the two-dimensional genus curve for the early, middle, and late epochs of reionization. It is found that the genus curve depends strongly on the ionized fraction of hydrogen in each model. The genus curves are significantly different for different reionization scenarios even when the ionized faction is the same. We find that the two-dimensional topology analysis method is a useful tool to constrain the reionization models. Our method can be applied to the future observations such as those of the Square Kilometre Array.
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
NASA Astrophysics Data System (ADS)
LE CHAT, G.; Kasper, J. C.; Cohen, O.; Spangler, S.
2013-05-01
Faraday rotation observations of natural radio sources allow remote diagnostics of the density and magnetic field of the solar corona. We use linear polarization observations made with the NRAO Very Large Array at frequencies of 1465 and 1665 MHz of 33 polarized radio sources occulted by the solar corona within 5 to 14 solar radii. The measurements were made during May 1997 (Mancuso and Spangler, 2000), March 2005 and april 2005 (Ingleby et al., 2005), corresponding to Carrington rotation number 1922, 1923, 2027 and 2028. We compare the observed Faraday rotation values with values extracted from MHD steady-state simulations of the solar corona using the BATS-R-US model. The simulations are driven by magnetogram data taken at the same time as the observed data. We present the agreement between the model and the Faraday rotation measurements, and we discuss the contraints imposed on models of the quiet corona and CMEs by these observations.
Kim, Tae K.; Pogorelov, Nikolai V.; Borovikov, Sergey N.; Clover, John M.; Jackson, Bernard V.; Yu, Hsiu-Shan
2012-11-20
Numerical modeling of the heliosphere is a critical component of space weather forecasting. The accuracy of heliospheric models can be improved by using realistic boundary conditions and confirming the results with in situ spacecraft measurements. To accurately reproduce the solar wind (SW) plasma flow near Earth, we need realistic, time-dependent boundary conditions at a fixed distance from the Sun. We may prepare such boundary conditions using SW speed and density determined from interplanetary scintillation (IPS) observations, magnetic field derived from photospheric magnetograms, and temperature estimated from its correlation with SW speed. In conclusion, we present here the time-dependent MHD simulation results obtained by using the 2011 IPS data from the Solar-Terrestrial Environment Laboratory as time-varying inner boundary conditions and compare the simulated data at Earth with OMNI data (spacecraft-interspersed, near-Earth solar wind data).
Broken Ergodicity in Two-Dimensional Homogeneous Magnetohydrodynamic Turbulence
NASA Technical Reports Server (NTRS)
Shebalin, John V.
2010-01-01
Two-dimensional (2-D) homogeneous magnetohydrodynamic (MHD) turbulence has many of the same qualitative features as three-dimensional (3-D) homogeneous MHD turbulence.The se features include several ideal invariants, along with the phenomenon of broken ergodicity. Broken ergodicity appears when certain modes act like random variables with mean values that are large compared to their standard deviations, indicating a coherent structure or dynamo.Recently, the origin of broken ergodicity in 3-D MHD turbulence that is manifest in the lowest wavenumbers was explained. Here, a detailed description of the origins of broken ergodicity in 2-D MHD turbulence is presented. It will be seen that broken ergodicity in ideal 2-D MHD turbulence can be manifest in the lowest wavenumbers of a finite numerical model for certain initial conditions or in the highest wavenumbers for another set of initial conditions.T he origins of broken ergodicity in ideal 2-D homogeneous MHD turbulence are found through an eigen analysis of the covariance matrices of the modal probability density functions.It will also be shown that when the lowest wavenumber magnetic field becomes quasi-stationary, the higher wavenumber modes can propagate as Alfven waves on these almost static large-scale magnetic structures
Two-Species, 3D, MHD Simulation of Europa's Interaction with Jupiter's Magnetosphere
NASA Technical Reports Server (NTRS)
Liu, Yifan; Nagy, Andrew F.; Kabin, Konstantin; Combi, Michael R.; DeZeeuw, Darren L.; Gombosi, Tamas I.; Powell, Kenneth G.
2000-01-01
The interaction of Europa with the Jovian a magnetosphere has been studied by using a two species in ideal magnetohydrodynamic (MHD) numerical model. This model considers the upstream plasma in the Jovian magnetosphere and the molecular oxygen ions in the ionosphere of Europa, separately. We present results a from simulation studies, which take into account impact ionization, recombination, and the effect of a possible induced dipole magnetic field of Europa. The total mass loading of the magnetospheric flow and the ionization frequency used in the model are consistent with the estimates of Europa's ionosphere and atmosphere. The multi-species MHD equations are solved by using a finite volume, high-order, Godunov-type method on an adoptively refined unstructured grid, which allows a detailed modeling of the region near Europa's surface, while still resolving both the upstream region and the satellite's wake. We have paid special attention to the wake of Europa, in order to be able to make comparisons with the Galileo's E4 flyby observations, as well as other model calculations. The calculated escape flux of a O2+ down the tail was found to be about 5.6 x 10(exp 25) s(sup -1).
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 λ concentrated in the COFC then diffuses to the core region so as to reduce the gradient in λ, relaxing in the direction of the Taylor state.
Proposal of a brand-new gyrokinetic algorithm for global MHD simulation
NASA Astrophysics Data System (ADS)
Naitou, Hiroshi; Kobayashi, Kenichi; Hashimoto, Hiroki; Andachi, Takehisa; Lee, Wei-Li; Tokuda, Shinji; Yagi, Masatoshi
2009-11-01
A new algorithm for the gyrokinetic PIC code is proposed. The basic equations are energy conserving and composed of (1) the gyrokinetic Vlasov (GKV) equation, (2) the Vortex equation, and (3) the generalized Ohm's law along the magnetic field. Equation (2) is used to advance electrostatic potential in time. Equation (3) is used to advance longitudinal component of vector potential in time as well as estimating longitudinal induced electric field to accelerate charged particles. The particle information is used to estimate pressure terms in equation (3). The idea was obtained in the process of reviewing the split-weight-scheme formalism. This algorithm was incorporated in the Gpic-MHD code. Preliminary results for the m=1/n=1 internal kink mode simulation in the cylindrical geometry indicate good energy conservation, quite low noise due to particle discreteness, and applicability to larger spatial scale and higher beta regimes. The advantage of new Gpic-MHD is that the lower order moments of the GKV equation are estimated by the moment equation while the particle information is used to evaluate the second order moment.
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.
NASA Astrophysics Data System (ADS)
Harvey, L. D. Danny
1992-06-01
A two-dimensional (latitude-depth) deep ocean model is presented which is coupled to a sea ice model and an Energy Balance Climate Model (EBCM), the latter having land-sea and surface-air resolution. The processes which occur in the ocean model are thermohaline overturning driven by the horizontal density gradient, shallow wind-driven overturning cells, convective overturning, and vertical and horizontal diffusion of heat and salt. The density field is determined from the temperature and salinity fields using a nonlinear equation of state. Mixed layer salinity is affected by evaporation, precipitation, runoff from continents, and sea ice freezing and melting, as well as by advective, convective, and diffusive exchanges with the deep ocean. The ocean model is first tested in an uncoupled mode, in which hemispherically symmetric mixed layer temperature and salinity, or salinity flux, are specified as upper boundary conditions. An experiment performed with previous models is repeated in which a mixed layer salinity perturbation is introduced in the polar half of one hemisphere after switching from a fixed salinity to a fixed salinity flux boundary condition. For small values of the vertical diffusion coefficient KV, the model undergoes self-sustained oscillations with a period of about 1500 years. With larger values of KV, the model locks into either an asymmetric mode with a single overturning cell spanning both hemispheres, or a symmetric quiescent state with downwelling near the equator, upwelling at high latitudes, and a warm deep ocean (depending on the value of KV). When the ocean model is forced with observed mixed layer temperature and salinity, no oscillations occur. The model successfully simulates the very weak meridional overturning and strong Antarctic Circumpolar Current at the latitudes of the Drake Passage. The coupled EBCM-deep ocean model displays internal oscillations with a period of 3000 years if the ocean fraction is uniform with latitude and KV
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
Lagrangian MHD Particle-in-Cell simulations of coronal interplanetary shocks driven by observations
NASA Astrophysics Data System (ADS)
Lapenta, Giovanni; Bacchini, Fabio; Bemporad, Alessandro; Susino, Roberto; Olshevskyi, Vyacheslav
2016-04-01
In this work, we compare the spatial distribution of the plasma parameters along the June 11, 1999 CME-driven shock front with the results obtained from a CME-like event simulated with the FLIPMHD3D code, based on the FLIP-MHD Particle-in-Cell (PiC) method. The observational data are retrieved from the combination of white-light (WL) coronagraphic data (for the upstream values) and the application of the Rankine-Hugoniot (RH) equations (for the downstream values). The comparison shows a higher compression ratio X and Alfvénic Mach number MA at the shock nose, and a stronger magnetic field deflection d towards the flanks, in agreement with observations. Then, we compare the spatial distribution of MA with the profiles obtained from the solutions of the shock adiabatic equation relating MA, X, and the angle between the upstream magnetic field and the shock front normal for the special cases of parallel and perpendicular shock, and with a semi-empirical expression for a generically oblique shock. The semi-empirical curve approximates the actual values of MA very well, if the effects of a non-negligible shock thickness and plasma-to magnetic pressure ratio are taken into account throughout the computation. Moreover, the simulated shock turns out to be supercritical at the nose and sub-critical at the flanks. Finally, we develop a new 1D Lagrangian ideal MHD method based on the GrAALE code, to simulate the ion-electron temperature decoupling due to the shock transit. Two models are used, a simple solar wind model and a variable-gamma model. Both produce results in agreement with observations, the second one being capable of introducing the physics responsible for the additional electron heating due to secondary effects (collisions, Alfvén waves, etc.). Work supported by the European Commission under the SWIFF project (swiff.eu)
NASA Technical Reports Server (NTRS)
Benyo, Theresa L.
2010-01-01
Preliminary flow matching has been demonstrated for a MHD energy bypass system on a supersonic turbojet engine. The Numerical Propulsion System Simulation (NPSS) environment was used to perform a thermodynamic cycle analysis to properly match the flows from an inlet to a MHD generator and from the exit of a supersonic turbojet to a MHD accelerator. Working with various operating conditions such as the enthalpy extraction ratio and isentropic efficiency of the MHD generator and MHD accelerator, interfacing studies were conducted between the pre-ionizers, the MHD generator, the turbojet engine, and the MHD accelerator. This paper briefly describes the NPSS environment used in this analysis and describes the NPSS analysis of a supersonic turbojet engine with a MHD generator/accelerator energy bypass system. Results from this study have shown that using MHD energy bypass in the flow path of a supersonic turbojet engine increases the useful Mach number operating range from 0 to 3.0 Mach (not using MHD) to an explored and desired range of 0 to 7.0 Mach.
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
NASA Technical Reports Server (NTRS)
Yung, Yuk L.; Shia, R. L.; Allen, M.; Zurek, R. W.; Crisp, D.; Wen, J. S.
1988-01-01
The bulk of O sub 3 destruction in the Antarctic stratosphere takes place in the lower stratosphere between 15 and 25 km. Both O sub 3 and the halogen reservoir species have their origins in the higher altitude region (20 to 30 km) in the equatorial and mid-latitude stratosphere. Using the Caltech-JPL two-dimensional residual circulation model, researchers investigate the growth of stratospheric halogen due to the increase of CFCl sub 3 and CF sub 2 Cl sub 2.
Behavior of fast earthward flow near the braking region: Hall MHD simulation
NASA Astrophysics Data System (ADS)
Lu, Xingqiang; Ma, Zhiwei; Guo, Wei
2016-10-01
Behavior of the fast earthward flow near the braking region in the magnetotail during a substorm is investigated using the Hall MHD simulation. The results indicate that the high-speed earthward plasma flow is associated with fast reconnection in the middle tail. The fast flow is mainly confined in the range -1.5RE < z < 1.5RE . In the region of -15RE < x < -9RE , due to intermittent magnetic reconnection, the earthward flow exhibits a fluctuating property, i.e., the flow is localized in space and is bursty in time. The pile-up of the magnetic flux and plasma in the near-Earth region leads to formation of the fast-flow braking region or dipolarization front. After colliding into the fast-flow braking region, a part of the Earth flow bounces back, and leads to an intermittent tailward flow in the near-Earth magnetotail.
3D MHD SIMULATION OF FLARE SUPRA-ARCADE DOWNFLOWS IN A TURBULENT CURRENT SHEET MEDIUM
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.
The magnetic topology of the plasmoid flux rope in a MHD-simulation of magnetotail reconnection
NASA Astrophysics Data System (ADS)
Birn, J.; Hesse, M.
On the basis of a 3D MHD simulation, the magnetic topology of a plasmoid that forms by a localized reconnection process in a magnetotail configuration (including a net dawn-dusk magnetic field component B sub y N is discussed. As a consequence of B sub y N not equalling 0, the plasmoid assumes a helical flux rope structure rather than an isolated island or bubble structure. Initially all field lines of the plasmoid flux rope remain connected with the earth, while at later times a gradually increasing amount of flux tubes becomes separated, connecting to either the distant boundary or to the flank boundaries. In this stage, topologically different flux tubes become tangled and wrapped around each other, consistent with predictions on the basis of an ad hoc plasmoid model.
The magnetic topology of the plasmoid flux rope in a MHD-simulation of magnetotail reconnection
NASA Astrophysics Data System (ADS)
Birn, J.; Hesse, M.
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 ByN. As a consequence of ByN ≠ 0 the plasmoid assumes a helical flux rope structure rather than an isolated island or bubble structure. Initially all field lines of the plasmoid flux rope remain connected with the Earth, while at later times a gradually increasing amount of flux tubes becomes separated, connecting to either the distant boundary or to the flank boundaries. In this stage topologically different flux tubes become tangled and wrapped around each other, consistent with predictions on the basis of an ad-hoc plasmoid model.
The magnetic topology of the plasmoid flux rope in a MHD simulation of magnetotail reconnection
NASA Astrophysics Data System (ADS)
Birn, J.; Hesse, M.
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 plasmoid gets a helical flux rope structure rather than an isolated island or bubble structure. Initially all field lines of the plasmoid flux rope remain connected with the Earth, while at later times a gradually increasing number 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 plasmoid models.
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.
Kim, Tae K.; Pogorelov, Nikolai V.; Borovikov, Sergey N.; ...
2012-11-20
Numerical modeling of the heliosphere is a critical component of space weather forecasting. The accuracy of heliospheric models can be improved by using realistic boundary conditions and confirming the results with in situ spacecraft measurements. To accurately reproduce the solar wind (SW) plasma flow near Earth, we need realistic, time-dependent boundary conditions at a fixed distance from the Sun. We may prepare such boundary conditions using SW speed and density determined from interplanetary scintillation (IPS) observations, magnetic field derived from photospheric magnetograms, and temperature estimated from its correlation with SW speed. In conclusion, we present here the time-dependent MHD simulationmore » results obtained by using the 2011 IPS data from the Solar-Terrestrial Environment Laboratory as time-varying inner boundary conditions and compare the simulated data at Earth with OMNI data (spacecraft-interspersed, near-Earth solar wind data).« less
Global simulations of protoplanetary disks with net magnetic flux. I. Non-ideal MHD case
NASA Astrophysics Data System (ADS)
Béthune, William; Lesur, Geoffroy; Ferreira, Jonathan
2017-04-01
Context. The planet-forming region of protoplanetary disks is cold, dense, and therefore weakly ionized. For this reason, magnetohydrodynamic (MHD) turbulence is thought to be mostly absent, and another mechanism has to be found to explain gas accretion. It has been proposed that magnetized winds, launched from the ionized disk surface, could drive accretion in the presence of a large-scale magnetic field. Aims: The efficiency and the impact of these surface winds on the disk structure is still highly uncertain. We present the first global simulations of a weakly ionized disk that exhibits large-scale magnetized winds. We also study the impact of self-organization, which was previously demonstrated only in non-stratified models. Methods: We perform numerical simulations of stratified disks with the PLUTO code. We compute the ionization fraction dynamically, and account for all three non-ideal MHD effects: ohmic and ambipolar diffusions, and the Hall drift. Simplified heating and cooling due to non-thermal radiation is also taken into account in the disk atmosphere. Results: We find that disks can be accreting or not, depending on the configuration of the large-scale magnetic field. Magnetothermal winds, driven both by magnetic acceleration and heating of the atmosphere, are obtained in the accreting case. In some cases, these winds are asymmetric, ejecting predominantly on one side of the disk. The wind mass loss rate depends primarily on the average ratio of magnetic to thermal pressure in the disk midplane. The non-accreting case is characterized by a meridional circulation, with accretion layers at the disk surface and decretion in the midplane. Finally, we observe self-organization, resulting in axisymmetric rings of density and associated pressure "bumps". The underlying mechanism and its impact on observable structures are discussed.
Cloaking two-dimensional fermions
Lin, De-Hone
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.
NASA Technical Reports Server (NTRS)
Jackman, Charles H.; Douglass, Anne R.; Stolarski, Richard S.; Guthrie, Paul D.; Thompson, A. M.
1990-01-01
A two dimensional (altitude and latitude) model of the atmosphere is used to investigate problems relating to the variability of the dynamics and temperature of the atmosphere on the ozone distribution, solar cycle variations of atmospheric constituents, the sensitivity of model results to tropospheric trace gas sources, and assessment computations of changes in ozone related to manmade influences. In a comparison between two dimensional model results in which the odd nitrogen family was transported together and model results in which the odd nitrogen species was transported separately, it was found that the family approximations are adequate for perturbation scenario calculations.
An MHD simulation of plasmoid instability in the dayside ionosphere of an unmagnetized planet
NASA Astrophysics Data System (ADS)
Hitoshi, S.; Terada, N.; Kasaba, Y.
2015-12-01
A numerical simulation of magnetic reconnection in the dayside ionosphere of an unmagnetized planet and a comparison of the size distribution of flux ropes obtained from simulation with that from observation will be reported. Flux ropes have been frequently observed in the dayside ionospheres of Venus and Mars[Russell and Elphic, 1979; Cloutier et al.,1999] and their radius has been found to be between 6 to 12 km near the subsolar location of Venus[Russell et al., 1990]. Dreher et al. [1995] suggested using an MHD simulation that reconnection caused by an IMF rotation can generate flux ropes at the Venus ionopause. However, Dreher et al. [1995] examined only the linear stage of reconnection, so the nonlinear stage that takes into consideration the vertical convection of the reconnection site along the intrinsic convection in the Venus ionosphere has yet to be investigated. In this study, using a 2-D multi-species MHD simulation, the spatiotemporal evolution of reconnection in the ionosphere of Venus is examined. The size distribution of flux ropes is also examined and the validity of the generation mechanism of flux ropes is discussed by comparing the rope size distribution with the observed one. In the ionosphere of Venus, our simulation result shows that plasmoid instability [Loureiro et al., 2007] occurs in a Sweet-Parker (SP) current sheet above the altitude where Lundquist number exceeds 106, and consequently many plasmoids are generated. In the nonlinear stage, secondary reconnections occur in the current sheets, which exist between adjacent pairs of plasmoids, and thus smaller flux ropes are created. It has been suggested that the smaller side of the size distribution increases as a result of hierarchical reconnections in the SP current sheet [Shibata et al., 2001]. The observational size distribution [Vignes et al., 2003] shows that the population of small flux ropes is larger than that of large ones and it is consistent with the simulation result. Through
ON THE ORIGIN OF THE TYPE II SPICULES: DYNAMIC THREE-DIMENSIONAL MHD SIMULATIONS
MartInez-Sykora, Juan; Hansteen, Viggo; Moreno-Insertis, Fernando E-mail: viggo.hansteen@astro.uio.no
2011-07-20
Recent high temporal and spatial resolution observations of the chromosphere have forced the definition of a new type of spicule, 'type II's', that are characterized by rising rapidly, having short lives, and by fading away at the end of their lifetimes. Here, we report on features found in realistic three-dimensional simulations of the outer solar atmosphere that resemble the observed type II spicules. These features evolve naturally from the simulations as a consequence of the magnetohydrodynamical evolution of the model atmosphere. The simulations span from the upper layer of the convection zone to the lower corona and include the emergence of a horizontal magnetic flux. The state-of-art Oslo Staggered Code is used to solve the full MHD equations with non-gray and non-LTE radiative transfer and thermal conduction along the magnetic field lines. We describe in detail the physics involved in a process which we consider a possible candidate for the driver mechanism that produces type II spicules. The modeled spicule is composed of material rapidly ejected from the chromosphere that rises into the corona while being heated. Its source lies in a region with large field gradients and intense electric currents, which lead to a strong Lorentz force that squeezes the chromospheric material, resulting in a vertical pressure gradient that propels the spicule along the magnetic field, as well as Joule heating, which heats the jet material, forcing it to fade.
Non-linear MHD Simulation of ELMs including Pellet Triggered ones for KSTAR tokamak
NASA Astrophysics Data System (ADS)
Han, Hyunsun; Park, G.; Strauss, H.; Kim, J. Y.
2011-10-01
Three-dimensional non-linear MHD simulations have been conducted to investigate the qualitative characteristics of ELM(Edge Localized Mode)s including pellet induced ones using the M3D code. A linearized velocity perturbation of initial equilibrium is employed to trigger the ELM instability for the simulation of natural ELM, while a density blob, which represents the ionized pellet ablation and is located within the edge pedestal, is adopted in an adiabatic condition for that of pellet induced one. The initial equilibrium is constructed based on a H-mode plasma of KSTAR(Korea Superconducting Tokamak Advanced Research) device. It is found that characteristics of natural ELM simulation are in qualitative agreement with the experimental observations including that density perturbation is much larger than temperature one during ELM instability. Regarding the pellet induced ELM, it is observed that the locally increased pressure due to the fast parallel heat conduction compared to the spread of density perturbation triggers the peeling-ballooning instability resulting in ELM-like relaxation. Detailed results will be presented in the discussion of underlying mechanism and application to KSTAR tokamak.
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.
Internetwork magnetic field as revealed by two-dimensional inversions
NASA Astrophysics Data System (ADS)
Danilovic, S.; van Noort, M.; Rempel, M.
2016-09-01
Context. Properties of magnetic field in the internetwork regions are still fairly unknown because of rather weak spectropolarimetric signals. Aims: We address the matter by using the two-dimensional (2D) inversion code, which is able to retrieve the information on smallest spatial scales up to the diffraction limit, while being less susceptible to noise than most of the previous methods used. Methods: Performance of the code and the impact of various effects on the retrieved field distribution is tested first on the realistic magneto-hydrodynamic (MHD) simulations. The best inversion scenario is then applied to the real data obtained by Spectropolarimeter (SP) on board Hinode. Results: Tests on simulations show that: (1) the best choice of node position ensures a decent retrieval of all parameters; (2) the code performs well for different configurations of magnetic field; (3) slightly different noise levels or slightly different defocus included in the spatial point spread function (PSF) produces no significant effect on the results; and (4) temporal integration shifts the field distribution to a stronger, more horizontally inclined field. Conclusions: Although the contribution of the weak field is slightly overestimated owing to noise, 2D inversions are able to recover well the overall distribution of the magnetic field strength. Application of the 2D inversion code on the Hinode SP internetwork observations reveals a monotonic field strength distribution. The mean field strength at optical depth unity is ~ 130 G. At higher layers, field strength drops as the field becomes more horizontal. Regarding the distribution of the field inclination, tests show that we cannot directly retrieve it with the observations and tools at hand, however, the obtained distributions are consistent with those expected from simulations with a quasi-isotropic field inclination after accounting for observational effects.
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.
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.
Kirigami for Two-Dimensional Electronic Membranes
NASA Astrophysics Data System (ADS)
Qi, Zenan; Bahamon, Dario; Campbell, David; Park, Harold
2015-03-01
Two-dimensional materials have recently drawn tremendous attention because of their unique properties. In this work, we introduce the notion of two-dimensional kirigami, where concepts that have been used almost exclusively for macroscale structures are applied to dramatically enhance their stretchability. Specifically, we show using classical molecular dynamics simulations that the yield and fracture strains of graphene and MoS2 can be enhanced by about a factor of three using kirigami as compared to standard monolayers. Finally, using graphene as an example, we demonstrate that the kirigami structure may open up interesting opportunities in coupling to the electronic behavior of 2D materials. Authors acknowledge Mechanical Engineering and Physics departments at Boston University, and Mackgrafe at Mackenzie Presbyterian University.
Cooperative two-dimensional directed transport
NASA Astrophysics Data System (ADS)
Zheng, Zhigang; Chen, Hongbin
2010-11-01
A mechanism for the cooperative directed transport in two-dimensional ratchet potentials is proposed. With the aid of mutual couplings among particles, coordinated unidirectional motion along the ratchet direction can be achieved by transforming the energy from the transversal rocking force (periodic or stochastic) to the work in the longitude direction. Analytical predictions on the relation between the current and other parameters for the ac-driven cases are given, which are in good agreement with numerical simulations. Stochastic driving forces can give rise to the resonant directional transport. The effect of the free length, which has been explored in experiments on the motility of bipedal molecular motors, is investigated for both the single- and double-channel cases. The mechanism and results proposed in this letter may both shed light on the collective locomotion of molecular motors and open ways on studies in two-dimensional collaborative ratchet dynamics.
Two-Dimensional NMR Lineshape Analysis
NASA Astrophysics Data System (ADS)
Waudby, Christopher A.; Ramos, Andres; Cabrita, Lisa D.; Christodoulou, John
2016-04-01
NMR titration experiments are a rich source of structural, mechanistic, thermodynamic and kinetic information on biomolecular interactions, which can be extracted through the quantitative analysis of resonance lineshapes. However, applications of such analyses are frequently limited by peak overlap inherent to complex biomolecular systems. Moreover, systematic errors may arise due to the analysis of two-dimensional data using theoretical frameworks developed for one-dimensional experiments. Here we introduce a more accurate and convenient method for the analysis of such data, based on the direct quantum mechanical simulation and fitting of entire two-dimensional experiments, which we implement in a new software tool, TITAN (TITration ANalysis). We expect the approach, which we demonstrate for a variety of protein-protein and protein-ligand interactions, to be particularly useful in providing information on multi-step or multi-component interactions.
Two-Dimensional NMR Lineshape Analysis
Waudby, Christopher A.; Ramos, Andres; Cabrita, Lisa D.; Christodoulou, John
2016-01-01
NMR titration experiments are a rich source of structural, mechanistic, thermodynamic and kinetic information on biomolecular interactions, which can be extracted through the quantitative analysis of resonance lineshapes. However, applications of such analyses are frequently limited by peak overlap inherent to complex biomolecular systems. Moreover, systematic errors may arise due to the analysis of two-dimensional data using theoretical frameworks developed for one-dimensional experiments. Here we introduce a more accurate and convenient method for the analysis of such data, based on the direct quantum mechanical simulation and fitting of entire two-dimensional experiments, which we implement in a new software tool, TITAN (TITration ANalysis). We expect the approach, which we demonstrate for a variety of protein-protein and protein-ligand interactions, to be particularly useful in providing information on multi-step or multi-component interactions. PMID:27109776
Two-dimensional thermofield bosonization
Amaral, R.L.P.G.
2005-12-15
The main objective of this paper was to obtain an operator realization for the bosonization of fermions in 1 + 1 dimensions, at finite, non-zero temperature T. This is achieved in the framework of the real-time formalism of Thermofield Dynamics. Formally, the results parallel those of the T = 0 case. The well-known two-dimensional Fermion-Boson correspondences at zero temperature are shown to hold also at finite temperature. To emphasize the usefulness of the operator realization for handling a large class of two-dimensional quantum field-theoretic problems, we contrast this global approach with the cumbersome calculation of the fermion-current two-point function in the imaginary-time formalism and real-time formalisms. The calculations also illustrate the very different ways in which the transmutation from Fermi-Dirac to Bose-Einstein statistics is realized.
Two-dimensional NMR spectrometry
Farrar, T.C.
1987-06-01
This article is the second in a two-part series. In part one (ANALYTICAL CHEMISTRY, May 15) the authors discussed one-dimensional nuclear magnetic resonance (NMR) spectra and some relatively advanced nuclear spin gymnastics experiments that provide a capability for selective sensitivity enhancements. In this article and overview and some applications of two-dimensional NMR experiments are presented. These powerful experiments are important complements to the one-dimensional experiments. As in the more sophisticated one-dimensional experiments, the two-dimensional experiments involve three distinct time periods: a preparation period, t/sub 0/; an evolution period, t/sub 1/; and a detection period, t/sub 2/.
Two dimensional unstable scar statistics.
Warne, Larry Kevin; Jorgenson, Roy Eberhardt; Kotulski, Joseph Daniel; Lee, Kelvin S. H. (ITT Industries/AES Los Angeles, CA)
2006-12-01
This report examines the localization of time harmonic high frequency modal fields in two dimensional cavities along periodic paths between opposing sides of the cavity. The cases where these orbits lead to unstable localized modes are known as scars. This paper examines the enhancements for these unstable orbits when the opposing mirrors are both convex and concave. In the latter case the construction includes the treatment of interior foci.
NASA Technical Reports Server (NTRS)
Juday, Richard D.
1992-01-01
Modified vernier scale gives accurate two-dimensional coordinates from maps, drawings, or cathode-ray-tube displays. Movable circular overlay rests on fixed rectangular-grid overlay. Pitch of circles nine-tenths that of grid and, for greatest accuracy, radii of circles large compared with pitch of grid. Scale enables user to interpolate between finest divisions of regularly spaced rule simply by observing which mark on auxiliary vernier rule aligns with mark on primary rule.
Two-Dimensional Potential Flows
NASA Technical Reports Server (NTRS)
Schaefer, Manfred; Tollmien, W.
1949-01-01
Contents include the following: Characteristic differential equations - initial and boundary conditions. Integration of the second characteristic differential equations. Direct application of Meyer's characteristic hodograph table for construction of two-dimensional potential flows. Prandtl-Busemann method. Development of the pressure variation for small deflection angles. Numerical table: relation between deflection, pressure, velocity, mach number and mach angle for isentropic changes of state according to Prandtl-Meyer for air (k = 1.405). References.
NASA Astrophysics Data System (ADS)
Sonnerup, Bengt U. Ö.; Denton, Richard E.; Hasegawa, Hiroshi; Swisdak, M.
2013-05-01
We re-examine the basic premises of a single-spacecraft data analysis method, developed by Sonnerup and Hasegawa (2005), for determining the axis orientation and proper frame velocity of quasi two-dimensional, quasi-steady structures of magnetic field and plasma. The method, which is based on Faraday's law, makes use of magnetic and electric field data measured by a single spacecraft traversing the structure, although in many circumstances the convection electric field, - v × B, can serve as a proxy for E. It has been used with success for flux ropes observed at the magnetopause but has usually failed to provide acceptable results when applied to real space data from reconnection events as well as to virtual data from numerical MHD simulations of such events. In the present paper, the reasons for these shortcomings are identified, analyzed, and discussed in detail. Certain basic properties of the method are presented in the form of five theorems, the last of which makes use of singular value decomposition to treat the special case where the magnetic variance matrix is non-invertible. These theorems are illustrated using data from analytical models of flux ropes and also from MHD simulations as well as a 2-D kinetic simulation of reconnection. The results make clear that the method requires the presence of a significant, non-removable electric field distribution in the plane transverse to the invariant direction and that it is sensitive to deviations from strict two-dimensionality and strict time stationarity.
The Biermann Battery In Cosmological Mhd Simulations Of Population III Star Formation
Xu, Hao; O' Shea, Brian W; Li, Hui; Li, Shengtai; Norman, Michael L; Collins, David C
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.
Simulating the Heliosphere with Kinetic Hydrogen and Dynamic MHD Source Terms
Heerikhuisen, Jacob; Pogorelov, Nikolai; Zank, Gary
2013-04-01
The interaction between the ionized plasma of the solar wind (SW) emanating from the sun and the partially ionized plasma of the local interstellar medium (LISM) creates the heliosphere. The heliospheric interface is characterized by the tangential discontinuity known as the heliopause that separates the SW and LISM plasmas, and a termination shock on the SW side along with a possible bow shock on the LISM side. Neutral Hydrogen of interstellar origin plays a critical role in shaping the heliospheric interface, since it freely traverses the heliopause. Charge-exchange between H-atoms and plasma protons couples the ions and neutrals, but the mean free paths are large, resulting in non-equilibrated energetic ion and neutral components. In our model, source terms for the MHD equations are generated using a kinetic approach for hydrogen, and the key computational challenge is to resolve these sources with sufficient statistics. For steady-state simulations, statistics can accumulate over arbitrarily long time intervals. In this paper we discuss an approach for improving the statistics in time-dependent calculations, and present results from simulations of the heliosphere where the SW conditions at the inner boundary of the computation vary according to an idealized solar cycle.
Simulating the Heliosphere with Kinetic Hydrogen and Dynamic MHD Source Terms
Heerikhuisen, Jacob; Pogorelov, Nikolai; Zank, Gary
2013-04-01
The interaction between the ionized plasma of the solar wind (SW) emanating from the sun and the partially ionized plasma of the local interstellar medium (LISM) creates the heliosphere. The heliospheric interface is characterized by the tangential discontinuity known as the heliopause that separates the SW and LISM plasmas, and a termination shock on the SW side along with a possible bow shock on the LISM side. Neutral Hydrogen of interstellar origin plays a critical role in shaping the heliospheric interface, since it freely traverses the heliopause. Charge-exchange between H-atoms and plasma protons couples the ions and neutrals, but themore » mean free paths are large, resulting in non-equilibrated energetic ion and neutral components. In our model, source terms for the MHD equations are generated using a kinetic approach for hydrogen, and the key computational challenge is to resolve these sources with sufficient statistics. For steady-state simulations, statistics can accumulate over arbitrarily long time intervals. In this paper we discuss an approach for improving the statistics in time-dependent calculations, and present results from simulations of the heliosphere where the SW conditions at the inner boundary of the computation vary according to an idealized solar cycle.« less
NASA Astrophysics Data System (ADS)
Kim, Tae K.; Pogorelov, Nikolai V.; Borovikov, Sergey N.; Clover, John M.; Jackson, Bernard V.; Yu, Hsiu-Shan
2012-11-01
Numerical modeling of the heliosphere is a critical component of space weather forecasting. The accuracy of heliospheric models can be improved by using realistic boundary conditions and confirming the results with in situ spacecraft measurements. To accurately reproduce the solar wind (SW) plasma flow near Earth, we need realistic, time-dependent boundary conditions at a fixed distance from the Sun. We may prepare such boundary conditions using SW speed and density determined from interplanetary scintillation (IPS) observations, magnetic field derived from photospheric magnetograms, and temperature estimated from its correlation with SW speed. Here, we present the time-dependent MHD simulation results obtained by using the 2011 IPS data from the Solar-Terrestrial Environment Laboratory as time-varying inner boundary conditions and compare the simulated data at Earth with OMNI data (spacecraft-interspersed, near-Earth solar wind data). At the request of the author, the PDF of the published article was replaced with a new file containing color figures. The scientific content is not affected by this change.
MHD simulations of magnetized laser-plasma interaction for laboratory astrophysics
NASA Astrophysics Data System (ADS)
Khiar, Benjamin; Ciardi, Andrea; Vinci, Tommaso; Revet, Guilhem; Fuchs, Julien; Higginson, Drew
2015-11-01
Laser-driven plasmas coupled with externally applied strong, steady-state, magnetic fields have applications that range from ICF to astrophysical studies of jet collimation, accretion shock dynamics in young stars and streaming instabilities in space plasmas. We have recently included the modelling of laser energy deposition in our three-dimensional, resistive two-temperature MHD code GORGON. The model assumes linear inverse-bremsstrahlung absorption and the laser propagation is done in the geometrical optics approximation. We present full scale numerical simulations of actual experiments performed on the ELFIE installation at LULI, including plasma generated from single and multiple laser plasmas embedded in a magnetic field of strength up to 20 T, and experiments and astrophysical simulations that have shown the viability of poloidal magnetic fields to directly result in the collimation of outflows and the formation of jets in astrophysical accreting systems, such as in young stellar objects. The authors acknowledge the support from the Ile-de-France DIM ACAV, from the LABEX Plas@par and from the ANR grant SILAMPA.
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.
3D Multifluid MHD simulation for Uranus and Neptune: the seasonal variations of their magnetosphere
NASA Astrophysics Data System (ADS)
Cao, X.; Paty, C. S.
2015-12-01
The interaction between Uranus' intrinsic magnetic field and the solar wind is quite different from the magnetospheric interactions of other planets. Uranus' large obliquity, coupled with the fact that its dipole moment is off-centered and highly tilted relative to the rotation axis, leads to unique and seasonally dependent interaction geometries with the solar wind. We present results from adapting a multifluid MHD simulation to examine these seasonally dependent geometries in terms of the global magnetospheric structure, magnetopause and bow shock location, and magnetotail configuration. The Voyager 2 spacecraft encountered Uranus near solstice, and was able to observe the magnetic field structure and plasma characteristics of a twisted magnetotail [Behannon et al., 1987]. We use such magnetometer and plasma observations as a basis for benchmarking our simulations for the solstice scenario. Auroral observations made by the Hubble Space Telescope during equinox [Lamy et al.,2012] give some indication of the magnetospheric interaction with the solar wind. We also demonstrate the structural difference of the magnetosphere between solstice and equinox seasons. The magnetosphere at equinox is quite distinct due to the orientation and rotation of the magnetic axis relative to the solar wind direction.
A three-dimensional high Mach number asymmetric magnetopause model from global MHD simulation
NASA Astrophysics Data System (ADS)
Liu, Z.-Q.; Lu, J. Y.; Wang, C.; Kabin, K.; Zhao, J. S.; Wang, M.; Han, J. P.; Wang, J. Y.; Zhao, M. X.
2015-07-01
The numerical results from a physics-based global magnetohydrodynamic (MHD) model are used to examine the effect of the interplanetary magnetic field (IMF), solar wind dynamic pressure, and dipole tilt angle on the size and shape of the magnetopause. The subsolar magnetopause is identified using the plasma velocity and density, the cusps are identified using the thermal pressure, and the whole shape of the magnetopause is determined with the three-dimensional streamlines traced through the simulation domain. The magnetopause surface obtained from the simulations is fitted with a three-dimensional surface function controlled by ten configuration parameters, which provide a description of the subsolar magnetopause, the cusp geometry, the flaring angle, the azimuthal asymmetry, the north-south asymmetry, and the twisting angle of the magnetopause. Effects of the IMF, solar wind dynamic pressure, and dipole tilt angle on the configuration parameters are analyzed and fitted by relatively simple functions. It is found that the solar wind dynamic pressure mainly affects the magnetopause size; the IMF mainly controls the magnetopause flaring angle, azimuthal asymmetry, and twisting angle; and the dipole tilt angle mainly affects the magnetopause north-south asymmetry and the cusp geometry. The model is validated by comparing with available empirical models and observational results, and it is demonstrated that the new model can describe the magnetopause for typical solar wind conditions.
Investigating Magnetic Activity in the Galactic Centre by Global MHD Simulation
NASA Astrophysics Data System (ADS)
Suzuki, Takeru K.; Fukui, Yasuo; Torii, Kazufumi; Machida, Mami; Matsumoto, Ryoji; Kakiuchi, Kensuke
2017-01-01
By performing a global magnetohydrodynamical (MHD) simulation for the Milky Way with an axisymmetric gravitational potential, we propose that spatially dependent amplification of magnetic fields possibly explains the observed noncircular motion of the gas in the Galactic centre (GC) region. The radial distribution of the rotation frequency in the bulge region is not monotonic in general. The amplification of the magnetic field is enhanced in regions with stronger differential rotation, because magnetorotational instability and field-line stretching are more effective. The strength of the amplified magnetic field reaches >~ 0.5 mG, and radial flows of the gas are excited by the inhomogeneous transport of angular momentum through turbulent magnetic field that is amplified in a spatially dependent manner. As a result, the simulated position-velocity diagram exhibits a time-dependent asymmetric parallelogram-shape owing to the intermittency of the magnetic turbulence; the present model provides a viable alternative to the bar-potential-driven model for the parallelogram shape of the central molecular zone. In addition, Parker instability (magnetic buoyancy) creates vertical magnetic structure, which would correspond to observed molecular loops, and frequently excited vertical flows. Furthermore, the time-averaged net gas flow is directed outward, whereas the flows are highly time dependent, which would contribute to the outflow from the bulge.
Extended MHD simulations of Rayleigh-Taylor instability with real frequency in a 2D slab
NASA Astrophysics Data System (ADS)
Goto, Ryosuke; Miura, Hideaki; Ito, Atsushi; Sato, Masahiko; Hatori, Tomoharu
2014-10-01
Small scale effects such as the Finite Larmor Radius (FLR) effect and the Hall term can change the linear and non-linear growth of the high wave number unstable modes of the pressure driven instability considerably. Here we consider a simple Rayleigh-Taylor (R-T) instability in a 2D slab, and study the effect of the Hall term and the FLR effect to the R-T instability by means of numerical simulations of the Braginskii-type extended MHD equations. As we have reported earlier, the linear growth rates of the high wave number modes are highly reduced when the Hall term and the FLR effect are added simultaneously. However, there appears little real frequency in the previous work. Since the diamagnetic drift associated with the real frequency is considered to affect the growth of the linear and nonlinear evolutions, we provide a new equilibrium in which appearance of the real frequency is expected and carry out numerical simulations. Influences of the real frequency on the growth rates as well as on the nonlinear mixing width for some combinations of the Hall and the FLR parameters are going to be presented.
Vanhille, Christian
2017-01-01
This work deals with a theoretical analysis about the possibility of using linear and nonlinear acoustic properties to modify ultrasound by adding gas bubbles of determined sizes in a liquid. We use a two-dimensional numerical model to evaluate the effect that one and several monodisperse bubble populations confined in restricted areas of a liquid have on ultrasound by calculating their nonlinear interaction. The filtering of an input ultrasonic pulse performed by a net of bubbly-liquid cells is analyzed. The generation of a low-frequency component from a single cell impinged by a two-frequency harmonic wave is also studied. These effects rely on the particular dispersive character of attenuation and nonlinearity of such bubbly fluids, which can be extremely high near bubble resonance. They allow us to observe how gas bubbles can change acoustic signals. Variations of the bubbly medium parameters induce alterations of the effects undergone by ultrasound. Results suggest that acoustic signals can be manipulated by bubbles. This capacity to achieve the modification and control of sound with oscillating gas bubbles introduces the concept of bubbly-liquid-based acoustic metamaterials (BLAMMs). PMID:28106748
NASA Astrophysics Data System (ADS)
Ostrikov, K. N.; Denysenko, I. B.; Tsakadze, E. L.; Xu, S.; Storer, R. G.
2002-11-01
This article presents the results on the diagnostics and numerical modeling of low-frequency (approx460 KHz) inductively coupled plasmas generated in a cylindrical metal chamber by an external flat spiral coil. Experimental data on the electron number densities and temperatures, electron energy distribution functions, and optical emission intensities of the abundant plasma species in low/intermediate pressure argon discharges are included. The spatial profiles of the plasma density, electron temperature, and excited argon species are computed, for different rf powers and working gas pressures, using the two-dimensional fluid approach. The model allows one to achieve a reasonable agreement between the computed and experimental data. The effect of the neutral gas temperature on the plasma parameters is also investigated. It is shown that neutral gas heating (at rf powers[greater-than-or-equal, slanted]0.55 kW) is one of the key factors that control the electron number density and temperature. The dependence of the average rf power loss, per electron-ion pair created, on the working gas pressure shows that the electron heat flux to the walls appears to be a critical factor in the total power loss in the discharge.
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
NUMERICAL SIMULATION OF PROPAGATION AND SCATTERING OF THE MHD WAVES IN SUNSPOTS
NASA Astrophysics Data System (ADS)
Parchevsky, K.; Kosovichev, A. G.; Khomenko, E.; Collados, M.
2009-12-01
We present comparison of numerical simulation results of MHD wave propagation in two different magnitostatic models of sunspots refferred to as "deep" and "shallow" models. The "deep" model has convex shape of magnetic field lines near the photosphere and non-zero horizorntal perturbations of the sound speed up to the bottom of the model (7.5 Mm). The "shallow" model has concave shape of the magnetic field lines near the photosphere and horizontally uniform sound speed below 2 Mm. Common feature of MHD waves behaviour in these two models is that for weak magnetic field (less than 1kG at the photosphere) waves reduce their amplitude when they reach the center of the sunspot and restore the amplitude when pass the center. For the "deep" model this effect is bigger than for the "shallow" model. The wave amplitude inside sunspots depends on the strength of the magnetic field. For the "shallow" model with photospheric magnetic field of 2.2 kG the wave amplitude inside the sunspot becomes bigger than outside (opposite to the weak magnetic field). The wave amplitude depends on the distance of the source from the sunspot center. For the "shallow" model and source distance of 9 Mm from the sunspot center the wave amplitude at some moment (when the wavefront passes the sunspot center) becomes bigger inside the sunspot than outside. For the source distance of 12 Mm the wave amplitude remains smaller inside the sunspot than outside for all moments of time. Using filtering technique we separated magnetoacoustic and magnetogravity waves. Simulations show that the sunspot changes the shape of the wave front and amplitude of the f-modes significantly stronger than the p-modes. It is shown, that inside the sunspot magnetoacoustic and magnetogravity waves are not spatially separated unlike the case of the horizontally uniform background model. Strong Alfven wave is generated at the wave source location in the "deep" model. This wave exists in the "shallow" model as well, but with
Numerical Simulation of Propagation and Transformation of the MHD Waves in Sunspots
NASA Astrophysics Data System (ADS)
Parchevsky, Konstantin; Zhao, J.; Kosovichev, A.
2010-05-01
Direct numerical simulation of propagation of MHD waves in stratified medium in regions with non-uniform magnetic field is very important for understanding of scattering and transformation of waves by sunspots. We present numerical simulations of wave propagation through the sunspot in 3D. We compare results propagation in two different magnitostatic models of sunspots refferred to as "deep" and "shallow" models. The "deep" model has convex shape of magnetic field lines near the photosphere and non-zero horizorntal perturbations of the sound speed up to the bottom of the model. The "shallow" model has concave shape of the magnetic field lines near the photosphere and horizontally uniform sound speed below 2 Mm. Waves reduce their amplitude when they reach the center of the sunspot and estore the amplitude when pass the center. For the "deep" model this effect is bigger than for the "shallow" model. The wave amplitude depends on the distance of the source from the sunspot center. For the "shallow" model and source distance of 9 Mm from the sunspot center the wave amplitude at some moment (when the wavefront passes the sunspot center) becomes bigger inside the sunspot than outside. For the source distance of 12 Mm the wave amplitude remains smaller inside the sunspot than outside for all moments of time. Using filtering technique we separated magnetoacoustic and magnetogravity waves. Simulations show that the sunspot changes the shape of the wave front and amplitude of the f-modes significantly stronger than the p-modes. It is shown, that inside the sunspot magnetoacoustic and magnetogravity waves are not spatially separated unlike the case of the horizontally uniform background model. We compared simulation results with the wave signals (Green's functions) extracted from the SOHO/MDI data for AR9787.
Matsuda, K.; Terada, N.; Katoh, Y.; Misawa, H.
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)
Reuter, K.; Jenko, F.; Forest, C. B.; Bayliss, R. A.
2008-08-01
A parallel implementation of a nonlinear pseudo-spectral MHD code for the simulation of turbulent dynamos in spherical geometry is reported. It employs a dual domain decomposition technique in both real and spectral space. It is shown that this method shows nearly ideal scaling going up to 128 CPUs on Beowulf-type clusters with fast interconnect. Furthermore, the potential of exploiting single precision arithmetic on standard x86 processors is examined. It is pointed out that the MHD code thereby achieves a maximum speedup of 1.7, whereas the validity of the computations is still granted. The combination of both measures will allow for the direct numerical simulation of highly turbulent cases ( 1500
NASA Astrophysics Data System (ADS)
Okkerse, M.; Kleijn, C. R.; van den Akker, H. E. A.; de Croon, M. H. J. M.; Marin, G. B.
2000-10-01
A two-dimensional model is presented for the hydrodynamics and chemistry of an oxy-acetylene torch reactor for chemical vapor deposition of diamond, and it is validated against spectroscopy and growth rate data from the literature. The model combines the laminar equations for flow, heat, and mass transfer with combustion and deposition chemistries, and includes multicomponent diffusion and thermodiffusion. A two-step solution approach is used. In the first step, a lumped chemistry model is used to calculate the flame shape, temperatures and hydrodynamics. In the second step, a detailed, 27 species / 119 elementary reactions gas phase chemistry model and a 41 species / 67 elementary reactions surface chemistry model are used to calculate radicals and intermediates concentrations in the gas phase and at the surface, as well as growth rates. Important experimental trends are predicted correctly, but there are some discrepancies. The main problem lies in the use of the Miller-Melius hydrocarbon combustion mechanism for rich oxy-acetylene flames. [J. A. Miller and C. F. Melius, Combustion and Flame 91, 21 (1992)]. Despite this problem, some aspects of the diamond growth process are clarified. It is demonstrated that gas-phase diffusion limitations play a minor role in the diamond growth process, which is determined by surface kinetics. Except for atomic hydrogen, gas phase diffusion is also of minor importance for the transport of species in and behind the flame front. Finally, it is shown that penetration of nitrogen from the ambient air into the flame cannot explain the observed changes at the center of the diamond films as reported in the literature.
Proceedings of the workshop on nonlinear MHD and extended MHD
1998-12-01
Nonlinear MHD simulations have proven their value in interpreting experimental results over the years. As magnetic fusion experiments reach higher performance regimes, more sophisticated experimental diagnostics coupled with ever expanding computer capabilities have increased both the need for and the feasibility of nonlinear global simulations using models more realistic than regular ideal and resistive MHD. Such extended-MHD nonlinear simulations have already begun to produce useful results. These studies are expected to lead to ever more comprehensive simulation models in the future and to play a vital role in fully understanding fusion plasmas. Topics include the following: (1) current state of nonlinear MHD and extended-MHD simulations; (2) comparisons to experimental data; (3) discussions between experimentalists and theorists; (4) /equations for extended-MHD models, kinetic-based closures; and (5) paths toward more comprehensive simulation models, etc. Selected papers have been indexed separately for inclusion in the Energy Science and Technology Database.
Thermodynamic MHD Simulations of Jets in the Solar Corona and Inner Heliosphere
NASA Astrophysics Data System (ADS)
Lionello, R.; Torok, T.; Titov, V. S.; Linker, J.; Mikic, Z.; Leake, J. E.; Linton, M.
2015-12-01
Coronal jets are transient, collimated plasma ejections that occur predominantly in coronal holes and are observed in EUV, soft X-ray, and occasionally in white-light coronagraphs. While these intriguing phenomena have been studied and modeled for more than two decades, the details of their formation mechanism(s) are not yet fully understood, and their potential role for the generation of the fast solar wind remains largely elusive. Here we present 3D MHD simulations of coronal jets which are performed in a large computational domain (up to 20 solar radii) and incorporate the effects of thermal conduction, radiative cooling, empirical coronal heating, and the solar wind. These features allow us to model the plasma properties and energy transfer of coronal jets in a more realistic manner than done so far, and to study the amount of energy and mass transported by these phenomena into the higher corona and inner heliosphere. In order to produce a jet, we consider a simple, purely radial background magnetic field and slowly introduce a magnetic flux rope into the coronal configuration by coupling our model to dynamic flux emergence simulations at the lower boundary of the computational domain. We find two types of jets in our simulations: a very impulsive event reminiscent of so-called blowout jets and a slowly developing, more extended event that produces a long-lasting signature in the corona. We present synthetic satellite images for both types of events and discuss their respective formation mechanisms. Our analysis is supported by a detailed investigation of the magnetic topology for the blowout-type case and of the transport of energy and plasma into the higher corona and inner heliosphere for the long-lasting event.
Monolithic multigrid methods for two-dimensional resistive magnetohydrodynamics
Adler, James H.; Benson, Thomas R.; Cyr, Eric C.; MacLachlan, Scott P.; Tuminaro, Raymond S.
2016-01-06
Magnetohydrodynamic (MHD) representations are used to model a wide range of plasma physics applications and are characterized by a nonlinear system of partial differential equations that strongly couples a charged fluid with the evolution of electromagnetic fields. The resulting linear systems that arise from discretization and linearization of the nonlinear problem are generally difficult to solve. In this paper, we investigate multigrid preconditioners for this system. We consider two well-known multigrid relaxation methods for incompressible fluid dynamics: Braess--Sarazin relaxation and Vanka relaxation. We first extend these to the context of steady-state one-fluid viscoresistive MHD. Then we compare the two relaxation procedures within a multigrid-preconditioned GMRES method employed within Newton's method. To isolate the effects of the different relaxation methods, we use structured grids, inf-sup stable finite elements, and geometric interpolation. Furthermore, we present convergence and timing results for a two-dimensional, steady-state test problem.
NASA Technical Reports Server (NTRS)
Yang, Kyung-Soo; Ferziger, Joel H.
1993-01-01
We apply the dynamic subgrid-scale model (DSGSM) to large-eddy simulation (LES) of turbulent channel flow with a square rib mounted on one wall. The Reynolds number (Re) is 3210 based on the mean velocity above the obstacle and the obstacle height. Near-wall structures are resolved with the no-slip boundary condition. The results show better agreement with direct numerical simulation (DNS) than LES with a fixed model constant, verifying the value of the DSGSM for simulating complex turbulent flows.
NASA Astrophysics Data System (ADS)
Leroy, Matthieu; Keppens, Rony
2016-04-01
The transfer of matter from the solar-wind to the Earth's magnetosphere during southward solar wind is mostly well understood but the processes governing the same phenomenon during northward solar wind remains to be fully apprehended. Numerous numerical studies have investigated the topic with many interesting results but most of these were considering two-dimensional situations with simplified magnetic configuration and often neglecting the inhomogeneities for the sake of clarity. Given the typical parameters at the magnetosphere-solar wind interface, the situation must be considered in the frame of Hall-MHD, due to the fact that the current layers widths and the gradient lengths can be in the order of the ion inertial length. As a consequence of Hall-MHD creating a third vector component from two planar ones, and also because magnetic perturbations can affect the field configuration at a distance in all directions and not only locally, three-dimensional treatment is necessary. In this spirit three-dimensional simulations of a configuration approaching the conditions leading to the development of Kelvin-Helmholtz instabilities at the flank of the magnetosphere during northward oriented solar-wind are performed as means to study the entry of solar-wind matter into Earth's magnetic field. In the scope of assessing the effect of the Hall-term in the physical processes, the simulations are also performed in the MHD frame. Furthermore the influence of the density and velocity jump through the shear layer on the rate of mass entering the magnetosphere is explored. Indeed, depending on the exact values of the physical quantities, the Kelvin-Helmholtz instability may have to compete with secondary instabilities and the non-linear phase may exhibit vortex merging and large-scale structures reorganisation, creating very different mixing layers, or generate different reconnection sites, locally and at a distance. These different configurations may have discernible signatures
Pressure of two-dimensional Yukawa liquids
NASA Astrophysics Data System (ADS)
Feng, Yan; Goree, J.; Liu, Bin; Wang, Lei; Tian, Wen-de
2016-06-01
A simple analytic expression for the pressure of a two-dimensional Yukawa liquid is found by fitting results from a molecular dynamics simulation. The results verify that the pressure can be written as the sum of a potential term which is a simple multiple of the Coulomb potential energy at a distance of the Wigner-Seitz radius, and a kinetic term which is a multiple of the one for an ideal gas. Dimensionless coefficients for each of these terms are found empirically, by fitting. The resulting analytic expression, with its empirically determined coefficients, is plotted as isochores, or curves of constant area. These results should be applicable to monolayer dusty plasmas.
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
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.
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.
NASA Astrophysics Data System (ADS)
Stark, D. J.; Yin, L.; Albright, B. J.; Guo, F.
2016-10-01
A PIC study of laser-ion acceleration via relativistic induced transparency points to how 2D-S (laser polarization in the simulation plane) and -P (out-of-plane) simulations may capture different physics characterizing these systems, visible in their entirety in (often cost-prohibitive) 3D simulations. The electron momentum anisotropy induced in the target by the laser pulse is dramatically different in the two 2D cases, manifesting in differences in polarization shift, electric field strength, density threshold for onset of relativistic induced transparency, and target expansion timescales. In particular, a trajectory analysis of individual electrons and ions may allow one to delineate the role of the fields and modes responsible for ion acceleration. With this information, we consider how 2D simulations might be used to develop, in some respects, a fully 3D understanding of the system. Work performed under the auspices of the U.S. DOE by the LANS, LLC, Los Alamos National Laboratory under Contract No. DE-AC52-06NA25396. Funding provided by the Los Alamos National Laboratory Directed Research and Development Program.
Two-dimensional quantum repeaters
NASA Astrophysics Data System (ADS)
Wallnöfer, J.; Zwerger, M.; Muschik, C.; Sangouard, N.; Dür, W.
2016-11-01
The endeavor to develop quantum networks gave rise to a rapidly developing field with far-reaching applications such as secure communication and the realization of distributed computing tasks. This ultimately calls for the creation of flexible multiuser structures that allow for quantum communication between arbitrary pairs of parties in the network and facilitate also multiuser applications. To address this challenge, we propose a two-dimensional quantum repeater architecture to establish long-distance entanglement shared between multiple communication partners in the presence of channel noise and imperfect local control operations. The scheme is based on the creation of self-similar multiqubit entanglement structures at growing scale, where variants of entanglement swapping and multiparty entanglement purification are combined to create high-fidelity entangled states. We show how such networks can be implemented using trapped ions in cavities.
Two-dimensional capillary origami
NASA Astrophysics Data System (ADS)
Brubaker, N. D.; Lega, J.
2016-01-01
We describe a global approach to the problem of capillary origami that captures all unfolded equilibrium configurations in the two-dimensional setting where the drop is not required to fully wet the flexible plate. We provide bifurcation diagrams showing the level of encapsulation of each equilibrium configuration as a function of the volume of liquid that it contains, as well as plots representing the energy of each equilibrium branch. These diagrams indicate at what volume level the liquid drop ceases to be attached to the endpoints of the plate, which depends on the value of the contact angle. As in the case of pinned contact points, three different parameter regimes are identified, one of which predicts instantaneous encapsulation for small initial volumes of liquid.
Smoothed MHD equations for numerical simulations of ideal quasi-neutral gas dynamic flows
NASA Astrophysics Data System (ADS)
Popov, Mikhail V.; Elizarova, Tatiana G.
2015-11-01
We introduce a mathematical model and related numerical method for numerical modeling of ideal magnetohydrodynamic (MHD) gas flows as an extension of previously known quasi-gasdynamic (QGD) equations. This approach is based on smoothing, or averaging of the original MHD equation system over a small time interval that leads to a new equation system, named quasi-MHD, or QMHD system. The QMHD equations are closely related to the original MHD system except for additional strongly non-linear dissipative τ-terms with a small parameter τ as a factor. The τ-terms depend on the solution itself and decrease in regions with the small space gradients of the solution. In this sense the QMHD system could be regarded as an approach with adaptive artificial dissipation. The QMHD is a generalization of regularized (or quasi-) gas dynamic equation system suggested in last three decades. In the QMHD numerical method the evolution of all physical variables is presented in a non-split divergence form. Divergence-free evolution of the magnetic field provides by using a constrained transport method based on Faraday's law of induction. Accuracy and convergence of the QMHD method is verified on a wide set of standard MHD tests including the 3D Orszag-Tang vortex flow.
Agatz, Annika; Brown, Colin D
2017-05-15
Mathematical models of pesticide fate and behaviour in soils have been developed over the last 30years. Most models simulate fate of pesticides in a 1-dimensional system successfully, supporting a range of applications where the prediction target is either bulk residues in soil or receiving compartments outside of the soil zone. Nevertheless, it has been argued that the 1-dimensional approach is limiting the application of knowledge on pesticide fate under specific pesticide placement strategies, such as seed, furrow and band applications to control pests and weeds. We report a new model (2-DROPS; 2-Dimensional ROots and Pesticide Simulation) parameterised for maize and we present simulations investigating the impact of pesticide properties (thiamethoxam, chlorpyrifos, clothianidin and tefluthrin), pesticide placement strategies (seed treatment, furrow, band and broadcast applications), and soil properties (two silty clay loam and two loam top soils with either silty clay loam, silt loam, sandy loam or unconsolidated bedrock in the lower horizons) on microscale pesticide distribution in the soil profile. 2-DROPS is to our knowledge the first model that simulates temporally- and spatially-explicit water and pesticide transport in the soil profile under the influence of explicit and stochastic development of root segments. This allows the model to describe microscale movement of pesticide in relation to root segments, and constitutes an important addition relative to existing models. The example runs demonstrate that the pesticide moves locally towards root segments due to water extraction for plant transpiration, that the water holding capacity of the top soil determines pesticide transport towards the soil surface in response to soil evaporation, and that the soil type influences the pesticide distribution zone in all directions. 2-DROPS offers more detailed information on microscale root and pesticide appearance compared to existing models and provides the
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.
Swain, Eric D.; Wolfert, Melinda A.; Bales, Jerad D.; Goodwin, Carl R.
2004-01-01
Successful restoration of the southern Florida ecosystem requires extensive knowledge of the physical characteristics and hydrologic processes controlling water flow and transport of constituents through extremely low-gradient freshwater marshes, shallow mangrove-fringed coastal creeks and tidal embayments, and near-shore marine waters. A sound, physically based numerical model can provide simulations of the differing hydrologic conditions that might result from various ecosystem restoration scenarios. Because hydrology and ecology are closely linked in southern Florida, hydrologic model results also can be used by ecologists to evaluate the degree of ecosystem restoration that could be achieved for various hydrologic conditions. A robust proven model, SWIFT2D, (Surface-Water Integrated Flow and Transport in Two Dimensions), was modified to simulate Southern Inland and Coastal Systems (SICS) hydrodynamics and transport conditions. Modifications include improvements to evapotranspiration and rainfall calculation and to the algorithms that describe flow through coastal creeks. Techniques used in this model should be applicable to other similar low-gradient marsh settings in southern Florida and elsewhere. Numerous investigations were conducted within the SICS area of southeastern Everglades National Park and northeastern Florida Bay to provide data and parameter values for model development and testing. The U.S. Geological Survey and the National Park Service supported investigations for quantification of evapotranspiration, vegetative resistance to flow, wind-induced flow, land elevations, vegetation classifications, salinity conditions, exchange of ground and surface waters, and flow and transport in coastal creeks and embayments. The good agreement that was achieved between measured and simulated water levels, flows, and salinities through minimal adjustment of empirical coefficients indicates that hydrologic processes within the SICS area are represented properly
Relativistic MHD simulations of core-collapse GRB jets: 3D instabilities and magnetic dissipation
NASA Astrophysics Data System (ADS)
Bromberg, Omer; Tchekhovskoy, Alexander
2016-02-01
Relativistic jets are associated with extreme astrophysical phenomena, like the core collapse of massive stars in gamma-ray bursts (GRBs) and the accretion on to supermassive black holes in active galactic nuclei. It is generally accepted that these jets are powered electromagnetically, by the magnetized rotation of a central compact object (black hole or neutron star). However, how the jets produce the observed emission and survive the propagation for many orders of magnitude in distance without being disrupted by current-driven instabilities is the subject of active debate. We carry out time-dependent 3D relativistic magnetohydrodynamic (MHD) simulations of relativistic, Poynting-flux-dominated jets. The jets are launched self-consistently by the rotation of a strongly magnetized central object. This determines the natural degree of azimuthal magnetic field winding, a crucial factor that controls jet stability. We find that the jets are susceptible to two types of instability: (i) a global, external kink mode that grows on long time-scales. It bodily twists the jet, reducing its propagation velocity. We show analytically that in flat density profiles, like the ones associated with galactic cores, the external mode grows and may stall the jet. In the steep profiles of stellar envelopes the external kink weakens as the jet propagates outward. (ii) a local, internal kink mode that grows over short time-scales and causes small-angle magnetic reconnection and conversion of about half of the jet electromagnetic energy flux into heat. We suggest that internal kink instability is the main dissipation mechanism responsible for powering GRB prompt emission.
Using Two-Ribbon Flare Observations and MHD Simulations to Constrain Flare Properties
NASA Astrophysics Data System (ADS)
Kazachenko, Maria D.; Lynch, Benjamin J.; Welsch, Brian
2016-05-01
Flare ribbons are emission structures that are frequently observed during flares in transition-region and chromospheric radiation. These typically straddle a polarity inversion line (PIL) of the radial magnetic field at the photosphere, and move apart as the flare progresses. The ribbon flux - the amount of unsigned photospheric magnetic flux swept out by flare ribbons - is thought to be related to the amount coronal magnetic reconnection, and hence provides a key diagnostic tool for understanding the physical processes at work in flares and CMEs. Previous measurements of the magnetic flux swept out by flare ribbons required time-consuming co-alignment between magnetograph and intensity data from different instruments, explaining why those studies only analyzed, at most, a few events. The launch of the Helioseismic and Magnetic Imager (HMI) and the Atmospheric Imaging Assembly (AIA), both aboard the Solar Dynamics Observatory (SDO), presented a rare opportunity to compile a much larger sample of flare-ribbon events than could readily be assembled before. We created a dataset of 363 events of both flare ribbon positions and fluxes, as a function of time, for all C9.-class and greater flares within 45 degrees of disk center observed by SDO from June 2010 till April 2015. For this purpose, we used vector magnetograms (2D magnetic field maps) from HMI and UV images from AIA. A critical problem with using unprocessed AIA data is the existence of spurious intensities in AIA data associated with strong flare emission, most notably "blooming" (spurious smearing of saturated signal into neighboring pixels, often in streaks). To overcome this difficulty, we have developed an algorithmic procedure that effectively excludes artifacts like blooming. We present our database and compare statistical properties of flare ribbons, e.g. evolutions of ribbon reconnection fluxes, reconnection flux rates and vertical currents with the properties from MHD simulations.
Two Dimensional Hydrodynamic Analysis of the Moose Creek Floodway
2012-09-01
ER D C/ CH L TR -1 2 -2 0 Two Dimensional Hydrodynamic Analysis of the Moose Creek Floodway C oa st al a n d H yd ra u lic s La b or at...distribution is unlimited. ERDC/CHL TR-12-20 September 2012 Two Dimensional Hydrodynamic Analysis of the Moose Creek Floodway Stephen H. Scott, Jeremy A...A two-dimensional Adaptive Hydraulics (AdH) hydrodynamic model was developed to simulate the Moose Creek Floodway. The Floodway is located
Malapaka, Shiva Kumar; Mueller, Wolf-Christian
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.
NASA Astrophysics Data System (ADS)
Ku, H. C.; Sibeck, D. G.; Wing, S.
2001-12-01
An accurate knowledge of the magnetosheath is essential for studies of the bow shock, magnetopause, and solar input into the magnetosphere. Gasdynamic models may not give sufficient accuracy whereas the cost/time constraints preclude running the 3-D MHD global simulations for numerous solar wind conditions. A 3-D magnetosheath MHD model is needed and presented as a viable alternative. The inner boundary of the model is the magnetopause, which has been previously determined from the pressure balance and exhibits a small indentation near the cusp regions. The initial position of the bow shock is taken from a gasdynamic model and subsequently adjusted when the magnetic field is included. The results of the gasdynamic and MHD models are compared with the following input parameters: the heat capacity ration γ = 2, the solar wind sonic Mach number, M∞ = 7, 9.81 (solar wind velocity v = 400 ; km ; s-1), temperature T = 105, 1.96 x 105 K, n = 10 ; cm-3, Bx = 10 \\cos θ \\cos φ ; nT, By = 10 \\cos θ sin φ ; nT, and Bz = 10 sin θ ; nT. There is a pronounced dawn-dusk asymmetry for both Mack numbers, and the presence of a strongly southward interplanetary magnetic field results in an equatorial belt of depressed depletion layer densities and plasma pressures between the cusp. The missing pressure is supplied by an equatorial band of enhanced magnetic field strengths. Near the subsolar point MHD densities fall to values 60% and 45 % of those in the gasdynamic models for M∞ = 9.81 and 7, resepctively. However, the standoff distance of bow shock increases significantly with stronger southward field component for low Mack numbers. By contrast, a standing shock wave attached to the the cusp becomes particularly noticeable for a strong dawn-dusk IMF orientation and high Mach numbers (M∞ = 9.81).
MHD simulations of DC helicity injection for current drive in tokamaks
Sovinec, C.R.; Prager, S.C.
1994-12-01
MHD computations of DC helicity injection in tokamak-like configurations show current drive with no ``loop voltage`` in a resistive, pressureless plasma. The self-consistently generated current profiles are unstable to resistive modes that partially relax the profile through the MHD dynamo mechanism. The current driven by the fluctuations leads to closed contours of average poloidal flux. However, the 1% fluctuation level is large enough to produce a region of stochastic magnetic field. A limited Lundquist number (S) scan from 2.5 {times} 10{sup 3} to 4 {times} 10{sup 4} indicates that both the fluctuation level and relaxation increase with S.
NASA Astrophysics Data System (ADS)
Takizuka, T.; Shimizu, K.; Hayashi, N.; Hosokawa, M.; Yagi, M.
2009-07-01
The plasma flow in the scrape-off-layer (SOL) plays an important role in particle control in magnetic fusion reactors. The flow is expected to expel helium ashes and to retain impurities in the divertor region, if it is directed towards the divertor plate. It has been experimentally observed, however, that the flow direction is sometimes opposite; from the outer plate side to the SOL middle side in the outer SOL region of tokamaks. In order to study these SOL flow patterns by fully taking account of the kinetic effects, a full particle code, PARASOL, is applied to a tokamak plasma with the upper-null point (UN) or lower-null point (LN) divertor configuration for the downward ion ∇B drift. PARASOL simulations for the medium aspect ratio (A = 5.5) reveal the variation of the flow pattern. For the UN case with the ion ∇B drift away from the null point, the flow velocity Vpar parallel to the magnetic field is formed almost in-out symmetrically. In the inner SOL region Vpar is directed to the inner divertor plate and in the outer SOL Vpar is directed to the outer plate. The stagnation point (Vpar = 0) is located symmetrically at the bottom. On the other hand for the LN case with the ion ∇B drift towards the null point, Vpar in the outer SOL region has a backward flow pattern. The stagnation point moves below the mid-plane of the outer SOL and Vpar in the mid-plane outer SOL is directed to the inner plate. These simulation results are very similar to the experimental results. Simulations are carried out by changing the aspect ratio and by artificially cutting the electric field. It is found that the banana motion of trapped ions is very important for the formation of the flow pattern in addition to the self-consistent electric field. The trapped-ion effects can be stronger than the electric-field effects for the standard tokamaks with A < 5.
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).
Physical Mechanisms of Two-Dimensional Turbulence
NASA Astrophysics Data System (ADS)
Ecke, Robert
2004-03-01
Turbulence has slowly yielded its mysteries through over 100 years of persistent effort. Recently experimental techniques and computation power have reached the stage where significant progress has been made on this very challenging problem. Two dimensional turbulence offers some real advantages in terms of reduced degrees of freedom such that the problem can now be thoroughly explored from many perspectives. Further, two-dimensional turbulence exhibits the basic phenomena of direct-enstrophy and inverse-energy cascades thought to apply to oceanic and atmospheric systems. We have investigated the properties of turbulence in two spatial dimensions using experimental measurements of the grid turbulence in a flowing soap film^1 and of the electromagnetically-forced turbulence in a thin salt layer floating on a dense immiscible fluid underlayer. We have also explored 2D turbulence using several different direct numerical simulations of homogeneous, isotropic turbulence in a periodic box^2. The data for both consist of high resolution fields of velocity; some are statistically independent sets and others are temporally resolved for dynamics. From this data we construct conventional Eulerian statistics, directly measure energy and enstrophy transfer^1, identify coherent structures in the flow, determine Lagrangian quantities, and calculate stretching fields. This comprehensive experimental and numerical characterization elucidates the physical mechanisms of two-dimensional turbulence. ^1 M.K. Rivera, W.B. Daniel and R.E. Ecke, Phys. Rev. Lett. 90, 104502 (2003). ^2 S. Chen, R.E. Ecke, G. Eyink, X. Wang, and Z. Xiao, Phys. Rev. Lett. 91, 214501 (2003).
NASA Astrophysics Data System (ADS)
Aricò, Costanza; Tucciarelli, Tullio
2009-03-01
A novel methodology for the simulation of 2D thermohaline double diffusive processes, driven by heterogeneous temperature and concentration fields in variable-density saturated porous media, is presented. The stream function is used to describe the flow field and it is defined in terms of mass flux. The partial differential equations governing system is given by the mass conservation equation of the fluid phase written in terms of the mass-based stream function, as well as by the advection-diffusion transport equations of the contaminant concentration and of the heat. The unknown variables are the stream function, the contaminant concentration and the temperature. The governing equations system is solved using a fractional time step procedure, splitting the convective components from the diffusive ones. In the case of existing scalar potential of the flow field, the convective components are solved using a finite volume marching in space and time (MAST) procedure; this solves a sequence of small systems of ordinary differential equations, one for each computational cell, according to the decreasing value of the scalar potential. In the case of variable-density groundwater transport problem, where a scalar potential of the flow field does not exist, a second MAST procedure has to be applied to solve again the ODEs according to the increasing value of a new function, called approximated potential. The diffusive components are solved using a standard Galerkin finite element method. The numerical scheme is validated using literature tests.
Two-dimensional Quantum Gravity
NASA Astrophysics Data System (ADS)
Rolf, Juri
1998-10-01
This Ph.D. thesis pursues two goals: The study of the geometrical structure of two-dimensional quantum gravity and in particular its fractal nature. To address these questions we review the continuum formalism of quantum gravity with special focus on the scaling properties of the theory. We discuss several concepts of fractal dimensions which characterize the extrinsic and intrinsic geometry of quantum gravity. This work is partly based on work done in collaboration with Jan Ambjørn, Dimitrij Boulatov, Jakob L. Nielsen and Yoshiyuki Watabiki (1997). The other goal is the discussion of the discretization of quantum gravity and to address the so called quantum failure of Regge calculus. We review dynamical triangulations and show that it agrees with the continuum theory in two dimensions. Then we discuss Regge calculus and prove that a continuum limit cannot be taken in a sensible way and that it does not reproduce continuum results. This work is partly based on work done in collaboration with Jan Ambjørn, Jakob L. Nielsen and George Savvidy (1997).
Giammarinaro, B.; Coulouvrat, F.; Pinton, G.
2016-01-01
Shear waves that propagate in soft solids, such as the brain, are strongly nonlinear and can develop into shock waves in less than one wavelength. We hypothesize that these shear shock waves could be responsible for certain types of traumatic brain injuries (TBI) and that the spherical geometry of the skull bone could focus shear waves deep in the brain, generating diffuse axonal injuries. Theoretical models and numerical methods that describe nonlinear polarized shear waves in soft solids such as the brain are presented. They include the cubic nonlinearities that are characteristic of soft solids and the specific types of nonclassical attenuation and dispersion observed in soft tissues and the brain. The numerical methods are validated with analytical solutions, where possible, and with self-similar scaling laws where no known solutions exist. Initial conditions based on a human head X-ray microtomography (CT) were used to simulate focused shear shock waves in the brain. Three regimes are investigated with shock wave formation distances of 2.54 m, 0.018 m, and 0.0064 m. We demonstrate that under realistic loading scenarios, with nonlinear properties consistent with measurements in the brain, and when the shock wave propagation distance and focal distance coincide, nonlinear propagation can easily overcome attenuation to generate shear shocks deep inside the brain. Due to these effects, the accelerations in the focal are larger by a factor of 15 compared to acceleration at the skull surface. These results suggest that shock wave focusing could be responsible for diffuse axonal injuries. PMID:26833489
NASA Astrophysics Data System (ADS)
Lusso, Christelle; Ern, Alexandre; Bouchut, François; Mangeney, Anne; Farin, Maxime; Roche, Olivier
2017-03-01
This work is devoted to numerical modeling and simulation of granular flows relevant to geophysical flows such as avalanches and debris flows. We consider an incompressible viscoplastic fluid, described by a rheology with pressure-dependent yield stress, in a 2D setting with a free surface. We implement a regularization method to deal with the singularity of the rheological law, using a mixed finite element approximation of the momentum and incompressibility equations, and an arbitrary Lagrangian Eulerian (ALE) formulation for the displacement of the domain. The free surface is evolved by taking care of its deposition onto the bottom and of preventing it from folding over itself. Several tests are performed to assess the efficiency of our method. The first test is dedicated to verify its accuracy and cost on a one-dimensional simple shear plug flow. On this configuration we setup rules for the choice of the numerical parameters. The second test aims to compare the results of our numerical method to those predicted by an augmented Lagrangian formulation in the case of the collapse and spreading of a granular column over a horizontal rigid bed. Finally we show the reliability of our method by comparing numerical predictions to data from experiments of granular collapse of both trapezoidal and rectangular columns over horizontal rigid or erodible granular bed made of the same material. We compare the evolution of the free surface, the velocity profiles, and the static-flowing interface. The results show the ability of our method to deal numerically with the front behavior of granular collapses over an erodible bed.
Large Scale Earth's Bow Shock with Northern IMF as Simulated by PIC Code in Parallel with MHD Model
NASA Astrophysics Data System (ADS)
Baraka, Suleiman
2016-06-01
In this paper, we propose a 3D kinetic model (particle-in-cell, PIC) for the description of the large scale Earth's bow shock. The proposed version is stable and does not require huge or extensive computer resources. Because PIC simulations work with scaled plasma and field parameters, we also propose to validate our code by comparing its results with the available MHD simulations under same scaled solar wind (SW) and (IMF) conditions. We report new results from the two models. In both codes the Earth's bow shock position is found to be ≈14.8 R E along the Sun-Earth line, and ≈29 R E on the dusk side. Those findings are consistent with past in situ observations. Both simulations reproduce the theoretical jump conditions at the shock. However, the PIC code density and temperature distributions are inflated and slightly shifted sunward when compared to the MHD results. Kinetic electron motions and reflected ions upstream may cause this sunward shift. Species distributions in the foreshock region are depicted within the transition of the shock (measured ≈2 c/ ω pi for Θ Bn = 90° and M MS = 4.7) and in the downstream. The size of the foot jump in the magnetic field at the shock is measured to be (1.7 c/ ω pi ). In the foreshocked region, the thermal velocity is found equal to 213 km s-1 at 15 R E and is equal to 63 km s -1 at 12 R E (magnetosheath region). Despite the large cell size of the current version of the PIC code, it is powerful to retain macrostructure of planets magnetospheres in very short time, thus it can be used for pedagogical test purposes. It is also likely complementary with MHD to deepen our understanding of the large scale magnetosphere.
Numerical linearized MHD model of flapping oscillations
NASA Astrophysics Data System (ADS)
Korovinskiy, D. B.; Ivanov, I. B.; Semenov, V. S.; Erkaev, N. V.; Kiehas, S. A.
2016-06-01
Kink-like magnetotail flapping oscillations in a Harris-like current sheet with earthward growing normal magnetic field component Bz are studied by means of time-dependent 2D linearized MHD numerical simulations. The dispersion relation and two-dimensional eigenfunctions are obtained. The results are compared with analytical estimates of the double-gradient model, which are found to be reliable for configurations with small Bz up to values ˜ 0.05 of the lobe magnetic field. Coupled with previous results, present simulations confirm that the earthward/tailward growth direction of the Bz component acts as a switch between stable/unstable regimes of the flapping mode, while the mode dispersion curve is the same in both cases. It is confirmed that flapping oscillations may be triggered by a simple Gaussian initial perturbation of the Vz velocity.
NASA Technical Reports Server (NTRS)
Ogino, T.; Walker, R. J.; Ashour-Abdalla, M.; Dawson, J. M.
1985-01-01
A three-dimensional MHD simulation code is used to model the magnetospheric configuration when the IMF has both a northward B(z) component and a B(y) component in the east-west direction. Projections of the plasma pressure, the field-aligned velocity, the field-aligned vorticity, and the field-aligned current along the magnetic field lines into the northern ionosphere are shown and discussed. Cross-sectional patterns of these parameters are shown. The results demonstrate that the B(y) component of the IMF strongly influences the plasma sheet configuration and the magnetospheric convection pattern.
NASA Astrophysics Data System (ADS)
Hayashi, K.; Hmi Team
2010-12-01
We will report results of the MHD simulation of the solar corona and solar wind using the HMI magnetic field data, especially focusing on a simulated eruption of a coronal streamer that reasonably corresponds to a large-scale coronal eruption event observed on August 1, 2010. The pre-event coronal situation is prepared through the time-relaxation MHD simulation using the synoptic map data of the solar surface magnetic field for a period of the Carrington Rotation 2098. Then, the global magnetic field evolutions from CR 2098 to 2099 are introduced in the simulation by means of a boundary model we recently developed, which enable to trace the sub-Alfvenic MHD responses of the corona numerically. The simulated coronal features include the formation of the two twisted coronal magnetic field structures along the magnetically inversion lines at the lowermost corona (coinciding the two observed filaments at west-north part of the solar disk) and the large-scale outward motions and decay of the closed-field streamer above the two twisted-field regions. Our MHD simulation model did not include the triggering event directly, and our simulations were done in somewhat low resolution in space. However, the reasonable success in reproducing coronal features relating a specific event in a well-known manner (using the synoptic map format data and the MHD simulation model) shows that the new dataset from HMI will be useful for the models, such as the MHD and the potential field models, as the previous dataset by SOHO/MDI.
The two-dimensional code image recognition based on wavelet transform
NASA Astrophysics Data System (ADS)
Wan, Hao; Peng, Cheng
2017-01-01
With the development of information technology, two-dimensional code is more and more widely used. In the technology of two-dimensional code recognition, the noise reduction of the two-dimensional code image is very important. Wavelet transform is applied to the noise reduction of two-dimensional code, and the corresponding Matlab experiment and simulation are made. The results show that the wavelet transform is simple and fast in the noise reduction of two-dimensional code. And it can commendably protect the details of the two-dimensional code image.
Cyclic thermal signature in a global MHD simulation of solar convection
NASA Astrophysics Data System (ADS)
Cossette, J.; Charbonneau, P.; Smolarkiewicz, P. K.
2013-12-01
Space-based observations have clearly established that total solar irradiance (TSI) varies on time scales from minutes to days and months as well as on the longer time scale of the 11-year solar cycle. The most conspicuous of these variations is arguably the slight increase of TSI (0.1%) at solar maxima relative to solar minima. Models that include contributions from surface solar magnetism alone (i.e. sunspots, faculae and magnetic network) have been very successful at reproducing the observed TSI fluctuations on time scales shorter than a year, but leave some doubts as to the origin of the longer decadal fluctuations. In particular, one school of thought argues that surface magnetism alone can explain the entire TSI variance; see (Lean & al. 1998, ApJ, 492, 390), whereas; the other emphasizes on taking into account the effect of a global modulation of solar thermal structure by magnetic activity; see (Li & al. 2003, ApJ, 591, 1267). Observationally, the potential for the occurrence of magnetically-modulated global structural changes is supported by a positive correlation between p-mode oscillation frequencies and the TSI cycle as well as by recent evidence for a long-term trend in the TSI record that is not seen in indicators of surface magnetism; see (Bhatnagar & al. 1999, ApJ, 521, 885; Fröhlich 2013, Space Sci Rev,176, 237). Additionally, 1D structural solar models have demonstrated that the inclusion of a magnetically-modulated turbulent mechanism could explain the observed p-mode oscillation frequency changes with great accuracy. However, these models relied upon an ad-hoc parametrization of the alleged process and therefore obtaining a complete physical picture of the modulating mechanism requires solving the equations governing the self-consistent evolution of the solar plasma. Here we present a global magnetohydrodynamical (MHD) simulation of solar convection extending over more than a millennium that produces large-scale solar-like axisymmetric magnetic
Numerical simulation of flare energy build-up and release via Joule dissipation. [solar MHD model
NASA Technical Reports Server (NTRS)
Wu, S. T.; Bao, J. J.; Wang, J. F.
1986-01-01
A new numerical MHD model is developed to study the evolution of an active region due to photospheric converging motion, which leads to magnetic-energy buildup in the form of electric current. Because this new MHD model has incorporated finite conductivity, the energy conversion occurs from magnetic mode to thermal mode through Joule dissipation. In order to test the causality relationship between the occurrence of flare and photospheric motion, a multiple-pole configuration with neutral point is used. Using these results it is found that in addition to the converging motion, the initial magnetic-field configuration and the redistribution of the magnetic flux at photospheric level enhance the possibility for the development of a flare.
A Three-Dimensional MHD Simulation of the Solar Wind for a Tilted-Dipole Magnetic Field on the Sun
NASA Technical Reports Server (NTRS)
Goldstein, Melvyn L.
2007-01-01
Using a three-dimensional MHD model, we simulate the global steady-state structure of the solar corona and solar wind for a dipole magnetic field on the Sun inclined by 30 degrees to the solar rotation axis. This represents the solar conditions typical for a declining phase of solar cycle. The computations can extend from the coronal base out to 100-AU and at large heliospheric distances includes the effects of interstellar neutral hydrogen and their interaction with solar wind protons. The simulations can model the formation of corotating interaction regions and the heliospheric current sheet. The simulations are also capable of describing very strong rarefaction regions that include embedded sub-Alfvenic regions that form on the trailing edge of a fast flows.
NASA Astrophysics Data System (ADS)
Krebs, I.; Jardin, S. C.; Günter, S.; Lackner, K.; Hoelzl, M.; Ferraro, N.
2016-10-01
We use the finite element 3D MHD code M3D-C1 to study large-scale instabilities in the center of tokamak plasmas. It has been shown that in 3D MHD simulations of plasmas with a flat central q 1 , an ideal interchange instability can develop that keeps the current density from peaking despite central heating. The instability yields a (m = 1 , n = 1) perturbation of the core plasma, i.a. a helical flow that flattens the central current density by (1) flattening the temperature profile and (2) combining with the perturbed magnetic field to generate a negative loop voltage through a dynamo effect. This might explain the ``flux-pumping'' effect observed in hybrid discharges. We study in which parameter range the two effects are strong enough to prevent sawtoothing. We describe a new regime of quasi-stationary oscillating states and analyze cases in between the stationary and the cycling regime in which the sawtooth behaviour is modified by the current flattening mechanisms. To connect to experimental observations, we have set up simulations starting with a scenario comparable to the current ramp-up phase.
Magnetohydrodynamic waves in two-dimensional prominences embedded in coronal arcades
Terradas, J.; Soler, R.; Díaz, A. J.; Oliver, R.; Ballester, J. L.
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.
NASA Astrophysics Data System (ADS)
Huang, Z.; Toth, G.; Gombosi, T. I.; Jia, X.; Rubin, M.; Hansen, K. C.; Fougere, N.; Bieler, A. M.; Shou, Y.; Altwegg, K.; Combi, M. R.; Tenishev, V.
2015-12-01
The neutral and plasma environment is critical in understanding the interaction of comet Churyumov-Gerasimenko (CG), the target of the Rosetta mission, and the solar wind. To serve this need and support the Rosetta mission, we develop a 3-D four fluid model, which is based on BATS-R-US within the SWMF (Space Weather Modeling Framework) that solves the governing multi-fluid MHD equations and the Euler equations for the neutral gas fluid. These equations describe the behavior and interactions of the cometary heavy ions, the solar wind protons, the electrons, and the neutrals. This model incorporates different mass loading processes, including photo and electron impact ionization, charge exchange, dissociative ion-electron recombination, and collisional interactions between different fluids. We simulate the near nucleus plasma and neutral gas environment near perihelion with a realistic shape model of CG and compare our simulation results with Rosetta observations.
Schmidt, J. M.; Cairns, Iver H.; Hillan, D. S.
2013-08-20
Type II solar radio bursts are the primary radio emissions generated by shocks and they are linked with impending space weather events at Earth. We simulate type II bursts by combining elaborate three-dimensional MHD simulations of realistic coronal mass ejections (CMEs) at the Sun with an analytic kinetic radiation theory developed recently. The modeling includes initialization with solar magnetic and active region fields reconstructed from magnetograms of the Sun, a flux rope of the initial CME dimensioned with STEREO spacecraft observations, and a solar wind driven with averaged empirical data. We demonstrate impressive accuracy in time, frequency, and intensity for the CME and type II burst observed on 2011 February 15. This implies real understanding of the physical processes involved regarding the radio emission excitation by shocks and supports the near-term development of a capability to predict and track these events for space weather prediction.
Modeling solar wind mass-loading in the vicinity of the Sun using 3-D MHD simulations
NASA Astrophysics Data System (ADS)
Rasca, A. P.; Horányi, M.; Oran, R.; Holst, B.
2014-01-01
Collisionless shocks due to mass-loading were first discussed to describe the solar wind flow around a cometary atmosphere, showing its choking effects on the flow. Recent observations have led to an increased interest in mass-loading occurring in the solar corona due to both sungrazing comets and collisional debris production by sunward migrating interplanetary dust particles. The 1-D simulations with a hydrodynamic model have illustrated the impact on the solar wind from abrupt mass-loading in the coronal region. Full 3-D magnetohydrodynamic (MHD) simulations using a solar corona model based on the Block-Adaptive-Tree-Solarwind-Roe-Upwind-Scheme code provide a more realistic coronal environment for modeling specific events applicable to modeling the mass-loaded coronal wind. A specific application is introduced modeling the mass-loading effects from a sungrazing comet.
NASA Technical Reports Server (NTRS)
Walker, Raymond J.; Ogino, Tatsuki
1988-01-01
A time-dependent three-dimensional MHD model was used to investigate the magnetospheric configuration as a function of the interplanetary magnetic field direction when it was in the y-z plane in geocentric solar magnetospheric coordinates. The model results show large global convection cells, tail lobe cells, high-latitude polarcap cells, and low latitude cells. The field-aligned currents generated in the model magnetosphere and the model convection system are compared with observations from low-altitude polar orbiting satellites.
Measuring Monotony in Two-Dimensional Samples
ERIC Educational Resources Information Center
Kachapova, Farida; Kachapov, Ilias
2010-01-01
This note introduces a monotony coefficient as a new measure of the monotone dependence in a two-dimensional sample. Some properties of this measure are derived. In particular, it is shown that the absolute value of the monotony coefficient for a two-dimensional sample is between /"r"/ and 1, where "r" is the Pearson's…
Electromagnetic two-dimensional analysis of trapped-ion eigenmodes
Kim, D.; Rewoldt, G.
1984-11-01
A two-dimensional electromagnetic analysis of the trapped-ion instability for the tokamak case with ..beta.. not equal to 0 has been made, based on previous work in the electrostatic limit. The quasineutrality condition and the component of Ampere's law along the equilibrium magnetic field are solved for the perturbed electrostatic potential and the component of the perturbed vector potential along the equilibrium magnetic field. The general integro-differential equations are converted into a matrix eigenvalue-eigenfunction problem by expanding in cubic B-spline finite elements in the minor radius and in Fourier harmonics in the poloidal angle. A model MHD equilibrium with circular, concentric magnetic surfaces and large aspect ratio is used which is consistent with our assemption that B << 1. The effect on the trapped-ion mode of including these electromagnetic extensions to the calculation is considered, and the temperature (and ..beta..) scaling of the mode frequency is shown and discussed.
Two-dimensional convective turbulence
Gruzinov, A.V.; Kukharkin, N.; Sudan, R.N.
1996-02-01
We show that 2D {bold E{times}B} ionospheric turbulence of the electron density in the equatorial electrojet is isomorphic to the viscous convection of an ordinary fluid in a porous medium due to temperature gradients. Numerical simulations reveal the strong anisotropy in the turbulence, which consists of rising hot bubbles and falling cool bubbles. These bubbles break up into fingers leading to the formation of stable shear flows. After reaching a quasisteady state, the omnidirectional energy spectrum approaches a {ital k}{sup {minus}2} behavior, rather than {ital k}{sup {minus}5/3} as expected from isotropic turbulence. Physical mechanisms that lead to anisotropy are analyzed. {copyright} {ital 1996 The American Physical Society.}
Two-dimensional discrete Coulomb alloy
NASA Astrophysics Data System (ADS)
Xiao, Yuqing; Thorpe, M. F.; Parkinson, J. B.
1999-01-01
We study an A1-xBx alloy on a two-dimensional triangular lattice. The ions A and B have different charges, with a background charge to ensure neutrality, and are constrained to lie at the discrete sites defined by a fixed triangular lattice. We study the various structures formed at different compositions x by doing computer simulations to find the lowest energy, using an energy minimization scheme, together with simulated annealing. Like ions try to avoid each other because of charge repulsion, which leads to structures, which are very different from those in a random alloy. At low concentrations, a triangular Wigner lattice is formed, which evolves continuously up to a concentration of x=1/3. For higher concentrations, 1/3<=x<=1/2 there are long polymer chains, with occasional branches. We show that there is a symmetry about x=1/2, which is the percolation point for nearest neighbors on the triangular lattice. At certain special stoichiometries, regular superlattices are formed, which usually have a slightly lower energy than a disordered configuration. The powder-diffraction patterns are calculated. The magnetic properties of this structure are also studied, and it is shown that the high-temperature susceptibility could be a useful diagnostic tool, in that it is very sensitive to the number of nearest-neighbor magnetic pairs. This work contributes to a better understanding of layered double hydroxides like Ni1-xAlx(OH)2(CO3)x/2.yH2O.
Silva, F. da
2008-10-15
The EU will supply the plasma position reflectometer for ITER. The system will have channels located at different poloidal positions, some of them obliquely viewing a plasma which has a poloidal density divergence and curvature, both adverse conditions for profile measurements. To understand the impact of such topology in the reconstruction of density profiles a full-wave two-dimensional finite-difference time domain O-mode code with the capability for frequency sweep was used. Simulations show that the reconstructed density profiles still meet the ITER radial accuracy specifications for plasma position (1 cm), except for the highest densities. Other adverse effects such as multireflections induced by the blanket, density fluctuations, and MHD activity were considered and a first understanding on their impact obtained.
Agapiou, A; Zorba, E; Mikedi, K; McGregor, L; Spiliopoulou, C; Statheropoulos, M
2015-07-09
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".
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
Monolithic multigrid methods for two-dimensional resistive magnetohydrodynamics
Adler, James H.; Benson, Thomas R.; Cyr, Eric C.; ...
2016-01-06
Magnetohydrodynamic (MHD) representations are used to model a wide range of plasma physics applications and are characterized by a nonlinear system of partial differential equations that strongly couples a charged fluid with the evolution of electromagnetic fields. The resulting linear systems that arise from discretization and linearization of the nonlinear problem are generally difficult to solve. In this paper, we investigate multigrid preconditioners for this system. We consider two well-known multigrid relaxation methods for incompressible fluid dynamics: Braess--Sarazin relaxation and Vanka relaxation. We first extend these to the context of steady-state one-fluid viscoresistive MHD. Then we compare the two relaxationmore » procedures within a multigrid-preconditioned GMRES method employed within Newton's method. To isolate the effects of the different relaxation methods, we use structured grids, inf-sup stable finite elements, and geometric interpolation. Furthermore, we present convergence and timing results for a two-dimensional, steady-state test problem.« less
Hall-MHD simulations of the Kelvin-Helmholtz instability at the solar wind/magnetosphere interface
NASA Astrophysics Data System (ADS)
Leroy, M. H. J.; Keppens, R.
2016-12-01
The process feeding the development of the boundary layer at the interface between the solar wind (SW) and the magnetosphere (MS) during northward interplanetary magnetic field is still not fully understood, though the Kelvin-Helmholtz instability (KHI) being the major actor is in good agreement with the observations so far. In this work, we study different configurations than can occur in the KHI scenario in a three-dimensional (3D) Hall-MHD setting, where the double mid-latitude reconnection (DMLR) process exposed by Faganello, Califano et al. is triggered by the equatorial roll-ups. Their previous work is extended here with a larger simulation box and the addition of a density contrast. The influence of the parameters on the growth rate of the KHI and thus the efficiency of the DMLR is assessed. The effect of the Hall term on the physical processes is also investigated.
NASA Astrophysics Data System (ADS)
Winters, Andrew R.; Derigs, Dominik; Gassner, Gregor J.; Walch, Stefanie
2017-03-01
We describe a unique averaging procedure to design an entropy stable dissipation operator for the ideal magnetohydrodynamic (MHD) and compressible Euler equations. Often in the derivation of an entropy conservative numerical flux function much care is taken in the design and averaging of the entropy conservative numerical flux. We demonstrate in this work that if the discrete dissipation operator is not carefully chosen as well it can have deleterious effects on the numerical approximation. This is particularly true for very strong shocks or high Mach number flows present, for example, in astrophysical simulations. We present the underlying technique of how to construct a unique averaging technique for the discrete dissipation operator. We also demonstrate numerically the increased robustness of the approximation.
Equilibrium state of a trapped two-dimensional Bose gas
Rath, Steffen P.; Yefsah, Tarik; Guenter, Kenneth J.; Cheneau, Marc; Desbuquois, Remi; Dalibard, Jean; Holzmann, Markus; Krauth, Werner
2010-07-15
We study experimentally and numerically the equilibrium density profiles of a trapped two-dimensional {sup 87}Rb Bose gas and investigate the equation of state of the homogeneous system using the local density approximation. We find a clear discrepancy between in situ measurements and quantum Monte Carlo simulations, which we attribute to a nonlinear variation of the optical density of the atomic cloud with its spatial density. However, good agreement between experiment and theory is recovered for the density profiles measured after time of flight, taking advantage of their self-similarity in a two-dimensional expansion.
Two-dimensional signal reconstruction: The correlation sampling method
Roman, H. E.
2007-12-15
An accurate approach for reconstructing a time-dependent two-dimensional signal from non-synchronized time series recorded at points located on a grid is discussed. The method, denoted as correlation sampling, improves the standard conditional sampling approach commonly employed in the study of turbulence in magnetoplasma devices. Its implementation is illustrated in the case of an artificial time-dependent signal constructed using a fractal algorithm that simulates a fluctuating surface. A statistical method is also discussed for distinguishing coherent (i.e., collective) from purely random (noisy) behavior for such two-dimensional fluctuating phenomena.
Vortices in the Two-Dimensional Simple Exclusion Process
NASA Astrophysics Data System (ADS)
Bodineau, T.; Derrida, B.; Lebowitz, Joel L.
2008-06-01
We show that the fluctuations of the partial current in two dimensional diffusive systems are dominated by vortices leading to a different scaling from the one predicted by the hydrodynamic large deviation theory. This is supported by exact computations of the variance of partial current fluctuations for the symmetric simple exclusion process on general graphs. On a two-dimensional torus, our exact expressions are compared to the results of numerical simulations. They confirm the logarithmic dependence on the system size of the fluctuations of the partial flux. The impact of the vortices on the validity of the fluctuation relation for partial currents is also discussed in an Appendix.
Two Dimensional Mechanism for Insect Hovering
Jane Wang, Z.
2000-09-04
Resolved computation of two dimensional insect hovering shows for the first time that a two dimensional hovering motion can generate enough lift to support a typical insect weight. The computation reveals a two dimensional mechanism of creating a downward dipole jet of counterrotating vortices, which are formed from leading and trailing edge vortices. The vortex dynamics further elucidates the role of the phase relation between the wing translation and rotation in lift generation and explains why the instantaneous forces can reach a periodic state after only a few strokes. The model predicts the lower limits in Reynolds number and amplitude above which the averaged forces are sufficient. (c) 2000 The American Physical Society.
2012-02-28
0.008 0.01 0.012 0 0.2 0.4 0.6 0.8 1 1.2 Time [s] M ac h N um be r a t N oz zl e E xi t Figure 6: Nozzle exit Mach number as a function of time...11 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.5 1 1.5 2 2.5 3 3.5 4 M ac h N um be r Distance from Throat [m] Mach number without MHD Generation Mach...flow by anMHDgenerator before reapplying it after the combustor via anMHDaccelerator, this energybypass concept could also be applied to the PDRE [16
Two-dimensional electronic spectroscopy using incoherent light: theoretical analysis.
Turner, Daniel B; Howey, Dylan J; Sutor, Erika J; Hendrickson, Rebecca A; Gealy, M W; Ulness, Darin J
2013-07-25
Electronic energy transfer in photosynthesis occurs over a range of time scales and under a variety of intermolecular coupling conditions. Recent work has shown that electronic coupling between chromophores can lead to coherent oscillations in two-dimensional electronic spectroscopy measurements of pigment-protein complexes measured with femtosecond laser pulses. A persistent issue in the field is to reconcile the results of measurements performed using femtosecond laser pulses with physiological illumination conditions. Noisy-light spectroscopy can begin to address this question. In this work we present the theoretical analysis of incoherent two-dimensional electronic spectroscopy, I((4)) 2D ES. Simulations reveal diagonal peaks, cross peaks, and coherent oscillations similar to those observed in femtosecond two-dimensional electronic spectroscopy experiments. The results also expose fundamental differences between the femtosecond-pulse and noisy-light techniques; the differences lead to new challenges and new opportunities.
A two-dimensional spin liquid in quantum kagome ice.
Carrasquilla, Juan; Hao, Zhihao; Melko, Roger G
2015-06-22
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.
Two-Dimensional Phononic Crystals: Disorder Matters.
Wagner, Markus R; Graczykowski, Bartlomiej; Reparaz, Juan Sebastian; El Sachat, Alexandros; Sledzinska, Marianna; Alzina, Francesc; Sotomayor Torres, Clivia M
2016-09-14
The design and fabrication of phononic crystals (PnCs) hold the key to control the propagation of heat and sound at the nanoscale. However, there is a lack of experimental studies addressing the impact of order/disorder on the phononic properties of PnCs. Here, we present a comparative investigation of the influence of disorder on the hypersonic and thermal properties of two-dimensional PnCs. PnCs of ordered and disordered lattices are fabricated of circular holes with equal filling fractions in free-standing Si membranes. Ultrafast pump and probe spectroscopy (asynchronous optical sampling) and Raman thermometry based on a novel two-laser approach are used to study the phononic properties in the gigahertz (GHz) and terahertz (THz) regime, respectively. Finite element method simulations of the phonon dispersion relation and three-dimensional displacement fields furthermore enable the unique identification of the different hypersonic vibrations. The increase of surface roughness and the introduction of short-range disorder are shown to modify the phonon dispersion and phonon coherence in the hypersonic (GHz) range without affecting the room-temperature thermal conductivity. On the basis of these findings, we suggest a criteria for predicting phonon coherence as a function of roughness and disorder.
Nonlinear tunneling in two-dimensional lattices
Brazhnyi, V. A.; Konotop, V. V.; Kuzmiak, V.; Shchesnovich, V. S.
2007-08-15
We present a thorough analysis of the nonlinear tunneling of Bose-Einstein condensates in static and accelerating two-dimensional lattices within the framework of the mean-field approximation. We deal with nonseparable lattices, considering different initial atomic distributions in highly symmetric states. For an analytical description of the condensate before instabilities develop, we derive several few-mode models, analyzing essentially both nonlinear and quasilinear regimes of tunneling. By direct numerical simulations, we show that two-mode models provide an accurate description of tunneling when either initially two states are populated or tunneling occurs between two stable states. Otherwise, a two-mode model may give only useful qualitative hints for understanding tunneling, but does not reproduce many features of the phenomenon. This reflects the crucial role of instabilities developed due to two-body interactions resulting in a non-negligible population of the higher bands. This effect becomes even more pronounced in the case of accelerating lattices. In the latter case we show that the direction of the acceleration is a relevant physical parameter which affects the tunneling by changing the atomic rates at different symmetric states and by changing the numbers of bands involved in the atomic transfer.
Holtschlag, D.J.; Koschik, J.A.
2005-01-01
Upper St. Clair River, which receives outflow from Lake Huron, is characterized by flow velocities that exceed 7 feet per second and significant channel curvature that creates complex flow patterns downstream from the Blue Water Bridge in the Port Huron, Michigan, and Sarnia, Ontario, area. Discrepancies were detected between depth-averaged velocities previously simulated by a two-dimensional (2D) hydrodynamic model and surface velocities determined from drifting buoy deployments. A detailed ADCP (acoustic Doppler current profiler) survey was done on Upper St. Clair River during July 1–3, 2003, to help resolve these discrepancies. As part of this study, a refined finite-element mesh of the hydrodynamic model used to identify source areas to public water intakes was developed for Upper St. Clair River. In addition, a numerical procedure was used to account for radial accelerations, which cause secondary flow patterns near channel bends. The refined model was recalibrated to better reproduce local velocities measured in the ADCP survey. ADCP data also were used to help resolve the remaining discrepancies between simulated and measured velocities and to describe variations in velocity with depth. Velocity data from ADCP surveys have significant local variability, and statistical processing is needed to compute reliable point estimates. In this study, velocity innovations were computed for seven depth layers posited within the river as the differences between measured and simulated velocities. For each layer, the spatial correlation of velocity innovations was characterized by use of variogram analysis. Results were used with kriging to compute expected innovations within each layer at applicable model nodes. Expected innovations were added to simulated velocities to form integrated velocities, which were used with reverse particle tracking to identify the expected flow path near a sewage outfall as a function of flow depth. Expected particle paths generated by use
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-σ (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 σ 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.
Deng, Wei; Zhang, Bing; Li, Hui; Li, Shengtai E-mail: zhang@physics.unlv.edu E-mail: sli@lanl.gov
2015-06-01
We perform 3D relativistic ideal magnetohydrodynamics (MHD) simulations to study the collisions between high-σ (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 σ 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.
Two-dimensional generalized Toda lattice
NASA Astrophysics Data System (ADS)
Mikhailov, A. V.; Olshanetsky, M. A.; Perelomov, A. M.
1981-12-01
The zero curvature representation is obtained for the two-dimensional generalized Toda lattices connected with semisimple Lie algebras. The reduction group and conservation laws are found and the mass spectrum is calculated.
Two-dimensional function photonic crystals
NASA Astrophysics Data System (ADS)
Liu, Xiao-Jing; Liang, Yu; Ma, Ji; Zhang, Si-Qi; Li, Hong; Wu, Xiang-Yao; Wu, Yi-Heng
2017-01-01
In this paper, we have studied two-dimensional function photonic crystals, in which the dielectric constants of medium columns are the functions of space coordinates , that can become true easily by electro-optical effect and optical kerr effect. We calculated the band gap structures of TE and TM waves, and found the TE (TM) wave band gaps of function photonic crystals are wider (narrower) than the conventional photonic crystals. For the two-dimensional function photonic crystals, when the dielectric constant functions change, the band gaps numbers, width and position should be changed, and the band gap structures of two-dimensional function photonic crystals can be adjusted flexibly, the needed band gap structures can be designed by the two-dimensional function photonic crystals, and it can be of help to design optical devices.
Two Dimensional Plasmonic Cavities on Moire Surfaces
NASA Astrophysics Data System (ADS)
Balci, Sinan; Kocabas, Askin; Karabiyik, Mustafa; Kocabas, Coskun; Aydinli, Atilla
2010-03-01
We investigate surface plasmon polariton (SPP) cavitiy modes on two dimensional Moire surfaces in the visible spectrum. Two dimensional hexagonal Moire surface can be recorded on a photoresist layer using Interference lithography (IL). Two sequential exposures at slightly different angles in IL generate one dimensional Moire surfaces. Further sequential exposure for the same sample at slightly different angles after turning the sample 60 degrees around its own axis generates two dimensional hexagonal Moire cavity. Spectroscopic reflection measurements have shown plasmonic band gaps and cavity states at all the azimuthal angles (omnidirectional cavity and band gap formation) investigated. The plasmonic band gap edge and the cavity states energies show six fold symmetry on the two dimensional Moire surface as measured in reflection measurements.
NASA Astrophysics Data System (ADS)
Kubota, Y.; Nagatsuma, T.; Den, M.; Tanaka, T.; Fujita, S.
2015-12-01
We are developing a real-time numerical simulator for the solar-wind-magnetosphere-ionosphere coupling system using next generation magnetosphere-ionosphere coupling global MHD simulation called REPPU (REProduce Plasma Universe) code. The feature of simulation has an advanced robustness to strong solar wind case because a triangular grid is used, which is able to calculate in the uniform accuracy over the whole region. Therefore we can simulate extreme event such as the Bastille day storm. The resolution is 7682 grids in the horizontal direction and 240 grids in the radial direction. The inner boundary of the simulation box is set at 2.6 Re. We investigate the reproduction of the magnetosphere-ionosphere coupling simulation in strong solar wind case. Therefore we compared the simulation results with the observation of the Bastille day storm event (2000/7/15), in which the solar wind velocity is above 1000 km/s and the value of Bz reached -60 nT. Especially, we focus the cross polar cap potential (CPCP) saturation and time variation because the CPCP represents the value of magnetospheric - ionospheric convection strength via region 1 current. The CPCP depends on solar wind electric field, dynamic pressure and ionospheric conductivity [Siscoe et al., 2002; Kivelson et al., 2008]. The model of Kivelson et al. [2008] shows a good reproduction to the CPCP variation. However their study assumes that the ionospheric conductivity is constant. The conductivity in our simulation of the Bastille day event is varied by the auroral activity. In this lecture, we discuss the effect of both the auroral conductance and solar EUV-driven conductance to CPCP saturation.
Two-dimensional order and disorder thermofields
Belvedere, L. V.
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.
Efficient Two-Dimensional-FFT Program
NASA Technical Reports Server (NTRS)
Miko, J.
1992-01-01
Program computes 64 X 64-point fast Fourier transform in less than 17 microseconds. Optimized 64 X 64 Point Two-Dimensional Fast Fourier Transform combines performance of real- and complex-valued one-dimensional fast Fourier transforms (FFT's) to execute two-dimensional FFT and coefficients of power spectrum. Coefficients used in many applications, including analyzing spectra, convolution, digital filtering, processing images, and compressing data. Source code written in C, 8086 Assembly, and Texas Instruments TMS320C30 Assembly languages.
Analytical estimates of turbulent MHD transport coefficients
NASA Technical Reports Server (NTRS)
Montgomery, D.; Hatori, T.
1984-01-01
Turbulent transfer rates from small-scale MHD excitations to large-scale Fourier modes are calculated algebraically, using the method of Biskamp and Welter. Three cases are considered: two-dimensional Navier-Stokes flows, two-dimensional incompressible MHD, and the weakly three-dimensional Strauss equations. In all cases, an initially large spectral gap between the small-scale and large-scale excitations is assumed, and attention focusses on the initial values of the back-transfer rates. The sign of the transfer is determined by the sign of an analytically calculable eddy viscosity and/or anomalous resistivity. We are able to confirm the results of Biskamp and Welter for the case of two-dimensional MHD, but find some differences for the case of the Strauss equations. It is argued that the Strauss equations may not exhibit an inverse cascade phenomenon for the spatially periodic case unless their initial spectra are such that the behavior is essentially that of two-dimensional MHD.
Two-Dimensional Optical Proximity Effects
NASA Astrophysics Data System (ADS)
Flanner, Philip D.; Subramanian, Shankar; Neureuther, Andrew R.
1986-08-01
In projection printing the proximity effects between adjacent two-dimensional features such as concentric elbows can be the limiting factor in designing layout rules. An aerial image simulation code based on the imaging algorithms in SAMPLE has been developed and used to investigate these proximity effects. The program accepts arbitrary polygonal shapes constructed of rectangular and triangular patches. The image is calculated using Hopkins transmission cross coefficient formulation and uses rapid integral evaluation techniques. The cpu time for this FORTRAN F77 program depends on the size of the mask and the partial coherence factor as 0.25[(1 + σ) 2A(NA/λ)2]2 seconds on a DEC VAX 11/780 using double precision, where A is the mask area, σ the coherence factor, NA the numerical aperture and λ the wavelength. The output intensity can be displayed with graphics tools such as UNIGRAFIX or cross-sectioned for input to SAMPLE development simulation along critical paths. Proximity effects in critical regions between features such as nested elbows, contacts near contacts and lines, and lines near large pads are studied. For small contacts studies show that a contact hole can be placed as close as 0.5λ/NA microns to another contact hole. For nested elbows the critical effect is the variation in intensity in the straight regions just adjacent to the corner. This undesirable variation is primarily due to the intrafeature intensity interactions and is not greatly influenced by the proximity of another nested elbow. For general feature shapes the proximity effects are reduced by increasing the partial coherence factor to 0.5 or higher but at the cost of reducing contrast and peak intensity. For contact masks a partial coherence of 0.3 is recommended for higher edge slope and peak intensities. Proximity effects of small defects are also illustrated.
Deng, Wei
2015-07-21
The question of the energy composition of the jets/outflows in high-energy astrophysical systems, e.g. GRBs, AGNs, is taken up first: Matter-flux-dominated (MFD), σ < 1, and/or Poynting-flux-dominated (PFD), σ >1? The standard fireball IS model and dissipative photosphere model are MFD, while the ICMART (Internal-Collision-induced MAgnetic Reconnection and Turbulence) model is PFD. Motivated by ICMART model and other relevant problems, such as “jets in a jet” model of AGNs, the author investigates the models from the EMF energy dissipation efficiency, relativistic outflow generation, and σ evolution points of view, and simulates collisions between high-σ blobs to mimic the situation of the interactions inside the PFD jets/outflows by using a 3D SRMHD code which solves the conservative form of the ideal MHD equations. σ_{b,f} is calculated from the simulation results (threshold = 1). The efficiency obtained from this hybrid method is similar to the efficiency got from the energy evolution of the simulations (35.2%). Efficiency is nearly σ independent, which is also confirmed by the hybrid method. σ_{b,i} - σ_{b,f} provides an interesting linear relationship. Results of several parameter studies of EMF energy dissipation efficiency are shown.
Two-dimensional inflow-wind solution of black hole accretion with an evenly symmetric magnetic field
NASA Astrophysics Data System (ADS)
Mosallanezhad, Amin; Bu, Defu; Yuan, Feng
2016-03-01
We solve the two-dimensional magnetohydrodynamic (MHD) equations of black hole accretion with the presence of magnetic field. The field includes a turbulent component, whose role is represented by the viscosity, and a large-scale ordered component. The latter is further assumed to be evenly symmetric with the equatorial plane. The equations are solved in the r - θ plane of a spherical coordinate by assuming time-steady and radially self-similar. An inflow-wind solution is found. Around the equatorial plane, the gas is inflowing; while above and below the equatorial plane at a certain critical θ angle, θ ˜ 47°, the inflow changes its direction of radial motion and becomes wind. The driving forces are analysed and found to be the centrifugal force and the gradient of gas and magnetic pressure. The properties of wind are also calculated. The specific angular momentum of wind is found to be significantly larger than that of inflow, thus wind can transfer angular momentum outward. These analytical results are compared to those obtained by the trajectory analysis based on MHD numerical simulation data and good agreements are found.
Localized reconnection in the magnetotail driven by lobe flow channels: Global MHD simulation
NASA Astrophysics Data System (ADS)
Nishimura, Y.; Lyons, L. R.
2016-02-01
Recent ionospheric measurements suggest polar cap flow channels often trigger nightside auroral brightening. However, measurements were limited to the ionosphere, and it was not understood if such flow channels can exist in the lobe and can trigger magnetotail reconnection in a localized cross-tail extent. We examined if localized flow channels can form self-consistently in a global MHD regime, and if so, how such flow channels originate and relate to localized magnetotail reconnection. We show that lobe convection became nonuniform with azimuthally narrow flow channels (enhanced dawn-dusk electric fields) of ~3 RE cross-tail width. The flow channels propagated from the dayside toward the plasma sheet as an interplanetary magnetic field (IMF) discontinuity swept tailward. The plasma sheet around the lobe flow channels became thinner with a similar cross-tail extent and then localized reconnection occurred. These results suggest that localized flow channels can propagate tailward across the lobe and drive localized magnetotail reconnection, that the cross-tail width of reconnection and resulting plasma sheet flow channels and dipolarization fronts are related to the width of inflow from the lobe, and that IMF discontinuities drive lobe flow channels.
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.
NASA Astrophysics Data System (ADS)
Park, K.; Ogino, T.; Lee, D.; Walker, R. J.; Kim, K.
2013-12-01
One of the significant problems in magnetospheric physics concerns the nature and properties of the processes which occur at the magnetopause boundary; in particular how energy, momentum, and plasma the magnetosphere receives from the solar wind. Basic processes are magnetic reconnection [Dungey, 1961] and viscouslike interaction, such as Kelvin-Helmholtz instability [Dungey 1955, Miura, 1984] and pressure-pulse driven [Sibeck et al. 1989]. In generally, magnetic reconnection occurs efficiently when the IMF is southward and the rate is largest where the magnetosheath magnetic field is antiparallel to the geomagnetic field. [Sonnerup, 1974; Crooker, 1979; Luhmann et al., 1984; Park et al., 2006, 2009]. The Kelvin-Helmholtz instability is driven by the velocity shear at the boundary, which occur frequently when the IMF is northward. Also variation of the magnetic field and the plasma properties is reported to be quasi-periodic with 2-3min [Otto and Fairfield, 2000] and period of vortex train with 3 to 4 minutes by global MHD simulation [Ogino, 2011]. The pressure-pulse is driven by the solar wind. And the observations of the magnetospheric magnetic field response show quasi-periodic with a period of 8 minutes [Sibeck et al., 1989; Kivelson and Chen, 1995]. There have been few studies of the vortices in the magnetospheric boundary under southward IMF condition. However it is not easy to find the generation mechanism and characteristic for vortices in complicated 3-dimensional space. Thus we have performed global MHD simulation for the steady solar wind and southward IMF conditions. From the simulation results, we find that the vortex occurs at R= 11.7Re (IMF Bz = -2 nT) and R= 10.2Re (IMF Bz = -10 nT) in the dayside magnetopause boundary. Also the vortex rotates counterclockwise in duskside magnetopause (clockwise in dawnside) and propagates tailward. Across the vortex, magnetic field and plasma properties clearly show quasi-periodic fluctuations with a period of 8
NASA Astrophysics Data System (ADS)
Zhai, X. M.; Yeung, P. K.
2016-11-01
Turbulence in an electrically conducting fluid in the limit of low magnetic Reynolds number is, because of the Lorentz force due to an external magnetic field, very different from classical turbulence at both the large scales and the small scales. The importance of minimizing finite domain-size effects on the large scale development has often tended to limit the Reynolds number reached in the past. In this work we use periodic domains stretched along the magnetic field with aspect ratio up to 8 and beyond. The initial state is obtained from decaying isotropic turbulence with large-eddy length scales of order 1% of the length of the domain. After a transient period the kinetic energy returns to a power law decay while the integral length scales in the direction parallel to the magnetic field show preferential growth. At early times the parallel velocity component becomes stronger than the other two but this anisotropy is subsequently reversed under the combined effects of anisotropic Joule dissipation and viscous dissipation. The small scales show characteristics of quasi two-dimensional behavior in the transverse plane. Results over a range of magnetic interaction parameters and Reynolds numbers are compared with known theoretical predictions. Supported by NSF Grant CBET-1510749 and supercomputer resources at TACC/XSEDE and ALCF.
Deng, Wei; Li, Hui; Zhang, Bing; ...
2015-05-29
We perform 3D relativistic ideal MHD simulations to study the collisions between high-σ (Poynting- ux-dominated) blobs which contain both poloidal and toroidal magnetic field components. This is meant to mimic the interactions inside a highly variable Poynting- ux-dominated jet. We discover a significant electromagnetic field (EMF) energy dissipation with an Alfvenic 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 themore » 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 σ values before and after the major EMF energy dissipation process. In conclusion, our results give support to the proposed astrophysical models that invoke signi cant magnetic energy dissipation in Poynting- ux-dominated jets, such as the internal collision-induced magnetic reconnection and turbulence (ICMART) model for GRBs, and reconnection triggered mini-jets model for AGNs.« less
Deng, Wei; Li, Hui; Zhang, Bing; Li, Shengtai
2015-05-29
We perform 3D relativistic ideal MHD simulations to study the collisions between high-σ (Poynting- ux-dominated) blobs which contain both poloidal and toroidal magnetic field components. This is meant to mimic the interactions inside a highly variable Poynting- ux-dominated jet. We discover a significant electromagnetic field (EMF) energy dissipation with an Alfvenic 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 σ values before and after the major EMF energy dissipation