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.
On the evolution of a magnetic flux rope: Two-dimensional MHD simulation results
NASA Astrophysics Data System (ADS)
Teh, W.-L.; Nakamura, T. K. M.; Nakamura, R.; Baumjohann, W.; Abdullah, M.
2015-10-01
We use the time-dependent, two-dimensional (2-D), ideal MHD equations to simulate and investigate the evolution of magnetic field and plasma profiles of the typical (T) and crater (C) magnetic flux ropes (FRs). The T-FR has a magnetic pressure peak at the center of the flux rope, while the C-FR has a local dip instead. The simulation starts with a 2-D magnetic flux rope in magnetohydrostatic equilibrium, where pressure gradient forces are balanced by Lorentz forces. The magnetic field and plasma pressure profiles for the initial flux rope are derived from the analytical solutions by Zhang et al. (2010). The initial flux rope starts to evolve when the force balance is broken by imposing pressure or magnetic field perturbations onto the equilibrium system. The pressure perturbations are produced by increasing/decreasing the internal plasma pressure of the flux rope, while the magnetic field perturbations are produced by increasing/decreasing the transverse magnetic fields across the flux rope. We conclude that a T-FR can be evolved into a C-FR and vice versa, if the perturbation strength is sufficient, and that the plasma pressure and density in the new equilibrium state could be either increased or decreased for the evolution of C-FR to T-FR and also for the evolution of T-FR to C-FR.
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. PMID:15142583
Comparative analysis of numerial methods for two-dimensional high-compression MHD-flow simulation
Aksenov, A.G.; Gerusov, A.V.
1995-01-01
The efficiency of the different numerical algorithms in solving the ideal MHD-equations in the presence of a transverse magnetic field is considered. As the testing problem for estimation of the algorithm efficiency, the dynamics of a noncylindrical skinned Z-pinch was used. The important features of the considered pinch are the high degree of plasma compression, the presence of the shock waves and contact discontinuities, and the unstable behavior of the plasma-magnetic field boundary. The new qualitative results were obtained by numerical simulation of the above problem with the help of a new algorithm. Particularly, the highly nonlinear stage of Rayleigh-Taylor instability at the plasma-magnetic field boundary was analyzed. The instability growth was found to result in the breaking of the plasma jets into vacuum along with the emergence of the magnetic field bubbles in the matter. 15 refs., 9 figs., 2 tabs.
Two-dimensional heat conducting simulation of plasma armatures
Huerta, M.A.; Boynton, G. . Dept. of Physics)
1991-01-01
This paper reports on our development of a two-dimensional MHD code to simulate internal motions in a railgun plasma armature. The authors use the equations of resistive MHD, with Ohmic heating, and radiation heat transport. The authors use a Flux Corrected Transport code to advance all quantities in time. Our runs show the development of complex flows, subsequent shedding of secondary arcs, and a drop in the acceleration of the armature.
A Two Dimensional MHD Code Using ALE Method for the Study of Pinch Dynamics
NASA Astrophysics Data System (ADS)
Wang, Ganghua; Kan, Mingxian; Sun, Chengwei; Xie, Long; Zhao, Hailong
2013-10-01
A two dimensional MHD code MDSC (Magnetically Driven Simulation Code) is developed using ALE method for the study of pinch dynamics. The MHD equations are solved in an operator split fashion or time-splitting technique. The thermal, magnetic diffusions and Lagrangian hydrodynamics are computed with mixed differencing scheme of explicit and implicit. Finite differences are computed with a finite volume technique, and a first-order accurate convection scheme was used. Examples of different seed perturbations showed that the code is successful. Project supported by the National Natural Science Foundation of China (Grant No.1172277).
Two-dimensional and three-dimensional time-dependent MHD model of extended corona
NASA Astrophysics Data System (ADS)
Wang, Ai-Hua
A new time-dependent, numerical, magnetohydrodynamic (MHD) model for the simulation on two-dimensional and three-dimensional coronal streamers and coronal holes from the solar surface (r = 1 solar radius) to 15 solar radius is presented. For the two-dimensional coronal streamer simulation, three examples are given for dipole, quadrupole, and hexapole (Legendre polynomials P1, P2, and P3) initial field topologies. For the two-dimensional coronal hole simulation, one example is given for a dipole initial field topology. For the three-dimensional coronal streamer simulation, one example is given for a spherical harmonic function (Y2)2 (spherical harmonical function) initial field topology. The computed physical variables 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 the present cases, the initial flow field is a polytropic, hydrodynamic solution to the steady state radial flow equation superimposed on a potential magnetic field. For the two-dimensional coronal streamers, different sizes and shapes were obtained. Inside the streamer the velocity is very small and the density is high. For the two-dimensional coronal hole the highest solar wind comes from the center of the hole. At 15 solar radius the radial flow speed is about 412 km/s. With theoretical extrapolation, it shows that the radial flow speed is in the range between 512-800 km/s at 1AU. Also, at the center of the hole the number density is low with the order of 105/cu cm at 2 solar radius. For the three-dimensional numerical model, the preliminary coronal streamer results are presented. In addition to the properties of the solutions, their accuracy is discussed.
Evolution of generalized two-dimensional magnetotail equilibria in ideal and resistive MHD
NASA Astrophysics Data System (ADS)
Merkin, V. G.; Sitnov, M. I.; Lyon, J. G.
2015-03-01
We present results of two-dimensional (2-D) magnetohydrodynamic (MHD) simulations of the terrestrial magnetotail. A regional adaptation of the Lyon-Fedder-Mobarry global MHD model is used. As initial conditions, we employ a class of asymptotic magnetotail equilibria with and without an accumulation of magnetic flux at the tailward end (a Bz hump). The former have been recently shown by full particle simulations to be unstable to a kinetic mode with formal properties of ion tearing. Thus, our goal here is to investigate the evolution of the same equilibria in the MHD approximation and assist in the physical interpretation of the kinetic simulations. This is additionally motivated by the energy principle considerations which suggest that if the system is unstable kinetically, it may also be unstable ideally. To seek dynamical MHD regimes similar to those observed in kinetic simulations, we implement two sets of boundary conditions (velocity balanced, VB, and momentum balanced, MB), one allowing plasma flows through the boundaries and the other inhibiting such flows. The use of more reflecting MB boundary conditions results in suppression of any significant dynamics, and we see no substantial changes beyond initial equilibrium relaxation. On the other hand, VB boundary conditions allow a more efficient relaxation of initial equilibrium and absorb subsequently generated plasma flows. With these boundary conditions we find the equilibrium without a flux accumulation (i.e., with constant magnetic field component normal to the current sheet) to develop an apparently resistive mode accompanied by tailward plasma flows. At the same time, the equilibria with a Bz hump of sufficiently large amplitude develop a different, ideal, mode characterized by spontaneous generation of earthward plasma flows and an exponential growth of the corresponding electric field. This growth is qualitatively similar to the corresponding fully kinetic simulations although no explosive growth of the earthward moving Bz peak is evident in the MHD calculations, just an earthward shift of a part of the initial flux accumulation. We discuss implications of our results for the possibility of existence and impact of such equilibria in the Earth's magnetotail and in global MHD simulations.
Two-dimensional 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.
Two-dimensional acoustic instability in open-cycle supersonic disk MHD generator
Matsuo, Tetsuji; Ishikawa, Motoo; Umoto, Juro
1995-12-31
Both the guide vanes of the outflow disk MHD generator and the multiple inlets of the inflow disk MHD generator induce inlet azimuthal fluctuations, whose propagation along the channel may cause r-{theta} two-dimensional magneto-acoustic instability. The present paper evaluates the growth rate of r-{theta} two-dimensional disturbance during the propagation along supersonic disk channels by means of a sensitivity analysis. The generator analyzed here is a coal-fired outflow supersonic disk MHD generator of commercial scale. The paper proposes a method of sensitivity analysis for the azimuthally nonuniform disturbance. The sensitivity analysis shows that both low and high frequency two-dimensional disturbances have higher growth rate than one-dimensional ones. Time-invariant inlet azimuthal disturbances can tremendously grow during the propagation, which means that the fluctuation induced by the guide vanes may be quite dangerous. The azimuthal direction of traveling waves much affects the growth rate of waves. Two-dimensional time-dependent calculations also show that slight inlet azimuthal disturbances grow large during the propagation along the channel.
Global magnetohydrodynamic simulation of the two-dimensional magnetosphere
NASA Technical Reports Server (NTRS)
Leboeuf, J. N.; Tajima, T.; Kennel, C. F.; Dawson, J. M.
1979-01-01
The time-dependent magnetohydrodynamic interaction of the solar wind with a two-dimensional dipole magnetic field has been simulated using a novel Lagrangian particle type of MHD code that can treat local low density or vacuum regions without numerical instability. This enables one to simulate the time-dependent magnetic tail. When the solar wind field is southward, a magnetic field line topology consistent with Dungey's model emerges in steady state. The tail, however, is short, and the x-points are only slightly shifted from their vacuum locations, because of strong numerical resistivity. Different configurations resulting from different relative orientations of the solar wind magnetic field and dipole axis are also presented. While the magnetic field is relatively steady, the density and flow in the magnetosheath are turbulent, as are the bow shock and magnetopause; the Kelvin-Helmholtz instability may account for these phenomena. We also model a 'substorm' as the passage of a rotational discontinuity in the solar wind over the dipole. Both 90 and 180 deg shifts to a southward solar wind field cause a violent readjustment of the magnetic tail which eventually settles down to the Dungey configuration.
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.
Numerical analysis of real gas MHD flow on two-dimensional self-field MPD thrusters
NASA Astrophysics Data System (ADS)
Xisto, Carlos M.; Páscoa, José C.; Oliveira, Paulo J.
2015-07-01
A self-field magnetoplasmadynamic (MPD) thruster is a low-thrust electric propulsion space-system that enables the usage of magnetohydrodynamic (MHD) principles for accelerating a plasma flow towards high speed exhaust velocities. It can produce an high specific impulse, making it suitable for long duration interplanetary space missions. In this paper numerical results obtained with a new code, which is being developed at C-MAST (Centre for Mechanical and Aerospace Technologies), for a two-dimensional self-field MPD thruster are presented. The numerical model is based on the macroscopic MHD equations for compressible and electrically resistive flow and is able to predict the two most important thrust mechanisms that are associated with this kind of propulsion system, namely the thermal thrust and the electromagnetic thrust. Moreover, due to the range of very high temperatures that could occur during the operation of the MPD, it also includes a real gas model for argon.
On the Transition from Two-Dimensional to Three-Dimensional MHD Turbulence
NASA Technical Reports Server (NTRS)
Thess, A.; Zikanov, Oleg
2004-01-01
We report a theoretical investigation of the robustness of two-dimensional inviscid MHD flows at low magnetic Reynolds numbers with respect to three-dimensional perturbations. We analyze three model problems, namely flow in the interior of a triaxial ellipsoid, an unbounded vortex with elliptical streamlines, and a vortex sheet parallel to the magnetic field. We demonstrate that motion perpendicular to the magnetic field with elliptical streamlines becomes unstable with respect to the elliptical instability once the velocity has reached a critical magnitude whose value tends to zero as the eccentricity of the streamlines becomes large. Furthermore, vortex sheets parallel to the magnetic field, which are unstable for any velocity and any magnetic field, are found to emit eddies with vorticity perpendicular to the magnetic field and with an aspect ratio proportional to N(sup 1/2). The results suggest that purely two-dimensional motion without Joule energy dissipation is a singular type of flow which does not represent the asymptotic behaviour of three-dimensional MHD turbulence in the limit of infinitely strong magnetic fields.
Simulated annealing applied to two-dimensional low-beta reduced magnetohydrodynamics
Chikasue, Y.; Furukawa, M.
2015-02-15
The simulated annealing (SA) method is applied to two-dimensional (2D) low-beta reduced magnetohydrodynamics (R-MHD). We have successfully obtained stationary states of the system numerically by the SA method with Casimir invariants preserved. Since the 2D low-beta R-MHD has two fields, the relaxation process becomes complex compared to a single field system such as 2D Euler flow. The obtained stationary state can have fine structure. We have found that the fine structure appears because the relaxation processes are different between kinetic energy and magnetic energy.
Reconstruction of two-dimensional coherent MHD structures in a space plasma: The theory
NASA Astrophysics Data System (ADS)
Sonnerup, Bengt U. .-.; Teh, Wai-Leong
2008-05-01
We develop basic theory for the reconstruction of two-dimensional, time-stationary, ideal, compressible MHD structures in a space plasma from data taken by a single spacecraft as the structures move past it. The MHD equations are solved as a spatial initial-value problem in a manner similar to that used in so-called Grad-Shafranov (GS) reconstruction (e.g., Sonnerup et al., 2006), the difference being that our new method can deal with general structures, not just those governed by a GS-like equation. The approach described here represents a first step toward reconstruction of 2D steady state reconnection configurations, viewed in a frame moving with the X-line: Resistive, electron pressure, and Hall terms are still missing in Ohm's law but resistive and Hall effects can, we argue, ultimately be included. A numerical algorithm to perform the integration has been developed. It is tested by generation of synthetic data from a virtual spacecraft moving through an exact, analytical, axisymmetric solution of the MHD equations; these data are then used for the reconstruction. The exact solution involves isentropic plasma flow at an angle to the magnetic field. In addition to pressure and density, all three magnetic field and flow components are activated in the solution, i.e., they all vary with radius. Results show that the new method works with acceptable accuracy in a rectangular region surrounding the spacecraft path, with the two long sides of the rectangle parallel to the path. As is the case for GS reconstruction, the length of the short sides is limited by spatially growing numerical instability inherent in this type of integration procedure. Applications to actual spacecraft (Cluster) data will be reported separately.
Two-dimensional numerical simulation of MPD flows
Martinez-Sanchez, M.; Chanty, J.M.G.
1987-05-01
A two-dimensional numerical model has been developed in order to analyze electromagnetic plasma accelerators also called Self-Field Magneto-Plasma-Dynamic Thrusters. This model uses a Magneto-Hydro-Dynamic description of the gas considered as a fully ionized, isothermal plasma, and takes into account the Hall effect (nonlinear conductivity) and the interaction between the magnetic field and the fluid dynamics of the plasma. The system of equations is discretized into finite volumes, and is solved by a Newton-Raphson scheme. Results from the MHD model were calculated for a mass flow rate of 6 g/s of argon and for currents up to ten kilo-Amperes. 29 references.
Two-dimensional MHD reconstruction for studying magnetic reconnection at the magnetopause
NASA Astrophysics Data System (ADS)
Teh, W.; Sonnerup, B.
2007-12-01
A new method for the reconstruction of two-dimensional, coherent structures in a space plasma is developed, using the ideal MHD equations. The reconstruction algorithm is similar to that used in Grad-Shafranov (GS) reconstruction, which is to solve the equations as a spatial initial-value problem. It is benchmarked with an exact analytical solution, in which the pressure, density, all three magnetic field and flow components are functions of radius only, and in which isentropic flow at an angle to the magnetic field is present. The reconstruction results show good agreement with the exact solution, with acceptably small errors within a strip of substantial width around the spacecraft trajectory. The reconstruction scheme is then applied to previously studied magnetopause reconnection events seen by Cluster. In contrast to the case of GS reconstruction, which is performed in the deHoffmann-Teller frame, we now use a frame co-moving with the X-line, in which the axial electric field should ideally be constant. The new reconstruction results are generally consistent with earlier interpretations. We also examine the possibility of including the Hall term in Ohms law by use of an iterative procedure.
Two-dimensional Simulations of Correlation Reflectometry in Fusion Plasmas
E.J. Valeo; G.J. Kramer; R. Nazikian
2001-07-05
A two-dimensional wave propagation code, developed specifically to simulate correlation reflectometry in large-scale fusion plasmas is described. The code makes use of separate computational methods in the vacuum, underdense and reflection regions of the plasma in order to obtain the high computational efficiency necessary for correlation analysis. Simulations of Tokamak Fusion Test Reactor (TFTR) plasma with internal transport barriers are presented and compared with one-dimensional full-wave simulations. It is shown that the two-dimensional simulations are remarkably similar to the results of the one-dimensional full-wave analysis for a wide range of turbulent correlation lengths. Implications for the interpretation of correlation reflectometer measurements in fusion plasma are discussed.
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
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.
A two-dimensional MHD global coronal model - Steady-state streamers
NASA Astrophysics Data System (ADS)
Wang, A.-H.; Wu, S. T.; Suess, S. T.; Poletto, G.
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.
Two-Dimensional Simulations of Thin-Silicon Solar Cells
Wang, T. H.; Page, M. R.; Ciszek, T. F.
2002-08-01
Quantitative analysis or numeric simulation on a cross-section of silicon devices offers many insights into understanding material problems and their effects on device performances as well as device structure optimizations. Such two-dimensional simulations on semiconductor devices are standard design practices and are routinely done with expensive software packages. The availability of less expensive software tools nowadays, such as MicroTec(R) for 2D modeling of semiconductor devices, affords us a more detailed examination of polycrystalline thin-silicon materials and solar cells.
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.
Two dimensional simulation of high power laser-surface interaction
Goldman, S.R.; Wilke, M.D.; Green, R.E.L.; Johnson, R.P.; Busch, G.E.
1998-08-01
For laser intensities in the range of 10{sup 8}--10{sup 9} W/cm{sup 2}, and pulse lengths of order 10 {micro}sec or longer, the authors have modified the inertial confinement fusion code Lasnex to simulate gaseous and some dense material aspects of the laser-matter interaction. The unique aspect of their treatment consists of an ablation model which defines a dense material-vapor interface and then calculates the mass flow across this interface. The model treats the dense material as a rigid two-dimensional mass and heat reservoir suppressing all hydrodynamic motion in the dense material. The computer simulations and additional post-processors provide predictions for measurements including impulse given to the target, pressures at the target interface, electron temperatures and densities in the vapor-plasma plume region, and emission of radiation from the target. The authors will present an analysis of some relatively well diagnosed experiments which have been useful in developing their modeling. The simulations match experimentally obtained target impulses, pressures at the target surface inside the laser spot, and radiation emission from the target to within about 20%. Hence their simulational technique appears to form a useful basis for further investigation of laser-surface interaction in this intensity, pulse-width range. This work is useful in many technical areas such as materials processing.
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.
Two-Dimensional Dynamic Simulation of a Continuous Foil Bearing
NASA Technical Reports Server (NTRS)
Braun, M. Jack; Choy, F. K.; Dzodzo, Milorad; Hsu, J.
1996-01-01
In this paper, the two dimensional(radial and circumferential) transient Navier-Stokes equations are used to solve the hydrodynamic problem in conjunction with the time dependent motion of the journal, and the deformable, spring supported foil. The elastic deformation of the foil and its supports are simulated by a finite element model. The time-dependent Navier-Stokes formulation is used to solve for the interaction between the fluid lubricant, the motion of the journal and the deformable foil boundary. The steady state, the quasi-transient and the full transient dynamic simulation of the foil-fluid journal interaction are examined on a comparative basis. For the steady state simulation, the fluid lubricant pressures are evaluated for a particular journal position, by means of an iterative scheme until convergence is achieved in both the fluid pressures and the corresponding foil deformation. For the quasi-transient case, the transient motion of the journal is calculated using a numerical integration scheme for the velocity and displacement of the journal. The deformation of the foil is evaluated through numerical iteration in feedback mode with the fluid film pressure generated by the journal motion until convergence at every time step is achieved. For the full transient simulation, a parallel real-time integration scheme is used to evaluate simultaneously the new journal position and the new deformed shape of the foil at each time step. The pressure of the fluid lubricant is iterated jointly with the corresponding journal position and the deformed foil geometry until convergence is achieved. A variable time-stepping Newmark-Beta integration procedure is used to evaluate the transient dynamics at each time step of the bearing.
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 ??} component of the viscous stress and consider various values of the viscous parameter ?. We find that when T {sub ??} is included, the rotational speed of the high-latitude flow decreases, while the density increases and decreases at the high and low latitudes, respectively. We calculate the radial profiles of inflow and outflow rates. We find that the inflow rate decreases inward, following a power law form of M-dot {sub in}?r{sup s}. The value of s depends on the magnitude of ? and is within the range of ?0.4-1.0. Correspondingly, the radial profile of density becomes flatter compared with the case of a constant M-dot (r). We find that the density profile can be described by ?(r)?r {sup p} and the value of p is almost same for a wide range of ? ranging from ? = 0.1 to 0.005. The inward decrease of inflow accretion rate is very similar to hot accretion flows, which is attributed to the mass loss in outflows. To study the origin of outflow, we analyze the convective stability of the slim disk. We find that depending on the value of ?, the flow is marginally stable (when ? is small) or unstable (when ? is large). This is different from the case of hydrodynamical hot accretion flow, where radiation is dynamically unimportant and the flow is always convectively unstable. We speculate that the reason for the difference is because radiation can stabilize convection. The origin of outflow is thus likely because of the joint function of convection and radiation, but further investigation is required.
NASA Astrophysics Data System (ADS)
Takasao, Shinsuke; Matsumoto, Takuma; Nakamura, Naoki; Shibata, Kazunari
2015-06-01
Solar flares are an explosive phenomenon where super-sonic flows and shocks are expected in and above the post-flare loops. To understand the dynamics of post-flare loops, a two-dimensional magnetohydrodynamic (2D MHD) simulation of a solar flare has been carried out. We found new shock structures in and above the post-flare loops, which were not resolved in the previous work by Yokoyama & Shibata. To study the dynamics of flows along the reconnected magnetic field, the kinematics and energetics of the plasma are investigated along selected field lines. It is found that shocks are crucial to determine the thermal and flow structures in the post-flare loops. On the basis of the 2D MHD simulation, we developed a new post-flare loop model, which we defined as the pseudo-2D MHD model. The model is based on the one-dimensional (1D) MHD equations, where all variables depend on one space dimension, and all the three components of the magnetic and velocity fields are considered. Our pseudo-2D model includes many features of the multi-dimensional MHD processes related to magnetic reconnection (particularly MHD shocks), which the previous 1D hydrodynamic models are not able to include. We compared the shock formation and energetics of a specific field line in the 2D calculation with those in our pseudo-2D MHD model, and found that they give similar results. This model will allow us to study the evolution of the post-flare loops in a wide parameter space without expensive computational cost or neglecting important physics associated with magnetic reconnection.
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 (?) 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 ? is 140 with a relatively large spread (? = 28). The average direction of propagation is: longitude (?n) = 194 and latitude (?n) = 7 (but = 27), where ?n = 0 is sunward and ?n = 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 the normal component of the magnetic field. There is little difference in any average parameter value according to type. However, the average appears to depend slightly on type with the for the RDs being smaller. The discontinuity type was shown to change commonly in either direction (TD to RD or RD to TD) between the two observing positions, i.e., ?40% of the time. It is not clear if these type-changes are spatial or temporal. Shortcomings of the analysis are (1) the need to impose an upper limit on the angular difference of the DD normals between the two observing positions (which eliminated most surfaces of very small radii of curvature), and (2) the inability to distinguish real curvature from shorter-scale surface variations, from only two spacecraft data sets. The results of the study should help to caution us as to the simplistic use of the planar DD surface assumption in projecting, to the distance of Earth's magnetosphere, a distantly observed DD surface (e.g., one near L1), especially for studies that depend on accurately predicting the timing and characteristics of magnetospheric events.
Riquelme, Mario A.; Quataert, Eliot; Sharma, Prateek; Spitkovsky, Anatoly E-mail: eliot@astro.berkeley.edu E-mail: anatoly@astro.princeton.edu
2012-08-10
The magnetorotational instability (MRI) is a crucial mechanism of angular momentum transport in a variety of astrophysical accretion disks. In systems accreting at well below the Eddington rate, such as the central black hole in the Milky Way (Sgr A*), the plasma in the disk is essentially collisionless. We present a nonlinear study of the collisionless MRI using first-principles particle-in-cell plasma simulations. We focus on local two-dimensional (axisymmetric) simulations, deferring more realistic three-dimensional simulations to future work. For simulations with net vertical magnetic flux, the MRI continuously amplifies the magnetic field, B, until the Alfven velocity, v{sub A} , is comparable to the speed of light, c (independent of the initial value of v{sub A} /c). This is consistent with the lack of saturation of MRI channel modes in analogous axisymmetric MHD simulations. The amplification of the magnetic field by the MRI generates a significant pressure anisotropy in the plasma (with the pressure perpendicular to B being larger than the parallel pressure). We find that this pressure anisotropy in turn excites mirror modes and that the volume-averaged pressure anisotropy remains near the threshold for mirror mode excitation. Particle energization is due to both reconnection and viscous heating associated with the pressure anisotropy. Reconnection produces a distinctive power-law component in the energy distribution function of the particles, indicating the likelihood of non-thermal ion and electron acceleration in collisionless accretion disks. This has important implications for interpreting the observed emission-from the radio to the gamma-rays-of systems such as Sgr A*.
NASA Astrophysics Data System (ADS)
Riquelme, Mario A.; Quataert, Eliot; Sharma, Prateek; Spitkovsky, Anatoly
2012-08-01
The magnetorotational instability (MRI) is a crucial mechanism of angular momentum transport in a variety of astrophysical accretion disks. In systems accreting at well below the Eddington rate, such as the central black hole in the Milky Way (Sgr A*), the plasma in the disk is essentially collisionless. We present a nonlinear study of the collisionless MRI using first-principles particle-in-cell plasma simulations. We focus on local two-dimensional (axisymmetric) simulations, deferring more realistic three-dimensional simulations to future work. For simulations with net vertical magnetic flux, the MRI continuously amplifies the magnetic field, B, until the Alfvn velocity, vA , is comparable to the speed of light, c (independent of the initial value of vA /c). This is consistent with the lack of saturation of MRI channel modes in analogous axisymmetric MHD simulations. The amplification of the magnetic field by the MRI generates a significant pressure anisotropy in the plasma (with the pressure perpendicular to B being larger than the parallel pressure). We find that this pressure anisotropy in turn excites mirror modes and that the volume-averaged pressure anisotropy remains near the threshold for mirror mode excitation. Particle energization is due to both reconnection and viscous heating associated with the pressure anisotropy. Reconnection produces a distinctive power-law component in the energy distribution function of the particles, indicating the likelihood of non-thermal ion and electron acceleration in collisionless accretion disks. This has important implications for interpreting the observed emissionfrom the radio to the gamma-raysof systems such as Sgr A*.
Two-dimensional radiation-magnetohydrodynamic simulations of SATURN imploding Z pinches
NASA Astrophysics Data System (ADS)
Hammer, James H.; Eddleman, James L.; Springer, Paul T.; Tabak, Max; Toor, Arthur; Wong, Keith L.; Zimmerman, George B.; Deeney, Chris; Humphreys, Russ; Nash, Thomas J.; Sanford, Thomas W. L.; Spielman, Rick B.; De Groot, John S.
1996-05-01
Z-pinch implosions driven by the SATURN device [D. D. Bloomquist et al., Proceedings of the 6th Institute of Electrical and Electronics Engineers (IEEE) Pulsed Power Conference, Arlington, VA, edited by P. J. Turchi and B. H. Bernstein (IEEE, New York, 1987), p. 310] at Sandia National Laboratory are modeled with a two-dimensional radiation magnetohydrodynamic (MHD) code, showing strong growth of the magneto-Rayleigh-Taylor (MRT) instability. Modeling of the linear and nonlinear development of MRT modes predicts growth of bubble-spike structures that increase the time span of stagnation and the resulting x-ray pulse width. Radiation is important in the pinch dynamics, keeping the sheath relatively cool during the run-in and releasing most of the stagnation energy. The calculations give x-ray pulse widths and magnitudes in reasonable agreement with experiments, but predict a radiating region that is too dense and radially localized at stagnation. We also consider peaked initial density profiles with constant imploding sheath velocity that should reduce MRT instability and improve performance. Krypton simulations show an output x-ray power ?80 TW for the peaked profile.
Two-dimensional magnetohydrodynamics simulations of young Type Ia supernova remnants
NASA Astrophysics Data System (ADS)
Fang, Jun; Zhang, Li
2012-08-01
Using two-dimensional magnetohydrodynamics (MHD) simulations, we investigate the dynamical properties of Type Ia supernova remnants (SNRs) evolved either in a uniform ambient medium or from an interaction with a dense clump. The initial conditions assume that the expansion of the supernova ejecta is of free inertia with a power-law density distribution in the outer part of the ejecta. To include the effects of the diffusive shock acceleration process and the escape of the accelerated particles from the shock front, we use different adiabatic indices in the simulations to study the dynamical evolution of the Type Ia SNRs. Moreover, we investigate the interactions of a SNR with either a small or a large clump. A double-shock structure with a contact discontinuity is produced as the ejecta flow supersonically in the ambient medium; Rayleigh-Taylor instability is clearly shown as fingers near the contact discontinuity in the contour maps of density, and a high density and a high magnetic field can be triggered because of the instability around the Rayleigh-Taylor fingers. We perform simulations with different adiabatic indices, and the results show that a narrower intershock region is produced with a smaller adiabatic index because a larger compression ratio for the SNR shock is induced. The influence of the Rayleigh-Taylor instability on the morphologies of both the forward and reverse shocks is more significant with a smaller adiabatic index. Finally, the simulations of a SNR interacting with a dense clump show that the morphology of the remnant is greatly twisted after the collision, and a filament with a high density and a high magnetic field can be produced as a SNR colliding with a large dense clump.
Two-dimensional simulations of the inertial electrostatic confinement device
NASA Astrophysics Data System (ADS)
Marocchino, Alberto; Lapenta, Giovanni; Evstatiev, Evstati; Nebel, Richard; Park, Jaeyoung
2006-04-01
We discuss the application of the CELESTE simulation package to the simulation of the experiments conducted at the Los Alamos Inertial Electrostatic Confinement (IEC) device. Recently considerable experimental advances have been made in understanding of the stability of the virtual cathode and in the physics of POPS. This momentous experimental advance requires a new simulation effort for explaining the new experimental findings, particularly in the area of stability of the configurations obtained experimentally. We have conducted a 2D stability study of the virtual cathode in the IEC device using the DEMOCRITUS package. DEMOCRITUS is a 2D general geometry electrostatic PIC code. In the present study we have done complete stability study and investigate the two-stream instability occuring in the IEC device.
Two dimensional quantum mechanical simulation of low dimensional tunneling devices
NASA Astrophysics Data System (ADS)
Alper, C.; Palestri, P.; Lattanzio, L.; Padilla, J. L.; Ionescu, A. M.
2015-11-01
We present a 2-D quantum mechanical simulation framework based on self-consistent solutions of the Schrödinger and Poisson equations, using the Finite Element Method followed by tunneling current (direct and phonon assisted) calculation in post-processing. The quantum mechanical model is applied to Germanium electron-hole bilayer tunnel FETs (EHBTFET). It is found that 2D direct tunneling through the underlap regions may degrade the subthreshold characteristic of such devices and requires careful device optimization to make the tunneling in the overlap region dominate over the parasitic paths. It is found that OFF and ON state currents for the EHBTFET can be classified as point and line tunneling respectively. Oxide thickness was found to have little impact on the magnitude of the ON current, whereas it impacts the OFF current.
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.
Two-dimensional Simulations of Pulsational Pair-instability Supernovae
NASA Astrophysics Data System (ADS)
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 ? 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 1050 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 ? 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.
One- and two-dimensional STEALTH simulations of fuel-pin transient response. Final report. [BWR; PWR
Wahi, K.K.
1980-08-01
This report presents an assessment of the adaptability of EPRI's one- and two-dimensional STEALTH computer codes to perform transient fuel rod analysis. The ability of the STEALTH code to simulate transient mechanical or thermomechanical loss-of-coolant accident is described. Analytic models of one- and two-dimensional formulations and features included in the two-dimensional simulation are discussed.
Numerical simulations of the two-dimensional multimode Richtmyer-Meshkov instability
NASA Astrophysics Data System (ADS)
Thornber, B.; Zhou, Y.
2015-03-01
The two-dimensional Richtmyer-Meshkov instability occurs as shock waves pass through a perturbed material interface, triggering transition to an inhomogeneous turbulence variable density flow. This paper presents a series of large-eddy-simulations of the two dimensional turbulent RM instability and compares the results to the fully three dimensional simulations. There are two aims for this paper, the first is to explore what numerical resolution is required for a statistically converged solution for a two dimensional inhomogeneous flow field. The second aim is to elucidate the key differences in flow physics between the two dimensional and three dimensional Richtmyer-Meshkov instabilities, particularly their asymptotic self-similar regime. Convergence is achieved using 64 independent realisations and grid resolutions up to 40962 in the plane. It is shown that for narrowband cases the growth rate ? = 0.48 which is substantially higher than the three-dimensional equivalent. Mix measures are consistently lower compared to three-dimensional, and the kinetic energy distribution is homogeneous at late time. The broadband case has a similar initial growth rate as the three-dimensional case, with a marginally lower ? = 0.63. Mix is similar in magnitude, but is reducing at late time. The spectra in both cases exhibit the dual-cascade expected from two-dimensional turbulence.
Numerical simulations of the two-dimensional multimode Richtmyer-Meshkov instability
Thornber, B.; Zhou, Y.
2015-03-15
The two-dimensional Richtmyer-Meshkov instability occurs as shock waves pass through a perturbed material interface, triggering transition to an inhomogeneous turbulence variable density flow. This paper presents a series of large-eddy-simulations of the two dimensional turbulent RM instability and compares the results to the fully three dimensional simulations. There are two aims for this paper, the first is to explore what numerical resolution is required for a statistically converged solution for a two dimensional inhomogeneous flow field. The second aim is to elucidate the key differences in flow physics between the two dimensional and three dimensional Richtmyer-Meshkov instabilities, particularly their asymptotic self-similar regime. Convergence is achieved using 64 independent realisations and grid resolutions up to 4096{sup 2} in the plane. It is shown that for narrowband cases the growth rate θ = 0.48 which is substantially higher than the three-dimensional equivalent. Mix measures are consistently lower compared to three-dimensional, and the kinetic energy distribution is homogeneous at late time. The broadband case has a similar initial growth rate as the three-dimensional case, with a marginally lower θ = 0.63. Mix is similar in magnitude, but is reducing at late time. The spectra in both cases exhibit the dual-cascade expected from two-dimensional turbulence.
Hybrid simulation of whistler excitation by electron beams in two-dimensional non-periodic domains
Woodroffe, J.R. Streltsov, A.V.
2014-11-01
We present a two-dimensional hybrid fluid-PIC scheme for the simulation of whistler wave excitation by relativistic electron beams. This scheme includes a number of features which are novel to simulations of this type, including non-periodic boundary conditions and fresh particle injection. Results from our model suggest that non-periodicity of the simulation domain results in the development of fundamentally different wave characteristics than are observed in periodic domains.
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.
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.
Evidence of Active MHD Instability in EULAG-MHD Simulations of Solar Convection
NASA Astrophysics Data System (ADS)
Lawson, Nicolas; Strugarek, Antoine; Charbonneau, Paul
2015-11-01
We investigate the possible development of magnetohydrodynamical instabilities in the EULAG-MHD “millennium simulation” of Passos & 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.
Two-dimensional direct numerical simulation of parametrically excited surface waves in viscous fluid
NASA Astrophysics Data System (ADS)
Murakami, Youichi; Chikano, Masatsugu
2001-01-01
Standing surface waves on a viscous fluid driven parametrically by a vertical harmonic oscillation are investigated, based on direct numerical simulations of the two-dimensional Navier-Stokes equation, together with appropriate boundary conditions. The condition for the onset of the waves in the experiments by Lioubashevski et al. [Phys. Rev. Lett. 76, 3959 (1996)] is reproduced by our numerical simulation. The time evolution and the flow structures are investigated in detail. The form of the surface elevation is analyzed and the dependence of the saturated amplitude on the forcing strength shows a normal bifurcation. Instead of a localized state, spatially uniform standing waves are formed in an extended system. Using initial perturbations of the uniform state, numerical simulations show that the uniform standing waves are stable to two-dimensional disturbances, which suggests that three-dimensionality is essential for the spatially localized state to occur.
Langevin simulations of two-dimensional vortex fluctuations: Anomalous dynamics and IV exponent
NASA Astrophysics Data System (ADS)
Holmlund, Kenneth; Minnhagen, Petter
1996-07-01
The dynamics of two-dimensional (2D) vortex fluctuations is investigated through simulations of the 2D Coulomb gas model in which vortices are represented by soft disks with logarithmic interactions. The simulations strongly support a recent suggestion that 2D vortex fluctuations obey an intrinsic anomalous dynamics manifested in a long-range 1/t tail in the vortex correlations. A nonlinear IV exponent a, which is different from the commonly used Ambegaokar-Halperin-Nelson-Siggia exponent aAHNS and is given by a=2aAHNS-3, is confirmed by the simulations. The results are discussed in the context of earlier simulations, experiments, and a phenomenological description.
Magnetotail reconnection, MHD theory and simulations
NASA Technical Reports Server (NTRS)
Birn, J.; Hesse, M.; Schindler, K.
1989-01-01
Magnetotail reconnection leading to plasmoid formation and ejection is discussed, emphasizing three-dimensional structures and deviations from earlier imposed symmetries, based on MHD simulations and topological considerations. In general, the separation of the plasmoid takes a finite amount of time. During this stage the plasmoid is characterized by filamentary structures of interwoven flux tubes with different topological connections.
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.
Relativistic MHD Simulations of Precessed Jets
NASA Technical Reports Server (NTRS)
Mizuno, Y.; Nishikawa, K.-I.; Hardee, P.; Koide, S.; Fishman, G. J.
2006-01-01
Relativistic jets are considered to be generated by magnetic fields in a rotating black hole with accretion disk. Consequently, resulting outflows contain magnetic fields in them and control the propagation of jets. We have performed 3D relativistic MHD simulations to investigate the stability and structure of precessed MHD jets with large Lorentz factor by using a newly developed 3D GRMHD code. We have performed simulations of supermagnetosonic jets surrounded by a fast wind. The simulation results reveal complex pressure structure inside the RMHD jet. The structure is produced by a combination of the helical surface and body modes excited by the precession as predicted theoretically. The wavelength of the body mode which occurs in an internal helical twist is much shorter than that of the helical twist surface mode. We will present some comparisons between the RMHD simulations and theoretical predictions, and potential observables and discuss the effect of wind.
An analytical model for simulating two-dimensional multispecies plume migration
NASA Astrophysics Data System (ADS)
Chen, Jui-Sheng; Liang, Ching-Ping; Liu, Chen-Wuing; Li, Loretta Y.
2016-02-01
The two-dimensional advection-dispersion equations coupled with sequential first-order decay reactions involving arbitrary number of species in groundwater system is considered to predict the two-dimensional plume behavior of decaying contaminant such as radionuclide and dissolved chlorinated solvent. Generalized analytical solutions in compact format are derived through the sequential application of the Laplace, finite Fourier cosine, and generalized integral transform to reduce the coupled partial differential equation system to a set of linear algebraic equations. The system of algebraic equations is next solved for each species in the transformed domain, and the solutions in the original domain are then obtained through consecutive integral transform inversions. Explicit form solutions for a special case are derived using the generalized analytical solutions and are compared with the numerical solutions. The analytical results indicate that the analytical solutions are robust, accurate and useful for simulation or screening tools to assess plume behaviors of decaying contaminants.
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.
Cell-dynamical simulation of magnetic hysteresis in the two-dimensional Ising system
NASA Astrophysics Data System (ADS)
Sengupta, Surajit; Marathe, Yatin; Puri, S.
1992-04-01
We present results from numerical simulations using a ``cell-dynamical system'' to obtain solutions to the time-dependent Ginzburg-Landau equation for a scalar, two-dimensional (2D), (?2)2 model in the presence of a sinusoidal external magnetic field. Our results confirm a recent scaling law proposed by Rao, Krishnamurthy, and Pandit [Phys. Rev. B 42, 856 (1990)], and are also in excellent agreement with recent Monte Carlo simulations of hysteretic behavior of 2D Ising spins by Lo and Pelcovits [Phys. Rev. A 42, 7471 (1990)].
Lattice Boltzmann simulations of a strongly interacting two-dimensional Fermi gas
NASA Astrophysics Data System (ADS)
Brewer, Jasmine; Mendoza, Miller; Young, Ryan E.; Romatschke, Paul
2016-01-01
We present fully nonlinear dissipative fluid dynamics simulations of a strongly interacting trapped two-dimensional Fermi gas using a lattice Boltzmann algorithm. We are able to simulate nonharmonic trapping potentials, temperature-dependent viscosities, as well as a discretized version of the ballistic (noninteracting) behavior. Our approach lends itself to direct comparison with experimental data, opening up the possibility of a precision determination of transport coefficients in the strongly interacting Fermi gas. Furthermore, we predict the presence of a strongly damped ("nonhydrodynamic") component in the quadrupole mode, which should be observable experimentally.
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.
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.
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.
Simulation of two-dimensional electronic spectra of phycoerythrin 545 at ambient temperature.
Leng, Xuan; Liang, Xian-Ting
2014-10-30
By using a hierarchical equations-of-motion approach, we reproduce the two-dimensional electronic spectra of phycoerythrin 545 from Rhodomonas CS24 at ambient temperature (294 K). The simulated spectra are in agreement with the experimental results reported in Wong et al. (Nat. Chem. 2012, 4, 396). The evolutions of cross peaks for rephasing spectra and diagonal peaks for nonrephasing spectra have also been plotted. The peaks oscillate with the population times, with frequencies, phases, and amplitudes of the oscillating curves also being qualitatively consistent with the experimental results. PMID:25299464
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.
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.
Tsuchiya, H.; Morisaki, T.; Komori, A.; Motojima, O.
2006-10-15
A sheet-shaped thermal lithium beam probe has been developed for two-dimensional density measurements in the edge region of the torus plasma. A numerical simulation was carried out to confirm the validity of the diagnostics for fast and transient phenomena such as edge localized modes or blobs, etc., where the velocity of blobs is faster than that of the probe beam. It was found in the simulation that the density of the blob itself is reconstructed to be low and unexpected ghosts appear in the reconstructed density profile near the blob, if the conventional reconstruction method is employed. These results invite our attention to the numerical errors in the density reconstruction process. On the other hand, the errors can be corrected by using the simulation results.
Observation of ion waves in two-dimensional particle simulation of field-assisted plasma expansion
Patel, K.
1997-05-01
We report the results of two-dimensional particle simulations (computer experiments) of finite plasma expansion between biased plane parallel electrodes. We show that the simulation produces results consistent with the existing one-dimensional analytical model. While the plasma expansion on the low-potential side is space-charge limited, on the opposite side it is due to ambipolar diffusion. The time-dependent simulated ion current to the electrode exhibits a modulation which has not been experimentally observed. This is identified to be a consequence of the oscillation in sheath front ion density which occurs because of the ion acoustic waves generated during the expansion. This modulation, which is greater at lower ion temperatures and nonuniform with respect to the electrode surface, can be used to estimate the transient number density in the plasma. Modifications to conventional experimental detection circuits which could help in the detection of these waves are presented. {copyright} {ital 1997 American Institute of Physics.}
Martinez-Sykora, Juan; De Pontieu, Bart; Hansteen, Viggo
2012-07-10
The bulk of the solar chromosphere is weakly ionized and interactions between ionized particles and neutral particles likely have significant consequences for the thermodynamics of the chromospheric plasma. We investigate the importance of introducing neutral particles into the MHD equations using numerical 2.5D radiative MHD simulations obtained with the Bifrost code. The models span the solar atmosphere from the upper layers of the convection zone to the low corona, and solve the full MHD equations with non-gray and non-LTE radiative transfer, and thermal conduction along the magnetic field. The effects of partial ionization are implemented using the generalized Ohm's law, i.e., we consider the effects of the Hall term and ambipolar diffusion in the induction equation. The approximations required in going from three fluids to the generalized Ohm's law are tested in our simulations. The Ohmic diffusion, Hall term, and ambipolar diffusion show strong variations in the chromosphere. These strong variations of the various magnetic diffusivities are absent or significantly underestimated when, as has been common for these types of studies, using the semi-empirical VAL-C model as a basis for estimates. In addition, we find that differences in estimating the magnitude of ambipolar diffusion arise depending on which method is used to calculate the ion-neutral collision frequency. These differences cause uncertainties in the different magnetic diffusivity terms. In the chromosphere, we find that the ambipolar diffusion is of the same order of magnitude or even larger than the numerical diffusion used to stabilize our code. As a consequence, ambipolar diffusion produces a strong impact on the modeled atmosphere. Perhaps more importantly, it suggests that at least in the chromospheric domain, self-consistent simulations of the solar atmosphere driven by magnetoconvection can accurately describe the impact of the dominant form of resistivity, i.e., ambipolar diffusion. This suggests that such simulations may be more realistic in their approach to the lower solar atmosphere (which directly drives the coronal volume) than previously assumed.
Vahedi, V.; Birdsall, C.K.; Lieberman, M.A.; DiPeso, G.; Rognlien, T.D.
1992-12-15
Weakly ionized processing plasmas are studied in two-dimensions using a bounded particle-in-cell (PIC) simulation code with a Monte Carlo Collision (MCC) package. The MCC package models the collisions between charged and neutral particles, which are needed to obtain a self-sustained plasma and the proper electron and ion energy loss mechanisms. A two-dimensional capacitive RF discharge is investigated in detail. Simple frequency scaling laws for predicting the behavior of some plasma parameters are derived and then compared with simulation results, finding good agreements. We find that as the drive frequency increases, the sheath width decreases, and the bulk plasma becomes more uniform, leading to a reduction of the ion angular spread at the target and an improvement of ion dose uniformity at the driven electrode.
Simulation study of chiral two dimensional ultraviolet (2DUV) spectroscopy of the protein backbone
Abramavicius, Darius; Jiang, Jun; Bulheller, Benjamin M.; Hirst, Jonathan D.; Mukamel, Shaul
2010-01-01
Amide n –π* and π-π* excitations around 200 nm are prominent spectroscopic signatures of the protein backbone, which are routinely used in ultraviolet (UV) circular dichroism for structure characterization. Recently developed ultrafast laser sources may be used to extend these studies to two dimensions (2D). We apply a new algorithm for modelling protein electronic transitions to simulate two-dimensional ultraviolet (2DUV) photon echo signals in this regime and to identify signatures of protein backbone secondary (and tertiary) structure. Simulated signals for a set of globular and fibrillar proteins and their specific regions reveal characteristic patterns of helical and sheet secondary structures. We investigate how these patterns vary and converge with the size of the structural motif. Specific chiral polarization configurations of the UV pulses are found to be sensitive to aspects of the protein structure. This information significantly augments that available from linear circular dichroism. PMID:20481498
NASA Astrophysics Data System (ADS)
Wang, Jhih-Huang; Lin, Gwo-Fong; Jhong, Bing-Chen
2014-05-01
The heavy rain brought by typhoons frequently causes inundation and results in property damage and loss of life. To mitigate hazards due to typhoons, typhoon events with rainfall data available are also collected. The physically based two-dimensional model, called FLO-2D, is employed to construct an inundation simulation model for evaluating the effect of the inundation hazard. An actual application is conducted to clearly simulate the inundation processes in the downstream of Zhuo-Shui River basin. The result of Manning's n value separated as agricultural land and town is correspond to the actual situation according to land use. Moreover, the inundation situation of 48 h rainfall is the worst in the downstream region. In conclusion, the inundation hazard caused by typhoon heavy rainfall often leads to loss of life and property damage.
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.
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-grit roughness to the LEWICE shapes produced greater losses than corresponding smooth ice shapes. Spoiler-ice with constant spanwise height caused larger performance losses than spoiler-ice with height scaled as a function of local chord length. Aerodynamic performance degradation due to the variable height spoiler-ice was similar to that obtained with the corresponding LEWICE shapes.
NASA Astrophysics Data System (ADS)
Brown, James H.
1993-10-01
Geophysical phenomena are often characterized by smooth continuous power spectral densities having a negative power law slope. Frequently, Fourier transform analysis has been employed to generate synthetic scenes from pseudorandom arrays by passing the stochastic data through a Fourier filter having the desired power spectral dependency. This report examines the possibility of producing two-dimensional synthetic structure by invoking autoregressive/moving average analysis, as contrasted with the Fourier method. Computations that apply multidimensional fast Fourier transforms to large data arrays consume enormous resources and time. An alternative method is needed to reduce the computational burden, achieve circular symmetry, account for correlations in all directions, and lend itself to producing nonstationary scenes. Future editions of the Phillips Laboratory Strategic High Altitude Atmospheric Radiance Code (SHARC) will feature an ability to calculate structured radiance. The method explored herein provides a process to construct a nonstationary database for SHARC that accurately simulates symmetric two-dimensional geophysical power spectra and takes into account correlations along the line of sight that existing methods approximate.
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.
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.
Kim, J.; McMurray, J. S.; Williams, C. C.; Slinkman, J.
1998-11-24
We report the results of a 2-step two-dimensional (2D) diffusion study by Scanning Capacitance Microscopy (SCM) and 2D TSUPREM IV process simulation. A quantitative 2D dopant profile of gate-like structures consisting heavily implanted n+ regions separated by a lighter doped n-type region underneath 0.56 {mu}m gates is measured with the SCM. The SCM is operated in the constant-change-in-capacitance mode. The 2-D SCM data is converted to dopant density through a physical model of the SCM/silicon interaction. This profile has been directly compared with 2D TSUPREM IV process simulation and used to calibrate the simulation parameters. The sample is then further subjected to an additional diffusion in a furnace for 80 minutes at 1000C. The SCM measurement is repeated on the diffused sample. This final 2D dopant profile is compared with a TSUPREM IV process simulation tuned to fit the earlier profile with no change in the parameters except the temperature and time for the additional diffusion. Our results indicate that there is still a significant disagreement between the two profiles in the lateral direction. TSUPREM IV simulation considerably underestimates the diffusion under the gate region.
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.
Two-Dimensional Numerical Simulation of Trapped Ion Mode and Drift Wave Turbulence.
NASA Astrophysics Data System (ADS)
Kingsbury, Owen Todd
The first chapter is the paper entitled "Two-dimensional numerical simulation of trapped electron mode turbulent transport in a tokamak". Trapped electrons are lumped into hot and cold fluids to treat temperature gradient effects. The ion temperature gradient and dissipative trapped electron modes were simultaneously present. A plasma particle pinch was found only at extremely low collisionalities and a heat conduction pinch was found at moderate collisionalities, although there was no energy flow pinch seen. The second chapter is the paper entitled "Two -dimensional numerical simulation of trapped ion mode turbulence in a tokamak". The simulation of long wavelength trapped ion mode turbulence was used to investigate Bohm (macroscopic) versus gyro-Bohm (microscopic) scaling behavior in tokamaks. A nonlinear two-field model of dissipative trapped ion turbulence evolving trapped ion and trapped electron density fluctuations showed gyro-Bohm-like scaling in contrast to earlier simulation work by Saison, Wimmel, and Sardei (Plasma Physics, Vol. 20, pp. 1 to 20, 1978). In fact nearly all features of trapped ion mode turbulence and transport originally posited by Kadomstev and Pogutse (Reviews of Plasma Physics, Vol. 5) were recovered. The third chapter is the paper entitled "Numerical simulation of drift waves and trapped ion modes". Simulations were used to study the interaction of trapped electron drift waves (DW) and trapped ion modes (TIM). Wavenumber (k) space was divided into long wave and short wave regions at a poloidal wavenumber corresponding to the ion bounce frequency. Two field models were used to describe trapped electron drift wave dynamics at short waves and trapped ion mode dynamics for long waves. The principal result of this study was that the TIM did not contribute to the diffusion significantly, regardless of the model for the nonlinear coupling to the DW. The appendix documents a sparsely populated k -space grid scheme that was invented to perform the TIM/DW simulations. The method did not give physical results and was not used. The argument in the appendix states that it is not possible to mock up the nonlinear convolutions in Fourier representation such that some of the modes need not be included.
NASA Astrophysics Data System (ADS)
Dwivedi, S. K.; Asay, J. R.; Gupta, Y. M.
2006-10-01
Two-dimensional (2D) mesoscale simulations of planar shock compression, followed by either reloading or unloading, are presented to examine and understand the quasielastic response observed experimentally in shocked polycrystalline aluminum. The simulations included a realistic representation of the grain ensembles in polycrystalline samples to identify heterogeneous deformation features deemed important to model the continuum measurements. The simulations were carried out using a 2D Lagrangian finite element code (ISP-TROTP) that incorporated elastic-plastic deformation in grain interiors and utilized a contact/cohesive methodology to analyze the response of finite strength grain boundaries. Local heterogeneous response due to mesoscale features was quantified by calculating appropriate material variables along in situ Lagrangian tracer lines and comparing the temporal variation of their mean values with results from 2D continuum simulations. A series of initial calculations ruled out effects due to finite element size and width of the representative volume element used in our simulations. Simulations using a variety of heterogeneities were performed to identify the heterogeneities that were most important for simulating the experimentally observed quasielastic response. These were inclusions, hardened grain boundaries, and microporosity. Mesoscale simulations incorporating these effects demonstrate that the shock-deformed state in polycrystalline aluminum is strongly heterogeneous with considerable variations in lateral stresses. The simulated velocity profiles for a representative reloading and unloading experimental configuration were found to agree well with experimental data, and suggest that hardened grain boundaries are the most likely source of mesoscale heterogeneities in shocked 6061-T6 aluminum. The calculated shear strength and shear stresses were also found to be in good agreement with the reported experimental values.
Simulating and exploring Weyl semimetal physics with cold atoms in a two-dimensional optical lattice
NASA Astrophysics Data System (ADS)
Zhang, Dan-Wei; Zhu, Shi-Liang; Wang, Z. D.
2015-07-01
We propose a scheme to simulate and explore Weyl semimetal physics with ultracold fermionic atoms in a two-dimensional square optical lattice subjected to experimentally realizable spin-orbit coupling and an artificial dimension from an external parameter space, which may increase experimental feasibility compared with the cases in three-dimensional optical lattices. It is shown that this system with a tight-binding model is able to describe essentially three-dimensional Weyl semimetals with tunable Weyl points. The relevant topological properties are also addressed by means of the Chern number and the gapless edge states. Furthermore, we illustrate that the mimicked Weyl points can be experimentally detected by measuring the atomic transfer fractions in a Bloch-Zener oscillation, and the characteristic topological invariant can be measured with the particle pumping approach.
Two-dimensional dynamic stall as simulated in a varying freestream
NASA Technical Reports Server (NTRS)
Pierce, G. A.; Kunz, D. L.; Malone, J. B.
1978-01-01
A low speed wind tunnel equipped with a axial gust generator to simulate the aerodynamic environment of a helicopter rotor was used to study the dynamic stall of a pitching blade in an effort to ascertain to what extent harmonic velocity perturbations in the freestream affect dynamic stall. The aerodynamic moment on a two dimensional, pitching blade model in both constant and pulsating airstream was measured. An operational analog computer was used to perform on-line data reduction and plots of moment versus angle of attack and work done by the moment were obtained. The data taken in the varying freestream were then compared to constant freestream data and to the results of two analytical methods. These comparisons show that the velocity perturbations have a significant effect on the pitching moment which can not be consistently predicted by the analytical methods, but had no drastic effect on the blade stability.
Brouwer, Darren H; Horvath, Matthew
2015-02-01
An improved NMR crystallography strategy is presented for determining the structures of network materials such as zeolites from just a single two-dimensional (2D) NMR correlation spectrum that probes nearest-neighbor interactions, combined with the unit cell parameters and space group information measured in a diffraction experiment. The correlation information contained within a 2D spectrum is converted into a "connectivity matrix" which is incorporated into a cost function whose minimum is searched for using a simulated annealing algorithm. The algorithm was extensively tested on over 150 zeolite frameworks from the International Zeolite Association database of zeolite structures and shown to be very robust and efficient in reconstructing the structures from connectivity information. The structure determination of the pure silica zeolites ITQ-4, Ferrierite, and Sigma-2 from experimental 2D (29)Si double-quantum NMR spectra and powder X-ray diffraction data using this improved approach is also presented. PMID:25466355
Simulation of femtosecond two-dimensional electronic spectra of conical intersections
NASA Astrophysics Data System (ADS)
Krčmář, Jindřich; Gelin, Maxim F.; Domcke, Wolfgang
2015-08-01
We have simulated femtosecond two-dimensional (2D) electronic spectra for an excited-state conical intersection using the wave-function version of the equation-of-motion phase-matching approach. We show that 2D spectra at fixed values of the waiting time provide information on the structure of the vibronic eigenstates of the conical intersection, while the evolution of the spectra with the waiting time reveals predominantly ground-state wave-packet dynamics. The results show that 2D spectra of conical intersection systems differ significantly from those obtained for chromophores with well separated excited-state potential-energy surfaces. The spectral signatures which can be attributed to conical intersections are discussed.
Percolation analysis of nonlinear structures in scale-free two-dimensional simulations
NASA Technical Reports Server (NTRS)
Dominik, Kurt G.; Shandarin, Sergei F.
1992-01-01
Results are presented of applying percolation analysis to several two-dimensional N-body models which simulate the formation of large-scale structure. Three parameters are estimated: total area (a(c)), total mass (M(C)), and percolation density (rho(c)) of the percolating structure at the percolation threshold for both unsmoothed and smoothed (with different scales L(s)) nonlinear with filamentary structures, confirming early speculations that this type of model has several features of filamentary-type distributions. Also, it is shown that, by properly applying smoothing techniques, many problems previously considered detrimental can be dealt with and overcome. Possible difficulties and prospects with the use of this method are discussed, specifically relating to techniques and methods already applied to CfA deep sky surveys. The success of this test in two dimensions and the potential for extrapolation to three dimensions is also discussed.
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].
Simulations of one- and two-dimensional complex plasmas using a modular, object-oriented code
Jefferson, R. A.; Cianciosa, M.; Thomas, E. Jr.
2010-11-15
In a complex plasma, charged microparticles ('dust') are added to a background of ions, electrons, and neutral particles. This dust fully interacts with the surrounding plasma and self-consistently alters the plasma environment leading to the emergence of new plasma behavior. Numerical tools that complement experimental investigations can provide important insights into the properties of complex plasmas. This paper discusses a newly developed code, named DEMON (dynamic exploration of microparticle clouds optimized numerically), for simulating a complex plasma. The DEMON code models the behavior of the charged particle component of a complex plasma in a uniform plasma background. The key feature of the DEMON code is the use of a modular force model that allows a wide variety of experimental configurations to be studied without varying the core code infrastructure. Examples of the flexibility of this modular approach are presented using examples of one- and two-dimensional complex plasmas.
NASA Astrophysics Data System (ADS)
Zhang, Jiao; Wang, Yanhui; Wang, Dezhen
2015-11-01
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 N2 impurities content could significantly influence the number of discharge channel, which is discussed in the paper.
Shocked Magnetotail: ARTEMIS Observations and MHD Simulations
NASA Astrophysics Data System (ADS)
Zhou, Xiaoyan
2015-04-01
Interplanetary shocks can cause magnetospheric disturbances on various scales including kinetic and MHD processes. In this paper we study a shock event using ARTEMIS in situ observations and OpenGGCM MHD simulations, which shows how significant effect of interplanetary shocks could be on the magnetotail. The two ARTEMIS spacecraft were located near the tail current sheet and lobe center at (-60, 1, -5Re_GSM) when the shock arrived and recorded an abrupt tail compression leading to significant enhancements in the plasma density, temperature, magnetic field strength, and cross-tail current density, as well as to tailward flows and current sheet crossings. About 10 min later, the spacecraft entered the sheath solar wind unexpectedly. Two hypotheses are considered: either the tail was cut off by the high solar wind ram pressure (~25-30 nPa), or the compressed tail was pushed aside by the appreciable dawnward solar wind flow imposed by the shock. OpenGGMC simulation results confirmed the second hypothesis and revealed that during this 10 min interval, the lobe center moved dawnward by ~12 Re and the tail width in Y was reduced from ~40 to 26 Re, which eventually exposed ARTEMIS to the sheath solar wind. Comparisons of plasma and magnetic parameters between ARTEMIS in situ observations and simulations showed a satisfied consistence.
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.
Two-Dimensional Simulations of Relativistic Extragalactic Jets Crossing an ISM/ICM Interface
NASA Astrophysics Data System (ADS)
Zhang, Hui-Min; Koide, Shinji; Sakai, Jun-Ichi
1999-08-01
We have performed two-dimensional relativistic hydrodynamical simulations of initially conical axisymmetric jets using a newly developed relativistic magnetohydrodynamic simulation code. The simulation code employs a simplified total variation diminishing method. These jets emerge from the atmospheres of active galaxies and then cross a pressure-matched interface into a hotter, but less-dense, intraclustermedium, whereupon they are accelerated and collimated. We compared the nonrelativistic and relativistic jets to find any relativistic effects in this kind of propagation processes. The simulation results show that there are clear relativistic effects as well as interface impacts in several aspects. Compared with a nonrelativistic jet propagating in a uniform medium, three results are notable: (1) when a jet propagates from a higher density medium region to lower density region, the variation in the amplitude of the Mach disk between concave and convex is greater; nonrelativistic jets show this feature more obviously; (2) the interface causes the jet to undergo a quasi-periodical shrinkage and expansion, which may correspond to a chain of knots in an extragalactic jet; (3) the jet head advance velocity formula, v_h={v_0sqrt eta }/({1+sqrt eta }), should be replaced by v_h={v_0gamma_0 sqrt eta }/{(1+gamma_0 sqrt eta )}, where v_0 and gamma_0 are the velocity of the inflowing jet fluid and its Lorentz factor, respectively, and eta is the initial ratio of jet density to medium density.
Gheisari, R.; Firoozabadi, M. M.; Mohammadi, H.
2014-01-15
A new idea to calculate ultracold neutron (UCN) production by using Monte Carlo simulation method to calculate the cold neutron (CN) flux and an analytical approach to calculate the UCN production from the simulated CN flux was given. A super-thermal source (UCN source) was modeled based on an arrangement of D{sub 2}O and solid D{sub 2} (sD{sub 2}). The D{sub 2}O was investigated as the neutron moderator, and sD{sub 2} as the converter. In order to determine the required parameters, a two-dimensional (2D) neutron balance equation written in Matlab was combined with the MCNPX simulation code. The 2D neutron-transport equation in cylindrical (ρ − z) geometry was considered for 330 neutron energy groups in the sD{sub 2}. The 2D balance equation for UCN and CN was solved using simulated CN flux as boundary value. The UCN source dimensions were calculated for the development of the next UCN source. In the optimal condition, the UCN flux and the UCN production rate (averaged over the sD{sub 2} volume) equal to 6.79 × 10{sup 6} cm{sup −2}s{sup −1} and 2.20 ×10{sup 5} cm{sup −3}s{sup −1}, respectively.
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.
Numerical Simulation of MHD Effect in Liquid Metal Blankets with Flow Channel Insert
NASA Astrophysics Data System (ADS)
Mao, J.; Pan, H. C.
2011-09-01
The magnetohydrodynamic effect in liquid metal blankets with flow channel insert and pressure equalization slot for fusion liquid metal blanket is studied by numerical simulation based on two dimensional fully developed flow model. The code is verified by comparing analytical solution and numerical solution of Hunt Case II. The velocity field and MHD pressure drop varying with electric conductivity of the FCI is analyzed. The result shows that the average velocity in central area of the cross section decreases with the increase of the electric conductivity of FCI. While the average velocity in gap zone is reverse. Comparing with MHD duct flow without FCI, MHD pressure drop is reduced significantly when the FCI material is electrically insulating.
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
Alzheimers disease (AD) is a neurodegenerative disorder characterized by the accumulation of plaque deposits in the human brain. The main component of these plaques consists of highly ordered structures called amyloid fibrils, formed by the amyloid ?-peptide (A?). The mechanism connecting A? and AD is yet undetermined. In a previous study, a coarse-grained united-residue model and molecular dynamics simulations were used to model the growth mechanism of A ? amyloid fibrils. Based on these simulations, a dock/lock mechanism was proposed, in which A? fibrils grow by adding monomers at either end of an amyloid fibril template. To examine the structures in the early time-scale formation and growth of amyloid fibrils, simulated two-dimensional ultraviolet spectroscopy is used. These early structures are monitored in the far ultraviolet regime (? = 190250 nm) in which the computed signals originate from the backbone n?* and ??* transitions. These signals show distinct cross-peak patterns that can be used, in combination with molecular dynamics, to monitor local dynamics and conformational changes in the secondary structure of A?-peptides. The protein geometry-correlated chiral xxxy signal and the non-chiral combined signal xyxy- xyyx were found to be sensitive to, and in agreement with, a dock/lock pathway. PMID:23214934
Two-Dimensional Hybrid-PIC Simulation of Magnetic Sail Including Interplanetary Magnetic Field
NASA Astrophysics Data System (ADS)
Matsumoto, Masaharu; Kajimura, Yoshihiro; Usui, Hideyuki; Funaki, Ikkoh; Shinohara, Iku
Solar wind plasma behavior and thrust of a magnetic sail under the condition with interplanetary magnetic field (IMF) are examined by time-dependent, two-dimensional, X-Y Cartesian, hybrid particle-in-cell (PIC) simulations. Magnetic sail is a propellant less propulsion system proposed for an interplanetary space flight. The thrust force is produced by the interaction between magnetic dipole field artificially generated by superconducting coils in a spacecraft and a solar wind. In the present simulations, the ratio of ion Larmor radius at the magnetopause to characteristic length of the magnetosphere is set to 0.1, and IMF strength is set to 0 and 10nT. As simulation results, magnetic reconnection occurs due to superposition of IMF and dipole field in the solar wind flow field. The reconnection points depend on the direction of IMF and those have an important role in the formation of shock wave. When IMF is perpendicular to the solar wind flow direction, the thrust acting on the spacecraft increases compared to the case without IMF. When IMF is parallel to the solar wind flow direction, lift force is generated on the spacecraft. These phenomena are attributed to the difference in location of magnetic reconnection point depending on the direction of IMF.
Simulation of Ozone and Long Lived Tracers in the GSFC Two-Dimensional Model
NASA Technical Reports Server (NTRS)
Fleming, Eric L.; Jackman, Charles H.; Considine, David B.; Stolarski, Richard S.
1999-01-01
The GSFC two-dimensional transport and chemistry model has been used for a wide variety of scientific and assessment studies of stratospheric ozone. Transport is a key element in the ozone simulations, and we have recently upgraded our model transport formulation to include much of the information about atmospheric transport processes available from existing data sets. To properly evaluate the model transport, it is desirable to examine the effects of transport and photochemistry separately. Recently, high quality observations of several long lived stratospheric tracers have become available from aircraft, balloon, and satellite measurement systems. This data provides a means to do a detailed model transport evaluation, as has been done in the recent Models and Measurements Intercomparison Project II. In this paper, we will discuss the GSFC 2D model simulations of ozone together with model-data comparisons of long lived tracers such as methane and the age of air transport diagnostic. We will show that the model can reproduce many of the transport-sensitive features observed in the stratosphere, and can compare reasonably well with measurements of both total ozone and long lived tracers simultaneously. We will also discuss the model deficiencies in simulating some of the detailed aspects of the observations.
NASA Astrophysics Data System (ADS)
Kawamura, E.; Lieberman, M. A.; Lichtenberg, A. J.; Graves, D. B.
2012-08-01
Plasma instabilities are observed in low-pressure inductive discharges in the transition between low density capacitively driven and high density inductively driven discharges when attaching gases are used. A two-dimensional hybrid fluid-analytic simulation is used to determine the space- and time-varying densities of electrons, positive and negative ions, and neutral species, and electron and neutral gas temperatures. The simulation includes both the capacitive and inductive coupling of the source coils to the plasma and the neutral gas dissociation and heating. The plasma is described using the time-dependent fluid equations, along with an analytical sheath model. The simulation is applied to an experiment in Cl2, in which gaps in the electron and positive ion densities versus power curves were observed, with our numerical results indicating the existence of an inductive-capacitive transition instability, corresponding approximately to the observed gaps. The fluid calculation captures various features that are not included in previous global instability models. A method is developed to match the numerical results to the global model formalism, which predicts the existence of the unstable mode, as numerically found. The time and space variations can be used to improve the global model formalism.
NASA Astrophysics Data System (ADS)
Peterson, D. L.; Bowers, R. L.; McLenithan, K. D.; Deeney, C.; Chandler, G. A.; Spielman, R. B.; Matzen, M. K.; Roderick, N. F.
1998-09-01
A two-dimensional (2-D) Eulerian Radiation-Magnetohydrodynamic (RMHD) code has been used to simulate imploding z pinches for three experiments fielded on the Los Alamos Pegasus II capacitor bank [J. C. Cochrane et al., Dense Z-Pinches, Third International Conference, London, United Kingdom 1993 (American Institute of Physics, New York, 1994), p. 381] and the Sandia Saturn accelerator [R. B. Spielman et al., Dense Z-Pinches, Second International Conference, Laguna Beach, 1989 (American Institute of Physics, New York, 1989), p. 3] and Z accelerator [R. B. Spielman et al., Phys. Plasmas 5, 2105 (1998)]. These simulations match the experimental results closely and illustrate how the code results may be used to track the flow of energy in the simulation and account for the amount of total radiated energy. The differences between the calculated radiated energy and power in 2-D simulations and those from zero-dimensional (0-D) and one-dimensional (1-D) Lagrangian simulations (which typically underpredict the total radiated energy and overpredict power) are due to the radially extended nature of the plasma shell, an effect which arises from the presence of magnetically driven Rayleigh-Taylor instabilities. The magnetic Rayleigh-Taylor instabilities differ substantially from hydrodynamically driven instabilities and typical measures of instability development such as e-folding times and mixing layer thickness are inapplicable or of limited value. A new measure of global instability development is introduced, tied to the imploding plasma mass, termed "fractional involved mass." Examples of this quantity are shown for the three experiments along with a discussion of the applicability of this measure.
Two-dimensional nonsteady viscous flow simulation on the Navier-Stokes computer miniNode
NASA Technical Reports Server (NTRS)
Nosenchuck, Daniel M.; Littman, Michael G.; Flannery, William
1986-01-01
The needs of large-scale scientific computation are outpacing the growth in performance of mainframe supercomputers. In particular, problems in fluid mechanics involving complex flow simulations require far more speed and capacity than that provided by current and proposed Class VI supercomputers. To address this concern, the Navier-Stokes Computer (NSC) was developed. The NSC is a parallel-processing machine, comprised of individual Nodes, each comparable in performance to current supercomputers. The global architecture is that of a hypercube, and a 128-Node NSC has been designed. New architectural features, such as a reconfigurable many-function ALU pipeline and a multifunction memory-ALU switch, have provided the capability to efficiently implement a wide range of algorithms. Efficient algorithms typically involve numerically intensive tasks, which often include conditional operations. These operations may be efficiently implemented on the NSC without, in general, sacrificing vector-processing speed. To illustrate the architecture, programming, and several of the capabilities of the NSC, the simulation of two-dimensional, nonsteady viscous flows on a prototype Node, called the miniNode, is presented.
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.
Recine, Greg . E-mail: gjr5y@virginia.edu; Rosen, Bernard; Cui, H.-L.
2005-11-01
We have constructed a lattice Wigner-Weyl code to expand the Buot-Jensen algorithm to calculation of electron transport in two-dimensional cylindrically symmetric structures. Almost all of the numerical simulations to date have dealt with the restricted problem of one-dimensional transport. In real devices, electrons are not confined to a single transport dimension and the coulombic potential is fully present and felt in three dimensions. We show the derivation of the 2D equation in cylindrical coordinates as well as approximations employed in the calculation of the four-dimensional convolution integral of the Wigner function and the potential. We work under the assumption that longitudinal transport is more dominant than radial transport and employ parallel processing techniques. The total transport is calculated in two steps: (1) transport the particles in the longitudinal direction in each shell separately, then (2) each shell exchanges particles with its nearest neighbor. Most of this work is concerned with the former step: A 1D space and 2D momentum transport problem. Time evolution simulations based on these method are presented for three different cases. Each case lead to numerical results consistent with expectations. Discussions of future improvements are discussed.
NASA Astrophysics Data System (ADS)
Ghasemi, Amirmahdi; Pathak, Ashish; Chiodi, Robert; Raessi, Mehdi
2013-11-01
Ocean waves represent a vast renewable energy resource, which is mostly untapped. We present a computational tool for simulation of the interactions between waves and two-dimensional oscillating solid bodies representing simple wave energy converters (WECs). The computational tool includes a multiphase flow solver, in which the two-step projection method with GPU acceleration is used to solve the Navier-Stokes equations. The fictitious domain method is used to capture the interactions of a moving rigid solid body with the two-fluid flow. The solid and liquid volumes are tracked using the volume-of-fluid (VOF) method, while the triple points and phase interfaces in three-phase cells are resolved. A consistent mass and momentum transport scheme is used to handle the large density ratio. We present results of two wave generation mechanisms with a piston or flap wave maker, where the theoretical and experimental results were used for validation. Then, simulation results of several simple devices representative of distinct WECs, including a bottom-hinged flap device as well as cylindrical or rectangular terminators are presented. The results are in good agreement with the available experimental data.
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.
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.
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
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.
NASA Astrophysics Data System (ADS)
Huang, Zhiming; Hao, Yanpeng; Yang, Lin; Han, Yongxia; Li, Licheng
2015-12-01
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)
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.
Simulated two-dimensional electronic spectroscopy of the eight-bacteriochlorophyll FMO complex
NASA Astrophysics Data System (ADS)
Yeh, Shu-Hao; Kais, Sabre
2014-12-01
The Fenna-Matthews-Olson (FMO) protein-pigment complex acts as a molecular wire conducting energy between the outer antenna system and the reaction center; it is an important photosynthetic system to study the transfer of excitonic energy. Recent crystallographic studies report the existence of an additional (eighth) bacteriochlorophyll a (BChl a) in some of the FMO monomers. To understand the functionality of this eighth BChl, we simulated the two-dimensional electronic spectra of both the 7-site (apo form) and the 8-site (holo form) variant of the FMO complex from green sulfur bacteria, Prosthecochloris aestuarii. By comparing the spectrum, it was found that the eighth BChl can affect two different excitonic energy transfer pathways: (1) it is directly involved in the first apo form pathway (6 ? 3 ? 1) by passing the excitonic energy to exciton 6; and (2) it facilitates an increase in the excitonic wave function overlap between excitons 4 and 5 in the second pathway (7 ? 4,5 ? 2 ? 1) and thus increases the possible downward sampling routes across the BChls.
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.
Lagrangian particle simulation of tracer dispersion in the lee of a schematic two-dimensional hill
Tinarelli, G.; Anfossi, D.; Brusasca, G.; Ferrero, E.; Giostra, U.; Morselli, M.G.; Moussafir, J.; Tampieri, F.; Trombetti, F. CNR, Turin Universita di Alessandria CNR, Bologna ARIA, Paris )
1994-06-01
Spray, a 3D Langrangian particle model for the simulation of complex flow dispersion, is presented. Its performance is tested against the Environmental Protection Agency wind tunnel concentration distribution of passive tracer released from elevated point sources, located in the lee region of a two-dimensional schematic hill, in a neutrally stratified boundary layer. Based on the measured values of the first two moments of the turbulent flow velocity, the mean fields are computed over a regular grid using a mass-consistent model, whereas the turbulence structure is simply interpolated. From these fields, trajectories of tracer particles are computed using a linear formulation of the Langevin equation, with a correlated, skewed forcing. The self-consistence test (well-mixed condition), aimed at maintaining an initially well-mixed particle distribution uniform in time, has shown satisfactory results in the region under study. The computed concentration field turns out to be in good agreement with the observed one. In detail, ground-level profiles and vertical cross sections of concentration are compared showing the important effects resulting from the topographic influence on the flow structure.
Magnetoconvection dynamics in a stratified layer. 1: Two-dimensional simulations and visualization
NASA Astrophysics Data System (ADS)
Lantz, Steven R.; Sudan, R. N.
1995-03-01
To gain insight in the problem of fluid convection below solar photosphere, time-dependent magnetohydrodynamic convection is studied by numerical simulation to the magneto-anelastic equations, a model appropiate for low Mach numbers. Numerical solutions to the equations are generated on a two-dimensional Cartesian mesh by a finite-difference, predictor-corrector algorithm. The thermodynamic properties of the fluid are held constant at the rigid, stress-free top and bottom boundaries of the computational box, while lateral boundaries are treated as periodic. In most runs the background polytropic fluid configuration is held fixed at Rayleigh number R = 5.44 times the critical value, Prandtl number P = 1.8, and aspect ratio a = 1, while the magnetic parameters are allowed to vary. The resulting dynamical behavior is shown to be strongly influenced by a horizontal magnetic field which is imposed at the bottom boundary. As the field strength increases from zero, an initially unsteady 'single-roll' state, featuring complex time dependence is replaced by a steady 'traveling-wave tilted state; then, an oscillatory or 'sloshing' state; then, a steady two-poll state with no tilting; and finally, a stationary state. Because the magnetic field is matched onto a potential field at the top boundary, it can penetrate into the nonconducting region above. By varying a magnetic diffusivity, the concentrations of weak magnetic fields at the top of these flows can be shown to be explainable in terms of an advection-diffusion balance.
Large Eddy Simulation of a turbulent flow in two dimensional dunes using an immersed boundary method
NASA Astrophysics Data System (ADS)
Agegnehu, Getnet; Smith, Heather D.
2013-11-01
The flow over dunes separates at the crest, generating a shear layer which has a big role for energy dissipation and formation of coherent structures. Large Eddy Simulations using bodyfitted and immersed boundary grids are performed to study the detailed flow dynamics that occurs in a fixed two dimensional dunes. We used a three-dimensional, non-hydrostatic solver; OpenFOAM for this study. The immersed boundary method was implemented using a discrete forcing approach with direct imposition of the boundary conditions. A periodic boundary condition is imposed in both the streamwise and spanwise directions. No-slip and free slip conditions are applied for the bottom and top walls respectively. The flow is forced with a pressure gradient which yields the mean velocity. The numerical results have been quantitatively compared with an experimental data for the mean flow and turbulence profiles. Resolved streamwise velocity profiles from both the immersed boundary and bodyfitted grids are in a good agreement with the experimental data. A good correlation of turbulent intensities and instantaneous flow fields are also observed between the two methods. It is also shown that the numerical model overestimates the vertical velocity profiles in the leeward side of the dune.
NASA Astrophysics Data System (ADS)
Reith, Daniel; Bucior, Katarzyna; Yelash, Leonid; Virnau, Peter; Binder, Kurt
2012-03-01
As a generic model system for phase separation in polymer solutions, a coarse-grained model for hexadecane/carbon dioxide mixtures has been studied in two-dimensional geometry. Both the phase diagram in equilibrium (obtained from a finite size scaling analysis of Monte Carlo data) and the kinetics of state changes caused by pressure jumps (studied by large scale molecular dynamics simulations) are presented. The results are compared to previous work where the same model was studied in three-dimensional geometry and under confinement in slit geometry. For deep quenches the characteristic length scale ?(t) of the formed domains grows with time t according to a power law close to \\ell (t)\\propto \\sqrt{t}. Since in this problem both the polymer density ?p and the solvent density ?s matter, the time evolution of the density distribution PL(?p,?s,t) in L L subboxes of the system is also analyzed. It is found that in the first stage of phase separation the system separates locally into low density carbon dioxide regions that contain no polymers and regions of high density polymer melt that are supersaturated with this solvent. The further coarsening proceeds via the growth of domains of rather irregular shapes. A brief comparison of our findings with results of other models is given.
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.
MHD Simulation Heliospheric Magnetic Fields and Turbulence
NASA Technical Reports Server (NTRS)
Roberts, D. Aaron
2005-01-01
This talk will present a summary of our results on simulations of heliospheric structure and dynamics. We use a three-dimensional MHD code in spherical coordinates to produce a solar wind containing a rotating, tilted heliospheric current sheet, fast-slow stream and microstream shear layers, waves, 2-D turbulence, and pressure balanced structures that are input to the inner (superAlfvenic) boundary. The evolution of various combinations of these has led to a deeper understanding of sector structure, magnetic holes, fluctuation anisotropies, and general turbulent evolution. We show how the sectors are likely to be connected, how spiral fields can arise, and how field line diffusion can be caused by waves with transverse structure and microstream shears.
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 ?m 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 a larger sand target). The deep penetration simulation predicted considerable instability with a trajectory change of approximately 45 when friction was considered in the dry sand medium. An overall conclusion of this work is that projectile penetration studies in geologic materials need to explicitly consider the heterogeneous or particulate nature of these materials.
Two-dimensional lattice Boltzmann model for magnetohydrodynamics.
Schaffenberger, Werner; Hanslmeier, Arnold
2002-10-01
We present a lattice Boltzmann model for the simulation of two-dimensional magnetohydro dynamic (MHD) flows. The model is an extension of a hydrodynamic lattice Boltzman model with 9 velocities on a square lattice resulting in a model with 17 velocities. Earlier lattice Boltzmann models for two-dimensional MHD used a bidirectional streaming rule. However, the use of such a bidirectional streaming rule is not necessary. In our model, the standard streaming rule is used, allowing smaller viscosities. To control the viscosity and the resistivity independently, a matrix collision operator is used. The model is then applied to the Hartmann flow, giving reasonable results. PMID:12443375
NASA Astrophysics Data System (ADS)
Sydorenko, D.; Rankin, R.; Kabin, K.
2009-12-01
This paper presents initial results based on kinetic extensions of a nonlinear two-dimensional (2D) multi-fluid (three ion species and fluid electrons) MHD model that is designed to study propagation of shear Alfven waves in low-altitude auroral flux tubes. It is intended to use the model for scientific support of the enhanced polar outflow probe e-POP/CASSIOPE spacecraft mission (launch scheduled in 2010). Effects of gravity, thermal pressure, and geomagnetic field curvature are included, while the parallel electric field along geomagnetic field lines is calculated under the assumption of plasma quasineutrality. The model has been used successfully to study excitation of eigenmodes of the ionospheric Alfven resonator (IAR) by an Alfven wave packet injected from the magnetospheric end of the simulated plasma region. The formation of density cavities due to the ponderomotive force of standing oscillations in the IAR [Sydorenko, Rankin, and Kabin, 2008], and excitation of double layers and ion-acoustic wave packets, has been demonstrated. The kinetic extension of the multi-fluid code involves replacing the fluid electron model with a kinetic module that solves the simplified drift-kinetic Vlasov equation for the electron velocity distribution function (EVDF). To avoid undue complexity, it is assumed that (i) the electrons move only along geomagnetic field lines and (ii) the electron magnetic moment is conserved. As a result, the evolution of the EVDF is reduced to the problem of advection in 2D phase space distance along the field line - velocity along the field line. This problem is solved using a semi-Lagrangian algorithm [Staniforth and Cote, 1991]. The kinetic simulation starts from the initial equilibrium state similar to [Ergun et al., 2000]. The equilibrium assumes that the plasma consists of two electron populations: cold electrons with isotropic EVDF originating from the ionosphere, and hot anisotropic electrons with a loss-cone EVDF coming from the high-altitude end. The loss-cone distribution is prone to strong numerical dispersion, which is compensated by tracing the interface of the EVDF in the coordinate-velocity phase space. Ergun R. E., C. W. Carlson, J. P. McFadden, F. S. Mozer, and R. J. Strangeway (2000), Geophys. Res. Lett., 27, 4053-4056. Staniforth A. and J. Cote (1991), Mon. Wea. Rev., 119, 2206-2223 Sydorenko, D., R. Rankin, and K. Kabin (2008), J. Geophys. Res., 113, A10206, doi:10.1029/2008JA013579.
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 Astrophysics Data System (ADS)
Caillol, Jean-Michel
2015-04-01
We present two methods for solving the electrostatics of point charges and multipoles on the surface of a sphere, i.e., in the space S 2 , with applications to numerical simulations of two-dimensional (2D) polar fluids. In the first approach, point charges are associated with uniform neutralizing backgrounds to form neutral pseudo-charges, while in the second, one instead considers bi-charges, i.e., dumbells of antipodal point charges of opposite signs. We establish the expressions of the electric potentials of pseudo- and bi-charges as isotropic solutions of the Laplace-Beltrami equation in S 2 . A multipolar expansion of pseudo- and bi-charge potentials leads to the electric potentials of mono- and bi-multipoles, respectively. These potentials constitute non-isotropic solutions of the Laplace-Beltrami equation, the general solution of which in spherical coordinates is recast under a new appealing form. We then focus on the case of mono- and bi-dipoles and build the theory of dielectric media in S 2 . We notably obtain the expression of the static dielectric constant of a uniform isotropic polar fluid living in S 2 in terms of the polarization fluctuations of subdomains of S 2 . We also derive the long range behavior of the equilibrium pair correlation function under the assumption that it is governed by macroscopic electrostatics. These theoretical developments find their application in Monte Carlo simulations of the 2D fluid of dipolar hard spheres. Some preliminary numerical experiments are discussed with a special emphasis on finite size effects, a careful study of the thermodynamic limit, and a check of the theoretical predictions for the asymptotic behavior of the pair correlation function.
NASA Technical Reports Server (NTRS)
Fleming, E. L.; Jackman, C. H.; Stolarski, R. S.; Considine, D. B.
1998-01-01
We have developed a new empirically-based transport algorithm for use in our GSFC two-dimensional transport and chemistry model. The new algorithm contains planetary wave statistics, and parameterizations to account for the effects due to gravity waves and equatorial Kelvin waves. As such, this scheme utilizes significantly more information compared to our previous algorithm which was based only on zonal mean temperatures and heating rates. The new model transport captures much of the qualitative structure and seasonal variability observed in long lived tracers, such as: isolation of the tropics and the southern hemisphere winter polar vortex; the well mixed surf-zone region of the winter sub-tropics and mid-latitudes; the latitudinal and seasonal variations of total ozone; and the seasonal variations of mesospheric H2O. The model also indicates a double peaked structure in methane associated with the semiannual oscillation in the tropical upper stratosphere. This feature is similar in phase but is significantly weaker in amplitude compared to the observations. The model simulations of carbon-14 and strontium-90 are in good agreement with observations, both in simulating the peak in mixing ratio at 20-25 km, and the decrease with altitude in mixing ratio above 25 km. We also find mostly good agreement between modeled and observed age of air determined from SF6 outside of the northern hemisphere polar vortex. However, observations inside the vortex reveal significantly older air compared to the model. This is consistent with the model deficiencies in simulating CH4 in the northern hemisphere winter high latitudes and illustrates the limitations of the current climatological zonal mean model formulation. The propagation of seasonal signals in water vapor and CO2 in the lower stratosphere showed general agreement in phase, and the model qualitatively captured the observed amplitude decrease in CO2 from the tropics to midlatitudes. However, the simulated seasonal amplitudes were attenuated too rapidly with altitude in the tropics. Overall, the simulations with the new transport formulation are in substantially better agreement with observations compared with our previous model transport.
Simulation of melting of two-dimensional Lennard-Jones solids
NASA Astrophysics Data System (ADS)
Wierschem, Keola; Manousakis, Efstratios
2011-06-01
We study the nature of melting of a two-dimensional (2D) Lennard-Jones solid using large-scale Monte Carlo simulation. We use systems of up to 102 400 particles to capture the decay of the correlation functions associated with translational order (TO) as well as the bond-orientational (BO) order. We study the role of dislocations and disclinations and their distribution functions. We computed the temperature dependence of the second moment of the TO parameter (?G) as well as of the order parameter ?6 associated with BO order. By applying finite-size scaling of these second moments, we determined the anomalous dimension critical exponents ?(T) and ?6(T) associated with power-law decay of the ?G and ?6 correlation functions. We also computed the temperature-dependent distribution of the order parameters ?G and ?6 on the complex plane that supports a two-stage melting with a hexatic phase as an intermediate phase. From the correlation functions of ?G and ?6, we extracted the corresponding temperature-dependent correlation lengths ?(T) and ?6(T). The analysis of our results leads to a consistent picture strongly supporting a two-stage melting scenario as predicted by the Kosterlitz, Thouless, Halperin, Nelson, and Young (KTHNY) theory where melting occurs via two continuous phase transitions, first from solid to a hexatic fluid at temperature Tm, and then from the hexatic fluid to an isotropic fluid at a critical temperature Ti. We find that ?(T) and ?6(T) have a distinctly different temperature dependence, each diverging at different temperature, and that their finite-size scaling properties are consistent with the KTHNY theory. We also used the temperature dependence of ? and ?6 and their theoretical bounds to provide estimates for the critical temperatures Tm and Ti, which can also be estimated using the Binder ratio. Our results are within error bars, the same as those extracted from the divergence of the correlation lengths.
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.
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
NASA Astrophysics Data System (ADS)
Lopez, A. R.; Baty, R. S.; Kashiwa, B. A.
Over the last several years, Sandia National Laboratories has had an interest in developing capabilities to predict the flow fields around vehicles entering or exiting the water at a wide range of speeds. Such prediction schemes have numerous engineering applications in the design of weapon systems. For example, such a scheme could be used to predict the forces and moments experienced by an air launched antisubmarine weapon on water entry. Furthermore, a water exit prediction capability could be used to model the complicated surface closure jet resulting from a missile being shot out of the water. The CCICE (Cell-Centered Implicit Continuous-fluid Eulerian) code developed at Los Alamos National Laboratory (LANL) was chosen to provide the fluid dynamics solver for high speed water entry and water exit problems. This implicit time marching, two dimensional, conservative, finite volume code solves the multi-material, compressible, inviscid fluid dynamics equations. The incompressible version of the CCICE code, CCMAC (Cell-Centered Marker and Cell), was chosen for low speed water entry and water exit problems in order to reduce the computational expense. These codes were chosen to take advantage of certain advances in numerical methods for computational fluid dynamics (CFD) that have taken place at LANL. Notable among these advances is the ability to perform implicit, multi-material, compressible flow simulations, with a fully cell-centered data structure. This means that a single set of control volumes are used, on which a discrete form of the conservation laws is satisfied. This is in control to the more classical staggered mesh methods, in which separate control volumes are defined for mass and momentum.
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.
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.
Two-dimensional simulation of Pinatubo aerosol and its effect on stratospheric ozone
NASA Technical Reports Server (NTRS)
Tie, Xuexi; Brasseur, Guy P.; Briegleb, Bruce; Granier, Claire
1994-01-01
This paper presents time-dependent simulations of the response of the stratosphere to the injection into the atmosphere of massive amounts of sulfur during the eruption of Mt. Pinatubo (The Philippines) in June 1991. The study is based on a coupled two-dimensional chemical-dynamical-radiative model to which a microphysical model for sulfate aerosol formation and fate has been added. The study suggests that, during the first year (July 1991 to June 1992) following the volcanic eruption, the observed changes in the ozone amount integrated between 65 deg S and 65 deg N were caused primarily by changes in the meridional circulation (associated with heating by the volcanic cloud in the tropics) and in the photolysis rate of molecules such as ozone (associated with backscattering of light by the cloud). During the second year after the eruption, as the aerosol was dispersed at all latitudes and, in particular, reached the polar region, the largest contribution to ozone reduction resulted from the heterogeneous chemical conversion of N2O5 and ClONO2 on the surface of the aerosol particles. The conversion of the latter compound, and hence the magnitude of the calculated ozone depletion, is highly dependent on the temperature in the lower stratosphere. Despite the fact that the surface area provided by aerosol particles decreased during the second year following the eruption, the calculated ozone depletion remained significant because the conversion of N2O5 is insensitive to the aerosol surface area density for values larger than 1-10 sq microns/cu cm (depending on latitude). The predicted reduction in ozone at 20 km in March during the third year (July 1993 to June 1994) of the model integration is smaller by a factor of 2 than it was during the second year.
Two-dimensional simulation of Pinatubo aerosol and its effect on stratospheric ozone
Tie, X.; Brasseur, G.P.; Briegleb, B.; Granier, C.
1994-10-01
This paper presents time-dependent simulations of the response of the stratosphere to the injection into the atmosphere of massive amounts of sulfur during the eruption of Mt. Pinatubo (The Philippines) in June 1991. The study is based on a coupled two-dimensional chemical-dynamical-radiative model to which a microphysical model for sulfate aerosol formation and fate has been added. The study suggests that, during the first year (July 1991 to June 1992) following the volcanic eruption, the observed changes in the ozone amount integrated between 65 deg S and 65 deg N were caused primarily by changes in the meridional circulation (associated with heating by the volcanic cloud in the tropics) and in the photolysis rate of molecules such as ozone (associated with backscattering of light by the cloud). During the second year after the eruption, as the aerosol was dispersed at all latitudes and, in particular, reached the polar region, the largest contribution to ozone reduction resulted from the heterogeneous chemical conversion of N2O5 and ClONO2 on the surface of the aerosol particles. The conversion of the latter compound, and hence the magnitude of the calculated ozone depletion, is highly dependent on the temperature in the lower stratosphere. Despite the fact that the surface area provided by aerosol particles decreased during the second year following the eruption, the calculated ozone depletion remained significant because the conversion of N2O5 is insensitive to the aerosol surface area density for values larger than 1-10 sq microns/cu cm (depending on latitude). The predicted reduction in ozone at 20 km in March during the third year (July 1993 to June 1994) of the model integration is smaller by a factor of 2 than it was during the second year.
Solar Wind Turbulence from MHD to Sub-ion Scales: High-resolution Hybrid Simulations
NASA Astrophysics Data System (ADS)
Franci, Luca; Verdini, Andrea; Matteini, Lorenzo; Landi, Simone; Hellinger, Petr
2015-05-01
We present results from a high-resolution and large-scale hybrid (fluid electrons and particle-in-cell protons) two-dimensional numerical simulation of decaying turbulence. Two distinct spectral regions (separated by a smooth break at proton scales) develop with clear power-law scaling, each one occupying about a decade in wavenumbers. The simulation results simultaneously exhibit several properties of the observed solar wind fluctuations: spectral indices of the magnetic, kinetic, and residual energy spectra in the magnetohydrodynamic (MHD) inertial range along with a flattening of the electric field spectrum, an increase in magnetic compressibility, and a strong coupling of the cascade with the density and the parallel component of the magnetic fluctuations at sub-proton scales. Our findings support the interpretation that in the solar wind, large-scale MHD fluctuations naturally evolve beyond proton scales into a turbulent regime that is governed by the generalized Ohms law.
NASA Astrophysics Data System (ADS)
Duan, Jennifer G.; Nanda, S. K.
2006-08-01
SummaryRiver-training structures, such as spur dikes, are effective engineered methods used to protect banks and improve aquatic habitat. This paper reports the development and application of a two-dimensional depth-averaged hydrodynamic model to simulate suspended sediment concentration distribution in a groyne field. The governing equations of flow hydrodynamic model are depth-averaged two-dimensional Reynold's averaged momentum equations and continuity equation in which the density of sediment laden-flow varies with the concentration of suspended sediment. The depth-averaged two-dimensional convection and diffusion equation was solved to obtain the depth-averaged suspended sediment concentration. The source term is the difference between suspended sediment entrainment and deposition from bed surface. One laboratory experiment was chosen to verify the simulated flow field around a groyne, and the other to verify the suspended sediment concentration distribution in a meandering channel. Then, the model utility was demonstrated in a field case study focusing on the confluence of the Kankakee and Iroquois Rivers in Illinois, United States, to simulate the distribution of suspended sediment concentration around spur dikes. Results demonstrated that the depth-averaged, two-dimensional model can approximately simulate the flow hydrodynamic field and concentration of suspended sediment. Spur dikes can be used to effectively relocate suspended sediment in alluvial channels.
Po, Hoi Chun; Zhou, Qi
2015-01-01
Bosons have a natural instinct to condense at zero temperature. It is a long-standing challenge to create a high-dimensional quantum liquid that does not exhibit long-range order at the ground state, as either extreme experimental parameters or sophisticated designs of microscopic Hamiltonians are required for suppressing the condensation. Here we show that synthetic gauge fields for ultracold atoms, using either the Raman scheme or shaken lattices, provide physicists a simple and practical scheme to produce a two-dimensional algebraic quantum liquid at the ground state. This quantum liquid arises at a critical Lifshitz point, where a two-dimensional quartic dispersion emerges in the momentum space, and many fundamental properties of two-dimensional bosons are changed in its proximity. Such an ideal simulator of the quantum Lifshitz model allows experimentalists to directly visualize and explore the deconfinement transition of topological excitations, an intriguing phenomenon that is difficult to access in other systems. PMID:26268154
NASA Astrophysics Data System (ADS)
Po, Hoi Chun; Zhou, Qi
2015-08-01
Bosons have a natural instinct to condense at zero temperature. It is a long-standing challenge to create a high-dimensional quantum liquid that does not exhibit long-range order at the ground state, as either extreme experimental parameters or sophisticated designs of microscopic Hamiltonians are required for suppressing the condensation. Here we show that synthetic gauge fields for ultracold atoms, using either the Raman scheme or shaken lattices, provide physicists a simple and practical scheme to produce a two-dimensional algebraic quantum liquid at the ground state. This quantum liquid arises at a critical Lifshitz point, where a two-dimensional quartic dispersion emerges in the momentum space, and many fundamental properties of two-dimensional bosons are changed in its proximity. Such an ideal simulator of the quantum Lifshitz model allows experimentalists to directly visualize and explore the deconfinement transition of topological excitations, an intriguing phenomenon that is difficult to access in other systems.
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
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.
Understanding the cause of IV kink in GaAs MESFET`s with two-dimensional numerical simulations
Wilson, M.R.; Zdebel, P.; Wennekers, P.; Anholt, R.
1995-12-31
High performance GaAs MESFET`s have been observed to exhibit kinks in their IV characteristics, particularly when high drain-source voltages are applied. Such characteristics make the design of circuits with high operating voltages difficult since this type of IV anomaly is typically not modeled by circuit simulators. This work has identified the cause of these kinks through the use of two-dimensional numerical device simulation with impact ionization. These simulations have also identified a potential device solution to IV kink. Furthermore, the results of this simulation work were verified by comparison with fabricated devices.
Numerical simulation model for the study of magneto-hydrodynamic (MHD) waves in a structured medium
Xiao, Y.
1988-01-01
This dissertation contains two basic parts: a formal development of a numerical simulation model for the study of MHD waves in a structured medium, and an application of the model to the investigation of the propagation of MHD waves in a magnetic slab and their interactions with nonmagnetic surroundings. The numerical model is a time-dependent, two-dimensional, and nonlinear MHD model with gravity and radiative energy loss. The corresponding numerical code is based on the newly developed SINIL (Semi-Implicit-Non-Iterative-Lagrangian) scheme. The MHD governing equations are discretized on a Lagrangian grid, using the control-volume method. The gas dynamic properties are solved explicitly, and the magnetic field is solved implicitly without using numerical iterations. Using this numerical model, three kinds of slab waves are studied, namely, kink type slab waves, sausage type slab waves, and kink-type single interface waves (which are considered as kink-type slab waves in the limit of infinite slab width). In this study, external acoustic waves can only be excited by internal body waves. The excitation of external acoustic waves represents the energy leakage from the internal magnetized region to the external field-free region.
Numerical simulations of thermal conductivity in dissipative two-dimensional Yukawa systems.
Khrustalyov, Yu V; Vaulina, O S
2012-04-01
Numerical data on the heat transfer constants in two-dimensional Yukawa systems were obtained. Numerical study of the thermal conductivity and diffusivity was carried out for the equilibrium systems with parameters close to conditions of laboratory experiments with dusty plasma. For calculations of heat transfer constants the Green-Kubo formulas were used. The influence of dissipation (friction) on the heat transfer processes in nonideal systems was investigated. The approximation of the coefficient of thermal conductivity is proposed. Comparison of the obtained results to the existing experimental and numerical data is discussed. PMID:22680584
Heat transfer coefficients in two-dimensional Yukawa systems (numerical simulations)
Khrustalyov, Yu. V. Vaulina, O. S.
2013-05-15
New data on heat transfer in two-dimensional Yukawa systems have been obtained. The results of a numerical study of the thermal conductivity for equilibrium systems with parameters close to the conditions of laboratory experiments in dusty plasma are presented. The Green-Kubo relations are used to calculate the heat transfer coefficients. The influence of dissipation (internal friction) on the heat transfer processes in nonideal systems is studied. New approximations are proposed for the thermal conductivity and diffusivity for nonideal dissipative systems. The results obtained are compared with the existing experimental and numerical data.
NASA Astrophysics Data System (ADS)
Komuro, Atsushi; Ono, Ryo
2014-04-01
Gas heating in an atmospheric-pressure streamer discharge was analysed by a two-dimensional streamer discharge simulation model describing internal molecular energy transfer. Our two-dimensional streamer simulation model incorporates concepts from the fast gas heating mechanism proposed by Popov (2011 J. Phys. D: Appl. Phys. 44 285201) and our self-developed state-to-state vibrational kinetics. In dry air, gas heating occurs mainly from electron-impact dissociation reactions of O2 molecules and from quenching processes of electronically excited N2(B 3?g, C 3?u) molecules and O(1D) atoms. In humid air, rapid vibration-to-translation transitions of H2O and the exothermicity of the OH formation reactions additionally increase the gas temperature. It is shown that gas heating during the discharge pulse increases with humidity.
Numerical simulation of the flow around two-dimensional partially cavitating hydrofoils
NASA Astrophysics Data System (ADS)
Celik, Fahri; Ozden, Yasemin Arikan; Bal, Sakir
2014-09-01
In the present study, a new approach is applied to the cavity prediction for two-dimensional (2D) hydrofoils by the potential based boundary element method (BEM). The boundary element method is treated with the source and doublet distributions on the panel surface and cavity surface by the use of the Dirichlet type boundary conditions. An iterative solution approach is used to determine the cavity shape on partially cavitating hydrofoils. In the case of a specified cavitation number and cavity length, the iterative solution method proceeds by addition or subtraction of a displacement thickness on the cavity surface of the hydrofoil. The appropriate cavity shape is obtained by the dynamic boundary condition of the cavity surface and the kinematic boundary condition of the whole foil surface including the cavity. For a given cavitation number the cavity length of the 2D hydrofoil is determined according to the minimum error criterion among different cavity lengths, which satisfies the dynamic boundary condition on the cavity surface. The NACA 16006, NACA 16012 and NACA 16015 hydrofoil sections are investigated for two angles of attack. The results are compared with other potential based boundary element codes, the PCPAN and a commercial CFD code (FLUENT). Consequently, it has been shown that the results obtained from the two dimensional approach are consistent with those obtained from the others.
Three Dimensional Simulations of Compressible Hall MHD Plasmas
Shaikh, Dastgeer; Shukla, P. K.
2008-10-15
We have developed three dimensional, time dependent, compressible, non-adiabatic, driven and massively parallelized Hall magnetohydrodynamic (MHD) simulations to investigate turbulent spectral cascades in a regime where characteristic lengthscales associated with plasma fluctuations are smaller than ion gyro radii. Such regime is ubiquitously present in solar wind and many other collisionless space plasmas. Particularly in the solar wind, the high time resolution databases identify a spectral break at the end of MHD inertial range spectrum that corresponds to a high frequency regime. In the regime, turbulent cascades cannot be explained by the usual MHD models. With the help of our 3D Hall MHD code, we find that characteristic turbulent interactions in the high frequency regime evolve typically on kinetic Alfven time scales. The turbulent fluctuation associated with kinetic Alfven interactions are compressive and anisotropic and possess equipartition of kinetic and magnetic energies.
Flight simulations of a two-dimensional flapping wing by the IB-LBM
NASA Astrophysics Data System (ADS)
Inamuro, Takaji; Kimura, Yusuke; Suzuki, Kosuke
2012-11-01
Two-dimensional symmetric flapping flight is investigated by the immersed boundary-lattice Boltzmann method. First, we investigate the effect of the Reynolds number 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. Secondly, we study the motion of the model with an initial rotational disturbance and find that the motion is rotationally unstable. That is, once the model starts rotating, the rotational motion rapidly increases due to a complicated vorticity field around the wings. Finally, we propose a simple way to control the rotational and horizontal motion by bending and flapping the tip of the wing. With the control we can achieve an upward stable motion in spite of the complicated vorticity field around the wings.
Brown, R C; Wyllie, R; Koller, S B; Goldschmidt, E A; Foss-Feig, M; Porto, J V
2015-05-01
The interplay of magnetic exchange interactions and tunneling underlies many complex quantum phenomena observed in real materials. We study nonequilibrium magnetization dynamics in an extended two-dimensional (2D) system by loading effective spin-1/2 bosons into a spin-dependent optical lattice and use the lattice to separately control the resonance conditions for tunneling and superexchange. After preparing a nonequilibrium antiferromagnetically ordered state, we observe relaxation dynamics governed by two well-separated rates, which scale with the parameters associated with superexchange and tunneling. With tunneling off-resonantly suppressed, we observe superexchange-dominated dynamics over two orders of magnitude in magnetic coupling strength. Our experiment will serve as a benchmark for future theoretical work as the detailed dynamics of this 2D, strongly correlated, and far-from-equilibrium quantum system remain out of reach of current computational techniques. PMID:25931552
Two-Dimensional Coupled Distributed Hydrologic-Hydraulic Model Simulation on Watershed
NASA Astrophysics Data System (ADS)
Cea, Miguel; Rodriguez, Martin
2015-10-01
The objective of this work is to develop a coupled distributed model that enables to analyze water movement in watershed as well as analyze the rainfall-runoff. More specifically, it allows to estimate the various hydrologic water cycle variables at each point of the watershed. In this paper, we have carried out a coupled model of a distributed hydrological and two-dimensional hydraulic models. We have incorporated a hydrological rainfall-runoff model calculated by cell based on the Soil Conservation Service (SCS) method to the hydraulic model, leaving it for the hydraulic model (GUAD2D) to conduct the transmission to downstream cells. The goal of the work is demonstrate the improved predictive capability of the coupled Hydrological-Hydraulic models in a watershed.
Guo, Xun; Zhang, Xitong; Zhao, Shijun; Huang, Qing; Xue, Jianming
2016-01-01
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. PMID:26602974
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)
Hybrid Vlasov-Maxwell simulations of two-dimensional turbulence in plasmas
Valentini, F.; Servidio, S.; Veltri, P.; Perrone, D.; Califano, F.; Matthaeus, W. H.
2014-08-15
Turbulence in plasmas is a very challenging problem since it involves wave-particle interactions, which are responsible for phenomena such as plasma dissipation, acceleration mechanisms, heating, temperature anisotropy, and so on. In this work, a hybrid Vlasov-Maxwell numerical code is employed to study local kinetic processes in a two-dimensional turbulent regime. In the present model, ions are treated as a kinetic species, while electrons are considered as a fluid. As recently reported in [S. Servidio, Phys. Rev. Lett. 108, 045001 (2012)], nearby regions of strong magnetic activity, kinetic effects manifest through a deformation of the ion velocity distribution function that consequently departs from the equilibrium Maxwellian configuration. Here, the structure of turbulence is investigated in detail in phase space, by evaluating the high-order moments of the particle velocity distribution, i.e., temperature, skewness, and kurtosis. This analysis provides quantitative information about the non-Maxwellian character of the system dynamics. This departure from local thermodynamic equilibrium triggers several processes commonly observed in many astrophysical and laboratory plasmas.
Two dimensional self-consistent fluid simulation of rf inductive sources
DiPeso, G.; Vahedi, V.; Hewett, D.W.; Rognlien, T.D.
1993-11-17
The two-dimensional (R - Z) electromagnetic code FMRZ has been written to model inductive sources self-consistently in time. The code models an argon plasma with momentum-transfer, excitation and ionization as electron-neutral reactions and scattering and charge-exchange for the ion-neutral reactions. The electrons and ions are treated as Maxwellian fluid species and a reduced set of Maxwell`s equations is used to advance the electromagnetic fields. The set of equations used in FMRZ is not subject to typical numerical constraints present in many time dynamic codes allowing one to choose appropriate the and space scales to resolve only the frequencies and scale lengths of interest. The model retains nonlinear driving terms which give rise to a pondermotive force that distorts the density profile. Density and power profiles will be used to illustrate the physical effects of various terms in the equations. Trends in average density and temperature compare well with an analytic model.
Simulation of the formation of two-dimensional Coulomb liquids and solids in dusty plasmas
Hwang, H.H.; Kushner, M.J.
1997-09-01
Dust particle transport in low-temperature plasmas has recently received considerable attention due to the desire to minimize contamination of wafers during plasma processing of microelectronics devices. Laser light scattering observations of dust particles near wafers in reactive-ion-etching (RIE) radio frequency (rf) discharges have revealed clouds which display collective behavior. These observations have motivated experimental studies of the Coulomb liquid and solid properties of these systems. In this paper, we present results from a two-dimensional model for dust particle transport in RIE rf discharges in which we include particle-particle Coulomb interactions. We predict the formation of Coulomb liquids and solids. These predictions are based both on values of {Gamma}{gt}2 (liquid) and {Gamma}{gt}170 (solid), where {Gamma} is the ratio of electrostatic potential energy to thermal energy, and on crystal-like structure in the pair correlation function. We find that Coulomb liquids and solids composed of trapped dust particles in RIE discharges are preferentially formed with increasing gas pressure, decreasing particle size, and decreasing rf power. We also observe the ejection of particles from dust crystals which completely fill trapping sites, as well as lattice disordering followed by annealing and refreezing. {copyright} {ital 1997 American Institute of Physics.}
Two-dimensional numerical model of two-layer shallow water equations for confluence simulation
NASA Astrophysics Data System (ADS)
Chen, Su-Chin; Peng, Szu-Hsien
2006-11-01
This study presents a finite-volume explicit method to solve 2D two-layer shallow water equations. This numerical model is intended to describe two-layer shallow flows in which the superposed layers differ in velocity, density and rheology in a two-dimensional domain. The rheological behavior of mudflow or debris flow is called the Bingham fluid. Thus, the shear stress on rigid bed can be derived from the constitutive equation. The computational approach adopts the HLL scheme, a novel approach for the purpose of computing a Godunov flux and solving the Riemann problem approximately proposed by Harten, Lax and van Leer, as a basic building block, treats the bottom slope by lateralizing the momentum flux, and refines the scheme using the Strang splitting to manage the frictional source term. This study successfully performed 2D two-layer shallow water computations on a rigid bed. The proposed numerical model can describe the variety of depths and velocities of substances including water and mud, when the hyperconcentrated tributary flows into the main river. The analytical results in this study will be valuable for further advanced research and for designing or planning hydraulic engineering structures.
Two-dimensional particle-in-cell simulations of transport in a magnetized electronegative plasma
Kawamura, E.; Lichtenberg, A. J.; Lieberman, M. A.
2010-11-15
Particle transport in a uniformly magnetized electronegative plasma is studied in two-dimensional (2D) geometry with insulating (dielectric) boundaries. A 2D particle-in-cell (PIC) code is employed, with the results compared to analytic one-dimensional models that approximate the end losses as volume losses. A modified oxygen reaction set is used to scale to the low densities used in PIC codes and also to approximately model other gases. The principal study is the limiting of the transverse electron flow due to strong electron magnetization. The plasma in the PIC calculation is maintained by axial currents that vary across the transverse dimension. For a cosine current profile nearly uniform electron temperature is obtained, which at the B-fields studied (600-1200 G) give a small but significant fraction (0.25 or less) of electron to negative ion transverse loss. For a more transverse-confined current, and approximating the higher mass and attachment reaction rate of iodine, the fraction of electron to negative ion transverse loss can be made very small. The models which have been constructed reasonably approximate the PIC results and indicate that the cross-field transport is nearly classical.
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.
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.
Sullivan, H.F.; Wright, J.L.; Fraser, R.A.
1996-12-31
A collaborative research project was undertaken to generate surface temperature profiles for the indoor side of seven different double- and triple-glazed insulated glazing units exposed to the ASHRAE winter design condition. Four research groups produced four sets of results in a blind study. Two sets were measured by means of thermography and two were generated using two-dimensional numerical simulation. In addition, each simulation group produced results using simplified methods. Companion papers each present results from the individual studies along with some observations and commentary. This paper, an overview, presents a compilation of results and provides the opportunity for a variety of comparisons. Good agreement was found among all four sets of data. Simplified simulation models also show promise. The reassurance offered by these accomplishments is important because both the measurement and simulation methods are in the early stages of development. In addition, details found in individual temperature profiles provide valuable insights regarding the mechanisms of window heat transfer.
MHD simulation of the planetary magnetospheres by using various scalar type supercomputer systems
NASA Astrophysics Data System (ADS)
Fukazawa, Keiichiro; Umeda, Takayuki; Ogino, Tatsuki; Walker, Raymond; Yumoto, Kiyohumi
Currently more than 85% of the "top 500" supercomputer systems in the world have adopted the "64-bit x86" processor architecture. However it is often mentioned that the performance of electromagnetic fluid codes is not as good on the scalar type computers (often less than 10% of peak performance efficiency) as compared to vector type computers. For instance our planetary magnetospheric magnetohydrodynamic code reached over 50% of performance efficiency on vector supercomputers. In this study we have carried out performance tuning and other measurements on massively parallel supercomputer systems with various types of scalar processors. We use the T2K open supercomputer at University of Tokyo (AMD Opteron processors), SR16000 at Kyushu University (IBM POWER6 processors), and FX1 (Fujitsu SPARC64VI processors) and HX600 (AMD Opteron processors) at Nagoya University. In this presentation, as a tuning technique, the MHD simulation model was run by using three decomposition methods for parallelization and one cache tuning method to find out which method is best for the MHD code. As a result we have obtained over 10% of peak performance efficiency using the T2K open supercomputer and we obtained much better performances with SR16000 and FX1, HX600 (over 20%). In particular we found that the two-dimensional decom-position of the MHD model is suitable for the T2K system and while for the SR16000 and FX1 cache tuned three-dimensional decomposition achieved the best performance. In this study we will show and compare the results of performance measurements and tuning techniques for MHD simulation codes of the planetary magnetospheres with scalar type supercomputers in detail. Finally we will present the latest simulation results of global planetary magnetosphere with high spatial resolution (three times the resolution of our current Saturn's model) using the result of performance tuning.
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.
One- and two-dimensional hybrid simulations of whistler mode waves in a dipole field
NASA Astrophysics Data System (ADS)
Wu, S.; Denton, R. E.; Liu, K.; Hudson, M. K.
2015-03-01
We simulate whistler mode waves using a hybrid code. There are four species in the simulations, hot electrons initialized with a bi-Maxwellian distribution with temperature in the direction perpendicular to background magnetic field greater than that in the parallel direction, warm isotropic electrons, cold inertialess fluid electrons, and protons as an immobile background. The density of the hot population is a small fraction of the total plasma density. Comparison between the dispersion relation of our model and other dispersion relations shows that our model is more accurate for lower frequency whistlers than for higher frequency whistlers. Simulations in 2-D Cartesian coordinates agree very well with those using a full dynamics code. In the 1-D simulations along the dipole magnetic field, the predicted frequency and wave number are observed. Rising tones are observed in the one-fourteenth scale simulations that have larger than realistic magnetic field spatial inhomogeneity. However, in the full-scale 1-D simulation in a dipole field, the waves are more broadband and do not exhibit rising tones. In the 2-D simulations in a meridional plane, the waves are generated with propagation approximately parallel to the background magnetic field. However, the wavefronts become oblique as they propagate to higher latitudes. Simulations with different plasma density profiles across L shell are performed to study the effect of the background density on whistler propagation.
Monte Carlo simulations of a model two-dimensional, two-patch colloidal particles
NASA Astrophysics Data System (ADS)
R?ysko, W.; Soko?owski, S.; Staszewski, T.
2015-08-01
We carried out Monte Carlo simulations of the two-patch colloids in two-dimensions. Similar model investigated theoretically in three-dimensions exhibited a re-entrant phase transition. Our simulations indicate that no re-entrant transition exists and the phase diagram for the system is of a swan-neck type and corresponds solely to the fluid-solid transition.
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
Hybrid Kinetic-MHD Simulations in General Geometry
NASA Astrophysics Data System (ADS)
Kim, Charlson C.; Parker, Scott E.; Sovinec, Carl R.
2003-10-01
We present a hybrid kinetic MHD model that is applicable to fusion relevent simulations. Previous research(Hsu ST, Sigmar DJ, PFB 4) 1492-1505, 1992 and simulation results suggest that the hot particle momentum contribution is not negligable and prompts reexamination of the hybrid kinetic MHD model equations(Cheng CZ, Johnson JR,JGR-S A-104) 413-427, 1999 typically used. The model equations have been applied to the NIMROD simulation(Sovinec CR, Gianakon TA, Held ED, et al., PoP 10) 1727-1732, 2003, a finite element, three dimensional, massively parallel, extended MHD simulation, capable of handling general geometries. A ? f PIC module has been incorporated into the NIMROD simulation to model the effects of a minority hot particle species on MHD instabilities. The details of the PIC implementation will be presented. As an example of the hybrid physics, a benchmark case of kinetic effects on the internal kink mode and the excitation of the fishbone mode will be presented. We also present performance results on various architectures.
NASA Technical Reports Server (NTRS)
Tsang, L.; Lou, S. H.; Chan, C. H.
1991-01-01
The extended boundary condition method is applied to Monte Carlo simulations of two-dimensional random rough surface scattering. The numerical results are compared with one-dimensional random rough surfaces obtained from the finite-element method. It is found that the mean scattered intensity from two-dimensional rough surfaces differs from that of one dimension for rough surfaces with large slopes.
Integrated Two-Dimensional DRACO Simulations of Cryogenic DT Target Performance on OMEGA
NASA Astrophysics Data System (ADS)
Hu, S. X.; Radha, P. B.; Goncharov, V. N.; Betti, R.; Epstein, R.; Marshall, F. J.; McCrory, R. L.; Meyerhofer, D. D.; Sangster, T. C.; Skupsky, S.
2013-10-01
Integrated simulations of cryogenic deuterium-tritium (DT) target implosions on OMEGA have been performed using the radiation-hydrodynamic code DRACO. Taking into account the known nonuniformities of target and laser irradiation, 2-D simulations examine the target performance of a variety of ignition-relevant implosions. The effects of cross-beam energy transfer and nonlocal heat transport are mimicked by a time-dependent flux limiter. DRACO simulations show good agreement with experiments in ?R , neutron yield, Ti, neutron rate, and x-ray images for the mid-adiabat (? ~ 4 ) implosions. For low-adiabat (? ~ 2) and high in-flight aspect ratio (IFAR > 24) implosions, the integrated simulations with the known nonuniformity sources cannot fully explain the reduction in target performance. Examinations of other possible nonuniformity sources and the thermal conductivity model will be presented. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.
Monte Carlo simulations of a model two-dimensional, two-patch colloidal particles.
R?ysko, W; Soko?owski, S; Staszewski, T
2015-08-14
We carried out Monte Carlo simulations of the two-patch colloids in two-dimensions. Similar model investigated theoretically in three-dimensions exhibited a re-entrant phase transition. Our simulations indicate that no re-entrant transition exists and the phase diagram for the system is of a swan-neck type and corresponds solely to the fluid-solid transition. PMID:26277147
Sheehey, P. ); Hammel, J.E.; Lindemuth, I.R.; Scudder, D.W.; Shlachter, J.S. ); Lovberg, R.H.; Riley, R.A. Jr. )
1992-11-01
Deuterium-fiber-initiated Z-pinch experiments have been simulated using a two-dimensional resistive magnetohydrodynamic model, which includes many important experimental details, such as cold-start'' initial conditions, thermal conduction, radiation, actual discharge current versus time, and grids of sufficient size and resolution to allow realistic development of the plasma. When the fiber becomes fully ionized (at a time depending on current ramp and fiber thickness), the simulations show rapidly developing [ital m]=0 instabilities, which originated in the corona surrounding the fiber, drive intense nonuniform heating and rapid expansion of the plasma column. Diagnostics generated from the simulation results, such as shadowgrams and interferograms, are in good agreement with experiment.
Lin, Zhenyi; Li, Wei; Gatebe, Charles; Poudyal, Rajesh; Stamnes, Knut
2016-02-20
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. PMID:26906570
Resistive MHD simulation of edge-localized-modes for double-null discharges in the MAST device
NASA Astrophysics Data System (ADS)
Pamela, S. J. P.; Huijsmans, G. T. A.; Kirk, A.; Chapman, I. T.; Harrison, J. R.; Scannell, R.; Thornton, A. J.; Becoulet, M.; Orain, F.; the MAST Team
2013-09-01
Recent development of the nonlinear magneto hydrodynamic (MHD) code JOREK has enabled the alignment of its two-dimensional finite-element grid along poloidal flux surfaces for double-null Grad-Shafranov equilibria. In previous works with the JOREK code, only single X-point plasmas were studied. The fast-camera diagnostic on MAST, which gives a global view of the pedestal filamentation during an ELM crash, clearly shows filaments travelling far into the scrape-off layer, as far as the first wall. Simulation of such a filament dynamics in MAST double-null plasmas is presented here and compared with experimental observations. In addition to direct comparison with the fast-camera images, general aspects of filaments are studied, such as their radial speed and composition. A qualitative validation of simulations is carried out against other diagnostics, such as the Thomson-scattering profiles or the infra-red camera images. Simulations are found to reproduce experimental edge localized modes in a reasonable manner, with similar energy losses and divertor heat-flux profiles. However, the MHD model used for those simulations is a reduced MHD model, which is likely approaching the limit of its applicability for the MAST device. Also, the absence of diamagnetic drift terms in the present MHD model results in nonlinear simulations being dominated by the highest mode number, and thus coupling with lower mode numbers is not observed.
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.
NASA Astrophysics Data System (ADS)
Lee, Kuang Wu; Buechner, Joerg
Two-dimensional particle-in-cell simulation of Weibel instability in a current-free return beam plasma system Lee, Kuang Wu and Joerg Buechner In the collisionless plasmas of stellar coro-nae and planetary magnetospheres return beams are generated in order to compensate strong flows of accelerated electrons. In this process return beams help to maintain charge neutrality in the electron downflow channels. In laser plasma experiments return beams beams are also observed to compensate injected electrons. In return-beam two-stream systems plasma insta-bilities are excited that cause an electron temperature anisotropy. The latter, in turn, can cause Weibel instability. Weibel instability leads to the excitation of electromagnetic and transverse waves which play a vital role in plasma transport in collisionless plasmas. While, according to previous investigations, electrostatic waves dominate during the initial stage of the instability evolution later strong anomalous (collisionless) transport converts kinetic energy into thermal energy. Finally, during a highly nonlinear stage, obliquely propagating electromagnetic waves are generated which, again, isotropize the system and drive it toward a new equilibrium. By means of solving the corrsponding linear dispersion analysis we obtained the stability conditions in a higher-dimensional return-beam system. Then we used a two-dimensional electromagnetic particle-in-cell (2D EM PIC) simulation code to study the nonlnear evolution of the instabilities and the waves, generated in the course of these processes.
MHD Pedestal Formation in Time-Dependent Simulations
NASA Astrophysics Data System (ADS)
Guazzotto, Luca; Betti, Riccardo; Jardin, Steve
2014-10-01
Finite toroidal and poloidal flows are routinely observed in the edge plasma region of tokamak experiments. MHD theory predicts that when the poloidal velocity is transonic with respect to the poloidal sound speed (csp ≡csBp / B , where Bp is the poloidal field) a transient will develop. After the end of the transient, a steady-state MHD pedestal in plasma density and pressure is left, with the height of the pedestal depending on the poloidal location. The formation of the MHD pedestal was demonstrated with time-dependent simulations with the resistive-MHD code SIM2D. In the present work, we explore the effect of additional physics on the formation of the pedestal. The advanced model implemented in M3DC1 is used to validate and extend SIM2D calculations. Since M3DC1, contrary to SIM2D, was not developed to study transonic transients, this also gives a strong independent verification of the correctness of the MHD pedestal model. Special focus is given to poloidal viscosity, which is already implemented in M3DC1 and is being implemented in SIM2D. Analytic calculations complement and support numerical results. Work supported by US Department of Energy Contract No. DE-FG02-93ER54215.
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.
Bezier surfaces and finite elements for MHD simulations
Czarny, Olivier
2008-08-10
A finite element method based on bicubic Bezier surfaces is applied to the simulation of MHD instabilities relevant to magnetically confined fusion. The major advantage of the new technique is that it allows a natural way to implement mesh refinement strategy, which is not supported by a pure Hermite formulation. Compared to a Lagrangian formulation the number of degrees of freedom is significantly reduced. The use of an isoparametric representation of the space coordinates allows an accurate alignment of the finite elements to the magnetic field line geometry in a tokamak plasma. The Bezier finite elements have been implemented in a MHD code using the non-linear reduced MHD model in toroidal geometry. As an illustration, results for Soloviev equilibrium and time-dependent current-hole computations are presented and discussed.
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.
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.…
One and two dimensional electromagnetic gyrokinetic PIC simulation by ?f method
NASA Astrophysics Data System (ADS)
Chen, C. M.; Nishimura, Y.; Cheng, C. Z.
2014-10-01
An electromagnetic gyrokinetic Particle-in-Cell simulation is studied aiming at long-wave-length magnetohydrodynamic instabilities. A fully nonlinear characteristic method (?f method) of electrostatic gyrokinetic theory is employed. For a one dimensional geometry, ``0.5 dimension'' is taken in `` y-direction'' of the configuration space and another ``0.5 dimension'' is taken in the ``vz-direction'' of the velocity space. Recent electromagnetic ?f simulation shows optimistic results. We revisit the importance of the conservation properties in the low dimensional geometries. This work is supported by National Science Council of Taiwan, NSC 100-2112-M-006-021-MY3 and NSC 103-2112-M-006-021-MY3.
A zero-equation turbulence model for two-dimensional hybrid Hall thruster simulations
NASA Astrophysics Data System (ADS)
Cappelli, Mark A.; Young, Christopher V.; Cha, Eunsun; Fernandez, Eduardo
2015-11-01
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.
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.
Two-dimensional particle-in-cell simulation of the expansion of a plasma into a rarefied medium
NASA Astrophysics Data System (ADS)
Sarri, G.; Murphy, G. C.; Dieckmann, M. E.; Bret, A.; Quinn, K.; Kourakis, I.; Borghesi, M.; Drury, L. O. C.; Ynnerman, A.
2011-07-01
The expansion of a dense plasma through a more rarefied ionized medium has been studied by means of two-dimensional particle-in-cell simulations. The initial conditions involve a density jump by a factor of 100, located in the middle of an otherwise equally dense electron-proton plasma with uniform proton and electron temperatures of 10 eV and 1 keV, respectively. Simulations show the creation of a purely electrostatic collisionless shock together with an ion-acoustic soliton tied to its downstream region. The shock front is seen to evolve in filamentary structures consistently with the onset of the ion-ion instability. Meanwhile, an un-magnetized drift instability is triggered in the core part of the dense plasma. Such results explain recent experimental laser-plasma experiments, carried out in similar conditions, and are of intrinsic relevance to non-relativistic shock scenarios in the solar and astrophysical systems.
Two-dimensional solar cell simulations by means of circuit modeling
Kerschaver, E. van; Nijs, J.; Mertens, R.; Ghannam, M.
1997-12-31
In this work, the authors present a circuit model to perform multidimensional solar cell simulations. This model allows for incorporating effects of lateral current flows in solar cells, keeping the required time and computer resources relatively low. The use and sensitivity of the model will be described based on its application towards the design of metallization patterns for locally passivated back surface structures. As a second application the authors present the usage of the model to study the influence of different cell parameters such as surface recombination velocities and cell thickness on its performance.
Mesh refinement in a two-dimensional large eddy simulation of a forced shear layer
NASA Technical Reports Server (NTRS)
Claus, R. W.; Huang, P. G.; Macinnes, J. M.
1989-01-01
A series of large eddy simulations are made of a forced shear layer and compared with experimental data. Several mesh densities were examined to separate the effect of numerical inaccuracy from modeling deficiencies. The turbulence model that was used to represent small scale, 3-D motions correctly predicted some gross features of the flow field, but appears to be structurally incorrect. The main effect of mesh refinement was to act as a filter on the scale of vortices that developed from the inflow boundary conditions.
NASA Astrophysics Data System (ADS)
Cao, Duc; Moses, Gregory; Delettrez, Jacques
2015-08-01
An implicit, non-local thermal conduction algorithm based on the algorithm developed by Schurtz, Nicolai, and Busquet (SNB) [Schurtz et al., Phys. Plasmas 7, 4238 (2000)] for non-local electron transport is presented and has been implemented in the radiation-hydrodynamics code DRACO. To study the model's effect on DRACO's predictive capability, simulations of shot 60 303 from OMEGA are completed using the iSNB model, and the computed shock speed vs. time is compared to experiment. Temperature outputs from the iSNB model are compared with the non-local transport model of Goncharov et al. [Phys. Plasmas 13, 012702 (2006)]. Effects on adiabat are also examined in a polar drive surrogate simulation. Results show that the iSNB model is not only capable of flux-limitation but also preheat prediction while remaining numerically robust and sacrificing little computational speed. Additionally, the results provide strong incentive to further modify key parameters within the SNB theory, namely, the newly introduced non-local mean free path. This research was supported by the Laboratory for Laser Energetics of the University of Rochester.
Two Dimensional Simulations of Plastic-Shell, Direct-Drive Implosions on OMEGA
Radha, P B; Goncharov, V N; Collins, T B; Delettrez, J A; Elbaz, Y; Glebov, V Y; Keck, R L; Keller, D E; Knauer, J P; Marozas, J A; Marshall, F J; McKenty, P W; Meyerhofer, D D; Regan, S P; Sangster, T C; Shvarts, D; Skupsky, S; Srebro, Y; Town, R J; Stoeckl, C
2004-09-27
Multidimensional hydrodynamic properties of high-adiabat direct-drive plastic-shell implosions on the OMEGA laser system [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] are investigated using the multidimensional hydrodynamic code, DRACO. Multimode simulations including the effects of nonuniform illumination and target roughness indicate that shell stability during the acceleration phase plays a critical role in determining target performance. For thick shells that remain integral during the acceleration phase, target yields are significantly reduced by the combination of the long-wavelength ({ell} < 10) modes due to surface roughness and beam imbalance and the intermediate modes (20 {le} {ell} {le} 50) due to single-beam nonuniformities. The neutron-production rate for these thick shells truncates relative to one-dimensional (1-D) predictions. The yield degradation in the thin shells is mainly due to shell breakup at short wavelengths ({lambda} {approx} {Delta}, where {Delta} is the in-flight shell thickness). The neutron-rate curves for the thinner shells have significantly lower amplitudes and a fall-off that is less steep than 1-D rates. DRACO simulation results are consistent with experimental observations.
Lefkoff, L.J.; Gorelick, S.M.
1987-01-01
A FORTRAN-77 computer program code that helps solve a variety of aquifer management problems involving the control of groundwater hydraulics. It is intended for use with any standard mathematical programming package that uses Mathematical Programming System input format. The computer program creates the input files to be used by the optimization program. These files contain all the hydrologic information and management objectives needed to solve the management problem. Used in conjunction with a mathematical programming code, the computer program identifies the pumping or recharge strategy that achieves a user 's management objective while maintaining groundwater hydraulic conditions within desired limits. The objective may be linear or quadratic, and may involve the minimization of pumping and recharge rates or of variable pumping costs. The problem may contain constraints on groundwater heads, gradients, and velocities for a complex, transient hydrologic system. Linear superposition of solutions to the transient, two-dimensional groundwater flow equation is used by the computer program in conjunction with the response matrix optimization method. A unit stress is applied at each decision well and transient responses at all control locations are computed using a modified version of the U.S. Geological Survey two dimensional aquifer simulation model. The program also computes discounted cost coefficients for the objective function and accounts for transient aquifer conditions. (Author 's abstract)
Two Dimensional 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.
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.
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.
A two-dimensional particle simulation of the magnetopause current layer
Berchem, J.; Okuda, H.
1988-11-01
We have developed a 2/1/2/-D (x, y, v/sub x/, v/sub y/, v/sub z/) electromagnetic code to study the formation and the stability of the magnetopause current layer. This code computes the trajectories of ion and electron particles in their self-consistently generated electromagnetic field and an externally imposed 2-D vacuum dipolar magnetic field. The results presented here are obtained for the simulation of the solar wind-magnetosphere interaction in the subsolar region of the equatorial plane. We observe the self-consistent establishment of a current layer resulting from both diamagnetic drift and E /times/ B drift due to the charge separation. The simulation results show that during the establishment of the current layer, its thickness is of the order of the hybrid gyroradius /rho//sub H/ = ..sqrt../rho//sub i//rho//sub e/ predicted by the Ferraro-Rosenbluth model. However, diagnostics indicate that the current sheet is subject to an instability which broadens the width of the current layer. Ripples with amplitudes of the order of the ion gyroradius appear at the interface between the field and the particles. These pertubations are observed both on the electrostatic field and on the compressional component of the magnetic field. This instability has a frequency of the order of the local ion cyclotron frequency. However, the modulation propagates in the same direction as the electron diamagnetic drift which indicates that the instability is not a classical gradient-driven instability, such as the lower hybrid or ion drift cyclotron instabilities. The nonlinear phase of the instability is characterized by the filamentation of the current layer which causes anomalous diffusion inside the central current sheet. 79 refs., 7 figs.
Nenov, Artur; Segarra-Mart, Javier; Giussani, Angelo; Conti, Irene; Rivalta, Ivan; Dumont, Elise; Jaiswal, Vishal K; Altavilla, Salvatore Flavio; Mukamel, Shaul; Garavelli, Marco
2015-01-01
The SOS//QM/MM [Rivalta et al., Int. J. Quant. Chem., 2014, 114, 85] method consists of an arsenal of computational tools allowing accurate simulation of one-dimensional (1D) and bi-dimensional (2D) electronic spectra of monomeric and dimeric systems with unprecedented details and accuracy. Prominent features like doubly excited local and excimer states, accessible in multi-photon processes, as well as charge-transfer states arise naturally through the fully quantum-mechanical description of the aggregates. In this contribution the SOS//QM/MM approach is extended to simulate time-resolved 2D spectra that can be used to characterize ultrafast excited state relaxation dynamics with atomistic details. We demonstrate how critical structures on the excited state potential energy surface, obtained through state-of-the-art quantum chemical computations, can be used as snapshots of the excited state relaxation dynamics to generate spectral fingerprints for different de-excitation channels. The approach is based on high-level multi-configurational wavefunction methods combined with non-linear response theory and incorporates the effects of the solvent/environment through hybrid quantum mechanics/molecular mechanics (QM/MM) techniques. Specifically, the protocol makes use of the second-order Perturbation Theory (CASPT2) on top of Complete Active Space Self Consistent Field (CASSCF) strategy to compute the high-lying excited states that can be accessed in different 2D experimental setups. As an example, the photophysics of the stacked adenine-adenine dimer in a double-stranded DNA is modeled through 2D near-ultraviolet (NUV) spectroscopy. PMID:25607949
Hall MHD Simulations of Comet 67P/Churyumov-Gerasimenko
NASA Astrophysics Data System (ADS)
Shou, Y.; Combi, M. R.; Rubin, M.; Hansen, K. C.; Toth, G.; Gombosi, T. I.
2012-12-01
Comets have highly eccentric orbits and a wide range of gas production rates and thus they are ideal subjects to study the interaction between the solar wind and nonmagnetized bodies. Hansen et al. (2007, Space Sci. Rev. 128, 133) used a fluid-based MHD model and a semi-kinetic hybrid particle model to study the plasma environment of comet 67P/Churyumov-Gerasimenko (CG), the Rosetta mission target comet, at different heliocentric distances. They showed that for such a weak comet at a large heliocentric distance, the length scales of the cometosheath and the bow shock are comparable to or smaller than the ion gyroradius, which violates the underlying assumption for a valid fluid description of the plasma. As a result, the classical ideal MHD model is not able to always give physical results, while the hybrid model, which accounts for the kinetic effects of ions with both cometary and solar wind origin, is more reliable. However, hybrid models are computationally expensive and the results can be noisy. A compromise approach is Hall MHD [Toth et al., 2008], which includes the Hall term in the MHD equations and allows for the decoupling of the ion and electron fluids. We use a single ion species Hall MHD model to simulate the plasma environment of comet 67P/CG and compare the results with the two models mentioned above. We find that the Hall effect is capable of reproducing some features of the hybrid model and thus extends the applicability of MHD. In addition, this study helps to identify the conditions and regions in the cometary plasma where the Hall effect is not negligible. This work is supported by NSF Planetary Astronomy grant AST0707283 and JPL subcontract 1266313 under NASA grant NMO710889.
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 Euler and Navier-Stokes Time accurate simulations of fan rotor flows
NASA Technical Reports Server (NTRS)
Boretti, A. A.
1990-01-01
Two numerical methods are presented which describe the unsteady flow field in the blade-to-blade plane of an axial fan rotor. These methods solve the compressible, time-dependent, Euler and the compressible, turbulent, time-dependent, Navier-Stokes conservation equations for mass, momentum, and energy. The Navier-Stokes equations are written in Favre-averaged form and are closed with an approximate two-equation turbulence model with low Reynolds number and compressibility effects included. The unsteady aerodynamic component is obtained by superposing inflow or outflow unsteadiness to the steady conditions through time-dependent boundary conditions. The integration in space is performed by using a finite volume scheme, and the integration in time is performed by using k-stage Runge-Kutta schemes, k = 2,5. The numerical integration algorithm allows the reduction of the computational cost of an unsteady simulation involving high frequency disturbances in both CPU time and memory requirements. Less than 200 sec of CPU time are required to advance the Euler equations in a computational grid made up of about 2000 grid during 10,000 time steps on a CRAY Y-MP computer, with a required memory of less than 0.3 megawords.
Two-dimensional Euler and Navier-Stokes Time accurate simulations of fan rotor flows
Boretti, A.A.
1990-07-01
Two numerical methods are presented which describe the unsteady flow field in the blade-to-blade plane of an axial fan rotor. These methods solve the compressible, time-dependent, Euler and the compressible, turbulent, time-dependent, Navier-Stokes conservation equations for mass, momentum, and energy. The Navier-Stokes equations are written in Favre-averaged form and are closed with an approximate two-equation turbulence model with low Reynolds number and compressibility effects included. The unsteady aerodynamic component is obtained by superposing inflow or outflow unsteadiness to the steady conditions through time-dependent boundary conditions. The integration in space is performed by using a finite volume scheme, and the integration in time is performed by using k-stage Runge-Kutta schemes, k = 2,5. The numerical integration algorithm allows the reduction of the computational cost of an unsteady simulation involving high frequency disturbances in both CPU time and memory requirements. Less than 200 sec of CPU time are required to advance the Euler equations in a computational grid made up of about 2000 grid during 10,000 time steps on a CRAY Y-MP computer, with a required memory of less than 0.3 megawords.
Voinovich, Peter; Merlen, Alain
2005-12-01
The effect of parametric wave phase conjugation (WPC) in application to ultrasound or acoustic waves in magnetostrictive solids has been addressed numerically by Ben Khelil et al. [J. Acoust. Soc. Am. 109, 75-83 (2001)] using 1-D unsteady formulation. Here the numerical method presented by Voinovich et al. [Shock waves 13(3), 221-230 (2003)] extends the analysis to the 2-D effects. The employed model describes universally elastic solids and liquids. A source term similar to Ben Khelil et al.'s accounts for the coupling between deformation and magnetostriction due to external periodic magnetic field. The compatibility between the isotropic constitutive law of the medium and the model of magnetostriction has been considered. Supplementary to the 1-D simulations, the present model involves longitudinal/transversal mode conversion at the sample boundaries and separate magnetic field coupling with dilatation and shear stress. The influence of those factors in a 2-D geometry on the potential output of a magneto-elastic wave phase conjugator is analyzed in this paper. The process under study includes propagation of a wave burst of a given frequency from a point source in a liquid into the active solid, amplification of the waves due to parametric resonance, and formation of time-reversed waves, their radiation into liquid, and focusing. The considered subject is particularly important for ultrasonic applications in acoustic imaging, nondestructive testing, or medical diagnostics and therapy. PMID:16419796
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.
NASA Astrophysics Data System (ADS)
Vlasis, Alkiviadis; Dessart, Luc; Audit, Edouard
2016-02-01
Some interacting supernovae (SNe) of type IIn show a sizeable continuum polarisation suggestive of a large scale asymmetry in the circumstellar medium (CSM) and/or the SN ejecta. Here, we extend the recent work of Dessart et al. on super-luminous SNe IIn and perform axially-symmetric (i.e., 2D) multi-group radiation hydrodynamics simulations to explore the impact of an imposed large scale density asymmetry. When the CSM is asymmetric, the latitudinal variation of the radial optical depth τ introduces a strong flux redistribution from the higher-density CSM regions, where the shock luminosity is larger, towards the lower-density CSM regions where photons escape more freely - this redistribution ceases when τ ≲ 1. Along directions where the CSM density is larger, the shock deceleration is stronger and its progression slower, producing a non-spherical cold-dense shell (CDS). For an oblate CSM density distribution, the photosphere (CDS) has an oblate (prolate) morphology when τ ≳ 1. When the CSM is symmetric and the ejecta asymmetric, the flux redistribution within the CSM now tends to damp the latitudinal variation of the luminosity at the shock. It then requires a larger ejecta asymmetry to produce a sizeable latitudinal variation in the emergent flux. When the interaction is between a SN ejecta and a relic disk, the luminosity boost at early times scales with the disk opening angle - forming a super-luminous SN IIn this way requires an unrealistically thick disk. In contrast, interaction with a disk of modest thickness/mass can yield a power that rivals radioactive decay of a standard SN II at nebular times.
Wu, Tianmin; Zhang, Ruiting; Li, Huanhuan; Zhuang, Wei E-mail: lijiangy@pku.edu.cn; Yang, Lijiang E-mail: lijiangy@pku.edu.cn
2014-02-07
We analyzed, based on the theoretical spectroscopic modeling, how the differences in the folding landscapes of two ?-hairpin peptides trpzip2 and trpzip4 are reflected in their thermal unfolding infrared measurements. The isotope-edited equilibrium FTIR and two dimensional infrared spectra of the two peptides were calculated, using the nonlinear exciton propagation method, at a series of temperatures. The spectra calculations were based on the configuration distributions generated using the GB{sup OBC} implicit solvent MD simulation and the integrated tempering sampling technique. Conformational analysis revealed the different local thermal stabilities for these two peptides, which suggested the different folding landscapes. Our study further suggested that the ellipticities of the isotope peaks in the coherent IR signals are more sensitive to these local stability differences compared with other spectral features such as the peak intensities. Our technique can thus be combined with the relevant experimental measurements to achieve a better understanding of the peptide folding behaviors.
NASA Astrophysics Data System (ADS)
Wu, Tianmin; Zhang, Ruiting; Li, Huanhuan; Yang, Lijiang; Zhuang, Wei
2014-02-01
We analyzed, based on the theoretical spectroscopic modeling, how the differences in the folding landscapes of two ?-hairpin peptides trpzip2 and trpzip4 are reflected in their thermal unfolding infrared measurements. The isotope-edited equilibrium FTIR and two dimensional infrared spectra of the two peptides were calculated, using the nonlinear exciton propagation method, at a series of temperatures. The spectra calculations were based on the configuration distributions generated using the GBOBC implicit solvent MD simulation and the integrated tempering sampling technique. Conformational analysis revealed the different local thermal stabilities for these two peptides, which suggested the different folding landscapes. Our study further suggested that the ellipticities of the isotope peaks in the coherent IR signals are more sensitive to these local stability differences compared with other spectral features such as the peak intensities. Our technique can thus be combined with the relevant experimental measurements to achieve a better understanding of the peptide folding behaviors.
A two-dimensional simulation of tritium transport in the vadose zone at the Nevada Test site
Ross, W.C.; Wheatcraft, S.W.
1994-09-01
The site of a 0.75-kiloton underground nuclear explosion, the Cambric event, was selected for the study of radionuclide transport in the hydrologic environment. Water samples from RNM-2S, a well located 91 m from Cambric, have been analyzed for tritium and other radionuclides since the initiation of pumping. Water from RNM-2S flows to Frenchman Lake via an unlined canal. Flume data indicate canal transmission losses of approximately 2m{sup 3}/day/meter of canal. To determine if infiltrating canal water might be recirculated by RNM-2S, and therefore provide an additional radionuclide input to water samples collected at RNM-2S, a two-dimensional variably saturated solute transport computer model (SATURN, Huyakorn et al., 1983) was used to simulate the movement of tritium from the canal to the water table. Results indicate that recirculated canal water has not had a significant effect on the breakthrough of tritium at RNM-2S.
Matsui, H.; Koike, Makoto; Kondo, Yutaka; Fast, Jerome D.; Takigawa, M.
2014-09-30
Number concentrations, size distributions, and mixing states of aerosols are essential parameters for accurate estimation of aerosol direct and indirect effects. In this study, we developed an aerosol module, designated Aerosol Two-dimensional bin module for foRmation and Aging Simulation (ATRAS), that can represent these parameters explicitly by considering new particle formation (NPF), black carbon (BC) aging, and secondary organic aerosol (SOA) processes. A two-dimensional bin representation is used for particles with dry diameters from 40 nm to 10 µm to resolve both aerosol size (12 bins) and BC mixing state (10 bins) for a total of 120 bins. The particles with diameters from 1 to 40 nm are resolved using an additional 8 size bins to calculate NPF. The ATRAS module was implemented in the WRF-chem model and applied to examine the sensitivity of simulated mass, number, size distributions, and optical and radiative parameters of aerosols to NPF, BC aging and SOA processes over East Asia during the spring of 2009. BC absorption enhancement by coating materials was about 50% over East Asia during the spring, and the contribution of SOA processes to the absorption enhancement was estimated to be 10 – 20% over northern East Asia and 20 – 35% over southern East Asia. A clear north-south contrast was also found between the impacts of NPF and SOA processes on cloud condensation nuclei (CCN) concentrations: NPF increased CCN concentrations at higher supersaturations (smaller particles) over northern East Asia, whereas SOA increased CCN concentrations at lower supersaturations (larger particles) over southern East Asia. Application of ATRAS to East Asia also showed that the impact of each process on each optical and radiative parameter depended strongly on the process and the parameter in question. The module can be used in the future as a benchmark model to evaluate the accuracy of simpler aerosol models and examine interactions between NPF, BC aging, and SOA processes under different meteorological conditions and emissions.
Fan, L; Fang, H; Lin, Z
2001-05-01
During immiscible-fluid displacement, the contact angle between the interface and the wall of a tube, as well as the velocity V of the contact line where a fluid interface intersects the wall of a tube, depends on the applied capillary pressure Pcap. In this paper, the contact line dynamics of immiscible-fluid displacement is simulated by using the lattice Boltzmann model in a two-dimensional capillary channel with an ideally smooth wall. The V dependence of the contact angle is studied for two different wetting cases. Our simulational results are in good agreement with those based on theoretical computations and with molecular dynamics simulations. In particular, the power-law behavior Pcap approximately Vx is found with an exponent x very close to 1. The simulations suggest that the lattice Boltzmann model may serve as an alternative reliable quantitative approach to study the contact line dynamics, and also may be a promising tool for investigating some other immiscible displacement related subjects. PMID:11414912
NASA Astrophysics Data System (ADS)
Fan, Lewen; Fang, Haiping; Lin, Zhifang
2001-05-01
During immiscible-fluid displacement, the contact angle between the interface and the wall of a tube, as well as the velocity V of the contact line where a fluid interface intersects the wall of a tube, depends on the applied capillary pressure Pcap. In this paper, the contact line dynamics of immiscible-fluid displacement is simulated by using the lattice Boltzmann model in a two-dimensional capillary channel with an ideally smooth wall. The V dependence of the contact angle is studied for two different wetting cases. Our simulational results are in good agreement with those based on theoretical computations and with molecular dynamics simulations. In particular, the power-law behavior Pcap~Vx is found with an exponent x very close to 1. The simulations suggest that the lattice Boltzmann model may serve as an alternative reliable quantitative approach to study the contact line dynamics, and also may be a promising tool for invesitgating some other immiscible displacement related subjects.
MHD Simulations of Plasma Thruster in application to VASIMR project
NASA Astrophysics Data System (ADS)
Novakowski, S. V.; Sagdeev, R. Z.; Chang-Diaz, F. R.; Ilin, A.
1998-11-01
The results of the computer simulation of the MHD processes occuring in the plasma of the thruster in VASIMR rocket (F. R. Chang-Diaz, Research Status of the Variable Specific Impulse Magnetoplasma Rocket, in Bull. of the APS, Vol. 42, No. 10, p. 2057 ) are presented. The geometry of the thruster chamber and the exaust region is considered and a set of self-consistent MHD equations are solved with the aid of the specifically developed computer code THRUSTER. Different configurations with a different magnetic nozzle shape are considered for the purpose of finding the optimal parameters for thruster efficiency. The results of the simulation, namely the data on the density, temperature and velocity profiles are compared to the experimental data. The role of effects due to self-consistent magnetic field of plasma are discussed.
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)
Lindley, Brandon; Wang, Qi; Zhang, Tianyu
2012-03-01
We develop a tricomponent (ternary) hydrodynamic model for multiphase flows of biomass and solvent mixtures, which we employ to simulate biofilm. In this model, the three predominant effective components in biofilms, which are the extracellular polymeric substance (EPS) network, the bacteria, and the effective solvent (consisting of the solvent and nutrient, etc.), are modeled explicitly. The tricomponent fluid mixture is assumed incompressible as a whole, while intercomponent mixing, dissipation, and conversion are allowed among the effective components. Bacterial growth and EPS production due to the growing bacterial population are modeled in the biomass transport equations. Bacterial decay due to starvation and natural causes is accounted for in the bacterial population dynamics to capture the possible bacterial population reduction due to the depletion of the nutrient. In the growth regime for biofilms, the mixture behaves like a multiphase viscous fluid, in which the molecular relaxation is negligible in the corresponding time scale. In this regime, the dynamics of biofilm growth in the solvent (water) are simulated using a two-dimensional finite difference solver that we developed, in which the distribution and evolution of the EPS and bacterial volume fractions are investigated. The hydrodynamic interaction between the biomass and the solvent flow field is also simulated in a shear cell environment, demonstrating the spatially and temporally heterogeneous distribution of the EPS and bacteria under shear. This model together with the numerical codes developed provides a predictive tool for studying biomass-flow interaction and other important biochemical interactions in the biofilm and solvent fluid mixture.
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. PMID:26241967
Evaluation of subgrid-scale models in large eddy simulation of flow past a two-dimensional block
NASA Astrophysics Data System (ADS)
Cheng, W. C.; Port-Agel, F.
2012-04-01
Large eddy simulations (LES) are performed to study flow past a two-dimensional (2D) block. An immersed boundary method (IBM) is developed and implemented to model the block in the simulation. The accuracy of the IBM method and the performance of four subgrid-scale (SGS) models are examined by comparing the results with wind tunnel experimental data from the literature. The SGS models that are tested include (a) the Smagorinsky model, (b) the Lagrangian dynamc model, (c) the scale-dependent Largrangian dynamic model, and (d) the modulated gradient model. Good agreement is observed between the experiments and the results from the scale-dependent Lagrangian dynamic model and the modulated gradient model. These models are able to reproduce the mean wind and turbulence statistics around the block. Moreover, the values of the eddy viscosity coefficient and scale-dependence coefficient obtained with the Lagrangian scale-dependent dynamic model are found to have strong spatial variability. Lower values of the eddy viscosity coefficient are found in regions of the flow with higher shear in order to account for the reduced length scales of the turbulence.
Yu, Zhicong; Noo, Frdric; Dennerlein, Frank; Wunderlich, Adam; Lauritsch, Gnter; Hornegger, Joachim
2012-01-01
Mathematical phantoms are essential for the development and early-stage evaluation of image reconstruction algorithms in x-ray computed tomography (CT). This note offers tools for computer simulations using a two-dimensional (2D) phantom that models the central axial slice through the FORBILD head phantom. Introduced in 1999, in response to a need for a more robust test, the FORBILD head phantom is now seen by many as the gold standard. However, the simple Shepp-Logan phantom is still heavily used by researchers working on 2D image reconstruction. Universal acceptance of the FORBILD head phantom may have been prevented by its significantly-higher complexity: software that allows computer simulations with the Shepp-Logan phantom is not readily applicable to the FORBILD head phantom. The tools offered here address this problem. They are designed for use with Matlab, as well as open-source variants, such as FreeMat and Octave, which are all widely used in both academia and industry. To get started, the interested user can simply copy and paste the codes from this PDF document into Matlab M-files. PMID:22713335
NASA 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.
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. PMID:26574458
NASA Astrophysics Data System (ADS)
Yu, Zhicong; Noo, Frdric; Dennerlein, Frank; Wunderlich, Adam; Lauritsch, Gnter; Hornegger, Joachim
2012-07-01
Mathematical phantoms are essential for the development and early stage evaluation of image reconstruction algorithms in x-ray computed tomography (CT). This note offers tools for computer simulations using a two-dimensional (2D) phantom that models the central axial slice through the FORBILD head phantom. Introduced in 1999, in response to a need for a more robust test, the FORBILD head phantom is now seen by many as the gold standard. However, the simple Shepp-Logan phantom is still heavily used by researchers working on 2D image reconstruction. Universal acceptance of the FORBILD head phantom may have been prevented by its significantly higher complexity: software that allows computer simulations with the Shepp-Logan phantom is not readily applicable to the FORBILD head phantom. The tools offered here address this problem. They are designed for use with Matlab, as well as open-source variants, such as FreeMat and Octave, which are all widely used in both academia and industry. To get started, the interested user can simply copy and paste the codes from this PDF document into Matlab M-files.
Takao, Yoshinori; Kusaba, Naoki; Eriguchi, Koji; Ono, Kouichi
2010-11-15
Two-dimensional axisymmetric particle-in-cell simulations with Monte Carlo collision calculations (PIC-MCC) have been conducted to investigate argon microplasma characteristics of a miniature inductively coupled plasma source with a 5-mm-diameter planar coil, where the radius and length are 5 mm and 6 mm, respectively. Coupling the rf-electromagnetic fields to the plasma is carried out based on a collisional model and a kinetic model. The former employs the cold-electron approximation and the latter incorporates warm-electron effects. The numerical analysis has been performed for pressures in the range 370-770 mTorr and at 450 MHz rf powers below 3.5 W, and then the PIC-MCC results are compared with available experimental data and fluid simulation results. The results show that a considerably thick sheath structure can be seen compared with the plasma reactor size and the electron energy distribution is non-Maxwellian over the entire plasma region. As a result, the distribution of the electron temperature is quite different from that obtained in the fluid model. The electron temperature as a function of rf power is in a reasonable agreement with experimental data. The pressure dependence of the plasma density shows different tendency between the collisional and kinetic model, implying noncollisional effects even at high pressures due to the high rf frequency, where the electron collision frequency is less than the rf driving frequency.
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)
Biswas, Rajib; Furtado, Jonathan; Bagchi, Biman
2013-10-01
We present computer simulation study of two-dimensional infrared spectroscopy (2D-IR) of water confined in reverse micelles (RMs) of various sizes. The present study is motivated by the need to understand the altered dynamics of confined water by performing layerwise decomposition of water, with an aim to quantify the relative contributions of different layers water molecules to the calculated 2D-IR spectrum. The 0-1 transition spectra clearly show substantial elongation, due to inhomogeneous broadening and incomplete spectral diffusion, along the diagonal in the surface water layer of different sized RMs. Fitting of the frequency fluctuation correlation functions reveal that the motion of the surface water molecules is sub-diffusive and indicate the constrained nature of their dynamics. This is further supported by two peak nature of the angular analogue of van Hove correlation function. With increasing system size, the water molecules become more diffusive in nature and spectral diffusion almost completes in the central layer of the larger size RMs. Comparisons between experiments and simulations establish the correspondence between the spectral decomposition available in experiments with the spatial decomposition available in simulations. Simulations also allow a quantitative exploration of the relative role of water, sodium ions, and sulfonate head groups in vibrational dephasing. Interestingly, the negative cross correlation between force on oxygen and hydrogen of O-H bond in bulk water significantly decreases in the surface layer of each RM. This negative cross correlation gradually increases in the central water pool with increasing RMs size and this is found to be partly responsible for the faster relaxation rate of water in the central pool.
NASA Astrophysics Data System (ADS)
Tie, Xuexi; Lin, Xing; Brasseur, Guy
1994-08-01
We have developed a coupled two-dimensional dynamical/chemical/microphysical model to study the global distribution of stratospheric sulfate aerosols. In particular, we use this model to simulate the global distribution of volcanic aerosols after the eruption of El Chichn in Mexico in April 1982. The simulated background aerosol distributions are highly dispersed, while a slight latitudinal gradient is also noticed. The calculated background aerosol surface area and mass are about 0.7 to 1.0 ?m2/cm3 and 0.3 to 0.5 parts per billion by mass, respectively, at midlatitude in the northern hemisphere, in fair agreement with available observations. After the eruption of El Chichn in April 1982, the stratospheric aerosol load rapidly increases in the tropics at an altitude of 20 to 25 km. The aerosol area in the tropics reaches a maximum 50 ?m2/cm3 in the lower stratosphere, which is about 70-100 times the background aerosol area. Six months after the eruption, volcanic aerosols spread out globally but are still centered in the tropics. One year after the eruption the enhanced aerosol begins to decrease and tends to become uniformly distributed in the lower stratosphere. Two years after the eruption the global aerosol is about 5 times the background aerosol load in the lower stratosphere. The e-folding time of the aerosol load is about 10 months in the tropics during the postvolcanic period. Compared to observations (in terms of spatial, temporal, and size distributions), the model quantitatively simulates the evolution of volcanic aerosol clouds. Thus this model could be a useful tool for studying the impacts of volcanic eruptions on stratospheric ozone and climate. Moreover, we find that for a model simulation in which the gas phase SO2 is the only material ejected by the eruption, the model substantially underestimates the volcanic aerosol load. Thus we expect that the direct ejection of sulfate aerosol particles may be a very important process.
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).
Ito, Hironobu; Tanimura, Yoshitaka
2016-02-21
Full classical molecular dynamics (MD) simulations of two-dimensional (2D) infrared-Raman and 2D Raman spectroscopies of liquid water were carried out to elucidate a mode-mode coupling mechanism using a polarizable water model for intermolecular and intramolecular vibrational spectroscopy (POLI2VS). This model is capable of describing both infrared and Raman spectra. Second-order response functions, which consist of one molecular polarizability and two molecular dipole moments for 2D IR-Raman and three molecular polarizabilities for 2D Raman spectroscopies, were calculated using an equilibrium-non-equilibrium hybrid MD approach. The obtained signals were analyzed using a multi-mode Brownian oscillator (BO) model with nonlinear system-bath interactions representing the intramolecular OH stretching, intramolecular HOH bending, hydrogen bonded (HB)-intermolecular librational motion and HB-intermolecular vibrational (translational) motion of liquid water. This model was applied through use of hierarchal Fokker-Planck equations. The qualitative features of the peak profiles in the 2D spectra obtained from the MD simulations are accurately reproduced with the BO model. This indicates that this model captures the essential features of the intermolecular and intramolecular motion. We elucidate the mechanisms governing the 2D signal profiles involving anharmonic mode-mode coupling, the nonlinearities of the polarizability and dipole moment, and the vibrational dephasing processes of liquid water even in the case that the 2D spectral peaks obtained from the MD simulation overlap or are unclear. The mode coupling peaks caused by electrical anharmonic coupling (EAHC) and mechanical anharmonic coupling (MAHC) are observed in all of the 2D spectra. We find that the strength of the MAHC between the OH-stretching and HB-intermolecular vibrational modes is comparable to that between the OH-stretching and HOH bending modes. Moreover, we find that this OH-stretching and HB-intermolecular vibrational coupling should be observed as off-diagonal cross peaks in the 2D spectra. PMID:26896979
Tie, X.; Lin, X.; Brasseur, G. |
1994-08-01
We have developed a coupled two-dimensional dynamical/chemical/microphysical model to study the global distribution of stratospheric sulfate aerosols. We use this model to simulate the global distribution of volcanic aerosols after the eruption of El Chichon in Mexico in April 1982. The simulated background aerosol distribution are highly dispersed, while a slight latitudinal gradient is also noticed. The calculated background aerosol surface area and mass are about 0.7 to 1.0 sq microns/cu cm and 0.3 to 0.5 parts per billion by mass, respectively, at midlatitude in the northern hemisphere, in fair agreement with available observations. After the eruption of El Chichon in April 1982, the stratospheric aerosol load rapidly increases in the tropics at an altitude of 20 to 25 km. The aerosol area in the tropics reaches a maximum 50 sq microns/ cu cm in the lower stratosphere, which is about 70-100 times the background aerosol area. Six months after the eruption, volcanic aerosols spread out globally but are still centered in the tropics. One year after the eruption the enhanced aerosol begins to decrease and tends to become uniformly distributed in the lower stratosphere. Two years after the eruption the global aerosol is about 5 times the background aerosol load in the lower stratosphere. The e-folding time of the aerosol load is about 10 months in the tropics during the postvolcanic period. Compared to observations (in terms of spatial, temporal, and size distributions), the model quantitatively simulates the evolution of volcanic aerosol clouds. Thus this model could be a useful tool for studying the impacts of volcanic eruptions on stratospheric ozone and climate.
NASA Astrophysics Data System (ADS)
Pan, Kuo-Chuan; Liebendrfer, 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 radiationhydrodynamic 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 ? 0.10.5 B (1 B ? 1051 erg) for all considered 2D models within approximately 100300 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 neutrinoelectron scattering during collapse will lead to a stronger explosion.
NASA Astrophysics Data System (ADS)
Ito, Hironobu; Tanimura, Yoshitaka
2016-02-01
Full classical molecular dynamics (MD) simulations of two-dimensional (2D) infrared-Raman and 2D Raman spectroscopies of liquid water were carried out to elucidate a mode-mode coupling mechanism using a polarizable water model for intermolecular and intramolecular vibrational spectroscopy (POLI2VS). This model is capable of describing both infrared and Raman spectra. Second-order response functions, which consist of one molecular polarizability and two molecular dipole moments for 2D IR-Raman and three molecular polarizabilities for 2D Raman spectroscopies, were calculated using an equilibrium-non-equilibrium hybrid MD approach. The obtained signals were analyzed using a multi-mode Brownian oscillator (BO) model with nonlinear system-bath interactions representing the intramolecular OH stretching, intramolecular HOH bending, hydrogen bonded (HB)-intermolecular librational motion and HB-intermolecular vibrational (translational) motion of liquid water. This model was applied through use of hierarchal Fokker-Planck equations. The qualitative features of the peak profiles in the 2D spectra obtained from the MD simulations are accurately reproduced with the BO model. This indicates that this model captures the essential features of the intermolecular and intramolecular motion. We elucidate the mechanisms governing the 2D signal profiles involving anharmonic mode-mode coupling, the nonlinearities of the polarizability and dipole moment, and the vibrational dephasing processes of liquid water even in the case that the 2D spectral peaks obtained from the MD simulation overlap or are unclear. The mode coupling peaks caused by electrical anharmonic coupling (EAHC) and mechanical anharmonic coupling (MAHC) are observed in all of the 2D spectra. We find that the strength of the MAHC between the OH-stretching and HB-intermolecular vibrational modes is comparable to that between the OH-stretching and HOH bending modes. Moreover, we find that this OH-stretching and HB-intermolecular vibrational coupling should be observed as off-diagonal cross peaks in the 2D spectra.
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
Mori, Takahiro; Kawamura, Hikaru
2008-05-01
Spatiotemporal correlations of the two-dimensional (2D) spring-block (Burridge-Knopoff) models of earthquakes with the long-range interblock interactions are extensively studied by means of numerical computer simulations. The long-range interaction derived from an elastic theory, which takes account of the effect of the elastic body adjacent to the fault plane, falls off with distance r as 1r;{3} . Comparison is made with the properties of the corresponding short-range models studied earlier. Seismic spatiotemporal correlations of the long-range models generally tend to be weaker than those of the short-range models. The magnitude distribution exhibits a "near-critical" behavior, i.e., a power-law-like behavior close to the Gutenberg-Richter law, for a wide parameter range with its B -value, B approximately 0.55 , insensitive to the model parameters, in sharp contrast to that of the 2D short-range model and those of the 1D short-range and long-range models where such a near-critical behavior is realized only by fine tuning the model parameters. In contrast to the short-range case, the mean stress drop at a seismic event of the long-range model is nearly independent of its magnitude, consistent with the observation. Large events often accompany foreshocks together with a doughnutlike quiescence as their precursors, while they hardly accompany aftershocks with almost negligible seismic correlations observed after the main shock. PMID:18643042
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 Nmes (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. PMID:17120637
Tian, Peifang; Devor, Anna; Sakadi?, Sava; Dale, Anders M.; Boas, David A.
2011-01-01
Absorption or fluorescence-based two-dimensional (2-D) optical imaging is widely employed in functional brain imaging. The image is a weighted sum of the real signal from the tissue at different depths. This weighting function is defined as depth sensitivity. Characterizing depth sensitivity and spatial resolution is important to better interpret the functional imaging data. However, due to light scattering and absorption in biological tissues, our knowledge of these is incomplete. We use Monte Carlo simulations to carry out a systematic study of spatial resolution and depth sensitivity for 2-D optical imaging methods with configurations typically encountered in functional brain imaging. We found the following: (i) the spatial resolution is <200 ?m for NA ?0.2 or focal plane depth ?300 ?m. (ii) More than 97% of the signal comes from the top 500 ?m of the tissue. (iii) For activated columns with lateral size larger than spatial resolution, changing numerical aperature (NA) and focal plane depth does not affect depth sensitivity. (iv) For either smaller columns or large columns covered by surface vessels, increasing NA and?or focal plane depth may improve depth sensitivity at deeper layers. Our results provide valuable guidance for the optimization of optical imaging systems and data interpretation. PMID:21280912
2015-01-01
Two-dimensional (2D) optical spectroscopy techniques based on ultrashort laser pulses have been recently extended to the optical domain in the ultraviolet (UV) spectral region. UV-active aromatic side chains can thus be used as local highly specific markers for tracking dynamics and structural rearrangements of proteins. Here we demonstrate that 2D electronic spectra of a model proteic system, a tetrapeptide with two aromatic side chains, contain enough structural information to distinguish between two different configurations with distant and vicinal side chains. For accurate simulations of the 2DUV spectra in solution, we combine a quantum mechanics/molecular mechanics approach based on wave function methods, accounting for interchromophores coupling and environmental effects, with nonlinear response theory. The proposed methodology reveals effects, such as charge transfer between vicinal aromatic residues that remain concealed in conventional exciton Hamiltonian approaches. Possible experimental setups are discussed, including multicolor experiments and signal manipulation techniques for limiting undesired background contributions and enhancing 2DUV signatures of specific electronic couplings. PMID:24803989
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
Nenov, Artur; Rivalta, Ivan; Cerullo, Giulio; Mukamel, Shaul; Garavelli, Marco
2014-02-20
Two-dimensional (2D) optical spectroscopy techniques based on ultrashort laser pulses have been recently extended to the optical domain in the ultraviolet (UV) spectral region. UV-active aromatic side chains can thus be used as local highly specific markers for tracking dynamics and structural rearrangements of proteins. Here we demonstrate that 2D electronic spectra of a model proteic system, a tetrapeptide with two aromatic side chains, contain enough structural information to distinguish between two different configurations with distant and vicinal side chains. For accurate simulations of the 2DUV spectra in solution, we combine a quantum mechanics/molecular mechanics approach based on wave function methods, accounting for interchromophores coupling and environmental effects, with nonlinear response theory. The proposed methodology reveals effects, such as charge transfer between vicinal aromatic residues that remain concealed in conventional exciton Hamiltonian approaches. Possible experimental setups are discussed, including multicolor experiments and signal manipulation techniques for limiting undesired background contributions and enhancing 2DUV signatures of specific electronic couplings. PMID:24803989
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.
Analysis and gyrokinetic simulation of MHD Alfven wave interactions
NASA Astrophysics Data System (ADS)
Nielson, Kevin Derek
The study of low-frequency turbulence in magnetized plasmas is a difficult problem due to both the enormous range of scales involved and the variety of physics encompassed over this range. Much of the progress that has been made in turbulence theory is based upon a result from incompressible magnetohydrodynamics (MHD), in which energy is only transferred from large scales to small via the collision of Alfven waves propagating oppositely along the mean magnetic field. Improvements in laboratory devices and satellite measurements have demonstrated that, while theories based on this premise are useful over inertial ranges, describing turbulence at scales that approach particle gyroscales requires new theory. In this thesis, we examine the limits of incompressible MHD theory in describing collisions between pairs of Alfven waves. This interaction represents the fundamental unit of plasma turbulence. To study this interaction, we develop an analytic theory describing the nonlinear evolution of interacting Alfven waves and compare this theory to simulations performed using the gyrokinetic code AstroGK. Gyrokinetics captures a much richer set of physics than that described by incompressible MHD, and is well-suited to describing Alfvenic turbulence around the ion gyroscale. We demonstrate that AstroGK is well suited to the study of physical Alfven waves by reproducing laboratory Alfven dispersion data collected using the LAPD. Additionally, we have developed an initialization alogrithm for use with AstroGK that allows exact Alfven eigenmodes to be initialized with user specified amplitudes and phases. We demonstrate that our analytic theory based upon incompressible MHD gives excellent agreement with gyrokinetic simulations for weakly turbulent collisions in the limit that k?rho i << 1. In this limit, agreement is observed in the time evolution of nonlinear products, and in the strength of nonlinear interaction with respect to polarization and scale. We also examine the effect of wave amplitude upon the validity of our analytic solution, exploring the nature of strong turbulence. In the kinetic limit where k? rhoi ? 1 where incompressible MHD is no longer a valid description, we illustrate how the nonlinear evolution departs from our analytic expression. The analytic theory we develop provides a framework from which more sophisticated of weak and strong inertial-range turbulence theories may be developed. Characterization of the limits of this theory may provide guidance in the development of kinetic Alfven wave turbulence.
NASA Technical Reports Server (NTRS)
Fleming, Eric L.; Jackman, Charles H.; Stolarski, Richard S.; Considine, David B.
1998-01-01
We have developed a new empirically-based transport algorithm for use in our GSFC two-dimensional transport and chemistry assessment model. The new algorithm contains planetary wave statistics, and parameterizations to account for the effects due to gravity waves and equatorial Kelvin waves. We will present an overview of the new algorithm, and show various model-data comparisons of long-lived tracers as part of the model validation. We will also show how the new algorithm gives substantially better agreement with observations compared to our previous model transport. The new model captures much of the qualitative structure and seasonal variability observed methane, water vapor, and total ozone. These include: isolation of the tropics and winter polar vortex, the well mixed surf-zone region of the winter sub-tropics and mid-latitudes, and the propagation of seasonal signals in the tropical lower stratosphere. Model simulations of carbon-14 and strontium-90 compare fairly well with observations in reproducing the peak in mixing ratio at 20-25 km, and the decrease with altitude in mixing ratio above 25 km. We also ran time dependent simulations of SF6 from which the model mean age of air values were derived. The oldest air (5.5 to 6 years) occurred in the high latitude upper stratosphere during fall and early winter of both hemispheres, and in the southern hemisphere lower stratosphere during late winter and early spring. The latitudinal gradient of the mean ages also compare well with ER-2 aircraft observations in the lower stratosphere.
NASA Technical Reports Server (NTRS)
Lu, Rong; Turco, Richard P.
1994-01-01
Over the southern California coastal region, observations of the vertical distributions of pollutants show that maximum concentrations can occur within temperature inversion layers well above the surface. A mesoscale model is used to study the dynamical phenomena that cause such layers, including sea breezes and mountain flows, and to study the characteristics of air pollutant transport in a coastal environment capped by a temperature inversion. The mathematical and physical structure of the model is described. Two-dimensional simulations corresponding to four configurations of coastal plains and mountains are discussed. The simulations reveal that pollutant transport over a coastal plain is strongly influenced by the topographic configuration, including the height of coastal mountains and their distance from the coastline. Sea breezes induced by land-sea thermal contrasts, as well as upslope winds induced along mountain flanks, both create vertical transport that can lead to the formation of elevated pollution layers. The sea-breeze circulation generates pollution layers by undercutting the mixed layer and lofting pollutants into the stable layer. Heating of mountain slopes acts to vent pollutants above the mountain ridge during the day; during the evening, pollutants can be injected directly into the inversion layer from the decaying upslope flows. In a land-sea configuration with mountains close to the coastline, the sea breeze and heated-mountain flow are strongly coupled. In the afternoon, this interaction can produce upslope flow from which polluted air is detrained into the inversion layer as a return circulation. When the mountains lie farther inland, however, pollutants may be trapped aloft when the mixed layer stabilizes in the late afternoon. As the nocturnal boundary layer forms over the coast in the evening, polluted mixed-layer air is effectively left behind in the inversion layer. In the Los Angeles Basin, the formation mechanism for elevated polluted layers is most similar to our cases with inland mountains.
NASA Astrophysics Data System (ADS)
Kercek, A.; Hillebrandt, W.; Truran, J. W.
1998-09-01
We present the results of two-dimensional calculations of turbulent nuclear burning of hydrogen-rich material accreted onto a white dwarf of 1.0 Msun. The main aim of the present paper is to investigate the question as to whether and how the general properties of the burning are affected by numerical resolution effects. In particular, we want to see whether or not convective overshooting into the surface layers of the C+O white dwarf can lead to self-enrichment of the initially solar composition of the hydrogen-rich envelope with carbon and oxygen from the underlying white dwarf core. Our explicit hydrodynamic code is based on the PPM-method and computes the onset of the thermonuclear runaway on a Cartesian grid. Only part of the white dwarf's surface is covered by the computational grid and curvature effects are ignored. In contrast to previous works we do not observe fast mixing of carbon and oxygen from the white dwarf's surface into the envelope by violent overshooting of large eddies. The main features of the flow fields in our simulations are the appearance of small persistent coherent structures of very high vorticity (and velocity) compared to the background flow. Their typical linear scales are about 10 to 20 grid zones and thus their physical size depends on the numerical resolution, i.e, their size decreases with increasing resolution. For the early phase of the thermonuclear runaway (TNR) they dominate the flow patterns and result in very little overshoot and mixing. Only at late times, after steady slow mixing and with increasing nuclear energy production, do these structures become weak, but show up again once hydrogen has mainly been burnt and the energy generation rate drops. On the other hand, there are no big differences between high and low resolution simulations, as far as the overall properties of the TNR are concerned. The two simulations which are presented here show only moderate differences in spatially integrated quantities such as laterally averaged temperature, energy generation rate, and chemical composition. We have not expanded both simulations equally long, but for the physical time under consideration the major difference seems to be that the highly resolved simulation is a bit less violent. In conclusion, we do find some self-enrichment, but on time-scales much longer than in previous calculations.
NASA Technical Reports Server (NTRS)
Dryer, M.; Smith, Z. K.; Coates, A. J.; Johnstone, A. D.
1991-01-01
Large disturbances in the interplanetary medium were observed by several spacecraft during a period of enhanced solar activity in early February 1986. The locations of six solar flares and the spacecraft considered here encompassed more than 100 deg of heliolongitude. These flares during the minimum of cycle 21 set the stage for an extensive multispacecraft comparison performed with a two-dimensional, MHD numerical experiment. The plasma instruments on the Giotto spacecraft, on its way to encounter Comet Halley in March 1986, made measurements of the solar wind for up to 8 hours/day during February. Solar wind measurements from the Johnstone Plasma Analyzer experiment on Giotto are compared with the MHD simulation of the interplanetary medium throughout these events. Using plasma data obtained by the IMP-8 satellite in addition, it appears that an extended period of high solar wind speed is required as well as the simulated flares to represent the interplanetary medium in this case. The plasma and magnetometer data from Vega-1 is compared with the MHD simulation. This comparison tends to support an interpretation that the major solar wind changes at both Giotto and Vega-1 on February 8, 1986 were due to a shock from a W 05 deg solar flare on February 6, 1986 (06:25 UT). The numerical experiment is considered, qualitatively, to resemble the observations at the former spacecraft, but it has less success at the latter one.
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 observations. They primarily differ in the depth of the thermocline. The generation of mode-two waves and the behaviour of the waves in shallow water is sensitive to this depth. Rotation affects the shoaling waves by reducing the amplitude of the leading waves via the radiation of long trailing inertia-gravity waves. The nonlinear-dispersive evolution of these inertia-gravity waves results in the formation of secondary mode-one wave packets.
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.
Relativistic MHD simulations of stellar core collapse and magnetars
NASA Astrophysics Data System (ADS)
Font, Jos A.; Cerd-Durn, Pablo; Gabler, Michael; Mller, Ewald; Stergioulas, Nikolaos
2011-02-01
We present results from simulations of magneto-rotational stellar core collapse along with Alfvn oscillations in magnetars. These simulations are performed with the CoCoA/CoCoNuT code, which is able to handle ideal MHD flows in dynamical spacetimes in general relativity. Our core collapse simulations highlight the importance of genuine magnetic effects, like the magneto-rotational instability, for the dynamics of the flow. For the modelling of magnetars we use the anelastic approximation to general relativistic MHD, which allows for an effective suppression of fluid modes and an accurate description of Alfvn waves. We further compute Alfvn oscillation frequencies along individual magnetic field lines with a semi-analytic approach. Our work confirms previous results based on perturbative approaches regarding the existence of two families of quasi-periodic oscillations (QPOs), with harmonics at integer multiples of the fundamental frequency. Additional material is presented in the accompanying contribution by Gabler et al (2010b) in these proceedings.
MHD simulations of boundary layer formation along the dayside Venus ionopause due to mass loading
NASA Astrophysics Data System (ADS)
McGary, J. E.; Pontius, D. H.
1994-02-01
A two-dimensional magnetohydrodynamic (MHD) simulation of mass-loaded solar wind flow around the dayside of Venus is presented. For conditions appropriate to a low-altitude ionopause the simulations show that mass loading from the pickup of oxygen ions produces a boundary layer of finite thickness along the ionopause. Within this layer the temperatures exhibit strong gradients normal to and away from the ionopause. Furthermore, there is a shear in the bulk flow velocity across the boundary layer, such that the (predominantly tangential) flow decreases in speed as the ionopause is approached and remains small along the ionopause, consistent with Pioneer Venus observations. The total mass density increases significantly as the flow approaches the ionopause, where the contribution of O(+) to the total number density is a few percent. Numerical simulations are carried out for various mass addition rates and demonstrate that the boundary layer develops when oxygen ion production exceeds approximately 2 x 105/cu m/s. For the upstream solar wind parameters and mass loading rates chosen for these simulations, the results are consistent with observations made on the dayside of Venus for average ionopause conditions near 300 km.
NASA Astrophysics Data System (ADS)
Chung, Tracy N. H.; Liu, Chun-Ho
2013-07-01
Flow resistance, ventilation, and pollutant removal for idealized two-dimensional (2D) street canyons of different building-height to street-width (aspect) ratios AR are examined using the friction factor f, air exchange rate (ACH), and pollutant exchange rate (PCH), respectively, calculated by large-eddy simulation (LES). The flows are basically classified into three characteristic regimes, namely isolated roughness, wake interference, and skimming flow, as functions of the aspect ratios. The LES results are validated by various experimental and numerical datasets available in the literature. The friction factor increases with decreasing aspect ratio and reaches a peak at AR = 0.1 in the isolated roughness regime and decreases thereafter. As with the friction factor, the ACH increases with decreasing aspect ratio in the wake interference and skimming flow regimes, signifying the improved aged air removal for a wider street canyon. The PCH exhibits a behaviour different from its ACH counterpart in the range of aspect ratios tested. Pollutants are most effectively removed from the street canyon with AR = 0.5. However, a minimum of PCH is found nearby at AR = 0.3, at which the pollutant removal is sharply weakened. Besides, the ACH and PCH are partitioned into the mean and turbulent components to compare their relative contributions. In line with our earlier Reynolds-averaged Navier-Stokes calculations (Liu et al., Atmos Environ 45:4763-4769, 2011), the current LES shows that the turbulent components contribute more to both ACH and PCH, consistently demonstrating the importance of atmospheric turbulence in the ventilation and pollutant removal for urban areas.
NASA Astrophysics Data System (ADS)
Richert, Alexander J. W.; Lyra, Wladimir; Boley, Aaron; Mac Low, Mordecai-Mark; Turner, Neal
2015-05-01
Recent observations of gaps and non-axisymmetric features in the dust distributions of transition disks have been interpreted as evidence of embedded massive protoplanets. However, comparing the predictions of planet-disk interaction models to the observed features has shown far from perfect agreement. This may be due to the strong approximations used for the predictions. For example, spiral arm fitting typically uses results that are based on low-mass planets in an isothermal gas. In this work, we describe two-dimensional, global, hydrodynamical simulations of disks with embedded protoplanets, with and without the assumption of local isothermality, for a range of planet-to-star mass ratios 1-10 {{M}J} for a 1 {{M}? } star. We use the Pencil Code in polar coordinates for our models. We find that the inner and outer spiral wakes of massive protoplanets (M? 5 {{M}J}) produce significant shock heating that can trigger buoyant instabilities. These drive sustained turbulence throughout the disk when they occur. The strength of this effect depends strongly on the mass of the planet and the thermal relaxation timescale; for a 10 {{M}J} planet embedded in a thin, purely adiabatic disk, the spirals, gaps, and vortices typically associated with planet-disk interactions are disrupted. We find that the effect is only weakly dependent on the initial radial temperature profile. The spirals that form in disks heated by the effects we have described may fit the spiral structures observed in transition disks better than the spirals predicted by linear isothermal theory.
Plasmoid dynamics in 3D resistive MHD simulations of magnetic reconnection
NASA Astrophysics Data System (ADS)
Samtaney, R.; Loureiro, N. F.; Uzdensky, D. A.; Schekochihin, A. A.
2012-04-01
Magnetic reconnection is a well known plasma process believed to lie at the heart of a variety of phenomena such as sub-storms in the Earth's magnetosphere, solar/stellar and accretion-disk flares, sawteeth activity in fusion devices, etc. During reconnection, the global magnetic field topology changes rapidly, leading to the violent release of magnetic energy. Over the past few years, the basic understanding of this fundamental process has undergone profound changes. The validity of the most basic, and widely accepted, reconnection paradigm - the famous Sweet-Parker (SP) model, which predicts that, in MHD, reconnection is extremely slow, its rate scaling as S-1/2, where S is the Lundquist number of the system - has been called into question as it was analytically demonstrated that, for S ? 1, SP-like current sheets are violently unstable to the formation of a large number of secondary islands, or plasmoids. Subsequent numerical simulations in 2D have confirmed the validity of the linear theory, and shown that plasmoids quickly grow to become wider than the thickness of the original SP current sheet, thus effectively changing the underlying reconnection geometry. Ensuing numerical work has revealed that the process of plasmoid formation, coalescence and ejection from the sheet drastically modifies the steady state picture assumed by Sweet and Parker, and leads to the unexpected result that MHD reconnection is independent of S. In this talk, we review these recent developments and present results from three-dimensional simulations of high-Lundquist number reconnection in the presence of a guide field. A parametric study varying the strength of the guide field is presented. Plasmoid flux and width distribution functions are quantified and compared with corresponding two dimensional simulations.
Judi, David R; Mcpherson, Timothy N; Burian, Steven J
2009-01-01
A grid resolution sensitivity analysis using a two-dimensional flood inundation model has been presented in this paper. Simulations for 6 dam breaches located randomly in the United States were run at 10,30,60,90, and 120 meter resolutions. The dams represent a range of topographic conditions, ranging from 0% slope to 1.5% downstream of the dam. Using 10 meter digital elevation model (DEM) simulation results as the baseline, the coarser simulation results were compared in terms of flood inundation area, peak depths, flood wave travel time, daytime and nighttime population in flooded area, and economic impacts. The results of the study were consistent with previous grid resolution studies in terms of inundated area, depths, and velocity impacts. The results showed that as grid resolution is decreased, the relative fit of inundated area between the baseline and coarser resolution decreased slightly. This is further characterized by increasing over prediction as well as increasing under prediction with decreasing resolution. Comparison of average peak depths showed that depths generally decreased as resolution decreased, as well as the velocity. It is, however, noted that the trends in depth and velocity showed less consistency than the inundation area metrics. This may indicate that for studies in which velocity and depths must be resolved more accurately (urban environments when flow around buildings is important in the calculation of drag effects), higher resolution DEM data should be used. Perhaps the most significant finding from this study is the perceived insensitivity of socio-economic impacts to grid resolution. The difference in population at risk (PAR) and economic cost generally remained within 10% of the estimated impacts using the high resolution DEM. This insensitivity has been attributed to over estimated flood area and associated socio-economic impacts compensating for under estimated flooded area and associated socio-economic impacts. The United States has many dams that are classified as high-hazard potential that need an emergency action plan (EAP). It has been found that the development of EAPs for all high-hazard dams is handicapped due to funding limitations. The majority of the cost associated with developing an EAP is determining the flooded area. The results of this study have shown that coarse resolution dam breach studies can be used to provide an acceptable estimate of the inundated area and economic impacts, with very little computational cost. Therefore, the solution to limited funding may be to perform coarse resolution dam breach studies on high-hazard potential dams and use the results to help prioritize the order in which detailed EAPs should be developed.
Understanding Accretion Disks through Three Dimensional Radiation MHD Simulations
NASA Astrophysics Data System (ADS)
Jiang, Yan-Fei
I study the structures and thermal properties of black hole accretion disks in the radiation pressure dominated regime. Angular momentum transfer in the disk is provided by the turbulence generated by the magneto-rotational instability (MRI), which is calculated self-consistently with a recently developed 3D radiation magneto-hydrodynamics (MHD) code based on Athena. This code, developed by my collaborators and myself, couples both the radiation momentum and energy source terms with the ideal MHD equations by modifying the standard Godunov method to handle the stiff radiation source terms. We solve the two momentum equations of the radiation transfer equations with a variable Eddington tensor (VET), which is calculated with a time independent short characteristic module. This code is well tested and accurate in both optically thin and optically thick regimes. It is also accurate for both radiation pressure and gas pressure dominated flows. With this code, I find that when photon viscosity becomes significant, the ratio between Maxwell stress and Reynolds stress from the MRI turbulence can increase significantly with radiation pressure. The thermal instability of the radiation pressure dominated disk is then studied with vertically stratified shearing box simulations. Unlike the previous results claiming that the radiation pressure dominated disk with MRI turbulence can reach a steady state without showing any unstable behavior, I find that the radiation pressure dominated disks always either collapse or expand until we have to stop the simulations. During the thermal runaway, the heating and cooling rates from the simulations are consistent with the general criterion of thermal instability. However, details of the thermal runaway are different from the predictions of the standard alpha disk model, as many assumptions in that model are not satisfied in the simulations. We also identify the key reasons why previous simulations do not find the instability. The thermal instability has many important implications for understanding the observations of both X-ray binaries and Active Galactic Nuclei (AGNs). However, direct comparisons between observations and the simulations require global radiation MHD simulations, which will be the main focus of my future work.
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.
Coupled simulation of kinetic pedestal growth and MHD ELM crash
Park, G-Y; Cummings, J.; Chang, C S; Podhorszki, Norbert; Klasky, Scott A; Ku, S.; Pankin, A.; Samtaney, Ravi; Shoshani, A.; Snyder, P.; Sugiyama, L.
2009-01-01
Edge pedestal height and the accompanying ELM crash are critical elements of ITER physics yet to be understood and predicted through high performance computing. An entirely self-consistent first principles simulation is being pursued as a long term research goal, and the plan is planned for completion in time for ITER operation. However, a proof-of-principle work has already been established using a computational tool that employs the best first principles physics available at the present time. A kinetic edge equilibrium code XGC0, which can simulate the neoclassically dominant pedestal growth from neutral ionization (using a phenomenological residual turbulence diffusion motion superposed upon the neoclassical particle motion) is coupled to an extended MHD code M3D, which can perform the nonlinear ELM crash. The stability boundary of the pedestal is checked by an ideal MHD linear peeling-ballooning code, which has been validated against many experimental data sets for the large scale (type I) ELMs onset boundary. The coupling workflow and scientific results to be enabled by it are described.
Coupled simulation of kinetic pedestal growth and MHD ELM crash
Park, G.; Cummings, J.; Chang, C. S.; Klasky, Scott A; Ku, S.; Podhorszki, Norbert; Pankin, A.; Samtaney, Ravi; Shoshani, A.; Snyder, P.; Strauss, H.; Sugiyama, L.; CPES Team, the
2007-01-01
Edge pedestal height and the accompanying ELM crash are critical elements of ITER physics yet to be understood and predicted through high performance computing. An entirely self-consistent first principles simulation is being pursued as a long term research goal, and the plan is planned for completion in time for ITER operation. However, a proof-of-principle work has already been established using a computational tool that employs the best first principles physics available at the present time. A kinetic edge equilibrium code XGC0, which can simulate the neoclassically dominant pedestal growth from neutral ionization (using a phenomenological residual turbulence diffusion motion superposed upon the neoclassical particle motion) is coupled to an extended MHD code M3D, which can perform the nonlinear ELM crash. The stability boundary of the pedestal is checked by an ideal MHD linear peeling-ballooning code, which has been validated against many experimental data sets for the large scale (type I) ELMs onset boundary. The coupling workflow and scientific results to be enabled by it are described.
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)
Forjan, Gary F.
2009-06-01
Explaining the nature of the million degree solar corona is a question that has been challenging astrophysicists for over 60 years. While many theories have been proposed to explain the nature of the heating mechanism, there is as yet no single answer to this question. An important step toward finding a solution would be to first determine where in the atmosphere the heating is occurring, for this would narrow the different theoretical possibilities for its cause. >From an observational standpoint, recent measurements by instruments on the Solar and Heliospheric Observatory (SOHO) and Transition Region and Coronal Explorer (TRACE) spacecraft revealed that many coronal loops in active regions on the sun are nearly isothermal in their coronal parts. Loop modeling using pseudo-stereoscopic methods applied to SOHO EIT data indicated that temperature gradients were much smaller than predicted from scaling laws. From these and other observations, some authors conclude that the heating results from processes operating in the chromospheric and transition regions. On the other hand, many observed loop properties may be explained by assuming that the heating mechanism is due to the idea of tangled magnetic fields combined with a growing instability that becomes turbulent and releases impulsive energy through magnetic reconnection. Some authors claim that these energy releases occur at higher altitudes in the corona and are responsible for supplying the majority of coronal heating. Clearly, current observations along with numerical modeling results are interpreted differently depending on the researcher and vigorous debate continues over the nature of the heating process and whether it is located near the chromosphere/lower transition region or in the corona. In this work we attempt to determine if there are observational discriminators derived through computer modeling that can distinguish where the heating occurs. To accomplish this we first use an astrophysical magneto-hydrodynamics computer code to model a solar flux tube having the physical conditions of a one million degree quiet sun corona. A series of experiments is then performed in which energy of various durations and peak intensities is injected at different locations along the flux tube. These experiments are evolved over time and the differences in the temperature, density and velocity profiles are observed. In performing the simulations, the details of the energy transport processes including thermal conduction, convection, radiative cooling, and the nature of the heating sources are studied. The purpose in examining these processes is that they give insight into the validity of various assumptions used by other authors in their analytical models of the corona. It is expected that the determination of the positional and temporal characteristics of the heating will lead to an understanding of the exact physical process responsible for the heating. Most work currently being done in coronal modeling is accomplished with limited one-dimensional codes that do not include a magnetic field. The primary justification for using such codes is that thermal conduction is constrained to operate only along the magnetic field lines. Our work uses a two-dimensional code and includes a magnetic field. This is more physically realistic and allows for the examination of any interaction between the plasma and the magnetic field. In the course of performing these experiments, a major computational goal was to develop the computer code needed to correctly model conduction only along the field lines and quantitatively compare the effects of isotropic vs. magnetic field-aligned thermal conduction on the evolution of the plasma in the flux tube. The results indicate that assuming all conduction is along the loop axis in one-dimensional loop models is more accurate than assuming isotropic conduction in multi-dimensional models. However, there are differences between the one-dimensional and two-dimensional models. Our work has produced three main results. First, we developed the techniques and computer code to model physically correct conduction as a vector quantity in multi-dimensional magnetohydrodynamic codes. Secondly, the results of our calculations under solar coronal conditions indicate that one-dimensional models are more accurate than two-dimensional models with isotropic conduction. Finally, there are differences in the dynamics of coronal loops depending on where energy release occurs but that there are currently no observations capable of detecting these differences.
MHD simulations of ram pressure stripping of a disk galaxy
NASA Astrophysics Data System (ADS)
Ramos, Mariana; Gomez, Gilberto
2015-08-01
The removal of the ISM of disk galaxies through ram pressure stripping (RPS) has been extensively studied in numerous simulations. These models show that this process has a significant impact on galaxy evolution (the truncation of the ISM will lead to a decrease in the star formation and the galaxy will become redder).Nevertheless, the role of the magnetic fields (MFs) on the dynamics of the gas in this process has been hardly studied, although the influence of magnetic fields on the large scale disk structure is well established. The presence of MFs produce a less compressible gas, thus increasing the scale height of the gas in the galaxy, that is, gas can be found farther away from the galactic potential well, which may lead to an easier removal of gas. We test this idea by performing a 3D MHD simulation of a disk galaxy that experiences RPS under the wind-tunnel approximation.
MHD Simulations of Earth's Bow Shock at low Mach Numbers: Standoff Distances
NASA Technical Reports Server (NTRS)
Cairns, Iver H.; Lyon, J. G.
1995-01-01
Global, three-dimensional, ideal MHD simulations of Earth's bow shock are reported for low Alfven Mach numbers M(sub A) and quasi-perpendicular magnetic field orientations. The simulations use a hard, infinitely conducting magnetopauause obstacle, with axisymmetric three-dimensional location given by scaled standard model, to directly address previous gasdynamic (GD) and field-aligned MHD (FA-MHD) work. Tests of the simulated shocks' density jumps X for 1.4 approx. less than MA approx. less than 10 and the high M(sub A) shock location, and reproduction of the GD relation between magnetosheath thickness and X for quasi-gasdynamic MHD runs with M(sub A) much greater than M(sub s), confirm that the MHD code is working correctly. The MHD simulations show the standoff distance a(sub s), increasing monotonically with decreasing M(sub A). Significantly larger a(sub s), are found at low M(sub A) than predicted by GD and phenomenological MHD models and FA-MHD simulations, as required qualitatively by observations. The GD and FA-MHD predictions err qualitatively, predicting either constant or decreasing a(sub s), with decreasing M(sub A). This qualitative difference between quasi- perpendicular MHD and FA-MHD simulations is direct evidence for a(sub s), depending on the magnetic field orientation Theta. The enhancement factor over the phenomenological MHD predictions at MA approx. 2.4 agrees quantitatively with one observatiorial estimate. A linear relationship is found between the magnetosheath thickness and X, modified both quantitatively and intrinsically by MHD effects from the GD result. The MHD and GD results agree in the high M(sub A) limit. An MHD theory is developed for a(sub s), restricted to sufficiently perpendicular Theta and high sonic Mach numbers M(sub s). It explains the simulation results with excellent accuracy. Observational and further simulation testing of this MHD theory, and of its predicted M(sub A), Theta, and M(sub s) effects, is desirable.
Final Report: "Large-Eddy Simulation of Anisotropic MHD Turbulence"
Zikanov, Oleg
2008-06-23
To acquire better understanding of turbulence in flows of liquid metals and other electrically conducting fluids in the presence of steady magnetic fields and to develop an accurate and physically adequate LES (large-eddy simulation) model for such flows. The scientific objectives formulated in the project proposal have been fully completed. Several new directions were initiated and advanced in the course of work. Particular achievements include a detailed study of transformation of turbulence caused by the imposed magnetic field, development of an LES model that accurately reproduces this transformation, and solution of several fundamental questions of the interaction between the magnetic field and fluid flows. Eight papers have been published in respected peer-reviewed journals, with two more papers currently undergoing review, and one in preparation for submission. A post-doctoral researcher and a graduate student have been trained in the areas of MHD, turbulence research, and computational methods. Close collaboration ties have been established with the MHD research centers in Germany and Belgium.
Simulations of Pulse Detonation Engines with MHD Thrust Augmentation
NASA Astrophysics Data System (ADS)
Zeineh, Christopher; Roth, Timothy; Cole, Lord; Karagozian, Ann; Cambier, Jean-Luc
2008-11-01
Pulse detonation rocket engines (PDREs) have received significant attention in recent years due to their potentially superior performance over constant-pressure engines. Yet unsteady chamber pressures cause the PDRE flow to be either over-expanded or under-expanded for the majority of the cycle, with substantial performance loss in atmospheric flight applications. The present computational studies examine the potential benefits of using magneto-hydrodynamic (MHD) thrust augmentation by extracting energy via a generator in the PDRE nozzle and applying it to a separate, secondary stream. In the present studies, which involve both transient quasi-1D and 2D numerical simulations, the energy extracted from the nozzle flow is directly applied to a by-pass air stream through an MHD accelerator. The air stream is first shocked by the under-expanded nozzle flow and raised to high temperature, allowing thermal ionization. The specific conditions for thrust augmentation are examined. Alternative configurations utilizing a magnetic piston in the PDRE chamber are also explored. Results show potential performance gains but with significant challenges, depending on the operating and flight conditions.
MHD Simulation of the HIT-SI Experiment
NASA Astrophysics Data System (ADS)
Marklin, George
2003-10-01
The Helicity Injected Torus (HIT) experiment at the University of Washington has been reconfigured into a high beta spheromak with steady state AC current drive [1]. Helicity is injected by two half torus Reversed Field Pinches (RFP's) connected to the ends of the cylindrically symmetric flux conserver, rotated by 90 degrees from each other. The RFP's are driven with sinusoidally varying voltage and flux. Each side has its voltage and flux in phase, but is 90 degrees out of phase from the other side. The helicity injection rate, which is proportional to the voltage times the flux, goes like sin(wt)^2 on one side and cos(wt)^2 on the other, making the total injection rate constant in time. The complex multiply connected 3-dimensional geometry of this device make it difficult to simulate with existing codes that typically use a structured mesh. This poster will describe a new 3D MHD simulation code and a new 3D Taylor state code which both use an unstructured finite element mesh. The mesh is generated from a CAD-like description of an arbitrary arrangement of 3D geometrical objects. Taylor states in the HIT-SI geometry will be shown for different combinations of fluxes in the two injectors. MHD simulation results will be shown starting from a Taylor state with uniform density and temperature and continuing through several cycles of time dependent helicity injection. Field line tracing plots will show the quality of the flux surfaces at various stages in the injection cycle. [1] T. R. Jarboe, Fusion Technology, vol. 36, p. 85, 1999
NASA Astrophysics Data System (ADS)
Passos, D. M. D. C.; Charbonneau, P.
2014-12-01
The steady advance in computer power has finally enabled us to explore the solar dynamo problem by means of 3D global magnetohydrodynamical (MHD) simulations of the convection zone.Using the EULAG-MHD code, we have succeeded in producing simulations of the Sun's magnetic activity cycles that resemble the observed evolutionary patterns of the large-scale solar magnetic field. In these simulations the anelastic ideal MHD equations are solved in a thick, rotating shell of electrically conducting fluid, under solar-like stratification and thermal forcing. Since these simulations are fully dynamical in all time and spatial resolved scales, they achieve highly turbulent regimes and naturally produce variable amplitude solutions.We have recently been able to produce a simulation that spans for 1650 years and that produced 40 complete sunspot like cycles, the longest of its kind so far.This allows to perform statistical studies and establish direct comparisons with the observed solar cycle. Some of the main similarities and differences between the statistical properties of simulated and observed cycles are presented here (e.g. evidence for Gnevyshev-Ohl patterns, Gleissberg modulation or hemispheric coupling). Additionally, by studying the behaviour of the large scale flows in the simulation (differential rotation and meridional circulation) we also find evidence for solar cycle modulation of the deep equatorward flow in the meridional circulation. This result is briefly discussed as well as its implications for current helioseismic measurement methodologies and for classical kinematic mean-field flux transport dynamo simulations.
NASA 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.
3D MHD disruptions simulations of tokamaks plasmas
NASA Astrophysics Data System (ADS)
Paccagnella, Roberto; Strauss, Hank; Breslau, Joshua
2008-11-01
Tokamaks Vertical Displacement Events (VDEs) and disruptions simulations in toroidal geometry by means of a single fluid visco-resistive magneto-hydro-dynamic (MHD) model are presented in this paper. The plasma model, implemented in the M3D code [1], is completed with the presence of a 2D homogeneous wall with finite resistivity. This allows the study of the relatively slowly growing magneto-hydro-dynamical perturbation, the resistive wall mode (RWM), which is, in this work, the main drive of the disruptions. Amplitudes and asymmetries of the halo currents pattern at the wall are also calculated and comparisons with tokamak experimental databases and predictions for ITER are given. [1] W. Park, E.V. Belova, G.Y. Fu, X.Z. Tang, H.R. Strauss, L.E. Sugiyama, Phys. Plasmas 6 (1999) 1796.
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.
NASA Technical Reports Server (NTRS)
Denton, R.; Sonnerup, B. U. O.; Swisdak, M.; Birn, J.; Drake, J. F.; Heese, M.
2012-01-01
When analyzing data from an array of spacecraft (such as Cluster or MMS) crossing a site of magnetic reconnection, it is desirable to be able to accurately determine the orientation of the reconnection site. If the reconnection is quasi-two dimensional, there are three key directions, the direction of maximum inhomogeneity (the direction across the reconnection site), the direction of the reconnecting component of the magnetic field, and the direction of rough invariance (the "out of plane" direction). Using simulated spacecraft observations of magnetic reconnection in the geomagnetic tail, we extend our previous tests of the direction-finding method developed by Shi et al. (2005) and the method to determine the structure velocity relative to the spacecraft Vstr. These methods require data from four proximate spacecraft. We add artificial noise and calibration errors to the simulation fields, and then use the perturbed gradient of the magnetic field B and perturbed time derivative dB/dt, as described by Denton et al. (2010). Three new simulations are examined: a weakly three-dimensional, i.e., quasi-two-dimensional, MHD simulation without a guide field, a quasi-two-dimensional MHD simulation with a guide field, and a two-dimensional full dynamics kinetic simulation with inherent noise so that the apparent minimum gradient was not exactly zero, even without added artificial errors. We also examined variations of the spacecraft trajectory for the kinetic simulation. The accuracy of the directions found varied depending on the simulation and spacecraft trajectory, but all the directions could be found within about 10 for all cases. Various aspects of the method were examined, including how to choose averaging intervals and the best intervals for determining the directions and velocity. For the kinetic simulation, we also investigated in detail how the errors in the inferred gradient directions from the unmodified Shi et al. method (using the unperturbed gradient) depended on the amplitude of the calibration errors. For an accuracy of 3 for the maximum gradient direction, the calibration errors could be as large as 3% of reconnection magnetic field, while for the same accuracy for the minimum gradient direction, the calibration errors could only be as large as 0.03% of the reconnection magnetic field. These results suggest that the maximum gradient direction can normally be determined by the unmodified Shi et al. method, while the modified method or some other method must be used to accurately determine the minimum gradient direction. The structure velocity was found with magnitude accurate to 2% and direction accurate to within 5%.
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.
CASIM : A Multi-fluid MHD Cometary Atmosphere Simulator
NASA Astrophysics Data System (ADS)
Benna, M.; Mahaffy, P. R.
2004-12-01
We present new results of our Cometary Atmosphere Simulation (CASIM) code that is presently under development to model the interaction of a cometary atmosphere with the solar wind. Several high-resolution 2-D simulations for a Halley-type comet are shown. In the current simulations we investigate more precisely the evolution of the interaction between the cometary atmosphere and the solar wind starting from the early stages of the comet outgassing ( 5. a.u.) to the peak of its activity ( 1.5 a.u.). Our code is based on the solution of the multi-fluid MHD equations using an efficient adaptively refined cartesian mesh solver that provides a very high resolution over a large space domain (simulation domain 10^8 km, highest resolution 25 m). The multi-fluid approach we chose leads to a more accurate representation of the cometary atmosphere since additional details of the interaction between the neutral gas and the plasma, and their resulting structures are revealed. In particular, the multi-fluid representation of the ion population gives an improved view of the coupling between heavy and light ions and the resulting coma boundaries at different spatial scales. This research is sponsored by NASA and the National Academies.
NASA Astrophysics Data System (ADS)
Lei, Jie; Zhu, Da-Peng; Xu, Ming-Chun; Hu, Shu-Jun
2015-10-01
By applying the on-site Coulomb interaction corrections on the anion:2p and the cation:3d electrons, we find that the GGA + U approach can completely compensate the underestimation of band gap of ZnO and GaN, two wide band gap semiconductors. Based on such approach, we investigate the electronic structure of ZnO/GaN (0001) heterostructure, particularly for the two dimensional electron gas formed near the polar interface. The polarization difference between ZnO and GaN induces the surface charge, resulting in the accumulation of band electrons on the N-polar interface.
Combis, Patrick; Cormont, Philippe; Hebert, David; Robin, Lucile; Rullier, Jean-Luc; Gallais, Laurent
2012-11-19
A self-consistent approach is proposed to determine the temperature dependent thermal conductivity k(T) of fused silica, for a range of temperatures up to material evaporation using a CO{sub 2} laser irradiation. Calculation of the temperature of silica using a two-dimensional axi-symmetric code was linked step by step as the laser power was increased with experimental measurements using infrared thermography. We show that previously reported k(T) does not reproduce the temporal profile as well as our adaptive fit which shows that k(T) evolves with slope discontinuities at the annealing temperature and the softening temperature.
NASA Astrophysics Data System (ADS)
Combis, Patrick; Cormont, Philippe; Gallais, Laurent; Hebert, David; Robin, Lucile; Rullier, Jean-Luc
2012-11-01
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 CO2 laser irradiation. Calculation of the temperature of silica using a two-dimensional axi-symmetric code was linked step by step as the laser power was increased with experimental measurements using infrared thermography. We show that previously reported k(T) does not reproduce the temporal profile as well as our adaptive fit which shows that k(T) evolves with slope discontinuities at the annealing temperature and the softening temperature.
NASA Astrophysics Data System (ADS)
Hur, Min Sup; Wurtele, Jonathan S.
2009-04-01
Focusing of an intense laser pulse produced by backward Raman pulse amplification (BRA) has been numerically studied using a two-dimensional, axisymmetric kinetic model. The two-dimensional averaged particle-in-cell (aPIC) simulation assumes slowly varying field envelopes and is comprised of one-dimensional sub-models that are coupled radially through laser diffraction. A converging 33 TW seed pulse was amplified up to 1 PW. The focusing of the seed pulse, even when particle trapping was important, was maintained. It was also found that the focusing properties of the pulse tail can lead to some rewidening of the longitudinal pulse duration and some ideas for eliminating this effect were suggested. Simulations performed for various plasma densities and temperatures exhibited robust amplification and pulse shortening.
MHD Simulations of the Plasma Flow in the Magnetic Nozzle
NASA Technical Reports Server (NTRS)
Smith, T. E. R.; Keidar, M.; Sankaran, K.; olzin, K. A.
2013-01-01
The magnetohydrodynamic (MHD) flow of plasma through a magnetic nozzle is simulated by solving the governing equations for the plasma flow in the presence of an static magnetic field representing the applied nozzle. This work will numerically investigate the flow and behavior of the plasma as the inlet plasma conditions and magnetic nozzle field strength are varied. The MHD simulations are useful for addressing issues such as plasma detachment and to can be used to gain insight into the physical processes present in plasma flows found in thrusters that use magnetic nozzles. In the model, the MHD equations for a plasma, with separate temperatures calculated for the electrons and ions, are integrated over a finite cell volume with flux through each face computed for each of the conserved variables (mass, momentum, magnetic flux, energy) [1]. Stokes theorem is used to convert the area integrals over the faces of each cell into line integrals around the boundaries of each face. The state of the plasma is described using models of the ionization level, ratio of specific heats, thermal conductivity, and plasma resistivity. Anisotropies in current conduction due to Hall effect are included, and the system is closed using a real-gas equation of state to describe the relationship between the plasma density, temperature, and pressure.A separate magnetostatic solver is used to calculate the applied magnetic field, which is assumed constant for these calculations. The total magnetic field is obtained through superposition of the solution for the applied magnetic field and the self-consistently computed induced magnetic fields that arise as the flowing plasma reacts to the presence of the applied field. A solution for the applied magnetic field is represented in Fig. 1 (from Ref. [2]), exhibiting the classic converging-diverging field pattern. Previous research was able to demonstrate effects such as back-emf at a super-Alfvenic flow, which significantly alters the shape of the magnetic field in both the near- and far-field regions. However, in that work the downstream domain was constrained to a channel of constant cross-sectional area. In the present work we seek to address this issue by modeling the downstream region with a domain that permits free expansion of the plasma, permitting a better evaluation of the downstream effects the applied field has on the plasma. The inlet boundary conditions and applied magnetic field values will also be varied to determine the effect the initial plasma energy content and applied magnetic field energy density have on the near- and far-field plasma properties on the MHD code. This will determine the effect of inlet boundary conditions on the results downstream and address issues related to the restrictive numerical domain previously used.
NASA Astrophysics Data System (ADS)
Wu, Benxin; Shin, Yung C.
2007-05-01
In laser shock peening (LSP) under a water-confinement regime, laser-matter interaction near the coating-water interface can induce very high pressures in the order of gigapascals, which can impart compressive residual stresses into metal workpieces to improve fatigue and corrosion properties. For axisymmetric laser spots with finite size, the pressure generation near the water-coating interface is a two dimensional process in nature. This is in particular the case for microscale LSP performed with very small laser spots, which is a very promising technique to improve the reliability performance of microdevices. However, models capable of predicting two dimensional (2D) spatial distributions of the induced pressures near the coating-water interface in LSP have rarely been reported in literature. In this paper, a predictive 2D axisymmetric model is developed by numerically solving the hydrodynamic equations, supplemented with appropriate equations of state of water and the coating material. The model can produce 2D spatial distributions of material responses near the water-coating interface in LSP, and is verified through comparisons with experimental measurements. The model calculation shows that the effect of radial release wave on pressure spatial distributions becomes more significant as the laser spot size decreases, indicating the importance of a 2D model, particularly for microscale LSP.
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.
MHD Simulation of RF Current Drive in MST
NASA Astrophysics Data System (ADS)
Goetz, J. A.; Hendries, E. R.; Anderson, J. K.; Forest, C. B.; Reusch, J. A.; Seltzman, A. H.; Sovinec, C. R.; Diem, S.; Harvey, R. W.
2013-10-01
Auxiliary current drive using the electron Bernstein wave (EBW) may advance the performance of the RFP. In prior computations, a hypothetical edge-localized current is shown to suppress tearing activity that governs transport in the RFP. Ideal conditions for tearing stabilization include reduced toroidal induction, and precise width and radial position of the current drive. To support MST EBW studies, an integrated modeling scheme incorporates ray tracing and Fokker-Plank predictions of auxiliary current into single fluid MHD. Simulations at low Lundquist number (S ~ 104) agree with the previous work but at MST-like S (S ~ 3 106) show unexpected results. The effect on the current profile by the rf-driven force decreases in magnitude and widens considerably as S increases. Simulations reproduce the experimentally observed periodic current profile relaxation events (sawteeth). With rf drive, reduction of tearing mode amplitudes is seen, but is limited to periods between each sawtooth, which persist with up to 10 MW of rf. Prolonged low tearing amplitudes are predicted with the combination of current drive and reduced toroidal loop voltage, consistent with previous conclusions. Finally, these simulations show that the resistivity profile has a strong effect on the optimal current drive profile for mode stabilization. Work supported by US DoE.
Moran, S. D.; Preketes, N. K.; Zhang, T. O.; Zanni, M. T.; Mukamel, S.
2013-01-01
Cataracts is a misfolding protein disease in which one of its major components is the γD-crystallin protein. The conformational structure of the aggregated γD-crystallin and the interactions that cause aggregation are largely unknown. A recent experimental two-dimensional infrared (2DIR) spectroscopy study determined that the C-terminal domain has a high propensity to form β-sheets whereas the N-terminal domain forms a disordered structure in the fiber state. We present a combined computational molecular dynamics (MD) and infrared spectroscopy study of the local dynamics of these domains. The computed 2DIR signals agree remarkably well with experiment. We show that both domains having a Greek key structural fold experience different electrostatic environments, which may be related to the fact that the C-terminal domain is more structurally stable than the N-terminal domain. We correlate the vibrational couplings to known energy dissipation mechanisms and reveal their origin. PMID:23972032
NASA Astrophysics Data System (ADS)
Fan, Shuangli; Zhong, Fan
2009-01-01
We study two-dimensional q -state random-bond Potts models for both q=8 and q=5 with a linearly varying temperature. By applying a successive Monte Carlo renormalization group procedure, both the static and dynamic critical exponents are obtained for randomness amplitudes (the strong to weak coupling ratio) of r0=3 , 10, 15, and 20. The correlation length exponent ? increases with disorder from less than to larger than unity and this variation is justified by the good collapse of the specific heat near the critical region. The specific heat exponent is obtained by the usual hyperscaling relation ?=2-d? and thus indicates no possibility of the activated dynamic scaling. Both r0 and q have effects on the critical dynamics of the disordered systems, which can be seen from variations of the rate exponent, the hysteresis exponent, and the dynamic critical exponent. Implications of these results are discussed.
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.
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.
Multifluid MHD Simulation of the Magnetosphere of Uranus
NASA Astrophysics Data System (ADS)
Cao, X.; Paty, C. S.
2013-12-01
The interaction between Uranus' intrinsic magnetic field and the solar wind is quite different from the magnetospheric interactions of the Earth, Mercury, Jupiter and Saturn due to several factors. 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 initial 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. Specifically we compare these characteristics modeled for solstice conditions, when the solar wind is directed nearly parallel to the rotation axis, and equinox conditions, when the solar wind is nearly perpendicular to the rotation axis. The Voyager 2 spacecraft encountered Uranus near solstice, and was able to observed the magnetic field structure and plasma characteristics of a twisted magnetotail [Behannon et al., 1987], and we use such magnetometer and plasma observations as a basis for benchmarking our simulations for the solstice scenario. The equinox geometry has no flyby observations for comparison, but recent auroral observations made by the Hubble Space Telescope [Lamy et al., 2012] give some indication of the magnetospheric interaction with the solar wind.
MHD simulations of the parametric decay of large-amplitude Alfven waves in the expanding solar wind
NASA Astrophysics Data System (ADS)
Del Zanna, Luca; Landi, Simone; Matteini, Lorenzo; Verdini, Andrea; Velli, Marco
2015-04-01
The nonlinear evolution and parametric decay of large-amplitude Alfven are investigated by performing two-dimensional, compressible MHD simulations within the expanding box model, to mimic the waves propagation in the solar wind plasma. The linear and nonlinear phases of the parametric decay instability are studied for both circularly polarized waves in parallel propagation and for arc-polarized waves in oblique propagation, in the monochromatic case and in the presence of a spectrum of modes. In the oblique case, direct excitation of daughter modes transverse to the local background field is observed, and this transverse cascade seems to be favored for monochromatic mother waves. The expansion effect reduces the instability growth rate, and it can even suppress its onset for the lowest frequency modes considered here, possibly explaining the persistence of these outgoing waves in the solar wind.
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.
Preliminary analysis of the dynamic heliosphere by MHD simulations
Washimi, H.; Zank, G. P.; Tanaka, T.
2006-09-26
A preliminary analysis of the dynamic heliosphere to estimate the termination shock (TS) distance from the sun around the time when Voyager 1 passed the termination shock at December 16, 2004 is performed by using MHD simulations. For input to this simulation, we use the Voyager 2 solar-wind data. We first find a stationary solution of the 3-D outer heliosphere by assigning a set of LISM parameters as our outer boundary conditions and then the dynamical analysis is performed. The model TS crossing is within 6 months of the observed date. The TS is pushed outward every time a high ram-pressure solar wind pulse arrives. After the end of the high ram-pressure wind, the TS shock shrinks inward. When the last Halloween event passed through the TS at DOY 250, 2004, the TS began to shrink inward very quickly and the TS crossed V1. The highest inward speed of the TS is over 400 km/s. The high ram-pressure solar wind transmitted through the TS becomes a high thermal-pressure plasma in the heliosheath, acting to push the TS inward. This suggests that the position of the TS is determined not only by the steady-state pressure balance condition between the solar wind ram-pressure and the LISM pressure, but by the dynamical ram pressure too. The period when the high ram-pressure solar wind arrives at the TS shock seems to correspond to the period of the TS particle event (Stone et al, 2005, Decker et al., 2005). The TS crossing date will be revised in future simulations using a more appropriate set of parameters for the LISM. This will enable us to undertake a detailed comparison of the simulation results with the TS particle events.
Observations and MHD Simulations for a Shocked Magnetotail
NASA Astrophysics Data System (ADS)
Zhou, X.; Zhou, X. Z.; Angelopoulos, V.; Raeder, J.; Oliveira, D.; Shi, Q.
2014-12-01
Recent studies disclosed that interplanetary shocks not only raise global auroral activity, but also cause significant tail disturbances, ranging from ULF wave excitation to abrupt cross-tail current sheet thinning and current density increase, generation of burst bulk flows and dipolarization fronts, and to magnetic reconnection enhancement. In addition, shocks can also cause significant deformation of the magnetotail at ~60 Re and beyond. In this paper we study a shock event using ARTEMIS in situ observations and OpenGGCM MHD simulations. The two ARTEMIS spacecraft were located near the tail current sheet and lobe center at (-60, 1, -5Re_GSM) when the shock arrived and recorded an abrupt tail compression leading to significant enhancements in the plasma density, temperature, magnetic field strength, and cross-tail current density, as well as to tailward flows. However, ~10 min later, the spacecraft entered the sheath solar wind unexpectedly. Two hypotheses are considered: either the tail was cut off by the high solar wind ram pressure (~25-30 nPa), or the compressed tail was pushed aside by the appreciable Vy solar wind flow component imposed by the shock. OpenGGMC simulation results confirmed the second hypothesis and disclosed that for this event the magnetic pressure played a dominant role at X=-60 Re for the compression. In addition to the shock normal direction and shock compression, the anisotropic (transverse) magnetic pressure also contributed to the significant reduction of the lobe Y dimension. Therefore, during this 10 min interval, the lobe center moved dawnward by ~12 Re and the tail width in Y was reduced from 40 to 26 Re, which eventually exposed ARTEMIS to the sheath solar wind. Comparisons of plasma and magnetic parameters between ARTEMIS in situ observations and simulations showed a satisfied consistence.
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.
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. PMID:25945848
Equilibrium Flows in Non-linear MHD Simulations of X-point Plasmas
Pamela, S.; Huysmans, G. T. A.
2008-11-01
In non-linear MHD simulations of ELMs, a radially localised, toroidally symmetric, poloidal flow layer exists in the H-mode pedestal region. This sheared flow layer could have a significant influence on the linear stability properties of MHD instabilities and their non-linear evolution. Using the non-linear MHD simulation code JOREK with reduced resistive MHD equations, we study the edge-localised poloidal flow in both circular and X-point tokamak plasmas at equilibrium (toroidal symmetry). For the circular case, an analytical interpretation is derived. In the simulations of X-point plasmas, the flow can have both m = 0 and m = 1 components. In fact, abrupt transitions take place between the two equilibrium states, accompanied by a strong increase in the kinetic energy. Similar transitions between equilibrium flow states have been predicted by Strauss for m = 0 poloidal flow patterns. Scalings are obtained for both the m = 1 and m = 0 flows.
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.
RANS Simulations of the Tilted Rig Experiment:A Two-dimensional Rayleigh-Taylor Instability Case
NASA Astrophysics Data System (ADS)
Denissen, Nicholas; Rollin, Bertran; Reisner, Jon; Andrews, Malcolm
2012-11-01
Modeling turbulent mixing due to unstable density stratification is of fundamental interest in many multiphysics applications. RANS models remain the tool of choice for efficient estimates of the effects of turbulence on complex problems. While many RANS models have been validated for canonical Rayleigh-Taylor turbulence, applications of interest often have non-planar/dynamic interfaces. This presentation will address the ability of a multispecies, compressible, turbulence model to compute RT mixing on a moving interface. The simulations are based on the tilted rocket-rig experiments designed to study mixing of fluids by the Rayleigh-Taylor instability. In this experiment, a tank containing two fluids of different densities is accelerated downward with the rig inclined by a few degrees off vertical. The RANS simulations are be compared to experiments, direct numerical simulations and large eddy simulations to analyze the model's ability to capture 2D flow features.
Relativistic MHD simulations of poynting flux-driven jets
Guan, Xiaoyue; Li, Hui; Li, Shengtai
2014-01-20
Relativistic, magnetized jets are observed to propagate to very large distances in many active galactic nuclei (AGNs). We use three-dimensional relativistic MHD simulations to study the propagation of Poynting flux-driven jets in AGNs. These jets are already assumed to be being launched from the vicinity (?10{sup 3} gravitational radii) of supermassive black holes. Jet injections are characterized by a model described in Li et al., and we follow the propagation of these jets to ?parsec scales. We find that these current-carrying jets are always collimated and mildly relativistic. When ?, the ratio of toroidal-to-poloidal magnetic flux injection, is large the jet is subject to nonaxisymmetric current-driven instabilities (CDI) which lead to substantial dissipation and reduced jet speed. However, even with the presence of instabilities, the jet is not disrupted and will continue to propagate to large distances. We suggest that the relatively weak impact by the instability is due to the nature of the instability being convective and the fact that the jet magnetic fields are rapidly evolving on Alfvnic time scales. We present the detailed jet properties and show that far from the jet launching region, a substantial amount of magnetic energy has been transformed into kinetic energy and thermal energy, producing a jet magnetization number ? < 1. In addition, we have also studied the effects of a gas pressure supported 'disk' surrounding the injection region, and qualitatively similar global jet behaviors were observed. We stress that jet collimation, CDIs, and the subsequent energy transitions are intrinsic features of current-carrying jets.
Relativistic MHD Simulations of Poynting Flux-driven Jets
NASA Astrophysics Data System (ADS)
Guan, Xiaoyue; Li, Hui; Li, Shengtai
2014-01-01
Relativistic, magnetized jets are observed to propagate to very large distances in many active galactic nuclei (AGNs). We use three-dimensional relativistic MHD simulations to study the propagation of Poynting flux-driven jets in AGNs. These jets are already assumed to be being launched from the vicinity (~103 gravitational radii) of supermassive black holes. Jet injections are characterized by a model described in Li et al., and we follow the propagation of these jets to ~parsec scales. We find that these current-carrying jets are always collimated and mildly relativistic. When ?, the ratio of toroidal-to-poloidal magnetic flux injection, is large the jet is subject to nonaxisymmetric current-driven instabilities (CDI) which lead to substantial dissipation and reduced jet speed. However, even with the presence of instabilities, the jet is not disrupted and will continue to propagate to large distances. We suggest that the relatively weak impact by the instability is due to the nature of the instability being convective and the fact that the jet magnetic fields are rapidly evolving on Alfvnic time scales. We present the detailed jet properties and show that far from the jet launching region, a substantial amount of magnetic energy has been transformed into kinetic energy and thermal energy, producing a jet magnetization number ? < 1. In addition, we have also studied the effects of a gas pressure supported "disk" surrounding the injection region, and qualitatively similar global jet behaviors were observed. We stress that jet collimation, CDIs, and the subsequent energy transitions are intrinsic features of current-carrying jets.
Substorm features in MHD (magnetohydrodynamics) simulations of magnetotail dynamics
Birn, J.; Hesse, M.
1990-01-01
We present a review and extended analysis of characteristic results from our nonideal three-dimensional MHD simulations of unstable magnetotail evolution, which develops without the necessity of external driving or prescribed localization on nonideal effects. These modes involve magnetic reconnection at a near-Earth site in the tail, consistent with the near-Earth neutral line model of substorms. The evolution tailward of the reconnection site is characterized by plasmoid formation and ejection into the far tail, plasma sheet thinning between the near-Earth neutral line (X line) and the departing plasmoid, and fast tailward flow, which occupies large sections of the plasma sheet at larger distance from the X line, while it occurs only in very limited space and time sections close to the X line. The region earthward of the X line is characterized by dipolarization, propagating from midnight toward the flank regions and, perhaps, tailward. It is associated with the signatures of the substorm current wedge: reduction and diversion of cross-tail current from a region surrounding the reconnection site and increase of Region 1 type field-aligned currents. A mapping of these currents to the Earth on the basis of an empirical magnetic field model shows good agreement of the mapped current system with the observed Region 1 field-aligned current system and its substorm associated changes, including also a nightward and equatorward shift of the peaks of the field-aligned current density. The evolution of the mappings of the boundaries of the closed field line region bears strong resemblance to the formation and expansion of he auroral bulge. The consistency of all of these details with observed substorm features strongly supports the idea that substorm evolution in the tail is that of a large scale nonideal instability.
Gustavsen, Arlid; Kohler, Christian; Dalehaug, Arvid; Arasteh, Dariush
2008-12-01
This paper assesses the accuracy of the simplified frame cavity conduction/convection and radiation models presented in ISO 15099 and used in software for rating and labeling window products. Temperatures and U-factors for typical horizontal window frames with internal cavities are compared; results from Computational Fluid Dynamics (CFD) simulations with detailed radiation modeling are used as a reference. Four different frames were studied. Two were made of polyvinyl chloride (PVC) and two of aluminum. For each frame, six different simulations were performed, two with a CFD code and four with a building-component thermal-simulation tool using the Finite Element Method (FEM). This FEM tool addresses convection using correlations from ISO 15099; it addressed radiation with either correlations from ISO 15099 or with a detailed, view-factor-based radiation model. Calculations were performed using the CFD code with and without fluid flow in the window frame cavities; the calculations without fluid flow were performed to verify that the CFD code and the building-component thermal-simulation tool produced consistent results. With the FEM-code, the practice of subdividing small frame cavities was examined, in some cases not subdividing, in some cases subdividing cavities with interconnections smaller than five millimeters (mm) (ISO 15099) and in some cases subdividing cavities with interconnections smaller than seven mm (a breakpoint that has been suggested in other studies). For the various frames, the calculated U-factors were found to be quite comparable (the maximum difference between the reference CFD simulation and the other simulations was found to be 13.2 percent). A maximum difference of 8.5 percent was found between the CFD simulation and the FEM simulation using ISO 15099 procedures. The ISO 15099 correlation works best for frames with high U-factors. For more efficient frames, the relative differences among various simulations are larger. Temperature was also compared, at selected locations on the frames. Small differences was found in the results from model to model. Finally, the effectiveness of the ISO cavity radiation algorithms was examined by comparing results from these algorithms to detailed radiation calculations (from both programs). Our results suggest that improvements in cavity heat transfer calculations can be obtained by using detailed radiation modeling (i.e. view-factor or ray-tracing models), and that incorporation of these strategies may be more important for improving the accuracy of results than the use of CFD modeling for horizontal cavities.
NASA Astrophysics Data System (ADS)
Li, Hong; Zhang, Wei; Zhang, Zhenguo; Chen, Xiaofei
2015-07-01
A discontinuous grid finite-difference (FD) method with non-uniform time step Runge-Kutta scheme on curvilinear collocated-grid is developed for seismic wave simulation. We introduce two transition zones: a spatial transition zone and a temporal transition zone, to exchange wavefield across the spatial and temporal discontinuous interfaces. A Gaussian filter is applied to suppress artificial numerical noise caused by down-sampling the wavefield from the finer grid to the coarser grid. We adapt the non-uniform time step Runge-Kutta scheme to a discontinuous grid FD method for further increasing the computational efficiency without losing the accuracy of time marching through the whole simulation region. When the topography is included in the modelling, we carry out the discontinuous grid method on a curvilinear collocated-grid to obtain a sufficiently accurate free-surface boundary condition implementation. Numerical tests show that the proposed method can sufficiently accurately simulate the seismic wave propagation on such grids and significantly reduce the computational resources consumption with respect to regular grids.
NASA Technical Reports Server (NTRS)
Fleming, Eric L.; Jackman, Charles H.; Considine, David B.
1999-01-01
We have adopted the transport scenarios used in Part 1 to examine the sensitivity of stratospheric aircraft perturbations to transport changes in our 2-D model. Changes to the strength of the residual circulation in the upper troposphere and stratosphere and changes to the lower stratospheric K(sub zz) had similar effects in that increasing the transport rates decreased the overall stratospheric residence time and reduced the magnitude of the negative perturbation response in total ozone. Increasing the stratospheric K(sub yy) increased the residence time and enhanced the global scale negative total ozone response. However, increasing K(sub yy) along with self-consistent increases in the corresponding planetary wave drive, which leads to a stronger residual circulation, more than compensates for the K(sub yy)-effect, and results in a significantly weaker perturbation response, relative to the base case, throughout the stratosphere. We found a relatively minor model perturbation response sensitivity to the magnitude of K(sub yy) in the tropical stratosphere, and only a very small sensitivity to the magnitude of the horizontal mixing across the tropopause and to the strength of the mesospheric gravity wave drag and diffusion. These transport simulations also revealed a generally strong correlation between passive NO(sub y) accumulation and age of air throughout the stratosphere, such that faster transport rates resulted in a younger mean age and a smaller NO(y) mass accumulation. However, specific variations in K(sub yy) and mesospheric gravity wave strength exhibited very little NO(sub y)-age correlation in the lower stratosphere, similar to 3-D model simulations performed in the recent NASA "Models and Measurements" II analysis. The base model transport, which gives the most favorable overall comparison with inert tracer observations, simulated a global/annual mean total ozone response of -0.59%, with only a slightly larger response in the northern compared to the southern hemisphere. For transport scenarios which gave tracer simulations within some agreement with measurements, the annual/globally averaged total ozone response ranged from -0.45% to -0.70%. Our previous 1995 model exhibited overly fast transport rates, resulting in a global/annually averaged perturbation total ozone response of -0.25%, which is significantly weaker compared to the 1999 model. This illustrates how transport deficiencies can bias model simulations of stratospheric aircraft.
NASA Astrophysics Data System (ADS)
Klimo, O.; Psikal, J.; Tikhonchuk, V. T.; Weber, S.
2014-05-01
Laser-plasma interaction and hot electron generation play a crucial role in the context of inertial confinement fusion and in particular in the shock-ignition concept. Here we present a fully kinetic large-scale two-dimensional simulation studying laser-plasma interaction and hot electron generation in a relatively long and hot coronal plasma. The simulation shows saturation of the reflectivity of an intense spike pulse and absorption taking place close to a quarter critical density in particular, due to cavitation and stimulated Raman scattering. The signatures of steady two-plasmon decay are observed, but the hot electron number produced by this instability is low in comparison with the other two processes. The spectral and angular distribution of the back-scattered light is presented and the energy and angular characteristics of hot electrons due to individual absorption processes are studied.
NASA Astrophysics Data System (ADS)
Gonzalez-Melchor, Minerva; Mendez, Arlette; Alejandre, Jose
2015-03-01
When the movement of particles is performed predominantly in two dimensions, the systems can be considered at a good extent as two-dimensional. For instance the lipids in a bilayer, micrometric particles in a quasi-two-dimensional colloidal suspension, colloids in a monolayer deposited on the air-water interface, and DNA complexes trapped at the water surface can be described at a first approach as bidimensional fluids. These systems are important for many applications in surface and colloidal science. In simulations where the explicit interface between liquid and vapor is present, the line tension can be directly computed. In this work we present molecular dynamics results obtained for the liquid/vapor coexistence curve of 2D Yukawa fluids and for the line tension. A comparison with the three-dimensional case is also presented.
Almarza, N. G.; Pekalski, J.; Ciach, A.
2014-04-28
The triangular lattice model with nearest-neighbor attraction and third-neighbor repulsion, introduced by Pekalski, Ciach, and Almarza [J. Chem. Phys. 140, 114701 (2014)] is studied by Monte Carlo simulation. Introduction of appropriate order parameters allowed us to construct a phase diagram, where different phases with patterns made of clusters, bubbles or stripes are thermodynamically stable. We observe, in particular, two distinct lamellar phasesthe 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.
Multiple Cusps under Northward IMF Conditions: Observations and MHD Simulations Compared
NASA Astrophysics Data System (ADS)
Zhang, H.; Siscoe, G.; Fritz, T. A.; Zong, Q.; Daly, P. W.; Reme, H.; Balogh, A.; Ridley, A. J.; Raeder, J.
2007-12-01
Multiple cusps have been observed by the Cluster spacecraft when the satellites were traveling outbound on Mar 21 and Mar 22, 2001. We conclude that multiple cusps are a temporal effect which is due to the change of the solar wind azimuthal flow (the wind sock effect). The cusp properties derived from two MHD codes, Open GGCM and BATSRUS, have been compared with the Cluster observations. We find that although the simulated magnetospheres are smaller than the real magnetosphere, the simulated magnetic fields and the amplitude of the model-derived plasma parameters (velocity, density, temperature and thermal pressure) agree well with Cluster observations. The MHD code successfully simulated the responses of the cusp positions to the solar wind azimuthal flow. This event is under northward IMF condition. The Geotail spacecraft observed the cold dense plasma when it crossed the dusk flank of the magnetotail. MHD code successfully simulated the formation of the cold sense plasma sheet on the flanks.
NASA Astrophysics Data System (ADS)
Lisjak, A.; Liu, Q.; Zhao, Q.; Mahabadi, O. K.; Grasselli, G.
2013-10-01
Stress waves, known as acoustic emissions (AEs), are released by localized inelastic deformation events during the progressive failure of brittle rocks. Although several numerical models have been developed to simulate the deformation and damage processes of rocks, such as non-linear stress-strain behaviour and localization of failure, only a limited number have been capable of providing quantitative information regarding the associated seismicity. Moreover, the majority of these studies have adopted a pseudo-static approach based on elastic strain energy dissipation that completely disregards elastodynamic effects. This paper describes a new AE modelling technique based on the combined finite-discrete element method (FEM/DEM), a numerical tool that simulates material failure by explicitly considering fracture nucleation and propagation in the modelling domain. Given the explicit time integration scheme of the solver, stress wave propagation and the effect of radiated seismic energy can be directly captured. Quasi-dynamic seismic information is extracted from a FEM/DEM model with a newly developed algorithm based on the monitoring of internal variables (e.g. relative displacements and kinetic energy) in proximity to propagating cracks. The AE of a wing crack propagation model based on this algorithm are cross-analysed by traveltime inversion and energy estimation from seismic recordings. Results indicate a good correlation of AE initiation times and locations, and scaling of energies, independently calculated with the two methods. Finally, the modelling technique is validated by simulating a laboratory compression test on a granite sample. The micromechanical parameters of the heterogeneous model are first calibrated to reproduce the macroscopic stress-strain response measured during standard laboratory tests. Subsequently, AE frequency-magnitude statistics, spatial clustering of source locations and the evolution of AE rate are investigated. The distribution of event magnitude tends to decay as power law while the spatial distribution of sources exhibits a fractal character, in agreement with experimental observations. Moreover, the model can capture the decrease of seismic b value associated with the macrorupture of the rock sample and the transition of AE spatial distribution from diffuse, in the pre-peak stage, to strongly localized at the peak and post-peak stages, as reported in a number of published laboratory studies. In future studies, the validated FEM/DEM-AE modelling technique will be used to obtain further insights into the micromechanics of rock failure with potential applications ranging from laboratory-scale microcracking to engineering-scale processes (e.g. excavations within mines, tunnels and caverns, petroleum and geothermal reservoirs) to tectonic earthquakes triggering.
NASA Technical Reports Server (NTRS)
Fleming, Eric L.; Jackman, Charles H.; Considine, David B.; Stolarski, Richard S.
1999-01-01
In this study, we examine the sensitivity of long lived tracers to changes in the base transport components in our 2-D model. Changes to the strength of the residual circulation in the upper troposphere and stratosphere and changes to the lower stratospheric K(sub zz) had similar effects in that increasing the transport rates decreased the overall stratospheric mean age, and increased the rate of removal of material from the stratosphere. Increasing the stratospheric K(sub yy) increased the mean age due to the greater recycling of air parcels through the middle atmosphere, via the residual circulation, before returning to the troposphere. However, increasing K(sub yy) along with self-consistent increases in the corresponding planetary wave drive, which leads to a stronger residual circulation, more than compensates for the K(sub yy)-effect, and produces significantly younger ages throughout the stratosphere. Simulations with very small tropical stratospheric K(sub yy) decreased the globally averaged age of air by as much as 25% in the middle and upper stratosphere, and resulted in substantially weaker vertical age gradients above 20 km in the extratropics. We found only very small stratospheric tracer sensitivity to the magnitude of the horizontal mixing across the tropopause, and to the strength of the mesospheric gravity wave drag and diffusion used in the model. We also investigated the transport influence on chemically active tracers and found a strong age-tracer correlation, both in concentration and calculated lifetimes. The base model transport gives the most favorable overall comparison with a variety of inert tracer observations, and provides a significant improvement over our previous 1995 model transport. Moderate changes to the base transport were found to provide modest agreement with some of the measurements. Transport scenarios with residence times ranging from moderately shorter to slightly longer relative to the base case simulated N2O lifetimes that were within the observational estimates of Volk et al. [1997]. However, only scenarios with rather fast transport rates were comparable with the Volk et al. estimates of CFCl3 lifetimes. This is inconsistent with model-measurement comparisons of mean age in which the base model or slightly slower transport rates compared the most favorably with balloon SF6 data. For all comparisons shown, large transport changes away from the base case resulted in simulations that were outside the range of measurements, and in many cases, far outside this range.
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.
Xu, X B; Fangohr, H; Gu, M; Chen, W; Wang, Z H; Zhou, F; Shi, D Q; Dou, S X
2014-03-19
We study the superconducting vortex states induced by the interplay of long-range Pearl repulsion and short-range intervortex attraction using Langevin dynamics simulations. We show that at low temperatures the vortices form an ordered Abrikosov lattice both in low and high fields. The vortices show distinctive modulated structures at intermediate fields depending on the effective intervortex attraction: ordered vortex chain and kagome-like vortex structures for weak attraction; bubble, stripe and antibubble lattices for strong attraction. Moreover, in the regime of the chain state, the vortices display structural transitions from chain to labyrinthine (or disordered chain) and/or to disordered states depending on the strength of the disorder. PMID:24589983
NASA Astrophysics Data System (ADS)
Perkins, L. J.; Logan, B. G.; Zimmerman, G. B.; Werner, C. J.
2013-07-01
We report for the first time on full 2-D radiation-hydrodynamic implosion simulations that explore the impact of highly compressed imposed magnetic fields on the ignition and burn of perturbed spherical implosions of ignition-scale cryogenic capsules. Using perturbations that highly convolute the cold fuel boundary of the hotspot and prevent ignition without applied fields, we impose initial axial seed fields of 20-100 T (potentially attainable using present experimental methods) that compress to greater than 4 104 T (400 MG) under implosion, thereby relaxing hotspot areal densities and pressures required for ignition and propagating burn by 50%. The compressed field is high enough to suppress transverse electron heat conduction, and to allow alphas to couple energy into the hotspot even when highly deformed by large low-mode amplitudes. This might permit the recovery of ignition, or at least significant alpha particle heating, in submarginal capsules that would otherwise fail because of adverse hydrodynamic instabilities.
NASA Astrophysics Data System (ADS)
Djouder, M.; Kermoun, F.; Mitiche, M. D.; Lamrous, O.
2016-01-01
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.
Perkins, L. J.; Logan, B. G.; Zimmerman, G. B.; Werner, C. J.
2013-07-15
We report for the first time on full 2-D radiation-hydrodynamic implosion simulations that explore the impact of highly compressed imposed magnetic fields on the ignition and burn of perturbed spherical implosions of ignition-scale cryogenic capsules. Using perturbations that highly convolute the cold fuel boundary of the hotspot and prevent ignition without applied fields, we impose initial axial seed fields of 20100 T (potentially attainable using present experimental methods) that compress to greater than 4 10{sup 4} T (400 MG) under implosion, thereby relaxing hotspot areal densities and pressures required for ignition and propagating burn by ?50%. The compressed field is high enough to suppress transverse electron heat conduction, and to allow alphas to couple energy into the hotspot even when highly deformed by large low-mode amplitudes. This might permit the recovery of ignition, or at least significant alpha particle heating, in submarginal capsules that would otherwise fail because of adverse hydrodynamic instabilities.
NASA Astrophysics Data System (ADS)
Skvortsova, Yulia; Wang, Gufeng; Geng, M. Lei
2006-11-01
Statistical correlation coefficient mapping has proven to be a useful technique in tissue classification for cancer diagnosis. The classification is achieved by comparing the correlation coefficients for an unknown to a set of selected tissue samples with known pathological conditions. Currently, the correlation coefficient threshold in the classification is empirically determined. In this paper, boundaries of statistical significance between different tissue pathological conditions are established through Bayesian analysis on the Fisher's z-transformed Pearson's correlation coefficients between tissue samples. Moreover, probability values are provided in assigning a tissue sample to a specific tissue clinical condition, which is more appreciable in clinical practices. The methodology is examined with a simulated tissue-phantom data set, yielding satisfactory diagnostic results.
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.
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 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
Extragalactic jets with helical magnetic fields: relativistic MHD simulations
NASA Astrophysics Data System (ADS)
Keppens, R.; Meliani, Z.; van der Holst, B.; Casse, F.
2008-08-01
Context: Extragalactic jets are judged to harbor dynamically important, organized magnetic fields that presumably aid in the collimation of the relativistic jet flows. Aims: We here explore the morphology of AGN jets pervaded by helical field and flow topologies by means of grid-adaptive, high-resolution numerical simulations. We concentrate on morphological features of the bow shock and the jet beam behind the Mach disk, for various jet Lorentz factors and magnetic field helicities. We investigate the influence of helical magnetic fields on jet beam propagation in an overdense external medium. We adopt a special relativistic magnetohydrodynamic (MHD) viewpoint on the shock-dominated AGN jet evolution. Due to the adaptive mesh refinement (AMR), we can concentrate on the long-term evolution of kinetic energy-dominated jets, with beam-averaged Lorentz factor ? ? 7, as they penetrate denser clouds. These jets have near-equipartition magnetic fields (with the thermal energy) and radially varying ?(R) profiles within the jet radius R
NASA Astrophysics Data System (ADS)
Beyer, C.; Ballarini, E.; Bauer, R.; Griebler, C.; Bauer, S.
2011-12-01
The biodegradation of oxidizable hydrocarbon contaminants in the subsurface requires the presence of compatible microbial communities as well as sufficient amounts of electron acceptors and nutrients. In this context, transverse mixing, driven by dispersion and diffusion, is one of the main mechanisms governing the availability of dissolved electron acceptors at a hydrocarbon plume fringe. Aerobic and anaerobic biodegradation of hydrocarbons limited by transverse mixing has been studied experimentally in 2D bench-scale flow-through tanks, filled with a saturated porous medium. Flow of groundwater through the tanks was induced by pumping water at one side through injection ports, and simultaneously extracting water at the other side of the tank. An ethylbenzene plume was established by injection through the central inlet port. A mixture of unlabeled and fully deuterium-labeled isotopomers was used in order to investigate the spatial distribution of degradation processes via monitoring of compound-specific stable isotope fractionation. In the first phase of the experiment, aerobic biodegradation was studied. For this purpose, the tank was recharged with water containing oxygen as a dissolved electron acceptor and the aerobic strain Pseudomonas putida F1 was inoculated. Later, nitrate was added to the recharge water as an additional electron acceptor and the denitrifying strain Aromatoleum aromaticum EbN1 was amended to study competitive aerobic/anaerobic biodegradation. A numerical reactive transport model of the experiment was set up for a model based interpretation of the observed degradation patterns. In a sensitivity analysis, the influence of the relevant hydrodynamic parameters on the observable distributions of ethylbenzene isotopomers, oxygen and nitrate was studied. Subsequent model calibration allowed for a good agreement with ethylbenzene concentrations measured at the tank outlet ports as well as oxygen concentrations, which were measured at several profiles perpendicular to the flow direction along the plume. Simulated microbial growth was strongest near the central tank inlet, where both, oxygen and ethylbenzene were available at high concentrations, and along the transverse mixing zone at the fringe of the developed ethylbenzene plume. Model based interpretation of the aerobic/anaerobic phase with competitive biodegradation proved to be ambiguous due to uncertainties regarding the actual stoichiometry of the specific denitrification reaction. Also, the simulated isotopic patterns were very sensitive to the assumed initial distribution of the A. aromaticum EbN1 biomass. Ethylbenzene concentrations and isotopic patterns predicted by the numerical model match the measurements quite well for the first half of the aerobic/anaerobic phase. A distinct increase in biodegradation dynamics later on hints at a change in biodegradation dynamics during the course of the experiment.
Xu, Yousheng; Liu, Yang; Xia, Yong; Wu, Fengmin
2008-10-01
A numerical simulation using the multiple relaxation time lattice-Boltzmann method is carried out for the purpose of investigating fluid flow over two vibrating side-by-side circular cylinders and the effect of moving the cylinders on the wake characteristics. As a benchmark problem to assess the validity and efficiency of the model, the calculation was carried out at Reynolds number of 200 and four pitch ratios (T/D , where D is the cylinder diameter while T is the center-to-center spacing between the two cylinders) of 1.2, 1.6, 2.2, and 3.2, respectively. The calculated results indicate that the vibration of the cylinder pair has significant influence on the wake patterns. When the amplitude of vibration is big enough, the vibration locks up the vortex shedding and formation. For each cylinder vibration frequency, there exists a threshold of vibration amplitude for the lock-up phenomenon. With the vibration frequency is increased, the threshold of vibration amplitude decreases. PMID:18999533
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.
A Comparison Study of Three CESE Schemes in MHD Simulation
NASA Astrophysics Data System (ADS)
Ji, Zhen; Zhou, Yu-Fen
2010-08-01
The space-time conservation element and solution element (CESE) scheme is a new second order numerical scheme based on the concept of space-time conservation integration. In order to further overcome excessive numerical damping due to small Courant-Friedrichs-Lewy (CFL) number and to obtain a high quality solution, a Courant number insensitive (CNIS) scheme and a high-order scheme have been proposed by Chang et al. for fluid mechanics problems recently. In this study, to explore the potential capability of applications of the CNIS CESE scheme and the high-order CESE scheme to magnetohydrodynamics (MHD) equations, several benchmark MHD problems are calculated in one and two dimensions: (i) Brio and Wu's shock tube, (ii) Dai and Woodward's case, (iii) the Orszag-Tang vortex problem, (iv) the Riemann problem. The numerical results just prove that the CNIS scheme is more accurate and can keep the divergence free condition of the magnetic field, even if the CFL number is < 1. Meanwhile, the tests show that the high order CESE scheme possesses the ability to solve MHD problems but is sensitive to the Courant number.
NASA Astrophysics Data System (ADS)
Tahir, N. A.; Kim, V.; Lamour, E.; Lomonosov, I. V.; Piriz, A. R.; Rozet, J. P.; Sthlker, 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)
Yoon, Hyun Jin; Ha, Chang Seung; Lee, Hae June
2008-11-01
A two-dimensional fluid simulation of Hg-Ne-Ar mixtures is developed for the study of flat fluorescent lamps (FFLs) for a backlight unit of a large-area liquid crystal display. The effects of control parameters, such as gas pressure, gap distance, driving voltage and frequency, and gas mixture ratio on discharge efficiency are investigated over the following parameter ranges: pressure of 10-100 Torr, Hg ratio of 0.3-2.0%, and driving voltage of 500-2000 V with a driving frequency of 10-100 kHz. In general, the luminance increases with driving voltage, Hg ratio, gas pressure, and the driving frequency. The luminance efficacy has optimal values for each parameter with proper steady state conditions for the enery loss mechanism and the creation and the transport of ultraviolet light.
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)
Kasama, Toshihiro; Nakajima, Anri
2009-10-01
To investigate the effect of charged substances on the properties of ion-sensitive field-effect transistors (ISFETs), the site percolation property of a finite-size two-dimensional square-lattice system was analyzed by Monte Carlo simulation. We found that the variation in the aspect ratio (width/length) of the channel leads to two important features: the sensitivity of the ISFET is enhanced with a decrease in width and/or an increase in length; however, ISFET having a rather wide and/or short channel produces the best performance in quantitative analysis. The results of this study would be applicable to the design of an ultrasensitive and quantitatively analyzable ISFET.
NASA Technical Reports Server (NTRS)
Rhee, Hyop S.; Begg, Lester L.; Wetch, Joseph R.; Jang, Jong H.; Juhasz, Albert J.
1990-01-01
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)
Shinagawa, H.; Tsugawa, T.; Matsumura, M.; Iyemori, T.; Saito, A.; Maruyama, T.; Jin, H.; Nishioka, M.; Otsuka, Y.
2013-10-01
Unusual ionospheric variations were observed in the M9.0 Tohoku-oki earthquake on 11 March 2011. Among various kinds of features in the ionosphere, significant depletion of total electron content (TEC) near the epicenter was observed after the earthquake. Although previous studies have suggested that the coseismic ionospheric variations are associated with atmospheric perturbation caused by vertical displacement of the sea surface, the mechanism of the TEC depletion has not been fully understood. In this paper, a two-dimensional nonlinear nonhydrostatic compressible atmosphere-ionosphere model is employed to investigate the ionospheric variations in the vicinity of the epicenter. The simulation results reveal that an impulsive pressure pulse produced by a sudden uplift of the sea surface leads to local atmospheric expansion in the thermosphere and that the expansion of the thermosphere combined with the effect of inclined magnetic field lines in the ionosphere causes the sudden TEC depletion above the epicenter region.
Modeling extreme (Carrington-type) space weather events using three-dimensional MHD code simulations
NASA Astrophysics Data System (ADS)
Ngwira, C. M.; Pulkkinen, A. A.; Kuznetsova, M. M.; Glocer, A.
2013-12-01
There is growing concern over possible severe societal consequences related to adverse space weather impacts on man-made technological infrastructure and systems. In the last two decades, significant progress has been made towards the modeling of space weather events. Three-dimensional (3-D) global magnetohydrodynamics (MHD) models have been at the forefront of this transition, and have played a critical role in advancing our understanding of space weather. However, the modeling of extreme space weather events is still a major challenge even for existing global MHD models. In this study, we introduce a specially adapted University of Michigan 3-D global MHD model for simulating extreme space weather events that have a ground footprint comparable (or larger) to the Carrington superstorm. Results are presented for an initial simulation run with ``very extreme'' constructed/idealized solar wind boundary conditions driving the magnetosphere. In particular, we describe the reaction of the magnetosphere-ionosphere system and the associated ground induced geoelectric field to such extreme driving conditions. We also discuss the results and what they might mean for the accuracy of the simulations. The model is further tested using input data for an observed space weather event to verify the MHD model consistence and to draw guidance for future work. This extreme space weather MHD model is designed specifically for practical application to the modeling of extreme geomagnetically induced electric fields, which can drive large currents in earth conductors such as power transmission grids.
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. PMID:25581402
Totsuji, Chieko; Miyake, Takashi; Nakanishi, Kenta; Tsuruta, Kenji; Totsuji, Hiroo
2009-01-28
A method for numerically simulating quantum systems is proposed and applied to the two-dimensional electron fluid at T = 0. This method maps quantum systems onto classical ones in the spirit of the classical-map hypernetted-chain theory and performs simulations on the latter. The results of the simulations are free from the assumption of the hypernetted-chain approximation and the neglect of the bridge diagrams. A merit of this method is the applicability to systems with geometrical complexity and finite sizes including the cases at finite temperatures. Monte Carlo and molecular dynamics simulations are performed corresponding to two previous proposals for the 'quantum' temperature and an improvement in the description of the diffraction effect. It is shown that one of these two proposals with the improved diffraction effect gives significantly better agreement with quantum Monte Carlo results reported previously for the range of 5?r(s)?40. These results may serve as the basis for the application of this method to finite non-periodic systems like quantum dots and systems at finite temperatures. PMID:21715808
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).
Two-Dimensional Colloidal Alloys
NASA Astrophysics Data System (ADS)
Law, Adam D.; Buzza, D. Martin A.; Horozov, Tommy S.
2011-03-01
We study the structure of mixed monolayers of large (3?m diameter) and small (1?m diameter) very hydrophobic silica particles at an octane-water interface as a function of the number fraction of small particles ?. We find that a rich variety of two-dimensional hexagonal super-lattices of large (A) and small (B) particles can be obtained in this system due to strong and long-range electrostatic repulsions through the nonpolar octane phase. The structures obtained for the different compositions are in good agreement with zero temperature calculations and finite temperature computer simulations.
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 ?m diameter) and small (1 ?m diameter) very hydrophobic silica particles at an octane-water interface as a function of the number fraction of small particles ?. We find that a rich variety of two-dimensional hexagonal super-lattices of large (A) and small (B) particles can be obtained in this system due to strong and long-range electrostatic repulsions through the nonpolar octane phase. The structures obtained for the different compositions are in good agreement with zero temperature calculations and finite temperature computer simulations. PMID:21517357
Liang, Xian-Ting
2014-07-28
A framework for simulating electronic spectra from photon-echo experiments is constructed by using a numerical path integral technique. This method is non-Markovian and nonperturbative and, more importantly, is not limited by a fixed form of the spectral density functions of the environment. Next, a two-dimensional (2D) third-order electronic spectrum of a dimer system is simulated. The spectrum is in agreement with the experimental and theoretical results previously reported [for example, M. Khalil, N. Demirdven, and A. Tokmakoff, Phys. Rev. Lett. 90, 047401 (2003)]. Finally, a 2D third-order electronic spectrum of the Fenna-Matthews-Olson (FMO) complex is simulated by using the Debye, Ohmic, and Adolphs and Renger spectral density functions. It is shown that this method can clearly produce the spectral signatures of the FMO complex by using only the Adolphs and Renger spectral density function. Plots of the evolution of the diagonal and cross-peaks show that they are oscillating with the population time.
Kato, Tsunehiko N.; Takabe, Hideaki
2010-09-20
A two-dimensional particle-in-cell simulation is performed to investigate weakly magnetized perpendicular shocks with a magnetization parameter of {sigma} = 6 x 10{sup -5}, which is equivalent to a high Alfven Mach number M{sub A} of {approx}130. It is shown that current filaments form in the foot region of the shock due to the ion-beam-Weibel instability (or the ion filamentation instability) and that they generate a strong magnetic field there. In the downstream region, these current filaments also generate a tangled magnetic field that is typically 15 times stronger than the upstream magnetic field. The thermal energies of electrons and ions in the downstream region are not in equipartition and their temperature ratio is T{sub e}/T{sub i} {approx} 0.3-0.4. Efficient electron acceleration was not observed in our simulation, although a fraction of the ions are accelerated slightly on reflection at the shock. The simulation results agree very well with the Rankine-Hugoniot relations. It is also shown that electrons and ions are heated in the foot region by the Buneman instability (for electrons) and the ion-acoustic instability (for both electrons and ions). However, the growth rate of the Buneman instability is significantly reduced due to the relatively high temperature of the reflected ions. For the same reason, ion-ion streaming instability does not grow in the foot region.
Ozbilgin, M.M.; Dickerman, D.C.
1984-01-01
The two-dimensional finite-difference model for simulation of groundwater flow was modified to enable simulation of surface-water/groundwater interactions during periods of low streamflow. Changes were made to the program code in order to calculate surface-water heads for, and flow either to or from, contiguous surface-water bodies; and to allow for more convenient data input. Methods of data input and output were modified and entries (RSORT and HDRIVER) were added to the COEF and CHECKI subroutines to calculate surface-water heads. A new subroutine CALC was added to the program which initiates surface-water calculations. If CALC is not specified as a simulation option, the program runs the original version. The subroutines which solve the ground-water flow equations were not changed. Recharge, evapotranspiration, surface-water inflow, number of wells, pumping rate, and pumping duration can be varied for any time period. The Manning formula was used to relate stream depth and discharge in surface-water streams. Interactions between surface water and ground water are represented by the leakage term in the ground-water flow and surface-water mass balance equations. Documentation includes a flow chart, data deck instructions, input data, output summary, and program listing. Numerical results from the modified program are in good agreement with published analytical results. (USGS)
NASA Astrophysics Data System (ADS)
Maire, Pierre-Henri; Abgrall, Rmi; Breil, Jrme; Loubre, Raphal; 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, Jrme; Loubre, Raphal; 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 elasticplastic 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.
Marocchino, A.; Atzeni, S.; Schiavi, A.
2014-01-15
In some regions of a laser driven inertial fusion target, the electron mean-free path can become comparable to or even longer than the electron temperature gradient scale-length. This can be particularly important in shock-ignited (SI) targets, where the laser-spike heated corona reaches temperatures of several keV. In this case, thermal conduction cannot be described by a simple local conductivity model and a Fick's law. Fluid codes usually employ flux-limited conduction models, which preserve causality, but lose important features of the thermal flow. A more accurate thermal flow modeling requires convolution-like non-local operators. In order to improve the simulation of SI targets, the non-local electron transport operator proposed by Schurtz-Nicolaï-Busquet [G. P. Schurtz et al., Phys. Plasmas 7, 4238 (2000)] has been implemented in the DUED fluid code. Both one-dimensional (1D) and two-dimensional (2D) simulations of SI targets have been performed. 1D simulations of the ablation phase highlight that while the shock profile and timing might be mocked up with a flux-limiter; the electron temperature profiles exhibit a relatively different behavior with no major effects on the final gain. The spike, instead, can only roughly be reproduced with a fixed flux-limiter value. 1D target gain is however unaffected, provided some minor tuning of laser pulses. 2D simulations show that the use of a non-local thermal conduction model does not affect the robustness to mispositioning of targets driven by quasi-uniform laser irradiation. 2D simulations performed with only two final polar intense spikes yield encouraging results and support further studies.
NASA Astrophysics Data System (ADS)
Marocchino, A.; Atzeni, S.; Schiavi, A.
2014-01-01
In some regions of a laser driven inertial fusion target, the electron mean-free path can become comparable to or even longer than the electron temperature gradient scale-length. This can be particularly important in shock-ignited (SI) targets, where the laser-spike heated corona reaches temperatures of several keV. In this case, thermal conduction cannot be described by a simple local conductivity model and a Fick's law. Fluid codes usually employ flux-limited conduction models, which preserve causality, but lose important features of the thermal flow. A more accurate thermal flow modeling requires convolution-like non-local operators. In order to improve the simulation of SI targets, the non-local electron transport operator proposed by Schurtz-Nicola-Busquet [G. P. Schurtz et al., Phys. Plasmas 7, 4238 (2000)] has been implemented in the DUED fluid code. Both one-dimensional (1D) and two-dimensional (2D) simulations of SI targets have been performed. 1D simulations of the ablation phase highlight that while the shock profile and timing might be mocked up with a flux-limiter; the electron temperature profiles exhibit a relatively different behavior with no major effects on the final gain. The spike, instead, can only roughly be reproduced with a fixed flux-limiter value. 1D target gain is however unaffected, provided some minor tuning of laser pulses. 2D simulations show that the use of a non-local thermal conduction model does not affect the robustness to mispositioning of targets driven by quasi-uniform laser irradiation. 2D simulations performed with only two final polar intense spikes yield encouraging results and support further studies.
NASA Astrophysics Data System (ADS)
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)
Jiang, Xun; Camp, Charles D.; Shia, Runlie; Noone, David; Walker, Christopher; Yung, Yuk L.
2004-08-01
The National Centers for Environmental Prediction-Department of Energy Reanalysis 2 data are used to calculate the monthly mean meridional circulation and eddy diffusivity from 1979 to 2002 for use in the California Institute of Technology-Jet Propulsion Laboratory two-dimensional (2-D) chemistry and transport model (CTM). This allows for an investigation of the impact of dynamics on the interannual variability of the tropical total column ozone for all years for which the Total Ozone Mapping Spectrometer and the Solar Backscatter Ultraviolet merged total ozone data are available. The first two empirical orthogonal functions (EOFs) of the deseasonalized and detrended stratospheric stream function capture 88% of the total variance on interannual timescales. The first EOF, accounting for over 70% of the interannual variance, is related to the quasi-biennial oscillation (QBO) and its interaction with annual cycles, the QBO-annual beat (QBO-AB). The 2-D CTM provides realistic simulations of the seasonal and interannual variability of ozone in the tropics. The equatorial ozone anomaly from the model is close to that derived from the observations. The phase and amplitude of the QBO are well captured by the model. The magnitude of the QBO signal is somewhat larger in the model than it is in the data. The QBO-AB found in the simulated ozone agrees well with that in the observed data.
NASA Astrophysics Data System (ADS)
Sharp, Leah Z.; Egorova, Dassia; Domcke, Wolfgang
2010-01-01
Two-dimensional (2D) photon-echo spectra of a single subunit of the Fenna-Matthews-Olson (FMO) bacteriochlorophyll trimer of Chlorobium tepidum are simulated, employing the equation-of-motion phase-matching approach (EOM-PMA). We consider a slightly extended version of the previously proposed Frenkel exciton model, which explicitly accounts for exciton coherences in the secular approximation. The study is motivated by a recent experiment reporting long-lived coherent oscillations in 2D transients [Engel et al., Nature 446, 782 (2007)] and aims primarily at accurate simulations of the spectroscopic signals, with the focus on oscillations of 2D peak intensities with population time. The EOM-PMA accurately accounts for finite pulse durations as well as pulse-overlap effects and does not invoke approximations apart from the weak-field limit for a given material system. The population relaxation parameters of the exciton model are taken from the literature. The effects of various dephasing mechanisms on coherence lifetimes are thoroughly studied. It is found that the experimentally detected multiple frequencies in peak oscillations cannot be reproduced by the employed FMO model, which calls for the development of a more sophisticated exciton model of the FMO complex.
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.
NASA Astrophysics Data System (ADS)
Kanevce, Ana; Kuciauskas, Darius; Levi, Dean H.; Allende Motz, Alyssa M.; Johnston, Steven W.
2015-07-01
We use two-dimensional numerical simulations to analyze high spatial resolution time-resolved spectroscopy data. This analysis is applied to two-photon excitation time-resolved photoluminescence (2PE-TRPL) but is broadly applicable to all microscopic time-resolved techniques. By solving time-dependent drift-diffusion equations, we gain insight into carrier dynamics and transport characteristics. Accurate understanding of measurement results establishes the limits and potential of the measurement and enhances its value as a characterization method. Diffusion of carriers outside of the collection volume can have a significant impact on the measured decay but can also provide an estimate of carrier mobility as well as lifetime. In addition to material parameters, the experimental conditions, such as spot size and injection level, can impact the measurement results. Although small spot size provides better resolution, it also increases the impact of diffusion on the decay; if the spot size is much smaller than the diffusion length, it impacts the entire decay. By reproducing experimental 2PE-TRPL decays, the simulations determine the bulk carrier lifetime from the data. The analysis is applied to single-crystal and heteroepitaxial CdTe, material important for solar cells, but it is also applicable to other semiconductors where carrier diffusion from the excitation volume could affect experimental measurements.
Phase transition-like behavior of magnetospheric substorms: Global MHD simulation results
NASA Astrophysics Data System (ADS)
Shao, X.; Sitnov, M. I.; Sharma, S. A.; Papadopoulos, K.; Goodrich, C. C.; Guzdar, P. N.; Milikh, G. M.; Wiltberger, M. J.; Lyon, J. G.
2003-01-01
Using nonlinear dynamical techniques, we statistically investigate whether the simulated substorms from global magnetohydrodynamic (MHD) models have a combination of global and multiscale features, revealed in substorm dynamics by [2000] and featured the phase transition-like behavior. We simulate seven intervals of total duration of 280 hours from the data set used in the above works [, 1985]. We analyze the input-output (vBs-pseudo AL index) system obtained from the global MHD model and compare the results to those inferred from the original set (vBs-observed AL index). The analysis of the coupled vBs-pseudo AL index system shows the first-order phase transition map, which is consistent with the map obtained for the vBs-observed AL index system. Although the comparison between observations and global MHD simulations for individual events may vary, the overall global transition pattern during the substorm cycle revealed by singular spectrum analysis (SSA) is statistically consistent between simulations and observations. The coupled vBs-pseudo AL index system also shows multiscale behavior (scale-invariant power law dependence) in SSA power spectrum. Besides, we find the critical exponent of the nonequilibrium transitions in the magnetosphere, which reflects the multiscale aspect of the substorm activity, different from power law frequency of autonomous systems. The exponent relates input and output parameters of the magnetosphere. We also discuss the limitations of the global MHD model in reproducing the multiscale behavior when compared to the real system.
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.
NASA Astrophysics Data System (ADS)
Liu, Hao-Ran; Ding, Hang
2015-08-01
We propose an approach to simulate flows with moving contact lines (MCLs) on curved substrates on a Cartesian mesh. The approach combines an immersed boundary method with a three-component diffuse-interface model and a characteristic MCL model. The immersed boundary method is able to accurately enforce the no-slip boundary condition at the solid surface, thereby circumventing the penetration of the gas and the liquid into the solid by convection. On the other hand, using the three-component diffuse-interface model can prevent the gas and liquid from infiltrating into the solid substrate through the diffusive fluxes during the interface evolution. A combination of these two methods appears to effectively conserve the mass of the phases in the computation. The characteristic MCL model not only allows the contact lines to move on the curved boundaries, but makes the gas-liquid interface to intersect the solid object at an angle in consistence with the prescribed contact angle, even with the variation of surface tangent at the solid substrate. We examine the performance of the approach through a variety of numerical experiments. The mass conservation and interface shapes at equilibrium were tested through the simulation of drop spreading on a circular cylinder. The dynamic behaviors of moving contact lines were validated by simulating the droplet spreading on a flat substrate, and we compared the numerical results against theoretical predictions and previous experimental observations. The method was also applied to the simulations of flows with curved boundaries and moving contact lines, such as drop impact on a sphere and water entry of a sphere. Finally, we studied the penetration process of a two-dimensional drop into a porous substrate that consists of a cluster of circular cylinders.
NASA Technical Reports Server (NTRS)
Wu, S. T.; Song, M. T.; Martens, P. C. H.; Dryer, M.
1991-01-01
A situation wherein a bipolar magnetic field embedded in a stratified solar atmosphere undergoes symmetrical shear motion at the footpoints is investigated via a 2D (nonplanar) MHD simulation. It was found that the vertical plasma flow velocities grow exponentially, leading to a new type of global MHD instability. The growth rate increases almost linearly until it reaches the same order of magnitude as the Alfven speed. Then a nonlinear MHD instability occurs beyond this point. It was found that the central loops are pinched by opposing Lorentz forces, and the outer closed loops stretch upward with the vertically-rising mass flow. The nonlinear dynamical shearing instability is illustrated by a numerical example that is given for three different values of the plasma beta that span several orders of magnitude.
MECHANISMS FOR MHD POYNTING FLUX GENERATION IN SIMULATIONS OF SOLAR PHOTOSPHERIC MAGNETOCONVECTION
Shelyag, S.; Mathioudakis, M.; Keenan, F. P.
2012-07-01
We investigate the generation mechanisms of MHD Poynting flux in the magnetized solar photosphere. Using radiative MHD modeling of the solar photosphere with initial magnetic configurations that differ in their field strength and geometry, we show the presence of two different mechanisms for MHD Poynting flux generation in simulations of solar photospheric magnetoconvection. The weaker mechanism is connected to vertical transport of weak horizontal magnetic fields in the convectively stable layers of the upper photosphere, while the stronger is the production of Poynting flux in strongly magnetized intergranular lanes experiencing horizontal vortex motions. These mechanisms may be responsible for the energy transport from the solar convection zone to the higher layers of the solar atmosphere.
Phase Transition-like Behavior of Magnetospheric Substorms: Global MHD Simulation Results
NASA Astrophysics Data System (ADS)
Shao, X.; Sitnov, M.; Sharma, A. S.; Papadopoulos, K.; Guzdar, P. N.; Goodrich, C. C.; Milikh, G. M.; Wiltberger, M. J.; Lyon, J. G.
2001-12-01
Because of their relevance to massive global energy loading and unloading, lots of observations and studies have been made for magnetic substorm events. Using nonlinear dynamical techniques, we investigate whether the simulated substorms from global MHD models have the non-equilibrium phase transition-like features revealed by \\markcite{Sitnov et al. [2000]}. We simulated 6 intervals of total duration of 240 hours from the same data set used in Sitnov et al. [2000]. We analyzed the input-output (vBs--pseudo-AL index) system obtained from the global MHD model and compared the results to those in \\markcite{Sitnov et al. [2000, 2001]}. The analysis of the coupled vBs--pseudo-AL index system shows the first-order phase transition map, which is consistent with the map obtained for the vBs--observed-AL index system from Sitnov et al. [2000]. The explanation lies in the cusp catastrophe model proposed by Lewis [1991]. Although, the comparison between observation and individual global MHD simulations may vary, the overall global transition pattern during the substorm cycle revealed by Singular Spectrum Analysis (SSA) is consistent between simulations and observations. This is an important validation of the global MHD simulations of the magnetosphere. The coupled vBs--pseudo-AL index system shows multi-scale behavior (scale-invarianet power-law dependence) in singular power spectrum. We found critical exponents of the non-equilibrium transitions in the magnetosphere, which reflect the multi-scale aspect of the substorm activity, different from power-law frequency of autonomous systems. The exponents relate input and output parameters of the magnetosphere and distinguish the second order phase transition model from the self-organized criticality model. We also discuss the limitations of the global MHD model in reproducing the multi-scale behavior when compared to the real system.
Oblique MHD cosmic-ray modified shocks: Two-fluid numerical simulations
NASA Technical Reports Server (NTRS)
Frank, Adam; Jones, T. W.; Ryu, Dongsu
1991-01-01
We present the first results of time dependent, two-fluid, cosmic-ray (CR) modified, MHD shock simulations. The calculations were carried out with a new numerical code for 1-D ideal MHD. By coupling this code with the CR energy transport equation we can simulate the time-dependent evolution of MHD shocks including the acceleration of the CR and their feedback on the shock structures. We report tests of the combined numerical method including comparisons with analytical steady state results published earlier by Webb, as well as internal consistency checks for more general MHD CR shock structures after they appear to have converged to dynamical steady states. We also present results from an initial time dependent simulation which extend the parameter space domain of previous analytical models. These new results support Webb's suggestion that equilibrium oblique shocks are less effective than parallel shocks in the acceleration of CR. However, for realistic models of anisotropic CR diffusion, oblique shocks may achieve dynamical equilibrium on shorter timescale than parallel shocks.
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.
Liu Xiangmei; Song Yuanhong; Xu Xiang; Wang Younian
2011-08-15
A two-dimensional (2D) self-consistent fluid model is developed to describe the formation, subsequent growth, transport, and charging mechanisms of nanoparticles in a capacitively coupled silane discharge applied by two very high frequency (VHF) sources with phase shift. In this discharge process, large anions are produced by a series of chemical reactions of anions with silane molecules, while the lower limit of the initial nanoparticles are taken as large anions (Si{sub 12}H{sub 25}{sup -} and Si{sub 12}H{sub 24}{sup -}) to directly link the coagulation module with the nucleation module. And then, by using the coagulation module, the particle number density quickly decreases over several orders of magnitude, whereas the particle size strongly increases. We investigate in particular the growth of the nanoparticles ranging in size from {approx}1 to 50 nm in coagulation processes. The influences of controlled phase shifts between VHF (50 MHz) voltages on the electron density, electron temperature, nanoparticle uniformity, and deposition rate, are carefully studied. It is found from our simulation that the plasma density and nanoparticle density become center high and more uniform as the phase shift increases from 0 to 180 deg. Moreover, the role of phase-shift control in the silane discharge diluted with hydrogen gas is also discussed.
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.
NASA Astrophysics Data System (ADS)
Shkurenkov, I. A.; Mankelevich, Yu A.; Rakhimova, T. V.
2013-02-01
The results of two-dimensional modelling of a radio-frequency dielectric barrier discharge (RF DBD) in a hydrogen-oxygen stoichiometric mixture under atmospheric pressure are presented. The production of active species and the possibility of ignition of the mixture are studied. It is shown that the production of active species in the discharge is enough to reduce the ignition temperature significantly. A detailed description of the ion production and loss is presented. The processes of electron attachment are very fast, while the detachment processes depend on the type of ion. The electron detachment, charge recombination, and conversion of negative and positive ions are very important here. The current discharge consists of breakdowns that occur in each half-period, and it resembles the standard DBDs of kilohertz frequency. The surface charge is not uniform over the electrode area and the RF DBD consists of micro-discharges, which are not so pronounced as in the DBDs of kilohertz frequency. Two additional types of RF DBDs, the dual-frequency RF DBD and frequency-modulated RF DBD, are simulated for the purpose of controlling the ratio between the input power absorbed by electrons and ions in this discharge.
Fan, Yu; Zou, Ying; Sun, Jizhong; Wang, Dezhen; Stirner, Thomas
2013-10-15
The influence of an applied magnetic field on plasma-related devices has a wide range of applications. Its effects on a plasma have been studied for years; however, there are still many issues that are not understood well. This paper reports a detailed kinetic study with the two-dimension-in-space and three-dimension-in-velocity particle-in-cell plus Monte Carlo collision method on the role of EB drift in a capacitive argon discharge, similar to the experiment of You et al.[Thin Solid Films 519, 6981 (2011)]. The parameters chosen in the present study for the external magnetic field are in a range common to many applications. Two basic configurations of the magnetic field are analyzed in detail: the magnetic field direction parallel to the electrode with or without a gradient. With an extensive parametric study, we give detailed influences of the drift on the collective behaviors of the plasma along a two-dimensional domain, which cannot be represented by a 1 spatial and 3 velocity dimensions model. By analyzing the results of the simulations, the occurring collisionless heating mechanism is explained well.
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)
Bloch, Edward; Uddin, Nabil; Gannon, Laura; Rantell, Khadija; Jain, Saurabh
2015-01-01
Background Stereopsis is believed to be advantageous for surgical tasks that require precise hand-eye coordination. We investigated the effects of short-term and long-term absence of stereopsis on motor task performance in three-dimensional (3D) and two-dimensional (2D) viewing conditions. Methods 30 participants with normal stereopsis and 15 participants with absent stereopsis performed a simulated surgical task both in free space under direct vision (3D) and via a monitor (2D), with both eyes open and one eye covered in each condition. Results The stereo-normal group scored higher, on average, than the stereo-absent group with both eyes open under direct vision (p<0.001). Both groups performed comparably in monocular and binocular monitor viewing conditions (p=0.579). Conclusions High-grade stereopsis confers an advantage when performing a fine motor task under direct vision. However, stereopsis does not appear advantageous to task performance under 2D viewing conditions, such as in video-assisted surgery. PMID:25185439
Hu Zhanghu; Song Yuanhong; Wang Younian
2010-08-15
A two-dimensional particle-in-cell (PIC) model is proposed to study the wake field and stopping power induced by a nonrelativistic charged particle moving perpendicular to the external magnetic field in two-component plasmas. The effects of the magnetic field on the wake potential and the stopping due to the polarization of both the plasma ions and electrons are discussed. The velocity fields of plasma ions and electrons are investigated, respectively, in the weak and strong magnetic field cases. Our simulation results show that in the case of weak magnetic field and high ion velocity, the wakes exhibit typical V-shaped cone structures and the opening cone angles decrease with the increasing ion velocity. As the magnetic field becomes strong, the wakes lose their typical V-shaped structures and become highly asymmetrical. Similar results can be obtained in the case of low ion velocity and strong magnetic field. In addition, stopping power is calculated and compared with previous one-dimensional and full three-dimensional PIC results.
NASA Astrophysics Data System (ADS)
Liu, Xiang-Mei; Song, Yuan-Hong; Xu, Xiang; Wang, You-Nian
2011-08-01
A two-dimensional (2D) self-consistent fluid model is developed to describe the formation, subsequent growth, transport, and charging mechanisms of nanoparticles in a capacitively coupled silane discharge applied by two very high frequency (VHF) sources with phase shift. In this discharge process, large anions are produced by a series of chemical reactions of anions with silane molecules, while the lower limit of the initial nanoparticles are taken as large anions (Si12H25- and Si12H24-) to directly link the coagulation module with the nucleation module. And then, by using the coagulation module, the particle number density quickly decreases over several orders of magnitude, whereas the particle size strongly increases. We investigate in particular the growth of the nanoparticles ranging in size from 1 to 50 nm in coagulation processes. The influences of controlled phase shifts between VHF (50 MHz) voltages on the electron density, electron temperature, nanoparticle uniformity, and deposition rate, are carefully studied. It is found from our simulation that the plasma density and nanoparticle density become center high and more uniform as the phase shift increases from 0 to 180. Moreover, the role of phase-shift control in the silane discharge diluted with hydrogen gas is also discussed.
Chaudhuri, Saptarishi; Roy, Sanjukta; Unnikrishnan, C. S.
2006-08-15
We discuss the implementation and characterization of the source of a slow, intense, and collimated beam of rubidium atoms. The cold atomic beam is produced by two-dimensional magneto-optical trapping in directions transverse to the atomic beam axis and unbalanced Doppler cooling in the axial direction. The vacuum design allows use of relatively low laser power and a considerably simplified assembly. The atomic beam has a high flux of about 2x10{sup 10} atoms/s at a total cooling laser power of 55 mW. It has a narrow longitudinal velocity distribution with mean velocity 15 m/s with full width at half maximum 3.5 m/s and has a low divergence of 26 mrad. The high flux enables ultrafast loading of about 10{sup 10} atoms into a three-dimensional (3D) magneto-optical trap within 500 ms. The variation of the atomic beam flux was studied as a function of the rubidium vapor pressure, cooling laser power, transverse cooling laser beam length, detuning of the cooling laser, and relative intensities of the cooling beams along the atomic beam axis. We also discuss a detailed comparison of our measurements of the cold atomic beam with a 3D numerical simulation.
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 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.
3D nonlinear MHD simulations of ultra-low q plasmas
NASA Astrophysics Data System (ADS)
Bonfiglio, D.; Cappello, S.; Piovan, R.; Zanotto, L.; Zuin, M.
2008-11-01
Magnetohydrodynamic (MHD) phenomena occurring in the ultra-low safety factor (ULq) configuration are investigated by means of 3D nonlinear MHD simulations. The ULq configuration, a screw pinch characterized by the edge safety factor qedge in the interval 0 < qedge < 1, is the intermediate state between the tokamak and the reversed field pinch. This numerical study, based on the simple frame of the visco-resistive pressureless MHD model, shows that ULq plasmas have the natural tendency to select discrete qedge values which are about the major rational numbers, suggesting plasma self-organization. Similar behaviour is observed in experimental ULq discharges, like those recently obtained exploiting the flexibility of the RFX-mod device. The transition of qedge from a major rational number to the next one occurs together with the development of a kink deformation of the plasma column, whose stabilization yields a nearly axisymmetric state with a rather flat q profile. Numerical simulations also show that it is possible to sustain either of the two conditions, namely, the saturated kink helical configuration and the axisymmetric one, by forcing qedge at a suitable value. Finally, the effects of this MHD phenomenology on the confinement properties of ULq plasmas are discussed.
NASA Astrophysics Data System (ADS)
Seo, Jeong Hyun; Eden, J. Gary
2006-12-01
Cylindrical microcavity plasma devices with diameters (D) in the 100-300?m range and a dielectric barrier structure similar to that described by Park et al. [J. Appl. Phys. 99, 026107 (2006)] for Al /Al2O3 devices have been investigated numerically. A two-dimensional fluid simulation of microplasmas in Ne/7% Xe gas mixtures with pD values (where p is the total gas pressure) in the 3-9Torrcm interval yields the temporal history of the spatially resolved electron and ion number densities in response to a 250kHz bipolar excitation wave form. Calculations show two distinct regions of plasma development, along the microcavity axis and near the wall, each of which dominates the plasma characteristics in separate pD regions. For low pD values (<4Torrcm ), the negative glow produced at the cavity wall extends to the microcavity axis which, in combination with the strong axial electric field, produces an intense glow discharge on axis. For 4?pD?6Torrcm, a weakened axial discharge is observed early in the life of the plasma but the radial variation of the electron density flattens. Further increases in the gas pressure (to the largest pD values investigated, 6-9Torrcm) result in the retreat of the negative glow to the vicinity of the microcavity wall, thereby producing a diffuse but annular discharge. Even at the higher pD values, the axial discharge appears to facilitate ignition of the negative glow. The predictions of the simulations are consistent with the behavior of Al /Al2O3 microplasma devices for which D =100-300?m.
Trinkunas, G; Holzwarth, A R
1994-02-01
Kinetic modeling of the exciton migration in the cyanobacterial photosystem I core complex from Synechococcus sp. was performed by an exact solution of the Pauli master equation for exciton motion. A square two-dimensional 10 x 10 pigment lattice and a Frster dipole-dipole coupling between chromophores was assumed. We calculated decay-associated spectra and lifetimes and compared them to the corresponding experimental data from picosecond fluorescence and transient absorption obtained by global analysis. Seven spectral chlorophyll(Chl) forms, identical in shape but shifted in their absorption maximums, were used to describe the non-homogeneous broadening of the PS I-100 particle absorption spectrum. The optimized Chl lattice arrangement best reproducing the experimental decay-associated spectra as well as the steady-state fluorescence spectrum indicated the long-wavelength-absorbing Chls forming a cluster in the corner of the lattice with the reaction center (RC) placed apart at a distance of two lattice constants. The variable parameters, i.e., the charge separation rate in the RC and the lattice constant a, were found to be optimal at kRC = 2.3 ps-1 and a = 1.14 nm, respectively. The surprising conclusions of the simulations is that Chls with absorption maxima as long a 724 nm have to be taken into account to describe the time-resolved spectra of this PS I particle properly. The dependencies of the exciton decay in the model PS I particle on the excitation wavelength and on the temperature are discussed. We also show that the excited state decay of similar PS I particles that lack the long-wavelength absorbing Chls is nearly mono-exponential. Various critical factors that limit the general reliability of the conclusions of such simulations are discussed in detail. PMID:8161695
Multiple Cusps under Northward IMF Conditions: Observations and MHD Simulations Compared
NASA Astrophysics Data System (ADS)
Zhang, H.; Fritz, T. A.; Zong, Q.; Siscoe, G.; Ridley, A. J.; Raeder, J.
2008-05-01
Multiple cusps have been observed by the Cluster spacecraft when the satellites were travelling outbound on Mar 21 and Mar 22, 2001. Evidences show that multiple cusps are a temporal effect which is due to the change of the solar wind azimuthal flow. The cusp properties derived from two MHD codes, Open GGCM and BATSRUS, have been compared with the Cluster observations. We find that although the simulated magnetospheres are smaller than the real magnetosphere, the simulated magnetic fields and the amplitude of the model-derived plasma parameters (velocity, density, temperature and thermal pressure) agree well with Cluster observations. The MHD code qualitatively simulated the responses of the cusp positions to the solar wind azimuthal flow (the wind sock effect).
Non-linear MHD simulations of ELMs in JET and quantitative comparisons to experiments
NASA Astrophysics Data System (ADS)
Pamela, S.; Eich, T.; Frassinetti, L.; Sieglin, B.; Saarelma, S.; Huijsmans, G.; Hoelzl, M.; Becoulet, M.; Orain, F.; Devaux, S.; Chapman, I.; Lupelli, I.; Solano, E.; Contributors, JET
2016-01-01
A subset of JET ITER-like wall (ILW) discharges, combining electron density and temperature as well as divertor heat flux measurements, has been collected for the validation of non-linear magnetohydrodynamic (MHD) simulations of edge-localised-modes (ELMs). This permits a quantitative comparison of simulation results against experiments, which is required for the validation of predicted ELM energy losses and divertor heat fluxes in future tokamaks like ITER. This paper presents the first results of such a quantitative comparison, and gives a perspective of what will be necessary to achieve full validation of non-linear codes like JOREK. In particular, the present study highlights the importance of pre-ELM equilibria and parallel energy transport models in MHD simulations, which form the underlying basis of ELM physics.
MHD simulation of the solar wind interaction with the magnetosphere of Mercury
NASA Astrophysics Data System (ADS)
Varela, Jacobo; Pantellini, Filippo; Moncuquet, Michel
2014-05-01
We show MHD simulations of the solar wind interaction with the magnetosphere of Mercury. We use the open source codes Pluto and MPI-AMRVAC in 3 dimensional spherical geometry. In order to appreciate the limits of the MHD approach in the context of Mercury's environment we do first compare our simulations with hybrid simulation (e.g. Trávníček et al, Icarus, 209, pp 11-22, 2010). We do also compare magnetic field profiles from the magnetometer on Messenger with profiles sampled along the corresponding spacecraft trajectory in the simulations. These comparisons show that despite the lack of kinetic effects, MHD simulation provide a more than fair description of the interaction of the solar wind with Mercury at low computational cost making it a useful tool to help decrypt data from current and future exploratory missions in the hermean magnetosphere (e.g. Bepi Colombo-MMO). The research leading to these results has received funding from the European Commission's Seventh Framework Programme (FP7/2007-2013) under the grant agreement SHOCK (project number 284515).
NASA Astrophysics Data System (ADS)
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 Technical Reports Server (NTRS)
Ngwira, Chigomezyo M.; Pulkkinen, Antti; Kuznetsova, Maria M.; Glocer, Alex
2014-01-01
There is a growing concern over possible severe societal consequences related to adverse space weather impacts on man-made technological infrastructure. In the last two decades, significant progress has been made toward the first-principles modeling of space weather events, and three-dimensional (3-D) global magnetohydrodynamics (MHD) models have been at the forefront of this transition, thereby playing a critical role in advancing our understanding of space weather. However, the modeling of extreme space weather events is still a major challenge even for the modern global MHD models. In this study, we introduce a specially adapted University of Michigan 3-D global MHD model for simulating extreme space weather events with a Dst footprint comparable to the Carrington superstorm of September 1859 based on the estimate by Tsurutani et. al., (2003). Results are presented for a simulation run with "very extreme" constructed/idealized solar wind boundary conditions driving the magnetosphere. In particular, we describe the reaction of the magnetosphere-ionosphere system and the associated induced geoelectric field on the ground to such extreme driving conditions. The model setup is further tested using input data for an observed space weather event of Halloween storm October 2003 to verify the MHD model consistence and to draw additional guidance for future work. This extreme space weather MHD model setup is designed specifically for practical application to the modeling of extreme geomagnetically induced electric fields, which can drive large currents in ground-based conductor systems such as power transmission grids. Therefore, our ultimate goal is to explore the level of geoelectric fields that can be induced from an assumed storm of the reported magnitude, i.e., Dst approx. = -1600 nT.
NASA Astrophysics Data System (ADS)
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.
Numerical Simulation of 3-D Supersonic Viscous Flow in an Experimental MHD Channel
NASA Technical Reports Server (NTRS)
Kato, Hiromasa; Tannehill, John C.; Gupta, Sumeet; Mehta, Unmeel B.
2004-01-01
The 3-D supersonic viscous flow in an experimental MHD channel has been numerically simulated. The experimental MHD channel is currently in operation at NASA Ames Research Center. The channel contains a nozzle section, a center section, and an accelerator section where magnetic and electric fields can be imposed on the flow. In recent tests, velocity increases of up to 40% have been achieved in the accelerator section. The flow in the channel is numerically computed using a new 3-D parabolized Navier-Stokes (PNS) algorithm that has been developed to efficiently compute MHD flows in the low magnetic Reynolds number regime. The MHD effects are modeled by introducing source terms into the PNS equations which can then be solved in a very e5uent manner. To account for upstream (elliptic) effects, the flowfield can be computed using multiple streamwise sweeps with an iterated PNS algorithm. The new algorithm has been used to compute two test cases that match the experimental conditions. In both cases, magnetic and electric fields are applied to the flow. The computed results are in good agreement with the available experimental data.
Modeling of substorm development with a kinematic effect by the global MHD simulations
NASA Astrophysics Data System (ADS)
den, Mitsue; Fujita, Shigeru; Tanaka, Takashi; Horiuchi, Ritoku
Magnetic reconnection is considered to play an important role in space phenomena such as substorm in the Earth's magnetosphere. Recently, Tanaka and Fujita reproduced substorm evoution process by numerical simulation with the global MHD code. In the MHD framework, the dissipation model is used for modeling of the kinetic effects. They found that the normalized reconnection viscosity, one of the dessipation model employed there, gave a large effect for the substorm development though that viscosity was assumed to be a constant parameter. It is well known that magnetric reconnection is controlled by microscopic kinetic mechanism. Horiuchi et al. investigated the roles of microscopic plasma instabilities on the violation of the frozen-in condition by examining the force balance equation based on explicit electromagnetic particle simulation for an ion-scale current sheet, and concluded that the growth of drift kink instability can create anomalous resistivity leading to the excitation of collisionless reconnection. They estimated the effective resistivity based on the particle simulation data. In this paper, we perform substorm simulation by using the global MHD code with this anomalous resistivity obtained in their microscopic approach istead of the emprical resistivity model, and investigate the relationship between the substorm development and the anomalous resistivity model.
NASA Technical Reports Server (NTRS)
Smith, Z.; Yeh, T.; Dryer, M.; Watanabe, T.; Oyama, K.
1987-01-01
During the period 3-10 February 1986 a series of major solar flares occurred on the Sun and several intense geomagnetic storms took place on the Earth. To examine the causality between the solar activity and the geomagnetic activity in this period, a magnetohydrodynamic (MHD) numerical simulation was performed using a 2 1/2 -D numerical code. In that period of February 1986, the Japanese spacecraft Sakigake was at 0.84 AU, 57 deg west of the Earth. Besides the in-situ measurements of the interplanetary plasma, Sakigake also provided Doppler scintillation observations. Comparisons between the results of the MHD simulation and the measurements made by the spacecraft Sakigake are presented.
An MHD Simulation of the Magnetosphere Based on the HLLD Approximate Riemann Solver
NASA Astrophysics Data System (ADS)
Miyoshi, T.; Kusano, K.
2005-12-01
A Harten-Lax-van Leer Discontinuities (HLLD) approximate Riemann solver, which was recently developed by Miyoshi and Kusano (2005), is improved for extended magnetohydrodynamic (MHD) equations that include a background potential field, multi-component plasmas, and an arbitrary equation of state, and is applied to the magnetospheric global simulation. The resolution of the HLLD solver is as well as the standard linearized Riemann solver, but the HLLD solver is more robust and efficient than the other linearized Riemann solver. The validity and efficiency of the HLLD solver for the magnetospheric simulation is carefully examined, and it is shown that the HLLD solver is more suitable for extended MHD than the other linealized Riemann solvers.
NASA Astrophysics Data System (ADS)
Kress, B. T.; Hudson, M. K.; Looper, M. D.; Lyon, J. G.; Goodrich, C. C.
2008-11-01
Test-particle trajectories are computed in fields from a global MHD magnetospheric model simulation of the 29 October 2003 Storm Commencement to investigate trapping and transport of solar energetic electrons (SEEs) in the magnetosphere during severe storms. SEEs are found to provide a source population for a newly formed belt of electrons in the Earth's inner zone radiation belts, which was observed following the 29 October 2003 storm. Energy and pitch angle distributions of the new belt are compared with results previously obtained [Kress, B.T., Hudson, M.K., Looper, M.D., Albert, J., Lyon, J.G., Goodrich, C.C., 2007. Global MHD test particle simulations of >10 MeV radiation belt electrons during storm sudden commencement. Journal of Geophysical Research 112, A09215, doi:10.1029/2006JA012218], where outer belt electrons were used as a source for the new belt.
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.
Direct Numerical Simulations of Nonlinear Evolution of MHD Instability in LHD
Miura, H.; Nakajima, N.; Hayashi, T.; Okamoto, M.
2006-11-30
Nonlinear evolutions of MHD instabilities in the large helical device are studied by means of direct numerical simulations under the vacuum configuration with the magnetic axis position R = 3.6m, including effects of its full three-dimensional geometry, flows parallel to the magnetic field lines and the fluid compressibility. The linear growth of the pressure-driven modes and their nonlinear saturations are observed. The linear growth brings about the flows parallel to the magnetic field lines as strong as the perpendicular flows. The fluid compressibility reduces the linear growth rate significantly. In the nonlinear saturation process, a qualitative difference is found in the behaviors of the parallel and perpendicular flows. The plasma appears to approach to a near-equilibrium state, keeping finite amplitudes of the parallel flow. Our numerical results highlight important roles of the parallel flow and compressibility in nonlinear MHD simulations in the large helical device.
3D simulations of disc winds extending radially self-similar MHD models
NASA Astrophysics Data System (ADS)
Stute, Matthias; Gracia, Jos; Vlahakis, Nektarios; Tsinganos, Kanaris; Mignone, Andrea; Massaglia, Silvano
2014-04-01
Disc winds originating from the inner parts of accretion discs are considered as the basic component of magnetically collimated outflows. The only available analytical magnetohydrodynamic (MHD) solutions to describe disc-driven jets are those characterized by the symmetry of radial self-similarity. However, radially self-similar MHD jet models, in general, have three geometrical shortcomings: (i) a singularity at the jet axis, (ii) the necessary assumption of axisymmetry and (iii) the non-existence of an intrinsic radial scale, i.e. the jets formally extend to radial infinity. Hence, numerical simulations are necessary to extend the analytical solutions towards the axis, by solving the full three-dimensional equations of MHD and impose a termination radius at finite radial distance. We focus here on studying the effects of relaxing the (ii) assumption of axisymmetry, i.e. of performing full 3D numerical simulations of a disc wind crossing all MHD critical surfaces. We compare the results of these runs with previous axisymmetric 2.5D simulations. The structure of the flow in all simulations shows strong similarities. The 3D runs reach a steady state and stay close to axisymmetry for most of the physical quantities, except for the poloidal magnetic field and the toroidal velocity which slightly deviate from axisymmetry. The latter quantities show signs of instabilities, which, however, are confined to the region inside the fast magnetosonic separatrix surface. The forces present in the flow, both of collimating and accelerating nature, are in good agreement in both the 2.5D and the 3D runs. We conclude that the analytical solution behaves well also after relaxing the basic assumption of axisymmetry.
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 center of the mean BP in both observations and simulations, consistent with the classical picture of a production of the asymmetry in the canopy. This is the first time that this has been found also in the internetwork. More or less vertical kilogauss magnetic fields are found for 98% of the synthetic BPs underlining that basically every BP is associated with kilogauss fields. At the continuum formation height, the simulated BPs are on average 190 K hotter than the mean quiet Sun, the mean BP field strength is found to be 1750 G, and the mean inclination is 17°, supporting the physical flux-tube paradigm to describe BPs. On average, the synthetic BPs harbor downflows increasing with depth. The origin of these downflows is not yet understood very well and needs further investigation.
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)
Burow, K. R.; Gamble, J. M.; Fujii, R.; Constantz, J.
2001-12-01
Water flowing through the Sacramento-San Joaquin River Delta supplies drinking water to more than 20 million people in California. Delta water contains elevated concentrations of dissolved organic carbon (DOC) from drainage through the delta peat soils, forming trihalomethanes when the water is chlorinated for drinking. Land subsidence caused by oxidation of the peat soils has led to increased pumping of drainage water from delta islands to maintain arable land. An agricultural field on Twitchell Island was flooded in 1997 to evaluate continuous flooding as a technique to mitigate subsidence. The effects of shallow flooding on DOC loads to the drain water must be determined to evaluate the feasibility of this technique. In this study, heat is used as a nonconservative tracer to determine shallow ground-water flux and calculate DOC loads to an adjacent drainage ditch. Temperature profiles and water levels were measured in 12 wells installed beneath the pond, in the pond, and in an adjacent drainage ditch from May 2000 to June 2001. The range in seasonal temperatures decreased with depth, but seasonal temperature variation was evident in wells screened as deep as 10 to 12 feet below land surface. A constant temperature of 17 degrees C was measured in wells 25 feet beneath the pond. Ground-water flux beneath the pond was quantified in a two-dimensional simulation of water and heat exchange using the SUTRA flow and transport model. The effective vertical hydraulic conductivity of the peat soils underlying the pond was estimated through model calibration. Calibrated hydraulic conductivity is higher (1E-5 m/sec) than estimates from slug tests (2E-6 m/sec). Modeled pond seepage is similar to that estimated from a water budget, although the total seepage determined from the water budget is within the range of error of the instrumentation. Overall, model results indicate that recharge from the pond flows along shallow flow paths and that travel times through the peat to the drainage ditch may be on the order of decades.
PROPERTIES OF UMBRAL DOTS AS MEASURED FROM THE NEW SOLAR TELESCOPE DATA AND MHD SIMULATIONS
Kilcik, A.; Yurchyshyn, V. B.; Abramenko, V.; Goode, P. R.; Cao, W.; Rempel, M.; Kitai, R.; Watanabe, H.
2012-02-01
We studied bright umbral dots (UDs) detected in a moderate size sunspot and compared their statistical properties to recent MHD models. The study is based on high-resolution data recorded by the New Solar Telescope at the Big Bear Solar Observatory and three-dimensional (3D) MHD simulations of sunspots. Observed UDs, living longer than 150 s, were detected and tracked in a 46 minute long data set, using an automatic detection code. A total of 1553 (620) UDs were detected in the photospheric (low chromospheric) data. Our main findings are (1) none of the analyzed UDs is precisely circular, (2) the diameter-intensity relationship only holds in bright umbral areas, and (3) UD velocities are inversely related to their lifetime. While nearly all photospheric UDs can be identified in the low chromospheric images, some small closely spaced UDs appear in the low chromosphere as a single cluster. Slow-moving and long-living UDs seem to exist in both the low chromosphere and photosphere, while fast-moving and short-living UDs are mainly detected in the photospheric images. Comparison to the 3D MHD simulations showed that both types of UDs display, on average, very similar statistical characteristics. However, (1) the average number of observed UDs per unit area is smaller than that of the model UDs, and (2) on average, the diameter of model UDs is slightly larger than that of observed ones.
Simulating MHD/Fluid type electromagnetic modes in the total-f gyrokinetic code XGC1
NASA Astrophysics Data System (ADS)
Lang, J.; Ku, S.-H.; Chang, C.-S.; Chen, Y.; Parker, S. E.
2014-10-01
For a more complete description of the MHD/fluid type mode activities including ELMs and neoclassical tearing modes, their interaction with the kinetic neoclassical and microturbulence dynamics needs to be simulated together. Evolution of the background profile should also be captured self-consistently. We report recent development activity of the MHD/fluid modes capability in the total-f gyrokinetic codes in the limit of small delta-B. Verification of the Alfven wave modes, low-n tearing modes, and transition from ITG to KBM modes will be presented. Plan for further development will be discussed. Important implication of the new development to the XGC1 program and fusion physics will also be discussed.
Neoclassical viscous stress tensor for non-linear MHD simulations with XTOR-2F
NASA Astrophysics Data System (ADS)
Mellet, N.; Maget, P.; Ltjens, H.; Meshcheriakov, D.; the Tore Supra Team
2013-04-01
The neoclassical viscous stress tensor is implemented in the non-linear MHD code XTOR-2F (Ltjens and Luciani 2010 J. Comput. Phys. 229 8130-43), allowing consistent bi-fluid simulations of MHD modes, including the metastable branch of neoclassical tearing modes (NTMs) (Carrera et al 1986 Phys. Fluids 29 899-902). Equilibrium flows and bootstrap current from the neoclassical theory are formally recovered in this Chew-Goldberger-Low formulation. The non-linear behaviour of the new model is verified on a test case coming from a Tore Supra non-inductive discharge. A NTM threshold that is larger than with the previous model is obtained. This is due to the fact that the velocity is now part of the bootstrap current and that it differs from the theoretical neoclassical value.
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.
An MHD Simulation of AR11944 Using Hmi Magnetic Field Data
NASA Astrophysics Data System (ADS)
Hayashi, K.
2014-12-01
We will present the results from the MHD simulation of the active region 11944 using series of the HMI magnetic field data as time-varying boundary condition on the solar photosphere. Our simulation model applies the concept of the characteristics, as in our previous studies, to all boundary surfaces, so that the influences of unphysical waves from outside will be prevented from entering the simulation domain. To the bottom boundary, specifically, the boundary treatments are applied so that the enforced time-evolution of the normal component of magnetic field satisfying the characteristics equations of the hyperbolic MHD system and preserving the divergence-free condition in the simulated volume. In this numerical chamber carefully prepared, we first set the potential field as the initial values of the magnetic field; then, the observation-based time-dependent boundary values will drive the system to form regions of twisted field lines with higher magnetic energy density than the initial potential field. We applied our model to the region 11944 and conducted a simulation, for a 24-hour span from 2014 January 6, 23 UT to examine the evolution of the magnetic field structures and accumulation of magnetic energy in the simulated system before and after an X flare (around Jan. 7 18 UT).
Wagner, Chad
2007-01-01
The use of one-dimensional hydraulic models currently is the standard method for estimating velocity fields through a bridge opening for scour computations and habitat assessment. Flood-flow contraction through bridge openings, however, is hydrodynamically two dimensional and often three dimensional. Although there is awareness of the utility of two-dimensional models to predict the complex hydraulic conditions at bridge structures, little guidance is available to indicate whether a one- or two-dimensional model will accurately estimate the hydraulic conditions at a bridge site. The U.S. Geological Survey, in cooperation with the North Carolina Department of Transportation, initiated a study in 2004 to compare one- and two-dimensional model results with field measurements at complex riverine and tidal bridges in North Carolina to evaluate the ability of each model to represent field conditions. The field data consisted of discharge and depth-averaged velocity profiles measured with an acoustic Doppler current profiler and surveyed water-surface profiles for two high-flow conditions. For the initial study site (U.S. Highway 13 over the Tar River at Greenville, North Carolina), the water-surface elevations and velocity distributions simulated by the one- and two-dimensional models showed appreciable disparity in the highly sinuous reach upstream from the U.S. Highway 13 bridge. Based on the available data from U.S. Geological Survey streamgaging stations and acoustic Doppler current profiler velocity data, the two-dimensional model more accurately simulated the water-surface elevations and the velocity distributions in the study reach, and contracted-flow magnitudes and direction through the bridge opening. To further compare the results of the one- and two-dimensional models, estimated hydraulic parameters (flow depths, velocities, attack angles, blocked flow width) for measured high-flow conditions were used to predict scour depths at the U.S. Highway 13 bridge by using established methods. Comparisons of pier-scour estimates from both models indicated that the scour estimates from the two-dimensional model were as much as twice the depth of the estimates from the one-dimensional model. These results can be attributed to higher approach velocities and the appreciable flow angles at the piers simulated by the two-dimensional model and verified in the field. Computed flood-frequency estimates of the 10-, 50-, 100-, and 500-year return-period floods on the Tar River at Greenville were also simulated with both the one- and two-dimensional models. The simulated water-surface profiles and velocity fields of the various return-period floods were used to compare the modeling approaches and provide information on what return-period discharges would result in road over-topping and(or) pressure flow. This information is essential in the design of new and replacement structures. The ability to accurately simulate water-surface elevations and velocity magnitudes and distributions at bridge crossings is essential in assuring that bridge plans balance public safety with the most cost-effective design. By compiling pertinent bridge-site characteristics and relating them to the results of several model-comparison studies, the framework for developing guidelines for selecting the most appropriate model for a given bridge site can be accomplished.
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.
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.
NASA Astrophysics Data System (ADS)
Shao, X.; Sitnov, M. I.; Sharma, A. S.; Papadopoulos, K.; Goodrich, C. C.; Guzdar, P. N.; Milikh, G. M.; Wiltberger, M. J.; Lyon, J. G.
2002-05-01
Studies of the magnetosphere during substorms based on the observational data of the solar wind and the geomagnetic indices have shown clear features of phase transition-like behavior [Sitnov et al., 2000]. The global MHD simulations of the events in the Bargatze et al. [1985] database are used to study the non-equilibrium phase transition-like features of substorms. We simulated 7 intervals of total duration of 280 hours from the same data set used in Sitnov et al. [2000]. From the simulations the AL index is computed from the maximum of the westward Hall current and is referred to as the pseudo-AL index. We analyzed the input-output (vBs-pseudo-AL index) system obtained from the global MHD model and compare the results to those in Sitnov et al. [2000, 2001]. The analysis of the coupled vBs-pseudo-AL index system shows the first-order phase transition characterizing global beahavior, similar to the case of vBs-observed-AL index [Sitnov et al., 2000]. Although, the comparison between observations and global MHD simulations for individual events may vary, the overall global transition pattern during the substorm cycle revealed by singular spectrum snalysis is statistically consistent between simulations and observations. The coupled vBs-pseudo-AL index system shows multi-scale behavior (scale-invariant power-law dependence) in singular power spectrum. We find critical exponents of the non-equilibrium transitions in the magnetosphere, which reflect the multi-scale aspect of the substorm activity, different from power-law frequency of autonomous systems. The exponents relate input and output parameters of the magnetosphere.
NASA Technical Reports Server (NTRS)
1982-01-01
Information on the Japanese National Aerospace Laboratory two dimensional transonic wind tunnel, completed at the end of 1979 is presented. Its construction is discussed in detail, and the wind tunnel structure, operation, test results, and future plans are presented.
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.
Simulations of MHD Dynamo With and Without the Reversal Surface
NASA Astrophysics Data System (ADS)
Martin, D.; Craig, D.; Reusch, J. A.
2014-03-01
Fluctuations in the Reversed Field Pinch (RFP) are dominated by Fourier mode numbers m=0 and m=1. The velocity and magnetic fluctuations drive a dynamo which redistributes current in the plasma. In experiments, m=0 modes and dynamo due to m=1 modes are highly dependent on the existence of the reversal surface in the plasma. We investigate the effects of reversal surface on magnetic and velocity fluctuations using a magnetohydrodynamic simulation to model the plasma with and without a reversal surface. We find that while m=0 modes are suppressed through the removal of the reversal surface, magnetic m=1 amplitudes are not affected. Velocity fluctuations for both modes decrease with the reversal surface removed. Work funded by USDOE.
Energy Science and Technology Software Center (ESTSC)
1997-11-18
QUENCH2D* is developed for the solution of general, non-linear, two-dimensional inverse heat transfer problems. This program provides estimates for the surface heat flux distribution and/or heat transfer coefficient as a function of time and space by using transient temperature measurements at appropriate interior points inside the quenched body. Two-dimensional planar and axisymmetric geometries such as turnbine disks and blades, clutch packs, and many other problems can be analyzed using QUENCH2D*.
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.
Extended MHD Simulation of Kelvin-Helmholtz Instability in a 2D Slab
NASA Astrophysics Data System (ADS)
Hatori, Tomoharu; Miura, Hideaki; Ito, Atsushi; Sato, Masahiko; Goto, Ryosuke
2013-10-01
Shear flow of plasma in magnetic confinement fusion devices can play important roles to achieve high-performance plasma.On one hand, it can improve plasma confinement.On the other hand, it can cause magnetohydrodynamic (MHD) instabilities such as Kelvin-Helmholtz (KH) instability.Although KH instability has been researched intensively in a (single-fluid) MHD theory, the effects of the ion inertia length (two-fluid effect) or finite Larmor radius (FLR effect) to KH modes have not yet been well investigated, especially for parameters suitable for magnetically confined plasmas.These small scale effects are important when the shear is strong, e.g. in the edge region of H-mode tokamaks.In this study, numerical simulations of the KH instability in a 2D slab are carried out by our nonlinear extended MHD code.Evolution of KH modes due to sheared-flow perpendicular to an equilibrium magnetic field is concerned.Two-fluid terms show stabilizing effect, while FLR terms destabilizing. Wave numbers that growth rates are affected by those effects vary by beta, which correspond to the ratio of the Larmor radius to the ion inertia length. Discussion about nonlinear evolution and saturation will be presented.
Simulation of 3-D Nonequilibrium Seeded Air Flow in the NASA-Ames MHD Channel
NASA Technical Reports Server (NTRS)
Gupta, Sumeet; Tannehill, John C.; Mehta, Unmeel B.
2004-01-01
The 3-D nonequilibrium seeded air flow in the NASA-Ames experimental MHD channel has been numerically simulated. The channel contains a nozzle section, a center section, and an accelerator section where magnetic and electric fields can be imposed on the flow. In recent tests, velocity increases of up to 40% have been achieved in the accelerator section. The flow in the channel is numerically computed us ing a 3-D parabolized Navier-Stokes (PNS) algorithm that has been developed to efficiently compute MHD flows in the low magnetic Reynolds number regime: The MHD effects are modeled by introducing source terms into the PNS equations which can then be solved in a very efficient manner. The algorithm has been extended in the present study to account for nonequilibrium seeded air flows. The electrical conductivity of the flow is determined using the program of Park. The new algorithm has been used to compute two test cases that match the experimental conditions. In both cases, magnetic and electric fields are applied to the seeded flow. The computed results are in good agreement with the experimental data.
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.
NASA Astrophysics Data System (ADS)
Ma, Z.; Bhattacharjee, A.; Forbes, T.
2005-12-01
During the last ten years, an eruptive flare model based on a loss of equilibrium in a coronal flux rope has been developed (Forbes and Priest 1995, Lin and Forbes 2000) and has been tested by observations from SOHO and RHESSI. We present fully self-consistent resistive and Hall MHD simulations of the model beginning from an equilibrium solution of the Grad-Shafranov equation in which a flux rope is nested in an arcade. The system is then driven by photospheric converging flows. It is found that the system evolves into a configuration with a thin current sheet which grows progressively thinner and longer, driving the flux rope upward. Magnetic reconnection in the thin current sheet eventually leads to the accelerated expulsion of the flux rope, as anticipated qualitatively by earlier theoretical calculations. In the resistive MHD model, the reconnection rate as well as the acceleration is controlled by the resistivity. In the Hall MHD model, the current sheet becomes thinner and more dynamic, the acceleration is faster and much more weakly dependent on the resistivity (at high values of the Lundquist number). Comparisons will be made with an eruptive event on 2003 November 18.
NASA Astrophysics Data System (ADS)
Borrero, J. M.; Lites, B. W.; Lagg, A.; Rezaei, R.; Rempel, M.
2014-12-01
Milne-Eddington (M-E) inversion codes for the radiative transfer equation are the most widely used tools to infer the magnetic field from observations of the polarization signals in photospheric and chromospheric spectral lines. Unfortunately, a comprehensive comparison between the different M-E codes available to the solar physics community is still missing, and so is a physical interpretation of their inferences. In this contribution we offer a comparison between three of those codes (VFISV, ASP/HAO, and HeLIx+). These codes are used to invert synthetic Stokes profiles that were previously obtained from realistic non-grey three-dimensional magnetohydrodynamical (3D MHD) simulations. The results of the inversion are compared with each other and with those from the MHD simulations. In the first case, the M-E codes retrieve values for the magnetic field strength, inclination and line-of-sight velocity that agree with each other within ?B ? 35 (Gauss), ?? ? 1.2, and ?v ? 10 m s-1, respectively. Additionally, M-E inversion codes agree with the numerical simulations, when compared at a fixed optical depth, within ?B ? 130 (Gauss), ?? ? 5, and ?v ? 320 m s-1. Finally, we show that employing generalized response functions to determine the height at which M-E codes measure physical parameters is more meaningful than comparing at a fixed geometrical height or optical depth. In this case the differences between M-E inferences and the 3D MHD simulations decrease to ?B ? 90 (Gauss), ?? ? 3, and ?v ? 90 m s-1.
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.
Galloway, Joel M.; Green, W. Reed
2007-01-01
Beaver Lake is considered a primary watershed of concern in the State of Arkansas. As such, information is needed to assess water quality, especially nutrient enrichment, nutrient-algal relations, turbidity, and sediment issues within the system. A previously calibrated two-dimensional, laterally averaged model of hydrodynamics and water quality was used for the evaluation of changes in input nutrient and sediment concentrations on the water quality of the reservoir for the period of April 2001 to April 2003. Nitrogen and phosphorus concentrations were increased and decreased and tested independently and simultaneously to examine the nutrient concentrations and algal response in the reservoir. Suspended-solids concentrations were increased and decreased to identify how solids are distributed in the reservoir, which can contribute to decreased water clarity. The Beaver Lake model also was evaluated using a conservative tracer. A conservative tracer was applied at various locations in the reservoir model to observe the fate and transport and how the reservoir might react to the introduction of a conservative substance, or a worst-case spill scenario. In particular, tracer concentrations were evaluated at the locations of the four public water-supply intakes in Beaver Lake. Nutrient concentrations in Beaver Lake increased proportionally with increases in loads from the three main tributaries. An increase of 10 times the calibrated daily input nitrogen and phosphorus in the three main tributaries resulted in daily mean total nitrogen concentrations in the epilimnion that were nearly 4 times greater than the calibration concentrations at site L2 and more than 2 times greater than the calibrated concentrations at site L5. Increases in daily input nitrogen in the three main tributaries independently did not correspond in substantial increases in concentrations of nitrogen in Beaver Lake. The greatest proportional increase in phosphorus occurred in the epilimnion at sites L3 and L4 and the least increase occurred at sites L2 and L5 when calibrated daily input phosphorus concentrations were increased. When orthophosphorus was increased in all three tributaries simultaneously by a factor of 10, daily mean orthophosphorus concentrations in the epilimnion of the reservoir were almost 11 times greater than the calibrated concentrations at sites L2 and L5, and 15 times greater in the epilimnion of the reservoir at sites L3 and L4. Phosphorus concentrations in Beaver Lake increased less when nitrogen and phosphorus were increased simultaneously than when phosphorus was increased independently. The greatest simulated increase in algal biomass (represented as chlorophyll a) occurred when nitrogen and phosphorus were increased simultaneously in the three main tributaries. On average, the chlorophyll a values only increased less than 1 microgram per liter when concentrations of nitrogen or phosphorous were increased independently by a factor of 10 at all three tributaries. In comparison, when nitrogen and phosphorus were increased simultaneously by a factor of 10 for all three tributaries, the chlorophyll a concentration increased by about 10 micrograms per liter on average, with a maximum increase of about 57 micrograms per liter in the epilimnion at site L3 in Beaver Lake. Changes in algal biomass with changes in input nitrogen and phosphorus were variable through time in the Beaver Lake model from April 2001 to April 2003. When calibrated daily input nitrogen and phosphorus concentrations were increased simultaneously for the three main tributaries, the increase in chlorophyll a concentration was the greatest in late spring and summer of 2002. Changes in calibrated daily input inorganic suspended solids concentrations were examined because of the effect they may have on water clarity in Beaver Lake. The increase in total suspended solids was greatest in the hypolimnion at the upstream end of Beaver Lake, and negligible changes
2.5d Mhd Simulations Of Winds From Red Giants Stars: Broadband Alfvn Waves
NASA Astrophysics Data System (ADS)
Airapetian, Vladimir; Carpenter, K.; Ofman, L.
2010-01-01
We present the numerical simulations of winds from evolved giant stars using a fully non-linear, time dependent, 2.5-dimensional magnetohydrodynamic (MHD) code. This study extends our previous fully non-linear MHD wind simulations to the parameter space that describes winds from red giant stars. In the current version of this Alfvn wave driven model, a wind is driven by randomly generated low-frequency non-linear Alfvn waves in a broadband frequency range at the base of the wind. We simulate freely propagated and partially reflected Alfvn waves in the gravitationally stratified atmosphere of a late-type giant star, in a self-consistent manner, until a steady-state wind is formed. Our simulations demonstrate that, unlike linear Alfven wave-driven wind models, a stellar wind model based on plasma acceleration due to low frequency broad-band non-linear Alfvn waves, can consistently reproduce the observed radial velocity profiles of the winds, their terminal velocities, the turbulent broadening of UV lines emitted from those winds and the observed mass loss rates. We find that conversion of non-linear transverse Alfvn waves into longitudinal magnetosonic waves plays the major role in depositing momentum and energy into the stellar wind. The fitting of mass-loss rates from ? Tau with the predicted rate suggests a highly anisotropic stellar wind in this evolved giant. The model also predicts a variation of the wind mass-loss rates on time scales of 1 month.
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.
Propagation of Pi2 pulsations through the braking region in global MHD simulations
NASA Astrophysics Data System (ADS)
Ream, J. B.; Walker, R. J.; Ashour-Abdalla, M.; El-Alaoui, M.; Wiltberger, M.; Kivelson, M. G.; Goldstein, M. L.
2015-12-01
We investigate the propagation of Pi2 period pulsations from their origin in the plasma sheet through the braking region, the region where the fast flows are slowed as they approach the inner edge of the plasma sheet. Our approach is to use both the University of California, Los Angeles (UCLA) and Lyon-Fedder-Mobarry (LFM) global magnetohydrodynamic (MHD) computer codes to simulate the Earth's magnetosphere during a substorm that occurred on 14 September 2004 when Pi2 pulsations were observed. We use two different MHD models in order to test the robustness of our conclusions about Pi2. The simulations are then compared with ground-based and satellite data. We find that the propagation of the pulsations in the simulations, especially through the braking region, depends strongly on the ionospheric models used at the inner boundary of the MHD models. With respect to typical observed values, the modeled conductances are high in the UCLA model and low in the LFM model. The different conductances affect the flows, producing stronger line tying that slows the flow in the braking region more in the UCLA model than in the LFM model. Therefore, perturbations are able to propagate much more freely into the inner magnetosphere in the LFM results. However, in both models Pi2 period perturbations travel with the dipolarization front (DF) that forms at the earthward edge of the flow channel, but as the DF slows in the braking region, -8≤x≤-6 RE, the Pi2 period perturbations begin to travel ahead of it into the inner magnetosphere. This indicates that the flow channels generate compressional waves with periods that fall within the Pi2 range and that, as the flows themselves are stopped in the braking region, the compressional wave continues to propagate into the inner magnetosphere.
NASA Astrophysics Data System (ADS)
Den, M.; Horiuchi, R.; Fujita, S.; Tanaka, T.
2011-12-01
Magnetic reconnection is considered to play an important role in space phenomena such as substorm in the Earth's magnetosphere. Tanaka and Fujita reproduced substorm evolution process by numerical simulation with the global MHD code [1]. In the MHD framework, the dissipation model is introduced for modeling of the kinetic effects. They found that the normalized reconnection viscosity, one of the dissipation model employed there, gave a large effect for the dipolarization, central phenomenon in the substorm development process, though that viscosity was assumed to be a constant parameter. It is well known that magnetic reconnection is controlled by microscopic kinetic mechanism. Frozen-in condition is broken due to particle kinetic effects and collisionless reconnection is triggered when current sheet is compressed as thin as ion kinetic scales under the influence of external driving flow [2, 3]. Horiuchi and his collaborators showed that reconnection electric field generated by microscopic physics evolves inside ion meandering scale so as to balance the flux inflow rate at the inflow boundary, which is controlled by macroscopic physics [2]. That is, effective resistivity generated through this process can be expressed by balance equation between micro and macro physics. In this paper, we perform substorm simulation by using the global MHD code developed by Tanaka [3] with this effective resistivity instead of the empirical resistivity model. We obtain the AE indices from simulation data, in which substorm onset can be seen clearly, and investigate the relationship between the substorm development and the effective resistivity model. [1] T. Tanaka, A, Nakamizo, A. Yoshikawa, S. Fujita, H. Shinagawa, H. Shimazu, T. Kikuchi, and K. K. Hashimoto, J. Geophys. Res. 115 (2010) A05220,doi:10.1029/2009JA014676. [2] W. Pei, R. Horiuchi, and T. Sato, Physics of Plasmas,Vol. 8 (2001), pp. 3251-3257. [3] A. Ishizawa, and R. Horiuchi, Phys. Rev. Lett., Vol. 95, 045003 (2005). [4] T. Tanaka, J. Comp. Phys. 111 (1994) 381.
NASA Astrophysics Data System (ADS)
Fei, Yue; Chan, Anthony A.; Elkington, Scot R.; Wiltberger, Michael J.
2006-12-01
In an MHD particle simulation of the September 1998 magnetic storm the evolution of the radiation belt electron radial flux profile appears to be diffusive, and diffusion caused by ULF waves has been invoked as the probable mechanism. In order to separate adiabatic and nonadiabatic effects and to investigate the radial diffusion mechanism during this storm, in this work we solve a radial diffusion equation with ULF wave diffusion coefficients and a time-dependent outer boundary condition, and the results are compared with the phase space density of the MHD particle simulation. The diffusion coefficients include contributions from both symmetric resonance modes (ω ≈ mωd, where ω is the wave frequency, m is the azimuthal wave number, and ωd is the bounce-averaged drift frequency) and asymmetric resonance modes (ω ≈ (m ± 1)ωd). ULF wave power spectral densities are obtained from a Fourier analysis of the electric and magnetic fields of the MHD simulation and are used in calculating the radial diffusion coefficients. The asymmetric diffusion coefficients are proportional to the magnetic field asymmetry, which is also calculated from the MHD field. The resulting diffusion coefficients vary with the radial coordinate L (the Roederer L-value) and with time during different phases of the storm. The last closed drift shell defines the location of the outer boundary. Both the location of the outer boundary and the value of the phase space density at the outer boundary are time-varying. The diffusion calculation simulates a 42-hour period during the 24-26 September 1998 magnetic storm, starting just before the storm sudden commencement and ending in the late recovery phase. The differential flux calculated in the MHD particle simulation is converted to phase space density. Phase space densities in both simulations (diffusion and MHD particle) are functions of Roederer L-value for fixed first and second adiabatic invariants. The Roederer L-value is calculated using drift shell tracing in the MHD magnetic field, and particles have zero second invariant. The radial diffusion calculation reproduces the main features of the MHD particle simulation quite well. The symmetric resonance modes dominate the radial diffusion, especially in the inner and middle L region, while the asymmetric resonances are more important in the outer region. Using both symmetric and asymmetric terms gives a better result than using only one or the other and is better than using a simple power law diffusion coefficient. We find that it is important to specify the value of the phase space density on the outer boundary dynamically in order to get better agreement between the radial diffusion simulation and the MHD particle simulation.
Relativistic modeling capabilities in PERSEUS extended MHD simulation code for HED plasmas
Hamlin, Nathaniel D.; Seyler, Charles E.
2014-12-15
We discuss the incorporation of relativistic modeling capabilities into the PERSEUS extended MHD simulation code for high-energy-density (HED) plasmas, and present the latest hybrid X-pinch simulation results. The use of fully relativistic equations enables the model to remain self-consistent in simulations of such relativistic phenomena as X-pinches and laser-plasma interactions. By suitable formulation of the relativistic generalized Ohm’s law as an evolution equation, we have reduced the recovery of primitive variables, a major technical challenge in relativistic codes, to a straightforward algebraic computation. Our code recovers expected results in the non-relativistic limit, and reveals new physics in the modeling of electron beam acceleration following an X-pinch. Through the use of a relaxation scheme, relativistic PERSEUS is able to handle nine orders of magnitude in density variation, making it the first fluid code, to our knowledge, that can simulate relativistic HED plasmas.
Relativistic modeling capabilities in PERSEUS extended MHD simulation code for HED plasmas
NASA Astrophysics Data System (ADS)
Hamlin, Nathaniel D.; Seyler, Charles E.
2014-12-01
We discuss the incorporation of relativistic modeling capabilities into the PERSEUS extended MHD simulation code for high-energy-density (HED) plasmas, and present the latest hybrid X-pinch simulation results. The use of fully relativistic equations enables the model to remain self-consistent in simulations of such relativistic phenomena as X-pinches and laser-plasma interactions. By suitable formulation of the relativistic generalized Ohm's law as an evolution equation, we have reduced the recovery of primitive variables, a major technical challenge in relativistic codes, to a straightforward algebraic computation. Our code recovers expected results in the non-relativistic limit, and reveals new physics in the modeling of electron beam acceleration following an X-pinch. Through the use of a relaxation scheme, relativistic PERSEUS is able to handle nine orders of magnitude in density variation, making it the first fluid code, to our knowledge, that can simulate relativistic HED plasmas.
An edge-based finite element scheme for MHD simulations on unstructured grids
NASA Astrophysics Data System (ADS)
Kerhcer, A. D.; Weigel, R. S.
2012-12-01
A new code for magnetohydrodynamic (MHD) simulations on unstructured grids is described. A modified formulation of the edge-based finite element method is implemented. The new formulation allows for a more robust treatment of boundary fluxes leading to more accurate results. The versatility and efficiency of the code is demonstrated on common test problems in one, two and three dimensions. Higher order solutions obtained with flux-corrected transport (FCT) techniques and Godunov methods will be discussed. The code is fully parallelized for use on GPUs, multi-core CPUs and workstation clusters.
3D MHD VDE and disruptions simulations of tokamaks plasmas including some ITER scenarios
NASA Astrophysics Data System (ADS)
Paccagnella, R.; Strauss, H. R.; Breslau, J.
2009-03-01
Tokamaks vertical displacement events (VDEs) and disruptions simulations in toroidal geometry by means of a single fluid visco-resistive magneto-hydro-dynamic (MHD) model are presented in this paper. The plasma model is completed with the presence of a 2D wall with finite resistivity which allows the study of the relatively slowly growing magnetic perturbation, the resistive wall mode (RWM), which is, in this paper, the main drive of the disruption evolution. Amplitudes and asymmetries of the halo currents pattern at the wall are also calculated and comparisons with tokamak experimental databases and predictions for ITER are given.
MHD simulation of a propagation of loop-like and bubble-like magnetic clouds
NASA Technical Reports Server (NTRS)
Vandas, M.; Fischer, S.; Pelant, P.; Dryer, M.; Smith, Z.; Detman, T.
1995-01-01
Propagation and evolution of magnetic clouds in the ambient solar wind flow is studied self-consistently using ideal MHD equations in three dimensions. Magnetic clouds as ideal force-free objects (cylinders or spheres) are ejected near the Sun and followed beyond the Earth's orbit. We investigate the influence of various initial parameters like the injection velocity, magnetic field strength, magnetic helicity, orientation of the clouds' axis, etc., on their propagation and evolution. We demonstrate that the injection velocity and magnetic field strength have a major influence on propagation. Simulation results are compared with analytical solutions of magnetic cloud evolution.
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
NIMROD Extended MHD Simulations of Reversed-Field Pinch Relaxation Dynamics
NASA Astrophysics Data System (ADS)
Sauppe, Joshua; Sovinec, Carl; Sarff, John; Triana, Joseph
2014-10-01
The nonlinear evolution and relaxation dynamics of an initially non-reversed two-fluid plasma in cylindrical geometry is investigated using the NIMROD code. The initial relaxation event brings the plasma to the characteristic reversed-field state. There is significant magnetic activity with MHD and Hall dynamos working together to relax the parallel current profile while the fluctuation-induced Lorentz force drives plasma flows. Subsequent events have considerably less magnetic activity and often have opposing MHD and Hall dynamos. The direction of the driven flows in these events differs from the initial event, and is consistent with experimental observations on the MST RFP. The nonlinear mode coupling during relaxation events is investigated, and the presence of the Hall dynamo is found to significantly alter the spectral power flow. Synthetic diagnostics are used to compare simulation results to experimental measurements of Hall dynamo mode structure with laser Faraday rotation and magnetic probes. At modest Lundquist number the time-scales of relaxation and drive are well-separated and the simulations are compared to two-fluid relaxation theories. Generalized two-fluid helicities are well-conserved relative to magnetic energy over the simulated relaxation events. Work supported by U.S. DoE and NSF.
Solar wind - Magnetosphere - Ionosphere Coupling in the GUMICS-4 Global MHD Simulation
NASA Astrophysics Data System (ADS)
Pulkkinen, T. I.; Palmroth, M.; Laitinen, T. V.; Janhunen, P.; Koskinen, H. E.
This presentation discusses the magnetosphere - ionosphere coupling dynamics during substorm evolution in a global MHD simulation GUMICS-4. The ionospheric and magnetospheric evolution is followed during observed substorm events that have been run using the actual solar wind and IMF as model initial and boundary conditions. In addition to the standard 5-min resolution output from the simulation, specific periods were rerun in a mode that saves the output every 20 seconds. This allows us to analyze changes in the magnetosphere and ionosphere at intervals corresponding roughly to the Alfven travel time between the ionosphere and high-altitude magnetosphere. We examine the effects of the solar wind dynamic pressure and the orientation of the interplanetary magnetic field on the energy input into the magnetosphere through the magnetopause surface and its dissipation in the ionosphere. In the ionosphere, maps of the Pedersen and Hall conductances, auroral precipitation power, Joule heating, polar cap potential, and field-aligned currents are used in the analysis. In the magnetosphere, the location and shape of the tail current sheet is characterized using physical parameters such as magnetic field, current density, plasma velocity, mass flux, and energy flux in a coordinate system defined by the sheet. The results are used to discuss, in the framework of the MHD simulation, the solar wind driving of magnetospheric activity and the role of near-tail reconnection in the energy dissipation in the ionosphere.
Two-dimensional material nanophotonics
NASA Astrophysics Data System (ADS)
Xia, Fengnian; Wang, Han; Xiao, Di; Dubey, Madan; Ramasubramaniam, Ashwin
2014-12-01
Two-dimensional materials exhibit diverse electronic properties, ranging from insulating hexagonal boron nitride and semiconducting transition metal dichalcogenides such as molybdenum disulphide, to semimetallic graphene. In this Review, we first discuss the optical properties and applications of various two-dimensional materials, and then cover two different approaches for enhancing their interactions with light: through their integration with external photonic structures, and through intrinsic polaritonic resonances. Finally, we present a narrow-bandgap layered material -- black phosphorus -- that serendipitously bridges the energy gap between the zero-bandgap graphene and the relatively large-bandgap transition metal dichalcogenides. The plethora of two-dimensional materials and their heterostructures, together with the array of available approaches for enhancing the light-matter interaction, offers the promise of scientific discoveries and nanophotonics technologies across a wide range of the electromagnetic spectrum.
MHD limits in non-inductive tokamak plasmas: simulations and comparison to experiments on Tore Supra
Maget, P.; Huysmans, G.; Ottaviani, M.; Garbet, X.; Moreau, Ph.; Segui, J.-L.; Luetjens, H.
2008-11-01
Non-inductive tokamak discharges with a flat or hollow current profile are prone to the triggering of large tearing modes when the minimum of the safety factor is just below a low order rational. This issue is of particular importance for discussing the optimal safety factor for MHD modes avoidance in Steady-State reactor plasmas. Different non-linear regimes of such magnetic configurations in Tore Supra are studied using the full MHD code XTOR. Numerical simulations show that the non-linear stage of the Double-Tearing Mode (DTM) is governed by the full reconnection model, but a single tearing mode in a low magnetic shear configuration can have a similar impact on the confinement. The different regimes observed experimentally are recovered in the simulations: a small amplitude (2,1) DTM for close resonant surfaces as seen in Tore Supra, a sawtooth-like behaviour of the (2,1) Double-Tearing Mode as first seen in TFTR, or a large amplitude (2,1) tearing mode that severely degrades the energy confinement, as reported in Tore Supra, JET or DIII-D. Situations where q{sub min}{approx_equal}1.5 with a stable n = 1 mode, as seen in Tore Supra longest discharges, seem to put specific constraints on the MHD model that is used. Indeed, curvature stabilisation without transport terms as could explain linear stability, but such effect vanishes in presence of heat transport. Electron diamagnetic rotation effect is investigated as a possible mechanism for n = 1 mode stabilization.
NASA Technical Reports Server (NTRS)
Ding, D. Q.; Denton, . E.; Hudson, M. K.; Lysak, R. L.
1995-01-01
The poloidal mode field line resonance in the Earth's dipole magnetic field is investigated using cold plasma ideal MHD simulations in dipole geometry. In order to excite the poloidal mode resonance, we use either an initial or a continuous velocity perturbation to drive the system. The perturbation is localized at magnetic shell L = 7 with plasma flow in the radial direction (electric field component in the azimuthal direction). It is found that with the initial perturbation alone, no polodial mode resonance can be obtained and the initially localized perturbation spreads out across all magnetic L shells. With the continuous perturbation, oscillating near the poloidal resonance frequency, a global-scale poloidal cavity mode can be obtained. For the first time, a localized guided poloidal mode resonance is obtained when a radial component of electric field is added to the initial perturbation such that the curl of the electric field is everywhere perpendicular to the background dipole magnetic field. During the localized poloidal resonance, plasma vortices parallel/antiparallel to the background dipole magnetic field B(sub 0). This circular flow, elongated radially, results in twisting of magnetic field flux tubes, which, in turn, leads to the slowdown of the circular plasma flow and reversal of the plasma vortices. The energy associated with the localized poloidal resonance is conserved as it shifts back and forth between the oscillating plasma vortices and the alternately twisted magnetic flux tubes. In the simulations the eigenfunctions associated with the localized poloidal resonance are grid-scale singular functions. This result indicates that ideal MHD is inadequate to describe the underlying problem and nonideal MHD effects are needed for mode broadening.
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.
Nonlinear MHD simulation of DC helicity injection in the Pegasus spherical tokamak
NASA Astrophysics Data System (ADS)
Bayliss, Adam; Sovinec, Carl
2006-10-01
DC helicity injection has been successfully employed in spherical tokamaks (ST's) to produce a tokamak-like plasma with either a poloidal-gap voltage known as coaxial helicity injection [HIT-II, NSTX] or a biased cathode gun configuration [CDX, PEGASUS]. In PEGASUS, the tokamak-like plasma which is subsequently ohmically driven is the product of a reversal of vacuum poloidal flux and a merger of gun-injected current filaments. A 3D nonlinear MHD computation using the NIMROD code [Sovinec et al. JCP 195, 355 (2004)] simulates the formation, merger, and relaxation of the gun-injected current filaments to the tokamak-like plasma. The reversal of poloidal flux due to the field induced by the helicity drive is reproduced and the MHD processes leading to the merger and relaxation of the current filaments are described. Over the lifetime of a helically-driven experimental shot (approximately 10ms), the extent to which the merged plasma exhibits amplication of poloidal flux and the injected current in the relaxed state, reported in PEGASUS, is explored. The results are compared with simulations of current drive in NSTX via coaxial helicity injection which exhibit an n=1 open field-line kink [Tang and Boozer, Phys. Plasmas 11, 2679 (2004)].
Observations and 3D MHD simulations of a solar active region jet
NASA Astrophysics Data System (ADS)
Gontikakis, C.; Archontis, V.; Tsinganos, K.
2009-11-01
Aims: We study an active region jet originating from NOAA 8531 on May 15 1999. We perform 3D MHD numerical simulations of magnetic flux emergence and its subsequent reconnection with preexisting magnetic flux. Then, we compare the physical properties of the observed jet with the reconnecting outflow produced in the numerical model. Methods: We report observations of this jet using a series of TRACE 171 filtergrams, simultaneous observations from SUMER in Ne viii 770 and C iv 1548 as well as MDI magnetograms. In the numerical simulation, the full compressible and resistive MHD equations are solved, including viscous and Ohmic heating. Results: A high-velocity upflow (?100 km s-1) is observed after the emergence of new magnetic flux at the edge of the active region. The jet is recorded over a range of temperatures between 105 K and 1.5 106 K. In our numerical experiments, we find that the jet is the result of magnetic reconnection between newly emerging flux and the preexisting magnetic field of the active region. Conclusions: The hot and high-velocity bidirectional flows occur as a result of the interaction between oppositely directed magnetic fields. Observations and numerical results are strongly suggestive of effective reconnection process being responsible for producing jets when emerging flux appears in solar active regions.
Chatterjee, Dipankar; Amiroudine, Sakir
2011-02-01
A comprehensive non-isothermal Lattice Boltzmann (LB) algorithm is proposed in this article to simulate the thermofluidic transport phenomena encountered in a direct-current (DC) magnetohydrodynamic (MHD) micropump. Inside the pump, an electrically conducting fluid is transported through the microchannel by the action of an electromagnetic Lorentz force evolved out as a consequence of the interaction between applied electric and magnetic fields. The fluid flow and thermal characteristics of the MHD micropump depend on several factors such as the channel geometry, electromagnetic field strength and electrical property of the conducting fluid. An involved analysis is carried out following the LB technique to understand the significant influences of the aforementioned controlling parameters on the overall transport phenomena. In the LB framework, the hydrodynamics is simulated by a distribution function, which obeys a single scalar kinetic equation associated with an externally imposed electromagnetic force field. The thermal history is monitored by a separate temperature distribution function through another scalar kinetic equation incorporating the Joule heating effect. Agreement with analytical, experimental and other available numerical results is found to be quantitative. PMID:21053082
Extended MHD simulations of infernal mode dynamics and coupling to tearing modes
NASA Astrophysics Data System (ADS)
Brunetti, D.; Graves, J. P.; Halpern, F. D.; Luciani, J.-F.; Ltjens, H.; Cooper, W. A.
2015-05-01
A numerical study of pressure driven magnetohydrodynamic (MHD) instabilities in a low-shear tight aspect ratio configuration is presented. When the magnetic shear is sufficiently small over an extended region in the core, enhanced instability occurs due to the coupling to poloidal sidebands, which itself occurs due to toroidicity. Numerical simulations have been performed with the initial value code XTOR-2F both in the ideal and resistive MHD frame. Two-fluid effects (plasma diamagnetic flows) have been retained as well. The predictions of the XTOR-2F code on the amplitude of the growth rate, and on the rotation frequency of the modes, have been compared with analytic linear theory of infernal modes. Qualitative agreement has been found between numerical and analytical results, in spite of the tight aspect ratio configuration. The intermediate scaling ? S-3/8, predicted by the linear theory (Brunetti et al 2014 Plasma Phys. Control. Fusion 56 075025), is recovered by the numerical results. A study of the nonlinear evolution of the magnetic island of the tearing sideband has been performed and the results from the simulations are compared with Rutherfords theory.
Stochastic models of two-dimensional fracture
NASA Astrophysics Data System (ADS)
Ausloos, M.; Kowalski, J. M.
1992-06-01
Two statistical models of (strictly two-dimensional) layer destruction are presented. The first is built as a strict percolation model with an added ``conservation law'' (conservation of mass) as physical constraint. The second allows for damped or limited fracture. Two successive fracture crack thresholds are considered. Percolation (i.e., fracture) probability and cluster distributions are studied by use of numerical simulations. Different fractal dimension, critical exponents for cluster distribution, and universality laws characterize both models.
Nonlinear MHD simulations of Quiescent H-mode plasmas in DIII-D
NASA Astrophysics Data System (ADS)
Liu, F.; Huijsmans, G. T. A.; Loarte, A.; Garofalo, A. M.; Solomon, W. M.; Snyder, P. B.; Hoelzl, M.; Zeng, L.
2015-09-01
In the Quiescent H-mode (QH-mode) regime, the edge harmonic oscillation (EHO), thought to be a saturated kink-peeling mode (KPM) driven unstable by current and rotation, is found in experiment to provide sufficient stationary edge particle transport to avoid the periodic expulsion of particles and energy by edge localized modes (ELMs). In this paper, both linear and nonlinear MHD modelling of QH-mode plasmas from the DIII-D tokamak have been investigated to understand the mechanism leading to the appearance of the EHO in QH-mode plasmas. For the first time nonlinear MHD simulations with low-n modes both with ideal wall and resistive wall boundary conditions have been carried out with the 3D non-linear MHD code JOREK. The results show, in agreement with the original conjectures, that in the non-linear phase, kink peeling modes are the main unstable modes in QH-mode plasmas of DIII-D and that the kink-peeling modes saturate non-linearly leading to a 3D stationary state. The characteristics of the kink-peeling modes, in terms of mode structure and associated decrease of the edge plasma density associated with them, are in good agreement with experimental measurements of the EHO in DIII-D. The effect of plasma resistivity, the role of plasma parallel rotation as well as the effect of the conductivity of the vacuum vessel wall on the destabilization and saturation of kink-peeling modes have been evaluated for experimental QH-mode plasma conditions in DIII-D.
Intermittency, dissipation, and scaling in two-dimensional magnetohydrodynamic turbulence
Merrifield, J. A.; Chapman, S. C.; Dendy, R. O.
2007-01-15
Direct numerical simulations (DNS) provide a means to test phenomenological models for the scaling properties of intermittent MHD turbulence. The well-known model of She and Leveque, when generalized to MHD, is in good agreement with the DNS in three dimensions, however, it does not coincide with DNS in two dimensions (2D). This is resolved here using the results of recent DNS of driven MHD turbulence in 2D which directly determine the scaling of the rate of dissipation. Specifically, a simple modification to generalized refined similarity is proposed that captures the results of the 2D MHD simulations. This leads to a new generalization of She and Leveque in MHD that is coincident with the DNS results in 2D. A key feature of this model is that the most intensely dissipating structures, which are responsible for the intermittency, are thread-like in 2D, independent of whether the underlying phenomenology of the cascade is Kolmogorov or Iroshnikov Kraichnan.
NASA Technical Reports Server (NTRS)
Benyo, Theresa L.
2011-01-01
Flow matching has been successfully achieved for an MHD energy bypass system on a supersonic turbojet engine. The Numerical Propulsion System Simulation (NPSS) environment helped perform a thermodynamic cycle analysis to properly match the flows from an inlet employing a MHD energy bypass system (consisting of an MHD generator and MHD accelerator) on a supersonic turbojet engine. Working with various operating conditions (such as the applied magnetic field, MHD generator length and flow conductivity), interfacing studies were conducted between the MHD generator, the turbojet engine, and the MHD accelerator. This paper briefly describes the NPSS environment used in this analysis. This paper further describes the analysis of a supersonic turbojet engine with an MHD generator/accelerator energy bypass system. Results from this study have shown that using MHD energy bypass in the flow path of a supersonic turbojet engine increases the useful Mach number operating range from 0 to 3.0 Mach (not using MHD) to a range of 0 to 7.0 Mach with specific net thrust range of 740 N-s/kg (at ambient Mach = 3.25) to 70 N-s/kg (at ambient Mach = 7). These results were achieved with an applied magnetic field of 2.5 Tesla and conductivity levels in a range from 2 mhos/m (ambient Mach = 7) to 5.5 mhos/m (ambient Mach = 3.5) for an MHD generator length of 3 m.
3D Dynamics of Magnetopause Reconnection Using Hall-MHD Global Simulations
NASA Astrophysics Data System (ADS)
Maynard, K.; Germaschewski, K.; Raeder, J.; Bhattacharjee, A.
2011-12-01
Magnetic reconnection at Earth's magnetopause and in the magnetotail is of crucial importance for the dynamics of the global magnetosphere and space weather. Even though the plasma conditions in the magnetosphere are largely in the collisionless regime, most of the existing research using global computational models employ single-fluid magnetohydrodynamics (MHD) with artificial resistivity. Studies of reconnection in simplified, two-dimensional geometries have established that two-fluid and kinetic effects can dramatically alter dynamics and reconnection rates when compared with single-fluid models. These enhanced models also introduce particular signatures, for example a quadrupolar out-of-plane magnetic field component that has already been observed in space by satellite measurements. However, results from simplified geometries cannot be translated directly to the dynamics of three-dimensional magnetospheric reconnection. For instance, magnetic flux originating from the solar wind and arriving at the magnetopause can either reconnect or be advected around the magnetosphere. In this study, we use a new version of the OpenGGCM code that incorporates the Hall term in a Generalized Ohm's Law to study magnetopause reconnection under synthetic solar wind conditions and investigate how reconnection rates and dynamics of flux transfer events depend on the strength of the Hall term. The OpenGGCM, a global model of Earth's magnetosphere, has recently been ported to exploit modern computing architectures like the Cell processor and SIMD capabilities of conventional processors using an automatic code generator. These enhancements provide us with the performance needed to include the computationally expensive Hall physics.
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.
Interaction of Cometary Material With the Solar Corona: EUV Observations and MHD Simulations
NASA Astrophysics Data System (ADS)
Liu, W.; Jia, Y.; Downs, C.; Schrijver, C.; Saint-Hilaire, P.; Battams, K.; Tarbell, T. D.; Shine, R. A.
2012-12-01
Extreme ultraviolet (EUV) emission from two recent sun-grazing comets, C/2011 N3 and C/2011 W3 (Lovejoy), has been observed in the solar corona for the first time by the SDO/AIA and STEREO/EUVI instruments (Schrijver et al. 2011). These observations provided a unique opportunity to investigate the interaction of the cometary material with the solar corona and probe their physical conditions. We present here EUV observations and MHD simulations on this subject, focusing on the deceleration of the cometary tail material within the corona. We found that despite their different local coronal environments, the two comets exhibited quite similar characteristics. The initial EUV emitting tail had a projected velocity of 100-200 km/s, which was much lower than the orbital velocity of 500-600 km/s in the plane-of-sky. This indicates that significant deceleration had taken place while the tail material was heated to coronal temperatures on the order of 1 MK before it started to emit in EUV (Bryans & Pesnell 2012). After its initial appearance, the tail further experienced a projected deceleration of ~1 km/s^2 (or 4 g_Sun). In particular, in the Lovejoy case, the tail appeared as clusters of bright parallel striations roughly at right angles to the orbit direction, suggestive of magnetic field lines illuminated by the plasma frozen onto them. These striations came to a stop and then accelerated in an opposite direction (seen in projection), approaching a constant velocity of ~50 km/s. These observations suggest that a Lorentz force from the coronal magnetic field was operating on the newly ionized cometary plasma. To test this hypothesis and understand tail deceleration mechanisms, we adopted a multi-fluid MHD model (Jia et al. 2012) to simulate the interaction between charged particles and the magnetized coronal plasma. We used potential extrapolation (Schrijver & DeRosa 2003) and a more sophisticated global MHD model (Lionello et al. 2009) to infer the magnetic field and plasma conditions of the corona along the comet's orbit as inputs to the simulations. We will compare the observations and simulation results, and discuss the implications for using sun-grazing comets as probes to the solar corona in the context of NASA's future Solar Probe Plus mission.
Two-dimensional flexible nanoelectronics
NASA Astrophysics Data System (ADS)
Akinwande, Deji; Petrone, Nicholas; Hone, James
2014-12-01
2014/2015 represents the tenth anniversary of modern graphene research. Over this decade, graphene has proven to be attractive for thin-film transistors owing to its remarkable electronic, optical, mechanical and thermal properties. Even its major drawback--zero bandgap--has resulted in something positive: a resurgence of interest in two-dimensional semiconductors, such as dichalcogenides and buckled nanomaterials with sizeable bandgaps. With the discovery of hexagonal boron nitride as an ideal dielectric, the materials are now in place to advance integrated flexible nanoelectronics, which uniquely take advantage of the unmatched portfolio of properties of two-dimensional crystals, beyond the capability of conventional thin films for ubiquitous flexible systems.
Two-dimensional 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.
MHD SIMULATIONS OF ACCRETION ONTO Sgr A*: QUIESCENT FLUCTUATIONS, OUTBURSTS, AND QUASIPERIODICITY
Chan Chikwan; Liu Siming; Fryer, Christopher L.; Psaltis, Dimitrios; Oezel, Feryal; Melia, Fulvio; Rockefeller, Gabriel
2009-08-10
High-resolution observations of Sgr A* have revealed a wide variety of phenomena, ranging from intense rapid flares to quasi-periodic oscillations (QPOs), making this object an ideal system to study the properties of low luminosity accreting black holes. In this paper, we use a pseudospectral algorithm to construct and evolve a three-dimensional magnetohydrodynamic (MHD) model of the accretion disk in Sgr A*. Assuming a hybrid thermal-nonthermal emission scheme and calibrating the parameters by observations, we show that the MHD turbulence in the environment of Sgr A* can by itself only produce factor two fluctuations in luminosity. These fluctuations cannot explain the magnitude of flares observed in this system. However, we also demonstrate that external forcing of the accretion disk, which may be generated by the 'clumpy material' raining down onto the disk from the large-scale flow, do produce outbursts qualitatively similar to those observed by XMM-Newton in X-rays and by ground-based facilities in the near infrared. Strong, but short-term QPOs emerge naturally in the simulated light curves. We attribute these to nonaxisymmetric density perturbations that emerge as the disk evolves back toward its quiescent state.
Sub-Alfvenic Non-Ideal MHD Turbulence Simulations with Ambipolar Diffusion: I. Turbulence Statistics
Klein, R I; Li, P S; McKee, C F; Fisher, R
2008-04-10
Most numerical investigations on the role of magnetic fields in turbulent molecular clouds (MCs) are based on ideal magneto-hydrodynamics (MHD). However, MCs are weakly ionized, so that the time scale required for the magnetic field to diffuse through the neutral component of the plasma by ambipolar diffusion (AD) can be comparable to the dynamical time scale. We have performed a series of 256{sup 3} and 512{sup 3} simulations on supersonic but sub-Alfvenic turbulent systems with AD using the Heavy-Ion Approximation developed in Li et al. (2006). Our calculations are based on the assumption that the number of ions is conserved, but we show that these results approximately apply to the case of time-dependent ionization in molecular clouds as well. Convergence studies allow us to determine the optimal value of the ionization mass fraction when using the heavy-ion approximation for low Mach number, sub-Alfvenic turbulent systems. We find that ambipolar diffusion steepens the velocity and magnetic power spectra compared to the ideal MHD case. Changes in the density PDF, total magnetic energy, and ionization fraction are determined as a function of the AD Reynolds number. The power spectra for the neutral gas properties of a strongly magnetized medium with a low AD Reynolds number are similar to those for a weakly magnetized medium; in particular, the power spectrum of the neutral velocity is close to that for Burgers turbulence.
3D MHD simulations of the flapping instability - magnetic reconnection interaction.
NASA Astrophysics Data System (ADS)
Divin, Andrey; Erkaev, Nikolay; Lapenta, Giovanni; Markidis, Stefano; Korovinskiy, Daniil; Semenov, Vladimir; Kubyshkina, Daria
Earth's magnetotail is susceptible to MHD-scale kink-like oscillations that bend the current sheet in the equatorial plane. An analytical theory developed recently suggests that the oscillations can exist if normal and tangential magnetic field gradients are non-zero, hence the name (double-gradient mode). The mode is stable if the product of these two gradients is positive, and unstable if the product is negative. The latter case was successfully reproduced recently by large-scale MHD simulations. In the present report we investigate the interaction of localised magnetic reconnection pulse and the flapping instability. Grad-Shafranov equation solution provides for the initial tail-like condition, and reconnection is started by adding anomalous resistivity at the current sheet center. Plasma flows significantly increase the local gradients at the jet front, leading to much faster flapping mode development. Notably, if the initial configuration is flapping unstable, then the reconnection jet shows evidences of a kink-like bending in the equatorial plane. In the nonlinear stage the front extent in the vertical ("Z" GSM) direction increases due to instability, hence local generation of the mode can lead to structuring of magnetotail dipolarization fronts and is of potential importance for tail dynamics.
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.
NASA Astrophysics Data System (ADS)
Kanki, Takashi; Nagata, Masayoshi; Kagei, Yasuhiro
2011-10-01
The dynamics of structures of magnetic field, current density, and plasma flow generated during multi-pulsed coaxial helicity injection in spherical torus is investigated by 3-D nonlinear MHD simulations. During the driven phase, the flux and current amplifications occur due to the merging and magnetic reconnection between the preexisting plasma in the confinement region and the ejected plasma from the gun region involving the n = 1 helical kink distortion of the central open flux column (COFC). Interestingly, the diamagnetic poloidal flow which tends toward the gun region is then observed due to the steep pressure gradients of the COFC generated by ohmic heating through an injection current winding around the inboard field lines, resulting in the formation of the strong poloidal flow shear at the interface between the COFC and the core region. This result is consistent with the flow shear observed in the HIST. During the decay phase, the configuration approaches the axisymmetric MHD equilibrium state without flow because of the dissipation of magnetic fluctuation energy to increase the closed flux surfaces, suggesting the generation of ordered magnetic field structure. The parallel current density ? concentrated in the COFC then diffuses to the core region so as to reduce the gradient in ?, relaxing in the direction of the Taylor state.
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 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.
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.
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.
NASA Astrophysics Data System (ADS)
Hayashi, Keiji; Washimi, H.; Tokumaru, M.
2012-05-01
The evolution of the inner heliosphere over a 9-year period from 2001 to 2009, from 50 Rs to 1250 Rs, is simulated by means of the time-dependent three-dimensional MHD simulation with a new treatment handling the observation-based temporally evolving boundary data. The inner boundary magnetic field is calculated from the solar surface magnetic field data made at Wilcox Solar Observatory (WSO), and the plasma speed data is from the maps constructed by means of the MHD tomography analysis using the interplanetary scintillation (IPS) data. The density and temperatures are determined by empirical relation functions that are derived from Helios data. In this way, all inner boundary values of the solar wind flowing outward are from measurements. The two ground-based observations, WSO magnetic field and IPS solar wind data, have been long conducted, and we used these two dataset to drive the simulation system over the 9-year span well covering the solar cycle 23. The simulated interplanetary MHD variables are compared with the in-situ measurements, OMNI (nearby the Earth) and the Ulysses. Overall, except the poloidal component of the magnetic field, the simulated MHD variables derived agree very well with the in-situ data.
Application of a 3D, Adaptive, Parallel, MHD Code to Supernova Remnant Simulations
NASA Astrophysics Data System (ADS)
Kominsky, P.; Drake, R. P.; Powell, K. G.
2001-05-01
We at Michigan have a computational model, BATS-R-US, which incorporates several modern features that make it suitable for calculations of supernova remnant evolution. In particular, it is a three-dimensional MHD model, using a method called the Multiscale Adaptive Upwind Scheme for MagnetoHydroDynamics (MAUS-MHD). It incorporates a data structure that allows for adaptive refinement of the mesh, even in massively parallel calculations. Its advanced Godunov method, a solution-adaptive, upwind, high-resolution scheme, incorporates a new, flux-based approach to the Riemann solver with improved numerical properties. This code has been successfully applied to several problems, including the simulation of comets and of planetary magnetospheres, in the 3D context of the Heliosphere. The code was developed under a NASA computational grand challenge grant to run very rapidly on parallel platforms. It is also now being used to study time-dependent systems such as the transport of particles and energy from solar coronal mass ejections to the Earth. We are in the process of modifying this code so that it can accommodate the very strong shocks present in supernova remnants. Our test case simulates the explosion of a star of 1.4 solar masses with an energy of 1 foe, in a uniform background medium. We have performed runs of 250,000 to 1 million cells on 8 nodes of an Origin 2000. These relatively coarse grids do not allow fine details of instabilities to become visible. Nevertheless, the macroscopic evolution of the shock is simulated well, with the forward and reverse shocks visible in velocity profiles. We will show our work to date. This work was supported by NASA through its GSRP program.
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.
A Real-time 3D Visualization of Global MHD Simulation for Space Weather Forecasting
NASA Astrophysics Data System (ADS)
Murata, K.; Matsuoka, D.; Kubo, T.; Shimazu, H.; Tanaka, T.; Fujita, S.; Watari, S.; Miyachi, H.; Yamamoto, K.; Kimura, E.; Ishikura, S.
2006-12-01
Recently, many satellites for communication networks and scientific observation are launched in the vicinity of the Earth (geo-space). The electromagnetic (EM) environments around the spacecraft are always influenced by the solar wind blowing from the Sun and induced electromagnetic fields. They occasionally cause various troubles or damages, such as electrification and interference, to the spacecraft. It is important to forecast the geo-space EM environment as well as the ground weather forecasting. Owing to the recent remarkable progresses of super-computer technologies, numerical simulations have become powerful research methods in the solar-terrestrial physics. For the necessity of space weather forecasting, NICT (National Institute of Information and Communications Technology) has developed a real-time global MHD simulation system of solar wind-magnetosphere-ionosphere couplings, which has been performed on a super-computer SX-6. The real-time solar wind parameters from the ACE spacecraft at every one minute are adopted as boundary conditions for the simulation. Simulation results (2-D plots) are updated every 1 minute on a NICT website. However, 3D visualization of simulation results is indispensable to forecast space weather more accurately. In the present study, we develop a real-time 3D webcite for the global MHD simulations. The 3-D visualization results of simulation results are updated every 20 minutes in the following three formats: (1)Streamlines of magnetic field lines, (2)Isosurface of temperature in the magnetosphere and (3)Isoline of conductivity and orthogonal plane of potential in the ionosphere. For the present study, we developed a 3-D viewer application working on Internet Explorer browser (ActiveX) is implemented, which was developed on the AVS/Express. Numerical data are saved in the HDF5 format data files every 1 minute. Users can easily search, retrieve and plot past simulation results (3D visualization data and numerical data) by using the STARS (Solar-terrestrial data Analysis and Reference System). The STARS is a data analysis system for satellite and ground-based observation data for solar-terrestrial physics.
Dayside Proton Aurora: Comparisons between Global MHD Simulations and Image Observations
NASA Technical Reports Server (NTRS)
Berchem, J.; Fuselier, S. A.; Petrinec, S.; Frey, H. U.; Burch, J. L.
2003-01-01
The IMAGE mission provides a unique opportunity to evaluate the accuracy of current global models of the solar wind interaction with the Earth's magnetosphere. In particular, images of proton auroras from the Far Ultraviolet Instrument (FUV) onboard the IMAGE spacecraft are well suited to support investigations of the response of the Earth's magnetosphere to interplanetary disturbances. Accordingly, we have modeled two events that occurred on June 8 and July 28, 2000, using plasma and magnetic field parameters measured upstream of the bow shock as input to three-dimensional magnetohydrodynamic (MHD) simulations. This paper begins with a discussion of images of proton auroras from the FUV SI-12 instrument in comparison with the simulation results. The comparison showed a very good agreement between intensifications in the auroral emissions measured by FUV SI-12 and the enhancement of plasma flows into the dayside ionosphere predicted by the global simulations. Subsequently, the IMAGE observations are analyzed in the context of the dayside magnetosphere's topological changes in magnetic field and plasma flows inferred from the simulation results. Finding include that the global dynamics of the auroral proton precipitation patterns observed by IMAGE are consistent with magnetic field reconnection occurring as a continuous process while the iMF changes in direction and the solar wind dynamic pressure varies. The global simulations also indicate that some of the transient patterns observed by IMAGE are consistent with sporadic reconnection processes. Global merging patterns found in the simulations agree with the antiparallel merging model. though locally component merging might broaden the merging region, especially in the region where shocked solar wind discontinuities first reach the magnetopause. Finally, the simulations predict the accretion of plasma near the bow shock in the regions threaded by newly open field lines on which plasma flows into the dayside ionosphere are enhanced. Overall the results of these initial comparisons between global MHD simulation results and IMAGE observations emphasize the interplay between reconnection and dynamic pressure processes at the dayside magnetopause. as well as the intricate connection between the bow shock and the auroral region.
The Dynamics of Two-Dimensional Foams
NASA Astrophysics Data System (ADS)
Chae, Jang Jin
This dissertation describes research on the structure and dynamics of two-dimensional foams. New experimental results are presented and new algorithms developed to study foam dynamics with particular emphasis on foams that evolve with significant rupture. In the introduction, basic principles and statistical properties of two-dimensional coarsening cellular patterns are reviewed. Theoretical and computational models which have been developed are also discussed. In Chapter 2, experimental results are presented for the relaxation of a two dimensional soap foam in which wall breakage is initiated through gentle warming of the foam cell. Significantly different phenomenology from the relaxation of non-breaking foams is observed. At a critical "break time," which depends on the temperature ramping rate and initial conditions, a large scale mechanical cascade of wall rupture sets in leading to a rapid disintegration of the foam. In Chapter 3, an efficient new algorithm for simulating the evolution of two-dimensional dry soap foams is presented. Our physically based model for the evolution is based on a combination of mass transfer, vertex movement, and edge relaxation. The stochastic nature of topological transitions due to numerical error has been carefully examined. In Chapter 4, simulations of breaking foams by this new algorithm are presented. The separation of vertex and edge movements permits a study of foam evolution that includes wall rupture. This evolution exhibits a sensitive dependence on both the type of breaking "rule" chosen as well as the initial conditions. The topological evolution is characterized in terms of certain "evolution exponents," and we show simulation results that agree with theoretical considerations. In Chapter 5, normal grain growth in anisotropic polycrystals is simulated using a new algorithm developed from the one used to simulate normal foams. The simulation results, without breakage, show a decrease in growth exponents which is due to the reduction in the mean surface energy during evolution. However, including breakage of low angle tilt grain boundaries substantially increases the growth exponents. These simulations highlight the fact that competition between anisotropic effects and boundary breakage can lead to a wide range of possible growth exponents.
Stil, Jeroen; Wityk, Nicole; Ouyed, Rachid; Taylor, A. R.
2009-08-10
We present three-dimensional magnetohydrodynamic (MHD) simulations of superbubbles, to study the importance of MHD effects in the interpretation of images from recent surveys of the Galactic plane. These simulations focus mainly on atmospheres defined by an exponential density distribution and the Dickey and Lockman density distribution. In each case, the magnetic field is parallel to the Galactic plane and we investigate cases with either infinite scale height (constant magnetic field) or a constant ratio of gas pressure to magnetic pressure. The three-dimensional structure of superbubbles in these simulations is discussed with emphasis on the axial ratio of the cavity as a function of magnetic field strength and the age of the bubble. We investigate systematic errors in the age of the bubble and scale height of the surrounding medium that may be introduced by modeling the data with purely hydrodynamic models. Age estimates derived with symmetric hydrodynamic models fitted to an asymmetric magnetized superbubble can differ by up to a factor of 4, depending on the direction of the line of sight. The scale height of the surrounding medium based on the Kompaneets model may be up to 50% lower than the actual scale height. We also present the first ever predictions of Faraday rotation by a magnetized superbubble based on three-dimensional MHD simulations. We emphasize the importance of MHD effects in the interpretation of observations of superbubbles.
NASA Technical Reports Server (NTRS)
Kuznetsova, M. M.; Sibeck, D. G.; Hesse, M.; Wang, Y.; Rastaetter, L.; Toth, G.; Ridley, A.
2009-01-01
We use the global magnetohydrodynamic (MHD) code BATS-R-US to model multipoint observations of Flux Transfer Event (FTE) signatures. Simulations with high spatial and temporal resolution predict that cavities of weak magnetic field strength protruding into the magnetosphere trail FTEs. These predictions are consistent with recently reported multi-point Cluster observations of traveling magnetopause erosion regions (TMERs).
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
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 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.
3D MHD Simulation of Flare Supra-Arcade Downflows in a Turbulent Current Sheet Medium
NASA Astrophysics Data System (ADS)
Ccere, 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.
Multi-fluid MHD simulation of the solar wind interaction with Venus
NASA Astrophysics Data System (ADS)
Nagy, A. F.; Najib, D.; Ma, Y.; Russell, C. T.; Toth, G.
2011-12-01
This paper reports on a new advanced multi-fluid MHD model that has recently been developed for Venus. The model is similar to the numerical model that was successfully applied to Mars (Najib et al., 2011). Mass densities, velocities and pressures of the protons and major ionosphere ion species (O+, O2+ and CO2+) are self-consistently calculated by solving the individual coupled continuity, momentum and energy equations. The various chemical reactions and ion-neutral collision processes are considered in the model. The simulation domain covers the region from 100 km altitude above the surface up to 16 RV in the tail. An adaptive spherical grid structure is constructed with radial resolution of about 10 km in the lower ionosphere. The model is applied to both solar-maximum and solar-minimum conditions and model results are compared in detail with multi-species single fluid model results.
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.
Modeling CME-shock-driven storms in 2012-2013: MHD test particle simulations
NASA Astrophysics Data System (ADS)
Hudson, M. K.; Paral, J.; Kress, B. T.; Wiltberger, M.; Baker, D. N.; Foster, J. C.; Turner, D. L.; Wygant, J. R.
2015-02-01
The Van Allen Probes spacecraft have provided detailed observations of the energetic particles and fields environment for coronal mass ejection (CME)-shock-driven storms in 2012 to 2013 which have now been modeled with MHD test particle simulations. The Van Allen Probes orbital plane longitude moved from the dawn sector in 2012 to near midnight and prenoon for equinoctial storms of 2013, providing particularly good measurements of the inductive electric field response to magnetopause compression for the 8 October 2013 CME-shock-driven storm. An abrupt decrease in the outer boundary of outer zone electrons coincided with inward motion of the magnetopause for both 17 March and 8 October 2013 storms, as was the case for storms shortly after launch. Modeling magnetopause dropout events in 2013 with electric field diagnostics that were not available for storms immediately following launch have improved our understanding of the complex role that ULF waves play in radial transport during such events.
MHD simulations of magnetic reconnection in a skewed three-dimensional tail configuration
NASA Technical Reports Server (NTRS)
Birn, J.; Hesse, M.
1991-01-01
The dynamic evolution of a nonsymmetric magnetotail configuration initiated by the sudden occurrence of (anomalous) resistivity are examined using a three-dimensional resistive MHD simulation developed by Birn (1990) that includes a net cross-tail field and thus breaks the mirror symmetry around the neutral sheet. Results show that the field evolution is similar to that of a symmetric configuration studied by Birn and Hones (1981), pointing to the formation and ejection of a plasmoid. On the other hand, the topological structure of the magnetic field, defined by the field line connections, was remarkably different from the symmetric case. The plasmoid in this case became 'open', connected initially with the earth but gradually becoming connected with the interplanetary field. The openness of the plasmoid and its magnetic connection with interplanetary field lines suggest the possibility of a heat flux out of the plasmoid on interconnected flux tubes.
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.
NASA Astrophysics Data System (ADS)
Kivelson, M.; Jia, X.
2013-12-01
In previous work we demonstrated that a magnetohydrodynamic (MHD) simulation of Saturn's magnetosphere in which periodicity is imposed by rotating vortical flows in the ionosphere reproduces many reported periodically varying properties of the system. Here we shall show that previously unreported features of the MHD simulation of Saturn's magnetosphere illuminate additional measured properties of the system. By averaging over a rotation period, we identify a global electric field whose magnitude is a few tenths of a mV/m (see Figure 1). The electric field intensity decreases with radial distance in the middle magnetosphere, consistent with drift speeds v=E/B of a few km/s towards the morning side and relatively independent of radial distance. The electric field within 10 RS in the equatorial plane is oriented from post-noon to post-midnight, in excellent agreement with observations [e.g., Thomsen et al., 2012; Andriopoulou et al., 2012, 2013; Wilson et al., 2013]. By following the electric field over a full rotation phase we identify oscillatory behavior whose magnitude is consistent with the reported fluctuations of measured electric fields. Of particular interest is the nature of the fast mode perturbations that produce periodic displacement of the magnetopause and flapping of the current sheet. Figure (2) shows the total perturbation pressure (the sum of magnetic and thermal pressure) in the equatorial plane at a rotation phase for which the ionospheric flow near noon is equatorward. By following the perturbations over a full rotation period, we demonstrate properties of the fast mode wave launched by the rotating flow structures and thereby characterize the 'cam' signal originally proposed by Espinosa et al. [2003].
Global evolution of Birkeland currents on 10 min timescales: MHD simulations and observations
NASA Astrophysics Data System (ADS)
Merkin, V. G.; Anderson, B. J.; Lyon, J. G.; Korth, H.; Wiltberger, M.; Motoba, T.
2013-08-01
In this paper we compare time-dependent global ionospheric field-aligned current (FAC) patterns on 10 min timescales inferred from the Active Magnetosphere and Polar Electrodynamics Response Experiment (AMPERE) with the high-resolution Lyon-Fedder-Mobarry (LFM) global magnetohydrodynamic (MHD) model. The improved LFM model yields temporally varying FAC patterns with a fine structure on the sub-100 km scale. The goal of the study is to explore the responses of observed and simulated FAC patterns and underlying magnetic perturbations to a succession of rapid transitions in the solar wind and Interplanetary Magnetic Field (IMF) parameters. To drive the simulations, we use the upstream Wind and Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft measurements recorded on 3 August 2010. For the time interval of interest (˜40 min following the impact of an interplanetary shock), the IMF is characterized by a BZ rotation from southward to northward direction under negative BY conditions. Through this case study analysis, it is found that the simulations have generally reproduced the salient characteristics of both the morphology and dynamics of the AMPERE FAC patterns. Due to the high resolution of the global model, the peak current densities are found to significantly (by a factor of 2-4) exceed those obtained from AMPERE. As a further quantitative analysis, the low-altitude magnetic perturbations measured by Iridium spacecraft and used to derive the AMPERE 2-D FAC patterns are also compared with the magnetic field variations calculated from the simulations. It is found that outside of localized regions of peak current densities, which mainly occur on the dayside and can fall between the Iridium tracks, the simulated magnetic perturbations closely follow the Iridium measurements. This demonstrates, in particular, that there is no systematic bias in the simulations to overestimate the magnetic perturbations and corresponding FAC densities. Overall, our results demonstrate that given sufficient resolution, contemporary global MHD models are capable of reproducing observed features of global ionospheric FAC distributions. This, in particular, suggests the feasibility of potential efforts to assimilate AMPERE observations in global magnetospheric models.
Multi-fluid MHD Cometary Atmosphere Simulation for Halley-type Comets.
NASA Astrophysics Data System (ADS)
Benna, M.; Mahaffy, P. R.
2004-11-01
We present new results of our Cometary Atmosphere Simulation (CASIM) code that is presently under development to model the interaction of a cometary atmosphere with the solar wind. Several high-resolution 2-D simulations for a Halley-type comet are shown. In the current simulations we investigate more precisely the evolution of the interaction between the cometary atmosphere and the solar wind starting from the early stages of the comet outgassing ( 5. a.u.) to the peak of its activity ( 1.5 a.u.). Our code is based on the solution of the multi-fluid MHD equations using an efficient adaptively refined cartesian mesh solver that provides a very high resolution over a large space domain (simulation domain 108 km, highest resolution 25 m). The multi-fluid approach we chose leads to a more accurate representation of the cometary atmosphere since additional details of the interaction between the neutral gas and the plasma, and their resulting structures are revealed. In particular, the multi-fluid representation of the ion population gives an improved view of the coupling between heavy and light ions and the resulting coma boundaries at different spatial scales. This research is sponsored by NASA and the National Academies.
NASA Astrophysics Data System (ADS)
Sonnerup, Bengt U. .; 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.
NASA Technical Reports Server (NTRS)
Birn, J.; Hones, E. W., Jr.; Schindler, K.
1986-01-01
The outflow from a reconnection region in a realistic magnetotail geometry is studied using a two-dimensional time-dependent, compressible, resistive MHD code. Two cases are emphasized: (1) the evolution of near-earth reconnection, which grows in the form of an internal unstable mode after gradual externally forced changes have initiated an anomalous dissipation process, and (2) the evolution of more distant reconnection under influence of a nonuniform inflow that forces reconnection to occur at a given location in the distant tail. In both cases, it is demonstrated that plasma flow is primarily parallel to the magnetic field in regions away from the localized area of reconnection and outside a narrow central layer.
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.
Llacer, J.; Chatterjee, A.; Batho, E.K.; Poskanzer, J.A.
1982-05-01
The characteristics and design of a high-accuracy and high-sensitivity 2-dimensional camera for the measurement of the end-point of the trajectory of accelerated heavy ion beams of positron emitter isotopes are described. Computer simulation methods have been used in order to insure that the design would meet the demanding criteria of ability to obtain the location of the centroid of a point source in the X-Y plane with errors smaller than 1 mm, with an activity of 100 nanoCi, in a counting time of 5 sec or less. A computer program which can be developed into a general purpose analysis tool for a large number of positron emitter camera configurations is described in its essential parts. The validation of basic simulation results with simple measurements is reported, and the use of the program to generate simulated images which include important second order effects due to detector material, geometry, septa, etc. is demonstrated. Comparison between simulated images and initial results with the completed instrument shows that the desired specifications have been met.
NASA Astrophysics Data System (ADS)
Olmi, B.; Del Zanna, L.; Amato, E.; Bucciantini, N.; Bandiera, R.
2015-09-01
Pulsar wind nebulae are among the most powerful particle accelerators in the Galaxy with acceleration efficiencies that reach up to 30% and maximum particle energies in the PeV range. In recent years relativistic axisymmetric MHD models have proven to be excellent tools for describing the physics of such objects, and particularly successful at explaining their high energy morphology, down to very fine details. Nevertheless, some important aspects of the physics of PWNe are still obscure: the mechanism(s) responsible for the acceleration of particles of all energies is (are) still unclear, and the origin of the lowest energy (radio emitting) particles is most mysterious. The correct interpretation of the origin of radio emitting particles is of fundamental importance, as this holds information about the amount of pair production in the pulsar magnetosphere, and hence on the role of pulsars as antimatter factories. On the other hand, the long lifetimes of these particles against synchrotron losses, allows them to travel far from their injection location, making their acceleration site difficult to constrain. As far as the highest energy (X and gamma-ray emitting) particles are concerned, their acceleration is commonly believed to occur at the pulsar wind termination shock. But since the upstream flow is thought to have non-uniform properties along the shock surface, important constraints on the acceleration mechanism(s) could come from exact knowledge of the location and flow properties where particles are being accelerated. We investigate in detail both topics by means of 2D numerical MHD simulations. Different assumptions on the origin of radio particles and more generally on the injection sites of all particles are considered, and the corresponding emission properties are computed. We discuss the physical constraints that can be inferred from comparison of the synthetic emission properties against multiwavelength observations of the PWN class prototype, the Crab Nebula.
The ideal tearing mode: 2D MHD simulations in the linear and nonlinear regimes
NASA Astrophysics Data System (ADS)
Landi, Simone; Del Zanna, Luca; Pucci, Fulvia; Velli, Marco; Papini, Emanuele
2015-04-01
We present compressible, resistive MHD numerical simulations of the linear and nonlinear evolution of the tearing instability, for both Harris sheet and force-free initial equilibrium configurations. We analyze the behavior of a current sheet with aspect ratio S1/3, where S is the Lundquist number. This scaling has been recently recognized to be the threshold for fast reconnection occurring on the ideal Alfvenic timescale, with a maximum growth rate that becomes asymptotically independent on S. Our simulations clearly confirm that the tearing instability maximum growth rate and the full dispersion relation are exactly those predicted by the linear theory, at least for the values of S explored here. In the nonlinear stage, we notice the rapid onset and subsequent coalescence of plasmoids, as observed in previous simulations of the Sweet-Parker reconnection scenario. These findings strongly support the idea that in a fully dynamic regime, as soon as current sheets develop and reach the critical threshold in their aspect ratio of S1/3 (occurring well before the Sweet-Parker configuration is able to form), the tearing mode is able to trigger fast reconnection and plasmoids formation on Alfvenic timescales, as required to explain the violent flare activity often observed in solar and astrophysical plasmas.
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.
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.
Two-dimensional NMR spectroscopy
Croasmun, W.R.; Carlson, R.M.K.
1987-01-01
Written for chemists and biochemists who are not NMR spectroscopists, but who wish to use the new techniques of two-dimensional NMR spectroscopy, this book brings together for the first time much of the practical and experimental data needed. It also serves as information source for industrial, academic, and graduate student researchers who already use NMR spectroscopy, but not yet in two dimensions. The authors describe the use of 2-D NMR in a wide variety of chemical and biochemical fields, among them peptides, steroids, oligo- and poly-saccharides, nucleic acids, natural products (including terpenoids, alkaloids, and coal-derived heterocyclics), and organic synthetic intermediates. They consider throughout the book both the advantages and limitations of using 2-D NMR.
Turbulent two-dimensional magnetohydrodynamics and conformal field theory
Rahimi Tabar, M.R.; Rouhani, S.
1996-03-01
We show that an infinite number of non-unitary minimal models may describe two dimensional turbulent magnetohydrodynamics (MHD), both in the presence and absence of the Alf{close_quote}ven effect. We argue that the existence of a critical dynamical index results in the Alf{close_quote}ven effect or equivalently the equipartition of energy. We show that there are an infinite number of conserved quantities in 2{ital D}{endash}{ital MHD} turbulent systems both in the limit of vanishing the viscocities and in force free case. In the force free case, using the non-unitary minimal model {ital M}{sub 2,7} we derive the correlation functions for the velocity stream function and magnetic flux function. Generalizing this simple model we find the exponents of the energy spectrum in the inertial range for a class of conformal field theories. Copyright {copyright} 1996 Academic Press, Inc.
A renormalization group analysis of two-dimensional magnetohydrodynamic turbulence
NASA Technical Reports Server (NTRS)
Liang, Wenli Z.; Diamond, P. H.
1993-01-01
The renormalization group (RNG) method is used to study the physics of two-dimensional (2D) magnetohydrodynamic (MHD) turbulence. It is shown that, for a turbulent magnetofluid in two dimensions, no RNG transformation fixed point exists on account of the coexistence of energy transfer to small scales and mean-square magnetic flux transfer to large scales. The absence of a fixed point renders the RNG method incapable of describing the 2D MHD system. A similar conclusion is reached for 2D hydrodynamics, where enstrophy flows to small scales and energy to large scales. These analyses suggest that the applicability of the RNG method to turbulent systems is intrinsically limited, especially in the case of systems with dual-direction transfer.
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.
Swain, Eric D.; Wolfert, Melinda A.; Bales, Jerad D.; Goodwin, Carl R.
2004-01-01
Successful restoration of the southern Florida ecosystem requires extensive knowledge of the physical characteristics and hydrologic processes controlling water flow and transport of constituents through extremely low-gradient freshwater marshes, shallow mangrove-fringed coastal creeks and tidal embayments, and near-shore marine waters. A sound, physically based numerical model can provide simulations of the differing hydrologic conditions that might result from various ecosystem restoration scenarios. Because hydrology and ecology are closely linked in southern Florida, hydrologic model results also can be used by ecologists to evaluate the degree of ecosystem restoration that could be achieved for various hydrologic conditions. A robust proven model, SWIFT2D, (Surface-Water Integrated Flow and Transport in Two Dimensions), was modified to simulate Southern Inland and Coastal Systems (SICS) hydrodynamics and transport conditions. Modifications include improvements to evapotranspiration and rainfall calculation and to the algorithms that describe flow through coastal creeks. Techniques used in this model should be applicable to other similar low-gradient marsh settings in southern Florida and elsewhere. Numerous investigations were conducted within the SICS area of southeastern Everglades National Park and northeastern Florida Bay to provide data and parameter values for model development and testing. The U.S. Geological Survey and the National Park Service supported investigations for quantification of evapotranspiration, vegetative resistance to flow, wind-induced flow, land elevations, vegetation classifications, salinity conditions, exchange of ground and surface waters, and flow and transport in coastal creeks and embayments. The good agreement that was achieved between measured and simulated water levels, flows, and salinities through minimal adjustment of empirical coefficients indicates that hydrologic processes within the SICS area are represented properly in the SWIFT2D model, and that the spatial and temporal resolution of these processes in the model is adequate. Sensitivity analyses were conducted to determine the effect of changes in boundary conditions and parameter values on simulation results, which aided in identifying areas of greatest uncertainty in the model. The parameter having the most uncertainty (most in need of further field study) was the flow coefficient for coastal creeks. Smaller uncertainties existed for wetlands frictional resistance and wind. Evapotranspiration and boundary inflows indicated the least uncertainty as determined by varying parameters used in their formulation and definition. Model results indicated that wind was important in reversing coastal creek flows. At Trout Creek (the major tributary connecting Taylor Slough wetlands with Florida Bay), flow in the landward direction was not simulated properly unless wind forcing was included in the simulation. Simulations also provided insight into the major influence that wind has on salinity mixing along the coast, the varying distribution of wetland flows at differing water levels, and the importance of topography in controlling flows to the coast. Slight topographic variations were shown to highly influence the routing of water. A multiple regression analysis was performed to relate inflows at the northern boundary of Taylor Slough bridge to a major pump station (S-332) north of the SICS model area. This analysis allows Taylor Slough bridge boundary conditions to be defined for the model from operating scenarios at S-332, which should facilitate use of the SICS model as an operational tool.
NASA Astrophysics Data System (ADS)
Washimi, Haruichi; Zank, Gary P.; Hu, Qiang; Webb, G. M.; Shinagawa, Hiroyuki
2011-09-01
In situ observations of the outer heliosphere by the Voyager 1 (V1) and Voyager 2 (V2) spacecrafts show highly variable behavior of the solar wind plasma in deep interplanetary space and the heliosheath (HS). We develop a dynamic and realistic model that satisfies both V1 and V2 observed crossing times and locations of the termination shock (TS) simultaneously, by performing a three-dimensional (3D) MHD simulation that includes the effects of neutral particles (Washimi et al. (2010)). Daily values of solar-wind speed and density observed by V2 were used so that short-term dynamical effects are reproduced in this simulation. Here, we compare the V1 observed high-energy charged particle flux data in the HS (Webber et al. (2009)) with our MHD simulation results to identify the flux increase/decrease associated with the March 2006 interplanetary shock events.
Numerical Simulation of Turbulent MHD Flows Using an Iterative PNS Algorithm
NASA Technical Reports Server (NTRS)
Kato, Hiromasa; Tannehill, John C.; Mehta, Unmeel B.
2003-01-01
A new parabolized Navier-Stokes (PNS) algorithm has been developed to efficiently compute magnetohydrodynamic (MHD) flows in the low magnetic Reynolds number regime. In this regime, the electrical conductivity is low and the induced magnetic field is negligible compared to the applied magnetic field. The MHD effects are modeled by introducing source terms into the PNS equation which can then be solved in a very efficient manner. To account for upstream (elliptic) effects, the flowfields are computed using multiple streamwise sweeps with an iterated PNS algorithm. Turbulence has been included by modifying the Baldwin-Lomax turbulence model to account for MHD effects. The new algorithm has been used to compute both laminar and turbulent, supersonic, MHD flows over flat plates and supersonic viscous flows in a rectangular MHD accelerator. The present results are in excellent agreement with previous complete Navier-Stokes calculations.
NASA Technical Reports Server (NTRS)
Kabin, K.; Hansen, K. C.; Gombosi, T. I.; Combi, M. R.; Linde, T. J.; DeZeeuw, D. L.; Groth, C. P. T.; Powell, K. G.; Nagy, A. F.
2000-01-01
Magnetohydrodynamics (MHD) provides an approximate description of a great variety of processes in space physics. Accurate numerical solutions of the MHD equations are still a challenge, but in the past decade a number of robust methods have appeared. Once these techniques made the direct solution of MHD equations feasible, a number of global three-dimensional models were designed and applied to many space physics objects. The range of these objects is truly astonishing, including active galactic nuclei, the heliosphere, the solar corona, and the solar wind interaction with planets, satellites, and comets. Outside the realm of space physics, MHD theory has been applied to such diverse problems as laboratory plasmas and electromagnetic casting of liquid metals. In this paper we present a broad spectrum of models of different phenomena in space science developed in the recent years at the University of Michigan. Although the physical systems addressed by these models are different, they all use the MHD equations as a unifying basis.
NASA Astrophysics Data System (ADS)
Kitiashvili, I.; Abramenko, V.; Goode, P. R.; Kosovichev, A.; Mansour, N.; Wray, A.; Yurchyshyn, V.
2012-12-01
Recent progress in observational capabilities and numerical modeling have provided unique high-resolution information demonstrating complicated dynamics and structures of turbulent flows and magnetic field on the Sun. The realistic approach to numerical simulations is based on physical first principles and takes into account compressible fluid flow in a highly stratified magnetized medium, 3D multi-bin radiative energy transfer between fluid elements, a real-gas equation of state, ionization, and excitation of all abundant species, magnetic effects and sub-grid turbulence. We present new results of 3D radiative MHD simulations of the upper solar convection zone and chromosphere that reveal a fundamental role of small-scale vortex dynamics, and compare the numerical results and predictions with observational results from the 1.6 m clear aperture New Solar Telescope (NST) at Big Bear Observatory. In particular, we investigate formation and dynamics of ubiquitous small-scale vortex tubes mostly concentrated in the intergranular lanes and their role in magnetic structuring and acoustic emission of the Sun. These whirlpool-like flows are characterized by very strong horizontal shear velocities (7 - 11 km/s) and downflows (~7 km/s), and are accompanied by sharp decreases in temperature, density and pressure at the surface. High-speed whirlpool flows can attract and capture other vortices, penetrate into the low chromosphere, and form stable magnetic flux tubes. The simulations also reveal a strong connection between acoustic wave excitation events and the dynamics of vortex tubes. In this talk, we will discuss different aspects of small-scale turbulent dynamics of the low atmosphere from the high-resolution simulations in comparison with recent NST observations, and the strategy for future synergies of numerical simulations and observations with large aperture solar telescopes.
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.
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.
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.
Mini-magnetosphere: Laboratory experiment, physical model and Hall MHD simulation
NASA Astrophysics Data System (ADS)
Shaikhislamov, I. F.; Antonov, V. M.; Zakharov, Yu. P.; Boyarintsev, E. L.; Melekhov, A. V.; Posukh, V. G.; Ponomarenko, A. G.
2013-08-01
Magnetosphere with a size comparable to the ion kinetic scales is investigated by means of laboratory experiment, analytical analysis and Hall MHD simulation. In experiment a specific magnetic field was observed which is non-coplanar to dipole field, does not change sign at dipole moment inversion and could be generated only via the quadratic Hall term. Magnetopause position and plasma stand off distance were found to be profoundly different between the experimental regimes with small and large ion inertia length. In the previous studies of a mini-magnetosphere by kinetic codes such novel features were observed as absence of the bow shock and plasma stopping at the Stoermer particle limit instead of the pressure balance distance. Proposed analytical model explains these features by Hall currents which tend to cancel magnetic field convection by ions. Performed numerical simulation shows a good agreement with experiment and analytical model. It gives detailed spatial structure of the Hall field and reveals that while ions penetrate deep inside mini-magnetosphere electrons overflow around it along magnetopause boundary.
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.
Radiative 3D MHD simulations of the spontaneous small-scale eruptions in the solar atmosphere
NASA Astrophysics Data System (ADS)
Kitiashvili, Irina N.
2015-08-01
Studying non-linear turbulent dynamics of the solar atmosphere is important for understanding mechanism of the solar and stellar brightness variations. High-resolution observations of the quiet Sun reveal ubiquitous distributions of high-speed jets, which are transport mass and energy into the solar corona and feeding the solar wind. However, the origin of these eruption events is still unknown. Using 3D realistic MHD numerical simulations we find that small-scale eruptions are produced by ubiquitous magnetized vortex tubes generated by the Sun's turbulent convection in subsurface layers. The swirling vortex tubes (resembling tornadoes) penetrate into the solar atmosphere, capture and stretch background magnetic field, and push the surrounding material up, generating shocks. Our simulations reveal complicated high-speed flow patterns and thermodynamic and magnetic structure in the erupting vortex tubes and shows that the eruptions are initiated in the subsurface layers and are driven by high-pressure gradients in the subphotosphere and photosphere and by the Lorentz force in the higher atmosphere layers. I will discuss about properties of these eruptions, their effects on brightness and spectral variations and comparison with observations.
NASA Technical Reports Server (NTRS)
Boriakoff, Valentin
1994-01-01
The goal of this project was the feasibility study of a particular architecture of a digital signal processing machine operating in real time which could do in a pipeline fashion the computation of the fast Fourier transform (FFT) of a time-domain sampled complex digital data stream. The particular architecture makes use of simple identical processors (called inner product processors) in a linear organization called a systolic array. Through computer simulation the new architecture to compute the FFT with systolic arrays was proved to be viable, and computed the FFT correctly and with the predicted particulars of operation. Integrated circuits to compute the operations expected of the vital node of the systolic architecture were proven feasible, and even with a 2 micron VLSI technology can execute the required operations in the required time. Actual construction of the integrated circuits was successful in one variant (fixed point) and unsuccessful in the other (floating point).
NASA Astrophysics Data System (ADS)
Szymkiewicz, Adam; Tisler, Witold; Burzy?ski, Kazimierz
2015-09-01
Flow in unsaturated porous media is commonly described by the Richards equation. This equation is strongly nonlinear due to interrelationships between water pressure head (negative in unsaturated conditions), water content and hydraulic conductivity. The accuracy of numerical solution of the Richards equation often depends on the method used to estimate average hydraulic conductivity between neighbouring nodes or cells of the numerical grid. The present paper discusses application of the computer simulation code VS2DI to three test problems concerning infiltration into an initially dry medium, using various methods for inter-cell conductivity calculation (arithmetic mean, geometric mean and upstream weighting). It is shown that the influence of the averaging method can be very large for coarse grid, but that it diminishes as cell size decreases. Overall, the arithmetic average produced the most reliable results for coarse grids. Moreover, the difference between results obtained with various methods is a convenient indicator of the adequacy of grid refinement.
Swillens, Abigail; Segers, Patrick; Torp, Hans; Lvstakken, Lasse
2010-01-01
Detailed imaging of complex blood flow may improve early diagnosis of cardiovascular disease. In clinical practice, non-invasive flow imaging has been limited to one-dimensional Doppler techniques. Searching for multi-dimensional estimators, research has given attention to speckle tracking (ST) and vector Doppler (VD). However, these techniques have yet to be validated for complex flow patterns as may arise in diseased arteries. In this work, the properties of ST and crossed-beam VD are compared with a ground truth for clinically relevant flow using an ultrasonic simulation environment coupled with the output from computational fluid dynamics (CFD). The statistical properties (n = 80) of ST and VD were first evaluated for stationary flow in a tube for varying vessel positions and angles, and for varying noise levels. The parameter study demonstrated VD to be a more robust axial velocity estimator, and similar results were obtained overall for the lateral velocity component. As an example, the relative standard deviation was 15% and 8% for ST compared with 3% and 10% for VD, for the axial and lateral velocity component, respectively. Further, performance was evaluated for pulsatile flow conditions in a stenosed carotid bifurcation model. A linear regression analysis showed that both methods overall had a good agreement to the CFD reference, however VD suffered from more spurious artifacts and was severely hampered by aliasing in parts of the cardiac cycle. ST was less accurate in estimating the axial component, but prevailed in estimating velocities well beyond the Nyquist range. Based on our simulations, both methods may be used to image complex flow behavior in the carotid bifurcation, however, considering also the scanning limitations of VD, ST may provide a more consistent and practical approach. Future work will entail in vitro and in vivo validation of these results. PMID:20178899
Formation and Eruption of an Active Region Sigmoid: NLFFF Modeling and MHD Simulation
NASA Astrophysics Data System (ADS)
Jiang, C.; Wu, S.; Feng, X.; Hu, Q.
2013-12-01
We present a magnetic analysis of the formation and eruption of an active region sigmoid in AR 11283 from 2011 September 4 to 6, which is jointly based on observations, static nonlinear force-free field (NLFFF) extrapolation and dynamic MHD simulation. A time sequence of NLFFF model's outputs are used to reproduce the evolution of the magnetic field of the region over three days leading to a X-class flare near the end of 2011 September 6. In the first day, a new bipolar emerges into the negative polarity of a pre-existing mature bipolar, forming a magnetic topology with a coronal null on the magnetic separatrix surface between the two flux system, while the field is still near potential at the end of the day. After then photospheric shearing and twisting build up non-potentiality in the embedded core region, with a flux rope (FR) formed there above the polarity inversion line by tether-cutting reconnection between the strongly sheared field lines. Within this duration, the core field has gained a magnetic free energy of ˜ 1032 erg. In this core a sigmoid is observed distinctly at 22:00 UT on September 6, closely before its eruption at 22:12 UT. Comparison of the SDO/AIA observations with coronal magnetic field suggests that the sigmoid is formed by emission due to enhanced current sheet along the BPSS (bald-patch separatrix surface, in which the field lines graze the line-tied photosphere at the neutral line) that separates the FR from the ambient flux. Quantitative inspection of the pre-eruption field on 22:00 UT suggests a mechanism for the eruption: tether cutting at the null triggers a torus instability of the FR--overlying field system. This pre-eruption NLFFF is then input into a time-dependent MHD model to simulate the fast magnetic evolution during eruption, which successfully reproduces the observations. The highly asymmetric magnetic environment along with the lateral location of the null leads to a strongly inclined non-radial direction of the eruption. The study of this kind provides important insights in a quantitative way to many open issues on the formation and eruption of sigmoidal FR.
Aoshima, Masayuki; Satoh, Akira
2006-01-01
Influences of the magnetic interaction between particles and the aspect ratio of particles on aggregate structures in a colloidal dispersion composed of rod-like ferromagnetic particles were investigated by means of the cluster-moving Monte Carlo method. The internal structures of the aggregates obtained in simulations were analyzed in terms of the number density distribution of the clusters and radial distribution functions. The results show that as the magnetic interaction between particles increases, many small clusters such as anti-parallel particle pairs, raft-like clusters, and small loop-like clusters are formed; these gather to form larger aggregates. In the case of a relatively strong magnetic interaction between particles, solid-like rectangular clusters are formed when the aspect ratio is approximately 2, since the suitable distance between magnetic charges enables particles to form a fundamental structure of two normal anti-parallel particle pairs. As the aspect ratio increases beyond 2, many more stable raft-like clusters are formed, since the increase in distance between magnetic charges makes the two normal anti-parallel particle pair structures unstable. For a significantly larger aspect ratio, large network microstructures are produced by the formation of many chain-like and loop-like structures. PMID:16038920
NASA Astrophysics Data System (ADS)
Okudur, O. O.; Vanstreels, K.; De Wolf, I.; Hangen, U.
2016-01-01
Continuous scaling of integrated circuits has led to the introduction of highly porous low dielectric constant (low-k) materials, whose inferior mechanical properties raise concerns regarding the reliability of integrated circuits. Nanoindentation is proven to be a straightforward method to study mechanical properties of films. However, in the case of low-k, the measurement and analysis are complex due to the porous nature of the films and reduced film thicknesses which give rise to substrate effects. A methodology that combines nanoindentation experiments with finite-element simulations is proposed and validated in this study to extract the substrate-free elastic modulus of porous ultra-thin low-k films. Furthermore, it is shown that imperfections of the nanoindentation probe significantly affect the finite-element results. An effective analytical method that captures the actual nanoindenter behavior upon indentation is proposed by taking both tip radius and conical imperfections into account. Using this method combined with finite element modeling, the elastic modulus of sub-100 nm thick low-k films is successfully extracted. Standard indentation tests clearly overestimated the actual modulus for such thin films, which emphasizes the importance of the proposed methodology.
Giammarinaro, B; Coulouvrat, F; Pinton, G
2016-04-01
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)
Reuter, K.; Jenko, F.; Forest, C. B.; Bayliss, R. A.
2008-08-01
A parallel implementation of a nonlinear pseudo-spectral MHD code for the simulation of turbulent dynamos in spherical geometry is reported. It employs a dual domain decomposition technique in both real and spectral space. It is shown that this method shows nearly ideal scaling going up to 128 CPUs on Beowulf-type clusters with fast interconnect. Furthermore, the potential of exploiting single precision arithmetic on standard x86 processors is examined. It is pointed out that the MHD code thereby achieves a maximum speedup of 1.7, whereas the validity of the computations is still granted. The combination of both measures will allow for the direct numerical simulation of highly turbulent cases ( 1500
Matsuda, K.; Terada, N.; Katoh, Y.; 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.
Analysis of Voyager observed high-energy electron fluxes in the heliosheath using MHD simulations
NASA Astrophysics Data System (ADS)
Washimi, H.; Webber, W. R.; Zank, G. P.; Hu, Q.; Florinski, V. A.; Adams, J. H.; Kubo, Y.
2011-12-01
The Voyager spacecraft (V1 and V2) observed electrons of 6-14 MeV in the heliosheath which showed several incidences of flux variation relative to a background of gradually increasing flux with distance from the Sun. The increasing flux of background electrons is thought to result from inward radial diffusion. We compare the temporal electron flux variation with dynamical phenomena in the heliosheath that are obtained from our MHD simulations. Because our simulation is based on V2 observed solar-wind data before V2 crossed the termination shock, this analysis is effective up to late 2008, i.e., about a year after the V2-crossing, during which disturbances, driven prior to the crossing time, survived in the heliosheath. Several electron flux variations correspond to times directly associated with interplanetary shock events. One noteworthy example corresponds to various times associated with the March 2006 interplanetary shock, these being the collision with the termination shock, the passage past the V1 spacecraft, and the collision with the region near the heliopause, as identified by W.R. Webber et al. (JGR, 114, A07108, 2009) for proton/helium of 7-200 MeV. Our simulations indicate that all other electron flux variations, except one, correspond well to the times when a shock-driven magneto-sonic pulse and its reflection in the heliosheath either passed across V1/V2, or collided with the termination shock or with the plasma sheet near the heliopause. This result suggests that these variations in the electron flux should be due to either direct or indirect effects of magnetosonic pulses in the heliosheath driven by interplanetary shocks.
NASA Astrophysics Data System (ADS)
Burckel, A.; Sauter, O.; Angioni, C.; Candy, J.; Fable, E.; Lapillonne, X.
2010-11-01
In order to better identify the role of the magnetic topology on ITG and TEM instabilities, different MHD equilibria with increasing complexity are calculated using the CHEASE code [1]. We start from the geometry of the s-? cyclone benchmark case [2], consider the corresponding circular numerical equilibrium, and then successively add a non zero value of a consistent with the kinetic profiles, an elongation of 1.68, a triangularity of 0.15, and finally an up-down asymmetry corresponding to a single-null diverted geometry. This gives the opportunity to study separately the effect of each main characteristics of the equilibrium on microinstabilities in core plasmas. Linear local electrostatic gyrokinetic simulations of these different numerical equilibria and of their corresponding analytical descriptions (Miller-type representations [3]) are performed using the codes GS2 [4, 5] and GYRO[6]. It is observed that each modification of the equilibrium has an influence on the results of gyrokinetic simulations. The effect of the ? parameter can compensate the stabilizing effect of an increase in the elongation. A comparison between the up-down symmetric shaped equilibrium and its corresponding diverted configuration show a non negligible effect on the growth rate of ITG and TEM turbulence. The comparison between the local Miller model and using a full equilibrium shows that it is mainly the indirect change of elongation in the plasma core which influences the results. The global aim is to provide well defined benchmark cases including real geometry and kinetic electrons physics, since this is not analyzed by the cyclone case. In addition, the goal is to define a procedure for testing of local simulations inspired by experimental constraints and results.
Properties of Ganymede's magnetosphere inferred from improved three-dimensional MHD simulations
NASA Astrophysics Data System (ADS)
Jia, Xianzhe; Walker, Raymond J.; Kivelson, Margaret G.; Khurana, Krishan K.; Linker, Jon A.
2009-09-01
We describe a three-dimensional single-fluid MHD simulation of Ganymede's magnetosphere that accords extremely well with the Galileo particles and fields measurements. Major improvements to our previously published model involve the modification of the inner boundary condition and the implementation of an anomalous resistivity model. The improved model couples the moon's ionosphere (with finite Pedersen conductance) with the magnetosphere self-consistently. The previous model applied only in the limit of unreasonably high ionospheric conductivity. We illustrate in detail the global convection pattern inferred from the new model and demonstrate some features of the convection that differ from that of the Earth's magnetosphere because Ganymede lacks a corotation electric field. Our new model does a better job of reproducing magnetic field and plasma observations from multiple Galileo passes, which sampled different external conditions and different regions of the magnetosphere. In particular, for a critical upstream pass (G8) during which the Galileo spacecraft entered onto closed field lines, the simulated magnetosphere provides an excellent fit to the measurements without the need for tuning the spacecraft trajectory. In comparison with the plasma measurements of the G2 flyby, our model also yields good agreement with the Galileo PLS observations and supports the conclusion reached by Vasyli?nas and Eviatar (2000) that the observed ionospheric outflow consists of oxygen ions. For constant external conditions, dynamic variations associated with magnetic reconnection on timescales of the order of tens of seconds are found over a large region near the magnetopause in the simulations. Future applications of our model, such as test particle tracing and investigating the behavior of the cross polar cap potential under different external and ionospheric conditions, will provide a more comprehensive understanding of Ganymede's magnetospheric environment.
NASA Astrophysics Data System (ADS)
Jia, X.; Walker, R. J.; Kivelson, M. G.; Khurana, K. K.; Linker, J. A.
2008-12-01
The Galileo spacecraft visited Ganymede six times passing through different regions of the moon's magnetosphere. On the two low latitude passes on the upstream side, the G8 and G28 flybys, the spacecraft detected large amplitude waves in the magnetic field at the magnetopause crossings. In particular, the wave amplitude was larger during the G8 pass in which the spacecraft passed closer to the nose of the upstream magnetopause than it did on the G28 pass. Whether the observed oscillations were spatial structures or resulted from temporal variations of the magnetopause is not clear although it has been proposed to be surface waves caused by the Kelvin-Helmholtz instabilities on the magnetopause (Kivelson et al., 1998). We have conducted three-dimensional MHD simulations, which model the interaction between the Jovian plasma and Ganymede's magnetosphere, that enable us to investigate the properties of Ganymede's magnetopause boundaries. We examine the temporal variation of the system in detail and find that for the conditions during the G8 pass, the magnetopause identified in our simulation oscillates in regions consistent with the locations where large amplitude oscillations were seen in the magnetometer data. Bursty plasma flows associated with magnetic reconnection occurring near the upstream equator are observed in the vicinity of the magnetopause in our simulations. Because the ambient Jovian magnetic field is always nearly anti- parallel to Ganymede's intrinsic field at the equator, we attribute the observed boundary oscillations to temporal variations associated with magnetic reconnection at the magnetopause. We have performed similar analyses on other passes and will present comparisons with the Galileo observations.
Analysis of Voyager Observed High-Energy Electron Fluxes in the Heliosheath Using MHD Simulations
NASA Technical Reports Server (NTRS)
Washimi, Haruichi; Webber, W. R.; Zank, Gary P.; Hu, Qiang; Florinski, Vladimir; Adams, James; Kubo, Yuki
2011-01-01
The Voyager spacecraft (V1 and V2) observed electrons of 6-14 MeV in the heliosheath which showed several incidences of flux variation relative to a background of gradually increasing flux with distance from the Sun. The increasing flux of background electrons is thought to result from inward radial diffusion. We compare the temporal electron flux variation with dynamical phenomena in the heliosheath that are obtained from our MHD simulations. Because our simulation is based on V2 observed plasma data before V2 crossed the termination shock, this analysis is effective up to late 2008, i.e., about a year after the V2-crossing, during which disturbances, driven prior to the crossing time, survived in the heliosheath. Several electron flux variations correspond to times directly associated with interplanetary shock events. One noteworthy example corresponds to various times associated with the March 2006 interplanetary shock, these being the collision with the termination shock, the passage past the V1 spacecraft, and the collision with the region near the heliopause, as identified by W.R. Webber et al. for proton/helium of 7-200 MeV. Our simulations indicate that all other electron flux variations, except one, correspond well to the times when a shock-driven magneto-sonic pulse and its reflection in the heliosheath either passed across V1/V2, or collided with the termination shock or with the plasma sheet near the heliopause. This result suggests that variation in the electron flux should be due to either direct or indirect effects of magnetosonic pulses in the heliosheath driven by interplanetary shocks
NASA Astrophysics Data System (ADS)
Hall, F.; Otto, A.
2003-12-01
We have studied the formation of thin current sheets during the growth phase of magnetospheric substorms. Our approach is based on the conservation of entropy of magnetic flux tubes during the slow quasi-static evolution of the magnetosphere seen during the growth phase. The growth phase is initiated by the erosion of closed dayside magnetic flux. This flux is replenished by convection of closed magnetic flux from the near-Earth tail region to the dayside. However, this process of magnetic flux replenishment is subject to the entropy constraints imposed on the slow quasi-static convection of magnetic flux tubes from the mid- and far-tail regions, first identified by Erickson and Wolf (1980). We argue that the depletion of flux from a finite reservoir in the near-Earth tail region leads to the observed current sheet thinning. We use three-dimensional MHD simulations to model the formation of the thin current sheet in the near-Earth region during the late growth phase of substorms.
Region 1 birkeland currents from a global MHD simulation of the magnetosphere
NASA Astrophysics Data System (ADS)
Fedder, J. A.;