Institute of Scientific and Technical Information of China (English)
JIANGuangde; DONGJiaqi
2003-01-01
A numerical simulation code has been established with particle simulation method in order to study the gyro-kinetic equations for the electrostatic electron temperature gradient modes in toroidal plasmas. The flowchart is given as well for the code. The fourth-order adaptive step-size scheme is adopted, that saves computer time and is simple. The calculation code is useful for the research of the electron temperature gradient instability.
Hallo, L.; Olazabal-Loumé, M.; Maire, P. H.; Breil, J.; Morse, R.-L.; Schurtz, G.
2006-06-01
This paper deals with ablation front instabilities simulations in the context of direct drive ICF. A simplified DT target, representative of realistic target on LIL is considered. We describe here two numerical approaches: the linear perturbation method using the perturbation codes Perle (planar) and Pansy (spherical) and the direct simulation method using our Bi-dimensional hydrodynamic code Chic. Numerical solutions are shown to converge, in good agreement with analytical models.
Energy Technology Data Exchange (ETDEWEB)
Hallo, L.; Olazabal-Loume, M.; Maire, P.H.; Breil, J.; Schurtz, G. [CELIA, 33 - Talence (France); Morse, R.L. [Arizona Univ., Dept. of Nuclear Engineering, Tucson (United States)
2006-06-15
This paper deals with ablation front instabilities simulations in the context of direct drive inertial confinement fusion. A simplified deuterium-tritium target, representative of realistic target on LIL (laser integration line at Megajoule laser facility) is considered. We describe here two numerical approaches: the linear perturbation method using the perturbation codes Perle (planar) and Pansy (spherical) and the direct simulation method using our bi-dimensional hydrodynamic code Chic. Our work shows a good behaviour of all methods even for large wavenumbers during the acceleration phase of the ablation front. We also point out a good agreement between model and numerical predictions at ablation front during the shock wave transit.
Study of the Kelvin-Helmholtz instability through simulation with the code Athena
Freitas-Lemes, P; Faúndez-Abans, M
2013-01-01
Kelvin-Helmholtz instabilities are common in astrophysical systems, ranging from jet black holes up to protoplanetary accretion disk. An astrophysical object with strong characteristics of the Kelvin-Helmholtz instability is Caraguejo Nebula, in which the material expansion was caused by the explosion of a supernova about 1000 years ago. This instability occurs at the boundary between two fluids of different densities when one of the fluids accelerated with respect to the other. In order to study this instability, we performed a simulation with the code ATHENA Eulerian mesh. For this simulation, we consider a square domain with periodic boundaries on the sides, and reflecting on the boundary of the top and bottom. The upper box is filled with a gas density {\\rho}=1.0, pressure P1 = 1.0, adiabatic index {\\gamma}=5/3, and velocity u1=0.03 in the x direction (to the right). The lower portion has a density {\\rho}=2.0, the same pressure, velocity, and adiabatic index, only in the opposite direction to the left. Sp...
Non-linear simulations of combustion instabilities with a quasi-1D Navier-Stokes code
Haugen, Nils Erland L; Sannan, Sigurd
2010-01-01
As lean premixed combustion systems are more susceptible to combustion instabilities than non-premixed systems, there is an increasing demand for improved numerical design tools that can predict the occurrence of combustion instabilities with high accuracy. The inherent non-linearities in combustion instabilities can be of crucial importance, and we here propose an approach in which the one-dimensional Navier-Stokes and scalar transport equations are solved for geometries of variable cross-section. The focus is on attached flames, and for this purpose a new phenomenological model for the unsteady heat release from a flame front is introduced. In the attached flame method (AFM) the heat release occurs over the full length of the flame. The non-linear code with the use of the AFM approach is validated against results from an experimental study of thermoacoustic instabilities in oxy-fuel flames by Ditaranto and Hals [Combustion and Flame, 146, 493-512 (2006)]. The numerical simulations are in accordance with the...
Numerical simulations of the Kelvin-Helmholtz instability with the Gadget-2 SPH code
Gabbasov, Ruslan F; Suarez-Cansino, Joel; Sigalotti, Leonardo Di G
2013-01-01
The method of Smoothed Particle Hydrodynamics (SPH) has been widely studied and implemented for a large variety of problems, ranging from astrophysics to fluid dynamics and elasticity problems in solids. However, the method is known to have several deficiencies and discrepancies in comparison with traditional mesh-based codes. In particular, there has been a discussion about its ability to reproduce the Kelvin-Helmholtz Instability in shearing flows. Several authors reported that they were able to reproduce correctly the instability by introducing some improvements to the algorithm. In this contribution, we compare the results of Read et al. (2010) implementation of the SPH algorithm with the original Gadget-2 N-body/SPH code.
Suppressing the Numerical Cherenkov Instability in FDTD PIC Codes
Godfrey, Brendan B
2014-01-01
A procedure for largely suppressing the numerical Cherenkov instability in finite difference time-domain (FDTD) particle-in-cell (PIC) simulations of cold, relativistic beams is derived, and residual growth rates computed and compared with WARP code simulation results. Sample laser-plasma acceleration simulation output is provided to further validate the new procedure.
Bates, J. W.; Schmitt, A. J.; Karasik, M.; Zalesak, S. T.
2016-12-01
The ablative Rayleigh-Taylor (RT) instability is a central issue in the performance of laser-accelerated inertial-confinement-fusion targets. Historically, the accurate numerical simulation of this instability has been a challenging task for many radiation hydrodynamics codes, particularly when it comes to capturing the ablatively stabilized region of the linear dispersion spectrum and modeling ab initio perturbations. Here, we present recent results from two-dimensional numerical simulations of the ablative RT instability in planar laser-ablated foils that were performed using the Eulerian code FastRad3D. Our study considers polystyrene, (cryogenic) deuterium-tritium, and beryllium target materials, quarter- and third-micron laser light, and low and high laser intensities. An initial single-mode surface perturbation is modeled in our simulations as a small modulation to the target mass density and the ablative RT growth-rate is calculated from the time history of areal-mass variations once the target reaches a steady-state acceleration. By performing a sequence of such simulations with different perturbation wavelengths, we generate a discrete dispersion spectrum for each of our examples and find that in all cases the linear RT growth-rate γ is well described by an expression of the form γ = α [ k g / ( 1 + ɛ k L m ) ] 1 / 2 - β k V a , where k is the perturbation wavenumber, g is the acceleration of the target, Lm is the minimum density scale-length, Va is the ablation velocity, and ɛ is either one or zero. The dimensionless coefficients α and β in the above formula depend on the particular target and laser parameters and are determined from two-dimensional simulation results through the use of a nonlinear curve-fitting procedure. While our findings are generally consistent with those of Betti et al. (Phys. Plasmas 5, 1446 (1998)), the ablative RT growth-rates predicted in this investigation are somewhat smaller than the values previously reported for the
Marx, Alain; Lütjens, Hinrich
2017-03-01
A hybrid MPI/OpenMP parallel version of the XTOR-2F code [Lütjens and Luciani, J. Comput. Phys. 229 (2010) 8130] solving the two-fluid MHD equations in full tokamak geometry by means of an iterative Newton-Krylov matrix-free method has been developed. The present work shows that the code has been parallelized significantly despite the numerical profile of the problem solved by XTOR-2F, i.e. a discretization with pseudo-spectral representations in all angular directions, the stiffness of the two-fluid stability problem in tokamaks, and the use of a direct LU decomposition to invert the physical pre-conditioner at every Krylov iteration of the solver. The execution time of the parallelized version is an order of magnitude smaller than the sequential one for low resolution cases, with an increasing speedup when the discretization mesh is refined. Moreover, it allows to perform simulations with higher resolutions, previously forbidden because of memory limitations.
Kinetic Simulations of Rayleigh-Taylor Instabilities
Sagert, Irina; Colbry, Dirk; Howell, Jim; Staber, Alec; Strother, Terrance
2014-01-01
We report on an ongoing project to develop a large scale Direct Simulation Monte Carlo code. The code is primarily aimed towards applications in astrophysics such as simulations of core-collapse supernovae. It has been tested on shock wave phenomena in the continuum limit and for matter out of equilibrium. In the current work we focus on the study of fluid instabilities. Like shock waves these are routinely used as test-cases for hydrodynamic codes and are discussed to play an important role in the explosion mechanism of core-collapse supernovae. As a first test we study the evolution of a single-mode Rayleigh-Taylor instability at the interface of a light and a heavy fluid in the presence of a gravitational acceleration. To suppress small-wavelength instabilities caused by the irregularity in the separation layer we use a large particle mean free path. The latter leads to the development of a diffusion layer as particles propagate from one fluid into the other. For small amplitudes, when the instability is i...
Control and simulation of thermoacoustic instabilities
Poinsot, Thierry
2014-11-01
Combustion instabilities (CI), due to thermoacoustic coupling between acoustic waves and chemical reaction, constitute a major danger for all combustion systems. They can drive the system to unstable states where the whole combustor can oscillate, vibrate, quench or in extreme cases explode or burn. Such phenomena are commonly observed in the final phases of development programs, leading to major difficulties and significant additional costs. One of the most famous examples of combustion instabilities is the F1 engine of the Apollo program which required more than 1000 engine tests to obtain a stable regime satisfying all other constraints (performance, ignition, etc). CIs constitute one of the most challenging problems in fluid mechanics: they combine turbulence, acoustics, chemistry, unsteady two-phase flow in complex geometries. Since combustion instabilities have been identified (more than hundred years ago), the combustion community has followed two paths: (1) improve our understanding of the phenomena controlling stability to build engines which would be ``stable by design'' and (2) give up on a detailed understanding of mechanisms and add control systems either in open or closed loop devices to inhibit unstable modes. Of course, understanding phenomena driving combustion instabilities to suppress them would be the most satisfying approach but there is no fully reliable theory or numerical method today which can predict whether a combustor will be stable or not before it is fired. This talk will present an overview of combustion instabilities phenomenology before focusing on: (1) active control methods for combustion instabilities and (2) recent methods to predict unstable modes in combustors. These methods are based on recent Large Eddy Simulation codes for compressible reacting flows on HPC systems but we will also describe recent fully analytical methods which provide new insights into unstable modes in annular combustion chambers. Support: European
Rayleigh-Taylor instability simulations with CRASH
Chou, C.-C.; Fryxell, B.; Drake, R. P.
2012-03-01
CRASH is a code package developed for the predictive study of radiative shocks. It is based on the BATSRUS MHD code used extensively for space-weather research. We desire to extend the applications of this code to the study of hydrodynamically unstable systems. We report here the results of Rayleigh-Taylor instability (RTI) simulations with CRASH, as a necessary step toward the study of such systems. Our goal, motivated by the previous comparison of simulations and experiment, is to be able to simulate the magnetic RTI with self-generated magnetic fields produced by the Biermann Battery effect. Here we show results for hydrodynamic RTI, comparing the effects of different solvers and numerical parameters. We find that the early-time behavior converges to the analytical result of the linear theory. We observe that the late-time morphology is sensitive to the numerical scheme and limiter beta. At low-resolution limit, the growth of RTI is highly dependent on the setup and resolution, which we attribute to the large numerical viscosity at low resolution.
Investigating the Magnetorotational Instability with Dedalus, and Open-Souce Hydrodynamics Code
Energy Technology Data Exchange (ETDEWEB)
Burns, Keaton J; /UC, Berkeley, aff SLAC
2012-08-31
The magnetorotational instability is a fluid instability that causes the onset of turbulence in discs with poloidal magnetic fields. It is believed to be an important mechanism in the physics of accretion discs, namely in its ability to transport angular momentum outward. A similar instability arising in systems with a helical magnetic field may be easier to produce in laboratory experiments using liquid sodium, but the applicability of this phenomenon to astrophysical discs is unclear. To explore and compare the properties of these standard and helical magnetorotational instabilities (MRI and HRMI, respectively), magnetohydrodynamic (MHD) capabilities were added to Dedalus, an open-source hydrodynamics simulator. Dedalus is a Python-based pseudospectral code that uses external libraries and parallelization with the goal of achieving speeds competitive with codes implemented in lower-level languages. This paper will outline the MHD equations as implemented in Dedalus, the steps taken to improve the performance of the code, and the status of MRI investigations using Dedalus.
Simulation of EAST vertical displacement events by tokamak simulation code
Qiu, Qinglai; Xiao, Bingjia; Guo, Yong; Liu, Lei; Xing, Zhe; Humphreys, D. A.
2016-10-01
Vertical instability is a potentially serious hazard for elongated plasma. In this paper, the tokamak simulation code (TSC) is used to simulate vertical displacement events (VDE) on the experimental advanced superconducting tokamak (EAST). Key parameters from simulations, including plasma current, plasma shape and position, flux contours and magnetic measurements match experimental data well. The growth rates simulated by TSC are in good agreement with TokSys results. In addition to modeling the free drift, an EAST fast vertical control model enables TSC to simulate the course of VDE recovery. The trajectories of the plasma current center and control currents on internal coils (IC) fit experimental data well.
Elimination of the numerical Cerenkov instability for spectral EM-PIC codes
Yu, Peicheng; Decyk, Viktor K; Fiuza, F; Vieira, Jorge; Tsung, Frank S; Fonseca, Ricardo A; Lu, Wei; Silva, Luis O; Mori, Warren B
2014-01-01
When using an electromagnetic particle-in-cell (EM-PIC) code to simulate a relativistically drifting plasma, a violent numerical instability known as the numerical Cerenkov instability (NCI) occurs. The NCI is due to the unphysical coupling of electromagnetic waves on a grid to wave-particle resonances, including aliased resonances, i.e., $\\omega + 2\\pi\\mu/\\Delta t=(k_1+ 2\\pi\
Numerical simulation of the hydrodynamic instability experiments and flow mixing
Institute of Scientific and Technical Information of China (English)
BAI JingSong; WANG Tao; LI Ping; ZOU LiYong; LIU CangLi
2009-01-01
Based on the numerical methods of volume of fluid (VOF) and piecewise parabolic method (PPM) and parallel circumstance of Message Passing Interface (MPI), a parallel multi-viscosity-fluid hydrodynamic code MVPPM (Multi-Viscosity-Fluid Piecewise Parabolic Method) is developed and performed to study the hydrodynamic instability and flow mixing. Firstly, the MVPPM code is verified and validated by simulating three instability cases: The first one is a Riemann problem of viscous flow on the shock tube;the second one is the hydrodynamic instability and mixing of gaseous flows under re-shocks; the third one is a half height experiment of interfacial instability, which is conducted on the AWE's shock tube. By comparing the numerical results with experimental data, good agreement is achieved. Then the MVPPM code is applied to simulate the two cases of the interfacial instabilities of jelly models accelerated by explosion products of a gaseous explosive mixture (GEM), which are adopted in our experiments. The first is implosive dynamic interfacial instability of cylindrical symmetry and mixing. The evolving process of inner and outer interfaces, and the late distribution of mixing mass caused by Rayleigh-Taylor (RT) instability in the center of different radius are given. The second is jelly layer experiment which is initialized with one periodic perturbation with different amplitude and wave length. It reveals the complex processes of evolution of interface, and presents the displacement of front face of jelly layer, bubble head and top of spike relative to initial equilibrium position vs. time. The numerical results are in excellent agreement with that experimental images, and show that the amplitude of initial perturbations affects the evolvement of fluid mixing zone (FMZ) growth rate extremely, especially at late times.
Numerical simulation of the hydrodynamic instability experiments and flow mixing
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
Based on the numerical methods of volume of fluid (VOF) and piecewise parabolic method (PPM) and parallel circumstance of Message Passing Interface (MPI),a parallel multi-viscosity-fluid hydrodynamic code MVPPM (Multi-Viscosity-Fluid Piecewise Parabolic Method) is developed and performed to study the hydrodynamic instability and flow mixing. Firstly,the MVPPM code is verified and validated by simulating three instability cases:The first one is a Riemann problem of viscous flow on the shock tube; the second one is the hydrodynamic instability and mixing of gaseous flows under re-shocks; the third one is a half height experiment of interfacial instability,which is conducted on the AWE’s shock tube. By comparing the numerical results with experimental data,good agreement is achieved. Then the MVPPM code is applied to simulate the two cases of the interfacial instabilities of jelly models acceler-ated by explosion products of a gaseous explosive mixture (GEM),which are adopted in our experi-ments. The first is implosive dynamic interfacial instability of cylindrical symmetry and mixing. The evolving process of inner and outer interfaces,and the late distribution of mixing mass caused by Rayleigh-Taylor (RT) instability in the center of different radius are given. The second is jelly layer ex-periment which is initialized with one periodic perturbation with different amplitude and wave length. It reveals the complex processes of evolution of interface,and presents the displacement of front face of jelly layer,bubble head and top of spike relative to initial equilibrium position vs. time. The numerical results are in excellent agreement with that experimental images,and show that the amplitude of initial perturbations affects the evolvement of fluid mixing zone (FMZ) growth rate extremely,especially at late times.
LFSC - Linac Feedback Simulation Code
Energy Technology Data Exchange (ETDEWEB)
Ivanov, Valentin; /Fermilab
2008-05-01
The computer program LFSC (
Magnetohydrodynamic Simulation Code CANS+: Assessments and Applications
Matsumoto, Yosuke; Kudoh, Yuki; Kawashima, Tomohisa; Matsumoto, Jin; Takahashi, Hiroyuki R; Minoshima, Takashi; Zenitani, Seiji; Miyoshi, Takahiro; Matsumoto, Ryoji
2016-01-01
We present a new magnetohydrodynamic (MHD) simulation code with the aim of providing accurate numerical solutions to astrophysical phenomena where discontinuities, shock waves, and turbulence are inherently important. The code implements the HLLD approximate Riemann solver, the fifth-order-monotonicity-preserving interpolation scheme, and the hyperbolic divergence cleaning method for a magnetic field. This choice of schemes significantly improved numerical accuracy and stability, and saved computational costs in multidimensional problems. Numerical tests of one- and two-dimensional problems showed the advantages of using the high-order scheme by comparing with results from a standard second-order TVD scheme. The present code enabled us to explore long-term evolution of a three-dimensional global accretion disk, in which compressible MHD turbulence saturated at much higher levels via the magneto-rotational instability than that given by the second-order scheme owing to the adoption of the high-resolution, nume...
Multidimensional Simulations of Rotating Pair Instability Supernovae
Chatzopoulos, E; Couch, S M
2013-01-01
We study the effects of rotation on the dynamics, energetics and Ni-56 production of Pair Instability Supernova explosions by performing rotating two-dimensional ("2.5-D") hydrodynamics simulations. We calculate the evolution of eight low metallicity (Z = 10^-3, 10^-4 Zsun) massive (135-245 Msun) PISN progenitors with initial surface rotational velocities 50% that of the critical Keplerian value using the stellar evolution code MESA. We allow for both the inclusion and the omission of the effects of magnetic fields in the angular momentum transport and in chemical mixing, resulting in slowly-rotating and rapidly-rotating final carbon-oxygen cores, respectively. Increased rotation for carbon-oxygen cores of the same mass and chemical stratification leads to less energetic PISN explosions that produce smaller amounts of Ni-56 due to the effect of the angular momentum barrier that develops and slows the dynamical collapse. We find a non-monotonic dependence of Ni-56 production on rotational velocity in situation...
Lessons Learned from Numerical Simulations of Interfacial Instabilities
Cook, Andrew
2015-11-01
Rayleigh-Taylor (RT), Richtmyer-Meshkov (RM) and Kelvin-Helmholtz (KH) instabilities serve as efficient mixing mechanisms in a wide variety of flows, from supernovae to jet engines. Over the past decade, we have used the Miranda code to temporally integrate the multi-component Navier-Stokes equations at spatial resolutions up to 29 billion grid points. The code employs 10th-order compact schemes for spatial derivatives, combined with 4th-order Runge-Kutta time advancement. Some of our major findings are as follows: The rate of growth of a mixing layer is equivalent to the net mass flux through the equi-molar plane. RT growth rates can be significantly reduced by adding shear. RT instability can produce shock waves. The growth rate of RM instability can be predicted from known interfacial perturbations. RM vortex projectiles can far outrun the mixing region. Thermal fluctuations in molecular dynamics simulations can seed instabilities along the braids in KH instability. And finally, enthalpy diffusion is essential in preserving the second law of thermodynamics. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
Electron cloud effects: codes and simulations at KEK
Ohmi, K
2013-01-01
Electron cloud effects had been studied at KEK-Photon Factory since 1995. e-p instability had been studied in proton rings since 1965 in BINP, ISR and PSR. Study of electron cloud effects with the present style, which was based on numerical simulations, started at 1995 in positron storage rings. The instability observed in KEKPF gave a strong impact to B factories, KEKB and PEPII, which were final stage of their design in those days. History of cure for electron cloud instability overlapped the progress of luminosity performance in KEKB. The studies on electron cloud codes and simulations in KEK are presented.
HADES, A Radiographic Simulation Code
Energy Technology Data Exchange (ETDEWEB)
Aufderheide, M.B.; Slone, D.M.; Schach von Wittenau, A.E.
2000-08-18
We describe features of the HADES radiographic simulation code. We begin with a discussion of why it is useful to simulate transmission radiography. The capabilities of HADES are described, followed by an application of HADES to a dynamic experiment recently performed at the Los Alamos Neutron Science Center. We describe quantitative comparisons between experimental data and HADES simulations using a copper step wedge. We conclude with a short discussion of future work planned for HADES.
Numerical instability in a 2D gyrokinetic code caused by divergent E X B flow
Energy Technology Data Exchange (ETDEWEB)
Byers, J.A.; Dimits, Y.M.; Langdon, A.B. [Lawrence Livermore National Lab., CA (United States)
1994-12-01
In this paper, a numerical instability first observed in an 2D electrostatic gyrokinetic code is described. The instability should also be present in some form in many versons of particle-in-cell simulation codes that employ guiding center drifts. A perturbation analysis of the instability is given and its results agree quantitatively with the observations from the gyrokinetic code in all respects. The basic mechanism is a false divergence of the E X B flow caused by the interpolation between the grid and the particles as coupled with the specific numerical method for calculating E = -{del} {phi}. Stability or instability depends in detail on the specific choice of particle interpolation method and field method. One common interpolation method, subtracted dipole, is stable. Other commonly used interpolation methods, linear and quadratic, are unstable when combined with a finite difference for the electric field. Linear and quadratic interpolation can be rendered stable if combined with another method for the electric field, the analytic differential of the interpolated potential.
Numerical Instability in a 2D Gyrokinetic Code Caused by Divergent E × B Flow
Byers, J. A.; Dimits, A. M.; Matsuda, Y.; Langdon, A. B.
1994-12-01
In this paper, a numerical instability first observed in a 2D electrostatic gyrokinetic code is described. The instability should also be present in some form in many versons of particle-in-cell simulation codes that employ guiding center drifts. A perturbation analysis of the instability is given and its results agree quantitatively with the observations from the gyrokinetic code in all respects. The basic mechanism is a false divergence of the E × B flow caused by the interpolation between the grid and the particles as coupled with the specific numerical method for calculating E - ∇φ. Stability or instability depends in detail on the specific choice of particle interpolation method and field method. One common interpolation method, subtracted dipole, is stable. Other commonly used interpolation methods, linear and quadratic, are unstable when combined with a finite difference for the electric field. Linear and quadratic interpolation can be rendered stable if combined with another method for the electric field, the analytic differential of the interpolated potential.
ALE simulation of Rayleigh-Taylor instability
Energy Technology Data Exchange (ETDEWEB)
Anbarlooei, H.R. [Univ. of Science and Technology, Dept. of Mechanical Engineering, Tehran (Iran, Islamic Republic of); Mazaheri, K. [Univ. of Tarbiyat Modares, Dept. of Mechanical Engineering, Tehran, (Iran, Islamic Republic of)]. E-mail: Kiumars@modares.ac.ir; Bidabadi, M. [Univ. of Science and Technology, Dept. of Mechanical Engineering, Tehran (Iran, Islamic Republic of)
2004-07-01
This paper investigates the use of an Arbitrary Lagrangian-Eulerian (ALE) technique for the simulation of a single mode Rayleigh-Taylor instability. A compatible Lagrangian algorithm is used on a simply connected quadrilateral grid in Lagrangian Phase. This algorithm includes subzonal pressures, which are used to control spurious grid motion, and an edge centered artificial viscosity. We use Reference Jacobians optimization based rezone algorithm in the rezoning phase of ALE method. Also a second order sign preserving method is used for remapping. To force monotonocity in remapping phase a Repair algorithm is used. Finally, for remapping of nodal variables we used a second order transformer to transfer these data to cell centers. It is shown that the usage of these algorithms for an ALE method can improve the simulation of a single mode Rayleigh-Taylor Instability. (author)
Numerical simulation of Richtmyer-Meshkov instability
Institute of Scientific and Technical Information of China (English)
FU Dexun; MA Yanwen; ZHANG Linbo; TIAN Baolin
2004-01-01
The compressible Navier-Stokes equations discretized with a fourth order accurate compact finite difference scheme with group velocity control are used to simulate the Richtmyer-Meshkov (R-M) instability problem produced by cylindrical shock-cylindrical material interface with shock Mach number Ms=1.2 and density ratio 1:20 (interior density/outer density). Effect of shock refraction, reflection, interaction of the reflected shock with the material interface, and effect of initial perturbation modes on R-M instability are investigated numerically. It is noted that the shock refraction is a main physical mechanism of the initial phase changing of the material surface. The multiple interactions of the reflected shock from the origin with the interface and the R-M instability near the material interface are the reason for formation of the spike-bubble structures. Different viscosities lead to different spike-bubble structure characteristics. The vortex pairing phenomenon is found in the initial double mode simulation. The mode interaction is the main factor of small structures production near the interface.
Computer Code for Nanostructure Simulation
Filikhin, Igor; Vlahovic, Branislav
2009-01-01
Due to their small size, nanostructures can have stress and thermal gradients that are larger than any macroscopic analogue. These gradients can lead to specific regions that are susceptible to failure via processes such as plastic deformation by dislocation emission, chemical debonding, and interfacial alloying. A program has been developed that rigorously simulates and predicts optoelectronic properties of nanostructures of virtually any geometrical complexity and material composition. It can be used in simulations of energy level structure, wave functions, density of states of spatially configured phonon-coupled electrons, excitons in quantum dots, quantum rings, quantum ring complexes, and more. The code can be used to calculate stress distributions and thermal transport properties for a variety of nanostructures and interfaces, transport and scattering at nanoscale interfaces and surfaces under various stress states, and alloy compositional gradients. The code allows users to perform modeling of charge transport processes through quantum-dot (QD) arrays as functions of inter-dot distance, array order versus disorder, QD orientation, shape, size, and chemical composition for applications in photovoltaics and physical properties of QD-based biochemical sensors. The code can be used to study the hot exciton formation/relation dynamics in arrays of QDs of different shapes and sizes at different temperatures. It also can be used to understand the relation among the deposition parameters and inherent stresses, strain deformation, heat flow, and failure of nanostructures.
Gyrokinetic simulation of driftwave instability in field-reversed configuration
Fulton, D. P.; Lau, C. K.; Schmitz, L.; Holod, I.; Lin, Z.; Tajima, T.; Binderbauer, M. W.
2016-05-01
Following the recent remarkable progress in magnetohydrodynamic (MHD) stability control in the C-2U advanced beam driven field-reversed configuration (FRC), turbulent transport has become one of the foremost obstacles on the path towards an FRC-based fusion reactor. Significant effort has been made to expand kinetic simulation capabilities in FRC magnetic geometry. The recently upgraded Gyrokinetic Toroidal Code (GTC) now accommodates realistic magnetic geometry from the C-2U experiment at Tri Alpha Energy, Inc. and is optimized to efficiently handle the FRC's magnetic field line orientation. Initial electrostatic GTC simulations find that ion-scale instabilities are linearly stable in the FRC core for realistic pressure gradient drives. Estimated instability thresholds from linear GTC simulations are qualitatively consistent with critical gradients determined from experimental Doppler backscattering fluctuation data, which also find ion scale modes to be depressed in the FRC core. Beyond GTC, A New Code (ANC) has been developed to accurately resolve the magnetic field separatrix and address the interaction between the core and scrape-off layer regions, which ultimately determines global plasma confinement in the FRC. The current status of ANC and future development targets are discussed.
Energy Technology Data Exchange (ETDEWEB)
Lartigue, G.
2004-11-15
The new european laws on pollutants emission impose more and more constraints to motorists. This is particularly true for gas turbines manufacturers, that must design motors operating with very fuel-lean mixtures. Doing so, pollutants formation is significantly reduced but the problem of combustion stability arises. Actually, combustion regimes that have a large excess of air are naturally more sensitive to combustion instabilities. Numerical predictions of these instabilities is thus a key issue for many industrial involved in energy production. This thesis work tries to show that recent numerical tools are now able to predict these combustion instabilities. Particularly, the Large Eddy Simulation method, when implemented in a compressible CFD code, is able to take into account the main processes involved in combustion instabilities, such as acoustics and flame/vortex interaction. This work describes a new formulation of a Large Eddy Simulation numerical code that enables to take into account very precisely thermodynamics and chemistry, that are essential in combustion phenomena. A validation of this work will be presented in a complex geometry (the PRECCINSTA burner). Our numerical results will be successfully compared with experimental data gathered at DLR Stuttgart (Germany). Moreover, a detailed analysis of the acoustics in this configuration will be presented, as well as its interaction with the combustion. For this acoustics analysis, another CERFACS code has been extensively used, the Helmholtz solver AVSP. (author)
Monte Carlo simulation code modernization
CERN. Geneva
2015-01-01
The continual development of sophisticated transport simulation algorithms allows increasingly accurate description of the effect of the passage of particles through matter. This modelling capability finds applications in a large spectrum of fields from medicine to astrophysics, and of course HEP. These new capabilities however come at the cost of a greater computational intensity of the new models, which has the effect of increasing the demands of computing resources. This is particularly true for HEP, where the demand for more simulation are driven by the need of both more accuracy and more precision, i.e. better models and more events. Usually HEP has relied on the "Moore's law" evolution, but since almost ten years the increase in clock speed has withered and computing capacity comes in the form of hardware architectures of many-core or accelerated processors. To harness these opportunities we need to adapt our code to concurrent programming models taking advantages of both SIMD and SIMT architectures. Th...
Comparison of computer codes for estimates of the symmetric coupled bunch instabilities growth times
Angal-Kalinin, Deepa
2002-01-01
The standard computer codes used for estimating the growth times of the symmetric coupled bunch instabilities are ZAP and BBI.The code Vlasov was earlier used for the LHC for the estimates of the coupled bunch instabilities growth time[1]. The results obtained by these three codes have been compared and the options under which their results can be compared are discussed. The differences in the input and the output for these three codes are given for a typical case.
Hydrodynamic Instability, Integrated Code, Laboratory Astrophysics, and Astrophysics
Takabe, Hideaki
2016-10-01
This is an article for the memorial lecture of Edward Teller Medal and is presented as memorial lecture at the IFSA03 conference held on September 12th, 2003, at Monterey, CA. The author focuses on his main contributions to fusion science and its extension to astrophysics in the field of theory and computation by picking up five topics. The first one is the anomalous resisitivity to hot electrons penetrating over-dense region through the ion wave turbulence driven by the return current compensating the current flow by the hot electrons. It is concluded that almost the same value of potential as the average kinetic energy of the hot electrons is realized to prevent the penetration of the hot electrons. The second is the ablative stabilization of Rayleigh-Taylor instability at ablation front and its dispersion relation so-called Takabe formula. This formula gave a principal guideline for stable target design. The author has developed an integrated code ILESTA (ID & 2D) for analyses and design of laser produced plasma including implosion dynamics. It is also applied to design high gain targets. The third is the development of the integrated code ILESTA. The forth is on Laboratory Astrophysics with intense lasers. This consists of two parts; one is review on its historical background and the other is on how we relate laser plasma to wide-ranging astrophysics and the purposes for promoting such research. In relation to one purpose, I gave a comment on anomalous transport of relativistic electrons in Fast Ignition laser fusion scheme. Finally, I briefly summarize recent activity in relation to application of the author's experience to the development of an integrated code for studying extreme phenomena in astrophysics.
One dimensional PIC simulation of relativistic Buneman instability
Rajawat, Roopendra Singh; Sengupta, Sudip
2016-10-01
Spatio-temporal evolution of the relativistic Buneman instability has been investigated in one dimension using an in-house developed particle-in-cell simulation code. Starting from the excitation of the instability, its evolution has been followed numerically till its quenching and beyond. The simulation results have been quantitatively compared with the fluid theory and are found to be in conformity with the well known fact that the maximum growth rate (γmax) reduces due to relativistic effects and varies with γ e 0 and m/M as γ m a x ˜ /√{ 3 } 2 √{ γ e 0 } ( /m 2 M ) 1 / 3 , where γ e 0 is the Lorentz factor associated with the initial electron drift velocity (v0) and (m/M) is the electron to ion mass ratio. Further it is observed that in contrast to the non-relativistic results [A. Hirose, Plasma Phys. 20, 481 (1978)] at the saturation point, the ratio of electrostatic field energy density ( ∑ k | E k | 2 / 8 π ) to initial drift kinetic energy density (W0) scales with γ e 0 as ˜ 1 / γe 0 2 . This novel result on the scaling of energy densities has been found to be in quantitative agreement with the scalings derived using fluid theory.
Relativistic Klystron Two-Beam Accelerator Simulation Code Development
Lidia, Steven; Ryne, Robert
1997-05-01
We present recent work on the development and testing of a 3-D simu- lation code for relativistic klystron two-beam accelerators (RK-TBAs). This new code utilizes symplectic integration techniques to push macro- particles, coupled to a circuit equation framework that advances the fields in the cavities. Space charge effects are calculated using a Green's function approach, and pipe wall effects are included in the electrostatic approximation. We present simulations of the LBNL/LLNL RK-TBA device, emphasizing cavity power development and beam dynamics, including the high- and low-frequency beam break-up instabilities.
Reactive transport codes for subsurface environmental simulation
Steefel, C.I.; Appelo, C.A.J.; Arora, B.; Kalbacher, D.; Kolditz, O.; Lagneau, V.; Lichtner, P.C.; Mayer, K.U.; Meeussen, J.C.L.; Molins, S.; Moulton, D.; Shao, D.; Simunek, J.; Spycher, N.; Yabusaki, S.B.; Yeh, G.T.
2015-01-01
A general description of the mathematical and numerical formulations used in modern numerical reactive transport codes relevant for subsurface environmental simulations is presented. The formulations are followed by short descriptions of commonly used and available subsurface simulators that conside
Energy Technology Data Exchange (ETDEWEB)
McClenaghan, J.; Lin, Z.; Holod, I.; Deng, W.; Wang, Z. [University of California, Irvine, California 92697 (United States)
2014-12-15
The gyrokinetic toroidal code (GTC) capability has been extended for simulating internal kink instability with kinetic effects in toroidal geometry. The global simulation domain covers the magnetic axis, which is necessary for simulating current-driven instabilities. GTC simulation in the fluid limit of the kink modes in cylindrical geometry is verified by benchmarking with a magnetohydrodynamic eigenvalue code. Gyrokinetic simulations of the kink modes in the toroidal geometry find that ion kinetic effects significantly reduce the growth rate even when the banana orbit width is much smaller than the radial width of the perturbed current layer at the mode rational surface.
Simulation and quasilinear theory of aperiodic ordinary mode instability
Energy Technology Data Exchange (ETDEWEB)
Seough, Jungjoon [Faculty of Human Development, University of Toyama, 3190, Gofuku, Toyama City, Toyama 930-8555 (Japan); International Research Fellow of the Japan Society for the Promotion of Science, Tokyo (Japan); Yoon, Peter H. [Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742 (United States); School of Space Research, Kyung Hee University, Yongin-Si, Gyeonggi-Do 446-701 (Korea, Republic of); Hwang, Junga [Korea Astronomy and Space Science Institute, Daejeon (Korea, Republic of); Department of Astronomy and Space Science, University of Science and Technology, Daejeon (Korea, Republic of); Nariyuki, Yasuhiro [Faculty of Human Development, University of Toyama, 3190, Gofuku, Toyama City, Toyama 930-8555 (Japan)
2015-08-15
The purely growing ordinary (O) mode instability driven by excessive parallel temperature anisotropy for high-beta plasmas was first discovered in the 1970s. This instability receives renewed attention because it may be applicable to the solar wind plasma. The electrons in the solar wind feature temperature anisotropies whose upper values are apparently limited by plasma instabilities. The O-mode instability may be important in this regard. Previous studies of O mode instability have been based on linear theory, but the actual solar wind electrons may be in saturated state. The present paper investigates the nonlinear saturation behavior of the O mode instability by means of one-dimensional particle-in-cell simulation and quasilinear theory. It is shown that the quasilinear method accurately reproduces the simulation results.
Direct Numerical Simulation of the Rayleigh-Taylor Instability with the Spectral Element Method
Institute of Scientific and Technical Information of China (English)
ZHANG Xu; TAN Duo-Wang
2009-01-01
A novel method is proposed to simulate Rayleigh-Taylor instabilities using a specially-developed unsteady threedimensional high-order spectral element method code.The numerical model used consists of Navier-Stokes equations and a transport-diffusive equation.The code is first validated with the results of linear stability perturbation theory.Then several characteristics of the Rayleigh-Taylor instabjJjties are studied using this three-dimensional unsteady code,inducling instantaneous turbulent structures and statistical turbulent mixing heights under different initial wave numbers.These results indicate that turbulent structures ofRayleigh-Taylor instabilities are strongly dependent on the initial conditions.The results also suggest that a high-order numerical method should provide the capability of sir.ulating small scale fluctuations of Rayleigh-Taylor instabilities of turbulent flows.
Particle-in-cell (PIC) simulations of beam instabilities in gyrotron beam tunnels
Energy Technology Data Exchange (ETDEWEB)
Tran, T.M.; Jost, G.; Appert, K.; Sauter, O. [Ecole Polytechnique Federale, Lausanne (Switzerland). Centre de Recherche en Physique des Plasma (CRPP); Wuthrich, S. [CRAY Research, PATP/PSE, Ecole Polytechnique Federale, Lausanne (Switzerland)
1995-10-01
Experimental observations seem to indicate that the beam velocity and energy spreads are larger than those calculated from the electron trajectory codes which do not take into account the effects of beam instabilities. On the other hand, parasitic oscillations of the beam with frequencies close to the electron cyclotron frequency {omega}{sub ce} have been observed experimentally, suggesting the possibility that instabilities can be excited in the beam tunnels and are responsible for the beam degradation. 2D electrostatic and electromagnetic time-dependent PIC codes have been developed to simulate the beam transport in the beam tunnel. The results of extensive parametric runs, using these codes (which were ported on the Cray T3D massively parallel computer), together with the role of the beam instabilities around {omega}{sub ce} on the beam degradation will be reported. (author) 2 figs., 9 refs.
Simulating Rayleigh-Taylor (RT) instability using PPM hydrodynamics @scale on Roadrunner (u)
Energy Technology Data Exchange (ETDEWEB)
Woodward, Paul R [Los Alamos National Laboratory; Dimonte, Guy [Los Alamos National Laboratory; Rockefeller, Gabriel M [Los Alamos National Laboratory; Fryer, Christopher L [Los Alamos National Laboratory; Dimonte, Guy [Los Alamos National Laboratory; Dai, W [Los Alamos National Laboratory; Kares, R. J. [Los Alamos National Laboratory
2011-01-05
The effect of initial conditions on the self-similar growth of the RT instability is investigated using a hydrodynamics code based on the piecewise-parabolic-method (PPM). The PPM code was converted to the hybrid architecture of Roadrunner in order to perform the simulations at extremely high speed and spatial resolution. This paper describes the code conversion to the Cell processor, the scaling studies to 12 CU's on Roadrunner and results on the dependence of the RT growth rate on initial conditions. The relevance of the Roadrunner implementation of this PPM code to other existing and anticipated computer architectures is also discussed.
One dimensional PIC simulation of relativistic Buneman instability
Rajawat, Roopendra Singh
2016-01-01
Spatio-temporal evolution of the relativistic Buneman instability has been investigated in one dimension using an in-house developed particle-in-cell simulation code. Starting from the excitation of the instability, its evolution has been followed numerically till its quenching and beyond. As compared to the well understood non-relativistic case, it is found that the maximum growth rate ($\\gamma_{max}$) reduces due to relativistic effects and varies with $\\gamma_{e0}$ and m/M as $\\gamma_{max} \\sim \\frac{\\sqrt{3}}{2\\sqrt{\\gamma_{e0}}}\\biglb(\\frac{m}{2M}\\bigrb)^{1/3}$, where $\\gamma_{e0}$ is Lorentz factor associated with the initial electron drift velocity ($v_{0}$) and (m/M) is the electron to ion mass ratio. Further it is observed that in contrast to the non-relativistic results[Hirose,Plasma Phys. 20, 481(1978)] at the saturation point, ratio of electrostatic field energy density ($\\sum\\limits_{k} |E_{k}|^{2}/8\\pi$) to initial drift kinetic energy density ($W_{0}$) scales with $\\gamma_{e0}$ as $\\sim 1/\\gamm...
Parametric instabilities of large-amplitude parallel propagating Alfven waves: 2-D PIC simulation
Nariyuki, Yasuhiro; Hada, Tohru
2008-01-01
We discuss the parametric instabilities of large-amplitude parallel propagating Alfven waves using the 2-D PIC simulation code. First, we confirmed the results in the past study [Sakai et al, 2005] that the electrons are heated due to the modified two stream instability and that the ions are heated by the parallel propagating ion acoustic waves. However, although the past study argued that such parallel propagating longitudinal waves are excited by transverse modulation of parent Alfven wave, we consider these waves are more likely to be generated by the usual, parallel decay instability. Further, we performed other simulation runs with different polarization of the parent Alfven waves or the different ion thermal velocity. Numerical results suggest that the electron heating by the modified two stream instability due to the large amplitude Alfven waves is unimportant with most parameter sets.
Nonlinear instability in simulations of Large Plasma Device turbulence
Friedman, B; Umansky, M V; Schaffner, D; Joseph, I
2013-01-01
Several simulations of turbulence in the Large Plasma Device (LAPD) [W. Gekelman et al., Rev. Sci. Inst. 62, 2875 (1991)] are energetically analyzed and compared with each other and with the experiment. The simulations use the same model, but different axial boundary conditions. They employ either periodic, zero-value, zero-derivative, or sheath axial boundaries. The linear stability physics is different between the scenarios because the various boundary conditions allow the drift wave instability to access different axial structures, and the sheath boundary simulation contains a conducting wall mode instability which is just as unstable as the drift waves. Nevertheless, the turbulence in all the simulations is relatively similar because it is primarily driven by a robust nonlinear instability that is the same for all cases. The nonlinear instability preferentially drives $k_\\parallel = 0$ potential energy fluctuations, which then three-wave couple to $k_\\parallel \
Methods for Simulating the Heavy Core Instability
Directory of Open Access Journals (Sweden)
Chang Philip
2013-04-01
Full Text Available Vortices have been proposed as the sites of planet formation, where dust collects and grows into planetesimals, the building blocks of planets. However, for very small dust particles that can be treated as a pressure-less fluid, we have recently discovered the “heavy core” instability, driven by the density gradient in the vortex. In order to understand the eventual outcome of this instability, we need to study its non-linear development. Here, we describe our ongoing work to develop highly accurate numerical models of a vortex with a density gradient embedded within a protoplanetary disk.
The stellar atmosphere simulation code Bifrost. Code description and validation
Gudiksen, B. V.; Carlsson, M.; Hansteen, V. H.; Hayek, W.; Leenaarts, J.; Martínez-Sykora, J.
2011-07-01
Context. Numerical simulations of stellar convection and photospheres have been developed to the point where detailed shapes of observed spectral lines can be explained. Stellar atmospheres are very complex, and very different physical regimes are present in the convection zone, photosphere, chromosphere, transition region and corona. To understand the details of the atmosphere it is necessary to simulate the whole atmosphere since the different layers interact strongly. These physical regimes are very diverse and it takes a highly efficient massively parallel numerical code to solve the associated equations. Aims: The design, implementation and validation of the massively parallel numerical code Bifrost for simulating stellar atmospheres from the convection zone to the corona. Methods: The code is subjected to a number of validation tests, among them the Sod shock tube test, the Orzag-Tang colliding shock test, boundary condition tests and tests of how the code treats magnetic field advection, chromospheric radiation, radiative transfer in an isothermal scattering atmosphere, hydrogen ionization and thermal conduction. Results.Bifrost completes the tests with good results and shows near linear efficiency scaling to thousands of computing cores.
Elimination of the numerical Cerenkov instability for spectral EM-PIC codes
Yu, Peicheng; Xu, Xinlu; Decyk, Viktor K.; Fiuza, Frederico; Vieira, Jorge; Tsung, Frank S.; Fonseca, Ricardo A.; Lu, Wei; Silva, Luis O.; Mori, Warren B.
2015-07-01
When using an electromagnetic particle-in-cell (EM-PIC) code to simulate a relativistically drifting plasma, a violent numerical instability known as the numerical Cerenkov instability (NCI) occurs. The NCI is due to the unphysical coupling of electromagnetic waves on a grid to wave-particle resonances, including aliased resonances, i.e., ω + 2 πμ / Δt =(k1 + 2 πν1 / Δx1) v0, where μ and ν1 refer to the time and space aliases and the plasma is drifting relativistically at velocity v0 in the 1 ˆ -direction. We extend our previous work Xu et al. (2013) by recasting the numerical dispersion relation of a relativistically drifting plasma into a form which shows explicitly how the instability results from the coupling modes which are purely transverse electromagnetic (EM) modes and purely longitudinal modes in the rest frame of the plasma for each time and space aliasing. The dispersion relation for each μ and ν1 is the product of the dispersion relation of these two modes set equal to a coupling term that vanishes in the continuous limit. The new form of the numerical dispersion relation provides an accurate method of systematically calculating the growth rate and location of the mode in the fundamental Brillouin zone for any Maxwell solver for each μ and ν1. We then focus on the spectral Maxwell solver and systematically discuss its NCI modes. We show that the second fastest growing NCI mode for the spectral solver corresponds to μ =ν1 = 0, that it has a growth rate approximately one order of magnitude smaller than the fastest growing μ = 0 and ν1 = 1 mode, and that its location in the k space fundamental Brillouin zone is sensitive to the grid size and time step. Based on these studies, strategies to systematically eliminate the NCI modes for a spectral solver are developed. We apply these strategies to both relativistic collisionless shock and LWFA simulations, and demonstrate that high-fidelity multi-dimensional simulations of drifting plasmas can
The stellar atmosphere simulation code Bifrost
Gudiksen, Boris V; Hansteen, Viggo H; Hayek, Wolfgang; Leenaarts, Jorrit; Martínez-Sykora, Juan
2011-01-01
Context: Numerical simulations of stellar convection and photospheres have been developed to the point where detailed shapes of observed spectral lines can be explained. Stellar atmospheres are very complex, and very different physical regimes are present in the convection zone, photosphere, chromosphere, transition region and corona. To understand the details of the atmosphere it is necessary to simulate the whole atmosphere since the different layers interact strongly. These physical regimes are very diverse and it takes a highly efficient massively parallel numerical code to solve the associated equations. Aims: The design, implementation and validation of the massively parallel numerical code Bifrost for simulating stellar atmospheres from the convection zone to the corona. Methods: The code is subjected to a number of validation tests, among them the Sod shock tube test, the Orzag-Tang colliding shock test, boundary condition tests and tests of how the code treats magnetic field advection, chromospheric ...
2D Implosion Simulations with a Kinetic Particle Code
Sagert, Irina; Strother, Terrance T
2016-01-01
We perform two-dimensional (2D) implosion simulations using a Monte Carlo kinetic particle code. The paper is motivated by the importance of non-equilibrium effects in inertial confinement fusion (ICF) capsule implosions. These cannot be fully captured by hydrodynamic simulations while kinetic methods, as the one presented in this study, are able to describe continuum and rarefied regimes within one approach. In the past, our code has been verified via traditional shock wave and fluid instability simulations. In the present work, we focus on setups that are closer to applications in ICF. We perform simple 2D disk implosion simulations using one particle species. The obtained results are compared to simulations using the hydrodynamics code RAGE. In a first study, the implosions are powered by energy deposition in the outer layers of the disk. We test the impact of the particle mean-free-path and find that while the width of the implosion shock broadens, its location as a function of time remains very similar. ...
Large-Eddy Simulation of combustion instabilities in a variable-length combustor
Garby, Romain; Selle, Laurent; Poinsot, Thierry
2013-01-01
This article presents a simulation of a model rocket combustor with continuously variable acoustic properties thanks to a variable-length injector tube. Fully compressible Large-Eddy Simulations are conducted using the AVBP code. An original flame stabilization mechanism is uncovered where the recirculation of hot gases in the corner recirculation zone creates a triple flame structure. An unstable operating point is then chosen to investigate the mechanism of the instability. The simulations are compared to experimental results in terms of frequency and mode structure. Two-dimensional axi-symmetric computations are compared to full 3D simulations in order to assess the validity of the axi-symmetry assumption for the prediction of mean and unsteady features of this flow. Despite the inaccuracies inherent to the 2D description of a turbulent flow, for this configuration and the particular operating point investigated, the axi-symmetric simulation qualitatively reproduces some features of the instability.
Large-eddy-simulation of 3-dimensional Rayleigh-Taylor instability in incompressible fluids
Institute of Scientific and Technical Information of China (English)
无
2002-01-01
The 3-dimensional incompressible Rayleigh-Taylor instability is numerically studied through the large-eddy-simulation (LES) approach based on the passive scalar transport model. Both the instantaneous velocity and the passive scalar fields excited by sinusoidal perturbation and random perturbation are simulated. A full treatment of the whole evolution process of the instability is addressed. To verify the reliability of the LES code, the averaged turbulent energy as well as the flux of passive scalar are calculated at both the resolved scale and the subgrid scale. Our results show good agreement with the experimental and other numerical work. The LES method has proved to be an effective approach to the Rayleigh-Taylor instability.
Mizuno, Yosuke; Lyubarsky, Yuri; ishikawa, Ken-Ichi; Hardee, Philip E.
2010-01-01
We have investigated the development of current-driven (CD) kink instability through three-dimensional relativistic MHD simulations. A static force-free equilibrium helical magnetic configuration is considered in order to study the influence of the initial configuration on the linear and nonlinear evolution of the instability. We found that the initial configuration is strongly distorted but not disrupted by the kink instability. The instability develops as predicted by linear theory. In the non-linear regime the kink amplitude continues to increase up to the terminal simulation time, albeit at different rates, for all but one simulation. The growth rate and nonlinear evolution of the CD kink instability depends moderately on the density profile and strongly on the magnetic pitch profile. The growth rate of the kink mode is reduced in the linear regime by an increase in the magnetic pitch with radius and the non-linear regime is reached at a later time than for constant helical pitch. On the other hand, the growth rate of the kink mode is increased in the linear regime by a decrease in the magnetic pitch with radius and reaches the non-linear regime sooner than the case with constant magnetic pitch. Kink amplitude growth in the non-linear regime for decreasing magnetic pitch leads to a slender helically twisted column wrapped by magnetic field. On the other hand, kink amplitude growth in the non-linear regime nearly ceases for increasing magnetic pitch.
Benchmarking and scaling studies of pseudospectral code Tarang for turbulence simulations
Indian Academy of Sciences (India)
Mahendra K Verma; Anando Chatterjee; K Sandeep Reddy; Rakesh K Yadav; Supriyo Paul; Mani Chandra; Ravi Samtaney
2013-10-01
Tarang is a general-purpose pseudospectral parallel code for simulating flows involving fluids, magnetohydrodynamics, and Rayleigh–Bénard convection in turbulence and instability regimes. In this paper we present code validation and benchmarking results of Tarang. We performed our simulations on 10243, 20483, and 40963 grids using the HPC system of IIT Kanpur and Shaheen of KAUST. We observe good `weak' and `strong' scaling for Tarang on these systems.
Benchmarking and scaling studies of pseudospectral code Tarang for turbulence simulations
VERMA, MAHENDRA K
2013-09-21
Tarang is a general-purpose pseudospectral parallel code for simulating flows involving fluids, magnetohydrodynamics, and Rayleigh–Bénard convection in turbulence and instability regimes. In this paper we present code validation and benchmarking results of Tarang. We performed our simulations on 10243, 20483, and 40963 grids using the HPC system of IIT Kanpur and Shaheen of KAUST. We observe good ‘weak’ and ‘strong’ scaling for Tarang on these systems.
On the Numerical Dispersion of Electromagnetic Particle-In-Cell Code : Finite Grid Instability
Meyers, M D; Zeng, Y; Yi, S A; Albright, B J
2014-01-01
The Particle-In-Cell (PIC) method is widely used in relativistic particle beam and laser plasma modeling. However, the PIC method exhibits numerical instabilities that can render unphysical simulation results or even destroy the simulation. For electromagnetic relativistic beam and plasma modeling, the most relevant numerical instabilities are the finite grid instability and the numerical Cherenkov instability. We review the numerical dispersion relation of the electromagnetic PIC algorithm to analyze the origin of these instabilities. We rigorously derive the faithful 3D numerical dispersion of the PIC algorithm, and then specialize to the Yee FDTD scheme. In particular, we account for the manner in which the PIC algorithm updates and samples the fields and distribution function. Temporal and spatial phase factors from solving Maxwell's equations on the Yee grid with the leapfrog scheme are also explicitly accounted for. Numerical solutions to the electrostatic-like modes in the 1D dispersion relation for a ...
Kinetic simulation of the electron-cyclotron maser instability: effect of a finite source size
Kuznetsov, A A
2012-01-01
The electron-cyclotron maser instability is widespread in the Universe, producing, e.g., radio emission of the magnetized planets and cool substellar objects. Diagnosing the parameters of astrophysical radio sources requires comprehensive nonlinear simulations of the radiation process. We simulate the electron-cyclotron maser instability in a very low-beta plasma. The model used takes into account the radiation escape from the source region and the particle flow through this region. We developed a kinetic code to simulate the time evolution of an electron distribution in a radio emission source. The model includes the terms describing the particle injection to and escape from the emission source region. The spatial escape of the emission from the source is taken into account by using a finite amplification time. The unstable electron distribution of the horseshoe type is considered. A number of simulations were performed for different parameter sets typical of the magnetospheres of planets and ultracool dwarf...
Simulation and quasilinear theory of proton firehose instability
Energy Technology Data Exchange (ETDEWEB)
Seough, Jungjoon [Korean Astronomy and Space Science Institute, Daejeon (Korea, Republic of); Faculty of Human Development, University of Toyama, 3190, Gofuku, Toyama City, Toyama, 930-8555 (Japan); Yoon, Peter H. [University of Maryland, College Park, Maryland 20742 (United States); School of Space Research, Kyung Hee University, Yongin, Gyeonggi 446-701 (Korea, Republic of); Hwang, Junga [Korean Astronomy and Space Science Institute, Daejeon (Korea, Republic of); Korea, University of Science and Technology, Daejeon (Korea, Republic of)
2015-01-15
The electromagnetic proton firehose instability is driven by excessive parallel temperature anisotropy, T{sub ∥} > T{sub ⊥} (or more precisely, parallel pressure anisotropy, P{sub ∥} > P{sub ⊥}) in high-beta plasmas. Together with kinetic instabilities driven by excessive perpendicular temperature anisotropy, namely, electromagnetic proton cyclotron and mirror instabilities, its role in providing the upper limit for the temperature anisotropy in the solar wind is well-known. A recent Letter [Seough et al., Phys. Rev. Lett. 110, 071103 (2013)] employed quasilinear kinetic theory for these instabilities to explain the observed temperature anisotropy upper bound in the solar wind. However, the validity of quasilinear approach has not been rigorously tested until recently. In a recent paper [Seough et al., Phys. Plasmas 21, 062118 (2014)], a comparative study is carried out for the first time in which quasilinear theory of proton cyclotron instability is tested against results obtained from the particle-in-cell simulation method, and it was demonstrated that the agreement was rather excellent. The present paper addresses the same issue involving the proton firehose instability. Unlike the proton cyclotron instability, however, it is found that the quasilinear approximation enjoys only a limited range of validity, especially for the wave dynamics and for the relatively high-beta regime. Possible causes and mechanisms responsible for the discrepancies are speculated and discussed.
Three-dimensional simulations of viscoelastic instability in polymeric filaments
DEFF Research Database (Denmark)
Rasmussen, Henrik Koblitz; Hassager, Ole
1999-01-01
The three-dimensional Langrangian integral method is used to simulate the elastic end-plate instability that occurs in the rapid extension of some polymeric filaments between parallel plates. It is demonstrated that the upper convected Maxwell model describes the essential features of the instabi...
Simulations of Rayleigh Taylor Instabilities in the presence of a Strong Radiative shock
Trantham, Matthew; Kuranz, Carolyn; Shvarts, Dov; Drake, R. P.
2016-10-01
Recent Supernova Rayleigh Taylor experiments on the National Ignition Facility (NIF) are relevant to the evolution of core-collapse supernovae in which red supergiant stars explode. Here we report simulations of these experiments using the CRASH code. The CRASH code, developed at the University of Michigan to design and analyze high-energy-density experiments, is an Eulerian code with block-adaptive mesh refinement, multigroup diffusive radiation transport, and electron heat conduction. We explore two cases, one in which the shock is strongly radiative, and another with negligible radiation. The experiments in all cases produced structures at embedded interfaces by the Rayleigh Taylor instability. The weaker shocked environment is cooler and the instability grows classically. The strongly radiative shock produces a warm environment near the instability, ablates the interface, and alters the growth. We compare the simulated results with the experimental data and attempt to explain the differences. This work is funded by the NNSA-DS and SC-OFES Joint Program in High-Energy-Density Laboratory Plasmas, Grant Number DE-NA0002956.
Large eddy simulation of a shocked gas cylinder instability induced turbulence
Institute of Scientific and Technical Information of China (English)
无
2010-01-01
The Navier-Stokes equations for compressible fluid are solved with the operator splitting technique and LES (large eddy simulation) with the Smagorinsky model. A computational code MVFT (multi-viscosity-fluid and turbulence) is developed to study hydrodynamic instability and the induced turbulent mixing for multi compressible fluid. In order to validate the code MVFT,the LANL’s shock tube experiment of shocked SF6 gas cylinder is simulated with the initial state of SF6 gas cylinder described by dissipative ITL (interface transition layer). It is shown that the width and height of gas cylinder calculated with MVFT are closer to the experimental results than RAGE,and that the velocities of upstream edge,downstream edge and vortex edge agree with the experimental results,and are appreciably smaller than the RAGE results. The code MVFT has been pre-liminarily validated.
Nishikawa, K.-I.; Ramirez-Ruiz, E.; Hededal, C.; Hardee, P.; Mizuno, Y.; Fishman, G. J.
2007-01-01
Using a 3-D relativistic particle-in-cell (RPIC) code, we have investigated particle acceleration associated with a relativistic electron-positron (cold) jet propagating into ambient electron-positron and electron-ion plasmas without initial magnetic fields in order to investigate the nonlinear stage of the Weibel instability. We have also performed simulations with broad Lorentz factor distribution of jet electrons and positrons, which are assumed to be created by the photon annihilation. The growth time and nonlinear saturation levels depend on the initial jet parallel velocity distributions and ambient plasma. Simulations show that the Weibel instability created in the collisionless shocks accelerates jet and ambient particles both perpendicular and parallel to the jet propagation direction. The nonlinear fluctuation amplitude of densities, currents, electric, and magnetic fields in the electron-ion ambient plasma are larger than those in the electron-positron ambient plasma. We have shown that plasma instabilities driven by these streaming electron-positron pairs are responsible for the excitation of near-equipartition, turbulent magnetic fields. These fields maintain a strong saturated level on timescales much longer than the electron skin depth at least for the duration of the simulations. Our results reveal the importance of the electromagnetic filamentation instability in ensuring an effective coupling between electron-positron pairs and ions, and may help explain the origin of large upstream fields in GRB shock.
Development and Test of 2.5-Dimensional Electromagnetic PIC Simulation Code
Lee, Sang-Yun; Lee, Ensang; Kim, Khan-Hyuk; Seon, Jongho; Lee, Dong-Hun; Ryu, Kwang-Sun
2015-03-01
We have developed a 2.5-dimensional electromagnetic particle simulation code using the particle-in-cell (PIC) method to investigate electromagnetic phenomena that occur in space plasmas. Our code is based on the leap-frog method and the centered difference method for integration and differentiation of the governing equations. We adopted the relativistic Buneman-Boris method to solve the Lorentz force equation and the Esirkepov method to calculate the current density while maintaining charge conservation. Using the developed code, we performed test simulations for electron two-stream instability and electron temperature anisotropy induced instability with the same initial parameters as used in previously reported studies. The test simulation results are almost identical with those of the previous papers.
Rossby Wave Instability of Thin Accretion Disks - III. Nonlinear Simulations
Li, H; Wendroff, B; Liska, R
2000-01-01
(abridged) We study the nonlinear evolution of the Rossby wave instability in thin disks using global 2D hydrodynamic simulations. The key questions we are addressing in this paper are: (1) What happens when the instability becomes nonlinear? Specifically, does it lead to vortex formation? (2) What is the detailed behavior of a vortex? (3) Can the instability sustain itself and can the vortex last a long time? Among various initial equilibria that we have examined, we generally find that there are three stages of the disk evolution: (1) The exponential growth of the initial small amplitude perturbations. This is in excellent agreement with the linear theory; (2) The production of large scale vortices and their interactions with the background flow, including shocks. Significant accretion is observed due to these vortices. (3) The coupling of Rossby waves/vortices with global spiral waves, which facilitates further accretion throughout the whole disk. Even after more than 20 revolutions at the radius of vortic...
On the Numerical Dispersion of Electromagnetic Particle-In-Cell Code : Finite Grid Instability
Energy Technology Data Exchange (ETDEWEB)
Meyers, Michael David [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Univ. of California, Los Angeles, CA (United States) Dept. of Physics and Astronomy; Huang, Chengkun [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Zeng, Yong [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Yi, Sunghwan [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Albright, Brian James [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2014-07-15
The Particle-In-Cell (PIC) method is widely used in relativistic particle beam and laser plasma modeling. However, the PIC method exhibits numerical instabilities that can render unphysical simulation results or even destroy the simulation. For electromagnetic relativistic beam and plasma modeling, the most relevant numerical instabilities are the finite grid instability and the numerical Cherenkov instability. We review the numerical dispersion relation of the electromagnetic PIC algorithm to analyze the origin of these instabilities. We rigorously derive the faithful 3D numerical dispersion of the PIC algorithm, and then specialize to the Yee FDTD scheme. In particular, we account for the manner in which the PIC algorithm updates and samples the fields and distribution function. Temporal and spatial phase factors from solving Maxwell's equations on the Yee grid with the leapfrog scheme are also explicitly accounted for. Numerical solutions to the electrostatic-like modes in the 1D dispersion relation for a cold drifting plasma are obtained for parameters of interest. In the succeeding analysis, we investigate how the finite grid instability arises from the interaction of the numerical 1D modes admitted in the system and their aliases. The most significant interaction is due critically to the correct representation of the operators in the dispersion relation. We obtain a simple analytic expression for the peak growth rate due to this interaction.
Direct Numerical Simulations of Type Ia Supernovae Flames I: The Landau-Darrieus Instability
Bell, J B; Rendleman, C A; Woosley, S E; Zingale, M A
2004-01-01
Planar flames are intrinsically unstable in open domains due to the thermal expansion across the burning front--the Landau-Darrieus instability. This instability leads to wrinkling and growth of the flame surface, and corresponding acceleration of the flame, until it is stabilized by cusp formation. We look at the Landau-Darrieus instability for C/O thermonuclear flames at conditions relevant to the late stages of a Type Ia supernova explosion. Two-dimensional direct numerical simulations of both single-mode and multi-mode perturbations using a low Mach number hydrodynamics code are presented. We show the effect of the instability on the flame speed as a function of both the density and domain size, demonstrate the existence of the small scale cutoff to the growth of the instability, and look for the proposed breakdown of the non-linear stabilization at low densities. The effects of curvature on the flame as quantified through measurements of the growth rate and computation of the corresponding Markstein numb...
Simulation of Kelvin-Helmholtz Instability with Flux-Corrected Transport Method
Institute of Scientific and Technical Information of China (English)
WANG Li-Feng; YE Wen-Hua; FAN Zheng-Feng; LI Ying-Jun
2009-01-01
The sixth-order accurate phase error flux-corrected transport numerical algorithm is introduced, and used to simulate Kelvin-Helmholtz instability. Linear growth rates of the simulation agree with the linear theories of Kelvin-Helmholtz instability. It indicates the validity and accuracy of this simulation method. The method also has good capturing ability of the instability interface deformation.
Energy Technology Data Exchange (ETDEWEB)
Kozmenkov, Y. [Helmholtz-Zentrum Dresden-Rossendorf e.V. (FZD), Institute of Safety Research, P.O.B. 510119, D-01324 Dresden (Germany); Institute of Physics and Power Engineering, Obninsk (Russian Federation); Rohde, U., E-mail: U.Rohde@hzdr.de [Helmholtz-Zentrum Dresden-Rossendorf e.V. (FZD), Institute of Safety Research, P.O.B. 510119, D-01324 Dresden (Germany); Manera, A. [Paul Scherrer Institute (Switzerland)
2012-02-15
Highlights: Black-Right-Pointing-Pointer We report about the simulation of flashing-induced instabilities in natural circulation systems. Black-Right-Pointing-Pointer Flashing-induced instabilities are of relevance for operation of pool-type reactors of small power at low pressure. Black-Right-Pointing-Pointer The RELAP5 code is validated against measurement data from natural circulation experiments. Black-Right-Pointing-Pointer The magnitude and frequency of the oscillations were reproduced in good agreement with the measurement data. - Abstract: This paper reports on the use of the RELAP5 code for the simulation of flashing-induced instabilities in natural circulation systems. The RELAP 5 code is intended to be used for the simulation of transient processes in the Russian RUTA reactor concept operating at atmospheric pressure with forced convection of coolant. However, during transient processes, natural circulation with flashing-induced instabilities might occur. The RELAP5 code is validated against measurement data from natural circulation experiments performed within the framework of a European project (NACUSP) on the CIRCUS facility. The facility, built at the Delft University of Technology in The Netherlands, is a water/steam 1:1 height-scaled loop of a typical natural-circulation-cooled BWR. It was shown that the RELAP5 code is able to model all relevant phenomena related to flashing induced instabilities. The magnitude and frequency of the oscillations were reproduced in a good agreement with the measurement data. The close correspondence to the experiments was reached by detailed modeling of all components of the CIRCUS facility including the heat exchanger, the buffer vessel and the steam dome at the top of the facility.
PIC simulations of the MagnetoRotational instability in electron-positron plasmas
Inchingolo, Giannandrea; Grismayer, Thomas; Loureiro, Nuno F.; Fonseca, Ricardo A.; Silva, Luis O.
2016-10-01
The magnetorotational instability (MRI) is a crucial mechanism of angular momentum transport in a variety of astrophysical scenarios, as e-e+ plasmas accretion disks nearness neutron stars and black holes. The MRI has been widely studied using MHD models and simulations, in order to understand the behavior of astrophysical fluids in a state of differential rotation. When the timescale for electron and ion collisions is longer than the inflow time in the disk, the plasma is macroscopically collisionless and MHD breaks down. This is the case of the limit of weak magnetic field, i.e., as the ratio of the ion cyclotron frequency to orbital frequency becomes small. Leveraging on the recent addition of the shearing co-rotating frames equations of motion and Maxwell's equations modules in our PIC code OSIRIS 3.0, we intend to present our recent results of the analysis of MRI in electron-positron plasma in the limit of weak magnetic field. We will recall the theoretical 1D linear model of Krolik et Zweibel that describes the behavior of MRI in the limit of weak magnetic field and use it to support our results. Moving to 2D simulations, the analysis of MRI via PIC code permits to investigate also how MRI will act in comparison with other Kinetic instabilities, like mirror instability.
Roberts, Michael Scott
The Rayleigh-Taylor instability is a buoyancy driven instability that takes place in a stratified fluid system with a constant acceleration directed from the heavy fluid into the light fluid. In this study, both experimental data and numerical simulations are presented. Experiments are performed primarily using a lithium-tungstate aqueous solution as the heavy liquid, but sometimes a calcium nitrate aqueous solution is used for comparison purposes. Experimental data is obtained for both miscible and immiscible fluid combinations. For the miscible experiments the light liquid is either ethanol or isopropanol, and for the immiscible experiments either silicone oil or trans-anethole is used. The resulting Atwood number is either 0.5 when the lithium-tungstate solution is used or 0.2 when the calcium nitrate solution is used. These fluid combinations are either forced or left unforced. The forced experiments have an initial perturbation imposed by vertically oscillating the liquid containing tank to produce Faraday waves at the interface. The unforced experiments rely on random interfacial fluctuations, due to background noise, to seed the instability. The liquid combination is partially enclosed in a test section that is accelerated downward along a vertical rail system causing the Rayleigh-Taylor instability. Accelerations of approximately 1g (with a weight and pulley system) or 10g (with a linear induction motor system) are experienced by the liquids. The tank is backlit and digitally recorded with high speed video cameras. These experiments are then simulated with the incompressible, Navier-Stokes code Miranda. The main focus of this study is the growth parameter (α) of the mixing region produced by the instability after it has become apparently self-similar and turbulent. The measured growth parameters are compared to determine the effects of miscibility and initial perturbations (of the small wavelength, finite bandwidth type used here). It is found that while
The ballistic transport instability in Saturn's rings III: numerical simulations
Latter, Henrik; Chupeau, Marie
2014-01-01
Saturn's inner B-ring and its C-ring support wavetrains of contrasting amplitudes but with similar length scales, 100-1000 km. In addition, the inner B-ring is punctuated by two intriguing `flat' regions between radii 93,000 km and 98,000 km in which the waves die out, whereas the C-ring waves coexist with a forest of plateaus, narrow ringlets, and gaps. In both regions the waves are probably generated by a large-scale linear instability whose origin lies in the meteoritic bombardment of the rings: the ballistic transport instability. In this paper, the third in a series, we numerically simulate the long-term nonlinear evolution of this instability in a convenient local model. Our C-ring simulations confirm that the unstable system forms low-amplitude wavetrains possessing a preferred band of wavelengths. B-ring simulations, on the other hand, exhibit localised nonlinear wave `packets' separated by linearly stable flat zones. Wave packets travel slowly while spreading in time, a result that suggests the obser...
Simulation of multibunch motion with the Headtail code and application to the CERN SPS and LHC
Mounet, N; Rumolo, G
2011-01-01
Multibunch instabilities due to beam-coupling impedance can be a critical limitation for synchrotrons operating with many bunches. It is particularly true for the LHC under nominal conditions, where according to theoretical predictions the 2808 bunches rely entirely on the performance of the transverse feedback system to remain stable. To study these instabilities, the HEADTAIL code has been extended to simulate the motion of many bunches under the action of wake fields. All the features already present in the single-bunch version of the code, such as synchrotron motion, chromaticity, amplitude detuning due to octupoles and the ability to load any kind of wake fields through tables, have remained available. This new code has been then parallelized in order to track thousands of bunches in a reasonable amount of time. The code was benchmarked against theory and exhibited a good agreement. We also show results for bunch trains in the LHC and compare them with beam-based measurements.
On the Numerical Dispersion of the Electromagnetic Particle-In-Cell Code: Finite Grid Instability
Meyers, M. D.; Huang, C.-K.; Zeng, Y.; Yi, S.; Albright, B. J.
2014-10-01
The widely used Particle-In-Cell (PIC) method in relativistic particle beam and laser plasma modeling is subject to numerical instabilities that can render unphysical simulation results or even destroy the simulation. For electromagnetic relativistic beam and plasma modeling, the most relevant numerical instabilities are the finite grid instability and the numerical Cherenkov instability. We rigorously derive the faithful 3D PIC numerical dispersion relation, and specialize to the Yee FDTD scheme. The manner in which the PIC algorithm updates and samples the fields and distribution function, along with any temporal and spatial phase factors, is accounted for. Numerical solutions to the 1D dispersion relation are obtained for parameters of interest. We investigate how the finite grid instability arises from the interaction of the numerical modes admitted in the system and their aliases. The most significant interaction is due critically to the correct placement of the operators in the dispersion relation. We obtain a simple analytic expression for the peak growth rates due to these interactions.
Simulations and model of the nonlinear Richtmyer-Meshkov instability (U)
Energy Technology Data Exchange (ETDEWEB)
Dimonte, Guy [Los Alamos National Laboratory
2009-01-01
The nonlinear evolution of the Richtmyer-Meshkov (RM) instability is investigated using numerical simulations with the FLASH code in two-dimensions (20). The purpose of the simulations is to develop a nonlinear model of the RM instability that is accurate to the regime of inertial confinement fusion (ICF) and ejecta formation, namely, at large Atwood number A and initial amplitude kh{sub o} (k {triple_bond} wavenumber) of the perturbation. The FLASH code is first validated by obtaining excellent agreement with RM experiments well into the nonlinear regime. The results are then compared with a variety of nonlinear models that are based on potential flow. We find that the models agree with simulations for moderate values of A and kh{sub o} but not for the values characteristic of ICF and ejecta formation. As a result, a new nonlinear model is developed that captures the simulation results consistent with potential flow and for a broader range of A and kh{sub o}.
Alya: Towards Exascale for Engineering Simulation Codes
Vazquez, Mariano; Koric, Seid; Artigues, Antoni; Aguado-Sierra, Jazmin; Aris, Ruth; Mira, Daniel; Calmet, Hadrien; Cucchietti, Fernando; Owen, Herbert; Taha, Ahmed; Cela, Jose Maria
2014-01-01
Alya is the BSC in-house HPC-based multi-physics simulation code. It is designed from scratch to run efficiently in parallel supercomputers, solving coupled problems. The target domain is engineering, with all its particular features: complex geome- tries and unstructured meshes, coupled multi-physics with exotic coupling schemes and Physical models, ill-posed problems, flexibility needs for rapidly including new models, etc. Since its conception in 2004, Alya has shown scaling behaviour in an increasing number of cores. In this paper, we present its performance up to 100.000 cores in Blue Waters, the NCSA supercomputer. The selected tests are representative of the engineering world, all the problematic features included: incompressible flow in a hu- man respiratory system, low Mach combustion problem in a kiln furnace and coupled electro-mechanical problem in a heart. We show scalability plots for all cases, discussing all the aspects of such kind of simulations, including solvers convergence.
The Parker Instability in a Thick Gaseous Disk II Numerical Simulations in 2D
Santillan, A; Franco, J; Martos, M A; Hong, S S; Ryu, D; Santillan, Alfredo; Kim, Jongsoo; Franco, Jose; Martos, Marco; Ryu, Dongsu
2000-01-01
We present 2D, ideal-MHD numerical simulations of the Parker instability in a multi-component warm disk model. The calculations were done using two numerical codes with different algorithms, TVD and ZEUS-3D. The outcome of the numerical experiments performed with both codes is very similar, and confirms the results of the linear analysis for the undular mode derived by Kim et al. (2000): the most unstable wavelength is about 3 kpc and its growth timescale is between 30-50 Myr (the growth rate is sensitive to the position of the upper boundary of the numerical grid). Thus, the time and length scales of this multicomponent disk model are substantially larger than those derived for thin disk models. We use three different types of perturbations, random, symmetric, and antisymmetric, to trigger the instability. The antisymmetric mode is dominant, and determines the minimum time for the onset of the nonlinear regime. The instability generates dense condensations and the final peak column density value in the antis...
Direct numerical simulations of type Ia supernovae flames I: The landau-darrieus instability
Energy Technology Data Exchange (ETDEWEB)
Bell, J.B.; Day, M.S.; Rendleman, C.A.; Woosley, S.E.; Zingale, M.
2003-11-24
Planar flames are intrinsically unstable in open domains due to the thermal expansion across the burning front--the Landau-Darrieus instability. This instability leads to wrinkling and growth of the flame surface, and corresponding acceleration of the flame, until it is stabilized by cusp formation. We look at the Landau-Darrieus in stability for C/O thermonuclear flames at conditions relevant to the late stages of a Type Ia supernova explosion. Two-dimensional direct numerical simulations of both single-mode and multi-mode perturbations using a low Mach number hydrodynamics code are presented. We show the effect of the instability on the flame speed as a function of both the density and domain size, demonstrate the existence of the small scale cutoff to the growth of the instability, and look for the proposed breakdown of the non-linear stabilization at low densities. The effects of curvature on the flame as quantified through measurements of the growth rate and computation of the corresponding Markstein number. While accelerations of a few percent are observed, they are too small to have any direct outcome on the supernova explosion.
Three-dimensional simulations of ablative hydrodynamic instabilities in indirectly driven targets
Energy Technology Data Exchange (ETDEWEB)
Marinak, M.M.; Tipton, R.E.; Remington, B.A. [and others
1996-06-01
To model ignition in a National Ignition Facility (NIF) capsule implosion, the authors must understand the behavior of instabilities that can cause breakup of the pellet shell. During a capsule implosion, shocks that transit the shell cause growth of perturbations at the surface or at an interface because of a Richtmyer-Meshkov type of instability. Following shock breakout, or earlier for a shaped pulse, the low-density ablated plasma accelerates the pusher, and the ablation front is Rayleigh-Taylor (RT) unstable. Ablation and finite density gradients have the effect of stabilizing the short wavelength modes. Unstable modes present on the outer surface grow and feed through to the inner surface. Once the shell encounters the rebounding shock from the capsule center, it decelerates and the inner surface becomes RT unstable. If perturbations grow large enough, pusher material mixes into the core, degrading implosion performance. Capsule designs for the NIF depend on ablative stabilization and saturation to prevent perturbations initially present on the capsule surface from growing large enough to quench ignition. Here, the authors examine the first simulations and experiments to study the effect of 3-D perturbation shape on instability growth and saturation in indirectly driven targets. The first section discusses HYDRA, the radiation hydrodynamics code developed for these simulations. The subsequent section examines 3-D shape effects in single-mode perturbations in planar foil simulations and experiments. A discussion of the evolution of multimode perturbations on planar foils is followed by a discussion of 3-D simulations of instability growth in Nova capsule implosions.
On the numerical dispersion of electromagnetic particle-in-cell code: Finite grid instability
Meyers, M. D.; Huang, C.-K.; Zeng, Y.; Yi, S. A.; Albright, B. J.
2015-09-01
The Particle-In-Cell (PIC) method is widely used in relativistic particle beam and laser plasma modeling. However, the PIC method exhibits numerical instabilities that can render unphysical simulation results or even destroy the simulation. For electromagnetic relativistic beam and plasma modeling, the most relevant numerical instabilities are the finite grid instability and the numerical Cherenkov instability. We review the numerical dispersion relation of the Electromagnetic PIC model. We rigorously derive the faithful 3-D numerical dispersion relation of the PIC model, for a simple, direct current deposition scheme, which does not conserve electric charge exactly. We then specialize to the Yee FDTD scheme. In particular, we clarify the presence of alias modes in an eigenmode analysis of the PIC model, which combines both discrete and continuous variables. The manner in which the PIC model updates and samples the fields and distribution function, together with the temporal and spatial phase factors from solving Maxwell's equations on the Yee grid with the leapfrog scheme, is explicitly accounted for. Numerical solutions to the electrostatic-like modes in the 1-D dispersion relation for a cold drifting plasma are obtained for parameters of interest. In the succeeding analysis, we investigate how the finite grid instability arises from the interaction of the numerical modes admitted in the system and their aliases. The most significant interaction is due critically to the correct representation of the operators in the dispersion relation. We obtain a simple analytic expression for the peak growth rate due to this interaction, which is then verified by simulation. We demonstrate that our analysis is readily extendable to charge conserving models.
Spiking network simulation code for petascale computers
Kunkel, Susanne; Schmidt, Maximilian; Eppler, Jochen M.; Plesser, Hans E.; Masumoto, Gen; Igarashi, Jun; Ishii, Shin; Fukai, Tomoki; Morrison, Abigail; Diesmann, Markus; Helias, Moritz
2014-01-01
Brain-scale networks exhibit a breathtaking heterogeneity in the dynamical properties and parameters of their constituents. At cellular resolution, the entities of theory are neurons and synapses and over the past decade researchers have learned to manage the heterogeneity of neurons and synapses with efficient data structures. Already early parallel simulation codes stored synapses in a distributed fashion such that a synapse solely consumes memory on the compute node harboring the target neuron. As petaflop computers with some 100,000 nodes become increasingly available for neuroscience, new challenges arise for neuronal network simulation software: Each neuron contacts on the order of 10,000 other neurons and thus has targets only on a fraction of all compute nodes; furthermore, for any given source neuron, at most a single synapse is typically created on any compute node. From the viewpoint of an individual compute node, the heterogeneity in the synaptic target lists thus collapses along two dimensions: the dimension of the types of synapses and the dimension of the number of synapses of a given type. Here we present a data structure taking advantage of this double collapse using metaprogramming techniques. After introducing the relevant scaling scenario for brain-scale simulations, we quantitatively discuss the performance on two supercomputers. We show that the novel architecture scales to the largest petascale supercomputers available today. PMID:25346682
Spiking network simulation code for petascale computers
Directory of Open Access Journals (Sweden)
Susanne eKunkel
2014-10-01
Full Text Available Brain-scale networks exhibit a breathtaking heterogeneity in the dynamical properties and parameters of their constituents. At cellular resolution, the entities of theory are neurons and synapses and over the past decade researchers have learned to manage the heterogeneity of neurons and synapses with efficient data structures. Already early parallel simulation codes stored synapses in a distributed fashion such that a synapse solely consumes memory on the compute node harboring the target neuron. As petaflop computers with some 100,000 nodes become increasingly available for neuroscience, new challenges arise for neuronal network simulation software: Each neuron contacts on the order of 10,000 other neurons and thus has targets only on a fraction of all compute nodes; furthermore, for any given source neuron, at most a single synapse is typically created on any compute node. From the viewpoint of an individual compute node, the heterogeneity in the synaptic target lists thus collapses along two dimensions: the dimension of the types of synapses and the dimension of the number of synapses of a given type. Here we present a data structure taking advantage of this double collapse using metaprogramming techniques. After introducing the relevant scaling scenario for brain-scale simulations, we quantitatively discuss the performance on two supercomputers. We show that the novel architecture scales to the largest petascale supercomputers available today.
The cosmological simulation code GADGET-2
Springel, V
2005-01-01
We discuss the cosmological simulation code GADGET-2, a new massively parallel TreeSPH code, capable of following a collisionless fluid with the N-body method, and an ideal gas by means of smoothed particle hydrodynamics (SPH). Our implementation of SPH manifestly conserves energy and entropy in regions free of dissipation, while allowing for fully adaptive smoothing lengths. Gravitational forces are computed with a hierarchical multipole expansion, which can optionally be applied in the form of a TreePM algorithm, where only short-range forces are computed with the `tree'-method while long-range forces are determined with Fourier techniques. Time integration is based on a quasi-symplectic scheme where long-range and short-range forces can be integrated with different timesteps. Individual and adaptive short-range timesteps may also be employed. The domain decomposition used in the parallelisation algorithm is based on a space-filling curve, resulting in high flexibility and tree force errors that do not depe...
Rosenberg, D.; Pouquet, A.; Germaschewski, K.; Ng, C. S.; Bhattacharjee, A.
2006-10-01
A recently developed spectral-element adaptive refinement incompressible magnetohydrodynamic (MHD) code is applied to simulate the problem of island coalescence instability (ICI) in 2D. The MHD solver is explicit, and uses the Elsasser formulation on high-order elements. It automatically takes advantage of the adaptive grid mechanics that have been described in [Rosenberg, Fournier, Fischer, Pouquet, J. Comp. Phys., 215, 59-80 (2006)], allowing both statically refined and dynamically refined grids. ICI is a MHD process that can produce strong current sheets and subsequent reconnection and heating in a high-Lundquist number plasma such as the solar corona [cf., Ng and Bhattacharjee, Phys. Plasmas, 5, 4028 (1998)]. Thus, it is desirable to use adaptive refinement grids to increase resolution, and to maintain accuracy at the same time. Results are compared with simulations using finite difference method with the same refinement grid, as well as pesudo-spectral simulations using uniform grid.
Simulation of the interchange instability in a magnetospheric substorm site
Directory of Open Access Journals (Sweden)
O. V. Mingalev
2006-07-01
Full Text Available We perform modeling of the interchange instability driven by longitudinal pressure asymmetry in the region of the pressure buildup that forms in the inner magnetosphere at the substorm growth phase. The simulation refers to the dawnward side of the Harang discontinuity and times after B_{z} IMF turning northward. The solution for the equilibrium state indicates tailward flows associated with vortices, which is in agreement with a previous finding of Ashour-Abdalla et al. (1999, 2002. We show that in the regions of equilibrium field-aligned currents (FACs, small initial perturbations in pV^{γ} (p is the isotropic plasma pressure, V is the unit magnetic flux tube volume, γ=5/3 the adiabatic exponent, set up as ripples inclined to azimuth, grow in time. For the background FAC of ~10^{-6} A/m^{2}, the linear growth rate of the instability is ~6 min. Starting from the 12th min of evolution, the perturbations exhibit nonlinear deformations, develop undulations and front steepening. An interesting peculiarity in the distribution of the associated small-scale FACs is that they become asymmetric with time. Specifically, the downward currents are more localised, reaching densities up to 15×10^{-6} A/m^{2} at the nonlinear stage. The upward FACs are more dispersed. When large enough, these currents are likely to produce the aurora. We also run our simulation for the initial perturbations of large transverse scales in order to demonstrate that the interchange instability can be responsible for pressure and cross-tail current spatial variations of great extent.
Directory of Open Access Journals (Sweden)
Hong Qin
2003-01-01
Full Text Available Two-stream instabilities in intense charged particle beams, described self-consistently by the nonlinear Vlasov-Maxwell equations, are studied using a 3D multispecies perturbative particle simulation method. The recently developed Beam Equilibrium, Stability and Transport code is used to simulate the linear and nonlinear properties of the electron-proton (e-p two-stream instability observed in the Proton Storage Ring (PSR experiment for a long, coasting beam. Simulations in a parameter regime characteristic of the PSR experiment show that the e-p instability has a dipole-mode structure, and that the growth rate is an increasing function of beam intensity, but a decreasing function of the longitudinal momentum spread. It is also shown that the instability threshold decreases with increasing fractional charge neutralization and increases with increasing axial momentum spread of the beam particles. In the nonlinear phase, the simulations show that the proton density perturbation first saturates at a relatively low level and subsequently grows to a higher level. Finally, the nonlinear space-charge-induced transverse tune spread, which introduces a major growth-rate reduction effect on the e-p instability, is studied for self-consistent equilibrium populations of protons and electrons.
Large eddy simulation requirements for the Richtmyer-Meshkov Instability
Olson, Britton J
2014-01-01
The shock induced mixing of two gases separated by a perturbed interface is investigated through Large Eddy Simulation (LES) and Direct Numerical Simulation (DNS). In a simulation, physical dissipation of the velocity field and species mass fraction often compete with numerical dissipation arising from the errors of the numerical method. In a DNS the computational mesh resolves all physical gradients of the flow and the relative effect of numerical dissipation is small. In LES, unresolved scales are present and numerical dissipation can have a large impact on the flow, depending on the computational mesh. A suite of simulations explores the space between these two extremes by studying the effects of grid resolution, Reynolds number and numerical method on the mixing process. Results from a DNS are shown using two different codes, which use a high- and low-order numerical method and show convergence in the temporal and spectral dependent quantities associated with mixing. Data from a coarse LES are also presen...
3D Convection-pulsation Simulations with the HERACLES Code
Felix, S.; Audit, E.; Dintrans, B.
2015-10-01
We present 3D simulations of the coupling between surface convection and pulsations due to the κ-mechanism in classical Cepheids of the red edge of Hertzsprung-Russell diagram's instability strip. We show that 3D convection is less powerful than 2D convection and does not quench the radiative pulsations, leading to an efficient 3D κ-mechanism. Thus, the 3D instability strip is closer to the observed one than the 1D or 2D were.
DSMC Simulations of the Rayleigh-Taylor Instability in Gases
Gallis, Michael; Koehler, Timothy; Torczynski, John; Plimpton, Steven
2015-11-01
The Direct Simulation Monte Carlo (DSMC) method of molecular gas dynamics is applied to simulate the Rayleigh-Taylor instability (RTI) in atmospheric-pressure monatomic gases (e.g., argon and helium). The computational domain is a 1 mm × 4 mm rectangle divided into 50-nm square cells. Each cell is populated with 1000 computational molecules, and time steps of 0.1 ns are used. Simulations are performed to quantify the growth of a single-mode perturbation on the interface as a function of the Atwood number and the gravitational acceleration. The DSMC results qualitatively reproduce all observed features of the RTI and are in reasonable quantitative agreement with existing theoretical and empirical models. Consistent with previous work in this field, the DSMC simulations indicate that the growth of the RTI follows a universal behavior. For cases with multiple-mode perturbations, the numbers of bubble-spike pairs that eventually appear are found to be in agreement with theoretical results for the most unstable wavelength. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
Energy Technology Data Exchange (ETDEWEB)
Boeuf, J.P.; Pitchford, L.C. [Universite Paul Sabatier, Toulouse (France); Morgan, W.L. [Kinema Research, Monument Colorado, CO (United States)
1995-12-31
The purpose of this communication is to present a 1-D fluid model of DC and RF discharges in 1-D and to show examples of results from this model in electronegative gases under conditions where the attachment-detachment-ionization instability appears in the body of the plasma. The codes corresponding to these models are referred to as belonging to the SIGLO (Simulation of GLOw discharges) series. The physical and numerical models have been formulated for especially rapid computation on a PC. The rapid computational times make this model suitable for parametric studies and the incorporation of on-line graphics (such as movies showing the evolution of the charged particle densities and electric field distributions) directly into the computer model. The results we present here are in CF4 for DC and RF (13.56 Mhz) applied voltages, for a pressure of 1 torr and a gap length of 4 cm. The conditions are close to those of Gogolides et al., and we illustrate here the possibility of attachment induced instabilities when detachment is significant. Detachment of the fluorine negative ion F- by CFP{sub x} radicals could be efficient in CF{sub 4} plasmas. In this paper we consider the detachment frequency due to CF{sub x} radicals as a parameters and study the structure and evolution of the discharge in the presence of attachment-detachment instabilities. The results show that for some values of the detachment frequency, the charged particle densities and field amplitude in the plasma of a RF discharge in CF{sub 4} do not reach constant (time independent) values but oscillates, at a frequency much lower than the applied voltage (typically on the order of 10 kHz in our conditions). The plasma column contains adjacent low field and strong field {open_quotes}domains{close_quotes} where the relative concentrations of electrons and negative ions are different.
Direct numerical simulations of type Ia supernovae flames II: The Rayleigh-Taylor instability
Energy Technology Data Exchange (ETDEWEB)
Bell, J.B.; Day, M.S.; Rendleman, C.A.; Woosley, S.E.; Zingale, M.
2004-01-12
A Type Ia supernova explosion likely begins as a nuclear runaway near the center of a carbon-oxygen white dwarf. The outward propagating flame is unstable to the Landau-Darrieus, Rayleigh-Taylor, and Kelvin-Helmholtz instabilities, which serve to accelerate it to a large fraction of the speed of sound. We investigate the Rayleigh-Taylor unstable flame at the transition from the flamelet regime to the distributed-burning regime, around densities of 10e7 gm/cc, through detailed, fully resolved simulations. A low Mach number, adaptive mesh hydrodynamics code is used to achieve the necessary resolution and long time scales. As the density is varied, we see a fundamental change in the character of the burning--at the low end of the density range the Rayleigh-Taylor instability dominates the burning, whereas at the high end the burning suppresses the instability. In all cases, significant acceleration of the flame is observed, limited only by the size of the domain we are able to study. We discuss the implications of these results on the potential for a deflagration to detonation transition.
Communication Systems Simulator with Error Correcting Codes Using MATLAB
Gomez, C.; Gonzalez, J. E.; Pardo, J. M.
2003-01-01
In this work, the characteristics of a simulator for channel coding techniques used in communication systems, are described. This software has been designed for engineering students in order to facilitate the understanding of how the error correcting codes work. To help students understand easily the concepts related to these kinds of codes, a…
Aspect ratio dependence in magnetorotational instability shearing box simulations
Bodo, G; Cattaneo, F; Rossi, P; Ferrari, A
2008-01-01
Aims: We study the changes in the properties of turbulence driven by the magnetorotational instability in a shearing box, as the computational domain size in the radial direction is varied relative to the height Methods: We perform 3D simulations in the shearing box approximation, with a net magnetic flux, and we consider computational domains with different aspect ratios Results: We find that in boxes of aspect ratio unity the transport of angular momentum is strongly intermittent and dominated by channel solutions in agreement with previous work. In contrast, in boxes with larger aspect ratio, the channel solutions and the associated intermittent behavior disappear. Conclusions: There is strong evidence that, as the aspect ratio becomes larger, the characteristics of the solution become aspect ratio independent. We conclude that shearing box calculations with aspect ratio unity or near unity may introduce spurious effects.
The stellar atmosphere simulation code Bifrost. Code description and validation
Gudiksen, B.V.; Carlsson, M.; Hansteen, V.H.; Hayek, W.; Leenaarts, J.|info:eu-repo/dai/nl/304837946; Martínez-Sykora, J.
2011-01-01
Context. Numerical simulations of stellar convection and photospheres have been developed to the point where detailed shapes of observed spectral lines can be explained. Stellar atmospheres are very complex, and very different physical regimes are present in the convection zone, photosphere,
Simulation of 2D Kinetic Effects in Plasmas using the Grid Based Continuum Code LOKI
Banks, Jeffrey; Berger, Richard; Chapman, Tom; Brunner, Stephan
2016-10-01
Kinetic simulation of multi-dimensional plasma waves through direct discretization of the Vlasov equation is a useful tool to study many physical interactions and is particularly attractive for situations where minimal fluctuation levels are desired, for instance, when measuring growth rates of plasma wave instabilities. However, direct discretization of phase space can be computationally expensive, and as a result there are few examples of published results using Vlasov codes in more than a single configuration space dimension. In an effort to fill this gap we have developed the Eulerian-based kinetic code LOKI that evolves the Vlasov-Poisson system in 2+2-dimensional phase space. The code is designed to reduce the cost of phase-space computation by using fully 4th order accurate conservative finite differencing, while retaining excellent parallel scalability that efficiently uses large scale computing resources. In this poster I will discuss the algorithms used in the code as well as some aspects of their parallel implementation using MPI. I will also overview simulation results of basic plasma wave instabilities relevant to laser plasma interaction, which have been obtained using the code.
Krause, M.; Camenzind, M.
2001-12-01
In the present paper, we examine the convergence behavior and inter-code reliability of astrophysical jet simulations in axial symmetry. We consider both pure hydrodynamic jets and jets with a dynamically significant magnetic field. The setups were chosen to match the setups of two other publications, and recomputed with the MHD code NIRVANA. We show that NIRVANA and the two other codes give comparable, but not identical results. We explain the differences by the different application of artificial viscosity in the three codes and numerical details, which can be summarized in a resolution effect, in the case without magnetic field: NIRVANA turns out to be a fair code of medium efficiency. It needs approximately twice the resolution as the code by Lind (Lind et al. 1989) and half the resolution as the code by Kössl (Kössl & Müller 1988). We find that some global properties of a hydrodynamical jet simulation, like e.g. the bow shock velocity, converge at 100 points per beam radius (ppb) with NIRVANA. The situation is quite different after switching on the toroidal magnetic field: in this case, global properties converge even at 10 ppb. In both cases, details of the inner jet structure and especially the terminal shock region are still insufficiently resolved, even at our highest resolution of 70 ppb in the magnetized case and 400 ppb for the pure hydrodynamic jet. The magnetized jet even suffers from a fatal retreat of the Mach disk towards the inflow boundary, which indicates that this simulation does not converge, in the end. This is also in definite disagreement with earlier simulations, and challenges further studies of the problem with other codes. In the case of our highest resolution simulation, we can report two new features: first, small scale Kelvin-Helmholtz instabilities are excited at the contact discontinuity next to the jet head. This slows down the development of the long wavelength Kelvin-Helmholtz instability and its turbulent cascade to smaller
Directory of Open Access Journals (Sweden)
E. Benedetto
2005-12-01
Full Text Available The electron cloud may cause transverse single-bunch instabilities of proton beams such as those in the Large Hadron Collider (LHC and the CERN Super Proton Synchrotron (SPS. We simulate these instabilities and the consequent emittance growth with the code HEADTAIL, which models the turn-by-turn interaction between the cloud and the beam. Recently some new features were added to the code, in particular, electric conducting boundary conditions at the chamber wall, transverse feedback, and variable beta functions. The sensitivity to several numerical parameters has been studied by varying the number of interaction points between the bunch and the cloud, the phase advance between them, and the number of macroparticles used to represent the protons and the electrons. We present simulation results for both LHC at injection and SPS with LHC-type beam, for different electron-cloud density levels, chromaticities, and bunch intensities. Two regimes with qualitatively different emittance growth are observed: above the threshold of the transverse mode-coupling (TMC type of instability there is a rapid blowup of the beam, while below this threshold a slow, long-term, emittance growth remains. The rise time of the TMC instability caused by the electron cloud is compared with results obtained using an equivalent broadband resonator impedance model, demonstrating reasonable agreement.
Software quality and process improvement in scientific simulation codes
Energy Technology Data Exchange (ETDEWEB)
Ambrosiano, J.; Webster, R. [Los Alamos National Lab., NM (United States)
1997-11-01
This report contains viewgraphs on the quest to develope better simulation code quality through process modeling and improvement. This study is based on the experience of the authors and interviews with ten subjects chosen from simulation code development teams at LANL. This study is descriptive rather than scientific.
A New Three-Dimensional Code for Simulation of Ion Beam Extraction: Ion Optics Simulator
Institute of Scientific and Technical Information of China (English)
JIN Dazhi; HUANG Tao; HU Quan; YANG Zhonghai
2008-01-01
A new thee-dimensional code, ion optics simulator (IOS), to simulate ion beam extraction is developed in visual C++ language. The theoretical model, the flowchart of code, and the results of calculation as an example are presented.
Fraschetti, Federico; Ballet, Jean; Decourchelle, Anne
2010-01-01
Context: The Rayleigh-Taylor instabilities generated by the deceleration of a supernova remnant during the ejecta-dominated phase are known to produce finger-like structures in the matter distribution which modify the geometry of the remnant. The morphology of supernova remnants is also expected to be modified when efficient particle acceleration occurs at their shocks. Aims: The impact of the Rayleigh-Taylor instabilities from the ejecta-dominated to the Sedov-Taylor phase is investigated over one octant of the supernova remnant. We also study the effect of efficient particle acceleration at the forward shock on the growth of the Rayleigh-Taylor instabilities. Methods: We modified the Adaptive Mesh Refinement code RAMSES to study with hydrodynamic numerical simulations the evolution of supernova remnants in the framework of an expanding reference frame. The adiabatic index of a relativistic gas between the forward shock and the contact discontinuity mimics the presence of accelerated particles. Results: The ...
Angulo, A. A.; Kuranz, C. C.; Drake, R. P.; Huntington, C. M.; Park, H.-S.; Remington, B. A.; Kalantar, D.; MacLaren, S.; Raman, K.; Miles, A.; Trantham, Matthew; Kline, J. L.; Flippo, K.; Doss, F. W.; Shvarts, D.
2016-10-01
This poster will describe simulations based on results from ongoing laboratory astrophysics experiments at the National Ignition Facility (NIF) relevant to the effects of radiative shock on hydrodynamically unstable surfaces. The experiments performed on NIF uniquely provide the necessary conditions required to emulate radiative shock that occurs in astrophysical systems. The core-collapse explosions of red supergiant stars is such an example wherein the interaction between the supernova ejecta and the circumstellar medium creates a region susceptible to Rayleigh-Taylor (R-T) instabilities. Radiative and nonradiative experiments were performed to show that R-T growth should be reduced by the effects of the radiative shocks that occur during this core-collapse. Simulations were performed using the radiation hydrodynamics code Hyades using the experimental conditions to find the mean interface acceleration of the instability and then further analyzed in the buoyancy drag model to observe how the material expansion contributes to the mix-layer growth. This work is funded by the NNSA-DS and SC-OFES Joint Program in High-Energy-Density Laboratory Plasmas under Grant Number DE-FG52-09NA29548.
Characteristics of gravity waves generated in a baroclinic instability simulation
Directory of Open Access Journals (Sweden)
Y.-H. Kim
2015-11-01
Full Text Available An idealized baroclinic instability case is simulated using a ~ 10 km resolution global model to investigate the characteristics of gravity waves (GWs generated in the baroclinic life cycle. Three groups of GWs (W1–W3 appear around the high-latitude surface trough at the mature stage of the baroclinic wave. They have horizontal and vertical wavelengths of 40–400 and 2.9–9.8 km, respectively, in the upper troposphere. The two-dimensional phase-velocity spectrum of the waves is arc-shaped with a peak at 17 m s−1 eastward, which is difficult for the waves to propagate upward through the tropospheric westerly jet. At the breaking stage of the baroclinic wave, a midlatitude surface low is isolated from the higher-latitude trough, and two groups of quasi-stationary GWs (W4 and W5 appear near the surface low. These waves have horizontal and vertical wavelengths of 60–400 and 4.9–14 km, respectively, and are able to propagate vertically for long distances. The generation mechanism of the simulated GWs is discussed.
The Particle Accelerator Simulation Code PyORBIT
Energy Technology Data Exchange (ETDEWEB)
Gorlov, Timofey V [ORNL; Holmes, Jeffrey A [ORNL; Cousineau, Sarah M [ORNL; Shishlo, Andrei P [ORNL
2015-01-01
The particle accelerator simulation code PyORBIT is presented. The structure, implementation, history, parallel and simulation capabilities, and future development of the code are discussed. The PyORBIT code is a new implementation and extension of algorithms of the original ORBIT code that was developed for the Spallation Neutron Source accelerator at the Oak Ridge National Laboratory. The PyORBIT code has a two level structure. The upper level uses the Python programming language to control the flow of intensive calculations performed by the lower level code implemented in the C++ language. The parallel capabilities are based on MPI communications. The PyORBIT is an open source code accessible to the public through the Google Open Source Projects Hosting service.
Code generation: a strategy for neural network simulators.
Goodman, Dan F M
2010-10-01
We demonstrate a technique for the design of neural network simulation software, runtime code generation. This technique can be used to give the user complete flexibility in specifying the mathematical model for their simulation in a high level way, along with the speed of code written in a low level language such as C+ +. It can also be used to write code only once but target different hardware platforms, including inexpensive high performance graphics processing units (GPUs). Code generation can be naturally combined with computer algebra systems to provide further simplification and optimisation of the generated code. The technique is quite general and could be applied to any simulation package. We demonstrate it with the 'Brian' simulator ( http://www.briansimulator.org ).
Characterization and Simulation of Thermoacoustic Instability in a Low Emissions Combustor Prototype
DeLaat, John C.; Paxson, Daniel E.
2008-01-01
Extensive research is being done toward the development of ultra-low-emissions combustors for aircraft gas turbine engines. However, these combustors have an increased susceptibility to thermoacoustic instabilities. This type of instability was recently observed in an advanced, low emissions combustor prototype installed in a NASA Glenn Research Center test stand. The instability produces pressure oscillations that grow with increasing fuel/air ratio, preventing full power operation. The instability behavior makes the combustor a potentially useful test bed for research into active control methods for combustion instability suppression. The instability behavior was characterized by operating the combustor at various pressures, temperatures, and fuel and air flows representative of operation within an aircraft gas turbine engine. Trends in instability behavior vs. operating condition have been identified and documented. A simulation developed at NASA Glenn captures the observed instability behavior. The physics-based simulation includes the relevant physical features of the combustor and test rig, employs a Sectored 1-D approach, includes simplified reaction equations, and provides time-accurate results. A computationally efficient method is used for area transitions, which decreases run times and allows the simulation to be used for parametric studies, including control method investigations. Simulation results show that the simulation exhibits a self-starting, self-sustained combustion instability and also replicates the experimentally observed instability trends vs. operating condition. Future plans are to use the simulation to investigate active control strategies to suppress combustion instabilities and then to experimentally demonstrate active instability suppression with the low emissions combustor prototype, enabling full power, stable operation.
DeLaat, John C.; Paxson, Daniel E.
2008-01-01
Extensive research is being done toward the development of ultra-low-emissions combustors for aircraft gas turbine engines. However, these combustors have an increased susceptibility to thermoacoustic instabilities. This type of instability was recently observed in an advanced, low emissions combustor prototype installed in a NASA Glenn Research Center test stand. The instability produces pressure oscillations that grow with increasing fuel/air ratio, preventing full power operation. The instability behavior makes the combustor a potentially useful test bed for research into active control methods for combustion instability suppression. The instability behavior was characterized by operating the combustor at various pressures, temperatures, and fuel and air flows representative of operation within an aircraft gas turbine engine. Trends in instability behavior versus operating condition have been identified and documented, and possible explanations for the trends provided. A simulation developed at NASA Glenn captures the observed instability behavior. The physics-based simulation includes the relevant physical features of the combustor and test rig, employs a Sectored 1-D approach, includes simplified reaction equations, and provides time-accurate results. A computationally efficient method is used for area transitions, which decreases run times and allows the simulation to be used for parametric studies, including control method investigations. Simulation results show that the simulation exhibits a self-starting, self-sustained combustion instability and also replicates the experimentally observed instability trends versus operating condition. Future plans are to use the simulation to investigate active control strategies to suppress combustion instabilities and then to experimentally demonstrate active instability suppression with the low emissions combustor prototype, enabling full power, stable operation.
Large eddy simulation of Rayleigh-Taylor instability using the arbitrary Lagrangian-Eulerian method
Energy Technology Data Exchange (ETDEWEB)
Darlington, R
1999-12-01
This research addresses the application of a large eddy simulation (LES) to Arbitrary Lagrangian Eulerian (ALE) simulations of Rayleigh-Taylor instability. First, ALE simulations of simplified Rayleigh-Taylor instability are studied. The advantages of ALE over Eulerian simulations are shown. Next, the behavior of the LES is examined in a more complicated ALE simulation of Rayleigh-Taylor instability. The effects of eddy viscosity and stochastic backscatter are examined. The LES is also coupled with ALE to increase grid resolution in areas where it is needed. Finally, the methods studied above are applied to two sets of experimental simulations. In these simulations, ALE allows the mesh to follow expanding experimental targets, while LES can be used to mimic the effect of unresolved instability modes.
Numerical instability due to relativistic plasma drift in EM-PIC simulations
Xu, Xinlu; Martins, Samual F; Tsung, Frank S; Decyk, Viktor K; Fonseca, Ricardo A; Lu, Wei; Silva, Luis O; Mori, Warren B
2012-01-01
The numerical instability observed in the Electromagnetic-Particle-in-cell (EM-PIC) simulations with a plasma drifting with relativistic velocities is studied using both theory and computer simulations. We derive the numerical dispersion relation for a cold plasma drifting with a relativistic velocity and find an instability attributed to the coupling between the beam modes of the drifting plasma and the electromagnetic modes in the system. The characteristic pattern of the instability in Fourier space for various simulation setups and Maxwell Equation solvers are explored by solving the corresponding numerical dispersion relations. Furthermore, based upon these characteristic patterns we derive an asymptotic expression for the instability growth rate. The results are compared against simulation results and good agreement is found. The results are used as a guide to develop possible approaches to mitigate the instability. We examine the use of a spectral solver and show that such a solver when combined with a...
Simulation of the Initial 3-D Instability of an Impacting Drop Vortex Ring
DEFF Research Database (Denmark)
Sigurdson, Lorenz; Wiwchar, Justin; Walther, Jens Honore
2013-01-01
Computational vortex particle method simulations of a perturbed vortex ring are performed to recreate and understand the instability seen in impacting water drop experiments. Three fundamentally different initial vorticity distributions are used to attempt to trigger a Widnall instability......, a Rayleigh centrifugal instability, or a vortex breakdown-type instability. Simulations which simply have a perturbed solitary ring result in an instability similar to that seen experimentally. Waviness of the core which would be expected from a Widnall instability is not visible. Adding an opposite......, though tests are not conclusive. Perhaps the opposite-signed secondary vortex was not strong enough or placed appropriately. Elliptical streamlines , as expected, are visible in the core of the solitary ring at early times. Support from the Canadian Natural Sciences and Engineering Research Council grant...
Laboratory experiments and numerical simulations on magnetic instabilities
Stefani, F; Kasprzyk, Ch; Paredes, A; Ruediger, G; Seilmayer, M
2016-01-01
Magnetic fields of planets, stars and galaxies are generated by self-excitation in moving electrically conducting fluids. Once produced, magnetic fields can play an active role in cosmic structure formation by destabilizing rotational flows that would be otherwise hydrodynamically stable. For a long time, both hydromagnetic dynamo action as well as magnetically triggered flow instabilities had been the subject of purely theoretical research. Meanwhile, however, the dynamo effect has been observed in large-scale liquid sodium experiments in Riga, Karlsruhe and Cadarache. In this paper, we summarize the results of some smaller liquid metal experiments devoted to various magnetic instabilities such as the helical and the azimuthal magnetorotational instability, the Tayler instability, and the different instabilities that appear in a magnetized spherical Couette flow. We conclude with an outlook on a large scale Tayler-Couette experiment using liquid sodium, and on the prospects to observe magnetically triggered ...
Energy Technology Data Exchange (ETDEWEB)
Ducros, F.
1996-06-12
Here is a study about fluid flows (the hydrodynamic part of codes modeling the plasma dynamics) showing great gradients and unsteady flows (Rayleigh-Taylor, Richtmyer-Meshkov). The numerical resolution of these problems needs codes able to simulate the transition at the turbulence. The code exposed here (NSMP), tries to answer to these demands by the resolution of Navier-Stokes equations. After the resolution of these equations are presented the consequences of the discretization of continuous equations of fluids mechanics and then a modeling of turbulence is introduced. The two last chapters are devoted to the simulation of Rayleigh-Taylor instabilities. (N.C.). 34 refs., 39 figs., 8 colour plates.
Shibata, M; Shibata, Masaru; Sekiguchi, Yu-ichirou
2005-01-01
We perform fully general relativistic simulations of rotating stellar core collapse in three spatial dimension. A parametric equation of state is adopted following Dimmelmeier et al. The early stage of the collapse is followed by an axisymmetric code. When the stellar core becomes compact enough, we start a 3-dimensional simulation adding a bar-mode nonaxisymmetric density perturbation. In the axisymmetric simulations, it is clarified that the maximum value of $\\beta \\equiv T/W$ achieved during the stellar collapse and depends sensitively on the velocity profile and total mass of the initial core, and equations of state. It is also found that for all the models with high degree of differential rotation, a funnel structure is formed around the rotational axis after the formation of neutron stars. For selected models in which the maximum value of $\\beta$ is larger than $\\sim 0.27$, 3-dimensional simulations are performed. It is found that the bar-mode dynamical instability sets in for the case that the followin...
Nonlinear Simulations of Coalescence Instability Using a Flux Difference Splitting Method
Ma, Jun; Qin, Hong; Yu, Zhi; Li, Dehui
2016-07-01
A flux difference splitting numerical scheme based on the finite volume method is applied to study ideal/resistive magnetohydrodynamics. The ideal/resistive MHD equations are cast as a set of hyperbolic conservation laws, and we develop a numerical capability to solve the weak solutions of these hyperbolic conservation laws by combining a multi-state Harten-Lax-Van Leer approximate Riemann solver with the hyperbolic divergence cleaning technique, high order shock-capturing reconstruction schemes, and a third order total variance diminishing Runge-Kutta time evolving scheme. The developed simulation code is applied to study the long time nonlinear evolution of the coalescence instability. It is verified that small structures in the instability oscillate with time and then merge into medium structures in a coherent manner. The medium structures then evolve and merge into large structures, and this trend continues through all scale-lengths. The physics of this interesting nonlinear dynamics is numerically analyzed. supported by the National Magnetic Confinement Fusion Science Program of China (Nos. 2013GB111002, 2013GB105003, 2013GB111000, 2014GB124005, 2015GB111003), National Natural Science Foundation of China (Nos. 11305171, 11405208), JSPS-NRF-NSFC A3 Foresight Program in the field of Plasma Physics (NSFC-11261140328), the Science Foundation of the Institute of Plasma Physics, Chinese Academy of Sciences (DSJJ-15-JC02) and the CAS Program for the Interdisciplinary Collaboration Team
Attal, Nitesh; Ramaprabhu, Praveen
2013-11-01
The interaction of a shock wave with a chemically reacting front is of importance to the design of supersonic combustors and scramjets where mixing from the Richtmyer-Meshkov Instability (RMI) could be tapped to increase combustion efficiency. We will describe results of shock-driven, reacting RMI of a sinusoidally perturbed, single-mode interface separating Hydrogen (fuel) and Oxygen at 300 K and 1625 K respectively. The non-premixed interface was accelerated by a Mach 1.2 shock traversing from the light (H2) to heavy (O2) fluid (Atwood number = 0.5) in a numerical shock tube of aspect ratio 12. The 2D simulations were performed using the compressible flow code FLASH, with modifications to handle detailed chemistry and temperature-dependent material properties. The initial thickness of the material interface was systematically varied to study the effect of the diffusion thickness on the flame and instability dynamics. Product formation and heat release as a result of chemical reactions were described according to the 9-species, 19-steps detailed reaction mechanism.
Large eddy simulation of combustion instability in a tripropellant air heater
Yuan, Lei; Shen, Chibing
2016-12-01
This research is motivated by the issue associated with high frequency combustion instability. Large eddy simulation was performed to investigate spontaneous combustion instability in an air/LO2/C2H5OH tripropellant air heater. The simulation predicts self-excited transverse oscillations. Overall behavior of combustion instability including pressure time histories, mode shapes, Rayleigh index and unsteady response of the injector were studied in detail. Special emphasis was given to the flame behavior, droplet trajectories, pressure evolutions, and formation of large-scale vortical structures during combustion instability in present air heater. Furthermore, in contrast to previous investigations, a new process is identified in the simulation that may feed energy into the acoustic mode and drive combustion instability.
Simulation of Water Chemistry using and Geochemistry Code, PHREEQE
Energy Technology Data Exchange (ETDEWEB)
Chi, J.H. [Korea Electric Power Research Institute, Taejeon (Korea)
2001-07-01
This report introduces principles and procedures of simulation for water chemistry using a geochemistry code, PHREEQE. As and example of the application of this code, we described the simulation procedure for titration of an aquatic sample with strong acid to investigate the state of Carbonates in aquatic solution. Major contents of this report are as follows; Concepts and principles of PHREEQE, Kinds of chemical reactions which may be properly simulated by PHREEQE, The definition and meaning of each input data, An example of simulation using PHREEQE. (author). 2 figs., 1 tab.
N-S Simulations of Crow-Type Instabilities in Vortex Wake
Zheng, Z. C.; Baek, K.
1999-01-01
Three-dimensional Navier-Stokes simulations of the Crow instability of wake vortices are conducted using large-eddy simulations without background turbulence. Sinusoidal displacement has been specified as the initial perturbation for the vortex system. The results have shown that the minimum Crow instability wavelength is about one vortex spacing shorter than predicted by Crow's linear stability theory. The planar- standing-wave-angle value and the amplitude indifference behavior agree with Crow's analysis. Simulations with periodicity in the axial direction have indicated minor influence of axial flow on the Crow instability.
N-S Simulations of Crow-Type Instabilities in Vortex Wake
Zheng, Z. C.; Baek, K.
1999-01-01
Three-dimensional Navier-Stokes simulations of the Crow instability of wake vortices are conducted using large-eddy simulations without background turbulence. Sinusoidal displacement has been specified as the initial perturbation for the vortex system. The results have shown that the minimum Crow instability wavelength is about one vortex spacing shorter than predicted by Crow's linear stability theory. The planar- standing-wave-angle value and the amplitude indifference behavior agree with Crow's analysis. Simulations with periodicity in the axial direction have indicated minor influence of axial flow on the Crow instability.
Advanced thermohydraulic simulation code for transients in LMFBRs (SSC-L code)
Energy Technology Data Exchange (ETDEWEB)
Agrawal, A.K.
1978-02-01
Physical models for various processes that are encountered in preaccident and transient simulation of thermohydraulic transients in the entire liquid metal fast breeder reactor (LMFBR) plant are described in this report. A computer code, SSC-L, was written as a part of the Super System Code (SSC) development project for the ''loop''-type designs of LMFBRs. This code has the self-starting capability, i.e., preaccident or steady-state calculations are performed internally. These results then serve as the starting point for the transient simulation.
Simulation of Instability at Transition Energy with a New Impedance Model for CERN PS
Wang, Na; Biancacci, Nicolo; Migliorati, Mauro; Persichelli, Serena; Sterbini, Guido
2016-01-01
Instabilities driven by the transverse impedance are proven to be one of the limitations for the high intensity reach of the CERN PS. Since several years, fast single bunch vertical instability at transition energy has been observed with the high intensity bunch serving the neu-tron Time-of-Flight facility (n-ToF). In order to better understand the instability mechanism, a dedicated meas-urement campaign took place. The results were compared with macro-particle simulations with PyHEADTAIL based on the new impedance model developed for the PS. Instability threshold and growth rate for different longitu-dinal emittances and beam intensities were studied.
Centromeric Non-coding Transcription: Opening the Black Box of Chromosomal Instability?
Cáceres-Gutiérrez, Rodrigo; Herrera, Luis A
2017-06-01
In eukaryotes, mitosis is tightly regulated to avoid the generation of numerical chromosome aberrations, or aneuploidies. The aneuploid phenotype is a consequence of chromosomal instability (CIN), i.e., an enhanced rate of chromosome segregation errors, which is frequently found in cancer cells and is associated with tumor aggressiveness and increased tumor cell survival potential. To avoid the generation of aneuploidies, cells rely on the spindle assembly checkpoint (SAC), a widely conserved mechanism that protects the genome against this type of error. This signaling pathway stops mitotic pro-gression before anaphase until all chromosomes are correctly attached to spindle microtubules. Howev-er, impairment of the SAC cannot account for the establishment of CIN because cells bearing this phe-notype have a functional SAC. Hence, in cells with CIN, anaphase is not triggered until all chromo-somes are correctly attached to spindle microtubules and congressed at the metaphase plate. Thus, an in-teresting question arises: What mechanisms actually mediate CIN in cancer cells? Recent research has shown that some pathways involved in chromosome segregation are closely associated to centromere-encoded non-coding RNA (cencRNA) and that these RNAs are deregulated in abnormal conditions, such as cancer. These mechanisms may provide new explanations for chromosome segregation errors. The present review discusses some of these findings and proposes novel mechanisms for the establish-ment of CIN based on regulation by cencRNA.
A methodology for the rigorous verification of plasma simulation codes
Riva, Fabio
2016-10-01
The methodology used to assess the reliability of numerical simulation codes constitutes the Verification and Validation (V&V) procedure. V&V is composed by two separate tasks: the verification, which is a mathematical issue targeted to assess that the physical model is correctly solved, and the validation, which determines the consistency of the code results, and therefore of the physical model, with experimental data. In the present talk we focus our attention on the verification, which in turn is composed by the code verification, targeted to assess that a physical model is correctly implemented in a simulation code, and the solution verification, that quantifies the numerical error affecting a simulation. Bridging the gap between plasma physics and other scientific domains, we introduced for the first time in our domain a rigorous methodology for the code verification, based on the method of manufactured solutions, as well as a solution verification based on the Richardson extrapolation. This methodology was applied to GBS, a three-dimensional fluid code based on a finite difference scheme, used to investigate the plasma turbulence in basic plasma physics experiments and in the tokamak scrape-off layer. Overcoming the difficulty of dealing with a numerical method intrinsically affected by statistical noise, we have now generalized the rigorous verification methodology to simulation codes based on the particle-in-cell algorithm, which are employed to solve Vlasov equation in the investigation of a number of plasma physics phenomena.
A multi-scale code for flexible hybrid simulations
Leukkunen, L; Lopez-Acevedo, O
2012-01-01
Multi-scale computer simulations combine the computationally efficient classical algorithms with more expensive but also more accurate ab-initio quantum mechanical algorithms. This work describes one implementation of multi-scale computations using the Atomistic Simulation Environment (ASE). This implementation can mix classical codes like LAMMPS and the Density Functional Theory-based GPAW. Any combination of codes linked via the ASE interface however can be mixed. We also introduce a framework to easily add classical force fields calculators for ASE using LAMMPS, which also allows harnessing the full performance of classical-only molecular dynamics. Our work makes it possible to combine different simulation codes, quantum mechanical or classical, with great ease and minimal coding effort.
Simulation of the frictional stick-slip instability
Mora, Peter; Place, David
1994-03-01
A lattice solid model capable of simulating rock friction, fracture and the associated seismic wave radiation is developed in order to study the origin of the stick-slip instability that is responsible for earthquakes. The model consists of a lattice of interacting particles. In order to study the effect of surface roughness on the frictional behavior of elastic blocks being rubbed past one another, the simplest possible particle interactions were specified corresponding to radially dependent elastic-brittle bonds. The model material can therefore be considered as round elastic grains with negligible friction between their surfaces. Although breaking of the bonds can occur, fracturing energy is not considered. Stick-slip behavior is observed in a numerical experiment involving 2D blocks with rough surfaces being rubbed past one another at a constant rate. Slip is initiated when two interlocking asperities push past one another exciting a slip pulse. The pulse fronts propagate with speeds ranging from the Rayleigh wave speed up to a value between the shear and compressional wave speeds in agreement with field observations and theoretical analyses of mode-II rupture. Slip rates are comparable to seismic rates in the initial part of one slip pulse whose front propagates at the Rayleigh wave speed. However, the slip rate is an order of magnitude higher in the main part of pulses, possibly because of the simplified model description that neglected intrinsic friction and the high rates at which the blocks were driven, or alternatively, uncertainty in slip rates obtained through the inversion of seismograms. Particle trajectories during slip have motions normal to the fault, indicating that the fault surfaces jump apart during the passage of the slip pulse. Normal motion is expected as the asperities on the two surfaces ride over one another. The form of the particle trajectories is similar to those observed in stick-slip experiments involving foam rubber blocks ( Brune
Coded source imaging simulation with visible light
Wang, Sheng; Zou, Yubin; Zhang, Xueshuang; Lu, Yuanrong; Guo, Zhiyu
2011-09-01
A coded source could increase the neutron flux with high L/ D ratio. It may benefit a neutron imaging system with low yield neutron source. Visible light CSI experiments were carried out to test the physical design and reconstruction algorithm. We used a non-mosaic Modified Uniformly Redundant Array (MURA) mask to project the shadow of black/white samples on a screen. A cooled-CCD camera was used to record the image on the screen. Different mask sizes and amplification factors were tested. The correlation, Wiener filter deconvolution and Richardson-Lucy maximum likelihood iteration algorithm were employed to reconstruct the object imaging from the original projection. The results show that CSI can benefit the low flux neutron imaging with high background noise.
Nonlinear electron-magnetohydrodynamic simulations of three dimensional current shear instability
Energy Technology Data Exchange (ETDEWEB)
Jain, Neeraj [Max Planck Institute for Solar System Research, Max-Planck-Str. 2, 37191 Katlenburg-Lindau (Germany); Das, Amita; Sengupta, Sudip; Kaw, Predhiman [Institute for Plasma Research, Bhat, Gandhinagar 382428 (India)
2012-09-15
This paper deals with detailed nonlinear electron-magnetohydrodynamic simulations of a three dimensional current shear driven instability in slab geometry. The simulations show the development of the instability in the current shear layer in the linear regime leading to the generation of electromagnetic turbulence in the nonlinear regime. The electromagnetic turbulence is first generated in the unstable shear layer and then spreads into the stable regions. The turbulence spectrum shows a new kind of anisotropy in which power transfer towards shorter scales occurs preferentially in the direction perpendicular to the electron flow. Results of the present three dimensional simulations of the current shear instability are compared with those of our earlier two dimensional simulations of sausage instability. It is found that the flattening of the mean velocity profile and thus reduction in the electron current due to generation of electromagnetic turbulence in the three dimensional case is more effective as compared to that in the two dimensional case.
Nonlinear evolution of mirror instability in the Earth's magnetosheath in pic simulations
Ahmadi, Narges
Mirror modes are large amplitude non-propagating structures frequently observed in the magnetosheath and they are generated in space plasma environments with proton temperature anisotropy of larger than one. The proton temperature anisotropy also drives the proton cyclotron instability which has larger linear growth rate than that of the mirror instability. Linear dispersion theory predicts that electron temperature anisotropy can enhance the mirror instability growth rate while leaving the proton cyclotron instability largely unaffected. Contrary to the hypothesis, electron temperature anisotropy leads to excitement of the electron whistler instability. Our results show that the electron whistler instability grows much faster than the mirror instability and quickly consumes the electron free energy, so that there is not enough electron temperature anisotropy left to significantly impact the evolution of the mirror instability. Observational studies have shown that the shape of mirror structures is related to local plasma parameters and distance to the mirror instability threshold. Mirror structures in the form of magnetic holes are observed when plasma is mirror stable or marginally mirror unstable and magnetic peaks are observed when plasma is mirror unstable. Mirror structures are created downstream of the quasi-perpendicular bow shock and they are convected toward the magnetopause. In the middle magnetosheath, where plasma is mirror unstable, mirror structures are dominated by magnetic peaks. Close to the magnetopause, plasma expansion makes the region mirror stable and magnetic peaks evolve to magnetic holes. We investigate the nonlinear evolution of mirror instability using expanding box Particle-in-Cell simulations. We change the plasma conditions by artificially enlarging the simulation box over time to make the plasma mirror stable and investigate the final nonlinear state of the mirror structures. We show that the direct nonlinear evolution of the mirror
Direct Numerical Simulation of Three-Dimensional Richtmyer-Meshkov Instability
Institute of Scientific and Technical Information of China (English)
FU De-Xun; MA Yan-Wen; LI Xin-Liang
2008-01-01
Direct numerical simulation(DNS)is used to study flow characteristics after interaction of a planar shock with a spherical media interface in each side of which the density is different.This interfacial instability is known as the Richtmyer-Meshkov(R-M)instability.The compressible Nayier-Stoke equations are discretized with group velocity control(GVC)modified fourth order accurate compact difference scheme.Three-dimensional numerical simulations are performed for R-M instability installed passing a shock through a spherical interface.Based on numerical results the characteristics of 3D R-M instability are analysed.The evaluation for distortion of the interface.the deformation of the incident shock wave and effects of refraction,reflection and diffraction are Dresented.The effects of the interfacial instability on produced vorticity and mixing is discussed.
Muon simulation codes MUSIC and MUSUN for underground physics
Kudryavtsev, V A
2008-01-01
The paper describes two Monte Carlo codes dedicated to muon simulations: MUSIC (MUon SImulation Code) and MUSUN (MUon Simulations UNderground). MUSIC is a package for muon transport through matter. It is particularly useful for propagating muons through large thickness of rock or water, for instance from the surface down to underground/underwater laboratory. MUSUN is designed to use the results of muon transport through rock/water to generate muons in or around underground laboratory taking into account their energy spectrum and angular distribution.
Muon simulation codes MUSIC and MUSUN for underground physics
Kudryavtsev, V. A.
2009-03-01
The paper describes two Monte Carlo codes dedicated to muon simulations: MUSIC (MUon SImulation Code) and MUSUN (MUon Simulations UNderground). MUSIC is a package for muon transport through matter. It is particularly useful for propagating muons through large thickness of rock or water, for instance from the surface down to underground/underwater laboratory. MUSUN is designed to use the results of muon transport through rock/water to generate muons in or around underground laboratory taking into account their energy spectrum and angular distribution.
HADES, A Code for Simulating a Variety of Radiographic Techniques
Energy Technology Data Exchange (ETDEWEB)
Aufderheide, M B; Henderson, G; von Wittenau, A; Slone, D M; Barty, A; Martz, Jr., H E
2004-10-28
It is often useful to simulate radiographic images in order to optimize imaging trade-offs and to test tomographic techniques. HADES is a code that simulates radiography using ray tracing techniques. Although originally developed to simulate X-Ray transmission radiography, HADES has grown to simulate neutron radiography over a wide range of energy, proton radiography in the 1 MeV to 100 GeV range, and recently phase contrast radiography using X-Rays in the keV energy range. HADES can simulate parallel-ray or cone-beam radiography through a variety of mesh types, as well as through collections of geometric objects. HADES was originally developed for nondestructive evaluation (NDE) applications, but could be a useful tool for simulation of portal imaging, proton therapy imaging, and synchrotron studies of tissue. In this paper we describe HADES' current capabilities and discuss plans for a major revision of the code.
Secondo, R; Venturini, M; Fox, J D; Rivetta, C H; Höfle, W
2011-01-01
Transverse Single-Bunch Instabilities due to Electron Cloud effect are limiting the operation at high current of the SPS at CERN. Recently a high-bandwidth Feedback System has been proposed as a possible solution to stabilize the beam and is currently under study. We analyze the dynamics of the bunch actively damped with a simple model of the Feedback in the macro-particle code WARP, in order to investigate the limitations of the System such as the minimum amount of power required to maintain stability. We discuss the feedback model, report on simulation results and present our plans for further development of the numerical model.
L-PICOLA: Fast dark matter simulation code
Howlett, Cullan; Manera, Marc; Percival, Will J.
2015-07-01
L-PICOLA generates and evolves a set of initial conditions into a dark matter field and can include primordial non-Gaussianity in the simulation and simulate the past lightcone at run-time, with optional replication of the simulation volume. It is a fast, distributed-memory, planar-parallel code. L-PICOLA is extremely useful for both current and next generation large-scale structure surveys.
Modane: A Design Support Tool for Numerical Simulation Codes
Directory of Open Access Journals (Sweden)
Lelandais Benoît
2016-07-01
Full Text Available The continual increasing power of supercomputers allows numerical simulation codes to take into account more complex physical phenomena. Therefore, physicists and mathematicians have to implement complex algorithms using cutting edge technologies and integrate them in large simulators. The CEA-DAM has been studying for several years the contribution of UML/MDE technologies in its simulators development cycle. The Modane application is one of the results of this work.
Advanced thermohydraulic simulation code for pool-type LMFBRs (SSC-P code)
Energy Technology Data Exchange (ETDEWEB)
Madni, I.K.; Cazzoli, E.G.
1980-09-01
Models for components and processes that are needed for simulation of thermohydraulic transient in a pool-type liquid metal fast breeder reactor (LMFBR) plant are described in this report. A computer code, SSC-P, has been developed as a part of the Super System Code (SSC) development project. A user's manual is being prepared as a separate document. 27 refs., 26 figs., 1 tab.
RAMSES-CH: A New Chemodynamical Code for Cosmological Simulations
Few, C. Gareth; Courty, Stephanie; Gibson, Brad K.; Kawata, Daisuke; Calura, Francesco; Teyssier, Romain
2012-01-01
We present a new chemodynamical code - Ramses-CH - for use in simulating the self-consistent evolution of chemical and hydrodynamical properties of galaxies within a fully cosmological framework. We build upon the adaptive mesh refinement code Ramses, which includes a treatment of self-gravity, hydrodynamics, star formation, radiative cooling, and supernovae feedback, to trace the dominant isotopes of C, N, O, Ne, Mg, Si, and Fe. We include the contribution of Type Ia and II supernovae, in ad...
RAMSES-CH: a new chemodynamical code for cosmological simulations
Few, C. G.; Courty, S.; Gibson, B. K.; Kawata, D; Calura, F.; Teyssier, R.
2012-01-01
We present a new chemodynamical code -RAMSES-CH- for use in simulating the self-consistent evolution of chemical and hydrodynamical properties of galaxies within a fully cosmological framework. We build upon the adaptive mesh refinement code RAMSES, which includes a treatment of self-gravity, hydrodynamics, star formation, radiative cooling and supernova feedback, to trace the dominant isotopes of C, N, O, Ne, Mg, Si and Fe. We include the contribution of Type Ia and Type II supernovae, in ad...
Miscible and immiscible liquid experiments and simulations on the Rayleigh-Taylor instability
Roberts, Michael; Mokler, Matthew; Cabot, William; Jacobs, Jeffrey
2011-11-01
Experiments and numerical simulations are presented in which an incompressible system of two liquids is accelerated to produce the Rayleigh-Taylor instability. In these experiments, the initially stable, stratified liquid combination is accelerated downward on a vertical rail system in one of two experimental apparatuses: an apparatus in which a system of weights and pulleys accelerates the liquid filled tank (which is affixed to a test sled), or a new apparatus which uses linear induction motors to accelerate the tank (which is attached to an aluminum plate) to produce much greater acceleration levels. Both miscible and immiscible liquid combinations are used. In both apparatuses the resulting fluid flows are visualized with backlit imaging using LED backlights in conjunction with monochrome high-speed video cameras, both of which travel with the moving fluid filled containers. Initial perturbations are either unforced and allowed to progress from background noise or forced by vertically oscillating the liquid combination to produce parametric internal waves. The results of these experiments are compared to numerical simulations performed using the CFD code Miranda.
Nexus: A modular workflow management system for quantum simulation codes
Krogel, Jaron T.
2016-01-01
The management of simulation workflows represents a significant task for the individual computational researcher. Automation of the required tasks involved in simulation work can decrease the overall time to solution and reduce sources of human error. A new simulation workflow management system, Nexus, is presented to address these issues. Nexus is capable of automated job management on workstations and resources at several major supercomputing centers. Its modular design allows many quantum simulation codes to be supported within the same framework. Current support includes quantum Monte Carlo calculations with QMCPACK, density functional theory calculations with Quantum Espresso or VASP, and quantum chemical calculations with GAMESS. Users can compose workflows through a transparent, text-based interface, resembling the input file of a typical simulation code. A usage example is provided to illustrate the process.
Direct simulation Monte Carlo investigation of the Rayleigh-Taylor instability
Gallis, M. A.; Koehler, T. P.; Torczynski, J. R.; Plimpton, S. J.
2016-08-01
The Rayleigh-Taylor instability (RTI) is investigated using the direct simulation Monte Carlo (DSMC) method of molecular gas dynamics. Here, fully resolved two-dimensional DSMC RTI simulations are performed to quantify the growth of flat and single-mode perturbed interfaces between two atmospheric-pressure monatomic gases as a function of the Atwood number and the gravitational acceleration. The DSMC simulations reproduce many qualitative features of the growth of the mixing layer and are in reasonable quantitative agreement with theoretical and empirical models in the linear, nonlinear, and self-similar regimes. In some of the simulations at late times, the instability enters the self-similar regime, in agreement with experimental observations. For the conditions simulated, diffusion can influence the initial instability growth significantly.
Proton temperature-anisotropy-driven instabilities in weakly collisional plasmas: Hybrid simulations
Hellinger, Petr
2014-01-01
Kinetic instabilities in weakly collisional, high beta plasmas are investigated using two-dimensional hybrid expanding box simulations with Coulomb collisions modeled through the Langevin equation (corresponding to the Fokker-Planck one). The expansion drives a parallel or perpendicular temperature anisotropy (depending on the orientation of the ambient magnetic field). For the chosen parameters the Coulomb collisions are important with respect to the driver but are not strong enough to keep the system stable with respect to instabilities driven by the proton temperature anisotropy. In the case of the parallel temperature anisotropy the dominant oblique fire hose instability efficiently reduces the anisotropy in a quasilinear manner. In the case of the perpendicular temperature anisotropy the dominant mirror instability generates coherent compressive structures which scatter protons and reduce the temperature anisotropy. For both the cases the instabilities generate temporarily enough wave energy so that the ...
Energy Technology Data Exchange (ETDEWEB)
Garcia-Fenoll, M.; Barrachina, T.; Miro, R.; Verdu, G.
2014-07-01
In this work, part of our works in the frame of the OECD/NEA Oskarshamn-2 (O{sub 2}) BWR Stability Benchmark for Coupled Code Calculations and Uncertainty Analysis in Modelling are shown. The objective is to simulate the instability event registered in February 1999 at the Swedish NPP Oskarshamn-2 with the coupled code RELAP5/PARCSv2.7. (Author)
Energy Technology Data Exchange (ETDEWEB)
Gómez, Daniel O.; DeLuca, Edward E. [Harvard-Smithsonian Center for Astrophysics, 60 Garden St, Cambridge, MA 02138 (United States); Mininni, Pablo D. [Departamento de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires and Instituto de Física de Buenos Aires, Ciudad Universitaria, 1428 Buenos Aires (Argentina)
2016-02-20
Recent high-resolution Atmospheric Imaging Assembly/Solar Dynamics Observatory images show evidence of the development of the Kelvin–Helmholtz (KH) instability, as coronal mass ejections (CMEs) expand in the ambient corona. A large-scale magnetic field mostly tangential to the interface is inferred, both on the CME and on the background sides. However, the magnetic field component along the shear flow is not strong enough to quench the instability. There is also observational evidence that the ambient corona is in a turbulent regime, and therefore the criteria for the development of the instability are a priori expected to differ from the laminar case. To study the evolution of the KH instability with a turbulent background, we perform three-dimensional simulations of the incompressible magnetohydrodynamic equations. The instability is driven by a velocity profile tangential to the CME–corona interface, which we simulate through a hyperbolic tangent profile. The turbulent background is generated by the application of a stationary stirring force. We compute the instability growth rate for different values of the turbulence intensity, and find that the role of turbulence is to attenuate the growth. The fact that KH instability is observed sets an upper limit on the correlation length of the coronal background turbulence.
Maestro and Castro: Simulation Codes for Astrophysical Flows
Zingale, Michael; Almgren, Ann; Beckner, Vince; Bell, John; Friesen, Brian; Jacobs, Adam; Katz, Maximilian P.; Malone, Christopher; Nonaka, Andrew; Zhang, Weiqun
2017-01-01
Stellar explosions are multiphysics problems—modeling them requires the coordinated input of gravity solvers, reaction networks, radiation transport, and hydrodynamics together with microphysics recipes to describe the physics of matter under extreme conditions. Furthermore, these models involve following a wide range of spatial and temporal scales, which puts tough demands on simulation codes. We developed the codes Maestro and Castro to meet the computational challenges of these problems. Maestro uses a low Mach number formulation of the hydrodynamics to efficiently model convection. Castro solves the fully compressible radiation hydrodynamics equations to capture the explosive phases of stellar phenomena. Both codes are built upon the BoxLib adaptive mesh refinement library, which prepares them for next-generation exascale computers. Common microphysics shared between the codes allows us to transfer a problem from the low Mach number regime in Maestro to the explosive regime in Castro. Importantly, both codes are freely available (https://github.com/BoxLib-Codes). We will describe the design of the codes and some of their science applications, as well as future development directions.Support for development was provided by NSF award AST-1211563 and DOE/Office of Nuclear Physics grant DE-FG02-87ER40317 to Stony Brook and by the Applied Mathematics Program of the DOE Office of Advance Scientific Computing Research under US DOE contract DE-AC02-05CH11231 to LBNL.
Simulating magnetised plasma with the versatile advection code
Keppens, R.; Toth, G.; Palma, J. M. L.; Dongarra, J.; Hernandez, V.
1999-01-01
Matter in the universe mainly consists of plasma. The dynamics of plasmas is controlled by magnetic fields. To simulate the evolution of magnetised plasma, we solve the equations of magnetohydrodynamics using the Versatile Advection Code (VAC). To demonstrate the versatility of VAC, we present calcu
Simulating magnetised plasma with the versatile advection code
Keppens, R.; Toth, G.; Palma, J. M. L.; Dongarra, J.; Hernandez, V.
1999-01-01
Matter in the universe mainly consists of plasma. The dynamics of plasmas is controlled by magnetic fields. To simulate the evolution of magnetised plasma, we solve the equations of magnetohydrodynamics using the Versatile Advection Code (VAC). To demonstrate the versatility of VAC, we present
Simulation techniques for spatially evolving instabilities in compressible flow over a flat plate
Wasistho, B.; Geurts, B.J.; Kuerten, J.G.M.
1997-01-01
In this paper we present numerical techniques suitable for a direct numerical simulation in the spatial setting. We demonstrate the application to the simulation of compressible flat plate flow instabilities. We compare second and fourth order accurate spatial discretization schemes in combination w
O'Neill, Sean M; Begelman, Mitchell C
2012-01-01
We present the results of a numerical investigation of current-driven instability in magnetized jets. Utilizing the well-tested, relativistic magnetohydrodynamic code Athena, we construct an ensemble of local, co-moving plasma columns in which initial radial force balance is achieved through various combinations of magnetic, pressure, and rotational forces. We then examine the resulting flow morphologies and energetics to determine the degree to which these systems become disrupted, the amount of kinetic energy amplification attained, and the non-linear saturation behaviors. Our most significant finding is that the details of initial force balance have a pronounced effect on the resulting flow morphology. Models in which the initial magnetic field is force-free deform, but do not become disrupted. Systems that achieve initial equilibrium by balancing pressure gradients and/or rotation against magnetic forces, however, tend to shred, mix, and develop turbulence. In all cases, the linear growth of current-drive...
Computed radiography simulation using the Monte Carlo code MCNPX
Energy Technology Data Exchange (ETDEWEB)
Correa, S.C.A. [Programa de Engenharia Nuclear/COPPE, Universidade Federal do Rio de Janeiro, Ilha do Fundao, Caixa Postal 68509, 21945-970, Rio de Janeiro, RJ (Brazil); Centro Universitario Estadual da Zona Oeste (CCMAT)/UEZO, Av. Manuel Caldeira de Alvarenga, 1203, Campo Grande, 23070-200, Rio de Janeiro, RJ (Brazil); Souza, E.M. [Programa de Engenharia Nuclear/COPPE, Universidade Federal do Rio de Janeiro, Ilha do Fundao, Caixa Postal 68509, 21945-970, Rio de Janeiro, RJ (Brazil); Silva, A.X., E-mail: ademir@con.ufrj.b [PEN/COPPE-DNC/Poli CT, Universidade Federal do Rio de Janeiro, Ilha do Fundao, Caixa Postal 68509, 21945-970, Rio de Janeiro, RJ (Brazil); Cassiano, D.H. [Instituto de Radioprotecao e Dosimetria/CNEN Av. Salvador Allende, s/n, Recreio, 22780-160, Rio de Janeiro, RJ (Brazil); Lopes, R.T. [Programa de Engenharia Nuclear/COPPE, Universidade Federal do Rio de Janeiro, Ilha do Fundao, Caixa Postal 68509, 21945-970, Rio de Janeiro, RJ (Brazil)
2010-09-15
Simulating X-ray images has been of great interest in recent years as it makes possible an analysis of how X-ray images are affected owing to relevant operating parameters. In this paper, a procedure for simulating computed radiographic images using the Monte Carlo code MCNPX is proposed. The sensitivity curve of the BaFBr image plate detector as well as the characteristic noise of a 16-bit computed radiography system were considered during the methodology's development. The results obtained confirm that the proposed procedure for simulating computed radiographic images is satisfactory, as it allows obtaining results comparable with experimental data.
Enhanced Verification Test Suite for Physics Simulation Codes
Energy Technology Data Exchange (ETDEWEB)
Kamm, J R; Brock, J S; Brandon, S T; Cotrell, D L; Johnson, B; Knupp, P; Rider, W; Trucano, T; Weirs, V G
2008-10-10
This document discusses problems with which to augment, in quantity and in quality, the existing tri-laboratory suite of verification problems used by Los Alamos National Laboratory (LANL), Lawrence Livermore National Laboratory (LLNL), and Sandia National Laboratories (SNL). The purpose of verification analysis is demonstrate whether the numerical results of the discretization algorithms in physics and engineering simulation codes provide correct solutions of the corresponding continuum equations. The key points of this document are: (1) Verification deals with mathematical correctness of the numerical algorithms in a code, while validation deals with physical correctness of a simulation in a regime of interest. This document is about verification. (2) The current seven-problem Tri-Laboratory Verification Test Suite, which has been used for approximately five years at the DOE WP laboratories, is limited. (3) Both the methodology for and technology used in verification analysis have evolved and been improved since the original test suite was proposed. (4) The proposed test problems are in three basic areas: (a) Hydrodynamics; (b) Transport processes; and (c) Dynamic strength-of-materials. (5) For several of the proposed problems we provide a 'strong sense verification benchmark', consisting of (i) a clear mathematical statement of the problem with sufficient information to run a computer simulation, (ii) an explanation of how the code result and benchmark solution are to be evaluated, and (iii) a description of the acceptance criterion for simulation code results. (6) It is proposed that the set of verification test problems with which any particular code be evaluated include some of the problems described in this document. Analysis of the proposed verification test problems constitutes part of a necessary--but not sufficient--step that builds confidence in physics and engineering simulation codes. More complicated test cases, including physics models of
Wang, LiFeng; Ye, WenHua; He, XianTu; Wu, JunFeng; Fan, ZhengFeng; Xue, Chuang; Guo, HongYu; Miao, WenYong; Yuan, YongTeng; Dong, JiaQin; Jia, Guo; Zhang, Jing; Li, YingJun; Liu, Jie; Wang, Min; Ding, YongKun; Zhang, WeiYan
2017-05-01
Inertial fusion energy (IFE) has been considered a promising, nearly inexhaustible source of sustainable carbon-free power for the world's energy future. It has long been recognized that the control of hydrodynamic instabilities is of critical importance for ignition and high-gain in the inertial-confinement fusion (ICF) hot-spot ignition scheme. In this mini-review, we summarize the progress of theoretical and simulation research of hydrodynamic instabilities in the ICF central hot-spot implosion in our group over the past decade. In order to obtain sufficient understanding of the growth of hydrodynamic instabilities in ICF, we first decompose the problem into different stages according to the implosion physics processes. The decomposed essential physics pro- cesses that are associated with ICF implosions, such as Rayleigh-Taylor instability (RTI), Richtmyer-Meshkov instability (RMI), Kelvin-Helmholtz instability (KHI), convergent geometry effects, as well as perturbation feed-through are reviewed. Analyti- cal models in planar, cylindrical, and spherical geometries have been established to study different physical aspects, including density-gradient, interface-coupling, geometry, and convergent effects. The influence of ablation in the presence of preheating on the RTI has been extensively studied by numerical simulations. The KHI considering the ablation effect has been discussed in detail for the first time. A series of single-mode ablative RTI experiments has been performed on the Shenguang-II laser facility. The theoretical and simulation research provides us the physical insights of linear and weakly nonlinear growths, and nonlinear evolutions of the hydrodynamic instabilities in ICF implosions, which has directly supported the research of ICF ignition target design. The ICF hot-spot ignition implosion design that uses several controlling features, based on our current understanding of hydrodynamic instabilities, to address shell implosion stability, has
A Systematic Look at Code Performance and System Simulation
Directory of Open Access Journals (Sweden)
G.Srikanth
2014-06-01
Full Text Available The most standard method in improvise a system’s efficiency in Digital communication is channel coding but this methods is not been able to extend its features for high speed links. Growing demands in network speeds are placing a large burden on the energy efficiency of high-speed links and render the benefit of channel coding for these systems a timely subject. The low error rates of interest and the presence of residual inter-symbol interference (ISI caused by hardware constraints impede the analysis and simulation of coded high-speed links. Focusing on the residual ISI and collective noise as the dominant error mechanisms, this paper analyzes error correlation through concepts of error region, channel signature, and correlation distance. This framework provides a deeper insight into joint error behaviors in high-speed links, extends the range of statistical simulation for coded high-speed links, and provides a case against the use of biased Monte Carlo methods in this setting. Finally, based on a hardware test bed, the performance of standard binary forward error correction and error detection schemes is evaluated, from which recommendations on coding for high-speed links are derived. Keywords:
Scrape-Off Layer Turbulence in Tokamaks Simulated with a Continuum Gyrokinetic Code
Hakim, A; Abel, I G; Hammett, G W; Stoltzfus-Dueck, T
2016-01-01
We are developing a new continuum gyrokinetic code, Gkeyll, for use in edge plasma simulations, and here present initial simulations of turbulence on open field lines with model sheath boundary conditions. The code implements an energy conserving discontinuous Galerkin scheme, applicable to a general class of Hamiltonian equations. Several applications to test problems have been done, including a calculation of the parallel heat-flux on divertor plates resulting from an ELM crash in JET, for a 1x/1v SOL scenario explored previously, where the ELM is modeled as a time-dependent intense upstream source. Here we present initial simulations of turbulence on open field lines in the LAPD linear plasma device. We have also done simulations in a helical open-field-line geometry. While various simplifications have been made at present, this still includes some of the key physics of SOL turbulence, such as bad-curvature drive for instabilities and rapid parallel losses with sheath boundary conditions. This is useful fo...
Simulation of Transverse Multi-Bunch Instabilities of Proton Beams in LHC
Koschik, Alexander; Zotter, Bruno
The CERN Large Hadron Collider (LHC) is designed for highest luminosity and therefore requires operation with a large number of bunches and high intensities. Its performance could be limited by the electromagnetic interaction between the charged particle beam and its surroundings which cause collective instabilities. This thesis describes methods of simulating and analyzing multi-bunch instabilities in circular accelerators and storage rings. The simulation models as well as analyzing tools presented here, also facilitate the interpretation of measurements in multi-bunch machines. The 3-dimensional, multi-bunch tracking program MultiTRISIM was developed, based on its single-bunch predecessor TRISIM3D. It allows the exploration of longrange effects in round or flat vacuum chambers for equidistant or uneven filling schemes. Previous computer simulations of collective effects concentrated mainly on instabilities of single or few bunches in electron storage rings. There, the strong radiation damping reduces the r...
Li, Yanggui; Geng, Xingguo; Wang, Heping; Zhuang, Xin; Ouyang, Jie
2016-06-01
The frontal instability of lock-exchange density currents is numerically investigated using dissipative particle dynamics (DPD) at the mesoscopic particle level. For modeling two-phase flow, the “color” repulsion model is adopted to describe binary fluids according to Rothman-Keller method. The present DPD simulation can reproduce the flow phenomena of lock-exchange density currents, including the lobe-and-cleft instability that appears at the head, as well as the formation of coherent billow structures at the interface behind the head due to the growth of Kelvin-Helmholtz instability. Furthermore, through the DPD simulation, some small-scale characteristics can be observed, which are difficult to be captured in macroscopic simulation and experiment.
Barker, Adrian J
2016-01-01
I present results from the first global hydrodynamical simulations of the elliptical instability in a tidally deformed gaseous planet (or star) with a free surface. The elliptical instability is potentially important for tidal evolution of the shortest-period hot Jupiters. I model the planet as a spin-orbit aligned or anti-aligned, and non-synchronously rotating, tidally deformed, homogeneous fluid body. A companion paper presented an analysis of the global modes and instabilities of such a planet. Here I focus on the nonlinear evolution of the elliptical instability. This is observed to produce bursts of turbulence that drive the planet towards synchronism with its orbit in an erratic manner. If the planetary spin is initially anti-aligned, the elliptical instability also drives spin-orbit alignment on a similar timescale as the spin synchronisation. The instability generates differential rotation inside the planet in the form of zonal flows, which play an important role in the saturation of the instability,...
Numerical instability due to relativistic plasma drift in EM-PIC simulations
Xu, Xinlu; Yu, Peicheng; Martins, Samual F.; Tsung, Frank S.; Decyk, Viktor K.; Vieira, Jorge; Fonseca, Ricardo A.; Lu, Wei; Silva, Luis O.; Mori, Warren B.
2013-11-01
The numerical instability observed in electromagnetic particle-in-cell (EM-PIC) simulations with a plasma drifting with relativistic velocities is studied using both theory and computer simulations. We derive the numerical dispersion relation for a cold plasma drifting with a relativistic velocity, and find an instability attributed to the intersection between beam resonances and the electromagnetic modes in the drifting plasma. The intersection can occur in the fundamental Brillouin zones when EM waves with phase velocities less than the speed of light exist, and from aliasing beam resonances and aliasing EM modes. The unstable modes are neither purely transverse nor longitudinal. The characteristic patterns of the instability in Fourier space for various simulation setups and Maxwell equation solvers are explored by solving the corresponding numerical dispersion relations. Furthermore, based upon these characteristic patterns, we derive an asymptotic expression for the instability growth rate. The asymptotic expression greatly speeds up the calculation of the instability growth rate and makes the parameter scans for minimal growth rate feasible even for full three dimensions. The results are compared against simulation results, and good agreements are found. These results can be used as a guide to develop possible approaches to mitigate the instability. We examine the use of a spectral solver and show that such a solver when combined with a low pass filter with a cutoff value of |k→| essentially eliminates the instability while not modifying modes of physical interest. The use of a spectral solver also provides minimal errors to electromagnetic modes in the lowest Brillouin zones.
Avara, Mark J; Bogdanović, Tamara
2013-01-01
The role played by magnetic fields in the intracluster medium (ICM) of galaxy clusters is complex. The weakly collisional nature of the ICM leads to thermal conduction that is channelled along field lines. This anisotropic heat conduction profoundly changes the stability of the ICM atmosphere, with convective stabilities being driven by temperature gradients of either sign. Here, we employ the Athena magnetohydrodynamic code to investigate the local non-linear behavior of the heat-flux driven buoyancy instability (HBI), relevant in the cores of cooling-core clusters where the temperature increases with radius. We study a grid of 2-d simulations that span a large range of initial magnetic field strengths and numerical resolutions. For very weak initial fields, we recover the previously known result that the HBI wraps the field in the horizontal direction thereby shutting off the heat flux. However, we find that simulations which begin with intermediate initial field strengths have a qualitatively different beh...
Kulkarni, Akshay K
2008-01-01
We present results of 3D simulations of MHD instabilities at the accretion disk-magnetosphere boundary. The instability is Rayleigh-Taylor, and develops for a fairly broad range of accretion rates and stellar rotation rates and magnetic fields. It manifests itself in the form of tall, thin tongues of plasma that penetrate the magnetosphere in the equatorial plane. The shape and number of the tongues changes with time on the inner-disk dynamical timescale. In contrast with funnel flows, which deposit matter mainly in the polar region, the tongues deposit matter much closer to the stellar equator. The instability appears for relatively small misalignment angles, $\\Theta\\lesssim30^\\circ$, between the star's rotation and magnetic axes, and is associated with higher accretion rates. The hot spots and light curves during accretion through instability are generally much more chaotic than during stable accretion. The unstable state of accretion has possible implications for quasi-periodic oscillations and intermitten...
Long-time simulations of the Kelvin-Helmholtz instability using an adaptive vortex method.
Sohn, Sung-Ik; Yoon, Daeki; Hwang, Woonjae
2010-10-01
The nonlinear evolution of an interface subject to a parallel shear flow is studied by the vortex sheet model. We perform long-time computations for the vortex sheet in density-stratified fluids by using the point vortex method and investigate late-time dynamics of the Kelvin-Helmholtz instability. We apply an adaptive point insertion procedure and a high-order shock-capturing scheme to the vortex method to handle the nonuniform distribution of point vortices and enhance the resolution. Our adaptive vortex method successfully simulates chaotically distorted interfaces of the Kelvin-Helmholtz instability with fine resolutions. The numerical results show that the Kelvin-Helmholtz instability evolves a secondary instability at a late time, distorting the internal rollup, and eventually develops to a disordered structure.
Scientific codes developed and used at GRS. Nuclear simulation chain
Energy Technology Data Exchange (ETDEWEB)
Schaffrath, Andreas; Sonnenkalb, Martin; Sievers, Juergen; Luther, Wolfgang; Velkov, Kiril [Gesellschaft fuer Anlagen und Reaktorsicherheit (GRS) gGmbH, Garching/Muenchen (Germany). Forschungszentrum
2016-05-15
Over 60 technical experts of the reactor safety research division of the Gesellschaft fuer Anlagen- und Reaktorsicherheit (GRS) gGmbH are developing and validating reliable methods and computer codes - summarized under the term nuclear simulation chain - for the safety-related assessment for all types of nuclear power plants (NPP) and other nuclear facilities considering the current state of science and technology. This nuclear simulation chain has to be able to simulate and assess all relevant physical processes and phenomena for all operating states and (severe) accidents. In the present contribution, the nuclear simulation chain developed and applied by GRS as well as selected examples of its application are presented. The latter demonstrate impressively the width of its scope and its performance. The GRS codes can be passed on request to other (national as well as international) organizations. This contributes to a worldwide increase of the nuclear safety standards. The code transfer is especially important for developing and emerging countries lacking the financial means and/or the necessary know-how for this purpose. At the end of this contribution, the respective course of action is described.
Numerical simulation of lowest-order short-crested wave instabilities
DEFF Research Database (Denmark)
Fuhrman, David R.; Madsen, Per A.; Bingham, Harry
2006-01-01
A numerical study of doubly periodic deep-water short-crested wave instabilities, arising from various quartet resonant interactions, is conducted using a high-order Boussinesq-type model. The model is first verified through a series of simulations involving classical class I plane wave...... demonstrates a reasonably similar evolution. These simulations consider the simplest physical situations involving three-dimensional instabilities of genuinely three-dimensional progressive waves, revealing qualitative differences from classical two-dimensional descriptions. This study is therefore...
Simulations of flashing experiments in TOPFLOW facility with TRACE code
Energy Technology Data Exchange (ETDEWEB)
Mikuž, Blaž, E-mail: blaz.mikuz@ijs.si [Jozef Stefan Institute, Reactor Engineering Division, Jamova cesta 39, 1000 Ljubljana (Slovenia); Tiselj, Iztok [Jozef Stefan Institute, Reactor Engineering Division, Jamova cesta 39, 1000 Ljubljana (Slovenia); Beyer, Matthias; Lucas, Dirk [Institute of Fluid Dynamics, Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstraße 400, 01328 Dresden (Germany)
2015-03-15
Highlights: • Two decompression experiments performed at TOPFLOW are simulated with a TRACE code. • The depressurization triggers flashing of the slightly undersaturated liquid water. • Pressure, temperature and void fractions are compared with measurements. • Prediction of the choked flow is the most critical parameter of simulations. • Good agreement with measurements at high initial pressure (i.e. 65 and 40 bars). - Abstract: The decompression experiments performed at TOPFLOW facility in 2010 have been reproduced using the latest best-estimate thermohydraulic system code TRACE (V 5.0 Patch 3). The main component of TOPFLOW facility was about 8 m long vertical tube with an inner diameter of 195.3 mm. The evaporation of liquid water to steam caused by depressurization was simulated using two different procedures: from stagnant water and during circulating of water in tubes. The liquid water was almost saturated at initial pressure values of 1.0, 2.0, 4.0 and 6.5 MPa. Our approach applies one-dimensional code to simulate all the important parts of the facility not just the vertical test section, where the measurements were taken. The obtained simulated pressure, temperature and void fractions are compared with measured values. The simulations of the first procedure (stagnant water at beginning) are in a good agreement with measurements, especially for the cases with longer transients and higher initial pressure, however, choked flow model through the blow-off valve had to be adjusted. There is a short transient (about 2 s) after the fast opening valve opens, which was not reproduced correctly with TRACE. The simulations of the second procedure (circulating water in a loop) correctly predict pressure and temperature decrease, but underpredict void fraction. No modification of the default TRACE choked flow model was needed for procedure B.
Simulation of EAST quasi-snowflake discharge by tokamak simulation code
Energy Technology Data Exchange (ETDEWEB)
Guo, Y., E-mail: yguo@ipp.ac.cn [Institute of Plasma Physics, Chinese Academy of Science, Hefei 230031 (China); Pironti, A. [CREATE, Università di Napoli Federico II, Università di Cassino and Università di Napoli Parthenope, Via Claudio 19, Napoli 80125 (Italy); Liu, L. [Institute of Plasma Physics, Chinese Academy of Science, Hefei 230031 (China); Xiao, B.J. [Institute of Plasma Physics, Chinese Academy of Science, Hefei 230031 (China); School of Nuclear Science and Technology, University of Science and Technology of China, Hefei 230026 (China); Albanese, R.; Ambrosino, R. [CREATE, Università di Napoli Federico II, Università di Cassino and Università di Napoli Parthenope, Via Claudio 19, Napoli 80125 (Italy); Luo, Z.P.; Yuan, Q.P. [Institute of Plasma Physics, Chinese Academy of Science, Hefei 230031 (China); Calabrò, G.; Crisanti, F. [ENEA UnitàTecnicaFusione, C.R. Frascati, Via E. Fermi 45, Frascati 00044, Roma (Italy); Xing, Z. [Institute of Plasma Physics, Chinese Academy of Science, Hefei 230031 (China)
2015-12-15
Highlights: • By tokamak simulation code (TSC), we reproduce the quasi-snowflake (QSF) discharge controlled by RZIp method. • Singular Value Decomposition (SVD) method, a way to decouple the PF current and control parameter, is implemented in TSC code. • TSC code is used to simulate the QSF shape control by SVD method. • The calculation results show SVD method is a good way for EAST QSF shape control. - Abstract: Both theory and experiment have proved Snowflake configuration could reduce the heat loads on divertor plate. Due to limitation of PF coils, EAST could only operate with quasi-snowflake (QSF). In 2014 EAST campaign, QSF has been achieved by RZIp control. The next important task is the QSF shape control. As tokamak discharge simulation code, Tokamak Simulation Code (TSC), which has been benchmarked by experimental data, is used to simulate EAST QSF discharge. Singular Value Decomposition (SVD) method, a way to decouple the PF current and control parameter, is implemented in TSC code to simulate the course of QSF shape control. The simulation results show SVD method is a good way for EAST QSF shape control.
Development of dynamic simulation code for fuel cycle fusion reactor
Energy Technology Data Exchange (ETDEWEB)
Aoki, Isao; Seki, Yasushi [Department of Fusion Engineering Research, Naka Fusion Research Establishment, Japan Atomic Energy Research Institute, Naka, Ibaraki (Japan); Sasaki, Makoto; Shintani, Kiyonori; Kim, Yeong-Chan
1999-02-01
A dynamic simulation code for fuel cycle of a fusion experimental reactor has been developed. The code follows the fuel inventory change with time in the plasma chamber and the fuel cycle system during 2 days pulse operation cycles. The time dependence of the fuel inventory distribution is evaluated considering the fuel burn and exhaust in the plasma chamber, purification and supply functions. For each subsystem of the plasma chamber and the fuel cycle system, the fuel inventory equation is written based on the equation of state considering the fuel burn and the function of exhaust, purification, and supply. The processing constants of subsystem for steady states were taken from the values in the ITER Conceptual Design Activity (CDA) report. Using this code, the time dependence of the fuel supply and inventory depending on the burn state and subsystem processing functions are shown. (author)
Simulations of Laboratory Astrophysics Experiments using the CRASH code
Trantham, Matthew; Kuranz, Carolyn; Fein, Jeff; Wan, Willow; Young, Rachel; Keiter, Paul; Drake, R. Paul
2015-11-01
Computer simulations can assist in the design and analysis of laboratory astrophysics experiments. The Center for Radiative Shock Hydrodynamics (CRASH) at the University of Michigan developed a code that has been used to design and analyze high-energy-density experiments on OMEGA, NIF, and other large laser facilities. This Eulerian code uses block-adaptive mesh refinement (AMR) with implicit multigroup radiation transport, electron heat conduction and laser ray tracing. This poster will demonstrate some of the experiments the CRASH code has helped design or analyze including: Kelvin-Helmholtz, Rayleigh-Taylor, magnetized flows, jets, and laser-produced plasmas. This work is funded by the following grants: DEFC52-08NA28616, DE-NA0001840, and DE-NA0002032.
Evaluation of the Aleph PIC Code on Benchmark Simulations
Boerner, Jeremiah; Pacheco, Jose; Grillet, Anne
2016-09-01
Aleph is a massively parallel, 3D unstructured mesh, Particle-in-Cell (PIC) code, developed to model low temperature plasma applications. In order to verify and validate performance, Aleph is benchmarked against a series of canonical problems to demonstrate statistical indistinguishability in the results. Here, a series of four problems is studied: Couette flows over a range of Knudsen number, sheath formation in an undriven plasma, the two-stream instability, and a capacitive discharge. These problems respectively exercise collisional processes, particle motion in electrostatic fields, electrostatic field solves coupled to particle motion, and a fully coupled reacting plasma. Favorable comparison with accepted results establishes confidence in Aleph's capability and accuracy as a general purpose PIC code. Finally, Aleph is used to investigate the sensitivity of a triggered vacuum gap switch to the particle injection conditions associated with arc breakdown at the trigger. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
Linear simulations of the cylindrical Richtmyer-Meshkov instability in magnetohydrodynamics
Bakhsh, Abeer
2016-03-09
Numerical simulations and analysis indicate that the Richtmyer-Meshkov instability(RMI) is suppressed in ideal magnetohydrodynamics(MHD) in Cartesian slab geometry. Motivated by the presence of hydrodynamic instabilities in inertial confinement fusion and suppression by means of a magnetic field, we investigate the RMI via linear MHD simulations in cylindrical geometry. The physical setup is that of a Chisnell-type converging shock interacting with a density interface with either axial or azimuthal (2D) perturbations. The linear stability is examined in the context of an initial value problem (with a time-varying base state) wherein the linearized ideal MHD equations are solved with an upwind numerical method. Linear simulations in the absence of a magnetic field indicate that RMI growth rate during the early time period is similar to that observed in Cartesian geometry. However, this RMI phase is short-lived and followed by a Rayleigh-Taylor instability phase with an accompanied exponential increase in the perturbation amplitude. We examine several strengths of the magnetic field (characterized by β=2p/B^2_r) and observe a significant suppression of the instability for β ≤ 4. The suppression of the instability is attributed to the transport of vorticity away from the interface by Alfvén fronts.
Parallelization of a Monte Carlo particle transport simulation code
Hadjidoukas, P.; Bousis, C.; Emfietzoglou, D.
2010-05-01
We have developed a high performance version of the Monte Carlo particle transport simulation code MC4. The original application code, developed in Visual Basic for Applications (VBA) for Microsoft Excel, was first rewritten in the C programming language for improving code portability. Several pseudo-random number generators have been also integrated and studied. The new MC4 version was then parallelized for shared and distributed-memory multiprocessor systems using the Message Passing Interface. Two parallel pseudo-random number generator libraries (SPRNG and DCMT) have been seamlessly integrated. The performance speedup of parallel MC4 has been studied on a variety of parallel computing architectures including an Intel Xeon server with 4 dual-core processors, a Sun cluster consisting of 16 nodes of 2 dual-core AMD Opteron processors and a 200 dual-processor HP cluster. For large problem size, which is limited only by the physical memory of the multiprocessor server, the speedup results are almost linear on all systems. We have validated the parallel implementation against the serial VBA and C implementations using the same random number generator. Our experimental results on the transport and energy loss of electrons in a water medium show that the serial and parallel codes are equivalent in accuracy. The present improvements allow for studying of higher particle energies with the use of more accurate physical models, and improve statistics as more particles tracks can be simulated in low response time.
RAMSES-CH: a new chemodynamical code for cosmological simulations
Few, C. G.; Courty, S.; Gibson, B. K.; Kawata, D.; Calura, F.; Teyssier, R.
2012-07-01
We present a new chemodynamical code -RAMSES-CH- for use in simulating the self-consistent evolution of chemical and hydrodynamical properties of galaxies within a fully cosmological framework. We build upon the adaptive mesh refinement code RAMSES, which includes a treatment of self-gravity, hydrodynamics, star formation, radiative cooling and supernova feedback, to trace the dominant isotopes of C, N, O, Ne, Mg, Si and Fe. We include the contribution of Type Ia and Type II supernovae, in addition to low- and intermediate-mass asymptotic giant branch stars, relaxing the instantaneous recycling approximation. The new chemical evolution modules are highly flexible and portable, lending themselves to ready exploration of variations in the underpinning stellar and nuclear physics. We apply RAMSES-CH to the cosmological simulation of a typical L★ galaxy, demonstrating the successful recovery of the basic empirical constraints regarding [α/Fe]-[Fe/H] and Type Ia/II supernova rates.
RAMSES-CH: A New Chemodynamical Code for Cosmological Simulations
Few, C Gareth; Gibson, Brad K; Kawata, Daisuke; Calura, Francesco; Teyssier, Romain
2012-01-01
We present a new chemodynamical code - Ramses-CH - for use in simulating the self-consistent evolution of chemical and hydrodynamical properties of galaxies within a fully cosmological framework. We build upon the adaptive mesh refinement code Ramses, which includes a treatment of self-gravity, hydrodynamics, star formation, radiative cooling, and supernovae feedback, to trace the dominant isotopes of C, N, O, Ne, Mg, Si, and Fe. We include the contribution of Type Ia and II supernovae, in addition to low- and intermediate-mass asymptotic giant branch stars, relaxing the instantaneous recycling approximation. The new chemical evolution modules are highly flexible and portable, lending themselves to ready exploration of variations in the underpining stellar and nuclear physics. We apply Ramses-CH to the cosmological simulation of a typical L\\star galaxy, demonstrating the successful recovery of the basic empirical constraints regarding, [{\\alpha}/Fe]-[Fe/H] and Type Ia/II supernovae rates.
Simulations of the Ion-Hose Instability for DARHT-II Long-Pulse Experiments
Chan, K C D
2004-01-01
Ion-hose effect has been described extensively in literatures. Computer simulations of the effect typically use particle-in-cell (PIC) computer codes or codes using the spread-mass formulation [1]. PIC simulations, though offering more reliable results, will require extended running time in large computers To support commissioning experiments in the DARHT-II induction linac in Los Alamos National Laboratory, we have modified a spread-mass code so that we can survey quickly the parameter space for the experiment. It can also be used to provide quick answers during experiment. The code was originally written by Genoni from Mission Research Corporation (MRC) for constant linac parameters. We have modified it so that parameters can have dependence along the length of the linac. In this paper, we will describe simulation results using this code for the DARHT-II commissioning experiment and also our benchmarking results comparing to LSP, a PIC code from MRC.
Low-temperature plasma simulations with the LSP PIC code
Carlsson, Johan; Khrabrov, Alex; Kaganovich, Igor; Keating, David; Selezneva, Svetlana; Sommerer, Timothy
2014-10-01
The LSP (Large-Scale Plasma) PIC-MCC code has been used to simulate several low-temperature plasma configurations, including a gas switch for high-power AC/DC conversion, a glow discharge and a Hall thruster. Simulation results will be presented with an emphasis on code comparison and validation against experiment. High-voltage, direct-current (HVDC) power transmission is becoming more common as it can reduce construction costs and power losses. Solid-state power-electronics devices are presently used, but it has been proposed that gas switches could become a compact, less costly, alternative. A gas-switch conversion device would be based on a glow discharge, with a magnetically insulated cold cathode. Its operation is similar to that of a sputtering magnetron, but with much higher pressure (0.1 to 0.3 Torr) in order to achieve high current density. We have performed 1D (axial) and 2D (axial/radial) simulations of such a gas switch using LSP. The 1D results were compared with results from the EDIPIC code. To test and compare the collision models used by the LSP and EDIPIC codes in more detail, a validation exercise was performed for the cathode fall of a glow discharge. We will also present some 2D (radial/azimuthal) LSP simulations of a Hall thruster. The information, data, or work presented herein was funded in part by the Advanced Research Projects Agency-Energy (ARPA-E), U.S. Department of Energy, under Award Number DE-AR0000298.
Enhanced verification test suite for physics simulation codes
Energy Technology Data Exchange (ETDEWEB)
Kamm, James R.; Brock, Jerry S.; Brandon, Scott T.; Cotrell, David L.; Johnson, Bryan; Knupp, Patrick; Rider, William J.; Trucano, Timothy G.; Weirs, V. Gregory
2008-09-01
This document discusses problems with which to augment, in quantity and in quality, the existing tri-laboratory suite of verification problems used by Los Alamos National Laboratory (LANL), Lawrence Livermore National Laboratory (LLNL), and Sandia National Laboratories (SNL). The purpose of verification analysis is demonstrate whether the numerical results of the discretization algorithms in physics and engineering simulation codes provide correct solutions of the corresponding continuum equations.
CHOLLA: A New Massively Parallel Hydrodynamics Code for Astrophysical Simulation
Schneider, Evan E.; Robertson, Brant E.
2015-04-01
We present Computational Hydrodynamics On ParaLLel Architectures (Cholla ), a new three-dimensional hydrodynamics code that harnesses the power of graphics processing units (GPUs) to accelerate astrophysical simulations. Cholla models the Euler equations on a static mesh using state-of-the-art techniques, including the unsplit Corner Transport Upwind algorithm, a variety of exact and approximate Riemann solvers, and multiple spatial reconstruction techniques including the piecewise parabolic method (PPM). Using GPUs, Cholla evolves the fluid properties of thousands of cells simultaneously and can update over 10 million cells per GPU-second while using an exact Riemann solver and PPM reconstruction. Owing to the massively parallel architecture of GPUs and the design of the Cholla code, astrophysical simulations with physically interesting grid resolutions (≳2563) can easily be computed on a single device. We use the Message Passing Interface library to extend calculations onto multiple devices and demonstrate nearly ideal scaling beyond 64 GPUs. A suite of test problems highlights the physical accuracy of our modeling and provides a useful comparison to other codes. We then use Cholla to simulate the interaction of a shock wave with a gas cloud in the interstellar medium, showing that the evolution of the cloud is highly dependent on its density structure. We reconcile the computed mixing time of a turbulent cloud with a realistic density distribution destroyed by a strong shock with the existing analytic theory for spherical cloud destruction by describing the system in terms of its median gas density.
Murphy, G C; Pelletier, Guy
2008-01-01
Magnetic reconnection plays a critical role in many astrophysical processes where high energy emission is observed, e.g. particle acceleration, relativistic accretion powered outflows, pulsar winds and probably in dissipation of Poynting flux in GRBs. The magnetic field acts as a reservoir of energy and can dissipate its energy to thermal and kinetic energy via the tearing mode instability. We have performed 3d nonlinear MHD simulations of the tearing mode instability in a current sheet. Results from a temporal stability analysis in both the linear regime and weakly nonlinear (Rutherford) regime are compared to the numerical simulations. We observe magnetic island formation, island merging and oscillation once the instability has saturated. The growth in the linear regime is exponential in agreement with linear theory. In the second, Rutherford regime the island width grows linearly with time. We find that thermal energy produced in the current sheet strongly dominates the kinetic energy. Finally preliminary ...
Direct Numerical Simulation of Electrokinetic Instability and Transition to Chaotic Motion
Demekhin, E A; Shelistov, V S
2013-01-01
A new type of instability - electrokinetic instability - and an unusual transition to chaotic motion near a charge-selective surface was studied by numerical integration of the Nernst-Planck-Poisson-Stokes system and a weakly nonlinear analysis near the threshold of instability. Two kinds of initial conditions were considered: (a) white noise initial conditions to mimic "room disturbances" and subsequent natural evolution of the solution; (b) an artificial monochromatic ion distribution with a fixed wave number to simulate regular wave patterns. The results were studied from the viewpoint of hydrodynamic stability and bifurcation theory. The threshold of electroconvective movement was found by the linear spectral stability theory, the results of which were confirmed by numerical simulation of the entire system. The following regimes, which replace each other as the potential drop between the selective surfaces increases, were obtained: one-dimensional steady solution; two-dimensional steady electroconvective ...
Numerical Simulation of Flow Instabilities in High Speed Multistage Compressors
Institute of Scientific and Technical Information of China (English)
JunHu; ThomasPeters; 等
1999-01-01
In the present paper,a nonlinear multi“actuator disk” model is proposed to analyze the dynamic behavior of flow instabilities,including rotating stall and surge,in high speed multistage axial compressors.The model describes the duct flow fields using two dimensional,compressible and unsteady Euler equations,and accounts for the influences of downstream plenum and throttle in the system as well.It replaces each blade row of multistage compressore with a disk.For numerical calculations,the time marching procedure,using MacCormack two steps scheme,is used.The main pupose of this paper is to predict the mechanism of two dimensional short wavelength rotating stall inception and the interation between blade rows in high speed multistage compressors.It has been demonstrated that the model has the ability to predict those phenomena,and the results show that some system parameters have a strong effect on the stall features as well.Results for a five stage high speed compressor are analyzed in detail,and comparison with the experimental data demonstrates that the model and calculating results are reliable.
Generating performance portable geoscientific simulation code with Firedrake (Invited)
Ham, D. A.; Bercea, G.; Cotter, C. J.; Kelly, P. H.; Loriant, N.; Luporini, F.; McRae, A. T.; Mitchell, L.; Rathgeber, F.
2013-12-01
This presentation will demonstrate how a change in simulation programming paradigm can be exploited to deliver sophisticated simulation capability which is far easier to programme than are conventional models, is capable of exploiting different emerging parallel hardware, and is tailored to the specific needs of geoscientific simulation. Geoscientific simulation represents a grand challenge computational task: many of the largest computers in the world are tasked with this field, and the requirements of resolution and complexity of scientists in this field are far from being sated. However, single thread performance has stalled, even sometimes decreased, over the last decade, and has been replaced by ever more parallel systems: both as conventional multicore CPUs and in the emerging world of accelerators. At the same time, the needs of scientists to couple ever-more complex dynamics and parametrisations into their models makes the model development task vastly more complex. The conventional approach of writing code in low level languages such as Fortran or C/C++ and then hand-coding parallelism for different platforms by adding library calls and directives forces the intermingling of the numerical code with its implementation. This results in an almost impossible set of skill requirements for developers, who must simultaneously be domain science experts, numericists, software engineers and parallelisation specialists. Even more critically, it requires code to be essentially rewritten for each emerging hardware platform. Since new platforms are emerging constantly, and since code owners do not usually control the procurement of the supercomputers on which they must run, this represents an unsustainable development load. The Firedrake system, conversely, offers the developer the opportunity to write PDE discretisations in the high-level mathematical language UFL from the FEniCS project (http://fenicsproject.org). Non-PDE model components, such as parametrisations
Electron Debye scale Kelvin-Helmholtz instability: Electrostatic particle-in-cell simulations
Lee, Sang-Yun; Lee, Ensang; Kim, Khan-Hyuk; Lee, Dong-Hun; Seon, Jongho; Jin, Ho
2015-12-01
In this paper, we investigated the electron Debye scale Kelvin-Helmholtz (KH) instability using two-dimensional electrostatic particle-in-cell simulations. We introduced a velocity shear layer with a thickness comparable to the electron Debye length and examined the generation of the KH instability. The KH instability occurs in a similar manner as observed in the KH instabilities in fluid or ion scales producing surface waves and rolled-up vortices. The strength and growth rate of the electron Debye scale KH instability is affected by the structure of the velocity shear layer. The strength depends on the magnitude of the velocity and the growth rate on the velocity gradient of the shear layer. However, the development of the electron Debye scale KH instability is mainly determined by the electric field generated by charge separation. Significant mixing of electrons occurs across the shear layer, and a fraction of electrons can penetrate deeply into the opposite side fairly far from the vortices across the shear layer.
Note on quantitatively correct simulations of the kinetic beam-plasma instability
Lotov, K V; Mesyats, E A; Snytnikov, A V; Vshivkov, V A
2014-01-01
A large number of model particles is shown necessary for quantitatively correct simulations of the kinetic beam-plasma instability with the clouds-in-cells method. The required number of particles scales inversely with the expected growth rate, as in the kinetic regime only a narrow interval of beam velocities is resonant with the wave.
Note on quantitatively correct simulations of the kinetic beam-plasma instability
Energy Technology Data Exchange (ETDEWEB)
Lotov, K. V.; Timofeev, I. V. [Budker Institute of Nuclear Physics SB RAS, 630090 Novosibirsk (Russian Federation); Novosibirsk State University, 630090 Novosibirsk (Russian Federation); Mesyats, E. A.; Snytnikov, A. V.; Vshivkov, V. A. [Institute of Computational Mathematics and Mathematical Geophysics SB RAS, 630090 Novosibirsk (Russian Federation)
2015-02-15
A large number of model particles are shown necessary for quantitatively correct simulations of the kinetic beam-plasma instability with the clouds-in-cells method. The required number of particles scales inversely with the expected growth rate, as only a narrow interval of beam velocities is resonant with the wave in the kinetic regime.
Stockem, A; Schlickeiser, R
2010-01-01
An instability driven by the thermal anisotropy of a single electron species is investigated in a 2D particle-in-cell (PIC) simulation. This instability is the one considered by Weibel and it differs from the beam driven filamentation instability. A comparison of the simulation results with analytic theory provides similar exponential growth rates of the magnetic field during the linear growth phase of the instability. We observe in accordance with previous works the growth of electric fields during the saturation phase of the instability. Some components of this electric field are not accounted for by the linearized theory. A single-fluid-based theory is used to determine the source of this nonlinear electric field. It is demonstrated that the magnetic stress tensor, which vanishes in a 1D geometry, is more important in this 2-dimensional model used here. The electric field grows to an amplitude, which yields a force on the electrons that is comparable to the magnetic one. The peak energy density of each mag...
Simulating the Rayleigh-Taylor instability in polymer fluids with dissipative particle dynamics
Li, Yanggui; Geng, Xingguo; Zhuang, Xin; Wang, Lihua; Ouyang, Jie
2016-04-01
The Rayleigh-Taylor (RT) instability that occurs in the flow of polymer fluids is numerically investigated with dissipative particle dynamics (DPD) method at the mesoscale particle level. For modeling two-phase flow, the Flory-Huggins parameter is introduced to model binary fluids. And the polymer chains in fluids are described by the modified FENE model that depicts both the elastic tension and the elastic repulsion between the adjacent beads with bond length as the equilibrium length of one segment. Besides, a bead repulsive potential is employed to capture entanglements between polymer chains. Through our model and numerical simulation, we research the dynamics behaviors of the RT instability in polymer fluid medium. Furthermore, we also explore the effects of polymer volume concentration, chain length, and extensibility on the evolution of RT instability. These simulation results show that increasing any of the parameters, concentration, chain length, and extensibility, the saturation length of spikes becomes longer, and the two polymer fluids have less mixture. On the contrary, for the case of low concentration, or short chain, or small extensibility, the spikes easily split and break up, and the RT instability pattern evolves into chaotic structure. These observations indicate that the polymer and its properties drastically modify the RT instability pattern.
Zhang, Haocheng; Li, Hui; Guo, Fan; Taylor, Greg
2017-02-01
Kink instabilities are likely to occur in the current-carrying magnetized plasma jets. Recent observations of the blazar radiation and polarization signatures suggest that the blazar emission region may be considerably magnetized. While the kink instability has been studied with first-principle magnetohydrodynamic (MHD) simulations, the corresponding time-dependent radiation and polarization signatures have not been investigated. In this paper, we perform comprehensive polarization-dependent radiation modeling of the kink instability in the blazar emission region based on relativistic MHD (RMHD) simulations. We find that the kink instability may give rise to strong flares with polarization angle (PA) swings or weak flares with polarization fluctuations, depending on the initial magnetic topology and magnetization. These findings are consistent with observations. Compared with the shock model, the kink model generates polarization signatures that are in better agreement with the general polarization observations. Therefore, we suggest that kink instabilities may widely exist in the jet environment and provide an efficient way to convert the magnetic energy and produce multiwavelength flares and polarization variations.
Institute of Scientific and Technical Information of China (English)
无
2010-01-01
A parallel algorithm and code MVFT(multi-viscous-fluid and turbulence) of large-eddy simulation(LES) is developed from our MVPPM(multi-viscous-fluid piecewise parabolic method),and performed to solve the multi compressible Navier-Stokes(N-S) equations.The effect of the unresolved subgrid-scale(SGS) motions on the large scales is represented by different SGS stress models in LES.A Richtmyer-Meshkov instability experiment of the evolution of a rectangular block of SF6,which occupies half of the height of the shock tube test section,following the interaction with a planar shock wave,is numerically and exhaustively simulated by this code.The comparison between experimental and simulated images of the evolving SF6 block shows that they are consistent.The numerical simulations reproduce the complex developing process of SF6 block,which grows overturningly.The geometric quantities that characterize the extents of SF6 block are also compared in detail between numerical simulations and experiment with good agreements between them,a quantitative demonstration of the developing law of SF6 block.There is an evident discrepancy between the three numerical simulations for the maximum position of the right edge of block at the late stage,because the right interface grows complicated and the dissipation is different for different SGS models.The SGS turbulent dissipation,molecular viscosity dissipation and SGS turbulent kinetic energy have been studied and analyzed.They have a similar distribution to the large eddy structures.The SGS turbulent dissipation is much greater than the molecular viscosity dissipation;the SGS turbulent dissipation of Vreman model is smaller than the Smagorinsky model.In general,the simulated results of Vreman SGS model are better compared with the dynamic viscosity and Smagorinsky SGS model.The vorticity and circulation deposition on the block interface have also been investigated.
Large-eddy-simulation of 3-dimensional Rayleigh-Taylor instability in incompressible fluids
Institute of Scientific and Technical Information of China (English)
WANG; Lili
2002-01-01
［1］Sharp, D. H., An overview of Rayleigh-Taylor instability, Physica D, 1984, 12: 3-18.［2］Baker, G. R., Meiron, D. I., Orszag, S. A., Vortex simulation of the Rayleigh-Taylor instability, Phys. Fluids, 1980, 23: 1485-1490.［3］Tryggvason, G., Numerical simulations of the Rayleigh-Taylor instability, J. Comput. Phys., 1988, 75: 253-282.［4］Mulder, W., Osher, S., Sethian, J., Computing interface motion in compressible gas dynamics, J. Comput. Phys., 1992, 100: 209-228.［5］Osher, S., Sethian, J., Fronts propagating with curvature-dependent speed: algorithms based on Hamilton-Jacobi formulations, J. Compput. Phys., 1988, 79(1): 12-49.［6］Li, X. L., Study of three-dimensional Rayleigh-Taylor instability in compressible fluids through level set method and parallel computation, Phys. Fluids, 1993, A(5): 1904-1913.［7］Holmes, R. L, Grove, J. W., Sharp, D. H., Numerical investigation of Richtmyer-Meshkov instability using front tracking, J. Fluid Mech., 1995, 301: 51-64.［8］Gardner, C., Glimm, J., McBryan, O. et al., The dynamics of bubble growth for Rayleigh-Taylor unstable interfaces, Phys. Fluids, 1988, 31: 447-465.［9］He Xiaoyi, Chen Shiyi, Zhang Raoyang, A lattice Boltzmann scheme for incompressible multiphase flow and its application in simulation of Rayleigh-Taylor instability, J. Comput Phys., 1999, 152: 642-663.［10］Li, X. L., Jin, B. X., Glimm, J., Numerical study for the three-dimensional Rayleigh-Taylor instability through the TVD/AC scheme and parallel computation, J. Comput. Phys., 1996, 126: 343-355.［11］Taylor, G. I., The stability of liquid surface when accelerated in a direction perpendicular to their planes, I, Proc. Roy. Soc., London, 1950, A201: 192-196.［12］Abarzhi, S. I., Stable steady flow in the Rayleigh-Taylor instability, Phs. Rev. Lett., 1998, 81: 337-340.［13］Zhang, Q., The motion of single-mode Rayleigh-Taylor unstable interfaces, IMPACT Comput. Sci. Eng., 1991, 3: 277-389.［14］Deardorff. J. W
Numerical simulations of evaporative instabilities in sessile drops of ethanol on heated substrates
Semenov, Sergey; Carle, Florian; Medale, Marc; Brutin, David
2015-11-01
The work is focussed on numerical simulations of thermo-convective instabilities in evaporating pinned sessile droplets of ethanol on heated substrates. Computed evaporation rate of a droplet is validated against parabolic flight experiments and semi-empirical theory presented here. To the best authors' knowledge, this is the first study which combines theoretical, experimental and computational approaches in convective evaporation of sessile droplets. The influence of gravity level on evaporation rate and contributions of different mechanisms of vapor transport (diffusion, Stefan flow, natural convection) are shown. The qualitative difference (in terms of developing thermo-convective instabilities) between steady-state and unsteady numerical approaches is demonstrated.
Necas, A.; Tajima, T.; Nicks, S.; Magee, R.; Clary, R.; Roche, T.; Tri Alpha Energy Team
2016-10-01
In Tri Alpha Energy's C-2U experiment, advanced beam-driven field-reversed configuration (FRC) plasmas were sustained via tangential neutral beam injection. The dominant fast ion population made a dramatic impact on the overall plasma performance. To explain an experimentally observed anomalous neutron signal (100x thermonuclear), we use EPOCH PIC code to simulate possible beam driven non-destructive instabilities that transfer energy from fast ions to the plasma, causing phase space bunching. We propose that the hydrogen beam ion population drives collective modes in the deuterium target plasma, giving rise to the instability and increased fusion rate. The instability changes character from electrostatic in the low beta edge to fully electromagnetic in the core, with an associated reduction in growth rates. The DD reactivity enhancement is calculated using a two-body correlation function and compared to the experimentally observed neutron yield. The high-energy tails in the distributions of the plasma deuterons and beam protons are observed via a mass-resolving Neutral Particle Analyzer (NPA) diagnostic. This observation is qualitatively consistent with EPOCH simulation of the beam-plasma instability.
A computer code to simulate X-ray imaging techniques
Energy Technology Data Exchange (ETDEWEB)
Duvauchelle, Philippe E-mail: philippe.duvauchelle@insa-lyon.fr; Freud, Nicolas; Kaftandjian, Valerie; Babot, Daniel
2000-09-01
A computer code was developed to simulate the operation of radiographic, radioscopic or tomographic devices. The simulation is based on ray-tracing techniques and on the X-ray attenuation law. The use of computer-aided drawing (CAD) models enables simulations to be carried out with complex three-dimensional (3D) objects and the geometry of every component of the imaging chain, from the source to the detector, can be defined. Geometric unsharpness, for example, can be easily taken into account, even in complex configurations. Automatic translations or rotations of the object can be performed to simulate radioscopic or tomographic image acquisition. Simulations can be carried out with monochromatic or polychromatic beam spectra. This feature enables, for example, the beam hardening phenomenon to be dealt with or dual energy imaging techniques to be studied. The simulation principle is completely deterministic and consequently the computed images present no photon noise. Nevertheless, the variance of the signal associated with each pixel of the detector can be determined, which enables contrast-to-noise ratio (CNR) maps to be computed, in order to predict quantitatively the detectability of defects in the inspected object. The CNR is a relevant indicator for optimizing the experimental parameters. This paper provides several examples of simulated images that illustrate some of the rich possibilities offered by our software. Depending on the simulation type, the computation time order of magnitude can vary from 0.1 s (simple radiographic projection) up to several hours (3D tomography) on a PC, with a 400 MHz microprocessor. Our simulation tool proves to be useful in developing new specific applications, in choosing the most suitable components when designing a new testing chain, and in saving time by reducing the number of experimental tests.
Gamma ray transport simulations using SGaRD code
Directory of Open Access Journals (Sweden)
Humbert Philippe
2017-01-01
Full Text Available SGaRD (Spectroscopy, Gamma rays, Rapid, Deterministic code is used for the fast calculation of the gamma-ray spectrum, produced by a spherical shielded source and measured by a detector. The photon source lines originate from the radioactive decay of the unstable isotopes. The leakage spectrum is separated in two parts: the uncollided component is transported by ray tracing, and the scattered component is calculated using a multigroup discrete ordinates method. The pulse height spectrum is then simulated by folding the leakage spectrum with the detector response function, which is precalculated for each considered detector type. An application to the simulation of the gamma spectrum produced by a natural uranium ball coated with plexiglass and measured using a NaI detector is presented. The SGaRD code is also used to infer the dimensions of a one-dimensional model of a shielded gamma ray source. The method is based on the simulation of the uncollided leakage current of discrete gamma lines that are produced by nuclear decay. The material thicknesses are computed with SGaRD using a fast ray-tracing algorithm embedded in a nonlinear multidimensional iterative optimization procedure that minimizes the error metric between calculated and measured signatures.
Axisymmetric Plume Simulations with NASA's DSMC Analysis Code
Stewart, B. D.; Lumpkin, F. E., III
2012-01-01
A comparison of axisymmetric Direct Simulation Monte Carlo (DSMC) Analysis Code (DAC) results to analytic and Computational Fluid Dynamics (CFD) solutions in the near continuum regime and to 3D DAC solutions in the rarefied regime for expansion plumes into a vacuum is performed to investigate the validity of the newest DAC axisymmetric implementation. This new implementation, based on the standard DSMC axisymmetric approach where the representative molecules are allowed to move in all three dimensions but are rotated back to the plane of symmetry by the end of the move step, has been fully integrated into the 3D-based DAC code and therefore retains all of DAC s features, such as being able to compute flow over complex geometries and to model chemistry. Axisymmetric DAC results for a spherically symmetric isentropic expansion are in very good agreement with a source flow analytic solution in the continuum regime and show departure from equilibrium downstream of the estimated breakdown location. Axisymmetric density contours also compare favorably against CFD results for the R1E thruster while temperature contours depart from equilibrium very rapidly away from the estimated breakdown surface. Finally, axisymmetric and 3D DAC results are in very good agreement over the entire plume region and, as expected, this new axisymmetric implementation shows a significant reduction in computer resources required to achieve accurate simulations for this problem over the 3D simulations.
Large-Eddy Simulation Code Developed for Propulsion Applications
DeBonis, James R.
2003-01-01
A large-eddy simulation (LES) code was developed at the NASA Glenn Research Center to provide more accurate and detailed computational analyses of propulsion flow fields. The accuracy of current computational fluid dynamics (CFD) methods is limited primarily by their inability to properly account for the turbulent motion present in virtually all propulsion flows. Because the efficiency and performance of a propulsion system are highly dependent on the details of this turbulent motion, it is critical for CFD to accurately model it. The LES code promises to give new CFD simulations an advantage over older methods by directly computing the large turbulent eddies, to correctly predict their effect on a propulsion system. Turbulent motion is a random, unsteady process whose behavior is difficult to predict through computer simulations. Current methods are based on Reynolds-Averaged Navier- Stokes (RANS) analyses that rely on models to represent the effect of turbulence within a flow field. The quality of the results depends on the quality of the model and its applicability to the type of flow field being studied. LES promises to be more accurate because it drastically reduces the amount of modeling necessary. It is the logical step toward improving turbulent flow predictions. In LES, the large-scale dominant turbulent motion is computed directly, leaving only the less significant small turbulent scales to be modeled. As part of the prediction, the LES method generates detailed information on the turbulence itself, providing important information for other applications, such as aeroacoustics. The LES code developed at Glenn for propulsion flow fields is being used to both analyze propulsion system components and test improved LES algorithms (subgrid-scale models, filters, and numerical schemes). The code solves the compressible Favre-filtered Navier- Stokes equations using an explicit fourth-order accurate numerical scheme, it incorporates a compressible form of
Liu, K.; Min, K.; Gary, S. P.; Wang, X.
2016-12-01
Linear dispersion analyses and two-dimensional electromagnetic particle-in-cell simulations are performed to study the kinetic plasma instabilities driven by a proton velocity ring with parameters (e.g., ring speed 10vA where vA is the Alfvén speed) relevant to the pickup ions in the distant solar wind. The results show that, besides the commonly expected Alfvén cyclotron instability with maximum growth at parallel propagation, mirror mode and ion Bernstein modes at oblique propagations are also unstable. While the enhanced waves from the Alfvén cyclotron instability mainly lead to pitch angle scattering of the ring protons, the other modes scatter the protons differently. The results also have implications for the pickup ions in the outer heliosheath.
Linear Simulations of the Cylindrical Richtmyer-Meshkov Instability in Hydrodynamics and MHD
Gao, Song
2013-05-01
The Richtmyer-Meshkov instability occurs when density-stratified interfaces are impulsively accelerated, typically by a shock wave. We present a numerical method to simulate the Richtmyer-Meshkov instability in cylindrical geometry. The ideal MHD equations are linearized about a time-dependent base state to yield linear partial differential equations governing the perturbed quantities. Convergence tests demonstrate that second order accuracy is achieved for smooth flows, and the order of accuracy is between first and second order for flows with discontinuities. Numerical results are presented for cases of interfaces with positive Atwood number and purely azimuthal perturbations. In hydrodynamics, the Richtmyer-Meshkov instability growth of perturbations is followed by a Rayleigh-Taylor growth phase. In MHD, numerical results indicate that the perturbations can be suppressed for sufficiently large perturbation wavenumbers and magnetic fields.
Energy Technology Data Exchange (ETDEWEB)
Ghizzo, A. [Institut Jean Lamour UMR 7163, Université de Lorraine, BP 239 F-54506 Vandoeuvre les Nancy (France)
2013-08-15
The saturation of the Weibel instability in the relativistic regime is investigated within the Hamiltonian reduction technique based on the multistream approach developed in paper I in the linear case and in paper II for the nonlinear saturation. In this work, the study is compared with results obtained by full kinetic 1D2V Vlasov-Maxwell simulations based on a semi-Lagrangian technique. For a temperature anisotropy, qualitatively different regimes are realized depending on the excitation of the longitudinal (plasma) electric field, in contrast with the existing theories of the Weibel instability based on their purely transverse characters. The emphasis here is on gaining a better understanding of the nonlinear aspects of the Weibel instability. The multistream model offers an alternate way to make calculations or numerical experiments more tractable, when only a few moments of the velocity distribution of the plasma are considered.
Energy Technology Data Exchange (ETDEWEB)
Brunner, S. [Centre de Recherches en Physique des Plasmas, Association Euratom-Confédération Suisse, Ecole Polytechnique Fédérale de Lausanne, Lausanne, (Switzerland); Berger, R. L. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Cohen, B. I. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Hausammann, L. [Centre de Recherches en Physique des Plasmas, Association Euratom-Confédération Suisse, Ecole Polytechnique Fédérale de Lausanne, Lausanne, (Switzerland); Valeo, E. J. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
2014-10-01
Kinetic Vlasov simulations of one-dimensional finite amplitude Electron Plasma Waves are performed in a multi-wavelength long system. A systematic study of the most unstable linear sideband mode, in particular its growth rate γ and quasi- wavenumber δk, is carried out by scanning the amplitude and wavenumber of the initial wave. Simulation results are successfully compared against numerical and analytical solutions to the reduced model by Kruer et al. [Phys. Rev. Lett. 23, 838 (1969)] for the Trapped Particle Instability (TPI). A model recently suggested by Dodin et al. [Phys. Rev. Lett. 110, 215006 (2013)], which in addition to the TPI accounts for the so-called Negative Mass Instability because of a more detailed representation of the trapped particle dynamics, is also studied and compared with simulations.
Computer code for the atomistic simulation of lattice defects and dynamics. [COMENT code
Energy Technology Data Exchange (ETDEWEB)
Schiffgens, J.O.; Graves, N.J.; Oster, C.A.
1980-04-01
This document has been prepared to satisfy the need for a detailed, up-to-date description of a computer code that can be used to simulate phenomena on an atomistic level. COMENT was written in FORTRAN IV and COMPASS (CDC assembly language) to solve the classical equations of motion for a large number of atoms interacting according to a given force law, and to perform the desired ancillary analysis of the resulting data. COMENT is a dual-purpose intended to describe static defect configurations as well as the detailed motion of atoms in a crystal lattice. It can be used to simulate the effect of temperature, impurities, and pre-existing defects on radiation-induced defect production mechanisms, defect migration, and defect stability.
Simulation of Code Spectrum and Code Flow of Cultured Neuronal Networks.
Tamura, Shinichi; Nishitani, Yoshi; Hosokawa, Chie; Miyoshi, Tomomitsu; Sawai, Hajime
2016-01-01
It has been shown that, in cultured neuronal networks on a multielectrode, pseudorandom-like sequences (codes) are detected, and they flow with some spatial decay constant. Each cultured neuronal network is characterized by a specific spectrum curve. That is, we may consider the spectrum curve as a "signature" of its associated neuronal network that is dependent on the characteristics of neurons and network configuration, including the weight distribution. In the present study, we used an integrate-and-fire model of neurons with intrinsic and instantaneous fluctuations of characteristics for performing a simulation of a code spectrum from multielectrodes on a 2D mesh neural network. We showed that it is possible to estimate the characteristics of neurons such as the distribution of number of neurons around each electrode and their refractory periods. Although this process is a reverse problem and theoretically the solutions are not sufficiently guaranteed, the parameters seem to be consistent with those of neurons. That is, the proposed neural network model may adequately reflect the behavior of a cultured neuronal network. Furthermore, such prospect is discussed that code analysis will provide a base of communication within a neural network that will also create a base of natural intelligence.
GOTHIC code simulation of thermal stratification in POOLEX facility
Energy Technology Data Exchange (ETDEWEB)
Li, H.; Kudinov, P. (Royal Institute of Technology (KTH) (Sweden))
2009-07-15
Pressure suppression pool is an important element of BWR containment. It serves as a heat sink and steam condenser to prevent containment pressure buildup during loss of coolant accident or safety relief valve opening during normal operations of a BWR. Insufficient mixing in the pool, in case of low mass flow rate of steam, can cause development of thermal stratification and reduction of pressure suppression pool capacity. For reliable prediction of mixing and stratification phenomena validation of simulation tools has to be performed. Data produced in POOLEX/PPOOLEX facility at Lappeenranta University of Technology about development of thermal stratification in a large scale model of a pressure suppression pool is used for GOTHIC lumped and distributed parameter validation. Sensitivity of GOTHIC solution to different boundary conditions and grid convergence study for 2D simulations of POOLEX STB-20 experiment are performed in the present study. CFD simulation was carried out with FLUENT code in order to get additional insights into physics of stratification phenomena. In order to support development of experimental procedures for new tests in the PPOOLEX facility lumped parameter pre-test GOTHIC simulations were performed. Simulations show that drywell and wetwell pressures can be kept within safety margins during a long transient necessary for development of thermal stratification. (au)
Movahed, Pooya
High-speed flows are prone to hydrodynamic interfacial instabilities that evolve to turbulence, thereby intensely mixing different fluids and dissipating energy. The lack of knowledge of these phenomena has impeded progress in a variety of disciplines. In science, a full understanding of mixing between heavy and light elements after the collapse of a supernova and between adjacent layers of different density in geophysical (atmospheric and oceanic) flows remains lacking. In engineering, the inability to achieve ignition in inertial fusion and efficient combustion constitute further examples of this lack of basic understanding of turbulent mixing. In this work, my goal is to develop accurate and efficient numerical schemes and employ them to study compressible turbulence and mixing generated by interactions between shocked (Richtmyer-Meshkov) and accelerated (Rayleigh-Taylor) interfaces, which play important roles in high-energy-density physics environments. To accomplish my goal, a hybrid high-order central/discontinuity-capturing finite difference scheme is first presented. The underlying principle is that, to accurately and efficiently represent both broadband motions and discontinuities, non-dissipative methods are used where the solution is smooth, while the more expensive and dissipative capturing schemes are applied near discontinuous regions. Thus, an accurate numerical sensor is developed to discriminate between smooth regions, shocks and material discontinuities, which all require a different treatment. The interface capturing approach is extended to central differences, such that smooth distributions of varying specific heats ratio can be simulated without generating spurious pressure oscillations. I verified and validated this approach against a stringent suite of problems including shocks, interfaces, turbulence and two-dimensional single-mode Richtmyer-Meshkov instability simulations. The three-dimensional code is shown to scale well up to 4000 cores
Merlin, Emiliano; Buonomo, Umberto; Grassi, Tommaso; Piovan, Lorenzo; Chiosi, Cesare
2009-01-01
We present EvoL, the new release of the Padova N-body code for cosmological simulations of galaxy formation and evolution. In this paper, the basic Tree + SPH code is presented and analysed, together with an overview on the software architectures. EvoL is a flexible parallel Fortran95 code, specifically designed for simulations of cosmological structure formation on cluster, galactic and sub-galactic scales. EvoL is a fully Lagrangian self-adaptive code, based on the classical Oct-tree and on...
Cook, J W S; Dendy, R O
2010-01-01
We present particle-in-cell (PIC) simulations of minority energetic protons in deuterium plasmas, which demonstrate a collective instability responsible for emission near the lower hybrid frequency and its harmonics. The simulations capture the lower hybrid drift instability in a regime relevant to tokamak fusion plasmas, and show further that the excited electromagnetic fields collectively and collisionlessly couple free energy from the protons to directed electron motion. This results in an asymmetric tail antiparallel to the magnetic field. We focus on obliquely propagating modes under conditions approximating the outer mid-plane edge in a large tokamak, through which there pass confined centrally born fusion products on banana orbits that have large radial excursions. A fully self-consistent electromagnetic relativistic PIC code representing all vector field quantities and particle velocities in three dimensions as functions of a single spatial dimension is used to model this situation, by evolving the in...
Riquelme, Mario; Verscharen, Daniel
2014-01-01
We use particle-in-cell (PIC) simulations to study the nonlinear evolution of ion velocity space instabilities in an idealized problem in which a background velocity shear continuously amplifies the magnetic field. We simulate the astrophysically relevant regime where the shear timescale is long compared to the ion cyclotron period, and the plasma beta is ~ 1-100. The background field amplification in our calculation is meant to mimic processes such as turbulent fluctuations or MHD-scale instabilities. The field amplification continuously drives a pressure anisotropy with the perpendicular pressure larger than the parallel pressure, and the plasma becomes unstable to the mirror and ion cyclotron instabilities. In all cases, the nonlinear state is dominated by the mirror instability, not the ion cyclotron instability, and the plasma pressure anisotropy saturates near the threshold for the linear mirror instability. The magnetic field fluctuations initially undergo exponential growth but saturate in a secular p...
The GBS code for tokamak scrape-off layer simulations
Halpern, F. D.; Ricci, P.; Jolliet, S.; Loizu, J.; Morales, J.; Mosetto, A.; Musil, F.; Riva, F.; Tran, T. M.; Wersal, C.
2016-06-01
We describe a new version of GBS, a 3D global, flux-driven plasma turbulence code to simulate the turbulent dynamics in the tokamak scrape-off layer (SOL), superseding the code presented by Ricci et al. (2012) [14]. The present work is driven by the objective of studying SOL turbulent dynamics in medium size tokamaks and beyond with a high-fidelity physics model. We emphasize an intertwining framework of improved physics models and the computational improvements that allow them. The model extensions include neutral atom physics, finite ion temperature, the addition of a closed field line region, and a non-Boussinesq treatment of the polarization drift. GBS has been completely refactored with the introduction of a 3-D Cartesian communicator and a scalable parallel multigrid solver. We report dramatically enhanced parallel scalability, with the possibility of treating electromagnetic fluctuations very efficiently. The method of manufactured solutions as a verification process has been carried out for this new code version, demonstrating the correct implementation of the physical model.
The GBS code for tokamak scrape-off layer simulations
Energy Technology Data Exchange (ETDEWEB)
Halpern, F.D., E-mail: federico.halpern@epfl.ch [Ecole Polytechnique Fédérale de Lausanne (EPFL), Swiss Plasma Center (SPC), CH-1015 Lausanne (Switzerland); Ricci, P.; Jolliet, S. [Ecole Polytechnique Fédérale de Lausanne (EPFL), Swiss Plasma Center (SPC), CH-1015 Lausanne (Switzerland); Loizu, J. [Max-Planck-Institut für Plasmaphysik, D-17491, Greifswald (Germany); Morales, J.; Mosetto, A.; Musil, F.; Riva, F.; Tran, T.M.; Wersal, C. [Ecole Polytechnique Fédérale de Lausanne (EPFL), Swiss Plasma Center (SPC), CH-1015 Lausanne (Switzerland)
2016-06-15
We describe a new version of GBS, a 3D global, flux-driven plasma turbulence code to simulate the turbulent dynamics in the tokamak scrape-off layer (SOL), superseding the code presented by Ricci et al. (2012) [14]. The present work is driven by the objective of studying SOL turbulent dynamics in medium size tokamaks and beyond with a high-fidelity physics model. We emphasize an intertwining framework of improved physics models and the computational improvements that allow them. The model extensions include neutral atom physics, finite ion temperature, the addition of a closed field line region, and a non-Boussinesq treatment of the polarization drift. GBS has been completely refactored with the introduction of a 3-D Cartesian communicator and a scalable parallel multigrid solver. We report dramatically enhanced parallel scalability, with the possibility of treating electromagnetic fluctuations very efficiently. The method of manufactured solutions as a verification process has been carried out for this new code version, demonstrating the correct implementation of the physical model.
Riquelme, Mario; Verscharen, Daniel
2016-01-01
In low-collisionality plasmas, velocity-space instabilities are a key mechanism providing an effective collisionality for the plasma. We use particle-in-cell (PIC) simulations to study the interplay between electron and ion-scale velocity-space instabilities and their effect on electron pressure anisotropy, viscous heating, and thermal conduction. The adiabatic invariance of the magnetic moment in low-collisionality plasmas leads to pressure anisotropy, $p_{\\perp,j} > p_{||,j}$, if the magnetic field $\\vec{B}$ is amplified ($p_{\\perp,j}$ and $p_{||,j}$ denote the pressure of species $j$ [electron, ion] perpendicular and parallel to $\\vec{B}$). If the resulting anisotropy is large enough, it can in turn trigger small-scale plasma instabilities. Our PIC simulations explore the nonlinear regime of the mirror, ion-cyclotron, and electron whistler instabilities, through continuous amplification of the magnetic field $|\\vec{B}|$ by an imposed shear in the plasma. In the regime $1 \\lesssim \\beta_j \\lesssim 20$ ($\\be...
EVIDENCE OF ACTIVE MHD INSTABILITY IN EULAG-MHD SIMULATIONS OF SOLAR CONVECTION
Energy Technology Data Exchange (ETDEWEB)
Lawson, Nicolas; Strugarek, Antoine; Charbonneau, Paul, E-mail: nicolas.laws@gmail.ca, E-mail: strugarek@astro.umontreal.ca, E-mail: paulchar@astro.umontreal.ca [Département de Physique, Université de Montréal, C.P. 6128 Succ. Centre-ville, Montréal, Qc H3C 3J7 (Canada)
2015-11-10
We investigate the possible development of magnetohydrodynamical instabilities in the EULAG-MHD “millennium simulation” of Passos and Charbonneau. This simulation sustains a large-scale magnetic cycle characterized by solar-like polarity reversals taking place on a regular multidecadal cadence, and in which zonally oriented bands of strong magnetic fields accumulate below the convective layers, in response to turbulent pumping from above in successive magnetic half-cycles. Key aspects of this simulation include low numerical dissipation and a strongly sub-adiabatic fluid layer underlying the convectively unstable layers corresponding to the modeled solar convection zone. These properties are conducive to the growth and development of two-dimensional instabilities that are otherwise suppressed by stronger dissipation. We find evidence for the action of a non-axisymmetric magnetoshear instability operating in the upper portions of the stably stratified fluid layers. We also investigate the possibility that the Tayler instability may be contributing to the destabilization of the large-scale axisymmetric magnetic component at high latitudes. On the basis of our analyses, we propose a global dynamo scenario whereby the magnetic cycle is driven primarily by turbulent dynamo action in the convecting layers, but MHD instabilities accelerate the dissipation of the magnetic field pumped down into the overshoot and stable layers, thus perhaps significantly influencing the magnetic cycle period. Support for this scenario is found in the distinct global dynamo behaviors observed in an otherwise identical EULAG-MHD simulations, using a different degree of sub-adiabaticity in the stable fluid layers underlying the convection zone.
Khomenko, E; de Vicente, A; Collados, M; Luna, M
2014-01-01
We study the Rayleigh-Taylor instability (RTI) at a prominence-corona transition region in a non-linear regime. Our aim is to understand how the presence of neutral atoms in the prominence plasma influences the instability growth rate, and the evolution of velocity, magnetic field vector and thermodynamic parameters of turbulent drops. We perform 2.5D numerical simulations of the instability initiated by a multi-mode perturbation at the corona-prominence interface using a single-fluid MHD approach including a generalized Ohm's law. The initial equilibrium configuration is purely hydrostatic and contains a homogeneous horizontal magnetic field forming an angle with the direction in which the plasma is perturbed. We analyze simulations with two different orientations of the magnetic field. For each field orientation we compare two simulations, one for the pure MHD case, and one including the ambipolar diffusion in the Ohm's law (AD case). Other than that, both simulations for each field orientation are identica...
Front instabilities and invasiveness of simulated avascular tumors.
Popławski, Nikodem J; Agero, Ubirajara; Gens, J Scott; Swat, Maciej; Glazier, James A; Anderson, Alexander R A
2009-07-01
We study the interface morphology of a 2D simulation of an avascular tumor composed of identical cells growing in an homogeneous healthy tissue matrix (TM), in order to understand the origin of the morphological changes often observed during real tumor growth. We use the Glazier-Graner-Hogeweg model, which treats tumor cells as extended, deformable objects, to study the effects of two parameters: a dimensionless diffusion-limitation parameter defined as the ratio of the tumor consumption rate to the substrate transport rate, and the tumor-TM surface tension. We model TM as a nondiffusing field, neglecting the TM pressure and haptotactic repulsion acting on a real growing tumor; thus, our model is appropriate for studying tumors with highly motile cells, e.g., gliomas. We show that the diffusion-limitation parameter determines whether the growing tumor develops a smooth (noninvasive) or fingered (invasive) interface, and that the sensitivity of tumor morphology to tumor-TM surface tension increases with the size of the dimensionless diffusion-limitation parameter. For large diffusion-limitation parameters, we find a transition (missed in previous work) between dendritic structures, produced when tumor-TM surface tension is high, and seaweed-like structures, produced when tumor-TM surface tension is low. This observation leads to a direct analogy between the mathematics and dynamics of tumors and those observed in nonbiological directional solidification. Our results are also consistent with the biological observation that hypoxia promotes invasive growth of tumor cells by inducing higher levels of receptors for scatter factors that weaken cell-cell adhesion and increase cell motility. These findings suggest that tumor morphology may have value in predicting the efficiency of antiangiogenic therapy in individual patients.
Mahdaoui, O.; Agassant, J.-F.; Laure, P.; Valette, R.; Silva, L.
2007-04-01
The polymer coextrusion process is a new method of sheet metal lining. It allows to substitute lacquers for steel protection in food packaging industry. The coextrusion process may exhibit flow instabilities at the interface between the two polymer layers. The objective of this study is to check the influence of processing and rheology parameters on the instabilities. Finite elements numerical simulations of the coextrusion allow to investigate various stable and instable flow configurations.
Electron proton instability in the CSNS ring
Institute of Scientific and Technical Information of China (English)
WANG Na; QIN Qing; LIU Yu-Dong
2009-01-01
The electron proton(e-p)instability has been observed in many proton accelerators.It will induce transverse beam size blow-up,cause beam loss and restrict the machine performance.Much research work has been done on the causes,dynamics and cures of this instability.A simulation code is developed to study the e-p instability in the ring of the China Spallation Neutron Source(CSNS).
Simulation of spreading with solidification: assessment synthesis of Thema code
Energy Technology Data Exchange (ETDEWEB)
Spindler, B.; Veteau, J.M. [CEA Grenoble, Direction de l' Energie Nucleaire, Dept. de Technologie Nucleaire, Service d' Etudes Thermohydrauliques et Technologiques, 38 (France)
2004-07-01
After a presentation of the models included in THEMA code, which simulates the spreading of a fluid with solidification, the whole assessment calculations are presented. The first series concerns the comparison with analytical or numerical solutions: dam break, conduction for the heat transfer in the substrate, crust growth. The second series concerns the comparison with the CORINE isothermal tests (simulating fluid at low temperature). The third series concerns the CORINE tests with heat transfer. The fourth series concerns the tests with simulating materials at medium or high temperature (RIT, KATS). The fifth series concerns the tests with prototypical materials (COMAS, FARO, VULCANO). Finally the blind simulations of the ECOKATS tests are presented. All the calculations are performed with the same physical models (THEMA version 2.5), without any variable tuning parameter according to the test under consideration. Sensitivity studies concern the influence of the viscosity model in the solidification interval, and for the tests with prototypical materials the inlet temperature and the solid fraction. The relative difference between the calculated and measured spreading areas is generally less than 20 % except for the test with prototypical materials, for which the assessment is not easy due to the large experimental uncertainties. The level of validation of THEMA is considered as satisfactory, taking into account the required accuracy. (authors)
Overview of the Tusas Code for Simulation of Dendritic Solidification
Energy Technology Data Exchange (ETDEWEB)
Trainer, Amelia J. [Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States); Newman, Christopher Kyle [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Francois, Marianne M. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2016-01-07
The aim of this project is to conduct a parametric investigation into the modeling of two dimensional dendrite solidification, using the phase field model. Specifically, we use the Tusas code, which is for coupled heat and phase-field simulation of dendritic solidification. Dendritic solidification, which may occur in the presence of an unstable solidification interface, results in treelike microstructures that often grow perpendicular to the rest of the growth front. The interface may become unstable if the enthalpy of the solid material is less than that of the liquid material, or if the solute is less soluble in solid than it is in liquid, potentially causing a partition [1]. A key motivation behind this research is that a broadened understanding of phase-field formulation and microstructural developments can be utilized for macroscopic simulations of phase change. This may be directly implemented as a part of the Telluride project at Los Alamos National Laboratory (LANL), through which a computational additive manufacturing simulation tool is being developed, ultimately to become part of the Advanced Simulation and Computing Program within the U.S. Department of Energy [2].
Badjin, D A; Manukovskiy, K V; Blinnikov, S I
2015-01-01
We describe our experience of modelling of the radiatively cooling shocks and their thin shells with various numerical tools in different physical and calculational setups. We have found that under certain physical conditions, the circular shaped shells show a strong bending instability and successive fragmentation on Cartesian grids soon after their formation, while remain almost unperturbed when simulated on polar meshes. We explain these results as an interplay of numerical perturbations superimposed by grids not aligned to the flow lines, and a physical Rayleigh--Taylor like instability of the thin shell inner boundary being accelerated during re-estabilshing of pressure balance within and behind the shell after preceding sudden temperature loss. This phenomenon also sets new requirements on further radiatively cooling shocks simulations in order to be physically correct and free of numerical artefacts.
Postural instability and motion sickness in a fixed-based flight simulator.
Stoffregen, T A; Hettinger, L J; Haas, M W; Roe, M M; Smart, L J
2000-01-01
We evaluated the prediction that postural instability would precede the subjective symptoms of motion sickness in a fixed-base flight simulator. Participants sat in a cockpit in a video projection dome and were exposed to optical flow that oscillated in the roll axis with exposure durations typical of flight simulation. The frequencies of oscillation were those that characterize spontaneous postural sway during stance. Head motion was measured prior to and during exposure to imposed optical flow. Of 14 participants, 6 were classified as motion sick, either during or after exposure to the optical oscillation. Prior to the onset of subjective symptoms, head motion among participants who later became sick was significantly greater than among participants who did not become motion sick. We argue that the results support the postural instability theory of motion sickness. Actual or potential applications include the prevention or mitigation of motion sickness in virtual environments.
Energy Technology Data Exchange (ETDEWEB)
Potocki, Mark L [Los Alamos National Laboratory; Hull, Lawrence M [Los Alamos National Laboratory
2010-01-01
The detonation of explosives with thin shells can cause the shells to expand to over 200% strain at strain rates on the order of 10{sup 4} s{sup -1} before failure. Experimental data indicate the development and growth of multiple plastic instabilities lead to the formation of failure and fragmentation in the near periodic pattern. Presented are comparisons of the onset of instabilities from simulations and experimental data. At Los Alamos National Laboratory material models have been evolving for several years to simulate high strain-rate behavior. Our models include the effects of shock heating and damage evolutions as well as failure. The current edition of one of our models uses a tabular EOS, the PTW strength model, a modified Gurson yield surface to compute damage evolution, and a Johnson-Cook failure model. Presented are some of the details of these models. An experiment confirmed the temperature discontinuities.
PIC simulation of a thermal anisotropy-driven Weibel instability in a circular rarefaction wave
Dieckmann, M E; Murphy, G C; Bret, A; Romagnani, L; Kourakis, I; Borghesi, M; Ynnerman, A; Drury, L O'C; 10.1088/1367-2630/14/2/023007
2012-01-01
The expansion of an initially unmagnetized planar rarefaction wave has recently been shown to trigger a thermal anisotropy-driven Weibel instability (TAWI), which can generate magnetic fields from noise levels. It is examined here if the TAWI can also grow in a curved rarefaction wave. The expansion of an initially unmagnetized circular plasma cloud, which consists of protons and hot electrons, into a vacuum is modelled for this purpose with a two-dimensional particle-in-cell (PIC) simulation. It is shown that the momentum transfer from the electrons to the radially accelerating protons can indeed trigger a TAWI. Radial current channels form and the aperiodic growth of a magnetowave is observed, which has a magnetic field that is oriented orthogonal to the simulation plane. The induced electric field implies that the electron density gradient is no longer parallel to the electric field. Evidence is presented here for that this electric field modification triggers a second magnetic instability, which results i...
Self-destructing Spiral Waves: Global Simulations of a Spiral-wave Instability in Accretion Disks
Bae, Jaehan; Nelson, Richard P.; Hartmann, Lee; Richard, Samuel
2016-09-01
We present results from a suite of three-dimensional global hydrodynamic simulations that shows that spiral density waves propagating in circumstellar disks are unstable to the growth of a parametric instability that leads to break down of the flow into turbulence. This spiral wave instability (SWI) arises from a resonant interaction between pairs of inertial waves, or inertial-gravity waves, and the background spiral wave. The development of the instability in the linear regime involves the growth of a broad spectrum of inertial modes, with growth rates on the order of the orbital time, and results in a nonlinear saturated state in which turbulent velocity perturbations are of a similar magnitude to those induced by the spiral wave. The turbulence induces angular momentum transport and vertical mixing at a rate that depends locally on the amplitude of the spiral wave (we obtain a stress parameter α ˜ 5 × 10-4 in our reference model). The instability is found to operate in a wide range of disk models, including those with isothermal or adiabatic equations of state, and in viscous disks where the dimensionless kinematic viscosity ν ≤ 10-5. This robustness suggests that the instability will have applications to a broad range of astrophysical disk-related phenomena, including those in close binary systems, planets embedded in protoplanetary disks (including Jupiter in our own solar system) and FU Orionis outburst models. Further work is required to determine the nature of the instability and to evaluate its observational consequences in physically more complete disk models than we have considered in this paper.
Lower-Hybrid Drift Instability Saturation Mechanisms in One-Dimensional Simulations,
1980-09-19
The linear properties and saturation mechanisms of the lower-hybrid drift instability have been investigated using a one-dimensional particle-hybrid simulation. For low drift velocities (V sub d much less than V sub ti), ion trapping and current relaxation (V sub d approaches limit of 0) are competing processes for stabilization. If the relative electron-ion drift velocity is kept constant in time , ion trapping causes
DEFF Research Database (Denmark)
Hansen, Anders L.; Lund, Erik; Pinho, Silvestre T.
2009-01-01
In this paper a hierarchical FE approach is utilized to simulate delamination in a composite plate loaded in uni-axial compression. Progressive delamination is modelled by use of cohesive interface elements that are automatically embedded. The non-linear problem is solved quasi-statically in which...... the interaction between material degradation and structural instability is solved iteratively. The effect of fibre bridging is studied numerically and in-plane failure is predicted using physically based failure criteria....
Riquelme, Mario A.; Quataert, Eliot; Verscharen, Daniel
2016-06-01
In low-collisionality plasmas, velocity-space instabilities are a key mechanism providing an effective collisionality for the plasma. We use particle-in-cell (PIC) simulations to study the interplay between electron- and ion-scale velocity-space instabilities and their effect on electron pressure anisotropy, viscous heating, and thermal conduction. The adiabatic invariance of the magnetic moment in low-collisionality plasmas leads to pressure anisotropy, {{Δ }}{p}j\\equiv {p}\\perp ,j-{p}\\parallel ,j\\gt 0, if the magnetic field {\\boldsymbol{B}} is amplified ({p}\\perp ,j and {p}\\parallel ,j denote the pressure of species j (electron, ion) perpendicular and parallel to {\\boldsymbol{B}}). If the resulting anisotropy is large enough, it can in turn trigger small-scale plasma instabilities. Our PIC simulations explore the nonlinear regime of the mirror, IC, and electron whistler instabilities, through continuous amplification of the magnetic field | {\\boldsymbol{B}}| by an imposed shear in the plasma. In the regime 1≲ {β }j≲ 20 ({β }j\\equiv 8π {p}j/| {\\boldsymbol{B}}{| }2), the saturated electron pressure anisotropy, {{Δ }}{p}{{e}}/{p}\\parallel ,{{e}}, is determined mainly by the (electron-lengthscale) whistler marginal stability condition, with a modest factor of ˜1.5-2 decrease due to the trapping of electrons into ion-lengthscale mirrors. We explicitly calculate the mean free path of the electrons and ions along the mean magnetic field and provide a simple physical prescription for the mean free path and thermal conductivity in low-collisionality β j ≳ 1 plasmas. Our results imply that velocity-space instabilities likely decrease the thermal conductivity of plasma in the outer parts of massive, hot, galaxy clusters. We also discuss the implications of our results for electron heating and thermal conduction in low-collisionality accretion flows onto black holes, including Sgr A* in the Galactic Center.
Lahaye, Noé; Paci, Alexandre; Smith, Stefan Llewellyn
2016-04-01
We examine the instability of lenticular vortices -- or lenses -- in a stratified rotating fluid. The simplest configuration is one in which the lenses overlay a deep layer and have a free surface, and this can be studied using a two-layer rotating shallow water model. We report results from laboratory experiments and high-resolution direct numerical simulations of the destabilization of vortices with constant potential vorticity, and compare these to a linear stability analysis. The stability properties of the system are governed by two parameters: the typical upper-layer potential vorticity and the size (depth) of the vortex. Good agreement is found between analytical, numerical and experimental results for the growth rate and wavenumber of the instability. The nonlinear saturation of the instability is associated with conversion from potential to kinetic energy and weak emission of gravity waves, giving rise to the formation of coherent vortex multipoles with trapped waves. The impact of flow in the lower layer is examined. In particular, it is shown that the growth rate can be strongly affected and the instability can be suppressed for certain types of weak co-rotating flow.
Self-Destructing Spiral Waves: Global Simulations of a Spiral Wave Instability in Accretion Disks
Bae, Jaehan; Hartmann, Lee; Richard, Samuel
2016-01-01
We present results from a suite of three-dimensional global hydrodynamic simulations which show that spiral density waves propagating in circumstellar disks are unstable to the growth of a parametric instability that leads to break-down of the flow into turbulence. This spiral wave instability (SWI) arises from a resonant interaction between pairs of inertial waves, or inertial-gravity waves, and the background spiral wave. The development of the instability in the linear regime involves the growth of a broad spectrum of inertial modes, with growth rates on the order of the orbital time, and results in a nonlinear saturated state in which turbulent velocity perturbations are of a similar magnitude to those induced by the spiral wave. The turbulence induces angular momentum transport, and vertical mixing, at a rate that depends locally on the amplitude of the spiral wave (we obtain a stress parameter $\\alpha \\sim 5 \\times 10^{-4}$ in our reference model). The instability is found to operate in a wide-range of ...
Large Eddy Simulations of Kelvin Helmholtz instabilities at high Reynolds number stratified flows
Brown, Dana; Goodman, Lou; Raessi, Mehdi
2015-11-01
Simulations of Kelvin Helmholtz Instabilities (KHI) at high Reynolds numbers are performed using the Large Eddy Simulation technique. Reynolds numbers up to 100,000 are achieved using our model. The resulting data set is used to examine the effect of Reynolds number on various statistics, including dissipation flux coefficient, turbulent kinetic energy budget, and Thorpe length scale. It is shown that KHI are qualitatively different at high Re, up to and including the onset of vortex pairing and billow collapse and quantitatively different afterward. The effect of Richardson number is also examined. The results are discussed as they apply to ocean experiments.
Neoclassical Simulation of Tokamak Plasmas using Continuum Gyrokinetc Code TEMPEST
Energy Technology Data Exchange (ETDEWEB)
Xu, X Q
2007-11-09
We present gyrokinetic neoclassical simulations of tokamak plasmas with self-consistent electric field for the first time using a fully nonlinear (full-f) continuum code TEMPEST in a circular geometry. A set of gyrokinetic equations are discretized on a five dimensional computational grid in phase space. The present implementation is a Method of Lines approach where the phase-space derivatives are discretized with finite differences and implicit backwards differencing formulas are used to advance the system in time. The fully nonlinear Boltzmann model is used for electrons. The neoclassical electric field is obtained by solving gyrokinetic Poisson equation with self-consistent poloidal variation. With our 4D ({psi}, {theta}, {epsilon}, {mu}) version of the TEMPEST code we compute radial particle and heat flux, the Geodesic-Acoustic Mode (GAM), and the development of neoclassical electric field, which we compare with neoclassical theory with a Lorentz collision model. The present work provides a numerical scheme and a new capability for self-consistently studying important aspects of neoclassical transport and rotations in toroidal magnetic fusion devices.
EMMA: an AMR cosmological simulation code with radiative transfer
Aubert, Dominique; Ocvirk, Pierre
2015-01-01
EMMA is a cosmological simulation code aimed at investigating the reionization epoch. It handles simultaneously collisionless and gas dynamics, as well as radiative transfer physics using a moment-based description with the M1 approximation. Field quantities are stored and computed on an adaptive 3D mesh and the spatial resolution can be dynamically modified based on physically-motivated criteria. Physical processes can be coupled at all spatial and temporal scales. We also introduce a new and optional approximation to handle radiation : the light is transported at the resolution of the non-refined grid and only once the dynamics have been fully updated, whereas thermo-chemical processes are still tracked on the refined elements. Such an approximation reduces the overheads induced by the treatment of radiation physics. A suite of standard tests are presented and passed by EMMA, providing a validation for its future use in studies of the reionization epoch. The code is parallel and is able to use graphics proc...
SIMULATE-4 multigroup nodal code with microscopic depletion model
Energy Technology Data Exchange (ETDEWEB)
Bahadir, T. [Studsvik Scandpower, Inc., Newton, MA (United States); Lindahl, St.O. [Studsvik Scandpower AB, Vasteras (Sweden); Palmtag, S.P. [Studsvik Scandpower, Inc., Idaho Falls, ID (United States)
2005-07-01
SIMULATE-4 is a three-dimensional multigroup analytical nodal code with microscopic depletion capability. It has been developed employing 'first principal models' thus avoiding ad hoc approximations. The multigroup diffusion equations or, optionally, the simplified P{sub 3} equations are solved. Cross sections are described by a hybrid microscopic-macroscopic model that includes approximately 50 heavy nuclides and fission products. Heterogeneities in the axial direction of an assembly are treated systematically. Radially, the assembly is divided into heterogeneous sub-meshes, thereby overcoming the shortcomings of spatially-averaged assembly cross sections and discontinuity factors generated with zero net-current boundary conditions. Numerical tests against higher order transport methods and critical experiments show substantial improvements compared to results of existing nodal models. (authors)
Simulating Turbulence Using the Astrophysical Discontinuous Galerkin Code TENET
Bauer, Andreas; Springel, Volker; Chandrashekar, Praveen; Pakmor, Rüdiger; Klingenberg, Christian
2016-01-01
In astrophysics, the two main methods traditionally in use for solving the Euler equations of ideal fluid dynamics are smoothed particle hydrodynamics and finite volume discretization on a stationary mesh. However, the goal to efficiently make use of future exascale machines with their ever higher degree of parallel concurrency motivates the search for more efficient and more accurate techniques for computing hydrodynamics. Discontinuous Galerkin (DG) methods represent a promising class of methods in this regard, as they can be straightforwardly extended to arbitrarily high order while requiring only small stencils. Especially for applications involving comparatively smooth problems, higher-order approaches promise significant gains in computational speed for reaching a desired target accuracy. Here, we introduce our new astrophysical DG code TENET designed for applications in cosmology, and discuss our first results for 3D simulations of subsonic turbulence. We show that our new DG implementation provides ac...
VISRAD, 3-D Target Design and Radiation Simulation Code
Golovkin, Igor; Macfarlane, Joseph; Golovkina, Viktoriya
2016-10-01
The 3-D view factor code VISRAD is widely used in designing HEDP experiments at major laser and pulsed-power facilities, including NIF, OMEGA, OMEGA-EP, ORION, LMJ, Z, and PLX. It simulates target designs by generating a 3-D grid of surface elements, utilizing a variety of 3-D primitives and surface removal algorithms, and can be used to compute the radiation flux throughout the surface element grid by computing element-to-element view factors and solving power balance equations. Target set-up and beam pointing are facilitated by allowing users to specify positions and angular orientations using a variety of coordinates systems (e.g., that of any laser beam, target component, or diagnostic port). Analytic modeling for laser beam spatial profiles for OMEGA DPPs and NIF CPPs is used to compute laser intensity profiles throughout the grid of surface elements. We will discuss recent improvements to the software package and plans for future developments.
Fu, X. R.; Cowee, M. M.; Liu, K.; Peter Gary, S.; Winske, D.
2014-04-01
The velocity space scattering of an anisotropic electron beam (T⊥b/T∥b>1) flowing along a background magnetic field B0 through a cold plasma is investigated using both linear theory and 2D particle-in-cell simulations. Here, ⊥ and ∥ represent the directions perpendicular and parallel to B0, respectively. In this scenario, we find that two primary instabilities contribute to the scattering in electron pitch angle: an electrostatic electron beam instability and a predominantly parallel-propagating electromagnetic whistler anisotropy instability. Our results show that at relative beam densities nb/ne≤0.05 and beam temperature anisotropies Tb ⊥/Tb ∥≤25, the electrostatic beam instability grows much faster than the whistler instabilities for a reasonably fast hot beam. The enhanced fluctuating fields from the beam instability scatter the beam electrons, slowing their average speed and increasing their parallel temperature, thereby increasing their pitch angles. In an inhomogeneous magnetic field, such as the geomagnetic field, this could result in beam electrons scattered out of the loss cone. After saturation of the electrostatic instability, the parallel-propagating whistler anisotropy instability shows appreciable growth, provided that the beam density and late-time anisotropy are sufficiently large. Although the whistler anisotropy instability acts to pitch-angle scatter the electrons, reducing perpendicular energy in favor of parallel energy, these changes are weak compared to the pitch-angle increases resulting from the deceleration of the beam due to the electrostatic instability.
The Plasma Simulation Code: A modern particle-in-cell code with patch-based load-balancing
Germaschewski, Kai; Fox, William; Abbott, Stephen; Ahmadi, Narges; Maynard, Kristofor; Wang, Liang; Ruhl, Hartmut; Bhattacharjee, Amitava
2016-08-01
This work describes the Plasma Simulation Code (PSC), an explicit, electromagnetic particle-in-cell code with support for different order particle shape functions. We review the basic components of the particle-in-cell method as well as the computational architecture of the PSC code that allows support for modular algorithms and data structure in the code. We then describe and analyze in detail a distinguishing feature of PSC: patch-based load balancing using space-filling curves which is shown to lead to major efficiency gains over unbalanced methods and a previously used simpler balancing method.
Merlin, Emiliano; Grassi, Tommaso; Piovan, Lorenzo; Chiosi, Cesare
2009-01-01
We present EvoL, the new release of the Padova N-body code for cosmological simulations of galaxy formation and evolution. In this paper, the basic Tree + SPH code is presented and analysed, together with an overview on the software architectures. EvoL is a flexible parallel Fortran95 code, specifically designed for simulations of cosmological structure formation on cluster, galactic and sub-galactic scales. EvoL is a fully Lagrangian self-adaptive code, based on the classical Oct-tree and on the Smoothed Particle Hydrodynamics algorithm. It includes special features such as adaptive softening lengths with correcting extra-terms, and modern formulations of SPH and artificial viscosity. It is designed to be run in parallel on multiple CPUs to optimize the performance and save computational time. We describe the code in detail, and present the results of a number of standard hydrodynamical tests.
Ferguson, Kevin; Sewell, Everest; Krivets, Vitaliy; Greenough, Jeffrey; Jacobs, Jeffrey
2016-11-01
Initial conditions for the Richtmyer-Meshkov instability (RMI) are measured in three dimensions in the University of Arizona Vertical Shock Tube using a moving magnet galvanometer system. The resulting volumetric data is used as initial conditions for the simulation of the RMI using ARES at Lawrence-Livermore National Laboratory (LLNL). The heavy gas is sulfur hexafluoride (SF6), and the light gas is air. The perturbations are generated by harmonically oscillating the gasses vertically using two loudspeakers mounted to the shock tube which cause Faraday resonance, producing a random short wavelength perturbation on the interface. Planar Mie scattering is used to illuminate the flow field through the addition of propylene glycol particles seeded in the heavy gas. An M=1.2 shock impulsively accelerates the interface, initiating instability growth. Images of the initial condition and instability growth are captured at a rate of 6 kHz using high speed cameras. Comparisons between experimental and simulation results, mixing diagnostics, and mixing zone growth are presented.
High order numerical simulations of the Richtmyer Meshkov instability in a relativistic fluid
Zanotti, Olindo
2014-01-01
We study the Richtmyer--Meshkov (RM) instability of a relativistic perfect fluid by means of high order numerical simulations with adaptive mesh refinement (AMR). The numerical scheme adopts a finite volume Weighted Essentially Non-Oscillatory (WENO) reconstruction to increase accuracy in space, a local space-time discontinuous Galerkin predictor method to obtain high order of accuracy in time and a high order one-step time update scheme together with a "cell-by-cell" space-time AMR strategy with time-accurate local time stepping. In this way, third order accurate (both in space and in time) numerical simulations of the RM instability are performed, spanning a wide parameter space. We present results both for the case in which a light fluid penetrates into a higher density one (Atwood number $A>0$), and for the case in which a heavy fluid penetrates into a lower density one (Atwood number $A<0$). We find that, for large Lorentz factors \\gamma_s of the incident shock wave, the relativistic RM instability is...
Large eddy simulations of flow instabilities in a stirred tank generate by a Rushton turbine
DEFF Research Database (Denmark)
Fan, Jianhua; Wang, Yundong; Fei, Weiyang
2007-01-01
The aim of this paper is to investigate the flow instabilities in a baffled, stirred tank generated by a single Rushton turbine by means of large eddy simulation (LES) and simulation using the k-ε turbulent model. A sliding mesh method was used for the coupling between the rotating...... that CFD simulations using k-ε model and LES approach agreed well with the DPIV measurement. Fluctuations of the radial and axial velocity were well predicted at different frequencies by the LES simulation. Velocity fluctuations of high frequencies were observed in the impeller region, while low...... computational time and computer memories. The results of the present work give better understanding to the mixing mechanisms in the mechanically agitated tank....
Energy Technology Data Exchange (ETDEWEB)
Jost, G.; Tran, T.M.; Appert, K. [Ecole Polytechnique Federale, Lausanne (Switzerland). Centre de Recherche en Physique des Plasma (CRPP); Wuethrich, S. [CRAY Research, PATP/PSE, EPFL, Lausanne (Switzerland)
1996-12-01
A two-dimensional PIC code aimed at the investigation of electron-cyclotron beam instabilities in gyrotrons and their effects on the beam quality is presented. The code is based on recently developed techniques for handling charge conservation and open boundaries and uses an electromagnetic field which is decomposed in its transverse magnetic (TM) and electric (TE) components. The code has been implemented on the massively parallel computer CRAY T3D, and on the CRAY Y-MP. (author) figs., tabs., refs.
Numerical simulations of thermal-chemical instabilities at the core-mantle boundary
Hansen, Ulrich; Yuen, David A.
1988-01-01
Numerical simulations of thermal-chemical instabilities in the D-double-prime layer at the core-mantle boundary are presented which show that strong lateral heterogeneities in the composition and density fields can be initiated and maintained dynamically if there is continuous replenishment of material from subduced slabs coming from the upper mantle. These chemical instabilities have a tendency to migrate laterally and may help to support core-mantle boundary topography with short and long wavelengths. The thermal-chemical flows produce a relatively stagnant D-double-prime layer with strong lateral and temporal variations in basal heat flux, which gives rise to thermal core-mantle interactions influencing the geodynamo.
Simulation of feedback instability in the coupled magnetosphere-ionosphere system
Hasegawa, Hiroki; Ohno, Nobuaki; Sato, Tetsuya
2010-08-01
Quiet auroral arcs formation has been investigated theoretically and numerically in a self-consistent dynamic way. By using a three-dimensional magneto-hydro-dynamics simulation of a dipole magnetosphere-ionosphere coupling system, it is shown that multiple longitudinally striated structures of the ionospheric plasma density and the field-aligned current are formed, resulting from nonlinear feedback instability. The areas where these structures appear are consistent with the prediction by the integrated feedback theory that includes the effects of the spatially non-uniform electric field and non-uniform plasma density. Effects of the difference of the field line lengths between the ionosphere and the magnetospheric equator over the auroral latitudes are also discussed on the feedback instability.
Relativistic MHD simulations of core-collapse GRB jets: 3D instabilities and magnetic dissipation
Bromberg, Omer
2015-01-01
Relativistic jets naturally occur in astrophysical systems that involve accretion onto compact objects, such as core collapse of massive stars in gamma-ray bursts (GRBs) and accretion onto supermassive black holes in active galactic nuclei (AGN). It is generally accepted that these jets are powered electromagnetically, by the magnetised rotation of a central compact object. However, how they produce the observed emission and survive the propagation for many orders of magnitude in distance without being disrupted by current-driven non-axisymmetric instabilities is the subject of active debate. We carry out time-dependent 3D relativistic magnetohydrodynamic simulations of relativistic, Poynting flux dominated jets. The jets are launched self-consistently by the rotation of a strongly magnetised central compact object. This determines the natural degree of azimuthal magnetic field winding, a crucial factor that controls jet stability. We find that the jets are susceptible to two types of instability: (i) a globa...
Beam-beam simulation code BBSIM for particle accelerators
Energy Technology Data Exchange (ETDEWEB)
Kim, Hyung J.; Sen, Tanaji; /Fermilab
2011-01-01
A highly efficient, fully parallelized, six-dimensional tracking model for simulating interactions of colliding hadron beams in high energy ring colliders and simulating schemes for mitigating their effects is described. The model uses the weak-strong approximation for calculating the head-on interactions when the test beam has lower intensity than the other beam, a look-up table for the efficient calculation of long-range beam-beam forces, and a self-consistent Poisson solver when both beams have comparable intensities. A performance test of the model in a parallel environment is presented. The code is used to calculate beam emittance and beam loss in the Tevatron at Fermilab and compared with measurements. They also present results from the studies of stwo schemes proposed to compensate the beam-beam interactions: (a) the compensation of long-range interactions in the Relativistic Heavy Ion Collider (RHIC) at Brookhaven and the Large Hadron Collider (LHC) at CERN with a current carrying wire, (b) the use of a low energy electron beam to compensate the head-on interactions in RHIC.
Beam-beam simulation code BBSIM for particle accelerators
Energy Technology Data Exchange (ETDEWEB)
Kim, Hyung J.; Sen, Tanaji; /Fermilab
2011-01-01
A highly efficient, fully parallelized, six-dimensional tracking model for simulating interactions of colliding hadron beams in high energy ring colliders and simulating schemes for mitigating their effects is described. The model uses the weak-strong approximation for calculating the head-on interactions when the test beam has lower intensity than the other beam, a look-up table for the efficient calculation of long-range beam-beam forces, and a self-consistent Poisson solver when both beams have comparable intensities. A performance test of the model in a parallel environment is presented. The code is used to calculate beam emittance and beam loss in the Tevatron at Fermilab and compared with measurements. They also present results from the studies of stwo schemes proposed to compensate the beam-beam interactions: (a) the compensation of long-range interactions in the Relativistic Heavy Ion Collider (RHIC) at Brookhaven and the Large Hadron Collider (LHC) at CERN with a current carrying wire, (b) the use of a low energy electron beam to compensate the head-on interactions in RHIC.
Energy Technology Data Exchange (ETDEWEB)
Bartosiewicz, Yann [Universite Catholique de Louvain (UCL), Faculty of Applied Sciences, Mechanical Engineering Department, TERM Division, Place du Levant 2, 1348 Louvain-la-Neuve (Belgium)], E-mail: yann.bartosiewicz@uclouvain.be; Lavieville, Jerome [Universite Catholique de Louvain (UCL), Faculty of Applied Sciences, Mechanical Engineering Department, TERM Division, Place du Levant 2, 1348 Louvain-la-Neuve (Belgium); Seynhaeve, Jean-Marie [Universite Catholique de Louvain (UCL), Faculty of Applied Sciences, Mechanical Engineering Department, TERM Division, Place du Levant 2, 1348 Louvain-la-Neuve (Belgium)], E-mail: jm.seynhaeve@uclouvain.be
2008-04-15
This paper presents some results concerning a first benchmark for the new European research code for thermal hydraulics computations: NEPTUNE{sub C}FD. This benchmark relies on the Thorpe experiment to model the occurrence of instabilities in a stratified two-phase flow. The first part of this work is to create a numerical trial case with the VOF approach. The results, in terms of time of onset of the instability, critical wave-number or wave phase speed, are rather good compared to linear inviscid theory and experimental data. Additional numerical tests showed the effect of the surface tension and density ratio on the growing dynamics of the instability and the structure of the waves. In the second part, a code to code (VOF/multi-field) comparison is performed for a case with zero surface tension. The results showed some discrepancies in terms of wave amplitudes, growing rates and a time shifting in the global dynamics. Afterward, two surface tension formulations are proposed in the multi-field approach. Both formulations provided similar results. The time for onset of the instability, the most amplified wave-number and its amplitude were in rather good agreement with the linear analysis and VOF results. However, the time-shifted dynamics was still observed.
Energy Technology Data Exchange (ETDEWEB)
Aoki, Isao; Seki, Yasushi [Japan Atomic Energy Research Inst., Naka, Ibaraki (Japan). Naka Fusion Research Establishment; Sasaki, Makoto; Shintani, Kiyonori; Kim, Yeong-Chan
1997-11-01
A dynamic simulation code for the fuel cycle of a fusion experimental reactor has been developed. The code follows the fuel inventory change with time in the plasma chamber and the fuel cycle system during a single pulse operation. The time dependence of the fuel inventory distribution is evaluated considering the fuel burn and exhaust in the plasma chamber, purification and supply functions. For each subsystem of the plasma chamber and the fuel cycle system, the fuel inventory equation is written based on the equation of state considering the function of fuel burn, exhaust, purification, and supply. The processing constants of subsystem for the steady states were taken from the values in the ITER Conceptual Design Activity (CDA) report. Using the code, the time dependence of the fuel supply and inventory depending on the burn state and subsystem processing functions are shown. (author)
Hughes, R. Scott; Wang, Joseph; Decyk, Viktor K.; Gary, S. Peter
2016-04-01
This paper investigates how the physics of the whistler anisotropy instability (WAI) is affected by variations in the electron thermal velocity vte, referred to here in terms of the ratio v̂ t e=vt e/c , where c is the speed of light. The WAI is driven by the electron condition RT>1 , where RT=Te ⊥/Te ∥ is the temperature anisotropy ratio and ⊥/∥ signify directions perpendicular/parallel to the background magnetic field B0 . While a typical value of v̂ t e in the solar wind is ˜0.005 , electromagnetic (EM) particle-in-cell (PIC) simulations often use a value near 0.1 in order to maximize the computational time step. In this study, a two-dimensional (2D) Darwin particle-in-cell (DPIC) code, MDPIC2, is used. The time step in the DPIC model is not affected by the choice of v̂ t e , making DPIC suited for this study. A series of simulations are carried out under the condition that the electron βe is held fixed, while v̂ t e is varied over the range 0.1 ≥v̂ t e≥0.025 . The results show that, with βe held fixed, the linear dispersion properties and the nonlinear saturation amplitude and pitch angle scattering rates associated with the WAI are insensitive to the value of v̂ t e . A supplementary investigation is conducted which characterizes how the WAI model is affected at various values of v̂ t e by noise associated with the limited number of particles in a typical PIC simulation. It is found that the evolution of the WAI is more strongly influenced by electrostatic noise as v̂ t e is decreased. The electrostatic noise level is inversely proportional to the number of particles per computational cell ( Nc ); this implies that the number of particles required to remove nonphysical effects from the PIC simulation increases as v̂ t e decreases. It is concluded that PIC simulations of this instability which use an artificially large value of v̂ t e accurately reproduce the response of a cooler plasma as long as a realistic value of βe is used
Jao, C.-S.; Hau, L.-N.
2016-11-01
Electrostatic streaming instabilities have been proposed as the generation mechanism for the electrostatic solitary waves observed in various space plasma environments. Past studies on the subject have been mostly based on the kinetic theory and particle simulations. In this paper, we extend our recent study based on one-dimensional fluid theory and particle simulations to two-dimensional regimes for both bi-streaming and bump-on-tail streaming instabilities in electron-ion plasmas. Both linear fluid theory and kinetic simulations show that for bi-streaming instability, the oblique unstable modes tend to be suppressed by the increasing background magnetic field, while for bump-on-tail instability, the growth rates of unstable oblique modes are increased with increasing background magnetic field. For both instabilities, the fluid theory gives rise to the linear growth rates and the wavelengths of unstable modes in good agreement with those obtained from the kinetic simulations. For unmagnetized and weakly magnetized systems, the formed electrostatic structures tend to diminish after the long evolution, while for relatively stronger magnetic field cases, the solitary waves may merge and evolve to steady one-dimensional structures. Comparisons between one and two-dimensional results are made and the effects of the ion-to-electron mass ratio are also examined based on the fluid theory and kinetic simulations. The study concludes that the fluid theory plays crucial seeding roles in the kinetic evolution of electrostatic streaming instabilities.
Wareing, C J; Falle, S A E G
2016-01-01
We have used the AMR hydrodynamic code, MG, to perform 3D magnetohydrodynamic simulations with self-gravity of stellar feedback in a sheet-like molecular cloud formed through the action of the thermal instability. We simulate the interaction of the mechanical energy input from a 15Msun star and a 40Msun star into a 100pc-diameter 17000Msun cloud with a corrugated sheet morphology that in projection appears filamentary. The stellar winds are introduced using appropriate Geneva stellar evolution models. In the 15Msun star case, the wind forms a narrow bipolar cavity with minimal effect on the parent cloud. In the 40Msun star case, the more powerful stellar wind creates a large cylindrical cavity through the centre of the cloud. After 12.5Myrs and 4.97Myrs respectively, the massive stars explode as supernovae (SNe). In the 15Msun star case, the SN material and energy is primarily deposited into the molecular cloud surroundings over 10^5 years before the SN remnant escapes the cloud. In the 40Msun star case, the ...
A comparative study of MONTEBURNS and MCNPX 2.6.0 codes in ADS simulations
Energy Technology Data Exchange (ETDEWEB)
Barros, Graiciany P.; Pereira, Claubia; Veloso, Maria A.F.; Velasquez, Carlos E.; Costa, Antonella L., E-mail: gbarros@ufmg.br, E-mail: claubia@nuclear.ufmg.br [Universidade Federal de Minas Gerais (UFMG), Belo Horizonte, MG (Brazil). Dept. de Engenharia Nuclear
2013-07-01
The possible use of the MONTEBURNS and MCNPX 2.6.0 codes in Accelerator-driven systems (ADSs) simulations for fuel evolution description is discussed. ADSs are investigated for fuel breeding and long-lived fission product transmutation so simulations of fuel evolution have a great relevance. The burnup/depletion capability is present in both studied codes. MONTEBURNS code links Monte Carlo N-Particle Transport Code (MCNP) to the radioactive decay burnup code ORIGEN2, whereas MCNPX depletion/ burnup capability is a linked process involving steady-state flux calculations by MCNPX and nuclide depletion calculations by CINDER90. A lead-cooled accelerator-driven system fueled with thorium was simulated and the results obtained using MONTEBURNS code and the results from MCNPX 2.6.0 code were compared. The system criticality and the variation of the actinide inventory during the burnup were evaluated and the results indicate a similar behavior between the results of each code. (author)
Rayleigh-Taylor instability in Magnetohydrodynamic Simulations of the Crab Nebula
Porth, Oliver; Keppens, Rony
2014-01-01
In this paper we discuss the development of Rayleigh-Taylor filaments in axisymmetric simulations of Pulsar wind nebulae (PWN). High-resolution adaptive mesh refinement magnetohydrodynamic (MHD) simulations are used to resolve the non-linear evolution of the instability. The typical separation of filaments is mediated by the turbulent flow in the nebula and hierarchical growth of the filaments. The strong magnetic dissipation and field-randomization found in recent global three-dimensional simulations of PWN suggests that magnetic tension is not strong enough to suppress the growth of RT filaments, in agreement with the observations of prominent filaments in the Crab nebula. The long-term axisymmetric results presented here confirm this finding.
Comparison of two- and three-dimensional simulations of miscible Rayleigh-Taylor instability
Energy Technology Data Exchange (ETDEWEB)
Cabot, W
2006-02-23
A comparison of two-dimensional and three-dimensional high-resolution numerical large-eddy simulations of planar, miscible Rayleigh-Taylor instability flows are presented. The resolution of the three-dimensional simulation is sufficient to attain a fully turbulent state. A number of different statistics from the mixing region (e.g., growth rates, PDFs, mixedness measures, and spectra) are used to demonstrate that two-dimensional flow simulations differ substantially from the three-dimensional one. It is found that the two-dimensional flow grows more quickly than its three-dimensional counterpart at late times, develops larger structures, and is much less well mixed. These findings are consistent with the concept of inverse cascade in two-dimensional flow, as well as the influence of a reduced effective Atwood number on miscible flow.
Energy Technology Data Exchange (ETDEWEB)
Horiuchi, Ritoku; Sato, Tetsuya [Theory and Computer Simulation Center, National Inst. for Fusion Science, Toki, Gifu (Japan)
1999-06-01
Generation of anomalous resistivity and dynamical development of collisionless reconnection in the vicinity of a magnetically neutral sheet are investigated by means of a three-dimensional particle simulation. For no external driving source, two different types of plasma instabilities are excited in the current layer. The lower hybrid drift instability (LHDI) is observed to grow in the periphery of current layer in an early period, while a drift kink instability (DKI) is triggered at the neutral sheet in a late period as a result of the nonlinear deformation of the current sheet by the LHDI. A reconnection electric field grows at the neutral sheet in accordance with the excitation of the DKI. When an external driving field exists, the convective electric field penetrates into the current layer through the particle kinetic effect and collisionless reconnection is triggered by the convective electric field earlier than the DKI is excited. It is also found that the anisotropic ion distribution is formed through the anomalous ion heating by the DKI. (author)
The Plasma Simulation Code: A modern particle-in-cell code with load-balancing and GPU support
Germaschewski, Kai; Ahmadi, Narges; Wang, Liang; Abbott, Stephen; Ruhl, Hartmut; Bhattacharjee, Amitava
2013-01-01
Recent increases in supercomputing power, driven by the multi-core revolution and accelerators such as the IBM Cell processor, graphics processing units (GPUs) and Intel's Many Integrated Core (MIC) technology have enabled kinetic simulations of plasmas at unprecedented resolutions, but changing HPC architectures also come with challenges for writing efficient numerical codes. This paper describes the Plasma Simulation Code (PSC), an explicit, electromagnetic particle-in-cell code with support for different order particle shape functions. We focus on two distinguishing feature of the code: patch-based load balancing using space-filling curves, and support for Nvidia GPUs, which achieves substantial speed-up of up to more than 6x on the Cray XK7 architecture compared to a CPU-only implementation.
Semi-global simulations of the magneto-rotational instability in core collapse supernovae
Obergaulinger, M; Müller, E; Aloy, M A
2008-01-01
Possible effects of magnetic fields in core collapse supernovae rely on an efficient amplification of the weak pre-collapse fields. The magneto-rotational instability (MRI) has been suggested to lead to rapid field growth. Although MRI studies exist for accretion discs, the application of their results to core collapse supernovae is inhibited as the physics of supernova cores is substantially different from that of accretion discs. We address the problem of growth and saturation of the MRI by means of semi-global simulations, which combine elements of global and local simulations by taking into account the presence of global background gradients and using a local computational grid. We analyze the dispersion relation of the MRI to identify different regimes of the instability. This analysis is complemented by simulations, where we consider a local computational box rotating at sub-Keplerian velocity, and where we allow for a radial entropy gradient. We identify six regimes of the MRI depending on the ratio of...
Energy Technology Data Exchange (ETDEWEB)
Reckinger, Scott James [Montana State Univ., Bozeman, MT (United States); Livescu, Daniel [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Vasilyev, Oleg V. [Univ. of Colorado, Boulder, CO (United States)
2016-09-02
A comprehensive numerical methodology has been developed that handles the challenges introduced by considering the compressive nature of Rayleigh-Taylor instability (RTI) systems, which include sharp interfacial density gradients on strongly stratified background states, acoustic wave generation and removal at computational boundaries, and stratification-dependent vorticity production. The computational framework is used to simulate two-dimensional single-mode RTI to extreme late-times for a wide range of flow compressibility and variable density effects. The results show that flow compressibility acts to reduce the growth of RTI for low Atwood numbers, as predicted from linear stability analysis.
Energy Technology Data Exchange (ETDEWEB)
Marxen, Olaf, E-mail: olaf.marxen@vki.ac.be [Center for Turbulence Research, Building 500, Stanford University, Stanford, CA 94305-3035 (United States); Aeronautics and Aerospace Department, von Karman Institute for Fluid Dynamics, Chaussée de Waterloo, 72, 1640 Rhode-St-Genèse (Belgium); Magin, Thierry E. [Aeronautics and Aerospace Department, von Karman Institute for Fluid Dynamics, Chaussée de Waterloo, 72, 1640 Rhode-St-Genèse (Belgium); Shaqfeh, Eric S.G.; Iaccarino, Gianluca [Center for Turbulence Research, Building 500, Stanford University, Stanford, CA 94305-3035 (United States)
2013-12-15
A new numerical method is presented here that allows to consider chemically reacting gases during the direct numerical simulation of a hypersonic fluid flow. The method comprises the direct coupling of a solver for the fluid mechanical model and a library providing the physio-chemical model. The numerical method for the fluid mechanical model integrates the compressible Navier–Stokes equations using an explicit time advancement scheme and high-order finite differences. This Navier–Stokes code can be applied to the investigation of laminar-turbulent transition and boundary-layer instability. The numerical method for the physio-chemical model provides thermodynamic and transport properties for different gases as well as chemical production rates, while here we exclusively consider a five species air mixture. The new method is verified for a number of test cases at Mach 10, including the one-dimensional high-temperature flow downstream of a normal shock, a hypersonic chemical reacting boundary layer in local thermodynamic equilibrium and a hypersonic reacting boundary layer with finite-rate chemistry. We are able to confirm that the diffusion flux plays an important role for a high-temperature boundary layer in local thermodynamic equilibrium. Moreover, we demonstrate that the flow for a case previously considered as a benchmark for the investigation of non-equilibrium chemistry can be regarded as frozen. Finally, the new method is applied to investigate the effect of finite-rate chemistry on boundary layer instability by considering the downstream evolution of a small-amplitude wave and comparing results with those obtained for a frozen gas as well as a gas in local thermodynamic equilibrium.
Migliorati, M
2015-01-01
The simulation of beam dynamics in presence of collective effects requires a strong computational effort to take into account, in a self consistent way, the wakefield acting on a given charge and produced by all the others. Generally this is done by means of a convolution integral or sum. Moreover, if the electromagnetic fields consist of resonant modes with high quality factors, responsible, for example, of coupled bunch instabilities, a charge is also affected by itself in previous turns, and a very long record of wakefield must be properly taken into account. In this paper we present a new simulation code for the longitudinal beam dynamics in a circular accelerator, which exploits an alternative approach to the currently used convolution sum, reducing the computing time and avoiding the issues related to the length of wakefield for coupled bunch instabilities. With this approach it is possible to simulate, without the need of a large computing power, simultaneously, the single and multi-bunch beam dynamics...
ANNarchy: a code generation approach to neural simulations on parallel hardware
Directory of Open Access Journals (Sweden)
Julien eVitay
2015-07-01
Full Text Available Many modern neural simulators focus on the simulation of networks of spiking neurons on parallel hardware. Another important framework in computational neuroscience, rate-coded neural networks, is mostly difficult or impossible to implement using these simulators. We present here the ANNarchy (Artificial Neural Networks architect neural simulator, which allows to easily define and simulate rate-coded and spiking networks, as well as combinations of both. The interface in Python has been designed to be close to the PyNN interface, while the definition of neuron and synapse models can be specified using an equation-oriented mathematical description similar to the Brian neural simulator. This information is used to generate C++ code that will efficiently perform the simulation on the chosen parallel hardware (multi-core system or graphical processing unit. Several numerical methods are available to transform ordinary differential equations into an efficient C++ code. We compare the parallel performance of the simulator to existing solutions.
ANNarchy: a code generation approach to neural simulations on parallel hardware.
Vitay, Julien; Dinkelbach, Helge Ü; Hamker, Fred H
2015-01-01
Many modern neural simulators focus on the simulation of networks of spiking neurons on parallel hardware. Another important framework in computational neuroscience, rate-coded neural networks, is mostly difficult or impossible to implement using these simulators. We present here the ANNarchy (Artificial Neural Networks architect) neural simulator, which allows to easily define and simulate rate-coded and spiking networks, as well as combinations of both. The interface in Python has been designed to be close to the PyNN interface, while the definition of neuron and synapse models can be specified using an equation-oriented mathematical description similar to the Brian neural simulator. This information is used to generate C++ code that will efficiently perform the simulation on the chosen parallel hardware (multi-core system or graphical processing unit). Several numerical methods are available to transform ordinary differential equations into an efficient C++code. We compare the parallel performance of the simulator to existing solutions.
Michikoshi, Shugo; Inutsuka, Shu-ichiro
2010-01-01
We investigate the formation process of planetesimals from the dust layer by the gravitational instability in the gas disk using local $N$-body simulations. The gas is modeled as a background laminar flow. We study the formation process of planetesimals and its dependence on the strength of the gas drag. Our simulation results show that the formation process is divided into three stages qualitatively: the formation of wake-like density structures, the creation of planetesimal seeds, and their collisional growth. The linear analysis of the dissipative gravitational instability shows that the dust layer is secularly unstable although Toomre's $Q$ value is larger than unity. However, in the initial stage, the growth time of the gravitational instability is longer than that of the dust sedimentation and the decrease in the velocity dispersion. Thus, the velocity dispersion decreases and the disk shrinks vertically. As the velocity dispersion becomes sufficiently small, the gravitational instability finally become...
Simulations of the C-2/C-2U Field Reversed Configurations with the Q2D code
Onofri, Marco; Dettrick, Sean; Barnes, Daniel; Tajima, Toshiki; TAE Team
2015-11-01
C-2U was built to sustain advanced beam-driven FRCs for 5 + ms. The Q2D transport code is used to simulate the evolution of C-2U discharges and to study sustainment via fast ion current and pressure, with the latter comparable to the thermal plasma pressure. The code solves the MHD equations together with source terms due to neutral beams, which are calculated by a Monte Carlo method. We compare simulations with experimental results obtained in the HPF14 regime of C-2 (6 neutral beams with energy of 20 keV and total power of 4.2 MW). All simulations start from an initial equilibrium and transport coefficients are chosen to match experimental data. The best agreement is obtained when utilizing an enhanced energy transfer between fast ions and the plasma, which may be an indication of anomalous heating due to beneficial beam-plasma instabilities. Similar simulations of C-2U (neutral beam power increased to 10 + MW and angled beam injection) are compared with experimental results, where a steady state has been obtained for 5 + ms, correlated with the neutral beam pulse and limited by engineering constraints.
Feasibility Analysis on Simulation of PLCS Malfunction Event using SPACE Code
Energy Technology Data Exchange (ETDEWEB)
Kim, Ung Soo; Lee, Cheol Shin; Sohn, Jong Joo [KEPCO-E and C, Daejeon (Korea, Republic of)
2011-10-15
A computer code named 'Safety and Performance Analysis Code (SPACE)' has been being developed in order to replace several existing computer codes used in designing nuclear power plant (NPP) in Korea. This SPACE code is a system code and should be able to simulate various plant events, needed for safety analysis of pressurized water reactors (PWRs), such as loss of coolant accident (LOCA), steam line break (SLB), feedwater line break (FLB), steam generator tube rupture (SGTR), and several anticipated operational occurrences (AOOs). Therefore, respective simulations of above events with the SPACE code should be verified and validated to utilize this code in the safety analysis. In this work, a feasibility analysis is performed for the simulation of pressurizer level control system (PLCS) malfunction event for the Shin-Kori units 3 and 4 (SKN 3 and 4)
Cai, Kai; Boley, Aaron C; Pickett, Megan K; Mejia, Annie C
2007-01-01
It is generally thought that protoplanetary disks embedded in envelopes are more massive and thus more susceptible to gravitational instabilities (GIs) than exposed disks. We present three-dimensional radiative hydrodynamics simulations of protoplanetary disks with the presence of envelope irradiation. For a disk with a radius of 40 AU and a mass of 0.07 Msun around a young star of 0.5 Msun, envelope irradiation tends to weaken and even suppress GIs as the irradiating flux is increased. The global mass transport induced by GIs is dominated by lower-order modes, and irradiation preferentially suppresses higher-order modes. As a result, gravitational torques and mass inflow rates are actually increased by mild irradiation. None of the simulations produce dense clumps or rapid cooling by convection, arguing against direct formation of giant planets by disk instability, at least in irradiated disks. However, dense gas rings and radial mass concentrations are produced, and these might be conducive to accelerated p...
Endeve, Eirik; Cardall, C.; Budiardja, R.; Beck, S.; Bejnood, A.; Mezzacappa, A.
2011-01-01
The stationary accretion shock instability (SASI) plays an important role in modern simulations of core-collapse supernovae. With the intent to study magnetic field generation and the possible impact of magnetic fields during the crucial nonlinear phase leading to the explosion of massive stars, we have carried out high-resolution, three-dimensional magnetohydrodynamic simulations of the SASI. Turbulent flows emerging from the operation of the spiral SASI mode result in exponential growth of the magnetic energy. From initial conditions in the range expected for slowly rotating progenitor stars, we find that saturation of the magnetic energy can occur within a typical explosion time scale. Implications for neutrino-powered supernovae and neutron star magnetization are considered.
Choudhury, Prakriti Pal
2015-01-01
We perform global linear stability analysis and idealized numerical simulations in global thermal balance to understand the condensation of cold gas from hot/virial atmospheres (coronae), in particular the intracluster medium (ICM). We pay particular attention to geometry (e.g., spherical versus plane-parallel) and the nature of the gravitational potential. Global linear analysis gives a similar value for the fastest growing thermal instability modes in spherical and Cartesian geometries. Simulations and observations suggest that cooling in halos critically depends on the ratio of the cooling time to the free-fall time ($t_{cool}/t_{ff}$). Extended cold gas condenses out of the ICM only if this ratio is smaller than a threshold value close to 10. Previous works highlighted the difference between the nature of cold gas condensation in spherical and plane-parallel atmospheres; namely, cold gas condensation appeared easier in spherical atmospheres. This apparent difference due to geometry arises because the prev...
SITA version 0. A simulation and code testing assistant for TOUGH2 and MARNIE
Energy Technology Data Exchange (ETDEWEB)
Seher, Holger; Navarro, Martin
2016-06-15
High quality standards have to be met by those numerical codes that are applied in long-term safety assessments for deep geological repositories for radioactive waste. The software environment SITA (''a simulation and code testing assistant for TOUGH2 and MARNIE'') has been developed by GRS in order to perform automated regression testing for the flow and transport simulators TOUGH2 and MARNIE. GRS uses the codes TOUGH2 and MARNIE in order to assess the performance of deep geological repositories for radioactive waste. With SITA, simulation results of TOUGH2 and MARNIE can be compared to analytical solutions and simulations results of other code versions. SITA uses data interfaces to operate with codes whose input and output depends on the code version. The present report is part of a wider GRS programme to assure and improve the quality of TOUGH2 and MARNIE. It addresses users as well as administrators of SITA.
DgSMC-B code: A robust and autonomous direct simulation Monte Carlo code for arbitrary geometries
Kargaran, H.; Minuchehr, A.; Zolfaghari, A.
2016-07-01
In this paper, we describe the structure of a new Direct Simulation Monte Carlo (DSMC) code that takes advantage of combinatorial geometry (CG) to simulate any rarefied gas flows Medias. The developed code, called DgSMC-B, has been written in FORTRAN90 language with capability of parallel processing using OpenMP framework. The DgSMC-B is capable of handling 3-dimensional (3D) geometries, which is created with first-and second-order surfaces. It performs independent particle tracking for the complex geometry without the intervention of mesh. In addition, it resolves the computational domain boundary and volume computing in border grids using hexahedral mesh. The developed code is robust and self-governing code, which does not use any separate code such as mesh generators. The results of six test cases have been presented to indicate its ability to deal with wide range of benchmark problems with sophisticated geometries such as airfoil NACA 0012. The DgSMC-B code demonstrates its performance and accuracy in a variety of problems. The results are found to be in good agreement with references and experimental data.
Weis, Matthew R.
Cylindrical liner implosions in the Magnetized Liner Inertial Fusion (MagLIF) concept are susceptible to the magneto-Rayleigh-Taylor instability (MRT). The danger of MRT enters in two phases, (1) during the main implosion, the outer surface of the liner is MRT unstable, and (2) during the short time period when the liner decelerates onto hot fuel, the inner surface becomes unstable. Growth of MRT on the outer surface may also feedthrough, which may seed the inner surface leading to high MRT growth in the second phase. If MRT growth becomes large enough, confinement of the fuel is lost. To characterize MRT we solve the linearized, ideal MHD equations in both planar and cylindrical geometries, including the presence of an axial magnetic field and the effects of sausage and kink modes (present in cylindrical coordinates only). In general, the total instability growth rates in cylindrical geometry are found to be larger than those in planar geometry. MRT and feedthrough is shown to be suppressed by strong magnetic field line bending (tension). However, for the same amount of field line bending, feedthrough is the most stabilized. Application of the planar and the cylindrical model to results from the Z-machine at Sandia National Laboratories is presented. Analytic MRT growth rates for a typical magnetized MagLIF-like implosion show the kink mode to be the fastest growing early and very late in the liner implosion (during deceleration). 1D HYDRA MHD simulations are used to generate realistic, evolving profiles (in density, pressure, and magnetic field) during the implosion from which instantaneous growth rates can be computed exactly, using either the planar or cylindrical analytic formulae developed in this thesis. Sophisticated 2D HYDRA MHD simulations were also performed to compare with the analytic theory and experimental results. In 2D, highly compressed axial magnetic fields can reduce the growth of perturbations at the fuel/liner interface during the implosion
Numerical Simulation of Multi-Material Mixing in an Inclined Interface Richtmyer-Meshkov Instability
Subramaniam, Akshay; Lele, Sanjiva
2015-11-01
The Richtmyer-Meshkov instability arises when a shock wave interacts with an interface separating two fluids. In this work, high fidelity simulations of shock induced multi-material mixing between N2 and CO2 in a shock tube are performed for a Mach 1.55 shock interacting with a planar material interface that is inclined with respect to the shock propagation direction. In the current configuration, unlike the classical perturbed flat interface case, the evolution of the interface is non-linear from early time onwards. Our previous simulations of this problem at multiple spatial resolutions have shown that very small 3D perturbations have a large effect on vortex breakdown mechanisms and hence fine scale turbulence. We propose a comparison of our simulations to the experiments performed at the Georgia Tech Shock Tube and Advanced Mixing Laboratory (STAML). Results before and after reshock of the interface will be shown. Results from simulations of a second case with a more complex initial interface will also be presented. Simulations shown are conducted with an extended version of the Miranda solver developed by Cook et al. (2007) which combines high-order compact finite differences with localized non-linear artificial properties for shock and interface capturing. This research is part of the Blue Waters sustained-petascale computing project, which is supported by the National Science Foundation (awards OCI-0725070 and ACI-1238993) and the state of Illinois.
Energy Technology Data Exchange (ETDEWEB)
Burkhardt, Joerg
2013-07-01
The courses and consequences of severe accidents in nuclear power plants are usually simulated with the help of so called Lumped Parameter-Codes which are especially designed for this purpose. These codes are able to simulate complex physical phenomena within short computing times since they are based on a simplified zone principle. Furthermore they are provided with a simplified flow model basis. This dissertation aims at the ability of the German Containment Code System (COCOSYS) to simulate local accumulations of hydrogen. During severe accidents with a melting reactor core (as in Harrisburg or Fukushima) hydrogen can be generated and then be released to the containment. In case of a local accumulation a detonation can occur that endangers the buildings integrity. The results show that the development and the erosion of these hydrogen accumulations based on bouant flows are qualitatively well simulated. From a systematic grid study general rules concerning the simulation of the stratification erosion have been derivated. Those have been applied and confirmed by several blind code-benchmarks. A detailed analysis has shown that the simulated erosion rate and the resistance of simulated hydrogen accumulations are directly related to the grid discretisation chosen by the user. Based upon this analysis a model concept has been developed, which is able to detect hydrogen accumulations and to determine their intensity of interaction with impinging flows by non-dimensional numbers. The erosion flow is controlled by adjusting local grid effects. The model is in the development phase.
Comparison of DAC and MONACO DSMC Codes with Flat Plate Simulation
Padilla, Jose F.
2010-01-01
Various implementations of the direct simulation Monte Carlo (DSMC) method exist in academia, government and industry. By comparing implementations, deficiencies and merits of each can be discovered. This document reports comparisons between DSMC Analysis Code (DAC) and MONACO. DAC is NASA's standard DSMC production code and MONACO is a research DSMC code developed in academia. These codes have various differences; in particular, they employ distinct computational grid definitions. In this study, DAC and MONACO are compared by having each simulate a blunted flat plate wind tunnel test, using an identical volume mesh. Simulation expense and DSMC metrics are compared. In addition, flow results are compared with available laboratory data. Overall, this study revealed that both codes, excluding grid adaptation, performed similarly. For parallel processing, DAC was generally more efficient. As expected, code accuracy was mainly dependent on physical models employed.
Riquelme, Mario A.; Quataert, Eliot; Verscharen, Daniel
2015-02-01
We use particle-in-cell simulations to study the nonlinear evolution of ion velocity space instabilities in an idealized problem in which a background velocity shear continuously amplifies the magnetic field. We simulate the astrophysically relevant regime where the shear timescale is long compared to the ion cyclotron period, and the plasma beta is β ~ 1-100. The background field amplification in our calculation is meant to mimic processes such as turbulent fluctuations or MHD-scale instabilities. The field amplification continuously drives a pressure anisotropy with p > p ∥ and the plasma becomes unstable to the mirror and ion cyclotron instabilities. In all cases, the nonlinear state is dominated by the mirror instability, not the ion cyclotron instability, and the plasma pressure anisotropy saturates near the threshold for the linear mirror instability. The magnetic field fluctuations initially undergo exponential growth but saturate in a secular phase in which the fluctuations grow on the same timescale as the background magnetic field (with δB ~ 0.3 langBrang in the secular phase). At early times, the ion magnetic moment is well-conserved but once the fluctuation amplitudes exceed δB ~ 0.1 langBrang, the magnetic moment is no longer conserved but instead changes on a timescale comparable to that of the mean magnetic field. We discuss the implications of our results for low-collisionality astrophysical plasmas, including the near-Earth solar wind and low-luminosity accretion disks around black holes.
Rodgers-Lee, Donna; Downes, Turlough P
2016-01-01
The redistribution of angular momentum is a long standing problem in our understanding of protoplanetary disk (PPD) evolution. The magnetorotational instability (MRI) is considered a likely mechanism. We present the results of a study involving multifluid global simulations including Ohmic dissipation, ambipolar diffusion and the Hall effect in a dynamic, self-consistent way. We focus on the turbulence resulting from the non-linear development of the MRI in radially stratified PPDs and compare with ideal MHD simulations. In the multifluid simulations the disk is initially set up to transition from a weak Hall dominated regime, where the Hall effect is the dominant non-ideal effect but approximately the same as or weaker than the inductive term, to a strong Hall dominated regime, where the Hall effect dominates the inductive term. As the simulations progress a substantial portion of the disk develops into a weak Hall dominated disk. We find a transition from turbulent to laminar flow in the inner regions of th...
Three-Dimensional DSMC Simulations of the Rayleigh-Taylor Instability in Gases
Koehler, T. P.; Gallis, M. A.; Torczynski, J. R.; Plimpton, S. J.
2016-11-01
The Direct Simulation Monte Carlo (DSMC) method of molecular gas dynamics is applied to simulate the Rayleigh-Taylor instability (RTI) in atmospheric-pressure monatomic gases (e.g., argon and helium). The computational domain is a 1-mm by 1-mm by 4-mm cuboid uniformly divided into 62.5 billion cubical cells. A total of 1 trillion computational molecules are used, and time steps of 0.1 ns are used. Simulations are performed to quantify the growth of perturbations on an initially flat interface as a function of the Atwood number. The DSMC results reproduce many features of the RTI and are in reasonable agreement with theoretical and empirical models. Consistent with previous work, the DSMC simulations indicate that the growth of the RTI follows a universal behavior. The numbers of bubble-spike pairs that eventually appear agree with theoretical values based on the most unstable wavelength and are independent of the statistical representation of the gas. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
Anomalous Doppler instability in tokamaks: first principles simulation and observations in MAST
Dendy, Richard; Lai, Alan; Chapman, Sandra
2015-11-01
The evolution in velocity space of minority suprathermal electron populations undergoing the anomalous Doppler instability (ADI) is investigated using fully nonlinear particle-in-cell simulations (W N Lai et al., Phys. Plasmas 20, 102122 (2013); and submitted (2015)) that self-consistently evolve particles and fields in a magnetized plasma. Electron trajectories during different stages of the ADI are captured, and are analyzed in relation to the excited electric fields and the overall velocity distribution of electrons. The time-evolution of the moments of the perpendicular electron distribution function is studied to test the range of applicability of analytical approximations that involve a quasilinear wave-driven diffusion operator. For some electrons, trapping and mirroring are observed during the saturation phase. Recent measurements of microwave and X-ray emission during edge localized mode (ELM) activity in the MAST tokamak imply acceleration of electrons parallel to the magnetic field combined with rapid acquisition of perpendicular momentum. This suggests (S J Freethy et al., Phys. Rev. Lett. 114, 125004 (2015)) that the ADI is operating on electrons accelerated by inductive electric fields generated by the initial ELM instability. Work supported in part by the RCUK Energy Programme and EPSRC.
Simulation of drift wave instability in field-reversed configurations using global magnetic geometry
Fulton, D. P.; Lau, C. K.; Lin, Z.; Tajima, T.; Holod, I.; the TAE Team
2016-10-01
Minimizing transport in the field-reversed configuration (FRC) is essential to enable FRC-based fusion reactors. Recently, significant progress on advanced beam-driven FRCs in C-2 and C-2U (at Tri Alpha Energy) provides opportunities to study transport properties using Doppler backscattering (DBS) measurements of turbulent fluctuations and kinetic particle-in-cell simulations of driftwaves in realistic equilibria via the Gyrokinetic Toroidal Code (GTC). Both measurements and simulations indicate relatively small fluctuations in the scrape-off layer (SOL). In the FRC core, local, single flux surface simulations reveal strong stabilization, while experiments indicate quiescent but finite fluctuations. One possible explanation is that turbulence may originate in the SOL and propagate at very low levels across the separatrix into the core. To test this hypothesis, a significant effort has been made to develop A New Code (ANC) based on GTC physics formulations, but using cylindrical coordinates which span the magnetic separatrix, including both core and SOL. Here, we present first results from global ANC simulations.
Numerical simulations of Kelvin-Helmholtz instability: a two-dimensional parametric study
Tian, Chunlin
2016-01-01
Using two-dimensional simulations, we numerically explore the dependences of Kelvin-Helmholtz instability upon various physical parameters, including viscosity, width of sheared layer, flow speed, and magnetic field strength. In most cases, a multi-vortex phase exists between the initial growth phase and final single-vortex phase. The parametric study shows that the evolutionary properties, such as phase duration and vortex dynamics, are generally sensitive to these parameters except in certain regimes. An interesting result is that for supersonic flows, the phase durations and saturation of velocity growth approach constant values asymptotically as the sonic Mach number increases. We confirm that the linear coupling between magnetic field and Kelvin-Helmholtz modes is negligible if the magnetic field is weak enough. The morphological behaviour suggests that the multi-vortex coalescence might be driven by the underlying wave-wave interaction. Based on these results, we make a preliminary discussion about seve...
Bhat, Pallavi; Blackman, Eric G
2016-01-01
We study the dynamo generation (exponential growth) of large scale (planar averaged) fields in unstratified shearing box simulations of the magnetorotational instability (MRI). In contrast to previous studies restricted to horizontal ($x$-$y$) averaging, we demonstrate the presence of large scale fields when either horizontal or vertical ($y$-$z$) averaging is employed. By computing planar averaged fields and power spectra, we find large scale dynamo action in the early MRI growth phase---a previously unidentified feature. Fast growing horizontal low modes and fiducial vertical modes over a narrow range of wave numbers amplify these planar averaged fields in the MRI growth phase, before turbulence sets in. The large scale field growth requires linear fluctuations but not nonlinear turbulence (as defined by mode-mode coupling) and grows as a direct global mode of the MRI. Only by vertical averaging, can it be shown that the growth of horizontal low wavenumber MRI modes directly feed-back to the initial vertica...
Simulations of octupole compensation of head-tail instability at the Tevatron
Energy Technology Data Exchange (ETDEWEB)
Meiqin Xiao; Tanaji Sen; Frank Schmidts
2003-05-28
The proton lifetime in the Tevatron depends sensitively on chromaticities. Too low chromaticities can make the beam unstable due to the weak head-tail instability. One way to compensate this effect is to introduce octupoles to create a larger amplitude dependent betatron tune spread. However, the use of octupoles will also introduce additional side effects such as second order chromaticity, differential tune shifts and chromaticities on both proton and anti-proton helices. The non-linear effects may also reduce the dynamic aperture. There are 67 octupoles in 4 different circuits in the Tevatron which may be used for this purpose. We report on a simulation study to find the best combinations of polarities and strengths of the octupoles.
Directory of Open Access Journals (Sweden)
Řidký Václav
2014-03-01
Full Text Available The work is devoted to 3D and 2D parallel numerical computation of pressure and velocity fields around an elastically supported airfoil self-oscillating due to interaction with the airflow. Numerical solution is computed in the OpenFOAM package, an open-source software package based on finite volume method. Movement of airfoil is described by translation and rotation, identified from experimental data. A new boundary condition for the 2DOF motion of the airfoil was implemented. The results of numerical simulations (velocity are compared with data measured in a wind tunnel, where a physical model of NACA0015 airfoil was mounted and tuned to exhibit the flutter instability. The experimental results were obtained previously in the Institute of Thermomechanics by interferographic measurements in a subsonic wind tunnel in Nový Knín.
Merkin, V. G.; Lyon, J.; Claudepierre, S. G.
2013-12-01
The Kelvin-Helmholtz Instability (KHI) has long been suggested to operate on the magnetospheric boundary, where the magnetosheath plasma streams past the magnetosphere. The instability is thought to be responsible for inducing various wave populations in the magnetosphere and for mass, momentum and energy transport across the magnetospheric boundary. Waves attributed to the KHI have been observed at the Earth's magnetosphere flanks as well as at Saturn and Mercury during spacecraft crossings, and remotely at boundaries of Coronal Mass Ejections (CMEs). Recent high-resolution global 3D magnetohydrodynamic (MHD) simulations of the magnetosphere confirm the existence of pronounced perturbations of the magnetospheric boundary, which are thought to be due to KHI. Such global simulations had been challenging in the past because of the need to encompass the entire magnetosphere, while sufficiently resolving the boundary layer. Here we present results of such a high-resolution simulation of the magnetosphere, using the Lyon-Fedder-Mobarry (LFM) model, under steady northward Interplanetary Magnetic Field (IMF) conditions. We find the magnetospheric boundary to be globally unstable, including the high-latitude boundary layer (meridional plane), where magnetic tension is apparently not sufficient to stabilize the growth of oscillations. Roughly beyond the terminator, global modes, coupled into the surface modes, become apparent, so that the entire body of the magnetosphere is engaged in an oscillatory motion. The wave vector of the surface oscillations has a component perpendicular to the background flow and tangential to the shear layer (in the equatorial plane, k_z component of the wave vector), which is consistent with the generation of field-aligned currents that flow on closed field lines between the inner portion of the boundary layer and the ionosphere. We calculate the distribution of wave power in the equatorial plane and find it consistent with the existence of a
Neutral Particle Transport in Cylindrical Plasma Simulated by a Monte Carlo Code
Institute of Scientific and Technical Information of China (English)
YU Deliang; YAN Longwen; ZHONG Guangwu; LU Jie; YI Ping
2007-01-01
A Monte Carlo code (MCHGAS) has been developed to investigate the neutral particle transport.The code can calculate the radial profile and energy spectrum of neutral particles in cylindrical plasmas.The calculation time of the code is dramatically reduced when the Splitting and Roulette schemes are applied. The plasma model of an infinite cylinder is assumed in the code,which is very convenient in simulating neutral particle transports in small and middle-sized tokamaks.The design of the multi-channel neutral particle analyser (NPA) on HL-2A can be optimized by using this code.
2005-01-01
Tech-X Corporation releases simulation code for solving complex problems in plasma physics : VORPAL code provides a robust environment for simulating plasma processes in high-energy physics, IC fabrications and material processing applications
Fairfield, Donald H.; Otto, A.
1999-01-01
On March 24, 1995 the Geotail spacecraft observed large fluctuations of the magnetic field and plasma properties in the Low Latitude Boundary Layer (LLBL) about 15 R(sub E) tailward of the dusk meridian. Although the magnetospheric and the magnetosheath field were strongly northward, the B(sub z) component showed strong short duration fluctuations in which B(sub z) could even reach negative values. We have used two-dimensional magnetohydrodynamic simulations with magnetospheric and magnetosheath input parameters specifically chosen for this. Geotail event to identify the processes which cause the observed boundary properties. It is shown that these fluctuations can be explained by the Kelvin-Helmholtz instability if the k vector of the instability has a component along the magnetic field direction. The simulation results show many of the characteristic properties of the Geotail observations. In particular, the quasi-periodic strong fluctuations are well explained by satellite crossings through the Kelvin-Helmholtz vortices. It is illustrated how the interior structure of the Kelvin-Helmholtz vortices leads to the rapid fluctuations in the Geotail observations. Our results suggest an average Kelvin-Helmholtz wavelength of about 5 R(sub E) with a vortex size of close to 2 R(sub E) for an average repetition time of 2.5 minutes. The growth time for these waves implies a source region of about 10 to 16 R(sub E) upstream from the location of the Geotail spacecraft (i.e., near the dusk meridian). The results also indicate a considerable mass transport of magnetosheath material into the magnetosphere by magnetic reconnection in the Kelvin-Helmholtz vortices.
Punzalan, Florencio Rusty; Kunieda, Yoshitoshi; Amano, Akira
2015-01-01
Clinical and experimental studies involving human hearts can have certain limitations. Methods such as computer simulations can be an important alternative or supplemental tool. Physiological simulation at the tissue or organ level typically involves the handling of partial differential equations (PDEs). Boundary conditions and distributed parameters, such as those used in pharmacokinetics simulation, add to the complexity of the PDE solution. These factors can tailor PDE solutions and their corresponding program code to specific problems. Boundary condition and parameter changes in the customized code are usually prone to errors and time-consuming. We propose a general approach for handling PDEs and boundary conditions in computational models using a replacement scheme for discretization. This study is an extension of a program generator that we introduced in a previous publication. The program generator can generate code for multi-cell simulations of cardiac electrophysiology. Improvements to the system allow it to handle simultaneous equations in the biological function model as well as implicit PDE numerical schemes. The replacement scheme involves substituting all partial differential terms with numerical solution equations. Once the model and boundary equations are discretized with the numerical solution scheme, instances of the equations are generated to undergo dependency analysis. The result of the dependency analysis is then used to generate the program code. The resulting program code are in Java or C programming language. To validate the automatic handling of boundary conditions in the program code generator, we generated simulation code using the FHN, Luo-Rudy 1, and Hund-Rudy cell models and run cell-to-cell coupling and action potential propagation simulations. One of the simulations is based on a published experiment and simulation results are compared with the experimental data. We conclude that the proposed program code generator can be used to
Directory of Open Access Journals (Sweden)
Florencio Rusty Punzalan
Full Text Available Clinical and experimental studies involving human hearts can have certain limitations. Methods such as computer simulations can be an important alternative or supplemental tool. Physiological simulation at the tissue or organ level typically involves the handling of partial differential equations (PDEs. Boundary conditions and distributed parameters, such as those used in pharmacokinetics simulation, add to the complexity of the PDE solution. These factors can tailor PDE solutions and their corresponding program code to specific problems. Boundary condition and parameter changes in the customized code are usually prone to errors and time-consuming. We propose a general approach for handling PDEs and boundary conditions in computational models using a replacement scheme for discretization. This study is an extension of a program generator that we introduced in a previous publication. The program generator can generate code for multi-cell simulations of cardiac electrophysiology. Improvements to the system allow it to handle simultaneous equations in the biological function model as well as implicit PDE numerical schemes. The replacement scheme involves substituting all partial differential terms with numerical solution equations. Once the model and boundary equations are discretized with the numerical solution scheme, instances of the equations are generated to undergo dependency analysis. The result of the dependency analysis is then used to generate the program code. The resulting program code are in Java or C programming language. To validate the automatic handling of boundary conditions in the program code generator, we generated simulation code using the FHN, Luo-Rudy 1, and Hund-Rudy cell models and run cell-to-cell coupling and action potential propagation simulations. One of the simulations is based on a published experiment and simulation results are compared with the experimental data. We conclude that the proposed program code
The FLUKA code: An accurate simulation tool for particle therapy
Battistoni, Giuseppe; Böhlen, Till T; Cerutti, Francesco; Chin, Mary Pik Wai; Dos Santos Augusto, Ricardo M; Ferrari, Alfredo; Garcia Ortega, Pablo; Kozlowska, Wioletta S; Magro, Giuseppe; Mairani, Andrea; Parodi, Katia; Sala, Paola R; Schoofs, Philippe; Tessonnier, Thomas; Vlachoudis, Vasilis
2016-01-01
Monte Carlo (MC) codes are increasingly spreading in the hadrontherapy community due to their detailed description of radiation transport and interaction with matter. The suitability of a MC code for application to hadrontherapy demands accurate and reliable physical models capable of handling all components of the expected radiation field. This becomes extremely important for correctly performing not only physical but also biologically-based dose calculations, especially in cases where ions heavier than protons are involved. In addition, accurate prediction of emerging secondary radiation is of utmost importance in innovative areas of research aiming at in-vivo treatment verification. This contribution will address the recent developments of the FLUKA MC code and its practical applications in this field. Refinements of the FLUKA nuclear models in the therapeutic energy interval lead to an improved description of the mixed radiation field as shown in the presented benchmarks against experimental data with bot...
Implementation and performance of FDPS: A Framework Developing Parallel Particle Simulation Codes
Iwasawa, Masaki; Hosono, Natsuki; Nitadori, Keigo; Muranushi, Takayuki; Makino, Junichiro
2016-01-01
We have developed FDPS (Framework for Developing Particle Simulator), which enables researchers and programmers to develop high-performance parallel particle simulation codes easily. The basic idea of FDPS is to separate the program code for complex parallelization including domain decomposition, redistribution of particles, and exchange of particle information for interaction calculation between nodes, from actual interaction calculation and orbital integration. FDPS provides the former part and the users write the latter. Thus, a user can implement a high-performance fully parallelized $N$-body code only in 120 lines. In this paper, we present the structure and implementation of FDPS, and describe its performance on three sample applications: disk galaxy simulation, cosmological simulation and Giant impact simulation. All codes show very good parallel efficiency and scalability on K computer and XC30. FDPS lets the researchers concentrate on the implementation of physics and mathematical schemes, without wa...
FARO and KROTOS code simulation and analysis at JRC Ispra
Energy Technology Data Exchange (ETDEWEB)
Annunziato, A.; Yerkess, A.; Addabbo, C. [European Commission-Joint Research Centre, Inst. for Systems, Informatics and Safety, 21020 Ispra (Italy)
1998-01-01
The paper summarizes relevant results from the pre and post test calculations of fuel coolant interaction and quenching tests performed in the FARO and KROTOS test facilities. The main analytical tools adopted at JRC Ispra are the COMETA and the TEXAS codes. COMETA pre and post test calculations of FARO Test L-20 as well as an application of the code to KROTOS test facility are presented. The analysis provides the need to account for H{sub 2} generation models into the pre-mixing calculations. In addition salient results from the application of TEXAS to FARO and KROTOS tests are shown. (author)
Simulation of direct contact condensation of steam jets based on interfacial instability theories
Heinze, David; Schulenberg, Thomas; Class, Andreas; Behnke, Lars
2014-11-01
A simulation model for the direct contact condensation of steam in subcooled water is presented that allows to determine major parameters of the process such as the jet penetration length. Entrainment of water by the steam jet is modeled based on the Kelvin-Helmholtz and Rayleigh-Taylor instability theories. Primary atomization due to acceleration of interfacial waves and secondary atomization due to aerodynamic forces account for the initial size of entrained droplets. The resulting steam-water two-phase flow is simulated based on a one-dimensional two-fluid model. An interfacial area transport equation is used to track changes of the interfacial area density due to droplet entrainment and steam condensation. Interfacial heat and mass transfer rates during condensation are calculated using the two-resistance model. The resulting two-phase flow equations constitute a system of ordinary differential equations which is discretized by means of an explicit Runge-Kutta method. The simulation results are in good agreement with published experimental data over a wide range of pool temperatures and mass flow rates. funded by RWE Power AG.
Energy Technology Data Exchange (ETDEWEB)
Ebrahimi, Fatima [Univ. of New Hampshire, Durham, NH (United States)
2014-07-31
Large-scale magnetic fields have been observed in widely different types of astrophysical objects. These magnetic fields are believed to be caused by the so-called dynamo effect. Could a large-scale magnetic field grow out of turbulence (i.e. the alpha dynamo effect)? How could the topological properties and the complexity of magnetic field as a global quantity, the so called magnetic helicity, be important in the dynamo effect? In addition to understanding the dynamo mechanism in astrophysical accretion disks, anomalous angular momentum transport has also been a longstanding problem in accretion disks and laboratory plasmas. To investigate both dynamo and momentum transport, we have performed both numerical modeling of laboratory experiments that are intended to simulate nature and modeling of configurations with direct relevance to astrophysical disks. Our simulations use fluid approximations (Magnetohydrodynamics - MHD model), where plasma is treated as a single fluid, or two fluids, in the presence of electromagnetic forces. Our major physics objective is to study the possibility of magnetic field generation (so called MRI small-scale and large-scale dynamos) and its role in Magneto-rotational Instability (MRI) saturation through nonlinear simulations in both MHD and Hall regimes.
Coupling methods for parallel running RELAPSim codes in nuclear power plant simulation
Energy Technology Data Exchange (ETDEWEB)
Li, Yankai; Lin, Meng, E-mail: linmeng@sjtu.edu.cn; Yang, Yanhua
2016-02-15
When the plant is modeled detailedly for high precision, it is hard to achieve real-time calculation for one single RELAP5 in a large-scale simulation. To improve the speed and ensure the precision of simulation at the same time, coupling methods for parallel running RELAPSim codes were proposed in this study. Explicit coupling method via coupling boundaries was realized based on a data-exchange and procedure-control environment. Compromise of synchronization frequency was well considered to improve the precision of simulation and guarantee the real-time simulation at the same time. The coupling methods were assessed using both single-phase flow models and two-phase flow models and good agreements were obtained between the splitting–coupling models and the integrated model. The mitigation of SGTR was performed as an integral application of the coupling models. A large-scope NPP simulator was developed adopting six splitting–coupling models of RELAPSim and other simulation codes. The coupling models could improve the speed of simulation significantly and make it possible for real-time calculation. In this paper, the coupling of the models in the engineering simulator is taken as an example to expound the coupling methods, i.e., coupling between parallel running RELAPSim codes, and coupling between RELAPSim code and other types of simulation codes. However, the coupling methods are also referable in other simulator, for example, a simulator employing ATHLETE instead of RELAP5, other logic code instead of SIMULINK. It is believed the coupling method is commonly used for NPP simulator regardless of the specific codes chosen in this paper.
Mizuno, Yosuke; Nishikawa, Ken-Ichi; Hardee, Philip E
2010-01-01
We have investigated the relaxation of a hydrostatic hot plasma column containing toroidal magnetic field by the Current-Driven (CD) kink instability as a model of pulsar wind nebulae. In our simulations the CD kink instability is excited by a small initial velocity perturbation and develops turbulent structure inside the hot plasma column. We demonstrate that, as envisioned by Begelman, the hoop stress declines and the initial gas pressure excess near the axis decreases. The magnetization parameter \\sigma, the ratio of the Poynting to the kinetic energy flux, declines from an initial value of 0.3 to about 0.01 when the CD kink instability saturates. Our simulations demonstrate that axisymmetric models strongly overestimate the elongation of the pulsar wind nebulae. Therefore, the previous requirement for an extremely low pulsar wind magnetization can be abandoned. The observed structure of the pulsar wind nebulae do not contradict the natural assumption that the magnetic energy flux still remains a good frac...
Simulation of LT Code in MATLAB%LT码的MATLAB仿真
Institute of Scientific and Technical Information of China (English)
陈国泰; 郑海峰; 陈国钦; 潘美莺; 廖延初
2011-01-01
After introducing the coding and decoding procession of LT code,a class of fountain code,the simulation program in MATLAB is presented and explained.With the simulation results based on three types of degree distributions for LT code,LT code and Raptor code are compared.%介绍了喷泉码中LT码的编码译码过程,提供了详细的MATLAB仿真代码和说明.通过对三种不同度分布的LT码进行性能仿真,并对仿真结果进行了分析,同时也对LT码和Raptor码进行了适当的比较.
A code to simulate nuclear reactor inventories and associated gamma-ray spectra.
Cresswell, A J; Allyson, J D; Sanderson, D C
2001-01-01
A computer code has been developed to simulate the gamma-ray spectra that would be measured by airborne gamma spectrometry (AGS) systems from sources containing short-lived fission products. The code uses simple numerical methods to simulate the production and decay of fission products and generates spectra for sodium iodide (NaI) detectors using Monte Carlo codes. A new Monte Carlo code using a virtual array of detectors to reduce simulation times for airborne geometries is described. Spectra generated for a short irradiation and laboratory geometry have been compared with an experimental data set. The agreement is good. Spectra have also been generated for airborne geometries and longer irradiation periods. The application of this code to generate AGS spectra for accident scenarios and their uses in the development and evaluation of spectral analysis methods for such situations are discussed.
GYSELA, a full-f global gyrokinetic Semi-Lagrangian code for ITG turbulence simulations
Grandgirard, V.; Sarazin, Y.; Garbet, X.; Dif-Pradalier, G.; Ghendrih, Ph.; Crouseilles, N.; Latu, G.; Sonnendrücker, E.; Besse, N.; Bertrand, P.
2006-11-01
This work addresses non-linear global gyrokinetic simulations of ion temperature gradient (ITG) driven turbulence with the GYSELA code. The particularity of GYSELA code is to use a fixed grid with a Semi-Lagrangian (SL) scheme and this for the entire distribution function. The 4D non-linear drift-kinetic version of the code already showns the interest of such a SL method which exhibits good properties of energy conservation in non-linear regime as well as an accurate description of fine spatial scales. The code has been upgrated to run 5D simulations of toroidal ITG turbulence. Linear benchmarks and non-linear first results prove that semi-lagrangian codes can be a credible alternative for gyrokinetic simulations.
Krause, M.; M. Camenzind
2001-01-01
In the present paper, we examine the convergence behavior and inter-code reliability of astrophysical jet simulations in axial symmetry. We consider both, pure hydrodynamic jets and jets with a dynamically significant magnetic field. The setups were chosen to match the setups of two other publications, and recomputed with the MHD code NIRVANA. We show that NIRVANA and the two other codes give comparable, but not identical results. We find that some global properties of a hydrodynamical jet si...
The 1963 Vajont landslide (Italy) simulated through a numerical 2D code
Zaniboni, Filippo; Ausilia Paparo, Maria; Elsen, Katharina; Tinti, Stefano
2013-04-01
On October 9th, 1963, a huge mass of about 260 million m3 collapsed along Mt. Toc flank into the artificial lake called Vajont and generated a gigantic wave that invested the town of Longarone (North-East Italy, about 100 km north of Venice), provoking about 2000 casualties. The event started a public debate on the responsibilities for the disaster, and also raised crucial issues for the scientific and engineering community, regarding reservoir flank instability and safety of the hydroelectric plant. The peculiar features of the event were immediately evident. The clay layers remained uncovered in the upper part of the detachment niche, supporting the hypothesis of a well-defined pre-existing sliding surface, that could explain the high falling velocity (around 20 m/s as a maximum) and the compactness of the deposit layers that were found to sit almost unperturbed on the bottom of the valley. The numerical study presented here contributes to the understanding of dynamics of the Vajont landslide. It is found that the accurate knowledge of the pre- and post-slide morphology provides tight constraints on the parameters of the numerical model, that are tuned to fit the observed deposit. Numerical simulations are carried out by means of the in-house built code UBO-BLOCK2. The initial sliding body is divided into a mesh of interacting volume-conserving blocks, whose motion is computed numerically. The friction coefficient at the base of the landslide is determined through a best fit search by maximizing the degree of overlapping between the calculated and observed deposits. Our best solution is also able to account for the observed slight easterly rotation of the mass, the different behaviors of the eastern and western part of the sliding surface and the retrogressive motion of the slide that after climbing up the opposite flank of the valley reverted velocity to settle down on the bottom of the valley.
OPR1000 Control Rod Drop Accident Simulation using the SPACE Code
Energy Technology Data Exchange (ETDEWEB)
Yang, Chang Keun; Ha, Sang Jun; Moon, Chan Kook [Korea Hydro and Nuclear Power, Daejeon (Korea, Republic of)
2012-05-15
The Korea nuclear industry has developed a best estimated two-phase three-filed thermal-hydraulic analysis code, SPACE (Safety and Performance Analysis Code for Nuclear Power Plants), for safety analysis and design of a PWR (Pressurized Water Reactor). As the first phase, the demo version of the SPACE code was released in March 2010. The code has been verified and improved according to the Validation and Verification (V and V) matrix prepared for the SPACE code as the second phase of the development. In this study, a Control Rod Drop accident has been simulated using the SPACE code as one aspect of the V and V work. The results from this test were compared with tests of the RETRAN and CESEC codes
Metropol, a computer code for the simulation of transport of contaminants with groundwater
Sauter FJ; Hassanizadeh SM; Leijnse A; Glasbergen P; Slot AFM
1990-01-01
In this report a description is given of the computer code METROPOL. This code simulates the three dimensional flow of groundwater with varying density and the simultaneous transport of contaminants in low concentration and is based on the finite element method. The basic equations for groundwater
Relativistic modeling capabilities in PERSEUS extended MHD simulation code for HED plasmas
Energy Technology Data Exchange (ETDEWEB)
Hamlin, Nathaniel D., E-mail: nh322@cornell.edu [438 Rhodes Hall, Cornell University, Ithaca, NY, 14853 (United States); Seyler, Charles E., E-mail: ces7@cornell.edu [Cornell University, Ithaca, NY, 14853 (United States)
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.
Duan, Zhe
2015-01-01
We report a study of spin dynamics based on simulations with the Polymorphic Tracking Code (PTC), exploring the dependence of the static polarization limit on various beam parameters and lattice settings for a practical RHIC lattice.
Medium-rate speech coding simulator for mobile satellite systems
Copperi, Maurizio; Perosino, F.; Rusina, F.; Albertengo, G.; Biglieri, E.
1986-01-01
Channel modeling and error protection schemes for speech coding are described. A residual excited linear predictive (RELP) coder for bit rates 4.8, 7.2, and 9.6 kbit/sec is outlined. The coder at 9.6 kbit/sec incorporates a number of channel error protection techniques, such as bit interleaving, error correction codes, and parameter repetition. Results of formal subjective experiments (DRT and DAM tests) under various channel conditions, reveal that the proposed coder outperforms conventional LPC-10 vocoders by 2 subjective categories, thus confirming the suitability of the RELP coder at 9.6 kbit/sec for good quality speech transmission in mobile satellite systems.
Cook, James; Chapman, Sandra; Dendy, Richard
2010-11-01
Particle-in-cell (PIC) simulations of fusion-born protons in deuterium plasmas demonstrate a key alpha channeling phenomenon for tokamak fusion plasmas. We focus on obliquely propagating modes at the plasma edge, excited by centrally born fusion products on banana orbits, known to be responsible for observations of ion cyclotron emission in JET and TFTR. A fully self-consistent electromagnetic 1D3V PIC code evolves a ring-beam distribution of 3MeV protons in a 10keV thermal deuterium-electron plasma with realistic mass ratio. A collective instability occurs, giving rise to electromagnetic field activity in the lower hybrid range of frequencies. Waves spontaneously excited by this lower hybrid drift instability undergo Landau damping on resonant electrons, drawing out an asymmetric tail in the distribution of electron parallel velocities, which constitutes a net current. These simulations demonstrate a key building block of some alpha channeling scenarios: the direct collisionless coupling of fusion product energy into a form which can help sustain the equilibrium of the tokamak.
Fast Ion Effects on Fishbones and n=1 Kinks in JET Simulated by a Non-perturbative NOVA-KN Code
Energy Technology Data Exchange (ETDEWEB)
N.N. Gorelenkov; C.Z. Cheng; V.G. Kiptily; M.J. Mantsinen; S.E. Sharapov; the JET-EFDA Contributors
2004-10-28
New global non-perturbative hybrid code, NOVA-KN, and simulations of resonant type modes in JET [Joint European Torus] plasmas driven by energetic H-minority ions are presented. The NOVA-KN code employs the ideal-MHD description for the background plasma and treats non-perturbatively the fast particle kinetic response, which includes the fast ion finite orbit width (FOW) effect. In particular, the n = 1 fishbone mode, which is in precession drift resonance with fast ions, is studied. The NOVA-KN code is applied to model an n = 1 (f = 50-80kHz) MHD activity observed recently in JET low density plasma discharges with high fast ion (H-minority) energy content generated during the ion cyclotron resonance heating (ICRH). This n = 1 MHD activity is interpreted as the instability of the n = 1 precession drift frequency fishbone modes.
ICOOL: A SIMULATION CODE FOR IONIZATION COOLING OF MUON BEAMS.
Energy Technology Data Exchange (ETDEWEB)
FERNOW,R.C.
1999-03-25
Current ideas [1,2] for designing a high luminosity muon collider require significant cooling of the phase space of the muon beams. The only known method that can cool the beams in a time comparable to the muon lifetime is ionization cooling [3,4]. This method requires directing the particles in the beam at a large angle through a low Z absorber material in a strong focusing magnetic channel and then restoring the longitudinal momentum with an rf cavity. We have developed a new 3-D tracking code ICOOL for examining possible configurations for muon cooling. A cooling system is described in terms of a series of longitudinal regions with associated material and field properties. The tracking takes place in a coordinate system that follows a reference orbit through the system. The code takes into account decays and interactions of {approx}50-500 MeV/c muons in matter. Material geometry regions include cylinders and wedges. A number of analytic models are provided for describing the field configurations. Simple diagnostics are built into the code, including calculation of emittances and correlations, longitudinal traces, histograms and scatter plots. A number of auxiliary files can be generated for post-processing analysis by the user.
Reckinger, Scott J.; Livescu, Daniel; Vasilyev, Oleg V.
2016-05-01
An investigation of compressible Rayleigh-Taylor instability (RTI) using Direct Numerical Simulations (DNS) requires efficient numerical methods, advanced boundary conditions, and consistent initialization in order to capture the wide range of scales and vortex dynamics present in the system, while reducing the computational impact associated with acoustic wave generation and the subsequent interaction with the flow. An advanced computational framework is presented that handles the challenges introduced by considering the compressive nature of RTI systems, which include sharp interfacial density gradients on strongly stratified background states, acoustic wave generation and removal at computational boundaries, and stratification dependent vorticity production. The foundation of the numerical methodology described here is the wavelet-based grid adaptivity of the Parallel Adaptive Wavelet Collocation Method (PAWCM) that maintains symmetry in single-mode RTI systems to extreme late-times. PAWCM is combined with a consistent initialization, which reduces the generation of acoustic disturbances, and effective boundary treatments, which prevent acoustic reflections. A dynamic time integration scheme that can handle highly nonlinear and potentially stiff systems, such as compressible RTI, completes the computational framework. The numerical methodology is used to simulate two-dimensional single-mode RTI to extreme late-times for a wide range of flow compressibility and variable density effects. The results show that flow compressibility acts to reduce the growth of RTI for low Atwood numbers, as predicted from linear stability analysis.
Fully-kinetic simulations of the Rayleigh-Taylor instability in high-energy-density plasmas
Alves, E. Paulo; Mori, Warren B.; Fiuza, Frederico
2016-10-01
The Rayleigh-Taylor instability (RTI) in high-energy-density (HED) plasmas is a central problem in a wide range of scenarios. It dictates, for instance, the dynamics of supernovae in astrophysical plasmas, and is also recognized as a critical challenge to achieving ignition in inertial confinement fusion. In some of these conditions the Larmor radius or Coulomb mean free path (m.f.p.) is finite, allowing kinetic effects to become important, and it is not fully clear how the development of the RTI deviates from standard hydrodynamic behavior. In order to obtain an accurate description of the RTI in these HED conditions it is essential to capture the self-consistent interplay between collisional and collisionless plasma processes, and the role of self-generated electric and magnetic fields. We have explored the dynamics of the RTI in HED plasma conditions using first-principles particle-in-cell simulations combined with Monte Carlo binary collisions. Our simulations capture the role of kinetic diffusion as well as the self-generated electric (e.g. space-charge) and magnetic (e.g. Biermann battery) fields on the growth rate and nonlinear evolution of the RTI for different plasma conditions. We will discuss how different collisional m.f.p. relative to the collisionless plasma skin depth affect the RTI development. This work was supported by the DOE Office of Science, Fusion Energy Science (FWP 100182).
Analytical model and MD simulation of nonlinear Richtmyer-Meshkov instability
Nishihara, Katsunobu; Abe, Motomi; Fukuda, Yuko; Zhakhovskii, Vasilii; Matsuoka, Chihiro
2001-10-01
We present two topics, an analytical model and moelrcular dynamic (MD) simulations of the Richtmyer-Meshokov instability (RMI). We have developled a selfconsistent analytical model that describes a nonlinear evolution of a vortex sheet in the two-dimensional RMI. The model consists of two kinematic boundary conditions, a modified Birkhoff-Rott equation and an equation for time evolution of circulation at the interface with a finite Atwood number. It is shown that the created vortcity on the interface has strong inhomogeneity, that causes locally streching and compression of the sheet. We discuss the dependence of the Atwood number on the nonlinear dynamics of the sheet. MD approache has been applied for converging shocks and RMI in a dense Lennard-Jones fluid in cylindrical geometry. MD method has fundamental advantages over hydrodymanic simulations such as no limitation of resolution in turbulent state. The appearance of Mach stems in the rippled shocks and turbulent mixing in RMI have been observed when the reflected shock passes through the unstable surface again. We discuss the mode number and Mach number dependence on the mixing.
Numerical simulation on macro-instability of coupling flow field structure in jet-stirred tank
Luan, D. Y.; Lu, J. P.; Bu, Q. X.; Zhang, S. F.; Zheng, S. X.
2016-05-01
The velocity field macro-instability (MI) can help to improve the mixing efficiency. In this work, the MI features of flow field induced by jet-stirred coupling action is studied by using computational fluid dynamics (CFD) simulations. The numerical simulation method of jet-stirred model was established based on standard turbulent equations, and the impeller rotation was modeled by means of the Sliding Mesh (SM) technology. The numerical results of test fluid (water) power consumption were compared with the data obtained by power test experiments. The effects of jet flow velocity and impeller speed on MI frequency were analyzed thoroughly. The results show that the calculated values of power consumption agree well with the experiment measured data, which validates the turbulent model, and the flow structure and MI frequency distribution are affected by both impeller speed and jet flow rate. The amplitude of MI frequency increases obviously with the increasing rotation speed of impeller and the eccentric jet rate, and it can be enhanced observably by eccentric jet rate, in condition of comparatively high impeller speed. At this time, the MI phenomenon disappears with the overall chaotic mixing.
Energy Technology Data Exchange (ETDEWEB)
Cordero Garcia, S.; Peco Espinosa, J.
2010-07-01
The fire simulation and analytical validation procedures have been gaining importance in the context of safety analysis and probabilistic deterministic Fire at Nuclear Power Plants. Meanwhile, the fire simulation codes have been accepted as valuable tools for risk analysis in fire protection. To evaluate the quality and predictability of the codes used in fire protection, they are validated with different experiments. This work is performed to find the dependency of the FDS output parameters against a certain input.
Rota, Christopher T; Wolf, Alexander J; Renken, Rochelle B; Gitzen, Robert A; Fantz, Debby K; Montgomery, Robert A; Olson, Matthew G; Vangilder, Larry D; Millspaugh, Joshua J
2016-12-01
We present predictor variables and R and Stan code for simulating and analyzing counts of Missouri Ozark herpetofauna in response to three forest management strategies. Our code performs four primary purposes: import predictor variables from spreadsheets; simulate synthetic response variables based on imported predictor variables and user-supplied values for data-generating parameters; format synthetic data for export to Stan; and analyze synthetic data.
Directory of Open Access Journals (Sweden)
Christopher T. Rota
2016-12-01
Full Text Available We present predictor variables and R and Stan code for simulating and analyzing counts of Missouri Ozark herpetofauna in response to three forest management strategies. Our code performs four primary purposes: import predictor variables from spreadsheets; simulate synthetic response variables based on imported predictor variables and user-supplied values for data-generating parameters; format synthetic data for export to Stan; and analyze synthetic data.
ARC Code TI: Mission Simulation ToolKit (MST)
National Aeronautics and Space Administration — The MST is a simulation framework, supporting the development of autonomy technology for planetary exploration vehicles. The MST provides a software test bed which...
Shukla, Chandrasekhar; Patel, Kartik
2016-01-01
We carry out Particle-in-Cell (PIC) simulations to study the instabilities associated with a 2-D sheared electron flow configuration against a neutralizing background of ions. Both weak and strong relativistic flow velocities are considered. In the weakly relativistic case, we observe the development of electromagnetic Kelvin Helmholtz instability with similar characteristics as that predicted by the electron Magnetohydrodynamic (EMHD) model. On other hand, in strong relativistic case the compressibility effects of electron fluid dominate and introduce upper hybrid electrostatic oscillations transverse to the flow which are very distinct from EMHD fluid behaviour. In the nonlinear regime, both weak and strong relativistic cases lead to turbulence with broad power law spectrum.
A Multi-Code Analysis Toolkit for Astrophysical Simulation Data
Turk, Matthew J.; Smith., Britton D.; Oishi, Jeffrey S.; Skory, Stephen; Skillman, Samuel W.; Abel, Tom; Norman, Michael L.
2010-01-01
The analysis of complex multiphysics astrophysical simulations presents a unique and rapidly growing set of challenges: reproducibility, parallelization, and vast increases in data size and complexity chief among them. In order to meet these challenges, and in order to open up new avenues for collaboration between users of multiple simulation platforms, we present yt (available at http://yt.enzotools.org/), an open source, community-developed astrophysical analysis and visualization toolkit. ...
Development of MCNPX-ESUT computer code for simulation of neutron/gamma pulse height distribution
Abolfazl Hosseini, Seyed; Vosoughi, Naser; Zangian, Mehdi
2015-05-01
In this paper, the development of the MCNPX-ESUT (MCNPX-Energy Engineering of Sharif University of Technology) computer code for simulation of neutron/gamma pulse height distribution is reported. Since liquid organic scintillators like NE-213 are well suited and routinely used for spectrometry in mixed neutron/gamma fields, this type of detectors is selected for simulation in the present study. The proposed algorithm for simulation includes four main steps. The first step is the modeling of the neutron/gamma particle transport and their interactions with the materials in the environment and detector volume. In the second step, the number of scintillation photons due to charged particles such as electrons, alphas, protons and carbon nuclei in the scintillator material is calculated. In the third step, the transport of scintillation photons in the scintillator and lightguide is simulated. Finally, the resolution corresponding to the experiment is considered in the last step of the simulation. Unlike the similar computer codes like SCINFUL, NRESP7 and PHRESP, the developed computer code is applicable to both neutron and gamma sources. Hence, the discrimination of neutron and gamma in the mixed fields may be performed using the MCNPX-ESUT computer code. The main feature of MCNPX-ESUT computer code is that the neutron/gamma pulse height simulation may be performed without needing any sort of post processing. In the present study, the pulse height distributions due to a monoenergetic neutron/gamma source in NE-213 detector using MCNPX-ESUT computer code is simulated. The simulated neutron pulse height distributions are validated through comparing with experimental data (Gohil et al. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 664 (2012) 304-309.) and the results obtained from similar computer codes like SCINFUL, NRESP7 and Geant4. The simulated gamma pulse height distribution for a 137Cs
The FLUKA Code: An Accurate Simulation Tool for Particle Therapy.
Battistoni, Giuseppe; Bauer, Julia; Boehlen, Till T; Cerutti, Francesco; Chin, Mary P W; Dos Santos Augusto, Ricardo; Ferrari, Alfredo; Ortega, Pablo G; Kozłowska, Wioletta; Magro, Giuseppe; Mairani, Andrea; Parodi, Katia; Sala, Paola R; Schoofs, Philippe; Tessonnier, Thomas; Vlachoudis, Vasilis
2016-01-01
Monte Carlo (MC) codes are increasingly spreading in the hadrontherapy community due to their detailed description of radiation transport and interaction with matter. The suitability of a MC code for application to hadrontherapy demands accurate and reliable physical models capable of handling all components of the expected radiation field. This becomes extremely important for correctly performing not only physical but also biologically based dose calculations, especially in cases where ions heavier than protons are involved. In addition, accurate prediction of emerging secondary radiation is of utmost importance in innovative areas of research aiming at in vivo treatment verification. This contribution will address the recent developments of the FLUKA MC code and its practical applications in this field. Refinements of the FLUKA nuclear models in the therapeutic energy interval lead to an improved description of the mixed radiation field as shown in the presented benchmarks against experimental data with both (4)He and (12)C ion beams. Accurate description of ionization energy losses and of particle scattering and interactions lead to the excellent agreement of calculated depth-dose profiles with those measured at leading European hadron therapy centers, both with proton and ion beams. In order to support the application of FLUKA in hospital-based environments, Flair, the FLUKA graphical interface, has been enhanced with the capability of translating CT DICOM images into voxel-based computational phantoms in a fast and well-structured way. The interface is capable of importing also radiotherapy treatment data described in DICOM RT standard. In addition, the interface is equipped with an intuitive PET scanner geometry generator and automatic recording of coincidence events. Clinically, similar cases will be presented both in terms of absorbed dose and biological dose calculations describing the various available features.
Large Eddy Simulation of Flow in Turbine Cascades Using LESTool and UNCLE Codes
Huang, P. G.
2004-01-01
During the period December 23,1997 and December August 31,2004, we accomplished the development of 2 CFD codes for DNS/LES/RANS simulation of turbine cascade flows, namely LESTool and UNCLE. LESTool is a structured code making use of 5th order upwind differencing scheme and UNCLE is a second-order-accuracy unstructured code. LESTool has both Dynamic SGS and Spalart's DES models and UNCLE makes use of URANS and DES models. The current report provides a description of methodologies used in the codes.
Large Eddy Simulation of Flow in Turbine Cascades Using LEST and UNCLE Codes
Ashpis, David (Technical Monitor); Huang, P. G.
2004-01-01
During the period December 23, 1997 and December August 31, 2004, we accomplished the development of 2 CFD codes for DNS/LES/RANS simulation of turbine cascade flows, namely LESTool and UNCLE. LESTool is a structured code making use of 5th order upwind differencing scheme and UNCLE is a second-order-accuracy unstructured code. LESTool has both Dynamic SGS and Sparlart's DES models and UNCLE makes use of URANS and DES models. The current report provides a description of methodologies used in the codes.
Energy Technology Data Exchange (ETDEWEB)
Pruess, Karsten
2003-08-08
Numerical simulation has become a widely practiced andaccepted technique for studying flow and transport processes in thevadose zone and other subsurface flow systems. This article discusses asuite of codes, developed primarily at Lawrence Berkeley NationalLaboratory (LBNL), with the capability to model multiphase flows withphase change. We summarize history and goals in the development of theTOUGH codes, and present the governing equations for multiphase,multicomponent flow. Special emphasis is given to space discretization bymeans of integral finite differences (IFD). Issues of code implementationand architecture are addressed, as well as code applications,maintenance, and future developments.
Winjum, B. J.; Banks, J. W.; Berger, R. L.; Cohen, B. I.; Chapman, T.; Hittinger, J. A. F.; Rozmus, W.; Strozzi, D. J.; Brunner, S.
2012-10-01
We present results on the kinetic filamentation of finite-width nonlinear electron plasma waves (EPW). Using 2D simulations with the PIC code BEPS, we excite a traveling EPW with a Gaussian transverse profile and a wavenumber k0λDe= 1/3. The transverse wavenumber spectrum broadens during transverse EPW localization for small width (but sufficiently large amplitude) waves, while the spectrum narrows to a dominant k as the initial EPW width increases to the plane-wave limit. For large EPW widths, filaments can grow and destroy the wave coherence before transverse localization destroys the wave; the filaments in turn evolve individually as self-focusing EPWs. Additionally, a transverse electric field develops that affects trapped electrons, and a beam-like distribution of untrapped electrons develops between filaments and on the sides of a localizing EPW. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and funded by the Laboratory Research and Development Program at LLNL under project tracking code 12-ERD-061. Supported also under Grants DE-FG52-09NA29552 and NSF-Phy-0904039. Simulations were performed on UCLA's Hoffman2 and NERSC's Hopper.
TreePM: A Code for Cosmological N-Body Simulations
Indian Academy of Sciences (India)
J. S. Bagla
2002-09-01
We describe the TreePM method for carrying out large N-Body simulations to study formation and evolution of the large scale structure in the Universe. This method is a combination of Barnes and Hut tree code and Particle-Mesh code. It combines the automatic inclusion of periodic boundary conditions of PM simulations with the high resolution of tree codes. This is done by splitting the gravitational force into a short range and a long range component. We describe the splitting of force between these two parts.We outline the key differences between TreePM and some other N-Body methods.
Simulation of loss of feedwater transient of MASLWR test facility by MARS-KS code
Energy Technology Data Exchange (ETDEWEB)
Park, Juyeop [Korea Institute of Nuclear Safety, Daejeon (Korea, Republic of)
2013-05-15
MASLWR test facility is a mock-up of a passive integral type reactor equipped with helical coil steam generator. Since SMART reactor which is being current developed domestically also adopts helical coil steam generator, KINS has joined this ICSP to evaluate performance of domestic regulatory audit thermal-hydraulic code (MARS-KS code) in various respects including wall-to-fluid heat transfer model modification implemented in the code by independent international experiment database. In the ICSP, two types of transient experiments have been focused and they are loss of feedwater transient with subsequent ADS operation and long term cooling (SP-2) and normal operating conditions at different power levels (SP-3). In the present study, KINS simulation results by the MARS-KS code (KS-002 version) for the SP-2 experiment are presented in detail and conclusions on MARS-KS code performance drawn through this simulation is described. Performance of the MARS-KS code is evaluated through the simulation of the loss of feedwater transient of the MASLWR test facility. Steady state run shows helical coil specific heat transfer models implemented in the code is reasonable. However, through the transient run, it is also found that three-dimensional effect within the HPC and axial conduction effect through the HTP are not well reproduced by the code.
Applications of the lahet simulation code to relativistic heavy ion detectors
Energy Technology Data Exchange (ETDEWEB)
Waters, L.; Gavron, A. [Los Alamos National Lab., NM (United States)
1991-12-31
The Los Alamos High Energy Transport (LAHET) simulation code has been applied to test beam data from the lead/scintillator Participant Calorimeter of BNL AGS experiment E814. The LAHET code treats hadronic interactions with the LANL version of the Oak Ridge code HETC. LAHET has now been expanded to handle hadrons with kinetic energies greater than 5 GeV with the FLUKA code, while HETC is used exclusively below 2.0 GeV. FLUKA is phased in linearly between 2.0 and 5.0 GeV. Transport of electrons and photons is done with EGS4, and an interface to the Los Alamos HMCNP3B library based code is provided to analyze neutrons with kinetic energies less than 20 MeV. Excellent agreement is found between the test data and simulation, and results for 2.46 GeV/c protons and pions are illustrated in this article.
Applications of the lahet simulation code to relativistic heavy ion detectors
Energy Technology Data Exchange (ETDEWEB)
Waters, L.; Gavron, A. [Los Alamos National Lab., NM (United States)
1991-12-31
The Los Alamos High Energy Transport (LAHET) simulation code has been applied to test beam data from the lead/scintillator Participant Calorimeter of BNL AGS experiment E814. The LAHET code treats hadronic interactions with the LANL version of the Oak Ridge code HETC. LAHET has now been expanded to handle hadrons with kinetic energies greater than 5 GeV with the FLUKA code, while HETC is used exclusively below 2.0 GeV. FLUKA is phased in linearly between 2.0 and 5.0 GeV. Transport of electrons and photons is done with EGS4, and an interface to the Los Alamos HMCNP3B library based code is provided to analyze neutrons with kinetic energies less than 20 MeV. Excellent agreement is found between the test data and simulation, and results for 2.46 GeV/c protons and pions are illustrated in this article.
Simulation and Optimization of VHDL code for FPGA-Based Design using Simulink
Directory of Open Access Journals (Sweden)
Naresh Grover
2014-06-01
Full Text Available Simulations and prototyping have been a very important part of the electronics industry since a very long time. In recent years, FPGA's have become increasingly important and have found their way into all kind of digital system design This paper presents a novel, easy and efficient approach of implementation and verification of VHDL code using Simulink and then to regenerate the optimized VHDL code again using Simulink. The VHDL code written for the complicated digital design of 32-bit floating point arithmetic unit has been synthesized on Xilinx, verified and simulated on Simulink. The same VHDL code in Modelsim was optimized using this approach and the optimized code so generated by Simulinkhas also been synthesized to compare the results. Power dissipations for both synthesized designs using Xilinx Power Estimator were also extracted for comparison.
Direct numerical simulation of electrokinetic instability and transition to chaotic motion
Energy Technology Data Exchange (ETDEWEB)
Demekhin, E. A., E-mail: edemekhi@gmail.com [Laboratory of Micro- and Nanofluidics, Moscow State University, Moscow 119192 (Russian Federation); Department of Computation Mathematics and Computer Science, Kuban State University, Krasnodar 350040 (Russian Federation); Institute of Mechanics, Moscow State University, Moscow 117192 (Russian Federation); Nikitin, N. V. [Institute of Mechanics, Moscow State University, Moscow 117192 (Russian Federation); Shelistov, V. S. [Institute of Mechanics, Moscow State University, Moscow 117192 (Russian Federation); Scientific Research Department, Kuban State University, Krasnodar 350040 (Russian Federation)
2013-12-15
A new type of instability—electrokinetic instability—and an unusual transition to chaotic motion near a charge-selective surface (semiselective electric membrane, electrode, or system of micro-/nanochannels) was studied by the numerical integration of the Nernst-Planck-Poisson-Stokes system and a weakly nonlinear analysis near the threshold of instability. A special finite-difference method was used for the space discretization along with a semi-implicit 31/3 -step Runge-Kutta scheme for the integration in time. Two kinds of initial conditions were considered: (a) white-noise initial conditions to mimic “room disturbances” and subsequent natural evolution of the solution, and (b) an artificial monochromatic ion distribution with a fixed wave number to simulate regular wave patterns. The results were studied from the viewpoint of hydrodynamic stability and bifurcation theory. The threshold of electroconvective movement was found by the linear spectral stability theory, the results of which were confirmed by numerical simulation of the entire system. Our weakly nonlinear analysis and numerical integration of the entire system predict possibility of both kinds of bifurcations at the critical point, supercritical and subcritical, depending on the system parameters. The following regimes, which replace each other as the potential drop between the selective surfaces increases, were obtained: one-dimensional steady solution, two-dimensional steady electroconvective vortices (stationary point in a proper phase space), unsteady vortices aperiodically changing their parameters (homoclinic contour), periodic motion (limit cycle), and chaotic motion. The transition to chaotic motion does not include Hopf bifurcation. The numerical resolution of the thin concentration polarization layer showed spike-like charge profiles along the surface, which could be, depending on the regime, either steady or aperiodically coalescent. The numerical investigation confirmed the
Hanasaki, Itsuo; Walther, Jens H.; Kawano, Satoyuki; Koumoutsakos, Petros
2010-11-01
We study shear-induced instabilities of lipid bilayers immersed in water using coarse-grained molecular dynamics simulations. The shear imposed by the flow of the water induces initially microscopic structural changes of the membrane, starting with tilting of the molecules in the direction of the shear. The tilting propagates in the spanwise direction when the shear rate exceeds a critical value and the membrane undergoes a bucklinglike deformation in the direction perpendicular to the shear. The bucklinglike undulation continues until a localized Kelvin-Helmholtz-like instability leads to membrane rupture. We study the different modes of membrane undulation using membranes of different geometries and quantify the relative importance of the bucklinglike bending and the Kelvin-Helmholtz-like instability of the membrane.
Parallelization of a beam dynamics code and first large scale radio frequency quadrupole simulations
Directory of Open Access Journals (Sweden)
J. Xu
2007-01-01
Full Text Available The design and operation support of hadron (proton and heavy-ion linear accelerators require substantial use of beam dynamics simulation tools. The beam dynamics code TRACK has been originally developed at Argonne National Laboratory (ANL to fulfill the special requirements of the rare isotope accelerator (RIA accelerator systems. From the beginning, the code has been developed to make it useful in the three stages of a linear accelerator project, namely, the design, commissioning, and operation of the machine. To realize this concept, the code has unique features such as end-to-end simulations from the ion source to the final beam destination and automatic procedures for tuning of a multiple charge state heavy-ion beam. The TRACK code has become a general beam dynamics code for hadron linacs and has found wide applications worldwide. Until recently, the code has remained serial except for a simple parallelization used for the simulation of multiple seeds to study the machine errors. To speed up computation, the TRACK Poisson solver has been parallelized. This paper discusses different parallel models for solving the Poisson equation with the primary goal to extend the scalability of the code onto 1024 and more processors of the new generation of supercomputers known as BlueGene (BG/L. Domain decomposition techniques have been adapted and incorporated into the parallel version of the TRACK code. To demonstrate the new capabilities of the parallelized TRACK code, the dynamics of a 45 mA proton beam represented by 10^{8} particles has been simulated through the 325 MHz radio frequency quadrupole and initial accelerator section of the proposed FNAL proton driver. The results show the benefits and advantages of large-scale parallel computing in beam dynamics simulations.
Hoelzl, M.; Huijsmans, G. T. A.; Merkel, P.; Atanasiu, C.; Lackner, K.; Nardon, E.; Aleynikova, K.; Liu, F.; Strumberger, E.; McAdams, R.; Chapman, I.; Fil, A.
2014-11-01
The dynamics of large scale plasma instabilities can be strongly influenced by the mutual interaction with currents flowing in conducting vessel structures. Especially eddy currents caused by time-varying magnetic perturbations and halo currents flowing directly from the plasma into the walls are important. The relevance of a resistive wall model is directly evident for Resistive Wall Modes (RWMs) or Vertical Displacement Events (VDEs). However, also the linear and non-linear properties of most other large-scale instabilities may be influenced significantly by the interaction with currents in conducting structures near the plasma. The understanding of halo currents arising during disruptions and VDEs, which are a serious concern for ITER as they may lead to strong asymmetric forces on vessel structures, could also benefit strongly from these non-linear modeling capabilities. Modeling the plasma dynamics and its interaction with wall currents requires solving the magneto-hydrodynamic (MHD) equations in realistic toroidal X-point geometry consistently coupled with a model for the vacuum region and the resistive conducting structures. With this in mind, the non-linear finite element MHD code JOREK [1, 2] has been coupled [3] with the resistive wall code STARWALL [4], which allows us to include the effects of eddy currents in 3D conducting structures in non-linear MHD simulations. This article summarizes the capabilities of the coupled JOREK-STARWALL system and presents benchmark results as well as first applications to non-linear simulations of RWMs, VDEs, disruptions triggered by massive gas injection, and Quiescent H-Mode. As an outlook, the perspectives for extending the model to halo currents are described.
The Karlsruhe extensive air shower simulation code CORSIKA.
Capdevielle, J. N.; Grieder, P.; Knapp, J.; Gabriel, P.; Gils, H. J.; Heck, D.; Mayer, H. J.; Oehlschläger, J.; Rebel, H.; Schatz, G.; Thouw, T.
1992-11-01
CORSIKA is a detailed simulation program for extensive air showers initiated by high energy cosmic particles. Primary protons and nuclei up to iron can be treated as well as photons. The reaction model for the hadronic interactions is based on the Dual Parton Model and relies on experimental data wherever possible. For electromagnetic interactions the shower program EGS4 may be used.
Dattoli, Giuseppe
2005-01-01
The coherent synchrotron radiation (CSR) is one of the main problems limiting the performance of high intensity electron accelerators. A code devoted to the analysis of this type of problems should be fast and reliable: conditions that are usually hardly achieved at the same time. In the past, codes based on Lie algebraic techniques have been very efficient to treat transport problem in accelerators. The extension of these method to the non-linear case is ideally suited to treat CSR instability problems. We report on the development of a numerical code, based on the solution of the Vlasov equation, with the inclusion of non-linear contribution due to wake field effects. The proposed solution method exploits an algebraic technique, using exponential operators implemented numerically in C++. We show that the integration procedure is capable of reproducing the onset of an instability and effects associated with bunching mechanisms leading to the growth of the instability itself. In addition, parametric studies a...
An Advanced simulation Code for Modeling Inductive Output Tubes
Energy Technology Data Exchange (ETDEWEB)
Thuc Bui; R. Lawrence Ives
2012-04-27
During the Phase I program, CCR completed several major building blocks for a 3D large signal, inductive output tube (IOT) code using modern computer language and programming techniques. These included a 3D, Helmholtz, time-harmonic, field solver with a fully functional graphical user interface (GUI), automeshing and adaptivity. Other building blocks included the improved electrostatic Poisson solver with temporal boundary conditions to provide temporal fields for the time-stepping particle pusher as well as the self electric field caused by time-varying space charge. The magnetostatic field solver was also updated to solve for the self magnetic field caused by time changing current density in the output cavity gap. The goal function to optimize an IOT cavity was also formulated, and the optimization methodologies were investigated.
Code modernization and modularization of APEX and SWAT watershed simulation models
SWAT (Soil and Water Assessment Tool) and APEX (Agricultural Policy / Environmental eXtender) are respectively large and small watershed simulation models derived from EPIC Environmental Policy Integrated Climate), a field-scale agroecology simulation model. All three models are coded in FORTRAN an...
Solar effect on the Rayleigh-Taylor instability growth rate as simulated by the NCAR TIEGCM
Wu, Qian
2017-04-01
The TIEGCM (Thermosphere Ionosphere Electrodynamics General Circulation Model) is used to investigate the solar effect on the equatorial ionospheric Rayleigh-Taylor (R-T) instability growth rate, which is responsible for the occurrence of the plasma bubbles. The R-T growth rate is calculated for the solar maximum year 2003 and minimum 2009. The growth rate is strongly dependent on the solar activity. During solar maximum, the pre-reversal enhancement is much stronger leading to higher R-T growth rate. The R-T growth rates from the TIEGCM follow the same solar dependence as the observed occurrence of equatorial plasma bubbles by DMSP satellites. The R-T growth rate also enhances when the day/night terminator is parallel to the magnetic field line near the equator. The R-T growth rate does not correlate well with the solar F10.7 index on a short time scale ( 10 days) because the field-line integrated electron content gradient cancels out the positive correlation between the vertical ion drift with the F10.7 index. The TIEGCM result shows the importance of the electron content gradient to the R-T growth rate and the plasma bubble occurrence. The bubble occurrence rates were estimated based on the vertical ion drift simulation results.
Li, Weidong; Gao, Yanfei; Bei, Hongbin
2016-01-01
As a commonly used method to enhance the ductility in bulk metallic glasses (BMGs), the introduction of geometric constraints blocks and confines the propagation of the shear bands, reduces the degree of plastic strain on each shear band so that the catastrophic failure is prevented or delayed, and promotes the formation of multiple shear bands. The clustering of multiple shear bands near notches is often interpreted as the reason for improved ductility. Experimental works on the shear band arrangements in notched metallic glasses have been extensively carried out, but a systematic theoretical study is lacking. Using instability theory that predicts the onset of strain localization and the free-volume-based finite element simulations that predict the evolution of shear bands, this work reveals various categories of shear band arrangements in double edge notched BMGs with respect to the mode mixity of the applied stress fields. A mechanistic explanation is thus provided to a number of related experiments and especially the correlation between various types of shear bands and the stress state. PMID:27721462
Li, Weidong; Gao, Yanfei; Bei, Hongbin
2016-10-01
As a commonly used method to enhance the ductility in bulk metallic glasses (BMGs), the introduction of geometric constraints blocks and confines the propagation of the shear bands, reduces the degree of plastic strain on each shear band so that the catastrophic failure is prevented or delayed, and promotes the formation of multiple shear bands. The clustering of multiple shear bands near notches is often interpreted as the reason for improved ductility. Experimental works on the shear band arrangements in notched metallic glasses have been extensively carried out, but a systematic theoretical study is lacking. Using instability theory that predicts the onset of strain localization and the free-volume-based finite element simulations that predict the evolution of shear bands, this work reveals various categories of shear band arrangements in double edge notched BMGs with respect to the mode mixity of the applied stress fields. A mechanistic explanation is thus provided to a number of related experiments and especially the correlation between various types of shear bands and the stress state.
Simulation of bundle test Quench-12 with integral code MELCOR
Energy Technology Data Exchange (ETDEWEB)
Duspiva, J. [Nuclear Research Inst., Rez plc (Czech Republic)
2011-07-01
The past NRI analyses cover the Quench-01, Quench-03 and Quench-06 with version MELCOR 1.8.5 (including reflood model), and Quench-01 and Quench-11 tests with the latest version MELCOR 1.8.6. The Quench-12 test is specific, because it has different bundle configuration related to the VVER bundle configuration with hexagonal grid of pins and also used E110 cladding material. Specificity of Quench-12 test is also in the used material of fuel rod cladding - E110. The test specificities are a reason for the highest concern, because the VVER reactors are operated in the Czech Republic. The new input model was developed with the taking into account all experience from previous simulations of the Quench bundle tests. The recent version MELCOR 1.8.6 YU{sub 2}911 was used for the simulation with slightly modified ELHEAT package. Sensitivity studies on input parameters and oxidation kinetics were performed. (author)
Process monitoring and simulation code verification using interactive computer animation
Energy Technology Data Exchange (ETDEWEB)
Curtis, J.N.; Beelman, R.J.; Schwieder, D.H.; Stewart, H.D.
1984-05-23
At the Idaho National Engineering Laboratory (INEL), EG and G Idaho, Inc., has developed techniques by which schematics, created for and displayed at color graphics terminals, can be driven by actual or calculated data. These input data cause changes to occur within the displayed schematic. This research is presently being done to develop a prototype to be used in nuclear power plant control rooms. Work stations have already been developed to analyze data that are produced during actual and simulated nuclear reactor experiments.
Vrnak, Daniel R.; Stueber, Thomas J.; Le, Dzu K.
2012-01-01
This report presents a method for running a dynamic legacy inlet simulation in concert with another dynamic simulation that uses a graphical interface. The legacy code, NASA's LArge Perturbation INlet (LAPIN) model, was coded using the FORTRAN 77 (The Portland Group, Lake Oswego, OR) programming language to run in a command shell similar to other applications that used the Microsoft Disk Operating System (MS-DOS) (Microsoft Corporation, Redmond, WA). Simulink (MathWorks, Natick, MA) is a dynamic simulation that runs on a modern graphical operating system. The product of this work has both simulations, LAPIN and Simulink, running synchronously on the same computer with periodic data exchanges. Implementing the method described in this paper avoided extensive changes to the legacy code and preserved its basic operating procedure. This paper presents a novel method that promotes inter-task data communication between the synchronously running processes.
2D and 3D Core-Collapse Supernovae Simulation Results Obtained with the CHIMERA Code
Bruenn, S W; Hix, W R; Blondin, J M; Marronetti, P; Messer, O E B; Dirk, C J; Yoshida, S
2010-01-01
Much progress in realistic modeling of core-collapse supernovae has occurred recently through the availability of multi-teraflop machines and the increasing sophistication of supernova codes. These improvements are enabling simulations with enough realism that the explosion mechanism, long a mystery, may soon be delineated. We briefly describe the CHIMERA code, a supernova code we have developed to simulate core-collapse supernovae in 1, 2, and 3 spatial dimensions. We then describe the results of an ongoing suite of 2D simulations initiated from a 12, 15, 20, and 25 solar mass progenitor. These have all exhibited explosions and are currently in the expanding phase with the shock at between 5,000 and 20,000 km. We also briefly describe an ongoing simulation in 3 spatial dimensions initiated from the 15 solar mass progenitor.
2D and 3D core-collapse supernovae simulation results obtained with the CHIMERA code
Energy Technology Data Exchange (ETDEWEB)
Bruenn, S W; Marronetti, P; Dirk, C J [Physics Department, Florida Atlantic University, 777 W. Glades Road, Boca Raton, FL 33431-0991 (United States); Mezzacappa, A; Hix, W R [Physics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6354 (United States); Blondin, J M [Department of Physics, North Carolina State University, Raleigh, NC 27695-8202 (United States); Messer, O E B [Center for Computational Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6354 (United States); Yoshida, S, E-mail: bruenn@fau.ed [Max-Planck-Institut fur Gravitationsphysik, Albert Einstein Institut, Golm (Germany)
2009-07-01
Much progress in realistic modeling of core-collapse supernovae has occurred recently through the availability of multi-teraflop machines and the increasing sophistication of supernova codes. These improvements are enabling simulations with enough realism that the explosion mechanism, long a mystery, may soon be delineated. We briefly describe the CHIMERA code, a supernova code we have developed to simulate core-collapse supernovae in 1, 2, and 3 spatial dimensions. We then describe the results of an ongoing suite of 2D simulations initiated from a 12, 15, 20, and 25 M{sub o-dot} progenitor. These have all exhibited explosions and are currently in the expanding phase with the shock at between 5,000 and 20,000 km. We also briefly describe an ongoing simulation in 3 spatial dimensions initiated from the 15 M{sub o-dot} progenitor.
MOCCA code for star cluster simulation: comparison with optical observations using COCOA
Askar, Abbas; Giersz, Mirek; Pych, Wojciech; Olech, Arkadiusz; Hypki, Arkadiusz
2016-02-01
We introduce and present preliminary results from COCOA (Cluster simulatiOn Comparison with ObservAtions) code for a star cluster after 12 Gyr of evolution simulated using the MOCCA code. The COCOA code is being developed to quickly compare results of numerical simulations of star clusters with observational data. We use COCOA to obtain parameters of the projected cluster model. For comparison, a FITS file of the projected cluster was provided to observers so that they could use their observational methods and techniques to obtain cluster parameters. The results show that the similarity of cluster parameters obtained through numerical simulations and observations depends significantly on the quality of observational data and photometric accuracy.
MOCCA Code for Star Cluster Simulation: Comparison with Optical Observations using COCOA
Askar, Abbas; Pych, Wojciech; Olech, Arkadiusz; Hypki, Arkadiusz
2015-01-01
We introduce and present preliminary results from COCOA (Cluster simulatiOn Comparison with ObservAtions) code for a star cluster after 12 Gyrs of evolution simulated using the MOCCA code. The COCOA code is being developed to quickly compare results of numerical simulations of star clusters with observational data. We use COCOA to obtain parameters of the projected cluster model. For comparison, a FITS file of the projected cluster was provided to observers so that they could use their observational methods and techniques to obtain cluster parameters. The results show that the similarity of cluster parameters obtained through numerical simulations and observations depends significantly on the quality of observational data and photometric accuracy.
Institute of Scientific and Technical Information of China (English)
CHEN Xianyan; Masahide KIMOTO
2009-01-01
Satellite observations of SSTs have revealed the existence of unstable waves in the equatorial eastern Pacific and Atlantic oceans. These waves have a 20-40-day periodicity with westward phase speeds of 0.4-0.6 m s-1 and wavelengths of 1000-2000 km during boreal summer and fall.They are generally called tropical instability waves (TIWs).This study investigates TIWs simulated by a high-resolution coupled atmosphere-ocean general circulation model (AOGCM).The horizontal resolution of the model is 120 km in the atmosphere,and 30 km longitude by 20 km latitude in the ocean.Model simulations show good agreement with the observed main features associated with TIWs.The results of energetics analysis reveal that barotropic energy conversion is responsible for providing the main energy source for TIWs by extracting energy from the meridional shear of the climatological-mean equatorial currents in the mixed layer.This deeper and northward-extended wave activity appears to gain its energy through baroclinic conversion via buoyancy work,which further contributes to the asymmetric distribution of TIWs.It is estimated that the strong cooling effect induced by equatorial upwelling is partially (～30%-40%)offset by the equatorward heat flux due to TIWs in the eastern tropical Pacific during the seasons when TIWs are active.The atmospheric mixed layer just above the sea surface responds to the waves with enhanced or reduced vertical mixing.Furthermore,the changes in turbulent mixing feed back to sea surface evaporation,favoring the westward propagation of TIWs.The atmosphere to the south of the Equator also responds to TIWs in a similar way,although TIWs are much weaker south of the Equator.
Bhat, Pallavi; Ebrahimi, Fatima; Blackman, Eric G.
2016-10-01
We study the dynamo generation (exponential growth) of large-scale (planar averaged) fields in unstratified shearing box simulations of the magnetorotational instability (MRI). In contrast to previous studies restricted to horizontal (x-y) averaging, we also demonstrate the presence of large-scale fields when vertical (y-z) averaging is employed instead. By computing space-time planar averaged fields and power spectra, we find large-scale dynamo action in the early MRI growth phase - a previously unidentified feature. Non-axisymmetric linear MRI modes with low horizontal wavenumbers and vertical wavenumbers near that of expected maximal growth, amplify the large-scale fields exponentially before turbulence and high wavenumber fluctuations arise. Thus the large-scale dynamo requires only linear fluctuations but not non-linear turbulence (as defined by mode-mode coupling). Vertical averaging also allows for monitoring the evolution of the large-scale vertical field and we find that a feedback from horizontal low wavenumber MRI modes provides a clue as to why the large-scale vertical field sustains against turbulent diffusion in the non-linear saturation regime. We compute the terms in the mean field equations to identify the individual contributions to large-scale field growth for both types of averaging. The large-scale fields obtained from vertical averaging are found to compare well with global simulations and quasi-linear analytical analysis from a previous study by Ebrahimi & Blackman. We discuss the potential implications of these new results for understanding the large-scale MRI dynamo saturation and turbulence.
Directory of Open Access Journals (Sweden)
Monteagudo Ángel
2011-02-01
Full Text Available Abstract Background As the canonical code is not universal, different theories about its origin and organization have appeared. The optimization or level of adaptation of the canonical genetic code was measured taking into account the harmful consequences resulting from point mutations leading to the replacement of one amino acid for another. There are two basic theories to measure the level of optimization: the statistical approach, which compares the canonical genetic code with many randomly generated alternative ones, and the engineering approach, which compares the canonical code with the best possible alternative. Results Here we used a genetic algorithm to search for better adapted hypothetical codes and as a method to guess the difficulty in finding such alternative codes, allowing to clearly situate the canonical code in the fitness landscape. This novel proposal of the use of evolutionary computing provides a new perspective in the open debate between the use of the statistical approach, which postulates that the genetic code conserves amino acid properties far better than expected from a random code, and the engineering approach, which tends to indicate that the canonical genetic code is still far from optimal. We used two models of hypothetical codes: one that reflects the known examples of codon reassignment and the model most used in the two approaches which reflects the current genetic code translation table. Although the standard code is far from a possible optimum considering both models, when the more realistic model of the codon reassignments was used, the evolutionary algorithm had more difficulty to overcome the efficiency of the canonical genetic code. Conclusions Simulated evolution clearly reveals that the canonical genetic code is far from optimal regarding its optimization. Nevertheless, the efficiency of the canonical code increases when mistranslations are taken into account with the two models, as indicated by the
Ricci, P.; Halpern, F. D.; Jolliet, S.; Loizu, J.; Mosetto, A.; Fasoli, A.; Furno, I.; Theiler, C.
2012-12-01
Based on the drift-reduced Braginskii equations, the Global Braginskii Solver, GBS, is able to model the scrape-off layer (SOL) plasma turbulence in terms of the interplay between the plasma outflow from the tokamak core, the turbulent transport, and the losses at the vessel. Model equations, the GBS numerical algorithm, and GBS simulation results are described. GBS has been first developed to model turbulence in basic plasma physics devices, such as linear and simple magnetized toroidal devices, which contain some of the main elements of SOL turbulence in a simplified setting. In this paper we summarize the findings obtained from the simulation carried out in these configurations and we report the first simulations of SOL turbulence. We also discuss the validation project that has been carried out together with the GBS development.
Srna - Monte Carlo codes for proton transport simulation in combined and voxelized geometries
Directory of Open Access Journals (Sweden)
Ilić Radovan D.
2002-01-01
Full Text Available This paper describes new Monte Carlo codes for proton transport simulations in complex geometrical forms and in materials of different composition. The SRNA codes were developed for three dimensional (3D dose distribution calculation in proton therapy and dosimetry. The model of these codes is based on the theory of proton multiple scattering and a simple model of compound nucleus decay. The developed package consists of two codes: SRNA-2KG and SRNA-VOX. The first code simulates proton transport in combined geometry that can be described by planes and second order surfaces. The second one uses the voxelized geometry of material zones and is specifically adopted for the application of patient computer tomography data. Transition probabilities for both codes are given by the SRNADAT program. In this paper, we will present the models and algorithms of our programs, as well as the results of the numerical experiments we have carried out applying them, along with the results of proton transport simulation obtained through the PETRA and GEANT programs. The simulation of the proton beam characterization by means of the Multi-Layer Faraday Cup and spatial distribution of positron emitters obtained by our program indicate the imminent application of Monte Carlo techniques in clinical practice.
Comparisons of the simulation results using different codes for ADS spallation target
Yu Hong Wei; Shen Qing Biao; Wan Jun Sheng; Zhao Zhi Xiang
2002-01-01
The calculations to the standard thick target were made by using different codes. The simulation of the thick Pb target with length of 60 cm, diameter of 20 cm bombarded with 800, 1000, 1500 and 2000 MeV energetic proton beam was carried out. The yields and the spectra of emitted neutron were studied. The spallation target was simulated by SNSP, SHIELD, DCM/CEM (Dubna Cascade Model /Cascade Evaporation Mode) and LAHET codes. The Simulation Results were compared with experiments. The comparisons show good agreement between the experiments and the SNSP simulated leakage neutron yield. The SHIELD simulated leakage neutron spectra are in good agreement with the LAHET and the DCM/CEM simulated leakage neutron spectra
The application of Geant4 simulation code for brachytherapy treatment
Agostinelli, S; Garelli, S; Paoli, G; Nieminen, P; Pia, M G
2000-01-01
Brachytherapy is a radiotherapeutic modality that makes use of radionuclides to deliver a high radiation dose to a well-defined volume while sparing surrounding healthy structures. At the National Institute for Cancer Research of Genova a High Dose Rate remote afterloading system provides Ir(192) endocavitary brachytherapy treatments. We studied the possibility to use the Geant4 Monte Carlo simulation toolkit in brachytherapy for calculation of complex physical parameters, not directly available by experiment al measurements, used in treatment planning dose deposition models.
Vencels, Juris; Delzanno, Gian Luca; Manzini, Gianmarco; Markidis, Stefano; Peng, Ivy Bo; Roytershteyn, Vadim
2016-05-01
We present the design and implementation of a spectral code, called SpectralPlasmaSolver (SPS), for the solution of the multi-dimensional Vlasov-Maxwell equations. The method is based on a Hermite-Fourier decomposition of the particle distribution function. The code is written in Fortran and uses the PETSc library for solving the non-linear equations and preconditioning and the FFTW library for the convolutions. SPS is parallelized for shared- memory machines using OpenMP. As a verification example, we discuss simulations of the two-dimensional Orszag-Tang vortex problem and successfully compare them against a fully kinetic Particle-In-Cell simulation. An assessment of the performance of the code is presented, showing a significant improvement in the code running-time achieved by preconditioning, while strong scaling tests show a factor of 10 speed-up using 16 threads.
Modification of PRETOR Code to Be Applied to Transport Simulation in Stellarators
Energy Technology Data Exchange (ETDEWEB)
Fontanet, J.; Castejon, F.; Dies, J.; Fontdecaba, J.; Alejaldre, C.
2001-07-01
The 1.5 D transport code PRETOR, that has been previously used to simulate tokamak plasmas, has been modified to perform transport analysis in stellarator geometry. The main modifications that have been introduced in the code are related with the magnetic equilibrium and with the modelling of energy and particle transport. Therefore, PRETOR- Stellarator version has been achieved and the code is suitable to perform simulations on stellarator plasmas. As an example, PRETOR- Stellarator has been used in the transport analysis of several Heliac Flexible TJ-II shots, and the results are compared with those obtained using PROCTR code. These results are also compared with the obtained using the tokamak version of PRETOR to show the importance of the introduced changes. (Author) 18 refs.
Comparative Design Studies for the BESSY FEL Program using the MEDUSA and GENESIS Simulation Codes
Freund, H
2005-01-01
The BESSY FEL is based on a seeded cascade of High Gain Harmonic Generation (HGHG) sections followed by an amplifier to produce coherent and stable short wavelength output. Here, we report on comparative design studies carried out using the MEDUSA [1], and GENESIS [2] simulation codes. These two codes have each been used to successfully predict a variety of FEL designs and have agreed well with a number of important experiments. In addition, they were included in a comparative study of FEL simulation [3] that reported substantial agreement between the codes for the specific configurations studied. However, these codes are based on different assumptions. GENESIS treats the particle dynamics using a wiggler-averaged orbit approximation, the transverse electromagnetic field is treated using a field solver, and harmonics are not included. MEDUSA does not use the wiggler-averaged orbit approximation to treat particle dynamics, the transverse fields are treated using a Gaussian modal superposition, and harmonics ar...
On the Quantification of Incertitude in Astrophysical Simulation Codes
Hoffman, Melissa; Katz, Maximilian P.; Willcox, Donald E.; Ferson, Scott; Swesty, F. Douglas; Calder, Alan
2017-01-01
We present a pedagogical study of uncertainty quantification (UQ) due to epistemic uncertainties (incertitude) in astrophysical modeling using the stellar evolution software instrument MESA (Modules and Experiments for Stellar Astrophysics). We present a general methodology for UQ and examine the specific case of stars evolving from the main sequence to carbon/oxygen white dwarfs. Our study considers two epistemic variables: the wind parameters during the Red Giant and Asymptotic Giant branch phases of evolution. We choose uncertainty intervals for each variable, and use these as input to MESA simulations. Treating MESA as a "black box," we apply two UQ techniques, Cauchy deviates and Quadratic Response Surface Models, to obtain bounds for the final white dwarf masses. Our study is a proof of concept applicable to other computational problems to enable a more robust understanding of incertitude. This work was supported in part by the US Department of Energy under grant DE-FG02-87ER40317.
Divergence-free MHD Simulations with the HERACLES Code
Directory of Open Access Journals (Sweden)
Vides J.
2013-12-01
Full Text Available Numerical simulations of the magnetohydrodynamics (MHD equations have played a significant role in plasma research over the years. The need of obtaining physical and stable solutions to these equations has led to the development of several schemes, all requiring to satisfy and preserve the divergence constraint of the magnetic field numerically. In this paper, we aim to show the importance of maintaining this constraint numerically. We investigate in particular the hyperbolic divergence cleaning technique applied to the ideal MHD equations on a collocated grid and compare it to the constrained transport technique that uses a staggered grid to maintain the property. The methods are implemented in the software HERACLES and several numerical tests are presented, where the robustness and accuracy of the different schemes can be directly compared.
ANL/HTP: a computer code for the simulation of heat pipe operation
Energy Technology Data Exchange (ETDEWEB)
McLennan, G.A.
1983-11-01
ANL/HTP is a computer code for the simulation of heat pipe operation, to predict heat pipe performance and temperature distributions during steady state operation. Source and sink temperatures and heat transfer coefficients can be set as input boundary conditions, and varied for parametric studies. Five code options are included to calculate performance for fixed operating conditions, or to vary any one of the four boundary conditions to determine the heat pipe limited performance. The performance limits included are viscous, sonic, entrainment capillary, and boiling, using the best available theories to model these effects. The code has built-in models for a number of wick configurations - open grooves, screen-covered grooves, screen-wrap, and arteries, with provision for expansion. The current version of the code includes the thermophysical properties of sodium as the working fluid in an expandable subroutine. The code-calculated performance agrees quite well with measured experiment data.
LEADS-DC: A computer code for intense dc beam nonlinear transport simulation
Institute of Scientific and Technical Information of China (English)
无
2011-01-01
An intense dc beam nonlinear transport code has been developed. The code is written in Visual FORTRAN 6.6 and has ~13000 lines. The particle distribution in the transverse cross section is uniform or Gaussian. The space charge forces are calculated by the PIC (particle in cell) scheme, and the effects of the applied fields on the particle motion are calculated with the Lie algebraic method through the third order approximation. Obviously,the solutions to the equations of particle motion are self-consistent. The results obtained from the theoretical analysis have been put in the computer code. Many optical beam elements are contained in the code. So, the code can simulate the intense dc particle motions in the beam transport lines, high voltage dc accelerators and ion implanters.
Bode, P; Bode, Paul; Ostriker, Jeremiah P.
2003-01-01
An improved implementation of an N-body code for simulating collisionless cosmological dynamics is presented. TPM (Tree-Particle-Mesh) combines the PM method on large scales with a tree code to handle particle-particle interactions at small separations. After the global PM forces are calculated, spatially distinct regions above a given density contrast are located; the tree code calculates the gravitational interactions inside these denser objects at higher spatial and temporal resolution. The new implementation includes individual particle time steps within trees, an improved treatment of tidal forces on trees, new criteria for higher force resolution and choice of time step, and parallel treatment of large trees. TPM is compared to P^3M and a tree code (GADGET) and is found to give equivalent results in significantly less time. The implementation is highly portable (requiring a Fortran compiler and MPI) and efficient on parallel machines. The source code can be found at http://astro.princeton.edu/~bode/TPM/
Energy Technology Data Exchange (ETDEWEB)
NONE
2001-01-01
In the report, research results discussed in 1999 fiscal year at Nuclear Code Evaluation Committee of Nuclear Code Research Committee were summarized. Present status of Monte Carlo simulation on nuclear energy study was described. Especially, besides of criticality, shielding and core analyses, present status of applications to risk and radiation damage analyses, high energy transport and nuclear theory calculations of Monte Carlo Method was described. The 18 papers are indexed individually. (J.P.N.)
Energy Technology Data Exchange (ETDEWEB)
Picard, Richard Roy [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Bhat, Kabekode Ghanasham [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2017-07-18
We examine sensitivity analysis and uncertainty quantification for molecular dynamics simulation. Extreme (large or small) output values for the LAMMPS code often occur at the boundaries of input regions, and uncertainties in those boundary values are overlooked by common SA methods. Similarly, input values for which code outputs are consistent with calibration data can also occur near boundaries. Upon applying approaches in the literature for imprecise probabilities (IPs), much more realistic results are obtained than for the complacent application of standard SA and code calibration.
Understanding Performance of Parallel Scientific Simulation Codes using Open|SpeedShop
Energy Technology Data Exchange (ETDEWEB)
Ghosh, K K
2011-11-07
Conclusions of this presentation are: (1) Open SpeedShop's (OSS) is convenient to use for large, parallel, scientific simulation codes; (2) Large codes benefit from uninstrumented execution; (3) Many experiments can be run in a short time - might need multiple shots e.g. usertime for caller-callee, hwcsamp for HW counters; (4) Decent idea of code's performance is easily obtained; (5) Statistical sampling calls for decent number of samples; and (6) HWC data is very useful for micro-analysis but can be tricky to analyze.
Energy Technology Data Exchange (ETDEWEB)
Takase, Haruhiko [Japan Atomic Energy Research Inst., Naka, Ibaraki (Japan). Naka Fusion Research Establishment; Senda, Ikuo
1999-04-01
A Toroidally Symmetric Plasma Simulation (TSPS) code has been developed for investigating the position and shape control on tokamak plasmas. The analyses of three-dimensional eddy currents on the conducting components around the plasma and the two-dimensional magneto-hydrodynamic (MHD) equilibrium are taken into account in this code. The code can analyze the plasma position and shape control during the minor disruption in which the deformation of plasma is not negligible. Using the ITER (International Thermonuclear Experimental Reactor) parameters, some examples of calculations are shown in this paper. (author)
Srna-Monte Carlo codes for proton transport simulation in combined and voxelized geometries
Ilic, R D; Stankovic, S J
2002-01-01
This paper describes new Monte Carlo codes for proton transport simulations in complex geometrical forms and in materials of different composition. The SRNA codes were developed for three dimensional (3D) dose distribution calculation in proton therapy and dosimetry. The model of these codes is based on the theory of proton multiple scattering and a simple model of compound nucleus decay. The developed package consists of two codes: SRNA-2KG and SRNA-VOX. The first code simulates proton transport in combined geometry that can be described by planes and second order surfaces. The second one uses the voxelized geometry of material zones and is specifically adopted for the application of patient computer tomography data. Transition probabilities for both codes are given by the SRNADAT program. In this paper, we will present the models and algorithms of our programs, as well as the results of the numerical experiments we have carried out applying them, along with the results of proton transport simulation obtaine...
Wareing, C J; Falle, S A E G; Van Loo, S
2016-01-01
We have used the AMR hydrodynamic code, MG, to perform 3D MHD simulations of the formation of clumpy and filamentary structure in a thermally unstable medium. A stationary thermally unstable spherical diffuse cloud with uniform density in pressure equilibrium with low density surroundings was seeded with random density variations and allowed to evolve. A range of magnetic field strengths threading the cloud have been explored, from beta=0.1 to beta=1.0 to the zero magnetic field case (beta=infinity), where beta is the ratio of thermal pressure to magnetic pressure. Once the density inhomogeneities had developed to the point where gravity started to become important, self-gravity was introduced to the simulation. With no magnetic field, clumps form within the cloud with aspect ratios of around unity, whereas in the presence of a relatively strong field (beta=0.1) these become filaments, then evolve into interconnected corrugated sheets that are predominantly perpendicular to the magnetic field. With magnetic a...
Lattice Boltzmann simulation of three-dimensional Rayleigh-Taylor instability
Liang, H.; Li, Q. X.; Shi, B. C.; Chai, Z. H.
2016-03-01
In this paper, the three-dimensional (3D) Rayleigh-Taylor instability (RTI) with low Atwood number (At=0.15 ) in a long square duct (12 W ×W ×W ) is studied by using a multiple-relaxation-time lattice Boltzmann (LB) multiphase model. The effect of the Reynolds number on the interfacial dynamics and bubble and spike amplitudes at late time is investigated in detail. The numerical results show that at sufficiently large Reynolds numbers, a sequence of stages in the 3D immiscible RTI can be observed, which includes the linear growth, terminal velocity growth, reacceleration, and chaotic development stages. At late stage, the RTI induces a very complicated topology structure of the interface, and an abundance of dissociative drops are also observed in the system. The bubble and spike velocities at late stage are unstable and their values have exceeded the predictions of the potential flow theory [V. N. Goncharov, Phys. Rev. Lett. 88, 134502 (2002), 10.1103/PhysRevLett.88.134502]. The acceleration of the bubble front is also measured and it is found that the normalized acceleration at late time fluctuates around a constant value of 0.16. When the Reynolds number is reduced to small values, some later stages cannot be reached sequentially. The interface becomes relatively smoothed and the bubble velocity at late time is approximate to a constant value, which coincides with the results of the extended Layzer model [S.-I. Sohn, Phys. Rev. E 80, 055302(R) (2009), 10.1103/PhysRevE.80.055302] and the modified potential theory [R. Banerjee, L. Mandal, S. Roy, M. Khan, and M. R. Guptae, Phys. Plasmas 18, 022109 (2011), 10.1063/1.3555523]. In our simulations, the Graphics Processing Unit (GPU) parallel computing is also used to relieve the massive computational cost.
Lin, Y.; Wing, S.; Johnson, J. R.; Wang, X. Y.; Perez, J. D.; Cheng, L.
2017-06-01
Global structure and evolution of flux tube entropy S, integrated over closed field lines, associated with magnetic reconnection in the magnetotail are investigated using the AuburN Global hybrId codE in three dimensions (3-D), ANGIE3D. Flux tubes with decreased entropy, or "bubbles," are found to be generated due to the sudden change of flux tube topology and thus volume in reconnection. By tracking the propagation of the entropy-depleted flux tubes, the roles of the entropy structure in plasma transport to the inner magnetosphere is examined with a self-consistent global hybrid simulation for the first time. The value of S first decreases due to the shortening of flux tubes and then increases due to local ion heating as the bubbles are injected earthward by interchange-ballooning instability, finally oscillating around an equilibrium radial distance where S is nearly the same as the ambient value. The pressure remains anisotropic and not constant along the flux tubes during their propagation with a nonzero heat flux along the field line throughout the duration of the simulation. The correlation of these bubbles with earthward fast flows and specific entropy s is also studied.
RAY-RAMSES: a code for ray tracing on the fly in N-body simulations
Barreira, Alexandre; Bose, Sownak; Li, Baojiu
2016-01-01
We present a ray tracing code to compute integrated cosmological observables on the fly in AMR N-body simulations. Unlike conventional ray tracing techniques, our code takes full advantage of the time and spatial resolution attained by the N-body simulation by computing the integrals along the line of sight on a cell-by-cell basis through the AMR simulation grid. Moroever, since it runs on the fly in the N-body run, our code can produce maps of the desired observables without storing large (or any) amounts of data for post-processing. We implemented our routines in the RAMSES N-body code and tested the implementation using an example of weak lensing simulation. We analyse basic statistics of lensing convergence maps and find good agreement with semi-analytical methods. The ray tracing methodology presented here can be used in several cosmological analysis such as Sunyaev-Zel'dovich and integrated Sachs-Wolfe effect studies as well as modified gravity. Our code can also be used in cross-checks of the more conv...
Min, Kyungguk; Liu, Kaijun
2016-01-01
Linear dispersion theory and electromagnetic particle-in-cell (PIC) simulations are used to investigate linear growth and nonlinear saturation of the proton velocity ring-driven instabilities, namely, ion Bernstein instability and Alfvén-cyclotron instability, which lead to fast magnetosonic waves and electromagnetic ion cyclotron waves in the inner magnetosphere, respectively. The proton velocity distribution is assumed to consist of 10% of a ring distribution and 90% of a low-temperature Maxwellian background. Here two cases with ring speeds vr/vA=1 and 2 (vA is the Alfvén speed) are examined in detail. For the two cases, linear theory predicts that the maximum growth rate γm of the Bernstein instability is 0.16Ωp and 0.19Ωp, respectively, and γm of the Alfvén-cyclotron instability is 0.045Ωp and 0.15Ωp, respectively, where Ωp is the proton cyclotron frequency. Two-dimensional PIC simulations are carried out for the two cases to examine the instability development and the corresponding evolution of the particle distributions. Initially, Bernstein waves develop and saturate with strong electrostatic fluctuations. Subsequently, electromagnetic Alfvén-cyclotron waves grow and saturate. Despite their smaller growth rate, the saturation levels of the Alfvén-cyclotron waves for both cases are larger than those of the Bernstein waves. Resonant interactions with the Bernstein waves lead to scattering of ring protons predominantly along the perpendicular velocity component (toward both decreasing and, at a lesser extent, increasing speeds) without substantial change of either the parallel temperature or the temperature anisotropy. Consequently, the Alfvén-cyclotron instability can still grow. Furthermore, the free energy resulting from the pitch angle scattering by the Alfvén-cyclotron waves is larger than the free energy resulting from the perpendicular energy scattering, thereby leading to the larger saturation level of the Alfvén-cyclotron waves.
Modeling of two-phase flow instabilities during startup transients utilizing RAMONA-4B methodology
Energy Technology Data Exchange (ETDEWEB)
Paniagua, J.; Rohatgi, U.S.; Prasad, V.
1996-10-01
RAMONA-4B code is currently under development for simulating thermal hydraulic instabilities that can occur in Boiling Water Reactors (BWRs) and the Simplified Boiling Water Reactor (SBWR). As one of the missions of RAMONA-4B is to simulate SBWR startup transients, where geysering or condensation-induced instability may be encountered, the code needs to be assessed for this application. This paper outlines the results of the assessments of the current version of RAMONA-4B and the modifications necessary for simulating the geysering or condensation-induced instability. The test selected for assessment are the geysering tests performed by Prof Aritomi (1993).
A new GPU-accelerated hydrodynamical code for numerical simulation of interacting galaxies
Igor, Kulikov
2013-01-01
In this paper a new scalable hydrodynamic code GPUPEGAS (GPU-accelerated PErformance Gas Astrophysic Simulation) for simulation of interacting galaxies is proposed. The code is based on combination of Godunov method as well as on the original implementation of FlIC method, specially adapted for GPU-implementation. Fast Fourier Transform is used for Poisson equation solution in GPUPEGAS. Software implementation of the above methods was tested on classical gas dynamics problems, new Aksenov's test and classical gravitational gas dynamics problems. Collisionless hydrodynamic approach was used for modelling of stars and dark matter. The scalability of GPUPEGAS computational accelerators is shown.
Energy Technology Data Exchange (ETDEWEB)
Serfontein, Dawid E., E-mail: Dawid.Serfontein@nwu.ac.za [School of Mechanical and Nuclear Engineering, North West University (PUK-Campus), PRIVATE BAG X6001 (Internal Post Box 360), Potchefstroom 2520 (South Africa); Mulder, Eben J. [School of Mechanical and Nuclear Engineering, North West University (South Africa); Reitsma, Frederik [Calvera Consultants (South Africa)
2014-05-01
A computer code was developed for the semi-automatic translation of input models for the VSOP-A diffusion neutronics simulation code to the format of the newer VSOP 99/05 code. In this paper, this algorithm is presented as a generic method for producing codes for the automatic translation of input models from the format of one code version to another, or even to that of a completely different code. Normally, such translations are done manually. However, input model files, such as for the VSOP codes, often are very large and may consist of many thousands of numeric entries that make no particular sense to the human eye. Therefore the task, of for instance nuclear regulators, to verify the accuracy of such translated files can be very difficult and cumbersome. This may cause translation errors not to be picked up, which may have disastrous consequences later on when a reactor with such a faulty design is built. Therefore a generic algorithm for producing such automatic translation codes may ease the translation and verification process to a great extent. It will also remove human error from the process, which may significantly enhance the accuracy and reliability of the process. The developed algorithm also automatically creates a verification log file which permanently record the names and values of each variable used, as well as the list of meanings of all the possible values. This should greatly facilitate reactor licensing applications.
Inclusion of models to describe severe accident conditions in the fuel simulation code DIONISIO
Energy Technology Data Exchange (ETDEWEB)
Lemes, Martín; Soba, Alejandro [Sección Códigos y Modelos, Gerencia Ciclo del Combustible Nuclear, Comisión Nacional de Energía Atómica, Avenida General Paz 1499, 1650 San Martín, Provincia de Buenos Aires (Argentina); Daverio, Hernando [Gerencia Reactores y Centrales Nucleares, Comisión Nacional de Energía Atómica, Avenida General Paz 1499, 1650 San Martín, Provincia de Buenos Aires (Argentina); Denis, Alicia [Sección Códigos y Modelos, Gerencia Ciclo del Combustible Nuclear, Comisión Nacional de Energía Atómica, Avenida General Paz 1499, 1650 San Martín, Provincia de Buenos Aires (Argentina)
2017-04-15
The simulation of fuel rod behavior is a complex task that demands not only accurate models to describe the numerous phenomena occurring in the pellet, cladding and internal rod atmosphere but also an adequate interconnection between them. In the last years several models have been incorporated to the DIONISIO code with the purpose of increasing its precision and reliability. After the regrettable events at Fukushima, the need for codes capable of simulating nuclear fuels under accident conditions has come forth. Heat removal occurs in a quite different way than during normal operation and this fact determines a completely new set of conditions for the fuel materials. A detailed description of the different regimes the coolant may exhibit in such a wide variety of scenarios requires a thermal-hydraulic formulation not suitable to be included in a fuel performance code. Moreover, there exist a number of reliable and famous codes that perform this task. Nevertheless, and keeping in mind the purpose of building a code focused on the fuel behavior, a subroutine was developed for the DIONISIO code that performs a simplified analysis of the coolant in a PWR, restricted to the more representative situations and provides to the fuel simulation the boundary conditions necessary to reproduce accidental situations. In the present work this subroutine is described and the results of different comparisons with experimental data and with thermal-hydraulic codes are offered. It is verified that, in spite of its comparative simplicity, the predictions of this module of DIONISIO do not differ significantly from those of the specific, complex codes.
FAST: a three-dimensional time-dependent FEL simulation code
Saldin, E L; Yurkov, M V
1999-01-01
In this report we briefly describe the three-dimensional, time-dependent FEL simulation code FAST. The equations of motion of the particles and Maxwell's equations are solved simultaneously taking into account the slippage effect. Radiation fields are calculated using an integral solution of Maxwell's equations. A special technique has been developed for fast calculations of the radiation field, drastically reducing the required CPU time. As a result, the developed code allows one to use a personal computer for time-dependent simulations. The code allows one to simulate the radiation from the electron bunch of any transverse and longitudinal bunch shape; to simulate simultaneously an external seed with superimposed noise in the electron beam; to take into account energy spread in the electron beam and the space charge fields; and to simulate a high-gain, high-efficiency FEL amplifier with a tapered undulator. It is important to note that there are no significant memory limitations in the developed code and an...
Energy Technology Data Exchange (ETDEWEB)
Patra, Anirban [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Tome, Carlos [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2016-03-23
This Milestone report shows good progress in interfacing VPSC with the FE codes ABAQUS and MOOSE, to perform component-level simulations of irradiation-induced deformation in Zirconium alloys. In this preliminary application, we have performed an irradiation growth simulation in the quarter geometry of a cladding tube. We have benchmarked VPSC-ABAQUS and VPSC-MOOSE predictions with VPSC-SA predictions to verify the accuracy of the VPSCFE interface. Predictions from the FE simulations are in general agreement with VPSC-SA simulations and also with experimental trends.
Zhang, Shuai; Morita, Koji; Shirakawa, Noriyuki; Yamamoto, Yuichi
The COMPASS code is designed based on the moving particle semi-implicit method to simulate various complex mesoscale phenomena relevant to core disruptive accidents of sodium-cooled fast reactors. In this study, a computational framework for fluid-solid mixture flow simulations was developed for the COMPASS code. The passively moving solid model was used to simulate hydrodynamic interactions between fluid and solids. Mechanical interactions between solids were modeled by the distinct element method. A multi-time-step algorithm was introduced to couple these two calculations. The proposed computational framework for fluid-solid mixture flow simulations was verified by the comparison between experimental and numerical studies on the water-dam break with multiple solid rods.
Simulation of positron backscattering and implantation profiles using Geant4 code
Institute of Scientific and Technical Information of China (English)
黄世娟; 潘子文; 刘建党; 韩荣典; 叶邦角
2015-01-01
For the proper interpretation of the experimental data produced in slow positron beam technique, the positron im-plantation properties are studied carefully using the latest Geant4 code. The simulated backscattering coefficients, the implantation profiles, and the median implantation depths for mono-energetic positrons with energy range from 1 keV to 50 keV normally incident on different crystals are reported. Compared with the previous experimental results, our simula-tion backscattering coefficients are in reasonable agreement, and we think that the accuracy may be related to the structures of the host materials in the Geant4 code. Based on the reasonable simulated backscattering coefficients, the adjustable parameters of the implantation profiles which are dependent on materials and implantation energies are obtained. The most important point is that we calculate the positron backscattering coefficients and median implantation depths in amorphous polymers for the first time and our simulations are in fairly good agreement with the previous experimental results.
A FEW ASPECTS REGARDING THE SIMULATION OF CONTRACT IN THE ROMANIAN CIVIL CODE
Directory of Open Access Journals (Sweden)
Tudor Vlad RĂDULESCU
2017-05-01
Full Text Available The article aims to analyze some key aspects of simulation in contracts, as regulated by the Romanian Civil Code . The process of simulation will be explained, based on the provisions of the previous Civil Code, but also with reference to the relevant provisions of the legislation of some European countries. The analyse will focus on the apparent act, and also on the secret one and a special emphasis on intention to simulate, animo simulandi, the key aspect of the matter. Also the effects of the simulation will be reviewed, both from the point of view of the parties and that of third parties, the concept of third parties having another meaning in this procedure.
GLAMER Part I: A Code for Gravitational Lensing Simulations with Adaptive Mesh Refinement
Metcalf, R Benton
2013-01-01
A computer code is described for the simulation of gravitational lensing data. The code incorporates adaptive mesh refinement in choosing which rays to shoot based on the requirements of the source size, location and surface brightness distribution or to find critical curves/caustics. A variety of source surface brightness models are implemented to represent galaxies and quasar emission regions. The lensing mass can be represented by point masses (stars), smoothed simulation particles, analytic halo models, pixelized mass maps or any combination of these. The deflection and beam distortions (convergence and shear) are calculated by modified tree algorithm when halos, point masses or particles are used and by FFT when mass maps are used. The combination of these methods allow for a very large dynamical range to be represented in a single simulation. Individual images of galaxies can be represented in a simulation that covers many square degrees. For an individual strongly lensed quasar, source sizes from the s...
A program code generator for multiphysics biological simulation using markup languages.
Amano, Akira; Kawabata, Masanari; Yamashita, Yoshiharu; Rusty Punzalan, Florencio; Shimayoshi, Takao; Kuwabara, Hiroaki; Kunieda, Yoshitoshi
2012-01-01
To cope with the complexity of the biological function simulation models, model representation with description language is becoming popular. However, simulation software itself becomes complex in these environment, thus, it is difficult to modify the simulation conditions, target computation resources or calculation methods. In the complex biological function simulation software, there are 1) model equations, 2) boundary conditions and 3) calculation schemes. Use of description model file is useful for first point and partly second point, however, third point is difficult to handle for various calculation schemes which is required for simulation models constructed from two or more elementary models. We introduce a simulation software generation system which use description language based description of coupling calculation scheme together with cell model description file. By using this software, we can easily generate biological simulation code with variety of coupling calculation schemes. To show the efficiency of our system, example of coupling calculation scheme with three elementary models are shown.
Silantyev, Denis A.; Lushnikov, Pavel M.; Rose, Harvey A.
2017-04-01
A nonlinear Langmuir wave in the kinetic regime k λ D ≳ 0.2 may have a filamentation instability, where k is the wavenumber and λD is the Debye length. The nonlinear stage of that instability develops into the filamentation of Langmuir waves which in turn leads to the saturation of the stimulated Raman scattering in laser-plasma interaction experiments. Here, we study the linear stage of the filamentation instability of the particular family (H. A. Rose and D. A. Russell, Phys. Plasmas 8, 4784 (2001)) of Bernstein-Greene-Kruskal (BGK) modes (I. B. Bernstein et al., Phys. Rev. 108, 546 (1957)) that is a bifurcation of the linear Langmuir wave. Performing direct 2 + 2D Vlasov-Poisson simulations of collisionless plasma, we find the growth rates of oblique modes of the electric field as a function of BGK's amplitude, wavenumber, and the angle of the oblique mode's wavevector relative to the BGK's wavevector. Simulation results are compared to theoretical predictions.
An introduction to LIME 1.0 and its use in coupling codes for multiphysics simulations.
Energy Technology Data Exchange (ETDEWEB)
Belcourt, Noel; Pawlowski, Roger Patrick; Schmidt, Rodney Cannon; Hooper, Russell Warren
2011-11-01
LIME is a small software package for creating multiphysics simulation codes. The name was formed as an acronym denoting 'Lightweight Integrating Multiphysics Environment for coupling codes.' LIME is intended to be especially useful when separate computer codes (which may be written in any standard computer language) already exist to solve different parts of a multiphysics problem. LIME provides the key high-level software (written in C++), a well defined approach (with example templates), and interface requirements to enable the assembly of multiple physics codes into a single coupled-multiphysics simulation code. In this report we introduce important software design characteristics of LIME, describe key components of a typical multiphysics application that might be created using LIME, and provide basic examples of its use - including the customized software that must be written by a user. We also describe the types of modifications that may be needed to individual physics codes in order for them to be incorporated into a LIME-based multiphysics application.
Simulation of hydrogen deflagration experiment – Benchmark exercise with lumped-parameter codes
Energy Technology Data Exchange (ETDEWEB)
Kljenak, Ivo, E-mail: ivo.kljenak@ijs.si [Jožef Stefan Institute, Jamova cesta 39, SI-1000 Ljubljana (Slovenia); Kuznetsov, Mikhail, E-mail: mike.kuznetsov@kit.edu [Karlsruhe Institute of Technology, Kaiserstraße 12, 76131 Karlsruhe (Germany); Kostka, Pal, E-mail: kostka@nubiki.hu [NUBIKI Nuclear Safety Research Institute, Konkoly-Thege Miklós út 29-33, 1121 Budapest (Hungary); Kubišova, Lubica, E-mail: lubica.kubisova@ujd.gov.sk [Nuclear Regulatory Authority of the Slovak Republic, Bajkalská 27, 82007 Bratislava (Slovakia); Maltsev, Mikhail, E-mail: maltsev_MB@aep.ru [JSC Atomenergoproekt, 1, st. Podolskykh Kursantov, Moscow (Russian Federation); Manzini, Giovanni, E-mail: giovanni.manzini@rse-web.it [Ricerca sul Sistema Energetico, Via Rubattino 54, 20134 Milano (Italy); Povilaitis, Mantas, E-mail: mantas.p@mail.lei.lt [Lithuania Energy Institute, Breslaujos g.3, 44403 Kaunas (Lithuania)
2015-03-15
Highlights: • Blind and open simulations of hydrogen combustion experiment in large-scale containment-like facility with different lumped-parameter codes. • Simulation of axial as well as radial flame propagation. • Confirmation of adequacy of lumped-parameter codes for safety analyses of actual nuclear power plants. - Abstract: An experiment on hydrogen deflagration (Upward Flame Propagation Experiment – UFPE) was proposed by the Jozef Stefan Institute (Slovenia) and performed in the HYKA A2 facility at the Karlsruhe Institute of Technology (Germany). The experimental results were used to organize a benchmark exercise for lumped-parameter codes. Six organizations (JSI, AEP, LEI, NUBIKI, RSE and UJD SR) participated in the benchmark exercise, using altogether four different computer codes: ANGAR, ASTEC, COCOSYS and ECART. Both blind and open simulations were performed. In general, all the codes provided satisfactory results of the pressure increase, whereas the results of the temperature show a wider dispersal. Concerning the flame axial and radial velocities, the results may be considered satisfactory, given the inherent simplification of the lumped-parameter description compared to the local instantaneous description.
Directory of Open Access Journals (Sweden)
Annamaria Buonomano
2016-04-01
Full Text Available In this paper details about the results of a code-to-code validation procedure of an in-house developed building simulation model, called DETECt, are reported. The tool was developed for research purposes in order to carry out dynamic building energy performance and parametric analyses by taking into account new building envelope integrated technologies, novel construction materials and innovative energy saving strategies. The reliability and accuracy of DETECt was appropriately tested by means of the standard BESTEST validation procedure. In the paper, details of this validation process are accurately described. A good agreement between the obtained results and all the reference data of the BESTEST qualification cases is achieved. In particular, the obtained results vs. standard BESTEST output are always within the provided ranges of confidence. In addition, several test cases output obtained by DETECt (e.g., dynamic profiles of indoor air and building surfaces temperature and heat fluxes and spatial trends of temperature across walls are provided.
Wareing, C. J.; Pittard, J. M.; Falle, S. A. E. G.; Van Loo, S.
2016-06-01
We have used the adaptive mesh refinement hydrodynamic code, MG, to perform idealized 3D magnetohydrodynamical simulations of the formation of clumpy and filamentary structure in a thermally unstable medium without turbulence. A stationary thermally unstable spherical diffuse atomic cloud with uniform density in pressure equilibrium with low density surroundings was seeded with random density variations and allowed to evolve. A range of magnetic field strengths threading the cloud have been explored, from β = 0.1 to 1.0 to the zero magnetic field case (β = ∞), where β is the ratio of thermal pressure to magnetic pressure. Once the density inhomogeneities had developed to the point where gravity started to become important, self-gravity was introduced to the simulation. With no magnetic field, clouds and clumps form within the cloud with aspect ratios of around unity, whereas in the presence of a relatively strong field (β = 0.1) these become filaments, then evolve into interconnected corrugated sheets that are predominantly perpendicular to the magnetic field. With magnetic and thermal pressure equality (β = 1.0), filaments, clouds and clumps are formed. At any particular instant, the projection of the 3D structure on to a plane parallel to the magnetic field, i.e. a line of sight perpendicular to the magnetic field, resembles the appearance of filamentary molecular clouds. The filament densities, widths, velocity dispersions and temperatures resemble those observed in molecular clouds. In contrast, in the strong field case β = 0.1, projection of the 3D structure along a line of sight parallel to the magnetic field reveals a remarkably uniform structure.
Lehe, Remi; Kirchen, Manuel; Godfrey, Brendan B.; Maier, Andreas R.; Vay, Jean-Luc
2016-11-01
Particle-in-cell (PIC) simulations of relativistic flowing plasmas are of key interest to several fields of physics (including, e.g., laser-wakefield acceleration, when viewed in a Lorentz-boosted frame) but remain sometimes infeasible due to the well-known numerical Cherenkov instability (NCI). In this article, we show that, for a plasma drifting at a uniform relativistic velocity, the NCI can be eliminated by simply integrating the PIC equations in Galilean coordinates that follow the plasma (also sometimes known as comoving coordinates) within a spectral analytical framework. The elimination of the NCI is verified empirically and confirmed by a theoretical analysis of the instability. Moreover, it is shown that this method is applicable both to Cartesian geometry and to cylindrical geometry with azimuthal Fourier decomposition.
Lehe, Remi; Godfrey, Brendan B; Maier, Andreas R; Vay, Jean-Luc
2016-01-01
Particle-In-Cell (PIC) simulations of relativistic flowing plasmas are of key interest to several fields of physics (including e.g. laser-wakefield acceleration, when viewed in a Lorentz-boosted frame), but remain sometimes infeasible due to the well-known numerical Cherenkov instability (NCI). In this article, we show that, for a plasma drifting at a uniform relativistic velocity, the NCI can be eliminated by simply integrating the PIC equations in Galilean coordinates that follow the plasma (also sometimes known as comoving coordinates) within a spectral analytical framework. The elimination of the NCI is verified empirically and confirmed by a theoretical analysis of the instability. Moreover, it is shown that this method is applicable both to Cartesian geometry and to cylindrical geometry with azimuthal Fourier decomposition.
Shukla, Chandrasekhar; Das, Amita; Patel, Kartik
2016-08-01
We carry out particle-in-cell simulations to study the instabilities associated with a 2-D sheared electron flow configuration against a neutralizing background of ions. Both weak and strong relativistic flow velocities are considered. In the weakly relativistic case, we observe the development of electromagnetic Kelvin-Helmholtz instability with similar characteristics as that predicted by the electron Magnetohydrodynamic (EMHD) model. On the contrary, in a strong relativistic case, the compressibility effects of electron fluid dominate and introduce upper hybrid electrostatic oscillations transverse to the flow which are very distinct from EMHD fluid behavior. In the nonlinear regime, both weak and strong relativistic cases lead to turbulence with broad power law spectrum.
Zhang, Weiqun; Wang, Peng
2008-01-01
Magnetic field strengths inferred for relativistic outflows including gamma-ray bursts (GRB) and active galactic nuclei (AGN) are larger than naively expected by orders of magnitude. We present three-dimensional relativistic magnetohydrodynamics (MHD) simulations demonstrating amplification and saturation of magnetic field by a macroscopic turbulent dynamo triggered by the Kelvin-Helmholtz shear instability. We find rapid growth of electromagnetic energy due to the stretching and folding of field lines in the turbulent velocity field resulting from non-linear development of the instability. Using conditions relevant for GRB internal shocks and late phases of GRB afterglow, we obtain amplification of the electromagnetic energy fraction to $\\epsilon_B \\sim 5 \\times 10^{-3}$. This value decays slowly after the shear is dissipated and appears to be largely independent of the initial field strength. The conditions required for operation of the dynamo are the presence of velocity shear and some seed magnetization b...
A New Code SORD for Simulation of Polarized Light Scattering in the Earth Atmosphere
Korkin, Sergey; Lyapustin, Alexei; Sinyuk, Aliaksandr; Holben, Brent
2016-01-01
We report a new publicly available radiative transfer (RT) code for numerical simulation of polarized light scattering in plane-parallel atmosphere of the Earth. Using 44 benchmark tests, we prove high accuracy of the new RT code, SORD (Successive ORDers of scattering). We describe capabilities of SORD and show run time for each test on two different machines. At present, SORD is supposed to work as part of the Aerosol Robotic NETwork (AERONET) inversion algorithm. For natural integration with the AERONET software, SORD is coded in Fortran 90/95. The code is available by email request from the corresponding (first) author or from ftp://climate1.gsfc.nasa.gov/skorkin/SORD/.
A PIC-MCC code for simulation of streamer propagation in air
DEFF Research Database (Denmark)
Chanrion, Olivier Arnaud; Neubert, Torsten
2008-01-01
A particle code has been developed to study the distribution and acceleration of electrons in electric discharges in air. The code can follow the evolution of a discharge from the initial stage of a single free electron in a background electric field to the formation of an electron avalanche...... particles are followed in a Cartesian mesh and the electric field is updated with Poisson's equation from the charged particle densities. Collisional processes between electrons and air molecules are simulated with a Monte Carlo technique, according to cross section probabilities. The code also includes...... photoionisation processes of air molecules by photons emitted by excited constituents. The paper describes the code and presents some results of streamer development at 70km altitude in the mesosphere where electrical discharges (sprites) are generated above severe thunderstorms and at ∼10km relevant...
X-ray simulation with the Monte Carlo code PENELOPE. Application to Quality Control.
Pozuelo, F; Gallardo, S; Querol, A; Verdú, G; Ródenas, J
2012-01-01
A realistic knowledge of the energy spectrum is very important in Quality Control (QC) of X-ray tubes in order to reduce dose to patients. However, due to the implicit difficulties to measure the X-ray spectrum accurately, it is not normally obtained in routine QC. Instead, some parameters are measured and/or calculated. PENELOPE and MCNP5 codes, based on the Monte Carlo method, can be used as complementary tools to verify parameters measured in QC. These codes allow estimating Bremsstrahlung and characteristic lines from the anode taking into account specific characteristics of equipment. They have been applied to simulate an X-ray spectrum. Results are compared with theoretical IPEM 78 spectrum. A sensitivity analysis has been developed to estimate the influence on simulated spectra of important parameters used in simulation codes. With this analysis it has been obtained that the FORCE factor is the most important parameter in PENELOPE simulations. FORCE factor, which is a variance reduction method, improves the simulation but produces hard increases of computer time. The value of FORCE should be optimized so that a good agreement of simulated and theoretical spectra is reached, but with a reduction of computer time. Quality parameters such as Half Value Layer (HVL) can be obtained with the PENELOPE model developed, but FORCE takes such a high value that computer time is hardly increased. On the other hand, depth dose assessment can be achieved with acceptable results for small values of FORCE.
The NEST Dry-Run Mode: Efficient Dynamic Analysis of Neuronal Network Simulation Code
Directory of Open Access Journals (Sweden)
Susanne Kunkel
2017-06-01
Full Text Available NEST is a simulator for spiking neuronal networks that commits to a general purpose approach: It allows for high flexibility in the design of network models, and its applications range from small-scale simulations on laptops to brain-scale simulations on supercomputers. Hence, developers need to test their code for various use cases and ensure that changes to code do not impair scalability. However, running a full set of benchmarks on a supercomputer takes up precious compute-time resources and can entail long queuing times. Here, we present the NEST dry-run mode, which enables comprehensive dynamic code analysis without requiring access to high-performance computing facilities. A dry-run simulation is carried out by a single process, which performs all simulation steps except communication as if it was part of a parallel environment with many processes. We show that measurements of memory usage and runtime of neuronal network simulations closely match the corresponding dry-run data. Furthermore, we demonstrate the successful application of the dry-run mode in the areas of profiling and performance modeling.
Parallelization issues of a code for physically-based simulation of fabrics
Romero, Sergio; Gutiérrez, Eladio; Romero, Luis F.; Plata, Oscar; Zapata, Emilio L.
2004-10-01
The simulation of fabrics, clothes, and flexible materials is an essential topic in computer animation of realistic virtual humans and dynamic sceneries. New emerging technologies, as interactive digital TV and multimedia products, make necessary the development of powerful tools to perform real-time simulations. Parallelism is one of such tools. When analyzing computationally fabric simulations we found these codes belonging to the complex class of irregular applications. Frequently this kind of codes includes reduction operations in their core, so that an important fraction of the computational time is spent on such operations. In fabric simulators these operations appear when evaluating forces, giving rise to the equation system to be solved. For this reason, this paper discusses only this phase of the simulation. This paper analyzes and evaluates different irregular reduction parallelization techniques on ccNUMA shared memory machines, applied to a real, physically-based, fabric simulator we have developed. Several issues are taken into account in order to achieve high code performance, as exploitation of data access locality and parallelism, as well as careful use of memory resources (memory overhead). In this paper we use the concept of data affinity to develop various efficient algorithms for reduction parallelization exploiting data locality.
Bierwage, Andreas; Spong, Donald A.
2009-05-01
Hybrid-MHD-Gyrokinetic Code (HMGC) [1] and the gyrofluid code TAEFL [2,3] are used for nonlinear simulation of Alfven Eigenmodes in Tokamak plasma. We compare results obtained in two cases: (I) a case designed for cross-code benchmark of TAE excitation; (II) a case based on a dedicated DIII-D shot #132707 where RSAE and TAE activity is observed. Differences between the numerical simulation results are discussed and future directions are outlined. [1] S. Briguglio, G. Vlad, F. Zonca and C. Kar, Phys. Plasmas 2 (1995) 3711. [2] D.A. Spong, B.A. Carreras and C.L. Hedrick, Phys. Fluids B4 (1992) 3316. [3] D.A. Spong, B.A. Carreras and C.L. Hedrick, Phys. Plasmas 1 (1994) 1503.
DEFF Research Database (Denmark)
Hernandez, Nestor; Pihl, Jeppe; Heide, Janus
One of the proven benets of Network Coding (NC) is to achieve the data capacity for multicast networks. However, even though there has been a signicant amount of research in this area, potentials demonstrators of these capabilities have not been widely shown or deployed. Thus, in this work we...... present a set of pre-computed ns-3 simulations to model the behaviour of Wurf.it, a Random Linear Network Coding (RLNC)-based reliable multicast solution for content distribution with cross-platform support. Wurf.it is based on Kodo, a C++11 network coding library that provides the primitive encoding...... demonstrator consists of stored simulations with ns-3 in a laptop and a Wurf.it implementation within a WiFi network. For the implementation, a video content from a mobile camera is distributed with low delay using SCORE to a set of heterogenous receivers (e.g. dierent platforms). Use cases of Wurf.it are mild...
An efficient simulation method of a cyclotron sector-focusing magnet using 2D Poisson code
Energy Technology Data Exchange (ETDEWEB)
Gad Elmowla, Khaled Mohamed M; Chai, Jong Seo, E-mail: jschai@skku.edu; Yeon, Yeong H; Kim, Sangbum; Ghergherehchi, Mitra
2016-10-01
In this paper we discuss design simulations of a spiral magnet using 2D Poisson code. The Independent Layers Method (ILM) is a new technique that was developed to enable the use of two-dimensional simulation code to calculate a non-symmetric 3-dimensional magnetic field. In ILM, the magnet pole is divided into successive independent layers, and the hill and valley shape around the azimuthal direction is implemented using a reference magnet. The normalization of the magnetic field in the reference magnet produces a profile that can be multiplied by the maximum magnetic field in the hill magnet, which is a dipole magnet made of the hills at the same radius. Both magnets are then calculated using the 2D Poisson SUPERFISH code. Then a fully three-dimensional magnetic field is produced using TOSCA for the original spiral magnet, and the comparison of the 2D and 3D results shows a good agreement between both.
The linear tearing instability in three dimensional, toroidal gyro-kinetic simulations
Energy Technology Data Exchange (ETDEWEB)
Hornsby, W. A., E-mail: william.hornsby@ipp.mpg.de; Migliano, P.; Buchholz, R.; Kroenert, L.; Weikl, A.; Peeters, A. G. [Theoretical Physics V, Department of Physics, Universitaet Bayreuth, Bayreuth D-95447 (Germany); Zarzoso, D.; Poli, E. [Max-Planck-Institut für Plasmaphysik, Boltzmannstrasse 2, D-85748 Garching bei München (Germany); Casson, F. J. [CCFE, Culham Science Centre, Abingdon, Oxon OX14 3DB (United Kingdom)
2015-02-15
Linear gyro-kinetic simulations of the classical tearing mode in three-dimensional toroidal geometry were performed using the global gyro-kinetic turbulence code, GKW. The results were benchmarked against a cylindrical ideal MHD and analytical theory calculations. The stability, growth rate, and frequency of the mode were investigated by varying the current profile, collisionality, and the pressure gradients. Both collisionless and semi-collisional tearing modes were found with a smooth transition between the two. A residual, finite, rotation frequency of the mode even in the absence of a pressure gradient is observed, which is attributed to toroidal finite Larmor-radius effects. When a pressure gradient is present at low collisionality, the mode rotates at the expected electron diamagnetic frequency. However, the island rotation reverses direction at high collisionality. The growth rate is found to follow a η{sup 1∕7} scaling with collisional resistivity in the semi-collisional regime, closely following the semi-collisional scaling found by Fitzpatrick. The stability of the mode closely follows the stability analysis as performed by Hastie et al. using the same current and safety factor profiles but for cylindrical geometry, however, here a modification due to toroidal coupling and pressure effects is seen.
Use of numerical simulation computer codes to fire problems in nuclear power plants in Finland
Energy Technology Data Exchange (ETDEWEB)
Keski-Rahkonen, O.; Eloranta, E. (Valtion Teknillinen Tutkimuskeskus, Espoo (Finland). Fire Technology Lab.); Huhtanen, R. (Valtion Teknillinen Tutkimuskeskus, Helsinki (Finland). Nuclear Engineering Lab.)
1991-03-01
Zone and field model codes are used for fire simulations, including nuclear facilities, in Finland. Here two examples are described: (a) calculation of evaporation rate of a pool fire (8 MW) in a compartment using FIRST, and calculation of an oil spill fire (180 MW) in a turbine hall using PHOENICS. (orig.).
Multi-dimensional free-electron laser simulation codes: a comparison study
Biedron, S G; Dejus, Roger J; Faatz, B; Freund, H P; Milton, S V; Nuhn, H D; Reiche, S
2000-01-01
A self-amplified spontaneous emission (SASE) free-electron laser (FEL) is under construction at the Advanced Photon Source (APS). Five FEL simulation codes were used in the design phase: GENESIS, GINGER, MEDUSA, RON, and TDA3D. Initial comparisons between each of these independent formulations show good agreement for the parameters of the APS SASE FEL.
Laboratory and numerical simulation of internal wave attractors and their instability.
Brouzet, Christophe; Dauxois, Thierry; Ermanyuk, Evgeny; Joubaud, Sylvain; Sibgatullin, Ilias
2015-04-01
Internal wave attractors are formed as result of focusing of internal gravity waves in a confined domain of stably stratified fluid due to peculiarities of reflections properties [1]. The energy injected into domain due to external perturbation, is concentrated along the path formed by the attractor. The existence of attractors was predicted theoretically and proved both experimentally and numerically [1-4]. Dynamics of attractors is greatly influenced by geometrical focusing, viscous dissipation and nonlinearity. The experimental setup features Schmidt number equal to 700 which impose constraints on resolution in numerical schemes. Also for investigation of stability on large time intervals (about 1000 periods of external forcing) numerical viscosity may have significant impact. For these reasons, we have chosen spectral element method for investigation of this problem, what allows to carefully follow the nonlinear dynamics. We present cross-comparison of experimental observations and numerical simulations of long-term behavior of wave attractors. Fourier analysis and subsequent application of Hilbert transform are used for filtering of spatial components of internal-wave field [5]. The observed dynamics shows a complicated coupling between the effects of local instability and global confinement of the fluid domain. The unstable attractor is shown to act as highly efficient mixing box providing the efficient energy pathway from global-scale excitation to small-scale wave motions and mixing. Acknowledgement, IS has been partially supported by Russian Ministry of Education and Science (agreement id RFMEFI60714X0090) and Russian Foundation for Basic Research, grant N 15-01-06363. EVE gratefully acknowledges his appointment as a Marie Curie incoming fellow at Laboratoire de physique ENS de Lyon. This work has been partially supported by the ONLITUR grant (ANR-2011-BS04-006-01) and achieved thanks to the resources of PSMN from ENS de Lyon 1. Maas, L. R. M. & Lam, F
Santos-Lima, R.; de Gouveia Dal Pino, E. M.; Falceta-Gonçalves, D. A.; Nakwacki, M. S.; Kowal, G.
2017-03-01
Statistical analysis of Faraday rotation measure (RM) maps of the intracluster medium (ICM) of galaxy clusters provides a unique tool to evaluate some spatial features of the magnetic fields there. Its combination with numerical simulations of magnetohydrodynamic (MHD) turbulence allows the diagnosis of the ICM turbulence. Being the ICM plasma weakly collisional, the thermal velocity distribution of the particles naturally develops anisotropies as a consequence of the large-scale motions and the conservation of the magnetic moment of the charged particles. A previous study (Paper I) analysed the impact of large-scale thermal anisotropy on the statistics of RM maps synthesized from simulations of turbulence; these simulations employed a collisionless MHD model that considered a tensor pressure with uniform anisotropy. In this work, we extend that analysis to a collisionless MHD model in which the thermal anisotropy develops according to the conservation of the magnetic moment of the thermal particles. We also consider the effect of anisotropy relaxation caused by the microscale mirror and firehose instabilities. We show that if the relaxation rate is fast enough to keep the anisotropy limited by the threshold values of the instabilities, the dispersion and power spectrum of the RM maps are indistinguishable from those obtained from collisional MHD. Otherwise, there is a reduction in the dispersion and steepening of the power spectrum of the RM maps (compared to the collisional case). Considering the first scenario, the use of collisional MHD simulations for modelling the RM statistics in the ICM becomes better justified.
Numerical simulation of lowest-order short-crested wave instabilities
DEFF Research Database (Denmark)
Fuhrman, David R.; Madsen, Per A.; Bingham, Harry
2006-01-01
instabilities. These correctly lead to well-known (nearly symmetric) recurrence cycles below a previously established breaking threshold steepness, and to an asymmetric evolution (characterized by a permanent transfer of energy to the lower side-band) above this threshold, with dissipation from a smoothing......-bands. At larger steepness, the evolution leads to a permanent downshift of both the mean and peak frequencies, driven in part by dissipation, effectively breaking the quasi-recurrence cycle. A single case involving a class Ib short-crested wave instability at relatively large steepness is also considered, which...
Code OK2—A simulation code of ion-beam illumination on an arbitrary shape and structure target
Ogoyski, A. I.; Kawata, S.; Someya, T.
2004-08-01
For computer simulations on heavy ion beam (HIB) irradiation on a spherical fuel pellet in heavy ion fusion (HIF) the code OK1 was developed and presented in [Comput. Phys. Commun. 157 (2004) 160-172]. The new code OK2 is a modified upgraded computer program for more common purposes in research fields of medical treatment, material processing as well as HIF. OK2 provides computational capabilities of a three-dimensional ion beam energy deposition on a target with an arbitrary shape and structure. Program summaryTitle of program: OK2 Catalogue identifier: ADTZ Other versions of this program [1] : Title of the program: OK1 Catalogue identifier: ADST Program summary URL:http://cpc.cs.qub.as.uk/summaries/ADTZ Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland Computer: PC (Pentium 4, ˜1 GHz or more recommended) Operating system: Windows or UNIX Program language used: C++ Memory required to execute with typical data: 2048 MB No. of bits in a word: 32 No. of processors used: 1CPU Has the code been vectorized or parallelized: No No. of bytes in distributed program, including test data: 17 334 No of lines in distributed program, including test date: 1487 Distribution format: tar gzip file Nature of physical problem: In research areas of HIF (Heavy Ion Beam Inertial Fusion) energy [1-4] and medical material sciences [5], ion energy deposition profiles need to be evaluated and calculated precisely. Due to a favorable energy deposition behavior of ions in matter [1-4] it is expected that ion beams would be one of preferable candidates in various fields including HIF and material processing. Especially in HIF for a successful fuel ignition and a sufficient fusion energy release, a stringent requirement is imposed on the HIB irradiation non-uniformity, which should be less than a few percent [4,6,7]. In order to meet this requirement we need to evaluate the uniformity of a realistic HIB irradiation and energy deposition pattern. The HIB
Energy Technology Data Exchange (ETDEWEB)
TP Clement
1999-06-24
RT3DV1 (Reactive Transport in 3-Dimensions) is computer code that solves the coupled partial differential equations that describe reactive-flow and transport of multiple mobile and/or immobile species in three-dimensional saturated groundwater systems. RT3D is a generalized multi-species version of the US Environmental Protection Agency (EPA) transport code, MT3D (Zheng, 1990). The current version of RT3D uses the advection and dispersion solvers from the DOD-1.5 (1997) version of MT3D. As with MT3D, RT3D also requires the groundwater flow code MODFLOW for computing spatial and temporal variations in groundwater head distribution. The RT3D code was originally developed to support the contaminant transport modeling efforts at natural attenuation demonstration sites. As a research tool, RT3D has also been used to model several laboratory and pilot-scale active bioremediation experiments. The performance of RT3D has been validated by comparing the code results against various numerical and analytical solutions. The code is currently being used to model field-scale natural attenuation at multiple sites. The RT3D code is unique in that it includes an implicit reaction solver that makes the code sufficiently flexible for simulating various types of chemical and microbial reaction kinetics. RT3D V1.0 supports seven pre-programmed reaction modules that can be used to simulate different types of reactive contaminants including benzene-toluene-xylene mixtures (BTEX), and chlorinated solvents such as tetrachloroethene (PCE) and trichloroethene (TCE). In addition, RT3D has a user-defined reaction option that can be used to simulate any other types of user-specified reactive transport systems. This report describes the mathematical details of the RT3D computer code and its input/output data structure. It is assumed that the user is familiar with the basics of groundwater flow and contaminant transport mechanics. In addition, RT3D users are expected to have some experience in
Phase 1 Validation Testing and Simulation for the WEC-Sim Open Source Code
Ruehl, K.; Michelen, C.; Gunawan, B.; Bosma, B.; Simmons, A.; Lomonaco, P.
2015-12-01
WEC-Sim is an open source code to model wave energy converters performance in operational waves, developed by Sandia and NREL and funded by the US DOE. The code is a time-domain modeling tool developed in MATLAB/SIMULINK using the multibody dynamics solver SimMechanics, and solves the WEC's governing equations of motion using the Cummins time-domain impulse response formulation in 6 degrees of freedom. The WEC-Sim code has undergone verification through code-to-code comparisons; however validation of the code has been limited to publicly available experimental data sets. While these data sets provide preliminary code validation, the experimental tests were not explicitly designed for code validation, and as a result are limited in their ability to validate the full functionality of the WEC-Sim code. Therefore, dedicated physical model tests for WEC-Sim validation have been performed. This presentation provides an overview of the WEC-Sim validation experimental wave tank tests performed at the Oregon State University's Directional Wave Basin at Hinsdale Wave Research Laboratory. Phase 1 of experimental testing was focused on device characterization and completed in Fall 2015. Phase 2 is focused on WEC performance and scheduled for Winter 2015/2016. These experimental tests were designed explicitly to validate the performance of WEC-Sim code, and its new feature additions. Upon completion, the WEC-Sim validation data set will be made publicly available to the wave energy community. For the physical model test, a controllable model of a floating wave energy converter has been designed and constructed. The instrumentation includes state-of-the-art devices to measure pressure fields, motions in 6 DOF, multi-axial load cells, torque transducers, position transducers, and encoders. The model also incorporates a fully programmable Power-Take-Off system which can be used to generate or absorb wave energy. Numerical simulations of the experiments using WEC-Sim will be
L-PICOLA: A parallel code for fast dark matter simulation
Howlett, C.; Manera, M.; Percival, W. J.
2015-09-01
Robust measurements based on current large-scale structure surveys require precise knowledge of statistical and systematic errors. This can be obtained from large numbers of realistic mock galaxy catalogues that mimic the observed distribution of galaxies within the survey volume. To this end we present a fast, distributed-memory, planar-parallel code, L-PICOLA, which can be used to generate and evolve a set of initial conditions into a dark matter field much faster than a full non-linear N-Body simulation. Additionally, L-PICOLA has the ability to include primordial non-Gaussianity in the simulation and simulate the past lightcone at run-time, with optional replication of the simulation volume. Through comparisons to fully non-linear N-Body simulations we find that our code can reproduce the z = 0 power spectrum and reduced bispectrum of dark matter to within 2% and 5% respectively on all scales of interest to measurements of Baryon Acoustic Oscillations and Redshift Space Distortions, but 3 orders of magnitude faster. The accuracy, speed and scalability of this code, alongside the additional features we have implemented, make it extremely useful for both current and next generation large-scale structure surveys. L-PICOLA is publicly available at https://cullanhowlett.github.io/l-picola.
Sen, WANG; Qiping, YUAN; Bingjia, XIAO
2017-03-01
Plasma control system (PCS), mainly developed for real-time feedback control calculation, plays a significant part during normal discharges in a magnetic fusion device, while the tokamak simulation code (TSC) is a nonlinear numerical model that studies the time evolution of an axisymmetric magnetized tokamak plasma. The motivation to combine these two codes for an integrated simulation is specified by the facts that the control system module in TSC is relatively simple compared to PCS, and meanwhile, newly-implemented control algorithms in PCS, before applied to experimental validations, require numerical validations against a tokamak plasma simulator that TSC can act as. In this paper, details of establishment of the integrated simulation framework between the EAST PCS and TSC are generically presented, and the poloidal power supply model and data acquisition model that have been implemented in this framework are described as well. In addition, the correctness of data interactions among the EAST PCS, Simulink and TSC is clearly confirmed during an interface test, and in a simulation test, the RZIP control scheme in the EAST PCS is numerically validated using this simulation platform. Supported by the National Magnetic Confinement Fusion Science Program of China (No. 2014GB103000) and the National Natural Science Foundation of China (No. 11205200).
Energy Technology Data Exchange (ETDEWEB)
Brucker, R.; Munoz, A.; Rodriguez, J.
2011-07-01
The scope of radiological analysis is to calculate the dose received by the public and by an operator in the control room in case of an accident. Simulation software are needed for that kind of analysis in order to solve differential equations (radionuclides transport equations), to simulate the accident scenario, and to calculate the dose. This article presents the main radionuclide transport codes (several cases simulated with RADTRAD v3.03 are detailed), dose calculation programs, and atmospheric dispersion coefficients calculation software. (Author) 10 refs.
Mixa, T.; Fritts, D. C.; Laughman, B.; Wang, L.; Kantha, L. H.
2015-12-01
Multiple observations provide compelling evidence that gravity wave dissipation events often occur in multi-scale environments having highly-structured wind and stability profiles extending from the stable boundary layer into the mesosphere and lower thermosphere. Such events tend to be highly localized and thus yield local energy and momentum deposition and efficient secondary gravity wave generation expected to have strong influences at higher altitudes [e.g., Fritts et al., 2013; Baumgarten and Fritts, 2014]. Lidars, radars, and airglow imagers typically cannot achieve the spatial resolution needed to fully quantify these small-scale instability dynamics. Hence, we employ high-resolution modeling to explore these dynamics in representative environments. Specifically, we describe numerical studies of gravity wave packets impinging on a sheet of high stratification and shear and the resulting instabilities and impacts on the gravity wave amplitude and momentum flux for various flow and gravity wave parameters. References: Baumgarten, Gerd, and David C. Fritts (2014). Quantifying Kelvin-Helmholtz instability dynamics observed in noctilucent clouds: 1. Methods and observations. Journal of Geophysical Research: Atmospheres, 119.15, 9324-9337. Fritts, D. C., Wang, L., & Werne, J. A. (2013). Gravity wave-fine structure interactions. Part I: Influences of fine structure form and orientation on flow evolution and instability. Journal of the Atmospheric Sciences, 70(12), 3710-3734.
Intercomparison of numerical simulation codes for geologic disposal of CO2
Energy Technology Data Exchange (ETDEWEB)
Pruess, Karsten; Garcia, Julio; Kovscek, Tony; Oldenburg, Curt; Rutqvist, Jonny; Steefel, Carl; Xu, Tianfu
2002-11-27
Numerical simulation codes were exercised on a suite of eight test problems that address CO2 disposal into geologic storage reservoirs, including depleted oil and gas reservoirs, and brine aquifers. Processes investigated include single- and multi-phase flow, gas diffusion, partitioning of CO2 into aqueous and oil phases, chemical interactions of CO2 with aqueous fluids and rock minerals, and mechanical changes due to changes in fluid pressures. Representation of fluid properties was also examined. In most cases results obtained from different simulation codes were in satisfactory agreement, providing confidence in the ability of current numerical simulation approaches to handle the physical and chemical processes that would be induced by CO2 disposal in geologic reservoirs. Some discrepancies were also identified and can be traced to differences in fluid property correlations, and space and time discretization.
Integrated fast ignition simulation of cone-guided target with three codes
Energy Technology Data Exchange (ETDEWEB)
Sakagami, H. [Hyogo Univ., Computer Engineering, Himeji, Hyogo (Japan); Johzaki, T.; Nagatomo, H.; Mima, K. [Osaka Univ., Institute of Laser Engineering, Suita, Osaka (Japan)
2004-07-01
It was reported that the fuel core was heated up to {approx} 0.8 keV in the fast ignition experiments with cone-guided targets, but they could not theoretically explain heating mechanisms and achievement of such high temperature. Thus simulations should play an important role in estimating the scheme performance, and we must simulate each phenomenon with individual codes and integrate them under the Fast Ignition Integrated Interconnecting code project. In the previous integrated simulations, fast electrons generated by the laser-plasma interaction were too hot to efficiently heat the core and we got only a 0.096 keV temperature rise. Including the density gap at the contact surface between the cone tip and the imploded plasma, the period of core heating became longer and the core was heated by 0.162 keV, about 69% higher increment compared with ignoring the density gap effect. (authors)
MOLOCH computer code for molecular-dynamics simulation of processes in condensed matter
Directory of Open Access Journals (Sweden)
Derbenev I.V.
2011-01-01
Full Text Available Theoretical and experimental investigation into properties of condensed matter is one of the mainstreams in RFNC-VNIITF scientific activity. The method of molecular dynamics (MD is an innovative method of theoretical materials science. Modern supercomputers allow the direct simulation of collective effects in multibillion atom sample, making it possible to model physical processes on the atomistic level, including material response to dynamic load, radiation damage, influence of defects and alloying additions upon material mechanical properties, or aging of actinides. During past ten years, the computer code MOLOCH has been developed at RFNC-VNIITF. It is a parallel code suitable for massive parallel computing. Modern programming techniques were used to make the code almost 100% efficient. Practically all instruments required for modelling were implemented in the code: a potential builder for different materials, simulation of physical processes in arbitrary 3D geometry, and calculated data processing. A set of tests was developed to analyse algorithms efficiency. It can be used to compare codes with different MD implementation between each other.
Passive stabilization in a linear MHD stability code
Energy Technology Data Exchange (ETDEWEB)
Todd, A.M.M.
1980-03-01
Utilizing a Galerkin procedure to calculate the vacuum contribution to the ideal MHD Lagrangian, the implementation of realistic boundary conditions are described in a linear stability code. The procedure permits calculation of the effect of arbitrary conducting structure on ideal MHD instabilities, as opposed to the prior use of an encircling shell. The passive stabilization of conducting coils on the tokamak vertical instability is calculated within the PEST code and gives excellent agreement with 2-D time dependent simulations of PDX.
Energy Technology Data Exchange (ETDEWEB)
Mead, W.C.
1980-09-11
Ion acoustic turbulence is examined as one mechanism which could contribute to the inhibition of electron thermal transport which has been inferred from many laser-plasma experiments. The behavior of the ion acoustic instability is discussed from the viewpoint of the literature of 2-dimensional particle-in-cell simulations. Simulation techniques, limitations, and reported saturation mechanisms and levels are discussed. A scaling law for the effective collision frequency ..nu..* can be fit to several workers' results to within an order-of-magnitude. The inferred ..nu..* is shown to be 1-2 orders-of-magnitude too small to account for the transport inhibition seen in Nd-laser-produced plasmas. Several differences between the simulation conditions and laser-produced plasma conditions are noted.
Energy Technology Data Exchange (ETDEWEB)
Hindi, Haitham; Prabhakar, Shyam; Fox, John D.; Linscott, Ivan; Teytelman, Dmitri; /SLAC
2011-08-31
We present a technique for the design and verification of efficient bunch-by-bunch controllers for damping longitudinal multibunch instabilities. The controllers attempt to optimize the use of available feedback amplifier power - one of the most expensive components of a feedback system - and define the limits of the closed loop system performance. Our design technique alternates between analytic computation of single bunch optimal controllers and verification on a multibunch numerical simulator. The simulator uses PEP-II parameters and identifies unstable coupled bunch modes, their growth rates and their damping rates with feedback. The results from the simulator are shown to be in reasonable agreement with analytical calculations based on the single bunch model. The technique is then used to evaluate the performance of a variety of controllers proposed for PEP-II.
Computer code simulations of explosions in flow networks and comparison with experiments
Gregory, W. S.; Nichols, B. D.; Moore, J. A.; Smith, P. R.; Steinke, R. G.; Idzorek, R. D.
1987-10-01
A program of experimental testing and computer code development for predicting the effects of explosions in air-cleaning systems is being carried out for the Department of Energy. This work is a combined effort by the Los Alamos National Laboratory and New Mexico State University (NMSU). Los Alamos has the lead responsibility in the project and develops the computer codes; NMSU performs the experimental testing. The emphasis in the program is on obtaining experimental data to verify the analytical work. The primary benefit of this work will be the development of a verified computer code that safety analysts can use to analyze the effects of hypothetical explosions in nuclear plant air cleaning systems. The experimental data show the combined effects of explosions in air-cleaning systems that contain all of the important air-cleaning elements (blowers, dampers, filters, ductwork, and cells). A small experimental set-up consisting of multiple rooms, ductwork, a damper, a filter, and a blower was constructed. Explosions were simulated with a shock tube, hydrogen/air-filled gas balloons, and blasting caps. Analytical predictions were made using the EVENT84 and NF85 computer codes. The EVENT84 code predictions were in good agreement with the effects of the hydrogen/air explosions, but they did not model the blasting cap explosions adequately. NF85 predicted shock entrance to and within the experimental set-up very well. The NF85 code was not used to model the hydrogen/air or blasting cap explosions.
A New Code for Numerical Simulation of MHD Astrophysical Flows With Chemistry
Kulikov, Igor; Protasov, Viktor
2016-01-01
The new code for numerical simulation of magnetic hydrodynamical astrophysical flows with consideration of chemical reactions is given in the paper. At the heart of the code - the new original low-dissipation numerical method based on a combination of operator splitting approach and piecewise-parabolic method on the local stencil. The details of the numerical method are described; the main tests and the scheme of parallel implementation are shown. The chemodynamics of the hydrogen while the turbulent formation of molecular clouds is modeled.
Hori, T.; Ichimura, T.
2015-12-01
Here we propose a system for monitoring and forecasting of crustal activity, especially great interplate earthquake generation and its preparation processes in subduction zone. Basically, we model great earthquake generation as frictional instability on the subjecting plate boundary. So, spatio-temporal variation in slip velocity on the plate interface should be monitored and forecasted. Although, we can obtain continuous dense surface deformation data on land and partly at the sea bottom, the data obtained are not fully utilized for monitoring and forecasting. It is necessary to develop a physics-based data analysis system including (1) a structural model with the 3D geometry of the plate interface and the material property such as elasticity and viscosity, (2) calculation code for crustal deformation and seismic wave propagation using (1), (3) inverse analysis or data assimilation code both for structure and fault slip using (1)&(2). To accomplish this, it is at least necessary to develop highly reliable large-scale simulation code to calculate crustal deformation and seismic wave propagation for 3D heterogeneous structure. Actually, Ichimura et al. (2014, SC14) has developed unstructured FE non-linear seismic wave simulation code, which achieved physics-based urban earthquake simulation enhanced by 10.7 BlnDOF x 30 K time-step. Ichimura et al. (2013, GJI) has developed high fidelity FEM simulation code with mesh generator to calculate crustal deformation in and around Japan with complicated surface topography and subducting plate geometry for 1km mesh. Further, for inverse analyses, Errol et al. (2012, BSSA) has developed waveform inversion code for modeling 3D crustal structure, and Agata et al. (2015, this meeting) has improved the high fidelity FEM code to apply an adjoint method for estimating fault slip and asthenosphere viscosity. Hence, we have large-scale simulation and analysis tools for monitoring. Furthermore, we are developing the methods for
Fu, Xiangrong; Cowee, Misa M.; Friedel, Reinhard H.; Funsten, Herbert O.; Gary, S. Peter; Hospodarsky, George B.; Kletzing, Craig; Kurth, William; Larsen, Brian A.; Liu, Kaijun; MacDonald, Elizabeth A.; Min, Kyungguk; Reeves, Geoffrey D.; Skoug, Ruth M.; Winske, Dan
2014-10-01
Magnetospheric banded chorus is enhanced whistler waves with frequencies ωrcell simulations in a magnetized, homogeneous, collisionless plasma to test the hypothesis that banded chorus is due to local linear growth of two branches of the whistler anisotropy instability excited by two distinct, anisotropic electron components of significantly different temperatures. The electron densities and temperatures are derived from Helium, Oxygen, Proton, and Electron instrument measurements on the Van Allen Probes A satellite during a banded chorus event on 1 November 2012. The observations are consistent with a three-component electron model consisting of a cold (a few tens of eV) population, a warm (a few hundred eV) anisotropic population, and a hot (a few keV) anisotropic population. The simulations use plasma and field parameters as measured from the satellite during this event except for two numbers: the anisotropies of the warm and the hot electron components are enhanced over the measured values in order to obtain relatively rapid instability growth. The simulations show that the warm component drives the quasi-electrostatic upper band chorus and that the hot component drives the electromagnetic lower band chorus; the gap at ˜Ωe/2 is a natural consequence of the growth of two whistler modes with different properties.
Fu, Xiangrong; Cowee, Misa M; Friedel, Reinhard H; Funsten, Herbert O; Gary, S Peter; Hospodarsky, George B; Kletzing, Craig; Kurth, William; Larsen, Brian A; Liu, Kaijun; MacDonald, Elizabeth A; Min, Kyungguk; Reeves, Geoffrey D; Skoug, Ruth M; Winske, Dan
2014-10-01
Magnetospheric banded chorus is enhanced whistler waves with frequencies ωr particle-in-cell simulations in a magnetized, homogeneous, collisionless plasma to test the hypothesis that banded chorus is due to local linear growth of two branches of the whistler anisotropy instability excited by two distinct, anisotropic electron components of significantly different temperatures. The electron densities and temperatures are derived from Helium, Oxygen, Proton, and Electron instrument measurements on the Van Allen Probes A satellite during a banded chorus event on 1 November 2012. The observations are consistent with a three-component electron model consisting of a cold (a few tens of eV) population, a warm (a few hundred eV) anisotropic population, and a hot (a few keV) anisotropic population. The simulations use plasma and field parameters as measured from the satellite during this event except for two numbers: the anisotropies of the warm and the hot electron components are enhanced over the measured values in order to obtain relatively rapid instability growth. The simulations show that the warm component drives the quasi-electrostatic upper band chorus and that the hot component drives the electromagnetic lower band chorus; the gap at ∼Ω e /2 is a natural consequence of the growth of two whistler modes with different properties.
Pair Instability Supernovae of Very Massive Population III Stars
Chen, Ke-Jung; Woosley, Stan; Almgren, Ann; Whalen, Daniel
2014-01-01
Numerical studies of primordial star formation suggest that the first stars in the universe may have been very massive. Stellar models indicate that non-rotating Population III stars with initial masses of 140-260 Msun die as highly energetic pair-instability supernovae. We present new two-dimensional simulations of primordial pair-instability supernovae done with the CASTRO code. Our simulations begin at earlier times than previous multidimensional models, at the onset of core collapse, to capture any dynamical instabilities that may be seeded by collapse and explosive burning. Such instabilities could enhance explosive yields by mixing hot ash with fuel, thereby accelerating nuclear burning, and affect the spectra of the supernova by dredging up heavy elements from greater depths in the star at early times. Our grid of models includes both blue supergiants and red supergiants over the range in progenitor mass expected for these events. We find that fluid instabilities driven by oxygen and helium burning ari...
Wang, Zhenyu; Lin, Yu; Wang, Xueyi; Tummel, Kurt; Chen, Liu
2016-07-01
The eigenmode stability properties of three-dimensional lower-hybrid-drift-instabilities (LHDI) in a Harris current sheet with a small but finite guide magnetic field have been systematically studied by employing the gyrokinetic electron and fully kinetic ion (GeFi) particle-in-cell (PIC) simulation model with a realistic ion-to-electron mass ratio mi/me . In contrast to the fully kinetic PIC simulation scheme, the fast electron cyclotron motion and plasma oscillations are systematically removed in the GeFi model, and hence one can employ the realistic mi/me . The GeFi simulations are benchmarked against and show excellent agreement with both the fully kinetic PIC simulation and the analytical eigenmode theory. Our studies indicate that, for small wavenumbers, ky, along the current direction, the most unstable eigenmodes are peaked at the location where k →.B → =0 , consistent with previous analytical and simulation studies. Here, B → is the equilibrium magnetic field and k → is the wavevector perpendicular to the nonuniformity direction. As ky increases, however, the most unstable eigenmodes are found to be peaked at k →.B → ≠0 . In addition, the simulation results indicate that varying mi/me , the current sheet width, and the guide magnetic field can affect the stability of LHDI. Simulations with the varying mass ratio confirm the lower hybrid frequency and wave number scalings.
Energy Technology Data Exchange (ETDEWEB)
Schultz, Peter Andrew
2011-12-01
The objective of the U.S. Department of Energy Office of Nuclear Energy Advanced Modeling and Simulation Waste Integrated Performance and Safety Codes (NEAMS Waste IPSC) is to provide an integrated suite of computational modeling and simulation (M&S) capabilities to quantitatively assess the long-term performance of waste forms in the engineered and geologic environments of a radioactive-waste storage facility or disposal repository. Achieving the objective of modeling the performance of a disposal scenario requires describing processes involved in waste form degradation and radionuclide release at the subcontinuum scale, beginning with mechanistic descriptions of chemical reactions and chemical kinetics at the atomic scale, and upscaling into effective, validated constitutive models for input to high-fidelity continuum scale codes for coupled multiphysics simulations of release and transport. Verification and validation (V&V) is required throughout the system to establish evidence-based metrics for the level of confidence in M&S codes and capabilities, including at the subcontiunuum scale and the constitutive models they inform or generate. This Report outlines the nature of the V&V challenge at the subcontinuum scale, an approach to incorporate V&V concepts into subcontinuum scale modeling and simulation (M&S), and a plan to incrementally incorporate effective V&V into subcontinuum scale M&S destined for use in the NEAMS Waste IPSC work flow to meet requirements of quantitative confidence in the constitutive models informed by subcontinuum scale phenomena.
SimCommSys: taking the errors out of error-correcting code simulations
Directory of Open Access Journals (Sweden)
Johann A. Briffa
2014-06-01
Full Text Available In this study, we present SimCommSys, a simulator of communication systems that we are releasing under an open source license. The core of the project is a set of C + + libraries defining communication system components and a distributed Monte Carlo simulator. Of principal interest is the error-control coding component, where various kinds of binary and non-binary codes are implemented, including turbo, LDPC, repeat-accumulate and Reed–Solomon. The project also contains a number of ready-to-build binaries implementing various stages of the communication system (such as the encoder and decoder, a complete simulator and a system benchmark. Finally, SimCommSys also provides a number of shell and python scripts to encapsulate routine use cases. As long as the required components are already available in SimCommSys, the user may simulate complete communication systems of their own design without any additional programming. The strict separation of development (needed only to implement new components and use (to simulate specific constructions encourages reproducibility of experimental work and reduces the likelihood of error. Following an overview of the framework, we provide some examples of how to use the framework, including the implementation of a simple codec, the specification of communication systems and their simulation.
Numerical simulations of magnetic Kelvin-Helmholtz instability at a twisted solar flux tube
Murawski, K.; Chmielewski, P.; Zaqarashvili, T. V.; Khomenko, E.
2016-07-01
The paper aims to study the response of a solar small-scale and weak magnetic flux tube to photospheric twisting motions. We numerically solve three-dimensional ideal magnetohydrodynamic equations to describe the evolution of the perturbation within the initially static flux tube, excited by twists in the azimuthal component of the velocity. These twists produce rotation of the magnetic field lines. Perturbation of magnetic field lines propagates upwardly, driving vertical and azimuthal flow as well as plasma compressions and rarefactions in the form of eddies. We conclude that these eddies result from the sheared azimuthal flow which seeds Kelvin-Helmholtz instability (KHI) between the flux tube and the ambient medium. Numerically obtained properties of the KHI confirm the analytical predictions for the occurrence of the instability.
Directory of Open Access Journals (Sweden)
F. Løvholt
2013-06-01
Full Text Available Tsunamis induced by rock slides plunging into fjords constitute a severe threat to local coastal communities. The rock slide impact may give rise to highly non-linear waves in the near field, and because the wave lengths are relatively short, frequency dispersion comes into play. Fjord systems are rugged with steep slopes, and modeling non-linear dispersive waves in this environment with simultaneous run-up is demanding. We have run an operational Boussinesq-type TVD (total variation diminishing model using different run-up formulations. Two different tests are considered, inundation on steep slopes and propagation in a trapezoidal channel. In addition, a set of Lagrangian models serves as reference models. Demanding test cases with solitary waves with amplitudes ranging from 0.1 to 0.5 were applied, and slopes were ranging from 10 to 50°. Different run-up formulations yielded clearly different accuracy and stability, and only some provided similar accuracy as the reference models. The test cases revealed that the model was prone to instabilities for large non-linearity and fine resolution. Some of the instabilities were linked with false breaking during the first positive inundation, which was not observed for the reference models. None of the models were able to handle the bore forming during drawdown, however. The instabilities are linked to short-crested undulations on the grid scale, and appear on fine resolution during inundation. As a consequence, convergence was not always obtained. It is reason to believe that the instability may be a general problem for Boussinesq models in fjords.
Large Eddy Simulations of Transverse Combustion Instability in a Multi-Element Injector
2016-07-27
treated as an ideal gas . Switching to a cubic equation of state and used a surrogate with a molecular weight which better approximates the actual...other provision of law , no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a... constant mass flow of warm combustion products. The transverse instability was established by artificially vibrating the side walls of the chamber. By
Rabie, M.; Franck, C. M.
2016-06-01
We present a freely available MATLAB code for the simulation of electron transport in arbitrary gas mixtures in the presence of uniform electric fields. For steady-state electron transport, the program provides the transport coefficients, reaction rates and the electron energy distribution function. The program uses established Monte Carlo techniques and is compatible with the electron scattering cross section files from the open-access Plasma Data Exchange Project LXCat. The code is written in object-oriented design, allowing the tracing and visualization of the spatiotemporal evolution of electron swarms and the temporal development of the mean energy and the electron number due to attachment and/or ionization processes. We benchmark our code with well-known model gases as well as the real gases argon, N2, O2, CF4, SF6 and mixtures of N2 and O2.
A new Monte Carlo code for absorption simulation of laser-skin tissue interaction
Institute of Scientific and Technical Information of China (English)
Afshan Shirkavand; Saeed Sarkar; Marjaneh Hejazi; Leila Ataie-Fashtami; Mohammad Reza Alinaghizadeh
2007-01-01
In laser clinical applications, the process of photon absorption and thermal energy diffusion in the target tissue and its surrounding tissue during laser irradiation are crucial. Such information allows the selection of proper operating parameters such as laser power, and exposure time for optimal therapeutic. The Monte Carlo method is a useful tool for studying laser-tissue interaction and simulation of energy absorption in tissue during laser irradiation. We use the principles of this technique and write a new code with MATLAB 6.5, and then validate it against Monte Carlo multi layer (MCML) code. The new code is proved to be with good accuracy. It can be used to calculate the total power bsorbed in the region of interest. This can be combined for heat modelling with other computerized programs.
Min, K.; Liu, K.; Gary, S. P.
2015-12-01
In the inner magnetosphere, the energy-dependent convection of ring current ions can lead to the ring-type proton velocity distributions with ∂fp(vperp)/∂vperp > 0 and ring speeds around the Alfvén speed. This ring-type velocity distribution is known to drive fast magnetosonic waves at propagation quasi-perpendicular to the background magnetic field B0 and, with sufficient temperature anisotropy, electromagnetic ion cyclotron (EMIC) waves at propagation parallel to B0. While there is an abundant literature on linear theory and computer simulations of EMIC waves driven by bi-Maxwellian ion distributions, the literature on the instabilities associated with ring-type proton velocity distributions in the inner magnetosphere is less substantial. Even less studied is the interplay of the two instabilities which lead to the growth of EMIC and fast magnetosonic waves, respectively. The goal of this paper is to provide a comprehensive picture of the instabilities responsible for the two types of waves and their interplay in the conditions of the inner magnetosphere, using linear dispersion theory and self-consistent particle-in-cell (PIC) simulations. For systematic analyses, two-component proton distributions fp = fr + fb are used, where fr represents a tenuous energetic proton velocity distribution with ∂fr(vperp)/∂vperp > 0 providing free energy and fb represents a dense Maxwellian background with sufficiently small beta corresponding to the inner magnetospheric condition. Both an ideal velocity ring and a partial shell with sinn-type pitch angle dependence will be considered for the fr component.
EMPulse, a new 3-D simulation code for electromagnetic pulse studies
Cohen, Bruce; Eng, Chester; Farmer, William; Friedman, Alex; Grote, David; Kruger, Hans; Larson, David
2016-10-01
EMPulse is a comprehensive and modern 3-D simulation code for electro-magnetic pulse (EMP) formation and propagation studies, being developed at LLNL as part of a suite of codes to study E1 EMP originating from prompt gamma rays. EMPulse builds upon the open-source Warp particle-in-cell code framework developed by members of this team and collaborators at other institutions. The goal of this endeavor is a new tool enabling the detailed and self-consistent study of multi-dimensional effects in geometries that have typically been treated only approximately. Here we present an overview of the project, the models and methods that have been developed and incorporated into EMPulse, tests of these models, comparisons to simulations undertaken in CHAP-lite (derived from the legacy code CHAP due to C. Longmire and co-workers), and some approaches to increased computational efficiency being studied within our project. This work was performed under the auspices of the U.S. DOE by Lawrence Livermore National Security, LLC, Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
Development of a space radiation Monte Carlo computer simulation based on the FLUKA and ROOT codes
Pinsky, L; Ferrari, A; Sala, P; Carminati, F; Brun, R
2001-01-01
This NASA funded project is proceeding to develop a Monte Carlo-based computer simulation of the radiation environment in space. With actual funding only initially in place at the end of May 2000, the study is still in the early stage of development. The general tasks have been identified and personnel have been selected. The code to be assembled will be based upon two major existing software packages. The radiation transport simulation will be accomplished by updating the FLUKA Monte Carlo program, and the user interface will employ the ROOT software being developed at CERN. The end-product will be a Monte Carlo-based code which will complement the existing analytic codes such as BRYNTRN/HZETRN presently used by NASA to evaluate the effects of radiation shielding in space. The planned code will possess the ability to evaluate the radiation environment for spacecraft and habitats in Earth orbit, in interplanetary space, on the lunar surface, or on a planetary surface such as Mars. Furthermore, it will be usef...
A high-resolution code for large eddy simulation of incompressible turbulent boundary layer flows
Cheng, Wan
2014-03-01
We describe a framework for large eddy simulation (LES) of incompressible turbulent boundary layers over a flat plate. This framework uses a fractional-step method with fourth-order finite difference on a staggered mesh. We present several laminar examples to establish the fourth-order accuracy and energy conservation property of the code. Furthermore, we implement a recycling method to generate turbulent inflow. We use the stretched spiral vortex subgrid-scale model and virtual wall model to simulate the turbulent boundary layer flow. We find that the case with Reθ ≈ 2.5 × 105 agrees well with available experimental measurements of wall friction, streamwise velocity profiles and turbulent intensities. We demonstrate that for cases with extremely large Reynolds numbers (Reθ = 1012), the present LES can reasonably predict the flow with a coarse mesh. The parallel implementation of the LES code demonstrates reasonable scaling on O(103) cores. © 2013 Elsevier Ltd.
Energy Technology Data Exchange (ETDEWEB)
Baes, C.F. III; Sharp, R.D.; Sjoreen, A.L.; Hermann, O.W.
1984-11-01
TERRA is a computer code which calculates concentrations of radionuclides and ingrowing daughters in surface and root-zone soil, produce and feed, beef, and milk from a given deposition rate at any location in the conterminous United States. The code is fully integrated with seven other computer codes which together comprise a Computerized Radiological Risk Investigation System, CRRIS. Output from either the long range (> 100 km) atmospheric dispersion code RETADD-II or the short range (<80 km) atmospheric dispersion code ANEMOS, in the form of radionuclide air concentrations and ground deposition rates by downwind location, serves as input to TERRA. User-defined deposition rates and air concentrations may also be provided as input to TERRA through use of the PRIMUS computer code. The environmental concentrations of radionuclides predicted by TERRA serve as input to the ANDROS computer code which calculates population and individual intakes, exposures, doses, and risks. TERRA incorporates models to calculate uptake from soil and atmospheric deposition on four groups of produce for human consumption and four groups of livestock feeds. During the environmental transport simulation, intermediate calculations of interception fraction for leafy vegetables, produce directly exposed to atmospherically depositing material, pasture, hay, and silage are made based on location-specific estimates of standing crop biomass. Pasture productivity is estimated by a model which considers the number and types of cattle and sheep, pasture area, and annual production of other forages (hay and silage) at a given location. Calculations are made of the fraction of grain imported from outside the assessment area. TERRA output includes the above calculations and estimated radionuclide concentrations in plant produce, milk, and a beef composite by location.
V. S. O. P. - Computer Code System for Reactor Physics and Fuel Cycle Simulation
Teuchert, E.; Hansen, U.; Haas, K. A.
1980-01-01
V .S .O .P . (Very Superior Old Programs) is a system of codes linked together for the simulation of reactor life histories. It comprisesneutron cross section libraries and processing routines, repeated neutron spectrum evaluation, 2-D diffusion calculation based onneutron flux synthesis with depletion and shut-down features, incore and out-of-pile fuel management, fuel cycle cost analysis, and thermal hydraulics (at present restricted to Pebble Bed HTRs). Various techniques have been employe...
N-MODY: A Code for Collisionless N-body Simulations in Modified Newtonian Dynamics
Londrillo, Pasquale; Nipoti, Carlo
2011-02-01
N-MODY is a parallel particle-mesh code for collisionless N-body simulations in modified Newtonian dynamics (MOND). N-MODY is based on a numerical potential solver in spherical coordinates that solves the non-linear MOND field equation, and is ideally suited to simulate isolated stellar systems. N-MODY can be used also to compute the MOND potential of arbitrary static density distributions. A few applications of N-MODY indicate that some astrophysically relevant dynamical processes are profoundly different in MOND and in Newtonian gravity with dark matter.
Fletcher, C. D.
The capability to perform thermal-hydraulic analyses of a space reactor using the ATHENA computer code is demonstrated. The fast reactor, liquid-lithium coolant loops, and lithium-filled heat pipes of the preliminary General electric SP-100 design were modeled with ATHENA. Two demonstration transient calculations were performed simulating accident conditions. Calculated results are available for display using the Nuclear Plant Analyzer color graphics analysis tool in addition to traditional plots. ATHENA-calculated results appear reasonable, both for steady state full power conditions, and for the two transients. This analysis represents the first known transient thermal-hydraulic simulation using an integral space reactor system model incorporating heat pipes.
Parallel code NSBC: Simulations of relativistic nuclei scattering by a bent crystal
Babaev, A. A.
2014-01-01
The presented program was designed to simulate the passage of relativistic nuclei through a bent crystal. Namely, the input data is related to a nuclei beam. The nuclei move into the crystal under planar channeling and quasichanneling conditions. The program realizes the numerical algorithm to evaluate the trajectory of nucleus in the bent crystal. The program output is formed by the projectile motion data including the angular distribution of nuclei behind the crystal. The program could be useful to simulate the particle tracking at the accelerator facilities used the crystal collimation systems. The code has been written on C++ and designed for the multiprocessor systems (clusters).
Institute of Scientific and Technical Information of China (English)
无
2002-01-01
Capacity both in uplink and downlink of TD-SCDMA (time division-synchronous code division multiple access)system is studied in a multi-cell environment. The theoretical expressions of the mean of intercell interference in uplinkand the mean of sum of power allocation in downlink are given, by which uplink and downlink capacity is analyzed.Furthermore, we give the simulation models for both uplink and downlink capacity. The results from theoretical analysisand simulation fit very well. In the end, the maximum number of users that TD-SCDMA system can serve for 12.2kspeech service is given.
Massey, J. L.
1976-01-01
The very low error probability obtained with long error-correcting codes results in a very small number of observed errors in simulation studies of practical size and renders the usual confidence interval techniques inapplicable to the observed error probability. A natural extension of the notion of a 'confidence interval' is made and applied to such determinations of error probability by simulation. An example is included to show the surprisingly great significance of as few as two decoding errors in a very large number of decoding trials.
Benchmarking of Simulation Codes Based on the Montague Resonance in the CERN Proton Synchrotron
Hofmann, Ingo; Cousineau, Sarah M; Franchetti, Giuliano; Giovannozzi, Massimo; Holmes, Jeffrey Alan; Jones, Frederick W; Luccio, Alfredo U; Machida, Shinji; Métral, E; Qiang, Ji; Ryne, Robert D; Spentzouris, Panagiotis
2005-01-01
Experimental data on emittance exchange by the space charge driven Montague resonance'' have been obtained at the CERN Proton Synchrotron in 2002-04 as a function of the working point. These data are used to advance the benchmarking of major simulation codes (ACCSIM, IMPACT, MICROMAP, ORBIT, SIMBAD, SIMPSONS, SYNERGIA) currently employed world-wide in the design or performance improvement of high intensity circular accelerators. In this paper we summarize the experimental findings and compare them with the first three steps of simulation results of the still progressing work.
Directory of Open Access Journals (Sweden)
S. Saha
2016-04-01
Full Text Available Combustion instability in solid propellant rocket motor is numerically simulated by implementing propellant response function with quasi steady homogeneous one dimensional formulation. The convolution integral of propellant response with pressure history is implemented through a user defined function in commercial computational fluid dynamics software. The methodology is validated against literature reported motor test and other simulation results. Computed amplitude of pressure fluctuations compare closely with the literarture data. The growth rate of pressure oscillations of a cylindrical grain solid rocket motor is determined for different response functions at the fundamental longitudinal frequency. It is observed that for response function more than a critical value, the motor exhibits exponential growth rate of pressure oscillations.
Henri, Pierre; Briand, Carine; Mangeney, André; 10.1029/2009JA014969
2013-01-01
Recent observation of large amplitude Langmuir waveforms during a Type III event in the solar wind have been interpreted as the signature of the electrostatic decay of beam-driven Langmuir waves. This mechanism is thought to be a first step to explain the generation of solar Type III radio emission. The threshold for this parametric instability in typical solar wind condition is investigated here by means of 1D-1V Vlasov-Poisson simulations. We show that the amplitude of the observed Langmuir beat-like waveforms is of the order of the effective threshold computed from the full kinetic simulations. The expected level of associated ion acoustic density fluctuations have also been computed for comparison with observations.
KULL: LLNL's ASCI Inertial Confinement Fusion Simulation Code
Energy Technology Data Exchange (ETDEWEB)
Rathkopf, J. A.; Miller, D. S.; Owen, J. M.; Zike, M. R.; Eltgroth, P. G.; Madsen, N. K.; McCandless, K. P.; Nowak, P. F.; Nemanic, M. K.; Gentile, N. A.; Stuart, L. M.; Keen, N. D.; Palmer, T. S.
2000-01-10
KULL is a three dimensional, time dependent radiation hydrodynamics simulation code under development at Lawrence Livermore National Laboratory. A part of the U.S. Department of Energy's Accelerated Strategic Computing Initiative (ASCI), KULL's purpose is to simulate the physical processes in Inertial Confinement Fusion (ICF) targets. The National Ignition Facility, where ICF experiments will be conducted, and ASCI are part of the experimental and computational components of DOE's Stockpile Stewardship Program. This paper provides an overview of ASCI and describes KULL, its hydrodynamic simulation capability and its three methods of simulating radiative transfer. Particular emphasis is given to the parallelization techniques essential to obtain the performance required of the Stockpile Stewardship Program and to exploit the massively parallel processor machines that ASCI is procuring.
YT: A Multi-Code Analysis Toolkit for Astrophysical Simulation Data
Energy Technology Data Exchange (ETDEWEB)
Turk, Matthew J.; /San Diego, CASS; Smith, Britton D.; /Michigan State U.; Oishi, Jeffrey S.; /KIPAC, Menlo Park /Stanford U., Phys. Dept.; Skory, Stephen; Skillman, Samuel W.; /Colorado U., CASA; Abel, Tom; /KIPAC, Menlo Park /Stanford U., Phys. Dept.; Norman, Michael L.; /aff San Diego, CASS
2011-06-23
The analysis of complex multiphysics astrophysical simulations presents a unique and rapidly growing set of challenges: reproducibility, parallelization, and vast increases in data size and complexity chief among them. In order to meet these challenges, and in order to open up new avenues for collaboration between users of multiple simulation platforms, we present yt (available at http://yt.enzotools.org/) an open source, community-developed astrophysical analysis and visualization toolkit. Analysis and visualization with yt are oriented around physically relevant quantities rather than quantities native to astrophysical simulation codes. While originally designed for handling Enzo's structure adaptive mesh refinement data, yt has been extended to work with several different simulation methods and simulation codes including Orion, RAMSES, and FLASH. We report on its methods for reading, handling, and visualizing data, including projections, multivariate volume rendering, multi-dimensional histograms, halo finding, light cone generation, and topologically connected isocontour identification. Furthermore, we discuss the underlying algorithms yt uses for processing and visualizing data, and its mechanisms for parallelization of analysis tasks.
Development Of Sputtering Models For Fluids-Based Plasma Simulation Codes
Veitzer, Seth; Beckwith, Kristian; Stoltz, Peter
2015-09-01
Rf-driven plasma devices such as ion sources and plasma processing devices for many industrial and research applications benefit from detailed numerical modeling. Simulation of these devices using explicit PIC codes is difficult due to inherent separations of time and spatial scales. One alternative type of model is fluid-based codes coupled with electromagnetics, that are applicable to modeling higher-density plasmas in the time domain, but can relax time step requirements. To accurately model plasma-surface processes, such as physical sputtering and secondary electron emission, kinetic particle models have been developed, where particles are emitted from a material surface due to plasma ion bombardment. In fluid models plasma properties are defined on a cell-by-cell basis, and distributions for individual particle properties are assumed. This adds a complexity to surface process modeling, which we describe here. We describe the implementation of sputtering models into the hydrodynamic plasma simulation code USim, as well as methods to improve the accuracy of fluids-based simulation of plasmas-surface interactions by better modeling of heat fluxes. This work was performed under the auspices of the Department of Energy, Office of Basic Energy Sciences Award #DE-SC0009585.
Energy Technology Data Exchange (ETDEWEB)
Kida, Takashi; Umeda, Miki; Sugikawa, Susumu [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment
2003-03-01
MOX dissolution using silver-mediated electrochemical method will be employed for the preparation of plutonium nitrate solution in the criticality safety experiments in the Nuclear Fuel Cycle Safety Engineering Research Facility (NUCEF). A simulation code for the MOX dissolution has been developed for the operating support. The present report describes the outline of the simulation code, a comparison with the experimental data and a parameter study on the MOX dissolution. The principle of this code is based on the Zundelevich's model for PuO{sub 2} dissolution using Ag(II). The influence of nitrous acid on the material balance of Ag(II) is taken into consideration and the surface area of MOX powder is evaluated by particle size distribution in this model. The comparison with experimental data was carried out to confirm the validity of this model. It was confirmed that the behavior of MOX dissolution could adequately be simulated using an appropriate MOX dissolution rate constant. It was found from the result of parameter studies that MOX particle size was major governing factor on the dissolution rate. (author)
TEMPEST code modifications and testing for erosion-resisting sludge simulations
Energy Technology Data Exchange (ETDEWEB)
Onishi, Y.; Trent, D.S.
1998-01-01
The TEMPEST computer code has been used to address many waste retrieval operational and safety questions regarding waste mobilization, mixing, and gas retention. Because the amount of sludge retrieved from the tank is directly related to the sludge yield strength and the shear stress acting upon it, it is important to incorporate the sludge yield strength into simulations of erosion-resisting tank waste retrieval operations. This report describes current efforts to modify the TEMPEST code to simulate pump jet mixing of erosion-resisting tank wastes and the models used to test for erosion of waste sludge with yield strength. Test results for solid deposition and diluent/slurry jet injection into sludge layers in simplified tank conditions show that the modified TEMPEST code has a basic ability to simulate both the mobility and immobility of the sludges with yield strength. Further testing, modification, calibration, and verification of the sludge mobilization/immobilization model are planned using erosion data as they apply to waste tank sludges.
Integrated code development for studying laser driven plasmas
Energy Technology Data Exchange (ETDEWEB)
Takabe, Hideaki; Nagatomo, Hideo; Sunahara, Atsusi; Ohnishi, Naofumi; Naruo, Syuji; Mima, Kunioki [Osaka Univ., Suita (Japan). Inst. of Laser Engineering
1998-03-01
Present status and plan for developing an integrated implosion code are briefly explained by focusing on motivation, numerical scheme and issues to be developed more. Highly nonlinear stage of Rayleigh-Taylor instability of ablation front by laser irradiation has been simulated so as to be compared with model experiments. Improvement in transport and rezoning/remapping algorithms in ILESTA code is described. (author)
Energy Technology Data Exchange (ETDEWEB)
Lee, Joon H.; Siegel, Malcolm Dean; Arguello, Jose Guadalupe, Jr.; Webb, Stephen Walter; Dewers, Thomas A.; Mariner, Paul E.; Edwards, Harold Carter; Fuller, Timothy J.; Freeze, Geoffrey A.; Jove-Colon, Carlos F.; Wang, Yifeng
2011-03-01
This report describes a gap analysis performed in the process of developing the Waste Integrated Performance and Safety Codes (IPSC) in support of the U.S. Department of Energy (DOE) Office of Nuclear Energy Advanced Modeling and Simulation (NEAMS) Campaign. The goal of the Waste IPSC is to develop an integrated suite of computational modeling and simulation capabilities to quantitatively assess the long-term performance of waste forms in the engineered and geologic environments of a radioactive waste storage or disposal system. The Waste IPSC will provide this simulation capability (1) for a range of disposal concepts, waste form types, engineered repository designs, and geologic settings, (2) for a range of time scales and distances, (3) with appropriate consideration of the inherent uncertainties, and (4) in accordance with rigorous verification, validation, and software quality requirements. The gap analyses documented in this report were are performed during an initial gap analysis to identify candidate codes and tools to support the development and integration of the Waste IPSC, and during follow-on activities that delved into more detailed assessments of the various codes that were acquired, studied, and tested. The current Waste IPSC strategy is to acquire and integrate the necessary Waste IPSC capabilities wherever feasible, and develop only those capabilities that cannot be acquired or suitably integrated, verified, or validated. The gap analysis indicates that significant capabilities may already exist in the existing THC codes although there is no single code able to fully account for all physical and chemical processes involved in a waste disposal system. Large gaps exist in modeling chemical processes and their couplings with other processes. The coupling of chemical processes with flow transport and mechanical deformation remains challenging. The data for extreme environments (e.g., for elevated temperature and high ionic strength media) that are
Improvements in the Monte Carlo code for simulating 4πβ(PC)-γ coincidence system measurements
Dias, M. S.; Takeda, M. N.; Toledo, F.; Brancaccio, F.; Tongu, M. L. O.; Koskinas, M. F.
2013-01-01
A Monte Carlo simulation code known as ESQUEMA has been developed by the Nuclear Metrology Laboratory (Laboratório de Metrologia Nuclear-LMN) in the Nuclear and Energy Research Institute (Instituto de Pesquisas Energéticas e Nucleares-IPEN) to be used as a benchmark for radionuclide standardization. The early version of this code simulated only β-γ and ec-γ emitters with reasonably high electron and X-ray energies. To extend the code to include other radionuclides and enable the code to be applied to software coincidence counting systems, several improvements have been made and are presented in this work.
R-T instability model of magnetic fluid and its numerical simulations
Institute of Scientific and Technical Information of China (English)
郑秋云; 李明军; 舒适
2008-01-01
The Rayleigh-Taylor(R-T) instability of ferrofluid has been the subject of recent research,because of its implications on the stability of stellar.By neglecting the viscosity and rotation of magnetic fluid,and assuming that the magnetic particles are irrotational and temperature insensitive,we obtain a simplified R-T instability model of magnetic fluid.For the interface tracing,we use five-order weighted essentially non-oscillatory(WENO) scheme to spatial direction and three-order TVD R-K method to time direction on the uniform mesh,respectively.If the direction of the external magnetic field is the same as that of gravity,the velocities of the interface will be increased.But if the direction of the external magnetic field is in opposition to the direction of gravity,the velocities of the interface will be decreased.When the direction of the external magnetic field is perpendicular to the direction of gravity,the symmetry of the interface will be destroyed.Because of the action which is produced by perpendicular external magnetic field,there are other bubbles at the boudaries which parallel the direction of gravity.When we increase the magnetic susceptibility of the magnetic fluids,the effects of external magnetic fields will be more distinct for the interface tracing.
V.S.O.P. (99/09) Computer Code System for Reactor Physics and Fuel Cycle Simulation; Version 2009
Rütten, H.-J.; Haas, K. A.; Brockmann, H.; Ohlig, U.; Pohl, C.; Scherer, W.
2010-01-01
V.S.O.P.(99/ 09) represents the further development of V.S.O.P.(99/ 05). Compared to its precursor, the code system has been improved again in many details. The main motivation for this new code version was to update the basic nuclear libraries used by the code system. Thus, all cross section libraries involved in the code have now been based on ENDF/B-VII. V.S.O.P. is a computer code system for the comprehensive numerical simulation of the physics of thermal reactors. It implies the setup of...
Institute of Scientific and Technical Information of China (English)
樊建华; 王运东; 费维扬
2007-01-01
The aim of this work is to investigate the flow instabilities in a baffled,stirred tank generated by a single Rushton turbine by means of large eddy simulation (LES).The sliding mesh method was used for the coupling between the rotating and the stationary frame of references.The calculations were carried out on the "Shengcao-21C" supercomputer using a computational fluid dynamics (CFD) code CFX5.The flow fields predicted by the LES simulation and the simulation using standard k-ε model were compared to the results from particle image velocimetry (PIV) measurements.It is shown that the CFD simulations using the LES approach and the standard k-ε model agree well with the PIV measurements.Fluctuations of the radial and axial velocity are predicted at different frequencies by the LES simulation.Velocity fluctuations of high frequencies are seen in the impeller region,while low frequencies velocity fluctuations are observed in the bulk flow.A low frequency velocity fluctuation with a nondimensional frequency of 0.027Hz is predicted by the LES simulation,which agrees with experimental investigations in the literature.Flow circulation patterns predicted by the LES simulation are asymmetric,stochastic and complex,spanning a large portion of the tanks and varying with time,While circulation patterns calculated by the simulation using the standard k-ε model are symmetric.The results of the present work give better understanding to the flow instabilities in the mechanically agitated tank.However,further analysis of the LES calculated velocity Series by means of fast Fourier transform (FFT) and/or spectra analysis are recommended in future work in order to gain more knowledge of the complicated flow phenomena.
Nishioka, S.; Mochalskyy, S.; Taccogna, F.; Hatayama, A.; Fantz, U.; Minelli, P.
2017-08-01
The development of the kinetic particle model for the extraction region in negative hydrogen ion sources is indispensable and helpful to clarify the H- beam extraction physics. Recently, various 3D kinetic particle codes have been developed to study the extraction mechanism. Direct comparison between each other has not yet been done. Therefore, we have carried out a code-to-code benchmark activity to validate our codes. In the present study, the progress in this benchmark activity is summarized. At present, the reasonable agreement with the result by each code have been obtained using realistic plasma parameters at least for the following items; (1) Potential profile in the case of the vacuum condition (2) Temporal evolution of extracted current densities and profiles of electric potential in the case of the plasma consisting of only electrons and positive ions.
A Python Code for the Emmanoulopoulos et al. [arXiv:1305.0304] Light Curve Simulation Algorithm
Connolly, S D
2015-01-01
I have created, for public use, a Python code allowing the simulation of light curves with any given power spectral density and any probability density function, following the algorithm described in Emmanoulopoulos et al. 2013. The simulated products have exactly the same variability and statistical properties as the observed light curves. The code and its documentation are available at: https://github.com/samconnolly/DELightcurveSimulation Note that a Mathematica code of the algorithm is given in Emmanoulopoulos et al. [arXiv:1305.0304
Yamada, Susumu; Kitamura, Akihiro; Kurikami, Hiroshi; Machida, Masahiko
2015-04-01
Fukushima Daiichi Nuclear Power Plant (FDNPP) accident on March 2011 released significant quantities of radionuclides to atmosphere. The most significant nuclide is radioactive cesium isotopes. Therefore, the movement of the cesium is one of the critical issues for the environmental assessment. Since the cesium is strongly sorbed by soil particles, the cesium transport can be regarded as the sediment transport which is mainly brought about by the aquatic system such as a river and a lake. In this research, our target is the sediment transport on Ogaki dam reservoir which is located in about 16 km northwest from FDNPP. The reservoir is one of the principal irrigation dam reservoirs in Fukushima Prefecture and its upstream river basin was heavily contaminated by radioactivity. We simulate the sediment transport on the reservoir using 2-D river simulation code named Nays2D originally developed by Shimizu et al. (The latest version of Nays2D is available as a code included in iRIC (http://i-ric.org/en/), which is a river flow and riverbed variation analysis software package). In general, a 2-D simulation code requires a huge amount of calculation time. Therefore, we parallelize the code and execute it on a parallel computer. We examine the relationship between the behavior of the sediment transport and the height of the reservoir exit. The simulation result shows that almost all the sand that enter into the reservoir deposit close to the entrance of the reservoir for any height of the exit. The amounts of silt depositing within the reservoir slightly increase by raising the height of the exit. However, that of the clay dramatically increases. Especially, more than half of the clay deposits, if the exit is sufficiently high. These results demonstrate that the water level of the reservoir has a strong influence on the amount of the clay discharged from the reservoir. As a result, we conclude that the tuning of the water level has a possibility for controlling the
Simulation of a Synthetic Jet in Quiescent Air Using TLNS3D Flow Code
Vatsa, Veer N.; Turkel, Eli
2007-01-01
Although the actuator geometry is highly three-dimensional, the outer flowfield is nominally two-dimensional because of the high aspect ratio of the rectangular slot. For the present study, this configuration is modeled as a two-dimensional problem. A multi-block structured grid available at the CFDVAL2004 website is used as a baseline grid. The periodic motion of the diaphragm is simulated by specifying a sinusoidal velocity at the diaphragm surface with a frequency of 450 Hz, corresponding to the experimental setup. The amplitude is chosen so that the maximum Mach number at the jet exit is approximately 0.1, to replicate the experimental conditions. At the solid walls zero slip, zero injection, adiabatic temperature and zero pressure gradient conditions are imposed. In the external region, symmetry conditions are imposed on the side (vertical) boundaries and far-field conditions are imposed on the top boundary. A nominal free-stream Mach number of 0.001 is imposed in the free stream to simulate incompressible flow conditions in the TLNS3D code, which solves compressible flow equations. The code was run in unsteady (URANS) mode until the periodicity was established. The time-mean quantities were obtained by running the code for at least another 15 periods and averaging the flow quantities over these periods. The phase-locked average of flow quantities were assumed to be coincident with their values during the last full time period.
Acceleration of a Particle-in-Cell Code for Space Plasma Simulations with OpenACC
Peng, Ivy Bo; Markidis, Stefano; Vaivads, Andris; Vencels, Juris; Deca, Jan; Lapenta, Giovanni; Hart, Alistair; Laure, Erwin
2015-04-01
We simulate space plasmas with the Particle-in-cell (PIC) method that uses computational particles to mimic electrons and protons in solar wind and in Earth magnetosphere. The magnetic and electric fields are computed by solving the Maxwell's equations on a computational grid. In each PIC simulation step, there are four major phases: interpolation of fields to particles, updating the location and velocity of each particle, interpolation of particles to grids and solving the Maxwell's equations on the grid. We use the iPIC3D code, which was implemented in C++, using both MPI and OpenMP, for our case study. By November 2014, heterogeneous systems using hardware accelerators such as Graphics Processing Unit (GPUs) and the Many Integrated Core (MIC) coprocessors for high performance computing continue growth in the top 500 most powerful supercomputers world wide. Scientific applications for numerical simulations need to adapt to using accelerators to achieve portability and scalability in the coming exascale systems. In our work, we conduct a case study of using OpenACC to offload the computation intensive parts: particle mover and interpolation of particles to grids, in a massively parallel Particle-in-Cell simulation code, iPIC3D, to multi-GPU systems. We use MPI for inter-node communication for halo exchange and communicating particles. We identify the most promising parts suitable for GPUs accelerator by profiling using CrayPAT. We implemented manual deep copy to address the challenges of porting C++ classes to GPU. We document the necessary changes in the exiting algorithms to adapt for GPU computation. We present the challenges and findings as well as our methodology for porting a Particle-in-Cell code to multi-GPU systems using OpenACC. In this work, we will present the challenges, findings and our methodology of porting a Particle-in-Cell code for space applications as follows: We profile the iPIC3D code by Cray Performance Analysis Tool (CrayPAT) and identify
Comparison of Geant4-DNA simulation of S-values with other Monte Carlo codes
Energy Technology Data Exchange (ETDEWEB)
André, T. [Université Bordeaux 1, CENBG, UMR 5797, F-33170 Gradignan (France); CNRS, IN2P3, CENBG, UMR 5797, F-33170 Gradignan (France); Morini, F. [Research Group of Theoretical Chemistry and Molecular Modelling, Hasselt University, Agoralaan Gebouw D, B-3590 Diepenbeek (Belgium); Karamitros, M. [Université Bordeaux 1, CENBG, UMR 5797, F-33170 Gradignan (France); CNRS, IN2P3, CENBG, UMR 5797, F-33170 Gradignan (France); CNRS, INCIA, UMR 5287, F-33400 Talence (France); Delorme, R. [LPSC, Université Joseph Fourier Grenoble 1, CNRS/IN2P3, Grenoble INP, 38026 Grenoble (France); CEA, LIST, F-91191 Gif-sur-Yvette (France); Le Loirec, C. [CEA, LIST, F-91191 Gif-sur-Yvette (France); Campos, L. [Departamento de Física, Universidade Federal de Sergipe, São Cristóvão (Brazil); Champion, C. [Université Bordeaux 1, CENBG, UMR 5797, F-33170 Gradignan (France); CNRS, IN2P3, CENBG, UMR 5797, F-33170 Gradignan (France); Groetz, J.-E.; Fromm, M. [Université de Franche-Comté, Laboratoire Chrono-Environnement, UMR CNRS 6249, Besançon (France); Bordage, M.-C. [Laboratoire Plasmas et Conversion d’Énergie, UMR 5213 CNRS-INPT-UPS, Université Paul Sabatier, Toulouse (France); Perrot, Y. [Laboratoire de Physique Corpusculaire, UMR 6533, Aubière (France); Barberet, Ph. [Université Bordeaux 1, CENBG, UMR 5797, F-33170 Gradignan (France); CNRS, IN2P3, CENBG, UMR 5797, F-33170 Gradignan (France); and others
2014-01-15
Monte Carlo simulations of S-values have been carried out with the Geant4-DNA extension of the Geant4 toolkit. The S-values have been simulated for monoenergetic electrons with energies ranging from 0.1 keV up to 20 keV, in liquid water spheres (for four radii, chosen between 10 nm and 1 μm), and for electrons emitted by five isotopes of iodine (131, 132, 133, 134 and 135), in liquid water spheres of varying radius (from 15 μm up to 250 μm). The results have been compared to those obtained from other Monte Carlo codes and from other published data. The use of the Kolmogorov–Smirnov test has allowed confirming the statistical compatibility of all simulation results.
Simulations of 3D LPI's relevant to IFE using the PIC code OSIRIS
Tsung, F. S.; Mori, W. B.; Winjum, B. J.
2014-10-01
We will study three dimensional effects of laser plasma instabilities, including backward raman scattering, the high frequency hybrid instability, and the two plasmon instability using OSIRIS in 3D Cartesian geometry and cylindrical 2D OSIRIS with azimuthal mode decompositions. With our new capabilities we hope to demonstrate that we are capable of studying single speckle physics relevant to IFE in an efficent manner.
Institute of Scientific and Technical Information of China (English)
无
2010-01-01
In this work, a large eddy simulation (LES) model, which includes momentum and heat source (or sink) inside the tree planting layer, is proposed for the simulation of flow in a street canyon with tree planting. Vegetation canopy layer simulation shows that this model can be used to simulate the velocity distribution and temperature variation inside the canopy layer. Effects of atmospheric instability on flow and pollutant distribution in a street canyon with tree planting of an aspect ratio of 0.5 are studied. Results show that compared with the canyon with no tree planting (or the exposed street canyon), the canyon with tree planting shows a reduced wind circulation and pollutant exchange rate (PER) at the top layer of the street canyon, which induces the increase in the pollutant concentrations near road surface, leeward wall and windward wall. When street canyon atmosphere is under a strongly unstable condition, wind velocity decreases while pollutant concentration is increased in the areas near the street canyon top, road surface, leeward and windward walls, compared with the wind velocity in the street canyon with the neutral stratification. When street canyon atmosphere is under a weakly unstable condition, wind velocity weakens near the street canyon top and windward wall, but strengthens near the road surface and leeward wall, and pollutant concentration is decreased near the leeward and windward walls and is increased between the two rows of trees. When the street canyon atmosphere is under an unstable condition, PER is lower than that under the neutral stratification.
Instability of P-waves just below the transition region in a global solar wind simulation
Grappin, R; Pinto, R; Wang, Y -M
2007-01-01
We investigate how wave propagation is modified by the presence of heat sources and sinks, in the simple 1D, hydrodynamical case, including chromosphere and solar wind. We integrate the time-dependent hydrodynamic equations of the solar wind with spherical symmetry, including conduction, radiative cooling and a prescribed mechanical heat flux. Once a quasi-stationary wind is established, we study the response of the system to pressure oscillations at the photospheric boundary. We use transparent boundary conditions. We find that wavepackets with high enough amplitude propagating upward from the photosphere implode just below the transition region. This implosion is due to the radiative cooling term generating pressure holes close to the wave crests of the wave, which make the wave collapse. In the case where heat sources and sinks are not present in the equations, the wave remains stable whatever the initial wave amplitude, which is compatible with published work. Instability should be observable when and whe...
The GENGA Code: Gravitational Encounters in N-body simulations with GPU Acceleration
Grimm, Simon L
2014-01-01
We describe a GPU implementation of a hybrid symplectic N-body integrator, GENGA (Gravitational ENcounters with Gpu Acceleration), designed to integrate planet and planetesimal dynamics in the late stage of planet formation and stability analysis of planetary systems. GENGA is based on the integration scheme of the Mercury code (Chambers 1999), which handles close encounters with very good energy conservation. It uses mixed variable integration (Wisdom & Holman 1991) when the motion is a perturbed Kepler orbit and combines this with a direct N-body Bulirsch-Stoer method during close encounters. The GENGA code supports three simulation modes: Integration of up to 2048 massive bodies, integration with up to a million test particles, or parallel integration of a large number of individual planetary systems. GENGA is written in CUDA C and runs on all Nvidia GPUs with compute capability of at least 2.0. All operations are performed in parallel, including the close encounter detection and the grouping of indepe...
Premar-2: a Monte Carlo code for radiative transport simulation in atmospheric environments
Energy Technology Data Exchange (ETDEWEB)
Cupini, E. [ENEA, Centro Ricerche Ezio Clementel, Bologna, (Italy). Dipt. Innovazione
1999-07-01
The peculiarities of the PREMAR-2 code, aimed at radiation transport Monte Carlo simulation in atmospheric environments in the infrared-ultraviolet frequency range, are described. With respect to the previously developed PREMAR code, besides plane multilayers, spherical multilayers and finite sequences of vertical layers, each one with its own atmospheric behaviour, are foreseen in the new code, together with the refraction phenomenon, so that long range, highly slanted paths can now be more faithfully taken into account. A zenithal angular dependence of the albedo coefficient has moreover been introduced. Lidar systems, with spatially independent source and telescope, are allowed again to be simulated, and, in this latest version of the code, sensitivity analyses to be performed. According to this last feasibility, consequences on radiation transport of small perturbations in physical components of the atmospheric environment may be analyze and the related effects on searched results estimated. The availability of a library of physical data (reaction coefficients, phase functions and refraction indexes) is required by the code, providing the essential features of the environment of interest needed of the Monte Carlo simulation. Variance reducing techniques have been enhanced in the Premar-2 code, by introducing, for instance, a local forced collision technique, especially apt to be used in Lidar system simulations. Encouraging comparisons between code and experimental results carried out at the Brasimone Centre of ENEA, have so far been obtained, even if further checks of the code are to be performed. [Italian] Nel presente rapporto vengono descritte le principali caratteristiche del codice di calcolo PREMAR-2, che esegue la simulazione Montecarlo del trasporto della radiazione elettromagnetica nell'atmosfera, nell'intervallo di frequenza che va dall'infrarosso all'ultravioletto. Rispetto al codice PREMAR precedentemente sviluppato, il codice
Validating a Monotonically-Integrated Large Eddy Simulation Code for Subsonic Jet Acoustics
Ingraham, Daniel; Bridges, James
2017-01-01
The results of subsonic jet validation cases for the Naval Research Lab's Jet Engine Noise REduction (JENRE) code are reported. Two set points from the Tanna matrix, set point 3 (Ma = 0.5, unheated) and set point 7 (Ma = 0.9, unheated) are attempted on three different meshes. After a brief discussion of the JENRE code and the meshes constructed for this work, the turbulent statistics for the axial velocity are presented and compared to experimental data, with favorable results. Preliminary simulations for set point 23 (Ma = 0.5, Tj=T1 = 1.764) on one of the meshes are also described. Finally, the proposed configuration for the farfield noise prediction with JENRE's Ffowcs-Williams Hawking solver are detailed.
A high-order public domain code for direct numerical simulations of turbulent combustion
Babkovskaia, N; Brandenburg, A
2010-01-01
A high-order scheme for direct numerical simulations of turbulent combustion is discussed. Its implementation in the massively parallel and publicly available Pencil Code is validated with the focus on hydrogen combustion. Ignition delay times (0D) and laminar flame velocities (1D) are calculated and compared with results from the commercially available Chemkin code. The scheme is verified to be fifth order in space. Upon doubling the resolution, a 32-fold increase in the accuracy of the flame front is demonstrated. Finally, also turbulent and spherical flame front velocities are calculated and the implementation of the non-reflecting so-called Navier-Stokes Characteristic Boundary Condition is validated in all three directions.
Modeling the Parker instability in a rotating plasma screw pinch
Khalzov, I V; Katz, N; Forest, C B; 10.1063/1.3684240
2012-01-01
We analytically and numerically study the analogue of the Parker (magnetic buoyancy) instability in a uniformly rotating plasma screw pinch confined in a cylinder. Uniform plasma rotation is imposed to create a centrifugal acceleration, which mimics the gravity required for the classical Parker instability. The goal of this study is to determine how the Parker instability could be unambiguously identified in a weakly magnetized, rapidly rotating screw pinch, in which the rotation provides an effective gravity and a radially varying azimuthal field is controlled to give conditions for which the plasma is magnetically buoyant to inward motion. We show that an axial magnetic field is also required to circumvent conventional current driven magnetohydrodynamic (MHD) instabilities such as the sausage and kink modes that would obscure the Parker instability. These conditions can be realized in the Madison Plasma Couette Experiment (MPCX). Simulations are performed using the extended MHD code NIMROD for an isothermal...
Xia, Yidong; Podgorney, Robert; Huang, Hai
2017-03-01
FALCON (Fracturing And Liquid CONvection) is a hybrid continuous/discontinuous Galerkin finite element geothermal reservoir simulation code based on the MOOSE (Multiphysics Object-Oriented Simulation Environment) framework being developed and used for multiphysics applications. In the present work, a suite of verification and validation (V&V) test problems for FALCON was defined to meet the design requirements, and solved to the interests of enhanced geothermal system modeling and simulation. The intent for this test problem suite is to provide baseline comparison data that demonstrates the performance of FALCON solution methods. The test problems vary in complexity from a single mechanical or thermal process, to coupled thermo-hydro-mechanical processes in geological porous medium. Numerical results obtained by FALCON agreed well with either the available analytical solutions or experimental data, indicating the verified and validated implementation of these capabilities in FALCON. Whenever possible, some form of solution verification has been attempted to identify sensitivities in the solution methods, and suggest best practices when using the FALCON code.
Boley, A C; Durisen, R H; Cai, K; Pickett, M K; D'Alessio, P
2006-01-01
This paper presents a fully three-dimensional radiative hydrodymanics simulation with realistic opacities for a gravitationally unstable 0.07 Msun disk around a 0.5 Msun star. We address the following aspects of disk evolution: the strength of gravitational instabilities under realistic cooling, mass transport in the disk that arises from GIs, comparisons between the gravitational and Reynolds stresses measured in the disk and those expected in an alpha-disk, and comparisons between the SED derived for the disk and SEDs derived from observationally determined parameters. The mass transport in this disk is dominated by global modes, and the cooling times are too long to permit fragmentation for all radii. Moreover, our results suggest a plausible explanation for the FU Ori outburst phenomenon.
Hooper, E. B.; Sovinec, C. R.
2016-10-01
An instability observed in whole-device, resistive magnetohydrodynamic simulations of the driven phase of coaxial helicity injection in the National Spherical Torus eXperiment is identified as a current-driven resistive mode in an unusual geometry that transiently generates a current sheet. The mode consists of plasma flow velocity and magnetic field eddies in a tube aligned with the magnetic field at the surface of the injected magnetic flux. At low plasma temperatures (˜10-20 eV), the mode is benign, but at high temperatures (˜100 eV) its amplitude undergoes relaxation oscillations, broadening the layer of injected current and flow at the surface of the injected toroidal flux and background plasma. The poloidal-field structure is affected and the magnetic surface closure is generally prevented while the mode undergoes relaxation oscillations during injection. This study describes the mode and uses linearized numerical computations and an analytic slab model to identify the unstable mode.
Ongaro, T. E.; Clarke, A.; Neri, A.; Voight, B.; Widiwijayanti, C.
2005-12-01
For the first time the dynamics of directed blasts from explosive lava-dome decompression have been investigated by means of transient, multiphase flow simulations in 2D and 3D. Multiphase flow models developed for the analysis of pyroclastic dispersal from explosive eruptions have been so far limited to 2D axisymmetric or Cartesian formulations which cannot properly account for important 3D features of the volcanic system such as complex morphology and fluid turbulence. Here we use a new parallel multiphase flow code, named PDAC (Pyroclastic Dispersal Analysis Code) (Esposti Ongaro et al., 2005), able to simulate the transient and 3D thermofluid-dynamics of pyroclastic dispersal produced by collapsing columns and volcanic blasts. The code solves the equations of the multiparticle flow model of Neri et al. (2003) on 3D domains extending up to several kilometres in 3D and includes a new description of the boundary conditions over topography which is automatically acquired from a DEM. The initial conditions are represented by a compact volume of gas and pyroclasts, with clasts of different sizes and densities, at high temperature and pressure. Different dome porosities and pressurization models were tested in 2D to assess the sensitivity of the results to the distribution of initial gas pressure, and to the total mass and energy stored in the dome, prior to 3D modeling. The simulations have used topographies appropriate for the 1997 Boxing Day directed blast on Montserrat, which eradicated the village of St. Patricks. Some simulations tested the runout of pyroclastic density currents over the ocean surface, corresponding to observations of over-water surges to several km distances at both locations. The PDAC code was used to perform 3D simulations of the explosive event on the actual volcano topography. The results highlight the strong topographic control on the propagation of the dense pyroclastic flows, the triggering of thermal instabilities, and the elutriation
Espinosa, G.; Rodríguez, R.; Gil, J. M.; Suzuki-Vidal, F.; Lebedev, S. V.; Ciardi, A.; Rubiano, J. G.; Martel, P.
2017-03-01
Numerical simulations of laboratory astrophysics experiments on plasma flows require plasma microscopic properties that are obtained by means of an atomic kinetic model. This fact implies a careful choice of the most suitable model for the experiment under analysis. Otherwise, the calculations could lead to inaccurate results and inappropriate conclusions. First, a study of the validity of the local thermodynamic equilibrium in the calculation of the average ionization, mean radiative properties, and cooling times of argon plasmas in a range of plasma conditions of interest in laboratory astrophysics experiments on radiative shocks is performed in this work. In the second part, we have made an analysis of the influence of the atomic kinetic model used to calculate plasma microscopic properties of experiments carried out on magpie on radiative bow shocks propagating in argon. The models considered were developed assuming both local and nonlocal thermodynamic equilibrium and, for the latter situation, we have considered in the kinetic model different effects such as external radiation field and plasma mixture. The microscopic properties studied were the average ionization, the charge state distributions, the monochromatic opacities and emissivities, the Planck mean opacity, and the radiative power loss. The microscopic study was made as a postprocess of a radiative-hydrodynamic simulation of the experiment. We have also performed a theoretical analysis of the influence of these atomic kinetic models in the criteria for the onset possibility of thermal instabilities due to radiative cooling in those experiments in which small structures were experimentally observed in the bow shock that could be due to this kind of instability.
Energy Technology Data Exchange (ETDEWEB)
Bertolotto, D.
2011-11-15
The current doctoral research is focused on the development and validation of a coupled computational tool, to combine the advantages of computational fluid dynamics (CFD) in analyzing complex flow fields and of state-of-the-art system codes employed for nuclear power plant (NPP) simulations. Such a tool can considerably enhance the analysis of NPP transient behavior, e.g. in the case of pressurized water reactor (PWR) accident scenarios such as Main Steam Line Break (MSLB) and boron dilution, in which strong coolant flow asymmetries and multi-dimensional mixing effects strongly influence the reactivity of the reactor core, as described in Chap. 1. To start with, a literature review on code coupling is presented in Chap. 2, together with the corresponding ongoing projects in the international community. Special reference is made to the framework in which this research has been carried out, i.e. the Paul Scherrer Institute's (PSI) project STARS (Steady-state and Transient Analysis Research for the Swiss reactors). In particular, the codes chosen for the coupling, i.e. the CFD code ANSYS CFX V11.0 and the system code US-NRC TRACE V5.0, are part of the STARS codes system. Their main features are also described in Chap. 2. The development of the coupled tool, named CFX/TRACE from the names of the two constitutive codes, has proven to be a complex and broad-based task, and therefore constraints had to be put on the target requirements, while keeping in mind a certain modularity to allow future extensions to be made with minimal efforts. After careful consideration, the coupling was defined to be on-line, parallel and with non-overlapping domains connected by an interface, which was developed through the Parallel Virtual Machines (PVM) software, as described in Chap. 3. Moreover, two numerical coupling schemes were implemented and tested: a sequential explicit scheme and a sequential semi-implicit scheme. Finally, it was decided that the coupling would be single
Numerical simulation of multi-material mixing in an inclined interface Richtmyer-Meshkov instability
Subramaniam, Akshay; Lele, Sanjiva K.
2017-01-01
In this work, high fidelity simulations of shock induced multi-material mixing between air and SF6 in a shock tube are performed for a Mach 1.5 shock interacting with a planar material interface that is inclined with respect to the shock propagating direction. In the current configuration, unlike the classical perturbed flat interface case, the evolution of the interface is fully non-linear from early time. The simulations attempt to replicate an experiment conducted at the Georgia Tech STAML. Tight coupling between numerics and flow physics and the large range of spatial scales make this a challenging problem to simulate numerically. Often, two dimensional simulations are performed to reduce the computational cost of these simulations. We show here that the effect of small three dimensional perturbations likely to be present in an experimental setting is not negligible. Full 3D simulations would have to be performed to do a proper comparison with experiments. Effect of grid resolution is also studied in the present work. Simulations shown are conducted with an extended version of the Miranda solver developed by Cook et. al [1] which combines high-order compact finite differences [2] with localized non-linear artificial properties for shock and interface capturing [3].
Global and Kinetic MHD Simulation by the Gpic-MHD Code
Institute of Scientific and Technical Information of China (English)
Hiroshi NAITOU; Yusuke YAMADA; Kenji KAJIWARA; Wei-li LEE; Shinji TOKUDA; Masatoshi YAGI
2011-01-01
In order to implement large-scale and high-beta tokamak simulation, a new algorithm of the electromagnetic gyrokinetic PIC （particle-in-cell） code was proposed and installed on the Gpic-MHD code [Gyrokinetic PIC code for magnetohydrodynamic （MHD） simulation]. In the new algorithm, the vorticity equation and the generalized Ohm＇s law along the magnetic field are derived from the basic equations of the gyrokinetic Vlasov, Poisson, and Ampere system and are used to describe the spatio-temporal evolution of the field quantities of the electrostatic potential φ and the longitudinal component of the vector potential Az. The basic algorithm is equivalent to solving the reduced-MHD-type equations with kinetic corrections, in which MHD physics related to Alfven modes are well described. The estimation of perturbed electron pressure from particle dynamics is dominant, while the effects of other moments are negligible. Another advantage of the algorithm is that the longitudinal induced electric field, ETz = -δAz/δt, is explicitly estimated by the generalized Ohm＇s law and used in the equations of motion. Furthermore, the particle velocities along the magnetic field are used （vz-formulation） instead of generalized momentums （pz-formulation）, hence there is no problem of ＇cancellation＇, which would otherwise appear when Az is estimated from the Ampere＇s law in the pz-formulation. The successful simulation of the collisionless internal kink mode by the new Gpic-MHD with realistic values of the large-scale and high-beta tokamaks revealed the usefulness of the new algorithm.
Numerical simulation of the Hall effect in magnetized accretion disks with the Pluto code
Nakhaei, Mohammad; Safaei, Ghasem; Abbassi, Shahram
2014-01-01
We investigate the Hall effect in a standard magnetized accretion disk which is accompanied by dissipation due to viscosity and magnetic resistivity. By considering an initial magnetic field, using the PLUTO code, we perform a numerical magnetohydrodynamic simulation in order to study the effect of Hall diffusion on the physical structure of the disk. Current density and temperature of the disk are significantly modified by Hall diffusion, but the global structure of the disk is not substantially affected. The changes in the current densities and temperature of the disk lead to a modification in the disk luminosity and radiation.
Simulation of Electron Trajectories in the Multicusp Ion Source Using Geantn4 Monte Carlo Code
Khodadadi Azadboni, Fatemeh; Sedaghatizade, Mahmood
2010-04-01
To optimize the multicusp ion source, understanding of transport properties of electrons is indispensable. Since the transport of electrons in the multicusp ion source is a three-dimensional problem, we use the 3D computer code Geant4, to model the particle trajectories. The goal is to study the effect of electron injection into a cylindrical gas chamber and the electron trajectories. The role of the magnetic filter in contemporary negative ion sources is analyzed. The conditions in the magnetic filter adjacent to the plasma electrode optimum for the generation, formation, and extraction of an H- ion beam are found. The simulation results are in good agreement with the experimental data.
DISCRETE DYNAMIC MODEL OF BEVEL GEAR – VERIFICATION THE PROGRAM SOURCE CODE FOR NUMERICAL SIMULATION
Directory of Open Access Journals (Sweden)
Krzysztof TWARDOCH
2014-06-01
Full Text Available In the article presented a new model of physical and mathematical bevel gear to study the influence of design parameters and operating factors on the dynamic state of the gear transmission. Discusses the process of verifying proper operation of copyright calculation program used to determine the solutions of the dynamic model of bevel gear. Presents the block diagram of a computing algorithm that was used to create a program for the numerical simulation. The program source code is written in an interactive environment to perform scientific and engineering calculations, MATLAB
2D hybrid simulations of super-diffusion at the magnetopause driven by Kelvin-Helmholtz instability
Energy Technology Data Exchange (ETDEWEB)
Cowee, Misa M [Los Alamos National Laboratory; Winske, Dan [Los Alamos National Laboratory; Gary, S Peter [Los Alamos National Laboratory
2009-01-01
This manuscript describes the self-consistent simulation of diffusion at the magnetopause driven by Kelvin-Helmholtz (KH) instability. Two-dimensional hybrid (kinetic ions, fluid electrons) simulations of the most KH-unstable configuration where the shear flow is oriented perpendicular to the uniform magnetic field are carried out. The motion of the simulation particles are tracked during the run and their mean-square displacement normal to the magnetopause is calculated from which diffusion coefficients are determined. The diffusion coefficients are found to be time dependent, with D{sub x} {proportional_to} t{sup {alpha}}, where {alpha} > 1. Additionally, the probability distribution functions (PDF) of the 'jump lengths' the particles make over time are found to be non-gaussian. Such time-dependent diffusion coefficients and non-gaussian PDF's have been associated with so-called 'super-diffusion', in which diffusive mixing of particles is enhanced over classical diffusion. The results indicate that while turbulence associated with the break-down of vortices contributes to this enhanced diffusion, it is the growth of large-scale, coherent vortices is the more important process in facilitating it.
2007-03-28
LST 035 0 o2 0O3 o2o ,0) 7 02 0! lO0 .0, 2 20,O 161) 20 200 110 110 22, 240 150 100 220 frequen•/, kHz ftequtnCy, kHr Fig. 2 Experimental, simulation...validated in simulations of supersonic and hypersonic steady base flows over a flat plate by Ma and Zhong [26], and Wang and Zhong [4]. 0 00’ 0.’ o2o
Numerical simulation of Ge solar cells using D-AMPS-1D code
Energy Technology Data Exchange (ETDEWEB)
Barrera, Marcela, E-mail: barrera@tandar.cnea.gov.ar [Comision Nacional de Energia Atomica, Avenida General Paz 1499, San Martin 1650, Buenos Aires (Argentina); Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET) (Argentina); Rubinelli, Francisco [Instituto de Desarrollo Tecnologico para la Industria Quimica (INTEC)-CONICET, Gueemes 3450, Santa Fe 3000 (Argentina); Rey-Stolle, Ignacio [Instituto de Energia Solar, Universidad Politecnica de Madrid, Avenida Complutense 30, Madrid 28040 (Spain); Pla, Juan [Comision Nacional de Energia Atomica, Avenida General Paz 1499, San Martin 1650, Buenos Aires (Argentina); Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET) (Argentina)
2012-08-15
A solar cell is a solid state device that converts the energy of sunlight directly into electricity by the photovoltaic effect. When light with photon energies greater than the band gap is absorbed by a semiconductor material, free electrons and free holes are generated by optical excitation in the material. The main characteristic of a photovoltaic device is the presence of internal electric field able to separate the free electrons and holes so they can pass out of the material to the external circuit before they recombine. Numerical simulation of photovoltaic devices plays a crucial role in their design, performance prediction, and comprehension of the fundamental phenomena ruling their operation. The electrical transport and the optical behavior of the solar cells discussed in this work were studied with the simulation code D-AMPS-1D. This software is an updated version of the one-dimensional (1D) simulation program Analysis of Microelectronic and Photonic Devices (AMPS) that was initially developed at The Penn State University, USA. Structures such as homojunctions, heterojunctions, multijunctions, etc., resulting from stacking layers of different materials can be studied by appropriately selecting characteristic parameters. In this work, examples of cells simulation made with D-AMPS-1D are shown. Particularly, results of Ge photovoltaic devices are presented. The role of the InGaP buffer on the device was studied. Moreover, a comparison of the simulated electrical parameters with experimental results was performed.
BlazeDEM3D-GPU A Large Scale DEM simulation code for GPUs
Govender, Nicolin; Wilke, Daniel; Pizette, Patrick; Khinast, Johannes
2017-06-01
Accurately predicting the dynamics of particulate materials is of importance to numerous scientific and industrial areas with applications ranging across particle scales from powder flow to ore crushing. Computational discrete element simulations is a viable option to aid in the understanding of particulate dynamics and design of devices such as mixers, silos and ball mills, as laboratory scale tests comes at a significant cost. However, the computational time required to simulate an industrial scale simulation which consists of tens of millions of particles can take months to complete on large CPU clusters, making the Discrete Element Method (DEM) unfeasible for industrial applications. Simulations are therefore typically restricted to tens of thousands of particles with highly detailed particle shapes or a few million of particles with often oversimplified particle shapes. However, a number of applications require accurate representation of the particle shape to capture the macroscopic behaviour of the particulate system. In this paper we give an overview of the recent extensions to the open source GPU based DEM code, BlazeDEM3D-GPU, that can simulate millions of polyhedra and tens of millions of spheres on a desktop computer with a single or multiple GPUs.
Harris, R.
2015-12-01
I summarize the progress by the Southern California Earthquake Center (SCEC) and U.S. Geological Survey (USGS) Dynamic Rupture Code Comparison Group, that examines if the results produced by multiple researchers' earthquake simulation codes agree with each other when computing benchmark scenarios of dynamically propagating earthquake ruptures. These types of computer simulations have no analytical solutions with which to compare, so we use qualitative and quantitative inter-code comparisons to check if they are operating satisfactorily. To date we have tested the codes against benchmark exercises that incorporate a range of features, including single and multiple planar faults, single rough faults, slip-weakening, rate-state, and thermal pressurization friction, elastic and visco-plastic off-fault behavior, complete stress drops that lead to extreme ground motion, heterogeneous initial stresses, and heterogeneous material (rock) structure. Our goal is reproducibility, and we focus on the types of earthquake-simulation assumptions that have been or will be used in basic studies of earthquake physics, or in direct applications to specific earthquake hazard problems. Our group's goals are to make sure that when our earthquake-simulation codes simulate these types of earthquake scenarios along with the resulting simulated strong ground shaking, that the codes are operating as expected. For more introductory information about our group and our work, please see our group's overview papers, Harris et al., Seismological Research Letters, 2009, and Harris et al., Seismological Research Letters, 2011, along with our website, scecdata.usc.edu/cvws.
Hassanein, A.; Sizyuk, T.
2008-11-01
Safe and reliable operation is still one of the major challenges in the development of the new generation of ITER-like fusion reactors. The deposited plasma energy during major disruptions, edge-localized modes (ELMs) and vertical displacement events (VDEs) causes significant surface erosion, possible structural failure and frequent plasma contamination. While plasma disruptions and ELM will have no significant thermal effects on the structural materials or coolant channels because of their short deposition time, VDEs having longer-duration time could have a destructive impact on these components. Therefore, modelling the response of structural materials to VDE has to integrate detailed energy deposition processes, surface vaporization, phase change and melting, heat conduction to coolant channels and critical heat flux criteria at the coolant channels. The HEIGHTS 3D upgraded computer package considers all the above processes to specifically study VDE in detail. Results of benchmarking with several known laboratory experiments prove the validity of HEIGHTS implemented models. Beryllium and tungsten are both considered surface coating materials along with copper structure and coolant channels using both smooth tubes with swirl tape insert. The design requirements and implications of plasma facing components are discussed along with recommendations to mitigate and reduce the effects of plasma instabilities on reactor components.
CRYSTAL simulation code and modeling of coherent effects in a bent crystal at the LHC
Energy Technology Data Exchange (ETDEWEB)
Sytov, A.I., E-mail: alex_sytov@mail.ru [Research Institute for Nuclear Problems, Belarusian State University, Bobruiskaya str., 11, 220030 Minsk (Belarus); INFN Sezione di Ferrara, Dipartimento di Fisica e Scienze della Terra, Università di Ferrara, Via Saragat 1, 44100 Ferrara (Italy); Tikhomirov, V.V., E-mail: vvtikh@mail.ru [Research Institute for Nuclear Problems, Belarusian State University, Bobruiskaya str., 11, 220030 Minsk (Belarus)
2015-07-15
A CRYSTAL simulation code for particle tracking in crystals is introduced. Its essence consists in both adequate and fast sampling of proton trajectories in crystals which is crucial for both correct description of experiments and quantitative prediction of new effects. The H8 single-pass experiment at the CERN SPS as well as 7 TeV proton deflection by a bent crystal at the LHC are simulated. We predict the existence of dechanneling peaks corresponding to the planar channeling oscillations as well as describe the possibility of their observation at high energies, specifically at the LHC energy. An effect of excess over the amorphous level of ionization losses in the channeling mode was also found at 7 TeV.
Reduced gravity boiling and condensing experiments simulated with the COBRA/TRAC computer code
Cuta, Judith M.; Krotiuk, William
1988-01-01
A series of reduced-gravity two-phase flow experiments has been conducted with a boiler/condenser apparatus in the NASA KC-135 aircraft in order to obtain basic thermal-hydraulic data applicable to analytical design tools. Several test points from the KC-135 tests were selected for simulation by means of the COBRA/TRAC two-fluid, three-field thermal-hydraulic computer code; the points were chosen for a 25-90 percent void-fraction range. The possible causes for the lack of agreement noted between simulations and experiments are explored, with attention to the physical characteristics of two-phase flow in one-G and near-zero-G conditions.
Simulation of high-energy radiation belt electron fluxes using NARMAX-VERB coupled codes.
Pakhotin, I P; Drozdov, A Y; Shprits, Y Y; Boynton, R J; Subbotin, D A; Balikhin, M A
2014-10-01
This study presents a fusion of data-driven and physics-driven methodologies of energetic electron flux forecasting in the outer radiation belt. Data-driven NARMAX (Nonlinear AutoRegressive Moving Averages with eXogenous inputs) model predictions for geosynchronous orbit fluxes have been used as an outer boundary condition to drive the physics-based Versatile Electron Radiation Belt (VERB) code, to simulate energetic electron fluxes in the outer radiation belt environment. The coupled system has been tested for three extended time periods totalling several weeks of observations. The time periods involved periods of quiet, moderate, and strong geomagnetic activity and captured a range of dynamics typical of the radiation belts. The model has successfully simulated energetic electron fluxes for various magnetospheric conditions. Physical mechanisms that may be responsible for the discrepancies between the model results and observations are discussed.
Comparison of a laboratory spectrum of Eu-152 with results of simulation using the MCNP code
Energy Technology Data Exchange (ETDEWEB)
Rodenas, J. [Departamento de Ingenieria Quimica y Nuclear, Universidad Politecnica de Valencia, Apartado 22012, E-46071 Valencia (Spain); Gallardo, S. [Departamento de Ingenieria Quimica y Nuclear, Universidad Politecnica de Valencia, Apartado 22012, E-46071 Valencia (Spain)], E-mail: sergalbe@iqn.upv.es; Ortiz, J. [Laboratorio de Radiactividad Ambiental, Universidad Politecnica de Valencia, Apartado 22012, E-46071 Valencia (Spain)
2007-09-21
Detectors used for gamma spectrometry must be calibrated for each geometry considered in environmental radioactivity laboratories. This calibration is performed using a standard solution containing gamma emitter sources. Nevertheless, the efficiency curves obtained are periodically checked using a source such as {sup 152}Eu emitting many gamma rays that cover a wide energy range (20-1500 keV). {sup 152}Eu presents a problem because it has a lot of peaks affected by True Coincidence Summing (TCS). Two experimental measures have been performed placing the source (a Marinelli beaker) at 0 and 10 cm from the detector. Both spectra are simulated by the MCNP 4C code, where the TCS is not reproduced. Therefore, the comparison between experimental and simulated peak net areas permits one to choose the most convenient peaks to check the efficiency curves of the detector.
CRYSTAL simulation code and modeling of coherent effects in a bent crystal at the LHC
Sytov, A. I.; Tikhomirov, V. V.
2015-07-01
A CRYSTAL simulation code for particle tracking in crystals is introduced. Its essence consists in both adequate and fast sampling of proton trajectories in crystals which is crucial for both correct description of experiments and quantitative prediction of new effects. The H8 single-pass experiment at the CERN SPS as well as 7 TeV proton deflection by a bent crystal at the LHC are simulated. We predict the existence of dechanneling peaks corresponding to the planar channeling oscillations as well as describe the possibility of their observation at high energies, specifically at the LHC energy. An effect of excess over the amorphous level of ionization losses in the channeling mode was also found at 7 TeV.
magnum.fe: A micromagnetic finite-element simulation code based on FEniCS
Abert, Claas; Exl, Lukas; Bruckner, Florian; Drews, André; Suess, Dieter
2013-11-01
We have developed a finite-element micromagnetic simulation code based on the FEniCS package called magnum.fe. Here we describe the numerical methods that are applied as well as their implementation with FEniCS. We apply a transformation method for the solution of the demagnetization-field problem. A semi-implicit weak formulation is used for the integration of the Landau-Lifshitz-Gilbert equation. Numerical experiments show the validity of simulation results. magnum.fe is open source and well documented. The broad feature range of the FEniCS package makes magnum.fe a good choice for the implementation of novel micromagnetic finite-element algorithms.
magnum.fe: A micromagnetic finite-element simulation code based on FEniCS
Abert, Claas; Bruckner, Florian; Drews, André; Suess, Dieter
2013-01-01
We have developed a finite-element micromagnetic simulation code based on the FEniCS package called magnum.fe. Here we describe the numerical methods that are applied as well as their implementation with FEniCS. We apply a transformation method for the solution of the demagnetization-field problem. A semi-implicit weak formulation is used for the integration of the Landau-Lifshitz-Gilbert equation. Numerical experiments show the validity of simulation results. magnum.fe is open source and well documented. The broad feature range of the FEniCS package makes magnum.fe a good choice for the implementation of novel micromagnetic finite-element algorithms.
A Particle In Cell code development for high current ion beam transport and plasma simulations
Joshi, N
2016-01-01
A simulation package employing a Particle in Cell (PIC) method is developed to study the high current beam transport and the dynamics of plasmas. This package includes subroutines those are suited for various planned projects at University of Frankfurt. In the framework of the storage ring project (F8SR) the code was written to describe the beam optics in toroidal magnetic fields. It is used to design an injection system for a ring with closed magnetic field lines. The generalized numerical model, in Cartesian coordinates is used to describe the intense ion beam transport through the chopper system in the low energy beam section of the FRANZ project. Especially for the chopper system, the Poisson equation is implemented with irregular geometries. The Particle In Cell model is further upgraded with a Monte Carlo Collision subroutine for simulation of plasma in the volume type ion source.
Simulation with the COREDIV code of JET discharges with the ITER-like wall
Energy Technology Data Exchange (ETDEWEB)
Telesca, G., E-mail: g.telesca@fz-juelich.de [Department of Applied Physics, Ghent University, Gent (Belgium); Zagorski, R. [Institute of Plasma Physics and Laser Microfusion, EURATOM/IPPLM Association, Warsaw (Poland); Brezinsek, S. [IEK-4, FZ Jülich GmbH, Association EURATOM-FZJ, TEC, Jülich (Germany); Brix, M.; Flanagan, J. [EURATOM/CCFE Fusion Association, Culham, Abingdon, Oxon OX14 3DB (United Kingdom); Ivanova-Stanik, I. [Institute of Plasma Physics and Laser Microfusion, EURATOM/IPPLM Association, Warsaw (Poland); Lehnen, M. [IEK-4, FZ Jülich GmbH, Association EURATOM-FZJ, TEC, Jülich (Germany); Stamp, M. [EURATOM/CCFE Fusion Association, Culham, Abingdon, Oxon OX14 3DB (United Kingdom); Van Oost, G. [Department of Applied Physics, Ghent University, Gent (Belgium)
2013-07-15
ICRF heated L-mode pulses of JET with the new ITER like wall are simulated for the first time with the transport code COREDIV. The model, which couples self-consistently the core with the SOL as well as the main plasma with impurities, outputs, from a limited number of inputs as the heating power, the average density and the confinement time, the core temperatures and densities profiles, the effective ion charge Z{sub eff}, the power radiated, the W fluxes and concentration and the plasma parameters on the divertor. Due to the slab geometry of the SOL, the Be flux cannot be calculated self-consistently, but it is given as an input, according to spectroscopic measurements in the divertor. Comparison of simulations with experimental data both of the core and of the SOL is generally satisfactorily, with the exception of Z{sub eff}, possibly due to radiofrequency-specific effects, which are not accounted for in the model.
Computer simulation of Angra-2 PWR nuclear reactor core using MCNPX code
Energy Technology Data Exchange (ETDEWEB)
Medeiros, Marcos P.C. de; Rebello, Wilson F., E-mail: eng.cavaliere@ime.eb.br, E-mail: rebello@ime.eb.br [Instituto Militar de Engenharia - Secao de Engenharia Nuclear, Rio de Janeiro, RJ (Brazil); Oliveira, Claudio L. [Universidade Gama Filho, Departamento de Matematica, Rio de Janeiro, RJ (Brazil); Vellozo, Sergio O., E-mail: vellozo@cbpf.br [Centro Tecnologico do Exercito. Divisao de Defesa Quimica, Biologica e Nuclear, Rio de Janeiro, RJ (Brazil); Silva, Ademir X. da, E-mail: ademir@nuclear.ufrj.br [Coordenacao dos Programas de Pos Gaduacao de Engenharia (COPPE/UFRJ), Rio de Janeiro, RJ (Brazil)
2011-07-01
In this work the MCNPX (Monte Carlo N-Particle Transport Code) code was used to develop a computerized model of the core of Angra 2 PWR (Pressurized Water Reactor) nuclear reactor. The model was created without any kind of homogenization, but using real geometric information and material composition of that reactor, obtained from the FSAR (Final Safety Analysis Report). The model is still being improved and the version presented in this work is validated by comparing values calculated by MCNPX with results calculated by others means and presented on FSAR. This paper shows the results already obtained to K{sub eff} and K{infinity}, general parameters of the core, considering the reactor operating under stationary conditions of initial testing and operation. Other stationary operation conditions have been simulated and, in all tested cases, there was a close agreement between values calculated computationally through this model and data presented on the FSAR, which were obtained by other codes. This model is expected to become a valuable tool for many future applications. (author)
Development of a Beam-Beam Simulation Code for e+e- Colliders
Zhang, Yuan
2005-01-01
BEPC will be upgraded into BEPCII, and the luminosity will be about 100 times higher. We developed a three dimensional strong-strong PIC code to study the beam-beam effects in BEPCII. The transportation through the arc is the same as that in Hirata's weak-strong code. The beam-beam force is computed directly by solving the Poisson equation using the FACR method, and the boundary potential is computed by circular convolution. The finite bunch length effect is included by longitudinal slices. An interpolation scheme is used to reduce the required slice number in simulations. The standard message passing interface (MPI) is used to parallelize the code. The computing time increases linearly with (n+1), where n is the slice number. The calculated luminosity of BEPCII at the design operating point is less than the design value. The best area in the tune space is near (0.505,0.57) according to the survey, where the degradation of luminosity can be improved.
Humphries, Stanley; Johnson, Kristin; Rick, Kyle; Liu, Zheng-jun; Goldberg, S. Nahum
2005-04-01
ETherm3 is a finite-element software suite for simulations of electrosurgery and RF thermal ablation processes. Program components cover the complete calculation process from mesh generation to solution analysis. The solutions employ three-dimensional conformal meshes to handle cluster probes and other asymmetric assemblies. The conformal-mesh approach is essential for high-accuracy surface integrals of net electrode currents. ETherm3 performs coupled calculations of RF electric fields in conductive dielectrics and thermal transport via dynamic solutions of the bioheat equation. The boundary-value RF field solution is updated periodically to reflect changes in material properties. ETherm3 features advanced material models with the option for arbitrary temperature variations of thermal and electrical conductivity, perfusion rate, and other quantities. The code handles irreversible changes by switching the material reference of individual elements at specified transition temperatures. ETherm3 is controlled through a versatile interpreter language to enable complex run sequences. The code can automatically maintain constant current or power, switch to different states in response to temperature or impedance information, and adjust parameters on the basis of user-supplied control functions. In this paper, we discuss the physical basis and novel features of the code suite and review application examples.
Verification and validation of the simulated radar image (SRIM) code radar cross section predictions
Stanley, Dale A.
1991-12-01
The objectives of this study were to verify and validate the Simulated Radar Image (SRIM) Code Version 4.0 monostatic radar cross section (RCS) predictions. SRIM, uses the theory of Physical Optics (PO) to predict backscatter for a user specified aspect angle. Target obscuration and multiple reflections are taken into account by sampling the target with ray tracing. The software verification and validation technique followed in this study entailed comparing the code predictions to closed form PO equations, other RCS prediction software packages, and measured data. The targets analyzed were a sphere, rectangular flat plate, circular flat plate, solid right circular cylinder, dihedral and trihedral corner reflectors, top hat, cone, prolate spheroid, and generic missile. SRIM RCS predictions are shown for each target as a function of frequency, aspect angle, and ray density. Also presented is an automation technique that enables the user to run SRIM sequentially over a range of azimuth angles. The FORTRAN code written by the author for the PO equations is also provided.
Traveling-wave-tube simulation: The IBC (Interactive Beam-Circuit) code
Energy Technology Data Exchange (ETDEWEB)
Morey, I.J.; Birdsall, C.K.
1989-09-26
Interactive Beam-Circuit (IBC) is a one-dimensional many particle simulation code which has been developed to run interactively on a PC or Workstation, and displaying most of the important physics of a traveling-wave-tube. The code is a substantial departure from previous efforts, since it follows all of the particles in the tube, rather than just those in one wavelength, as commonly done. This step allows for nonperiodic inputs in time, a nonuniform line and a large set of spatial diagnostics. The primary aim is to complement a microwave tube lecture course, although past experience has shown that such codes readily become research tools. Simple finite difference methods are used to model the fields of the coupled slow-wave transmission line. The coupling between the beam and the transmission line is based upon the finite difference equations of Brillouin. The space-charge effects are included, in a manner similar to that used by Hess; the original part is use of particle-in-cell techniques to model the space-charge fields. 11 refs., 11 figs.
Software Abstractions and Methodologies for HPC Simulation Codes on Future Architectures
Directory of Open Access Journals (Sweden)
Anshu Dubey
2014-07-01
Full Text Available Simulations with multi-physics modeling have become crucial to many science and engineering fields, and multi-physics capable scientific software is as important to these fields as instruments and facilities are to experimental sciences. The current generation of mature multi-physics codes would have sustainably served their target communities with modest amount of ongoing investment for enhancing capabilities. However, the revolution occurring in the hardware architecture has made it necessary to tackle the parallelism and performance management in these codes at multiple levels. The requirements of various levels are often at cross-purposes with one another, and therefore hugely complicate the software design. All of these considerations make it essential to approach this challenge cooperatively as a community. We conducted a series of workshops under an NSF-SI2 conceptualization grant to get input from various stakeholders, and to identify broad approaches that might lead to a solution. In this position paper we detail the major concerns articulated by the application code developers, and emerging trends in utilization of programming abstractions that we found through these workshops.
Simulating polarized Galactic synchrotron emission at all frequencies, the Hammurabi code
Waelkens, A; Reinecke, M; Kitaura, F S; Ensslin, T A
2008-01-01
We present a publicly available code called Hammurabi for generating mock polarized observations of Galactic synchrotron emission for telescopes like LOFAR, SKA, Planck and WMAP, based on model inputs for the Galactic magnetic field (GMF), the cosmic-ray density distribution and the thermal electron density. We also present mock UHECR deflection measure (UDM) maps based on model inputs for the GMF. In future, when UHECR sources are identified, this will allow us to define UDM as a GMF probe in a similar way as polarized radio sources permit us to define rotation measures. To demonstrate the code's abilities mock observations are compared to real data as a means to constrain the input parameters of our simulations with a focus on large-scale magnetic field properties. As expected, attempts at trying to model the synchrotron, UHECR deflection and RM input parameters, show that any additional observational data set greatly increases the constraints on the models. The hammurabi code addresses this by allowing to ...