scholarly journals Building and Auto-Tuning Computing Kernels: Experimenting with Boast and Starpu in the Gysela Code

2018 ◽  
Vol 63 ◽  
pp. 152-178
Author(s):  
Julien Bigot ◽  
Virginie Grandgirard ◽  
Guillaume Latu ◽  
Jean-Francois Mehaut ◽  
Luís Felipe Millani ◽  
...  
Keyword(s):  
Turbulent Transport ◽  
Building Blocks ◽  
Tokamak Plasma ◽  
Computational Domain ◽  
Major Goal ◽  
Five Dimensions ◽  
Performance Portability ◽  
Automated Process ◽  
Auto Tuning ◽  
Specific Computation

Modeling turbulent transport is a major goal in order to predict confinement performance in a tokamak plasma. The gyrokinetic framework considers a computational domain in five dimensions to look at kinetic issues in a plasma; this leads to huge computational needs. Therefore, optimization of the code is an especially important aspect, especially since coprocessors and complex manycore architectures are foreseen as building blocks for Exascale systems. This project aims to evaluate the applicability of two auto-tuning approaches with the BOAST and StarPU tools on the GYSELA code in order to circumvent performance portability issues. A specific computation intensive kernel is considered in order to evaluate the benefit of these methods. StarPU enables to match the performance and even sometimes outperform the hand-optimized version of the code while leaving scheduling choices to an automated process. BOAST on the other hand reveals to be well suited to get a gain in terms of execution time on four architectures. Speedups in-between 1.9 and 5.7 are obtained on a cornerstone computation intensive kernel.

scholarly journals COMPARISON BETWEEN 2D TURBULENCE MODEL ESEL AND EXPERIMENTAL DATA FROM AUG AND COMPASS TOKAMAKS

2015 ◽  
Vol 55 (2) ◽  
pp. 128-135 ◽  
Author(s):  
Peter Ondac ◽  
Jan Horacek ◽  
Jakub Seidl ◽  
Petr Vondrácek ◽  
Hans Werner Müller ◽  
...  
Keyword(s):  
Turbulent Transport ◽  
Plasma Potential ◽  
Density Fluctuations ◽  
Tokamak Plasma ◽  
Plasma Parameters ◽  
Fluid Turbulence ◽  
Radial Profiles ◽  
Parallel Dynamics ◽  
Two Machines ◽  
Probe Measurements

<!-- p, li { white-space: pre-wrap; } --><p style="text-indent: 0px; margin: 0px;">In this article we have used the 2D fluid turbulence numerical model, ESEL, to simulate turbulent transport in edge tokamak plasma. Basic plasma parameters from the ASDEX Upgrade and COMPASS tokamaks are used as input for the model, and the output is compared with experimental observations obtained by reciprocating probe measurements from the two machines. Agreements were found in radial profiles of mean plasma potential and temperature, and in a level of density fluctuations. Disagreements, however, were found in the level of plasma potential and temperature fluctuations. This implicates a need for an extension of the ESEL model from 2D to 3D to fully resolve the parallel dynamics, and the coupling from the plasma to the sheath.</p>

scholarly journals On rising magnetic flux tube and formation of sunspots in a deep domain

2020 ◽  
Vol 494 (2) ◽  
pp. 2523-2537 ◽  
Author(s):  
H Hotta ◽  
H Iijima
Keyword(s):  
Flux Tube ◽  
Temperature Region ◽  
Convection Zone ◽  
Solar Surface ◽  
Turbulent Transport ◽  
Numerical Code ◽  
Magnetic Flux Tube ◽  
Computational Domain ◽  
Divergent Flow ◽  
Horizontal Flux

ABSTRACT We investigate the rising flux tube and the formation of sunspots in an unprecedentedly deep computational domain that covers the whole convection zone with a radiative magnetohydrodynamics simulation. Previous calculations had shallow computational boxes (&lt;30 Mm) and convection zones at a depth of 200 Mm. By using our new numerical code Radition and RSST for Deep Dynamics(r2d2), we succeed in covering the whole convection zone and reproduce the formation of the sunspot from a simple horizontal flux tube because of the turbulent thermal convection. The main findings are as follows. (1) The rising speed of the flux tube is larger than the upward convection velocity because of the low density caused by the magnetic pressure and the suppression of the mixing. (2) The rising speed of the flux tube exceeds 250 m s−1 at a depth of 18 Mm, while we do not see any clear evidence of the divergent flow 3 h before the emergence at the solar surface. (3) Initially, the root of the flux tube is filled with the downflows, and then the upflow fills the centre of the flux tube during the formation of the sunspot. (4) The essential mechanisms for the formation of the sunspot are the coherent inflow and the turbulent transport. (5) The low-temperature region is extended to a depth of at least 40 Mm in the matured sunspot, with the high-temperature region in the centre of the flux tube. Some of the findings indicate the importance of the deep computational domain for the flux emergence simulations.

Non-linear MHD modelling of Edge Localized Modes suppression by Resonant Magnetic Perturbations in ITER

2022 ◽  
Author(s):  
Marina Becoulet ◽  
Guido Huijsmans ◽  
Chantal Passeron ◽  
Yueqiang Liu ◽  
Todd E Evans ◽  
...  
Keyword(s):  
Turbulent Transport ◽  
Heat Fluxes ◽  
Total Power ◽  
Computational Domain ◽  
Localized Modes ◽  
Mode Behavior ◽  
Non Linear ◽  
Magnetic Perturbations ◽  
Edge Localized Modes ◽  
Resonant Magnetic Perturbations

Abstract Edge Localized Modes (ELMs) suppression by Resonant Magnetic Perturbations (RMPs) was studied with the non-linear MHD code JOREK for the ITER H-mode scenarios at 15MA,12.5MA,10MA/5.3T. The main aim of this work was to demonstrate that ELMs can be suppressed by RMPs while the divertor 3D footprints of heat and particle fluxes remain within divertor material limits. The unstable peeling-ballooning modes responsible for ELMs without RMPs were modelled first for each scenario using numerically accessible parameters for ITER. Then the stabilization of ELMs by RMPs was modelled with the same parameters. RMP spectra, optimized by the linear MHD MARS-F code, with main toroidal harmonics N=2, N=3, N=4 have been used as boundary conditions of the computational domain of JOREK, including realistic RMP coils, main plasma, Scrape Off Layer (SOL) divertor and realistic first wall. The model includes all relevant plasma flows: toroidal rotation, two fluid diamagnetic effects and neoclassical poloidal friction. With RMPs, the main toroidal harmonic and the non-linearly coupled harmonics remain dominant at the plasma edge, producing saturated modes and a continuous MHD turbulent transport thereby avoiding ELM crashes in all scenarios considered here. The threshold for ELM suppression was found at a maximum RMP coils current of 45kAt-60kAt compared to the coils maximum capability of 90kAt. In the high beta poloidal steady-state 10MA/5.3T scenario, a rotating QH-mode without ELMs was observed even without RMPs. In this scenario with RMPs N=3, N=4 at 20kAt maximum current in RMP coils, similar QH-mode behavior was observed however with dominant edge harmonic corresponding to the main toroidal number of RMPs. The 3D footprints with RMPs show the characteristic splitting with the main RMP toroidal symmetry. The maximum radial extension of the footprints typically was ~20 cm in inner divertor and ~40 cm in outer divertor with stationary heat fluxes decreasing further out from the initial strike point from ~5MW/m2 to ~1MW/m2 assuming a total power in the divertor and walls is 50MW.

Effects of the location of a biased limiter on turbulent transport in the IR-T1 tokamak plasma

2017 ◽  
Vol 71 (9) ◽  
Author(s):  
Ramin Alipour ◽  
Mahmood Ghoranneviss ◽  
Ahmad Salar Elahi ◽  
Sakineh Meshkani
Keyword(s):  
Turbulent Transport ◽  
Tokamak Plasma

Analysis of the radial and poloidal turbulent transport in the edge tokamak plasma

2013 ◽  
Vol 79 (5) ◽  
pp. 647-655 ◽  
Author(s):  
S. MESHKANI ◽  
M. GHORANNEVISS ◽  
M. LAFOUTI ◽  
A. SALAR ELAHI
Keyword(s):  
Magnetic Field ◽  
Turbulent Transport ◽  
Edge Plasma ◽  
Tokamak Plasma ◽  
Spectral Features ◽  
Negative Bias ◽  
Langmuir Probes ◽  
Negative Bias Voltage ◽  
Helical Magnetic Field ◽  
Transport Method

AbstractIn this paper, turbulent transport in the edge plasma of the IR-T1 tokamak (r/a = 0.9) in the presence of a resonant helical magnetic field (RHF) and a biased limiter has been investigated and analyzed. The time evolution of potential fluctuation, and electric field and turbulent transport have been measured by using two arrays of the Langmuir probes in both the radial and poloidal directions. The experiments have been done in different regimes such as limiter biasing and RHF, and both of them. The analyses have been done by the fast Fourier transport method and their spectral features are obtained with the help of the standard autocorrelation technique. The results show that radial turbulent transport decreases about 60% after positive biasing application, while it increases about 40% after negative biasing. The effect of positive biasing on poloidal turbulent transport displays an increase of about 55%, while the negative bias voltage decreases the poloidal turbulent transport about 30%. Consequently, confinement is improved and plasma density rises significantly due to the applied positive biasing in IR-T1. However, the results are reversed when negative biasing is applied. Also, in this work, the results of the applied RHF (L = 3) are compared with biasing results and analyzed.

scholarly journals Landing Gear Aerodynamic Noise Prediction Using Building-Cube Method

2012 ◽  
Vol 2012 ◽  
pp. 1-16 ◽  
Author(s):  
Daisuke Sasaki ◽  
Deguchi Akihito ◽  
Hiroshi Onda ◽  
Kazuhiro Nakahashi
Keyword(s):  
Large Scale ◽  
Building Blocks ◽  
Landing Gear ◽  
Experimental Result ◽  
Aerodynamic Noise ◽  
Noise Prediction ◽  
Computational Domain ◽  
Flow Solver ◽  
Flow Acceleration ◽  
Geometry Model

Landing gear noise prediction method is developed using Building-Cube Method (BCM). The BCM is a multiblock-structured Cartesian mesh flow solver, which aims to enable practical large-scale computation. The computational domain is composed of assemblage of various sizes of building blocks where small blocks are used to capture flow features in detail. Because of Cartesian-based mesh, easy and fast mesh generation for complicated geometries is achieved. The airframe noise is predicted through the coupling of incompressible Navier-Stokes flow solver and the aeroacoustic analogy-based Curle’s equation. In this paper, Curle’s equation in noncompact form is introduced to predict the acoustic sound from an object in flow. This approach is applied to JAXA Landing gear Evaluation Geometry model to investigate the influence of the detail components to flows and aerodynamic noises. The position of torque link and the wheel cap geometry are changed to discuss the influence. The present method showed good agreement with the preceding experimental result and proved that difference of the complicated components to far field noise was estimated. The result also shows that the torque link position highly affects the flow acceleration at the axle region between two wheels, which causes the change in SPL at observation point.

scholarly journals Beyond Democracy-Dictatorship Measures: A New Framework Capturing Executive Bases of Power, 1789–2016

2019 ◽  
Vol 17 (1) ◽  
pp. 66-84 ◽  
Author(s):  
Jan Teorell ◽  
Staffan I. Lindberg
Keyword(s):  
Building Blocks ◽  
Authoritarian Regimes ◽  
Five Dimensions ◽  
Direct Election ◽  
Bases Of Power ◽  
Regime Types ◽  
Heads Of State ◽  
Heads Of Government ◽  
Ruling Party ◽  
New Framework

We attempt to integrate the literatures on authoritarian regime types and democratic forms of government. We propose a theoretical framework of five dimensions of executive appointment and dismissal that can be applied in both more democratic and more authoritarian regimes: the hereditary, military, ruling party, direct election, and confidence dimensions, respectively. Relying on the Varieties of Democracy data, we provide measures of these five dimensions for 3,937 individual heads of state and 2,874 heads of government from 192 countries across the globe from 1789 to the present. After presenting descriptive evidence of their prevalence, variation, and relationship to extant regime typologies, a set of exploratory probes gauge the extent to which the five dimensions can predict levels of repression, corruption, and executive survival, controlling for aspects of democracy. This leads to generation of a set of original hypotheses that we hope can serve as building blocks for explanatory theory. We conclude by discussing some limitations of these novel data.

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