Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Ina, Takuya*; Idomura, Yasuhiro; Imamura, Toshiyuki*; Yamashita, Susumu; Onodera, Naoyuki
Proceedings of 12th Workshop on Latest Advances in Scalable Algorithms for Large-Scale Systems ScalA21) (Internet), 8 Pages, 2021/11
Times Cited Count：1 Percentile：50.67(Computer Science, Software Engineering)A new mixed-precision preconditioner based on the iterative refinement (IR) method is developed for preconditioned conjugate gradient (P-CG) and multigrid preconditioned conjugate gradient (MGCG) solvers in a multi-phase thermal-hydraulic CFD code JUPITER. In the IR preconditioner, all data is stored in FP16 to reduce memory access, while all computation is performed in FP32. The hybrid FP16/32 implementation keeps the similar convergence property as FP32, while the computational performance is close to FP16. The developed solvers are optimized on Fugaku (A64FX), and applied to ill-conditioned matrices in JUPITER. The P-CG and MGCG solvers with the new IR preconditioner show excellent strong scaling up to 8,000 nodes, and at 8,000 nodes, they are respectively accelerated up to 4.86
and 2.39 from the conventional ones on Oakforest-PACS (KNL).
Idomura, Yasuhiro
no journal, ,
Under the Post-K project, a Gyrokinetic Toroidal 5D full-f Eulerian code GT5D has been developed towards exascale burning plasma simulations on the Post-K machine. In this talk, we review the present status on new computational techniques on GT5D. The main computing part of GT5D is given by Krylov based sparse matrix solvers for a semi-implicit time integration. We have ported computing kernels of these solvers on a prototype machine of FUGAKU and on V100 GPU, and confirmed that almost ideal performance gains are achieved on these state-of-the-art many core and GPU architectures.
Idomura, Yasuhiro
no journal, ,
A new synergy effect between neoclassical and turbulent particle transports in ion temperature gradient driven turbulence is investigated using the Gyrokinetic Toroidal 5D full-f Eulerian code GT5D. It is found that in addition to turbulent particle transport, enhanced neoclassical particle transport due to the new synergy effect through the ambipolar condition makes a significant contribution to particle transport of bulk and impurity ions. This mechanism does not work for temperature, and selectively enhances only particle transport.
Idomura, Yasuhiro
no journal, ,
The multi-phase multi-component thermal hydraulics code JUPITER, the urban wind analysis code CityLBM, and the in-situ visualization software In-Situ PBVR were ported and optimized on Fugaku, and their performances were evaluated. The performance of JUPITER, which is implemented in C, was compared against Oakforest-PACS, and a reasonable speedup due to the improved hardware was confirmed. In addition, the performance was further improved by using FP16 SIMD operations on A64FX. On the other hand, Fujitsu C compiler had many optimization issues on CityLBM, which is implemented in C++, and its performance was two orders of magnitudes slower than Tsubame, when the same number of computing nodes are used. Finally, we constructed an in-situ visualization environment on Fugaku using In-Situ PBVR, which was released as an open source software.
Watanabe, Tomohiko*; Idomura, Yasuhiro; Todo, Yasushi*; Honda, Mitsuru*
no journal, ,
During the initial start-up phase of the supercomputer Fugaku, we have launched a simulation project to explore physics of burning plasma confinement, that is, turbulent transport of particles, momentum, energy, impurity ions and hydrogen isotopes, and confinement of energetic particles, in collaboration with data science approaches. In prior to the project, we have upgraded and optimized three major fusion plasma simulation codes, GKV, GT5D and MEGA, which solve the kinetic plasma dynamics on multi-dimensional phase space, achieving the high computational performance on Fugaku. The flux tube gyrokinetic code, GKV, is applied to simulations of the multi-scale turbulence in multiple ion species plasma and the turbulent transport of heavy impurity ions. The global full-f gyrokinetic code, GT5D, is employed to explore non-local turbulent transport and intrinsic plasma rotation. The kinetic-MHD hybrid code, MEGA, is used for studying confinement of energetic ions, and has also been extended to introduce kinetic dynamics of bulk ions. In the project, data science approaches are also promoted to improve transport modeling and efficiency of the simulation research.
Idomura, Yasuhiro
no journal, ,
We analyze turbulence transition between linear and saturated Ohmic confinement (LOC-SOC) regimes using the global full-f gyrokinetic simulation code GT5D on the Fugaku supercomputer. The LOC-SOC transition is characterized by the change of intrinsic rotation profiles with a density ramp. This feature is reproduced by numerical experiments, and its mechanism is clarified. The change of collisionality, which depends on the density, induces a transition of dominant micro-instability from trapped electron modes (TEMs) to ion temperature gradient driven modes (ITGs). TEMs and ITGs have different asymmetries in turbulent spectra with respect to the wavenumber in the direction of the magnetic field, leading to the change of momentum transport in the LOC-SOC transition.
