Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Hasegawa, Yuta; Aoki, Takayuki*; Kobayashi, Hiromichi*; Idomura, Yasuhiro; Onodera, Naoyuki
no journal, ,
We developed a block-structured static adaptive mesh refinement (AMR) CFD code for the aerodynamics simulation using the lattice Boltzmann method on GPU supercomputers. The data structure of AMR was based on the forest-of-octrees, and the domain partitioning algorithm was based on space-filling curves (SFCs). To reduce the halo data communication, we introduced the tree cutting approach, which divided the global domains with a few octrees into small sub-domains with many octrees, leading to a hierarchical domain partitioning approach with the coarse structured block and the fine SFC partitioning in each block. The tree cutting improved the locality of the sub-divided domain, and reduced both the amount of communication data and the number of connections of the halo communication. In the strong scaling test on the Tesla V100 GPU supercomputer, the tree cutting approach showed 
1.82 speedup at the performance of 2207 MLUPS (mega-lattice update per second) on 128 GPUs.
Onodera, Naoyuki; Idomura, Yasuhiro; Hasegawa, Yuta; Nakayama, Hiromasa; Shimokawabe, Takashi*; Aoki, Takayuki*
no journal, ,
This paper presents a novel data assimilation method in realistic turbulent boundary layer simulations for the realization of a wind digital twin. We have developed a plume dispersion simulation code named CityLBM based on a lattice Boltzmann method. CityLBM enables a real time ensemble simulation for several km square area by applying locally mesh-refinement method on GPU supercomputers. Mesoscale wind boundary conditions produced by a Weather Research and Forecasting Model are given as boundary conditions in CityLBM by using a nudging data assimilation method. In this study, we propose a dynamic nudging data assimilation method, where a particle filter optimizes the nudging coefficient based on the observation data. This approach gave reasonable agreements in vertical profiles of the wind speed, the wind direction, and the turbulent intensity compared to the observation data throughout the day, and enabled all-day simulations, where atmospheric conditions change significantly.
Wang, Z.; Sugiyama, Tomoyuki
no journal, ,
Tsuru, Tomohito; Lobzenko, I.
no journal, ,
Dislocation has been regarded as the essential lattice defect in plastic deformation, especially in metallic materials. The fundamental properties of the dislocation core have a dominant influence on the intrinsic ductility or brittleness of materials. The interaction between dislocations and other crystal defects plays a critical role in determining the mechanical properties of metals. Especially, plastic deformation in BCC metals is achieved by a fundamental motion of screw dislocations through a kink mechanism. In the present study, we evaluated softening/strengthening behavior of dilute and highly-concentrated BCC alloys by the first-principles calculations. The introduction of dislocations within our periodic cell was accomplished by applying a continuum linear elastic theory solution for the periodic dislocation dipole array. Then, we proposed new analytical models describing the kink process of screw dislocations, in which the fundamental properties are evaluated by the electronic structure calculations. The analytical models based on the solid solution and the line-tension model were applied efficiently to predict the fundamental mechanical properties.
Sugihara, Kenta; Onodera, Naoyuki; Idomura, Yasuhiro; Yamashita, Susumu
no journal, ,
A multi-phase multi-component thermal-hydraulic simulation code JUPITER has been developed to analyze the molten material behavior under severe accident conditions in nuclear reactors. In JUPITER, the THINC/WLIC method was implemented as an interface tracking method, which enabled us to accurately calculate the dynamics of the multiphase interface of the molten material at relatively low flow velocity. However, when JUPITER is applied to air-water two phase flows in fuel bundles, there is a problem that the Volume of Fluid (VOF) value is stripped from the interface and small VOF values drift in turbulent flows where coalescence and separation of the interface are active. To improve the interface tracking method of the JUPITER code, the applicability of the phase-field method has been investigated. In this study, the phase-field method is applied to the JUPITER code and the droplet oscillation phenomena are analyzed. The numerical results are compared with the theoretical solution to clarify the sensitivity of the phase-field method to its hyper parameters such as the mobility and the interface width.