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Hasegawa, Yuta; Onodera, Naoyuki; Asahi, Yuichi; Idomura, Yasuhiro
Dai-35-Kai Suchi Ryutai Rikigaku Shimpojiumu Koen Rombunshu (Internet), 3 Pages, 2021/12
We are developing a real-time urban wind simulation code called CityLBM. In this paper, a performance measurement of the CityLBM was carried out using Tesla A100 GPUs. To optimize the communication with heterogeneous network architectures of intra-node (NVlink) and inter-node (Infiniband) connection, we designed blocked two dimensional domain partitioning with 2 
2 or 2 4 subdomains, which are confined within each node. The strong scaling with 2.4 billion grids was tested. The result showed good strong scalability and performance, leading to 2.81 speedup from 80 GPUs to 256 GPUs and 1.15 speedup with the blocked domain partitioning. Finally, the simulation with 1 m resolution and 5.7 km 5.7 km horizontal region exceeded the real-time performance, where the computational speed was 
faster than the real-time.
Onodera, Naoyuki; Idomura, Yasuhiro; Hasegawa, Yuta; Nakayama, Hiromasa
Dai-35-Kai Suchi Ryutai Rikigaku Shimpojiumu Koen Rombunshu (Internet), 3 Pages, 2021/12
A detailed wind simulation is very important for designing smart cities. Since a lot of tall buildings and complex structures make the air flow turbulent in urban cities, large-scale CFD simulations are needed. We develop a GPU-based CFD code based on a Lattice Boltzmann Method (LBM) with a block-based Adaptive Mesh Refinement (AMR) method. In order to reproduce real wind conditions, the wind condition and ground temperature of the mesoscale weather forecasting model are given as boundary conditions. In this research, a surface heat flux model based on the Monin-Obukhov similarity theory was introduced to improve the calculation accuracy. We conducted a detailed wind simulation in Oklahoma City. By executing this computation, wind conditions in the urban area were reproduced with good accuracy.