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Journal Articles

Development of a design optimization framework for sodium-cooled fast reactors, 3; Development of a prototype with user interface

Doda, Norihiro; Nakamine, Yoshiaki*; Yoshimura, Kazuo; Kuwagaki, Kazuki; Hamase, Erina; Yokoyama, Kenji; Kikuchi, Norihiro; Mori, Takero; Hashidate, Ryuta; Tanaka, Masaaki

Keisan Kogaku Koenkai Rombunshu (CD-ROM), 29, 6 Pages, 2024/06

As a part of the development of the "Advanced Reactor Knowledge- and AI-aided Design Integration Approach through the whole plant lifecycle (ARKADIA)" to utilize the knowledge obtained through the sodium-cooled fast reactors (SFRs) and combine the latest numerical simulation technologies, ARKADIA-Design is being developed to support the optimization of SFRs in the conceptual design stage. ARKADIA-Design consists of three systems of Virtual Plant Life System (VLS), Enhanced and AI-aided optimization System (EAS), and Knowledge Management System (KMS). A design optimization framework controls the linkage among the three systems through the interfaces in each system. In this study, we have developed a prototype of the framework for core design optimization using the coupled analysis functions in VLS and optimization control function in the linkage of EAS and VLS to investigate the applicability of the framework to the SFR design optimization process.

Journal Articles

Data assimilation experiment of flow around three-dimensional square cylinder using LBM-LETKF with small number of observation points

Hasegawa, Yuta; Idomura, Yasuhiro; Onodera, Naoyuki

Keisan Kogaku Koenkai Rombunshu (CD-ROM), 29, 4 Pages, 2024/06

We implemented the ensemble data assimilation (DA) of turbulence by using the mesh-refined lattice Boltzmann method with the local ensemble transform Kalman filter (LBM-LETKF). We examined the accuracy of the data assimilation against a turbulent flow around a three-dimensional square cylinder. The DA error was comparable or less than the observation noise when the observation interval was a half of the period of the K$'{a}$rm$'{a}$n vortex street and the number of observation points was 0.195% of computational grid points. The LBM-LETKF enables DA of turbulence with spatially- and temporally- sparse observations.

Journal Articles

Compressible Navier-Stokes formulation for accelerating Poisson solver of gas-liquid two-phase fluid simulations

Onodera, Naoyuki; Sugihara, Kenta; Ina, Takuya; Idomura, Yasuhiro

Keisan Kogaku Koenkai Rombunshu (CD-ROM), 29, 3 Pages, 2024/06

Gas-liquid two-phase flow analysis is one of the most important research topics in nuclear engineering because it is essential for safety evaluation and reactor design. However, it requires large-scale multi-scale simulations, and advanced numerical approaches are needed. To meet this challenge, we have continued to develop the Poisson solver for the multiphase flow analysis code JUPITER. In this study, we aim to improve the convergence of the pressure Poisson solver by formulating the Navier-Stokes equation without using the incompressible approximation. The convergence performance was measured on 8 GPUs for bubbly flow analysis in a circular tube. The results show that the computation time and the number of iterations are reduced by half compared to those using the incompressible approximation, which indicates the usefulness of the formulation in the present study.

Journal Articles

Development of a design optimization framework for sodium-cooled fast reactors, 2; Development of optimization analysis control function

Doda, Norihiro; Nakamine, Yoshiaki*; Kuwagaki, Kazuki; Hamase, Erina; Kikuchi, Norihiro; Yoshimura, Kazuo; Matsushita, Kentaro; Tanaka, Masaaki

Keisan Kogaku Koenkai Rombunshu (CD-ROM), 28, 5 Pages, 2023/05

As a part of the development of the "Advanced Reactor Knowledge- and AI-aided Design Integration Approach through the whole plant lifecycle (ARKADIA)" to automatically optimize the life cycle of innovative nuclear reactors including fast reactors, ARKADIA-design is being developed to support the optimization of fast reactor in the conceptual design stage. ARKADIA-Design consists of three systems (Virtual plant Life System (VLS), Evaluation assistance and Application System (EAS), and Knowledge Management System (KMS)). A design optimization framework controls the connection between the three systems through the interfaces in each system. This paper reports on the development of an optimization analysis control function that performs design optimization analysis combining plant behavior analysis by VLS and optimization study by EAS.

Journal Articles

Parameter optimization for urban wind simulation using ensemble Kalman filter

Onodera, Naoyuki; Idomura, Yasuhiro; Hasegawa, Yuta; Asahi, Yuichi; Inagaki, Atsushi*; Shimose, Kenichi*; Hirano, Kohin*

Keisan Kogaku Koenkai Rombunshu (CD-ROM), 28, 4 Pages, 2023/05

We have developed a multi-scale wind simulation code named CityLBM that can resolve entire cities to detailed streets. CityLBM enables a real time ensemble simulation for several km square area by applying the locally mesh-refined lattice Boltzmann method on GPU supercomputers. On the other hand, real-world wind simulations contain complex boundary conditions that cannot be modeled, so data assimilation techniques are needed to reflect observed data in the simulation. This study proposes an optimization method for ground surface temperature bias based on an ensemble Kalman filter to reproduce wind conditions within urban city blocks. As a verification of CityLBM, an Observing System Simulation Experiment (OSSE) is conducted for the central Tokyo area to estimate boundary conditions from observed near-surface temperature values.

Journal Articles

Machine learning models for sub-grid-scale (SGS) term

Asahi, Yuichi; Maeyama, Shinya*; Fujii, Keisuke*

Keisan Kogaku Koenkai Rombunshu (CD-ROM), 28, 4 Pages, 2023/05

We have developed a deep-learning model to surrogate the effect of small-scale on large-scale fluctuations. We have constructed the sub-grid-scale (SGS) models based on the Mori-Zwanzig projection operatormethod and neural networks. We have performed large eddy simulations (LESs) of the Kuramoto-Sivashinsky turbulence with these SGS models. We have demonstrated that the time averaged energy spectrumof LESs agree with that of the dynamic numerical simulation (DNS).

Journal Articles

Data assimilation of two-dimensional isotropic turbulence by lattice Boltzmann method and local ensemble transform Kalman filter (LBM-LETKF)

Hasegawa, Yuta; Onodera, Naoyuki; Asahi, Yuichi; Idomura, Yasuhiro

Keisan Kogaku Koenkai Rombunshu (CD-ROM), 28, 5 Pages, 2023/05

We implemented and investigated the data assimilation (DA) of two-dimensional isotropic turbulence using the lattice Boltzmann method and the local ensemble transform Kalman filter (LBM-LETKF). We carried out the numerical experiment with 256$$^{2}$$ grids, 256$$^{2}$$ or less observation points, 10% root mean square (RMS) observation noise in the velocity observation, and 4, 16, or 64 ensemble members. The numerical experiment showed that the accuracy of the LETKF was better than the nudging DA with both dense and sparse observation. The lack of observation points caused the numerical instability in the LETKF, but such a numerical instability can be suppressed by increasing the number of ensemble members. In the sparse observation case (8$$times$$8 observation points) with 64 ensemble members, the root means squared error (RMSE) of the velocity in the LBM-LETKF was smaller than the RMS of the observation noise, while the nudging DA required 32$$times$$32 observation points to obtain the same accuracy. Overall, the LETKF with sufficiently large number of ensemble members was highly accurate and robust, thus, the LETKF was a good choice for the DA of turbulent flows using the LBM.

Journal Articles

GPU implementation of local ensemble transform Kalman filter (LETKF) with two-dimensional lattice Boltzmann method

Hasegawa, Yuta; Onodera, Naoyuki; Asahi, Yuichi; Idomura, Yasuhiro

Keisan Kogaku Koenkai Rombunshu (CD-ROM), 27, 4 Pages, 2022/06

We developed GPU implementation of ensemble data assimilation (DA) using the local ensemble transform Kalman filter (LETKF) with the lattice Boltzmann method (LBM). The performance test was carried out upto 32 ensembles of two-dimensional isotropic turbulence simulations using the D2Q9 LBM. The computational cost of the LETKF was less than or nearly equal to that of the LBM upto eight ensembles, while the former exceeded the latter at larger ensembles. At 32 ensembles, their computational costs per cycle were respectively 28.3 msec and 5.39 msec. These results suggested that further speedup of the LETKF is needed for practical 3D LBM simulations.

Journal Articles

Optimization of phase field variables in gas-liquid two-phase flow problems

Sugihara, Kenta; Onodera, Naoyuki; Idomura, Yasuhiro; Yamashita, Susumu

Keisan Kogaku Koenkai Rombunshu (CD-ROM), 27, 5 Pages, 2022/06

The phase-field method has been successfully applied to various multi-phase flow problems as an interface tracking method for gas-liquid interfaces. However, the accuracy of the phase-field method depends on hyper-parameters, which are empirically adjusted for each problem. The phase-field method sustains sharp interfaces by the balance between the numerical viscosity of the advection term and the interface modification by the diffusion and anti-diffusion terms. Based on this fact, we propose a method for deriving the optimal hyper-parameters in a non-empirical manner by performing a basic error analysis of the interface advection.

Journal Articles

Parameter optimization for generating atmospheric boundary layers by using the locally mesh-refined lattice Boltzmann method

Onodera, Naoyuki; Idomura, Yasuhiro; Hasegawa, Yuta; Shimokawabe, Takashi*; Aoki, Takayuki*

Keisan Kogaku Koenkai Rombunshu (CD-ROM), 27, 4 Pages, 2022/06

We have developed a wind simulation code named CityLBM to realize wind digital twins. Mesoscale wind conditions are given as boundary conditions in CityLBM by using a nudging data assimilation method. It is found that conventional approaches with constant nudging coefficients fail to reproduce turbulent intensity in long time simulations, where atmospheric stability conditions change significantly. We propose a dynamic parameter optimization method for the nudging coefficient based on a particle filter. CityLBM was validated against plume dispersion experiments in the complex urban environment of Oklahoma City. The nudging coefficient was updated to reduce the error of the turbulent intensity between the simulation and the observation, and the atmospheric boundary layer was reproduced throughout the day.

Journal Articles

Performance measurement of an urban wind simulation code with the Locally Mesh-Refined Lattice Boltzmann Method over NVIDIA and AMD GPUs

Asahi, Yuichi; Onodera, Naoyuki; Hasegawa, Yuta; Shimokawabe, Takashi*; Shiba, Hayato*; Idomura, Yasuhiro

Keisan Kogaku Koenkai Rombunshu (CD-ROM), 27, 5 Pages, 2022/06

We have ported the GPU accelerated Lattice Boltzmann Method code "CityLBM" to AMD MI100 GPU. We present the performance of CityLBM achieved on NVIDIA P100, V100, A100 GPUs and AMDMI100 GPU. Using the host to host MPI communications, the performance on MI100 GPU is around 20% better than on V100 GPU. It has turned out that most of the kernels are successfully accelerated except for interpolation kernels for Adaptive Mesh Refinement (AMR) method.

Journal Articles

Development of a design optimization framework for sodium-cooled fast reactors; Development of coupled analysis control function

Doda, Norihiro; Nakamine, Yoshiaki*; Igawa, Kenichi*; Iwasaki, Takashi*; Murakami, Satoshi*; Tanaka, Masaaki

Keisan Kogaku Koenkai Rombunshu (CD-ROM), 27, 6 Pages, 2022/06

As a part of the development of the "Advanced Reactor Knowledge- and AI-aided Design Integration Approach through the whole plant lifecycle (ARKADIA)" to automatically optimize the life cycle of innovative nuclear reactors including fast reactors, ARKADIA-design is being developed to support the optimization of fast reactor design in the conceptual stage. ARKADIA-Design consists of three systems (Virtual plant Life System (VLS), Evaluation assistance and Application System (EAS), and Knowledge Management System (KMS)). A design optimization framework controls the cooperation between the three systems through the interfaces in each system. This paper reports on the development status of the "VLS interface," which has a control function of coupling analysis codes in VLS.

Journal Articles

Improved domain partitioning on tree-based mesh-refined lattice Boltzmann method

Hasegawa, Yuta; Aoki, Takayuki*; Kobayashi, Hiromichi*; Idomura, Yasuhiro; Onodera, Naoyuki

Keisan Kogaku Koenkai Rombunshu (CD-ROM), 26, 6 Pages, 2021/05

We introduce an improved domain partitioning method called "tree cutting approach" for the aerodynamics simulation code based on the lattice Boltzmann method (LBM) with the forest-of-octrees-based local mesh refinement (LMR). The conventional domain partitioning algorithm based on the space-filling curve (SFC), which is widely used in LMR, caused a costly halo data communication which became a bottleneck of our aerodynamics simulation on the GPU-based supercomputers. Our tree cutting approach adopts a hybrid domain partitioning with the coarse structured block decomposition and the SFC partitioning in each block. This hybrid approach improved the locality and the topology of the partitioned sub-domains and reduced the amount of the halo communication to one-third of the original SFC approach. The code achieved $$times 1.23$$ speedup on 8 GPUs, and achieved $$times 1.82$$ speedup at the performance of 2207 MLUPS (mega-lattice update per second) on 128 GPUs with strong scaling test.

Journal Articles

The Examination of advanced analysis method on unsteady gas entrainment vortex applying AMR method

Matsushita, Kentaro; Fujisaki, Tatsuya*; Ezure, Toshiki; Tanaka, Masaaki; Uchida, Mao*; Sakai, Takaaki*

Keisan Kogaku Koenkai Rombunshu (CD-ROM), 26, 6 Pages, 2021/05

For the gas entrainment vortex at the free surface in sodium-cooled fast reactors, development of the numerical analysis method to evaluate amount of the gas entrainment from the free surface has been developing. In this paper, the automatic creation of analysis meshes which can suppress the calculation cost while maintaining the prediction accuracy of the vortex shape is investigated, and the adaptive mesh refinement (AMR) method is examined to the creation of analysis mesh applying to the unsteady vortex system. The refined mesh based on the criterion evaluated by vorticity, Q-value as second invariant of the velocity and the discriminant for the eigen equation of the velocity gradient tensor is considered, and it found that the AMR method based on Q-value can refine the analysis meshes most efficiently.

Journal Articles

Multi-resolution steady flow prediction with convolutional neural networks

Asahi, Yuichi; Hatayama, Sora*; Shimokawabe, Takashi*; Onodera, Naoyuki; Hasegawa, Yuta; Idomura, Yasuhiro

Keisan Kogaku Koenkai Rombunshu (CD-ROM), 26, 4 Pages, 2021/05

We develop a convolutional neural network model to predict the multi-resolution steady flow. Based on the state-of-the-art image-to-image translation model Pix2PixHD, our model can predict the high resolution flow field from the signed distance function. By patching the high resolution data, the memory requirements in our model is suppressed compared to Pix2PixHD.

Journal Articles

Acceleration of locally mesh allocated Poisson solver using mixed precision

Onodera, Naoyuki; Idomura, Yasuhiro; Hasegawa, Yuta; Shimokawabe, Takashi*; Aoki, Takayuki*

Keisan Kogaku Koenkai Rombunshu (CD-ROM), 26, 3 Pages, 2021/05

We develop a mixed-precision preconditioner for the pressure Poisson equation in a two-phase flow CFD code JUPITER-AMR. The multi-grid (MG) preconditioner is constructed based on the geometric MG method with a three- stage V-cycle, and a cache-reuse SOR (CR-SOR) method at each stage. The numerical experiments are conducted for two-phase flows in a fuel bundle of a nuclear reactor. The MG-CG solver in single-precision shows the same convergence histories as double-precision, which is about 75% of the computational time in double-precision. In the strong scaling test, the MG-CG solver in single-precision is accelerated by 1.88 times between 32 and 96 GPUs.

Journal Articles

Development of neutronics, thermal-hydraulics, and structure mechanics coupled analysis method on integrated numerical analysis for design optimization support in fast reactor

Doda, Norihiro; Uwaba, Tomoyuki; Nemoto, Toshiyuki*; Yokoyama, Kenji; Tanaka, Masaaki

Keisan Kogaku Koenkai Rombunshu (CD-ROM), 26, 4 Pages, 2021/05

For design optimization of fast reactors, in order to consider the feedback reactivity due to thermal deformation of the core when the core temperature rises, which could not be considered in the conventional design analysis, a neutronics, thermal-hydraulics, and structure mechanics coupled analysis method has been developed. Neutronics code, plant dynamics code, and structural mechanics code are coupled by a control module in python script. This paper outlines the coupling method of analysis codes and the results of its application to an experiment in an actual plant.

Journal Articles

Development of neutronics and thermal-hydraulics coupled analysis method on platform for design optimization in fast reactor

Doda, Norihiro; Hamase, Erina; Yokoyama, Kenji; Tanaka, Masaaki

Keisan Kogaku Koenkai Rombunshu (CD-ROM), 25, 4 Pages, 2020/06

With the aim of advancing the design optimization in fast reactors, neutronics and thermal-hydraulics coupled analysis method which can consider the temporal change of neutron flux distribution in the core has been developed. A three-dimensional neutronics analysis code and a plant dynamics analysis code are coupled on a platform using Python programing. In this report, outlines of the coupling method of analysis codes, the results of its application to the actual plant under a virtual accidental condition, and the future development is described.

Journal Articles

Ensemble wind simulation using a mesh-refined lattice Boltzmann method

Hasegawa, Yuta; Onodera, Naoyuki; Idomura, Yasuhiro

Keisan Kogaku Koenkai Rombunshu (CD-ROM), 25, 4 Pages, 2020/06

We developed a GPU-based CFD code using a mesh-refined lattice Boltzmann method (LBM), which enables ensemble simulations for wind and plume dispersion in urban cities. The code is tuned for Pascal or Volta GPU architectures, and is able to perform real-time wind simulations with several kilometers square region and several meters of grid resolution. We examined the developed code against the field experiment JU2003 in Oklahoma City. In the comparison, wind conditions showed good agreements, and the ensemble-averaged and maximum values of tracer concentration satisfied the factor 2 agreements.

Journal Articles

GPU-acceleration of locally mesh allocated Poisson solver

Onodera, Naoyuki; Idomura, Yasuhiro; Ali, Y.*; Shimokawabe, Takashi*; Aoki, Takayuki*

Keisan Kogaku Koenkai Rombunshu (CD-ROM), 25, 4 Pages, 2020/06

We have developed the stencil-based CFD code JUPITER for simulating three-dimensional multiphase flows. A GPU-accelerated Poisson solver based on the preconditioned conjugate gradient (P-CG) method with a multigrid preconditioner was developed for the JUPITER with block-structured AMR mesh. All Poisson kernels were implemented using CUDA, and the GPU kernel function is well tuned to achieve high performance on GPU supercomputers. The developed multigrid solver shows good convergence of about 1/7 compared with the original P-CG method, and $$times$$3 speed up is achieved with strong scaling test from 8 to 216 GPUs on TSUBAME 3.0.

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