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Nishida, Akemi; Suzuki, Yoshio; Yamada, Tomonori; Kino, Chiaki; Uzawa, Ken*; Miyamura, Hiroko; Kawamura, Takuma; Takemiya, Hiroshi; Nakajima, Norihiro
RIST News, (54), p.33 - 37, 2013/01
Nuclear plants are complicated and huge structures and consist of a large number of parts. To simulate the behavior of such a complicated huge structure, it becomes important the viewpoint as a general system including pre-post-processing. Therefore, the CCSE proposed an approach for assembly structure analysis and implemented a framework of a full-scale 3D vibration simulator for an entire nuclear plant. Until now, we performed numerical experiments using the data of a building and equipment of HTTR, Oarai R&D Center, JAEA, and demonstrated that earthquake response simulation of large-scale structure as an entire nuclear plant was possible so far. In this report, the framework of the full-scale 3D vibration simulator, the assembly structure analysis approach and visualization technology for an evaluation of the results are shown. And finally, an example of application of the simulator for probabilistic risk assessment, PRA, started from 2011, is shown.
Uzawa, Ken
Proceedings of 9th International Conference on Flow Dynamics (ICFD 2012) (USB Flash Drive), p.392 - 393, 2012/09
To prevent anomalous events of equipment and structures in a spent fuel pool from occurring, it is essential to comprehend overflow of water and fluid pressure caused by sloshing. For this purpose, it is necessary to quantitatively evaluate turbulent dissipation near water surface and inner structures instead of an empirical value which depends on size of each pool. In this research, we test the efficacy of turbulence models by performing numerical simulation of sloshing in a rectangular pool to evaluate turbulent dissipation based on action mechanism. A conservation equation of turbulent kinetic energy of LES model is derived and compared contributions turbulent dissipation terms to the kinetic energy. I demonstrated that the reproducibility of turbulence near wall in the Large Eddy Simulation is the best.
Uzawa, Ken; Watanabe, Tadashi*
Journal of Power and Energy Systems (Internet), 6(2), p.229 - 240, 2012/06
To prevent anomalous events of equipment and structures in a spent fuel pool from occurring, it is essential to comprehend overflow of water and fluid pressure caused by sloshing. For this purpose, it is necessary to quantitatively evaluate turbulent dissipation near water surface and inner structures instead of an empirical value which depends on size of each pool. Therefore, we test the efficacy of turbulence models by performing numerical simulation of dam break phenomenon as an elementary process of a sloshing to evaluate turbulent dissipation based on action mechanism. In this research, we derived a conservation equation of turbulent kinetic energy of RANS models and compared contributions of pressure, gravity and turbulent dissipation terms to the kinetic energy. As a result, we demonstrated that turbulent dissipation term is a predominant factor on the dynamics of dam break flow and turbulent dissipation is overestimated in eddy viscosity model.
Uzawa, Ken
Nagare, 31(3), p.271 - 276, 2012/06
To prevent anomalous events of equipment and structures in a spent fuel pool from occurring, it is essential to comprehend overflow of water and fluid pressure caused by sloshing. For this purpose, it is necessary to quantitatively evaluate turbulent dissipation near water surface and inner structures instead of an empirical value which depends on size of each pool. In this research, we test the efficacy of turbulence models by performing numerical simulation of dam break phenomenon and sloshing in a rectangular pool to evaluate turbulent dissipation based on action mechanism. As a result, we demonstrated that numerical heights by Reynolds stress model and Large Eddy Simulation are in well agreement with experimental value.
Suzuki, Yoshio; Nishida, Akemi; Uzawa, Ken; Nakajima, Norihiro
Keisan Kogaku Koenkai Rombunshu (CD-ROM), 17, 4 Pages, 2012/05
Our goal is to evaluate the validity of results obtained from seismic simulation of entire nuclear plant, and then to estimate real behavior. In this study, we have established a trial tool to enable a zooming analysis from a combining analysis of ground-building-equipments (beam model) to an assembly structural analysis of equipments (solid model) in order to compare results of beam model and solid model. By applying the tool to analysis of a cantilever model with various cross sections, we have confirmed that results of solid model well coincide with theoretical solutions and results of beam model.
Uzawa, Ken; Watanabe, Tadashi; Nishida, Akemi; Suzuki, Yoshio; Takemiya, Hiroshi
High Performance Computing on Vector Systems 2011, p.171 - 184, 2012/01
The Center for Computational Science and E-systems (CCSE) has been promoting researches and developments for the full-scale 3D vibration simulator of an entire nuclear power plant, which is a virtual plant vibration simulator on inter-connected supercomputers. Application example of the vibration simulator to High Temperature Engineering Test Reactor (HTTR) and recent progress of collaborative work for JST-CREST program "Multiscale and multiphysics earthquake-proof simulation" are shown. This year, we started to implement the analysis capability of fluid effects to the vibration simulator. We have presented a two-phase flow model for analyzing a sloshing and suggested importance of turbulent effect to estimate the flow impact on the structure more precisely.
Uzawa, Ken; Watanabe, Tadashi
Proceedings of 19th International Conference on Nuclear Engineering (ICONE-19) (CD-ROM), 8 Pages, 2011/10
When a spent fuel pool suffered from a huge seismic acceleration, a sloshing may occur and causes overflow of water and damage of structure. To prevent these phenomena from occurring, effects of turbulence on a sloshing height and fluid pressure on the structure should be taken into account, however they are not fully quantitatively evaluated. Therefore, we have performed numerical simulations of a dam break problem as an elementary process of the sloshing based on the Launder-Gibson (LG) model, which is one of Reynolds-averaged Navier-Stokes equations. Until now, we found that a fluid pressure based on the LG model is in good agreement with experimental fluid pressure. In this research, we have confirmed same results by performing Large Eddy Simulation (LES). We found that the overflow of water is an order of magnitude more accurate than previous work.
Uzawa, Ken; Watanabe, Tadashi; Nishida, Akemi; Takemiya, Hiroshi
Proceedings of Joint International Conference of 7th Supercomputing in Nuclear Application and 3rd Monte Carlo (SNA + MC 2010) (USB Flash Drive), 6 Pages, 2010/10
When big response acceleration is added to air-liquid two-phase flow in nuclear reactor plant, large deformation of the interface configuration with breakup/coalescence of bubbles and micro-scale turbulence near the interface may change heat transfer and void fraction distribution in the reactor core. Now we have been developed a numerical tool for detailed analysis of the two-phase flow based on OpenFOAM which is an open source computational fluid dynamics software package to sophisticate "Three-Dimensional Virtual Plant Vibration Simulator". In this report, we show the validity of OpenFOAM by comparing results obtained by OpenFOAM with those obtained by experimental results. Findings for turbulent effects near the interface on dynamics of the two-phase flow are also reported.
Li, J.*; Uzawa, Ken*; Lin, Z.*; Kishimoto, Yasuaki; Miyato, Naoaki; Matsumoto, Taro; Dong, J. Q.*
Proceedings of 21st IAEA Fusion Energy Conference (FEC 2006) (CD-ROM), 8 Pages, 2007/03
The dynamics of secondary, anisotropic coherent structures behaving as a stationary wave, including zonal/mean flows, streamers and low-frequency long wavelength fluctuations, in multiple-scale turbulence in tokamak plasmas is investigated by performing 3D simulations as well as 2D modeling analyses. The role of nonlinear mode coupling is specifically discussed as a ubiquitous principal interaction mechanism in the dual processes of the generation and back-action of secondary structures on ITG and ETG turbulence. Here two new results are evidently presented on the importance of the mode coupling interaction: (1) While secondary zonal flows and long wavelength modes are generated through nonlinear mode coupling, the same back-action process can deform the spectral distribution in inertia range from the power-law scaling into an exponential-law dependence. The turbulence may be reduced due to the local and/or nonlocal free energy transfer to stable region. (2) Streamer-like long wavelength fluctuations driven by the most unstable ETG modes, can saturate slab ETG turbulence through producing a 
-mode coupling that corresponds to the toroidal mode coupling in tokamak plasma, suggesting a low ETG fluctuation level and electron transport. Furthermore, the effect of ITG generated zonal flows regarded as a wave-type mean flow on the generation of zonal flows in ETG turbulence is also discussed with an emphasis on the role of nonlinear mode coupling.
Suzuki, Yoshio; Uzawa, Ken; Nishida, Akemi; Nakajima, Norihiro
no journal, ,
no abstracts in English
Suzuki, Yoshio; Hoshi, Yoshiyuki*; Sakamoto, Kensaku; Uzawa, Ken; Nishida, Akemi; Nakajima, Norihiro
no journal, ,
no abstracts in English
Uzawa, Ken
no journal, ,
When a spent fuel pool suffered from the earthquake, a sloshing may occur and causes overflow of water and damage of structure. To prevent these phenomena from occurring, effects of turbulence on a sloshing height and fluid pressure on the structure should be taken into account, however they are not fully quantitatively evaluated. In this work, numerical simulations of a dam break problem as an elementary process of the sloshing have been performed based on the Launder-Gibson (LG) model. As a result, a fluid pressure based on the LG model is in good agreement with experimental fluid pressure. It is also found that the effect of turbulent viscous dissipation on the fluid pressure near two-phase surface is comparable to that of the bulk fluid.
Nakajima, Norihiro; Kawamura, Takuma; Takemiya, Hiroshi; Uzawa, Ken; Idomura, Yasuhiro; Yamada, Susumu
no journal, ,
In the International Conference SC '11 (The Annual Conference for High Performance Computing, Networking, Storage and Analysis), it is exhibited and presented as the achievement of research and development in Center of Computational Science and e-Systems of JAEA, that is, in structural analyses, quake-proof analyses, materials simulations, computer science in nuclear engineering, and applications in nuclear science.
Suzuki, Yoshio; Uzawa, Ken; Nishida, Akemi; Nakajima, Norihiro
no journal, ,
We focus on the R&D of "three-dimensional vibration simulator for an entire nuclear plant" to confirm more quantitatively a seismic margin of nuclear plant under an earthquake over design earthquake ground motion, and thus, to enhance its security and safety. Here, one of the most crucial problems is to reduce and quantify uncertainty in order to evaluate the validity of simulation results. To enable this, we try to establish a framework including (1) coupling analysis of ground, building, and equipments to exclude an assumption of vibration state of building and equipments, (2) assembly structure analysis to exclude an assumption of interaction between parts, (3) zooming analysis of parts to make a model highly precise step by step, and (4) coupling analysis of fluid and structure to exclude an assumption of fluid dynamics.
Uzawa, Ken
no journal, ,
To prevent anomalous events of equipment and structures in a spent fuel pool from occurring, it is essential to comprehend overflow of water and fluid pressure caused by sloshing. For this purpose, it is necessary to quantitatively evaluate turbulent dissipation near water surface and inner structures instead of an empirical value which depends on size of each pool. In this research, we test the efficacy of turbulence models by performing numerical simulation of sloshing in a rectangular pool to evaluate turbulent dissipation based on action mechanism. As a result, we demonstrated that three-dimensional property of free-surface is prominent in the Large Eddy Simulation (LES), resulting that numerical pressure by the LES is well agreement with experimental value.
Uzawa, Ken
no journal, ,
CCSE/JAEA promotes the research and development of the three-dimensional vibration simulator for seismic evaluation of a nuclear power plant (NPP) to further improve reliability of seismic safety of NPPs. We started R&D of fluid analysis capability to analyze seismic fluid phenomena such as sloshing as one of element technologies of the three-dimensional vibration simulator since last year. In the past, conservative estimation using an empirical damping factor has been employed to estimate effect of turbulent eddies. In this research, we examined the effect of turbulent eddies on dynamics of both static and dynamic two-phase validation models as the first step of sloshing. As a result, a Reynolds stress model is well agreement with experimental results. We suggested that simulation method to accurately solve turbulent flow field is effective in qualitatively evaluate the sloshing dynamics.
Uzawa, Ken
no journal, ,
CCSE/JAEA promotes the research and development of the three-dimensional vibration simulator for seismic evaluation of a nuclear power plant (NPP) to further improve reliability of seismic safety of NPPs. We started R&D of fluid analysis capability as one of element technologies of the three-dimensional vibration simulator since last year. Especially, we have investigated a two-phase flow simulation code to analyze sloshing under earthquake. In this research, we achieved speed-up up to approximately 92.8% in parallel calculation using 1024 cores by improving communication method for MPI communication. We elucidated that simulation method to accurately solve turbulent flow field is effective in qualitatively evaluate the decay of sloshing.
Uzawa, Ken
no journal, ,
CCSE/JAEA promotes the research and development of the three-dimensional vibration simulator for seismic evaluation of a nuclear power plant (NPP) to further improve reliability of seismic safety of NPPs. We started R&D of fluid analysis capability as one of element technologies of the three-dimensional vibration simulator since last year. Especially, we have investigated a two-phase flow simulation code to analyze sloshing under earthquake. In this research, we achieved high parallel efficiency up to approximately 950.2 in parallel calculation using 1024 cores by improving an environment for massive parallel calculation. The technical feasibility for massive sloshing simulation including effect of turbulence is more or less established.
Nishida, Akemi; Suzuki, Yoshio; Kino, Chiaki; Uzawa, Ken
no journal, ,
At center for computational science and e-systems, Japan Atomic Energy Agency, R&D about three dimensional full scale vibration simulator considering environment such as structural, fluid, heat, etc. of nuclear plant an entire are performed. In this report, outline of the R&D especially assembly structure analysis which needs to combine huge number of component in nuclear plant, and fluid-structure interaction method we started recently, is shown.
