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Nakayama, Hiromasa; Takemi, Tetsuya*; Nagai, Haruyasu
Advances in Science & Research (Internet), 11, p.75 - 81, 2014/07
Times Cited Count：9 Percentile：97.6(Multidisciplinary Sciences)We have developed a local-scale high-resolution atmospheric dispersion model using Large-Eddy Simulation and tried to introduce it into SPEEDI-MP. In this study, our objectives are to first create a numerical model for LES on atmospheric dispersion in spatially-developing stable and unstable boundary layer flows which and compare to the existing wind tunnel experimental data. Based on the comparison, we discuss the basic performance of the LES model.
Kim, K.; Yamashita, Takao*
Proceedings of International Symposium on Fluvial and Coastal Disasters (CD-ROM), 8 Pages, 2005/12
Authors developed the wind-wave-surge coupled numerical model for storm surge simulation and made clear its availability for storm surges in the extremely shallow water. The developed model consists of the meso-scale atmospheric circulation models (MM5), ocean wave model (WW3) and ocean circulation model (POM). An additional sea surface stress, the whitecap wave breaking stress, was introduced in the model to consider the processes of energy transfer from wind to current through whitecap breaking. The conducted hindcast of storm surge in this study clearly showed the importance of energy transfer path via whitecap dissipation of wind waves in the generation mechanism of mean current in the extremely shallow water. This model was applied to the simulation of storm surges and waves in the Bay of Bengal for the cyclone in 1991. The importance of wave effects on wind-induced current fields in the extremely shallow water was also made clear in this research.
Kim, K.; Yamashita, Takao*
Kaigan Kogaku Rombunshu, 52(1), p.211 - 215, 2005/10
no abstracts in English
Nagai, Haruyasu; Kobayashi, Takuya; Tsuzuki, Katsunori; Kim, K.
no journal, ,
no abstracts in English
Nakayama, Hiromasa; Takemi, Tetsuya*; Nagai, Haruyasu
no journal, ,
Atmospheric dispersion within urban area resulting from accidental or intentional releases of hazardous materials is of great concern to public health. For investigating plume dispersion behaviours in urban areas, a numerical modelling is a useful tool. Therefore, we have developed local-scale high-resolution atmospheric dispersion model using large-eddy simulation (LOHDIM-LES) and investigated the basic performance in comparison to wind tunnel experimental data. Furthermore, we have attempted to extend our model to turbulent flows and plume dispersion within actual urban areas under realistic meteorological conditions. In this paper, our objective is to apply to the Joint URBAN 2003 field experiment and evaluate the basic performance of the LES model coupled to a mesoscale meteorological simulation model.
Nakayama, Hiromasa; Takemi, Tetsuya*; Nagai, Haruyasu
no journal, ,
we perform LESs of plume dispersion under stable and unstable boundary layers. In our model, the inflow turbulence is generated by the recycling method in a driver region and the target temperature profile is imposed at the exit of the driver region. Here, buoyancy effects modeled by Boussinesq approximation are incorporated into the downstream region of the driver region and numerical simulations of various thermally stratified boundary layer flows are performed. A tracer gas is emitted from a point source in a region where the boundary layers are fully developed and LESs of plume dispersion are carried out. Our objective is to compare our LES results of turbulence structures, plume concentrations and plume spreads to wind tunnel experimental data and theoretical values, and investigate the basic performance of the model.
Nakayama, Hiromasa; Takemi, Tetsuya*; Nagai, Haruyasu
no journal, ,
In order to simulate wind flows within and over urban areas under real meteorological conditions, coupling technique between NWP and LES-based CFD models is considered to be promising. Therefore, in coupling between both models, we applied a recycling technique to a strong wind event in Tokyo owing to the landfall of a major typhoon and compared with the observed data of time series of wind speed at a certain height. Although the observed ranges of wind fluctuations and gust factors were well reproduced in the LES, the effectiveness of this coupling approach has not been fully evaluated. In this study, we apply to the field experiments, the Joint Urban 2003 held at the central district of Oklahoma City on July 2003, and examine the coupling approach in comparison to the observed data in detail.
Nakayama, Hiromasa; Takemi, Tetsuya*; Nagai, Haruyasu
no journal, ,
The Fukushima Daiichi Nuclear Power Plant (FDNPP) consists of various buildings and structures over complex hilly terrain. For simulating wind flows over various arrangements of obstacles over complex surface geometries, a computational fluid dynamics (CFD) technique has been commonly used. An approach to couple LES-based CFD model with a meso-scale meteorological model (MM) should be a next-generation real-time prediction system to simulate turbulent winds over complex surface geometries under real meteorological conditions. One of the important issues to be solved to couple LES and MM models is to impose time-dependent turbulent inflow data for LESs from the MM model outputs, because the MM models are not able to reproduce high-frequency turbulent fluctuations appropriate to drive LES models. Therefore, the recycling method proposed by Kataoka and Mizuno (2002) is applied to coupling between MM and LES models. In this study, we apply the coupling calculation to prediction of turbulent winds during the FDNPP accident and report detailed information on turbulent structures under the influence of buildings and complex surface geometries.
