• Journal of Aerospace System Engineering
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• v.10 no.4
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• pp.35-40
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• 2016

Mid-course correction maneuvers (MCCMs) are necessary to correct the launch-vehicle dispersion to go to the Moon. There were 3 or 4 MCCMs needed for a direct transfer trajectory. But the strategy for MCCMs of the phasing-loop trajectory is different, because it has a longer trans-lunar trajectory than direct transfer does. An orbiter using a phasing-loop trajectory has several rotations of the Earth, so the orbiter has several good places, such as perigee and apogee, to correct the launch-vehicle dispersion. Although launch dispersion is relatively high, the launch vehicle is not as accurate as we expected. A good MCCM strategy can overcome the high dispersion by using small-magnitude correction maneuvers. This paper describes the phasing-loops sequence and strategy to correct high launch-vehicle dispersions.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.3
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• pp.8-14
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• 2003

The particle dispersion in the turbulent mixing layer has been numerically investigated to clarify the effect of the velocity ratio in the large-scale vortical structures. In this study the LES with subgrid-scale model is employed. The Lagrangian method to predict the particle motion is applied. The particles of 10, 50, 150, 200${\mu}m$ in mean diameter were loaded into the origin of the mixing layer. It is shown that the characteristics of flow and growth rate are strongly dependent on the variation of the velocity ratio. It is also shown the relationship between the Stokes number and the particle dispersion. As a result, in the case of St~1 the particle dispersion is faster than the diffustion of the flow field while in the cases of both St<<1 and St>>1 it is shown that the particle dispersion in lower than the diffusion of the flow filed.

• Nuclear Engineering and Technology
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• v.46 no.4
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• pp.557-568
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• 2014

This paper presents the results of an analysis of wind characteristics and atmosphere dispersion modeling that are based on computational simulation and part of a preliminary study evaluating environmental radiation monitoring system (ERMS) positions within the Barakah nuclear power plant (BNPP). The return period of extreme wind speed was estimated using the Weibull distribution over the life time of the BNPP. In the annual meteorological modeling, the winds from the north and west accounted for more than 90 % of the wind directions. Seasonal effects were not represented. However, a discrepancy in the tendency between daytime and nighttime was observed. Six variations of cesium-137 ($^{137}Cs$) dispersion test were simulated under severe accident condition. The $^{137}Cs$ dispersion was strongly influenced by the direction and speed of the main wind. A virtual receptor was set and calculated for observation of the $^{137}Cs$ movement and accumulation. The results of the surface roughness effect demonstrated that the deposition of $^{137}Cs$ was affected by surface condition. The results of these studies offer useful information for developing environmental radiation monitoring systems (ERMSs) for the BNPP and can be used to assess the environmental effects of new nuclear power plant.

• Journal of Korean Society for Geospatial Information Science
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• v.14 no.1 s.35
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• pp.57-63
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• 2006

The purpose of this study is to correct data on 3 intersection ranging from Kwangchun INT. to Nongsung INT. by the means of VTR recording and site survey and to measure the responsiveness of performance index by diversifying the platoon dispersion factor in signal progression simulation. The results are as follows : 1. The value of platoon dispersion factor was 0.28-0.33. The value in up stream is lower than that of in down stream even on the same intersection. 2. The platoon index showed big changes, though performance index didn't according to platoon dispersion factor. Therefore the value of platoon dispersion factor which is inner variable in T7F can be fixed for 0.34. 3. There was only little divergence in performance index changes according to platoon dispersion factor in designing the progression or T7F model.

• Journal of Ocean Engineering and Technology
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• v.27 no.5
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• pp.105-114
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• 2013

Lots of orders of special vessels and offshore plants for developing the resources in deepwater have been increased in recent. Because the most of accidents on those structures are caused by fire and explosion, many researchers have been investigated quantitatively to predict the cause and effect of fire and explosion based on both experiments and numerical simulations. The first step of the evaluation procedures leading to fire and explosion is to predict the dispersion of flammable or toxic material, in which the released material mixes with surrounding air and be diluted. In particular turbulent mixing, but density differences due to molecular weight or temperature as well as diffusion will contribute to the mixing. In the present paper, the numerical simulation of hydrogen dispersion inside a simple-shaped offshore structure was performed using a commercial CFD program, ANSYS-CFX. The simulated results for concentration of released hydrogen are compared to those of experiment and other simulation in Jordan et al.(2007). As a result, it is seen that the present simulation results are closer to the experiments than other simulation ones. Also it seems that the hydrogen dispersion is closely related to turbulent mixing and the selection of the turbulence model properly is significantly of importance to the reproduction of dispersion phenomena.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.11a
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• pp.459-462
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• 2008

In manufacture of slurry fuel, the effects of process parameters on the carbon dispersion stability have been investigated. The particle size and contents of the carbon slurry taken from 3 (top, medium, bottom) positions in fuel reservoir were analyzed to estimate the dispersion of the carbon in Jet A-1. Through the application of various additives, it was found that NB463S84 additive showed the best dispersion and stability of carbon at accelerated gravity condition. The mixer performance was compared by the observation of height change of carbon-containing layer and measurement of particle sizes at the same conditions. Application of the mixing conditions obtained from the lab-scale to bench scale manufacture confirmed the practical feasibility of our research.

• Applied Chemistry for Engineering
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• v.21 no.3
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• pp.311-316
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• 2010

This study aimed to prepare antimony-doped tin oxide (ATO) dispersion with high stability. The methods to achieve this goal were sought by investigating the changes of ATO particle size, size distribution, dispersion property as wet ball milling treatment time increased. And the changes of wet ball milled ATO dispersion property were also investigated, as pH increased. The changes of ATO particle size and size distribution, according to wet ball milling treatment time were evaluated with laser diffraction particle size analyzer and scanning electron microscope (SEM). The changes of ATO dispersion property, as wet ball milling treatment time and pH increased, were evaluated with zeta potential analysis and Turbiscan. By 60 min wet ball milling treatment time, ATO particle size decreased and size distribution became narrower, as the treatment time increased. After 60 min milling, the ATO particle size decreased to less than 30% of the initial size and the size distribution was narrowed to $0.1{\sim}5{\mu}m$ from $1{\sim}35{\mu}m$. However, more than 60 min milling, ATO particles aggregated and the particle size increased. ATO dispersion stability also increased as the treatment time and pH increased because the reduced particle size increased particle surface energy and repulsion between particles and the increased pH enhanced particle surface ionization. Hence, after proper length of wet ball milling treatment, highly stable ATO dispersion can be prepared, as increasing pH of the dispersion.

• Journal of the Korean Society for Marine Environment & Energy
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• v.11 no.1
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• pp.13-23
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• 2008

In coastal region, eutrophication, Do deficit and red tide are frequently occurred by influx of fresh water. When the fresh water containing pollutants is discharged into the sea, the surrounding water is contaminated by dispersion of freshwater flowing into coastal waters. The prediction and analysis about the dispersion process of the discharged fresh water should be conducted. A modeling system using GUI was developed to simulate hydrodynamic flow and fresh water dispersion in coastal waters and to analyze the results efficiently. The modeling module of the system includes a tide model using a finite element method and a fresh water dispersion model using a particle-tracking method. This system was applied to predict the tidal currents and fresh water dispersion in Mokpo coastal zone. To verify accuracy of the hydrodynamic model, the simulation results were compared with observed sea level and time variations of tidal currents showing a good agreement. The fresh water dispersion was verified with observed salinity distribution. The dispersion model also was verified with analytic solutions with advection-diffusion problems in 1-dimensional and 2-dimensional simple domain. The system is operated on GUI environment, to ease the model handling such as inputting data and displaying results. Therefore, anyone can use the system conveniently and observe easily and accurately the simulation results by using graphic functions included in the system. This system can be used widely to decrease the environmental disaster induced by inflow of fresh water into coastal waters.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.20 no.44
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• pp.207-215
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• 1997

This paper deals with a comparison between Taguchi's accumulation analysis method and Nair test on the ordered categorical data from an industrial experiment for quality improvement. a result of Taguchi's accumulation analysis method is shown to have reasonable power for detecting location effects, while Nair test identifies the location and dispersion effects separately, Accordingly, Taguchi's accumulation analysis needs to develop methods for detecting dispersion effects as well as location effects. In addition this paper rewmmends models for analyzing ordered categorical data, for examples, the cumulative legit model, mean response model etc Successively simple, reasonable methods should be introduced more likely to be used by the practitioners.

• Journal of the Society of Naval Architects of Korea
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• v.55 no.1
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• pp.83-91
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• 2018

In this paper, usefulness of marine radar for water waves measurement in coastal waters is presented. We installed a marine radar to acquire radar images of water wave around light beacon at Jujeon in Ulsan. Also, a series of analysis procedures for obtaining the wave information from the acquired image is described with a schematic diagram. We compared analysis results of radar images with measurement values using wave height gauge at light beacon. In order to improve accuracy of analysis results, detailed water depth information is essential. In conclusion, in case of the use of radar for water waves measurement, it is shown that it is very necessary to increase the accuracy of measurement by consideration of the water depth in the dispersion relation of water waves.