• 한국해양공학회지
• /
• 제14권2호
• /
• pp.44-52
• /
• 2000

The dispersion of surface oil is generally described as a break-up of oil slick into small oil droplets. These small droplets are subjected to turbulence and vertical circulation so that it can be entrained into subsurface. Sometimes they tend to be submerged into sea bottom permanently. The diameter of oil droplets is a critical parameter to determine their behavioral characteristics under water surface. At the same time the variations of droplet stability depends on the weathering of it. That is why the weathered oil has different mechanism from the unweathered one. The variability of physical properties of oil including viscosity and density contribute to interfere with effective separation of oil and emulsion droplets in water. Also in the presence of interactions among the droplets there are coalescing or coagulating effects on the dispersion process of droplets.

• 대한조선학회논문집
• /
• 제56권6호
• /
• pp.515-522
• /
• 2019

Since Liquefied Natural Gas (LNG) is normally carried at 1.1 bar pressure and at -163℃, special Cargo Containment System (CCS) are used. As LNG carrier is becoming larger, typical LNG insulation systems adopt a method to increase the thickness of insulation panel to reduce sloshing load and Boil-off Rate (BOR). However, this will decrease LNG cargo volume and increase insulation material costs. In this paper, silica aerogel, glass bubble were synthesized in polyurethane foam to increase volumetric efficiency by improving mechanical and thermal performance of insulation. In order to increase dispersibility of particles, ultrasonic dispersion was used. Dynamic impact test, quasi-static compression test at room temperature (20℃) and cryogenic temperature (-163℃) was evaluated. To evaluate the thermal performance, the thermal conductivity at room temperature (20℃) was measured. As a result, specimens without ultrasonic dispersion have a little effect on strength under the compressive load, although they show high mechanical performance under the impact load. In contrast, specimens with ultrasonic dispersion have significantly increased impact strength and compressive strength. Recently, as the density of Polyurethane foam (PUF) has been increasing, these results can be a method for improving the mechanical and thermal performance of insulation panel.

• 한국재료학회지
• /
• 제26권3호
• /
• pp.136-142
• /
• 2016

To study the dispersion factors of silica sol prepared from fumed silica powder, we prepared silica sol under an aqueous system using a batch type bead mill. The dispersion properties of silica sol have a close relationship to dispersion factors such as pH, milling time and speed, the size and amount of zirconia beads, the solid content of fumed silica, and the shape and diameter of the milling impellers. Especially, the silica particles in silica sol were found to show dispersion stability on a pH value above 7, due to the electrostatic repulsion between the particles having a high zeta potential value. The shape and diameter of the impellers installed in the bead mill for the dispersion of fumed silica was very important in reducing the particle size of the aggregated silica. The median particle size ($D_{50}$) of silica sol obtained after milling was also optimized according to the variation of the size and amount of the zirconia beads that were used as the grinding medium, and according to the solid content of fumed silica. The dispersion properties of silica sol were investigated using zeta potential, turbiscan, particle size analyzer, and transmission electron microscopy.

• 한국안전학회지
• /
• 제37권2호
• /
• pp.1-9
• /
• 2022

Most factories deal with toxic or flammable chemicals in their industrial processes. These hazardous substances pose a risk of leakage due to accidents, such as fire and explosion. In the event of chemical release, massive casualties and property damage can result; hence, quantitative risk prediction and assessment are necessary. Several methods are available for evaluating chemical dispersion in the atmosphere, and most analyses are considered neutral in dispersion models and under far-field wind condition. The foregoing assumption renders a model valid only after a considerable time has elapsed from the moment chemicals are released or dispersed from a source. Hence, an initial dispersion model is required to assess risk quantitatively and predict the extent of damage because the most dangerous locations are those near a leak source. In this study, the dispersion model for initial consequence analysis was developed with three-dimensional unsteady advective diffusion equation. In this expression, instantaneous leakage is assumed as a puff, and wind velocity is considered as a coordinate transform in the solution. To minimize the buoyant force, ethane is used as leaked fuel, and two different diffusion coefficients are introduced. The calculated concentration field with a molecular diffusion coefficient shows a moving circular iso-line in the horizontal plane. The maximum concentration decreases as time progresses and distance increases. In the case of using a coefficient for turbulent diffusion, the dispersion along the wind velocity direction is enhanced, and an elliptic iso-contour line is found. The result yielded by a widely used commercial program, ALOHA, was compared with the end point of the lower explosion limit. In the future, we plan to build a more accurate and general initial risk assessment model by considering the turbulence diffusion and buoyancy effect on dispersion.

• 한국환경과학회지
• /
• 제13권10호
• /
• pp.891-902
• /
• 2004

In order to predict air pollution and Yellow-sand dispersion precisely, it is necessary to clarify the sensitivity of meteorological field input interval. Therefore numerical experiment by atmospheric dynamic model(RAMS) and atmospheric dispersion model(PDAS) was performed for evaluating the effect of temporal and spatial resolution of meteorological data on particle dispersion. The results are as follows: 1) Base on the result of RAMS simulation, surface wind direction and speed can either synchronize upper wind or not. If surface wind and upper wind do not synchronize, precise prediction of Yellow-sand dispersion is strongly associated with upwelling process of sand of particle. 2) There is no significant discrepance in distribution of particle under usage of difference temporal resolution of meteorological information at early time of simulation, but the difference of distribution of particles become large as time goes by. 3) There is little difference between calculated particles distributions in dispersion experiments with high temporal resolution of meteorological data. On the other hand, low resolution of meteorological data occur the quantitative difference of particle density and there is strong tendency to the quantitative difference.

• KSTLE International Journal
• /
• 제6권1호
• /
• pp.28-32
• /
• 2005

The electrorheoloRical (ER) fluids are composed of a colloidal dispersion of polarizable particles in insulating oil, and it's the rheological property changes by the applied electric field. These changed are reversible and occur fast within a fewmilliseconds. The ER properties of the ER fluid such as increment of viscosity and yield stress come from the particle chain structure induced by electric fleld. When formulating the ER fluid for a speciflc application, some requirement must besatisfled, which are high yield stress under electric field, rapid response, and dispersion stability. While this characteristic makes valuable ER fluids in valious industrial applications, their lung term and quiescent application has been limited because ofproblems with particle sedimentation. In an effort to overcome sedimentation problem of ER fluids, the anhydrous ER materials of monodispersed hollow polyaniline (PANI) and adipate derivative respectively with submicron-sized suspension providing wide operating temperature range and other advantage were synthesized in a four-step procedure. The ER fluidswere characterized by FT-lR, TGA, DLS, SEM, and TEM. Stability of the suspensions was examined by an UV spectroscopy.The rheological and electrical properties of the suspension were investigated Couette-type rheometer with a high voltagegenerator, current density, and conductivity. And the behavior of ER suspensions was observed by a video camera attached toan optical microscope under 3kV/mm. The suspensions showed good ER properties, durability, and particle dispersion.

• 대한지하수환경학회지
• /
• 제2권2호
• /
• pp.49-57
• /
• 1995

지하수에 대한삼중수소농도의 측정치가 발표된 충청남도 청양, 제주도 지역 및 미국 조지아지역에 대해 평균체제시간을 계산하는 지하수연령측정 모델인 PFM, CMM, DBM과 평균체제시간과 분산매개변수를 동시에 계산하는 DNM, DM( $C_{FF}$ )모델을 적용하여 그 결과를 비교하였다. 입력자료인 강우의 삼중수소 농도의 부족한 측정자료를 보완하기 위하여 한국의 포항, 카나다의 오타와지역의 강수자료를 이용하여 입력함수를 작성하였다. 내재적으로 적은 분산을 가정하는 PFM과 DBM모델에 의한 결과는 유사하게 계산되었으며, 동일한 지역에서도 특이하게 높은 농도를 보이는 지점은 CMM에 의한 계산이 되지 않았다. 평균체제시간과 분산매개변수가 동시에 계산된 DNM과 DM( $C_{FF}$ )모델의 결과는 PFM, CMM, DBM의 결과를 이용하여 매개변수값을 한정시켰다. 동일지역에서도 삼중수소농도의 변화가 큰 경우는 각 지점마다 특징적인 지하수유동특성을 보이는 것으로 판단되어, 전 지 역에 걸쳐 동일한 모델을 일률적으로 적용하는 것은 바람직하지 않은 것으로 사료된다.

• Journal of Radiation Protection and Research
• /
• 제22권4호
• /
• pp.273-288
• /
• 1997

우리나라 원전이 위치하고 있는 해안지역에서 빈번히 발생하는 해륙풍 등과 같은 국지순환에 따른 방사성 물질의 대기확산 특성을 알아보기 위해 월성원전 주변지역을 대상으로 삼차원 해륙풍 모델과 라그랑지안 입자확산모델을 이용하여 봄철 약한 북풍이 부는 맑은 날과 강한 북풍이 부는 맑은 날에 대해 방사성 물질 확산에 관한 삼차원 시뮬레이션을 수행하였다. 시뮬레이션 결과, 해륙풍과 같은 국지순환의 발달여부에 따라 방사성 입자의 대기확산이 서로 다르게 나타남을 알 수 있었다. 또한 해륙풍의 해풍과 육풍의 풍향교체에 따른 입자의 재순환 현상이 대기중 농도분포에 중요한 역할을 하는 것을 확인할 수 있었다.

• 한국전자파학회논문지
• /
• 제22권4호
• /
• pp.407-415
• /
• 2011

본 논문에서는 등방성(isotropic) 특성과 작은 분산 오차(low dispersion error)를 갖는 3차원 등방성 시간 영역 유한 차분법(ID-FDTD: Isotropic Dispersion Finite Difference Time Domain) 방법의 stability condition과 광대역 해석 특성에 대해 논의하였다. 3차원 ID-FDTD 방법은 기존의 Yee FDTD 방법의 비등방성 특성과 큰 분산 오차를 개선하기 위해 제안되었다. 기존 연구에서는 3차원 ID-FDTD 방법의 stability condition을 수치적으로 계산하였지만, 이에 대한 검증이 충분히 이뤄지지 않은 상태이다. 이에 본 논문에서는 단일 주파수와 광대역 주파수 신호를 입력원으로 한 모의 실험 환경에서 3차원 ID-FDTD 방법의 stability condition 검증을 수행하였다. 또한 광대역 특성에 대해 3차원 ID-FDTD 방법과 유사한 알고리즘들을 비교 분석해 해보았고, 마지막으로 3D ID-FDTD을 적용하여 대형 크기 구 모델에 대해 radar cross section(RCS) 해석을 수행함으로써, 실질적 해석을 통한 알고리즘 검증 및 분석을 마무리 하였다.

• 한국지하수토양환경학회지:지하수토양환경
• /
• 제20권2호
• /
• pp.10-21
• /
• 2015

The present study introduces a novel numerical approach for solving dispersion dominated problems with Cauchy boundary condition in an Eulerian-Lagrangian scheme. The study reveals the incapability of traditional Neuman approach to address the dispersion dominated problems with Cauchy boundary condition, even though it can produce reliable solution in the advection dominated regime. Also, the proposed numerical approach is applied to a real field problem of radioactive contaminant migration from radioactive waste repository which is a major current waste management issue. The performance of the proposed numerical approach is evaluated by comparing the results with numerical solutions of traditional FDM (Finite Difference Method), Neuman approach, and the analytical solution. The results show that the proposed numerical approach yields better and reliable solution for dispersion dominated regime, specifically for Peclet Numbers of less than 0.1. The proposed numerical approach is validated by applying to a real field problem of radioactive contaminant migration from radioactive waste repository of varying Peclet Number from 0.003 to 34.5. The numerical results of Neuman approach overestimates the concentration value with an order of 100 than the proposed approach during the assessment of radioactive contaminant transport from nuclear waste repository. The overestimation of concentration value could be due to the assumption that dispersion is negligible. Also our application problem confirms the existence of real field situation with advection dominated condition and dispersion dominated condition simultaneously as well as the significance or advantage of the proposed approach in the real field problem.