• Journal of Soil and Groundwater Environment
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• v.11 no.1
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• pp.37-44
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• 2006

This study summarizes advantages and disadvantages of numerical methods and compares ELLAM and LEZOOMPC to develop an efficient numerical modeling technique on contaminant transport. Eulerian-Lagrangian method and Eulerian method are commonly used numerical techniques. However Eulerian-Lagrangian method does not conserve mass globally and fails to treat boundary in a straightforward manner. Also, Eulerian method has restrictions on the size of Courant number and mesh Peclet number because of time truncation error. ELLAM (Eulerian Lagrangian Localized Adjoint Method) which has been popularly used for past 10 years in numerical modeling, is known for overcoming these numerical problems of Eulerian-Lagrangian method and Eulerian method. However, this study investigates advantages and disadvantages of ELLAM and suggests a change for the better. To figure out the disadvantages of ELLAM, the results of ELLAM, LEZOOMPC (Lagrangian-Eulerian ZOOMing Peak and valley Capturing), and visual MODFLOW are compared for four examples having different mesh Peclet numbers. The result of ELLAM generates numerical oscillation at infinite of mesh Peclet number, but that of LEZOOMPC yields accurate simulations. The simulation results suggest that the numerical error of ELLAM could be alleviated by adopting some schemes in LEZOOMPC. In other words, the numerical model which combines ELLAM with backward particle tracking, forward particle tracking, adaptively local zooming, and peak/valley capturing of LEZOOMPC can be developed for not only overcoming the numerical error of ELLAM, but also keeping the numerical advantage of ELLAM.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2005.04a
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• pp.135-138
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• 2005

최근에 ELLAM 기법을 이용한 오염물 거동 문제를 많은 사람들이 다루어 오고 있다. ELLAM 기법은 기존의 Eulerian-Lagrangian 방식에서 일어나는 질량보존 문제점과 일반경계조건의 체계적인 적용 한계점을 극복하였다. 그러나 본 연구에서는 이 방식의 장단점을 네 개의 예제를 통하여 다른 모델들과 비교 검토하여 ELLAM의 수치적 고찰을 수행하고자 한다. 예제 수행 결과 Mesh Peclet Number가 무한대일때 ELLAM은 수치확산 및 수치진동과 같은 수치오차로 인해 음수의 농도 값을 갖거나 1 보다 큰 농도를 갖는 경향을 보인다. 그러나 Mesh Peclet Number 50 일때는 전체적으로 해석해와 잘 일치함을 볼 수 있다. 반면, LEZOOMPC(Lagrangian-Eulerian ZOOMing Peak and valley Capturing)는 항상 좋은 결과를 보여주고 있다. 따라서 위의 결과를 종합하여 볼 패 ELLAM의 단점은 LEZOOMPC의 성질을 이용하여 개선 및 보완될 수 있음을 간접적으로 시사해준다. 즉 LEZOOMPC에서 사용되는 선택적 국부 격자 세립화 과정을 이용하면 ELLAM에시 일어나는 다양한 수치오차를 줄일 수 있을 것이라고 판단된다.

• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.167-170
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• 2004

본 논문에서는 수중익 버블 캐비테이션과 날개 끝 볼텍스 캐비테이션의 거동 및 소음을 Eulerian-Lagrangian 기법을 이용하여 수치적으로 해석하였다. Eulerian-Lagrangian 기법은 캐비테이션 버블이 유동장에 미치는 영향이 거의 없다는 가정하에 유동장과 캐비테이션 거동을 일방으로 연계하여 해석하는 방식이다. 수중익 버블 캐비테이션 해석을 위한 유동장은 비압축성 RAMS 방정식을 해석하여 구하고 날개 끝 볼텍스 캐비테이션 유동장은 일반적 CFD 기법의 큰 수치 소산으로 그 특성이 잘 나타나지 않으므로 Sculley 볼텍스 모델을 이용하여 해석한다. 해석한 유동장 정보를 입력치로 하고 버블의 지배 방정식인 Rayleigh-Plesset 방정식과 Newton의 제2법칙에 근거한 궤적 방정식을 연계하여 캐비테이션의 성장-붕괴와 운동을 예측한다. 계산된 거동 정보를 이용하여 버블 캐비테이션과 날개 끝 볼텍스 캐비테이션의 소음을 예측하였다. 본 연구는 수중 운동체에서 발생하는 캐비테이션의 거동과 소음의 특성을 파악하고 그에 따른 대비책을 마련하는 기본 연구로서 활용할 수 있을 것이다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.05a
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• pp.173-176
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• 2009

The Arbitrary Lagrangian-Eulerian(ALE, in short) method is the new description of continum motion, which combines the advantages of the classical kinematical descriptions, i.e. Lagrangian and Eulerian description, while minimizing their respective drawbacks. In this paper, the ALE description is adapted to simulate fluid-structure interaction problems. An automatic re-mesh algorithm and a fluid-structure coupling process are included to analyze the interaction and moving motion during the 2-D axisymmetric solid rocket interior FSI phenomena simulation.

• Journal of Korea Water Resources Association
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• v.52 no.12
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• pp.1047-1055
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• 2019

Various types of numerical modeling techniques are used to predict the behavior of pollutants under various water environmental conditions in the event of a water pollutant accident. Among them, a hydraulic model that can consider water flow characteristics is the most basic and very important. The process of evaluating whether the hydraulic model accurately predicts the applied river characteristics is very important. In the verification of the modeling result, the measuring data are often used in the river. Currently, ADCP and FlowTrackers are widely used to measure the flow velocity of rivers. However, ADCP is not accurate when the depth is less than 0.6 m and also when the ratio of irreversibility near the surface is more than 40%. Futhermore, FlowTracker has a limitation in measuring at high depth and high velocity due to the direct measurement method in rivers. Simuation results, which are validated by these methods, are not reliable for low depth conditions of low flowrate and high velocity conditions of high flowrate. In this study, Lagrangian GPS floaters which measures physical quantity of water according to particle movement is used without the conventional method measured by Eulerian technique. The verification method of the model results was studied by comparing the simulation results of the hydraulic model with the velocities measured using the GPS floaters. When comparing the traveling distance of the GPS floaters with the traveling distance of the LPT simulations, the average error rate was 13.6% on distances, and the average error rate was 3.2% on velocities except for the stagnant section. Therefore, GPS floaters can be used for a correction and verification method of hydraulic model simulations.

• Journal of the Korean Society for Marine Environment & Energy
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• v.10 no.4
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• pp.218-226
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• 2007

In modern naval ships, the design of submarines has continually evolved to improve survivability and it is also important to design ship against shock response. Exiting underwater ship design has been peformed due to results of static analysis considering shock acceleration by simple method. However, it can not be anticipated good assesment. The present study applied the Arbitrary Lagrangian-Eulerian (ALE) technique, a fluid-structure interaction approach, to simulate an underwater explosion and investigate the survival capability of a damaged submarine liquefied oxygen tank. The Lagrangian-Eulerian coupling algorithm and the equations of state for explosives and seawater were also reviewed. It is shown that underwater explosion analysis using the ALE technique can accurately evaluate structural damage after attack. This procedure could be applied quantitatively to real structural design.

• The Journal of the Korea institute of electronic communication sciences
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• v.18 no.6
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• pp.1009-1014
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• 2023

Comprehensive observations of the Euler method and the Lagrangian method were performed in order to obtain high-resolution observation data in space and time for the complex environment of new city. The two radiosondes, which measure meteorological parameters using Lagrangian methods, produced air pressure, wind speed and wind direction. They were generally consistent with each other even if the observation points or times were different. The temperature measured by the sensor exposed to the air during the day was relatively high as the altitude increased due to the influence of solar radiation. The temporal difference in wind direction and speed was found in the comparison of Euler's wind profiler data with radiosonde data. When the wind field is horizontally in homogeneous, this result implies the need to consider the advection component to compare the data of the two observation methods. In this study, a method of using observation data at different times for each altitude section depending on the observation period of the Euler method is proposed to effectively compare the data of the two observation methods.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.112-113
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• 2021

하천으로 유입되는 오염물질은 유수의 흐름에 따라 이송되며 혼합된다. 이러한 오염물질의 해석을 위해서는 확산 또는 분산계수 산정이 필요하다. 오염물질의 거동과 관련된 실험적 연구는 방사선 동위원소와 형광성 물질을 이용하여 수행되어 왔으나, 추적자 실험은 많은 비용 및 인력을 요하며, 고정식으로 설치한 계측장비로부터 수집한 시계열 농도자료만을 이용하여 분석하기 때문에 공간적 분포에 대한 자료 취득은 어렵다는 한계가 있다. 하천의 오염물질을 모니터링하기 위해서는 공간을 이동하는 입자의 관점에서 물리량을 표현하는 Lagrangian 방식보다 특정 위치에서 물리량 변화를 표현하는 Eulerian 방식이 적합하다. 그러나 드론을 활용한 하천원격탐사 연구의 대부분은 이동식 플랫폼으로 활용되어 특정 시간에 공간적 분광특성의 분포 파악이 한정적이며, 동일 지점에서 분광특성의 시간적 변화를 파악할 수 없다. 따라서 본 연구에서는 기존의 면단위를 측정하는 이동식 플랫폼의 한계를 극복하고 하천 모니터링에 적합한 Eulerian 방식을 적용하기 위하여 CCTV 형태의 고정식 초분광촬영 플랫폼을 도입하였다. 본 연구에서는 하천으로 유입되는 오염물질의 거동을 분석하기 위하여 자연하천에서 형광성물질인 Rhodamine WT를 이용하여 추적자 실험을 수행하였으며, 접촉식 센서를 활용한 농도측정과 동시에 드론과 초분광센서를 활용하여 CCTV 형태의 고정식 초분광영상을 획득하였다. 실험결과 도출된 전통적인 방식의 분산계수 산정과 시공간 초분광영상을 활용한 분산계수 산정을 비교하여 오염물질 거동 분석에 초분광영상 활용의 가능성을 검토하였다. 본 연구에서 제시한 드론기반 시공간 초분광영상 기법을 교량이나 기타 하천구조물에 초분광 센서를 설치하여 CCTV형식으로 활용할 경우, 공단이나 하·폐수 처리장 등의 점오염원이 밀집해 있는 지역에 직접 설치하여 화학사고의 감지 및 오염물질의 유출 확인 및 조류, 부유사 등의 다양한 수질항목의 농도 변화 감지가 가능하고, 수심변화 감지로 장기적으로 활용할 경우 특정 지점에서의 하상변동 조사가 가능하다. 또한, 오염물질의 유출 사고 발생 등의 사람이 직접 접근이 불가능한 지역에 드론을 활용하여 초분광센서를 이용한 오염물질 감지가 가능할 것으로 판단된다.

• Clean Technology
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• v.25 no.3
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• pp.206-222
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• 2019

Recently, various multiphase flows have been developed, and among them some models have been commercialized. However, most of them have been developed based on a pressure-based approach; therefore, various numerical difficulties were involved inherently. Accordingly, in order to overcome these numerical difficulties, a multiphase flow model, MultiPhaSe flow (MPS), following a fractional-flow based approach was developed. In this study, by combining a contaminant transport module describing an enhanced dissolution effect of a surfactant with MPS, a MultiPhaSe flow and TranSport (MPSTS) model was developed. The developed model was verified using the analytical solution of Clement. The MPSTS model can simulate the process of surfactant enhanced aquifer remediation including interphase mass transfer and contaminant transport in multiphase flow by using the coupled particle tracking method and Lagrangian-Eulerian method. In this study, a surfactant was used in a non aqueous phase liquid (NAPL) contaminated area, and the effect of hydro-geological heterogeneity in the layered media on remediation efficiency was studied using the developed model. According to the numerical simulation, when hydraulic conductivity in a lower layer is 10 times, 20 times, and 50 times larger than that in an upper layer, the concentration of dissolved diesel in the lower layer is much higher than that in the upper layer because the surfactant moves faster along the lower layer owing to preferential flow; thus, the surfactant enhances dissolution of residual non aqueous phase liquid in the lower layer.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.6
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• pp.2073-2082
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• 1991

The vaporization and combustion of liquid spray in a cylindrical shape combustor was studied numerically. Mixture of liquid drops and air was assumed to be ejected from the center-hole and assisting air from the concentric annulus with swirling. Eulerian-Lagrangian scheme was adopted for the two phase calculation, and the interactions between the phases were considered with the PSIC model. Also adopted were the infinite conductivity model for drop vaporization, the equation of Arrhenius and the eddy break-up model for reaction rate, and the k-epsilon model for turbulence calculations. Gas flow patterns, drop trajectories and contours of temperature and mass fractions of the gas species were predicted with swirl number, drop diameter, and equivalence ratio taken as parameters. Calculations show that the vaporization and the consequent combustion efficiency enhance with the increase of the swirl number and/or with the decrease of drop size, and the higher maximum temperature is attained with the higher equivalence ratio.