• 대기
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• 제21권4호
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• pp.391-404
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• 2011

This study investigates the impact of cumulus parameterization scheme (CPS) with different horizontal grid sizes on the simulation of the local heavy rainfall case over the Korean Peninsula. The Weather Research and Forecasting (WRF)-based real-time forecast system of the Joint Center for High-impact Weather and Climate Research (JHWC) is used. Three CPSs are used for sensitivity experiments: the BMJ (Betts-Miller-Janjic), GD (Grell-Devenyi ensemble), and KF (Kain-Fritsch) CPSs. The heavy rainfall case selected in this study is characterized by low-level jet and low-level transport of warm and moist air. In 27-km simulations (DM1), simulated precipitation is overestimated in the experiment with BMJ scheme, and it is underestimated with GD scheme. The experiment with KF scheme shows well-developed precipitation cells in the southern and the central region of the Korean Peninsula, which are similar to the observations. All schemes show wet bias and cold bias in the lower troposphere. The simulated rainfall in 27-km horizontal resolution has influence on rainfall forecast in 9-km horizontal resolution, so the statements on 27-km horizontal resolution can be applied to 9-km horizontal resolution. In the sensitivity experiments of CPS for DM3 (3-km resolution), the experiment with BMJ scheme shows better heavy rainfall forecast than the other experiments. The experiments with CPS in 3-km horizontal resolution improve rainfall forecasts compared to the experiments without CPS, especially in rainfall distribution. The experiments with CPS show lower LCL(Lifted Condensation Level) than those without CPS at the maximum rainfall point, and weaker vertical velocity is simulated in the experiments with CPS compared to the experiments without CPS. It means that CPS suppresses convective instability and influences mainly convective rainfall. Consequently, heavy rainfall simulation with BMJ CPS is better than the other CPSs, and even in 3-km horizontal resolution, CPS should be applied to control convective instability. This conclusion can be generalized by conducting more experiments for a variety of cases over the Korean Peninsula.

• 한국해양공학회지
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• 제27권1호
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• pp.1-8
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• 2013

This paper presents the results of experimental and numerical research on the slamming phenomenon. Two experimental techniques were proposed in this study. The traditional free drop tests were carried out. However, the free drop tests done in this study using an LM guide showed excellent repeatability, unlike those of other researchers. The coefficients of variation for the drop test done in this experiment were less than 0.1. The other experimental technique proposed in this study was a novel concept that used a pneumatic cylinder. The pneumatic cylinder could accelerate the specimen over a very short distance from the free surface. As a result, high rates of repeatability were achieved. In the numerical study, the development of in-house code and utilization of commercial code were carried out. The in-house code developed was based on the boundary element method. It is a potential code. This was mostly applied to the computation of the wedge entry problem. The commercial code utilized was FLUENT. Most of the previous slamming research was done under the assumption of a constant body velocity all through the impact process, which is not realistic at all. However, the interaction of a fluid and body were taken into account by employing a user-defined function in this study. The experimental and numerical results were compared. The in-house code based on BEM showed better agreement than that of the FLUENT computation when it cames to the wedge computation. However, the FLUENT proved that it could deal with a very complex geometry while BEM could not. The proposed experimental and numerical procedures were shown to be very promising tools for dealing with slamming problems.

• International Journal of Aeronautical and Space Sciences
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• 제16권1호
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• pp.1-7
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• 2015

In order to provide some references for suitability of carrier-based aircrafts, this paper studies the flow field of exhaust jets and its impact on the flight deck. The geometrical models of aircraft carrier and carrier-based aircrafts are firstly built, on which unstructured tetrahedral meshes are generated for numerical analysis. Then, this paper simulates the flow field of exhaust jets to evaluate its impact on the Jet Blast Deflector (JBD) and the flight deck, when four carrier-based aircrafts are ready to start off in the bow. The standard k-${\varepsilon}$ equations, three-dimension N-S equations and the Computational Fluid Dynamics (CFD) theory are used in the analysis process. To solve the equations, the thermal coupling of the wind and the jet flow are also considered. The velocity and temperature distributions are provided with the simulation of the CFD software, FLUENT. The results indicate that: (1) this analytical method can be used to simulate aerodynamic problems with complex geometrical models, and the results are of high reliability; (2) the safety working area, the installation scheme of the JBD and the arrangement of the take-off position can be optimized through analysis.

• 한국음향학회지
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• 제37권2호
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• pp.92-98
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• 2018

본 논문은 모형 프로펠러를 대상으로 공동수조 시험, 수중 충격시험, 유한요소해석 및 전산유체해석에 기반하여 수행한 명음 발생 메커니즘 연구이다. 선미 유동을 모사하기 위해 반류망, 프로펠러 및 방향타를 설치하고 수중청음기와 가속도계로 프로펠러 명음 현상의 발생과 소멸을 계측하였다. 유한요소해석을 통해 프로펠러 날개의 고유진동수를 예측하고 접촉 및 비접촉식 충격시험으로 이를 검증하였다. RANS(Reynolds Averaged Navier-Stokes) 방정식 기반 전산유체해석을 통하여 프로펠러 날개 각 단면의 유속과 유효 받음각을 계산하였으며, DES(Detached Eddy Simulation) 기반 고해상도 해석을 통해 명음 발생 위치에서 2-D 날개 단면 뒷전의 와류흘림주파수(vortex shedding frequency) 계산을 수행하였다. 수치적으로 예측된 와류흘림주파수는 모형시험으로 계측한 명음 발생 주파수 및 날개 고유진동수와 일치함을 확인하였다.

• 상하수도학회지
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• 제26권5호
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• pp.669-683
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• 2012

The water supply pipes are buried across wide range of areas, so it is hard to spot them using excavation and takes a large amount of expense. Thus, there is a high risk for direct research and application, accompanying many difficulties in implementation of them. Therefore, it is more economical and convenient to use indirect evaluation variables than direct evaluation of the buried pipes in assessing the degree of pipe deterioration. To assess the degree of pipe deterioration using the indirect evaluation variables, it should be done first to identify how and to what extent they affect the degree of deterioration. This study measured the evaluation variables for pipe deterioration using the pipe endoscope and analyzed the measurement results and the degree of impact on the pipes. In addition, this study attempted to evaluate the adequateness of the pipe deterioration evaluation using the indirect variables based on the analysis results. The evaluation variables measured through the pipe endoscope were the thickness of sediments, size of scale, degree of desquamation and condition of connections. For the indirect evaluation variables, the data such as the property data from GIS pipe network map as well as the material, diameter, age and pipe lining material of the pipe, road type, leakage frequency, average water velocity and water pressure using the leakage repair records was collected. Using the collected data, this study comparatively analyzed the indirect evaluation variables for the degree of pipe deterioration and the results from the pipe endoscope to choose appropriate variables for pipe deterioration evaluation and calculated the weights of the indirect variables on the degree of deterioration. The results showed that the order of the impact of indirect variables on deterioration was pipe age > pipe lining material > road type > leakage frequency > average water velocity with their weights of 0.45, 0.20, 0.15, 0.10, and 0.10, respectively. Conclusively, the results suggest that the measures of sediment thickness, scale size, degree of desquamation and condition of connections are appropriate for the evaluation of pipe deterioration and sufficient for the analysis of the impact of the indirect variables on deterioration.

• Geomechanics and Engineering
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• 제8권3호
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• pp.415-440
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• 2015

In the present case study, High Strain Dynamic Testing of piles is conducted at 3 different locations of Kolkata city of India. The raw field data acquired is analyzed using Pile Driving Analyzer (PDA) and CAPWAP (Case Pile Wave Analysis Programme) computer software and load settlement curves along with variation of force and velocity with time is obtained. A finite difference based numerical software FLAC3D has been used for simulating the field conditions by simulating similar soil-pile models for each case. The net pile displacement and ultimate pile capacity determined from the field tests and estimated by using numerical analyses are compared. It is seen that the ultimate capacity of the pile computed using FLAC3D differs from the field test results by around 9%, thereby indicating the efficiency of FLAC3D as reliable numerical software for analyzing pile foundations subjected to impact loading. Moreover, various parameters like top layers of cohesive soil varying from soft to stiff consistency, pile length, pile diameter, pile impedance and critical height of fall of the hammer have been found to influence both pile displacement and net pile capacity substantially. It may, therefore, be suggested to include the test in relevant IS code of practice.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2011년도 추계학술대회 초록집
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• pp.97.1-97.1
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• 2011

Dimethyl ether (DME) is an attractive fuel as a hydrogen carrier for mobile PEMFC applications. However, its reforming technologies are rarely studied especially by using autothermal reforming (ATR) method. This work explored the impact of operating conditions to the performance of DME ATR. Temperature, Steam to carbon ratio(SCR), Oxygen to carbon ratio(OCR) and Gas hourly space velocity(GHSV) were considered as the operating conditions. As results, conversion efficiency was increased as the temperature increased, but saturated around $700^{\circ}C$. There was no significant effect of SCR on conversion efficiency, but high SCR led reactions in endothermic manner. High OCR substantially suppressed conversion efficiency, but it helped to sustain the temperature by stimulating exothermic reactions. Conversion efficiency was decreased as GHSV increased. The optimized operating conditions was suggested: $700^{\circ}C$, SCR of 1.5, OCR of 0.45 and GHSV below 15000/h and conversion efficiency was ~85% at the conditions.

• 한국자동차공학회논문집
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• 제14권3호
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• pp.22-27
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• 2006

As the regulation and assessment program for safety of passengers become stringent, automakers are required to develop lighter and safer vehicles. In order to fulfill both requirements which conflict with each other, automobile and steel companies have proposed the application of AHSS(Advance High Strength Steel) such as DP, TRIP and martensite steel. ULSAB-AVC model is one of the most remarkable reactions to offer solutions with the use of steel for the challenge to improve simultaneously the fuel efficiency, passenger safety, vehicle performance and affordability. This paper is concerned with the crash analysis of ULSAB-AVC model according to the US-SINCAP in order to compare the effectiveness between the model with AHSS and that with conventional steels. The crashworthiness is investigated by comparing the deformed shape of the cabin room, the energy absorption characteristics and the intrusion velocity of a car.

• 한국정밀공학회지
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• 제33권12호
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• pp.1039-1045
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• 2016

We investigated the protection capability of a plate against high speed projectiles demonstrating collision and penetration behaviors by finite element analysis. The element erosion method was used for penetration analysis, which showed that the speed of the projectile was slightly reduced by the collision with the protection plate. Protection capability was measured by the projectile's attitude angle change because the damage of our tanks by projectiles was also dependent on the projectile-tank collision angle. When the length of the protection plate was sufficiently long, the projectile was severely deformed and incapacitated. In the case of a small plate, the projectile was deformed only in the collision region. Thus, projection capability was investigated by the change of attitude angle. The effect of collision angle, velocity, and length of the plate on the rotational and vertical velocities of the projectile was investigated.

• 한국추진공학회지
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• 제19권3호
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• pp.96-102
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• 2015

기존에 사용되고 있는 대부분의 추진물질들은 연소 시 이산화탄소, 염산가스 등의 환경유해 물질을 다량 발생시킨다. 본 연구에서는 이러한 문제점을 개선하기 위한 테트라진 계열의 저탄소 고질소 화합물인 DAAT의 합성공정을 확립하였다. 또한, 문헌에 빠져있는 구체적인 공정법 및 특성 분석 결과를 서술하였다. 그리고 분광분석(NMR, IR)을 통한 DAAT의 구조분석과 열, 충격, 마찰 안정성을 측정하였고, Gaussian 09와 EXPLO5를 이용하여 생성열과 폭발 특성(폭압, 폭속) 등을 계산하였다.