• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.7
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• pp.33-39
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• 2005

A mathematical model, GUNBLAST, of blast waves emitted from a gun muzzle is established, and structural response analyses for the blast load are performed. The blast wave can be divided into two kinds of waves, free field and reflected blast waves. In this research, the free field blast wave model is established by the use of a scaling approach, and the reflected blast wave is calculated by using the oblique shock theory and computational fluid dynamic calculation. GUNBLAST is applied to two kinds of structural models. To investigate the effect of the muzzle distance from a structural surface, the blast waves on a plate for various muzzle distances are compared to uniform loads. Moreover, the transient response analysis of an aircraft wing model with a 12.7mm gun is carried out by using MSC/NASTRAN. From the results, it can be shown that the blast wave can cause broad random vibration and high frequency damage to equipments mounted in the aircraft.

• Journal of the Korea Concrete Institute
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• v.14 no.2
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• pp.266-274
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• 2002

The impact-echo test, which is to evaluate the integrity of concrete and masonry structures nondestructively, is an excellent method in the practical application. However, there are cases that the Impact-Echo testing nay result in the low reliability. In this study, the reliability of the Impact-Echo testing was investigated through the numerical simulation of the Impact-Echo testing. The finite element analysis and the analysis based on the dynamic stiffness matrix method was incorporated for the numerical simulation, in which the cases of a sandwiched shear stiffness, an incr＋easing or decreasing stiffness, and a homogeneous stiffness. Based on the results of the analysis were considered, this study proposed the approaches to Improve the reliability of the Impact-Echo testing.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.1
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• pp.195-201
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• 2006

The wave load and its influence on the response of offshore structure have been well investigated through the statistical approach based on the linear theory. The linear approach has a limitation to apply the extreme condition such as freak wave, which corresponds to extreme value of wave spectrum. The main topic of present study is to develop an efficient numerical method to predict wave load induced by extreme wave. As a numerical method, finite element method based on variational principle is adopted. The frequency-focusing method is applied to generate the extreme wave in the numerical wave tank. The wave load on the bottom mounted vertical cylinder is investigated. The hydroelastic response of the vertical cylinder is also investigated so as to compare the wave loads with the rigid body case in the extreme wave condition.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.1
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• pp.75.1-75.1
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• 2013

자체의 중력 효과를 고려하는 구대칭 완전 유체 전산모사 연구를 위해 일반상대론적 유체역학 코드를 이 분야 연구자들을 위한 공개용으로 개발하였다. 이 코드는 3+1 ADM(Arnowitt-Deser-Misner) 공식과 등방 공간 좌표를 사용하였다. 시공간 기하를 구하기 위해 극한값 썰기 (maximal slicing) 조건과 함께 세 개의 제한 방정식을 풀었고, 시공간을 채우는 물질인 유체는 근사 리만 해법을 사용한 HRSC (high resolution shock capturing) 기법으로 오일러 관찰자 시점에서 풀었다. 이 코드의 수렴성과 정확성을 검증하기 위해 상대론적인 구대칭 충격파 비교 분석, 블랙홀로 빨려 들어가는 상대론적 구대칭 강착, TOV(Tolman-Oppenheimer-Volkoff) 별 및 OS (Oppenheimer-Snyder) 붕괴 코드 테스트를 수행하였다. 특히, 이 코드의 동적 진화 테스트인 OS 붕괴의 경우 해석적인 해와 결과를 비교하기 위하여 좌표변환을 수치 계산으로 수행하였다. 아인슈타인의 일반상대성 이론을 넘어서는 변형된 중력이론 중 하나로 최근 제시된 EiBI(Eddington-inspired Born-Infeld) 이론에서 TOV 별의 해가 일반상대성 이론과 어떠한 차이를 보이는지 살펴 보았고, 그 이론에서도 물질이 붕괴하여 블랙홀을 만드는 경우 특이점이 형성되는지 고찰해 보았다.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.83-83
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• 2022

여러 분야의 연구자들이 지진해일의 위험에 대한 경각심을 가지고, 지진해일의 발생, 전파 그리고 수리현상을 해석하기 위해 많은 노력을 기울이고 있다. 해안지역에서 직접적인 피해를 입히는 지진해일의 충격파, 처오름, 월파, 침수 등에 관한 연구에 유사한 파형 특성을 가진 고립파를 많이 사용한다. 고립파는 비선형성과 분산이 균형을 이루는 가정에서 Korteweg-de Vries(KdV) 방정식을 만족하는 안정적인 이론파이다. 고립파의 파형분포는 수심에 의해 결정되고, 일정 수심 이상에서는 지진해일을 대신해 사용할 수 있다. 그러나 수심이 낮은 천해에서는 주기와 파장이 비현실적으로 짧아짐으로 지진해일을 대신하기에는 무리가 있다. 본 연구에서는 지진해일의 처오름 특성을 분석하기 위한 1:20 불투과성 경사면이 포함된 수치파동수조를 구성한다. 먼저, 일본 NOWPHAS(Nationwide Ocean Wave information network for Ports and HArbourS)의 관측자료를 이용하여 2011 동일본 지진해일과 고립파의 파형분포를 비교한다. 그리고 다양한 파형의 지진해일 생성할 수 있게 개발된 조파방법을 수치파동수조에 도입하여 수치해석을 수행한다. 수치해석결과, 지진해일의 처오름 높이가 고립파에 비해 최대 1.8배, 최소 1.13배, 평균 1.56배 증가한다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.5
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• pp.32-40
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• 2002

The study of nonlinear gas transport in rarefied condition or associated with the microscale length of the geometry has emerged as an interesting topic in recent years. Along with the DSMC method, several fluid dynamic models that come under the general category of the moment method or the Chapman-Enskog method have been used for this type of problem. In the present study, on the basis of Eu's generalized hydrodynamics, computational models for diatomic gases are developed. The rotational nonequilibrium effect is included by introducing excess normal stress associated with the bulk viscosity of the gas. The new models are applied to study the one-dimensional shock structure and the multi-dimensional rarefied hypersonic flow about a blunt body. The results indicate that the bulk viscosity plays a considerable role in fundamental flow problems such as the shock structure and shear flow. An excellent agreement with experiment is observed for the inverse shock density thickness.

• International Journal of Highway Engineering
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• v.11 no.1
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• pp.145-151
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• 2009

Current highway design standards is based on the safety under the free flow condition. The length of deceleration lane is also determined in terms of the deceleration distance which is necessary for the driers to adjust the vehicle speed from the speed limit on the main road to that on the exit ramp of the interchange. However, the queues are frequently developed on the deceleration, and the following vehicles to exit must decelerate on the main road. It may cause delay on the main road and traffic accidents. This study is to suggest a methodology to minimize such problems with the shock-wave theory. The queue length of exiting vehicles can be estimated by the design speeds, traffic volumes of main road and the exiting ramp, and the countermeasures to the operational problems. According to the results, the queue length can be shortened to 80% by upgrading the design speed of exit ramp as the amount of 10km/h. Fifty percent of queue length can be shortened by adding an additional lane on the ramp to two lanes.

• Journal of the Society of Naval Architects of Korea
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• v.29 no.4
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• pp.152-172
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• 1992

The ship sailing among waves are suffered the various wave loads that comes from its motion throughout its life. Because there are dynamic, the analysis of ship structure must be considered as the dynamic problem precisely. In the rationally-based design, the dynamic structural analysis is carried out using dynamic wave loads provided from the results of the ship mouton calculation as the rigid body. This method is based on the linear theory assumed low wave height and small amplitude of motion. But at the rough sea condition, high wave height, relatively ship's depth, is induced the large ship motion, so the ship section configulation below water line is rapidly changed at each time. This results in non-linear problem. Considering above situation in this paper, the strength analysis method is introduced for the hull glider among waves considering non-linear hydrodynamic forces. This paper considers that the overall or primary level of the ship structural dynamic loading and dynamic response provided from the non-linear wave forces, and bottom and bow flare impact forces estimated by momentum slamming theory, in which the ship is idealized as a hollow thin-walled box beam using thin-walled beam theory and the finite element method. This method is applied to 40,000 Ton Double-Skin Tanker and attention is paid to the influence of the response of ship speed, wave length and wave height compared with linear strip theory.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.2
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• pp.35.3-35.3
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• 2021

은하의 형성 과정은 천체물리학의 오랜 난제다. NewHorizon, Illustris-TNG, FIRE 등 다양한 수치실험이 사실적인 은하의 모습을 재현하고자 상상 이상의 노력을 해왔고, 일부 물리적 특성을 구현함으로써 희망적인 메세지도 주었다. 그러나 은하의 진화를 결정하는 핵심 물리과정들에 대한 이해는 여전히 불만족스럽다. 시대를 달리하며 유행처럼 제시된 중력 충격파, 초신성, 그리고 복사 피드백 과정 모두 사실적인 은하를 재현하는 데 안정적으로 작용하지 않는 것처럼 보인다. 이 발표에서는 교착상태에 빠진 듯한 현 상황을 타개하기 위해 우리 연구팀이 최근 시작한 수치실험들을 소개하고, 이론 모델의 문제점을 파악하기 위해 주시하고 있는 은하의 관측적 특성에 대해 이야기 해보고자 한다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.12 no.2
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• pp.21-33
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• 1992

Under the intense-impulsive loading, structures are subjected to the wide range of pressures at an instantaneous time. The constitutive laws capable to describe the material behavior under the extreme pressure as well as the low pressure are necessary for the analysis of the structural behavior under the intense -impulsive loadings. In this study, two plastic models, the pressure independent Von-Mises model and the pressure dependent Drucker-Prager model, are employed for the wave propagation analysis. Governing equations of this study are conservation equations of momentum and mass in Lagrangian coordinate system which is fixed to the material. Due to the shock-front which violates the continuity assumptions inherent in the differential equations numerical artificial viscosity is used to spread the shock front over several computational zones. These equations are solved by Finite Difference Method with discretized time and space coordinates. The associate normality flow rule as a plastic theory is implemented to find the plastic strains.