• 한국강구조학회 논문집
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• 제12권3호통권46호
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• pp.303-315
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• 2000

본 논문에서는 일반화된 21개 강성 매트릭스의 독립 변수를 모두 사용하였고 비등방성 3차원 탄성체의 지배 방정식 및 수치 해석 근사식을 유도하였다. 일반화된 3차원 해석은 2차원 해석의 제한성을 극복하는 정밀해를 보여줄 수 있으며, 두꺼운 보나 판, 또는 쉘에서 전단 변형 효과에 의한 처짐의 증가 효과를 더욱 정밀하게 해석할 수 있다. 따라서 본 논문은 3차원 비등방성 탄성체에 대하여 다양한 경계조건에 따른 유한 차분식을 유도하였으며 이를 전산화하여 해석 프로그램을 개발하였다. 특히, 본 논문에서는 자유경계조건에 대하여 개선된 유한차분법의 적용 방식을 제시하였다. 또한 탄성체의 각 방향 자유경계면에서 경계조건을 해결할 수 있는 일반화된 방식을 제시하였다. 몇가지 수치예제를 통하여 이러한 유한차분 경계처리 방식에 의한 비등방성 3차원 탄성체 해석의 타당성 및 거동을 분석하였다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제6권4호
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• pp.1197-1208
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• 2014

The problem of the oblique water entry of a three dimensional body is considered. Wagner theory is the theoretical framework. Applications are discussed for an elliptic paraboloid entering an initially flat free surface. A dedicated experimental campaign yields a data base for comparisons. In the present analysis, pressure, force and dynamics of the wetted surface expansion are assessed.

• 천문학회보
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• 제43권1호
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• pp.46.3-47
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• 2018

We present a general N-body exasolar system simulator in anticipation of upcoming searches for exoplanets and even exomoons by next generation telescopes such as James Webb Space Telescope. For habitable zones, traditionally defined by temperature, we here address the essential problem of dynamical stability of planetary orbits. Illustrative examples are presented on P-type orbits in stellar binary systems, that should be fairly common as in Kepler 16b. Specific attention is paid to reduced orbital lifetimes of exoplanets in the habitable zone by the stellar binary, that is propoesed by Maurice van Putten (2017). Especially, we focused on a classic work of complex three-body problem that is well known by Dvorak(1986). We charge his elliptic restricted three-body problem to extend unrestricted three-body problem to look into dynamical motions in view of circumbinary planet, furthermore, we suggest that opposite angular orientation of the planet is relative to the stability of orbits. In here, counter-rotation case is relatively more faster than co-rotation case for being stable. As a result, we find that various initial conditions and thresholds to approach dynamical stability and unstability with unexpectable isolated islands over enormous parameter space. Even, superkeplerian effect of binary is important to habitability of the exoplanet and we can verify that superfaster binary doesn't effect on th planet and increases survivality of planet around the binary.

• 한국항공우주학회지
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• 제43권8호
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• pp.692-698
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• 2015

본 논문에서는 원형 제한 3체 문제의 불변위상공간을 이용하여 지구-달 또는 행성간의 궤적을 설계하고 해석하는 기법을 소개한다. 2체 문제를 조합하는 고전적인 방식 대신에 원형 제한 3체 문제에 대한 운동방정식, 궤적의 동적 특성, 평형점 주변의 리아프누프 궤도와 불변위상공간의 특성을 기술한다. 원형 제한 3체 문제의 불변위상공간을 이용했을 때, 지구-달 시스템의 궤적설계 방식과 태양-목성 시스템의 경계면에서의 초기조건에 따른 궤적 특성을 수치 시뮬레이션을 통해 확인한다. 본 논문에서 제안한 원형 제한 3체 문제의 불변위상공간을 이용한 궤적설계 기법은 저추력 또는 저에너지를 이용한 달탐사 또는 행성탐사 임무 등에 활용 가능할 것이다.

• 천문학논총
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• 제30권2호
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• pp.297-299
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• 2015

In this paper we have examined the linear stability of triangular equilibrium points in the photogravitational restricted three body problem when both primaries are triaxial rigid bodies, the bigger one an oblate spheroid and source of radiation. The orbits about the Lagrangian equilibrium points are important for scientific investigation. A number of space missions have been completed and some are being proposed by various space agencies. We analyze the periodic motion in the neighbourhood of the Lagrangian equilibrium points as a function of the value of the mass parameter. Periodic orbits of an infinitesimal mass in the vicinity of the equilibrium points are studied analytically and numerically. The linear stability of triangular equilibrium points in the photogravitational restricted three body problem with Poynting-Robertson drag when both primaries are oblate spheroids has been examined by A. Kumar (2007). We have found the equations of motion and triangular equilibrium points for our problem. With the help of the characteristic equation we have discussed stability conditions. Finally, triangular equilibrium points are stable in the linear sense. It is further seen that the triangular points have long or short periodic elliptical orbits in the same range of ${\mu}$.

• 천문학논총
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• 제30권2호
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• pp.295-296
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• 2015

This study deals with the generalization of the Elliptic Restricted Three-Body Problem (ER3BP) by considering the effects of radiation and oblate spheroid primaries. This may illustrate a gas giant exoplanet orbiting its host star with eccentric orbit. In the three dimensional case, this generalization may possess two additional equilibrium points ($L_{6,7}$, out-of-plane). We determine the existence of $L_{6,7}$ in ER3BP under the effects of radiation (bigger primary) and oblateness (small primary). We analytically derive the locations of $L_{6,7}$ and assume initial approximations of (${\mu}-1$, ${\pm}\sqrt{3A_2}$), where ${\mu}$ and $A_2$ are the mass parameter and oblateness factor, respectively. The fixed locations are then determined. Our results show that the locations of $L_{6,7}$ are periodic and affected by $A_2$ and the radiation factor ($q_1$).

• 한국위성정보통신학회논문지
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• 제5권2호
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• pp.50-56
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• 2010

이제까지 수행된 우주 탐사 임무에서 임무 궤도의 설계는 행성 혹은 위성과 인공위성의 2체 문제 (two-body problem)에 기초한 Hohmann transfer를 기반으로 하는 Patched Conic Approximation 방식이 주로 사용되어져 왔다. Hohmann transfer는 원 궤도에서 다른 원 궤도로 천이할 수 있는 타원 천이 궤도의 설계 방식으로서, Patched Conic Approximation은 태양계를 여러 개의 2체 문제로 분해하고 각기 분해된 2체 시스템 사이의 Hohmann 천이 궤도를 설계하여 조합함으로써 행성 간의 임무 궤도를 설계하는 방식이다. 이 방식은 하나의 행성만을 고려했을 때, 즉 행성과 인공위성의 2체 문제일 때, 가장 효율적인 천이 방식으로 알려져 있고 현재까지의 우주 탐사 임무 설계에 주로 이용되고 있다. 하지만, 우주 탐사 임무가 점차 다양화되고 소형 위성을 이용한 임무 수행의 필요성이 증가함에 따라 기존의 Patched Conic Approximation은 요구되는 연료의 양이 크다는 점과 원뿔꼴(conic) 특성을 가지는 궤도만을 표현할 수 있다는 점에서 한계점을 보이기 시작하고 있다. 이에 반해 3체 동역학의 기하학적 특성은 기존의 태양계의 패러다임을 획기적으로 변화시킨다. 개념적으로는 요구되는 에너지가 매우 적은 에너지로 태양계를 모두 연결하는 궤도를 구성할 수 있기 때문이다. 본 논문에서는2체문제 기반의 임무 궤도 설계 기술의 한계성에서 벗어나 유연하고 효율적인 탐사 임무를 설계한다.

• 대한기계학회논문집A
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• 제20권5호
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• pp.1486-1497
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• 1996

The problem of determining the 3-demensional motion of any two rough bodies after a collision involves some rather long analysis and yet in some points it differs essentially from the corresponding problem in tdwo dimensions. We consider a special problem where two rough ellipsolids moving in any manner collide, and analyze the three dimensional impact process with Coulomb friction and Poisson's hypothesis. The differential equations that describe that process of the impact induce a flow in the tangent velocity space, the flow patterns characterize the possible impact cases. By using the graphic method in impulse space and numerical integration thchnique, we analyzed the impact process inall the possible cases and presented the algorithm for determining the post-impact motion. The principles could be applied to the general problem in three dimensions. We verified the effectiveness of the analysis results by simulating the numerous significant examples.

• Journal of Ship and Ocean Technology
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• 제7권2호
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• pp.1-19
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• 2003

This paper introduces a unified theory for the radiation problem of adjacent multiple floating bodies. The particular case of interest is the multiple slender bodies that their centerlines are parallel. The infinite-and finite-depth unified theories for the single-body problem are extended to solve each sub-problem of multiple bodies. The present method is valid for deep water and moderate water depth, and applicable for individually floating bodies as well as multimaran-type vehicles. For the validation of the present method, the heave and pitch hydrodynamic coefficients for two adjacent ships are compared with the results of a three-dimensional method, and an excellent agreement is shown. The application includes the hydrodynamic coefficients and motion RAOs of four trimarans which have different longitudinal and transverse arrangements for sidehulls.

• 천문학논총
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• 제30권2호
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• pp.293-294
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• 2015

This work considers the elliptic restricted three-body problem under effects of radiation of the bigger primary, and an oblate spheroid for the smaller primary to mimic an exoplanetary system with a gas giant planet. Under the influences of both effects we look for the existence of the triangular equilibrium points and the influences of the radiation and oblateness on the locations and motion of the points. We set the system in a normalized rotating coordinate system and derive equations of motion for the third infinitesimal object. Our study shows that the effects modify the equilateral/isosceles triangle shape with respect to the primaries. The triangular points also have non-planar motion with period depending on the value of the planet oblateness.