• 한국전산유체공학회:학술대회논문집
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• 2011.05a
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• pp.428-433
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• 2011

In this paper, a prediction method for dynamic stability derivatives is studied using steady state simulations in rotational coordinates. The simulations require the extension of a standard CFD formulations based on inertial coordinate. A new CFD code based on the method are developed. Flows induced by steady circular motions of airfoils with a constant pitch rate are simulated with the code. From the numerical simulations, the pitch rate derivatives are obtained at various Mach numbers, and the results are compared with other numerical results. The numerical simulations show that the new code are capable of predicting dynamic stability derivatives.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.21 no.5
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• pp.475-482
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• 2008

This paper indicates that the use of Euler angles lacks in its consistency and exactness of analysis when it was applied to incorporate the rotational equation of motion for rotor systems by previous researcher. Kinetic energy and angular velocity are different from case to case depending on the way of choosing Euler angles and thus only the linear system has been investigated even though the rotor system has a very nonlinear behavior. A new methodology is applied by using both spherical coordinate and quaternion in the rotor rotation to overcome weaknesses of Euler angles and shows its superiority It is found through numerical examples that the use of quaternion will be a more useful and valid tool to derive the numerical model of the rotor system.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.5
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• pp.395-404
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• 2012

This paper presents computations of the dynamic derivatives of three dimensional flight vehicle configurations using CFD. The pitch dynamic derivatives are computed from the pitch sinusoidal motion, while the roll damping is computed based on steady state calculation using a non-inertial frame method. The Basic Finner and the SDM(Standard Dynamic Model) are chosen for the benchmark tests against other numerical and experimental results. For the flow calculations, a 3-D Euler solver that can be run both on the non-inertial frame and on the inertial frame is developed. A dual-time stepping method is applied for the unsteady time accurate simulations. A good agreement of pitch-roll dynamic derivatives with previously published numerical results and the experimental results is observed.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.27 no.1
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• pp.693-700
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• 2009

For real-time precise GPS data processing such as a long baseline network RTK (Real-Time Kinematic) survey, PPP (Precise Point Positioning) and monitoring of ionospheric/tropospheric delays, it is necessary to guarantee accuracy comparable to IGS (International GNSS Service) precise orbit with no latency. As a preliminary study for determining near real-time satellite orbits, the general procedures of satellite orbit determination, especially the dynamic approach, were studied. In addition, the transformation between terrestrial and inertial reference frames was tested to integrate acceleration. The IAU 1976/1980 precession/nutation model showed a consistency of 0.05 mas with IAU 2000A model. Since the IAU 2000A model has a large number of nutation components, it took more time to compute the transformation matrix. The classical method with IAU 2000A model was two times faster than the NRO (non-rotating origin) approach, while there is no practical difference between two transformation matrices.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.5 no.1
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• pp.21-30
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• 1985

The tension leg platform (TLP) is a kind of compliant structures, and is also a type of moored stable platform with a buoyancy exceeding the weight because of having tensioned vertical anchor cables. In this paper, among the various kinds of tension leg structures, Deep Oil Technology (DOT) TLP was analyzed because it has large-displacement portions of the immersed surface such as vertical corner pontoons and small-diameter elongated members such as cross-bracing. It also has results of hydraulic model tests, comparable with theorectical analysis. Because of the vertical axes of symmetry in the three vertical buoyant legs and because there are no larger horizontal buoyant members between these three vertical members, it was decided to develop a numerical algorithm which would predict the dynamic response of the DOT TLP using the previously developed numerical algorithm Floating Vessel Response Simulation (FVRS) for vertically axisymmetric bodies of revolution. In addition, a linearized hydroelastic Morison equation subroutine would be developed to account for the hydrodynamic pressure forces on the small member cross bracing. Interaction between the large buoyant members or small member cross bracings is considered to be negligible and is not included in the analysis. The dynamic response of the DOT TLP in the surge mode is compared with the results of the TLP algorithm for various combinations of diffraction and Morison forces and moments. The results which include the Morison equation are better than the results for diffraction only. This is because the vertically axisymmetric buoyant members are only marginally large enough to consider diffractions effects. The prototype TLP results are expected to be more inertially dominated.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.11
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• pp.1-8
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• 2006

A steady prediction method is presented to compute dynamic damping coefficients for axisymmetric projectiles. Viscous flow analysis is essential to the steady method using a zero-spin coning motion in the inertial coordinate frame. The present method is applied to compute the pitching moment and the pitch-damping moment coefficients for the Army-Navy Spinning Rocket. The results are in good agreement with the parabolized Navier-Stokes data, range data, and unsteady prediction data. Predictions for Secant-Ogive-Cylinder configurations are performed to investigate effects of afterbody geometries. To investigate the geometrical effect and flow physics, the longitudinal developments of the coefficients are examined in detail.

• Aerospace Engineering and Technology
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• v.5 no.2
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• pp.149-158
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• 2006

A review has been made on what kind of method can be applied to predict the dynamic derivatives of the separated PLF(Payload Fairing) halves of a launch vehicle in consideration of technology and budget. An optimal approach is selected considering the geometric characteristics of the PLF halves, the aerodynamic conditions and the required accuracy. The time history of aerodynamic force/moment coefficients are obtained for the forced harmonic motions by solving the unsteady Euler equations derived with respect to the inertial reference frame. and the dynamic derivatives are deduced by integration of the aerodynamic coefficients for one period. In this research, the dynamic derivatives are presented for 0.6$\leq$ M $\leq$2.0, $-180^{\circ}$ $\leq$$\alpha$ $\leq$$180^{\circ}$ and $-90 ^{\circ}$$\leq$$\beta$$\leq$$90 ^{\circ}$.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.3
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• pp.220-227
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• 2019

The satellites in orbit use a sun reference vector from solar model based the ephemeris. To get the ephemeris, we use DE-Series, an ephemeris developed by the Jet Propulsion Laboratory (JPL), or the reference vector generation formula proposed by Vallado. The DE-Series provides the numerical coefficients of Chebyshev polynomials, which have the advantage of high precision, but there is a computational burden on the satellite. The Vallado's method has low accuracy, although the sun vector can be easily obtained through the sun vector generation equation. In this paper, we have developed a program to provide the Chebyshev polynomial coefficients to obtain the sun position coordinates in the inertial coordinate system. The proposed method can improve the accuracy compared to the conventional method and can be used for high - performance, high - precision nano satellite missions.

• Journal of the KSME
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• v.21 no.1
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• pp.21-31
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• 1981

원자력발전소의 원자로냉각재 압력경계의 건전성과 안정성을 확보하기 위하여 법적 요구조건을 설정함에 있어 파괴역학이 어떻게 적용되었는 가를 설명하였다. 이를 요약하면 다음과 같다. 1) 압력경계에 사용되는 재료의 $RT_{NDT}$를 정의하였다. 이는 무연성천이온도와 같은 개 념의 것으로, 앞으로 재료의 파괴인성은 이 $RT_{NDT}$에 대한 상대온도의 함수로 주어진다. 2)비연성파괴를 방지하기 위한 설계조건으로서 선형탄성 파괴역학에 근거한 조건식을 인용하였다. 여기서 조건식이란 능력확대계수의 합계가 어떠한 조건에서도 이러한 조건식을 만족한다는 것을 해석적으로 확인하고 규제당국의 승인을 받아야 한다. 3) 가동중검사에 발견된 결함으로 합격수준을 초과하는 것은 파괴역학적으로 해석하여 구조적 으로 안전하다는 것은 파괴역학적으로 해석하여 구조적으로 안전하다는 것을 입증하여야 한다. 이때 결함은 원자로의 가동과 더불어 성장하므로 수명기간중 피로파괴에 이를 것인지의 여부도 평가하여야 한다. 이때의 대조균열성장률은 Paris의 power law에 따른다. 4) 고속중성자 (E>1. 0MeV)에 의한 조사취화를 감시하기 위하여 감시시험계획을 사전에 수립 하고 이에 따라 감시시험을 수행하여 조사에 수립하고 이에 따라 감시시험을 수행하여 조사에 의한 원자로용기 재료의 파괴인성의 저하를 평가하여 이를 고려한 충분한 안전여유를 갖는 운 전조건 즉, 압력-온도 한계곡선을 산출하여야 한다. 이때의 취화 정도는 DELTA. $RT_{NDT}$ 와 Upper Shelf Energy의 감소로 나타낸다. 또한, 압력-온도 한계곡선은 선형관성 파괴역학에 입각한 조건식을 이용하여 해당 온도에서의 압력을 산출한다. System을 개발 사용하기 위하여 기존 전자계산소를 이용하는 방법이 바람직하며 System의 도입은 자체운영을 결정하기 전에 경제적인 여건 등 여러가지 문제를 검토하여야 한다. 특히 Turn Key Base로 System를 도입할 경우에는 System의 도입목 적과 사용빈도, 앞으로의 확장성 현재 설계및 생산 과정과의 마찰가능성, 유지보수문제 등을 신 중히 검토하여야 한다. 이제 기계공업도 전자계산기를 이해하고 사용하므로 서 발전할 수 있는 단계가 되었다. 예로부터 좋은 공구를 개발하여 적절히 사용하는 것이 기계공업 발전의 첩경이 었다. 전자계산기는 현대 기술이 개발한 가장 강력하고 사용하기 좋은 공구이다.점에서 피로구열의 안정성장을 논하고, 과거 10여년간의 피로 crack문제에 대한 연구방법, 실험방법 등을 소개하는 방향으로 고 를 진행시켜 나가겠다.에 그 효과가 증대됨을 알 수 있었다.적용한 임상실험이 수행되어야 할 것이다. 또한 위치결정에서 획득한 좌표값의 정확성을 알아보기 위해서 팬톰을 이용한 방사선조사 실험이 추후에 실행되어져야 할 것이다. 그리고 제작된 프레임에 Rotating X선 시스템과 내부 장기의 움직임을 계량화하고 PTV에서의 최적 여유폭을 설정함으로써 정위 방사선수술 및 3 차원 업체 방사선치료에 대한 병소 위치측정과 환자의 자세에 대한 setup 오차측정 결정에 도움이 될 수 있을 것이라고 사료된다. 상대적으로 우수한 것으로 나타났으며, 혼합충전재는 암모니아의 경우 코코넛과 펄라이트의 비율이 7：3인 혼합 재료 3번과 소나무수피와 펄라이트의 비율이 7：3인 혼합 재료 6번에서 다른 혼합 재료에 비하여 우수한 것으로 나타났다. 4. 코코넛과 소나무수피의 경우 암모니아 가스에 대한 흡착 능력은 거의 비슷한 것으로 사료되며,