• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.40 no.11
• /
• pp.948-956
• /
• 2012

This paper presents the computations of the longitudinal and directional stability derivatives for the SDM(Standard Dynamic Model). The static and dynamic derivatives are evaluated at once using forced harmonic oscillations in the pitch and yaw directions. For the numerical simulations, a 3-D Euler solver that uses a dual time stepping method for unsteady time accurate simulations is applied. This work investigates the variation of the derivatives in terms of the Mach number and the several motion parameters. Good agreement of the pitch and yaw stability derivatives with previously published numerical results and experimental results are observed.

• KCID journal
• /
• v.3 no.1
• /
• pp.40-52
• /
• 1996

This study was conducted to simulate long series of synthetic monthly flows by harmonic synthetic and harmonic regression models and to make a comparison of statistical parameters between observed and synthetic flows of six watersheds in Yeong San and Seo

• Proceedings of the Optical Society of Korea Conference
• /
• 2000.02a
• /
• pp.306-307
• /
• 2000

1962년 Armstrong 등에 의해 second harmonic generation(SHG) 의 이론이 완성된 후 SHG 효율을 높이기 위한 방법으로 비선형성이 큰 물질의 개발과 더불어 위상정합(phase matching)을 만족시키는 여러가지 방법이 연구 되었다. 특히 위상정합의 경우 지금까지는 복굴절을 이용하는 방법이 널리 사용되었으나 이 경우 입사광의 파장이 제한적이고, 많은 무기물 결정에서 비선형광학계수의 가장 큰 텐서 성분인 $d_{zzz}$를 사용할 수 없다는 단점을 가지고 있다. 반면 유사위상정합(Quasi-phase matching:QPM) 은 비선형광학계수( $d_{zzz}$)의 방향을 결맞음 길이(coherence length)마다 분극반전 시켜주어 2차 조화파의 진폭을 길이방향으로 계속 증가시키는 방법으로 구역반전된 길이를 조절하면 거의 모든 파장에 대해 비임계 위상정합( $d_{zzz}$ 사용)이 가능하고, 2차 조화파가 기본파의 전파경로에서 벗어나는 walk-off 현상이 없어 SHG 전환효율을 극대화할 수 있다. (중략). (중략)

• Aerospace Engineering and Technology
• /
• v.5 no.2
• /
• pp.149-158
• /
• 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}$.

• Economic and Environmental Geology
• /
• v.41 no.2
• /
• pp.211-217
• /
• 2008

The gravity anomalies that observed by ground and shipborne survey and calculated from GRACE satellite are combined by using spherical cap harmonic analysis (SCHA). In this study, ground gravity data from Korea Institute of Geoscience and Mineral Resource(KIGAM) and shipborne gravity data from National Ocean Research Institute(NORI) and Korea Ocean Research and Development institute(KORDI) were used. L-2 level GRACE Gravity Model (GGM02C) was also used for satellite gravity anomaly. The ground and shipborne surveyed data were combined and gridded using Krigging method with 0.05 degree interval and GRACE data were also gridded using the same method with 0.05 degree to harmonize with the resolution of SCHA that has coefficient up to 80. Generalized Minimal Residual(GMRES) inversion method was implemented for calculating the coefficients of SCHA using the gridded ground and satellite gravity anomalies that had 0 km and 50 km altitude, respectively. The results of inversion method showed good correlation of 0.950 and 0.995 with original ground and satellite data. The gravity anomaly using SCHA satisfies Laplace's equation, therefore, using these SCHA coefficients, gravity anomaly can be calculated at any altitude. In this study, gravity anomaly was calculated from 10 km to 60 km altitude and each altitude, very stable results were shown. The ground and shipborne gravity data that have higher resolution and satellite data in long wavelength are harmonized well with SCHA coefficients and successfully applied in South Korea area. If more continuous survey and muti-altitude surveyed data like airborne data available, more precise gravity anomaly can be acquired using SCHA method.

• Composites Research
• /
• v.12 no.2
• /
• pp.26-35
• /
• 1999

This paper presents the vibration damping characteristic of a single lap joint beam with partial dampers analyzed using the model strain energy method and the harmonic response analysis which were based on a finite element model. The two finite element analysis methods exhibited very similar results of the resonant frequency and system loss factor which were comparable to those by the theoretical analysis. Effects of the location of partial dampers and elastic moduli and thickness of their layers on the system loss factor were studied. The damping effects due to changes of modules and loss factor of the viscoelastic layer in lap joint and partial dampers were also studied. Consequently, the geometrical and material conditions at maximizing the system loss factor were suggested.

• Proceedings of the Korea Air Pollution Research Association Conference
• /
• 2005.11a
• /
• pp.463-465
• /
• 2005

• 대한방사선치료학회:학술대회논문집
• /
• 1998.06a
• /
• pp.30-30
• /
• 1998

• Proceedings of the Acoustical Society of Korea Conference
• /
• 1992.06a
• /
• pp.96-99
• /
• 1992

섬유강화 복합재료의 동탄성계수와 감쇠특성을 규명하기 위하여 랜덤하게 분포된 무한 실린더 형상의 산란체를 가진 매질내에서, 조화운동을 하는 압축 및 SV탄성파의 전파에 관하여 연구하였다. 단일 실린더에 대한 산란계수로부터 La의 준결정근사법을 이용하여 다중산란에 관한 이론을 유도하였고, 매질내에서의 파동전파 특성을 내포하는 분산관계식을 얻었다. 수치적으로 분산관계식의 해를 구함으로써 2 차원 유효체적강성, 횡방향 유효전단강성 및 각 파동의 전파에 따른 감쇠계수를 주파수와 체적비의 함수로서 제시하였다.

• Economic and Environmental Geology
• /
• v.49 no.4
• /
• pp.269-280
• /
• 2016

I presented three vector crustal magnetic anomaly components and six gradients by using spherical Slepian functions over the cap area of $20^{\circ}$ of radius centered on the South Pole. The Swarm mission, launched by European Space Agency(ESA) in November of 2013, was planned to put three satellites into the low-Earth orbits, two in parallel in East-West direction and one in cross-over of the higher altitude. This orbit configuration will make the gradient measurements possible in North-South direction, vertical direction, as well as E-W direction. The gravity satellites, such as GRACE and GOCE, have already implemented their gradient measurements for recovering the accurate gravity of the Earth and its temporal variation due to mass changes on the subsurface. However, the magnetic gradients have little been applied since Swarm launched. A localized magnetic modeling method is useful in taking an account for a region where data availability was limited or of interest was special. In particular, computation to get the localized solutions is much more efficient and it has an advantage of presenting high frequency anomaly features with numbers of solutions fewer than the global ones. Besides, these localized basis functions that were done by a linear transformation of the spherical harmonic functions, are orthogonal so that they can be used for power spectrum analysis by transforming the global spherical harmonic coefficients. I anticipate in scientific and technical progress in the localized modeling with the gradient measurements from Swarm and here will do discussion on the results of the localized solution to represent the three vector and six gradient anomalies over the Antarctic area from the synthetic data derived from a global solution of the spherical harmonics for the crustal magnetic anomalies of Swarm measurements.