• Journal of the Korean Society of Hazard Mitigation
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• v.9 no.3
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• pp.49-57
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• 2009

To minimze the degree of damage for the SMART highway's punctuality and safety after car-barrier collisions, the impact condition for longitudinal barriers of SMART highway was determined to be quite larger than the existing maximum impact condition. The impact condition consists of impact vehicles, impact velocities, and impact angles. To consider the occupant safety of passenger cars as much as possible, a small car with high risk during impact was selected as the impact vehicle for the evaluation of occupant risk. The impact velocity was determined to be 20% larger than the existing maximum impact velocity in order to include accident impact velocities as much as possible. The impact angle was determined to include most of expected accident impact angles. Computer simulations using various impact conditions were conducted for the existing domestic highest-performance medium and roadside barrier. How the suggested impact condition has an effect on the occupant safety was investigated. The existing domestic highest-performance medium and roadside barriers could not satisfy the suggested impact condition. New high-performance longitudinal barriers are required to minimize the degree of damage for the SMART highway's punctuality and safety after car-barrier collisions.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.3
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• pp.225-231
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• 2020

Recently, there has been an increasing demand for SAR satellite as it can be operated regardless of the weather condition. In general, main reflector of the SAR is formed of multiple deployable panels to increase performance in the constrained payload envelope. By nature, deployable structure lacks structural stiffness and it is vulnerable to external disturbances and excitation. In particular, SAR satellites may have high levels of vibration occurring at the antenna reflecting surface due to higher angular rate requirements. During image capturing it is important to keep high surface accuracy of the reflector for the quality of images. In this research, a performance degradation of deployable SAR antenna due to structural deformation is analyzed. Panels for main reflectors are assumed to be flexible structures and multi-body simulation environment is established. Then, deflection of the panel is calculated while the satellite performs maneuvers. In addition, antenna gain and beam pointing error are analyzed to determine how these deflections affect antenna performance and mission.

• Journal of Bio-Environment Control
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• v.15 no.2
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• pp.162-166
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• 2006

The objectives of this study were to determine the effect of cultivation time on the incidence of brown fruit stem (BFS) in glasshouse sweet pepper (cv. Special) and to investigate environmental causes of this disorder. The plants transplanted on 31 August (T1) showed more incidence of BFS than those on 24 November (T2) (6.1% vs.2.9%; P<0.01). The BFS symptom began to appear after completion of fruit enlargement, more often around fruit coloring period. Comparing the environmental factors between T1 and T2, with their data collected for 3 weeks around fruit coloring period, the factor that was most likely responsible for BFS incidence was found to be the night-time humidity deficit (HD) ($1.9g{\cdot}m^{-3}\;vs\;2.9g{\cdot}m^{-3}HD$). These results were reconfirmed as T1 was compared to the plants (T3) that were transplanted at a similar time of the following year to T1, but designed to reduce BSF by increasing air HD via heating at night. That is,T3 had much higher night-time HD than T1 ($5.9g{\cdot}m^{-3}\;vs\;1.9g{\cdot}m^{-3}HD$), and showed no incidence of BFS. These results indicated that, to prevent BFS incidence in the winter-harvesting sweet pepper plants, air humidity at night should be controlled low, especially for the fruit coloring period after fruit enlargement period is completed.

• Journal of Korean Society of Steel Construction
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• v.13 no.4
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• pp.407-417
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• 2001

To secure good visibility various steel flexible barriers were introduced and constructed in the area where a highway runs in parallel with a railroad. However, none of the flexible barriers was proven to satisfy the performance criteria for the impact condition of $14tonf-80km/h-15^{\circ}$ set forth by Korea design guide. Thus, in this study, the impact performance of the flexible barriers was investigated by using Barrier VII program, which was most widely used for the preliminary design of barriers. From the analytical results, it has been found that none of the barriers satisfied the stiffness requirement while the Type C barrier showed stiffer behavior than the others. Thus, the way to strengthen the installed Type C barrier was experimentally investigated. The method of partially filling concreter inside the pst was efficient to satisfy the performance criteria for the impact condition of $14tonf-80km/h-15^{\circ}$.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.6
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• pp.110-117
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• 2003

The operational characteristics of the landing gear retraction/extension depend on the complexity of design variables operational/environmental conditions. In order to meet the requirements of minimum stow area and performance, the integration of the landing gear system requires operational kinematic and dynamic analysis considering an effect of its related system. This study investigates operational dynamic behaviors of the T-50 landing gear system using ADAMS. Taking into account for various operational/environmental conditions, an analysis of dynamic behavior on the landing gear operational characteristics is performed with experience derived from a wide range of proprietary designs. Analytical results are presented for discussing the effects of temperature, aerodynamic and maneuver load on normal/emergency operation of the landing gears and doors. This analysis leads us to the conclusion that the proposed program is shown to be a better quantitative one that apply to a new development and troubleshooting of the landing gear system.

• Journal of Radiation Protection and Research
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• v.22 no.3
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• pp.135-141
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• 1997

The study of anneal characteristics is important for TL dosimeter to reuse. To obtain the annealing condition of the recently developed, new TL dosimeter, LiF:Mg,Cu,Na,Si Teflon Tills in a disk type (diameter 4.5 mm, thickness about $90mg/cm^2$), we studied for pre-irradiation annealing, readout procedure and post-readout annealing, in order. The gamma irradiations were carried out with a $^{60}Co$, dose of 0.1 Gy. We have used the method that observe the variation of thermoluminescent(TL) intensity of these Teflon TLDs over repeated cycles by changing both anneal temperature and anneal time with the TLD reader and the oven. There is a 5% loss in sensitivity over the ten repeated readouts by the annealing condition:pre-irradiation annealing at $80^{\circ}C$ for one hour, readout to $280^{\circ}C$ and post-readout annealing at $270^{\circ}C$ for 20 seconds.

• Proceedings of the Korean Vacuum Society Conference
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• 2000.02a
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• pp.90-90
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• 2000

이온빔을 이용한 리소그래피의 경우 미크론 이하의 미세구조를 형성할 수 있는 유용한 수단으로서 방사광 X-선과 함께 주목을 받고 있으며, 이와 같은 미세구조 제작은 MEMS (Micro Electro-Mechanical System) 개발에 있어서 매우 중요하다. 그러나 이온빔을 이용한 리소그래피에 대한 연구가 많이 이루어져 있지 않은 상태이다. MeV급 양정사 빔을 이용한 리소그래피의 가능성을 확인하기 위하여 기본적인 실험을 수행하였으며, 최적 이온빔 조사 조건 및 최적 현상 조건을 도출하였다. Resist로는 PMMA를 사용하였으며, 1.8 MeV 양성자 빔을 사용하여 50$\mu\textrm{m}$ 깊이의 구조물을 만들었다. 1.8MeV 양성자 빔의 조사선량이 7x1013ions/cm2 이상이 되면 PMMA 내부에 기포가 형성되므로 적정 조사선량을 4x1013 ions/cm2으로 결정하였다. 또한 선량을 4x1013ions/cm2 으로 고정하고 선량률을 변화시켜주면 선량률이 8x1011ions/cm2S 일 때부터 시료에 기포나 터짐 현상 등의 문제가 발생하였으며 5x1010~~1x1010ions/cm2s 의 선량률이 조사시간, 결함측면에서 가장 적합한 영역임을 알 수 있었다. 현상제로는 20% morpholine, 5% etanolamine 60% diethylenglykol-monobutylether, 15% 증류수를 혼합하여 사용하였다. 현상 온도를 30~5$0^{\circ}C$로 변화시켜서 현상을 한 결과, 4$0^{\circ}C$에서 현상 소요시간은 1시간 이내이며 SEM으로 관찰된 표면의 상태도 제일 양호한 결과를 보였다. 82 mesh 밀도, 선굵기 60$\mu\textrm{m}$, 크기 20x20 mm인 백금 망을 마스크로 사용하여 실제 3차원 미세구조를 제작하여 보았다. 그림 1에서 제작된 구조물의 SEM 사진을 보여주었으며, 식각된 면의 조도가 매우 뛰어나며 모서리의 직각성도 우수함을 확인할 수 있다. 이와 같이 도출된 시험 조건을 기초로 하여 리소그래피 후에 전기 도금을 이용한 금속 몰드 제작 및 이온빔 리소그래피 장점을 최대한 살릴수 있는 미세구조 제작에 대한 연구를 계속 추진할 계획이다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.1
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• pp.21-30
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• 2021

Mid-course trajectory of the missiles equipped with seeker should be designed to detect target within FOV of seeker and to maximize the maneuverability at the point of transition to terminal guidance phase. Because the trajectory optimization problems are generally hard to obtain the analytic solutions due to its own nonlinearity with several constraints, the various numerical methods have been presented so far. In this paper, mid-course trajectory optimization problem for boost-glide missiles is calculated by using SOCP (Second-Order Cone Programming) which is one of convex optimization methods. At first, control variable augmentation scheme with a control constraint is suggested to reduce state variables of missile dynamics. And it is reformulated using a normalized time approach to cope with a free final time problem and boost time problem. Then, partial linearization and lossless convexification are used to convexify dynamic equation and control constraint, respectively. Finally, the results of the proposed method are compared with those of state-of-the-art nonlinear optimization method for verification.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.12
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• pp.867-875
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• 2022

The preliminary mission analysis of a lunar lander, which is mounted on the upper stage of a Korean space launch vehicle, is performed when landing on the moon through a trans-lunar injection maneuver after being injected into the earth's low orbit by th launcher in this paper. Both direct landing and orbital landing methods, which have each advantage and disadvantages, are applied and their transfer orbit characteristics are analyzed according to the launch date when launching in lunar October 2030. We also analyzed the launch dates which satisfying eclipse conditions, solar elevation conditions, and tracking time intervals such as the US lunar lander Surveyor-1. The obtained results show that the most appropriate launch date is the 4th day of lunar October in case of direct landing method, and the 3rd day in case of indirect landing method, since the argument of perigee of the trans-lunar injection orbit and eclipse conditions are favorable in the dates.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.259-259
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• 2009

박막태양전지의 효율을 높이기 위한 방법 중 입사된 태양광의 흡수율을 높이기 위한 방법으로 전지의 표면구조를 제어하는 기술이 최근에 활발히 연구되고 있다. 본 연구에서는 박막태양전지의 저가화와 고효율화를 위하여 투명전도막으로 응용되고있는 ZnO박막의 증착속도를 높이는 공정변수의 영향과 수광효과를 개선하기 위하여 최적의 표면구조를 가지는 ZnO박막 증착조건을 찾고자 증착 공정변수에 대하여 실험하였다. 공정변수의 조절에 따라 표면구조의 제어가 가능하였으며 우수한 광학적 특성과 500nm/min 의 높은 증착속도를 얻을 수 있었다. 또한 표면구조와 전기적, 광학적 특성이 긴밀한 관계를 가지는 것을 알 수 있었다. 실험된 공정 변수는 기판온도, 공정압력, 플라즈마 파워, 원료 가스 조성 이며 공정변수에 따른 전기적, 광학적, 구조적, 특성은 FE-SEM, 4Point-probe, XRD, UV-spectroscopy를 이용하여 분석하였다.