• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.7
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• pp.29-36
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• 2004

In this work, the effect of composite couplings on hub loads of a hingeless rotor in forward flight is investigated. The hingeless composite rotor blade is idealized as a laminated thin-walled box-beam. The nonclassical effects such as transverse shear, torsional warping are considered in the structural formulation. The nonlinear differential equations of motion are obtained by applying Hamilton's principle. The blade response and hub loads are calculated using a finite element formulation in space and time. The aerodynamic forces acting on the blade are calculated by quasi-steady strip theory. The theory includes the effects of reversed flow and compressibility. The magnitude of elastic couplings obtained by MSC/NASTRAN is compared with the classical pitch-flap $({\delta}3)$ or $pitch-lag({\alpha}1)$ coupling. It is found that the elastic couplings have a substantial effect on the behavior of $N_b/rev$ hub loads. Nearly 10 to 40% of hub loads is reduced by appropriately tailoring the fiber orientation angles in the laminae of the composite blade.

• Magazine of the Korea Concrete Institute
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• v.6 no.4
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• pp.153-160
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• 1994

Ten Half precast concrete slabs reinforced with welded deformed wire fabric were tested under two concentrated loads to investigate the flexural moment and ductile capacity. The test variables were the compressive strength of topping concrete, quantitative roughness, and reinforcernent ratio. The effects of each test variables were studied separately. Test results were as followings. The ultimate strength design method is applicable to predict flexural strength for Half P.C. concrete slab with welded deformed wire fabric and quantitative roughness. It is proper to consider 0.0035 strain ;is yielding stress of the welded deformed wire fabric. The ductility index of Half precast concrete slab with welded deformed wire fabric showed lower value. Therefore to enhance the ductility capacity the normal defomed bar should be used with the welded deformed wire fabric for the longitudinal reinforcement.

• The Korean Journal of Air & Space Law and Policy
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• v.22 no.1
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• pp.29-54
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• 2007

Nuclear Power Sources(NPS) have been used since 1961 for the purpose of generating energy for space objects and have since then been recognized as particularly suited essential to some space operations. In January 1978 a malfuctioning Soviet nuclear powered satellite, Cosmos 954, re-entered the earth's atmosphere and disintegrated, scattering radioactive debris over a wide area of the Canadian Northwest Territory. This incident provided some reasons to international legal scholars to make some principles to regulate using NPS in outer space. In 1992 General Assembly adopted "Principles Relevant to the Use of Nuclear Power Sources in Outer Space". These NPS Principles set out certain legal and regulatory requirements on the use of nuclear and radioactive power sources for non-propulsive purposes. Although these principles, called 'soft laws', are not legal norms, they have much enfluences on state practices such as 1983 DBS Principles(Principles Governing the Use by States of Artificial Earth Satellites for International Direct Television Broadcasting), 1986 RS Principles(Principles Relating to Remote Sensing of the Earth from Space) and 1996 Declaration on International Cooperation in the Exploration and Use of Outer Space for the Benefit and in the Interests of all States, Taking into Particular Account the Needs of Developing Countries. As far as 1963 Declaration of Legal Principles Governing the Activities of States in the Exploration and Use of Outer Space is concerned the main points such as free use of outer space, non-appropriation of celestial bodies, application of international law to outer space etc. have become customary international law binding all states. NPS Principles might have similar characters according to states' willingness to respect them.

• The Korean Journal of Air & Space Law and Policy
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• no.spc
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• pp.35-58
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• 2007

Nuclear Power Sources(NPS) have been used since 1961 for the purpose of generating energy for space objects and have since then been recognized as particularly suited essential to some space operations. In January 1978 a malfuctioning Soviet nuclear powered satellite, Cosmos 954, re-entered the earth's atmosphere and disintegrated, scattering radioactive debris over a wide area of the Canadian Northwest Territory. This incident provided some reasons to international legal scholars to make some principles to regulate using NPS in outer space. In 1992 General Assembly adopted "Principles Relevant to the Use of Nuclear Power Sources in Outer Space". These NPS Principles set out certain legal and regulatory requirements on the use of nuclear and radioactive power sources for non-propulsive purposes. Although these principles, called 'soft laws', are not legal norms, they have much enfluences on state practices such as 1983 DBS Principles(Principles Governing the Use by States of Artificial Earth Satellites for International Direct Television Broadcasting), 1986 RS Principles(Principles Relating to Remote Sensing of the Earth from Space) and 1996 Declaration on International Cooperation in the Exploration and Use of Outer Space for the Benefit and in the Interests of all States, Taking into Particular Account the Needs of Developing Countries. As far as 1963 Declaration of Legal Principles Governing the Activities of States in the Exploration and Use of Outer Space is concerned the main points such as free use of outer space, non-appropriation of celestial bodies, application of international law to outer space etc. have become customary international law binding all states. NPS Principles might have similar characters according to states' willingness to respect them.

• Korean Journal of Materials Research
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• v.3 no.6
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• pp.645-651
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• 1993

The growth of semi-insulating(SI) high resistant undoped GaAs epilayer has been studied to solve the problems ocurring when GaAs IC is fabricated by the widely used ion implantation directly into the SI GaAs substrate. The EPD ditribution of the SI substrates has been examined, and the suitability of the buffer layers grown by MOCVD and MBE, respectively, has been tested for IC fabrication through leakage current measurement. IJngated FET has been fabricated on the SI epilayer and leakage current through the buffer layer has been measured. In the case of MOCVD grown 1$\mu\textrm{m}$-thick buffer layer, the leakage current is as small as about 270nA/mm, and this value does not affect the pinch-off of FET. In this case, the epilayer quality is affected by the substrate defects because the leakage current distribution is coincided with the EPD distribution of the SI substrate. The 2$\mu\textrm{m}$-thick buffer layer grown by MBE, however, has the better quality, and shows the lower leakage current(40nA/mrn) and higher uniformity.

• Journal of the Korea Concrete Institute
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• v.19 no.1
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• pp.19-26
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• 2007

Until recently Korea is considered to be immune from the earthquake hazard because it is located for away from the active fault. However, we have noticed that recent strong earthquakes inflicted enormous losses on human lives and nation's economy all over the world. Hence, there has been raised the importance of the earthquake resistant design for various infrastructures. In this research, new methodologies for the seismic design and performance assessment of reinforced concrete(RC) bridge pier were proposed from experimental results of 82 circular RC bridge piers and 54 rectangular RC bridge piers tested in domestic and aboard. New seismic design method was based on the concept of the limited ductile design, which could be practically used for low or moderate seismic regions like Korea. Further study for the seismic safety of RC bridge piers was carried out to enhance the seismic performance of aged RC bridge piers, which were designed and constructed before implementing the 1992 seismic design provision in Korea. New formula for the seismic performance assessment of RC bridge piers was proposed and practically used for the decision on the need of repair and retrofit of many aged RC bridge piers.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.27-27
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• 2021

세굴은 유체와 유사의 상호작용으로 발생하는 중요한 자연 현상 중 하나로, 구조 및 지반 붕괴, 홍수, 생태계 파괴 등의 문제를 야기할 수 있다. 이러한 세굴 현상을 예측하기 위해 많은 수치적 연구가 진행되어왔지만, 대부분의 연구가 기존 격자기반방법인 유한체적법 (FVM)과 개별요소법 (DEM)이 연성된 모델을 이용하였고, 이는 격자 의존도로 인한 정확도와 효율성의 문제점을 보였다. 해결책으로 입자기반 유체해석 방법인 약압축성 SPH (WCSPH)와 개별요소법의 결합모델을 이용한 모의가 연구되어 왔지만, 단순 밀도차를 활용한 유체해석방법이 압력의 불안정성을 야기하여 유사의 운동에도 영향을 주는 결과를 보였다. 또한, 개별요소법의 특성상 모의 입자의 크기를 실제 실험 입자의 크기와 동일하게 설정하면서 입자수가 지나치게 증가해 계산의 효율성이 현저히 낮아지게 되었고, 이로 인해 실제 자연 지형에 적용하는데 어려움을 보여주었다. 본 연구에서는 향상된 세굴 수치모의해석을 위해 반복법을 통해 안정적인 유체 압력을 계산하는 비압축성 SPH (ISPH)와 개별요소법을 연성한 ISPH-DEM 모델을 사용하였다. 또한, 계산속도 향상을 위해 하나의 입자가 다수의 작은 입자의 움직임을 대표하는 Coarse-grained 방법을 적용하여 기존 모델을 개선하였다. 개선된 모델을 NFLOW ISPH PURPLE 소프트웨어를 이용하여 세굴 현상을 수치 모의하였고 실험 결과와 검증을 진행한 결과, 세굴의 깊이, 너비, 형상 등을 비교하였을 때 약 10% 이내의 오차를 보였고, Coarse-grained 방법을 통한 입자 수 감소로 최소 13배 증가된 해석 속도를 보였다. 이를 통해 본 연구에서 제시된 모델이 실제 자연 지형에서의 적용가능성을 확인할 수 있었다.

• The Optical Journal
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• s.101
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• pp.57-63
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• 2006

지금까지 재현성이나 안정성이 문제가 되어온 경면 연삭이나 연성 모드 연삭도 ELID 연삭법의 개발에 따라 실용화되기 시작하고 있다. 부드러운 지석으로 피삭재 표면을 문지르듯이 가공한 기존의 다듬질 연삭은 예리하게 돌출된 미세한 지립에 의해 삭둑삭둑 잘리며 능률적으로 경면화되고 초정밀화 될 수 있는 신가공 기술로 변해 왔다. 또 절삭 가공의 이미지로 난가공재를 깎는 고능률 연삭도 실용 단계로 들어섰다. ELID 법의 본격적인 보급을 위해 관련된 제조업체의 협력으로 주변 기술의 정비가 진행되고 있지만 ELID 연삭 조건을 최적화하려면 작업 목적의 설정과 구성 요소의 선정을 좀더 명확하게 한 다음 적용할 기계 정밀도·성능, 기능과의 적합성을 검토할 필요가 있다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2010.10a
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• pp.523-524
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• 2010

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2010.10a
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• pp.535-536
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• 2010