• 산업기술연구
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• 제20권B호
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• pp.45-53
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• 2000

A numerical study is done on the thrust vector control using gaseous secondary injection in the rocket nozzle. A commercial code, PHOENICS, is used to simulate the rocket nozzle flow. A $45^{\circ}-15^{\circ}$ conical nozzle is adopted to do numerical experiments. The flow in a rocket nozzle is assumed a steady, compressible, viscous flow. The exhaust gas of the rocket motor is used as an injectant to control the thrust vector of rocket at the constant rate of secondary injection flow. The injection location which is on the wall of rocket is chosen as a primary numerical variable. Computational results say that if the injection position is too close to nozzle throat, the reflected shock occurs. On the other hand, the more mass flow rate of injection is needed to get enough side thrust when the injection position is moved too far from the throat.

• 전기학회논문지
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• 제59권7호
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• pp.1309-1313
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• 2010

In this paper, we propose a novel guidance law for controlling an UAV(Unmanned Air-Vehicle) to follow a reference line in vertical plane. A kinematics model representing the relative motion of the UAV to the reference line is derived. And then LQR(Linear Quadratic Regulator) theory is applied to the model to derive the VLFG(Vertical Line Following Guidance) law. The resultant guidance law forms a gain-scheduling controller scheduled by a simple parameter $\sigma$ which is a function of the UAV's velocity, axial acceleration, gravity, and the slope of the reference line. Also derived is a stability condition for the $\sigma$ variation based on Lyapunov theory. Simulation results show that the proposed guidance law can be applied effectively to UAV guidance algorithm design.

• E2M - 전기 전자와 첨단 소재
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• 제9권10호
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• pp.1060-1065
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• 1996

We have studied the magnetoresistance phenomena on spin valve thin films of antiferromagnetic NiO/CoO. Interlayer coupling oscillates between the antiferrocoupling and ferrocoupling with the variation of Cu thickness. The exchange coupling strength between NiO (antiferromagnetic) and NiFe(ferromagnetic) as a function of NiO texture and interface roughness is investigated by CoO insertion. CoO has significantly higher anisotropy in the (111) plane and interface roughness. It seems that the MR-ratio is increased by CoO inserted films. From the AFM and XRD data, the increase of MR-ratio and exchange field is influenced by the roughness of CoO.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2002년도 봄 학술발표회 논문집
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• pp.99-106
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• 2002

This paper presents an analytical investigation on the behavior of simple span integral abutment bridge. An integral abutment bridge is a simple span or multiple span continuous deck type bridge having the deck integral with the abutment wall. Although the temperature variation and earth pressure are the major attributor to the total stress in integral abutment bridge, the superstructure has been designed by modeling it as a simple or continuous beam In order to investigate the effect of temperature change and earth pressure on the superstructure of integral bridge, the simple span integral bridge is modeled as a plane frame element. Performing frame analysis, the variations of bending moment and axial force of superstructure due to the various loading combination are investigated with respect to the flexural rigidity of piles, and the bending moment and axial force obtained by frame analysis are compared with the maximum bending moment obtained by conventional design method and initial prestressing force respectively.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2010년도 한국우주과학회보 제19권1호
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• pp.41.1-41.1
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• 2010

A bipolar magnetic field perturbation in the meridional plane was observed when the Polar spacecraft crossed the plasmapause near the midnight, which was identified by a clear jump in density and temperature, from the plasmasheet to the plasmasphere. The bipolar variation shows a negative-then-positive polarity. To examine the bipolar magnetic field perturbation at the plasmapause, we assume one-dimensional model with physical quantities varying along a direction normal to the plasmapause and employ two-fluid approach for the tangential plasmapause. That is, the magnetic fields on both sides are parallel. Considering Ampere's law and pressure balance relation, we have a perturbed magnetic field, which is consistent with the observation at the plasmapause.

• 한국조명전기설비학회:학술대회논문집
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• 한국조명전기설비학회 2009년도 춘계학술대회 논문집
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• pp.270-272
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• 2009

This paper presents a basic data of the surface discharge characteristics for solid dielectric under non-uniform field in $N_2/O_2$ mixture gas. Used electrodes are needle and plane. Used solid dielectric is expoxy resin. With the variation of the mixture rates of the gas by 80[%]:20[%], 60[%]:40[%] and 40[%]:60[%] in same condition, we can obtain different surface dielectric strength. Increased Pressure and thickness caused increased surface dielectric strength.

• Computers and Concrete
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• 제27권3호
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• pp.269-282
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• 2021

A dynamic analytical solution for a simply supported, rectangular functionally graded plate with a porous middle layer under time-dependent load based on a refined third-order shear deformation theory with a cubic variation of in-plane displacements according to the thickness and linear/quadratic transverse displacement is presented. The solution achieved in the trigonometric series form and rests on the Green's function method. Two porosity types and their influence on material properties, and mechanical behavior are considered. The network of pores is assumed to be empty or filled with low-pressure air, and the material properties are calculated using the power-law distribution idealization. Numerical calculations have been carried out to demonstrate the accuracy of the kinematic model for the dynamic problem, the effect of porosity, thickness of porous layers, power-law index, and type of loading on the dynamic response of an imperfect functionally graded material plate.

• 대한치과교정학회지
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• 제33권1호
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• pp.41-49
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• 2003

골격성 III급 부정교합자는 부적절한 악골 위치에서 기능 교합을 유지하기 위해 치아의 경사도와 수직적 위치가 변화하게 된다. 이러한 치성보상은 전치부 및 구치부 전반에 걸쳐 일어나며, 현재 보편적으로 시행되고 있는 악교정수술을 위한 술전교정시 이를 제거하여 각 골격 구조내에서 치아들이 적절히 위치되도록 하여야 한다. 전치부 치성보상에 관한 측모 두부방사선 사진을 이용한 연구는 많이 시행되어졌으나, 구치부 경사도에 관한 연구는 미미 한 실정이다. 이에 본 연구는 성인 골격성 III급 부정교합자의 전후방적, 수직적 악골 부조화에 따른 폭경 부조화 및 구치 경사도 변화를 알아보기 위해 진단 모형상에서 상하악 견치, 제1소구치, 제1대구치 부위의 기저골 폭경을 측정하여 상악에 대한 하악의 비율을 구하였으며, 모형 을 삭제하여 좌우 구치간 경사도를 측정하였다. 악골 부조화 심화에 따른 기저골 폭경 비율과 제1대구치 협설 경사도 변화의 상관관계를 조사하여 다음과 같은 결론을 얻었다. 1. 골격성 III급 부정교합자의 악골의 전후방적 부조화가 심화될수록 상하악 구치간 각도합이 증가하여 치성보상이 많이 일어났으며, 특히 하악 구치가 설측 경사되는 치성보상을 보였다(p<0.001). 2. 골격성 III급 부정교합자의 악골의 수직적 부조화 및 폭경 부조화와 구치부 치성보상 간에는 유의할만한 상관성이 없었다. 3. 골격성 III급 부정교합자의 전후방적, 수직적 부조화의 심화와 기저골 폭경 부조화는 유의할만한 상관성이 없었다.

• Steel and Composite Structures
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• 제9권4호
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• pp.381-395
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• 2009

This paper presents the details of an advanced Finite Element (FE) analysis of a plane steel portal frame with semi-rigid beam-to-column connections subjected cyclic loading. In spite of several component models on cyclic behaviour of connections presented in the literature, works on numerical investigations on cyclic behaviour of full scale frames are rather scarce. This paper presents the evolution of an FE model which deals comprehensively with the issues related to cyclic behaviour of full scale steel frames using ABAQUS software. In the material modeling, combined kinematic/isotropic hardening model and isotropic hardening model along with Von Mises criteria are used. Connection non-linearity is also considered in the analysis. The bolt slip which happens in friction grip connection is modeled. The bolt load variation during loading, which is a pivotal issue in reality, has been taken care in the present model. This aspect, according to the knowledge of the authors, has been first time reported in the literature. The numerically predicted results using the methodology evolved in the present study, for the cyclic behaviour of a cantilever beam and a rigid frame, are validated with experimental results available in the literature. The moment-rotation and deflection responses of the evolved model, match well with experimental results. This proves that the methodology for evolving the steel frame and connection model presented in this paper is closer to real frame behaviour as evident from the good comparison and hence paves the way for further parametric studies on cyclic behaviour of flexibly connected frames.

• 한국전자파학회논문지
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• 제10권4호
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• pp.582-593
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• 1999

본 논문에서는 무궁화 III호 위성체용 Ka-밴드 다이플렉서의 설계를 위해 모드매칭법에 의해 산란행렬을 계산하여 설계한 필터의 전달특성을 분석하고, 대칭적 유도성 아이리스 구조와 전계면 금속삽입 구조로 설계된 2개의 대역통과 필터를 자계면 T-접합에 의한 합성방법으로 Ka 밴드 위성체용 다이플렉서를 설계, 제작 하여 그 설계 방법에 대한 타당성 여부를 검증하였다 제작된 다이플렉서는 위성체에서 송.수선 펼터의 개별 사용에 따른 크기 및 무게의 증가를 효과적으로 감소시킬 수 있으며, 송선필터의 경우 아이리스를 도파관 자계변 외벽으로 돌출시키는 구조로 설계함으로써 펼터 자체가 방열판 구실을 하여 고전력 전송에 따른 펼터 의 특성 변화를 최소화하였다. 또한 대부분의 도파관 펼터에서 동작특성을 보정하기 위해 사용되는 미세 보정 나사의 사용을 배제함으로써 제작의 단순화와 위성체용으로서의 내구성과 선뢰도를 향상시켰다. 제작된 Ka-밴드 위성체용 다이플렉서는 2개의 펼터(Rx : $30.485\pm0.4 GHz$, Tx : $20.755\pm0.4 GHz$) 모두 통과대역에 서 1.2 dB 미만의 삽입손실(insertion loss)과 15dB 보다 좋은 반사손실(return loss) 특성을 얻었고, 송.수신 필터간 65dB 이상의 분리도(isolation)를 나타내었다.