• 한국항행학회논문지
• /
• 제18권1호
• /
• pp.7-13
• /
• 2014

본 논문에서는 GPS 전파 간섭 신호의 한 종류인 기만 신호를 검출하는 기법을 제안한다. 본 논문에서 기만의 대상이 되는 신호에는 민간에 구조가 공개된 GPS L1 C/A 신호로 선정하였으며 GPS L1 C/A 기만 신호의 영향을 분석하고 이를 통해서 기만 신호 검출 기법을 제안한다. 제안하는 기만 신호 검출 기법은 상관함수가 왜곡된 정도로 기만 신호의 인가를 판단한다. 기만 신호의 판단기준은 수신기 열잡음의 통계적 특성으로부터 정량적인 수치로 계산된 임계값을 이용하였다. 제안하는 기법을 검증하기 위한 시뮬레이션은 MATLAB을 기반으로 구성하였으며 기만 신호에 의한 상관함수 왜곡 및 코드 위상 오차를 확인하였다. 그리고 본 논문에서 제안하는 기만 신호 검출 기법을 적용하여 기만 신호의 검출 시뮬레이션을 수행하여 제안하는 기법에 의한 기만 신호 검출성능을 확인하였다.

• 대한조선학회논문집
• /
• 제58권1호
• /
• pp.17-23
• /
• 2021

The membrane-type Liquefied Natural Gas (LNG) cargo tank is equipped with a double barrier to seal the LNG, of which the secondary barrier serves to prevent LNG leakage and mainly uses fiber-reinforced composite materials. However, the composite materials have thermal expansion anisotropy, which deteriorates shape distortion and mechanical performance due to repeated thermal loads caused by temperature changes between cryogenic and ambient during the unloading of LNG. Therefore, in this study, the longitudinal thermal expansion characteristics of the composite materials were obtained using a vertical thermo-mechanical analyzer, and the elastic modulus was obtained through the tensile test for each temperature to perform thermal load analysis for each direction. This is considered that it is useful to secure reliability from the viewpoint of the design of materials for a LNG cargo hold.

• 한국산업융합학회 논문집
• /
• 제7권1호
• /
• pp.55-62
• /
• 2004

The presence of cutting fluid for cutting tool and workpiece leads a temperature decrease, and reduces tool wear and residual stress. Moreover, it disposes chips from cutting area, and reduces thermal distortion. However, in manufacturing, cutting fluid used in cutting process is undesirable for both human and environmental aspect. Also, it's not economic for cutting cost. This paper studied experimentally the effects of cutting parameters on the characteristics of mist generation in turning. The results of experiment are as follows: 1) The more severe cutting conditions the more mist generate, 2) The ratio of weight concentrations of cutting fluid nearly have no an effect on the amounts of mist generation 3) The size of SMD is not affected by cutting parameters.

• 항공우주시스템공학회지
• /
• 제2권2호
• /
• pp.28-34
• /
• 2008

This paper describes the performance characteristics of flow and structure in the post-chamber and nozzle. Using the computational fluid dynamics (CFD) technique, the stress and compressible flow fields in the downstream of the post chamber and nozzle were numerically calculated. Besides, the stress characteristics at the wall of post-chamber and nozzle were investigated under different thickness (2mm, 5mm and 10mm) of the nozzle wall. The stress pattern demonstrates that the strength of nozzle wall having 10mm is safer than that of 5mm or 2mm according to von Mises stress irrespective to the pressure field

• 한국가스학회지
• /
• 제8권3호
• /
• pp.8-15
• /
• 2004

본 논문은 내부탱크 바닥판의 중심부에서 바닥판의 가장자리인 코너부로 연결되는 반경 방향의 거리를 따라서 바닥판에 걸리는 von Mises 응력, 변위량, 회전 뒤틀림 모멘트를 나타내고 있다. 계산결과에 의하면 내부탱크를 냉각하는 초기과정에서 LNG의 충진율, 즉 LNG와 직접 접촉하는 반경방향 거리는 내부탱크의 바닥판에 대하여 중요한 영향을 미치게 된다. 내부탱크에 공급된 $-162^{\circ}C$의 액상 LNG와 내부에서 증발된 $-80^{\circ}C$의 LNG 가스가 내부탱크의 바닥판과 환상판, 측벽면 등에 접촉하면서 온도차 하중에 의한 열적거동 특성을 위치에 따라 서로 다르게 보여주고 있다. 유한요소해석 결과로부터, LNG의 증발가스와 초저온 액체($-162^{\circ}C$)에 의한 온도차는 바닥판의 열적 불안정성을 일으키는 원인으로 작용하며, 이러한 열적 뒤틀림 현상은 내부탱크 시스템의 안전성을 위협할 수도 있다.

• Nuclear Engineering and Technology
• /
• 제53권12호
• /
• pp.3918-3929
• /
• 2021

In this study, we experimentally investigate of a two-phase natural circulation loop that functions as a passive containment cooling system (PCCS). The experimental apparatus comprises two loops: a hot loop, for simulating containment under severe accidents, and a natural circulation loop, for simulating the PCCS. The experiment is conducted by controlling the pressure and inlet temperature of the hot loop in the range of 0.59-0.69 MPa (abs) and 119.6-158.8 ℃, respectively. The heat balance of the hot loop is established and compared with a natural circulation loop to assess the thermal reliability of the experimental apparatus, and an additional system is installed to measure the vapor mass flow rate. Furthermore, the thermal-hydraulic characteristics are considered in terms of a temperature, mass flow rate, heat transfer coefficient (HTC), etc. The flow rate of the natural circulation loop is induced primarily by flashing, and a distortion is observed in the local HTC because of the fully develop as well as subcooled boiling. As a result, we present the amount of heat capacity that the PCCS can passively remove according to the experimental conditions and compared the heat transfer performance using Chen's and Dittus-Boelter correlation.

• 천문학회보
• /
• 제46권1호
• /
• pp.38.3-38.3
• /
• 2021

We are developing an optomechanical design of infrared telescope for the CubeSat and Unmanned Aerial Vehicle (UAV) which adapts the Linear Astigmatism Free- Three Mirror System in the confocal off-axis condition. The small entrance pupil (diameter of 40 mm) and the fast telescope (f-number of 1.9) can survey large areas. The telescope structure consists of three mirror modules and a sensor module, which are assembled on the base frame. The mirror structure has duplex layers to minimize a surface deformation and physical size of a mirror mount. All the optomechanical parts and three freeform mirrors are made from the same material, i.e., aluminum 6061-T6. The Coefficient of Thermal Expansion matching single material structure makes the imaging performance to be independent of the thermal expansion. We investigated structural characteristics against external loads through Finite Element Analysis. We confirmed the mirror surface distortion by the gravity and screw tightening, and the overall contraction/expansion following the external temperature environment change (from -30℃ to +30℃).

• 한국레이저가공학회지
• /
• 제15권1호
• /
• pp.10-14
• /
• 2012

Pulse laser welding was performed on C22 metal bellows. The results can be summarized as follows: Laser welded metal bellows had less thermal distortion, narrow HAZ, high aspect ratio in comparison with other welding processes like TIG, Plasma welding. Laser welded bellows has higher tensile strengths than that C22 base metal. The value of hardness in laser weld metal was measured 100-120 Hv, it was decreased compared to the base metal. It is reasoned that due to the annealed by heat input during the laser welding.

• 한국레이저가공학회지
• /
• 제1권1호
• /
• pp.11-17
• /
• 1998

The electron beam welding system has the advantages of the high power density, narrow welding section, and small thermal distortion of a workpiece. Recently, the electron beam welding system is widely used to the airplane engineering, nuclear power plant, and automobile industry. In the present paper, the structural analyses on the vacuum chamber of the electron beam welding system are performed by the F.E.M. analysis. The stiffening characteristics on the geometric shape, stiffener height and stiffener span are investigated. The deflection of the stiffened vacuum chamber under pressure is minimized by longitudinal and transverse stiffeners which are continuous in both direction.

• 한국진공학회지
• /
• 제4권1호
• /
• pp.12-17
• /
• 1995

Diamondlike carbon(DLC)films having good characteristics in mechanical and optical properties, were synthesized by rf-plasma enhanced chemical vapor deposition method. Methane, methane-hydrogen, or methane-argon were used as source gases. The infrared transparency and composition of the films were investigate. Especially, the anti-reflection effect of KLC film in infrared region was confirmed by depositing it on Ge/Si sample. When DLC films were deposited on the plastic substrates and thermal distortion, which were originated before and during deposition, respectively, played a role as a crack source of the films.