• 한국군사과학기술학회지
• /
• 제17권3호
• /
• pp.304-310
• /
• 2014

Based on atmosphere weather data by balloon in Osan and Gwangju area, if icing condition occurs in weather environment of altitude range where helicopter is operated was analyzed in quantitative way. Yearly icing occurrence frequency for daytime during recent three years was average 102 days in Osan, average 91 days in Gwangju. Icing weather environment to highly affect operation of helicopter varies a little according to analysis methods but icing intensity at MDT level was calculated in all the methods, and 14.5~38 times was suggested in Osan; 2.5~30 times in Gwangju. Icing at MDT level was calculated in common in all the analysis methods through wide periods such as Jan., Feb., Mar., and Nov. in Osan. In Gwangju, icing at MDT level was suggested focusing on Jan. only. Therefore, military helicopter developed in Korea is required to strive obtaining certificate of airworthiness about icing condition at MDT level for implementation of perfect operational mission and safe operation.

• 한국위성정보통신학회논문지
• /
• 제9권3호
• /
• pp.104-108
• /
• 2014

한국형발사체의 표면에 장착되는 UHF-대역 안테나의 표면에 발생하는 결빙을 모델링하고, 이러한 결빙이 안테나의 공진주파수, 반사손실 및 방사패턴 등의 주요 특성에 미치는 영향을 분석하였다. 안테나 표면결빙을 모델링하기 위해 $-180^{\circ}C$의 얼음층에 대한 비유전율을 추출하였고 추출된 비유전율을 이용하여 안테나 표면결빙 모델을 제안하였다. 중심주파수가 UHF-대역인 안테나 표면에 1mm의 결빙이 되었을 경우의 표면결빙 모델을 적용하여 시뮬레이션 한 결과, 표면결빙에 의해 안테나의 공진주파수가 21MHz 하향 되었고, 방사패턴도 전 방향에 대해 전체적으로 10dB 이상의 성능저하가 발생되었다. 따라서 실제 안테나 표면에 결빙이 발생할 경우 안테나 성능에 심각한 영향을 미칠 것으로 판단된다.

• Archives of Metallurgy and Materials
• /
• 제65권3호
• /
• pp.1011-1014
• /
• 2020

Ice formed on radome surfaces causes communication disruption due to radio-frequency interference (RFI), which reveals the importance of de-icing systems for radomes. As a radome de-icing application, in this work, carbon nanotube (CNT) thin films were fabricated using a spray-coating method, and influence of process parameters on RF transmittance and electrothermal properties was investigated. With the increase of spraying time, sheet resistance of the fabricated film decreases, which results in a decrease of the RF transmittance and improvement of the heating performance. Also, the de-icing capability of the fabricated CNT film was evaluated at -20℃, and efficient removal of ice under cold conditions was demonstrated.

• Journal of Advanced Marine Engineering and Technology
• /
• 제25권5호
• /
• pp.1051-1057
• /
• 2001

In this paper, we deal with three types of modelling method for the analysis of galloping in power transmission line (PTL). The single mass model is obtained under linearization method and it is applied into f-order model. On these models, the nature frequencies of PTL are obtained and it makes an effects on the galloping directly. In simulation, we verify that the maximum magnitude of nature frequency depends on the galloping distance of PTL. Also from the analysis of frequency response, a few of reduction method for galloping are introduced which is effected by distance of PTL, wind velocity and icing types.

• 콘크리트학회논문집
• /
• 제15권4호
• /
• pp.606-614
• /
• 2003

본 연구는 서울시에 위치한 콘크리트 교량 바닥판의 제빙화학제로 인한 열화속도를 추정하기 위하여 제빙화학제 사용현황을 조사하고 실구조물 조사에 의한 표면 염소이온량 누적정도와 염소이온 확산계수의 확률 분포적 특성을 고려하여 국내 환경에 적합한 내구수명 예측을 수행하였다. 연구결과, 무작위성을 나타내는 표면 염소이온량과 염소이온 확산계수는 각각 규모매개변수 0.192, 29.828, 형상매개변수 7.899, 1.983을 갖는 gamma 분포가 형성되었다. 표면 염소이온량은 평균 1.5kg/㎥이며 약70%의 확률수준에서 1∼2kg/㎥까지 농축되었다. 본 연구결과를 종합하여 볼 때 콘크리트 교량 바닥판의 설계내구수명이 20년 이상이 되려면 필요한 피복두께는 최소 26mm 이상으로 시공되어야 하며 고내구성 콘크리트로 타설하여 염소이온 확산계수를 감소시키는 것이 유효할 것으로 판단된다.

• 한국항공운항학회지
• /
• 제18권3호
• /
• pp.34-41
• /
• 2010

'Aviation Safety' is the state in which the risk of harm to persons or of property damage is reduced to, and maintained at or below, an acceptable level through a continuing process of hazard identification and risk management in the aviation field. 'Risk' is the assessed potential for adverse consequences resulting from a hazard and 'Risk assessment' involves consideration of both the frequency and the severity of any adverse consequence. This study focused on the risk frequency about a case airport which does not meet the 'Runway end safety area' requirement of ICAO SARPs and Korea standards and used 'RSA risk model' for estimating the risk frequency. As results of this study, risk frequency of the runway end safety areas in the case airport is higher than that of 'Runway end safety area' requirement of ICAO SARPs and Korea standards, which means that alternatives for risk frequency mitigation to a level as low as reasonably practicable is required in the case airport. The optimum solution analysed from this study is to impose restriction of aircraft operation when the runway condition is poor(icing condition) and also it snows in the case airport.

• Wind and Structures
• /
• 제18권2호
• /
• pp.135-154
• /
• 2014

Aerodynamic characteristics of crescent and D-shape bundled conductors were measured by high frequency force balance technique in the wind tunnel. The drag and lift coefficients of each sub-conductor and the whole bundled conductors were presented under various attack angles of wind. The galloping possibility of bundled conductors is discussed based on the Den Hartog criterion. The influence of icing thickness, initial ice accretion angle and sub-conductor on the aerodynamic properties were investigated. Based on the measured aerodynamic force coefficients, a computationally efficient finite element method is also implemented to analyze galloping of iced bundled conductors. The analysis results show that each sub-conductor of the bundled conductor has its own galloping feature due to the use of aerodynamic forces measured separately for every single sub-conductors.

• 대한전기학회논문지
• /
• 제41권4호
• /
• pp.339-345
• /
• 1992

Estimates of maximum amplitudes of conductor galloping are needed in order to determine appropriate phase-to-phase clearances on the overhead lines. One approach to obtaining these estimates is through the use of mathematical models of conductor galloping. Unfortunately, the models that consider both vertical conductor motion (Den Hartog type) and torsional conductor motion are often too complex for practical use. However, the estimates of maximum amplitude obtained from galloping models that assume only vertical (Den Hartog type) conductor motion tend to be too conservative. This paper presents the DF method to obtain the estimates of the amplitude and the frequency of galloping limit cycle, along with the wind pressure at which they occur, from a nonlinear dynamic model that considers both Den Hartog type and torsional conductor motion. From these results, the useful data for the line design guide and further insight into the mechanism of the conductor galloping are obtained.

• Wind and Structures
• /
• 제22권2호
• /
• pp.253-272
• /
• 2016

The paper concerns with the method and results of wind tunnel investigations of the Strouhal number (St) of a stationary iced cable model of cable-supported bridges with respect to different angles of wind attack. The investigations were conducted in the Climatic Wind Tunnel Laboratory of the Czech Academy of Sciences in $Tel{\check{c}}$. The methodology leading to the experimental icing of the inclined cable model was prepared in a climatic section of the laboratory. The shape of the ice on the cable was registered by a photogrammetry method. A section of an iced cable model with a smaller scale was reproduced with a 3D printing procedure for subsequent aerodynamic investigations. The St values were determined within the range of the Reynolds number (Re) between $2.4{\cdot}10^4$ and $16.5{\cdot}10^4$, based on the dominant vortex shedding frequencies measured in the wake of the model. The model was oriented at three principal angles of wind attack for each of selected Re values. The flow regimes were distinguished for each model configuration. In order to recognize the tunnel blockage effect the St of a circular smooth cylinder was also tested. Good agreement with the reported values in the subcritical Re range of a circular cylinder was obtained. The knowledge of the flow regimes of the airflow around an iced cable and the associated St values could constitute a basis to formulate a mathematical description of the vortex-induced force acting on the iced cable of a cable-supported bridge and could allow predicting the cable response due to the vortex excitation phenomenon.

• 대한정형외과학회지
• /
• 제55권2호
• /
• pp.117-126
• /
• 2020

슬관절의 퇴행성 관절염에서 슬관절 전치환술은 널리 시행되고 있고 그 빈도도 점점 증가되고 있다. 수술 후 일상생활로의 복귀, 근력 및 운동범위의 회복 등 기능 회복을 위한 노력이 이루어져야 하고 이는 환자 요인, 수술 술기 및 재활 등 다양한 관점에서 접근해야 한다. 환자의 연령이나 비만의 정도, 성별, 대퇴사두근의 근력 등이 수술 후 기능 회복에 영향을 줄 수 있고 환자의 기대치나 만족도 같은 정신적인 상태도 영향을 준다. 기능 회복을 위하여 수술 전부터 환자교육 및 통증 조절, 대퇴사두근 근력의 강화 같은 치료를 시행할 수 있다. 수술 후 냉찜질 및 압박, 경피적 전기 신경 자극 치료, 신경근육 전기 자극 치료, 저주파 저강도 자기장 치료, 대퇴사두근의 근력운동, 관절범위 운동과 같은 물리치료도 적용할 수 있다. 최근에는 수중에서 근력과 균형감각을 회복시키는 수 치료도 점점 시행되는 추세이다. 이런 기능 회복을 위한 치료들은 수술 후 단기적으로만 시행될게 아니라 장기적으로 꾸준히 시행되는 것이 중요하며 술자는 환자의 상태나, 순응도, 사회적, 심리적 상황 등을 고려하여 적절히 적용하여야 한다.