• 대한조선학회논문집
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• 제56권2호
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• pp.135-142
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• 2019

Ice accretions on the ship equipment and areas are the most common issues for vessels operating in cold climate and ice-covered waters and it has effect on the vessel safety and operability of equipment and systems, thus ship machineries and structures exposed to low temperature environments should satisfy the winterization requirements specified in ice class rules. The main objective of this study is to review the state-of-the-art of winterization trend for vessels navigating in ice-covered waters. The hazard of icing and how ice accretions affect operations and safety are investigated firstly, and then winterized notations for each classification are summarized. In addition, winterization methods currently used in vessels operating in ice-covered waters are investigated for a better understanding of effective approach and its application. This information will provide a framework for future winterization issues to mitigate the ice accretion phenomena.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2009년 춘계학술대회논문집
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• pp.27-30
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• 2009

The aerodynamic performance of aircraft in icing condition can deteriorate considerably by contamination of aerodynamic and propulsive systems due to icing accretions on aircraft surfaces. A computational analysis based on the Eulerian description was performed on an airfoil to investigate effects of ice accretions on airfoil aerodynamics. A water droplet with liquid water concentration ($0.00075kg/m^3$) and mean volume diameter ($20{\mu}m$) was considered and applied to various angles of attack to investigate the stall angle decrease and the drag increment.

• Wind and Structures
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• 제15권5호
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• pp.385-407
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• 2012

Bridge hanger vibrations have been reported under icy conditions. In this paper, the results from a series of static and dynamic wind tunnel tests on a circular cylinder representing a bridge hanger with simulated thin ice accretions are presented. The experiments focus on ice accretions produced for wind perpendicular to the cylinder at velocities below 30 m/s and for temperatures between $-5^{\circ}C$ and $-1^{\circ}C$. Aerodynamic drag, lift and moment coefficients are obtained from the static tests, whilst mean and fluctuating responses are obtained from the dynamic tests. The influence of varying surface roughness is also examined. The static force coefficients are used to predict parameter regions where aerodynamic instability of the iced bridge hanger might be expected to occur, through use of an adapted theoretical 3-DOF quasi-steady galloping instability model, which accounts for sectional axial rotation. A comparison between the 3-DOF model and the instabilities found through two degree-of-freedom (2-DOF) dynamic tests is presented. It is shown that, although there is good agreement between the instabilities found through use of the quasi-steady theory and the dynamic tests, discrepancies exist-indicating the possible inability of quasi-steady theory to fully predict these vibrational instabilities.

• Wind and Structures
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• 제23권3호
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• pp.253-273
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• 2016

Ice accretions on stay cables may result in the instable vibration of galloping, which would affect the safety of cable-stayed bridges. A large number of studies have investigated the galloping vibrations of transmission lines. However, the obtained aerodynamics in transmission lines cannot be directly applied to the stay cables on cable-stayed bridges. In this study, linear and nonlinear single degree-of-freedom models were introduced to obtain the critical galloping wind velocity of iced stay cables where the aerodynamic lift and drag coefficients were identified in the wind tunnel tests. Specifically, six ice shapes were discussed using section models with geometric scale 1:1. The results presented obvious sudden decrease regions of the aerodynamic lift coefficient for all six test models. Numerical analyses of iced stay cables associated to a medium-span cable-stayed bridge were carried out to evaluate the potential galloping instability. The obtained nonlinear critical wind velocity for a 243-meter-long stay cable is much lower than the design wind velocity. The calculated linear critical wind velocity is even lower. In addition, numerical analyses demonstrated that increasing structural damping could effectively mitigate the galloping vibrations of iced stay cables.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2011년 춘계학술대회논문집
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• pp.465-468
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• 2011

Ice accretion on aircraft surface can greatly deteriorate the safety of aircraft. In particular, it can be a cause of impediment for aircraft performances such as aerodynamic characteristics, control, and engine. Numerical simulation of icing accretion based on the state-of-art CFD techniques can be alternative to expensive icing wind tunnel test or flight test. In this study, icing conditions are defined in order to predict the ice accretions around the air intake of aircraft. Then the range and amount of ice accretion on the intake in icing wind tunnel were investigated In addition, a study on the size effect of icing wind tunnel was conducted in order to check the compatibility with the real in-flight test environment.

• 천문학회보
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• 제43권1호
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• pp.45.3-46
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• 2018

Although mass accretion from the disk to the central protostar is a key process of low mass star formation, the accretion mechanism is still poorly understood. To investigate "episodic accretion", which has been suggested as an accretion mechanism in low mass star formation, we have carried out near-infrared spectroscopic observations of three very low-luminosity objects (VeLLOs) and one background source, using InfraRed Camera onboard the AKARI space telescope. The ice absorption features of $H_2O$, $CO_2$, and CO were detected around the wavelengths of 3.0, 4.26, and $4.67{\mu}m$, respectively. In addition, we revealed the XCN ice feature, which is attributed to high energy UV photons produced by the episodic burst accretion. The comparisons of the ice abundances of our targets with those of other YSOs observed previously with AKARI IRC imply that the three VeLLOs had experienced burst accretions although they are now in a very quiescent phase.

• 한국항공우주학회지
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• 제42권2호
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• pp.134-143
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• 2014

추운 기후에서 운영되는 풍력터빈 시스템의 표면에 발생한 결빙으로 인하여 공기역학적 성능이 크게 저하될 수 있다. 이러한 결빙은 양력감소 및 항력증가를 야기하고, 발전효율에 부정적인 영향을 미치게 된다. 이로 인하여 풍력발전기의 성능저하 또는 과부하, 무게중심의 변화에 따른 과도진동, 결빙파편이 지상으로 떨어질 경우의 안전성 문제, 계기의 결빙으로 인한 계기 측정오차, 최악의 경우 풍력 시스템 정지 등의 문제가 발생한다. 본 연구에서는 결빙증식이 풍력 발전기의 공력특성에 미치는 영향을 CFD 기법을 이용해 분석하였다. 또한 결빙증식 결과를 바탕으로 BEM 기법을 적용시켜 삼차원 블레이드에 대한 공력성능을 계산하였다. 결빙의 두께는 상대적인 속도차이에 의해 블레이드 중심에서 끝단으로 갈수록 증가함을 알 수 있었고, 공기의 속도가 결빙증식에 미치는 주요 인자임을 확인하였다.

• 한국항공우주학회지
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• 제38권6호
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• pp.530-536
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• 2010

비행 중 대기조건에 의한 결빙은 항공기 안전성과 직결되며, 특히 항공기 표면 발생 결빙은 공력 특성 변화를 야기하여 제어면 성능을 저해하는 요소가 된다. KC-100 항공기의 결빙에 의한 공력 영향성 조사를 위해 결빙 전문 CFD 코드인 FENSAP-ICE를 이용하였다. 항공기의 공력 특성을 대표하는 주날개 단면 익형을 먼저 고려하고 다음으로 전기체형상에 대해 결빙 해석을 수행하였다. 또한 Anti-Icing 및 De-Icing 장치 설계를 위해 항공기 부품별 결빙 영역 및 결빙 증식 크기를 조사하였다. 결빙 영역은 주날개 및 수평 꼬리날개의 앞전에서 단면 코드길이 기준 약 7.07%, 11.2% 범위를 나타냈고, Wind Shield의 경우 약 16.7%에서 결빙이 발생하였다. 결빙에 의한 공력특성 변화의 경우, 받음각 0도에서 KC-100 항공기의 양력은 64.3% 감소한 반면 항력은 55.2% 증가하였다.

• 한국항공우주학회지
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• 제41권4호
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• pp.253-260
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• 2013

회전익기의 공기흡입구 주위 표면에 발생한 결빙은 엔진의 성능을 저해하는 요인으로 비행 안전성에 심각한 영향을 끼칠 수 있다. 항공기 표면에 발생하는 결빙현상을 분석하는데 많은 비용이 소요되는 결빙 풍동 시험 및 비행시험에 비해 전산유체역학을 기반으로 한 결빙 시뮬레이션은 매우 효과적인 도구가 될 수 있다. 본 연구에서는 결빙조건에서 회전익기 공기흡입구 부근에 설치된 방빙장치의 작동 유무에 따른 결빙의 양과 발생 영역을 CFD 예측기법 및 결빙 풍동시험을 통해 분석하였다. 방빙장치를 작동시킨 경우 공기 흡입구 표면에서의 결빙의 질량과 최대 두께가 약 80% 이상 감소하는 것을 확인하였다.