• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2005년도 추계학술대회 논문집
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• pp.135-140
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• 2005

항만과 해역에 설치되는 수직벽의 일례로 육상 및 유입되는 오염수의 오염 유출 방지를 위한 차수기능을 갖는 차수벽과 교량이나 댐, 갑문 둥의 하천 또는 해양구조물을 축조하는 동안 물이 들어오는 것을 방지하기 위하여 임시로 설치되는 가물막이(cofferdam)벽 등이 있다 이들 차단벽의 구조역학적인 설계 인자 중 유입수 유동 특성과 설치 지역의 지반 특성이 중요한 의미를 가진다고 판단된다. 본 연구에서는 이러한 수직 차단벽 주위의 유체역학적 특성 파악의 일례로 수직벽의 하단에 틈새를 갖는 파공(perforation)이 발생하였을 때 이들 파공의 개도율 변화에 따른 유동특성을 고찰하는 하나의 방안으로 입자영상유속계(Particle Image Velocimetry)를 이용하여 수직벽 후류 특성을 실험적으로 고찰하였다.

• 한국항공우주학회지
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• 제37권2호
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• pp.139-146
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• 2009

능동 비틀림 제어기법을 이용한 복합재료 로터 블레이드의 헬리콥터 진동억제에 대한 수치연구를 수행하였다. 허브에 작용하는 진동하중 억제를 위해 복합재료 블레이드의 탄성 연계와 함께 압전 소재의 전단변형 메커니즘을 이용하였다. 로터 블레이드는 표면에 압전 작동기를 부착한 박벽 상자형 단면을 갖는 복합재료 보로 모델링하였다. 회전익에 대한 지배 운동방정식은 Hamilton 원리를 이용하여 구성하였고, 공력하중은 자유후류모델을 포함하는 비정상 공력 이론을 이용하여 구했다. 다양한 탄성연계 적층과 능동 작동기를 부착한 복합재료 블레이드에 대해 허브진동 하중 특성을 고찰하였다. 수치해석 결과 최적 제어 알고리듬을 적용하여 $N_b$/rev 진동하중을 대폭 줄일 수 있음을 보였다.

• 스마트미디어저널
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• 제8권4호
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• pp.38-45
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• 2019

회전익 드론의 후류에서 발생하는 강한 유동과 살포되는 농약 노즐에서의 스프레이 유동이 동반될 경우, 극심한 기체의 요동과 함께 액적 유동은 바람의 영향을 크게 받게 된다. 특히 액적은 공기역학적인 항력의 영향을 받기 때문에 단순한 제자리 비행과는 달리 전진 비행을 할 경우 또는 측풍을 받고 있을 경우, 살포 영역에 큰 변화가 발생한다. 이로 인하여 드론을 활용한 농약살포에는 보다 큰 비산의 위험성이나 위치간의 낙하분산에 차이가 커져 효율성이 떨어질 수 있는 문제가 생긴다. 따라서 적절한 수치 모델링과 이를 적용한 전산 시뮬레이션을 통하여 다양한 비행 및 대기 조건을 적용할 수 있는 예측 도구가 필요하다. 본 연구에서는 로터에서 나오는 강한 하풍과 드론의 비행속도에 따른 액적 유동 특성에 대해 실험 및 수치해석을 진행하였으며, 액적이 분포하는 확률밀도함수를 구하여 서로 비교함으로써 농약살포용 드론에서 액적을 살포할 시 효율성을 증진시킬 수 있는 분사 시스템을 구축하고자 한다.

• 한국항해항만학회지
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• 제32권6호
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• pp.453-458
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• 2008

원형실린더에 크기가 다른 제어봉을 부착하여 2차원 단면 유통특성에 대해서 시간평균유동장을 계측하여 근접후류 제어에 관하여 PIV기법을 적용하여 연구를 수행하였다. 모델시험은 각각 크기가 다른 제어봉을 적용하였으며($d/D=0.1{\sim}d/D=0.5$) 레이놀즈수는 원형실린더의 직경을 기준으로 Re=15,000으로 적용하였다. 유동장의 속도분포론 획득하기 위해 2프레임 상호상관법을 이용하였다. 실험에 적용된 원형실린더(D=50mm)에 제어봉을 부착한 결과를 상호 비교함으로서 시간평균속도분포와 제어봉에 의한 유동제어 효과를 알 수 있었다.

• Journal of Ship and Ocean Technology
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• 제10권4호
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• pp.1-11
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• 2006

The finite volume based multi-block RANS code, WAVIS developed at MOERI is applied to the numerical self-propulsion test. WAVIS uses the cell-centered finite volume method for discretization of the governing equations. The realizable $k-{\epsilon}$ turbulence model with a wall function is employed for the turbulence closure. The free surface is captured with the two-phase level set method and body forces are used to model the effects of a propeller without resolving the detail blade flow. The propeller forces are obtained using an unsteady lifting surface method based on potential flow theory. The numerical procedure followed the self-propulsion model experiment based on the 1978 ITTC performance prediction method. The self-propulsion point is obtained iteratively through balancing the propeller thrust, the ship hull resistance and towing force that is correction for Reynolds number difference between the model and full scale. The unsteady lifting surface code is also iterated until the propeller induced velocity is converged in order to obtain the propeller force. The self-propulsion characteristics such as thrust deduction, wake fraction, propeller efficiency, and hull efficiency are compared with the experimental data of the practical container ship. The present paper shows that hybrid RANS and potential flow based numerical method is promising to predict the self-propulsion parameters of practical ships as a useful tool for the hull form and propeller design.

• 한국항공우주학회지
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• 제47권2호
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• pp.81-89
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• 2019

본 연구는 쿼드 틸트 프로펠러(Quad Tilt Propeller)형상의 탠덤날개 항공기의 전진비행 조건을 풍동실험하여 전방 날개 및 프로펠러가 후방날개에 작용하는 공력 간섭효과를 분석하였다. 6축 밸런스시스템을 이용해 전기체의 힘을 측정하였고 날개뿌리에 부착된 스트레인게이지를 이용하여 각 날개의 굽힘모멘트를 측정하였다. 12홀 프로브를 이용해 날개 및 프로펠러 후류의 유동장을 측정하였으며, 털실과 스모크를 이용한 유동가시화 실험을 통해 유동 특징을 정성적으로 확인하였다. 요소별 공력간섭 현상을 측정하기 위해 프로펠러 부착 조합을 바꿔가며 전방날개와 프로펠러가 후방날개에 작용하는 영향을 분석하였다.

• Applied Microscopy
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• 제49권
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• pp.3.1-3.7
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• 2019

Graphene, which is one of the most promising materials for its state-of-the-art applications, has received extensive attention because of its superior mechanical properties. However, there is little experimental evidence related to the mechanical properties of graphene at the atomic level because of the challenges associated with transferring atomically-thin two-dimensional (2D) materials onto microelectromechanical systems (MEMS) devices. In this study, we show successful dry transfer with a gel material of a stable, clean, and free-standing exfoliated graphene film onto a push-to-pull (PTP) device, which is a MEMS device used for uniaxial tensile testing in in situ transmission electron microscopy (TEM). Through the results of optical microscopy, Raman spectroscopy, and TEM, we demonstrate high quality exfoliated graphene on the PTP device. Finally, the stress-strain results corresponding to propagating cracks in folded graphene were simultaneously obtained during the tensile tests in TEM. The zigzag and armchair edges of graphene confirmed that the fracture occurred in association with the hexagonal lattice structure of graphene while the tensile testing. In the wake of the results, we envision the dedicated preparation and in situ TEM tensile experiments advance the understanding of the relationship between the mechanical properties and structural characteristics of 2D materials.

• Clinical and Experimental Emergency Medicine
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• 제5권4호
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• pp.240-248
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• 2018

Objective Determine differences between faculty, residents, and nurses regarding night shift preparation, performance, recovery, and perception of emotional and physical health effects. Methods Survey study performed at an urban university medical center emergency department with an accredited residency program in emergency medicine. Results Forty-seven faculty, 37 residents, and 90 nurses completed the survey. There was no difference in use of physical sleep aids between groups, except nurses utilized blackout curtains more (69%) than residents (60%) and faculty (45%). Bedroom temperature preference was similar. The routine use of pharmacologic sleep aids differed: nurses and residents (both 38%) compared to faculty (13%). Residents routinely used melatonin more (79%) than did faculty (33%) and nurses (38%). Faculty preferred not to eat (45%), whereas residents (24%) preferred a full meal. The majority (>72%) in all groups drank coffee before their night shift and reported feeling tired despite their routine, with 4:00 a.m. as median nadir. Faculty reported a higher rate (41%) of falling asleep while driving compared to residents (14%) and nurses (32%), but the accident rate (3% to 6%) did not differ significantly. All had similar opinions regarding night shift-associated health effects. However, faculty reported lower level of satisfaction working night shifts, whereas nurses agreed less than the other groups regarding increased risk of drug and alcohol dependence. Conclusion Faculty, residents, and nurses shared many characteristics. Faculty tended to not use pharmacologic sleep aids, not eat before their shift, fall asleep at a higher rate while driving home, and enjoy night shift work less.

• The Korean Journal of Pain
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• 제34권2호
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• pp.241-245
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• 2021

Background: It has been reported that a new type of headache may develop as a result of face mask use during the COVID-19 pandemic. The aim of this study is to investigate the clinical features of face mask-related headache during the COVID-19 pandemic. Methods: This is a cross-sectional study carried out on healthcare workers at the Afyonkarahisar Health Sciences University. The number of workers at our university was established. Sample size was calculated using the G*Power program. A questionnaire consisting of questions relating to pre-existing headache, an aggravation in headache, and de-novo headache was filled out by 3 neurologists with all participants. Results: Data was collected from a total of 375 participants, after the exclusion of 5 individuals who refused to participate. Out of all participants, 26 (6.9%) used a filtering mask, 274 (73.1%) used a surgical mask, 75 (20.0%) participants used a combination of both masks. The number of participants with preexisting headache was 114 (30.4%) had pre-existing headache. Of those with pre-existing headache, 77 (67.5%) healthcare workers had reported an aggravation in their headache after mask use. De-novo headache was observed in 116 (30.9%) of participants. De-novo headache characteristics included throbbing in 17 (14.7%) participants and pressing in 99 (85.3%) participants. In addition, symptoms such as tachypnea, sleep disturbance, and fatigue were found to be significantly higher. Conclusions: This study indicates that healthcare workers develop headaches due to use of masks during the COVID-19 outbreak.

• 한국입자에어로졸학회지
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• 제17권4호
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• pp.81-89
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• 2021

Understanding particle-laden flow around cylindrical bodies is essential for the better design of various applications such as filters. In this study, laminar flows around two tandem cylinders and the motions of particles in the flow are numerically investigated at low Reynolds numbers. We aim to reveal the effects of the spacing between cylinders, Reynolds number and particle Stokes number on the characteristics of particle trajectories. When the cylinders are placed close, the unsteady flow inside the inter-cylinder gap at Re = 100 shows a considerable modification. However, the steady recirculation flow in the wake at Re = 10 and 40 shows an insignificant change. The change in the flow structure leads to the variation of particle dispersion pattern, particularly of small Stokes number particles. However, the dispersion of particles with a large Stokes number is hardly affected by the flow structure. As a result, few particles are observed in the cylinder gap regardless of the cylinder spacing and the Reynolds number. The deposition efficiency of the upstream cylinder shows no difference from that of a single cylinder, increasing as the Stokes number increases. However, the deposition on the downstream cylinder is found only at Re = 100 with large spacing. At this time, the deposition efficiency is generally small compared to that of an upstream cylinder, and the deposition location is also changed with no deposited particles near the stagnation point.