• 한국항공우주학회지
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• 제38권7호
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• pp.647-654
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• 2010

본 연구에서는 날갯짓 비행체 날개의 유체-구조 연계를 고려한 설계나 날갯짓 비행체의 비행 동역학 및 제어 시뮬레이션에 적용 가능한 효율적인 공력모델을 제안하고, 풍동 실험을 통해 공력모델의 특성을 검증하고자 한다. 날갯짓 비행체는 저 레이놀즈 수 영역의 비정상 유동장의 지배를 받기 때문에, 이 영역에서 날개 운동에 따른 공력을 효과적으로 측정할 수 있도록 풍동실험장치를 설계 및 개발하였다. 본 연구의 실험장치 특성상 힘을 측정하는 2축-로드셀은 비관성계에 있기 때문에, 순수한 날개의 공력을 측정하기 위해서는 관성력을 보정해주어야 하며, 이에 대한 방법론을 수립하였다. 최종적으로 유동속도, 날개의 운동 주파수 및 고정 받음각에 따라 날개에 작용하는 양력 및 항력의 평균값 및 평균 제곱근 값을 비교함으로서 실험결과와 공력모델의 특성을 비교 검증하였다.

• 한국산학기술학회논문지
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• 제19권2호
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• pp.302-310
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• 2018

본 연구는 청소년의 다문화 수용성의 영향을 미치는 요인들 사이의 관계를 확인하고 모델을 구축하기 위해 시도되었다. 이 연구는 2016 한국아동 청소년 패널조사(korean children and youth panel survey: kcps)의 자료 중 7차년도 자료를 이용하였으며, 청소년 본인 1881명 중 응답률이 불충분한 101명을 제외한 1780명을 최종 분석에 활용 하였다. 본 연구의 자료분석은 SPSS 22와 Amos Program 22를 이용하여 유의수준 .05 수준에서 분석하였으며, 대상자의 인구학적 특성과 연구변수의 특성을 파악하기 위해 기술 통계 분석(descriptive analysis)을 실시하였다. 가설적 모형의 적합도 검증 및 가설 검증은 최대우도법(maximum likelihood estimate)을 사용하였으며 모형 적합도 평가는 $X^2$ 통계량, GFI, AGFI, CFI, IFI, RMSEA를 이용하였다. 본 연구의 모형은 우수한 모델 적합도를 나타내었으며, 자아탄력성, 또래관계, 공동체 의식은 청소년의 다문화 수용성에 영향을 주는 요인임을 확인 할 수 있었다. 따라서 청소년의 다문화 수용성을 증진시키기 위해, 자아탄력성, 또래관계, 공동체 의식을 높일 수 있는 혼합형 중재가 필요할 것임을 제안한다.

• Steel and Composite Structures
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• 제34권5호
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• pp.699-713
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• 2020

The aerodynamic performance of long-span cable-stayed bridges is much dependent on its geometrical configuration and countermeasure strategies. In present study, the aerodynamic performance of three composite cable-stayed bridges with different tower configurations and passive aerodynamic countermeasure strategies is systematically investigated by conducting a series of wind tunnel tests in conjunction with theoretical analysis. The structural characteristics of three composite bridges were firstly introduced, and then their stationary aerodynamic performance and wind-vibration performance (i.e., flutter performance, VIV performance and buffeting responses) were analyzed, respectively. The results show that the bridge with three symmetric towers (i.e., Bridge I) has the lowest natural frequencies among the three bridges, while the bridge with two symmetric towers (i.e., Bridge II) has the highest natural frequencies. Furthermore, the Bridge II has better stationary aerodynamic performance compared to two other bridges due to its relatively large drag force and lift moment coefficients, and the improvement in stationary aerodynamic performance resulting from the application of different countermeasures is limited. In contrast, it demonstrates that the application of both downward vertical central stabilizers (UDVCS) and horizontal guide plates (HGP) could potentially significantly improve the flutter and vortex-induced vibration (VIV) performance of the bridge with two asymmetric towers (i.e., Bridge III), while the combination of vertical interquartile stabilizers (VIS) and airflow-depressing boards (ADB) has the capacity of improving the VIV performance of Bridge II.

• 대한조선학회논문집
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• 제36권3호
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• pp.41-49
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• 1999

초고속선의 추진기로 새로이 주목받고 있는 공기유입 물제트 추진기에 대한 타당성을 검토하였다. 본 추진기는 벤틸레이션 상태에서 작동되므로 완전캐비테이션 단면을 사용하여 로터를 설계하였다. 즉 쐐기형(wedge type) 단면과 캐비테이터형(cavitator type) 단면을 갖는 로터 2종류를 설계 제작하여 모형시험을 수행하였다. 로터는 일반적으로 덕트-프로펠러에서 채택하고 있는 Kaplan형 프로펠러 형상을 선택하였다. 캐비테이션 터널 시험부를 개조하여 공기유입 물제트 추진기의 단독특성시험을 수행하였으며, 레이져 유속계를 이용하여 노즐 내부 속도를 엄밀하게 계측하였다. 단독특성 시험은 개조된 캐비테이션 터널의 시험부에서 수행되었으며 완전침수(fully-submerged)상태와 자유분출(free-jet)상태에서 수행되었다. 자유분출상태에서는 후류공기가 유입되어 벤틸레이션 현상이 발생하였으며, 특히 캐비테이터형 단면을 갖는 KP447 로터의 경우 낮은 전진계수에서 작동시킬 경우 완전캐비테이션이 발생하여 성능특성이 크게 변화하였다. 날개 압력면의 뒷날 부근에 높이가 다른 띠를 각각 부착시켜 양력 증가장치로 사용하였으며 이에 의한 추력과 토오크 변화를 계측하였다.

• Journal of Advanced Marine Engineering and Technology
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• 제32권1호
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• pp.82-93
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• 2008

The flowfield behind two cylinders and flow-induced noise generated from the cylinders in various arrangement are numerically investigated based on the finite difference lattice Boltzmann model with 21 velocity bits. which is introduced a flexible specific heat ${\gamma}$ to simulate diatomic gases like air. In an isolated cylinder with two type of mesh. some flow parameters such as Strouhal number $S_t$ and acoustic pressure ${\Delta}p$ simulated from the solution are given and quantitatively compared with those provided the previous works. The effects of the center-to-center pitch ratio $L_{cc}/d=2.0$ in staggered circular cylinders as shown in Fig. 1 and angles of incidence ${\alpha}=30^{\circ}(T_{cc}/d=0.5)$, $45^{\circ}(T_{cc}/d =0.707)$ and $60^{\circ}\;(T_{cc}/d=0.866)$, respectively, are studied. Our analysis focuses on the small-scale instabilities of vortex shedding, which occurs in staggered arrangement. With the results of drag $C_d$ and lift $C_l$ coefficients and vorticity contours. the mechanisms of the interference phenomenon and its interaction with the two-dimensional vortical structures are present in the flowfields under $Re\;{\le}\;200$. The results show that we successively capture very small pressure fluctuations, with the same frequency of vortex shedding, much smaller than the whole pressure fluctuation around pairs of circular cylinders. The upstream cylinder behaves like an isolated single cylinder, while the downstream one experiences wake-induced flutter. It is expected that, therefore, the relative position of the downstream cylinder has significant effects on the flow-induce noise, hydrodynamic force and vortex shedding characteristics of the cylinders.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2003년도 추계학술대회 논문집
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• pp.39-42
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• 2003

Leading edge extension(LEX) in a highly swept shape applied to a delta wing features the modern air-fighters. The LEX vortices generated upon the upper surface of the wing at high angle of attack enhance the lift force of the delta wing by way of increased negative suction pressure over the surfaces. The present 3-D stereo PIV includes the Identification of 2-D cross-correlation equation, stereo matching of 2-D velocity vectors of two cameras, accurate calculation of 3-D velocity vectors by homogeneous coordinate system, removal of error vectors by a statistical method followed by a continuity equation criterion and so on. A delta wing model with or without LEX was immersed in a circulating water channel. Two high-resolution, high-speed digital cameras$(1280pixel\times1024pixel)$ were used to allow the time-resolved animation work. The present dynamic stereo PIV represents the complicated vortex behavior, especially, in terms of time-dependent characteristics of the vortices at given measuring sections. Quantities such as three velocity vector components, vorticity and other flow information can be easily visualized via the 3D time-resolved post-processing to make the easy understanding of the LEX effect or vortex emerging and collapse which are important phenomena occurring in the field of delta wing aerodynamics.

• 대한기계학회논문집A
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• 제35권5호
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• pp.487-494
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• 2011

LNG / LNG-FPSO선박에 사용되는 안전밸브는 배관 시스템으로부터 유체를 방출하여 시스템의 압력을 일정하게 유지시키는데 중요한 역할을 한다. 이러한 안전밸브의 기능적 특성으로 인해 유출계수는 밸브의 성능 중 가장 큰 비중을 차지하며, 선급의 인정을 받기 위해서는 0.8이상의 유출계수가 요구되고 있다. 밸브 성능을 향상시키기 위해서 밸브 내부에서 발생하는 유동특성에 대한 정확한 이해가 필요함에도 불구하고 대부분의 밸브 설계의 경우 현장 작업자들의 경험과 실험에 의한 시행착오에 의존하고 있다. 본 논문에서는 안전밸브에 대한 유동해석을 통해 밸브 내부에 발생하는 압축성 유동현상을 고찰하였고, 실험과 해석에 의한 유출계수를 비교하여 유동해석의 타당성을 검증하였으며, 안전밸브를 지나는 공기의 질량유량을 예측하기 위한 유동해석 모델을 확립하였다.

• 대한후두음성언어의학회지
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• 제11권1호
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• pp.51-60
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• 2000

Background and Objectives : Quality of life(QOL) is a construct representing physical, mental and social well-being. QOL has been used as a device for measuring the severity of health-related condition and treatment outcomes. As the social welfare system develops, the attention to QOL increases as well. The aims of this study was to examine whether the patients with voice disorder perceived significantly more the effects of voice disorder on QOL than nonpatient group did and if any, identify the sociodemographic risk factors influencing QOL of patients. Materials and Methods : This study asked 113 adults with voice disorders who were enrolled in Voice Clinic in the Department of Otolaryngology, Kangbuk Samsung Hospital between lune 1998 and January 1999 and 111 nonpatients to complete a questionnaire designed to elicit information about the effete of voice disorders on quality of lift. The questionnaire included items concerning sociodemographic areas, voice symptoms, job, effects of voice disorders on QOL domains(work, social, psychological, physical, and communication areas), potential risk factors to exposures, familial and medical history of voice disorders. Results : The sociodemographic characteristics of the patient group are as follows : (1) 75.2% of total patient group were female and the rest were male. (2) Age of total patient group ranged from 20 to 65 years. Hoarseness was the most commonly reported complaints, followed by complaints of high note difficulties during singing and voice fatigue. The patient group perceived effects of voice disorders on the areas of work, social, psychological, physical and communication more adversely than the comparison group did (p＜0.05). QOL impairments were evaluated as a function of age, gender, education, and income, controlling other independent effects. The results were that (1) age was significantly associated with work problems and (2) gender and income were significantly associated with psychological problems. Conclusions : The findings indicated that the patients with voice disorders would perceive markedly adverse effect on all QOL domains, that is, work, social, psychological, physical, communicational areas. Therefore, the results of study suggest that lurker investigations about the nature of voice disorders, the prevention, treatment, and coping strategies are needed in the future.

• 한국식품영양학회지
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• 제19권4호
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• pp.515-525
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• 2006

Survey was done to total 250 people to analyze characteristics of water quality in 5 widely used mineral water springs-(Teajosan(a), Leechungmukong(b), Onju(c), Yeongin(d), Crown(e))-in Chung-nam area and local mineral water usage. And the content of mineral and physico-chemical properties were compared in 5 sites. The largest users of mineral water spring was $40{\sim}50's$ of ages. Among those mineral water spring users, 52.5% had regular dietary habit and 32% showed improvement in lift habit after using mineral water spring. The mineral water spring users were engaged in student, housewife, professional, self-employed, etc. Those who were highly interested in health were likely to use mineral spring water more often regardless of age and occupation. Five mineral water springs differed in contents of mineral. The average content of minerals was $Ca\;28.5mg/{\ell},\;K\;1.5mg/{\ell},\;Mg\;5.3mg/{\ell},\;Na\;14.3mg/{\ell}$. 'K index' was an indicator of healthy water, and 'O index' was an indicator of tasty water. According to K indek and O index, waters of a b, c and e area were classified as 'tasty and healthy water', and water of e area had the highest values in both K and O index d area was classified as 'tasty water.'

• 한국전산유체공학회지
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• 제18권3호
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• pp.8-13
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• 2013

Drag reduction of a running vehicle is very important issue for the energy savings and emission reduction of its power train. Especially for a solar powered electric vehicle, the drag reduction and weight lightening are two serious problems to be solved to extend its driving distance under the given energy condition. In this study, the ground effect of an airfoil shaped road vehicle was studied for an optimum body design of an ultra-light solar powered electric vehicle. Clark-Y airfoil type was adopted to the body shape of the model vehicle to reduce aerodynamic drag. From the study, it was found that the drag of the model vehicle was reduced as the height(h) between ground and the lower surface of the model vehicle was decreased. It is due to the reduction of the down-wash decreasing the induced drag of the vehicle. The lift was also decreased as the height decreased. It is due to the turbulent boundary layer developed beneath the vehicle body. The drag is classified into two types; the form and friction drag. The fraction of form drag to friction one is 76 to 24 on the model vehicle. As the height(h) of the model vehicle from the ground surface increases the form drag also increases but the friction drag is in reverse.