• 한국지구과학회지
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• 제32권4호
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• pp.402-410
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• 2011

본 논문에서는 IRAS 07280-1829 적외선원과 이를 둘러싸고 있는 분자운에 대해 수행된 $^{12}CO$와 $^{13}CO$ 1-0 분자선 관측결과와 기존의 적외선 자료를 이용하여 이 적외선원의 생성환경에 관해 연구하였다. 관측자료로부터 얻어진 적외선원의 파장별 에너지분포의 기울기(${\alpha}$=1.16)와 복사온도(145 K), 그리고 광도(${\sim}2.9{\times}10^4L_{\odot}$)는 이 적외선 천체가 CLASS I형의 중량급원시성임을 의미한다. 이 적외선원방향에서 관측된 두 CO 분자선에서 보이는 넓은 속도 성분은 분자분출류의 존재를 암시한다. 적외선원을 감싸고 있으리라 짐작되는 분자운A에서 측정된 여기온도는 9-22 K, 질량은 약 ~180 $M_{\odot}$인 것으로 보아 이 분자운이 전형적인 적외선 암흑분자운(Infrared-dark clouds)의 물리적 특성을 가짐을 보았다. 이 분자운의 질량은 비리알 질량보다 10배 이상 작은 값으로 계산되었는데 이것은 여기에 어린 원시성이 이미 생성되고 있다는 관측사실에 모순된다. 이는 아마도 분자운A가 교란운동(turbulence) 혹은 강한 자기장에 의해 지배되는 환경 가운데에 중량급원시성 IRAS 07280-1829을 생성하고 있음을 의미하는 것 일수도 있는 것으로 해석하였다.

• Wind and Structures
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• 제23권5호
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• pp.465-483
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• 2016

This study aims to enhance the understanding of the surface pressure distribution around rectangular bodies, by considering aspects such as the suction pressure at the leading edge on the top and side faces when the body aspect ratio and wind direction are changed. We carried out wind tunnel measurements and numerical simulations of flow around a series of rectangular bodies (a cube and two rectangular bodies) that were placed in a deep turbulent boundary layer. Based on a modern numerical platform, the Navier-Stokes equations with the typical two-equation model (i.e., the standard $k-{\varepsilon}$ model) were solved, and the results were compared with the wind tunnel measurement data. Regarding the turbulence model, the results of the $k-{\varepsilon}$ model are in overall agreement with the experimental results, including the existing data. However, because of the blockage effects in the computational domain, the pressure recovery region is underpredicted compared to the experimental data. In addition, the $k-{\varepsilon}$ model sometimes will fail to capture the exact flow features. The primary emphasis in this study is on the flow characteristics around rectangular bodies with various aspect ratios and approaching wind directions. The aspect ratio and wind direction influence the type of wake that is generated and ultimately the structural loading and pressure, and in particular, the structural excitation. The results show that the surface pressure variation is highly dependent upon the approaching wind direction, especially on the top and side faces of the cube. In addition, the transverse width has a substantial effect on the variations in surface pressure around the bodies, while the longitudinal length has less influence compared to the transverse width.

• International Journal of Fluid Machinery and Systems
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• 제2권4호
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• pp.363-374
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• 2009

The 2D flow around 13 similar stay-vane profiles with different trailing edge geometries is investigated to determinate the main characteristics of the excitation forces for each one of them and their respective dynamic behaviors when modeled as a free-oscillating system. The main goal is avoid problems with cracks of hydraulic turbines components. A stay vane profile with a history of cracks was selected as the basis for this work. The commercial finite-volume code $FLUENT^{(R)}$ was employed in the simulations of the stationary profiles and, then, modified to take into account the transversal motion of elastically mounted profiles with equivalent structural stiffness and damping. The k-$\omega$ SST turbulence model is employed in all simulations and a deforming mesh technique used for models with profile motion. The static-model simulations were carried out for each one of the 13 geometries using a constant far field flow velocity value in order to determine the lift force oscillating frequency and amplitude as a function of the geometry. The free-oscillating stay-vane simulations were run with a low mass-damping parameter ($m^*{\xi}=0.0072$) and a single mean flow velocity value (5m/s). The structural bending stiffness of the stay-vane is defined by the Reduced Velocity parameter (Vr). The dynamic analyses were divided into two sets. The first set of simulations was carried out only for one profile with $2{\leq}Vr{\leq}12$. The second set of simulations focused on determining the behavior of each one of the 13 profiles in resonance.

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