• Journal of Advanced Marine Engineering and Technology
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• 제15권3호
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• pp.45-56
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• 1991

This paper describes characteristics of the flow pattern of the flow past a rectangular cylinder experimentally investigated. The width-to-length ratio of the section varried from 2 to4. For the statistical treatment, autocorrelation coefficient, probability density function and power spectral density function are obtained by the digital processing technic through on-line system with a hot wire anemometer. As a results, it was found that strong periodic coherent eddies structure is sustained to about 20H downstream from the cylinder. And nearer the cylinder in the wake, the number of turbulent eddies of a large scale coherent structure are comparatively much more dominant than that of a small scale one. By the analysis of power spectrum, It was cleared that there exists a certain range of the width to length ratio between 2.5 and 3 of which the flow pattern changes abruptly with a sudden discontinuity in Strouhal number.

• 한국기계기술학회지
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• 제13권2호
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• pp.101-106
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• 2011

In this study, the velocity distribution according to upper side coner shape of underwater construction with rectangular cylinder was measured with PIV method and the wake flow characteristics was considered. According to the coner shape, the flow pattern of wake flow was also differed greatly and the step-shaped coner of cut-off ratio B/H=0.06 was similar in the slope shape in result.

• Steel and Composite Structures
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• 제20권6호
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• pp.1323-1343
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• 2016

This paper presents the results of an extensive numerical analysis program devoted to the investigation of the mechanical behaviour of bolted ball-cylinder joints. The analysis program is developed by means of finite element (FE) models implemented in the non-linear code ABAQUS. The FE models have been accurately calibrated on the basis of available experimental results. It is indicated that the FE models could be used effectively to describe the mechanical performance of bolted ball-cylinder joints, including failure modes, stress distributions and load-displacement curves. Therefore, the proposed FE models could be regarded as an efficient and accurate tool to investigate the mechanical behavior of bolted ball-cylinder joints. In addition, to develop a further investigation, parametric studies were performed, varying the dimensions of hollow cylinders, rectangular tubes, convex washers and ribbed stiffener. It is found that the dimensions of hollow cylinders, rectangular tubes and ribbed stiffener influenced the mechanical behaviour of bolted ball-cylinder joints significantly. On the contrary, the effects of the dimensions of convex washers were negligible.

• 치과방사선
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• 제25권2호
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• pp.297-308
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• 1995

This study was designed to measure the absorbed dose to organs of special interest from full mouth with intraoral film(l4 films) and to compare the five periapical techniques. Thermoluminescent crystals(TLD-100 chip) were located in brain, orbit, bone marrow of mandibular ramus, bone marrow of mandibular body, bone marrow of 4th cervical spine, parotid gland, submandibular gland and thyroid gland. X -ray machine was operated at 70kVp and round collimating film holding device(XCP) and rectangular collimating film holding device(Precision Instrument) were used. The distance from the X-ray focus to the open end of the collimator was 8 inch, 12 inch and 16 inch. The results were as follows : 1. The absorbed dose was the highest in bone marrow of mandibular body(5.656mGy) and the lowest in brain (0.050mGy). 2. Generally, the lowest absorbed dose was measured from 16 inch cylinder, rectangular collimating film holding device with paralleling technique. But, in bone marrow of mandibular body and the floor of mouth, the highest absorbed dose was measured from 12 inch cylinder, rectangular collimating film holding device with paralleling techniques. 3. Comparing of five intraoral radiographic techniques, it was appeared statistically significant reduction of the absorbed doses measured with rectangular collimating film holding device compared to XCP film holding device (P<0.05). 4. No statistically significant reduction in the absorbed dose was found as cylinder length was changed(P>0.05).

• 수산해양기술연구
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• 제58권2호
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• pp.95-105
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• 2022

In this study, the fishery status of the octopus pot fishery in the east coastal sea were investigated, and the fishing performance of each pot shape was compared and analyzed. The fishery status survey was conducted through listening surveys at Jukbyeon Port, Uljin Port and Pohang Daebo Port in Gyeongbuk Province, and the amount of fishing gear used, fishing method, size and loss of octopus pot fishery was investigated. On the east coastal sea, octopus is one of the commercially important fish stocks and is caught in inshore pots, inshore combos, inshore gillnets and offshore pots. Among these fishing methods, pot fishing yields the highest catch. The shape of the pot differs depending on the region. In Uljin (Jukbyeon Port and Hupo Port), Gyeongbuk, rectangular type net pots are mainly used, and in Pohang (Daebo Port) in Gyeongbuk, drum-type pots are mostly used. Enteroctopus dofleini accounts for more than 90% of the catch of octopus. For the octopus fishing performance test by trap type, three types of traps (rectangular pot, drum pot and cylinder pot) were used on the coastal sea of Pohang Daebo. As a result, the total catch by pot shape was shown in the order of rectangular-type pot > drum-type pot > cylinder-type pot. The catch of octopus, the target species, was in the following order: rectangular-type pot > drum-type pot > cylinder-type pot. Such result shows a significant difference (Mann-Whitney test, p<0.05).

• Wind and Structures
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• 제26권5호
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• pp.293-304
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• 2018

A numerical study is conducted on the flow characteristics of a rectangular cylinder (chord-to-width ratio C/W = 2 - 10) mounted close to a rigid wall at gap-to-width ratios G/W = 0.25 - 6.25. The effects of G/W and C/W on the Strouhal number, vortex structure, and time-mean drag and lift forces are examined. The results reveal that both G/W and C/W have strong influences on vortex structure, which significantly affects the forces on the cylinder. An increase in G/W leads to four different flow regimes, namely no vortex street flow (G/W < 0.75), single-row vortex street flow ($0.75{\leq}G/W{\leq}1.25$), inverted two-row vortex street flow ($1.25<G/W{\leq}2.5$), and two-row vortex street flow (G/W > 2.5). Both Strouhal number and time-mean drag are more sensitive to C/W than to G/W. For a given G/W, Strouhal number grows with C/W while time-mean drag decays with C/W, the growth and decay being large between C/W = 2 and 4. The time-mean drag is largest in the single-row vortex street regime, contributed by a large pressure on the front surface, regardless of C/W. A higher C/W, in general, leads to a higher time-mean lift. The maximum time-mean lift occurs for C/W = 10 at G/W = 0.75, while the minimum time-mean lift appears for C/W = 2 at the same G/W. The impact of C/W on the time-mean lift is more substantial in single-row vortex regime. The effect of G/W on the time-mean lift is larger at a larger C/W.

• Wind and Structures
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• 제38권1호
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• pp.59-74
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• 2024

Large Eddy Simulation (LES) is used to explore the influence of vibration frequency and amplitude on the aerodynamic performance of a rectangular cylinder with an aspect ratio of B/D=5 (B: breadth; D: depth of cylinder) at a Reynolds number of 22,000 near resonance frequency. In smooth flow conditions, the research employs a sequence of three-dimensional simulations under forced vibration with diverse frequency ratios f_e / f_o = 0.8-1.2 (f_e : oscillation frequency; f_o : Strouhal frequency when the rectangular cylinder is stationary ) and oscillation amplitudes A_h/D = 0.05 - 0.3. The individual influences of f_e / f_o and A_h/D on the characteristics of integrated and distributed aerodynamic forces are the focal points of discussion. For the integrated aerodynamic force, particular emphasis is placed on the analysis of the dependence of velocity-proportional component C₁ and displacement-proportional component C₂ of unsteady aerodynamic force on amplitude and frequency ratio. Near the resonance frequency, the dependencies of C₁ and C₂ on amplitude are stronger than that of frequency ratio. For the distributed aerodynamic force, the increase in frequency and amplitude promotes the position of the main vortex core and reattachment to the leading edge in the streamwise direction. In the spanwise direction, vibration enhances the spanwise correlation of aerodynamic force to weaken the three-dimensional effect of the flow field, and a lower frequency ratio and larger amplitude amplify this effect.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2004년도 유체기계 연구개발 발표회 논문집
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• pp.629-634
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• 2004

Cavities are inevitable structures in automobile configuration. The flow-induced noise is generated from the wheel housing section by the interaction between a rotating wheel and the unsteady flows in the cavity. In this research the wheel housing was assumed by a rectangular cavity for simplification. We measured the radiated sound from the 2-D cavity without cylinder and from the rotating cylinder in the cavity by using the sound source localization method with an acoustic mirror system. In the 2-D cavity case of low Mach number(Ma=0.029), the sound sources were found to be located near the leading edge of cavity due to the shear layer instabilities. Comparing the cases of the rotating and the non-rotating cylinder, it is observed that the sound Pressure levels around the rotating cylinder in the cavity increased and the main acoustic sources were located at the rear section of the rotating wheel.

• 해양환경안전학회지
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• 제20권6호
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• pp.760-767
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• 2014

본 연구에서는 길이가 다른 장방형 실린더 사이에서 발생하는 제트류가 후류에 미치는 영향을 알아보기 위해 회류수조에서 PIV기법을 사용하여 실험을 실시하였다. 장방형 실린더의 높이(h)와 실린더 사이의 간격(gap)은 10mm이며 폭(B)은 300mm로 하였다. 유동방향의 모델의 길이(L)는 30mm, 60mm, 90mm 및 120mm를 각각 적용하였으며, 모델의 높이(H=30mm)를 기준으로 길이의 비가 1, 2, 3,및 4이다. 유입유동은 조류의 수심에 따른 차이를 감안하여 모델의 높이(H)를 기준으로 $Re=1.4{\times}10^4$, $Re=2.0{\times}10^4$, $Re=2.9{\times}10^4$를 각각 적용하였으며. 유동계측을 위한 영역은 실린더 후방으로 모델 높이의 5배까지 설정하였다. 실험결과 유속이 증가함에 따라 와의 크기가 후류영역으로 증가하며, 근접 후류에서는 장방형 구조물일수록 관통류의 속도성분이 증가하는 특성을 나타냈다. 또한 후류로 갈수록 속도결손은 유입유동이 증가할수록 종횡비가 작은 경우에 크게 나타났다.

• 한국전산유체공학회지
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• 제10권1호
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• pp.1-7
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• 2005

Three-dimensional numerical analysis of the flow around rectangular cylinders with various side ratios, D/H, from 0.2 to 2.0, was carried out for Reynolds number of 10³ by using a multi-directional finite difference method on a regular-arranged multi-grid. The predicted results are in good agreement with the experimental data. It is found that fluid dynamic characteristics of rectangular cylinders alternate between the high-pressure mode and the low-pressure mode of the base pressure for D/H=0.2-0.6. We show that this phenomenon is induced by the change of the flow pattern around rectangular cylinders.