• 한국항공우주학회지
• /
• 제33권8호
• /
• pp.42-49
• /
• 2005

아음속풍동 폐쇄형 시험부의 벽면효과 보정을 위한 새로운 blockage 보정 기법을 개발하였다. 개발된 보정 기법은 실속항력계수와 separation blockage의 비선형 관계를 이용하여 선형 양력곡선 기울기 영역에서 후실속 영역까지 실시간으로 보정이 가능하게 하였다. 본 연구에서 제시한 방법은 bluff body 시험 결과를 사용하는 고전적 방법과 벽면압력측정 방법과 비교하여 그 타당성을 검증하였다. 그 결과 본 연구에서 제시한 보정 방법은 실속 및 후실속 영역에서 bluff body 방법보다 우수한 보정 결과를 보이며 벽면압력측정 방법과 같은 정확도로 보정됨을 확인할 수 있었다.

• Wind and Structures
• /
• 제1권4호
• /
• pp.351-364
• /
• 1998

In wind tunnel experiments, the blockage effect is a very important factor which affects the test results significantly. A number of investigations into this problem, especially on the blockage correction of drag coefficient, have been carried out in the past. However, only a limited number of works have been reported on the wind tunnel blockage effect on wind-induced vibration although it is considered to be fairly important. This paper discusses the aerodynamic characteristics of the square model and square model with corner cut based on a series of the wind tunnel tests with various blockage ratios and angles of attack. From the test results, the aerodynamic behavior of square models with up to 10% blockage ratio are almost the same and square models with up to 10% blockage ratio can be tested as a group which behaves similarly.

• Wind and Structures
• /
• 제12권6호
• /
• pp.541-551
• /
• 2009

This paper explains how to correctly measure the drag coefficient of a circular cylinder in wind tunnels with large blockage ratios and for the sub-critical to the super-critical flow regimes. When dealing with large blockage ratios, the drag has to be corrected for wall constraints. Different formulations for correcting blockage effect are compared for each flow regime based on drag measurements of smooth circular cylinders performed in a wind tunnel for three different blockage ratios. None of the correction model known in the literature is valid for all the flow regimes. To optimize the correction and reduce the scatter of the results, different correction models should be combined depending on the flow regime. In the sub-critical regime, the best results are obtained using Allen and Vincenti's formula or Maskell's theory with ${\varepsilon}$=0.96. In the super-critical regime, one should prefer using Glauert's formula with G=0.6 or the model of Modi and El-Sherbiny. The change in the formulations appears at the flow transition with a variation of the wake pattern when passing from sub-critical to super-critical flow regimes. This parameter being not considered in the known blockage corrections, these theories are not valid for all the flow regimes.

• 대한조선학회논문집
• /
• 제57권3호
• /
• pp.133-139
• /
• 2020

In order to study the resistance test technique for the submerged body in Large Cavitation Tunnel (LCT), DARPA Suboff, submarine model publicly available was manufactured. DTRC released the resistance test data of DARPA Suboff conducted at ship speeds up to 18.0 knots in high-speed towing tank in 1990. As LCT is considered restricted waterways with walls, the resistance test results must be corrected with three wall blockage effects called buoyancy effect, solid blockage effect and wake blockage effect. Before correction, the resistance of LCT was 16~20 % higher than that of DTRC. After correction, the resistance and the resistance coefficients were compared with those of DTRC. The corrected resistance of LCT shows good agreement with that of DTRC. The residual resistance coefficient shows the difference according to the calculation method of buoyancy and frictional resistance coefficient. This paper suggests the best way for the calculation of residual resistance coefficient, On the basis of the present study, it is thought that the operating conditions for the propeller cavitation and noise tests can be drawn through LCT tests.

• 한국위성정보통신학회논문지
• /
• 제11권1호
• /
• pp.6-11
• /
• 2016

본 논문에서는 3세대 디지털 사이니지 대용량 고속 서비스 제공에 필요한 IEEE802.11n 표준 기반 40MHz 채널 대역폭을 사용하는 광대역 무선랜에 대한 동일채널, 인접채널, 인적차폐(Body Blockage)에 의한 채널 간섭 영향을 분석 하였다. 모의실험 결과, 동일채널 간섭기기와는 63m 이상의 보호 이격거리에서 78개 이내의 간섭기기와 운용이 가능하고, 인접채널들과는 61m 이상에서 80개 이내, 간섭채널이 동시에 존재하는 멀티채널에서는 97m 이상의 보호 이격거리가 필요함을 확인 하였다. 또한 간섭완화 기법을 통해 동일채널 간섭에서 빔포밍 적용시 51m로 개선되었고, CR(Cognitive Radio) 적용시 40m로 개선됨을 확인 하였다. 인적차폐 영향시, 채널 대역폭 조절, 간섭 보호 비(C/I) 조절, 빔포밍, 전력제어 기법을 통해 인적차폐로 인한 감쇄가 완화됨을 확인 하였다.

• 한국산업융합학회 논문집
• /
• 제24권5호
• /
• pp.573-579
• /
• 2021

In this study, flow analysis was performed on three types of strainers for ships with different flow rates to predict the pressure drop of the strainer due to the filter of strainer. In the case of flow analysis, the flow analysis was performed by applying the porous media method by applying the resistance value derived by Ergun's equation to the filter position. As a result of the analysis, it was found that when the dimensions of the strainer body were small, the influence of the flow rate on the pressure drop was large. In addition, the amount of pressure drop and the flow rate are almost linearly proportional, and an analysis formula that can predict the amount of pressure drop was derived. In order to predict the amount of pressure drop of the strainer when blockage exist in the strainer filter, the analysis was performed by introducing the resistance ratio to derive the prediction equation. Using this equation, it is thought that it will be possible to predict the performance of the strainer due to blockage in the future strainer design and field application.

• 대한조선학회논문집
• /
• 제58권2호
• /
• pp.58-65
• /
• 2021

In order to study the self-propulsion test and analysis techniques for the submerged body in Large Cavitation Tunnel (LCT). DARPA Suboff, a submarine model publicly available was manufactured. The resistance results of DARPA Suboff was acquired from the LCT tests and compared with those of DTRC. After the wall blockage correction, the resistance results of LCT were in good agreement with those of DTRC. On the basis of the resistance results of LCT, the self-propulsion tests were conducted in LCT. The test objective was to get the full-scale propeller operating conditions for the propeller cavitation and noise tests. The test results of DARPA Suboff were analyzed in a way similar to the analysis techniques of those of the Towing Tank (TT). Another submerged body, for which self-propulsion tests were conducted in TT, was selected for results verification. The results of LCT were in good agreement with those of TT. On the basis of the present study, it is thought that the operating conditions for the full-scale submerged body can be drawn through LCT tests.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 1998년도 추계 학술대회논문집
• /
• pp.160-166
• /
• 1998

In this paper, incompressible two-dimensional Navier-Stokes equations are numerically solved for the study of steady laminar flow around a body with the wall effect. A second-order finite difference method is used for the spatial discretization on the nonstaggered grid system and the 4-stage Runge-Kutta scheme for the numerical integration in time. The pressure field is obtained by solving the pressure-Poisson equation with the Neumann boundary condition. To investigate the wall effect, numerical computations are carried out for the NACA 0012 section at the various blockage ratios. The pressure and skin friction on the foil surface, velocity pronto in its wake and drag coefficient are investigated as functions of the blockage ratio.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 1995년도 창립기념학술대회
• /
• pp.30-36
• /
• 1995

An axisymmetric flow induced by a train moving into a tunnel is numerically simulated. The effect of train shape on wavefront of a compression wave created by a train is investigated parametrically using several model trains having the same nose shape but different blockage. The zonal method combined with the Fortified Solution Algorithm (FSA) is employed as a numerical algorithm to solve this moving body problem. The computational result is compared with the experimental data. Good agreement is obtained, which justifies the present computational approach. The compression waves created by the model trains are compared and the result shows that the pressure gradient of the wavefront of the compression wave becomes small in the case of small blockage even though the nose shape is same. The wavefront is not determined solely by the cross-sectional area distribution of the train nose.

• International Journal of Naval Architecture and Ocean Engineering
• /
• 제2권2호
• /
• pp.57-67
• /
• 2010

Experimental investigations were carried out on an Axi-symmetric Body Model fitted with Pump-jet Propulsor (PJP) in the Cavitation Tunnel at Naval Science and Technological Laboratory (NSTL). The tests were intended for evaluating the propulsion characteristics of the body and propulsor. The self propulsion point of the model for two configurations was determined after finding the corrections for tunnel blockage effects and differences in model length at zero trim. The results were found to match closely with the towing tank results. The rotor and stator torques also matched closely over full range of experiment. Further experiments were carried out on the body at $4.5^{\circ}$ angle of trim to investigate the propulsive performance and assess the operational difficulties in the sea. The results indicated an increase in resistance and decrease in rotor thrust; but the balance of torques between the rotor and stator was undisturbed, causing no concern to vehicle roll.