• Wind and Structures
• /
• 제15권4호
• /
• pp.345-354
• /
• 2012

This work discusses the wind stability requirements specified by UN Reg. 27 on emergency car warning triangles, which are of mandatory use in many countries. Wind tunnel experiments have been carried out in order to determine aerodynamic coefficients of commercial warning triangles and the friction coefficients between the triangle legs and an asphalt base that fulfils the roughness requirements stated by Reg. 27 for wind stability certification. The wind stability specifications for warning triangles are reviewed, compared with pressure field measurements and discussed. Results of wind tunnel tests and comparison with field measurements reported in the literature show that the requirements could be excessively conservative.

• 대한교통학회지
• /
• 제27권1호
• /
• pp.43-51
• /
• 2009

이 논문은 타이어-노면간 마찰계수(drag factor)와 노면에 발생된 스키드마크를 통해 제동직전 속도(pre-braking speed) 산정을 정확하게 하기 위한 방법론을 제시하고자 한다. 제동직전 속도(pre-braking speed)와 활주직전 속도(pre-skidding speed)간 어떠한 상관관계가 있는지 판단하기 위해 실차 주행 및 제동실험을 통해 데이터가 수집되었다. 두 대의 차량에 fifth wheel(오륜) 장비, 스피드건, vericom 2000 등 다양한 측정장비를 탑재하여 제동실험이 수행되었으며, 자동차 속도, 제동거리, 활주거리, 감속도 등이 정밀 측정되었다. 실험자료의 분석을 통해 노면 마찰계수값과 활주직전 속도를 산정하고, 이후 활주직전 속도와 제동직전 속도를 비교하여 이들간의 상관관계를 규명하였다. 결과적으로 산정된 마찰계수값은 현재 일반적으로 적용되고 있는 0.8보다 높았으며, 제동직전 속도는 활주직전 속도보다 $5{\sim}10km/h$ 정도 높은 것으로 나타났다. 향후에는 다양한 차종과 노면조건에 대한 후속실험을 통해 더욱 정교한 한국형 분석모형의 개발과 실무적용이 필요할 것으로 판단된다.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2007년도 춘계학술대회B
• /
• pp.2660-2665
• /
• 2007

Turbulent boundary-layer over a micro-riblet film(MRF) was investigated experimentally. The MRF has sharp V-shaped micro scale grooves of $300{\mu}m$ in width and $176.8{\mu}m$ in height. Particle image velocimetry(PIV) system was employed to measure velocity fields of flow over the MRF coated plate. Flow over a smooth plate was also measured for comparison. The PIV measurements were taken in the streamwise wall-normal planes at Re$\theta$= 985 and 2342. Vortex structures of the flow were analyzed by extracting the swirling strength as an unambiguous vortex-identification criterion. As a result the number of spanwise vortices with clockwise(negative) rotation decreases rapidly in the near-wall region(y<0.2h), but decreases slowly in the outer region(0.2h

• 한국군사과학기술학회지
• /
• 제6권4호
• /
• pp.29-37
• /
• 2003

Using a wind tunnel testing, the aerodynamic load characteristics of an elliptic airfoil was described. The experimental data was obtained for angles of attack $-20^{\circ}$ to $+20^{\circ}$ with $2^{\circ}$ increments at a chord Reynolds number of $0.99{\times}105$ and $2.48{\times}105$. For each test case, chordwise suction pressure distributions and wake surveys were obtained. Static pressure measurements were made over a 10 sec averaging time at a 10 Hz sampling rate. For each case, wake survey was conducted with a pilot-static probe at 1.0c downstream from the trailing edge at very fine spacing to resolve the wake velocity deficit profile. As can be expected, suction pressure coefficient was increased with angle of attack. The normal force, CNmax, appeared peak value at the incidence angle of $12^{\circ}~14^{\circ}$, and the significant increase in profile drag at this range of angles of attack.

• Wind and Structures
• /
• 제28권6호
• /
• pp.355-367
• /
• 2019

Control of horseshoe vortex in the circular cylinder-plate juncture using vortex generator (VG) was studied at $Re_D$(where D is the diameter of the cylinder) = $2.05{\times}10^5$. Impact of a number of parameters e.g., the shape of the VG's, number of VG pairs (n), spacing between the VG and the cylinder leading edge (L), lateral gap between the trailing edges of a VG pair (g), streamwise gap between two VG pairs ($S_{VG}$) and the spacing between the two VG's in parallel arrangement ($Z_{VG}$) etc. were investigated on the horseshoe vortex control. The study is conducted using surface oil flow visualization and surface pressure measurements in low speed wind tunnel. It is observed that all the parameters studied have significant control effect, either by reduction in separation region or by lowering the adverse pressure along the symmetric axis upstream of the juncture.

• 대한기계학회논문집B
• /
• 제37권6호
• /
• pp.567-575
• /
• 2013

외부경계층 수직 날의 마찰저항 저감 기구를 규명하기 위하여 회류수조에서 시간분해 입자영상유속계로 측정된 비정상 유동장에 POD 분석을 실시하였다. 최근의 PIV 결과에서는 수직날 평면 및 수직날 사이 평면에서 각각 2.73%, 7.95%의 마찰저항 저감효과가 발견되었다. 본 연구에서는 수직날 배열이 난류조직구조에 미치는 영향을 POD 방법을 통하여 분석하였다. 난류유동의 조직적인 와구조가 수직날에 의하여 절단, 변형되고 비정상 거동이 난류경계층에서의 마찰저항 저감 기구와 밀접하게 관련된 것으로 관찰되었다.

• 한국산학기술학회논문지
• /
• 제12권2호
• /
• pp.944-951
• /
• 2011

본 논문은 ADCP 계측기기 부근에서 음향학적인 그리고 ADCP 계기로 인해 발생하는 흐름의 교란에 기인한 속도 오차에 대한 원인들을 실험 및 수치모의를 통해 고찰한다. 실험실에서의 연구는 선박에 탑재되지 않은 독립된 ADCP에 대해 수행하였고, 수평 및 수직면에서 ADCP에 의해 유발되는 흐름 교란은 ADV를 이용하여 관측하였다. 그리고 ADCP와 ADV의 동시적 측정이 ADCP계측에 있어 추가적인 계측기기 부근의 영향들을 고려하기 위해 수행되었다. 수치모의는 ADCP가 선박에 탑재되었을 때 ADCP 계기 부근에 발생하는 잠재적인 오차에 대해 연구하기 위해 설계되었다. 수치해석 기법 사용된 LES (Large Eddy Simulation)는 선박에 탑재된 ADCP에 작용하는 항력과 계기와 선박의 막음효과에 의해 발생하는 흐름의 교란의 크기와 범위를 모의하였다. 결과로 ADCP에 의해 관측된 속도는 계측기기 하단의 제한된 범위 내에서 일정 정도 오차를 보였고 교란되지 않은 하천의 흐름 조건에 따라 오차가 실질적으로 다르게 나타났다.

• 한국군사과학기술학회지
• /
• 제11권2호
• /
• pp.144-151
• /
• 2008

An experimental study has been conducted to investigate the effects of circular damage hole on the characteristics of airfoil performance. The damage on a wing created from a hit by anti-air artillery was modeled as a circular hole. Force balance measurements and static pressure measurements on the wing surface were carried out for the cases of having damage holes of 10% chord size at quarter chord and/or half chord positions. All experiments were conducted at Reynolds number of $2.85\times10^5$ based on the chord length. The surface pressure data show big pressure alterations near the circular damage holes. This abnormal surface pressure distribution produces shear stress that could lead to the acceleration of the structural degradation of the wing around the circular damage hole. However, in spite of the existence of circular damage holes, the measured force data indicated the only a slight decrease in lift accompanied by increase in drag compared to the results of undamaged one. The influence of damage hole on the aerodynamic performance was increased as the location of damage moved to the leading edge. The effect on the control force was insignificant when the damaged size was not large.

• 대한조선학회지
• /
• 제19권2호
• /
• pp.19-25
• /
• 1982

Several formulae have been proposed to estimate the viscous resistance of ships by wake surveys. Both the total head and the velocity should be measured. The integration of he total head loss shows over estimations of the resistance by about 10%. Therefore measurements of the velocity are required, which need much more works. A simple method is suggested in this paper to take accout of the velocity-defect from the measured total head. It gives reasonable estimations of the viscous resistance within the experimental accuracy. Experimental data of a low-drag body of revolution in the wind-tunnel and Series 60 model, CB=0.6 in the tank are used to verify the suggested formula.

• 천문학회보
• /
• 제40권2호
• /
• pp.45.2-45.2
• /
• 2015

It is obvious that there are plentiful of dust particles in the interplanetary spaces of the Solar System (IDPs), based on micrometeor craters, zodiacal light and direct measurements on the spacecraft. Because of photon drag and planetary perturbations, these particles are continuously falling to the Sun or planets, therefore continuous source of the IDPs are required. We studied the fractional contribution of each type of solar system objects to the IDPs complex through the optical properties of the potential dust sources and the zodiacal light. We found that more than 90% of the IDPs are originated from cometary nuclei. This result is discussed through the comparison with the dynamic simulation, micrometeors mineralogy and near-infrared spectrum of the zodiacal light. In addition, we introduce our new project on the numerical simulation for the dust particles ejected from the cometary nuclei, to verify the conclusion of dominant cometary contribution and its detailed consequences.