• 한국항공우주학회지
• /
• 제39권6호
• /
• pp.481-486
• /
• 2011

결빙 관련 풍동 시험은 과냉각된 액적과 모델의 상사성을 고려하여 실제 크기 모델에 대해 풍동 시험이 이루어져야 하나 풍동 시험장의 공간적 제한으로 전기체에 대한 항공기 결빙은 제한적 혹은 항공기 구성품 단위별로 풍동 시험이 수행된다. 제한된 공간의 결빙 풍동 시험장에서 전기체 형상과 유사한 축적율과 결빙 영역을 조사하기 위해 본 연구에서는 일차적으로 실제 크기의 익형에 대해 Truncated Flapped 개념을 적용하였다. Flap의 변위각에 따른 압력 분포와 축적율의 경향성을 실제 크기의 익형과 Truncated Flapped 익형을 비교한 결과 정량적, 정성적으로 매우 유사한 경향을 나타냄을 확인하였다.

• 한국항공우주학회지
• /
• 제33권7호
• /
• pp.1-8
• /
• 2005

풍동 시험부 비정상 벽면효과에 대한 연구를 위해 폐쇄형 시험부내의 원형 실린더 주위 유동장에 대한 수치적 연구를 수행하였다. 수치기법은 Roe의 flux-difference-splitting을 사용한 격자점 중심 유한체적법과 이중시간 전진 기법을 사용하는 내재적 시간적분법을 사용하였다. 계산 결과 폐쇄형 시험부에는 실린더 주위 비정상 유동장에 압력구배를 강화시켜 실린더의 양력 및 항력의 진폭을 크게 하고, 실린더 뒷전에서의 기저압력을 작게 하여 항력을 증가시키는 벽면효과가 있음을 확인하였다. 또한, 이러한 시험부 벽면은 실린더 와류 shedding 주파수를 커지게 하는 효과가 있다. 시험부 벽면에서의 압력은 벽면효과가 포함된 shedding 주파수를 기본으로 하는 고조파 현상을 보인다.

• 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.

• Wind and Structures
• /
• 제27권3호
• /
• pp.163-173
• /
• 2018

The design wind pressure for low-rise buildings in the ASCE 7-10 is defined by procedures that are categorized into the Main Wind Force-Resisting System (MWFRS) and the Components and Cladding (C&C). Some of these procedures were originally developed based on steel portal frames of industrial buildings, while the residential structures are a completely different structural system, most of which are designed as low-rise light-frame wood constructions. The purpose of this study is to discuss the rationality (or irrationality) of the extension of the wind loads calculated by the ASCE 7-10 to the light-frame wood residential buildings that represent the most vulnerable structures under extreme wind conditions. To serve this purpose, the same approach as used in the development of Chapter 28 of the ASCE 7-10 that envelops peak responses is adopted in the present study. Database-assisted design (DAD) methodology is used by applying the dynamic wind loads from Louisiana State University (LSU) database on a typical residential building model to assess the applicability of the standard by comparing the induced responses. Rather than the postulated critical member demands on the industrial building such as the bending moments at the knee, the maximum values at the critical points for wood frame buildings under wind loads are used as indicators for the comparison. Then, the critical members are identified through these indicators in terms of the displacement or the uplift force at connections and roof envelope. As a result, some situations for each of the ASCE 7 procedures yielding unconservative wind loads on the typical low-rise residential building are identified.

• Wind and Structures
• /
• 제25권3호
• /
• pp.233-259
• /
• 2017

Investigations on simulated near-surface atmospheric boundary layer (ABL) in an open-jet facility are carried out by conducting experimental tests on small-scale models of low-rise buildings. The objectives of the current study are: (1) to determine the optimal location of test buildings from the exit of the open-jet facility, and (2) to investigate the scale effect on the aerodynamic pressure characteristics. Based on the results, the newly built open-jet facility is well capable of producing mean wind speed and turbulence profiles representing open-terrain conditions. The results show that the proximity of the test model to the open-jet governs the length of the separation bubble as well as the peak roof pressures. However, test models placed at a horizontal distance of 2.5H (H is height of the wind field) from the exit of the open-jet, with a width that is half the width of the wind field and a length of 1H, have consistent mean and peak pressure coefficients when compared with available results from wind tunnel testing. In addition, testing models with as large as 16% blockage ratio is feasible within the open-jet facility. This reveals the importance of open-jet facilities as a robust tool to alleviate the scale restrictions involved in physical investigations of flow pattern around civil engineering structures. The results and findings of this study are useful for putting forward recommendations and guidelines for testing protocols at open-jet facilities, eventually helping the progress of enhanced standard provisions on the design of low-rise buildings for wind.

• 자원환경지질
• /
• 제31권6호
• /
• pp.535-545
• /
• 1998

Various geophysical methods have been applied to the survey of the lava tunnel of Manjanggul in Cheju Island to study the effectiveness of each method in investigating underground tunnels. The surveys employing gravity, magnetic, electrical, AMT and VLF methods were carried out along seven profiles across the Manjanggul; especially, all the five methods were used on one representative profile. Several aspects of different methods pertinent to their use in investigation of underground tunnels have been noted. The electrical method employing the dipole-dipole array appeared to be the most effective one among five methods. Therefore, we have tested the electrical method more carefully by using various electrode spacings, and obtained successful resistivity sections showing the existence of lava tunnels. The gravity method provided relatively successful responses associated with the tunnel although the gravity readings were contaminated by wind blowing during the survey. The gravity data were also useful for the quantitative modeling study. The magnetic data were also successful in delineating the tunnel qualitatively. The AMT data were not successful because the used frequency band was not appropriate in detecting very shallow target. The VLF data were severely influenced by the neighboring noise sources such as power lines and were not successful in detecting the tunnel responses. The comprehensive result of electrical, gravity and magnetic surveys suggests that undiscovered lava tunnels may exist adjacent to the Manjanggul.

• 대한조선학회논문집
• /
• 제43권4호
• /
• pp.431-439
• /
• 2006

Due to the limitation of size of the test section, blockage effects could not be avoided in the model test of yacht sails for common wind tunnels. In this paper, a numerical analysis is performed to investigate the blockage effects on the lift and drag forces measured from wind tunnel experiments for a 30 feet sloop yacht sail. Complex airflows around the jib and main sails including three-dimensional flow separations are calculated for various close-hauled conditions. It is found that the blockage of a wind tunnel changes the flow separation and consequently the lift and drag forces of the sails, especially the main sail, reduce and increase, respectively, due to the blockage effects.

• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 2007년 가을학술발표회
• /
• pp.639-653
• /
• 2007

Offshore geotechnical site investigation of the seabed ground has been a key factor of the successful construction of various types of offshore structures like as sea-crossing bridges, submerged tunnels, and other marine facilities. Offshore investigations are not easy tasks because of the wave, wind, tidal ebb and flows, and others. Recent developments of offshore equipment including platforms and testing devices like as maine cone penetrator have inspired us to get more reliable characteristics of the seafloor. General information on the offshore site investigations and technical trends concerned are introduced.

• Nuclear Engineering and Technology
• /
• 제44권1호
• /
• pp.1-8
• /
• 2012

Thermal plasma technology has been at the center of major developments over the past century. It has found numerous applications ranging from aerospace materials testing to nanopowder synthesis and processing. In the present review highlights of principal breakthroughs in this field are presented with emphasis on an analysis of the basic phenomena involved, and the potential of the technology for industrial scale applications.

• 한국철도학회:학술대회논문집
• /
• 한국철도학회 2000년도 춘계학술대회 논문집
• /
• pp.495-502
• /
• 2000

For the tunnel design of the first class on new Seoul-Chunchon railway, we investigated for train speeds to run through tunnels without ear-discomfort of passenger in cabin by application of numerical analysis. Also we analyzed the effect of the wind speed induced by train in tunnel that is very harmful to the workers on railroad and the effect of the air-pressure fluctuations which get the fatigue to the tunnel lining and the car body.