• 한국방재안전학회논문집
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• 제6권2호
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• pp.49-56
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• 2013

본 논문에서는 재난변동풍하중을 받는 고층건물의 예비설계과정에서 필요로 하는 자료를 얻기 위하여 경계층풍동 실험을 실시했다. 먼저 본 실험에 앞서 경계층풍동내의 자연풍을 얻기 위하여 확산장치를 이용했고, 이로부터 평균풍속 수직분포, 난류강도, 파워스펙트럼으로 입증했으며, 이 후 변장비 1:2 강체모형을 이용 경계층풍동실험을 실시한 결과로부터 다음과 같은 결론을 얻을 수 있었다. 1. 경계층풍동에서의 평균풍속 및 난류강도의 수직분포가 자연풍과 같이 잘 실현되었다. 2. 변동풍속 스펙트럼은 Von Karman spectrum과 비교한 결과 잘 일치했다. 3. 변동압력 스펙트럼에서 풍상면의 피크분포는 0.01-0.1 Hz영역에서 발생했고, 풍후면은 0.1 Hz영역에서 발생했다. 4. 자기상관계수는 재난변동풍하중의 작용시간이 증가하면 정성확률과정으로 분포하는 사실을 알 수 있었다.

• 설비공학논문집
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• 제3권3호
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• pp.161-167
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• 1991

This paper presents the results of some measurement of the fluctuating velocity field in the turbulent boundary layer disturbed by a triangular prism and discusses the discovery of the disturbed boundary layer. A prism of height 8mm was used for experiments. The streamwise location of the prism was fixed at 1200mm downstream from the leading edge and the space between the prism center and the wall was set at three different values, 6, 15 and 33.5mm. The results show that the near-wall region of the disturbed boundary layer recovers original state much more quickly than the outer region. In the case h=6mm the recovery is faster than the other cases. Moreover, it was found that peak of fluctuating velocities moves outwards somewhat rapidly with increasing ${\times}$ mainly due to the turbulent diffusion of the fluctuating velocity.

• Journal of applied mathematics & informatics
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• 제10권1_2호
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• pp.175-191
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• 2002

The equations of a polar fluid of hydromagnetic fluctuating through a porous medium axe cast into matrix form using the state space and Laplace transform techniques the resulting formulation is applied to a variety of problems. The solution to a problem of an electrically conducting polar fluid in the presence of a transverse magnetic field and to a problem for the flow between two parallel fixed plates is obtained. The inversion of the Laplace transforms is carried out using a numerical approach. Numerical results for the velocity, angular velocity distribution and the induced magnetic field are given and illustrated graphically for each problems.

• 대한기계학회논문집
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• 제10권5호
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• pp.706-712
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• 1986

본 연구는 맥동류의 진동 속도가 평균 유속에 비하여 매우 작은 경우로서 Re- ynolbs수가 40 이하 층류유동에 관한 것이다. 부력은 무시하고 비압축성의 점성유체 에 관한 비정상 Navier-Stokes 방정식과 에너지방정식의 선형 섭동방정식을 구하고, 진동성분의 복소진폭을 수치적으로 풀어서 저항력과 함께 열전달 응답의 진폭과 위상 을 구하였다.

• 한국방재안전학회논문집
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• 제8권1호
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• pp.29-37
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• 2015

우리나라 전체 재해의 60%이상은 태풍과 같은 바람재난으로부터 발생하고 있으며, 이러한 자연 재해로부터 구조물이나 외장재의 안전과 사용성 측면에서의 내풍설계 과정에서는 풍속스펙트럼의 평가가 요구된다. 본 논문에서는 최근 우리나라를 통과한 태풍 2003년 매미, 2010년 곰파스, 2012년 템빈의 변동풍속자료로부터 난류의 특성을 알아보기 위하여 6개의 대표지점을 여수, 서울, 청주, 원주, 대구, 속초로 선정했다. 선정된 각 지점에 대한 태풍의 변동풍속자료는 기상청으로부터 획득했다. 기상청으로부터 획득한 변동풍속 자료는 연최대순간풍속과 연최대평균퐁속이 같은 날 발생했기 때문에 각 모집단의 표본 1440개 중 년최대순간풍속이 속하는 740개 풍속자료를 10분 평균풍속으로 가정하여 난류특성을 비교 검토하였다.

• 대한기계학회논문집B
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• 제28권2호
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• pp.181-188
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• 2004

The frequency characteristics in an axial flow fan operating at a design and three off-design operating conditions have been investigated by measuring the velocity fluctuation of a tip leakage vortex and a wake flow. Two hot-wire probe sensors rotating with the fan rotor. a fixed and a moving ones, were introduced to obtain a cross-correlation coefficient between two sensors as well as the fluctuating velocity. The results show that the spectral peaks due to the fluctuating velocity near the rotor tip are mainly observed in the reverse flow region of higher flow rates than those in the peak pressure operating condition. However, no peak frequency presents near the rotor tip for near stall condition. Detailed wake flow just downstream of the rotor blade was also measured by the rotating hot-wire sensor. The peak frequency of a high velocity fluctuation due to Karman vortex shedding in the wake region is mainly observed at the higher flow rate condition than that in the design point.

• Wind and Structures
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• 제9권2호
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• pp.109-124
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• 2006

This paper describes the characteristics of the fluctuating lift forces when a circular cylinder vibrates in the cross-flow direction. The response characteristics on elastically supported the circular cylinder was first examined by a free-vibration test. Next, flow-induced vibrations obtained by the free-vibration test were reproduced by a forced-vibration test, and then the characteristics of the fluctuating lift forces, the work done by the fluctuating lift, the behavior of the rolling-up of the separated shear layers were investigated on the basis of the visualized flow patterns. The main findings were that (i) the fluctuating lift forces become considerably large than those of a stationary circular cylinder, (ii) negative pressure generates on the surface of the circular cylinder when the rolling-up of separated shear layer begins, (iii) the phase between the fluctuating lift force and the cylinder displacement changes abruptly as the reduced velocity $U_r$ increases, and (iv) whether the generating cross-flow vibration becomes divergent or convergent can be described based on the work done by the fluctuating lift force. Furthermore, it was found that the generation of cross-flow vibration can be perfectly suppressed when the small tripping rods are installed on the surface of the circular cylinder.

• Wind and Structures
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• 제17권4호
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• pp.379-397
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• 2013

Large Eddy Simulations (LES) were carried out to investigate the aerodynamic characteristics of a rectangular cylinder with side ratio B/D=5 at Reynolds number Re=22,000 (based on cylinder thickness). Particular attention was devoted to the effects of velocity shear in the oncoming flow. Time-averaged and unsteady flow patterns around the cylinder were studied to enhance understanding of the effects of velocity shear. The simulation results showed that the Strouhal number has no significant variation with oncoming velocity shear, while the peak fluctuation frequency of the drag coefficient becomes identical to that of the lift coefficient with increase in velocity shear. The intermittently-reattached flow that features the aerodynamics of the 5:1 rectangular cylinder in non-shear flow becomes more stably reattached on the high-velocity side, and more stably separated on the low-velocity side. Both the mean and fluctuating drag coefficients increase slightly with increase in velocity shear. The mean and fluctuating lift and moment coefficients increase almost linearly with velocity shear. Lift force acts from the high-velocity side to the low-velocity side, which is similar to that of a circular cylinder but opposite to that of a square cylinder under the same oncoming shear flow.

• Wind and Structures
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• 제20권4호
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• pp.579-607
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• 2015

A Combination Random Flow Generation (CRFG) technique for obtaining the fluctuating inflow boundary conditions for Large Eddy Simulation (LES) is proposed. The CRFG technique was developed by combining the typical RFG technique with a novel calculation of k and ${\varepsilon}$ to estimate the length- and time-scales (l, ${\tau}$) of the target fluctuating turbulence field used as the inflow boundary conditions. Through comparatively analyzing the CRFG technique and other existing numerical/experimental results, the CRFG technique was verified for the generation of turbulent wind velocity fields with prescribed turbulent statistics. Using the turbulent velocity fluctuations generated by the CRFG technique, a series of LESs were conducted to investigate the wind flow around S-, R-, L- and U-shaped building models. As the pressures of the models were also measured in wind tunnel tests, the validity of the LES, and the effectiveness of the inflow boundary generated by the CRFG techniques were evaluated through comparing the simulation results to the wind tunnel measurements. The comparison showed that the LES accurately and reliably simulates the wind-induced pressure distributions on the building surfaces, which indirectly validates the CRFG technique in generating realistic fluctuating wind velocities for use in the LES. In addition to the pressure distribution, the LES results were investigated in terms of wind velocity profiles around the building models to reveal the wind flow dynamics around bluff bodies. The LES results quantitatively showed the decay of the bluff body influence when the flow moves away from the building model.

• 한국방재안전학회논문집
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• 제8권1호
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• pp.39-46
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• 2015

시공간적으로 불규칙하게 작용하는 태풍의 변동풍속은 지표면의 조도에 의해 많은 영향을 받으며, 이러한 불규칙한 변동풍속을 받는 저층 중층 고층건물의 안전 및 사용성의 평가는 이와 관련한 많은 파라미터에 의해 평가되고 있다. 최근 우리나라를 통과한 태풍 매미(2003), 곰파스(2010), 템빈(2012)의 변동풍속자료로부터 난류의 특성 및 스펙트럼의 평가를 알아 보기 위하여 6개의 대표지점을 선정했고, 선정된 각 지점에 대한 변동풍속자료는 기상청으로부터 획득했지만, 이 자료는 지상 10m 높이에서 관측되었고 1분의 평균자료이다. 이러한 기상청의 자료는 실측자료이기는 하나 1분 평균에 의한 진동수의 영역별 영향이 평균화될 수 있고, 높이에 따른 변동풍속의 특성을 잘 나타내지 못하고 있다. 따라서 본 논문에서는 고층건물에 영향을 미치는 지상 200m 높이에서의 변동풍속에 대한 확률분포, 난류특성 및 스펙트럼을 평가하기 위하여 기상청 자료와 Monte Carlo Simulation 방법을 이용하여 변동풍속을 해석한 후 비교 검토하였다.