• 한국도로학회논문집
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• 제15권5호
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• pp.21-29
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• 2013

PURPOSES: Simulation of aggregate slump test using equivalent sphere particle in DEM and its validity evaluation against lab aggregate slump test METHODS : In this research, aggregate slump tests are performed and compared with DEM simulation. To utilize spheric particles in YADE, equivalent sphere diameter concept is applied. As verification measures, the volume in slump cone filled with aggregate is used and it is compared with volume in slump cone filled with equivalent sphere particle. Slump height and diameter are also used to evaluate the suggested numerical method with equivalent concept RESULTS : Simulation test results show good agrement with lab test results in terms of loose packing volume, height and diameter of slumped particle clump. CONCLUSIONS : It is concluded that numerical simulation using DEM is applicable to evaluate the effect of aggregate morphological property in loose packing and optimum gradation determination based on the aggregate slump test simulation result.

• 한국자동차공학회논문집
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• 제15권1호
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• pp.116-124
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• 2007

An optical method to measure the size and number density of soot aggregates in diesel exhaust has been proposed in this study. Two laser beams in co-axial alignment transmit a soot loaded exhaust gas flow, and the transmittance at each wavelength is detected by a photo diode simultaneously. The volume equivalent diameter and number density of soot aggregates in the optical path can be theoretically given by the transmittance values measured at two wavelengths. A test conducted by a single cylinder, 4 cycle, small and DI diesel engine shows that the temporal variations of the size and number density of soot aggregates in the diesel exhaust can be measured by the proposed method at a transient mode operation. It is found that the volume equivalent diameter varied temporally from 70 to 110 nm during the period that high soot concentration is observed. One can also conclude that the optical length longer than 1 m in the dynamic range regarding this method is preferable for measuring soot concentration at the level of $1\;mg/m^3$.

• 한국분무공학회지
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• 제20권4호
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• pp.261-267
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• 2015

The main purpose of this study is to provide the information of soot generation of toluene fuel droplet. To achieve this, this paper provides the experimental results on the different initial diameter of toluene droplet combustion characteristics conducted under equivalent ambient pressure ($P_{amb}$) and oxygen concentration ($O_2$) conditions. Visualization of single fuel droplet was performed with high resolution CCD camera and visualization system. At the same time, ambient pressure ($P_{amb}$) and oxygen concentration ($O_2$) were maintained by ambient condition control system. Soot volume fraction ($f_v$) was analyzed and compared on the basis of intensity ratio ($I/I_0$) of background image. The result of soot generation was almost the same regardless of initial droplet diameter since thermophoretic flux is not much changed under the same ambient conditions. Soot standoff ratio (SSR) of 2 mm diameter showed unstable variation characteristics due to the short available measuring time.

• 한국화재소방학회논문지
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• 제22권3호
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• pp.272-277
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• 2008

본 연구는 분기배관을 물계통 소화설비에 적용할 경우 정확한 등가길이를 제시하고자 수행하였다. 등가길이 측정위치를 예측하고자 분기배관의 압력강하에 대해 유한체적법을 이용하여 확인한 후 측정위치를 결정하였고 그 위치에서 압력손실시험을 실시하였다. 측정된 값의 정확성을 판단하기 위해 해석결과와 비교하였고 두 값이 유사함을 알 수 있었다. 본 연구의 결과로 분기배관의 압력손실측정위치를 주방향의 입구측은 주배관 호칭의 20배, 출구측은 주배관 호칭의 10배, 분기방향의 출구측은 주배관 호칭의 20배로 제안하였다.

• Journal of Mechanical Science and Technology
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• 제17권6호
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• pp.925-934
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• 2003

An experimental study is performed to investigate the characteristics of near wake flow behind a circular cylinder with serrated fins using a constant temperature anemometer and flow visualization. Various vortex shedding modes are observed. Fin height and pitch are closely related to the vortex shedding frequency after a certain transient Reynolds number. The through velocity across the fins decreases with increasing fin height and decreasing fin pitch. Vortex shedding is affected strongly by the velocity distribution just on top of the finned tube. The weaker gradient of velocity distribution is shown as increasing the freestream velocity and the fin height, while decreasing the fin pitch. The weaker velocity gradient delays the entrainment flow and weakens its strength. As a result of this phenomenon, vortex shedding is decreased. The effective diameter is defined as a virtual circular cylinder diameter taking into account the volume of fins, while the hydraulic diameter is proposed to cover the effect of friction by the fin surfaces. The Strouhal number based upon the effective diameters seems to correlate well with that of a circular cylinder without fins. After a certain transient Reynolds number, the trend of the Strouhal number can be estimated by checking the ratio of effective diameter to inner diameter. The normalized velocity and turbulent intensity distributions with the hydraulic diameter exhibit the best correlation with the circular cylinder's data.

• 대한기계학회논문집B
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• 제41권6호
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• pp.389-395
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• 2017

본 연구는 정적 연소 조건에서 Octane 단일 연료 액적의 매연 생성 거동에 관한 정보를 제공하기 위해 수행하였다. 이를 위해 동일한 분위기 압력($P_{amb}$) 1.0 atm과 산소 농도($O_2$) 21%, 질소 농도($N_2$) 79% 조건에서 초기 액적 직경($d_0$) 변화에 따른 Octane 액적의 매연 생성 특성 실험 결과를 제시하였다. Octane 액적 연소 가시화는 초고속 카메라를 사용하여 촬영하였고, 분위기 조건은 제어 시스템에 의해 동일한 조건을 유지하였다. Octane 액적 연소 결과, 매연 생성량은 동일한 분위기 조건에서 초기 액적 직경 변화의 영향이 크게 나타나지 않았다. 또한, 매연 체적 분율 최댓값($f_{vmax}$)은 $135^{\circ}{\sim}315^{\circ}$ 측정 방향에서 높은 결과를 보였다. 이는 액적 점화 이후 Igniter의 이동 과정에서 생성된 Soot-tail로 인해 매연 체적분율 결과가 증가된 것으로 나타났다.

• Nuclear Engineering and Technology
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• 제39권4호
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• pp.313-326
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• 2007

In this paper, an algorithm to reconstruct two orthogonal images into a three-dimensional image is developed in order to measure the bubble size and volume in a two-phase boiling flow. The central-active contour model originally proposed by P. $Szczypi\'{n}ski$ and P. Strumillo is modified to reduce the dependence on the initial reference point and to increase the contour stability. The modified model is then applied to the algorithm to extract the object boundary. This improved central contour model could be applied to obscure objects using a variable threshold value. The extracted boundaries from each image are merged into a three-dimensional image through the developed algorithm. It is shown that the object reconstructed using the developed algorithm is very similar or identical to the real object. Various values such as volume and surface area are calculated for the reconstructed images and the developed algorithm is qualitatively verified using real images from rubber clay experiments and quantitatively verified by simulation using imaginary images. Finally, the developed algorithm is applied to measure the size and volume of vapor bubbles condensing in a subcooled boiling flow.

• 한국자동차공학회논문집
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• 제8권1호
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• pp.10-16
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• 2000

Spatially resolved liquid volume fractions from a set of line-of-sight laser diffraction measurements for axisymmetric sprays generated from a pintle-type gasoline injector have been tomographically reconstructed by Abel transformation, Fourier transformation and onion peeling method. Spatially resolved liquid volume fractions classified into 32 size groups were translated characteristics of SI engine fuel sprays. These data were also obtained from the phase Doppler measurements for the same sprays. The comparison between laser deffraction measurements and transformation reconstructs more reasonable spatially resolved characteristics for axisymmetric sprays as well as for asymmetric sprays.

• Computers and Concrete
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• 제5권6호
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• pp.509-524
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• 2008

Containment structures not only are leak-tight barriers, but also may be subjected to impacts caused by tornado-generated projectiles, aircraft crashes or the fragments of missile warhead. This paper presents the results of an experimental study of the impact resistance of steel fiber-reinforced concrete against 45 g projectiles at velocity around 2500 m/s. An explosively formed projectile (EFP) was designed to generate an equivalent missile fragment. The formation and velocity of EFP are measured by flash x-ray. A switch made of double-layered thin copper sheets controlled the exposure time of each flash x-ray. The influence of the fiber volume fraction on the crater diameter of concrete slab and the residual velocity of the projectile were studied. The residual velocity of the projectile decreased as the fiber volume fractions increased. In this work, the residual velocity of the projectile was to 44% that of plain concrete when the fiber volume fraction exceeded 1.5%. Based on the present finding, steel fiber reinforced concrete with the fiber volume fraction exceeding 1.5% appear to be more efficient in protection against high velocity fragment impact.

• 한국방재학회 논문집
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• 제10권2호
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• pp.31-37
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• 2010

본 연구는 디지털 이미지 처리 기법을 이용하여 2차원 이미지를 3차원으로 변환하기 위하여 형상변환계수 및 등가직경이론을 제안하였고, 이를 이용하여 수정입도분포곡선을 작성하였다. 연구에 이용된 골재는 천연골재(해변자갈) 2종 및 쇄석골재 2종 등 총 4종의 골재를 이용하였다. 4종의 골재에 대한 편평비는 각각 0.30, 0.36, 0.47 및 0.83으로 측정되었다. 형상변환계수는 각각 0.77, 0.78, 0.84 및 0.92로 결정되었다. 형상변환계수에 디지털이미지 처리기법에서 구한 입경을 곱하여 입자의 크기를 보정하였다. 보정된 입자크기를 이용하여 보정된 체적 및 중량을 구하여 수정입도곡선을 작성하였다.