• Wind and Structures
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• 제11권5호
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• pp.345-359
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• 2008

An experimental investigation of the flow over the rectangular body located in close proximity to a ground board was reported using the particle image velocimetry (PIV) technique. The present experiments were conducted in a closed-loop open surface water channel with the Reynolds number, $Re_H=1.2{\times}10^4$ based on the model height. In addition to the PIV measurements, flow visualization studies were also carried out. The PIV technique provided instantaneous and time-averaged velocity vectors map, vorticity contours, streamline topology and turbulent quantities at various locations in the near wake. In the vertical symmetry plane, the upperbody flow is separated from the sharp top leading edge of the model and formed a large reverse flow region on the upper surface of the model. The flow structure downstream of the model has asymmetric double vortices. In the horizontal symmetry plane, identical separated flow regions occur on both vertical side walls and a pair of primary recirculatory bubbles dominates the wake region.

• Earthquakes and Structures
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• 제12권5호
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• pp.583-589
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• 2017

In this study, result of a field investigation of railway traffic-induced vibrations is provided to examine acceptability levels of ground vibration and to evaluate the serviceability of a liquid-storage tank. Free field attenuation of the amplitudes as a function of distance is derived by six accelerometers and compared with a well-known half-space Bornitz's analytical solution which considers the loss of the amplitude of waves due to geometrical damping and material damping of Rayleigh. Bornitz's solution tends to overlap vertical free field vibration compared with in-situ measured records. The vibrations of the liquid-storage tank were compared with the USA, Federal Transportation Railroad Administration (FTA) criteria for acceptable ground-borne vibrations and with the criteria in DIN 4150-3 German standard. Comparing the thresholds stated in DIN 4150-3, absolute peak particle velocities are within the safe limits, however according to FTA velocity level at the top of the water tank exceeds the allowable limits. Furthermore, it is intended to indicate experimentally the effect of the kinematic interaction caused by the foundation of the structure on the free-field vibrations.

• 한국군사과학기술학회지
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• 제23권1호
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• pp.37-42
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• 2020

This study is for a bulletproof experiment through speed acceleration of steel ball(2.385 mm) at the laboratory level. The secondary propulsion method is used for speed acceleration, which uses a sabot assembly consisting of a sabot body, a plunger, water, and a sabot cap. At the core of the secondary drive, it is important that the energy in the water of the private particle is transferred well to the steel ball. The experiment was conducted by selecting a plunger that pushes water and water charged with variables. judging that the longer the contact time, the greater the energy transferred to the steel ball. As a result of experiments with each variable, the amount of water does not affect the speed acceleration efficiency of the steel ball and, when the length of the plunger is increased by 200 %, the speed of the steel ball can be accelerated up to 130 m/s.

• 한국방재학회 논문집
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• 제10권6호
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• pp.175-183
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• 2010

본 연구에서는 LDV시스템을 이용하여 부유식 방파제 주변의 유동장의 변화를 수리모형실험을 통해 분석하였다. LDV시스템은 유체의 유속을 측정하기 위해 다양한 수리모형실험에서 폭넓게 사용되어왔다. LDV시스템을 이용하면 측정시간이 오래 걸리는 단점이 있지만, 측정한 자료를 가공하지 않고 정확한 유속장을 제시할 수 있다는 장점이 있다. 방파제의 형상과 흘수를 달리하여 수리모형실험을 수행하였으며, 유동장과 와류의 상관관계를 분석하였다. 또한, 연직 2차원 Navier-Stokes 방정식 모형을 이용하여 수치모형실험을 수행하였으며, 수치모형실험 결과와 수리모형실험 결과를 비교분석하였다.

• 한국재료학회지
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• 제12권2호
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• pp.129-134
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• 2002

The optimum condition for fabricating cordierite disc type filter element was deduced. Cordierite monolith was used as starting material for filter element because it has many advantages such as high thermal shock resistance and good catalytic activity compared with $TiO_2$and SiC. The contents of organic additives and foaming agent were optimized to control the porosity and mechanical strength of cordierite filter. Among the required properties to be adopted as filter elements, the pressure drop and NOx removal efficiency were investigated depending on processing variables. It was found that pressure drop depends on particle size distribution of cordierite monolith and organic additives added as forming agent. The pressure drop at 5cm/sec of face velocity was in the range of 15~655mm$H_2O$ at room temperature. The NOx removal efficiency of catalytic filter with $V_2O_5$ as catalyst was over 85% at $450^{\circ}C$.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2006년도 제27회 추계학술대회논문집
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• pp.146-149
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• 2006

단일액체추진제 하이드라진 추력기의 인젝터로부터 발생하는 분무 특성을 파악하기 위해 입자영상유속계 및 레이저 도플러 유속계 기법을 적용하였다. 입자영상유속계를 이용하여 순간 평면 이미지를 획득하고 이 영상 자료를 통해 압력에 따른 분무정도 및 인젝터 분무성능을 판단하였다. 영상 이미지에서 누락된 분무 입자의 속도 및 입경 계측을 위해 레이저 도플러 유속계 계측방법을 적용하였다. 계측된 두 실험결과를 비교함으로써 분무 특성에 대한 명확한 이해 뿐만 아니라 인젝터 설계 변수 도출이 본 연구의 목적이다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2009년도 제33회 추계학술대회논문집
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• pp.202-206
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• 2009

고속회전 연료분사시스템의 분무특성을 연구하였다. 분무특성에 영향을 주는 직렬식 분무오리피스의 직경을 각각 1mm, 2mm, 3mm, 4mm, 5mm와 분무오리피스 수를 3개, 6개, 12개로 변화시켜가며 분무특성 연구를 수행하였다. PDPA 측정 시스템을 이용하여 분무입자의 크기와 속도, 분무분포 등을 측정하였고, 고속카메라를 이용하여 분무가시화를 수행하였다. 실험결과, 분무오리피스로부터 분출된 단일 액주의 길이는 회전속도에 의해 제어되며, 분무입자의 크기(SMD)는 분무오리피스의 직경과 수가 증가함에 따라 작아지는 경향을 보였다. 결국 분무입자의 크기를 제어하는 기본 메커니즘은 분무 오리피스내의 액막의 두께에 의해 결정됨을 알 수 있었다.

• 한국분무공학회지
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• 제8권1호
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• pp.16-22
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• 2003

Zeta potential measurements of colloid particles suspended in a liquid are performed by a Zeta Meter developed. There are many applications of colloid stability in spray technology, paints, wastewater treatment, and pharmaceuticalse. Zeta potentials of charged particles are obtained by measuring the electrophoretic velocities of the particles using video enhanced microscopy and image analysis program. The values of zeta potential of polystyrene latex(PSL), $silica(SiO_2)$M, polyvinylidence difluoride(PVDF), silicon nitride, and alumina particles in deionized (DI) water were measured to be -40.5, -31.9, -25.2, -15.1 and -10.1mV, respectively. The particles having high zeta potential less than -20 mV are stable in DI water, because the double layers of them have strong repulsive forces mutually, and the particles having low zeta potential over -20mV are unstable due to Van Der Waals forces. Silica(>20nm), PSL, aluminum and PVDF particles were found to be stable that would remain separate and well disperse, while silicon nitride and alumina particles were found to be unstable that would gradually agglomerate in DI water.

• 대한기계학회논문집B
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• 제23권1호
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• pp.92-103
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• 1999

The fuel spray behavior in the intake port of an electronic control port irijection gasoline engine has a strong influence on engine performance, exhaust emission and fuel consumption. Thus, in this study, fuel spray behavior and flow characteristics of the air assist gasoline spray injected into a suction flow in a simulated rectangular intake port have boon investigated. Macro-behavior of spray characteristics was investigated by means of visualization and the measurements of SMD and velocity were made by PDPA. For analysis the flow field with droplets size, droplets are classified five droplets size groups. As a result, the normal distance of suction flow increasing, the relatively large droplets distribution and SMD increase because small droplets easily follow suction flow. Near impinging wail, after impinging against the wall, secondary atomized small droplets of D < $30{\mu}m$ bound from the wall. And the increasement of suction flow progress to the large droplets of D > $100{\mu}m$ distribution. Therefore, SMD are apparently increased near impinging wall, Z/d = 9.0.

• 대한기계학회논문집B
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• 제23권1호
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• pp.123-130
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• 1999

The objective of the current study is to understand steady 3-dimensional flow phenomena in a bifurcated duct experimentally. A bifurcation model is fabricated with transparent acrylic resin to visualize the whole flow field with the PIV system. The gray level cross-correlation method is applied to the image processing algorithm. The subpixel and the area interpolation methods are used to obtain the final velocity vectors. The finite volume predictions are used to analyze the flow patterns in the bifurcation model. The results of the computer simulation and the PIV experiment for three-dimensional flow show the recirculation zone and the formation of the paired secondary flow distal to the apex of the bifurcation model. The results obtained with the two methods also show that the branch flow strongly strikes the inner wall due to the inertial effect and accompanied helical motion as it flows toward the outer wall.