• Proceedings of the Korea Water Resources Association Conference
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• 2008.05a
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• pp.1779-1783
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• 2008

영상해석을 통한 흐름해석의 방법인 Large-Scale Particle Image Velocimetry (LSPIV)는 실험실내의 소규모 흐름해석에 이용하던 Particle Image Velocimetry (PIV)를 자연하천이나 실험실에서 넓은 영역($4m^2{\sim}45,000m^2$)에 적용할 수 있도록 확장시킨 것으로 지난 10여년전부터 세계적으로 널리 이에 대한 연구가 진행되고 있다. PIV는 seeding, illumination, recording 그리고 image processing으로 구성된다. LSPIV(Large Scale PIV)는 PIV의 기본원리를 근거로 하여 기존의 PIV에 비하여 실험실 내에서의 수리모형실험이나 일반 하천에서의 유속측정과 같은 큰 규모의 흐름해석을 할 수 있도록 seeding, illumination에 대한 조정이 필요 하고, 촬영된 image에 대한 왜곡을 없애는 작업이 필요하다. LSPIV는 PIV의 네 가지 단계를 포함하여 seeding, illumination, recording, image transformation, image processing 및 post-processing의 여섯 단계로 구성되어진다 (Li, 2002). LSPIV의 적용시 각 단계마다 유속계산시 오차를 발생시키는 27가지의 요인들이 존재하고 있는바 (Kim, 2006), 본 연구에서는 이들 중 실내의 실험실에서 파악이 가능한 인자들에 대해 그들 각각의 인자들이 유속 측정에 미치는 오차의 정도를 파악하고자 하였다. 본 연구에서는 LSPIV의 적용시 이용되는 이미지의 개수와 이미지 촬영시 적용된 이미지의 해상도에 따른 오차의 발생 정도를 조사하였다. 이미지 촬영에 있어서 비디오카메라를 이용할 경우 촬영시간에 따라 많은 수의 이미지를 취득할 수 있은바 이미지의 수에 따른 유속계산오차를 파악하고자 하였다. 또한 디지털 카메라를 이용할 경우 여러 가지 이미지 해상도를 이용할 수 있으므로 적용한 이미지 해상도에 따른 유속계산에 미치는 오차의 크기를 파악하고자 하였다. 이미지의 갯수가 유속계산시 미치는 오차의 영향의 정도를 조사하기 위해서 초당 30 frame을 촬영할 수 있는 비디오카메라를 이용하여 91초 동안 촬영된 이미지로부터 매 5번째의 이미지를 추출하여 455개의 이미지를 준비하였고 이로부터 이미지수를 10, 50, 100, 200, 300, 400의 순서로 증가시키면서 이미지 개수로부터 나타나는 유속계산 오차를 조사한 결과 이미지의 개수가 50매 이상인 경우는 이로 인한 오차가 1% 이하로 감소함을 파악하였다. 촬영된 이미지의 해상도가 유속계산시 미치는 영향을 조사하기 위해 디지털카메라를 적용하여 세가지 이미지 해상도(640*480, 1280*960, 2048*1536 pixel)로 변화시키면서 유속측정 오차를 분석한 결과 저해상도의 이미지를 이용한 경우 고해상도 이미지를 이용한 경우와 비교하여 3% 가량의 차이를 나타내었다.

• Proceedings of the Korea Water Resources Association Conference
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• 2010.05a
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• pp.483-487
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• 2010

하천에서 물이 비교적 빠른 속도로 흘러가면 압력 변동, 하상의 조도, 하천내 구조물 등의 영향에 의해 수면이 끊임없이 변형을 일으키며 수면에 작은 물결(수면 파문)이 생긴다. 이러한 수면 파문은 유수에 의해 유수의 평균 유속으로 이류되며, 이 때문에 인간이 유수의 흐름을 시각적으로 인식할 수 있다. 이러한 표면 파문은 적절한 영상 분석을 하면 표면 유속 측정의 추적자로 이용할 수 있다. 본 연구는 유수 표면을 연속된 영상을 촬영하고, 일련의 영상을 시공간 영상(space-time image)으로 만든 뒤, 휘도 경사법(graylevel gradient method)으로 유속 벡터를 추출하는 새로운 방법을 제시하였다. 이 분석 과정은 기존의 입자 영상 유속계(PIV, Particle Image Velocimetry) 기법을 이용하는 방법보다 훨씬 간단하고 분석 시간도 크게 절약할 수 있다. 또한, 수면 파문의 전파에 따른 중력파의 영향을 시공간 영상의 처리 과정에서 잡음으로 간주하여 처리할 수 있다는 장점을 가지고 있다. 개발된 루틴을 표면 영상 유속계(SIV, Surface Image Velocimtery)에 구현하여 새로운 영상 유속계를 개발하였다. 시공간 영상 분속을 이용하는 새로운 영상 유속계를 실험실 수로의 영상 자료에 적용하여 그 정확도, 적용성, 장단점 등을 분석하였다. 제안된 방법에 의한 평균류 산정 결과는 물리적으로 타당하며, 저속 또는 저휘도에서의 분석 성능이 뛰어난 것으로 밝혀졌다. 다만, 이방향 흐름의 분석에서는 문제가 있는 것이 밝혀졌다.

• Journal of Magnetics
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• v.16 no.4
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• pp.444-448
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• 2011

In the present study, we separated the marker particles from the suspending particle mixture solution using isotacho-electrophoresis technique, a novel quantitative ionic particle separation method, in the microchannel. A multiple stacking zone of the suspending particle was visualized with variations in electric field strength, pH value and concentration of the ionic solution. In particular, the electrophoretic mobility of ionic particle (fluorescein) was estimated based on the electrophoretic velocity value measured by the particle image velocimetry. As a result, isotacho-electrophoresis zones were clearly visualized as going downstream in the electric field. The particle migration velocity increased proportional to the applied voltage increase; it was also affected by the pH value variations in the ionic solution.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2002.04a
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• pp.64-64
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• 2002

Two dimensional velocity distributions outside a Mach 2.0 supersonic nozzle have been investigated using digital particle image velocimetry (PIV). Mean velocities, turbulence intensities, vorticity field and volume dilatation field are obtained from 300 instantaneous PIV images using 0.33 $\mu\textrm{m}$ $TiO_2$ particle. The seeding particle of larger size, 1.4 $\mu\textrm{m}$ $TiO_2$, is also used for the experimental measurements of velocity lag downstream of shock waves according to particle sizes. The results have been compared and analyzed with schlieren photographs and computational fluid dynamics (CFD) results for the velocity distribution, the locations of shock waves and over-expanded shock structure. It was shown that the locations of normal shock and shock waves can be resolved by the axial or radial velocities, and the velocity lag is more significantly increased due to particle inertia as a particle size increases. And it was also found that over-expanded shock structures call be predicted by volume dilatation fields, and streamwise turbulence intensities are influenced significantly by normal shock waves.

• Journal of Advanced Marine Engineering and Technology
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• v.17 no.4
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• pp.28-37
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• 1993

Flow characteristics within the three-dimensional square cavity are studied experimentally by adopting PIV(Particle Image Velocimetry). A new method for tracking the same particle pairs in the consecutive flow image is suggested resulting in more effective acquisition of the velocity vectors. Two methods for supplying the shearing stress within the cavity are developed by continuous moving belt and 2-dimensional plane Poiseuille flow. The effect of TGL vortex in the case of belt-moving flow is remarkable owing to the distribution of the kinetic energy in the spanwise direction. But, for the plane Poiseuille flow, velocity profiles similar to a forced vortex are obtained and its tendency increases with the Reynolds number.

• 한국가시화정보학회:학술대회논문집
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• 2001.12a
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• pp.123-137
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• 2001

PIV (particle image velocimetry) systems use a camera to take snapshots of particles carried by a fluid at some precise instants. Signal processing methods are then used to compute the flow velocity field. In this paper, the design of the camera objective (optics) is addressed. The optimization is done in order to maximize the signal-to-noise ratio of in-focus particles. Four different kinds of noise are considered: photon shot noise, thermal and read noise, background glow shot noise, and noise made by the other particles. A semi-empirical model for the lens aberrations of a two-doublet objective is first addressed, since further, it is shown that lens aberrations (low f-value $f_{\#}$) should be used instead of the Fraunhofer diffraction (high f-value) for the fitting of the particle image size with the pixel size. Other important conclusions of the paper include the expression of optimum values for the magnification M, for the exposure period $\tau$ and for the pixel size $\xi$.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.507-510
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• 2002

An algorithm of 3-D particle image velocimetry(3D-PIV) was developed for the measurement of 3-D velocity Held of complex flows. The measurement system consists of two or three CCD camera and one RGB image grabber. Flows size is $1500{\times}100{\times}180(mm)$, particle is Nylon12(1mm) and illuminator is Hollogen type lamp(100w). The stereo photogrammetry is adopted for the three dimensional geometrical mesurement of tracer particle. For the stereo-pair matching, the camera parameters should be decide in advance by a camera calibration. Camera parameter calculation equation is collinearity equation. In order to calculate the particle 3-D position based on the stereo photograrnrnetry, the eleven parameters of each camera should be obtained by the calibration of the camera. Epipolar line is used for stereo pair matching. The 3-D position of particle is calculated from the three camera parameters, centers of projection of the three cameras, and photographic coordinates of a particle, which is based on the collinear condition. To find velocity vector used 3-D position data of the first frame and the second frame. To extract error vector applied continuity equation. This study developed of various 3D-PIV animation technique.

• International Journal of Aeronautical and Space Sciences
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• v.12 no.3
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• pp.296-304
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• 2011

In order to design a shear coaxial injector of solid particles with water, basic experiments on a particle laden jet are necessary. The purpose of the present study is to understand the effect of particle loading ratio on the particle spray characteristics (i.e. spreading angle, distribution of particle number density, velocity profiles, and particle developing region length). Hydro-reactive Al2O3 particles with a primary particle diameter of 35~50 ${\mu}m$ are used in this experiment. An automated particle feeder was designed to supply constant particle mass flowrates. Air is used as the carrier gas. To determine the air velocity at the orifice exit, tracers (aluminum oxide, 0.5~2 ${\mu}m$ primary diameter) are also supplied by a tracer feeder. A plain orifice type injector with 3 mm diameter, and 20 mm length was adopted. Particle image velocimetry is used to measure the mean and fluctuating velocity components along the axial and radial directions.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.7
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• pp.1741-1748
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• 1995

A new particle tracking algorithm using the concept of match probability between two consequent image frames has been developed to obtain an instantaneous 2-dimensional velocity field. A computer simulation has been carried out to check the performance and usefulness of the developed algorithm by comparing with the conventional 4-frame Particle Tracking Velocimetry(PTV) method. As a result the newly developed algorithm shows very good performance. Although the major part of the developed algorithm is time-consuming iterative updating routine of match probability, computational elapse time to get the resonable results is a very short compared with the 4-frame PTv.Additionally, the present 2-frame PTV algorithm recovers more velocity vectors and has higher dynamic range and lower error ratio compared with the conventional 4-frame PTV.

• Journal of the Korean Society of Visualization
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• v.4 no.2
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• pp.59-68
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• 2006

We have evaluated the performances of the following six interpolation schemes used for win-dow deformation in particle image velocimetry (PIV): the linear, quadratic, B-spline, cubic, sinc, Lagrange interpolations. Artificially generated images comprised of particles of diameter in a range pixel were investigated. Three particle diameters were selected for detailed evaluation: pixel with a constant particle concentration $0.02particle/pixel^2$. Two flow patterns were considered: uniform and shear flows. The mean and random errors, and the computation times of the interpolation schemes were determined and compared.