• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.6
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• pp.19-26
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• 2002

The objective of this study is to examine a DI(Direct Injection) gasoline spray development process under different ambient pressures using PIV(Particle Image Velocimetry). fuel spray experiments were performed within a constant volume chamber. The spray structure, velocity maps, velocity and vorticity contours were obtained to investigate its spray characteristics. It was found that higher ambient pressure has a significant effect on radial growth of the spray. The position which has a maximum velocity moved from the spray edge to the spray center as ambient pressure was increased. Higher ambient pressure moved a maximum vorticity position upward of the spray.

• Journal of Advanced Marine Engineering and Technology
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• v.29 no.4
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• pp.453-460
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• 2005

Experiments were conducted to investigate the effect of the surface roughness on the flat plate turbulent boundary layer. The square rods were installed at the leading edge to make surface roughness. The particle image velocimetry was used to measure the mean velocities and velocity fluctuation component. All measurements were made over a range of w/k=1. 2 5 and $Re_x=80.000{\sim}360,000$. Friction velocity was measured by using Clauser plot method. The level of turbulent intensities on roughness surface appears more strongly than that of turbulent intensities on flat plate. A correlation of boundary layer thickness in term of $Re_x$ and w/k are presented.

• Journal of Power System Engineering
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• v.3 no.2
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• pp.13-19
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• 1999

The purpose of the present experimental study is to apply multi-point simultaneous measurement by PIV(Particle Image Velocimetry) to high-speed flow region within a domestic boiler circulation pump. Two different kinds of flow rate($27{\ell}/min,\;19{\ell}/min$)are selected as experimental condition. A volute casing and Impeller made of transparent Polycarbonate were made for the easy access of the illumination laser via fiber optical line and cylinder lens assembly to the measuring region. A CCD camera is syncronized with AOM to acquire clear original particle images. Optimized cross correlation identification to obtain velocity vectors is implemented by direct calculation of correlation coefficients. The instantaneous and time-mean velocity distribution, velocity profile and kinetic energy are represented quantitatively at the full-scale region for the deeper understanding of the unsteady flow characteristics in a commercial circulation pump.

• Journal of Power System Engineering
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• v.9 no.4
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• pp.45-50
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• 2005

Characteristics of flows at T-junction duct with and without orifices are investigated in this paper. Experiments and PIV visualization were carried out for several flow rates. Two-dimensional PIV experimental apparatus was decided by numerical analysis. PIV visualization was also coded to visualize flow fields at junctions for two-dimensional case. For the PIV visualization system, Grey-Level Cross-Correlation particle tracking algorithm was used to calculate the flow fields. Vinyl chloride polymer particles of $100{\sim}150{\mu}m$ of diameter are used in this visualization. The PIV visualization results showed relatively good agreement with Experimental data.

• Korean Journal of Metals and Materials
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• v.47 no.1
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• pp.7-12
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• 2009

The detailed quantitative microstructural data on the cracking of coarse constituent particles in 7075 (T651) series wrought Al-alloys have been studied using the utility of a novel digital image processing technique, where the particle cracks are generated due to monotonic loading. The microstructural parameters such as number density, volume fraction, size distribution, first nearest neighbor distribution, and two-point correlation function have been quantitatively characterized using the developed technique and such data are very useful to verify and study the theoretical models for the damage evolution and fracture of Al-alloys. The data suggests useful relationships for damage modeling such as a linear relationship between particle cracking and strain exists for the uniaxial tensile loading condition, where the larger particles crack preferentially.

• Journal of the Society of Naval Architects of Korea
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• v.45 no.1
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• pp.42-53
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• 2008

The two dimensional PIV (particle image velocimetry) measurement technique is applied to water flow in a narrow cavitation tunnel. The nearly homogeneous and isotropic turbulent flows are generated by the honeycomb installed in the tunnel and visualized with a PIV technique. The velocities in the measurement plane at the tunnel centerline 184cm downward from the honeycomb were measured and calculated by an image correlation technique. The turbulent properties are evaluated and each term in the turbulent kinetic energy equation is calculated for the conditions with different internal pressures. Lowering the internal pressure gives an effect on the turbulent flow due to growing bubbles which are resolved in the water. The turbulent kinetic energy in the measurement plane is decayed much slower than those of other research results carried out with wind tunnels. With decreasing the tunnel internal pressures the turbulent intensities are increased about 1.5 times and the anisotropic tendency is also increased.

• Ecology and Resilient Infrastructure
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• v.8 no.1
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• pp.1-8
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• 2021

A surface image velocimeter (SIV) measures the velocity of a particle group by calculating the intensity distribution of the particle group in two consecutive images of the water surface using a cross-correlation method. Therefore, to increase the accuracy of the flow velocity calculated by a SIV, it is important to accurately calculate the displacement of the particle group in the images. In other words, the change in the physical distance of the particle group in the two images to be analyzed must be accurately calculated. In the image of an actual river taken using a camera, camera lens distortion inevitably occurs, which affects the displacement calculation in the image. In this study, we analyzed the effect of camera lens distortion on the displacement calculation using a dense and uniformly spaced grid board. The results showed that the camera lens distortion gradually increased in the radial direction from the center of the image. The displacement calculation error reached 8.10% at the outer edge of the image and was within 5% at the center of the image. In the future, camera lens distortion correction can be applied to improve the accuracy of river surface flow rate measurements.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.1
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• pp.21-28
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• 2000

Although commercial PIV systems have been widely used for the non-intrusive velocity field measurement of fluid flows, they are still under development and have considerable room for improvement. In this study, a single-frame double-exposure PIV system using a high-resolution CCD camera was developed. A pulsed Nd:Yag laser and high-resolution CCD camera were synchronized by a home-made control circuit. In order to resolve the directional ambiguity problem encountered in the single-frame PIV technique, the second particle image was genuinely shifted in the CCD sensor array during the time interval dt. The velocity vector field was determined by calculating the displacement vector at each interrogation window using cross-correlation with 50% overlapping. In order to check the effect of spatial resolution of CCD camera on the accuracy of PIV velocity field measurement, the developed PIV system with three different resolution modes of the CCD camera (512 ${\times}$ 512, lK ${\times}$ IK, 2K ${\times}$ 2K) was applied to a turbulent flow which simulate the Zn plating process of a steel strip. The experimental model consists of a snout and a moving belt. Aluminum flakes about $1{\mu}m$ diameter were used as scattering particles for the liquid flow in the zinc pot and the gas flow above the zinc surface was seeded with atomized olive oil with an average diameter of 1-$3{\mu}m$. Velocity field measurements were carried out at the strip speed $V_s$=1.0 m/s. The 2K ${\times}$ 2K high-resolution PIV technique was significantly superior compared to the smaller pixel resolution PIV system. For the cases of 512 ${\times}$ 512 and 1K ${\times}$ 1K pixel resolution PIV system, it was difficult to get accurate flow structure of viscous flow near the wall and small vortex structure in the region of large velocity gradient.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.6
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• pp.874-887
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• 1998

A 2-frame PTV (particle tracking velocimetry) system using the concept of match probability between two consequent image frames has been developed to obtain instantaneous velocity fields. The overall 2-frame PTV system including image pre-processing, tracking algorithm and post-processing routine was implemented to apply to real flows. The developed 2-frame PTV system has several advantages such as high recovery ratio of velocity vectors, low error ratio and small computational time compared with the conventional 4-frame PTV and the FFT-based cross-correlation PIV technique. The 2-frame PTV system was applied to a turbulent channel flow over a rectangular block to check its reliability and usefulness. Total 96 sequential image frames have been captured and processed to get both mean and fluctuating velocity vector fields over the recirculating region. The mean velocity and turbulent intensity profiles were well agreed with hte LDV measurements in the separated region behind the block. Time-averaged reattachment length is about 6.3 times of the block height.

• Journal of Advanced Marine Engineering and Technology
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• v.27 no.3
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• pp.395-404
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• 2003

Quantitative data of the temperature and velocity were obtained simultaneously by using liquid crystal tracer. PIV(Particle Image Velocimety) based on a grey-level cross-correlation method was used for visualizing and analysis of the flow field. The temperature gradient was obtained by applying the color-image processing to a visualized image, and a neural-network a1gorithm was applied to the color-to-temperature calibration. This simultaneous measurement was applied to the Rayleigh-Bernard convection. This paper describes the method, and presents the quantitative visualization of Rayleigh-Bernard convection and the effect of aspect ratio and viscosity. Also the experimental results were compared with the numerical results.