• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.6
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• pp.477-483
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• 2016

Velocity profiles of laminar, transition and turbulent boundary layers were investigated by using Particle Image Velocimetry(PIV) measurements on the flat plate at Mach 2.96. The Schlieren visualization and PIV measurements are also used to confirm whether the oblique shock wave generated from the leading edge affects the flow field over the flat plate. The laminar velocity profile measured from the experiment was well matched with the compressible Blasius solution. The velocity profile of the transition boundary layer was well correlated with the theoretical turbulent velocity profile from near the wall and the transition began from Re = $1.41{\times}106$. For the turbulent boundary layer, considering compressibility effects, the Van Driest-transformed velocity satisfies the incompressible log-law. It is found that the log region is extended farther in the wall-normal direction compared to the log region in incompressible boundary layer.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.19 no.6
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• pp.606-613
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• 2007

This study investigates the behavior of a plunging wave and its associated runup and overtopping through velocity measurements and suggests an empirical formula for overtopping velocities on a structure. The plunging wave breaking in front of the structure generates very bubbly flow fields. For measurements of the two phase flow field of the breaking wave, particle image velocimetry and a modified optical method were employed. The obtained velocity fields were discussed in respect of the process of wave impinging, runup and overtopping. The overtopping velocity distribution is found to have a nonlinear profile showing a maximum magnitude at its front part. The relationship of self-similarity among dimensionless parameters is observed and used to obtain the regression formula to depict the overtopping velocity.

• Journal of the Society of Naval Architects of Korea
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• v.53 no.5
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• pp.371-379
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• 2016

In the ship design process, ship motion and propulsion performance in sea waves became very important issues. Especially, prediction of ship propulsion performance during real operation is an important challenge to ship owners for economic operation in terms of fuel consumption and route-time evaluation. Therefore, it should be considered in the early design stages of the ship. It is thought that the averaged value and fluctuation of effective inflow velocity to the propeller have a great effect on the propulsion performance in waves. However, even for the nominal velocity distribution, very few results have been presented due to some technical difficulties in experiments. In this study, flow measurements near the propeller plane using a stereo PIV system were performed. Phase-averaged flow fields on the propeller plane of a KVLCC2 model ship in waves were measured in the towing tank by using the stereo PIV system and a phase synchronizer with heave motion. The experiment was carried out at fully loaded condition with making surge, heave and pitch motions free at a forward speed corresponding to Fr=0.142 (Re=2.55×106) in various head waves and calm water condition. The phase averaged nominal velocity fields obtained from the measurements are discussed with respect to effects of wave orbital velocity and ship motion. The low velocity region is affected by pressure gradient and ship motion.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.7
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• pp.992-997
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• 2012

In this paper, we were analyzed the vibration characteristics of the three-phase cast resin transformer using less than 50% of load in the field. Most of the cast resin transformer is less than 50% in the domestic field is used for load conditions. Consisting of a solid insulator cast resin transformer is generating lots of noise and vibration. In addition, because it is affected by Joule 's heat is used in light load conditions. As a results, the transformer vibrations at frequencies below about from 200Hz to 500Hz were detected. Vibration velocity depends on the load variations were found. Load up to approximately 20-30% in most cases the vibration velocity was found at 4,000 ${\mu}m/s$ or less, 8,000 ${\mu}m/s$ or more. Vibration frequency at light load conditions were generated at the 120Hz, 240Hz, 360Hz and 480Hz. At the load condition of from 10% to 20%, vibration velocity is higher than another. Most of the vibration velocity were identified at the 1,000 ${\mu}m/s$ or less. Using the vibration frequency and velocity measurements data, the load on the cast resin transformer analyzed the correlation of the burden. Therefore, this data could be found in the vibration characteristics of the light-load conditions. If the field measurements using the data perform diagnostics on the transformer, it's expected to be very effective.

• International Journal of Vascular Biomedical Engineering
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• v.1 no.2
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• pp.30-35
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• 2003

Flow characteristics of blood flow in a micro channel were investigated experimentally using a micro-PIV (Particle Image Velocimetry) velocity field measurement technique. The main objective of this study was to understand the real blood flow in micron-sized blood vessels. The Reynolds number based on the hydraulic diameter of micro-channel for deionized (DI) water was about Re=0.34. For each experimental condition, 100 instantaneous velocity fields were captured and ensemble-averaged to get the spatial distributions of mean velocity. In addition, the motion of RBC (Red Blood Cell) was visualized with a high-speed CCD camera. The captured flow images of nano-scale fluorescent tracer particles in DI water were clear and gave good velocity tracking-ability. However, there were substantial velocity variations in the central region of real blood flow in a micro-channel due to the presence of red blood cells.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.7
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• pp.930-937
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• 2011

The characteristics of mean velocity and turbulence have been analyzed in the circular open channel flow using PIV measurement data for a wide range of water depth. The measured data are fitted to a velocity distribution function over the whole depth of the open channel. Reynolds shear stress and mean velocity in wall unit are compared with the analytic models for fully-developed turbulent boundary layer. Both the mean velocity and Reynolds shear stress have different distributions from the two-dimensional boundary layer flow when the water depth increases over 50% since the influence of the side wall penetrates more deeply into the free surface. The cross-stream Reynolds normal stress also has considerably different distribution in view of its peak value and decreasing rate in the outer region whether the water depth is higher than 50% or not.

• Journal of Industrial Technology
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• v.17
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• pp.51-72
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• 1997

The sound velocity measurements can permit much higher precision than that obtainable in the direct PVT experiments in addition to producing static and dynamic properties simultaneously, and thus the study on the sound velocity has been considered as another important approach to a fundamental understanding and description of the structure of fluids. This review deals with what have been done on studies of the sound velocity for evaluating thermodynamic properties with an emphasis on the development of the methods to extract the thermodynamic properties from the experimental data on sound velocity.

• Journal of the Society of Naval Architects of Korea
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• v.40 no.5
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• pp.17-25
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• 2003

Velocity field behind a container ship model with a rotating propeller has been investigated using PIV (particle image velocimetry) system. Four hundred instantaneous velocity fields were measured at 4 different blade phases and ensemble-averaged to investigate the spatial evolution of vortical structure of near wake within one propeller diameter downstream. The phase-averaged mean velocity fields show the potential wake and the viscous wake formed due to the boundary layers developed on the blade surfaces. The interaction between bilge vortex developed along the hull surface and the tangential velocity component of incoming flow causes to have asymmetric flow structure in the transverse plane.

• Journal of Advanced Marine Engineering and Technology
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• v.15 no.1
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• pp.71-74
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• 1991

Uncertainty analyses accompanied by the measurement of the velocity vectors in 3-D cavity flows are carried out. Twenty-one elemental errors are esimated or calculated according to the ANIS/ASME uncertainty analysis manual. Error components associater with the PIV(Particle Imaging Velocimetry) are reasonably small and the errors caused by the flow characteristics are fairly large, which confirm the reliability of the PIV measurement and also give good information to the planning phase of the experiment by discriminating the most critical parameter. The present study reveals that vector length expressed by pixels is the most influential. Calculated relative uncertainty for the all experimental conditions is ranging about 5-10% in terms of the representative velocity 0.5U. U is here the belt velocity on the cavity apparatus. Approximating equations to show the relative rss uncertainties are given and graphic representations are followed for the easier understanding of the uncertainty, existing in the velocity profiles of the cavity flow.

• Proceedings of the KOSOMBE Conference
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• v.1994 no.12
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• pp.153-156
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• 1994

An in vitro steady flow experiment was performed in order to test the accuracy of velocity measurement obtained through a pulsed Doppler echocardiography. A flow phantom was designed for the use in a wide velocity range at a given flow rate. The results showed that the pulsed Doppler velocity measurement obtained in this flow phantom is accurate at low flow rates. However, ultrasound velocity measurement should be performed under a careful considerations of PRF and Doppler gain settings, especially at higher flow rates.