• Journal of Advanced Marine Engineering and Technology
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• v.37 no.5
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• pp.510-519
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• 2013

In this study, the spray characteristics of a pressure swirl atomizer classified into a liquid sheet-type swirl nozzle for Urea-SCR system were investigated experimentally with the variation of injection pressure. The length to diameter ratio ($l_o/d$) of the nozzle was 3.1, and the swirler was set inside the nozzle tip to give injecting fluid angular momentum. The injection duration of the nozzle was controlled by PWM (pulse width modulation) modes. The development processes of the spray were imaged by a 2-D PIV system, and the change of spray angle was measured. The atomization characteristics, including axial velocity and SMD, were measured using a 2-D PDA system with the injection pressures at room temperature and ambient pressure conditions. As the experimental results, the injection pressure had a significant impact on the spray structure showing a different shape around the spray leading edge, and the smaller SMD was observed with increasing injection pressures, which was similar to that of the previous work.

• 한국가시화정보학회:학술대회논문집
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• 2004.11a
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• pp.5-9
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• 2004

An experimental study is performed turbulent swirling flow behind a crcular cylinder using 2-D PIV technique. The Reynolds number investigated is 15,000. The mean velocity vector, time mean axial velocity, turbulence intensity, kinetic energy and Reynolds shear stress behind the cylinder are measured before and behind the cylinder along the test tube.

• Journal of Mechanical Science and Technology
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• v.18 no.12
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• pp.2265-2272
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• 2004

The aquaculture tank is used for breeding fish in sea water which was pumped up to land. The flow characteristics in the aquaculture were investigated with varying the tank geometry and flow rate. The numerical analysis has been employed for calculating the velocity and temperature distributions in a water tank of rectangular type. The finite volume method and SIMPLE algorithm with 3-dimensional standard $\kappa$-$\varepsilon$ turbulence model were used for the numerical analysis. For comparison with experimental results, the PIV system was applied to visualize the flow patterns quantitatively. The numerical results showed good agreements with the experimental results. The mean velocity and temperature versus aquarium depth were represented for various circulating flow rates. Especially, the aquaculture environment is recommended that the aquarium depth has to be d=0.5 m, and this case is the condition of higher velocity and temperature in winter season.

• Journal of the Korean Society of Visualization
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• v.7 no.2
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• pp.64-71
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• 2010

The flow and noise characteristics of wake behind wind-turbine blades have been investigated experimentally using a two-frame particle image velocimetry (PIV) technique. Experiments were carried out in a POSTECH subsonic large wind-tunnel ($1.8^W{\times}1.5^H{\times}4.3^L\;m^3$) with KBP-750D (3-blade type) wind-turbine model at a freestream velocity of $U_o\;=\;15\;m/s$ and a tip speed ratio $\lambda\;=\;6.14$ (2933 rpm). The wind-turbine blades are connected to an AC servo motor, brake, encoder and torque meter to control the rotational speed and to extract a synchronization signal for PIV measurements. The wake flow was measured at four azimuth angles ($\phi\;=\;0^{\circ}$, $30^{\circ}$, $60^{\circ}$ and $90^{\circ}$) of the wind-turbine blade. The dominant flow structure of the wake is large-scale tip vortices. The turbulent statistics such as turbulent intensity are weakened as the flow goes downstream due to turbulent dissipation. The dominant peak frequency of the noise signal is identical to the rotation frequency of blades. The noise seems to be mainly induced by the tip vortices.

• Wind and Structures
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• v.35 no.1
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• pp.1-20
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• 2022

This research work presents an experimental study's outcomes to reveal the impact of an O-ring on the flow control over a sphere placed in a turbulent boundary layer. The investigation is performed quantitatively and qualitatively using particle image velocimetry (PIV) and dye visualization. The sphere model having a diamater of 42.5 mm is located in a turbulent boundary layer flow over a smooth plate for gap ratios of 0≤G/D≤1.5 at Reynolds number of 5 × 10³. Flow characteristics, including patterns of instantaneous vorticity, streaklines, time-averaged streamlines, velocity vectors, velocity fluctuations, Reynolds stress correlations, and turbulence kinetic energy (), are compared and discussed for a naked sphere and spheres having O-rings. The boundary layer velocity gradient and proximity of the sphere to the flat plate profoundly influence the flow dynamics. At proximity ratios of G/D=0.1 and 0.25, a wall jet is formed between lower side of the sphere and flat plate, and velocity fluctuations increase in regions close to the wall. At G/D=0.25, the jet flow also induces local flow separations on the flat plate. At higher proximity ratios, the velocity gradient of the boundary layer causes asymmetries in the mean flow characteristics and turbulence values in the wake region. It is observed that the O-ring with various placement angles (𝜃) on the sphere has a considerable alteration in the flow structure and turbulence statistics on the wake. At lower placement angles, where the O-ring is closer to the forward stagnation point of the sphere, the flow control performance of the O-ring is limited; however, its impact on the flow separation becomes pronounced as it is moved away from the forward stagnation point. At G/D=1.50 for O-ring diameters of 4.7 (2 mm) and 7 (3 mm) percent of the sphere diameter, the -ring exhibits remarkable flow control at 𝜃=50° and 𝜃=55° before laminar flow separation occurrence on the sphere surface, respectively. This conclusion is yielded from narrowed wakes and reductions in turbulence statistics compared to the naked sphere model. The O-ring with a diameter of 3 mm and placement angle of 50° exhibits the most effective flow control. It decreases, in sequence, streamwise velocity fluctuations and length of wake recovery region by 45% and 40%, respectively, which can be evaluated as source of decrement in drag force.

• Wind and Structures
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• v.19 no.4
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• pp.389-404
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• 2014

The flow characteristics of a circular cylinder surrounded by an outer permeable cylinder were experimentally investigated using Particle Image Velocimetry Technique in deep water flow. In order to consider the effects of diameter and porosity of the outer cylinder on flow structures of the inner cylinder, five different outer cylinder diameters (D=37.5, 52.5, 60, 75 and 90 mm) and eight different porosities (${\beta}$=0.4, 0.5, 0.6, 0.65, 0.7, 0.75, 0.8 and 0.85) were selected. During the experiments, the diameter of inner cylinder was kept constant as d=30 mm. The depth-averaged free-stream velocity was adjusted as U=0.156 m/s, which corresponds to the Reynolds number of Re=5000 based on the inner cylinder diameter. It has been concluded that both the outer permeable cylinder diameter and the porosity have important influences on the attenuation of vortex shedding in the wake region. The presence of outer permeable cylinder decreases the magnitude of Reynolds shear stress and turbulent kinetic energy compared to the bare cylinder case. Moreover, the spectral analysis of vortex shedding frequency has revealed that the dominant frequency of vortex shedding downstream of the cylinder arrangement also reduces substantially due to the weakened Karman shear layer instability.

• Clinical and Experimental Pediatrics
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• v.48 no.7
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• pp.723-730
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• 2005

Purpose : This study was performed to characterize the etiology and clinical features of acute viral lower-respiratory tract infections(LRI). Methods : Etiologic agents and clinical features of acute viral LRI were studied from October. 2003 through March. 2004 in hospitalized children with LRI(253 cases) at Samsung Cheil Hospital. The viruses were identified by indirect immunofluorescent method. Medical records of patients with proven viral LRI were reviewed retrospectively. Results : Ninety two cases(36.4%) were confirmed as viral infections. The identified pathogens were respiratory syncytial virus(RSV, 76.0%), adenovirus(ADV, 12.0%), influenza virus type A(INFA, 9.8 %), influenza virus type B(INFB, 1.1%) and parainfluenza virus(PIV, 1.1%). Eight four point eight% of patients were younger than 2 years of age. Clinical diagnosis of LRI were pneumonia(56.5%), bronchiolitis(35.9%), tracheobronchitis(4.3%) and croup(3.3%). The clinical symptoms and signs were cough(98.8%), rhinorrhea(82.6%), fever(70.7%), rale(67.4%), wheezing(29.3%), chest retraction(28.3%) and cyanosis(4.3%). The severe respiratory symptoms and signs were more common in RSV-infected patients, even cyanosis could be observed. Seventeen point four percent of patient had fever of $38.5^{\circ}C$ or higher and their most common etiologic agent was INFA(66.7%). Twenty three point nine percent had fever more than 5 days and common etiologic agent was INFA(77.8%). The elevated WBC count($>14{\times}10^3/{\mu}L$) was in 14.1%, and common etiologic agents were INFA(22.2%) and ADV(18.2%). C-reactive protein(CRP >4.0 mg/dL) was increased in 13.0%, and common in ADV(63.6 %). Increased aspartate aminotransferase(AST)/alanine aminotransferase(ALT) was detected in 10.9%, and the most common etiologic agent was RSV(12.9%). Conclusion : The common agents of acute viral LRI were RSV, ADV and INF, respectively. Because the etiologic agents present variable clinical features, it may be helpful to treat and to evaluate acute viral LRI that we should understand their etiologic variability.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.15 no.1
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• pp.41-50
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• 2010

We have developed an in-situ benthic chamber (BelcI) for use in coastal studies that can be deployed from a small boat. It is expected that BelcI will be useful in studying the benthic boundary layer because of its flexibility. BelcI is divided into three main areas: 1) frame and body chamber, 2) water sampler, and 3) stirring devices, electric controller, and data acquisition technology. To maximize in-situ use, the frame is constructed from two layers that consist of square cells. All electronic parts (motor controller, pA meter, data acquisition, etc.) are low-power consumers so that the external power supply can be safely removed from the system. The hydrodynamics of BelcI, measured by PIV (particle image velocimetry), show a typical "radial-flow impeller" pattern. Mixing time of water in the chamber is about 30 s, and shear velocity ($u^*$) near the bottom layer was calculated at $0.32\;cm\;s^{-1}$. Measurements of diffusivity boundary layer thickness showed a range of $180-230\;{\mu}m$. Sediment oxygen consumption rate, measured in-situ，was $84\;mmol\;O_2\;m^{-2}\;d_{-1}$, more than two times higher than on-board incubation results. Benthic fluxes assessed from in-situ incubation were estimated as follows: nitrate + nitrite = $0.18\;{\pm}\;0.07\;mmol\;m^{-2}\;d^{-1}$ ammonium $23\;{\pm}\;1\;mmol\;m^{-2}\;d^{-1}$ phosphate = $0.09\;{\pm}\;0.02\;mmol\;m^{-2}\;d^{-1}$ and silicate = $23\;{\pm}\;1\;mmol\;m^{-2}\;d^{-1}$.

• Journal of Mechanical Science and Technology
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• v.15 no.4
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• pp.500-509
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• 2001

Offshore subsea pipelines must be stable against external loadings, which are mostly due to waves and currents. To determine the stability of a subsea pipeline on the seabed, the Morrison equation has been applied with prediction of inertia and drag forces. When the pipeline is placed in a trench, the force acting on it is reduced considerably. Therefore, to consider the stability of a pipeline in a trench, one must employ reduction factors. To investigate the stability of various trenches, we numerically simulated flows over various trenches and compared them with experimental data from PIV (Particle Image Velocimetry) measurements. The present results were produced ar Reynolds numbers ranging from 6$\times$10$^3$to 3$\times$10(sub)5 based on the diameter of the cylinder. Quasi-periodic flow patterns computed by large-eddy simulation were compared with experimental data in terms of mean flow characteristics fro typical trench configurations (W/H=1 and H/D=3, 4). The stability for various trench conditions was addressed in terms of mean amplitudes of oscillating lift and drag, and the reduction factor for each case was suggested for pipeline design.

• Journal of the Society of Naval Architects of Korea
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• v.52 no.4
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• pp.356-363
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• 2015

Microbubbles moving in the turbulent boundary layer are visualized and investigated in the point of frictional drag reduction. The turbulent boundary layer is formed beneath the surface of the 2-D flat plate located in the tunnel test section. The microbubble generator produces mean bubble diameter of 30 – 50 μm. To capture the micro-bubbles passing through the tiny measurement area of 5.6 mm² to 200 mm², the shadowgraphy system is employed appropriately to illuminate bubbles. The velocity field of bubbles reveals that Reynolds stress is reduced in the boundary layer by microbubbles’ activity. To understand the contribution of microbubbles to the drag reduction rate more, much smaller field-of-view is required to visualize the bubble behaviors and to find the 2-D void fraction in the inner boundary layer.