• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.5
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• pp.1262-1275
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• 1993

The drag reduction effect of a freely-rotatable splitter plate was experimentally investigated in the 2-D wake behind a circular cylinder. By arranging the splitter plate to be aparted with a certain gap from the cylinder, the splitter plate was able to be aligned itself automatically to the flow direction in the tested range of 6.2$\times$$10^3$$\times$$10^4$. As a result, it was proven that the self-adjustable splitter plate always reduced effectively the drag imposed on the body against any arbitrary flow directions. In a specific range of Reynolds numbers, the drag reduction effect was dependent not only on the length of the splitter plate but also on the gap distance between the plate and the trailing edge of the body. For a splitter plate with a specific length, there existed a unique optimum range of gap distance to obtain successfully the drag reduction effect, however, the optimum range of gap distance was dependent on Reynolds number.

• Fibers and Polymers
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• v.2 no.4
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• pp.203-211
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• 2001

Residual stresses were predicted by a flow analysis in the mold cavity and residual stress distribution in the injection molded product was measured. Flow field was analyzed by the hybrid FEM/FDM method, using the Hele Shaw approximation. The Modified Cross model was used to determine the dependence of the viscosity on the temperature and the shear rate. The specific volume of the polymer melt which varies with the pressure and temperature fields was calculated by the Tait\`s state equation. Flow analysis results such as pressure, temperature, and the location of the liquid-solid interface were used as the input of the stress analysis. In order to calculate more accurate gap-wise temperature field, a coordinate transformation technique was used. The residual stress distribution in the gap-wise temperature field, a coordinate transformation technique was used. The residual stress distribution in the gap-wise direction was predicted in two cases, the free quenching, under the assumption that the shrinkage of the injection molded product occurs within the mold cavity and that the solid polymer is elastic. Effects of the initial flow rate, packing pressure, and mold temperature on the residual stress distribution was discussed. Experimental results were also obtained by the layer removal method for molded polypropylene.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.10 s.115
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• pp.1057-1066
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• 2006

Acoustic streaming Induced by longitudinal vibration at 30 kHz is visualized for a test fluid flow between the stationary glass plate and ultrasonic vibrating surface with particle imaging velocimetry (PIV) To measure an increase in the velocity of air flow due to acoustic streaming, the velocity of air flow in a gap between the heat source and ultrasonic vibrator is obtained quantitatively using PIV. The ultrasonic wave propagating into air in the gap generates steady-state secondary vortex called acoustic streaming which enhances convective cooling of the stationary heat source. Heat transfer through air in the gap is represented by experimental convective heat transfer coefficient with respect to the gap. Theoretical analysis shows that gaps for maximum heat transfer enhancement are the multiple of half wavelength. Optimal gaps for the actual design are experimentally found to be half wavelength and one wavelength. A drastic temperature variation exists for the local axial direction of the vibrator according to the measurement of the temperature distribution in the gap. The acoustic streaming velocity of the test fluid in the gap is at maximum when the gap agrees with the multiples of half wavelength of the ultrasonic wave, which are specifically 6 mm and 12 mm.

• Journal of Radiation Industry
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• v.9 no.3
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• pp.131-135
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• 2015

The flow characteristics of fluid were measured using radioactive tracer in pilot scale digester with tray motion mixer. In consideration of the detection volume of the detector and the size of the digester, 20 detectors were installed in the digester. The radioactive tracer eluted 8 mCi of $^{68}Ga$ from $^{68}Ge/^{68}Ga$ generator was injected into the digester bottom. After radiotracer injection, the flow pattern was measured on the basis of the initial movement of the tracer until its diffusion completely. Most of tracer moved to the wall along the bottom of the digester, and then rose along the wall. The other tracer moved up along the mixer, and then moved to the wall direction along the surface.

• Journal of the Korean Society for Railway
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• v.19 no.1
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• pp.11-19
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• 2016

The flows around a high speed train are very important because they could affect the aerodynamic characteristics such as drag and acoustic noise. Especially the boundary layer of flows could represent the characteristic of flows around the high speed train. Most previous studies have focused on the boundary layer region along the train length direction for the side of the train and underbody. The measurement and analysis of the boundary layer for the roof side is also very important because it could determine the flow inlet condition for the pantograph. In this study, the roof boundary layer was measured with a 1/20 scaled model of the next generation high speed train, and the results were compared with full-scaled computational fluid dynamics results to confirm their validity. As a result, it was confirmed that the flow inlet condition for the pantograph is about 85% of the train speed. Additionally, the characteristics of the boundary layer, which increases along the train direction, was also analyzed.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.47 no.4
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• pp.411-418
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• 2011

As a fish way is a structure for fish migrating well toward upper stream due to breaking river flow by a dam or dammed pool, the specific fish's swimming ability is one of the main factors in making a plan and managing it. In addition, it also needs to understand the current field in fish road to evaluate its performance. This study is aimed to analyze the swimming patterns with current velocity changes using a Particle Imaging Velocimetry (PIV) in order to understand the swimming ability of silver fish (Plecoglossus altivelis) that is one of the fishes migrating through the fish way of Nakdong River, and to analyze the 2 dimensional current field near to silver fish at swimming momentum. The results showed that average values of tail beat frequencies for continuous swimming with current velocity were 2.8 Hz at 0.3 m/s, 3.2 Hz at 0.4 m/s, 3.8 Hz at 0.5 m/s, respectively. The wake would be produced by direction turning of fish's tail fin and its magnitude would be verified by the difference of pressure. The pressure turbulent flow produced by its tail beat would be made in both sides, and then, the magnitude of wake should be the source of moving direction. The swimming momentum will help to support the primary factor in making a suitable design for specific fish species migrating toward the district river.

• Proceedings of the Korean Nuclear Society Conference
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• 1999.05a
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• pp.104-104
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• 1999

The local heat transfer coefficient is experimentally investigated for the reflux condensation in a countercurrent flow between the steam-air mixture and the condensate. A single vertical tube has a geometry which is a length of 2.4m, inner diameter of 16.56mm and outer diameter of 19.05mm and is made of stainless steel. Air is used as a noncondensible gas. The secondary side is installed in the form of coolant block around vertical tube and the heat by primary condensation is transferred to the coolant water. The local temperatures are measured at 15 locations in the vertical direction and each location has 3 measurement points in the radial direction, which are installed at the tube center, at the outer wall and at the coolant side. In three different pressures, the 27 sets of data are obtained in the range of inlet steam flow rate 1.348 -3.282kg/hr, of inlet air mass fraction 11.8 -55.0%. The local heat transfer coefficient increases as the increase of inlet steam flow rate and decreases as the decrease of inlet air mass fraction. As an increase of the system pressure, the active condensing region is contracted and the heat transfer capability in this region is magnified. The empirical correlation is developed represented with the 165 sets of local heat transfer data. As a result, the Jacob number and film Reynolds number are dominant parameters to govern the local heat transfer coefficient. The rms error is 17. 7% between the results by the experiment and by the correlation.

• Wind and Structures
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• v.21 no.2
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• pp.119-158
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• 2015

The characteristics of the coherence functions of X axial, Y axial, and RZ axial (i.e., body axis) wind forces on the Shanghai World Trade Centre - a 492 m super-tall building with section varying along height are studied via a synchronous multi-pressure measurement of the rigid model in wind tunnel simulating of the turbulent, and the corresponding mathematical expressions are proposed there from. The investigations show that the mathematical expressions of coherence functions in across-wind and torsional-wind directions can be constructed by superimposition of a modified exponential decay function and a peak function caused by turbulent flow and vortex shedding respectively, while that in along-wind direction need only be constructed by the former, similar to that of wind speed. Moreover, an inductive analysis method is proposed to summarize the fitted parameters of the wind force coherence functions of every two measurement levels of altitudes. The comparisons of the first three order generalized force spectra show that the proposed mathematical expressions accord with the experimental results well. Later, the influences of coherence functions on wind-induced dynamic responses are analyzed in detail based on the proposed mathematical expressions and the frequency-domain method of random vibration theory.

• Wind and Structures
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• v.18 no.3
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• pp.295-320
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• 2014

The characteristics of amplitudes and power spectra of X axial, Y axial, and RZ axial (i.e., body axis) wind forces on a 492 m high-rise building with a section varying along height in typical wind directions are studied via a rigid model wind tunnel test of pressure measurement. Then the corresponding mathematical expressions of power spectra of X axial (across-wind), Y axial (along-wind) and torsional wind forces in $315^{\circ}$ wind directions are proposed. The investigation shows that the mathematical expressions of wind force spectra of the main structure in across-wind and torsional directions can be constructed by the superimposition of an modified wind spectrum function and a peak function caused by turbulent flow and vortex shedding, respectively. While that in along-wind direction can only be constructed by the former and is similar to wind spectrum. Moreover, the fitted parameters of the wind load spectra of each measurement level of altitude are summarized, and the unified parametric results are obtained. The comparisons of the first three order generalized force spectra show that the proposed mathematical expressions accord with the experimental results well.

• Journal of the Korean Geophysical Society
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• v.8 no.4
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• pp.201-205
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• 2005

Turbulent fluxes of heat, water vapor, and CO2 have been measured since August, 2003 at Dasan Station (78o 55’ N, 11o50’E) in the Arctic. These data can allow us to better understand the interactions between the Polar ecosystems and the atmosphere together with those at King Sejong Station in the Antarctic. Due to the buildings and measurement platforms around the flux tower, it is required to evaluate how they influence measured flux data. By using one-year turbulence statistics data and footprint model, flux footprint climatology was analyzed together with data availability. The upwind distance of source area ranged from 150 to 300 m, where the buildings and measurement platforms existed. However, flow distortion due to them may be not a major factor to reduce the data availability significantly. Based on, the dominant wind direction of SW and footprint climatology, the location of flux tower is considered suitable for flux measurement.