• Proceedings of the KSRS Conference
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• v.2
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• pp.672-675
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• 2006

The geostrophic current component is estimated from the sea surface velocity observed by the long-range High-Frequency Ocean Radar (HF radar) system in the upstream of the Kuroshio, by comparing with geostrophic velocity determined from along-track T/P and Jason-1 altimetry data. However, the sea surface velocity of the HF radar (HF velocity) contains not only the geostrophic current but also the ageostrophic current such as tidal current and wind-driven Ekman current. Tidal current component is first extracted by the harmonic analysis of the time series of the HF velocity. Then, the Ekman current is further estimated from daily wind data of IFREMER by applying the least-square method to the residual difference between the HF velocity and the altimetry geostrophic velocity. As a result, the Ekman current in the HF velocity is estimated as 1.32 % of the wind speed and as rotated 45$^{\circ}$ clockwise to the wind direction. These parameters are found almost common in the Kuroshio area and in the Open Ocean. After these corrections, the geostrophic velocity component in the HF velocity agrees well with the altimetry geostrophic velocity.

• Ocean and Polar Research
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• v.25 no.spc3
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• pp.399-408
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• 2003

The behavior of Suspended Sediment Concentrations (SSC) around a silt screen in a microtidal coastal area was hydrodynamically measured. The current speed at the mid-layer about 30m downstream of the screen reduces to about half that at the same distance upstream. It was caused by the contraction of the vertical section due to the screen. Even during a relatively weak storm period the SSC increases to that of the value caused by dredging. Section-averaged SSC at the downstream of the screen is higher by about 60% than that at the upstream, suggesting that the silt screen plays an adverse effect rather than a constructive role in the reduction of SSC generated by dredging.

• Journal of Institute of Control, Robotics and Systems
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• v.14 no.2
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• pp.205-211
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• 2008

This paper describes the method aimed at establishing the equipment measuring the parameter of Cable Network by Best proper Cable Modem and PDA through RS232 interface. In this paper, we propose our creative experimental configuration and develope the Cable Modem (DOCSIS 2.0) superior more performing than the referred Cable Modem (DOCSIS 1.0, 1.1) and the measuring equipment of HFC network compositing of Cable Modem and PDA through RS232 interface. This equipment analyzes Upstream (U/S) and Downstream (D/S) Signal quality and generates the signal of Upstream by CW signal. The paper also provides the experimental results to check the Best Proper Cable Modem and the displayed screen for parameters for SNR, BER and the demodulated IQ diagram of 256QAM through LCD of PDA. Henceforth, it'll be possible to support a variety of the functions for E-mail, Internet, the speed test of WEB connection and the transmission of the measured result real time by PDA.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.4B
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• pp.257-269
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• 2003

S(Synchrous)-DMT(Discrete Multi Tone) is an emerging cable modem technology applicable to the upstream channel for high speed multimedia communication. In this paper we analyze the transmitting and receiving process of S-DMT scheme and derive bit error probability of S-DMT scheme in the $\varepsilon$-mixture impulse noise model which appropriately reflects impulse noise model which approproately reflects impulse noise characteristics of upstream channel. The analysis results show a good match with the simulation results. We also compare Eb/No gain performance of S-DMT with TDMA in 16-, 32-, 64-QAM.

• Proceedings of the KIEE Conference
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• 2005.07b
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• pp.972-974
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• 2005

The present work deals with the theoretical study of the effects of copper vapours resulting from the erosion of the electrodes on the properties of a SF6 arc in a Laval nozzle. Computations have been done for a DC arc of 1000A with upstream gas pressure of 3.75MPa. The arc plasma is assumed to be in local thermodynamic equilibrium(LTE). The sheath and non-equilibrium region around the electrodes are not considered in this model. However, its effects on the energy flux into the electrodes are estimated from some experimental and theoretical data. The turbulence effects are calculated using the Prandtl mixing length model. A conservation equation for the copper vapour concentration is solved together with the governing equations for mass, momentum and energy of the gas mixture. Comparisons were made between the results with and without electrodes erosion. It has been found that the presence of copper vapours cools down the arc temperature due to the combined effects of increased radiation and increased electrical conductivity. The copper vapour distribution is very sensitive to the turbulent parameter. The erosion of upstream electrode(cathode) has larger effects on the arc compared to the downstream electrode(anode) as the copper vapour eroded from the anode cannot diffuse against the high-speed axial flow.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.10a
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• pp.119-123
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• 2013

We conduct the research for reducing aeroacoustic noise occurred when a vehicle operates in high speed situation without modifying the structural configuration such as deforming A-pillar's side curvature. We introduce PAU (Pneumatic Auxiliary Unit) which is a sort of air duct using intake air through radiator grill. According to our research, we can reduce overall noise levels around the surface of HSM (Hyundai Simplified Model). When a vehicleruns 100km/s, area-weighted acoustic power level (AWAPL) indicates 33dB without PAU. However with PAU, coverall AWAPL is decreased to 29dB which means we can improvesilentness approximately 12% compared to ordinary case. Moreover we conduct similar implementation to steering situation especially about yawing. In varioussituations, -10, 0, 10 degree of yawing, we observe 10% reduction in the upstream region of HSM but little increase in downstream region. It seems that inlet air overlap turbulent kinetic energy to surrounding flow. Even though downstream region's noise is louder than upstream region, overall AWAPL is still lower than conventional condition. We also apply this scheme to the real vehicle situation, then we get reasonable output which can support our research outputs.

• Wind and Structures
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• v.28 no.6
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• pp.355-367
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• 2019

Control of horseshoe vortex in the circular cylinder-plate juncture using vortex generator (VG) was studied at $Re_D$(where D is the diameter of the cylinder) = $2.05{\times}10^5$. Impact of a number of parameters e.g., the shape of the VG's, number of VG pairs (n), spacing between the VG and the cylinder leading edge (L), lateral gap between the trailing edges of a VG pair (g), streamwise gap between two VG pairs ($S_{VG}$) and the spacing between the two VG's in parallel arrangement ($Z_{VG}$) etc. were investigated on the horseshoe vortex control. The study is conducted using surface oil flow visualization and surface pressure measurements in low speed wind tunnel. It is observed that all the parameters studied have significant control effect, either by reduction in separation region or by lowering the adverse pressure along the symmetric axis upstream of the juncture.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.11a
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• pp.378-381
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• 2009

A rotating stall, an instable phenomenon of compressor, brings about reducing the pressure rise, the efficiency of compressor and a mechanical demage. In order to improve instability and extend operating range, it was performed that a stability enhancement experiment applying air injection method at the 4-stage low-speed axial compressor. The coanda nozzle was used to inject air in axial direction at rotor tip and 8 injectors were set up at regular interval at the upstream of 1st stage rotor. At 80% speed, injectors were worked before rotating stall happened. As injecting the 5.4% air of mode inception flow rate, the stability of compressor operation enhanced about 4%.

• Journal of Advanced Marine Engineering and Technology
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• v.31 no.6
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• pp.687-693
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• 2007

It has been known that one of the main obstacles of improving the performance of positive displacement hydraulic turbine is pressure pulsation which occurs at the regions upstream and downstream of the turbine. In order to suppress the pressure pulsation. occurrence reason of the pressure pulsation should be understood in detail Therefore. this study aims to establish a CFD analysis method by which the phenomena of unsteady pressure pulsation can be examined with high accuracy. Internal flow field of the turbine is modeled simply to generalize the relation between the pressure pulsation and internal flow. The results show that the Present CFD method adopting unsteady calculation can be applied successfully to the analysis of the Phenomena of Pressure Pulsation. Occurrence of the Pressure pulsation is due to the difference of the rotational speed of turbine rotors When driving rotor rotates by uniform speed and fellowing rotor rotates by variable speed, very large Pressure pulsation occurs within the turbine periodically.

• International Journal of Highway Engineering
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• v.11 no.2
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• pp.217-228
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• 2009

Sections under the influence of merging in an uninterrupted facility create irregular interaction between vehicles, such as lane change, speed acceleration and deceleration because of the merging of ramp traffic flows which have traffic characteristics different from those of the main line. This causes a confused traffic flow phenomenon(turbulence), which is considered an unstable traffic characteristic between various continuous points in consideration of v conditions. In this study, in merge influence sections, detectors by lane-point were installed to create time and space-series -traffic data. The least significant difference(LSD), as the criteria for discriminating a significant speed change between points, was calculated to examine the turbulence. As a result, turbulence in merge influence section was found to change the zones of such occurrence and the seriousness levels according to traffic condition. Thus, the maximum merge influence section due to the turbulence was created in the traffic condition before congestion when traffic increases. According to characteristics of changes in speed, merge influence section was divided into upstream 100m$\sim$downstream 100m(a section of speed reduction), and downstream 100m$\sim$downstream 400m(a section of reduced speed maintenance and acceleration).