• Journal of Korea Water Resources Association
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• v.36 no.6
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• pp.971-984
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• 2003

This paper presents the hydraulic analysis of the air entrainment by the weir types. For the weir types, the stepped weir, the labyrinth weir and the gate underflow weir were selected, and the oxygen transfer efficiency was estimated by the site investigation and the hydraulic model tests. The most effective type for the oxygen transfer was stepped weir The more steps the stepped weir had, the higher efficiency it revealed. Oxygen transfer was proportional to the flow velocity, the Froude number, and the flow discharge in order. Hydraulic model tests showed that a nappe flow occurred at small flow rates. The concurrent condition of a nappe flow and a skimming flow occurred as flow rate increases, nappe flow at the upper part and skimming flow at the lower part. In the region of nappe flow, air inception occurred from the step edges due to flow separation, and air entrainment was made through a free-falling nappe, an air pocket, a nappe impact and a subsequent hydraulic jump. In the region of skimming flow, air entrainment occurred by the variation of water surface over the steps, but it was relatively small compared with nappe flow.

• Explosives and Blasting
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• v.16 no.4
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• pp.29-39
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• 1998

A case study was made on in site vibration velocity data collected for two months in the construction area of the Daeduck cultural City Hall. Taegu The geology over the area shows distributions of weathered and some crack developed hornfels of mud-shale in the upper part, underlain by less weathered and hard compact quartzite. For the period of 2 months of blasting event, the vibration velocities were measured and these data were analysed for K and n for three different period the test period, first month and second month. The data for the test period show that K and n are 2464 and 1.621 with the cube root method, and 7154 and 1.791 with the sqare root one, respectively. The data for the first month collected mostly from blasting in the upper hornfels show that K and n are 1668 and 1,492 for the cube root and 1219 and 1,366 for the square root, respectively. Such a significant decrease in the K and n values from the test period through the first month for the weathered and comparatively well crack developed rocks hard and compact lower quartzite, may be due to difference in attenuation of waves propagating through physically different media. Therefore, for more effective safety design and blasting, it seems that it may be n to adopt appropriate K and n values, with getting lower step by step while proceeding the operation. In the meantime, the attenuation rate of K and n together with SD cross point for the cube and square root methods indicates that the cube root one appears to be more applicable than the square root for this area with limited distance(The maximum is 100m).

• Proceedings of the KIEE Conference
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• 1992.07b
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• pp.1211-1214
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• 1992

AC servo motor drives, Fara DS series, proposed in this paper can be effectively used in robots, CNC machine tools, and FA system with AC servo motors as actuators. The inverter of the AC servo drive consists of IGBT (Insulated Gate Bipolar Transistor) which have high switching frequency. Noises and vibrations generated in variable speed control of AC servo motors can be greatly reduced due to their high switching frequencies. In the developed servo drive, maximum torque is always generated in the whole speed range by compensating phase shift, which results from the nonlinearies of the AC servo motor during abrupt acceleration and deceleration. Abundant protection functions are provided to prevent abnormal state of the servo motor, and furthermore diverse user options are considered provided for the effective application. The proposed AC servo motor drive is designed to minimize velocity variation with respect to external load, supply voltage, environmental temperature, and humidity, so can be widely used in the fields of factory automation including robots and CNC msachine tools.

• Journal of Conservation Science
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• v.33 no.6
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• pp.467-483
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• 2017

In this study, the degradation properties by temperature stress of $Araldite^{(R)}$ rapid-curing epoxy resin used for inorganic cultural heritages, was identified. The tensile and tensile shear strength of durability decreased for 12,624 hours at temperatures of $40{\sim}60^{\circ}C$. In terms of stability of external stress and temperature, the slow-curing epoxy was superior to the rapid-curing epoxy, and cultural heritage conservation plans should therefore consider the strength and stress properties of restoration materials. Color differences increased for 12,624 hours at temperatures of $40{\sim}60^{\circ}C$, and glossiness decreased. Both color and gloss stability were weak, which necessitates the improvement of optical properties. Thermal properties (weight loss, decomposition temperature, and glass transition temperature) of adhesives are linked to mechanical properties. Interfacial properties of the adherend and water vapor transmission rates of adhesives are linked to performance variation. For porous media (ceramics, brick, and stone), isothermal and isohumid environments are important. For outdoor artifacts on display in museums, changes in physical properties by exposure to varying environmental conditions need to be minimized. These results can be used as baseline data in the study of the degradation velocity and lifetime prediction of rapid-curing epoxy resin for the restoration of cultural heritages.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.8
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• pp.120-125
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• 2002

In the preceding tests using the KSR-III Sub.(I) engines, it was observed that the heat resistant capability of the engines was not enough for the mission. So Sub.(I) Mod. engines were designed and tested. The Sub.(I) Mod. engines have three major design parameters - the arrangement of main injectors, the impinging angle of main injectors and thermal barrier coating. More than twenty experiments were carried on to evaluate engine performance and heat resistance capability with respect to design parameters. In this study, the test results are introduced. Analysing the result of Sub.(I) engine tests, it is found that decreasing the impinging angle, adopting the H-type arrangement(rather than radial type arrangement) and adopting the thermal barrier coating can increase heat resistance capacity substantially. Also, engine performance evaluation is conducted using specific impulse and characteristic velocity parameter. The results show that the performance variation is small(about 5%) and the performance is better in the case of radial arrangement. It is suspected that these phenomena are caused by the change of flame structure atomization mixing characteristic of sprays and the distortion of recirculation zone. Also from the low frequency instability point of view, it is observed that reducing the impinging angle and adopting the H type arrangement can increase the instability characteristics.

• Korean Journal of Environmental Biology
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• v.24 no.2 s.62
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• pp.201-211
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• 2006

55 zooplankton taxa including 35 copepoda were observed in the Uldolmok waterway during the sampling period from August 2003 to April 2004. Neritic species showed the seasonal species fluctuation, and oceanic warm-water species occurred throughout the year. The number of taxa tended to increase at the flood tide from low tide to high tide, and to decrease at the ebb tide from high tide to low tide. Therefore, species composition of zooplankton in the Uldolmok waterway seemed to be affected by the inflow of oceanic waters with oceanic species all the year round. Total abundance of zooplankton ranged from 104 (February 2004) to 2,717 indiv. $m^{-3}$ (August 2003). According to the tidal cycle, the change of total abundance was more irregular and variable in November 2003 and February 2004 than August 2003 and April 2004. In August 2003 and April 2004, total abundance was low at the strong tide, and was high at low and high tide when tidal current was weak. Average abundances of dominant species such as Paracalanus indicus, Cirripedia nauplii and Acartia hongi were on the order of twice higher at ebb tide than flood tide. However, their abundances were also subject to wide fluctuation within flood tide and ebb tide. The changes of environmental parameters such as water temperature, salinity and chlorophyll-a concentration were negligible along the tidal periods in the Uldolmok waterway. Therefore, the advection, transfer and loss of zooplankton population derived from strong tidal current and eddy formed by the local difference of tidal velocity lead temporal variation of zooplankton community more complex and variable in the Uldolmok waterway.

• Applied Chemistry for Engineering
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• v.9 no.7
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• pp.950-955
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• 1998

The objective of this study was to investigate the effect of running time, operating pressure, feed concentration and circulation rate on the permeation flux and the rejection rate in cross-flow ultrafiltration of polyethylene glycol(PEG) solution of molecular weight($M_w$) 8000 and 20000. The membranes used for this study were MWCO(Molecular Weight Cut-off) of 6 K and 20 K. The experiments were performed at the operating pressures of 7, 14 and 28 psi, the circulation rates of 1000 mL/min and 2000 mL/min, and the feed concentration of 100 mg/L and 1000 mg/L. At a constant pressure, the permeation flux and the observed rejection($R_o$) appeared to be approximately constant within the range of running time, 0~480 min. The permeation flux increased with increasing the operating pressure, and it increased with decreasing the feed concentration and decreasing Mw of PEG at a given pressure. On the other hand, $R_o$ decreased slightly with increasing the operating pressure. However, $R_o$ increased with increasing the feed concentration and increasing of $M_w$ of PEG at a given pressure. The variation in circulation rates did not cause any significant influence on the permeation flux. Increasing of circulation rate caused the increase of $R_o$, and $\alpha$ was increased substantially with the decrease of $M_w$ of PEG. The dimensionless parameter. permeability ratio($\alpha$), which was used to investigate flux-pressure behavior, was increased with the increase in circulation rate and operating presure. The value of $\alpha$ was less than 1 in all cases. The estimated intrinsic rejection(R). which was obtained from mass transfer coefficient, was decreased with the increase of operating pressure. However R increased with the increase of linear velocity of feed and $M_w$ of PEG.

• Journal of Astronomy and Space Sciences
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• v.19 no.1
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• pp.25-30
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• 2002

Black hole binary candidates are known to be composed of a black hole with 10 $M_{\odot}$ and a K or M type companion. Because the companion is believed to fill the Roche lobe that is very aspherical, the light curves of black hole binaries are characterized by an ellipsoidal variation. It has been known that the ellipsoidal light curves exhibit asymmetric maximum brightness at the orbital phases 0.25 and 0.75, which has been attributed to star spots or the hot impact points of the accretion flow on to the accretion disk around the black hole. In this paper, it is pointed out that the special relativistic beaming effect contributes to the asymmetry of several percent often observed in the light curves. The typical orbital velocity 400 km $s^{-1}$ observed in black hole binaries may induce the temperature difference $\DeltaT/T$ ~ 1/400 of the late type companion star in the observer`s rest frame, because of the special relativistic Doppler beaming effect. This difference in temperature can result in several per cent of brightness sensitively dependent on the wavelength band, which is comparable to what has been observed in most black hole binary candidates. Considering the significant contribution of the special relativistic Doppler beaming effect, we conclude that the estimation of the sizes and temperatures of the star spots or the hot impact point needs serious revision.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.8
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• pp.4068-4076
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• 2013

The wheel-rail interaction forces are influenced by the velocity of vehicle, wheel load, alignment (curve radius, cant etc). For the safety of track structure, it is required to evaluate the influences for track and influential factors. Recently, the HEMU 430-X, which was developed by Next Generation High-Speed Rail Development R&D Project, achieved 421.4km/h in a test run of Daegu.Busan section of the Gyeongbu high speed rail on March in 2013. In the case of additional speed-up test on Test-Bed Section(Gongju.Jeongeup: KP 100~128km Osong starting point), the analysis of track forces is required for outer rail by the increase of dynamic force and centrifugal force of vehicle. In this paper, the vehicle speed variation on HSL line is evaluated by TPS analysis considering the tractive effort of HEMU 430-X, tested running resistance and alignment of Honam HSR. And the track forces are evaluated by centrifugal force and impact factor on curved track.

• Journal of Navigation and Port Research
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• v.36 no.10
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• pp.839-844
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• 2012

Anemometer is a meteorological instrument that measures wind direction and wind speed in real time, and is mounted to the cranes that are used at ports, shipbuilding yards, off-shore structure, or construction sites that are influenced by wind, and it is used in conjunction with the safety system. Load cell-type anemometer measures the wind direction through the ratio of load between 4 positions by mounting the thin plate to 4 load cells, and measures wind velocity through the summation of loads. According to previous research, the load ratio between two adjacent windswept with respect to the wind direction has unstable value due to vortex around windswept. This causes the result that increases an error on the wind direction. In this study we compared and analyzed the difference between the load ratio with respect to three type windswept shapes in order to suggest the proper windswept shape to reduce this error. The computational fluid flow analysis is carried out with ANSYS CFX to analyze the load ratio between three windswept shapes. Wind direction was adopted as the design variable, and selected 9 wind direction conditions from $0^{\circ}{\sim}90^{\circ}$ with $11.25^{\circ}$ interval for computational fluid flow analysis.