• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.3
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• pp.258-263
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• 2008

Performance of injector equiped with screw type swirler which is suitable for supersonic cruise engine combustor was investigated using theoretical, numerical, and experimental methods. Based on discharge coefficient and spray angle which represent the performance of injectors, the geometrical parameters which affect these performance parameters were defined, control group injectors were designed, and variation of performance parameters according to the geometrical parameters were examined. Within the defined range, measured value of performance of injectors was smaller than result of theoretical prediction, and prediction result from numerical simulation using VOF method agreed with the result of experiments very well. The viscous barrier was not observed, and minimum discharge coefficient and maximum spray angle, 0.05 and 104 respectively, was obtained for this type of injector.

• Ocean and Polar Research
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• v.36 no.4
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• pp.395-405
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• 2014

A 570 cm-long sediment core was retrieved at $9^{\circ}57^{\prime}N$ and $131^{\circ}42^{\prime}W$ in 5,080 m water depth from the northeast equatorial Pacific and its stratigraphy was established with $^{10}Be/^9Be$ and paleomagnetic measurements. Successive AF demagnetization reveals eight geomagnetic field reversals. In the reference geologic time scale, the eight reversal events correspond to an age of about 4.5 Ma. However, $^{10}Be/^9Be$-based age yields 9.5 Ma at a depth of 372 cm. Such a large discrepancy in determined ages is attributed to an extremely low sedimentation rate, 0.4 mm/kyr on average, of the study core and resultant loss or smoothing of geomagnetic fields. The composite age model reveals a wide range in the sedimentation rate - varying from 0.1 to 2.4 mm/kyr. However, the sedimentation rate shows systematic variation depending on sedimentary facies (Unit II and III), which suggests that each lithologic unit has a unique provenance and transport mechanism. At depths of 110-80 cm with a sedimentation rate of about 0.1 mm/kyr, ancient geomagnetic field reversal events of at least a 1.8 Myr time span have not been recorded, which indicates the probable existence of a hiatus in the interval. Such a sedimentary hiatus is observed widely in the deep-sea sediments of the NE equatorial Pacific.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.47 no.1
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• pp.59-61
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• 2014

We conducted eight surveys in the northern East China Sea (ECS) in winter (February - April), summer (July), and autumn (October) 2004-2009, to investigate the seasonal distribution of T. pacificus. A total of 482 paralarvae, ranging in mantle length (ML) from 1.0 - 17.0 mm, were collected at 73 out of 181 stations. There were higher numbers of paralarvae during the winter and summer months than in the autumn. There was significant seasonal variation in the paralarval mantle lengths; mantle lengths were longer in winter (April) than in summer (July). The position of oceanic fronts in the study area played an important role in restricting paralarval distribution along the inshore edge of the Tsushima Warm Current (TWC). When the TWC expanded to western Jeju Island in winter and autumn, the paralarval distribution range extended to include western Jeju Island. However, when the TWC was located southeast of Jeju Island in the summer, paralarvae were distributed along the frontal zone off southeast Jeju Island. Sites at which paralarval mantle length was <2.0 mm ML indicated that the spawning ground were likely to be within the northern ECS in winter and summer, but north of the study area in autumn.

• Journal of The Institute of Information and Telecommunication Facilities Engineering
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• v.4 no.2
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• pp.29-36
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• 2005

All-optical fiber-type $2{\times}32$ splitters for an Ethernet PON (passive optical network) were fabricated by using a FBT (fiber biconical tapered) process and the performance of the splitters was tested in upstream transmission of the EPON system. The $2{\times}32$ splitters was obtained by cascading $1{\times}4$ splitters fabricated by a conventional FBT process and showed -18 dB of insertion loss with 1.5 dB uniformity of output power at each channel and -0.1 dB of polarization dependent loss. The insertion loss variation was below 0.1 dB at the temperature range of $-40^{\circ}C\;to\;80^{\circ}C$. For upstream channel transmission test in the EPON system were a Zig board and a burst mode receiver. Zenko-made optical module was used for the burst mode receiver by adding functions of serializer/deserializer and clock data recovery, a Virtex II pro20 chipset and Vitesse VSC7123 were used in the Zig board for characterizing the burst mode and in the clock data recovery chipset, respectively. Startup acquisition lock time and data acquisition lock time were measured to be 670ns and 400ns, respectively, in the upstream channel transmission of the EPON system adapting the $2{\times}32$ splitter fabricated in this work.

• 한국지구물리탐사학회:학술대회논문집
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• 2005.05a
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• pp.37-42
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• 2005

We analyzed spectral attenuation of coda waves and estimated coda Q values in the crust of the Korean peninsula. 574 NS-component seismograms registered by the Korea Meteorological Administration (KMA) and Korea Institute of Geology, Mining and Materials (KIGAM) seismic networks with epicentral distances less than 100 km and sampling rate greater than 80 Hz were selected for this study. We estimated coda Q values using the single isotropic scattering model at center frequencies of 1.5, 3, 6, 9, 12, 15, and 18 Hz with 20 s time window starting from double of the S-wave arrival times. Estimated coda Q value at 1 Hz ($Q_0$) and n value range 50 to 250 and 0.5 to 1.0, respectively, and they are well correlated with the regional geology in the Korean peninsula. The $Q_0$ values in western Korea agree well with those of eastern China.

• Journal of the Korea Concrete Institute
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• v.26 no.3
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• pp.343-350
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• 2014

A probabilistic construction stage analysis using the Monte Carlo Simulation was performed to address the effects of uncertainty regarding the material properties, environmental factors, and applied forces. In the previous research, creep and shrinkage were assumed to be completely independent random variables. However, because of the common influencing factors in the material models for the creep and shrinkage estimation, strong correlation between creep and shrinkage can be presumed. In this paper, an Monte Carlo Simulation using CEB-FIB creep and shrinkage equations were performed to actually evaluate the correlation coefficient between two phenomena, and then another Monte Carlo Simulation to evaluate the statistical properties of axial strain affected by partially correlated random variables including the material properties, environmental factors, and applied forces. The results of Monte Carlo Simulation were compared with measured strains of a column on a first story in a 58-story building. Comparison indicated that the variation due to the uncertainty related with the material properties were most severe. And measured strains was within the range of mean+standard deviation.

• Journal of Bio-Environment Control
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• v.16 no.4
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• pp.297-302
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• 2007

Discharge variations of perforated hose and drip irrigation systems were examined to evaluate irrigation uniformity at different pressures and length of branch line. Evaluation using statistical uniformity indicated that button drippers performed at excellent level but drip tapes and drip hoses were a little lower level. Nominal discharge of drip irrigation systems showed at the high side within the range of regulating pressure provided by the manufacturer. It is desirable that the length of branch line for drip hose, drip tape, and button dripper should be limited to 50 m, 70 m, and 100 m, respectively. Irrigation uniformity of perforated hoses showed very low level. So it is recommended that the length of branch line for perforated hoses should be limited to $30{\sim}35m$.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.5
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• pp.707-713
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• 2013

Coupling bolts have replaced conventional fitted bolts in applications where the operator's safety during assembly/disassembly is of concern or where the cost of process interruption is significant. Coupling bolts have been installed on rotating flange couplings in a wide range of marine and power applications worldwide. Their use has been approved by all leading international and national classification societies and regulatory bodies. A coupling bolt is a hydraulically tensioned fitted bolt that creates a stable and rigid link between coupling flanges and simplifies assembly and disassembly. We measure the bolt dimensions for reverse engineering and study the standard of assembly-load using a mechanical formula in order to localize a coupling bolt for a shaft in a power plant. We experimentally obtain the friction coefficient and confirm the condition of bolt sets through structure analysis. We show the variation of contact pressure for the shape parameter in order to consider the result when redesigning a bolt.

• Elastomers and Composites
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• v.43 no.3
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• pp.157-165
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• 2008

Suspension polymerization was carried out to synthesize poly(butyl methacrylate) (PBMA) composite particles containing carbon black. Water was selected as a reaction medium, hydrophobic silica as a stabilizer and azobisisobutyronitrile as an initiator. Concentration of stabilizer was varied from 0.67 to 2.55 weight% with respect to the water, and that of initiator was varied from 0.25 to 3.00 weight% with respect to the butyl methacrylate (BMA) monomer. All polymerization reactions were conducted at 75$^{\circ}C$. It is found that stabilizer concentration has no impact on reaction kinetics, while an increase in initiator concentration enhances polymerization reaction rate. Increase of carbon black concentration from 1 to 3 to 5 wt% into PBMA displayed progressive decrease in reaction conversion. The particle diameter of PBMA composite particles containing carbon black was found to be between 5 and 30 ${\mu}m$. Glass transition was determined to range from 23.8 to 24.7$^{\circ}C$, irrespective of variation in the concentration of stabilizer, initiator or carbon black.

• Journal of Korean Society of Steel Construction
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• v.18 no.6
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• pp.769-782
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• 2006

As the ambient vibration test (AVT) of railway bridges has a limited range of speed, it has a limitation in examining the dynamic behavior of bridges accordingto speed. Thus, in order to analyze the correlation between the speed of a train passing over a bridge and the bridge's dynamic response, we conducted a speed-increasing experiment using a real diesel locomotive. To analyze the acceleration response characteristics, we attached seven vertical accelerometers at equal intervals throughout the entire section of the bridge except the supports, and one horizontal accelerometer to the middle span. Linear variable differential transformers (LVDT) were installed at the bridge's center in both vertical and horizontal directions to investigate the vertical and horizontal behaviors. The test train was statically loaded at the center and at the end of the bridge. And its speed was increased from 5 km/h to 90 km/h. With data obtained from the experiment, the vibration level was evaluated in each direction by the filtering frequency, and the level of horizontal vibration was examined in comparison with vertical vibration. The displacement and wheel load variation was analyzed by speed.