• The Journal of the Acoustical Society of Korea
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• v.37 no.6
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• pp.451-456
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• 2018

UAComm (Underwater Acoustic Communication) is an active research area, and many experiment has been performed to develop UAComm system. In this paper, we investigate the possibility of modifying and applying VirTEX (Virtual Time series EXperiment) to medium long range MIMO (Multiple-Input Multiple-Output) UAComm of about 20 km range for the analysis and performance prediction of UAComm system. Since VirTEX is a time-domain simulator, the generated time series can be used in HILS (Hardware In the Loop Simulation) to develop UAComm system. The developed package is verified through comparing with the sea-going FAF05 (Focused Acoustic Field 2005) experimental data. The developed simulator can be used to predict the performance of UAComm system, and even replace the expensive sea-going experiment.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.37 no.4
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• pp.372-376
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• 1992

This experiment was conducted to determine hay making time on the drying period, hay moisture content, hay loss content, yield and forage quality of Italian ryegrass in paddy field. Plant height increased rapidly from middle of April, and leaf weight rate were 55.6% at April 20 and 18.9% at May 30. Moisture content and loss content of hay were 17.1-20.5% and 10.2-15.0%, respectively, at drying for 4 days from May 10 to May 30. As the growth stage later, crude protein, fat and ash contents reduced, but crude fiber and NFE contents increased. Dry matter and TDN yield at the cutting of May 20 and May 30 increased to 17-18% and 5-11%, respectively, than those of April 20＋May 30.

• Journal of Hydrogen and New Energy
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• v.34 no.2
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• pp.132-140
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• 2023

In this study, rotary magnet holder (RMH) was manufactured to analyze the ion transport effect according to the rotating magnetic field for the hydrogen production efficiency by alkaline water electrolyte. In the experiment, the voltage signal according to the magnet arrangement inside the RMH, the rotation speed, and the rotation time was measured using the voltage measurement module. As a result of the voltage signal measurement experiment, the average potential difference increased as the rotation speed of the RMH increased. Through the results of the voltage signal measurement experiment, the most efficient magnet arrangement (case 2) was applied to the RMH to conduct a water electrolysis experiment. A 20% NaOH aqueous solution was filled in the electrolytic cell, and a direct current 2 V constant voltage was applied to measure the current value according to the RMH rotation to compare the hydrogen generation amount. When rotating at 100 RPM, the hydrogen production efficiency increased by 8.06% compared to when not rotating. Considering the area exceeding +25 mA, which was not measured at the beginning of the experiment, an increase in hydrogen production of about 10% or more can be expected.

• Journal of the Korea Institute of Building Construction
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• v.5 no.1 s.15
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• pp.105-109
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• 2005

Classified with concrete as placing ways - direct ways, sheath way - and placing directing flange direction, web direction - is analyzed section and strength of hardened concrete. The results of this study is belows the more fluid of concrete, the more useful to top-down method. To minimize the voids of the reverse placement joints, It is more effect to use the sheath method than direct method in concrete placement. If the joint face is a plane, it is impossible to extract the air bubbles which caused voids, so we should consider about this, and decide to select which type of joints.

• Journal of Korean Port Research
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• v.14 no.3
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• pp.353-360
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• 2000

In this study a drift prediction model based on fluid dynamics theory is introduced. The essential effects of environmental loads and target characteristics are taken into account from a fluid dynamics point of view. The governing equations of motion are derived from Netwon's law of dynamics. In the mathematical formulation only three degrees of freedom(surge, sway, yaw) of the drifting object are assumed and the environmental loads considered are the forces and moments by wind and current. A computer algorithm for this model is implemented to obtain the numerical result in the time domain. The preliminary tests for model verification are conducted and the results are compared with the field experiment data as well as leeway formula suggested from the field test data.

• The Korean Journal of Ecology
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• v.6 no.4
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• pp.250-256
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• 1983

Dehiscence of ginseng seeds under the various conditions, growing experiment in the different soil conditions, and growing experiment with extracts obtained by water passed the pot of 4 year ginseng plants were performed. The results obtained are as follows: The survival rate of ginseng plants in the soil of ginseng field sterilized by MIYAZAWA's method was higher than that of the non-sterilized, but lower than that of the control. The survival rate of ginseng plants on the sterilized soil of ginseng field was lower than that on the surrounding soil. The growth of ginseng plants cultivated with the water passed through the pot-planted 4-year-old ginseng plants was strongly inhibited in comparison with the control. Besides biological cause, chemical products excreted from the root of ginseng plants might be the important factors of soil sickness in the successive cultivation of the same plants.

• Transactions of the Korean Society of Automotive Engineers
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• v.3 no.3
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• pp.46-57
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• 1995

The aim of the present study is to provide fundamental informations for the development of magneticfluid actuator. To achieve the aim, oscillation characteristics of the magneticfluid plug are investigated by experiment for the various length and position of the magneticfluid plug and the frequency of magnetic field. The oscillation characteristics are obtained. Amplitude, natural frequency, phase shift and damping ratio, are compared with theoretical values. From the study, the following conclusive remarks can be made. The experimental equation for the magnetic field is obtained. The critical magneticfluid length exists and its value is about 70mm. The range of the damping ratio and fluid loss coefficient obtained by experiment are 0.1~0.2 and 30~100, respectively. Comparison between experimental and theoretical results of oscillation characteristics shows good agreement in the high frequency range. Meanwhile, in the low frequency range, there appears little discrepancies(5% in the frequency and amplitude and 10% in phase difference and damping ratio) with each other.

• Journal of the Korean Society of Marine Environment & Safety
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• v.7 no.2
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• pp.13-22
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• 2001

We studied the characteristics of marine casualties within the area under control of Korea National Maritime Police and leeway of drifting vessel. According to 5 years＇(1995~1999) data of casualties, it was found that the occurrence of casualties by fishing boats ranked the highest and a considerable numbers of casualties took place more than 20 miles off the shore. From a result of field experiment of G/T 50 tons vessel off Busan harbor on Apr. 26~28, 2000, we computed that the linear equation of leeway speed(cm/s) was 1.01$\times$U(U : wind speed in m/s)+11.36 with correlation coefficient between wind speed and leeway speed being 0.252 and we found leeway angle range from $+87^{\circ}$(right) to $-78^{\circ}$(left ) of the downwind direction.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2000.11a
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• pp.63-71
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• 2000

In this study a drift prediction model based on fluid dynamics theory is introduced. The essential effects of environmental loads and target characteristics are taken into account from a fluid dynamics point of view. The governing equations of motion are derived from Newton's law of dynamics. In the mathematical formulation only three degrees of freedom(surge, sway, yaw) of the drifting object are assumed and the environmental loads considered are the forces and moments by wind and current. A computer algorithm for this model is implemented to obtain the numerical result in the time domain. The preliminary tests for model verification are conducted and the results are compared with the field experiment data as well as leeway formula suggested from the field test data.

• Interaction and multiscale mechanics
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• v.3 no.4
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• pp.373-387
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• 2010

This study is intended to assess low frequency sound radiated from a viaduct under normal traffic. The bridge comprises steel box girders and wide cantilever decks on which vehicles pass. The low frequency sound and the acceleration response of the bridge under normal traffic are measured to investigate how bridge vibrations affect the low frequency sound observed near the bridge. Observations demonstrate that strong relationships exist between frequency characteristic of bridge's acceleration response and the sound pressure level of low frequency sound. A noteworthy point is that the dynamic feature of the sound pressure level is mostly affected by dynamic feature of the span locating near the observation point.