• 한국도로학회:학술대회논문집
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• 2005.11a
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• pp.239-244
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• 2005

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2000.10a
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• pp.118-122
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• 2000

In this study, Ringing is investigated by continuous wavelet transform. Ringing is considered to be one of the typical transient phenomena in the field of ocean engineering. The wavelet analysis is adopted to analyze ringing from the point that wavelet analysis is capable of frequency analysis as well as time domain analysis. The use mother wavelet is the Morlet wavelet. The relation between the frequency of the time series and that of wavelet can be clearly defined with Mor1et wavelet. Experimental data obtained by other researchers was used. The wave height time series and acceleration times series of the surface piercing cylinder were analyzed. The results show that the proposed scheme can detect typical frequency region by the time domain analysis which could hardly be detected if one relied on the frequency analysis.

• Journal of Industrial Technology
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• v.15
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• pp.123-135
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• 1995

In this paper, we performed the modeling of a tunable three section DFB-LD with continuous phase using the coupled-wave equation. It was also proposed new modeling method for ${\lambda}/4$ phase shifted one. We got the characteristics of oscillation wavelength, gain, and photon density profiles according to parameters such as coupling coefficient K and current into the third sections for two case of continuous phase and ${\lambda}/4$ shifted phase one. The simulations for ${\lambda}/4$ phase shifted tunable three section DFB-LD prove that the continuous tuning range is about 4.2nm for $K=120cm^{-1}$, $L=180{\mu}m$, and the oscillation mode be within the stop-bands. Also when changed a current of both end sections, it is shown that a photon density reaches the maximum at the center.

• Journal of the Korea Institute of Military Science and Technology
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• v.20 no.1
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• pp.63-71
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• 2017

During the sea trial test, we discovered EMI(Electromagnetic Interference) between MIL-SATCOM parabolic antenna and ES(Electronic Warfare Support) omni antenna. Emitted side lobe of CW(Continuous Wave) from MIL-SATCOM raises the threshold level of ES omni antenna. Therefore detection rate of ES is decreased. To solve this problem, the path of side lobe of CW from MIL-SATCOM should be blocked using EMI shield. This paper presents the method how to calculate the size of EMI shield, material, and optimized deployment. The test of the EMI shield effect was performed on a surface ship. After installing EMI shield, EMI has been decreased significantly. This paper will provide a method how to design EMI shield and a way to verify the result.

• Journal of the Korea Institute of Military Science and Technology
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• v.19 no.6
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• pp.690-697
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• 2016

EOIS(electro-optical imaging system) is the main target of the laser weapon. Specially, the image sensor will be vulnerable because EOIS focuses the incident laser beam onto the image sensor. Accordingly, the laser-induced damage of the image sensor needs to be identified for the counter-measure against the laser attack. In this study, the laser-induced damage of the CCD image sensor irradiated by the CW(continuous wave) NIR(near infrared) laser was experimentally investigated and mechanisms of those damage occurrences were analyzed. In the experiment, the near infrared CW fiber laser was used as a laser source. As the fluence, which is the product of the irradiance and the irradiation time, increased, the permanent damages such as discoloration and breakdown appeared sequentially. The discoloration occurred when the color filter was damaged and then the breakdown occurred when the photodiode and substrate were damaged. From the experimental results, LIDTs(laser-induced damage thresholds) of damages were roughly determined.

• Journal of the Korea Institute of Military Science and Technology
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• v.18 no.3
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• pp.293-299
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• 2015

We analyzed the damage effect on Glass Fibre Reinforced Plastics(GFRP) under air flow by irradiation of continuous wave near-IR laser. Damage process and temporal temperature distribution were demonstrated and material characteristics were observed with laser intensity, surface flow speed and angle. Surface temperature on GFRP rapidly increased with laser intensity, and the damaged pattern was different with flow characteristics. In case of no flow, penetration on GFRP by burning and flame generation after laser irradiation was appeared at once. GFRP was penetrated by the heat generated from resin ignition. In case of laser irradiation under flow, a flame generated after burning extinguished at once by flow and penetration pattern on GFRP were differently shown with flow angle. From the results, we presented the damage process and its mechanism.

• Korean Journal of Optics and Photonics
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• v.13 no.1
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• pp.65-69
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• 2002

A continuous wave deuterium fluoride (DF) chemical laser was designed and manufactured, and we have achieved DF laser beam generation with the maximum output power of 101 W. The gain medium is vibration-rotationally excited DF molecules produced by F+D$_2$ cold reaction through supersonic diffusion mixing in an optical cavity. F atoms are produced in a combustor by F$_2$+ H$_2$ reaction and injected into the cavity through a supersonic nozzle. The optimal chemical efficiency was measured to be 5.12% and specific power to be 96.5 J/g.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.35 no.3
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• pp.284-290
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• 1999

This paper describes a Frequency Shift Keying (FSK) modulator and demodulator and the experimented underwater data ommunication equipment to transfer the analog echo signal in real-time from an underwater vehicle to the mother ship. The system consists of an echo signal transfer unit equipped to the vehicle and an ultrasonic receiver equipped on the ship. The former includes an ultrasonic transceiver unit of 180kHz for echo detection and a continuous wave transmitter of 50kHz with a FSK modulator for echo transmission to the ship. The latter includes an ultrasonic receiver of 50kHz and the FSK demodulator. The results of experiment are as follows. 1. The characteristics of the FSK modulating and demodulating circuits designed with the use of C-MOS IC 4046 was good and confirmed its usefulness in underwater data communication system.2. The prototype ultrasonic transceiver unit shows profitable driving power while the pulse duration was short less than 3 msec, but it was found that the driving power is not sufficient while the long pulse duration or continuous wave is used. The gain of the ultrasonic receiver was 80 dB and the receiving bandwidth 700Hz (at - 3 dB point).3. It was found that the system designed by the author has some possibility to use in underwater echo transfer.4. At the FSK modulator, the widths of voltage and frequency which represent linearity were 3.5 V, 1600Hz, respectively, at the FSK demodulator 2.6 V, 700Hz, respectively.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.35 no.3
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• pp.285-285
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• 1999

This paper describes a Frequency Shift Keying (FSK) modulator and demodulator and the experimented underwater data ommunication equipment to transfer the analog echo signal in real-time from an underwater vehicle to the mother ship. The system consists of an echo signal transfer unit equipped to the vehicle and an ultrasonic receiver equipped on the ship. The former includes an ultrasonic transceiver unit of 180kHz for echo detection and a continuous wave transmitter of 50kHz with a FSK modulator for echo transmission to the ship. The latter includes an ultrasonic receiver of 50kHz and the FSK demodulator. The results of experiment are as follows. 1. The characteristics of the FSK modulating and demodulating circuits designed with the use of C-MOS IC 4046 was good and confirmed its usefulness in underwater data communication system.2. The prototype ultrasonic transceiver unit shows profitable driving power while the pulse duration was short less than 3 msec, but it was found that the driving power is not sufficient while the long pulse duration or continuous wave is used. The gain of the ultrasonic receiver was 80 dB and the receiving bandwidth 700Hz (at - 3 dB point).3. It was found that the system designed by the author has some possibility to use in underwater echo transfer.4. At the FSK modulator, the widths of voltage and frequency which represent linearity were 3.5 V, 1600Hz, respectively, at the FSK demodulator 2.6 V, 700Hz, respectively.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.12 no.3
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• pp.58-67
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• 2003

Welding characteristics of austienite 304 stainless and SM45C using a continuous wave Nd:YAG laser n experimentally investigated Laser beam welding is increasingly being used in welding of structural steels. The laser welding process is one of the most advanced manufacturing technologies owing to its high speed and deep penetration. The thermal cycles associated with laser welding are generally much Inter than those involved in conventional welding processes, leading to a rather small weld zone. Experiments are performed for 304 stainless steel plates changing several process parameter such as laser power, welding speed, shielding gas flow rate, presence of surface pollution, with fixed or variable gap and misalignment between the similar and dissimilar and plates, etc. The Nd:YAG laser welding process is one of the most advanced manufacturing technologies owing to its high speed and penetration. This paper describes the weld ability of SM45C carbon steel for machine structural use by Nd:YAG laser. The follow conclusions can be drawn that laser power and welding speed have a pronounced effect on size and shape of the fusion zone. Increase in welding speed resulted in an increase in weld depth/aspect ratio and hence a decrease in the fusion zone size. The penetration depth increased with the increase in laser power.