• The Journal of the Acoustical Society of Korea
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• v.27 no.3
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• pp.103-110
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• 2008

Strategically, the Patrol Killer Medium (PKM) ought to run at high speed that produces largely vibration by propeller, in a consequence, the vibration gradually deterioratescrews' working condition and increases the possibility of SONAR detection. In this paper, we propose the propeller damper, which is one of waysto reduce the vibration induced by the propeller, and simulate the ability of the damper numerically. The propeller damper was designed to apply to an isolated plate at the bottom flat board of ship which is directly affected by the fluctuating pressure. The dynamic pressure for the stern part of the PKM is calculated by using the DnV rule and the numerical analysis when the propeller damper applied or not, is performed with ANSYS at the isolated plate that simplified. From the analysis, the damping effect of the proposed propeller damper is confirmed and the reduction ratio for each compartment is estimated based on the experimental data in the PKM.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.2
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• pp.127-132
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• 2003

This paper presents a new model that can precisely simulate the attenuation characteristics of the voltage-controlled PIN diode attenuators. After carefully investigating the problems in the conventional PIN diode models, a new PIN diode model was proposed and verified with experimental data. The proposed model is well operated when it is used in the voltage-controlled mode as well as current-controlled mode, and is simple and straightforward model, since the PN junction diode of this model has the same curve as that of the PIN diode. This model is very effective to design voltage-controlled attenuator and its implementation in commercial simulators is simple and accurate. This model will allow RF and Microwave designers to better use the PIN diodes in various circuits.

• Proceedings of the Optical Society of Korea Conference
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• 2002.07a
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• pp.60-61
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• 2002

Laser-induced incandescence (LII) 측정법은 조사된 레이저에 의하여 입자가 가열됨에 따라서, 그 온도에 상응하는 흑체복사의 시간적 감소추이가 입자의 크기에 따라서 달리 나타나는 것을 이용하여 입자의 크기를 측정하는 방법이다. LII 감쇄법은 레이저에 의하여 가열된 입자의 에너지 균형 상관식에서 입자의 크기가 클수록 신호의 감쇄속도가 느리고, LII 신호의 감쇄비가 실험적으로 입자의 크기에 비례한다는 사실을 이용하여 연소진단에 응용되어 왔다. (중략)

• Journal of the Korean Regional Science Association
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• v.31 no.2
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• pp.47-61
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• 2015

The purpose of this study to empirical analysis of the effects of distance-decay for the relocated firms in the Seoul Metropolitan Area(SMA). In addition, this study was constructed distance-decay function for the relocated firms by industrial types using a general distance-decay function. The data of relocated firms in the SMA extracted from the spatial database which was constructed in an previous research. The industrial type divided into 3 parts which are construction, manufacturing, and service. The result of empirical analysis by each industrial type of the effect of distance-decay, the explanatory power($R^2$) of the each function were all high. In the construction, the adjusted $R^2$ of the distance-decay function was 0.728, the manufacturing was 0.802 and the service was 0.812. It means the effect of distance decay for the relocated firms in construction industrial type more big than the effects of distance decay for the manufacturing and service industrial types.

• Journal of Wetlands Research
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• v.23 no.2
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• pp.173-182
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• 2021

It is important to extract and assess low-flow recession characteristics for water resources management in the upper reaches of a stream. It is difficult to express the groundwater flow recession characteristics for streamflow synthetically. The linear recession model has been widely used by baseflow recession analysis for reason of simplicity and convenience, but recent studies show that nonlinear recession models fit well, and the relationship between the reservoir storage of shallow unconfined aquifers and the groundwater discharge was to be identified as nonlinear in the literature based on the analysis of numerous streamflow recession curves. The objective of the study is to decode these nonlinear characteristics, including evaporation loss, storage, and recharge of groundwater using streamflow. By analyzing the observed time series of streamflow from the study area, which is the Pyeongchang River basin in Korea, the main components of the underlying groundwater balance, namely, discharge, evaporation loss, storage, and recharge, can be identified and quantified. As a result of the study, depletion of groundwater by evapotranspiration losses through the water uptake of tree roots was found to bias the recession curves and the estimated reservoir parameters. The seasonality of both rainfall and potential evaporation, analysis of the recession curves, stratified according to time of the year, allowed the quantification of evapotranspiration loss as a function of a calendar month and stored groundwater storage.

• Journal of the Institute of Convergence Signal Processing
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• v.2 no.2
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• pp.68-74
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• 2001

A design and implementation method for the UHF-band(800MHz) variable attenuator using the 3dB coupler is proposed. The 90 degree, 3-dB Coupler is used for the variable attenuator. The principal theory for the 3-dB coupler is introduced. The 3-dB Coupler is designed by the mathematical analysis and a computer simulation tool. A PIN diode is used for the variable resistor at UHF-band. The variable attenuator using the 3-dB coupler and the PIN diode is designed and implemented. The measured results for the variable attenuator by a network analyzer show that the insertion loss is below -l0dB, and the continuous variable attenuation range is about 10dB.

• Korean Journal of Materials Research
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• v.3 no.6
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• pp.585-592
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• 1993

The effects of grain size and microstructure on the ultrasonic attenuation was investigated with SCM440 steel quenched and tempered at various temperatures. The ultrasonic attenuation was primarily due to the grain boundary scattering and the ultrasonic attenuation coeffecient increased with increasing grain size. In the meantime, it was found that the ultrasonic attenuation coefficient decreased with increasing tempering temperature. The dependence of ultrasonic attenuation coefficient on the frequency of ultrasonic wave had linear relationship on a log-log scale and was proportional to the Roney's equation.

• Aerospace Engineering and Technology
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• v.13 no.2
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• pp.73-79
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• 2014

During developing cubesat flight software, Communication test between cubesat and ground station is needed. For this, we have constructed indoor ground station without outdoor antenna for decreasing total cost and time. In this time, if output power of ground station is high, it will affect for cubesat transceiver to be fail. For solving this problem, ground station must be designed for output power of it to be lower than input power of cubesat satellite, and it must be verified. In this paper, first, we describe cubesat indoor ground station using UHF and VHF. Second, we describe output power decreasing test for indoor operation of ground station by attaching attenuators in the end of the output connector.

• Journal of the Korea Institute of Military Science and Technology
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• v.2 no.1
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• pp.30-37
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• 1999

Transmissivity and the signal loss in soil are computed. An electric field expression for the inhomogeneous complex media modelled by two layers is shown as an integral form. Volume scattering occurs in inhomogeneous media, and iterative Born approximation is used to analyze this scattering effect. The degree of randomness is controlled by specifying the variance and correlation length. Expression for the transmissivity and the signal loss is presented as the parameter of soil moisture contents, soil particle radius, temperature and frequency. The analysis shows that big deviation in signal loss depends on the temperature variation remarkably and the physical reason of unusual level is explained.

• 한국지구물리탐사학회:학술대회논문집
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• 2006.06a
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• pp.247-252
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• 2006

This study analysed the sensitivity of the attenuation functions for the seismic hazard estimation. For the seismic hazard estimation, this study used HAZUS software, which is developed originally by FEMA(USA). The scenario earthquake ($M_w=6.0$) is located the Hongsung area, where one of the recent macro earthquakes occurred in 1978. The area for seismic hazard estimation is assumed to be Boryung city in Choongnam-do. Three attenuation functions were applied for the sensitivity analysis. The results show that the attenuation functions have much influences on the seismic hazard on the various types of buildings. Therefore the attenuation function is very important factor for the seismic hazard estimation.