• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.1
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• pp.217-223
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• 2019

In this study, the acceleration changes of the surrounding ground when crushed stones were installed in a strip-type were analyzed using the 1-G shaking table test. The ground was constructed from clay, and the foundation was installed using crushed stone of strip-type form. The response acceleration and response spectrum for various input seismic motions were analyzed. The change in acceleration was examined according to the adjacent distance to the strip-type crushed stone foundation. In the Hachinohe seismic motion results, there was no significant decrease in acceleration, but the maximum response acceleration for the two seismic motions was inversely proportional to the distance from the crushed stone foundation. As a result of the response spectrum analysis, the attenuation period in the long period and the short period input wave were different from each other, and the change in response spectrum affected the maximum acceleration value. As the distance from the crushed stone foundation was increased, the attenuation was larger in the period between 0.08 and 0.5 sec in the Hachinohe seismic motion, the attenuation was larger in the period of less than 0.2 seconds in the Northridge seismic motion.

• The Journal of the Acoustical Society of Korea
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• v.29 no.4
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• pp.223-228
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• 2010

High-frequency bottom loss measurements for grazing angle of $82^{\circ}$ in frequency range 17-40 kHz were made in Jinhae bay in the southern part of Korea. Observations of bottom loss showed the strong variation as a function of frequency, which were compared to the predicted values using two-layered sediment reflection model. The geoacoustic parameters including sound speed, density and attenuation coefficient for the second sediment layer were predicted from the empirical relations with the mean grain size obtained from sediment core analysis. The geoacoustic parameters for the surficial sediment layer were inverted using Monte Carlo inversion algorithm. A sensitivity study for the geoacoustic parameters showed that the thickness of surficial sediment layer was most sensitive to the variation of the bottom loss.

• Journal of Soil and Groundwater Environment
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• v.13 no.6
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• pp.85-92
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• 2008

Water in Soyang River is an essential source for citizens of Chuncheon and Seoul areas. In 2006, turbid water in Soyang River aggravated by the typhoon Ewiniar, sustained for over 280 days unlike conventional years, then which interrupted water supply of Chuncheon and Seoul areas. Soil erosion derived from high cool lands constituting about 55% of Soyang River area is considered one of main causes for the turbid water, including imprudent development of mountainous area, road expansion, and road construction for forestry. According to analysis of turbidity, precipitation and reservoir level in Soyang River region for June 2006${\sim}$August 2008, the turbidity showed a peak correlation (r = 0.28) at a lag time of 49 days and especially did an excellent correlation (r = 0.60) with the reservoir level at a lag of 4 days. In the meantime, a critical turbidity of 31 NTU at Soyanggang Dam was estimated, over which would cause turbid water at Paldang Dam. In addition, a master recession curve was suggested, from which sustaining time of turbid water can be predicted.

• Journal of the Korean Society for Marine Environment & Energy
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• v.18 no.3
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• pp.216-222
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• 2015

A previous velocity measurement system for marine sediment had several problems such as the errors occurred when picking first arrival time and the inconvenient measurement procedure. In order to resolve these problems, we developed a new acoustic properties measurement system by using PXI (PCI eXtentions for Instrumentation) module based on LabVIEW. To verify the new system, we measured the velocity and attenuation of sediment using the new system in a parallel with the previous system under the same experimental environment. The result of measurement showed 1~2% margin of error for the velocity as well as similar attenuation values. We concluded that the new system can efficiently measure the acoustic properties of marine sediment. It also has an advantage to construct the database of acoustic data and raw signal.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.2A
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• pp.97-108
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• 2012

Dynamic responses were measured using long-term monitoring system for Uldolmok tidal current pilot power plant which is one of jacket-type offshore structures. Among the dynamic quantities, the tilt angle was chosen because the low frequency response components can be precisely measured by dynamic tiltmeter, and the natural frequencies and modal damping ratio were successfully identified using proposed LS-FDD (least squared frequency domain decomposition) method. And the effects of tidal height and tidal current velocity on the variation of natural frequencies and modal damping ratios were investigated in time and frequency domain. Also the non-parametric models were tested to model the relationship between tidal conditions and modal properties such as natural frequencies and damping ratios.

• Journal of the Korea Society for Simulation
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• v.24 no.4
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• pp.35-41
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• 2015

Recoil system for 40mm automatic gun is a device developed to absorb the shock of explosion. It is impossible to conduct pinpoint strike due to recoil if very high explosive shock, which is generated when an automatic gun fires shells, can't be absorbed. This study covers development and verification of analysis model for recoil system by utilizing a multi-domain software. The research process is as in the following. First, an analysis model is developed to verify damping characteristics through understanding of design intention. Second, environment which is identical to a field test is set up on analysis tool after putting explosive force that is measured through the test into the analysis model. Finally, the analysis model for recoil system using the multi-domain software is verified if it has effectiveness with a comparison between internal pressure of the recoil system along with displacement of gun barrel and the field test result.

• The Journal of the Korea institute of electronic communication sciences
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• v.18 no.6
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• pp.1103-1108
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• 2023

In this paper, we propose a new algorithm for attenuating the background noises in acoustic signal. This algorithm improves the noise attenuation performance by using the FNN(: Full-connected Neural Network) deep learning algorithm instead of the existing adaptive filter after wavelet transform. After wavelet transforming the input signal for each short-time period, noise is removed from a single input audio signal containing noise by using a 1024-1024-512-neuron FNN deep learning model. This transforms the time-domain voice signal into the time-frequency domain so that the noise characteristics are well expressed, and effectively predicts voice in a noisy environment through supervised learning using the conversion parameter of the pure voice signal for the conversion parameter. In order to verify the performance of the noise reduction system proposed in this study, a simulation program using Tensorflow and Keras libraries was written and a simulation was performed. As a result of the experiment, the proposed deep learning algorithm improved Mean Square Error (MSE) by 30% compared to the case of using the existing adaptive filter and by 20% compared to the case of using the STFT(: Short-Time Fourier Transform) transform effect was obtained.

• Journal of KSNVE
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• v.6 no.3
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• pp.267-273
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• 1996

이 글은 소음 진동분야에 종사하는 분들에게 압전형 지능구조물을 소개하면서 소음 분야의 응용예 및 활용 가능성 그리고 앞으로의 과제들을 알리고자 한다. 지능 구조물이란 감지기(sensor)와 가진기(actuator) 그리고 제어기(control logic)가 구조물에 합해져서 능동적인 기능을 갖고 있는 것으로서 주위 환경의 변화를 감지하여 이에 대처하는 거동을 하는 구조물이다. 예를 들어, 기계적인 지능구조물은 그 위치 나 속도 또는 구조물의 강성도나 감쇠 성질을 변화시키는 구조물이다. 따라서 이러한 적응력을 갖춘 구조물은 많은 공학 분야에 큰 영향을 주고 있으며 소음제어 분야에 있어서도 큰 기대가 된다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2001.05a
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• pp.157-160
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• 2001

본 논문은 근거리에서의 차량간 통신에 밀리미터나 광전파를 분석하는데 효과적인 Ray Tracing방법을 도입하여 오율특성을 분석하였다. 분석환경으로는 간섭신호에 강한 장점을 지니며 산소흡수에 의한 감쇠가 크며 주파수 재사용효율이 좋은 60GHz 대역에서의 비트오율을 분석하였다. 전파모델로 지면반사파, 콘크리트벽에 의한 반사와 옆 도로를 달리는 차량에 의한 반사를 고려한 Two-Ray 라이시안 채널에서의 다중접속자에 의한 DS/CDMA 시스템의 비트오율특성을 분석하여 검토하였다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1991.04a
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• pp.169-173
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• 1991

최근 자동화기술의 발달에 따라 산업용 로보트팔의 경량화, 고속화를 실행하 게 되는 경우와 우주, 원자력발전소 등과 같은 특수한 환경하에서 매니퓰레 이터(manipulator)를 제어하게 되는 경우가 많아지고 있는데, 이때 팔의 강성 이 충분하지 않으면 위치결정시 목표점에서의 과도진동이 발생하게 되어 위 치결정정도와 작업효율이 저하된다. 그러므로 이러한 경량화된 장비들의 진 동특성을 파악하고 운동시 발생하는 진동을 효율적으로 제어할 수 있는 제 어기(controller)를 설계하여 잔류진동을 감쇠시키므로써 위치결정시간을 줄 일 수 있고, 전체 작업행정시간이 단축되므로써 작업ㅎ류을 향상시키는 효과 를 가져오게 된다. 이때 원하고자 하는 제어를 하기 위해서는 제어대상 (plant)의 계규명(system identification)을 정확히 하여야 하는데 해석적으로 계를 규명하기가 까다로운 경우 제어기를 설계하는 것이 사실상 어렵게 되 므로 이러한 경우 실험적인 방법으로 주파수응답함수(frequency response function)를 구해 계의 모형(model)을 구하는 방법이 널리 사용되고 있다. 이 분야에 있어서 기존의 논문들은 팔의 변위를 측정하여 진동을 제어하나 이 러한 방법들은 간헐적으로 움직이는 산업장비(예:로보트의 팔)의 과도응답을 제어하기에는 부적합하다. 따라서 본 연구에서는 이러한 장비들의 과도응답 을 효과적으로 제어할 수 있도록 가속도계를 사용, 가속도를 측정하여 변위 를 제어하고자 한다.