• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.8
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• pp.1422-1430
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• 2016

Researches for oceans are limited to military purpose such as underwater sound detection and tracking system. Underwater acoustic communications with low-probability-of-interception (LPI) covert characteristics were received much attention recently. Covert communications are conducted at a low received signal-to-noise ratio to prevent interception or detection by an eavesdropper. This paper proposed optimal covert communication model based on direct sequence spread spectrum for underwater environments. Spread spectrum signals may be used for data transmission on underwater acoustic channels to achieve reliable transmission by suppressing the detrimental effect of interference and self-interference due to jamming and multipath propagation. The characteristics of the underwater acoustic channel present special problems in the design of covert communication systems. To improve performance and probability of interception, we applied BCJR(Bahl, Cocke, Jelinek, Raviv) decoding method and the direct sequence spread spectrum technology in low SNR. Also, we compared the performance between conventional model and proposed model based on turbo equalization by simulation and lake experiment.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.14 no.4
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• pp.1-7
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• 2000

In this paper, we study a cause of malfunction of switch to control drive motor in DFMS(Digital Flux Mapping System) which can measure incore neutron flux of the nuclear plant, and develope a method to solve this problem. DFMS has the type of generating contact signal by mechanical switch lever, which is operated whenever thimble detector inserted or withdrawed through thimble Guide Tube. However the characteristics of the lever tend to be changed by mechanical degrade or bad environment and the lever finally generates errotic contact signal. Therefore we installed electric coil ass'yin the outside of Guide Tube instead of mechanical switch assy's. In addition we applied resonance effect to control circuit and installed condenser in the input of power supply to protect noise and interference. After completion of this improvement, we tested this improved device repetitively under the various conditions. In conclusion, we identified the generation of the desired contact signal and the prevention of detector failure through plant surveillance test during normal plant operation.

• Journal of the Korea Convergence Society
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• v.10 no.8
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• pp.145-151
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• 2019

In this study, the effects were analyzed by applying the vibration absorption liner into the guide rail bracket as a part of method to reduce the vibration and noise on the high-rise apartment. As the result of vibration absorption liner performance, it was checked that the level of vibration and noise was reduced around 65.49% in the car side and around 90.05% in the counterweight side. Therefore, the vibration absorption effect by the vibration absorption liner of elevator guide rail bracket became fairly good. In case of the vibration absorption liner application, there was an effect on the reduction of 7.26 to 22.22% at hoistway section area, 3,840,000 to 9,780000 KRW at the cost of material and installation by comparing with the damping beam application. Also, in case of the vibration absorption liner application with light weight instead of damping beam with heavy weight, it was thought to become significant effect at preventing the safety from the accidents on installation site.

• Geophysics and Geophysical Exploration
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• v.25 no.1
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• pp.14-25
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• 2022

The passive surface wave method measures seismic signals from ambient noises or vibrations of natural phenomena without using an artificial source. Since passive sources are usually in lower frequencies than artificial ones being able to ensure the information on deeper geological structures, the passive surface wave method can investigate deeper geological structures. In the passive method, frequency dispersion curves are obtained after data acquisition, and the dispersion curves are analyzed by assuming 1D-layered earth, which is like the method of active surface wave survey. However, when computing dispersion curves, the passive method first obtains and analyzes coherence curves of received signals from a set of receivers based on spatial autocorrelation. In this review, we explain how passive surface wave methods measure signals, and make data processing and interpretation, before analyzing field application cases.

• Journal of the Korea institute for structural maintenance and inspection
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• v.28 no.5
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• pp.1-9
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• 2024

Recently, the TBM tunnel construction method has been in the spotlight as tunnel excavation under urban areas such as the Metropolitan Rapid Transit (GTX) has been actively carried out. Although the construction cost of the TBM tunnel is high, it is relatively free from noise and vibration compared to the NATM tunnel method, so it is well known to be a suitable construction method for application to the lower part of urban areas. In particular, when the stratum passes through the shallow section, it can have a great impact on existing upper structures and obstacles, so accurate numerical analysis considering various variables is required when designing the TBM tunnel. Unlike other tunnel construction methods, TBM tunnels build linings by assembling factory-made segments. Unlike NATM tunnels, segment lining has connections between segments, so how to the connection status between segments is reflected can have a significant impact on securing the reliability of analysis results. Therefore, in this paper, a segment joint model(Janssen Model) was applied to the lining for seismic analysis of the TBM tunnel, and the tunnel's behavioral characteristics were analyzed after numerical analysis using nonlinear models according to urban railway seismic design standards.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.48 no.1
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• pp.91-98
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• 2012

This study is aimed to utilize a basic data for setting up an allowable air noise with IMO standard in accommodation and working areas of 24m longer fishing vessels. The air noise in accommodation and working areas of 300 tons class squid-jigger were evaluated and the levels were compared to the allowable levels of IMO. The results indicated that the maximum range of noise levels was estimated to be between 54.8dB (A) and 83.2dB, and the correlation between the distance from the main engine to measuring point and the maximum noise level of each point was shown to be y=-13.8log (r)+92.91 ($r^2=0.821$). In addition, except the case of making an accommodation area near to the engine room in 24m longer jigging vessels, it was evaluated that the accommodation noise regulation of 1,600 tons international voyage vessels with 60dB (A) or an improved noise level with 65dB (A) could be properly applied.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.144.1-144.1
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• 2010

현재의 세계 자동차 시장은 석유 자원의 고갈과 전자화로 높은 연비의 기술적 성숙을 요구하고 있으며, 이는 미래 자동차 기술의 전동화를 가속시키고 있음에 따라 종래 엔진부하로 사용되는 시스템 및 유압시스템의 전동화 기술추이가 지속적으로 증가하고 있다. 이중 엔진 부하 메커니즘의 하나인 엔진 쿨링 팬 분야는 소비용량이 크고, 고 연비증감 기술증진의 전동화에 따른 차량 성능개선의 효과가 높아 실용 전동화 용의성에 의해 새로운 최우선 차량 전동부하로 나타나고 있다. 특히, 대형 차량(버스, 트럭)의 엔진 Cooling Fan 시스템은 차량 연비저감의 주요원 중에 하나로 대두되고 있으며, 도시 소음의 주된 요인이 되고 있어 전동화 기술개발의 필요성이 매우 높다. 전동 Cooling Fan 시스템은 종래 엔진 구동형 시스템에 비하여 엔진부하를 감소시킬 수 있고, 차량 연비향상 및 유해배출 가스를 저감시킴으로 기술적, 환경적 개발효과가 매우 높다. 본 연구에서는 쿨링팬 고출력 BLDC모터 설계제작에 관한 내용과, 최적 팬 블레이드 설계제작, 마지막으로 개발 전동 쿨링팬 성능평가에 관한 내용이 포함되어 있다.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.3 no.2
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• pp.103-113
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• 1991

This paper presents a method for estimating the noise source contribution of a pulse combustion burner in a multiple input system where the input sources may be coherent each other. By coherence function method, it is found that the biggest part of the noise source in the pulse combustion burner is generated by the part of the combustion chamber. This analysis is modeled as three input / single output system because the noise generating mechanism of the pulse combustion burner is very complicated. The coherence function method is proved to be useful tool for the identification of noise source. The overall levels of the radiated source pressure by coherence function method are compared with those measured and calculated by the frequency response function approach. The experimental results have shown a good agreement with the results calculated by the coherence function method when the input sources are coherent strongly each other. The estimation of shield effect by FRF method indicates that significant reduction can be achieved in sound radiation if only transmission path generated by the part of combustion chamber is acoustically shield.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.205-205
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• 2009

태양광 발전은 다른 발전방식과는 달리 연료비가 불필요하고 대기오염이나 폐기물 발생이 없으며 부위가 반도체 소자이고 제어부가 전자제품이므로 기계적인 진동과 소음 등의 공해가 전혀 없는 에너지원이다. 그러나 태양광 발전은 에너지 밀도가 낮아 일사량, 온도, 계절 등 기상조건의 작은 변화에도 발전량의 편차가 심하고 출력이 불안정하여 상용전원과의 연계나 별도의 축전설비 또는 발전설비 없이 독립적으로 사용하기에는 다소 무리가 있다는 단점이 있다. 따라서 본 논문에서는 이러한 문제점을 해결하기 위해서 1년 동안 실증운전을 통한 종합적인 운전특성 데이터, 태양전지 어레이 출력의 전압 전류, 교류 전력 및 전력량, 일사량 및 모듈의 온도, 외기온도 등 분석기간 동안 수집된 운전 데이터를 이용하여 태양이 태양전지 모듈에 입사되는 각과 발전량 즉 태양 전지 어레이 형태와 발전량과의 상관관계를 정량적으로 규명하여 태양광 발전시스템의 설계 및 시공의 최적화가 이루어질 수 있도록 하였다.

• Journal of Environmental Science International
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• v.15 no.3
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• pp.287-292
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• 2006

The purpose of this paper is to evaluate the noise level and source, reduce the subway line II noise. As a result of measurement of subway line II in Busan the highest value section of uproad line was from Jigegol to Motgol by 89 dB(A). The sections of conversation and listening interference(over 80 dB(A)) were 21 sections(55%) of 38 sections. Among these sections, 15 sections(71%) were produced rolling noise, 3 sections(14%) squeal noise, 2 sections(10%) braking noise and 1 section(5%) fan noise, and then a main noise source was the rolling noise. In case of downroad line, the highest value section was from Busan Metro Art Museum to Centum city, Motgol to Jigegol by 88 dB(A). The sections of conversation and listening interference(over 80 dB(A)) were 18 sections(47%) of 38 sections. Among these sections, 15 sections(83%) produced rolling noise, 2 sections(11%) squeal noise and 1 section(6%) braking noise were investigated in this study. and then a main noise source was the rolling noise.