• Smart Structures and Systems
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• 제19권3호
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• pp.335-340
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• 2017

Fiber Bragg grating (FBG) sensors are applied to structural health monitoring (SHM) in many areas due to their unique advantages such as ease of multiplexing and capability of absolute measurement. However, they are exposed to cyclic thermal load, generally in the temperature range of $-20^{\circ}C$ to $60^{\circ}C$, in railways during a long-term SHM and the cyclic thermal load can affect the mechanical strength of FBGs. In this paper, the effects of both cyclic thermal load and the reflectivity of FBGs on the mechanical strength are investigated though tension tests of FBG specimens after they are aged in a thermal chamber with temperature changes in a range from $-20^{\circ}C$ to $60^{\circ}C$ for 300 cycles. Results from tension tests reveal that the mechanical strength of FBGs decreases about 8% as the thermal cycle increases to 100 cycles; the mechanical strength then remains steady until 300 cycles. Otherwise, the mechanical strength of FBGs with reflectivity of 6dB (70%) and 10dB (90%) exhibits degradation values of about 6% and 12%, respectively, compared to that with reflectivity of 3dB (50%) at 300 cycles. SEM photos of the Bragg grating parts also show defects that cause their strength degradation. Consequently, it should be considered that mechanical strength of FBGs can be degraded by both thermal cycles and the reflectivity if the FBGs are exposed to repetitive thermal load during a long-term SHM.

• 한국농공학회논문집
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• 제64권3호
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• pp.33-43
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• 2022

South Korea's agricultural nitrogen balance and phosphorus balance rank first and second, respectively, among OECD countries, and proper nutrient management is required to preserve the water quality of rivers and lakes. This study evaluates the effects of furrow mulching on the reduction of non-point source pollution (NPS) load from a sloped upland. The study site was Wanju-gun, Jeollabuk-do, and the survey period was from 2018 to 2019. The slope of the testbed was 13%, and the soil type was sandy loam. The cropping system consisted of maize-autumn Chinese cabbage rotation. The testbed was composed of bare soil (bare), control (Cont.), furrow vegetation mulching (FVM), and furrow nonwoven fabric mulching (FFM) plots. Runoff was collected for each rainfall event with a 1/100 sampler, and the NPS load was calculated by measuring the concentrations of SS, T-N, and T-P. The NPS load was then analyzed for the entire monitoring and crop cultivation periods. During the monitoring period, the effect of reducing the NPS load was 1.5%~44.5% for FVM and 13.1%~55.2% for FFM. During the crop cultivation period, it was 1.2%~80.5% for FVM and 27.0%~65.1% for FFM, indicating that FFM was more effective than FVM. As the NPS load was fairly high during the crop conversion period, an appropriate management method needs to be implemented during this period.

• 대한전기학회논문지:전력기술부문A
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• 제52권7호
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• pp.414-420
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• 2003

The domestic needs for larger capability of power sources are increasing to cope with the expanding power load which results from the industrial developments & the progressed life style. In summer, the peak load is mainly due to the non-industrial reasons such as air-conditioners and other cooling equipments. To cover the concentrated peak load in stable, the power transmission lines should be more constructed and efficiently operated. The ampacity design of the underground cable system is generally following international standards such as IEC287, IEC60853 and JCS168 which regards the shape of 100% daily full power loads. It is not so efficient to neglect the real shapes of load curves generally below 60~70% of full load. The dynamic (real time) rating system tends to be used with the measured thermal parameters which make it possible to calculate the maximum ampacity within required periods. In this paper, the CTM(Conductor Temperature Monitoring) which is the base of dynamic rating systems for tunnel environment is proposed by a design of lumped thermal network ($\pi$-type thermal model) and distribution temperature sensor attached configuration, including the estimation results of its performances by load cycle test on 345kV single phase XLPE cable.

• 한국지반공학회논문집
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• 제27권6호
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• pp.17-26
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• 2011

그라운드 앵커공법은 현재 우리나라에서 가장 일반적으로 사용되는 사면보강공법들 중 하나이다. 그러므로 앵커로 보강된 사면의 안정성을 장기간 확인하기 위해서는 그라운드 앵커의 긴장력을 측정하는 것이 매우 중요하다. 그러나 전통적인 로드 셀 방식의 측정기술을 제외하고는 특별한 기술이 개발된 것이 없다. 본 논문에서는 지반구조물의 보강을 위해 널리 사용되는 그라운드 앵커의 단기 및 장기 장력을 측정하기 위해 기존에 현장에서 주로 사용되는 스트레인게이지 또는 V/W 타입 로드 셀을 대체할 수 있는 새로운 방법에 대하여 기술하였다. 사용된 센서는 스트레인게이지 또는 V/W타입의 센서에 비해 크기가 작고 내구성이 우수하며 전자기파에 의한 노이즈 발생이 없는 광섬유 브래그격자(Fiber Bragg Grating ; FBG)센서이다. FBG 센서를 내장한 7연 강연선을 이용하여 원하는 위치에서 변형률 감지가 가능한 인장형 앵커를 제작하고 앵커 정착장을 연암과 화강풍화토 지반조건에 각각 2세트(set)씩 시공하여 현장인발실험을 수행하였다. 재하-제하단계를 포함하는 전 하중단계에서 FBG센서로 측정된 변형률로부터 장력 모니터링을 수행하였고 기존 로드 셀로 측정된 결과와 비교하였다. 현장 인발실험 결과, 제안된 광섬유 센서를 이용한 그라운드 앵커의 시공 중 긴장력 측정결과 실내 UTM 결과와 달리 약간의 차이가 있으나 실용적인 차원에서는 충분히 활용 가능한 것으로 확인되었다.

• 한국농공학회논문집
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• 제57권2호
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• pp.27-36
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• 2015

The objective of this paper was to quantitatively analyze the effect of concentrated animal feeding operations (CAFO) NPS pollution on a small watershed water quality. Monitoring was conducted from March to October, 2013. Monthly flow rate and selected water quality at each monitoring site were measured during dry days. Rainy day monitoring also was conducted. Modeling was conducted to evaluate the effect of CAFO NPS pollution on the water quality at the watershed outlet. The highest and mean concentration of selected water quality indices during rainy days were higher than those in dry days in general. The highest TN concentration measured at the CAFP pollution discharge point was 237.831 mg/L. The results revealed that the CAFO NPS pollution sources could be equally blamed for the water quality degradation of the stream. However, the effect of the NPS pollution from CAFOs seemed not to be very influential to the watershed water quality at the outlet. SWAT modeling revealed that the TN load was reduced by 18.95 %, 23.39 % and 30.53 % at the watershed outlet if the TN load at the CAFO NPS pollution discharge point reduced by 20 %, 40 % and 60 %, respectively. It was thought that the natural attenuation processes played an important role. The modeling was based only on the assumption of the load reduction and not verified by the monitored data. Therefore, it was suggested that a long term monitoring studies for the evaluation of the impact of CAFO NPS pollution on the watershed water quality be conducted.

• 한국농공학회논문집
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• 제47권3호
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• pp.77-86
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• 2005

A monitoring study has been conducted to identify hydrologic conditions, water quality and nutrient loading characteristics of small watershed in Juam Lake. Climate data of the watershed were collected; flow rate was measured and water quality sampling was conducted at the watershed outlet for this study. Water quality data revealed that T-P concentrations meet I grade of lake water quality standard during non-storm period, but degraded up to II-III grade of lake water quality standard during storm period. The observed T-N concentrations always exceeded lake water quality standard. Therefore, T-P was identified as limiting chemical constituent for eutrophication of Juam Lake. T-P concentration of non-storm period also revealed that point source pollution is not serious in the watershed. Three year monitoring results showed that the observed T-N losses were $10.85\~18.88$ kg/ha and T-P losses were $0.028\~0.323$ kg/ha during six month (Mar. - Oct.), respectively. Major portion of runoff amount discharged by a few storm events a year and nutrient load showed apparent seasonal variation. Huge runoff amounts were generated by intense storms, which make application of water treatment or detention facilities ineffective. Monitoring results confirmed that water quality improvement by abating nonpoint source pollution in rural watershed of monsoon climate should be focused on source control. T-P losses from paddy field seemed to consist of significant amount of total load from study watershed. Therefore, management of drainage from paddy field is considered to be important for preventing algal blooming problem in Juam Lake.

• 전기학회논문지
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• 제59권10호
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• pp.1741-1747
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• 2010

The development of overload management systems for distribution transformers offers new opportunities for improving the reliability of distribution systems. It allows network planners to optimize the system resource utilization and investment cost. Such an improvement in the flexibility of the distribution network is only possible if the operator has more accurate knowledge of the realtime conditions of distribution transformers. In this paper, we present an improved overload decision system for distribution transformers using realtime monitoring data. Our study can be categorized into two parts: (a) improvement in the criteria for judging the overload conditions of distribution transformers and (b) development of an overload evaluation system using realtime monitoring data. In order to determine the overload criteria, overload experiments are performed on sample transformers; the results of these experiments are used to define the relationship between the transformer overload and the increase in the top-oil temperature. To verify the accuracy of the experimental results, field tests are performed using specially manufactured transformers, the loads and top-oil temperatures of which can be measured. For arriving at online overload decisions, we propose methods whereby the measured load curve can be converted into an overload characteristic curve and the overload time can be calculated for any load condition. The developed system is able to evaluate the overload for individual distribution transformers and calculate the losses using realtime monitoring data.

• 한국통신학회논문지
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• 제39C권7호
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• pp.608-614
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• 2014

이 논문에서는 비간섭 전력 부하 감시에 알맞은 패턴 인식 시스템을 다룬다. 전력 신호의 고차 적률 정보를 써서 전기기구를 효과적으로 분별하여 인식할 수 있는 새로운 특징 추출 방법을 제안한다. 동작 특성이 비슷한 두 전기기구를 제안한 고차 적률 특징과 커널 판별 분석을 쓰는 패턴 인식 시스템이 효과적으로 분별하여 인식할 수 있다는 것을 모의실험으로 보인다.

• 인터넷정보학회논문지
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• 제7권3호
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• pp.53-60
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• 2006

인터넷을 통해 전송되는 트래픽의 양이 지속적으로 증가하고 있기 때문에 네트워크 트래픽 모니터링 시스템이 모든 패킷을 실시간으로 분석하기는 어렵다. 피어-투피어(P2P), 스트리밍 미디어, 메신저 등과 같이 동적으로 포트 번호를 할당받는 애플리케이션의 사용이 늘어나면서, 사용자들은 이들이 유발하는 트래픽을 분석하기를 원하고 있다. 이 같은 고수준의 분석을 위해서는 각 패킷마다 많은 처리 시간이 필요로 한다. 본 논문에서 부하 차단기를 이용하여 패킷의 수를 제한할 것을 제안한다. 선택된 패킷은 어떤 애플리케이션이 생성한 것인지 식별된 후, 정의된 애플리케이션 계층의 프로토콜에 따라 분석된다.

• 한국터널지하공간학회 논문집
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• 제19권6호
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• pp.905-913
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• 2017

세그먼트 라이닝 설계시 고려하는 하중은 자중, 연직하중, 수평하중, 지반반력, 수압, 뒤채움 주입압, 부력 등이 있으며, 이 가운데 토압과 수압은 세그먼트 라이닝 설계시 콘크리트 강도, 세그먼트 라이닝의 두께 및 철근량 등을 결정하는데 가장 큰 영향을 미치는 주요 인자이다. 따라서 본 연구에서는 쉴드터널 시공단계별 계측결과를 토대로 세그먼트 라이닝에 발생하는 휨모멘트 계산하였으며, 이를 역해석 결과와 비교분석을 통하여 세그먼트 라이닝에 작용하는 토압 등을 분석하였다.