• Structural Engineering and Mechanics
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• 제89권3호
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• pp.309-321
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• 2024

In this paper, the effect of semi-rigid connections on the stability bearing capacity of cross-bracings in steel tubular transmission towers is investigated. Herein, a prediction method based on the hybrid model which is a combination of particle swarm optimization (PSO) and backpropagation neural network (BPNN) is proposed to accurately predict the stability bearing capacity of cross-bracings with semi-rigid connections and to efficiently conduct its probabilistic assessment. Firstly, the establishment of the finite element (FE) model of cross-bracings with semi-rigid connections is developed on the basis of the development of the mechanical model. Then, a dataset of 7425 samples generated by the FE model is used to train and test the PSO-BPNN model, and the accuracy of the proposed method is evaluated. Finally, the probabilistic assessment for the stability bearing capacity of cross-bracings with semi-rigid connections is conducted based on the proposed method and the Monte Carlo simulation, in which the geometric and material properties including the outer diameter and thickness of cross-sections and the yield strength of steel are considered as random variables. The results indicate that the proposed method based on the PSO-BPNN model has high accuracy in predicting the stability bearing capacity of cross-bracings with semi-rigid connections. Meanwhile, the semi-rigid connections could enhance the stability bearing capacity of cross-bracings and the reliability of cross-bracings would significantly increase after considering semi-rigid connections.

• 한국통신학회논문지
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• 제35권6B호
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• pp.867-874
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• 2010

무선 센서 네트워크에서는 멀티 홉 전송동안 높은 패킷 손실률이 발생하기 때문에 신뢰성 있는 데이터 전송방안이 필요하다. 특히, 화재 경보 시스템과 같은 event-driven 데이터가 발생하는 경우, 신뢰성 있는 데이터 전송을 위해서는 손실된 패킷을 복원하기 위한 재전송 방안이 제공되어야 한다. 손실된 데이터의 재전송은 데이터를 캐쉬하고 있는 노드에 요청이 되기 때문에, 데이터를 캐쉬하고 있는 노드는 모든 데이터 패킷을 버퍼에서 유지하고 있어야 한다. 그러나 일반적으로 센서 네트워크의 노드들은 제한된 자원을 가지 있다. 따라서 신뢰성 있는 데이터 전송을 위해서는 손실 패킷의 재전송 방안과 노드의 버퍼 관리 기법이 함께 제공되어야 한다. 본 논문에서는 전송 데이터의 신뢰도에 따라 데이터의 캐쉬지점을 결정하여 손실된 데이터를 복원하는 손실 복원 기법을 사용하는 데이터 전송에서의 효율적인 버퍼 관리기법을 제안하고, 컴퓨터 시뮬레이션을 통하여 제안하는 방안의 우수성을 검증하였다.

• 한국정보과학회논문지:정보통신
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• 제31권2호
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• pp.224-232
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• 2004

최선의 전송(best-effort) 방식을 택하는 멀티캐스트 전송에서 신뢰성을 제공하기 위한 연구 중 데이타 채널과는 독립적인 계층적 제어 트리를 통하여 신뢰성을 제공하는 연구는 높은 확장성을 보장하는 것으로 알려져 있다. 그러나 하위 네트워크 계층의 트리에서 토폴로지 형성에 관한 명시적 정보를 제공하지 않는 상태에서 형성된 전송계층의 논리적 제어트리는 네트워크 계층의 트리 토폴로지와 일치하지 않아서 링크를 비효율적으로 사용할 가능성이 있다. 본 논문에서 제안한 라우터의 지원을 받아 제어트리를 구성하는 기법은 중복되는 데이타를 없애고 링크의 효율성을 향상시키는데 그 목적이 있으며, 제어트리에 사용되는 메시지 타입을 검사하는 기능 확장만을 요구함으로써 사용의 용이성을 증가시켰다.

• 한국통신학회논문지
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• 제37A권12호
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• pp.1065-1075
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• 2012

For the purpose of providing high data rate real-time services, radio transmission technologies (RTT) for ship ad-hoc network (SANET) based on the Recommendation ITU-R 1842-1 are designed. Physical layer parameters of SANET are contrived to meet the requirements of the specification. In order to improve the link reliability for SANET, in this paper, we investigate the performance of the SANET with the multiple antennas, where receive combining (RC), transmit diversity (TD), and beamforming (BF) are employed, respectively. Based on the analysis of the packet error rate (PER) under the highly correlated maritime wireless channel model, we select the efficient multiple antenna schemes for SANET to improve the link reliability. In addition, the optimal MCS levels for the single-carrier (SC) SANET with the bandwidth of 25 kHz, and the multi-carrier (MC) SANET with the bandwidth of 50 kHz and 100 kHz are finalized.

• Journal of Power Electronics
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• 제12권1호
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• pp.208-214
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• 2012

This paper presents a novel approach based on the loci of instantaneous symmetrical components called "Wing Shape" which requires the measurement of three input stator currents and voltages to diagnose interturn insulation faults in three phase induction motors operating under different loading conditions. In this methodology, the effect of unbalanced supply conditions, constructional imbalances and measurement errors are also investigated. The sizes of the wings determine the loading on the motor and the travel of the wings while their areas determine the degree of severity of the faults. This approach is also applied to detect open circuit faults or single phasing conditions in induction motors. In order to validate this method, experimental results are presented for a 5 hp squirrel cage induction motor. The proposed technique helps improve the reliability, efficiency, and safety of the motor system and industrial plant. It also allows maintenance to be performed in a more efficient manner, since the course of action can be determined based on the type and severity of the fault.

• 대한전기학회논문지:전력기술부문A
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• 제51권5호
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• pp.209-216
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• 2002

Recently, there is greater demand for stable supply of electric power as higher level of our living. It becomes the important problem that the cause of fault in power system is found out in early stage, if once it occurs. In this respect, accurate classification of arcing faults in power systems is vitally important. This paper presents a new classification method for arcing faults in power system. To obtain data of various faults including high impedance fault(HIF) and low impedance fault(LIF), HIF model with the ZnO arrester is adopted and implemented within the overall transmission system model based on the electromagnetic transients program(EMTP). Results of phase plane trajectory if Clarke modal transformation using postfault current and voltage are utilized to classify types of arcing faults. The performance of the proposed method is tested on a typical 154 kV korean transmission system under various fault conditions. As can be seen from results, phase plane trajectory of postfault current should be combined with that of o component from Clarke modal transformation to give reliability of clear fault classification. Thus the proposed method can classify arcing faults including LIFs and HIFs accurately in power systems.

• 한국통신학회논문지
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• 제32권5A호
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• pp.475-483
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• 2007

OFDMA 상향 시스템은 DVB-RCT를 위해 채택되었는데, OFDM과 동일하게 다중 경로 페이딩 영향에 강하고 성능 열화 없이 수신 가능하다는 이점을 갖는다. 이 시스템의 QoS를 향상시키기 위해 기존의 MIMO시스템이 많이 연구되었으나 다중송수신 안테나를 이용하는 이들 STC, MRC 등은 다중안테나를 사용하는 데에 따른 하드웨어 복잡도 증가, 고비용, 공간상의 제약 등 여러 가지 문제점을 안고 있다. 따라서 이들을 극복하면서 QoS도 만족시킬 수 있는 새로운 기법이 필요하다. 따라서 이 논문에서는 단일 안테나를 사용하는 OFDMA 기반의 DVB-RCT 시스템을 위하여 기존의 다중 송수신 기법들의 단점을 극복하고 현존 시스템을 이용할 수 있는 협동 전송 기법을 제안한다. OFDMA 상향 시스템 기반의 단일 안테나 DVB-RCT 시스템에 제안된 협동 전송 기법을 적용함으로써, 위에서 언급한 기존 기법들의 단점들을 극복하고 MIMO 시스템과 같이 성능을 향상 시킬 수 있다.

• 한국통신학회논문지
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• 제21권11호
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• pp.2869-2885
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• 1996

There werer many researches on the switch system for high speed netowrk such as B-ISDN and the server system for the multimedia services respectively. But, in case of simple connection of these two systems, we have to suffer the bottlenck problem of data transmission, and pay the wasteful expenditure because of duplicated architecture of both systems such as interconnecting network at the switch and the server. Therefore, we propse the unified architecture of switehces and servers, which can be used as switches and servers simultaneously. This is based on the hybercube structure. The links are used iterconnection network of switch system, and each node has the subscriber subsystem and the server subsystem. The proposed architecure has the benifits as follows; the easy espansion of capacity due to the scalability,the simple system development and maintenance because of the equivalance of each nodes, the high reliability against the fault of nodes and links due to the existence of the many alternative links between nodes, the easy flow and QoS managment due to the non-blocking data transmission between any two nodes, the flexible adaptation for additional new services owing to simple insertion server board to node. In this paper, we present overal configuration and node component of proposed architecture, and the procesing flow for the various services.

• Journal of Electrical Engineering and Technology
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• 제11권4호
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• pp.951-960
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• 2016

Tower insulators in electric power transmission network play a crucial role in preserving the reliability of the system. Electrical utilities frequently face the problem of flashover of insulators due to pollution deposition on their surface. Several research works based on leakage current (LC) measurement has been already carried out in developing diagnostic techniques for these insulators. Since the LC signal is highly intermittent in nature, estimation of pollution severity based on LC signal measurement over a short period of time will not produce accurate results. Reports on the measurement and analysis of LC signals over a long period of time is scanty. This paper attempts to use Random Forest (RF) classifier, which produces accurate results on large data bases, to analyze the pollution severity of high voltage tower insulators. Leakage current characteristics over a long period of time were measured in the laboratory on porcelain insulator. Pollution experiments were conducted at 11 kV AC voltage. Time domain analysis and wavelet transform technique were used to extract both basic features and histogram features of the LC signal. RF model was trained and tested with a variety of LC signals measured over a lengthy period of time and it is noticed that the proposed RF model based pollution severity classifier is efficient and will be helpful to electrical utilities for real time implementation.

• 한국정보처리학회:학술대회논문집
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• 한국정보처리학회 2009년도 춘계학술발표대회
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• pp.1178-1181
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• 2009

Geographic forwarding algorithms을 사용하는 Georouting protocol에서는 route maintenance을 위해서 고정된 주기마다 beacon message을 이웃노드에 전송하는 fixed periodical beacon based route algorithm을 사용하여 mobile node 정보를 습득한다. Fixed periodical beacon scheme에서의 기존 연구 이슈는 이웃노드 정보의 신뢰성을 유지하기 위해서 다양한 mobility environment 환경에 맞도록 beacon 전송주기를 적절히 결정하는 연구가 진행되어 왔다. 이와 같은 연구에서는 long periodical interval 사용 시 이웃노드의 위치정보 error을 발생시킬 확률이 높으며 또한 short periodical interval 의 경우 네트워크 내에 high route overhead 을 유발시키는 단점을 가지고 있다. 따라서 고정된 주기 방법은 다양한 mobility environment에 잘 적용되지 못하며 또한 mobility environment 에서 발생하는 route maintenance 내에 이웃노드 정보에 대한 불확실성 문제가 빈번이 발생하여 경로 설정에 잘못된 정보를 제공하여 경로 신뢰성(path reliability)과 낮은 전송률 (transmission rate)을 야기한다. 본 논문에서는 이런 이웃노드 정보의 불확실성 문제를 극복하기 위해서 mobile node가 스스로 자신의 위치를 체크하여 routing table을 능동적으로 갱신하는 방법을 이용하여 이 문제를 극복할 수 있도록 하였다. 모의 실험은 ns2를 이용하여 실시하였으며 결과는 low/high mobility scenario에서는 기존 방법 보다 routing overhead 을 줄이면서 높은 전송률 (transmission rate)을 보인다.