• 디지털산업정보학회논문지
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• 제14권1호
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• pp.35-43
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• 2018

MANET composed of only wireless nodes is increasingly utilized in various fields. However, it is exposed to many security vulnerabilities because it doesn't have any infrastructure and transmits data by using multi-hop method. Therefore, MANET should be applied the intrusion detection technique that can detect efficiently malicious nodes and decrease impacts of various attacks. In this paper, we propose a distributed intrusion detection technique that can detect the various attacks while improving the efficiency of attack detection and reducing the false positive rate. The proposed technique uses the cluster structure to manage the information in the center and monitor the traffic of their neighbor nodes directly in all nodes. We use three parameters for attack detection. We also applied an efficient authentication technique using only key exchange without the help of CA in order to provide integrity when exchanging information between cluster heads. This makes it possible to free the forgery of information about trust information of the nodes and attack nodes. The superiority of the proposed technique can be confirmed through comparative experiments with existing intrusion detection techniques.

• Smart Structures and Systems
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• 제2권3호
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• pp.225-235
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• 2006

With the discovery in plants of the proteinaceous forisome crystalloid (Knoblauch, et al. 2003), a novel, non-living, ATP-independent biological material became available to the designer of smart materials for advanced actuating and sensing. The in vitro studies of Knoblauch, et al. show that forisomes (2-4 micron wide and 10-40 micron long) can be repeatedly stimulated to contract and expand anisotropically by shifting either the ambient pH or the ambient calcium ion concentration. Because of their unique abilities to develop and reverse strains greater than 20% in time periods less than one second, forisomes have the potential to outperform current smart materials as advanced, biomimetic, multi-functional, smart sensors or actuators. Probing forisome material properties is an immediate need to lay the foundation for synthesizing forisomebased smart materials for health monitoring of structural integrity in civil infrastructure and for aerospace hardware. Microfluidics is a growing, vibrant technology with increasingly diverse applications. Here, we use microfluidics to study the surface interaction between forisome and substrate and the conformational dynamics of forisomes within a confined geometry to lay the foundation for forisome-based smart materials synthesis in controlled and repeatable environment.

• 한국구조물진단유지관리공학회 논문집
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• 제4권4호
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• pp.109-119
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• 2000

PVDF film sensor was applied to measure the stress concentration for monitoring the structural integrity. The strain calibration of this film sensor was performed by the bending test of aluminum beam. The PVDF sensor and the electrical strain gage were bonded on the beam. When the beam was loaded, the output of electrical strain gage was compared with the output of the PVDF sensor. The waveform of PVDF sensor output was shown as the same form of the output of electrical strain gage. The gain was determined as 1.7 by comparing these two signals to determine the exact value of the strain. In order to experiment the stress concentration, the stress field was analyzed by finite element analysis. The tensile test of notched steel specimens was conducted to develop the measurement technique of stress concentration. The output voltage ratio between the PVDF sensor near the notch and the PVDF sensor far from the notch could give the information about the load bearing capacity of steel specimen.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2015년도 추계학술대회
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• pp.266-267
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• 2015

해상 활동에 있어서 해상교통의 핵심정보인 항법신호의 안전을 강화하기 위하여, 본 논문에서는 국내에서 발생한 전파간섭 발생 사례와 영향, 그리고 DGNSS 기준국 무결성 기능의 한계에 대해 조사하고 그 대응방안을 운영자 및 선박 운항자 관점에서 분석한다. 그 대안의 하나로서 항만 항법신호(PNT)의 무결성 감시 기술과 그 신뢰도를 결정하여 사용자에게 제공하기 위한 항만 PNT 무결성 감시 서비스에 대해 소개한다. 그리고 특정 항만에 항법신호 감시 시스템을 구축하여, 개발 시스템의 시범 운영 테스트를 통해 그 실용화 가능성을 제시한다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1998년도 하계학술대회 논문집 A
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• pp.186-188
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• 1998

Acoustic emission monitoring on two racetrack superconducting field winding coil was performed during excitation and quenches to diagnose the integrity of the field winding coils. Two field windings were not impregnated with epoxy The results confirm that the acoustic emission signals are mainly due to conductor motions which cause premature quenching of the winding. The quench current of modified racetrack type field winding coil (Type B) are more higher than that of conventional field winding coil (Type A).

• Earthquakes and Structures
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• 제8권4호
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• pp.843-857
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• 2015

System identification is regarded as the most basic technique for structural health monitoring to evaluate structural integrity. Although many system identification techniques extracting mode information (e.g., mode frequency and mode shape) have been proposed so far, it is also desired to identify physical parameters (e.g., stiffness and damping). As for high-rise buildings subjected to long-period ground motions, system identification for evaluating only the shear stiffness based on a shear model does not seem to be an appropriate solution to the system identification problem due to the influence of overall bending response. In this paper, a system identification algorithm using a shear-bending model developed in the previous paper is revised to identify both shear and bending stiffnesses. In this algorithm, an ARX (Auto-Regressive eXogenous) model corresponding to the transfer function for interstory accelerations is applied for identifying physical parameters. For the experimental verification of the proposed system identification framework, vibration tests for a 3-story steel mini-structure are conducted. The test structure is specifically designed to measure horizontal accelerations including both shear and bending responses. In order to obtain reliable results, system identification theories for two different inputs are investigated; (a) base input motion by a modal shaker, (b) unknown forced input on the top floor.

• Computers and Concrete
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• 제13권2호
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• pp.209-220
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• 2014

Vibration based damage detection is very popular in the civil engineering area. Especially, special structures like dams, long-span bridges and high-rise buildings, need continues monitoring in terms of mechanical properties of material, static and dynamic behavior. It has been stated in the International Commission on Large Dams that more than half of the large concrete dams were constructed more than 50 years ago and the old dams have subjected to repeating loads such as earthquake, overflow, blast, etc.,. So, some unexpected failures may occur and catastrophic damages may be taken place because of theloss of strength, stiffness and other physical properties of concrete. Therefore, these dams need repairs provided with global damage evaluation in order to preserve structural integrity. The paper aims to show the effectiveness of the model updating method for global damage detection on a laboratory arch dam model. Ambient vibration test is used in order to determine the experimental dynamic characteristics. The initial finite element model is updated according to the experimentally determined natural frequencies and mode shapes. The web thickness is selected as updating parameter in the damage evaluation. It is observed from the study that the damage case is revealed with high accuracy and a good match is attained between the estimated and the real damage cases by model updating method.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2006년도 International Symposium on GPS/GNSS Vol.1
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• pp.361-365
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• 2006

High ionospheric spatial gradient during ionospheric storm is most concern for the landing approach with GNSS (Global Navigation Satellite System) augmentation systems. In case of the GBAS (Ground-Based Augmentation System), the ionospheric storm causes sudden increase of the ionospheric delay difference between a ground facility and a user (aircraft), and the aircraft position error increases significantly. Since the ionosphere behavior and the storm effect depend on geographic location, understanding the ionospheric storm behavior at specific regional area is crucial for the GNSS augmentation system development and implementation. Korea Aerospace Research Institute and collaborating universities have been developing an integrity monitoring test bed for GBAS research and for future regional augmentation system development. By using the dense GPS (Global Positioning System) networks in Korea, a regional ionosphere map is constructed for finding detailed aspect of the ionosphere variation. Preliminary analysis on the ionospheric gradient variation during a recent storm period is performed and the results are discussed.

• 비파괴검사학회지
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• 제24권4호
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• pp.396-409
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• 2004

음향방출기술(acoustic emission technology)은 종래의 기존 비파괴검사법과는 달리 가동중인 설비의 건전성을 평가할 수 있으며 실시간으로 설비 상태의 진단이 가능한 실시간 감시기법이다. 즉 기존 비파괴검사법과는 달리 가동중인 설비에 대해 원격으로 결함을 탐지하고 결함 위치를 판정할 수 있는 연속감시 기능을 가진 비파괴 신기술로 최근 연구개발이 활발히 진행되고 있는 방법이다. 이러한 장점 때문에 대형 산업설비의 각종 기기들에 대한 감시 및 진단에 활용하고 있으며, 그 활용도가 점점 확대되고 있는 추세에 있다. 특히 종합적인 산업설비로 구성되어 있는 발전설비의 진단과 감시에 가장 효과적인 방법이라 할 수 있겠다. 본 논문에서는 원자력 화력 수력발전소 등의 발전설비에 대해 현재 적용중인 음향방출기술과 새로운 적용기술에 대해 서술하였다.

• Nuclear Engineering and Technology
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• 제53권6호
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• pp.1846-1857
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• 2021

Ultrasonic nondestructive testing is important for monitoring the structural integrity of dissimilar metal welds (DMWs) in pressure vessels and piping in nuclear power plants. However, there is a low probability of crack detection via inspection of DMWs using ultrasonic waves because the grain structures (grain orientations) of the weld area cause distortion and splitting of ultrasonic beams propagating in anisotropic media. To overcome this issue, the grain orientation should be known, and a precise ultrasonic wave simulation technique in anisotropic media is required to model the distortion and splitting of the waves accurately. In this study, a method for nondestructive prediction of the DMW grain orientations is presented for accurate simulation of ultrasonic wave propagation behavior in the weld area. The ultrasonic wave propagation behavior in anisotropic media is simulated via finite-element analysis when ultrasonic waves propagate in a transversely isotropic material. In addition, a methodology to predict the DMW grain orientation is proposed that employs a simulation technique for ultrasonic wave propagation behavior calculation and an optimization technique. The simulated ultrasonic wave behaviors with the grain orientations predicted via the proposed method demonstrate its usefulness. Moreover, the method can be used to determine the focal law in DMWs.