• Nuclear Engineering and Technology
• /
• 제52권11호
• /
• pp.2638-2651
• /
• 2020

Nozzle corner cracks present at the intersection of reactor pressure vessels (RPVs) and inlet or outlet nozzles have been a persistent problem for a number of years. The fracture analysis of such nozzle corner cracks is very important and critical for the efficient design and assessment of the structural integrity of RPVs. This paper aims to perform an engineering critical assessment of RPVs with nozzle corner cracks subjected to several transients accompanied by pressurized thermal shocks. The critical crack size of the RPV model with nozzle corner cracks under transient loading is evaluated on failure assessment curve. In particular, the influence of cladding on the crack initiation of nozzle corner crack under thermal transients is studied. The influence of primary internal pressure and secondary thermal stress on the stress field at nozzle corner and SIF at crack front is analyzed. Finally, the influence of different crack size and crack shape on the final critical crack size is analyzed.

• Smart Structures and Systems
• /
• 제12권3_4호
• /
• pp.427-440
• /
• 2013

A growing need has developed in the United States to obtain more specific knowledge on the structural integrity of infrastructure due to aging service lives, heavier and more frequent loading conditions, and durability issues. This need has spurred extensive research in the area of structural health monitoring over the past few decades. Several structural health monitoring techniques have been developed that are capable of locating damage in structures using modal strain energy of mode shapes. Typically in the past, bending strain energy has been used in these methods since it is a dominant vibrational mode in many structures and is easily measured. Additionally, there may be cases, such as pipes, shafts, or certain bridges, where structures exhibit significant torsional behavior as well. In this research, torsional strain energy is used to locate damage. The damage index method is used on two numerical models; a cantilevered steel pipe and a simply-supported steel plate girder bridge. Torsion damage indices are compared to bending damage indices to assess their effectiveness at locating damage. The torsion strain energy method is capable of accurately locating damage and providing additional valuable information to both of the structures' behaviors.

• Smart Structures and Systems
• /
• 제29권2호
• /
• pp.361-374
• /
• 2022

As civil infrastructure has continued to age worldwide, its structural integrity has been threatened owing to material deteriorations and continual loadings from the external environment. Structural Health Monitoring (SHM) has emerged as a cost-efficient method for ensuring structural safety and durability. As SHM research has gradually addressed an increasing number of structure-related problems, it has become difficult to understand the changing research topic trends. Although previous review papers have analyzed research trends on specific SHM topics, these studies have faced challenges in providing (1) consistent insights regarding macroscopic SHM research trends, (2) empirical evidence for research topic changes in overall SHM fields, and (3) methodological validations for the insights. To overcome these challenges, this study proposes a framework tailored to capturing the trends of research topics in SHM through a bibliometric and network analysis. The framework is applied to track SHM research topics over 15 years by identifying both quantitative and relational changes in the author keywords provided from representative SHM journals. The results of this study confirm that overall SHM research has become diversified and multi-disciplinary. Especially, the rapidly growing research topics are tightly related to applying machine learning and computer vision techniques to solve SHM-related issues. In addition, the research topic network indicates that damage detection and vibration control have been both steadily and actively studied in SHM research.

• 항공우주시스템공학회지
• /
• 제18권3호
• /
• pp.65-69
• /
• 2024

본 연구에서는 대형상용차 및 트레일러에 적용되는 브레이크 챔버의 압력을 실시간으로 모니터링하는 핵심부품인 센서 컨트롤 박스에 대하여 전산해석 프로그램인 ANSYS Workbench R2021 [7]을 활용하여 진동시험 규격인 KS R1034의 시험 조건을 기초로 고유진동수 및 진동에 의한 구조적 안전성을 분석하였다. 모달 해석을 통해 5Hz ~ 100Hz 주파수 영역에서 공진점을 검출하였고, 조화해석을 통해 33Hz ~ 67 Hz의 결과값을 비교하였다.

• Journal of information and communication convergence engineering
• /
• 제8권2호
• /
• pp.129-135
• /
• 2010

Wireless sensor networks (WSNs) are an emerging technology and offers economically viable monitoring solution to many challenging applications. However, deploying new technology in hostile environment, without considering security in mind has often proved to be unreasonably unsecured. Apparently, security techniques face many critical challenges in WSNs like data security and secrecy due to its hostile deployment nature. In order to resolve security in WSNs, we propose a novel and efficient secure framework called TriSec: a secure data framework for wireless sensor networks to attain high level of security. TriSec provides data confidentiality, authentication and data integrity to sensor networks. TriSec supports node-to-node encryption using PingPong-128 stream cipher based-privacy. A new PingPong-MAC (PP-MAC) is incorporated with PingPong stream cipher to make TriSec framework more secure. PingPong-128 is fast keystream generation and it is very suitable for sensor network environment. We have implemented the proposed scheme on wireless sensor platform and our result shows their feasibility.

• Journal of Information Processing Systems
• /
• 제3권2호
• /
• pp.82-88
• /
• 2007

Web services are the new building block of today's Internet, and provides interoperability among heterogeneous distributed systems. Recently in web services environment, security has become one of the most critical issues. The hackers attack one of fragile point and can misuse legitimate user privilege because all of the connected devices provide services for the user control and monitoring in real time. Also, the users of web services must temporarily delegate some or all of their rights to agents in order to perform actions on their behalf. This fact risks the exposure of user privacy information. In this paper, we propose secure delegation model based on SAML that provides confidentiality and integrity about the user information in distributed systems. In order to support privacy protection, service confidentiality, and assertion integrity, encryption and a digital signature mechanism is deployed. We build web service management server based on XACML, in order to manage services and policies of web service providers.

• Smart Structures and Systems
• /
• 제26권4호
• /
• pp.419-433
• /
• 2020

Investigation of structural integrity has been a critical issue in the field of civil engineering for years. Visual inspection is one of the most available methods to explore deteriorative components in structures. Still, this method is not applicable to invisible damage of structures. Alternatively, system identification methods are capable of tracking modal properties of structures over time. The deviation of these dynamic properties can serve as indicators to access structural integrity. In this study, a modal tracking technique using frequency-domain system identification from seismic responses of structures is proposed. The method first segments the measured signals into overlapped sequential portions and then establishes multiple Hankel matrices. Each Hankel matrix is then converted to the frequency domain, and a temporal-average frequency-domain Hankel matrix can be calculated. This study also proposes the frequency band selection that can divide the frequency-domain Hankel matrix into several portions in accordance with referenced natural frequencies. Once these referenced natural frequencies are unavailable, the first few right singular vectors by the singular value decomposition can offer these references. Finally, the frequency-domain stochastic subspace identification tracks the natural frequencies and mode shapes of structures through quick stabilization diagrams. To evaluate performance of the proposed method, a numerical study is carried out. Moreover, the long-term monitoring strong motion records at a specific site are exploited to assess the tracking performance. As seen in results, the proposed method is capable of tracking modal properties through seismic responses of structures.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2006년도 제37회 하계학술대회 논문집 B
• /
• pp.1136-1137
• /
• 2006

통합항해시스템이라 함은 자동화된 선박의 운용에 관한 것으로, 다양한 항해 센서(GPS, Gyro, Speed Log, echo sounder)를 이용하여 선박의 항해에 필요한 각종 정보를 입수하여 최적의 항로를 설정해주고, 운항의 안정성과 효율을 극대화시키는 시스템을 지칭한다. 즉, 선박의 운항에 필요한 다수의 모듈들을 독립적으로 운용하는 것이 아니라 이를 통합된 형태로 운용하여 효율을 극대화시키는 시스템이 통합항해시스템이라 할 수 있다. 통합항해시스템은 다양한 항해 센서들과 항해 시스템으로 구성되며, 다양한 항해 데이터들은 항해 센서로부터 수신하여 처리하는 동작을 수행한다. 즉, 통합항해시스템은 다수의 센서들로부터 수신된 정보를 평가하고 잠재적 위험과 무결성 저하에 대해서는 적절한 경고를 제공하여야한다. 따라서, 항해센서 데이터의 유효성(Validity) 및 모호성(Plausibility) 검사와 무결성 감시(Integrity Monitoring)는 통합항해시스템의 필수적 기능이라 할 수 있다. 본 연구에서는 IEC 61924 규격에 의한 항해센서로부터 수신된 항해데이터가 정확하고 유효함을 가지는 지에 대한 가치평가의 척도와 독립적인 데이터 소스로부터 데이터를 비교하여 검증하는 무결성, 정확도 이내의 정보를 완전하고 명확한 방법으로 사용자에게 제공하는 무결성 감시의 방법을 제시하며, 항해센서들에 의해 취득되는 항해 데이터의 무결성 검사를 통한 유효성, 적용가능성, 무결성의 평가방법을 기술한다.

• Smart Structures and Systems
• /
• 제18권4호
• /
• pp.643-662
• /
• 2016

The monitoring of structural integrity of pipeline tapered thread connections is of great significance in terms of safe operation in the industry. In order to detect effectively the loosening degree of tapered thread connection, an active sensing method using piezoceramic transducers was developed based on time reversal technique in this paper. As the piezoeramic transducers can be either as actuators or sensors to generate or detect stress waves, the energy transmission for tapered thread connection was analyzed. Subsequently, the detection principle for tapered thread connection based on time reversal was introduced. Finally, the inherent relationship between the contact area and tightness degree of tapered thread connection for the pipe structural model was investigated. Seven different contact area scenarios were tested. Each scenario was created by loosening connectors ranging from 3 turns to 4.5 turns in the right tapered threads when the contact area in the left tapered threads were 4.5 turns. The experiments were separately conducted with a highly noisy environment and various excitation signal amplitudes. The results show the focused peaks based on time reversal have the monotonously rising trend with the increase of the contact areas of tapered threads within an acceptable monitoring resolution for metal pipes. Compared with the energy method, the proposed time reversal based method to monitor tapered threads loosening demonstrates to be more robust in rejecting noise in Structural Health Monitoring (SHM) applications.

• 한국컴퓨터정보학회논문지
• /
• 제26권2호
• /
• pp.45-52
• /
• 2021

본 논문에서는 모니터링 단체의 특징기반 필터링 기반의 음원 이용 모니터링 도구에서 음원 이용 내역을 블록체인에 기록하도록 하는 블록체인 기반의 주배시 음원 이용 모니터링 정보 생성 방법을 제안한다. 주배시 음원이란 방송사의 방송콘텐츠에 삽입된 음원으로서 통상 음원과 마찬가지로 하나의 창작물로서 인정되며 음원의 권리를 가지고 있는 작사, 작곡가 등이 존재하며 방송에서 음원이 이용된 만큼 모든 권리자가 이에 따른 저작권료를 분배받는다. 하지만 주배시 음원 이용에 대한 정확하지 않은 모니터링 결과와 이에 따른 이용 내역에 대한 누락 및 투명하지 않는 정산 방식에 관한 문제가 발생하고 있다. 본 논문을 통하여 제안한 정보생성 방식을 이용하면 정확한 음원 이용 내역이 생성 가능하고 블록에 저장된 내역이 변경이나 누락 없이 저장되고 투명하지 않는 정산방식을 스마트 계약에 의해 처리하여 투명한 정산 및 분배가 가능하다.