• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2005년도 추계학술대회 논문집
• /
• pp.394-399
• /
• 2005

In this paper, a structural damage identification method (SDIM) is developed to identify the line crack-like directional damages generated within a cylindrical shell. First, the equations of motion fur a damaged cylindrical shell are derived. Based on a theory of continuum damage mechanics, a small material volume containing a directional damage is represented by the effective orthotropic elastic stiffness, which is dependent of the size and the orientation of the damage with respect to the global coordinates. The present SDIM is then derived from the frequency response function (FRF) directly solved from the dynamic equations of the damaged cylindrical shell. In contrast with most existing SDIMs which require the modal parameters measured in both intact and damaged states, the present SDIM requires only the FRF-data measured in damaged state. By virtue of utilizing FRF-data, one may choose as many sets of excitation frequency and FRF measurement point as needed to acquire a sufficient number of equations fer damage identification analysis. The numerically simulated damage identification tests are conducted to study the feasibility of the present SDIM.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2005년도 추계 학술대회논문집(수송기계편)
• /
• pp.77-80
• /
• 2005

This paper presents a theoretical and experimental study on the damage identification of structures. In civil and aerospace, significant work has been done in the area of detecting damage in structures by using changes in the dynamic response of the structure. In this paper a method based on the changes in the strain energy of the structure will be discussed. To evaluate the effectiveness of the method it will be applied to both beam and LNG(liquefied natural gas) carrier.

• 한국철도학회:학술대회논문집
• /
• 한국철도학회 2008년도 춘계학술대회 논문집
• /
• pp.56-64
• /
• 2008

To maintain effectively the functionality of major railroad facilities such as bridges, identifying and evaluating damage in a structure and taking appropriate action via continuous structural health monitoring are very important. However, most damage identification methods for structural health monitoring developed to date utilize modal domain responses which inevitably contain errors in transforming the domain of responses. In this paper, a damage identification method using time-domain operational deflection shapes is proposed. Since the proposed method utilizes time-domain responses, the error in the process of transformation to response domain can be avoided, and the accuracy of structural health evaluation can be improved. The feasibility of the proposed method is verified via a numerical example of a simple bridge structure.

• 한국전산구조공학회:학술대회논문집
• /
• 한국전산구조공학회 2007년도 정기 학술대회 논문집
• /
• pp.669-674
• /
• 2007

To develop a promising hybrid structural health monitoring (SHM) system, a combined use of structural vibration and electro-mechanical (EM) impedance is proposed. The hybrid SHM system is designed to use vibration characteristics as global index and EM impedance as local index. The proposed health monitoring scheme is implemented into prestressed concrete (PSC) girder bridges for which a series of damage scenarios are designed to simulate various prestress-loss situations at which the target bridges car experience during their service life. The measured experimental results, modal parameters and electro-magnetic impedance signatures, are carefully analyzed to recognize the occurrence of damage and furthermore to indicate its location.

• Structural Engineering and Mechanics
• /
• 제17권3_4호
• /
• pp.467-482
• /
• 2004

One of the uncertain damage parameters to jeopardize the safety of existing PSC bridges is the loss of the prestress force. A substantial prestress-loss can lead to severe problems in the serviceability and safety of the PSC bridges. In this paper, a nondestructive method to detect prestress-loss in beam-type PSC bridges using a few natural frequencies is presented. An analytical model is formulated to estimate changes in natural frequencies of the PSC bridges under various prestress forces. Also, an inverse-solution algorithm is proposed to detect the prestress-loss by measuring the changes in natural frequencies. The feasibility of the proposed approach is evaluated using PSC beams for which a few natural frequencies were experimentally measured for a set of prestress-loss cases. Numerical models of two-span continuous PSC beams are also examined to verify that the proposed algorithm works on more complicated cases.

• Structural Monitoring and Maintenance
• /
• 제3권1호
• /
• pp.33-49
• /
• 2016

Structural Health Monitoring (SHM) has been attracting numerous research efforts around the world because it targets at monitoring structural conditions and performance to prevent catastrophic failure, and to provide quantitative data for engineers and infrastructure owners to design a reliable and economical asset management strategy. In the past decade, with supports from Australian Research Council (ARC), Cooperative Research Center for Infrastructure and Engineering Asset Management (CIEAM), CSIRO and industry partners, intensive research works have been conducted in the School of Civil, Environmental and Mining Engineering, University of Western Australia and Centre for Infrastructural Monitoring and Protection, Curtin University on various techniques of SHM. The researches include the development of hardware, software and various algorithms, such as various signal processing techniques for operational modal analysis, modal analysis toolbox, non-model based methods for assessing the shear connection in composite bridges and identifying the free spanning and supports conditions of pipelines, vibration based structural damage identification and model updating approaches considering uncertainty and noise effects, structural identification under moving loads, guided wave propagation technique for detecting debonding damage, and relative displacement sensors for SHM in composite and steel truss bridges. This paper aims at summarizing and reviewing the recent research advances on SHM of civil infrastructure in Western Australia.

• 한국생산제조학회지
• /
• 제24권6호
• /
• pp.632-638
• /
• 2015

Many failures have been reported in gas turbine facilities owing to repeated startups and prolonged use of the turbines. In this study, the causes and mechanism of fatigue failure in the first blade of a gas turbine were analyzed using a finite element method to calculate the centrifugal force, bending force, and a modal analysis based on the stress-stiffening effect and harmonic response under the operating conditions. The results show that, fatigue damage was caused by the resonance conditions encountered, in which the first natural frequency declined along with an increase in the metal temperature of the blade. The position of the expected fatigue damage was shown to match the actual position of the cracking at the root area of the blade, which was on the concave side. In addition, the equivalence fatigue stress was observed to approach the fatigue limit.

• Smart Structures and Systems
• /
• 제21권2호
• /
• pp.171-185
• /
• 2018

Maintenance of deteriorated bridge structures has always been one of the challenging issues in developing countries as it is directly related to daily life of people including trade and economy. An effective maintenance strategy is highly dependent on timely inspections on the bridge health condition. This study is intended to investigate an approach for detecting bridge damage for the long-term health monitoring by use of copula theory. Long-term measured data for the seven-span plate-Gerber bridge is investigated. Autoregressive time series models constructed for the observed accelerations taken from the bridge are utilized for the computation of damage indicator for the bridge. The copula model is used to analyze the statistical changes associated with the modal parameters. The changes in the modal parameters with the time are identified by the copula statistical properties. Applicability of the proposed method is also discussed based on a comparison study among other approaches.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2013년도 추계학술대회 논문집
• /
• pp.320-324
• /
• 2013

A crack identification method using an equivalent bending stiffness for cracked beam and committee of neural networks is presented. The equivalent bending stiffness is constructed based on an energy method for a straight thin-walled pipe, which has a through-the-thickness crack, subjected to bending. Several numerical analysis for a steel cantilever pipe using the equivalent bending stiffness are carried out to extract the natural frequencies and mode shapes of the cracked beam. The extracted modal properties are used in constructing a training patterns of a neural network. The input to the neural network consists of the modal properties and the output is composed of the crack location and size. Multiple neural networks are constructed and each individual network is trained independently with different initial synaptic weights. Then, the estimated crack locations and sizes from different neural networks are averaged. Experimental crack detection is carried out for 3 damage cases using the proposed method, and the identified crack locations and sizes agree reasonably well with the exact values.

• 한국산학기술학회논문지
• /
• 제18권8호
• /
• pp.64-71
• /
• 2017

본 연구에서는 재킷식 해상풍력터빈 지지구조물의 효과적인 건전성 모니터링을 위하여, 손상에 의한 구조물의 모드 특성 변화 및 군집신경망기법을 이용한 손상추정기법을 제안한다. 실용적 적용을 위하여 제한된 계측자료를 활용하고, 구조적으로 중요하며 손상이 발생될 확률이 큰 것으로 판단되는 중요부재를 대상으로 손상을 추정한다. 즉, 재킷식 지지구조물은 부재 개수가 많기 때문에, 모든 부재를 적절히 식별하기 위해서는 이에 상당하는 많은 수의 계측 데이터 채널 및 센서를 설치해야 한다. 이는 건전성 모니터링의 경제적 및 실용적인 측면에서 적절치 않다고 판단되며, 본 연구에서는 중요 구조부재에 대하여 제한된 계측자료를 활용하여 집중적으로 손상추정을 수행하기 위한 연구를 수행한다. 5 MW 해상풍력터빈에 적용될 수 있는 재킷식 해상풍력터빈 지지구조물을 모델링한 후, 수치 시뮬레이션을 수행하여 신경망의 훈련패턴을 생성한다. 이후, 군집신경망기법을 이용하여 중요부재에 대한 손상위치 및 손상정도를 20가지 손상경우에 대하여 추정한 결과, 모든 손상 경우에 대하여 성공적으로 손상을 판정할 수 있었으며, 군집신경망기법을 적용함으로써 추청결과의 정확성이 향상됨을 알 수 있었다. 또한 실험연구를 통하여 기법을 검증하였는데, 3가지 손상경우에 대하여 손상을 추정한 결과 합리적으로 손상을 추정할 수 있었다.