• Transactions of the Korean Society of Mechanical Engineers A
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• 제28권10호
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• pp.1467-1474
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• 2004

In this study, a new damage identification method for beam-like structures with a fatigue crack is proposed. which does not require comparative measurement on an intact structure but require several measurements at different level of excitation forces on the cracked structure. The idea comes from the fact that dynamic behavior of a structure with a fatigue crack changes with the level of the excitation force. The 2$^{nd}$ spatial derivatives of frequency response functions along the longitudinal direction of a beam are used as the sensitive indicator of crack existence. Then, weighting function is employed in the averaging process in frequency domain to account for the modal participation of the differences between the dynamic behavior of a beam with a fatigue crack at the low excitation and one at the high excitation. Subsequently, a damage index is defined such that the location and level of the crack may be identified. It is shown from the analysis of vibration measurements in this study that comparison of frequency response characteristics of a beam with a single fatigue crack at different level of excitation forces enables an effective detection of the crack.

• Journal of Ocean Engineering and Technology
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• 제30권3호
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• pp.161-168
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• 2016

This paper presents a methodology through which the time series of the dynamic response of mooring line tension can be predicted without relying on a time-consuming nonlinear time-domain analysis. The mooring line tension for the target short-term sea states was predicted using a Hammerstein-Wiener model, a popular system identification scheme, based upon the pre-calculated motion-tension time history data for some selected short-term sea states that do not overlap with the targeted ones. The obtained mooring line tension was further processed, and a fatigue damage comparison was made between the predicted and calculated values. The results showed that the predicted time series of the mooring line tension matched the calculated one fairly well. Thus, it is expected that the methodology may be employed to enhance the efficiency of mooring line tension analysis.

• Journal of the Computational Structural Engineering Institute of Korea
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• 제12권3호
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• pp.331-343
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• 1999

본 논문에서는 새로이 유도된 진동기초 손상검색방법을 제시하고, 제한적인 모드특성치가 측정된 구조물을 대상으로 이 알고리즘의 적합성과 손상예측의 정확도를 검증하고자 하였다. 먼저, 기존의 Kim과 Stubbs에 의해 발표된 손상발견 알고리즘들을 검토하였으며, 이 알고리즘들의 적용한계와 오류적 가정을 극복할 수 있는 손상검색 알고리즘을 새로이 유도하였다. 다음으로, 손상발생 전후에 소수의 진동모드 특성치가 측정된 2경간 연속보를 대상으로 손상예측실험을 수행하여, 이들 손상검색 알고리즘의 손상예측 정확도를 분석하였다. 기존의 손상검색 알고리즘에 비하여 새로이 유도된 손상검색 알고리즘의 손상예측 정확도가 향상된 것으로 분석되었다.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 한국전산구조공학회 1996년도 가을 학술발표회 논문집
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• pp.147-155
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• 1996

The purpose of present study is to propose a improved damage detection and assessment algorithm that has its basis on the method of system identification. In this approach, the complete sets of modes or displacements are not needed since the error response function involves only the difference between components of those vectors. The present approach also allows the use of composite data which is constitute of static displacements and eigenmodes. The effectiveness of the proposed statistical system identification method is investigated through simulated studies. A series of tests for predetermined damaged cantilever beam and bowstring truss structure have been conducted to verify the proposed method.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 한국전산구조공학회 2003년도 봄 학술발표회 논문집
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• pp.95-102
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• 2003

To define an analytical model for a structural system or to assess damage in the system, system identification(SI) methods have been developed and widely applied. The paper presents a method of determining optimal sensor location(OSL) based on the maximum likelihood approach, which is applicable to modal SI methods. To estimate unknown parameters reliably, it is necessary that the information provided by the experiment should be maximized. By applying the Cramer-Rao inequality, a Fisher information matrix in terms of the probability density function of measurements is obtained from a lower bound of the estimation error. The paper also proposes a scheme of determining of OSL on damaged structures by using maximum strain energy factor. Simulation studies have carried out to investigate the proposed OSL algorithm for both undamaged and damaged structures.

• Structural Engineering and Mechanics
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• 제35권6호
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• pp.773-789
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• 2010

It is well known that the analytical vibration characteristic of a cracked beam depends largely on the crack model. In the forward analysis, an improved and simplified approach in modeling discrete open cracks in beams is presented. The effective length of the crack zone on both sides of a crack with stiffness reduction is formulated in terms of the crack depth. Both free and forced vibrations of cracked beams are studied in this paper and the results from the proposed modified crack model and other existing models are compared. The modified crack model gives very accurate predictions in the modal frequencies and time responses of the beams particularly with overlaps in the effective lengths with reduced stiffness. In the inverse analysis, the response sensitivity with respect to damage parameters (the location and depth of crack, etc.) is derived. And the dynamic response sensitivity is used to update the damage parameters. The identified results from both numerical simulations and experiment work illustrate the effectiveness of the proposed method.

• Proceedings of the SCSK Conference
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• 대한화장품학회 2003년도 IFSCC Conference Proceeding Book II
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• pp.448-455
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• 2003

Because cosmetics are applied directly to human skin, contamination of such products by microorganisms should be carefully avoided. Since cosmetics are usually kept at room temperature and contain large amounts of nitrogen and carbon sources, they may easily become contaminated by a variety of microorganisms, such as bacteria, filamentous fungi, and yeasts. The rapid and accurate identification of these microorganisms is essential to prevent further expansion of such contamination and the damage it causes. However, more than 30 days and laboratory skills are usually necessary in order to identify microorganisms in cosmetic materials. These time and labor constraints may allow further damage of the cosmetic products and thereby harm the consumer.(omitted)

• Journal of the Korea Institute of Information Security & Cryptology
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• 제24권4호
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• pp.721-737
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• 2014

The Resident Registration Number(RRN) system has been effectively acted as a national identification system since it was enforced. On the other hand, there are some problems such as leakages of personal informations including RRNs on a large scale and each RRN makes a pair with each person in all areas of the society. Nevertheless leakages of them might cause a big damage, there is no radical countermeasure for they are never changed in actual fact. In Republic of Korea, a RRN acts as a primary key of a database, so it has to be protected by severing the connectivity between leaked RRNs and the other personal data. In this paper, the Unconnected Random Personal Identification Number system is proposed for preventing damage of data spills by removing a dependency which the RRN has. Furthermore, this paper suggests the solutions against some potential issues in the system.

• Smart Structures and Systems
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• 제16권1호
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• pp.163-181
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• 2015

This research investigates the structural health monitoring of nonlinear structures after a major seismic event. It considers the identification of flag-shaped or pinched hysteresis behavior in response to structures as a more general case of a normal hysteresis curve without pinching. The method is based on the overall least squares methods and the log likelihood ratio test. In particular, the structural response is divided into different loading and unloading sub-half cycles. The overall least squares analysis is first implemented to obtain the minimum residual mean square estimates of structural parameters for each sub-half cycle with the number of segments assumed. The log likelihood ratio test is used to assess the likelihood of these nonlinear segments being true representations in the presence of noise and model error. The resulting regression coefficients for identified segmented regression models are finally used to obtain stiffness, yielding deformation and energy dissipation parameters. The performance of the method is illustrated using a single degree of freedom system and a suite of 20 earthquake records. RMS noise of 5%, 10%, 15% and 20% is added to the response data to assess the robustness of the identification routine. The proposed method is computationally efficient and accurate in identifying the damage parameters within 10% average of the known values even with 20% added noise. The method requires no user input and could thus be automated and performed in real-time for each sub-half cycle, with results available effectively immediately after an event as well as during an event, if required.

• Smart Structures and Systems
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• 제32권1호
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• pp.9-21
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• 2023

The parameters of civil engineering structures have time-variant characteristics during their service. When extremely large external excitations, such as earthquake excitation to buildings or overweight vehicles to bridges, apply to structures, sudden or gradual damage may be caused. It is crucially necessary to detect the occurrence time and severity of the damage. The unscented Kalman filter (UKF), as one efficient estimator, is usually used to conduct the recursive identification of parameters. However, the conventional UKF algorithm has a weak tracking ability for time-variant structural parameters. To improve the identification ability of time-variant parameters, an adaptive UKF with forgetting factor (AUKF-FF) algorithm, in which the state covariance, innovation covariance and cross covariance are updated simultaneously with the help of the forgetting factor, is proposed. To verify the effectiveness of the method, this paper conducted two case studies as follows: the identification of time-variant parameters of a simply supported bridge when the vehicle passing, and the model updating of a six-story concrete frame structure with field test during the Yangbi earthquake excitation in Yunnan Province, China. The comparison results of the numerical studies show that the proposed method is superior to the conventional UKF algorithm for the time-variant parameter identification in convergence speed, accuracy and adaptability to the sampling frequency. The field test studies demonstrate that the proposed method can provide suggestions for solving practical problems.