• 제목/요약/키워드: Weighted damage

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Structural damage identification based on transmissibility assurance criterion and weighted Schatten-p regularization

  • Zhong, Xian;Yu, Ling
    • Structural Engineering and Mechanics
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    • 제82권6호
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    • pp.771-783
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    • 2022
  • Structural damage identification (SDI) methods have been proposed to monitor the safety of structures. However, the traditional SDI methods using modal parameters, such as natural frequencies and mode shapes, are not sensitive enough to structural damage. To tackle this problem, this paper proposes a new SDI method based on transmissibility assurance criterion (TAC) and weighted Schatten-p norm regularization. Firstly, the transmissibility function (TF) has been proved a useful damage index, which can effectively detect structural damage under unknown excitations. Inspired by the modal assurance criterion (MAC), TF and MAC are combined to construct a new damage index, so called as TAC, which is introduced into the objective function together with modal parameters. In addition, the weighted Schatten-p norm regularization method is adopted to improve the ill-posedness of the SDI inverse problem. To evaluate the effectiveness of the proposed method, some numerical simulations and experimental studies in laboratory are carried out. The results show that the proposed method has a high SDI accuracy, especially for weak damages of structures, it can precisely achieve damage locations and quantifications with a good robustness.

포름알데히드에 의한 금속시편의 손상 특성 (Damage Characteristics of Metal Specimens by Formaldehyde)

  • 김명남;임보아;이선명
    • 보존과학회지
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    • 제31권3호
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    • pp.287-298
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    • 2015
  • 포름알데히드의 금속 손상은 보편적으로 알려진 것에 비해 손상농도와 손상정도의 정량화는 명확하지 않다. 본 연구는 금속시편(은, 구리, 철, 납, 황동)을 대상으로 가스부식시험기를 이용하여 포름알데히드 0.5, 1, 10, 100, 500ppm 농도에서의 손상, 손상농도에서 온 습도 조건에 따른 손상 가중, 손상농도에서 열화금속시편의 손상을 광학적, 화학적, 물리적 측정방법으로 평가하였다. 이 결과, 포름알데히드 농도 500ppm/day에서 납시편의 광학적, 화학적, 물리적 손상과 전체금속시편의 광학적 손상이 확인되었다. 기본조건($25^{\circ}C$, 50%), 고온조건($30^{\circ}C$, 50%)에서는 일부시편의 광학적 손상이 가중되었고, 고온 고습조건($30^{\circ}C$, 80%), 고습조건($25^{\circ}C$, 80%)에서는 납시편의 화학적 손상이 각각 2.8배, 1.3배 가중되었다. 열화금속시편의 포름산이온 농도 결과, 철시편, 황동시편의 부식 생성물은 포름알데히드 가스와 활발히 반응하는 것으로 나타났으며, 납시편의 표면 산화막은 포름알데히드 가스와의 반응을 감소시키거나 차단하는 것으로 확인되었다.

AHP 기법을 활용한 위험물 수송의 최적경로산정 (Applying the Analytic Hierarchy Process to Select the Optimal Route for Hazardous Material Transport)

  • 손유진;배상훈
    • 한국지리정보학회지
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    • 제13권4호
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    • pp.67-77
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    • 2010
  • 석유화학산업의 성장으로 석유화학물의 수송량이 증가하였다. 이는 위험물 사고건수의 증가를 초래하였다. 위험물 사고의 70% 이상이 수송 중 발생하며, 경로선택과정에서 수송경로의 선택에 따라 피해규모를 줄일 수 있지만 위험물 수송경로관련 연구는 미비한 실정이다. 본 연구의 목적은 전문가의 의견을 반영한 적정 위험물 수송경로의 선정을 통해 사고 발생시 피해규모를 최소화 하는데 있다. 이에 계층분석법(AHP)을 통하여 도출된 가중치를 위험도에 적용하여 최소 위험도 경로를 도출하였다. 그 결과 가중치 적용 경로의 경우 최단경로에 비해 인구위험도는 33.4%인 0.608, 환경위험도는 21.8% 감소한 0.168, 사회위험도는 1521.7%인 0.35가 감소하였다. 가중치 미적용 노선과 가중치 적용 노선을 비교하면, 가중치 적용 노선의 인구위험도는 2.6% 감소하였다. 본 연구를 통해 전문가의 의견을 반영한 가중치의 적용으로 위험도를 감소시키면서 인구피해규모를 최소화 하는 최적경로를 도출할 수 있었다.

Delamination identification of laminated composite plates using measured mode shapes

  • Xu, Yongfeng;Chen, Da-Ming;Zhu, Weidong;Li, Guoyi;Chattopadhyay, Aditi
    • Smart Structures and Systems
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    • 제23권2호
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    • pp.195-205
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    • 2019
  • An accurate non-model-based method for delamination identification of laminated composite plates is proposed in this work. A weighted mode shape damage index is formulated using squared weighted difference between a measured mode shape of a composite plate with delamination and one from a polynomial that fits the measured mode shape of the composite plate with a proper order. Weighted mode shape damage indices associated with at least two measured mode shapes of the same mode are synthesized to formulate a synthetic mode shape damage index to exclude some false positive identification results due to measurement noise and error. An auxiliary mode shape damage index is proposed to further assist delamination identification, by which some false negative identification results can be excluded and edges of a delamination area can be accurately and completely identified. Both numerical and experimental examples are presented to investigate effectiveness of the proposed method, and it is shown that edges of a delamination area in composite plates can be accurately and completely identified when measured mode shapes are contaminated by measurement noise and error. In the experimental example, identification results of a composite plate with delamination from the proposed method are validated by its C-scan image.

Electron Microscopy and MR Imaging Findings in Embolic Effects

  • Park Byung-Rae;Koo Bong-Oh
    • 대한의생명과학회지
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    • 제10권4호
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    • pp.367-373
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    • 2004
  • Evaluated the hyperacute embolic effects of triolein and oleic acid in cat brains by using MR image and electron microscopy. In fat embolism, free fatty acid is more toxic than neutral fat in terms of tissue damage. T2-Weighted imaging, diffusion-weighted imaging, and contrast-enhanced T1-weighted imaging were performed in cat brains after the injection of triolein (group 1, n=8) or oleic acid (group 2, n=10) into the internal carotid artery. MR image were quantitatively assessed by comparing the lesions with their counterparts on T2-weighted images, apparent diffusion coefficient (ADC) maps, and contrast-enhanced T1-weighted images. Electron microscopic findings in group 1 were compared with those in group 2. Qualitatively, MR images revealed two types of lesions. Type 1 lesions were hyperintense on diffusion-weighted images and hypointense of ADC maps. Type 2 lesions were isointense or mildly hyperintense on diffusion-weighted images and isointense on ADC maps. Quantitatively, the signal intensity rations of type 1 lesions in group 2 specimens were significantly higher on T2-weighted images (P=.013)/(P=.027) and lower on ADC maps compared with those of group 1. Electron microscopy of type 1 lesions in both groups revealed more prominent widening of the perivascular space and swelling of the neural cells in groups 1. MR and electron microscopic data on cerebral fat embolism induced by either triolein or oleic acid revealed characteristics suggestive of both vasogenic and cytotoxic edema in the hyperacute stage. Tissue damage appeared more severe in the oleic acid group than in the triolein group.

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Ensemble-based deep learning for autonomous bridge component and damage segmentation leveraging Nested Reg-UNet

  • Abhishek Subedi;Wen Tang;Tarutal Ghosh Mondal;Rih-Teng Wu;Mohammad R. Jahanshahi
    • Smart Structures and Systems
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    • 제31권4호
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    • pp.335-349
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    • 2023
  • Bridges constantly undergo deterioration and damage, the most common ones being concrete damage and exposed rebar. Periodic inspection of bridges to identify damages can aid in their quick remediation. Likewise, identifying components can provide context for damage assessment and help gauge a bridge's state of interaction with its surroundings. Current inspection techniques rely on manual site visits, which can be time-consuming and costly. More recently, robotic inspection assisted by autonomous data analytics based on Computer Vision (CV) and Artificial Intelligence (AI) has been viewed as a suitable alternative to manual inspection because of its efficiency and accuracy. To aid research in this avenue, this study performs a comparative assessment of different architectures, loss functions, and ensembling strategies for the autonomous segmentation of bridge components and damages. The experiments lead to several interesting discoveries. Nested Reg-UNet architecture is found to outperform five other state-of-the-art architectures in both damage and component segmentation tasks. The architecture is built by combining a Nested UNet style dense configuration with a pretrained RegNet encoder. In terms of the mean Intersection over Union (mIoU) metric, the Nested Reg-UNet architecture provides an improvement of 2.86% on the damage segmentation task and 1.66% on the component segmentation task compared to the state-of-the-art UNet architecture. Furthermore, it is demonstrated that incorporating the Lovasz-Softmax loss function to counter class imbalance can boost performance by 3.44% in the component segmentation task over the most employed alternative, weighted Cross Entropy (wCE). Finally, weighted softmax ensembling is found to be quite effective when used synchronously with the Nested Reg-UNet architecture by providing mIoU improvement of 0.74% in the component segmentation task and 1.14% in the damage segmentation task over a single-architecture baseline. Overall, the best mIoU of 92.50% for the component segmentation task and 84.19% for the damage segmentation task validate the feasibility of these techniques for autonomous bridge component and damage segmentation using RGB images.

A new damage index for seismic fragility analysis of reinforced concrete columns

  • Kang, Jun Won;Lee, Jeeho
    • Structural Engineering and Mechanics
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    • 제60권5호
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    • pp.875-890
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    • 2016
  • A new structural damage index for seismic fragility analysis of reinforced concrete columns is developed based on a local tensile damage variable of the Lee and Fenves plastic-damage model. The proposed damage index is formulated from the nonlinear regression of experimental column test data. In contrast to the response-based damage index, the proposed damage index is well-defined in the form of a single monotonically-increasing function of the volume weighted average of local damage distribution, and provides the necessary computability and objectivity. It is shown that the present damage index can be appropriately zoned to be used in seismic fragility analysis. An application example in the computational seismic fragility evaluation of reinforced concrete columns validates the effectiveness of the proposed damage index.

Enhanced Robust Cooperative Spectrum Sensing in Cognitive Radio

  • Zhu, Feng;Seo, Seung-Woo
    • Journal of Communications and Networks
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    • 제11권2호
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    • pp.122-133
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    • 2009
  • As wireless spectrum resources become more scarce while some portions of frequency bands suffer from low utilization, the design of cognitive radio (CR) has recently been urged, which allows opportunistic usage of licensed bands for secondary users without interference with primary users. Spectrum sensing is fundamental for a secondary user to find a specific available spectrum hole. Cooperative spectrum sensing is more accurate and more widely used since it obtains helpful reports from nodes in different locations. However, if some nodes are compromised and report false sensing data to the fusion center on purpose, the accuracy of decisions made by the fusion center can be heavily impaired. Weighted sequential probability ratio test (WSPRT), based on a credit evaluation system to restrict damage caused by malicious nodes, was proposed to address such a spectrum sensing data falsification (SSDF) attack at the price of introducing four times more sampling numbers. In this paper, we propose two new schemes, named enhanced weighted sequential probability ratio test (EWSPRT) and enhanced weighted sequential zero/one test (EWSZOT), which are robust against SSDF attack. By incorporating a new weight module and a new test module, both schemes have much less sampling numbers than WSPRT. Simulation results show that when holding comparable error rates, the numbers of EWSPRT and EWSZOT are 40% and 75% lower than WSPRT, respectively. We also provide theoretical analysis models to support the performance improvement estimates of the new schemes.

기 개발된 굴착식 터널의 지진취약도 모델 적용성 평가 (Evaluation of pre-developed seismic fragility models of bored tunnels)

  • 양승훈;곽동엽
    • 한국터널지하공간학회 논문집
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    • 제25권3호
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    • pp.187-200
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    • 2023
  • 본 연구에서는 주변 환경에 따른 굴착식 터널의 지진취약도 변화에 대한 분석을 진행하고 대표 지진취약도 모델을 제시하였다. 기 개발된 굴착식 터널의 지진취약도 모델들에 대한 분석을 진행한 후 각 모델들에 가중치를 부여하여 주변 환경에 맞게 새로 가중조합한 모델을 개발하였다. 주변 환경은 굴착식 터널 주변의 지반조건과 매설 깊이를 고려하였다. 지진취약도 곡선의 피해 발생 확률은 최대지반가속도(PGA)를 매개변수로 하여 결정된다. PGA가 0.3 g일 때 매설 깊이가 50 m이하의 조건에서는 경미한 손상을 초과하는 피해 확률이 20%, 매설 깊이가 50 m 이상 100 m 이하의 조건에서는 피해 확률이 10%, 매설 깊이 100 m 이상의 조건에서는 피해 확률이 3% 이하로 매설 깊이에 따라 피해 확률이 점차 낮아지는 것을 확인하였다. 또한 주변 지반이 토양으로 되어있을 때보다 암반으로 되어있을 때 동일한 지표의 PGA에 대해 같은 매설 깊이에서 피해 확률이 크게 나타나며, 매설 깊이가 깊어질수록 피해 확률이 작아진다. 이 연구는 향후 터널의 종합적 지진취약도 함수 개발에 유용하게 사용될 것으로 기대된다.

High Signal Intensities on T1-Weighted MRI as a Biomarker of Manganese

  • Kim, Yang-Ho
    • 한국환경보건학회:학술대회논문집
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    • 한국환경보건학회 2005년도 국제학술대회
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    • pp.105-139
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    • 2005
  • Increased signal in T1-weighted images was observed in the experimental manganese (Mn) poisoning of the non-human primate and a patient with Mn neurointoxication. However, our study showed that the increased signals in magnetic resonance images (MRI) were highly prevalent (41.6%) in Mn-exposed workers. Blood Mn concentration correlated with pallidal index. These changes in MRI tend to disappear following the withdrawal from the source of Mn accumulation, despite permanent neurological damage. Thus increased signal intensities on a T1-weighted image reflect exposure to Mn, but not necessarily manganism. Our study also showed that the concentration of Mn required to produce increased signal intensities on MRI is much lower than the threshold necessary to result in overt clinical signs of manganism. Increased signal intensities in the globus pallidus were determined by manganese accumulation in the animal experiment. Reanalysis of the previous data with the structural equation model revealed that pallidal index (Pl) on MRI reflects target organ dose of occupational Mn exposure

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