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Nonlinear damage detection using linear ARMA models with classification algorithms
Liujie Chen,Ling Yu,Jiyang Fu,Ching-Tai Ng 국제구조공학회 2020 Smart Structures and Systems, An International Jou Vol.26 No.1
Majority of the damage in engineering structures is nonlinear. Damage sensitive features (DSFs) extracted by traditional methods from linear time series models cannot effectively handle nonlinearity induced by structural damage. A new DSF is proposed based on vector space cosine similarity (VSCS), which combines K-means cluster analysis and Bayesian discrimination to detect nonlinear structural damage. A reference autoregressive moving average (ARMA) model is built based on measured acceleration data. This study first considers an existing DSF, residual standard deviation (RSD). The DSF is further advanced using the VSCS, and then the advanced VSCS is classified using K-means cluster analysis and Bayes discriminant analysis, respectively. The performance of the proposed approach is then verified using experimental data from a three-story shear building structure, and compared with the results of existing RSD. It is demonstrated that combining the linear ARMA model and the advanced VSCS, with cluster analysis and Bayes discriminant analysis, respectively, is an effective approach for detection of nonlinear damage. This approach improves the reliability and accuracy of the nonlinear damage detection using the linear model and significantly reduces the computational cost. The results indicate that the proposed approach is potential to be a promising damage detection technique.
Scavenging Effects of Tea Catechins on Superoxide and Hydroxy Radical
Park Jaeil,Liuji Chen,Xianqiang Yang,Shengrong Shen,Yuefei Wang,Ryu Beung Ho 한국생명과학회 2002 Journal of Life Science Vol.12 No.2
Tea catechins, the most important compounds in tea polyphenols, can efficiently scavenge superoxide anion free-radical (O₂-·), hydroxyl radical. (·OH) The mechanism of scavenging active oxygen free radicals was investigated by ESR spin trapping technique and Chemiluminescence. Results showed that various tea catechins constitute an antioxidant cycle in accordance with the decreasing order of the first reductive potential, and produce the effect of cooperative strength each other. Esterificated catechins could scavenge active oxygen free radicals more effectively than the non-esterificated ones. When ·OH and O₂-·- were scavenged by (-)-epigallocatechin gallate [(-)- EGCG], the stoichiometric factors were 6, and the rate constants of scavenging reaction reached 7.71x10(6) and 3.52x10(11) L mmol-¹ S-¹, respectively. In the mean time, tea catechins could scavenge superoxide anion fiee radical (O₂-·) and hydroxyl radical (·OH) in a dose dependent manner. But at higher concentration or pH value, tea catechins can induce the prooxidant.
Stress evaluation of tubular structures using torsional guided wave mixing
Ching-Tai Ng,Carman Yeung,Tingyuan Yin,Liujie Chen 국제구조공학회 2022 Smart Structures and Systems, An International Jou Vol.30 No.6
This study aims at numerically and experimentally investigating torsional guided wave mixing with weak material nonlinearity under acoustoelastic effect in tubular structures. The acoustoelastic effect on single central frequency guided wave propagation in structures has been well-established. However, the acoustoelastic on guided wave mixing has not been fully explored. This study employs a three-dimensional (3D) finite element (FE) model to simulate the effect of stress on guided wave mixing in tubular structures. The nonlinear strain energy function and theory of incremental deformation are implemented in the 3D FE model to simulate the guided wave mixing with weak material nonlinearity under acoustoelastic effect. Experiments are carried out to measure the nonlinear features, such as combinational harmonics and second harmonics in related to different levels of applied stresses. The experimental results are compared with the 3D FE simulation. The results show that the generation combinational harmonic at sum frequency provides valuable stress information for tubular structures, and also useful for damage diagnosis. The findings of this study provide physical insights into the effect of applied stresses on the combinational harmonic generation due to wave mixing. The results are important for applying the guided wave mixing for in-situ monitoring of structures, which are subjected to different levels of loadings under operational condition.