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RISS 인기검색어
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- 저자 : Yongjian Liu (검색결과 6 건)
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Fault diagnosis of rolling bearing using a refined composite multiscale weighted permutation entropy
Yongjian Li,Qiuming Gao,Peng Li,Jihua Liu,Yingmou Zhu 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.5
The health status information of rolling bearings is often contained in vibration signals, but it is difficult to detect bearing defects directly through vibration signals. To effectively extract the key feature information hidden in the original signal, this paper proposes the refined composite multiscale weighted permutation entropy (RCMWPE) method to efficiently characterize the operating state of the bearing. The proposed method focuses on two aspects:the improved version reduces the dependence of entropy on the length of the original time series, and the error caused by considering the amplitude information is suppressed. The performance of the proposed method is evaluated by synthetic signals and real bearing data, and compared with other traditional methods. By analyzing bearing signals of different fault types and different degrees of damage, it is verified that the proposed method can obtain more stable and reliable results and achieve higher fault diagnosis accuracy.
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Refined composite multiscale fuzzy entropy: Localized defect detection of rolling element bearing
Yongjian Li,Bingrong Miao,Weihua Zhang,Peng Chen,Jihua Liu,Xiaoliang Jiang 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.1
We proposed an appealing method based on refined composite multiscale fuzzy entropy (RCMFE), infinite feature selection (Inf-FS) algorithm, and support vector machine (SVM) for implementing localized defect detection to keep the downtime and extended damage caused by incipient failure of bearing at a minimum. As a useful approach, multiscale fuzzy entropy (MFE) was utilized to measure the complexity and dynamic changes of signals. However, an inaccurate entropy value would be yielded with the increase of scale factor. Here, as an improvement version of MFE, the RCMFE was proposed to address the shortcomings in the case of short time series. For this novel method, we conducted a full investigation of the effects and robustness by comparing the proposed method with two other entropybased approaches using synthetic signals and real data. Results indicate that the proposed algorithm outperforms the other approaches in terms of reliability and stability. The RCMFE values of bearing signals from one healthy condition and seven fault states are calculated as diagnostic information. Moreover, an intelligent fault identification method was constructed by combining the Inf-FS algorithm and SVM classifier. Experimental results show the usefulness of the proposed strategy.
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A Fast Adjustment Method of Magnetically Controlled Reactor with Multi-taps
Mengsen Liu,Yongjian Li,Hezhe Gao,Xuehai Gong Korean Magnetics Society 2018 Journal of Magnetics Vol.23 No.4
Magnetically controlled reactor (MCR) can compensate the capacitive reactive power generated by transmission line and enhance the stability of power supply, which is widely used in ultrahigh-voltage (UHV) power systems. In this paper, a novel structure for MCR with multi-taps is proposed. The MCR with multi-taps can switch its taps based on operation condition. The higher tap ratio is used to adjust the reactive power, and the lower tap ratio is fit for the stable grid. A switching algorithm is designed to make it work harmoniously and flexibly. For the adjustment of reactive power, this novel structure can perform better in regulated time without using higher tap ratios in practical operation, compared with the traditional structures.
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Analysis and Research on Space Vector Over-modulation Strategy of Indirect Matrix Converter
Wenshen Wang,Shanhu Li,Xu Liu,Yongjian Li,Yiping Liu 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5
In this paper, based on the characteristics of six space vector modulation methods, a variety of Space Vector Over-modulation strategies with voltage transfer ratio of 1.05 for indirect matrix converter is proposed. Firstly, the six space vector modulation methods are combined by adjusting the phase of the input current vector and the amplitude and phase of the output voltage vector. Secondly, the limit input current and output voltage vector characteristics, the limit fundamental voltage amplitude and the main low-frequency harmonic components of the input and output under the six modulation methods are analyzed in detail. According to the limit characteristics of the six modulation methods and the principle of limit vector superposition, multiple space vector over-modulation strategies based on single-mode, doublemode and multi-mode are proposed. Finally, the characteristics of the six space vector modulation methods are verified by experiments.
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Qianying Zhao,Jiaxin Yang,Dongyan Cao,Jiangna Han,Kaifeng Xu,Yongjian Liu,Keng Shen 대한부인종양학회 2016 Journal of Gynecologic Oncology Vol.27 No.3
Objective: To explore the appropriate treatment of malignant germ cell tumor (MGCT) in thefemale genital system, and to analyze the factors influencing both therapeutic response andsurvival outcome. Methods: A cohort of 230-Chinese women diagnosed with MGCT of the genital systemwas retrospectively reviewed and prospectively followed. The demographic and pathologicalfeatures, extent of disease and surgery, treatment efficiency, recurrence and survival wereanalyzed. Results: MGCTs from different genital origins shared a similar therapeutic strategy andresponse, except that all eight vaginal cases were infantile yolk sac tumors. The patients’ curerate following the initial treatment, 5-year overall survival and disease-free survival (DFS)were 85.02%, 95.00%, and 86.00%, respectively. Although more extensive excision couldenhance the remission rate; it did not improve the patients’ survival. Instead, the level of themedical institution, extent of surgery and disease were independent prognostic factors forrelapse (p<0.05). Approximately 20% of patients had recurrent or refractory disease, morethan half of whom were in remission following secondary cytoreductive surgery with salvagechemotherapy. Conclusion: Fertility-sparing surgery with or without standardized PEB/PVB (cisplatin,etoposide/vincristine, and bleomycin) chemotherapy is applicable for female MGCTsof different origins. Comprehensive staging is not required; nor is excessive debulkingsuggested. Appropriate cytoreduction by surgery and antineoplastic medicine at anexperienced medical institution can bring about an excellent prognosis for these patients.
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