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- 저자 : Jianzhong Hu (검색결과 4 건)
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Hu, Xing,Zhang, Jianzhong,Deng, Fujin,Chen, Gui,Chen, Qiang,Din, Zaki ud The Korean Institute of Power Electronics 2020 JOURNAL OF POWER ELECTRONICS Vol.20 No.5
Circulating current exists among phases or between the DC link and the three phases in a modular multilevel converter (MMC). Suppression control of the alternating components in circulating current is a critical issue for the stable and efficient operation of an MMC. Due to the redundancy and symmetry of MMCs, some of the self-redundant states of MMCs can be used to suppress the alternating components in circulating current without affecting the output performance of the converter. In this paper, a theoretical derivation of the boundary of redundant states is given. Then a suppression strategy for circulating current is proposed based on prediction control and the boundary of redundant states. The selection range of the redundant states is narrowed in this case, which reduces the computation burden when compared to the original method and ensures excellent performance in the suppression of circulating current. Simulations and experiments are carried out to verify the effectiveness of the proposed strategy.
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Jian Chen,Jianzhong Li,Qingqing Dong,Jiutian Xue,Ge Hu 한국항공우주학회 2023 International Journal of Aeronautical and Space Sc Vol.24 No.3
To meet the qualification of temperature rise and reduce emissions, a high temperature rise combustor which is based on RQL (rich-burn/quick-quench/lean-burn) under different primary holes structure had been used to investigate the flow characteristic and combustion performance. The flow field was measured by PIV (particle imaging velocimetry) under different primary holes structure at normal temperature and pressure, and the combustion and emissions performances were simulated under the same conditions in this paper. The results show that the flow field, the airflow mixing effectiveness in the quench zone airflow, the distribution of temperature, the emission and the combustion efficiency change obviously with the primary holes structure. The maximum central recirculation zone height with staggered structure (Case-II) is about 23% higher than that with symmetrical structure. The central recirculation zone length is reduced by 36% and the velocity gradient in the rich zone is increased when the primary holes structure is symmetrical with three holes (Case-I). The insufficient penetration of primary jets has a negative impact to the efficient mixing of the quench zone airflow. Therefore, the symmetrical structure of primary holes is used, increasing the number of holes while reducing the area of single-hole will have a negative impact on the efficient mixing of the quench zone airflow. In addition, when the primary holes structure is symmetrical with four holes (Case-III), the combustion efficiency was reduced by 0.07% and 0.03%, and the maximum emission index of NO was increased by 14% and 19%, respectively, compared with the Case-I and Case-II. On the contrary, the maximum emission index of CO and soot were reduced in rich zone.
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Tanishima Shinji,Weishi Li,Jianzhong Hu,Jie Zhao,Huilin Yang,Nagashima Hideki 대한척추외과학회 2022 Asian Spine Journal Vol.16 No.3
Study Design: This is a multicenter, prospective study.Purpose: This study aimed to evaluate the reproducibility of the walking test for patients with lumbar spinal stenosis (LSS).Overview of Literature: Walking test is one of the useful procedures to investigate cauda equina syndrome with lumbar spinal stenosis. One the other hands, there were few studies to investigate the reproducibility of this test.Methods: In this study, we prospectively examined 70 LSS patients with intermittent claudication symptoms at a multicenter outpatient clinic. A walking test was administered at baseline and week 4 to assess patients’ walking distance and lower limb pain and numbness. Immediately after the walking test, patients were asked to use the Visual Analog Scale (VAS) to rate their pain and numbness in the front, back, outside, inside, and hip of the lower legs. The reproducibility of the walking test was evaluated using Cohen’s κ analysis and intraclass correlation coefficients (ICCs). Meanwhile, the Swiss Spinal Stenosis (SSS) Questionnaire was used to evaluate the severity of the stenosis.Results: The walking distance ICC at baseline and at week 4 remained unchanged at 0.7, with acceptable interobserver reliabilities for lower limb pain and numbness in both legs. The average VAS score for lower leg pain was 23.2±25.2 mm at baseline and 27.4±28.8 mm at week 4, while the corresponding average VAS score for numbness was 23.4±26.7 mm at baseline and 24.8±25.2 mm at week 4. The ICC score was 0.7 for leg pain and 0.7 for numbness. The mean SSS was 30.2±5.5 at baseline and 29.2±5.2 at week 4, and there was no significant difference in the severity.Conclusions: The walking test for LSS has acceptable reproducibility.
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Zhongyuan Su,Yaoming Zhang,Minping Jia,Feiyun Xu,Jianzhong Hu 대한기계학회 2011 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.25 No.2
An improved singular value decomposition method of gear fault identification based on Hilbert-Huang transform was proposed to overcome the problem of reconstructing a feature matrix of singular value decomposition. The method includes three steps. First, the instantaneous frequency and amplitude matrices were acquired by Hilbert-Huang transform from faulted gear signals. Second, after the matrices were decomposed by singular value decomposition, the defined distances of singular value vectors and the optimal threshold of the distance for classification were calculated. Third, the fault characteristics of a gearbox were identified and classified by the threshold of the distances. The result demonstrates that the proposed method effectively identifies the gear fault and can realize an automatic gear fault diagnosis.
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