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- 저자 : ( Mengmeng Zheng ) (검색결과 5 건)
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Mengmeng Wu,Wenxiang Zhao,Jinghua Ji,Junqiang Zheng,Jianhua Luo 한국자기학회 2018 Journal of Magnetics Vol.23 No.2
Fractional-slot concentrated windings (FSCWs) are characterized with many advantages. However, their magnetic fields have rich space harmonics. These harmonics, especially tooth harmonics, have negative effect on machine performances. This paper proposes a new method to reduce the tooth harmonics in FSCW permanent-magnet (PM) machine, in which the magnetic distribution in air-gap will be affected by winding span radian. Also, a new stator structure is designed on the method. By using the new stator design, each order tooth harmonic can be reduced significantly and the working harmonic can also be increased slightly. Simultaneously, the unbalanced radial magnetic force can be significantly weakened. The basic principle of tooth harmonic reduction method can be analyzed by using the stator structure of the FSCW machine with single layer windings. Then, a three phase 18-slot/16-pole FSCW machine with double layer windings is newly designed, which can effectively weaken the tooth harmonic components of FSCW machines. It is shown that, under the fixed electrical and geometrical constrains, the designed FSCW machine has better performances, such as loss, vibration and noise, than the conventional ones.
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Investigation on characteristics of pressure fluctuation in a centrifugal pump with clearance flow
Lulu Zheng,Xiaoping Chen,Wei Zhang,Zu-chao Zhu,Jinglei Qu,Mengmeng Wang,Xiaojie Ma,Xueli Cheng 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.9
Clearance flow has great impact on pressure fluctuation of centrifugal pumps. Numerical calculations are performed to study the pressure fluctuation characteristics of centrifugal pump with wear ring clearance, especially in the regions of interaction between main flow and clearance flow (IMC) and clearance. The accuracy of numerical calculations is illustrated by comparing the experiments of performance and pressure fluctuation. Results show that, in clearance region the pressure fluctuation is still governed by blade passing frequency (f BPF ). Its amplitude of dominate frequency of pressure fluctuation becomes larger as the probe approaches the impeller exit. In IMC region, the pressure fluctuation at impeller outlet is dominated by f BPF . However, the dominate frequency at the entrance of impeller is less than f BPF . In addition, as the flow rate increased, the amplitude of dominate frequency of pressure fluctuation increases at impeller entrance, whereas an inverse trend is observed at wear ring clearance region.
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Qiuliang Cai,Lei Tong,Jingjing Zhang,Jie Zheng,Mengmeng He,Jiamei Lin,Xiaoqiu Chen,Hang Xiao 대한환경공학회 2019 Environmental Engineering Research Vol.24 No.4
Air pollution has attracted ever-increasing attention because of its substantial influence on air quality and human health. To better understand the characteristics of long-range transported pollution, the single particle chemical composition and size were investigated by the single particle aerosol mass spectrometry in Fuzhou, China from 17th to 22nd January, 2016. The results showed that the haze was mainly caused by the transport of cold air mass under higher wind speed (10 m·s<SUP>-1</SUP>) from the Yangtze River Delta region to Fuzhou. The number concentration elevated from 1,000 to 4,500 #·h<SUP>-1</SUP>, and the composition of mobile source and secondary aerosol increased from 24.3% to 30.9% and from 16.0% to 22.5%, respectively. Then, the haze was eliminated by the clean air mass from the sea as indicated by a sharp decrease of particle number concentration from 4,500 to 1,000 #·h<SUP>-1</SUP>. The composition of secondary aerosol and mobile sources decreased from 29.3% to 23.5% and from 30.9% to 23.1%, respectively. The particles with the size ranging from 0.5 to 1.5 ㎛ were mainly in the accumulation mode. The stationary source, mobile source, and secondary aerosol contributed to over 70% of the potential sources. These results will help to understand the physical and chemical characteristics of long- range transported pollutants.
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( Qiang Zhang ),( Yujuan Li ),( Fangxue Xu ),( Mengmeng Zheng ),( Xiaozhi Xi ),( Xuelan Zhang ),( Chunchao Han ) 한국균학회 2017 Mycobiology Vol.45 No.2
Different endophytes isolated from the seeds of Sophora flavescens were tested for their ability to produce matrine production. Response surface methodology (RSM) was applied to optimize the medium components for the endophytic fungus. Results indicated that endophyte Aspergillus terreus had the ability to produce matrine. The single factor tests demonstrated that potato starch was the best carbon source and the combination of peptone and NH<sub>4</sub>NO<sub>3</sub> was the optimal nitrogen source for A. terreus. The model of RSM predicted to gain the maximal matrine production at 20.67 μg/L, when the potato starch was 160.68 g/L, peptone was 24.96 g/L and NH<sub>4</sub>NO<sub>3</sub> was 2.11 g/L. When cultured in the optimal medium, the matrine yield was an average of 20.63 ± 0.11 μg/L, which was consistent with the model prediction. This study offered an alternative source for the matrine production by endophytic fungus fermentation and may have far-reaching prospect and value.
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Spatial Regionalization on Surface Ozone in the Yangtze River Delta of China
Lei Tong,Hang Xiao,Hui Yi,Yu Liu,Jie Zheng,Cenyan Huang,Mengmeng He 한국기상학회 2022 Asia-Pacific Journal of Atmospheric Sciences Vol.58 No.2
In order to better understand the tempo-spatial characteristics of surface ozone (O3) on the regional scale of Yangtze River Delta (YRD), China, cluster analysis was applied to surface O3 monitored from 2016 to 2017 at 110 state-controlled stations. Eight spatial regions with distinct patterns of O3 variations were identified. The exceedances over the Grade I (100 μg/m3) andGrade II (160μg/m3) National Ambient Air Quality Standard of maximum daily average 8 h O3 (MDA8 O3) varied within 99~192 and 1~41 days, respectively, for different subregions. The central and east YRD were the most polluted subregions with higher incidence of O3 episodes, while the southwest and southeast YRD were relatively clean. The spatial disparity of O3 over YRD was strongly affected by local emissions, with larger precursor emissions contributing to higher frequencies of O3 pollution and larger amplitudes of temporal variations. The regionalO3 pollution mainly occurred in spring, with higher peaks ofMDA8O3 being observed duringApril ~May for most subregions. While for east YRD, O3 pollution was most serious in summer, when its monthly MDA8 O3 reached the highest value (141.0 μg/m3). During thewhole study period, the spatial differences of weekly/monthly amplitudes ofMDA8O3 were similar to those of NO2 among the eight subregions, indicating the significant influence of NO2 on O3 over YRD on the yearly timescale. This influence was especially evident in warm seasons for the coastal subregions, where O3 production was controlled by NOx. While for the west inland subregion, O3was less affected by NO2 variation, indicating a NOx-saturated characteristic of O3 formation.
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