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- 저자 : Dongjiang (검색결과 4 건)
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Dongjiang Han,Changliang Tang,Long Hao,Jinfu Yang 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.11
Vibrations, particularly low-frequency vibrations caused by self-excited gas films, significantly affect the safety and economy of turbomachinery, which becomes dangerous at high rotational speeds. This experimental study focuses on the dynamic characteristics of a Permanent magnet (PM) disk-type motor rotor supported by gas aerostatic bearings. Nonlinear dynamic behavior, including double low frequency and gas film half whirling, was analyzed in the experiments. The dynamic features of double low frequency and gas whirling are described in the paper. The most important finding is that the sum of the whirling ratios of low frequencies 1 and 2 is always 1.00. The occurrence mechanism requires further study. The effects of bearing supply gas pressure on the dynamic response characteristics of the multi-disk PM rotor are implemented to improve rotor stability.
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Zhenxing Yang,Dongjiang Pan,Jianjun Zhou,Jian Chen,Zhenchuan Sun,Haining Liu 대한토목학회 2020 KSCE Journal of Civil Engineering Vol.24 No.4
This paper conducts a simulation experiment research on cutter-head vibration characteristics by evaluating a soft-hard mixed stratum (the upper layer is silty soil, whereas the lower layer is moderately weathered granite of maximum uniaxial compressive strength (UCS) 142.0 MPa and slightly weathered granite of maximum 210.0 MPa). The ratios of hard rock and soil within the tunnel face were designed to be 1:1 and 1:2. Then, the cutter-head and stratum model were subjected to vibration analysis by reasonably deployed accelerometers. Results show that: 1) different conditions of heterogeneous strata mainly affected the acceleration amplitude and frequency distribution of cutter-head, in other words, the stronger hard rock, the larger the strength difference between the hard rock and soil within a tunnel face, the larger the vibration acceleration and the more concentrated the vibration frequency distribution; 2) the radial and circumferential vibration acceleration of the cutter-head in different positions were not largely different; however, axial accelerations were largely different. The axial vibration accelerations first increased and then decreased along the radial direction of cutter-head. Considering the difference between Multi-Mode Boring Test System and real cutter-head structure, the radius of joint between the cutter-head and the flange plate should be reasonably increased according to the ratio of hard rock in tunnel face; 3) with the increasing difference between the strength of the hard rock and soil, the circumferential and axial vibration acceleration multiplied. Thus, the soil remarkably reduces the vibration of the cutter-head. These results can provide some evidence of potential application for advancing manufacturing practice for cutter-head and disc cutter of shield machine.
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Seismic reliability of concrete rectangular liquid storage structures
Xuansheng Cheng,Peicun He,Dongjiang Yu 국제구조공학회 2019 Structural Engineering and Mechanics, An Int'l Jou Vol.70 No.5
To analyze the seismic reliability of concrete rectangular liquid storage structures (CRLSSs), assuming that the wall thickness and internal liquid depth of CRLSSs are random variables, calculation models of CRLSSs are established by using the Monte Carlo finite element method (FEM). The principal stresses of the over-ground and buried CRLSSs are calculated under three rare fortification intensities, and the failure probabilities of CRLSSs are obtained. The results show that the seismic reliability increases with the increase of wall thickness, whereas it decreases with the increase of liquid depth. Between the two random factors, the seismic reliability of CRLSSs is more sensitive to the change in wall thickness. Compared with the over-ground CRLSS, the buried CRLSS has better reliability.
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Direct catalytic conversion of glucose and cellulose
Li, Zhenhuan,Su, Kunmei,Ren, Jun,Yang, Dongjiang,Cheng, Bowen,Kim, Chan Kyung,Yao, Xiangdong The Royal Society of Chemistry 2018 GREEN CHEMISTRY Vol.20 No.4
<P>Biomass product 5-hydroxymethylfurfural (5-HMF) can be used to synthesize a broad range of value added compounds currently derived from petroleum. Thus, the effective conversion of glucose or cellulose (the major components of biomass) into fuels and chemical commodities has been capturing increasing attention. Previous studies have been extensively focused on a two-step process for producing 5-HMF from glucose or cellulose, <I>i.e.</I>, the isomerization of glucose into fructose and then the dehydration of fructose. We herein discovered that heterogeneous sulfonated poly(phenylene sulfide) (SPPS) containing strong Brønsted acid sites is able to convert glucose and cellulose into 5-HMF with a high yield in ionic liquids (ILs). The optimal activity of glucose conversion to 5-HMF achieves a yield of 87.2% after 4 h reaction at 140 °C. For direct cellulose conversion, a 5-HMF yield of 68.2% can be achieved. The reaction mechanism over the SPPS catalyst in ILs was studied by DFT calculations, and the results indicated that the SO3H group of SPPS plays a crucial role in glucose conversion into 5-HMF, and it acts as a proton donor as a Brønsted acid and functions as a proton acceptor as the conjugate base. Furthermore, the anions and cations of ILs together with SO3H-SPPS helped in stabilizing the reaction intermediates and transition states, which also resulted in glucose facile conversion into 5-HMF. The new catalyst system highlights new opportunities offered by optimizing the production of 5-HMF directly from glucose and cellulose.</P>
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