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Accuracy analysis for machine tool spindles considering full parallel connections and form errors based on skin model shapes
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Over‐dispersed count data in crop and agronomy research
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- 저자 : Guojun Zhu (검색결과 4 건)
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Influence of pump start-up mode on the stability of mixed-flow pumps
Zhenbo Tang,Guojun Zhu,Jianjun Feng,Yajun Wu,Kai Liu,Qiang Lu 대한기계학회 2023 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.37 No.6
To analyse the influence of the start-up mode on the stability of the mixed-flow pump, start-up experiments are performed. And the external characteristic parameters, pressure fluctuation and shaft vibration data are collected by a multi-channel synchronous signal acquisition system during start-up. These data are analyzed by the time-frequency analysis method and wavelet partial coherence analysis method. Results reveal a positive correlation between the impeller angular acceleration and the time change rate of external characteristic parameters. During the start-up process, the variation law of the external characteristic parameters similar with the law of impeller rotating speed rise. The amplitude of the shaft vibration has a positive correlation with the start-up acceleration of the impeller. The influence of guide vane pressure fluctuations on the shaft vibrations is greater within 0~2 s after the start of the mixedflow pump. With the strart-up time extension, the partial coherence between the shaft vibration and the pressure fluctuations in guide vane is enhanced in low frequency band, which increases the risk of flow-induced vibration of the pump shaft.
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Yan Sina,Luo Xingqi,Feng Jianjun,Zhu Guojun,Zhang Lefu,Chen Senlin 한국유체기계학회 2019 International journal of fluid machinery and syste Vol.12 No.1
In order to study the influence of inlet gas volume fraction (IGVF) on performance of a gas-liquid centrifugal pump, three-dimensional turbulent flow of a single-stage gas-liquid centrifugal pump has been simulated by using computational fluid dynamics (CFD). Both steady and unsteady simulations have been conducted for different inlet gas volume fraction conditions of the pump. The gas phase distribution, the internal flow field and pressure field of the pump were obtained with inhomogeneous two-fluid model. The result showed that many gas accumulation zones accompanied vortices appears in the impeller as IGVF increases, and surge would occur as IGVF reaches a certain value. The change of IGVF would change the magnitude and direction of the impeller radial force.
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Effects of N2 addition on nanocrystalline diamond films by HFCVD in Ar/CH4 gas mixture
Sobia Allah Rakha,Zhou Xintai,Dezhang Zhu,Yu Guojun 한국물리학회 2010 Current Applied Physics Vol.10 No.1
Nanocrystalline diamond (NCD) films were grown on silicon substrates by hot filament chemical vapor deposition in Ar/N2/CH4 gas mixtures. The effects of seeding process prior to deposition, the total gas pressure, and concentration of nitrogen on the grain size, morphology and bonding nature in HFCVD technique were investigated. The results indicated that a low total gas pressure is favorable for nanosized diamond crystallites. Films micrograph obtained from scanning electron microscopy showed diamond nanograins elongated with the addition of nitrogen in the plasma. Crystal structure investigations were carried out by X-ray diffraction measurements for deposited films. An increase in the size of crystallite is also observed from XRD measurements in NCD film when nitrogen was added in plasma. From Raman spectra, it was observed that the relative intensity of G peak increases indicating more graphite content after nitrogen added in the plasma. The effects of the nitrogen incorporation in nanocrystalline films in HFCVD are discussed.
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Like Wang,Xingqi Luo,Jinling Lu,Jianjun Feng,Guojun Zhu,Wei Wang,Kai Wang 대한기계학회 2023 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.37 No.9
Tidal energy is an important renewable energy that uses the potential energy created by the rising and falling of ocean tides to generate electricity. The tip leakage vortex (TLV) and cavitation caused by the tip leakage flow have adverse effects on the energy conversion efficiency and stable operation of the tubular turbine. The selection of the tip clearance shape is critical. Therefore, the effects of four different combinations of asymmetrical tip clearance shapes on the energy and cavitation characteristics of hydrofoils are studied in this paper. The results show that the TLV remains unchanged when tipwall and endwall are sinusoidal and cosine curve shaped, respectively. When tip clearance is the combination of a flat tipwall and a sinusoidal endwall, the lift-drag ratio decreases by 10.72 %. The high shear stress region of tipwall near leading edge decreases. The flow resistance of the leakage flow decreases, and the leakage flow becomes more serious. The cavitation volume is 2.5 times that under the original flat tip clearance. When tip clearance is the combination of a flat tipwall and a cosine endwall, and the lift-drag ratio increases by 9.67 %. The shear stress increases, the leakage flow decreases. The swirling strength around the center of the vortex core is weakened. The cavitation volume is 3.81, with a decrease of nearly 30 %. A proper asymmetrical tip clearance can effectively improve the energy performance and cavitation characteristics of hydrofoils. This study provides theoretical support for the design and optimization of hydraulic machine with tip clearance.
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