Comparative study of tip leakage vortex trajectory and cavitation in an axial flow pump with various tip clearances

Xi Shen,Desheng Zhang,Bin Xu,Haoran Wu,Peng Wang,Weidong Shi 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.3

In order to analyze the effect of blade tip-gap size on the tip leakage vortex (TLV) dynamics and TLV-induced cavitation, a scaled axial flow pump model was created and numerically studied by the combination of an improved SST k-ω turbulence model and a homogeneous cavitation model. The trajectories of TLV core was obtained by using the swirling strength method at different tip-gap sizes vary significantly. The scale of TLV increases as the tip-gap size increases, and the starting point of TLV is sliding further downstream along the blade chord. The angle between the blade suction surface and the TLV also presented an increasing trend with the tip-gap size. The statistics of the velocity normal to the tip chord, as well as the turbulent kinetic energy (KTE) distributions were employed to illustrate a more disordered flow field, which was generated in the tip clearance in a larger amount of leaking flow due to the increased tip-gap size. The in-plain static pressure and vapor volume fraction distributions at different blade chord sections, coupled with three-dimensional cavitation patterns among three tip gaps, are further analyzed to verify the wandering motion of TLV, which shows good agreement with the visualization experiment. Considering the adverse effect of the TLV cavitation, a small tip gap is recommended for improving the axial flow pump performance.

Partly Random Multiple Weighting Matrices Selection for Orthogonal Random Beamforming

Tan, Li,Li, Zhongcai,Xu, Chao,Wang, Desheng The Korea Institute of Information and Commucation 2016 Journal of communications and networks Vol.18 No.6

In the multi-user multiple-input multiple-output (MIMO) system, orthogonal random beamforming (ORBF) scheme is proposed to serve multiple users simultaneously in order to achieve the multi-user diversity gain. The opportunistic space-division multiple access system (OSDMA-S) scheme performs multiple weighting matrices during the training phase and chooses the best weighting matrix to be used to broadcast data during the transmitting phase. The OSDMA-S scheme works better than the original ORBF by decreasing the inter-user interference during the transmitting phase. To save more time in the training phase, a partly random multiple weighting matrices selection scheme is proposed in this paper. In our proposed scheme, the Base Station does not need to use several unitary matrices to broadcast pilot symbol. Actually, only one broadcasting operation is needed. Each subscriber generates several virtual equivalent channels with a set of pre-saved unitary matrices and the channel status information gained from the broadcasting operation. The signal-to-interference and noise ratio (SINR) of each beam in each virtual equivalent channel is calculated and fed back to the base station for the weighting matrix selection and multi-user scheduling. According to the theoretical analysis, the proposed scheme relatively expands the transmitting phase and reduces the interactive complexity between the Base Station and subscribers. The asymptotic analysis and the simulation results show that the proposed scheme improves the throughput performance of the multi-user MIMO system.

A C3 continuous double circumscribed corner rounding method for five-axis linear tool path with improved kinematics performance

Yan Guangwen,Zhang Desheng,Xu Jinting,Sun Yuwen 한국CDE학회 2023 Journal of computational design and engineering Vol.10 No.4

Corner rounding methods have been widely developed to pursue the smooth motions of machine tools. However, most corner rounding methods, which adopt the double inscribed transitions, still remain an inherent issue of retaining large curvatures of transition curves. Even for those double circumscribed transitions-based methods with relatively small curvatures, they also constrain excessively the transition lengths and are limited to a low-order continuity, deteriorating the feedrate and jerk of machine tools. For addressing these problems, a C3 continuous double circumscribed corner rounding (DCCR) method is proposed for five-axis linear tool path. In this method, the C3 continuous double circumscribed B-splines are specially designed to round the corners of tool position and tool orientation, whose transition lengths are analytically determined by jointly constraining the approximation errors, overlaps elimination, and parameter synchronization. Moreover, the excessive constrains of transition lengths imposed by traditional methods are alleviated by fully considering the effects of overlaps and parameter synchronization, and the jerk of rotary axes is also limited with a high-order continuity. Compared to the existing double inscribed corner rounding (DICR) and DCCR methods, experiment results demonstrate that our method can improve further the feedrate while limiting the jerk of machine tools.

Increased Expression of EMMPRIN and VEGF in the Rat Brain after Gamma Irradiation

Ming Wei,Hong Li,Huiling Huang,Desheng Xu,Dashi Zhi,Dong Liu,Yipei Zhang 대한의학회 2012 Journal of Korean medical science Vol.27 No.3

The extracellular matrix metalloproteinase inducer (EMMPRIN) has been known to play a key regulatory role in pathological angiogenesis. A elevated activation of vascular endothelial growth factor (VEGF) following radiation injury has been shown to mediate blood-brain barrier (BBB) breakdown. However, the roles of EMMPRIN and VEGF in radiation-induced brain injury after gamma knife surgery (GKS) are not clearly understood. In this study, we investigated EMMPRIN changes in a rat model of radiation injury following GKS and examined potential associations between EMMPRIN and VEGF expression. Adult male rats were subjected to cerebral radiation injury by GKS under anesthesia. We found that EMMPRIN and VEGF expression were markedly upregulated in the target area at 8-12 weeks after GKS compared with the control group by western blot,immunohistochemistry, and RT-PCR analysis. Immunofluorescent double staining demonstrated that EMMPRIN signals colocalized with caspase-3 and VEGF-positive cells. Our data also demonstrated that increased EMMPRIN expression was correlated with increased VEGF levels in a temporal manner. This is the first study to show that EMMPRIN and VEGF may play a role in radiation injuries of the central nervous system after GKS.

Partly Random Multiple Weighting Matrices Selection for Orthogonal Random Beamforming

Li Tan,Zhongcai Li,Chao Xu,Desheng Wang 한국통신학회 2016 Journal of communications and networks Vol.18 No.6

In the multi-user multiple-input multiple-output(MIMO) system, orthogonal random beamforming (ORBF)scheme is proposed to serve multiple users simultaneously in orderto achieve the multi-user diversity gain. The opportunistic spacedivisionmultiple access system (OSDMA-S) scheme performs multipleweighting matrices during the training phase and choosesthe best weighting matrix to be used to broadcast data during thetransmitting phase. The OSDMA-S scheme works better than theoriginal ORBF by decreasing the inter-user interference duringthe transmitting phase. To save more time in the training phase,a partly random multiple weighting matrices selection scheme isproposed in this paper. In our proposed scheme, the Base Stationdoes not need to use several unitary matrices to broadcast pilotsymbol. Actually, only one broadcasting operation is needed. Each subscriber generates several virtual equivalent channels witha set of pre-saved unitary matrices and the channel status informationgained from the broadcasting operation. The signal-tointerferenceand noise ratio (SINR) of each beam in each virtualequivalent channel is calculated and fed back to the base stationfor the weighting matrix selection and multi-user scheduling. Accordingto the theoretical analysis, the proposed scheme relativelyexpands the transmitting phase and reduces the interactive complexitybetween the Base Station and subscribers. The asymptoticanalysis and the simulation results show that the proposed schemeimproves the throughput performance of the multi-user MIMOsystem.