Analysis of coasting-down hydrodynamic characteristics of sodium pump in the primary circuit of fast reactor

Yang Congxin,Luo Xin,Qian Chen 한국유체기계학회 2022 International journal of fluid machinery and syste Vol.15 No.2

The variation of coasting-down hydrodynamic characteristics of the sodium pump in the primary circuit of fast reactor is related to the safe and stable operation of nuclear power plant. In order to explore the variation rule of performance parameters during the coasting-down process, the prototype of the sodium pump (Vertical double suction coaxial in and out submersible pump) in the primary circuit of fast reactor was taken as the research object in this paper. Based on the N-S equation and the RNG k-ε turbulence model, the Fluent software was used. The UDF function was written to carry out unsteady numerical calculation on the coasting-down process of sodium pump, and the variation rule of rotating speed, flow rate, head, torque and pressure with time in the coasting-down process was obtained. The results show that during the coasting-down process,the time for the model pump rotating speed to drop to half (296.5 r/min) is more than 15 s, and the time to drop to the minimum (112 r/min) is more than 74 s, which meets the nuclear safety standards. The flow rate ratio and the rotating speed ratio have the same change law, the head ratio and the torque ratio have the same change law, and the decline speed of the head ratio and torque ratio is greater than the rotating speed ratio and the flow rate ratio, which conforms to the similarity law of the pump. During the coasting-down process, the energy of the model pump pressure pulsation is mainly concentrated at middle and low frequencies. With the increase of the coasting-down time, the amplitude of pressure pulsation decreases gradually, and the uniformity of pressure distribution at circumferential direction decreases gradually. In addition, under the influence of pressure pulsation and the complexity of flow passage of the flow components, the head has a pulsating downward trend.

A New Shape Adaptation Scheme to Affine Invariant Detector

( Congxin Liu ),( Jie Yang ),( Yue Zhou ),( Deying Feng ) 한국인터넷정보학회 2010 KSII Transactions on Internet and Information Syst Vol.4 No.6

In this paper, we propose a new affine shape adaptation scheme for the affine invariant feature detector, in which the convergence stability is still an opening problem. This paper examines the relation between the integration scale matrix of next iteration and the current second moment matrix and finds that the convergence stability of the method can be improved by adjusting the relation between the two matrices instead of keeping them always proportional as proposed by previous methods. By estimating and updating the shape of the integration kernel and differentiation kernel in each iteration based on the anisotropy of the current second moment matrix, we propose a coarse-to-fine affine shape adaptation scheme which is able to adjust the pace of convergence and enable the process to converge smoothly. The feature matching experiments demonstrate that the proposed approach obtains an improvement in convergence ratio and repeatability compared with the current schemes with relatively fixed integration kernel.

PPD: A Robust Low-computation Local Descriptor for Mobile Image Retrieval

( Congxin Liu ),( Jie Yang ),( Deying Feng ) 한국인터넷정보학회 2010 KSII Transactions on Internet and Information Syst Vol.4 No.3

This paper proposes an efficient and yet powerful local descriptor called phase-space partition based descriptor (PPD). This descriptor is designed for the mobile image matching and retrieval. PPD, which is inspired from SIFT, also encodes the salient aspects of the image gradient in the neighborhood around an interest point. However, without employing SIFT`s smoothed gradient orientation histogram, we apply the region based gradient statistics in phase space to the construction of a feature representation, which allows to reduce much computation requirements. The feature matching experiments demonstrate that PPD achieves favorable performance close to that of SIFT and faster building and matching. We also present results showing that the use of PPD descriptors in a mobile image retrieval application results in a comparable performance to SIFT.

Pim Protein Kinase-3 Is Regulated by TNF-α and Promotes Endothelial Cell Sprouting

Handong Yang,Yinfang Wang,Hang Qian,Peng Zhang,Congxin Huang 한국분자세포생물학회 2011 Molecules and cells Vol.32 No.3

Tumor necrosis factor-α (TNF-α) plays an important role in pathological angiogenesis associated with inflammatory response. Pim-3 kinase belonging to serine/threonine protein kinases is a potent suppressor of myc-induced apoptosis. We have recently demonstrated that Pim-3 plays an essential role in endothelial cell (EC) spreading and migration. In this study, we showed that TNF-α transiently increased Pim-3 mRNA expression, and this was mediated through Tumor necrosis factor-α receptor-1 (TNFR1)pathway in ECs. TNF-α could promote stabilization of Pim-3 mRNA in ECs. Small-interfering RNA (siRNA)-mediated gene knockdown of Pim-3 significantly impaired TNF-α-induced formation of EC membrane protrusions in vitro. Furthermore, Pim-3 silencing inhibited EC sprouting in subcutaneous Matrigel in vivo. eNOS mRNA abundance was lower in Pim-3 siRNA transfected ECs compared with the control ECs. These observations suggest that Pim-3plays a role in TNF-α-induced angiogenesis.

Patterning of CVD Diamond Films For MEMS Application

Wang, Xiaodong,Yang, Yirong,Ren, Congxin,Mao, Minyao,Wang, Weiyuan The Korean Vacuum Society 1998 Applied Science and Convergence Technology Vol.7 No.1

To apply diamond films in microelectromechanical systems(MEMS), it is necessary to develop the patterning technologies of diamond films in the micrometer scale. In this paper, three different kinds of technologies for patterning CVD diamond films carried out by us were demonstrated: selective growth by improved diamond nucleation in DC bias-enhanced microwave plasma chemical vapor deposition (MPCVD) system, selective growth of seeding using diamond-particle-mixed photoresist, and selective etching of oxygen ion beam using Al as the mask. It was show that high selectivity and precise patterns had been achieved, and all the processes were compatible with IC process.

Numerical Simulation of Unsteady Cavitation in a High-speed Water Jet

Guoyi Peng,Kunihiro Okada,Congxin Yang,Yasuyuki Oguma,Seiji Shimizu 한국유체기계학회 2016 International journal of fluid machinery and syste Vol.9 No.1

Concerning the numerical simulation of high-speed water jet with intensive cavitation this paper presents a practical compressible mixture flow method by coupling a simplified estimation of bubble cavitation and a compressible mixture flow computation. The mean flow of two-phase mixture is calculated by URANS for compressible fluid. The intensity of cavitation in a local field is evaluated by the volume fraction of gas phase varying with the mean flow, and the effect of cavitation on the flow turbulence is considered by applying a density correction to the evaluation of eddy viscosity. High-speed submerged water jets issuing from a sheathed sharp-edge orifice nozzle are treated when the cavitation number, σ = 0.1, and the computation result is compared with experimental data The result reveals that cavitation occurs initially at the entrance of orifice and bubble cloud develops gradually while flowing downstream along the shear layer. Developed bubble cloud breaks up and then sheds downstream periodically near the sheath exit. The pattern of cavitation cloud shedding evaluated by simulation agrees experimental one, and the possibility to capture the unsteadily shedding of cavitation clouds is demonstrated. The decay of core velocity in cavitating jet is delayed greatly compared to that in no-activation jet, and the effect of the nozzle sheath is demonstrated.

Effect of Balance Drum Clearance on the Flow in the last stage Impeller Back Sidewall gap

Qian Chen,Luo Xin,Yang Congxin,Wang Bin 한국유체기계학회 2020 International journal of fluid machinery and syste Vol.13 No.2

In order to study the effect of balance drum clearance on flow distribution in back sidewall gap of last-stage impeller, numerical calculation of a multistage pump was carried out. The accuracy of the numerical calculation method was verified with the external characteristic test. The axial distribution of the radial velocity at the inlet and the bottom of the back sidewall gap at different angles was plotted. The results showed that the radial velocity near the impeller flows radially to the outlet of the impeller, and the radial velocity near the pump shell flows radially to the hub. Influenced by the high-turbulent energy fluid at the outlet of the impeller, there are obvious eddy current movement at the inlet of the back sidewall gap, and the radial velocity increases with the increase of the balance drum clearance. When the flow rate increases from 0.5Q to 1.5Q, the radial velocity decreases gradually at the same angle. The results can provide a reference for the pump design and optimization.

Numerical Simulation of Unsteady Cavitation in a High-speed Water Jet

Peng, Guoyi,Okada, Kunihiro,Yang, Congxin,Oguma, Yasuyuki,Shimizu, Seiji Korean Society for Fluid machinery 2016 International journal of fluid machinery and syste Vol.9 No.1

Concerning the numerical simulation of high-speed water jet with intensive cavitation this paper presents a practical compressible mixture flow method by coupling a simplified estimation of bubble cavitation and a compressible mixture flow computation. The mean flow of two-phase mixture is calculated by URANS for compressible fluid. The intensity of cavitation in a local field is evaluated by the volume fraction of gas phase varying with the mean flow, and the effect of cavitation on the flow turbulence is considered by applying a density correction to the evaluation of eddy viscosity. High-speed submerged water jets issuing from a sheathed sharp-edge orifice nozzle are treated when the cavitation number, ${\sigma}=0.1$, and the computation result is compared with experimental data The result reveals that cavitation occurs initially at the entrance of orifice and bubble cloud develops gradually while flowing downstream along the shear layer. Developed bubble cloud breaks up and then sheds downstream periodically near the sheath exit. The pattern of cavitation cloud shedding evaluated by simulation agrees experimental one, and the possibility to capture the unsteadily shedding of cavitation clouds is demonstrated. The decay of core velocity in cavitating jet is delayed greatly compared to that in no-activation jet, and the effect of the nozzle sheath is demonstrated.

Multi-Objective Optimization of Multistage Pump Balance Drum System Based on BP Neural Network and Genetic Algorithm

Qian Chen,Luo Xin,Ling Zuguang,Yang Congxin 한국유체기계학회 2021 International journal of fluid machinery and syste Vol.14 No.1

The axial force balancing capacity of a balance drum is a key factor affecting the life of multi-stage centrifugal pumps. In this paper, a double shell segmental multistage pump is taken as the research object. The hydraulic performance and axial force performance are set as the optimization objectives, and the performance data are obtained by numerical simulation with FLUENT software. The BP neural network is used to establish the prediction model of structural parameters of the balance system, hydraulic performance and residual axial force performance, and it is used as the adaptive value evaluation model of genetic algorithm to solve the optimal value in the sample space. The results show that the radial clearance of the balance drum and the balance tube orifice flowmeter, the axial width of the balance cavity are the significant factors affecting the hydraulic performance and axial force performance of the multistage pump. When the radial clearance of the balance drum is 0.1mm, the clearance of the orifice flowmeter is 1.95mm, and the axial width of the balance cavity is 55mm, the multi-stage pump has the best hydraulic performance and the smallest residual axial force. The vortex band in the balance cavity can increase the amount of the fluid spin and enhance the axial force balancing capacity of the balance drum. The greater the area occupied by the negative high-rotation fluid in the balance cavity, the stronger the ability of the balance drum to balance the axial force. The test results show that compared with the prototype multistage pump, at nominal flow rate, the head and efficiency of the optimized model are increased by 0.71% and 1.63% respectively, and the bearing temperature and vibration speed of the multi-stage pump are significantly reduced.