Browsing by Author "Zhou, Ling"
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Item A High-Resolution Network with Strip Attention for Retinal Vessel Segmentation(2023) Ye, Zhipin; Liu, Yingqian; Jing, Teng; He, Zhaoming; Zhou, LingAccurate segmentation of retinal vessels is an essential prerequisite for the subsequent analysis of fundus images. Recently, a number of methods based on deep learning have been proposed and shown to demonstrate promising segmentation performance, especially U-Net and its variants. However, tiny vessels and low-contrast vessels are hard to detect due to the issues of a loss of spatial details caused by consecutive down-sample operations and inadequate fusion of multi-level features caused by vanilla skip connections. To address these issues and enhance the segmentation precision of retinal vessels, we propose a novel high-resolution network with strip attention. Instead of the U-Net-shaped architecture, the proposed network follows an HRNet-shaped architecture as the basic network, learning high-resolution representations throughout the training process. In addition, a strip attention module including a horizontal attention mechanism and a vertical attention mechanism is designed to obtain long-range dependencies in the horizontal and vertical directions by calculating the similarity between each pixel and all pixels in the same row and the same column, respectively. For effective multi-layer feature fusion, we incorporate the strip attention module into the basic network to dynamically guide adjacent hierarchical features. Experimental results on the DRIVE and STARE datasets show that the proposed method can extract more tiny vessels and low-contrast vessels compared with existing mainstream methods, achieving accuracies of 96.16% and 97.08% and sensitivities of 82.68% and 89.36%, respectively. The proposed method has the potential to aid in the analysis of fundus images.Item Influence of impeller gap drainage width on the performance of low specific speed centrifugal pump(2021) Wei, Yangyang; Yang, Yang (TTU); Zhou, Ling; Jiang, Lei; Shi, Weidong; Huang, GaoyangThe centrifugal pump is one of the most important pieces of energy‐consuming equipment in various hydraulic engineering applications. This paper takes a low specific speed centrifugal pump as the research object. Based on the research method combining numerical calculation and experimental verification, the influence of the gap drainage structure on the performance of the low specific speed centrifugal pump and its internal flow field distribution were investigated. The flow field inside the low specific speed centrifugal pump impeller under different gap widths was stud-ied. The comparison between the numerical calculation results and the experimental results con-firms that the numerical calculations in this paper have high accuracy. It was found that the gap drainage will reduce the head of the low specific speed centrifugal pump, but increase its hydraulic efficiency. Using a smaller gap width could greatly improve the performance of the low specific speed centrifugal pump on the basis of a slight reduction in the head. The high‐pressure leakage flow at the gap flows from the blade pressure surface to the suction surface can effectively suppress the low‐pressure area at the impeller inlet. The flow rate of the high‐pressure leakage flow increases with the gap width. Excessive gap width may cause a low‐pressure zone at the inlet of the previous flow passage. These results could serve as a reference for the subsequent gap design to further improve the operating stability of the low specific speed centrifugal pump.Item Numerical calculation of energy performance and transient characteristics of centrifugal pump under gas-liquid two-phase condition(2020) Zhou, Ling; Han, Yong; Lv, Wanning; Yang, Yang (TTU); Zhu, Yong; Song, XiangyuThe unstable operation of a centrifugal pump under the gas-liquid two-phase condition seriously affects its performance and reliability. In order to study the gas phase distribution and the unsteady force in an impeller, based on the Euler-Euler heterogeneous flow model, the steady and unsteady numerical calculations of the gas-liquid two-phase full flow field in a centrifugal pump was carried out, and the simulation results were compared with the test data. The results show that the test results are in good agreement with the simulation data, which proves the accuracy of the numerical calculation method. The energy performance curve of the model pump decreases with the increase of the gas content, which illustrates a serious impact on the performance under the part-load operating condition. The results reveal that the high-efficiency-operating range become narrow, as the gas content increases. The gas phase is mainly distributed on the suction surface of the impeller blades. When the gas content reaches a certain value, the gas phase separation occurs. As the inlet gas content increases, the radial force on the impeller blades decreases. The pattern of the pressure pulsation is similar to that under pure water and low gas content conditions, and the number of peaks during the pulsation is equal to the number of the impeller blades. After the gas content reaches a certain value, the pressure fluctuates disorderly and the magnitude and the direction of radial force change frequently, which are detrimental to the operation stability of the pump. The intensity of the pressure pulsations in the impeller flow channel continues to increase in the direction of the flow under pure water conditions. The pressure pulsation intensities at the blade inlet and the volute tongue become more severe with the increase of the gas content.Item Optimal Design of Slit Impeller for Low Specific Speed Centrifugal Pump Based on Orthogonal Test(2021) Yang, Yang; Zhou, Ling; Zhou, Hongtao; Lv, Wanning; Wang, Jian; Shi, Weidong; He, ZhaomingMarine centrifugal pumps are mostly used on board ship, for transferring liquid from one point to another. Based on the combination of orthogonal testing and numerical simulation, this paper optimizes the structure of a drainage trough for a typical low-specific speed centrifugal pump, determines the priority of the various geometric factors of the drainage trough on the pump performance, and obtains the optimal impeller drainage trough scheme. The influence of drainage tank structure on the internal flow of a low-specific speed centrifugal pump is also analyzed. First, based on the experimental validation of the initial model, it is determined that the numerical simulation method used in this paper is highly accurate in predicting the performance of low-specific speed centrifugal pumps. Secondly, based on the three factors and four levels of the impeller drainage trough in the orthogonal test, the orthogonal test plan is determined and the orthogonal test results are analyzed. This work found that slit diameter and slit width have a large impact on the performance of low-specific speed centrifugal pumps, while long and short vane lap lengths have less impact. Finally, we compared the internal flow distribution between the initial model and the optimized model, and found that the slit structure could effectively reduce the pressure difference between the suction side and the pressure side of the blade. By weakening the large-scale vortex in the flow path and reducing the hydraulic losses, the drainage trough impellers obtained based on orthogonal tests can significantly improve the hydraulic efficiency of low-specific speed centrifugal pumps.Item Two-phase flow investigation of sewage pumps with different tip clearance via computational fluid dynamics and multi-factor ANOVA(2024) Yang, Yang; Wang, Hui; Hu, Qixiang; Ji, Leilei; He, Zhaoming (TTU); Shi, Weidong; Song, Xiangyu; Zhou, LingSewage pumps are widely utilized in various applications, including municipal wastewater treatment plants, industrial processes, and residential sewage systems. These pumps are specifically designed to handle the transportation of mixtures consisting of solid and liquid components, commonly observed as two-phase flow. In this study, semi-open sewage pumps with varying clearance sizes have been examined through adjustment of the geometrical model. Multi-factor analysis of variance is employed to investigate the combined influence of different two-phase flow conditions and tip clearance sizes on the performance of sewage pumps. The results show that the performance of the pump decreases significantly as the clearance size increases. Also, the sensitivity of pump efficiency to variations in tip clearance size is contingent upon the flow rate. Under part-load conditions, both particle concentration and clearance size exhibit a notable effect on efficiency. The two-phase flow will greatly enhance the intensity of the unsteady flow near the inlet and outlet of the semi-open impeller, which is the main reason for the performance degradation of the sewage pump. The findings of this research provide valuable insights for enhancing the hydraulic performance and operational stability of semi-open sewage pumps operating under two-phase flow conditions.