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RISS 인기검색어
- 검색키워드
- 저자 : Zhiwu Jiang (검색결과 4 건)
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Instability analysis under part-load conditions in centrifugal pump
Weixiang Ye,Renfang Huang,Zhiwu Jiang,Xiaojun Li,ZuChao Zhu,Xianwu Luo 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.1
In this study, a centrifugal pump with a specific speed of 39.12 m×min -1 ×m 3 s -1 is treated to analyze the flow instability under part-load conditions by numerical simulation and experimental test. For calculations, the RANS method, coupled with the k-ω SST turbulence model, is adopted. Numerical results at different operation points are compared with available experimental data, such as hydraulic performance and flow field information by particle image velocimetry. The numerical and experiment results agree well. The flow simulation indicates a strong reverse flow at the passage upstream impeller inlet, and the energy loss in the impeller is the largest under partload conditions among all flow components in the pump. In one impeller revolution, one blade-to-blade flow passage is always nearly blocked off by the rotating stall occurring at the impeller inlet for each instant, and the blockage induces a jet flow with large velocity at the next blade-to-blade flow passage along the rotational direction of the impeller. The blockage and the jet flow in the blade-to-blade flow passages will make the flow unstable inside the impeller and cause performance breakdown and pressure vibration under part-load conditions for the pump.
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Meng, Yicun,Wang, Zhiwu,Jiang, Pingping,Wang, Wei,Chen, Fanji,Yan, Guozheng The Korean Institute of Power Electronics 2020 JOURNAL OF POWER ELECTRONICS Vol.20 No.4
Wireless power transfer (WPT) systems based on magnetic resonance provides a possible method to supply energy for implantable medical devices, such as gastrointestinal robots and wireless capsule endoscopes. However, low power transfer efficiency (PTE) (most researches show it to be lower than 3%) and poor power received stability are the key limitation of WPT systems in such applications. Three-coil WPT systems are regarded as an effective method to improve the power transfer efficiency and power received of gastrointestinal robots. Thus, an analytical model of a three-coil inductive link was established in this paper. Then the power transfer efficiency of load coil was optimized by changing the coil turns and raising a novel coil configuration: a Helmholtz-like load coil. As a result, the power transfer efficiency and power deliver to load (PDL) of this three-coil WPT system are tremendously improved. To verify the proposed design, a prototype simulated the gastrointestinal robot working situation and it was implemented for an experimental test. The results obtained from the experimental test demonstrate that the proposed three-coil WPT system with 9 turns load coil and 40 turns receiving coil achieves a PTE of 4.32% and a PDL of 541.5 mW. Moreover, the best PTE attained by the novel Helmholtz-like load coil was 6.45% and the PDL was 845 mW.
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Ding Han,Guozheng Yan,Zhiwu Wang,Pingping Jiang,Lin Yan 한국정밀공학회 2023 International Journal of Precision Engineering and Vol.24 No.6
A wireless power transfer system for targeted therapy microrobots has been received more attention recently. However, it usually fails to work due to weak coupling caused by misalignment in position and angle between the transmitting coil and the receiving coil. It will not be tolerated even if it occurs at certain angles. To address this issue, a three-dimensional hybrid transmitting coil, combining a fixed Helmholtz coil pair and an adjustable curved rectangular coil pair, is proposed. Based on the novel structure, the proposed hybrid transmitting coil could produce a three-dimensional magnetic field, realizing well coupled with the receiving coil embedded on the microrobot at any posture. To verify the efficiency and practical applicability of the transmitting coil proposed in this paper, we build the coil model via both analytical calculation and simulation analysis. Finally, the designed hybrid transmitting coil is also implemented in the wireless power transfer system with a receiving coil. The magnetic field distribution indicates that a large and uniform magnetic field could be obtained. The experimental results demonstrate that in the central zone of the transmitting coil, 300 × 200 mm, the magnetic field distribution is uniform, which can meet the requirements of the microrobot system working area. And the maximum output efficiency and power can be reached at 5% and 1001 mW, respectively. What's more, the proposed hybrid transmitting coil has solved the weak coupling problem due to misalignment in position and angle with which the electromagnetic energy decays quickly.
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Shear strength evaluation of RC solid piers of high-speed railway bridges in China
Wei Guo,Chao Fan,Yao Cui,Chen Zeng,Lizhong Jiang,Zhiwu Yu 국제구조공학회 2021 Structural Engineering and Mechanics, An Int'l Jou Vol.78 No.4
Piers are the main lateral force-resisting members of high-speed railway (HSR) bridges used in China and are characterized by low axial load ratios, low longitudinal reinforcement ratios, low stirrup ratios, and high shear span ratios. It is well known that flexural, flexural-shear, and shear failures of piers may occur during an earthquake. In this study, a new shear strength model was developed to simulate the seismic failure of HSR solid piers accurately. First, low cyclic-loading test data of solid piers obtained in recent years were collected to set up a database for model verification. Second, based on the test database, the applicability of existing shear strength models was evaluated. Finally, a new shear strength model for HSR solid piers with round-ended cross-sections was derived based on the truss model and ultimate equilibrium theory. In comparison with existing models, it was demonstrated that the proposed model could be used to predict the shear strength of HSR piers more accurately.
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