Dynamic Analyses of the Hydro-Turbine Generator Shafting System Considering the Hydraulic Instability

Hydraulic instability is a complex factor causing the vibration of hydro-turbine generator shafting system (HGSS), and the mechanism is the uneven distribution of flow along the circumference. The common reasons for this phenomenon include the inconsistency of the blade exit flow angle, the relay stroke and the guide vane opening. This paper mainly focuses on the research of the hydraulic instability caused by the inconsistency of the blade exit flow angle. Firstly, based on the Kutta-Joukowski theorem, the hydraulic unbalance force model is firstly presented. Then, considering the chain reaction among the hydraulic, mechanical and electrical instability, a combined nonlinear mathematical model of the HGSS is established. Finally, by using numerical simulation, the dynamic characteristics of the HGSS with the changing of the deviation of the blade exit flow angle, the blade exit diameter and the guide vane opening angle are analyzed. Moreover, it is found that the hydraulic instability determines the overall changing trend of the shafting dynamic behaviors. In addition, some stable ranges of the HGSS are distinguished. But above all, these results can efficiently provide a reference for the design and manufacture of hydro-turbine blades and the operation of hydropower stations

Nonlinear Hydraulic Vibration Modeling and Dynamic Analysis of Hydro-Turbine Generator Unit with Multiple Faults

Hydraulic vibration is a critical factor affecting the stability and health of the hydro-turbine generator unit (HGU). This paper investigates the nonlinear dynamic characteristics of the HGU occurring from the hydraulic vibration. First, using the turbulence flow model, the lift and drag coefficients of the asymmetric airfoil blades are calculated at different Reynolds numbers and angles of attack. Based on the lift and drag coefficients of the asymmetric airfoil blade, a novel nonlinear mathematical model of asymmetric hydraulic forces is proposed for the asymmetric airfoil blade. Then, combining mechanic and electric asymmetric excitations, a coupled nonlinear mathematical model of the HGU is built using Lagrange equations. Moreover, the correctness of this model is verified. Finally, dynamic behaviors of the HGU changing with attack angle, deviation of the outlet blade angle, outlet guide vane angle, and Reynolds number are analyzed by bifurcation diagrams. It is found that increasing the Reynolds number can enhance the hydraulic vibration, which can lead to more complex nonlinear bifurcation and chaotic motions. In addition, some interesting physical phenomena of HGU under critical ranges and values are obtained. More importantly, these results could give theoretical guidance in the designing and stability research of hydropower units

Nonlinear Hydraulic Vibration Modeling and Dynamic Analysis of Hydro-Turbine Generator Unit with Multiple Faults

Hydraulic vibration is a critical factor affecting the stability and health of the hydro-turbine generator unit (HGU). This paper investigates the nonlinear dynamic characteristics of the HGU occurring from the hydraulic vibration. First, using the turbulence flow model, the lift and drag coefficients of the asymmetric airfoil blades are calculated at different Reynolds numbers and angles of attack. Based on the lift and drag coefficients of the asymmetric airfoil blade, a novel nonlinear mathematical model of asymmetric hydraulic forces is proposed for the asymmetric airfoil blade. Then, combining mechanic and electric asymmetric excitations, a coupled nonlinear mathematical model of the HGU is built using Lagrange equations. Moreover, the correctness of this model is verified. Finally, dynamic behaviors of the HGU changing with attack angle, deviation of the outlet blade angle, outlet guide vane angle, and Reynolds number are analyzed by bifurcation diagrams. It is found that increasing the Reynolds number can enhance the hydraulic vibration, which can lead to more complex nonlinear bifurcation and chaotic motions. In addition, some interesting physical phenomena of HGU under critical ranges and values are obtained. More importantly, these results could give theoretical guidance in the designing and stability research of hydropower units

Dynamic Analyses of the Hydro-Turbine Generator Shafting System Considering the Hydraulic Instability

Hydraulic instability is a complex factor causing the vibration of hydro-turbine generator shafting system (HGSS), and the mechanism is the uneven distribution of flow along the circumference. The common reasons for this phenomenon include the inconsistency of the blade exit flow angle, the relay stroke and the guide vane opening. This paper mainly focuses on the research of the hydraulic instability caused by the inconsistency of the blade exit flow angle. Firstly, based on the Kutta-Joukowski theorem, the hydraulic unbalance force model is firstly presented. Then, considering the chain reaction among the hydraulic, mechanical and electrical instability, a combined nonlinear mathematical model of the HGSS is established. Finally, by using numerical simulation, the dynamic characteristics of the HGSS with the changing of the deviation of the blade exit flow angle, the blade exit diameter and the guide vane opening angle are analyzed. Moreover, it is found that the hydraulic instability determines the overall changing trend of the shafting dynamic behaviors. In addition, some stable ranges of the HGSS are distinguished. But above all, these results can efficiently provide a reference for the design and manufacture of hydro-turbine blades and the operation of hydropower stations

The risk of acute and early HIV (AEH) infection among MSM with different behaviour trajectories: an open cohort study in Tianjin, China, 2011–2019

Abstract Background Acute and early HIV (AEH) infection is characterized by a high viral load and infectivity. Approximately 50% of cases of HIV-1 transmission occur during AEH. Understanding sexual behaviour trajectories would be useful for predicting changes in the risk of HIV acquisition. However, few studies have investigated sexual behaviour trajectories and their association with AEH acquisition. This study identified behaviour trajectories among men who have sex with men (MSM), determined the risk of AEH infection, and compared risk factors between different behaviour trajectories. Methods The study was based on an ongoing prospective open cohort of voluntary HIV counselling and testing (VHCT) among MSM in Tianjin, China. From 2011 to 2019, 1974 MSM were recruited. Group-based trajectory modelling (GBTM) was used to identify behaviour trajectories by constructing a sexual risk behaviour score. Logistic regression and generalized estimating equation (GEE) were used to compare the risk of AEH infection and risk factors for different behaviour trajectories. All data analyses were performed using SAS 9.4. Results The incidence of AEH infection was 1.76/100 person-years, with 64 AEH infections documented in 3633 person-years of follow-up. Three sexual behaviour trajectories were identified: CL (consistently low risk, 35.46%), CH (consistently high risk, 42.71%) and HTL (high to low risk, 21.83%). MSM in the HTL and CH groups had higher AEH infection rates than MSM in the CL group (6.73%, 3.08% and 1.28%, respectively), with ORs of 5.54 (2.60, 11.82) and 2.44 (1.14, 5.25), respectively. MSM aged 30–50 years old and MSM who underwent HIV testing in the last year were more likely to be in the CH group and HTL group. In addition, the HTL group was characterized by a lower likelihood of local registration and a higher likelihood of working as a MSW. Conclusion MSM in the CH group and the HTL group had a higher risk of AEH infection. In the future, VHCT should be performed more often among younger MSM, and HIV counselling should be given the same priority as HIV testing. In addition, VHCT combined with PrEP may have a better preventive impact on MSM with a high risk of AEH infection

Subgenome parallel selection is associated with morphotype diversification and convergent crop domestication in Brassica rapa and Brassica oleracea

Brassica species, including crops such as cabbage, turnip and oilseed, display enormous phenotypic variation. Brassica genomes have all undergone a whole-genome triplication (WGT) event with unknown effects on phenotype diversification. We resequenced 199 Brassica rapa and 119 Brassica oleracea accessions representing various morphotypes and identified signals of selection at the mesohexaploid subgenome level. For cabbage morphotypes with their typical leaf-heading trait, we identified four subgenome loci that show signs of parallel selection among subgenomes within B. rapa, as well as four such loci within B. oleracea. Fifteen subgenome loci are under selection and are shared by these two species. We also detected strong subgenome parallel selection linked to the domestication of the tuberous morphotypes, turnip (B. rapa) and kohlrabi (B. oleracea). Overall, we demonstrated that the mesohexaploidization of the two Brassica genomes contributed to their diversification into heading and tuber-forming morphotypes through convergent subgenome parallel selection of paralogous genes