External Characteristic Parameters Research Articles

Analysis of Cavitation-Induced Unsteady Flow Conditions in Francis Turbines under High-Load Conditions

Hydraulic vibrations in Francis turbines caused by cavitation profoundly impact the overall hydraulic performance and operational stability. Therefore, to investigate the influence of cavitation phenomena under high-load conditions, a three-dimensional unsteady numerical simulation is carried out for a Francis turbine with different head operating conditions, which is combined with the SST k-w turbulence model and two-phase flow cavitation model to capture the evolution of cavitation under high-load conditions. Additionally, utilizing entropy production theory, the hydraulic losses of the Francis turbine during cavitation development are assessed. Contrary to the pressure-drop method, the entropy production theory can quantitatively reflect the characteristics of the local hydraulic loss distribution, with a calculated error coefficient τ not exceeding 2%. The specific findings include: the primary sources of energy loss inside the turbine are the airfoil cavitation and cavitation vortex rope, constituting 26% and 71% of the total hydraulic losses, respectively. According to the comparison with model tests, the vapor volume fraction (VVF) inside the draft tube fluctuates periodically under high-load conditions, causing low-frequency pressure pulsation in the turbine’s power, flow rate, and other external characteristic parameters at 0.37 Hz, and the runner radial force fluctuates at a frequency of 1.85 Hz.

Safety Study Based on the Aging Mechanism of Retired Lithium Batteries

Aiming at the problem of battery aging and capacity change during the charging and discharging cycle of decommissioned ternary lithium batteries, it is proposed to study lithium batteries from two different perspectives: macro and micro. Select the appropriate external characteristic parameters to carry out a large number of charge and discharge cycle experiments with different magnifications for the decommissioned ternary lithium battery, and observe the capacity and internal resistance of the lithium battery from a macroscopic perspective. For the battery disassembly experiment, the angle analyzes the changes in the internal material of the battery. The results show that the experimental verification of decommissioned lithium batteries can accurately analyze the reasons affecting battery aging and capacity change, so as to reduce the safety hazards of cascade use of batteries and extend the service life of batteries to provide data guidance and suggestions.

Multi-scale analysis for accelerated degradation mechanisms of cylindrical LiFePO4/graphite batteries under distinct positions of jelly roll

Lithium iron phosphate (LFP) batteries are widely used in the electric vehicle due to the great chemical stability and cost advantages. Fluctuations in the environment and driving conditions lead to a deterioration in battery performance that is inevitable. In addition, due to the winding manufacturing characteristics of cylindrical battery electrodes, the uneven distribution of current and temperature accelerates the aging process. In this paper, the cross-comparison aging test of cylindrical LFP batteries is designed, in which three kinds of constant current and two different dynamic working conditions are used for accelerated aging test at high temperature. The aging behavior and mechanism are investigated quantitatively by combination of in-situ electrochemical test and ex-situ Post-Mortem methods. During the long-term cycle of the battery, external characteristic parameters such as capacity, internal resistance, and open circuit voltage are periodically checked up. Until the capacity retention falls below 80%, the batteries are disassembled to sample the electrodes at the specified positions from the jelly roll. The material morphology changes of electrodes are observed by scanning electron microscopy. The half-cell tests were produced to obtain material-level aging information based on performance tests. This multi-scale analytical method enables the detailed process of performance loss, which guides performance prediction and safety diagnostics.

Research on the state of health estimation of lithium-ion batteries for energy storage based on XGB-AKF method

With the advantages of high energy density, long cycle life and high stability, lithium-ion batteries have been used in a large number of fields such as electric vehicles and grid scale energy storage. To ensure the safe and reliable operation of battery systems, it is important to make an accurate and rapid estimation of the state of health (SOH) of Li-ion cells. A Li-ion cell is a complex nonlinear dynamic system. The SOH of a Li-ion can not be measured directly in actual working conditions; it can only be estimated indirectly by external characteristic parameters that reflects the extent of cell aging. It is difficult to ensure the reliability of method based on a single aging feature or model. Therefore, this paper proposes a multi-feature SOH estimation method that combines data-driven XGBoost and a Kalman filter. Firstly, a principal component analysis algorithm to reconstruct multiple battery aging features based on data is used, and an XGBoost online estimation model incorporating multiple features based on the reconstructed feature data is constructed. Finally, the joint optimal estimation of SOH of Li-ion cells by introducing a time-domain Kalman filter based on the real-time correction of the XGBoost model is achieved in this method. The results show that the method improves the accuracy and robustness of the estimation model and achieves a high-precision joint estimation of SOH for Li-ion cells.

Numerical study on the energy performance of an axial-flow pump with different wall roughness

Pumping stations play an important role in China’s South-to-North Water Diversion, agricultural irrigation, and municipal drainage. Some pumping station units have been put into operation for long periods with improper operation and require maintenance. Moreover, the surfaces of the flow components have been worn and corroded, leading to an increase in the relative roughness and a decrease in the hydraulic performance efficiencies of pumping station units. In this work, we performed field measurements and numerical simulations to study the influence of the wall roughness on the hydraulic performance of slanted axial-flow pump devices under multiple working conditions. The effects of the wall roughness of the impeller chamber on the hydraulic performance of the pump, the guide vane chamber, and the inlet and outlet flow channel were investigated. Wall roughness had the largest influence on the hydraulic performance of the pump and the smallest influence on the inlet and outlet flow channels. For devices with different roughness values on the impeller chamber wall under different flow rate conditions, the performance of the pump device worsened under the large-flow-rate condition, and the device performance was better under the small-flow-rate and designed flow conditions. The efficiency of the slanted axial-flow pump device decreased significantly as the flow rate increased. Under the same flow rate condition, the performance of the device with Ra = 5 μm was similar to that with a smooth wall, where Ra is the roughness of the wall. With the increase in the roughness, the uniformity of the axial velocity distribution coefficient decreased, and the velocity-weighted average drift angle increased. External characteristic parameters, such as the torque and the static pressure, on the blade pressure surface gradually decreased with the increase in the wall roughness. A large roughness could induce instability of the wall flow and enhance the turbulent kinetic energy near the blade surface.

A novel method for state of health estimation of lithium-ion batteries based on improved LSTM and health indicators extraction

State of health (SOH) is a crucial challenge to guarantee the reliability and safety of the electric vehicles (EVs), due to the complex aging mechanism. A novel SOH estimation method based on improved long short-term memory (LSTM) and health indicators (HIs) extraction from charging-discharging process is proposed in this paper. In order to overcome the limitation of the measurement of battery capacity in real application, some external characteristic parameters related to voltage, current and temperature are selected from charging-discharging process as HIs to describe the aging mechanism of the batteries. After that, Pearson correlation coefficient is employed to select the HIs, which have high correlations with battery capacity. And neighborhood component analysis (NCA) is used to eliminate redundant information of HIs with high correlation in order to reduce computational burden. Aiming at the problem of hyperparameter selection in LSTM models, differential evolution grey wolf optimizer (DEGWO) is proposed in this paper for hyperparameters optimization. Compared with traditional grey wolf optimizer, which is easy to fall into local optimality, DEGWO updates the population through mutation, crossover and screening operations to obtain the global optimal solution and improve the global search ability. The proposed method is verified based on the dataset of the battery from NASA and MIT. The simulations indicate that the proposed method has higher accuracy for different kinds of batteries. The estimation errors for both datasets are within 1%. Compared with other methods, the estimation evaluation indicators such as RMSE, MAE and MAPE of the proposed method are within 1%, which is much less than the estimation results obtained by other methods. And determination coefficient R2 is above 0.95, which means the proposed method has batter fitting performance. It is also indicated that the method proposed in this paper has higher accuracy, better robustness and generalization.

Study on the Cluster Selection Method of Echelon Utilization Power Battery Based on Confidence Interval Estimation

In order to improve the screening accuracy of decommissioned power batteries and reduce the regulation errors of batteries in the process of echelon utilization, a cascade batteries selection method based on confidence interval probability prediction is proposed. Firstly, according to the internal and external characteristic parameters, residual capacity, state of health (SOH) and other historical parameters, K-means clustering is used to divide static clusters of retired power batteries with similar parameters. Secondly, the bootstrap probability method is used to analyze the deviation subset of SOH estimation in echelon utilization process, and the probability interval density function of SOH subset is established. Finally, further optimization grouping is carried out according to the predicted SOH characteristics. By comparative analysis, the influence of confidence interval estimation on the screening accuracy is determined, and the effectiveness of the proposed screening method is determined. The consistency of dynamic characteristics is improved while the static parameters are similar in the screening process, which lays a foundation for accurate regulation of retired power battery echelon utilization.

Numerical Simulation of Transient Characteristics of Start-Up Transition Process of Large Vertical Siphon Axial Flow Pump Station

In order to explore the transient characteristics of the large-scale vertical siphon axial flow pumping station during the start-up and exhaust process, numerical simulations were carried out on the start-up process of the axial flow pumping station under the two starting modes of pre-opening the vacuum breaking valve and keeping the vacuum breaking valve closed. The calculation results show that during the start-up phase of the unit, the flow separation phenomenon of the impeller channel of the pump device with the vacuum breaking valve closed is serious, the large-scale vortex in the guide vane blocks the flow channel, and the instantaneous impact on the blade surface is strong. The flow field of the pump device with pre-open vacuum failure valve is obviously less affected by the instantaneous impact characteristics during the start-up of the pump. The range of high entropy production area in the impeller channel is reduced, the duration of high entropy production area is significantly shortened, and the instantaneous impact on the blade surface is weak. Under the two starting modes, the internal flow field of the pump device is similar in the evolutionary law. The unstable flow phenomenon of the pump device is most prominent in the weir flow stage. The maximum instantaneous impact on the blade surface also mainly occurs in the weir flow stage. A very small part of the remaining gas in the siphon formation stage is difficult to discharge and takes a long time. After the pump device is exhausted and enters a stable operation state, the external characteristic parameters are in good agreement with the test results. Compared with the starting method in which the vacuum breaking valve is kept closed, the method of pre-opening the vacuum breaking valve reduces the maximum starting head by 20% and the exhaust time by 43%. The pre-open vacuum breaking valve effectively avoids the system instability caused by the start-up and exhaust of the pump device.

Health Evaluation Method of Supercapacitor Based on Data Mining

With the wide application of super capacitor energy storage system as energy storage device on urban rail trains, the problem of its safe operation has attracted great attention. In order to ensure the reliability of the supercapacitor energy storage system, it is necessary to evaluate its health effectively. In view of the fact that the existing model-based supercapacitor evaluation methods are difficult to establish a reasonable and accurate model and the parameter estimation is complex, a data-driven supercapacitor health evaluation method is proposed. In this method, based on the data of voltage, current, temperature and external characteristic parameters of charge and discharge of supercapacitor, the weighted Euclidean distance formula is introduced, the mixed weighted Euclidean distance is calculated, and the comprehensive evaluation index of supercapacitor health state is obtained. It can quickly and effectively evaluate the health status of supercapacitors.

Analysis on Energy Loss Characteristic of a Bidirectional Tubular Turbine Based on Entropy Generation Theory

To obtain the external characteristic parameters and the distribution of hydraulic loss, ANSYS CFX code is used to for numerical simulations of a tidal bidirectional tubular turbine under positive and reverse conditions. The method of entropy generation analysis is used to obtain the energy loss in the unit and its local entropy generation rate. Besides, the influence of the shaft inclination in the guide vane on the tubular turbine is explored. The results show that there is a certain connection between the traditional hydraulic loss analysis and entropy generation analysis. Entropy generation could be adopted for the measurement of hydraulic loss with its distribution. The total entropy production is dominated by the runner under positive optimal condition, while the ones in the runner and the intake are the highest under reverse optimal condition. In addition, the greater the shaft inclination angle of the guide vane, the larger the total entropy production on the blade surface of the runner under the positive condition.

Analysis of the Influence of Different Bionic Structures on the Noise Reduction Performance of the Centrifugal Pump.

The strong noise generated during the operation of the centrifugal pump harms the pump group and people. In order to decrease the noise of the centrifugal pump, a specific speed of 117.3 of the centrifugal pump is chosen as a research object. The bionic modification of centrifugal pump blades is carried out to explore the influence of different bionic structures on the noise reduction performance of centrifugal pumps. The internal flow field and internal sound field of bionic blades are studied by numerical calculation and test methods. The test is carried out on a closed pump test platform which includes external characteristics and a flow noise test system. The effects of two different bionic structures on the external characteristics, acoustic amplitude–frequency characteristics and flow field structure of a centrifugal pump, are analyzed. The results show that the pit structure has little influence on the external characteristic parameters, while the sawtooth structure has a relatively great influence. The noise reduction effect of the pit structure is aimed at the wide-band noise, while the sawtooth structure is aimed at the discrete noise of the blade-passing frequency (BPF) and its frequency doubling. The noise reduction ability of the sawtooth structure is not suitable for high-frequency bands.

Numerical Research on Performance of High-Speed Partial Emission Pump

The high-speed partial emission pump is a small flow and high-head pump, which has been widely used. To study the main factors affecting the performance of high-speed partial emission pumps, numerical simulation methods were used to calculate the performance parameters of high-speed partial emission pumps with and without inducers, and the external characteristic parameters were verified through comparison test values. The results show that the head of the high-speed partial emission pump with inducer is nearly 15 m higher than that of the high-speed partial emission pump without inducer. Considering the influence of air in the high-speed partial emission pump on the working performance, the two-phase flow with different flow rates, different particle sizes, and different concentrations was calculated, and the different liquid phase distributions, liquid phase velocity vector diagrams, and external characteristic curve were compared. The results show that under the same flow condition, the gas-phase particle diameter has the most severe influence on the external characteristic.

The Numerical Analysis of Hydrodynamic Characteristics of Ducted Propeller by using SST k-ω Model

Hydrodynamic characteristics of the four-blade ducted propeller are numerically simulated by CFD method. The hydrodynamic performance of the propeller is analyzed by the SST k-ω Model, including the external characteristic parameters such as thrust and torque. The forward velocity at the propeller surface of the ducted propeller, the distribution of the induced velocity along the propeller surface, and the relationship between the propeller thrust and the surrounding velocity field are analyzed. The pressure distribution on the inner wall of the conduct is complicated. The pressure in the front half of the inner wall is small and large in the rear half. Axial, radial and tangential velocity distributions of sections at different distances from the paddle surface are calculated. The velocities on the dorsal side of the propellers are significantly higher than that on the foliar side and lower near the conduit.

Transient flow analysis in axial-flow pump system during stoppage

Axial-flow pumps with siphon outlet are widely used in South-to-North Water Transfer Project of China for the excellent characteristics and good performance in stopping period. The reverse rotational speed and the head of impeller are the key parameters for the system’s safety in stoppage. In this article, the computational fluid dynamics method was used for three-dimensional unsteady numerical simulations. The method based on volume of fluid model was executed on geometrical model of the whole flow system to get the variation laws of internal and external characteristic parameters. Through numerical calculation, the variation laws of the parameters were got in the pump operating condition, braking condition, and turbine condition, and the maximum reverse speed of the impeller was 203.0 r/min (−0.947 times the rated speed). Compared with the designed mode, when the air valve was opened in advance, the pump system would go through the weir flow state first, and a higher head of impeller would be got as a result. When the air valve refused to open, the pump system would get into runaway state. Comparisons of the calculated and measured results indicate the proposed computational fluid dynamics method is reliable in the simulation of the transient flow in axial-flow pump system.

Study on SOC Estimation Based on Circular Optimization for RBF Neural Network

This paper proposed a circular particle swarm optimization least squares (CPSOLS) method which is consisted of the regularized least squares (RLS) method and the adaptive particle swarm optimization (APSO) algorithm. The RLS algorithm optimized the parameters of the RBF network, aiming at the phenomenon of RLS trapping in the local minimum, introduced the penalty factor and used the global optimization ability of the particle swarm optimization algorithm to make it out of the local minimum; simplified the structure of the RBF network and improved the generalization ability of the network. The APSO algorithm weakened the precocious converge phenomena of the particle swarm optimization algorithm, adopted the adaptive selection of the nonlinear dynamic inertia weight which is guided by the control factor of the battery external characteristic temperature parameters, optimized the link weight of the RBF network, improved the state of charge (SOC) estimation accuracy and real-time performance of the RBF network. Using the Arbin multifunctional battery test system BT2000 to collect the sample data of the battery external characteristic parameters, and using the sample data to train and optimize the RBF neural network, and estimate the SOC of the batteries. The results showed that the optimized RBF network improved the SOC estimation accuracy and real-time performance.

Limits of acceptable changing the torque converters parameters in the manufacturing control of blades wheels

The article deals with the question of manufacturing the blades wheels for three-wheel single-stage torque converters designed for automatic transmissions of wheeled vehicles. In the control of series-produced blades wheels for modern torque converters, the most difficult task is to check blades dimensions. Centrifugal pump and centripetal turbine wheels of Allison type torque converters have closed interblade channels, access to which for standard measuring instruments is rather difficult. The application of present-day instruments for such parts, in particular, the control using of universal measuring manipulators with three or more coordinates, makes it possible to check the geometry only in the area near input and output blade tips, which is not sufficient. The integrated control method which is based on the experimental determination of external characteristic parameters for newly manufactured torque converters is proposed. The question of determining the acceptable change limits of external characteristic parameters when checking the quality of blade wheel manufacturing is considered as well. It is proposed to determine the acceptable change limits on the base of quantitative evaluation of parameter deviation influence on vehicle acceleration dynamics

Numerical study on the effects of uneven bottom topography on freak waves

A numerical model is built by using an improved VOF method coupled with an incompressible Navier–Stokes solver. Exploiting the model, the freak wave formation due to the dispersive focusing mechanism is investigated numerically without uneven bottoms and in presence of uneven bottoms. During the freak wave transformation over an uneven bottom in finite water, combined effects of shoaling, refraction and reflection can modify the external characteristics of freak waves, and also can complicate the energy transfers. Furthermore, wavelet analysis method is adopted to analyze the behavior of the instantaneous energy structure of freak waves. It is found that when the bottoms vary in height, the external characteristic parameters and high frequency energy show a similar trend, but the value may be quite different due to the difference in local characteristic of the bottom.

Research on the Relationships between Blade Angles and External Characteristics of a Centimeter Scale Pneumatic Turbine

A pneumatic motor based on the principle of reaction micro turbine has been developed with a rotor diameter of 24 mm. The turbine motor includes a planet-gear reducer with gear ratio of 6.5, generates a maximum mechanical power of 248W with total efficiency 60%. It has been tested to speeds up to 10,000rpm on shaft end. Based on the developed cm-scale micro reaction turbine motors prototype, the mathematical models about the blade angles and its external characteristic parameters were built and carried out, and then their relationships are researched and obtained when the blade angles change within possible ranges.