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Based on the panel data of 284 prefecture-level city in China from 2005 to 2019, this paper measures the urban capital allocation efficiency and takes smart city construction as a quasi-natural experiment. The multi-period difference-in-differences (DID) model has been built to verify the internal mechanism and practical effect of smart city construction driving the optimal allocation of capital. The results show that the construction of smart cities has significantly improved the efficiency of capital allocation, and the conclusion remains valid after a series of robustness tests; Mechanism analysis shows that strengthening environmental regulations and improving innovation capabilities, together with the construction of smart cities, have promoted the improvement of capital allocation efficiency; The heterogeneity analysis indicates that the effect of smart city construction on capital allocation efficiency is influenced by the administrative level and regional heterogeneity characteristics of the city. This paper provides empirical evidence for the policy effectiveness of smart city construction and provides policy enlightenment on how to optimize capital allocation. • The construction of smart cities significantly alleviates urban capital mismatch. • The transaction cost effects, environmental regulation effects, and innovation capability effects are important mechanisms. • The correction effect is influenced by the administrative level and regional characteristics. [ABSTRACT FROM AUTHOR]

Precise prediction of PV power in the short term is crucial for maintaining power system stability and balance. However, the performance of conventional time series prediction models on short-term long series prediction is scarcely sufficient because of the stochastic and turbulent character of PV power data. This work suggests a PV short-term power forecast model based on weather type, AHA-VMD-MPE decomposition reconstruction, and improved Informer combination to tackle this issue. Firstly, a SUM-ApEn-K-mean++ multidimensional clustering method to group the dataset by weather conditions. Then an AHA-VMD-MPE decomposition model is proposed to decompose the historical power data Finally the Informer model is improved and the improved model is utilized to predict the PV power under various weather conditions. The model exhibits great accuracy and stability in short-term PV power prediction, as demonstrated by the experimental results, which were validated using measured data from many PV power plants. • A weather typing method based on SUM-ApEn-K-means++ has been proposed. • A sequence decomposition method based on AHA-VMD-MPE has been proposed. • The improved Informer model has been applied to short-term PV forecasting. • Validation has been performed on multiple time scales. [ABSTRACT FROM AUTHOR]

The effect of surface roughness on the transient characteristics of the hydrodynamic cylindrical bearing during startup is studied. A mixed lubrication model considering both asperity contact and hydrodynamic fluid flow is solved. The asperity contact pressure is obtained by the Greenwood-Williamson (GW) contact model. The hydrodynamic pressure is calculated by modified average Reynolds equation with finite element method (FEM). The transient movement of the journal center, the transient average film thickness, the hydrodynamic pressure and the contact pressure are presented for different surface roughnesses. The contact time and contact zone in different types of surface roughness are obtained. The influences of the standard deviation of asperity height ( σ ) and rough surface patterns on these parameters are analyzed. The results show that the surface roughness has an important influence on the transient characteristics of the bearing during the initial period of startup. [ABSTRACT FROM AUTHOR]

The dynamic contact behavior of hydrodynamic journal bearings during start-up is investigated. The hydrodynamic oil force and asperity contact force are obtained by solving the mixed lubrication model. The motion of the journal center, the contact time, and the lift-off speed of the bearing are determined. The effects of the relative clearance and acceleration time are discussed. The result shows that the hydrodynamic oil force increases sharply during the early stage of the start-up process, leading to a sharp decrease in the contact force. An increase in the relative clearance of the bearing generates a decrease in both the contact force and the contact time. Also, a high start-up acceleration leads to a sharp decrease in the contact force. [ABSTRACT FROM AUTHOR]

In present work, in order to optimize partial slip zone for heavily loaded journal bearings, an isothermal hydrodynamic model considering wall slip occurring at oil-bush interface is built. Two-component slip model is utilized to calculate slip velocity. The performances of the journal bearing in different slip zone shapes and eccentricity ratios are evaluated. The optimal slip parameters in a range of eccentricity ratios are selected by considering their effects on hydrodynamic behavior, such as load carrying capacity and friction coefficient/torque. In addition, the application of optimal partial slip zone is presented. Results show that the optimal range of slip zone in high eccentricity ratio is quite restricted. The slip zone should be located at the convergent region of the film. The circumferential end of slip zone should locate at the convergent region and be close to the position of minimum film thickness. It is better to widen the axial length of slip zone, i.e. maximum rectangular shape could better improve bearing performance. • An isothermal hydrodynamic model considering wall slip occurring at oil-bush interface is built. • The performances of journal bearing in different slip zone shapes and eccentricity ratios are evaluated. • The optimal slip parameters in a constant load are selected with considering a range of eccentricity ratios. • The application of optimized partial slip zone in specific operations is presented. [ABSTRACT FROM AUTHOR]