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It is significant to predict the vibration trend of a hydropower generator unit (HGU) based on historical data for the stable operation of units and the maintenance of power system safety. Therefore, a novel combined model based on ensemble empirical mode decomposition (EEMD), sample entropy (SE), a Gaussian process regression (GPR) model and an autoregressive moving average model (ARMA) is proposed. Firstly, according to the non-linear and non-stationary characteristics of the vibration series, the vibration time series is decomposed into a single component and relatively stable subsequences using EEMD. Then, the SE algorithm reconstructs the subsequences with similar complexity to reduce the number of prediction sequences. Moreover, after judging the stationarity test of the reconstructed sequence, the GPR model and ARMA model are used to predict the non-stationary and stable subsequences, respectively. Finally, the predicted values of each subsequence are synthesised. Furthermore, five related methods are employed to evaluate the effectiveness of the proposed approach. The results illustrate that: (1) compared with EEMD only, EEMD combined with SE can improve prediction accuracy; (2) the reconstruction strategy based on SE can reduce the influence of false modes and improve the prediction accuracy; and (3) the prediction effect of the hybrid prediction model, which reduces the influence of accidental factors, is better than that of a single model in predicting the vibration sequence of an HGU.

To master the basic characteristics of steady-state cornering for a semitrailer, this paper summarises the current modelling methods for handling and stability and discusses their limitations. The classical linear mathematical model for a two-degree-of-freedom (DOF) handling and stability system is used to develop a new model. Analysis methods are proposed to introduce the influence of the camber angle and body roll into the model parameters. Thus, a mathematical model for the lateral stability of semitrailer with five DOFs is established. At the same time, a modified formula to calculate the stability factor of the semitrailer is developed with a MATLAB model to solve the dynamic state equation. The mathematical model, which considers the body roll and the changes in the camber angle caused by roll, compares the turning radius ratio and yaw rate as the evaluation index with the classical linear mathematical model of a two-DOF system. The vehicle parameters for three different types of semi-tractor trailers are used to calculate and compare two mathematical models for handling and stability using real vehicle test data. The results show that the new modelling and analysis method proposed in this paper has a high calculation accuracy and fast calculation speed, is clear and concise, and is consistent with the real vehicle test data. In addition, the accuracy of the new mathematical model for handling and stability and the improved stability factor are verified.

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