At present, traditional data-driven nonlinear system modeling methods primarily focus on model fitting and application. In this context, this paper constructs an upper boundary model based on least squares support vector regression (LSSVR) for the maximum tolerable output of a critical parameter from the system, which is influenced by uncertainty. The study delves into the relationship between the balance of model accuracy and sparsity, and its effect on the model output. First, by utilizing the optimization problem of LSSVR, the original equality linear constraints are transformed into inequality constraints that satisfy the upper boundary model. Next, to improve the model’s accuracy, an inequality constraint based on the approximation error between the predicted output of the upper bound model and the actual output is introduced. Meanwhile, the LSSVR’s weight L₂-norm is employed to control the complexity of the upper boundary model’s structure, thereby constructing a new objective function and establishing a new optimization problem that satisfies the inequality constraints of the upper bound model. Finally, the Lagrangian function is introduced into the optimization problem, and the Karush-Kuhn-Tucker conditions are used to derive the corresponding dual optimization problem, which is then converted into a standard quadratic programming problem to solve for the parameters of the upper bound model. Since the new optimization problem satisfies convexity, the solution for the model coefficients is globally optimal. The effectiveness and superiority of the proposed method are validated through experimental analysis, where the maximum approximation error, root mean square error, and sparsity-related metrics are used to reflect the model’s accuracy and sparsity characteristics.

Large diameter wedge gate valves are commonly used in petroleum and chemical pipeline systems, where they endure a coupled load of dynamic pressure from the medium and thermal loads. This coupled load not only exacerbates the structural deformation of the valve but also increases the friction wear between the valve stem and the valve cover. Additionally, it may affect the fluid flow pattern, and, in severe cases, may induce flow-induced vibration, leading to valve stem fracture issues. Aiming at the problem of valve stem fracture in the practical engineering application of DN1 200 mm large-caliber gate valve, this paper uses the process discrete analysis method to divide the position of multi-valve plate, adopts ANSYS numerical simulation technology to visualize the flow characteristics of flow field in the gate valve, and employs Fourier signal analysis method to reveal the pressure pulsation response in fluid domain. Then, the modal analysis and harmonic response analysis of the valve pipeline flow system are carried out, and the resonance characteristics of valve stem and gate plate with multi-physical field coupling under specific stroke are studied. The results show that, when the gate valve opens/closes and the stroke is small, the large Karman vortex street and backflow phenomenon are generated due to the disturbance of the gate plate after the valve, the fluid pressure pulsation increases and the flow condition is disordered, which induces the valve pipeline flow system to produce a large common amplitude value, resulting in the fracture of the valve stem. Therefore, this paper proposes and verifies that the addition of expansion pipe can alleviate the vortex and backflow behind the valve, reduce the pressure pulsation and avoid the flow-induced resonance. Qualitative and quantitative analyses are finally performed to determine the expansion pipe size to weaken the fluid pressure pulsation and the common amplitude value. The comparative study shows that the vibration reduction effect is the best when the diameter of the expansion pipe is 1.3 times that of the pipe (1 560 mm) and when the length of the expansion pipe equals the diameter of the pipe (1 200 mm). The obtained results have certain guiding significance for the vibration reduction optimization research of large-caliber gate valves.

Addressing the issues of long computation time and low efficiency in numerical solutions for turbulent noise intensity in conventional air/water medium, a neural network prediction model for bluff body/cavity turbulent noise intensity in air/water medium under similar flow conditions was established. This model efficiently predicts aerodynamic noise intensity at the same Reynolds number based on underwater noise intensity, providing technical support for the efficient prediction and control methods of turbulent noise intensity in air/water medium, as well as the research on the interchangeability of noise testing medium. Particle image velocimetry experiments were conducted to measure the flow velocity around open-slot cylinders, validating the effectiveness of the numerical methods. A numerical model for turbulent noise intensity in air/water medium was constructed using the large eddy simulation method, achieving an average velocity calculation error of less than 2.25% and a Strouhal number error of 0.89% between test and simulated values. The numerical model generated 1 338 data points, which were used to construct a training sample dataset. Then, a backpropagation (BP) neural network was built based on key flow parameters to map the relationship between turbulent noise in air/water medium. The Levenberg-Marquardt algorithm was employed to train the predictive model, with the Sigmoid function selected as the activation function. The network comprises 8 input neurons, 1 output neuron, and a single hidden layer. The results demonstrate that the proposed BP neural network prediction model can predict aerodynamic noise intensity at the same Reynolds number as underwater noise intensity, with a maximum prediction error of less than 6.21 dB and an average error of 0.44 dB; that the model exhibits good generalization ability, with an error of 0.27 dB at irregular points in the test set; and that, under comparable hardware conditions, the numerical solution method required approximately 30 hours for computation, while the BP neural network prediction model took only 70 seconds, significantly improving the computational efficiency.

In order to reveal the influence factors of regulating valve’s service life in coal liquefaction, and ensure the safety and stability of coal liquefaction system operation, numerical simulations were carried out based on turbulence model, cavitation model and discrete phase model to address the complex multiphase flow problem of gas liquid solid. In the investigation, the distribution characteristics of erosion wear and cavitation inside the valve were studied, and the coupled damage rate of cavitation erosion in key parts of the valve core was obtained. Then, the coupled cavitation erosion wear behavior of solid multiphase flow in the flow channel during the operation of the regulating valve was reproduced through experiments, and the damage morphology of the metal tin valve core under continuous cavitation erosion composite action was analyzed. Finally, the damage degree of tin valve cores under different working conditions was quantitatively evaluated using roughness values, and the impact fatigue and composite damage mechanism of valve core surfaces were explored. The results show that the main area where cavitation occurs in the coal liquefaction regulating valve is from the throttle port to the head of the valve core. The range of cavitation increases with the increase of inlet pressure, and the cavitation intensity also increases accordingly. Under different import pressures, the extreme value of the surface erosion rate of the valve core appears at the head of the valve core, with a maximum erosion wear rate of 1.42 × 10^-4 kg/(m²·s), which is more than 10 times that of other erosion areas. The reason is that the high-speed fluid backflow at the head of the valve core carries particles and impacts the head of the valve core, while the collapse of bubbles impacts the surface of the valve core. In addition, it is also found that the surface of the regulating valve core, which works for a long time under the coupling effect of erosion and cavitation, exhibits characteristic morphology such as grooves and corrosion points.

Due to their small size, low cost and high reliability, permanent magnet synchronous motors have been widely used in the fields of industrial production, transportation and household appliances. Electrolytic capacitor is the middle part of drive system connecting the power grid and the motor. Its life is easily affected by external factors such as environmental temperature and humidity, which seriously restricts the stability and reliability of the motor products. Therefore, the drive system without electrolytic capacitor has become the research hotspot at home and abroad. Scholars have proposed various control strategies for achieving high power factor, suppressing current harmonics, and stabling motor operation. In this paper, the factors affecting the power quality and motor performance of drive system without electrolytic capacitor are analyzed, the advantages and disadvantages of different control strategies are compared, the control strategies for optimizing system performance are summarized, and the driving technology of permanent magnet synchronous motor without electrolytic capacitor is prospected. There comes to the following conclusions: at present, the current power quality is improved mainly through the optimization of motor control algorithm, but the existing methods, such as indirect power control, direct power control, compensation phase current’s non-ideal characteristics and regenerative energy control, all have some limitations; the improvement of motor performance is mainly carried out by the traditional control strategies based on constant bus voltage, such as weak magnetic control and over-modulation, while simultaneously suppressing beat phenomenon and ensuring stable operation of the motor, thus, it is necessary to further consider whether the power factor and current harmonics meet the standards in the subsequent research. Moreover, it is pointed that the comprehensive performance control of non-electrolytic capacitor motor, which takes into account both power quality and motor performance, is the biggest problem faced by the current non-electrolytic capacitor control system. Therefore, it is necessary to carry out a collaborative control for the power grid and the motor to rationally allocate functions and avoid conflicts.