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In this paper we present a novel, closed three-dimensional (3D) random vortex dynamics system, which is equivalent to the Navier--Stokes equations for incompressible viscous fluid flows. The new random vortex dynamics system consists of a stochastic differential equation which is, in contrast with the two-dimensional random vortex dynamics equations, coupled with a finite-dimensional ordinary functional differential equation. This new random vortex system paves the way for devising new numerical schemes (random vortex methods) for solving three-dimensional incompressible fluid flow equations by Monte Carlo simulations. In order to derive the 3D random vortex dynamics equations, we have developed two powerful tools: the first is the duality of the conditional distributions of a couple of Taylor diffusions, which provides a path space version of integration by parts; the second is a forward type Feynman--Kac formula representing solutions to nonlinear parabolic equations in terms of functional integration. These technical tools and the underlying ideas are likely to be useful in treating other nonlinear problems., 21 pages, 3 figures, 1 table

The Huge vibration data are generated continuously by many sensors in daily high-speed rotating machinery operations. Accurate online prediction based on big vibration data streaming can reduce the risks related to failures and avoid service disruptions. This paper presents a hybrid nonlinear autoregressive network with exogenous inputs (NARX) model to forecast the remaining useful life of ball bearings through health index based on big vibration data streaming. This approach is validated by a real data from PRONOSTIA experimentation platform and industrial test rig compared with backpropagation neural network (BP), Elman and general regression neural network (GRNN) prediction model. Root mean square error, mean absolute error and correlation coefficient were used as performance indexes to evaluate the prediction accuracy of these models. The mean absolute error, the root mean square error and the correlation coefficient of hybrid NARX model evaluation index are 2.04, 2.85 and 0.98 respectively. It shows that the model presented in this paper has higher prediction accuracy. It can meet the needs of actual ball bearing remaining useful life prediction and also provide reference in other fields.

The health condition assessment of Electric Multiple Unit (EMU) traction motor ball bearing is one of the key issues of high-speed train running safety. In order to assess health condition of EMU traction motor ball bearing, an online-sequential extreme learning machine algorithm based on TensorFlow (TOSELM) is proposed. Samples data set is divided into normal condition and fault condition using vibration data of ball bearings. This paper uses health condition accuracy rate index to evaluate TOSELM algorithm performance. The proposed approach is verified by public data set and private data set. The experiment results show the proposed method is an effective method for ball bearing health status assessment.

The transient thermal performance of rolling bearings affects the mechanical performance and system safety of traction motors. Most of the traditional empirical formulas used in temperature analysis have been simplified and cannot be completely applied to the calculation of heat generation and convection heat transfer coefficients. Based on the comparative analysis of finite element transient temperature and experimental data, this paper proposes a correction method of mathematical model and derives an accurate calculation formula for the heat generation and lubricant convection heat transfer coefficient of ball bearings applicable for the non-driving end in the traction motor of a high-speed EMU (Electric Multiple Unit). The accuracy of the results has been verified by durability experiment data. In addition, with changes in speed, radial load and other factors taken into account, we have analyzed the influence of these time-varying factors on ball bearing temperature, as well as the temperature distribution law of each component in a grease-lubricated bearing, in a bid to lay a foundation for follow-up research on the heat transfer laws of traction motors and rolling bearings.

Due to the complexity of the structures and magnetic field distribution in the end region of large turbogenerators, using a 330-MW water-hydrogen-hydrogen cooled turbogenerator as an example, the 3-D mathematical and geometry models of the nonlinear transient eddy current field were given. Taking the nonlinearity of the core material and the influences of noncontact between the copper screen and the clamping plate, as well as the shape of stator end windings into consideration, the 3-D transient electromagnetic field was calculated, and the losses of different metal parts were obtained by the finite-element method. The calculated power losses were applied to the thermal field as heat sources. Temperatures of the copper screen were gained. The calculated results of copper screen were well coincident with the test data. Hence, the calculated results are accurate, and the method of calculation is effective.

Since the structure of a large capacity turbogenerator is complex in the end region, accurate calculation about the leakage magnetic field becomes a key factor in the design. In this paper, a 330-MW level turbogenerator is electromagnetically analyzed and investigated with different metal screens in the end region. Its nonlinear transient electromagnetic field and eddy current loss were calculated by using the time step finite-element method (FEM). The influences of metal screen materials on the electromagnetic field and eddy current loss were compared and analyzed. All of these will contribute to the turbogenerator engineering design. Using the loss gained by the magnetic field calculation as a heat source, the thermal field of the end region with a copper screen was calculated. Compared with the test data, the calculated temperature results match well with the measured data.

The voltage unbalance can introduce the torque ripples for a doubly fed induction generator (DFIG), which may bring the stress on the drive train. Thus, this paper proposes a direct power control (DPC) strategy of a DFIG for torque ripples suppression under unbalanced grid voltage conditions. Under the unbalanced grid voltage conditions, the stator reactive power pulsations are proportional to the torque ripples, the torque ripples can be suppressed by smoothing the reactive power. Then, a reduced-order generalized integrator (ROGI) for the negative-sequence components was added to the reactive power control loop, thereby constructing a proportional-integral (PI) plus a ROGI (PI+ROGI) regulator. Finally, the simulation results were provided to validate the satisfactory steady-state performance and the fast dynamic responses of the proposed DPC scheme.

This paper has proposed a novel (Integral-Proportional) I-P controller in speed control of a permanent magnet synchronous machine (PMSM) drive system, it removes the side effects such as slow dynamic response of the conventional I-P controller and maintains the advantages in the meantime. Theoretical studies for the conventional P-I, I-P and the proposed controllers in the s-domain and z-domain are presented, and the transfer functions of them are derived. The responses of the controllers to step input reference and sudden change in reference speed and load are analysed in simulation and experiment. Both the simulation and the experimental results show the effectiveness of the proposed controller.

The DFIG is excited by converter which is connected rotor. The performance of wind turbine is depended on the matching conditions of the DFIG and converter. And the DFIG equivalent circuit parameter will influence the generator electromagnetic design. Based on the equivalent circuit and the test data, this paper put forward a kind of theory and calculation method to separate the equivalent circuit parameter of DFIG, and the rationality of this method is proved by comparing the result of test and calculation.

The doubly excited brushless reluctance machine (DEBRM) is a new type of reluctance machine and is attractive for converter-fed variable speed drive applications and variablespeed constant-frequency generating systems. The DEBRM system features not only simplicity, robustness and reliability of the reluctance or cage-rotor inductance machines, but a much smaller power electronic converter, compared to a conventional AC induction machine. This paper bases on winding function theory, establish the linear model of the DEBRM to calculate the air-gap flux distribution and winding flux linkages of the two sets of stator windings. The self and mutual inductance of the two stator windings is computed for equivalent circuit derivation, and the DEBRM torque capabilities are investigated with 3-pole rotor machine. All the results are used to highlight the common principles of electromechanical energy conversion for the DEBRMs with unconventional magnetic structures and provide insights into the optimal design and control of a practical DEBRM.

The variable-frequency induction motor used in electric vehicle is investigated in this paper. Firstly the design method of a voltage inverter-fed induction motor is introduced, and then the calculation methods of electromagnetic parameter are presented and programmed in VB (Visual Basic) software. Based on the geometrical dimensions and parameters, a simulation model in the vector control system is used to predict the performances of this machine. The comparison between the simulation results and the experimental results shows that the performances of the design machine are matched for its application.

This paper presents a design for sliding mode-PI current regulators that may be used to switched reluctance motor (SRM) drives. Based on the linear model and the actual magnetization curves for the SRM simulation, the sliding mode-PI control of SRM is given to execute the current regulation. A high-performance fully digital controller has been designed for the control of SRM built for vehicle propulsion. The SRM is specifically designed and built to have high density and low noise. The controller is designed to maximize the machine efficiency, the peak overload capability, and to minimize torque ripple at low speed. The effectiveness of sliding mode-PI of SRM is researched. Experimental results demonstrate that sliding mode-PI control of SRM drives for KV has excellent performance.

We consider a queueing network with two classes of customers and three workstations, each consists of one server and one buffer. One workstation is in the first stage and two parallel workstations in the second stage. Each workstation in the second stage receives customers from its own arrival stream. The buffer in the first stage consists of sufficient customers of both classes. A reward is earned whenever the first stage accepts a customer and a holding cost is incurred by a customer in the queue in the second stage. The objective is to dynamically select the class of customer to be next served at the first stage, based on the state of the system, so as to maximize the average benefit over an infinite horizon. In the paper, a fuzzy approach is presented to solve this complex problem. Simulation shows that the approach is efficient and promising.