A piezo-windmill excited by rotating magnets was presented to harvest energy from wind of low speed and wide range speed. The exciting force exerting on the piezo-windmill is general periodic ...(inharmonic). An analytical model for performance evaluation was established based on Fourier series as well as superposition principle and simulated to obtain the influence of system parameters on the response of the piezo-cantilever in terms of the number of optimal rotary speeds and the relative amplitude ratio. A prototype was fabricated and tested to prove the analysis results. The research results show that, under other parameters given, there are multiple optimal rotary/wind speeds for the amplitude-ratio/generated-voltage to achieve peak. With the increasing of the number of exciting magnets, the number of the optimal rotary/wind speeds decreases. There is a moderate quantity of exciting magnets for the peak amplitude-ratio/generated-voltage to achieve maximum. Besides, with the increasing of proof mass, the optimal speeds decreases, and the relative amplitude-ratio/generated-voltage increases.
•A piezo-windmill excited by rotating magnets is presented to harvest wind energy.•Excitation force exerting on piezo-windmill is general periodic instead of harmonic.•Analytical model of evaluating piezo-windmill under general periodic force is built.•There are multiple optimal wind-speed ranges for the amplitude ratio to achieve peak.•The influence of the number of exciting magnets on the piezo-windmill is obtained.
•A stereo-camera 3D-DIC system for full-field vibration measurements is presented.•The optical setup is based on two low frame rate cameras and a multimedia projector.•A down-sampling approach is ...used to overcome the Nyquist-Shannon theorem limitation.•Fringe projection is introduced to solve the stereo matching problem.•An innovative time-domain image filtering is proposed to enhance measurement results.•3D vibration amplitudes lower than 10 μm at 6.5 kHz have been measured with a 178 fps camera.
The digital image correlation (DIC) was used in this paper to obtain full-field measurements of a target vibrating at a frequency higher than the maximum cameras’ frame rate. The down-sampling technique was implemented to compensate for the cameras’ moderate frame rate, thus getting an accurate displacement acquisition even at 6.5 kHz. Two innovative methods to support the DIC application were introduced. The use of fringe projection (or structured light), initially applied on the sample at rest, reduced the effort and time required for the stereo matching task’s solution and improved this setting’s accuracy and reliability. Additionally, a new time-domain image filtering was proposed and tested to improve the quality of the obtained DIC maps. In combination with the down-sampling, the effect of this filtering technique was tested in this work at (approx.) 2500 and 6500 Hz by measuring the response of a bladed disk to sinusoidal excitation. Evidence of improved results was observed for both frequencies for amplitudes in the range of 10 µm.
In order to investigate the interaction effect between the transient wear behavior and the lubrication characteristics of the main bearing in low-speed diesel engine under the actual working ...condition, a coupling model of mixed elastohydrodynamic transient lubrication and time-varying wear is constructed. The transient lubrication model considering the journal misalignment and elastic-plastic asperity contact is used to consider the lubrication characteristics of the main bearing. The wear mechanism of the main bearing material (Babbitt alloy) is found to be surface fatigue wear mainly by the experiments under the equivalent lubrication state, thus the wear model is based on the fatigue damage theory. Several experiments were conducted to verify the accuracy of the coupled model. It is found that the wear gradually increases with increases with wear time, and meanwhile, the lubrication characteristics also change with the wear status. In addition, the effect of the parameters including radius clearance, rotation speed, journal misalignment and bearing loads on the properties of lubrication and wear were investigated. This work would provide practical support for the investigation of wear and lubrication behavior under actual low-speed diesel engine operation.
•A coupling analysis model of mixed elastohydrodynamic transient lubrication and time-varying wear of the main bearing under actual dynamic load was established.•The wear mechanism of the main bearing material is found to be surface fatigue wear mainly by the experiments under the equivalent lubrication state of actual condition in low-speed diesel engine.•The verifications of axis orbit, friction coefficient and wear depth indicate the accuracy of the coupling model.•The improvement of bearing lubrication performance after stable wear under actual working conditions was revealed.
In this paper, a simple signal injection method is proposed for sensorless control of permanent-magnet synchronous machine (PMSM) at a low speed, which ideally requires one voltage vector only for ...position estimation. The proposed method is easy to implement, resulting in low computation burden. No filters are needed for extracting the high-frequency current signals for position estimation. The use of low-pass filters (LPFs) in the current control loop to obtain the fundamental current component is not necessary. Therefore, the control bandwidth of the inner current control loop may not need to be sacrificed. The proposed method may also be further developed to inject two opposite voltage vectors to reduce the effects of inverter voltage error on the position estimation accuracy. The effectiveness of the proposed method is demonstrated by comparing with other sensorless control method. Theoretical analysis and experimental results are given for validating the proposed new sensorless control method.
Ni-Cr-W matrix cermet composites were prepared using powder metallurgical technology, and their microstructures, phase compositions, and mechanical properties were determined. Specifically, the ...tribological performances of the Ni-Cr-W composites were evaluated at a speed of 0.5 mm/s from room temperature to 800 °C, and their friction-reducing mechanism was clarified. The results showed that the NiCrW/Al2O3/Ag composite had the highest mechanical strength, with a 94.5 % increase in tensile strength compared to NiCrW/Al2O3. The NiCrW/Al2O3/SrCO3 composite exhibited the best high-temperature tribological performance because the chemical reaction on the friction surface generated new lubricating phases consisting of NiO, WO2, WO3, and Sr2CrO4. These acted synergistically lubricate and anti-wear with the Al2O3, Cr2O3, and NiCr2O4, and formed a continuous glaze layer on the wear surface. Furthermore, the multiple roles of nano-alumina in the obtained composite and its service in friction were discussed.
Abstract
In the ballistic performance testing field of human body protection and armor protection, aiming at the demand of sub-caliber launch of assembled ammunition with the mass range of 4 ~ 16 g ...and velocity range of 280 ~ 500 m/s, establish the mathematical model of interior ballistic with MATLAB, calculate the interior ballistic state, and analyze the influence law of the change of charge parameters and projectile mass with the launch velocity. The results show that the propellant does not burn completely as the small-mass projectile leaves the barrel; under the same chamber volume, the projectile velocity increases with the charge mass, and this trend gradually decrease with the increasing chamber volume; under the same charge mass, the projectile velocity decreases with the increase of chamber volume, and this trend gradually increases with the increasing charge mass; under the same projectile mass, the projectile velocity decreases with the increase of charge mass, and this trend remains basically unchanged as the projectile mass increases. The analysis and calculation results are verified by the firing test. The results show that although there are differences between the actual charge quality and the calculation results, the obtained velocity changing trend is basically consistent with the trend revealed by the calculation results. The analysis and verification results can provide guidance for understanding the influencing factors affecting the launch of sub-caliber low-speed projectile, and have positive significance for improving the ballistic performance testing ability and promoting the development of the protection industry.
This paper describes end-winding heat transfer under forced external cooling, a cooling arrangement which is not commonly studied in literature. The average end-winding heat transfer under different ...rotational speeds and external coolant supply is studied through the use of computational fluid dynamics. As a result of the analysis, an analytical expression for the combined effect of rotation and external forced cooling is proposed. Finally, the established expression is used in an lumped-parameter thermal-network analysis and resulting temperatures are compared with corresponding measurements.
This article presents a sensorless motor drive scheme by a fusion of the electrical model-based estimation and the mechanical model-based observer with respect to the position servo with a heavy ...load. The signal injection is applied to extract the position information from the magnetic saliency. However, in the low-speed and heavy-load scenarios, the position observability degenerates in the electrical model due to the core saturation. Nevertheless, the mechanical motion states, including the rotor position, can always be adequately extracted from the mechanical motion model. The extended Kalman filter (EKF) is adopted to fuse the information from the mechanical motion perception and the signal injection-based estimation so that the speed estimate quality gets significant improvement especially when the core saturation occurs. A disturbance-rejection mechanism is introduced to resist the parameter inaccuracy and inconstancy of the EKF model. The fused estimates are applied with a model predictive control in the speed loop to realize the servo control. The sensorless scheme is validated in a heavy-load pendulum servo bench, 200% of the machine rating torque, driven by a surface-mounted permanent-magnet synchronous machine.
Vibration signal always performs poorly in the fault diagnosis of low-speed rolling bearings. The fact that rolling bearings running under different speed conditions further increases the difficulty ...of fault diagnosis on low-speed bearing. To address the above problems, this article proposes a fault diagnosis method for low-speed rolling bearings based on acoustic emission (AE) signal and subspace embedded feature distribution alignment (SADA). First, the AE signal of low-speed rolling bearing is collected and the spectral dataset is constructed. Second, subspace alignment is used to align the basis vectors for both domains in order to prevent feature distortion. Then, a base classifier is trained to predict the pseudolabels of the target domain, which is used to quantitatively estimate the weight of the edge distribution and conditional distribution of the two domains for adaption. Finally, following the structural risk minimization (SRM) framework, a kernel function is constructed to establish the classifier f , which iteratively updates the pseudolabels in the target domain and obtains the coefficient matrix of the final framework to complete the identification task. The feasibility and effectiveness of the proposed method are verified by two AE datasets of low-speed rolling bearing.
In an industrial environment, a large part of the solutions used in machine parks is based on rotating systems. Therefore, the branches of diagnostics in this area are subjected to extensive research ...so that they effect with more and more new solutions. This article presents the problem of selected most common faults in a low-speed machinery environment. Presented chapters define the concept of symptoms and diagnostics and define its goals. Selected issues of the analysis of diagnostic signals were also discussed.
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