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As the modern industry rapidly advances toward digitalization, networking, and intelligence, intelligent fault diagnosis technology has become a necessary measure to ensure the safe and stable operation of mechanical equipment and effectively avoid major disaster accidents and huge economic losses caused by mechanical equipment failure. As the "power heart" of hydraulic transmission systems, hydraulic piston pumps (HPPs) occupy an important position in aerospace, navigation, national defense, industry, and many other high-tech fields due to their high-rated pressure, compact structure, high efficiency, convenient flow regulation, and other advantages. Faults in HPPs can create serious hazards. In this paper, the research on fault recognition technology for HPPs is reviewed. Firstly, the existing fault diagnosis methods are described, and the typical fault types and mechanisms of HPPs are introduced. Then, the current research achievements regarding fault diagnosis in HPPs are summarized based on three aspects: the traditional intelligent fault diagnosis method, the modern intelligent fault diagnosis method, and the combined intelligent fault diagnosis method. Finally, the future development trend of fault identification methods for HPPs is discussed and summarized. This work provides a reference for developing intelligent, efficient, and accurate fault recognition methods for HPPs. Moreover, this review will help to increase the safety, stability, and reliability of HPPs and promote the implementation of hydraulic transmission technology in the era of intelligent operation and maintenance. [ABSTRACT FROM AUTHOR]

The analytical model for tornado vortices is crucial in both the wind field characterization and the tornado-resistant design of civil structures. The objective of this study is to derive a novel three-dimensional analytical tornado model from the vortex governing equations simplified based on the force balance analysis in tornado-like vortices (TLVs). First, TLVs with different swirl ratios are generated in a numerical simulator utilizing the large-eddy simulation. Then, the forces in the axisymmetric vortex governing equations are calculated for time-averaged TLVs. The governing equations in the single-cell TLV are simplified by ignoring some significantly small terms. Finally, a novel three-dimensional analytical tornado model, which contains the radial, tangential, and vertical velocity as well as the pressure, has been proposed and validated. The result shows that the force balance in the single-cell TLV is simpler than that in TLVs with larger swirl ratios. In the single-cell TLV, the viscous forces in the radial and vertical directions can be neglected, while the tangential viscous force remains to play an important role in the force balance. The proposed model mitigates the limitations of existing models in describing single-cell tornado vortices, such as only two-dimensional velocity being given, the neglection of the vertical shear effects near the ground, and the infinite velocity at high altitudes. It shows good agreement with the numerical and experimental TLVs as well as the real tornado. [ABSTRACT FROM AUTHOR]

Large-scale modern wind turbines at standstill are prone to vortex-induced vibrations. In this study, we propose the use of the aero-damping map to investigate the complex vibration responses of the wind turbine airfoil at 90° of attack angle with different levels of structural dampings. The vibration amplitude and response frequency in the lock-in condition and soft lock-in conditions agree well with the contour line on which the sum of aerodynamic damping and structural damping is equal to zero. The mechanism of frequency soft lock-in is explored from the aspect of energy transfer that when the equilibrium state cannot be maintained at the natural frequency due to high structural damping, the system locks to a frequency between the natural frequency and vortex shedding frequency of the stationary airfoil to achieve lower aerodynamic damping and more energy absorption from the air. The transient response of the beat vibration is also investigated with the aero-damping map combined with the dynamic mode decomposition method. It is found that the lock-in mode and von Kármán mode coexist in the unsteady flow field during beat vibration. The competition between the two modes causes the system to be in an intermittent state of alternating frequency lock-in stage with lower aerodynamic damping and unlock-in stage with higher aerodynamic damping, hence resulting in the amplitude amplification and attenuation alternately. [ABSTRACT FROM AUTHOR]

Light field particle image velocimetry (LF-PIV) can measure the three-dimensional (3D) flow field via a single perspective and hence is very attractive for applications with limited optical access. However, the flow velocity measurement via single-camera LF-PIV shows poor accuracy in the depth direction due to the particle reconstruction elongation effect. This study proposes a solution based on a dual-camera LF-PIV system along with an ordered-subset simultaneous algebraic reconstruction technique (OS-SART). The proposed system improves the spatial resolution in the depth direction and reduces the reconstruction elongation. The OS-SART also reduces the computational time brought by the dual-camera LF-PIV. Numerical reconstructions of the particle fields and Gaussian ring vortex field are first performed to evaluate the reconstruction accuracy and efficiency of the proposed system. Experiments on a circular jet flow are conducted to further validate the velocity measurement accuracy. Results indicate that the particle reconstruction elongation is reduced more than 10 times compared to the single-camera LF-PIV and the reconstruction efficiency is improved at least twice compared to the conventional SART. The accuracy is improved significantly for the ring vortex and 3D jet flow fields compared to the single-camera system. It is therefore demonstrated that the proposed system is capable of measuring the 3D flow field fast and accurately. [ABSTRACT FROM AUTHOR]