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Improved deep convolution neural network (CNN) for the identification of defects in the centrifugal pump using acoustic images

This work addresses the challenging problem of finite-time fault tolerant attitude stabilization control for the rigid spacecraft attitude control system without the angular velocity measurements, in the presence of external disturbances and actuator failures. Consider the severe circumstances with above failures and uncertainties, a novel continuous finite-time Extended State Observer is first established to observe the attitude angular velocity and the synthetic failure simultaneously. Unlike the existing observers, the finite-time methodology and Extended State Observer are utilized, to achieve the finite-time uniformly ultimately bounded stability of the attitude angular velocity and extended state observation errors. Furthermore, a novel continuous finite-time attitude controller is developed by using the nonsingular terminal sliding mode control and super-twisting method. The main feature of this work stems from our use of multiply advanced techniques or methodologies that enables the finite-time stability of the closed-loop attitude control system and the designed control scheme is continuous with the property of chattering restraining. Finally, numerical simulation results are presented to illustrate the effectiveness and fine performances of the finite-time observer and controller for the attitude control system.

Finite-time Extended State Observer based fault tolerant output feedback control for attitude stabilization.

Application of flow control strategy of blowing, synthetic and plasma jet actuators in vertical axis wind turbines

The aerodynamics and flow physics of a NACA 4412 airfoil in ground effect for a wide range of angles of attack from −4 to 20 deg are investigated by numerical simulations. The compressible Reynolds-averaged Navier–Stokes equations and shear-stress transport k-ω turbulence model equations are solved using the finite-volume method. Analyses of the computed results show that the angle of attack versus height (above the ground) plane can be divided into three regions based on the sign of the lift increment value: region I of positive ground effect, and regions II and III of negative ground effect. For low-to-moderate angles of attack, when the ride height is reduced, the airflow is blocked in the convergent passage between the lower surface of the airfoil and the ground, resulting in increase of pressure on the lower surface of the airfoil. As a consequence, the effective angle of attack decreases, and there is less upward deflection of the streamlines, resulting in an increase in pressure on the upper surfac...

Airfoil Aerodynamics in Ground Effect for Wide Range of Angles of Attack

It is necessary to study the influence of atmospheric disturbance on aircraft motion for the motion compensation sensitivity requirements of airborne SAR. Most motion compensation study for airborne SAR is focusing on the effects of assuming motion errors on SAR images from the early years of airborne SAR development. In this paper, based on power spectra density (PSD) method, the spectra of aircraft motion that containing all the response motion information due to atmospheric disturbance can be calculated from the given spectra of the atmospheric turbulence and the transfer function between aircraft motion and atmospheric turbulence. As an example, one common atmospheric turbulence model is applied to get the lateral/longitudinal uncontrolled and controlled aircraft motion. At low frequency domain, our results show that the controlled aircraft motion is suppressed in comparison with the uncontrolled aircraft motion as wished; whereas, at high frequency domain, there is no difference between the spectra of controlled and uncontrolled aircraft motion, i.e., each has a scaling behavior with a scaling exponent corresponding exactly to the atmospheric turbulence model. Based on these aircraft motion analysis, an acceptable residual motion error is predicted from the motion compensation requirements, which suggests that motion compensation for airborne SAR is unavoidable and should pay more attention on the medium frequency range.

Studying atmospheric turbulence effects on aircraft motion for airborne SAR motion compensation requirements

Conditional Sampling and Wavelet Analysis in Early Stage of Step-Generated Transition

\n The varying speed impact of wedge bodies on a water surface is studied numerically and theoretically to provide a fast and accurate prediction of the pressure on the wedge surface and the motion of wedge bodies during the free impact, which can be a two-dimensional (2D) model for the strip theory or 2D + t strategy. The fluid is assumed to be incompressible, inviscid, with negligible gravity effect and surface tension effect. The computational fluid dynamics (CFD) method is based on the volume of fluid (VOF) method and global moving mesh (GMM) method. Various cases of a varying speed impact are shown for the CFD method, and a linear relationship between the pressure coefficient Cp and a dimensionless variable K is observed. To clearly explain the linear relationship between Cp and K, we follow the potential theory to derive the Cp expression based on several assumptions on the free surface drawn from the CFD results. The Cp expression and the motion of wedge bodies for a free impact derived from it are considered as an approximate solution for a varying speed impact. The approximate solution is compared with the existing analytical models and the published experimental data. The approximate solution can work well for different deadrise angles, while the existing analytical models can only be used for small deadrise angles. Good agreement is also obtained between the approximate solution and the experimental test results, including the time history of wedge acceleration and the pressure on the wedge surface.

Numerical and Theoretical Study on the Varying Speed Impact of Wedge Bodies on a Water Surface

By using the finite volume method with volume of fluid model and global dynamic mesh technique, the effects of Froude number and geometry on the water entry process of a 2-D ellipse are investigated numerically. For the time history of the vertical force, the computational fluid dynamics (CFD) results match the experimental data much better than the classical potential-flow theories due to the consideration of the viscosity, turbulence, surface tension, gravity, and compressibility. The results show that the position of peak pressure on ellipse shifts from the spray root to the bottom of ellipse at a critical time. The critical time changes with the geometry and Froude number. By studying the vertical force, the ellipse water entry process can be divided into the initial and late stages based on the critical dimensionless time of about 0.1. The geometry of the ellipse plays a dominant role in the initial stage, while the Froude number is more important in the late stage of entry. The classical Wagner theory is extended to the ellipse water entry, and the predicted maximum value of vertical force coefficient in the initial stage is 4πa/b that matches the CFD results very well, where a and b are the horizontal axis and vertical axis of the ellipse parallel and perpendicular to the initial calm water surface, respectively.

Effects of Froude number and geometry on water entry of a 2-D ellipse

In the traditional high-lift system design process, the aerodynamics optimization design and mechanism design are decoupled, which often introduces contradiction and trade-off between them. In this...

Peiqing Liu

Papers

Studying atmospheric turbulence effects on aircraft motion for airborne SAR motion compensation requirements

Conditional Sampling and Wavelet Analysis in Early Stage of Step-Generated Transition

Numerical and Theoretical Study on the Varying Speed Impact of Wedge Bodies on a Water Surface

Effects of Froude number and geometry on water entry of a 2-D ellipse

Two-Dimensional New-Type High-Lift Systems with Link/Straight Track Mechanism Coupling Downward Deflection of Spoiler