Feasibility Of Active Control Research Articles

Analysis of hydrofoil rotation control method for improving the propulsion performance of wave-powered boats considering the effect of currents

The wave-powered boat is a kind of mobile marine platform that can convert wave energy into thrust through the rotation of the hydrofoils. The rotation control method of the hydrofoil has a significant impact on the propulsion performance of wave powered-boats when considering ocean currents. In this paper, by establishing an equivalent instantaneous optimization model for the motion of the hydrofoil, the rotation angle that can obtain the maximum thrust is analyzed, and the relationship between the rotation angle, hydrofoil motion velocity as well as the current velocity is obtained. Subsequently, the propulsion performance of the hydrofoil under the active control method is compared with that under the passive control method through the fluid-multibody coupled analysis, and the motion parameters of the hydrofoil are explored, thus the feasibility of active control when considering the ocean currents is verified. It can be seen that the active control method based on the optimal rotation angle equation can significantly improve the propulsion performance of the wave-powered boat in the presence of currents. Under the passive control method, either increasing the stiffness or increasing the co-current velocity will make the rotation process of the hydrofoil fluctuate and disorderly. In contrast, the active control method can stabilize the rotation process of the hydrofoil, and the hydrofoil is always in a position where the maximum thrust can be obtained during rotation, thus making the propulsion performance better. The relevant research in this paper can provide a reference for similar research of the wave-powered boat.

Dispersion engineering of infrared epsilon-near-zero modes by strong coupling to optical cavities

Abstract Epsilon-near-zero (ENZ) materials have recently emerged as a promising platform for infrared nanophotonics. A significant challenge in the design of ENZ-based optics is to control the dispersion of ENZ modes that otherwise have a flat profile near the ENZ frequency. Strong coupling with an optical cavity is a promising approach to ENZ dispersion engineering, which however has limitations due to the lack of tunability or nanofabrication demands of the cavity employed. Here, we theoretically and numerically show that much of the limitations of previous approaches can be overcome by strongly coupling the ENZ mode to an unpatterned Fabry–Perot cavity. We demonstrate this unprecedented ENZ dispersion control in coupled cavities by designing tunable infrared polarizers that can absorb s and reflect p-polarized components, or vice versa, for almost any oblique angle of incidence, i.e. omnidirectional polarizers. The feasibility of active control is also demonstrated using a phase change material within the cavity, which predicts dynamic switchability of polariton dispersions across multiple resonant levels at mid-infrared wavelengths. These results are expected to advance the current understanding of strongly coupled ENZ interactions and demonstrate their potential in tailoring dispersions for active and passive control of light.

Active vibration suppression at bearing pedestals in an elastically supported shafting system via non-contact electromagnetic actuators

The bearings are important paths for the shaft vibration transmitting to the hull structure. A new scenario based on non-contact electromagnetic actuators mounted at bearing pedestals is proposed to suppress the vibration transmission from the shaft to the elastic foundation. The dynamic model of a shafting system with the non-contact electromagnetic actuators is established on the Hamilton’s principle. With this model, the influence of the displacement stiffnesses of the electromagnetic actuators on the vibration transmission is discussed, and the feasibility of active control is investigated. A multi-harmonic vibration suppression method is adopted and the performance is evaluated. Numerical results show that the vertical control by the electromagnetic actuators is able to attenuate the vibration transmission from the shaft to the foundation. With the addition of horizontal control, the foundation vibration is further decreased due to the reduction of power flow generated by the moments between the bearing pedestals and foundation. The results of a proof-of-principle experiment have also verified the effectiveness of the vertical control by the non-contact electromagnetic actuators in vibration transmission suppression and the foundation acceleration responses are remarkably reduced.

Active vibration control of a shaft bracket-plate coupled system

Active vibration control of a shaft bracket-plate coupled system is investigated. The vibration of the plate is controlled with electromagnetic vibration absorbers (EVAs), which are mounted around the feet of the shaft bracket to impede the transmission of vibration from the bracket apex to the plate. A dynamic model is established on the Timoshenko beam theory and the Kirchhoff thin plate theory to reveal the mechanism of vibration transmission. It is exhibited that all the induced forces and moments at the coupling points contribute much to the transverse responses of the plate. The feasibility of active control with the EVAs is evaluated numerically based on the controllability of the plate vibration. It is demonstrated that the two-point in-plane control is able to attenuate the plate vibration under the excitation of in-plane disturbance forces, while the multi-point control is effective in reducing the plate vibration regardless of the directions of disturbance forces. An experimental system is built to verify the performance of the two-point in-plane control. The results have shown that with the help of adaptive control, the two-point in-plane control is capable of suppressing the vibration of the foundation induced by the in-plane forces acting on the shaft bracket.

Simulation and experiment on lateral vibration transmission control of a shafting system with active stern support

An active stern support is proposed to suppress lateral vibration transmission in the shaft-hull system of underwater vehicles subjected to the excitation of propeller forces. The active stern support uses six active struts instead of a common bearing support to suppress vibration transmission from the shaft to the hull. The dynamic model of a shaft-hull system embedded with the active stern support is established on the Timoshenko beam theory and the FRF (frequency response function)-based synthesis method. Based on this model, the characteristics of vibration transmission in the system and the feasibility of active control are analyzed. An adaptive control algorithm is constructed and the performance of vibration suppression is evaluated. An experimental system is built as well to verify the effectiveness of the control method. Numerical and experimental results show that the active stern support is able to suppress the transmission of lateral vibration induced by the propeller forces, and the attenuation of the normal vibration of the hull structure can be achieved.

Influence of Acoustic Blockage on Flutter Instability in a Transonic Nozzle

In order to predict oscillating loads on a structure, time-linearized methods are fast enough to be routinely used in design and optimization steps of a turbomachine stage. In this work, frequency-domain time-linearized Navier–Stokes computations are proposed to predict the unsteady separated flow generated by an oscillating bump in a transonic nozzle. The influence of regressive pressure waves on the aeroelastic stability is investigated. This case is representative of flutter of a compressor blade submitted to downstream stator potential effects. The influence of frequency is first investigated on a generic oscillating bump to identify the most unstable configuration. Introducing backward traveling pressure waves, it is then showed that aeroelastic stability of the system depends on the phase shift between the wave's source and the bump motion. Finally, feasibility of active control through backward traveling pressure waves is evaluated. The results show a high stabilizing effect even for low amplitude, opening new perspectives for the active control of choke flutter.

A Compact Active Control System for Tonal Noise Reduction in Axial Fans

The objective of this paper is to show the feasibility of active control of tonal noise from automotive engine cooling fans using a single unbaffled loudspeaker in front of the fan. A simplified model is described for preliminary design using this configuration. A single input single output (SISO) filtered X-LMS has been implemented to control the first tones in real time. At the error microphone, the sound pressure attenuation at blade passage frequency (BPF) and its first harmonics are reduced down to the broadband noise level. At low frequency, for large sound wavelength compared to the fan radius, the sound radiation is reduced in all directions, since the dipolar directivity of the secondary noise emitted by the unbaffled loudspeaker is similar to the directivity of the primary noise emitted by the fan.

Active Control of Low Frequency Buzz-Saw Tones; Theory and Experiment

This paper discusses some theoretical and experimental issues related to the active control of buzz-saw tones radiated from an aircraft engine inlet at takeoff. Buzz-saw tones occur when the rotor tip speed becomes supersonic. It arises due to the formation of shocks at the blade tips, which then propagate non-linearly along the engine duct. Buzz-saw noise comprises a series of tones harmonically related to the shaft rotation frequency (Engine Orders). Moreover, it has been shown that the noise at each Engine Order comprises just one single spinning mode. Whilst there has been considerable work aimed at assessing the feasibility of active control for reducing the tones due to rotor – stator interaction, buzz-saw noise has been overlooked. This is surprising given the low frequencies at which Buzz-Saw noise occurs, and its simple modal content, which both suggest that buzz-saw noise is particularly suited to active control. This paper describes various control strategies for reducing buzz-saw noise. The paper concludes with the results of a laboratory experiment aimed at demonstrated experimentally the effectiveness with which a single spinning mode, characteristic of an EO = 3 buzz-saw tone, can be controlled. Reductions in excess of 14dB are reported at some frequencies.

Analytical development of a robust controller for smart structural systems

This paper aims at demonstrating the feasibility of active control of beams with a multiobjective state-feedback control technique. The multiobjective state-feedback controller is designed on a linear matrix inequality (LMI) approach for the multiobjective synthesis. The design objectives are to achieve a mix ofH∞ performance andH2 performance satisfying constraints on the closed-loop pole locations in the face of model uncertainties. The controller is also designed to reject the effects of the noise and external of disturbances. For the theoretical analysis, the governing equation of motion is derived by Hamilton’s principle to describe the dynamics of a smart structural system. Numerical examples are presented to demonstrate the effectiveness of the integrated robust controller in damping out the multiple vibration modes of the piezo/beam system.