LAMINATED PIEZOELECTRIC PLATE FOR ACTIVE UNDERWATER ACOUSTIC CONTROL

The pressure reflected from a bi-laminated piezoelectric plate hasbeen determined using the Thomson-Haskell matrix method. The plate iscomposed of a piezoelectric layer with grounded vacuum and An elasticlayer in contact with the fluid. An incident plane wave in the fluidmedium strikes the plate at dif- Ferent angles. The required electricpotential across the piezoelectric layer to cancel the reflectionfrom the Fluid/elastic boundary has been determined for thepiezoelectric material PZT-5 at various thickness parame- Ters andincident frequencies.

LAMINATED VISCOELASTIC PLATE WITH INCLUSIONS FOR PASSIVE UNDER-WATER ACOUSTIC CONTROL

The effectiveness of a fluid-loaded sandwiched viscoelastic layerin suppressing acoustic scat- tering and radiation has been estimatedusing the Thomson-Haskell matrix method. The GU (Gaunaurd andUberall) resonance theory has been adopted to handle three types ofviscoelastic substrates with air -filled in- Clusions. The effects ofthe varying thickness of the substrates, the volume fractions of theinclusions and fre- Quencies of incident waves have been studied todetermine the optimal strategies of signal reduction. In theInvestigation, the monopole resonance phenomena of the inclusionshave been taken into account.

Researches on active structural acoustic control by radiation modes

Based on the radiation modes, an active control strategy is presented for sound radiation from elastic structures with an example of simply supported rectangular panel. The physical characteristics and mathematical meaning of the radiation modes are analyzed. The radiation efficiency of radiation mode falls off very rapidly with the increase of modes order at low frequency. A new control strategy is developed in which by canceling the adjoint coef- ficient of the first k radiation modes, the sound powers of the first k radiation modes is zero theoratically. The numerical calculation is made by using point force actuators as control forces.

Active Control of Structurally Radiated Sound from an Elastic Cylindrical Shell

A numerical and experimental study was presented on active control of structurally radiated sound from an elastic cylindrical shell.An analytical model was developed for the active structural acoustic control (ASAC) of the cylindrical shell.Both global and local control strategies were considered.The optimal control forces corresponding to each control strategy were obtained by using the linear quadratic optimal control theory.Numerical simulations were performed to examine and analyze the control performance under different control strategies.The results show that global sound attenuation of the cylindrical shell at resonance frequencies can be achieved by using point force as the control input of the ASAC system.Better control performance can be obtained under the control strategy of minimization of the radiated sound power.However,control spillover may occur at off-resonance frequencies with the control strategy of structural kinetic energy minimization in terms of the radiated sound power.Considerable levels of global sound attenuation can also be achieved in the on-resonance cases with the local control strategy,i.e.,minimization of the mean-square velocity of finite discrete locations.An ASAC experiment using an FXLMS algorithm was implemented,agreement was observed between the numerical and experimental results,and successful attenuation of structural vibration and radiated sound was achieved.

Experimental investigation on active acoustic flutter control

Experimenial studies on active acoustic fiutter control are carried out successfully in wind-tunnel after the theoretical study The experdrients verify the theory presented in the reference[1] and give valuable experimeotal results which predict a prondsing future of applying new techology and new ideas to the area of vibration induced by flow.

The design and experimental investigation of control system for acoustic liner with adjustable impedance

A kind of new acoustic liner with adjustable impedance has been proposed. At the same time, a set of control system has been designed for this kind of liner. Many experimental results have been obtained based on this control system. In fact, the present investigation shows the possibi1ity of active control of sound absorption coefficient or impedance of a liner according to external sound source condition by means of a standing wave tube. The experimental results show that the sound absorption coefficient of the liner can keep optimal under any sound source condition by controlling the cavity depth and the flow rate through the perforated plate of the liner. In addition, hoth the resistance and the reactance of the liner can also be controlled independently corresponding to any given condition. which is necessary to control unsteady How in turbomachinery.

Studies on the Aeroacoustics of Turbomachinery

In this paper, the research work on aeroacoustics in turbomachinery done in the Thermoturbomachinery institute, Department of Power Machinery Engineering, Shanghai Jiao Tong University, for the past 15 years is summarized. It includes: aeroacoustic similarity law and correction ofnon--similarity) mechanism of acoustic control of separated flow, aerodynamic and aeroacoustic comprehensive optimum calculation, and the influence of inlet turbulence and inlet distortion.

Comparison of smart panels for tonal and broadband vibration and sound transmission active control

This paper presents a comprehensive overview of the principal features of smart panels equipped with feed-forward and feedback systems for the control of the flexural response and sound transmission due respectively to tonal and to stochastic broadband disturbances.The smart panels are equipped with two types of actuators:first,distributed piezoelectric actuators formed either by small piezoelectric patches or large piezoelectric films bonded on the panels and second,point actuators formed by proof-mass electromagnetic transducers.Also,the panels encompass three types of sensors:first,small capacitive microphone sensors placed in front of the panels;second,distributed piezoelectric sensors formed by large piezoelectric films bonded on the panels and third point sensors formed by miniaturized accelerometers.The proposed systems implement both single-channel and multi-channel feed-forward and feedback control architectures.The study shows that,the vibration and sound radiation control performance of both feed-forward and feedback systems critically depends on the sensor-actuator configurations.