Kenneth D. Frampton

Acoustic self-localization in a distributed sensor network

The purpose of this paper is to present a technique for determining the coordinate locations of nodes in a distributed sensor network. This technique is based on the time difference of arrival (TDOA) of acoustic signals. In this scheme, several sound sources of known locations transmit while each node in the sensor network records the wave front time-of-arrival. Data from the nodes are transmitted to a central processor and the nonlinear TDOA equations are solved. Computational simulation results are presented in order to quantify the solution behavior and its sensitivity to likely error sources. Results based on experimentally collected data are also presented in order to demonstrate the potential for this approach in solving the self-localization problem.

The scaling of acoustic streaming for application in micro-fluidic devices

Abstract Recent interest in MEMS devices in general, and in micro-fluidic devices specifically, has spurred a great deal of research into the behavior of fluids in very small-scale devices. Many novel techniques have been proposed for the propulsion of fluids in small scales devices including peristaltic and electrokinetic. More recently, investigations have considered the use of acoustic streaming: that is, the imposition of steady fluid momentum via nonlinear acoustic effects. The purpose of this manuscript is to overview the physics of acoustic streaming, discus the various physical phenomena which generate the effect, and to highlight the favorable scaling issues of acoustic streaming that make it a viable alternative in micro-fluidic devices.

AEROELASTIC STRUCTURAL ACOUSTIC COUPLING : IMPLICATIONS ON THE CONTROL OF TURBULENT BOUNDARY-LAYER NOISE TRANSMISSION

A method of formulating a model to evaluate the aeroelastic structural acoustic response of a panel subjected to turbulent boundary layer (TBL) noise sources and coupled with full potential flow aerodynamics is presented. Reduced-order models of both the aerodynamics and the structural acoustic coupling are presented such that a state-variable realization of the entire system dynamics can be developed for future active control system design and synthesis with modern and robust control theory. Results from this study demonstrate the importance of including aeroelastic coupling in modeling the structural acoustic response of panels for interior noise control on modern aircraft. At subsonic flow conditions, the aeroelastic coupling serves to increase the transmission loss across the panel with increasing Mach number; however, the power spectrum of the TBL noise source increases with increasing Mach number as well and thus offsets this benefit to some degree. Results from this study also serve to demonstrate that for future analysis of robust stability and performance, variations in the plant dynamics due to variations in flow conditions must be considered in the design of broadband, feedback, active structural acoustic control systems.

POWER FLOW IN AN AEROELASTIC PLATE BACKED BY A REVERBERANT CAVITY

This paper investigates the modeling of an elastic plate coupled to a reverberant acoustic enclosure and subjected to convected fluid loading. The primary objective of this work is to quantify the effects of variations in external fluid convection velocity on power flow from the plate. The plate power flow constituents consist of injected power due to turbulent boundary layer (TBL) pressure disturbance, sound power radiated to the convected flow, sound power radiated to a reverberant cavity, and power dissipated through structural damping. Results indicate that variations in the convected fluid loading can significantly alter the balance in power flow. These results demonstrate the importance of including the effects of convected fluid loading in modeling the sound transmission through plates. Results also indicate that convected fluid loading serves to decrease the sound power radiated to the cavity as the external flow velocity increases. This effect, however, is overwhelmed by the increase in turbulent...

Active Control of Panel Flutter with Piezoelectric Transducers

This article investigates the active control of panel flutter with piezoelectric transducers and including linearized potential flow aerodynamics. The aerodynamic modeling is accomplished by approximating the aerodynamic generalized forces with infinite impulse response filters. These filters are coupled to the in vacuo panel dynamic system in feedback, thus, creating a coupled, aeroelastic system. The panel model is developed from a Rayleigh-Ritz approach and includes the mass and stiffness effects of a piezoelectric transducer. Acting as a self-sensing actuator, the piezoelectric transducer is used to implement direct rate feedback control. Results of an analytical implementation of this control system demonstrate a significant increase in the flutter boundaries.

State-space modeling for aeroelastic panels with linearized potential flow aerodynamic loading

This article presents a new method for the state-space modeling of aeroelastic panels subject to linearized potential flow aerodynamic loading. This is accomplished by approximating the aerodynamic generalized forces on the panel with discrete, infinite impulse response (IIR) filters. The IIR filters are created using Pronys method for a least-squares-fit to the aerodynamic influence functions. These filters are coupled to the in vacuo panel dynamic system as feedback, creating a coupled, aeroelastic system. The accuracy of the model is established by comparing the panel flutter boundaries of the approximate system with those found in past studies.

Smart double panel with decentralised active damping units for the control of sound transmission

This paper presents a theoretical study of decentralized velocity feedback control systems for the reduction of sound transmission through double panels. The system studied consists of two plates which are coupled acoustically by the air in the cavity between them and structurally by four elastic mounts. The geometrical and material properties of the double panel have been chosen so as to approximate a section of an aircraft fuselage skin. The outer panel of the skin (the source panel) is excited by oblique plane waves and the consequent sound power radiated from the inner panel (the radiating panel) is calculated. First, a parametric study of passive sound transmission of double panels with different geometrical and material properties is carried out. Second, active vibration control is implemented using 16 decentralized direct velocity feedback loops. Performance of such a control system is assessed for four control cases. The first two cases deal with skyhook force actuators with collocated velocity sensors, which implement active damping either on the source panel or on the radiating panel. In the third case, skyhook actuators and collocated velocity sensors are located on both panels. Finally, an approach using actuators that react between the two panels with collocated relative velocity sensors is considered.

Sound Transmission Through an Aeroelastic Plate into a Cavity

Sound transmission through a convected fluid loaded plate, i.e., aeroelastic plate, backed by a reverberant acoustic cavity is investigated. The plate and cavity are modeled using Galerkins method while the aerodynamic forces on the plate are approximated with a singular value decomposition method. Analytical results indicate that variations in the external flow velocity can significantly affect the sound transmission. The mechanism by which these effects occur is discussed. Also discussed is the importance of including the cavity coupling toward calculating the transmitted sound.

State-space modeling of aerodynamic forces on plate using singular value decomposition

This technique employs the singular value decomposition of a block Hankel matrix constructed from the aerodynamic matrix impulse response resulting in a system that has common global poles

EXPERIMENTS ON CONTROL OF LIMIT CYCLE OSCILLATIONS IN A TYPICAL SECTION

The experimental application of active control to reduce or eliminate limit-cycle oscillations in a typical section airfoil is presented. The test rig consists of a three-degree-of-freedom typical section which has free play in the e ap restoring stiffness. Such a free play was intended to mimic that associated with control surface mechanism backlashinarealsystem.Controliseffectedby meansofanactuatoractingonthee ap.AlinearquadraticGaussian optimization scheme is used to design a compensator that will accomplish three goals: 1 ) reduce or eliminate limitcycle oscillations, 2 ) increase the e utter boundary, and 3 ) be robust to variations in the e ow velocity. Although the typical section isa nonlineardynamicsystem, thecontrol system design wasbased on thelineartypical section with no freeplay. The results presented indicatethat each ofthesegoalswas accomplished. More specie cally, limit-cycle oscillations were eliminated, the e utter velocity was increased by 17%, and the control system was stable over a wide range of e ow conditions.