B. Cazzolato

Active control of sound transmission using structural error sensing

The active minimization of harmonic sound transmission into an arbitrarily shaped enclosure using error signals derived from structural vibration sensors is investigated numerically. It is shown that by considering the dynamics of the coupled system, it is possible to derive a set of “structural radiation” modes which are orthogonal with respect to the global potential energy of the coupled acoustic space and which can be sensed by structural vibration sensors. Minimization of the amplitudes of the “radiation modes” is thus guaranteed to minimize the interior acoustic potential energy. The coupled vibro-acoustic system under investigation is modelled using finite element analysis which allows systems with complex geometries to be investigated rather than limiting the analysis to simple analytically tractable systems. Issues regarding the practical implementation of sensing the orthonormal sets of structural radiation modes are discussed. Specific examples relating to the minimization of the total acoustic...

Linear-Parameter-Varying Control of an Improved Three-Degree-of-Freedom Aeroelastic Model

Aeroelasticity is a broad term that describes the often complex interactions between aerodynamics and structural mechanics. The active control of aeroelastic phenomena is of particular research interest as it can lead to a reduction in weight and an increase in performance of an airframe. For more background on the analysis and control of aeroelastic systems, the reader is referred to the article by Mukhopadhyay [1]. A two degree-of-freedom wing section that is allowed to pitch and plunge due to supporting translational and torsional springs has often been used as a testbed for novel aeroelastic control methodologies. Two such apparatus are commonly used for the experimental validation of these methodologies; the Benchmark Active Control Technologies (BACT) wing [1, 2], and the Nonlinear Aeroelastic Test Apparatus (NATA) [3, 4]. This work focusses on the NATA platform, and presents an improved dynamic model along with a dynamic-less state-feedback Linear Parameter Vary-

Active Structural-Acoustic Control of a Rocket Fairing Using Proof-Mass Actuators

The feasibility of using proof-mass actuators to control noise transmission actively into a small rocket fairing, given practical constraints on actuator power and mass, is explored. The modal-interaction approach was used to develop a fully coupled structural-acoustic state-space model that relates the out-of-plane structural modal velocities to the spatially varying pressure response in the cavity. The dynamics of the proof-mass actuators were included in the structural-acoustic model. The modal-interaction approach also allowed the decomposition of the acoustic response into radiation modes, which proved essential for determining the optimal locations for sensors and actuators. Numerical simulations using linear quadratic Gaussian controllers with collocated proof-mass actuators and displacementsensorsdemonstrated approximately 4.2 dB of attenuation overthe300-Hz bandwidth forthegivenactuatorconstraints.However,thiswasonly slightly morethantheattenuationprovidedby thepassive effects of the proof-mass actuators, which was approximately 3.5 dB.

An Alternative Nonlinear Control Law for the Global Stabilization of the PVTOL Vehicle

A popular method for the control of the planar vertical takeoff and landing vehicle (PVTOL) is to cast the system into the form of a cascade nonlinear system with an exponentially stable linear subsystem, as suggested by Olfati-Saber in 2002. This idea has since been incorporated into many other published works. The contribution of this note is to demonstrate an alternative cascade structure, achieved by minimizing the interconnection term between closed-loop subsystems. Global stability of the proposed controller is proven, and simulation results suggest improved performance of this new approach as compared to that previously published.

A multipole array magnetic spring

This paper presents research on a magnetic spring concept, which has application to the development of a vibration isolation table. Features of the design are scalable, noncontact load bearing and a single degree of instability.

A Review of Virtual Sensing Algorithms for Active Noise Control

Traditional local active noise control systems minimise the measured acoustic pres- sure to generate a zone of quiet at the physical error sensor location. The resulting zone of quiet is generally limited in size and this requires the physical error sensor be placed at the desired location of attenuation, which is often inconvenient. To overcome this, a number of virtual sensing algorithms have been developed for active noise control. Using the physical error signal, the control signal and knowledge of the system, these virtual sensing algorithms estimate the error signal at a location that is remote from the physical error sensor, referred to as the virtual location. Instead of minimising the physical error signal, the estimated error sig- nal is minimised with the active noise control system to generate a zone of quiet at the virtual location. This paper will review a number of virtual sensing algorithms developed for active noise control. Additionally, the performance of these virtual sensing algorithms in numerical simulations and in experiments is discussed and compared.

Active noise control in a pure tone diffuse sound field using virtual sensing

Local active noise control systems generate a zone of quiet at the physical error sensor using one or more secondary sources to cancel acoustic pressure and its spatial derivatives at the sensor location. The resulting zone of quiet is generally limited in size and as such, placement of the error sensor at the location of desired attenuation is required, which is often inconvenient. Virtual acoustic sensors overcome this by projecting the zone of quiet away from the physical sensor to a remote location. The work described here investigates the effectiveness of using virtual sensors in a pure tone diffuse sound field. Stochastically optimal virtual microphones and virtual energy density sensors are developed for use in diffuse sound fields. Analytical expressions for the controlled sound field generated with a number of control strategies are presented. These expressions allow the optimal control performance to be predicted. Results of numerical simulations and experimental measurements made in a reverberation chamber are also presented and compared.

A Simplified Force Equation for Coaxial Cylindrical Magnets and Thin Coils

A recently-published equation for calculating the force between coaxial cylindrical magnets is presented in simplified form. The revised equation is now very compact: it is defined with fewer parameters and contains fewer terms than the original equation. The new equation is purely real, unlike the original which contained imaginary components. As a result of the simplifications, the new equation is demonstrably faster to evaluate than the original, improving its utility for parametric optimization. A reference implementation is provided for Matlab and Mathematica.

Feedback control of structurally radiated sound into enclosed spaces using structural sensing

A technique is developed that addresses sensor and actuator placement and feedback control of structural/acoustic problems that can be described as a flexible structure surrounding an acoustic cavity. Specifically, this work is directed at the space launch vehicle problem, where it is assumed that it is not possible to obtain, in advance of a required control output, a coherent measurement of the disturbance or to directly measure the quantity to be controlled. These assumptions necessitate the use of structural sensing to predict the sound pressure in the cavity and of feedback control to reduce the radiated sound. A method for selecting sensor and actuator positions based on a transformation of the problem into radiation modes is covered as well as an optimal feedback control approach which allows the control of radiated pressure into a defined subvolume of the cavity using only structural actuators and sensors. Finally, an example problem is completed which draws on all of the theoretical development t...

Structural radiation mode sensing for active control of sound radiation into enclosed spaces

In the recent article by Cazzolato and Hansen [J. Acoust. Soc. Am. 104, 2878–2889 (1998)] it was shown that it is possible to derive for a structure some set of surface velocity distributions, referred to as radiation modes, which are orthogonal in terms of their contributions to the acoustic potential energy of a coupled cavity. The technique used an orthonormal decomposition to derive an expression for the radiation modes which was based on prior work for free-field sound radiation. It will be shown in the following letter that for the special case involving the calculation of global internal potential energy it is possible to use a simple approach which requires no orthonormal decomposition since the expression for the global potential energy is already in a form that can be easily diagonalized.