Marc Michau

A Plane and Thin Panel with Representative Simply Supported Boundary Conditions for Laboratory Vibroacoustic Tests

A technique to setup a simply supported rectangular plane panel for laboratory vibroacoustic tests is described and validated. For a given panel fixed to thin vertical supports, a dimensionless parameter is proposed to size these supports following a desired frequency precision compared to theoretical eigenfrequencies of a panel with such boundary conditions. A numerical study confirms the potential of this design parameter. Detailed instructions for assembling a panel with adequate thin vertical supports on a rigid frame are then given. Finally, three laboratory cases are described which illustrate possible experimental vibroacoustic applications using a panel assembled following previous guidelines. The design parameter viability is experimentally confirmed, and all obtained results depicted good agreement with analytical solutions and numerical predictions.

Decentralized complex envelope controller for ASAC by virtual mechanical impedances

The problem of Active Structural Acoustic Control (ASAC) is to attenuate the radiated sound power by energy injection using structural actuators to modify deflection shapes. Collocated and dual actuator-sensor pairs allow the feedback problem to be formulated as the implementation of virtual mechanical impedances. The approach is based on a two-step process: (1) the virtual impedance is derived from measurements of the primary sound and transfer functions; (2) the centralized or decentralized complex envelope controller is designed to ensure stable feedback loops. Experiments are performed on a curved composite aircraft panel comprising a window. The proposed approach leads to the implementation of active virtual impedances and unstable compensators. An increased kinetic energy of the panel is observed, thus demonstrating that the control inputs needs to provide vibrational energy to achieve sound power reduction (2.7dB).

Optimal virtual mechanical impedances for the vibroacoustic active control of a thin plate

In order to reduce the acoustic power radiated by a flexible panel, dual colocated actuator / sensor pairs are used to modify its vibration. The control strategy implemented for harmonic disturbances leads to locally impose a virtual mechanical impedance to the structure, using the linear relation between the actuator input and the control output of each pair. This virtual mechanical impedance is computed in order to minimize the radiated acoustic power. The proposed approach consists in two steps: (1) the matrix of optimal virtual mechanical impedance is calculated by measuring the primary disturbance and the transfer functions between actuators and structural/acoustic sensors and (2) the virtual mechanical impedance objective is achieved using a real-time integral controller. It is shown that such an optimal control approach leads to better sound power reduction than a classical active damping strategy where the virtual mechanical impedance is defined as real positive. Theoretical and experimental results are compared, also showing that the method proposed here is robust regarding variations of the primary disturbance.

Virtual mechanical impedance approach for the active structural acoustic control of panels

This work investigates harmonic Active Structural Acoustic Control of flexural panels using structural, collocated and dual actuator-sensor pairs. Two types of transducer technologies are envisioned: (1) thin piezoelectric actuators and sensors; (2) electrodynamic inertial actuators and transverse velocity sensors. The control strategy is to locally impose a complex, virtual mechanical impedance to the structure via a linear relation between the actuator input and sensor output of each pair, at each frequency of interest. This virtual impedance is optimized to minimize the sound radiation of the structure at the corresponding frequency. The approach is implemented as a two-step process: (1) the optimal virtual impedance matrix is derived from identification of the primary sound and transfer functions between the control actuators, structural sensors and far-field acoustic sensors; (2) the optimal virtual impedance matrix is imposed using a real-time, iterative controller. Numerical and experimental result...