Numerical investigation towards the control of flexural waves using structural intensity for an active barrier of structure-borne sound

Abstract

Noise is often generated in different parts of a structure than where it is perceived, e.g. cabin noise caused by engine or APU of aircraft. Passive materials can reduce noise, but are mainly effective in a higher frequency range and require additional mass. Active systems in turn address low frequency noise, targeting different measures (sound pressure, vibration velocity, radiated sound power). Another approach is the focus on structural intensity (SI), i.e. transmitted power per unit area. Hereby, an active barrier for structure-borne sound can attenuate the downstream structure and avoid noise emission. Therefore, a real-time measurement of SI is crucial. It can be estimated using accelerometer arrays with different levels of simplifications. The presented numerical study assesses these methods, addressing the actuator and error sensor placement on a plate structure. A linear feed-forward filter is implemented, hence the SI it is split into its linearly dependent components. The necessary amount of control forces and virtual error sensors is assessed, with respect to dependencies on wavelength and the type of SI components. The study shows an advantage of SI control compared to a conventional velocity control. A small number of error sensor positions and actuators can achieve a higher global attenuation. Simplified and more robust methods for SI estimation are favorable for a practical implementation. For example by controlling only velocity and angular rate or bending moments, a rather high attenuation can be achieved.