Neven Alujević

Smart Double Panel for the Sound Radiation Control: Blended Velocity Feedback

In this paper an active damping method using blended velocity feedback for the reduction of sound transmission through a simplified aircraft double panel is considered. The double panel consists of a source and a radiating panel, which are coupled acoustically by the air in the cavity between them and structurally by four elastic mounts. The double panel is equipped with an array of nine voice-coil actuators that can react against the two panels. A velocity sensor is mounted at both panel junctions of each actuator. The outputs from the sensors on the source and radiating panels are weighted by factors α and 1 - α, respectively. The two weighted signals are then subtracted and combined into the error signal fed back to the actuator via a constant amplification gain. The stability and performance of such a decentralized velocity feedback system are analyzed experimentally as a function of the weighting factor α. Reductions between -10 and -18 dB in the radiated sound power have been measured at low-frequency resonances of the double panel, depending on the weighting factor implemented.

Dynamic analysis and ℋ2 optimisation of a piezo-based tuned vibration absorber:

In this article, a piezo-based tuned vibration absorber is proposed and theoretically analysed. The proposed device consists of a proof mass, a piezoelectric actuator and a resilient element (spring). An equivalent mechanical model where the piezoelectric element is connected to a general circuit composed of a resistor, an inductor and a capacitor in series (RLC) is presented to illustrate the coupling of the electrical components with the mechanical systems. Based on the mechanical replacement model, a C or L circuit can be used to realise a piezo-based tuned vibration neutraliser, while with an RC or RL circuit the piezo-based tuned vibration absorber can be considered as a piezo-based tuned mass damper. For the C and L circuits, tuning strategies are derived to adjust the shunt capacitance and inductance to track the disturbance frequency. In the case of RC and RL shunt circuits, an ℋ2 optimisation criterion is used for tuning the piezo-based tuned mass damper. Closed-form expressions for the optimal tuning parameters are provided in this article.

Adaptive-passive control of structure-borne noise of rotating machinery using a pair of shunted inertial actuators

In this article, two piezo-based rotating inertial actuators are considered for the suppression of the structure-borne noise radiated from rotating machinery. Each inertial actuator comprises a piezoelectric stack element shunted with the Antoniou’s gyrator circuit. This type of electrical circuit can be used to emulate a variable inductance. By varying the shunt inductance it is possible to realise two tuneable vibration neutralisers to suppress tonal frequency vibrations of a slowly rotating machine. Also, reductions in the noise radiated from the machine housing can be achieved. First, a theoretical study is performed using a simplified lumped parameter model of the system at hand. The simplified model consists of a rotating shaft and two perpendicularly mounted shunted piezo-based rotating inertial actuators. Second, the shunted piezo-based rotating inertial actuators are tested on an experimental test bed comprising a rotating shaft mounted in a frame. The noise is radiated by a plate that is attached to the frame. The experimental results show that a reduction of 11 dB on the disturbance force transmitted from the rotating shaft through the bearing to the housing can be achieved. This also generates a reduction of 9 dB for the plate vibration and the radiated noise.

Active control of Turbulent Boundary Layer sound transmission into a vehicle interior

In high speed automotive, aerospace, and railway transportation, the turbulent boundary layer (TBL) is one of the most important sources of interior noise. The stochastic pressure distribution associated with the turbulence is able to excite significantly structural vibration of vehicle exterior panels. They radiate sound into the vehicle through the interior panels. Therefore, the air flow noise becomes very influential when it comes to the noise vibration and harshness assessment of a vehicle, in particular at low frequencies. Normally, passive solutions, such as sound absorbing materials, are used for reducing the TBL-induced noise transmission into a vehicle interior, which generally improve the structure sound isolation performance. These can achieve excellent isolation performance at higher frequencies, but are unable to deal with the low-frequency interior noise components. In this paper, active control of TBL noise transmission through an acoustically coupled double panel system into a rectangular cavity is examined theoretically. The Corcos model of the TBL pressure distribution is used to model the disturbance. The disturbance is rejected by an active vibration isolation unit reacting between the exterior and the interior panels. Significant reductions of the low-frequency vibrations of the interior panel and the sound pressure in the cavity are observed.

Self-tuneable velocity feedback for active isolation of random vibrations in subcritical two degree of freedom systems

It has been previously shown that skyhook damping can be used to actively reduce vibration transmission between masses in supercritical 2 degree of freedom (dof) systems. The method is based on measuring the absolute velocity of the clean body, multiplying it by a negative gain, and feeding the result back to a force actuator reacting between the clean and the dirty body. This approach results in a broadband vibration isolation. For subcritical 2 dof systems this is normally not possible due to control stability problems. These stability problems can be mitigated by including an appropriate amount of relative damping between the clean and the dirty body in addition to the absolute damping. This approach has been referred to as blended velocity feedback. In this paper the application of the blended velocity feedback on subcritical 2 dof systems is investigated using an auto-tuning controller. An algorithm to gradually change the relative and absolute feedback gains until the active isolation performance reaches its best by applying an optimal combination of the two gains is applied. There is only one such optimal combination which minimises the kinetic energy of the clean body, and consequently the performance surface has a global minimum. Furthermore there are no local minima so a trial and error algorithm could be applied. Although in the frequency domain finding the minimum of the performance surface is straightforward, in the time domain the determining the clean body mean squared velocity can take a considerable time per step of the algorithm, such that the convergence of the trial and error algorithm can be relatively slow. It is hypothesized that more sophisticated algorithms may speed-up the convergence but this would be at cost of using a model-based approach.

Adaptive-passive control of noise radiation of gear-box systems using a pair of shunted piezo-based rotating inertial actuators

In this paper, two Piezo-Based Rotating Inertial Actuators (PBRIAs) are considered for the suppression of the structureborne noise radiated from rotating machinery. Each inertial actuator comprises a piezoelectric stack element shunted with the Antoniou’s gyrator circuit. This type of electrical circuit can be used to emulate a variable inductance. By varying the shunt inductance it is possible to realize two tuneable vibration neutralizers in order to suppress single frequency vibrations of a slowly rotating shaft. As a consequence, reductions in the sound radiated from the machine housing can be also achieved. First a theoretical study is performed using a simplified lumped parameter model of the system at hand. The simplified model consists of a rotating shaft and two perpendicularly mounted shunted PBRIAs. Secondly, the shunted PBRIA is tested on an experimental test bed comprising a rotating shaft mounted in a frame. The noise is radiated by a plate that is attached to the frame. The experimental results show that a reduction of 11 dB on the disturbance force transmitted from the rotating shaft through the bearing to the housing can be achieved. This also generates a reduction of 9 dB for the plate vibration and the radiated noise.