Final Report Summary - SPRINT (SPRiNT - Smart Panels for the Reduction of Noise Transmission) Significant components of the interior noise in high speed vehicles are caused by the Turbulent Boundary Layer (TBL) disturbances which are inherently random and broadband. In fact, aircraft cabin noise during cruise is dominated by the TBL noise components. The noise is generated by the airflow over the fuselage surface and transmitted to the vehicle interior especially through vibration and sound radiation of panels of the aircraft fuselage. This problem is traditionally solved passively, by applying sound absorbing materials onto the panels. However, the low-frequency effectiveness of passive treatments is not sufficient. For this reason an interest has grown in using active noise transmission control. It can be implemented through smart panels with embedded sensor-actuator pairs which apply decentralised velocity feedback control. Such control generates active damping and thus significantly decreases the sound transmission at low frequencies, where it is dominated by resonances of fuselage panels. The major challenge in development of smart panels with decentralised velocity feedback control loops is the stability of practical systems, which limits the maximum feedback gain, and thus the maximum performance. Furthermore, due to the cross-talk between the control units, the increase in the number of feedback loops does not necessarily lead to the increase in global performance, as the maximum stable gain tends to decrease. In that case, there is a danger that unnecessary mass is added to the structure. Therefore the three objectives of the project SPRiNT are: to improve on the stability of the feedback loops, to investigate ways to reduce mass added to the structure by the active control system components, and finally, to optimize the number of control units per smart panel area. This will be done theoretically by numerical simulations and experimentally on prototype smart panels.Since the beginning of the project the work performed can be summarized as follows. A mathematical model has been built which allows for simulation of the sound transmission through a smart double panel system equipped with decentralised velocity feedback control units. This model has been first used to perform simulations with ideal velocity sensors and force actuators. The model has also been adjusted to include the frequency response functions of miniature voice coil actuators and accelerometer sensors. In addition, extensive preparations were performed to build the electromechanical test rig and the controller unit. Finally, the testing rig was built in a form of an acoustic aquarium, with the smart double panel on top, together with a miniature electronic controller with very low energy consumption. The electromechanical testing rig can be seen on the attached photographs. This testing rig can be used to perform experimental analyses of the efficiency of the investigated control approach to reduce noise transmission through the smart structure.The main results achieved include the development of the mathematical model, the manufacturing of the testing rig and the electronic controller. This means that the 1st milestone has been achieved as indicated in the work plan for the project. In addition, the work on the project progressed more quickly than planned such that the manufacturing of the electronic controller (which was planned through months 13 through 24) has been completed by the month 18. It was possible to make this controller rather miniature controller with low energy consumption (see the attached documents).The final results are expected to enable successful demonstration of a very interesting and novel active control technique. In addition, the experimental validation of the proposed active control method using the completed testing rig will significantly increase the knowledge on the effectiveness of the method, and potential mechanisms for improving the method. It is very likely that further high quality publications in peer review journals will result from the experimental research to be performed. This, in turn, will enable the researcher to become more independent scientist.
