Report

Teaser, summary, work performed and final results

Periodic Reporting for period 2 - TAVAC (Technologies for Active Vibration and Acoustic Comfort)

Teaser

There are two related important challenges faced in new aircraft development. Challenge 1: The comfort of passengers should be continuously improved. Challenge 2: Most importantly, as more powerful and efficient aircraft engines are introduced and new light-weight airframes...

Summary

There are two related important challenges faced in new aircraft development. Challenge 1: The comfort of passengers should be continuously improved. Challenge 2: Most importantly, as more powerful and efficient aircraft engines are introduced and new light-weight airframes are adopted the intensity of engine and airframe vibrations is increased while the damping capacity of the fuselage is reduced, hence, the vibration and noise level in the cabin are increased, setting a barrier in the improvement of airframe and engine efficiency. To address both challenges, special noise cancellation techniques should be employed. The project aims to improve existing airframes and engine technology and efficiency, while sustaining the high level of the customer comfort through the introduction of novel integrated active technologies of noise and vibration reduction. This is accommodated in two discrete, but highly related directions: (1) Active vibration isolation and control; and (2) Active noise control. The project aims to technically improve current successful approaches and to adapt them for increased passenger comfort in business jets. The project objectives can be summarized as:
• Obj. 1: Develop an Active Vibration Control System to accommodate engine vibrations using active engine mounts.
• Obj. 2: Develop an Active Noise Cancelation System to reduce noise discomfort in the passenger area.
• Obj. 3: Develop an Active Vibration Control System to attenuate aerodynamic vibrations transferred to passenger area via the fuselage floor.

Work performed

In WP1, an experimental setup was manufactured and tested presenting similar modal characteristics with the designed prototype. The experimental results, proved the efficiency of the proposed concept to substantially decrease drastically (up to 12dB) the resulting acceleration on the steel plate (representing the aircraft fuselage). The concept efficiency was proved on a resonance of the system due to the high levels of “grass” noise introduced on the response from the electromechanical shaker and the piezoelectric actuator. The later was a more demanding case than cancelation on the N1 frequency. Introduction of filters will additionally prove the concept on the N1 frequency of interest, and is on-going work. The concept efficiency was presented on a single mount along a single direction (normal to the plane of the steel plate). Additional tests are planned to be performed with actuators on two mounts, or along the axial directions. The completion of a control feedback algorithm is expected to provide autonomously the optimum phase difference and applied piezoelectric force magnitude, further improving the system performance
In WP2, an integrated ANC system has been implemented and experimentally tested. The ANC system is based on a conventional FxLMS algorithm for reliability and simplicity reasons and it has been tested through different noise signals, aiming to a local adaptive noise cancellation. The ANC system implemented can successfully reduce the overall noise level of noise up to 23 dB at the nominal ear position D and the spectrum peak amplitude of noise up to 20 dB at the nominal ear position D. The proposed spatial H/W arrangement (microphones and loudspeakers) of the ANCS achieves significant performance of ANC system building a quiet zone far away for the error microphone and close to a desired location (passenger’s ear). So, it is not important the error microphone to be placed closed to the ear in order the zone of quietness to be achieved in the vicinity of it. The total weight of the H/W (FPGA controller, microphones, loudspeaker, amplifiers and power supply) is about 9 Kgrs. It is therefore expected that the system can meet the project requirements, i.e. to offer at least a 10 dB reduction at the engine rotation speed. Moreover, the system offers the potential for an overall 15 dB noise reduction under specific conditions. Further improvements are possible, both in the HW and the SW system components. The work in WP2 has been cocluded.
In WP3, in order to fix the discrepancies of our previous model regarding the effect of the inductance, a new model was formulated and the experiments where repeated using white noise excitation instead of a swept sine. Initially, a simplified two degrees of freedom experiment was designed, in order to test the performance of the SATMD in a more controlled setup. The excitation was modified to white noise replacing in such a way the previous sinusoidal disturbance – a proposition suggested by the topic manager. The new type of excitation helped to improve the measured signal and avoid unwanted noise caused by the inductor. Multiple cases where examined with different resistive and inductive loads. Subsequently, the experimental responses were validated by the improved numerical algorithm. The next step was to repeat the investigation on the lab scale prototype presented earlier. The experimental procedure of the two degrees of freedom system was repeated using white noise excitation and inductors ranging from 50 to 300mH. The experimental data were then validated to the simulations from our new model which were also in agreement. We can thus conclude that our model is able to predict the effect of the SATMD on any structure, assuming that the provided data allow the simulation of its baseline response.

Final results

In the active engine and fuselage vibration control the project will provide the following progress beyond the SoA:

• Will utilize solid-state d33 stacked PZT actuators; also low-cost, light-weight piezopolymer dynamic sensors and/or MEMS accelerometers. The proposed solid-state actuators and sensors will drastically improve effectiveness, reduce power amplifier requirements, eliminate the need of signal conditioning, and will drastically reduce the weight of the actuator-sensor system.
• provide a robust design and optimization methodology, relying on FEA numerical tools, which will enable the optimization of the actuator-sensor network based on the modal-attenuation and filtering concept.
• provide an integrated virtual-testing simulation capability which will predict the attenuated dynamic response of the aircraft structure to the fuselage-floor, coupled with the actuator, sensor and controller systems.

The local ANC control at a headrest will offer the following innovative features:
• Efficient sub band adaptive filtering algorithm (SAF) for the optimum combination of narrow-band and broadband ANC.
• Efficient cross-talk cancellation through 3D binaural audio approaches (head tracking possibility of the EAP design, BACCH algorithm)

The developed Active Vibration & anti-Noise Control Systems will become available to industry, SMEs and research community through strategic partnerships and marketing plan. Research results will be disseminated to technology stakeholders (CleanSky partners, industry, research organizations and academia) to enhance composite structure impact knowledge and improve the passenger comfort in business jets. The project is expected to have a major effect on the development of applied technologies for enhanced aircraft performance, a key priority of the CleanSky program and the EU Flightpath 2050 Vision for Aviation. The proposed AVNC concept is very promising because it will enhance passenger comfort, the quality of air-travel and provided services and will offer a competitive advantage for the new regional aircraft.

Website & more info

More info: http://www.miltech.gr/tavac.html.