Martin Radestock

Optimization, design and structural testing of a high deformable morphing leading edge of an active blown high lift system

The future generation of high lift devices hast to play a part in reducing the noise footprint and increasing the performance for start and landing of transport aircrafts. To contribute to these goals, an active blown Coandă-flap based high lift system is investigated within the German national Collaborative Research Centre 880 as an alternative to the state of the art slats and flaps. A key part of this system is an adaptive gapless droop nose with an exceedingly high grade of leading edge morphing. The design and construction of this component is based on a structural optimization framework, developed at German Aerospace Center (DLR). The framework consists of two hierarchical design steps, an optimization of the hybrid composite skin layout with integral T-stringers, acting as joints to the inner actuation mechanism and the kinematic optimization of the latter. This paper describes a full scale hybrid composite morphing droop nose and its structural tests. The results of these tests will finally be compared with the results of the finite element simulation and applied for the validation of the optimization framework.

Experimental Realization of a Sound Radiation Filter for Feedforward Control to Improve Active Structural Acoustic Control Systems

Due to the strengthened CO2 and NOx regulations, future vehicles have to be lightweight and efficient. But, lightweight structures are prone to vibrations and radiate sound efficiently. Therefore, many active control approaches are studied to lower noise radiation besides the passive methods. One active approach for reducing Sound radiation from structures is the active structural acoustic control (ASAC). Since the early 90’s, several theoretical studies regarding ASAC systems were presented, but only very little experimental investigations can be found for this alternative to passive damping solutions. The theoretical simulations show promising results of ASAC systems compared to active vibration control approaches. So, for that reason in this paper an experiment is conducted to investigate the performance of an ASAC system in the frequency range up to 600 Hz. A regular sensor grid of 24 accelerometers that are interconnected to establish six radiation signals is applied to an aluminum plate. The plate is excited by a point force and the feedforward control system counteracts these vibrations with 2 inertial actuators. The radiated sound power can be reduced by 4 dB integrated over the targeted frequency band. Compared to an active vibration control system which results only in a 0.2 dB decreased sound radiation, the ASAC system is beneficial. Furthermore, the filter length and the causality aspect of the experiments are analyzed in order to investigate the digital signal processing requirements. It can be shown that short filters are sufficient for an ASAC System compared to the filter length needed for an AVC system. In the last part of this paper some technical simplifications are investigated in order to reduce the complexity of the sound Radiation filters. It is shown that the high pass filters needed to model the radiation efficiency can be neglected with a very small loss of performance.

Acoustic design of boundary segments in aircraft fuselages using topology optimization and a specialized acoustic pressure function

In most aviation applications, a major cost benefit can be achieved by a reduction of the system weight. Often the acoustic properties of the fuselage structure are not in the focus of the primary design process, too. A final correction of poor acoustic properties is usually done using insulation mats in the chamber between the primary and secondary shell. It is plausible that a more sophisticated material distribution in that area can result in a substantially reduced weight. Topology optimization is a well-known approach to reduce material of compliant structures. In this paper an adaption of this method to acoustic problems is investigated. The gap full of insulation mats is suitably parameterized to achieve different material distributions. To find advantageous configurations, the objective in the underlying topology optimization is chosen to obtain good acoustic pressure patterns in the aircraft cabin. An important task in the optimization is an adequate Finite Element model of the system. This can usually not be obtained from commercially available programs due to the lack of special sensitivity data with respect to the design parameters. Therefore an appropriate implementation of the algorithm has been done, exploiting the vector and matrix capabilities in the MATLABQ environment. Finally some new aspects of the Finite Element implementation will also be presented, since they are interesting on its own and can be generalized to efficiently solve other partial differential equations as well.