The belt-rib concept for lifting surfaces with variable camber evolved at DLR recently as one of the most promising solutions for the adaptive wing. With the belt-rib idea the adaptive wing issue is approached in a new way: instead of a "mechatronic" solution with hinges or linear bearings a "structronic" solution is chosen, where distributed flexibility allows the desired shape changes. The resulting system is not only easier to maintain due to the absence of wear, but also is structurally more reliable and substantially lighter.The new concept evolves from the classical wing structure. The classical rib, which is in charge of the wing section's stiffness, is replaced by a "belt rib," which allows camber changes within given limits while leaving the remaining in-plane stiffness properties of the section widely unchanged.The evolution of the belt-rib concept was accompanied by experimental tests on different prototypes. After a first development stage, in which mainly the system's shape adaptability and the overall stiffness properties were investigated, further steps followed, focused on manufacturing, weight optimization and strength aspects.Recent developments dealt with the construction of a model with solid-state hinges, realized as hybrid glass fiber-carbon-fiber reinforced composite structure. The model is actuated mechanically by cables, which can be replaced by multifunctional actuators-like shape memory wires-in the future.The paper opens with an introduction about shape control of aerospace structures and variable camber in particular, in which the major advantages of a "structronic" approach with respect to classical solutions are discussed. Then the fundamentals of the belt-rib concept are sketched, with some significant results of the feasibility proof phase, followed by the description of the last developments. The conclusion summarizes the potential of a structronic approach to shape control with an outline of possible future work.
This paper deals with the mathematical framework of near-field acoustic holography based on finite elements in application to the acoustic response of a fluid within a closed cavity to the enclosure boundary conditions. The finite element method is an effective implementation of the modal approach for arbitrary geometries and provides advantages for certain wavenumber intervals in rooms. An inverse implementation of the direct problem can benefit from using generalized coordinates with modally reduced system matrices. A solution can be obtained via singular value decomposition together with Tikhonov regularization. This paper investigates acoustic mode spectrums of acoustic transfer functions, which has a major effect on the reconstruction of particle velocities from given sound pressures in a simple cavity model. It is found that the largest considered modal wavenumber in the acoustic transfer matrix should be twice the maximum excitation wavenumber. Furthermore, the relation between reconstruction errors and the detectability of evanescent waves depending on the wavenumber of excitation is considered. The proposed method is validated experimentally by reconstructing particle velocities on the inner boundaries of an Airbus A400M fuselage based on measurements of the inner pressure field. Results are compared with structural velocities measured with a laser Doppler vibrometer.
The use of thin monolithic piezoceramic patches as actuators and sensors for adaptive structures is well known and has been described in literature. Nevertheless the manufacturing of adaptive structures is still very challenging. During the manufacturing process it is often necessary to apply high mechanical loads on the extreme brittle piezoceramic material. As a result very often cracks in the piezoceramic material make the structure uselessness. This problem becomes serious when large scale structures with many actuators and sensors are considered. To come to more reliable results the use of encapsulated piezoceramic actuators and sensors came into focus. Within the German industrial project “Adaptronik” a new modular concept has been developed to pre-encapsulate different kinds of piezoceramic materials before further processing. During this manufacturing step the piezoceramic material is provided with a mechanical stabilization, an electrical insulation, electrodes and reliable electric contacts. The multifunctional elements are characterized by an increased damage tolerance, good long term properties and an easy handling. Due to the modular concept, the multifunctional elements can be designed to meet a great variety of different requirements. This involves for example driving voltages, size and shape of the elements and the piezoceramic material itself. The manufacturing of curved elements was demonstrated. A technology to bond these elements on spatial curved surfaces and to integrate them into fiber composite structures was developed. Experiments have been carried out to investigate the active and passive properties of the multifunctional elements and their interaction with structural components.
The belt-rib concept for lifting surfaces with variable camber evolved at DLR recently as one of the most promising solutions for the adaptive wing. With the belt-rib idea the adaptive wing issue is approached in a new way: instead of a "mechatronic" solution with hinges or linear bearings a "structronic" solution is chosen, where defined, distributed flexibility allow the desired shape changes. The new concept evolves from the classical wing structure. The classical rib, which is in charge of the wing section's stiffness, is replaced by a "belt rib", which allows camber changes within given limits while leaving the remaining in-plane stiffness properties of the section widely unchanged.The evolution of the belt-rib concept was accompanied by experimental tests on different prototypes. The last developments concern the construction of a model with solid-state hinges, realized as hybrid glass fibercarbon-fiber reinforced composite structure. The model is actuated mechanically by Bowden cables, which can be replaced by shape memory wires in the next development stage.In this paper, the fundamentals of the concept and the most relevant results of the first developments are reported. A description of the new belt-rib design follows, which was implemented in a new prototype. The description of the experimental strength proof and an outline of further development work conclude the paper.
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