German Institute of Composite Structures and Adaptive Systems

Braunschweig, Germany

German Institute of Composite Structures and Adaptive Systems

Braunschweig, Germany
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Gardner A.D.,German Aerospace Center | Opitz S.,German Institute of Composite Structures and Adaptive Systems | Wolf C.C.,German Aerospace Center | Merz C.B.,German Aerospace Center
CEAS Aeronautical Journal | Year: 2017

A back-flow flap attached to the suction side of an airfoil is investigated in both passively and actively actuated modes for the control of dynamic stall. This method of dynamic stall control has low power requirements and no parasitic drag when not actuated. Experiments in a low-speed wind tunnel at 50 m/s were used to characterize the reduction in dynamic stall hysteresis using pressure measurements on the midline airfoil section. It was found that the pitching moment peak is reduced by an average of 25% for all deep stall test cases for active actuation of the flap, while for passive actuation the pitching moment peak is reduced by 19%. In each case the maximum lift remained the same, while the peak drag increased by an average of 2.5% for the active flap, and by 0.9% for the passive flap. With the flap closed at low angles of attack, the reference values of the airfoil are retained. © 2017, Deutsches Zentrum für Luft- und Raumfahrt e.V.

Weiss L.,German Institute of Composite Structures and Adaptive Systems
DLR Deutsches Zentrum fur Luft- und Raumfahrt e.V. - Forschungsberichte | Year: 2017

At the initial phase of the design process, only static and equivalent static loads are considered in the structural layout of an aircraft composite fuselage. Therefore, the dynamic structural behaviour of a composite fuselage under crash load conditions is an inappropriate result of a static structural layout. This thesis provides a novel method based on the intelligent application of structural modelling and optimisation techniques to overcome this lacking feature in the design process. Therein, the key innovation is to consider static and crash loads simultaneously at the initial design phase of composite design. The novel method is based on evolutionary computation techniques applied on structural simulation in order to include energy absorption or deformation work characteristics immanent to composite materials and composite design within a multi-objective optimisation approach for an overall system response. The proposed method includes the systematic transfer of design information from the initial design phase to the preliminary design. Based on the systematic transfer, the prototypical development of an adaptive deformation element for the purpose of deformation control and energy absorption is conducted.

Hoffmann F.,German Aerospace Center | Keimer R.,German Institute of Composite Structures and Adaptive Systems | Riemenschneider J.,German Institute of Composite Structures and Adaptive Systems
CEAS Aeronautical Journal | Year: 2016

DLR has been researching on active twist rotor blade control for at least 15 years now. This research work included the design and manufacturing of model rotor blades within the blade skin integrated actuators. As a main subject, numerical benefit studies with respect to rotor noise, vibration, and performance were carried out with DLR’s rotor simulation code S4. Since this simulation code is based on a modal synthesis, it uses the natural blade frequencies and mode shapes to model the blade dynamics. Both, natural blade frequencies and mode shapes, are computed in advance employing a finite element beam model of the blade. Each beam element possesses certain structural properties that are derived from an ANSYS model for certain cross sections of the blade. Since model rotor blades are built for wind tunnel testing, they are highly instrumented with sensors and therefore vary in their structural properties along span. Modifications in the structural properties due to the instrumentation are not included in the ANSYS model. However, to account for these variations, two experimental methods have been developed. They allow the determination of the real values for the most important structural blade properties such that the structural blade model is improved. The paper describes the experimental methods, as well as the development of an advanced structural blade model for rotor simulation purposes. It shows a validation of the structural blade model based on the measured non-rotating and rotating frequencies. © 2015, Deutsches Zentrum für Luft- und Raumfahrt e.V.

Barth T.,Braunschweig Institute of Technology | Scholz P.,Braunschweig Institute of Technology | Scholz P.,Institute of Fluid Mechanics | Wierach P.,German Aerospace Center | Wierach P.,German Institute of Composite Structures and Adaptive Systems
AIAA Journal | Year: 2011

This paper describes a study of dynamical vane vortex generators in a flow over a flat plate. Fluidic vortex generators are more effective when operated dynamically. Thus, it is the aim of this study to find out whether mechanical vortex generators are also superior under dynamic operating conditions. The motion of the vortex generators is generated by piezoceramic actuators constructed in a bimorph configuration, which consists of a carbon-fiber bar covered with piezoceramic face actuators. The actuators exploit the longitudinal piezoelectric effect (d33 effect), they are operated in resonance to reach the required displacement and generate a sinusoidal motion of the vortex generators. Vortex generators and actuators were integrated into a flat plate in a low-speed wind tunnel. A stereo particle image velocimetry system was used to record phase-locked flowfields that were analyzed using vortex classification methods. It was found that the transient development of the vortex core position and circulation is very different from that of static vanes. While vortices from static vortex generators are able to survive over a considerable distance, the vortices from dynamically driven ones decay faster. It is argued that the dynamic vortices have a greater ability to reorganize the momentum in the turbulent boundary layer. Copyright © 2010 by Peter Scholz.

Elishakoff I.,Florida Atlantic University | Kriegesmann B.,Leibniz University of Hanover | Kriegesmann B.,Institute of Structural Analysis | Rolfes R.,Leibniz University of Hanover | And 5 more authors.
AIAA Journal | Year: 2012

Hybrid optimization and antioptimization of the buckling load of composite cylindrical shells is conducted. The methodology, which has been developed in previous works, is applied to a set of cylindrical composite shells, tested at German Aerospace Center. Furthermore, the existing approach is enhanced to fit within the design-optimization scheme. The shells possess traditional imperfections in the form of Fourier series coefficients of their initial imperfection profile. Additionally, two nontraditional imperfections are included in the analysis. The available experimental data is enclosed by either 11-dimensional hyperrectangle or hyperellipsoid. The minimum buckling load of the ensemble of such shells is determined by the antioptimization procedure. Then, this minimum load is maximized by varying the laminate angle. It is shown that the proposed method is a viable and relatively simple alternative to probabilistic approaches and successfully supplements them. It is shown that the proposed method is a successful supplement to probabilistic methods and the deterministic single-buckle approach, because it is deterministic in nature and thus could appeal to engineers and investigators alike, and it takes into account the actual scatter of input data. Copyright © 2011 by the American Institute of Aeronautics and Astronautics, Inc.

Rudenko A.,German Aerospace Center | Rudenko A.,German Institute of Composite Structures and Adaptive Systems | Monner H.P.,German Aerospace Center | Monner H.P.,German Institute of Composite Structures and Adaptive Systems | And 2 more authors.
22nd AIAA/ASME/AHS Adaptive Structures Conference | Year: 2014

A detailed analysis of today's commercial aircrafts determines an increased demand for high lift systems that cannot be provided by prevailing evolutionary technology development. This especially applies to the topics of noise reduction and performance increase for start and landing. An active blown Coandǎ-flap based high lift system, which is investigated within the German national Collaborative Research Centre 880, would be an alternative to today's slats and flaps and promises to contribute to those goals. An adaptive gapless droop nose with an exceedingly high grade of leading edge morphing is proven to be a key part of such a system, and thus a structural optimization framework for this technology is developed by the DLR The content of this paper is formed by the detailed presentation of the framework for optimization of a composite skin combined with an actuation kinematics.

Willberg C.,German Aerospace Center | Duczek S.,Otto Von Guericke University of Magdeburg | Vivar-Perez J.M.,German Institute of Composite Structures and Adaptive Systems | Ahmad Z.A.B.,University of Technology Malaysia
Applied Mechanics Reviews | Year: 2015

This paper reviews the state-of-the-art in numerical wave propagation analysis. The main focus in that regard is on guided wave-based structural health monitoring (SHM) applications. A brief introduction to SHM and SHM-related problems is given, and various numerical methods are then discussed and assessed with respect to their capability of simulating guided wave propagation phenomena. A detailed evaluation of the following methods is compiled: (i) analytical methods, (ii) semi-analytical methods, (iii) the local interaction simulation approach (LISA), (iv) finite element methods (FEMs), and (v) miscellaneous methods such as mass-spring lattice models (MSLMs), boundary element methods (BEMs), and fictitious domain methods. In the framework of the FEM, both time and frequency domain approaches are covered, and the advantages of using high order shape functions are also examined. Copyright © 2015 by ASME.

Monner H.P.,German Aerospace Center | Riemenschneider J.,German Institute of Composite Structures and Adaptive Systems | Kintscher M.,German Institute of Composite Structures and Adaptive Systems
Collection of Technical Papers - AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference | Year: 2012

The future generation of high lift devices for transport aircrafts has to contribute to the reduction of noise during landing and a reduction of drag during cruise flight. Also it has to be compatible with affords for natural laminar flow on the wing. A smart gapless droop nose would be an alternative to today's slats and promises to contribute to those goals. A consortium of Airbus, EADS-IW, CASSIDIAN and DLR developed such a smart leading edge in the framework of the fourth German national research program in aeronautics. This paper describes a 1:1 3D fiber reinforced flexible smart droop nose and its ground test. The results of these tests will finally be compared with the results of the finite element simulation. © 2012 AIAA.

Ucan H.,German Institute of Composite Structures and Adaptive Systems
JEC Composites Magazine | Year: 2012

Given the demands of the aviation industry, the challenges of the carbon fibre reinforced plastics (CFRP) industry cannot be met with the current technology. This paper introduces a new concept to improve the autodave process in order to achieve high part quality and productivity at low part cost and with low scrap rates.

Riemenschneider J.,German Institute of Composite Structures and Adaptive Systems | Keimer R.,German Institute of Composite Structures and Adaptive Systems | Kalow S.,German Institute of Composite Structures and Adaptive Systems
39th European Rotorcraft Forum 2013, ERF 2013 | Year: 2013

Model rotor blades are needed to validate numerical models and simulation tools. In order to do so, a proper characterization of the model rotor blades is urgently needed. Over the years a set of techniques was developed to characterize properties of active twist blades. Most of the methods can be applied to standard passive blades as well. Active twist rotor blades have been developed for the use in secondary rotor control such as higher harmonic control (HHC) and individual blade control (IBC). The basic principle of such blades is the implementation of piezoelectric actuators into the blades, using different types of coupling, causing the blades to twist. At the DLR model scale blades have been manufactured to demonstrate the feasibility of such systems. This paper is describing the experimental characterization methods for active twist blades. Both the elastic and mass related properties are discussed as well as the actuation behavior - especially for very low frequencies. © 2013 by the American Helicopter Society International, Inc. All rights reserved.

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