German Institute of Composite Structures and Adaptive Systems

Braunschweig, Germany

German Institute of Composite Structures and Adaptive Systems

Braunschweig, Germany
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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.


Riemenschneider J.,German Institute of Composite Structures and Adaptive Systems | Schulz M.,German Institute of Composite Structures and Adaptive Systems | Pohl M.,German Institute of Composite Structures and Adaptive Systems
ASME 2012 Conference on Smart Materials, Adaptive Structures and Intelligent Systems, SMASIS 2012 | Year: 2012

Active Twist Rotor Blades for helicopter main rotors have been developed for the use in secondary 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 causing the blades to twist. At the DLR such types of active twist blades have been designed for quite some years. Several model scale blades have been manufactured to demonstrate the feasibility of such systems. This paper presents a new set of rotor blades (4 m diameter) which is designed to go into a wind tunnel experiment within the "STAR" consortium. In this paper it is discussed, what kind of other applications for such blades - equipped with piezoceramic actuators - can be considered. Besides the capability to twist at frequencies of 1 through 6/rev, there is always the option of statically changing the pretwist of the blade, which will influence the figure of merrit. The idea is to use blade integrated actuators as part of electromechanical absorbers has been discussed recently. Using certain electrical networks, the structural behavior of the rotor blade can be significantly influenced. The effectiveness of such systems was experimentally investigated using a twist blade. In this paper results of a rotating blade with aerodynamic damping is shown for the first time. Different types of shunt networks have been investigated as presented in [1] before: At first an oscillating circuit was established coupling the capacitive piezoelectric actuators with an inductivity. If the setup is tuned right, this results in a significant decrease of the amplitues of a single frequency, e.g. torsional eigenfrequencies. In a next step a virtual "negative capacity" was used to dissipate the vibrating energy in the electrical circuit. Such an element shows the same amplitude response as the capacity, but the phase is shifted by 180 deg compared to a "regular capacity". The advantage of this method is the effectiveness over a broad frequency range. That way several modes can be influenced at the same time. Finally, a first evaluation of the influence of these measures on the vibration level of a complete rotor was carried out. Copyright © 2012 by ASME.


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.


Algermissen S.,German Institute of Composite Structures and Adaptive Systems | Unruh O.,German Institute of Composite Structures and Adaptive Systems | Haase T.,German Institute of Composite Structures and Adaptive Systems | Monner H.P.,German Institute of Composite Structures and Adaptive Systems
21st International Congress on Sound and Vibration 2014, ICSV 2014 | Year: 2014

In future aircraft well-established jet engines could be substituted by contra rotating open rotor (CROR) propulsion systems. Due to their fuel efficiency they are able to reduce costs and CO2 emissions significantly. But up to now the high noise emission of CROR engines in certain frequency bands impede dissemination on the market. This conflict can be solved by the implementation of modern noise reduction techniques like Active Structural Acoustic Control (ASAC) in aircraft. In this paper an approach for the reduction of noise transmission through a section of a fuselage is presented. The experimental aircraft Dornier 728 of the DLR is equipped with an ASAC system. The system is mounted on a side panel including two windows and covers an area of 1000 × 1500 mm2. Sensors on the inner fuselage measure the normal acceleration in specified points of the structure. A narrow-band robust controller calculates the desired actuator signals to reduce the sound transmission at the specific CROR bands in the bandwidth from 1 to 500 Hz. Since the Dornier 728 aircraft has no CROR engines, their acoustic excitations have to be synthesized. A 112-channel loudspeaker array is placed close to the fuselage. The loudspeakers are driven with synthesized signals and produce a complex CROR sound pressure field on the outer side of the fuselage. The synthesized excitation gives the opportunity to test the ASAC system with realistic loads. Beside a detailed description of the ASAC realization and the algorithms, the results of the experiments and the effectiveness of the control concept are shown.

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