Buckling is an important design constraint in light-weight structures as it may result in the collapse of an
entire structure. When a mechanical beam column is loaded above its critical buckling load, it may buckle. In
addition, if the actual loading is not fully known, stability becomes highly uncertain. To control uncertainty
in buckling, an approach is presented to actively stabilise a slender flat column sensitive to buckling. For this
purpose, actively controlled forces applied by piezoelectric actuators located close to the column's clamped
base stabilise the column against buckling at critical loading. In order to design a controller to stabilise the
column, a mathematical model of the postcritically loaded system is needed. Simulating postbuckling behaviour
is important to study the effect of axial loads above the critical axial buckling load within active buckling
control. Within this postbuckling model, different kinds of uncertainty may occur: i) error in estimation of
model parameters such as mass, damping and stiffness, ii) non-linearities e. g. in the assumption of curvature of
the column's deflection shapes and many more. In this paper, numerical simulations based on the mathematical
model for the postcritically axially loaded column are compared to a mathematical model based on experiments
of the actively stabilised postcritically loaded real column system using closed loop identification. The motivation
to develop an experimentally validated mathematical model is to develop of a model based stabilising control
algorithm for a real postcritically axially loaded beam column.
This paper gives a general view on some aspects of the influence of uncertainty in model-based monitoring of loadcarrying
structures. The advantages and relevance of monitoring for the prediction of reliability will be clarified and the
difference between uncertainty and reliability is discussed. Solving inverse Problems is a particular challenge in
monitoring systems. Therefore, different categories of inverse problems are discussed. A generally valid extended
difference equation, which describes the transfer behavior of the structure, will be derived as the basis for digital signal
processing of model-based monitoring. This equation also considers changes in the structures dynamic properties, e.g
due to damage or temperature. With this equation, the influence of uncertainty due to measurement noise to the
functionability of monitoring is discussed and some possibilities are shown to control this uncertainty when determining
ideal sensor-positions for monitoring.
The reliability assessment of complex adaptive systems requires the identification of dominant input parameters and the
quantitative evaluation of the associated effects on the system performance. This can be achieved using experimental and
numerical sensitivity analysis methods. In this paper a simulation based approach is presented, assessing the system
performance of an active vibration isolation device with respect to parameter variations, such as temperature, load
amplitude, material properties and geometry dimensions of the structural elements. The modeling of the active system is
described utilizing the Finite Element Method and a Krylov Subspace based model order reduction scheme. The
implemented Morris screening technique and variance based sensitivity analysis are discussed. For the example of an
active vibration system the sensitivity analysis strategy is outlined and it is shown that a quantitative assessment of the
system performance considering large scale parameter variations is provided.
The reliability assessment of complex active systems requires simulation methods, which reproduce complex system
performance and also account for failure and fatigue scenarios. More and more, test methods traditionally carried out
experimentally are replaced by computational or 'virtual' methods. Reliability of these complex adaptive systems is hard
to estimate for several reasons. A priori undetermined interaction between various influencing parameters, unknown
fatigue properties of the multifunctional materials employed in sensors and actuators and very complex system
performance requirements make it difficult to predict under which circumstances the system may fail. Sensitivity
Analysis (SA) of the comprehensive adaptive system model has proven to be a valuable tool for the identification and
assessment of scenarios that are relevant for system reliability. For the example of an active oil pan, which is equipped
with piezoelectric sensors and actuators to suppress structural vibrations, the method is outlined.
The mission of the Fraunhofer Gesellschaft, one of the biggest research facilities in Germany, is to identify technologies with a high impact potential for commercial applications and to take all necessary steps to successfully promote them by performing cooperative industrial research activities. One of these technologies is called smart structures, also known as adaptive structures. Most recently, Fraunhofer decided to strategically extend its portfolio to include this technology and summarize its R&D activities in the FIT (Fraunhofer Innovation Topics) ADAPTRONIK. To improve Fraunhofer's competencies in adaptronics, especially with respect to system design and implementation, the Fraunhofer internal project MAVO FASPAS was launched in 2003. Now, after 3 years of work, the project comes to a close. This article discusses some major project results.
In 1997 the BMBF announced a highly paid competition for future oriented key technologies and their industrial utilization. 230 proposals from industrial enterprises and research establishments were submitted. An independent group of experts selected altogether only 5 projects which were proposed to the BMBF. One of these projects was the major project ADAPTRONICS which is funded from 1998 to 2002 with a total volume of 25,000,000 EURO. This project is under the direction of the DLR and focuses on the integration of piezoelectric fibers and patches into lightweight structures aiming at active vibration and noise reduction, shape control and micro positioning. The main project target is the implementation of this technology in different industrial branches like the automotive industry, rail technology, mechanical engineering, medical engineering, and aerospace technology. This paper will give an overview of the recent progress and the next steps in the various tasks.
Within the framework of an idea competition for future-oriented key technologies and their industrial utilization, in 1997 BMBF called for project proposals from industries and research for so-called 'Leitprojekte'. An independent group of experts selected few project proposals from the many submitted, and proposed them to BMBF for promotion. One of these projects is the BMBF-Leitprojekt ADAPTRONIK which is introduced in this paper. Adaptronics describes the field of technology focusing on the development of a new class of so-called smart structures. The Leitprojekt ADAPTRONIK consists of 24 partners from industry and research institutes and is conducted under the responsibility of the German Aerospace Center (DLR). The project focuses on the development and structure-conforming integration of piezoelectric fibers and patches in structures for lightweight construction. It is aimed at active vibration and noise reduction, contour deformation and micro-positioning in the very sense of adaptronics in various industrial applications. The project targets are prototype assemblies from the fields of automotive industry, rail vehicles, mechanical engineering, medical engineering, and aerospace. In the paper the content, the status and an outlook will be presented.
In contrast to conventional lightweight material like aluminum or titanium, fiber composites offer the possibility to integrate functional elements directly into the material. Thus, multifunctional materials are developed which have the ability to serve more than the load-carrying function. As there is extensive work on the field of integration of thin piezoceramic platse and foils into carbon fiber reinforced polymeres, this will be focused on in this paper. First, the design of an active carbon fiber composite with integrated piezoceramic is shown. Different fiber layups and connecting methods to supply the piezoceramic are discussed. A sophisticated processing technology for active composite materials, the so-called DP-RTM (Differential Pressure - Resin Transfer Moulding), is presented. Various damage mechanisms may reduce or even destroy the sensing and actuaing capabilities of the piezoceramic material. Therefore the capability of high resolution non-destructive methods to evaluate manufacturing defects as well as defects resulting from mechanical overload is presented. Finally two applications are discussed in more detail to demonstrate the potential of the active composite material. Representing static applications an active composite plate is shown which has an infinite bending stiffness up to a certain load. A second active composite plate is used for active noise control.
In 1997 BMBF, within the framework of an idea competition for future-oriented key technologies and their industrial utilization, called for project proposals from industries and research for so-called 'Leitprojekts'. An independent group of experts selected few project proposals form the many submitted, and prosed them to BMBF for promotion. One of these projects is the BMBF-Leitprojekt ADAPTRONIK which is introduced in this paper. The Leitprojekt ADAPTRONIK which is conducted under the responsibility of Deutsches Zentrum fuer Luft-und Raumfahrt e.V. in Brunswick, focuses on the strucutre-conforming integration of piezoelectric fibers and patches in structures for lightweight construction. It is aimed at active vibration and noise reduction, contour deformation and micro-positioning in the very sense of adaptronics in various industrial applications. The project targets are prototype assemblies from the fields of automotive industry, rail vehicles, mechanical engineering, medical engineering, and aerospace.
Civil transport airplanes fly with fixed geometry wings optimized only for one design point described by altitude, Mach number and airplane weight. These parameters vary continuously during flight, to which means the wing geometry seldom is optimal. According to aerodynamic investigations a chordwide variation of the wing camber leads to improvements in operational flexibility, buffet boundaries and performance resulting in reduction of fuel consumption. A spanwise differential camber variation allows to gain control over spanwise lift distributions reducing wing root bending moments. This paper describes the design of flexible Fowler flaps for an adaptive wing to be used in civil transport aircraft that allows both a chordwise as well as spanwise differential camber variation during flight. Since both lower and upper skins are flexed by active ribs, the camber variation is achieved with a smooth contour and without any additional gaps.