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design optimization process, which includes besides the modeling of the coupled system of the flight dynamics,
also the structural dynamics, the actuators of the control surfaces and the sensors as well as the effects of the
digital flight control systems.
Results from structural mode coupling investigations from Eurofighter Aircraft are presented. Analytical and
experimental methods to avoid structural mode coupling on ground and during flight are described. Especially
the design of structural notch filters to minimize interaction between structure and flight control system is outlined
using a mathematical model of the elastic aircraft. The paper explains design procedures, design and clearance
requirements, test procedures and the correlation between mathematical model predictions and structural
coupling tests as well as the aeroservoelatic model update using on ground and in flight structural coupling test
results.
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SESSION B3A IMPROVED SIMULATION
Chair: Fabio Soares (Embraer)
Title: Simulation tools for assessing the reliability and robustness of shell structures
Authors: Prof. M. Oberguggenberger
University of Innsbruck
Time: November 4, 2009 4:00 pm
Room: Lumen
This presentation addresses the longstanding question of assessing the reliability and safety of design of shell
structures. As a rule, computational costs of computing e.g. the buckling behavior of complex shell structures as
arising in aerospace applications are extremely high. We argue that the most useful approach consists in sampling
based sensitivity analysis. In the past years, we developed a pool of Monte Carlo methods for sensitivity
analysis. The methods are based on artificial random variations of the decisive input and shape parameters
and a statistical evaluation of the effects on the outputs.
Relatively small sample sizes suffice for the required accuracy of the statistical indicators. Nevertheless, the
issue of accelerating the computations remains an important one. We are currently engaged in a large research
project that aims at improving computational efficiency and widening the scope of the stochastic models
for the parameter variations. This research project ACOSTA (Advanced Concept for Structure Analysis of large
light weight structures) is carried out jointly with Intales GmbH Engineering Solutions and two departments at
the University of Innsbruck (Mathematics, Civil Engineering), supported by the Austrian Research Promotion
Agency. The project focuses on the buckling behavior of the frontskirt of the ARIANE 5 launcher under various
loading and flight scenarios, and the development of new and faster numerical algorithms.
We report about two major new developments in sensitivity analysis. The first one concerns the combination
of Monte Carlo simulation methods with iterative solvers. We succeeded to show that it is possible to save a
significant amount of computing time by performing a load incremental procedure with an initial set of input
parameters and starting the random variations at a later time, when a larger percentage of the ultimate load is
reached. Our experiments showed that this approach does not disturb the accuracy of the statistical indicators.
We also gained understanding of how and when the random variations should be entered in the iterations.
The second development is about incorporating correlation in the sensitivity analysis. On the one hand, an a
posteriori correlation analysis of output variables and their sensitivities allows searching for the most important
indicators of failure. On the other hand, existing correlations of input parameters can be modelled by copulas;
spatial random variations of parameters across the structures can be modelled by random fields. We extended
our computer codes to include both methods (copulas, random fields). This admits the introduction of further
indicators and thus a more complete sensitivity analysis.
We believe that our methods contribute to progress in the area of simulation, focusing especially on robustness,
safety and improvement of design.
Title: CÆSAM CAE centric Application Framework Application to
AIRBUS Stress Analysis Tool
Authors: G. Malherbe, Y. Radovcic, D. Granville, M. Balzano
SAMTECH, Airbus
Time: November 4, 2009 4:20 pm
Room: Lumen
Aeronautical industry is currently facing high industrial challenges: cycle reduction, high simulation fidelity
(composites challenge…), find a new way of working in a world wide organization, cost reduction, improvement
of aircraft Simulation Lifecycle Management.
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To answer these challenges in Aircraft Structural Analysis, SAMTECH developed CÆSAM (an acronym for
„Computer Aided Engineering by SAMTECH“), a CAE centric open Application Framework. CÆSAM allows
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