Aeroelasticity and sizing in a multilevel modeling approach for preliminary design

Abstract

In the preliminary design phase, aircraft are described with a limited level of detail, the focus being on fast investigation of a large number of cases and quickly changing configurations and parameters. An evaluation chain at preliminary design usually consists of a number of different methods, including analytical equations (e.g., for range), frequency response (e.g., for handling qualities), and time simulations. It is a highly coupled, iterative process. In many cases the analysis environments for preliminary design are heterogeneous, incorporating methods and tools ranging from standard software to in-house solutions.

Process chains are very much adapted to the specific needs of a group or a company, and interactions of analysis methods are performed manually or are hard coded in the process. Some attempts have been made to generate a more coherent process chain for preliminary design. For an industrial use, one of the major motivations of re-examining the existing design loops is the need for modularity of the used analysis methods. In the same environment, the designer wants to be able to execute analysis modules with varying complexity, for example, to change a description of the structure from a mass or beam element type to a small finite element representation, without having to change the complete process.

As part of the VIVACE / Prelude case study, the Simulation Toolbox task was aimed at a modularization of the preliminary design loop. An outline of a modular design environment had been defined by the industrial partner at the outset of the project. As a representative example for an analysis element, a module for nonlinear time-domain simulation was selected to be implemented. The module is based on a multibody simulation approach, which is well suited for the preliminary design task. This is because it is focused on models of medium level of complexity, and also because it has inherent capabilities for fast parameter variation and for a simple coupling of engineering disciplines, especially rigid body flight mechanics, structural dynamics, and aerodynamics.

In the majority of cases, dynamic aeroelastic deformations are neglected at an early aircraft design stage. However, as aircraft become increasingly more flexible (resulting from the application of new materials and structural optimization), the introduction of aircraft elasticity is expected to greatly increase the reliability of the analysis results even earlier in the design process than previously possible. An example is the calculation of dynamic (maneuver) loads where an introduction of aeroelastic effects can significantly change the results. The sample application presented in this chapter has been taken from that field.