Calculations Showing the Influence of Aerodynamic Damping on Binary Wing Flutter
The influence of damping is examined by comparing the flutter critical speeds and frequencies obtained using the complete equations of motion and those obtained when all the damping terms are omitted. The calculations are made for binary flexure-torsion flutter of a wing in incompressible flow and the comparisons extend over ranges of values of the principal parameters. When the ratio of air density to wing density is high, the damping terms are found to raise the flutter speed by a large amount. But when the ratio of air density to wing density is low, a condition often occurring in practice, it appears that, over a wide range of parameter variation, the flutter speed obtained in the absence of damping is reasonably close to that obtained from the complete equations. Further experience is obviously needed before any general conclusions can be re~¢hed, but the present results offer some hope of reducing either the extent of, or the accuracy needed in, the aerodynamic information used for wing flutter calculations. It is pointed out that with constant aerodynamic coefficients the flutter speed for an undamped system is independent of the wing density.
Approximate Formulae for Flutter Prediction
On the basis of certain simplifying assumptions a general equation can be developed that provides an estimate of the flutter speed of a binary system. The equation includes aerodynamic stiffness derivatives, and in the absence of reliable derivatives for oscillatory motion it is suggested that derivatives derived from steady flow measurements can be used. The equation is applied to derive specific formulae for main surface flexure‐torsion flutter. The effects of compressibility on the derivatives for this particular case is deduced, and the derivatives are then used to estimate certain general effects of compressibility on flutter. It appears that many of the generally accepted features of flutter in the transonic region can be established by this approach, but the application of the formula is limited by the lack of reliable data for aerodynamic stiffness derivatives. A concentrated effort to establish these derivative values is likely to be more rewarding in the long run than flutter tests on innumerable models to establish overall flutter trends of limited application.
An Optimization Approach to Occupant Safety and Fuel Economy in Vehicle Design
1. Abstract A major challenge in automotive design is the creation of safe vehicles with minimal environmental impact. This study presents a modeling framework for evaluating and optimizing body designs for improved occupant safety and fuel efficiency. Vehicle body mass is considered as the main link between safety and sustainability. The modeling framework includes frontal crash energy absorption, restraint system design and fuel economy. Preliminary results indicate a Pareto-optimal curve between safety and sustainability may exist when other factors are not taken into account. A more complete modeling framework that includes more sophisticated sustainability and safety metrics, cost and other market considerations, is suggested in order to support better design and regulatory decisions. 2. Keywords: Automotive body structures, fuel economy, occupant safety, optimal vehicle design, restraint systems