Structural Topology Optimization Of Rudder Surface Considering The Flutter Performance

Structural flutter problem, involving aeroelastic and structural dynamics, is an important but hard-to-predict self-excited vibration which always causes paroxysmal destruction to a structure. Rudder surface of aircraft always encounters flutter during its hypersonic flight. Whereas, only mass balance and local stiffness strengthen are available to rudder surface’s flutter suppress at present. Both of them are belong to the passive flutter suppress and always increase the weight of the rudder surface. Active flutter suppress is a method utilizing exterior control systems. The inherent time delay and instability induced by them are serious threats to the safety of aircraft. Although too many simulations and tunnel experiments about active flutter suppress have been done, only few can be really applied to aircraft flight. In order to improve flutter speed and simultaneously lighten its weight, structural topology optimization is applied to the design of the rudder surface in our work.Theories about flutter analysis and structural topology optimization are presented and three optimization models are constructed based on the characteristics of exiting commercial software for the flutter property optimization of a rudder surface. Firstly, the two models respectively based on flutter damping constraint and bending/twist modal frequency splitting are carried out for the rudder surface optimization. The flutter damping constraint based model executed on the Nastran platform significantly increases the flutter speed but only an undesirable topology configuration is achieved. While the bending/twist modal frequency splitting based model carried out on the Optistruct platform gets an applicable topology configuration but without obviously improvement on flutter property and mass lightening. For obtaining a desirable rudder surface topology configuration, a two-stage optimization model which successively uses the flutter damping and the frequency-splitting as constraint is proposed after the serious comparison of the previous optimization models. The results from this two-stage optimization model indicate that both flutter speed and lightweight of the rudder surface are promoted dramatically. A desirable rudder surface topology configuration with high flutter speed as an intrinsic property is achieved by introducing topology optimization into its design, which is an effective method to settle the aeroelastic stability problem of the rudder surface.