Effects of structural nonlinearities on limit cycle response of aerodynamic surfaces

D e f i n i n g t h e f l u t t e r and divergence c h a r a c t e r i s t i c s o f aerodynamic surfaces i s a bas ic requirement i n assur ing s t r u c t u r a l and performance i n t e g r i t y o f a g iven design f o r I t s opera t iona l environment. Divergence and f l u t t e r phenomena a re uns tab le motions w i t h inc reas ing ampl i tude. For systems c o n t a i n i n g s t r u c t u r a l n o n l l n e a r i t l e s , another mode o f a e r o e l a s t i c response -l i m i t c y c l e o s c i l l a t i o n -may be present . The p o t e n t i a l o f l i m i t c y c l e response i s o f importance s ince these o s c i l l a t i o n s may occur w i t h i n the aerodynamlc su r face f l u t t e r and divergence f l i g h t envelope and may lead t o f a t i g u e damage o f the system even though a e r o e l a s t i c i n s t a b i l i t y i s n o t encountered. This paper presents an asymptot ic expansion approx imat ion technique which was developed t o p r e d i c t t h l s type l i m i t c y c l e response f o r aerodynamic surfaces w i t h d i s c r e t e s t r u c t u r a l n o n l l n e a r i t i e s . As a p a r t o f t h i s i n v e s t i g a t i o n . numerical s i m u l a t i o n r e s u l t s were used t o eva lua te the adequacy o f the asymptot ic expansion s o l u t i o n s t o the non l inear problem. Several numerical i n t e g r a t i o n techniques were evaluated, on a comparat ive bas is , f o r p r e d i c t i n g the l i m i t c y c l e response o f the non l inear system.