Modal coordinates for aeroelastic analysis with large local structural variations

Abstract

Time domain aeroelastic equations of motion are formulated in a way that allows large local structural variations with a state-space model that is based on a relatively small number of generalized coordinates. Freefree or restrained vibration modes are first calculated for a nominal finite element model loaded with relatively large fictitious masses located at the area of structural variations. These modes and the associated oscillatory aerodynamic force coefficient matrices are used to construct a time-domain model for a basic aeroelastic case where the fictitious mass contribution to the generalized mass matrix is removed. High-accuracy aeroelastic investigations of the effects of structural variations can then be performed by simply introducing mass, stiffness, and damping coupling terms. It is shown that the number of modes required for the investigation of large stiffness variations is substantially lower than that required when fictitious masses are not used, and only slightly larger than the number of modes required for direct aeroelastic analysis of a single structural case.