MODAL COORDINATES FOR AEROELASTIC ANALYSIS WITH LARGE LOCAL STRUCTURAL VARIATIONS

Time domain aeroelastic equations of motion are formulated in a way th at allows large local structural variations with a state-space model t hat is based on a relatively small number of generalized coordinates. Free-free or restrained vibration modes are first calculated for a nom inal finite element model loaded with relatively large fictitious mass es located at the area of structural variations. These modes and the a ssociated oscillatory aerodynamic force coefficient matrices are used to construct a time-domain model for a basic aeroelastic case where th e fictitious mass contribution to the generalized mass matrix is remov ed. High-accuracy aeroelastic investigations of the effects of structu ral variations can then be performed by simply introducing mass, stiff ness, and damping coupling terms. It is shown that the number of modes required for the investigation of large stiffness variations is subst antially 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.