Besah and L%u 



VI. CONCLUSIONS 



Strut flutter occurs in two different hydroelastic modes. At 

 low values of generalized mass ratio flutter occurs in a predominantly- 

 first bending mode shape with the qualitative characteristics of the 

 "new mode" previously described. At higher values of generalized 

 mass ratio, flutter occurs in a predominantly first torsion mode shape 

 with the qualitative characteristics "mode 2" described in the text. 

 The flutter mode of a strut can be determined by examining the mode 

 shape of the second vibration mode of a strut in water, except in a 

 transition region where strong coupling interferes with this identifi- 

 cation. 



Flutter speed predictions using the present analysis are ge- 

 nerally inaccurate. In the bending flutter region, flutter is often pre- 

 dicted to occur in the wrong mode so that flutter speed predictions 

 cannot be used. In the torsional flutter region, the accuracy of flutter 

 speed predictions is dependent on the value of torsional mass ratio. 

 Predicted mode shapes and frequencies are nearly always accurate 

 when three-dimensional hydrodynamic loading is used. 



Foils attached to a strut in an- inverted-T configuration have a 

 strong effect on the flutter characteristics of the strut. Further in- 

 vestigation of foil effects is needed. 



NOTATION 



a nondimensional distance from midchord to elastic axis, 



measured perpendicular to elastic axis, positive aft as 

 fraction of semichord b 



a nondimensional distance from midchord to local aero- 



dynamic center (for steady flow) measured perpendicular 

 to elastic axis, positive aft as a fraction of semichord b 



b semichord measured perpendicular to elastic axis 



[_Cj damping matrix of strut 



\qS\ effective damping matrix of the strut-fluid system 



C(k) complex Theodorsen circulation function 



C p local lift slope for a strip perpendicular to elastic axis 



in steady flow 



366 



