Besch and Liu 



Prominent among unconventional ships are hydrofoil craft and surface 

 effect ships. Flutter is a recognized problem for the strut-foil systems 

 of hydrofoil craft. The rudders contemplated for surface effect ships 

 may be similarly vulnerable. 



Much research has been done on the flutter of strut models 

 analogous to the above systems. The initial demonstration of strut 

 flutter was made by Hillborne[l]in 1958. Further experimental work has 

 often been accompanied by difficulties, including models that wouldn't 

 flutter, models that were destroyed by flutter or divergence, and facil- 

 ity limitations. Numerous theoretical analyses have been produced, but 

 none has been successful in predicting all experimental results conser- 

 vatively. 



Out of these efforts have come many clues to the nature of strut 

 flutter. By combining previous results with some recent experimental 

 and theoretical work we have produced a concept of flutter involving 

 two different flutter regions. This paper will discuss existing flutter 

 data from the standpoint of two flutter regions, and will present cal- 

 culations which indicate the origin of the two regions. The expected ac- 

 curacy of flutter speed predictions within each region will be described. 



Existing data deals with a large number of simple struts, and a 

 small number of struts with tip pods, some with foils forming an in- 

 verted-T configuration. A sample configuration is shown in Figure 1. 

 All tested configurations have been small-scale models. Most discus- 

 sion will be devoted to simple struts and struts with pods. One strut 

 with foils has been included. 



All struts were cantilever supported from an effectively rigid 

 foundation, so that the structural characteristics of the system were 

 those of a cantilever beam in which both bending and twisting could 

 occur. Because of the relatively high aspect ratio and thin profile of 

 the struts, bending consisted of displacements perpendicular to the 

 plane of the strut, while twisting occurred about a spanwise elastic 

 axis. Vibration modes of the struts consisted of a series of modes 

 which could usually be identified as predominantly bending or predo- 

 minantly twisting or torsion. 



The mode shapes of the struts at flutter inception could also be 

 characterized as predominantly bending or torsion. In most cases, 

 struts displayed either bending or torsional oscillations at flutter. 



[lj References are listed on page 393 



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