HYDROFOIL INSTABILITY AT LOW MASS DENSITY RATIOS
1964
Caporali, R L | Brunelle, E J
A study is made of the low mass-density ratio hydroelastic behavior of fully wetted lifting surfaces of sufficiently high aspect ratio to justify the fundamental assumptions of twodimensional, unsteady hydrodynamic fluid forces and the concept of a rigid streamwise section. Hence, this study is particularly applicable to lifting surfaces in marine usage. In particular, the strut supports of hydrofoil boats which operate at sub-cavitating speeds may be regarded as typical of the hydroelastic systems toward which this investigation is directed. Part I concerns the low mass-density ratio flutter behavior of the two-degree-of-freedom 'typical section' and shows that there exists a critical mass-density ratio below which the classic 'typical section' analysis will predict no dynamic stabilities. However, some extremely sensitive cause and effect relationships are noted. Part II deals with the low mass-density ratio hydroelastic behavior of fully wetted, uniform, cantilever struts or other lifting surfaces, both with and without an angle of sweepback. It was ascertained that the low massdensity ratio flutter behavior of such structures can be properly predicted only if the spanwise character of the strut is explicitly included in the mathematical model used in the analysis. It is shown that a positive non-zero sweep angle is essential for low mass-density ratio bendingtorsion flutter of uniform cantilevered struts to occur.
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