VIBRATION ANALYSIS OF ISOTROPIC AND COMPOSITE STIFFENED PRESSURE HULLS UNDER INITIAL STRESS

Stiffened isotropic and composite pressure hulls are extensively used in underwater scenario. 2D cad models of isotropic and composite hull are evaluated in Ansys 17 workbench software for buckling and vibration behavior under initial stress. Rib width variation from 10 to 50mm in isotropic pressure hull resulted in increased free vibration frequency, while the reverse trend is observed in the composite hull. Increased radial pressure alone or hydro-static pressure on the hulls caused the frequencies to diminish and finally attain zero value at buckling pressure for both types of hulls under investigation. However the rate at which frequency decreased with increase in pressure is more pronounced in metal hull than in composite hulls indicating gradual reduction in overall stiffness of structure due to external pressure loading unlike in isotropic hulls. Frequency variation under initial stress is analyzed for identical metal pressure hull in 2D and 3D CAD and it is observed that deviation in free vibration frequencies is as high as 18%, higher values being obtained for 2D model.