Any pressure hull invariably has imperfections as a result of the manufacturing procedure. Imperfections in a spherical pressure hull are the basis for localized buckling and deformation behavior. Numerical analysis and analytical calculations are carried out to predict
the buckling behavior and strength of a pressure hull made of titanium alloy (Ti-6Al-4V) for both perfect and imperfect pressure hulls. Finite element analysis is carried out for different imperfection angles to see the effect on strength and buckling. Results of numerical analysis show that
there is considerable reduction in both buckling pressure and strength as a result of imperfections. Hence, allowable deviation due to imperfection for a spherical pressure hull has to be considered for thickness calculations.Abbreviations:P external pressure (Design
pressure)Dm mean diameter of the pressure hullRm mean radius of the pressure hullRi imperfect radius of the pressure hullt thickness of the pressure hullΔR imperfect
deviationδ imperfection angleσ hoop stressPy pressure at yield strength of the materialPb buckling pressureE Young’s modulus of the materialμ Poisson’s
ratioMSW meters of sea waterAPDL ANSYS Parametric Design Language
Manned submersibles are underwater vehicles. These vehicles are equipped with an atmospheric pressure casing called a spherical pressure hull, which can accommodate up to three people. The spherical pressure hull facilitates safe passage to high-pressure environments.
It has circular openings that serve as viewports to enable underwater viewing and intervention. The regions near the openings are the weakest in the pressure hull and must be reinforced. Reinforcement of the viewports is performed using the area replacement method. The amount of material removed
from the viewport opening must be replaced along the axis of symmetry of the opening. This is the minimum amount of material that must be placed along the circumference of the viewports. Reinforced viewports in the pressure hull are analyzed using finite element analysis, and the stresses
are classified into primary and secondary stresses. The reinforcements of the viewports are carried out in such a way that the calculated primary and secondary stresses are below the permissible limits.Abbreviations:P ‐ External pressure (design pressure)Dm
‐ Mean diameter of the pressure hullRm ‐ Mean radius of the pressure hullt ‐ Thickness of the pressure hullσ ‐ Hoop stressPy ‐ Pressure at yield strength of the materialPb
‐ Buckling pressureE ‐ Young’s modulus of the materialγ ‐ Poisson’s ratioMSW ‐ Meters of sea water
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