POST-BUCKLING ANALYSIS OF UNDERWATER VESSELS

Abstract

Most of the underwater vessels are designed to avoid buckling. This in turn adds to the weight and hence cost and performance of the vessels. This cost can be reduced if nonlinear and post buckling behavior of the vessels is carried out. In certain cases, the stiffness in the system can be introduced that will avoid large deformations and the resulting plastic strain. One form of this stiffness can come from structures contained by the vessels. In this way the lower buckling mode of the vessel can be filtered out and it will be able to withstand higher buckling pressures. Extensive work has been done on the postbuckling and buckling behavior of vessels to find out the critical load and the postbuckling strength of the structure. The objective of this research is to study the nonlinear buckling behavior of shell within shell structures .The postbuckling behavior of the outer shell will be studied resulting in the contact between the two cylinders and the critical buckling load of the complete model will be found out. The lower buckling mode will be filtered out by the introduction of nonlinear stiffness from the contained structure. Interaction of the vessel with the contained structure will also be studied. The system was modeled in ANSYS and linear buckling analyses was carried out first to determine the Eigen buckling modes of the individual cylinders. Complete nonlinear solution using the complete model was obtained. Geometric (large deformation), and element (contact) nonlinearities were included in the analysis. The buckling load of the structure was found out. As a result of nonlinear buckling analysis, we found out the outer cylinder has a finite postbuckling strength .Because of which it deformed and came in contact with the inner cylinder and the complete system collapsed at the critical load of the structure. The buckling load is higher than the buckling load of the individual cylinders which is an indication that the first buckling mode has been filtered out.