Collapse of thick-walled cylinders under external hydrostatic pressure

The paper presents an in-depth study that has not been done before, and is deemed to be very important in ocean engineering. The paper analyses the buckling of several thick-walled circular tubes under external hydrostatic pressure, using the computer software ANSYS for elastic and plastic buckling; together with Ross's method for determining the best buckling prediction method suitable for real life application; for the first time. Several selected tubes from the experimental data were analysed by Eigen buckling and ANSYS nonlinear analysis. The ANSYS nonlinear analyses included material and geometrical nonlinearity. Besides using ANSYS, Ross's Design Chart was used to test its capabilities, and then compared with the experimental data to determine whether it was safer or not than the ANSYS nonlinear predicted? ANSYS nonlinear proved to be most convincing, but not quite as reliable or easy to use as Ross's nonlinear analysis. The reason was that Ross's methods were based on over a century's work of experimentation, and used the simple, but reliable von Mises formula; together with Windenburg's thinness ratio, whereas, ANSYS suffered somewhat from numerical instability; as a result of applying the finite element method to large plastic strains; and manipulating very large and small numbers together. The details from this study, together with Ross's design chart will one day enable large submarines to be designed to descend to 11.52 km below the sea level, that is, to the bottom of the Mariana's Trench. Moreover, such deep diving submarines may be useful in retrieving the 10,000 billion tonnes of methane hydrates, lying below the sea bed; together with other minerals and precious metals, etc.