Keywords: cylinders, external pressure, buckling, finite elements, ANSYS.

This paper reports on a theoretical investigation into the buckling characteristics of six series of ring-stiffened circular cylinders that experienced general instability when subjected to external hydrostatic pressure. Each series contains between three to five models with the same internal and external diameters, but with different sizes of and numbers of ring-stiffeners. Four series contained models that were machined to a high degree of precision from steel, while the other two series contained models machined to a high degree of precision also, but from aluminium alloy. The theoretical investigation focused on obtaining critical buckling pressure values P_cr, for each model with the well-known Kendrick's Part I and Part III theories. Also using the computer package ANSYS, which is based on the finite element method. Each ring-stiffened cylinder was modelled and subjected to external pressure to obtain the respective critical buckling pressures, namely P_cr. The thinness ratio lambda¹, which was derived by the senior author, together with a dimensionless quantity called the plastic knockdown factor (PKD), which were calculated for each model. The plastic knockdown factor was calculated by dividing the critical buckling pressure P_cr, by the experimental buckling pressure, namely P_exp, obtained from previous experiments carried out; mostly at the University of Portsmouth. The thinness ratio was used because vessels such as these, which have small but significant random out-of-circularity, defy "exact" theoretical analysis and it is because of this that the design charts were produced. It is true that vessels such as these, which have larger and more regular distributions of initial out-of-circularity can be successfully analysed by "exact" theoretical methods. Three design charts were constructed by plotting the reciprocal of the thinness ratio (1/lambda¹) against the plastic knockdown factor (P_cr/P_exp), using results from Kendrick Part I, Kendrick Part III, and ANSYS.

This work is presented for the first time in the present paper. Comparison between Kendrick's theories and experimentally obtained results was good.

A typical pressure vessel consists of cylinders, cones and domes. This structure appears in the form of thin-walled pressure vessel because of their practical use in mechanical engineering design [1]. Perhaps the pressure vessel that can withstand uniform external pressure most efficiently, from the structural point of view, is the thin-walled spherical shell, but most underwater pressure vessel are not in this shape, because other shapes lend themselves more readily for other important purposes besides structural efficiency.

The study of the strength of ring-reinforced circular cylinders under uniform external pressure is very important in the design of pressure vessels that can be used to build submarine or submersibles. Scientists have been researching for faster and more efficient methods of determining design parameters for ring-stiffened circular cylinders; this is the main theme of the present paper.

1

Ross, C.T.F, Pressure Vessels: External Pressure Technology, Horwood Publishing Ltd., Chichester, UK, 2001.

purchase the full-text of this paper (price £20)

go to the previous paper
go to the next paper
return to the table of contents
return to the book description
purchase this book (price £145 +P&P)