Modelling and behaviour of cylindrical shell structures with helical features

• Cylindrical shells with helical features are not widely studied computationally.
• The study proposes a robust and powerful method of parametric helical meshing.
• Method is illustrated on the post-buckling behaviour of axially-compressed cylinder.
• Imperfection sensitivity of spirally welded cylinder is investigated.

Spiral welding or bonding is a particularly efficient and cost-effective method of constructing continuous tubes. However the understanding of the mechanics of such structures is not yet well developed. This is in no small part due to the difficulties involved in their computational analysis.Cylindrical shells are traditionally modelled using rectangular finite elements oriented parallel to the meridional and circumferential axes. However, spiral features are particularly challenging to model because such features are not orthogonal to the axes of the cylinder. Commercial finite element pre-processors often struggle to mesh these with anything other than a free triangulation. A superior mesh would consist of well-conditioned rectangular elements oriented orthogonally with respect to the axes of the helix, termed a ‘helical mesh’, but this requires significant programming effort. A helical mesh is particularly important if features of the shell such as geometric imperfections, residual stresses, weld material and heat affected zones, and bonding in systems using adhesives are required to follow the helical form. Helically wound structural forms are widely used in different applications that demand continuous cylindrical forms. The most common uses in structural engineering are in spiral wound tubes, piles, chimneys and pipelines.This paper describes a powerful computational procedure developed by the authors to generate high quality helical meshes. Special emphasis is placed on the modelling of geometric deviations defined relative to the helix, appropriate for the analysis of spiral welded and stiffened tubes. The effect of helical meshing is illustrated using benchmark examples of perfect and imperfect cylinders under axial compression.