Technical Note 5 - Contact Modelling Options

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Technical Note 5 - Contact Modelling Options

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Overview

This technical note provides an overview of the contact modelling options available in PipeLay. There are five possible options: Simple (the default), Standard, Pivoting-Bed, Non-Pivoting Bed and Roller which are summarised as follows:

Simple (Option 1). This “single-point elastic contact” option provides the simplest modelling strategy. The support is always associated with the same node and no frictional effects are modelled. It allows relatively large time steps and relatively coarse FE meshes to be used.

Standard (Option 2). This “single-point moving elastic contact” option is an extension of the “single-point elastic contact” option, where the support point can alternate between various nodes as the pipeline moves in the axial direction. Frictional effects are also accounted for, modelled using a non-linear spring approach.

Bed Support

oPivoting (Option 2 enhanced). This “single-point moving distributed elastic contact” option is an extension of the “single-point moving elastic contact” option, with the exception that the bending stiffness of the element(s) in close proximity to the point support is augmented. This effectively applies the support over a finite length rather than just at a single point. The direction of support is aligned perpendicular to the pipeline at the support point.

oNon-Pivoting (Option 3). This “multiple-point moving elastic contact” option provides the most accurate modelling strategy, and is an extension of the “single-point moving elastic contact” option, with the exception that contact can occur over several nodes, simulating a length of pipeline in contact with a rollerbox.

Roller (Option 4). This “singe-point elastic contact with adaptive support rotations” option is identical to the “single-point elastic contact” option except that the orientations of the individual supports continuously adapt to match the orientation of the pipeline resting on them. This means that all reactions imparted by the supports on the pipeline are in the radial (or perpendicular) direction and so do not induce any axial load into the line.  

The rollerbox contact modelling options provided by PipeLay range from a relatively simple contact model capable of modelling the most important aspects of the response of the pipeline/stinger system, up to a more sophisticated and realistic model that is capable of capturing the detailed characteristics of the pipeline/stinger interaction, including relative axial and transverse pipe motion with anisotropic friction effects.

As model complexity increases, so too does the effect on simulation run-times. The simple contact model gives the user the option to run a large number of load cases in a short period of time, for example in the preliminary design phase when a number of configurations may be under investigation. The detailed contact model can then be used in subsequent analyses to investigate the performance of specific configurations.

An important consideration is that all of the rollerbox contact modelling options in PipeLay are now based on elastic contact surfaces. In early versions of the software, very small timesteps were required in order to accurately capture intermittent impact with rollerboxes modelled as rigid surfaces, leading to long simulation run-times. More recent versions offer significant improvements in run-time performance of analyses involving pipeline/stinger interaction.

Further articles go into detail on the general contact modelling strategy and the calculation of optimum support contact stiffness.