Support Best Practice

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Support Best Practice

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1.For Double V-Supports avoid using single flat surfaces as they have no lateral restraint and so any vessel roller/yaw motion during analysis will cause the pipe to slide off the supports. If you are modelling V-Shaped supports set the L1 surface and possibly the L3 surface to zero length, while if you are modelling U-Shaped only the L3 surface needs to have a zero length.

2.Zero-Gap O Supports are ideal for modelling the lateral and vertical restraint of tensioner tracks (axial restraint comes from the Tensioner component itself). Also, the Zero-Gap O Support location and restraint always automatically adapts to account for the diameter of the pipeline and so it does not need changes to its inputs to reflect changes to diameter.

3.O-Shaped Supports are typically used on J-lay towers, in particular for modelling bell-mouths. They can be used for tensioners as well, but unlike the Zero-Gap O Support their inputs (roller length) are dependent on pipeline diameter. In other words, if the pipeline diameter changes then the roller length input needs to be adapted so as to keep the O-Shaped Support in suitable contact with the pipeline.

4.Some general advice on the PipeLay contact modelling strategy is as follows:

a.The Contact Ramp, as specified on Constants dialog of the Project component (defaults to 0.1m), is used to numerically build up the contact reaction/stiffness over a finite distance before actual support contact is made by the pipeline. It represents a numerical cushion so as to avoid sudden impact type loads acting on the pipeline when contact is made and thereby helping to limit solution stability issues during dynamics (Refer to Technical Note 5 for more details). This being said the Contact Ramp is only of real use when either:        

i.You are letting PipeLay calculate optimum support stiffness value itself.

ii.You are trying to model non-linear or relatively low support stiffness values.

For large or rigid support stiffness (>= 10000 kN/m) the Contact Ramp offers no benefit as the numerical cushion is too stiff and should be set to zero length so as to stop the pipeline sitting statically above the support contact surfaces.

Contact Ramp

Contact Ramp

 

Metric Constants

Metric Constants

 

b.Avoid specifying huge support stiffness values (>= 100,000 kN/m) as they do not provide any extra restraint to the pipeline and numerically they can require more solution iterations. If supports are rigid in reality then stiffness values in the range of 10,000 to 50,000 kN/m effectively achieve rigid conditions in a PipeLay analysis and anything larger is generally unwarranted.

c.Remember that the support stiffness input is applied to each contact surface on the support and so in the case of a V-Shaped support the net vertical stiffness is greater than the support stiffness value itself.