Vessel Best Practice

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Vessel Best Practice

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1.When defining vessel data, such as support or stinger locations, keep the intended position of the origin for the vessel axis system in mind (locations are relative to this).

2.The relationship between the origins for the vessel and stinger axis systems is important to understand/establish. For simplicity you should consider coinciding the origin and axes of the stinger axis system with those of the vessel axis system. For example, you could put both axis origins/systems at the stern of the vessel on deck height as this would make migration of support data from packages like OFFPIPE easier.

3.The specified support locations refer to the bottom of the support and not the bottom of the pipeline. This is particularly relevant for V-Shaped supports where there is always a gap between the bottom of the pipe and the bottom of the support due to the geometry of the V-Shape. With this in mind it may be necessary apply fine tune offsets to the support locations if the provided coordinates refer to the bottom of the pipeline. Also, if a V-Shaped support is beside a Zero-Gap O support (as is often the case around tenisoners) and both supports have the same elevation then the pipeline may well sit higher over the V-Shaped support relative to the Zero-Gap O support, which in turn may cause localised bending of the pipeline. Again a fine tune offset can rectify this misalignment. Note that a bottom of pipe support location option may be introduced in a future version.

 

support_location_v-shaped

 

support_locations

 

4.Try to use a vessel profile as much as possible, even if it is just a Standard Vessel Profile or a box shaped User Vessel Profile, as it gives a sense of scale to the model and also highlights where the origins, reference points, stinger and supports are located.

5.When defining radii of curvature for different regions along the vessel and stinger please keep the following in mind:

a.Supports are only moved to the radii if their Fine Tune Offset location input is set to [CALCULATED].

b.The direction in which the supports are moved to the radii can be controlled by the Fine Tune Direction input. The default direction is perpendicular to the support angle and if the support angle is left empty (calculated by the UI) then the direction of movement is perpendicular to the corresponding radius.

c.Each radius of curvature is applied incrementally, meaning that all appropriate supports are initially moved onto the first radius (the one with a tangent point furthest along the vessel positive Y axis) then the necessary supports for the second radius are moved again and so on until all radii have been applied.

d.Suitable minimum radii can be determined using the cross section properties of the pipeline and an allowable bending strain values. Generally, some of the vessel supports are in reality fixed along a common line so if a particularly small bend radius is being targeted then there may have to be a gradual transition from the line to the minimum radius. This is typically achieved using a series of radii of reducing sizes. Also, as the pipeline approaches the stinger tip it may be necessary to align the final few supports along a tangent to the minimum radius. This can be done by setting the final radius to a very large value, for example 999m.

e.Depending on the level of tension load acting across the supports during the FE analysis you may find that the target minimum bend radius/maximum bend strain is surpassed due to local concentration effects over the supports. If this is an issue, you can request the analysis to automatically optimise or fine tune the support elevations further, so as to overcome the concentration effects. The final support positions can then be extracted for checking after the analysis has completed. Analysis optimisation is turned off or on using the corresponding drop down on the Radii of Curvature dialog. There is a run time penalty with analysis optimisation so it is recommended to run your analysis first without optimisation and then gauge the need for it upon reviewing the initial results.

radii_of_curvature

6.After creating a Vessel component add it immediately to an empty Model component and use the different viewpoints to check that everything is as expected. Also, use the Support Data button to extract to/check in Excel the support locations and applied offsets to achieve any specified radii of curvature. Optionally, you can enable the Show Radii of Curvature tick box to draw any applied radii of curvatures for supports.

model_view

 

support_data

 

7.For horizontal firing lines consider ignoring any supports on the forward side of the tensioner system. The pipe in this region is not generating or undergoing significant loading and so it does not add any benefit to the analysis; rather it just increases the number of elements and run time unnecessarily.

8.For simplicity and efficiency consider modelling multi-tensioner systems with just a single tensioner component. This should be possible if all of the tensioners are in close proximity to one another. You can also still leave the tensioner supports in place, but just use one tensioner component.

9.Vessel Motion best practice is discussed under Environment, Motion & Loading specific components.