Stinger Best Practice

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Stinger Best Practice

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1.When defining support locations remember to keep the intended position of the origin for the stinger axis system on the vessel in mind (locations are relative to this). The same applies to the orientation of the stinger axes, by default the stinger Y axis points in the opposite direction the vessel Y axis. Note that the support locations for all S-lay stingers can either be left as specified on the Stinger and/or Stinger Section components or alternatively they can be adjusted by the UI so as to map them to various radii of curvature along the vessel, as defined on the Vessel component. This latter approach is discussed later under the Vessel Component section.

stinger_coordinate_system

 

2.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_origin

 

suppoet_locations_explicit_rigid_s-lay

 

4.For Articulated S-lay stingers the following points are worth highlighting:

a.The specified Section Orientations are just starting positions for the stinger sections. These positions may change during the analysis depending on the loads acting on the sections and the stiffness of the connections between them.

 articulated_s-lay_sections

 

b.When you are using non-linear flex joints for connecting the stinger sections and the Section Deformation option on the Stinger component is set to Specified Orientation then the flex joint curves are with respect to the defined section orientations. This means the zero moment/angle point on the flex joints curves correspond to the input section orientations and if the input orientations are changed then so too should the curves in order to ensure consistency. If however the Section Deformation option is set to Horizontal then the curves are always with respect to the horizontal axis (zero points correspond to horizontal) and so are independent of section orientation inputs.

 

       section_deformation

 

c.When trying to model rotational stops on flex joints then it is best to use the automatic non-linear curve option as this allows for the simple specification of allowable free rotation angles with the corresponding moment-angle curves then automatically calculated by the PipeLay user interface.

 

flex_joint

 

d.If the net buoyancy (buoyancy minus ballast) of the stinger sections is known/fixed and the resulting section angles are unknown then it is best to position the sections with mean or best guess initial orientations. The aim is to keep the amount of movement during the analysis to a minimum, thus improving run time and solution stability. If the opposite is the case where the net buoyancy is unknown, but the desired section angles are known then the user can adopt either of the following approaches:

i.Set the section angles to the desired values, but initially model the connections between the sections as rigid by just assigning a large linear stiffness to the flex joints. Run the static analysis on the initial model and using the output review the loads acting on the stinger sections. Using these loads and a suitable hand calculation determine suitable buoyancy/ballast values for the sections. Then apply the calculated values to the model and re-run the analysis with the original flexible flex joints included.

ii.Rather than performing a manual calculation, just let PipeLay automatically calculate suitable net buoyancy values itself by setting the Optimise Buoyancy option on the Stinger component to Yes. The automatic calculation is similar to the manual one and it will report both the level of applied net buoyancy as well as any deviation from the specified section orientations/angles. Please refer to the Articulated S-Lay Stinger article for a full outline of the automatic buoyancy calculation process.

 

articulated_stinger_buoyancy