OrcaFlex Examples - E Pipelay and Recovery

E01 OrcaLay Plus Lateral Restraint.zip (6.5 MB) – Description PDF (142 KB)

This model is based on the simple method used in OrcaLay for multiple static analyses of lay configurations. The reactions between the lay pipe and the stinger rollers are generated by Tether type Link objects, which have strength in tension only. This has the advantage of speed and simplicity over more detailed treatments, but does not allow for movement at the tensioner. It therefore represents the common situation where the pipe is held fixed during welding operations.

The OrcaLay model is two-dimensional and consequently has tethers in the vertical plane only. This model extends the idea by adding tethers to provide lateral restraint as well as vertical and can therefore deal with three-dimensional motions due to out-of-plane environmental conditions.

This type of model is not suitable for modelling the situation where the tensioner allows axial movement of the pipe because the roller locations (Link connections) would move with the pipe which is unrealistic.

The method allows for lift off the rollers, but in setting up the geometry implicitly assumes the pipe lies on the stinger over its entire length. Any significant departure from this condition will lead to some inaccuracy in the geometry. Nonetheless, it does provide a simple and robust technique for modelling many pipelay operations.

E02 Rigid Hinged Stinger.zip (8.8 MB) – Description PDF (279 KB)

This model represents a rigid stinger hinged off the back of a lay vessel with the rollers not represented as individual supports but as a continuous support with a constant radius of curvature. This support is provided in the model by a set of elastic solid shapes. The lay pipe is supported laterally by additional elastic solids.

Because the interaction between the lay pipe and the stinger can tolerate axial movement of the pipe, this model allows the pipe to move in and out of the two tensioners. The model therefore represents the situation where welding operations have been suspended and the pipe is moving relative to the vessel so as to limit stresses. Modelling both tensioners is not generally necessary, but it has been done here to demonstrate how easily it can be done.

The method allows for lift off the stinger and axial movement of the line. However the individual loads applied to the pipe are approximated by contact with a continuous curved surface, so local loads due to rollers are neglected. Nonetheless the model provides a quick method of assessing how a stinger set-up will behave before embarking on more detailed analysis.

E03 Rigid Hinged Stinger with Rollers.zip (16.6 MB) – Description PDF (563 KB)

This model represents a rigid stinger hinged off the back of a lay vessel with the rollers represented as individual supports modelled as pairs of single segment lines with clashing enabled. There are rollers on both stinger and the lay barge. The lay pipe is restrained laterally by the V-shaped configuration of the roller lines.

Line clashing is not applied in statics, so measures are required to control the position of the lay pipe during this part of the calculation. The dynamic simulation is carried out in two stages: firstly the line is lowered onto the rollers by fictitious winches without wave environment. This simulation is run for long enough for the system to settle and the final state is preserved to provide the initial conditions for subsequent cases including wave motion.

Because the clashing interaction between the lay pipe and the stinger can tolerate axial movement of the pipe, this model allows the pipe to move in and out of the tensioner. The model therefore represents the situation where welding operations have been suspended and the pipe is moving relative to the vessel so as to limit stresses. Note the clashing interaction between lay pipe and rollers is frictionless.

The method allows for lift off the stinger and axial movement of the line. The individual rollers are modelled explicitly and represented by lines that will generate a reaction force when the lay pipe contacts them. It therefore provides a detailed model of the pipe lay operation with all relevant features accurately represented.

E04 Articulated Stinger.zip (20.2 MB) – Description PDF (234 KB)

This model represents a three-section articulated stinger hinged off the back of a lay vessel with the rollers represented as individual supports modelled as single segment lines with clashing enabled. In general there would be rollers on both stinger sections and the lay barge. The lay pipe is restrained laterally by vertical supports on the final stinger section.

Line clashing is not applied in statics, so measures are required to control the position of the lay pipe during this part of the calculation. Consequently the dynamic simulation is carried out in two stages: firstly the line is lowered onto the rollers by fictitious winches without wave environment. This simulation is run for long enough for the system to settle and the final state is preserved to provide the initial conditions for subsequent cases including wave motion.

Because the clashing interaction between the lay pipe and the stinger can tolerate axial movement of the pipe, this model allows the pipe to move in and out of the tensioner. The model therefore represents the situation where welding operations have been suspended and the pipe is moving relative to the vessel so as to limit stresses.

E05 Pipe Davit Lift.zip (30.0 MB) – Description PDF (305 KB)

The free end of a steel pipe is lifted from the seabed by davits to bring it alongside a workboat. The lift is modelled dynamically in small waves and no current.

E06 Midline Pull-up.zip (2.2 MB) – Description PDF (266 KB)

A long umbilical cable is laid on the seabed. The mid point is then lifted a short distance, e.g. to position the umbilical in a plough prior to burial. The lift is carried out in still water.