OrcaFlex Manual - Orcina

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System Modelling: Data and Results, Lines
Note: A line can be an inner line in more than one contact relationship, but only if either (a) the outer
line involved is the same in all those relationships, or (b) the outer lines involved all have their
Contents Method set to be free-flooding, and each inner line node is inside at most one of those
outer lines at any one time. This option (b) allows contact relationships to be set up to model pullin
of a single inner line through multiple free-flooding outer lines, providing each inner line node
leaves one outer line before entering the next outer line.
Warnings: The containment modelling does not apply to any attachments to the inner line. So any attached
clumps, drag chains, stiffeners or 6d buoys will experience external fluid conditions that ignore any
containment of the inner node to which they are attached. Attachments to any contained inner
node will therefore – probably wrongly – be subject to fluid loading based on the fluid density,
pressure and kinematics of the sea, not those of the fluid contents of the containing line.
The line results Relative Velocity, Normal Relative Velocity, Axial Relative Velocity, Strouhal
Frequency, Reynolds Number, Seabed Normal Resistance and Seabed Normal Resistance/D (when
the default linear seabed resistance model is used) do not take into account line containment. They
therefore report the fluid conditions or seabed interaction that the node would have experienced if
it had been fully exposed to the environment. The relative velocity and seabed resistance results
reported are scaled by each node's containment scaling factor in order to arrive at the conditions
actually applied during the simulation. Often, the node is completely contained, and therefore the
environmental velocity and seabed resistance values are scaled down to zero. These effects
therefore do not affect fully contained nodes at all during the simulation.
Note that you should take care if any VIV modelling, wake interference or lift forces due to seabed proximity are
specified for an inner line section for which containment might occur. Specifically:
� Any VIV modelling and lift forces specified in the data will be disabled on an inner line node whenever any
amount of the length of line modelled by the node is contained, and so shielded, by the outer line. An inner line
node that enters into, or emerges from, an outer line end during the simulation will therefore experience a
discontinuity when the force from these effects is suddenly disabled (when entering containment) or re-enabled
(when emerging from containment).
� Any Wake interference effects specified in the data are not affected by inner line containment – they will
continue to be included even if the inner line node is contained within the outer line. The inner line nodes will
therefore still generate wake, if that is specified in the data, and will still react to any wake from upstream lines
that generate wake. This is not appropropriate for any inner line nodes that are contained, since they will be
shielded by the outer line. So it is therefore recommended that you do not specify wake generation or wake
reaction for any inner line section that will be contained at any time during the simulation.
Data
Line contact data for all lines in the model are specified on a single data form with two pages: Relationships and
Penetrator Locations.
Relationships
Penetrating Line, Penetrating Line Is, Splined Line
These three choices select two lines from those present in the model, and specify the contact and containment
relationship between them.
The splined line will present a curved cylindrical contact surface to the penetrators attached to the penetrating line,
and the curved cylinder axis will follow a smooth spline curve that follows and passes through the nodes of the
splined line.
Penetrators on the penetrating line, as specified by the Penetrator Locations data, will then come into contact with
this surface if they meet it, and experience reaction and friction forces that are calculated using the Normal
Stiffness and Shear Stiffness. The splined line contact surface will be either the external or internal surface of its
curved cylinder, depending on whether the penetrating line is specified to be Inside, Outside or Around the splined
line. For more detail on how this interaction is modelled, see the modelling page.
Penetrator Locations
Penetrators are attached to some or all of the nodes of the penetrating line. The default behaviour is to attach a
penetrator at every node on the penetrating line, at the node centre. Alternatively, the distribution and position of