Stinger Section - Flexible/Flexible Hydro
You can model this type of stinger section, by setting the topmost drop-down box, Section Type, to Flexible or Flexible Hydro.
If you are defining a flexible stinger section, the Properties dialog has significantly more inputs, as shown in the figure below.
Flexible Stinger Section Properties
The Length, Bending Stiffness, Axial Stiffness, Torsional Stiffness and Weight in Air inputs are mandatory. You may also associate Buoyancy with the stinger section. This Buoyancy can be internally computed by the user interface based on suitable inputs for Displaced Volume and Ballast, or alternatively you can manually specify a particular value. Note that if the Displaced Volume input is omitted then the internally computed Buoyancy corresponds to zero. Note also that the Ballast entry defaults to zero.
It is worth highlighting that Buoyancy values are important for Articulated S-Lay stingers and while you should specify such values upfront, or indeed get the user interface to calculate them for you, it is also possible to get the PipeLay analysis engine to optimise the Buoyancy of each stinger section in order to achieve a certain set of desired section angles for the stinger. This optimisation process is discussed under the Stinger component in a later article.
In terms of hydrodynamic inputs, the Drag Diameter, Normal Drag and Normal Inertia are mandatory. The Tangential Drag, Tangential Added Mass and Normal Added Mass are optional inputs, and PipeLay computes default values for these entries if omitted.
For a flexible hydro stinger section the hydrodynamic inputs outlined in the last paragraph are omitted from the Properties dialog, except for the Drag Diameter which is still used for display purposes in related animation files. Instead, the sections hydrodynamic characteristics are defined in Hydrodynamic Properties dialog. All other Properties inputs for the flexible hydro section type are the same as those for the previously discussed flexible section.
In the case of a Flexible Hydro stinger section you have the option to specify relatively complex hydrodynamic properties in the Hydrodynamic Properties dialog. As stinger sections can be relatively arbitrary in shape the specification of hydrodynamic properties can be significantly more complicated than that required for a Pipe Section or Cable component, which you can assume to be circular in cross-section. For example, the hydrodynamic properties of the stinger section may be very different in the vertical and horizontal directions. For this reason, the hydrodynamic coefficients for a Flexible Hydro section can be specified separately for each of three directions; one vertical, and two horizontal. Furthermore, for each direction, the data can be specified as three products as follows:
•CdAd (drag coefficient by frontal area) – for the hydrodynamic loading due to relative fluid/stinger section velocity
•CmVin (inertia coefficient by reference volume) – for the hydrodynamic loading due to stinger section acceleration
•CaVin (added mass coefficient by reference volume) – for the hydrodynamic loading due to water particle acceleration
This means the hydrodynamic properties of a Flexible Hydro stinger section can be characterised by nine hydrodynamic coefficients or products.