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Tensioners

The tensioner is a custom component that allows modelling tensioning devices for rigid risers. Each tensioner consists in an assembly of cables and tension properties. They are characterized by the following parameters :

  • Name: Enter the name of the Tensioner component.

  • Number of tensioner units: the number of cables or tensioning jacks.

  • Dynamic tension limit: DTL for each tensioner - this value will be used when running drilling riser preliminary stability analysis according to API Recommended Practice 16Q.

  • Tensioning force: the total tension imposed at the riser or telescopic joint outer barrel (TJOB) top.

  • Tensioner system dynamic stiffness: The percentage change in top tension induced by a 1m vertical displacement of the vessel (heave). The actual cable stiffness K depends on the percentage p and the tension T as K = p/100*T . Zero means that the top tension does not vary as the riser moves vertically.

  • Connection points diameters: the upper and lower tensioners (cables or jacks) connection points are distributed around two circles which have diameters Dtop and Dbottom respectively.

  • Connection points azimuths: On the diameters previously defined the points of connections for each tensioner are defined by their azimuth angle with respect to the global X-axis, expressed in degrees. These angle are counted positive anti-clockwise when seen from above. The number of lines in the table is adjusted according to the number of tensioners specified above ("Number of tensioner units").

  • Primary points: The tensioner object may be connected to other objects (drilling riser, OB, drillship) through two primary nodes. These two points must have been previously created and belong to another object in the model : primary points of lines or fairleads for example. The nodes coordinates may not be modified directly, and the corresponding edit boxes remain grayed. Selecting the object, connection point and type of boundary conditions may be done exactly as when connecting, and selection is as per a generic line using "Linked to" and "Attach point". The co-ordinates, although grayed-out because they are not modifiable, are updated according to the selected points.

Conventions applicable to load intensity:

The loading direction depends on the tensioning force value sign:

  • Positive tension: The force is acting from the secondary point towards the first primary point. A reaction force is acting from the first primary point towards the secondary point (see figure 1 below).

  • Negative tension: The forces directions correspond to figure 2.

Note that the default names of the primary points (TopTens and BotTens) are adequate for standard tensioner devices where the tensioning units are pulling the riser upwards. In this case, the tensioning force value should be positive.

For a particular tensioning system pushing the riser (as for hydraulic jacks pinned at a deck below the riser connection (see figure 3), the tensioning force value should be negative.

Note

The local reference frame (x,y) will coincide with the reference frame of the object to which the tensioner is connected (local Reference frame of the drillship, otherwise global frame).

Note

In the nominal position, the tensioner system must be vertical (same fleet angle for all the cables). If the user tries to connect the tensioner with a misalignment, the following warning is displayed and the connection aborts :

Once the tensioner has been connected, if the user moves one end so that the two ends are not vertically aligned any more, the following warning is displayed and the tensioner is disconnected:

Note

Once the tensioner has been created, the following entities are automatically created and added in the Types and Model trees :

  • One Cable/chain properties type
  • One object tensioner whose name has been previously given
  • As many cable objects as previously defined
  • One loading object.