1. Pipe-in-pipe contact input

  • Fluid loading on inner pipe: Determines if the inner pipe is exposed to environmental loading or kinematics based on relative movement between inner and outer pipe.

1.1. Pipe specification

The position of the master pipe in the pipe-in-pipe contact pair. This option decides if the outer or inner pipe should be the master pipe.

The contact between the master pipe and the slave pipe will be applied between a node on the master pipe and an element in the slave pipe. This results in nodal loads along the master pipe and discrete element loads along the slave pipe. The number of artificial contact elements is equal to number of nodes in the master pipe.

The master line and the slave line is specified by

  • line id, first and last segment number

or

1.2. Contact force characteristics

  • Stiffness type, Options Linear or Non-linear:

    • Linear : Single value input

    • Non-linear: A table of force/displacement pairs must be entered.

    • Contact compression stiffness between the master and slave pipe. The contact stiffness, specified as stiffness per unit length along the master pipe, should be chosen large enough, but not stiffer than necessary. Very high stiffness values may lead to long run-times, instability and high-frequency numerical noise. When selecting the stiffness it may be useful to consider penetration for a characteristic force and also the convergence of the results that are of interest.

Input for dynamic analysis only (i.e. not applied in static analysis):

  • Relative damping level (RELDAM): Relative damping at estimated eigenperiod in the master, slave and contact spring system.

  • Damping: damping coefficient per unit length of master pipe. Damping is only applied in the radial direction.

  • Spring friction stiffness (STIFF) : Associated with static friction coefficient. The stiffness used when loading friction forces.

  • Static friction : Static friction coefficient

  • Dynamic (sliding) friction : Dynamic sliding friction coefficient

  • Axial friction switch: Controls if the axial friction between master and slave is included.

  • Rotational friction switch: Controls if the rotational friction between master and slave is included.

  • Velocity limit for change from static to dynamic friction

Based on specified damping level the stiffness proportional damping coefficient is calculated by

Static friction, Dynamic (sliding) friction and Velocity limit are only applied if Axial friction switch is activated.
Rotational friction switch requires that Axial friction switch is activated.
\[a_2=2\times \mathrm{RELDAM}\times \sqrt{\frac{\mathrm{AMS\_M+AMS\_S}}{\mathrm{STIFF}}}\]

where

  • \(\mathrm {AMS_M}\) and \(\mathrm {AMS_S}\) are structural mass per unit length of the master pipe and the slave pipe respectively

  • \(\mathrm {STIFF}\) is contact spring stiffness per unit length.

1.3. Contact spring stiffness

  • Contact spring stiffness: Spring compression stiffness per unit length