1. Pipe-in-pipe contact

Describes input for Pipe-in-pipe contact

This data group is optional and is available for Arbitrary Systems only.

In the following the input parameters are described. A maximum of 400 pipe-in-pipe specifications may be given. The input lines in this group must be given in one block for each pipe-in-pipe pair.

1.1. Data group identifier, one input line

PIPE IN PIPE

1.2. Pipe-in-pipe identifier, one input line

IDPIPE CHLOAD

  • IDPIPE: character(16): Pipe-in-pipe identifier

  • CHLOAD: character(4), default: EXPO: Fluid loading on inner pipe

    • = 'EXPO': Exposed. The inner pipe is exposed to external environmental loading; buoyancy and wave kinematics.

    • = 'SHCL': Sheltered closed. The inner pipe is sheltered from external loading, but subjected to fluid loads from the inner fluid. The velocity and acceleration of the inner fluid follows the local transverse motion of the outer pipe.

1.3. Specification of master pipe, one input line

For master pipe defined by a single line
CHMAST LINE-ID ISEGF_M ISEGL_M

  • CHMAST : character(4): = LINE

  • LINE-ID: character(8): Reference to line identifier

  • ISEGF_M: integer, default: 1: First local segment in line for master pipe

  • ISEGL_M: integer, default: NSEG: Last local segment in line for master pipe

For master pipe defined by a main riser line
CHMAST = MRL  MRL-ID

  • CHMAST: character(4): = MRL

  • MRL-ID: character(8): Reference to main riser line identifier

1.4. Specification of slave pipe, one input line

For slave pipe defined by a single line
CHSLAV = LINE  LINE-ID ISEGF_S ISEGL_S

  • CHSLAV : character(4): = LINE

  • LINE-ID: character(8): Reference to line identifier

  • ISEGF_S: integer, default: 1: First local segment in line for slave pipe

  • ISEGL_S: integer, default: NSEG: Last local segment in line for slave pipe

Note that the slave pipe may not contain connectors.

For slave pipe defined by a main riser line
CHSLAV = MRL  MRL-ID

  • CHMAST: character(4): = MRL

  • MRL-ID: character(8): Reference to main riser line identifier

Note that the slave pipe may not contain connectors.

1.5. Specification of contact force characteristics, one input line

CHPOS IKS RELDAM DAMP STIFFR FRICST FRICDY CHAXI CHROT VELLIM

  • CHPOS: character: Position of master pipe

    • = INNER

    • = OUTER

  • IKS: integer: Stiffness code for radial contact force

    • = 1: Constant contact compression stiffness

    • = N: Table with N pairs of contact force - displacement to be specified

  • RELDAM: real: Desired relative damping level at estimated eigen period in pipe, pipe and contact spring system (see below) \(\mathrm {[1]}\). Damping is only applied in the radial direction. Not used in static analysis.

  • DAMP: real: Dash pot damping coefficient per unit length of master pipe \(\mathrm {[FT/L^2]}\). Damping is only applied in the radial direction. Not used in static analysis.

  • STIFFR: real: Spring stiffness associated with the static friction coefficient FRICST, \(\mathrm {[F/L^2]}\). The spring stiffness is applied in the ring and axial directions until the spring force exceeds the static friction force. Not used in static analysis. Dummy if CHAXI = OFF.

  • FRICST: real: Static friction coefficient \(\mathrm {[1]}\). Not used in static analysis. Dummy if CHAXI = OFF.

  • FRICDY: real: Dynamic sliding friction coefficient \(\mathrm {[1]}\). FRICDY ⇐ FRICST. Not used in static analysis. Dummy if CHAXI = OFF.

  • CHAXI: character: Control parameter for friction caused by translational displacements. Not used in static analysis.

    • = ON

    • = OFF

  • CHROT: character: Control parameter for friction caused by rotation. Not used in static analysis.

    • = ON. Requires CHAXI = ON

    • = OFF

  • VELLIM: real: Velocity limit for determining that sliding has stopped \(\mathrm {[L/T]}\). If the relative sliding velocity between the pipes falls below VELLIM, the spring stiffness STFFR is applied. Should be small, but not zero. Not used in static analysis. Dummy if CHAXI = OFF.

Contact spring stiffness; IKS = 1, one input line
STIFF

  • STIFF: real: Spring compression stiffness per unit length \(\mathrm {[F/L^2]}\)

Contact spring stiffness; IKS > 1, one input line
FS(1) ZS(1) ........ FS(N) ZS(N)

  • FS(1): real: Contact force per unit length corresponding to the gap ZS(1) \(\mathrm {[F/L]}\). A negative value is a force apposing penetration.

  • ZS(1): real: Gap between the pipes \(\mathrm {[L]}\), A negative values indicates contact.

ZS(i) must be given in increasing order

All FS and ZS values should be negative, as the ZS values are understood to be the gap between the two pipes. If no negative values are given, linear extrapolation will be done from the two smallest ZS values.

Please note that the sign convention of this input is planned changed in future versions!