Page 139 - Pipelines and Risers

112 Chapter 8

displacement, regardless of axial constraints and boundary effects. The waves are represented
by a 3 hours storm with a build-up time of half an hour.

The attributes of PONDUS are summarized below:

PiDe structure:
straight pipeline on horizontal seabottom (no free spans)
two degree of freedom (lateral deflection & rotation about global vertical axis) at each
nodal point
variable pipe mechanical and geometric properties along the pipe
variable end conditions (free, fixes or spring)
constant axial force in space along the pipe
tension effects: optional (the pipe may have an initial axial force which may increase due
to lateral deflection)
pressure effects (the pressure will contribute to the effective axial force and
internal pressure may give tensile stress along the pipe axis)
temperature effects (increased temperature may give compressive stress along the pipe
axis)
nodal linear springs and nodal masses may be specified
no stiffness contribution from concrete coating

Soil force:
- simple Coulomb friction model
- comprehensive soil models for sand and clay
- soil properties may vary along the route
- soil force in pipe axis direction is not considered

Hvdrodvnamic force (horizontal and lift):
- several force models available
- relative velocity is considered (optional)
- regular and irregular waves with a user defined direction relative to the pipe. Time series
for velocity, acceleration and coefficients along the pipe for irregular waves must be
generated in separate modules (WAVESIM, PREPONDUS) and stored on file
- constant current (normal to the pipe) in time. Possible modifications due to boundary layer
effects may be included in the value for current velocity

SDecified force:
- a distributed force may be specified, constant along the pipe but varying in time (linear- or
sine-functions)