PONDUS

PONDUS is a computer program that computes the dynamic lateral response of offshore pipelines subjected to wave and current action on a horizontal seabed.

PONDUS is a FEM formulation, based on 2-D elements which solves, in the time domain, the equations of motion of the pipeline in the horizontal plane using small deflection theory, but accounting for bending deformation effects on axial forces.

PONDUS features calculation of kinematics from 3-D irregular waves, several hydrodynamic force models, models for partial burial, non-linear, time dependent interaction between pipeline and soil (sand and clay) and non-linear pipeline material properties (for boundary elements).

This allows for detailed analysis of specific pipeline sections subjected to specified environmental conditions.

The PONDUS program system consists of four programs or modules. A complete dynamic response analysis of the pipeline must include a run of all modules. However, an efficient data base system simplifies the work during a complete study by storing input data and intermediate results (e.g. water particle velocities and accelerations).

The attributes of PONDUS are summarized below:

Pipe Structure

  • Straight pipeline on horizontal sea-bottom (no free spans).
  • Two degrees of freedom (lateral deflection and rotation about global vertical axis) at each nodal point.
  • Variable pipe mechanical and geometric properties along the pipe.
  • Variable end conditions (free, fixed or spring).
  • Constant axial force in space along the pipe.
  • Tension effects: optional (the pipe may have an initial axial force that 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.
  • Non-linear material description for “boundary elements” (optional).

Soil Force

  • Elasto-plastic model with possible hardening and softening effects for clay and coarse sand (transverse to pipeline).
  • Transverse soil properties may vary along the pipe.
  • Axial soil force along the pipe is not considered.

Hydrodynamic Force (lift force included)

  • Several force models available.
  • Relative velocity between pipe and fluid at each node is considered (optional).
  • Regular and irregular waves with user-defined direction relative to the pipe.
  • Constant current (normal to the pipe) in time.

Numerical Method

  • Finite element formulation with straight beam elements with two degrees of freedom at each node (rotation and transverse displacement).
  •  Small deflection theory (small rotations) for the beam elements with linear material behaviour (no updating of nodal coordinates).
  • Geometric stiffness is included.
  • Solution in time domain using the Newmark method and incremental formulation.
  • Rayleigh damping may be specified for the pipe.
  • Damping in the linear range of the soil may be specified.
  • Concentrated mass formulation.
  • Constant time step (user specified).
  • Simple trapezoidal integration for the distributed loading along the beam elements (nodal forces only, no moments).

Published March 8, 2006

Egil Giertsen
egil.giertsen@marintek.sintef.no 
Direct phone: +47 73 59 20 81

Fax: +47 73 59 26 60