Overview of Load Effects

The following physical effects contribute to system loads:

  • weight and inertia, governed by line mass, including any pipe contents and external wrapping

  • hydrostatic forces, dependent on pressure gradients

  • hydrodynamic forces, dependent on wave, current and structure motions

  • forced motion of line, dependent on vessel motions

  • aerodynamic forces, dependent on wind and structure motions

Since the analysis is based on a beam model with pressure-independent cross section properties, the hydrostatic pressure level does not affect the static or dynamic equilibrium condition, hence the pressure gradients are sufficient.

All loads are applied either as distributed line loads (force/length) or as point loads.

The following sections give an outline of essential features of the implemented load models.

With regard to surface-piercing structures, two classes of hydrodynamic load models are used:

  1. Hydrostatic and hydrodynamic loads are applied on a length equal to the submerged length of the component axis, i.e. the volume forces are concentrated in the pipe axis.

  2. Hydrostatic and hydrodynamic forces are distributed according to the actual diameter, or shape of the buoyancy volume. Thus, the cross section can be partly submerged, and structures such as floating hoses and fish cages can be modelled.

For submerged structures, and also for surface-piercing normal pipes and cables, the first class is used, and generally this cross section is referred to in the subsequent discussion. The second class is referred to as a "partly submerged" cross section.