Compose wave/current loading

General description:

Through this function the wave/current loadings on the pipeline are specified. Load factors can be specified in the next function (design function 5), where the various loading components are combined into loading combinations.

Function description:

The sea state considered is 3 dimensional for waves and 2 dimensional for currents. In the required table ENVLOAD the occurrence of waves and/or current is indicated. Waves are characterised by height, period, direction, position and type of crest and wave theory (in table WAVE). Wave profiles may be long- or shortcrested and according to Airy (1st order) or Stokes (5th order) theory. For the time being no combination of Stokes and shortcrestedness is allowed.

A current profile can be specified either as an exponential curve or by a number of profile values over the water depth (tables CURRENT and CURPROF). The water depth is considered to be constant and is calculated from W-LEVEL and G-LEVEL. When these levels vary, an average depth is determined for the elements in open water only. A warning is given if variations are large.

The influence of (weight) coatings and marine growth, resulting in increase of the structural pipe diameter, can be taken into account (table OUTDIAM), as well as the dynamic amplification of forces due to vibration of pipe spans (table DYNAMPL) and the influence of nearby stream disturbing members, e.g. jacket members (table DISMEM).

In table PROPENV the specific weight of the sea water and the acceleration of gravity has to be specified only if different from the default values.

If dynamic amplification due to free span vibrations is taken into account, the pipe weight in air must be given (table AIRWGHT), differing from DEADW (design function 3.1) which includes buoyancy. From the weight in air the mass of the pipeline is determined.

The function generates a wave profile (table WAPROF) and water velocities and accelerations (table VELACC). Wave and current velocities are added vectorially and resolved in directions perpendicular and parallel to the pipeline axis at the mid points of the pipeline elements. The latter is also applicable to the wave accelerations. By means of the Morison equation wave / current forces are calculated from the velocities, accelerations and the hydrodynamic coefficients specified in table C-DML and reported in table HYDROCO.

When table DYNAMPL exists, dynamic amplification factors (DAF's) are calculated (table AMPLFAC) by which the hydrodynamic forces are multiplied. Wave slamming is taken into account in the zone between wave crest and trough depending on the pipe orientation. Hydrodynamic forces parallel to the pipeline are neglected. The resulting wave/current forces per unit of length are reported in table WAFOR in the global X-Y-Z coordinate system.

H4103, last changed: 11/4/2020

See also: