Wave Best Practice

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Wave Best Practice

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1.Sanitise wave height and period inputs for the given scenario to see if they are physically plausible. For example, installation would never occur with 6m high waves in 10m water depth. Analysing such extreme conditions would be pointless and would require small time steps etc. in order to maintain convergence.

2.Remember wave direction is a global entity and is not specific to the vessel, unlike wave heading. The difference between wave direction and wave heading is highlighted in the following figure (heading on left hand side, direction on right hand side) and this should be kept in mind when defining wave components. If the vessel is pointing along the global Y axis then a 0 degree wave heading (incident on the bow) corresponds to 180 degree wave direction.

wave_heading

3.Be aware that shallow water waves can have hydrodynamic effects on the seabed portion of a pipeline and so you may see more dynamic seabed tension variation than in a deep water case. These effects can be removed by reducing the drag diameter of the pipeline on the seabed.

4.Typically in a standard analysis a single dominant wave direction is specified; however multi-direction waves with energy spreading are an option for more detailed analysis.

5.In terms of random sea spectrum discretisation the default inputs provided in the PipeLay user interface are usually sufficient. For the equal area discretisation option users should typically request 20 to 100 harmonics; the more harmonics the more detail is captured on the spectrum.

6.Remember that regular waves use an amplitude input rather than a height input as per the random seas. Two times the amplitude equals the wave height.

7.Further best practice advice on wave loadings is provided in a later section where the Installation Stages tab of the Analysis component is discussed.