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Vessel and RAO Data

Three sets of inputs are required to completely define the response of a floating vessel to the ambient wave field. The first set defines the vessel initial position, that is, the location of the vessel prior to the application of any vessel offset or dynamic motions. This information is defined in terms of the location of the vessel reference point (the point at which the RAOs are defined), and initial yaw orientation of the vessel. Refer to Basic Vessel Concepts for further information on this feature.

The second set of inputs is used to specify the offset of the vessel from its initial position and orientation. These entries are optional and are only specified if the vessel is offset from its initial location and orientation before the commencement of the dynamic analysis. Flexcom offers a full 6 degree of freedom offset capability, comprising three translations and three rotations. This facility will be illustrated later, in Vessel Offset Analyses. Refer to Vessel Offsets for further information on this feature.

The third set of inputs is the full vessel RAOs and phase angles in all vessel degrees of freedom. Given the vessel initial position, offset and RAOs, in addition to the time history of wave elevation, the motion of the reference point in response to the wave field throughout an analysis can be calculated, and from this the motion of the point(s) on the structure attached to the vessel. As the RAO data may be quite extensive, it is typically stored in a separate file which is simply referenced by the main keyword file. The file with RAO data already exists in the Worked example folder, and is named RAO.incx. This should be copied into the folder for this project. Refer to High Frequency RAO Motions for further information on this feature.

You may also optionally associate a structural profile with the vessel. While does not affect analysis results, it does add considerably to the visual appeal of the structural animation. A range of standard vessel profiles are provided; the FPSO profile being particularly suited to this worked example.

The completed specification of vessel data for the FPSO in this example is specified as shown in the figure below. Note that all vessel data (apart from vessel offsets) is specified in the $MODEL section of the file.

Vessel Data

Refer to the *VESSEL, INTEGRATED keyword for further information on these data inputs.