Initial RIFLEX Analysis

RIFLEX modules INPMOD and STAMOD must be run successfully prior to a VIV analysis utilising VIVANA. Information on how to give input to RIFLEX is given in the RIFLEX User Guide, but the following rules should also be observed:

  • Always use 3D beam elements. A later version of the program will possibly allow for 3D cable elements (no rotational degrees of freedom).

  • Always use a 2D current profile, i.e. the direction of the current must be the same at all levels. Theory for the application of 3D current in VIV analysis does not yet exist.

  • The current profile to be used must be directed perpendicular or parallel to the riser plane.

  • The user may decide whether to apply the current load in the static analysis or not. VIV response will be calculated as long as a current profile is specified, but the results will generally depend upon whether the current load is applied or not. The current profile to be used is selected on the STAMOD input file, see the RIFLEX User Guide, and this is also where the user may choose to apply the load or not.

  • The riser should be modelled as one of the following (see the RIFLEX User Guide for a description):

    • SA system (standard system, no bottom contact)

    • SB system (standard system, bottom contact)

    • AR system (arbitrary systems)

  • Specifying regular or irregular waves on the INPMOD input file will have no effect on the VIV response analysis.

  • Vessel motions will likewise have no effect on the VIV response analysis.