VIV analysis

OrcaFlex offers a variety of modelling options for the analysis of vortex induced vibration (VIV) of lines, including both frequency domain and time domain approaches. The VIV modelling features have been developed in co-operation with academics in the UK and USA.

A separate user guide for the time domain VIV models is available (time domain VIV models.pdf).

Available VIV models

OrcaFlex provides facilities for using the following different VIV models:

• SHEAR7. OrcaFlex provides facilities for exporting SHEAR7 data and modes files based on an OrcaFlex model. SHEAR7 can be run separately using these files as input, or called directly from OrcaFlex.
• VIVA. OrcaFlex can create VIVA data and modes files based on an OrcaFlex model. Again, VIVA can be run separately with these files as input, or executed directly from OrcaFlex.
• Two wake oscillator models: the Milan model and the Iwan and Blevins model.
• Two vortex tracking models.

Of all these models, SHEAR7 and VIVA are the two main programs in current use in the industry. Neither is an Orcina program: they are completely independent, written and distributed by other companies, so to use them you must purchase and install them on your machine. They are both frequency domain models, so they only analyse steady state conditions.

The other models are built into OrcaFlex so no further software is needed. They are all time domain models, and so are not limited to steady state conditions.

Using VIV models

You choose which VIV model to use (if any) on the VIV page on the line data form. There are separate choices for the static and dynamic analyses: the frequency domain models are only applicable to statics, and the time domain models only to dynamics.