OrcaFlex

- Discretisation & Convergence

Discretisation

• Why Worry?

– Too fine and the run takes longer – Too coarse and behaviour is missed or wrong • Check Static Model Visually – Does it look like too much or too little?

– Make finer in regions such as touchdown, near solids, near step changes in the properties – Make coarser in regions where little happens, deep water catenary suspended lengths for example www.orcina.com

OrcaFlex User Group, 2005 Slide 1 of 5

OrcaFlex

- Discretisation & Convergence

Discretisation

• Check Dynamic Model Visually – Are lines passing through solids, catching on the edge or failing to follow the profile?

– Does the line seem to kink rather than curve – Are nodes bouncing on the seabed?

• Check Results – Tension Time History: ‘Spiky’ or high frequency variation – Tension Range Graph: Euler limit infringed and high compression – Curvature Range Graph: Smooth variation www.orcina.com

OrcaFlex User Group, 2005 Slide 2 of 5

OrcaFlex

- Discretisation & Convergence

Statics Convergence

• Where to get information – Message Box – Statics Progress Window – Out-of-Balance Loads (Shift+Ctrl+Y) – Your eyes Slide 3 of 5 www.orcina.com

OrcaFlex User Group, 2005

OrcaFlex

- Discretisation & Convergence

Statics Convergence

• What to look out for – Object overshoot - more damping. @ Min 1-1.5, Max 10-100 in steps OR bad 1st guess – Statically indeterminate Buoys - Check DofF or give an out of-balance force – Circling solution but never quite reaching it - increase tolerance (care!) – Multiple dependent objects - fix some, run simulation, then save final positions. Then start again with all free.

www.orcina.com

OrcaFlex User Group, 2005 Slide 4 of 5

OrcaFlex

- Discretisation & Convergence

Statics Convergence

• If all else fails?

– Fix the objects and let it settle dynamically – Contact us for help!

www.orcina.com

OrcaFlex User Group, 2005 Slide 5 of 5