1. Integration Schemes Explicit Integration: Xn+1 – Xn = Dt . F(Xn)
Simple, no iteration required
Time-step limited, i.e. is conditionally stable
Good for short-duration phenomena (clashing & snatching)
Conditional stability  ’guaranteed’ accuracy
Implicit Integration: Xn+1 – Xn = Dt . F(Xn+1)
Stable, large time-steps, but requires iteration
Can lose accuracy,at large time steps - this needs to be assessed
Can miss short-duration phenomena (contact, axial waves, etc)
An implicit integration scheme for OrcaFlex is under development

2. Time Step Determination
Recommended Value:
1/20th of the smallest nodal natural period in the model
Alternative Approaches:
Increase smallest nodal period
Push our luck & use larger time steps

3. Increasing Nodal Natural Period
Which Component Dominates?
Axial Stiffness:
Reduce stiffness generally, avoiding excessive stretch
Reduce stiffness locally in areas requiring fine segmentation
Bending Stiffness:
Use longer segments, provided system allows it (check). This has a double effect as decreases the number of nodes as well as increasing time step.
Consider modelling termination heads etc. with buoys

4. Increasing Time Step Default Value: Trial and Error Approach:
Based on experience rather than theory
Errs on the conservative side
Trial and Error Approach:
Try twice recommended value
Try three times recommended value
Keep increasing until code diverges
Caveat: Very occasionally produces noisy results - Check

5. General Run Time Considerations
Interactions between Objects:
Shapes and Seabed: Avoid excessive contact stiffness
Line clashing: Use clash energy as a measure of severity of impact
Only enable line clashing where needed
Torsion Modelling:
Do you really need it? Do a check run and find out
Live Graphs during Simulations:
Don’t have more than you need, especially range graphs.
Random Sea Cases: Outer Time Step:
Recommended value may be unnecessarily small for stiff systems.