Mike Pettit
Ansys Employee

Hello Greg,

To answer questions 1 and 2: the stability analysis takes all of the steady forces acting on a structure (buoyancy, weight, current, wind, mooring tensions, drift force due to waves etc), and then finds a position for the structure where all of those forces are in equilibrium. Therefore, when we start a time domain calculation from this position, we avoid a large initial acceleration on the structure because the net force is already zero.

Naturally this only works if the steady forces acting in the time domain calculation are the same as they were in the stability analysis. So, the Aqwa editor allows you to define environment conditions in the stability analysis, and then right-click > Propagate them into any connected Hydrodynamic Response systems, to ensure that the environment is consistent between the analyses.

To be clear, the stability analysis is not stepping through time - it is iterating towards a convergence where all of the forces are balanced. A time domain analysis linked to a stability analysis will still start at t = 0.

Generally, if your time domain calculations do not include drift forces (i.e. the Analysis Type is set to 'Irregular Wave Response' or 'Regular Wave Response', or there is no Irregular Wave defined) and all of the other steady forces are the same (i.e. same current/wind definition, or no current/wind), then you can start each time domain analysis from the same stability analysis:

If your time domain calculations do include drift forces (i.e. the Analysis Type is set to 'Irregular Wave Response with Slow Drift' or 'Slow Drift Only', and there is at least one Irregular Wave defined) or any of the other steady forces are different between analyses (i.e. different current/wind definitions), then you should start each time domain analysis from its own stability analysis:

To answer your other questions:

3. I'm afraid AqwaGS does not have a capability to add a legend like this - you have to keep track of which dataset is which. However, I should mention that since Release 2021 R1, the Aqwa Workbench editor allows you to plot data from different systems within the same project:

4. I'm afraid there is no function to draw the strakes on the spar, either in Aqwa Workbench or AqwaGS.

5. The Morison discs are usually added at the ends of Morison tube elements, so the default added mass and drag coefficients assume that only one side of the disc is wetted. You might consider doubling the added mass and drag if both sides of the disc are immersed.

I hope this helps!

Cheers, Mike