Reply To: Gettiing problem with interacting structures have moved too far

[Mike Pettit]

Hello,

The fender definition may be correct in your model. The problem you are encountering now is related to the hydrodynamic interaction between the Spar and Torus structures. In the Hydrodynamic Diffraction analysis, the Aqwa solver calculates the radiation and diffraction effects for each structure, but also the interaction effect: the heave motion of the torus generates a radiated wave that affects the forces acting on the spar, while the diffraction effect of the spar will affect the wave forces on the torus. In other words, the frequency-dependent added mass and radiation damping matrices calculated by Aqwa are extended to include the degrees of freedom of both structures (i.e. 12x12 instead of 6x6).

However, the hydrodynamic interaction effect is only calculated for the structures in their definition positions in the Hydrodynamic Diffraction analysis. In the time domain, as the structures move relative to one another, the interaction effects between them are not recalculated. Therefore the Aqwa solver applies a limit to the relative motion that it will allow in the time domain, because the results become unreliable when the relative motion is too large. Also, this limit is more restrictive when the structures are close together in the Hydrodynamic Diffraction analysis. In your case the solver probably stops when the torus vertical position changes due to the passing incident wave.

To avoid this problem, you could consider turning off the interaction effect. This may not be unreasonable, as the spar motion is dampened (small radiation term) and is quite small in diameter (small diffraction term). To turn off hydrodynamic interaction, click on the Hydrodynamic Diffraction Structure Selection, then click on Interacting Structure Group 1, click on some empty space in the Graphical Window (to deselect the structures) and then click Apply. The field should change from 'All' to 'None'. You will need to re-run the Hydrodynamic Diffraction analysis, but this should allow you to run the time domain analysis without any problems.

I hope this helps.

Mike