Free Motion excessive time

DRiver · March 17, 2022, 06:19

Hi. Currently, I'm running a couple of full-scale ship resistance simulations. I have been using the Free motion model, as well as the Equilibrium model for the Z_Translation and Y_Rotation degrees of freedom. But, with both models, the physical time of the simulation is very high. I have run up to 200 seconds and the DFBI moment is oscillating around zero, but it's still in the order of 1E+05 N*m.

Until now, I have tried these two models, also I have tried increasing the moment of inertia up to 2x and 4x the one calculated for the ship. None of these solutions have reduced the physical time required to reach the equilibrium.

Do you know any condition, model or parameter that I could adjust to significantly reduce the physical time of these simulations?

Thank you.

Aeronautics El. K. · March 27, 2022, 18:15

In my experience the free motion is a lot more time consuming than the equilibrium. However, even with the equilibrium, perhaps 200 seconds are not enough. Let it run longer.
But I have noticed a similar behaviour generally, like what you mentioned.

March 17, 2022, 06:19	Free Motion excessive time	#1
DRiver New Member Daniel Riveros Join Date: Nov 2015 Location: Genoa, Italy Posts: 14 Rep Power: 10	Hi. Currently, I'm running a couple of full-scale ship resistance simulations. I have been using the Free motion model, as well as the Equilibrium model for the Z_Translation and Y_Rotation degrees of freedom. But, with both models, the physical time of the simulation is very high. I have run up to 200 seconds and the DFBI moment is oscillating around zero, but it's still in the order of 1E+05 Nm. Until now, I have tried these two models, also I have tried increasing the moment of inertia up to 2x and 4x the one calculated for the ship. None of these solutions have reduced the physical time required to reach the equilibrium. Do you know any condition, model or parameter that I could adjust to significantly reduce the physical time of these simulations? Thank you. Last edited by DRiver; March 21, 2022 at 09:40.*

March 27, 2022, 18:15		#2
Aeronautics El. K. Senior Member Lefteris Join Date: Oct 2011 Location: UK Posts: 337 Rep Power: 15	In my experience the free motion is a lot more time consuming than the equilibrium. However, even with the equilibrium, perhaps 200 seconds are not enough. Let it run longer. But I have noticed a similar behaviour generally, like what you mentioned. DRiver likes this. __________________ Lefteris

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