about GMO and STL

March 5, 2009, 03:57

dear friends

i have a big prolem with the FLOW 3D software, we recently take the license and i am very new to the company, i am trying many times to simulate a GMO of a ship and also some other parts but i always take a huge ammount of errors.... firstly , i create the part in solidworks, then i save it as stl and then i check it with the stl check software, the check tells me that everything is ok, then the simulation starts but when the gmo reach the sea level.... we have a dissaster,,,,, the solver can not solve... it always dingrease the timestep....

can you tell me what is not correct?

and also can i apply a spring force on a gmo????????

thanks a lot edwards

March 5, 2009, 15:08

Hi~ It would be best if you sent your prepin to FLOW-3D support to better understand your problem.

At this moment you cannot add a spring force on a GMO but word has it you will be able to with the v94 release.

MC

ttynjala · March 18, 2009, 02:49

Might be totally unrelated to your problem too but had a bit similar symptoms when I experimented with pressure coupled objects floating on fluid (i.e. a 'ship'). When the object hit the fluid the timestep size dived to some 1e-10 and then finally failure due to convergence problem.

It turned out my problem was that I gave the moment of inertia for the 'ship' using TJMVB(m,i,j) but the values I gave were way too small (documentation didn't say anything about units to use so I just put in something..). Because of the very low moment of inertia the ship 'tilted' VERY easily causing the convergence problem. Increasing the values to about 1000x solved the problem for me. But as said - might (or might not) be totally unrelated to your problem.

melissa · March 18, 2009, 09:01

FLOW-3D(R) does not use units so the user must stay consistent throughout. In the manual the mass moment of inertia tensor equation is given. The English units would be
slug-in^2.

stefmascio · March 24, 2009, 11:20

hello edward,
are you using the implicit or the explicit solver for the GMO model?
The explicit is unstable for floating boats, you should use the implicit one.

(I've registered too some bad behaviour of the gmo when the moments of inertia were too small, and I don't know much why. Luckly if you are interested in the steady state condition you can set the values you want)

Stefano

March 5, 2009, 03:57	about GMO and STL	#1
edward Guest Posts: n/a	dear friends i have a big prolem with the FLOW 3D software, we recently take the license and i am very new to the company, i am trying many times to simulate a GMO of a ship and also some other parts but i always take a huge ammount of errors.... firstly , i create the part in solidworks, then i save it as stl and then i check it with the stl check software, the check tells me that everything is ok, then the simulation starts but when the gmo reach the sea level.... we have a dissaster,,,,, the solver can not solve... it always dingrease the timestep.... can you tell me what is not correct? and also can i apply a spring force on a gmo???????? thanks a lot edwards

March 5, 2009, 15:08	Re: about GMO and STL	#2
MC Guest Posts: n/a	Hi~ It would be best if you sent your prepin to FLOW-3D support to better understand your problem. At this moment you cannot add a spring force on a GMO but word has it you will be able to with the v94 release. MC

March 18, 2009, 02:49	Re: about GMO and STL	#3
ttynjala New Member Tuomas Tynjälä Join Date: Mar 2009 Location: Espoo, Finland Posts: 1 Rep Power: 0	Might be totally unrelated to your problem too but had a bit similar symptoms when I experimented with pressure coupled objects floating on fluid (i.e. a 'ship'). When the object hit the fluid the timestep size dived to some 1e-10 and then finally failure due to convergence problem. It turned out my problem was that I gave the moment of inertia for the 'ship' using TJMVB(m,i,j) but the values I gave were way too small (documentation didn't say anything about units to use so I just put in something..). Because of the very low moment of inertia the ship 'tilted' VERY easily causing the convergence problem. Increasing the values to about 1000x solved the problem for me. But as said - might (or might not) be totally unrelated to your problem.

March 18, 2009, 09:01	Units for mass moment of inertia	#4
melissa Member MC Join Date: Mar 2009 Posts: 56 Rep Power: 17	FLOW-3D(R) does not use units so the user must stay consistent throughout. In the manual the mass moment of inertia tensor equation is given. The English units would be slug-in^2.

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March 24, 2009, 11:20		#5
stefmascio Member Stefano Join Date: Mar 2009 Posts: 59 Rep Power: 17	hello edward, are you using the implicit or the explicit solver for the GMO model? The explicit is unstable for floating boats, you should use the implicit one. (I've registered too some bad behaviour of the gmo when the moments of inertia were too small, and I don't know much why. Luckly if you are interested in the steady state condition you can set the values you want) Stefano