numerical singularity in modal analysis of ship

[amolpanchal]

Can you please let me know why i am getting numerical singularity in modal analysis of ship?

 

[rob768]

unrestrained? disconnect nodes? Do a static analysis (gravity) first to make an integreity check.

 

[amolpanchal]

Thanks for reply, Rob!

Actually i am solving this model in Abaqus. This model was unrestrained as i wanted to find its rigid body modes, but when i was solving this model for 0.0 to 5Hz, i was getting this error. Later i solved this model for 0.1 to 10 hz and its solved. So the question is why it happened and how to find rigid body modes now?

Thanks,
Amol

 

[rob768]

out of curiosity: why would you want to find rigid body modes of a ship? Are you sending it into deep space? Otherwise it makes no sense..

 

[amolpanchal]

just to see its pitch/roll/yaw mode.

but why abaqus is not solving this model when i used 0.0 to 10 Hz?

 

[rob768]

I don't know. I don't use abaqus so i am not familiar with the program. I assume it generates an error code or description?
If you're looking for rigid body modes, 10 Hz is a lot. Expect real modes within 10 Hz. Can you try other programs?
also: try fixing it at both end and do a gravity load (static) calculation. Doesn't mean a thing but will tell whether the model is correct or not.

I know in one program i once used, i had to indicate i was looking for rigid body modes, or otherwise the program came back in error.

good luck

 

[amolpanchal]

okay. thanks!
but the model seems to be right as it is solved with inertia relief