Motion Induced Stress Analysis

[hthomson]

Hi,

I often have to review steel weldments for structural integrity which are located on a moving vessel (Pitch, Roll, Heave etc). Previously I have calculated the forces induced due to the vessel motion and added teh forces to the model in a static analysis which works okay and has passed 3rd party verification in the past.

However I feel like it should be possible to miss out the hand calcs and input the vessel motion into Creo directly (i.e. pitches 8 degs in 5 secs, rolls 8 degs in 5 secs, heaves 10m in 10 secs etc etc..) and have it spit out the the resulting stresses. Can Creo do this (dynamic analysis?) and if so any pointers?

I previously posted this at: Motion Induced Stress Analysis but didnt know how to move it to here so have posted twice.

Thanks,

Hugh

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[ehaenen]

Hi Hugh

It seems to me that all your examples can be described using an acceleration. You can define this using a gravity load (heave), or a centrifugal load (pitch/ roll). you will have to find a way to constrain your structure though. You can use the location where the vessel is mounted to the thing that supports the vessel (a ship?).

Although: pitching 8 degrees in 5 seconds is a velocity, that in itself will not cause a stress (it's a constant motion) it's the acceleration that does it.

does this help?

Erik

[SylvainA.]

Hello.

You may have a look at : https://support.ptc.com/appserver/cs/view/solution.jsp?n=CS103225&art_lang=en&posno=1&q=mechanism%20load&ProductFamily=C…

[hthomson]

Hi,

Thank you for the link. This looks like something I could make use off. Will need to spend a while getting to grips with it but looks to be worth the time. Apologies for the delay in reply. I haven't had a chance to look at this yet. Chris Hutcheon‌

[346gnu]

Hi,

Maximum accelerations are at maximum angles (zero velocity).

Do your standards give these envelopes for the relevant location on the ship?

If they do, create a csys as max roll/pitch and point your 3 gravity basis vectors in these directions.

The basis vector directions can reverse and so you have a permutated set of angles and gravities.

[hthomson]

Hi Charles,

It merely states that...

"Unit motion due to wind, current, and wave loads shall be included in the design loads".

It does also state that ""Where vessel motion characteristic is not available, conservative maximum pitch and roll accelerations of 0.35g can be considered" however I normally have all the data to hand so I go through the motions (pun intended) of working out he loads.

I do think that between your post and Sylvain's post I should be able to work a more efficient means of calculating the stresss due to vessel motion...if I can get the time away from other projects to do so.

Thank you for your guidance. Chris Hutcheon

tag:

Hugh

[346gnu]

0.35g seems quite a lot.

Rough weather then.