FEA Lifting problem

[RobJV]

I have a fairly "simple" FEA problem that is causing constraint issues for me.  I will simplify the description:  20ft x 6ft steel lid with 6" flanges all around.  The lid has 4 lifting lugs close to the corners that will allow lifting from a single point.  I want to see the affects of the lift through the plate.

I can do the forces by hand but am having issues figuring out where to place constraints to mimic this problem.  If I place a single fixed constraint at bottom face of lid, then of course I don't see the affects of the forces that will be exhibited longitudinally through the plate.  If I use sliding constraints obviously there will not be enough constraints.  This should be quite simple but has me perplexed.  Any idea?  

Thanks,

Rob

[dan_inv09]

I would probably model chains, but ...

If you fix one lug and have the others sliding, how would that work?

[RobJV]

Thanks for your response.  I don't see how going through the extra work of modelling chains is going to help me at all though.

I tried fixing one lug and creating frictionless constraints (in the direction of chain pull) on the other lugs and this gives results that seem plausible - I will investigate further.  

Thanks.

[dan_inv09]

I didn't mean you would have to constrain all the little links, but I would make something to approximate the hook in the lifting lug. Then you could fix the other ends.

Unless the people doing the lifting have some sort of spreaders, the angle of the chains could be a significant factor (and it would change as the thing deformed).

[RobJV]

Yes - I understand what you are saying about the chain - I will try playing with some way of constraining to see if I can then leave my calculated forces out of the FEA altogether.  I will try modelling a single link as my lugs are d-links that i can then rotate to proper orientation .  (I am also trying to avoid a spreader bar as it will probably not be necessary in my case pending FEA results.)

Thanks.

[blair]

If you can determine the angle of the lift chains, it's quite simple to determine the force vetor components. Or just model long lift bars/single links to a central connection.

[JDMather]

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@RobJV wrote:

.. Any idea?  

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Here is an idea, attach your file here.

[RobJV]

Hi Blair,

That is essentially what I ended up doing.  Thanks.

Rob

[RobJV]

I was waiting for your canned response.   Normally I would attach it but could not in this instance.  Thanks though.

Rob

[dan_inv09]

But how do you constrain it if you are putting in a lift force?

You have to constrain one (the end of the "chains") or more (see above (if that worked)) lift points and use the force of gravity, dont'you?

[blair]

Apply forces to the lift points using the "Vector" function as long as you don't introduce Gravity.

[dan_inv09]

I understand that, but doesn't it need some sort of a constraint somewhere?

[dan_inv09]

[dan_inv09]

Now, if you want to simulate what would happen if you're cranking on the crane but some bozo missed one of the bolts, then I can understand using just vectors.

[JDMather]

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@RobJV wrote:

I was waiting for your canned response. ....

Rob

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I kept this example very simple, but can't you simply add the 4 corner force vectors directed to single point that counteract the force of gravity?

If it is balanced out (lifting forces and gravity) no constraints needed - simply set to Detect and eliminate Rigid Body Motion.

(the force glyph in the center is Gravity)

[RobJV]

Thanks for taking a look.  I ended up modelling a single link of chain on each D-Link lifting lug and just move the link to accomodate different angles of lifting which Dan clued me into.  (I simply show gravity and place fixed constraints on all the chain links.)

You picture shows my initial setup but I could not figure out how to accomplish it without constraints and doesn't your way also require me to precalculate all the force vectors? - I know it is simple in this case but would rather let the computer do all the work  I will examine your way further as well.  I guess if all my "Y" up force vectors equals the weight of the assembly it would work?  

Rob

[RobJV]

Also, doesn't it complain about lack of constraints regardless or does the setting you talk about take care of that?

[dan_inv09]

[dan_inv09]

I finally found it!