Moving load model in a simply supported beam 1

[giacuni]

Hello!
I am doing a simple model: a moving load along a simply supported beam as depicted in the figure below

Basically, I've modeled the moving load as a load applied at a reference point and then used a boundary conditions in order to move it.

The model works. The problem is that I doesn't have a satisifed result.
In the figure below is possible to see that the result obtained with ABAQUS (DYNAMIC ABAQUS) is different from the one that I expect (DYNAMIC EXACT).
The Figure shows the displacement observed from the mid-span point of the beam versus vehicle position. (at t=0 the load is at the left-point (x=0 meter) and at the
end of the analysis the load is at the right-point (x=34 meter).
It seems that, at the end of the analysis (when the load reached the right end of the beam) the displacement is not zero (but it should be of course).

What do you think is the problem?
I can share the script file if you need.
Thanks in advance

 

[StefCon]

Hi,
Have you checked the energies (history output)? Maybe they can give a clue.

Best regards,

 

[giacuni]

Hi, thanks for the interest.
Here is the plot of the energies:

What can I see is that:
- the total energy (ETOTAL) is linear (and may be this is not good thing as I remember that should be better if it was constant).
- the artificial strain (ALLAE), the damping dissipation (AALVD) are negligible compared to the strain energy (ALLSE) (and that is good as I remember)

But I don't catch any clue.
Sorry, I'm just a beginner.

Kind regards

 

[IceBreakerSours]

Zoom in on the final ~0.53 seconds of the analysis. Which time integrator is chosen for the dynamic run? Upload the file.

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[StefCon]

Is it ALLVD that peaks at the end? If you are using damping, try reducing it and see if it makes a difference.
If you are using implicit dynamics you can try changing the energy dissipation in the step (presence of contacts for example defaults to a rather high energy dissipation).
Explicit is the usual (mass scaling, double precision...).

Please let us know how you solve it.

Good luck!

 

[giacuni]

Thanks for the interest.

The ALLKE peaks at the end. The ALLVE is constant to zero. What does it tell that?

I used an implicit dynamic analysis. I used a beam with 100 elements.
I chose as time step: 0.00499266 seconds. Which is the time that occurs to the load to go to an element to an other element.
Here is the script: Link

 

[IceBreakerSours]

I am not sure why you chose to specify displacement (with a ramped up time variation), instead of constant velocity. This is quite likely transients in the beginning and the end of Step-2 because of unwanted acceleration. Plot the double differentiation of the displacement output (preferably, history output).

Also, I think the contact algorithm may be missing the beam profile thickness (almost) entirely. I am always a little iffy about contact between rigid surfaces and line elements (I have filed a couple of bug reports on this myself). Please make sure you are using the latest version of Abaqus.

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[giacuni]

Thanks for your answer.
I take this opportunity to wish you merry Christmas.

Back to the problem.
1. I have tried to use the velocity boundary condition instead of the displacement boundary condition but the result is the same.
2. I have the version Abaqus/CAE 6.14-5 (of the University). I can't get a recent version.

I have tried to plot three graphs:
1. The contact pressure between the contact point and the beam

2. The contact open between the contact point and the beam

3. The acceleration of the contact point

It seems all right to me the acceleration.
I have checked with and without the interaction properties "allow separation after contact" but I have the same result in terms of the contact opening.

I really don't understand what is the problem. It seems a really easy model to do but it is actually very tricky...

 

[IceBreakerSours]

Your beam has a certain thickness and COPEN seems to show penetrating surfaces towards the end of the analysis and a bit of noisy response, in general. I am not sure if contact is taking the thickness of the beam in to account or not. You can request Abaqus/CAE or Abaqus/Viewer to display the beam thickness and see what I am trying to get at.

Also, read "Contact diagnostics in an Abaqus/Standard analysis" in the documentation for some diagnostics.

I am curious why you need to discretize the domain with 100 beam elements. Can you not get away with just one beam element? If not, why so?

You are a couple of versions behind, by the way. That is not to say that your issue will be resolved just by upgrading.

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[Shz713]

Hi there,
have you found solution to your problem?
Try to use B31 elements and for the moving point load, to avoid jumps you need to define it in a way that when reaches specific node the displacement are not exceeded exaggeratedly.

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