moving mass

[andreamordini]

Hi all,

what is in your opoinion the best way to model a mass moving on a line meshed with beam elements?

thanks in advance,

andrea


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Andrea Mordini, Civil Engineer, Ph.D.

http://www.andreamordini.com

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[doatis]

If it were me, I would make sure that my beam had multiple divisions in it. At each node, I would place a mass21 element. As I walked through each substep, I would use the ekill/ealive to remove/add masses to the current load step.

Now, depending on what you're doing, you may need to divide that line into many beam segments in order to get the appropriate resolution.

What is the real intent of your analysis? If you're just using the mass to apply inertial loads to your beam, you're better off using tabular loading. You should know the mass, and the acceleration, so you know the force. Define a table that relates your force magnitude to time/position and go from their.

Hope this helps,
Doug

 

[doatis]

D'oh, sorry for the typo. Obviously my last sentence should be "...time/position and go from there."

Coffee hasn't kicked in yet.

 

[andreamordini]

Hallo doatis

thanks for your response.
This could be a good idea, but what about if I have more than one moving mass and if the mass values are different?
For example one train passing on a bridge with the first wagon heavier than the second...
I tried to define all the masses and to connect them with the nodes on the bridge by using the CP or CE command but there's a numerical problem and I don't know why...

andrea

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Andrea Mordini, Civil Engineer, Ph.D.

http://www.andreamordini.com

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[Stringmaker]

Do the effects of the static loading make up a large portion of your total stress state? This sounds more like a transient dynamic type of analysis that is better done with a code like DYNA.

 

[andreamordini]

Finally I solved my problem.
I define the masses I need and I put some constraints on them. Then, when the masses enter the bridge, I release the constraint and I create a CP between the first mass and the first node on the bridge. In the subsequent step, I delete the CP and I create a new one with the next node on the bridge.
The CP commands can be used in the SOLU processor.

Hope this helps the next one solving the same problem.

andrea

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Andrea Mordini, Civil Engineer, Ph.D.

http://www.andreamordini.com

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