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michalacadova
10-12-2010, 05:00 AM
Hi,
I went through the contact example co21 (co07) end I have a question concerning the loading curve. On the attached picture there is the load curve of X and Z prescribed displacement (in the Preview) and the real X and Z displacement measured in Postview. In Preview, both displacements are in the same time step (step01). But that would mean, that both movements are in the same time, but that is not right! One displacement follows the other. So I would do it in two different time steps. It is possible, that the Preview load the *.feb file wrongly, so it looks like both displacement are in the same time step, but they should be in two different steps?

My second question is what would be the best way to model several cycles (tens, even hundreds) of this problem?

Michala

michalacadova
10-12-2010, 05:35 AM
One more remark – when I look at the code itself (.*feb) the, lad curves are set as follow

<LoadData>
<loadcurve id="1">
<loadpoint>0,0</loadpoint>
<loadpoint>1,0.1</loadpoint>
<loadpoint>4,0.1</loadpoint>
</loadcurve>
<loadcurve id="2">
<loadpoint>0,0</loadpoint>
<loadpoint>1,0</loadpoint>
<loadpoint>4,3</loadpoint>
</loadcurve>
<loadcurve id="3">
<loadpoint>0,0</loadpoint>
<loadpoint>1,-0.35</loadpoint>
<loadpoint>4,-0.35</loadpoint>
</loadcurve>
</LoadData>

This is how I think it should be set up. But then, I cannot see these settings in the Preview. Is the febio file OK, but the loaded Preview file not? However, I still don’t know, what the first load curve represent (id 1). It is the velocity, or the acceleration, or something else?

Michala

PS: I am aware of the fact, that I have lately asked lots of (even maybe silly) questions and I really appreciate your responses. There is nobody in my lab working with Febio, so this is the only way how to get some responses and the way how to understand this effective tool for solving biomechanical problems. Thanks!

michalacadova
10-12-2010, 07:41 AM
I have another question concerning this case. When I try to run the febio file (I have attached it) it says: FATAL ERROR: unrecognized tag “fix” <line 4592>. What’s the problem with it? I have checked it and the structure seem the same as in the example :(.

Michala

maas
10-12-2010, 03:35 PM
Hi Michala,

The reason for the FATAL ERROR is that you have a fixed boundary condition in a Step definition and currently FEBio does not allow that. To prevent this, you need to define all fixed BC's in the Initial step in PreView. In fact, if you only have one analysis step I would place all the BC's in the Initial step.

There is also a bug in PreView that places the BC's in the first analysis step when reading an FEBio file instead of the Initial step. I will try to fix this as soon as I find the time. I guess this is how the problem started.

About the loadcurve with id=1, it looks indeed like this curve is not being used. I think it is a remnant of an older version of the file so you can just ignore that.

Hope this helps.

Cheers,

Steve.