Fix Boundary in Multi-Step Analysis
issueid=725 07-13-2015 03:38 PM
Junior Member
Fix Boundary in Multi-Step Analysis


I don't know whether it's a bug or a feature that's not yet implemented. I have a file with two steps: swelling then compression. I'd like to fix one surface during the second step. Which means that this surface can move/deform during the swelling step but should be fixed as soon as the second step starts.

I think I used the correct code in the Step section:
		    <fix bc="xy">
				<node id="9"/>
				<node id="10"/>
				<node id="41"/>
				<node id="42"/>
				<node id="73"/>
				<node id="74"/>
				<node id="105"/>
				<node id="106"/>
				<node id="137"/>
				<node id="138"/>
				<node id="169"/>
				<node id="170"/>
				<node id="201"/>
				<node id="203"/>
				<node id="233"/>
				<node id="234"/>
				<node id="265"/>
				<node id="266"/>
				<node id="297"/>
				<node id="298"/>
But FEBio 2.3.0 (and also 2.4) fails to launch the file: "FATAL ERROR: unrecognized tag "fix" (line 1024)"

Thanks for any help you can provide.


Issue Details
Issue Number 725
Project FEBio
Category Unknown
Status Not a Bug
Priority Unknown
Affected Version Unknown
Fixed Version (none)
Users able to reproduce bug 0
Users unable to reproduce bug 0
Assigned Users (none)
Tags (none)

07-14-2015 09:58 AM
Lead Code Developer
Hi Antoine,

Fixed BC's are not supported yet in a multi-step analysis. I can look into adding that, but I don't think the fixed BC is what you need. The fixed BC enforce a zero displacement with respect to the reference configuration so if you were to use it in a second step it would simply force the boundary back to its original, undeformed position.

Instead, you could use a zero prescribed BC and set the type to relative.
<prescribe bc="x" type="relative" lc="1">
    <node id="9">1</node>
    <node id="298">1</node>
Then, you just define a zero load curve to make sure the nodes remain in their current position.



07-14-2015 10:01 AM
Junior Member
Hi Steve,

I totally forgot the relative attribute. It's indeed what I wanted in this case. Thanks again for your help.



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