COMSOL Forums: Local Edge System
http://www.comsol.com/community/forums/general/thread/33212/
Most recent forum messagesTue, 08 Jan 2013 11:38:11 +0000COMSOL Forums: Local Edge Systemhttp://www.comsol.com/shared/images/logos/comsol_logo.gif
http://www.comsol.com/community/forums/general/thread/33212/
Re: Local Edge System
http://www.comsol.com/community/forums/general/thread/33212/#p93298
Hello,<br />
<br />
I still couldn't figure out how to compute the derivative along a certain edge. I looked at the beam equation view and there the derivative is accessed by the expression "mod1.umod1.vmod1.wts". The s at the end seems to compute the derivative of the local w variable in the edge direction. Sadly i wasn't able to apply this to an own weak formulation on an edge. Do you have an idea, how this might be done?<br />
<br />
Thank you very much.<br />
<br />
Jan KaulTue, 08 Jan 2013 11:38:11 +000033212.1357645091.93298Re: Local Edge System
http://www.comsol.com/community/forums/general/thread/33212/#p91627
Hi<br />
<br />
I have some problems understanding what you are doing<br />
<br />
1) define materials on the domains and the edge, now you have a mix of undefined material variables and local user defined for part of it<br />
<br />
2) the edge load of the solid is probably not d(u,x), first d(u,x) is ux in COMSOL (check the equations view), then u is the dependent variable of the "solid", I suspect you want the dependent variables of your "beam" that is u2x<br />
<br />
3) why use a rigid connector and not just a "fixed" BC for the solid (and the beam) ?<br />
<br />
I would suggest that you solve the two independently and look at the variables in specific plots, then you can combine them, probably it will be clearer.<br />
<br />
As validation you should draw your beam as solid and solve the "solid" as a 2 material case and then compare with the use of your beam<br />
<br />
--<br />
Good luck<br />
IvarTue, 04 Dec 2012 18:58:36 +000033212.1354647516.91627Re: Local Edge System
http://www.comsol.com/community/forums/general/thread/33212/#p91588
Thank you Hendrik,<br />
<br />
that changes a lot. But actually for my case it would suffice to access the derivatives of the displacement field of the solid, which should be usual Lagrange tetrahedrons. I thought that if I want to compute the derivatives using the u variable of the solid mechanics physics instead of the u2 variable of the beam physics comsol would automaticly use the shape-functions of the solid.<br />
<br />
kind regards<br />
<br />
Jan KaulTue, 04 Dec 2012 07:59:14 +000033212.1354607954.91588Re: Local Edge System
http://www.comsol.com/community/forums/general/thread/33212/#p91586
Hello Ivar,<br />
<br />
I'm really sorry to bother you so often, but i can't seem to be able to compute the derivatives, no matter how I tried it. The reason for my question is that I want to apply an Edge Load depending on the derivative of u. I attached my Model, so that you might have a look at it.<br />
The critical part is the Edge Load in the Solid Mechanics Physics, which seems to be zero although I multiplied it with a very big number.<br />
<br />
I thank you very much for your time and hope that I won't be bothering you for a while after that.<br />
<br />
kind regards<br />
<br />
Jan KaulTue, 04 Dec 2012 07:42:44 +000033212.1354606964.91586Re: Local Edge System
http://www.comsol.com/community/forums/general/thread/33212/#p91585
Hi,<br />
<br />
<div class="quote"><br />
<br />
Is there a way to compute the derivative of along the edge(beam), because although my beam is in the direction of z, uz doesn't seem to work.<br />
<br />
</div><br />
<br />
Derivatives with respect to spatial directions cannot be computed for the beam elements, nor can the tangential derivative operator dtang() be used. The beams use a special ('Hernitian') element formulation. A derivative like uz for a beam element in the z direction is however the same as the degree of freedom thy. In the beam element the derivatives of the transverse displacements are actually degrees of freedom.<br />
<br />
Regards,<br />
HenrikTue, 04 Dec 2012 07:41:21 +000033212.1354606881.91585Re: Local Edge System
http://www.comsol.com/community/forums/general/thread/33212/#p91527
Hi<br />
<br />
isnt it what was just said above, in the beam theory the beam "edge" is "x", you have a coordinate change with the beam physics<br />
<br />
--<br />
Good luck<br />
IvarMon, 03 Dec 2012 14:16:08 +000033212.1354544168.91527Re: Local Edge System
http://www.comsol.com/community/forums/general/thread/33212/#p91502
Thank you very much for your reply.<br />
<br />
Is there a way to compute the derivative of along the edge(beam), because although my beam is in the direction of z, uz doesn't seem to work.<br />
<br />
kind regards<br />
<br />
Jan KaulMon, 03 Dec 2012 08:32:23 +000033212.1354523543.91502Re: Local Edge System
http://www.comsol.com/community/forums/general/thread/33212/#p91191
Hi,<br />
<br />
Concerning the original question about directions in Local Edge System:<br />
<br />
<div class="quote"><br />
<br />
I'm trying to implement a "Predescribed Displacement" Condition on an Edge using the local Edge Coordinate system. But i have the Problem that i couldn't find a reference to the "Local Edge System" and therefore I'm not sure which coordinate direction lies in the direction of the edge. And additionally i don't really know how the directions are called.<br />
<br />
</div><br />
<br />
Local edge systems are available for some loads and boundary conditions in the Beam and Shell interfaces. Your question does not tell which, and the definitions differ:<br />
<br />
Beam:<br />
<br />
The local edge system is the same as the beam coordinate system as specified by the Section Orientation subfeature under Cross Section Data.<br />
<br />
Shell:<br />
<br />
The first direction (xl) is along the edge.<br />
The third direction (zl) is the same as the shell normal direction.<br />
The second direction (yl) is in the plane of the shell, and formed by the cross product zl X xl.<br />
<br />
In both cases you can examine the directions by adding Arrow Line plots under a 3D Plot group. If you do not have any results yet (which you would not have during input data preparation) you need to add a Study, then Show Default Solver, and run until Compile Equations. Now you will have a data set which contains the geometrical information required.<br />
<br />
Regards,<br />
HenrikTue, 27 Nov 2012 13:11:38 +000033212.1354021898.91191Re: Local Edge System
http://www.comsol.com/community/forums/general/thread/33212/#p91181
Thank you very much Ivar!<br />
<br />
I solved my problem using the intop Operator.<br />
<br />
Jan KaulTue, 27 Nov 2012 11:05:03 +000033212.1354014303.91181Re: Local Edge System
http://www.comsol.com/community/forums/general/thread/33212/#p91177
Hi<br />
<br />
in COMSOL Solid physics u,v,w are the displacement field (implicitely u(x,y,z),v(x,y,z) ...) but you do not address u,v,w like that, you can define in the post processing a line graph on a solved Data set, then select an Edge entity and type u in the expression, this will give you the displacement u(x,y,z) along the edge for all (x,y,z) belonging to the selected edge.<br />
<br />
by default COMSOL show this w.r.t. the arc length (s)*total_arc_length, but you might change the horizontal scale and define your own expression (scalar) based on any value, including x,y,z ...<br />
<br />
in COMSOL if you want to know a dependent value at "point" location you need to define a "point integration" operator and select your point and "integrate" (as sum_over_i=1to1 => value at i=1) so the integration of "u" over a point at location (x0,y0,z0) is u(x0,y0,z0).<br />
<br />
but now I have a doubt how you could implement this for "s" and get u(s=0) for a given edge over to a variable <br />
<br />
--<br />
Good luck<br />
IvarTue, 27 Nov 2012 09:49:58 +000033212.1354009798.91177Re: Local Edge System
http://www.comsol.com/community/forums/general/thread/33212/#p91164
Hello,<br />
<br />
Thank you very much Ivar. Is there a way to get for example u(s=0)?<br />
<br />
kind regards<br />
<br />
Jan KaulTue, 27 Nov 2012 09:03:48 +000033212.1354007028.91164Re: Local Edge System
http://www.comsol.com/community/forums/general/thread/33212/#p91133
Hi<br />
<br />
the local variable for edges is "s" going from 0 to 1 along the arrow direction (COMSOL decides how) and you need to turn on the arrow plot in the view options to see the direction<br />
<br />
--<br />
Good luck<br />
IvarMon, 26 Nov 2012 18:33:07 +000033212.1353954787.91133Local Edge System
http://www.comsol.com/community/forums/general/thread/33212/#p91090
Hello,<br />
<br />
I'm trying to implement a "Predescribed Displacement" Condition on an Edge using the local Edge Coordinate system. But i have the Problem that i couldn't find a reference to the "Local Edge System" and therefore I'm not sure which coordinate direction lies in the direction of the edge. And additionally i don't really know how the directions are called.<br />
<br />
I really appreciate your help.<br />
<br />
Jan KaulMon, 26 Nov 2012 08:41:54 +000033212.1353919314.91090