Thickness dependancy in extrusion

General discussions about how to formulate a script for FlexPDE.

Thickness dependancy in extrusion

Hello,

I wonder if there is a dependancy between different layers when extruding along the z-axis.
In my model i have two endplates, one at the top and one at the bottom of another material. But whenever the thickness of this endplates exceed 10% of the thickness of the material inbetween, the mesh gets destroyed while simulating from time t=0 to t=1 with a constant load in z-direction on the top plate.

I realised this by using the LIMITED REGION function and restricted the endplates to Layer 1 & 3 and the Material inbetween to Layer 2.
Like this:

extrusion z = -2.7, -2.5, 2.5, 2.7

Limited Region 1
Layer 1
Layer 3

/Geometrydefinition here

Limited Region 2
Layer 2

/Geometrydefintion here

In this example, the geometry of region 1 and region 2 are the same. Just the material differs and thus i use the different layers.

Simon
SJanssen

Posts: 6
Joined: Tue Jan 03, 2017 4:05 am

Re: Thickness dependancy in extrusion

I made an example to show what exactly i mean (see attachment).
If I choose the plates thickness (layer 1 and 5) to be 0.1 ("quader_stack_d1e-1") the script seems to work, if I choose the thickness to be greater ("quader_stack_d1"), it does not work anymore.
Attachments
SJanssen

Posts: 6
Joined: Tue Jan 03, 2017 4:05 am

Re: Thickness dependancy in extrusion

So far I figured out, that - at least in my case - the trouble seems to be caused by the combination of a load BC on uz and a value BC on hp on the surface between topplate and the middle part. So what I tried so far is:

value(uz) = something & value(hp) = something: works
value(uz) = something & load(hp) = something: works
load(uz) = something & value(hp) = something: does not work

I would really appreciate any help.
Thank you,
Simon
SJanssen

Posts: 6
Joined: Tue Jan 03, 2017 4:05 am

Re: Thickness dependancy in extrusion

This problem is unlikely due to layer thickness changes. There are a couple other issues that should be addressed first.

1) It is difficult to determine how FlexPDE will interpret a natural boundary condition because of the convoluted dependencies expressed in the equations. For example, VF variables appear not to be PDEs at all, but definitions. The U variables are defined by steady state equations but there are references to their time derivatives in other equations. If your variable is time dependent, FlexPDE is expecting a more direct statement in the general form of dt(variable) = F(variables, derivatives, etc). Your equations are likely to confuse the equation analysis.

2) Your script violates the rules for 3D domain construction. Your region 1 and 2 describe the same region. They should be combined. See Help sections "User Guide | Using FlexPDE in Three Dimensions" and "Technical Notes | Extrusions in 3D".
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