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jsmith
New member
Username: jsmith

Post Number: 1
Registered: 07-2010
Posted on Monday, July 12, 2010 - 02:26 am:   

Hello,

I would like to impose periodic BCs on all lateral sides of a 3D body (i.e. in both x and y). I believe my script is correct but I get an error which I cannot understand.

I start from the example "TWO-WAY_PERIODIC.PDE" which works in 2D, and simply extrude in the third dimension (in z). The script fails with an "Incomplete Bounding Mesh" message.

!------------ script

title '3D TWO-WAY PERIODIC BOUNDARY TEST'

COORDINATES
Cartesian3 ('x','y','z') { coordinate system, 1D,2D,3D, etc }

variables
u

definitions
k = 1
h=0
x0=0.4 x1=0.9 { right box x-coordinates }
x2=-0.5 x3=0.0 { left box x-coordinates }
y0=-0.7 y1 = -0.3 {y-coordinates for both boxes }

equations
u : div(K*grad(u)) + h = 0

EXTRUSION
SURFACE 'Bottom' z=-1/2
LAYER 'everything'
SURFACE 'Top' z=1/2

boundaries
region 1
{ Periodic bottom boundary }
start(-1,-1)
periodic(x,y+2) line to(0.95,-1)
{ New "line" spec breaks periocity }
{ optional: natural(u) = normal(K*grad(u)) }
line to (1,-1)
{ Periodic right boundary }
periodic(x-2,y) arc(center=-1,0) to (1,1)
{ Images of non-periodic stub and periodic bottom boundry }
line to (0.95,1) to (-1,1)
{ Image of periodic right boundary }
arc(center= -3,0) to close
{ off-center hot box }
start(x0,y0)
value(u)=1 line to (x1,y0) to (x1,y1) to (x0,y1) to close
{ off-center cold box }
start(x2,y0)
value(u)=-1 line to (x3,y0) to (x3,y1) to (x2,y1) to close

monitors
grid(x,y) ON z=0
contour(u) ON z=0
plots
grid(x,y) ON z=0
contour(u) ON z=0
end

!------------ end script

Help appreciated!

PS.
I use the student version.

I also tried a different strategy: periodic extrusion in z and imposing periodicity only in one lateral dimension. This corresponds to a rotation of my desired configuration. It failed with a similar message.

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mgnelson
Moderator
Username: mgnelson

Post Number: 200
Registered: 07-2007
Posted on Tuesday, July 13, 2010 - 01:24 pm:   

This appears to be a bug in FlexPDE. We will look into it and hopefully have it fixed in the next maintenance release (v6.14).
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rgnelson
Moderator
Username: rgnelson

Post Number: 1383
Registered: 06-2003
Posted on Thursday, July 15, 2010 - 02:18 pm:   

Actually, the example as distributed violates the rules of periodicity. It has two-way periodicity at the left corners, but somehow succeeds in 2D. (This is probably an accident of periodic reference ordering).

If you put a gap at each end of the horizontal boundaries, the problem runs successfully in 3D. See attached.

We will try to clarify the diagnostics so that FlexPDE will either run the script correctly or issue a diagnostic report identifying the multiple periodicity.


application/octet-stream
3d_periodic2.pde (1.2 k)

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