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lee (leemu215)
Member
Username: leemu215

Post Number: 8
Registered: 06-2008
Posted on Monday, July 21, 2008 - 05:42 am:   

The FlexPDE 5 allows the definition of mesh-moving equations,it is only a method for adaptive mesh,or we can use this new function to solve some new problems?

Thanks very much!
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Robert G. Nelson (rgnelson)
Moderator
Username: rgnelson

Post Number: 1151
Registered: 06-2003
Posted on Monday, July 21, 2008 - 01:00 pm:   

I don't understand the question.

The Arbitrary Lagrange/Eulerian facility in FlexPDE 5 allows you to program motion into the finite element mesh. As with all facilities of FlexPDE, it is your choice how to drive the motion.

This capability is independent of the adaptive mesh refinement, which is applied by default in FlexPDE 5.

See "Help | User_Guide | Moving_Meshes" and the examples in the "Samples | Moving_Mesh" folder.
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lee (leemu215)
Member
Username: leemu215

Post Number: 9
Registered: 06-2008
Posted on Tuesday, July 22, 2008 - 03:45 am:   

Thanx.
In the example "Help | User_Guide | Moving_Meshes| 2D_Cyl_Piston"
Why pho and p have no Boundary condition,when I apply one ,it shows error"more than allowed variables"?
Btw,what is the physical meaning of the equation
'P: dt(P) + u*dr(P)+v*dz(P) + gamma*P*(dr(r*u)/r+dz(v)) = smoother*div(grad(P))'in this example.
Thanks for your help recently!!
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lee (leemu215)
Member
Username: leemu215

Post Number: 10
Registered: 06-2008
Posted on Tuesday, July 22, 2008 - 05:45 am:   

is this equation the same with the one I upload?
application/mswordeuler equation
euler equation.doc (35.3 k)
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lee (leemu215)
Member
Username: leemu215

Post Number: 11
Registered: 06-2008
Posted on Tuesday, July 22, 2008 - 09:04 am:   

"1. The default boundary condition when none is stated is NATURAL()=0. "
dose it mean ,if the boundary condition is NATURAL()=0 ,we do not need to specify the BC?
I tried with simple problem,the result is not the same.
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Marek Nelson (mgnelson)
Moderator
Username: mgnelson

Post Number: 54
Registered: 07-2007
Posted on Tuesday, July 22, 2008 - 11:32 pm:   

1)
It sounds like you have placed the boundary condition in the EQUATIONS section. You need to state BCs in the boundary path inside the BOUNDARIES section.

2)
The P equation in this problem is time dependent behavior of the pressure of a perfect gas. Our P equation as shown in our sample should be equivalent to your E equation in the case of a perfect gas. We also added the smoothing term as a noise filter.

3)
If no BC is stated, then the default is NATURAL()=0. With the caveat that a stated BC will be applied to all subsequent paths until explicitly changed. See "boundary conditions" in the Help index. So, in your simple problem, if you first stated some BC other than NATURAL()=0, that BC will continue until changed. Then if you add the natural somewhere, you have changed the BCs.

e.g.
START () VALUE()=1
LINE TO () TO () TO () TO CLOSE

is not the same as
START () VALUE()=1
LINE TO () TO () NATURAL()=0
LINE TO () TO CLOSE

The first will apply VALUE()=1 to all four line segments. If, in the second, you add NATURAL, the value is applied to the first two sides and natural to the last two sides and the solution will be different.
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lee (leemu215)
Member
Username: leemu215

Post Number: 12
Registered: 06-2008
Posted on Tuesday, July 29, 2008 - 04:20 am:   

thax very much!
But in the example "2d_cyl_piston.pde" when I add natural(P)=0 it will still cause trouble.
application/octet-stream
2d_cyl_piston.pde (4.4 k)
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Marek Nelson (mgnelson)
Moderator
Username: mgnelson

Post Number: 55
Registered: 07-2007
Posted on Tuesday, July 29, 2008 - 03:49 pm:   

Addition of the NATURAL(P)=0 in this script has no effect (as expected) when I run version 5.0.23 on Windows.

What version of FlexPDE are you running and on what platform?
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lee (leemu215)
Member
Username: leemu215

Post Number: 13
Registered: 06-2008
Posted on Wednesday, August 06, 2008 - 04:31 am:   

I also download version 5.0.23,and run it on Windows XP ,when I add natural(P)=0 in the example "2d_cyl_piston.pde".then the same problem comes:error:More than allowed Number of Variables.
ps:I use a student license.
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Marek Nelson (mgnelson)
Moderator
Username: mgnelson

Post Number: 59
Registered: 07-2007
Posted on Wednesday, August 06, 2008 - 02:39 pm:   

The student license is limited to five equations (see www.pdesolutions.com/student5.html ). The 2d_cyl_piston problem has six equations.

The sample files are keyed so that they can run in demo mode without restriction. You can change numerical values in the samples without breaking the key, but you cannot add or remove text (like adding your natural statement.)

By adding text, you have broken the sample key and then you are running on a student license, which cannot run six equations.

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