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Old   June 18, 2009, 20:58
Default nodes position through time
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Hi there,

i did a simulation in order to reproduce a experiment that involves wave propagation in water and also fluid structure interaction. This one consists on a confined fluid, in which pressure waves propagate through the fluid until finding a compliant wall. Those waves give moviment to the compliant wall that are measured.
I simulated this system and now I want to validate my model comparing the results with the experimental results. In my simulation I can observe the motion of wall, what I want to compare with my experimental data. The problem is that I dont know how. I mean, how does CFX solves the mesh motion? Is possible using CEL to get the coordinates of the nodes of a specific 2d region for each instant? If not, how can I get the node coordinates depending on time that I can observe using CFX-Post?
Any idea or tip on that direction will be very well received! Thank you in advance.
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Old   June 18, 2009, 23:12
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Hi,

You can get CFD-Post to display the X/Y/Z coordinate of the wall patch. If you want to extract the absolute positions for external analysis of you can get that out of CFD-Post using the export command.

Was the simulation done as an FSI simulation? If so then the mesh motion comes from the deformations predicted by the FEA solver.

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Old   June 19, 2009, 05:28
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Hi Mr. Horrocks,

thanks for your fast answer. I am using MFX and I set in my FEA (ANSYS Mechanical) only two boundary conditions.
!============================
!...
!BC1 - fix the boards of my "plate"
sf,boards,all,all,0
!BC2 - set FSI
sf,plate,fsin,1
!...
!============================
then I set the CFX simulation especifying by CEL the mesh displacement that generate the pressure waves. And also set the FSI region.
Therefore, I am looking for the mesh displacement in both sides. It is also to check if the exchange between CFX and ANSYS is ok for me. Due to convergence and stability I changed some settings, relaxation for example, and now I need to evaluate those changes. (some advises on that field has also high value to me!)

Back to my doubts, I could get from some points but it was a hard work getting those data and exporting. Is it possible to get x,y,z from each node in a 2D region through time using that approach you suggested? Does that approach permit exporting the data x(t),y(t),z(t) from each node in the surface?

Thanks
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Old   June 19, 2009, 07:14
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Hi,

You can get the x/y/z location of every point on a patch at every time step by one of two ways, neither of them are nice:

1) Make a monitor point on each point. Then you can output the x/y/z location of it through the solver manager
2) output a results file every time step. Then export the x/y/z points from CFD-Post.

This will generate a huge file and I wonder why you would bother. CFD-Post is post-processing software designed so you don't need to handle large datasets elsewhere. Why do you want to export it anyway?

Glenn Horrocks
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Old   June 19, 2009, 07:50
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Some parts of my surfaces present opposite displacements of other parts, what can give me a null volume displaced. But it is not what really happens. To avoid that, i want to use a RMS value from my displaced volume. As we are applying to the experimental data. Maybe it is possible using CEL, is it?
In my case, the second way is better, I think! You mean, trn file for each step? I already ran the simulation outputing for every step, (And you are right... it generates a huge file, but it is already there). And as I understood, what I have in that files, among other information, is the node position in each step. Then, can I export those data all together or do I need to export point by point? I mean, is possible to have a "surface" coordinates for each timestep or do I need to export each node position (P,i= x(t), y(t), z(t); where i is node index)? What I want to do is:
1 - define some very small areas using the nodes position (from three nodes position I can define the position of a element of area);
2 - take the component y of that element position;
3 - make the product of that component by the respective element of area;
4 - make the summation of that product for each element of area.
It gives me a volume, that can become zero because some position phase differences among the elements. And it is what I want to avoid applying the rms value of that product.

If you have any idea to make my work more effective, i will be really grate,

Smagmon

Last edited by smagmon; June 19, 2009 at 08:19.
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Old   June 20, 2009, 07:00
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Why do you want to export the data? You can do this calculation in CFD-Post (or as a monitor point during a solver run) then you don't need to export anything. MUCH easier and more efficient. Have a look in the reference manual under the CEL Expression language for the types of functions you can do in CEL.

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Old   June 23, 2009, 06:22
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Hi,
Thanks for the tip. I will try to do that, I am learning with the reference material.

Sorry for not replying until now. I was out for a couple days.
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