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Need help for the “FFD_SURFACE_POINTS”

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Old   January 22, 2014, 02:08
Default Need help for the “FFD_SURFACE_POINTS”
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Yufei ZHANG
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In the ONERA M6 optimization test case (V3.0.00 test case folder: TestCases\optimization_rans\steady_oneram6\), the grid file (mesh_ONERAM6_turb.su2) includes the FFD control parameters.
The “FFD_CORNER_POINTS” and “FFD_CONTROL_POINTS” is easy for understanding. But the “FFD_SURFACE_POINTS” is quite confusing. The point indexes are the indexes of the wing surface grid, but the coordinates are not on the wing surface (as shown in the figure).

Is the FFD_SURFACE_POINTS necessary? Is there any tutorial for the FFD definition?

When I use the FFD function with my own grid, the SU2_MDC couldn’t generate the deformed mesh, because the maximum difference of the original and deformed surface grids is very large, even when all of the geometry parameters are 0. I think the problem comes from the FFD_SURFACE_POINTS definition.

Thank you for your help!
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Old   January 23, 2014, 01:29
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It seems that there is a transformation relationship between the FFD_CONTROL_POINTS and the FFD_SURFACE_POINTS. If the FFD box is a unitary box (x, y, z) = ([0,1], [0,1], [0,1]), the output of SU2_MDC is correct when the coordinates of FFD_SURFACE_POINTS are equal to the surface grid points. If the FFD box is not a unitary box, the FFD_SURFACE_POINTS need to be transformed by a relation. But the relation is not clear.
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Old   January 28, 2014, 16:44
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Trent Lukaczyk
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FFD_SURFACE_POINTS identify which surface grid points are inside the FFD box, and their (u,v,w) parametric location inside the box.
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Old   January 29, 2014, 20:51
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Quote:
Originally Posted by rktchip View Post
FFD_SURFACE_POINTS identify which surface grid points are inside the FFD box, and their (u,v,w) parametric location inside the box.
Dear rktchip,

Thank you for your reply.
How to define the (u,v,w) parametric location? Is there a transformation tool or code? Thank you!
flyyufei
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Old   January 30, 2014, 13:40
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Tommy Chen
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Quote:
Originally Posted by flyyufei View Post
Dear rktchip,

Thank you for your reply.
How to define the (u,v,w) parametric location? Is there a transformation tool or code? Thank you!
flyyufei
Hi Yufei

Are you from the Tsinghua University ?

actually the FFD transformation algorithm could be found in a classicla paper,
http://pages.cpsc.ucalgary.ca/~blob/...others/ffd.pdf
and also http://www.cse.iitd.ernet.in/~pkalra/csl783/ch14ffd.pdf

Cheers
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Old   January 30, 2014, 13:55
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Tommy Chen
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Quote:
Originally Posted by flyyufei View Post
Dear rktchip,

Thank you for your reply.
How to define the (u,v,w) parametric location? Is there a transformation tool or code? Thank you!
flyyufei
Actually the parametric location is like sort of the (u,v) parameters in NURBS methods, to define the relatively location within the FFD control volume
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Old   February 5, 2014, 21:04
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Yufei ZHANG
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Hi Tommy,
Thank you very much for your help. I apologize for my late reply because of the Chinese Spring Festival.
I’m from Tsinghua University in Beijing. How did you know?



Quote:
Originally Posted by Tommy Chen View Post
Hi Yufei

Are you from the Tsinghua University ?

actually the FFD transformation algorithm could be found in a classicla paper,
http://pages.cpsc.ucalgary.ca/~blob/...others/ffd.pdf
and also http://www.cse.iitd.ernet.in/~pkalra/csl783/ch14ffd.pdf

Cheers
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Old   February 12, 2014, 14:17
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Thomas D. Economon
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Hi,

Currently, the code uses the 8 control points and the degree for each direction (i,j,k) to compute the locations of the FFD_CONTROL_POINTS (basically just the locations of each {i,j,k} of the structured box) and the FFD_SURFACE_POINTS automatically, i.e., no user intervention is required for FFD_CONTROL_POINTS or FFD_SURFACE_POINTS, only for FFD_CORNER_POINTS.

Therefore, after creating your mesh and supplying the basic definition of the box (degree and corner points), run SU2_MDC with DV_KIND= NO_DEFORMATION in the configuration file, and the remaining information (FFD_CONTROL_POINTS and FFD_SURFACE_POINTS) will be populated automatically for you.

All the best,
Tom
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Old   February 20, 2014, 07:31
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Yufei ZHANG
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Thank you! It works!

Quote:
Originally Posted by economon View Post
Hi,

Currently, the code uses the 8 control points and the degree for each direction (i,j,k) to compute the locations of the FFD_CONTROL_POINTS (basically just the locations of each {i,j,k} of the structured box) and the FFD_SURFACE_POINTS automatically, i.e., no user intervention is required for FFD_CONTROL_POINTS or FFD_SURFACE_POINTS, only for FFD_CORNER_POINTS.

Therefore, after creating your mesh and supplying the basic definition of the box (degree and corner points), run SU2_MDC with DV_KIND= NO_DEFORMATION in the configuration file, and the remaining information (FFD_CONTROL_POINTS and FFD_SURFACE_POINTS) will be populated automatically for you.

All the best,
Tom
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