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Surface Sampling

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Old   July 22, 2014, 12:23
Default Surface Sampling
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Dear Foamers,

I have an engine case where I need to extract velocities on different cut planes.
To do that I am using sample utility in OpenFoam with a format raw (which gives the coordinates and the velocity components). Later I am plotting the 2D velocity vectors in Matlab. But since the mesh is not an evenly spaced grid , I am having some issues in creating the contours and vectors.

My question is there a way I could get the velocities on a regular grid (like remapping the sampled velocity on an evenly spaced grid)? Or a surface write format which writes the sampled data at regular intervals given a dx , a dy and start and end points? I am aware that line sampling can do that, but I need surface sampling in this case.

Thanks for your time.
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Old   August 6, 2014, 14:12
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Well I had to provide a cloud of points using set sampling to get what I wanted.It works but creating a cloud is not fun, especially if the domain is big and we want to sample at many points.

Thanks !
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Old   August 6, 2014, 14:22
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Another question is that when we provide the coordinates of several points to sample, and say a point A(0.5,0.5,0.5) lies outside our solution domain , then the sample utility does not output any value at that point (I am using "raw" write format).

All I want is that OpenFOAM outputs "NaN" values at all those points which lie outside the domain. Does anyone have an idea about how to accomplish this?

Thanks in advance !
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Old   October 26, 2020, 14:18
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Quote:
Originally Posted by AA29 View Post
Another question is that when we provide the coordinates of several points to sample, and say a point A(0.5,0.5,0.5) lies outside our solution domain , then the sample utility does not output any value at that point (I am using "raw" write format).

All I want is that OpenFOAM outputs "NaN" values at all those points which lie outside the domain. Does anyone have an idea about how to accomplish this?

Thanks in advance !
Hi, I am wondering if you were able to make OpenFOAM output NAN for the points which are outside your domain. Thanks.
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Old   September 21, 2021, 08:16
Default Sample on array of points
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I also needed to sample on set of points on a surface and found a solution.


It's possible to sample on a surface drawn in a CAD program (I use blender), which is exported as stl. If you draw the points where you need to sample and connect them as a surface, it is possible to sample on these points.

You can then add to your controlDict (openfoam.com v2012):
Code:
planesVelocity
{
     type            surfaces;
     libs ("libfieldFunctionObjects.so");
     enabled         true;
     writeControl    runTime;//Writes data every writeInterval seconds of     simulated time. 
     writeInterval 0.001;
     interpolationScheme cellPoint;
     surfaceFormat raw;
     surfaces
     (
         y0
         {
             type            sampledTriSurfaceMesh;
             surface         y0.stl;
             interpolate     true;
             source insideCells;
         }            
     );
     fields
     (   
         U 
         turbulenceProperties:R
     );
}
For the setting source I find:
source=insideCells, interpolate=true Per surface point interpolate cell containing it.
https://cpp.openfoam.org/v4/classFoa...rfaceMesh.html . The stl file is located in constant/triSurface

I didn't check thoroughly, but values outside the domain seem missing. I will write a script (Python) to add the missing coordinates and set them to NaN.
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