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probe and sample point in same place producing different data

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Old   May 9, 2015, 08:34
Default probe and sample point in same place producing different data
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Hi,

In a case I'm running I have put a probe in a particular location to record velocity at run time, and have also put a sampleDict entry at the same location to record velocity post-solving. Obviously the data produced from both SHOULD be identical, but it's not, does anyone know why? Is it something to do with the fact that the solver (pimpleFoam) is running in parallel? I seem to remember someone telling me in the past to use average(U) or something when solving in parallel?

Below are the probe and sampleDict entries:

probe (located in system/controlDict):
Code:
actuator_probe
    {
        type            probes;
        functionObjectLibs ("libsampling.so");
        enabled         true;
        outputControl   outputTime; //timeStep;
        outputInterval  1;
        probeLocations
        (
            (-0.015 0 0.5)
        );
        fields
        (
            U
        );
    }
(this locates a velocity probe at (-0.015 0 0) - note that the case is 2D).

sampleDict entry (located in system/sampleDict):
Code:
actuator_velocity
    {
        type        uniform;
        axis        z;

        start       (-0.015 0 0);
        end         (-0.015 0 1);
        nPoints     3;
    }
(this locates a line with three points in the 'z' dimension (being a 2D case this essentially acts as a point location) between (-0.015 0 0) and (-0.015 0 1) - so I just use the middle point on the line as a point measurement).

So the data they record SHOULD be the same, and yet it is not.

Any ideas? Thank you.
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Old   May 13, 2015, 12:41
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Anyone?
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Old   November 30, 2015, 11:31
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I still haven't got to the bottom of this - I've attached an image which shows plots of velocity (x & y components) recorded at a certain location (-0.015, 0, 0.5) on the domain, and of vorticity (z component) recorded at a certain location (0, -0.5, 0.5), using both a probe and sampling.

Interestingly, the velocities recorded with probe and sample (at (-0.015, 0, 0.5)) don't appear to agree at all, yet the vorticity recorded at (0, -0.5, 0.5) seem to pretty much agree, although not perfectly (which I don't understand).

Also, the velocity recordings are actually on a boundary where I have prescribed a sinusoidal oscillatory velocity boundary condition using groovyBC, so I know what the recording SHOULD BE as I was the one that specified it, and the sampled data (black line) DOES agree with this - so I trust the data I obtain through sampling, but not through using a probe.

Anyone able to shed some light?
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Old   May 2, 2016, 02:35
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Hey,
I am looking to probe vorticity during run-time, does the probes utility allow this or ( I have seen in some ancient posts here) do I need to create a new probe for vorticity. If you have ine the latter, can your share your code ( createProbes.H etc) ?

Cheers,
D
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