Strange limit in velocity

[brouwe...@gmail.com]

Hi everybody,

I noticed a strange limit in velocity by OPenPIV which is clearly related to the size of the interrogation windows and their overlap. I would like to know what causes this limitation as in theory the size of the windows should allow for greater velocities.

More details can be found in the enclosed word file.

Images, scripts and results are provided in the zip file.

Thanks in advance for any suggestions or help.

Kind regards,

Bart Brouwers

[brouwe...@gmail.com]

Hereby the zip file

[Alex Liberzon]

Could you please specify which openpiv version you run? it seems that you use something < 0.23 or so, I am trying now with 0.25.0 and there are many inconsistencies.

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[Alex Liberzon]

One remark before we can get deeper into the example, the basic maximum displacement is the 1/2 * window size and the recommended is 1/4 of the window size. could you please run the code with the window sizes chosen to be 4*expected_displacement?

Thanks

[brouwe...@gmail.com]

Hi Alex,

Indeed I am using  a VKI customized version of OpenPIV, which is modified starting from your OpenPIV version 0.22.3.   

Kind regards,

Bart

Op vrijdag 3 maart 2023 om 18:21:20 UTC+1 schreef alex.l...@gmail.com:

[Alex Liberzon]

I see, could you please share this repo with us? I wonder what's VKI customized version and what we might need to adjust in the newer OpenPIV versions.

Meanwhile, I think that OpenPIV does not have any maximum displacement limitation, this is just the basic assumption of the window size - it is strongly recommended to have a window size 4 times the maximum displacement expected. The window deformation and multi-grid part, along with the option to non-square, rectangular windows, would help to deal with the high dynamic range of displacements in case like yours, where some parts of the image have different imaging resolutions.

Alex

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