Changes between Version 12 and Version 13 of Tutorial/AdvancedParticleImagingVelocimetry2


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Timestamp:
Aug 28, 2013, 11:53:54 AM (8 years ago)
Author:
sommeria
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  • Tutorial/AdvancedParticleImagingVelocimetry2

    v12 v13  
    1 This is an example using more advanced tools than the simple example .... and .... Image pre_processing and merging of mutiple fields is used to optimise PIV in the case of a narrow parietal jet (produced by convection in a cavity).
     1This is an example using more advanced tools than the simple example [wiki:"Tutorial: Particle Image Velocimetry" Tutorial: Particle Image Velocimetry]. Image pre_processing and merging of mutiple fields is used to optimise PIV in the case of a narrow parietal jet (produced by convection in a cavity).
    22Open the example UVMAT_DEMO6_PIVconvection (accessible on http://servforge.legi.grenoble-inp.fr/pub/soft-uvmat/).
    33
     
    99
    1010= mask =
    11 Open the original image with uvmat, selecting the transform option 'phys'.  withCreate a mask polygon by the menu bar command Projection object/mask_polygon. Set the option 'mask_outside' and introduce the coordinates of the four corners in Coord (like for geometry calib). Plot the polygon. Then create the corresponding mask by '''Tools/make mask'''.
     11Open the original image with uvmat, selecting the transform option 'phys'. Create a mask polygon by the menu bar command Projection object/mask_polygon. Set the option 'mask_outside' and introduce the coordinates of the four corners in '''Coord''' (like for geometry calib). Plot the polygon. Then create the corresponding mask by '''Tools/make mask'''. The default name is 'mask_1.png' in the subfolder Dalsa1.mask.
    1212
    1313= sub_background =
    1414We observe parasitic light rays on the images which correspond to fixed features, leading possibly to spurious velocity vectors equal to 0. To eliminate those we use sub_bacground.
    1515Open the image with 'series' and select the program 'sub_background'. This function is not provided in the default menu, so you need to use the last menu option 'more...', and select the function in the sub-folder 'series/' of the package uvmat. This option is then preserved in the menu for later use.
    16 Then run sub_background over the whole index range in i and j, using the default parameters. Answer Yes to the quaestion 'apply levels', which will conveniently rescale the image brightness after background removal.
     16Then run sub_background over the whole index range in i and j, using the default parameters. Answer Yes to the question 'apply levels', which will conveniently rescale the image brightness after background removal.
    1717
    1818= first PIV =
     19Do PIV  on the the whole image series, selecting all the options from Civ1 to Patch2 (see [wiki:"Tutorial: Particle Image Velocimetry" Tutorial: Particle Image Velocimetry] for an introduction).
     20
     21Choose the pair 'j=1-2' which provides the smaller time interval (100 ms), a good choice to capture correlations in a first try (although higher precision can be obtained with a larger time interval if the correlation is still of good quality).
     22
     23Select the Mask 'mask_1.png' previously created.
     24
     25Looking at the results with uvmat, we global flow fetures. We notice hower that the thin parietal plume is not properly resolved while the precision in the interior is poor because of the small displacement within the frame pair. So the next step will be to perform two PIV series optimized for each sub-region and merge them.
    1926
    2027= making two masks =
     
    3643
    3744= merging data on a common grid =
    38 create a projection grid in phys coordinates. For that open a velocity field with uvmat, displayed in phys coordinates. Use the upper bar menu option Projection object/plane. Then in the GUI '''set_object''', choose the option !ProjMode=interp_lin. Choose a mesh 0.2 cm in each direction, ranging from 0 to 58.8 in x and 0 to 55 in y. Press REFRESH to see the result of projection in the GUI view_field. Check the option '''nb_vec/4''' to reduce the number of vectors displayed on the plot.
     45create a projection grid in phys coordinates. For that open a velocity field with uvmat, displayed in phys coordinates. Use the upper bar menu option Projection object/plane. Then in the GUI '''set_object''', choose the option !ProjMode=interp_lin. Choose a mesh 0.1 cm in each direction, ranging from 0 to 58.8 in x and 0 to 55 in y. Press REFRESH to see the result of projection in the GUI view_field. Check the option '''nb_vec/4''' to reduce the number of vectors displayed on the plot.
     46
    3947Now in series open the PIV file Dalsa1.sback.civ_bulk as input. Then append the second file Dalsa1.sback.civ_plume using the menu bar selection '''Open/Browse append...'''.
    40 Set FieldTransform to 'phys', and selection Projection Object. The plane is then incorporated in series.
     48
     49Set '''!FieldTransform''' to 'phys', and select '''Projection Object'''. The plane for projection is then incorporated in '''series'''.
     50
     51It is also advised to introduce masks in the interpolation process so that each field is interpolated in its range of validity. This is done by selecting the option '''Mask'''. Use the browser to fill the table of masks, in accordance with the table of input file series.
     52
     53= merging data using thin plate shell =
     54The previously used linear interpolation does not provide field derivatives. For that purpose, we proceed as previouisly but use the option '''!ProjMode''' ='interp_tps' for the projection plane in '''set_object'''.
     55
     56In the GUI '''series''', select simultaneously the fields vec(U,V), curl(U,V) and div(U,V) to get the vorticity and divergence in addition to velocity. The calculation is significantly longer that for interp_lin, so in the demo we use a resolution DX=DY=0.2 cm for the projection plane (instead of 0.1 cm).
     57
     58Open the resulting files with uvmat. Selct a vector (components U, V) or a scalar curl or div to visualize the different fields.