Changes between Version 50 and Version 51 of Tutorial/AdvancedParticleImagingVelocimetry2


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Timestamp:
Jan 30, 2015, 2:37:42 PM (10 years ago)
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vaillant1p
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  • Tutorial/AdvancedParticleImagingVelocimetry2

    v50 v51  
    22
    33= [wiki:Tutorial] / Advanced Particle Imaging Velocimetry =
    4 This is an example using more advanced tools than the simple example [wiki:Tutorial/ParticleImageVelocimetry 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). Open the example UVMAT_DEMO6_PIVconvection (accessible on http://servforge.legi.grenoble-inp.fr/pub/soft-uvmat/).
     4This is an example using more advanced tools than the simple example [wiki:Tutorial/ParticleImageVelocimetry Tutorial: Particle Image Velocimetry]. Image pre_processing and merging of multiple fields is used to optimise PIV in the case of a narrow parietal jet (produced by convection in a cavity). Open the example 'UVMAT_DEMO6_PIVconvection/Dalsa1' (accessible on http://servforge.legi.grenoble-inp.fr/pub/soft-uvmat/).
    55
    66= Calibration =
    7 Perform the geometric calibration by marking the four box corners with the mouse, as described in [wiki:Tutorial/GeometricCalibration Tutorial: geometric calibration], section 'calibration with reference points'. Alternatively, you can skip this operation by using the reference file 'Dalsa1.ref.xml' provided, removing the extension '.ref' to make it active.
     7Perform the geometric calibration by selecting the four box corners with the mouse, as described in [wiki:Tutorial/GeometricCalibration Tutorial: geometric calibration], section 'calibration with reference points'. Alternatively, you can skip this operation by using the reference file 'Dalsa1.ref.xml' provided, removing the extension '.ref' to make it active.
    88
    99= Mask =
    … …  
    1111
    1212= Sub_background =
    13 We 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_background'''.  In the GUI '''uvmat''', select '''[Run/field series]'''. Then 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.  Then 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.
     13We 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 the '''[Action]''' function 'sub_background'.  In the GUI '''uvmat''', select '''[Run/field series]'''. Then 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.  Then '''[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.
    1414
    1515= First PIV =
    16 Do a PIV on the whole image series, optained with '''sub_background''' (stored in a 'Dalsa1.sback' subfolder), selecting all the options from Civ1 to Patch2 (see [wiki:Tutorial/ParticleImageVelocimetry Tutorial: Particle Image Velocimetry] for an introduction).
     16Do a PIV on the whole image series, optained with 'sub_background' (stored in a 'Dalsa1.sback' subfolder), selecting all the options from '''[CIV1]''' to '''[PATCH2]''' (see [wiki:Tutorial/ParticleImageVelocimetry Tutorial: Particle Image Velocimetry] for an introduction).
    1717
    1818Choose 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).
    1919
    20 Select the check box Mask and open the file 'mask_1.png' previously created.
     20Select the check box '''[Mask]''' and open the file 'mask_1.png' previously created.
    2121
    2222Looking at the results with '''uvmat''', we see the global flow features. We notice however 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.
    … …  
    2626
    2727= PIV on the parietal plume =
    28 Open an image of the subfolder Dalsa1.sback (for instance Dalsa1_1_1.png) and open the GUI '''series''' to change the name at the bottom '''output !SubDir''' by 'Dalsa1.sback.civ_bulk'.
    29 
    30 Click then on 'civ_series' in the '''[Action]''' list to open the GUI '''civ_input'''. Choose the following parameters:
     28Open an image of the subfolder Dalsa1.sback (for instance Dalsa1_1_1.png) and open the GUI '''series/civ_series'''. Choose the following parameters:
    3129
    3230 * pair j=1-2 for Civ1 and Civ2 : it minimises the time interval which is needed to capture the large velocity in the plume.
    … …  
    3735 * For Civ2, same parameters !CorrBox, auto-grid and Mask.
    3836 * For patch and Fix, default parameters.
     37 * Make sure the images go from i=60 to i=150.
     38
     39Select '''[OK]''' and in the GUI '''series''' change the name at the bottom '''[output !SubDir]''' by 'Dalsa1.sback.civ_bulk'.
    3940
    4041= PIV on the interior =
    41 Select the pair j=1-3 to deal with the small velocities (considering that the parietal plume has been masked). Then use the default parameters.
     42Select the pair j=1-3 to deal with the small velocities (considering that the parietal plume has been masked). Then use the default parameters to '''[RUN]''' the PIV calculation with the 'mask_bulk.png' mask.
    4243
    4344= Merging data on a common grid =
    4445Create a projection grid in phys coordinates. For that purpose, open a velocity field of 'Dalsa1.sback.civ_bulk' 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''' in '''view_field''' to reduce the number of vectors displayed on the plot.
    4546
    46 Now 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...]'''. Select '''[!ActionName]'''= 'merge_proj'. Set '''[!FieldTransform]''' to 'phys', and select the check box '''Projection Object'''. The plane for projection is then incorporated in '''series'''. It 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 check box '''Mask'''. Use the browser to fill the table of masks, in accordance with the table of input file series. Press '''[RUN]''' to launch the calculation. Then press '''[STATUS]''' to see the result with '''uvmat'''.
     47Now 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...]'''. Select '''[!ActionName]'''= 'merge_proj'. Set '''[!FieldTransform]''' to 'phys', and select the check box '''Projection Object'''. The plane for projection is then incorporated in '''series'''. It 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 check box '''Mask'''. Use the browser to fill the table of masks, in accordance with the order of the files in the table of input file series. Press '''[RUN]''' to launch the calculation. Then press '''[STATUS]''' to see the result with '''uvmat'''. Select the coordinates you want on the figure with '''get_field''' and click on '''[OK]'''.
    4748
    4849= Merging data using thin plate spline =
    4950The 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'''. To reach this GUI using the same projection object as before just select the check box '''edit''' in the GUI '''series''' to open the GUI '''set_object'''. Change the option '''[!ProjMode]''' and click on '''[REFRESH]'''.
    5051
    51 In the GUI '''series''', select simultaneously the fields 'vec(U,V)', 'curl(U,V)' and 'div(U,V)' (using the keyboard Ctrl button) 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).
     52In the GUI '''series''', select simultaneously the fields 'vec(U,V)', 'curl(U,V)' and 'div(U,V)' (using the keyboard Ctrl button) 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 '''[Mesh]''' resolution DX=DY=0.2 cm for the projection plane (instead of 0.1 cm).
    5253
    5354Open the resulting files with '''uvmat'''. Select a vector (components U, V) or a scalar curl or div to visualize the different fields.