Changes between Version 22 and Version 23 of Tutorial/AdvancedParticleImagingVelocimetry


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Timestamp:
Jan 28, 2015, 10:24:56 PM (6 years ago)
Author:
sommeria
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  • Tutorial/AdvancedParticleImagingVelocimetry

    v22 v23  
    11[[TracNav(Tutorial/TOC)]]
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    3 = [wiki:Tutorial] / Advanced Particle Imaging Velocimetry =
    4 This example illustrates advanced procedures for particle Image Velocimetry (PIV), see [https://servforge.legi.grenoble-inp.fr/projects/soft-uvmat/wiki/Tutorial/ParticleImageVelocimetry#TutorialParticleImageVelocimetry: TutorialParticleImageVelocimetry] for a first introduction to PIV.
     3= [wiki:Tutorial] / Correlation Image Velocimetry for a turbulent series =
     4This example applies Particle Image Velocimetry (PIV) to a turbulent jet, see [https://servforge.legi.grenoble-inp.fr/projects/soft-uvmat/wiki/Tutorial/ParticleImageVelocimetry#TutorialParticleImageVelocimetry: TutorialParticleImageVelocimetry] for a first introduction to PIV.
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    66== Visual check ==
    7 Launch the GUI '''uvmat''' and open an image in ''UVMAT_DEMO03_PIVchallenge_2005C/images'' , which represents a jet (images from PIV challenge, ref...). Images are organized in pairs, denoted with labels a, b with a short time interval  Dt=0.01 ms, with interval 2 ms between two successive pairs. The timing and geometric calibration has been provided in the xml file images.xml, in the same way as discussed in section .. for a single pair.
     7Launch the GUI '''uvmat''' and open an image in ''UVMAT_DEMO03_PIVchallenge_2005C/images'' , which represents a jet (images from PIV challenge, ref...). Images are organized in pairs, denoted with labels a, b with a short time interval  Dt=0.01 ms, with interval 2 ms between two successive pairs. The timing and geometric calibration has been provided in the xml file ''images.xml'', in the same way as discussed in the introductory example of tutorial 5.
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    9 check the image pair between a and b, then between 1 and 2, dt is displayed while the time is displayed in the upper right edit box.
     9Check the image pair between a and b, then between 1 and 2, dt is displayed while the time is displayed in the upper right edit box.
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    11 '''Civ:''' import the parameters stored in ...
     11== Civ ==
     12Open the GUI '''series/civ_input'''  and import the processing parameters stored in ''UVMAT_DEMO03_PIVchallenge_2005C\Images.civ\0_XML\c001a.xml''
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    13 small displacement of the order of 1 pixel, so small search box.
     14The seeding density is not excellent, so we keep the default correlation box [25 25]. The displacement in image pair is of the order of 1 to 2 pixels, so we use a small search box. The correlation box is slightly reduced for Civ2, [21 x21] to improve the spatial resolution. A fairly low smoothing parameter is chosen for Patch to avoid smoothing of the inherently noisy turbulent flow.
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    15 Check filter, compare filter2 and civ2, make transverse cut...
     16== merge proj''' ''' ==
     17To properly process data, a projection of the velocity fields on a grid is needed, preferentially in physical coordinates. Create this grid in the GUI uvmat by opening the velocity field, then select '''[Projection object/plane]''' in the upper menu bar, and select '''[wiki:ProjMode !ProjMode]'''='interp_tps' in the GUI '''set_object'''. A grid mesh of 0.05 cm is proposed, corresponding to the vector density. Adjust the min and max in each direction for instance x=[-1.5:1.3] and y=![0:2.9]. Press REFRESH to see the result of projection/interpolation on the grid. Press SAVE to backup the content of the GUI '''set_object''' as an xml file.
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    17 '''merge proj: '''
     19Now activate '''Run/series''' in the upper menu bar of '''uvmat''' and select the '''ACTION''' 'merge_proj'. Select the box '''[Projection Object]''' so that the plane in '''set_object''' is incorporated. If '''set_object''' has been closed, then open its backup as an xml file with the browser. Select the transform 'phys' in the menu '''[! [wiki:FieldTransform "FieldTransform]"]'''. Select the indices i from first_i=1 to last_i=99. In the menu ! FieldName select simultaneously the options 'vec(U,V)', 'curl(U,V)', 'div(U,V)' (using the key 'Ctrl'). Note that the whole configuration of '''series''' can be retrieved by the menu bar command '''[Import Config]''', opening ''Images.ref.civ.mproj/0_XML/c_1-99.xml''. Press RUN to start the projection, preferably with '''[run mode]'''='background' to keep free the current Matlab session.
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    19 define a physical grid for the final results, select (U,V0 and curl , div, use '''[!ProjMode]''' =interp_tps
     21The projected fields are written as netcdf files in the folder images.civ.mproj. Those can be opened by uvmat. The list of 'variables' appear in a GUI '''get_field'''. Selecting the variables 'U', 'V', 'curl'... in the table variables, we can see their dimensions in the right hand column. They are structured as two-component arrays (y,x) unlike the raw PIV results. Select the plot option 'scalar' or 'vector', and the quantity to plot in uvmat, as well as the variables used as coordinates, here 'coord_x' and 'coord_y'.
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    21 launch merge_proj: results are obtained as 2D matrices, open with uvmat. Select U in get_field.
     23== turbulent  statistics ==
     24From these files, basis turbulence statistics can be provided by the function 'turb_stat' to be selected in the menu '''ACTION''' of series: select the option 'more...' which gives access to a browser from which this function, located in the folder UVMAT/series can be selected. Then run the calculation and visualise the different fields with uvmat, after selection by get_field: for instance the average of V gives the mean jet structure. The field uvmean clearly shows the structure of the Reynolds stress across the jet, positive on one side and negative on the other side, corresponding on the radial eddy diffusion of the jet. ''''''
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    23 No info left on the PIV process after projection. This is the start for the scientific analysis.
     26== time series in a single netcdf file ==
     27For further data processing it can be convenient to merge all fields in a single netcdf file. This can be done by opening the previous results in series and applying the '''ACTION ''''time_series'. Select for instance the variables 'U' and 'V' as 'scalars'. No projection object is needed at this stage, so '''[Projection Object] '''must be unselected.
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    25 '''time_series:'''
    26 
    27 '''turb_stat:'''
    28 
     29 The result is obtained as a single netcdf file ''images.civ.mproj.tseries/c_1-99.nc''. Opening this file by uvmat, we observe that the arrays U and V are now with 3 components, (time, y, x). A plane of cut (x,y) is displayed in uvmat, whose z coordinate (here the time) can be moved by the [z slider] in the GUI '''set_object'''.