Changes between Version 10 and Version 11 of Tutorial/ParticleImageVelocimetry


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Timestamp:
Dec 9, 2014, 11:52:40 PM (6 years ago)
Author:
sommeria
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  • Tutorial/ParticleImageVelocimetry

    v10 v11  
    1010Particle Image Velocimetry (PIV) measures the displacement of features in a pair of images. Visual evidence of feature displacement between the two images is a prerequisite  for the success of the computation. To observe this motion, write the file indices 1 and 2 in the boxes '''[i1]''' and '''[i2]''' respectively, in the frame '''[File Indices]''' on the left. Then push the red button '''[<-->]''' in the frame '''[Navigate]''', see figure. The image then alternatively switches from 1 to 2. The speed of motion can be adjusted with the slider '''[speed]'''. Press '''[STOP]''' to stop the motion.
    1111
    12 <doc138|center>
     12[[Image(movie1-2.JPG)]]
    1313
    1414== Launching PIV ==
     
    1919The PIV operation depends on several parameters, but the default values proposed by the GUI provide a good first approach in many cases. Press '''[RUN] ''' to get the result. The button is then colored in grey until the computation is finished. The operation produces a  file with format netcdf, extension '''.nc''', in a subdirectory called ''''CIV' ''' by default. The file name ends with index string '_1-2' indicating that it results from images 1 and 2. The file name and its status is indicated in a new figure '''civ_status'''. Press the file name to open it with uvmat, or use the browser of '''uvmat'''.
    2020
    21 <doc137|center>
     21[[Image(Civ_1.JPG)]]
    2222
    2323= Monitoring PIV results =
     
    4343== Derived fields ==
    4444
    45 Other field representations are available, selected in the menu '''[Fields]''' at the top of the GUI. For instance the option 'u' provides a (false) color map of the x wise velocity component. A contour plot can be obtained instead of a color map by selecting the option 'contour' in the menu '''[!ListContour]''' in the frame''' [Scalar] '''. Then select the contour interval, for instance 0.5. The result is shown in the following figure.  <doc145|center>
     45Other field representations are available, selected in the menu '''[Fields]''' at the top of the GUI. For instance the option 'u' provides a (false) color map of the x wise velocity component. A contour plot can be obtained instead of a color map by selecting the option 'contour' in the menu '''[!ListContour]''' in the frame''' [Scalar] '''. Then select the contour interval, for instance 0.5. The result is shown in the following figure.
     46
     47[[Image(contours.JPG)]]
    4648
    4749To get the vorticity field, 'vort' , and other spatial derivatives, you need to come back to the GUI CIV, select the check boxes '''[FIX1] ''' and  '''[PATCH1] ''' , and press '''[RUN]'''. This will produce an interpolated velocity field and their spatial derivatives in the same netcdf file.  After this operation vorticity can be visualized in the GUI  '''uvmat''', selecting the option  '''[vort] ''' in the popup  menu '''[Fields]'''. The color code can be adjusted by the edit box '''[MinA] ''' (saturated blue color below this value) and '''[MaxA]''' (saturated red color beyond this value).
     
    124126The following figure shows the final vorticity field, in which the vorticity roll up in the wake of the sphere is clearly visible. A zoom near a vortex shows the vorticity superposed with velocity vectors.
    125127
     128[[Image(vort_civ3.jpg)]]
     129[[Image(vort_vel_zoom.jpg)]]
     130
    126131== Fix and patch ==
    127132