Changes between Version 48 and Version 49 of Tutorial/ParticleImageVelocimetry
- Timestamp:
- Mar 23, 2015, 5:42:41 PM (10 years ago)
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Tutorial/ParticleImageVelocimetry
v48 v49 7 7 The Particle Image Velocimetry (PIV) computation 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. 8 8 9 9 [[Image(movie1-2.JPG)]] 10 10 11 11 == Launching PIV == … … 16 16 The operation produces a file with format netcdf, named with extension '.nc', in a folder called 'Images.civ'. This can be viewed by pressing '''[STATUS] '''in the GUI '''series''', which displays the result file 'frame_1-2.nc'. The index string '_1-2' indicates that it results from images 1 and 2. Select the file name and press '''[OPEN]''' to open it directly with '''uvmat''', or use the browser of '''uvmat'''. 17 17 18 18 [[Image(Civ_1.JPG)]] 19 19 20 20 == Visualizing the velocity fields == … … 41 41 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. 42 42 43 43 [[Image(contours.JPG)]] 44 44 45 45 == Spatial derivatives == 46 To get the vorticity field, 'curl', and other spatial derivatives, you need to come back to the GUI''' series''' with images in '''[Input Files]''' and '''[Action]''' as 'civ_series'. In''' civ_input''', select the check boxes '''[FIX1] ''' and '''[PATCH1] ''', validate the input with '''[OK]''', then press '''[RUN]''' in the GUI '''series'''. A question box appears to warn about the existence of the result file, answer '''[OK]''' to refresh it with the new data. Otherwise the results are stored in a new subdirectory with extension '.civ1', so the previous results are not erased (you can modify this extension by editing the boxe '''[!OutputDirExt]''' in the GUI '''series'''. 46 47 47 To get the vorticity field, 'curl', and other spatial derivatives, you need to come back to the GUI''' series''' with images in '''[Input Files]''' and '''[Action]''' as 'civ_series'. In''' civ_input''', select the check boxes '''[FIX1] ''' and '''[PATCH1] ''', validate the input with '''[OK]''', then press '''[RUN]''' in the GUI '''series'''. A question box appears to warn about the existence of the result file, answer '''[OK]''' to refresh it with the new data. Otherwise the results are stored in a new subdirectory with extension '.civ1', so the previous results are not erased (you can modify this extension by editing the boxe '''[!OutputDirExt]''' in the GUI '''series'''. 48 49 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 '''[!FieldName]'''. 48 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 'curl' in the popup menu '''[!FieldName]'''. 50 49 51 50 == Superposing image and vectors == … … 54 53 [[Image(Tutorial5 - Image+Vectors.png)]] 55 54 56 Similarly, the velocity vectors can be superposed to the vorticity field, selecting ' vort'''' ''' in '''[!FieldName_1]''' instead of 'image'''''''.'''55 Similarly, the velocity vectors can be superposed to the vorticity field, selecting 'curl' in '''[!FieldName_1]''' instead of 'image'. 57 56 58 57 == From pixel displacement to physical velocity ==
