| 97 | | '''Particle Imaging Velocimetry (PIV)''' ''A Spectra-Physics Millennia ProS 6W YAG continuous laser (532 nm) in conjunction with 2 cameras was used to provide PIV images. The laser light sheet was brought in parallel to the bottom of the tank. The light sheet can then be racked in the vertical through a series of steps through the use of a motorized traverse (tilted at 3.5 degrees to match the slope of the channel) and a mirror set at 45 degrees. The laser has another set of optics to point the light sheet down at the mirror, producing the light sheet. There is a glass window that enables the laser beam to go through the surface of the water tank. A 3D animation of the laser is in the ‘videos’ subfolder of the Photos folder. The laser light sheet positions are then synchronized with the PIV cameras. The field of view extends from close to the upstream end of the first bend, towards the mid-point of the second bend.'' |
| 98 | | |
| 99 | | ''Later experiments used larger seeding particles, 200 micron polystyrene particles for the flow seeding. These work very well for these situations where the measurement area is larger than 2 square metres. The three PIV cameras consist of one Falcon1 camera (Falcon 4M, CMOS 2432*1728 pixels, 10 bits) over the upstream part – with a 35 mm objective lens, PCO2 over the first bend with a 35 mm objective lens, and PCO3 over the most downstream part of the PIV measurement area, which has a 20 mm objective lens. 15 slices in the vertical are taken, each containing 20 images and these are repeated 10 times. Four different times between frames are used, since the velocities were not known a priori and vary as a function of height in the gravity current. So as such, no specific frame rate is used. All this is in the .xml files which can be read by a text editor. The two PCO cameras are PCO.edge5.5 CMOS cameras (2560*2160 pixels). The general approach is to have the lowest slice at approximately 2 cm above the floor, and then there are 2.5 cm heights between each successive level. These varied over time however, so there are a number of slightly different setups – see below. The sequence starts at the highest point, and then steps down through the flow, to the bottom, before switching back to the top again. Heights of laser slices (22/09/16 – 2.5 cm but after that 12/10/2016 and 14/10/2016 and 19/10/2016 all at basal 2 cm).'' |
| | 101 | '''Particle Imaging Velocimetry (PIV)''' A Spectra-Physics Millennia ProS 6W YAG continuous laser (532 nm) in conjunction with 2 cameras was used to provide PIV images. The laser light sheet was brought in parallel to the bottom of the tank in case of the slope front experiments and tilted by 2% to match the slope of the channel in case of the ice front experiments. The light sheet can then be racked in the vertical through a series of steps through the use of a motorized traverse and a mirror set at 45 degrees. The laser has another set of optics to point the light sheet down at the mirror, producing the light sheet. The laser light sheet positions are then synchronized with the PIV cameras. The laser light sheets cover the whole topography, but are slighlty bended towards the sides, so that they are closer to the bottom at the source and at the end of the topography compared to the middle. Also a vertical laser was used together with a vertical camera to observe the flow in a cross section. The three PIV cameras consist of: |
| | 102 | - one Falcon1 camera ''(Falcon 4M, CMOS 2432*1728 pixels, 10 bits)'' as the vertical camera – with a 35 mm objective lens.[[BR]] |
| | 103 | |
| | 104 | - PCO1 (PCO.edge5.5 CMOS cameras (2560*2160 pixels)) with a 35 mm objective lens overlooking the part in front of the source in the slope front experiments and the ice shelf in the ice front experiments.[[BR]] |
| | 105 | |
| | 106 | - PCO2 (PCO.edge5.5 CMOS cameras (2560*2160 pixels)) with 20 mm objective lens overlooking the continental self and trough in the slope front experiments and the channel in the ice front experiments.[[BR]] |
| | 107 | |
| | 108 | After experiment 26 of the slope front expriments, 60 micron particles were used for the flow seeding. The number of slices were adjusted to the need of the experiment and is listed in the file LIST_OF_EXPERIMENTS.xlxs. The number of slices, dt between the images, exposure time (either 20-50), the number of images and the number of scans had to be decided before each experiments. The slope front experiments also contained series of images at one horizontal slice to better observe the evolution of the flow. The vertical laser was turned on after a steady flow was established/ at the end of the experiment. |
| | 109 | |
| | 110 | During horizontal PIV, the vertical camera was turned on (with the same acquisition as the PCO1 and PCO2) to produce an .xml file that contains information on the time, dt, exposure time, times for the scanning. During some experiments, this .xml file was missing (technical mistake or if we stopped the acquisition before it was done), so that .xml files from other experiments have to be used and modified to fit the setup. However, the starting time is not correct then. |
| | 111 | |
| 193 | | 1. '''Convert .tif into .png[[BR]]'''In Run>Field series you can open any ''.tif'' of the desired folder (Warning : you should not take the im.tif but any im@XXXX.tif is working). Then in the ''Action'' part you should select ''extract_multitif'', if the Input button is in pink you should click on it and give to the software the'' Falcon.xml'' that you extracted earlier (If that doesn't exist, copy one ''.xml'' file from a previous experiment and change the set |
| | 218 | 1. '''Convert .tif into .png[[BR]]'''In Run>Field series you can open any ''.tif'' of the desired folder (Warning : you should not take the im.tif but any im@XXXX.tif is working). Then in the ''Action'' part you should select ''extract_multitif'', if the Input button is in pink you should click on it and give to the software the'' Falcon.xml'' that you extracted earlier (If that doesn't exist, copy one ''.xml'' file from a previous experiment and change the setting manually. Once it is done you can click on RUN, don't forget to select ''cluster_oar'' in the run mode, the action will be much faster. When it is done a new folder called PCOY.png is created in your EXPXX folder and contains all the png. [[BR]]For''' SCANS''': Check that the right number of slices is registered! To do so, click on ''check_data_files'' in the'' Action'' part and type the right number of slices in ''nb_slices i'' |
| 213 | | * ''Each ‘PIV’ folder contains subfolders for each of the 3 PIV cameras: Dalsa (sometimes Falcon1 – it’s the same thing); PCO2; PCO3 [these are named after the different brands of camera]. Other folders include PCO2.png and PCO3.png which contain processes images of the PCO cameras that are in a non-bespoke format. Other folders that can be within the Camera folder include: Dalsa.sback; Dalsa.sback_1; PCO2.png.civ; PCO2.png.civ_1; PCO2.png.civ_2; PCO2.png.sback: PCO2.png.sback_1; PCO3.png.sback_1. .sback files refer to those files where the background has been subtracted, then civ_1 contains images with the first PIV iteration as processed in UVMAT (Joel’s code) and shows the raw data – with or without the rejected vectors; vectors are shown in four colours, blue = best, green = medium, red = poor, and pink = false. A box can be clicked to hide the false vectors. Civ_2 uses a spline interpretation to interpolate between vectors, so long as they are close enough to the surrounding vectors. Then interpolates all the vectors onto a regular grid. Times for the .png images are in the XML files, or netcdf files.'' |
| | 238 | * ''Each ‘PIV’ folder contains subfolders for each of the 3 PIV cameras: Dalsa (sometimes Falcon1 – it’s the same thing); PCO1; PCO2 [these are named after the different brands of camera]. Other folders include PCO1.png and PCO2.png which contain processes images of the PCO cameras that are in a non-bespoke format. Other folders that can be within the Camera folder include: Dalsa.sback; Dalsa.sback_1; PCO2.png.civ; PCO2.png.civ_1; PCO2.png.civ_2; PCO2.png.sback: PCO2.png.sback_1; PCO3.png.sback_1. .sback files refer to those files where the background has been subtracted, then civ_1 contains images with the first PIV iteration as processed in UVMAT (Joel’s code) and shows the raw data – with or without the rejected vectors; vectors are shown in four colours, blue = best, green = medium, red = poor, and pink = false. A box can be clicked to hide the false vectors. Civ_2 uses a spline interpretation to interpolate between vectors, so long as they are close enough to the surrounding vectors. Then interpolates all the vectors onto a regular grid. Times for the .png images are in the XML files, or netcdf files.'' |
