# Changes between Version 4 and Version 5 of WikiStart

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Sep 8, 2017, 1:52:48 PM (3 years ago)
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• ## WikiStart

 v4 By definition we will use Ox and Oy axis to define the along slope and the cross slope axis. The central reference point (0,0) along the slope is chosen to be the first "land" corner downstream of the source. Positive u - direction corresponds to the along slope flow direction, while positive  v - direction is directed onshelf. 2.3.2 Reference axis for ice front experiments 2.4 References axis along the wall (horizontal and vertical) By definition we will use Ox and Oy axis to define the along shore and the cross shore axis. The central reference point (0,0) along the wall is chosen to be the closest point to the center of the tank (also labeled '''M0'''). Positive direction corresponds to the mean wave or the mean flow direction. == 2.3.2 Reference axis for ice front experiments == == 2.4 References axis along the wall (horizontal and vertical) - Nadine add image! == By definition we will use Ox and Oy axis to define the along shore and the cross shore axis. The central reference point (0,0) along the wall is chosen to be the closest point to the center of the tank (also labeled '''M0?'''). Positive direction corresponds to the mean wave or the mean flow direction. __We use seven references points along the wall to quantify the impact of the free surface deformation and the possible vertical deviation of the laser sheet???__ ||$\nu$||Viscosity||$10^-^6m^2s^-^1$ ^|||| ||$L$||Total length of the wall||$\ m$|||| ||$W_{Source}$||Width of source (inner)||$23\ cm$|||| == 2.5 Variable Parameters == == 2.7 Definition of the relevant non-dimensional numbers == Rossby number, $Ro =$. Froud number (equivalent Fd), $Fd = Umax/fRd = Umax/C$. where C is the maximum phase speed of internal gravity waves $C=sqrt(g'H1)$ Wave Froude number $Fdwave = Umax/VTRW$ where VTRW is the maximum phase speed of Topographic Rossby Wave $VTRW=???$ Rossby number, $Ro = U/W/f$. ??, $H* = .....$.  (Reference) Depth of baroclinic current ($H_{BC}=...$ (Reference) Internal rossby radius ($\lambda_i = sqrt (g' H_{BC})/f$. = 3 - Instrumentation and data acquisition = '''Density profiler (DP)''' '''Particle Imaging Velocimetry (PIV)''' A Spectra-Physics Millennia ProS 6W YAG continuous laser (532 nm) in conjunction with 3 cameras was used to provide PIV images. The laser light sheet was brought in parallel to the floor of the channel. 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. '''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. 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).