1 Overview 2 Details of the Model Construction - Canada France ...

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6 Experimental methodology 6.1 Dyes The dye was injected using electric micro-pumps provided by UWAL. Dyes were “Lucky” brand concentrated food colouring supplied by UWAL. The dye was sourced from a 1 liter container on the input side of the pump and the dye flow was started/interrupted using a hose clamp on the output side. The 1.2 mm inner diameter stainless steel dye probe lines were connected to the dye source using an assortment of flexible hoses that were slipped on and off the dye probes as necessary. For the tests where probes B1-B5 were alternately fired, aquarium air-line gang valves were used to redirect the dye to the individual probes. In a single day of testing it was unusual to use more than 1 litre of each of the red and blue food coloring dyes when only flushing tests were being performed. The dyes were diluted in ratios near 50:1 to obtain a good balance between visibility and minimal use of the dye which would eventually cloud up the water. Change-out of the water was performed on a daily basis and required approximately 1.5-2 hours to complete. It was found necessary to flush the tunnel and then immediately refill it in order to avoid getting air trapped in the plastic straws that make up the flow straightener. The trapped air in the flow straightener results in small bubbles being entrained in the flow which significantly reduces the transparency of the water. The only solution when this happens is to flush out the straws using a hose. However, this results in large amounts of trapped sediment being flushed from the straws, which (at least in our one attempt at this procedure) muddies the water beyond usability for testing. Tests requiring relatively small amounts of dye (i.e. flushing time tests) were generally performed early in the day when the water was still clear. Flow visualization tests requiring continuous dye input over several seconds were performed at the end of the day when the dye had significantly clouded the water. The red and blue dyes were selected based on their better contrast in the water as suggested by Robert Gordon, with red being more visible than blue. The method used for initiating the dye injection was to first turn on the micro-pumps, wait a few seconds for the output pressure to build up and then simultaneously open the hose clamps to begin the dye injection (this was generally controlled by Karun). In this way, if more than one dye color was used, the dyes would be injected simultaneously to within a few 100 ms. It is important to note this as some of the video footage appears to indicate that the blue and red dyes (e.g. for the A3 & A5 probe flushing time tests) enter the chamber at very different times. This is an illusion caused by the strong flow along the dome floor in certain slit to wind orientations compounded by the mezzanine blocking the camera's view of the dome floor. 6.2 Lighting The model was lit from one side with three 500 W halogen light fixtures. Two of the light fixtures were placed approximately 50 cm above floor level (~35 cm below the bottom of the tank) while the third fixture (a spot light) was at tank level aimed towards the downstream tank direction. With this arrangement, reflections were avoided from the vantage point of the cameras. However, some shadowing is visible due to partial blocking of the spot light by the storyboard (this is particularly evident in the bottom camera views). A white fluorescent light panel (part of the UWAL water tunnel setup) was placed on the side of the tunnel opposite the “side-view” camera.
6.3 Video capture Two Panasonic Lumix ZS7 digital cameras were used for the video capture. This camera was selected based on a combination of video quality (1280:720 @ 30 Hz), flexibility (10X optical zoom), price ($200) and ready availability. The video was captured in AVCHD “Lite” format (.MTS file extension) with the highest compression mode selected to minimize the amount of data to be handled later. It was determined that these settings would not reduce the quality of the captured video in a meaningful way. The optical stabilization and GPS modes of the camera were disabled to maximize battery run time. Between the two cameras, three spare batteries were used with a typical run-time on a single charge being approximately two hours. The time required to charge the battery was ~1 hour. Both cameras were mounted on high quality, sturdy tripods. One camera viewed through the side of the tunnel (the “sideview” camera), while the other was mounted close to the floor below the test section and looking up through the bottom window (the “bottom view” camera). The side view camera was mounted upside down so that the dome orientation appears correct in the video but the storyboard text is inverted. Two storyboards were made visible in the side-view video frame, each describing the relevant details of the experimental setup for that video. The storyboard is correct in all instances except for the “boundary layer investigation” experiment (described below) where the dome angle appearing on the board is 0 degrees but is in fact at 90 degrees (which is clear from the video). White board markers and erasers were used to edit the storyboards (seen in Figure 12). 6.4 The capture sequence Each video capture instance generally followed the sequence below: • The side-view camera was started first with the operator (Marc Baril) simultaneously calling out, “Start”. This call-out is not always heard on the video. • The bottom-view camera was started with the operator (Tom Benedict) calling out, “Rolling”. At this point both cameras were capturing video. • The dye probe operator (Karun Thanjavur) would start the slower of the two dye pumps running (assuming two dyes were used), wait a few seconds and then start the faster pump. We then waited a couple of seconds for the pressure in both dye lines to build up. The hose clamps on both lines were then released simultaneously with Karun calling out, “Open”. Usually, either Marc Baril, Robert Gordon or a UWAL student would assist with the task of opening one of the hose clamps. For flushing time tests, the dye injection lasted for ~3sec, after which the hose clamps were shut off (on the call, “close”), and the dye pumps turned off. For flow visualization, dye flow was maintained long enough to provide adequate footage of the flow pattern that was being investigated. For visualizing the flow upstream and downstream of the dome simultaneously, dye was injected through the downstream B7 probe first, then B6 (with B7 still running); after a few seconds of both probes injecting, B7 was turned off, then B6 a few seconds later. For flow visualization around the dome using probes B1 to B5, the output of the micro-pump was connected to an aquarium air-line gang valve which then fed all five probes. In this test, for the sake of visual clarity, dye was injected through only one probe at a time by opening the appropriate valve. 7 Determination of the Operating Tunnel Flow Speed The first experiment carried out involved the determination of the water flow speed in the channel
Page 1 and 2: Canada-France-Hawaii Telescope Corp
Page 3 and 4: Figure 3: Vent dimensions in inches
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Page 7 and 8: 4 Dye Probe Locations Dye probe por
Page 9: gradually narrows down over a lengt
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Page 17 and 18: 10 Lessons learned • A dome shutt
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