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

dye probe was held near each vent location to visualize the entrainment of dye towards and into the
unvented dome model.
8.4 Turbulence Generator Investigation
Robert Breidenthal suggested that if we wished to increase the level of turbulent layer up to the level of
the dome that we could install some turbulence generators upwind of the dome. In practice this is
unlikely to be feasible, however to give this idea a try we cut a sawtooth shaped turbulence generator
board out of corrugated plastic poster-board with teeth 38 mm tall and 19 mm wide at the base. This
structure was held on the upstream edge of the model base plate and the flow was visualized using dye
probe B6. The depth of the turbulence generator in the water was varied to determine at what point it
had an effect on the vortex on the upstream side of the observatory base. The turbulence generator
board is shown in Figure 15.
9 Basic Data Product
The files were saved in the AVCHD Lite format of the Panasonic ZS7 cameras. There were a few
issues around using the files in this format. For one, the AVCHD format is not commonly supported by
older video display software; this is a fairly easy problem to work around. Secondly, we wished to use
MATLAB to automatically process the video to determine the flushing times in a more quantitative
way, however this video format is not supported by MATLAB. Thirdly, the 720p HD format video was
unnecessarily large for most common use and precluded easy distribution on inexpensive data media
(e.g. DVD disks).
The video files were first renamed and organized in a self-explanatory and intuitive path structure that
makes it easy to navigate to the video pertaining to a specific experimental configuration. These files
were then converted using the SUPER video conversion tool to a AVI format using the following
settings:
• Format: AVI
• Output video codec: DivX
• Output audio codec: mp3
• Video scale size: 640 x 360 pixels
• Frame per sec: 14.985 Hz
• Bitrate: 9600 kbps
• Options: Hi-quality
• Audio: 1 Channel, 22050 Hz sampling, 96 kbps bitrate
• MEncoder and DirectShow decode selected (the latter only works for the Windows OS).
Down-conversion from the nominal 60 Hz (30 Hz actual!) frame rate to 15 Hz was necessary to ensure
normal playback speed of the video. Conversion to the actual 30 Hz frame rate of the video resulted in
video that played back at approximately twice the correct speed; this was found for at least 4
conversion packages tried. This problem is related to the decoders of the AVCHD Lite format ignoring
a bit that indicates that each 30 Hz frame should be played twice to achieve the nominal 60 Hz
playback.