servo-electric drive motors and magnetic linear encoders. Integrating these two
systems with the multichannel, closed-loop, digital control system results in a
fully automated 3-D bathymetric survey system.
Lateral Boundaries
Design of the upstream and downstream lateral boundaries was a challenge,
since the longshore current has to flow out of the upstream flow channels and
into the downstream flow channels while wave diffraction into the flow channels
needs to be minimized. Wave guides were designed to allow current to flow
under the impermeable wave guide, and the height of the opening beneath each
wave guide could be adjusted. The height of the opening beneath the wave
guides was selected after several trial and error iterations. At the upstream
boundary, a constant 0.15-m-high opening beneath the wave guide was used. At
the downstream boundary, the bottom edge of the wave guide was set at
approximately the minimum wave trough elevation. Therefore, at the
downstream boundary, the height of the opening beneath the wave guide
increased with increasing water depth. In Appendix B, Figures B-9 and B-10
show the downstream and upstream wave guides, respectively, with the facility
drained. Wave guides were not used at the ends of the four most shoreward flow
channels, because of the shallow-water depth and a desire to minimize
obstructions to longshore sediment transport in shallow water.
In addition to the wave guides, a matrix of 0.1-m-diam rigid polyvinyl
chloride pipe was installed in the flow channels at the downstream and upstream
ends of the facility. At the downstream end of the facility, the matrix of pipe was
installed immediately upstream of the vertical turbine pumps to absorb the
residual wave energy that entered beneath the wave guides and to minimize wave
reflection in the flow channels (Appendix B, Figure B-11). At the upstream end
of the facility, the matrix of pipe was installed immediately behind the wave
guide to direct the discharge from the pumps to the upstream boundary of the
beach (Appendix B, Figure B-10). At both ends of the facility, the matrices of
pipes extended through the entire water column and across the full width of each
channel. Svendsen (1991) discussed similar concepts.
Control and Data Acquisition Room
Real-time control and data acquisition of the many different types of
equipment and instrumentation in the LSTF are conducted from the control room,
located at the downdrift end of the facility (Figure 9). Real-time control of the
wave generators and instrumentation bridge as well as data collection from the
wave gauges, current meters, and the beach profile indicator are carried out using
the computer located in the lower left corner of this photograph. The computer
to the right is dedicated to data acquisition and real-time display of the in-line
flow sensors, which measure the discharge of the pumps. The 20 flow channels
and vertical turbine pumps for externally recirculating the longshore current can
be seen in the foreground, through the window of the control room. The
instrumentation bridge and the testing region of the facility can be seen in the
upper left corner of the photograph.
12
Chapter 2
Overview of the Laboratory Facility
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