13 Vibration-Based Scour Monitoring: Prototype Design, Laboratory Experiments and Field Deployment 143 Fig. 13.9 Performance comparison of VTP and TDR devices in a flood event 0 50 100 150 200 250 300 350 -160 -140 -120 -100 -80 -60 -40 -20 0 4/6/14 0:00 4/7/14 0:00 4/8/14 0:00 4/9/14 0:00 4/10/14 0:00 Water Surface Elevation (cm) Bed Elevation (cm) Time (M/D/Y hh:mm) VTP TDR Water Surface Elevation Fig. 13.10 Performance comparison of VTP and TDR devices in consecutive flood events 80 90 100 110 120 130 140 150 -160 -140 -120 -100 -80 -60 -40 -20 0 4/15/14 0:00 4/17/14 0:00 4/19/14 0:00 4/21/14 0:00 4/23/14 0:00 Water Surface Elevation (cm) Bed Elevation (cm) Time (M/D/Y hh:mm) VTP TDR Water Surface Elevation This study presented a new instrumentation system that can determine scour formation and refill in real time while remaining insensitive to many of the conditions that negatively affect the available scour monitoring systems. In the proposed methodology, a support pipe is furnished with uniformly distributed vibration-based turbulent pressure sensors, referred to as VTPs, along its length. The pipe is then buried in the channel bed. The VTPs contain accelerometers allowing the time history acceleration response of the plate to be measured to determine if the material surrounding the VTP is water or sediment. Measured accelerations are significantly higher for the VTPs that are located in the flow compared to those that are located in the sediment due to the natural excitations resulting from the dynamic pressure in the flow associated with turbulent fluctuations. Hence, measuring the profile of the acceleration response for VTPs distributed along a bridge pier makes it possible to determine the location of the water/sediment interface. The experimental measurements conducted in the laboratory demonstrated that the mean-square response of the VTPs located in the channel flow is one to two orders of magnitude higher than that of the VTPs located in the sediment. Furthermore, the formation of scour is observed to improve the distinction between the sensors in the sediment and flow as the turbulence in the scour hole is higher than that in the flow channel. Performance of VTP device is also evaluated through field investigation. Results reveal that VTP can be used to measure bed elevation accurately. VTP device responds to the bed change due to flood event and can record both scour and
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