Laboratory Measurements of Water Level and Waves in Hurricane Wind Conditions
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Offenbacher, Ethan Riley
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Abstract
This study focuses on the behavior of three common methods of measuring water surface elevation used in physical wave experiments, namely: capacitance wave gauges, ultrasonic distance meters (UDMs), and underwater pressure sensors, under hurricane wind conditions. The experiments analyzed in this study were conducted at the University of Miami in their SUSTAIN wind-wave storm simulator as part of NICHE, a broader NSF funded project to inform the design of a future full-scale wind-wave facility. In these experiments, four different wave conditions (along with a wind-only baseline) were run in both fresh and salt water in a range of windspeeds up to what is experienced in a Saffir-Simpson category 5 hurricane, with instrumentation placed at three locations along the length of the flume.
Analysis of the results reveals several notable trends that may be useful in the design and analysis of future wind-wave experiments. The UDM derived wave parameters generally agree with their capacitance wave gauge derived counterparts at fan speeds below ~24 m/s for all wave conditions tested, although with higher variability and a lower signal-to-noise ratio. However, the UDM data is largely unreliable and increasingly dominated by noise in winds at and above 36 m/s. The average water levels observed by different sensors in the same location diverged at higher wind speeds, with UDMs trending lower than capacitance gauges. A significant increase in air pressure was observed in the flume at higher windspeeds, up to the equivalent of 13 cm of water column, and noise in the underwater pressure data prevented the resolution of wave data finer than the average water level. Although differences in average wave heights and water levels were observed by the capacitance gauges in freshwater and saltwater, these are likely the result of instrumentation issues particular to this experimental setup and not representative of capacitance wave gauges as a whole. The overall data does not suggest a physical difference in the behavior of the wind-wave interaction on a macro-scale in freshwater and saltwater distinguishable by the instrument setup used in this experiment.
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2024-05-17
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