Measuring wave impact induced pressures with a pressure mapping system

Abstract

The use of a pressuremapping system formeasuring wave impact induced pressures is evaluated in this paper. A set-up and a calibrationmethodology are suggested and employed for thiswork. The system is validated against pressure transducer and load cell measurements and for a range of waves breaking on a vertical seawall. For a large number (120 measurements for each case considered) of breaking and broken waves interacting with the wall, the peak pressure (Ppeak) profiles and the pressure distribution maps reported by the system agree wellwith results acquired using pressure transducers. Although the pressuremapping system tends to underestimate Ppeak, differences on themean of the 3, 5 and 10 highest Ppeak rangewithin±10%, while for themajority of the measurements the error on the integral of the acting pressures (the acting force compared with the force measured by the load cell) ranges within ±20%. It is concluded, that through careful calibration and set-up the pressure mapping system has the capacity to provide pressure distribution maps with a good accuracy. It is not, however, considered to constitute the absolute alternative to pressure transducers and thus a combined use is suggested for applications where a very high level of accuracy is required.Postprint (author's final draft

Variability of wave impact measurements on vertical breakwaters

“…The highly turbulent environment and the air/water mixture during wave breaking add further difficulty to the measurements. Furthermore, even if an almost perfect repeatability of the generated wave is guaranteed, this does not translate into perfect repeatability of the impact conditions (Stagonas et al, 2016).…”

“…Due to these uncertainties, generating correct measurements of wave impact loads on marine structures is probably one of the biggest challenges for coastal and maritime hydraulic modellers. Stagonas, Marzeddu, Gironella, and Sánchez-Arcilla (2016) performed a series of experiments to validate a pressure mapping system against classical measurements (pressure arrays and load cells). Their work showed that the spatial distribution of these impacts is characterized by pressure hot spots that appear slightly above the still water level (SWL).…”

“…According to Bullock et al (2007), an unexpected behaviour of the measured loads at laboratory and prototype scales should not be excluded, due to the complex interactions occurring in the presence of air/water mixtures in a highly turbulent medium. A review of the literature on hydraulic tests dealing with waveinduced impact forces and pressures (Bullock et al, 2007;Marzeddu et al, 2014;Stagonas et al, 2016) revealed a limited understanding of the results variability, suggesting the need of a larger number of test repetitions for statistically robust and comparable datasets.…”

“…In many wave-impact hydraulic studies (e.g. Marzeddu et al, 2014;Stagonas et al, 2016), waves are generated by piston or flap wavemakers moving according to the linear wave theory (Biésel & Suquet, 1951). However, some studies (Goda, 1967(Goda, , 1997Morison, Crooke, & Washington, 1953;Oliveira, Sachez-Arcilla, Gironella, & Madsen, 2017) reported the presence of secondary harmonic free waves for extreme long wave conditions, when the waves were generated by sinusoidally moving a paddle.…”

Analysis of Fluid Flow Impact Oscillatory Pressures With Air Entrapment at Structures

“…At the present time these forces are not fully understood and the long term durability of coastal defences is difficult to determine (Oumeraci et al, 1993), (Wemmenhove et al, 2015), (Alagan Chella et al, 2015). In addition to these short duration impulse impact pressures, resonant oscillatory pressure signals have been observed in many experimental studies (Bagnold, 1939), (Hattori et al, 1994), (Sabeur et al, 1998), (Peregrine, 2003), (Stagonas et al, 2016). These oscillations manifest themselves subsequent to the initial wave impact with solid or porous walls and may be a source of much damage and deterioration to the structural integrity of coastal defences.…”