Field Measurements of Impact Pressures in Surf

Abstract

Field measurements were made of the vertical distribution of impact pressures exerted by breaking waves. Four distinct types are recognized and compared. These are near-breaking wave, plunging breaker, spilling breaker and post-breaking bore. The measurements were obtained by placing a 6 foot aluminum flat plate, backed by a cylinder in the surf zone, so that the fiat faced the approaching breakers. Five sensors were placed at one foot intervals on the flat. The sensors consisted of strain gage mounted aluminum diaphragms. Results indicated that impact pressure is significantly influenced by breaker type. The bore generated the largest impact pressures, followed in decreasing order by plunging breaker, spilling breaker and near breaking wave. In the vertical array, the largest impact pressures were recorded at or near the top, except for the bore where the reverse occurred. A qualitative explanation is given of various phenomena associated with impact pressures, by considering breaker mechanics.

Fixed and moored bodies in steep and breaking waves using SPH with the Froude–Krylov approximation

“…This raises an interesting point regarding the stages of breaking where the maximum loading occurs. Early experimental works have recorded maximum forces due to the post-breaking roller (Miller et al 1974). In contrast, recent experimental (Wienke and Oumeraci 2005) and numerical work (Hildebrandt and Schlurmann 2012) reports the maximum force on the cylinder at the point of overturning-where the plunging jet [or breaker tongue as in Wienke and Oumeraci (2005)] has a horizontal velocity and the front of the wave crest is vertical.…”

“…Breaking waves are likely, and, despite being the subject of sustained research for seven decades, there is still debate over the loads and forces exerted. For example , Miller et al (1974) and Morison et al (1953) reported that the post-breaking bore impact exerts the greatest force. However, Wienke and Oumeraci (2005) state loading is maximum at start of breaking where overturning begins and the incipient breaking jet remains horizontal.…”

Sedimentology of rocky shorelines: 3.

“…On a very gentle bottom slope, broken waves can reform and break multiple times. The bores of plunging breakers have been shown to produce greater pressure than the bores of spilling breakers (Morison et al, 1954;Miller et al, 1974). Homma and Horikawa (1965a,b) suggest that the height of a broken wave in the surf zone is 0.78 h, where h is the water depth, given that the bottom slope is greater than 1:30.…”