Impact pressures of sea waves

Abstract

Following previous work (by P. Blackmore, 1982, at Plymouth Polytechnic) more detailed pressure measurements were taken at Ilfracombe, North Devon and at a new site, Bovisand, near Plymouth. In both cases a beach array of transducers was used to enable a determination of wave characteristics for correlation with impact pressures. At both sites, the tidal variations were exploited to obtain depth dependent parameters such as wave steepness and their effect on impact pressure magnitude and variation. The bulk of the readings come from Ilfracombe, as storm damage brought a temporary halt to work at Bovisand. The wave profile can be characterised by the relevant wave theory using a linear approximation for deep water waves, but requiring a non-linear approach for-shallow water waves. Computer programs were developed to extract appropriate measurements from experimental data using digitally processed time series analysis for the purpose of comparing with values obtained from linear and non-linear modelling methods. The main aspects studied included, the impact pressures with their magnitude, duration and frequency of occurrence. Probability distributions have been used to provide a prediction of the extreme value of wave height for the data analysed. A dual loading pattern involving high intensity impacts together with prolonged secondary pressures was highlighted in this research as direct loading on the sea wall. The experimental results have shown that components of the loading pattern produce pressure distributions of equal importance.