<p>Air bubbles entrain into the water during wave breaking. The impact of the aerated region on forces has been studied only briefly by other researchers, which might be due to difficulties of the measurements. The air entrainment might be important to include in e.g. numerical models of wave kinematics. Including air entrainment in force estimates is complex, however, since it is extremely difficult to isolate the effect of air entrainment in breaking waves and thus also to evaluate the effects.</p><p>The forces on marine and offshore structures are often affected by spilling breakers. The spilling breaker is characterised by a roller of mixed air and water that progresses approximately with wave celerity. This high speed in the top of the wave has the potential to induce high wave loads on upper parts of the structures. This study analysed the effect of the air content on the forces. The analyses used the Morison equation to examine the effect of the percentage of air on the forces. An experimental set-up was developed to include the injection of air into an otherwise calm water body. The air-injection did introduce a high level a turbulence. It was possible to assess the amount of air content in the water for different amounts of air-injection. In the mixture of air and water the force on an oscillating square cylinder was measured for different levels of air-content, - also in the case without air. The measurements indicated that force coefficients for clear water could be use in the Morison equations as long as the density for water was replaced by the density for the mixture of air and water.</p>

Effect of Air Fraction on Force Coefficients in Oscillatory Flow

Paper Proceedings: https://asmedigitalcollection.asme.org/OMAE/OMAE2021/volume/85116

OMAE 2021

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