The effect of aeration on the maximum pressure during wave impacts on a horizontal overhang

The effect of aeration on the maximum pressure during wave impacts on a horizontal overhang: An experimental and numerical study of the effect of aeration on the maximum impact on a horizontal overhang.

van Gent, Koen (TU Delft Mechanical, Maritime and Materials Engineering)

Wellens, P.R. (mentor)
Helmons, R.L.J. (graduation committee)

Delft University of Technology

Offshore and Dredging Engineering

2023-07-06

When waves break, air and water mix and small air bubbles are formed in the water, creating aeration. The mixture of air and water alters the behavior of the fluid. Traditionally, it has been assumed that aeration has a damping effect on impact, as exemplified by the use of air bubbles in the swimming pool below the Olympic 10m platform and during synchronized 10m platform jumps to reduce the force exerted on the swimmer's body.

However, in recent years, it has been found that this assumption does not hold true in all situations involving aeration. When treating aerated water as a non-compressible fluid, it does exhibit a damping effect on impact. However, when treating aerated water as a compressible fluid, the speed of sound of the mixture can actually change with implications for the propagation of density waves. This means that an aerated water impact can feature pressure oscillations that increase the force instead of reducing it. Consequently, hydraulic structures that have been or will be constructed with the assumption that aeration only has a damping effect, may be affected.

Understanding the effect of wave-induced aeration on a horizontal platform is crucial for the design of new hydraulic structures in a more efficient and cost-effective manner. This research aims to determine the maximum force experienced by a horizontal surface during an aerated wave impact. The investigation involves using a numerical method, followed by a series of self-conducted small-scale sloshing experiments. The simulations contribute in two ways: they aid in understanding the problem and the magnitude of forces acting on the experimental setup, and they assist in verifying the experimental results once the experiments are completed. For the experiments, a new tank layout has been designed to facilitate the creation of aerated water inside the tank. The tank is used for conducting experiments where aerated wave impacts are compared to non-aerated wave impacts for different wave impacts. The experimental results confirm both the effect of pressure reduction due to aeration when the aeration level is near to 4%, as well the effect that the maximum pressure can increase for aeration levels between 1 and 2%.

Aeration
horizontal overhang
wave pressure

http://resolver.tudelft.nl/uuid:1a46bf5e-a9f2-4484-8cdd-a0cd4b483127

Student theses

master thesis

© 2023 Koen van Gent