Abstract
An existing 2-dimensional multiphase flow model has been adapted to serve as a tool for predicting dynamic velocity and density profiles in air and water under wavy conditions. The ambition has been to handle wind and wave velocities relevant for hurricane Category 5 wind conditions (U10 > 70 m/s). The output from the model will be used as inlet boundary conditions for more detailed flow simulations to obtain loads on structural elements relevant to the Nautical Sunrise, or similar, projects.
A wavemaker and a beach model were implemented to enable realistic conditions. This allowed simulations of laboratory experiments, performed at the SUSTAIN facility, Miami, USA. Some model parameters related to droplet entrainment were tuned. Satisfactory comparison of model versus experiment was found for velocity profiles, turbulent kinetic energy, surface level gradient, and air pressure gradient below the ceiling. The wave amplitudes seemed to be underestimated at the location of the main sensors, because of numerical dissipation (damping) of the waves. As a result, the predicted load amplitudes on the lowest experimental load cell were underpredicted. Out of three experimental load cells only the lower one was directly impacted by waves. For the two higher load cells the predictions compared well with the experiments.
It was found that the main contribution to the dynamic pressures in the flow was due to wave impacts and that the dispersed droplets had a minor contribution to the effective density of the air.
Two large scale real sea test cased were computed. Wave amplitudes were around 5 m. The water depth was 50 m, with 150 m of atmosphere above. Dynamic profiles of velocities, phase volume fractions and dynamic pressures were demonstrated and can be delivered as input to detailed load simulations.
An overall conclusion is that waves are more important than wind when it comes to forces on a floating construction.