Graduation of Jesse Swagemakers

20 oktober 2022 12:00 t/m 14:00 - Locatie: CiTG - Lecture Hall E | Zet in mijn agenda

Wave breaking induced drift: An experimental and theoretical prediction in deepwater unidirectional waves

  • Professor of graduation: Dr. Ir. T.S. van den Bremer
    Supervisors: Dr. Ir. M.A. Schipper (TU Delft), Dr. Ir. R. Calvert (TU Delft/University of Edinburgh)

     

In this thesis, the contribution of the wave-breaking-induced transport to the total wave-induced transport at the surface of a deep-water unidirectional irregular sea is quantified. Accurately capturing the contribution of the wave-breaking-induced transport is crucial for predicting the course of marine pollution in the ocean. Thus, a theoretical model is developed, which computes the transport of individual breaking wave groups from surface elevation measurements of a deep-water unidirectional irregular sea. The contribution of the wave-breaking-induced transport to the total wave-induced transport is then defined by an enhancement factor. This enhancement factor shows how much the total surface transport in a wave field without breaking wave groups is enhanced by the transport of breaking wave groups.

The model that is developed is an extension of the relationship from research by Sinnis et al. (2021). In their research, they defined a relationship between the transport of isolated breaking wave groups and the wave group characteristics. The transport relation from Sinnis et al. was applied to the breaking wave groups from surface elevation measurements of a deep water irregular sea. In order to do this, the surface elevation spectrum was approximated by multiple Gaussian wave groups. From the Gaussian wave groups, the wave group characteristics could be determined. The breaking waves were identified based on a steepness threshold for the wave groups. The wave-breaking-induced transport was calculated for all individual breaking wave groups.

dditionally, experiments were carried out to validate the theoretical model. The experiments were performed in the Atlantic Basin of Deltares. In this facility, unidirectional irregular waves were generated. During the experiments, an overhead camera filmed the behavior of Lagrangian particles floating on top of the waves. The particles were tracked using OpenCV and their trajectories were obtained. Because the particles in breaking waves travel faster than in non-breaking waves, a velocity threshold was used to identify the breaking waves in the trajectories. From the identified breaking waves the wave-breaking-induced transport was quantified.

For the validation of the theoretical model, the number of breaking waves, the strength of the breaking events, and the enhancement factor were compared. The results showed that all values were in the same order of magnitude and that the wave-breaking-induced transport enhanced the surface transport for non-breaking waves by a factor up to 1.5. Besides, a sensitivity analysis on the relevant parameters showed that the deviation remains within 10% from the mean.

In conclusion, the theoretical model gave reasonable predictions of the contribution of the wavebreaking-induced transport. Hence, this framework can be fruitful grounds for further extension of the breaking induced drift in the ocean.

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