Abstract
Acknowledgements
List of Symbols and Abbreviations
Chapter 1 Introduction
1.1 General introduction
1.2 Scope of the study
1.3 Organization of the study
Chapter 2 Literature review
2.1 Introduction
2.2 Equilibrium ripple characteristics
2.3 Predictions of transient ripple dimensions and hysteresis
2.4 Defects
2.5 Vortex dynamics
2.5.1 Laboratory experiments
2.5.2 Numerical simulations
2.6 Flow three-dimensionality over regular ripples
Chapter 3 Laboratory experiments on the role of hysteresis, defect dynamics and initial perturbation on wave-generated ripple
development
3.1 Introduction
3.2 Methodology
3.2.1 Experiment setup
3.2.2 Bedform analysis
3.3 Results
3.3.1 Changes in wave height and wave period
3.3.2 Influence of initial perturbation
3.4 Discussion
3.4.1 Initial ripple development
3.4.2 Defects and hysteresis
3.4.3 Modelling of the equilibrium ripple wavelength
3.5 Conclusions
Chapter 4 Investigating the response of wave-generated ripples to changes in wave forcing
4. 1 Introduction
4.2 Methodology
4.3 Results and discussions
4.3.1 Dependence of the hysteresis time scale on wave orbital diameter and mobility number
4.3.2 Threshold value of the Shields parameter for ripple readjustment
4.3.3 Effects of defect density and defect interactions on bedform evolution
4.4 Conclusions
Chapter 5 Three-dimensional flow structures over ripples: laboratory measurements and numerical modelling
5.1 Introduction
5.1.1 Wave-generated ripples
5.1.2 Vortex dynamics
5.1.3 Three-dimensionality in flow structures
5.2 Methodology
5.2.1 Laboratory experiments
5.2.2 High-resolution Large Eddy Simulation model
5.3 Results
5.3.1 Streamwise comparison
5.3.2 Vortex structures in the spanwise direction
5.3.3 Vortex strength
5.4 Discussion
5.4.1 Velocity at the ripple crest
5.4.2 Vortex structures
5.4.3 Implications for morphodynamics
5.4.4 Limitations
5.5 Conclusions
Chapter 6 High-resolution large eddy simulations of vortex dynamics over ripple defects
6.1 Introduction
6.1.1 Influence of defects on hysteresis
6.1.2 Hydrodynamics over wave-generated ripples
6.2 Methodology
6.3 Results
6.3.1 Velocity and vortieity field
6.3.2 Vortex characteristics
6.3.3 Shear stress distribution
6.4 Discussion
6.4.1 Maximum velocity at ripple crest
6.4.2 Vortex dynamics
6.4.3 Implieations for morphodynamics
6.5 Conclusions
Chapter 7 Conclusions and future work
7.1 Conclusions
7.2 Future work
References
Appendix A Other relevant parameters in Exp. 1 and Exp. 2
Appendix B Bedform patterns and three-dimensional flow patterns