**5. Conclusions**

The temporal evolution of seabed scour around monopile foundation of a Darrieus-type tidal current turbine is presented in the current study. The temporal scour depth and scour profiles are obtained by experimental measurement using 3D printed models with di fferent rotor radius and tip clearance. Based on experimental data and analysis, empirical equations for temporal evolution of scour depth around turbine is proposed. By comparison analysis with other existing equations for other scour types, the influence of turbine rotor and tip clearance on the development of seabed scour is discussed. The evidence of turbine rotor accelerates the mean velocity and increases the turbulence intensity between turbine and seabed. The scour hole size is amplified. The conclusions are as follows.


Our empirical model for temporal scour induced by Darrieus-type tidal current turbine has some limits. The model mainly considers the impact of tip clearance and rotor radius. Other influential parameters for scour, like sediment diameter and inlet velocity are considered as conventional conditions in our model. In these general conditions, our model shows grea<sup>t</sup> agreemen<sup>t</sup> with existed experimental data. However, there is some errors using the equation to calculate temporal scour development in some extreme conditions. In the future, it is suggested to study other parameters affecting the temporal and spatial development of scour induced by tidal current turbine.

**Author Contributions:** W.H.L., long term research series in tidal turbine and ship propeller jet induced scour with former supervisors M.D. and G.H.; C.S. and W.H.L. contributed to establish temporal scour equation of Darrieus type tidal turbine; C.S. wrote the manuscript with recommendations and validations from W.H.L., S.S.L., M.D. and G.H.

**Funding:** This research was funded by Natural Science Foundation of Tianjin City: 18JCYBJC21900 and The APC was funded by Natural Science Foundation of Tianjin City: 18JCYBJC21900.

**Acknowledgments:** The authors wish to extend their gratitude to School of Civil Engineering in Tianjin University for laboratory space; Queen's University Belfast, University of Plymouth, University of Oxford, Dalian University of Technology, University of Malaya (HIR ENG47), Universiti Teknologi Malaysia, and Southern University College for their past support; and professional bodies EI, IEI, IET, BCS, IEM, IEAust, ASCE, ECUK, BEM, FEANI, AFEO, MINDS and academy AAET for membership support and available resources.

**Conflicts of Interest:** The authors declare no conflict of interest.
