The monopile-wheel composite foundation is an innovative type of offshore wind turbine (OWT) foundation with good bearing capacity. The foundation is subjected to cyclic loads from wind, waves, and tides, so it is necessary to study its horizontal cyclic characteristics. By introducing cyclic degradation constitutive and Rayleigh damping parameters, numerical models are generated and validated by comparing with laboratory experiment results. The laws of horizontal accumulated displacement of the composite foundation are then explored through changes in the cycle amplitude, number, wheel diameter, height of loading point and pre -vertical load. The main findings are that the composite foundation is more likely to reach a stable displacement under constant amplitude cyclic loading compared to that of monopile. Under transient dynamic response (74 % of the horizontal ultimate bearing capacity), accumulated displacement will increase rapidly regardless of the foundation form. The composite foundation has smaller hysteresis loop area and slower accumulation rate of bending moment. The soil pressure weakening of the monopile mainly occurs in front of the pile, while that of the composite foundation mainly occurs under the wheel. After cyclic loading, the V - H envelopes for the composite foundation contract unevenly inwards. Above these, prediction methods for the cumulative displacement, maximum bending moment and V - H envelopes for composite foundation considering cyclic degradation are proposed.

With the development of offshore wind power energy, the monopile-wheel composite foundation has attracted wide attentions from scholars as an innovative foundation for offshore wind turbines (OWTs). And in offshore engineering, the local scouring usually tends to weaken the bearing capacity by moving surrounding soil till even become a non-negligible reason for some engineering disasters. To explore this effect of local scour qualitatively and quantitatively, the scouring morphology of the monopile-friction wheel composite foundations under unidirectional flow are obtained by means of CFD. Then, a 3D finite element model is developed to estimate the bearing behaviors and deformation characteristics with the consideration of various scouring conditions. Both internal forces and failure envelopes under H-T combined loads are also obtained through numerical analysis. The results reveal that key scouring parameters significantly affect the bearing capacity and envelopes shrinkage of the composite foundation. In particular, the scouring depth has the greatest effect on lateral and torsional bearing behaviors of 15%-32% and 24%-58%, respectively, followed successively by the scouring angle and extent. And the loading point height has a noticeable impact on the lateral resistance of the composite foundation. The findings provide valuable insights into understanding the load bearing behaviors of composite foundations and their practical application in engineering.