Introduction  As a new type of clean and renewable energy, wind power attracts widely attention. With the development of wind power from land to sea, offshore floating wind power has developed rapidly.

  Method  In this paper, the commercial software ANSYS-AQWA was used to numerically analyze the dynamic response of the OC4 DeepCwind semi-submersible floating wind turbine under typical sea condition of the South China Sea. The equivalent load method was used to caluclate the aerodynamic loads, and potential flow theory was used to calculate the hydrodynamic loads on the platform and the mooring force on the mooring lines.

  Results  The results shows the surge and motion response will increase significantly when one mooring line is lost. This may cause the loss control of the platform. When two mooring lines are lost, the motion response will increase appropriately during a certain time. Therefore, it is recommended to use redundant mooring system, i. g. several mooring lines in one group, to have enough time to replace the damaged mooring line.

  Conclusion  This work provides a certain reference to the development of offshore wind power in deep water. Further research is needed to study the mechanism of flooded columns damaged and their numerical modeling methods.