# Validation mooring lines - Comparison FRyDoM / DeeplinesWind¶

## Test case¶

In this benchmark, a Floating Offshore Wind Turbine (FOWT) platform with three mooring lines anchored to the bottom are considered. The platform is fixed or mooved with prescribed harmonic motion. The tension results of the three mooring lines at the fairleads and anchor points are compared to DeeplinesWind [DLW2013] simulation.

The water depth is set equal to 200 m, the gravity acceleration is 9.81 m/s^2 and the water density is 1025 kg/m^3.

### Mooring lines properties¶

The mechanical properties and morison coefficients of the mooring lines are listed in the next table.

Properties | Value |
---|---|

Diameter (m) | 0.0766 |

Length (m) | 835.5 |

Axial stiffness (N) | 7.536E+08 |

Linear density (kg/m) | 113.35 |

Drag coeff. (normal) | 1.1 |

Drag coeff. (tangential) | |

Added mass (normal) | |

Added mass (tangential) |

### Failead positions¶

The following table gives the cartesian coordinates of the fairlead in the platform reference frame.

Fairlead | Position (in body reference frame) |
---|---|

T1 | {20.435, 35.4, -14} |

T2 | {-40.87, 0., -14} |

T3 | {20.435, -35.4, -14} |

### Anchor positions¶

The following table gives the cartesian coordinates of the anchor point in the world reference frame.

Anchor | Position (in world reference frame) |
---|---|

G1 | {418.8, 725.383, -200} |

G2 | {-837.6, 0., -200} |

G3 | {418.8, -725.383, -200} |

### Environment set¶

The following table gives the environment simulated for the different comparison studies

Motion | Waves | Current |
---|---|---|

Harmonic surge (T=50s ; A=10m) | No | No |

Harmonic heave (T=30s ; A=5m) | No | No |

No | Regular wave (T=27s : A=5m ; dir = 0 deg) | No |

No | Regular wave (T=27s ; A=5m ; dir = 90 deg) | No |

No | No | yes |

No | No | yes |

## Results¶

### Imposed surge motion¶

The motion of the platform is harmonic in surge, with a time period equal to 50 seconds and an amplitude of 10 meters. Other degrees of freedom are fixed.

In the next figures we compare the tension of the three mooring lines at the corresponding fairleads between FRyDoM and DeeplinesWind

In the next figures we compare the tension of the three mooring lines at the anchor points between FRyDoM and DeeplinesWind

One can observe that the non-linearties are important on the dynamic of the mooring line and well capture in FRyDoM. The results of FRyDoM are very close to the results from the benchmark model with a mean relative difference about 3.2%, 4.1% and 3.2% for respectively the tension of the mooring lines 1, 2 and 3 at the fairleads. At the anchor points, the differences are about 3.9%, 4.7% and 3.9% for respectively the mooring lines 1, 2 and 3.

### Imposed heave motion¶

The motion of the platform is harmonic in heave, with a time period equal to 30 seconds and an amplitude of 5 meters. Other degrees of freedom are fixed.

In the next figures we compare the tension of the three mooring lines at the fairleads between FRyDoM and DeeplinesWind.

In the next figures we compare the tension of the three mooring lines at the anchor points between FRyDoM and DeeplinesWind.

The tensions of the mooring lines simulated by FRyDoM follow the time evolution of the tensions given by the benchmark model with a constant offset around 4E+04 N. The non-linearities are correctly predicted. The origin of the offset is investigated.

### Regular waves¶

(in progress)

### Uniform Current¶

(in progress)