# Coupled Analysis of Offshore Wind Turbine Jacket Structures with Pile-Soil-Structure Interaction Using FAST v8 and X-SEA

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## Abstract

**:**

## 1. Introduction

## 2. Coupled Analysis of Turbine and Support Structure

#### 2.1. Brief Introduction of Offshore Structural Analysis Software X-SEA

#### 2.2. Coupled Dynamic Analysis of Turbine and Support Structures

#### 2.3. Pile-Soil-Structure Interaction

- (1)
- The pile-soil-structure interaction (PSSI), the nonlinear soil behavior is simulated as a nonlinear soil spring by using P-Y, T-Z and Q-Z curve data according to the American Petroleum Institute.
- (2)
- The pile-soil interaction (PSI), similar to the pile-soil-structure interaction, the pile-soil interaction simulated the nonlinear soil behavior using P-Y, T-Z and Q-Z curve as a nonlinear soil spring.

## 3. Numerical Examples

#### 3.1. Verification of Jacket Support Structure for NREL 5MW Offshore Wind Turbine

^{3}. The jacket foundation model is illustrated in Figure 4. Thar model has 12 joints and 112 elements. The joint numbers 61–64 were the fixed boundary conditions located on the seabed. The joint numbers 24, 28, 32, 36, 54, 55 and 56 were the transition pieces or interface joints to transfer the loads and motions within the X-SEA program. The geometry and material properties of the jacket structure are given in Table 3. The same wave forces produced by Airy wave theory were applied to both X-SEA and FAST v8 substructure models [9]. The resulted dynamic lateral reaction forces in the x- and y-directions and the vertical reaction force in the z-direction are compared in Figure 5, Figure 6 and Figure 7, respectively. Figure 8, Figure 9 and Figure 10 compare the resulted dynamic reaction moment capacity on the jacket support structure about x-, y- and z-directions, respectively. These reaction forces and moments resulted from X-SEA and FAST v8 substructure models in good agreement.

#### 3.2. Coupled Dynamic Analysis of Turbine and Support Structure

#### 3.3. Dynamic Coupled Analysis of Turbine and Support Structure-Pile-Soil Interaction

## 4. Concluding Remarks

## Author Contributions

## Funding

## Conflicts of Interest

## References

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**Figure 5.**Comparison of the dynamic lateral reaction force capacity on the jacket support structure in the x-direction resulted from X-SEA and FAST v8 programs.

**Figure 6.**Comparison of the dynamic lateral reaction force capacity on the jacket support structure in the y-direction resulted from X-SEA and FAST v8 programs.

**Figure 7.**Comparison of the dynamic vertical reaction force capacity on the jacket support structure in the z-direction resulted from X-SEA and FAST v8 programs.

**Figure 8.**Comparison of the dynamic reaction moment capacity on the jacket support structure about the x-direction resulted from X-SEA and FAST v8 programs.

**Figure 9.**Comparison of the dynamic reaction moment capacity on the jacket support structure about the y-direction resulted from X-SEA and FAST v8 programs.

**Figure 10.**Comparison of the dynamic vertical reaction moment capacity on the jacket support structure about the z-direction resulted from X-SEA and FAST v8 programs.

**Figure 11.**Comparison of displacements in the x-direction resulted from coupled and uncoupled analyses from the X-SEA program.

**Figure 12.**Comparison of displacement in the y-direction resulted from coupled and uncoupled analyses from the X-SEA program.

**Figure 15.**A comparison of the natural frequencies between the piled support structure and fixed support structure.

**Figure 16.**A comparison of the displacement on the fixed support structure, piled-support structure and pile superelement models in the x-direction.

**Figure 17.**A comparison of the displacement on the fixed support structure, pile support structure and pile superelement models in the y-direction.

**Figure 18.**The maximum distribution of displacement along the pile length in the lateral direction (x).

**Figure 19.**The maximum distribution of displacement along the pile length in the transverse direction (y).

Solution Features of X-SEA |
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Environmental load (wave, current, wind, marine growth, buoyancy, earthquake, self-weight etc.) |

Regular (five kinds) and irregular wave (PM and JONSWAP Spectrum) |

3D linear diffraction wave theory (shell and solid element) |

Static analysis with load combinations |

Frequency analysis |

Three-dimensional prestressed concrete analysis using 3D solid and shell element |

Geometrical and material nonlinear analysis of frame, shell and solid elements |

Nonlinear time history dynamics (dynamics of large deformation of elastoplastic analysis using frame, shell and solid elements) |

Pile-soil-interaction foundation analysis (P-Y, T-Z and Q-Z) |

Dynamic analysis in time domain and frequency domain |

COG (center of gravity) |

Automatic calculation of Stress Concentration Factor (SCF) with local joint flexibility |

Fatigue damage analysis in time and frequency domain |

Mooring analysis with seabed contact for floating offshore structures |

Multiple calculation of FAST v8 wind turbine loads |

Coupled analysis of FAST v8 and offshore structural analysis |

Code checking (AISC, API, Euro Code 3, Norsok, DNV and IEC wind) |

Hydrodynamic Analysis | ||
---|---|---|

X-SEA Element | Material Property | |

Shell element | XSHELL3-QSI: 3 node quasi-conforming XSHELL4-ANS: 4 node assume natural strain | Elastoplastic: Von Mises with strain hardening, Ivanov-Yulishin, Concrete elasto-plastic and elasto-plastic fracture, laminate composite, concrete creep |

Frame element | XFRAME: 2 node frame element with warping (7 dof, shear deformation, tapered, offset) | Elasto-plastic: Von Mises, concrete creep |

Solid element | XSOLID4T & XSOLID10T: 4 and 10 node, tetrahedral XSOLID8-EAS: EAS 8 node | Elasto-plastic: Von Mises, Mohr-Coulomb, Drucker-Prager, Tresca |

Truss element | XTRUSS: 2 node three-dimensional element | Elasto-plastic: Von Mises |

Cable element | XCABLE–Parbolic XCABLE–Catenary XCABLE-Mooring | 5-point nonlinear model |

Spring element | XSPRING: 3D Spring | |

Link Element | Gap, hook, gap-hook | |

Interface element | 1D, 2D, 3D (bond-slip element) | |

Tendon element | 3D prestressing tendon |

Parameter | Value |
---|---|

Outer diameter of a leg [m] | 1.200 |

Wall thickness of a leg [m] | 0.045 |

Outer diameter of a diagonal [m] | 0.800 |

Wall thickness of a diagonal [m] | 0.035 |

Young’s modulus [N/m^{2}] | 2.1 × 10^{11} |

Density [kg/m^{3}] | 7850 |

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**MDPI and ACS Style**

Plodpradit, P.; Dinh, V.N.; Kim, K.-D. Coupled Analysis of Offshore Wind Turbine Jacket Structures with Pile-Soil-Structure Interaction Using FAST v8 and X-SEA. *Appl. Sci.* **2019**, *9*, 1633.
https://doi.org/10.3390/app9081633

**AMA Style**

Plodpradit P, Dinh VN, Kim K-D. Coupled Analysis of Offshore Wind Turbine Jacket Structures with Pile-Soil-Structure Interaction Using FAST v8 and X-SEA. *Applied Sciences*. 2019; 9(8):1633.
https://doi.org/10.3390/app9081633

**Chicago/Turabian Style**

Plodpradit, Pasin, Van Nguyen Dinh, and Ki-Du Kim. 2019. "Coupled Analysis of Offshore Wind Turbine Jacket Structures with Pile-Soil-Structure Interaction Using FAST v8 and X-SEA" *Applied Sciences* 9, no. 8: 1633.
https://doi.org/10.3390/app9081633