# Technical Definition of the TetraSpar Demonstrator Floating Wind Turbine Foundation

^{1}

^{2}

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Design Requirements

- Design for scalable, industrialized production
- -
- Key components should be scalable to accommodate turbines in the 15 MW+ scale, which is anticipated to be the average turbine size in the late 2020s when FOWT is commercialized.
- -
- Components designed for industrialized production in order to capture benefits of learning curves and volume manufacturing.

- Minimize works to be done at port of embarkation
- -
- Port space is often scarce and costs relatively high for storage and assembly of FOWTs, possibly becoming a limiting factor for widespread buildout of FOWT.
- -
- In order to maintain pace of FOWT installation at the offshore site, fast component assembly and commissioning would be possible.

- Eliminate need for highly specialized, bespoke vessels
- -
- One of the big upsides of FOWTs is the opportunity to utilize relatively small, local vessels and cranes for assembly and installation, making offshore wind more accessible for locations that are not near existing supply chain.
- -
- Possibility to use relatively small, nonspecialized vessels also provides opportunity for increased local content in construction of offshore wind projects.

#### TetraSpar Design Philosophy

## 3. Demonstrator Site Description

#### Metocean Conditions

## 4. Global System Overview

## 5. Component Description

#### 5.1. Floater

#### 5.2. Keel

#### 5.3. Suspension System

#### 5.4. Mooring System

#### 5.5. Wind Turbine

## 6. Conclusions

## Author Contributions

## Funding

## Conflicts of Interest

## References

- Walsh, C.; Ramírez, L.; Fraile, D.; Brindley, G. Offshore Wind in Europe—Key Trends and Statistics 2019; Wind Europe: Brussels, Belgium, 2020. [Google Scholar]
- Carbon Trust. Floating Offshore Wind: Market and Technology Review. 2015. Available online: https://www.carbontrust.com/resources/floating-offshore-wind-market-technology-review (accessed on 10 July 2020).
- WindEurope. Floating Offshore Wind Energy: A Policy Blueprint for Europe. 2018. Available online: https://windeurope.org/policy/position-papers/floating-offshore-wind-energy-a-policy-blueprint-for-europe/ (accessed on 25 March 2020).
- Principle Power, Inc. WindFloat. Available online: http://http://www.principlepowerinc.com/en/windfloat (accessed on 3 June 2020).
- IDEOL. Floating Offshore Wind. Available online: https://www.ideol-offshore.com/en (accessed on 3 June 2020).
- Equinor. Hywind. Available online: https://www.equinor.com/en/what-we-do/floating-wind/how-hywind-works.html (accessed on 3 June 2020).
- Andersen, M.T.; Tetu, A.; Stiesdal, H. Economic Potential of Industrializing Floating Wind Turbine Foundations. In Proceedings of the ASME 2018 37th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, Madrid, Spain, 17–22 June 2018. [Google Scholar]
- IEC. IEC 61400-1:2019 Wind Energy Generation Systems—Part 1: Design Requirements; IEC: Geneva, Switzerland, 2019. [Google Scholar]
- Standards Norway. NORSOK Standard N-003: Actions and Action Effects; Standards Norway: Lysaker, Norway, 2007. [Google Scholar]
- Torsethaugen, K.; Haver, S. Simplified double peak spectral model for ocean waves. In Proceedings of the Fourteenth International Offshore and Polar Engineering Conference, Toulon, France, 23–28 May 2004. [Google Scholar]

Item | Unit | Value |
---|---|---|

Water depth | (m) | 220.0 m |

ULS (50-year) | ||

Wind speed at hub height | (m/s) | 45.9 |

Significant wave height (${H}_{s}$) | (m) | 12.9 |

Peak wave period (${T}_{p}$) | (s) | 16.0 |

Current velocity | (m/s) | 1.7 |

ALS (1000-year) | ||

Wind speed at hub height | (m/s) | 45.9 |

Significant wave height (${H}_{s}$) | (m) | 15.5 |

Peak wave period (${T}_{p}$) | (s) | 17.5 |

Current velocity | (m/s) | 1.9 |

**Table 2.**Operational metocean conditions for fatigue limit state (FLS) calculations. Three peak wave periods are defined corresponding to the mean value of the probability sectors defined by the values in the indices.

Item | Unit | Value | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|

Wind speed at hub height | (m/s) | 4.00 | 6.00 | 8.00 | 10.00 | 12.00 | 14.00 | 16.00 | 18.00 | 20.00 | 22.00 | 24.00 | 26.00 |

Wave height (${H}_{s}$) | (m) | 0.64 | 0.95 | 1.31 | 1.71 | 2.15 | 2.64 | 3.15 | 3.70 | 4.27 | 4.87 | 5.50 | 6.16 |

Wave period (${T}_{p,0-25}$) | (s) | 4.82 | 5.20 | 5.59 | 5.99 | 6.41 | 6.91 | 7.35 | 7.86 | 8.31 | 8.84 | 9.37 | 9.90 |

Wave period (${T}_{p,25-75}$) | (s) | 7.51 | 7.88 | 8.28 | 8.64 | 9.01 | 9.42 | 9.78 | 10.19 | 10.60 | 11.01 | 11.42 | 11.87 |

Wave period (${T}_{p,75-100}$) | (s) | 11.86 | 12.09 | 12.39 | 12.58 | 12.76 | 12.94 | 13.11 | 13.29 | 13.56 | 13.75 | 13.95 | 14.25 |

Current velocity | (m/s) | 0.12 | 0.19 | 0.25 | 0.32 | 0.39 | 0.45 | 0.52 | 0.59 | 0.66 | 0.73 | 0.80 | 0.87 |

Item | Unit | Value |
---|---|---|

Overall mass incl. ballast | (tons) | 5471 |

Overall vertical center of gravity below MWL | (m) | 40.0 |

Draft | (m) | 66.0 |

Height of foundation-tower interface, above MWL | (m) | 16.0 |

Item | Unit | Value |
---|---|---|

Floater mass incl. ballast water and additional components | (tons) | 1340 |

Floater vertical center of gravity wrt. MWL | (m) | −9.2 |

Distance from MWL to bottom of floater | (m) | 16.0 |

Floater roll mass moment of inertia wrt. CoG | (kgm${}^{2}$) | $442.5\times {10}^{6}$ |

Floater pitch mass moment of inertia wrt. CoG | (kgm${}^{2}$) | $442.2\times {10}^{6}$ |

Floater yaw mass moment of inertia wrt. CoG | (kgm${}^{2}$) | $532.2\times {10}^{6}$ |

Item | Unit | Value |
---|---|---|

Center column diameter | (m) | 4.3 |

Center column equivalent length | (m) | 30.6 |

Center column coordinates wrt. MWL | (m) | (0.0; 0.0; −14.6)–(0.0; 0.0; 16.0) |

Radial brace diameter | (m) | 3.5 |

Radial brace equivalent length | (m) | 32.8 |

Radial brace mode coordinates wrt. MWL | (m) | (2.5; 0.0; −14.0)–(35.3; 0.0; −14.0) |

(−1.2; 2.2; −14.0)–(−17.6; 30.6; −14) | ||

(−1.2; −2.2; −14)–(−17.6; −30.6;−14) | ||

Diagonal brace diameter | (m) | 2.2 |

Diagonal brace equivalent length | (m) | 38.9 |

Diagonal brace node coordinates wrt. MWL | (m) | (3.1; 0.0; 14.1)–(32.4; 0.0; −11.5) |

(−1.5; 2.7; 14.1)–(−16.2; 28.0; −11.5) | ||

(−1.5; −2.7; 14.1)–(−16.2; −28.0; −11.5) | ||

Lateral brace diameter | (m) | 4.0 |

Lateral brace equivalent length | (m) | 49.2 |

Lateral brace node coordinates wrt. MWL | (m) | (30.5; 3.5; −14.0)–(−12.2; 28.1; −14.0) |

(−18.3; 24.6; −14.0)–(−18.3; −24.6; −14) | ||

(−12.2; −28.1; −14.0)–(30.5; −3.5; −14.0) |

Item | Unit | Value |
---|---|---|

Keel mass incl. ballast water | (tons) | 3696 |

Vertical distance from MWL to keel horizontal centerline | (m) | 64.0 |

Keel roll mass moment of inertia wrt. CoG | (kgm${}^{2}$) | $1.443\times {10}^{9}$ |

Keel pitch mass moment of inertia wrt. CoG | (kgm${}^{2}$) | $1.443\times {10}^{9}$ |

Keel yaw mass moment of inertia wrt. CoG | (kgm${}^{2}$) | $2.878\times {10}^{9}$ |

Keel equivalent cylinder length | (m) | 56.4 |

Keel cylinder diameter | (m) | 4.1 |

Keel brace node coordinates wrt. MWL | (m) | (20.0; −28.2; −64.0)–(20.0; 28.2; −64.0) |

(14.4; 31.4; −64.0)–(−34.4; 3.2; −64) | ||

(−34.4; −3.2; −64.0)–(14.4; −31.4; −64.0) |

**Table 7.**Mechanical properties of the suspension lines, with definition of fairlead coordinates and line connectivity.

Item | Unit | Value |
---|---|---|

Linetype | (-) | Synthetic rope bundle |

Buoyancy diameter | (mm) | 119.0 |

Unstretched length | (m) | 60.0 |

Submerged mass | (kg/m) | −0.44 |

Dry mass | (kg/m) | 11.0 |

Axial Stiffness | (kN) | 506,667.0 |

Floater Suspension (FS) fairlead coordinates (wrt. MWL) | ||

FS1 | (m) | (35.6; −1.2; −15.8) |

FS2 | (m) | (−16.8; −31.5; −15.8) |

FS3 | (m) | (−18.8; −30.3; −15.8) |

FS4 | (m) | (−18.8; 30.3; −15.8) |

FS5 | (m) | (−16.8; 31.4; −15.8) |

FS6 | (m) | (35.6; 1.2; −15.8) |

Keel fairlead (KF) coordinates (wrt. MWL) | ||

KF1 | (m) | (19.8; −32.7; −64.0) |

KF2 | (m) | (18.4; −33.5; −64.0) |

KF3 | (m) | (−38.2; −0.8; −64.0) |

KF4 | (m) | (−38.2; 0.8; −64.0) |

KF5 | (m) | (18.4; 33.5; −64.0) |

KF6 | (m) | (19.8; 32.7; −64.0) |

Connectivity | ||

Suspension line 1 | FS1-KF1 | |

Suspension line 2 | FS2-KF2 | |

Suspension line 3 | FS3-KF3 | |

Suspension line 4 | FS4- KF4 | |

Suspension line 5 | FS5-KF5 | |

Suspension line 6 | FS6-KF6 |

Item | Unit | Value |
---|---|---|

Anchor radius | (m) | 630.0 |

Anchor node coordinates wrt. MWL | (m) | (630.0; 0.0; −220.0) |

(−215.5; −592.0; −220.0) | ||

(−315.0; 545.6; −220.0) | ||

Mooring fairlead node coordinates wrt. MWL | (m) | (36.3; 0.0; −12.4) |

(−18.1; −31.4; −12.4) | ||

(−18.1; 31.4; −12.4) | ||

Segment lengths of each mooring line | ||

Fairlead | (-) | |

Linetype1 | (m) | 80.0 |

Linetype2 | (m) | 6.0 |

Linetype1 | (m) | 140.0 |

Linetype3 | (m) | 145.5 |

Linetype4 | (m) | 30.0 |

Linetype2 | (m) | 270.0 |

Anchor | (-) |

Item | Unit | Value |
---|---|---|

Linetype1 | ||

Linetype | (-) | Synthetic rope |

Buoyancy diameter | (mm) | 108.0 |

Submerged weight | (N/m) | 2.2 |

Axial Stiffness | (kN) | $4.45\times {10}^{5}$ |

Linetype2 | ||

Linetype | (-) | Mooring chain |

Buoyancy diameter | (mm) | 202 |

Submerged weight | (N/m) | 2139.6 |

Axial Stiffness | (kN) | $1.15\times {10}^{6}$ |

Linetype3 | ||

Linetype | (-) | Mooring chain |

Buoyancy diameter | (mm) | 234 |

Submerged weight | (N/m) | 2872.0 |

Axial Stiffness | (kN) | $1.55\times {10}^{6}$ |

Linetype4 | ||

Linetype | (-) | Mooring chain w. clump weights |

Buoyancy diameter | (mm) | 698 |

Submerged weight | (N/m) | 19,515.0 |

Axial Stiffness | (kN) | $1.06\times {10}^{6}$ |

Item | Unit | Value |
---|---|---|

Tower base above MWL | (m) | 16.0 |

Rotor and nacelle (RNA) mass | (tons) | ∼200.0 |

RNA CoG wrt. tower base | (m) | (3.75; 0.0; 72.1) |

Total tower mass | (tons) | 235 |

Vertical tower CoG above tower base | (m) | 26.4 |

Tower length | (m) | 71.6 |

Tower roll MoI wrt. CoG | (kgm${}^{2}$) | $89.38\times {10}^{6}$ |

Tower pitch MoI wrt. CoG | (kgm${}^{2}$) | $89.38\times {10}^{6}$ |

Tower yaw MoI wrt. CoG | (kgm${}^{2}$) | $489.85\times {10}^{3}$ |

Tower base diameter | (m) | 4.3 |

Tower top diameter | (m) | 3.6 |

© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

## Share and Cite

**MDPI and ACS Style**

Borg, M.; Walkusch Jensen, M.; Urquhart, S.; Andersen, M.T.; Thomsen, J.B.; Stiesdal, H.
Technical Definition of the TetraSpar Demonstrator Floating Wind Turbine Foundation. *Energies* **2020**, *13*, 4911.
https://doi.org/10.3390/en13184911

**AMA Style**

Borg M, Walkusch Jensen M, Urquhart S, Andersen MT, Thomsen JB, Stiesdal H.
Technical Definition of the TetraSpar Demonstrator Floating Wind Turbine Foundation. *Energies*. 2020; 13(18):4911.
https://doi.org/10.3390/en13184911

**Chicago/Turabian Style**

Borg, Michael, Morten Walkusch Jensen, Scott Urquhart, Morten Thøtt Andersen, Jonas Bjerg Thomsen, and Henrik Stiesdal.
2020. "Technical Definition of the TetraSpar Demonstrator Floating Wind Turbine Foundation" *Energies* 13, no. 18: 4911.
https://doi.org/10.3390/en13184911