Parametric Sensitivity Analysis of Mooring Chains of a Floating Offshore Wind Turbine in Shallow Water
Abstract
:1. Introduction
2. Model and Methodology
2.1. Parameters of the Floating Offshore Wind Turbine
2.2. Design of Mooring Chains in Shallow Water
2.3. Analysis Method
3. Testing Cases Setting
4. Results and Discussion
4.1. Length of Mooring Chains
4.1.1. Static Characteristics Analysis
4.1.2. Dynamic Characteristics Analysis
4.2. Nominal Diameter of Mooring Chains
4.2.1. Static Characteristics Analysis
4.2.2. Dynamic Characteristics Analysis
4.3. Clump Weights of Mooring Chains
4.3.1. Static Characteristics Analysis
4.3.2. Dynamic Characteristics Analysis
5. Conclusions
- (1)
- A shorter mooring chain has a larger pre-tension, but the tension of the mooring chain increases more significantly with the same offset of the FOWT with more obvious nonlinear characteristics, which is not conducive to mooring safety. In addition, it is found that the horizontal motion of a FOWT is strongly affected by the length of the mooring chain. A too long mooring chain causes a significant offset of the FOWT, while a too short mooring chain quickly increases the tension of the mooring chain. Therefore, it is crucial to design the appropriate length of the mooring chains to ensure the operation and safety of FOWTs.
- (2)
- The mooring chain with the larger nominal diameter has larger tension force under the same platform offset, but the spatial shape of the mooring chains with different nominal diameters is almost the same. The change in the nominal diameter of the mooring chain has a certain impact on the dynamic responses of the FOWT. As the nominal diameter of the mooring chain increases, the mean and maximum values of the horizontal movement of the FOWT will decrease, but it is not as significant as the impact from the change in the mooring chain length.
- (3)
- By analyzing the weight and position of the clump weights, it is evident that increasing the weight of clump weights improves the pre-tension of the mooring chain. Additionally, a heavier clump weight results in a shorter lying section under the same displacement of the FOWT. When the weight of the clump weight remains unchanged, positioning the clump weights as close to the touchdown point on the seabed as possible can improve the restoring force of the mooring system. Additionally, the horizontal restoring force provided by a design scheme with multiple counterweights is greater than that with only a single counterweight. Moreover, a reasonable layout of clump weights attached to mooring chains can effectively restrain the “slack-taut” effect of mooring chains in shallow water. This article only explores the influence of some key mooring chain parameters, such as mooring chain length, nominal diameter, and suspension clump weights, to reveal the nonlinear characteristics of mooring chains of a FOWT in shallow water. Within a limited range of design parameters, a suitable design scheme was selected, providing a certain reference for mooring chain design in shallow water. In addition, as a matter of fact, wave nonlinearity becomes more pronounced as the water depth decreases. According to DNV-RP-C205 [29], the Stokes waves may be more appropriate for describing the extreme wave conditions in the study rather than linear wave models.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
References
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Unit | Value | |
---|---|---|
Mass of blades | kg | 230,717 |
Mass of nacelle | kg | 446,006 |
Mass of tower | kg | 1.257 × 106 |
Height of tower | m | 104.63 |
Mass of concrete platform (excl. tower and mooring systems) | kg | 2.1709 × 107 |
Center of gravity | m | −15.225 |
Draft | m | 22.0 |
Displacement | m3 | 2.3509 × 104 |
Iterm | Grade R3 | Grade R3S | Grade R4 | Grade R4S | Grade R5 |
---|---|---|---|---|---|
Proof load, stud link (kN) | 0.0156D2 (44-0.08D) | 0.0180D2 (44-0.08D) | 0.0216D2 (44-0.08D) | 0.0240D2 (44-0.08D) | 0.0251D2 (44-0.08D) |
Proof load, studless (kN) | 0.0156D2 (44-0.08D) | 0.0174D2 (44-0.08D) | 0.0192D2 (44-0.08D) | 0.0213D2 (44-0.08D) | 0.0223D2 (44-0.08D) |
Breaking load (kN) | 0.0223D2 (44-0.08D) | 0.0249D2 (44-0.08D) | 0.0274D2 (44-0.08D) | 0.0304D2 (44-0.08D) | 0.0320D2 (44-0.08D) |
Weight, stud link (kg/m) | 0.0219D2 | ||||
Five-link length (mm) | Minimum 22D and Maximum 22.55D |
Item | Unit | Chain I | Chain II | Chain III |
---|---|---|---|---|
Nominal diameter | m | 0.137 | 0.127 | 0.117 |
Mass of chains per unit length (in air) | kg/m | 411.041 | 353.225 | 299.789 |
Weight of chains per unit length (in water) | N/m | 3505.4 | 3012.4 | 2556.6 |
Equivalent hydro-diameter | m | 0.257 | 0.239 | 0.220 |
Axial stiffness (EA) | N | 1.6510 × 109 | 1.4188 × 109 | 1.2041 × 109 |
Proof load | kN | 1.3395 × 104 | 1.1789 × 104 | 1.0242 × 104 |
Breaking load | kN | 1.6992 × 104 | 1.4955 × 104 | 1.2993 × 104 |
Item | Values |
---|---|
Quantity of mooring lines | 3 |
Angle between adjacent mooring chains | 120° |
Vertical distance from fairlead to water surface (m) | 9.5 |
Radius of fairlead from centerline of floating body (m) | 44 |
Vertical distance between anchor point and water surface z (m) | −44 |
Horizontal distance between anchor point and fairlead x (m) | 634.184 |
Radius from anchor point to center line of floating body (m) | 678.18 |
Length of unextended mooring chain (m) | 637 |
Seabed stiffness (Pa/m) | 3.0 × 106 |
Seabed damping (PaS/m) | 3.0 × 105 |
Load Cases | Still Water | Rated Operation | Extreme Shutdown |
---|---|---|---|
(DLC. 1) | (DLC. 2) | (DLC. 3) | |
Direction (deg) | 0.0 | 0.0 | 90.0 |
Wind speed (m/s) | 0.0 | 11.4 | 56.2 |
Wind shear index | 0.0 | 0.067 | 0.096 |
Significant wave height (m) | 0.0 | 1.75 | 11.53 |
Wave period (s) | 0.0 | 7.5 | 14.93 |
Peak elevation parameter | 0.0 | 3.3 | 3.3 |
Current speed (m/s) | 0.0 | 0.46 | 1.19 |
L(m) | 637 | 647 | 652 | 657 | |
---|---|---|---|---|---|
D (mm) | |||||
117 | EUR 377,310 | EUR 383,234 | EUR 386,195 | EUR 389,157 | |
127 | EUR 444,564 | EUR 451,543 | EUR 455,033 | EUR 458,522 | |
137 | EUR 517,331 | EUR 525,452 | EUR 529,513 | EUR 533,573 |
Design Factors | Static Characteristics | Dynamic Characteristics |
---|---|---|
Length |
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Nominal diameter |
|
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Clump weights |
|
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Chen, J.; Wang, C.; Wu, X.; Feng, F.; Li, Y. Parametric Sensitivity Analysis of Mooring Chains of a Floating Offshore Wind Turbine in Shallow Water. J. Mar. Sci. Eng. 2024, 12, 2202. https://doi.org/10.3390/jmse12122202
Chen J, Wang C, Wu X, Feng F, Li Y. Parametric Sensitivity Analysis of Mooring Chains of a Floating Offshore Wind Turbine in Shallow Water. Journal of Marine Science and Engineering. 2024; 12(12):2202. https://doi.org/10.3390/jmse12122202
Chicago/Turabian StyleChen, Jiahao, Chuanfu Wang, Xiaodi Wu, Fan Feng, and Yan Li. 2024. "Parametric Sensitivity Analysis of Mooring Chains of a Floating Offshore Wind Turbine in Shallow Water" Journal of Marine Science and Engineering 12, no. 12: 2202. https://doi.org/10.3390/jmse12122202
APA StyleChen, J., Wang, C., Wu, X., Feng, F., & Li, Y. (2024). Parametric Sensitivity Analysis of Mooring Chains of a Floating Offshore Wind Turbine in Shallow Water. Journal of Marine Science and Engineering, 12(12), 2202. https://doi.org/10.3390/jmse12122202