the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 18 Dec 2023
Fatigue life evaluation of offshore wind turbines considering scour and passive structural control
Abstract. Offshore wind turbine (OWT) support structures are exposed to the risk of fatigue damages and scour, and this risk can be effectively mitigated by installing structural control devices such as tuned mass dampers (TMDs). However, time-varying scour altering OWTs’ dynamic characteristics has an impact on the TMD design and fatigue life, which was rarely studied before. In this paper, a simplified modal model was used to investigate the influence of scour and a TMD on the fatigue life evaluation of a 5 MW OWT’s support structure, and the parameters of the TMD were obtained by either a traditional method or a newly developed optimization technique. This optimization technique aims at finding optimal parameters of the TMD which maximizes the fatigue life of a hotspot at the mudline, and effect of time-varying scour can be considered. Results show that scour can decrease the fatigue life by about 26 %, and the TMD can effectively suppress vibration and increase the fatigue life. Further, it is found that the fatigue life can be extended by 7.2 % with the TMD optimized by the proposed optimization technique, compared to that with the traditionally optimized TMD which does not take the change of dynamic characteristics into account.
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RC1: 'Comment on wes-2023-149', Anonymous Referee #1, 21 Dec 2023
The authors investigate the effects of passive TMDs on the fatigue behavior of monopile wind turbines. A parameter optimization method has been developed for designing TMDs, taking into account scour-related changes in the dynamics of wind turbines. The paper presents a numerical case study of a 5-MW monopile wind turbine. The topic is interesting. Below are some comments to further improve the paper:
1. In Section 2.1, the combined soil and structural damping is presented as 1% without elaboration. This figure seems quite low for soil. Also, how is this implemented in Rayleigh damping?
2. In Equations 1 and 2, there is ambiguity regarding dimensions. How are "C_T" and "K_T" defined, and how do they differ from "c_T" and "k_T"? Since the TMD should have one DOF, how is the "u_T" vector defined?
3. In Section 2.4, the forces on the right side of Equation 6 are nonlinear, and their truncation essentially linearizes them. Please elaborate on this and clarify this step in the manuscript.
4. According to Section 3, the studied TMD operates in the FA direction, and the SS direction is uncontrolled. This should be mentioned in the Abstract, Introduction, and Conclusion sections.
5. The mass ratio of the TMD, chosen as 1% in the study, is quite low and could result in unfeasible TMD displacement. This effect should be discussed.
6. Section 4.5 presents additional results with the TMD (FOT), optimized considering overall fatigue performance. These results should be integrated into Section 4.4 and presented alongside the TMD optimized for the initial state of the structure. This would allow, for example, the inclusion of a third and fourth curve in Figure 9, showing results incorporating TMDs optimized by FOT."Some further points are
7. Title: Consider the alternative, "Effect of Scour on the Fatigue Life of Offshore Wind Turbines and Its Prevention Through Passive Structural Control."
8. Abstract: The text requires editing. Some sentences are difficult to understand and contain grammatical errors. For example, ""... either by a traditional method or a newly developed ..."" should be ""... both a traditional method and a newly developed ... are presented.". Additionally, the sentence "... scour can decrease the fatigue life by about 26%, and the TMD can ... increase the fatigue life," lacks complete information about the effect of TMD. Also, the tenses change inconsistently throughout the text.
9. In the Introduction, the literature review includes vibration control systems only up to 2021. Recent years have seen accelerated developments, including floating and monopile OWTs. Presenting these up-to-date examples would more clearly define the research gap.
10. Again in the Introduction, the paper's contribution should be stated in the present tense: "In this study, ABAQUS is used ..." Furthermore, it is unclear what the FE model in MATLAB includes. The text mentions considering the scour effect, but the previous sentence stated ABAQUS was used for SSI.
11. The paragraph mentioned above should first introduce the objectives of the study. Currently, it summarizes only the methodology. The overall purpose should be clarified as: "The aim of the present study is to ... (investigate the effect of scour ... introduce an optimization method for TMDs ... through a case study involving a monopile 5 MW wind turbine.)"
12. At the end of the Introduction, the structure of the paper should be outlined: "The remainder of the paper is organized as follows: Section 2 describes ..."
13. In Figures 9 and 10, adding a grid or labeling significant values on both curves would be helpful.
14. In Figures, try to use vector graphics for better resolution.
15. There are quite a few self-citations (e.g., Chen 2018- Chen 2021: 6 times). Please, check the necessity of these references.Citation: https://doi.org/10.5194/wes-2023-149-RC1 - AC1: 'Reply on RC1', Chao Chen, 07 Feb 2024
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RC2: 'Comment on wes-2023-149', Anonymous Referee #2, 05 Jan 2024
- AC2: 'Reply on RC2', Chao Chen, 07 Feb 2024
Status: closed
-
RC1: 'Comment on wes-2023-149', Anonymous Referee #1, 21 Dec 2023
The authors investigate the effects of passive TMDs on the fatigue behavior of monopile wind turbines. A parameter optimization method has been developed for designing TMDs, taking into account scour-related changes in the dynamics of wind turbines. The paper presents a numerical case study of a 5-MW monopile wind turbine. The topic is interesting. Below are some comments to further improve the paper:
1. In Section 2.1, the combined soil and structural damping is presented as 1% without elaboration. This figure seems quite low for soil. Also, how is this implemented in Rayleigh damping?
2. In Equations 1 and 2, there is ambiguity regarding dimensions. How are "C_T" and "K_T" defined, and how do they differ from "c_T" and "k_T"? Since the TMD should have one DOF, how is the "u_T" vector defined?
3. In Section 2.4, the forces on the right side of Equation 6 are nonlinear, and their truncation essentially linearizes them. Please elaborate on this and clarify this step in the manuscript.
4. According to Section 3, the studied TMD operates in the FA direction, and the SS direction is uncontrolled. This should be mentioned in the Abstract, Introduction, and Conclusion sections.
5. The mass ratio of the TMD, chosen as 1% in the study, is quite low and could result in unfeasible TMD displacement. This effect should be discussed.
6. Section 4.5 presents additional results with the TMD (FOT), optimized considering overall fatigue performance. These results should be integrated into Section 4.4 and presented alongside the TMD optimized for the initial state of the structure. This would allow, for example, the inclusion of a third and fourth curve in Figure 9, showing results incorporating TMDs optimized by FOT."Some further points are
7. Title: Consider the alternative, "Effect of Scour on the Fatigue Life of Offshore Wind Turbines and Its Prevention Through Passive Structural Control."
8. Abstract: The text requires editing. Some sentences are difficult to understand and contain grammatical errors. For example, ""... either by a traditional method or a newly developed ..."" should be ""... both a traditional method and a newly developed ... are presented.". Additionally, the sentence "... scour can decrease the fatigue life by about 26%, and the TMD can ... increase the fatigue life," lacks complete information about the effect of TMD. Also, the tenses change inconsistently throughout the text.
9. In the Introduction, the literature review includes vibration control systems only up to 2021. Recent years have seen accelerated developments, including floating and monopile OWTs. Presenting these up-to-date examples would more clearly define the research gap.
10. Again in the Introduction, the paper's contribution should be stated in the present tense: "In this study, ABAQUS is used ..." Furthermore, it is unclear what the FE model in MATLAB includes. The text mentions considering the scour effect, but the previous sentence stated ABAQUS was used for SSI.
11. The paragraph mentioned above should first introduce the objectives of the study. Currently, it summarizes only the methodology. The overall purpose should be clarified as: "The aim of the present study is to ... (investigate the effect of scour ... introduce an optimization method for TMDs ... through a case study involving a monopile 5 MW wind turbine.)"
12. At the end of the Introduction, the structure of the paper should be outlined: "The remainder of the paper is organized as follows: Section 2 describes ..."
13. In Figures 9 and 10, adding a grid or labeling significant values on both curves would be helpful.
14. In Figures, try to use vector graphics for better resolution.
15. There are quite a few self-citations (e.g., Chen 2018- Chen 2021: 6 times). Please, check the necessity of these references.Citation: https://doi.org/10.5194/wes-2023-149-RC1 - AC1: 'Reply on RC1', Chao Chen, 07 Feb 2024
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RC2: 'Comment on wes-2023-149', Anonymous Referee #2, 05 Jan 2024
- AC2: 'Reply on RC2', Chao Chen, 07 Feb 2024
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