the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 12 Feb 2024
Anomalous Response of Floating Offshore Wind Turbine to Wind and Waves
Abstract. We study the Floating Offshore Wind Turbine (FOWT) dynamic response to high wind velocity scenarios utilizing an extensive Markov Chain Monte Carlo simulation involving 10,000 trials of a reduced model from Betti et al. (2014) with a blade-pitch PID controller. The research emphasizes analysis of extreme events in surge, pitch and heave of FOWT, identifying and categorizing them based on their statistics, correlations and causal relations to wind and waves. A significant insight is the differentiation of anomalies into short-correlated and long-correlated types, with the latter primarily influenced by wind conditions. For example, one of our findings is that while specific wave conditions may amplify anomalies, wind remains the predominant factor in long-term anomalous pitch behaviors. We anticipate that further development of this analysis of the operation's critical extreme events will be pivotal for advancing control strategies and design considerations in FOWTs, accommodating the turbulent environment they encounter.
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CC1: 'Comment on wes-2024-14', Howard Yu, 15 Feb 2024
Publisher’s note: the content of this comment was removed on 15 February 2024 since the comment function was misused.
Disclaimer: this community comment is written by an individual and does not necessarily reflect the opinion of their employer.Citation: https://doi.org/10.5194/wes-2024-14-CC1 -
RC1: 'Comment on wes-2024-14', Anonymous Referee #1, 26 Feb 2024
This paper demonstrates some analysis of the anomalous response of FOWT based on a linear model developed by an earlier work by Betti et al. (2014). The novelty of the paper could be strengthened. From my understanding, the linear FOWT model was adapted from Betti et al. (2014). The authors conducted some investigation of detuning the blade pitch controller. Subsequently, 10000 Monte Carlo simulation was carried out in the linear models and the analysis was mainly based on these simulation results. The novelty of this work could be better emphasised, and I recommend a major revision to clearly articulate its uniqueness and establish a stronger link with existing literature.
- Section 1. The motivation can be improved. Why is the anomalous response of FOWT important? Why can’t other models perform such a task? The link between the first and second paragraphs is weak.
- The format of citations can be improved. The current format is quite disturbing when reading.
- “Each controller operates independently, and within each region, only one variable is altered.” This sentence is not true. Most of the controllers do not operate independently, and more than one variable is altered. For example, in the above-rated wind region, the generator torque can follow the Constant Power strategy, instead of Constant Torque.
- Page 5, lines 80, 81 and 82. Q → Q_\alpha?
- Equation 8. Why is there a minus sign?
- Equation 13. There is an assumption of 100% efficiency in the generator.
- Page 9 “This observation appears counter-intuitive as it implies that the net wind thrust acting on the structure is lower in higher wind speed conditions.” This is not counter-intuitive if one knows the basics of wind turbine operations. The thrust curve against the wind speed has a negative slope in the above-rated wind region due to the blade pitch, as the authors pointed out later. Please remove the word “counter-intuitive”.
- Page 11. Please define a_p and a_i as detuning parameters. It is confusing to see Equation (17) and wondering what a_p and a_i are.
- Page 11. Line 202. “We start with ai = 1, and calculate the average rotor speed where the averaging is over time (25 min).” Wouldn’t using standard deviation be better in this case? Or is it because the convergency for the rotor speed took a long time and that’s why the averaged rotor speed was used?
- Page 11. Line 204. “tuned”→” fine-tuned”
- Page 13. I wonder why a duration of 1500 seconds was chosen. Why not a 10-minute time-series? Also, was the transient at the beginning discarded?
- “FIG. 13 presents the probability density function (PDF), which depicts the overall distribution of individual states (grey)” Is the grey area representing the mean of each time series? Or is it a distribution of all data points? If latter, at what time step?
- Fig 14-40. The figures are generally too small to read. I encouraged the authors to use bigger figures or zoom in to highlight the meaningful part. Or maybe think about how to present them in an innovative way.
Citation: https://doi.org/10.5194/wes-2024-14-RC1 - CC2: 'Reply on RC1', Michael Chertkov, 11 Mar 2024
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RC2: 'Comment on wes-2024-14', Anonymous Referee #2, 11 Mar 2024
This paper demonstrates some analysis of the anomalous response of FOWT based on a linear model developed by an earlier work by Betti et al. (2014). Firstly, the results based on simulations using a linear model on FOWTs are not enough to be sufficient for demonstrating the results due to highly coupled non-linearities in the FOWTs. Secondly, the novelty of the paper could be strengthened. From my understanding, the linear FOWT model was adapted from Betti et al. (2014). The authors only conducted some investigation of detuning the blade pitch controller. Subsequently, 10000 Monte Carlo simulation was carried out in the linear models and the analysis was mainly based on these simulation results.
A simulation model based on only 7 states is too simple to capture the dynamic response of a FOWTs. And the aerodynamics are model based on simply Cp-lambda curve is not sufficient to simulate the FOWT system response. Furthermore, the flexibility of the blades are missing which is very important for a FOWT. So in conclusion, the model needs to be extended.
Apart from the general comments, there are many major mistakes in the paper:
- For example, at line 63, the author mentioned "The mechanical part of the Betti model is stated in terms of the six Degrees Of Freedom (DOF) – three “coordinates" – surge, heave and pitch – and their “velocities". ". This statement is wrong. Based on the authors' description, the model has actually only three DOFs. Or, you can mention it has 6 states. The velocities are not DoFs. They are part of states of a state-space model.
- Equation (12) is wrong. In the equation, the wind speed should be the undisturbed incoming wind speed instead of the local relatvie wind speed at blade. The same mistake happens for the equation 8 and 15.
Some of specific comments (I only listed some of the major mistakes) for the authors to consider:
- Line 21: The format of citations needs to be improved. With the author name at the end of the sentence is very confusing when reading.
- Line 25: The argument of selecting TLP is quite weak, which can not represent the complicity of a FOWT, in which the pitch, surge and roll motion of the platform is actually very crucial response of FOWT.
- Line 29 - 33: In your explanation, actually, one important Region which lies in between below-rated and above-rated is missing. Actually, this region is even more crucial for having anomalous event on FOWTs. Furthermore, the statement of the control strategy in this paragraph is not very accurate.
- Line 46: "mainframe FOWT", "mainframe" is not the correct terminology. You should use platform or floater;
- Figure 14 to 40 are too small to read. It should be presented in a better way which can reveal the important/meaningful part of the results
The novelty and the quality of this work need to be considerably improved before it can be accepted for publication. And I suggest a major revision including the corrections on all the fundamental mistakes. Afterward, the author can resubmit it for a new round of review.
Citation: https://doi.org/10.5194/wes-2024-14-RC2 - AC1: 'Reply on RC2', Michael Chertkov, 20 Mar 2024
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