Fatigue Stress Estimation for Submerged and Sub-Soil Welds of Offshore Wind Turbines on Monopiles Using Modal Expansion

Round 1

Reviewer 1 Report

The manuscript is well written and could be of interest to the readers both from industry and academia. The data analysis is very thorough and well described. I particularly found the discussions regarding the challenges associated with sensor deployment on wind turbines very informative. It was demonstrated that the presented model works quite well for wind speeds below 7 m/s and performs relatively poorly under extreme loading scenarios. The authors may include further discussion on the possible sources of this divergence besides the measurement variability.

Author Response

Dear,

Many thanks for reviewing our research. I would like to address your question about possible sources of poor estimation accuracy for extreme wind speed: As seen in Fig.13 the relative error on DES for high wind speed is not necessarily elevated. However since fatigue weighs large cycles higher the influence of those low wind speed high spread conditions is relatively small while a small number of samples dominates the error on fatigue. The poor performance of specific sensors e.g. TP 5m 35/215 deg. is later connected to an estimation bias which can be removed by altering the mode shape components. TP sensors not featuring such a bias estimate DES already very accurate. For MP sensors a much smaller dataset was available, which was also different for each MP sensor. Thus, the error on fatigue is very sensitive to the performance in only a few timestamps. The estimation model is very straightforward with time invariant features, low sampling rate of SCADA and the modal model being identified from a single condition. Considering these limitations a scatter of estimation quality is expected and a larger data set should help confirming. Also, we altered the results and conclusions slightly to emphasize this point. Attached you can find the revised manuscript in pdf format.

Author Response File: Author Response.pdf

Reviewer 2 Report

In the beginning, I would like to thank you for the opportunity to review this publication. Both the topic and the publication itself seem clear and well-edited.

The presented publication has the correct structure, i.e. an introduction with a description of the problem, then the authors described the research methods and materials on which the publication was based. The division into sub-chapters is correct and allows for a clear separation of selected issues described in the above-mentioned chapter. Then there is a chapter on results, which is also in the correct form. Unfortunately, the results are presented not very clearly (poor quality of the presented graphics, eg Figs. 10-13).
The presented experiment was planned and carried out correctly. The authors also performed an error analysis, thanks to which it was possible to evaluate the obtained results.
There are minor stylistic and formatting errors in the paper (eg in line 304, the word "First" should be in lower case or it should be preceded by a period and not a colon). There is no space between 14.5 and m / s on line 201.
In formatting, it is worth standardizing the notation of units. If in the content (e.g. line 201, 303, or 408) there is a record of speed m / s, then the same record should also appear in the graphs (and not, as it was written in ms-1).
If you decide to write units on the graphs, they should be described in all drawings (the unit is missing in Figure 5).

Author Response

Dear,

Many thanks for reviewing our research. Your corrections are very appreciated and we tried to implement all of them. Following your wish for clarification of the results chapter we altered the manuscript to improve readability and language. Also we reworked all illustrations which now feature a higher visual quality and contain the appropriate units on all axes. Note, that some axes do not contain tick labels due to confidentiality concerns. Attached you can find the revised manuscript in pdf format.

Author Response File: Author Response.pdf