Field Observations of Scour Behavior around an Oscillating Water Column Wave Energy Converter

Round 1

Reviewer 1 Report

JSME-1599976

Title: Field observations of scour behavior around an Oscillating Water Column Wave Energy Converter

The paper presents measurements of scour around an OWC deployed at King Island, Australia in 2021. The scope of the paper is rather small, with Fig. 15 being the main result in my view. However, openly published measurements, footage and data of fullscale WECs deployed in real offshore environments is very rare, and of great relevance for the wave energy sector, both in academia and industry. This fact in itself points towards an acceptance decision. However, there are some issues with the paper that should be addressed, and I therefore recommend that a major revision takes place before the paper can be accepted.

 

1. It might be true that scour has not been studied to a large extent for wave energy systems, but it has for sure been studied for similar offshore structures. The biggest shortcoming of the paper is that no results from offshore wind or other more established offshore industries are reviewed and compared with the results presented in the paper. As a starting point, see for instance:

 

Bolle, A., Haerens, P., Trouw, K., & Smits, J. (2010). Scour around gravity-based wind turbine foundations-prototype measurements. In Coasts, marine structures and breakwaters: Adapting to change: Proceedings of the 9th international conference organised by the Institution of Civil Engineers and held in Edinburgh on 16 to 18 September 2009 (pp. 103-114). Thomas Telford Ltd.

 

Bolle, A., Mercelis, P., Goossens, W., & Haerens, P. (2010). Scour monitoring and scour protection solution for offshore gravity based foundations. In Scour and Erosion (pp. 491-500).

 

Mayall, R. O., Byrne, B. W., Burd, H. J., McAdam, R. A., Cassie, P., & Whitehouse, R. J. S. (2018, October). Modelling of foundation response to scour and scour protection for offshore wind turbine structures. In Scour and Erosion IX: Proceedings of the 9th International Conference on Scour and Erosion (ICSE 2018), November 5-8, 2018, Taipei, Taiwan (p. 405). CRC Press.

 

Petersen, T. U., Sumer, B. M., Fredsøe, J., Raaijmakers, T. C., & Schouten, J. J. (2015). Edge scour at scour protections around piles in the marine environment—Laboratory and field investigation. Coastal Engineering, 106, 42-72.

 

Tavouktsoglou, N. S., Harris, J. M., Simons, R. R., & Whitehouse, R. J. S. (2017). Equilibrium scour-depth prediction around cylindrical structures. Journal of Waterway, Port, Coastal, and Ocean Engineering, 143(5), 04017017.

 

Van Eijk, T. F. A. (2016). Gravity Based Foundation: Scour and design optimisation. Master thesis, TU Delft.

 

Whitehouse, R. J., Sutherland, J., & Harris, J. M. (2011, December). Evaluating scour at marine gravity foundations. In Proceedings of the Institution of Civil Engineers-Maritime Engineering (Vol. 164, No. 4, pp. 143-157). Thomas Telford Ltd.

 

Yu, T., Zhang, Y., Zhang, S., Shi, Z., Chen, X., Xu, Y., & Tang, Y. (2019). Experimental study on scour around a composite bucket foundation due to waves and current. Ocean Engineering, 189, 106302.

 

Currently in the paper, one small reference is made to Whitehouse et al. (2010), saying that “A similar event (settlement caused by scour undermining the structure foundation) for a different gravity structure was also observed”. I would recommend that the authors do a more profound job in evaluating the results against comparable studies. Are the results expected from similar studies in offshore engineering?

 

2. Related to the above comment is the connection to the earlier paper by Lancester et al. (EWTEC 2021) on scour prediction of the same device, based on both numerical and experimental modelling. Some references to the earlier results are included in the present paper, but they are quite vague “likely to contribute to scour in these locations and was previously predicted by Lancaster” or “Lancaster, et al. [15]. It is likely that vortices form at the back corners of the pontoons”. This could be done more explicitly, for instance by including some of the results from the earlier paper and comparing against new data. Ideally of course, the experimentally measured data should be complemented by numerical simulations, but I understand if the authors find it outside of the scope to carry out a new numerical study for this paper. But if relevant, the results from Lancester et al. (2021) could be used here.

 

3. More information on the WEC should be provided, preferably in a table with mass, length, rated power, etc.

 

4. The paper also lacks a discussion on implications of scour for the WEC performance. How could the detected scour affect the energy absorption and reliability of the device?

 

5. The scientific value of the photos is rather low, and they are often not clear. However, I would still recommend to keep them, but to help the reader by explaining in the caption more details of the pictures and the conclusions that can be drawn from them.

 

6. The level of English is mostly satisfactory, but it should benefit from a proof-reading of a proficient English speaker. There are a number of sentences throughout the paper that are unclear or strangely formulated and could be improved, for instance: “... has been deployed near continuously ...”

 

7. The paper is generally well-structured and transparent. Please make sure that the formatting agrees with the template for the journal; e.g., should text in tables be left-aligned or centered.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

The research is of great significance to practical engineering，and the results show some innovative points which will provide valuable information. I recommend this manuscript to be published if the following points could be well addressed:

1. The reason for taking wave measurements should be clarifeid. The connection between scour and wave condition should be analyzed. Why not consider the influence of tidal current?
2. The conclusions are specificly drawn for the King Island OWC WEC. Can the conclusions be widely used?
3. The scour measurements or monitor technology should be summarized ssystematically.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors have done a good job in revising the paper. All my comments have been adequately addressed.