Suction Bucket Pile–Soil–Structure Interactions of Offshore Wind Turbine Jacket Foundations Using Coupled Dynamic Analysis
Round 1
Reviewer 1 Report
In this paper, the soil-structure interaction modeling of suction bucket foundations, used to install offshore wind turbine substructures in intermediate water depths, is discussed in the broadest sense. In general, this topic is of high interest both to the research as well as to offshore wind and petrol industry, as this foundation type offers some advantages compared to pile foundations.
However, this manuscript struggles with two problems: First, it does not feature new results that may lead to innovations or findings. What is actually performed in this study? It is not an approach to coupled simulations of wind turbine structures, it is a comparison of two foundation modeling approaches. Second (which is more problematic), the scientific quality of the manuscript is, in the current state, low from my point of view. To be more specific, when dealing with simulation of wind turbines, a comprehensive and deep knowledge of the entire system behavior (from rotor blade tip to foundation) is required to obtain meaningful results. However, in this manuscript trivial perceptions are discussed quite extensively, while potentially interesting findings are not approached. I do not believe that this is irreparable, but the manuscript needs a profound revision to be suitable for consideration as a printed version.
If the authors want to revise this manuscript, I rather recommend to discuss the approach and results with experts (for instance on scientific confereces, which is unfortunately hard in the current situation) than just processing my comments (and the comments from other reviewers, if present) step by step. Another advise is to survey the relevant literature in this field much deeper.
General comments:
- Consider proof-reading for the entire manuscript.
- Please do not introduce abbreviations, if they are not used in the text. Example: "... finite elements (FEM)" (page 2, line 58). By the way, "FEM" is the "abbreviation" for "finite-element method".
- The formating of almost all figures is different. Consider harmonizing figures at least concerning font types and sizes.
- Figures 5 and 6: There seems to be a problem displaying your sketches (I tested it with two different PDF readers). Has nobody cross-checked this.
Specific comments:
1. Introduction
- I do not believe that your introduction gives a comprehensive overview of the state of the art in this field, particularly concerning offshore wind turbine substructures. After reading this, it looks like there are monopiles, tripods, and jackets, all with specific advantages and drawbacks. However, the reality is much more complicated and the market shares of these structures actually depend highly on economical considerations, probably more than on technical ones. Consider enhancing this section citing relevant and international references.
- For the reader, it is not or only very difficult to see why a suction bucket foundation is beneficial compared to other foundation types. To be honest, this is a kind of introduction that does not motivate to continue reading.
2. Coupled analysis of turbine and support structure
- Is this a co-simulation or loose coupling approach? For me, it looks like you are performing a co-simulation and to be fair, this kind of approach is not coupled. For this reason, I propose reconsidering the title of the paper.
- Natively, FAST v8 comes with a module for substructures called SubDyn and there are works on the integration of foundations in SubDyn, some of them also discussing suction buckets. As a consequence, I am missing a verification and comparison to these approaches. What can you do better and what is new in your approach?
4. Pile-soil structure interaction
- What is a "member"?
- Your equations of motion comprise only matrices in diagonal form, implying you decouple tower, substructure, and piles in your computation. What is the benefit compared to the approaches known from literature?
- How do you obtain your damping values?
- You say "Obtaining a closed-form solution would require iterations over
soil stiffness until it converges to..." Can you elaborate on that?
6. Numerical study
- Is it correct that you do not consider wind loads in your study? If so, the significance of your study is very low, because the loads at the interface between rotor-nacelle assembly and tower are much higher than the wave loads on the structure. If not, why is there no information about the wind states? I am very much concerned that I have to write this when reviewing a study in the field of wind energy.
- What do you mean by linear current? Constant current from sea bed to mean sea level? How do you consider effects like scour, marine growth, breaking waves, corrosion, etc. in your models?
- Can you discuss the simulation time of 60 seconds, which is very low for a study of this kind?
- Many figures showing kinematic responses are shown, but at least not discussed. In fact, these figures illustrate more or less nothing, because the dependency on nonlinear system behavior is completely neglected.
Author Response
Dear Reviewer
I really appreciate your comments about the paper. I have revised all the paper based on your comments.
Please see the attachment.
Thank you.
Ki-du Kim
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Please find comments in the attached file.
A general comments is that more information must be added regarding the soil spring model that are implemented. In particular how nonlinear plastic and accumulated soil responce are modelled. If the rotational spring consepth is used for the suction bucket soil interaction, the metodology for determination of these springs must be included.
Comments for author File: Comments.pdf
Author Response
Dear reviewer
I really apprecite your comments about the paper.
I have revised the paper based on your all comments.
Please see the attachment.
Thank you
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Please find reply the the authors responce attached.
Comments for author File: Comments.pdf
Author Response
Dear Reviewer
I appreciate you again reagriding comments.
I have revised the paper based on all your comments and attached the answers and new revised paper.
Thank you
Ki-Du Kim
Author Response File: Author Response.pdf
