Flexible Riser Tensile Armor Modelling Method and Application to Fatigue Analysis
Round 1
Reviewer 1 Report
It is very good paper that showed the flexible riser was tested and modelled using ANSYS FEA for stress check. however, The FEA model included all structural layers for one full pitch length, and meshed with more than 10 million elements. so, please mentioned what RAM PC?
and the Contact surfaces were defined between adjacent layers, with internal 342 friction coefficient 0.1, so, from my personal experience is 0.3, mentioned why you have used 0.1.
The 5% match came because you have used 0.1 friction factor?
It is very good paper that showed the flexible riser was tested and modelled using ANSYS FEA for stress check. however, The FEA model included all structural layers for one full pitch length, and meshed with more than 10 million elements. so, please mentioned what RAM PC?
and the Contact surfaces were defined between adjacent layers, with internal 342 friction coefficient 0.1, so, from my personal experience is 0.3, mentioned why you have used 0.1.
The 5% match came because you have used 0.1 friction factor?
Author Response
Thank you very much for taking the time to review the paper, and our comment responses are as follows:
- We used a 32G RAM 2.3G Hz PC to run the FEA cases. For the tension only cases, computational time is around 2hrs, when bending involved, it takes more than half a day. Usually the most time consuming part is not the computational time, it is the time to twick the model to get a converged solution, it may take days and weeks.
- This flexible pipe we worked on has anti-wearing tape between armor wire layer #1 / armor wire layer #2, the tapes would reduce the friction between armor wire layers, and 0.1 is a reasonable estimation.
- Higher friction factor may yield different results, it could be further assessed, due to time and funding limitation, we will leave it to future research work.
Reviewer 2 Report
This paper introduces a 3D curved bar theory-based stress calculation method for flexible structures- helix armour and applies it to flexible riser fatigue analysis. The method considers the helical geometry, frictional hysteretic effect, and all stress components of the tensile armour under tension and bending load. The method is validated by FEA and compared with literature data. Then, the math model was used for the fatigue assessment and the lifetime extension evaluation of an 8" flexible riser. According to the authors, the proposed method can be used for other multi-scale risers' models and helix structures.
The review paper comprises two parts; the first one concerns stress analyses based on the analytical equations and comparison with FEA results and the literature data. This part can be acceptable, but improvement needs to be made in the quality of the work as follows:
1) The equations should be rewritten in a form that they are easier to analyse. They have different fonts in size and are written in a complicated way to read and analyse.
2) The FEA model needs to be explained so that the reader can understand how it was built. It was said that Ansys and Abaqus were used, but there is no justification for why they were both used in one analysis.
3) I do not see a novelty in this part of the paper; for me, it is an engineering application of existing methods.
The second part concern the application of the flexible riser and its fatigue analysis. This part needs to be significantly rewritten. Here, numerous elements are not clear to me, and they are listed here:
4) Ansys and Abaqus, according to the authors, were used for stress analysis; why both in one analysis?
5) The fatigue analysis was described too briefly, and it is impossible to understand how it was carried out.
6) The FEA model of the analysed riser looks very complex, but more of the modelling details are not presented. Based on the text, I cannot understand how the FEA model
was built. I only have a rough idea of what has been done, and only that I have done similar things before; for a reader who is not too familiar with the subject, the description would not be clear.
7) The pictures, for example, Fig. 12, could be of better quality and must be improved because they are blurred.
8 ) The remaining fatigue life of 2140 years needs to be discussed more because the analysis does not consider the statistical nature of the fatigue phenomenon. The presentation of life without proper comments could be too optimistic and, therefore, risky for the structure.
9) Not all references are used in the paper's text; this need to be corrected.
10) I suggest looking at the paper's conclusions and highlighting the proposed method's novelty.
I recommend proofreading the whole text to improve minor grammar errors. Generally, the English of the paper is acceptable.
Author Response
please see the attached file for the comment responses.
Author Response File: 
Author Response.pdf
Round 2
Reviewer 2 Report
The following improvements are needed to implement:
+ For putting a non-breaking space between numbers and units (like 125 Nm or 5 Te)
+ For consistency with curvature units, see lines 260, 261, 324, 356 and Table 4.
+ Formating of literature references is inconsistent, and I think it does not fulfil the journal's requirements; please see the recommendation of the journal.
+ Please reformat all equations so that they look more professional. Please see, for example, the article: Xuan, S.; Zhan, C.; Liu, Z.; Zhao, Q.; Guo, W. Numerical Research on Global Ice Loads of Maneuvering Captive Motion in Level Ice. J. Mar. Sci. Eng. 2021, 9, 1404. https://doi.org/10.3390/jmse9121404
Minor corrections are needed; therefore, proofreading is recommended.
Author Response
Thanks again for the review and comments, responses are:
- We have added space between numbers and units throughout the paper
- All curvature units were corrected to 1/m
- Reference section has been fully reformatted
- All equations have been reformatted. Because we are working on the MS Word format, we had experience before that different users may see different format when opening the same MS Word file, which could be related to MS Word settings of each user.
Also the paper has been through proofreading again by the authors, a minor grammar error has been corrected in this revision.
