The Effect of Ice Floe on the Strength, Stability, and Fatigue of Hybrid Flexible Risers in the Arctic Sea
Round 1
Reviewer 1 Report
This paper introduces an effect of ice floe on the fatique of the carbon fibre composites through simulation and subsequent recommendations to improve the life of these hybrid composites under artic conditions. I recommend correcting formal adjustments such as readability, clarity of images and numbering of images. However, the results obtained by numerical simulation are presented in sufficient detail, and I think this article can be published based on the following personal view points.
However, I have some comments and questions before final acceptance:
1. “Analysis methodology”, page 4. …analysis…I think there is a typo or an unfinished thought.
2. “Static analysis”, page 5 and until the end of the paper “The various load cases considered for global analysis are presented in Error! Reference source not found..“ You should solve the problem with your references.
3. “1.3.2. Dynamic analysis”, page 8, Figure 1 and until the end of the paper. The legibility of the descriptions in the individual figures is very poor. It is essential to edit the images in the entire document in a readable form.
4. “1.3.3. Load cases with floating ice configurations”, page 9. Would it be possible to provide the stiffness (material) properties of ice?
5. “1.4. Local Analysis”, page 10, Figure 3. I cannot see any difference between Fig. 3(b) and (c). Can you comment on it?
6. “1.4.1. Assumptions”, page 11. I would appreciate to give the material properties in the paper, so that the readers can check the values.
7. “1.4.2. Loading”, page 11. “Design pressure applied to the internal surface (34.47MPa)“...Why 34.47 MPa? Can you justified this value?
Author Response
Dear reviewer,
Thank you very much for your constructive suggestion. It really helped us improve the manuscript. Please see our replies below in red.
However, I have some comments and questions before final acceptance:
- “Analysis methodology”, page 4. …analysis…I think there is a typo or an unfinished thought.
We have modified it. There was an incomplete sentence.
- “Static analysis”, page 5 and until the end of the paper “The various load cases considered for global analysis are presented in Error! Reference source not found..“ You should solve the problem with your references.
Referencing software was not working for some reason when submitted. We have now fixed the problem. Thanks very much.
- “1.3.2. Dynamic analysis”, page 8, Figure 1 and until the end of the paper. The legibility of the descriptions in the individual figures is very poor. It is essential to edit the images in the entire document in a readable form.
We have now changed the figure to improve the legibility of the description and increased the DPI.
- “1.3.3. Load cases with floating ice configurations”, page 9. Would it be possible to provide the stiffness (material) properties of ice?
We have added ice stiffness in section 2.1.4. All changes are highlighted in yellow in manuscript.
- “1.4. Local Analysis”, page 10, Figure 3. I cannot see any difference between Fig. 3(b) and (c). Can you comment on it?
They are taken from different angles so the arrow seems to be in the same direction.
- “1.4.1. Assumptions”, page 11. I would appreciate to give the material properties in the paper, so that the readers can check the values.
Material properties are added in Table 6.
- “1.4.2. Loading”, page 11. “Design pressure applied to the internal surface (34.47MPa)“...Why 34.47 MPa? Can you justified this value?
It is mentioned the in manuscript how the pressure was calculated. It was pressure due to the column of the water (equivalent to sea depth at the location).
Thanks once again for the useful comments,
Sincerely,
Ketan
Reviewer 2 Report
The paper covers an interesting topic, relevant to flexible risers in the challenging artic conditions. This paper focuses on the mechanical properties of the hybrid composite flexible risers with composite pressure armour.
However, the model presentation is unclear, there is no detailed information about the model to prove the accuracy of the data, and the paper is very poorly written, described and formatted. It needs to reconsider after major revision in order to be recommended for publication. The remarks are described below:
1. All the titles for tables should be placed above the corresponding table.
2. ''The minimum bending radius (MBR) is therefore limited to 3.35 m to avoid straining the CFRP layers further than the matrix cracking.''. Are the values of ''3.35 m'' referred to from the literature?
3. ''As CFRP layers tend to start fail with initiation of microcracks.''. Add reference.
4. ''the operator considered using a Submerged Turret Riser System (STR) for the project 15The STR system'' It seem to have missed the full point between ''15'' and ''The''.
5. The article format is too poor, such as:
''Subsequently, the local FEA static analysis methodology of 0.5 m section composite layer is presented. analysis''.
''All dimensions and material information are used from previous work4''
''Section 1.3, M is moment and EI is bending stiffness whereβ2 is curvature, where
critical curvature is 
''
Too many ''Error! Reference source not found.'' are found in this article.
The format above Figure 2.
''20mm'', ''34.47MPa'', ''5m'', ''6m'', '' 736MPa''
6. Please list the dimensions and material properties of the flexible riser in tables.
7. For better understanding, please add some figures to describe the flexible riser with a carbon fibre reinforced polymer pressure armour layer and the Submerged Turret Riser System.
8. Acronyms should be applied (Explained) when it first appears in the text, e.g. “TDP”.
9. Please add the Vessel RAO from the supplement to the article, so that the reader can easily and conveniently understand the far, near and cross.
10. Add more detailed explanations for Table 1 and Table 2.
11. Quality of figures and graphs is poor.
12. Please list the stiffness properties of ice and buoys.
13. Section1.3.2, 0° current, 180° current and the current 90-degree, the same format should be used to describe degree.
14. Section 1.4, ''assumed 880 and 00 in alternate layer'', the superscript is ''°'', not ''0''.
15. Section 1.6.1,''Table 19 to Table 24 in supplementary information provides the results for MBR along the riser arclength.'' Table 19 to Table 24 are not included in supplementary.
16. Section 1.10.1 ''Figure 1: Hoop stress through the layers.'', it is not Figure 1. Check the number of all the figures.
17. ''This evaluation considers the effects of the Arctic environment on the hybrid composite riser, specifically its impact on the strength and stability performance.''. How to consider the impact on stability performance?
18. ''External Pressure applied to the depth where the MBR occurred taking from global analysis.''. What is the value of the external pressure? In the global analysis, the external pressure is forced on the outer sheath of the flexible riser.
19. Section 1.10.3,''The maximum tension was found to be 850kN in worst case scenario as mentioned in dynamic analysis. It is worth noted that the tension share of the composite layer came to 42.15kN.''. How do the authors calculate that the tension load applied on the composite layer is 42.15 kN? Please describe the calculation process in detail.
20. Why choose this ice floes parameters and not others?
21. Why the composite pressure sheath has to withstand the bending moments experienced by the full riser? From reference 4, the riser also includes external polymer sheath, tensile armor and internal polymer sheath. What are the outer sheath and composite pressure sheath? The pressure sheath is the CFRP? The author must specify in detail which layers are included in the composite riser.
22. The description of finite element model is not clear.
Author Response
Please see attached.
Author Response File: 
Author Response.pdf
Round 2
Reviewer 1 Report
I do not have any comments and I agree with publication of this article.
Reviewer 2 Report
This manuscript can be accepted in current form.
