Lightweight Structural Concepts in Bearing Quasi-Static Ice Hull Interaction Loads

Round 1

Reviewer 1 Report

This paper investigates lightweight structural concepts including metal grillage, sandwich panel and stiffened sandwich panel, subject to ice loading. The  topic is of value and conclusions are supported by sound calculations and FE analysis. There are a few comments which need to be addressed.

One fundamental assumption here is that ice loading is quasi-static. I found it difficult to accept this claim. As shown in Figure 1b, during the process leading to flexural failure, the load increases rapidly in a relatively short time. By 'Quasi-static' it means history-independent. This of course makes it possible to run a large number of simulation and approach the research question in such manner. But whether a quasi-static simulation really represent the loading scenario reasonably is not justified by the authors. The authors are suggested to run one or several dynamic loading simulation with realistic ice load evolution and compare the result with that obtained from quasi-static simulation. This gives confidence to the approach adopted in this paper.

I could not get how the HPZ is used in the simulations. It seems that HPZ does not appear from Section 4 on. Also line 180-181 is unclear how it relates to the work in this paper.

Why 32cm corresponds to load height of 25cm? FSICR ice class IB can resist 60cm ice. For 32cm it seems that ice class 1C is enough.

Figure 5b the simulations differ considerably with experiments. Later it is claimed in line 227 that it agrees qualitatively well. However, since the authors are comparing different concepts, a qualitatively well agreement may not be sufficient.

I recommend the discussion to include some statements on the cost of different concepts, as that usually drives the practicality of structural design.

Some editorial issues:

a. 'alternate' -> 'alternative'

b. In the title there is a '.' at the end, which should be removed

c. There are ten keywords, which should be reduced as some of them overlaps

d. 'P' in eq.(3) not explained

e. The references are not in good format. Please correct that.

Author Response

Dear Reviewer,

Thank you for sharing your thoughts with us. You have raised some interesting observations. We will try our best to answer them. Please find our answers marked in blue. The corresponding updates in the manuscript are marked with comment bubbles.

This paper investigates lightweight structural concepts including metal grillage, sandwich panel and stiffened sandwich panel, subject to ice loading. The  topic is of value and conclusions are supported by sound calculations and FE analysis. There are a few comments which need to be addressed.

One fundamental assumption here is that ice loading is quasi-static. I found it difficult to accept this claim. As shown in Figure 1b, during the process leading to flexural failure, the load increases rapidly in a relatively short time. By 'Quasi-static' it means history-independent. This of course makes it possible to run a large number of simulation and approach the research question in such manner. But whether a quasi-static simulation really represent the loading scenario reasonably is not justified by the authors. The authors are suggested to run one or several dynamic loading simulation with realistic ice load evolution and compare the result with that obtained from quasi-static simulation. This gives confidence to the approach adopted in this paper.

Thank you for bringing this point. There are three thoughts behind our supposed assumption.

1. In this study we proposed a composite consisting of three layers. This study focuses on finding candidates for the quasi-static layer. The subsequent paper will focus on candidates for the dynamic impact resistant layer. When combined together, they will be able to withstand the full spectrum of load cases seen during ice-hull interaction. This is represented in Figure 2 in the manuscript.
2. FSICR rules prescribe applying a static load patch for direct calculations.
3. In literature, we see studies that have idealised ice pressure as quasi-static [1, 2].

These points are now incorporated in the manuscript.

Your suggestion on comparing with a dynamic loading simulation with realistic ice load evolution is interesting. However, the ice properties and characteristics, load evolution and vessel advance velocity corresponding to FSICR prescribed pressure are not known. This makes it unreasonable to compare dynamic and quasi-static solutions. Our proposal of separately investigating quasi-static and dynamic components would help capturing ice-hull interaction reasonably.

I could not get how the HPZ is used in the simulations. It seems that HPZ does not appear from Section 4 on. Also line 180-181 is unclear how it relates to the work in this paper.

HPZ area is defined in the middle of the nominal pressure area (Figure 4b in manuscript). The dimensions of the HPZ is sourced from the work done in Zhang, Cheemakurthy [3] on using a probabilistic approach to estimate the loading conditions in Sweden. The load magnitudes in the nominal and HPZ area are taken according to FSICR rules.

The above mentioned details are now incorporated in the manuscript.

Why 32cm corresponds to load height of 25cm? FSICR ice class IB can resist 60cm ice. For 32cm it seems that ice class 1C is enough.

A 95% operational time window corresponds to an ice thickness of 50 cm according to data collected in [4]. The 32 cm mentioned here was calculated using a Weibull distribution in [3]. Assuming a conservative approach, we chose 50 cm. This corresponded to class 1B. In the manuscript, we have updated this information and added a thickness distribution figure to support this claim.

The load height can be much lesser than the corresponding ice thickness. The observation is explained in Riska and Kämäräinen [5]’s study. In our study we have taken the FSICR load height recommendation for class 1B as 0.25 m.

These details are now incorporated in the manuscript.

Figure 5b the simulations differ considerably with experiments. Later it is claimed in line 227 that it agrees qualitatively well. However, since the authors are comparing different concepts, a qualitatively well agreement may not be sufficient.

Considering the large number of cases, validating them all is practically not feasible. Instead, we chose to validate the FE model to be as close as possible to experimental data found in literature. The dataset used in our paper includes some uncertainties which is also highlighted in the reference study [6].

These points are now incorporated in the manuscript.

I recommend the discussion to include some statements on the cost of different concepts, as that usually drives the practicality of structural design.

Thank you for the recommendation. This is now included in the discussion section.

Some editorial issues:

1. 'alternate' -> 'alternative'
2. In the title there is a '.' at the end, which should be removed
3. There are ten keywords, which should be reduced as some of them overlaps
4. 'P' in eq.(3) not explained
5. The references are not in good format. Please correct that.

Thank you for this recommendation. These points and the reference list has been updated.

We thank you for taking the time in reviewing our paper.  Please feel free to discuss with us on our replies.

We wish you a pleasant weekend.

Kind Regards,

Harsha Cheemakurthy, Zuheir Barsoum, Magnus Burman and Karl Garme

REFERENCES

1. Discusser O, Fukasawa T, Discussers F, Boon B, Zakky A, Constantinescu A, et al., editors. QUASI-STATIC RESPONSE. Proceedings of the 20th International Ship and Offshore Structures Congress (ISSC 2018) Volume 3: Discussions; 2020: IOS Press;
2. Wang B, Yu H-C, Basu R, editors. Ship and ice collision modeling and strength evaluation of LNG ship structure. International Conference on Offshore Mechanics and Arctic Engineering; 2008.https://doi.org/10.1115/OMAE2008-57134
3. Zhang M, Cheemakurthy H, Ehlers S, Franz von Bock und Polach R, Garme K, Burman M. Ice pressure prediction based on the probabilistic method for ice-going vessels in inland waterways. Journal of Offshore Mechanics and Arctic Engineering. 2019;141(2). https://doi.org/10.1115/1.4041015.
4. Cheemakurthy H, Zhang M, Garme K, Barsoum Z, editors. Nonlinear Finite Element Analysis of Inland-Waterway Barge in Fresh Water Ice Conditions. The 29th International Ocean and Polar Engineering Conference; 2019: OnePetro;
5. Riska K, Kämäräinen J, editors. A review of ice loading and the evolution of the finnish-swedish ice class rules. Proceedings of the SNAME Annual Meeting and Expo November; 2011
6. Zhu S, Chai GB. Damage and failure mode maps of composite sandwich panel subjected to quasi-static indentation and low velocity impact. Composite structures. 2013;101:204-14. https://doi.org/10.1016/j.compstruct.2013.02.010.

Reviewer 2 Report

The developed study is of high quality and has the potential for a significant impact on marine industry. It presents an extended and robust analysis concerning three different possible innovative solutions to provide ice-class vessels with both lightweight properties and suitable resistence to ice impact. The background of the work was well established and the presentation of methods and results is clear and scientifically strong. The performed parametric analysis as well as the identification of significant parameters provide readers with a wide range of information and support the sccientific soundness of the study. The results have the potential to have an impact on the industrial sectos interested in lightweight ice-class vessels development as well as on the institutions responsible for rules and regulations on marine structures design. In conclusion, I consider the paper suitable for publication without any further revisions. The description of the methodology and the presentation of the results is clear and robust.

No revision are required. Only a typo was detected: on page 3 line 102 “Figure 3” sould be replaced with “Figure 2”.

Author Response

Dear Reviewer,

We thank you for sharing your thoughts. It is heartening to know that the work will contribute towards the development of lightweight ice going vessels. We continue to work in this field and would be glad to hear your opinion for future work. We have made the typo correction as indicated by you.

We wish you a pleasant weekend.

Kind Regards,

Harsha Cheemakurthy, Zuheir Barsoum, Magnus Burman and Karl Garme.