A Multidisciplinary Computational Framework for Topology Optimisation of Offshore Helidecks

Round 1

Reviewer 1 Report

This paper presents a multidisciplinary computational framework for topology  optimization of offshore helidecks. The focus of this paper is on the simple optimization problem of compliance minimization under volume constraints. The presentation of the results also does not look very professional. This manuscript reads more like the technical report on the ongoing project than a stand-alone paper. It is very difficult for me to grasp the contribution of the paper. For these reasons, I am inclined to rejecting this paper.

Author Response

We appreciate the reviewer’s point of view however we would like to mention that the main novelty and contribution of our work to the field is the multidisciplinary approach that we have adopted. We developed a computational framework to optimise the helideck supporting structure, which incorporates:

1. Extreme value analysis of maximum gust speed, based on available data since 1853 at the UK Met Office stations close to the lighthouse location,
2. Extreme wind load calculation using computational fluid dynamics (CFD) and
3. Design computational framework to design the lightest structure with the lowest compliance.

The entire framework is developed to design a structure using Aluminium to maintain the offshore harsh environmental conditions.

We believe the presentation of the results are in line with the requirements of Journal of Marine Science and Engineering.

The reviewers also mentioned in their report that extensive editing of English language and style required. We respect the reviewer’s point of view, but we would like to disagree this point of view. Three of the manuscript authors who reviewed the manuscript before submission are native English speakers and the rest are professionals who have been working in academia for years and published several papers.

Reviewer 2 Report

The resolution of the figures used in the thesis should be corrected.

The most important structural strength evaluation of a helideck is the aluminium decking. It is essential to verify the structural strength according to the landing position of the helideck, but there is no such content in the study. Please add the relevant contents. 

In order to evaluate the safety of a structure, it must be evaluated based on a reasonable load combination. Please add relevant information.

 

Author Response

1. The resolution of the figures used in the thesis should be corrected.

Thanks for your observation. We replaced low quality figures (Figure 2 and 3) and we hope the current version would be accepted. However, we would like to mention that the design documents of the current helideck and the lighthouse itself are rather old documents (over 50 years old for the helideck and over 150 years for the lighthouse) with low graphical quality.

2. The most important structural strength evaluation of a helideck is the aluminium decking. It is essential to verify the structural strength according to the landing position of the helideck, but there is no such content in the study. Please add the relevant contents.

Thanks for your comment. We agree with the reviewer. We considered the worst load case (i.e. edge landing) in our design framework. We added the relevant description section 2.6.3 lines 412 to 414.

3. In order to evaluate the safety of a structure, it must be evaluated based on a reasonable load combination. Please add relevant information.

Thanks for your comment. We combined all loads which are mentioned in section 2.6.3. All loads are applied on the structure simultaneously according to CAP 437. We added adverb “simultaneously” in line 408 to make it clear and avoid any confusion.

Reviewer 3 Report

1. In the abstract of this study, carbon steel-based helidecks were previously used, but it is recently described that aluminum helidecks are used. I think an engineering rationale for this should be added.

2. Overall, it is necessary to increase the resolution of the photo. (especially Figures 2 and 3)

3. In the case of aluminum welding, many defects occur for various reasons. How was the uncertainty about this reflected in numerical analysis and your research? An explanation for this is absolutely necessary.

4. 3D beam element was used in FE structural analysis, is there any particular reason for using this element? I think it is necessary to explain the differentiation from other existing methods or elements.

Author Response

1. In the abstract of this study, carbon steel-based helidecks were previously used, but it is recently described that aluminum helidecks are used. I think an engineering rationale for this should be added.

Thanks for your comment. We described the reason of considering Aluminium for the new generation of helidecks in section 2.6.1 lines 337 to 345. However due to limited numbers of words (maximum length of abstract is 300 words) we could not address this in the abstract. We hope this could be accepted by the reviewer.

2. Overall, it is necessary to increase the resolution of the photo. (especially Figures 2 and 3).

Thanks for your observation. We replaced low quality figures (Figure 2 and 3) and we hope the current version would be accepted. However, we would like to mention that the design documents of the current helideck and the lighthouse itself are rather old documents (over 50 years old for the helideck and over 150 years for the lighthouse) with low graphical quality.

3. In the case of aluminum welding, many defects occur for various reasons. How was the uncertainty about this reflected in numerical analysis and your research? An explanation for this is absolutely necessary.

Thanks for your comment. We adopted Aluminium material properties from Eurocode 9 standard Table 3.2 where the Heat Affected Zone (HAZ) properties are included for extruded profiles. We already mentioned in the manuscript section 2.6.1 line 343 that “The selected material has yield stress of 260 and 125 MPa according to Eurocode 9 for extruded and welded sections respectively (26)”.

 

4. 3D beam element was used in FE structural analysis, is there any particular reason for using this element? I think it is necessary to explain the differentiation from other existing methods or elements.

Thanks for your comment. The main reason of using beam elements is that the helideck is made of beam components. However, we validated our FE method/element against experimental modal analysis. In section 3.3 we showed that our simulations/model can predict the behaviour of current helideck properly therefore we concluded that using 3D beam elements is a suitable method to simulate these structures.

Round 2

Reviewer 1 Report

The revised paper is well improved and can be accepted for publication.

Reviewer 3 Report

I accept this paper.