Assessment of the Roll Derivatives of Different Surface Ships Based on Numerical Pure Roll Simulation

Round 1

Reviewer 1 Report

I am attaching the corrected pdf file for just one correction.

Comments for author File: Comments.pdf

Author Response

We are very grateful for your comments on the manuscript. Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our research. We have studied the comments carefully and have made the correction which we hope to meet with approval. The main corrections in the paper and the responses to the reviewer’s comments are as follows:

Author Response File: Author Response.pdf

Reviewer 2 Report

The paper uses numerical pure roll simulations to assess roll derivatives of a ship to be employed in 4-DoF manoeuvring simulations. The paper is well-structured and well-written. The proposed method has been tested on several types of vessels having high speed and limited GM comparing, for two of them, the results with experimental ones from previous studies. The following minor issues shall be addressed to improve the quality of the manuscript:

1. Authors might consider adding a flowchart to summarise the whole methodology applied in the paper.

2. Table 2: How the values of p' and phi_0 have been chosen? Please, add a discussion about the suitability of their ranges considered in the study.

3. Figure 3: the 3D models do not allow reproduction of the results of the paper. Please, add the lines plan or, at least, the body plan of the studied ships.

4. Figure 4: it seems that there are some mistakes in the Figure texts. Please, check.

5. Figure 6: The responses for Y' does not resemble a sinusoid. Is it still acceptable to apply Fourier analysis? A comparison of the results of Fourier analysis with numerical simulations and related discussion is recommended.

5. Figures 17 and 18: the results obtained for K_in and K_out for ships other than the catamaran are not well reported. Please, add a separate graph in order to appreciate the fitting for all these vessels.

6. In the text there are some typos (e.g. line 83, line 304, ecc.). Please, fix them.

If these issues are properly addressed, it is suggested to accept the paper without further review.

Author Response

We are very grateful for your comments on the manuscript. Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our research. We have studied the comments carefully and have made the correction which we hope to meet with approval. The main corrections in the paper and the responses to the reviewer’s comments are as follows:

Author Response File: Author Response.pdf

Reviewer 3 Report

The authors present an interesting approach for using CFD to obtain motion derivatives for ship rolling, which can be difficult to obtain from model experiments or other methods. The CFD simulations seem to be done using state-of-the-art methods, with regard to analyzing grid sizes, and sensitivity on the results. 

There are some areas where the paper could be improved... 

Throughout the paper there seems to be some confusion between the terms roll moment and roll motions. In general a low roll restoring moment results in high roll motions. For example, in lines 13 and 15 imply that a high roll moment is dangerous, whereas a ship with a high roll restoring moment will be least susceptible to capsize. 

Table 2 should have units added for the parameters. 

In general, there should be a nomenclature section to define the variables, or they should be specifically defined in the text. This would help in interpreting the results (e.g. Figures 6 to 12). 

The paper could be improved by addressing the following two comments;

1. The CFD simulations were carried out for model scale. The authors should discuss how the derivatives change when going to full scale, or if they are they directly scalable if viscous effects at full scale are not introduced? 

2. The comparison of the results against model experiments is quite weak. Based on the results in Table 5 we see that for the container ship, Yp agrees to within 6.5% and Kp within 7.5%, which might be considered acceptable agreement. However, for ONRT the magnitude of Kp is calculated to be less than one quarter of the value obtained from other sources. Is this really acceptable? What were the causes of this large variation, and how will it effect predictions made using CFD? There are no comparisons given for the other ships. How will the authors address this gap? 

Author Response

We are very grateful for your comments on the manuscript. Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our research. We have studied the comments carefully and have made the correction which we hope to meet with approval. The main corrections in the paper and the responses to the reviewer’s comments are as follows:

Author Response File: Author Response.pdf