Theoretical Analysis Method for Roll Motion of Popup Data Communication Beacons
Round 1
Reviewer 1 Report
1. It was mentioned in the abstract that the effect of the roll angle on data transmission is crucial. However, the paper discusses only the roll motion of PDCB. The maximum roll angle to effectively data transmission has yet to be discussed.
2. The sentence on page 2, line 54 to 55 need to be re-formulated because the meaning is unclear.
3. The right-hand side of equation 2.2.1 should be a function of time.
4. Detail explanation including the mathematical derivative to obtain the equation 2.2.28 should be included in the manuscript.
5. Figure 4 shows that the PDCB has an initial roll angle. Therefore, the roll angle is always positive. The factors that induce the initial roll angle should be explained in the manuscript.
6. The righting arm as a function of roll angle can be theoretically calculated. This is important to verify the assumption formula obtained in equation 2.2.18.
7. On page 8, lines 268 – 271. Those conclusions should be supported by data obtained from numerical calculation and analysis. There are no calculation results for the damping moment given in the manuscript. The drag force induced by the wave acting on the PDCB as wave force is different from the damping moment, which depends on the body characteristics. The damping moment as a function of angular velocity and roll angle should be included in the manuscript.
8. The assumption used in the paper is not consistent. Some parts use the assumption of small roll amplitude with the linear damping moment. However, in the other parts, the damping and the restoring moment are assumed to be nonlinear.
9. On page 8, line 277 mentions that the natural roll period of PDCB is 5 seconds. How to obtain this period.
10. Figure 5 shows the dimension of the model but the draught was not mentioned. The draught is important to investigate the model’s equilibrium before conducting the simulation.
11. On page 9, lines 294 – 300 concluded that the maximum roll angle was 23 degrees. A longer simulation duration is necessary because the roll amplitude increases with time. The curve shows an irregular motion rather than a regular roll motion. In cases of simulation conduction in regular waves, the comparison cannot be performed by using the average.
12. To compare the results of the three methods, Figure 10 should be written in the same phase angle. Otherwise, it is very difficult to make the comparison.
Comments for author File: 
Comments.pdf
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 2 Report
The reviewer wants to thank the authors for the paper investing the behaviour of a floating data communication beacon under wave conditions and concluding on the data transfer due to the motion response under waves. S/he has some suggestions and questions:
*1) Line (L) 61: The density of the floating material is described but nothing else. At least provide a total mass of such a single cylinder.
*2) L100: Here the variables are described but later in the paper this is not always the case. Please check the full paper for this.
*3) L107: It is not clear why this weave height of 0.183 m was chosen. Maximum capacity of the testing facility? Please clarify this.
*4) L127: Liny et al. [?] please include the number of the reference.
*5) Figure 4: Why does the motion start with a roll angle of 28 or so degree? And with an increasing value? Sorry, if the reviewer missed this in the paper.
*6) Figure 6 and general: Please provide further information for the numerical model. At least the size of the numerical tank and how reflections were absorbed. Plus did the authors use a full six-degree-of-freedom solver or was only one or more open? How large was the mesh in relation to the diameter? Mesh study?
*7) Figure 7 and general: Is there definitely no reflected wave in the tank? Maybe plot a wave gauge in addition to the motion response to understand the different changes.
*8) The comparison in Figure 10 should start with time 0 equal the first movement of the floating device due to the first wave. This should be time 0. In addition, such a fully developed motion response can be presented.
*9) The discussion should go deeper and discuss the individual methodological approach.
The reviewer is looking forward to reading the paper again. Thank you!
no big mistakes but please check the descriptions of the variables.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Thank you very much for the revised manuscript. For validation or verification means, the results of numerical simulation, analytical solution and the model experiment should be compared at the same time duration. Not only for a specific range of time as shown in Figure 11. It will be better if the comparison is performed starting from 0 second to 90 seconds.
The time domain of roll motion obtained by the model experiment from 0 seconds to 90 seconds was not shown in the article. The authors are suggested to show the time domain of the model experiment in the article.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 2 Report
The reviewer thanks the authors for their comments, answers and corrections. The quality of the paper could be improved.
*a) Referring to point 5 and figure 4: Yes, understood. There is an initial motion but clearly, there is a first further increase of the angle, and this cannot be caused by the damping force. At the moment, this seems an initial angle including an increasing motion is provided as the initial condition at time t equal 0 seconds. The authors did not answer this question and please explain this in more detail.
*b) The sub numberings in section 3.1.1 and 3.1.2 are not needed. Please make those new sections better readable and coherent. Please start with the models, how the motion is included, how large the fluid domain is (including the boundary conditions) and what was done to prove the mesh independence. Furthermore, the time discretisation as well as the needed time for a stable motion response while not being affected by reflections should be discussed.
*c) Referring to the old point 7: The reviewer disagrees with the comment on the reflected waves. Numerical simulations can also be affected by reflections if the boundary conditions are not properly implemented. Please show this while running the numerical tank without the floating body and wave only for a longer time allowing it to reach a potential reflected wave in the measurement probe.
*d) Referring to the old point 8 figure 10 and now figure 11: The reviewer is not sure what is only marked as deleted or if there are now two figures nevertheless, neither of the figures shows the full process of the starting of the motion. Please show the initial start of the motion and again a second figure of the detail of the fully developed motion response. The first response is critical to understand that the numerical model fully captures all effects including the maximum angle of the motions. … the reviewer understands that for the communication the long-time response is more important but for the validation the first peak is critical. Therefore the reviewer suggests presenting both.
Thank you. The reviewer is looking forward to the answers.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 3
Reviewer 2 Report
Thank you!
