Research on the Vibration and Wave Propagation in Ship-Borne Tethered UAV Using Stress Wave Method

Round 1

Reviewer 1 Report

This research addresses the vibration characteristics of ship-borne tethered UAVs under taut-slack conditions by using the Hamilton’s principle and dimensional analysis. The goal was to see if the numerical results and the experimental results match closely and whether the impact of equilibrium curvature has any relationship with the longitudinal and transverse waves. Therefore, the main question of this research covers generating the governing equations for the UAVs for vibration characteristics, developing the experimental model and from there, finding the connection between the excitation and natural frequencies and between the impact of equilibrium curvature to longitudinal and transverse waves.  

To the reviewer’s understanding and based on the context present in this manuscript, the topic seems original, although relationship between excitation and natural frequencies are investigated by the researchers in the past for many vibration problems. It seems that it does not address any specific gap in the field up to the current context.  

So far, there is not that much significant study conducted on the dynamic behavior analysis of the ship-borne tethered UAVs under taut-slack conditions because of the influence of the ship motion at one end and attached to the UAV platform at the other end. Therefore, this research adds the corresponding wave dynamics equations for the ship-borne tethered UAVs. In addition, this research adds a numerical analysis of the tension and velocity of ship-borne tethered UAVs under the conditions of the ship's heaving which is performed by the characteristic line technique.

When developing the mathematical model, the authors can consider a nonlinear material model for further improvement. The current research includes a linearly elastic model.  

The authors presented various types of results and arguments in this paper including the variation of dynamic strain with frequency, dynamic tension spectrum, variation of dynamic strain with amplitude, and dynamic tension and distribution diagrams to represent their results. In addition, the authors performed dimensional analysis to conduct experimental research on the tethered UAVs. From all these types of results, it seems that the conclusions of the research regarding the investigation of the dynamic characteristics of the ship-borne tethered UAVs are consistent with the results and evidence presented. Also, in the model experiment, for the constant excitation frequency, the maximum dynamic tension at different positions of the tethered UAV system fluctuates and increases which is consistent with the theoretical results.

The references seem appropriate. Some references are cited from papers published within the last three years and overall looks appropriate.  

The general format of the tables and figures looks standard. However, the reviewer is not sure about the specific format requirement of the journal and therefore, prefers to comment only on the general format of the tables and figures. 

This paper is well written and can be recommended for publication.

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

In the reviewed paper vibration behavior of ship-borne tethered UAVs under taut-slack conditions is discussed. A set of wave dynamics equations for the ship-borne tethered UAVs are created, and a numerical analysis of the tension and velocity of ship-borne tethered UAVs under the conditions of the ship's heaving is carried out via the characteristic line technique.

The issues discussed in the work are in line with contemporary research trends in the field. Unfortunately the authors did not clearly and lucidly highlight new and original elements of their work.

My critical remarks concerned mainly the editorial side of the work.

Firstly, please the add nomenclature.
Secondly, taking into account the number of formulas and variables, nomenclature should be introduced.The legends in Figs. 4, 5, 7, 14 are incomplete (no units for the ordinates). Please complete this. The descriptions under Figs. 8 and 9 require correction. There is no clear distinction between the analyzed cases. The descriptions and legends of Figs. mentioned in the review comentary are unclear or hardly legible (e.g. which result is for working condition 1.4 and which result is for working condition 1.5 in the Fig. 9). Table 2 does not include the units of the presented physical quantities (etc).
In the opinion of the reviewer, the simulation results should be properly compared with the results of experimental tests (there is no measure of model compliance with the results of experimental tests). I have not found a criterion for comparing the simulation results with the results of experimental research (and it would be good to have such data in the paper).

The conclusions and references generally look good.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Dear Authors,

 Tethered UAVs have a wider range of potential applications and the benefits of lengthy hovering durations and plentiful power over regular UAVs. There are few studies on the dynamic response of ship-borne tethered UAVs under taut-slack conditions due to its complex dynamic boundary condition from the ship motion and the UAV platform. Based on this and considering the actual engineering problems, it is very important to research the vibration and wave propagation in ship-borne tethered UAV. Moreover, it is interested to apply stress wave method dealing with this problem and the computational and experimental models are quite useful, and I am recommending that your paper be considered for publication in drones. However, there are some issues with the work. The principal ones include:

 

(1) In lines 134 to 135 of page 4, as you stated, the in-plane equations of motion are coupled with each other, but are the out of plane equations coupled? And why do you only consider the boundary conditions of the in-plane equations.

 

(2) In lines 156-157, suggest giving the equation deducing process more detailed.

 

(3) In lines 223-226, it is interested as that the responses change from only the longitudinal wave to coupling characteristics of a transverse wave and longitudinal wave, and could you increase to simulate this change in the Numerical simulation Section, because it may give a significant impact on the stability of the system.

 

(4) Suggest giving introduction of the characteristic line numerical method more detailed, for example add some references about this method.

 

(5) the subtitle of Figures 5, 6 and 8 are tedious and repetitive, for example, suggest Figure 5 as The number and magnitude of the amplitudes and frequency response curve of top dynamic strain at different excitation frequencies, (a) ? = 0.24Hz, Ae = 2m, (b)…, (c) …and (d).

 

(6) In lines 294-297, you stated that “Figure 5(b) shows that when the excitation frequency approaches the first natural frequency, the amplitude jumps from the single-periodic component to the multi-periodic component, subharmonic responses, and the multiply periodic response and subharmonic response appear”, Is this conclusion universal? And could you give its reason by theory qualitatively, then it will be more rigorous and systematic.

Comments for author File: Comments.pdf

Author Response

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Round 2

Reviewer 2 Report

Manuscript can be published in the present form.

Reviewer 3 Report

The authors have substantially and satisfactory revised the manuscript according to the reviewer's comments. This revised manuscript can be accepted for publication.