Guidance-Based Path Following of an Underactuated Ship Based on Event-Triggered Sliding Mode Control

Round 1

Reviewer 1 Report

In this paper underactuated dynamics of ship motion is studied. The extended state observer (ESO), is also used to design controller. The trigger time event-triggered mechanism (ETM) is included and Lyapunov theory is used to show that closed-loop signals are bounded.

     ·         Introduction is extensive enough

·         The kinematic model is unclear (in eq 2 is unclear, please reconsider the form  “a tan 2[..]” and also the notation for derivative describing partial derivative; in eq (8) we have “arctan” probably for the same function and explain notation for \psi_d; the conclusion from (10) unknown for c₁ and \Delta_2, so on.).

·         Please review the transition from eq 24 to eq 25 and explain the significance of the parameer \rho.

·         Please rewrite the equations in better format in section 3 at least (line after eq 12 is totally corrupted). Write few words about Lyapunov theorem used in eq (27) (and over the paper for Lyapunov functions defined)

·         The last line of the Table 1 is on other page

·         Review English

Comments for author File: Comments.pdf

Author Response

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Reviewer 2 Report

The authors have proposed an event-triggered SMC based control for ships coupled with state-observer. The paper is interesting and theoretical development is good. However, it lacks evidence on the improvement over state-of-the-art. In this direction, the following suggestions should be noted for the revised version:

1. The authors need to revise the literature survey as it misses some recent works on ships which employs state observer ("A switching control perspective on the offshore construction scenario of heavy-lift vessels", "Robustifying dynamic positioning of crane vessels for heavy lifting operation", "Observer-based robust control for dynamic positioning of large-scale heavy lift vessels").

2. Authors need to sufficiently motivate why event-triggering is required in ship control. Generally, it is a slow system and resources in practice for ships is sufficient. Then, what is the need of such mechanism?

3. The proposed controller does not address parametric uncertainty, whereas, current literature can address them for ship either in robust (see the above mentioned work) or adaptive ("An adaptive control framework for underactuated switched euler-lagrange systems") way.

4. Authors need to give comparative simulation with existing results. 

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The kinematic model remains unclear (in eq 2 is unclear, please reconsider the form  “a tan 2[..]” and also the notation for derivative describing partial derivative; in eq (8) we have “arctan” probably for the same function a; the conclusion from (10) unknown for c₁ and \Delta_2, so on.). 

Write few words about Lyapunov theorem used

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

No further comments

Author Response

Thank you very much for your approval of this paper.