Design and Analysis of a Variable Buoyancy System for Efficient Hovering Control of Underwater Vehicles with State Feedback Controller
Round 1
Reviewer 1 Report
The paper describe the design and analysis of a VBS for an AUV.
I find this paper hard to evaluate. There is obviously a merit in the wide scope and extensive documentation searching process, but I consider the actual contribution as unclear due to the information dispersion. The paper goes into low level details in many sections that, from my point of view, are not necessary, while the novelty of the proposal is not sufficiently justified.
For example, aspects like the battery selection, the DC motor characteristics, the pump scheme, the vehicle model formulation or the control algorithm are described in detail, but no relevant contributions seem to be present there.
The term proposal is used both for the analysis/design methodology, the specific solution or the control system. I would recommend a more concise paper focussed into the actual contribution the authors want to claim.
If the focus is going to be put in the design process, the methodology should be better described. Additional justification would be necessary to better describe the novelty of the proposal. In the present form, it looks just a sequence of selection steps for particular requirements.
If the focus is going to be put in the vehicle and VBS, it should be compared with solutions with similar characteristics. I have the impression that too different vehicles are selected for comparison, leading to unfair conclusions.
If the focus is going to be put in the control algorithm, more extensive simulations should be performed, analysing other alternative methods. Also, additional robustness/stability analysis is missing here.
Conveniently presented, maybe 2-3 papers could be derived from this work.
The English writing needs also extensive revision in order to ease paper readability. Perhaps I'm missing some relevant aspects of the work because of this.
Author Response
Please see Author_Closure_JMSE_20_03_2020.pdf.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
This manuscript presents a system for controlling the buoyancy of an underwater vehicle, and the control algorithm itself.
First of all, language must be thoroughly reviewed, preferably by a English native speaker.
The paper is well structured, but maybe it goes down to a too basic level in some explanations. A priori knowledge of the problem and technical skills on the reader's side can be expected.
Generally speaking, LQR control is a very well known law, some other control structures getting more profit of the buoyancy system could have been explored.
On the other hand, no comments on the extrapolation of simulation results to a possible actual implementation of the system have been provided, even though building and instrumentation details are provided all through the manuscript
Specific comments follow:
Fig. 6 does not provide information on materials, just raw labels showing mi (i=1...8).m. Further details must be provided.
Fig. 7 looks pixelated. A much better version of this graphic must be provided.
The same stands for Fig. 9
Eqs 18 and 19 have non-readable parts (subindexes). They must be fixed.
There is an unexpected question mark in Eq 2. The same can be observed in many other equations. This must be fixed.
The sentence in line 576 has no point in a scientific work
Onwards reference to Eq 34 in line 589 must be avoided, it decreases readability. Moreover, eq 28 has nothing to do with control, it's just the generic state space matrix equation for a linear system.
The rule of the overline in state model variables is not clear, it would be much better to avoid it for readability. Moreover, it's common to use bold case letters to specify that a variable is defined as a vector or a matrix. Plain case letters are reserved for scalar variables.
In general terms, LQR is very poorly explained. E.g.: Eq 29 must be an integral, and, given that the solution to LQR is obtained through eq 31, which happens to be the MARE, this integral must come with an infinite horizon limit. In addition, it has been stated that is a reference following problem in lines 574 and 575, Eq 29 must be shaped as the non-zero reference case, and therefore the solution to the overall LQR must include an input stage that depends on matrix S.
The sentence in lines 622 and 623 is not understandable: ens 24 and 28 are the same, a state model; 24 is the explicit form of 28. One is not solving the other.
It has to be explained where the values for the matrix coefficients came from
Eq 34 is not consistent with eq 24
Time scale in fig 12 is very poorly chosen: most of the 3000 s the system is in steady state. Graphics must focus on transient modes, reducing drastically the time scale, i.e. providing only the information depicted in fig 13
Author Response
Please see Author_Closure_JMSE_20_03_2020.pdf.
Author Response File: Author Response.pdf
Reviewer 3 Report
The paper deals with the design of a variable buoyancy system to be applied to AUV.
The subject is interesting, but the paper is very difficult to read, just for example, the words 'Etc.' and 'i.e' are used 19 and 56 times ,respectively.
The Introduction is fragmented in three paragraphs, with a very general sentences about AUV at the beginning, a section related to background in which are listed the main areas of power consumption and some hints about buoyancy change and a section dealing with a critical review of what have been done by other Authors. A real state of the art is missing.
Some more work is needed to make evident the reliability of the designed system, also for other but the Authors stated it at the end of the conclusion.
The paper is more similar to a technical report rather than a scientific paper, but the proposed concept seems to be promising.
In the following some minor remarks:
General comment: Please not use ' ' to define variables or parameters in the text.
line 12: Please, delete "but"
line 14: Please, delete "Autonomous Underwater Vehicles (AUVs)
line 30: Please, delete the empty space between "a" and "desired"
line 54: Please, rephrase using "consumption defined by Zhao et al. [2]"
line 103: Please, delete the empty space between "any" and "performance"
line 158: Please, use "ability" instead of "to be able"
line 160: Please, use "integration of" instead of "to integrate the"
line 163: Please, use "compensation" instead of "to compensate"
line 191: It seems to me an empty line, please verify.
line 216: Please, use the small letter for Cylindrical
line 229: Equation 2, verify the symbol for equal and add a parenthesis before π
line 281: Please define equation as 4 and accordingly change all other equation number.
lines 283 and 286: Please, use the small letter for Power
line 290: Please, use the capital letter after the full stop.
line 301: Please, insert number (6) in line 300 and not in line 301
line 337: the verb is missing, please verify.
lines 507-508 and 536. please verify the used symbols, they are not intelligible in the manuscript
Author Response
Please see Author_Closure_JMSE_20_03_2020.pdf.
Round 2
Reviewer 1 Report
The paper has been improved in some aspects. However, I still paper contribution as unclear.
The authors have modified the paper contribution section:
"our focus in this paper is to investigate the detailed design and development analysis of VBS which control the continuous mass flow rate. Mass metric analysis of the scalable design of VBS for different buoyancy capacity and computer simulation analysis of hovering performance of AUV integrated with designed VBS using efficient state feedback controller are studied in-detail."
I consider that to give more support to that comment, additional simulation performance analysis is required. The stability margin seems to be small, and alternative weighting matrices should be tested in order to evaluate the robustness, since model uncertainties could lead to poor performance in real implementation.
To better illustrate design scalability, a second AUV design example could be presented and simulated.
Author Response
Please see the file: Author_Closure_2_JMSE_28_03_2020.pdf.
Author Response File: Author Response.pdf
Reviewer 2 Report
After the modifications introduced by the authors to the manuscript, I think that it reaches the quality standards to be published in this journal
Author Response
Please see the file: Author_Closure_2_JMSE_28_03_2020.pdf.
Author Response File: Author Response.pdf
Round 3
Reviewer 1 Report
I consider the authors have improved sufficiently the paper for publication.
English writing still needs to be revised. The abstract, for example, contains several mistakes, specially in the second half.
Along the paper, there are several sentences using the structure "although/though/however ... but ..." incorrectly.
The verb show is used wrongly in form "shows" several times.
Correct "as following".
Author Response
Please see the file: Author_Closure_3_JMSE_02_04_2020.pdf.
Author Response File: Author Response.pdf
