Numerical Study of the Fish-like Robot Swimming in Fluid with High Reynolds Number: Immersed Boundary Method

Round 1

Reviewer 1 Report

The paper proposes an immersed boundary method, superior in handling the moving boundary conditions, is employed to simulate the movement of a fish-like robot swimming in high Reynolds number flows through a combination with the RANS turbulence model.

Following comments needed to be addressed by the authors,

1. The literature review is poor. Highlight and discuss the potential real-world applications of the robot. Authors are encouraged to add more literature to highlight the novelty of the proposed work. 
2. Add a figure that shows the appearance and hardware model of the robot in a figure. 
3. Add a discussion on how you match the actuator parameters of the model in compliance with available market hardware. 
4. Typos and grammatical errors can be seen. Please proofread the paper to correct the issues.
   

 

Author Response

Response to Reviewer 1 Comments

Manuscript Number: actuators-1727412

Article Title: Numerical Study of the Fish-like Robot Swimming in fluid with High Reynolds Number Immersed Boundary Method

 

We sincerely appreciate all the valuable comments and suggestions on our manuscript from the Editor and the Reviewers and thanks a lot for allowing us to revise and improve our manuscript. We have addressed all the comments carefully as follows. The corresponding revised manuscript with amendment tracks, highlighted in color blue, is prepared and attached with the new submission. In addition, a clean revised version is also provided to ease the manuscript readability. Please see the attachment.

 

Reviewer 1#:

The paper proposes an immersed boundary method, superior in handling the moving boundary conditions, is employed to simulate the movement of a fish-like robot swimming in high Reynolds number flows through a combination with the RANS turbulence model. Following comments needed to be addressed by the authors.

Response: We thank you very much for your detailed review and constructive comments and suggestions. We carefully followed the comments and suggestions and made the corresponding modifications to improve the manuscript. The detailed replies are given as the following.

 

Point 1: The paper proposes an immersed boundary method, superior in handling the moving boundary conditions, is employed to simulate the movement of a fish-like robot swimming in high Reynolds number flows through a combination with the RANS turbulence model. Following comments needed to be addressed by the authors.

Response 1: Thank you very much for your valuable advice. We have carefully polished the introduction by adding more references relating to the study methods, the novelty, and the applications of underwater fish-like robots as highlighted in the color blue. The complementary references are listed as follows.

1. Aracri, S.; Giorgio-Serchi, F.; Suaria, G.; Sayed, M.E.; Stokes, A.A. Soft robots for ocean exploration and offshore operations: a perspective. Soft Robotics, 2021.
2. Giorgio-Serchi, F,; Weymouth, G.D. Drag cancellation by added-mass pumping. J. JFM 2016, 798.
3. Weymouth, G.; Giorgioserchi, F.; Analytic modeling of a size-changing swimmer. 2018.
4. Armanini, C.; Farman M.; Calisti, M.; Serchi, F.G.; Renda, F. Flagellate Underwater Robotics at Macroscale: Design, Modeling, and Characterization. 2021.
5. Maertens, A.P.; Triantafyllou M.S.; Yue, D. Efficiency of Fish Propulsion. Bioinspiration & Biomimetics 2015, 10, 4.
6. Weymouth, G.D.; Yue, K.P. Conservative Volume-of-Fluid method for free-surface simulations on Cartesian-grids. J comput phys 2010, 229, 8, 2853-2865.

 

Point 2: Add a figure that shows the appearance and hardware model of the robot in a figure.

Response 2: Thank you very much for your constructive suggestion. As highlighted in blue color, we have added the hardware model of the robot fish in Figure 5 in Section 3.3. In addition, the related contents in the main text are also modified accordingly.

 

Point 3: Add a discussion on how you match the actuator parameters of the model in compliance with available market hardware.

Response 3: Thank you very much. The proposed numerical model figured out the lift and the drag coefficients at different Reynolds numbers as precise as the ones obtained from the available market hardware. The corresponding statement is added to the main text as highlighted in blue color on page 12.

 

Point 4: Typos and grammatical errors can be seen. Please proofread the paper to correct the issues.

Response 4: Thank you very much for your great advice. We have scrupulously modified the improper spellings and grammar throughout the article, as highlighted in the color green in the main text, to ensure the readability of the article.

 

 

 

Author Response File: Author Response.pdf

Reviewer 2 Report

This manuscript reports on the development and testing of an IBM with RANS-based turbulence modelling for capturing the fsi response of self-propelled bioinspired mechanisms. The manuscript does not have any major fault from a technical perspective and it is presented quite nicely and rigorously. My main concern with this manuscript is the lack of novelty. The utilization of many different kind of boundary-deformation techniques for solid-fluid coupling have been tested and in this respect this manuscript is not novel. The use of CFD models for bioinspired mechanical system is also not novel. Therefore, if the authors are looking to provide a further added value to their manuscript, they need to include additional scenarios or metrics which can be of relevance to the robotics field and which are not readily available from existing experimental data. I am listing below a number of possible addition which the authors can work on:

1) RANS model are good for certain type of applications, but IBM models have been often used with implicit-LES turbulence models which provide much better accuracy over a broad range of Re. The authors should at least cite these works and their implication for bioinspired fluid mechanics, an e xamples is Weymouth and Yue, "Conservative Volume-of-fluid method for free-surface simulations on cartesian grids" JCP.

2) if the authors intend to use their IBM for biosinpired vehicle design, they should have a better look at what the state-of-the-art is with bioinspired systems used in the aquatic environment and use that as a way to highlight the needs from a modelling perspective. I refer the authors to Aracri et al. "Soft Robots for Ocean Exploration and Offshore operation: a perspective", Soft Robotics and encourage the authors to review some novel robotics prototype which could provide an interesting case study for their CFD analysis such as flagellate-inspired robots (Armanini et al. "Flagellate Underwater Robotics at Macroscale: Design, Modeling, and Characterization", IEEE - TRO) or squid-inspired robots (Weymouth et al. "Analytical modelling of a size-changing swimmer" IUTAM Symposium on Critical flow dynamics involving moving/deformable structures with design applications).

3) speaking of IBM and turbulence models, the authors should consider recent work on highly-derformable and highly dynamics systems which have been modelled with such computational models. An example is Giorgio-Serchi & Weymouth "Drag cancellation by added-mass pumping", JFM.

4) the authors need to use their code to not only model the basic fluid mechanics paramters, but particularly those parameters which are relevant for robotics design; this in particular entails the mechanical output power, the quasi-propulsive efficiency, the froude-efficiency, the thrust. I think this will be much more informative that the contourplots provided in fig.8, 9, 10.

5) the number one added-value that a fast numerical model like this one can provide is to study the efficiency peak at various St values. The robotics research on improved thrust output and efficiency in fish-inspired robots focuses on how to maximize these parameters by modifying the elasticity of the tail. I recommend the authors to look at  manuscripts such as Maertens "Efficiency of fish propulsion", JCP and recent advances on efficiency optimization, such as Bujard et al. "A resonant squid-inspired robot unlock biological propulsive efficiency" Science Robotics.

Author Response

Response to Reviewer 2 Comments

Manuscript Number: actuators-1727412

Article Title: Numerical Study of the Fish-like Robot Swimming in fluid with High Reynolds Number Immersed Boundary Method

 

We sincerely appreciate all the valuable comments and suggestions on our manuscript from the Editor and the Reviewers and thanks a lot for allowing us to revise and improve our manuscript. We have addressed all the comments carefully as follows. The corresponding revised manuscript with amendment tracks, highlighted in color red, is prepared and attached with the new submission. In addition, a clean revised version is also provided to ease the manuscript readability. Please see the attachment.

 

Reviewer 2#:

This manuscript reports on the development and testing of an IBM with RANS-based turbulence modelling for capturing the fsi response of self-propelled bioinspired mechanisms. The manuscript does not have any major fault from a technical perspective and it is presented quite nicely and rigorously. My main concern with this manuscript is the lack of novelty. The utilization of many different kind of boundary-deformation techniques for solid-fluid coupling have been tested and in this respect this manuscript is not novel. The use of CFD models for bioinspired mechanical system is also not novel. Therefore, if the authors are looking to provide a further added value to their manuscript, they need to include additional scenarios or metrics which can be of relevance to the robotics field and which are not readily available from existing experimental data. I am listing below a number of possible addition which the authors can work on.

Response: We thank you very much for your constructive and insightful suggestions and comments. The manuscript has been carefully revised accordingly. The detailed replies are given as follows.

 

Point 1: RANS model are good for certain type of applications, but IBM models have been often used with implicit-LES turbulence models which provide much better accuracy over a broad range of Re. The authors should at least cite these works and their implication for bioinspired fluid mechanics, an examples is Weymouth and Yue, "Conservative Volume-of-fluid method for free-surface simulations on cartesian grids" JCP.

Response 1: Thank you very much for your comments and suggestions. In this paper, the direct force method of immersion boundary method was used to study the high Reynolds number. The direct force method was combined with the turbulence model k-ε, and the feasibility of the program was verified by the flow around a cylinder.

As suggested, the article “Conservative Volume-of-Fluid method for free-surface simulations on Cartesian-grids. J comput phys 2010”, as numbered as [18], is added to the introduction to make our review on the study of the fish-like robots more complete. In future studies, we will try to use the IBM model in conjunction with the implicit LES turbulence model to cover a larger Re range.

18. Weymouth, G.D.; Yue, K.P. Conservative Volume-of-Fluid method for free-surface simulations on Cartesian-grids. J comput phys 2010, 229, 8, 2853-2865.

 

Point 2: if the authors intend to use their IBM for biosinpired vehicle design, they should have a better look at what the state-of-the-art is with bioinspired systems used in the aquatic environment and use that as a way to highlight the needs from a modelling perspective. I refer the authors to Aracri et al. "Soft Robots for Ocean Exploration and Offshore operation: a perspective", Soft Robotics and encourage the authors to review some novel robotics prototype which could provide an interesting case study for their CFD analysis such as flagellate-inspired robots (Armanini et al. "Flagellate Underwater Robotics at Macroscale: Design, Modeling, and Characterization", IEEE - TRO) or squid-inspired robots (Weymouth et al. "Analytical modelling of a size-changing swimmer" IUTAM Symposium on Critical flow dynamics involving moving/deformable structures with design applications).

Response 2: Thank you very much for your valuable recommendation on the related references. Those references listed as follows are added at proper locations in the introduction. Correspondingly, some statements about the reference are also summarized in the introduction as highlighted in the color blue.

1. Aracri, S.; Giorgio-Serchi, F.; Suaria, G.; Sayed, M.E.; Stokes, A.A. Soft robots for ocean exploration and offshore operations: a perspective. Soft Robotics, 2021.
2. Weymouth, G.; Giorgioserchi, F.; Analytic modeling of a size-changing swimmer. 2018.
3. Armanini, C.; Farman M.; Calisti, M.; Serchi, F.G.; Renda, F. Flagellate Underwater Robotics at Macroscale: Design, Modeling, and Characterization. 2021.

Importantly, we will extend the application of the direct relay method to a wider range of bionic soft robots in future work.

 

Point 3: speaking of IBM and turbulence models, the authors should consider recent work on highly-derformable and highly dynamics systems which have been modelled with such computational models. An example is Giorgio-Serchi & Weymouth "Drag cancellation by added-mass pumping", JFM.

 

Response 3: Thank you very much for your suggestion. The recommended work using the IBM and turbulence models to simulate the highly deformable and highly dynamics systems is added in the introduction as numbered as [7]. In addition, the corresponding statement is also added as highlighted in the color blue.

7. Giorgio-Serchi, F,; Weymouth, G.D. Drag cancellation by added-mass pumping. J. JFM 2016, 798.

 

Point 4: the authors need to use their code to not only model the basic fluid mechanics paramters, but particularly those parameters which are relevant for robotics design; this in particular entails the mechanical output power, the quasi-propulsive efficiency, the froude-efficiency, the thrust. I think this will be much more informative that the contourplots provided in fig.8, 9, 10.

Response 4: Thank you very much for your constructive comment. We would like to say this work was initially designed to utilize the immersed boundary method of the direct force method to simulate the fish-like robots swimming in fluids. The applicability of the calculation algorithm in the turbulence model was considered. Those points reflect the novelty of this paper. As suggested, we will explore and extend the further application of the numerical methods to facilitate the design of robotic fish in the next step.

 

Point 5: the number one added-value that a fast numerical model like this one can provide is to study the efficiency peak at various St values. The robotics research on improved thrust output and efficiency in fish-inspired robots focuses on how to maximize these parameters by modifying the elasticity of the tail. I recommend the authors to look at manuscripts such as Maertens "Efficiency of fish propulsion", JCP and recent advances on efficiency optimization, such as Bujard et al. "A resonant squid-inspired robot unlock biological propulsive efficiency" Science Robotics.

Response 5: Thank you very much for your valuable advice. The content of the suggested article is of great significance to us, and we put it in the introduction as numbered as [16]. In addition, the corresponding statement is also added in the introduction as highlighted in the color blue. We will also continue to study the peak efficiency under different St values in the next step. And consider how to maximize these parameters by changing the elasticity of the tail.

16. Maertens, A.P.; Triantafyllou M.S.; Yue, D. Efficiency of Fish Propulsion. Bioinspiration & Biomimetics 2015, 10, 4.

 

 

 

 

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The authors followed some of my recommendations and provided some editing of the manuscript. They did not produce additional data nor did they revise the presentation of the data which they had produced earlier. The overall quality of the manuscript has improved mainly from an editing perspective rather than content-wise. I appreciate the author's effort to complement the literature to provide a broader background to the work.