Hydrodynamics and Musculature Actuation of Fish during a Fast Start
Round 1
Reviewer 1 Report
In this paper, the hydrodynamics of a crucian carp during a fast-start (C-type) were studied using three-dimensional CFD modeling. The study confirms previous observations of jet formation and vortex ring generation during the preparation and propulsion stages. An interesting observation of a vortex ring generated by the head during propulsion was also made. Overall, this paper is well written. I recommend this paper for publication after minor revisions. Please address the following comments:
Page 4, section 3: Please also briefly mentioned the discretization method you are using in the sovler (e.g. finite difference, finite volume, or finite element) as well as the numerical order used in the simulation.
Page 5, section 4: "f" and "ez" in Figure 4 & equations 3.1-3.2 should be explicitly defined.
Figure 5 (b-d) & Figure 6: The figures are presented at low resolution.
Equation 5: Why is this written in component-wise instead of vector form? e.g. C = F / (0.5 \rho U2 S)
Figure 8: What is the mesh resolution at this wake region? Is this resolution good enough to resolve the wake structure? Looking at the mesh in Figure 3 (b), it seems to me that the wake region has low mesh resolution along the x direction.
minor text issues:
Page 4, 2 (c): missing "." after the sentence "Therefore,we need to adjust the curve to ensure the conservation of linear and angular momentum" and missing space in ",we"
Page 5, section 4: missing space after the period in "... we calculated the internal torque T along the fish body.The internal torque, ... "
Author Response
Please see the attachment
Author Response File: 
Author Response.docx
Reviewer 2 Report
1) please carefully check the typos, e.g., "In this paper, we obtained the hydrodynamics of fish fast-start through three-dimensional CFD, then quantitatively analyze the patterns of musculature activation using the internal torque.", the tense of first-half and second-half sentence are different.
2) please elaborate the relevance of Ref. [17-22] with current study more specifically.
3) please provide the model validation with experimental results.
4) as for Page 4, please indicate why the Reynolds number is selected with about 4000 instead of around 8000;
5) the title of subsection 6.1 needs to be removed, because there is no other subsections.
6) in section 7, what is the results if the Reynolds number is further increased to 12,000.
7) please indicate what is the internal relations between internal torque and Reynolds number.
8) please provide primary findings with key data in "Abstract" and "Conclusions".
Author Response
Please see the attachment.
Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
It is recommended to be published as the authors addressed all the comments.
