Optimization of a Twistable Hovering Flapping Wing Inspired by Giant Hummingbirds Using the Unsteady Blade Element Theory
Round 1
Reviewer 1 Report
Dear Editor,
This manuscript, titled “Optimization of a twistable hovering flapping wing inspired 2 by giant hummingbirds using the Unsteady Blade Element 3 Theory”, focussed on designing energy-efficient flapping wings by building an optimisation model that considers geometric and kinematic parameters, vertical force constraint and energy consumption. The optimised design parameters showed that large geometrical parameters, medium amplitude of flapping angle and low frequency are key features for hummingbird-inspired flapping wings with higher Reynolds numbers. Sensitivity analysis identified wing length, flapping frequency and amplitude as the three key parameters for force generation and power consumption.
Finally, I would recommend the publication of this manuscript in Applied Sciences after the major revisions are conducted based on the comments below.
1) The contributions of the paper should to be stressed more.
2) The literature review is inadequate, and it is vital to emphasise the novelty of this study. Therefore, I strongly recommend expanding the literature review. The paper contains new original research that deserves to be highlighted. To ensure a comprehensive review, especially since this paper focuses on the dynamics of the blades to some extent, it is crucial to refer to some structural dynamics studies not mentioned in the introduction. The following can serve as examples: 10.3390/vibration4010001, 10.1016/j.renene.2021.11.006, 10.1002/we.1939, and 10.1115/GT2020-14821.
3) The manuscript should be improved regarding the language. There are significant language errors, typos and inconsistencies such as the title’s capitalisation.
4) Please insert more figures and improve the current ones in section 2 to describe the problem so that the reader finds it easier to follow.
5) For Figures 5 and similar figures, a legend is recommended and colourcode the plots. Please also expand the physical interpretation of the results.
Author Response
Please see the attachment.Author Response File: 
Author Response.pdf
Reviewer 2 Report
The paper by Dong et al. describes an optimization method, based on a blade element model, for the design of a flapping, twisting, hummingbird inspired wing. The paper is interesting and nicely written. The authors have done a good job describing a relatively complex issue very coherently. I’ve listed below some minor typos but I have no major issues with the manuscript. The two comment I will make are 1) that the description of the surrogate optimization method is difficult to understand for readers not familiar with the method. 2) it is one thing to calculate the optimal linear wing twist and another to design a flexible wing that twists that way in a flapping drone. The gap between theory and application is rather wide.
Lines 119 Remove the period and use lower case for a in “And”
Line 127 extra length, or offset but not “extra offset”
Line 229 “during the downstroke” instead of “during the downstroke stroke”
Line 242 This is not an equation, missing Cd = ?
Line 343 what is a “plat” wing
Line 486-487 Translation, pronation and pronation should be Translation, pronation and supination
Fig. 4b According to the figure (red arrows) pronation follows supination at t=0.5. These are movement and they should be separated by the downstroke. If you use a different definition please explain in in the legend. It is not clear
Line 554. Those should be these
Line 723-754 ????
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
The paper presents the optimization methodology of twistable wing for hovering flapping wing using unsteady blade element theory and numerical methods, it also presents the sensitivity analysis of various wing morphological and kinematic parameters. The authors utilize surrogate optimization models for determining optimal wing design for minimizing power density (objective function) required for wing motion. Further the plots discussed in sensitivity analysis section (3.2) seem to indicate that global minima has not been achieved. Some of the major observations are mentioned below:
Line 18 The abstract mentions higher Reynolds number, whereas in Line 362 the Reynolds number is restricted to 19000.
Line 72-74 Estimate of computation cost versus solution fidelity of both the methodologies may be given.
Line 76-78 It is stated that the literature suggests that triangular profiled wing results in least power consumption, whereas the elliptical profile is chosen for current research. The reason should be explained.
Line 90-92 It is stated that the literature suggests passively twistable wing and flat wing have similar results. The current research results also did not establish twist as a significant morphological parameter. The reason for considering twist as a potentially important design parameter should be detailed.
Line 101 Grammatical error
Line 105 Technically sound reason for selecting elliptical wing may be detailed
Line 154 Reference needs to be included
Figure 3 & Line 189-190 The irregular oscillations in rotation profiles that have been attributed to structural vibrations need more deliberation.
Sec 2.2 A significant portion of this section is a reproduction from literature. This section can be structured in a much more concise manner with using appropriate reference
Line 486-487 Pronation is repeated
Sec 3.3 and Figure 5 The plots discussed in sensitivity analysis seem to indicate that global minima has not been achieved, as the most of these present a liner change in both vertical force and power with variation with any given parameter. Further, it might be more meaningful to combine both vertical force and power required into a single parameter.
Line 648 This text should be refereeing to Figure 6.
The conclusions presented in section 4 needs to be justified in light of the comments provided above.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
I do not have any further comments and recommend publication of this manuscript.
Author Response
Thank you for your careful reading, helpful comments, and constructive suggestions.
Reviewer 3 Report
Overall the paper quality has improved, but still, there are few points that need to be addressed before the paper becomes acceptable.
See the attached file for detailed comments.
Comments for author File: Comments.pdf
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
