Surface Patterns for Drag Modification in Volleyballs

Round 1

Reviewer 1 Report

This an interesting paper but there is something wrong with the range calculations of around 150 m. If a ball is launched at 15 m/s at 25 degrees in a vacuum, the range will be 17.6 m. So how can the range possibly be 150 m?

Fig 3(a) does not look realistic. Can you provide a realistic y vs x trajectory?

When these problems are fixed I can review again.

Author Response

A1. This an interesting paper but there is something wrong with the range calculations of around 150 m. If a ball is launched at 15 m/s at 25 degrees in a vacuum, the range will be 17.6 m. So how can the range possibly be 150 m?

---The range was actually ~15 m. Fig. 3(c) and its caption were revised (see Page 7 in the revised text).

A2. Fig 3(a) does not look realistic. Can you provide a realistic y vs x trajectory? When these problems are fixed I can review again.

---Fig. 3(a) shows a schematic view of flight trajectory. The real data were summarized in Fig. 3(c), based on measurements of horizontal (H) and lateral (L) distances.

Reviewer 2 Report

See attached file.

Comments for author File: Comments.pdf

Author Response

B1. Page 1: “At low speeds, the wake is large and the drag is high, while for a ball moving faster than a certain speed, the wake suddenly shrinks and the drag plummets.” Replace “drag” with “drag coefficient”.

---Corrected (Page 2 in the revised text).

B2. Page 2, second line from the bottom: life coefficient -> lift coefficient

---Corrected (Page 4 in the revised text).

B3. Section 2 “Experiments”:

B3-1. force measurement on a sphere are largely influenced by the type of support used for the sphere. Give details about the support (in figure 2 top-right it is shown that the balls are supported from the back: mention it in the text). What is the diameter of the rod? Please specify it.

---Actually, the ball was supported from the back support that was made of a rod with 0.8 m length and 0.02 m width. We added this comment in the revised text (Page 4).

B3-2. Give (quantitative) details about the difference between “Conventional” and “Surface-modified” volleyballs.

---The main features of conventional and surface-modified balls were same as follows: their diameters were 21 cm, circumferences 65-67 cm, and weights 260-280 g. The difference was given as follows: six-panel and smooth surface for conventional balls (Adidas AV514RB and Mizuno 9OV80027), while six-panel and hexagon-patterned surface (Molten V5M5000) and eight-panel and dimpled surface (Mikasa MVA200CEV) for surface-modified balls. We added the ball details in the revised text (Page 4).

B3-3. Perform an uncertainty analysis of the drag coefficient results reported in figure 2.

---Two additional data for each case were added in Fig. 2 to check out the experimental uncertainty. As clearly seen, all the data were reproduced. For clarity, Fig. 2 and its caption were revised (Page 5).

B4. Page 5: “and their flight distances can be controlled to have the longest distance (Molten) or the shortest distance (Mikasa)”. It is not clear how the flight distances can be controlled via modification of the surface of the volleyballs. Please explain or provide a criterion.

---The flight distance modification by surface pattern was explained in the following paragraph (Page 8). We just added the comment before starting the paragraph like: “The flight distance modification by surface pattern may be explained by the drag coefficients.”

B5. General comment: I could not grasp on what basis the authors make conclusions on the isotropy or anisotropy of the aerodynamics of the different volleyballs tested. In my opinion, since the authors do not show the results of lift and side forces, no conclusions can be drawn on whether the aerodynamics of the volleyballs is isotropic or anisotropic.

---We added the results of lift and side forces in Fig. 4 (newly added). This figure shows that the isotropy of the aerodynamics would be relevant to the isotropy of the surface pattern (see Fig. 4 and Page 8).

Round 2

Reviewer 1 Report

This paper presents results of testing the aerodynamics of different volleyballs. I am happy to accept the paper with a few minor corrections, as indicated on the annotated pdf version of the revision (attached).

Comments for author File: Comments.pdf

Author Response

This paper presents results of testing the aerodynamics of different volleyballs. I am happy to accept the paper with a few minor corrections, as indicated on the annotated pdf version of the revision.

A1. “A turbulent ow pulls straight back on the ball and slow it down.”

---Changed as “A turbulent flow causes to slow the ball down.” (Page 2)

A2. “The rapid decrease in the drag force is known as drag crisis, which is responsible for why volleyballs can swerve unpredictably by as much as a meter.”

---Changed as “The rapid decrease in the drag force is known as drag crisis.” (Page 2)

A3. “would be”

---Changed as “are” (Page 2)

A4. “166 ~ 172 m” and “127 ~ 141 m”

---Changed as “16.6 ~ 17.2 m” and “12.7 ~ 14.1 m” (Page 6)

A5. “Therefor”

---Changed as “Therefore” (Page 8)

Reviewer 2 Report

I thank the authors for having addressed my comments. I can now recommend the paper for publication.

Author Response

I thank the authors for having addressed my comments. I can now recommend the paper for publication.

---We are very grateful for the final recommendation for publication.