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Near the onset of convection in a plane layer of fluid, the flow takes the form of counter-rotating rolls. The rolls are identical, and their axes are parallel. Grammatically, which of the following sentences is wrong, and which is preferable?

  1. The rolls axes are parallel.
  2. The rolls' axes are parallel.
  3. The roll axes are parallel.

The same question about the following 3 sentences:

  1. The rolls orientation is horizontal.
  2. The rolls' orientation is horizontal.
  3. The roll orientation is horizontal.

(Grammatically, here the situation is slightly different, since "axes" is in the plural and "orientation" in the singular form, which probably may affect the answer.)

Vlad
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    I would avoid that form and use "the axes of these rolls" and "the orientation of these rolls" instead – TimR Jan 30 '24 at 15:43
  • The copyeditor prefers variants 2 in both cases. I prefer variants 1, because they are shorter; both variants 1 and 3 are used in the literature, but not often. However, the editor's correction probably suggest that they are not grammatically correct. – Vlad Jan 30 '24 at 15:54
  • I prefer "The flow of a fluid takes the form of counter-rotating rolls. The rolls are identical, and their axes are parallel." – Yorik Jan 30 '24 at 15:58
  • All right, but I'd like to check whether something is formally wrong with variants 1-3! :) – Vlad Jan 30 '24 at 16:04
  • I think this requires a level of domain knowledge outside the scope of this site. – alphabet Jan 30 '24 at 16:05
  • I do not think so. Maybe I should not have written the first 2 introductory sentences. The case is simple: you have many identical rolls, whose axes are parallel. Are variants 1-3 good enough to express this idea from the point of view of grammar? – Vlad Jan 30 '24 at 16:09
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    There are many rolls, and presumably each of them has an orientation (even if they're all the same), so you should say "the rolls' orientations are horizontal." (Although if you decide on version 3, you don't need to pluralize.) – Peter Shor Jan 30 '24 at 16:22
  • It's normal to use "roll axis" rather than "rolls axis". There are at least 10 identical questions already so I won't post this as an answer. – Stuart F Jan 30 '24 at 16:46
  • I'm seeing convective roll. – Lambie Jan 30 '24 at 17:11
  • In the research environment, everybody understands what kind of rolls are meant, so it is not really necessary to use this adjective. In a textbook, once you call them solemnly "convective rolls" as you are seeing, and then switch to just "rolls". – Vlad Jan 30 '24 at 17:44
  • "Rolls axis" is out of question, because there are as many axes as there are rolls. Please give references to the identical qns. – Vlad Jan 30 '24 at 17:47
  • This is the kind of context where it might make sense to just use: " "the axes of the rolls" – Lambie Jan 30 '24 at 17:58
  • These aren't rolls, and they therefore don't have a roll's axis. And even if they were rolls and did have a roll axis, the roll axis of a roll would not be the axis of vortex circulation. You have totally botched the nomenclature. A roll's roll axis would be at 90 degrees to the roll's axis. See why we don't want to call 'em rolls? – Phil Sweet Jan 30 '24 at 21:08
  • Phil, this convective pattern is called "rolls" for at least 60 years (I would guess, more than that). They do have axes, both in the geometric (they are bodies of revolution) and mechanical (the axes about fluid is rotating) sense. – Vlad Jan 30 '24 at 22:02
  • And that's why it's important to use the proper nomenclature for body frames and earth reference frames and fluid frames. You have vorticity, and it begins to organize itself into stable macro structures such as cells and tubes. These structures start to form stable groups, with alternating vorticity adding to the overall stability of the system. So that's what you end up with - the most stable ensemble being manifest. – Phil Sweet Jan 30 '24 at 22:20
  • I have no problem calling a sky full of radiata clouds rolls. But when you want to start looking at the anatomy and orientation of a single tube, it's time to switch to the standard vector notation and nomenclature for 3d fluid flow. – Phil Sweet Jan 30 '24 at 22:22

1 Answers1

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Variant 1, your preference, is the only ungrammatical one.

It would not be grammatical to use the plural noun rolls attributively as an adjective. Sometimes plural nouns are used in that way, but this is not one of those times.

As I commented above, I would avoid the possessive form and use "the axes of these rolls" and "the orientation of these rolls" instead.

I would also not use the singular noun as attributive adjective unless it is well established and everyone already knows what the phrase means. Is everyone agreed that "roll orientation" refers to the position of its axis relative to ... to what? gravity? Is the orientation the same in outer space as it is on earth?

TimR
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  • Orientation is not a position. An axis is a line. The orientation of a line is its direction. It is up to you to choose, in which terms you will discuss the direction. Convection in the outer space is very different from that on the surface of the Earth, because gravity is an important ingredient of the process. I am not sure the rolls will be observed there. Got your message re the possessive forms. – Vlad Jan 30 '24 at 22:09
  • Yes, position was a bad choice of word. Perpendicular to the gravitational vector? – TimR Jan 30 '24 at 22:14
  • If the fluid layer is horizontal and there is no rotation, then yes, the axes are normal to the vector of gravity. – Vlad Jan 30 '24 at 22:18
  • Indeed, this was discussed previously, e.g. here: https://english.stackexchange.com/questions/7807/when-are-attributive-nouns-plural?noredirect=1&lq=1 . Conclusions: "roll" and "rolls'" are acceptable (fine with me, because variants 3 are the shortest). And there is a tendency in modern English and in the scientific literature to tolerate modifying nouns in plural, so variant 1 will also be acceptable soon. :) – Vlad Jan 30 '24 at 23:31
  • Think what you like, but it's not acceptable here, IMO. Did you visit the link in my answer at "Sometimes"? – TimR Jan 31 '24 at 00:34