What's the name for a 3d U shape?

Question

Imagine a tube, split in half laterally, discarding one of the halves. Does the remaining shape have a name? Like this .

@Couchy311 >implying we allow equivalence under ambient isotopy.
Then the homotopy theorist comes and calls it a point smh. — Jackozee Hakkiuz, May 15 '19 at 02:46
Are you referring to something like this? I'd like to know as well. — QuasarChaser, May 15 '19 at 03:00
@ExtremeRaider That's looks like the tip of an elliptic paraboloid. — Jackozee Hakkiuz, May 15 '19 at 03:03
@JackozeeHakkiuz so it's not the same shape that the OP is referring to? — QuasarChaser, May 15 '19 at 03:03
The description sounds like a semicircular cylinder to me. @Pink Sweetener could you post a picture? — Jackozee Hakkiuz, May 15 '19 at 03:05
@ExtremeRaider No closer to this, except the curve is half of a circle. — Pink Sweetener, May 15 '19 at 04:16
I think @JackozeeHakkiuz is the closest so far with "halfpipe". Of course, a real world halfpipe is inside of a box, where as the shape I describe is round on the outside. I've added a new picture to the question. — Pink Sweetener, May 15 '19 at 04:20
Does it look like this picture https://math.stackexchange.com/questions/531608/how-to-find-the-center-of-mass-of-half-a-torus — Q the Platypus, May 15 '19 at 04:37
@QthePlatypus nope, it's got corners, like in the image above. — Pink Sweetener, May 15 '19 at 04:41

score 3 · Accepted Answer · answered May 15 '19 at 04:34

I don't have a formal name for it but circle with a smaller circle cut out of it is an "annulus". Extruding a shape into 3d with a rectangle makes it a prism so the full shape would be "annula-prism" and a half version of the shape would be a "semi-annula-prism".

If the tube is round rather then rectangular (so it looks like a donut) it is a half-torus.

What's the name for a 3d U shape?

1 Answers1