Helical strakes on flexible riser

Hi, can i ask how to do the helical strakes on flexible riser with constant height and different pitch? I managed to do the strakes using helix and pipe but the helical strakes on the riser have its on height. My design should have three-start of square-shaped helical strakes but i only manage to do only one start. Can anyone gives me an idea how to solve this?


Hi -
Just some clarifications…
You have posted this question in the Rhino Developer > rhino3dm category. That might be the wrong category for a question related to geometry creation. Are you writing a program and, if so, in which language?

In any case, it would be easier for others to help you if you post what you have managed to do so far.

Oh it seems like i posted in wrong category. I am asking for geometry creation. I am so sorry for the inconvenience.

Hi -

In that case, if you create one of them, you can simply use ArrayPolar to create 2 copies in a polar array. Please post your file if you wonder about anything else.

This is where i managed to do so far. One start of helical strakes with round cross-sectional. I need to do a domain, tube with 2 or 3 number of start of helical strakes with square shaped cross-sectional. I also have trouble in doing the boolean difference between the tube and the strakes. I want to eliminate the inner part of the strakes but when i do the boolean difference, the whole domain is disappear. I need to redo the domain again. Do you have any idea how to solve this? TRIAL 1.3dm (823.4 KB)

Hello - is the attached something like what you need?

TRIAL 1_maybe.3dm (781.5 KB)


Hi, omg yes. This the square sectional that i need. Can you teach me how to do it?

Thank you so much for helping me.

Hello -

  1. CPlane > Curve to the end of the helix

  2. Rectangle > Center start at 0,0,0

  3. Sweep1 > Roadlike

  4. Cap the result


Please see http://docs.mcneel.com/rhino/6/training-level1/en-us/Default.htm


1 Like

Alright thank you so much.

Hi, how you adjust these point? I cannot sweep the geometry.

Hi -

You click on the point to select it and then click again to place it somewhere else.

From your picture, adjusting that point won’t really change anything. Can you post your file and explain what is going wrong?

So i am trying to do 3 helical strakes at one domain with triangle-sectioned strake. I But I dont have the idea how to do the strakes without intersect which each other. The pitch between the 3 strakes are 5mm. I already did the triangle to do the closed sweep on the rail but I stuck on how to do the 3 strakes without intersect all of them. The picture I attached is the top view of desired design but i change it to triangle-sectioned strake. I need to do the 3 starts of the strakes but i dont know how. CASE STUDY 0.5D.3dm (32.2 KB)
.cross section

You can draw a helix with 15 mm pitch.
Then a triangle on the end of the helix. The command to use here is Polygon, with the option ‘AroundCurve’ in the command line…

Once you have the swept surface, type cap.

Then PolarArray the surface 3 times.

CASE STUDY 0.5D.3dm (299.3 KB)