Nurbs surface (Infinite Plate with circular hole)

Hi everybody.. Im new in here and Im stuck trying to make the surface of a infinite plate with circular hole.

I made the nurbs curves, but dont know why, when I try to create the surface from those boundaries, the part of the circle loses the weight (0.707) in that control point (see the picture), so.. is it posible to create a NURBS surface (not an ordinary one)?

Im trying to work on an Isogeometric Analysis so I need the exact geometry.

Other problem is the mesh.. the mesh created does not use NURBS functions, it just aproximates the shape so its not exact.. is there a way to make a nurbs mesh (pshysical and control mesh)?

Thank you! I hope I can solve this, its really urgent

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Replies to This Discussion

Permalink Reply by Pieter Segeren on January 15, 2016 at 6:20pm

Hi Giuliana, try connecting the PlanarSurface component to the curves you've just joined
(these are planar curves, right?)

Permalink Reply by Giuliana Galaz on January 16, 2016 at 11:53am

thanks!!! :)

Permalink Reply by peter fotiadis on January 16, 2016 at 12:21am

See this as well

Attachments:

Rectangle_VS_something_V1.gh, 15 KB

Permalink Reply by peter fotiadis on January 16, 2016 at 12:52am

Added some fun more

Attachments:

Rectangle_VS_something_V2.gh, 128 KB

Permalink Reply by Giuliana Galaz on January 16, 2016 at 11:52am

Thank you peter :)

Permalink Reply by Giuliana Galaz on January 21, 2016 at 9:40am

Peter.. This surface created it seems its not a NURBS surface .. I made an script to obtain a nurbs surface from that one and what i got whas just a rectangle .. I dont know why but I cant build a nurb surface from that curves

The script that I used was:

Private Sub RunScript(ByVal x As Surface, ByRef A As Object)

A = x.ToNurbsSurface
End Sub

Besides .. when I use the "surface points", the control points and weights are not the same than the ones from "control points" (of the edge curves).

What I really need to obtain is something like this:

(im sorry for my english, I am from Chile)

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Permalink Reply by peter fotiadis on January 21, 2016 at 10:10am

Er ... the thing that you've displayed initially is a trimmed "surface" meaning a Brep (== a "surface" PLUS the trimming info). Your script gets the underlying surface (form the Brep) thus ... the rectangle.

I'll modify a bit the def in order to get what you want. But we are talking about a collection of surfaces and obviously NOT a "single" one. For instance for the "general" (so to speak) case we have 3 surfaces:

Do you want to use code for that? And why you need surfaces instead of a Brep ? (maybe for subdividing ?? if yes you can do that with another approach).

Permalink Reply by peter fotiadis on January 21, 2016 at 11:00am

Get this that works ONLY with the At Corner mode and yields (obviously) 2 untrimmed surfaces. In plain English: something with 4 edges that can being divided in U/V etc etc.

With some work more it could work with the other mode (Anywhere) as well yielding 3 surfaces.

Obviously when the cutter is a polygon ... well ... that's another animal, he he.

Still I can't get the whole scope of this ... but anyway

Attachments:

Rectangle_VS_something_V2A.gh, 143 KB

Permalink Reply by Giuliana Galaz on January 21, 2016 at 11:08am

It`s because I'm using Rhino to obtain the parameters of a surface:

- control points

- weights

- knot vectors

but until now I have been able only to obtain those parameters from curves, not from surfaces, that's what made me think that rhino does no work with nurbs surfaces, cause I couldnt been able to obtain those parameters from any surface.

Also I need to mesh the surface but with nurbs functions (not lagrange) .. I dont know yet if that is possible in grasshopper.

I've been struggling so long and I'm running out of time :/

Permalink Reply by peter fotiadis on January 21, 2016 at 12:22pm

Wait a minute:

1. Is the - a bit naive - demo provided (V2A) OK with the scope? or at last the scope as described with regard the initial question of yours (one circle at some polygon corner).

2. By mesh the surface(s) you mean divide them eh? And what means "any" surface? (probably something that "looks" like a surface ... but in fact is a trimmed one? [Brep] or a collection of trimmed ones? [Breps]).

3. Do you understand the difference between a "surface" and a Brep?

Suggestion: provide some sketches (by hand and/or by any means) that describe what you have in mind.

Permalink Reply by Giuliana Galaz on January 21, 2016 at 12:59pm

mmm .. the demo provided (V2A) works very good, but.. can I make a surface like that without the dividing line?.. why does the properties of the surface changes wheter I use Edge Surface or boundary surfaces? .. they dont work the same way?

see the surface you created know delivers me the correct control points, but I dont know whats really the difference between that surface and the one I was creating by using the boundary surface.

(I dont really understand the difference between a surface and a Brep)

Im working with a new analysis of finite elements .. so by mesh I do mean to divide the surface.. but the difference is than when you use the classical finite elemente method, the mesh is generated by polinomial functions, and they dont fit exactly the geometry, however the Isogeometric Analysis (thats what Im using) generate the mesh with NURBS functions and they fit exactly the original geometry.

If I succeeded this mesh, the division of the surface in two surfaces would be those you show in the demo.. and then I can refine that mesh into smaller elements each time. This mesh is achieved by inserting control points in the surface

Permalink Reply by Daniel González Abalde on January 21, 2016 at 1:03pm

Rhino si que trabaja con superficies nurbs, ya que su núcleo es la librería OpenNURBS, pero eso no quiere decir que todas las superficies sean nurbs.

El problema que tienes creo que es que el componente boundary surface no funciona como tu crees. Este crea una superficie plana a partir de un grupo de curvas planas, éstas se unen y encierran un espacio, los parámetros nurbs no están involucrados. Eso creo.

Solo necesitas el componente "surface points" para conocer los parámetros nurbs de la superficie.

Rhino no tiene mallas con funciones nurbs, de hecho es la primera vez que oigo eso. Tienes alguna documentación para que pueda ver funciones nurbs en mallas como las que tu quieres obtener?