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lost.identity May 17, 2009 08:22

Smoothing a curve

I'm trying to draw a smooth curve through a set of points.

The problem is I do not know the actual equation of the curve. All I've got is a set of digitized data points and these data points does not follow a smooth curve (i.e. some of them are displaced a few millimeters).

In ICEM I try to draw a curve through the points hoping that it would make a spline through them so that the curve would smooth even if the points are not. However, I find that the curve is not smooth either.

Does anyone know how I can smooth the curve?


kepeng July 5, 2009 04:12

hi, have you find the actual equation of the curves, which build from points?

I am interest in it too.

lost.identity July 5, 2009 07:55

I was able to obtain an engineering drawing of the part.

The problem that I find with ICEM is that you draw everything from coordinate points.

I used another software to draw the geometry since I now know the exact dimensions and the curvature. Then I obtained those points from this program and then imported it into ICEM.

It works now. Also, since ICEM does not have any dimensions, it's best to draw things in millimeters. This increase the tolerance and the curves you draw will be more likely to pass through the points. Afterward you can convert them back into meters by re-scaling.

kepeng July 5, 2009 19:49

en, your solution is the very good.
The capability of geometry building in ICEM is relatively weak to the CAD system, such as AUTOCad, UG.
I want to build a simple curve in ICEM from knowing points. This geometry is too simple to using other CAD systems, and it can be accomplished automatically in ICEM using the function of replay script.
However, the problem is that the equation of the curve is unknown for me. So I cannot make sure the curve generated by ICEM is the correct one.
Maybe I need to give this up and turn to your method.

lost.identity July 7, 2009 05:33

Yes, if you don't know the equation of the curve it will be difficult to do it.

When I didn't know the equation I had to digitize the image. I used a program called TechDig (I can't find that program online now but there are a lot of other programs that can do the same thing).

The problem with this method is that it is difficult to get your points to lie on a smooth curve. In my case I had to manually pick out the points, there's an automatic option as well which didn't work for me.

I suppose if you don't know the equation of the curve it will be difficult to draw it in CAD.

kepeng July 12, 2009 22:40

I query the engineering of ANSYS in China about this problem. but he knows only here used the Bspline, but didnot know any further information about the equations used in ICEM

Maybe i should compare the curve generated in ICEM with different format Bspline to find the correct one?

Furthermore, as indicated here: " ". Maybe the defaults Bspline used in ICEM.

What should the defaults be?
If there are no pressing reasons for doing otherwise, your B-spline should be defined as follows:
  • k=4 (cubic);
  • no multiple control points;
  • uniform (for a closed curve) or open uniform (for an open curve) knot vector.

lost.identity July 13, 2009 05:23

Yeah the curve generation tool in ICEM is a Bspline. So if you have a set of points it will try to draw a Bspline through them. However, I noticed that Bspline will go through each and every point, so if the points are not on a smooth curve the spline is not smooth either.

I guess the first thing is getting the points to lie on a smooth curve. The only way you can do this is if you know the equation or you know how to generate it somehow.

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