Curvature continuity analysis

[CADfan]

Dear all,

I am facing, some problem in the Curvature continuity. Here to create an airfoil profile, i used three curves,one top curve, one bottom curve and a nose curve.(conic curve). All the curves are tangent to each other, but the curvature continuity condition are not satisfied. Can somebody give me, a clue to make the curves to have curvature continuous. See the airfoil profile with curvature spikes in the attachment.

And also what is preferred values for the minimum and maximum curvature values to have the smooth curve.



Thanks,

CADfan

 

[Jacoolo]

if you accept to make the airfoil made of 3 curves by "hand" I would replace them with the one, or more created inside ISDX(Creo 2.0) which allows for higher order curves than default 3 deg.

explicitly, the default order of spline in Pro/E causes such problem. I think you can solve this problem a little bit by controling the polygon of spline in sketcher within extra relations, but take it in mind that, this has it own pros and cons

to evalaute this solution(control polygon driven by relations), please check following posts of jeff4136

http://www.mcadcentral.com/search.php?searchid=93095

http://www.mcadcentral.com/creo-tips-tricks-part-modeling/16559-vss-b-spline-secti-ns.html

http://www.mcadcentral.com/creo-tips-tricks-part-modeling/6555-c-nic-secti-ns.html

 

[CADfan]

Thanks muadib3d. I was looking for the different solutions. I try your suggestions.Thanks again.


CADfan

 

[tobbo]

"All the curves are tangent to each other, but the curvature continuity condition are not satisfied" . Well i guess not because they are tangent and dont have a curvature condition...

If you specify curvature instead of tangency you will get closer to what what you want. You can either replace the "nose curve" with a "curve thrue points" and set it to be curvature at the ends, or , as Jacek says , use Isdx to create either just the nose curve, or perhaps all three curves. If you will use three curves, then you will probably have to tweak them a bit to get a smoother graph.

Using creo2 will give you the opportunity to create highorder curve (above deg3) , and that mght be helpful for this case

//Tobias

 

[cpoirier]

I have a question. What will be the result if you select all 3 curves and convert to a spline?
Chris

 

[Jacoolo]

the result would be the one bezier curve(spline), with tangency/curvature maintained all along. Sometimes it is as solution, sometimes not.

 

[CADfan]

Tobias,
Thanks a lot for your suggestion.But if i select two curve where it joins and right click on the screen, the tangency and coincident options only shown. OK i try to use ISDX.


Thanks,

CADfan

 

[CADfan]

curvature continuity on single curve

Jacek,Tobias Larsson & Chris,

Here is the airfoil with single curve. As Jacek &Tobias Larsson said, both tangency and curvature continuity maintained in the single curve. And i realized that it need some practice to adjust the control polygon to bring the smooth curvature. Still i couldn't overcome a kink which is marked on the attached image. Hope this issued will be solved if ISDX is used.

Thanks,

CADfan

 

[Jacoolo]

first - I suppose "the kink" reflects the place you inserted a point in the spline while creating it

second - I assume indicated by you point in the graph does not relate to real area on the spline, imho this is the point where curvature changes the direction between positive/negative values.

third - I doubt you can obtain the curvature plot(no kinks) with desired plot of curve within default Pro/Engineer 3 deg bezier curve(spline)

you should accept it or take advantage of higher order curves(different software or ISDX in Creo 2.0)

 

[CADfan]

Jacek,

You are absolutely correct for all three points.

First - To maintain the airfoil shape, i inserted a point where the kink shown on the curature spike. If i delete that point, the curvature becomes smooth, but it doesn't maintain the airfoil shape

Second- You are right.Once, after posting my reply i noticed that, i marked in the wrong location in the curvature graph.

Third- I manually adjusted the control polycon to get the desired plot. But i realized that, this may not be the cutting edge method to proceed. Then i stopped. I am not familiar with ISDX. Hope i can get both correct shape and curvature continuity when using ISDX


Thanks a lot for your support.


Thanks,

CADfan

 

[tobbo]

when making splines, try to always minimize the number of points and use polygons instead to adjust the shape. Even if you are just making a "C" , do it with a 2 point spline and tweak it with polygons. Makes "better" (more clean) surfaces.

//Tobias