Cross Sectional Area of a .stl file

[sammybrush]

Hello,
I am trying to calculate the coefficient of drag of a couple of components. This is only a very basic CFD analysis that I want to undertake.

To calculate the coefficient of drag, I would like to find the largest cross sectional area of the model.

The models that I have been supplied with are .stl files, which I understand are sterolitograhy models. I do not have access to the original models.

Is there anyway of finding the cross sectional area of a .stl file within solidworks?

I have tried to extract the edges of the model and then I was going to project them onto a surface, but I cannot extract the edges of the model.

Many Thanks

 

[CorBlimeyLimey]

Are you using the Import as > Solid Body option when opening the file?

 

[sammybrush]

I have been importing it as a 'Graphics body' when I change the option to a 'surface body' I get an error saying
"The STL model has too many surfaces - Please import this model as a Graphics body"

I presume that my supplied model is generated with too many surfaces and I need to get the number of surfaces reduced?

 

[CorBlimeyLimey]

I'll take that as a "No".

 

[rfus]

big poly models bring SW to its knees, as it is a parametric NURBS based modeler, and it treats each triangle as a surface. If you have a large, high tolerance, faceted stl poly model, you are not going to have much luck with SW. If you have premium, you can bring it in using scanto3d.

Alternatives to consider. SW will bring in lots of points. You can use programs like accutrans to convert the stl into xyz's and just import all the verticies into SW through the use of the points import macro. thread559-183201
These points can be used in combo with the graphics body to build your profile.

Rhino is free for 25 saves

http://www.rhino3d.com/

. You can use it to make a cross sections. You basically need a different tool to work with poly's though.

Do you want to use cosmos to calculate the drag or do you have other FEA tools?

rfus

 

[sammybrush]

CorBlimeyLimey - yeah that is a no

rfus - I will have a look at the import point cloud and rhino. Many Thanks

I am using Phoenics to calculate the drag, but i want the frontal area to have an estimate of the answer using some hand calcs.

cheers

 

[rfus]

If you can post the files, I will cut them with my RE polygon modeling tools for you if they are not that complicated, where you need them cut.

 

[sammybrush]

Many thanks, but i do not want to burden you with extra work.
I will try and look at it myself and if i have any problems i will let you know.
Thank you very much

 

[Russell67]

If all you are concerned with is the area (l x w) then why not create a drawing, take a cross section of the area you would like, export this to a dxf at a 1:1 scale, then use this sketch to create a part and calculate the area from there.

If you are interested in volume then take smaller slices import the sketches to planes and create lines and build the part from there.

 

[MNuttall]

I had a similar problem trying to work with a large STL file. I spoke to our VAR about it and learned that Solidworks supports a maximum of 20,000 faces in a solid model and 100,000 faces in a surface model (I think I've got those numbers right). Apparently that is inherent in the parasolid format.
We purchased a license of Rhino so that we could work with it.

 

[rfus]

You are right with the 100K on the surface body. I proved it back in 2004 using this app (btw, this app rules):

http://www.daylongraphics.com/products/leveller/

exporting a grid in stl format creates twice as many triangles as there are grid nodes. found 100K to be the limit.

rfus

 

[SnowCrash]

Okay, make an assembly of the SW conversion of your .stl part with a big envelope that encloses the solid. Then make a cavity with it. You can then take cross sections of the resulting hole, or back fill with another part. Sort of like virtual lost wax casting.
"assume a spherical cow . . . "

--
Hardie "Crashj" Johnson
SW 2008 SP4
Nvidia Quadro FX 1000
AMD Athalon 1.8 GHz 2 Gig RAM

 

[dgowans]

SnowCrash,

Doesn't your method assume that the STL file can be imported with the solid body option enabled? If the STL can be imported in this manner the cross section can be generated directly with no need to use the cavity function. Did I miss something???