Volume Measurement

[Anonymous]

I'm trying validate the accuracy of a 3d model by measuring the volume of an ellipsoid cap shape shown below (green section).

With the specified dimensions, according to the calculation the expected volume should be 706.858 cubic units,

Fusion 360 doesn't provide a simple method to create an ellipsoid shape. To create the equivalent object with Fusion 360 I created 3 orthogonal Ellipses and used the loft tool based on the technique shown here http://autode.sk/1X0rfqB . The volume measurement from properties reports a volume measurement of 686 not the 706 value I was expecting. I attempted the drawing several times but the never achieved the expected value.

Not giving up, I repeated the exercise using 3 orthogonal circles and the loft tool to create the quadrant of a sphere. Again the volume measurements differ from the expected calculated value.

One other point, mirroring a quadrant of the sphere using this loft method does not produce a smooth hemisphere. A visible seam in noticeable at the join which could account for the difference in the volume measurement.

Any help to resolve this issue to obtain the correct volume measurement would be appreciated.

[wilkhui]

Hi Graham - thanks for raising this, we'll have a look.

Indy

[wilkhui]

Oops, looks like we need to update that video to avoid making the seam..!

You'll need to create extruded support surfaces from those input edges, which will allow you to set G2 boundary conditions like so:

Unfortunately you won't be able to add a third G2 condition (on Rail1 in my picture) because it causes a mathematical conflict. So you'll still get a seam if you tried to mirror the lower half 

It's possible that this T-Splines method is more accurate, I'll give it a shot and report back.

Thanks for your patience!

Indy

[wilkhui]

The T-Splines method is certainly closer..!

[Anonymous]

Thanks Wilkhu for the response. The T-Splines method is definitely closer to the expected value.

One of our CAD designers tried to create the same part using SW. I've attached the volume measurement output for reference.

[wilkhui]

Hi Graham,

Sorry about the delay in responding!

A simpler way to get the ellipsoid is to use non-uniform scaling on a sphere. I recorded a Screencast to show how, hopefully the below helps:

Cheers,

Indy