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No correlation to hand calculation-Newbie Problem

Posted Jun 24, 2011, 12:17 p.m. EDT Structural Mechanics Version 3.5a 5 Replies

Frank Modica
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Hi,
I am trying to familiarize myself with COMSOL by running very simple simulations that can be checked by hand calculation.

Simple Compressive Stress Problem

Square Bar
1" x 1" cross section (in X and Y dir)
10" long (in Z dir)
10000 lb. compressive force on top 1" x 1" area
Fixed Boundary Condition on bottom 1" x 1" area
Aluminum (Modulus 10,000,000 psi, for COMSOL Material Library)

Deflection at top should be

Deflection= [(Force/Area)/(Modulus/Init Length)] = 0.010"

COMSOL Result 2.5*10^-5 inches

FEA Performed in Solidworks Simulation (COSMOS) gave predicted result.

Thank You In Advance for your counsel
5 Replies Last Post Jun 24, 2011, 6:43 p.m. EDT
Jeff Hiller COMSOL Employee

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Posted: 1 decade ago Jun 24, 2011, 12:53 p.m. EDT
Without seeing your file, it's hard to say. Can you post it?
My wild guess: your geometry may be drawn in meters (that's the default) rather than inches.
Without seeing your file, it's hard to say. Can you post it? My wild guess: your geometry may be drawn in meters (that's the default) rather than inches.
Frank Modica
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Posted: 1 decade ago Jun 24, 2011, 2:43 p.m. EDT
Jean-Francois,

Thank you for the reply. I measured the edges and they report 1 x 1 x 10 as I intended. I created the geometry via the Draw->Block command.

I am posting the file.

This brings up another problem I had. I initially brought the geometry (a 1" x 1" x 10" block) in through the Solidworks interface. The grid showed in meters, depicting the geometry as approximately .025m x .025m x .250m. I got funky results. When I measured the edges, they were .0508" x .0508" x .5080". This was a Solidworks 2010 model.

I am also posting the simple CAD Import problem.

Regards

Frank
Jean-Francois, Thank you for the reply. I measured the edges and they report 1 x 1 x 10 as I intended. I created the geometry via the Draw->Block command. I am posting the file. This brings up another problem I had. I initially brought the geometry (a 1" x 1" x 10" block) in through the Solidworks interface. The grid showed in meters, depicting the geometry as approximately .025m x .025m x .250m. I got funky results. When I measured the edges, they were .0508" x .0508" x .5080". This was a Solidworks 2010 model. I am also posting the simple CAD Import problem. Regards Frank
Jeff Hiller COMSOL Employee

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Posted: 1 decade ago Jun 24, 2011, 4:24 p.m. EDT
It looks like the load in the file you sent is set not to 1e4[psi] but to 1e4[(in.lb/s^2)/in^2]. Once you set it to 1e4[psi] you get the expected result.

The doubling of dimensions is something that I remember hearing about a while back and which I believed was fixed since. Have you tested this on the current version, 4.2?
It looks like the load in the file you sent is set not to 1e4[psi] but to 1e4[(in.lb/s^2)/in^2]. Once you set it to 1e4[psi] you get the expected result. The doubling of dimensions is something that I remember hearing about a while back and which I believed was fixed since. Have you tested this on the current version, 4.2?
Frank Modica
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Posted: 1 decade ago Jun 24, 2011, 4:43 p.m. EDT
Jean-Francois,

I see. Thank you.

How can I input a total load on a boundary, without having to calculate the x-sectional area?

In many cases one knows the total force readily, and would simply like to impose a boundary condition of that force over that arbitrary area.

Regards,

Frank
Jean-Francois, I see. Thank you. How can I input a total load on a boundary, without having to calculate the x-sectional area? In many cases one knows the total force readily, and would simply like to impose a boundary condition of that force over that arbitrary area. Regards, Frank
Jeff Hiller COMSOL Employee

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Posted: 1 decade ago Jun 24, 2011, 6:43 p.m. EDT
In v3.5a, you can have the software compute the surface area for you by way of an integration coupling variable. It's a bit clunky, but it works.
In v4.2, you have the option of providing the total force and the software does the rest for you, see screen shot.
In v3.5a, you can have the software compute the surface area for you by way of an integration coupling variable. It's a bit clunky, but it works. In v4.2, you have the option of providing the total force and the software does the rest for you, see screen shot.

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