Mesh Control – A Double Edged Sword

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When running simulations, mesh density is important.  Coarser meshes solve faster but are less
accurate; while finer meshes are the opposite, slow but accurate.  While one way to reach the middle ground is to
have the density right in the middle, a more accurate way would be to use mesh
control.  Stress concentrations most commonly
occur along edges, especially sharp edges. 
On edges and other areas where accuracy is important, mesh control is a
great way to keep that accuracy while keeping time down as well.  To demonstrate this, a tensile test was
simulated with a notch cut into it.  

Tensile test

Simulations were then completed in mesh densities of coarse,
in the middle, and fine with simulation time, mesh element size, and maximum
stress were measured.

Course
Coarse

Regular
In the Middle

Fine
Fine

Mesh Size

Time

Max Element Size

Max Stress

Course

>1
sec

10.06 mm

433.2
MPa

Regular

4 sec

5.03 mm

469.1
MPa

Fine

54 sec

2.52 mm

479.9
MPa

Once these simulations were complete, three simulations were
done using mesh control on the notch using a regular mesh size for the rest of
the part.

Mesh 1Mesh Control 1

Mesh 2
Mesh Control 2

Mesh 3
Mesh Control 3

Mesh Size

Time

Mesh Control Size

Max Stress

Mesh Control 1

4 sec

2.52 mm

571 MPa

Mesh Control 2

5 sec

1
mm

693.8 MPa

Mesh Control 3

115 sec

.05 mm

33205
MPa

In the first instance of using mesh control, with the mesh
control size being equal to the fine max element size, the stress found was
very accurate, coming close to that found in previous tests.  As the mesh control size was decreased
however, a new problem
developed.  The stress found grew at an
alarming rate.  The yield strength of
this material is 620.4 MPa.  According to
the studies done with mesh control, the part breaks easily while in all
actuality does not.

Mesh control is an invaluable tool in being accurate and
saving time.  It is important however to
not try and refine the mesh too much, or else the entire simulation will be
rendered useless.

Chad Whitbeck – Applications Engineer

Computer Aided Technology Inc.