Torsional mass moments of inertia for CROD and CBAR elements (Nastran)

If you are working with Simcenter Nastran, you can use the TORSIN parameter to optionally include the torsional mass moment of inertia in the CROD and CBAR element mass matrices. By default, Simcenter Nastran does not calculate torsional mass for CROD or CBAR elements, though it does for CBEAM elements. This can lead to differences when you compare results between equivalent models.

The TORSIN box in the Solution Parameters dialog box (available from the Modeling Objects Manager dialog box) lets you control the setting for this parameter:

• If you enter 0, the software does not include the torsional mass moment of inertia for CROD and CBAR elements (the default).

• If you enter 1, the software includes the torsional mass moment of inertia for CROD and CBAR elements.

• If you enter 2, the software includes the torsional mass moment of inertia for CBAR elements only.

• If you enter 3, the software includes the torsional mass moment of inertia for CROD elements only.

For more information, see Specifying parameters for Nastran analyses.

CBAR axial torsional mass moment of inertia calculation

Simcenter Nastran calculates the CBAR axial torsional mass moment of inertia similarly to the CBEAM element using the equation:

Ixx = ρL(I1+I2)

where:

Ixx = torsional mass moment of inertia

ρ = density

L = the length of the element

I1 and I2 = area moments of inertia

CROD axial torsional mass moment of inertia calculation

Simcenter Nastran calculates the CROD axial torsional mass moment of inertia using the equation:

Ixx = ρLIx

where Ix = J = torsional constant.

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Torsional mass moments of inertia for CROD and CBAR elements (Nastran), Simcenter 3D 2021.1 Series

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