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12-17-2013 02:24 PM

Hi,

I am trying to apply an enforced rotation (on a hollow cylinder) on 3D solid hexa.

I used a RBE2 element to connect the inner diameter of the cylinder to a node in the middle of the cylinder.

I constrained the middle node on all translations (pinned) and used a enforced rotation on the middle node, but nothing happens, it doesnt rotate...

What am I doing wrong?

Thanks.

Solved! Go to Solution.

8 REPLIES

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12-18-2013 02:36 AM

Hello,

What you describe should return a fatal error: if your boundary conditions are limited to a pinned node your model is not sufficiently constrained, you need 6 fixed DOFs, and, equally important, if enforcing a rotation you first need to constrain the corresponding rotation DOF. In NASTRAN terms an SPCD is preceded by an SPC. FEMAP issues the following warning message if this isn't the case:

"Node XX, DOF Y is not constrained but has Enforced Displacement applied."

Last (but unlkely) check your RBE2: remember that 3D elements' nodes have no rotation, therefore limiting your RBE2 to rotation DOFs wouldn't work.

Hope this helps

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12-18-2013 07:39 AM - edited 12-18-2013 07:42 AM

Sorry for the partial information...

The middle node is constrained in all translations, the bottom and top of the cylinder are constrained so that they are free only to slide on their plane (to allow the rotation).

I am using sol 601 so constraining the rotation on the middle node is not necessary for my understanding.

Regarding your last point - in order to provide rotation I need to unconstrain the rotational DOFs?

But then I will have all DOFs free of constraint, what will cause rotation?

Thanks.

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12-19-2013 11:05 AM

With Nastran, ANY node that has an enforced displacement or rotation has to have that degree of freedom constrained. This includes SOL601. So in your case, if the rotation is about the local Z axis, that node must have it's Z rotation constrained.

Best Regards,

Chip Fricke

Best Regards,

Chip Fricke

Principal Applications Engineer - Femap Product Development

Chip Fricke

Principal Applications Engineer - Femap Product Development

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12-26-2013 02:23 AM

Hi Chio,

Thanks, I did constrained it and it did help.

This raises a question, when I used "displacement" load in advanced non-linear - It is not needed to constrain the displaced DOF, and everything works just fine, what is the difference between "displacement" load and the "enforced rotation" load in this matter?

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12-26-2013 06:27 AM

Hello!,

Is the same, is a way of talking: in FEMAP "**Displacement**" under "**Loads**" is what we refer as "**Enforced Displacement of Translation**".

Best regards,

Blas.

Blas Molero Hidalgo, Ingeniero Industrial, Director

IBERISA • 48004 BILBAO (SPAIN)

WEB: http://www.iberisa.com

Blog Femap-NX Nastran: http://iberisa.wordpress.com/

IBERISA • 48004 BILBAO (SPAIN)

WEB: http://www.iberisa.com

Blog Femap-NX Nastran: http://iberisa.wordpress.com/

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12-26-2013 09:35 AM

Hi Blas,

So why is it not necessary to constrain the DOF if I use "displacement" in sol 601?

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12-28-2013 12:37 PM

Dear Assafwei,

With Advanced NonLinear (SOL601) module you do not need to constrain the DOF where you prescribed an enforced displacement of translation or rotation because is not used the NX Nastran solver, but ADINA solver.

To clarify this better, with NX NASTRAN there are two methods available to you for specifying an enforced displacement at a component.

- The first method is to enter the value of the enforced displacement directly on an
**SPC**entry. - The alternate method (used in FEMAP) to enforce a displacement at a component is
**to use the SPCD Bulk Data entry**. The SPCD entry is actually a force, not a constraint, but it is used in conjunction with an SPC entry to enforce the displacement. When you use an SPCD entry, internal forces are computed that are applied to the structure to produce the desired enforced displacements.

**Grid points with an enforced displacement using the SPCD entry must also appear on an SPC or an SPC1 Bulk Data entry.**

The SPCD method of enforcing a nonzero constraint is more efficient than using an SPC entry alone when you're using multiple subcases that specify different constraint conditions. Note also that when you use an SPCD entry, the displacement values entered on the SPC entry are ignored. The software only uses the SPCD values.

Best regards,

Blas.

Blas Molero Hidalgo, Ingeniero Industrial, Director

IBERISA • 48004 BILBAO (SPAIN)

WEB: http://www.iberisa.com

Blog Femap-NX Nastran: http://iberisa.wordpress.com/

IBERISA • 48004 BILBAO (SPAIN)

WEB: http://www.iberisa.com

Blog Femap-NX Nastran: http://iberisa.wordpress.com/

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12-28-2013 12:50 PM

Thanks Blas!

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