Explicit MPC in Nastran

[InFeA]

Hi all,

Please explain the difference between RBE2 and Explicit MPc's. When do we need to use the explicit MPC's.

Thanks in Advance..

Madhu

 

[johnhors]

An RBE2 is a Rigid Body Element, in which nodes can be rigidly attached to each other. It adds an infinite stiffness to the model at these nodes.

A MPC is a Multi-Point Constraint, in which multiple nodes can be constrained.

The two have nothing in common. The RBE2 does not constrain a model, the MPC does not add any stiffness to the model.

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[InFeA]

Hi Johnhors,

Thanks for the response.

Madhu

 

[BlasMolero]

Dear Karanam05,
The RBE2 (Rigid Body Element, type 2) element with FEMAP & NX NASTRAN defines a rigid body whose independent degrees of freedom are specified at a single point and whose dependent degrees of freedom are specified at an arbitrary number of points. The RBE2 element uses constraint equations to couple the motion of the dependent degrees of freedom to the motion of the independent degrees of freedom. Consequently, RBE2 elements do not contribute directly to the stiffness matrix of the structure and ill-conditioning is avoided.

The RBE2 provides a very convenient tool for rigidly connecting the same components of several grid points together.

MPC are Rigid constraint that involves user-selected degrees-of-freedom at both grid points and at scalar points. The coefficients in the equation of constraint are computed and input by the user.

In NX Nastran from SIEMENS PLM (and with others "nastran" I suppose to run a similar way), you can use either MPCs or R-type elements (RBE2, RBE3, etc..) to model rigid bodies and rigid constraints. The MPC entry provides considerable generality but lacks user convenience. Specifically, you must supply the coefficients in the equations of constraint defined through the MPC entry. With R-type elements, NX Nastran automatically generates a constraint equation (an internal MPC equation) for each dependent degree of freedom.

Typical applications that use RBE2 entries are:
• Rigid Bulkhead
• Evaluation of Resultant Loads
• Connection of a Bar Element to a Shell
• “Bearing” Loads and remote Masses (this is more proper for RBE3)

Typical applications that use MPC entries are:
• Relative Motion
• Incompressible Fluid in an Elastic Container

Best regards,
Blas.



~~~~~~~~~~~~~~~~~~~~~~
Blas Molero Hidalgo
Ingeniero Industrial
Director

IBERISA
48011 BILBAO (SPAIN)
WEB:

http://www.iberisa.com

 

[InFeA]

Hello Blas,

Thanks for the reply.


Regards,
Madhu