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Applying a moment Directly

Creator
Creator

Hello,

 

Starting off with a little background, the analysis I’m attempting to run is a bolted Monopole that is about 60 ft tall subject to wind loading. Now I’m not wanting to model 60ft of pole structure otherwise I’d be waiting for the analysis to finish for days so instead i cut the pole leaving a couple of inches protruding above the weld.  I have a direct shear value I’m going to add to the pipe, with an additional moment (across the highlighted area) I’d like to add to representing the reaction the pipe provides. I'm still pretty fresh moving from Abaqus to FEMAP so I’m still learning the ends and outs. I've got the model setup with the shear loading but cannot seem to figure out the bending moment portion. Any help would be greatly appreciated. 

 

I have attached an image which shows the configuration along with the highlighted area representing the area which the shear and moment are to be applied to. 

 

-Jerod

7 REPLIES

Re: Applying a moment Directly

Solution Partner Phenom Solution Partner Phenom
Solution Partner Phenom

Dear Jerod,

You can apply any loading at the surface meshing with an spider rigid RBE3 element, make sure to activate ALL the six DOFs at the DEPENDENT node (the center node). Also, make sure to activate only the translational DOFs TX, TY, TZ at the INDEPENDENT nodes.

rbe3-dof.png

rbe3.png

Best regards,
Blas.

PD
1.- To reduce the model size by a factor of 10 and increase the solution accuracy at the same time I strongly success to mesh with HEX 8-nodes elements.
2.- To learn more about RBE2/RBE3 elements visit my blog in the following address:
https://iberisa.wordpress.com/2015/10/13/rbe2-vs-rbe3-on-femap-with-nx-nastran/

 

Blas Molero Hidalgo, Ingeniero Industrial, Director
IBERISA • 48004 BILBAO (SPAIN)
WEB: http://www.iberisa.com
Blog Femap-NX Nastran: http://iberisa.wordpress.com/

Re: Applying a moment Directly

Creator
Creator

Blas,

 

Thank you for your prompt reply. I'm still figuring out all the features and lingo of FEMAP, but I’m guessing RBE3 elements are similar to Abaqus's feature of tying a surface/node-set/element to a single node. That way you can toy with that one node which in return translates to your tied region? Just wanting to make sure I understand the logic behind RBE3. 

 

-Jerod

Re: Applying a moment Directly

Siemens Genius Siemens Genius
Siemens Genius

Here's a little info from the NX Nastran Element Library Reference:

"The RBE3 element is a powerful tool for distributing applied loads and mass in a model. Unlike the RBAR and RBE2 elements, the RBE3 doesn’t add additional stiffness to your structure. Forces and moments applied to reference points are distributed to a set of independent degrees of freedom based on the RBE3 geometry and local weight factors."

Re: Applying a moment Directly

Creator
Creator

Blas,

 

I'm having difficulty defining the point i wish to tie the region to. I have attached an image of what i'm talking about. If i use the "new node at center" its going to throw the controlling node at the COG and not at the center of the pipe. What is the best way to define a new node for this purpose? 

 

-Jerod

Re: Applying a moment Directly

Siemens Phenom Siemens Phenom
Siemens Phenom

From your screen shot, it appears that you can apply a Torque load to surfaces.  You define an axis to apply the torque load around.

Best Regards,
Chip Fricke
Principal Applications Engineer - Femap Product Development

Re: Applying a moment Directly

Creator
Creator

Chip,

 

The first image i sent only had the shear loading put onto it, i quickly learned trying to add a moment directly to this surface was not working. I'm attempting now to tie this region to a single node and add both the shear (X direction) force and the bending moment loading (about the Y axis).  I understand you need to apply the torque about an axis but first i'm trying to tie this region together. Is this not the correct approach?

 

-jerod

Re: Applying a moment Directly

Siemens Phenom Siemens Phenom
Siemens Phenom

Chip is correct, the Moment Load in FEMAP gets expanded to nodal moments.  For a solid mesh, there are no DOFs in rotation, therefore they don't do anything.  Use the Torque load in FEMAP, it expands into nodal forces to achieve the torque specified.

 

Mark.