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Developing Breakout Models in FEMAP

This presentation includes:

• Definition of Breakout Models

• When to use breakouts

• [Tutorial] Adding a pass-through in a wing rib

• [Tutorial] Adding boss to orthogrid pressure plate

Presenter: Ryan Tatman

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Presentation Summary

• SDA Overview

• Breakout Definition

• When to use breakouts

• Example - Adding a pass-through in a wing rib

• Example – Adding boss to orthogrid pressure plate

• Conclusions

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What is a breakout model?

• A breakout model is an analysis model created to represent a portion of a large structure in order to get more specific information.

Example: Assessing the stress concentration in the joint shown below

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When is a breakout model needed?

• When a small design change requires analysis

– When a small portion of a large design needs to be iteratively designed

– When a feature is added to an existing part

• When examination of localized stress risers is needed

– When the size of a model does not allow for the fidelity needed in specific locations

– When stress information is needed for a fillet or pad-up in a plate model

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Example - Small Design Change

• Adding a pass-through to a wing rib VIEW THE DEMONSTRATION

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Map Output from Model

• Model -> Load -> Map Output from Model

Source Model

Elements/Nodes to take results from

Output sets to take results from

What data to take

What to do if there is no data for a node or element in target model

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Example – Local Stress Riser

• Large orthogrid pressure plate with bolted exterior supports

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Popular Options

• Hex-Mesh the area of the model

– No element doubling

– Element penetration

– Element skins

• Pull nodal displacements and rotations from the analysis and create SPCDs to apply on solid meshed breakout

• Integrate solid meshed breakout into full model

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Control – Plate Only Model

VIEW THE DEMONSTRATION

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Control – Full Solid Model

VIEW THE DEMONSTRATION

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Hex Mesh – No Element Doubling

Pros:• Accurate stiffness• Accurate massCons:• No moment supported at

junction• Potentially unconservative• Potentially incorrect load pathLimitations:• Solid Elements cannot resolve

moments at its nodes so all plate-solid interactions are hinges

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Hex Mesh – Element Penetration

Pros:• Can support moment at

junctionCons:• Heightened mass• Artificially stiff• Artificially strong• Unconservative

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Hex Mesh – Element Skins

Pros:• Can support moment at

junctionCons:• Heightened mass• Artificially stiff• Artificially strong• Unconservative

Note: a thinner skin can be used to lessen this effect, but thin skins behave like no element doubling, leading to a potentially incorrect load path.

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Solid Breakout – Interface Nodes

Pros:• Quick to model• Accurate massCons:• Potentially incorrect stress

• Artificially high stress if stiffness increased

• Artificially low stress if stiffness decreased

• Fairly accurate stress if stiffness is not significantly changed

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Solid Breakout – Zipped In

Pros:• Accurate stress • Accurate massCons:• Slower to model• Requires more solution time

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Conclusions

• “Map output from model” is a quick way to set up loads on a breakout

– Try to keep nodes in original location (use mesh refine, not remesh)

– Try to keep breakout stiffness similar to original model if using enforced displacements

• Plate to solid transitions can work in some instances, but have limitations

• “Dummy elements” can be used for ballpark estimates if needed, but will often give inaccurate results

• “Zipped in” breakout models will give the most consistently accurate results

– Grow breakout model by at least three elements lengths from the point of interest

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Additional Resource

What New book published Fall 2014

Why Learning with the help documentation can be like drinking from a fire hose. Learning Femap succinctly covers the bases on using Femap without being a “bible”.

Covers Introduction Femap Application Interface Modeling/ Pre-Processing Analysis Post-Processing Programming Femap

How Explanation of features Numerous illustrations Annotated examples Guided tutorials

Learning FemapISBN 978-1-4951-2963-6By Eric Gustafson (eric@structures.aero), Senior Aerospace Stress Analyst, SDAAvailable online at www.learningfea.com

$49.99

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Contact Us:

Contact:

Marty Sivic

Email:msivic@structures.aero

Website:http://structures.aero/

Phone: (724) 382-5290

Try FEMAP For Free!

Download a free 45-day trial of FEMAP with NX Nastran

• Full FEMAP capabilities• All Nastran solution sequences included• (http://structures.aero/femap-trial/)

Presenter:

Ryan Tatman

Email:rtatman@structures.aero

Website:http://structures.aero/

Phone: (703) 935-2818

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About SDA (aka “Structures.Aero”)

• SDA was founded in 1997 and provides expert aerospace structural analysis

• We serve a variety of industries

• We specialize in composites, and developing strong, lightweight structures that are readily manufacturable

• Low level support up through developing test plans and advanced stress analysis

• Typical support programs include small to large UAVs, manned and unmanned spacecraft, naval structures

• Our team consists of over a dozen B.S., M.S., and PhD level engineers

• SDA is located in Sterling, VA, just north of Dulles Airport near Washington DC

Learn more about

Structural Design and Analysis

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Typical Projects We Support

• Some of our previous projects include:– Aircraft

• Aurora Excalibur

• MHADD ARES

• Vanilla VA1

• Lockheed Constellation restoration for Lufthansa

– Spacecraft

• NASA NESC Composite Crew Module (CCM)

• NASA NESC Max Launch Abort System (MLAS)

• NASA James Webb Space Telescope/IEC

• NASA Orion Heatshield mass reduction for NESC

• NASA Orion Crew Module (with Lockheed)

• NASA WFIRST Telescope for Goddard

Aerosonde

Heatshield

Shadow M2

CCM

Orion Crew Module

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Partnerships

Siemens Value Added Reseller Collier Research Corporation Reseller

FEMAP NX Nastran

Fibersim Solid Edge

HyperSizer Pro

HyperSizerExpress

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APPENDIX: TUTORIAL WALKTHROUGHS

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Small Design Change Example Walkthrough

• First we used the “Draw Erase Selective Mesh – Property” command (new in 11.3).

• This allows the user to selectively hide elements and surfaces using a variety of options

• Next we used the “Create New Group” command followed by the “Group Element ID - by Property” command to select the rib

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Small Design Change Example Walkthrough

• “Add Related Elements” adds all entities needed to fully define the group

• We then created a new modfem

• File -> Merge lets you merge portions of models into other models

• We chose our model then clicked “All Off” because we don’t want the entire model

• We then went to the “Entity selection” section and chose “From Group” and picked our group

• Clicking “Add Related Entities” then “Update All” completes the action

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Small Design Change Example Walkthrough

• We then used the “Element Refine” tool to refine our mesh (new in 11.3)

• We chose the 4:1 pattern with the Add/Refine Action and used Area Drag to select all of our elements.

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Small Design Change Example Walkthrough

• The “Map Output From Model” command is going to bring loads from our full model into our breakout model.

• We chose to use nodal displacements in this breakout

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Small Design Change Example Walkthrough

• We applied these loads to the perimeter nodes as well as creating a new pinned constraint.

• The breakout is now set up and ready to be run

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Local Stress Riser Example Walkthrough

• First, we defined our breakout location by creating a square with the “Rectangle” Command

• The “Solid – Slice” Command lets us slice our solid into the size of our breakout.

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Local Stress Riser Example Walkthrough

• After deleting the geometry and mesh we no longer needed, we used the “Mesh –Geometry – Solid” command to mesh our solid

• The “Connect – Rigid” command was used to connect our plates to our solids

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Local Stress Riser Example Walkthrough

• The source nodes are on the plate elements and the target nodes are on the solid elements

• We used RBE2s in the webinar, but RBE3s can be used as well. Which RBE to use can depend on its application in your breakout

• The bolt interface RBE was updated to connect to the new solid mesh using the “Modify – Edit – Element” Command.

• The model is finished and ready to run