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Unrestricted © Siemens AG 2015

Femap Symposium Series 2015 Femap Symposium Series 2015

April 14, Sterling VA, USA

FEMAP Freebody Deep-Dive

Femap Symposium 2015 Sterling, VA – Co-Hosted with SDA, Inc.

ZEN Feb 9-13 2015

Restricted © Siemens AG 2015 All rights reserved.

Siemens PLM Software

FEMAP Freebody Deep Dive

Topics

• What is a Freebody?

• Recovering Grid Point Forces in NASTRAN

• Understanding Grid Point Force Output

• Freebodies in FEMAP

• Using the FEMAP Freebody Toolbox

• FEMAP Freebody Options

• Global / Local Modelling with Freebodies

• Additional Topics

ZEN Feb 9-13 2015



What is a Freebody?

Freebodies provide an insight into nodal forces and moments that are a result of

surrounding finite element entities

• In FEMAP, freebodies can be

used to display a balanced set

of loads on a structure or

calculate the load across an

interface

• Freebodies are commonly used

when modeling practices dictate

that the resulting FE mesh is a “coarse-grid” mesh and is suitable as an

“internal loads” model

• Commonly modeled structures are often too complicated to model in

sufficient detail to obtain useable stresses

• Allows for forces / moments to be extracted for detail stress analysis

• Freebodies are heavily used (but not limited to) in the aerospace industry

ZEN Feb 9-13 2015



Recovering Grid Point Forces in NASTRAN

Enabling GPFORCE Output in NASTRAN Case Control

• Turning on the NASTRAN GPFORCE

case control request is required to

take full advantage of the FEMAP

Freebody Tool

• Analysis Manager

• Master Requests and Conditions

• Output Requests

• Force Balance

• GPFORCE requests can return a large

amount of data, so this option

is not enabled by default

ZEN Feb 9-13 2015



Recovering Grid Point Forces in NASTRAN

Enabling GPFORCE Output in NASTRAN Case Control

• FEMAP can work with a reduced set

of data including applied load (OLOAD),

constraint force (SPCFORCE), and

constraint equation (MPCFORCE)

• This is generally not recommended

unless only a generic freebody

display of the entire structure is

all that’s required

• Additionally, care should be taken when

not requesting GPFORCE data for

the entire model

ZEN Feb 9-13 2015



Understanding Grid Point Force Output

NASTRAN F06 Output

• When the results destination is set to “Print Only” or “Print and PostProcess”

GPFORCE data can be viewed in the F06 file

• Note that it is still recommended to read GPFORCE data into FEMAP from

the OP2 file, not the F06 file

• Search for “G R I D P O I N T F O R C E B A L A N C E”

G R I D P O I N T F O R C E B A L A N C E

POINT-ID ELEMENT-ID SOURCE T1 T2 T3 R1 R2 R3

1 F-OF-SPC 4.169596E-02 1.031393E+00 -5.078434E+01 0.0 0.0 0.0

1 267 QUAD4 1.213303E-01 5.287078E+00 -1.944031E+01 2.078351E-03 5.017486E-01 4.834255E-04

1 268 QUAD4 -1.630262E-01 -6.318471E+00 7.022465E+01 -2.078351E-03 -5.017486E-01 -4.834255E-04

1 *TOTALS* 9.436896E-16 -6.306067E-14 2.557954E-13 1.934217E-16 0.0 -2.333203E-16

0 2 267 QUAD4 -7.904667E-01 -1.515594E+02 3.756228E+02 1.975718E-01 5.075642E-01 1.493221E-02

2 268 QUAD4 -3.752280E-01 -1.348000E+02 -4.464662E+02 1.780457E-01 -5.262242E-01 2.671471E-02

2 269 QUAD4 5.058178E-01 1.277458E+02 2.504629E+00 -1.799477E-01 -1.129834E-01 -4.392642E-02

2 270 QUAD4 6.598768E-01 1.586136E+02 6.833877E+01 -1.956698E-01 1.316434E-01 2.279495E-03

2 *TOTALS* -1.798561E-14 -1.136868E-12 7.389644E-13 6.383782E-16 1.493250E-14 5.551115E-17

0 3 269 QUAD4 -2.833224E-01 -7.450614E+01 3.083269E+02 1.501767E-01 -1.241496E-01 2.011796E-02

3 270 QUAD4 -2.021358E-01 -4.297056E+01 -3.489907E+02 1.569770E-01 1.129076E-01 4.146868E-02

3 271 QUAD4 1.617432E-01 5.205509E+01 -2.303685E+01 -1.572558E-01 -2.788103E-01 -1.574009E-02

3 272 QUAD4 3.237150E-01 6.542161E+01 6.370063E+01 -1.498980E-01 2.900524E-01 -4.584655E-02

3 *TOTALS* 1.049161E-14 8.540724E-12 -2.700062E-13 1.665335E-16 -2.886580E-15 8.326673E-17

ZEN Feb 9-13 2015




NASTRAN F06 Output

• GPFORCE results are listed per grid and include Fxyz (T1, T2, T3) and Mxyz

(R1, R2, R3)

• Results are separated into 4 different categories, plus a summation

• Elemental (discrete; per connecting flexible element)

• Applied (total forces / moments applied on node; single quantity per node)

• F-of-SPC (SPC forces on node; single quantity per node)

• F-of-MPC (MPC forces on node, including both constraint equations and

RBE contributions; single quantity per node)

• *TOTALS* (total summation of all contributions; single quantity per node)

• For the majority of cases, this value should be near zero, indicating

equilibrium at the node

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How GPFO Relates to Structure

• Freebody output can be very dependent on the nodes and elements included

in the summation

• Determining which nodes and elements are to be used is varies based on how

the model was idealized as well as what specific quantity is desired

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Freebodies in FEMAP

Freebodies in FEMAP exist as creatable objects, like nodes, elements, etc.

• They persist in the database

• This is a huge benefit for recreating freebody displays in the future

• Can help reduce analysis errors and rework

• Any number of freebodies can be displayed simultaneously

• Many tools exist to automate free-body-related tasks, such as creating loads

and substructure modeling

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Freebodies in FEMAP

FEMAP Freebody Types – There are 3 separate types of freebodies in FEMAP

• Freebody – user selects the elements, FEMAP automatically selects related

nodes. Intended to display a balanced set of loads on a discrete piece of

structure

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Freebodies in FEMAP


• Interface Load – user selects both nodes and elements and FEMAP

calculates a summation of loads and forces across the interface and displays

as a single vector

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Freebodies in FEMAP


• Section Cut – similar to interface load, a summed load across an interface is

displayed and calculated, however node and element selection is automated

by FEMAP. The user selects a “cutting plane”, defined by a plane, vector or a

curve. The cutting plane can be dynamically located within the model

ZEN Feb 9-13 2015



Freebodies in FEMAP

Freebody Contributions

• Freebody contributions in FEMAP are split into six categories

• Applied – represents applied loads

• Reaction – results of SPC forces

• MultiPoint Reaction – results of MPC forces

• Peripheral Elements – effects of elements

surrounding selected elements

• Freebody Elements – effects of elements

selected by the user or by FEMAP

• Nodal Summation – nodal summation values

from the solver, not FEMAP calculated values

• Default contributions are Applied, Reaction, MultiPoint Reaction and

Peripheral elements

• This provides forces and moments acting on the selected structure

ZEN Feb 9-13 2015



Freebodies in FEMAP

Freebody Result Vectors – As previously mentioned, the NASTRAN GPFORCE

request is recommended to fully take advantage of the freebody tool, however

the result quantities may be obtained from several different quantities

The italicized rows above represent default output requests in FEMAP and are

sufficient for displaying a balanced freebody on the entire structure

Primary Secondary

Applied GPFORCE OLOAD

SPC GPFORCE SPCFORCE

MPC GPFORCE MPCFORCE

Elemental GPFORCE None

Nodal Summation GPFORCE None

ZEN Feb 9-13 2015



Using the FEMAP Freebody Toolbox

Accessing the Freebody Toolbox

• The Freebody Toolbox is located in the

PostProcessing toolbox and can only

be accessed when results are present in

the model

Global Settings – These controls affect all

freebodies in the model. Control global display

of freebodies, select output set (tied to contour

and deform) and enable data summation on

nodes

Freebody Settings – These controls are

related to individual freebodies, such as

selecting nodes and elements

View Settings – These are global settings that

affect freebody visualization (symbol sizes,

vector scaling, etc.). Same as found in View

Options (F6)

ZEN Feb 9-13 2015




Creating a New Freebody

• In the Freebody Toolbox, new Freebodies are created within the Freebody

Manager

• The New Freebody dialog allows for setup of basic settings, such as freebody

type, vector display, and contribution selection

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Creating a New Freebody

• Any of the settings applied in the New Freebody dialog can be changed at any

time within the toolbox

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Accessing Different Freebodies

• Multiple Freebodies can be displayed at any

time however, only a single freebody can be

active at any time within the toolbox

• Use the drop-down menu to change the active

freebody and modify settings

• Display of individual freebodies can be

controlled with the “Is Visible” checkbox as

well as with the Visibility Quick View Dialog

ZEN Feb 9-13 2015




Freebody Vector Types

• Depending on the freebody type, there are vector quantities for nodal vectors

and a single total summation vector

• Nodal Vectors

• Displays the summation at each node, based on the selected freebody

contributions

• Available for all freebody types

• Total Summation Vector

• Displays the total summation across all nodes at a pre-defined position.

The selected position does not affect summed force calculations, but will

affect summed moment calculations due to the difference in moment arms

• Available for Interface Load and Section Cut freebodies

• Both force and moment vectors are available and can be individually toggled

• Vectors can be displayed as either components or resultant vectors

• Individual components can be toggled on and off

ZEN Feb 9-13 2015




Freebody Vector Visualization

Visibility Quick Toggle Buttons

• All On / All Off

• Forces On/Off

• Moments On/Off

• Toggle between resultant/component

• Select summation location (interface load

and section cut only)

ZEN Feb 9-13 2015




Freebody Vector Visualization

Detail Options

• Additional detailed options for visualization

can be found by expanding the Total

Summation Vector and Nodal Vector(s)

nodes

• Select components displayed (Fx, Fy, Fz),

(Mx, My, Mz)

• Select components included in calculation

(interface load and section cut only)

ZEN Feb 9-13 2015




Freebody Coordinate Systems

• The selected freebody coordinate system

controls the coordinate system for both nodal

vectors and the total summation vector (if

applicable) for the selected freebody

• Nodal vectors may optionally be displayed in

the nodal output coordinate system

• If no nodal output system was specified on

the node, the default coordinate system used

is the global rectangular system

ZEN Feb 9-13 2015




Freebody Mode

• When using “Freebody Mode”, the user selects

elements and FEMAP will automatically select

related nodes

• This mode is designed to display a balanced

set of loads on a selected set of elements

• Entities may be selected manually (default) or

inferred for a selected group

• The default contribution selections will display

forces/moments acting on the selected

elements

Select Elements

Highlight Selected Elements

Reset Element Selection

ZEN Feb 9-13 2015




Display of balanced set of loads on wingpost model. All elements in the model

were selected for this display

ZEN Feb 9-13 2015




Interface Load Mode

• Interface load freebodies display nodal

vectors for selected nodes as well as a total

summation vector at a selected location

• Unlike freebody mode freebodies, interface

load freebodies are not likely to be in

equilibrium

• In addition to element selection, nodes must

be selected manually – FEMAP does not infer

them based on the selected elements

• When selected entities from a group, both

the nodes and elements of interest must

exist in the group

ZEN Feb 9-13 2015




Interface Load Mode – Selecting Nodes

Select Nodes

Highlight Selected Nodes

Reset Node Selection

Locate Summation Vector at Node Centroid Select Free Edge Nodes

When selecting elements, any elements

may be selected, however only those

connected to the selected nodes will be

used

ZEN Feb 9-13 2015




Interface Load – Selecting Components in Summation

• Individual force and moment contributions

that are included in the total summation

vector calculation can be toggled on and off

• By default, all force and all moment vectors

are included in the calculation

• Changes made here will affect the total

summation calculation

• Turning on and off certain contributions

is dependent on how the model was

idealized ; it is up to the analyst to

understand how the FE model correlates

to real-world structure

ZEN Feb 9-13 2015




Interface Load Display, Showing Summed Shear Load at a Rib

ZEN Feb 9-13 2015




Section Cut Mode

• An extension to Interface Load mode

• The user defines a cutting plane in the

model and the contributing freebody

nodes and elements are determined

automatically

• Total summation location can be placed at

• Plane/path intersection

• Nodal centroid

• Static location

• Nodal and total summation vectors can

optionally be aligned tangent to the path

without having to create additional

coordinate systems

ZEN Feb 9-13 2015




Freebody Section Cut Modes

Plane: Cutting plane is defined via base

point and normal vector. Path is defined as

the normal vector; cutting plane will always

be normal to the path

Plane / Vector: Similar to Plane, however an

additional vector is defined for the path. The

cutting plane will always remain co-planar to

the original plane and does not have to be

normal to the path

Vector: Cutting plane is normal to the

defined vector. Path is the defined vector;

cutting plane will always be normal to the

path

Curve: Cutting plane is normal to the

tangent vector at a point along the plane.

Cutting plane will always be normal to the

tangent vector

ZEN Feb 9-13 2015




Section cut defined using plane

ZEN Feb 9-13 2015




Section cut defined using curve

ZEN Feb 9-13 2015




Additional Section Cut options

• Slider tool can be used to move the cutting

plane along the length of the path

interactively within the available entities

• Section cut entities may be limited to a

specific group or selected from the entire

model, and can be limited to a search

distance from the base location of the

cutting plane

• The cutting plane can optionally be given a

thickness tolerance that will allow for

accurate selection of entities that are

slightly out-of-plane

• Clipped entities can either be included or

excluded from the summation calculations

ZEN Feb 9-13 2015




Cut plane initial position Cut plane moved along the path

Freebody nodes

Freebody elements

ZEN Feb 9-13 2015




Freebody Tools

1 2 3 4 5

1 – List freebody to message window

2 – List freebody to data table

3 – List freebody summation to message

window (interface load / section cut)

4 – List freebody summation to data table

(interface load / section cut)

5 – Freebody validation tool; warns user

when freebody results are potentially

missing from the model

ZEN Feb 9-13 2015



Global-Local Modeling with Freebodies

The freebody Multi-Model Load from Freebody tool automates the creation of

global-local models

• Used to map freebody loads from a coarse grid

model to a fine grid model and automatically

create connections with RBE3 elements

• Start with a balanced freebody in a coarse model

• FEMAP can automatically locate suitable target

nodes in the fine grid FEM and will connect with

RBE3 elements

• Once properly constrained, the detail FEM is

ready to run with a mapped set of loads

• The detail FEM must exist in the same space as

the part in the coarse grid FEM

ZEN Feb 9-13 2015




Define Target Model Parameters

Freebody loads can be applied to target

nodes based according to

• Existing nodes (IDs must match)

• Closest node in space to source

node

• Existing nodes to be connected with

RBE3 elements

• User can define target nodes or

FEMAP can automatically find

• Search distance can be limited

• Maximum nodes to map can be

limited

ZEN Feb 9-13 2015




ZEN Feb 9-13 2015



Additional Topics – Freebodies with

NX Nastran Glue / Contact

As of NX Nastran v10.1, the GPFORCE output request does not include

contributions from glue or contact in the F06 or OP2 data block

• The result is a nodal imbalance that is the summation of all other contributions

• Nodes that are affected by glue or contact will not be in equilibrium

• The nodal summation quantity is equal and opposite to the existing

summation

G R I D P O I N T F O R C E B A L A N C E

POINT-ID ELEMENT-ID SOURCE T1 T2 T3 R1 R2 R3

0 686 821 HEXA -7.854530E-03 5.974986E-02 7.854530E-03 0.0 0.0 0.0

686 822 HEXA -4.059431E-03 4.661321E-02 2.316282E-02 0.0 0.0 0.0

686 827 HEXA 7.568718E-03 -6.126883E-02 -7.568719E-03 0.0 0.0 0.0

686 828 HEXA -2.503399E-02 -9.182400E-02 -3.478359E-03 0.0 0.0 0.0

686 857 HEXA -2.316282E-02 4.661320E-02 4.059429E-03 0.0 0.0 0.0

686 858 HEXA -1.751655E-03 6.132058E-02 1.751656E-03 0.0 0.0 0.0

686 863 HEXA 3.478360E-03 -9.182400E-02 2.503399E-02 0.0 0.0 0.0

686 864 HEXA 5.081535E-02 3.061997E-02 -5.081535E-02 0.0 0.0 0.0

686 *TOTALS* -1.318390E-16 5.620504E-16 -4.440892E-16 0.0 0.0 0.0

0 10000 468 HEXA 2.385245E-17 5.842150E-02 3.122502E-17 0.0 0.0 0.0

10000 *TOTALS* 2.385245E-17 5.842150E-02 3.122502E-17 0.0 0.0 0.0

ZEN Feb 9-13 2015





In FEMAP 11.2, the ability to reverse the nodal summation value was added,

allowing the nodal imbalance to be treated as a separate contribution in the

equal-and-opposite direction

• This option should only be used if the

cause of the imbalance is a result of

data missing from the GPFO table

and not as a result of mechanism at

the node

ZEN Feb 9-13 2015





Default contributions Freebody elements / nodal summation

Freebody elements + nodal summation Reversed nodal summation

ZEN Feb 9-13 2015



Additional Topics – Load from Freebody Tool

Freebody results can be used to create loads within an existing model using the

Model->Load->From Freebody tool

• Works with all freebody modes

• For interface load and section cut

freebodies, total summation load

can be created at a new node in

the model

• Loads can be created in an

existing load set as well as

in a new load set

ZEN Feb 9-13 2015




Freebody Loads

ZEN Feb 9-13 2015




Created Loads

ZEN Feb 9-13 2015



Additional Topics – Sum Data on Nodes Option

By default, freebody vectors at each node are displayed as a summation of the

selected components

• A global setting allows for nodal

quantities to be displayed as

individual contributions. It affects

all displayed freebodies

• This allows for comparison to

• F06 data, as well as troubleshooting

of models

• This option is best used with

the element shrink view option

ZEN Feb 9-13 2015



Additional Topics – Sum Data on Nodes Option

ID: 342

Source Fx Fy Fz Mx My Mz

ELEM 8 -4.12634 -2.76307 -130.752 46.32936 47.4351 -1.88713

ELEM 182 -18.5132 142.901 -466.199 0.280101 0.999626 0.022155

ELEM 80 208.315 34.15445 109.5391 0.067844 0.091289 -0.06195

ZEN Feb 9-13 2015



Q and A

ZEN Feb 9-13 2015



Contact Info

At Siemens:

Patrick Kriengsiri

FEMAP Development

411 Eagleview Blvd

Exton, PA 19341

404-353-6596

[email protected]

At SDA:

Russ Hilley

Staff Structural Analysis Engineer

46030 Manekin Plaza Ste. 120

Sterling, VA 20166

678-780-9578

[email protected]

mailto:[email protected]

mailto:[email protected]

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