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DENEL AERONAUTICS 1 DENEL AERONAUTICS Topology Optimization of Additive Manufactured GPS bracket Niël Agenbag Date: 10 July 2019

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DENEL AERONAUTICS

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DENEL AERONAUTICS

Topology Optimization of Additive Manufactured GPS bracket

Niël Agenbag

Date: 10 July 2019

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Introduction

• Using topology optimization to re-design a mounting bracket

from a sheet metal design to a 3D printable design, having

half the original weight

• The original design is sheetmetal

• This work forms part of an AISI project used to develop Design

for Additive Manufacturing (DfAM)

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Introduction

• Intention is to show step by step how to use SOL 200 – make it

accessible to new user

• Illustrate the pitfalls that were encountered

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Introduction

• GPS bracket and antenna location

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Introduction

• GPS existing bracket sheet metal concept

GPS

Mountin

g

fasteners

Bracket

mount

holes

Holes for

looms (should

be left open)

Sheetmetal

mass: 76.6g

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Introduction

• Loads

• Component is subjected to the following inertial loads:

• Mass has to be minimized for these loads.

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Definitions SOL 200

• Topology (layout and load-path study)

• Topometry (element by element sizing optimization)

• Topography (finite element grids are moved as normal vectors

to the shell surface or the user's given direction)

We will use this

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Tools

The following software was chosen to analyze the component:

• MSC.Apex to create the model

• MSC.Patran to set up SOL 200 optimization

• MSC.NASTRAN to run SOL 200 optimization

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MSC.Apex

Apex screenshot of geometry and mesh

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Modelling strategy

• Model the GPS as a point mass

• Connect the point mass to bracket using RBE2

• The dependent nodes of this RBE is connected

to another RBE2 that is connected to the bore of

the fastener

• The mounting hole nodes of the bracket are

connected to a central node using an RBE3.

Central node is constrained using SPC

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Modelling strategy

• Model the elements of the component using

HEX8 elements

• The mount fasteners are constrained using SPC

in local x, y, z as well as the rotational out of

plane moments. It is not constrained in the

moment direction of the rotation of the fastener

(constrained in direction 1,2,3,4,5 of local coord

in picture below)

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MSC.Patran

First perform linear static run (Good practice and shows low stresses)

Unstressed

design region

as expected

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MSC.Patran

Set up optimization

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MSC.Patran

Set up optimization: Groups for design space and non-design

space

Non-design

space:

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MSC.Patran

Set up optimization

Design space (can

be changed by

optimization):

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MSC.Patran

Set up optimization: Get current mass and calculate what it

should be after optimization

• Density specified in [tonnes/m3] for further dynamic analysis

• Design space mass = 494.87g

• Non-design space mass = 2.79g

• GPS mass = 127.6g

• Existing sheetmetal bracket = 76.6g.

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MSC.Patran

Set up optimization: Get current mass and calculate what it

should be after optimization

• Final mass target for design space = 35g

• This is a 50% mass saving

• BUT

• the mass constraint is specified in terms of the total mass of the

model (494.87g + 2.79g + 127.6g = 625g)

• Therefore the mass fraction that the optimizing algorithm must

aim for is: 35g/625g = 0.056 > round down to 0.05.

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MSC.Patran

Set up optimization: Menus

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MSC.Patran

Set up optimization

Starting

volume

fraction

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MSC.Patran

Set up optimization

Goal

function

Mass

constraint

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MSC.Patran

Set up analysis

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MSC.Patran

Set up optimization: Algorithm can be set up here

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MSC.Patran

Set up optimization: Issues

• There were some issues with the native Patran BDF where it

wrote out the DRESP2 card with incorrect parameters. This has

to be manually corrected using a text editor. This is important

to note with Patran 2019. Potentially this will be fixed in later

versions. The DRESP2 card is written out incorrectly by Patran to

be in the long format, but it enters to long integers in the C2

and C3 column of the DRESP2 card. The defaults are

acceptable in the DRESP2 card and the defaults are loaded

whenthe C2 and C3 columns are left blank. The card should

be changed to be as follows for the above example:

DRESP2 1 COMPL AVG

DRESP1 20 30 40 50 60 70

The result was run and imported. The result is shown in the

following picture:

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Baseline results Coarse model RBE2

Results: Elements

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Baseline results Coarse model RBE2

Results (using Patran Insight tool to get surfaces)

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RBE2 results fine model

Now rerun the same model setup with a finer mesh:

This is to check for mesh convergence

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RBE2 results fine model

Splits bracket in 2 parts, but it is not allowed to stress subsystems

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RBE2 results fine model

Issues:

The larger model had memory issues, so the "METHOD" option

needed to be changed to 4 where it was 1 as written out with

Patran in the BDF. It gives the following error in the F06 file:

*** SYSTEM INFORMATION MESSAGE 7603 (DMKCRS)

METHOD I IS SELECTED BY THE PROGRAM TO PERFORM TRIPLE MATRIX PRODUCT

*** SYSTEM INFORMATION MESSAGE 7603 (DMKCRS)

METHOD I IS SELECTED BY THE PROGRAM TO PERFORM TRIPLE MATRIX PRODUCT

*** USER WARNING MESSAGE 7510 (ADS9P4S)

MSCADS DESIRED STORAGE REQUIRES TO INCREASE OPEN CORE BY AT LEAST 136120667358

WORDS

WILL ATTEMPT TO OPTIMIZE WITH AVAILABLE STORAGE

*** USER WARNING MESSAGE 7510 (ADS9P4S)

MSCADS MINIMUM STORAGE REQUIRES TO INCREASE OPEN CORE BY AT LEAST 26591772018

WORDS

WILL ATTEMPT TO OPTIMIZE WITH AVAILABLE STORAGE

*** SYSTEM FATAL MESSAGE 7510 (ADS9P4S)

INSUFFICIENT MEMORY AVAILABLE FOR OPTIMIZER MSCADS

USER ACTION: SWITCH TO METHOD =4 OR REDUCE SIZE OF DESIGN MODEL

0FATAL ERROR

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RBE2 results fine model

Issues:

It can be fixed using the following BDF entry (simply change

METHOD to 4):

$ ...OPTIMIZATION CONTROL

DOPTPRM* DESMAX 50 FSDMAX 0

* P1 0 P2 13

* METHOD 4 OPTCOD MSCADS

* CONV1 .001 CONV2 1.-20

* CONVDV .001 CONVPR .01

* DELP .2 DELX .5

* DPMIN .01 DXMIN .05

* CT -.03 GMAX .005

* CTMIN .003

*

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RBE3 results fine model

Rerun the fine model with RBE3:

This makes the load path go below the whole GPS again:

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RBE3 results redo model

Redo design space and use RBE3 and mass element to model

GPS

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RBE3 results redo model

Redo design space and use RBE3 and mass element to model

GPS

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Important to note

Notes:

• The number of iterations of optimization can easily exceed the

default, so set number of iterations to a high value, typically

50:$ ...OPTIMIZATION CONTROL

DOPTPRM* DESMAX 50 FSDMAX 0

* P1 0 P2 13

* METHOD 4 OPTCOD MSCADS

* CONV1 .001 CONV2 1.-20

* CONVDV .001 CONVPR .01

* DELP .2 DELX .5

* DPMIN .01 DXMIN .05

* CT -.03 GMAX .005

* CTMIN .003

*

• It is noteworthy that *.xdb should be selected as the output

format. Both HDF5 and OP2 files are imported by Patran and

made part of the DB file. This takes an inordinate amount of

time, whereas the XDB immediately attaches immediately. It is

therefore important to choose the XDB output:

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Important to note

Choose XDB:

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Important to note

Notes:

• Additional to the XDB run, the BDF was rerun TOPVAR with the

"STRESS" optional entry of the TOPVAR card set to 5 MPa. This

was done to check if it had an influence on the outcome of

the optimization. This entry will prevent the optimization from

having an element with a stress above 5 MPa.

$ $$ $$ $$ $$ $$ $

TOPVAR* 1 PSOLID PSOLID .7

* .5 2

* STRESS 5.0

• The bracket stresses were all below 5MPa

• This is useful for cases where fatigue endurance limit is

important. Stresses can be kept below endurance limit by the

optimizer.

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Final mass

Before and after

The optimization was run as before and the final iteration

(number 32) showed a bracket with a mass of 19.5g.

This is a significant improvement over the sheetmetal bracket

that was 76g.

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Design Loop

Overlay of exported elements and design in CATIA

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Design Loop

• Exported the elements as IGES from Patran

• Import IGES into CATIA

• Designer uses the IGES element geometry

• Designs a new bracket with the guidelines

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Design Loop

Part design iteration 1 from design:

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Design Loop

Future work as part of design loop:

• Perform a linear static FEA in order to guide the designer as to

where to remove material

• Remove material at low stress regions, typically at center span

of rods

• Perform a final linear static FEA for the stress report

• 3D Print final design

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Conclusions

• NASTRAN SOL 200 is a useful tool for identification of the critical

load path using

• Combinations of load cases

• Frequency response criteria (not covered in this

presentation)

• Stiffness criteria

• It is important to note that the finite element modelling

strategy (eg. RBE2 vs RBE3) can influence the SOL200 outcome

(the load path)

• NASTRAN SOL 200 can be used in the Design for Additive

Manufacturing (DfAM) workflow because it can be used in the

optimization of components

• Significant mass savings are possible using SOL 200

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Conclusion

THE END

QUESTIONS