topology optimization using nx nastran & simcenter · nx nastran results • for each subcase,...

Topology Optimization using

NX Nastran & SimcenterGuy Wills

Simcenter 3D Topology Optimization Product Manager

Realize innovation.Restricted © Siemens AG 2017

Unrestricted © Siemens AG 20182017.MM.DD Siemens PLM Software

Topology Optimization for Analysts – Highlights

• Created to enable CAE Analysts to use advanced CAE and optimization

functionality to execute design concept studies.

• Topology Optimization embedded into NX Nastran. Based on industry proven

Optimization architecture (SOL200).

• Topology Optimization workflow integrated into Simcenter 3D Engineering

Desktop to aid the model construction and post processing of the results.

• Multi-discipline optimization with a mix of solution types in the same

optimization.

• Geometry shape control (Manufacturing Constraints).

• Lattice zone prediction – Designing for Lattices.

• Smoothed facet model

available to guide further

design work.

Mesh with

Lattice

Changes included

in CAD with

Lattice


Why Topology Optimization ?

Wikipedia… Topology Optimization is a mathematical method that optimizes material layout within a

given design space, for a given set of loads, boundary conditions and constraints with the goal of

maximizing the performance of the system.

Part and assembly design has increasing complex functional, operating and light-weighting

requirements. Topology Optimization is one method to guide the user to an optimal design.

Topology Optimization also enables the user to view more design concepts, this is because novel

shapes are produced that have not previously been considered.

Optimization Examples:

• Maximze stiffness (strength), while keeping the design mass between upper and lower

boundaries and the first flexible normal mode above a specified frequency.


Topology Optimization Workflow

Topology Optimization is a solution using multiple steps in a workflow.

This is not a fixed workflow and in practise, there will be variations.

CAD Part/AssyBuild the FE

ModelSOL200 Top Opt Solution

Design/Frozen Area(s)

Objective

ConstraintsManufacturing

ConstraintsSolution

ParametersResults Study

Results Selection

Verification of Selected Results

Output of Smoothed Geometry

Further Design Work based on Topology Optimized results


Build the FE Model

• Topology Optimization starts with an FE model to describe the

design areas and the surrounding scenery parts

• Many alternative methods available to build the model:

a) Orphan mesh (no CAD)

b) Single CAD part and single FEM

c) CAD assembly and single FEM or an AFEM

• Consider the model to be constructed in two parts

• Design Area

• Elements acted on by the Optimizer

• 2D Shell and 3D solid elements only

• Scenery Elements

• Scenery elements can be any NX Nastran elements

Green = Design Area Elements

Blue = Scenery Elements


NX Nastran SOL200 Topology Optimization Solution

• New NX Nastran SOL200 solution type

• Multiple solutions can be run based

on the same model to study the effects

of different options and values

Note:

It’s is good practise to create separate test solutions

of the different subcases, then re-use the loads and

constraints in the SOL200 Topology Optimization

solution.



• Supports multiple subcase types in the

SAME optimization.

• Linear Statics

• Normal Modes

• Direct Frequency

• Modal Frequency

• Each subcase can have its own Output

Requests, Case Control Parameters &

User Defined Text.

• Models that require multiple loadcases,

create one solution Subcase per loadcase.

Solution subcase options


Example Multiple Solution Optimization

Linear Statics Linear Statics &

Normal Modes

Linear Statics

Setup

Linear Statics &

Normal Modes Setup

Linear Statics &

Normal Modes

Linear Statics



• Optimization Solution options

• Topology Optimization Parameters to

control the optimization, for example

convergence criteria.

• Max Design Cycles to stop the solution if

not converged.

• Penalty Law to change the calculation

method.

• Recovery Option to decide which

optimization iteration results to retain.


Design and Frozen Areas

• Design Area

• The Design Area contains the elements the Optimizer can

operate on. The remainder of the model is implicitly

Frozen.

• Many Designs Areas (connected or disconnected) are

allowed.

• Can contain Elements, Mesh, Polygon Body or Selection

Recipe.

• Only 2D shell and 3D solid elements are allowed in the

Design Area(s).

• Frozen Area

• For some models it is easier to identify the elements that

are not to be changed by the Optimizer, and the remainder

of the model is implicitly the Design Area.


Topology Optimization Objective

• Only one Optimization Objective can be used in a solution.

• At the Global level

• For Responses that are global

• Within a Subcase

• For Responses that are specific to that Subcase

Objective at the Global

or Subcase level


Topology Optimization Objective

Standard and Advanced creation options example

Standard Method Advanced Method


Topology Optimization Constraints

• Constraints can be applied at the Global and/or at the Subcase level.

• At the Global level

• For Responses that are global

• Within a Subcase

• For Responses that are specific

to that Subcase

Constraints at the Global

and Subcase level


Topology Optimization Constraints

Standard and Advanced creation options examples

Standard Method

Advanced Method


Topology Optimization Responses

Objectives and Constraints reference a

Response. This is how the NX Nastran

“measures” the model during the Optimization.

The Responses listed all have sub-options, eg

reference Physical Properties, DOF, Nodes

etc.

Total Model Weight

Design Area Weight

Total Model Volume

Compliance

Normal Modes

Bucking Modes

Displacement

Strain

Stress

Force

SPC Force

Composite Strain

Composite Stress

Composite Failure

Acoustic Pressure

Eigenvalue Modes

Complex Eigenvalue Modes

Frequency Response Force

Frequency Response SPCForce

Frequency Response Stress

Frequency Response Displacement

Frequency Response Velocity

Frequency Response Acceleration

Random Response Displacement

Random Response Velocity

Random Response Acceleration

Transient Response Displacement

Transient Response Velocity

Transient Response Acceleration

List of Responses available


Topology Optimization Responses

Example Reponses


Advanced Objective and Constraint Construction

NX Nastran provides the following cards that can be used to create more complex

constructions for the Objective and Constraints

NX Nastran Card Section Description

SET Control List of DRESP1 responses.

DRSPAN Control Exclusively assigns a SET of DRESP1 responses to a specific subcase.

DRESP2 Bulk Defines equation responses that are used for the objective and/or design constraints.

DRESP3 Bulk Defines responses to be evaluated in an external user-supplied program.

DEQTN Bulk Defines one or more equations.

DLINK Bulk Relates one design variable to one or more other design variables.

DSCREEN Bulk Defines screening data for constraint deletion.

DESVAR Bulk Defines a design variable.

DTABLE Bulk Defines a table of real constants that are used in equations.


Advanced Objective and Constraint Construction

Examples:

• Taking the Compliance response from 3 subcases and make the sum the Objective.

• Taking the Displacement response from 3 subcases and averaging them as a global Constraint.

• Introduce a variable that is intendant to the model data.

• Introduce a table of constants to be used in multiple equations.


Topology Optimization Manufacturing Constraints

• Manufacturing Constraints are used to control the

optimization to produce a specific effect.

• Planar Symmetry

• Cyclic Symmetry

• Maximum Member Size

• Minimum Member Size

• Casting Die Direction

• Extrusion

• Max Overhang Angle (for AM)

• Multiple MC’s can be included in the

same Optimization.

• No check is made for conflicting MC’s

(ie Planer and Rotational Symmetry).


Topology Optimization Manufacturing Constraints

– Planar & Cyclic Symmetry

• Planar Symmetry & Cyclic Symmetry dictate

how the Topology Optimization changes

elements independently to the mesh

distribution.

Without Planer

Symmetry

With Planer

Symmetry

With Cyclic

Symmetry


Topology Optimization Manufacturing Constraints – Max & Min

Member Size

• Max & Min Member Size

• Max & Min size of the trusses created by the optimization.

Without Max

Member Size

With Max

Member Size

Without Min

Member Size

With Min

Member Size


Topology Optimization Manufacturing Constraints – Casting Die

Direction

• The optimization process does not create any internal cavities or undercuts

that would make it impossible to remove the part from the mold.

• For molds that have two halves, the user can specify the direction in which

each half is separated from the part.

Casting Plane, Pull

direction along hole

centrelines


Topology Optimization Manufacturing Constraints – Extrusion

• Constant cross section normal to specified vector

Without Extrusion

constraint

With Extrusion

constraint


Topology Optimization Manufacturing Constraints – Overhang

Angle

• Ensures that there is sufficient structural integrity as the part is built

layer by layer using 3D printing technology.

• The user can specify the maximum angle for any trusses,

protrusions, or slopes relative to the base plate normal vector, as

well as the minimum thickness for any portions of the body.

With

Overhang Angle

Build

Direction

Without

Overhang Angle


Topology Optimization Solution Parameters

Topology Optimization Parameters

• Shared list with SOL200 Design Optimization

• Used to control convergence and outputs


Topology Optimization Solution Parameters

Results Recovery to specify which design

cycles are included in the .OP2 results. Initial

is Design Cycle 0 with no Optimization.

• Initial and Best

• Initial with Skipped Cycles

• See Parameter “Cycle Skip Count”

for more information.

• Initial and All Improved

• Every cycle that shows an

improvement over the previous

cycle.


NX Nastran Results

• For each Subcase, results requested for each Design Cycle are

Recovered and can be used for normal post processing as

required.

• During the optimization process, NX Nastran reduces the Young's

Modulus and density of each of the elements in the design area,

giving each element a Normalized Material Density value ranging

from 0.0 to 1.0

• The Loadcase Independent Results holds the Normalized Mass

Density results for each optimization cycle requested.

• These are used to view the Topology Optimization results:

• Using the normal Post View commands.

• Using the Material Density Results display.


NX Nastran Results – Material Results Display

• Material Density Display

• To streamline the process of selecting the final elements to define

the optimized geometry.

• Dynamic Smoothing is a Nodal Average.


NX Nastran Results – Results Display

• Post View options can also be applied to the Material Density Display.


Verification Solution of the Topology Optimization Results

Verification solution is a copy of the original solution that includes only the

elements selected by the Solid Area bound value.

Subset Group for

Verification Solution

Set DESMAX=0 to only make

first non=optimization iteration

Subset Group selected for export


Export of Results – Smoothed or Unsmoothed

• Laplacian Smoothing

• The elements are further smoothed based on their proximity to

one another.

• Smoothing Level

• Sets a factor that determines the number of times to run the

smoothing algorithm. Higher values produce greater smoothing,

but also shrink the model.

• Output files are stored in the same folder as the .sim file.

• Export (Smoothed or Unsmoothed)

• STL faceted model of the external faces

• Nastran input BDF file with shell elements of the external faces

Note: For solid elements, the external faces are exported as

facets or shells.


Further Design Work

Import STL as Convergent body

• Edit Convergent body as required

• Use as guidance for design work


Designing for an Additive Manufactured Lattice

• Currently Lattices used for light-weighting are applied to parts that have previously been

designed using traditional methods or Topology Optimization. This changes the

structural performance of the component.

• Adding a Lattice definition to the Topology Optimization enables the

user to design for the optimal locations for Lattices to be applied.


Topology Optimization with Lattices also Requires a Workflow

Approach

Build Model

SOL200 Top Opt Solution

• Select Lattice typeSetup & Solve

Model

Results Selection

• Solid & Lattice Zone Bounds

Create Verification Solution

Export

• STL for Solid & Lattice Zones

• Density .csv

3-matics

• Import data

• Generate solid zone

• Generate Lattice

3-matics

• Export NXN input of Lattice as Beams

Verification Solution

• Append & connect Lattice to Verification solution

Solve Verification model

Note:-

For details please consult the following documentation

• Simcenter Help

• NX Nastran Design Sensitivity and Optimization User's Guide

• NX Nastran Quick Reference Guide


Selecting the Lattice Type

The Lattice Penalty Law enables the user to select

the type of Lattice. This selects a Penalty Law curve

that plots the unique normalized elasticity vs relative

density relationship.

• Body Centered Cubic (BCC)

• Face Centered Cubic (FCC)

• Edge of Face Centered Cubic (EDGE)

• Octahedral (OCTA)

• FCC + OCTA (OCTET)

• BCC + EDGE (BCCUB)

• FCC + EDGE (FCCUB)

• BCC + FCC (BC-FC)

• BCC + FCC + EDGE (BFECB)

BCC FCC EDGE

OCTA OCTET BCCUB

FCCUB BC-FC BFECB


Solid & Lattice Zones

Result is two Zones

• Solid (green)

• Lattice (orange)

No lattices are actually created. The

external faces are exported as STL file

along with a Density map .csv

The Solid and Lattice zones are

imported into 3-matics from Materialize

to complete the Lattice creation and

optimization.

• The faceted model can be exported

back to NX.

• NX Nastran tetrahedral, beams and

rigid connections elements can be

exported back to Simcenter.

Mesh with no

Lattice

Mesh with

Lattice

Changes included

in CAD with

Lattice


Summary

• Topology Optimization embedded into NX Nastran. Based on industry proven

Optimization architecture (SOL200).

• Topology Optimization workflow integrated into Simcenter 3D Engineering

Desktop to aid the model construction and post processing of the results.

• Comprehensive set of model responses for the Optimization Objective and

Constraints.

• Smoothed facet model available to guide further design work.

• Lattice zone prediction – Designing for Lattices.

Mesh with

Lattice

Changes included

in CAD with

Lattice

Guy WillsProduct Manager

Simcenter 3D Engineering Desktop

E-mail:

[email protected]

Realize innovation.

topology optimization using nx nastran & simcenter · nx nastran results • for each subcase,...

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