# adams-to-nastran - msc • there is a need for model translation from adams to fea 5/26/2011 4...

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Adams-to-Nastran

Jose L Ortiz, PhD.Adams User MeetingMunich - May 19, 2011

Agenda

Overview

Manual and Scripted Translation

Theoretical Background

Implementation Details

Example

Q&A

5/26/2011 2

Overview Introducing Adams-to-Nastran

Manual and Scripted Translation

Theoretical Background

Implementation Details

Example

Q&A

Agenda

5/26/2011 3

Overview

There is a need for model translation from Adams to FEA

5/26/2011 4

Multibody Dynamics System modelAdams

Finite Element Analysis modelFEA

Overview

Introducing Adams-to-Nastran

Performs an automatic model translation (export) from Adams to FEA

Available for the past 2 releases

As of today, an MD license and a LINEAR license are required

Available only in the Adams/Solver C++

5/26/2011 5

Overview

Introducing Adams-to-Nastran (cont.)

The export process creates a set of fully editable *.bdf files

Old black box option still available

Minor limitations in the type or complexity of the Adams model Models with non holonomic constraints

Tool can be used from shell and from Adams/View

5/26/2011 6

Overview

Introducing Adams-to-Nastran (cont.)

There is no need to modify the Adams model

There is no need to change your processes

Export job can be triggered at any operating point

Export job is a high fidelity translation Accurate kinematics Matching eigenvalues (static cases only)

5/26/2011 7

Overview

Introducing Adams-to-Nastran (cont.)

Users can use an optional configuration file to fine tune translation

Current release exports to linear FEA codes

5/26/2011 8

Overview

Example CAE process

5/26/2011 9

Motion analysis

FEA

translation

Create Adams model

Adams

NVH Optimization

Overview

Manual and Scripted Translation Problems Limitations

Theoretical Background

Implementation Details

Example

Q&A

Agenda

5/26/2011 10

Manual and Scripted Translation

Manual translation Error prone Time consuming (300 man hours for chassis prototype) Inaccurate

5/26/2011 11

Manual and Scripted Translation

Manual translation Error prone Time consuming (300 man hours for chassis prototype) Inaccurate

Scripted (user-written script) Limitations. Cumbersome Inaccurate

5/26/2011 12

Manual and Scripted Translation

Why inaccurate? Kinematic configuration is hard to reproduce

5/26/2011 13

Manual and Scripted Translation

Why inaccurate? Kinematic configuration is hard to reproduce

Eigenvalues computed by FEA code do not matcheigenvalues computed by Adams

5/26/2011 14

3.78

MBD FEA

7.23

Manual and Scripted Translation

Why inaccurate? Kinematic configuration is hard to reproduce

Eigenvalues computed by FEA code do not matcheigenvalues computed by Adams

Structural coupling can be compromised

5/26/2011 15

Manual and Scripted Translation

Why inaccurate? A thorough theoretical study showed that

(1) High fidelity translations require mathematical informationnot available to users

5/26/2011 16

Manual and Scripted Translation

Why inaccurate? A thorough theoretical study showed that

(1) High fidelity translations require mathematical informationnot available to users

Example:

MOTION/1, JOINT=2, FU=DX(7,8)-DZ(11,23)

5/26/2011 17

Manual and Scripted Translation

Why inaccurate? A thorough theoretical study showed that

(1) High fidelity translations require mathematical informationnot available to users

(2) Linear FEA codes use linear constraint equations

5/26/2011 18

Overview

Manual and Scripted Translation

Theoretical Background Overview Governing equations in Adams Governing equations in Nastran Example

Implementation Details

Example

Q&A

Agenda

5/26/2011 19

Theoretical Background

Overview

Automatic. The translation is another simulation job

5/26/2011 20

Theoretical Background

Overview

Automatic. The translation is another simulation job

Command:

SIMULATE/DYN, END=1.0, STEP=10LINEAR/EXPORT, TYPE=WHITEBOX, FILE=abc.nas

5/26/2011 21

Theoretical Background

Overview

Automatic. The translation is another simulation job

Adams/View:

5/26/2011 22

Theoretical Background

Overview

Automatic. The translation is another simulation job

Adams/View:

5/26/2011 23

Theoretical Background

Overview

Automatic. The translation is another simulation job

Accurate. Exact kinematics

5/26/2011 24

Theoretical Background

Overview

Automatic. The translation is another simulation job

Accurate. Exact kinematics

Overcomes FEA limitations

5/26/2011 25

Theoretical Background

Overview

Automatic. The translation is another simulation job

Accurate. Exact kinematics

Overcomes FEA limitations

Matching eigenvalues guaranteed for static cases

5/26/2011 26

Theoretical Background

Basic idea

Linearize the Adams model at the operating point

5/26/2011 27

Theoretical Background

Basic idea

Linearize the Adams model at the operating point

Linearize the Adams model using Nastran coordinates

5/26/2011 28

Theoretical Background

Basic idea

Linearize the Adams model at the operating point

Linearize the Adams model using Nastran coordinates

Identify inertia elements, constraint equations and forces

5/26/2011 29

Theoretical Background

Basic idea

Linearize the Adams model at the operating point

Linearize the Adams model using Nastran coordinates

Identify inertia elements, constraint equations and forces

Will the equations assembled by Nastran match?

5/26/2011 30

Theoretical Background

Basic idea

Linearize the Adams model at the operating point

Linearize the Adams model using Nastran coordinates

Identify inertia elements, constraint equations and forces

Will the equations assembled by Nastran match?

Need to examine the equations of motion in more detail

5/26/2011 31

Theoretical Background

Governing equations in Adams Simplified version

5/26/2011 32

Nastran coordinates

used!

Non linear equations!

Theoretical Background

Governing equations in Adams (cont.) Simplified version

Partitioning

5/26/2011 33

Theoretical Background

Governing equations in Adams (cont.) Simplified version

Partitioning

Defining P

5/26/2011 34

This P is non linear!

Theoretical Background

Governing equations in Adams (cont.) Eliminating Lagrange multipliers

5/26/2011 35

Non linear equations!

Theoretical Background

Governing equations in Adams (cont.) Eliminating Lagrange multipliers

Differentiating constraints

5/26/2011 36

Non linear equations!

Theoretical Background

Governing equations in Adams (cont.) Eliminating Lagrange multipliers

Differentiating constraints

Dependent accelerations

5/26/2011 37

Theoretical Background

Governing equations in Adams (cont.) Reduced ODE

First and second derivatives of dependent states can be found from constraint equations

Linearization done in terms of Nastran coordinates

5/26/2011 38

Theoretical Background

Governing equations in Adams (cont.) Reduced ODE

First and second derivatives of dependent states can be found from constraint equations

Linearization done in terms of Nastran coordinates

Exact linearization of ODE. In variational form

5/26/2011 39

Linearized equations!

Theoretical Background

Governing equations in Nastran Partitioned equations of motion (linear)

5/26/2011 40

Theoretical Background

Governing equations in Nastran (cont.) Partitioned equations of motion (linear)

Constraints (linear)

5/26/2011 41

Theoretical Background

Governing equations in Nastran (cont.) Partitioned equations of motion (linear)

Constraints (linear)

Defining P (this P is a constant)

5/26/2011 42

This P is a constant!

Theoretical Background

Governing equations in Nastran (cont.) Dependent accelerations

5/26/2011 43

Theoretical Background

Governing equations in Nastran (cont.) Dependent accelerations

Reduced ODE

5/26/2011 44

Theoretical Background

Governing equations in Nastran (cont.) Dependent accelerations

Reduced ODE

Final form

5/26/2011 45

Theoretical Background

Adams and Nastran equations

5/26/2011 46

Adams

Nastran

This P is a constant!

This P is non linear!

Theoretical Background

Linearized Adams and Nastran equations

5/26/2011 47

Adams

Nastran

uuv

TTTT

fffMMvMMMMvMMMM

PPPPPPPPPPP

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