Gaëtan Kerschen, Professeur, ULg - Laboratoire de structures et systèmes spatiaux

Jeudi 10 novembre

Votre modèle est en désaccord avec vos mesures de vibration ? Un voile levé sur les vibrations non-linéaires.

LIEGE CREATIVE, en partenariat avec :

Gaëtan Kerschen

Space Structures and Systems Lab.

Aerospace and Mechanical Eng. Dept.

University of Liège

Votre modèle est en désaccord avec vos

mesures de vibration ?

Un voile levé sur les vibrations non-linéaires

2

Aerospace and Mechanical Engineering Dept.

Founded in the 1960s, 25 professors, 100 researchers.

Materials, solid & fracture mechanics, aerodynamics &

aeroelasticity, fluid dynamics, vibrations, space structures,

propulsion, thermodynamics.

Subsonic wind tunnel (1.5m x 2m test section).

Master of Aerospace Engineering (full-English).

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1960-1980: FEM and

SAMCEF software

F. de Veubeke

1980-2000: flexible multibody

dynamics (MECANO)

M. Géradin

2000-date: 4 Professors active in vibrations,

O. Bruls, J.C. Golinval, G. Dimitradis, GK.

Long-standing Tradition in Vibrations @ ULg

Spin-offs: SAMTECH

Open Engineering

V2i

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Space Structures and Systems Lab (S3L)

Nonlinear vibrations

Frequency

Energy

Bifurcations

(Aero)space structures

Orbital mechanics &

mission analysis Nanosatellites

5

Outline

The virtual prototyping era & nonlinearities.

Aircraft fly, so what ?

The proposed philosophy.

The F-16 aircraft.

NOLISYS, a two-day-old start-up.

6

Maturity of the Finite Element Method

The vibrations and resonances of complex structures

such as full-scale aircraft and bridges can be effectively

predicted using the finite element method.

Airbus A350WXB

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The Virtual Prototyping Era

A model can predict the behavior of a structure before the

existence of the first prototype.

Using models, we can access non measurable information

(e.g., stress).

Particular operational conditions (e.g., earthquakes) that are

difficult to reproduce experimentally can be simulated.

Test design (e.g., sensor and actuator placement).

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Typically, Linear Behavior Is Assumed

A X

B Y

A+B X+Y LIN

LIN

LIN

Output

Input

No unpleasant surprise

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Nonlinear System ?

A X

B Y

A+B ??? NL

NL

NL

Output

Input

Nonlinear

Linear

Weak

impact

Strong

impact

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Bolts, joints and gaps Elastomers and composites

Friction and contact Large amplitudes

Common Types of Nonlinearities

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Outline

The virtual prototyping era & nonlinearities.

Aircraft fly, so what ?

The proposed philosophy.

The F-16 aircraft.

NOLISYS, a two-day-old start-up.

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Aircraft Fly But …

Impact: Flight envelope (performance) is limited or fatigue issues.

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Satellite Fly But …

5 20 30 70-100

0

100

Accel.

Sweep frequency (Hz)

Acc.

(m/s2)

0.1 g

1 g excitation

Tests @ Airbus Defence and

Space with Siemens and S3L

Impact: « unpleasant » surprise, troubleshooting needed.

Dangerous resonance

popping up out of the blue

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Certification Process for a New Aircraft

DECISION

Tests Tests

Models

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Nonlinearities of Airbus A400M Revealed During Tests

Failure of commercial linear software (Siemens-LMS):

…during the A400M GVT, highly force-dependent resonances were

systematically fitted by means of two structural modes…

Impact: Nonlinearities slowed down aircraft certification.

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Environmental Pressure Mounts Further

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You Are Nonlinear !

Load

Extension Toe region:

normal range Linear Yield

Human cadaveric

anterior cruciate

ligament in knee

joint (Dr. Ziv,

MAE, Buffalo)

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Outline

The virtual prototyping era & nonlinearities.

Aircraft fly, so what ?

The proposed philosophy.

The F-16 aircraft.

NOLISYS, a two-day-old start-up.

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Our Philosophy: From Measurements to Design

IDENTIFY MEASURE

VIBRATION

MEASUREMENTS

Identify nonlinear

connections early on

UNDERSTAND

DESIGN HYBRID

MODELING

LINEAR FINITE

ELEMENT MODEL

Compute nonlinear

features and responses

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More than 15 Years of Developments @ S3L

MEASURE

VIBRATION

MEASUREMENTS

Dedicated,

early, tests

IDENTIFY

Detection

Location

Visualization

Exp. modeling

UNDERSTAND

Nonlinear

modes

Nonlinear freq.

responses

DESIGN

Optimization

LINEAR FINITE

ELEMENT MODEL

HYBRID

MODELING

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1. Yes or No ?

2. What ? Where ? How ?

3. How much ?

xxxxxfnl ,sin,),( 3

?

333 3,2.1,1.0),( xxxxxfnl ?

We Seek an Experimental Model for the Nonlinearity

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The NI2D Software Integrates These Methods

Today the only software dedicated to the experimental

& numerical analysis of nonlinear vibrations.

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The virtual prototyping era & nonlinearities.

Aircraft fly, so what ?

The proposed philosophy.

The F-16 aircraft.

NOLISYS, a two-day-old start-up.

Outline of the Presentation

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Testing of a Full-Scale F-16 Aircraft

Belgian airforce base.

Collaboration with

Siemens LMS.

Right missile Connection with the wing

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Sensor Set-Up (>160 Accelerometers)

But only a few sensors for the

dedicated nonlinear tests

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Nonlinearity Has a Beneficial Effect Here

Frequency (Hz)

4 2 6

-40

-60

-80 8 10

-20

10 N RMS

100 N RMS

Output

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Low level,

10N

High level,

100N

A Map for Nonlinearity Location

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Visualization of the Nonlinearity

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The Observed Nonlinearities

-4 -3 -2 -1 0 1 2 3 4

x 10-4

-5

-4

-3

-2

-1

0

1

2

3

4

5Force level: 67 N rms

Relative displacement (m)

- A

ccele

ration (

m/s

2)

-0.04 -0.03 -0.02 -0.01 0 0.01 0.02 0.03-2.5

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5Force level: 67 N rms

Relative velocity (m/s)

- A

ccele

ration (

m/s

2)

Right missile Connection with the wing

Friction

Joint

opening

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Linear main structure =

fairly easy to model

numerically.

Nonlinear component =

difficult to model numerically.

Data-Driven and Computer-Aided Models Integrated

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The virtual prototyping era & nonlinearities.

Aircraft fly, so what ?

Nonlinearities & the proposed philosophy.

The F-16 aircraft.

NOLISYS, a two-day-old start-up.

Outline of the Presentation

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The NOLISYS Spin-Off Company

April 2016: First Spin-Off from the Walloon Region

(with support from Siemens, V2i & GDTECH)

Nov. 2016: SPRL (T. Detroux, managing director).

≤ 2018: Creation of a SA.

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Our Activities

NI2D® software

(owned by ULg)

Consultancy

Training

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Training Activities

With international industrial attendees: Airbus Toulouse, Airbus Defence and

Space, Bruel & Kjaer, US Air Force, MAG-IAS, Sandia National Labs.

1st-3rd ed., Liège, 2015-2016

4th ed., Los Angeles, 2017

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Concluding Remarks

Nonlinearity is pervasive in engineering structures:

Main economic benefits:

► Reduce time-to-market.

► Avoid painful troubleshooting.

► Better performance by exploiting nonlinearity early on.

► Limit performance (F-16).

► Slow down the design cycle and testing campaigns (A400M).

► Hinder product certification.

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The Quest for Lighter and Lighter Structures

No resonances.

Early 1900s

Dynamic design (LIN) Dynamic design (NL) Static design

Resonances under control.

No nonlinearity

HEAVY

STRUCTURES

Today Tomorrow

Resonances & nonlinearity

under control.

LIGHT

STRUCTURES

ULTRA-LIGHT

STRUCTURES

Performance Environment

Merci pour votre attention.

Gaëtan Kerschen,

Space Structures and Systems Lab.

Aerospace and Mechanical Eng. Dept.

University of Liège