Acoustic Simulation with Actran

11 October 2012

Jonathan Jacqmot (jonathan.jacqmot@fft.be)– Free Field Technologies

• A quick introduction about Free Field Technologies

(FFT)

• The Actran software for acoustic, vibro-acoustic and

aero-acoustic simulations

• Some case studies

• Conclusions

• Questions are more than welcome !

Agenda

• Free Field Technologies (FFT) is the technical leader in acoustic, vibro-

acoustic and aero-acoustic CAE

• The company has three main activities

– Development of the Actran software suite

– Provision of related services: training, consulting, technology transfer, methodology

development, installation and performance tuning, custom developments, CAE

process automation

– Research in acoustic CAE and related fields

• Free Field Technologies operates from its headquarters in Mont-Saint-

Guibert (near Brussels), Belgium, and from its offices in Toulouse,

France, Tokyo, Japan, and Troy, MI, USA.

• Actran is used by over 300 industrial customers worldwide.

• FFT joined MSC Software Corporation in September 2011 and became a

wholly owned subsidiary of MSC.

Free Field Technologies

Some of our Automotive Customers

Some of our Aerospace Customers

Some Other References

• Noise is becoming a dominant

problematic for different reasons

• Stringent norms

– The norms defined by States are more

and more restrictive

– It sometimes becomes the dimensioning

factor: Airbus A380

• Comfort

– Acoustic comfort (car or aircraft cabin for

instance) is a marketing argument today

• Damages

– In the conception of spatial structures, a

high level of noise can lead to damages

until the break-down of the structure

Why acoustics ?

Evolution of allowed pass-by noise levels from 1970 to 2000

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1970 1977 1984 1992 2000

Accep

tab

le l

evels

(d

B)

• Acoustics as well as weak vibro-acoustic coupling

– Acoustic finite elements, infinite elements & PML

– Including visco-thermal loss effects

– Convected wave propagation (flow + temperature)

• Excitations imported from MSC Nastran or others

• Results provided (among others)

– Acoustic pressure, intensity and power

– Power distribution and radiation efficiency

• Applications

– Engine: power train and auxiliaries (oilpan,

manifold, exhaust, …)

– Engine compartment insulation

– Any vibrating / radiating component

• Can be further extended using vibro-acoustics and aero-acoustics

features

Actran Acoustics Features

• Infinite elements are:

– « finite » elements

– covering an unbounded domain

– with appropriate high order shape

functions in the radial direction

• Infinite elements:

– ensure there are no wave reflections

at the FE/IE interface

– provide accurate acoustic results

beyond the FE domain

Few Words about Infinite Elements

S

P

1 3

P’ P’’

• Shells & solids

– Visco-elastic shells & solids

– Piezo-electric elements (electric excitation,

mechanical response)

– Stiffeners, beams and mass-spring systems

• Porous elements: based on Biot model

– Model foam, rock wool, fibers...

– Most complete : Porous UP Model

• Vibrating skeleton surrounded by a fluid

• 3 + 1 = 4 degrees of freedom per node

– Other models : Delaney-Bazley, Miki, Rigid porous,

Lump porous

– Material properties (frequency dependent):

• Foam skeleton properties

• Fluid properties

• Foam properties : tortuosity, resistivity, porosity, …

• Local & global indicators, including energy

balance statements

Structural and Porous Elements Library

• A CFD computation (URANS, LES, DNS, …) is used to determine

the flow

• The sound sources are calculated from these results

– Use of Lighthill’s analogy

– Standard simplifying assumptions

Actran AeroAcoustics: Lighthill’s Analogy

Source domain Ws (quadrupoles/dipoles)

CAA domain W (Actran, FEM)

NRBC at Ge

Gs

Wa

Ge

Solid boundary at Gs

Actran AeroAcoustics: Process Overview

Easy to use procedure - CFD

and acoustic computational

chains are decoupled

Efficient procedure - mapping

strategy (integration

technique). A pure acoustic

meshing criterion is sufficient:

there is no need for a

refinement of the mesh in the

sources zone

Robust procedure Actran

directly reads native CFD files

• Import meshes from Nastran, Patran or

others

• Setup of fluid (and/or solid) domains

• Definition of boundary conditions

– Spherical, cylindrical, plane sources

– Modal ducts

– Import from Nastran or others

– Random (diffuse, turbulent, rain)

– …

• Specification of

– Frequency range

– Microphone locations

– Post processing meshes

• Manage and monitor calculation

Actran VI for Pre-Processing

• Visualization of

– Sound pressure

– Displacements

– Density

– Velocity

– Mapping quality

• Multiple visualization modules

Actran VI for Post-Processing

Maps Iso lines/surfaces Vectors Deformations

Source: FFT

• Plots of frequency response functions (FRF) of

– Sound pressure level

– Transmission loss

– …

• Polar/directional plots

• Waterfall diagrams

– FRF (color) per RPM over frequency

Actran VI for Post-Processing

Vibro-Acoustic Application Reviews

Powertrain Radiation

• This project: a complete truck powertrain, length around 2.5 meters

• The structure vibration levels are computed with an external FEA solver

• The results (velocities or displacements) are used as the excitation of

the acoustic radiation problem solved by Actran

• Several RPM’s of the power train are considered

• The numerical results are compared with measurements

Introduction

Reference :

Experimental Validation of an Efficient Procedure for Large Acoustic Radiation

Problems, M.Gustafsson, J.Jacqmot, S.Caro - ISMA 2010 conference

• In the following, we only focus on the acoustic computations

Computation Process

3. Post Processing and Analysis

2. Acoustic computations (Actran) 1. Vibration modes and participation

factors

Maps

Binary

files

FRF Waterfall

• Acoustic measurements have been done to assess the accuracy

of both the structural computation and acoustic radiation.

• For the complete set of frequency, regimes and microphones, a

maximum of 2dB difference has been detected.

Powertrain: Experimental Validation

(Normalised results)

Magnus Gustafsson et. All. : Experimental Validation of an Efficient Procedure for Large Acoustic Radiation

Problems, ISMA 2010

• 500 Hz

• 1500 Hz

Maps of the acoustic fields

Panel Contribution

Transmission Loss through Windows

• The transmission through windows is of main importance in

automotive industry as it is one of the weakest points of

transmission.

• The number of parameters is very limited :

– glass material properties are difficult to modify

– multi-layered side windows would largely increase the weight

– shape is defined by design studio

• This study is focused on the seals connecting the window to the

car structure

Context

• Baffled

• Incident space : Rayleigh

• Transmitted space : infinite FEM

• 600×600 mm² plate glass

• 2-material glass run channel (2.2m long)

Structural 3D model (dynamic analysis)

Vibro-acoustic model

glass run

channel glass incident

power

transmitted

power

air (I-FEM)

Transmission Index of sealed window

Wtr

• Measurement of the transmitted acoustic power at 10cm from

glass gives higher TL and critical frequency.

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30

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45

50

100 1000 10000

Frequence (Hz)

TL

(d

B)

Puissance transmise à la surface du vitrage

Puissance transmise à 10 cm du vitrage

Mesures

Glass thickness of 3,85 mm

Transmitted power evaluation

TL based absolute transmitted power

TL base on transmitted power evaluated as in XP set-up

TL Measurements

• Several design proposals simulated

Ranking of design proposal by simulation

TL Champ Diffus

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30

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45

50

100 1000 10000

Frequency (Hz)

TL

(d

B)

Coulisse B9 P3 Initiale

Coulisse B9 P3 Géométrie n°1

Coulisse B9 P3 Géométrie n°2

Coulisse B9 P3 Géométrie n°3

É paisseur de vitrage de 3,85 mm

most effective design

Product improvement

Automotive Panel Submitted to Various

Excitation

• Automotive panels need to be

– as light as possible to decrease the fuel consumption

– as isolating as possible to increase the passengers’ comfort

• New materials and new designs must be used to fit with both

requirements

• Plastic Omnium produces these kinds of panels

Context

• Road noise transmission at 90 kph on rear floor :

– tyre / road : airborne noise

– road vibration : structure-borne noise

Noise Source

tyre / road road vibration

• Structure & airborne transmission : excitation mode

– airborne through diffuse sound field (Wi ~ 1 Pa²)

– structure borne through a dynamic force (F = 1N)

Actran Excitation

• Actran can rank the two propagation paths

• Actran can define which part of the panel is

the most contributing

• User can then focus the improvement on the

most relevant part of the product !

Results

Frequency [Hz] Frequency [Hz]

Satellite Exposed to Lift-off Pressure

Field

• At lift-off, components like satellites carried on launchers are exposed to intense acoustic excitation that can damage their structures

• In the frame of an ESA driven project, Dutch Space is seeking for improving the prediction of the response of a folded solar array loaded by an Acoustic Diffuse Field

• The objective of the study is to compare the vibro-acoustic response of a folded solar array loaded by an Acoustic Diffuse Field :

– Measured in a reverberant chamber (Dutch Space)

– Simulated with the Infinite/Finite Element solver Actran (Free Field Technologies)

Application Review - ATV Solar Array

Study Objectives

• Structure modeled in modal coordinates

– Existing Dutch Space model

– Modes extracted with NASTRAN (SOL103)

• The air layers and the surrounding air are modeled

together in physical coordinates

– Meshed with the real thickness

– Take visco-thermal effects into account (Beltman model)

• Fluid / Structure coupling taken into account (between

each panel and fluid layer)

Application Review - ATV Solar Array

Numerical Model

Infinite Elements (NRBC)

Panels

FE Air Domain

• Influence of the air layers and Acoustic Diffuse Field models

Application Review - ATV Solar Array

Results

Hybrid representation closer to

measurements on the complete

frequency range

Full Model = full modal

representation

Second Model = hybrid

modal/physical representation

Aero-Acoustic Application Reviews

Application Review - Rod Airfoil

Experimental setup

• Cylinder: ∅ = 10 mm

• Airfoil: NACA 0012,

c = 100 mm

• Span: 300 mm

• Far field measurements:

R = 1.85 m

Experimental data

• Geometric and hydrodynamic

boundary conditions

• Velocity profiles and spectra

• Wall pressure and far field spectra

• Acoustic mesh should resolve up to 5kHz

• Acoustic wave length @ 5kHz : 0.068m

• 4 quadratic elements / λ: Δx = 0.017m

• Slight mesh refinement at cylinder

boundary and leading edge to capture

the boundary curvature

• Acoustic model contains 588 000 cells

• 1 232kdof have to be computed with an

IFE interpolation order of 10

Acoustic Model

Rigid walls

Mapping region

Infinite elements

Modal duct

Δx = 17mm

PSD pressure in the far field at R = 1.85 m and θ = 90°

Acoustics Results

• Very good agreement with experimental data

• Characteristic fits extremely well over the

whole spectra

• Far field PSD peak is 4 dB too high

• This might be due to not fully statistical

converged results:

Sim.: 5 avg. of 25Hz // Exp.: 200 avg. of 4Hz

• Objective: post-process complex, unsteady CFD

results and compute the flow noise of a HVAC duct

system

• Example: Fluent + Actran

• Real duct with register – CPU stats

– CFD: 15h

– CAA: 6h

– Target: 3kHz

• Our unique strategy ensures excellent results

Application Review - Instrument Panel Duct

ACTRAN TEST

• Volskswagen Passat

• Window = visco-elastic shell, seals = visco-elastic solids

• Trim components into the cavity using admittance

Application Review - Side-Mirror Noise

Sound p

ressure

Level [d

B]

“A comparison between the effects of the Turbulent and the Acoustic wall pressure fluctuations inside a car”, M. Cabrol,

Y. Detandt, M. Hartmann, A. Mutzke, 18th AIAA/CEAS Aeroacoustics Conference, Colorado Springs, Colorado, 2012

• Electronics

• Loudspeakers

• Headsets, telephones, microphones,

• Underwater acoustics

• Shipbuilding

• Compressors

• Construction

– Glass structures

– Multi-layered construction panels

• Etc

• Contact us if you need more information !!

Actran can also be used for…

• MSC Acoustic Engineering Services are

offered from

– FFT’s offices in Belgium, France, Japan & USA

– Or through any local MSC office

• Several highly skilled staff with thorough

acoustics and structural dynamics background

• Deep experience in numerical acoustics, vibro-

acoustics and aero-acoustics consultancy

projects for the automotive and aerospace

industry such as intake and exhaust noise,

NVH of trimmed body, engine noise radiation,

HVAC noise, Side Mirror Noise, windows

transparency, …

• Also skilled in using other CAE software and

high-performance computing resources

• Please take a look to our dedicated leaflet

MSC Acoustic Services

• Actran offers a complete numerical solution to perform efficient

acoustic design study for all the industrial applications

• From acoustics to vibro-acoustics to aero-acoustic studies

• All the modules have intensively validated by our customers:

many publications can be downloaded on our website

(www.fft.be)

• Very efficient solvers combined to different types of parallelism

in order to perform fast simulations

• Actran can be directly plugged at the end of your structural or

CFD analysis

• MSC & FFT teams also provide engineering acoustic services,

on-site or off-site

Conclusions