Introduction to Actran

for Acoustics Radiation Analysis

November 21st, 2012

Chanhee Jeong

Agenda

• Introduction to Actran

• Acoustic Radiation Analysis with Actran

– Weakly Coupled Vibro-Acoustics

– Computational Process

– Key Ingredients of the Actran Model

– Example of Application

• Live Demo in Actran VI

• Conclusion

• Q&A

The Actran Software Suite

Actran Vibro-Acoustics Actran Aero-Acoustics Actran TM

Actran Acoustics

Actran DGM

Actr

an V

I

Actran for Nastran

Actran Acoustics Module

Actran Vibro-Acoustics Actran Aero-Acoustics Actran TM

Actran Acoustics

Actran DGM

Actr

an V

I

Actran for Nastran

FE domain

IE domain

Actran Solver

• Acoustic FEM/IFEM approach

• Multi-purpose toolbox: several computational sequences

– Direct Frequency Response

– Modal Frequency Response – for interior problems

– Hybrid Modal-Physical Response – the best of both worlds

– Modal Extraction – for undamped structure or cavity

– + Compressible Flow –potential flow solver

– + Frequency response using a time domain LEE Solver

– + Transient solver

• Linux or Windows platforms

• Direct & iterative solvers, multiple load & restart

• Several types of parallelism available

Actran Acoustics Features

• Acoustics as well as weak vibro-acoustic coupling

– Acoustic finite elements, infinite elements

– 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

Few Words about Infinite Elements

• 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

S

P

1 3

P’ P’’

Vibro-Acoustics - One-Way or Two-Way

Coupling

Structure

Air

Vibration

induces

noise

Noise

induces

vibration

One-way coupling

(no feedback)

Two-way coupling

(feedback)

OK KO

Sub-marine under water Engine radiating in free field

Computation Process

3. Post Processing and Analysis = Actran VI

2. Acoustic computations = Actran 1. Structural FEA Analysis = MSC Nastran

Maps

Mesh

&

results

files

FRF Waterfall

Acoustic Radiation Procedure

• An acoustic boundary condition is created from the vibration

levels computed by Nastran.

• The MSC Nastran mesh is different than the acoustic mesh

mapping is required

• This feature is called BC Mesh (stands for Boundary Condition

Mesh)

BC_MESH feature Acoustic Radiation

structure mesh

displacement field

acoustic mesh

Preparation of the Acoustic Mesh

• A 3D finite element mesh is a requirement to support the acoustic

analysis

• The element size must be small enough to capture the smallest acoustic

wavelength and the small fluctuations very close to the structure

use of 4 linear element per wavelength thanks to optimized

integration rules

• The meshing process is easy

– Create a closed surface mesh (BC_MESH) very close around the structural model

(wrapping)

– Create a surface mesh at a distance D (~0.3 x size of object) of the structure to

support the infinite elements

– Automatic 3D mesh in between

cf

3D elements

Infinite Elements Surface

BC_MESH Surface

Supported Quantities & Formats

• Type of vibration data compatible with Actran

– Acceleration, Velocity or Displacement

– Vector (3 directions) or Normal to the surface

• Can be expressed in physical quantities or under the form of

mode shapes and participation factors

• The different realizations corresponding to the different RPMs

will be automatically handled by Actran to output results for each

RPM available in the structure results file

Structure Soft. Vibration Participation Factors Modes

MSC Nastran OP2 / Punch Punch OP2

ANSYS RST MCF RST

IDEAS UNV - -

Actran OP2 / NFF - -

ABAQUS ODB - -

Output specifications

field points

(microphones) field mesh

Results – Output Specification

• Virtual microphones can be located

anywhere in the finite and/or infinite

element domain

• Multiple control surfaces to compute the

radiated power

• Maps for different frequencies

– on the acoustic mesh or/and

– on a mesh dedicated to the post-processing

(named field mesh in Actran)

– plot acoustic pressure, acoustic intensity,

etc.

Power Evaluation from Microphones - ISO 3744

• The computation of the radiated power

from a set microphones is normalized

through the standard ISO 3744

• Actran VI has function to automatically

define the field points location according

to the standard ISO 3744 (sphere,

hemisphere, box)

• Easy reproduction of experimental set-up

Waterfall Diagrams

• “Waterfall” are diagrams where the

response is plot versus both

frequencies and the engine orders

(RPM)

• Such diagram can be obtained after a

single Actran computation thanks to

the multi-load case capability

• Some phenomena can be identified as

system dependant (vertical lines on

the waterfall), e.g. structure modes, …

• Some phenomena can be identified as

excitation dependant (diagonal lines

on the waterfall)

Example – Gearbox Application Case

• Two models are built in order to simulate:

– the radiation in complete free field

– the radiation in semi free field (reflecting floor

located at -700mm in Z direction).

• Goal : assess the effect of the floor

BC_MESH

Surface

Finite

Elements Infinite

Element

Interface

Actran Output specification

Microphones

Field Mesh

Floor Effect on Sound Pressure Levels

x y

z

C

D

A

B E

Point A Point B

Point E Point C

Floor Effect on the Directivity (3000Hz)

With Floor Without Floor

Real

part of

the

pressure

SPL

Floor effect - =

-

-

=

=

Actran Demo Seat back, relax and enjoy the flight

Thank you!