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!
Top Related