Acoustic Simulation Seminar

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Acoustic Simulation Seminar
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BEASY Home Ashurst Lodge
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Administrative Issues

• Fire Exits
• Assembly point by flagpoles
• Toilets
• Messages
• Reception

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Computational Mechanics

• Group formed in 1978
• Headquarters -
• Southampton England
• Billerica Massachusetts USA
• Main Activities -
• Software
• Publishing
• Training
• Research Development

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Group Activities
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Computational Mechanics Worldwide

• Clients in over forty countries
• Head office in Southampton,UK
• North American office in Billerica Massachusetts
• Software and services partners worldwide

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BEASY

• Development of BEASY Software
• Sales and Marketing of BEASY products
• Support services
• Customisation services
• Training
• Consultancy
• Software development and R D

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BEASY support service

• www site for news and updates
• email support
• ftp for updates and support
• Hot line support service
• Training courses and seminars
• In company training service
• Newsletter
• User Group meetings
• Maintenance
• Consultancy

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Mathematical Modelling and Numerical Methods

• Our team of engineers offers
• extensive expertise and experience of modelling
  problems in many different application areas
• a thorough understanding of computer and
  numerical methods and their associated
  limitations
• customised simulation tools and software
  development
• intelligent application of modelling tools and
  analysis of results
• the development of new techniques

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Project Management

• Partial list of clients
• Rolls-Royce (UK)
• GKN Westland Helicopters (UK)
• Shell (Netherlands)
• General Electric (USA)
• Conoco (Norway)
• United States Navy (USA)
• European Space Agency (Netherlands)
• Ford (USA)
• Honda (Japan)
• Hamilton Standard United Technologies (USA)

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Our Clients

• A selected list of our clients is given below

• BAESystems (UK)
• Alstom Power (Switzerland)
• Ford (USA)
• Ansto (Australia)
• Clay Technology (Sweden)
• Rolls-Royce (UK)
• Volkswagen (Germany)
• Agusta Westland (UK)
• Alfa Avio (Italy)
• Boeing (USA)
• KOGAS (Korea)
• Suzuki (Japan)
• NPL (UK)

• Hamilton Sundstrand United Technologies (USA)
• NASA (USA)
• Kockums (Sweden)
• Chevron (USA)
• US Navy (USA)
• Defence Evaluation Research Agency (UK)
• Engage (UK)
• Mobil (USA)
• Bombardier (Canada)
• Cyfronet (Poland)
• DSTO (Australia)

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BEASY Applications Areas
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BEASY Products

• BEASY Mechanical Design
• Stress, thermal and contact simulation
• BEASY Fatigue and Crack Growth
• Crack growth simulation and multi site damage
• BEASY Corrosion and CP
• Corrosion control simulation and interference
  prediction
• BEASY CRM
• Corrosion simulation,ICCP and related electric
  and magnetic fields
• BEASY ECOAT
• Simulation of electrochemical coating processes
• BEASY Acoustic Design
• Acoustic simulation

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BEM Technology

• BEASY solutions are for the most part based on
  Boundary Element Method Technology (BEM)
• BEM is a technique similar to the Finite Element
  Method (FEM)
• However it is based on an Integral Equations
  methodology which provides substantial benefits
  for many applications
• Simplified Modelling
• Accurate modelling of small features and details
• Simplified modelling of large regions and
  infinite boundaries
• Accurate representation of surface phenomena

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How BEM can help

• Ease of use and faster data preparation gives
  substantial reduction in analysis costs
• Boundary-only model integrates well with CAD
  models
• Small details and features can be easily
  incorporated
• High Accuracy gives increased confidence in the
  product quality and reliability

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BEM Basics

• With BEASY you only need to define elements on
  the BOUNDARY or SURFACE
• BOUNDARY ELEMENTS

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Model only the Surface or Boundary
The BEASY Model describes only the Surface
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BEASY Results
Deformed Shape
Stress Distribution
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Brief Overview of Technology

• Mechanical Design
• Stress, thermal analysis to predict performance
  and durability
• Contact Simulation
• Predict load transfer characteristics and wear
• Fatigue and Crack Growth
• Predict integrity and life
• Corrosion and CP
• Predict effectiveness of corrosion control
  measures
• Electrocoating
• Optimise coating processes

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Brake Caliper
Bolt Hole Fixed in 3 Coord. Directions
Symmetry Plane
13.8 MPa Pressure Applied as Normal Traction in
Bore (including Pockets)
two zone model with 1520 elements
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Von Mises Stress
446 MPa (avg. mesh point value)
359 MPa (avg. mesh point value)
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BEASY-Non-conforming Contact

• Fixities

All displacement components set to zero
All displacement components set to zero
All displacement components set to zero
This position is Corner A
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BEASY-Non-conforming Contact
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BEASY-Non-conforming Contact

• Principal stress

Two regions where contact pressure is high
Two regions where contact pressure is high
This position is Corner A
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Structural Integrity Assessment

• All structures contain flaws to some extent, E.G.
  As a result of
• The manufacturing process
• The fabrication
• Localised in-service damage
• Numerical fracture mechanics answers the
  following questions
• Will the crack grow ?
• Will it grow in an unstable fast or slow manner ?
• If growth is stable, at what rate will it grow ?
• To what size can the crack grow before becoming
  unstable ?

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Initial Boundary Element Mesh
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Crack Growth Results After Applying Loading Cycles
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Detailed View Of Crack Growth From Bolt Holes
ADVANCING CRACKS
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Actual Crack Growth Pattern During Experimental
Testing
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Electrochemical Coating

• BEASY can be used to predict the performance of
  coating processes
• In this model there is
• a single plate anode
• Two plates close together to be coated
• Results include
• Coating thickness distribution
• Potential and current fields

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Coating Performance With Time
T.03
T17
T.15
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Corrosion Control
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Modelling Is Simple As Only the Wetted Area of
the Ship is Modelled
BEASY can predict the effectiveness of corrosion
control measures.
For defence applications it can also predict the
corrosion related electric and magnetic fields
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BEASY Modelling Products

• BEASY
• Includes its own modelling and visualisation
  tools
• BEASY PATRAN
• Create and visualise BEASY models in PATRAN
• BEASY IDEAS
• Create and visualise BEASY models in IDEAS
• BEASY NASTRAN
• Convert NASTRAN bulk data files to BEASY models

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BEASY Acoustic Design
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BEASY Acoustic Design

• What can BEASY Acoustic Design Do ?

Architectural Acoustics
Sound Radiation
Vibro Acoustics
Wheel Noise
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BEASY Acoustic Design

• Prediction of Interior Exterior Noise Fields
• Noise Control and Reduction
• Structural Acoustic Scattering and Radiation
• Vibro Acoustics
• Panel Contribution Analysis
• Architectural and Environmental Acoustic Design

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BEASY Acoustic Design

• Vehicle Acoustic Design
• Modelling of Reflective, Absorbing Open
  Boundaries
• Multi Region Analysis
• Acoustic Diagnostic sensitivity Analysis
• Prediction of Sound Power, Pressure and Intensity

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BEASY Acoustic Design

• Sound Propagation through Absorbing Material
• Noise Analysis of Soft and Rigid Half Space
• Multi Frequency Analysis
• Prediction of Acoustic Efficiency
• Allowing for Complex Frequency, Density and Speed
  of Sound
• NASTRAN Interface

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Vehicle Sound Reduction

• Predicted sound pressure level in vehicle. Note
  cut away elements to reveal the internal details
  of the seat models

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Acoustic Problem Types

• BEASY can Solve
• Interior Acoustic Problems
• Exterior Acoustic Problems
• Coupled Exterior and Interior Acoustic Problems

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Applications

• The Acoustic Domain is Surrounded by the Boundary
• Muffler
• Passenger Compartment Acoustics
• Room Acoustics
• Acoustic Cavities

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Exterior Problems

• Boundary of the problem surrounded by the
  acoustic domain
• Radiation problems
• Scattering problems

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Acoustic Zones

• BEASY can model multiple acoustic regions e.g.
• Vehicles
• Engine Compartment
• Passenger's Cabin
• Interior/exterior coupled

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Acoustic Zones

• You may use Multi Zone Facility for
• Coupling Regions with Different Acoustic
  Properties
• Coupling Regions of Different Types E.g. Interior
  Exterior
• Reducing the Computer Resources Requirement

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Surface Conditions

• BEASY can Model different Surface Conditions

Baffles
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BEASY Acoustic Boundary Conditions

• Complex Pressure
• Complex Velocity
• Complex Surface Velocity
• Complex Velocity Potential
• Complex Acceleration
• Complex Impedance
• Complex Admittance

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Sound Absorbent Boundaries
Panels can be sound absorbent
Impedance or Admittance
User specifies the structure velocity and
impedance or Admittance
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Open Fully Absorbent Boundaries
Sound is free to leak from the interior
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Fully Reflecting Boundaries
Velocity set to Zero
Sound is Reflected Back to the Domain
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Features of BEASY Acoustic

• Employs Advanced BE methods to Solve Acoustic
  Problems
• Comprehensive BE Element Library
• Comprehensive Boundary Conditions Type
• Error Analysis to evaluate the Accuracy of the
  Results
• Comprehensive Data Check
• Step_Wise Analysis Options and Restart

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Advantages of BEASY for Acoustics

• Describe only the surface of structure
• Easy to model geometrical complexity
• with reduced cost
• Easy to Interface with CAD Systems
• Exterior problems with Infinite boundaries
• Reduced number of degrees of freedom
• particularly for high frequencies
• Accurate solution

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Theoretical Introduction and Verification Example
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Theoretical Foundations

• Acoustic Wave propagation
• Where u(x,t) Velocity Potential
• c Speed of Sound
• b(x,t) Noise Source
• x and t Position and Time variable

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Theoretical Foundations

• Acoustic pressure
• Where mass density of the acoustic media
• Velocity

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Theoretical Foundations

• Assuming time harmonic
• Transform from the time to frequency domain
• Where k w/c the wave number
• w angular frequency

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Theoretical Foundations

• The resulting BEM Equations at the specified
  frequency w are
• Where
• u Velocity Potential
• q Normal Velocity
• Note all values are complex

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Diagnostic Analysis

• From BE Internal Point equation
• Where
• v velocity on the boundary
• p pressure on the boundary
• g and h are the influence coefficients

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Diagnostic Analysis

• Contribution to the pressure at a point due to
  the pressure on one element
• Pressure h p
• Similarly the contribution due to the velocity of
  one surface element
• Pressure g v

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Sensitivity

• The influence terms g and h enable us to compute
  the sensitivity
• The change in the pressure due to a unit change
  in the surface velocity
• Eg How much do I have to reduce the velocity on
  element n to reduce the sound level at this point
  by 10

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Verification Examples

• Multi zone Piston with complex materials
• Features
• High Accuracy
• Multiple Acoustic Regions
• Sound Absorbing Materials

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Multi Zone Piston

• Multi Zone problem with different materials
• Acoustic propagation through porous
• material with complex properties

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Multi Zone Piston
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Sound Pressure Level
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Acoustic Pressure at Surface of Piston
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Acoustic Pressure at Surface of Piston
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Transmission Loss Assessment
C. Calì1, R. Citarella1, A.Galasso2 2Elasis
S.C.p.A. (FIAT GROUP), Pomigliano (NA),
ITALY 1Dept. of Mechanical Engineering,
University of Salerno, ITALY
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Transmission Loss Assessment

• One of the most valuable criteria for vehicle
  quality assessment is based on acoustic emission
  levels
• A car is judged comfortable depending upon the
  noise level transmitted inside
• Consequently there is a general attention to
  design criteria aimed to improve the
  structural-acoustic behaviour
• Such design approach, based on experimental and
  numerical procedures, enables the
• prediction of noise emissions
• correlation with the structural vibration sources

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Experimental Set Up

• A rectangular panel is placed as a separation
  between
• A reverberant room, where a uniform acoustic
  field is artificially generated
• An anechoic room where it is possible to measure
  the transmitted (by the panel vibrations)
  acoustic field
• In the reverberant room a rotating microphone
  provides the pressure level frequency spectrum

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FEM Model of Panel

.

Loaded side by a spatially uniform pressure, as
provided by the frequency spectrum
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BEM Model of the Cavity
Vibrating Panel
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First Vibration Mode
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Dynamic Analysis

• The procedure starts with the dynamic assessment
  of the component behaviour by an FEM modal
  analysis
• The results are compared with the experimental
  measurements in order to validate the model.

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FEM Panel Model

• The FEM panel model is fully constrained on 32
  uniformly spaced points along the borders,
  consistent with the welding points applied to the
  real panel
• The following input data were used
• Panel dimensions 1760x1020x2 mm
• Material steel
• Density 7850 kg/m3
• Damping 0.005
• Young modulus 2.1E05 N/mm2
• Poisson ratio 0.3
• ANSYS element type Shell 63

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BEM Acoustic Analysis

• For the acoustic analysis, the BEM mesh has to be
  sufficiently refined depending on the higher
  frequency of interest (at least four quadratic
  elements per wavelength)
• For the acoustic analysis, the modelled fluid
  properties are the following
• density 1.22 kg/m3
• sound speed 344 m/s
• reference pressure 2E-0.5 N/m2

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Transmission Loss
Predicted
Experimental
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Difference Between Numerical and Experimental
Transmission Loss
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Summary

• Satisfactory agreement is obtained between the
  numerical procedure and with the experimental
  data.
• The FEM-BEM coupled approach can be easily
  applied to solve vibration acoustic problems
• A more refined FEM and BEM mesh is required if
  higher frequencies are to be studied
• The same procedure can be applied to complex
  components such as car bodies.

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Panel Contribution Analysis
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Acoustic Simulation

• First Generation
• Analysis Tool to predict acoustic fields
• Second Generation
• Design Tool to Evaluate Diagnostic and Solution
  Sensitivities
• Panel Contributions

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Diagnostic Analysis What does it tell us ?

• Acoustic analysis predicts the sound field
• Diagnostics/Panel Contributions predict
• How much sound each part of the structure is
  Directly and Indirectly generating at a given
  position ?
• What are the major contributors to the sound
  level at any position ?
• What is the sensitivity of the sound level to
  changes in surface Conditions ?
• What is the contribution from each structural
  panel ?

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Panel Contributions
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Direct and Indirect Contributions

• In most cases the sound from a vibrating
  structural panel travels Directly and Indirectly
  to the diagnostic point (Eg Drivers ear)
• It reflects from other surfaces
• BEASY can compute both the Direct and Indirect
  Contribution by a powerful analytic technique

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True Contribution
Includes both direct and indirect contributions
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Acoustic Diagnostic Application

• Sound Signature of an Under Water Vehicle

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Diagnostic Analysis Under Water Vehicle

• Underwater Vehicle near a sound source
• The objective is to
• determine the quantity of sound entering the
  vehicle
• determine the sound level at an observation point
  outside the vehicle
• determine how much of the sound level at the
  observation point is contributed by the
  structural surfaces inside the vehicle
• ie How much sound enters the vehicle and is
  reflected back

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BEM Model
External surface of vessel
Sea
Open Compartment
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Sound Pressure Level Surrounding The Vessel
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Panel Contributions

• Contribution of each element on the inside
  surface of the vessel to the sound level at the
  observation point

The element colour indicates how much sound each
element contributes
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Acoustic Pressure Contribution

• The contributions of the two end panels to the
  sound level at the observation point. Each panel
  contributes over 3 to the sound level.

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Acoustic Diagnostic Application

• Acoustic Design of a Vehicle Interior

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Acoustic Design of an automobile

• In this application the vibration of the vehicle
  structure is driving the acoustic field
• The structure vibration can be obtained from
• A FEM model of the vehicle structure
• A user specified velocity
• A measurement system
• The objective is to predict the sound levels and
  determine the parts of the structure which must
  be modified to reduce the sound level

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Sound Pressure Level in Vehicle
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Diagnostic Analysis

• Objective
• To determine the contributions to the sound
  perceived by the driver

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Panel Contributions
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Redistributed Velocity Contribution
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Sensitivity Analysis of a Car's Cabin

• The influence coefficients can also be displayed
• They provide information on the sensitivity of
  the sound level at the observation point to the
  velocity of individual elements or panels

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Redistributed Velocity Influence

• Contour display of the influence (sensitivity) of
  sound level at the drivers ear to the velocity of
  each element

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Redistributed Velocity Contribution

• Contour display of the true contribution of each
  element to the sound level at the drivers ear

SPL
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Automobile Diagnostic Analysis

• Objective To determine the contributions to the
  sound perceived by rear seat passenger

Passenger position
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Redistributed Velocity Contribution

• Contour display of the influence (sensitivity) of
  sound level at the passengers ear to the velocity
  of each element

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Redistributed Velocity Contribution
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Diagnostic Analysis

• Acoustic analysis predicts the sound field
• Diagnostics predict
• How much sound each part of the structure is
  Directly and Indirectly generating at a given
  position ?
• What are the major contributors to the sound
  level at any position ?
• What is the sensitivity of the sound level to
  changes in surface Conditions ?

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Applications
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Architectural Acoustics

• Objective
• Predict the sound propagation through a building
• Procedure
• The BEM model describes the surfaces of the
  building.
• Each surface can have its own properties. eg
• Impedance
• Each room can be described as an acoustic zone
  which can have its own acoustic properties. eg
• Speed of sound
• Density
• The noise source can be defined as
• Point source or line source
• Vibrating structure

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BEM Model of the Building
Zone Interfaces
Room 3
Room 1
Room 2
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Sound Pressure Level on Structure
Noise source inside room 1
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Sound Pressure Level on Structure
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Acoustic Surfaces Impedance

• Objective
• Determine the impact of acoustic impedance
  conditions of the surface of the structure on the
  acoustic performance
• Procedure
• Define the surface of the structure with elements
• Specify the surface conditions using the
  impedance values
• Define the noise sources

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Predicting Acoustic Performance
BEM Model
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Predicted Sound Pressure
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Predicted Sound Pressure
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Sound Sources

• Objective
• Determine the sound field in a room with multiple
  speakers
• Procedure
• Define the BEM mesh of the surface
• Define impedance values of the surfaces
• Define any number of acoustic sources
• Define the display plane

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Sound Sources
Speakers
BEM Mesh of the Room
Display Plane
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Sound Pressure Levels on the Display Plane
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Noise Radiated From a Wheel

• Objectives
• Determine the noise radiated from a wheel due to
  its vibration
• Procedure
• Define the BEM surface elements
• Input the structural velocities from the FEM
  model
• Define the display planes

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BEM Model of a Wheel
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Predicted Sound Level on Wheel
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Sound Level on Display Surfaces
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Vibro Acoustics

• Objective
• To compute the acoustic response in the air
  surrounding the structure
• Procedure
• Develop the BEM model of the surface of the
  structure
• Import the surface velocities from the structural
  FEM analysis or measurement system
• Select the range of frequencies to be studied
• Define how the results are to be viewed

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BEM Mesh on the Structure
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Cylindrical Display Surface
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Sound Pressure at 300 Hz
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Acoustic Radiation

• Results can be displayed on the display planes or
  on the structure
• Results can include
• Sound Pressure Level
• Velocities
• Energy
• etc
• Displays can include
• Contours
• Graphs
• Tables

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Sound Pressure Level at 250 Hz
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Sound Pressure Level at 150 Hz
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Acoustic Radiation

• Results from different frequencies can be
  displayed

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Sound Pressure Level at250 Hz
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Sound Pressure Level at 150 Hz
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Sound Pressure Level at 50 Hz
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Underwater Acoustic Study

• In this application the acoustic fields
  surrounding a boat are predicted
• The noise source is part of the structure
  vibrating

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BEM Model
BEM Mesh
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Sound Pressure Level Near The Boat
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Surrounding Acoustic Fields
Sound Pressure Level
Z Velocity
X Velocity
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Pump NoiseStudy
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BEM Mesh on the Pump
Structural Vibration data is used to predict the
radiated noise
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Predicted SPL Near the Pump
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Predicted Radiated Noise
SPL contour in the air near the pump
Pump
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Fan NoiseStudy
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Industrial Fan

• The objective was to predict
• The noise generated by a fan
• The root cause of the noise

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Modelling Methodology

• FEM model used to predict the vibration of the
  fan
• NASTRAN bulk data including GRIDs and CQUAD4s
• NASTRAN punch file with structural velocity
  information
• BEASY computes the vibro acoustic solution

142
Model Data

• Distances in M
• Speeds in M/second
• Air Density1.25 Kg/m3
• Sound Speed600m/second
• Reference Pressure 1.E-8 Pa

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BEASY- Modelling 1

• Bulk data file read into the BEASY User Interface

Each CQUAD4 converted into a quadrilateral surface
144
BEASY- Modelling 2

• Some parts removed for this evaluation
• Surfaces reversed as necessary

Openings in fan casing
Openings in fan casing
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BEASY- Modelling 3

• Fan casing has internal partitions

Surfaces cut-away to show internal partition
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BEASY- Modelling 5

• Zones defined

Fan interior part 1
Fan exterior (infinite)
Fan interior part 2
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BEASY- Modelling 4

• Extra surfaces created as necessary

Surfaces created to close the openings
Surfaces created to close the openings
Surfaces created to close the openings
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BEASY- Modelling 6

• The CQUAD4 elements from the bulk data file were
  meshed with QUAD9 elements
• Materials properties defined

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BEASY- Modelling 7

• Group created containing elements for which
  structural velocity Boundary Conditions are
  required from the NASTRAN result file
• Element geometry file written containing
  details of the elements

Elements on which structural velocities are NOT
required
Elements on which structural velocities are NOT
required
Elements on which structural velocities are NOT
required
Elements on which structural velocities are NOT
required
150
BEASY- Modelling 8

• BEASY automatically applies NASTRAN structural
  velocities to the element geometry file.
• Selected frequency75 Hz

Arrows show velocity components
151
BEASY- Results 1

• Sound pressure level outside the fan

152
BEASY- Results 2
Sound pressure level inside the fan
153
BEASY- Results 3

• Sound pressure level inside the fan

154
BEASY- Results 4
SPL radiating away from the fan
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BEASY- Simplified Model

• Part of the fan removed
• New (bigger) surfaces created
• Model of only the outside of the fan

Mesh of 290 elements
22 surfaces
156
BEASY- Results 5

• Simplified model Sound pressure level

157
BEASY- Panel Contribution 1
Panel Contribution Analysis activated
Array of internal points at which contribution is
required
Array of internal points at which contribution is
required
Array of points at which contribution is required
158
BEASY- Results 6
Panel Contribution analysis predicts Contribution
to SPL at one of the target points
Target point
Target point
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BEASY- Summary

• Easy translation of geometry from bulk data file
  into BEASY
• Structural velocities automatically extracted
  from NASTRAN results files
• Clear visualisation of the acoustics field allows
  identification of source of the noise
• Panel Contribution analysis
• gives precise information on
• which parts of structure
• contribute most noise
• to selected target locations

160
Summary

• BEASY employs Boundary Element Method to Solve
  Wide Range of Industrial and Environmental
  Acoustic Problems
• BEASY allows Multiple Acoustic Zones
• BEASY supports wide range of Acoustic Boundary
  Conditions
• BEASY provides a Comprehensive Element Library

161
Summary

• BEASY provides Powerful Diagnostic Analysis
• BEASY Provides Acoustic Sensitivity Analysis
• The advantages of the BEASY approach is clear
  
• Simple modeling
• Reduced problem size
• Flexible modeling
• High accuracy

162
Next Step

• As you can see from this short overview BEASY
  provides effective solutions to an important
  range of problems
• Benefits include
• Improved quality of predictions
• Reduced cost
• BEASY provides an effective solution to many
  problems which could not be solved in a cost
  effective way with other technologies
• To find out more contact your nearest BEASY
  representative

163
Contact Information
Email info_at_beasy.com Web www.beasy.com Europe C
omputational Mechanics BEASY Ashurst Lodge
Ashurst, Southampton, SO40 7AA, UK Tel 44 (0) 238
029 3223 Fax [phone] North
America Computational Mechanics Inc 25 Bridge
Street, Billerica, Ma 01821 Tel [phone]
5841 Fax [phone]