6469739

Airborne Sound of ElectricalMachines using Symmetric

Matrices in ANSYS 14 ANSYS CONFERENCE & 29. CADFEM USERS’ MEETING

20th October 2011Dipl.-Ing. Steffen Peters, CADFEM GmbH

Dipl.-Ing. Fatmir Hetemi, Universität MünchenLucas Kostetzer, Eng., ESSS

FFEEAAAAMM GmbH Forschungszentrum für Elektrische Antriebstechnik und Aktorik München

Kooperationspartner der

Airborne Sound of Electrical Machines in ANSYS 14

Contents

- 1 -

Motivation FSI Coupling Methods Coupling Performance for a Flat Plate Test Case: Electric Motor Workflow from Electromagnetics to Acoustics FSI Setup Discussion of Results Coupling Performance for E-Motor

Conclusions & Outlook


MOTIVATION


Motivation (I/II)

Noise in electric motors ( 3 types) Aerodynamics ( cooling fan, moving parts) Bearings and mechanical connections Electromagnetic

Present objective Numerical study of electromagnetic

induced vibration and noise of a permanent magnet motor

Team University of defense of Munich

Machine data, experimental Electromagnetism expertise

CADFEM/ESSS Modeling and simulation expertise


Motivation (II/II)

- 4 -

Acoustic simulation of electric drives requires coupled physics Magnetic forces excite motor structure to radiate so un d

ANSYS MaxwellMagnetic Field

ANSYS MechanicalStructural Dynamics

Efficient load transfer or coupling between solvers (inkl. FFT) Efficient solution of acoustic field

Forces (FFT)

ANSYS MechanicalAcoustic Field

Displacements


FSI COUPLING METHODS


Fluid-Structure-Interaction (FSI) Coupling Methods

- 6 -

Weak coupling (one-way coupling) No feedback of the sound field on the structure Decoupling into two separate tasks: structure and fluid/acoustics Sufficient in many cases In preparation, but currently no push-button solution in ANSYS

Strong coupling (two-way coupling) Required for couplings with notable feedback from fluid

E.g., Light weighted structures and/or heavy fluids (water) Non-linear behavior requires staggered solution (CFD-Mechanical) Linear solution in ANSYS Mechanical via FSI matrix coupling

Two possible implementations Symmetric system matrix Unsymmetric system matrix

In this investigation we’ll have a closer look at the symmetric and unsymmetric coupling of structure dynamics and acoustic field

1-Way

2-Way


- 7 -

Acoustic FSI: Unsymmetric Implementation

Putting structure and fluid fields together we end up with the unsymmetric coupled (u,p) formulated FSI matrix system for solving elasto-acoustic

hydro-elastic problems

The unsymmetric matrices require a special solver for transient, harmonic and modal analysis High consumption of memory and CPU time

m+mf

c+cf

k+kf

F(t)+pf(t)

u(t), v(t)


Acoustic FSI: Symmetric Implementation

FSI/MMo 8

Symmetric (u,p,φ) formulations of the FSI problem available by Sigrist (DCN propulsion, France) and Garreau (ANSYS France) Basic idea: introduce an additional DOF in terms of fluid displacement potential to

get larger but symmetric system matrices use standard symmetric solvers to solve the problem in physical space due to the symmetry of all matrices real modes will result

Released feature and default coupling algorithm in ANSYS 14 Hidden beta feature until then Now fully validated and released

additional DOF: SP01


COUPLING PERFORMANCE


Flat Plate: Comparison of Coupling Performance

- 10 -

Simple test case for performance evaluation 531 structural, 13180 acoustic nodes 22 frequencies (0..100Hz) Pressure excitation on structure Infinity (Robin) boundary condition on fluid exterior

FSI coupling Symmetric matrix formulation Unsymmetric matrix formulation

Boundary Conditions Sound Pressure


Flat Plate: Comparison of Coupling Performance

11

Symmetric coupling performance comes close to one-way performance 1-way coupling applied by 1D script for APDL, no 3D yet Symmetric coupling applied to real test case of an electric motor

Unsym Sym Struct full Struct MSUP* Air Sum full Sum MSUP*

Max Total Memory Used [MB] 1010.00 794.00 563.00 543.00 641.00 641.00 641.00

Solution CPU Time [s] 151.00 90.00 5.50 3.00 56.22 61.72 59.22

Solution Elapsed Time [s] 188.00 108.00 20.00 8.00 68.00 88.00 76.00

*MSUP = Modal Superposition


TEST CASE: ELECTRIC MOTOR


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Machine description

Synchronous machine BSM 3-4000

Machine type Brushless Permanent Magnet AC motor

Rated Output Power (kW) 0. 8

Rated Voltage (V) 200

Number of Poles 4

Stator teeth 24

Rated Speed (rpm) 1000

Circuit ( 3 phases) 33.3Hz

Type of Circuit Y3

Characteristic frequencies• frot=1000rpm/60 =16.66Hz• fcurrent=33.33HzFrom machine design• max rotational speed is 4000rpm• frot, max=66.66Hz

Source: [Universität der Bundeswehr München]


Workflow in detail – 1. Electromagnetics

Inputs Machine data (2D) Mechanical load and conditions Circuit input (current/voltage)

Results exchange (output) Forces acting at each stator tooth over the time

Per tooth we have a radial and tangential force that is transformed to frequency domain (FFT) One real and imaginary part per force

4 .csv files per tooth


Workflow in detail – 2. Structural Dynamics

Inputs Machine data (3D) Forces spectrum from

electromagnetic simulation External field conditions (acoustics)

Results exchange (output) Displacement field at the housing

per each solved frequency Sound field

Sound pressure Sound pressure level Sound power Sound power level


ELECTROMAGNETICSIn brief. More details in presentation by S. Fink @ EM Session


Maxwell 2D Results: Magnetic Field


Maxwell 2D Results – Force calculation

Expressions to calculate force density at the air gap Radial Force density [Nm-2]

Tangential Force density [Nm-2]

Integration location Line integral per tooth

trt BBf0

1

22

021

trr BBf

11 Line tdeptht dlfLF

11 Line rdepthr dlfLF

@¼ of the air gap

zoom


Maxwell 2D Results: Force Analysis

Fast Fourier Transformation performed by Maxwell output interfaceWritten to CSV files (Re(F) & Im(F) vs. freq.) per tooth

11 Line tdeptht dlfLF

11 Line rdepthr dlfLF

FFT of forces

Conversion from time domain into frequencydomain


STRUCTURAL DYNAMICS


Modal Analysis: Structural Behavior

To gain better insight into the possible stuctural response a modal analysis was performed Dominant modes Mode2: 2016Hz ( first resonance frequency of this machine)

There are more frequencies in the mode 2: (2057,2483,2761Hz) Mode 3: 5208Hz, 5241Hz Mode 4: 5532Hz, 5541Hz

Mode2: 2016Hz Mode3: 5208Hz Mode4: 5532Hz


Damping ratio effect on vibration

Housing X direction displacement

No effect of damping except for the resonance frequencies Good design Comparison to measurements would return true damping values

Highest amplitude in the low frequency band

66.6Hz

Experimental measurments pending


ACOUSTICS


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Fully coupled Setup

Geometry in 3D: Machine structure (stator, winding body & housing) Air enclosure for acoustics (created in DesignModeler)

Input: radial and tangential force on stator teeth Forces spectrum from electromagnetic

simulation (Maxwell) Boundary conditions Asymmetric MPC contact between structure and fluid Infinity (Robin) boundary condition on fluid exterior Force mapping by pilot node

APDL script Remote force on pilot node (one per tooth) Force applied at the remote points

From .csv table FSI coupling via symmetric matrix approach


Coupled Acoustics Setup in ANSYS Workbench 14

- 25 -

Acoustic domain, boundary conditions and result evaluationset up via GUI extension for acoustics (next slide)

Air Domain

Exterior BC

FSI BC

Far-fieldpostprocessing

User definedresults: SP, SPL


Coupled Acoustics Setup in ANSYS Workbench 14

ACT Acoustics module available for Mechanical Editor ACT allows for fast adaption and extension (also < release cycle) No more need to do acoustics in APDL

For more details on ACT / Application Customization Toolkit for ANSYS 14 ANSYS Programming & Customization sessions


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Acoustic Field Results

Sound pressure level and sound pressure at 2500 Hz


- 28 -

Acoustic Field Results

Sound pressure animation at 2500 Hz


- 29 -

Acoustic Results

Radiated sound power level [W] Integral quantity Independent of location

of measurement Independent of environment

Sound pressure level SPL [dB] Local quantity at microphones Depends on location

of measurement (micro) May depend on measurement

environment (echoic / unechoic,…)


Radiation Efficiency

- 30 -

Structural deformation Highest peaks in low freq. band

Sound pressure level Highest peaks in mid to

high frequency band

Low radiation efficiency in low frequency bands Structural dynamics calculation alone

is insufficient for prediction of sound


E-MOTOR: COUPLING PERFORMANCE


E-Motor: Comparison of Coupling Performance

- 32 -

Simplified mesh test case for performance evaluation 99866 (quadratic) structural, 14035 acoustic (linear) nodes 10 frequencies (0..4000Hz) for this comparison Force excitation from Maxwell on stator teeth Asymmetric MPC contact between structure and fluid Infinity (Robin) boundary condition on fluid exterior

FSI coupling Symmetric matrix formulation Unsymmetric matrix formulation

Sound PressureMesh


E-Motor: Comparison of Coupling Performance

33

One-way coupling still to be done in 3D

Symmetric coupling performance >2x faster than with unsymmetric coupling

Unsym Sym

Max Total Memory Used [MB] 17435.00 9516.00

Solution CPU Time [s] 11170.00 4805.00

Solution Elapsed Time [s] 4434.00 1700.00


Conclusions & Outlook

- 34 -

Acoustics accomplishes virtual prototyping Better physical understanding of…

Electromagnetics Vibration Acoustics

Symmetric matrix implementation in ANSYS 14 Significantly faster than unsymmetic approach Nearly as fast as 1-way coupling when solving

harmonic response with full matrices But… No re-use of existing results No MSUP for structure side 3D-implementation of 1-way coupling to be

done via APDL and ACT ANSYS Workbench ACT Acoustics extension Provides GUI accessibility of acoustic setup

6469739

Documents

acoustic fsi

ansys conference

weak coupling oneway

sound field

motor structure

p formulated fsi matrix

structure dynamics

symmetric system matrices