FEA ANALYSIS
OPTIMIZER
INTEROPERABILITY
SERVICE
General-purpose multiphysics design and analysis
software for a wide range of
applications
Automatically selects and
manages multiple goalseeking algorithms
Built-in circuit modelling and
interfaces to leading CAD
packages
Technical support, training and
consultancy services available
for software usage and
applications
30th Anniversary Event
Multi-Physics for Electrical Machines
By Dan ILEA
Overview
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Multi-physics simulation for Electrical Machines
– Definitions
– Electrical Machines and Multi-physics
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Challenges of multi-physics simulation
– Electromagnetics
– Thermal
– Multi-physics coupling
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Multi-physics in Opera – future steps
Multi-Physics for Electrical Machines
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Multi-physics simulation
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Definition:
= Continuum physics that depends on the behaviour of one or more other continuum
physics
– May be sequential
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EM analysis => Forces => Stress analysis => Deflection
– May have mutual dependence
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EM analysis => Heat => Thermal analysis => Temperature rise
Updated material properties
Multi-Physics for Electrical Machines
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Iterative process
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Multi-physics simulation for Electrical Machines
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Electrical Machines and Multi-Physics
– Rare earth magnets
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Offer a high power density
Sensitive to temperature and vibration
– Insulation fatigue
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Thermal and Stress effects have a compounded effect
EPSRC FUTURE Vehicles project: http://www.futurevehicles.ac.uk/index.html
– Reliability
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Safety – automotive, aeronautic and other transport applications
Cost – off shore wind energy generation
Multi-Physics for Electrical Machines
EUGM 2014
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Multi-physics simulation for Electrical Machines
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Electrical Machines and Multi-Physics
– Specific requirements from the automotive domain:
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Harsh operation conditions
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Highly non-uniform driving cycles
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High speed machines
Improvements in computer hardware and multi-core PC’s now make the full
multi-physics characterisation of electrical machines realistic
Multi-Physics for Electrical Machines
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Challenges of multi-physics simulation
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Electromagnetics
– Opera-2d and 3d solvers for EM have been
widely validated for all machine types
– Opera-2d offers a reliable and quick first
validation for the majority of cases
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Steady-state and transient operation
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Mechanically coupled motion
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Co-simulations (MATLAB/Simulink)
Multi-Physics for Electrical Machines
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Challenges of multi-physics simulation
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However, when solving other physics (Thermal, Stress) or coupled multi-physics
full 3d models are needed
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Solving complex 3d EM problems can be extremely time-consuming
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Mechanically coupled movement
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Starting and transient operation
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Complex control strategies
SOLUTION:
– Solve 2d EM problem => Import model into Opera-3d => Solve other physics
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Feasible for some cases
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Cumbersome, less efficient and prone to user errors
Multi-Physics for Electrical Machines
EUGM 2014
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2d Slice Option
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New Symmetry option in the Modeller (available only through ME3d)
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Creates a 2d slice from the full 3d model for quick analysis
Multi-Physics for Electrical Machines
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2d Slice Option
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The full model is preserved; completely reversible operation
Solve 2d slice for transient simulations
Multi-Physics for Electrical Machines
Solve full 3d model when needed (e.g. thermal, stress,…)
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2d Slice Option
Considerably speed-up your analyses
4000
3500
3394
3000
Solution time [s]
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2500
2000
1500
1000
742
500
77
21
2d slice
2d slice
with
rotational
symmetry
0
reflection
symmetry
reflection
with
rotational
symmetry
Similar solution times to 2d
Multi-Physics for Electrical Machines
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Thermal analysis
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Inherently a 3d problem
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Opera uses thermal conductivities, heat transfer BC and thermal contact
resistances to define the model space
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Two major problems when analysing machines:
– What happens in the gap?
– How to model conductors?
Multi-Physics for Electrical Machines
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Thermal analysis - Boundaries
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Designer needs to supply the heat transfer boundary conditions
– Outer boundary
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Relatively easy to calculate using analytical data or from existing measurements
Outer heat transfer
coefficient BC
Multi-Physics for Electrical Machines
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Thermal analysis - Boundaries
– Internal boundaries
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More complicated to calculate the Heat Transfer Coefficients (HTC), especially on the
surface of the Gap
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HTC dependent on the type of cooling, rpm, gas pressure and temperature, etc.
Gap heat transfer
coefficient BC
Multi-Physics for Electrical Machines
EUGM 2014
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HTC calculation tool
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New tool for calculating the heat transfer
coefficient for machine gap
– Two different types of cooling:
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Natural
Forced
– Analytical calculation of the HTC of the gap based
on the gap geometry, machine speed and cooling
gas properties
– Developed in collaboration with City University
London
Multi-Physics for Electrical Machines
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HTC calculation tool
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New tool for calculating the heat transfer coefficient for machine gap
(continued)
– Automatically applies calculated value to the selected boundary
Multi-Physics for Electrical Machines
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Thermal analysis
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Accurate modelling of conductors for thermal solution
– Critical since most heating is produced in this region (copper losses)
– Very difficult:
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Conductors consist of materials with very different thermal properties:
– Wire (usually copper), Insulator, Resins…
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Fill factor has a big impact on the thermal conductivities in the region
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Conductors have multiple turns
– Individually modelling each turn along with each section of insulation is rarely
feasible
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Geometry of end windings is sometimes difficult to model
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Thermal analysis - Conductors
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A compound thermal conductivity for the material in the slot can be
calculated:
– 𝑆𝑙𝑜𝑡𝑇𝑐 =
𝐶𝑜𝑝𝑝𝑒𝑟𝑇ℎ𝐶 ∗𝐾𝐶𝑢 +𝐼𝑛𝑠𝑢𝑙𝑎𝑡𝑜𝑟𝑇ℎ𝐶 ∗𝐾𝑖 +𝑅𝑒𝑠𝑖𝑛𝑇ℎ𝐶 ∗𝐾𝑟
3
, where:
– CopperThC, InsulatorThC and ResinThC are the copper, insulation and resin thermal
conductivities, respectively
– Kcu, Ki and Kr are the relative proportion of the area occupied by the copper,
insulation and resin, respectively so that:
𝐾𝐶𝑢 + 𝐾𝑖 + 𝐾𝑟 = 𝐹𝑖𝑙𝑙 𝑓𝑎𝑐𝑡𝑜𝑟
Multi-Physics for Electrical Machines
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Thermal analysis - Conductors
Motor Cover
Slot material (compound
conductor thermal conductivity)
Magnet
Multi-Physics for Electrical Machines
Stator iron
Rotor iron
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Thermal analysis - Conductors
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Compound thermal conductivity applied to the region including the end
windings
“Air” (Low thermal
conductivity)
Slot material
(compound conductor
thermal conductivity
Motor Cover
Multi-Physics for Electrical Machines
EUGM 2014
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Thermal analysis - Conductors
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Meshed Conductors – Heat source (I2R)
Meshed conductors = heat source
Multi-Physics for Electrical Machines
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Thermal analysis
Temperature and heat flux vectors produced by copper losses (one phase)
Multi-Physics for Electrical Machines
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Multi-physics coupling
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Using tables
– Passing field information between simulations
– Typical scenario
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Solve EM solution
Create thermal op3
Read thermal op3 into Post
Create table of element centroids
Read solved EM into Post
Create table file with loss values from EM at thermal centroids
Re-read thermal op3
Import loss values into thermal
Solve thermal database
– Allows different mesh, symmetries and include only necessary components
Multi-Physics for Electrical Machines
EUGM 2014
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Multi-physics coupling
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Multi-physics analysis
– “Fields” passed directly between analyses
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Automatic calculation
– “One stop” definition of material properties, boundary conditions, volume
properties, symmetry for all analyses
– Same mesh used for all simulations
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Stress / Thermal will ignore AIR
Multi-Physics for Electrical Machines
EUGM 2014
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Multi-physics coupling
Multi-Physics for Electrical Machines
EUGM 2014
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Multi-physics coupling
•Material properties
•Volume properties
•Boundary conditions
•Symmetry
Multi-Physics for Electrical Machines
EUGM 2014
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Multi-physics coupling
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All non-transient analysis simulations
– Magnetostatics (TOSCA)
– Steady-state AC (ELEKTRA-SS)
– Velocity (ELEKTRA-VL)
– High Frequency (Soprano-SS / Soprano-EV)
– Space Charge (SCALA)
– Static Thermal (TEMPO-ST)
– Static Stress (STRESS-ST)
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Transient Electromagnetic (ELEKTRA-TR) at Time=0
– Allows deflections of meshed coils to be calculated in static stress analysis
Multi-Physics for Electrical Machines
EUGM 2014
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Multi-physics – Future steps
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Extend multi-physics coupling to transient simulations
– Include post-processing of transient analyses during simulations
– Allow for more parameters to be passed between the various analyses
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Extending 2d slice integration
– Extrapolate results from slice onto the full model
– Solve reduced EM model and map directly to the full model for other physics
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More Parallel
Multi-Physics for Electrical Machines
EUGM 2014
Cobham Technical Services