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Simulation of Thermal-Structure Interaction
Kyle C. Koppenhoefer, Ph.D. Principal
ALTASIM TECHNOLOGIES
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Shankar Krishnan, Ph.D. Applications Engineer
COMSOL
Agenda
• Introduction to Thermal-Structure Interaction
• Simulating with COMSOL Multiphysics® • Thermal-Structural Examples, Design
Challenges, and Solutions • Live Demo
– Shrink Fitting • Q&A Session • How To
– Try COMSOL Multiphysics – Contact Us
Electric current and heat flow through the contacting surfaces of a switch
Thermal-Structure Interactions
Power generation Electronics and MEMS Automotive
Biomedical Aerospace
Simulating an Application
• Conception and understanding – Enables innovation
• Design and optimization
– Achieve the highest possible performance
• Testing and verification
– Virtual testing is much faster than testing physical prototypes Heating Circuit
Model tree Provides instant access to any part of the model settings • CAD/Geometry • Materials • Physics • Mesh • Solve • Results
The COMSOL Desktop®
Graphics Ultrafast graphic presentation, stunning visualization
COMSOL Desktop Straightforward to use, it gives full insight and control over the modeling process
Poll Question #1
How important is Thermal-Structure Interaction in your simulations?
• Very important - most of my simulations require some form of thermal-
structure interaction
• Important – when it is present, the interaction is important
• Somewhat important – but I don’t tend to work on coupled analysis
• Not important – None involve thermal-structure interaction
Thermal Expansion
l l + Δ l
Δ l = α(T-Tref)l
Heat
α
T-Tref
Δ l/l
Cool
Automatic and Manual Couplings Between Thermal and Structural Simulations
Nonlinear and Anisotropic Material Properties
Plastic, Viscoelastic, Viscoplastic Materials and Creep
Dynamic Effects
σ
ε
Tensile stress cools down Compressive stress heats up
Structural damping manifests as vibration-induced heating
Thermoelastic damping in MEMS devices
Adding More Physical Effects
Electromagnetic Heating and Thermal Expansion
Joule heating in electronics Induction heating furnace RF heating in a waveguide
Customized Multiphysics Interactions
Stress-optics: Thermal-stress-induced difference in refractive index between x and y-directions
Heating circuit: Electrical, thermal, and structural coupling between solid and shell
Thermal-Structure Interaction
Kyle C. Koppenhoefer, Ph.D. Principal
AltaSim Technologies, LLC
Overview
• Thermal-structural interaction examples • Design challenges • Coupling of temperature/deformation • Computational tools necessary for solving • Structural example problem • Shrink fit demonstration
THERMAL-STRUCTURAL EXAMPLES
Thermal-Structural Interaction Electronics
Turbines
Heat Treatment of Metals
Pressure Vessels Shrink-Fitting
THERMAL-STRUCTURAL DESIGN CHALLENGES
Thermal-Structural Design Challenges
• Material damage that is a function of temperature (e.g., yielding, creep)
• Mechanical damage due to constrained thermal growth – Mechanical constraints – Spatial temperature gradients – Material property variations (e.g., CTE)
• Spatial variations • Variations with temperature
Turbines
Constrained Thermal Growth
Δ l = α(T-Tref)l
∆𝒍𝒍
= 𝜶 𝑻 − 𝑻𝒓𝒓𝒓
𝜺𝒕𝒕𝒓𝒓𝒕𝒕𝒍 = 𝜶 𝑻 − 𝑻𝒓𝒓𝒓
𝜺𝒕𝒓𝒎𝒕 = 𝜺𝒕𝒕𝒕𝒕𝒍 − 𝜺𝒕𝒕𝒓𝒓𝒕𝒕𝒍
𝝈 = 𝑬𝜺𝒕𝒓𝒎𝒕
l l + Δ l
Heat
Cool
Thermal strain produces displacement Mechanical strain produces stress
THERMAL-STRUCTURAL COUPLING
Thermal-Structural Interaction
Sequentially Coupled
Turbines
Fully Coupled
Loosely Coupled
Temperature → Deformation Examples: • Pressure vessel w/ different fluids • Beam buckling due to thermal load
Temperature ↔ Deformation Examples: • Forging • Contact changes due to deformation
Examples: • Frictional heating (e.g., disk brakes)
COMPUTATIONAL TOOL – KEY FEATURES
Key Features
• Thermal and structural analysis within same software – Thermal analysis includes conduction, convection, and
radiation – Elastic, plastic structural response – Ability to model phase changes – Solution methods
• Steady state analysis • Transient analysis
– Sequential coupling • Apply temperatures from thermal analysis to structural
– Two-way coupling • Mechanical contact • Thermal contact • Heat source due to plastic strain
Key Features
• Material properties – Thermal
• Thermal conductivity • Density • Specific heat (transient) • Latent heat of transformation (temperature range)
– Structural • Elastic modulus • Poisson’s ratio • Yield Strength
– Temperature dependent material properties
Thermal Contact
• Evaluates heat conduction across two contacting surfaces
• Contact localized at asperities due to surface roughness
• Heat flux on boundaries
Tu
Td
Thermal Contact
• Three components of conductance
– Constriction conductance (hc) – Gap conductance (hg) – Gap radiation (hr) – h = hc+ hg+ hr
• Friction heat , Qfric, is a heat source term that is partitioned between the two surface using the surface roughness term, r – r=0.5 for identical surfaces
Thermal Contact
• Cooper-Mikic-Yovanovich (CMY) Correlation – Isotropic surface roughness – Plastic deformation of the surface asperities
• Mikic Elastic Correlation – Isotropic surface roughness – Elastic deformation of the surface asperities
• User Defined – Define constriction conductance directly
Cooper-Mikic-Yovanovich
• Constriction conductance
THERMAL-STRUCTURAL EXAMPLE
Example Problem – Shrink Fitting
• Railroad wheels assembled via shrink fit onto axle
• Axle critical for railway vehicle safety
• Fretting fatigue at fit interface is significant failure mode
• Safety insured by regular inspection of axels
• High contact stress can accelerate fretting fatigue
Example Problem – Key Features
• Two-way coupled problem due to contact – Mechanical contact – Thermal contact
• Temperature-dependent plasticity • Transient thermal and mechanical analysis • Parametric studies on geometry variations
Live Demonstration
• Please wait while the content is loading • Demonstration of shrink fit problem setup
Poll Question #2
What type of thermal-structure interaction are you interested in simulating?
• Thermal expansion – including thermal stress
• Nonlinear materials – viscoelastic, creep, etc.
• Thermal contact – to account for surface effects
• Other multiphysics – involves electromagnetic heating, convective cooling, etc.
• More than one of the above
Q&A Session
Product Suite – COMSOL 4.4
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