Multiphysics Couplings
When two physics talk to each other: heat bends structures, fluids push panels, voltages squeeze crystals.
1. What's in this domain?
| Coupling | What talks to what | Example question |
|---|---|---|
| Thermo-mechanical | temperature → expansion → stress | "Will the exhaust manifold crack from heat?" |
| One-way FSI (CFD→FEA) | fluid pressure map → structural load | "Wind loading on this panel — deflection?" |
| Piezo | voltage ↔ mechanical strain | "How much does this actuator stroke at 100 V?" |
| Electromagnetics (magnetostatics) | currents → fields/forces | "Force on this armature?" |
2. When do I use it?
| Use when | Don't use for |
|---|---|
| Thermo-mechanical: heat causes expansion, constrained expansion causes stress | Single physics only (use Static or Thermal) |
| FSI: you have a CFD pressure map and want structural response | Full CFD simulation (use external CFD) |
| Piezo: piezoelectric actuators or sensors | Non-piezo materials |
| Electromagnetics: magnetic forces on current-carrying parts | High-frequency EM (RF/microwave) |
Use cases
| Problem Type | Industry | Example |
|---|---|---|
| Flow-induced vibration | Energy/Chemical | Heat exchanger tube vibration |
| Piezoelectric actuation | Aerospace/Automotive | Fuel injector actuator |
| Motor design | Automotive/Energy | Magnetic field analysis |
| High-temperature creep | Power plants | Turbine blade creep life |
| MEMS sensors | Electronics | Accelerometer design |
| Magnetic levitation | Transportation | Maglev force analysis |
3. The flow
Thermo-Mechanical
- Run thermal analysis first (steady or transient)
- Simulate → Thermo-Mechanical — uses temperature field as load
- Results — stress from constrained expansion
FSI
- Import pressure map from CFD
- Boundary — map pressure to structural faces
- Simulate → Static Structural
- Results — deflection from fluid pressure
Piezo
- Design — geometry
- Boundary — piezo material + voltage + mechanical BCs
- Simulate → Piezo
- Results — strain from voltage
Electromagnetics
- Design — geometry
- Boundary — current sources + materials
- Simulate → Electromagnetics
- Results — B-field, forces
4. Reading your results
Thermo-Mechanical
| Result | Meaning |
|---|---|
| Thermal stress | Stress from constrained expansion |
| Temperature field | Input from thermal analysis |
FSI
| Result | Meaning |
|---|---|
| Deflection | Structural response to fluid pressure |
| Stress | Combined mechanical + fluid loading |
Piezo
| Result | Meaning |
|---|---|
| Strain | Mechanical deformation from voltage |
| Electric field | Voltage distribution |
Electromagnetics
| Result | Meaning |
|---|---|
| B-field | Magnetic flux density |
| Force | Lorentz force on conductors |
5. Boundaries of truth
What's validated
| Case | Reference | Error |
|---|---|---|
| Thermo-mechanical staggered | Published | < 3% |
| Piezo d33 | Published | < 2% |
| Magnetostatics (Ampère) | Analytical | < 1% |
| FSI cantilever pressure | Published | < 5% |
What's NOT covered
- Two-way FSI — one-way only (CFD→FEA)
- Transient multiphysics — steady-state coupling only
- Nonlinear piezo — linear piezoelectricity only
- Time-varying electromagnetics — magnetostatics only
See also
- [Thermal](thermal.md) — for thermal analysis alone
- [Static Structural](static-structural.md) — for structural analysis alone
- [Dynamics](dynamics.md) — for dynamic coupling
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