Acoustics
How sound and pressure waves travel through fluids and structures.
1. What is it?
Acoustic analysis solves the Helmholtz equation — the wave equation in frequency domain — for pressure waves in a fluid region:
- Resonant modes of a cavity (room, duct, bottle): at which frequencies does the air column ring?
- Pressure field from a vibrating boundary: where are loud spots?
"This duct: what's its first acoustic resonance? Will the fan tone hit it?"
2. When do I use it?
| Use when | Don't use for |
|---|---|
| Interior noise, duct acoustics, cavity resonances | Outdoor propagation over terrain |
| Simple radiation questions | Absorption design |
| Room modes, Helmholtz resonators | CFD-level flow-noise (aeroacoustics) |
Use cases
| Problem Type | Industry | Example |
|---|---|---|
| Muffler design | Automotive | Exhaust silencer tuning |
| Room acoustics | Architecture | Concert hall modes |
| Cabin noise | Aircraft | Fuselage acoustic modes |
| HVAC duct silencing | Building Services | Duct resonator design |
| Speaker enclosure | Consumer Electronics | Box resonance analysis |
| Sonar transducer | Defence | Underwater acoustic modes |
3. The flow
- Design — geometry of the fluid region
- Boundary — material (density, speed of sound) + walls + excitation
- Mesh — generate (6+ elements per wavelength)
- Simulate → Acoustics → set frequency range
- Results — resonant modes, pressure field
4. Reading your results
Resonant Modes
| Result | Meaning |
|---|---|
| Natural frequency | Frequency at which the cavity rings |
| Mode shape | Pressure distribution at that frequency |
Pressure Field
| Color | Meaning |
|---|---|
| Blue | Low pressure |
| Red | High pressure |
5. Boundaries of truth
What's validated
| Case | Reference | Error |
|---|---|---|
| 1D duct resonance | Analytical | < 1% |
| 2D cavity modes | Published | < 2% |
What's NOT covered
- Outdoor propagation — infinite domains
- Aeroacoustics — flow-generated noise
- Absorbing materials — rigid walls only
- Structural coupling — fluid-only
See also
- [Multiphysics](multiphysics.md) — for fluid-structure coupling
- [Dynamics](dynamics.md) — for structural vibration
Keep exploring
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