Example5 Resonance in Cavity

General

The resonance of sound waves excited in a cavity is analyzed.
The sound waves radiated from the cavity are peaked when the excitation frequency matches the cavity’s resonant frequency.
Unless specified in the list below, the default conditions will be applied.

Analysis Space

Item	Settings
Analysis Space	Axisymmetric
Model unit	mm

Analysis Conditions

Item	Settings
Solver	Acoustic Analysis [Mach]
Analysis Type	Harmonic analysis
Options	N/A

The tab setting is listed below.

Tabs	Setting Item	Settings
	Frequency	Minimum: 1,000[Hz] Maximum: 10,000[Hz]
Harmonic analysis	Sweep Type	Division number: 190
	Sweep Setting	Select Fast sweep.

Open boundary	Coordinates of Origin	x = 0 z = 0

Model

It is axisymmetric, so just right half of the section is created with a sheet body and defined as air. The open boundary is set on the perimeter of the quadrant circle representing the surface of the cavity.

The speed is set as the boundary condition on the bottom of the cavity.

Body Attributes and Materials

Body Number/Type	Body Attribute Name	Material Name
8/Sheet	AIR	000_Air(*)

* Available from the Material DB

Boundary Conditions

The “speed” boundary condition is set on the bottom and the “open boundary” condition is set on the perimeter.

Boundary Condition Name/Topology	Tab	Boundary Condition Type	Settings
v/Edge	Acoustic	Speed	1[m/s]
Open/Face	Acoustic	Open boundary

Results

The Figure below is the frequency plot of the sound pressure level [dB] at x=0, Z=10.

It is peaked at 8.9[kHz].

It is very close to 8.46[kHz], the result calculated from the Helmholtz resonance equation below.

C: Sound speed, V: Volume of cavity

The gradation contour of the sound pressure level at 8.6[Hz] is shown below.

The sound pressure is quite high in the cavity.

See other Acoustic Analysis examples.