Example3 Interference of Sound Waves(2D)

General

The interference of sound waves from two sources is analyzed.
The interference pattern is solved.
“Field Superposition Setting” function is used to analyze the change in the field when the phase of the driving source is changed.
Unless specified in the list below, the default conditions will be applied.

Analysis Space

Item	Setting
Analysis Space	2D
Model unit	m

Analysis Conditions

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

The harmonic analysis tab is set up as follows.

The sound waves propagate outside the analysis region. Therefore the “open boundary” condition below is applied initially.

Tab	Setting Item	Setting
Harmonic analysis	Frequency	Minimum: 1000[Hz] Maximum: 2000[Hz]
	Sweep Type	Select Linear step by division number. Division number: 1
	Sweep Setting	Deselect Fast sweep.
	Enable each port’s individual weight setting for the superposed field display	Select
Open Boundary Tab	Type	Absorbing boundary
	Order of Absorbing Boundary	1st degree
	Coordinates of Origin	x = z = 0

Model

The model is created in 2D. A semi-circle and two rectangle sheet bodies form the air.
The “pressure” boundary condition is set on the sound generators. The “open boundary” is set on the perimeter of the semi circle.

Body Attributes and Materials

Body Number/Type	Body Attribute Name	Material Name
5/Sheet	Air	000_Air(*)

* Available from the Material DB

Boundary Conditions

The boundary conditions of open boundary and pressure are set.

Boundary Condition Name/Topology	Tab	Boundary Condition Type	Setting
Open/Face	Acoustic	Open boundary
V1/Face	Acoustic	Pressure	-1[Pa]
V2/Face	Acoustic	Pressure	-1[Pa]

Results

Shown below are the gradation contours of the particle speed at 1000[Hz] and 2000[Hz].

Frequency: 1000[Hz]

Frequency: 2000[Hz]

The interference pattern varies with the frequency.

Next, change the coefficient in the Field Superposition Setting and see its effect. Open the “Field Superposition Setting” dialog box.

The boundary condition names for each driving source (V1, V2) and the corresponding coefficients will appear in the (MAG PHASE) formats.

Initially, (MAG=1.0, PHASE=0.0[deg]) will show up. In this Exercise, we change PHSE of V2 to 0,45,90,180[deg]

and see the change in the field.

The figures below are with the fields set to 1000[Hz], Particle velocity, Magnitude, Absolute, and Linear.

The minimum value of the contour diagram is set to 0[mm/s] and the maximum value to 5[mm/s]. For the easy viewing, the contour is set

with “Gradation contour with color division” selected. By changing the PHASE,

the pattern of the contour is changed. The directivity changes according to the pattern change of the contour as shown below.

Calculation conditions of the directivity are as follows.

Observation point: r=1[m], φmin=0.0[deg], φmax=0.0[deg], φstep=0, θmin=0.0[deg], θmax=180[deg], θstep=60

Display: Select Sound pressure level[dB] and select YZ plane for Reflective. (Calculation is based on the assumption that the wall parallel with Z axis is extending a long distance)

Horizontal axis: Select θ

See other Acoustic Analysis examples.