This document discusses modeling and simulating sound propagation inside a rigid-walled rectangular cavity using ANSYS. It describes: 1. Setting up a finite element model of a rigid-walled rectangular cavity with dimensions of 0.5m x 0.3m x 1.1m, along with an acoustic source and receiver located within the cavity. 2. Performing a modal analysis in ANSYS to calculate the undamped natural frequencies and mode shapes of the cavity. 3. Conducting a harmonic response analysis to calculate the acoustic pressure at the receiver location due to the acoustic source, using the modal superposition method.

1. SOUND INSIDE A RIGID-WALLED
CAVITY
ANSYS WORKBENCH 15.0
sanjeet kumar singh

2. Learning outcomes
1. Calculate the undamped natural frequencies of a rigid walled cavity using
ANSYS.
2. Use the FLUID 130 Fluid element in ANYS to model rigid wall cavity.
3. Sound pressure level at a receiver inside a rigid-wall rectangular cavity due to an
acoustic volume velocity source, using the modal summation method.
4. Mode shape of a rigid-wall rectangular cavity
5. Conduct a harmonic response analysis in ANSYS

3. Rigid-walled rectangular cavity with an acoustic volume velocity source and receiver to
measure the resulting sound pressure
y
x
z
Sound Source
Receiver

4. Parameters of a Rigid-walled Cavity
Description Parameter Value (m)
Cavity:
Length X
Length Y
Length Z
Lx
Ly
Lz
0.5 m
0.3 m
1.1 m
Acoustic Source:
Location X
Location Y
Location Z
Xs
Ys
Zs
0.15 m
0.12 m
0.0 m
Acoustic Receiver
Location X
Location Y
Location Z
Xb
Yb
Zb
0.3 m
0.105 m
0.715 m
Fluid :
Speed of sound
Density
Number of modes
C0
ρ0
Na
343 m/s
1.21 kg/m3
500 no units

7. The mess in finite element model will create nodes at the location of the source and receiver, and
use hard key point points in the mess, which will create a key-point at a desired location and can
not be changed. However, mapped meshing is not supported when hard key-points are used, so it
is not possible to create a regular mesh with brick elements.

8. Undamped natural frequencies of a rigid walled cavity using ANSYS
40 natural
frequencies of the
cavity
The 18th mode will be (1,1,2) mode. ANSYS does not have an in-built mechanism for
determining the modal indices of acoustic(or structure) responses and therefore these have to
be determined by viewing the response of the system and the user has to recognize the mode
shape and appropriate model index

9. Harmonic response analysis in ANSYS
1. In harmonic analysis, calculate the acoustic pressure response within the cavity using the full
method and an acoustic mass source.
2. Calculate the pressure response at the receiver location.

10. Under the harmonic response (B5) branch, click on
the analysis setting branch. Change all the setting
according to show in the figure. Solution intervals
500, which will give a frequency spacing of 1 Hz.
Save MAPDL db to yes as the database is needed for
post-processing of the acoustic results.

11. Define two named selection objects that correspond to the nodes where the acoustic source and
microphone are located as listed in table in slide no 4.
The worksheet (Model (A4,B4)-insert-Named selection-row scoping method-worksheet) use to
select a node by initially selecting a group of nodes and then filtering the set. After the filtering
operation, one node remaining in the selection set.

12. The name selection have been defined for the nodes for the acoustic source and
microphone, the acoustic source is defined and acoustic pressure can be calculated at the
microphone.

13. Sound pressure level at Receiver (microphone )