Example: Acoustics in Coupled Rooms. Introduction The sound transmission across a building element...
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Transcript of Example: Acoustics in Coupled Rooms. Introduction The sound transmission across a building element...
Example:Acoustics in Coupled Rooms
Introduction
• The sound transmission across a building element sample is simulated.
• The setup is similar to the one stipulated by the ISO 15186/3 standard as implemented at the Icelandic Building Research Institute (IBRI) in Reykjavik.
• This example shows how Extended Multiphysics can be used to split a model into separate exchangeable modules.
• In particular, a 2D model of the sample is inserted into the 3D test bench.
Acoustics in Coupled Rooms
Geometry
Acoustics in Coupled Rooms – Problem Definition
• In the 3D geometry, the rooms are modeled as much further apart than they really are.
• The rooms are connected via the sample plate, which is modeled in a separate 2D geometry.
Sending room
Receiving room
Sound source
Sample plate
Domain Equations – Acoustics
• Frequency domain acoustics is goverened by a slightly modified Helmholtz’s equation for the acoustic pressure, p.
• Material properties are density, 0, and speed of sound, c.
• Note that the density cannot be eliminated from the equation unless it is a global constant
Acoustics in Coupled Rooms – Problem Definition
fpc
p
2,0)(
20
2
0
Domain Equations – Structure
• As a simple example, a 1 cm thick, homogenous steel plate is used as sample.
• The plate is modeled using plate elements of Reissner-Mindlin type.
• The pressure difference between the rooms enter the plate equations as a surface load.
Acoustics in Coupled Rooms – Problem Definition
Specified normal acceleration,given by plate movement
Boundary Conditions – Acoustics
• The natural boundary condition corresponds to inward normal acceleration. Three types are used:
Acoustics in Coupled Rooms – Problem Definition
00
p
n
pZ
ipn
0
ap
n
0
Hard wall
Specified impedance, partly absorbing
Boundary Conditions – Structure
Acoustics in Coupled Rooms – Problem Definition
• The plate is mounted in the opening between the rooms using wooden spacers and wedges.
• Where the plate is in contact with the spacers, it is considered free to rotate, but not to move.
• The rest of the gap between plate and niche wall is filled with a soft sound absorbing material that does not restrict the plate’s movements.
Results
Acoustics in Coupled Rooms – Results
• The instantaneous pressure pattern is shown as isosurfaces.
• The wall color represents the sound pressure level in the two rooms (in dB).
Results
Acoustics in Coupled Rooms – Results
• The sound reduction index is not a smooth function of frequency.
• This is probably due to the absence of damping in the source room and the sample plate causing pronounced resonance effects.