Defining acoustic load sets, sources, and pressures (FEM acoustics)

You can define acoustic sources and acoustic loads in Simcenter Nastran FEM acoustic and vibro-acoustic analyses in SOL 108 - Direct Frequency and SOL 111 - Modal Frequency Response solutions.

Acoustic source loads

Acoustic waves are longitudinal waves that are generated by the volumetric expansion or contraction of the fluid medium, such as air or water. The expansion or contraction is caused by an excitation of the system.

An acoustic source is modeled as one or two oscillating spheres, a single direction radiating acoustic wave in an infinite acoustic field, or an acoustic source generated by interaction of fluid flow with rigid surfaces. You can use the Acoustic Load Set command in conjunction with the Acoustic Monopole, Acoustic Dipole, Acoustic Plane Wave, or Surface Dipole command to simulate a stationary acoustic source in space.

Examples of acoustic sources include:

• A small speaker in a small rigid box that emits sounds at a low frequency.

• An engine inside an anechoic chamber.

• An engine exhaust pipe outlet.

• Obstructions in ducts, such as flaps, grills, and so on, and elbows in an HVAC system.

You can use options in the Acoustic Load Set dialog box to specify a name, label, and description.

The Acoustic Load Set command corresponds to the Simcenter Nastran ALOAD case control command.

After you define the acoustic load set, you can use the right-click command New to create acoustic sources on nodes or arbitrarily in space. The software adds the acoustic source to the acoustic load set.

For example, you may want to enable the acoustic source only on specified nodes so that you can study the contribution of each acoustic source independently.

The Acoustic Monopole command corresponds to the Simcenter Nastran ACPOLE1 bulk entry.

The Acoustic Dipole command corresponds to the Simcenter Nastran ACPOLE2 bulk entry.

The Acoustic Plane Wave command corresponds to the Simcenter Nastran ACPLNW bulk entry.

The Surface Dipole command corresponds to the Simcenter Nastran ACSPO2 bulk entry.

For more information, see:

• ALOAD in the Simcenter Nastran Quick Reference Guide.

• ACPOLE1 in the Simcenter Nastran Quick Reference Guide.

• ACPOLE2 in the Simcenter Nastran Quick Reference Guide.

• ACPLNW in the Simcenter Nastran Quick Reference Guide.

• ACSPO2 in the Simcenter Nastran Quick Reference Guide.

• Defining acoustic loads in the Simcenter Nastran Acoustic User's Guide.

• Acoustic source loading in the Simcenter Nastran Acoustic User's Guide.

Acoustic pressure loads

You can define an enforced pressure load that the software applies to the nodes in the acoustic fluid. You can use the Frequency Excitation Load Set command in conjunction with the Enforced Acoustic Pressure command to define the acoustic pressure.

You can use options in the Frequency Excitation Load Set dialog box to define the scaling factor for the acoustic pressure. You can specify a complex scaling factor:

• A constant value, either with real and imaginary parts or by magnitude and phase angle.

• A varying value through a table field in which the magnitude of the pressure varies with frequency.

The Frequency Excitation Load Set command corresponds to the Simcenter Nastran RLOAD1 and RLOAD2 bulk data entries.

After you define the frequency load set, you can use the options in the Enforced Acoustic Pressure dialog box to:

• Select the fluid nodes to which to apply the acoustic pressure.

• Define the magnitude of the pressure.

• Assign specific pressure values to individual nodes.

For more information, see:

• RLOAD1 and RLOAD2 in the Simcenter Nastran Quick Reference Guide

• SPCD in the Simcenter Nastran Quick Reference Guide

Where do I find it?

Creating an Acoustic Load Set or Frequency Excitation Load Set

Application	Pre/Post
Prerequisites	A Simulation file as the work part and displayed partSimcenter Nastran as the specified solverAcoustic or Vibro-Acoustic as the specified analysis typeSOL 108 - Direct Frequency or SOL 111 - Modal Frequency Response as the specified solution type
Simulation Navigator	Right-click the Solver Sets node→New→Acoustic Load Set or Frequency Excitation Load Set
Location in dialog box	Frequency Excitation Load Set dialog box→Type list→Enforced Acoustic Pressure

Adding an Acoustic Monopole, Acoustic Dipole, Acoustic Plane Wave, Surface Dipole, or Enforced Acoustic Pressure

Application	Pre/Post
Prerequisites	A Simulation file as the work part and displayed partSimcenter Nastran as the specified solverAcoustic or Vibro-Acoustic as the specified analysis typeFEMAO as the specified method for surface dipoleSOL 108 - Direct Frequency or SOL 111 - Modal Frequency Response as the specified solution type
Command Finder	Acoustic Monopole Acoustic Dipole Acoustic Plane Wave Surface Dipole Enforced Acoustic Pressure

How do I

Create an acoustic source load

Create an acoustic absorber

Learn more

Boundary conditions overview (FEM acoustics)

Creating acoustic constraints

Random loading for acoustic and vibro-acoustic analysis (FEM acoustics)

Look up more details

Acoustic Load Set dialog box

Quick links

Command reference

Pre/Post video examples

Bulk Entry Descriptions

Simcenter 3D tutorials

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Related Topics

Acoustic source loading

Defining acoustic load sets, sources, and pressures (FEM acoustics), Simcenter 3D 2021.1 Series

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