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

Random loading for acoustic and vibro-acoustic models lets you analyze simulation scenarios such as:

• Panel transmission loss, which is typically used for acoustic studies in the transportation industry.

• Virtual vibration testing of a spacecraft fixed-base excitation or diffuse acoustic field excitation.

• Road noise, which is typically used for analyzing cabin noise (vibrations) from probabilistic excitation by the road.

You can analyze acoustic and vibro-acoustic models for random loading using SOL 108 Direct Frequency Response and SOL 111 Modal Frequency Response.

Random loading

• Distributed acoustic plane wavesYou use the Distributed Acoustic Plane Waves random load to define an incident acoustic field that impinges on the model with a given pressure amplitude as the load. The distributed acoustic plane wave load is composed of a set of plane waves that create a diffuse field. The plane wave sets are automatically generated in spherical or hemispherical constellations surrounding the model.**Distributed Acoustic Plane Waves Display (full sphere)**Distributed Acoustic Plane Waves Display (hemisphere)

• Power spectral density factorsYou use Power Spectral Density Factors to create random loads. The factors indicate auto- and cross-power spectral density between (regular, deterministic) frequency response subcases. These subcases can represent unit load cases, but the subcases can also contain a more complex combination of loads.

Random subcases (solution steps)

• Subcase – Random Distributed Acoustic Plane WavesYou use the Subcase – Random Distributed Acoustic Plane Waves solution step to define distributed acoustic plane waves loading for acoustic and vibro-acoustic analysis.You use the Subcase – Random Distributed Acoustic Plane Waves solution step to apply an acoustic diffuse field. The random loading (distributed acoustic plane waves) is applied with acoustic plane wave sets.You can define the output requests, forcing frequencies, case control parameters (PARAM), and case control user-defined text parameters.

• Subcase - RandomYou use the Subcase - Random solution step to prescribe the power spectral density (PSD) factors between already defined (normal, deterministic) subcases that contain force, vibration, or acoustic loads. You can specify auto-power and cross-power spectral density factors (RANDPS).You can define output requests and forcing frequencies, as well as autocorrelation function time lag constants, case control parameters (PARAM), and case control user-defined text parameters.

Modeling objects

• Autocorrelation Function Time Lag specifies an autocorrelation (ATOC) describer in one or many output requests.

• Cross-Power Spectral Density/Cross-Correlation Function Output allows you to request the cross-power spectral density and cross-correlation function between different responses, for example, stress, force, acceleration (for structural or vibro-acoustic analysis types), or pressure cross spectral density response (for acoustic or vibro-acoustic analysis types).

• Power Spectral Density Factors defines power spectral density/cross spectral density (PSD/CSD) factors between frequency response subcases, by creating and referencing one or many unique instances of a power spectral density factors modeling object (RANDPS).

Output requests

You can request the following PSD outputs in SORT1 or SORT2 format for all output requests:

• Acoustic Incident Power

• Acoustic Transmitted Power

• Acoustic Transmission Loss

• Cross-Power Spectral Density/Cross-Correlation Function

Plot results

You can plot the following results in scenario-based post-processing:

• SORT1 or SORT2 PSD results

• SORT1 RMS results

• SORT2 CSD results

• SORT2 results for acoustic power and transmission loss

Where do I find it?

Creating distributed acoustic plane waves

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 typeSOL108 Direct Frequency Response and SOL111 Modal Frequency Response as the specified solution typeSubcase-Random Distributed Acoustic Plane Waves as the specified solution step
Simulation Navigator	Expand the Subcase-Random Distributed Acoustic Plane Waves solution step node of an active solution→right-click the Loads container→New Load→Distributed Acoustic Plane Waves

Creating an autocorrelation function time lag or power spectral density factors

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 typeSOL108 Direct Frequency Response or SOL111 Modal Frequency Response as the specified solution typeSubcase-Random as the specified solution step
Command Finder	Modeling Objects
Location in dialog box	Modeling Objects Manager dialog box→Type list→Autocorrelation Function Time Lag or Power Spectral Density Factors

Creating a cross-power spectral density/cross-correlation function output

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 typeSOL108 Direct Frequency Response or SOL111 Modal Frequency Response as the specified solution typeSubcase-Random Distributed Acoustic Plane Waves or Subcase-Random as the specified solution step
Command Finder	Modeling Objects
Location in dialog box	Modeling Objects Manager dialog box→Type list→Cross-Power Spectral Density/Cross-Correlation Function Output

Defining output requests for random loading of acoustic and vibro-acoustic solutions

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 typeSOL108 Direct Frequency Response or SOL111 Modal Frequency Response as the specified solution typeSubcase-Random Distributed Acoustic Plane Waves or Subcase-Random as the specified solution step
Simulation Navigator	Expand the Solution node of an active solution→right-click the Subcase node→Edit
Location in dialog box	Solution Step dialog box→Output Requests→Create Modeling Object→

How do I

Create an acoustic source load

Create an acoustic absorber

Learn more

Boundary conditions overview (FEM acoustics)

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

Creating acoustic constraints

Quick links

Command reference

Pre/Post video examples

Bulk Entry Descriptions

Simcenter 3D tutorials

Browse Simcenter 3D help by product area

Random loading for acoustic and vibro-acoustic analysis (FEM acoustics), Simcenter 3D 2021.1 Series

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