Estimating component vibrations by using measured or computed pressure fields

Acoustic Transfer Vectors (ATVs) are matrices of transfer functions between the normal velocities on an acoustic mesh envelope used as coupling surface with a structural mesh, and the pressure at microphone locations. In direct acoustics, you can use ATVs in conjunction with input vibrations on a structure to calculate the vibro-acoustic response at microphones and obtain the acoustic pressure.

In some cases, the input vibrations and measurement data might not be available due to lack of suitable locations for accelerometers on a component, or accelerometers might damage the component, or vice versa (for example, for hot components).

However, you can retrieve these input vibrations by using the Inverse Numerical Acoustics solution in the Simcenter 3D Noise and Vibration environment. The Inverse Numerical Acoustics solution uses the inverse of the ATV concept to localize and quantify acoustic sources from measured or computed pressure in the near field.

A typical application is to calculate the estimated velocities of an engine as a standalone component, use these velocities as boundary conditions on the component placed in a complete vehicle assembly, and then calculate new acoustic pressures at different microphone locations.

Regularization and Computation of the L-Curves

The Inverse Numerical Acoustics solution solves an underdetermined problem, which provides a solution of normal velocities that reproduce the pressures used as input in the inverse problem well, but which might deviate to some extent from the exact reproduction of normal velocities. To avoid large numerical errors, truncation is used to remove the smallest singular values from the singular value decomposition method applied to the ATV matrix. You can achieve this regularization by manually defining a threshold in function of frequency, or through an L-curve algorithm:

• Manual lets you define a tolerance for singular value removal by using a field.Note: The software removes singular values that are smaller than a threshold percentage of the maximum singular value before the numerical inversion.

• Adaptive Pruning Method lets you define the optimal cut-off percentage tolerance at each frequency. When you use this method, the software also outputs residual norms and residual values.

Where do I find it?

Creating Simcenter 3D Noise and Vibration Simulation files

Application	Pre/Post
Prerequisites	An assembly FEM file as the work part and displayed partA FEM or BEM file represented as an ATV SetA FEM file represented as a Mode Set
Command Finder	New Simulation
Simulation Navigator	Right-click the assembly FEM file→New Simulation

Creating Inverse Numerical Acoustics solutions

Application	Pre/Post
Prerequisites	A Simulation file as the work part and displayed partAn assembly FEM fileA BEM or FEM file represented as an ATV SetAn external file that contains measured or computed, acoustic pressuresSimcenter 3D Noise and Vibration as the specified solverVibro-Acoustic as the specified analysis typeInverse Numerical Acoustics as the specified solution type
Command Finder	Solution
Simulation Navigator	Right-click the Simulation file→New Solution

Creating Inverse Numerical Acoustics Output Requests

Application	Pre/Post
Prerequisites	A Simulation file as the work part and displayed partAn assembly FEM fileA BEM or FEM file represented as an ATV SetAn external file that contains measured or computed, acoustic pressuresSimcenter 3D Noise and Vibration as the specified solverVibro-Acoustic as the specified analysis typeInverse Numerical Acoustics Output Requests as the specified solution type
Command Finder	Modeling Objects
Simulation Navigator	Right-click the Modeling Objects node→Modeling Objects
Location in dialog box	Type list→Inverse Numerical Acoustics Output Requests

Specifying regularization

Application	Pre/Post
Prerequisites	A Simulation file as the work part and displayed partAn assembly FEM fileA BEM or FEM file represented as an ATV SetAn external file that contains measured or computed, acoustic pressuresSimcenter 3D Noise and Vibration as the specified solverVibro-Acoustic as the specified analysis typeInverse Numerical Acoustics as the specified solution type
Command Finder	Modeling Objects
Simulation Navigator	Right-click the Modeling Objects node→Modeling Objects
Location in dialog box	Type list→Regularization

How do I

Replace different FEM files with an Acoustics BEM ATV set

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Estimating component vibrations by using measured or computed pressure fields, Simcenter 3D 2021.1 Series

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