Acoustics Module Updates

For users of the Acoustics Module, COMSOL Multiphysics® version 5.5 includes a new Elastic Waves, Time Explicit Physics interface, multiphysics couplings for acoustic-structure interaction with the time explicit formulation, and a Port boundary condition for the Thermoviscous Acoustics, Frequency Domain interface. Learn more about these and many more Acoustics Module updates below.

New Elastic Waves, Time Explicit Physics Interface

The new Elastic Waves, Time Explicit physics interface is based on the discontinuous Galerkin time explicit method and enables efficient multicore computations of elastic wave propagation in solids. Features are included to provide realistic material data including anisotropy and damping. The interface is suited for modeling ultrasound propagation in solids, such as with transducers and sensors, and for nondestructive testing (NDT) applications, and is applicable to any acoustically large system that involves transient propagation over many wavelengths, which includes seismic wave propagation in soil and rock.

You can see the new interface used in the following models:

The COMSOL Multiphysics UI with the Settings window open for the Elastic Waves, Time Explicit interface and a plot showing seismic waves at 5 seconds. Using the Elastic Waves, Time Explicit interface User interface for the new Elastic Waves, Time Explicit interface shown here in a model of seismic waves propagating in the soil.

Multiphysics for Acoustic-Structure Interaction with the Time Explicit Interfaces

For large transient acoustic-structure interaction simulations, a new Acoustic-Structure Interaction, Time Explicit multiphysics coupling is available. This coupling connects the Pressure Acoustics, Time Explicit and new Elastic Waves, Time Explicit physics interfaces. To take full advantage of the time explicit formulation, the use of nonconforming meshes is essential when coupling domains with different properties. This is achieved through the new Pair Acoustic-Structure Boundary, Time Explicit multiphysics coupling that handles geometric assemblies. The use of nonconforming meshes is a natural extension and use of the properties of the discontinuous elements. You can see this functionality used in the Immersion Ultrasonic Testing Setup model.

The COMSOL Multiphysics UI with the Settings window open for the Pair Acoustic-Structure Boundary, Time Explicit multiphysics coupling and a model in the Graphics window. Using the Pair Acoustic-Structure Boundary, Time Explicit multiphysics coupling In the new Immersion Ultrasonic Testing Setup model, you can see the settings for the new Pair Acoustic-Structure Boundary, Time Explicit multiphysics coupling feature.

Material Discontinuity, Pair Conditions, and Dissipation for the Acoustic Time Explicit Interfaces

The fluid acoustics interfaces that are based on the discontinuous Galerkin time explicit method now have the option to include dissipation. Dissipation plays an important role when modeling high-frequency applications like ultrasound imaging and flowmeters. The new option exists for the Pressure Acoustics, Time Explicit and Convected Wave Equation, Time Explicit interface.

The Pressure Acoustics, Time Explicit interface now includes a Material Discontinuity (interior) boundary condition and a Continuity pair feature. These are used to handle jumps in material properties for a union with a conforming mesh, or an assembly using a nonconforming mesh, respectively. You can see the Material Discontinuity feature in the Isotropic-Anisotropic Sample: Elastic Wave Propagation model.

The Settings window for the Material Discontinuity feature with the Boundary Selection section open and a pressure plot for a model shown to the right. Using the Material Discontinuity feature Use of the Material Discontinuity feature to couple an isotropic and an anisotropic solid material.

Ports for Thermoviscous Acoustics

A new Port boundary condition has been added to the Thermoviscous Acoustics, Frequency Domain interface, used to excite and absorb acoustic waves that enter or leave waveguide structures in microacoustic applications. The port conditions provide a near-perfect, nonreflecting radiation condition for waveguide inlets/outlets, including the viscous and thermal boundary layers. In many cases, using the new Port condition provides superior ease of use and accuracy compared to an impedance condition or a perfectly matched layer (PML) configuration. When working with small acoustic subsystems, two Port conditions are used and combined to automatically compute the scattering matrix, transfer matrix, and impedance matrix relating the inlet to the outlet. These are all simplified lumped representations of subsystems typically used to efficiently analyze their integration into a full system. You can see this feature in the Wax Guard Acoustics: Transfer Matrix Computation model.

The Settings window for the Port feature is shown with the Port Properties section open and the list of port types is shown. Using the Port feature for thermoviscous acoustics modeling Use of the new Port feature in the Thermoviscous Acoustics, Frequency Domain physics interface. There are three options for the port type: User defined, Numeric, and Circular.

Updated Port Feature in Pressure Acoustics

The Port condition is now available in 2D for the Pressure Acoustics, Frequency Domain interface, and has a User defined option and a Slit option to define the mode shapes. In general, when a port sweep is performed and two ports are used, one at the inlet and one at the outlet, the transfer matrix and the impedance matrix of the system are automatically computed. In COMSOL Multiphysics® version 5.5, new transmission loss variables are automatically generated for the transmission between two or more ports. The port sweep functionality now also works when an inner sweep is performed over the port number. You can see this feature used in the Shape Optimization of an Acoustic Demultiplexer model.

Background Fluid Flow Coupling and Mapping Study for Aeroacoustics

The new Background Fluid Flow Coupling multiphysics coupling and dedicated Mapping study features are added in version 5.5 to automate and simplify the coupling of a CFD model and a convected acoustic model. This includes the linearized Navier-Stokes, linearized Euler, and convected wave equation physics. The multiphysics coupling and mapping ensure that the computed CFD solution is correctly mapped from the fluid flow mesh to the acoustics mesh, while also taking care of different discretization orders. The mapping and interpolation are essential to avoid introducing numerical noise into the acoustic model, where the reactive terms are especially important to treat correctly.

You can see this functionality used in the following models:

The Background Fluid Flow Coupling settings are shown with the Variables to Map section open for a Helmholtz resonator model. Coupling flow and acoustics Use the Background Fluid Flow Coupling multiphysics coupling and the Mapping study, seen in the Model Builder window, to couple flow and acoustics, as seen in the Helmholtz Resonator with Flow tutorial model.

Anisotropic Materials in Pressure Acoustics Interfaces

The new Anisotropic Acoustics feature for pressure acoustics makes it possible to define fluids with an effective anisotoropic density and a scalar effective bulk modulus. With this feature you can set up homogenized material properties for metamaterials and define effective fluid properties of porous and fibrous materials that have anisotropic structures. The effective density can be defined as having an Isotropic, Diagonal, or Symmetric structure. You can see this new feature in the Acoustic Cloaking model.

Lorentz Coupling for Modeling Electroacoustic Transducers

The Lorentz Coupling feature supports a two-way coupling between the Magnetic Fields and Solid Mechanics interfaces. The Lorentz force is determined by computing the cross product of the current density, J, and the magnetic flux, B, in the volume of the domain, which is then applied on the mechanics side as a volumetric force. At the same time, the velocity is taken from the Solid Mechanics interface and applied in the Magnetic Fields interface, as a Lorentz velocity term. The feature automatically handles the frames and moving mesh effects.

This feature is intended for conductive, nonmagnetizable domains (typically, copper coils), and when combined with the Acoustic-Structure Boundary multiphysics coupling, enables you to model electroacoustic transducers. It is available in 2D, 2D axisymmetry, and 3D, for Time Dependent, Frequency Domain (Perturbation), and Eigenfrequency analysis. This functionality requires the AC/DC Module together with one of the Structural Mechanics Module, Acoustics Module, or MEMS Module. You can see this functionality used in the Loudspeaker Driver — Frequency-Domain Analysis and Loudspeaker Driver — Transient Analysis models.

The Settings window for the Lorentz Coupling feature is open and a loudspeaker driver model is plotted to the right. Using the Lorentz Coupling multiphysics feature Use of the Lorentz Coupling multiphysics feature for the electromechanical coupling on the voice coil in a loudspeaker driver.

Acoustic-Pipe Acoustic Connection Multiphysics Coupling

With the new Acoustic-Pipe Acoustic Connection multiphysics coupling, you can couple the pressure acoustics interfaces to the pipe acoustics interfaces in both frequency and time domain simulations. The coupling is defined between a point in the pipe interface and a boundary in the pressure acoustics interface. You can see this functionality used in the Probe Tube Microphone and Acoustics of a Pipe System with 3D Bend and Junction models.

The COMSOL Multiphysics UI with the Settings window open for the Acoustic-Pipe Acoustic Connection multiphysics coupling and a pipe system model in the Graphics window. Using the Acoustics-Pipe Acoustic Connection multiphysics coupling Use of the new Acoustics-Pipe Acoustic Connection multiphysics coupling in the Acoustics of a Pipe System with 3D Bend and Junction tutorial model.

Acoustic-Structure Couplings for Layered Shells

The multiphysics couplings between acoustics and structures have been extended to support the Layered Shell physics interface. With this functionality, you can model vibroacoustic problems involving composite materials and other layered structures. Note that you need the Composite Materials Module to enable this functionality.

The Layered Shell interface is now supported for the following multiphysics couplings:

  • Acoustic-Structure Boundary
  • Thermoviscous Acoustic-Structure Boundary
  • Aeroacoustic-Structure Boundary
  • Porous-Structure Boundary

Improved Acoustophoretic Force

The Acoustophoretic Force feature has been renamed Acoustophoretic Radiation Force. This feature has new force expressions that are more accurate, because they account for the viscous and thermal boundary layers that form around particles in an acoustic pressure field. You can now specify whether the particles are solid or liquid. Then you can choose a Thermodynamic loss model: Ideal, Viscous, or Thermoviscous. The feature can be combined with both pressure acoustics and thermoviscous acoustics to model particle sorting and other acoustofluidic applications. You can see this new feature in the Acoustic Levitator and Acoustic Streaming in a Microchannel Cross Section models.

News in Ray Acoustics

Preview Grid Release Positions

When you release particles from a grid of points using the Release from Grid feature, you can now preview the initial particle positions in the Graphics window. In the Initial Coordinates section of the Settings window, click the Preview Initial Coordinates button to view the initial particle coordinates as a grid of points. Click the Preview Initial Extents button to view the spatial extents of the initial coordinates as a bounding box. These buttons allow you to check the initial particle positions before running a study.

In addition, when you right-click a Study node and click Get Initial Value, you can preview the initial particle positions and velocities for all release types.

The COMSOL Multiphysics UI showing a model where the initial particle coordinates are viewed as a grid of points. Initial particle coordinates viewed as a point grid Graphics window after clicking the Preview Initial Coordinates button.
The COMSOL Multiphysics UI showing a model where the spatial extents of the initial particle coordinates are shown as a bounding box. Initial particle coordinates' spatial extents Graphics window after clicking the Preview Initial Extents button.

New Release Type: Hexapolar Cone

When you release rays in a cone, a new type of Conical distribution is available: Hexapolar. For the Hexapolar cone option, rays are released at uniformly distributed angles from the cone axis, with each ring having six more rays than the previous one.

Rays released in a cone shape visualized with arrows of rainbow coloring, seen from the side so the arrows point to the right. Hexapolar cone: Side view Hexapolar-cone-based release, side view.
Rays released in a cone shape visualized with arrows of rainbow coloring, seen from the front so the arrows point at the viewer. Hexapolar cone: Front view Hexapolar-cone-based release, front view.

Isotropic Scattering Wall Condition

You can now select Isotropic scattering as the wall condition when particles hit boundaries in the geometry. Like the Diffuse scattering condition, the Isotropic scattering condition causes particles to be reflected with randomly sampled velocity directions around the surface normal. However, whereas the Diffuse scattering condition uses a probability distribution based on the cosine law, the Isotropic scattering condition follows a probability distribution that gives equal flux across any differential solid angle in the hemisphere.

The diffuse scattering wall condition is compared to the isotropic scattering wall condition. Scattering wall condition comparison Comparison of the diffuse (left) and isotropic (right) scattering wall conditions. Each side shows a distribution of 1000 particles.


Renamed Ray Release Features

Ray release features have been renamed in COMSOL Multiphysics® version 5.5. The Inlet is now called Release from Boundary, and the Inlet on Axis (in 2D axisymmetric models) is now called Release from Symmetry Axis.

The COMSOL Multiphysics UI in version 5.5 showing the Release from Boundary and Release from Symmetry Axis ray release features. Showing the updated ray release feature names Choice of boundary features in the Geometrical Optics interface in a 2D axisymmetric geometry.

Improvements to Iterative Solver Suggestions in Acoustics

The auto-generated solver suggestions have been improved for models that include interfaces from the Acoustics Module together with multiphysics couplings. Additionally, the Lagrange multiplier variables are handled correctly by the Vanka preconditioner when necessary. Common iterative solver suggestions are now set up for the following couplings and combination of couplings:

  • Acoustic BEM-FEM Boundary
  • Acoustic-Structure Boundary
  • Thermoviscous Acoustic-Structure Boundary
  • Acoustic-Thermoviscous Acoustic Boundary
  • Aeroacoustic-Structure Boundary
  • Piezoelectric Coupling
  • Solid-Shell Connection

Other default and solver suggestion improvements include an iterative solver suggestion for the Compressible Potential Flow interface. A new Stationary-Frequency and Stationary-Transient solver configuration is available when coupling Compressible Potential Flow and Linearized Potential Flow in a convected acoustics simulation. A second iterative solver suggestion is now added for models to couple Pressure Acoustics to Solid Mechanics with the Acoustic-Structure Boundary multiphysics coupling. Lastly, a better default solver has been added for the Linearized Euler interfaces. You can see some of these improvements used in the Loudspeaker Driver in a Vented Enclosure model.

A loudspeaker driver is modeled in COMSOL Multiphysics and the Settings window is open for the Suggested Iterative Solver with the General section open. Using the Suggested Iterative Solver in a model Use of the Suggested Iterative Solver in the Loudspeaker Driver in a Vented Loudspeaker Enclosure tutorial model.

New Solvers for Large Acoustic Problems

For frequency-domains simulations modeled with the Pressure Acoustics, Frequency Domain interface, two specialized iterative solver methods have been introduced for simulating finite element method models at high frequencies. First, the domain decomposition method now supports the use of absorbing boundary conditions for the domain boundaries, which is important for cluster computations using domain decomposition for frequency-domain acoustics. Second, the new complex Shifted Laplacian (SL) method can be used for both the normal multigrid preconditoner and the domain decomposition method. The multigrid alternative is the best option for large models when not using a cluster.

With this new functionality, you can solve significantly larger models in acoustics than before. For example, a car cabin interior acoustic model can now be solved up to 7 kHz, solving 83.5 million DOFs using 105 GB of RAM, whereas it would only converge for up to about 3 kHz in earlier versions of the software. This corresponds to an order of magnitude larger simulation due to the fact that frequency domain acoustics scales with approximately the cube of the frequency. You can see this functionality used in the Car Cabin Acoustics — Frequency Domain analysis model.

A model of the inside of a car cabin showing the acoustics response in a red, white, and blue color table. Car cabin interior acoustics The acoustics response of a car cabin interior solved at 7 kHz using the new complex Shifted Laplacian solver.

Restructure of the Model Wizard Tree and Application Library

With the introduction of the new Elastic Waves, Time Explicit interface, the physics interface locations in the Model Wizard tree have been updated with two new branches: Elastic Waves and Pipe Acoustics. To get a better overview of the existing and the many new tutorial models, the Application Library categories have also been updated with new categories:

  • Elastic Waves
  • Tutorials, Pressure Acoustics
  • Tutorials, Pipe Acoustics
  • Tutorials, Thermoviscous Acoustics

Important Enhancements in the Acoustics Module

  • In the Exterior Field Calculation feature
    • The location of an infinite symmetry and antisymmetry plane can be specified by entering an offset value
  • Postprocessing news
    • The Octave Band plots have the option of using 1/6 octaves
    • The reference direction can be set in 1D Radiation Pattern plots of 2D models
    • The Directivity plot comes with a true logarithmic axis and has moved to 1D plot groups
  • For the Exclude Edges and Exclude Points options
    • Added for all constraint type boundary conditions (Dirichlet conditions) in the following interfaces:
      • Thermoviscous Acoustics interface
      • Linearized Navier-Stokes interface
      • Linearized Euler interface
    • Handle over-constrained problems and simplify certain combinations of boundary conditions
    • Available when the View Advanced Physics option is selected
  • The unit "rayl" used for the specific acoustic impedance
    • Available in the SI unit: [rayl]
    • Available in the cgs unit: [rayls_cgs]
  • Surface stress variables exist on both exterior and interior boundaries in the following interfaces:
    • Thermoviscous Acoustics interface
    • Linearized Navier-Stokes interface
  • A new Absorption Coefficient option is available for the impedance boundary condition
    • Simplifies the input of certain measured surface impedance data
      • Useful in the higher frequency range
    • Available for all pressure acoustics interfaces
  • The Characteristic specific impedance condition in pressure acoustics interfaces
    • Works for waves propagating at a given angle toward the boundary
    • A priori knowledge of the solved problem can improve the simple nonreflective conditions significantly

Extended Support for Jiles–Atherton Hysteresis

The nonlinear Magnetostrictive Material has been extended to include the Jiles–Atherton model of magnetic hysteresis. The model is suitable for investigating the hysteretic loss effects in applications such as power transformers and rotating electric machines. The model parameters are related to microscopic physical effects in magnetic materials and they can also be estimated based on experimental data.

Additionally, the Jiles–Atherton material model for magnetic hysteresis has been extended to support parametric stationary studies (in addition to the previously available Time Dependent analysis). Ferromagnetic hysteresis is for low-to-moderate frequencies, rate-independent, and can be analyzed using a parametric stationary study, for example when studying magnetization and demagnetization. This functionality requires the AC/DC Module together with one of the Structural Mechanics Module, Acoustics Module, or MEMS Module.

The Settings window for Magnetostrictive Material 1 is shown next to a point graph for a hysteretic magnetostrictive model. Modeling magnetic hysteresis Settings for the hysteretic magnetostrictive model, together with hysteresis loops generated from simulation.

Visualization of Loads

Applied mechanical loads are now available as default plots in all structural mechanics physics interfaces. The loads plots are solution dependent, so both arrow directions and colors are updated when a dataset is updated with a new solution. Even abstract loads, such as forces and moments applied to rigid connectors and rigid domains are plotted at their true point of application. A new arrow type, used for plotting applied moments, has been introduced for this functionality. More than 100 models are updated with this new functionality.

Three tube models with red arrows visualizing various mechanical loads. Visualizing loads on a tube Three sets of loads plotted on a model of a tube.

New Tutorial Models

Version 5.5 brings several new and updated tutorial models.