Simcenter 3D Ray Acoustics environment

You can use the Simcenter 3D Ray Acoustics environment to efficiently solve high-frequency acoustic models, where the wavelength is much smaller than the dimensions of the space it propagates within. Unlike FEM acoustics and Acoustics BEM, Ray Acoustics is not bounded by an upper frequency limit or the model size. The lower frequency limit of this solution starts typically at medium high-frequencies. For example, for a car cavity the applicable frequency range is between 500 Hz and 20 kHz (audible frequency).

When the acoustic wavelength is small compared to the traveled distance, the acoustic energy propagation can be considered to propagate along lines called rays. These sound rays are conceptually similar to light rays. This means that you can analyze problems with geometrical acoustics similar to geometrical optics. Geometrical acoustics requires only a surface discretization of the model and a coarse representation of, for example, geometric details and curvatures. Therefore, ray acoustics can solve these minimally discretized models faster than equivalent FEM or BEM models.

Typically, you can use ray acoustics in any industry. Ray acoustic analysis is especially useful for sound quality design of rooms and cabins, and acoustic sensor design, such as parking sensors or sonar.

When you work in the Simcenter 3D Ray Acoustics environment, you can create a model that contains:

• Acoustic fluid meshes of triangular or quadrilateral elements and reference fluid properties, such as speed of sound, mass density, and relative humidity.

• Microphone meshes.

• Acoustic sources.

Supported loads

This environment supports the incoherent (phase-less) acoustic source Noise Ray Source, and the coherent acoustic sources Point Ray Source and Panel Ray Source.

You can define:

• A Noise Ray Source by specifying acoustic pressure and adding it to one subcase to model background noise. Background noise is any sound other than the actively monitored sound.The software adds the noise generated by the source to the frequency response at each microphone. Thus, the background noise affects the impulse response, binaural impulse response, and the sound quality criteria results. Examples of background noises are environmental noises such as waves, traffic noise, alarms, humans talking, animal noises, and so on.

• A spherical Point Ray Source by specifying:Directionality in spherical coordinates with complex field values that depend on frequencies and angles.Magnitude of type power or pressure.Time delay to account for the delay of sound from a sound source arriving at a receiver, or the time delay between different sound sources. The time delay affects impulse response results, such as beam tracing or hybrid impulse results, and echograms.

• A hemispherical Point Ray Source by specifying directionality, direction with a CSYS, magnitude of type power or pressure, and time delay.

• A Panel Ray Source by specifying on which acoustic fluid elements to create the source, a direction, time delay, and a magnitude of type power, pressure, or intensity.Note: The software exports the Panel Ray Source as hemispherical point ray sources that are located in the center of gravity of the selected acoustic fluid elements. Those sources point in the same direction as the element normals.

• For the magnitude of a Point Ray Source or Panel Ray Source, by specifying:A constant complex excitation with real and imaginary parts.A constant complex excitation with magnitude and phase angle.A frequency-dependent complex field value.

Note:

For the directionality of the Point Ray Source, you can also use a directionality field exported from an acoustic or vibro-acoustic Nastran, Nastran with FEMAO, or acoustic or vibro-acoustic BEM solution. For information on creating directionality fields, see Automatically create directionality fields.

Supported simulation objects

This environment supports the definition of:

• An Acoustic Absorber simulation object with:Impedance to model complex soundproofing materials on the structural surface.Surface Coefficients properties to model complex soundproofing or transmitting materials on the structural surface. You specify the following coefficients:Only an Alpha Coefficient (\alpha ) to account for absorbed acoustic energy.Only a Delta Coefficient (\delta ) to account for diffusely reflected acoustic energy.Only a Tau Coefficient (\tau ), which is equivalent to \alpha equal 1, to account for the absorbed acoustic energy that is partially transmitted. You can enter a constant value of, for example, 0 to indicate an opaque surface that absorbs all acoustic energy or a constant value of 1 to indicate a transparent surface that transmits all acoustic energy. Because \alpha equals 1, the surface does not reflect any of the incoming energy.The surface does the following:Diffusely transmits energy when \tau is greater than 0, and equal to or less than 1.Diffusely absorbs energy. The software calculates the absorbed energy from (1, - ,\tau ) x incoming energy.You can also enter the following extreme values:0 to indicate an opaque surface that does not transmit acoustic energy.1 to indicate a transparent surface that transmits all acoustic energy.The transmission loss (TL) is calculated fromTL, = ,10,{\log _{10}}\left( {\frac{1}{\tau }} \right),[dB]Note: The Acoustic Absorber simulation object also supports a frequency-dependent \tau coefficient for other analyses. In a Ray Acoustics analysis, when rays are transmitted, the phase of the propagation is also transmitted. This phase shift is independent of the incident angle.Both \alpha and \tau coefficients to account for specular reflected, absorbed, and transmitted energy. The surface then:Diffusely absorbs energy when \alpha is greater than 0, and is equal or less than 1.Diffusely transmits energy when \tau is greater than 0, and is equal or less than \alpha .Reflects specular energy calculated from (1, - ,\alpha ) x incoming energy.\alpha , \delta , and \tau coefficients to account for specular reflected, diffuse reflected, absorbed, and transmitted energy. The surface then:Diffusely absorbs energy when \alpha is greater than 0, but is equal or less than 1.Diffusely transmits energy when \tau is greater than 0, but is equal or less than \alpha .Reflects specular energy calculated from (1 - \alpha )(1 - \delta ) x incoming energy.Reflects diffuse energy calculated from (1 - \alpha ),\delta x incoming energy.Fully Absorbent Material property to exclude rays that enter inside cavities during the geometrical computation.

• A Diffraction simulation object to specify diffractions on element edges or faces of acoustic fluid elements to account for the spreading of rays. You can specify whether the diffraction occurs only in the forward or shadow area of the selected elements, or on which dihedron side the software computes diffraction.

• A Smooth Surface simulation object to specify smooth surfaces. For example, when a surface with a continuous normal exists in your model, you can use the Smooth Surface simulation object to ensure that the software considers this surface when a ray is reflected on that surface.

Supported modeling objects

This environment supports the modeling objects:

• Forcing Frequencies to specify the list of forcing frequencies to be solved in frequency response problems.

• Physical Solver Parameters to control whether to account for air absorption.

• Particle Solver Parameters to specify parameters for a particle tracing solution.

• Wide Bands to specify the bands for calculating and outputting particle tracing results.

• Time Sampling to specify the time sampling for the integration of the particle trajectory.

• Output Requests to request acoustic pressure results at microphone nodes, ray paths, echograms, binaural impulse results (BIRs), BIR sound quality criterium, and for a particle tracing solution sound quality criteria to recover from the acoustic response solution. For the BIR results, the software also creates an audio file in WAV format (*.wav) for each selected microphone. The WAV files are stored in the Simulation file directory.For more information about ray paths, echograms, and BIRs, see Post-processing of results.

Note:

To request a particle tracing solution, you must select the Enable Particle Tracing check box in an active solution or solution step. For information about particle tracing, see Particle tracing solutions.

Supported solution types

This environment supports the Acoustic Response solution type, which also lets you request the conversion of results to time domain.

Supported solver parameters

You can control the location of the solver, parallel processing, and amount of reflections, diffractions, and beam subdivisions to be computed.

Post-processing of results

You can post-process the results that you requested with the Output Requests modeling object using the Scenario Based Data-Visualization Navigator. For example, you can post-process the following results with the:

• Ray Path Analysis post-processing scenario:Ray paths at specified times or across a range of values. The following shows the ray paths displayed. The last ray is displayed in red with a larger line widthRay pathsEchograms that show on a timeline the different ray path attachments and their individual sound pressure contribution, which help you to understand the overall acoustics of an enclosure. An example of an echogram is shown below.Echogram - XY plot of sound pressure over timeYou can create an echogram for each receiver and each forcing frequency. This lets you show the contribution and arrival time of the different rays for each frequency in relation to the position of each receiver. Echograms can provide information about the acoustical impressions a person perceives, for example, in a room.For example, amplitude of reflections that do not seem to decrease can indicate that flutter echo persists in the room. A flutter echo originates when, for example, in a concert hall, the sound is allowed to bounce back and forth between the wall behind the stage and the wall behind the audience. To avoid this kind of flutter echo, you can apply damping.Ray paths and an echogram stacked in one view. The ray paths are displayed in the upper half of the view and the echogram in the lower half. Because the plots are synchronized, you can probe a value in the echogram and let the software display the associated ray path in the upper plot. The following figure below shows an example of synchronized plots, where the software displays an echogram and only the ray path of a probed value.Synchronized plots of ray path and echogram

• Function Plots post-processing scenario BIR results at selected microphones. Because BIRs integrate (Kemar-based) head-related transfer functions, they let you characterize how left and right ears receive sound from the acoustic environment that is determined by, for example, acoustic sources, scene, and so on. The computation of the BIRs depend on the relative position of the right and left ears with respect to the acoustic environment. To define the relative position, you specify the following positive axes of an absolute or local coordinate system, where the XY plane is parallel to the bird's eye view of a human head:X-axis is along the human central vision direction and points away from the head.Y-axis forms a horizontal line between the human ears and points away from the left ear.Z-axis is normal to the XY plane pointing out of the top of the head.The following figure below shows an example of a function plot, where the software displays the overlayed BIR graphs of the left and right ear channels.BIR - XY plot of sound pressure over time for both channels

Where do I find it?

Application	Pre/Post
Prerequisites	A Simulation file as the work part and displayed partSimcenter 3D Ray Acoustics as the specified solver
Command Finder	Solution
Simulation Navigator	Right-click the Simulation file→New Solution

How do I

Automatically create directionality fields

Learn more

Particle tracing solutions

Ray Acoustics workflow

Remote solving workflow (Linux)

Quick links

Command reference

Pre/Post video examples

Bulk Entry Descriptions

Simcenter 3D tutorials

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Simcenter 3D Ray Acoustics environment, Simcenter 3D 2021.1 Series

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