Creating duct modes workflow

Create the acoustic model

You should have a model of your duct system meshed with only fluid elements. Your duct inlets and outlets should be modeled as circular, annular, or rectangular.

You will need to create a microphone mesh on your model in order to output acoustic results such as pressure. See Capturing acoustic results.

Create an acoustic SOL 108 direct frequency response solution

1. In the Simulation Navigator, right-click your Simulation file, and choose New Solution.

2. In the Solution dialog box, set the Analysis Type to Acoustic, and the Solution Type to SOL 108 Direct Frequency Response.

3. On the Bulk Data tab, select the Enable Adaptive Order for Acoustic Elements check box .

4. Optional: Adjust the FEMAO settings Adaptation Rule (ACADAPT) and Order Limit (ACORDER).

5. On the Case Control tab, click ,  Create Modeling Object (Output Requests).

6. In the Acoustic Output Request dialog box, enable the Transmission Coefficients and Transmission Loss check box for the Duct Modes output.

7. Click OK.

8. In the Solution dialog box, on the Case Control tab, (Forcing Frequencies) , click Create Forcing Frequencies.

9. Enter your forcing frequencies and then click OK.

10. In the List group, click  to add the forcing frequencies modeling object.

11. Click Close to close the Modeling Objects Manager dialog box.

12. In the Solution Step dialog box, create a subcase for the type of duct mode load you are defining by selecting one of the following subcase types under Step:Subcase - Specific Duct Modes****Subcase - Distributed Duct Modes

13. Click OK.

14. Optional: You can create additional subcases by right-clicking the solution and selecting New Subcase.

Create a Duct mode load

1. Expand the Subcase node of an active solution, right-click the Loads container, and choose New Load.Depending on your subcase type, you will only have one load option: Specific Duct Mode or Distributed Duct Mode

2. In the Specific Duct Mode or Distributed Duct Mode dialog box, click Create Region .

3. In the Region dialog box, in the Region Objects group, select the fluid element faces that represent a duct inlet.

4. In the Shape group, select whether your duct inlet is Circular, Annular, or Rectangular.

5. Optional: In the Parameters group, you can offset your duct mode load axially by entering a value in Axial Offset Value.

6. In the Transverse Axis group, when Define Transverse Axis Automatically is selected, the software determines the duct axis direction. You can turn this option off to manually define the duct axis direction.

7. Click OK to close the Region dialog box.

8. In the Duct Mode Amplitude group, when defining a Specific Duct Mode, in Azimuthal / X Order and Radial / Y Order, define the duct mode order relative to the two duct cross section directions.Note: Azimuthal / X Order and Radial / Y Order do not apply to the Distributed Duct Mode.

9. In Measure Type, select the units of the duct mode amplitude as Acoustic intensity, Acoustic power, or Pressure.

10. In Format, specify the format of the duct mode amplitude complex data pair as Real/Imaginary, Magnitude/Phase, or Field. The Field choice allows you to specify frequency dependent complex data pairs.

11. Depending on what you selected in Format, enter either the Real / Imaginary or the Magnitude/Phase complex data pair.

12. Click OK to close the dialog box.

Create an Anechoic End Duct (AED) or Automatically Matched Layer (AML)

To allow the acoustic waves to exit a duct system boundary without reflections, you can:

• Define the Anechoic End Duct (AED) Simulation Object on a duct outlet. You can use this option when you are only interested in results within the duct system, and not exterior acoustic radiation.

• Define the Automatically Matched Layer (AML) at the outlet. When the AML is defined, the acoustic energy at the outlet can radiate to exterior microphone locations. You can use this option when you are interested in results within the duct system, and exterior acoustic radiation.See Create an automatically matched layer.

The following procedure is for the Anechoic End Duct (AED).

1. Right-click the Simulation Objects container of an active solution and choose New Simulation Object→Anechoic End Duct.

2. In the Anechoic End Duct dialog box, click Create Region .

3. On the Region dialog box, in the Region Objects group, select the fluid element faces that represent a duct outlet.

4. In the Shape group, select whether your duct outlet is Circular, Annular, or Rectangular.

5. Click OK to close the dialog box.

Solve the Solution

1. Right-click the Solution and choose Solve.

2. When the solve is complete, close all the information windows.

3. Post-process the solution using a Post-Processing Scenario.For more information, see Scenario-based post-processing.

Learn more

Duct mode load

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Creating duct modes workflow, Simcenter 3D 2021.1 Series

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