Defining pressure and power data in dB

For table fields with Frequency selected as the independent domain, and Pressure or a power variable such as Power (x1) selected for the dependent domain, you can do the following:

• Convert the tabular data for pressure or power values to dB.

• Enter the tabular data for pressure or power values in dB.

The pressure and power tabular data can be real or complex. If the pressure or power tabular data is complex, it must be in magnitude/phase format and the software performs the dB calculations on the magnitude only.

The software uses the following equation to convert tabular data for pressure or power to dB:

{P_{dB}} = {S_f},{\log {10}}\left( {\frac{P}{{{P{ref}}}}} \right)

where:

{P_{dB}}

Pressure or power in dB

{S_f}

dB scaling factor

P

Pressure or power

{P_{ref}}

Reference pressure or power

When the software converts tabular data for pressure or power values to dB, if the units for pressure or power differ from those of the reference pressure or power, respectively, it converts the pressure or power units for the tabular data to the units of the reference pressure or power before calculating the values in dB.

For example, suppose the pressure is 8 MPa, the reference pressure is 0.00002 Pa, and the dB scaling factor is 10. The software computes the pressure in dB as follows:

{P_{dB}} = 10{\log _{10}}\left( {\frac{{8 \times {{10}^6}}}{{0.00002}}} \right) = 116.02,{\rm{dB}}

When the software performs a table lookup, it interpolates the values for pressure or power in the units of the reference pressure or power. Thus, when you enter the tabular data for pressure or power values in dB, the software uses the following equation to convert the values in dB to values in the units of the reference pressure or power:

P = {P_{ref}}{10^{\left( {\frac{{{P_{dB}}}}{{{S_f}}}} \right)}}

For example, suppose you create a table field for frequency versus pressure, with the tabular data for pressure in dB. If the tabular data for the table is (2,3) and (4,8), the dB scaling factor is 10, and the reference pressure is 0.00002 Pa, the software computes the table lookup value for a frequency of 3 as follows:

The software begins by converting the pressure data in dB to pressure in Pa.

P = 0.00002\left( {{{10}^{\left( {\frac{3}{{10}}} \right)}}} \right) = 0.0000399,{\rm{Pa}}

P = 0.00002\left( {{{10}^{\left( {\frac{8}{{10}}} \right)}}} \right) = 0.0001262,{\rm{Pa}}

The software then interpolates the values using the selected interpolation method. Thus, if in the Table Field dialog box, Interpolation is set to Linear, and Algorithm is set to Linear Linear, the software calculates the lookup as follows:

\left( {\frac{{{P_{lookup}} - 0.0000399}}{{3 - 2}}} \right) = \left( {\frac{{0.0001262 - 0.0000399}}{{4 - 2}}} \right),,,,, \to ,,,,,{P_{lookup}} = 0.0000831,{\rm{Pa}}

Where do I find it?

Converting pressure or power data to dB

Application	Pre/Post
Prerequisites	The Table Field dialog box open with Frequency selected as the independent domain, Pressure or a power variable such as Power (x1) selected for the dependent domain, and the Data Points table populated
Location in dialog box	In the Data Points table, right-click the pressure or power column heading→dB Scaling

Entering pressure or power data in dB

Application	Pre/Post
Prerequisites	The Table Field dialog box open with Frequency selected as the independent domain, and Pressure or a power variable such as Power (x1) selected for the dependent domain
Location in dialog box	In the Data Points table, right-click the pressure or power column heading→dB Scaling→enter the tabular data

Changing dB scaling factor

Application	Pre/Post
Prerequisites	The Table Field dialog box open with Frequency selected as the independent domain, Pressure or a power variable such as Power (x1) selected for the dependent domain, and dB Scaling selected
Location in dialog box	In the dB Options group, from the dB Scaling Factor list, select the dB scaling factor

Changing dB reference pressure of power

Application	Pre/Post
Prerequisites	The Table Field dialog box open with Frequency selected as the independent domain, Pressure or a power variable such as Power (x1) selected for the dependent domain, and dB Scaling selected
Location in dialog box	In the dB Options group, in the dB Reference box, type the reference pressure

How do I

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Defining pressure and power data in dB, Simcenter 3D 2021.1 Series

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