Working with Surface Spectra Field Functions

Importing a .trn file registers the following field functions:

Time History:
Fourier Transform:

The time history and field functions can be displayed in a scene, by setting the appropriate field function as a scalar displayer.

Using the Time History Field Functions

The .trn import registers a number of time history field functions relating to the exported field data.

These field functions have mostly read-only properties, except that the Time History:Pressure field function lets you select a filter type, which activates a FIR Filter sub-node.

Using the Fourier Transform Field Function

The import registers an FFT field function, relating to the exported scalar data. This field function has a number of properties that allow you to control the Fourier transform, in addition to the base properties of a typical field function.

Fourier Transform Field Function Properties

Fft Input Start Time

The start time (in seconds) for the time sampling for this object. If you have multiple FTs, you can vary the settings of this property to sample multiple time intervals from the simulation run.

Fft Input Cut-off time

The end time (in seconds) for the time sampling for this object. If you have multiple FTs, you can vary the settings of this property to sample multiple time intervals from the simulation run.

Amplitude Function

Specifies the amplitude function that is generated. These functions are all standard for this type of analysis.

Note	The function domain is limited to positive frequencies.

Power Spectral Density (Pa^2/Hz)

Frequency-domain description of the signal power.

Power Spectral Density (dB/Hz)

Sound pressure in decibels per hertz. Adds the Reference Sound Pressure node.

Sound Pressure Level

Sound pressure in decibels. Adds the Reference Sound Pressure node.

Root Mean Square

The square root of the Power Spectral Density.

A-Weighted Sound Pressure Level

Weights the Sound Pressure Level with the A-scale function, for loudness less than 55 phons (at 1000 Hz, 1 phon = 1 dB). This option is typically for problems that involve the frequency range for human hearing. Adds the Reference Sound Pressure node.

B-Weighted Sound Pressure Level

Weights the Sound Pressure Level with the B-scale function, for loudness of 55-85 phons. Adds the Reference Sound Pressure node.

C-Weighted Sound Pressure Level

Weights the Sound Pressure Level with the C-scale function, for loudness greater than 85 phons. Adds the Reference Sound Pressure node.

Frequency Range Type

Specifies the frequency function that is used. The sub-node that is contained within the FT field function is used to define the input for each frequency range type.

Frequency Value

Frequency in Hz. You specify a single value.

Frequency Range

Frequency in Hz over a range of values. You specify the lower and upper limits.

Octave Bands

Discrete frequency bands corresponding to different octaves within hearing range. Each successive band represents twice the range of the previous one. The current frequency band defines the hearing range.

3rd Octave Bands

Discrete frequency bands corresponding to one-third of each octave within hearing range. The current frequency band defines the hearing range.

Analysis Blocks

Specifies the number of analysis blocks used.

Overlap Factor

Sets the overlap factor between blocks, if any, in a range from 0 to 0.9. This overlap allows for smooth transitions between blocks.

Field update

When On, updates the FT field function when the display time or when a field function property is changed. The Off option can reduce the amount of time that is taken to update the results.

Window Function

Specifies the window function applied to the FT. The window function makes the signal periodic: it is guaranteed to be zero at both start and end. For most cases, apply a window function to a signal before applying an FT for best results. Available options:

None: This default setting leaves the data set function without a window function until you select one of the other options in this list.
Hamming: See Eqn. (543).
Hann (Hanning): See Eqn. (544).
Bartlett: See Eqn. (545).
Blackman: See Eqn. (546).

Nyquist Frequency

A read-only value in Hz.

Filter Type

Specifies the type of filter that is applied.

None

Does not use a filter.

Band pass filter

Keeps frequencies between low and high cut-off levels. Adds an Ideal Filter sub-node in which you can set these levels.

Band stop filter

Discards frequencies between low and high cut-off levels. Adds an Ideal Filter sub-node in which you can set these levels.

Dimensions

A read-only value of the dimensions that Simcenter STAR-CCM+ calculates for the FT field function.