Forcing Frequencies dialog box (Nastran)

This modeling object lets you specify forcing frequencies for a frequency response analysis and corresponds to the FREQ, FREQ1, FREQ2, FREQ3, FREQ4, or FREQ5 bulk entry depending upon the options you choose in the Forcing Frequencies or Forcing Frequencies - Modal dialog box.

For more information on the bulk entries used for forcing frequencies, see Solution Frequencies in Basic Dynamic Analysis User's Guide.

Common options in Forcing Frequencies and Forcing Frequencies - Modal dialog boxes

Modeling Object
Name	Defines the modeling object name.
Label	Specifies a unique numerical identifier for the modeling object.
Properties
Description	Lets you enter a brief description. Click to open a text editor where you can enter a longer description.
Frequency List
Frequency List Form	Specifies the form of the FREQi bulk entry to use in frequency response solutions.

Forcing Frequencies options

Frequency List
Frequency List	Appears when Frequency List Form is set to Individual Frequencies (FREQ).Specifies the frequency unit. Hz is the default.Note: This corresponds to the Fi field in the FREQ bulk entry.
Frequency List box	Appears when Frequency List Form is set to Individual Frequencies (FREQ).Lets you specify as many frequencies as you need.Enter the frequencies to include. Separate them by commas or spaces.You can also Cut, Copy, and Paste the frequencies.
Linear Sweep Defined by	Appears when Frequency List Form is set to Linear Sweep (FREQ1).Specifies the frequency range.Number of StepsLets you set values for First Frequency (F1 field in the FREQ1 bulk entry), Step Value (DF field in the FREQ1 bulk entry), and Number of Steps (NDF field in the FREQ1 bulk entry).Step ValueLets you set values for Start Frequency (F1 field in the FREQ1 bulk entry), End Frequency After, and Step Value (DF field in the FREQ1 bulk entry).Note: When the End Frequency After value does not fit into the sweep definition, the software includes the next valid frequency in the frequency list.For example, if Start Frequency is 100, End Frequency After is 200, and Step Value is 75, the software exports 100, 175, and the next valid frequency, which is 250.When the End Frequency After value is greater than Start Frequency, the software generates one interval.
Linear Sweep by RPM Defined by	Appears when Frequency List Form is set to Linear Sweep by RPM (FREQ).Specifies the forcing frequencies for an order-cut solution step or subcase from an RPM sweep. Each order-cut subcase may have different forcing frequencies. The software extracts the order number from the solution step name and uses the order number to find the RPMs and its related frequencies.Number of StepsLets you set values for First RPM, RPM Step Value, and Number of Steps.Step ValueLets you set values for Start RPM, End RPM After, and RPM Step Value.Note: When the End RPM After value does not fit into the sweep definition, the software includes the next valid RPM in the RPM list.For example, if Start RPM is 100,End RPM After is 200, and RPM Step Value is 75, the software uses 100, 175, and the next valid RPM, which is 250, to find related forcing frequencies.If the Step Value is greater than the difference of Start RPM and End RPM After, the software searches for frequencies at only the two RPMs: Start RPM and Start RPM + Step Value.
Logarithmic Sweep Defined by	Appears when Frequency List Form is set to Logarithmic Sweep (FREQ2).Specifies the frequency range.IntervalLets you set values for First Frequency (F1 field in the FREQ2 bulk entry), Last Frequency (F2 field in the FREQ2 bulk entry), and Number of Logarithmic Intervals (NF field in the FREQ2 bulk entry).BaseLets you set values for Start Frequency (F1 field in the FREQ2 bulk entry), End Frequency After (F2 field in the FREQ2 bulk entry), and Base of Logarithm (NF field in the FREQ2 bulk entry).Note: When the End Frequency After value does not fit into the sweep definition, the software includes the next valid frequency in the frequency list. For example, if Start Frequency is 100,End Frequency After is 200, and Base of Logarithm is 75, the software exports 100, 175, and the next valid frequency, which is 250.When the End Frequency After value is greater than Start Frequency, the software generates one interval.
Lower Center Frequency	Appears when Frequency List Form is set to Octave (FREQ), 1/3 Octave (FREQ), or 1/12 Octave (FREQ).Lets you enter the lower center frequency value of the frequency range.
Upper Center Frequency	Appears when Frequency List Form is set to Octave (FREQ), 1/3 Octave (FREQ), or 1/12 Octave (FREQ).Lets you enter the upper center frequency value of the frequency range.
Limit Frequency Range	Appears when Frequency List Form is set to Use Frequencies from All Loads (FREQ).Use Frequencies from All Loads combines all the frequencies defined for the solution and all subcases. When the same forcing frequencies exist at the subcase levels and solution level, the subcase setting takes priority over the solution's setting. You can have multiple combinations of forcing frequencies at the subcase level. The software then creates a union of the defined frequencies.Selecting this check box lets you set the range of forcing frequencies you are interested in. To limit the range of the forcing frequencies, enter values in the From and To boxes.
Advanced
Appears when Frequency List Form is set to Linear Sweep by RPM (FREQ) or Use Frequencies from All Loads (FREQ).
Frequency Tolerance	The software uses the frequency tolerance value to discard forcing frequencies that fall within the tolerance.For example, if the frequency tolerance value is set to 1 Hz and the software finds 200 Hz and 200.9 Hz forcing frequencies, the software filters out the second frequency.

Forcing Frequencies - Modal options

Lower Bound	Appears when Frequency List Form is set to Interpolated Between Natural Frequencies (FREQ3), Spread Around Natural Frequencies (FREQ4), or Fractions of Natural Frequencies (FREQ5).Lets you enter the lower bound of the frequency range in cycles per unit of time.Note: This corresponds to the F1 field in the FREQ3, FREQ4, or FREQ5 bulk entry.
Upper Bound	Appears when Frequency List Form is set to Interpolated Between Natural Frequencies (FREQ3), Spread Around Natural Frequencies (FREQ4), or Fractions of Natural Frequencies (FREQ5).Lets you enter the upper bound of the frequency range in cycles per unit of time.Note: This corresponds to the F2 field in the FREQ3, FREQ4, or FREQ5 bulk entries.
Interpolation Between Frequencies	Appears when Frequency List Form is set to Interpolated Between Natural Frequencies (FREQ3).Controls the type of interpolation between the frequencies.LINEARUses linear interpolation between the frequencies.LOGUses logarithmic interpolation between the frequencies.Note: This corresponds to the TYPE field in the FREQ3 bulk entry.
Number of Excitation Frequencies	Appears when Frequency List Form is set to Interpolated Between Natural Frequencies (FREQ3).Lets you enter the number of excitation frequencies within each subrange of frequencies through the end points.Note: This corresponds to the NEF field in the FREQ3 bulk entry.
Cluster	Appears when Frequency List Form is set to Interpolated Between Natural Frequencies (FREQ3).Lets you enter a factor that controls the clustering of the excitation frequency near the end of the range. Enter a real number greater than 0.0.For example:Cluster value is greater than 1.0Provides closer spacing of the excitation frequency near the end of the frequency range.Cluster value is less than 1.0Provides closer spacing of the excitation frequency near the center of the frequency range.Note: See the description of the CLUSTER field in the FREQ3 bulk entry for more information and a usage example.
Frequency Spread	Appears when Frequency List Form is set to Spread Around Natural Frequencies (FREQ4).Lets you enter the amount of spread around each natural frequency. The spread is the +/- amount specified for each mode which occurs between the specified Lower Bound and Upper Bound for the frequency range.Note: This corresponds to the FSPD field in the FREQ4 bulk entry.
Number of Evenly Spaced Frequencies	Appears when Frequency List Form is set to Spread Around Natural Frequencies (FREQ4).Lets you enter the number of evenly spaced frequencies per spread mode. Enter an integer greater than 0. If you enter an even value, the software uses the Number of Evenly Spaced Frequencies + 1.Note: This corresponds to the NFM field in the FREQ4 bulk entry.
Fractions of the Natural Frequencies box	Appears when Frequency List Form is set to Fractions of Natural Frequencies (FREQ5).Lets you specify fractions of the natural frequencies between the specified Lower Bound and Upper Bound for the frequency range.Enter real numbers greater than 0.0. Separate them by commas or spaces.You can also Cut, Copy, and Paste the frequencies.Note: This corresponds to the FRi field in the FREQ5 bulk entry.

Learn more

Specifying forcing frequencies for a frequency response analysis

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Forcing Frequencies dialog box (Nastran), Simcenter 3D 2021.1 Series

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