Defining Harmonic Response Steps

You can define a harmonic response step to perform a mode-based analysis that calculates the steady-state dynamic linearized response of a system to harmonic excitation. The app calculates the response based on the system's eigenfrequencies and mode shapes, which it must first extract by using the eigenfrequency extraction procedure in a preceding frequency step.

This task shows you how to:

See Also
About Harmonic Response Steps
In Other Guides
Analysis Cases and Steps

Define Harmonic Response Steps Using the Frequency Increment Interval Type

  1. From the Procedures section of the action bar, click Harmonic Response Step .
  2. Optional: Enter a descriptive Name.
  3. From the Projection type options, specify one of the following options:
    OptionDescription
    None Creates a mode-based harmonic response step.
    All frequencies Projects the dynamic equations onto the modal subspace at each frequency requested on the data lines.
    Center frequencies Projects the dynamic equations onto the modal subspace for all frequencies requested. The app performs the projection using modal properties evaluated at the center frequency determined on a logarithmic or linear scale.
    Lower/upper range values Projects the dynamic equations onto the modal subspace at the lower limit of each frequency range and at the upper limit of the last frequency range.
  4. From the Interval type options, select Frequency increment.
  5. From the Scale options, specify one of the following options:
    OptionDescription
    Linear The Abaqus solvers divide the frequency ranges using a linear scale.
    Logarithmic The Abaqus solvers divide the frequency ranges using a logarithmic scale.
  6. Enter the following values in the data table:
    OptionDescription
    Lower (Hz) Lower limit of the frequency range or a single frequency, in cycles/time.
    Upper (Hz) Upper limit of the frequency range, in cycles/time.
    Frequency Increment (Hz) Number of frequency units in each interval of the frequency range. This value should be a number that is divisible by (Upper – Lower).
  7. Optional: From the Damping options, select one of the following options:
    OptionDescription
    Use structural material and element damping Indicates that the damping forces are intended to represent frictional effects. Select this option for models involving materials that exhibit frictional behavior or where local frictional effects are present throughout the model, such as dry rubbing of joints in a multi-link structure.
    Use viscous material and element damping Indicates that the damping forces are intended to represent viscous frictional effects. Select this option for models involving materials that exhibit viscous frictional behavior.
  8. To select the eigenmodes to be used for this step, see Selecting Eigenmodes for Mode-Based Procedures.
  9. Click OK.

Define Harmonic Response Steps Using the Eigenfrequency Increment Interval Type

  1. From the Procedures section of the action bar, click Harmonic Response Step .
  2. Optional: Enter a descriptive Name.
  3. From the Projection type options, specify one of the following options:
    OptionDescription
    None Creates a mode-based harmonic response step.
    All frequencies Projects the dynamic equations onto the modal subspace at each frequency requested on the data lines.
    Center frequencies Projects the dynamic equations onto the modal subspace for all frequencies requested. The app performs the projection using modal properties evaluated at the center frequency determined on a logarithmic or linear scale.
    Lower/upper range values Projects the dynamic equations onto the modal subspace at the lower limit of each frequency range and at the upper limit of the last frequency range.
  4. From the Interval type options, select Eigenfrequency.
  5. From the Scale options, specify one of the following options:
    OptionDescription
    Linear The Abaqus solvers divide the frequency ranges using a linear scale.
    Logarithmic The Abaqus solvers divide the frequency ranges using a logarithmic scale.
  6. Enter the following values in the data table:
    OptionDescription
    Lower (Hz) Lower limit of the frequency range or a single frequency, in cycles/time.
    Upper (Hz) Upper limit of the frequency range, in cycles/time.
    Number of Points Number of points in the frequency range at which results should be given, including the end points, in the following intervals:
    • From the lower limit of the frequency range to the first eigenfrequency in the range
    • In each interval from eigenfrequency to eigenfrequency
    • From the highest eigenfrequency in the range to the upper limit of the range
    The minimum number of points is 2 and the default value is 20.

    Bias

    You should enter a bias parameter only if results are requested at four or more frequency points. Any bias value less than 1.0 causes closer spacing of the results points toward the middle of the interval, while values greater than 1.0 provide spacing closer to the end of the interval. Biasing the results points toward the ends of the intervals provides better resolution in those regions.

    Using a bias value is recommended for eigenfrequency intervals because the ends of each interval are the eigenfrequencies where the response amplitudes vary most rapidly.

    The default bias parameter is 3.0.
    Scale Factor Enter a frequency scale factor. All frequency points, except the lower and upper limit of the frequency range, are multiplied by this factor. The default scale factor is 1.0.
  7. Optional: From the Damping options, select one of the following options:
    OptionDescription
    Use structural material and element damping Indicates that the damping forces are intended to represent frictional effects. You should select this option for models involving materials that exhibit frictional behavior or where local frictional effects are present throughout the model, such as dry rubbing of joints in a multi-link structure.
    Use viscous material and element damping Indicates that the damping forces are intended to represent viscous frictional effects. You should select this option for models involving materials that exhibit viscous frictional behavior.
  8. To select the eigenmodes to be used for this step, see Selecting Eigenmodes for Mode-Based Procedures.
  9. Click OK.

Define Harmonic Response Steps Using the Direct Range Interval Type

  1. From the Procedures section of the action bar, click Harmonic Response Step .
  2. Optional: Enter a descriptive Name.
  3. From the Projection type options, specify one of the following options:
    OptionDescription
    None Creates a mode-based harmonic response step.
    All frequencies Projects the dynamic equations onto the modal subspace at each frequency requested on the data lines.
    Center frequencies Projects the dynamic equations onto the modal subspace for all frequencies requested. The app performs the projection using modal properties evaluated at the center frequency determined on a logarithmic or linear scale.
    Lower/upper range values Projects the dynamic equations onto the modal subspace at the lower limit of each frequency range and at the upper limit of the last frequency range.
  4. From the Interval type options, select Direct Range.
  5. From the Scale options, specify one of the following options:
    OptionDescription
    Linear The Abaqus solvers divide the frequency ranges using a linear scale.
    Logarithmic The Abaqus solvers divide the frequency ranges using a logarithmic scale.
  6. Enter the following values in the data table:
    OptionDescription
    Lower (Hz) Lower limit of the frequency range or a single frequency, in cycles/time.
    Upper (Hz) Upper limit of the frequency range, in cycles/time.
    Number of Points Total number of points in the frequency range at which results should be given, including the end points. The minimum number of points is 2 and the default value is 20.
    Bias

    You should enter a bias parameter only if results are requested at four or more frequency points. Any bias value less than 1.0 causes closer spacing of the results points toward the middle of the interval, while values greater than 1.0 provide spacing closer to the end of the interval. Biasing the results points toward the ends of the intervals provides better resolution in those regions.

    The default bias parameter is 1.0.
  7. Optional: From the Damping options, select one of the following options:
    OptionDescription
    Use structural material and element damping Indicates that the damping forces are intended to represent frictional effects. You should select this option for models involving materials that exhibit frictional behavior or where local frictional effects are present throughout the model, such as dry rubbing of joints in a multi-link structure.
    Use viscous material and element damping Indicates that the damping forces are intended to represent viscous frictional effects. You should select this option for models involving materials that exhibit viscous frictional behavior.
  8. To select the eigenmodes to be used for this step, see Selecting Eigenmodes for Mode-Based Procedures.
  9. Click OK.

Define Harmonic Response Steps Using the Frequency Spread Interval Type

  1. From the Procedures section of the action bar, click Harmonic Response Step .
  2. Optional: Enter a descriptive Name.
  3. From the Projection type options, specify one of the following options:
    OptionDescription
    None Creates a mode-based harmonic response step.
    All frequencies Projects the dynamic equations onto the modal subspace at each frequency requested on the data lines.
    Center frequencies Projects the dynamic equations onto the modal subspace for all frequencies requested. The app performs the projection using modal properties evaluated at the center frequency determined on a logarithmic or linear scale.
    Lower/upper range values Projects the dynamic equations onto the modal subspace at the lower limit of each frequency range and at the upper limit of the last frequency range.
  4. From the Interval type options, select Frequency Spread.
  5. Enter the following values in the data table:
    OptionDescription
    Lower (Hz) Lower limit of the frequency range or a single frequency, in cycles/time.
    Upper (Hz) Upper limit of the frequency range, in cycles/time.
    Number of Points Total number of equally spaced points around the eigenfrequency at which results should be given, including the eigenfrequency and endpoints. The minimum value and default number of points is 3.0.
    Scale Factor Enter a frequency scale factor. All the frequency points, except the lower and upper limit of the frequency range, are multiplied by this factor. The default scale factor is 1.0.
    Spread Enter a frequency spread. This determines the spread as a fractional value of each eigenfrequency in the specified range. The value must be greater than 0.0 and less than 1.0. The default spread is 0.1.
  6. Optional: From the Damping options, select one of the following options:
    OptionDescription
    Use structural material and element damping Indicates that the damping forces are intended to represent frictional effects. You should select this option for models involving materials that exhibit frictional behavior or where local frictional effects are present throughout the model, such as dry rubbing of joints in a multi-link structure.
    Use viscous material and element damping Indicates that the damping forces are intended to represent viscous frictional effects. You should select this option for models involving materials that exhibit viscous frictional behavior.
  7. To select the eigenmodes to be used for this step, see Selecting Eigenmodes for Mode-Based Procedures.
  8. Click OK.