Defining Direct Harmonic Response Steps

You can use a direct harmonic response step to compute the steady-state harmonic response directly in terms of the physical degrees of freedom of the model.

By default, a direct harmonic response step computes the complex response.

This task shows you how to:

See Also
About Direct Harmonic Response Steps

Define Direct Harmonic Response Steps Using the Frequency Increment Interval Type

  1. From the Procedures section of the action bar, click Direct Harmonic Response .
  2. Optional: Enter a descriptive Name.
  3. Set the Interval Type to Frequency Increment.

  4. From the Scale options, specify one of the following:
    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.
  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.
    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).
  6. Optional: Select Include friction-induced damping effects.
  7. Optional: From the Global Damping options, select one of the following options:
    OptionDescription
    None Does not include global damping.
    Structural and Acoustic Includes structural and acoustic damping.
    Structural only Includes structural damping only.
    Acoustic only Includes acoustic damping only.
  8. If you have selected global damping, specify the following
    1. In the Mass Proportional field, enter the alpha factor to create global Rayleigh mass-proportional damping.
    2. In the Stiffness proportional field, enter the beta factor to create global Rayleigh stiffness-proportional damping.
    3. In the Stiffness proportional structural field, enter the s-global factor to create frequency-independent, stiffness-proportional, structural damping.
  9. 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 multilink 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.

Define Direct Harmonic Response Steps Using the Eigenfrequency Interval Type

  1. From the Procedures section of the action bar, click Direct Harmonic Response .
  2. Optional: Enter a descriptive Name.
  3. Set the Interval Type to Frequency Increment.

  4. From the Scale options, specify one of the following:
    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.
  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 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.
  6. Optional: Select Include friction-induced damping effects.
  7. Optional: From the Global Damping options, select one of the following options:
    OptionDescription
    None Does not include global damping.
    Structural and Acoustic Includes structural and acoustic damping.
    Structural only Includes structural damping only.
    Acoustic only Includes acoustic damping only.
  8. If you have selected global damping, specify the following
    1. In the Mass Proportional field, enter the alpha factor to create global Rayleigh mass-proportional damping.
    2. In the Stiffness proportional field, enter the beta factor to create global Rayleigh stiffness-proportional damping.
    3. In the Stiffness proportional structural field, enter the s-global factor to create frequency-independent, stiffness-proportional, structural damping.
  9. Optional: From the Damping options, enable any 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 multilink 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.

Define Direct Harmonic Response Steps Using the Direct Range Interval Type

  1. From the Procedures section of the action bar, click Direct Harmonic Response .
  2. Optional: Enter a descriptive Name.
  3. Set the Interval Type to Frequency Increment.

  4. From the Scale options, specify one of the following:
    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.
  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 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

    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.
  6. Optional: Select Include friction-induced damping effects.
  7. Optional: From the Global Damping options, select one of the following options:
    OptionDescription
    None Does not include global damping.
    Structural and Acoustic Includes structural and acoustic damping.
    Structural only Includes structural damping only.
    Acoustic only Includes acoustic damping only.
  8. If you have selected global damping, specify the following
    1. In the Mass Proportional field, enter the alpha factor to create global Rayleigh mass-proportional damping.
    2. In the Stiffness proportional field, enter the beta factor to create global Rayleigh stiffness-proportional damping.
    3. In the Stiffness proportional structural field, enter the s-global factor to create frequency-independent, stiffness-proportional, structural damping.
  9. 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 multilink 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.

Define Direct Harmonic Response Steps Using the Frequency Spread Interval Type

  1. From the Procedures section of the action bar, click Direct Harmonic Response .
  2. Optional: Enter a descriptive Name.
  3. Set the Interval Type to Frequency Increment.

  4. 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.
  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: Select Include friction-induced damping effects.
  7. Optional: From the Global Damping options, select one of the following options:
    OptionDescription
    None Does not include global damping.
    Structural and Acoustic Includes structural and acoustic damping.
    Structural only Includes structural damping only.
    Acoustic only Includes acoustic damping only.
  8. If you have selected global damping, specify the following
    1. In the Mass Proportional field, enter the alpha factor to create global Rayleigh mass-proportional damping.
    2. In the Stiffness proportional field, enter the beta factor to create global Rayleigh stiffness-proportional damping.
    3. In the Stiffness proportional structural field, enter the s-global factor to create frequency-independent, stiffness-proportional, structural damping.
  9. 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 multilink 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.