Models the addition of one or more tuned vibration absorbers to a structure.
A tuned absorber is used to suppress the amplitude of a particular resonance, or mode of vibration.
If the frequency of the tuned absorber is tuned to be close to the frequency of a structural resonance, the tuned absorber will "split" the original resonance into two resonances with lower amplitudes.
A tuned absorber is modeled using a mass, spring, and damper. The SDM method and sub-structuring is used to attach the tuned absorber mass to a structure using the spring and damper.
SDM calculates the new modes which result from attaching a tuned absorber mass to the structure with a spring and damper .
The new modes reflect the influence of the Tuned Absorber on the modes of the structure.
A Tuned Absorber s defined by the following parameters,
Absorber direction of motion
Absorber mass
Absorber frequency (should be "close" to the frequency of the mode to be suppressed)
Absorber damping (optional. An estimate of the percent of critical damping of the Absorber)
The Tuned Absorber FEA mass is attached to a Point & direction of a structure model using an FEA spring. The stiffness of the spring is calculated using the formula,
FEA spring stiffness = Absorber FEA mass x (Absorber Frequency)2
The using SDM to calculate the new modes, the following items are required,
A Shape Table containing UMM mode shapes of the unmodified structure.
A structure model containing the Point & direction where the Tuned Absorber will be attached.
Mass, Force & Length units (chosen on the Units tab in the File | Structure Options box), that match the Force & Length units of the UMM mode shapes.
The UMM mode shapes must animate correctly on the structure model before using them with this command.
When this command is executed, the following dialog box will open;
Tuned Absorber Dialog Box.
Select the Shape Table containing the UMM mode shapes of the unmodified structure from the UMM Shapes to Modify list.
Select the Number of Absorbers to be attached to the structure.
For each Absorber,
Select a Structure DOF for attaching the Absorber
Enter an Absorber Mass into the spreadsheet
Enter the Absorber Frequency into the spreadsheet
(optionally) Enter the Absorber Damping into the spreadsheet
After all Absorber parameters have been entered, press the Calculate New Modes button.
When the SDM calculation is completed, all Tuned Absorbers defined in the dialog box will have been added as new Point Masses to the structure model.
The Shape Table selection box will open allowing you to save the new UMM mode shapes of the modified structure.