What is a Modal Model?

A Modal Model A Modal Model is a set of mode shapes that have been scaled so that they preserve the dynamic properties of a structure. Two types of modal models are used in ME'scope, Residue mode shapes and Unit Modal Mass (UMM) mode shapes. Residue mode shapes are obtained by curve fitting a set of calibrated FRFs. UMM mode shapes are obtained by re-scaling a set of Residue mode shapes. Modal models are used for SDM calculations, FEA Model Updating, FRF synthesis, and MIMO calculations. is a set of mode shapes that has been scaled to preserve the mass, stiffness & damping properties of a structure.

In ME'scope, Residue A Residue is one of the three modal parameters (frequency & damping are the other two) obtained during FRF-based curve fitting. A Residue is the numerator term in the partial fraction expansion of the FRFcurve fitting model. A Residue is also referred to as the "strength" of the mode. Residue units are the FRF engineering units multiplied by Hz (or radians per second). Typical Residue units are g's/N-sec. mode shapes are obtained by curve fitting a set of FRFs.

• A Modal Model of Residue mode shapes is obtained by curve fitting a set of calibrated FRFs, or by re-scaling UMM mode shapes. (see Tools | Scaling | UMM to Residue Shapes in the Basic Modal Analysis commands chapter.)

• A Modal Model of UMM mode shapes is obtained by re-scaled a set of Residue mode shapes , or by re-scaling Residue mode shapes

• A Modal Model of UMM mode shapes is obtained by solving for the modes of an FEA FEA is an acronym for Finite Element Analysis. FEA involves creating an FEA model by adding FEA elements (called FEA Objects in ME'scope) to a structure model. The FEA model can be solved for its FEA modes, and also used for other analyses in ME'scope. model. (see FEA | Calculate FEA Modes in the FEA commands chapter)

Uses of a Modal Model

A Modal Model is required as input by the following commands in ME'scope,

1. Modes | Synthesize FRFs in a Data Block or Tools | Synthesize FRFs in a Shape Table

2. Transform | MIMO | Outputs in a Data Block

3. Transform | MIMO | Inputs in a Data Block

4. Transform | MIMO | Sinusoidal ODS ODS is an acronym for Operating Deflection Shape. An ODS is the deformation of a structure at two or more locations and/or directions due to its own operational forces and/or other applied forces. A time domain ODS characterizes the structural deformation at a specific time. A frequency domain ODS characterizes the structural deformation at a specific frequency. An ODS is a summation of contributions of the mode shapes of all resonances being excited by the specific operating condition. in a Data Block or Tools | Sinusoidal ODS in a Shape Table

5. SDM SDM is an acronym for Structural Dynamics Modification. SDM is an algorithm that uses the modes of an unmodified structure together with FEA Objects that model structural modifications, and calculates the modes of the modified structure. SDM is very fast and provides useful results even when a modal model has only a few modes in it. | Calculate New Modes in a Structure window

6. SDM | Modal Sensitivity in a Structure window

7. SDM | Add Tuned Absorber in a Structure window

8. FEA | FEA Model Updating in a Structure window

9. FEA | Calculate Updated FEA Modes in a Structure window