ODS's of a Plate

In this tutorial, we will build a model of a flat plate and display frequency-based 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.'s in animation on the model.

video

The following steps will be carried out to display the ODS's of the flat plate;

1. Create a model of the test article including all of its test points

2. Import FRF An FRF (Frequency Response Function) is a cross-channel frequency domain function that defines the dynamic properties of a structure between an excitation Force and the Response caused by that force. An FRF is defined as the ratio (Response DFT / Force DFT). The FRF is a special case of a Transfer Function, where the response is the numerator (Output) and the force is the denominator (Input). measurements taken from the test article into a Data Block file One or more measurements with a common time or frequency axis. Time domain measurements are real valued. Frequency domain measurements are complex valued. Each measurement has a unique measurement number (M#). M#s are displayed in the first column of the M#s spreadsheet in a Data Block window. M#s are used by the Animation equations at each Point for displaying M# data at the current cursor position.

3. Assign the FRF measurements (M# M# is an abbreviation for Measurement Number. Each measurement function in a Data Block or Acquisition window has a unique M#. Also, each shape component in a Shape Table window has a unique M#. Each M# in the connected Animation Source must be Assigned to a DOF of the structure model in order to display shapes from the Source in animation. Each un-measured DOF on the model is animated by creating an M# Interpolation using nearby Measured and Fixed DOFs.s) to points & directions (DOFs) on the model where the measurements were made

4. Display ODS's in animation on the plate model from the cursor position in the FRFs

5. Position the cursor at a resonance peak to display an approximation of the mode shape for that resonance

NOTE:  When an ODS is displayed from the cursor at or near a resonant peak in a set of FRFs, it is usually dominated by the resonance and is therefore a close approximation of the mode shape Modes are used to characterize resonant vibration in structures. Each mode has a natural frequency, damping value, and a mode shape. The mode shape is a standing wave deformation of the structure at its natural (resonant or modal) frequency. An ODS is a summation of contributions fof all of the mode shapes of the modes being excited in a structure. associated with the resonance.

Animating an ODS at a Resonance Peak.