Operating Deflection Shape (ODS)

Operating Deflection Shape (ODS) – is a term often used in the structural engineering analysis, known as ODS analysis. ODS analysis is a method used for visualisation of the vibration response of a machine or structure as influenced by its own operating forces, or extraneous forces (tidal, wind) and presents the data in an animated 3D wireframe mesh format.

The Operating Deflection Shape (ODS) method relies on the forces of the system or other influential forces (centrifugal force, wind, etc) as opposed to modal analysis which is the study of the vibration response of a machine under a known external forcing load. ODS can be measured in the Time Domain (Magnitude and Phase only), or the Frequency Domain (Frequency, Magnitude and Phase).

One application for a time based ODS would be for the assessment (and visualisation) of the amplitude and motion characteristics of a Compound Bow as it is drawn and released. A time based ODS would show the deflection of the bow before during and after the bow is released with the passage of time. It would not show any frequency content. This data could then be used to calculate the vibration exposure to the person using the bow. It can also be used for the assessment of the deck of a vessel due to the pitch, roll and awe of the vessel in the sea.

Frequency based ODS are more commonly used for the assessment (and visualisation) of machinery and structures to help identify possible natural frequencies of the structure during operating conditions. This method does provide the frequency and phase information although does not provide the time waveform data. The animation is generated by referencing all measurement positions to a fixed coordinate in a 3D wire frame mesh, and then referencing each fixed coordinate to a single fixed coordinate position. The FRF’s measured at each of the measurement positions are assigned to their respective coordinate position in the 3d wire frame mesh. Measurements using Frequency based ODS cannot be used during transient running speeds, and should be performed when the machine is operating at a constant speed.