Operating Deflection Shapes Analysis
Operating Deflection Shapes (ODS) analysis is used for determination of the vibration pattern of a structure under given operating conditions. Vibration measurements are performed at different points and directions on the structure and the vibration pattern can be shown as an animated geometry model of the structure or listed in a shape table.
Any ODS is a combination of the forcing function acting on the structure and the dynamic properties of the structure. The forcing function depends on the operating conditions, which for machinery could be influenced by e.g. engine speed, load, pressure, temperature and flow. Ambient forces from waves, wind and traffic might also apply for civil engineering structures.
ODS analysis can be divided into threee types:
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Time ODS
Time ODS is used to investigate the vibration pattern of a structure as a function of time. In contrast to Spectral ODS and Run-up/down ODS, where the vibration pattern of a single frequency or order, is investigated, Time ODS includes all frequencies in the analysed frequency range. Time ODS is very useful to give an overall ODS at a given point in time whether the signal is stationary or non-stationary e.g. transient signals.
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Spectral ODS
Spectral ODS is used to investigate the vibration pattern of a structure for a specific frequency or order component. For frequency component investigations, FFT analysis is used and the conditions must be stationary. For order component investigations, order analysis (tracking) is used to eliminate `smearing' of spectral components in cases of almost stationary conditions. The ODS of different spectral components (frequencies or orders) is subsequently extracted, shown in a shape table and animated.
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Run-up/down ODS
Run-up/down ODS is used to investigate the vibration pattern of a structure for specific order components as a function of rotational speed. The order components can either be defined beforehand (pre-slices) and/or taken out as slices from e.g. contour plots (post-slices). Run-up/down ODS is very useful for relating a structure’s noise and vibration behaviour to the rotational parts of an engine.
The Structural Dynamic Test Consultants
Modal Test Consultant (MTC) Type 7753 and Operating Deflection Shapes Test Consultant (ODSTC) Type 7765 are PULSE applications developed to simplify and dramatically reduce the time required to perform structural dynamic measurements. Together they are referred to as Structural Dynamic Test Consultants. The ODS Test Consultant supports Time ODS and Spectral ODS and can be upgraded with options for Run-up/down ODS (BZ-5612) and Animation (BZ-5613). Analysis can be performed in real-time or as post-processing of recorded time histories.
The Structural Dynamic Test Consultants utilise the PULSE multi-analysis platform. They are graphically driven and easily controlled, linking the measurement directly to the on-screen test object geometry. These features, together with highly effective tools for setup, measurement and validation, make testing fast and reliable. ODS results can be animated directly in ODSTC and FRFs directly in MTC. The data generated (time, spectra, geometry and DOF information) can be used directly by your chosen post-processing package, such as PULSE Reflex Modal Analysis, I-deas® Test or ME'scopeVEStm (both available through Brüel & Kjær)
