OMA+ODS of rotating systems | vRotorModal

The Rotational OMA+ODS package was developed with the aim of conducting structural dynamic investigations on rotating components during operation. In addition to the classic operational deflection shape analysis (ODS), the operational modal analysis (OMA) is a novel tool that enables the determination of modal parameters (natural frequency, mode shape, and damping) during operation. Data acquisition is carried out using vibration sensors attached to the test object and rotating during operation.

The vibration signals can be transmitted either via telemetry or via slip rings. As an alternative to these technologies, MAUL-THEET offers compact, autonomous front ends for slowly rotating test objects. These front ends are applied directly to the rotating test object and transmit the vibration signals via Wi-Fi.

By detecting the angular position using a speed sensor, the position of the co-rotating sensors can be calculated at any time. This allows signal blocks for local angular ranges to be created and analyzed. This data is stored and can then be evaluated using the vRotorModal analysis program.

In operational modal analysis, complete datasets for the operational modal analysis algorithms are fully automatically generated using tachometer and reference channels. These datasets contain

• The geometry in the form of points, lines and surfaces
• The assignment of the degrees of freedom to the measurement data
• The measurement data in the form of time courses

 

The data sets are analyzed in vRotorModal. The following algorithms are available to determine the modal variables

• Frequency Domain Decomposition (FDD)
• Enhanced Frequency Domain Decomposition (EFDD)
• Stochastic Subspace Identification (SSI)

 

The calculated modal sizes can be listed and animated using extensive graphic functions. Furthermore, the following tools are available for validating the modal variables

• Superposition of natural vibration forms
• Stability maps
• Modal Assurance Criteria (MAC)

In operational deflection shape analysis, time blocks of varying lengths can be extracted by adjustable circumferential segmentation of sensor positions. These time blocks are transformed into the frequency domain via FFT after window evaluation (e.g., Hanning). Taking into account the angular positions of the sensors, a coordinate transformation is performed, and, as in classical operational deflection shape analysis, the auto- and cross-spectra are computed.

In addition to the representation of the operational deflection shapes by animated wireframe animations, Rotational ODS provides other useful output options

• Polar plot amplitude vs. rotation angle
• Amplitude ratio vs. rotation angle
• Frequency vs. rotation angle
• Phase vs. rotation angle
• Waterfall and contour display per revolution

The Rotational OMA+ODS package can be used, among other things, to identify modal variables in situ, i.e. for relevant operating states. These modal variables can be used to compare simulation models (model updating). The process has been successfully used, for example, for rotating brake systems with different operating parameters (speed, brake pressure, etc.).

The Rotational OMA+ODS package was developed in close collaboration with our customers for use on rotating brake systems. We are pleased to now be able to offer the Rotational OMA+ODS system in a fully developed form.