OMA rotating systems | vRotorModal

The Rotational OMA+ODS package was developed with the aim of carrying out structural dynamic studies on rotating components during operation. In addition to the classic operating deflection shape analysis (ODS), the operating modal analysis (OMA) is a new tool that enables the determination of the modal variables (natural frequency, natural shape and damping) during operation. The measurement data is recorded by vibration sensors that are installed on the rotor and rotate during operation. The vibration signals can be transmitted either via telemetry or with slip rings. As an alternative to these techniques, MAUL-THEET offers compact, autonomous front ends for slowly rotating test objects, which are applied directly to the rotating test object and transmit the vibration signals via WLAN. By detecting the angular position using a speed sensor, the position of the rotating sensors can be calculated at any time. This means that the signal blocks can be formed and analyzed for local angular ranges. This data is saved and can then be evaluated using the MAUL-THEET vRotorModal analysis program.

With rotational OMA (operational modal analysis), complete data sets for the operating modal analysis algorithms are generated fully automatically using tachometer and reference channels. These records 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)

With rotational ODS (operating deflection shape analysis), time blocks of different lengths can be extracted through an adjustable circumferential division of the transducer positions. After window evaluation (e.g. Hanning), these time blocks are transformed into the frequency domain using FFT. Taking the angular position of the sensors into account, a coordinate transformation and, as in the classic operating deflection shape analysis, the auto and cross spectrum are formed. In addition to displaying the operating mode shapes using 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.