Modal passport of dynamically loaded structures: application to composite blades

Abstract

Close relation of modal properties to mechanical properties of structures presents interest for applied research and solutions of Structural Health Monitoring (SHM) tasks. The paper considers application of analytical and modal analysis techniques for structural research and monitoring of composite blades as well as required measurement tools. The Roving Hummer Technique (RHT) and Operational Modal Analysis OMA) were admitted as optimal methods for modal properties estimation, but 3-axial accelerometers and vibration deformation sensors -as most acceptable measurement tools. There is discussion of methodology and technical aspects required for modal properties estimation of static and rotating blades. Samples of composite blades preparation for measurements and equipment applied for testing are considered. Authors discuss the modal passport concept as the platform for applied studies of modal properties and for diagnostic purposes including Structural Health Monitoring (SHM) of operating structures. Typical modal passport structure is described as the set of modal parameters that are common for same type of blades and generalized dependences of modal parameters from operational factors. The paper discusses the principles of modal passport application for a particular blade based on its individual modal properties. There are conclusions about application of typical modal passport in industry.

Health Monitoring of Serial Structures Applying Piezoelectric Film Sensors and Modal Passport

“…The latter is not thicker than the films/wires and smooths out the roughness. Trial applications of piezo films into composite blades [ 19 , 26 , 27 ] demonstrated workability of such technical solutions in operational conditions. For instance, the measurement system remained functional at rotating frequencies up to 25 rev/sec, with no discernible effect on the aerodynamic profile.…”

“…For a test case, the typical testing procedure, which simulates ambient excitation, complements the recording procedure. The typical OMA [ 19 ] algorithms 3 are used to estimate the modal parameters from the sensor signals. These algorithms, which are realized by some OMA estimators in Frequency and Time Domains, compute the modal parameters.…”

“…Different OMA approaches to modal identification consider both stochastic subspace [ 14 ] and frequency domain decomposition [ 15 ] techniques. There are many cases of OMA applications [ 16 ] in aviation, for instance, for the airplane [ 17 ], for helicopter structures [ 18 ] and for blades [ 19 ], as well as for wind generator blades [ 20 ]. Successful trials attest to OMA techniques being the most promising approach to SHM of operating objects.…”

Wavelet-Based Output-Only Damage Detection of Composite Structures

“…Then, an operator estimates the modal parameters of the structure. The resulting parameters together with the possible external operational factors, such as static loads, temperature or speed of rotation (blades), are input to a modal passport [21,22], where the past measurements are stored. Modal parameters in a reference or intact structural state together with their deviations due to operational factors form a "signature" of a structure that is unique to this structure or for structures of this type.…”