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"Complex dynamic interactions of nonlinear, multistage and localization phenomena in turbine engines: development and validation of efficient and accurate modeling techniques."

Final Report Summary - UPGRADE (Complex dynamic interactions of nonlinear, multistage and localization phenomena in turbine engines: development and validation of efficient and accurate modeling techniques.)

Current and next-generation turbine engines will increasingly depend on onboard health monitoring and prognosis systems to help ensure the reliability, safety, and readiness of air vehicles. To effectively interpret the measurement data required for monitoring and prognosis of turbine engines, efficient models that have been experimentally validated and show to capture the essential complex dynamic interactions of nonlinear, multistage, and localization phenomena are mandatory.

In the proposed research project, advanced structural dynamic models and experimental validations will be developed for turbine engine rotors, which will directly support the emerging structural health monitoring and system prognosis needs of aerospace industry.

The main goals of the proposed research are:

• To model and predict the nonlinear vibration response of a rotor with cracked blades or blades damaged by a foreign object, including accounting for random mistuning and multistage coupling.

• To provide a fundamental physical understanding of localization phenomena in rotors due to individual and combined effects of mistuning and foreign object damage and/or cracks.

• To identify localization phenomena and nonlinear vibration characteristics strongly associated with cracks so that they can be exploited for structural health monitoring and damage detection.

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During the project, the following activities have been performed:

- A numerical code for the forced response analysis has been implemented in order to produce a data base of numerical results to be used as inputs for cracked/damaged blades identification algorithms.

- Development of reduced order modeling techniques to reduce the run time of the nonlinear analysis of structures (like bladed disks) with intermittent contacts (like cracks)

- Development of a cracked blade identification method for mistuned blade disks for on-line detection of high cycle fatigue cracks

- Implementation of a reduced order modeling technique, originally developed at the University of Michigan for single-stage mistuned bladed disks, to mistuned multi-stage assemblies with a cracked blade.

- Mechanical design of a test rig for the experimental validation of the models and methods developed during the first reporting period.

- Dynamic analysis of mistuned multi-stage bladed disks with a cracked blade with the objective of assessing indirect damage identification strategies.

- Experimental validation of cracked blade detection algorithm by means of mockup bladed disks.

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The main results achieved in the project are:

- Development and numerical validation of a family of reduction methods for the forced response analysis of cracked structures.

- Development of blade crack detection method for mistuned and cracked bladed disks, based on the projection of crack sensitive isolated mode shapes of the system on a basis made of corresponding isolated mode shapes of the tuned pristine system.

- Experimental validation of cracked blade detection method for damaged bladed disks.

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The modeling techniques developed in the UPGRADE project will contribute to fundamental physical understanding of localization phenomena in rotors due to individual and combined effects of mistuning and damage and therefore to the development of innovative and advanced motoring systems, meeting some of the challenges included in the ‘ACARE: A vision for 2020’ UE document about the aeronautics and air transport, mostly in terms of ‘Responding to society needs’, in the fields of Quality and affordability and Safety.

The proposed research will directly support both established and emerging practices in damage assessment of aerospace vehicles. The techniques developed will thus help to enable critical maintenance and repair decisions by the flight line maintenance manager/officer. Furthermore, these techniques will contribute to the reduction of the development time for new air and space vehicles through increased use of modeling and simulation. Some specific benefits of the proposed research include:

- Fundamentally new capabilities for predicting the response of rotors with cracked blades, which make an
important impact on increasing operational capabilities and readiness of engines and air vehicles.

- More efficient yet higher fidelity predictions of nonlinear vibration response of cracked structures, which
provide a quantum leap for estimating fracture propagation and fatigue life in complex structural and
fluid-structural systems.

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Contact details:

Dr Stefano Zucca (Marie Curie Fellow)
Politecnico di Torino
Department of Mechanical and Aerospace Engineering
email: stefano.zucca@polito.it

Prof. Bogdan Epureanu
University of Michigan (Ann Arbor)
Department of Mechanical Engineering
email: epureanu@umich.edu

Prof. Muzio Gola
Politecnico di Torino
Department of Mechanical and Aerospace Engineering
email: muzio.gola@polito.it