Operational Modal Analysis of Torsional Modes in Rotating Machinery

2014 ◽  
Author(s):  
Eoin Peter Carden ◽  
Mattias Lindblad
Keyword(s):  
Modal Analysis ◽  
Case Studies ◽  
Rotating Machinery ◽  
Operational Modal Analysis ◽  
Modal Testing ◽  
Damping Factor ◽  
Industrial Practice ◽  
Marine Propulsion ◽  
Lateral Modes ◽  
Marine Propulsion System

Traditional experimental modal testing techniques rely on controlled and measured excitation together with measured responses in order to identify the mode shape, natural frequency and damping factor of each mode. Applying a controlled and measured excitation to a rotor train when in operation is logistically difficult and especially challenging in the field. Operational modal analysis (OMA) identifies the modal parameters of a system from measurement of response due to some (unknown) excitation. OMA has proven successful over the past several decades on non-rotating structures but has relatively rarely been applied to rotating machinery. Case studies are presented demonstrating the use of OMA in identifying torsional modes on an electric motor driven reciprocating compressor, on a diesel engine driven fire water pump and on a marine propulsion system. In contrast to lateral modes, torsional modes of rotor trains are typically not speed dependent. However phenomena exist whereby the torsional modes may be different at stand still, off-load and at different loads. The case studies provide examples of such phenomena and also of significant differences between predicted and measured behaviour which suggests that improvements in industrial practice would be beneficial. Such improvements should be based on reconciliation of measured and predicted behaviour and OMA offers a valuable tool to facilitate this. OMA provides a significant benefit in investigating and understanding torsional behaviour in operation.

Operational Modal Analysis of Torsional Modes in Rotating Machinery

2014 ◽  
Vol 137 (2) ◽  
Author(s):  
Eoin Peter Carden ◽  
Mattias Lindblad
Keyword(s):  
Modal Analysis ◽  
Case Studies ◽  
Rotating Machinery ◽  
Operational Modal Analysis ◽  
Modal Testing ◽  
Damping Factor ◽  
Industrial Practice ◽  
Marine Propulsion ◽  
Lateral Modes ◽  
Marine Propulsion System

Traditional experimental modal testing techniques rely on controlled and measured excitation together with measured responses in order to identify the mode shape, natural frequency, and damping factor of each mode. Applying a controlled and measured excitation to a rotor train when in operation is logistically difficult and especially challenging in the field. Operational modal analysis (OMA) identifies the modal parameters of a system from measurement of response due to some (unknown) excitation. OMA has proven successful over the past several decades on nonrotating structures but has relatively rarely been applied to rotating machinery. Case studies are presented demonstrating the use of OMA in identifying torsional modes on an electric motor driven reciprocating compressor, on a diesel engine driven fire water pump, and on a marine propulsion system. In contrast to lateral modes, torsional modes of rotor trains are typically not speed dependent. However, phenomena exist whereby the torsional modes may be different at stand still, off-load and at different loads. The case studies provide examples of such phenomena and also of significant differences between predicted and measured behavior which suggests that improvements in industrial practice would be beneficial. Such improvements should be based on reconciliation of measured and predicted behavior and OMA offers a valuable tool to facilitate this. OMA provides a significant benefit in investigating and understanding torsional behavior in operation.

Operational Modal Analysis of Lateral Rotordynamic Modes of Rotating Machinery

2014 ◽  
Author(s):  
Eoin Peter Carden ◽  
Stefano Morosi
Keyword(s):  
Modal Analysis ◽  
Rotating Machinery ◽  
Operational Modal Analysis ◽  
Modal Testing ◽  
Normal Operation ◽  
Stability Margins ◽  
Normal Production ◽  
Testing Techniques ◽  
Excitation Force ◽  
Operational Range

The lateral rotordynamic response of turbomachinery is typically speed dependent due to hydrodynamic lubricated bearings, seals, gyroscopic and centrifugal effects, etc. Rotordynamic tools are used to predict the behavior of the machine during operation, however validating these results is challenging. Traditional experimental modal testing techniques rely on controlled and measured excitation together with measured responses. However, during operation this is unpractical, as the actual excitation force is rarely known. Operational modal analysis (OMA) can identify the modal parameters of a system over its entire operational range from measurement of response due to some (unknown) excitation. OMA has proven successful on non-rotating structures, but has seldom been applied to rotating machinery. Three case studies are presented demonstrating the use of OMA in identifying lateral rotors modes based on measurements from existing radial proximity probes during normal production undertaken as part of commissioning campaigns. Challenges encountered in using and interpreting OMA results are discussed. The results show that proximity probe data acquired during normal operation may be used as input to OMA for the assessment of stability margins of rotating machinery, to produce experimentally derived Campbell diagrams and to identify backwards as well as forwards whirling modes.

scholarly journals Monitoring historical masonry structures with operational modal analysis: Two case studies

2010 ◽  
Vol 24 (5) ◽  
pp. 1291-1305 ◽  
Author(s):  
L.F. Ramos ◽  
L. Marques ◽  
P.B. Lourenço ◽  
G. De Roeck ◽  
A. Campos-Costa ◽  
...  
Keyword(s):  
Modal Analysis ◽  
Case Studies ◽  
Operational Modal Analysis ◽  
Masonry Structures ◽  
Historical Masonry

Synergistic application of operational modal analysis and ambient noise deconvolution interferometry for structural and damage identification in historic masonry structures: three case studies of Italian architectural heritage

2019 ◽  
Vol 19 (4) ◽  
pp. 1250-1272 ◽  
Author(s):  
Enrique García-Macías ◽  
Alban Kita ◽  
Filippo Ubertini
Keyword(s):  
Modal Analysis ◽  
Case Studies ◽  
Ambient Noise ◽  
Damage Identification ◽  
Operational Modal Analysis ◽  
Bell Tower ◽  
Wave Velocities ◽  
Historic Structures ◽  
Deconvolution Interferometry

Conservation techniques within the framework of structural health monitoring, particularly through dynamic measurements and operational modal analysis, are becoming popular for condition-based maintenance and decision-making in historic structures. Nonetheless, while effective for giving insight into the overall behaviour of structures, these techniques may fail at detecting local damages with limited effects on the modal features of the system. In this regard, the analysis of propagating waves throughout the structure poses an attractive alternative for data-driven damage identification. Specifically, some encouraging results have been reported on the application of seismic interferometry to reinforced concrete structures, albeit the number of works concerning ambient vibrations is far scarce, and practically nonexistent in the realm of historic structures. In this light, this article explores the synergistic application of operational modal analysis and ambient noise deconvolution interferometry for the structural identification of historic structures through three different case studies, namely the Sciri Tower in Perugia, the Consoli Palace in Gubbio and the bell-tower of the Basilica of San Pietro in Perugia. The first case study represents a typical example of a masonry tower inserted into a building aggregate, while the second one constitutes a particular case of a monumental masonry palace. The presented results and discussion cover diverse aspects of the identification of wave velocities, signal processing strategies, effects of dispersion and robustness of the identification. Finally, the case study of the bell-tower of the Basilica of San Pietro illustrates the application of operational modal analysis and deconvolution interferometry for damage identification. To do so, two different ambient vibration tests conducted before and after the 2016 Central Italy seismic sequence are studied. The results show concentrated reductions in the wave velocities in the area of the belfry, which demonstrates that deconvolution interferometry constitutes a complementary technique to operational modal analysis for damage localization and, to some extent, damage quantification.

Response and Operational Modal Analysis from Wind Tunnel Test of the EOLO Flexible Aircraft

2021 ◽  
Author(s):  
David F. Castillo Zuñiga ◽  
Alain Giacobini Souza ◽  
Roberto G. da Silva ◽  
Luiz Carlos Sandoval Góes
Keyword(s):  
Wind Tunnel ◽  
Modal Analysis ◽  
Wind Tunnel Test ◽  
Operational Modal Analysis ◽  
Flexible Aircraft

scholarly journals Full-Field Operational Modal Analysis of an Aircraft Composite Panel from the Dynamic Response in Multi-Impact Test

Sensors ◽  
2021 ◽  
Vol 21 (5) ◽  
pp. 1602
Author(s):  
Ángel Molina-Viedma ◽  
Elías López-Alba ◽  
Luis Felipe-Sesé ◽  
Francisco Díaz
Keyword(s):  
Modal Analysis ◽  
Energy Absorption ◽  
High Speed ◽  
Operational Modal Analysis ◽  
Modal Identification ◽  
Image Correlation ◽  
Composite Panel ◽  
Impact Excitation ◽  
Full Field ◽  
The Impact

Experimental characterization and validation of skin components in aircraft entails multiple evaluations (structural, aerodynamic, acoustic, etc.) and expensive campaigns. They require different rigs and equipment to perform the necessary tests. Two of the main dynamic characterizations include the energy absorption under impact forcing and the identification of modal parameters through the vibration response under any broadband excitation, which also includes impacts. This work exploits the response of a stiffened aircraft composite panel submitted to a multi-impact excitation, which is intended for impact and energy absorption analysis. Based on the high stiffness of composite materials, the study worked under the assumption that the global response to the multi-impact excitation is linear with small strains, neglecting the nonlinear behavior produced by local damage generation. Then, modal identification could be performed. The vibration after the impact was measured by high-speed 3D digital image correlation and employed for full-field operational modal analysis. Multiple modes were characterized in a wide spectrum, exploiting the advantages of the full-field noninvasive techniques. These results described a consistent modal behavior of the panel along with good indicators of mode separation given by the auto modal assurance criterion (Auto-MAC). Hence, it illustrates the possibility of performing these dynamic characterizations in a single test, offering additional information while reducing time and investment during the validation of these structures.

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