Operational modal analysis deals with the estimation of modal parameters from vibration data obtained in operational rather than laboratory conditions. This paper extensively reviews operational modal analysis approaches and related system identification methods. First, the mathematical models employed in identification are related to the equations of motion, and their modal structure is revealed. Then, strategies that are common to the vast majority of identification algorithms are discussed before detailing some powerful algorithms. The extraction and validation of modal parameter estimates and their uncertainties from the identified system models is discussed as well. Finally, different modal analysis approaches and algorithms are compared in an extensive Monte Carlo simulation study.

System Identification Methods for (Operational) Modal Analysis: Review and Comparison

Increased concern for environment has led to the search for more environment friendly sources of energy. Wind energy can be a viable option in this regard. Vertical axis wind turbines offer promising solution for areas away from the integrated grid systems. However, they have certain drawbacks associated with different configurations. This paper reviews various configurations of VAWT along with their merits and demerits. Moreover, design techniques employed for VAWT design have also been reviewed along with their results. It was learned that coefficient of power (CP) for various configurations is different and can be optimized with reference to Tip Speed Ratio. Latest emerging design techniques can be helpful in this optimization. Furthermore, flow field around the blade can also be investigated with the help of these design techniques for safe operation.

Vertical axis wind turbine-a review of various configurations and design techniques

Operational modal analysis in the presence of harmonic excitation

Identification of modal parameters from transmissibility measurements

The stability of high-speed machining operations determines the reliability of machine tools and the quality of machined parts. Chatter-free cutting conditions are difficult to predict as they require accurately estimated dynamic modal parameters. A spectrogram analysis and impact tests for different configurations of the machine tools were conducted to compare the modal parameters at 0 rpm tests and during machining tests. Variations of between 2% and 8% were observed for the natural frequencies and between 2 and 10 times for the damping ratios. The operational modal analysis (OMA) is considered as a powerful tool for dynamic modal parameter estimations during machining operations. A complete methodology for applying this technique for machining operations was detailed. It was demonstrate how the OMA can be industrially exploited. The proposed approach was successfully applied during the high-speed machining of the 7075-T6 aluminum alloy to extract machine-tool parameters. Two different numerical approaches were used: the autoregressive moving average method (ARMA) and the least square complex exponential method (LSCE), both of which generated similar results. The dynamic parameters found using the operational modal analysis were used to predict machine dynamic stability lobes, and through experimental validation, it was shown that some depths of cut that are stable with standard stability lobes become unstable with dynamic stability lobes.

Estimation of machine-tool dynamic parameters during machining operation through operational modal analysis

A modified Ibrahim time domain algorithm for operational modal analysis including harmonic excitation

Modified ERA method for operational modal analysis in the presence of harmonic excitations

Modified SSTD method to account for harmonic excitations during operational modal analysis

Measuring and analysis procedures are presented in this paper to study the first two sweet spots of a tennis racket. After a brief description of sweet spots in racket, we describe the experimental procedures applied in this work. Reproducing realistically the boundary conditions at the grip of the racket is a major difficulty that is tackled here in a simple manner. Instrumentation and signal processing issues are discussed. Using digital filtering to extract time domain signals and comparing time signals from different locations on a racket, mode shapes have been identified. Test results are presented and sweet spots are identified for rackets with large and small heads, and for high or low string tension.

Prasenjit Mohanty

Papers

Operational modal analysis in the presence of harmonic excitation

A modified Ibrahim time domain algorithm for operational modal analysis including harmonic excitation

Modified ERA method for operational modal analysis in the presence of harmonic excitations

Modified SSTD method to account for harmonic excitations during operational modal analysis

Measuring sweet spots of tennis rackets