Dynamic response of trackside structures due to the aerodynamic effects produced by passing trains

The correct evaluation of the dynamic response of trackside structures is relevant for several technical issues including the design of wind/noise barriers and structures used as support platforms for equipment that are sensitive to vibration. The vibration of trackside structures is produced both by the seismic action generated by the passing train, as well as by the aerodynamic loads. To proceed towards the formulation of a mathematical model able to predict the dynamic behavior of trackside structures, an experimental campaign on a steel frame located close to a railway has been carried out. The dynamic response of the structure, the vibration of the foundation and the pressure generated by the train passage have been analyzed through a time-frequency representation. On the basis of these results a non-dimensional model representing the aerodynamic response of trackside structures has been developed and its maximum response has been represented through a response spectrum borrowing a familiar concept from earthquake engineering

Modal Identification of Bladed Disks by Time-Frequency Analysis of the Nonsynchronous Response

In some circumstances, it is impossible to exploit resonance crossings to identify the modal properties of rotor disks. In these cases, the identification process must rely on nonsynchronous vibrations and becomes challenging for two reasons. First, the signals are weak (compared to the levels measured during resonance crossings) and random, thus an averaging procedure is necessary. Second, the dynamical system is time-variant due to the variation of the rotor speed. This paper presents a modal identification procedure formulated in the framework of the time-frequency analysis. A region of the time-frequency plane is stretched to map the system into a fictitious linear time-invariant (LTI) system. Then, the power spectral density function (PSD) of the response is computed by an averaging procedure. Finally, the modal properties are estimated through an output-only modal identification algorithm. The procedure is applied to simulated and experimental data regarding a bladed disk of a steam turbine

Modal identification of dynamically coupled bladed disks in run-up tests

The spin test is a standard industrial practice employed for the qualification of rotor blades and disks. The expected results are the modal properties of blades and assemblages at different rotation velocities. If a significant dynamic coupling among the blades exists, global vibration modes appear, reflecting into a set of closely spaced natural frequencies for each mode family. In case of perfectly-Tuned bladed disks, the circumferential structure of the mode shapes is known and can be exploited during the identification process so that traditional single-dof models may be applied. On the contrary, the mode irregularities produced by mistuning prevents the use of single-dof models requiring the development of more sophisticated approaches. In this work, we propose a multi-dof identification technique organized as follow: 1) the FRF of the bladed disk in the neighborhood of a resonance crossing is identified by the wavelet transform of the measured response; 2) the modal parameters of the system are estimated using a mixed stochastic-deterministic subspace algorithm formulated in the frequency domain. The procedure is validated using a realistic numerical simulation