Examination of Rail Dampers with Respect to Noise and Vibration Mitigation

Nowadays there are more and more possibilities to mitigate noise and vibration emitted by railway transport to the lower levels. Among them, rail dampers with highly viscous properties placed on the rail web, fixed with adhesives or other methods, appeared as a new element in the railway superstructure. The elements are applied to reduce noise and vibration by transforming the vibration energy of the rail web into heat, through their large internal friction. Many companies produce rail web elements and apply them with success abroad. Domestic manufacturers have already appeared in Hungary; however, the installation of these elements is still very limited. This publication is intended to introduce the rail dampers and to demonstrate their efficiency through laboratory and field measurements. Experimental modal analysis was used during the laboratory test to determine the eigenfrequencies, the damping factors and the mode shapes of an experimental rail section, thus analyzing the vibration damping and noise reduction effect of the elements. Field measurements were also carried out at a segment installed with rail web elements in Hungary and its vicinity, under standardized conditions. By averaging measured noise level values for various types of trains, comparable noise reduction of the investigated rail web element can be achieved. The laboratory and field test results confirmed that the rail web elements can be suitable for rolling noise reduction and vibration damping in most of the cases. The results of the measurements provide guidance and information for future development of the elements

Torsional modal analysis of single shaft systems by using a novel vibroacoustic model of a permanent magnet synchronous motor

In this paper a novel torsional experimental modal analysis method based on a new vibroacoustic modeling methodology of a permanent magnet synchronous motor (PMSM) is presented. This methodology accurately describes torsional vibration conditions of a PMSM in case of single-phase pulsating current excitation, in conjunction with small angular displacement of the rotor. The test rig and the modal analysis results are briefly outlined, and an experimental validation consisting of a torque time-frequency (signature) analysis is introduced. The main advantage of the proposed method is that it does not require an external broadband torque source; since the PMSM is part of the investigated system

A finite element model of the tuning slot of labial organ pipes

An acoustic model suitable for the characterization of tuning slots of labial organ pipes is presented in this paper. Since the tuning slot arrangement is similar (but not identical) to that of toneholes in woodwind instruments, the adaptability of the well-established tonehole model for the specific problem is examined. A numerical model utilizing the finite element (FE) and perfectly matched layer techniques is set up for the simulation of tuning slots with design parameters varying over a wide range. Analytical tonehole models and the proposed numerical tuning slot model are both combined with analytical one-dimensional waveguide models to predict the acoustic behavior of tuning slot pipes. Comparison to measurements carried out on experimental pipes proves that the hybrid waveguide/FE model can predict the most important properties of the tuning slot pipe with good accuracy. The finite element method (FEM) also overcomes the limitations of traditional tonehole models relying on the equivalent T-circuit approximation. By means of the FE model the eigenfrequency-structure and its impact on the character of the sound can be foretold in the design phase, by which a more efficient scaling of tuning slot pipes can be achieved

Acoustic behavior of tuning slots of labial organ pipes

The effect of tuning slots on the sound characteristics of labial organ pipes is investigated in this paper by means of laboratory experiments. Besides changing the pitch of the pipe, the tuning slot also plays an important role in forming the timbre. The objectives of this contribution are to document the influence of tuning slots built with different geometries on the pipe sound and to validate the observed tendencies by means of reproducible experiments. It is found that the measured steady state sound spectra show unique characteristics, typical only for tuning slot organ pipes. By separately adjusting the geometrical parameters of the tuning slots on experimental pipes, the impact of each scaling parameter on the steady state spectrum is determined. It is shown that the scaling procedures used currently in organ building practice do not provide sufficient control over the sound characteristics, leaving the capabilities provided by the tuning slot unexploited. Subjective comparison made by organ builders of sound recordings of various setups confirms that the observed sound quality of tuning slot pipes is strongly dependent on the scaling of the slot

Active noise control in agricultural machines

Agricultural machines generate a complex noise field with significant low-frequency components. The demands for good sound comfort of the driver inside cabins of these machines are continuously growing. Since passive control techniques are not able to efficiently reduce the low-frequency noise in the cabin, active noise control techniques are being explored. A zone of quiet around the ears of the driver is quested through the use of secondary loudspeakers. This paper studies three different control strategies: feedforward control, feedforward control with feedback compensation and feedback control. The practical setup and the control algorithm of each control technique is discussed. The practical results, the advantages and the restrictions of the three techniques are compared.status: publishe