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Published Articles

The Volume 7, No 4, December 2002

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Active Control of Lateral Vibrations of a Railway Carriage

Sven Johansson, Lars Hakansson, Per Perssa! on and Ingvar Claesson


As trains are designed for higher and higher speeds the problems of railway carriage vibration are continually on the increase. Lateral vibrations in a railway carriage are noticeable to passengers if the vibration frequencies are lower than approximately 20 Hz. Below this frequency discomfort is a common problem for the passengers and below approximately 1 Hz motion sickness is a problem. The passive solution of stiffening the carriage chassis to shift the vibrational frequencies higher results in increased manufacturing and running costs, and opposes higher travel speeds due to additional weight. Semi-passive solutions such as modifying the structural dynamics of the carriage body by decoupling heavy underfloor equipment do not reduce the vibrations sufficiently. How- ever, by appending a multi-reference feedforward active vibration control system, one way expect a substantial reduction in the lateral vibration level. Using a dynamic computer model of a railway carriage to simulate the lateral vibration, and using as input bogie acceleration data measured on a running train, multiple-input/single- output coherence spectra were shown to constitute a suitable set of reference signals for an active control system. Control simulations based on the Feedforward Multiple-Input/Single-Output Filtered-x LMS Algorithm were carried out using different reference signal combinations. The control results indicate lateral vibration at- tenuation on the order of 15 dB at the desired frequency of 10 Hz.

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Development of Seismic Accelerometers with Bending Deformations of the Sensing Elements

A.A. Bazhenov, S.A. Lobastov, V.I. Yarovikov, I.N. Didenkulov


The authors present the basic requirements and principles for the design of highly ? sensitive piezo-accelerome- ters which have bending bimorph elements supported by central cylindrical rods. The technique presented for the design of piezoelectric sensors with sensitive elements subjected to bending deformations allows one to opti- mise the assembly parameters of the sensors. Calculations agree well with experimental data. The technique con- sidered has wide versatility and it is physically illustrative for the design not only piezo-accelerometers but also of other types of piezoelectric sensors of the mechanical values.

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Sound Radiation Efficiency of a Baffled Rectangular Plate Excited by Harmonic Point Forces Using its Surface Resistance Matrix

Jorge P. Arenas, Malcolm J. Crocker


In this paper the use of the acoustic radiation matrix is described. This matrix can be combined with the volume velocity vector on a discretised vibration surface to predict the total sound power radiated from the structure. In order to do so, the vibrating structure is simulated by a finite number of small piston sources flush-mounted on the surface. A definition of the acoustic radiation resistance matrix is presented and its main properties are dis- cussed. The sound radiation from simply-supported and clamped-clamped plates was calculated numerically. Results are presented for the radiation efficiency of the natural modes of the plate when it is excited by a har- monic point force. The volume velocity distribution on the plate was calculated using a matrix approach. The vi- bration response of the clamped-clamped plate was determined using an approach based on the virtual work principle. In addition, experimental results for a real clamped aluminium plate are presented. The sound power radiated and the radiation efficiency were calculated from measurements of the normal velocity on the plate at discrete points without measuring the sound field. The sound power radiated from the plate and its radiation effi- ciency were measured directly using the classical sound intensity method, in order to test the accuracy of the re- sistance matrix approach. An expression to transform the velocities into vibration cross-spectra is presented in order to deal with the phase determination.

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Study of Noise in a Small Spanish Town

J.M. Barrigon Morillas, V. Gomez Escobar, J.A. Mendez Sierra and R. VĂ­lchez Gomez


A study is presented of noise in Navalmoral de la Mata, a small town of Extremadura, Spain. The town was di- vided into a 200 m square grid and noise levels were measured at the nodes of this grid. The study was per- formed in the two months of August and September 1999 in order to compare a vacation and a non-vacation pe- riod. Unlike other studies, no major differences were found. The predictive capacity of the measurement model by grid was analysed by comparing the simple grid map (taking the value for a square to be the average of the values at the corners) and the isoline map obtained by a standard interpolation routine with test measurements at points within some of the squares. Agreement was poor, and the isoline map gave only a slight improvement. Even when the size of a part of the grid was reduced to 100 m, the predictive capacity remained low, even though this involved a fourfold increase in time and resources. The noise levels here were lower than in other Spanish towns of similar size but in more developed parts of the country, reflecting the influence of a region?s socio-economic situation.

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An Approach for Crack Detection in Beams on Elastic Foundations using Frequency Measurements

D.P. Patil and S.K. Maiti


In this paper a method has been proposed for the detection of open cracks based on frequency measurements on slender beams? on continuous and discontinuous elastic foundations. The cracks are represented by massless rotational springs. The foundation is represented by a Winkler spring. The approach exploits the transfer matrix method (TMM) to advantage and assumes slender beams in which the shear deformation and rotational inertia are negligible. Both forward and inverse problems are solved and results are presented. In forward problems, the frequencies are determined by giving the rotational spring stiffness as an input. In the inverse analysis, a method is employed to detect the location and size of a crack by providing the natural frequencies as inputs. Numerical case studies are presented to demonstrate the method?s effectiveness. The natural frequencies required for the inverse analysis are computed using a finite element program. A three-node interface finite element is used to take care of the foundation stiffness. It appears finally that the method can detect the location of a normal crack of size 10% or more of the section depth with an error less than 3%. The crack size can also be predicted with an error less than about 6%.

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