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Published Articles

The Volume 15, No 3, September 2010

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Building Response due to Ground Vibration - Simple Prediction Model Based on Experience with Detailed Models and Measurements

Lutz Auersch


Construction work, such as pile driving and soil compaction, or road and railway traffic excite nearby buildings, and the perceptible or audible vibration can be a nuisance for nearby inhabitants. A simplified building model has been created for these situations, which includes the effects of soil-structure interaction, the low-frequency amplification along the height of the building as well as the high-frequency reduction and the floor resonances. The model consists of one wall for all supporting structures (walls and columns) and one floor for each storey. The effect of different floor resonance frequencies is included in a stochastic procedure. The soil is modelled by a spring and a viscous damper, and the free-field amplitudes of the soil are applied under this soil element.
The model can be calculated by transfer matrices or in a continuous wave-type version where an analytical solution can be evaluated numerically. The building response in the high-frequency (acoustic) region is calculated as mean values over wider frequency bands. The approach to an infinite building model can be found for these high frequencies and the corresponding soil-structure transfer can be described by the ratio of impedances at foundation level.
The rules for choosing the parameters to obtain realistic results are derived from complex calculations for example, for the stiffness and damping of building foundations and many measurements as for the damping of floor resonances. The influences on the floor resonance from the soil (damping) and the supporting structure (detuning) are important. Some more effects will be discussed by the simplified and detailed models and by measurements to establish a good understanding of ground-induced building vibrations.

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Element Level Identification of a Viscously Damped System

Subrata Chakraborty, Sajal Roy


The modal data-based system identification (SI) algorithms normally consider the free vibration equation of motion of the dynamic system without damping for the identification of damage of existing structures. The present study intends to assess the damage of existing structures, including the effect of damping. The primary objective is to develop the equation error approach-based SI algorithm to identify both the stiffness properties and the damping parameters. The viscous damping model, which is computationally affordable and widely applicable to non-conservative systems, is considered for this objective. The formulation is hinged on the use of free vibration response in which the error norm of the eigen equation with damping is minimized. The SI algorithm is demonstrated through numerically-simulated modal data, which are obtained by the finite element analysis. The Monte Carlo simulation-based error sensitivity study confirms the consistency and robustness of the proposed algorithm.

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Role of an Artificial Neural Network and a Wavelet Transform for Condition Monitoring of the Combined Faults of Unbalance and Cracked Rotors

H. K. Srinivas, K. S. Srinivasan, K. N. Umesh


The vibration analysis of rotating machinery indicates the condition of potential faults such as unbalance, bent shaft, shaft crack, bearing clearance, rotor rub, misalignment, looseness, oil whirl and whip, and other malfunctions. More than one fault can occur in a rotor. This paper describes the application of an artificial neural network (ANN) and wavelet transform (WT) for the prediction of the effect of the combined faults of unbalance and shaft crack on the frequency components of the vibration signature of the rotating machinery. The experimental data of the frequency components and the corresponding root mean square (RMS) velocity (amplitude) data are used as inputs to train the ANN, which consists of a three-layered network. The ANN is trained using an improved multilayer feed forward back propagation Levenberg-Marquardt algorithm. In particular, the overall success rates achieved were 99.78% for unbalance, 99.81% for shaft crack, and 99.45% for the combined faults of unbalance and shaft crack. The wavelet transform approach enables instant to instant observation of different frequency components over the full spectrum. A new technique combining the WT with ANN performs three general tasks: data acquisition, feature extraction, and fault identification. This method is tested successfully for the individual and combined faults of unbalance and shaft crack at a success rate of 99.9%.

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Investigation of Low-Frequency Sound Colouration Treatments in Small Rooms by Means of Finite Element Analysis

Christos Sevastiadis, George Kalliris, George Papanikolaou


Acoustics in small rooms suffer from resonances in low frequencies, resulting in the well-known sound colouration problem. In the present work, the finite element method was used to investigate specific case studies of proposed treatments of this problem. The treatments are based on techniques that make use of three basic mechanisms: wavelength, boundary impedance, and active control. The quality of the treatments is evaluated using two spatial statistical measures of the sound pressure level frequency responses regularly sampled in the listening area. The results demonstrate the advantage of the impedance- and active control mechanism-based techniques. Resonant panels and multiple source excitation treatments improve the sound field flatness.

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Applicability of a Classical Perturbation Technique for Perturbation Parameters with Large Values

Igor V. Andrianov, Jan Awrejcewicz


In this letter we will illustrate and discuss some problems regarding the validity and accuracy of the perturbationlike methods applied to systems with weak and strong non-linearities.

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