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Published Articles


The Volume 12, No 3, September 2007




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Frequency-response Analysis of Shear Vibration of Long Structures due to Surface Excitation

S. K. Chakraborty, S. K. Sarkar, S. P. Bhattacharya


https://doi.org/10.20855/ijav.2007.12.3212


The article presents a qualitative and quantitative analysis of the dynamic response of long structures, such as long and high-rise building. A two-dimensional linear model of a building is devised. In this model, the building is represented as a constrained anisotropic plate subjected to base excitation. Consequently, the displacement of the plate is governed by a 2D wave equation with corresponding boundary conditions. The dynamic response of the system, due to base excitation, is being analysed by expanding the displacements in terms of the corresponding eigenfunctions. Also, an analytical expression describing the building motion of translational type is presented. Further analysis is then conducted to determine the response to rotation at the base of the building. The investigation reveals the existence of wave passage effect during the dynamic response of the structure under the optimum conditions on frequencies (low or high) for proper analysis of the resulting deformation of the foundation.


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A One-dimensional Model for Prediction of Breakout Noise from a Finite Rectangular Duct with different Acoustic Boundary Conditions

B. Venkatesham, Ardhendu G. Pathak and M. L. Munjal


https://doi.org/10.20855/ijav.2007.12.3213


This paper describes a simple one-dimensional predictive model for breakout noise from a thin rectangular duct with different end conditions like anechoic termination, rigid-end, and open-end termination. This model incorporates acoustic reflection effects in the duct internal sound field by using standing wave pattern with the transfer matrix approach. The coupling phenomenon is modelled making use of a common axial wave number for acoustic waves inside and flexural waves in the walls of the duct. The noise radiated from the rectangular duct is modelled as a finite-length line source. This standing wave analytical model has been compared with numerical model, the corresponding progressive wave model, and experimental results available in the literature. The effect of coupling in acoustic modes and flexural modes has been discussed.


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Design of Command Shaper using Gain-delay Units and Particle Swarm Optimisation Algorithm for Vibration Control of Flexible Systems

M. S. Alam, M. O. Tokhi


https://doi.org/10.20855/ijav.2007.12.3214


Conventional command shaping methods involve convolving a desired command with a sequence of impulses that may prove computationally expensive or unsuitable for online applications. Moreover, a priori knowledge of the system parameters, such as resonance frequencies and associated damping ratios, is required to design the exact sequence of impulses to produce a command that results in zero residual vibration. A new command shaping method is proposed in this paper using gain and delay units. Assuming that, no prior information is available about the system, a new variant of particle swarm optimisation (PSO) algorithm is proposed and used to derive the gain and delay values. The effect of the total number of delay and gain units is also analysed. Moreover, an adaptive control strategy is developed based on the proposed command shaping technique where the PSO is used to adjust the controller parameters online. A twin rotor (experimental flexible) system is used for assessment and evaluation of the control strategy. The effectiveness of the technique is assessed both in the time domain and the frequency domains.


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Cyclostationary Modelling of Reciprocating Compressors and Application to Valve Fault Detection

R. Zouari, J. Antoni, J. L. Ille, M. Sidahmed, M. Willaert, M. Watremetz


https://doi.org/10.20855/ijav.2007.12.3215


This paper presents a methodology for identifying events and valve faults in reciprocating compressors based on cyclostationary modelling of their vibration. The discussion in this paper first concerns the resampling of the time signals and then their decomposition into periodic and random parts. Secondly, the second-order cyclostationarity of the random part is exploited to construct an angular frequency map of the vibration energy by means of the Wigner-Ville spectrum based on cyclic averaging. From this energy representation, a correlation procedure between sensors is followed in order to identify the angular and spectral bands where coherent events occur in the compressor cycle. Additionally, it allows the extraction of pertinent and simple indicators for detecting fault signatures in valves; these can be used in condition monitoring.


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