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Published Articles

The Volume 18, No 4, December 2013

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A Two-Stage Adaptive Algorithm in the Frequency Domain for a Multichannel Feedforward Active Noise Control System

Min ZHU, Huigang WANG, Guoyue CHEN and Kenji MUTO


The reference paths between original sources and reference sensors in multichannel feedforward active noise control (ANC) systems are often ignored by most ANC algorithms. Therefore, a two-stage adaptive algorithm in the frequency domain is proposed to deal with several of the more complicated cases, specifically addressing instances when the reference sensors must be placed far away from the noise sources. This two-stage system includes a blind pre-processing system cascaded with a traditional MFxLMS system; both systems operate in the frequency domain. The new algorithm can eliminate the effect of reference paths by performing blind pre-processing independently. The MFxLMS algorithm in the following stage can achieve faster convergence than the traditional algorithm without blind pre-processing. The computational complexity of the proposed algorithm is analysed and a numerical simulation using impulse responses measured in a real reverberant room is performed to verify the convergence performance of the proposed algorithm.

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On Parametric Response Characteristics of Beams With Multiple Transverse Cracks

U.K. Mishra and S.K. Sahu


This study deals with the parametric instability of a beam with multiple cracks. The variation of buckling load and dynamic stability regions, with respect to relative crack depth and position of cracks, are analysed using FEM. The loading on the beam is considered to be axial with a simple harmonic fluctuation with respect to time. The equation of motion represents a system of second order differential equations with periodic coefficients of the Mathieu-Hill type. The development of the regions of instability arises from Floquet's theory, and the periodic solution is obtained by Bolotin's approach using the finite element method. The stiffness matrix of the cracked beam element is obtained from the flexibility matrix of the intact beam, and the additional flexibility matrix due to the crack. The frequencies of vibration and buckling loads of the cracked cantilever beams reduce with the increase in crack depth and number of cracks. The onset of instability occurs earlier with the introduction of more cracks. The instability region for the crack location nearer to the fixed end occurs at a lower excitation frequency of the cracked beam. The vibration and instability results can be used as a technique for structural health monitoring or testing of structural integrity, performance, and safety.

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Prediction of Ground Vibrations Induced by Urban Railway Traffic: An Analysis of the Coupling Assumptions Between Vehicle, Track, Soil, and Buildings

Georges Kouroussis, Laurent Van Parys, Calogero Conti and Olivier Verlinden


This paper is concerned with the problem of ground vibrations induced by railway traffic and its modelling through a decoupled approach, using only the finite element modelling for evaluating the ground waves propagation. The vehicle/track dynamics is calculated separately. An important modelling aspect is undoubtedly the track/soil interaction, which can play an important role in the generation of seismic waves. To avoid excessive computational resources, a coupled lumped mass model (CLM model) of the soil has been recently developed and is considered in this study. The influence of ballast and soil stiffnesses is presented, in order to confirm the range of validity of the CLM model. Combined with a discrete two layer model of the track, it offers the possibility of working with a simple compound track/soil model. A comprehensive analysis is provided to show the benefit of the finite element model with the proper radiation conditions at infinity, for analysing the structural response of a building located in the vicinity of the track. Focusing on typical results based on the tram of Brussels, the effects of track/soil and soil/structure coupling are investigated. Modal analyses of the vehicle and the building are presented in order to understand the effects of seismic wave amplification, especially when the source contains frequencies close to the natural frequencies of the building.

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Design and Development of a ?-Synthesis Controller for a Flexible Robotic Manipulator, Modelled as a Rotating Euler-Bernoulli Beam

Hamed Moradi, Gholamreza Vossoughi, Firooz Bakhtiari Nejad and Mohammad T. Ahmadian


In this paper, a robust control strategy for a robotic manipulator, modelled as a cantilever rotating Euler-Bernoulli beam, is developed. Imprecision in the payload mass, unknown properties of the manipulator link, and torque disturbance are included as the sources of uncertainty. The objective is to achieve a desired angular rotation while the vibration of the manipulator tip is suppressed and the control system remains in a stable region. The control input of the system is an external driving torque. For formulation of the continuous system, the mode summation technique is used and equations of motion are described in the Laplace domain. Then, unstructured uncertainties are included in the form of multiplicative input uncertainty. The $mu$-synthesis control approach is used and an $H_infty$ optimal robust controller is developed based on the DK-iteration algorithm. Results show that the designed controller guarantees the robust stability and performance of the perturbed system against existing uncertainties. Consequently, stability of the closed-loop system, disturbance rejection, and trajectory tracking performance are achieved.

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Parametric shock analysis of spade-less lightweight wheeled military vehicles subjected to cannon firing impact: feasibility study of spade removal

Ashkan Haji Hosseinloo, Nader Vahdati, Fook Fah Yap


Tracked military vehicles are being replaced by their lightweight wheeled counterparts in many armies around the world. However, mounting high caliber artillery guns on light wheeled vehicles may bring about some problems such as crew discomfort, vehicle slide, lift-off, turnover, etc. To avoid these problems, spades are used to connect the vehicle to the ground which in turn reduces the vehicle mobility. Furthermore, optimum spade design for different vehicles and soils is a hard job if at all possible. In this paper a spade-less four-wheel vehicle with mounted mortar is modeled and effects of firing impact amplitude, duration and elevation angle on the vehicle response are investigated. It is found that all of the likely problems can be avoided if appropriate precautions are taken except the firing inaccuracy at very high bomb charges. Therefore, for many cases it is feasible to remove the spades.

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Rotating group design for vane pump flow ripple reduction

Leonardo Zanetti-Rocha, Samir N.Y. Gerges, D. Nigel Johnston, Jorge P. Arenas


It is well known that the hydraulic pump is the main source of noise in hydraulic power steering systems. This noise is produced by the pulsating flow transmitted through the fluid due to the cyclic pumping mechanism. This flow ripple and pressure ripple propagate through the hydraulic circuit interacting in a complex way with other parts of the vehicle. This process generates annoying audible noise inside the vehicle. This work addresses a new approach of flow ripple reduction by tuning the pump rotating group. The method consists in making the outlet flow as steady as possible by modifying the rotating group geometry. A MatLab/Simulink based pump model has been created according to the new geometrical characteristics and their numerical results are compared with the regular pump ones. In addition, a flow ripple experimental test was conducted using the Secondary Source Method to validate the numerically predicted results of the regular pump. The results of the new design showed significant amplitude reduction of the flow ripple amplitudes at different operating conditions. In particular, the flow ripple reduction at the first harmonic attains almost 20 dB when pump runs at parking manoeuvres operation condition (1000 rpm at 50 bar of backpressure).

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