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Published Articles

The Volume 18, No 1, March 2013

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Sinem Öztürk, Haluk Erol


The growing demand for highly efficient household appliances has driven the need for tools to predict, evaluate\cbox{,} and optimize both existing and new designs. Improving the design of the residential kitchen hood requires in-depth knowledge of the structure. In particular, the dynamic behaviour of the structure during the working period needs to be studied carefully during the design stage. A tool for predicting the structure-borne noise behaviour would save a considerable amount of time, reduce the number of prototypes that need to be built, and decrease the development costs. This paper concentrates on reducing the noise generated from the vibrating structure of a residential kitchen hood by using both numerical and experimental methods. Normal modes of the structure were identified, and the results agree well with the finite-element model. To validate the finite\cbox{ }element model, an operational deflection-shape analysis of the structure was performed by using the laser Doppler vibrometry method. This study presents the finite element model and the experimental results of a kitchen hood. This study that the contribution of structure-borne noise from the vibrating panels to the overall kitchen hood noise levels is significant, especially at low frequencies. Thus, panel vibration is a critical design consideration for end users because of its relationship to noise and comfort.

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Performance of base isolated building subjected to stochastic earthquake considering system under parameter uncertainty

Sudib Kumar Mishra and Subrata Chakraborty


Base isolation has long been established as an effective tool for improving the seismic performance of structures. The effect of parameter uncertainty on the performance of base isolated structure is investigated in the present study. With the aid of the matrix perturbation theory and first-order Taylor series expansion, the total probability concept is used to evaluate the unconditional response of the system under parameter uncertainty. To do so, the conditional second-order information of responses are obtained by time domain nonlinear random vibration analysis through stochastic linearization. The implications of parametric uncertainty are illustrated in terms of the responses of interest in design applications. The lead rubber bearing isolator, isolating a multistoried building frame, is considered for numerical elucidation. It is observed that, although the randomness in a seismic event dominates, the uncertainty in the system parameters also affects the stochastic responses of the system. Particularly, the variance of the stochastic responses due to parameter uncertainty is notable.

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Experimental verification of drill string vibration suppression using adaptive self tuning controller

F. Abdul Majeed, H. Karki, M. Karkoub, Y. L. Abdel Magid


Drill bit whirl is a common phenomenon in rotary drilling rigs. It causes severe drill collar damage and borehole enlargement, leading to an irrevocable decrease in drilling efficiency. The majority of the research in this field concentrates on designing new drill bits or placing shock absorbers near the bottom hole assembly to minimize the damage caused by drill bit whirling. However, practically, vibrations in rotary drilling are minimized by tuning the upper rotary table speed or varying the weight on drill bit. This work explores the design and implementation of an adaptive controller to minimize vibrations of drill bits, particularly bit whirl. The developed controller achieves the vibration mitigation by varying the upper rotary speed. Moreover, the developed control law takes into account the vibrational frequencies and critical operating speeds of the drill string, thus also being capable of avoiding resonant vibrations. Experimental results are provided to prove the vibration mitigation capability of the developed controller.

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An Outward-Wave-Favouring Finite Element-Based Strategy for Exterior Acoustical Problems

C. S. Jog


This work presents a finite element-based strategy for exterior acoustical problems based on an assumed pressure form that favours outgoing waves. The resulting governing equation, weak formulation, and finite element formulation are developed both for coupled and uncoupled problems. The developed elements are very similar to conventional elements in that they are based on the standard Galerkin variational formulation and use standard Lagrange interpolation functions and standard Gaussian quadrature. In addition and in contrast to wave envelope formulations and their extensions, the developed elements can be used in the immediate vicinity of the radiator/scatterer. The method is similar to the perfectly matched layer (PML) method in the sense that each layer of elements added around the radiator absorbs acoustical waves so that no boundary condition needs to be applied at the outermost boundary where the domain is truncated. By comparing against strategies such as the PML and wave-envelope methods, we show that the relative accuracy, both in the near and far-field results, is considerably higher.

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The Prediction of Nonlinear Responses and Active Stiffness Control of Moving Slender Continua Subjected to Dynamic Loadings in a Vertical Host Structure

Stefan Kaczmarczyk and Philip Picton


Slender continua such as long ropes, cables, and belts are used as tension and payload-carrying members in various engineering applications. They are deployed in terrestrial mine/underground equipment and high-rise building installations through to tethered offshore tension members, tethered space satellite systems and rotating momentum-exchange tethers in Earth's orbit. The slender continua are inherently nonlinear, leading to large nonlinear responses with passages through resonances taking place when the time-varying natural frequencies of the system approach the frequency of the inertial load resulting from the dynamic loadings. In this paper, the lateral nonlinear dynamic behaviour of long slender continua moving at speed in a tall host structures is analysed. A mathematical model comprising non-stationary, nonlinear ordinary differential equations is used to describe the dynamic behaviour of the system equipped with a multi-modal active stiffness controller. The active control is implemented by an axial motion of the support, which results in substantial reduction of the response.

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