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Published Articles

The Volume 17, No 4, December 2012

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An Experimental Study of Delayed Positive Feedback Control for a Flexible Plate

Liu Kun, Chen Long-Xiang, Cai Guo-Ping


Active vibration control generally produces negative feedback, while positive feedback may cause degradation of control efficiency and even make a control system unstable. The current study indicates that positive feedback can also benefit the control if appropriate time delay is intentionally introduced into the control system. This is the so-called delayed positive feedback control technique. So far, most of the work on this technique is theoretical, and few are experimental in nature. This paper presents a theoretical and experimental study of the delayed positive feedback control technique using a flexible plate as the research object. The positive feedback weighting coefficient is designed using the optimal control method. The available time delay is determined by analyzing the maximal real part of characteristic roots of the system. A DSP-based experiment system and experimental data processing are described in detail. The simulation and experimental results indicate that the delayed positive feedback control may effectively reduce the plate vibration if the time delay is appropriately selected.

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An Assessment of Airport Environmental Noise Action Plans with Some Financial Aspects: The Case of Athens International Eleftherios Venizelos

Konstantinos Vogiatzis


Environmental noise is an important environmental factor responsible for the degradation of the urban environment and the quality of life especially in countries where climatic conditions allow for outdoor activities and night life. Athens International Airport (AIA), "Eleftherios Venizelos," is one of the most modern, most functional, and safest airports in the world and constitutes the largest hub of air travel in southeastern Europe, encouraging strong ?nancial and social development in the Athens greater area. AIA in collaboration with the University of Thessaly executed a complete study of aircraft noise according to the European Directive 49/2002 (ED 2002/49, 2002) under the auspices of the Ministry of Environment, Energy and Climate Change, and the Hellenic Civil Aviation Authority. In this article, an analytical evaluation and an in-depth assessment of environmental noise action plans aiming, among other aspects, for the sound insulation of buildings where noise annoyance is an issue, are presented, based on 2006 and 2011 Strategic Noise Maps for both EU noise indicators Lden and Lnight . Furthermore, a statistical analysis of predicted versus measured noise levels based on the existing AIA Noise Monitoring System, is also assessed.

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Vibration Modal Analysis of a Thin Folded Elastic Structure using a Levy-type Solution

E. Segovia, B. Ferrer, J. Ramis, J. Martinez, and J.P. Arenas


In this technical note, an approximated analytical Levy-type solution for the system of differential equations that governs the vibration of a thin folded structure is presented. The folded structure is composed of thin plates and thin curved circular panels attached by their straight sides. Hinged and arbitrary boundary conditions at curved edges and straight edges, respectively, were used. In order to test the proposed analytical approach, numerical experiments using commercial finite element method (FEM) software were developed for a particular folded struc- ture commonly found in Air Motion Transformer loudspeakers. It is found that the first two natural frequencies of this structure obtained with the analytical approach differed by less than 2% from those obtained using FEM. In addition, the analytical mode shape is almost identical to that obtained by FEM.

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Investigation of the Relation Between Friction Material Abrasive Properties and the Squeal Noise Tendency in Automotive Disc Brake Systems

Luciano T. Matozo, Alberto Tamagna, Hazim A. Al-Qureshi, Ademir R. Menetrier, Paulo E. Varante


Automotive brake systems are very often susceptible to generating high-frequency noises as a result of a self- excited vibration. This phenomenon is generically referred to as brake squeal noise and is the subject of many studies which intend to identify and describe its exciting mechanism and to propose counter measures to avoid its occurrence. One key subject yet to be explored about squeal noise generation is the relation between friction material characteristics and its occurrence propensity. This work presents the development of an empirical equation obtained by dimensional analysis (Buckingham theorem) capable of linking the squeal noise occurrence with four main properties of the friction composite: abrasive hardness, particle size and concentration, and also composite compressibility. Experimental results were obtained by testing six different friction material formulations, in which the concentration of an abrasive or its hardness or its particle size was altered in order to explore the impact of these variables on the squeal noise occurrence. The noise generation was accessed by testing the friction materials using a standard disc brake system in an inertial dynamometer under a specially developed test procedure. The obtained results validated the proposed equation, which proved to be capable of identifying the squeal noise occurrence tendency.

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Free Vibration of Circular Plates with Elastic Edge Support and Resting on an Elastic Foundation

L. Bhaskara Rao, C. Kameswara Rao


An analytical study is presented for the vibration characteristics of thin circular plates with rotational elastic edge support and resting on an elastic foundation. The Winkler model was used to describe this foundation. The exact analytical method is used to derive the frequency equation of the plate with elastic support and resting on this foundation. Parametric investigations of the vibration of circular plates with an restrained elastically edge against rotation and resting on an elastic foundation have been carried out with respect to various rotational stiffness pa- rameters, foundation stiffness parameters, and boundary conditions. Twelve vibration modes are presented. The location of the stepped region with respect to rotational restraint changed very little and moved from the range of 0.014 26† [10.006 204 8‡ ]–1 134.227 [10.025 94] to 0.017 58 [14.001 133]–6 352.958 2 [14.658 356]. Here, † represents the rotational spring stiffness ratio, and ‡ represents the foundation stiffness ratio. Extensive data are tabulated so that pertinent conclusions can be arrived at on the influence of rotational edge restraint and the foun- dation parameters of a Winkler foundation on the natural frequencies of uniform thin isotropic circular plates.

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