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Published Articles


The Volume 14, No 4, December 2009




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Selection and Designing of Command Shaper for Vibration Control of Flexible Manipulators: A Multi-objective Optimization Approach

Shafiul Alam, Osman Tokhi


https://doi.org/10.20855/ijav.2009.14.4248


This paper presents a selection and design scheme of multimodal command shapers using the multi-objective genetic algorithm (MOGA). A control scheme comprised of a command shaper and a collocated proportional- derivative control is employed in order to reduce end-point vibration without sacrificing the system?s response speed. Command shaping causes a delay in the system?s response and, also, reduces system vibration and, in this manner, the amount of vibration reduction and the response delay conflict with each other. Conventional meth- ods can hardly provide a solution that satisfies several design objectives demanded by practical applications due to the competing nature of these objectives. Furthermore, the selection of a shaping technique is crucial since robustness and computational complexity depend on the shaping technique. This paper proposes a combined ap- proach to selecting and designing command shapers using MOGA. A comparative assessment of the performance of the proposed approach with the conventional single-objective and weighted-sum genetic algorithm optimization approaches is also provided. The proposed technique can provide a wide range of solutions in a single run to conflicting design objectives and satisfy associated goals.


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A Module Based Active Noise Control System for Ventilation Systems, Part I: Influence of Measurement Noise on the Performance and Convergence of the Filtered-x LMS Algorithm

Martin Larsson, Sven Johansson, Ingvar Claesson and Lars Hakansson


https://doi.org/10.20855/ijav.2009.14.4249


Low noise level is an essential feature when installing ventilation systems today. To achieve attenuation over a broad frequency range, the passive silencers traditionally used to attenuate ventilation noise can be combined with an active noise control (ANC) system. To insure reliable operation and desirable levels of attenuation when applying ANC to duct noise, it is highly important to be able to suppress the contamination of the microphone signals due to the turbulent pressure fluctuations, which arise as the microphones are exposed to the airflow in the duct. This paper is the first in a series of two regarding the problem of turbulence-induced noise originating from the airflow inside the ducts. Part I is concerned with theoretical and experimental investigations of the influence of the turbulence-induced noise on the adaptive algorithm in the ANC system. Part II is concerned with the design and the investigations of microphone installations for turbulence suppression and the results concerning the performance of an ANC system with the different microphone installations are presented. Some of the results were obtained at an acoustic laboratory according to an ISO-standard. The attenuation achieved with ANC was approximately 15-25 dB between 50-315 Hz, even for airflow speeds up to 20 m/s.


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A Module-Based Active Noise Control System for Ventilation Systems, Part II: Performance Evaluation

Martin Larsson, Sven Johansson, Ingvar Claesson and Lars Hakansson


https://doi.org/10.20855/ijav.2009.14.4250


To utilize the full noise-attenuation potential of an active noise control (ANC) system applied to duct noise, it is important to be able to minimize the turbulence-induced noise in the microphone signals. This is the second paper in a series of two, that treats the problem of turbulence-induced noise originating from the airflow inside the ducts, when applying ANC to ducts. Part I contains theoretical and experimental investigations of the influence of the turbulence-induced noise on the filtered-x LMS algorithm used in the ANC system. Part II (the present paper) is concerned with the design and investigations of microphone installations, which produce a sufficient amount of turbulence suppression while also meeting industry requirements. These requirements are, for example, that the microphone installations should be based on standard ventilation parts, and that they should be easily installed and maintained. Furthermore, results concerning the performance of an ANC system with different microphone installations are presented. Some of the results were obtained at an acoustic laboratory according to an ISO standard. The attenuation achieved with ANC was approximately 15-25 dB between 50-315 Hz, even for airflow speeds up to 20 m/s.


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Proportional Controller-based Active Suspension System

Kumar M. Senthil, Rajamanickam Ranjith, Gopalan Sankar, Balasubramaniam Sidharth


https://doi.org/10.20855/ijav.2009.14.4251


The aim of this paper is to develop an active suspension system using a proportional control system. Traditionally, automotive suspension system design has been a compromise between three conflicting criteria: passenger comfort, suspension travel, and road-holding. In conventional suspension systems, a passenger experiences discomfort when a vehicle runs over a bump on the road and vibration is not completely isolated. To overcome this problem, an active suspension system has been developed. A quarter-car model has been used for developing the system, and the hardware-in-loop (HIL) technique is used. In this research, experiments were conducted on both active and passive suspension systems, and performance characteristics were evaluated. It was found that the active suspension is capable of dampening most of the vibrations from the unsprung mass and provides the passenger with the maximum comfort level. The quarter-car model can also be used as a computerized test rig for testing suspension systems in industries.


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Noise Levels Produced by Agricultural Machinery and Different Farming Processes

Dimitrios Karamousantas, Theodoros Varzakas, Andreas Kanakis, Basile C. Dalamagas


https://doi.org/10.20855/ijav.2009.14.4252


A characteristic trait of Greek agriculture the last 20 years has been its intense mechanisation. Agricultural ma- chineries are used in almost all phases of daily farming activities in small and large households for a few hours or for as long as 12 or 15 hours. The produced noise usually constitutes danger for the health and the safety of operators. Moreover, it increases the level of environmental noise, particularly in regions of general residence, as well as in tourist regions. Sound-pressure levels produced during the operation of agriculture machineries under different farming processes have been measured. Measurements taken at the height of the operator have been re- lated to European damage-risk criteria, to the requirements of the national legislation for noise protection, and to the maximum environmental permissible noise levels. The result is that permissible noise criteria cannot be met during farming processes. One octave and one-third octave bandwidth measurements have shown the noise content in low-frequency octave band centre frequencies.


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Active Control in Vehicles and in the Inner Ear: a Review

Stephen J. Elliott


https://doi.org/10.20855/ijav.2009.14.4253


The low frequency sound inside a number of aircraft and cars is now attenuated using commercial active sound? control systems. These operate either using loudspeakers to directly drive the sound field, or with shakers acting on the structure to modify its vibration and, hence, reduce excitation of the sound field. As the structure becomes larger, the number of actuators and sensors required for effective control rises sig- nificantly. Conventional, fully coupled control systems then become costly in terms of weight and sensitivity to individual failures. An alternative strategy of distributing the control over multiple local controllers will be disucssed, which has been shown to be effective in a number of cases. The workings of the inner ear also provide a remarkable natural example of decentralised active vibration con- trol, who?s aim is to enhance the motion within the cochlea. A simple model for this cochlear amplifier will be described, in which each of the outer hair cells act as local control loops, and its use illustrated in predicting the otoacoustic emissions generated by the ear as a result of this mechanism. These emissions are used clinically to screen the hearing of young children, so it is important to understand how they are generated within the cochlea.


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