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Published Articles

The Volume 19, No 4, December 2014

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Adaptive Resonant Vibration Control of a Piezoelectric Flexible Plate Implementing Filtered-X LMS Algorithm

Zhi-cheng Qiu, Biao Ma


Vibration in aerospace structures can lead to structural damage. To solve this problem, the implementation of active vibration control must be considered. This paper investigates active vibration control under the persistent resonant excitation of a clamped-clamped piezoelectric plate system. The finite element method (FEM) and ANSYS modal analysis methods are utilized to obtain the dynamics model and mode shapes of the plate. A two-norm criterion is used for optimal placement of piezoelectric sensors and actuators, taking into account the non-controlled modes to reduce spillover problems. A genetic algorithm (GA) is used to search the optimal locations of actuators/sensors. Then, a proportional derivative (PD) control algorithm and a filtered-X least mean square (filtered-X LMS) feed-forward control algorithm are designed for the system. Subsequently, numerical simulations with optimal placement of actuators and sensors are carried out to compare the performance of the controllers. Finally, experiments are conducted. The experimental results demonstrate that the designed filtered-X LMS control algorithms can suppress the resonant vibration better than that of the PD control.

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Control of MR Damper Connected Buildings by Output Feedback

Gokarna B. Motra and Naresh K. Chandiramani


The control of seismic response of buildings connected by a magnetorheological (MR) damper is studied. The desired control force is obtained using Linear Quadratic Gaussian (LQG) control based on the feedback of states estimated via measured outputs or Optimal Static Output Feedback (OSOF) control using the direct feedback of measured outputs. The damper input voltage is predicted using a Recurrent Neural Network (RNN), which proves more effective than the Clipped Voltage Law (CVL). Various sensor configurations and state weightings are considered to obtain effective control. LQG-RNN/OSOF-RNN yield significant reduction in response and base shear and require much less control effort compared to passive-on control with saturation voltage. Compared to passive-off control, they are very effective in attenuating maximum-peak/RMS responses and storeywise responses of the flexible building, except for max-peak accelerations that increase slightly. However, passive-off control is unable to transfer base shear to the stiffer building. LQG-RNN/OSOF-RNN also yield control at least as effective as LQR-RNN by deploying much fewer sensors but using a somewhat higher damper force. They are mostly comparable to each other, but OSOF-RNN requires an order-of-magnitude less CPU time for the control loop. Effective control is possible using few sensors.

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Use of a New Modified Acoustic Model to Investigate Mean Flow Effects on Underwater Sound Sources

Mohammad Riahi, Norouz M. Nouri, Ali Valipour


In this investigation, by introducing a relatively comprehensive acoustic equations system, the possibility of a more precise time and spatial pattern for sound wave propagation in fluid was revealed. Since the conservation equation is known as a fundamental equation for obtaining the wave equation, initially, by using scale analysis, the differential terms and weight coefficients are converted into the dimensionless form. Then, by assuming the amplitudes of the sound sources are small and by utilizing the perturbation technique, these dimensionless equations are converted into different orders based on the order of acoustical fluctuations. Consequently, it was shown that the obtained first order equations are representative of acoustical equations. Also, the results are indicative of the first order equations being coupled with the leading order ones. Comparison of the obtained acoustic the equations of the present study are capable of considering velocity, viscosity, and density changes of the background fluid flow. In the end, the effects of the flow velocity with a different Mach number on the acoustical distribution pattern that stemmed from different sound sources have been studied for several benchmarks.

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A Note on the Influence of Intermediate Restraints and Hinges in Frequencies and Mode Shapes of Beams

Raffo, J. L. and Grossi, R. O.


This note deals with the free transverse vibration of a beam with two arbitrarily located internal hinges, four intermediate elastic restraints, and ends elastically restrained against rotation and translation. The method of separation of variables is used for the determination of the exact frequencies and mode shapes. New results are presented for different boundary conditions and restraint conditions in the internal hinges. The mathematical model is also used to study the influence on the frequencies and mode shapes of varying intermediate supports that are located at the nodal points of higher modes. A detailed numerical study on the effects of the locations of intermediate translational restraints and their stiffness' on the natural frequencies and mode shapes is performed for different boundary conditions. The effect of the presence of the internal hinges is also analysed. Graphs and tables of the non-dimensional frequencies and the corresponding mode shapes are given in order to illustrate the behaviour of frequency parameters and the presence of mode shape switching.

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Passive Vibration Isolation by Compliant Mechanism Using Topology Optimization

V. Vijayan, T. Karthikeyan, M. Udayakumar and K.Chellamuthu


Compliant mechanisms have been designed for various types of applications to transmit desired forces and motions. In this paper, we explore an application of compliant mechanisms for passive vibration isolation systems. For this, a compliant isolator is used to cancel undesired disturbances, resulting in attenuated output amplitude. A compliant mechanism is equipped with an isolator, while a compliant mechanism also functions as a transmission of force and controls the amount of displacement that is transmitted from it. It can be used as passive vibration isolation. Here, by introducing compliance into the connection, the transmission of applied forces is reduced at some frequencies at the expense of increasing transmission at other frequencies. While transmitted force is the key parameter from the receiver's perspective, motion at the isolated machine is uninteresting. The force transmissibility is numerically identical to the motion transmissibility. The structural optimization approach is focused on the determination of the topology, shape, and size of the mechanism. The building blocks are used to optimize a structure for force transmission. The flexible building blocks method is used for the optimal design of compliant mechanisms. This approach is used to establish the actuator model of the block and its validation by commercial finite element software. A library of compliant elements is proposed in FlexIn. These blocks are limited in number, and the basis is composed of 36 elements. The force transmitted to the rigid foundation through the isolator is reduced in order to avoid the transmission of vibration to other machines. The preliminary results of FEA from ANSYS demonstrate that compliant mechanism can be effectively used to reduce the amount of force transmitted to the surface.

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Blind Source Separation Research Based on the Feature Distance Using Evolutionary Algorithms

Yang Yang, Xiuqin Wang and Di Zhang


Without any information on the mixing system, the blind source separation (BSS) technique efficiently separates mixed signals. The approach called evolutionary algorithms was used for the BSS problem in this paper. The fitness function based on the feature distance and kurtosis was proposed to measure the degree of the separated signals in this paper. Compared with the traditional algorithm in the BSS problem, the mathematical calculation and the physical significance of the separated signals are both taken into consideration in the proposed method. Therefore, the separated signals could have great correlation with the original individual signal and could be used in the additional signal processing step with good signal property. Experimental results on mixed spoken signals indicated that the established evolutionary algorithm of particle swarm optimization (PSO) and genetic algorithm (GA) could effectively solve the BSS problem from the signal feature distance and independence measurement. The study in this paper was implemented with MATLAB language.

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Boundary Condition Identification of a Plate on Elastic Support

Hamid Ahmadian, Morteza Esfandiar, Hassan Jalali


The behaviour of mechanical structures in low frequencies is strongly affected by the existence of the boundary conditions. It is not usually possible to provide ideal boundary conditions, i.e. simply supported or clamped, for structures. Therefore the real structures are mostly constrained by elastic supports. Constructing an accurate mathematical or numerical model for a structure requires the knowledge of the support parameters. In this paper, a new method is proposed for the parameter identification of a rectangular plate constrained by elastic support. The method relies on the free vibration solution of the plate dynamics subjected to elastic boundary conditions and employs the optimization toolbox of MATLAB.

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