Papers by Keyword: Vibration Control

Abstract: In the present work, a smart structure is being investigated, where a functionally graded carbon nanotube-reinforced composite (FG-CNTRC) plate is equipped with piezoelectric actuators to provide vibration control. Due to their high mechanical properties coupled with lightweight, FG-CNTRCs are mainly used in the aerospace industry and in advanced engineering applications. The CNTs have a linear and non-linear distribution along the thickness of the plate and are distributed according to five configurations, namely: UD, FG-X, FG-O, FG-A and FG-V. The first order shear deformation (FOSD) theory is considered in the formulation of a 9-node quadratic finite element with 5 degrees-of-freedom per node, and an additional degree of freedom is provided for the piezoelectric layer. The model developed in this study assesses the free vibration behavior and controls the nanocomposite plate deflection through the electromechanical coupling factor piezoelectric. In addition, it investigates: (i) the effect of the plate configuration, (ii) the CNT volume fraction, (iii) the CNT destruction patterns, (iv) the linear and nonlinear distribution of CNTs, (v) the number of CNTRC ply, (vi) the boundary conditions and (vii) the dimensions with different locations of actuators. The results obtained show the first natural frequencies for all configurations, which are considered to be in good agreement with those available in the literature and illustrate that the effective stiffness of the nanocomposite plates can be improved further when the reinforcement is dispersed according to the FG-X pattern. In addition, for the case of the deflection control analysis, results indicate that the distributed piezoelectric layers (actuators) attenuate the deflection of the CNTRC to the desired tolerance. It is noted that patches with partial coverage compared to the case of total coverage of piezoelectric layers require more electrical power to reach the same level of attenuation. The developed numerical model is intended to be used in a variety of potential advanced engineering applications.

Abstract: In this research, a shear-mode MR damper that can replace conventional passive damper of a front-loaded washing machine is designed, manufactured and an experiment based model is employed to characterize hysteresis behavior of the damper. Firstly, an optimized MR damper for front loaded washing machine is manufactured and an experimental system is set up for testing hysteresis behaviour of the damper. The experimental test is then conducted and presented. From experiential results, hysteresis of the damper is investigated and a suitable hysteresis model is proposed for the damper. The proposed hysteresis model of damper is then evaluated through experimental results.

Abstract: Robot simulation has developed quickly in recent decades. Along with the development of computer science, a lot of simulation soft-wares have been created to perform many purposes such as studying kinematic, dynamic, and off-line program to avoid obstacle on manipulator robots. The main objective of this study is therefore to analyze kinematic, dynamic characteristics of an R-R robotic manipulator in order to control this robot. Newton-Euler method was used to calculate the torque acting on each joint of the robot. Then, a numerical model of the robot was established by a multi-body dynamics software to compare with the results obtained by Newton-Euler theory. After that, a feed-forward control system was created by RecurDyn/CoLink to control the end-effector of the robot following a desired trajectory. The results showed that this research can be used for efficient simulation of structural kinematics, dynamics as well as control of the real manipulator robot with the robot structure in a virtual environment.

Abstract: In this study, we have investigated the band structure of elastic waves propagating in a phononic crystal, consisting of an epoxy matrix reinforced by Al₂O₃ inclusions in a square and hexagonal lattices. We also studied the influence of the inclusion geometry cross section – circular, hollow circular, square and rotated square with a 45° angle of rotation with respect to the x, y axes. The plane wave expansion (PWE) method is used to solve the wave equation considering the wave propagation in the xy plane (longitudinal-transverse vibration, XY mode, and transverse vibration, Z mode). The complete band gaps between the XY and Z modes are observed to circular, square and rotated square cross section inclusion and the best performance is for rotated square cross section inclusion in a square lattice. We suggest that the Al₂O₃/epoxy composite is feasible for vibrations management.

Abstract: Modern structures undergo considerably large responses when subjected to external loading owing to the tall, lighter and flexible nature of these structures. Due to this and the instability that may be induced, any vibrating system either civil or mechanical has the disability of being utilised to its maximum efficiency. This necessitates the response control of such structures and systems for many reasons. Different methods have been used for this response control from the past, which includes passive, active and hybrid control devices and strategies. Linear procedures and models used in this context have their own limitations since all real systems are basically nonlinear. This has been understood well in advance and hence, many control techniques have been devised to cater for non-linear behaviour from early mid-19^th century. Predicting the post-yield behaviour of civil engineering structures as well as controlling their vibrations using non-linear systems are ever challenging problems, especially when subjected to random excitations such as wind and earthquake. This paper presents the state of the art of non-linear devices and strategies for vibration control of structures and systems. It briefly discusses the control strategies and devices used in practise emphasising the merits and demerits of each of them. The use of control devices with linear plus cubic spring, hyperbolic sine spring, Belleville non-linear softening spring in parallel with viscous damper for the control of vibration is presented. The use of frequency energy dependence in the design of absorber and the use of power absorption ratio and kinetic energy of non-linear oscillator for the design of non-linear absorber, which is vastly explored in the recent years are outlined. A newer but efficient method in modelling non-linear system by the use of nonlinear targeted energy transfer is also discussed.

Abstract: A magnetic-fluid tuned liquid column damper (MF-TLCD) is a semi-active damper that has a magnetic fluid column in U-pipe as an additional vibration system. An MF-TLCD can suppress structural vibrations at a wide frequency range by applying a magnetic field. In this study, we performed vibration experiments for three types of U-pipes and assessed the effects on MF-TLCD performance caused by different damping forces on the liquid column.

Abstract: The purpose of this study is to evaluate and compare the effectiveness of friction dampers and tuned mass dampers (TMD) using numerical simulations. Wind and earthquake loads are simulated on a 15-story model building structure in which a friction damper and/or a TMD are installed. The idealized one-dimensional structure with a friction damper at each story and/or a TMD at the top of the building is subjected to a simulated load, and the displacement and acceleration responses of the structure are measured. The outcomes show that a TMD is more useful to control the vibration of the building from a wind load and a friction damper is more suitable for loads created by large accelerations such as those found during seismic events. This study provides verification on the performance of friction dampers and TMDs according to each of the two load types, wind and earthquake, through numerical simulations.

Abstract: The goal of this work is to describe a control procedure that simplifies the implementation and improves the performance of feedback active control on a planar structure. The article presents a design, development and experimental verification of an active feedback vibration control system of circular plate with the application of xPC Target platform. Vibrations of the plate are measured using MFC sensors. The control input is applied to the plate by a MFC disk, attached to the plate in its center. The plate vibrations were excited by a loudspeaker or by a second MFC actuator placed at a certain distance from the center of the disc.The basic philosophy is the off-line identification of the best model for the controlled process [1] and the subsequent synthesis of the controller. There are many classical strategies that can be used when a mathematical model is available, for instance, poles allocation or optimal control (LQR), used also by the authors [2, 3]. This article proposes an approach to design an effective controller for vibration suppression of a circular plate with the use of the pole placement method. For the considered system a linear discrete model obtained by parametric identification method for the data measured in a separate experiment has been designated. This model was used to develop the 6-th order digital controller which was implemented on xPC Target platform. Before implementation of the chosen control law design on real plant the simulations in Simulink/Matlab were performed. In order to investigate the influence of the implemented controller on the plate vibrations suppression the 3D scanning vibrometer has been used. The obtained simulation and experimental results, corresponding to the developed active vibration control system have been presented, compared and analyzed.

Abstract: Dynamic characteristics of numerical control (NC) machine tools, such as natural frequency and vibration property, directly affect machining efficiency and finished surface quality. In general, low-order natural frequencies of critical components have significant influences on machine tool’s performances. The headstock is the most important component of the machine tool. The reliability, cutting stability, and machining accuracy of a machining center largely depend on the structure and dynamic characteristics of the headstock. First, in order to obtain the natural frequencies and vibration characteristics of the headstock of a vertical machining center, modal test and vibration test in free running and cutting conditions were carried out by means of the dynamic signal collection and analysis system. According to the modal test, the first six natural frequencies of the headstock were obtained, which can not only guide the working speed, but also act as the reference of structural optimization aiming at frequency-shift. Secondly, by means of the vibration test, the vibration characteristics of the headstock were obtained and the main vibration sources were found out. Finally the corresponding vibration reduction plans were proposed in this paper. That provides the reference for improving the performance of the overall unit.

Abstract: In the paper, the problem of designing of mechatronic discrete systems for vibration control has been investigated and generalized. As the design method, the synthesis has been used. Main focus of the paper is given to formalization of the mechatronic structures that contains elements with negative values on different stages of the synthesis process. The study is done based on different distributions methods of dynamical characteristics, dimensionless transformation and retransformation algorithm, simultaneously with verification of possible configurations of connections of piezostack actuators with external electric networks. As the result, various classifications of mechatronic discrete systems and general design constrains have been presented and discussed.