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The vibration suppression of structures using a semi-active mass damper is investigated in this study. A magnetorheological (MR)-damper is utilized to design the semi-actively controlled mass damper. The inverse MR-damper model is developed on the basis of an improved LuGre friction model, and combined with a designed [H.sub.2]/Linear-Quadratic-Gaussian ([H.sub.2]/LQG) controller, in order to control the command current of the MR-damper to suppress structural vibration levels effectively. Illustrated examples are considered to investigate the vibration suppression effectiveness of a semi-active mass damper with a MR-damper, using the developed control methodology. The simulation results were compared with those reported in literature in order to validate the presented methodology. [DOI: 10.1115/1.4000969] Keywords: semi-active mass damper, [H.sub.2]LQG controller, magnetorheological (MR)-damper, clipped-optimal controller, improved LuGre friction model, inverse MRdamper model

Byline: M.T. Ahmadian (Center of Excellence in Design, Robotics and Automation, School of Mechanical Engineering, Sharif University of Technology, Tehran, Iran); R.A. Jafari-Talookolaei (Center of Excellence in Design, Robotics and [...]

Byline: P.A. Hassanpour (Department of Mechanical and Industrial Engineering, University of Toronto, 5 King's College Road, Toronto, ON, Canada, M5S 3G8); W.L. Cleghorn (Department of Mechanical and Industrial Engineering, University [...]

The single-reference/multiple-output active noise control (ANC) of the accurate physical model of an acoustic duct system, developed earlier by the authors [1] is investigated. An adaptive feedforward algorithm is developed that minimizes a generic cost function consisting of the p-norm of the error vector. A computer model of a multi-channel ANC system, with the tonal and sweep sine input signals, is established, and the results for different single-input/single-output (SISO) configurations (error microphone and secondary source locations) of the ANC system are compared. The dynamic response of the single-reference/multiple-output ANC systems, using the Minimax and MEFXLMS algorithms, is studied and the effect of the acoustical feedback neutralization in the multi-channel ANC system is examined. Simulation results demonstrate that the multi-channel adaptive feedforward ANC system with the Minimax algorithm has a superior performance to that of the same system with the MEFXLMS algorithm. However, the total noise reduction of the Minimax algorithm, compared with that of the MEFXLMS, is much dependent on the frequency content of the input signal [DOI: 10.1115/l.1636772]

Based on the closed-form solution of a one-dimensional wave equation, the primary, secondary and acoustic feedback paths for the active control of sound in an acoustic duct have been investigated. Accurate models for the condenser microphone and loudspeaker, which include both the electro-mechanical and mechano-acoustical couplings as well as acoustical damping, have been considered. A generalized form of the filtered-x least mean square (FXLMS) algorithm that uses a more general recursive adaptive weight update equation to improve the performance of the FXLMS algorithm has been developed. Computer simulations were carried out to investigate the performance of acoustical feedback and feedback neutralization as well as the effect of boundary conditions on the performance of active noise control (ANC) systems. Comparisons of the simulation results were carried out. [DOI: 10.1115/1.1400117]

A procedure in designing optimal Dynamic Vibration Absorbers (DVA) for a structurally damped beam system subjected to an arbitrary distributed harmonic force excitation, is presented. The Timoshenko beam theory is used to assess the effects of rotatory inertia and shear deformation. The method provides flexibility of choosing the number of absorbers depending upon the number of significant modes which are to be suppressed. Uniform cross-sectional area is considered for the beam and each absorber is modeled as a spring-mass-damper system. For each absorber with a selected mass, the optimum stiffness and damping coefficients are determined in order to minimize the beam dynamic response at the resonant frequencies for which they are operated. For this purpose, absorbers each tuned to a different resonance, are used to suppress any arbitrarily number of resonances of the beam. The interaction between absorbers is also accounted for in the analysis. The optimum tuning and damping ratios of the absorbers, each tuned to the mode of concern, are determined numerically by solving a min-max problem. The Direct Updated Method is used in optimization procedure and the results show that the optimum values of the absorber parameters depend upon various factors, namely: the position of the applied force, the location where the absorbers are attached, the position at which the beam response should be minimized, and also the beam characteristics such as boundary conditions, rotatory inertia, shear deformation, structural damping, and cross sectional geometry. Through the given examples, the feasibility of using proposed study is demonstrated to minimize the beam dynamic response over a broad frequency range. The resulting curves giving the non-dimensional absorber parameters can be used for practical applications, and some interesting conclusions can be drown from the study of them.

The transverse oscillatory motion of a simple beam with one end fixed while driven harmonically at the other end along its longitudinal axis is investigated. For a special case of zero value for the rigidity of beam, the problem reduces to that of a vibrating string with its corresponding equation of motion. The sufficient condition for the periodic solution of the beam was determined using the Green's function and Schauder's fixed point theorem. The criterion for the stability of the system is well defined and the condition for which the performance of the beam behaves as a nonlinear function is stated.

Byline: M. Ansari, E. Esmailzadeh, D. Younesian A comprehensive parametric study is performed on the longitudinal dynamics of a freight train based on different nonlinear time-domain models. The effect of different parameters, such as the couplers stiffness and damping, train speed, train acceleration, load distribution pattern, on the longitudinal train dynamics are investigated. Moreover, the effect of an empty wagon and its position, on the overall longitudinal train dynamics is discussed. A computer simulation model is developed to determine the optimum placement of the second locomotive in order to obtain the lowest longitudinal forces. Further study is carried out to determine the best type of automatic couplers.

The study of free in-plane vibration of curved beams, using different beam theories, is more challenging than that of straight beams, since the structural deformations in curved beams depend not only on the rotation and radial displacements, but also on the coupled tangential displacement caused by the curvature of structures. A critical review of the publications on the free in-plane vibration of curved beams to demonstrate the state of the art has been presented. The governing differential equations of motion for the curved beams, based on different hypotheses (including and excluding the axial extensity, rotary inertia and the shear deformation), were discussed and different approaches to solve the developed equations of motion have been identified. Finally, a systematic comparison of the dynamic properties of curved beams evaluated with various forms of curvatures based on different hypotheses were presented. [ABSTRACT FROM AUTHOR]