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Abstract: The objective of this paper is to improve the predictivity of squeal simulations by introducing uncertainty and robustness concepts during simulations. Complex eigenvalue analysis is a traditional way to detect numerically the unstable modes that can be associated with extensive vibration and noise pollution. This simulation, for which associated computational times are compatible with the design phase, is known to be insufficiently predictive. We first propose a complete strategy that relies on the integration of random fields into the contact interface, complex eigenvalue calculations, probabilistic analysis and a robustness criterion. Next, this strategy is applied to study the instabilities of a complete industrial brake system. Experimental comparisons highlight the efficiency of the improved squeal detection methodology. [Copyright &y& Elsevier]

Abstract: A robust feature extraction scheme for the rolling element bearing (REB) fault diagnosis is proposed by combining the envelope extraction and the independent component analysis (ICA). In the present approach, the envelope extraction is not only utilized to obtain the impulsive component corresponding to the faults from the REB, but also to reduce the dimension of vibration sources included in the sensor-picked signals. Consequently, the difficulty for applying the ICA algorithm under the conditions that the sensor number is limited and the source number is unknown can be successfully eliminated. Then, the ICA algorithm is employed to separate the envelopes according to the independence of vibration sources. Finally, the vibration features related to the REB faults can be separated from disturbances and clearly exposed by the envelope spectrum. Simulations and experimental tests are conducted to validate the proposed method. [Copyright &y& Elsevier]

Abstract: The present study aims at proposing an innovative phase control methodology for semi-active tuned mass dampers (SA-TMDs) that intend to minimize the off-tuned problems associated with passive tuned mass dampers (P-TMDs). The phase control algorithm is first developed, the essential of which is to apply the variable friction force to slow down the mass block at specific moments when the phase lag of the SA-TMD with respect to the structure is different from 90°, resulting in the SA-TMD back to the desired phase lag, i.e., −90° phase deviation, so that the SA-TMD has the maximum power flow to reduce the structural vibration. The feasibility of the application of the phase control in SA-TMDs is verified by performing numerical analyses of a simplified Taipei 101 structure model with a SA-TMD subjected to sinusoidal loads and design level wind loads. The numerical simulation results show that the SA-TMD implemented with phase control can enable the mass block to vibrate in a manner with a phase lag close to the −90° when the structure model is under sinusoidal excitations with frequencies different from the structural fundamental mode. The SA-TMD with phase control not only exhibits better performance than the optimal P-TMD in terms of suppressing the structural vibration, but also enhances its robustness, particularly when the SA-TMD is off-tuned to the structure. [Copyright &y& Elsevier]

Abstract: The main goal of this paper is to propose the single input robust adaptive sliding mode controllers to accomplish synchronization and anti-synchronization between two identical Φ 6 Duffing or Van der Pol oscillators with unmodel dynamics and external disturbances. Unlike directly eliminating the nonlinear dynamics by active control and sliding mode control in the literature, the proposed sliding mode controllers include the equivalent control part, which is only proportional to the synchronized error states, and the switching control part, where the discontinuous control functions have adaptive feedback gains. Sufficient conditions are provided based on the Lyapunov stability theorem and numerical simulations are performed to verify the effectiveness of presented schemes. [Copyright &y& Elsevier]

Abstract: Several important applications use nonlinear feedback methods for synthetically inducing self-excited oscillations in mechanical systems. The van der Pol and saturation function type feedback methods are widely used. The effects of time-delay on the self-excited oscillation of single and two degrees-of-freedom systems under nonlinear feedback have been studied in this paper. It is shown that a single degree-of-freedom oscillator with the van der Pol type nonlinear feedback can produce unbounded response in presence of time-delay. In general, an uncontrolled time-delay in the feedback changes the state of oscillations in an uncertain manner. Therefore, a bounded saturation type feedback with controllable time-delay is proposed for inducing self-excited oscillations. The feedback signal is essentially an infinite weighted sum of a nonlinear function of the state variables of the system measured at equal intervals in the past. More recent is the measurement, higher is the weight. Thus, the feedback signal uses a large amount of information about the past history of the dynamics. Such a control signal can be realized in practice by a recursive means. The control law allows three parameters to be varied namely, the time-delay, feedback and recursive gains. Multiple time scale analysis is used to plot amplitude vs. time-delay curves. Time-delay can be controlled to vary the amplitude of oscillation as well as to switch the oscillation from one mode to the other in a two degrees-of-freedom system. It is shown that a higher recursive gain can exercise a better and a more robust control on the amplitude of oscillation of the system. Analytical results are compared with the results of numerical simulations. [Copyright &y& Elsevier]

Abstract: Methods of passing through resonance zones in mechanical systems are discussed and a new method based on the speed-gradient energy control of two subsystems (rotor and support) is presented. Two typical problems of passing through resonance for one- and two-dimensional motion of the support are posed and analyzed by computer simulation. The control algorithms based on the speed-gradient method and averaging allow one to significantly reduce the required level of the controlling torque. The proposed algorithms have a small number of design parameters. Compared with the known algorithms the proposed ones are more simple for design and exhibit stronger robustness properties. [ABSTRACT FROM AUTHOR]

Abstract: A novel time-delayed acceleration feedback method of controlling friction-induced instability is proposed. A single degree-of-freedom mechanical oscillator on a moving belt represents the basic friction-driven system. The control force is synthesized based on an infinite weighted sum of the acceleration of the vibrating mass measured at regular intervals in the past. Such a control force can be effectively produced by the recursive summation of the time-delayed acceleration and the time-delayed control signal, and hence the technique is termed as the recursive time-delayed acceleration feedback control. The local stability analysis of the equilibrium reveals nontrivial and beneficial influences of the recursive gain on the system performance. Robustness of the control is shown to improve with the increasing value of the recursive gain. A multiple time scale based analysis of the system elucidates the role of the recursive gain in enhancing the amount of dissipation produced by the control action. The influences of the time-delay and the control gain on the optimized performance of the system are also discussed. Numerical simulations of the system equations corroborate the analytical results. The present method is believed to be applicable to any self-excited system having a large degree of instability that is not removable by an ordinary time-delayed feedback. [Copyright &y& Elsevier]