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By simultaneously considering the supported truss configuration optimization and optimal attitude–vibration control in rigid–flexible coupling (RFC) structure, this study proposes a novel integrated uncertain optimal structure-control design strategy with interval uncertainties. Based on the principle of energy equivalence, the flexible support truss of the RFC structure is simplified using an equivalent beam model, which can significantly reduce the degree of freedom of the model and improve design efficiency on the premise of satisfying the analysis accuracy of the static and dynamic characteristics of the complete truss structure. The Lagrangian method is applied to establish an RFC structure model including a central rigid body, equivalent flexible truss and free end mass. Given the difficulty of quantifying the multi-source uncertainty encountered by actual RFC structures, the structural optimization and control system design in this study considers them as interval uncertainty. As long as the uncertainty bounds are known, the uncertainty propagation in the integrated design strategy can be quantified using interval dimension-wise analysis. The time-independent interval reliability-based frequency constraint and time-dependent interval reliability-based dynamic response constraint are both constituted for the proposed integrated uncertain optimal design strategy, which is solved using an advanced multi-objective optimization algorithm. One numerical example is applied to verify the proposed method. An optimum integrated design layout with a lightweight truss configuration and a low energy consumption control system is obtained.

Traditional structures adopt a split design with vibration control, energy harvesting and monitoring, which is difficult to meet the needs of technological development. The development of new structure from a single function to a multifunctional integration structure requires that the structure not only has the characteristics of low-frequency vibration control and energy harvesting, but also takes into account functions such as sensing, fault diagnosis and health monitoring. Given the continuously growing trend of multifunctional integration research, this paper presents the latest review on multifunctional integration of nonlinear vibration control, energy harvesting and monitoring. This is an interdisciplinary topic related to structural dynamics, mechanical design and power electronics, which has great prospects in various potential applications. The nonlinear design of new multifunctional integration structure is an essential step in the development of vibration control and energy harvesting, and is one of the most effective technical means to improve performance in low-frequency excitation environments. Therefore, the main implementation methods of nonlinear vibration control are discussed in detail. Subsequently, different strategies for nonlinear vibration energy harvesting and the challenges faced by wireless sensor network monitoring are described. On this basis, the research status, engineering applications and research trends of multifunctional integration structure are introduced in detail.

This paper investigates the forced vibration and dynamic stability of a simply supported axially moving beam coupled to a nonlinear energy sink with the aim of passive vibration control. The equations of motion of the coupled system are solved using harmonic balance and pseudo-arc-length continuation methods. The impacts of the beam velocity, excitation frequency, and magnitude of the external force on the behavior of the system are studied. It is observed that the absorber should be designed in a way that the strongly modulated response (SMR) and weakly modulated response occur in the response of the system when the moving beam is excited near its primary resonances. The results show that the saddle node and Hopf bifurcations boundaries, as well as the absorber performance, would be reduced by increasing the beam velocity. It is also realized that the excitation frequency in which the response of the system enters the SMR region is decreased by enhancing the beam velocity, as well as the magnitude of the external force. Using the results of this paper, one can readily simulate the vibration control of simply supported moving beams utilizing a nonlinear energy sink.

This paper investigates the high-performance attitude control and active vibration suppression problem for flexible spacecraft in the presence of external disturbances. The active vibration control usually depends on additional sensors and actuators, which will highly increase the difficulty of practical application. In order to reduce the implementation complexity, the piezoelectric sensors are not adopted, but instead a modal observer is introduced to estimate the modal information. Based on the observed modal information and the prescribed performance design process, an adaptive attitude controller is developed, which has the capabilities of rejecting disturbances as well as possessing predetermined transient and steady-state control performance. Similarly, an active controller is constructed to deal with the vibrations induced by attitude motions. It can be proved that by constraining the estimations of the modal variables, the actual modal coordinate will also be constrained with expected attenuation characteristics. The stability of the entire closed-loop system is analyzed by the Lyapunov theory. Simulation results in different cases show the effectiveness and performance of the proposed algorithms.

An improved pendulum tuned mass damper with nonlinear cable tension, known as the prestressed tuned mass damper (PSTMD), has been proposed and investigated for mitigating excessive vibrations of offshore wind turbines (OWTs) across a frequency range. Unlike conventional nonlinear TMDs constructed with nonlinearity springs or dampers, the nonlinearity in the PSTMD originates from the geometric properties of its prestressing cables. This study extends the development of the device to a bi-directional PSTMD, considering the distinct nonlinear-memoryless-amplification (NMA) behavior for integrated vibration control in an OWT system, by means of the theoretical analysis and numerical simulation approaches. A mathematical model is derived to describe the nonlinear tensile forces of the cables in the bi-directional PSTMD, and a dynamical nonlinear model of the OWT with proposed PSTMD is established to account for aero-hydrodynamic loadings. NMA dynamic behavior under harmonic loads is examined via using the Newton–Raphson algorithm to explore the integrated vibration control of bi-directional PSTMD under wind–wave loads. Numerical simulations are conducted to demonstrate the effectiveness of the nonlinear bi-directional PSTMD in suppressing vibrations of the OWT system under both harmonic and wind–wave excitations. The analysis results indicate that the bi-directional PSTMD, considering the NMA behavior, effectively mitigates the frequency detuning phenomenon at the natural frequency of the OWT system. Furthermore, the study reveals that this approach offers significant advantages in vibration mitigation compared to a linear system.

This review of MRF (magnetorheological fluids or MR fluids) brings out the challenges in methods of preparation, difficulties encountered in storage and use, and possible solutions to overcome the challenges.Magnetorheological fluid in the rheological fluid domain has found use due to its ability to change its shear strength based on the applied magnetic field. Magnetorheological fluids are composed of magnetizable micron-sized iron particles and a non-magnetizable base or carrier fluid along with additives to counter sedimentation and agglomeration.Magnetorheological fluids can respond to external stimuli by undergoing changes in physical properties thus enabling several improved modifications in the existing technology enhancing their application versatility and utility. Thus, magnetorheological fluid, a rheological material whose viscosity undergoes apparent changes on application of magnetic field, is considered as a smart material. Such materials can be used for active and semi-active control of engineering systems.Many studies on the designs of systems incorporating MR fluids, mainly for vibration control and also for other applications including brakes, clutches, dynamometers, aircraft landing gears, and helicopter lag dampers, have emerged over last couple of decades. However, the preparation as well as the maintenance of magnetorheological fluids involves several challenges. Sedimentation is a major challenge, even when stored for moderate periods of time. A comprehensive review is made on the problems confronted in the preparation of magnetorheological fluids as well as sustenance of the properties, for use, over a long period of time. Other problems encountered include agglomeration and in-use thickening (IUT) as well as rusting and crusting. Of interest is the mitigation of these problems so as to prepare fluids with satisfactory properties, and such solutions are reviewed here. The control of magnetorheological fluids and the applications of interest are also reviewed.The review covers additives for overcoming challenges in the preparation and use of magnetorheological fluids that include incrustation, sedimentation, agglomeration, and also oxidation of the particles. The methodology to prepare the fluid along with the process for adding selected additives was reviewed. The results showed an improvement in the reduction of sedimentation and other problems decreasing comparatively. A set of additives for addressing the specific challenges has been summarized. Experiments were carried out to establish the sedimentation rates for compositions with varying fractions of additives.The review also analyzes briefly the gaps in studies on MR fluids and covers present developments and future application areas such as haptic devices.

This paper proposes a novel model-free reinforcement learning (RL) control algorithm for a semi-active tunable vibration absorber (TVA) with nonlinear properties that are operated under nonstationary and multi-frequency excitations. The research addresses two critical challenges in vibration absorber control that are often treated separately: (i) the time-varying and nonlinear stiffness-damping characteristics, and (ii) the complex and nonstationary nature of real-world excitations. To address these challenges, a modified Q-learning algorithm is proposed by integrating vibration-domain knowledge derived from Parseval’s theorem and frequency response functions. This integration not only enables the controller to effectively minimize vibration energy without requiring an explicit model of the plant but also significantly reduces the computational complexity of the learning process. The proposed controller is experimentally validated under nonstationary multi-frequency excitation using a semi-active TVA with highly time-variant stiffness and damping properties. Experimental results demonstrated accurate real-time control performance, achieving an R-squared value of 0.994 compared to an optimal control baseline, and up to 58% reduction in vibration energy. These results provide strong evidence that reinforcement learning control strategies, when guided by vibration-domain knowledge, can offer generalizable, efficient, and adaptive solutions to complex mechanical vibration control problems.

Satellite borne flexible structure is a multi-degree-of-freedom system, which contains complex dynamic characteristics such as time-varying parameters, geometric nonlinearity, gap nonlinearity, and so on. Flexible structure suspension typically results in geometric nonlinearity. The oscillation equation with nonlinear term is established according to the law of motion of a nonlinear pendulum and considering the influence of medium swing angle and lateral force. The perturbation approach is used to get the relationship between vibration frequency and the nonlinear term, and the impact of factors on vibration characteristics is investigated. The satellite borne flexible structure’s active vibration control (AVC) system is then established. Considering proportional differential (PD) or fuzzy control adjustment, variable step size least mean square (VSS-LMS) adaptive filtering algorithm is used to calculate the control signal, and considering the influence of geometric nonlinearity, the actuator is used to suppress the vibration of the satellite borne flexible structure. Finally, the vibration response’s amplitude under steady-state excitation significantly decreases as an outcome of the vibration control simulation.

A nonlinear energy sink (NES) passively reduces transient vibration energy of a typically impact loaded mechanical system. It is locally connected to the vibrating system through a nonlinear connecting stiffness. For a NES to perform efficiently, through targeted energy transfer (TET), the vibration levels need to exceed a well-defined threshold, below which the NES performs poorly. This threshold can be lowered by considering a NES with a bi-stable connecting stiffness. A bi-stable NES (BNES) has two stable equilibria. Besides vibrating in TET regime, a BNES can also vibrate chaotically or close to one of its equilibria, called intra-well vibrations. However, during both chaotic and intra-well vibrations, the mitigating performance of the BNES is poor. Here, a novel tuning method is developed, which finds the boundary between chaotic and TET regime, such that the BNES avoids the chaos and operates with the more performant TET. This boundary is found by numerically calculating the Lyapunov exponent, a measure for chaos. To quantify performance, two algebraic expressions, requiring no simulations, are derived in the paper expressing the speed of vibration mitigation and expressing the residual vibration energy left after TET. The result is a generic tuning methodology that not only ensures the BNES operates in the efficient TET regime, but also guarantees optimal speed of vibration mitigation. The developed performances measures in function of the NES’s parameters are to the point and easy to use. The tuned BNES shows a superior robustness w.r.t detuning compared to the linear vibration absorbers.

This paper deals with the active vibration control of composite cantilever beam. Based on the finite element method and Golla–Hughes–McTavish (GHM) model, the system dynamics equation is established. Models are simplified in physical and modal space because of unobservable and uncontrollable. Based on the particle swarm optimization (PSO) algorithm, the linear quadratic regulator (LQR) feedback gain was optimized. The effect of system vibration damping under different controller parameters, piezoelectric-constrained layer position and excitation signal was studied. The study show that the optimal feedback gain of the controller can effectively balance the control effect and the control cost. The closer the piezoelectric layer and viscoelastic layer are to the fixed end, the better the system control effect and the smaller the control cost. The reduced-order model has a good control effect on different excitation signals.