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Large amplitude vibrations are often associated with geometric nonlinearity. These nonlinear systems are usually controlled using linear controllers, such as positive position feedback (PPF). Nonlinear control has also often been limited to single-input single-output (SISO) architectures. The present study develops a nonlinear PPF controller implemented with both a SISO and a multiple-input multiple-output (MIMO) architecture on a real experimental set-up, consisting of a clamped composite sandwich beam. The controller aimed to reduce the vibration amplitude observed when the structure was subject to a stepped-sine excitation in the frequency neighborhood of the first natural frequency for different force excitation levels. The developed nonlinear controller is based on a linear PPF controller to which a cubic term was added since the system under study is of hardening type. The control parameters were selected by optimization of the reduction of the vibration at low excitation amplitude. The nonlinear MIMO and SISO versions of the controller were compared to linear MIMO and SISO versions, which omitted the cubic term but maintained the other parameters. The nonlinear controllers were found to outperform the linear ones, and the MIMO versions of each controller also outperformed the SISO ones. Overall, the experimental evidence shows that a nonlinear MIMO PPF controller should be preferred for the application under study. [ABSTRACT FROM AUTHOR]

This work investigates the application of an external adaptive tensioning (EAT) system for high-speed railway (HSR) bridges. The design of HSR bridges involves strict displacement and acceleration limits, which typically results in oversizing. The EAT system comprises under-deck cables deviated by compressive struts that are equipped with linear actuators. Since the cable is eccentric to the bridge neutral axis, tensioning the under-deck cables by adjusting the length of the linear actuators generates a bending moment that counteracts the effect of the external loads. The response under variable loading is reduced by computing the actuator commands with a linear quadratic regulator (LQR). Numerical results show that active control through the EAT system allows satisfying displacement and acceleration limits, which otherwise cannot be met without increasing the stiffness and mass of the bridge. A significant reduction of the response is achieved when resonance conditions occur. In addition, peak stresses are significantly reduced, showing the potential for fatigue-life extension. Parametric analyses comparing different bridge depths and spans, EAT system dimensions, controller parameters and actuator placement are carried out to investigate system efficacy. Results show that the adaptive bridge solution can achieve up to 32% mass savings compared to an equivalent passive bridge. • Integrated design-control methodology for adaptive high-speed railway bridges. • Conceptualization of a new type of external adaptive tensioning (EAT) system. • Limit states are met through active control provided by the EAT system. • Lower mass and environmental impacts for new bridges. • Potential for service life extension of new and existing bridges by retrofitting. [ABSTRACT FROM AUTHOR]

This paper presents a novel approach to active chatter control in milling operations using a new concept called the virtual inerter-based dynamic vibration absorber (VIDVA). While passive control methods, such as tuned mass damper (TMDs), have their merits, they may not provide optimal performance and adaptability in certain scenarios. Moreover, the realisation of an idealised inerter-based absorber as a localisation addition can be a difficult task to achieve. In response of these challenges, the integration of the inerter concept into virtual passive absorber (VPA) control to improve chatter stability performance is proposed. Four IDVAs are numerically evaluated to enhance the absolute chatter stability limit, and the numerical results are experimentally validated using cutting tests with a proof-mass actuator providing the control force. The study also includes robustness and actuator saturation analysis to provide a comprehensive evaluation of the proposed virtual IDVA. The findings demonstrate that the virtual IDVA offers improved chatter suppression performance, making it a promising solution for active chatter control and application of IDVAs in milling operations. • A virtual passive inerter-based absorber is proposed for chatter suppression. • A robustness analysis is presented, applicable also passive control methods. • Actuator saturation is evaluated for chatter suppression. • Inerter-based absorbers are more preferable than TMDs in virtual active controls. [ABSTRACT FROM AUTHOR]

• A novel coarse–fine parallel vibration isolation pointing platform (CFPP) is proposed to achieve pointing adjustment and active vibration isolation for optical payloads. • Designed a coarse- and fine-stage parallel scheme. Conducted kinematic and dynamic analyses to ensure its effectiveness. • Feedback active vibration isolation algorithm based on H-infinity loop forming, and proved control system stability. • Designed the prototype and experimentally verified the wide range of pointing adjustment and active vibration isolation function. A coarse and fine parallel vibration isolation pointing platform (CFPP) is proposed, which can realize a wide range of motion and active vibration isolation for space optical payload. First the coarse and fine parallel connection scheme is designed based on the Stewart generalized configuration. Kinematic and constraint analyses are performed to determine the two operation modes of the platform. The platform is then structurally designed. System dynamics model is established based on the Lagrange method, and the dynamic disturbance characteristics are analyzed. Next, the active vibration isolation control algorithm based on H∞ loop shaping is designed. The stability of the control system is analyzed. Finally, the prototype is constructed, and the three-axis pointing range test and active vibration isolation experiments in four attitudes are carried out, and the experimental results show that the designed pointing vibration isolation system with coarse and fine stages in parallel can achieve a 7° movement range of the three axes, and it has a maximum vibration isolation capacity of 20 dB for the disturbance in the frequency band of 2–20 Hz. It has great application prospects in the direction of miniaturization and integration of space optical payload in the future. [ABSTRACT FROM AUTHOR]

• Possible substantial deterioration in vibration suppression due to a negligible loop delay. • Control correction for loop delay to achieve complete vibration suppression. • Full exploitation of the strength of the distributed delayed control while considering the loop delay. • New multiple-delay perspectives for analytical parametric tuning, stability analysis, and exact optimization. We generalize the distributed delayed resonator (DDR) concept by incorporating the previously unutilized but inevitable feedback loop delay, thus creating a so-called multiple-delay distributed delayed resonator (MD-DDR) for complete vibration suppression. The necessary parameter tuning and control stability analysis become more involved but remain analytically solvable. Particularly, we take the operability of control parameters imposed by hardware as an explicit condition for parameter tuning and show that the loop delay (even if it is small) can lead to incomplete vibration suppression and, counter-intuitively, even no suppression if the excitation frequency exceeds a threshold value. On the other hand, such negative effects are neutralized by correcting control parameters. The loop delay is then intentionally augmented to seek enhanced performance, yielding a considerably extended operable frequency band for the desired complete vibration suppression. Furthermore, it is optimized to expedite response speed by achieving the leftmost placement of the dominant (i.e., the rightmost) characteristic root. Instead of applying a brute-force sweeping procedure as in the previous works, we analyze the dominant root locus and seek if the jump phenomenon occurs to conduct exact optimization at a low computational cost. Finally, extensive comparisons using actual experimental parameters are performed to explore various effects of the loop delay on vibration suppression and the benefits of the proposed MD-DDR in handling such issues over the conventional DDR that treats a single delay. This study fully exploits the strength of the distributed delayed control logic, moving the DDR concept closer to real applications and aiming to establish a broader design and analysis framework for the delayed resonator from a multiple-delay perspective. [ABSTRACT FROM AUTHOR]

Current offshore wind turbine installation and positioning methods require mechanical equipment attached on the lifted components and human intervention. The present paper studies the development of a contactless motion compensation technique by investigating a magnetically controlled pendulum. The technique involves the interaction of a magnetic pendulum with an electromagnetic actuator. Two control modes are considered: the imposition of a desired motion to the mass and the motion attenuation of a prescribed pivot excitation. The numerical model is validated and calibrated against experiments and demonstrates excellent predictive capabilities. The control exerted is effective for a broad range of excitation frequencies and amplitudes. Important parameters associated with the performance of the technique such as the separation distance of the magnets and the saturation of the controller are identified. The controllability regions for effective control depending on the characteristics of the excitation are derived. The force amplitude of the contactless actuator is comparable to currently-used active tugger line control systems, but with the additional advantage of both attractive and repulsive forces. The findings of this paper illuminate the path for the further development of a non-contact control technique which has the potential to increase the efficiency of offshore wind installations. • Contactless position control for offshore wind turbines: a proof of concept. • Pendulum motion control via magnetic interaction. • Additional control authority with both repulsive and attracting forces. • Efficient control for the desired motion of a pendulum mass for a fixed or moving pivot. • Estimated force amplitude comparable to active tugger control systems. [ABSTRACT FROM AUTHOR]

This work is aimed to develop a lateral vibration attenuation mechanism for a rotor system using an axial control strategy with resonance detuning, allowing the rotor to operate through its critical speeds without exciting its resonances. An efficient control mechanism via controllable tensile axial loads applied using linear actuators and thrust bearings, was proposed to suppress rotor vibration without unnecessary continuous control force applications, in contrast to active vibration control strategies. The control strategy using resonance detuning caused the shifting of resonance to a higher frequency by regulating the rotor lateral stiffness using the axial control mechanism. The efficacy of the actuation mechanism in mitigating rotor lateral vibration was investigated through simulation and experimental studies, demonstrating the effectiveness of the control mechanism in allowing a rotor to operate over a wide operational working range over its first critical speed without a continuous application of control forces. It was experimentally demonstrated that the proposed control strategy allowed the rotor system to bypass its critical speed without exciting its resonance. The control mechanism has shown high-responsiveness to an immediate change in axial load to suppress rotor vibration, while achieving a degree of robustness in ensuring the worst-case vibration suppression performance against the variation in rotor disc offset, mass, and eccentricity by selecting an appropriate level of axial load. [ABSTRACT FROM AUTHOR]

In this paper, the combination of a nonlinear system and a robust sliding-mode controller with sliding integral surface is studied. This controller is composed of a linear part and a nonlinear part defined by a non-smooth function. Calculating the frequency response curve of such a system can be time-consuming and difficult using time integration methods. An original algorithm based on the harmonic balance method and capable of directly calculating the periodic solutions of a robust sliding-mode controller with sliding integral surface is proposed. In addition, the classical numerical methods for continuation of nonlinear frequency response curves and stability calculation of periodic solutions have been adapted to take into account the integral component of the control law. Finally, experimental validations on a non-linear structure have been carried out, attesting to the efficiency of the proposed controller and the robustness of the proposed numerical tools. • Nonlinear system coupled with sliding mode control law. • Original algorithm for periodic solutions based on the harmonic balance method. • Continuation and stability of nonlinear frequency response curves. • Comprehensive bifurcation tracking to assess the influence of the nonlinear controller. • Experimental validation on a non-linear structure. [ABSTRACT FROM AUTHOR]

In an active vibration control (AVC) system, the secondary path can generally only be identified when the system has been built. The performance of a typical adaptive feedforward control system using the filtered-x least mean square (FxLMS) algorithm is heavily dependent upon the dynamic characteristics of the secondary path. It would, therefore, be helpful for engineers to have knowledge of this behavior early in the design process. In this paper, pre-identification of the secondary path is proposed, which means its offline identification model can be obtained without installing the AVC equipment. This can save both time and money. In the pre-identification process, the secondary path is split into three parts. The first part includes the actuator and related electrical equipment. The frequency response function of this part can be identified after the hardware has been selected. The second part involves the dynamic behavior of the structure to be controlled, which is identified by impact excitation using a specially developed pneumatic impact harmer. The third part concerns the analogue/digital and digital/analogue converters whose effect on the secondary path is offset by a phase shift corresponding to half the sampling time. In this paper, the pre-identification process of the secondary path components is described, and some experiments are conducted to verify the feasibility of the approach and to demonstrate the significance of the pre-identification results. This mainly involves predicting the control performance and optimizing the parameters of the control system. Combined with the simulation of the control system, the approach proposed can improve the work efficiency of large-scale engineering projects and reduce the cost of testing. [ABSTRACT FROM AUTHOR]

In this paper, an analysis model of adaptive active vibration control system of composite laminated plate using macro fiber composite (MFC) piezoelectric patches is presented, and the experimental testing is carried out. Electromechanical coupling equations of the composite laminated plate are established by considering the influence of the mass and stiffness of MFC piezoelectric patches. The adaptive active vibration control scheme for composite laminated plate based on the filtered-x least mean square (FxLMS) algorithm is proposed. The accuracy of the present analysis model is validated by the results of experimental test and finite element method (FEM). It can be found that the vibration responses nearby the first and second natural frequencies of the composite laminated plate can be rapidly and greatly suppressed by the adaptive active control system and experimental test. Moreover, the dynamic responses of the composite plate under multi-frequency excitation and random excitation can be fast controlled by the presented adaptive active control system. The novelty of this work is that a theoritical analysis model of adaptive closed-loop control system based on the MFC piezoelectric patches is presented for vibration suppression of composite laminated plate, and the effectiveness of the proposed adaptive active model are validated by experimental testing. [ABSTRACT FROM AUTHOR]

A hybrid controller is proposed to control the vibration of a cantilever structure. The hybrid adaptive controller combines sliding mode controller (SMC) and proportional-derivative (PD) controller. Meanwhile, a type-2 fuzzy neural network (T2FNN) with a zero-order consequent part and certain center is applied to SMC due to the unknown of the controlled object. The initial parameters of T2FNN are obtained through the identification by an SMC-theory based T2FNN. The adaption laws of the controller and T2FNN are given through Lyapunov stability. The state space equation of the beam is established for simulation. The proposed controller is applied to vibration control of a cantilever beam bonded with piezoelectric actuator to verify its effectiveness. The simulation and experiment results show excellent control performance of disturbance rejection and vibration suppression of the proposed controller. [ABSTRACT FROM AUTHOR]

The rotor mass imbalance is common in rotating machinery, which can lead to the synchronous vibration in the magnetically suspended centrifugal compressor (MSCC) system. This work proposes a synchronous vibration control method based on the optimal notch filter. Firstly, the dynamics of the magnetically suspended rotor (MSR) system with mass imbalance is modeled. Then phase-shift notch filter for the synchronous vibration suppression is designed according to theoretical stability analysis of the whole system. Furthermore, in order to optimize the dynamic performance of the notch filter, its phase angle is taken as the variable to be optimized. Taking the integral of the absolute value of time multiplies current as the objective function, the optimized design flow of the phase angle is given. The proposed optimized method does not rely on accurate mathematical model, and is more direct. Finally, the simulation and experiment results demonstrate the effectiveness of the optimal notch filter and also prove the system stability. [ABSTRACT FROM AUTHOR]

• Electrohydraulic shaking table (EHST) system includes servo and target controller. • The effective frequency bandwidth is extended by new designed servo controller. • An adaptive power level control algorithm is proposed for target control. • Experiment was conducted on a 3-ton EHST system with a 1.2 m × 1.2 m table. • The results show the system can finally match the target within an accuracy of ±3 dB. Active vibration control using electrohydraulic shaking table (EHST) system is widely applied in civil engineering, automotive industry, environmental vibration testing and other situations where large actuating forces are needed. However, the electrohydraulic actuators (actuating systems) often suffer from drawbacks of limited frequency bandwidth, varying system parameters and so forth. In view of the limits mentioned above, this study hopes to seek out proper solutions to minimize the influence from those drawbacks. We first design a full state feedback-feedforward servo controller, which is able to extend the frequency bandwidth of EHST system, by constructing the analytical models of the servo valve and hydraulic cylinder. Numerical simulations show that the proposed servo controller is able to compensate for the attenuation-band of hydraulic cylinder and thus improve the upper frequency limit of the whole system to a degree that is higher than the natural frequency of servo valve. Afterwards, we propose a frequency domain adaptive power level control (APLC) algorithm for solving the problem of parametric variations of EHST system in application of power level control (i.e., simulate vibration based on certain power spectrum). Numerical simulations show that although APLC algorithm is not able to get exactly same spectrum and waveform at every independent trial, the power level of every trail will finally converge to the target power spectrum. Finally, an experimental validation was conducted based on an EHST system with 3 ton maximum force and 1.2 m × 1.2 m horizontal table. The results show that the proposed algorithms have greatly improved the effective bandwidth and the power level of the controlled system response can finally match the target power spectrum within an accuracy of ±3 dB. [ABSTRACT FROM AUTHOR]

This paper deals with optimization of the sizing, location and orientation of the piezo-fiber reinforced composite (PFRC) actuators and active vibration control of the smart composite plates using particle-swarm optimized self-tuning fuzzy logic controller. The optimization criteria for optimal sizing, location and orientation of the PFRC actuators is based on the Gramian controllability matrix and the optimization process is performed by involving the limitation of the plates masses increase. Optimal configurations of five PFRC actuators for active vibration control of the first six modes of cantilever symmetric ((90°/0°/90°/0°) S), antisymmetric cross-ply ((90°/0°/90°/0°/90°/0°/90°/0°)) and antisymmetric angle-ply ((45°/-45°/45°/-45°/45°/-45°/45°/-45°)) composite plates are found using the particle swarm optimization. The detailed analysis of influences of the PFRC layer orientation and position (top or bottom side of composite plates), as well as bending-extension coupling of antisymmetric laminates on controllabilities is also performed. The experimental study is performed in order to validate this behavior on controllabilities of antisymmetric laminates. The particle swarm-optimized self-tuning fuzzy logic controller (FLC) adapted for the multiple-input multiple-output (MIMO) control is implemented for active vibration suppression of the plates. The membership functions as well as output matrices are optimized using the particle swarm optimization. The Mamdani and the zero-order Takagi–Sugeno–Kang fuzzy inference methods are employed and their performances are examined and compared. In order to represent the efficiency of the proposed controller, results obtained using the proposed particle swarm optimized self-tuning FLC are compared with the corresponding results in the case of the linear quadratic regulator (LQR) optimal control strategy. • Optimization of placement, sizing and orientation of PFRC actuators on smart composite plates. • Analysis of influence of PFRC fiber orientation on controllability of composite plates. • Active vibration control of smart composite plates using self-tuning fuzzy logic controller. • Optimization of membership functions and output matrices using Particle swarm optimization algorithm. [ABSTRACT FROM AUTHOR]

• Generic problem of vibration distribution is formulated particularly targeting active control of vibration with both suppression and harvesting simultaneously. • Vibration distribution is considered for vibrating systems with a networked structure. • Active control is achieved via topology feedback. • Significant problem of solution existence is answered and used to probe performance limit. Vibration control and energy harvesting have been extensively investigated over the past decades. Recent engineering applications motivate a new requirement where vibrations are required to be distributed in a designated specification. This vibration distribution requirement represents a generic problem where both vibration control and energy harvesting need be brought in a par. This paper presents a systematic investigation to this important problem. Fundamental issues associated with vibration distribution under specifications, constraints handling, as well as dynamics and/or topology feedback designs etc are disseminated. Important results are obtained with extensive remarks providing guidance for applications. The corresponding claims are verified through numerical examples. [ABSTRACT FROM AUTHOR]

• Semi-active control technique of joint variable stiffness was proposed. • The joint mechanism exhibits compact structure, based on direct drive principle. • Joint torsional stiffness changes, and then frequency-shift phenomenon occurs. • The major frequency bandwidth of interference signal was 0.06–0.63 Hz. • The low frequency vibration of flexible appendages can be attenuated robustly. With the advancement of space technology, space flexible jointed appendages have been applied widely. The low-frequency vibration problem is inevitable because of the external disturbances or attitude maneuvering in micro-gravity environment. In this study, an innovative joint mechanism was proposed and a new methodology for semi-active technique of joint variable stiffness control was utilized to suppress the low-frequency vibration of flexible jointed appendages. The joint mechanism, based on the direct drive principle, exhibits a compact structure and integrates with an electro-permanent-magnet driving mechanism. First, the concept design of joint mechanism is introduced. Second, dynamic equations of active joint and two flexible plates are obtained using Lagrange equation and assumed mode method. Finally, two types of non-contact periodic vibration excitation methods along rotation direction are proposed. A self-made electro–magnetic vibration exciter was employed to achieve single-frequency excitation, and two fans were placed on both sides of flexible appendages to induce multi-frequency excitation. According to numerical simulations and experimental results, when the joint torsional stiffness changes, frequency-shift phenomenon occurs, and the natural frequency of the system varies subsequently. Furthermore, the experimental results demonstrated that the major frequency bandwidth of interference signal was 0.06–0.63 Hz with a significant vibration attenuation of 5.41–26.94 dB for joint-1 and 5.63–16.48 dB for joint-2 in effective bandwidth. The low frequency vibration of flexible appendages system can be attenuated robustly, which verifies the effectiveness of this semi-active methodology. [ABSTRACT FROM AUTHOR]

• This article addresses the adaptive inverse control of boring bar chatter in internal turning process. • The feedback Filtered-x Normalized Least Mean Square algorithm is implemented in practice. • The parameters of controller are obtained from impact tests, without a priori knowledge of cutting dynamics. • The feedback FxNLMS controller suppresses the self-excited chatter vibrations by at least 70 dBs. • The boundary of stability in internal turning process is raised by at least 10 folds. In this article, adaptive inverse control of chatter vibrations in internal turning process is addressed. The active boring bar is composed of a slender steel cutting tool, an electrodynamic shaker as controllable actuator and an IEPE accelerometer as feedback sensor. The SISO control system actuates in the direction normal to the cut surface. A novel adaptive inverse control algorithm is presented in this paper. This algorithm is mainly used in the feed-forward Active Noise Control (ANC) applications and is known as the Filtered-x Normalized Least Mean Square (FxNLMS). In order to extend the application of adaptive inverse control algorithms in the field of Active Vibration Control (AVC), the FxNLMS algorithm with feedback architecture is suggested for the specific problem of chatter suppression in internal turning operations. The performance of developed adaptive feedback controller is experimentally verified during the internal turning of Aluminum alloy 6063-T6. The value of critical limiting depth of cut is anticipated to be nearly 0.2 [mm] for the slender boring bar. However, the stable cutting process is conducted by the active boring bar in the presence of adaptive controller up to depth of cut 2 [mm]. That is, the boundary of stability is enhanced by at least 10 folds. It has been observed that the amplitude of chatter vibrations is efficiently suppressed adjacent to the fundamental resonance peak of the active boring bar. In addition, the feedback FxNLMS controller effectively attenuates the boring bar's vibration by at least 70 dBs. Moreover, the periodic chatter marks are eliminated from the surface texture of workpiece and the roughness of cut surface is remarkably improved. The obtained results suggest that the practical application of adaptive inverse control algorithms for chatter rejection can be extended to other machining processes as well. [ABSTRACT FROM AUTHOR]

In the present work, an efficient one-dimensional finite element (1D-FE) framework considering layerwise mechanics with full electro-mechanical coupling has been developed for the laminated smart sandwich beams submitted to active damping. Nonlinear constitutive relations of piezo-thermo-elasticity at large electric field with temperature-dependent material properties have been considered. The efficient layerwise theory (ELWT) considers the normal deformation of the piezoelectric sensing/actuating patches/layers due to the more significant value of piezoelectric strain coefficient d 33. The electric potential variation across the thickness of the PZT sensor/actuator has been assumed quadratic. The state space format of the dynamical system has been constructed based on a reduced order model in modal space. The feedback linearization approach has been applied to the nonlinear system of equations to design an equivalent linear optimal control strategy. An experimental facility has been developed to test the accuracy of the present nonlinear FE model. This facility consists of a thermal chamber with a heating system, air gun, actuation & sensing units with band-pass filters, a smart sandwich beam equipped with PZT-SP5H patches, a data acquisition system, and a computer with LabVIEW software. Open- and closed-loop responses from the present 1D-FE model have been compared with those obtained through experimentation at different temperatures. It has been observed that the current nonlinear FE model correctly captures the dynamic behavior of the vibrating smart sandwich beam at different operating temperatures and strong electric field. The study shows a strong dependence of the PZT materials on thermal chamber temperature and actuation field. New results for a smart sandwich beam are also presented to study the performance of PZT-SP5H patches as sensors/actuators for nonlinear active shape and vibration control in a thermal environment. The effect of piezoelectric actuator/sensor thickness, patch size, position, and applied mechanical load on the active shape and vibration control has been discussed. • Coupled FE formulation for nonlinear smart sandwich beam in thermal environment. • Nonlinear active control of vibration employing feedback linearization. • Experimental validation of the nonlinear FE model. • Effectiveness of PZT actuators in strong electric and thermal field. [ABSTRACT FROM AUTHOR]

Model uncertainties, external excitations and complex boundary conditions, etc. present in the control system lead to poor robustness of the controller. Therefore, an extended state observer (ESO) is utilized to compensate for these disturbances. However, a conventional ESO is not sufficiently capable to deal with rapid periodic disturbances. A frequency-shaped linear quadratic regulator (FSLQR) is, hence, developed by employing a frequency independent cost function according to the disturbance spectrum. In addition, knowing that periodic disturbances may have unknown or varying frequencies, a frequency-adaptive mechanism is introduced to address such issues, which enables the proposed method to mitigate the influences of frequency deviations. This is the first attempt to introduce frequency shaping technology into the control framework based on extended state observer. The control scheme of the introduced approach is general, but is conveyed here using solely an all-clamped plate structure with an inertial actuator, which is considered a typically benchmark for vibration phenomenon. The effectiveness and advantage of the proposed strategy are validated with comparative experimental studies on a hardware-in-the-loop laboratory testbed and a theoretical analysis based on Lyapunov theorem. Compared with the classical method based on ESO, the vibration experimental results demonstrate that the control performance of the first mode and the second mode are improved, both having upgraded approximately 6 dB. [ABSTRACT FROM AUTHOR]

Positive Position Feedback (PPF) is an active vibration control algorithm widely employed for the vibration mitigation of thin-walled structures equipped with active flexural patches. Fractional order PPF (FOPPF) is a recent development of PPF that has been shown to achieve substantially better spillover characteristics, thanks to the inclusion of fractional calculus. However, so far, FOPPF literature has focused almost exclusively on single-input–single-output (SISO) applications, with little consideration of multiple-input-multiple-output (MIMO) capabilities and no experimental work on the subject. To fill this gap, a MIMO FOPPF control architecture was tested numerically and experimentally on a cantilever composite sandwich beam of rectangular section. The feedback algorithm involved two piezoelectric actuators and two piezoelectric sensors in a collocated configuration for the control of the lowest four resonances of the beam, excited by a random external excitation. The participation matrices, necessary for the simulation of the response of the electromechanical system, were obtained with a recently developed experimental method. The fractional orders of derivation, together with other controller parameters such as gain, resonant frequency and damping ratio, were chosen according to an optimization algorithm aimed at the vibration amplitude reduction of the first four resonances of the controlled system. As a result, the performance of the vibration control resulted superior to the equivalent PPF with integer exponents, both in simulations and experiments. [ABSTRACT FROM AUTHOR]

[Display omitted] • A model-free vibration control strategy is examined. • New parameter tuning technique is constructed for the model-free controller. • The proposed tuning method is more efficient than a previous one. • The effectiveness of the present method is verified by experiments. In active vibration control, controller tuning is necessary to obtain a sufficient damping performance. This study presents an efficient tuning technique for model-free vibration controller based on a virtual controlled object (VCO). A model-free vibration control system is constructed by using an actuator model and the VCO. A reference controlled object (RCO), which is a designer-defined single-degree-of-freedom (SDOF) structure, is used to tune the VCO-controller offline. A novel parameter tuning technique based on the RCO and the simultaneous perturbation stochastic approximation (SPSA) is proposed considering the difference in scale of the tuning parameters. The proposed tuning scheme automatically determines the tuning parameter of the controller without manual trial-and-errors such as experiments with actual plants and is much faster than previous methods. Therefore, the proposed method significantly enhances the practicability of the VCO-based model-free vibration suppression, bridging the gap between the basic study of the VCO-method and its implementation. The effectiveness of the proposed method is verified by applying it to the VCO-based H 2 controller. [ABSTRACT FROM AUTHOR]

The use of Machine Learning (ML) has rapidly spread across several fields of applied sciences, having encountered many applications in Structural Dynamics and Vibroacoustic (SD&V). An advantage of ML algorithms compared to traditional techniques is that physical phenomena can be modeled using only sampled data from either measurements or simulations. This is particularly important in SD&V when the model of the studied phenomenon is either unknown or computationally expensive to simulate. This paper presents a survey on the application of ML algorithms in three classical problems of SD&V: structural health monitoring, active control of noise and vibration, and vibroacoustic product design. In structural health monitoring, ML is employed to extract damage-sensitive features from sampled data and to detect, localize, assess, and forecast failures in the structure. In active control of noise and vibration, ML techniques are used in the identification of state-space models of the controlled system, dimensionality reduction of existing models, and design of controllers. In vibroacoustic product design, ML algorithms can create surrogates that are faster to evaluate than physics-based models. The methodologies considered in this work are analyzed in terms of their strength and limitations for each of the three considered SD&V problems. Moreover, the paper considers the role of digital twins and physics-guided ML to overcome current challenges and lay the foundations for future research in the field. • Review of machine learning applied in vibroacoustic and structural dynamics. • Basic principles of the machine learning methods commonly used are presented. • Control, structural health monitoring and design are the most relevant applications. • The current implementation scenario and challenges are reviewed for each application. • This article sheds light on trends and research opportunities merging both fields. [ABSTRACT FROM AUTHOR]

Bistable structures exhibit a unique snap-through behaviour, which is widely used in different engineering disciplines. Some bistable systems have the ability to change dynamic characteristics such as the depth of the potential wells, distribution of the stable equilibrium points, and symmetry of the potential function, but only for the initial assembly. Therefore, this study presents a novel tunable electromagnetic bistable system (EBS), which can be adjusted online. An EBS is composed of a mechanical spring and an electromagnetic negative-stiffness unit in parallel. To characterise such a system, a static model was developed using the filament method, and the dynamic response was calculated using the harmonic balance method to better understand the EBS tunability. We conducted a series of studies aimed at revealing the effects of the geometric parameters, initial conditions, and excitation level on the dynamic characteristics. Finally, a switch between the interwell and intrawell oscillations of the actively tunable EBS was experimentally demonstrated, improving applications such as adaptive energy harvesting and active vibration control. [Display omitted] • A tunable electromagnetic bistable structure which can be controlled online is proposed. • The nonlinear dynamic characteristic is investigated by 5th HBM and numerical method. • The vibration mode can be switched between interwell and intrawell oscillation by adjusting the coils current. • The symmetry of potential function of the system can be adjusted online as needed. • The prototype is developed to verify the tunability. [ABSTRACT FROM AUTHOR]

Highlights • Developed two receptance-based methods for torsional receptance measurement. • Only a few receptances of the T-block and the coupled structure are required. • Successfully obtained high-quality torsional FRFs on a two-disc rotor-bearing rig. • Eliminated the appearance of bending resonances in the estimated torsional FRFs. • Incorporating the rotational accelerometer enhances the method's robustness. Abstract Identification of torsional receptances of shaft structures has been a challenge. This paper presents a method for measuring or estimating high-quality torsional receptances using two different methods based on the Receptance Decoupling Technique. In both methods, a T-block needs to be attached to facilitate the generation of torsion, and only the numerical receptance data of the T-block cast in a simple theoretical model and a few measured receptance data of the assembled system are required. Both methods are studied and assessed in numerical simulation, and the more robust method is further validated in experiments. The usage of rotational accelerometer is shown to significantly improve the quality of the estimation when the noise level is high. It is demonstrated that high-quality torsional receptances can be indirectly measured with high repeatability using the proposed method and thus can be used subsequently to identify torsional modal parameters, update finite element models, make structural modifications, or implement active torsional vibration control. Due to ubiquitous use of rotating machines, this novel method has significant applications. [ABSTRACT FROM AUTHOR]

Highlights • The implementation of multichannel adaptive active vibration control system is discussed. • A novel multichannel FXLMS algorithm with online secondary path modeling is designed. • New variable step-size and auxiliary noise power scheduling strategy are presented. • Details concerning experimental setup and piezoelectric smart plate are disclosed. • Vibration reduction of smart cantilever plate with a high convergence rate. Abstract Reducing the vibration of smart structures based on adaptive active vibration control (AAVC) has been extensively studied in recent years, because it is a light weight and effective method for reducing low-frequency structural vibrations. The multi-channel AAVC methodology based on the filtered-X least mean square (FXLMS) algorithm is widely implemented in active control applications owing to its self-adjustment ability to adapt to dynamically varying structures. In this paper, a new multi-channel FXLMS with online secondary path modelling (SPM) is designed based on the auxiliary random noise technique. Through a defined indirect error signal, the proposed variable step-size (VSS) strategies can ensure that every online SPM filter and every active control filter have their own exclusive step size to update the coefficients. Moreover, the proposed auxiliary noise power scheduling (ANPS) strategy can ensure that the variation rules of auxiliary noise power applied to different secondary paths are different. A complete multi-channel AAVC real-time experimental system based on NI compact RIO is set up to conduct the experimental investigation. A series of AAVC control experiments on a piezoelectric smart cantilever plate with PZT sensors and actuators are conducted to demonstrate the validity and efficiency of the proposed method. The experimental results show that the vibration of the smart cantilever plate could be effectively attenuated with a high convergence rate. The proposed methodology has an important advantage in applications where active vibration control of piezoelectric smart structures is required. [ABSTRACT FROM AUTHOR]

Highlights • A two-link flexible manipulator experimental apparatus is constructed. • A Takagi-Sugeno model based fuzzy neural network controller is investigated. • A generalized minimum variance self-tuning control algorithm is designed. • Experiments are conducted on vibration suppression using the designed schemes. Abstract This paper presents experimental investigations on active vibration control of a two-link flexible manipulator (TLFM), utilizing a generalized minimum variance self-tuning control (GMVSTC) and Takagi-Sugeno model based fuzzy neural network control (TS-FNN) schemes. The GMVSTC algorithm consists of an on-line identifier in the form of controlled autoregressive moving average model and a vibration control signal generator, and the TS-FNN control algorithm generates control actions taking full advantages of fuzzy logic controller and a neural controller. Experimental setup of the two-link flexible manipulator is constructed. Experimental comparison research on vibration attenuation is conducted during and after the motor motion, to verify the designed controllers. The effectiveness of the designed controllers is evaluated in terms of vibration suppression as compared to that of the classical PD control. The experimental results demonstrate that the designed controller can damp out both the large and the small amplitude vibration of a two-link flexible manipulator more quickly than that the traditional linear PD controller, especially for the small amplitude residual vibration. [ABSTRACT FROM AUTHOR]

This paper proposes a Model Reference Command Shaping (MRCS) approach for an effective vibration and oscillation control of multimode flexible systems. The proposed MRCS is designed based on a reference model and avoids the need for measurement or estimation of several modes of frequency and damping ratio as in the case of other input shaping and command shaping approaches. To test the effectiveness and robustness, the designed MRCS is implemented for oscillation control of a double-pendulum overhead crane. Simulations on a nonlinear crane model and experiments using a laboratory overhead crane are carried out under two cases, without and with payload hoisting. Without a prior knowledge of the system frequency and damping ratio, the MRCS is shown to provide the highest reductions in the overall hook and payload oscillations when compared to the multimode Zero Vibration and Zero Vibration Derivative shapers designed based on the Average Travel Length approach. In addition, the MRCS is more robust towards changes in the frequency during payload hoisting and changes in the payload mass. It is envisaged that the proposed method can be useful in designing effective vibration control of multimode flexible systems. [ABSTRACT FROM AUTHOR]

Noise legislations and the increasing customer demands determine the NVH (Noise Vibration and Harshness) development of modern commercial vehicles. In order to meet the stringent legislative requirements for the vehicle noise emission, exact knowledge of all vehicle noise sources and their acoustic behavior is required. The development of new analysis tools to investigate the vibroacoustic behaviour within vehicle development process is of essential importance to achieve better products in combination with time and cost reduction. This paper discusses the application of an experimental multi-point and multi-DOF energy flow analysis (EFA) methodology for the NVH assessment and ranking of vibro-acoustic sources. The methodology consists of two steps in which the system mobility matrix are obtained by direct measurements whereas the dynamic loads under operational conditions are obtained through an inverse procedure. A finite difference technique is used to distinguish between degrees of freedom. A practical example is given for a gearbox, for which the noise paths from the gears through the gear-supporting shafts and bearings into the gearbox housing has been experimentally assessed in terms of energy flows. This paper also discusses the accuracy and limits of the methodology. [ABSTRACT FROM AUTHOR]

Abstract This paper presents a disturbance feedforward control strategy for active vibration isolation systems that have internal isolator dynamics. The structure of the feedforward controller follows from modeling, but to achieve robust performance the tuning of the controller parameters will be based on measurement data. More specifically, the controller poles, which correspond to internal isolator dynamics, are obtained offline from system identification experiments, while the controller zeros are obtained from online self-tuning using measured sampled-data systems. Self-tuning is used to reduce parameter uncertainty when having too limited identification possibilities, and to account automatically for the effect of noise amplification. Measurement results obtained from an industrial vibration isolation system show that residual vibrations are largely reduced up to the level of output noise limitations. [ABSTRACT FROM AUTHOR]

Abstract The combination of adaptive feedforward with adaptive feedback disturbance compensation has been suggested since a number of years as a potential solution for improving the performance of active vibration control systems. Unfortunately, as shown in the present paper there is a strong coupling between adaptive feedback and adaptive feedforward which may lead to instabilities and new algorithms which take into account this interaction are proposed in the paper. These algorithms take advantage of the Youla-Kučera parametrization of the feedback controller and feedforward compensator. First, the adaptive feedback algorithm is presented alone. Then, the adaptive feedforward algorithm is designed taking into account the feedback controller's presence in the loop. Stability of the complete scheme is obtained by appropriately filtering the regressor vectors in order to take into account a strictly positive real condition. Experimental results obtained on a relevant test-bench illustrate the performance of this approach to active vibration control. Comparison with adaptive feedback alone, with adaptive feedforward alone and adaptive feedforward + fixed feedback are provided. [ABSTRACT FROM AUTHOR]

A decentralized simple adaptive control is proposed for the vibration suppression of large space structures (LSS) with distributed actuators and sensors. The LSS is viewed as a set of connected substructures so that the dynamic substructuring method can be applied to establish the equations of motion for the LSS. Then, extraction and contraction of the subsystems are performed to form the perturbed equations of motion for each substructure. An output feedback control law only requiring the information of the local sensors is designed based on the simple adaptive control method. The stability of the overall system is rigorously proven. [ABSTRACT FROM AUTHOR]

• A novel analysis method based on the complex-factor model is proposed to analyze the vibration characteristics of the MSB due to the unbalance terms, and the precise vibration models are established. • The cross-feedback control model using the complex-exponential function method is proposed to effectively control the low-frequency precession and the high-frequency nutation of the MSB. • In comparison to the commonly used complex-factor cross-feedback model, the proposed complex-exponential function cross-feedback model could further reduce the precession amplitude by 38.88%, and mitigate the nutation by 60.42%. The research of vibration characteristics and active control methods of the magnetically suspended blower (MSB) are conducted for mitigation of the vibration amplitudes and the dynamic displacements of rotor shaft of the MSB at high speed. Firstly, the dynamic models with four degrees of freedom (DOFs) of the rotor shaft in the MSB are established. Secondly, the vibration characteristics of rotor shaft considering the rotor unbalance and misalignment are analyzed using the complex-factor model. Furthermore, the complex-factor and complex-exponential function cross-feedback models are respectively used to suppress the vibration amplitudes and the dynamic displacements of rotor shaft. Both numerical simulation and experimental tests of the cross-feedback model are conducted to verify the models. It is shown that a wide cutoff frequency of low-pass filter (LPF) could mitigate the precession, and a wide cutoff frequency of high-pass filter (HPF) could suppress the nutation. The proposed complex-exponential function cross-feedback model could be used to reduce the precession amplitude of the rotor shaft by 38.88%, and mitigate its nutation by 60.42%. [ABSTRACT FROM AUTHOR]

• Use of the particle swarm optimization method to tune an active controller. • The active controller has 44 parameters to tune. • The controller is connected to a composite plate with 8 piezoelectric materials. • Experiments show an average vibration attenuation of 68.88% on the first 8 modes. • Experiments show a maximum attenuation of 90.0% on the 8th mode. The Particle Swarm Optimization (PSO) algorithm is employed to tune the Multiple-Input Multiple-Output (MIMO) Positive Position Feedback (PPF) controller to reduce vibrations on a composite sandwich plate with free boundary conditions, equipped with piezoelectric actuators and sensors. The PSO algorithm determines the value of forty-four parameters describing the transfer functions of the MIMO PPF controllers. The solution found by the PSO code depends on the cost-function employed. In this work, two cost functions are investigated. The first function minimizes the time necessary for free vibrations to decay to zero, while the second function minimizes the area under the resonance peaks of the frequency response of the controlled plate. For both cost-function cases, the parameters found by the PSO algorithm are determined through simulations based on a reduced-order model of the structure. Once the parameters are determined, they are loaded on a real-time prototyping board and employed to dampen the vibrations of the sandwich plate tested in laboratory experiments. The compatibility of simulations and experiments was verified at various points on the surface of the plate, and vibration reductions up to 90% of the uncontrolled amplitude were achieved experimentally for the first eight modes. The absence of spillover on following modes was verified in simulations and experiments. [ABSTRACT FROM AUTHOR]

Active control strategies have been widely used in micro-vibration isolation with higher performance requirements. Aiming at the problem of insufficient vibration isolation performance due to time delay in feedback control, the ground-based feedforward active control is introduced to compensate in advance for higher pursuit. However, the inaccuracy of the feedforward control reference model severely restricts the vibration isolation performance. With the assistance of RBF neural network algorithm for accurate real-time identification of online model, a feedforward-feedback dual-loop active hybrid control (DAHC) strategy based on the RBF-RLS adaptive algorithm is proposed in this paper. The adaptive feedforward control uses the RBF neural network algorithm to identify the accurate model of the system online, and input it to the transverse filter of the RLS adaptive control algorithm for recursive calculation, which can effectively reduce the system error caused by the inaccuracy of the model. The experimental results show that the accuracy of online model affects the amplitude attenuation performance by 57.1%. DAHC strategy can greatly reduce the resonance peak by 25.02 dB in micro-vibration. Real applicative experiment further proves the effectiveness of our proposed algorithm. [ABSTRACT FROM AUTHOR]

Acoustic coatings with periodically arranged internal cavities have been successfully applied in submarines for the purpose of decoupling water from vibration of underwater structures, and thus reducing underwater sound radiation. Previous publications on decoupling acoustic coatings with cavities are mainly focused on the case of coatings with specific shaped cavities, including cylindrical and conical cavities. To explore better decoupling performance, an optimal design of acoustic coating with complex shaped cavities is attempted in this paper. An equivalent fluid model is proposed to characterize coatings with general axisymmetrical cavities. By employing the equivalent fluid model, an analytical vibroacoustic model is further developed for the prediction of sound radiation from an infinite plate covered with an equivalent fluid layer (as a replacement of original coating) and immersed in water. Numerical examples are provided to verify the equivalent fluid model. Based on a combining use of the analytical vibroacoustic model and a differential evolution algorithm, optimal designs for acoustic coatings with cavities are conducted. Numerical results demonstrate that the decoupling performance of acoustic coating can be significantly improved by employing special axisymmetrical cavities as compared to traditional cylindrical cavities. [ABSTRACT FROM AUTHOR]

This paper presents a theoretical study on passive and active vibration isolation schemes using inerter elements in a two degree of freedom (DOF) mechanical system. The aim of the work is to discuss basic capabilities and limitations of the vibration control systems at hand using simple and physically transparent models. Broad frequency band dynamic excitation of the source DOF is assumed. The purpose of the isolator system is to prevent vibration transmission to the receiving DOF. The frequency averaged kinetic energy of the receiving mass is used as the metric for vibration isolation quality. It is shown that the use of inerter element in the passive vibration isolation scheme can enhance the isolation effect. In the active case, a feedback disturbance rejection scheme is considered. Here, the error signal is the receiving body absolute velocity which is directly fed to a reactive force actuator between the source and the receiving bodies. In such a scheme, the so-called subcritical vibration isolation problems exist. These problems are characterised by the uncoupled natural frequency of the receiving body larger than the uncoupled natural frequency of the source body. In subcritical vibration isolation problems, the performance of the active control is limited by poor stability margins. This is because the stable feedback gain is restricted in a narrow range between a minimum and a maximum. However, with the inclusion of an inerter in the isolator, one of the two stability margins can be opened. This enables large, theoretically unlimited negative feedback gains and large active damping of the receiving body vibration. A simple expression for the required inertance is derived. [ABSTRACT FROM AUTHOR]

Paraboloidal membrane shells of revolution are commonly used as key components for advanced aerospace structures and aviation mechanical systems. Due to their high flexibility and low damping property, active vibration control is of significant importance for these in-orbit membrane structures. To explore the dynamic control behavior of space flexible paraboloidal membrane shells, precision distributed actuation and control effectiveness of free-floating paraboloidal membrane shells with piezoelectric actuators are investigated. Governing equations of the shell structronic system are presented first. Then, distributed control forces and control actions are formulated. A transverse mode shape function of the paraboloidal shell based on the membrane approximation theory and specified boundary condition is assumed in the modal control force analysis. The actuator induced modal control forces on the paraboloidal shell are derived. The expressions of microscopic local modal control forces are obtained by shrinking the actuator area into infinitesimal and the four control components are investigated respectively to predict the spatial microscopic actuation behavior. Geometric parameter (height-radius ratio and shell thickness) effects on the modal actuation behavior are explored when evaluating the micro-control efficiency. Four different cases are discussed and the results reveal the fact that shallow (e.g., antennas/reflectors) and deep (e.g., rocket/missile fairing) paraboloidal shells exhibit totally different modal actuation behaviors due to their curvature differences. Analytical results in this paper can serve as guidelines for optimal actuator placement for vibration control of different paraboloidal structures. [ABSTRACT FROM AUTHOR]

This paper presents a theoretical study of an inertial actuator connected to an accelerometer by a local feedback loop for active vibration control on a floating raft. On the criterion of the minimum power transmission from the vibratory machines to the flexible foundation in the floating raft, the best mounting positions for the inertial actuator on the intermediate mass of the floating raft are investigated. Simulation results indicate that the best mounting positions for the inertial actuator vary with frequency. To control time-varying excitations of vibratory machines on a floating raft effectively, an automatic control system based on real-time measurement of a cost function and automatically searching the best mounting position of the inertial actuator is proposed. To the best of our knowledge, it is the first time that an automatic control system is proposed to move an actuator automatically for controlling a time-varying excitation. [ABSTRACT FROM AUTHOR]

In this paper, Active Vibration Control (AVC) of a rectangular carbon fibre composite plate with free edges is presented. The plate is subjected to out-of-plane excitation by a modal vibration exciter and controlled by Macro Fibre Composite (MFC) transducers. Vibration measurements are performed by using a Laser Doppler Vibrometer (LDV) system. A fractional-order Positive Position Feedback (PPF) compensator is proposed, implemented and compared to the standard integer-order PPF. MFC actuator and sensor are positioned on the plate based on maximal modal strain criterion, so as to control the second natural mode of the plate. Both integer and fractional-order PPF allowed for the effective control of the second mode of vibration. However, the newly proposed fractional-order controller is found to be more efficient in achieving the same performance with less actuation voltage. Moreover, it shows promising performance in reducing spillover effect due to uncontrolled modes. [ABSTRACT FROM AUTHOR]

Viscoelastic materials have played an important role in passive vibration control. Nevertheless, the use of such materials in supports of rotating machines, aiming at controlling vibration, is more recent, mainly when these supports present additional complexities like multiple degrees of freedom and require accurate models to predict the dynamic behavior of viscoelastic materials working in a broad band of frequencies and temperatures. Previously, the authors propose a methodology for an optimal design of viscoelastic supports (VES) for vibration suppression in rotordynamics, which improves the dynamic prediction accuracy, the speed calculation, and the modeling of VES as complex structures. However, a comprehensive numerical study of the dynamics of rotor-VES systems, regarding the types and combinations of translational and rotational degrees of freedom (DOFs), accompanied by the corresponding experimental validation, is still lacking. This paper presents such a study considering different types and combinations of DOFs in addition to the simulation of their number of additional masses/inertias, as well as the kind and association of the applied viscoelastic materials (VEMs). The results - regarding unbalance frequency response, transmissibility and displacement due to static loads - lead to: 1) considering VES as complex structures which allow improving the efficacy in passive vibration control; 2) acknowledging the best configuration concerning DOFs and VEM choice and association for a practical application concerning passive vibration control and load resistance. The specific outcomes of the conducted experimental validation attest the accuracy of the proposed methodology. [ABSTRACT FROM AUTHOR]

In the field of active noise and vibration control (ANVC), a considerable part of unwelcome noise and vibration is resulted from rotational machines, making the spectrum of response signal multiple-frequency. Narrowband filtered-x least mean square (NFXLMS) is a very popular algorithm to suppress such noise and vibration. It has good performance since a priori-knowledge of fundamental frequency of the noise source (called reference frequency) is adopted. However, if the priori-knowledge is inaccurate, the control performance will be dramatically degraded. This phenomenon is called reference frequency mismatch (RFM). In this paper, a novel narrowband ANVC algorithm with orthogonal pair-wise reference frequency regulator is proposed to compensate for the RFM problem. Firstly, the RFM phenomenon in traditional NFXLMS is closely investigated both analytically and numerically. The results show that RFM changes the parameter estimation problem of the adaptive controller into a parameter tracking problem. Then, adaptive sinusoidal oscillators with output rectification are introduced as the reference frequency regulator to compensate for the RFM problem. The simulation results show that the proposed algorithm can dramatically suppress the multiple-frequency noise and vibration with an improved convergence rate whether or not there is RFM. Finally, case studies using experimental data are conducted under the conditions of none, small and large RFM. The shaft radial run-out signal of a rotor test-platform is applied to simulate the primary noise, and an IIR model identified from a real steel structure is applied to simulate the secondary path. The results further verify the robustness and effectiveness of the proposed algorithm. [ABSTRACT FROM AUTHOR]

Miniaturized vibrating MEMS devices, active (receivers or emitters) or passive devices, and their use for either new applications (hearing, meta-materials, consumer devices,…) or metrological purposes under non-standard conditions, are involved today in several acoustic domains. More in-depth characterisation than the classical ones available until now are needed. In this context, the paper presents analytical and numerical approaches for describing the behaviour of three kinds of planar micro-beams of rectangular shape (suspended rigid or clamped elastic planar beam) loaded by a backing cavity or a fluid-gap, surrounded by very thin slits, and excited by an incident acoustic field. The analytical approach accounts for the coupling between the vibrating structure and the acoustic field in the backing cavity, the thermal and viscous diffusion processes in the boundary layers in the slits and the cavity, the modal behaviour for the vibrating structure, and the non-uniformity of the acoustic field in the backing cavity which is modelled in using an integral formulation with a suitable Green's function. Benchmark solutions are proposed in terms of beam motion (from which the sensitivity, input impedance, and pressure transfer function can be calculated). A numerical implementation (FEM) is handled against which the analytical results are tested. [ABSTRACT FROM AUTHOR]

Active control of structural sound radiation is a promising technique to overcome the poor passive acoustic isolation performance of lightweight structures in the low–frequency region. Active structural acoustic control commonly aims at the suppression of the far–field radiated sound power. This paper is concerned with the active control of sound radiation into acoustic enclosures. Experimental results of a coupled rectangular plate-fluid system under stochastic excitation are presented. The amplitudes of the frequency-independent interior radiation modes are determined in real-time using a set of structural vibration sensors, for the purpose of estimating their contribution to the acoustic potential energy in the enclosure. This approach is validated by acoustic measurements inside the cavity. Utilizing a feedback control approach, a broadband reduction of the global acoustic response inside the enclosure is achieved. [ABSTRACT FROM AUTHOR]

The effectiveness of common algorithms for feedforward compensation of narrowband disturbance depends mainly on the model quality. To avoid this dependency several direct adaptive control algorithms without explicitly identified secondary path models have been developed over the last years. However an overview of their properties and a comparison of their performances in a standardized benchmark is still lacking. In this paper the three most promising algorithms are modified for narrowband feedforward vibration control for the use in rotating machinery. As in this application the reference signal is generated using the frequency measurement from a speed sensor it can be assumed that there is no coupling between reference measurement and the secondary path. First the algorithms are tested in simulation, then they are implemented on a test rig for active vibration control of unbalance induced rotor vibration. In simulation as well as for the test rig the performances of the algorithms are compared to each other. Advantages and drawbacks of the algorithms are discussed and practical instructions for implementation are given. The work is intended to serve as starting point and motivation for future research in this field of study. [ABSTRACT FROM AUTHOR]

Vibroacoustical systems as well as their behavior are coupled by nature. However, it may be of first interest for engineers to work on decoupled models, so that behavior of the structural/acoustic sub-system can be easily predicted and investigated. This work focuses on a virtual decoupling approach for vibroacoustics, with the objective to reconstruct decoupled and reduced system matrices from coupled experimental measurements. As a promising identification technique, the properness enforcement method has been developed in the literature for both symmetric and non-symmetric systems. During the decoupling process, however, this methodology still needs to be improved from two aspects: 1) the introduction of an additional correlation process so that the structural/acoustic sub-model can be correctly extracted from the coupled system; and 2) the additional optimization step after the complex vectors are approximately corrected by the properness enforcement method. These two key points are addressed by an integrated framework containing three aspects (i.e. identification, optimization, and correlation), which are specially designed for vibroacoustical applications. The finally identified system matrices of a decoupled and reduced equivalent system can exhibit the same behavior as the experimentally measured one. A simulated example is first presented to illustrate the use of this approach in detail. Then an experimental case study is used to demonstrate its feasibility in engineering applications. [ABSTRACT FROM AUTHOR]

High-performance vibration control is always preferred for cable structures that are inherently flexible and susceptible to dynamic excitations. Among different control categories, active control generally surpasses the other types of control (i.e., passive, semi-active, etc.) in terms of control performance. However, its large energy consumption and the potential instability concern hinder its wide-spread applications in relevant fields. In this regard, we propose a novel power-oriented adaptive self-powered active control system to address these concerns without compromising active control performance. In particular, this study explores the full potential of the newly proposed system analytically and numerically via a case study of a 135 m full-scale bridge cable. Moreover, its control performance is meticulously compared with that of an emerging passive controller, namely, an optimal inerter damper. Simulation results confirm that the proposed system successfully realized a considerably enhanced and broadband vibration mitigation performance than an optimal inerter damper without requiring an external energy supply. Slight modifications to the setup can further enable an easy transfer to other applications, shedding light on its promising future. [ABSTRACT FROM AUTHOR]

Positive Position Feedback (PPF) is one of the leading algorithms for the active suppression of the mechanical vibrations of thin-walled structures. The ease of integration with piezoelectric patches and its modal characteristics are among its main assets. In Multi-Input Multi-Output (MIMO) architectures, however, the passage from the physical signals of piezoelectric transducers to modal coordinates is required; this is achieved by placing participation matrices between sensors, controllers and actuators. The determination of these matrices is non-trivial, especially when the number of actuators is different from the number of modes to be controlled. Usually, the construction of an electromechanical Finite Element (FE) or reduced-order model is required to estimate the participation matrices. In this work, a method for the estimation of the participation matrices based on experimental measurements only is proposed. For the sake of generality, a bidimensional structure – a composite plate – with free edges (and thus with rigid body motions) was considered, and the vibration of eight vibration modes was suppressed by using four sensors and four actuators, in a non-collocated configuration. The simplified experimental identification of the electromechanical coupling allowed the numerical simulation of the uncontrolled and controlled vibrations of the plate when the latter was subjected to an external disturbance. The resulting PPF AVC achieved a reduction of several decibels in the vibration amplitude of all the eight modes under consideration, with negligible spillover over the following normal modes in laboratory experiments. The vibration reduction was verified in correspondence of several points across the surface of the plate in presence of a pseudo-random excitation. The proposed experimental identification technique simplifies considerably the design of PPF controls, eliminating the need for electromechanical modeling and opening the door to a more widespread use of Active Vibration Control (AVC) techniques. [ABSTRACT FROM AUTHOR]

We consider the stability analysis and controller design for a novel active vibration suppression technique, what we call the fractional-order delayed resonator (FODR), to suppress the oscillations from a single-degree-of-freedom mechanical structure. The parameterized control formulas for the associated gain and delay are firstly proposed. Then, an analytical procedure is presented to perform the complete stability analysis for the FODR alone and the coupled system. For practical implementation, the fractional feedback controller is realized by an integer-order approximate transfer function. Then, we introduce a novel control strategy named "order scheduling", which treats the order as a tunable parameter, to enhance the control flexibility. The results show that this powerful technique can widen the feasible frequency band, improve the vibration control speed, and enhance the stability robustness of the system. Finally, three numerical cases show the viability of the proposed scheme. • A new active vibration control strategy by fractional-order delayed feedback. • Cancellation the integer-order restriction on feedback for the delayed resonator. • Stability analysis for the feasible frequency map and stability robustness. • Enhancement of vibration-absorption performance by the order scheduling control. [ABSTRACT FROM AUTHOR]

The challenge of inducing stable and robust nonreciprocal transmission of sound is seen as an important milestone on the path towards developing active acoustic metamaterials. Structures that can transmit sound or vibration in a nonreciprocal manner may be considered analogous to an electrical diode and could be useful in many applications, such as noise control and the development of invisible acoustic sensors and acoustic cloaking. This paper focuses on conceptual development and experimental validation of an active metamaterial cell that does not obey the reciprocity principle. The structural cell considered, when activated, significantly attenuates vibration transmission through it in one direction and increases it in the opposite direction. The effect is present in a broad frequency band. The loss of reciprocity is induced by using two concurrent velocity feedback loops with non-collocated sensor-actuator pairs. Inertial accelerometers with time-integrated outputs are used in conjunction with miniature electrodynamic force actuators. The study is first carried out theoretically, using an electromechanically fully coupled lumped parameter model of an otherwise flexible active structure. The derived model is used to conduct analysis of the control system stability and performance. Given that a non-collocated transducer arrangement is considered, special attention is paid to the selection of parameters of the passive system which ensure satisfactory gain margins when the system is made active. In fact, criteria for unconditional stability are derived analytically, in terms of two simple inequalities for the system with idealised sensor-actuator pairs. For realistic transducers, however, unconditional stability is not possible. Nevertheless, if the two inequalities are respected, useful gain margins of the active system can be expected. This is validated experimentally using a dedicated 3D-printed measurement test rig. A substantial reduction of vibration transmission in the desired direction, accompanied by an increase in the opposite one, is recorded experimentally. These results suggest that the control scheme proposed could be used to design an active acoustic metamaterial, which would enable the significantly different transmission of sound depending on the direction it enters such a system. [ABSTRACT FROM AUTHOR]

Active vibration control of flexible structures has received considerable attention in the latest decades. However, several related control problems remain open to new investigations such as robust performance, spillover instability, and structural changes due to damage. Specifically in the case of damage, it may significantly aggravate closed-loop performance. Damage-tolerant active control is a recent research area that includes structural damage effect reduction in the controller design requirements. This paper presents a novel control method based on a modal double-loop controller design, aiming for vibration reduction of noncollocated flexible structures subject to damage and encompassing online reconfigurability. The first controller is designed for the healthy system in order to comply with predefined performance and robustness requirements, based on modal H ∞ norm. The second controller complements the closed-loop performance if the structure is damaged. A reconfigurable modal technique is adopted to design the second controller, using online modal structural parameter change information to update the controller. To assess the proposed method, finite element models are developed for a case study structure, including health and damage conditions. Results show the effectiveness of the methodology along with performance improvement compared to single-loop controllers based on regular H ∞ and modal H ∞ approaches. [ABSTRACT FROM AUTHOR]