Journal of Sound and Vibration最新文献

In the active control literature, the question of how to objectively and comprehensively compare system performance has received little attention. In most cases, comparisons are only made on a paper-specific application and cannot be extended to new cases. A unified method for intensive comparison of algorithm performance is proposed in this work. It is based on the definition of 9 indicators, aiming to quantify the speed of the control and its ability to reduce energy in the desired frequency range, without amplifying energy outside this range. Two descriptors describe the performance in the transient regime and the others describe the steady state performance of the control. The algorithms used to estimate these indicators are designed to rely on a small number of parameters and to be as robust as possible. Then, a procedure to get a satisfactory index from these indicators is provided. This procedure adapts to the user’s needs by allowing him to choose the test signals and to adjust the weighting of the indicators in the calculation of the satisfactory index. Two feedforward adaptive control algorithms for vibration cancellation are compared using this method. The first is the well-known Filtered-x Least Mean Square (FxLMS) and the second is based on a central controller using the Youla–Kučera parameterisation. Test signals are recorded from an experimental test bench consisting of a cantilever beam driven by a vibration shaker at one end and controlled by an actuator at the other end. The results show that the proposed descriptors can be used to quantify known behaviours such as the waterbed effect. They also show that neither of the two algorithms tested can be considered inherently better, as the procedure can recommend one or the other depending on the user’s requirements. Unlike other methods previously published, the evaluation protocol proposed in this paper is designed to enable the performance of a wide range of active control algorithms to be compared and quantified, whatever the application.

Dynamical systems with high damping efficiency in a wide frequency band can be useful on a small scale – for harvesting energy from ambient vibrations, and on a large scale – for damping harmful vibrations of mechanical structures. In this paper we present an assessment of the quality of solutions and damping efficiency of systems with fractional order derivatives. To simulate the fractional system the fourth-order Runge–Kutta method and Grünwald–Letnikov methods are used. We propose a coefficient for assessing the quality of solutions to fractional systems by reference to the quality of the calculated energy balance. As an exemplary system we study the Duffing model with embedded additional fractional-order derivative terms. Based on this coefficient, intervals of key numerical simulation parameters are determined to ensure the appropriate quality for the calculations of energy flows and energy balance. The determined values of these parameters are then used in tests of the damping efficiency of the studied system. Our results show that by modifying the fractional terms it is possible to configure a system that exhibits a “broadband effect”, i.e. a system that is characterized by high-amplitude vibrations and, consequently, high energy efficiency in a wide range of excitation frequencies.

Protecting seismic isolated equipment or buildings in a near-fault area is challenging because of the strong long-period velocity components of near-fault ground motions. These long-period pulses can cause excessive base displacement of conventional seismic isolation systems. In this study, an electromagnetic seismic isolation system with flywheels (EMSIS-FW) was experimentally investigated to reduce the base displacement of isolation systems during near-fault earthquakes. The EMSIS-FW consists of a sliding platform and rotary electromagnetic (EM) dampers, which can provide an EM damping force. With an additional flywheel installed on each EM damper, its moment of inertia can offer a considerable inertance for the EMSIS-FW. The inertance generated by the flywheel can be hundreds of times larger than its mass. Accordingly, the isolation frequency can be adjusted using different-sized flywheels. A prototype EMSIS-FW was designed and manufactured. A theoretical model was also developed to predict its dynamic behavior. Through shaking table tests, this study provided experimental verification of the effectiveness of inertance on isolation systems subjected to near-fault ground motions. The experimental results indicate that an increase in inertance reduces the isolation displacement, but it may increase the isolation acceleration during a typical far-field ground motion. In addition, the accuracy of the theoretical model was verified using the shaking table test.

Hybrid membrane resonator (HMR) as a typical metamaterial-based absorber with acoustic hard boundary condition (AHBC) has demonstrated excellent noise absorption abilities, but the challenge lies in achieving broadband absorption of ultralow-frequency noise in the tens of Hz to 150 Hz regime. In this research, we investigate systematically the absorption characteristics, absorption mechanisms, and casual optimality of an HMR with three openings in lower surface of the cavity, which functioned as an acoustic soft boundary condition (ASBC). Compared to the well-studied HMR with AHBC, a new absorption mechanism, which states that most energy dissipates occur in the opening region rather than in the membrane, has been found first. As a result, the HMR with ASBC can demonstrate outstanding ultralow-frequency sound absorption performance with a very small thickness, and the full width at half maximum of the HMR can be enlarged over 7 times. Furthermore, the causal inequalities of the absorbers with ideal AHBC and ASBC are derived based on the Cauchy integral and causality principle. The causal optimality of the proposed absorber is also achieved. This research provides valuable guidelines for the design of excellent ultralow-frequency sound absorbers which could contribute to solving the major issue of noise reduction.

The identification of mode shapes of structures through Operational Modal Analysis (OMA) often requires the application of data merging techniques to compensate for the lack of information on mode shapes scaling factors, which is inherent in OMA. In this paper, we propose a novel mode shape identification approach for structures having planes with rigid-like behavior, such as steel or reinforced concrete buildings with rigid floors. The approach is based on a theoretical model that generalizes the mechanical features of the structures under considerations. We show that the mode shapes of the model can be reconstructed starting from two components, i.e., modal centers of rotation and modal rotations; modal rotations depend on scaling factors of mode shapes, while modal centers of rotation turn out to be invariant with respect to mode shape scaling. Afterwards, we develop a method for identifying modal centers of rotation and modal rotations from experimental data, and then for reconstructing mode shapes. Numerical experiments have been performed to assess the capability of the approach with respect to a structural specimen having known modal properties. Compared with classic merging techniques, our approach enables a significant simplification of the experimental setup and a deeper analysis of mode shapes.

As a critical component in turbomachinery, such as aero-engines, bladed disks frequently experience mistuning due to various factors, leading to localized vibrations and increased risk of high-cycle fatigue. To enable online mistuning identification and dynamic response prediction of rotating bladed disks, this paper proposes a variable-speed reduced order model (VSROM) that accounts for varying rotational speeds and a response-based mistuning identification method. By parameterizing the stiffness matrix of the bladed disk as a polynomial and assuming the tuned system's mode shapes are minimally affected by speed, the VSROM can be developed using the Component Mode Mistuning method. Additionally, leveraging the VSROM, a response-based mistuning identification method is proposed, capable of identifying mistuning at any speed. The effectiveness and accuracy of the VSROM and mistuning identification method are validated through numerical simulations. The dynamic response of the mistuned system is predicted using the VSROM, and the results are compared with those obtained from the existing reduced order model that accounts for varying speeds, as well as from the full-order finite element model. The results demonstrate that the proposed VSROM offers superior prediction accuracy and computational efficiency. Moreover, mistuning identification at different speeds shows good agreement with the actual mistuning values. The proposed VSROM and mistuning identification method hold significant potential for online vibration monitoring of rotating bladed disks.

An automatic ball balancer (ABB) is a device that is used to automatically balance an eccentric rotor; these are typically used in rotary machines with unknown or variable imbalances. The typical construction of an ABB consists of several balls in a ring race. The balls can move freely inside the race, which changes the eccentricity radius and phase angles relative to the rotor. The automatic balancing process requires an ABB unit to be installed on an eccentric rotor's axis; thus, its application is quite limited and usually requires the redesign of a rotary machine. This paper presents a new method for eliminating vibrations in rotary machines by using multiple ABBs that are mounted away from the rotor's axis. In this application, ABBs can be considered to be unbalanced rotary masses with adjustable eccentricity radii and phases. Theoretically, this ability allows for the total reduction of the inertial force from an eccentric rotor; however, the parameters of the ABBs must be set correctly. The process of setting the eccentricity radius and phase in each ABB occurs due to a self-synchronization phenomenon and generally depends on the physical parameters of either a rotary machine or ABBs. Both analytical and numerical investigations that were based on the mathematical model of a system of a rotary machine with a pair of ABBs allowed us to formulate basic rules to apply such a system in existing rotary machines without interference on the rotors.

Quasi-zero stiffness (QZS) isolators can effectively suppress low-frequency vibration due to high-static-low-dynamic stiffness (HSLDS) characteristics. The existence of nonlinearity induces intricate nonlinear phenomena in QZS isolators, particularly under conditions of small damping and large excitation. These nonlinear characteristics can seriously affect the vibration isolation performance, which has rarely been focused on in existing studies. This study examines a typical QZS isolator with nonlinear damping. The modified incremental harmonic balance (IHB) method is applied to directly analyze its dynamic characteristics and investigate the suppression of the subharmonic response. The dynamic analysis results indicate multiple subharmonic vibration intervals, including the 1/2, the 1/3, and the 1/9 subharmonic vibration. The basin of attraction at different excitation frequencies shows that subharmonic vibration is highly likely to occur. The effect of different damping on the transmissibility proves to be different. Simultaneously, rational parameter matching can guarantee the absence of subharmonic vibration while maintaining the primary resonance frequency and amplitude unchanged. The research results of this study provide theoretical support for the parameter selection of QZS isolators. In addition, the higher-order approximations of most isolators have the same form, so these results can guide other QZS isolators in suppressing subharmonic vibrations and improving their operating range.

The dynamic performance of maglev vehicle-bridge coupled systems subjected to random guideway irregularity, especially the levitation stability of the running vehicle subsystem, is a critical issue affecting the safe operation and the comfort riding of maglev railways. This study is devoted to stochastic optimization of the levitation control system considering the coupled vibration of maglev vehicle and bridge under the random guideway irregularity. To alleviate the computational burden in the stochastic optimization process, the explicit expressions of the critical responses of the maglev vehicle-bridge coupled systems and the sensitivities of critical responses with respect to the feedback gains of the proportional-integral-derivative (PID) levitation controller are respectively constructed in terms of the guideway irregularity by virtue of the dimension-reduced formulation capability of the explicit time-domain method (ETDM), enabling stochastic dynamic analysis and stochastic sensitivity analysis to be executed at high efficiency. The stochastic optimization problem is formulated as the minimization of the standard deviation of the air gap variation with the constraint on the standard deviation of the current variation, and the optimal values of the PID gains are searched by the gradient-based method of moving asymptotes (MMA), in which the statistical moments and moment sensitivities of the critical responses required in the optimization process are obtained by ETDM. A numerical example with a 2-degree-of-freedom maglev vehicle moving on a multi-span simply-supported bridge is used to demonstrate the efficacy of ETDM for the stochastic analysis of maglev vehicle-bridge coupled systems under guideway irregularity. An engineering example involving a 3-car maglev train traversing a multi-span simply-supported bridge is further presented to show the effectiveness of the ETDM-based approach for the stochastic optimization of large-scale engineering problems. The levitation stability of the maglev train under the action of random guideway irregularity is considerably improved with the use of optimal feedback gains.