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This paper presents a simulation method that is used to study subcritical vibrations of a tube roll in a paper machine. This study employs asymmetric 3D beam elements based on the Timoshenko beam theory. An asymmetric beam model accounts for varying stiffness and mass distributions. Additionally, a detailed rolling element bearing model defines the excitations arising from the set of spherical roller bearings at both ends of the rotor. The results obtained from the simulation model are compared against the results from the measurements. The results indicate that the waviness of the bearing rolling surfaces contributes significantly to the subcritical vibrations while the asymmetric properties of the tube roll have only a fractional effect on the studied vibrations. [ABSTRACT FROM AUTHOR]

• The influence of machining vibration and process parameter on the surface roughness is considered in the prediction model. • Highly correlated features to surface roughness are extracted using combined GRA and MIC. • Extreme learning machine algorithm with high accuracy and efficiency is applied to predict the machined workpiece surface roughness. • The predictive surface roughness at the entire processing area is achieved by the proposed method. Surface roughness of mechanical parts plays an essential role in the practical application. Due to the complexity of the machining process, establishing a comprehensive theoretical model that can accurately simulate the real machined surface is challenging. Therefore, data-driven prediction methods are both practically useful and scientifically sound. This paper proposes an approach of using extreme learning machine (ELM) to predict surface roughness based on the monitored vibration signals, which can achieve the prediction of the surface roughness at any position of the machined surface, rather than using a single value to evaluate the processing quality under specific situations. To ensure the accuracy of the vibration intensity representation, the amplitude of monitored signals is compensated, accounting for varying positions and timings. The linear relationship between the spindle speed and acceleration is investigated to mitigate the impact of machining parameters on the monitored acceleration. Combined with grey relational analysis and mutual information coefficient, 18 features substantially linked to the surface roughness are selected from all extracted features and then used as the inputs for an ELM-based predictive decision-making system. The results indicate that the average and minimum errors of the developed method are 5.09% and 1.03%, respectively, demonstrating its accuracy and feasibility. In contrast to other machine learning models of SVR and ANN, the proposed method in this paper exhibits optimal predictive precision and efficiency, suggesting its potential application in the fast response of quality control. [ABSTRACT FROM AUTHOR]

• The precise parameters transfer matrix method exhibits excellent accuracy and applicability. • The effect of moment of inertia on the band calculation accuracy is smaller than that of shear deformation. • Both Young's modulus difference and density difference jointly affect the bandgap characteristics. • The appropriate axial wall pressure is beneficial for the low-frequency broadband design. The phononic crystal theory provides a novel approach for effectively controlling the bending vibrations in fluid-filled pipelines. This paper innovatively proposes the precise parameters transfer matrix method to investigate the band calculation accuracy and bandgap characteristics of fluid-filled periodic pipelines with various beam types. Firstly, the differential equations for bending vibration of fluid-filled pipelines are established based on deformation and force analysis. The parameters of the system state are precisely represented by the structural form of multiplying the constitutive matrix with the derivative matrix. Combined with Bloch's theorem, the novel precise parameters transfer matrix method for calculating the band structure is proposed. Secondly, the validity of this method is verified through a comparison with finite element simulation results. A detailed analysis is provided regarding the mechanism of bandgap formation and the effect of fluid filling on the band structure. Then, the influence of shear deformation, moment of inertia, and their coupling on the band calculation accuracy for fluid-filled periodic pipelines is studied based on various beam theories. Finally, it delves into the bandgap characteristics of fluid-filled periodic pipelines under different material parameters, structural parameters, and excitation conditions. This research offers valuable insights for the structural design and vibration damping application in fluid-filled periodic pipelines, providing theoretical support for accurately determining their bandgaps. [Display omitted] [ABSTRACT FROM AUTHOR]

• A control method based on the non-simplified equations of motion of the lattice sandwich structures with considering the effects of the sensors and actuators is established. • The effects of active feedback control on the band-gaps of the pyramidal core lattice sandwich structures based on the non-simplified equations of motion are investigated. • The results show that the proposed simple control strategy is sufficiently accurate, highly efficient and can significantly expand the band-gaps. In this paper, we propose a simple active adaptive feedback (AAF) control strategy to enhance the vibration mitigation and isolation properties of the conventional pyramid-core lattice sandwich structures (PSSs) and the modified chessboard-designed pyramid-core lattice sandwich structures (CPSSs) via the lead zirconate titanate (PZT) ceramic patches. The proposed simple AAF control strategy is based on the active feedback (AF) control by relating the AF control parameters to the frequency. Firstly, the effects of the AF control parameters on the band structures are analyzed. Subsequently, the mathematical expressions of the frequency-dependent AAF control parameters are derived by the curve fitting technique. The results show that the proposed simple AAF control strategy is sufficiently accurate, highly efficient and can significantly expand the band-gaps compared to the conventional AF control, hence leading to improved vibration mitigation and isolation properties of the PSSs and CPSSs. The proposed simple AAF control strategy provides a simplified and generalized method to enhance the vibration mitigation and isolation properties of the lightweight lattice sandwich structures (LSSs) while maintaining their high stiffness-to-density ratio, which may offer various potential applications in engineering sciences. [ABSTRACT FROM AUTHOR]

Fatigue Damage Spectra (FDS) and Extreme Response Spectra (ERS) are well-established tools for characterizing and evaluating the impact of vibration loads on mechanical structures. While this is particularly valuable in producing test-tailored specifications, their current application is limited to uniaxial analysis despite evidence indicating their inadequacy in representing real-world loads, which are often multiaxial. The proposed method offers a system-oriented approach to characterize and compare multiaxial environments in terms of their severity, independently or not of any physical structure. In addition, it introduces a generalization of the FDS and ERS, referred to as Fatigue Damage multi-Spectrum (FDmS) and Extreme Response multi-Spectrum (ERmS) respectively. These extensions allows for the consideration of multiaxial phenomena, such as correlation and modal proximity. Finally, this paper demonstrates through several case studies the method's capability to capture phenomena not addressed by established uniaxial approaches. [ABSTRACT FROM AUTHOR]

• This paper proposes a particle damping equivalent method based on force chain for simulating the behavior of PD. • The newly proposed method considers the contact between particles and the motion state of particles. • The shaking table test and corresponding numerical simulation are conducted under high-frequency vibration condition. • The effectiveness and superiority of the method are demonstrated and the particle motion state is confirmed. A particle damping equivalent method based on force chain is newly proposed for simulating the behavior of particle damper (PD) with higher accuracy. Compared with other existing equivalent methods, this method considers the contact between particles and evaluates the particle motion state. Firstly, the particle damping equivalent method based on the theory of force chain and contact model is proposed, and the simulation process of the equivalent method is described. Then, this equivalent method is adopted to simulate the high frequency vibration of pipe installed with PD using SAP2000 software. The simulated vibration response exhibits excellent agreement with experimental results, validating the effectiveness of the proposed equivalent method. Finally, based on the calculation results, it is observed that the particle motion state of the PD in the experiment is quasi-static. This further shows that the particle chain in the damper under high frequency vibration can ignore the wave propagation behavior, which aligns with the assumption of the particle contact model. [ABSTRACT FROM AUTHOR]

Vibratory offshore pile driving offers a potential solution for reducing the underwater noise generated during the installation of foundation piles compared to using impact hammers. Existing noise prediction models are specifically tailored to impact pile driving scenarios. This paper introduces a novel methodology for underwater noise predictions during vibratory pile driving. A non-linear driveability model is utilised to derive realistic non-linear interface friction forces, which are then incorporated into a noise prediction model. The study emphasises the significance of integrating a driveability analysis, revealing substantial differences from traditional models that assume perfect contact between the pile and soil. The authors argue that the proposed model provides more realistic outcomes when considering smooth driving without refusal, in contrast to traditional models designed for impact piling. The results illustrate noticeable deviations in pressure levels and seabed vibrations between the linear and presented methods at the driving frequency and its superharmonics. Furthermore, the research demonstrates that the noise field is highly sensitive to variations in system dynamics and excitation spectrum during driving, using both small- and large-diameter monopiles as examples. This research contributes to developing more effective driving techniques to reduce underwater noise pollution and facilitate sustainable offshore wind turbine installations. • Underwater sound predictions for offshore vibratory pile driving. • Non-linear friction interface forces describing pile–soil interaction. • Importance of accurate pile–soil interface friction modelling on underwater noise. • Utilising a driveability model for underwater noise predictions. • Underwater noise field comparison with linear models. [ABSTRACT FROM AUTHOR]

A washing machine is a household appliance that has an interesting and complex dynamical behavior, which can be well described by a set of nonlinear differential equations. When analyzing the dynamics of a washing machine, the steady state motion (periodic solution) is an important response to consider and can be evaluated as a solution of a periodic boundary-value problem. The unbalance generated by the unevenly distribution of clothes during centrifugation is highly random and, therefore, a stochastic model is necessary to take this characteristic into account. The novelty of this paper consists in the analysis of a washing machine dynamics considering the uncertainty in the unbalance. Therefore, a stochastic model is proposed for the dynamics of a washing machine. The steady state solutions are calculated using the shooting method combined with a sequential continuation to evaluate it across all the spin speeds of the machine. The probability distributions of the washing machine vibration at those different spin speeds are approximated using Monte Carlo simulations. The impact of the random unbalance in the vibration amplitude of the washing machine is also investigated and consists in a key input for the fatigue design of many components. [ABSTRACT FROM AUTHOR]

The paper deals with a novel design and investigation of a compact six degrees of freedom active vibration absorber with six identical eigenfrequencies. The objective is to entirely suppress vibration of a machine structure with six motion components, three translational and three rotational. The geometry of the spatial unifrequency absorber is based on a Stewart platform structure equipped with six active legs. Variants of this structure are analyzed. The six identical eigenfrequencies are finally reached by exerting active forces by actuators in the absorber legs, which actually produce active negative torsional stiffness. Achieving the unifrequency absorber with the help of a correction feedback brings variability to an optimization of the absorber design solution. In the next step, an active delayed resonator feedback is implemented to compensate the damping and to correct stiffness imperfections of the legs. The overall concept and design procedure are validated on a simulation case study including spectral analysis of arising infinite-dimensional system. • Compact six degrees of freedom active vibration absorber developed. • Stewart platform structure with springs and voice-coils used. • Mechanical properties, correction feedback and time delayed feedbacks optimized. • Absorber entirely suppress fully spatial vibrations of the primary structure. [ABSTRACT FROM AUTHOR]

Machine tool vibrations impose severe limitations on industry. Recent progress in solving for the stability behavior of delay differential equations and in modeling milling operations with time delay differential equations has provided the potential to significantly reduce the aforementioned limitations. However, industry has yet to widely adopt the current academic knowledge due to the cost barriers in implementing this knowledge. Some of these cost prohibitive tasks include time-consuming experimental cutting tests used to calibrate model force parameters and experimental modal tests for every combination of tool, tool holder, tool length, spindle, and machine. This paper introduces an alternative approach whereby the vibration behavior of a milling tool during cutting is used to obtain the necessary model parameters for the common delay differential equation models of milling. • Method to estimate milling model parameters from experimental time series. • Estimated parameters used to predict stability chart for range of cutting conditions. • Stability predictions show close match with experimental results. • Extends the spectral element method to incorporate steady-state vibration. • Automated approach for instrumented milling that makes manual modal test unnecessary. [ABSTRACT FROM AUTHOR]

The current image processing techniques heavily rely on classic windows for suppressing spectral leakage. However, the limited capability of these classic windows to suppress spectral leakage restricts their application in the field of high-precision measurement. This paper proposes a novel family of windows capable of suppressing spectral leakage associated with the Moiré fringes pattern, thereby enhancing the accuracy of lithography alignment. Specifically, a novel two-dimensional Hanning self-convolution window is introduced, which is derived from the Hanning window to inherit its advantage of ultra-rapid sidelobe decay. The behaviors of the main lobe and desirable sidelobes of the 1st- to 4th-order are examined. Additionally, a novel fringe phase extraction algorithm is established based on the proposed window, which demonstrates high accuracy and efficiency. Simulation and experimental results validate the feasibility and practicality of the proposed window. In particular, the proposed window outperforms classic windows in suppressing spectral leakage, thereby successfully enhancing the phase extraction accuracy to achieve high-precision misalignment measurement at the sub-2-nm level (1.47 nm @ 3σ criterion). The proposed method can be easily extended to other real engineering applications utilizing fringe to achieve high-precision measurements, such as fringe projection profilometry, damage detection, and visual mechanical vibration monitoring. [ABSTRACT FROM AUTHOR]

In recent years, there has been a growing interest in the development of ground-based Synthetic Aperture Radars (GBSAR) for the purpose of monitoring structural displacements. GBSAR offers high-resolution monitoring over a wide area and can capture data every few minutes. However, compact high-frequency multiple input multiple output (MIMO) radars have emerged as an alternative for monitoring sub-second displacements, such as structural vibrations. MIMO radar has sub-second acquisition interval. However, it has limited cross-range resolution compared to GBSAR, and interference between antennas and presence of multiple scatterers in the scene can cause strong sidelobes in the processed data. On the other hand, GBSAR utilizes a long synthetic aperture to achieve high cross-range resolution. However, due to its longer data acquisition time compared to MIMO radar, conventional methods are insufficient for detecting scatterers' sub-second displacements that occur during the data acquisition process. This study proposes a method to effectively monitor sub-second or sub-minute displacements using GBSAR signals. The proposed method enhances the conventional radar interferometric processes by employing spectral estimation, allowing for multi-dimensional detection of targets' azimuth angle, linear displacement, and vibrational characteristics. Consequently, this method improves both the processing of MIMO radar data and enables high-resolution fast displacement monitoring from GBSAR signals. The paper presents the theoretical details and mathematical formulations of the proposed method for both MIMO radar and GBSAR imaging modes. To evaluate the effectiveness of the proposed method, numerical simulations and real experiments are conducted. The experimental results validate the capability of the proposed method in both GBSAR and MIMO configuration modes for high-resolution monitoring of fast linear displacements and vibrations. The results exhibit promising signal-to-noise ratio (SNR) and peak-to-sidelobe ratio (PSLR) values. [ABSTRACT FROM AUTHOR]

Rolling element bearings are vital parts for rotating machinery. When a defect occurs on the surface of the bearing raceway or rolling element, giving rise to the abnormal vibration of the bearing and even the rotating machine. Thus, it is of great significance to understand the vibration characteristics of the bearing for fault diagnosis and machine condition monitoring. In recent decades, researches on defect-induced bearing vibration in machine condition monitoring have attracted increasing attention. Model-based investigation is a highly useful method for enhancing our understanding of defect-induced vibration and fault excitation mechanism of the bearing. It also serves as a basis for establishing the theory of bearing failure. With this in mind, a novel dynamic model of deep groove ball bearing (DGBB) with a localized outer race defect is proposed in this paper. In this model, the additional displacement excitation which is modelled as a piecewise function based on kinematics is considered, and the angle-based contact force is developed and modelled as a piecewise function taking into account the angular position, collision velocity, and impact force. In addition, an analytical formulation of the angle-varying effective stiffness matrix of the DGBB with a localized raceway defect of varying size is established. The proposed dynamic model is used to study the influences of different defect scenarios (i.e. angular positions and widths) on the time-varying contact stiffness, contact force, spectral characteristics, and bearing vibrations. The comparisons between the simulations and the experiments show that the proposed model is effective. • A physics and kinematics analyses based nonlinear dynamic model is proposed for defective deep groove ball bearing. • An angle-varying contact force model is deduced considering the striking force resulting from the collision of the rolling element with the trailing edge of the defect. • The time-varying additional displacement is modelled by introducing both the disconnection velocity of the rolling element from the leading edge and the angular velocity of the rolling element around the leading edge. • The contact stiffness, contact force, and contact deformation of the defective bearing are deduced and their angle-induced variations are analysed, as well as the bearing vibration behaviours. [ABSTRACT FROM AUTHOR]

• A new semi-analytical method is proposed for the fluid-conveying parallel pipeline with soft nonlinear clamp support model. • The proposed model simulates the vertical hysteretic restoring force of clamp using the Bouc-Wen model. The parameters were identified using the Particle Swarm Optimization (PSO) with experimental and simulation errors as the objective function. • This paper utilized multiple validation methods to verify the proposed model, modal experiment, sweep frequency and fixed frequency experiments and ANSYS software were used to verify the proposed model. • The model proposed in this paper is versatile and can be validated through experiments and simulations by adjusting the position of the dual clamp. Clamp is a crucial support structure to secure and connect the parallel pipeline system. Since the metal felt of the clamp is composed of metal rubber material, as well as the clamp structure using bolted connections, clamp is prone to cause nonlinear force during vibration. Nevertheless, no relevant paper has been reported to study the influence of soft nonlinearity of clamps on parallel pipelines. To bridge this gap, the present study introduces a novel semi-analytical dynamic model that effectively considers the influences of nonlinear clamps in parallel pipeline systems. The proposed model simulates the clamp's vertical hysteretic restoring force using the Bouc-Wen model. The clamp parameters are identified using Particle Swarm Optimization (PSO) with experimental and simulation errors as the objective function. Subsequently, the model is then validated by conducting modal and response tests. The numerical results are consistent with the experimental results. In order to prove the validation of the proposed model, experiments are conducted using dual clamps at different positions, and it can be observed that the nonlinear parameters of the clamps still meet the accuracy requirements. Moreover, the influences of fluid parameters on frequency are compared with the ANSYS software and the proposed model, and the influence trends exhibit consistency. By considering the nonlinear effects of clamps, the proposed model facilitates enhanced accuracy in predicting vibration responses. [ABSTRACT FROM AUTHOR]

Highlights • A unique human body inspired anti-vibration system is presented. • The muscle function of human body is explored as special nonlinear stiffness and damping units. • The rotation motion of upper body or arm swinging are employed in a simple but effective passive anti-vibration design. • Some nonlinear features are discovered for the first time leading to very beneficial vibration isolation. Abstract This paper presents a unique human body inspired passive vibration isolation system with a special coupled nonlinear inertia design. This human body inspired anti-vibration structure with nonlinear inertia consists of a compact X-shaped structure with a horizontally-installed spring system to simulate the functions of legs and muscles, and a compact rotational unit to mimic the arms swinging (or upper body movement) and/or muscle extension-flexion motion during human walking. It is particularly focused on the beneficial nonlinear effect incurred by the rotational unit, including a nonlinear equivalent mass and a very special nonlinear inertia incurred conservative force. It is shown that, the nonlinear properties (in equivalent stiffness, damping and mass simultaneously) can obviously improve the vibration isolation at low frequencies and/or in a broadband frequency range, and increase the stability of the mass center of the overall isolation system during vibration, irrespective of the loading and excitation conditions. The muscle function and swinging arms of human body are for the first time employed with an innovative and simple mechanical design for vibration control and successfully validated by experimental prototypes for their excellent beneficial nonlinear features. This paper presents a unique simple passive and adjustable anti-vibration solution of great potential in extensive engineering applications. [ABSTRACT FROM AUTHOR]

Highlights • Presents a unified model of piezoelectric vibration energy harvesters. • Demonstrates that the same power limit applies to all circuit interfaces. • Explains the power behaviors of energy harvesters through the impedance plot. • Derives analytical expressions of critical coupling for SEH and SSHI interfaces. • Compares the power characteristic of REH, SEH and SSHI energy harvesting interfaces. Abstract This paper presents a unified model of piezoelectric vibration energy harvesters through the use of a generalized electrical impedance that represents various energy harvesting interfaces, providing a universal platform for the analysis and discussion of energy harvesters. The unified model is based on the equivalent circuit analysis that utilizes the impedance electromechanical analogy to convert the system into the electrical domain entirely, where the model is formulated and analyzed. Firstly, the common behaviors of energy harvesters under this unified model are discussed, and the concept of power limit is discussed. The power limit represents the maximum possible power that could be harvested by an energy harvester regardless of the type of the circuit interface. The condition to reach this power limit is obtained by applying the impedance matching technique. Secondly, three representative energy harvesting interfaces, i.e., resistive (REH), standard (SEH), and synchronized switch harvesting on inductor (SSHI), are discussed separately, including their corresponding forms of the generalized electrical impedance and associated system behaviors. As an important contribution, a clear explanation of the system behavior is offered through an impedance plot that graphically illustrates the relationship between the system tuning and the harvested power. Thirdly, the effect of the system electrometrical coupling on power behaviors is discussed. As another important contribution, this paper derives and presents the analytical expressions of the critical coupling of the interfaces, which is the minimum coupling required to reach the power limit and also the parameter used to define the coupling state, i.e., weakly, critically, or strongly, of a system. In particular, the analytical expressions for the SEH and SSHI interfaces are presented for the first time in the research community. Lastly, the system behaviors and critical coupling of the three energy harvesting interfaces are compared and discussed. The SSHI interface has the lowest critical coupling, which explains its superior power harvesting capability for weakly coupled systems. [ABSTRACT FROM AUTHOR]

Highlights • The influence of the number of blades on the instantaneous aerodynamic torque is investigated. • The effect of the solidity on the wind turbine dynamic response is studied in non-stationary regime. • The number of blades significantly affects the overall Darrieus turbine dynamic behavior. • A new methodology, coupling aerodynamic phenomena with mechanical vibration, is introduced. • Optimum rotor configuration is achieved. Abstract Dynamic behavior of a Darrieus-type vertical axis wind turbine geared transmission system taking into account variable gear mesh stiffness and the external aerodynamic torque excitation is carried out in the present paper. The aerodynamic torque is obtained by a complete campaign of simulations based on Reynolds Averaged Navier-Stokes unsteady calculations for two, three and four-bladed rotor architectures. A three-dimensional model of a one-stage bevel spur gear system is developed. For each proposed rotor configuration, the effect of the number of blades on both aerodynamic performance and dynamic vibration of the Darrieus turbine geared transmission system is discussed at several tip speed ratios in non-stationary operation. The main originality of the present paper is to establish a correlation between the aerodynamic parts and the dynamic vibration of the gearing system by studying the effect of some design parameters on the dynamic vibration of the Darrieus turbine gearing system in non-stationary regime. This new methodology of simulation makes considerable progress in the understanding of the wind turbine dynamic vibration, which is an important issue. The number of the blades is the core problem of wind turbine engineering. In this paper, the numerical results show that the number of blades significantly affects the turbine efficiency and the dynamic response of the studied wind turbine gearing system in non-stationary regime. [ABSTRACT FROM AUTHOR]

Abstract A vibration absorber, also known as a tuned mass damper (TMD), is a passive vibration control device. This is achieved by attaching a secondary oscillator to a primary oscillator. In general, the aim is to reduce the vibration of the primary oscillator by suitably choosing the parameters of the secondary oscillator. The effectiveness of a TMD depends on (a) optimised the value of the tuned parameters, and (b) the nature of ambient damping of the absorber. They theory of TMD when the secondary and the primary oscillators are undamped or viscously damped is well developed. This paper presents an analytical approach to obtain optimal parameters of a TMD when the vibration absorber is viscoelastically damped. Classical results on viscously damped vibration absorbers can be obtained as a special case of the general results reduced in the paper. It is shown that by using a viscoelastically damped TMD, it is possible to obtain superior vibration absorption compared to an equivalent viscously damped TMD. [ABSTRACT FROM AUTHOR]

Abstract In a cable-stayed bridge, the employment of magnetorheological (MR) dampers among stay cables are steadily increasing for mitigation of rain-wind induced vibration. A major problem for the practical application of these devices is to develop a suitable algorithm that effectively suppresses the vibration of stay cables with basic calculations and minimal feedback requirement. This paper discusses an optimal equivalent control algorithm for vibration mitigation of stay cables based on the linear quadratic regulator (LQR). The control algorithm is anticipated to effectively reduce the risk of structural response amplification, which is due to the control forces along the direction of MR damper motion. Furthermore, this algorithm approximates the optimal LQR control forces through equivalent stiffness and damping, resulting in a significant reduction in the calculative effort of the optimal control forces. Hence, it is proved as a great significance for the MR semi-active control system application in the field of practical engineering. In the proposed equivalent control technique, control performance is evaluated by the vibration control problem faced by wind induced stay cable of the Second Nanjing Yangtze River Bridge. The results demonstrate that the MR semi-active control algorithm as proposed in this paper performs better than that of optimal passive control with almost achieving the level of LQR control with minimal feedbacks requirements. [ABSTRACT FROM AUTHOR]

Abstract In this paper, the vibratory dynamics of a system consists of a rotor and a stator with friction at the interface is studied. The main goal is to study how taking into account the deviation of the relative velocities associated with each point of the interface (rotor/stator) influences the model. The inclusion of this deviation, not usually modeled for this type of system, allows taking the friction plane into account. However, introducing this mechanism in a model with a friction interface leads to damping that in turn has an impact on the values and the convergence of the amplitudes of vibration. In addition, the deviation has a significant impact only when the rotation frequency of the rotating part is low. Thus this paper also focuses on the separation occurring at the interface. The method used to take this separation into account is presented. The addition of this separation in the model makes it possible to obtain more physically realistic limit cycles in the case of high rotation frequency. These two phenomena are combined in order to obtain physical amplitudes. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Air and thermoelastic damping contribution is small in the macro volume region. • Strong relation observed between material damping and critically damped stress. • Different trending curves and large errors when using constant damping assumption. • Presence of an optimum mass ratio when using low magnetization value. • Preference on the frequency tuning method depends on the magnetization value. Abstract Often when optimising a vibration energy harvester, the mechanical damping is given little significance and is usually assumed to be a constant. This paper analyses the importance of mechanical damping variation in modelling the behaviour of a cantilever beam-based electromagnetic resonator. It is shown that for beam volumes above 100 mm3, material damping dominates thermoelastic and air damping, hence becoming the major contributor towards the mechanical damping. A novel method is proposed to define material damping in terms of the maximum critically damped stress at resonance. The new method is shown to be simpler and more accurate than previous methods. Using the developed governing equations, the conditions of optimum load resistance are derived for two particular cases. A comparison is made between the mechanical damping model and the constant mechanical damping assumption in terms of maximum power output. Different trends were noted between the two compared methods, suggesting that the constant mechanical damping assumption can lead to large errors in power prediction. Further analysis describes the existence of an optimum mass ratio for electromagnetic resonators operating under a low magnetisation parameter. Lastly, this paper shows that different frequency tuning methods are preferable under different operating conditions. [ABSTRACT FROM AUTHOR]

Abstract A new multi-impulse robust shaper (MIR) is put forward to control the residual vibration of the flexible system actively in this paper. This technique designs a sequence of impulses according to the undamped natural frequency and the damping ratio of the flexible system to shape the input command. The input command shaped by MIR shaper can suppress the transient vibration and residual vibration and is robust to modeling errors in natural frequency and damping ratio of the flexible system to some extent. The shaped input command by MIR shaper can also suppress the high mode residual vibration under a certain level in a wide range of normalized frequency. The characteristic of the proposed MIR shaper is investigated in this paper, which shows a good advantage and broad application with comparison to the traditional ZV shaper, ZVD shaper and EI shapers. [ABSTRACT FROM AUTHOR]

Abstract Uniform acoustic waveguides in initially quiescent inhomogeneous media are governed by Bergmann's wave equation. The transverse modes are independent of the ambient gradient, but there is a void of papers on the cut-on conditions of the higher order axial modes. This paper presents a sufficient cut-on condition and discusses its application to hard-walled ducts in which the mean temperature varies linearly and exponentially along the duct axis. [ABSTRACT FROM AUTHOR]

Fractional derivative is increasingly being deployed to improve existing mathematical models due to its unique capability in describing anomalous behavior and memory effects which are common characteristics of natural phenomena. Improved vibration analysis has been accomplished by introducing fractional derivatives to model viscoelastic damping and vibration propagation through complex media and much research has been carried out to date. However, much of these existing research efforts have been sporadic to the best and there remains a pressing need to develop a consistent and systematic theoretical framework for vibration analysis of fractional systems to synergize for more productive and coordinated efforts in the area. This paper seeks to address some fundamental issues to facilitate further development such as the definition of general form of a fractional vibration system, its eigenvalue problem and methods of solution, definition of frequency response functions and applicability of conventional modal analysis, equivalent eigensystem and its more efficient eigensolution. With these important issues being resolved to clear the myth, vibration studies of fractional systems can be encouraged and expected to grow in a more fruitful direction. New methods developed and concepts discussed in the paper have all been validated through realistic numerical case studies based on a practical GARTEUR structure with viscoelastic supports modeled using fractional derivatives. [ABSTRACT FROM AUTHOR]

A method for non-parametric identification of systems with asymmetric non-linear restoring forces is proposed in this paper. The method, named the zero-crossing method for systems with asymmetric restoring forces (ZCA), is an extension of zero-crossing methods and allows identification of backbones, damping curves and restoring elastic and dissipative forces from a resonant decay response. The validity of the proposed method is firstly demonstrated on three simulated resonant decay responses of the systems with off-centre clearance, bilinear and quadratic stiffness. Then, the method is applied to experimental data from a micro-electro-mechanical resonator in order to quantify its non-linear damping and stiffness effects. Throughout the paper the proposed method is also compared with the Hilbert vibration decomposition to demonstrate that the ZCA yields more accurate results with much less effort. [ABSTRACT FROM AUTHOR]

Highlights • A novel propagation distance prediction method for surface periodic vibration is developed. • A new fundamental frequency estimation algorithm based on cepstrum is proposed. • The fundamental frequency energy percentage feature (FBEP) is developed for vibration signal representation. • Analyses on the FBEP feature distribution and its relationship to propagation distance are presented. Abstract Earth surface vibration signal processing becomes attractive recently due to its significance in source detection and localization, which can be adopted in a number of real world applications, such as footstep detection, underground pipeline network surveillance, etc. In this paper, we investigate the distance estimation problem for earth surface periodic vibration signal localization. The signal attenuation principle between the propagation distance and the signal frequency is exploited and a novel frequency band energy percentage (FBEP) feature is developed to characterize the energy distribution property within different frequency bands of different propagation distances. To obtain the fundamental frequency of periodic vibrations, the cepstrum approach is employed. An enhanced computationally efficient k nearest neighborhood (EH-kNN) algorithm is developed to perform the distance estimation. Experiments on real periodic vibration signals generated by an electric hammer under different collecting distances and transmission medias are conducted to show the superiority of the proposed distance estimation method in this paper. [ABSTRACT FROM AUTHOR]

Abstract In this paper, the control of roll vibration and vertical vibration of a seat suspension caused by uneven road under both sides of tyres is studied. The heavy duty vehicles are generally working under severe conditions, where the uneven road can cause roll vibration and vertical vibration of the vehicle body and can have an effect on seat suspension. The conventional single-degree of freedom (single-DOF) seat suspension can only isolate the vertical vibration while the roll vibration will be totally transferred to the driver's body. The high magnitude of driver body's lateral acceleration caused by roll vibration will influence drivers' health and have a negative effect on ride comfort. A two-layer multiple-DOF active seat suspension, which has a z-axis DOF in the bottom layer and a roll DOF in the top layer, is proposed in this paper. A non-singular terminal sliding controller is designed to control the top-layer to reduce the lateral acceleration and roll acceleration by tracking a desired roll angle. An H ∞ controller with disturbance compensation is applied to control the bottom-layer for vertical vibration isolation. Both controllers use the variables which can be measured or estimated in the practical application as feedback signals. Two inertial measurement units (IMUs) MPU9250 are used in order to estimate the rotary angles of the top and base platforms of the two-layer multiple-DOF active seat suspension. The effectiveness of the seat suspension and control method is validated by both simulations and experiments. A single-DOF active seat suspension and a well-tuned conventional passive one are applied for comparison. Based on ISO 2631, the vibration total value of frequency weighted root mean square (FW-RMS) acceleration of the multiple-DOF active seat surface has 29.8% and 23.6% reductions for evaluating its influence on health and ride comfort, respectively, when compared with the single-DOF active one. The proposed vibration isolation method can effectively reduce the whole body vibration (WBV) of heavy duty vehicle drivers, and it shows high potential for practical application. [ABSTRACT FROM AUTHOR]

In the paper a theoretical analysis is deduced regarding vibration control of large induction motors – power rating ≥1 MW – with roller bearings, using actuators between motor feet and a soft steel frame foundation. Based on a multibody model, the mathematical coherences are shown, including the feedback control system. Afterwards a numerical example of a soft mounted, converter driven, 2-pole induction motor (1.6 MW) with ball bearings is presented, where the bearing housing vibrations and the foundation vibrations are analyzed with and without control system. It could be shown, that without vibration control system the operating speed range cannot be used completely because of resonances, caused by the soft foundation. Therefore, critical speed areas occur, where steady state operation is not possible. However, with the vibration control system, the whole operating speed range can be used. The aim of the paper is to show the capability of using a vibration control system with actuators between motor feet and a soft foundation, for avoiding off-limits areas for the operation speed of large induction motors. [ABSTRACT FROM AUTHOR]

This paper deals with the problem of applying electromagnetic devices of the motional type to improve the dynamic stability of a pipe conveying air. When the flow velocity reaches a critical value, the steady equilibrium position becomes unstable, and self-excited lateral vibrations arise. In contrast, electromagnetic devices of the transformer type have been demonstrated to be highly effective in the passive stabilization of such a system, as well as the active stabilization of similar non-conservative systems with a follower force. In the present paper, we apply a pair of motional devices made of a conducting plate which is attached to the pipe and moves together with it within the perpendicular magnetic field generated by the controlled electromagnets. This motion generates eddy currents in the plates and a drag force of a viscous character. In this setting, we first investigate the possibility of designing a stabilizing control within the region of the magnetic field where every passive solution results in an unstable or conservative state. For that purpose, we determine a practical condition justifying the existence of a stabilizing control for a given set of system parameters. Later we pose and solve an optimal control problem aiming at stabilizing the system with the optimal rate of decrease of the system's energy. The solution is examined by means of numerical simulations performed within the three regions of the flow velocity: low subcritical, where the Coriolis acceleration of the conveyed fluid generates the predominate damping force; high subcritical, where the inertia of the fluid begins to dominate the dynamics of the system; and low supercritical, where unstable flutter vibrations start to arise. The effectiveness of the designed optimal controller is validated by comparisons with the corresponding passive solutions. [ABSTRACT FROM AUTHOR]

When conducting multi-input multi-output (MIMO) random vibration environment test, response spectral lines of under test article may exceed their tolerances and some of them can hardly be controlled by control algorithms. The cause of this phenomenon is the high level noises in the input forces, which are induced by the inverse of the ill-conditioned frequency response function matrices. These spectral lines may even trigger the instability of control algorithms and eventually result in an accidental test shutoff. The classical control algorithm for MIMO random vibration environment test contributed by Smallwood is analyzed theoretically and experimentally in the paper to reveal its weakness on dealing with this kind of error. An updated algorithm is proposed on the basis of inverse theory to overcome the difficulty of controlling these stubborn spectral lines. The main idea of the work is to reduce the level of noise components in input forces by regularizing singular values of ill-conditioned frequency response function matrices. An adjusting rule is set up according to the auto-power spectra tolerances. A simulation and an experiment are supplied in the paper to verify the effectiveness of the updated algorithm, the results are satisfactory. [ABSTRACT FROM AUTHOR]

Scaling laws are used to scale-up calculation or measurement results from a prototype structure to those of an original structure or vice versa. The scaling laws of mechanical structures are usually obtained from their equations of motion or from a dimensional analysis. This paper proposes scaling laws that are represented by a power law. The power law is directly deduced from the Π -theorem of similitude theory and the coefficients of the power law are obtained from first order sensitivities (sensitivity-based scaling laws). Among existing similitude analysis methods such as dimensional analysis the sensitivity-based scaling laws can be directly obtained from a model without a priori knowledge of its scaling behavior, e.g., from a finite element (FE) model. The applicability of the sensitivity-based scaling laws is demonstrated in three case studies. A simply supported rectangular plate subject to mechanical vibrations is modeled by an analytical approach based on the Kirchhoff plate theory and by an FE model based on the Mindlin-Reissner theory. The plate’s dimensions are considered as design parameters for the sensitivity-based scaling laws. It is found in the first case study that the sensitivity-based scaling laws exactly predict the natural frequencies and the mean squared transfer admittances of scaled models from those of the original plate. This is in agreement with current literature and, thus, the method proposed in this paper can be considered verified. In the second case study the sensitivity-based scaling laws are directly obtained from the FE model. A good accuracy of the predicted vibration responses of the scaled models is found since (1) the scaled model and the original one are in similitude, i.e., the mode shape order and the damping are kept, and (2) the scaled plate can still be considered thin. The latter is assessed by the length (or width) to thickness ratios of the investigated plates and a lower bound is proposed. The third case study comprises a simplified car undercarriage to demonstrate the applicability of the method in practical design engineering. Besides the geometry parameters the material properties are incorporated in the sensitivity-based scaling laws as well. It is found that the natural frequencies as well as the vibration velocities at an arbitrarily chosen receiver point of the scaled models can be accurately predicted from those of the original one for complete similitude conditions. [ABSTRACT FROM AUTHOR]

External gear pumps are one of the most commonly used types of positive displacement machines in high pressure hydraulic control systems, fuel-injection and fuel transport systems. Despite many merits of the traditional external gear pump design with involute teeth, the significant flow non-uniformity intrinsic of such design is considered to be a detrimental aspect, since it causes undesired noise emissions and mechanical vibrations. A disruptive concept of continuous-contact helical gear pumps (CCHGP) was proposed and successfully commercialized in the recent past. Such concept was proven to have clear advantages in terms of noise emissions. However, a clear interpretation of the displacing action and the transient features of the delivery flow was never addressed in past literature. This paper addresses this gap by first discussing the family of gear profiles suitable for implementing the CCHGP design. Subsequently, an analysis on the kinematic flow ripple is given, showing how such design concept can reduce or even eliminate the kinematic flow pulsations. The paper also presents a numerical approach for modelling the operation of CCHGPs, starting from the modeling of the geometric features necessary for a fluid dynamic analysis based on a lumped parameter approach. For model validation purposes, a commercial CCHGP was tested at the authors’ research center, and the simulation results were compared against the experiments, to show the level of accuracy of the model, as well as it potentials for future design studies. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel three-dimensional finite element model of the pipe conveying fluid is developed. • There is a qualitative difference between the in-plane and out-of-plane natural vibration. • The critical condition of buckling instability the curved pipe is clarified. • Initial curvatures have significant effects on the spatial vibration characteristics of the pipe. Due to the lack of advanced models and analytical methods, the study of pipe conveying fluid usually only considers the in-plane vibration of straight pipe. In order to fully understand the dynamic characteristics of curved pipe, it is necessary to establish the three-dimensional (3D) dynamic model. However, there are still few 3D modeling methods for the curved pipe. In this paper, based on the absolute nodal coordinate formulation (ANCF), a 3D finite element model for the curved pipe is developed. The nonlinear dynamic equations of the pipe system are derived by using the extended Lagrange equations. The natural frequencies and modes are calculated by linearizing the equations. The established model and the adopted method are verified through the comparison with relevant literature and ANSYS simulation. Furthermore, the effects of the relevant parameters on the natural vibration of curved pipe are discussed. The in-plane and out-of-plane natural vibration characteristics of curved pipe are compared and summarized for the first time. Finally, the advantages of the proposed model are outlined by the comparison with the planar dynamic model. The results provide new information about the effect of initial curvatures on the spatial vibration characteristics of pipes. In conclusion, this paper provides a novel dynamic model for studying the spatial vibration of the curved pipe. In the meantime, the results of this paper can also can guide for the research of the vibration of curved pipes in engineering. [ABSTRACT FROM AUTHOR]

• Higher temperature weakens the stability to pulsation velocity in subcritical region. • Higher temperature enhances the stability to pulsation velocity in supercritical region. • Higher temperature enhances the nonlinearity in subritical region. • Higher temperature weakens the nonlinearity in supercritical region. Parametric resonance is a kind of specific fluid-induced vibration for pipes conveying fluid. This paper focuses on revealing the qualitative characteristics of parametric resonances of the pipe with pulsating fluid speed in thermal environment, and compares the differences between the resonance characteristics in subcritical and supercritical regions. According to the generalized Hamilton's principle, the partial-differential-integral governing equation of a straight pipe is established. Under simply-supported boundary conditions, the non-trivial equilibrium configuration is obtained analytically. The governing equation of a supercritical pipe is derived by coordinate substitution on the basis of the new equilibrium configuration. The approximate analytical solution of parametric resonance for a pipe conveying fluid in a thermal environment is obtained by using the direct multi-scale method. The approximate analytical solution is verified to be reliable by using the Runge-Kutta method. The stability bounds of the parameters inducing parametric resonance are investigated via the introduced analytical method. The results show that the influence of temperature increment on sub-harmonic resonance is non-monotonic. In the subcritical region, when the temperature increment increases, the unstable region widens. This means that the system is more prone to parametric resonance, and the response amplitude decreases. In the supercritical region, when the temperature increment increases, the unstable bandwidth decreases, and the response amplitude increases. When viscous damping is increased or the average velocity is decreased, the sub-critical instability region decreases, and the supercritical instability region increases. With the increase in the pulsation velocity, the unstable bandwidth of subcritical and supercritical regions will increase, and parametric resonance is more likely to occur. [ABSTRACT FROM AUTHOR]

The quasi-Zero Stiffness (QZS) isolation system is a typical nonlinear isolation system, which has high static stiffness characteristics to improve the bearing capacity and deformation resistance, and its low dynamic stiffness characteristics can reduce the inherent frequency of the system to realize a wider vibration isolation frequency band, so it has a more excellent low-frequency vibration isolation performance compared with the linear system. In this paper, a horizontal QZS isolator is constructed based on a pre-compressed oblique spring system, and two sets of the horizontal QZS isolators are mechanically assembled to work together to achieve a bi-directional horizontal QZS isolation system. Considering that the construction of two sets of horizontal vibration isolators is approximately the same, we focus on one of the isolators for the static analysis and derive the parameter conditions to be satisfied for achieving quasi-zero stiffness characteristics. We considered the effect of each adjustable parameter of the horizontal vibration isolator on the mechanical performance of the QZS system, and sought to optimize the QZS interval to improve the vibration isolation performance. A comparative study of the dynamical properties between the QZS system with ordinary and optimized parameters, as well as the equivalent linear system, is further carried out by means of nonlinear approximate analysis. Finally, the dynamic characteristics of the bi-directional horizontal QZS system and the equivalent linear system are compared by shaker tests on the prototype device, which proved the excellent vibration isolation performance of the proposed QZS isolation system. [ABSTRACT FROM AUTHOR]

Tuned mass dampers (TMDs) have proven effective in suppressing structural vibration. In existing research on vortex-induced vibration (VIV) control of flexible structures, only one mode is commonly considered at the time, and only basic aerodynamic force models, which can struggle to model amplitude-dependent damping, are considered. However, flexible structures, such as multi-span bridges, exhibit multiple modes with closely spaced frequencies. Neglecting secondary modes may introduce calculation inaccuracies, as these modes can impose additional stiffness, thereby influencing the performance of TMD. This paper presents a framework to optimize the performance of multiple TMDs in the context of multi-mode VIV control for a flexible structure. A multi-span bridge is used as a case study, and the secondary modes and nonlinear aerodynamic effects are considered. The governing equations for the force-structure-MTMDs system are derived in modal coordinates using a polynomial model to model the aerodynamic force. A novel method to calculate the contribution of each mode to determine the minimum number of secondary modes to be considered is proposed. The optimal parameters of MTMDs are obtained using a global optimization method and compared with mode-by-mode design results. Robustness analysis is conducted to verify the effectiveness of the optimization framework. The results show that the polynomial model accurately predicts the amplitude after TMD installation. Secondary modes significantly affect the optimal parameters of TMDs, and the optimized results exhibit better control performance than the mode-by-mode design results. • Introduce a novel framework for optimizing multiple TMDs for flexible structures. • Consider the secondary modes of the structure and nonlinear aerodynamic effects. • Verify the applicability of TMD design using the polynomial nonlinear force model. • Develop a quantitative indicator to determine the minimum number of secondary modes. • Showcase improved performance of the optimized TMDs compared to mode-by-mode design. [ABSTRACT FROM AUTHOR]

[Display omitted] • A generalized method is proposed to measure eccentricity of multiple rotary parts. • Proposed lever mechanism with a ball probe can measure arbitrary cross-sections. • Method solution algorithm can obtain the eccentricity efficiently and effectively. • The proposed method has the advantages of anti-interference and batch inspection. Rotary parts are crucial to transmission equipment. Measuring and analyzing the eccentricity of rotary parts enables the monitoring of vibrations in machinery, ensures smooth operation, and reduces equipment maintenance costs. The accurate measurement and modification of eccentricity are the premise to ensure rotary parts' quality, however, existing measurement methods are computationally inefficient, complex, and expensive to implement, and limited in scope. In this paper, a novel and generalized precision measurement method is proposed to accurately and efficiently evaluate rotary parts' eccentricity parameters, including attitude angle, eccentricity, and eccentric angle. This precision measurement method includes a lever measuring mechanism with a spherical probe and a corresponding efficient signal processing algorithm. The measuring mechanism has a simple structure and can effectively measure arbitrary cross-sections, and its design and optimization principles are investigated and presented thoroughly. The signal processing algorithm can efficiently extract eccentricity parameters of measured cross-sections. This proposed method has proven to overcome the limitations of literacy methods and exhibits generality and anti-interference. Simulation calculation and experimental verification are used to evaluate the effectiveness, computation efficiency, applicability, and repeatability. The proposed method exhibits tremendous potential in a diverse range of applications, such as detecting eccentricity and correcting errors for mechanical measurements, aerospace, equipment manufacturing, and other related fields. [ABSTRACT FROM AUTHOR]

A novel instantaneous frequency (IF) tracking method for non-stationary measured signals with single-frequency, multi-frequency, and harmonic-frequency is presented in this paper. Firstly, the deficiency of the mainstream time-domain IF tracking methods, such as adaptive notch filter (ANF) and Extended Kalman Filter (EKF), etc., are analyzed. Then the relationship of the amplitude, frequency, and signal value of a periodic signal in adjacent time intervals is derived, the influence of amplitude change on IF tracking results is verified, and a new state-space model for the IF tracking of a non-stationary measured signal is constructed by using the adjacent non-stationary measured signal, signal amplitude, and frequency, and the EKF is used to update the state of the model. After that, a series of non-stationary signals whose amplitude, frequency, and phase change linearly, nonlinearly, and mutation over time are designed to verify the IF tracking performance of the proposed algorithm. From the simulation results and 1000 times Monte Carlo simulation results, the proposed algorithm has faster convergence speed, higher convergence accuracy, and better robustness, compared with mainstream time-domain frequency tracking algorithms, such as ANF and EKF. Based on the proposed single-frequency IF tracking model, a multi-frequency signal IF tracking model is constructed to track the IF of non-stationary measured signals containing multiple frequency components. The effectiveness of the proposed multi-frequency IF tracking algorithm for multi-frequency signal and harmonic signal IF tracking is verified by simulation cases. After that, some experimental cases are given to further verify the feasibility of the proposed IF tracking algorithm. From the experimental results, the effectiveness of the proposed algorithm is compared with other time-domain algorithms. In addition, the initial value of frequency is set to zero in all the processes of simulation and experiment, which effectively avoids the influence of the initial condition of frequency on the IF tracking result. [ABSTRACT FROM AUTHOR]

• Stress-stiffening in local resonances of rotating acoustic metamaterials can be captured using a stress stiffening function. • Rotating acoustic metamaterials with beam-tip-mass resonators support band gaps that depend linearly on the rotational speed. • Resonator parameters can be chosen such that band gaps of the metamaterial self-adjust to the synchronous vibration frequency, resulting in attenuation over a wide range of frequencies and thus rotational speeds. The rotation of mechanical systems can greatly change their modal and wave propagation response. In the classic example of the Foucault pendulum, the Coriolis force from the Earth's rotation causes the pendulum path to appear deflected to an observer on Earth. More recently, Coriolis forces and gyroscopic effects from rotation have been shown to break time-reversal symmetry, induce non-reciprocity, and change the band structure of phononic crystals. However, rotation also introduces centrifugal forces that can considerably affect the vibration response through stress stiffening and spin softening effects. Although this is well studied in the field of rotor dynamics, the effects of centrifugal forces on the dynamic behavior of acoustic metamaterials (AMs) are still unexplored. In this paper, we study the dependence of torsional band gaps on rotational speed in a rotating shaft with attached local resonances. Different from previous studies, we explicitly consider the effects of stress stiffening in local resonances by introducing a stress stiffening function in a reduced order model of the rotating AM. We then calculate the stress stiffening function for beam-tip-mass resonators and show that these resonators have a resonant frequency that scales linearly with the rotational speed in the asymptotic limit, which in turn causes the band gaps of the AM to depend linearly on the rotational speed. Motivated by the presence of synchronous vibrations in rotating machinery, in which frequency is also linearly dependent on rotational speed, we show that this rotating AM supports band gaps that self-adjust to the synchronous vibration frequency, resulting in attenuation over a wide range of frequencies and thus rotational speeds. Finally, we validate the reduced order model of the rotating AM using 3D finite element analysis. This work contributes a foundational understanding of the effects of rotation in AMs and builds a connection between the AM and rotor dynamics communities, with the potential to introduce novel vibration control in rotor dynamics problems. [ABSTRACT FROM AUTHOR]

Fault diagnosis techniques (FDT) face the challenge of implementing model learning in the presence of limited, imbalanced, or non-ideal data, which is a fundamental and crucial problem that hinders their applications in real industrial scenarios. In this paper, a novel deep neural network (DNN), densely-connected semi-Bayesian network (DSBNet) is proposed to implement feature learning of vibration signals for machinery fault diagnosis in non-ideal data scenarios. Firstly, deep Bayesian learning is embedded into the multi-scale semi-Bayesian block (MSBB) of DSBNet as a local feature extraction and enhancement module. The re-parameterization operations of Bayesian convolutional layers in MSBB perform uncertainty inference on the features by learning the mean and variance of the Gaussian convolution kernel, achieving local expansion and enhancement of network features. Furthermore, convolutional features are integrated into MSBB to generate multi-scale semi-Bayesian features. An adaptive selector based on the multi-class and multi-scale attention mechanism is proposed to enhance effective semi-Bayesian features and suppress redundant features. The proposed methodology facilitates the adaptive end-to-end training of DSBNet, which enables it to match the scale of the current dataset and achieve optimal performance. The effectiveness of DSBNet is verified on two testbeds and multiple in-service computing devices in real industry. The testing results illustrate that DSBNet outperforms other state-of-the-art DNNs, especially in the non-ideal training data scenarios. [ABSTRACT FROM AUTHOR]

This paper investigates multi-resonant electromagnetic shunts applied to base isolation for dual-function vibration damping and energy harvesting. Two multi-mode shunt circuit configurations, namely parallel and series, are proposed and optimized based on the H 2 criteria. The root-mean-square (RMS) value of the relative displacement between the base and the primary structure is minimized. Practically, this will improve the safety of base-isolated buildings subjected the broad bandwidth ground acceleration. Case studies of a base-isolated building are conducted in both the frequency and time domains to investigate the effectiveness of multi-resonant electromagnetic shunts under recorded earthquake signals. It shows that both multi-mode shunt circuits outperform traditional single mode shunt circuits by suppressing the first and the second vibration modes simultaneously. Moreover, for the same stiffness ratio, the parallel shunt circuit is more effective at harvesting energy and suppressing vibration, and can more robustly handle parameter mistuning than the series shunt circuit. Furthermore, this paper discusses experimental validation of the effectiveness of multi-resonant electromagnetic shunts for vibration damping and energy harvesting on a scaled-down base isolation system. [ABSTRACT FROM AUTHOR]

In this paper a critical review of literature on applications of Active Magnetic Bearings (AMBs) systems in flexible rotordynamic systems have been presented. AMBs find various applications in rotating machinery; however, this paper mainly focuses on works in vibration suppression and associated with the condition monitoring using AMBs. It briefly introduces reader to the AMB working principle, provides details of various hardware components of a typical rotor-AMB test rig, and presents a background of traditional methods of vibration suppression in flexible rotors and the condition monitoring. It then moves on to summarize the basic features of AMB integrated flexible rotor test rigs available in literature with necessary instrumentation and its main objectives. A couple of lookup tables provide summary of important information of test rigs in papers within the scope of this article. Finally, future directions in AMB research within the paper’s scope have been suggested. [ABSTRACT FROM AUTHOR]

This paper presents a novel approach to detect the milling chatter based on Variational Mode Decomposition (VMD) and energy entropy. VMD has already been employed in feature extraction from non-stationary signals. The parameters like number of modes (K) and the quadratic penalty (α) need to be selected empirically when raw signal is decomposed by VMD. Aimed at solving the problem how to select K and α, the automatic selection method of VMD’s based on kurtosis is proposed in this paper. When chatter occurs in the milling process, energy will be absorbed to chatter frequency bands. To detect the chatter frequency bands automatically, the chatter detection method based on energy entropy is presented. The vibration signal containing chatter frequency is simulated and three groups of experiments which represent three cutting conditions are conducted. To verify the effectiveness of method presented by this paper, chatter feather extraction has been successfully employed on simulation signals and experimental signals. The simulation and experimental results show that the proposed method can effectively detect the chatter. [ABSTRACT FROM AUTHOR]

In the field of vibration, driving point receptance is a well-established and widely applied concept. However, as demonstrated in this paper, when a driving point receptance is calculated using the finite element (FE) method with solid elements, it does not converge as the FE mesh becomes finer, suggesting that there is a singularity. Hence, the concept of driving point receptance deserves a rigorous examination. In this paper, it is firstly shown that, for a point harmonic force applied on the surface of an elastic half-space, the Boussinesq formula can be applied to calculate the displacement amplitude of the surface if the response point is sufficiently close to the load. Secondly, by applying the Betti reciprocal theorem, it is shown that the displacement of an elastic body near a point harmonic force can be decomposed into two parts, with the first one being the displacement of an elastic half-space. This decomposition is useful, since it provides a solid basis for the introduction of a contact spring between a wheel and a rail in interaction. However, according to the Boussinesq formula, this decomposition also leads to the conclusion that a driving point receptance is infinite (singular), and would be undefinable. Nevertheless, driving point receptances have been calculated using different methods. Since the singularity identified in this paper was not appreciated, no account was given to the singularity in these calculations. Thus, the validity of these calculation methods must be examined. This constructs the third part of the paper. As the final development of the paper, the above decomposition is utilised to define and determine driving point receptances required for dealing with wheel/rail interactions. [ABSTRACT FROM AUTHOR]

This paper extends previous work by the authors ( Journal of Sound and Vibration , 395:294-316,2017) on the acoustic field inside an annular duct with acoustic lining carrying mean axial and swirling flow so as to allow for non-uniform mean entropy, as would be found for instance in the turbine stage of an aeroengine. The main aim of this paper is to understand the effect of a non-uniform entropy on both the eigenmodes of the flow and the Green’s function, which will allow noise prediction once we have identified acoustic sources. We first derive a new acoustic analogy in isentropic swirling flow, which allows us to derive the equation the tailored Green’s function satisfies. The eigenmodes are split into two distinct families, acoustic and hydrodynamic modes, and are computed using different analytical methods; in the limit of high reduced frequency using the WKB method for the acoustic modes; and by considering a Frobenius expansion for the hydrodynamic modes. These are then compared with numerical results, with excellent agreement for all eigenmodes. The Green’s function is also calculating analytically using the realistic limit of high reduced frequency, again with excellent agreement compared to numerical calculations. We see that for both the eigenmodes and Green’s function the effect of non-uniform mean entropy is significant. [ABSTRACT FROM AUTHOR]

In rotating machine diagnosis different spectral tools are used to analyse vibration signals. Despite the good diagnostic performance such tools are usually refined, computationally complex to implement and require oversight of an expert user. This paper introduces an intuitive and easy to implement method for vibration analysis: amplitude cyclic frequency decomposition. This method firstly separates vibration signals accordingly to their spectral amplitudes and secondly uses the squared envelope spectrum to reveal the presence of cyclostationarity in each amplitude level. The intuitive idea is that in a rotating machine different components contribute vibrations at different amplitudes, for instance defective bearings contribute a very weak signal in contrast to gears. This paper also introduces a new quantity, the decomposition squared envelope spectrum, which enables separation between the components of a rotating machine. The amplitude cyclic frequency decomposition and the decomposition squared envelope spectrum are tested on real word signals, both at stationary and varying speeds, using data from a wind turbine gearbox and an aircraft engine. In addition a benchmark comparison to the spectral correlation method is presented. [ABSTRACT FROM AUTHOR]

This paper aims to investigate the effectiveness of using the torsional vibration signal as a diagnostic tool for planetary gearbox faults detection. The traditional approach for condition monitoring of the planetary gear uses a stationary transducer mounted on the ring gear casing to measure all the vibration data when the planet gears pass by with the rotation of the carrier arm. However, the time variant vibration transfer paths between the stationary transducer and the rotating planet gear modulate the resultant vibration spectra and make it complex. Torsional vibration signals are theoretically free from this modulation effect and therefore, it is expected to be much easier and more effective to diagnose planetary gear faults using the fault diagnostic information extracted from the torsional vibration. In this paper, a 20 degree of freedom planetary gear lumped-parameter model was developed to obtain the gear dynamic response. In the model, the gear mesh stiffness variations are the main internal vibration generation mechanism and the finite element models were developed for calculation of the sun-planet and ring-planet gear mesh stiffnesses. Gear faults on different components were created in the finite element models to calculate the resultant gear mesh stiffnesses, which were incorporated into the planetary gear model later on to obtain the faulted vibration signal. Some advanced signal processing techniques were utilized to analyses the fault diagnostic results from the torsional vibration. It was found that the planetary gear torsional vibration not only successfully detected the gear fault, but also had the potential to indicate the location of the gear fault. As a result, the planetary gear torsional vibration can be considered an effective alternative approach for planetary gear condition monitoring. [ABSTRACT FROM AUTHOR]

Aesthetics and functionality requirements have caused most buildings to be asymmetric in recent times. Such buildings exhibit complex vibration characteristics under dynamic loads as there is coupling between the lateral and torsional components of vibration, and are referred to as torsionally coupled buildings. These buildings require three dimensional modelling and analysis. In spite of much recent research and some successful applications of vibration based damage detection methods to civil structures in recent years, the applications to asymmetric buildings has been a challenging task for structural engineers. There has been relatively little research on detecting and locating damage specific to torsionally coupled asymmetric buildings. This paper aims to compare the difference in vibration behaviour between symmetric and asymmetric buildings and then use the vibration characteristics for predicting damage in them. The need for developing a special method to detect damage in asymmetric buildings thus becomes evident. Towards this end, this paper modifies the traditional modal strain energy based damage index by decomposing the mode shapes into their lateral and vertical components and to form component specific damage indices. The improved approach is then developed by combining the modified strain energy based damage indices with the modal flexibility method which was modified to suit three dimensional structures to form a new damage indicator. The procedure is illustrated through numerical studies conducted on three dimensional five-story symmetric and asymmetric frame structures with the same layout, after validating the modelling techniques through experimental testing of a laboratory scale asymmetric building model. Vibration parameters obtained from finite element analysis of the intact and damaged building models are then applied into the proposed algorithms for detecting and locating the single and multiple damages in these buildings. The results obtained from a number of different damage scenarios confirm the feasibility of the proposed vibration based damage detection method for three dimensional asymmetric buildings. [ABSTRACT FROM AUTHOR]

The knowledge of dynamic loads acting on a structure is always required for many practical engineering problems, such as structural strength analysis, health monitoring and fault diagnosis, and vibration isolation. In this paper, we present an online input force time history reconstruction algorithm using Dynamic Principal Component Analysis (DPCA) from the acceleration time history response measurements using moving windows. We also present an optimal sensor placement algorithm to place limited sensors at dynamically sensitive spatial locations. The major advantage of the proposed input force identification algorithm is that it does not require finite element idealization of structure unlike the earlier formulations and therefore free from physical modelling errors. We have considered three numerical examples to validate the accuracy of the proposed DPCA based method. Effects of measurement noise, multiple force identification, different kinds of loading, incomplete measurements, and high noise levels are investigated in detail. Parametric studies have been carried out to arrive at optimal window size and also the percentage of window overlap. Studies presented in this paper clearly establish the merits of the proposed algorithm for online load identification. [ABSTRACT FROM AUTHOR]

The paper discusses the conclusions obtained from a research centered on a vibration-powered milli- or micro generator (MG) operating as a harvester to yield the maximum amount of energy transferred by the vibration of an independent system. The investigation expands on the results proposed within papers that theoretically define the properties characterizing the basic configurations of a generator based on applied Faraday’s law of induction. We compared two basic principles of circuit closing in a magnetic circuit that, fully or partially, utilizes a ferromagnetic material, and a large number of generator design solutions were examined and tested. In the given context, the article brings a compact survey of the rules facilitating energy transformation and the designing of harvesters. [ABSTRACT FROM AUTHOR]