Search

In this paper, an integrated model is presented to study the axial–torsional dynamics of a distributed drill string. The coupled axial and torsional drill string dynamics typically lead to severe phenomena such as bit-bounce and stick–slip, which are the main causes of failure and efficiency reduction. The top-drive dynamics and the Bottom Hole Assembly (BHA) dynamics are interconnected through the drill pipes. In order to preserve the infinite-dimensional feature of the drill pipes in the mathematical modeling, a distributed model in terms of Delay Differential Algebraic Equations (DDAE) is proposed to represent the dynamics of the drill string. The bit-rock interaction, which consists of the cutting and the frictional components, is responsible for the coupling between the axial and torsional dynamics. A rate-independent bit-rock interaction law is employed for both cutting and frictional components. In order to capture the global bit motion, including multiple regenerative effects, the well-bottom depth function is used to determine the depth of cut. The well-bottom pattern evolution is formulated through algebraic equations rather than Partial Differential Equations (PDEs). A new formulation for the linearized drill string system in terms of Neutral-type Delay Differential Integral Equations (NDDIEs) is proposed to investigate the initiation of the oscillations around the nominal operation. By this formulation, the local stability of the distributed system is studied by determining the right-most eigenvalue of the linearized dynamics. A simulation-based case study reflecting real-life scenarios is presented to investigate the dynamical behavior of the system under different operating conditions. • Delay Differential Algebraic Equations (DDAEs) for the distributed drill-string. • Neutral-type Delay Differential Integral Equations for the linearized dynamics. • A new comprehensive approach for determining the depth of cut. • Investigating the effect of different time-delays on the stability characteristics. [ABSTRACT FROM AUTHOR]

The robustness of dynamical systems against external perturbations is crucial in engineering; however, it is often overlooked for the lack of methods for rapidly computing it. This paper proposes a novel algorithm for estimating the robustness of systems subject to time delay. More precisely, the algorithm iteratively estimates the so-called local integrity measure (LIM), that is, the radius of the largest hypersphere centered at the fixed point and located within its basin of attraction. Since time-delayed systems are infinite dimensional, initial conditions are restricted to a constrained type of initial functions. The semi-discretization method is used for rapidly simulating the dynamics of the systems, while trajectories are classified as converging or diverging using a subdivision of the reduced phase space into cells. The algorithm was tested on four different mechanical systems, and in all cases it very quickly provided an accurate estimation of the LIM. Moreover, it enabled the study of LIM trends in a multi-dimensional parameter space, which would have been unfeasible with alternative methods. This breakthrough in computational efficiency has important implications for engineering design, allowing for careful consideration of dynamical integrity and enhancing the safety and reliability of engineered systems, especially in the presence of time delays. • An algorithm for estimating the dynamical integrity of equilibria is developed. • The algorithm works for time-delayed dynamical systems. • The algorithm works iteratively, it is very quick and has no memory issues. • It enables one to consider dynamical integrity during engineering design. • Several case studies demonstrate the effectiveness of the algorithm. [ABSTRACT FROM AUTHOR]

The identification of vibration sources is a subject that has already been widely studied and exploited by both the scientific community and the industries. The methods were initially intended for the identification of vibration sources on different structures like beam, plates and shells, but they are also used today for the characterization of materials or defect detection. This paper proposes an improvement of the corrected force analysis technique (CFAT) published several years ago and based on the force analysis technique (FAT). Inverse methods are redefined in the polar coordinates which are more suited to the problem of circular filtering. Polar inverse methods will be applied on the case of a car window excited by a turbulent flow by simulations and experiments. [ABSTRACT FROM AUTHOR]

• A path integration method based on decoupling probability mapping is proposed. • A novel one-step transition probability density function matrix is constructed. • The case of multiple impulses within a one-step transition interval is handled. • The randomness of impulse instants is fully considered. • An idea is provided for various stochastic systems satisfying Markov properties. In this paper, a new path integration method is proposed for stochastic dynamical systems excited by Poisson white noise. An efficient one-step transition probability density function (TPDF) matrix is constructed based on a decoupling probability mapping. The new method can handle the case of multiple impulses occurring in a one-step transition time interval and considers the randomness of the impulse instant, which compensates for a drawback of previous path integration methods. The probability mapping realizes the decoupling of randomness and the one-step TPDF matrix, which can be extended to general stochastic systems satisfying the Markov property. The stochastic responses of two dynamical systems excited by Poisson white noises for different mean arrival rates are obtained by using the new path integration method, and MC simulations prove that the new method is very effective, and it maintains good accuracy even for large mean arrival rates. [ABSTRACT FROM AUTHOR]

• A SAFE-PML model is developed to predict SAW propagation in prestressed media. • Effects of material anisotropy and residual stress on SAWs are studied. • The proposed SAFE-PML model is used for two practical examples. • The relationship between two types of acoustoelastic theories is discussed. Dispersion of broadband surface acoustic waves (SAWs) is often used for the nondestructive evaluation of near-surface elastic properties of materials. The accurate forward model of SAW propagation is essential for inversion. In this paper, we present a combining semi-analytical finite element (SAFE) and perfectly matched layer method for accurately predicting the phase velocity dispersion, attenuation and polarization modes of SAWs in any prestressed anisotropic layered half-space. Equations of motion are formulated based on the Biot's theory of small deformations influenced by initial stress, so it does not matter whether the residual stress results from hyperelastic transformations. The simulated results are firstly validated by the solutions from the exact three-dimensional elasticity theory-based method. The SAFE method is then used to discuss the effect of material anisotropy and residual stress on the SAWs. Finally, the method is applied to two practical examples. The differences and similarities of two common types of acoustoelastic theories are also discussed. [ABSTRACT FROM AUTHOR]

Rotating machines are often subjected to fluctuating torques, which causes rotor vibrations, early wear and noise pollution. These vibrations can be reduced using centrifugal pendulum vibration absorbers (CPVAs), which are passive devices made of several bodies (pendulums) oscillating along a given path and rotating relatively to a rotor. Previous studies showed that the dynamics of these devices is subjected to instabilities leading to a localisation of the motion of the pendulums. In this paper, the localised behaviour of a CPVA made of two pendulums allowed to rotate about their centre of mass is investigated. To this aim, a dynamical model based on an analytic perturbation method is established. The aim of this model is to highlight some special features of the localised response, such as the appearance of quasi-periodic regimes. The case studies showed that in some special cases, localisation can improve the filtering efficiency as compared to a unison motion. The validity of the model was confirmed through a comparison with numerical resolutions of the system's dynamics. • The periodic response and stability of a CPVA with rocking pendulums are analysed. • The localised pendulums' response is investigated in details analytically. • An advanced stability analysis is proposed to compute analytically Neimark–Sacker bifurcations. • The analytical results are validated using numerical resolution methods. • Quasi-periodic and chaotic solutions are observed numerically. [ABSTRACT FROM AUTHOR]

• A synchronization approach for structural health monitoring data is introduced. • Time lags are estimated from the slopes of cross spectral density phase plots. • The proposed approach is applied at the post-processing stage. • Time lag estimation is robust in the presence of non-proportional damping. • The applicability of the approach is tested with simulations and real-world data. Since the advent of structural health monitoring (SHM), vibration analysis has been one of the most popular strategies for yielding modal information of structures, such as eigenfrequencies and mode shapes. As a result of the relatively high sampling rates adopted in vibration analysis, obtaining accurate modal information requires absolute synchronization of structural response data. Despite the advances in sensing technologies and synchronization protocols, synchronization discrepancies in structural response data may occur due to drifting in internal clocks of independent data acquisition units. Particularly in wireless SHM, in which each wireless sensor node essentially operates as an independent data acquisition unit, mitigating clock drifting has been an area of intensive research. This paper addresses the issue of data synchronization from a physics-based perspective, aiming to add an additional synchronization check at the post-sampling stage. Specifically, a frequency-domain synchronization approach is reported, which builds upon the relationship between time lags in structural response data and the cross spectral density phase angles. Validation tests are conducted using simulations of a multi-degree-of-freedom oscillator and data collected from a full-scale road bridge, demonstrating the capability of the approach to estimate time lags between SHM data even in the presence of non-proportional damping, thus overcoming a common limitation of other synchronization methods. The frequency-domain synchronization approach is intended to complement synchronization protocols in extracting accurate modal information. [ABSTRACT FROM AUTHOR]

This paper presents an analytic solution for the aerodynamic noise generated by a traveling wavepacket passing near the edge of a rigid semi-infinite flat plate. The solution is derived in the time domain for a wavepacket of either constant or spatially-varying wavenumber, for which novel closed-form expressions are obtained for the incident and scattered sound fields. The case of a varying wavepacket constitutes a surrogate model for turbulent flow distortions caused by the edge region and its geometry. This modeling approach permits a relaxation of the frozen gust assumption that is commonly used in the analytical prediction of trailing-edge noise, whereby the local vorticity is assumed to be unaffected by the edge. Our results shed light on the role that spatial variations of the vortical field near the trailing edge have on the incident and scattered sound contributions to the acoustic far field. In particular, we find that the wavenumber modification has a significant effect on the incident field but not on the scattered field amplitude. However, the phase difference between the incident and scattered fields depends strongly on the spatial variation in the wavepacket wavenumber, which leads to a variation in the sound level and directivity of the total pressure field. • Wavenumber modification used to study effect of relaxing the frozen gust assumption. • Novel closed-form expressions derived for the far field acoustic pressure. • Scattered field amplitude is not affected by wavenumber modification near the edge. • Wavenumber modification affects the incident field amplitude and phase difference. [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]

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]

Vision-based measurement is an emerging method for vibration tests due to its non-contact nature and high spatial resolution, which make the full-field measurement possible. Conventional vision-based measurement requires two or more cameras to produce an out-of-plane response measurement. However, the additional cost of another camera and synchronization system makes applying this kind of measurement method to real-world engineering projects more challenging. This paper presents a single-camera method for measuring the out-of-plane vibration of plate structures. To accomplish that, the image variation induced by the motion of a plane is represented using a motion-parametric homography. Under the Lucas–Kanade framework, the motion-parametric homographies are estimated separately for each region of interest (ROI) between images, and the out-of-plane displacement response is obtained concurrently. The proposed method's results are confirmed in good agreement with those of the laser Doppler vibrometer through an impact test on a steel plate structure. • Simultaneous identification of full-field out-of-plane displacement of plate structures from videos. • Based on a combination of motion-parametric homography and Lucas–Kanade algorithms. • Monocular, no need for a second camera. • Enables extraction of full-field vibration modes of plate structures. • Validated by laboratory experiments with Laser Doppler Vibrometer. [ABSTRACT FROM AUTHOR]

• The seal-vibrissa-shaped cylinder can weaken the regular vortex shedding in its wake. • The seal-vibrissa-shaped cylinder can mitigate the spanwise coherence of wake vortices. • The seal-vibrissa-shaped cylinder can suppresses the fluctuations on cylinder surfaces. • The seal-vibrissa-shaped cylinder can reduce the aerodynamic noise by inhibiting its tonal peak. • The configurations of seal-vibrissa-shaped cylinder can be applied for aerodynamic noise control of cylindrical-like bars. Inspired by the special structure of seal vibrissae and their ability to effectively suppress vortex-induced vibrations, this paper studies the characteristics of flow and aerodynamic noise generated around a seal-vibrissa-shaped cylinder at a Reynolds number (based on the hydrodynamic diameter and freestream velocity) of 6 × 104 using the delayed detached-eddy simulation model combined with the acoustic analogy approach. The far-field aerodynamic noise has also been measured at Reynolds numbers of 6 × 104∼1.2 × 105 in an anechoic wind tunnel to compare the seal-vibrissa-shaped cylinder with cylindrical and elliptical bars of the same characteristic dimensions. The calculated spectra of aerodynamic noise agree well with the wind tunnel measurements, verifying the accuracy of the numerical simulations. It is found that the three-dimensional flow separations introduced by the alternative saddle and nodal planes of the seal-vibrissa-shaped cylinder inhibit shear layer interactions and reduce the spanwise coherence, resulting in a wake with no dominant coherent structures and thus suppressing pressure fluctuations on the solid surfaces. The configuration of seal-vibrissa-shaped cylinder eliminates the regular Kármán vortex street which generally occurs in a cylinder wake, and consequently inhibits the tonal peak in the aerodynamic noise. The sound pressure level is also reduced in most frequencies. The consistency of the normalized spectra of the far-field aerodynamic noise and the vortex shedding frequency at different inflow speeds demonstrates the high accuracy of the anechoic wind tunnel measurements. Compared with cylinders with circular or elliptical cross sections, the seal-vibrissa-shaped cylinder effectively reduces the flow-induced noise by, respectively, 13 dB or 11 dB for a far-field receiver of 90° at Reynolds number of 6 × 104, showing great potential in reducing aerodynamic noise. [ABSTRACT FROM AUTHOR]

• A novel light-powered self-oscillating liquid crystal elastomer (LCE) bow is established. • The swing of the light-powered LCE bow has two motion regimes: self-oscillation regime and static regime. • The critical conditions for triggering the self-oscillation are numerically obtained. • The amplitude of the self-excited oscillation can be controlled by several parameters. The self-oscillating system is capable of harvesting energy directly from a steady external environment to maintain its own continuous motion, without the need for an additional controller. It has potential application value in the fields such as micromachines, soft robotics and sensors. Currently, existing self-oscillating systems are relatively complex and difficult to fabricate and control, which limits their practical applications. In this paper, we present a novel light-powered self-oscillating liquid crystal elastomer (LCE) bow, composed of one LCE fiber, two cantilever beams and two masses, that can self-oscillate continuously and periodically under steady illumination. Considering the well-established dynamic LCE model and beam theory, we formulate the governing equation of the self-oscillating LCE bow and theoretically investigate its dynamics. Numerical calculations predict that the LCE bow always develops into one of two motion regimes: either static or self-oscillation. The self-oscillation is maintained by the LCE fiber which absorbs light energy to compensate for the damping dissipation. The control strategies and design principles for amplitude, frequency and equilibrium position of the self-oscillation are also investigated in details. The suggested LCE bow offers potential advantages in terms of simple structure, customizable size, flexible regulation and easy assembly, and these findings are expected to provide insights for the design and utilization of self-oscillating LCE bows in autonomous robots, energy harvesters, sensors and bionic design. [Display omitted] [ABSTRACT FROM AUTHOR]

Frequency-domain expressions of sound pressure field radiated by moving source were derived successfully only for some special moving trajectories in the literature. In this paper, a frequency-domain expression of sound pressure field radiated by monopole source with general moving trajectory is firstly derived. This expression has a simple mathematical form, where the sound pressure spectrum is written as a Fourier transformation of free-field frequency-domain Green functions along the trajectory. This expression is subsequently verified through theoretical and numerical verification. In theoretical verification, this expression is degenerated into the known analytical solution in each case with special moving trajectories. In numerical verification, the sound pressure spectra calculated via this expression are consistent with those calculated via a time-domain numerical method in cases without known analytical solutions. This expression is finally applied to enable the mode composition beamforming method to localize a rotating source with time-variant rotation speed. • An analytical frequency-domain expression of sound pressure field is derived. • New expression uses Fourier transformation of free-field Green functions. • New expression enables theoretical analysis of source with general moving trajectory. • New expression has higher computational efficiency than time-domain methods. • New expression enables MCB to localize source with non-constant rotation speed. [ABSTRACT FROM AUTHOR]

The self-synchronization of rotors in a nonlinear system has both academic and practical importance because of its applicability as a source of excitation for vibratory machines. Although the characteristics of such self-synchronization can be clarified by analyzing the periodic solutions of the equations of motion, only self-synchronization corresponding to the stable periodic solution is realized in actual systems. The stability of the solution is thus one of the most important characteristics of self-synchronization. In this paper, to stabilize periodic solutions suitable for application to vibratory machines, the effects of the damping of the rigid body and the moment of inertia of the rotors on stability are examined using a system that consists of two unbalanced rotors installed in a rigid body. High-precision analysis conducted using the shooting method shows that it is possible to stabilize the instabilities caused by period-doubling and Hopf bifurcations while keeping other characteristics, such as the synchronous frequency and the rigid body amplitude, mostly unchanged. The findings of this study can serve as a guide to extending the range of stable periodic solutions and are thus expected to be useful in the design of systems that utilize the self-synchronization of rotors. [ABSTRACT FROM AUTHOR]

• A rotor-SFDs-casing model is built to study the diving-climbing maneuver numerically. • Flexible casing changes the support characteristics of a rotor system. • The deflection will appear in the rotor vibrations during diving-climbing maneuver. • There are additional components in the vibration due to the SFDs and flexible casing. • Results illustrate the effect of flexible casing and SFDs is considerable for dynamics. The thin-walled casing and squeeze film damper (SFD) of an aero-engine have significant effects on the vibration of the rotor during maneuvering flight. However, few studies have been conducted on the vibration responses of a rotor-damper-casing coupling system under this condition. This paper uses Lagrange's principle to derive the equation of motion for a rotor system that considers the flexible casing and static eccentricity of the SFDs during maneuvering flight. The model of a casing is established, and the frequency response functions (FRFs) with pre-stress are calculated by converting the flight parameters to pre-stress. Then, the FRFs are generated for various flight statuses and combined with the rotor finite element model using the linear interpolation method. The vibrations of a dual-rotor system during the diving-climbing maneuver are calculated by the Hilber-Hughes-Taylor- α (HHT- α) method. The results indicate that the deflection will appear in the rotor vibrations during maneuvering flight. The flexible supports of a casing make the vibration transfer between the High Pressure and Low Pressure rotors, and there are harmonic and subharmonic components in the vibrations of a rotor-damper-casing coupling system. Due to the influence of a flexible casing, the vibrations of a rotor vary at different speeds under the diving-climbing maneuver, even if the speed is far from the critical speed. This study illustrates the significance of considering the flexible casing and the SFD during maneuvering flight. [Display omitted] [ABSTRACT FROM AUTHOR]

• Surrogate modeling assisted by nonintrusive polar transformations is formulated. • Variabilities of Campbell diagram, mode shape and orbit are comparatively studied. • Effects of rotation direction and its interaction with uncertainties are clarified. • Novel evolution patterns in the natural characteristics and dynamics are observed. Aeroengines are usually designed with a dual-rotor configuration for the rotating part. A dual-rotor system has coupling characteristics introduced by an inter-shaft bearing, and the rotating direction of the rotors has critical influences on the performance. It becomes more complicated when the inevitable uncertainties of the dual-frequency excited dynamical system are considered. This paper delivers a comprehensive study of the natural characteristics and dynamic responses of a dual-rotor system with an inter-shaft bearing considering the non-random parametric uncertainties under co- and counter-rotating conditions. To this end, the finite element modeling and the deterministic solutions of a dual-rotor system are established. Then, the polynomial surrogate function is constructed for the desired natural characteristics and dynamic responses under non-random uncertainty. The polar interpolation technique is implemented to compute uncertain shaft orbits, overcoming difficulties in the traditional frequency-sense measure. Intensive case studies for different interval uncertain parameters are carried out and the results are comparatively discussed. It is found that the mass unbalance uncertainties only affect the respective modes excited by the rotor where the unbalance is located. The shaft stiffness has global uncertainty effects on the Campbell diagram, mode shapes, time history, shaft orbit and responses. Uncertainties in the inter-shaft bearing stiffness and speed ratio generally influence higher-order modes. The results of the present work gain insights into the modal characteristics and dynamical behaviors of the dual-rotor system under complex parametric uncertainties. [ABSTRACT FROM AUTHOR]

• A semi-analytical model is proposed for arbitrary spatially closed-coupled plates. • The model is available for arbitrary constraint conditions and curved edges. • The modal tests on the frustum/pyramid-like built-up plates are carried out. • The excellent prediction accuracy and useful parametric conclusions are achieved. A semi-analytical method and related experiments are present in this paper to investigate the free vibration characteristics of the closed-coupled plates with arbitrary spatial coupling angles and curved edges, which are the widely used structural form but researched for the first time. By combining the penalty function method with flexible setting virtual spring stiffness functions and the comprehensive relative motion relation matrices along the edges of the plates system, various types of boundary and spatial coupling connection conditions in practical engineering can be constructed. The semi-analytical solution formulas for the entire vibration model are established by using the first-order shear deformation theory (FSDT) and the two-dimensional Jacobian differential quadrature method (JDQM). To fulfill the requirements of integral operations for displacement approximation functions, the irregular domain mapping technique is employed to transform the irregular solving domain into the regular basic domain. The accuracy and applicability of the present method in predicting eigenfrequencies and mode shapes are proved by hammer modal tests concerning four pyramid/frustum-like built-up plates, comparisons with results from the open literature, as well as the finite element method (FEM) simulations of several specially designed cases. Moreover, many meaningful conclusions are drawn regarding the effects of spatial geometric parameters on the free vibration characteristics of spatially closed-coupled plates with curved edges. [Display omitted] [ABSTRACT FROM AUTHOR]

• Dynamics and stability of coupled bogies with specific couplings and stabilizers are analyzed. • Complexly modeled flexibly supported infinite coupled beam-layer reaction is used. • The improved version of Principle of Argument and D-decomposition method is discussed. • New phenomena of effect of change the viscous damping in coupling has been discovered. • The technical solutions of specific couplings are presented, and their benefits are discussed. A comprehensive investigation was carried out to analyze the vibration stability of a coupled bogie system moving uniformly along a complexly modeled flexibly supported infinite high-order shear deformable coupled beam system on a viscoelastic base. The main contribution of this study involves a comparative analysis of the specific coupling of the bogie system with and without the proposed additional stabilizer, in comparison to conventional cases. The study demonstrates significant benefits of the newly proposed options of dual coupling and additional stabilizers in terms of stability. Another contribution of the study is the feasibility of the proposed unconventional models in technical practice. A phenomenon has been discovered that increasing the viscous damping in a special coupling leads to the occurrence of motion instability in the mechanical system. The paper also presents a novel technical solution for connecting moving objects at high speeds. The benefits of the additional oscillator as a stabilizer are extensively illustrated through numerous different examples. It is well-known that when the velocity of masses, such as the bogie or any other complex oscillator, exceeds the minimum velocity at which waves propagate in the beam, the oscillation of the system may become unstable. Therefore, it is crucial to determine the conditions and stable regions of motion that involve specific combinations of system parameters. The region of instability is identified within the parameter space of the system using the D-decomposition technique and the argument principle. The bogie is specifically connected to another bogie in two new ways: with an additional stabilizer allowing double transverse displacement and providing an additional contact with the base, or with a specific coupling that enables simultaneous rotational and transverse displacement at the contact point. The analysis reveals two key findings. First, the additional mechanical stabilizer allows for the widest range of permissible suspension stiffness (largest stability region) when the connection is conventional. Second, enabling transverse displacement in the couplings results in a stable regime of motion at much lower suspension stiffness compared to other cases. [ABSTRACT FROM AUTHOR]

• Multibody system transfer matrix method for fast vibration analysis of ABH structures with complex topology. • A novel graded reinforced double-leaf acoustic black holes (GRD-ABH) structure with enhanced broadband low-frequency vibration isolation and structural stiffness. • Analytical derivation of the natural frequencies and the steady-state responses of the GRD-ABH structures. • Verification of the theoretical results by finite element method and experiments The acoustic black hole (ABH) has aroused great interest and shown high potential of application in broadband vibration control using a lightweight structure. Yet conventional ABHs still suffer from intrinsic weak structural stiffness and poor broadband low-frequency performance. Besides, there is a lack of effective computational methods for the design of complex or composite ABH structures with practically required properties. In this paper, the vibration isolation of a beam with embedded graded reinforced double-leaf ABH (GRD-ABH) structures is investigated, focusing on improving both broadband low-frequency vibration isolation performance and the structural stiffness. The multibody system transfer matrix method (MSTMM) is proposed to model and simulate the compound ABH beam, which is treated as a multibody system with complex topology. Both the free and forced vibration analysis of the GRD-ABH are conducted and the results are compared with the finite element method (FEM), thus validating the correctness and high computation efficiency of the MSTMM. The results show that the GRD-ABH beam can simultaneously enhance a broadband low-frequency vibration isolation effect and the structural stiffness compared with the conventional periodic reinforced double-leaf ABH beam. The experiment further verified the correctness of the MSTMM and the effectiveness of the vibration isolation effect of the proposed GRD-ABH beam. The proposed theoretical approach and the graded reinforced double-leaf design provide the basis for solving the vibration isolation problem of more complex ABH structures. [ABSTRACT FROM AUTHOR]

• Nonlinear dynamics of deterministic rotor system with rub-impact fault under maneuvering flight are investigated. • Interval responses of uncertain rotor system under maneuvering flight are analyzed from the perspective of displacement and impact force. • The effects of geometrical nonlinearity and maneuvering flight on rub-impact responses are revealed. Maneuvering motion inevitably leads to parametric excitations and inertial forces, which greatly aggravates the whirling motion of rotor system and then induces rub-impact fault between rotor and stator. Under this circumstance, rotor dynamic analysis under maneuvering conditions is of considerable importance for safe and efficient functioning of rotating machinery. Furthermore, the uncertainties are inherently present in mechanical systems due to wear, properties variations and working condition evolutions. The main objective of this paper is to investigate the nonlinear characteristics and interval responses of deterministic and uncertain rotor systems under maneuvering motion. Due to whirling motion with large amplitude, the geometrical nonlinearity of shaft and rub-impact nonlinearity are considered in the rotor system. Then the equations of motion of deterministic rotor system with rub-impact under maneuvering motion are theoretically derived according to the Lagrange's equation. On this basis, the parametric uncertainties of disk eccentricity and flight maneuvers involved in the rotor system are described by the Chebyshev interval algorithm. After that the nonlinear dynamic characteristics of deterministic rotor system under maneuvering motion are numerically solved and analyzed in terms of bifurcation diagram, time histories, whirling orbit, Poincaré map and frequency spectrum. Additionally, the interval responses of vibration displacement and impact force at different rotational speeds are further examined. [ABSTRACT FROM AUTHOR]

• A semi-analytical analysis method for the dynamic characteristics of kilometre-scale ultra large spacecraft is presented; • Combined with the equivalent linearization method, the equivalent mass and stiffness of geometrically large deformation beams are given; • The dynamic stiffness matrix of geometrically large deformation beam is derived for the first time. Ultra-kilometre and super-flexible spacecraft are the important development trends in the future. Classical multi-body dynamics and structural dynamics analysis theory have some limitations in dynamic modelling and solution of large deformation structures. In this paper, an improved dynamic stiffness method (DSM) is proposed to deal with the dynamical modelling and solution of ultra-kilometre spacecraft. The method retains the high accuracy and efficiency of the original DSM in dealing with continuous dynamical systems and breaks through the limitations of the original method in dealing with large deformation structures by introducing equivalent linearization techniques. Results show that the modal frequencies and mode shapes in this paper agree well with finite element solutions, and the maximum deviation is less than 1%; Besides, with the increase of spacecraft length, the structure has entered the nonlinear stage from the linear stage, the fundamental frequency of the structure will be lower than 0.001Hz, and the influence of structure length, density, and the mass of additional cabins on natural frequencies is less significant than that in linear stage. The proposed dynamic analysis framework can be further employed in the dynamic response and vibration control problems of super large spacecraft. [ABSTRACT FROM AUTHOR]

• A rubbing force model considering abradable coatings was established. • Effects of coating wear and blade bending on intrusion depth. • The deformation of the blade was measured by experimental method. • More accurate grating displacement sensors measure the feed. • The model can be used to study rubbing with or without coating. Aiming at the phenomenon that blade bending deformation and coating wear are rarely considered in existing rubbing force models, a blade-casing rubbing model based on the Archard wear model was established in this paper. First, the bending deformation of the blade was deduced according to the torque balance relationship, the equivalent deformation of the coated casing was analysed using the equivalent stiffness method, and the clearance between the blade and casing was calculated with the consideration of coating wear based on the Archard model. Second, the influences of the casing stiffness, blade size, and Young's modulus of the coating on the rubbing force were analysed and compared with the existing rubbing force models. Subsequently, a rubbing force characterisation test bench was built considering the AlSi-polyester coating. A strain gauge was used to analyse the blade deformation, the rubbing force was compensated based on the acceleration sensor, and a grating displacement sensor was used to measure the penetration depth, which made the relative error between the experimental and simulation results was less than 15%. Finally, the rubbing force model was applied to the rotor–blade–casing system, and the influence of coating and coating wear on the dynamic characteristics of the rotor system is analyzed. The results show that the model proposed in this paper is more suitable for the rub-impact faults of the elastic blade with an abradable coating on the casing surface. The rubbing force model considering the coating wear is beneficial to accurately predict the rubbing force. [ABSTRACT FROM AUTHOR]

This paper presents a boundary element method for calculating the sound pressure level on and above a ground-board placed on an infinite ground plane with constant impedance. This method uses the Green's function for the Helmholtz equation in a half-space bounded by an infinite impedance plane and therefore avoids the complications which occur when modeling the ground as a finite impedance plane (which results in diffraction from the edges of the ground plane). Two formulations are presented: the first one models a finite thickness ground-board, whilst the second one models a zero-thickness ground-board with the upper surface coplanar with the ground plane. The method is validated against an equivalent finite element method simulation and example calculations are presented for typical ground-board designs used for outdoor noise measurements on different ground impedance planes and incidence angles. It is shown that the sound pressure level on the upper surface of a ground-board placed on a non-rigid ground can vary significantly and that this variation is dependant on the ground impedance, angle of incidence and frequency. These findings are consistent with previous investigations and highlight the fact that noise measurements made using ground-board mounted microphones on a non-rigid ground are dependant on the impedance of the surrounding ground surface. The method presented in this paper could be used to develop corrections to straightforwardly account for this effect. [ABSTRACT FROM AUTHOR]

• Firstly use the zero-phase filtering technique to remove the edge effect of component response extracted from vehicle's response. • Propose the three-step mode shape correction method (MSCM) to remove the shifting and shrinking effects of the mode shapes identified. • Propose the trial-and-error method for accurately determining the damping ratio of the bridge with no subjective judgment. • The proposed technique can accurately identify the modal properties of damped bridges with no prior knowledge of bridge damping. • Field proof is conducted to verify the efficacy of the proposed technique. A novel method is proposed to simultaneously identify the mode shapes and damping ratios of a damped bridge using a single-axle scanning vehicle. This paper starts with the theoretical formulation for the vehicle-bridge system. Then the zero-phase filtering technique is adopted to extract the component response that is free of the edge effect from the test vehicle's response. To remove the shifting and shrinking effects caused by bridge damping on mode shapes, a novel three-step mode shape correction method (MSCM) is newly proposed, which does not require prior knowledge of the bridge damping. In addition, a trial-and-error approach is newly proposed for objectively calculating the bridge damping ratio. The feasibility of the proposed method is verified by theoretical studies and field proof. New findings of the paper include: (a) all the mode shapes produced by the MSCM do not show any shifting or shrinking phenomena as previously encountered, (b) the proposed method can accurately determine the first few modal properties of damped bridges with damping ratio up to 5%, and (c) the modal properties identified by the proposed method are validated by results from theory and field measurement for a three-span continuous bridge. [ABSTRACT FROM AUTHOR]

• A novel tapered beam micro-gyroscope is developed. • Static analysis and natural frequency solution of the system are carried out and the influences of the system parameters on the pull-in voltage are discussed. • Frequency-response analysis of the tapered beam micro-gyroscope with considering the nonlinearity of electrostatic force is investigated. • An approach to enhance the bandwidth and sensitivity of micro-gyroscope can be proposed by using the nonlinear factors and tapered beam structure. In this paper, nonlinearity is used to enhance the sensitivity and bandwidth performance of tapered beam micro-gyroscopes. Considering the electrostatic force nonlinearity and fringing field effects, the governing equations of system are derived by Euler angular transformation and Hamilton principle. The influences of parameters such as the shape factors and DC voltage on static deflection, pull-in voltage and natural frequency of tapered beam micro-gyroscope are analyzed by the Adomian decomposition method (ADM). Galerkin discretization is performed on the governing equations of the tapered beam micro-gyroscope. Frequency-response equation of the system is deduced and solved by applying the method of multi-scale (MMS). The convergence analysis of the frequency response curve is performed, and then verified by the Runge-Kutta method. Finally, the performance of the tapered beam micro-gyroscope is analyzed in terms of bandwidth, sensitivity, and calibration curve nonlinearity under the different shape factors. The maximum amplitude of response in the driving and sensing directions increases significantly with the change of shape factors of the tapered beam in the dynamics analysis. Compared with the straight beam micro-gyroscope, the tapered beam micro-gyroscope has the higher amplitude and pronounced nonlinear characteristics. Due to the electrostatic force nonlinearity, the amplitude of motion in the driving direction has a high response over a wide frequency band, while also effectively increasing the detection bandwidth. In addition, the nonlinear micro-gyroscope has less loss of sensitivity performance during damping fluctuations. Therefore, in view of the contradiction between bandwidth and sensitivity of the traditional micro-gyroscope, this paper proposes a solution from the perspective of structural design and nonlinear characteristics of the tapered beam micro-gyroscope. [Display omitted] [ABSTRACT FROM AUTHOR]

• Working principles of seismic electromagnetic tunable vibration absorbers (EM-TVAs). • Scaling analysis of EM-TVAs electro-mechanical properties. • Scaling analysis of EM-TVAs tuning. • Tonal flexural vibration control of a fuselage section with a rising number of smaller scale EM-TVAs. • Broadband flexural vibration control of a fuselage section with a rising number of smaller scale EM-TVAs This paper presents a case study on the tuning and flexural vibration control effects generated either by many-small-scale or few-large-scale electromagnetic tuneable vibration absorbers on a model section of an aircraft fuselage structure. The absorbers are formed by a coil-magnet seismic transducer connected to a tuneable resistive-inductive shunt. The control of both tonal and broad-band disturbances is investigated with reference to the number, and thus the size, of the units. The principal aim of the paper is to address the key question on whether, for a fixed total weight of the absorbers, it would be preferable to have a small number of comparatively larger and heavier units or a greater number of comparatively smaller and lighter units. To this end, the first part of the paper presents a comprehensive scaling analysis based on fundamental principles of the physical properties and tuning laws of the electromagnetic tuneable vibration absorbers. Then, the second part of the paper presents a simulation study on the optimal-tuning and the vibration control effects of setups with 4, 8, 16, 32 electromagnetic tuneable vibration absorbers whose total weight is kept equal to 6% of the weight of a model fuselage structure. The study shows that arrangements with many small-scale units produce larger vibration control effects than setups formed by comparatively fewer, larger scale, units. However, the operation frequency range of the EM-TVAs tends to shift to higher frequencies with downsizing. Moreover, the size of the optimal shunt inductance that would guarantee the tuning of the EM-TVAs tends to grow as the unit is downscaled such that an artificially large inductor may be required. [ABSTRACT FROM AUTHOR]

This paper presents an investigation of the non-minimum phase (NMP) zeros in the single input single output (SISO) transfer function of three-DoF (degrees of freedom) damped flexible linear time-invariant (LTI) systems under the assumption of classical damping. It is well-known that when all the modal residue signs of any multi-DoF damped flexible LTI system are the same, NMP zeros never occur in the system dynamics for any value of system parameters including modal residue, modal frequency and modal damping ratio. However, when all the modal residue signs are not the same, then additional conditions in terms of the system parameters are required to guarantee the elimination of NMP zeros. In this paper, the zero loci of a three-DoF damped flexible LTI system are developed to derive the sufficient and necessary conditions for the elimination of all NMP zeros. These conditions can be employed in the robust physical design of flexible systems, i.e., as long as these conditions are satisfied, the elimination of NMP zeros is guaranteed even when the system parameters undergo variations. [ABSTRACT FROM AUTHOR]

This paper presents a new design of a perforated plate-type acoustic metamaterial (PAM) to evade the influence of membrane pre-tension on the acoustic performance of metamaterials and to enable air ventilation while achieving the designated sound insulation. The study embarks on the analysis of sound insulation mechanism of a typical perforated membrane-type acoustic metamaterial (MAM) from the acoustic context, and discloses that sound transmission loss (STL) peaks of a perforated MAM are due to the strong wave interference between sound sources transmitted through the orifice(s) and the membrane(s). The sound insulation mechanism is explored further in the study by an acoustic impedance analysis of a perforated metamaterial using an electro-acoustic analogy in the latter part of the paper, and the result confirms that the STL peaks of a perforated PAM (or MAM) are indeed the outcome of a strong sound interference. The study also compares an experiment test and a finite element simulation on the sound transmission of a perforated PAM based on the new design. The result confirms that the new perforated PAM can yield a good broadband STL at relatively low frequencies. A practical application using the perforated PAM design is applied to reduce the noise propagation from the compressor compartment of a commercial refrigerator. The test result verifies the effectiveness of the design in terms of both sound reduction and air ventilation. [ABSTRACT FROM AUTHOR]

• We propose a new moving force identification method with two levels of regularization in time-frequency domain. • Noise-enhancement is clarified by the mechanism of stochastic resonance. • Filtered input signals may result in worse identification results. It is well-known that the response matrix in moving force identification (MFI) is ill-posed, so the identified force is apt to be affected by measurement noise. The effect of noise could be mitigated to some extent by traditional regularization methods, which do not distinguish between white noise and colored noise. However, this paper addresses that adding certain types of white noise can be helpful in suppressing the influence of colored noise because stochastic resonance (SR) can occur due to the interaction between the white noise and the nonlinear process of the MFI. With these understandings, this paper proposes a new MFI method that has two levels of regularization. In the first level, the response matrix is transformed to the time-frequency domain by wavelets with high time-frequency resolution. Thus, the new response matrix is more robust because the major frequency components are more prominent. In the second level, the element-wise Bayesian regularization is adopted to apply regularization on each force element. As regularization weights are determined by the measurement with noise, optimal weights can be obtained by adding certain white noise. This noise enhancement effect is demonstrated by several numerical simulations. Then, the performance of the proposed method is further validated in experimental studies. [ABSTRACT FROM AUTHOR]

The present research addresses the dynamic behaviour of an air spring with a pipeline connected to a reservoir in a frequency range up to 400 Hz, in which structure-borne vibration transmission may occur due to both the structural behaviour of the bellows and fluid dynamics in the pneumatic circuit of the suspension. Based on experimental results, three frequency ranges are distinguished where different resonances of the suspension appear: low (up to 30 Hz) due to the air flow between the bellows and the surge reservoir, intermediate (30–150 Hz) due to the formation of standing waves in the pipeline and high (beyond 150 Hz) due to the structural dynamics of the bellows. A novel modelling technique to predict the dynamic behaviour of the pneumatic system in all these frequency ranges is presented and validated: this consists of an enhanced Finite Element Model (FEM) considering the structural properties of the bellows and the effect of pressurised air in the bellows and in the reservoir, coupled to a model of fluid exchange between the two main air volumes which is defined using a VUFLUIDECH user subroutine developed in ABAQUS. The study focusses on the axial dynamic stiffness of the pneumatic suspension, which plays a key role in determining the transmissibility of the suspension. However, the mathematical model introduced in the paper is capable of predicting also the vibration modes of the suspension in shear and rotation, which may be relevant in some applications, e.g. when air springs are used in vehicle suspensions. • A novel dynamic model for the bellows-pipeline-reservoir pneumatic system is proposed. • The model extends the frequency range of an air suspension to 400 Hz. • Numerical to experimental comparisons are presented in the paper. • A physical explanation for resonances in the pneumatic suspension is proposed. [ABSTRACT FROM AUTHOR]

The vibro-acoustic response of complex structures with uncertain properties is a problem of great concern for modern industries. In recent years, much research has been devoted to the prediction of this response in the mid-frequency range where, because neither finite element analysis nor statistical energy analysis are appropriate, a hybrid deterministic-statistical approach becomes a suitable solution. Despite its potential, the existence of systems with active components that are too complex to be modelled numerically can limit the application of the method. However, it may still be possible to measure the dynamical response of these structures experimentally. This paper is hence concerned with the possibility of integrating experimental data into a hybrid deterministic-statistical method. To explain the new methodology, two similar case studies, consisting of a deterministic source structure that is coupled to a statistical plate receiver using passive isolators, are used. For each case, the vibratory excitation, characterised using in-situ blocked force measurements, the source structure mobility, and the isolators stiffness are experimentally determined and inserted in the proposed hybrid model of the system. The paper explains the techniques used for obtaining the considered experimental data and the theoretical model proposed for describing the systems. To validate the proposed approach, the predicted vibration response of the receiver plate is compared to the one obtained by experimentally randomising the plate in both case studies. The results show that a good agreement is obtained, both for the ensemble average response of the receiver structure and for the ensemble variance of this response. Moreover, the upper confidence bounds predicted by the hybrid method enclose well the ensemble of experimental results. The cause of some narrow-band differences observed between the predicted response and the experimental measurements is finally discussed. It is therefore concluded that the capabilities of the hybrid deterministic-statistical method can be clearly enhanced through the incorporation of experimental data prescribing active sub-systems. [ABSTRACT FROM AUTHOR]

The Acoustic Black Hole (ABH) effect is the phenomenon in which the wave velocity gradually decreases to zero when the bending wave propagates in wedge-like structures, such that no reflection occurs. This means that in the ideal scenario, flexural wave not reflects and the energy is totally captured at the tip of the wedge structure. ABH structures have great potential in the fields of vibration control and energy harvesting due to this phenomenon. In this paper, the semi-analytical method is adopted to establish the dynamical model of the one-dimensional cylindrical beam with ABH feature and arbitrary boundary condition. In order to investigate the effect of energy aggregating, the proportion of the kinetic or stain energy trapped in the arbitrary vicinity of the edge, as compared to that of the whole beam is defined and analyzed in detail. The main purpose of this paper is to analyze the different energy concentration effect between the tapered cylindrical beam and the wedge-like rectangular beam and hence to provide guidance for their applications in vibration control and energy harvesting. Numerical results show that considerable kinetic and strain energy are collected either in the tapered cylindrical beam or in the wedge-like rectangular beam. However, the energy density at the tip of the tapered cylindrical beam is obviously larger than that at the edge of the wedge-like rectangular beam. This means that vibration attenuation is increased when the same amount of viscoelastic material is adhered to the tip of the tapered cylindrical beams compared to the case of the wedge-like rectangular beams. Moreover, changing the excitation location on the tapered beam can also enhance energy concentration for different frequency bands. The theoretical model developed and new findings in this paper give rise to innovative applications of ABH beam structures in engineering and open new horizons to explore in the future. [ABSTRACT FROM AUTHOR]

Acoustic black hole (ABH), a thin wedge-shaped structure tapered according to the power-law of power (m) greater than or equal to two, has received much attention to the researchers in wave dynamics due to its potential as a light and effective absorber of elastic waves propagating in beams or plates. In this paper, the Euler-Bernoulli equation for the ABH is reformulated into the form of a generalized hypergeometric differential equation for m > 2. Then, the exact solution is derived in terms of generalized hypergeometric functions (p F q) where p = 0 and q = 3 by dividing the power m into four cases. The derived exact solution is in linearly independent and regular form for arbitrary m. In addition, by using the exact solution, the displacement field of a uniform beam with an ABH and the reflection coefficient from an ABH are calculated to demonstrate the applicability of the present exact solution. This paper aims at providing a mathematical and theoretical basis for the study of the ABHs. [ABSTRACT FROM AUTHOR]

Abstract Experimental system identification through modal analysis is often conducted by assuming linear constitutive laws and kinematic relationships. Significant prediction errors from these identified models can occur when the amplitude dependent contribution of nonlinearities is ignored. In this paper, the impact of such nonlinearities on the parameter identification and accuracy of a linear model is shown to depend significantly on the experimental procedures. Using modal analysis techniques and focusing on vibration near the fundamental mode, a cantilevered beam is modeled as a single degree of freedom oscillator with parameters to be determined through experimental system identification. Various testing procedures are described in detail and used to demonstrate the impact of nonlinearities on the outcome of different system identification processes. The signal control methods compared are (1) open loop, (2) constant input, and (3) constant response excitation. Forcing types considered are single point and distributed. Nonlinearities in experimental response are shown for all procedures, and it is demonstrated that the observed character and degree of the nonlinearities vary depending on the testing procedure. The paper makes various recommendations for experimental system identification procedures using linear structural models, which include developing empirical models for parameter shifts due to nonlinearities and using constant response tests to minimize nonlinear effects in the measured system response. By implementing these identification methods, parameter variations can be included in the linear model to significantly reduce predicted response and parameter errors for weakly nonlinear second-order systems. [ABSTRACT FROM AUTHOR]

Abstract In the present paper, the modelling, analysis and identification of various system faults in the presence of angular misalignment in coupled rotor-train systems integrated with an auxiliary AMB support has been presented. The method discussed in the paper quantifies the effect of misalignment by way of estimation of additive coupling stiffness (ACS). The novelty of the present paper lies in the modelling of a rotor-train-AMB system with two 4-dof simple rotors, each with an offset disc to have gyroscopic effects. With the combination of flexible coupling and weight dominance assumption the dynamic behaviour of rotor-bearing-coupling-AMB system has been characterized by the eight generalized coordinates of the two rotors. The coupling's angular stiffness has been modelled as the sum of direct stiffness and a time varying ACS, whose magnitude is affected by the amount of angular misalignment. A steering function has been selected such that the forced reponse due to coupling misalignment yields both odd and even harmonics in full spectrum. An identification algorithm based on least-squares regression technique in frequency domain has been developed using the forward and backward harmonics of rotor vibration and AMB current for the estimation of coupling direct stiffness, coupling additive stiffness, unbalance magnitude and its phase, equivalent viscous damping in each rotor, current and displacement constants of AMB. The assessment of severity of angular misalignment from the magnitude of estimated ACS is a novel deviation that has potential for practical application. [ABSTRACT FROM AUTHOR]

Abstract In this paper three formulations based on an Eulerian approach are presented to obtain the dynamic response of an elastic solid of revolution, which rotates around its main axis at constant angular velocity. The formulations are especially suitable for the study of the interaction of a solid with a non-rotating structure, such as occurs in the coupled dynamics of a railway wheelset with the track. With respect to previous publications that may adopt similar hypotheses, this paper proposes more compact formulations and eliminates certain numerical problems associated with the presence of second-order derivatives with respect to the spatial coordinates. Three different models are developed depending the basis function that represents the displacements associated with the deformation; these basis functions are: (1) the shape functions that are used in the three dimensional finite element (FE) method; (2) the undamped mode shapes of the solid; (3) the shape functions that are adopted in the axisymmetric FE approach. Comparisons are shown of calculations carried out using these models. These show the existence of modal veering when analysing the Campbell diagram for a railway wheel. [ABSTRACT FROM AUTHOR]

Abstract The sensor placement methods for the modal identification are usually based on the prediction error between the measured and the structural model responses. Generally, the prediction errors, which are caused by the model error and the measurement noise, are assumed to be a Gaussian random vector together. This paper proposes a conditional information entropy based sensor placement method to separately investigate the influences of the measurement noise and the model error on the sensor placement. The changes in the element stiffness matrices are used to represent the model error. To quantify the uncertainty in the modal identification result, the conventional information entropy method is not suitable, due to the uncertainty in the Fisher matrix caused by the uncertain model error. This paper proposes a conditional information entropy index to quantify the uncertainty in the modal identification result with uncertain Fisher matrices. The optimal sensor placement corresponds to the one that maximizes the conditional information entropy index value over the set of all possible sensor placements. The conventional information entropy method can be seen as a special case of the proposed conditional information entropy method. In addition, the proposed sensor placement method can be applied to the placement of the multidimensional sensors. The simply supported beam and a bridge benchmark structure are used to explain the sensor placement method, and the redundancy threshold can be set to avoid redundant information provided by closely spaced sensors. Highlights • A conditional information entropy based sensor placement method is proposed. • The model error and the measurement noise are separately considered. • The uncertainty in modal identification is quantified by the proposed CIE index. • The model error is represented by the perturbation in the element stiffness. • The proposed method can be applied to multidimensional sensors. [ABSTRACT FROM AUTHOR]

Abstract Quadratic pencils λ 2 M + λ C + K , where M , C , and K are n × n real matrices, arise in a broad range of important applications. Its spectral properties affect the vibration behavior of the underlying system which often consists of many elements coupled together through an intricate network of inter-connectivities. It is known that an n -degree-of-freedom system with semi-simple eigenvalues can be reduced to, without tampering with the innate vibration properties, n mutually independent single-degree-of-freedom subsystems, referred to as total decoupling. This paper revisits the problem with the additional constraint that the masses should stay invariant throughout the reduction process. Rescaling the masses if necessary, M is assumed to be the identity matrix. Isospectral flows are derived to either totally or partially decouple C and K to independent units of modules. Indeed, the same framework can be tailored to handle any kinds of desired structure. Two new results are obtained. First, the global convergence is guaranteed by using the Łojasiewicz gradient inequality. Second, bounds on errors due to numerical integration and floating-point arithmetic calculation are derived, which can be used for assessing the quality of the transformation. Numerical experiments on four distinct scenarios are given to demonstrate the capabilities of the framework of handling the decoupling problem. [ABSTRACT FROM AUTHOR]

Abstract A normalized Bouc-Wen model is adopt in the modelling to describe the hysteresis of magneto-rheological (MR) damper. An efficient parameters identification method of normalized Bouc-Wen model for MR damper is introduced in this paper. The parameters identification method of normalized Bouc-Wen model proposed in this paper is divided into three steps. Firstly, the physical meaning of normalized Bouc-Wen model are fully taken into consideration and the least-squares method is used to identify the parameters. Then, a Genetic Algorithm (GA) is utilized to identify the remaining parameters with an appropriate fitness function. The simulation results show that, compared to the other two method, the method proposed in this paper is more accurate, more efficient and less sensitive to data noise. [ABSTRACT FROM AUTHOR]

Abstract The phenomenon of pressure pulsations in pipeline systems caused by centrifugal pumps or reciprocating compressors are known to have detrimental effects on industrial applications. These pulsations can cause fluctuating loads on critical components in the pipeline which can ultimately lead to premature fatigue failure. This paper presents an experimental investigation of the attenuation mechanism of a Herschel-Quincke (HQ) device and its effectiveness in damping pressure pulsations when applied to a resonant piping system. When an HQ device with a length proportional to the wavelength of the targeted pulsation frequency within the main piping system is placed at acoustic pressure anti-nodes, the second acoustic mode of an open-open pipe is formed within the HQ device. This, in turn, transfers acoustic energy from the main pipeline to the HQ device in order to sustain the auxiliary resonant system. Additionally, it forces the acoustic pressure anti-nodes in the main piping system to become acoustic pressure nodes, which disrupts the resonance condition, and an anti-resonant mode is created in the main pipeline system at the targeted pulsation frequency. Additionally, the transmission loss of the HQ device was found to normalize linearly with the diameter ratio of the HQ device. Moreover, the effectiveness of multiple HQ devices on the attenuation of pressure pulsations in pipelines was investigated. For larger main pipe diameters, an HQ device can be divided into several smaller devices while maintaining the same total cross-sectional area and achieving nearly identical values of attenuation. The presence of mean flow and the directionality between the pressure pulsation and the mean flow has a minimal effect for low Mach number (M < 0.1). The results presented in this paper provide some practical considerations for the implementation of HQ devices in industrial pipeline systems under resonant conditions. Highlights • Transmission loss experimentally normalized with device to pipeline diameter ratio. • Optimal results achieved for device placement at a pressure anti-node of a resonant system. • Minimal mean flow effect on device performance for low Mach numbers/diameter ratios. • Second acoustic mode of an open-open pipe is formed within the HQ device. • Dividing a HQ device into multiple smaller devices can yield nearly identical values of attenuation. [ABSTRACT FROM AUTHOR]

Abstract With recent advancement of robotic technology, mobile wireless devices have made a paradigm shift in cost-effective and faster deployment of sensors towards health monitoring of large-scale infrastructure. A wide range of system identification methods has been developed by the researchers to accurately identify unknown structural parameters from the measured vibration data. However, most of these techniques are suitable only when all key locations of the structure are instrumented. In case of decentralized mobile sensing network where a sensor is autonomously moved from one location to another, only a single sensor is available at a particular time. In this paper, a newer time-frequency analysis method, namely Empirical Mode Decomposition (EMD), is explored and improved to undertake system identification using single channel measurement. Traditional EMD results in significant mode-mixing while analyzing closely-spaced modes and data with measurement noise. In this paper, Time-Varying Filtering based Empirical Mode Decomposition (TVF-EMD) is proposed to perform modal identification using decentralized sensing approach. The proposed method is fully adaptive and suitable for automation since it uses only one channel of data at a time. The proposed method is verified using a suite of numerical, experimental and full-scale studies using wireless sensors in a decentralized manner. [ABSTRACT FROM AUTHOR]

Abstract The physical parameters of the contact interfaces, such as preload and surface roughness quality, significantly affect the stiffness of joints. Knowledge of the relationship between these interface parameters and the equivalent stiffness allows joints to be considered in the design stages of complex structures. Hence, this paper considers the effect of contact interface parameters on the identified equivalent stiffness parameters of joint models. First, a new generic joint model is proposed to model the contact interfaces. Then, the ability of three different joint models, including the new model proposed in this paper, to capture the linear effects of contact interfaces under different preloads and surface roughness qualities is investigated. Finally, it is concluded that the preload and surface roughness quality control the normal and shearing stiffness of the joint models respectively. Experimental investigations also reveal that a complex mechanism governs the energy dissipation in the contact interface. Highlights • A new joint model representing surface roughness and preload effects is introduced. • Joint element stiffness model is obtained using decomposition of stiffness matrix. • The accuracy of the joint model is assessed using numerical and experimental data. • Experimental data reveal a complex mechanism for energy dissipation in the joint. [ABSTRACT FROM AUTHOR]

Abstract In everyday, practical, multibody, dynamic simulations, any savings in computational time are welcome. The aim of this paper is to develop an analytical mathematical approach to be used on a low-order element to reduce the computational costs. In this paper the Bernoulli-Euler beam energy formulation is expressed with an absolute nodal coordinate formulation (ANCF) and the general integral equation due to internal strain and bend generalized elastic forces is derived and expressed with the pre-computed matrices. The derived matrices, together with the Gauss quadrature integration, minimize the number of numerical operations when performing a dynamic time simulation. The equations are general and can be used for a cable element, without any restrictions on the strain-bend-displacement relationship. The proposed equations are implemented in the ANCF dynamic model, and the presented numerical results show that savings in the computational time can be achieved. [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 A modified mode-superposition method (MMSM) was presented in this paper to solve the free vibration problem of the "unconstrained" beams that the conventional mode-superposition method (CMSM) cannot easily tackle. For convenience, a beam without any attachments is called the "bare" beam, and the beam carrying any concentrated elements (CEs) is called the "loaded" beam, in this paper. Furthermore, the mode-superposition method (MSM) with only the "elastic" modes of the bare beam considered is called the CMSM, and the MSM with both the "elastic" and the "rigid-body" modes considered is called the MMSM. From the existing literature, one finds that the CMSM is one of the effective approaches for the free vibration analysis of a "constrained" bare beam (such as the C-C, P-P, or C-F beam) carrying various CEs, where "C, P and F" denote the abbreviations of "clamped, pinned and free", respectively. However, the CMSM is not available for that of an "unconstrained" bare beam (such as the F-F beam) carrying various CEs. For this reason, this paper presented a MMSM to solve the title problem so that one can easily obtain the natural frequencies and mode shapes for both the "rigid-body" motions and the "elastic" vibrations of the F-F loaded Timoshenko beam. The main difference between a "constrained" bare beam and an "unconstrained" one is that the free vibration responses of latter consist of the "rigid-body" motions and those of the former do not, so that the coupling effect between the "rigid-body" motions and the "elastic" vibrations" of the F-F loaded beam are not considered by using the CMSM. To confirm the correctness of the presented theory and the developed computer program for this paper, all numerical results obtained from the MMSM are compared with those obtained from the finite element method (FEM) and good agreement is achieved. Numerical examples reveal that the CMSM can provide neither any information regarding the "rigid-body" motions nor the accurate natural frequencies and mode shapes for the "elastic" vibrations of a F-F loaded beam, and all the above-mentioned drawbacks of the CMSM have been improved by the presented MMSM. [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]

Abstract This paper proposes a numerical method to model wave scattering by local inhomogeneities in elastic open waveguides. The damaged zone of the waveguide and its vicinity are described by a finite-element model. This model is coupled on the cross-section boundaries to a modal representation of the field propagating along the waveguide axis in the undamaged parts, yielding transparent boundary conditions. However, open waveguides are unbounded in the transverse direction, which complicates both the numerical resolution and the physical analysis. Theoretically, the wave fields are described by a discrete sum of trapped modes and two continuous sums on radiation modes. The latter is sometimes approximated by a discrete sum of leaky modes, which grow at infinity in the transverse direction. In this paper, a Perfectly Matched Layer (PML) of finite thickness is introduced to absorb outgoing waves in the transverse direction, yielding three types of discrete modes: trapped modes, leaky modes and PML modes (PML modes oscillate mainly inside the layer and are non-intrinsic to the physics). Two numerical test cases are considered: the scattering at the junction between a closed and an open cylindrical waveguides and the scattering by an axisymmetrical notch. Good agreement with literature results is found. In particular, the influence of PML modes on the scattered field is highlighted through numerical tests. Due to the lack of power orthogonality of leaky modes, it is also shown that the modal cross power can become significant, which complicates the scattering analysis of open waveguides. Finally, the generality of the proposed method is discussed through a three-dimensional test case considering an embedded bar with an oblique break. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Abstract It is well-known that the convective wave equation with a uniform mean flow can be transformed into a standard wave equation without flow by a Prandtl-Glauert-Lorentz type transformation. This paper examines the boundary condition to be used in the transformed coordinates for acoustic scattering by rigid bodies. Recently, based on the energy conservation equation for acoustic waves propagating in a uniform flow, a new solid wall boundary condition, dubbed the Zero Energy Flux (ZEF) solid surface boundary condition, has been proposed. Instead of the commonly used solid surface boundary condition that the normal acoustic velocity be zero, the ZEF condition requires that the acoustic energy flux be zero. In this paper, we point out that when formulated in the acoustic velocity potential and under the ZEF boundary condition, the normal derivative of the velocity potential remains to be zero when computed in the transformed coordinates. As such, numerical methods developed for solving the standard wave equation can be directly applied to the convective wave equation through a use of the Prandtl-Glauert-Lorentz transformation. Utilization of the transformation is particularly beneficial for numerical methods based on the boundary integral formulation because of the simplified kernel function in the transformed coordinates, for both the time domain and the frequency domain approaches. Useful relations for applying the transformation are derived and numerical examples that demonstrate the effectiveness of the transformation and ZEF boundary condition are presented. [ABSTRACT FROM AUTHOR]