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The stochastic responses and the asymptotic stability with probability 1 of vibro-impact systems with friction under wideband noise excitation were investigated. The Zhuravlev non-smooth transformation and the stochastic averaging method were extended to obtain the steady-state probability density functions of the system. The accuracy of the method was verified through comparison of the theoretical results with those from the Monte Carlo simulations. The effects of the friction force and the vibro-impact restitution coefficient on the system responses were studied. Furthermore, The Lyapunov exponent of the linearized averaged It8 equation was derived and the stability of the trivial solution was determined with the Lyapunov exponent. The results show that, changing the frictional coefficient and the vibro-impact restitution coefficient could adjust the system stochastic stability [ABSTRACT FROM AUTHOR]

Since RF breakdown is one of the primary limitations to improving the performances of RF accelerators, extensive efforts have been dedicated to locating the breakdowns. However, most existing methods rely on specialized techniques, resulting in high financial burdens. Although the method based on transient response of transmission line (TL) is suitable for facilities with sporadic recoverable breakdowns, practical operations are susceptible to notable errors. This study revisits the fundamental theories of lossless TL and investigates the wave process to understand the characteristics of the reversed pulse induced by the breakdowns. By utilizing steady-state response of the TL and employing phasor method, we derive analytical formulas to determine the exact location of breakdowns within the faulty cell for constant-gradient TW accelerator. Furthermore, the derived formulas demonstrate their independence from RF phase, thereby distinguishing them from traditional phase-based methods. Additionally, experimental validations are conducted at the HUST injector, and the results confirm the consistency of the analysis. Thus, the proposed method represents a promising improvement over the TL-based approaches and serves as a valuable complement to current techniques. Importantly, this method demonstrates particular advantages for constructed TW accelerators seeking to achieve a balance among high performance, low costs, and compact layouts.

Parametric excitation is a unique type of excitation that arises from the time-varying parameters of a dynamical system, typically induced by the periodic movements of the system components. However, the structure-moving subsystems problem creates a new type of parametric excitation where the subsystems do not have exact periodic movements. Under the circumstances, dimension of the mathematical model of such a system exhibits time dependency, which prohibits the employment of conventional analytical methods to predict its stability. In this paper, we propose a novel Generalized Sequential State Equation Method that provides a distinct solution framework for analysis of the subsystem-induced parametric resonance. With the time-domain system partition and state mapping, the proposed method reconfigures the coupled system with a sequence of state space equations and solves them chronologically. The proposed method relaxes the single-subsystem-assumption in its original form and applies to a general scenario where the subsystems travel with arbitrary characteristic period. With the proposed method, occurrences of the subsystem-induced parametric resonance are precisely predicted via a set of analytical stability criteria and the steady state response is determined in an exact analytical form. • Novel generalized sequential state equation method for parametric resonance with arbitrary characteristic period. • The proposed method advances the existing method by lifting the constraints on the inter-distance between subsystems. • Determining the stability of a moving subsystem induced parametric vibration via analytical stability criteria. • Delivering the exact waveform of the steady state of a parametrically excited structure in a general manner. • Investigating the characteristics of the subsystem induced parametric resonance in a multidimensional parameter space. [ABSTRACT FROM AUTHOR]

We formulate a particle and force level, activated dynamics-based statistical mechanical theory for the continuous startup nonlinear shear rheology of ultradense glass-forming hard sphere fluids and colloidal suspensions in the context of the elastically collective nonlinear Langevin equation approach and a generalized Maxwell model constitutive equation. Activated structural relaxation is described as a coupled local-nonlocal event involving caging and longer range collective elasticity which controls the characteristic stress relaxation time. Theoretical predictions for the deformation-induced enhancement of mobility, the onset of relaxation acceleration at remarkably low values of stress, strain, or shear rate, apparent power law thinning of the steady-state structural relaxation time and viscosity, a nonvanishing activation barrier in the shear thinning regime, an apparent Herschel–Buckley form of the shear rate dependence of the steady-state shear stress, exponential growth of different measures of a yield or flow stress with packing fraction, and reduced fragility and dynamic heterogeneity under deformation were previously shown to be in good agreement with experiments. The central new question we address here is the defining feature of the transient response—the stress overshoot. In contrast to the steady-state flow regime, understanding the transient response requires an explicit treatment of the coupled nonequilibrium evolution of structure, elastic modulus, and stress relaxation time. We formulate a new quantitative model for this aspect in a physically motivated and computationally tractable manner. Theoretical predictions for the stress overshoot are shown to be in good agreement with experimental observations in the metastable ultradense regime of hard sphere colloidal suspensions as a function of shear rate and packing fraction, and accounting for deformation-assisted activated motion appears to be crucial for both the transient and steady-state responses. [ABSTRACT FROM AUTHOR]

With the rapid development of pumped storage, the vibration problems caused by the operation of power stations have become increasingly prominent. In this paper, a large-scale pumped-storage power station is taken as the research object, and a three-dimensional refined finite element model of the underground powerhouse including the surrounding rock mass is established. Based on the analysis of the vibration source of the powerhouse and the water diversion pipeline, the modal and dynamic response analysis of the underground powerhouse of the hydropower station is carried out, and the distribution law of the larger vibration displacement position is revealed. The calculation results show that under the premise that the vibration source is selected reasonably and the numerical model is accurate, the main frequency of the underground powerhouse structure can be obtained more accurately. After optimizing the design of the underground powerhouse based on the calculation results, the resonance problem of the underground powerhouse of the hydropower station can be avoided. The dynamic elastic modulus of the rock mass around the underground powerhouse has little influence on the mode shape of the powerhouse, but has a great influence on its fundamental frequency. When the dynamic elastic modulus of the rock mass increases by 50%, the fundamental frequency of the plant increases by about 29%. At the same time, the mode shape of each order of the underground powerhouse structure does not change much, mainly manifested as the vibration of the beam system structure, which is mainly caused by the stiffness of the beam system components being much smaller than the structural stiffness of the windshield, machine pier, and mass concrete around the volute. The research results can provide references for the design of underground powerhouses of large-scale pumped-storage power stations and the analysis of vibration problems. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Xinyang Normal University Natural Science Edition is the property of Journal of Xinyang Normal University Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This article is concerned with thermal vibration behaviors of the functionally graded material–stepped cylindrical shell coupled with annular plate, including free vibration, transient response, and steady state response. The stepped cylindrical shell is divided into N s segments at locations of thickness and radius variations, which is coupled with N p annular plates. The boundary and coupling conditions are achieved by introducing the artificial virtual spring technology. Under the framework of FSDT, the displacement function of arbitrary shell segment and annular plate is expanded with Chebyshev polynomials and Fourier series for circumferential direction. Compared with results obtained by the finite element method and the references, a series of numerical examples and validations are presented to verify the convergence and accuracy of the current method. The effects of the relevant parameters containing the geometric parameters, boundary conditions, various loadings, and the thermal environment are investigated in detail. [ABSTRACT FROM AUTHOR]

This paper has been proposed to simulate the transient model of 3- cage rotor induction motor based on winding function approach (WF A). According to this method the motor is assumed to be consist of an ele.ctrical circuits on both stator and rotor. The magneto motive forces (MMF) that have been generated by these circuits play a role for coupling them together. Then mutual and self-inductances will be easily computed using WF A. Two types of WF A have been used to build and simulate the model of the induction motor. In the one part type, it's assumed that the coupling JvINIF between stator and rotor have a non-sinusoidal shapes according to the actual windings distribution over the motor slots. While in second prut type the generated MMF in ru·e assumed to have sinusoidal wavefonn. TI1e suggested models may be used to simulate the dynamic as well as steady state performance of a faulty and non-faulty motor. A simulation of the suggested models that consists of m-rotor bars and n-stator phases multiple coupled circuit-based has been perfonned using matlab m.file and the results of the motor ctment have been proved in its nonlineru· way by using \VF A. [ABSTRACT FROM AUTHOR]

Copyright of Engineering Mechanics / Gongcheng Lixue is the property of Engineering Mechanics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract The objective of this paper is to present a numerical scheme for applying nonlinear modal synthesis to study the dynamic performance of assembled structures with a frictional interface. A generalized Masing model is introduced to describe the frictional mechanism in steady state to enable obtaining the harmonic components of the friction force. By employing the concept of nonlinear modes based on normal form theory, a reduction technique based on branch modes can be applied to obtain a reduced order model. Both complex nonlinear modes and real nonlinear modes depending on the modal amplitude are used in the nonlinear modal synthesis approach, leading to a particular damping term representing energy dissipation due to friction. The implementation of the nonlinear modal synthesis combined with the generalized Masing model provides a simple, fast and efficient numerical method for describing the nonlinear performance of structures with dry friction devices. The proposed approach is applied to three increasingly complex case studies. Numerical simulations are carried out to demonstrate the efficiency and reliability of the method. [ABSTRACT FROM AUTHOR]

Due to the out of phase vibration of the internal units, unusual frequency dependent extreme properties, such as negative effective mass, can be perceived in a metamaterial. However, the performance of the linear metamaterial is limited to a narrow bandwidth due to the dependency on linear resonance. In this paper, this main limitation of the metamaterial is addressed by introducing the piecewise linear impacting oscillator at the mass-in-mass resonating unit. The impacting system dissipates energy and consequently attenuates the vibration of the main structure due to the counteraction of the external excitation by the resulting impulse force. Attenuation bandwidths can be increased in higher and lower frequency side for impact metamaterial as it can attenuate the two transmission peaks. In the lower frequency side attenuation bandwidth can be increased 50% and in the higher frequency side it theoretically becomes infinite. Therefore, impacting metamaterial can be considered as a potential solution towards low frequency and wideband vibration isolator. This paper also thoroughly discussed different nonlinear responses in each units of metamaterial chain. [ABSTRACT FROM AUTHOR]

Vibration transmission through a mass-in-mass unit is frequency dependent due to the difference in phase between the internal resonator and the surrounding structure. Generally, the attenuation band is confined between the two-transmission bands for a linear resonating metamaterial. In the case of a linear metamaterial, the attenuation band can be widened up to a certain limit by tuning the material properties, but cannot be extended infinitely by removing the 2nd transmission band. An impacting resonator can attenuate the vibration of the metamaterial due to the counteraction of the external excitation by the resulting impulse force and due to the presence of the sub and super-harmonic and chaotic responses. This paper theoretically elucidates that an impact metamaterial can results zero averaged effective mass for the multi-periodic type impacting vibration as in these frequency ranges vibration becomes essentially out of phase. Most importantly, an impacting metamaterial has a potential to extend the attenuation bandwidth by reducing the vibration of the main structure even for the minimal mass ratio. The scope of the paper is limited to analysis of a single building block of the impacting metamaterial to provide better insight comprehension of the effect of impacting oscillation inside a metamaterial unit more systematically. [ABSTRACT FROM AUTHOR]

The enzymatic biofuel cells (EBFCs) are considered as an attractive candidate for powering future implantable medical devices. In this study, a computational model of EBFCs based on three-dimensional (3-D) interdigitated microelectrode arrays was conducted. The main focus of this research is to investigate the effect of different designs and spatial distributions of the microelectrode arrays on mass transport of fuels, enzymatic reaction rate, open circuit output potential and current density. To optimize the performance of the EBFCs, numerical simulations have been performed for cylindrical electrodes with various electrode heights and well widths. Optimized cell performance was obtained when the well width is half of the height of the 3-D electrode. In addition, semi-elliptical shaped electrode is preferred based on the results from current density and resistive heating simulation.

This paper describes a simple and fast numerical procedure to study the steady state responses of assembled structures with nonlinearities along continuous interfaces. The proposed strategy is based on a generalized nonlinear modal superposition approach supplemented by a double modal synthesis strategy. The reduced nonlinear modes are derived by combining a single nonlinear mode method with reduction techniques relying on branch modes. The modal parameters containing essential nonlinear information are determined and then employed to calculate the stationary responses of the nonlinear system subjected to various types of excitation. The advantages of the proposed nonlinear modal synthesis are mainly derived in three ways: (1) computational costs are considerably reduced, when analyzing large assembled systems with weak nonlinearities, through the use of reduced nonlinear modes; (2) based on the interpolation models of nonlinear modal parameters, the nonlinear modes introduced during the first step can be employed to analyze the same system under various external loads without having to reanalyze the entire system; and (3) the nonlinear effects can be investigated from a modal point of view by analyzing these nonlinear modal parameters. The proposed strategy is applied to an assembled system composed of plates and nonlinear rubber interfaces. Simulation results have proven the efficiency of this hybrid nonlinear modal synthesis, and the computation time has also been significantly reduced. [ABSTRACT FROM AUTHOR]

The major purpose of this study is to research the local rub fault transfer mechanism in rotor system, that is, the influence of local faults on the whole rotor system. The proposed rotor model is based on Euler-Bernoulli beam finite elements. The dynamic model takes into account the gyroscopic moment of rotor as well as the elastic support. The local rub fault is equivalent to external excitation in the equations of motion. The local rub fault transfer mechanism derives from the harmonic balance theory by the relationship between the harmonic components of vibration response and the frequency domain response matrices. The response of any other nodes in the rotor system is obtained by the transfer mechanism. Effectiveness and robustness of the transfer mechanism are verified by numerical simulation and experiments. The transfer mechanism has a good applicability for the main vibration faults in rotor system such as rub, misalignment and crack. [ABSTRACT FROM AUTHOR]

This paper proposes an improved analytical model for the study of steady-state performance of droop-controlled VSC-MTDC systems. When power disturbances occur, such as those imposed by normal changes in power settings and converter outages, the powers of the converters with droop control may hit their limits and hence such converters no longer contribute to power sharing, which should be paid special attention when analyzing the impacts of power disturbances on the performance of multi-terminal HVDC (MTDC) systems. Based on the bisection algorithm and superposition principle, the proposed analytical model provides an easy way to estimate the results of power distributions, dc voltage deviations, and power loss variations of the MTDC system taking converter outage and converter overload into account. Simulations of a modified New England 39-bus system incorporating a four-terminal MTDC system are carried out for validating the proposed analytical model. [ABSTRACT FROM AUTHOR]

Impacting events are discontinuous and non-smooth in nature; thus, resulting in various forms of complex nonlinear dynamics. A numerical algorithm has been developed based on the analytical solution to distinguish different classes of impacting responses. The main advantages of the solver are that it can either stop the integration process after automatically identifying the steady state solution or continue until the maximum time is reached in case of the chaotic type response. To identify the frequency of higher periodic response, a periodicity coefficient has been defined as the frequency ratio of excitation and the system's response. The effect of coefficient of restitution on the different dynamic responses is also discussed within the scope of the paper. The amplitude of the vibration of the main mass is reduced due to the presence of the multi-periodic and chaotic impacting responses for a wide range of excitation frequencies. These characteristics make impact dampers ideal for applications in wideband vibration insulation and a unit of wideband nonlinear metamaterial. [ABSTRACT FROM AUTHOR]

Lateral vibration of rotors can be significantly reduced by inserting the damping elements between the shaft and the casing. The theoretical analysis, confirmed by computational simulations, shows that to achieve the optimum compromise between attenuation of the oscillation amplitude and magnitude of the forces transmitted through the coupling elements between the rotor and the stationary part, the damping effect must be controllable. For this purpose, the squeeze film dampers lubricated by magnetorheological fluid can be applied. The damping effect is controlled by the change of intensity of the magnetic field in the lubricating film. This article presents a procedure developed for investigation of the steady state response of rigid rotors coupled with the casing by flexible elements and short magnetorheological dampers. Their lateral vibration is governed by nonlinear (due to the damping forces) equations of motion. The steady state solution is obtained by application of a collocation method, which arrives at solving a set of nonlinear algebraic equations. The pressure distribution in the oil film is described by a Reynolds equation modified for the case of short dampers and Bingham fluid. Components of the damping force are calculated by integration of the pressure distribution around the circumference and along the length of the damper. The developed procedure makes possible to determine the steady state response of rotors excited by their unbalance, to determine magnitude of the forces transmitted through the coupling elements in the supports into the stationary part and is intended for proposing the control of the damping effect to achieve optimum performance of the dampers.