Resonance Region Research Articles

Vibration mitigation and energy harvesting of vibro–impact dielectric elastomer oscillators

Dielectric elastomers (DEs), as a type of intelligent materials, have the characteristics of light weight, high energy density, high conversion efficiency, and damping effect, and thus can achieve the potential dual–use value of concurrent vibration mitigation (VM) and energy harvesting (EH) by combining with mechanical structures. This paper investigates the vibro–impact dielectric elastomer oscillator (VI DEO) and the proposed rolling VI DEO (RVI DEO) to achieve or enhance the potential dual–use value of DE oscillators. First, the schematics of the VI DEO and the RVI DEO are elaborated in detail. Then, the two dynamics analysis models of the linear oscillator (LO)–VI DEO and LO–RVI DEO systems are developed. On this basis, the VM and EH performances of the two DE oscillators under transient and harmonic excitations are numerically studied. It is demonstrated that the two DE oscillators have the most effective VM performance when the LO–VI DEO and LO–RVI DEO systems behave most efficiently in the 1:1 resonance vibro–impact regime with targeted energy transfer (TET). Hence, to achieve this response regime, the influences of the parameters such as the ball's mass, impact distance, pre–stretched ratio and friction coefficient of the two DE oscillators on their VM and EH performances are investigated one by one. The research results show that the most effective VM can only be achieved by adjusting the ball's mass, and the largest output power is generated in the resonance region. Hence, we further perform multi–parameter optimization to find the two DE oscillators with the best performance. Based on the multi–parameter optimization results, the performances of the two optimal oscillators are evaluated under mid–energy level harmonic and variable–frequency excitations with different amplitudes, and it is proved that both optimal DE oscillators not only have good performances, but also the RVI DEO has a better robustness.

The Contributions to Registration Efficiency of The Fast Neutron Reactions on The Nuclei of The Heavy Oxide Scintillators

The results of the study of the contributions of the interaction reactions of fast neutron sources of 239Pu-Be and 252Cf to the counting efficiency of registration by oxide scintillators CdWO4, ZnWO4, Bi4Ge3O12 and Gd2SiO5, presented. The amount of gamma quanta per input neutron emitted from final nuclei excited in the reactions of inelastic scattering (n, nʹγ)in, resonant scattering (n, n)res and capture (n, γ)res and radiation capture (n, γ)cap was measured. PMT R1307 operating in single-electron mode was used as a photodetector, the background rate was ~ 5*103 s-1. The measured efficiency ε for scintillators ø40x40 mm was 752 for ZWO, 532 for CWO, 37 for GSO, and 23 for BGO in "counts/neutron" units, measurement error rate ~ 3-5%. The formation of the detector response is influenced by the parameters of the scintillator nuclei, such as the values of the interaction cross sections in the resonance region, the density of nuclear levels of the final nuclei, the lifetime of excited nuclear states, the upper limit of the resonance region of the cross section, as well as the scintillation time and geometric parameters of the scintillators. A phenomenological model of the response of an oxide scintillator to fast neutrons is proposed.

Investigation on the 1:2:3 internal resonance of high dimensional nonlinear dynamic system for FGGP reinforced rotating pre-twisted blade under the aerodynamic forces

The study of internal resonances is one of the main research areas in nonlinear dynamics. The energy transfer behaviors between multiple vibrational modes caused by internal resonances lead to complex nonlinear vibration behaviors. In this paper, the rotating blade is modeled as a functionally graded graphene platelet (FGGP) reinforced rotating pre-twisted plate. The nonlinear vibration of a high dimensional nonlinear dynamic system for FGGP reinforced rotating pre-twisted blade under the aerodynamic forces with 1:2:3 internal resonance is investigated. The axial excitations on the blade are primarily caused by axial aerodynamic force in the tip clearance and contact forces at the top of the blade. The subsonic airflow is treated as a transverse excitation and is calculated using the vortex lattice method. Rayleigh-Ritz method is used to obtain the mode shapes of the rotating composite pre-twisted blade. The three-degree-of-freedom ordinary differential equations of the rotating FGGP reinforced pre-twisted plate are derived by using Lagrange equation. Based on the multiscale method, the averaged equations of the rotating FGGP reinforced pre-twisted plate in the case of primary resonance and 1:2:3 internal resonance under axial and transverse excitations are acquired. We present a discussion on the amplitude-frequency response, force-amplitude response, bifurcations, and chaotic motions of a rotating FGGP reinforced pre-twisted cantilever plate under both axial and transverse excitations. A crescent-shaped independent resonance region is found in the amplitude-frequency response curves. The system exhibits complex nonlinear vibration behavior as axial or transverse excitation amplitude changes.

Dynamic modeling and nonlinear analysis for lateral–torsional coupling vibration in an unbalanced rotor system

Imbalance is a common problem in rotating machinery. In addition to the unbalanced force, lateral–torsional coupling vibration can also be induced by the mass imbalance. However, the related nonlinear behaviors and coupling mechanism are still not well understood, especially when lateral-angular motion is incorporated in a model. In this paper, a model for coupling lateral and torsional vibrations of an unbalanced rotor is developed by Lagrangian dynamics, in which the coupling of lateral-angular and torsional motions is first considered. Based on the model, the lateral responses, torsional responses, coupling excitation characteristics and coupling mechanisms are investigated in detail. The results show that mass imbalance can lead to nonlinear time-varying characteristics in the dynamic equations. When the imbalance is small, the lateral vibration can be degraded to a traditional imbalance problem. Meantime, very small transient torsional vibration with torsional natural frequency ft in frequency domain can be observed at the beginning. The coupling excitation applying on the torsional DOF caused by the lateral synchronous whirling is demonstrated to behave the feature of static torque, consequently, there actually exists no steady-state torsional vibration in small unbalanced rotor. Under largely unbalanced conditions, both resonant and unstable behavior can be observed in the lateral and torsional responses. The combined resonance is induced by the lateral translational–torsional coupling, while the instability is caused by lateral angular–torsional coupling. By increasing the lateral damping, the instability phenomenon can be suppressed, and the lateral amplitude in the resonance region can be effectively reduced.

Theoretical and numerical studies on stability of multiple eccentric rotors uniformly distributed along the circumference of two rigid bodies

This paper aims at studying synchronization, stability and motion characteristics of a new generalized dynamical model with two rigid bodies (RBs), driven by multiple eccentric rotors (ERs) uniformly distributed on the circumference of two different RBs. Using Lagrange’s equation, the motion differential equations of the system are deduced. The generalized theoretical analytical expressions of the criteria for implementing synchronization and stable operation of multiple ERs are obtained. Based on the above theoretical results, and taking the present dynamical model with six ERs for example, numerical qualitative discussions are given to deeply reveal the stable states and motion characteristics of the system in different resonant regions. The simulations are further carried out quantitatively, which verifies the validity of the above theoretical and numerical qualitative results. It is shown that, in the sub-resonant state with respect to the natural frequency of the main vibrating system, the stable zero phase difference between arbitrary two ERs on each RB can be achieved, in this case, the relative circular motion of two RBs with anti-phase is realized. This paper can lay a foundation for designing some new types of large scale high-frequency vibrating ball mills with high supply power.

Vibration energy characters study of a soft-core beam system coupled through nonlinear coupling layers

To ascertain the potential impact of nonlinear coupling layers on the vibration control of composite beam systems, this study develops a vibration analysis model of a nonlinear coupling-layered soft-core beam system. Ascertain the accuracy of the vibration responses computed by the soft-core beam system using the Galerkin truncation method (GTM) in comparison to the results obtained through alternative methods. The correct calculation results indicate that nonlinear coupling layers are the cause of nonlinear phenomena in the soft-core beam system. Nonlinear coupling layers are responsible for nonlinear phenomena of the soft-core beam system, such as peak-jumping and the region with multiple continuous amplitudes, according to numerical results. To reduce vibrations in the soft-core beam system's resonance regions, reasonable parameters for the nonlinear coupling layers are advantageous. When the soft-core beam system is excited at a single frequency, the kinetic energy responses include converted values of nonlinear coupling layers. Using nonlinear coupling layers, it is possible to establish an effective parameter range for the vibration energy control of the soft-core beam system. The utilization of reasonable parameters in nonlinear coupling layers can effectively mitigate the vibration energy of a soft-core beam system that is excited at a single frequency. The soft-core beam system induces the desired energy transfer phenomena at specific time intervals and under particular conditions.

Dark matter in the Higgs resonance region

Dark matter in the Higgs resonance region

The interaction between cross-flow induced vibration and convection heat transfer in tube bundle at subcritical Reynolds number

This work numerically investigates the interaction between flow-induced vibration (FIV) and forced convection heat transfer in tube bundle with a pitch ratio of 1.5 at subcritical Reynolds number (Re = 5 × 103-3 × 104). The range of reduced velocity is 0.53 ≤ Vr ≤ 2.71. The mass-damping parameter of coupling system is 0.07. The three-dimensional refined FIV simulation considering fluid viscous damping has been validated by the literature experiment to capture three continuous FIV mechanisms, namely turbulence-induced vibration, vortex-induced resonance and fluidelastic instability. The heat transfer and pressure drop in tube bundle are validated by the experiment. The coupling of Navier-Stokes equations, energy equations and vibration equations is solved by under-relaxation algorithm. The results of vibration response, the change of damping for the coupling system, flow field and temperature field, heat transfer and pressure drop are presented and delineated in this paper. The results show that for the low velocity turbulence-induced vibration, the interaction between FIV and flow heat transfer is negligible due to the weak fluid–solid interaction. In vortex-induced resonance region, the wall heating makes each row tube be out of phase by affecting the vortex shedding and reduces the positive feedback of resonance, which reduces the amplitude. The wall heating reduces the damping of coupling system, which causes an earlier transition from vortex-induced resonance to fluidelastic instability and a faster increase of amplitude in fluidelastic instability. In both vortex-induced resonance and fluidelastic instability, the vibration of tube bundle dominates the vortex shedding by the natural frequency, and further dominates the change of heat transfer. The best performance of enhanced heat transfer induced by FIV is located in vortex-induced resonance region, in which the time–space averaged Nusselt number is increased by 8.83%. Due to the redistribution of flow field and the elimination of deflective flow pattern, compared with vortex-induced resonance, the increasing ratio of heat transfer induced by FIV is lower and the increasing ratio of pressure drop induced by FIV is higher in the fluidelastic instability.

Influence of Meta-Atom Geometry on the Occurrence of Local Resonance Regions in Two-Dimensional Finite Phononic Structures

Influence of Meta-Atom Geometry on the Occurrence of Local Resonance Regions in Two-Dimensional Finite Phononic Structures

The correction of instrument transformer ferroresonance model in IEC standard and study on resonance interval based on transformer damping

The traditional ferromagnetic resonance model of the inductive voltage transformer in the IEC/TR 61869-102 transformer standard ignores the DC resistance of the transformer. The author believes that ignoring the damping effect of the transformer itself is not justified. Based on this, the model is modified, and the corresponding differential equation is derived. Through simulation and field testing, it is found that the DC resistance of the transformer has a damping effect on resonant overvoltage and resonant overcurrent. Moreover, with an increase in DC resistance, the ferromagnetic resonance region decreases. By increasing the DC resistance of the voltage transformer, it helps to reduce the ferromagnetic resonance interval as well as the inrush current.

State-to-state rovibrational transition rates for CO2 in the bend mode in collisions with He atoms.

Modeling environments that are not in local thermal equilibrium, such as protoplanetary disks or planetary atmospheres, with molecular spectroscopic data from space telescopes requires knowledge of the rate coefficients of rovibrationally inelastic molecular collisions. Here, we present such rate coefficients in a temperature range from 10 to 500K for collisions of CO2 with He atoms in which CO2 is (de)excited in the bend mode. They are obtained from numerically exact coupled-channel (CC) calculations as well as from calculations with the less demanding coupled-states approximation (CSA) and the vibrational close-coupling rotational infinite-order sudden (VCC-IOS) method. All of the calculations are based on a newly calculated accurate abinitio four-dimensional CO2-He potential surface including the CO2 bend (ν2) mode. We find that the rovibrationally inelastic collision cross sections and rate coefficients from the CSA and VCC-IOS calculations agree to within 50% with the CC results at the rotational state-to-state level, except for the smaller ones and in the low energy resonance region, and to within 20% for the overall vibrational quenching rates except for temperatures below 50K where resonances provide a substantial contribution. Our CC quenching rates agree with the most recent experimental data within the error bars. We also compared our results with data from Clary et al. calculated in the 1980s with the CSA [A. J. Banks and D. C. Clary, J. Chem. Phys. 86, 802 (1987)] and VCC-IOS [D. C. Clary, J. Chem. Phys. 78, 4915 (1983)] methods and a simple atom-atom model potential based on abinitio Hartree-Fock calculations and found that their cross sections agree fairly well with ours for collision energies above 500 cm-1, but that the inclusion of long range attractive dispersion interactions is crucial to obtain reliable cross sections at lower energies and rate coefficients at lower temperatures.

Dual-mode coupling resonance and dynamic stability of axially moving ferromagnetic thin plate strips in alternating magnetic field

This paper investigates the dual-mode coupling resonance and dynamic stability of axially moving ferromagnetic thin plate strips in alternating magnetic field. According to the basic electromagnetic theory and the magnetoelastic mechanics model, Lorentz electromagnetic force and torque generated by eddy current effect and the magnetizing force generated by magnetization are determined for the ferromagnetic plate strip. Introducing Von Karman geometric nonlinearity, the nonlinear governing equation of axially moving ferromagnetic plate strips under the combined action of mechanical load and magnetizing force is established by Hamilton's principle. For the simply supported plate strip, Galerkin method and the multi-scale method are employed to solve the modal coupling resonance dominated by electromagnetic excitation, obtaining the amplitude-frequency response equations. The stability of resonance responses is analyzed by the Lyapunov stability theory. Through parametric research, the amplitude-frequency characteristic curves, bifurcation diagrams and Lyapunov exponent spectra of each mode are plotted; the effect of different parameters on vibration characteristics and dynamic stability under the modal coupling is analyzed for the system. The results show that as one of the modal amplitudes enters the resonance region, the other modal amplitude decays into the "collapse" region due to energy exchange between modes; each modal amplitudes has more complex multi-valued and jumping phenomena for the nonlinear coupling effect. The increase in velocity will affect the stability of system; the enhancement of magnetic field will make the system change into chaos at high velocity.

Nonlinear interaction of electromagnetic wave with electron acoustic wave in plasma

An analysis on the nonlinear interaction of electromagnetic waves with electron acoustic waves is performed in plasma with two different temperature electron fluids in the presence of a neutralizing static ion background. A newly structured Zakharov’s equations are derived employing two fluid two-time scale theory. These coupled Zakharov’s equations describe the weakly nonlinear interaction of em wave perturbation with electron acoustic waves while propagating through plasma. In the low frequency or adiabatic limit, these Zakharov’s equations may be unified to produce a modified NLSE. A solution of the equation, novel in the literature, is derived following the method shown by Kudryashov. In a resonant regime, the modified NLSE reduces to NLSE. Though a stable solution exists for both cases, instability analysis shows caviton instability may arise. The threshold value of the electric field, at which instability sets in, is virtually zero for the resonant region whereas, apart from that region there is a threshold value of the electric field, determined by the frequency difference of em wave and electron plasma wave. Experimental observations support these results. This study is relevant for laser-plasma interaction and astrophysical and space plasma.

One‐Step Electrochemical Fabrication of 3D Gold Nanotrees with Enhanced Broadband Plasmonic Excited Carriers for Photoelectrochemical Reactions

AbstractPlasmonic nanostructures that generate hot carriers and induce catalytic chemical transformations are ideal candidates for solar energy utilization. However, the existing nanostructures require multistep synthesis procedures and generate fewer hot carriers due to their narrow resonance region and limited hotspots, restricting their usage in plasmonic catalysis. Inspired by the light‐harvesting behavior of the trees, the current work reports a one‐step fabrication strategy via electrodeposition for direct anisotropic growth of the 3D gold nanotrees with tunable size, branches, and height. The as‐synthesized nanostructures with broadband light absorption and plentiful hotspots can significantly foster hot carrier generation. The improved hot electron generation of 3D gold nanotrees is confirmed by in situ surface‐enhanced Raman spectroscopy for the dimerization reaction of 4‐nitrothiophenol. The energetic hot holes generated by the 3D gold nanotrees facilitate water oxidation and exhibit 18.6 times higher catalytic efficiency than Au film under 625 nm. Meanwhile, the photoelectrochemical catalysis of 3D gold nanotrees shows better performance compared with conventional Au nanospheres. This work opens up a promising avenue for fundamental studies of plasmonic catalysis via a wide variety of 3D gold nanotrees.

Super-High-Frequency Bulk Acoustic Resonators Based on Aluminum Scandium Nitride for Wideband Applications.

Despite the dominance of bulk acoustic wave (BAW) filters in the high-frequency market due to their superior performance and compatible integration process, the advent of the 5G era brings up new challenges to meet the ever-growing demands on high-frequency and large bandwidth. Al1-xScxN piezoelectric films with high Sc concentration are particularly desirable to achieve an increased electromechanical coupling (Kt2) for BAW resonators and also a larger bandwidth for filters. In this paper, we designed and fabricated the Al1-xScxN-based BAW resonators with Sc concentrations as high as 30%. The symmetry of the resonance region, border frame structure and thickness ratio of the piezoelectric stack are thoroughly examined for lateral modes suppression and resonant performance optimization. Benefiting from the 30% Sc doping, the fabricated BAW resonators demonstrate a large effective electromechanical coupling (Keff2) of 17.8% at 4.75 GHz parallel resonant frequency. Moreover, the temperature coefficient of frequency (TCF) of the device is obtained as -22.9 ppm/°C, indicating reasonable temperature stability. Our results show that BAW resonators based on highly doped Al1-xScxN piezoelectric film have great potential for high-frequency and large bandwidth applications.

A sensitivity-improved amplitude method for determining film thickness based on the partial reflection waves

A sensitivity-improved reflection coefficient amplitude method for determining wide-range lubricating oil film thickness is proposed based on partial reflection waves, which are obtained by removing the first reflection wave. Numerical analysis and experimental testing are conducted to verify the proposed method. The results show the lubricating oil film thickness ranging from the spring model region to the resonant region can be calculated based on the proposed partial-wave reflection coefficient amplitude method. In comparison to the existing reflection coefficient amplitude method, the measurement accuracy of the lubricating oil film thickness is significantly improved for the transition region which locates between the spring model region and the resonant region, for instance, the observed maximum relative error is decreased to 9% from 60%.

Reflection of the Electromagnetic Wave from the Region of Electron Cyclotron Absorption in Thermonuclear Plasma

A new approach to the problem of the passage of the extraordinary wave through the region of the electron–cyclotron resonance in inhomogeneous plasma was considered in the framework of the full set of Maxwell’s equations, taking into account the effects of spatial dispersion and resonance dissipation. For the model one-dimensional geometry, field distributions were calculated in the vicinity of the cyclotron resonance at the second harmonic for the normal incidence of the extraordinary wave and the reflection, transmission, and absorption coefficients were found depending on the parameters of the resonance region. As a result, the fine effect of the reflection of electromagnetic radiation from the cyclotron resonance region in transparent plasma was described and the results were compared with the observations of this effect in the experiments on the microwave heating of the plasma at the L-2M stellarator.

Reflection of the Electromagnetic Wave from the Region of Electron Cyclotron Absorption in Thermonuclear Plasma

A new approach to the problem of the passage of the extraordinary wave through the region of the electron–cyclotron resonance in inhomogeneous plasma was considered in the framework of the full set of Maxwell’s equations, taking into account the effects of spatial dispersion and resonance dissipation. For the model one-dimensional geometry, field distributions were calculated in the vicinity of the cyclotron resonance at the second harmonic for the normal incidence of the extraordinary wave and the reflection, transmission, and absorption coefficients were found depending on the parameters of the resonance region. As a result, the fine effect of the reflection of electromagnetic radiation from the cyclotron resonance region in transparent plasma was described and the results were compared with the observations of this effect in the experiments on the microwave heating of the plasma at the L-2M stellarator.

Enhancement of stimulated Brillouin scattering in multiple resonance regions by two-color light in inhomogeneous flowing plasmas

The effects of two-color light on stimulated Brillouin scattering (SBS) in an inhomogeneous flowing plasma have been investigated. The three-wave match of SBS is satisfied at multiple spatial locations and the multiple resonance regions occur when the two-color laser incident on an inhomogeneous flowing plasma, leading to multiple scattering of scattered light, which results in an enhancement of the reflectivity of the laser rather than a significant decrease. If the distance between the resonance points is smaller than the resonance length of SBS, the ion acoustic waves generated at different locations are coupled to each other, which enhances SBS. A model of multiple regions resonance of SBS is presented, and a one-dimensional Vlasov–Maxwell code is employed to verify the enhancement.

Non-linear Dynamic Characteristics of High-Speed Wheel-Rail Interface Considering Surface Topography and Liquid Medium

In this work, the force-deflection characteristics, and the nonlinear vibration of the wheel-rail interaction with surface roughness and liquid medium are studied. The statistical micro-contact Greenwood and Williamson model is used to characterize the rough surface. The load sharing theory is used to determine the analytical elastic contact force-deflection and damping force-deflection relationships, which are further approximated by power law functions. The nonlinear contact stiffness and damping characteristics are illustrated for different rough surface topographies and running speeds. The natural frequency is solved by assuming small covariates and defining time variables of different scales. Effects of surface topography and liquid medium on the natural frequency of the wheel-rail interface system are studied. The first-order harmonic responses under harmonic excitation are further determined as well as the jump-up and jump-down responses for different rough surface topographies, excitation loads, liquid mediums and running speeds. It is shown that the resonance region and the peak value of the vibration amplitude increase as the surface roughness, running speed and excitation load increase; whilst the jump-up and jump-down frequencies decrease. In addition, the system can change from a monostable to a bistable structure when surface roughness and excitation force increase and large limit cycle oscillation can occur.