Vibrational Coupling Research Articles

The comprehensive effect of friction self-excited and modal vibration on polygonal wear of high-speed train wheels

Wheel polygon wear has emerged as a critical issue in the development of high-speed trains in China, but the mechanism underlying its formation remains unknown. The formation mechanism and its effect factors of wheel polygonalization are investigated in depth in this paper using theoretical analysis and numerical simulation. A longitudinal self-excited vibration and vertical modal vibration coupling model of wheel-rail is established, considering the comprehensive effects of wheelset flexibility, vehicle spring mass, and foundation under rail. The critical condition of the system Hopf bifurcation is determined by theoretical analysis, and the longitudinal vibration characteristics of the wheel are studied using numerical simulation. Furthermore, the influence factors on wheel polygonalization are investigated. The research method makes a useful attempt to unify the relevant viewpoints of resonance theory and self-excited vibration theory, and the research results have theoretical guiding significance and engineering reference value for the prediction and suppression of wheel polygonal wear.

Study on Suppression of Transverse Mechanical Coupling of Rectangular Double-Laminated Bending Vibration Elements

Rectangular double-laminated piezoelectric elements are widely used in low frequency transducers. At present, most of these piezoelectric elements use a piezoelectric ceramic laminated structure. In this work, the bending vibration properties of double-laminated piezoelectric ceramic elements with different transverse dimensions were analyzed by the finite element method. It was found that there was a strong transverse mechanical coupling, and the transverse dimensions had a great effect on the bending vibration. To suppress the transverse mechanical coupling effect, a double-laminated piezoelectric element based on a 2-2 piezoelectric composite was designed. The simulation results show that the bending vibration performance of the double-laminated composite element is not affected by the transverse size. The 2-2 piezoelectric composite double-laminated and ceramic elements were prepared. In addition, simulation and experimental results indicate that the transverse mechanical coupling of the bending vibration of the piezoelectric composite double-laminated element is effectively suppressed, the vibration frequency is reduced by about 100 Hz, and the vibration displacement is increased by 2.2 times, in comparison with the piezoelectric ceramic double-laminated element.

Forced vibration analysis model for pumped storage power station based on the 1D–3D coupling and pipe walls vibration

AbstractHydraulic vibration is a common phenomenon in pumped storage power stations (PSPS) and hydropower plants. Evaluating the performance of the PSPS and water conveyance system under the hydraulic vibration condition is significant for the safety of the electric power and the PSPS system. In this study, the one‐dimensional (1D) and three‐dimensional (3D) coupling model for the entire PSPS system is established based on the open‐source software OpenFOAM and in‐house C++ codes. The coupling data exchange is realized by writing and reading files. The coupling model is validated by comparing the results with the pure 1D method under small load disturbance conditions. The forced vibration source is modeled by the pipe walls vibration method in the 3D region, and the 1D method takes charge of other parts in the PSPS system. The combination of the pipe walls vibration and 1D–3D coupling could fully consider the incident and reflected characteristics of the pressure waves. The established model could evaluate the overall performance of the PSPS system under forced vibration. Sensitive analysis of the vibration magnitude is carried out, and the results are consistent with the theoretical analysis, demonstrating that the established model is applicable for the forced vibration analysis.

Local mode analysis of characteristic vibrational coupling in nucleobases and Watson–Crick base pairs of DNA

Two-dimensional infrared spectroscopy has reported highly delocalized in-plane base vibrations in the fingerprint region of nucleotide monophosphates, suggesting the involvement of base pair C=O and C=C ring bonds and considerable interaction between C=O bond stretches. The high delocalization results in congested vibrational spectra, which complicates the assignment of the peaks. This congestion also extends to Watson–Crick base pairs. We applied in this work the characterization of normal mode procedure, a special feature of our local mode analysis, and could for the first time identify the C=O and C=C bonds being engaged in base pair coupling and quantify their contribution to each of the delocalized fingerprint vibration. In addition, a detailed and quantitative description of the hydrogen bonds involved in the Watson–Crick base pairs was provided. Based on the results of this study, we developed a new protocol to elucidate on the assignment of bands in the vibrational spectra of nucleic acids by probing the vibrational space for specific interactions between functional groups prior to and upon base pairing. This protocol will aid to fill the gap between deoxyribonucleic acid structural information and vibrational spectroscopy experiments by facilitating the interpretation of spectra on a quantitative basis.

Anion Doping Delays Nonradiative Electron-Hole Recombination in Cs-Based All-Inorganic Perovskites: Time Domain ab Initio Analysis.

Using time-domain density functional theory combined with nonadiabatic (NA) molecular dynamics, we demonstrate that composition engineering of the X-site anions has a strong influence on the nonradiative electron-hole recombination and thermodynamic stability of cesium-based all-inorganic perovskites. Partial substitution of iodine(I) with bromine (Br) and acetate (Ac) anions reduces the NA electron-vibrational coupling by minimizing the overlap between the electron and hole wave functions and suppressing atomic fluctuations. The doping also widens the energy gap to further reduce the NA coupling and to enhance the open-circuit voltage of perovskite solar cells. These factors increase the charge carrier lifetime by an order of magnitude and improve structural stability in the series CsPbI1.88BrAc0.12 > CsPbI2Br > CsPbI3. The fundamental atomistic insights into the influence of anion doping on the photophysical properties of the all-inorganic lead halide perovskites guide the design of efficient optoelectronic materials.

Dynamic analysis and vibration control for a maglev vehicle-guideway coupling system with experimental verification

Maglev trains are strongly nonlinear, open-loop unstable, and flexible track systems. Vehicle-guideway self-excited vibration, which occurs mainly due to the deflection of the flexible guideway, may take place when a train is levitated on the guideway, even if the train is stationary. In this research, maglev vehicle-guideway coupling vibration is studied by employing the Hopf bifurcation criterion. First, the nonlinear dynamic model is presented with consideration of the flexibility of the guideway. To avoid the massive computations required to solve all the eigenvalues when analyzing system stability, the stability criterion of the Hopf bifurcation for the maglev system is proposed and proven with strict mathematical analysis. Based on the proposed lemma, the bifurcation points of the maglev system are calculated, and the critical points of the coupling vibration are found. Next, the influence law of the parameters of the guideway on the vehicle-guideway coupling vibration is analyzed with theoretical and numerical simulation. Then the influence law and the system stability range of the control parameters are analyzed to suppress the coupled vibration. Finally, the effectiveness of the proposed theory is verified by experiments.

Multidimensional Quantum Dynamical Simulation of Infrared Spectra under Polaritonic Vibrational Strong Coupling.

Recent experimental and theoretical studies demonstrate that the chemical reactivity of molecules can be modified inside an optical cavity. Here, we provide a theoretical framework for conducting multidimensional quantum simulations of the infrared (IR) spectra for molecules interacting with cavity modes. A single water molecule under polaritonic vibrational strong coupling serves as an illustrative example. Combined with accurate potential energy and dipole moment surfaces, our cavity vibrational self-consistent field/virtual state configuration interaction (cav-VSCF/VCI) approach can predict the IR spectra when the molecule is inside or outside the cavity. The spectral signatures of Rabi splittings and shifts of certain bands are found to be strongly dependent on the frequency and polarization direction of the cavity modes. Analyses of the simulated spectra show that polaritonic vibrational strong coupling can induce unconventional couplings among the molecule's vibrational modes, suggesting that intramolecular vibrational energy transfer can be significantly accelerated by the cavity.

Dynamic and vibration characteristics of flexible robot manipulator under complex electromechanical coupling

Aiming at the complex electromechanical coupling effect at the joints of RP (rotating parallel) flexible robot, the electromechanical coupling dynamics and vibration response characteristics driven by AC servo motor, as well as the dynamic starting characteristics of the motor are studied. The physical model including electromagnetic and mechanical system coupling is established, and the dynamic model of the whole system is derived based on the overall electromechanical coupling effect and Lagrange Maxwell equation. With the help of Matlab/Simulink, a virtual simulation platform is built to analyze the output speed characteristics of the motor drive end and the motion of the moving base. Finally, through the joint simulation of Matlab/Simulink dynamic simulation model and Adams/controls virtual prototype model, the vibration characteristics of flexible manipulator under electromechanical coupling are obtained. The simulation results show that the electromechanical coupling effect of the motor drive end has a significant impact on the dynamic characteristics of the flexible manipulator. The conclusions obtained are of great value for improving the chiral energy of flexible machinery.

Generalized Resonance Energy Transfer Theory: Applications to Vibrational Energy Flow in Optical Cavities.

A general rate theory for resonance energy transfer (gRET) is formulated to incorporate any degrees of freedom (e.g., rotation, vibration, exciton, and polariton) as well as coherently coupled composite donor or acceptor states. The compact rate expression allows us to establish useful relationships: (i) detailed balance condition when the donor and acceptor are at the same temperature; (ii) proportionality to the product of dipole correlation tensors, which is not necessarily equivalent to spectral overlap; (iii) scaling with the effective coherent size, i.e., the number of coherently coupled molecules or modes; (iv) decomposition of collective rate in homogeneous systems into the monomer and coherence contributions such that the ratio of the two defines the quantum enhancement factor F; (v) spatial and orientational dependences as derived from the interaction potential. For the special case of exciton transfer, the general rate formalism reduces to FRET or its multichromophoric extension. When applied to cavity-assisted vibrational energy transfer between molecules or within a molecule, the general rate expression provides an intuitive explanation of intriguing phenomena such as cooperativity, resonance, and nonlinearity in the collective vibrational strong coupling (VSC) regime, as demonstrated in recent simulations. The relevance of gRET to cavity-catalyzed reactions and intramolecular vibrational redistribution is discussed and will lead to further theoretical developments.

Unified master equation for molecules in phonon and radiation baths

We have developed a unified quantum optical master equation that includes the dissipative mechanisms of an impurity molecule in crystals. Our theory applies generally to polyatomic molecules where several vibrational modes give rise to intramolecular vibrational redistributions. The usual assumption on identical shapes of the nuclear potentials in ground and excited electronic states and the rotating wave approximation have been relaxed, i.e. the vibrational coordinates are different in the ground and excited states, with counter-rotating terms included for generality. Linear vibrational coupling to the lattice phonons accounts for dissipations via non-radiative transitions. The interaction of a molecule with photons includes Herzberg–Teller coupling as the first order non-Condon interaction where the transition dipole matrix elements depend linearly on vibrational coordinates. We obtain new cross terms as the result of mixing the terms from the zeroth-order (Condon) and first-order (non-Condon) approximations. The corresponding Lamb shifts for all Liouvilleans are derived explicitly including the contributions of counter-rotating terms. The computed absorption and emission spectra for carbon monoxide is in good agreement with experimental data. We use our unified model to obtain the spectra for nitrogen dioxide, demonstrating the capability of our theory to incorporate all typical dissipative relaxation and decoherence mechanisms for polyatomic molecules. The molecular quantum master equation is a promising theory for studying molecular quantum memory.

The Train-Bridge Coupled Vibration Analysis of a Long-Span Prestressed Concrete Continuous Beam Bridge under Creep Deformation Effect

The track smoothness of high-speed railroads is severely limited to ensure train performance. The concrete continuous girder bridge is deformed to influence the smoothness of the bridge decks and track caused by creep bulge. There is a need to research the impact of beam creep on the dynamical response of bridge and train operation safety. This paper used Midas software to calculate the long-term deformation of large-span prestressed concrete continuous beam bridges under concrete creep and shrinkage. The train-bridge coupled system was established by adopting self-programming software. Thereafter, the large-term deformation results of the main girder are considered as track irregularity input into the vibration equation of the train-bridge system. The safety of the train operation was evaluated by calculating the dynamic response of the bridge and analyzing the criteria of train running safety. It was shown that the indicators of the large-span bridge are within the allowable code values under all working conditions. The bridge deformation under creep has an impact on the displacement and acceleration response of the bridge when a high-speed train passes through. There is no noticeable impact of creep deformation on the operational performance of trains. Nevertheless, the criteria for assessing the safety of trains’ operation, such as derailment factor, wheel load differences, lateral wheel forces, and vehicle acceleration, have been increased.

Cavity-enabled enhancement of ultrafast intramolecular vibrational redistribution over pseudorotation.

Vibrational strong coupling (VSC) between molecular vibrations and microcavity photons yields a few polaritons (light-matter modes) and many dark modes (with negligible photonic character). Although VSC is reported to alter thermally activated chemical reactions, its mechanisms remain opaque. To elucidate this problem, we followed ultrafast dynamics of a simple unimolecular vibrational energy exchange in iron pentacarbonyl [Fe(CO)₅] under VSC, which showed two competing channels: pseudorotation and intramolecular vibrational-energy redistribution (IVR). We found that under polariton excitation, energy exchange was overall accelerated, with IVR becoming faster and pseudorotation being slowed down. However, dark-mode excitation revealed unchanged dynamics compared with those outside of the cavity, with pseudorotation dominating. Thus, despite controversies around thermally activated VSC modified chemistry, our work shows that VSC can indeed alter chemistry through a nonequilibrium preparation of polaritons.

Accurate and efficient band-gap predictions for metal halide perovskites at finite temperature

We develop a computationally efficient scheme to accurately determine finite-temperature band gaps for metal halide perovskites belonging to the class ABX3 (A = Rb, Cs; B = Ge, Sn, Pb; and X = F, Cl, Br, I). First, an initial estimate of the band gap is provided for the ideal crystalline structure through the use of a range-separated hybrid functional, in which the parameters are determined non-empirically from the electron density and the high-frequency dielectric constant. Next, we consider two kinds of band-gap corrections to account for spin-orbit coupling and thermal vibrations including zero-point motions. In particular, the latter effect is accounted for through the special displacement method, which consists in using a single distorted configuration obtained from the vibrational frequencies and eigenmodes, thereby avoiding lengthy molecular dynamics. The sequential consideration of both corrections systematically improves the band gaps, reaching a mean absolute error of 0.17 eV with respect to experimental values. The computational efficiency of our scheme stems from the fact that only a single calculation at the hybrid-functional level is required and that it is sufficient to evaluate the corrections at the semilocal level of theory. Our scheme is thus convenient for the screening of large databases of metal halide perovskites, including large-size systems.

A novel evaluation of train running safety on the HSR bridges under earthquakes based on the observed track deformation rate

Safe operation of the trains on the high-speed railway bridge requires the railway line to have a high level of track regularity. High-speed railway bridges can deform unevenly under horizontal earthquakes, and the solid instantaneous deformation of the track can cause the train to derail. This paper develops a refined nonlinear model of the train-track-bridge coupling vibration subjected to seismic shaking to capture as comprehensively as possible the impact of the transient deformation of the track on the train operation at each moment and position. In addition, the risk factors and derailment characteristics are investigated in depth. The findings showed that the earthquake caused the bridge's girder ends to undergo severe dislocation and rotation, which facilitates the derailment of a train. Moreover, the vibration coupling between the train and the bridge becomes strong after bearing shear pin failure. Based on the statistical results of derailment causes, a novel index for evaluating the train running safety on the high-speed railway bridge is proposed. Besides, the engineering applications of this index are also introduced. Indeed, this new index can be used as the lower limit for evaluating train derailment on HSR bridges during earthquakes.

Remote near-field spectroscopy of vibrational strong coupling between organic molecules and phononic nanoresonators

Phonon polariton (PhP) nanoresonators can dramatically enhance the coupling of molecular vibrations and infrared light, enabling ultrasensitive spectroscopies and strong coupling with minute amounts of matter. So far, this coupling and the resulting localized hybrid polariton modes have been studied only by far-field spectroscopy, preventing access to modal near-field patterns and dark modes, which could further our fundamental understanding of nanoscale vibrational strong coupling (VSC). Here we use infrared near-field spectroscopy to study the coupling between the localized modes of PhP nanoresonators made of h-BN and molecular vibrations. For a most direct probing of the resonator-molecule coupling, we avoid the direct near-field interaction between tip and molecules by probing the molecule-free part of partially molecule-covered nanoresonators, which we refer to as remote near-field probing. We obtain spatially and spectrally resolved maps of the hybrid polariton modes, as well as the corresponding coupling strengths, demonstrating VSC on a single PhP nanoresonator level. Our work paves the way for near-field spectroscopy of VSC phenomena not accessible by conventional techniques.

Internal Resonance of the Coupling Electromechanical Systems Based on Josephson Junction Effects.

The internal resonances of the coupling vibration among electro-dynamic modes of an NEMS are studied for the coupling resonators connected on a Josephson junction. The methodology adopted involves coupling a resonator connected on a Josephson junction. The mathematical model of the coupled system is then obtained by considering the regulatory nonlinear effect of the phase difference of that Josephson junction. The resulting dynamic differential equation is deduced by considering the nonlinear terms of the Josephson junction and the nanobeam. The multi-scale method is then used to obtain the 1:1:1 resonant amplitude-frequency response equation of the coupled electromechanical system. The influence of the phase difference of the Josephson junction, magnetic field, external excitation and other factors are analyzed based on the internal resonant amplitude of the coupled system. The simulation results illustrate that the changes in the values of the magnetic field, excitation amplitude and divided resistances can lead to a remarkable change in the values of the nanobeam frequency and amplitude. The internal resonance principle is used to generate a mutual conversion and amplification among electrical signals and mechanical signals. This research provides a theoretical framework and a numerical approach for improving the sensitivity of magnetic quality detection.

Influence of Electromagnet-Rail Coupling on Vertical Dynamics of EMS Maglev Trains

Active control is essential for EMS maglev trains to achieve stable suspension. Currently, the main line's suspension performs well, but in areas with low track stiffness, such as the garage, turnouts, and other lines, unexpected coupling vibration is more likely to occur. Control parameters, vehicle parameters, and rail parameters are all closely related to this phenomenon. In this study, the vehicle-rail coupling dynamic equation with secondary suspension system is first established, and used to disclose the effects of different parameters on the electromagnet-rail coupling vibration of the EMS maglev train. Next, the authors adopted the proportional-derivative (PD) controller, and proposed the concept of maglev train control frequency. Next, a general simulation model was established based on the MATLAB/Simulink, and numerical simulation was carried out to reveal how the secondary suspension frequency, the control frequency and the rail frequency affect the electromagnet-rail coupling vibration. The research results provide a reference for the design of maglev trains, controllers, and tracks, laying a theoretical basis for the maintenance of maglev commercial lines.

Influence of Vibrational Strong Coupling on an Ordered Liquid Crystal

Vibrational strong coupling and the formation of vibrational polaritons are a result of strong light-matter interaction between a cavity photon and a molecular vibrational mode. The Rabi splitting parameter, which reflects the microscopic light-matter interaction strength, reveals information about the molecular alignment and concerted vibrational motion inside the cavity. We have investigated vibrational strong coupling of 4-cyano-4'-octylbiphenyl liquid crystal molecules in isotropic and smectic A phases. We observed a ∼30% change in the Rabi splitting with the phase transition from isotropic to smectic A by controlling the temperature, together with the onset of polarization-dependent anisotropy of the Rabi splitting in the smectic A phase. Based on the estimated orientational distribution function, we show that the observed Rabi splitting difference in the isotropic and smectic A phases can only be explained by taking into account the influence of collective vibrational motion in the cavity, which affects the molecular properties under the vibrational strong coupling regime.

Calculated attenuated total reflection (ATR) for analyzing surface plasmon polaritons

The electromagnetic waves propagate in the interface between metal and dielectric can be simply called surface plasmon polariton. The surface plasmon polaritons were produced by the coupling of incoming electromagnetic waves and collective vibrations of free charges on metal surface. The generation of surface polaritons may be done using attenuated total reflection (ATR) method which was based on total internal reflection. The method can be performed numerically by analyzing reflections on each involved interfaces. The generated surface plasmon polaritons were represented by the appearance of the dip in the ATR spectroscopy. In this paper, we presented the ATR spectroscopy for surface plasmon polaritons generated on gold-castor oil interface. The results showed the predicted dispersion relation from calculated ATR of the surface plasmons polaritons were in good agreement with the dispersion relation from the theory.

Order of magnitude reduction in Joule heating of single molecular junctions between graphene electrodes.

Maintaining stability of single-molecular junctions (SMJs) in the presence of current flow is a prerequisite for their potential device applications. However, theoretical understanding of nonequilibrium heat transport in current-carrying SMJs is a challenging problem due to the different kinds of nonlinear interactions involved, including electron-vibration and anharmonic vibrational coupling. Here, we overcome this challenge by accelerating Langevin-type current-induced molecular dynamics using machine-learning potential derived from density functional theory. We show that SMJs with graphene electrodes generate an order of magnitude less heating than those with gold electrodes. This is rooted in the better phonon spectral overlap of graphene with molecular vibrations, rendering harmonic phonon heat transport being dominant. In contrast, in a spectrally mismatched junction with gold electrodes, anharmonic coupling becomes important to transport heat away from the molecule to surrounding electrodes. Our work paves the way for studying current-induced heat transport and energy redistribution in realistic SMJs.