Vibrational States Research Articles

Nonlinear unsteady aerodynamic forces prediction and aeroelastic analysis of wind-induced bridge response at multiple wind speeds: A deep learning-based reduced-order model

Machine learning-based aerodynamic reduced-order models (ROMs) combine high accuracy with extremely low computational costs, making them highly effective in predicting nonlinear and unsteady bridge aerodynamic forces. Although several machine learning-based nonlinear aerodynamic models have been developed, the majority are built on a single wind speed parameter. However, in nonlinear aerodynamic prediction and aeroelastic analysis of bridges, the variability in incoming wind speed significantly influences the computed results. A ROM relying solely on a single wind speed lacks the ability to accurately forecast the intricate dynamic behaviors arising from changes in wind speed. When the incoming wind speed changes, the model's prediction accuracy significantly decreases. Usually, it is necessary to establish a new database and train a new model, which not only increases time and cost but also greatly reduces the convenience of the ROM. Addressing this challenge, this study proposes a multiple-wind-speed (MWS) nonlinear unsteady bridge aerodynamic model based on the LSTM deep neural network. Taking the Taohuayu Yellow River Bridge in the Henan Province of China as an example, the modeling process of the proposed MWS-ROM is demonstrated, along with non-linear aerodynamic predictions of the deck under various conditions and aerodynamic-elastic analysis of the deck under different wind speeds. The research results show that the trained LSTM network can accurately predict the nonlinear aerodynamic forces of bridges under single and double degrees of freedom vibration conditions. The MWS-ROM performed well in predicting convergent vibrations at low wind speeds and limits cycle oscillations at high wind speeds, aligning closely with results from the CFD full-order model. Compared to CFD, the aerodynamic ROM based on the LSTM network significantly enhances computational efficiency, consequently boosting the convenience and efficiency of bridge flutter analysis. Additionally, the methodology proposed herein can be extended for wind-induced vibration control and response prediction in other types of deck sections.

Coarse-grained modeling of high-enthalpy air flows based on the updated vibrational state-to-state kinetics

The state-to-state (StS) model can accurately describe high-temperature thermochemical nonequilibrium flows. For the five-species air gas mixture, we develop a comprehensive database for the state-specific rate coefficients for temperatures 300–25 000 K in this paper. The database incorporates recent molecular dynamics simulations (based on the ab initio potential energy surfaces) in the literature, and theoretical methods, including the forced harmonic oscillator model and the Marrone–Treanor model, are employed to complement the rate coefficients that are unavailable from molecular dynamics calculations. The post-shock StS simulations using the present database agree with the experimental NO infrared radiation. Based on this updated StS kinetics database, we investigate the post-shock high-enthalpy air flows by employing both the StS and coarse-grained models (CGM). The CGM, which lumps molecular vibrational states into groups, shows results that align with the StS model, even utilizing only two groups for each molecule. However, the CGM-1G model, with only one group per molecule and belonging to the multi-temperature model (but uses StS kinetics), fails to reproduce the StS results. Analysis of vibrational energy source terms for different kinetic processes and fractions of vibrational groups reveals that the deficiency of the CGM-1G model stems from the overestimation of high-lying vibrational states, leading to higher dissociation rates and increased consumption of vibrational energy in dissociation. Furthermore, the presence of the Zeldovich-exchange processes indirectly facilitates energy transfer in N2 and O2, a phenomenon not observed in binary gas systems. These findings have important implications for developing the reduced-order model based on coarse-grained treatment.

Bismorpholin-4-ium tetrabromo-cadmium metal-organic single crystal delivering Crystal structure, physicochemical properties and Characterizations for Optoelectronic Applications

For the development of nonlinear optical (NLO) materials, compositions of cadmium chloride (CC) and Morpholinium bromide (MB) molecules were utilized to form metal-organic materials. Morpholinium bromide was incorporated with cadmium metal to have electron charge transfer by constructing acentric structures that take advantage of strong third-order nonlinear optical properties. Bis Morpholinium cadmium bromide (BMCB) crystals were synthesized by a slow evaporation method (SEST). The BMCB crystal belongs to monoclinic P21/c space group with four molecules in the unit cell (a=6.7607(4) Å, b=16.5811(2) Å, c=14.9744(2) Å, β=94.136(3) ° and Z=4). The grown BMCB crystal phase purity and crystallinity were further investigated using powder X-ray diffraction (PXRD) analysis. Using Fourier transform infrared (FTIR) spectroscopy, the functional groups and their vibrational states were evaluated. From the results obtained from UV-vis-NIR spectral analysis, it is clear that the title compound is transparent in the visible range with the lower cut-off wavelength of 254 nm. The TG-DTA measurement has been used to evaluate thermal stability. Microhardness measurements were carried out to evaluate the mechanical stability of the grown crystal. The third-order nonlinear optical (NLO) characteristics were studied using Z-scan technique. The grown crystal exhibits outstanding third-order NLO response and wide laser damage threshold (LDT), which are crucial characteristics for developing practical NLO devices. The findings consequently open a novel path for the logical design of enormous, thermally stable and NLO-active metal-organic complexes for NLO applications.

Numerical analysis of sloshing effects in cryogenic liquefied-hydrogen storage tanks for trains under various vibration conditions

This study examines the effects of hydrogen sloshing on internal pressure, temperature, and fluid behavior liquefied-hydrogen storage tanks designed for train usage by applying the natural frequency and frequency conditions from train vibration test standards. Notably, it investigates the impact on BOG generation using a transient volume-of-fluid phase change model. Here, simulations were conducted at vibrations of 0, 0.53, 1.53, and 3 Hz, which were established using sine wave acceleration. The results demonstrated that sloshing increased with higher frequencies, thereby resulting in a more intense heat transfer between the wall of the tanks and free surface of hydrogen and an increase in the BOG generation. Compared to the 0 Hz baseline, BOG generation increased by 13, 44, and 66 % at 0.53, 1.53, and 3 Hz, respectively.

Mechanical simulation and electrical performance analysis of high current connectors

Abstract Automotive high-current connectors are one of the key components in new energy vehicles, used for transmitting high currents within the vehicle. However, vibration is unavoidable during the actual operation of connectors. This vibration directly affects the contact pressure between the connector’s contact points, thereby influencing the electrical contact performance of the connector. This paper simplifies the contact components of the electrical connector using a cantilever beam model and conducts theoretical calculations of the contact pressure. Utilizing Ansys Workbench simulation software, the study investigates the contact pressure of the electrical connector under static and various sinusoidal vibration conditions, followed by sinusoidal frequency sweep vibration experiments. The research findings indicate that under vibration conditions, the contact pressure is lower than that under static conditions, and the electrical resistance fluctuates during the vibration process.

Effects of droplet dynamical behavior in flow channel of proton exchange membrane fuel cell under vibration conditions on cell performance

Effects of droplet dynamical behavior in flow channel of proton exchange membrane fuel cell under vibration conditions on cell performance

Investigating the impact of system parameters on flow-induced vibration hard galloping based on deep neural network

Abstract In this paper, a classification model is established for the flow-induced vibration response based on the numerical and experimental data, using a deep neural network-based machine learning approach. The model effectively distinguishes between hard galloping and soft galloping in flow-induced vibrations by identifying the corresponding range of system parameters. Moreover, a regression model is established to determine the relationship between the critical reduced velocity of hard galloping and system parameters, then an exploratory function strategy is utilized to establish the functional relationship between the critical reduced velocity of the hard galloping and the system parameters. The results reveal that the system parameter range with the occurrence of hard galloping is fn<0.85Uζ>-0.1fn+0.19. Additionally, the functional relationship between the critical reduced velocity and system parameters facilitates the adjustment of vibration states in flow-induced vibrations and enables deeper investigation into the phenomenon of hard galloping.

High-Resolution Continuous-Wave Laser Spectroscopy of Long-Lived Rydberg States in NO.

High-resolution continuous-wave (cw) laser spectroscopy of nitric oxide (NO) molecules has been performed to study and characterize the energy-level structure of and effects of electric fields on the high Rydberg states. The experiments were carried out with molecules flowing through a room temperature gas cell. Rydberg-state photoexcitation was implemented using the resonance enhanced three-color three-photon excitation scheme. Excited molecules were detected by high-sensitivity optogalvanic methods. Detailed measurements were made of Rydberg states with principal quantum numbers n = 22 and 32 in the series converging to the lowest rotational and vibrational state of the NO+ cation. The experimental data were compared with the results of numerical calculations which provided insight into the orbital angular momentum character of the intermediate H 2Σ+ state, improved determinations of the nf and ng quantum defects, a bound on the magnitude of the nh quantum defect, and information on the decay rates of the nf and ng Rydberg states. These measurements represent a step-change in laser spectroscopic studies of high Rydberg states in small atmospheric molecules. They open opportunities for more detailed studies of slow decay processes of Rydberg NO molecules confined in electrostatic traps, the synthesis of ultralong range Rydberg bimolecules, and the development of optical methods for trace gas detection.

Ternary Association Reaction of Vibrationally Cold N2+ Ions in Ambient Helium.

The rate coefficients for the ternary association reaction of vibrationally cold N2+ ions with N2 and He were measured in an afterglow plasma in the temperature range of 140-250 K: kN4+ = (1.02 ± 0.39)(300/T)(1.28±0.08) × 10-29 cm6 s-1. The rotational and vibrational state populations of N2+ ions were probed in situ by time-resolved cavity ring-down spectroscopy. The rate coefficient for Penning ionization of N2 by helium metastable atoms was also determined: km = [(2.70 ± 0.17) + (84.3 ± 5.9)e-(877±36)/T] × 10-11 cm3 s-1.

Isotopic species, vibrational states and nuclear quadrupole splitting in CH[formula omitted]Cl[formula omitted] from rotational spectroscopy at 8–18 GHz

The present work fills several significant gaps in the study of the rotational spectrum of the methylene chloride molecule. Two Fourier transform microwave spectrometers were used, providing complementary coverage of the 8–18 GHz region, at room temperature and in supersonic expansion. Hyperfine resolved measurements were made and fitted for ground states of the CH235Cl2, CH235Cl37Cl, CH237Cl2, and 13CH235Cl2 isotopic species, as well as for nine different excited vibrational states. Transitions in the v4=2, v4=3, v3=1, v9=1 states in CH235Cl2, and transitions in excited states of the ν4 mode in 35Cl37Cl and 37Cl2 isotopic species have been assigned for the first time. Vibrational and isotopic dependence of nuclear quadrupole coupling constants was identified. The v3=1 and v9=1 states in CH235Cl2 were found to be significantly coupled by c-axis Coriolis interaction, while transitions in v4=2 and v4=3 states exhibited hyperfine mediated perturbations enhancing the determination of the χab parameter and allowing assessment of its vibrational dependence.

Two-temperature thermochemical nonequilibrium model based on the coarse-grained treatment of molecular vibrational states.

Although the high-fidelity state-to-state (StS) model accurately describes high-temperature thermochemical nonequilibrium flows, its practical application is hindered by the prohibitively high computational cost. In this paper, we develop a reduced-order model that leverages the widelyused two-temperature (2T) framework and a coarse-grained treatment of molecular vibrational states to achieve accuracy comparable to the StS model while ensuring computational efficiency. We observe that the multigroup coarse-grained model (CGM), lumping vibrational energy levels into several groups, yields results close to the StS model for the high-temperature postshock oxygen flows, even using only two groups. However, theone-group CGM (CGM-1G), equivalent to the 2T model but using the StS kinetics, fails to approximate the StS results. Analysis of microscopic group properties reveals that the failure of the CGM-1G stems from the inability to capture the non-Boltzmann effects of mid-to-high vibrational levels, overestimating apparent dissociation rates and vibrational energy loss in the dissociation-dominated region. We then propose an analytical distribution function of vibrational groups by incorporating Treanor-like terms and an additional linear term (addressing the dissociation depletion of high-lying levels). Building upon this algebraic group distribution function and reconstructing vibrational levels within each group using the vibrational temperature, we develop a new 2T model called CG2T, which demonstrates accuracy much closer (than the CGM-1G) to the StS results for the postshock oxygen flows with varying degrees of thermochemical nonequilibrium. Moreover, a fullyconnected neural network is pretrained to substitute the module for the mass and vibrational energy source terms to enhance computational efficiency, achieving about 30-fold speedup in the CG2T model without sacrificing accuracy.

Study on vibration fatigue of lifeguard in a metro bogie and methodology for damage estimation based on the measured acceleration

The lifeguard is more like a cantilever beam installed on the end of bogie frame, used to remove foreign body on the rail. Due to severe vibration condition, the lifeguard has been reported to be subjected to fatigue failure by railway operators. This paper thus studied on fatigue failure mechanisms of lifeguard through both the field test and numerical simulation. In the field test, the vibration acceleration and dynamic stress developed on the lifeguard were measured to identify main contributors to the fatigue failure. The test results showed that the structural resonance arising from the rail corrugation-induced high frequency impact serves as the main causal factor. To better understanding the failure mechanism, a numerical model considering the flexibility of lifeguard was established to determine the stress field of lifeguard based on the modal method, which was further used to estimate the residual fatigue lifetime for given loading conditions. The results showed that the obtained dynamic stress for given position on lifeguard is quite comparable with those obtained through the field test. Based on the obtained dynamic stress, the fatigue damage was further estimated and concluded that the fatigue lifetime of lifeguard is much less than the designed lifetime under the considered loading condition. The rail grinding and the structural improvement are thus suggested to mitigate the vibration fatigue of lifeguard.

The Creation of Remote Spin Entanglement with a Nanomechanical Cantilever

We consider the creation of entanglement between remote electron spins using a magnetic nanoparticle attached to a cantilever tip (CT). We assume that the frequency of the CT vibrations matches the Larmor frequency of the spin (CT–spin resonance). Under the conditions of CT–spin resonance, the CT–spin system is described using the Jaynes–Cummings model. In this work, using the evolution operator of the Jaynes–Cummings model, we show that a movable CT can create an entangled state between remote spins. The most striking result is that the entanglement between the remote spins can be achieved without measuring the vibrational state of the CT.

Imaging study of O3 photodissociation in the Huggins band.

We report a velocity-mapped ion imaging study of the photodissociation of O3 in the Huggins band. The O(3PJ) images show evidence for three electronic channels producing O2(X3Σg-), O2(a1∆g), and O2(b1Σg+) state fragments, with the latter two arising from the spin-forbidden photodissociation of O3. Forward convolution simulations of the derived total translational energy distributions permit extraction of the vibrational state distribution for each O2 electronic state. All these distributions peak near v = 0 and decrease monotonically with the vibrational state. The wavelength-dependent branching of the three electronic channels has been determined and is approximately constant over the wavelength region studied (322-328nm). We have observed that the O2 electronic state branching ratios depend on the coincident O(3PJ) spin-orbit state, and the O2(b1Σg+) state is particularly sensitive. These results are qualitatively consistent with previous calculations on the coupling of the initially excited state to dissociative states by Rosenwaks and Grebenshchikov [J. Phys. Chem. A. 114, 9809-9819 (2010)]. The spatial anisotropy of the three dissociation channels has been determined through analysis of the O(3P0) angular distributions. The results are consistent with recent calculations but differ from previous experimental reports. The experimental results provide detailed information on the dissociation dynamics and should motivate new calculations.

Cavity ring-down spectroscopy of 14N216O near 0.83 µm

The cavity ring-down spectra (CRDS) of nitrous oxide were recorded at a pressure of 10 hPa in the 11,937–12,223 cm-1 range with a threshold sensitivity to absorption coefficient of the order of 6.5 × 10–11 cm-1. Three bands (ν1+5ν3, 6ν1+2ν3, and 3ν1+4ν3) were detected. The line centers and intensities were recovered from the observed spectra. The spectroscopic constants of the upper vibrational states and the vibrational transition dipole moment parameters were fitted to the measured line positions and intensities, respectively. It was found that the 3ν1+4ν3 band is in the interpolyad Coriolis resonance interaction with the 7ν1+7ν21 band. This interaction leads to the appearance in the spectra of the four extra lines of the 7ν1+7ν21 band.

Distinguishing laser-induced dissociation pathways of O 2 molecule based on alignment-dependent dissociation spectra in intense laser fields

We experimentally investigate the dissociative single ionization process, O 2 → O + + O, of aligned O 2 molecule in intense laser fields. The yield of a vibrational structure in the kinetic energy release spectra is measured as a function of alignment angle. By quantitative comparison of the measured angle-dependent dissociation probability with the simulation of a classical model that considers ionization and thus additional interaction within the laser pulse, we are able to distinguish the dissociation pathway that contribute to the vibrational structure. It is found that for a relative low laser intensity, the vibrational structure are produced from the dissociation pathway of a 4Π u → f 4Π g − 1ω. As the laser intensity increases, the increasing of the population probability of higher vibrational states and the absorbtion probability of more photons makes another two dissociation pathways open and become dominant.

Performance compensation model of turbine flowmeter under vibration conditions

Vibration conditions will affect the performance of the turbine flowmeters, resulting in inaccurate or unstable measurement results. A DN10 turbine flowmeter is taken as an example to study the influence rule of vibration conditions on the turbine flowmeter performance. An experimental facility is built to simulate the vibration conditions with amplitude ranging from 35 mm to 90 mm and frequency ranging from 0 Hz to 4 Hz. A simulation method for simulating a turbine flowmeter under vibration conditions based on a dynamic coordinate system and 6DOF (Six Degrees of Freedom) is proposed. Based on the experiments and CFD (Computational Fluid Dynamics) simulation, the results show that the average meter factor of the turbine flowmeter under vibration conditions is larger than that under non-vibration conditions. The average meter factor increases with vibration amplitude and vibration frequency. The maximum relative error of the measured flow rate is 9.73 %. To reduce the measurement error, a performance compensation model of the turbine flowmeter applied to vibration conditions is proposed. The meter factor increment is taken as the dependent variable, and the frequency, amplitude, and flow rate are taken as independent variables. The results show that compared to the original model, the relative error of the turbine flowmeter with the compensation model shows an average reduction of 76.61 %.

Updated ultraviolet fluorescence efficiencies of CS: Evidence for model discrepancies in the enhancement of NUV-derived CS abundances in comets

Observations of carbon monosulfide (CS) have a long history serving as a remote proxy for atomic sulfur, and more broadly, one of the sulfur reservoirs in cometary bodies. Recently, systematic discrepancies between NUV- and radio-derived CS abundances have been found to exceed a factor of 2–5, with NUV-derived abundances appearing enhanced for a wide array of comets. Interpretation of cometary CS emission in the ultraviolet has relied on a murky and ill-documented lineage of calculations whose accuracy can be difficult to assess. We report new fluorescence efficiencies of the CS radical, utilizing a rovibrational structure with vibrational states up to v=8 and rotational states up to N=100. The models utilize a new set of band transition rates derived from laboratory electron impact experiments. Benchmark comparisons to IUE observations of C/1979 Y1 (Bradfield) show favorable agreement with the fluorescence models. The present results affirm the accuracy of the historical record of CS abundances derived via ultraviolet CS emission in comets with IUE and HST, but do not explain the consistent enhancement of NUV-derived CS abundances relative to the radio measurements during the same apparitions. Alternative explanations of the factor of 2–5 discrepancy between NUV- and radio-derived CS abundances are discussed, as well as possible connections to sulfur reservoirs in protoplanetary disks. The model code and computed fluorescence efficiencies are made publicly available on the Zenodo service.

Study on the friction loss behavior of a wire rope and liner mating pair interface under vibration conditions

PurposeThis study aims to study the influence of friction influencing factors between the wire rope and the liner on the safe use of the wire rope, which can provide guidance for the reliability design of the lifting system with strong dynamic response such as high speed, heavy load, etc., and improve the friction-driven stability of the system.Design/methodology/approachIn this paper, the friction mechanism of wire rope and liner under the condition of excitation is investigated by means of wire rope-liner friction-vibration experimental platform and dynamic viscoelastic test of liner.FindingsThe results show that: With increasing excitation frequency, the friction between the three liner materials (G30, K25, PU) and the wire rope decreased, and the wear of the surface shape of the liners was greater. The dynamic thermomechanical analysis (DMA) test results showed that the viscoelasticity of the three liner materials increased when the frequency was increased.Research limitations/implicationsWire ropes are widely used in deep shaft hoisting and building elevators. Its operational reliability depends on whether there is sufficient friction between the wire rope and the friction liner, and whether the friction liner has good wear resistance. The study of the friction between the wire rope and the liner influencing factors is of great significance for the safe service of the wire rope.Practical implicationsThe related results can provide guidance for the reliability design of lifting systems with strong dynamic response, such as high speed and heavy load, to improve the friction drive stability of the system.Originality/valueWith the increase of mining depth, to improve the transportation efficiency of the hoist used in deep and ultra-deep mines, as well as to ensure the safety and reliability of its operation, it is crucial that the large friction hoisting equipment has sufficient friction between the wire rope and the friction lining, as well as whether the friction lining has a good abrasion resistance.

DFT insight into the structural, vibrational, and electronic properties of thin [110] Ge nanowires as anodic material for Li batteries

Germanium nanowires could be used to improve as anodic materials since their charge rate is better than that of the current graphite electrodes. In this work, we present a Density Functional Theory study of the effect of interstitial Li atoms on the vibrational, electronic, and mechanical properties of ultrathin hydrogen-passivated Ge nanowires (HGeNWs) with diamond structure, grown along the [110] crystallographic direction, and with a diameter of ∼14.4 Å. The interstitial Li atoms were placed at the tetrahedral positions (Td) reported as the more favorable ones. The phonon band structure of the HGeNWs reveals the existence of high frequency vibrations due to the hydrogen atoms at the nanowire surface. The effect of one interstitial Li atom in the nanowire leads to the apparition of three flat phonon bands almost independent of the collective vibrational states of the nanowire, reflecting a weak interaction between the Li atom and the neighboring ones; and a shift of the high vibrational modes to lower frequencies that results in more dispersive states. The electronic band structure confirms a transition from semiconducting to metallic behavior by adding a single Li interstitial atom per unit cell. The formation energies indicate that the nanowires with interstitial Li atoms are stable, and the average binding energy per Li atom slightly increases as a function of the concentration of Li atoms. The insertion of Li atoms in the nanowire leads to a volumetric expansion, without fracture or broken bonds. Even more, the redistribution of the electronic charge due to the Li atoms give the Ge-Ge bonds more axial elasticity and the values of the modulus of Young are almost constant for all studied concentrations of Li atoms. These theoretical results indicate an improvement of mechanical and electronic properties of Ge nanowires through the addition of interstitial Li atoms that could be important for their use as anodes in rechargeable Li batteries.