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The safe and stable operation of the transformer is the key to ensure the reliable operation of the power grid. Loose windings will produce a vibration acceleration signal with twice the power supply frequency signal, i.e., 100 Hz, as the main spectral component. The realization of transformer winding vibration acceleration detection can effectively determine the operating status of the transformer winding. In this report, a dual-cantilever beam Fiber Bragg Grating (FBG) vibration acceleration sensor for transformer winding with a two-point package structure was designed based on theoretical analysis and finite element simulation of COMSOL Multiphysics software. Through the demodulation of the center wavelength change to achieve the detection of external vibration acceleration and to achieve the vibration acceleration sensitivity of 37.813 pm/g at 100 Hz, linearity up to 99.97%, cross-sensitivity is less than 17.4%. The resonant frequency of the sensor is 134 Hz, and the sensitivity of the vibration acceleration at the resonant frequency point is 425.52 pm/g. The sensor is installed under the transformer to measure the vibration acceleration of the transformer winding. The vibration component under 100 Hz frequency could be obviously captured, and the FFT of the center wavelength captured the amplitude signal to realize the measurement of the vibration acceleration of the transformer winding less than 0.02 g micro-vibration acceleration, which could satisfy the general vibration range of the transformer winding. [ABSTRACT FROM AUTHOR]

A Mach 1.5 non-reactive flow in a cavity-stabilized combustor of a model scramjet is studied via a direct-numerical simulation approach, and the analysis is focused on the interaction among boundary layer, free shear-layer above the cavity and shock wave. It is found that the impingement of the free shear-layer on the aft wall of the cavity leads to strong turbulence kinetic energy, high local pressure, and a fan of compression waves. The compression waves evolve into an oblique shock, which reflects between the upper and lower walls and interacts with the boundary layers attached to the two walls. The analysis of the turbulence production reveals that the amplification of turbulence in the core of the shear-layer and around the reattachment point is mainly due to the shear production, but the deceleration production mechanism presents a significant impact in the regions above the aft wall of the cavity and around the shock interaction points. The very low frequency commonly observed in shock wave/boundary layer interactions is not observed in the present research, which might be due to the low Reynolds number of the studied case. [ABSTRACT FROM AUTHOR]

In this paper, the effect of the secondary flow induced by convergent–divergent riblets in supersonic turbulent boundary layers over a 24° compression ramp at Mach number 2.9 is studied via direct numerical simulation. Two riblet cases with the wavelength Λ being 1.1δ and 1.65δ (δ is the boundary layer thickness) are conducted to examine their impact on the secondary rolling motion, momentum transfer, turbulent fluctuations, flow separation, and unsteady shock motion. As the flow develops over the riblet section, both the size and intensity of the secondary rolling motion tend to increase. For the riblet case with Λ / δ = 1.1 , a single rolling mode is observed within a half wavelength, while a pair of co-rotating vortical structures is obtained for Λ / δ = 1.65. Both rolling patterns lead to an apparent spanwise variation of the flow field. The results reveal that the secondary flow contributes to the increase of both the mean momentum flux and turbulent fluctuations. By using the spanwise averaging, the mean momentum flux contributed from the dispersive stress and compressible effect caused by the secondary flow is identified. Both components appear to enhance the near-wall momentum mixing, and a larger enhancement is observed for Λ / δ = 1.1 , where the intensity of the secondary flow is stronger. Compared to the baseline case, the area of the separation zone at Λ / δ = 1.1 and Λ / δ = 1.65 is decreased by 56% and 38%, respectively. For all the cases, the low-frequency motion near the foot of the shock is observed. In comparison, the frequency of the low-frequency motion for the riblet case is two times higher than that in the baseline case, owing to the reduction of the separation area and length. [ABSTRACT FROM AUTHOR]

In this paper, a section of convergent–divergent (C–D) riblets is applied upstream of a compression ramp in a supersonic turbulent boundary layer in a Mach 2.9 flow with a Reynolds number of R e θ = 2240. Direct numerical simulations are undertaken to examine the impact of C–D riblets on the shock wave/boundary layer interaction and the feasibility of using them to mitigate flow separation. Over the riblet section, a large-scale secondary roll mode is produced by C–D riblets with the downwelling motion occurring around the diverging region and upwelling motion near the converging region. This consequently leads to a spanwise heterogeneity in mean quantities and turbulent structures over the riblet section and also in the interaction zone. Compared with the baseline case, the area of the separation zone for the riblet case experiences a dramatic local reduction of 92% in the diverging region, owing to the downwelling motion that injects the high-momentum fluid toward the wall and the near-wall spanwise velocity that transports the low-momentum fluid away. The enhanced upwelling motion around the converging region induced by C–D riblets, on the one hand, contributes to the decrease of the near-wall momentum and subsequently the increase of the local separation area. On the other hand, the upwelling motion effectively reduces the incoming Mach number upstream of the compression corner. This appears to reduce the strength of the separation shock, leading to a more gradual compression of the incoming flow that helps ease the enlargement of the separation area nearby. Overall, the area of the mean flow separation is reduced by 56%, indicating an effective flow separation control by the C–D riblets. [ABSTRACT FROM AUTHOR]

Direct numerical simulations of a turbulent channel flow developing over convergent–divergent (C–D) riblets are performed at a Reynolds number of Reb = 2800, based on the half channel height δ and the bulk velocity. To gain an in-depth understanding of the origin of the drag generated by C–D riblets, a drag decomposition method is derived from kinetic energy principle for a turbulent channel flow with wall roughness. C–D riblets with a wavelength, Λ, ranging from 0.25 δ to 1.5 δ , are examined to understand the influence of secondary flow motions on the drag. It is found that as Λ increases, the intensity of the secondary flow motion increases first and then decreases, peaking at Λ / δ = 1. At Λ / δ ≥ 1 , some heterogeneity appears in the spanwise direction for the turbulent kinetic energy (TKE) and vortical structures, with the strongest enhancement occurring around regions of upwelling. All the riblet cases examined here exhibit an increased drag compared to the smooth wall case. From the energy dissipation/production point of view, such a drag increase is dominated by the TKE production and the viscous dissipation wake component. While the drag contribution from the TKE production shear component decreases as Λ increases, the drag contribution from the wake component of both the TKE production and viscous dissipation follows the same trend as the intensity of the secondary flow motion. From the work point of view, the drag increase in the riblet case at Λ / δ = 0.25 comes mainly from the work of the Reynolds shear stresses, whereas at Λ / δ ≥ 1 , the drag augmentation is dominated by the work of the dispersive stresses. At Λ / δ = 0.5 , both components play an important role in the increase in the drag, which also exhibits a peak. [ABSTRACT FROM AUTHOR]

Robust detection of acoustically quiet, slow-moving, small unmanned aerial vehicles is challenging. A biologically inspired vision approach applied to the acoustic detection of unmanned aerial vehicles is proposed and demonstrated. The early vision system of insects significantly enhances signal-to-noise ratios in complex, cluttered, and low-light (noisy) scenes. Traditional time-frequency analysis allows acoustic signals to be visualized as images using spectrograms and correlograms. The signals of interest in these representations of acoustic signals, such as linearly related harmonics or broadband correlation peaks, essentially offer equivalence to meaningful image patterns immersed in noise. By applying a model of the photoreceptor stage of the hoverfly vision system, it is shown that the acoustic patterns can be enhanced and noise greatly suppressed. Compared with traditional narrowband and broadband techniques, the bio-inspired processing can extend the maximum detectable distance of the small and medium-sized unmanned aerial vehicles by between 30% and 50%, while simultaneously increasing the accuracy of flight parameter and trajectory estimations. [ABSTRACT FROM AUTHOR]

A planar duct flow configuration with a cross-flow injected from a longitudinal slit close to the upper wall of the duct is studied by using a direct numerical simulation approach to explore the underlying flow mechanism in relation to the tip-leakage vortex (TLV), which is one of the most important flow phenomena in turbomachinery. Major characteristics of TLV in a rotor of turbomachinery are identified in the current flow model. The analysis of mean and instantaneous flow fields reveals that the interaction between the main (axial) flow and jet (cross) flow is the primary source of the generation of the TLV. The evolution of the TLV is then investigated, and a vortex breakup phenomenon is identified. The evolution of TLV can be divided into three phases, i.e., the formation phase, the breakup phase, and the diffusion phase. Mean streamlines and turbulence kinetic energy (TKE) budgets are analyzed, showing that the high TKE central spot in the formation phase is due to the interaction between highly swirling vortex filaments and mean velocity gradient. In the outer part of the TLV, the TKE is mainly produced in the shear-layer and transported toward the center by the turbulence transport. [ABSTRACT FROM AUTHOR]

Compares surface hopping and mean field approaches for simulating proton transfer reactions. Molecular dynamics with quantum transitions method used for calculations in the surface hopping method; Consistency between quantum probabilities and the fraction of trajectories in each adiabatic state.

Presents a general minimal model for proton-coupled electron transfer (PCET) reactions in solution. Three coupled degrees of freedom that represent an electron, proton and solvent coordinate; Concerted mechanism in which the proton and electron are transferred simultaneously; Sequential and surface hopping methods; Role of nonadiabatic effects.

Two-dimensional time-dependent wave packet calculations are carried out on a collinear model of the I2(B)–Ar complex to investigate the possible kinematic origin of the one-atom cage effect in small van der Waals molecules. Three different excitation wavelengths are considered (496.5, 488, and 476.5 nm), and the dynamics are assumed to be restricted to the I2 B state electronic surface, with no nonadiabatic transitions following the pump excitation. Good agreement with experiment is obtained. To investigate the sensitivity of observable final state distributions on the weak intermolecular potential between I2 and Ar, three slightly different B state I–Ar interactions are employed for the case of 488 nm excitation. It is found that relatively small changes in the form and magnitude of the weak van der Waals interactions can have a large effect on the final state distributions. These results suggest that the experimental data on I2–Ar photodissociation–recombination can be explained by a purely kinematic one-atom cage effect on the B state electronic surface for a collinear population of I2–Ar clusters, without the need to introduce nonadiabatic electronic effects. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In this paper, we develop a method for accurately modeling ultrafast molecular dynamics and pump–probe spectroscopy using classical trajectory simulations. The approach is based on a semiclassical limit of the Liouville formulation of quantum mechanics. Expressions for the nonstationary classical phase space probability density created by an ultrashort laser pulse on an excited electronic state, and the observable fluorescence signal resulting from a pump–probe experiment, are derived in the weak-field limit using perturbation theory. By introducing additional approximations, these expressions are cast in a form that can be directly implemented using classical trajectory integration and ensemble averaging. The method is tested against multisurface time-dependent quantum mechanical wave packet calculations for a one-dimensional model system representing I2 photodissociation-recombination in a static Ar lattice. Nearly quantitative agreement between the exact calculations and the trajectory-based method is obtained. Although demonstrated for a one-dimensional system, the method is easily incorporated in conventional molecular dynamics programs, allowing efficient treatment of many-body ultrafast dynamics and spectroscopy. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We describe an approximate method for treating the mixed quantum-classical (QC) dynamics of many-body systems on N coupled electronic surfaces. The approach is based on calculating N×N reduced Hamiltonian matrices for the classical and quantal degrees of freedom by partial averaging, and then solving the appropriate equations of motion—Hamilton’s equations or the Schrödinger equation—self-consistently. The degrees of freedom requiring a quantum mechanical description are treated using a multistate Schrödinger equation with classically averaged effective time-dependent Hamiltonians and off-diagonal couplings. The classical degrees of freedom are treated by propagating N ensembles of trajectories, one on each electronic surface, using N reduced classical Hamiltonians defined in terms of the expectation value of the full Hamiltonian calculated using the evolving quantum wave functions. An ansatz is proposed to approximately estimate classical off-diagonal density matrix elements required for calculating the classically averaged interactions that couple quantum wave functions on different electronic states. We present the theory and then test it for a simple two-dimensional and two-state model system. Exact quantum and multiconfiguration time-dependent self-consistent-field (MCTDSCF) calculations are carried out to evaluate the QC performance. Good agreement between the MCTDSCF and QC results is obtained for the model considered. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In this work, we explore the applicability of a multiconfiguration version of the time-dependent Hartree approximation in photodissociation dynamics. A two-dimensional model system based on the A-band photodissociation of ICN is used. The propagation of the wave packet, which is expanded on grids, is carried out using pseudospectral methods and a predictor–corrector integrator. It is found that the quantum state resolved quantities, such as the final CN rotational distribution, require many more configurations than averaged quantities like the absorption spectrum. The calculated results from this work agree well with previous quantum calculations. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The vibrational predissociation of a van der Waals complex (Cl2Ne) is studied using a method based on the multiconfiguration time-dependent Hartree approximation. The three-dimensional wave function is first expanded to the time-independent Cl2 vibrational bases and the Hartree approximation is then imposed on the channel wave functions. The wave packets are propagated for a few picoseconds and five configurations are found to give convergent results. The decay lifetimes, product state distributions and the wave packet dynamics are compared with exact results and the agreement is found to be generally satisfactory. It is found that the decay depends sensitively on the quality of the initial resonance wave function and the single configuration TDH gives only a crude approximation of the dissociation dynamics. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A multiconfiguration time-dependent Hartree method is applied to study the photodissociation dynamics of methyl iodide on a MgO surface. The surface is assumed to be rigid and the dissociation is restricted in orientations parallel to the surface normal. Two active mathematical dimensions and two electronic states are included in our model. The dynamics of the fragments (the methyl radical and iodine atom) are complicated by the so-called ‘‘chattering effect’’ and by nonadiabatic transitions between the two dissociative states of CH3I. It is shown from the comparison with exact calculations that the single configuration time-dependent Hartree approximation fails to give an accurate description of the dynamics. The failure of the Hartree approximation, which is due to the neglect of direct spatial correlations between modes, can be effectively corrected by including a few additional configurations. Our results show that four configurations are sufficient to provide an accurate description of the complex dissociation dynamics of the CH3I/MgO system. [ABSTRACT FROM AUTHOR]

Photodissociation dynamics of HBr adsorbed on a LiF(001) surface are investigated using both exact and time-dependent Hartree (TDH) methods on realistic potential energy surfaces. The dissociation dynamics are restricted in two dimensions and two coupled dissociative states of the adsorbate are included. The wave packets are propagated on numerical grids, and fast Fourier transform (FFT) and discrete variable representation (DVR) are used to calculate the action of the Hamiltonian. In the TDH treatment, each excited electronic state is represented by a single nuclear configuration. Final radial, angular, and momentum distributions of the H fragment are calculated. Comparisons between the exact and TDH results reveal that the agreement between the two is generally reasonable and is better for highly averaged quantities. Results also show that nonadiabatic transition dynamics are correctly reproduced by the TDH approximation. Finally, the calculated results are found consistent with the experimental observations. [ABSTRACT FROM AUTHOR]

An empirical two-plus-three-body potential, developed by Murrell and co-workers [J. N. Murrell and R. A. Rodriguez-Ruiz, Mol. Phys. 71, 823 (1990)], is applied to the study of fcc aluminum. The parameters in the potential are derived by fitting the experimental phonon-dispersion curves and elastic constants. Calculations, using this potential, on a number of one-, two- and three-dimensional extended systems give results which are in quantitative agreement with recent ab initio calculations [I. J. Robertson, M. C. Payne, and V. Heine, Europhys. Lett. 15, 301 (1991)]. Calculations on small- and medium-sized aluminum clusters give cluster geometries and growth patterns which agree qualitatively with previous ab initio molecular-orbital and density-functional studies. [ABSTRACT FROM AUTHOR]

A validated method based on Haidinger fringes has been proposed to measure the optical constants for thin-walled glass cells. The method can significantly enhance measurement accuracy by utilizing the reflected spectrum to determine the optical constants of the sample. The reflected light off the inner and the outer surfaces of the cell combined together and formed the interferential pattern (Haidinger fringes) detected by the photodiodes. Taking into account that the sample in our experiment is a sealed cell, we deliberately set the incident angle to a non-zero value. First, the measurement principle has been analyzed, and subsequently, the relevant experimental platform has been established. To reduce random errors, we recalibrated the relationship between the frequency of the laser and the operating temperature. Furthermore, the incident angle has been accurately estimated using the method of non-linear least squares. Finally, the weighted average, considering correlated uncertainties for all measurements, is 1.873 ± 0.005 016 mm, which showcases clear advantages over conventional mechanical methods that risk potential damages. [ABSTRACT FROM AUTHOR]

An implicit large-eddy simulation is carried out to study turbulent boundary-layer separation from a backward-facing rounded ramp with active wall actuation control. This method, called spanwise alternating distributed strips control, is imposed onto the flat plate surface upstream of a rounded ramp by alternatively applying out-of-phase control and in-phase control to the wall-normal velocity component in the spanwise direction. As a result, the local turbulence intensity is alternatively suppressed and enhanced, leading to the creation of vertical shear-layers, which is responsible for the presence of large-scale streamwise vortices. These vortices exert a predominant influence on the suppression of the flow separation. The interaction between the large-scale vortices and the downstream recirculation zone and free shear-layer is studied by examining flow statistics. It is found that in comparison with the non-controlled case, the flow separation is delayed, the reattachment point is shifted upstream, and the length of the mean recirculation zone is reduced up to 8.49%. The optimal control case is achieved with narrow in-phase control strips. An in-depth analysis shows that the delay of the flow separation is attributed to the activation of the near-wall turbulence by the in-phase control strips and the improvement of the reattachment location is mainly due to the large-scale streamwise vortices, which enhance the momentum transport between the main flow and separated region. [ABSTRACT FROM AUTHOR]

This paper investigates the problem of the exponential cluster synchronization of coupled impulsive genetic oscillators with external disturbances and communication delay. Based on the Kronecker product, some new cluster synchronization criteria for coupled impulsive genetic oscillators with attenuation level are derived. The derived results are related to the impulsive strength, and the derived results also indicate that the maximal allowable bound of time delay is inversely proportional to the decay rate, the decay rate is proportional to the couple strength, the maximal allowable bound of time delay is proportional to attenuation level, and the attenuation level is inversely proportional to the couple strength. Moreover, the case when the feedback have different self-delay is also investigated. Finally, numerical examples are given to illustrate the effectiveness of the derived results. [ABSTRACT FROM AUTHOR]

Presents an accurate Fresnel diffraction model for a pulsed laser induced thermal lens effect in mode-mismatched crossed-beam configuration. Calculation of the diffraction field of the probe beam; Achievement of the thermal lens signal maximum; Intensity profile of the probe beam at detection plane.

In this paper, multiobjective synchronization of chaotic systems is investigated by especially simultaneously minimizing optimization of control cost and convergence speed. The coupling form and coupling strength are optimized by an improved multiobjective evolutionary approach that includes a hybrid chromosome representation. The hybrid encoding scheme combines binary representation with real number representation. The constraints on the coupling form are also considered by converting the multiobjective synchronization into a multiobjective constraint problem. In addition, the performances of the adaptive learning method and non-dominated sorting genetic algorithm-II as well as the effectiveness and contributions of the proposed approach are analyzed and validated through the Rössler system in a chaotic or hyperchaotic regime and delayed chaotic neural networks. [ABSTRACT FROM AUTHOR]

In this paper, the delay-distribution-dependent stability is derived for the stochastic genetic regulatory networks (GRNs) with a finite set delay characterization and interval parameter uncertainties. One important feature of the obtained results here is that the time-varying delays are assumed to be random and the sum of the occurrence probabilities of the delays is assumed to be 1. By employing a new Lyapunov-Krasovskii functional dependent on auxiliary delay parameters which allow the time-varying delays to be not differentiable, less conservative mean-square stochastic stability criteria are obtained. Finally, two examples are given to illustrate the effectiveness and superiority of the derived results. [ABSTRACT FROM AUTHOR]

In this paper, we study the controllability of networks with different numbers of communities and various strengths of community structure. By means of simulations, we show that the degree descending pinning scheme performs best among several considered pinning schemes under a small number of pinned nodes, while the degree ascending pinning scheme is becoming more powerful by increasing the number of pinned nodes. It is found that increasing the number of communities or reducing the strength of community structure is beneficial for the enhancement of the controllability. Moreover, it is revealed that the pinning scheme with evenly distributed pinned nodes among communities outperforms other kinds of considered pinning schemes. [ABSTRACT FROM AUTHOR]