Lumped parameter model for resonant frequency estimation of a thermoacoustic engine with gas-liquid coupling oscillation

Gas-liquid coupling oscillation is a novel approach to reducing the resonant frequency and to elevating the pressure amplitude of a thermoacoustic engine.If a thermoacoustic engine is used to drive low-frequency pulse tube refrigerators,the frequency matching between the thermoacoustic engine and the refrigerator plays an important role.Based on an acoustic-electric analogy,a lumped parameter model is proposed to estimate the resonant frequency of a standing-wave thermoacoustic engine with gas-liquid coupling oscillation.Furthermore,a simplified lumped parameter model is also developed to reduce the computation complexity.The resonant frequency dependence on the mean pressure,the gas space volume,and the water column length is computed and analyzed.The impact of different working gases on the resonant frequency is also discussed.The effectiveness of the models is validated by comparing the computed results with the experimental data of the gas-liquid coupling oscillation system.An increase in the mean working pressure can lead to a rise in the resonant frequency,and a lower resonant frequency can be achieved by elongating the liquid column.In comparison with nitrogen and argon,carbon dioxide can realize a lower frequency due to a smaller specific heat ratio.

Chimera states of phase oscillator populations with nonlocal higher-order couplings

The chimera states underlying many realistic dynamical processes have attracted ample attention in the area of dynamical systems.Here, we generalize the Kuramoto model with nonlocal coupling incorporating higher-order interactions encoded with simplicial complexes.Previous works have shown that higher-order interactions promote coherent states.However, we uncover the fact that the introduced higher-order couplings can significantly enhance the emergence of the incoherent state.Remarkably, we identify that the chimera states arise as a result of multi-attractors in dynamic states.Importantly, we review that the increasing higher-order interactions can significantly shape the emergent probability of chimera states.All the observed results can be well described in terms of the dimension reduction method.This study is a step forward in highlighting the importance of nonlocal higher-order couplings, which might provide control strategies for the occurrence of spatial-temporal patterns in networked systems.

Air–Sea Coupling Enhances the East Asian Winter Climate Response to the Atlantic Multidecadal Oscillation

A simple air-sea coupled model, the atmospheric general circulation model （AGCM） of the National Centers for Environmental Prediction coupled to a mixed-layer slab ocean model, is employed to investigate the impact of air-sea coupling on the signals of the Atlantic Multidecadal Oscillation （AMO）. A regional coupling strategy is applied, in which coupling is switched off in the extratropical North Atlantic Ocean but switched on in the open oceans elsewhere. The coupled model is forced with warm-phase AMO SST anomalies, and the modeled responses are compared with those from parallel uncoupled AGCM experiments with the same SST forcing. The results suggest that the regionally coupled responses not only resemble the AGCM simulation, but also have a stronger intensity. In comparison, the coupled responses bear greater similarity to the observational composite anomaly. Thus, air-sea coupling enhances the responses of the East Asian winter climate to the AMO. To determine the mechanism responsible for the coupling amplification, an additional set of AGCM experiments, forced with the AMO-induced tropical SST anomalies, is conducted. The SST anomalies are extracted from the simulated AMO-induced SST response in the regionally coupled model. The results suggest that the SST anomalies contribute to the coupling amplification. Thus, tropical air-sea coupling feedback tends to enhance the responses of the East Asian winter climate to the AMO.

Effects of air-sea coupling on the eastward propagating boreal winter intraseasonal oscillation over the tropical Indian Ocean

The effects of air-sea coupling over the tropical Indian Ocean（TIO） on the eastward propagating boreal winter intraseasonal oscillation（MJO） are investigated by comparing a fully coupled and a partially decoupled Indian Ocean experiment using the SINTEX-F coupled model.Air-sea coupling over the TIO significantly enhances the intensity of the eastward propagations of the MJO along the5°-10°S zonal areas.The zonal asymmetry of the SST anomaly（SSTA） is responsible for the enhanced eastward propagation.A positive SSTA appears to the east of the MJO convection,which results in the boundary layer moisture convergence and positively feeds back to the MJO convection.In addition,the air-sea interaction effect on the eastward propagation of the MJO is related to the interannual variations of the TIO.Air-sea coupling enhances（reduces） the eastward-propagating spectrum during the negative Indian Ocean dipole mode and positive Indian Ocean basin mode.Such phase dependence is attributed to the role of the background mean westerly in affecting the wind-evaporation-SST feedback.Air-sea coupling（decoupling） enhances（reduces） the zonal asymmetry of the low-level specific humidity,and thus the eastward propagation spectrum of the MJO.

On the Couplings between Chebyshev Coefficients as Derived from the Monthly Mean Geopotential Fields at 500 hPa over East Asia and the Southern Oscillation

The first six Chebyshev polynomial coefficients (i.e., A00, A01, A10, A11, A02, A20) were derived from monthly mean geopotential height over East Asia for the period 1951-1983. Spectral analysis of these coefficients reveals relative maxima of power in the frequency bands of 200 months (- 16.7 years), 25 months (the quasi-biennial oscillation), 5-6 months, and 2-3 months. Cross-spectral characteristics between Chebyshev coefficients and the Southern Oscillation Index (SOI) were also explored. Coherence spectrum for the zonal and meridional circulation index (A01 and A 10) with the SOI was significant near 4 years, the QBO, and 2-3 months. Some physical explanations were offered for the spatial linkages (i.e., teleconnections) between the SO and atmospheric circulation anomalies overEast Asia.

THE REGIONAL AIR-SEA COUPLED OSCILLATION IN THE SOUTH CHINA SEA

This study examined the regional air sea coupled interaction in the South China Sea (SCS), based on the 1979-1995 NCEP/NCAR reanalysis data of sea surface temperature (SST) and meridional wind (V component). Singular value decomposition (SVD) and single field principal component analysis (PCA) were employed to analyse the SST and V anomalies and compare the results with each other. It was found that the leading mode of SVD explained a predominant amount of squared covariance between the SST and meridional wind V, and that the time series expansion coefficients of the first mode between SST and V from PCA and SVD resembled very much each other. This infers that the meridional wind, as an indicator of Asian monsoon, is closely related with the SST through the air sea interaction in the SCS. The spatial patterns of the first mode of SST and V exhibit ellipse shaped variance in the SCS center and a NE SW oriented main axis, which are much similar to those in winter season. These results show that the most active center for both V and SST is in the SCS, which suggests that a regional air sea coupled oscillation possibly exists there for the whole year and is noticeable especially during the winter season. So the SCS is a very important region for the forming of the Asian Monsoon and the climate of the west Pacific.

Twentieth-century Pacific Decadal Oscillation simulated by CMIP5 coupled models

The authors examine the spatial and temporal characteristics of the simulated Pacific Decadal Oscillation （PDO） in 109 historical （i.e. all forcings） simulations derived from 25 coupled models within CMIPS. Compared with observations, most simulations successfully simulate the observed PDO pattern and its teleconnections to the SSTs in the tropical and southern Pacific. BNU-ESM, CanESM2, CCSM4, CESM 1 -FASTCHEM, FGOALS-g2, GFDL CM3, MIROCS, and NorESM 1 -M show better performance. Compared with the temporal phases of the observed PDO in the twentieth century, only five simulations -- from CNRM^CMS, CSIRO Mk3o6.0, HadCM3, and IPSL-CMSA-LR -- simulate an evolution of the PDO similar to that derived from observation, which suggests that current coupled models can barely reproduce the observed phase shifting of the PDO. To capture characteristics of the observed PDO in the twentieth century, a requirement is that all the relevant external forcings are included in the models. How to add realistic oceanic initial states into the model may be another key point.

One- and Two-Mode Combination Squeezing Operator for Two Harmonic Oscillators with Coordinate-Momentum Coupling

By virtue of the technique of integration within an ordered product of operators, we derive the normal ordering expansion of a one- and two-mode combination squeezing operator for two harmonic oscillators with coordinate- momentum coupling. It turns out that this squeezing operator just diagonalizes the Hamiltonian H=p^21/2m1＋m1ω^21x^21/2＋p^222m2＋m2ω^22x^22/2-λx2p1 so its ground state is a one- and two-mode combination squeezed state. Quantum fluctuation in the ground state is calculated.

Analysis of the Oscillating Mechanism of an Aerial Work Platform Based on ADAMS Hydraulic-Mechanical Coupling Simulation

Rigid model of the aerial work platform and hydraulic model of the oscillating mechanism were established with ADAMS. The simulation of two parameters, cy-linder force and oil chamber pressure, was carried out. The simulation result is useful to the design of the oscillating mechanism.

Tunable, continuous-wave single-resonant optical parametric oscillator with output coupling for resonant wave

We present a continuous-wave singly-resonant optical parametric oscillator with 1.5% output coupling of the reso- nant signal wave, based on an angle-polished MgO-doped periodically poled lithium niobate （MgO：PPLN）, pumped by a commercial Nd：YVO4 laser at 1064 nm. The output-coupled optical parametric oscillator delivers a maximum total output power of 4.19 W with 42.8% extraction efficiency, across a tuning range of 1717 nm in the near- and mid-infrared region. This indicates improvements of 1.87 W in output power, 19.1% in extraction efficiency and 213 nm in tuning range exten- sion in comparison with the optical parametric oscillator with no output coupling, while at the expense of increasing the oscillation threshold by a factor of - 2. Moreover, it is confirmed that the finite output coupling also contributes to the reduction of the thermal effects in crystal.

Phase synchronization and synchronization frequency of two-coupled van der Pol oscillators with delayed coupling

In this paper, phase synchronization and the frequency of two synchronized van der Pol oscillators with delay coupling are studied. The dynamics of such a system are obtained using the describing function method, and the necessary conditions for phase synchronization are also achieved. Finding the vicinity of the synchronization frequency is the major advantage of the describing function method over other traditional methods. The equations obtained based on this method justify the phenomenon of the synchronization of coupled oscillators on a frequency either higher, between, or lower than the highest, in between, or lowest natural frequency of the aggregate oscillators. Several numerical examples simulate the different cases versus the various synchronization frequency delays.

Time Delay Induced Oscillation: An Example on a Class of <i>n</i>Coupled Van Der Pol Oscillators Model with Delays

In this paper, a class of n coupled van der Pol oscillator model with delays is considered. By employing an analysis approach, some sufficient conditions to guarantee the existence of stability and oscillations for themodel are obtained. Examples are provided to demonstrate the results.

Thermokinetic Oscillation of a Two-step Reacting System Coupled with Thermal Conduction and Apparent

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Periodic electron oscillation in coupled two-dimensional lattices

We study the time evolution of electron wavepacket in the coupled two-dimensional(2D)lattices with mirror symmetry,utilizing the tight-binding Hamiltonian framework.We show analytically that the wavepacket of an electron initially located on one atomic layer in the coupled 2D square lattices exhibits a periodic oscillation in both the transverse and longitudinal directions.The frequency of this oscillation is determined by the strength of the interlayer hopping.Additionally,we provide numerical evidence that a damped periodic oscillation occurs in the coupled 2D disordered lattices with degree of disorderW,with the decay time being inversely proportional to the square ofW and the frequency change being proportional to the square of W,which is similar to the case in the coupled 1D disordered lattices.Our numerical results further confirm that the periodic and damped periodic electron oscillations are universal,independent of lattice geometry,as demonstrated in AA-stacked bilayer and tri-layer graphene systems.Unlike the Bloch oscillation driven by electric fields,the periodic oscillation induced by interlayer coupling does not require the application of an electric field,has an ultrafast periodicity much shorter than the electron decoherence time in real materials,and can be tuned by adjusting the interlayer coupling.Our findings pave the way for future observation of periodic electron oscillation in material systems at the atomic scale.

Collective Behavior of a Ring of Van Der Pol Oscillators under Gaussian and Random Coupling Schemes

The collective behavior of a ring of coupled identical van der Pol oscillators is numerically studied in this work. Constant, gaussian and random distributions of the coupling parameter along the ring are considered. Three values of the oscillators constant are assumed in order to cover from quasilinear to nonlinear dynamic performance. Single and multiple coupled frequencies are obtained using power spectra of the long term time series. Phase portraits are obtained from numerical simulations, and the coupled behavior is analyzed, compared and discussed.

Coupled Two-Dimensional Atomic Oscillation in an Anharmonic Trap

In atomic dynamics, oscillation Mong different axes can be studied separately in the harmonic trap. When the trap is not harmonic, motion in different directions may couple together. In this work, we observe a two- dimensional oscillation by exciting atoms in one direction, where the atoms are transferred to an anharmonic region. Theoretical calculations are coincident to the experimental results. These oscillations in two dimensions not only can be used to measure trap parameters but also have potential applications in atomic interferometry and precise measurements.

Discrete-Time Dynamic Image Segmentation Using Oscillators with Adaptive Coupling

In this study, we propose a novel discrete-time coupled model to generate oscillatory responses via periodic points with a high periodic order. Our coupled system comprises one-dimensional oscillators based on the Rulkov map and a single globally coupled oscillator. Because the waveform of a one-dimensional oscillator has sharply defined peaks, the coupled system can be applied to dynamic image segmentation. Our proposed system iteratively transforms the coupling of each oscillator based on an input value that corresponds to the pixel value of an input image. This approach enables our system to segment image regions in which pixel values gradually change with respect to a connected region. We conducted a bifurcation analysis of a single oscillator and a three-coupled model. Through simulations, we demonstrated that our system works well for gray-level images with three isolated image regions.

Characteristic of Torsional Vibration of Mill Main Drive Excited by Electromechanical Coupling

In the study of electromechanical coupling vibration of mill main drive system, the influence of electrical system on the mechanical transmission is considered generally, however the research for the mechanism of electromechanical interaction is lacked. In order to research the electromechanical coupling resonance of main drive system on the F3 mill in a plant, the cycloconverter and synchronous motor are modeled and simulated by the MTLAB/SIMUL1NK firstly, simulation result show that the current harmonic of the cycloconverter can lead to the pulsating torque of motor output. Then the natural characteristics of the mechanical drive system are calculated by ANSYS, the result show that the modal frequency contains the component which is close to the coupling vibration frequency of 42Hz. According to the simulation result of the mechanical and electrical system, the closed loop feedback model including the two systems are built, and the mechanism analysis of electromechanical coupling presents that there is the interaction between the current harmonic of electrical system and the speed of the mechanical drive system. At last, by building and computing the equivalent nonlinear dynamics model of the mechanical drive system, the dynamic characteristics of system changing with the stiffness, damping coefficient and the electromagnetic torque are obtained. Such electromechanical interaction process is suggested to consider in research of mill vibration, which can induce strong coupling vibration behavior in the rolling mill drive system.

The construction of conserved quantities for linearly coupled oscillators and study of symmetries about the conserved quantities

In this paper, the conserved quantities are constructed using two methods. The first method is by making an ansatz of the conserved quantity and then using the definition of Poisson bracket to obtain the coefficients in the ansatz. The main procedure for the second method is given as follows. Firstly, the coupled terms in Lagrangian are eliminated by changing the coordinate scales and rotating the coordinate axes, secondly, the conserved quantities are obtain in new coordinate directly, and at last, the conserved quantities are expressed in the original coordinates by using the inverse transform of the coordinates. The Noether symmetry and Lie symmetry of the infinitesimal transformations about the conserved quantities are also studied in this paper.

Asymptotic solving method for sea-air coupled oscillator ENSO model

The ENSO is an interannual phenomenon involved in the tropical Pacific ocean-atmosphere interaction. In this article, we create an asymptotic solving method for the nonlinear system of the ENSO model. The asymptotic solution is obtained. And then we can furnish weather forecasts theoretically and other behaviors and rules for the atmosphere- ocean oscillator of the ENSO.