Oscillatory Systems Research Articles

Imaging quantum oscillations and millitesla pseudomagnetic fields in graphene

The exceptional control of the electronic energy bands in atomically thin quantum materials has led to the discovery of several emergent phenomena1. However, at present there is no versatile method for mapping the local band structure in advanced two-dimensional materials devices in which the active layer is commonly embedded in the insulating layers and metallic gates. Using a scanning superconducting quantum interference device, here we image the de Haas–van Alphen quantum oscillations in a model system, the Bernal-stacked trilayer graphene with dual gates, which shows several highly tunable bands2–4. By resolving thermodynamic quantum oscillations spanning more than 100 Landau levels in low magnetic fields, we reconstruct the band structure and its evolution with the displacement field with excellent precision and nanoscale spatial resolution. Moreover, by developing Landau-level interferometry, we show shear-strain-induced pseudomagnetic fields and map their spatial dependence. In contrast to artificially induced large strain, which leads to pseudomagnetic fields of hundreds of tesla5–7, we detect naturally occurring pseudomagnetic fields as low as 1 mT corresponding to graphene twisting by 1 millidegree, two orders of magnitude lower than the typical angle disorder in twisted bilayer graphene8–11. This ability to resolve the local band structure and strain at the nanoscale level enables the characterization and use of tunable band engineering in practical van der Waals devices.

Unified AC/DC hybrid admittance modelling and oscillation stability analysis for interlinking voltage source converter system

AbstractThe voltage source converter (VSC) interlinking AC and DC power networks is a core equipment in AC/DC hybrid power systems. To analyze the stability of this system based on the impedance method, it is necessary to establish the hybrid AC/DC admittance model of interlinking VSC. This paper presents a unified and systematic AC/DC hybrid admittance modelling framework which is widely applicable to different control methods of interlinking VSCs. The hybrid admittance models for interlinking VSCs under PQ control, VdcIq control, and Vf control are explicitly formulated, with their elements individually reflecting the dynamics of the AC side, DC side, and the interaction between them. Subsequently, the impedance network model of interlinking VSC systems is formulated based on the hybrid admittance, and furthermore the frequency‐domain modal analysis is performed to analyze the system oscillation stability. Finally, frequency scanning and time‐domain simulation results in MATLAB/Simulink are provided to validate the effectiveness of the modelling and oscillation stability analysis method.

Analysis of medium-frequency oscillation based on bifurcation theory and joint modelling of SVG and direct-drive wind turbine

With the expansion of wind power clusters in power system, medium and high frequency oscillations in wind farm area are preliminarily emerging. At present, linear analysis such as impedance analysis are mainly used to analyse the grid-connected oscillation of renewable energy generation. However, the explanation of the oscillation mechanism is not intuitive and does not take into account the nonlinearity of converter. Considering the influence of external loop control of SVG and direct-drive wind turbine on the medium-frequency characteristics of the parallel system, a reduced-order nonlinear model under voltage time scale is established. The conjoint analysis of Jacobi matrix, bifurcation diagram and phase space trajectory are applied to study the influence rule of machine-side output power and short-circuit ratio on the oscillation behaviour of the parallel system. In addition, the oscillation evolution process is analysed from the dynamic standpoint. It is found that the system operates on the limit-loop state when the medium-frequency oscillation occurs, which reveals the mapping relationship between the oscillation amplitude and the limit-loop trajectory. The experimental results ultimately validate the theoretical analysis conducted on the StarSim-HIL (hardware-in-the-loop) experiment platform.

Geometric Blow-Up for Folded Limit Cycle Manifolds in Three Time-Scale Systems

Geometric singular perturbation theory provides a powerful mathematical framework for the analysis of ‘stationary’ multiple time-scale systems which possess a critical manifold, i.e. a smooth manifold of steady states for the limiting fast subsystem, particularly when combined with a method of desingularisation known as blow-up. The theory for ‘oscillatory’ multiple time-scale systems which possess a limit cycle manifold instead of (or in addition to) a critical manifold is less developed, particularly in the non-normally hyperbolic regime. We use the blow-up method to analyse the global oscillatory transition near a regular folded limit cycle manifold in a class of three time-scale ‘semi-oscillatory’ systems with two small parameters. The systems considered behave like oscillatory systems as the smallest perturbation parameter tends to zero, and stationary systems as both perturbation parameters tend to zero. The additional time-scale structure is crucial for the applicability of the blow-up method, which cannot be applied directly to the two time-scale oscillatory counterpart of the problem. Our methods allow us to describe the asymptotics and strong contractivity of all solutions which traverse a neighbourhood of the global singularity. Our main results cover a range of different cases with respect to the relative time-scale of the angular dynamics and the parameter drift. We demonstrate the applicability of our results for systems with periodic forcing in the slow equation, in particular for a class of Liénard equations. Finally, we consider a toy model used to study tipping phenomena in climate systems with periodic forcing in the fast equation, which violates the conditions of our main results, in order to demonstrate the applicability of classical (two time-scale) theory for problems of this kind.

Robust limit cycle control for finite-time generation of sustained oscillations in nonlinear systems with mixed dead-zone and saturation

This paper suggests a novel limit cycle control technique, based on the finite-time stability scheme, for producing sustained oscillations in a class of nonlinear complex systems. The considered systems are constrained to input dead-zone and saturation simultaneously and suffer from non-vanishing perturbations due to model uncertainties, and external disturbances. For this purpose, an innovative sliding manifold is proposed based on the topology of the wanted limit cycle which provides the conditions for developing the finite time stability concept for limit sets. With the aid of the finite-time command filter and the cooperation of the sliding mode control (SMC) method with the backstepping technique, a robust controller is constructed which guarantees the finite-time convergence of phase trajectories of the closed-loop system toward the wanted limit cycle. This leads to the creation of sustained oscillations, with the desirable amplitude and frequency, in the system's output. The stability analysis is proved based on the Lyapunov approach through the set stability concept. Finally, the effectiveness of the suggested methodology is confirmed by a variety of simulations.

Performance Evaluation of Optimally Placed SVC for Dynamic Stability of the Power System

Given the complexity of power systems, particularly in the deregulated power industry found in Nigeria, a consistent, safe, controllable, and high-quality power supply is required. The loss of the system's overall damping torque, which reduces the system's susceptibility to fluctuations and problems with dynamic stability, is one of the key downsides of network expansion. Flexible AC transmission systems (FACTS) controllers have been used to overcome problems with power system stability control. In order to improve dynamic stability, this study investigates how the generator's rotor angle, speed, voltage magnitude profile, and real power affect how well SVC operates under the effect of a three-phase fault. With a fault introduced on Bus 33 (Geregu Substation) and SVC placed optimally on Bus 21 (Jos Transmission Station) using voltage stability sensitivity factor (VSSF) after the simulation of continuation power flow (CPF), the 48-bus power system network in Nigeria was modeled using commercial PSAT software in a MATLAB environment. The power system's oscillation was significantly reduced, and the voltage profile was enhanced for power system dynamic stability, per simulation results with and without SVC.

Direct current power system stabilizers for HVDC grids: Current status

AbstractA power system stabilizer (PSS) is a control system integrated into the control structure of specific generation units within AC grids. It monitors current, voltage, and machine shaft speed. Analysing these variables, the PSS generates appropriate control signals to the voltage regulator unit, aiming to damp system oscillations. With the advancement of high‐voltage direct current (HVDC) overlaid high‐voltage alternative current (HVAC) grids, it is anticipated that direct current power system stabilizers (DC‐PSS) will be developed to perform a similar role as their AC counterparts. DC‐PSS will be responsible for monitoring and controlling DC voltage levels, ensuring stable operations. This paper focuses on DC‐PSS in HVDC grids, designed to ensure stable operation and mitigate voltage fluctuations. Unlike conventional AC power systems, HVDC includes only DC voltage and power. The input signal for DC‐PSS is the variations in DC voltage, and the output signal is proportional to the power changes at the specific bus where the DC‐PSS is installed, aiming to minimize DC voltage oscillations. These characteristics pose significant challenges in DC‐PSS. The paper addresses the challenges and highlights issues such as inertia and low‐frequency oscillations associated with DC‐PSS. Various control methods are presented and a comparison is made among these methods.

Establishing an integrated, four-dimensional quality assessment system for traditional Chinese medicine: A case study of Shuanghuanglian oral liquid

The quality of traditional Chinese medicine (TCM) is the premise to ensure its safety and effectiveness in clinical application. In this study, a complete quality control system for four-dimensional fingerprinting of TCM was innovatively constructed based on multiple detection techniques, and the quality of Shuanghuanglian oral liquid (SHL) was evaluated. Electrochemical fingerprinting (ECFP) as an emerging method without pretreatment provides rich and quantifiable information for SHL samples. The first quantitative ECFP of SHL was developed by the B-Z oscillation system. Eight characteristic parameters were analyzed and a good linear relationship was found between the oscillation lifetime and sample volume, by which the calculated values of the added sample volume (VL) showed different fluctuations between samples. What is more, high-performance liquid chromatography five-wavelength fusion fingerprint (HPLC-FWFP), GC fingerprint (GC-FP), and UV quantum fingerprint (UV-QFP) was established. Meanwhile, the purity of the peaks of the HPLC-FWFP was verified by the dual-wavelength absorption coefficient ratio spectrum (DWAR). Equal weighted ratio quantitative fingerprinting method (EWRQFM) was successfully proposed to extract all potential features for the overall quality assessment of the samples. Finally, a comprehensive evaluation strategy was proposed, namely the variation coefficient weighting algorithm (VCWA). The results of qualitative and quantitative evaluation of HPLC-FWFP, GC-FP, electrochemical quantum fingerprints (EC-QFP), and UV-QFP were integrated by this method. The established evaluation system is also a suitable strategy to control the quality of other TCM preparations.

Method of creation a digital twin of a vibration protection process

Various approaches to building digital twins are considered. The data-based approach has a big disadvantage due to need of the huge amount of information. The system-based ap-proach can not be used in some cases due to the lack of a mathematically justified method. One of such cases is a ball vibration absorber but they can be really useful for the vibration protection of high-rise flexible objects. The purpose of the research is to develop an algorithmic method of creating digital twins of the vibration protection process, which will provide the possibility of determining the optimal control parameters of the ball vibration absorber. The paper examines small steady oscillations of the dynamic system "supporting body - ball vibration absorber". Under the condition of small forced oscillations, the equation of the amplitude-frequency characteristic of the linear anti-vibration system was obtained. In view of the use in construction, the input and output parameters of the method of building a digital twin of a flexible structure were described and analyzed, as well as the methods of obtaining them. As a result of the evaluation of the speed of the method, a modification of the search way for the optimal parameters of the digital twin was proposed. The comparative analysis showed the high efficiency of the proposed anti-vibration sys-tem with optimally adjusted parameters of the digital twin. The proposed method allows to reduce the maximum value of the amplitude by approximately four times. Modifications of the method made it possible to speed it up by an average of three times, reduce the load on the processor and handle cases when finding the optimal parameters of a digital twin is a rather difficult analytical problem. The input and output parameters of the method and ways of obtaining them were de-scribed and analyzed. A comparative numerical analysis showed the high efficiency of the functioning of such a vibration protection system with optimally adjusted parameters of the ball vibration absorber.

Type series of resonant vibration equipment for concrete mixtures compaction and its main parameters calculation method

Introduction. Increasing the energy efficiency of vibration technology poses a number of challenges for its developers. A promising direction for reducing energy costs for driving vibration machines is the use of the resonance phenomenon. Due to the dynamic properties of the oscillatory system, it is possible to significantly reduce the power consumption of resonant vibration equipment, and in some cases, improve the quality of the products. The purpose of this article is to develop a standard range of resonant vibration equipment for compacting concrete mixtures and a methodology for calculating its main parameters.The object of research is the oscillatory system of a vibrating machine, consisting of two masses connected by the elastic and dissipative elements. In addition, the first mass is connected to a fixed base through elastic and dissipative elements.Materials and methods. The basic principles of theoretical mechanics, mathematical modelling and statistical processing of results were used in the research.Results. According to the research results, it was established that with an increase in the mass ratio of the oscillatory system, the dynamic coefficient decreases, and the width of the resonant zone increases. The regression equations are given. It has been established that with increasing rigidity of the working body, the dynamic coefficient decreases, and the horizontal section on the frequency response, the width of which does not change significantly, shifts to the region of higher frequencies. With an increase in the damping coefficient, the dynamic coefficient decreases, and the width of the resonant zone and the frequency range practically do not change. A wide range of nomenclature and masses of precast reinforced concrete justifies the development of a standard-size range of resonant vibration equipment. A standard range of light (up to 2 tons), medium (2-6 tons) and heavy (6-10 tons) types has been developed. Based on the analysis and generalization of research results, a method for calculating resonant vibration equipment for compacting concrete mixtures has been developed, which makes possible to increase its energy efficiency.

Analytical modeling and numerical analysis of thermoelastic damping in ultrathin elastic films due to surface effects

Analytical techniques used for estimating thermoelastic damping by incorporating both mechanical and thermal interactions between surfaces and the rest of the bulk are intricate and challenging due to the limited understanding of the damping mechanisms in extra-thin films subjected to forced vibrations. This paper proposes a modified model to analytically calculate the thermoelastic damping of ultrathin elastic films due to surface effects and analyzes the thermoelastic damping variation with different factors through numerical experiments on two materials. The model considers surface stresses derived from the elastic surface theory using Kirchhoff's kinetic hypothesis and determines thermoelastic damping by considering thermal dissipation and elastic potential energy. The results show that surface effects significantly influence the thermoelastic damping of the film, and the specific behavior of a thin film’s thermoelastic damping with respect to film thickness is impacted by various factors, including material property, the variation range of film thickness, and the forced vibration frequency. This study provides insights into the thermoelastic damping behavior of thin films and has important implications for the development of nanoscale oscillators in MEMS or NEMS systems.

Newton’s Second Law on Positive Real Line R_+

In this work, a classical particle that moves on will be investigated by using the affine commutator relation which corresponds to the Poisson bracket in classical mechanics where the equation of motions and the Newton’s second law will be modified. Two example of physical systems will be studied further using the modified Newton’s second law namely free particle and harmonic oscillator. The result concludes that for a free particle, the force on is no longer zero and a linear force due positive real line and fixed momentum. While, classical dynamics on for simple harmonic oscillator system is a qubic force.

Topologically originated optical analog of electromagnetically induced reflectance in Dirac semi-metal based photonic structure

The optical analog of the electromagnetically induced reflectance (EIR) effect was theoretically studied in an active topological photonic structure comprising Dirac semi-metal and topological photonic crystal. The destructive interference between the optical Tamm state and topological edge state results in an induced reflection. It was known that the EIR-like effect occurs in a system having a radiative state and a metastable state. Topological protection is used here to achieve a metastable state, so an effective design of the EIR-like effect was possible. The observed EIR-like effect was modeled as a coupled oscillator system. The use of bulk Dirac semi-metal makes this an active photonic system at terahertz frequencies where the Fermi energy can act as a tunable and controlling parameter through which the induced transparency can be varied.

Nonmonotonic enhancement of diversity-induced resonance in systems of mobile oscillators.

Diversity is omnipresent in natural and synthetic extended systems, the phenomenon of diversity-induced resonance (DIR), wherein a moderate degree of the diversity can provoke an optimal collective response, provides researchers a brand-new strategy to amplify and utilize the weak signal. As yet the relevant advances focus mostly on the ideal situations where the interactions among elements are uncorrelated with the physical proximity of agents. Such a consideration overlooks interactions mediated by the motion of agents in space. Here, we investigate the signal response of an ensemble of spatial mobile heterogeneous bistable oscillators with two canonical interacting modes: dynamic and preset. The oscillators are considered as mass points and perform random walks in a two-dimensional square plane. Under the dynamic scheme, the oscillators can only interact with other oscillators within a fixed vision radius. For the preset circumstance, the interaction among oscillators occurs only when all of them are in a predefined region at the same moment. We find that the DIR can be obtained in both situations. Additionally, the strength of resonance nonmonotonically rises with respect to the increase of moving speed, and the optimal resonance is acquired by an intermediate magnitude of speed. Finally, we propose reduced equations to guarantee the occurrence of such mobility-optimized DIR on the basis of the fast switching approximation theory and also examine the robustness of such phenomenon through the excitable FitzHugh-Nagumo model and a different spatial motion mechanism. Our results reveal for the first time that the DIR can be optimized by the spatial mobility and thus has promising potential application in the communication of mobile agents.

Coupled drillstring dynamics modeling using 3D field-consistent corotational beam elements

Drilling is essential to extract subsurface hydrocarbons and geothermal energy, or store waste fluids/gases underground. Drilling efficiency directly affects the economics of well construction, and is to a large extent determined by the non-productive time (NPT) associated with downhole tool failure, bit wear/damage, unexpected drillstring vibrations, and insufficient surface-to-bottom energy transfer. Various models have been developed since the 1960s to understand and mitigate undesired drilling system oscillations to ensure efficient drilling operations and help optimize the well design. Significant recent advancements in drilling engineering technology, sensor development, and data science make it possible to develop and apply a faster and more comprehensive drilling system dynamic model that can be used for real-time drilling optimization and automation.In this study, a novel control-oriented physic-based drillstring dynamic modeling framework is developed using 3D field-consistent corotational beam elements with an updated Lagrangian formulation. The structure and element kinematics are firstly derived in global and local coordinate systems respectively, based on which the system dynamics are formulated by integrating the element stiffness, damping, and mass matrices. Different drilling boundary conditions and forms of external loads, including bit-rock interaction, wellbore-drillstring contact, stabilizers, bottom hole assembly (BHA) eccentricities, and gravity/buoyancy are defined within the modeling framework. The numerical accuracy of the model with linear/quintic beam elements is discussed and verified in four different static/dynamic loading cases, which are typically used for beam analysis. Simulations of different drilling scenarios, including dynamics during the pipe connection process, bit on/off bottom process, and pipe rocking during slide drilling, are conducted for an actual L-shape well configuration with comparison to field data. The simulated drillstring tri-axial vibrations exhibit diverse characteristics and patterns in terms of oscillation amplitudes, frequencies, and modes at varying depths, generating valuable understanding of potential drilling dysfunctions and insights for real-time drilling optimization and automation.

Multi-dimensional opinion chaos synchronization based on multi-layer complex networks

Abstract In complex networks, the interactions of opinions are significantly affected by network structure. Moreover, multi-layer networks, which contain multiple subsystems and different types of interactions, are considered to have a stronger ability to simulate various real-world systems than traditional single-layer complex networks. Based on this motivation, this article attempts to show how to achieve complete synchronization of multi-dimensional opinions in a multi-layer network topology where the opinions of nodes have Rössler chaotic dynamics. A first step in investigating the synchronization of multi-layer complex networks is to propose a multi-dimensional opinion evolution model. In this article, the multi-layer complex network model combining the Rössler oscillation system is built, which provides us a tool for insight into the nodes complexity in multi-layer networks. Furthermore, a general criterion for globally exponentially asymptotic synchronization of multi-layer complex networks is provided using multiple Lyapunov stability theories. We illustrate the reliability of the model and the correctness of the criterion by Runge-Kutta (RK4) simulation. These findings shed new light on some interesting phenomena in society and help decision-makers predict the prevalence of hot topics and public opinions.

Network percolation provides early warnings of abrupt changes in coupled oscillatory systems: An explanatory analysis.

Functional networks are powerful tools to study statistical interdependency structures in spatially extended or multivariable systems. They have been used to get insights into the dynamics of complex systems in various areas of science. In particular, percolation properties of correlation networks have been employed to identify early warning signals of critical transitions. In this work, we further investigate the corresponding potential of percolation measures for the anticipation of different types of sudden shifts in the state of coupled irregularly oscillating systems. As a paradigmatic model system, we study the dynamics of a ring of diffusively coupled noisy FitzHugh-Nagumo oscillators and show that, when the oscillators are nearly completely synchronized, the percolation-based precursors successfully provide very early warnings of the rapid switches between the two states of the system. We clarify the mechanisms behind the percolation transition by separating global trends given by the mean-field behavior from the synchronization of individual stochastic fluctuations. We then apply the same methodology to real-world data of sea surface temperature anomalies during different phases of the El Niño-Southern Oscillation. This leads to a better understanding of the factors that make percolation precursors effective as early warning indicators of incipient El Niño and La Niña events.

Skilful predictions of the Summer North Atlantic Oscillation

The Summer North Atlantic Oscillation is the primary mode of atmospheric variability in the North Atlantic region and has a significant influence on regional European, North American and Asian summer climate. However, current dynamical seasonal prediction systems show no significant Summer North Atlantic Oscillation prediction skill, leaving society ill-prepared for extreme summers. Here we show an unexpected role for the stratosphere in driving the Summer North Atlantic Oscillation in both observations and climate prediction systems. The anomalous strength of the lower stratosphere polar vortex in late spring is found to propagate downwards and influence the Summer North Atlantic Oscillation. Windows of opportunity are identified for useful levels of Summer North Atlantic Oscillation prediction skill, both in the 50% of years when the late spring polar vortex is anomalously strong/weak and possibly earlier if a sudden stratospheric warming event occurs in late winter. However, we show that model dynamical signals are spuriously weak, requiring large ensembles to obtain robust signals and we identify a summer ‘signal-to-noise paradox’ as found in winter atmospheric circulation Our results open possibilities for a range of new summer climate services, including for agriculture, water management and health sectors.

Time-delay-induced spiral chimeras on a spherical surface of globally coupled oscillators.

We consider globally coupled networks of identical oscillators, located on the surface of a sphere with interaction time delays, and show that the distance-dependent time delays play a key role for the spiral chimeras to occur as a generic state in different systems of coupled oscillators. For the phase oscillator system, we analyze the existence and stability of stationary solutions along the Ott-Antonsen invariant manifold to find the bifurcation structure of the spiral chimera state. We demonstrate via an extensive numerical experiment that the time-delay-induced spiral chimeras are also present for coupled networks of the Stuart-Landau and Van der Pol oscillators in the same parameter regime as that of phase oscillators, with a series of evenly spaced band-type regions. It is found that the spiral chimera state occurs as a consequence of a resonant-type interplay between the intrinsic period of an individual oscillator and the interaction time delay as a topological structure property.

Cryogenic distribution system design for cryomodules and cavities test in HIAF project

ABSTRACT High-intensity heavy-ion accelerator facility (HIAF) is an accelerator-driven high-current heavy ion facility, currently under construction in Guangdong, China. The proton linear accelerator of HIAF linac has 96 superconducting cavities and 17 cryomodules cooled by 2 K saturated superfluid helium. Cryogenic tests should be carried out in a test cryogenic system prior to the online operation of each cavity and cryomodule. The cryogenic distribution system (CDS) is the main part of the test cryogenic system, which is used for transporting cryogenic fluid between helium refrigerator and test terminals. A specific CDS is developed due to the long cryogenic test time. Each test terminal can be independently cooled and heated up, saving quite a bit of time without impacting the others. This article provides comprehensive explanations for the process design, process analysis, and special structure design which enhance the system’s maintainability. Furthermore, particular technical designs, such as measuring system, helium guard, and elimination of thermoacoustic oscillations, are described in detail.