Periodic Forcing Research Articles

Rural Non-farm Sector Employment in the North-Eastern Region of India: Determinants and Implications for Well-being

The article analyses the causal relationship between rural non-farm employment (RNFE) and the well-being of the people in India’s North-Eastern Region (NER). When India experienced a decline in poverty, specifically during the post-liberalisation period, the reduction of poverty was lower in the NER, with a wide variation at the state level in the region than in the rest of the country. However, the structural shift in occupations and livelihoods in NER has been sharper than in other parts of the country. In this context, this article aims to contribute to an understanding of the issue of occupational diversification in NER. Based on data from three rounds of the National Sample Survey (NSS) Employment and Unemployment Survey and two rounds of the Periodic Labour Force Survey (PLFS), that is, the PLFS of 2017–2018 and 2019–2020. The 2SLS regression analysis highlights the higher inclination of young persons with technical education, people belonging to large families, and females in rural NER towards seeking livelihoods in the non-farm sector. JEL Codes: P46, M51, I21, E24

Reconstruction of the Fourier expansion of a periodic force acting on an oscillator

Reconstruction of the Fourier expansion of a periodic force acting on an oscillator

Suppression and frequency control of repetitive spiking in the FitzHugh-Nagumo model.

The FitzHugh-Nagumo equationis a simple model equationthat exhibits spiking. The output signal of a neuron is represented in the spiking frequency or firing rate. We consider a few control methods for spiking from the viewpoint of nonlinear dynamics. The repetitive spiking can be suppressed in the FitzHugh-Nagumo model by the periodic sinusoidal force with high frequency. We study the transition to the suppressed state numerically and perform a linear stability analysis to understand the suppression of the spiking. Next, we study coupled FitzHugh-Nagumo equations. We find that the periodic forcing makes the system chaotic, and the desynchronization induced by chaos weakens the total output of spiking in a certain parameter range. Finally, we propose a method of feedback control for the spiking frequency. We can get the desired spiking and bursting frequency using this feedback control. The feedback control method is analyzed using a mapping for the input.

Dust ion acoustic waves with Cairns–Tsallis electrons in the framework of damped Zakharov–Kuznetsov equation in the presence of external periodic force

Dust ion acoustic waves with Cairns–Tsallis electrons in the framework of damped Zakharov–Kuznetsov equation in the presence of external periodic force

Modelling the effect of the tidal cycle on the high phytoplankton biomass area of Cape Trafalgar (SW Iberian Peninsula)

Physical–biological interactions in the ocean are known to be crucial for understanding ecosystem processes. This is particularly relevant in the highly dynamic coastal regions, where the biogeochemical processes associated with higher-frequency perturbations such as tidal waves play a key role in primary production. In this study, we examine the influence of the tide-topography interaction on the high productivity area of Cape Trafalgar (NW limit of the Strait of Gibraltar, Iberian Peninsula) using a high-resolution ocean circulation model coupled to an ecosystem model. The obtained results highlight the relevance of the tidal cycle explaining the high phytoplankton biomass that characterises this region through an active and periodic forcing, resulting in a pulsating upwelling system. Our model shows that the interaction of the westward zonal component of the tidal current (uvel) with the submarine ridge (i.e., Barbate High) that characterises this region, which is perpendicular to the coast, results in the pumping of deep, cold, salty, and nutrient-rich waters to the well-illuminated subsurface waters, fuelling phytoplankton growth. At the same time, the interaction of the westward tidal current with the ridge leads to the development of a cyclonic eddy, which enables the redistribution of the upwelled waters over and to the east of Barbate High. The fortnightly tidal period has been identified as the most influential because (an effective) tidal-pumping process only takes place when the westward uvel is ∼ 0.42 m s−1, a condition attained between ∼ 3 days before and after the moment of maximum tidal flow during spring tides. Simultaneously, the energy and the associated horizontal and vertical mixing of the cyclonic gyre also vary with the tidal cycle, being stronger during spring tides. Both tidally driven processes, i.e., the cyclical upslope advection of deep nutrient-rich water and the influence of the cyclonic gyre, are the main mechanisms that lead to the development of a persistent phytoplankton-rich tongue over Barbate High. Consequently, Cape Trafalgar acts as a source of nutrient- and phytoplankton-rich waters to the surrounding waters.

Magnetoacoustic Heating of Plasma Caused by Periodic Magnetosound Perturbations with Discontinuities in a Quasi-Isentropic Magnetic Gas

The magnetoacoustic heating of a plasma by harmonic or periodic saw-tooth perturbations at a transducer is theoretically studied. The planar fast and slow magnetosound waves are considered. The wave vector may form an arbitrary angle θ with the equilibrium straight magnetic strength. In view of variable θ and plasma-β, the description of magnetosound perturbations and relative magnetosound heating is fairly difficult. The scenario of heating depends not only on plasma-β and θ, but also on a balance between nonlinear attenuation at the shock front and inflow of energy into a system. Under some conditions, the average over the magnetosound period force of heating may tend to a positive or negative limit, or may tend to zero, or may remain constant when the distance from a transducer tends to infinity. Dynamics of temperature specifying heating differs in thermally stable and unstable cases and occurs unusually in the isentropically unstable flows.

Numerical explorations of the vortex-induced vibration of a streamlined box girder with water-filled barriers

The present study aims to investigate the charactefristics of vortex-induced vibrations (VIVs) of a streamlined box girder equipped with water-filled barriers (WFBs) through two-dimensional computational fluid dynamics (CFD) simulations. Initially, the VIV behavior of the bridge section is examined by considering various positions of WFBs and angles of attack (α), focusing on parameters involving vibration amplitude, surface pressure distribution, and flow field. Subsequently, in order to reveal the underlying VIV mechanism, the bridge section with WFBs commonly positioned was chosen to evaluate the contribution or inhibition of wind loads on specific regions around the bridge's surface to VIV, based on the pressure distribution and energy input process characteristics. The numerical results demonstrate that if the WFBs are positioned closer to the railing on the windward side of the bridge, as α shifts from negative to positive, the separated vortex on the upper surface of the bridge section tends to be larger. Additionally, the shedding of vortices at the tail of the deck becomes more pronounced, creating a greater periodic force on the bridge section and making it more vulnerable to VIV. The mean and standard deviations of pressure coefficients, as well as the predominant frequencies of the distributed pressures, are closely correlated with various stages of the VIV development process. The occurrence of VIV is actively triggered by the wind load acting on the upper surface upstream and lower surface downstream, while conversely, the wind load acting on the downstream of the upper surface and the upstream of the lower surface tends to inhibit the VIV. Moreover, it is worth noting that the growth rate of energy consumption on the downstream of upper surface is more significant than that of energy consumption in other regions, which makes a main effect on limiting the amplitude of VIV.

Disparate energy sources for slow and fast Dansgaard–Oeschger cycles

Abstract. During the Late Pleistocene, Dansgaard–Oeschger (DO) cycles triggered warming events that were as abrupt as the present-day human-induced warming. However, in the absence of a periodic forcing operating on millennial timescales, the main energy sources of DO cycles remain debated. Here, we identify the energy sources of DO cycles by applying a bispectral analysis to the North Greenland Ice Core Project (NGRIP) oxygen isotope (δ18Oice) record; a 123 kyr long proxy record of air temperatures (Tair) over Greenland. For both modes of DO cyclicity – slow and fast – we detect disparate energy sources. Slow DO cycles, marked by multi-millennial periodicities in the 12.5 to 2.5 kyr bandwidth, receive energy from astronomical periodicities. Fast DO cycles, characterized by millennial periodicities in the 1.5 ± 0.5 kyr range, receive energy from centennial periodicities. We propose cryospheric and oceanic mechanisms that facilitate the transfer of energy from known sources to slow and fast DO cycles, respectively. Our findings stress the importance of understanding energy-transfer mechanisms across a broad range of timescales to explain the origins of climate cycles without primary periodic energy sources.

Effects of Diagonal Friction Dampers on Behavior of a Building

In this study, the effect of the friction damper location on the earthquake behavior of a building was investigated. Diagonal braced friction dampers were placed on different floors, and the changes in building behavior were examined. For this purpose, a scaled experimental building model with five floors, with a single span in the x and y directions, was used. Numerical model validation was carried out by taking into account the experimental and numerical period values obtained via the effect of free vibration. The period, peak displacement, and maximum shear force of the friction dampers, arranged in various configurations, were compared using the numerical model in conjunction with three different earthquake acceleration records. According to the investigations, the damper performance of the design changes depending on the earthquake acceleration that is affecting the building. Friction dampers located on the lower floors are more effective at reducing period, peak displacement, and floor shear forces than those located on the upper floors.

Forward and Adjoint Modeling of Sensitivities to Periodic Forcings in Groundwater Flow and Transport

Forward and Adjoint Modeling of Sensitivities to Periodic Forcings in Groundwater Flow and Transport

Failure analysis of the pure carbon strip affected by dynamic contact force during current-carrying sliding

The pure carbon strip is widely used in high-speed Electro Mechanical Units (EMUs) transit. Dynamic contact between the pantograph and the catenary produces internal cracks in the pure carbon strip, which results in the break of the pantograph and interruption of power transmission. The tribological properties and failure mechanism of the pure carbon strip is studied in this paper. The current-carrying tribology experiments were carried out on a flexible loading test rig. It is found that the dynamic contact in pantograph/catenary system produces regular influence on arc discharge and current transmission. The cracks and arc erosion are the most important failure mechanisms subjected to the periodic vertical contact force. The carbon fibers in the strip became orderly arranged honeycomb-structures after oxidation and sublimation. These honeycomb-structures distributed nearby the pores and induced the initiation and propagation of cracks. Therefore, preparing high-strength carbon fibers and eliminating the combination gap between the carbon fibers and the carbon matrix are recommended to prevent the failure of pure carbon strip. Results in this paper are expected to provide data support for the failure analysis and manufacturing technology to the pure carbon strip, as well as providing theoretical supports to the locomotives in service.

Reconstruction of the Fourier expansion of a periodic force acting on an oscillator

Reconstruction of the Fourier expansion of a periodic force acting on an oscillator

Design and analytical evaluation of an impact-based four-point bending configuration for piezoelectric energy harvesting

Aiming toward improved energy conversion in piezoelectric energy harvesters, this study investigates four-point bending (FPB) energy harvesters (FPB-EH) to explore their prominent features and characteristics. The FPB configuration innovatively extends energy harvesting capabilities relative to conventional cantilever beams. The FPB-EH comprises a composite piezoelectric beam that rests on two supports of a fixed clamp, excited by contact force applied at two contact lines on a moving clamp. A comprehensive analytical electromechanical model for the vibrating energy harvester is presented with unique modeling features, including multi-beam sections and multi-mode-shape functions. Solutions of the analytical model are presented for a wide range of contact force types, including steady-state solutions for harmonic forces, impact forces, periodic and non-periodic arbitrary forces. This comprehensive model progresses the state-of-the-art piezoelectric modeling knowledge and is readily applicable to various energy harvesting configurations. The model is validated against experimental results and finite element analysis. Next, a parametric study was performed to evaluate the effects of various FPB characteristics, including the fixed and moving clamp spans, the waveform, and the period-time of contact force. The results indicate that the FPB configuration can enhance energy conversion efficiency and normalized output energy by factors of over 3 and 6, respectively. Finally, guidance is given for selecting between cantilever and four-point bending configurations.

Traveling wave structures and analysis of bifurcation and chaos theory for Biswas–Milovic Model in conjunction with Kudryshov’s law of refractive index

The present study investigates the generalized Biswas–Milovic model using Kudryshov’s law of refractive index by employing the G′/(bG′+G+a)-Expansion method. This technique facilitates the extraction of singular exponential, trigonometric and kink soliton solutions for the model under examination. The outcomes are subsequently presented as 2D, 3D, and contour plots. Additionally, the model is transformed into a planner dynamical system, and the bifurcation theory is utilized to explore all potential parameter dependencies of the governing model. The chaotic behavior of dynamical systems is also studied by adding an external periodic force. The phase portraits of the obtained findings are also displayed. The results demonstrate the rich and sophisticated behavior of dynamical systems and emphasized the significance of exact solutions for determining their behavior.

Deep learning powered long-term warning systems for reservoir landslides

The reservoir landslides are characterized by repeated phases of acceleration and isokinetic deformation under long-term periodic external forces. The state-of-the-art research lacks reliable prediction methods and judgment of their evolution stages. This work promotes the application of the deep learning algorithm and landslide evolution model in long-term warning systems. The test site is the Sifangbei landslide in the Three Gorges reservoir area of China. The main innovative features are: (i) the displacement of the landslide is considered as the prediction target, and the optimal model (i.e., conditioning factors and hyper-parameters combination) driven by the deep learning framework is used for spatial prediction; (ii) different warning methods (from both literature and current practice) are compared to single out the one that can best describe the evolution stage of the reservoir landslide; and (iii) deep learning model and adaptive evolution model are combined to analyze the temporal-spatial kinematic characteristics and evolution trend of the landslide under extreme scenarios related to rainfall and reservoir water levels. The results show that the predicted displacements of the lower and central part of the landslide are respectively controlled by reservoir water level and rainfall; the five-stage evolution model can capture the long-term evolution trend of the Sifangbei landslide; under extreme scenarios, landslide deformation exhibits step-like characteristics and is more likely to start from the middle of the lower portion of the unstable area. These models represent the up-to-date steps of a long-term research plan. The gathered knowledge can be used to analyze the spatial evolution characteristics of landslides and promote the setup of long-term warning systems. Furthermore, the results show that combining the proposed deep learning and evolution methods provides forecast information that could help adjusting short-term warning strategies in such a complex risk area as the Three Gorges Reservoir.

A Novel Data-Driven Feature Extraction Strategy and Its Application in Looseness Detection of Rotor-Bearing System

During the service of rotating machinery, the pedestal bolts are prone to looseness due to the vibration environment, which affects the performance of rotating machinery and generate potential safety hazard. To monitor the occurrence and deterioration of the pedestal looseness in time, this paper proposes a data-driven diagnosis strategy for the rotor-bearing system. Firstly, the finite element model of a rotor-bearing system is established, which considers the piecewise nonlinear force caused by pedestal looseness. Taking the vibration response as output and periodic unbalanced force as input, the system’s NARX (Nonlinear Auto-Regressive with exogenous inputs) model is identified. Then GALEs (Generalized Associated Linear Equations) are used to evaluate NOFRFs (Nonlinear Output Frequency Response Functions) of the NARX model. Based on the first three-order NOFRFs, the analytical expression of the second-order optimal weighted contribution rate is derived and used as a new health indicator. The simulation results show that compared with the conventional NOFRFs-based health indicator, the new indicator is more sensitive to weak looseness. Finally, a rotor-bearing test rig was built, and the pedestal looseness was performed. The experiment results show that as the degree of looseness increases, the new indicator SRm shows a monotonous upward trend, increasing from 0.48 in no looseness to 0.90 in severe looseness, a rise of 89.7%. However, the traditional indicator Fe2 has no monotonicity, which further verifies the sensitivity of the first three-order NOFRFs-based second-order optimal weighted contribution rate and the effectiveness of the proposed data-driven feature extraction strategy.

Periodic Traction Force Fluctuations Suppression Strategy of Maglev Train Based on Flux Linkage Observation and Harmonic Current Injection

To suppress the periodic traction force fluctuations of maglev train caused by the current harmonics and the excitation flux linkage harmonics of long stator linear synchronous motor (LSLSM), a strategy based on flux linkage observation and harmonic current injection is proposed in this paper. First, the mathematical models of the LSLSM in single feed (SF) and double feed (DF) modes are established and simplified. Then, considering the characteristics of variable frequency and phase lag of the LSLSM, an improved discrete resonant controller (RSC) with pole correction and whole frequency domain phase compensation is designed to suppress the traction force fluctuation caused by current harmonics. To suppress the traction force fluctuations caused by the flux linkage harmonics, a sliding mode flux linkage observer (SMFO) is designed and combined with an adaptive notch filter (ANF) to estimate specific flux linkage harmonics in real-time. By analyzing the flux linkage component in the traction force equation, appropriate harmonic currents are injected and tracked by the RSC. Hardware-in-the-loop (HIL) experiments verify the effectiveness of the proposed strategy.

Study on the Vibration Displacement of Hydraulic Pipeline System Excited by Fluid Impact

Hydraulic impact had an effect on pipeline vibration displacement, so it was important to study the external lateral impact periodic force on fluid-structure coupling vibration displacement of hydraulic pipeline. Based on Bernoulli beam model, the fluid-structure coupling vibration equation of flexible pipeline was established by analyzing the stress of flexible pipeline under the action of internal flow. The hydraulic system pipeline was simulated whether the pipeline was subject to periodic impact force. The displacement-time curves in x, y and z directions of vibration monitoring points of hydraulic flexible pipelines were obtained, and the maximum displacement-time curves of fluid-structure coupling vibration under different pressure hydraulic impact were obtained. The simulation results were shown that the vibration of monitoring points in x, y and z directions of hydraulic impact pressure increased and the total displacement of the pipeline middle section of the hydraulic system decrease continuously, and then they tend to stabilize after a period of attenuation. The maximum displacement value of the X-direction monitoring point in the middle part of the hydraulic system pipeline was 9.5e −5 m, and the displacement vibration was stable at 0.135s. The maximum y-displacement was 3.1e −4m, and the vibration was stable at 0.2 s. The maximum z displacement was 1.32e-4 m, and the vibration was stable at 0.36 s. The total displacement was 3.35e −4 m, and the vibration was stable at 0.43s. Increasing the impact pressure, the maximum displacement of the hydraulic pipeline vibrations were larger, and the attenuation of the maximum values were faster. The research results provide a reference for the hydraulic system to prevent pressure shock and reduce vibration.

Frequency Synchronization of Heterogeneous Second-Order Forced Kuramoto Oscillator Networks: A Differential Inequality Approach

This paper is concerned with frequency synchronization of heterogeneous second-order forced Kuramoto oscillator networks. Under this model, each second-order oscillator is driven by a periodic external force and its dynamics will be affected by the inertia and the damping coefficient. By introducing the second-order differential inequality, we first show that this model exhibits frequency synchronization for any initial data if the amplitude of force is large and the inertia is small. In case that the amplitude of force is not large, we prove that this model still can drive frequency synchronization provided that the coupling strength is large and the initial configuration is confined to a sector. Comparison studies with existing synchronization conditions are made to indicate that these proposed criteria seem to be less conservative. A desynchronization for large inertia is shown in our numerical experiment.

Nonergodic Brownian oscillator: low-frequency response

An undisturbed Brownian oscillator may not reach thermal equilibrium with the thermal bath due to the formation of a localized normal mode. The latter may emerge when the spectrum of the thermal bath has a finite upper bound ω 0 and the oscillator natural frequency exceeds a critical value , which depends on the specific form of the bath spectrum. We consider the response of the oscillator with and without a localized mode to the external periodic force with frequency Ω lower than ω 0. The results complement those obtained earlier for the high-frequency response at and require a different mathematical approach. The signature property of the high-frequency response is resonance when the external force frequency Ω coincides with the frequency of the localized mode . In the low-frequency domain the condition of resonance cannot be met (since ). Yet, in the limits and , the oscillator shows a peculiar quasi-resonance response with an amplitude increasing with time sublinearly.