Dynamic Behavior Of System Research Articles

Static and dynamic nonlinear behavior of a multistable structural system consisting of two coupled von Mises trusses

Recent years have witnessed a growing interest in multistable structures. In most cases it is attained by a sequence of bistable elements. However, little is known on their nonlinear static and dynamic responses. In this work a detailed static and dynamic nonlinear analysis of a multistable structural system consisting of two coupled bistable von Mises trusses is conducted to enlighten the complex behavior of these systems. For this, the exact nonlinear equilibrium equations and equations of motion in their dimensionless forms are obtained through the principle of stationary potential energy and Hamilton’s principle, respectively, considering a linear elastic material. Using continuation algorithms, the nonlinear equilibrium paths are obtained. The stability of each configuration is analyzed using the principle of minimum potential energy. Multiple equilibrium paths of the coupled system are identified, leading to several coexisting stable and unstable solutions, bifurcations and potential wells which are closely connected to the symmetries of the system. It is shown that the number of coexisting solutions increases exponentially with the number of bistable units. The effect of unavoidable imperfections is also clarified. The nonlinear dynamics and bifurcations of the system under harmonic forcing and static pre-load are then studied. Bifurcation diagrams, Poincaré maps and cross-sections of the basins of attraction are used to study the influence of coexisting attractors due to multiple potential wells, resonances and bifurcations. The coexisting responses can merge giving rise to several types of cross-well motions, the threshold value being closely connected with the limit point load of the coupled system. The increase in coexisting solutions leads to increasingly complex basins of attraction with broad fractal regions. On the one hand, the complexity of the bifurcation scenarios seems valuable in several applications to encode information, to respond to external forcing and to switch between different states. On the other hand, multiple attractors and their fractal basins can lead to the loss of global stability and dynamic integrity due to the small uncorrupted basins surrounding each attractor. Thus, the knowledge of the static and dynamic behavior of multistable systems is of great significance to either inducing or avoiding this phenomenon or making use of it.

Low-Frequency Defense Strategy for Wind Turbine Participating in Power Grid Frequency Adjustment

With the continuous increase of wind power permeability, the dynamic behavior of the power system also changes, which also has a great impact on the setting of the low-frequency load-shedding scheme. The original low-frequency load-shedding scheme has no good adaptability to the system of high-permeability wind power. So, this article analyzes the principles of wind turbines in power grid frequency control. This paper expounds on the principle of low-frequency load-shedding strategy in the power system configuration. Connecting with the actual operation of the grid simulation, simulation results show that wind turbines in power grid frequency modulation can significantly reduce the low-frequency load shedding process of loads and wind power in frequency modulation of low-frequency with a positive impact.

Analysis of Dynamic Characteristics of Attached High Rise Risers

The exhaust chimney of third-generation nuclear power units is a typical attached high-rise riser structure. In this paper, the simplified mechanical model and dynamic model of China’s third-generation nuclear power Hualong-1 VNA system, including multiple nonlinear factors, are established for the first time. The DTM (differential transformation method) was first applied to solve the natural vibration characteristics of a multi-point constrained variable cross-section riser structure, and the effects of variable cross-section, variable mass, variable axial force, and different elastic constraint parameters on the natural vibration characteristics of the system were studied. The dynamic behavior of the VNA system under the combined action of internal flow velocity, vortex excitation, and foundation excitation was studied. The results show that the outer diameter function of the VNA system pipeline should be designed as a quadratic function or a near quadratic multi-segment constant value function. The “limiting” effect of constraining large stiffness can force low-order vibration modes with high constraint stiffness to jump to high-order vibration modes with low constraint stiffness. The elastic constraint arrangement scheme with near center symmetry can make the system vibration mode present a half stable and half-curved form. A new optimization design scheme has been proposed regarding the layout and stiffness parameters of the VNA system guide bracket. This can enable the VNA system pipeline to avoid severe oscillations near the response extreme values caused by multiple frequency excitations of seismic loads under design and accident conditions and ensure the service life of the equipment.

Development of the equivalent Great Britain 36-zone power system for frequency control studies

This paper presents a dynamic model of the equivalent Great Britain (GB) 36-zone power system, which can be used for reliable and realistic assessment of emerging load frequency control mechanisms. Flexible architecture of the presented dynamic test system permits a broad range of security of supply and small-signal stability studies for design of future power grids. It can be particularly useful for academic research, but also for undertaking feasibility studies in power industries. The proposed dynamic test system, which is obtained through network reduction of the original full-scale GB transmission power system developed by National Grid Electricity System Operator (NGESO) Company, provides detailed information about the GB power system. In this regard, the required data and modelling approaches to develop the 36-zone system are provided in detail. The presented dynamic test system represents the system topology, impedance characteristics and electromechanical oscillations of the original GB power system however, it is not an exact equivalent of the master GB system. Illustrative dynamic models of the key system components, including synchronous generators, automatic voltage regulators, power system stabilizers, hydro and steam turbines models along with speed governing systems are presented. Dynamic behavior of 36-zone test system in response to infeed loss contingencies is investigated. Particularly, the impact of changes in the system inertia on the system electromechanical modes is examined using the modal analysis approach. In this context, the mode shape concept is employed to determine dominant generators and contribution of different zones in the low frequency oscillations. Moreover, time-domain simulations are undertaken to validate the modal analysis results. Additionally, the condition of different zones from the viewpoint of frequency nadir and maximum rate of change of frequency for various contingencies and extreme cases are examined.

Identification of Nonlinear Behavior of Bridge Structures Using Time Series Analysis of Vibration Signals

ABSTRACT One of the most widely used linear techniques for solving damage identification problems and prediction of the system dynamic behavior is modal testing and analysis. However, most of real structures exhibit nonlinear behavior during their lifetime caused by a number of various reasons. The presence of nonlinearity in a structural system changes its dynamic characteristics; hence, the use of linear techniques is improper for prediction of the system behavior. In this paper, a vibration-based nonlinearity identification technique was proposed to identify early changes in a dynamic system prior to significant damages. This technique combines the time series Autoregressive Moving Average with Exogenous Inputs (ARMAX) modelling, probability theory, and Fuzzy C-Means (FCM) clustering algorithm to categorize the linear and nonlinear dynamic behaviors of a dynamic system. The technique aims to categorize the linear and nonlinear behaviors of a structure, when it is subjected to various levels of excitation source. To show the validity of the proposed method, a series of shake table tests was performed on a six-span steel truss bridge model. The bridge model was excited using different amplitudes of ground motion to control the nonlinearity degree of rubber-based supports. It can be concluded from the analysis results that the new vibration-based nonlinearity identification technique was able to identify nonlinear behavior of the bridge model once it was subjected to different levels of earthquake excitations. This algorithm was able to categorize the linear and nonlinear behaviors of the bridge model and define a specific threshold for different excitation sources.

Physical system behavior and energy flow analysis of a solar driven hydrogen production plant based on two-step thermochemical redox cycles

Two-step thermochemical water splitting using concentrated solar power offers promising potential for green hydrogen production as a part of a future sustainable energy economy. In this study, a system and energy flow analysis of a large scale 250 kW reactor prototype is presented by using a complex 3D-simulation model. Thus, the physical dynamic system behavior and potential efficiency improvements are discussed with respect to plant design and operational strategy. Regarding the plant design, different kind of heat losses as well as the influence of reactor design parameters and material modifications are analyzed. Regarding the operational strategy, crucial control parameters as cycle durations, temperatures, and mass flow rates are varied in a broad range and analyzed with respect to plant efficiency. By comparing commonly used operational strategies, the temperature swing operation turns out to be by far more efficient than any isothermal or near-isothermal operation for the current plant concept.

Dynamic responses of a conceptual two-dimensional airfoil in hypersonic flows with random perturbations

This paper investigates a conceptual pitch–plunge airfoil in hypersonic flows with both structural and aerodynamic nonlinearity, meanwhile the effects of irregular fluctuations in the flow and external random loads modeled as a Gaussian white noise are considered. The dynamic responses of the airfoil model especially the bifurcation behaviors are analyzed via the harmonic balance method for the deterministic case. We found the airfoil system undergo both subcritical and supercritical Hopf bifurcations. Subsequently, the effects of stochasticity on the dynamical behaviors of the hypersonic airfoil system are explored in the regimes of subcritical and supercritical Hopf bifurcations depending on the system parameters. Several interesting phenomena are triggered under random perturbations such as intermittency and stochastic transition between the low-amplitude oscillation state and the undesirable high-amplitude oscillation state. These dynamics are further characterized via the probability density function and time history. This work will provide new insights into the safety and reliability design of hypersonic aircraft.

Stability and Performance of an Undersea Kite Operating in a Turbulent Flow Field

In this article, we examine the effects of flow disturbances resulting from turbulence on the dynamic behavior of an underwater energy-harvesting kite system that executes periodic figure-8 flight. Due to the periodic nature of the kite’s operation, we begin by assessing orbital stability using the Floquet analysis and stroboscopic intersection analysis of a Poincaré section, with the former analysis performed on a simplified “unifoil” model and the latter performed on a six-degree-of-freedom (6-DOF)/flexible tether model. With periodic stability established, a frequency-domain analysis based on a linearization about the kite’s path is used to predict the quality of flight path tracking as a function of the turbulence frequency. To validate the accuracy of these simulation-based predictions under flow disturbances, we compare the predictions of the kite’s behavior against the results of small-scale tow testing experiments performed in a controlled pool environment.

A Prediction Based Replica Selection Strategy for Reducing Tail Latency in Geo-Distributed Systems

The deployment of modern applications in geo-distributed systems results in performance fluctuation which is a consequence of long-tail latency. To deliver high-quality services these applications always strive to adapt to the changing situation and an appropriate replica selection strategy is one efficient way to achieve this. Several replica selection strategies have already been developed but none of them are efficient enough to reduce tail latency and adapt to the dynamic environment of the geo-distributed systems. In this paper, we present the design and implementation of a prediction based replica selection strategy for reducing tail latency in geo-distributed systems. We have meticulously designed the proposed strategy to adapt to the dynamic behavior of the distributed system. For evaluating its effectiveness in reducing tail latency and adapting to the dynamic behavior of the geo-distributed systems we perform some extensive experiments in a 15 nodes Cassandra cluster that is deployed on Amazon EC2 over 5 geographical regions. For generating test datasets and workloads we use industry-standard Yahoo Cloud Serving Benchmark (YCSB). Our experimental results show that the proposed strategy not only reduces tail latency but also increases the overall throughput of the systems.

An Efficient and Effective WEC Power Take-Off System

A numerical model for a hydraulic wave energy converter power take-off is developed in this study. The system architecture is described and the mathematical model for each component is presented. The accumulators are not used as energy storage devices. Instead, they are used to reduce the stiffness of the system, increase the response time, and improve the controllability. The numerical model was implemented using MATLAB/Simulink. The design variables selected for this study are the maximum displacement in the hydraulic motors, and the shaft inertia. The effect of these design variables on system performance is studied using latin-hypercube sampling to generate the cases to be simulated. The displacement in the hydraulic devices is used as a control input to adjust the pressure in the hydraulic cylinder and then change the force acting on the floating body. The desired force is calculated by a high level controller that estimates the force value to achieve impedance matching in the WEC. The torque in the electric generator is used to control the shaft speed. The system was designed to actively use reactive power flow to maximize the electric power output in the generator. The model developed in this study is a complete wave-to-wire model based on a co-design approach that considers the effect of all the different subsystems on the dynamic behavior of the whole WEC system. Twelve different wave conditions were tested. The most critical metric for this study is the electric power in the generator, which is the objective function of the optimization that was performed for all the wave conditions defined as case study. The wave-to-wire efficiency, which includes the complete wave energy to electrical energy conversion chain, is also calculated in this work.

A new 3D hidden conservative chaotic system with multistability and its circuit implementation

A novel three-dimensional conservative system without an equilibrium point is constructed by replacing the square term x 2 + y 2 in the Vaidyanathan - Sundarapandian oscillator with a simple absolute value term |x|. The system is analyzed in detail by using time-domain waveform plots, bifurcation plots, Lyapunov exponent spectra, spectral entropy (SE), and C0 complexity. It is found that the system has rich dynamic behaviors: multiple phase trajectories can be tuned by only one parameter and multistability due to initial value sensitivity. The system shows that it can yield eight heterogeneous trajectories coexistent at different initial conditions, including periodic, quasi-periodic, and chaotic states. Additionally, the transient behavior was also observed. Finally, the experimental circuit was implemented, verifying both the physical realizability and the rich dynamic behaviors of the proposed system. With high complexity and sensitivity of parameter and initial condition, the proposed system is useful in image encryption and secure communication.

Dynamic behavior of railway Vehicle-Ballasted track system with unsupported sleepers based on the hybrid DEM-MBD method

In order to understand dynamic effect of the unsupported sleepers on railway substructure at the meso-macroscopic scales, this paper develops a dynamics analysis framework combining the discrete element method (DEM) and the multi-body dynamics method (MBD). Firstly, a DEM model of ballasted tracks is built by the PFC software (The full name is Particle Flow Code, which is based on the general discrete element (DEM) framework and code software) for capturing meso-macro mechanical behavior, while a MBD model of electric locomotive is presented for simulating accurately dynamic wheel loads. A numerical simulation program is compiled by the FISH Language to implement two-way coupling calculation between the DEM model and the MBD model. Then, experimental validation is carried out by comparing the dynamic response results obtained from the ShuoHuang Heavy-haul Railway Line field dynamics test with the simulation results adopting a hybrid DEM-MBD model and the classical railway vehicle-track hybrid dynamics model (VTCD model) known as Zhai’s model. Finally, the hybrid DEM-MBD model is used to simulate dynamic responses of the locomotive and ballasted tracks considering 0 ∼ 5 pieces of unsupported sleepers. Simulated results show that the acceleration of 1st and 2nd wheelset begin to increase when running to the position of one sleeper-space in front of hanging area and increase to the maximum when running to the edge of hanging area. In addition, it is necessary to pay attention to the variation of acceleration amplitude near the characteristic frequency excited by the distance between bogie pivot centers. The contact stress in well-supported area adjacent to both ends of hanging area increases greatly when the number of unsupported sleepers is greater than 3.

Dynamical Analysis of the Incommensurate Fractional-Order Hopfield Neural Network System and Its Digital Circuit Realization

Dynamical analysis of the incommensurate fractional-order neural network is a novel topic in the field of chaos research. This article investigates a Hopfield neural network (HNN) system in view of incommensurate fractional orders. Using the Adomian decomposition method (ADM) algorithm, the solution of the incommensurate fractional-order Hopfield neural network (FOHNN) system is solved. The equilibrium point of the system is discussed, and the dissipative characteristics are verified and discussed. By varying the order values of the proposed system, different dynamical behaviors of the incommensurate FOHNN system are explored and discussed via bifurcation diagrams, the Lyapunov exponent spectrum, complexity, etc. Finally, using the DSP platform to implement the system, the results are in good agreement with those of the simulation. The actual results indicate that the system shows many complex and interesting phenomena, such as attractor coexistence and an inversion property, with dynamic changes of the order of q0, q1, and q2. These phenomena provide important insights for simulating complex neural system states in pathological conditions and provide the theoretical basis for the later study of incommensurate fractional-order neural network systems.

Memristive field effect in a single and multilayer neural network with different connection topologies

The network connectivities play an important role in displaying the vastly different collective dynamics in many complex systems. To demonstrate the presence of different dynamical states and their transition, we consider Hindmarsh-Rose neurons, which are linked up by electromagnetic interactions. The dynamical behaviors of the proposed system are specifically explored under three distinct network connectivities: Regular(RG), small-world (SW), and random (RAND) interactions. We discover that increasing coupling intensity illustrates the dynamical transition from the desynchronization state to the traveling wave state for all the considered network interactions. Particularly, the regular network shows the emergence of spatial symmetric patterns that transit to a homogeneous steady state while increasing the strength of magnetic field interaction. In addition, the transition from an asymmetric pattern to an in-homogeneous steady state is noticed for small-world and random networks. The investigation is then extended to a three-layer multiplex network in which nodes interact electromagnetically within (intra-) layers and magnetically between (inter-) layers, since many complex networks in the real world have large numbers of nodes organized (or located) in different subnetworks. We show that increasing the coupling intensity leads to synchronization in all layers and, eventually, a rest state at high coupling strength.

Hyperchaos, constraints and its stability control in a 6D hyperchaotic particle motion system

Firstly, a novel six-dimensional (6D) hyperchaotic particle motion system is formulated. The equilibrium points and their characteristics, Poincaré sections, Lyapunov exponents, bifurcations and multi-periodic windows are studied. Secondly, we present two nonholonomic constrained systems. In order to analyze the particle motion trajectories under constraints, the explicit equations for constrained systems are given. Based on Lyapunov exponents, Poincaré maps and bifurcations, we can see that the different hyperchaotic phenomena of the particle motion can be generated by introducing nonholonomic constraints. Finally, the stability control of the 6D hyperchaotic particle motion system is realized by separately using constraint control method and linear feedback control method. Numerical simulations of the dynamical behaviors of the six-dimensional hyperchaotic particle motion system are carried out in order to illustrate the complex phenomena of the systems and verify the analysis results.

Examining the relationships between supply, demand, and environmental policies for science and technology innovation using a system simulation model

The development of science and technology has been increasingly linked with the implementation of science and technology innovation (STI) policies with important strategic significance for promoting national and regional innovation. In actual implementation, many types of STI policies are often combined for a joint effect; however, existing studies tend to focus on the effect of a single policy. The system simulation method can break through the limitations of traditional methods in model assumptions and establish a model that is as close to reality as possible. Notably, it is unusual to use the system simulation method to investigate STI policies. Using a system simulation model, this study conducts a detailed analysis to examine the complex causal relationships of STI systems and study the impact and mechanism of STI policy from a systematic perspective. This study quantifies various STI policies, establishing a simulation model to reflect the dynamic behavior of the regional STI policy system. The empirical results demonstrate that when a single type of policy is examined, the STI supply policy has the most significant impact on promoting STI and economic development. When various STI policies are combined, the combination of supply and demand policies has the greatest promotional effect on STI and economic development, whereas the combination of demand and environmental policies has the least promotional effect on STI and economic development. The results also show that the combined effect of various STI policies is not based on the simple addition of the effects of various policies, as there is an apparent synergy phenomenon in the combined STI effects. This study contributes to the existing literature and provides practical insights for policymakers and policy enthusiasts to understand the relationships between STI supply, demand, and environmental policies to advance policy effectiveness and promote sustainable development.

Sizing of a solar and hydrogen-based integrated energy system of a stand-alone house in Izmir

The current work presents the design and modeling of a solar and hydrogen energy-based integrated energy system that provides the electricity demand of a stand-alone house located in Izmir, Türkiye. This system is mainly comprised of photovoltaic (PV) cells, battery banks, a PEM electrolyzer (PEM-El), a hydrogen (H2) compressor, and a pressurized hydrogen tank. Electricity produced from PV cells was either used in the PEM-El for hydrogen production or stored in the batteries to meet the required energy during low solar radiation or night time. The H2 produced by the electrolyzer was pressurized with a compressor and stored in pressure tanks at a pressure of 350 bar. A zero-dimensional (0-D) mathematical approach was applied for the system component modeling. An energy management strategy was incorporated into the model to investigate the dynamic behavior of the integrated system. Parametric studies were then conducted for different numbers of PV and batteries. It was found that the amount of hydrogen produced is higher in summer (28.58 kg with 20 PV-30 batteries in June, 47.69 kg with 30 PV-20 batteries in July, and 66.96 kg with 40 PV-30 batteries in August). On the other hand, hydrogen produced is lower in winter (11.60 kg with 20 PV-10 batteries in December, 21.82 kg with 30 PV-20 batteries in January, and 32.20 kg with 40 PV-30 batteries in February). In addition, an economic analysis was conducted for the hybrid system.

Application of Modular Expression of Bond Space in Muzzle Disturbance Analysis

In order to simulate the complex dynamic behavior of automata system and analyze muzzle disturbance, a modular dynamic model of automata was established based on bond space theory. The bond space modules of the cradle, gun box, barrel and projectile were defined, and the state equations of each module of the automata were deduced in terms of momentum space vector and position change space vector and their first derivative. The whole model is established by connecting the generalized potential source and generalized flow source of each module. On this basis, the muzzle disturbance analysis is carried out by solving the model, and the simulation results are consistent with the test results of the continuous firing test. It shows that the muzzle disturbance analysis model based on the modular representation of bond space is correct, and provides a new method for the dynamic analysis of the projectile and gun coupling launching system.

On the stability of viscoelastic tapered rotors with internal flow

In this paper, the stability of viscoelastic tapered rotors with internal flow is investigated. The constitutive equation of the viscoelastic material is described on the basis of the Kelvin–Voigt model. Using Hamilton's principle, the governing equation of motion for the rotor system is formulated. The Galerkin discretization technique is then employed to discrete the partial differential equations. Thus, the complex frequencies in the first two modes of the simply supported rotor system are calculated, which are utilized to discriminate the stability of the system. Then, the stability evolution process of the system is analyzed. Also, the divergence flow velocity and spinning speed are computed numerically. Finally, a comprehensive parametric discussion is carried out to evaluate the effect of parameters such as hollowness ratio, mass ratio, taper ratio, and viscosity coefficient on the stability and critical spinning speed of the fluid–structure interaction system. The results show that for a viscoelastic tapered rotor with the internal flow, the rotor experiences a stability evolution of “stable-first mode divergence-stable-first mode flutter-first mode divergence-first mode flutter.” The dynamic behavior of the rotor system depends strongly on the mass ratio, hollowness ratio, taper ratio, flow velocity, and viscoelasticity of the material.

Evaluating the inertia of the Jordanian power grid

The increasing penetration of renewable energy sources in power grids has resulted in the need for a comprehensive evaluation of their impact on the dynamic behavior of the power system, including its inertia. This study aimed to evaluate the inertia of the current Jordanian power system at different penetration levels of renewable energy sources using DIgSILENT PowerFactory simulation software. In this study, the value of the constant inertia was calculated to be 8.755 s. The results were analyzed to determine the effect of renewable energy penetration on the inertia of the power system. The findings provide valuable information for the development of control strategies for integrating renewable energy sources into the Jordanian power system, ensuring stability and reliability in the power system operation. This study contributes to the understanding of the impact of renewable energy sources on power system inertia and supports the development of renewable energy integration strategies.