System Dynamic Behavior Research Articles

Methods for improving the efficiency of a wind power plant and reliable estimation of output control parameters and disturbances

A method for controlling a wind power plant based on the use of the optimization model that takes account of the drive vibration loading under different operating modes of the power unit is validated. The transfer functions of the rotor systems dynamic links are proposed, taking account of the influence of wind speed and electrical load, the block diagram of the control system and the transient process graph of the angular velocity regulating of the installation generator rotor. To ensure the reliability of the output control parameters and disturbing influences estimation, the determining method substantiation of the dynamic links correlation coefficients for the wind power plant rotor system is performed. These coefficients are necessary to develop models of the system dynamic behavior used in the modification of the wind power plant automated control in order to reduce the vibrations of all rotor systems elements under different operating modes of the power unit that will improve the reliability of modern wind turbines. The correlation function parameters to determine the correlation dependences for the measured values of wind speed and electrical load are found. Formulas are derived for determining the spectral density of input and output random processes at changing wind speed and electrical load, as well as the mutual spectral density of input and output random processes for dynamic links of rotor systems (rotary blades, rotor, generator, gearbox) based on the block diagram of the entire process in order to determine the correlation degree of transfer functions. The analysis of the input and output signals of the transfer functions with respect to their coherence is carried out from a correlation coefficients calculation of the rotor systems dynamic links. This makes it possible to describe the transfer function within the framework of the vibration fields analysis for the unit as a whole. Keywords wind power plant, control, rotor system, vibration, correlation coefficient

Innovative Load Shedding Scheme to Restore Synchronous Generator-Based Microgrids During FIDVR

Fault induced voltage recovery (FIDVR) phenomenon may occur in microgrids ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula> Gs) and distribution systems due to the induction motors (IMs) behavior after system voltage sags especially short circuit faults. For the case that motors reaccelerate, system voltage may recover to its nominal value after few seconds. However, it may remain low during motor stalling condition, which result in unstable (non-recoverable) FIDVR. In this paper, an adaptive load shedding scheme is proposed to mitigate unstable FIDVR in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula> Gs containing synchronous dispersed generators (SDGs) to enhance system dynamic behavior. Derivative of the imaginary part of equivalent admittance seen from the distribution feeders with respect to time is utilized to discriminate stable FIDVR from unstable ones. In addition, a new criterion is proposed to determine SDG stability margin during the FIDVR phenomenon. Then, a new load shedding scheme is presented based on the proposed SDG stability margin and IM reacceleration index. Moreover, the load shedding time delay is adaptively calculated based on motor reacceleration time. Performance of the proposed method is evaluated by comprehensive simulation studies on two realistic networks. These investigations fairly reveal security and reliability of the proposed method in various conditions.

Concurrent Monitoring and Isolation of Static Deviations and Dynamic Anomalies with a Sparsity Constraint

In modern process industries, elaborate monitoring and isolation of various disturbances and faults are needed for reliable and efficient system operation. The classic process-monitoring and fault-diagnosis methods can grasp the correlation between variables, and thus, only take care of abnormal situations caused by the corruption of the correlation relationship. However, dynamics anomalies are even more noteworthy as they reflect more internal details of the system dynamic behaviour under specific situations, and more importantly, can cause severe failures and spread to a broader range of areas while evolving over time. In this paper, a monitoring-and-isolation strategy is proposed to concurrently detect and isolate faults of static deviations and dynamic anomalies. The natural sparsity of the faulty variables is used to overcome the limitations of unknown fault directions and insufficient erroneous measurements, thereby translating the isolation problem into a quadratic programming problem with a sparsity constraint and solved by the least absolute shrinkage and selection operator (LASSO). The case study shows the advantages of the proposed method in monitoring and isolating static deviations and dynamic anomalies.

Route to chaos in whispering gallery mode coupled opto-mechanical systems

In opto-mechanical systems, the nonlinearity caused by radiation pressure can lead to various abundant dynamical phenomena such as chaos. Chaos is an important branch of nonlinear dynamics, and researchers focus on understanding the transitions from order to chaos in different systems. In this paper, we investigate the chaotic dynamics in a system consisting of two evanescently coupled identical cavity opto-mechanical subsystems, where the optical fields are in whispering gallery modes. To thoroughly analyze the transition from order to chaos in our system, we utilize the bifurcation diagrams, the Lyapunov exponents, and phase space trajectories to characterize the system properties. It is found that the coupling strength between the two opto-mechanical subsystems plays a crucial role in determining the systemic dynamic behaviors. There are two routes to chaos in our system i.e. the period-doubling transition and the quasiperiodic transition. These routes correspond to strong coupling and weak coupling between the two opto-mechanical subsystems, respectively. Furthermore, the results show that the synchronization between the oscillations in the two opto-mechanical subsystems can occur under strong coupling. In this situation, the dynamic behaviors of the two opto-mechanical subsystems are exactly identical and the manipulation of the coupling strength is equivalent to the tuning of the frequency detuning between the cavity fields and their corresponding driving fields. Consequently, the coupled system behaves as a single opto-mechanical system, enabling a period-doubling transition to chaos through increasing the coupling strength. In the case of weak coupling, the dynamics of the two opto-mechanical subsystems are no longer synchronized, and the coupled system dynamic behaviors unfold in an eight-dimensional phase space. The limit cycles experience the Hopf bifurcation, resulting in the emergence of a toric attractor. Within a certain range of parameters, i.e. appropriate frequency detunings, the two-dimensional torus becomes unstable as coupling strength increases, leading to a quasiperiodic transition into chaos in our coupled opto-mechanical system.

Stability Analysis of Bipolar LVDC Grid

The study and regulation of bipolar DC structures covered by asymmetrical action, the DC symmetric part approach is implemented. This approach is an expansion of the standard principle of symmetrical components in three phase AC-controlled networks. In typical and differential modes, the asymmetrical voltage and current in the positive and negative poles are separated into symmetric segments. For each mode, an analogous circuit is imitative, which produces decoupled case circuits. As a consequence, it provides autonomous recommendations of each situation and offers an informative mode of a bipolar DC power system's static and dynamic behavior. A common methodology which is relevant to numerous cases of device scheme is the DC symmetrical portion process. An improved common-mode voltage control scheme is defined as an example. By incorporating active damping regulation, it suppresses common mode LC resonance and decreases common-mode impedance to enhance power efficiency and stability of voltage. Matlab/Simulink effects validate the main theoretical assumptions.

Time-delay feedback control of an axially moving nanoscale beam with time-dependent velocity

The paper is concerned with the nonlinear subharmonic resonance of an axially moving nanoscale beam with time-dependent velocity controlled by displacement and velocity time delay. To gain a thorough understanding of the system, the frequency response equation is first obtained using the multiple scales method. The stable intervals of the system's zero and non-zero solutions, as well as the necessary and sufficient conditions for Hopf bifurcation are specified. Then, the effects of nonlocal parameter, displacement feedback gain coefficient, velocity feedback gain coefficient, displacement and velocity time delay on the system's dynamic behaviors are discussed. The analysis demonstrates that the nonlocal parameters can not only reduce the amplitude of the system, but also change the stable regions of the non-zero solution. Furthermore, the time delay parameters can affect the number, amplitude, and stability of non-zero solutions. If the time delay parameters are chosen within the optimal value range, both positive and negative time delay feedback can effectively control system stability. These research results will serve as a theoretical reference for the design and optimization of axially moving nanostructures.

Fractional order system dynamical behaviors with Beddington-DeAngelis functional response

The present study proposes a fractional order prey-predator model with Beddington-DeAngelis functional response, that the Caputo fractional derivative is applied. There is exploration of the solutions' existence, uniqueness, non-negativity, and boundedness. Stability of all feasible equilibrium points is determined locally by the use of Matignon's condition. Moreover, we also provide sufficient conditions to assure global asymptotic stability for both the predator-extinction equilibrium point and the positive equilibrium point, with selecting a relevant Lyapunov function and the incidence of Hopf-bifurcation is also displayed. Finally, the fractional order effect on the stability behavior of systems is investigated theoretically and also illustrated numerically to support theoretical results.

Memristor synapse-coupled piecewise-linear simplified Hopfield neural network: Dynamics analysis and circuit implementation

Electromagnetic induction current is generated between the adjacent neurons in neural network caused by the existence of membrane potential difference. Memristor is the fourth fundamental electric element, which can mimic the behavior of neural synapses and simulate the electromagnetic induction effect. In this paper, in order to simplify practical implementation, the commonly used hyperbolic tangent activation function of Hopfield neural network (HNN) is replaced by a piecewise-linear function, and a simple bi-neuron-based memristor synapse-coupled HNN is proposed. Theoretical analysis and numerical simulation results illustrate that the memsirstive HNN possesses five equilibria including one unstable saddle-focus, two unstable saddle points, and two stable node points (or node-foci). Local attraction basins and phase plane plots show that the memristive HNN model behaves multistability of coexisting chaos, periodic limit cycles, and stable point attractors. Various system dynamical behaviors affected by parameters of the piecewise-linear activation function, memristor coupling strength, and initial conditions of the neurons are investigated by numerical simulations. Furthermore, an analog circuit of the memristive HNN model is simply designed, which is easier for hardware implementation as the piecewise-linear activation function can be implemented by simple op-amp-based module. Finally, the experimental results verify the correctness of the design and analyses.

Dynamic investigation of centralized and decentralized storage systems for a district heating network

District heating is an efficient and promising way to cover the residential space-heating and domestic hot water needs, resulting in economic and environmental benefits, especially if operated by renewable power stations, when compared to fossil fuels. In this direction, the present study investigates in detail a district heating network with novel decentralized storage for domestic hot water (enerboxx scenario), over centralized storage systems, applying a specific schedule-based approach for the coordinated hot water tank charging. The goal of this design is to properly control the system by charging it at predetermined time periods during the day aiming at i) diminishing the thermal losses and ii) reducing the thermal demand from the grid, over the period of a day. The simulation is conducted with a newly developed component-based tool, called INTEMA, which is based on the Modelica language. This encompasses the ability to discretize with high temporal resolution and adjustable time steps the overall grid configuration, with the support of customizable level of detail models for simulating key system components such as the storage tanks, the piping and the dwelling needs, as well as the application of an advanced control system over the district heating network and the dwellings. More specifically, a combined control system that controls both operating parameters in the network and inside the dwellings is applied. The developed system model is verified against available data for a standard centralized storage system (reference scenario) and afterwards, the novel decentralized design is compared against corresponding results of the standard system, as concerns key operational parameters; indicatively the temperature levels of the hot water and the heat load demand. The analysis is conducted for a heating network of 9 dwellings in Austria, which have an underfloor heating system, a system for covering the domestic hot water demand, considering also that each of these 9 dwellings is characterized by a unique demand profile. It was found that the decentralized approach leads to lower demand and there are energy savings of 18 % compared to the reference scenario, while the thermal losses are reduced by about 22 %. Moreover, a parametric study regarding the storage tank volume and the heat exchanger thermal transmittance in the tank is conducted, in order to examine the impact of these design parameters on the system dynamic behavior.

A continuous contact force model for the impact analysis of hard and soft materials

• A new continuous contact model is proposed with high accuracy. • The new model can simulate impacts with remaining surface deformation after impact. • The new model can simulate impacts with zero separation indentation. • The model is verified by two published experimental data and typical contact models. Impacts with remaining surface deformation or zero indentation at the separation time are common in mechanical systems with hard and soft materials, and corresponding contact force models have been established for these two types of collision phenomena, but there is a lack of models that can simulate both types of impacts. A new continuous contact model is proposed that can simulate these two types of collisions with high accuracy. By constructing an approximate equation, the new model is developed based on the typical equation of continuous contact models. Two published experiments related to two types of collisions are used for model validation; in addition, typical continuous models for the impact analysis of two types of collisions are utilized for the comparison. The validation and comparison show that the new model can simulate the impact with remaining surface deformation or zero separation indentation with high accuracy. The influences of the restitution coefficient and remaining surface deformation ratio on the system dynamic behaviors have also been investigated. The new model will be helpful for the dynamic simulation of mechanical systems with contact-impacts phenomena involving hard materials and soft materials.

Consideration of multi-variable uncertainty using the GPC method for the dynamic study of a two-stage gearbox of a wind turbine

This paper deals with the problem of the uncertainties interaction in the design parameters of a two-stage gearbox of a wind turbine. The purpose of the dynamic study is to minimize the linear displacements in order to have more stability. The uncertainty consideration using a unique parameter, allowed the identification of the influence of this latter on the dynamic response, in addition to its extreme values. The examination of multivariate parameters investigates the interaction of these parameters. Thus, the gear system dynamic behavior was studied by taking into account the uncertainty with a suggested diagram: uncoupled form to evaluate the impact of each parameter and coupled form based on the progressive interaction of uncertain dynamic parameters using the multivariate uncertainty method. For this purpose, the generalized polynomial chaos approach (GPC) was applied to simulate the dynamic behavior of the wind turbine gearbox. The obtained results were then verified using Monte Carlo simulations.

Developing a system dynamic plus framework for water-land-society nexus modeling within urban socio-hydrologic systems

System dynamics models facilitate the sustainable management of urban socio-hydrologic systems by capturing the synergies between water, land, and urban society However, SD models depend heavily upon both quantitative and qualitative data to characterize the feedback loops in complex systems. This study aims to improve the capability of SD in problem conceptualization and scenario analysis within socio-hydrologic systems. Applying the Driver, Pressure, State, Impact, Response (DPSIR) and system archetypes coupled with SD models facilitate capturing interactions among disparate but interconnected subsystems driving the system's dynamic behavior. To explore this methodology, the SD+ has been applied to develop a Water-Land-Society Nexus model within the Isfahan City located in arid and semi-arid Central Iran. The results demonstrated that the continuation of the existing management policies will cause a severe water shortage due to increase in urban land uses as well as growing water demand. The Isfahan's water shortage has the characteristics of the Shifting the Burden system archetype, in which symptomatic solutions alleviate the problem symptom in the short-term, causing significant side effects in the long-run. Supplying more water through water transfer and wastewater reuse decreases water shortage, leading to increasing the water demand as well as the limited access to water.

Prediction and diagnostics of crises and critical states in an unusual vibro-impact system with soft impact

In nonlinear dynamical systems, whenchanging control parameters, critical states may occur. To predict these undesirable events, it is necessary to study the system dynamic behavior with changing in different control parameters. Two-body 2-DOF vibro-impact system is under consideration. The huge mass of the upper body, which can break away from the lower one and be in “free flight” for a short time, may be attributed to its specific and is a cause to consider it unusual. Some changes in the parameters of both external loading and the system itself can increase the efficiency of the machine, the mathematical model of which is the considered vibro-impact system. But the same changes lead to appearance of unwanted nonlinear phenomena, such as permanent sustained chaos, transient chaos, crisis-induced intermittency, and coexisting regimes with larger oscillatory amplitudes. The article shows their occurrence, traces the precursors, carries out their diagnostics by both traditional and less common methods. The description of many numerical experiments is accompanied by numerous figures and tables that clearly and convincingly demonstrate the results obtained.

System analysis of water-energy-food nexus of Bundelkhand region, India

Abstract The challenges in drought-hit Bundelkhand are stemming from policy constraints and insecurity of water, energy, and food resources, which have triggered mass migration, unemployment, indebtedness, and farmer suicide. Among the surveyed households of Banda District, 21% have no electricity, 90% are using fuelwood and cow dung for cooking purposes, 70% are engaged in agriculture, per capita food consumption is very low, and 51% of the households are using less than 40 lpcd (liters per capita per day) of water. The research methodology is unique is tailored to the WEF nexus approach. It analyzes the primary data of 534 households, 33 experts (Delphi Technique), and the secondary data of 189 articles. The Causal Loop Diagrams capture the system's dynamic behavior and establishes interconnectedness of the identified control parameters using the systems approach. Major parameters for agricultural production are productivity, productive area, and cropping intensity, while major water demand comes from agriculture, industrial, and domestic use. The energy sector is identified as the most challenging in this region, and the total generation comes from solar, biogas, fossil fuels, and organic fuels. This study concludes with findings suggesting urgent actions to be taken for regional sustainability and policy recommendations at the local level.

Comparison of the theoretical elements and application characteristics of STAMP, FRAM, and 24Model: A major hazardous chemical explosion accident

Owing to the flammable, explosive, and toxic characteristics of hazardous chemicals, chemical accidents always result in significant losses. Analysis of the parameters of process safety is an effective way to prevent hazardous chemical accidents and reduce losses. To promote the application of systemic accident models in practice, in this study, we clarify the theoretical elements of such models based on the development of system thinking and system science. Then, we discuss the characteristics of a new systemic model called 24Model and its systems thinking. We explore the differences in the practical application of different systemic models (System-Theoretic Accident Model and Processes (STAMP), Functional Resonance Accident Model (FRAM), and 24Model by analyzing a major hazardous chemical explosion accident that occurred in Tianjiayi Chemical Co., Ltd. in China. The results show that the elements of the systemic accident model are the system structure, component relationship, and dynamic behaviors. 24Model is proven to be a new systemic accident model developed by utilizing sequential models. The comparative results of the three analysis methods show that FRAM is suitable for accident prediction rather than accident analysis. STAMP and 24Model perform better in terms of the usability and reliability of accident analysis. Although STAMP fails to elaborately indicate the internal organizational causes of the accident, it is suitable for a small number of accidents in socio-technical systems. 24Model is a structured method for accident analysis and safety management frame of organization. With the classified accident causes and fewer training resources, it is more suitable for a number of accidents statistics and analysis. Finally, a universal frame to prevent hazardous chemical accidents is provided for companies and regulators.

Structural rule-based modeling with granular computing

In order to analyze the dynamic behaviors of complex systems in the era of big data, a new rule-based modeling approach is proposed in this paper. This approach considers structural information mining and granular computing (GrC) in rule-based modeling, it also aims at utilizing granular fuzzy intervals to reflect systems’ behaviors on uncertainty. Major contributions can be summarized as three points. First, using DBSCAN’s advantages in clustering arbitrarily-shaped data, DBSCAN is applied to extract structural information as the basis of rules in complex systems. Second, GrC is leveraged for rule formation and effective rule-based modeling, e.g. granules constructed in input space to refine structural DBSCAN clusters, granular intervals constructed in output space with the principle of justifiable granulating to reflect system dynamic behaviors. Third, experimental analysis based on three different design scenarios was studied on both synthetic data and publicly available datasets. Through comparative discussion, the proposed approach can outperform the conventional rule-based models, specifically having an improvement ratio of 0.18% to 1.48% on the proposed comprehensive indicator. Therefore, it can be concluded that the proposed approach has the feasibility and advantages of reflecting the structural and uncertainty characteristics of system dynamic analysis.

Fractional order mathematical model of monkeypox transmission dynamics

In this paper, we present a deterministic mathematical model of monkeypox virus by using both classical and fractional-order differential equations. The model includes all of the possible interactions that contribute to disease spread in the population. We investigate the model's stability results in the disease-free case when R 0 < 1. When R 0 < 1, we show that the model is stable, otherwise it is unstable. To obtain the best fit that describes the dynamics of this disease in Nigeria, the model is fitted using the nonlinear least square method on cumulative reported cases of monkeypox virus from Nigeria between January to December 2019. Furthermore, adequate conditions for the existence and uniqueness of the solution of the model have been proved. We run numerous simulations of the proposed monkeypox model with varied input parameters to investigate the intricate dynamics of monkeypox infection under the effect of various system input parameters. We investigate the system's dynamical behavior to develop appropriate infection control policies. This allows the public to understand the significance of control parameters in the eradication of monkeypox in the population. Lowering the order of fractional derivatives has resulted in significant modifications. To the community's policymakers, we offered numerous parameters for the control of monkeypox.

Scientific Model of Vocational Education Teaching Method in Differential Nonlinearity

Abstract This paper uses nonlinear differential equations to establish a relationship model between enrollment, education, and employment in vocational education. In this paper, the local stability of the vocational education system is analyzed utilizing nonlinear differential theory and numerical simulation. At the same time, we carried out a numerical simulation of the system’s dynamic behavior. Through numerical simulation research, it is found that the model has peculiar nonlinear behavior and dynamic characteristics when its parameters take some specific values. Finally, we get the critical condition of the stability of the vocational education system according to the model established in the article.

Analysis of wireless English multimedia communication based on spatial state model equation

Abstract In order to improve the quality of wireless English multimedia communication, according to the characteristics of space multimedia communication environment and communication equipment, this paper proposes a wireless English synchronous QoS control algorithm with low complexity and easy implementation. Using RTCPSRRTP timestamp and NTP absolute timestamp, the wireless English RTP timestamp is mapped to the same absolute reference clock (sender system time) respectively, and the wireless English synchronization detection decision rule is established according to the synchronization QoS performance requirements between wireless English media. Wireless English synchronization control system model at the receiver. At the receiving end, the wireless English stream is the main media stream and the video stream is the slave media stream. The synchronization detection and judgment is implemented in real time before the video frame is played. The synchronization between audio and video media is realized by corresponding synchronization control of wireless English playback. State space model reflects all the information of system dynamic behavior and is a complete description of system behavior. The state space model has a wide range of applications. It is not only suitable for SISO linear constant systems, but also suitable for nonlinear systems, time-varying systems, MIMO systems and stochastic systems. The more outstanding advantage is that the state space model adopts local calculation and uses the state variables inside the system to describe its dynamic characteristics. This property of local calculation not only greatly simplifies the mathematical expression of multi-dimensional system, but also facilitates the analysis and research of the system. The air link rate of the wireless transceiver is set to 512Kbps. The video is encoded based on H.264 and the audio is encoded based on G.729 Speech coding standard. Compared with the wireless English media synchronization control algorithm based on RTP / RTCP, the results show that the RMSE value after adopting the synchronization algorithm in this paper is reduced by 60.09% and 77.69% at most; Compared with the wireless English media synchronization control algorithm based on RTP / RTCP, the synchronization performance of this algorithm is better than the wireless English media synchronization control algorithm. The RMSE value is reduced by 2% on average and 5.2% at most. In addition, the synchronization control algorithm between wireless English media performs synchronization control by losing frames or pausing decoding before video decoding at the receiver, which affects the quality of wireless English video decoding and reconstruction.

Design and circuit implementations of multimemristive hyperchaotic system

To enhance the order and Kolmogorov entropy of the memristive hyperchaotic system and improve the realizability of the circuit, a sixth-order memristive hyperchaotic system that consists of two flux-controlled memristors and one charge-controlled memristor is designed. Combined with Lyapunov exponential spectrum, phase trajectory diagram and bifurcation diagram, dynamic characteristics of the system are analyzed, and the effects of system control parameters and initial state on the system dynamic behavior are explored. Equivalent circuit models of flux-controlled and charge-controlled memristors with cubic nonlinear characteristics are constructed by the basic operation modules, and the hardware simulation design of the memristive hyperchaotic system is completed. The experimental results show that the proposed system can exhibit kinds of attractors, such as periodic-loop, single-scroll, double-scroll and superposition by adjusting system control parameters, and the system can show the behavior of period doubling bifurcation entering chaos and anti-period doubling exiting chaos under the different system initial states, which corresponds to the multistable coexistence phenomena of the system, such as quasi-period and hyperchaos. Meanwhile, the sixth-order hyperchaotic system is implemented by hardware circuit simulation. The phase diagrams of the circuit simulation are consistent with that of the numerical simulation, which verifies the physical realizability of the hyperchaotic system. Based on the strong initial value sensitivity and large K entropy, the memristive hyperchaotic system can be applied to the image encryption, and the confidentiality and security of images can be effectively enhanced.