Nonlinear Stability and Boundedness of Approximately Symmetric Large-Scale Systems

Multi-objective analysis of hospital delivery systems

In this article, we deal with thermal convection in an inclined porous layer modelled by the Brinkman Law. Inertial effects are taken into account, and the physically significant rigid boundary conditions are imposed. This model is an extension of the work by Rees & Bassom (Rees & Bassom 2000 Acta Mech. 144, 103-118 (doi:10.1007/BF01181831)), where Darcy's Law is adopted, and only linear instability is investigated. It also completes the work of Falsaperla & Mulone (Falsaperla & Mulone 2018 Ric. Mat. 144, 1-17 (doi:10.1007/s11587-018-0371-2)), where the case of stress-free boundary conditions is studied and the inertial terms are absent. In this model, the basic laminar solution for the velocity is a combination of hyperbolic and polynomial functions, which makes the linear and nonlinear analysis much more complex. The original features of the paper are the following: we study three-dimensional perturbations, providing critical surfaces for the linear and nonlinear analyses; we study nonlinear stability with the Lyapunov method and, for the first time in the case of inclined layers, we compute the critical nonlinear Rayleigh regions by solving the associated variational maximum problem; we give some estimates of global nonlinear asymptotical stability; we study linear instability and nonlinear stability also with the presence of the inertial term, i.e. for a finite Va.

Construction of approximate reasoning model for dynamic CPS network and system parameter identification

A nonlinear stability analysis for rotating magnetized ferrofluid heated from below

A nonlinear (energy) stability analysis is performed for a rotating magnetized ferrofluid layer heated from below saturating a porous medium, in the stress-free boundary case. By introducing a generalized energy functional, a rigorous nonlinear stability result for a thermoconvective rotating magnetized ferrofluid is derived. The mathematical emphasis is on how to control the nonlinear terms caused by magnetic body force. It is found that the nonlinear critical stability magnetic thermal Rayleigh number does not coincide with that of linear instability analysis, and thus indicates that the subcritical instabilities are possible. However, it is noted that, in case of non-ferrofluid, global nonlinear stability Rayleigh number is exactly the same as that for linear instability. For lower values of magnetic parameters, this coincidence is immediately lost. The effect of magnetic parameter, M 3, medium permeability, D a , and rotation, $$T_{A_1}$$ , on subcritical instability region has also been analyzed. It is shown that with the increase of magnetic parameter, M 3, and Darcy number, D a , the subcritical instability region between the two theories decreases quickly while with the increase of Taylor number, $$T_{A_1} $$ , the subcritical region expands. We also demonstrate coupling between the buoyancy and magnetic forces in the presence of rotation in nonlinear energy stability analysis as well as in linear instability analysis.

Technical advances in ubiquitous sensing, embedded computing, and wireless communication are leading to a new generation of engineered systems called cyber-physical systems (CPS). This field is attracting more and more attention from researchers, practitioners, as well as the governments. Technically, cyber-physical systems are integrations of computation, networking, and physical dynamics, in which embedded devices are massively networked to sense, monitor and control the physical world. CPS has been regarded as the next computing revolution. This revolution will be featured by the envisioned transform that CPS will make on how we interact with the physical world. To facilitate unprecedented interactions between human beings and the physical world, sensor networks will become a crucial ingredient of CPS due to the need for coupling geographically distributed computing devices with physical elements. The proliferation of affordable sensor network technologies has significantly contributed to recent progress in CPS. On the other hand, the unique features of CPS (e.g. cyber-physical coupling driven by new demands and applications) give rise to a lot of open challenges for design and deployment of sensor networks in such systems. In particular, high-confidence CPS requires the employed sensor networks to support real-time, dependable, safe, secure, and efficient operations. In this issue we are focused on latest research results in wireless sensor networks (WSNs) that address key issues related to high-confidence cyber-physical systems and applications. In response to our call-for-papers, we have received 36 submissions, out of which 15 papers are finally accepted as a result of thorough review process by international experts in respective areas. The selection provides a glimpse of the state-of-the-art research in the field. In the paper Game Theoretic Approach for Interuser Interference Reduction in Body Sensor Networks, Wu et al present a decentralized inter-user interference reduction scheme with non-cooperative game for body sensor networks (BSNs). A no-regret learning algorithm for reducing the effect of the inter-user interference with low power consumption is proposed. The correctness and effectiveness of the proposed scheme are theoretically proved, and experimental results demonstrate that the effect of inter-user interference can be reduced effectively with low power consumption.

<div class="section abstract"><div class="htmlview paragraph">This paper presents nonlinear bifurcation stability analysis of articulated vehicles with active trailer differential braking (ATDB) systems. ATDB systems have been proposed to improve stability of articulated vehicle systems to prevent unstable motion modes, e.g., jack-knifing, trailer sway and rollover. Generally, behaviors of a nonlinear dynamic system may change with varying parameters; a stable equilibrium can become unstable and a periodic oscillation may occur or a new equilibrium may appear making the previous equilibrium unstable once the parameters vary. The value of a parameter, at which these changes occur, is known as “bifurcation value” and the parameter is known as the “bifurcation parameter”. Conventionally, nonlinear bifurcation analysis approach is applied to examine the nonlinear dynamic characteristics of single-unit vehicles, e.g., cars, trucks, etc. Little attention has been paid to investigate the feasibility and effectiveness of the bifurcation analysis method for nonlinear stability analysis of articulated vehicles under varied operating conditions, e.g., varied forward speed and trailer payload. This motivates the research to examine stability boundaries of equilibrium and limit cycles in the parameter space and to predict qualitative changes in system’s behaviour (bifurcations) occurring at their equilibrium points. To this end, a nonlinear yaw-roll model with 6 degrees of freedom (DOF) is generated to simulate the nonlinear dynamics of articulated vehicles. The nonlinear yaw-roll model is also used to design an ATDB controller based on a fuzzy logic control technique. The bifurcation analysis based on the phase-plane method is conducted to evaluate the yaw and roll stability of the articulated vehicle. Built upon the conventional bifurcation analysis for single-unit vehicles, an innovative bifurcation analysis technique is developed in order to effectively assess the nonlinear stability of articulated vehicles. The applicability and effectiveness of the newly developed technique is examined and demonstrated.</div></div>

Cyber-physical systems (CPS) are considered the integration of physical systems in the real world and control software in computing systems. In CPS, the real world and the computing systems are connected through networks with real-time information exchange. The introduction of networking technologies in CPS has substantial advantages in terms of system efficiency, scalability, maintenance, and many more. However, CPS are vulnerable to malicious attackers intruding on the network. The attackers aim to destroy the physical systems with cyber-physical attacks, in which the main objective is to remotely cause malfunctions in physical systems through networks. Therefore, extensive research on cyber-physical security has been conducted to detect cyber-physical attacks and guarantee the stability of the physical systems under cyber-physical attacks. In this survey, we conduct an exhaustive review of the literature on threats to CPS and on resilient CPS design strategies. First, we discuss the structure of CPS, considering physical dynamics, computing systems, and networks. Then, we provide a taxonomy of cyber-physical attacks with three properties (attack space, attack location, and stealthiness). These three attributes represent the requirements for the implementation of cyber-physical attacks. We review existing studies on anomaly-detection strategies against cyber-physical attacks in terms of physics, networks, and machine learning techniques. Moreover, we analyze the impact of typical cyber-physical attacks and the constraints on attack implementations. In particular, for each of the well-established cyber-physical attacks, we present numerical examples that clearly illustrate the time responses of the physical systems with a conventional physics-based anomaly detector. We also review advances in the typical cyber-physical attacks and the detection methods for these attacks. Furthermore, we review resilient CPS designs in the context of control theory, network management, and data-driven technologies. We conclude the survey by identifying future research directions.

Rail transit is a typical Cyber-physical Systems (CPS). The study of urban rail transit CPS was carried out with the introduction of CPS into the urban rail transit system. Based on the analysis of CPS, the fundamental architecture of urban rail transit CPS was designed and the functions of corresponding layers were explained. The system model of urban rail transit CPS was proposed. The functions of the model and the interaction between each model were explained. The issue of heterogeneous networks integration in rail transit system and train system was analyzed. Meanwhile, according to the actual demand of security monitoring and management of train running, network controller between WSN and control bus was designed and verified. The results show that the network controller can well achieve data exchange between WSN and train network.

Benefitting from the advances in sensor nets, wireless communication, and embedded systems, the cyber-physical system (CPS) has been implemented in many practical areas. The cyber world and the physical world in CPS are closely linked and merged, guaranteeing the reliable and efficient performance of the physical world. The service-oriented CPS has been the hot research and development. In this paper, we present a novel velocity-profile prediction method based on the specific CPS architecture. Three main efforts have been made. First, a CPS architecture which is appropriate for velocity-profile prediction is built. Second, the hybrid velocity-profile prediction (HVPP) method is developed based on the exclusive CPS architecture. The HVPP method accomplishes the velocity-profile prediction by cooperatively employing different control units in CPS. Third, a case study in a plug-in hybrid electric vehicle (PHEV) is performed to evaluate the effect of CPS-based service in the real application. Results of the case study demonstrate that the HVPP method can improve the fuel economy of PHEV significantly.

Reliability assessment of a power system with cyber-physical interactive operation of photovoltaic systems

Sensor devices have been widely applied to variety applications, including internet of things (IoT), cyber physical systems (CPS) and environmental monitoring systems. Because all sensing data in such applications are very important for data analysis and mining in a host machine, sensor devices are equipped with non-volatile memory (NVM) [1] and nonvolatile processor [2], [3] to prevent sensing data in sensor nodes from data loss. As a result, sensing data can be permanently stored in a sensor device without the risk of data loss even if the battery of the sensor device is run out. Based on such observations, the lifetime of a sensor network should be redefined due to non-volatile technologies, such as NVM and NV processor. Conventionally, the lifetime of a sensor network is the time at which the first sensor node uses up its battery due to the consideration of sensor network QoS [4], [5]. However, since sensing data can be permanently stored in a local drive, the lifetime of a sensor network should be redefined as the time at which the first out-of-date data is produced in a sensor node. If the battery of a sensor node is run out but the sensor node does not contain any out-of-date data, the sensor node will be regarded as a moribund node. If all moribund nodes can be rescued by a rechargeable technology, the sensor network will be immortal. Such observations motivate us to design an energy-efficient solution to achieve the goal of immortal sensor network by exploiting the benefits of wireless charging vehicle.

For implementation of Cyber-Physical Systems (CPS) simulation, interoperability between physical and cyber system are required. IEEE High Level Architecture (HLA) is standard for distributed simulation interoperability, and ETSI Machine-to-Machine (M2M) is standard for integration between physical machines. In this paper, we propose M2MHLA adaptor to integrate HLA-based simulations and M2M physical machines. M2M-HLA adaptor is located between HLA simulation systems and M2M systems. This adaptor transforms HLA data to M2M data and M2M data to HLA data. We propose sequence structure between M2M-HLA APIs for interconnection, data type definition and transformation method and time management method for design and implementation M2M-HLA adaptor. Because of M2M-HLA adaptor allows interoperability between different cyber systems and physical systems, this would extend the scope of CPS simulation system and increase its utilization.

This paper proposes an integration framework for a sensors network in cyber-physical systems. The framework proposed is still an effort in development to ease the integration and management of software and hardware for sensor networks in cyber-physical systems. The parameters, modeling process and implementation of the framework presented in this work correspond to the first step of the modeling. Such step focuses on analysis and treatment of the functional requirements of the uses for the wireless sensor networks combined with a refined vision of the architecture and its main components.

We propose a gradient-based online optimization framework for solving stochastic programming problems that frequently arise in the context of cyber-physical and robotic systems. Our problem formulation accommodates constraints that model the evolution of a cyber-physical system, which has, in general, a continuous state and action space, is nonlinear, and where the state is only partially observed. We also incorporate an approximate model of the dynamics as prior knowledge into the learning process and show that even rough estimates of the dynamics can significantly improve the convergence of our algorithms. Our online optimization framework encompasses both gradient descent and quasi-Newton methods, and we provide a unified convergence analysis of our algorithms in a non-convex setting. We also characterize the impact of modeling errors in the system dynamics on the convergence rate of the algorithms. Finally, we evaluate our algorithms in simulations of a flexible beam, a four-legged walking robot, and in real-world experiments with a ping-pong playing robot.