Modeling Of Cyber-physical Systems Research Articles

Modeling and Vulnerability Analysis of Spatially Embedded Heterogeneous Cyber-Physical Systems With Functional Dependency

Modern infrastructures are always spatially embedded and coupled with auxiliary information systems to form heterogeneous cyber-physical systems (CPSs). In this paper, considering the spatial information and overlap of components, a heterogeneous cyber-physical system model with weak dependency is proposed, in which the two networks overlap geographically and have heterogeneous models. Based on the connectivity between their dependent cyber nodes and the control center, the physical edges are classified as controllable or uncontrollable, corresponding to global and local load transfer strategies, respectively. Combined with coordinated DoS (deny of service) attacks on cyber nodes, the system vulnerability under physical edge-removal and edge-overload scenarios is investigated. It can be concluded that although the two networks are weakly dependent without direct failure-induced dependency, a fragmented cyber system can still aggravate the failure of the physical system. In the edge-removal scenario, deliberately attacking high-load edges produces better results, while imposing extra load on low-load edges performs better in the edge-overload scenario. In addition, blocking specific cyber nodes that make attacked edges or their adjacent edges uncontrollable can effectively improve the attack effect. This model might yield insight into modeling and protecting spatial cyber-physical systems.

Features of virtual duplicate creation of the turning process

The interdisciplinary approach of MC-SUITE implementation of the Industry 4.0 concept and the main requirements for digital models (virtual duplicates) of cyber-physical systems regarding virtual processes compliance to the real ones and the possibility of real-time operation have been described. The main condition for creating an adequate dynamic model of technological processing system (TPS) interaction with the cutting process has been defined and a model for such interaction for the longitudinal turning has been developed. On example of developed turning process structural scheme the possibility of describing the interaction of the TPS input parameters (cutting depth and longitudinal feed) with the output parameters (deformations in the respective directions) due to changes in the model internal parameters in a form of cutting force components have been demonstrated. Such representation of the model allows virtual turning process adjusting by specifying the cutting stiffness and functional dependences for the cutting forces components based on the results of intelligent analytical processing of the monitoring results of the TPS operation.

Survey on test case generation, selection and prioritization for cyber‐physical systems

SummaryA cyber‐physical system (CPS) is a collection of computing devices that communicate with each other, operate in the target environment via actuators and interact with the physical world through sensors in a feedback loop. CPSs need to be safe and reliable and function in accordance with their requirements. Testing, focusing on a CPS model and/or its code, is the primary approach used by engineers to achieve this. Generating, selecting and prioritizing test cases that can reveal faults in CPSs, from the wide range of possible input values and stimuli that affect their operation, are of central importance in this process. To date, however, in our search of the literature, we have found no comprehensive survey of research on test case generation, selection and prioritization for CPSs. In this article, therefore, we report the results of a survey of approaches for generating, selecting and prioritizing test cases for CPSs; the results illustrate the progress that has been made on these approaches to date, the properties that characterize the approaches and the challenges that remain open in these areas of research.

Electric heater mathematical model for cyber-physical systems

The article discusses the heat and mass transfer dynamic model for an electric heater with lumped parameters, which allows transient processes simulation for the main influences. The proposed model is recommended to be used in cyber-physical systems for forecasting and evaluating the effectiveness of control systems integrated into a single information management system. The developed model can be used by specialists for the analysis and synthesis of control systems for balanced ventilation systems or industrial air conditioners. As an example, a numerical simulation of transient processes along the action main channels for an electric heater HE 36/2 manufactured by VTS CLIMA was carried out. The significant advantage of the proposed model is the possibility for using it for the synthesis and analysis of multidimensional control systems.

Multi-paradigm modeling for cyber–physical systems: A systematic mapping review

Cyber–Physical Systems (CPS) are heterogeneous and require cross-domain expertise to model. The complexity of these systems leads to questions about prevalent modeling approaches, their ability to integrate heterogeneous models, and their relevance to the application domains and stakeholders. The methodology for Multi-Paradigm Modeling (MPM) of CPS is not yet fully established and standardized, and researchers apply existing methods for modeling of complex systems and introducing their own. No systematic review has been previously performed to create an overview of the field on the methods used for MPM of CPS. In this paper, we present a systematic mapping study that determines the models, formalisms, and development processes used over the last decade. Additionally, to determine the knowledge necessary for developing CPS, our review studied the background of actors involved in modeling and authors of surveyed studies. The results of the survey show a tendency to reuse multiple existing formalisms and their associated paradigms, in addition to a tendency towards applying transformations between models. These findings suggest that MPM is becoming a essential approach to model CPS, and highlight the importance of future integration of models, standardization of development process and education.

Manufacturing Execution System Integration through the Standardization of a Common Service Model for Cyber-Physical Production Systems

Digital transformation and artificial intelligence are creating an opportunity for innovation across all levels of industry and are transforming the world of work by enabling factories to embrace cutting edge Information Technologies (ITs) into their manufacturing processes. Manufacturing Execution Systems (MESs) are abandoning their traditional role of legacy executing middle-ware for embracing the much wider vision of functional interoperability enablers among autonomous, distributed, and collaborative Cyber-Physical Production System (CPPS). In this paper, we propose a basic methodology for universally modeling, digitalizing, and integrating services offered by a variety of isolated workcells into a single, standardized, and augmented production system. The result is a reliable, reconfigurable, and interoperable manufacturing architecture, which privileges Open Platform Communications Unified Architecture (OPC UA) and its rich possibilities for information modeling at a higher level of the common service interoperability, along with Message Queuing Telemetry Transport (MQTT) lightweight protocols at lower levels of data exchange. The proposed MES architecture has been demonstrated and validated in several use-cases at a research manufacturing laboratory of excellence for industrial testbeds.

Digital twins as run-time predictive models for the resilience of cyber-physical systems: a conceptual framework.

Digital twins (DT) are emerging as an extremely promising paradigm for run-time modelling and performability prediction of cyber-physical systems (CPS) in various domains. Although several different definitions and industrial applications of DT exist, ranging from purely visual three-dimensional models to predictive maintenance tools, in this paper, we focus on data-driven evaluation and prediction of critical dependability attributes such as safety. To that end, we introduce a conceptual framework based on autonomic systems to host DT run-time models based on a structured and systematic approach. We argue that the convergence between DT and self-adaptation is the key to building smarter, resilient and trustworthy CPS that can self-monitor, self-diagnose and—ultimately—self-heal. The conceptual framework eases dependability assessment, which is essential for the certification of autonomous CPS operating with artificial intelligence and machine learning in critical applications.This article is part of the theme issue ‘Towards symbiotic autonomous systems’.

Adaptive observer-based attack location and defense strategy in smart grid

This article mainly focuses on the attack location and defense of cyber-physical power systems under dynamic load altering attacks. Taking the smart grid as an example, first, the cyber-physical power system model under attack is established to provide conditions for attack detection. On this basis, an adaptive observer with [Formula: see text] performance is designed to realize detection and location through residual signal and attack estimation, respectively. Furthermore, a power redistribution strategy based on optimal economic scheduling is presented to realize attack defense by means of the observer data. Finally, theoretical analysis proves the feasibility of the algorithm, and simulation cases prove the effectiveness of attack location and defense strategies.

Categorical Semantics of Cyber-Physical Systems Theory

Cyber-physical systems require the construction and management of various models to assure their correct, safe, and secure operation. These various models are necessary because of the coupled physical and computational dynamics present in cyber-physical systems. However, to date the different model views of cyber-physical systems are largely related informally, which raises issues with the degree of formal consistency between those various models of requirements, system behavior, and system architecture. We present a category-theoretic framework to make different types of composition explicit in the modeling and analysis of cyber-physical systems, which could assist in verifying the system as a whole. This compositional framework for cyber-physical systems gives rise to unified system models, where system behavior is hierarchically decomposed and related to a system architecture using the systems-as-algebras paradigm. As part of this paradigm, we show that an algebra of (safety) contracts generalizes over the state of the art, providing more uniform mathematical tools for constraining the behavior over a richer set of composite cyber-physical system models, which has the potential of minimizing or eliminating hazardous behavior.

Modeling of Time-Delayed Distributed Cyber-Physical Power Systems for Small-Signal Stability Analysis

Compared with a power system under centralized control, a power system under fully distributed control has stronger interdependence between its physical side and cyber side. Such a system is a typical cyber-physical system (CPS). The time delay problem is one of the most critical issues in the application of distributed control for power systems. First, a distributed information flow model is established considering multiple sources of time delay, especially the communication delay between neighboring agents. Second, combining the dynamics of physical power systems, a general model of time-delayed CPS under fully distributed control is proposed, especially for inverter-based microgrids. Third, the stability of the time-delayed CPS is analyzed based on the proposed model with a critical eigenvalue tracking algorithm. A real-world microgrid with DGs under fully distributed frequency control is tested for small-signal stability analysis. The findings show that the stability of the distributed CPS with multiple sources of time delay depends on not only the absolute value of time delays but also the coordination of time delays and that the delay merging property in centralized mode is not relevant in a distributed CPS. The accuracy of the model and the obtained stability margin are verified by Simulink simulations.

Multi-State Reliability Assessment Model of Base-Load Cyber-Physical Energy Systems (CPES) during Flexible Operation Considering the Aging of Cyber Components

Cyber-Physical Energy Systems (CPESs) are energy systems which rely on cyber components for energy production, transmission and distribution control, and other functions. With the penetration of Renewable Energy Sources (RESs), CPESs are required to provide flexible operation (e.g., load-following, frequency regulation) to respond to any sudden imbalance of the power grid, due to the variability in power generation by RESs. This raises concerns on the reliability of CPESs traditionally used as base-load facilities, such as Nuclear Power Plants (NPPs), which were not designed for flexible operation, and more so, since traditionally only hardware components aging and stochastic failures have been considered for the reliability assessment, whereas the contribution of the degradation and aging of the cyber components of CPSs has been neglected. In this paper, we propose a multi-state model that integrates the hardware components stochastic failures with the aging of cyber components, and quantify the unreliability of CPES in load-following operations under normal/emergency conditions. To show the application of the reliability assessment model, we consider the case of the Control Rod System (CRS) of a NPP typically used for a base-load energy supply.

Model design as a new socio-cyber-physical systems creating mechanism

The purpose of this work is to consider the methodology of designing intellectual models of cyber-physical social systems that take into account the cybernetic properties of the hardware, software and the human factor specifics of the system developers and users. To ensure customizable solutions, model design process is based on systems analysis. This methodology can be implemented by optimizing the objective tree, which determines the development vector of the model being designed based on their importance; the information tree, which determines the structure of the knowledge base optimized by the cost of resources used; the task tree, which allows optimizing the development of the cyber-physical social systems based on the results of analyzing the criteria of the two trees. Intellectual properties of the model being designed are determined by automating the management of its development vector in accordance with the dynamics of the utility of its specific goals. Due to practical limitations on the amount of resources available, the task is to optimize the plan for creating a cyber-physical social system that maximizes the solution value with limited cost. The choice between more precise algorithms that are not applicable given fuzzy limitations caused by human factor allows solving the problems faster than when using deterministic or heuristic methods.

Coordinated Cyber-Attack Detection Model of Cyber-Physical Power System Based on the Operating State Data Link

Existing coordinated cyber-attack detection methods have low detection accuracy and efficiency and poor generalization ability due to difficulties dealing with unbalanced attack data samples, high data dimensionality, and noisy data sets. This paper proposes a model for cyber and physical data fusion using a data link for detecting attacks on a Cyber–Physical Power System (CPPS). The two-step principal component analysis (PCA) is used for classifying the system’s operating status. An adaptive synthetic sampling algorithm is used to reduce the imbalance in the categories’ samples. The loss function is improved according to the feature intensity difference of the attack event, and an integrated classifier is established using a classification algorithm based on the cost-sensitive gradient boosting decision tree (CS-GBDT). The simulation results show that the proposed method provides higher accuracy, recall, and F-Score than comparable algorithms.

Cyber‐physical component ranking for risk sensitivity analysis using betweenness centrality

This article proposes a model for critical component ranking in power system risk analysis using a proposed cyber-physical betweenness centrality (CPBC) index. Risk assessment, as part of the contingency analysis, is a critical activity that can identify and evaluate component outages that lead to system vulnerability, aiding operators to improve resilience. A power system cyber-physical risk assessment model is proposed that calculates and offers an efficient protection strategy to the system operator based on component vulnerability to adversaries and the impact of compromised assets on the system operation. We present the CPBC index, which traverses generated attack graphs to rank components according to their importance in reducing adversary impact on the power system. The CPBC extends upon betweenness centrality and integrates into analysis, the services and security cost of communications between system components, as well as the likelihood of component exploitation as an adversary medium to the target relays. The proposed model recommends actions, taking into account the interconnections between cyber and physical components as well as cyber-induced Common Vulnerabilities and Exposure scores associated with these connections, thus protecting critical components. The proposed model is implemented on the Cyber-Physical Situational Awareness 8-substation and extended IEEE 300-bus cyber-physical power system models, and results are presented on the impacts of the proposed component ranking model on the security-aware operation of the power system.

An actor-based framework for asynchronous event-based cyber-physical systems

In cyber-physical systems like automotive systems, there are components like sensors, actuators, and controllers that communicate asynchronously with each other. The computational model of actors supports modeling distributed asynchronously communicating systems. We propose the Hybrid Rebeca language to support the modeling of cyber-physical systems. Hybrid Rebeca is an extension of the actor-based language Rebeca. In this extension, physical actors are introduced as new computational entities to encapsulate physical behaviors. To support various means of communication among the entities, the network is explicitly modeled as a separate entity from actors. We develop a tool to derive hybrid automata as the basis for the analysis of Hybrid Rebeca models. We demonstrate the applicability of our approach through a case study in the domain of automotive systems. We use the SpaceEx framework for reachability analysis of the case study. Compared to hybrid automata, our results show that for event-based asynchronous models hybrid Rebeca improves analyzability by reducing the number of real variables, and increases modularity and hence, minimizes the number of changes caused by a modification in the model.

Ontological models of cyber physical systems

A version of developing an ontological model of a cyber physical system of the high level is offered in this paper. The description of the individual elements used in the developed ontological model is presented. The basic formular description of the high level ontology in the logical language of predicates is given. Realizations of particular cases of cyber physical systems are also given using three examples: a conveyor system for processing parts based on Festo, Smart Grids and Part Sequence Sorting System. For each of the models shown, a complete description of the indoor units is provided. Ontological models are based on the use of the concept of functional-block implementation, since this method is the most successful at present. As an intermediate model for adding rules, Prolog is used, whereof transmission into a set of function blocks will take place in the future.

Metrological support integration in conditions of digital transformation

The article formulates the problems of the development of measurement control regulators in digital platforms. Attention is paid to the role of the digital revolution and metrology on the economy of enterprises and the transformation of the service sector model as a whole. Attention is paid to the impact of the digital revolution and metrology on the economy. The article presents and substantiates the policy of introduction of metrological support for innovative development in the context of the digital cybernetic revolution. The proposed policy pays attention to the consideration of the fundamental model of cyber-physical systems, as a technological basis for the implementation of a new industrial evolution in metrological context. The importance of organizing of measurement principles in network infrastructure and communication protocols in the context of economic transformation is emphasized. A model of the use and implementation of chaos engineering and information technologies in metrological apparatus is considered.

Parallel simulation of cyber-physical systems

Model-based design (MBD) in systems engineering is a well-accepted technique to abstract, analyze, verify, and validate complex systems. In MBD, we design a mathematical model of the system to virtually execute and test systems via model simulations to understand the system dynamics better. Computing model simulations has their challenges; one is to ensure that the simulation trajectory preserves the model semantics. Besides, computing many simulation trajectories over a long time-horizon must be time efficient for rapid respond to system engineers. In this work, we address these challenges in simulating models of cyber-physical systems (CPS), particularly systems possessing mixed discrete–continuous dynamics. We focus on the subclass of CPS’s hybrid automata models, where Jump predicates are restricted to polygonal constraints and present a numerical simulation engine that can efficiently compute many random simulations in parallel by exploiting the parallel computing capability in modern multicore processors. Our simulation engine implements a lock-free parallel breadth-first-search (BFS)-like algorithm and is implemented in the model-checking tool XSpeed. In addition, an application of our simulation engine in property verification of CPS models has been illustrated on two benchmarks. Some model coverage metrics have been defined that users of the tool can specify to set the desired thoroughness of testing with simulations. We demonstrate the performance gains of our simulation engine over SpaceEx and CORA, the modern model checkers and simulators for affine hybrid systems.

Analysis of cascading failures of power cyber-physical systems considering false data injection attacks

This study considers the performance impacts of false data injection attacks on the cascading failures of a power cyber-physical system, and identifies vulnerable nodes. First, considering the monitoring and control functions of a cyber network and power flow characteristics of a power network, a power cyber-physical system model is established. Then, the influences of a false data attack on the decision-making and control processes of the cyber network communication processes are studied, and a cascading failure analysis process is proposed for the cyber-attack environment. In addition, a vulnerability evaluation index is defined from two perspectives, i.e., the topology integrity and power network operation characteristics. Moreover, the effectiveness of a power flow betweenness assessment for vulnerable nodes in the cyber- physical environment is verified based on comparing the node power flow betweenness and vulnerability assessment index. Finally, an IEEE14-bus power network is selected for constructing a power cyber-physical system. Simulations show that both the uplink communication channel and downlink communication channel suffer from false data attacks, which affect the ability of the cyber network to suppress the propagation of cascading failures, and expand the scale of the cascading failures. The vulnerability evaluation index is calculated for each node, so as to verify the effectiveness of identifying vulnerable nodes based on the power flow betweenness.

Formalized description of cyber-physical systems models using temporary non-deterministic automata

The principles of building finite state automata taking into account temporal logic were considered. In this case, time delays of the input symbol are added to the elements of the finite state automaton, which allow the automaton to change its state without producing an output symbol, as well as delays of the output symbol that determine the necessary time interval for the corresponding transition. The main approaches to the definition of the concept of a process, such as “process is a state” and “process is a transition”, which are characterized by the principles of signal processing, taking into account the possibility of saving the state and forming a queue for signal processing, are distinguished. The scientific novelty of this article lies in the approach to the formation of a hierarchical cyber system and the use of temporary SNDA. This method allows to synchronize processes in multithreaded data processing in complex organized, multilevel systems and excludes the possibility of unstable operation, and also improves the performance of the entire complex. As a visual representation of the model of the created principle of temporal non-deterministic automata, a system of grinding and transferring grain in a mill was used.