Simulation Of Cyber-physical Systems Research Articles

Equation-Based Modeling with Modelica – Principles and Future Challenges

Modelica is a well-established, open standard for the modeling and simulation of cyber-physical systems. Since it is based on equations, this modeling language is applicable to a multitude of physical domains and especially suited for complex physical systems and their control. This paper provides a brief introduction on the kind of equation-based modelling promoted by Modelica and its underlying core principles. The paper then describes its current state in development and outlines the most important technology trends for its future development.

Design of Multidisciplinary Cyber Physical Systems

A cyber-physical system (CPS) is a system of collaborating computational elements that control and interact with physical entities. These systems can be found in areas such as aerospace, automotive, energy, healthcare, manufacturing, entertainment, and consumer appliances, and can also be categorized as embedded systems, mechatronics, and smart X. In embedded systems the emphasis is on the computational elements, while mechatronic systems focus on the link between the computational and physical elements in terms of mechanical, electronics, control engineering and computer science domains. The design of cyber physical systems (mechatronics, embedded systems, smart X, etc.) is quite distinctive from any other designs, because they address highly complex multidisciplinary issues related to the combination of product/system/service (Rauniyar & Tanik, 2010). The inherent complexity in the design task due to the multidisciplinary aspects of CPS put high stress on engineers’ creativity to produce more innovative solutions. These challenges are known by the Engineering Design community in mechatronics (TorrySmith et al., 2013) but are exacerbated by the added layers of the cyber communication between the different objects, as well as the several challenges of possible IT service design which are of a different engineering nature (Dargahi et al., 2012; Wang, 2012). Therefore, assisting design engineers in design tasks as well as reducing the intrinsic complexity of the modeling is of crucial importance. This can be achieved by either design support tools or new methodologies that would make the design easier and simpler. The papers in this this special issue present the state of the art and advanced techniques related to the development, modelling and simulation of complex CPS. We cover controller design using system architecture, video servoing of robotic systems as well as characterisation of an instrumented dynamic flexible structure. The first paper written by Alvarez Cabrera and Tomiyama entitled “Architecture-Level Representation and Analysis of Regulatory Controller Configuration for Complex Mechatronic Systems” provides a method for automatically extracting information that is relevant for the controller design activities from a model that represents architecture-level information and concerns, and shows how the extracted information can be analyzed for control design purposes. Control design is closely linked to several subsystems within the cyber physical system, and the authors put architecture-level models at the core of the design activities of the control systems. The main contributions of this paper are the use of an architecture model and the extraction of information relevant to control design from it, while the control analysis process is taken from existing linear structured system techniques. The authors’ work provides great insight into how to improve control design, an inherently multidisciplinary, from improvements in the communication and exchange of updated design information between stakeholders during product development of CPS. The second paper, entitled “A Comparative Study on Eye-In-Hand Image-Based Visual Servoing; Stereo vs. Mono” written by Mohebbi et al. presents an application in visual servoing robotics, where

SimConnect and SimTalk for distributed cyber-physical system simulation

Real-time embedded and cyber-physical systems challenge simulation disciplines due to the heterogeneous tools used to model components in the system exploration and design phases. Termed “heterogeneity,” the mixed-model problem challenges multi-simulator coordination, where event causality must be preserved among simulators with different models of computation, signals, criteria for time advancement, and levels of abstraction. SimConnect and SimTalk enable heterogeneous, distributed, hardware/software co-simulation with a simplified backplane approach, emphasizing the simulation of software interacting with simulated world-model electrical, mechanical, and physical effects. The structure of SimConnect and SimTalk is described, adhering to the properties of a Kahn Process Network. Application of the tools to the coordination of three different simulators (TExaS, Ngspice, and Simulink) is presented to simulate closed-loop, hardware/software-based, Proportional-Integral-Derivative/Pulse-Width-Modulated control of a direct current motor. Results demonstrate agreement among simulator coordinations with configurable tradeoffs in speed versus accuracy.

Using complex event processing for modelling and simulation of cyber-physical systems

We consider critical infrastructures as cyber-physical systems (CPS). Although simulations play an important role for CPS, no single simulator is available to simulate different depending CI. Therefore, interoperability of simulators in federated simulations is an important requirement. For modelling and simulation of CPS behaviour, both physical and control aspects have to be considered. CPS control is essentially based on events, states and reactions. Today there are mature numerical simulations for physical behaviours, whereas control is frequently treated in a restricted and ad-hoc manner. We present and analyse different simulator integration approaches based on explicit semantic models and show how they improve the modelling and simulation capabilities of federated simulations in CPS. We demonstrate how complex event processing and reactive rules allow the description of CPS behaviour on the event and action level and the integration of control into federated simulations.

A Study on Design of Communication Protocol for CPS Simulation

The term “cyber-physical system (CPS)” refers to a computing system that integrates physical processes and computational devices via a network. There are many physical and computational devices in a CPS, which can function automatically through inter-device interactions. Because a CPS is usually used for large-scale complex systems, to ensure reliable CPS operation, its design and execution should be verified through simulations. For CPS simulation, a communication protocol should be established for data transmission between physical systems and the corresponding simulation models during the simulation, including control algorithms for regulating differences between the two systems. First, because physical systems and simulation models are advanced in real time and logical time, respectively, time regulation methods should be included in the control algorithm. Second, to simulate various types of physical systems, a flexible simulation environment, independent of the operating environment such as the type of communication middleware, is required. In this paper, we propose a communication protocol for data transmission between physical systems and simulation models via a middle layer that contains the policies for handling the two different clocks of each system: virtual and real. The proposed communication protocol can be used not only for communication between the two systems but also for overcoming the problems caused by the differences in their operating environments. The contribution of this work is in that it defines a communication protocol and proposes methods for controlling different types of systems.

A model-based software development method for automotive cyber-physical systems

The development of automotive cyber-physical systems (CPS) software needs to consider not only functional requirements, but also non-functional requirements and the interaction with physical environment. In this paper, a model-based software development method for automotive CPS (MoBDAC) is presented. The main contributions of this paper are threefold. First, MoBDAC covers the whole development workflow of automotive CPS software from modeling and simulation to code generation. Automatic tools are used to improve the development efficiency. Second, MoBDAC extracts nonfunctional requirements and deals with them in the implementation model level and source code level, which helps to correctly manage and meet non-functional requirements. Third, MoBDAC defines three kinds of relations between uncertain physical environment events and software internal actions in automotive CPS, and uses Model Modifier to integrate the interaction with physical environment. Moreover, we illustrate the development workflow of MoBDAC by an example of a power window development.

Generic framework for design, modeling and simulation of cyber physical systems

Wireless technologies have contributed to extensive development of many kinds of applications that enable cost-effective and intelligent monitoring and control of physical environments, objects, activities such as smart buildings, home or industry automation, and remote patient care. These kinds of applications often require support of heterogeneous physical environments and large-scale systems mixing several different types of monitoring and control. In addition to heterogeneity and scalability support, mobility support is crucial in the development of these software systems. Although much research has addressed design, modeling and simulation of such systems, most solutions usually do not cover all requirements from different domains. Rather, these solutions restrict the development environment and reduce flexibility of design by enforcing the use of a specific software platform and tightly-coupled tools. This paper presents problems and challenges of Cyber Physical Systems (CPS) like the aforementioned applications, and discusses features and benefits of a generic framework to enable design, modeling and simulation of large-scale, heterogeneous CPS systems in an integrated manner.