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In this paper we present an experience report for the RMQFMU, a plug and play tool, that enables feeding data to/from an FMI2-based co-simulation environment based on the AMQP protocol. Bridging the co-simulation to an external environment allows on one side to feed historical data to the co-simulation, serving different purposes, such as visualisation and/or data analysis. On the other side, such a tool facilitates the realisation of the digital twin concept by coupling co-simulation and hardware/robots close to real-time. In the paper we present limitations of the initial version of the RMQFMU with respect to the capability of bridging co-simulation with the real world. To provide the desired functionality of the tool, we present in a step-by-step fashion how these limitations, and subsequent limitations, are alleviated. We perform various experiments in order to give reason to the modifications carried out. Finally, we report on two case-studies where we have adopted the RMQFMU, and provide guidelines meant to aid practitioners in its use., To be submitted in brief format to 19th overture workshop

To demystify the Digital Twin concept, we built a simple yet representative thermal incubator system. The incubator is an insulated box fitted with a heatbed, and complete with a software system for communication, a controller, and simulation models. We developed two simulation models to predict the temperature inside the incubator, one with two free parameters and one with four free parameters. Our experiments showed that the latter model was better at predicting the thermal inertia of the heatbed itself, which makes it more appropriate for further development of the digital twin. The hardware and software used in this case study are available open source, providing an accessible platform for those who want to develop and verify their own techniques for digital twins.

This volume contains the papers presented at the 19th International Overture Workshop, which was held in an hybrid format: online and physically at Aarhus, Denmark on 22th October 2021. This event was the latest in a series of workshops around the Vienna Development Method (VDM), the open-source project Overture, and related tools and formalisms. VDM is one of the longest established formal methods for systems development. A lively community of researchers and practitioners has grown up in academia and industry around the modelling languages (VDM-SL, VDM++, VDM-RT, CML) and tools (VDMTools, Overture, VDM VSCode extension, Crescendo, Symphony, the INTO-CPS chain, and ViennaTalk). Together, these provide a platform for work on modelling and analysis technology that includes static and dynamic analysis, test generation, execution support, and model checking. This workshop provided updates on the emerging technology of VDM/Overture, including collaboration infrastructure, collaborative modelling and co-simulation for Cyber-Physical Systems.

In this work, we present the initial steps in the development of a digital twin of the agricultural autonomous vehicle, Robotti. A model of the vehicle dynamics is initially developed in the open-source multi-physics code, Chrono, and then wrapped as a Functional Mock-up Unit. We provide an overview of the envisioned digital twin system and a description of currently implemented features. The dynamic system of the vehicle chassis is characterised by the implementation of a revolute joint that ensures wheel–surface contact in uneven terrain. The vehicle dynamics model is applied for testing two scenarios describing the loads on the vehicle as a consequence of this mechanism. Finally, we give pointers to future work on modelling the Robotti and the establishment of a digital twin.

The accuracy of the result of a co-simulation is dependent on the correct initialization of all the simulation units. In this work, we consider co-simulation where the simulation units are described as Functional Mock-up Units (FMU). The Functional Mock-up Interface (FMI) specification specifies constraints to the initialization of variables in the scope of a single FMU. However, it does not consider the initialization of interconnected variables between instances of FMUs. Such interconnected variables place particular constraints on the initialization order of the FMUs. The approach taken to calculate a correct initialization order is based on predicates from the FMI specification and the topological ordering of both internal connections and interconnected variables. The approach supports the initialization of co-simulation scenarios containing algebraic loops using fixed point iteration. The approach has been realized as a plugin for the open-source INTO-CPS Maestro 2 Co-simulation framework. It has been tested for various scenarios and compared to an existing Initializer that has been validated through academic and industrial application.

Simulation-based analyses of cyber-physical systems are increasingly vital. Co-simulation is one such technique that enables the coupling of specialized simulation tools through an orchestration algorithm. The orchestrator dictates how each simulation tool should simulate its corresponding subsystem. Obtaining correct simulation results requires an implementation-aware orchestration algorithm tailored to the specific scenario, without the orchestrator knowing each simulation tool’s implementation. Such an algorithm should stabilize algebraic loops, perform time step negotiation, and adhere to each simulation tool’s implementation. This paper describes an approach and implementation to prove that a given orchestration algorithm respects all contracts related to the simulation units’ implementation. The approach has been applied to an industrial case study and other complex scenarios. The tool and results are available online.

Automated monitoring of deployed Cyber-physical Systems while they are operating can assist in detecting misbehavior. One way to achieve such monitoring is via co-simulation of a modelled system that corresponds to the deployed system. A necessary element in the realization of such a concept is data brokering between the systems. Our work addresses the topic of brokering external data into an Functional Mock-up Interface (FMI) 2.0 enabled co-simulation via a Functional Mock-up Unit (a simulation unit) called RabbitMQ FMU that outputs messages from an external message queue into the FMI enabled co-simulation.Our contribution includes a formal specification that captures the semantics of RabbitMQ FMU and ensures a maximum delay on the messages relayed to the co-simulation even through an unreliable network. This formal specification is then used to generate test cases that exercise all states and transitions of the formal specification. The implementation is then subjected to these test cases to verify that it is a refinement of the specification. The verification procedure is ongoing and currently the implementation has successfully been subjected to 1,539,246 tests. The RabbitMQ FMU provides a general and self-contained solution to brokering external data into and FMI-enabled co-simulation with guaranteed delays.

Co-simulation consists of the theory and techniques to enable global simulation of a coupled system via the composition of simulators. Despite the large number of applications and growing interest in the challenges, the field remains fragmented into multiple application domains, with limited sharing of knowledge. This tutorial aims at introducing co-simulation of continuous systems, targeted at researchers new to the field.

Despite the large number of applications and growing interest in the challenges that co-simulation poses, the field is fragmented into multiple application domains, with limited sharing of knowledge. This demo promotes a deeper understanding of a well known stabilization feature in co-simulation, which is used in the INTO-CPS tool chain. We develop the techniques that explain the empirical results of instability of the double mass-spring-damper system, and how to the stabilization feature improves the results. Moreover, we show how the restrictions of the Functional Mock-up Interface Standard impacts stability.

International audience; In the engineering of heterogeneous systems, there have always been challenges related to ensuring a common understanding of the interfaces between the constituent systems.

It is essential to find new ways of enabling experts in different disciplines to collaborate more efficient in the development of ever more complex systems, under increasing market pressures. One possible solution for this challenge is to use a heterogeneous model-based approach where different teams can produce their conventional models and carry out their usual mono-disciplinary analysis, but in addition, the different models can be coupled for simulation (co-simulation), allowing the study of the global behavior of the system. Due to its potential, co-simulation is being studied in many different disciplines but with limited sharing of findings. Our aim with this work is to summarize, bridge, and enhance future research in this multidisciplinary area. We provide an overview of co-simulation approaches, research challenges, and research opportunities, together with a detailed taxonomy with different aspects of the state of the art of co-simulation and classification for the past five years. The main research needs identified are: finding generic approaches for modular, stable and accurate coupling of simulation units; and expressing the adaptations required to ensure that the coupling is correct., Comment: 157 pages, about 30 figures