| 1. |
- Cremona, Fabio, et al.
(författare)
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Hybrid co-simulation : it's about time
- 2019
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Ingår i: Software and Systems Modeling. - : Springer Nature. - 1619-1366 .- 1619-1374. ; 18:3, s. 1655-1679
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Tidskriftsartikel (refereegranskat)abstract
- Model-based design methodologies are commonly used in industry for the development of complex cyber-physical systems (CPSs). There are many different languages, tools, and formalisms for model-based design, each with its strengths and weaknesses. Instead of accepting some weaknesses of a particular tool, an alternative is to embrace heterogeneity, and to develop tool integration platforms and protocols to leverage the strengths from different environments. A fairly recent attempt in this direction is the functional mock-up interface (FMI) standard that includes support for co-simulation. Although this standard has reached acceptance in industry, it provides only limited support for simulating systems that mix continuous and discrete behavior, which are typical of CPS. This paper identifies the representation of time as a key problem, because the FMI representation does not support well the discrete events that typically occur at the cyber-physical boundary. We analyze alternatives for representing time in hybrid co-simulation and conclude that a superdense model of time using integers only solves many of these problems. We show how an execution engine can pick an adequate time resolution, and how disparities between time representations internal to co-simulated components and the resulting effects of time quantization can be managed. We propose a concrete extension to the FMI standard for supporting hybrid co-simulation that includes integer time, automatic choice of time resolution, and the use of absent signals. We explain how these extensions can be implemented modularly within the frameworks of existing simulation environments.
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| 2. |
- Cremona, Fabio, et al.
(författare)
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Step Revision in Hybrid Co-simulation with FMI
- 2016
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Ingår i: Proceedings of the 14th ACM-IEEE International Conference on formal Methods and Models for System Design (MEMOCODE). - : IEEE conference proceedings. - 9781509027910
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Konferensbidrag (refereegranskat)abstract
- This paper presents a master algorithm for co-simulation of hybrid systems using the Functional Mock-up Interface (FMI) standard. Our algorithm introduces step revision to achieve an accurate and precise handling of mixtures of continuous-time and discrete-event signals, particularly in the situation where components are unable to accurately extrapolate their input. Step revision provides an efficient means to respect the error bounds of numerical approximation algorithms that operate inside co-simulated FMUs. We first explain the most fundamental issues associated with hybrid co-simulation and analyze them in the framework of FMI. We demonstrate the necessity for step revision to address some of these issues and formally describe a master algorithm that supports it. Finally, we present experimental results obtained through our reference implementation that is part of our publicly available open-source toolchain called FIDE.
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| 3. |
- Lohstroh, Marten, et al.
(författare)
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Logical Time for Reactive Software
- 2023
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Ingår i: Proceedings of 2023 Cyber-Physical Systems and Internet-of-Things Week, CPS-IoT Week 2023. - : Association for Computing Machinery (ACM). ; , s. 313-318
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Konferensbidrag (refereegranskat)abstract
- Timing is an essential feature of reactive software. It is not just a performance metric, but rather forms a core part of the semantics of programs. This paper argues for a notion of logical time that serves as an engineering model to complement a notion of physical time, which models the physical passage of time. Programming models that embrace logical time can provide deterministic concurrency, better analyzability, and practical realizations of timing-sensitive applications. We give definitions for physical and logical time and review some languages and formalisms that embrace logical time.
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