Requirements for hybrid cosimulation standards

Abstract

This paper defines a suite of requirements for future hybrid cosimulation standards, and specifically provides guidance for development of a hybrid cosimulation version of the Functional Mockup Interface (FMI). A cosimulation standard defines interfaces that enable diverse simulation tools to interoperate. Specifically, one tool defines a component that forms part of a simulation model in another tool. We focus on components with inputs and outputs that are functions of time, and specifically on mixtures of discrete events and continuous time signals. This hybrid mixture is not well supported by existing cosimulation standards, and specifically not by FMI 2.0, for reasons that are explained in this paper. The paper defines a suite of test components, giving a mathematical model of an ideal behavior, plus a discussion of practical implementation considerations. The discussion includes acceptance criteria by which we can determine whether a standard supports definition of each component. In addition, we define a set of test compositions that define requirements for coordination between components, including consistent handling of timed events.

Hybrid co-simulation: it’s about time

“…Broman et al [8] give the model shown in Fig. 1 as a "simplest possible" nontrivial illustration of the challenges of hybrid co-simulation.…”

“…For instance, the "getMaxStepSize" function of [7] is similar to the D ("deadline") function of [48]. Followup work includes [8], which proposes a collection of test cases together with acceptance criteria that can be used to determine whether a hybrid co-simulation technique is acceptable. Tripakis [47] investigates techniques to bridge the semantic gap between various formalisms (state machines, discrete-event models, dataflow, etc.)…”

“…In contrast to the above quote from Broman et al [8], and to avoid confusion with the term precision in measurement theory, henceforth we will in this article use the term resolution instead of precision to denote the grain at which we can tell apart two distinct time stamps. Note that properties 2 and 3 are not satisfied by floatingpoint numbers due to rounding errors [21].…”

“…The current standard for co-simulation (version 2.0 [38]), however, is unable to correctly simulate many mixed discrete and continuous behaviors, limiting its utility in current form for model-based design for CPS [8]. As a consequence, the community-driven standardization process is considering another mechanism called hybrid co-simulation that strives for the loose coupling of co-simulation, but with support for discrete and discontinuous signals and instantaneous events.…”

“…Instead of accepting some weaknesses of a particular tool, an alternative Communicated by Prof. J. Sztipanovits, M. Broy, and H. Daembkes. This work is partially based on previous work published by the authors [7,8,15] 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.…”