Reconciling interoperability with efficient Verification and Validation within open source simulation environments

Abstract

A Cyber-Physical System (CPS) comprises physical as well as software subsystems. Simulation-based approaches are typically used to support design and Verification and Validation (V&V) of CPSs in several domains such as: aerospace, defence, automotive, smart grid and healthcare. Accordingly, many simulation-based tools are available to support CPS design. This, on one side, enables designers to choose the toolchain that best suits their needs, on the other side poses huge interoperability challenges when one needs to simulate CPSs whose subsystems have been designed and modelled using different toolchains. To overcome such an interoperability problem, in 2010 the Functional Mock-up Interface (FMI) has been proposed as an open standard to support both Model Exchange (ME) and Co-Simulation (CS) of simulation models created with different toolchains. FMI has been adopted by several modelling and simulation environments. Models adhering to such a standard are called Functional Mock-up Units (FMUs). Indeed FMUs play an essential role in defining complex CPSs through, e.g., the System Structure and Parametrization (SSP) standard.Simulation-based V&V of CPSs typically requires exploring different simulation scenarios (i.e., exogenous input sequences to the CPS under design). Many such scenarios have a shared prefix. Accordingly, to avoid simulating many times such shared prefixes, the simulator state at the end of a shared prefix is saved and then restored and used as a start state for the simulation of the next scenario. In this context, an important FMI feature is the capability to save and restore the internal FMU state on demand. This is crucial to increase efficiency of simulation-based V&V. Unfortunately, the implementation of this feature is not mandatory and it is available only within some commercial software. As a result, the interoperability enabled by the FMI standard cannot be fully exploited for V&V when using open-source simulation environments.

Model‐driven engineering for simulation models interoperability: A case study in space industry

“…Also, several approaches were proposed for integrating model‐based co‐simulation technologies (e.g., Reference 34). In 2010 the Functional Mock‐up Interface (FMI) was proposed and adopted as an open standard to support both model exchange and co‐simulations of simulation models created with different tool chains (see, e.g., Reference 35 or for a full list 36 . Reference 37 proposed the development of an interface between architectural models and the co‐simulation framework in the domain of complex smart grid.…”

Optimizing Highly-Parallel Simulation-Based Verification of Cyber-Physical Systems

“…It is a mixed-mode analog circuit converting the DC input voltage (denoted as V i ) to a desired DC output voltage (V o ), often used off-chip to scale down the typical laptop battery voltage (12-24 V) to the few volts needed by, e.g., a laptop processor (the load) as well as on-chip to support dynamic voltage and frequency scaling in multicore processors (see, e.g., [40]). A BDC converter is self-regulating, i.e., it is able to maintain the desired output voltage V o notwithstanding variations in the input voltage V i or in the load R. We used a Modelica model of the fuzzy logic-based BDC controller of [47], converted into an FMU 2.0 object via the JModelica extension in [45].…”

Any-Horizon Uniform Random Sampling and Enumeration of Constrained Scenarios for Simulation-Based Formal Verification

“…The latter are opaque binary objects defining dynamical systems according to the Functional Mock-up Interface (FMI) open standard for model exchange. As such, FMUs can be automatically generated from 100+ different simulation platforms, including Modelica simulators (also open source implementations via, e.g., [60]), Mathworks Stateflow/Simulink, and SBML (via, e.g., the tool in [41]).…”

“…This means it needs to access only the monitor initial state and input space, and to repeatedly invoke the monitor transition function (and get the resulting states, even if as opaque objects). Saving and restoring monitor states during search is implemented either within our software (for Python-defined monitors) or by exploiting the FMI API (for FMU-defined monitors, for which we used the implementation in [60]).…”