Graham Hemingway

Rapid synthesis of high-level architecture-based heterogeneous simulation: a model-based integration approach

Virtual evaluation of complex command and control concepts demands the use of heterogeneous simulation environments. Development challenges include how to integrate multiple simulation engines with varying semantics and how to integrate simulation models and manage the complex interactions between them. While existing simulation frameworks may provide many of the required run-time services needed to coordinate among multiple simulation engines, they lack an overarching integration approach that connects and relates the interoperability of heterogeneous domain models and their interactions. This paper outlines some of the challenges encountered in developing a command and control simulation environment and discusses our use of the Generic Modeling Environment tool suite to create a model-based integration approach that allows for rapid synthesis of complex high-level architecture-based simulation environments.

Automated synthesis of Time-Triggered Architecture-based TrueTime models for platform effects simulation and analysis

The TrueTime toolbox simulates real-time control systems, including platform-specific details like process scheduling, task execution and network communications. Analysis using these models provides insight into platform-induced timing effects, such as jitter and delay. For safety-critical applications, the Time-Triggered Architecture (TTA) has been shown to provide the necessary services to create robust, fault-tolerant control systems. Communication induced timing effects still need to be simulated and analyzed even for TTA-compliant models. The process of adapting time-invariant control system models, through the inclusion of platform specifics, into TTA-based TrueTime models requires significant manual effort and detailed knowledge of the desired platforms execution semantics. In this paper, we present an extension of the Embedded Systems Modeling Language (ESMoL) tool chain that automatically synthesizes TTA-based TrueTime models. In our tools, timeinvariant Simulink models are imported into the ESMoL modeling environment where they are annotated with details of the desired deployment platforms. A constraint-based offline scheduler then generates the static TTA execution schedules. Finally, we synthesize new TrueTime models that encapsulate all of the TTA execution semantics. Using this approach it is possible to rapidly prototype, evaluate, and modify controller designs and their hardware platforms to better understand deployment induced performance and timing effects.

Model-based integration technology for next generation electric grid simulations

Simulation-based evaluation of the behavior of the electric grid is complex, as it involves multiple, heterogeneous, interacting cyber-physical system like domains. Each simulation domain has sophisticated tools, but their integration into a coherent framework is a very difficult, time-consuming, laborintensive, and error-prone task. This means that computational studies cannot be done rapidly and the process does not provide timely answers to the planners, operators and policy makers. Furthermore, grid behavior has to be tested against a number of scenarios and situations, meaning that a huge number of simulations must be executed covering the potential space of possibilities. Designing and efficiently deploying such computational experiments by utilizing multi-domain tools for integrated smart grid is a major challenge. This paper addresses these important issues by integrating multiple modeling tools from diverse domains in a single coherent framework for integrated simulation of smart grids.

Model-based tool-chain infrastructure for automated analysis of embedded systems

In many safety-critical applications of embedded systems, the system dynamics exhibits hybrid behaviors. To enable automatic analysis of these embedded systems, many analysis tools have been developed based on hybrid automata model. These tools are constructed by their own domain-specific modeling languages (DSMLs) but they are different in various aspects. To enable meaningful semantic interpretation of DSMLs, we propose an infrastructure for semantic anchoring that facilitates the transformational specification of DSML semantics. In the semantic anchoring infrastructure, the semantics of a DSML can be anchored to a well-defined semantic unit, which captures the operational semantics of hybrid automaton, via model transformation. The Abstract State Machine (ASM) is used as the underlying formal framework for the semantic unit. The semantics of a DSML is defined by specifying the transformation between the abstract syntax metamodel of the DSML and that of the semantic unit. The infrastructure can also enable model exchange among DSMLs while referring to the common semantic unit. Hence, hybrid automata based DSMLs can be integrated to form a meaningful tool chain by deploying this proposed infrastructure. In this paper, we demonstrate how effective the tool-chain infrastructure is by considering a practical case study involving the hybrid automata DSMLs, HyVisual and ReachLab.

Online stability validation using sector analysis

Our previous work has explored the use of compositional stabilization techniques for embedded flight control software[9] based on passivity properties of controller components and systems. Zames[21] presented a compositional behavior-bounding technique for evaluating stability of nonlinear systems based on real intervals representing cones (sectors) that bound possible component behaviors. Many innovations in control theory have developed from his insights. We present a novel use of his sector bound theory to validate the stability of embedded control implementations online. The sector analysis can be implemented as a computationally efficient check of stability for different parts of a control design. The advantage of the online application of this technique is that it takes into account software platform effects that impact stability, such as time delays, quantization, and data integrity. We present a brief overview of the sector concept, our compatible control design approach, application of the technique to model-based embedded control software design, an example of its use to find design defects, and insights that may be drawn from our investigation so far. In the present work we only consider software (discrete-time) control of nonlinear continuous-time systems without switching.

Towards incremental cycle analysis in ESMoL distributed control system models

We consider the problem of incremental cycle analysis for dataflow models in the Embedded Systems Modeling Language (ESMoL). This is an example of a syntactic property which does not lend itself to compositional analysis. We give a general form of a cycle enumeration algorithm that makes use of graph hierarchy to improve analysis efficiency. Our framework also stores simple connectivity information in the model to accelerate future cycle analyses when additional components are added or modifications are made. An extended version of this work gives a mapping from a term algebraic model of the ESMoL component model and logical dataflow sublanguages to the analysis framework, and an evaluation on a fixed-wing aircraft controller model[7]. Integrated cycle analysis aids well-formedness checking during model construction in the ESMoL tool suite.