Roger Burkhart

Integrating Models and Simulations of Continuous Dynamics into SysML

In this paper, we combine modeling constructs from SysML and Modelica to improve the support for Model-Based Systems Engineering (MBSE). The Object Management Group has recently developed the Systems Modeling Language (OMG SysML™). This visual modeling language provides a comprehensive set of diagrams and constructs for modeling many common aspects of systems engineering problems, such as system requirements, structures, functions, and behaviors. Complementin g these SysML constructs, the Modelica language has emerged as a standard for modeling the continuous dynamics of systems in terms of hybrid discreteevent and differential algebraic equation systems. In this paper, the synergy between SysML and Modelica is explored at three different levels: the de finition of continuous dynamics models in SysML; the use of a triple graph grammar to maintain a bidirectional mapping between these SysML constructs and the corresponding Modelica models; and the integration of simulation experiments with othe r SysML constructs to support MBSE. Throughout the paper, an example of a car suspension is used t o demonstrate these contributions.

MODELING CONTINUOUS SYSTEM DYNAMICS IN SYSML

In this paper, we present a formal approach to modeling continuous system dynamics in SysML using differential algebraic equations (DAE’s). To support model-based design, the Object Management Group has recently developed the Systems Modeling Language (OMG SysML™). The language is well-suited for modeling many different aspects of largescale, multidisciplinary engineering projects. It allows systems designers to capture information concerning system requirements, tests, structures, functions, and behaviors. However, SysML lacks explicit support for modeling continuous system dynamics using DAE’s. Such models are important for representing system behavior resulting from energy or signal exchange between system components. We introduce support for modeling system dynamics in the form of a language mapping between SysML and Modelica, an equation-based, object-oriented behavioral simulation language. The bidirectional mapping provides support for creating system dynamics models in SysML that can exist alongside other SysML information models, but that can also be transformed into executable simulations by a Modelica solver. To illustrate the approach, we provide an example SysML model of a hydraulic pump.

Combining Mathematical Programming and SysML for Automated Component Sizing of Hydraulic Systems

In this paper, we present a framework for automated component sizing to extend a designers ability to evaluate a particular configuration during the architecture exploration phase of a design process. Component sizing is a hard problem to solve, both from a computational and modeling aspect. This is because of competing objectives, requirements from multiple disciplines, and the need to find a good solution quickly for the architecture being considered. In current approaches, designers rely on heuristics and iterate over the multiple objectives and requirements until a satisfactory solution is found. To improve on this state of practice, we introduce advances in the following two areas: (a) solving the problem efficiently so that all of the imposed requirements are satisfied simultaneously and the solution obtained is mathematically optimal and (b) modeling a component sizing problem in a manner that is convenient to designers. An acausal, algebraic, equation-based, declarative modeling approach using mathematical programming (GAMS) is taken to solve these problems more efficiently. The object management group systems modeling language (OMG SysML™) is used to model component sizing problems in order to facilitate problem formulation, model reuse and automatic generation of low-level code that can be solved using GAMS and its solvers. This framework is demonstrated by applying it to an example of a hydraulic log splitter. Based on this initial example, we discuss two advantages of this framework—total time taken in solving multiple scenarios for a given configuration and the graphical representation of a problem in SysML.