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The Netherlands has one of the largest flower auctions. Due to the anticipated enlargement of the auction, distribution system capacity was researched using discrete event simulation. Results indicate that the current system will not be adequate for the needs of the expanded auction. Suggestions for increased efficiency are included, as is a schematic of the simulation model. Transit and buffer times are simplified or ignored in this model. The model is translated into a computer program using the Simulation of Logistics Elements (SOLE) program, which drives from Discrete Event Modeling on SIMULA (DEMOS). The model can simulate a typical six hour auction day. Data from almost twenty thousand deals daily is input. Validation was achieved through a comparison of model output to real output on different days. Graphs and tables are featured.

Abstract: Different modeling formalisms for timed and hybrid systems exist, each of which addresses a specific set of problems, and has its own set of features. These formalisms and tools can be used in each stage of the embedded systems development, to verify and validate various requirements. The Compositional Interchange Format (CIF), is a formalism based on hybrid automata, which are composed using process algebraic operators. CIF aims to establish interoperability among a wide range of formalisms and tools by means of model transformations and co-simulation, which avoids the need for implementing many bilateral translators. This work presents the syntax and formal semantics of CIF. The semantics is shown to be compositional, and proven to preserve certain algebraic properties, which express our intuition about the behavior of the language operators. In addition we show how CIF operators can be combined to implement widely used constructs present in other timed and hybrid formalisms, and we illustrate the applicability of the formalism by developing several examples. Based on the formal specification of CIF, an Eclipse based simulation environment has been developed. We expect this work to serve as the basis for the formal definition of semantic preserving transformations between various languages for the specification of timed and hybrid systems. [Copyright &y& Elsevier]

Abstract: Supervisory control theory enables control system designers to specify a model of the uncontrolled system in combination with control requirements, and subsequently use a synthesis algorithm for automatic controller generation. The use of supervisory control synthesis can significantly reduce development time of supervisory controllers as a result of unambiguous specification of control requirements, and synthesis of controllers that by definition are nonblocking and satisfy the control requirements. This is especially important for evolving systems, where requirements change frequently. For successful industrial application, the specification formalism should be expressive and intuitive enough to be used by domain experts, who define control requirements, and software experts, who implement control requirements and synthesize controllers. This paper defines such a supervisory control specification formalism that consists of automata, synchronizing actions, guards, updates, invariants, independent and dependent variables, where the values of the dependent variables can be defined in terms of functions on the independent variables. We also show how the language enables systematic, compositional specification of a control system for a patient communication system of an MRI scanner. We show that our specification formalism can deal with both event-based and state-based interfaces. To support systematic, modular specification of models for supervisory control synthesis, we introduce state trackers that record sequences of events in terms of states. The synthesized supervisor has been successfully validated by means of interactive user guided simulation. [Copyright &y& Elsevier]

The design of a high-volume printer for professional use is rather complex. The design of the paper path and the timing of sheets is frequently reengineered as the design of the printer components progresses. This paper presents an optimization model for the combined paper path and timing design problem. The paper path is an optimal physical dimensioning problem, while the timing is an open-loop optimal control problem. The coupled optimization problem is formulated as a simultaneous analysis and design (SAND) problem using a direct transcription of the optimal control problem. Benefits of the chosen formulation for industrial application are the ease of setting up the optimization model for arbitrary printer configurations, and the short computation times. Results of an industrial case are presented. [ABSTRACT FROM AUTHOR]

The complexity of the design of supervisory controllers for today's high-tech systems is ever increasing with the rise in demands for higher safety and functionality. Supervisory control synthesis enables the design engineer to automatically generate a supervisory controller from a model of the plant and a model of the controller requirements. Although supervisory control theory is an active research area, the number of industrial applications remains relatively low. One of the main reasons for this is the lack of guidelines for practical applications of supervisory control theory, especially in case of large-scale systems with numerous components and complex dependencies. In this paper, guidelines are given for the process of obtaining and validating a supervisory controller, more specifically for large-scale systems with isomorphisms. Systems with isomorphisms are systems with a high degree of symmetry and repetitiveness in their components, such as manufacturing lines with parallel processing lines or infrastructural systems with repeating modules. This paper shows how coordination between the steps in obtaining a supervisory controller for a large-scale system improves the efficiency of the process and quality of the end result, and how the isomorphism of components in the system can be exploited in these steps. This process is demonstrated in this paper by a case study related to the Eerste Heinenoordtunnel, a road tunnel in the Netherlands. The case study shows the steps of modeling the plant and the controller requirements, performing model reduction based on isomorphisms in the system, synthesizing the supervisory controller, and validating the controller by means of simulation. • A supervisor for a road tunnel is synthesized with 10257 states. • Parameter-based modeling is introduced as an accessible modeling method. • The model is reduced using isomorphisms decreasing the synthesis time by a factor 210. • The synthesized supervisor is validated by means of visualized simulations. [ABSTRACT FROM AUTHOR]

Abstract: The hybrid χ (Chi) formalism integrates concepts from dynamics and control theory with concepts from computer science, in particular from process algebra and hybrid automata. It integrates ease of modeling with a straightforward, structured operational semantics. Its ‘consistent equation semantics’ enforces state changes to be consistent with delay predicates, that combine the invariant and flow clauses of hybrid automata. Ease of modeling is ensured by means of the following concepts: (1) different classes of variables: discrete and continuous, of subclass jumping or non-jumping, and algebraic; (2) strong time determinism of alternative composition in combination with delayable guards; (3) integration of urgent and non-urgent actions; (4) differential algebraic equations as a process term as in mathematics; (5) steady-state initialization; and 6) several user-friendly syntactic extensions. Furthermore, the χ formalism incorporates several concepts for complex system specification: (1) process terms for scoping that integrate abstraction, local variables, local channels and local recursion definitions; (2) process definition and instantiation that enable process re-use, encapsulation, hierarchical and/or modular composition of processes; and (3) different interaction mechanisms: handshake synchronization and synchronous communication that allow interaction between processes without sharing variables, and shared variables that enable modular composition of continuous-time or hybrid processes. The syntax and semantics are illustrated using several examples. [Copyright &y& Elsevier]

Abstract: Nowadays, due to increasing system complexity and growing competition and costs, industry makes high demands on powerful techniques used to design and analyze manufacturing systems. One of the most popular techniques to do performance analysis is simulation. However, simulation-based analysis cannot guarantee the correctness of a system, so it is less suitable for functional analysis. Our research focuses on examining other methods to do performance analysis and functional analysis, and trying to combine the two. One of the approaches is to translate a simulation model that is used for performance analysis to a model written in an input language of an existing verification tool. We translate a χ [D.A. van Beek, K.L. Man, M.A. Reniers, J.E. Rooda, R.R.H. Schiffelers, Syntax and Consistent Equation Semantics of Hybrid Chi, CS-Report 04-37, Eindhoven University of Technology, 2004] simulation model of a turntable system into models written in the input languages of the tools CADP [J.-C. Fernandez, H. Garavel, A. Kerbrat, L. Mounier, R. Mateescu, M. Sighireanu, CADP—a protocol validation and verification toolbox, in: Proceedings of the 8th Conference on Computer Aided Verification (CAV’96), Lecture Notes in Computer Science, vol. 1102, 1996, pp. 437–440], Spin [G.J. Holzmann, The SPIN Model Checker, Addison-Wesley, 2003] and Uppaal [K.G. Larsen, P. Pettersson, W.Yi, Uppaal in a nutshell, Int. J. Software Tools for Technology Transfer 1 (1–2) (1997) 134–152] and do a functional analysis with each of them. This allows us to evaluate the usefulness of these tools for the functional analysis of χ models. We compare the input formalisms, the expressiveness of the temporal logics, and the algorithmic techniques for model checking that are used in those tools. [Copyright &y& Elsevier]