Digital twins: State-of-the-art future directions for modelling and simulation in engineering dynamics applications

This paper presents a review of the state-of-the-art for digital twins in the application domain of engineering dynamics. The focus on applications in dynamics, is because: (i) they offer some of the most challenging aspects of creating an effective digital twin, and (ii) they are relevant to important industrial applications such as energy generation and transport systems. The history of the digital twin is discussed first, along with a review of the associated literature; the process of synthesising a digital twin is then considered, including definition of the aims and objectives of the digital twin. An example of the asset management phase for a wind turbine is included in order to demonstrate how the synthesis process might be applied in practice. In order to illustrate modelling issues arising in the construction of a digital twin, a detailed case study is presented, based on a physical twin which is a small-scale three-storey structure. This case study shows the progression towards a digital twin highlighting key processes including: system identification, data-augmented modelling and verification and validation. Finally, a discussion of some open research problems and technological challenges is given, including: workflow, joints, uncertainty management and the quantification of trust. In a companion paper, as part of this special issue, a mathematical framework for digital twin applications is developed, and together the authors believe this represents a firm framework for developing digital twin applications in the area of engineering dynamics

Model Checking Commitment-Governed Compositions of Web Services

We propose a new approach towards verifying compositions of web services using model checking. In order to perform such a verification, we transform the web service composition into a Multi-Agent System (MAS) model where the process in charge of the composition and the participating services are represented by agents. We model the behavior of the resulting MAS using the extended Interpreted Systems Programming Language (ISPL+), the dedicated language of the MCMAS+ model checker for MAS. We use commitments between agents to regulate and reason about messages between composite web services. The properties against which the compositions are verified are expressed in the Computation Tree Logic of Commitments (CTLC), an extension of the branching logic CTL that supports commitment modalities. We describe BPEL2ISPL+, a tool we developed to perform the automatic transformation from the web service composition described in Business Process Execution Language (BPEL) into a verifiable MAS model described in ISPL+. The BPEL2ISPL+ tool is applied to a concrete BPEL web service composition and its accurate representation in ISPL+ is obtained. The CTLC properties used to verify the compositions regulated by commitments are represented along with the agents abstracting the participating web services. The MCMAS+ model checker is used to verify the model against these properties, providing thus a new approach to model check agent-based web service compositions governed by commitments

Realisierungsmethodik von applikationsspezifischen Softcore FPGA-Lösungen: in Abhänigkeit von algorithmischen Anforderungen im Einsatzgebiet eingebetteter Systeme

Die vorliegende Dissertation befasst sich mit Prinzipien, Methodiken, Techniken und Realisierungen zur systematischen Entwicklung von komplexen eingebetteten Systemen unter Verwendung von Softcore Prozessoren. Die adressierte Aufgabendomäne ist vor allem die echtzeitkritische Daten- und Bildverarbeitung. Notwendig sind neue Lösungen aufgrund immer leistungsfähigerer eingebetteter Systeme, mit deren Hilfe Aufgabenfelder bedient werden können, die bisher mit diesen Systemen nicht umsetzbar waren. Aufbauend auf den Darstellungen bereits existierender Modelle und Verfahren, wie z. B. dem V-Modell oder dem Hardware-Software Co-Design, wird eine spezielle Realisierungsmethodik für applikationsspezifische Softcore FPGA-Lösungen in Abhängigkeit von algorithmischen Anforderungen in der Aufgabendomäne erarbeitet. In diesem Zusammenhang wird eine Softcore-Bibliothek mit an diese Domäne angepassten Eigenschaften konzipiert und umgesetzt. Das dabei verwendete modellbasierte Vorgehen ermöglicht durch eine hierarchische Beschreibung und Validierung eine zeit- und kosteneffiziente Entwicklung komplexer Systeme. Für jede Abstraktionsebene werden Modelle vorgestellt, die jeweils auf dieser alle notwendigen Anforderungen zur frühzeitigen Fehlererkennung und Fehlervermeidung sowie eine automatisierte Codegenerierung und Optimierungen sinnvoll umsetzen. Durch gezielte Festlegung einzuhaltender Kriterien und Entwicklungsschritte wird dabei in jeder Komponente der Toolchain eine bestmögliche Kombination von zeit- und kosteneffizienter Entwicklung mit der Sicherstellung der Einhaltung harter Echtzeiteigenschaften sowie einer Maximierung der Wiederverwendbarkeit, erreicht. Dabei spielt die Anpassbarkeit der eingebetteten Systeme mit Hilfe von partieller Rekonfiguration, mit der das dynamische Austauschen von Teilen des Softcores oder sogar ganzer Softcore Prozessoren zur Laufzeit ermöglicht wird, eine wichtige Rolle. Es erfolgen ein praktischer Nachweis der Funktionalität der erarbeiteten Modelle sowie ausführliche Experimente über die zeitlichen Anforderungen bei der partiellen Rekonfiguration von Softcore Prozessoren. Die praktischen Ergebnisse der Arbeit zeigen deutlich die Effizienz der Entwicklung von Lösungen mit der konzipierten und umgesetzten Toolchain sowie die Relevanz und Einsetzbarkeit der partiellen Rekonfiguration in diesem Gebiet.This dissertation focuses on principles, methods, techniques and realizations for the systematic development of complex embedded systems using softcore processors. The addressed domain is primarily real-time-critical data and image processing. New solutions are needed due to the increasing performance of embedded systems, allowing for a range of applications that were previously not solvable with these systems. Building on the concepts of already existing models and methods, e.g. the V-model or hardware-software-co-design, a special realization methodology for application-specific softcore FPGA solutions is developed, in conjunction with algorithmic requirements in the addressed domain. In this context, a softcore library with characteristics tailored to this domain is designed and implemented. Through a hierarchical description and validation, the model-based approach used in this thesis enables the time- and cost-efficient development of complex systems. For each abstraction level, models are presented that provide all necessary requisites for early error detection and prevention, as well as mostly automated code generation and code optimization. By defining relevant criteria and development steps, a parsimonious development with respect to time and cost is achieved in each component of the toolchain. This ensures strict adherence to the hard real-time properties and maximizes the reusability of the modules implemented for a specific project. The adaptability of the embedded systems through using partial reconfiguration plays an important role. Partial reconfiguration enables dynamic replacement of parts of the softcore or even entire softcore processors at runtime. A practical evaluation of the functionality of the developed models as well an extensive array of experiments concerning the time requirements for the partial reconfiguration of softcore processors are presented. The practical results of this thesis clearly demonstrate the efficiency of developing solutions with the designed and realized toolchain, as well as the relevance and applicability of partial reconfiguration in the addressed domain