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  • 1.
    Hällqvist, Robert
    Linköping University, Department of Management and Engineering, Fluid and Mechatronic Systems. Linköping University, Faculty of Science & Engineering.
    On Standardized Model Integration: Automated Validation in Aircraft System Simulation2019Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Designing modern aircraft is not an easy task. Today, it is not enough to optimize aircraft sub-systems at a sub-system level. Instead, a holistic approach is taken whereby the constituent sub-systems need to be designed for the best joint performance. The State-of-the-Art (SotA) in simulating and exchanging simulation models is moving forward at a fast pace. As such, the feasible use of simulation models has increased and additional benefits can be exploited, such as analysing coupled sub-systems in simulators. Furthermore, if aircraft sub-system simulation models are to be utilized to their fullest extent, opensource tooling and the use of open standards, interoperability between domain specific modeling tools, alongside robust and automated processes for model Verification and Validation (V&V) are required.

    The financial and safety related risks associated with aircraft development and operation require well founded design and operational decisions. If those decisions are to be founded upon information provided by models and simulators, then the credibility of that information needs to be assessed and communicated. Today, the large number of sensors available in modern aircraft enable model validation and credibility assessment on a different scale than what has been possible up to this point. This thesis aims to identify and address challenges to allow for automated, independent, and objective methods of integrating sub-system models into simulators while assessing and conveying the constituent models aggregated credibility.

    The results of the work include a proposed method for presenting the individual models’ aggregated credibility in a simulator. As the communicated credibility of simulators here relies on the credibility of each included model, the assembly procedure itself cannot introduce unknown discrepancies with respect to the System of Interest (SoI). Available methods for the accurate simulation of coupled models are therefore exploited and tailored to the applications of aircraft development under consideration. Finally, a framework for automated model validation is outlined, supporting on-line simulator credibility assessment according to the presented proposed method.

    List of papers
    1. A Concept for Credibility Assessment of Aircraft System Simulators
    Open this publication in new window or tab >>A Concept for Credibility Assessment of Aircraft System Simulators
    2016 (English)In: JOURNAL OF AEROSPACE INFORMATION SYSTEMS, ISSN 1940-3151, Vol. 13, no 6, p. 219-233Article in journal (Refereed) Published
    Abstract [en]

    An efficient methodology for verification, validation, and credibility assessment of simulation models and simulator applications is an enabler for the aeronautical industrys increasing reliance on modeling and simulation in system design and verification and on training. As a complement to traditional document-centric approaches, this paper presents a method for credibility assessment of simulator applications, in which credibility information is presented to end users directly during simulation. The central idea is that each model in a simulator is extended with a metamodel describing different aspects of credibility. The metamodel includes a number of static credibility measures and a dynamic measure that may vary during simulation. The concept is implemented and tested in two system simulators for the Saab Gripen fighter aircraft. According to the evaluation, the concept facilitates an intuitive overview of model dependencies, as well as credibility information for individual models and for a simulator as a whole. This implies a support for detecting test plan deficiencies or that a simulator configuration is not a suitable platform for the execution of a particular test. Furthermore, model developers and end users are encouraged to reflect upon central credibility aspects like intended use, model fidelity, and test worthiness in their daily work.

    Place, publisher, year, edition, pages
    AMER INST AERONAUTICS ASTRONAUTICS, 2016
    National Category
    Other Electrical Engineering, Electronic Engineering, Information Engineering
    Identifiers
    urn:nbn:se:liu:diva-131716 (URN)10.2514/1.I010391 (DOI)000382152400002 ()
    Note

    Funding Agencies|Saab Aeronautics; National Aviation Engineering Research Programme (NFFP)

    Available from: 2016-10-03 Created: 2016-09-30 Last updated: 2019-12-19
    2. METHODS FOR AUTOMATING MODEL VALIDATION: STEADY-STATE IDENTIFICATION APPLIED ON GRIPEN FIGHTER ENVIRONMENTAL CONTROL SYSTEM MEASUREMENTS
    Open this publication in new window or tab >>METHODS FOR AUTOMATING MODEL VALIDATION: STEADY-STATE IDENTIFICATION APPLIED ON GRIPEN FIGHTER ENVIRONMENTAL CONTROL SYSTEM MEASUREMENTS
    2016 (English)In: Proceedings of the 30th congress of the International Council  of the Aeronautical Sciences, 2016Conference paper, Published paper (Refereed)
    Abstract [en]

    Model Validation and Verification (V&V) has historically often been considered a final step in the model development process. However, to justify model-based design decisions throughout the entire system development process, a methodology for continuous model V&V is essential. That is, model V&V activities should be fast and easy to reiterate as new information becomes available. Using a high fidelity simulation model of the Environmental Control System (ECS) in the Saab Gripen fighter aircraft as a guiding example, this paper further extends to an existing semiautomatic framework for model steady-state validation developed during ECS model validation efforts. Generic methods for identification of steady-state operation are a prerequisite for steady-state validation of industry grade physics based models against insitu measurements. Four different established methods for steady-state identification are investigated and compared: steady-state conditions on the standard deviation estimated from in-situ measurements, conditions on the variation coefficient, t-test on the slope of a simple regression line, and comparison of differently estimated variances. The methods’ applicability, on ECS measurements in particular, is evaluated utilizing steady-state identification needs defined during Gripen ECS model validation activities.

    Model Validation and Verification (V&V) has historically often been considered a final step in the model development process. However, to justify model-based design decisions throughout the entire system development process, a methodology for continuous model V&V is essential. That is, model V&V activities should be fast and easy to reiterate as new information becomes available.

    Using a high fidelity simulation model of the Environmental Control System (ECS) in the Saab Gripen fighter aircraft as a guiding example, this paper further extends to an existing semi-automatic framework for model steady-state validation developed during ECS model validation efforts. Generic methods for identification of steady-state operation are a prerequisite for steady-state validation of industry grade physics based models against in-situ measurements. Four different established methods for steady-state identification are investigated and compared: steady-state conditions on the standard deviation estimated from in-situ measurements, conditions on the variation coefficient, t-test on the slope of a simple regression line, and comparison of differently estimated variances. The methods’ applicability, on ECS measurements in particular, is evaluated utilizing steady-state identification needs defined during Gripen ECS model validation activities.

    Keywords
    Gripen, Steady-state identification, Automating model validation, Historical data validation
    National Category
    Aerospace Engineering
    Identifiers
    urn:nbn:se:liu:diva-142397 (URN)978-3-932182-85-3 (ISBN)
    Conference
    The 30th congress of the The International Council of the Aeronautical Sciences
    Projects
    OpenCPS
    Available from: 2017-10-30 Created: 2017-10-30 Last updated: 2019-12-19
    3. TLM-Based Asynchronous Co-simulation with the Functional Mockup Interface
    Open this publication in new window or tab >>TLM-Based Asynchronous Co-simulation with the Functional Mockup Interface
    2017 (English)In: Proceedings of the IUTAM Symposium on Solver-Coupling and Co-Simulation, Darmstadt, Germany, September 18-20, 2017 / [ed] Bernhard Schweizer, Switzerland, 2017Conference paper, Published paper (Refereed)
    Abstract [en]

    Numerical stability is a key aspect in co-simulation of physical systems. Decoupling a system into independent sub-models will introduce time delays on interface variables. By utilizing physical time delays for decoupling, affecting the numerical stability can be avoided. This requires interpolation, to allow solvers to request input variables for the time slot where they are needed. The FMI for co-simulation standard does not support fine-grained interpolation using interpolation tables. Here, various modifications to the FMI standard are suggested for improved handling of interpolation. Mechanical and thermodynamic models are used to demonstrate the need for interpolation, as well as to provide an industrial context. It is shown that the suggested improvements are able to stabilize the otherwise unstable connections.

    Place, publisher, year, edition, pages
    Switzerland: , 2017
    Series
    IUTAM Bookseries, E-ISSN 1875-3493 ; 35
    Keywords
    Co-simulation, FMI, TLM, Numerical stability
    National Category
    Other Electrical Engineering, Electronic Engineering, Information Engineering
    Identifiers
    urn:nbn:se:liu:diva-157342 (URN)10.1007/978-3-030-14883-6_2 (DOI)000493506100002 ()978-3-030-14882-9 (ISBN)978-3-030-14883-6 (ISBN)
    Conference
    IUTAM Symposium on Solver-Coupling and Co-Simulation
    Available from: 2019-06-10 Created: 2019-06-10 Last updated: 2019-12-19
    4. A Novel FMI and TLM-based Desktop Simulator for Detailed Studies of Thermal Pilot Comfort
    Open this publication in new window or tab >>A Novel FMI and TLM-based Desktop Simulator for Detailed Studies of Thermal Pilot Comfort
    Show others...
    2018 (English)In: ICAS congress proceeding, International Council of the Aeronautical Sciences , 2018, article id ICAS2018_0203Conference paper, Published paper (Other academic)
    Abstract [en]

    Modelling and Simulation is key in aircraft system development. This paper presents a novel, multi-purpose, desktop simulator that can be used for detailed studies of the overall performance of coupled sub-systems, preliminary control design, and multidisciplinary optimization. Here, interoperability between industrially relevant tools for model development and simulation is established via the Functional Mockup Interface (FMI) and System Structure and Parametrization (SSP) standards. Robust and distributed simulation is enabled via the Transmission Line element Method (TLM). The advantages of the presented simulator are demonstrated via an industrially relevant use-case where simulations of pilot thermal comfort are coupled to Environmental Control System (ECS) steadystate and transient performance.

    Place, publisher, year, edition, pages
    International Council of the Aeronautical Sciences, 2018
    Keywords
    OMSimulator; FMI; TLM; Pilot Thermal Comfort; Modelling and Simulation
    National Category
    Applied Mechanics Other Electrical Engineering, Electronic Engineering, Information Engineering
    Identifiers
    urn:nbn:se:liu:diva-152897 (URN)9783932182884 (ISBN)
    Conference
    31st Congress of the International Council of the Aeronautical Sciences,Belo Horizonte, Brazil, September 9-14, 2018
    Available from: 2018-11-27 Created: 2018-11-27 Last updated: 2020-01-16Bibliographically approved
  • 2.
    Hällqvist, Robert
    et al.
    Systems Simulation and Concept Design, Saab Aeronautics, Linköping, Sweden.
    Braun, Robert
    Linköping University, Department of Management and Engineering, Fluid and Mechatronic Systems. Linköping University, Faculty of Science & Engineering.
    Krus, Petter
    Linköping University, Department of Management and Engineering, Fluid and Mechatronic Systems. Linköping University, Faculty of Science & Engineering.
    Early Insights on FMI-based Co-Simulation of Aircraft Vehicle Systems2017In: Proceedings of 15:th Scandinavian International Conference on Fluid Power, June 7-9, 2017, Linköping, Sweden / [ed] Petter Krus, Liselott Eriksson and Magnus Sethson, Linköping: Linköping University Electronic Press, 2017, Vol. 144, p. 262-270Conference paper (Other academic)
    Abstract [en]

    Modelling and Simulation is extensively used for aircraft vehicle system development at Saab Aeronautics in Linköping, Sweden. There is an increased desire to simulate interacting sub-systems together in order to reveal, and get an understanding of, the present cross-coupling effects early on in the development cycle of aircraft vehicle systems. The co-simulation methods implemented at Saab require a significant amount of manual effort, resulting in scarcely updated simulation models, and challenges associated with simulation model scalability, etc. The Functional Mock-up Interface (FMI) standard is identified as a possible enabler for efficient and standardized export and co-simulation of simulation models developed in a wide variety of tools. However, the ability to export industrially relevant models in a standardized way is merely the first step in simulating the targeted coupled sub-systems. Selecting a platform for efficient simulation of the system under investigation is the next step. Here, a strategy for adapting coupled Modelica models of aircraft vehicle systems to TLM-based simulation is presented. An industry-grade application example is developed, implementing this strategy, to be used for preliminary investigation and evaluation of a cosimulation framework supporting the Transmission Line element Method (TLM). This application example comprises a prototype of a small-scale aircraft vehicle systems simulator. Examples of aircraft vehicle systems are environmental control systems, fuel systems, and hydraulic systems. The tightly coupled models included in the application example are developed in Dymola, OpenModelica, and Matlab/Simulink. The application example is implemented in the commercial modelling tool Dymola to provide a reference for a TLM-based master simulation tool, supporting both FMI and TLM. The TLM-based master simulation tool TLMSimulator is investigated in terms of model import according to the FMI standard with respect to a specified set of industrial needs and requirements.

  • 3.
    Hällqvist, Robert
    et al.
    Saab Aeronautics, Linköping, Sweden.
    Eek, Magnus
    Saab Aeronautics, Linköping, Sweden.
    Braun, Robert
    Linköping University, Department of Management and Engineering, Fluid and Mechatronic Systems. Linköping University, Faculty of Science & Engineering.
    Krus, Petter
    Linköping University, Department of Management and Engineering, Fluid and Mechatronic Systems. Linköping University, Faculty of Science & Engineering.
    METHODS FOR AUTOMATING MODEL VALIDATION: STEADY-STATE IDENTIFICATION APPLIED ON GRIPEN FIGHTER ENVIRONMENTAL CONTROL SYSTEM MEASUREMENTS2016In: Proceedings of the 30th congress of the International Council  of the Aeronautical Sciences, 2016Conference paper (Refereed)
    Abstract [en]

    Model Validation and Verification (V&V) has historically often been considered a final step in the model development process. However, to justify model-based design decisions throughout the entire system development process, a methodology for continuous model V&V is essential. That is, model V&V activities should be fast and easy to reiterate as new information becomes available. Using a high fidelity simulation model of the Environmental Control System (ECS) in the Saab Gripen fighter aircraft as a guiding example, this paper further extends to an existing semiautomatic framework for model steady-state validation developed during ECS model validation efforts. Generic methods for identification of steady-state operation are a prerequisite for steady-state validation of industry grade physics based models against insitu measurements. Four different established methods for steady-state identification are investigated and compared: steady-state conditions on the standard deviation estimated from in-situ measurements, conditions on the variation coefficient, t-test on the slope of a simple regression line, and comparison of differently estimated variances. The methods’ applicability, on ECS measurements in particular, is evaluated utilizing steady-state identification needs defined during Gripen ECS model validation activities.

    Model Validation and Verification (V&V) has historically often been considered a final step in the model development process. However, to justify model-based design decisions throughout the entire system development process, a methodology for continuous model V&V is essential. That is, model V&V activities should be fast and easy to reiterate as new information becomes available.

    Using a high fidelity simulation model of the Environmental Control System (ECS) in the Saab Gripen fighter aircraft as a guiding example, this paper further extends to an existing semi-automatic framework for model steady-state validation developed during ECS model validation efforts. Generic methods for identification of steady-state operation are a prerequisite for steady-state validation of industry grade physics based models against in-situ measurements. Four different established methods for steady-state identification are investigated and compared: steady-state conditions on the standard deviation estimated from in-situ measurements, conditions on the variation coefficient, t-test on the slope of a simple regression line, and comparison of differently estimated variances. The methods’ applicability, on ECS measurements in particular, is evaluated utilizing steady-state identification needs defined during Gripen ECS model validation activities.

  • 4.
    Hällqvist, Robert
    et al.
    Saab Aeronautics, Linköping, Sweden.
    Eek, Magnus
    Saab Aeronautics, Linköping, Sweden.
    Lind, Ingela
    Saab Aeronautics, Linköping, Sweden.
    Gavel, Hampus
    Saab Aeronautics, Linköping, Sweden.
    Validation Techniques Applied on the Saab Gripen FighterEnvironmental Control System Model2015In: Proceedings of the 56th SIMS / [ed] Lena Buffoni, Adrian Pop, and Bernhard Thiele, Linköping, 2015, p. 199-210, article id ecp15119199Conference paper (Refereed)
    Abstract [en]

    The Environmental Control System (ECS) of the Saab Gripen fighter provides a number of vital functions, such as provision of coolant air to the avionics, comfort air to the cockpit, and pressurization of the aircraft fuel system. To support system design, a detailed simulation model has been developed in the Modelica-based tool Dymola. The model needs to be a “good system representation”, during both steady-state operation and relevant dynamic events, if reliable predictions are to be made regarding cooling performance, static loads in terms of pressure and temperature, and various other types of system analyses. A framework for semi-automatic validation of the ECS model against measurements is developed and described in this paper. The framework extends a proposed formal methodology of semi-automaticmodel validation against in-situ measurements to the model development process implemented at Saab.Applied methods for validating the model in steady-state operation and during relevant dynamic events are presented in detail. The developed framework includes automatic filtering of measurement points defined as steady-state operation and visualization techniques applied on validation experiments conducted in the previously mentioned points. The proposed framework both simplify continuous validation throughout the system development process and enables a smooth transition towards a more independent verification and validation process.

  • 5.
    Hällqvist, Robert
    et al.
    Systems Simulation and Concept Design, Saab Aeronautics, Linköping, Sweden.
    Schminder, Jörg
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering.
    Eek, Magnus
    Systems Simulation and Concept Design, Saab Aeronautics, Linköping, Sweden.
    Braun, Robert
    Linköping University, Department of Management and Engineering, Fluid and Mechatronic Systems. Linköping University, Faculty of Science & Engineering.
    Gårdhagen, Roland
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering.
    Krus, Petter
    Linköping University, Department of Management and Engineering, Fluid and Mechatronic Systems. Linköping University, Faculty of Science & Engineering.
    A Novel FMI and TLM-based Desktop Simulator for Detailed Studies of Thermal Pilot Comfort2018In: ICAS congress proceeding, International Council of the Aeronautical Sciences , 2018, article id ICAS2018_0203Conference paper (Other academic)
    Abstract [en]

    Modelling and Simulation is key in aircraft system development. This paper presents a novel, multi-purpose, desktop simulator that can be used for detailed studies of the overall performance of coupled sub-systems, preliminary control design, and multidisciplinary optimization. Here, interoperability between industrially relevant tools for model development and simulation is established via the Functional Mockup Interface (FMI) and System Structure and Parametrization (SSP) standards. Robust and distributed simulation is enabled via the Transmission Line element Method (TLM). The advantages of the presented simulator are demonstrated via an industrially relevant use-case where simulations of pilot thermal comfort are coupled to Environmental Control System (ECS) steadystate and transient performance.

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