In the past, aircraft energy systems had only marginal relevance during the early design of commercial aircraft. The design problem was decomposed hierarchically based on a conventional architecture using pneumatic, hydraulic, and electric secondary power. Requirements were allocated and the actual design of individual aircraft energy systems was established in isolation downstream in the design process. Today, this approach is in question, as airframers realize that global optimization of the entire aircraft is the only remaining way to achieve substantial improvements in the total aircraft package. The ongoing integration of aircraft energy systems architecture design leads toward the reduced use of hydraulic and pneumatic secondary power, and a "More Electric Aircraft". At the same time, business relationships change from "purchaser and supplier"-cooperations to risksharing partnerships. These changes require methods and tools to support designing globally optimized architectures. As a contribution toward this overall goal, the objective of this thesis is to develop and implement a design methodology for the air conditioning system (Environmental Control System), which imposes key requirements on the aircraft energy systems architecture. The proposed concept is based on a physics-based design methodology. Herein, energyoptimal open-loop control has to be defined. Otherwise, a rigorous assessment using aircraftlevel metrics cannot be established. For this purpose, inverse-modeling approaches are introduced. These allow establishing energy-optimal open-loop control concurrently with optimal aircraft energy system architecture. As a physics-based design methodology requires a substantial modeling effort, flexibility and reusability of mathematical plant models are of pivotal importance. For this purpose, the equation-based object-oriented modeling language Modelica is adopted. In this regard, substantial contributions are made to further improve the robustness of the code generated from such modeling languages. In particular, robustness issues in established non-causal thermo-fluid interfaces ("connectors") are identified. Based on a rigorous analysis, a robust yet user-friendly interface called "stream connectors" is proposed. Additionally, robustness issues with steadystate initialization are addressed. In order to analyze this problem, a quantitative metric is proposed. Then, a probability-one homotopy method is introduced to equation-based objectoriented modeling languages. Using theorems from topology, the established method guarantees convergence with probability one. This property is demonstrated on a number of case studies. Exploiting these improvements, a robust and flexible modeling and simulation framework for Environmental Control Systems and general cooling systems is implemented. It covers both conventional low-speed fluid dynamics as well as high-speed gas dynamics. Building on this modeling and simulation framework and the proposed design methodology, a physics-based design environment for Environmental Control Systems and aircraft energy systems in general is implemented. It can be applied to conventional and unconventional system architectures alike.


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    Title :

    Device-oriented modeling and simulation in aircraft energy systems design


    Contributors:

    Publication date :

    2012


    Size :

    191 Seiten, 89 Bilder, 10 Tabellen, 202 Quellen



    Type of media :

    Theses


    Type of material :

    Print


    Language :

    English




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