Mavris, Dimitri N.

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Now showing 1 - 10 of 24
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    Assessment of Uncertainty in Aerospace Propulsion System Design and Simulation
    (Georgia Institute of Technology, 2003-12) Mavris, Dimitri N. ; Roth, Bryce Alexander
    The subject of uncertainty analysis in complex systems design is a broad and bourgeoning field of study. This paper focuses on only three very specific areas of current propulsion research wherein uncertainty plays a pivotal role in the problem formulation. The first is probabilistic approaches to matching engine cycle models to test data. Engine cycle models must have a high confidence of representing the actual engine performance accurately. These models must be matched in the presence of measurement, manufacturing, and other sources of uncertainty. Moreover, the optimal model match tends to change with time such that the problem is stochastic in nature. Current efforts are focusing on using Bayesian statistics to enable a comprehensive (stochastic) treatment of the problem. The second research area of interest is probabilistic analysis methods for estimation of part life in life-limited gas turbine engines. There are many sources of uncertainty in estimating part life, including material properties, material cleanliness/flaw size, part loads, and usage profile. Moreover, life limited parts are subject to accumulated damage over time, and the damage accumulation rate is a strong function of vehicle mission profile and usage. Current efforts are therefore aimed at linking detailed part analysis (finite element and materials models) with higher-level system and mission-level parameters to enable rapid and accurate analysis with the least possible effort. Finally, the role of uncertainty in engine materials selection and insertion is discussed. The materials development process for critical turbine engine parts is very lengthy and subject to considerable uncertainty with regards to the optimal balance of materials properties required for a given application. This is an area of research that will benefit from the development of materials selection methods designed to yield robust materials applicable to the greatest possible number of engines.
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    Estimation of Turbofan Engine Performance Model Accuracy and Confidence Bounds
    (Georgia Institute of Technology, 2003-09) Roth, Bryce Alexander ; Mavris, Dimitri N. ; Doel, David L.
    This paper explores the application of Inference and Bayesian Updating principles as a means to efficiently incorporate probabilistic data into the turbine engine status model matching process. This approach allows efficient estimation of nominal model match parameters from test data and also enables quantification of model accuracy and confidence bounds. The basic concepts are developed in detail and formulated into a status matching approach. This method is then applied to a simple surrogate matching problem using a cantilever beam matching exercise to illustrate the methods in a clear and easy-to-understand way. Typical results are presented and are directly analogous to status matching of a gas turbine engine cycle model.
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    A Method for Thermodynamic Work Potential Analysis of Aircraft Engines
    (Georgia Institute of Technology, 2002-07) Roth, Bryce Alexander ; McDonald, Robert Alan ; Mavris, Dimitri N.
    The objective of this paper is to provide a tool to facilitate the application of thermodynamic work potential methods to aircraft and engine analysis. This starts with a discussion of the theoretical background underlying these methods, which is then used to derive various equations useful for thermodynamic analysis of aircraft engines. The work potential analysis method is implemented in the form of a set of working charts and tables than can be used to graphically evaluate work potential stored in high-enthalpy gas. The range of validity for these charts is 300 to 36,000 oR, pressures between 0.01 and 100 atm, and fuel-air ratios from zero to stoichiometric. The derivations and charts assume mixtures of Jet-A and air as the working fluid. The thermodynamic properties presented in these charts were calculated based upon standard thermodynamic curve fits.
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    Adaptive Selection of Aircraft Engine Technologies in the Presence of Risk
    (Georgia Institute of Technology, 2002-06) Roth, Bryce Alexander ; Graham, Matthew ; Mavris, Dimitri N. ; Macsotai, Noel I.
    The objective of this paper is to describe a method for selecting optimal engine technology solution sets while simultaneously accounting for the presence of technology risk. This method uses a genetic algorithm in conjunction with Technology Identification, Evaluation, and Selection methods to find optimal combinations of technologies. The unique feature of this method is that the technology evaluation itself is probabilistic in nature. This allows the performance impact and associated risk of each technology to be quantified in terms of a distribution on key engine technology metrics. The resulting method can best be characterized as a concurrent genetic algorithm/Monte Carlo analysis that yields a performance- and risk-optimal technology solution set. This solution set is inherently a robust solution because the method will naturally strive to find those technologies representing the best compromise between performance improvement and technology risk. Finally, a practical demonstration of the method and accompanying results is given for a typical commercial aircraft engine technology selection problem.
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    A Stochastic Approach to Designing Affordable, Environmentally Acceptable Systems
    (Georgia Institute of Technology, 2002-01) Roth, Bryce Alexander ; Mavris, Dimitri N.
    The objective of this paper is to give an overview of current research thrusts focused on meeting the challenges associated with designing complex systems. Such systems must be capable of simultaneously meeting future needs for affordable, environmentally acceptable systems. These requirements for increased environmental compatibility, increased performance, and decreased cost are all fundamentally contradictory, and there is consequently a need for new design philosophies and methods capable of synthesizing acceptable solutions from a landscape of innumerable possibilities. In 1997, researchers at the Georgia Institute of Technology began responding to this need by exploring new methods for systems design under a base of funding provided by the NSF, ONR, and others. Many of these initiatives have since shown outstanding promise as stepping stones in the path to development of comprehensive methods to design affordable, environmentally acceptable systems. This paper describes five of these research thrusts in detail and illustrates opportunities for transition of these methods into industrial practice and educational curricula.
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    Adaptive Selection of Pareto Optimal Engine Technology Solution Sets
    (Georgia Institute of Technology, 2002) Roth, Bryce Alexander ; Graham, Matthew ; Mavris, Dimitri N. ; Macsotai, Noel I.
    Successful selection of propulsion system technologies for development and incorporation into new engine designs requires careful balance among many competing design objectives (i.e. performance, cost, risk, etc.). One seldom has sufficient development resources available to fully explore all promising concepts and must therefore choose a few technologies that show the greatest promise to meet program objectives. This paper describes a method of selecting optimal combinations of engine technologies. This method employs a technology impact forecasting environment in conjunction with genetic algorithms to find Pareto-optimal technology solution sets. These results are illustrated using Technology State Transition Diagrams to show how technologies move into and out of the Pareto-optimal sets. An edge search procedure is introduced as a means to efficiently characterize the objective space, the results of which are presented in the form of ternary plots. These plots show how technologies benefit multiple (oftenconflicting) objectives and help find robust or compromise technology combinations. Finally, these methods are applied to select engine technology combinations for a commercial engine system of current interest.
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    Commercial Engine Architecture Selection in the Presence of Uncertainty and Evolving Requirements
    (Georgia Institute of Technology, 2001-09) Roth, Bryce Alexander ; Mavris, Dimitri N.
    The objective of this paper is to discuss a few challenges foreseeable for future aircraft engine designs and briefly survey ongoing research that addresses these challenges. Emphasis is placed on methods for selecting commercial engine architectures. Four fundamental needs are identified and discussed at length: uncertainty in the design process, strategic business decisions in the context of engine design, complexity of future propulsion systems, and integration of new technologies into next-generation products. Probabilistic techniques are suggested as an analytical means to quantify the impact of uncertainty and to allow for uncertainty-mitigating decisions in the design process. Advanced engineering models in conjunction with ideas from complexity theory and game theory are a possible means of addressing the larger strategic business decisions as they pertain to architecture selection. Thermodynamic work potential methods are proposed as a basis for dealing with increased complexity. Finally, the role of technology identification, evaluation, and selection methods in engine technology studies is discussed.
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    Minimizing Vehicle Environmental and Economic Cost Via Thermodynamic Work Potential
    (Georgia Institute of Technology, 2001-01) Roth, Bryce Alexander ; Mavris, Dimitri N.
    The objective of this paper is to highlight several research opportunities currently being pursued at Georgia Tech to advance the state-of-the-art in vehicle design methods by applying the concept of thermodynamic work potential. The paper begins with a broad definition of thermodynamic work potential and describes several attributes that make it useful for vehicle design. Among these attributes are the ability to link aerothermodynamic performance and vehicle mass together in a "unified theory of vehicle design," as well as the ability to provide a means for explicitly calculating vehicle operating cost accountability. In addition, work potential methods are suggested as an excellent framework from which to conduct technology risk and benefit studies.
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    A Work Availability Perspective of Turbofan Engine Performance
    (Georgia Institute of Technology, 2001-01) Roth, Bryce Alexander ; Mavris, Dimitri N.
    This paper presents a work availability perspective on the thermodynamic performance of the turbofan engine and contrasts this with the classic presentation, which describes performance based primarily on cycle efficiency. It is shown that the availability perspective leads to a more fundamental understanding of the basic problem, this being to maximize the conversion of work potential stored in the fuel into useful work output. The discussion specifically addresses the impact of primary turbofan cycle parameters on usage and loss of work potential. It is shown that cycle pressure ratio governs exhaust heat losses, turbine inlet temperature governs non-equilibrium combustion losses, and fan pressure ratio governs loss due to residual exhaust kinetic energy. Finally, simplified loss calculation methods applicable to any turbofan engine are presented and the method is applied to the analysis of cycle losses in the Northrop F-5E propulsion system.
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    Adaptive Selection of Engine Technology Solution Sets from a Large Combinatorial Space
    (Georgia Institute of Technology, 2001) Roth, Bryce Alexander ; German, Brian Joseph ; Mavris, Dimitri N. ; Macsotai, Noel I.
    This paper describes a method to assist in selecting technology concepts from amongst a pool of candidates such that the resulting concepts yield the best compromise between conflicting sign performance and technology risk. The heart of this method is a unique technology impact forecasting environment that is used in conjunction with a genetic algorithm as a tool to efficiently explore the technology combinatorial space. The technique is applied to a commercial turbofan engine technology selection problem of practical interest. A pool of forty technology concepts is proposed and evaluated, the objective being to determine which subset of technologies is the best candidate to go forward into development given conflicting objectives on performance, engine manufacturing cost, and design risk (i.e. cumulative technology readiness). Introduction manufacturing cost, design risk, etc. School of Aerospace, Georgia Tech. Member, AIAA. Director, ASDL. Associate Fellow, AIAA.