http://hdl.handle.net/1721.1/7759 Wed, 19 Jun 2013 15:16:52 GMT 2013-06-19T15:16:52Z http://hdl.handle.net/1721.1/79343 Improved continuous-time higher harmonic control using [Eta] [infinity] methods Fan, Frank H. (Frank Hsiao) The helicopter is a versatile aircraft that can take-off and land vertically, hover efficiently, and maneuver in confined space. This versatility is enabled by the main rotor, which also causes undesired harmonic vibration during operation. This unwanted vibration has a negative impact on the practicality of the helicopter and also increases its operational cost. Passive control techniques have been applied to helicopter vibration suppression, but these methods are generally heavy and are not robust to changes in operating conditions. Feedback control offers the advantages of robustness and potentially higher performance over passive control techniques, and amongst the various feedback schemes, Shaw's higher harmonic control algorithm has been shown to be an effective method for attenuating harmonic disturbance in helicopters. In this thesis, the higher harmonic disturbance algorithm is further developed to achieve improved performance. One goal in this thesis is to determine the importance of periodicity in the helicopter rotor dynamics for control synthesis. Based on the analysis of wind tunnel data and simulation results, we conclude the helicopter rotor can be modeled reasonably well as linear and time-invariant for control design purposes. Modeling the helicopter rotor as linear time-invariant allows us to apply linear control theory concepts to the higher harmonic control problem. Another goal in this thesis is to find the limits of performance in harmonic disturbance rejection. To achieve this goal, we first define the metrics to measure the performance of the controller in terms of response speed and robustness to changes in the plant dynamics. The performance metrics are incorporated into an [Eta] [infinity] control problem. For a given plant, the resulting [Eta] [infinity] controller achieves the maximum performance, thus allowing us to identify the performance limitation in harmonic disturbance rejection. However, the [Eta] [infinity] controllers are of high order, and may have unstable poles, leading us to develop a design method to generate stable, fixed-order, and high performance controllers. Both the [Eta] [infinity] and the fixed-order controllers are designed for constant flight conditions. A gain-scheduled control law is used to reduce the vibration throughout the flight envelope. The gain-scheduling is accomplished by blending the outputs from fixed-order controllers designed for different flight conditions. The structure of the fixed-order controller allows the usage of a previously developed anti-windup scheme, and the blending function results in a bumpless full flight envelope control law. Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2013.; This thesis was scanned as part of an electronic thesis pilot project.; In title on title-page, "[Eta]" appears as the upper-case Greek letter; and, "[infinity]" appears as the symbol. Cataloged from PDF version of thesis.; Includes bibliographical references (p. 171-181). Tue, 01 Jan 2013 00:00:00 GMT http://hdl.handle.net/1721.1/79343 2013-01-01T00:00:00Z http://hdl.handle.net/1721.1/79342 Analysis, modeling and control of the airport departure process Simaiakis, Ioannis Increased air traffic demand over the past two decades has resulted in significant increases in surface congestion at major airports in the United States. The overall objective of this thesis is to mitigate the adverse effects of airport surface congestion, including increased taxi-out times, fuel burn, and emissions. The thesis tackles this objective in three steps: The first part deals with the analysis of departure operations and the characterization of airport capacity; the second part develops a new model of the departure process; and the third part of the thesis proposes and tests, both on the field and in simulations, algorithms for the control of the departure process. The characterization and estimation of airport capacity is essential for the successful management of congestion. This thesis proposes a new parametric method for estimating the departure capacity of a runway system, the most constrained element of most airports. The insights gained from the proposed technique are demonstrated through a case study of Boston Logan International Airport (BOS). Subsequently, the methodology is generalized to the study of interactions among the three main airports of the New York Metroplex, namely, John F. Kennedy International Airport (JFK), Newark Liberty International Airport (EWR) and LaGuardia Airport (LGA). The individual capacities of the three airports are estimated, dependencies between their operations are identified, and the capacity of the Metroplex as a whole is characterized. The thesis also identifies opportunities for improving the operational capacity of the Metroplex without significant redesign of the airspace. The proposed methodology is finally used to assess the relationship between route availability during convective weather and the capacity of LGA. The second part of the thesis develops a novel analytical model of the departure process. The modeling procedure includes the estimation of unimpeded taxi-out time distributions, and the development of a stochastic and dynamic queuing model of the departure runway(s), based on the transient analysis of D(t)=Ek(t)=1 queuing systems. The parameters of the runway service process are estimated using operational data. Using the aircraft pushback schedule as input, the model predicts the expected runway schedule and the takeoff times. It also estimates the expected queuing delay and its variance for each light, along with the congestion level of the airport, sizes of the departure queues, and the departure throughput. The model is trained using data from EWR in 2011, and is subsequently used to predict taxi-out times at EWR in 2007 and 2010. The final part of this thesis proposes dynamic programming algorithms for controlling the departure process, given the current operating environment. These algorithms, called Pushback Rate Control protocols, predict the departure throughput of the airport, and recommend a rate at which to release pushbacks from the gate in order to control congestion. The thesis describes the design and field-testing of a variant of Pushback Rate Control at BOS in 2011, and the development of a decision-support tool for its implementation. The analysis shows that during 8 four-hour test periods, fuel use was reduced by an estimated 9 US tons (2,650 US gallons), and taxi-out times were reduced by an average of 5.3 min for the 144 flights that were held at the gate. The thesis concludes with simulations of the Pushback Rate Control protocol at Philadelphia International Airport (PHL), one of the most congested airports in the US, and a discussion of the potential benefits and implementation challenges. Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2013.; This electronic version was submitted and approved by the author's academic department as part of an electronic thesis pilot project. The certified thesis is available in the Institute Archives and Special Collections.; Cataloged from department-submitted PDF version of thesis.; Includes bibliographical references (p. 305-313). Tue, 01 Jan 2013 00:00:00 GMT http://hdl.handle.net/1721.1/79342 2013-01-01T00:00:00Z http://hdl.handle.net/1721.1/79341 Influence strategies for systems of systems Shah, Nirav Bharat, 1979- Distributed decision making has been identified as a source of managerial complexity for leaders of systems of systems (SoS). A new framework, AIR (Anticipation-Influence-Reaction), is proposed to capture the feedback relationships between the decisions made by constituents and those made by the managers of the SoS. AIR is then used to develop a five-member set of basic influences that can bring about changes in constituent behavior thus modifying the SoS. These influences, the 5 Is, are Incentives, Information, Infrastructure, Integration, and Institutions. AIR and the influences are demonstrated through qualitative application to real-world SoSs and quantitatively through simulation of an inter-modal freight transport network. It is found that cooperation between competing constituents, i.e., rail and truck carriers, can be quite fragile and sensitive to the SoS context. Careful, dynamic planning of influence strategies is needed to maintain SoS behavior in the face of constituents who are driven by self-interest and a limited, local perspective of the SoS. Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2013.; This electronic version was submitted and approved by the author's academic department as part of an electronic thesis pilot project. The certified thesis is available in the Institute Archives and Special Collections.; Cataloged from department-submitted PDF version of thesis.; Includes bibliographical references (p. 141-149). Tue, 01 Jan 2013 00:00:00 GMT http://hdl.handle.net/1721.1/79341 2013-01-01T00:00:00Z http://hdl.handle.net/1721.1/79340 An approach to analyze tradeoffs for aerospace system design and operation O'Neill, Michael Gregory There are important tradeoffs that need to be considered for the design and operation of aerospace systems. In addition to tradeoffs, there may also be multiple stakeholders of interest to the system and each may have different preferences as to the balance amongst the tradeoffs under consideration. A tradeoff hyperspace is created when there are three or more tradeoff dimensions and this increases the challenge associated with resolving the hyperspace in order to determine the best design and operation of a system. The corresponding objectives of this research are to develop a framework to analyze tradeoff hyperspaces and to account for the preferences of multiple stakeholders in this framework. The framework developed in this research is called the Tradeoff Analysis Framework and its applicability was evaluated through analyzing three different case studies in the aerospace domain, each progressively more complex in terms of applying the framework and exploring the impact of certain types or change, or innovation in the system of interest. The first case study analyzed the impact of changing aircraft cruise operations and one facet of the case study explored the impact of imposing a hypothetical tax on aircraftproduced contrails. From this study it was determined that airlines will change their behavior (i.e., their perceived value-optimal cruise trajectory) in response to a tax placed on producing contrails where, the higher the tax, the less contrails they choose to produce. The second case study explored the impact of changes in aircraft approach procedures into Boston-Logan airport. In this study, there were multiple stakeholders, each with different preferences as to the balance amongst the performance and environmental tradeoffs considered. A key result from this study was that competing stakeholder preferences could be partially resolved, which led to the design new approach procedures that were beneficial to all stakeholders. The third and last case study examined the tradeoffs associated with using fractionated spacecraft for remote sensing space missions. Here, the current paradigm is monolithic spacecraft and it was found that despite fractionated spacecraft demonstrating more value-robustness than a comparable monolith, they fail to stay value-competitive to monoliths in terms of absolute value delivered. In particular, this occurs because presently the enabling technologies required for fractionated spacecraft are not yet mature and reliable enough at the performance levels needed for them to become viable alternatives to monoliths. Along with insights gained in the case studies about the systems of interest, through applying the Tradeoff Analysis Framework insights were gained with respect to implementing the framework. These insights form the methodological contributions of this research since they offer opportunities to learn about the breadth of potential framework applicability and areas for subsequent improvements in the framework for future use. Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2013.; This electronic version was submitted and approved by the author's academic department as part of an electronic thesis pilot project. The certified thesis is available in the Institute Archives and Special Collections.; Cataloged from department-submitted PDF version of thesis.; Includes bibliographical references (p. 181-189). Tue, 01 Jan 2013 00:00:00 GMT http://hdl.handle.net/1721.1/79340 2013-01-01T00:00:00Z