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On improving efficiency of flight using optimization
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics. (Division of flight dynamics)
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, optimization is used to improve the performance of aircraft. The focus is on operating current generation aircraft more efficiently rather than designing new aircraft. Drag minimization and aircraft trajectory optimization is used to increase efficiency. Optimization methods are implemented and evaluated on different problem formulations.

The first part of the thesis presents a drag minimization strategy using multiple control surfaces distributed across the span of an elastic wing. Aeroelasticity is exploited to reduce drag for a wide range of flight conditions. A method to minimize drag during a long distance flight is developed and tested in a wind tunnel environment. The method is based on continuously changing the control surface deflections to obtain a more beneficial load distribution from a drag point of view for the current flight condition. In a second study, the method is extended to include the angle of attack as a variable together with the control surface deflections in the drag minimization algorithm. Extensive wind tunnel testing demonstrates the possibility to reduce drag significantly with the presented method for a wide range of flight conditions.

The second topic in the thesis is optimizing the aircraft trajectory. The emissions from the aircraft engine are modeled as smooth functions suitable for optimization using published certification data. These emissions are combined in different environmental indices and used as objective functions in the aircraft trajectory optimization problem. The optimization problem is formulated by discretizing the trajectory in time. The resulting large scale nonlinear optimization problem is solved using a sequential quadratic programming method. The trajectory optimization problem is first studied using a model of the Boeing 737 and the results show that the optimal trajectory depends significantly on the definition of the environmental objective function. A method to treat restricted airspace is also presented and evaluated using a model of the Swedish Air Force trainer SK60. The results show that the method for imposing airspace constraints on the flight path works well, especially when the initial point for the optimization is feasible.

 

Place, publisher, year, edition, pages
Stockholm: KTH , 2009. , p. 37
Series
Trita-AVE, ISSN 1651-7660 ; 2009:45
National Category
Vehicle Engineering
Identifiers
URN: urn:nbn:se:kth:diva-10958OAI: oai:DiVA.org:kth-10958DiVA, id: diva2:233077
Public defence
2009-09-22, F3, KTH, Lindstedtsvägen 26, Stockholm, 10:15 (English)
Opponent
Supervisors
Note
QC 20100720Available from: 2009-09-04 Created: 2009-08-27 Last updated: 2010-07-20Bibliographically approved
List of papers
1. Real time drag minimization using redundant control surfaces
Open this publication in new window or tab >>Real time drag minimization using redundant control surfaces
2006 (English)In: Aerospace Science and Technology, ISSN 1270-9638, E-ISSN 1626-3219, Vol. 10, no 7, p. 574-580Article in journal (Refereed) Published
Abstract [en]

A method for minimizing the drag of a wind tunnel model with multiple control surfaces is presented. The minimization is performed in the wind tunnel and measurements are performed in real time. Real time measurements introduce difficulties such as noise in the signals, hysteresis and problems with repeatability of the function evaluations. The lack of a numerical function to minimize therefore puts certain demands on the optimization method, and hence a derivative free method, often referred to as a generating set search method, is used. The proposed method is generalized to take both linear equality constraints as well as linear inequality constraints into account. The generating set search method is implemented in the wind tunnel and tests show that the drag can be decreased while satisfying the constraints.

Keywords
Performance optimization, Real time computing, Wind tunnel testing, Direct search method
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-10953 (URN)10.1016/j.ast.2006.05.002 (DOI)000241577500003 ()2-s2.0-33749664340 (Scopus ID)
Note
QC 20100720Available from: 2009-08-27 Created: 2009-08-27 Last updated: 2017-12-13Bibliographically approved
2. Airspace constraints in aircraft emission trajectory optimization
Open this publication in new window or tab >>Airspace constraints in aircraft emission trajectory optimization
(English)Manuscript (preprint) (Other academic)
Abstract [en]

This paper describes a method for handling restricted airspace in trajectory optimization problems while maintaining the full dynamics of the aircraft model. The discussion is limited to the local solution of the optimization problem. The topological problem of determining which side of the restricted regions the aircraft trajectory should take can be seen as more of a preprocessing stage determining, for example, the shortest path. The trajectory optimization is performed with environmental objective functions describing the emissions from the aircraft engine. Results from two cases are presented. The first case is flying in the vicinity of an airport during the approach and avoiding flying directly above urban areas. The second case involves a long distance flight with a large region of restricted airspace in the way. Both cases are performed with a model of the Swedish Air Force trainer SK60. The results show that the solution, and the solution time, depend significantly on the initial starting guess. With a feasible starting guess, the efficiency of the optimization algorithm is not too degraded due to the nonconvex airspace constraints.

 

Keywords
Tractory optimization, nonconvex airspace constraints, emissions
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-10956 (URN)
Note
QC 20100720Available from: 2009-08-27 Created: 2009-08-27 Last updated: 2010-07-20Bibliographically approved
3. Performance optimization of flexible wings using multiple control surfaces
Open this publication in new window or tab >>Performance optimization of flexible wings using multiple control surfaces
2009 (English)In: International forum on aeroelasticity and structural dynamics, 2009, p. 1-15Conference paper, Published paper (Other academic)
Abstract [en]

In this study, the performance of a flexible wing with multiple control surfaces is optimized for different flight conditions. A wind tunnel model with 16 independent control surfaces is used as the test case. The problem is posed as a nonlinear optimization problem with the measured drag as the objective. The variables are the control surface deflections and the angle of attack. Using direct measurements and hardware in the optimization loop causes several difficulties such as problems with repeatability and drift in the measured signal. Constraints include maintaining the lift as well as bounds on the control surface deflections and the angle of attack. No computational estimation of the drag is performed. Instead, experimental measurements of the drag are used to perform the optimization during the wind tunnel test using a generating set search method. Including the angle of attack as a variable makes the lift constraint slightly nonlinear. An extension to the generating set search method is discussed and implemented to treat this nonlinearity. The algorithm makes the wing adapt to the current flight condition to improve performance. The experimental evaluation of the method shows that the drag is significantly reduced within a wide range of flight conditions.

Keywords
Performance optimization, Nonlinear constraints, Generating set search, derivative-free optimization, drag minimization, wind tunnel testing
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-10954 (URN)
Note
QC 20100617Available from: 2009-08-27 Created: 2009-08-27 Last updated: 2010-07-20Bibliographically approved
4. Reducing emissions using aircraft trajectory optimization
Open this publication in new window or tab >>Reducing emissions using aircraft trajectory optimization
(English)In: Aerospace Science and Technology, ISSN 1270-9638, E-ISSN 1626-3219Article in journal (Other academic) Submitted
Abstract [en]

Optimal aircraft trajectories reducing engine emissions are computed using numerical optimization. The emissions from the jet engine are modeled as functions of the aircraft altitude, airspeed and throttle setting. Combining the emission models with a performance model of the aircraft, the optimization problem is formulated with the objective of reducing emissions for a given distance flight. The resulting problem, involving a system of differential and algebraic equations, is discretized using collocation and the optimization problem is solved using sequential quadratic programming. Different objectives are investigated, such as minimizing the total emissions of carbon dioxide, carbon monoxide, oxides of nitrogen and hydrocarbons during a flight. Methods from life cycle impact assessment are used to weigh the different emissions to an index and several different indices are used and compared. A model of the Boeing 737-600 is used to illustrate the developed optimization method. The results show that the trajectories differ significantly depending on the chosen objective. Using a combination of objectives at different altitudes may give the most appropriate problem formulation.

Keywords
Trajectory optimization, Boeing fuel flow method, Emissions index
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-10955 (URN)
Note
QS 20120327Available from: 2009-08-27 Created: 2009-08-27 Last updated: 2017-12-13Bibliographically approved

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