14th AIAA Aviation Technology, Integration, and Operations Conference, 2014
ABSTRACT This paper presents a systemic approach that combines ideas from system science, system ... more ABSTRACT This paper presents a systemic approach that combines ideas from system science, system engineering and complex networks theory to analyze the nature of passenger air transportation. Two fundamental properties of a system are function and structure. The function of air transport is to transport passengers from origin to destination, and the structure is how this function is provided, i.e. the flight network. Finding an appropriate approach to study the interdependence between function and structure is of prime importance when investigating complex systems such as air transportation. For this task, a conceptual multi-layered network model, called the Z- model, helps in ordering different system viewpoints. The model places function and structure on different layers of interest. It also distinguishes between a latent function, an inherent internal structure and the coupled realized function-structure layers. The latter is the main focus of this paper and it is shown that this part of the system can either be understood as a bi-level network or a set of network paths. The Z- model provides a framework to interpret real world system peculiarities that includes static properties, temporal integration and airline operational relationships. The use case here is Intra-North American passenger air transport. It is found that during the last ten year, the temporal detour of passengers on markets with long travel time improved at the cost of temporal detour of passengers with lower travel time. This is in part attributed to an increase in directness and the changed collaboration behavior of airlines. An airport centrality metric that takes function-structure interdependence into account can help explain anomalies found in previous investigations of air transportation as a complex system.
The purpose of this paper is to study assortativity in global airline collaboration, i.e. whether... more The purpose of this paper is to study assortativity in global airline collaboration, i.e. whether similar airlines tend to collaborate or not. To access more markets and to offer an extended network with better connectivity, airlines collaborate (e.g. in alliances). This paper takes a three step approach. First, a clustering method calculates proximity according to operational, economic and fleet-related attributes. Second, a network community detection algorithm groups airlines to find distinct collaboration classes, based on passengers transferred between airlines. The third step compares the similarity and collaboration classes by measuring their statistical difference according to a mutual information metric. Understanding the relationship between similarity and collaboration provides valuable insight for long-term airline operations planning and policy makers that need to extrapolate future developments in the airline industry. The ultimate goal of this approach is to better un...
Recent international goals for the future development of aviation emphasize the improvement of pe... more Recent international goals for the future development of aviation emphasize the improvement of performance metrics of air transportation systems. Since traditional design processes typically target only individual system elements, like aircraft or air transportation networks, it appears desirable to integrate these different efforts into a single optimization approach. High- fidelity design tools for individual systems are computationally expensive. However, conceptual design methods are typically relatively time efficient. Therefore, this paper introduces an optimization approach that combines conceptual aircraft and network design. The approach couples both tasks by those aircraft requirements that are also relevant for network design, such as aircraft range and capacity. The idea is to provide a subsequent, more detailed aircraft design process with requirement values that appear promising to improve an entire air transportation system. This investigation is exploratory because i...
In aerospace systems design, conflicting dis-ciplines and technologies are always involved in the... more In aerospace systems design, conflicting dis-ciplines and technologies are always involved in the design process. Multi-Criteria Decision Analysis (MCDA) techniques can be helpful to effectively deal with such situations and make wise design decisions. In this paper, the feasibil-ity and added values of applying the MCDA tech-niques in aircraft design are explored. A new op-timization framework incorporating MCDA tech-niques in aircraft conceptual design process is es-tablished. An improved MCDA method is uti-lized to aggregate the multiple design criteria into one composite figure of merit, which serves as an objective function in the optimization pro-cess. It is demonstrated that the suitable MCDA method with improvement provides a better ob-jective function for the optimization than the tra-ditional weighted sum method. Considering that the inherent uncertainties and subjectivities of the weighting factors have crucial impacts on the design solution, surrogate models for the mult...
2014 IEEE International Systems Conference Proceedings, 2014
ABSTRACT Many global socio-economic systems are based on flows of information, energy or matter. ... more ABSTRACT Many global socio-economic systems are based on flows of information, energy or matter. Typically, various organizations and institutions plan, design, implement and operate part of the physical infrastructure necessary to enable the flow, but none of them are the central controlling instance. Collaboration in such self-organized complex systems of flow enables broader market and system connectivity, at the cost of increasing complexity and risk. This paper studies collaborative operator interdependencies by transforming the operators’ networks to the network of operators. The proposed approach analyzes collaboration in systems of flow according to four aspects: quantifying collaboration magnitude, evaluating diversity, finding the most important collaborators and illustrating the large-scale structure of collaboration. The presented use case is commercial air transport between Europe and North America, and vice versa. It is found that, while the flow becomes more direct, there is an increasing probability that a connection occurred among different airlines. The proposed method was also able to display the cyclic dynamics of collaboration heterogeneity and identify the most collaborative airlines. A visualization of the network-of-operators illustrates the large-scale structure of collaboration for the system-ofinterest. This collaboration network is able to capture real world peculiarities such as formation and separation in airline alliances and mergers in a quantitative way.
14th AIAA Aviation Technology, Integration, and Operations Conference, 2014
ABSTRACT This paper presents a systemic approach that combines ideas from system science, system ... more ABSTRACT This paper presents a systemic approach that combines ideas from system science, system engineering and complex networks theory to analyze the nature of passenger air transportation. Two fundamental properties of a system are function and structure. The function of air transport is to transport passengers from origin to destination, and the structure is how this function is provided, i.e. the flight network. Finding an appropriate approach to study the interdependence between function and structure is of prime importance when investigating complex systems such as air transportation. For this task, a conceptual multi-layered network model, called the Z- model, helps in ordering different system viewpoints. The model places function and structure on different layers of interest. It also distinguishes between a latent function, an inherent internal structure and the coupled realized function-structure layers. The latter is the main focus of this paper and it is shown that this part of the system can either be understood as a bi-level network or a set of network paths. The Z- model provides a framework to interpret real world system peculiarities that includes static properties, temporal integration and airline operational relationships. The use case here is Intra-North American passenger air transport. It is found that during the last ten year, the temporal detour of passengers on markets with long travel time improved at the cost of temporal detour of passengers with lower travel time. This is in part attributed to an increase in directness and the changed collaboration behavior of airlines. An airport centrality metric that takes function-structure interdependence into account can help explain anomalies found in previous investigations of air transportation as a complex system.
The purpose of this paper is to study assortativity in global airline collaboration, i.e. whether... more The purpose of this paper is to study assortativity in global airline collaboration, i.e. whether similar airlines tend to collaborate or not. To access more markets and to offer an extended network with better connectivity, airlines collaborate (e.g. in alliances). This paper takes a three step approach. First, a clustering method calculates proximity according to operational, economic and fleet-related attributes. Second, a network community detection algorithm groups airlines to find distinct collaboration classes, based on passengers transferred between airlines. The third step compares the similarity and collaboration classes by measuring their statistical difference according to a mutual information metric. Understanding the relationship between similarity and collaboration provides valuable insight for long-term airline operations planning and policy makers that need to extrapolate future developments in the airline industry. The ultimate goal of this approach is to better un...
Recent international goals for the future development of aviation emphasize the improvement of pe... more Recent international goals for the future development of aviation emphasize the improvement of performance metrics of air transportation systems. Since traditional design processes typically target only individual system elements, like aircraft or air transportation networks, it appears desirable to integrate these different efforts into a single optimization approach. High- fidelity design tools for individual systems are computationally expensive. However, conceptual design methods are typically relatively time efficient. Therefore, this paper introduces an optimization approach that combines conceptual aircraft and network design. The approach couples both tasks by those aircraft requirements that are also relevant for network design, such as aircraft range and capacity. The idea is to provide a subsequent, more detailed aircraft design process with requirement values that appear promising to improve an entire air transportation system. This investigation is exploratory because i...
In aerospace systems design, conflicting dis-ciplines and technologies are always involved in the... more In aerospace systems design, conflicting dis-ciplines and technologies are always involved in the design process. Multi-Criteria Decision Analysis (MCDA) techniques can be helpful to effectively deal with such situations and make wise design decisions. In this paper, the feasibil-ity and added values of applying the MCDA tech-niques in aircraft design are explored. A new op-timization framework incorporating MCDA tech-niques in aircraft conceptual design process is es-tablished. An improved MCDA method is uti-lized to aggregate the multiple design criteria into one composite figure of merit, which serves as an objective function in the optimization pro-cess. It is demonstrated that the suitable MCDA method with improvement provides a better ob-jective function for the optimization than the tra-ditional weighted sum method. Considering that the inherent uncertainties and subjectivities of the weighting factors have crucial impacts on the design solution, surrogate models for the mult...
2014 IEEE International Systems Conference Proceedings, 2014
ABSTRACT Many global socio-economic systems are based on flows of information, energy or matter. ... more ABSTRACT Many global socio-economic systems are based on flows of information, energy or matter. Typically, various organizations and institutions plan, design, implement and operate part of the physical infrastructure necessary to enable the flow, but none of them are the central controlling instance. Collaboration in such self-organized complex systems of flow enables broader market and system connectivity, at the cost of increasing complexity and risk. This paper studies collaborative operator interdependencies by transforming the operators’ networks to the network of operators. The proposed approach analyzes collaboration in systems of flow according to four aspects: quantifying collaboration magnitude, evaluating diversity, finding the most important collaborators and illustrating the large-scale structure of collaboration. The presented use case is commercial air transport between Europe and North America, and vice versa. It is found that, while the flow becomes more direct, there is an increasing probability that a connection occurred among different airlines. The proposed method was also able to display the cyclic dynamics of collaboration heterogeneity and identify the most collaborative airlines. A visualization of the network-of-operators illustrates the large-scale structure of collaboration for the system-ofinterest. This collaboration network is able to capture real world peculiarities such as formation and separation in airline alliances and mergers in a quantitative way.
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Papers by Stephan Lehner