User equilibrium, system optimum, and externalities in time-dependent road networks

This paper develops a comprehensive framework for analysing and calculating user equilibrium, system optimum, and externalities in time-dependent road networks. Under dynamic user equilibrium, traffic is assigned such that for each origin-destination pair in the network, the individual travel costs experienced by each traveller, no matter which combination of travel route and departure time he/she chooses, are equal and minimal. The system optimal flow is determined by solving a state-dependent optimal control problem, which assigns traffic such that the total system cost of the network system is minimized. The externalities are derived by using a novel sensitivity analysis. The analyses developed in this paper can work with general travel cost functions. Numerical examples are provided for illustration and discussion. Finally, some concluding remarks are given

Analysis of dynamic traffic models and assignments

This paper develops a comprehensive framework for analysing and solving traffic models and assignments in dynamic setting. Traffic models capture the time-varying travel times and flows on a road network and traffic assignments represent the corresponding responses of travellers. There are two different kinds of traffic assignments: dynamic user equilibrium and dynamic system optimum. Under dynamic user equilibrium, traffic is assigned such that for each origin-destination pair in the network, the individual travel costs experienced by each traveller, no matter which combination of travel route and departure time he/she chooses, are equal and minimal. The system optimum assigns traffic such that the total system cost of the network system is minimized. The system optimal traffic pattern provides a useful benchmark for evaluating various transport policy measures such as implementing dynamic road tolls. This system optimal assignment is formulated as a state-dependent optimal control problem. The analysis developed in this paper is novel and it can work with general travel cost functions. Numerical examples are provided for illustration and discussion. Finally, some concluding remarks are given

Resource Management Algorithms for Computing Hardware Design and Operations: From Circuits to Systems

The complexity of computation hardware has increased at an unprecedented rate for the last few decades. On the computer chip level, we have entered the era of multi/many-core processors made of billions of transistors. With transistor budget of this scale, many functions are integrated into a single chip. As such, chips today consist of many heterogeneous cores with intensive interaction among these cores. On the circuit level, with the end of Dennard scaling, continuously shrinking process technology has imposed a grand challenge on power density. The variation of circuit further exacerbated the problem by consuming a substantial time margin. On the system level, the rise of Warehouse Scale Computers and Data Centers have put resource management into new perspective. The ability of dynamically provision computation resource in these gigantic systems is crucial to their performance. In this thesis, three different resource management algorithms are discussed. The first algorithm assigns adaptivity resource to circuit blocks with a constraint on the overhead. The adaptivity improves resilience of the circuit to variation in a cost-effective way. The second algorithm manages the link bandwidth resource in application specific Networks-on-Chip. Quality-of-Service is guaranteed for time-critical traffic in the algorithm with an emphasis on power. The third algorithm manages the computation resource of the data center with precaution on the ill states of the system. Q-learning is employed to meet the dynamic nature of the system and Linear Temporal Logic is leveraged as a tool to describe temporal constraints. All three algorithms are evaluated by various experiments. The experimental results are compared to several previous work and show the advantage of our methods

Single-machine scheduling with stepwise tardiness costs and release times

We study a scheduling problem that belongs to the yard operations component of the railroad planning problems, namely the hump sequencing problem. The scheduling problem is characterized as a single-machine problem with stepwise tardiness cost objectives. This is a new scheduling criterion which is also relevant in the context of traditional machine scheduling problems. We produce complexity results that characterize some cases of the problem as pseudo-polynomially solvable. For the difficult-to-solve cases of the problem, we develop mathematical programming formulations, and propose heuristic algorithms. We test the formulations and heuristic algorithms on randomly generated single-machine scheduling problems and real-life datasets for the hump sequencing problem. Our experiments show promising results for both sets of problems

Optimal Orchestration of Virtual Network Functions

-The emergence of Network Functions Virtualization (NFV) is bringing a set of novel algorithmic challenges in the operation of communication networks. NFV introduces volatility in the management of network functions, which can be dynamically orchestrated, i.e., placed, resized, etc. Virtual Network Functions (VNFs) can belong to VNF chains, where nodes in a chain can serve multiple demands coming from the network edges. In this paper, we formally define the VNF placement and routing (VNF-PR) problem, proposing a versatile linear programming formulation that is able to accommodate specific features and constraints of NFV infrastructures, and that is substantially different from existing virtual network embedding formulations in the state of the art. We also design a math-heuristic able to scale with multiple objectives and large instances. By extensive simulations, we draw conclusions on the trade-off achievable between classical traffic engineering (TE) and NFV infrastructure efficiency goals, evaluating both Internet access and Virtual Private Network (VPN) demands. We do also quantitatively compare the performance of our VNF-PR heuristic with the classical Virtual Network Embedding (VNE) approach proposed for NFV orchestration, showing the computational differences, and how our approach can provide a more stable and closer-to-optimum solution

System optimal traffic assignment with departure time choice

This thesis investigates analytical dynamic system optimal assignment with departure time choice in a rigorous and original way. Dynamic system optimal assignment is formulated here as a state-dependent optimal control problem. A fixed volume of traffic is assigned to departure times and routes such that the total system travel cost is minimized. Although the system optimal assignment is not a realistic representation of traffic, it provides a bound on performance and shows how the transport planner or engineer can make the best use of the road system, and as such it is a useful benchmark for evaluating various transport policy measures. The analysis shows that to operate the transport system optimally, each traveller in the system should consider the dynamic externality that he or she imposes on the system from the time of his or her entry. To capture this dynamic externality, we develop a novel sensitivity analysis of travel cost. Solution algorithms are developed to calculate the dynamic externality and traffic assignments based on the analyses. We also investigate alternative solution strategies and the effect of time discretization on the quality of calculated assignments. Numerical examples are given and the characteristics of the results are discussed. Calculating dynamic system optimal assignment and the associated optimal toll could be too difficult for practical implementation. We therefore consider some practical tolling strategies for dynamic management of network traffic. The tolling strategies considered in this thesis include both uniform and congestion-based tolling strategies, which are compared with the dynamic system optimal toll so that their performance can be evaluated. In deriving the tolling strategies, it is assumed that we have an exact model for the underlying traffic behaviour. In reality, we do not have such information so that the robustness of a toll calculation method is an important issue to be investigated in practice. It is found that the tolls calculated by using divided linear traffic models can perform well over a wide range of scenarios. The divided linear travel time models thus should receive more attention in the future research on robust dynamic traffic control strategies design. In conclusion, this thesis contributes to the literature on dynamic traffic modelling and management, and to support further analysis and model development in this area

Airport airside balanced capacity usage and planning

U doktorskoj disertaciji je predložen postupak za analizu kapaciteta vazdušne strane aerodroma, za zadata fizička i operativna ograničenja, i zadate karakteristike potražnje. Ovaj postupak podrazumeva povezivanje (postojećeg) modela za procenu kapaciteta sistema poletno-sletnih staza sa (proširenim) modelom za procenu kapaciteta pristanišne platforme, kroz njihovu funkcionalnu vezu. Cilj ove doktorske disertacije je bio vrednovanje i, po potrebi, modifikovanje i proširenje postojećih modela za procenu kapaciteta platforme, kao i definisanje funkcionalne veze između poletno-sletne staze i platforme za različite tipove saobraćaja. Postojeći modeli su prošireni tako da uzimaju u obzir ograničenja po tipu aviona i korisnicima (npr. aviokompanije), kao i po vrsti saobraćaja. U cilju analize osetljivosti, predlažene su obvojnice za prikazivanje kapaciteta platforme određene konfiguracije, u zavisnosti od strukture potražnje u odnosu na glavne uticajne faktore. Analiza je obuhvatila dva osnovna tipa aerodroma sa aspekta njihove uloge u mrežama vazdušnog saobraćaja, a to su: izvorno-ciljni aerodromi, sa dominantnim saobraćajem od-tačke-do-tačke, i hub aerodromi, sa dominantnim transfernim saobraćajem za koji je karakteristično da se koncentriše u talase. Dodatno su analizirani i aerodromi na kojima postoje oba tipa saobraćaja. Rezultati disertacije pokazuju da se za izvorno-ciljne aerodrome može koristiti standardni pristup prilikom analize ukupnog kapaciteta vazdušne strane aerodroma, u kome se poletno-sletna staza i pristanišna platforma posmatraju odvojeno, pri čemu manji kapacitet nameće ograničenje ukupnog kapaciteta. Sa druge strane, u slučaju hub aerodroma kapacitet platforme i kapacitet poletno-sletne staze se ne mogu posmatrati nezavisno jedan od drugog. S tim u skladu, u ovoj doktorskoj disertaciji predložen je model za procenu kapaciteta platforme na hub aerodromima, koji pored konfiguracije platforme i strukture potražnje uzima u obzir i kapacitet poletno-sletne staze, kao i parametre koji opisuju talasnu strukturu saobraćaja...The thesis proposes an approach to analyzing the capacity of the existing (built) system under given physical and operational constraints and for given demand characteristics. The approach considers the linking of the (existing) runway capacity model with the (extended) apron capacity model, through the runway-apron functional relationship. The objective of the thesis was to evaluate and, if necessary, to modify/expand the existing apron capacity estimation models, as well as to define functional relationship between the runway system and apron(s). Existing apron capacity models are modified to include constraints on both aircraft classes and users (e.g. airlines), considering also different traffic types. The thesis also suggests apron capacity envelopes to illustrate sensitivity of apron capacity to changes in the demand structure with respect to dominant users, provided for a given apron configuration. Two general airport categories with respect to the role of the airport in the air transport network are analyzed: origin-destination airports (serving primarily point-to-point flights) and hub airports (serving primarily airline/alliance coordinated flights). Furthermore, the thesis also considers the co-existence of point-to-point and coordinated flights at a single airport. The results of the thesis show that the common approach in the overall airside capacity analysis can be applied at origin-destination airports: the runway system and apron(s) can be observed independently of each other, deriving the conclusion on the overall airside capacity by comparing the two. On the other hand, the finding of the thesis is that capacities of the runway system and apron(s) at the hub airports have to be observed linked to each other. Consequently, a model to estimate apron capacity at hub airport is offered in the thesis. In addition to apron configuration and demand structure it also takes into consideration: hubbing parameters and the runway system performance..