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High-resolution relaxation approximations to second-order macroscopic traffic flow models

(Elsevier, 2014) Delis Anargyros; Δελης Αναργυρος; Nikolos Ioannis; Νικολος Ιωαννης; Papageorgiou Markos; Παπαγεωργιου Μαρκος

A novel numerical approach for the approximation of several, widely applied, macroscopic traffic flow models is presented. A relaxation-type approximation of second-order nonequilibrium models, written in conservation or balance law form, is considered. Using the relaxation approximation, the nonlinear equations are transformed to a semi-linear diagonilizable problem with linear characteristic variables and stiff source terms. To discretize the resulting relaxation system, low- and high-resolution reconstructions in space and implicit–explicit Runge–Kutta time integration schemes are considered. The family of spatial discretizations includes a second-order MUSCL scheme and a fifth-order WENO scheme, and a detailed formulation of the scheme is presented. Emphasis is given on the WENO scheme and its performance for solving the different traffic models. To demonstrate the effectiveness of the proposed approach, extensive numerical tests are performed for the different models. The computations reported here demonstrate the simplicity and versatility of relaxation schemes as solvers for macroscopic traffic flow models.

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Mainstream traffic flow control on freeways using variable speed limits

(ANPET - Associação Nacional de Pesquisa e Ensino em Transportes, 2013) Carlson Rodrigo Castelan; Papamichail Ioannis; Παπαμιχαηλ Ιωαννης; Papageorgiou Markos; Παπαγεωργιου Μαρκος

Mainstream Traffic Flow Control (MTFC), enabled via variable speed limits, is a control concept for real-time freeway traffic management. The benefits of MTFC for efficient freeway traffic flow have been demonstrated recently using an optimal control approach and a feedback control approach. In this paper, both control approaches are reviewed and applied to a freeway network in a simulation environment. The validated network model used reflects an actual freeway (a ring-road), fed with actual (measured) demands. The optimal and feedback control results are discussed, compared and demonstrated to improve significantly the system performance. In particular, the feedback control scheme is deemed suitable for immediate practical application as it takes into account operational requirements and constraints, while its results are shown to be satisfactory. In addition, the control system performance was not very sensitive to variations of the parameters of the feedback controller. This result indicates that the burden associated with fine tuning of the controller may be reduced in the field.

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Fuzzy control optimized by a Multi-Objective Differential Evolution algorithm for vibration suppression of smart structures

(Elsevier, 2015) Georgios E. Stavroulakis; Yannis Marinakis; Magdalene Marinaki; Marinaki Magdalini; Μαρινακη Μαγδαληνη; Marinakis Ioannis; Μαρινακης Ιωαννης

Smart structures include elements of active, passive or hybrid control. The fuzzy control is considered which is a suitable tool for the systematic development of active control strategies. A new Multi-Objective Differential Evolution algorithm for the calculation of the free parameters in active control systems is proposed and tested. In particular, the usage of MODE with a combination of continuous and discrete variables for the optimal design of the controller is proposed. Numerical applications on smart piezoelastic beams are presented. The results obtained are compared with the ones obtained with the fuzzy controller optimized by a MOPSO algorithm.

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Nonaqueous liquid pool dissolution in three-dimensional heterogeneous subsurface formations

(2003) Chrysikopoulos Constantinos; Χρυσικοπουλος Κωνσταντινος; E.T. Vogler; W.M.J. Bao

A three-dimensional numerical flow and contaminant transport model is developed to investigate the effect of variable hydraulic conductivity on average mass transfer coefficients associated with the dissolution of dense nonaqueous phase liquid (DNAPL) pools in heterogeneous, water-saturated subsurface formations. Randomly generated, threedimensional hydraulic conductivity fields are used to represent a heterogeneous confined aquifer. Model simulations indicate that the average mass transfer coefficient is inversely proportional to the variance of the log-transformed hydraulic conductivity. A power law correlation relating the Sherwood number to the variance of the log-transformed hydraulic conductivity and appropriate Peclet numbers is developed. A reasonable fit between predicted and numerically determined mass transfer coefficients is observed

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Learning model-free robot control by a Monte Carlo EM algorithm

(Springer Verlag, 2009) Toussaint Marc; Kontes Georgios; Piperidis Savvas; Πιπεριδης Σαββας; Vlassis Nikos

We address the problem of learning robot control by model-free reinforcement learning (RL). We adopt the probabilistic model of Vlassis and Toussaint (2009) for model-free RL, and we propose a Monte Carlo EM algorithm (MCEM) for control learning that searches directly in the space of controller parameters using information obtained from randomly generated robot trajectories. MCEM is related to, and generalizes, the PoWER algorithm of Kober and Peters (2009). In the finite-horizon case MCEM reduces precisely to PoWER, but MCEM can also handle the discounted infinite-horizon case. An interesting result is that the infinite-horizon case can be viewed as a ‘randomized’ version of the finite-horizon case, in the sense that the length of each sampled trajectory is a random draw from an appropriately constructed geometric distribution. We provide some preliminary experiments demonstrating the effects of fixed (PoWER) vs randomized (MCEM) horizon length in two simulated and one real robot control tasks.

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Integrated feedback ramp metering and mainstream traffic flow control on motorways using variable speed limits

(Elsevier, 2014) Carlson Rodrigo Castelan; Papamichail Ioannis; Παπαμιχαηλ Ιωαννης; Papageorgiou Markos; Παπαγεωργιου Μαρκος

Ramp metering (RM) is the most direct and efficient tool for the motorway traffic flow management. However, because of the usually short length of the on-ramps, RM is typically deactivated to avoid interference of the created ramp queue with adjacent street traffic. By the integration of local RM with mainstream traffic flow control (MTFC) enabled via variable speed limits (VSL), control operation upstream of active bottlenecks could be continued even if the on-ramp is full or if the RM lower bound has been reached. Such integration is proposed via the extension of an existing local cascade feedback controller for MTFC-VSL by use of a split-range-like scheme that allows different control periods for RM and MTFC-VSL. The new integrated controller remains simple yet efficient and suitable for field implementation. The controller is evaluated in simulation for a real motorway infrastructure (a ring-road) fed with real (measured) demands and compared to stand-alone RM or MTFC-VSL, both with feedback and optimal control results. The controller’s performance is shown to meet the specifications and to approach the optimal control results for the investigated scenario.

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A dinuclear double-helical complex of potassium ions with acompartmental bridging ligand containing two terdentate N-donorfragments

(Royal Society of Chemistry, 1997) Elefteria Psillakis; Johná C Jeffery; Joná A McCleverty; Michaelá D Ward

Recently helicates have become a well known structural motif in supramolecular coordination chemistry.1–4 They are of particular interest not just for their appealing structures but also because of the processes of molecular recognition and self- assembly that are required for their formation. Their formation requires (i) ligands which contain several discrete metal-ion binding domains, and (ii) metal ions with specific preferences for particular coordination geometries that match the ligand binding sites.

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Global exponential stability for discrete-time networks with applications to traffic networks

(Institute of Electrical and Electronics Engineers, 2015) Karafyllis Iason; Καραφυλλης Ιασων; Papageorgiou Markos; Παπαγεωργιου Μαρκος

This paper provides sufficient conditions for global asymptotic stability and global exponential stability, which can be applied to nonlinear, large-scale, uncertain discrete-time networks. The conditions are derived by means of vector Lyapunov functions. The obtained results are applied to traffic networks for the derivation of sufficient conditions of global exponential stability of the uncongested equilibrium point of the network. Specific results and algorithms are provided for freeway traffic models. Various examples illustrate the applicability of the obtained results.

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Microsimulation analysis of practical aspects of traffic control with variable speed limits

(Institute of Electrical and Electronics Engineers, 2015) Papageorgiou Markos; Παπαγεωργιου Μαρκος; Muller Eduardo Rauh; Carlson Rodrigo Castelan; Kraus Werner

Mainstream traffic flow control (MTFC) with variable speed limits (VSLs) is a freeway traffic control method that aims to maximize throughput by regulating the mainstream flow upstream from a bottleneck. Previous studies in a macroscopic simulator have shown optimal and feedback MTFC potential to improve traffic conditions. In this paper, local feedback MTFC is applied in microscopic simulation for an on-ramp merge bottleneck. Traffic behavior reveals important aspects that had not been previously captured in macroscopic simulation. Mainly, the more realistic VSL application at specific points instead of along an entire freeway section produces a slower traffic response to speed limit changes. In addition, the nonlinear capacity flow/speed limit relation observed in the microscopic model is more pronounced than what was observed at the macroscopic level. After appropriate modifications in the control law, significant improvements in traffic conditions are obtained.

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