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• Archiv 02-14

Running projects

• MI7

  Routing Structures and Periodic Timetabling

  Prof. Dr. Ralf Borndörfer

  Project heads: Prof. Dr. Ralf Borndörfer
  Project members: Dr. Niels Lindner
  Duration: 01.06.2017 - 31.12.2019
  Status: running
  Located at: Konrad-Zuse-Zentrum für Informationstechnik Berlin
  

  Description

  The integration of passenger route choices in traffic planning problems taps essential optimization potentials that cannot be neglected. In this project, we approach this topic by mainly focusing on the timetabling problem: The aim is to efficiently find optimal solutions for the integrated timetabling and passenger routing problem. The research focuses on three work packages: the timetabling problem itself, efficient routing algorithms, and the identification and exploitation of routing structures.
  
  http://www.zib.de/projects/routing-structures-and-periodic-timetabling

• MI8

  Understanding and Improving Traffic with Uncertain Demands

  Prof. Dr. Max Klimm

  Project heads: Prof. Dr. Max Klimm
  Project members: Philipp Warode
  Duration: 01.06.2017 - 31.12.2019
  Status: running
  Located at: Humboldt Universität Berlin
  

  Description

  Traffic and logistic networks are among the most vital infrastructures of modern civilization providing access to economic activities, work, health care, and social and cultural life. However, the huge benefits of private and commercial traffic are accompanied by severe burdens in terms of congestion, exhaust gas pollution and land consumption. In the past years, we witnessed the emergence of several new car-related technologies that have the potential to fundamentally change the way traffic networks are managed and used: navigation devices with real-time information allow each traffic participant to make an informed decision concerning the route choice; electrical and hybrid vehicles allow mobility with reduced carbon-dioxide footprint; car-to-car and car-to-infrastructure communications pave the way to a more coordinated traffic, ultimately culminating in the use of autonomous vehicles. The ubiquity of navigation devices and car communication today produces a wealth of data concerning the traffic demand, its elasticity, and the travel times, making these pieces of information available to the system designer. However, the mathematical theory of traffic equilibria typically assumes a fixed travel demand that is then distributed in the network according to the equilibrium concept in question. The restriction to a single demand matrix may be useful when modeling a particular traffic scenario (e.g. a rush hour situation). However, when designing the overall network or when installing road-pricing schemes that are active for a long time period it is much more sensible to analyze the overall performance of the system, i.e., to study the average travel with respect to the empirical distribution of travel demands over a given time span. This is the main question addressed in this project.
  
  https://www.wiwi.hu-berlin.de/de/professuren/quantitativ/or/projects/unknown-demands/

• MI10

  Acyclic network flows

  Dr. Benjamin Hiller / Prof. Dr. Thorsten Koch / Prof. Dr. Martin Skutella

  Project heads: Dr. Benjamin Hiller / Prof. Dr. Thorsten Koch / Prof. Dr. Martin Skutella
  Project members: Dr. Kai-Helge Becker
  Duration: 01.06.2017 - 31.12.2019
  Status: running
  Located at: Konrad-Zuse-Zentrum für Informationstechnik Berlin
  

  Description

  Utility and infrastructure networks are at the heart of our daily life and we are taking their proper working for granted. To provide this service, network operators face difficult planning and operational problems. The complexity of the considered optimization problems increases for several reasons, for instance because geographically bigger networks are considered or the detail level is increased. For large networks, providing globally optimal solutions or at least good bounds for assessing solution quality is still a big challenge. This project addresses this challenge for so-called potential-driven nonlinear network flow problems that are a key model for infrastructure networks for fluids, e.g. water and gas. These problems feature a so-called potential for each node, and the flow on an arc is related to the difference of the potential of its end nodes. In particular, flow is always directed from higher to lower potential, i.e. the potentials induce an acylic orientation of the arcs. This observation is the motivation for this project: We study network flow problems with the additional requirement of acyclic flows: If each network arc is oriented in the direction of flow over this arc, then there is no directed cycle in the resulting network. This is an interesting combinatorial structure that arises from nonconvex nonlinear constraints and thus links combinatorial and continuous optimization. The aim of this project is to develop algorithmic techniques to exploit this structure to improve global optimization methods for large-scale nonlinear flow problems.
  
  http://www.zib.de/projects/acyclic-network-flows

• MI12

  Dynamic Models and Algorithms for Equilibria in Traffic Networks

  Prof. Dr. Martin Skutella

  Project heads: Prof. Dr. Martin Skutella
  Project members: Leon Sering
  Duration: 01.06.2017 - 31.12.2019
  Status: running
  Located at: Technische Universität Berlin
  

  Description

  The efficiency of private transport is of particular importance for densely populated metropolitan areas. In light of ever growing traffic volumes, road infrastructure constitutes a scarce resource that must be used as effectively as possible. In this context, the availability of data and, associated therewith, the development of future technologies such as autonomously guided vehicles dramatically change the way users act and interact. This project wants to address some of the challenges occurring in these next generation traffic networks.
  
  http://www.tu-berlin.de/?id=186306

• MI-CH1

  Robust Optimization of Load Balancing in the Operating Theatre

  Dr. Guillaume Sagnol

  Project heads: Dr. Guillaume Sagnol
  Project members: Daniel Schmidt genannt Waldschmidt
  Duration: 01.06.2017 - 31.12.2019
  Status: running
  Located at: Technische Universität Berlin
  

  Description

  The operating theater (OT) is one of the most expensive hospital resources, and its management is a very complex task, which involves combinatorial aspects in an uncertain environment (surgical durations, emergency cases, availability of recovery beds). This project is concerned with the tactical (middle-term) planning of the OT, which aims at maximizing the utilization of resources in the OT, balancing the workload over the different operating sessions, and ensuring an equitable access and treatment duration to all patients.
  
  http://www.coga.tu-berlin.de/v_menue/projects/mi_ch1

• MI-AP6

  Parameter identification, sensor localization and quantification of uncertainties

  Prof. Dr. Michael Hintermüller

  Project heads: Prof. Dr. Michael Hintermüller
  Project members: -
  Duration: 01.10.2014 - 30.06.2022
  Status: running
  Located at: Humboldt Universität Berlin
  

  Description

  The project work concentrates on modeling aspects as well as the conception and analysis of robust numerical methods for solving inverse problems for switching (or hybrid) systems of partial differential equations on graphs. In this context, the graph typically represents a transportation network for a specific substance or commodity. In accordance with the focus application of this collaborative research center (CRC), the main emphasis lies on networks transporting for (natural) gas. The project pursues several research goals:
  
  The identification of unknown parameters (e.g. the Darcy friction factor) and the detection of anomalies (leakage). the optimal arrangement of sensors in the network for a robustifying the identification tasks the quantification of uncertainties in the identified parameters or in other statistically relevant quantities.
  
  Within the CRC, this project will collaborate with other subprojects on (constrained) optimal control problems for hyperbolic or hybrid systems and their numerical realization, and on numerical methods for the identification of the friction coefficient. It will equip the hierarchy of models considered with the CRC with relevant physical parameters or statistical information resulting from solving various identification problems. The project participates in demonstrator D2.
  
  http://trr154.fau.de/index.php/en/subprojects/b02e

• MI-AP7

  Controlled coupling of mixed integer-continuous models with modeled uncertainties

  Prof. Dr. Volker Mehrmann

  Project heads: Prof. Dr. Volker Mehrmann
  Project members: -
  Duration: 01.10.2014 - 30.06.2022
  Status: running
  Located at: Technische Universität Berlin
  

  Description

  The aim of project B03 is the development of a new methodology for the coupling of widely different mathematical models in a network. Moreover, error controllers are developed on the basis of modeled errors and uncertainties using the example of gas networks. These errors and uncertainties in submodels of the complex network are balanced in the overall simulation. Therefore, measures for the errors and uncertainties should be modeled for every submodel and made comparable. This can only succeed on the basis of a detailed model hierarchy, see Figure 1. All the errors and uncertainties in the simulation and optimisation are considered as an error in the finest modeling level using a backward error analysis in the model hierarchy. The estimated error in the finest level forms the mathematical basis for the development of a robust coupling controller. The controller should allow us to control the overall error in such a way that a prescribed simulation or optimisation goal is achieved within a desired tolerance.
  
  http://trr154.fau.de/index.php/en/subprojects/b03e

• MI-AP8

  Nonlinear chance constraints in gas transportation problems

  PD Dr. René Henrion

  Project heads: PD Dr. René Henrion
  Project members: -
  Duration: 01.10.2014 - 30.06.2022
  Status: running
  Located at: Weierstraß-Institut
  

  Description

  The aim of this project consists in applying nonlinear probabilistic constraints to optimization problems in gas transportation assuming that the underlying random parameter obeys a multivariate and continuous distribution. Doing so, a robust in the sense of probability design of gas transport shall be facilitated. Stochastic optimization is the appropriate mathematical discipline to cope with uncertainty when looking for optimal decisions under random perturbations of some nominal parameters. Among different modeling options, probabilistic constraints hold a key position first of all in engineering applications. The solution of optimization problems with nonlinear probabilistic constraints with continuous multivariate distributions can be considered as new ground both from the theoretical and – at least for interesting dimension - from the numerical perspectives. Moreover, in the present project, we deal with implicit probabilistic constraints where the relation between decision and random parameter is established only by additional variables via some equation system. Although gas network problems with uncertain injection and consumption provide a very natural motivation for the research in this project, the mathematical insight to be expected has an impact on quite different applications as well, for instance, on optimization problems of power management, particularly those related with renewable energies. Beyond this, optimal control problems governed by PDEs and subjected to random state constraints promise being a potential application of implicit probabilistic constraints. In its first phase the project will investigate optimization problems arising from a simple stationary gas network model (RNET-ISO4) subject to random loads. Here the probabilistic constraint ensures the technical feasibility of loads with a specified probability. In the longer perspective, the consideration of dynamic probabilistic constraints for time-dependent decisions and of binary variables shall be pursued.
  
  http://trr154.fau.de/index.php/en/subprojects/b04e

• MI-AP9

  Hierarchical PDAE-surrogate-modeling and stabil PDAE-network-discretization for simulating large non-stationary gas networks

  Prof. Dr. Caren Tischendorf

  Project heads: Prof. Dr. Caren Tischendorf
  Project members: -
  Duration: 01.10.2014 - 30.06.2022
  Status: running
  Located at: Humboldt Universität Berlin
  

  Description

  This subproject focuses on the development and analysis of models and methods for a stable and fast simulation of huge transient gasnetworks, which will also be used for an efficient parameter optimization and control of the network. The main aspects are the development of a numerical discretization in space and time that is adjusted to the topology of the network as well as a hierarchical modelling of several elements (pipes, compressors ect.) and subnet-structures.
  For the complete network as a coupled system of nonlinear partial differential equations and algebraic equations (PDAE) we consider approximations by a spatial semi-discretization. We strive for a determination and classification of topology depending critera for the index of the time dependend differential algebraic system. Topology- and controldepending spatial discretizations will be determinded, that lead to DAEs of index 1, in order to diminish the influence of perturbations for the DAE system best possible. Moreover we want to establish a perturbationanalysis as well as existence and uniquness results for die PDAE-model. Here, the time and pressure/flow-depending control-states that can change the variable structure (dynamic as well as static) for certain points in time and for certain states of the network will be a major challange.
  As a method, we focus on a Galerkin-Approach in space followed by a discretization in time of the resulting DAE with implicit or semi-implicit methods respectively, such that the algebraic constraints hold for the current point in time. Continuationmethods and space-mapping techniques are used for the initialisation to guarantee good convergence behaviour. Furthermore, to satisfy the control requirements of the systems and to enable the handling of huge networks, this subproject aims at the enhancement of the simulation speed. It is planed to detect characteristic subnetstructures and derive parameter dependen transient surrogate models with suitable error estimators by applying model order reduction methods. These input-ouput models as dynamic systems of ODEs will be coupled with die complete PDAE model in one model hierarchy.
  
  http://trr154.fau.de/index.php/en/subprojects/c02e

• MI-AP17

  Efficient network flow methods for non-steady-state gasflows

  Prof. Dr. Martin Skutella

  Project heads: Prof. Dr. Martin Skutella
  Project members: -
  Duration: 01.10.2014 - 30.06.2022
  Status: running
  Located at: Technische Universität Berlin
  

  Description

  The goal of this subproject is to apply network flow theory to simplified models for gas pipelines and related transportation networks. Network flow theory has proven itself to be a powerful and valueable tool for solving complex problems in many areas of application, like traffic networks, telecommunication networks, and logistic networks. All of these networks can be designed and operated using network flow algorithms, which exhibit a very efficient runtime behaviour, making them capable of handling the large instances occuring in practice. In this subproject, we strive to employ network flow algorithms for solving problems in gas and related networks. Conventional network flow theory is insufficient to describe gas networks, since it neither accounts for pressures in nodes, nor for the non-linear dependency of the flow from the pressure in nodes. However, there are several problems in gas networks which occur in a similar form in network flow theory and are known and well understood there, for example generalized or length-bounded flows. Furthermore, non-linear relationships in other aspects like for example the flow velocity in traffic networks, have been studied and solved by network flow theory. As a base for our models we use a model based on the Weymouth equations, which can be solved using convex minimum cost flows. This flow model and its solution techniques can be generalized from the stationary to the transient case, analogous to how classic network flows can be generalized to dynamic network flows. For solving dynamic networks (approximately), there are useful techniques known from network flow theory, e.g. adaptive time-expanded networks, which have a great number of applications. These techniques are to be made useable for transient gas flows in this subproject. Gas networks usually contain a number of active elements - valves, compressors, and so on - which require integral decisions which have a significant impact on the gas flow. Therefore, these elements have to be incorporated in the network flow model. This can be handled by Branch & Bound based methods, or by adaption of techniques from network design. For Branch & Bound based techniques it is crucial to identify infeasible solutions as fast as possible. In gas networks, this means identifying partial configurations of active elements which imply infeasiblity. Therefore, analysis of infeasiblity will be a focus of the research done in this subproject. By developing efficient models and solution techniques for gas networks and characterizing infeasibility in these models, this subproject will contribute for Demonstrator 1, with a special focus on large gas networks.
  
  http://trr154.fau.de/index.php/en/subprojects/a07e