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Homberger J.,Stuttgart University of Applied Sciences
Electronic Commerce Research | Year: 2011

A new generic mechanism to coordinate decentral planning of a group of independent and self-interested decision makers, who are searching for an agreeable contract regarding multiple interdependent issues, in the case of asymmetric information is presented. The basic idea of the mechanism is that the group members cooperatively carry out an evolutionary search in the contract space. Therefore the (1,λ)-selection procedure, which is used in many evolutionary strategies, is combined with the Borda maximin voting rule, which has been applied successfully in group decision making. The proposed mechanism is realized, applied and evaluated for production coordination in a supply chain. A decentralized variant of the multi-level uncapacitated lot-sizing problem (MLULSP) is taken as the production model. For the evaluation 95 problem instances are generated based on MLULSP instances taken from the literature, with problem sizes varying from 5 to 500 items, from 12 to 52 periods. Experimental results show that the proposed mechanism is effective to determine fair cost distributions. © 2010 Springer Science+Business Media, LLC. Source


Eicker U.,Stuttgart University of Applied Sciences
Applied Energy | Year: 2010

One of the first rehabilitated passive energy standard office buildings in Europe was extensively monitored over two years to analyse the cooling performance of a ground heat exchanger and mechanical night ventilation together with the summer comfort in the building. To increase the storage mass in the light weight top floor, phase change materials (PCM) were used in the ceiling and wall construction. The earth heat exchanger installed at a low depth of 1.2 m has an excellent electrical cooling coefficient of performance of 18, but with an average cooling power of about 1.5 kW does not contribute significantly to cooling load removal. Mechanical night ventilation with 2 air changes also delivered cold at a good coefficient of performance of 6 with 14 kW maximum power. However, the night air exchange was too low to completely discharge the ceilings, so that the PCM material was not effective in a warm period of several days. In the ground floor offices the heat removal through the floor to ground of 2-3 W m-2 K-1 was in the same order of magnitude than the charging heat flux of the ceilings. The number of hours above 26 °C was about 10% of all office hours. The energy performance of the building is excellent with a total primary energy consumption for heating and electricity of 107-115 kW h m-2 a-1, without computing equipment only 40-45 kW h m-2 a-1. © 2009 Elsevier Ltd. All rights reserved. Source


Homberger J.,Stuttgart University of Applied Sciences
4OR | Year: 2010

An automated negotiation mechanism for decentralized production coordination is presented and evaluated. The coordination problem contains a set of self-interested software agents, representing the production facilities of a supply chain, searching for a mutually agreeable production plan, while taking private information into account. The negotiation mechanism is applied and evaluated using a multi-facility production coordination problem, which is a reformulation of the well-known multi-level uncapacitated lot-sizing problem (MLULSP). The basic element of the mechanism is a decentralized simulated annealing method, consisting of a transition rule carried out by a neutral mediator agent and a cooperative acceptance rule carried out by negotiating agents. We use 176 benchmark problems from relevant literature for the evaluation. Experimental results show that the proposed negotiation mechanism comes close to those results which are obtained by centralized planning. Furthermore, the developed simulated annealing method applied in a single, centralized planning task is competitive with the best known solution methods for the MLULSP. It was possible to compute new best solutions for 24 of the benchmark problems. © 2009 Springer-Verlag. Source


Fink A.,Helmut Schmidt University | Homberger J.,Stuttgart University of Applied Sciences
Flexible Services and Manufacturing Journal | Year: 2013

We consider a multi-agent extension of the non-preemptive single-mode resource-constrained project scheduling problem with discounted cash flow objectives. Such a problem setting is related to project scheduling problems which involve different autonomous firms where project activities are uniquely assigned to the project parties (agents). Taking into account opportunistic agents and the resulting information asymmetry we propose a general decentralized negotiation approach which uses ideas from ant colony optimization. In the course of the negotiation the agents iteratively vote on proposed project schedules without disclosing preference information regarding cash flow values. Computational experiments serve to analyze the agent-based coordination mechanism in comparison to other approaches from the literature. The proposed mechanism turns out as an effective method for coordinating self-interested agents with conflicting goals which collaborate in resource-constrained projects. © 2012 Springer Science+Business Media, LLC. Source


Xu Z.,Polytechnic University of Turin | Coors V.,Stuttgart University of Applied Sciences
Building and Environment | Year: 2012

Constructing and improving urban residential areas is an eternal critical subject in the process of the whole urban development which is connected with a series of challenges and problems. During the past decades, urban residential development has speed up extremely with massive population mobility in cities. The purpose of this study is to propose an integrated approach for sustainability assessment of urban residential development, considering sustainability indicators, housing equilibrium and building visualization. Firstly based on merging DPSIR (Driving Forces, Pressure, State, Impact and Response) framework and Analytic Hierarchy Process (AHP), the indicators were systematized for the sustainability modeling. Due to the urban activities cause impacts not only on local level but also a broader scale, a simulation model, using System Dynamics (SD) methodology, was structured to quantitatively investigate the developmental tendency of the indicators. And then the estimated results were displayed in 2D density maps in ArcGIS and 3D visualization in CityEngine. A real case study was presented for the Stuttgart Region of the state of Baden-Württemberg in Southern Germany and its Plieningen district to experience the usefulness and feasibility of the developed approach. The integration of GIS, SD model and 3D visualization, called GISSD system here, can better explain the interaction and the variation of the sustainability indicators for residential development. Hence it is able to support the Decision Maker to view the sustainable level of urban residential areas more comprehensively. © 2011 Elsevier Ltd. Source

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