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A normative proposal for obtaining a suitable multiattribute generalized cost in routing problems

100%

Lopez F. , Fernandez E.

2002

tom Vol. 27, No. 1

17-26

Up to now, the routing problem with physical planning, (choosing the best route linking each pair of adjacent nodes belonging to a road network), has been solved only using an imprecise heuristic approach. In this paper we present a normative method which uses some proxy variables for modeling the main attributes, and is based on a set of rational axioms which provides a good framework for clearing Decision Maker's preferences and beliefs, following the paradigm of Decision Analysis. This method has been successfully applied in practical decision making.

An improved method for deriving final ranking from a fuzzy preference relation via multiobjective optimization

100%

Fernandez E. , Olmedo R.

2003

tom Vol. 28, No. 3

143-157

Methods for deriving final ranking from a fuzzy preference relation do not perform well in presence of irrelevant alternatives or in case of complex graphs with numerous circuits. Recently some approaches based on the idea of reducing differences between a global model of preferences and a final ranking via multiobjective optimization with an evolutionary algorithm have been proposed. In this work a new method is presented based on similar ideas but improving them. The multiobjective optimization problem is separated into two steps and solved with a better model of preferences, also using an evolutionary algorithm simpler than the former. These improvements allow us to obtain better compromise solutions in a simpler way than the previous proposals.

Bismuth Hall thruster I: Simulation-suggested design and performance

80%

Scharfe D. B. , Scharfe M. K. , Capelli M. A. , Fernandez E.

2008

tom Vol. 49, no 3-4

329-348

A two-dimensional radial-axial hybrid simulation of the xenon-fueled Stanford Hall Thruster has been adapted to model a bismuth-fed thruster with varying channel geometry. The simulation treats the electrons as a quasi-one-dimensional fluid and the neutrals and ions as discrete superparticles advanced using a particle-in-cell (PIC) approach. Since experimental data of the electron cross-field mobility does not exist for the bismuth-fueled thruster, a model for electron transport based on shear suppression of plasma turbulence is used to compute a mobility from simulated plasma properties. While the bismuth propellant showed poor performance with an 8 cm channel length, results improved significantly as the simulated channel was shortened to 3.3 and 2.4 cm. The simulation of bismuth propellant at the shortest channel length provided significantly improved ionization fraction, thrust, efficiency, and thrust-to-power compared to xenon propellant on either the 8 cm or 2.4 cm channel, as can be expected due to the higher atomic mass and lower ionization potential of bismuth. With results indicating that optimal performance of the bismuth thruster occurs with a sub-3 cm channel length, such a design is suggested for a developing laboratory-model bismuth thruster.