358 research outputs found
A hierarchical solution approach for a multicommodity distribution problem under a special cost structure
Cataloged from PDF version of article.Motivated by the spare parts distribution system of a major automotive manufacturer in Turkey, we consider a multicommodity distribution problem from a central depot to a number of geographically dispersed demand points. The distribution of the items is carried out by a set of identical vehicles. The demand of each demand point can be satisfied by several vehicles and a single vehicle is allowed to serve multiple demand points. For a given vehicle, the cost structure is dictated by the farthest demand point from the depot among all demand points served by that vehicle. The objective is to satisfy the demand of each demand point with the minimum total distribution cost. We present a novel integer linear programming formulation of the problem as a variant of the network design problem. The resulting optimization problem becomes computationally infeasible for real-life problems due to the large number of integer variables. In an attempt to circumvent this disadvantage of using the direct formulation especially for larger problems, we propose a Hierarchical Approach that is aimed at solving the problem in two stages using partial demand aggregation followed by a disaggregation scheme. We study the properties of the solution returned by the Hierarchical Approach. We perform computational studies on a data set adapted from a major automotive manufacturer in Turkey. Our results reveal that the Hierarchical Approach significantly outperforms the direct formulation approach in terms of both the running time and the quality of the resulting solution especially on large instances. © 2012 Elsevier Ltd. All rights reserved
Fiber optical network design problems : case for Turkey
Ankara : The Department of Industrial Engineering and the Graduate School of Engineering and Science of Bilkent University, 2013.Thesis (Master's) -- Bilkent University, 2013.Includes bibliographical references leaves 102-110.The problems within scope of this thesis are based on an application arising from one of
the largest Internet service providers operating in Turkey. There are mainly two different
problems: the green field design and copper field re-design. In the green field design
problem, the aim is to design a least cost fiber optical network from scratch that will
provide high bandwidth Internet access from a given central station to a set of
aggregated demand nodes. Such an access can be provided either directly by installing
fibers or indirectly by utilizing passive splitters. Insertion loss, bandwidth level and
distance limitations should simultaneously be considered in order to provide a least cost
design to enable the required service level. On the other hand, in the re-design of the
copper field application, the aim is to improve the current service level by augmenting
the network through fiber optical wires. Copper rings in the existing infrastructure are
augmented with cabinets and direct fiber links from cabinets to demand nodes provide
the required coverage to distant nodes. Mathematical models are constructed for both
problem specifications. Extensive computational results based on real data from Kartal
(45 points) and Bakırköy (74 points) districts in Istanbul show that the proposed models
are viable exact solution methodologies for moderate dimensions.Yazar, BaşakM.S
Telecommunications for a deregulated power industry
Telecommunication plays a very important role in the effective monitoring and control of the power grid. Deregulation of the US power industry has enabled utilities to explore various communication options and advanced technologies. Utilities are increasingly investing in distributed resources, dynamic real-time monitoring, automated meter reading, and value added services like home energy management systems and broadband access for its customers. Telecommunication options like power line communications (PLC) and satellites are fast replacing legacy telephone and microwave systems in the US.;The objective of this thesis is to study the communication options that are available for utilities today. Phasor measurement units (PMUs) are analyzed in detail and communication delays due to the use of PMUs in wide area measurement systems (WAMS) are also studied. The highlight of this thesis is a close look at the characteristics of the power line channel by presenting a power line channel model and the use of digital modulation techniques like SS and OFDM, which help overcome the effects of such a hostile medium of communication. (Abstract shortened by UMI.)
Future manned systems advanced avionics study
COTS+ was defined in this study as commercial off-the-shelf (COTS) products, ruggedized and militarized components, and COTS technology. This study cites the benefits of integrating COTS+ in space, postulates a COTS+ integration methodology, and develops requirements and an architecture to achieve integration. Developmental needs and concerns were identified throughout the study; these needs, concerns, and recommendations relative to their abatement are subsequently presented for further action and study. The COTS+ concept appears workable in part or in totality. No COTS+ technology gaps were identified; however, radiation tolerance was cited as a concern, and the deferred maintenance issue resurfaced. Further study is recommended to explore COTS+ cost-effectiveness, maintenance philosophy, needs, concerns, and utility metrics. The generation of a development plan to further investigate and integrate COTS+ technology is recommended. A COTS+ transitional integration program is recommended. Sponsoring and establishing technology maturation programs and COTS+ engineering and standards committees are deemed necessary and are recommended for furthering COTS+ integration in space
A hierarchical solution approach for a multicommodity distribution problem under a special cost structure
Motivated by the spare parts distribution system of a major automotive manufacturer in Turkey, we consider a multicommodity distribution problem from a central depot to a number of geographically dispersed demand points. The distribution of the items is carried out by a set of identical vehicles. The demand of each demand point can be satisfied by several vehicles and a single vehicle is allowed to serve multiple demand points. For a given vehicle, the cost structure is dictated by the farthest demand point from the depot among all demand points served by that vehicle. The objective is to satisfy the demand of each demand point with the minimum total distribution cost. We present a novel integer linear programming formulation of the problem as a variant of the network design problem. The resulting optimization problem becomes computationally infeasible for real-life problems due to the large number of integer variables. In an attempt to circumvent this disadvantage of using the direct formulation especially for larger problems, we propose a Hierarchical Approach that is aimed at solving the problem in two stages using partial demand aggregation followed by a disaggregation scheme. We study the properties of the solution returned by the Hierarchical Approach. We perform computational studies on a data set adapted from a major automotive manufacturer in Turkey. Our results reveal that the Hierarchical Approach significantly outperforms the direct formulation approach in terms of both the running time and the quality of the resulting solution especially on large instances. © 2012 Elsevier Ltd. All rights reserved
Index to 1983 NASA Tech Briefs, volume 8, numbers 1-4
Short announcements of new technology derived from the R&D activities of NASA are presented. These briefs emphasize information considered likely to be transferrable across industrial, regional, or disciplinary lines and are issued to encourage commercial application. This index for 1983 Tech Briefs contains abstracts and four indexes: subject, personal author, originating center, and Tech Brief Number. The following areas are covered: electronic components and circuits, electronic systems, physical sciences, materials, life sciences, mechanics, machinery, fabrication technology, and mathematics and information sciences
Operations Research in action
Wie der Titel bereits andeutet bezieht sich diese Dissertation auf ein Operations Research
Projekt, dass der Ä Osterreichische Telekommunikationsanbieter Telekom Austria in den Jahren
2006 bis 2009 durchfÄuhrte. Die wachsende Zahl von Internet Nutzern, neue Anwendungen im
Internet und die zunehmende Konkurrenz von mobilem Internet zwingen Festnetzbetreiber wie
Telekom Austria ihre Produkte fÄur den Internet Zugang mit hÄoheren Bandbreiten zu versehen.
ZwangslÄau¯g mÄussen die Zugangsnetze verbessert werden, was nur mit hohen Investitionskosten
erreichbar ist. Aus diesem Grund kommt der kostenoptimalen Planung solcher Netzwerke eine
zentrale Rolle zu.
Ein wesentliches Projektziel war es, den Planungsprozess mit Methoden der diskreten Optimie-
rung aus dem Bereich Network Design zu unterstÄutzen. Die Ergebnisse, die in dieser Disserta-
tion beschrieben werden, beschÄaftigen sich mit Algorithmen aus dem Gebiet Facility Location
(Bestimmung von Versorgungsstandorten). Vor der PrÄasentation der dazugehÄorigen Theorie
und ihrer Anwendung auf die gestellten Problem werden zweitere grÄundlich analysiert.
ZunÄachst wird der Telekommunikationsmarkt bis 2009 mit speziellem Fokus auf den Zeitraum
zwischen 2006 und 2009 beschrieben. Die Telekommunikationsindustrie hatte bereits einige
Strategien zur Verbesserung der Netzwerkinfrastruktur entwickelt. Ihre Relevanz fÄur die ge-
stellten Probleme wird herausgearbeitet Dem folgt eine Au°istung der Problemspezi¯kationen,
wie sie in der Evaluierungsphase des Projekts mit den beteiligten Anwendern erstellt wurde. Mit
Hilfe eines dynamischen Programmes wird die gestellte Fragestellung unter BerÄucksichtigung
aller Spezi¯kationen gelÄost. Eine Au°istung von Bedingungen, wann dieser Algorithmus die
optimale LÄosung liefert, und die dazugehÄorigen Beweise beschlie¼en Kapitel 1.
In der Folge stellte sich allerdings heraus, dass die Praktiker mit dieser ersten LÄosung nicht
zufrieden waren. Die Liste der Spezi¯kationen war nicht vollstÄandig. Sie musste verÄandert und
erweitert werden. Mangelnde E±zienz machte die LÄosungen fÄur die Praxis unbrauchbar. Die
LÄosungen enthielten Versorgungsstandorte, die minder ausgelastet waren (underutilized), d.h.
diesen Standorten waren zu wenige Kunden zugeordnet worden. Solche Lokationen mussten
aus den LÄosungen entfernt werden. Dann aber waren die Verbleibenden so zu repositionieren,
dass die Versorgung mit einer vorgegebenen MindestÄubertragungsrate fÄur die grÄo¼tmÄogliche
Menge an Kunden sichergestellt werden konnte. Diese Strategie wurde mit Hilfe des Konzepts
der k-Mediane umgesetzt: Unter der Nebenbedingung, dass die Anzahl der Standorte durch
eine Konstante k beschrÄankt ist, wird die optimale Zuordnung von Kunden zu Versorgungs-
standorten, d.h. ihre Versorgung, gesucht. Anschlie¼end lÄost man dann k-Median Probleme fÄur
verschiedene Werte von k und bestimmt die Mindestauslastungen und Versorgungsraten, die
diese LÄosungen erzielen. Dieses Vorgehen versetzt den Anwender in die Lage unter verschie-
denen LÄosungen zwischen e±zienter Auslastung der Versorgungsstandorten und der HÄohe der
Versorgungsraten balancieren zu kÄonnen.
In Kapitel 2 werden zunÄachst die Ereignisse und Diskussionen beschrieben, die eine ÄAnderung
der LÄosungsstrategie notwendig machten, und die geÄanderten bzw. neuen Spezi¯kationen wer-
den prÄasentiert. Dem folgt die Vorstellung der Theorie der k-Mediane inklusive der Beschrei-
bung eines Algorithmus aus der Literatur. Am Ende des zweiten Kapitels wird eine Variante
dieses Algorithmus entwickelt, der fÄur die spezi¯schen Anforderungen noch besser geeignet ist:
Der Algorithmus aus der Literatur fÄugt Lokationen schrittweise in die LÄosung ein, d.h. pro
Iteration erhÄoht sich die Anzahl der Versorgungsstandorte um einen, bis die maximale Anzahl
von Lokationen erreicht ist. Im Falle von Zugangsnetzen ist die zu erwartende Anzahl von
Standorten aber eher gro¼. Daher ist es vorteilhafter die gewÄunschte Anzahl von oben, durch
Reduktion der Anzahl von Versorgungsstandorten in der LÄosung zu erreichen.
Kapitel 3 liefert eine extensive empirische Analyse von 106 verschiedenen Zugangsnetzen. Kon-
kreter Zweck dieser Demonstration ist es einen Eindruck zu vermittelt, wie man die entwickel-
ten und adaptierten Methoden bei der Vorbereitung des Planungsprozesses einsetzen kann.
So ist es einerseits mÄoglich strategischen Fragestellungen vorab zu analysieren (z.B. E®ekt
der Erzwingung des HV Kreises, Balance zwischen Auslastung der Versorgungsstandorte und
der Versorgungsrate), und andererseits VorschlÄage fÄur passende Planungsprozesse fÄur die An-
wender zu entwickeln (z.B. durch Laufzeitanalysen). ZusÄatzlich werden die beiden Methoden
zur LÄosung des k-Median Problems, die in dieser Abreit vorgestellt werden, noch bzgl. ihres
Laufzeitverhaltens verglichen.As indicated by the title this thesis is based on an Operations Research project which was
conducted at the Austrian telecommunications provider Telekom Austria between 2006 and
2009. An increasing number of internet users, new internet applications and the growing
competition of mobile internet access force ¯xed line providers like Telekom Austria to o®er
higher rates for data transmission via their access networks. As a consequence access nets
have to be improved which leads to investments of signi¯cant size. Therefore, minimizing such
investments by a cost optimal planning of networks becomes a key issue.
The main goal of the project was to support the planning process by utilizing discrete opti-
mization methods from the ¯eld of network design. The key results which are presented in
this thesis are algorithms for facility location. However, before dealing with the theory and the
solutions | in practice as well as in this thesis | a thorough analysis of the stated problem is
undertaken.
To begin with the telecommunication market before 2006 and especially between 2006 and
2009 is reviewed to provide some background information. The industry had already developed
di®erent strategies to improve ¯xed line infrastructure. Their relevance for the stated problem
is presented. Furthermore, the most important problem speci¯cations as they were gathered
in cooperation with the practitioners are listed and discussed in detail. A ¯rst solution was
based on a dynamic program for solving the facility location problem which was derived from
the speci¯cations. The statement of conditions for the optimality of this algorithm and their
proofs conclude Chapter 1.
It turned out that this ¯rst solution did not provide the desired result. It rather fostered the
discussion process between operations researches and practitioners. New speci¯cations were
added to the existing list. The planners dismissed these ¯rst solutions because they were not
e±cient enough. These solutions contained facilities which were underutilized, i.e. too few
customers were assigned to such facilities. To overcome this problem facilities of low utilization
had to be removed from the solutions. The remaining facilities were rearranged in a way to
maximize the coverage with a certain minimum transmission rate. This strategy was realized
by adapting the concept of the k-median problem: The number of facilities is bounded whereas
simultaneously the number of optimally supplied customers is maximized. Then for di®erent
bounds the minimum facility utilization is reported. That way the practitioner is enabled to
¯nd the optimal balance between e±cient facility utilization and coverage of customer demands.
After sketching the events and discussions which made further development necessary and
listing the additional speci¯cations, the theory of the k-median problem is presented and a
basic algorithm from the literature is cited. For the speci¯c requirements of the given problem
a variant of the algorithm is developed and described at the end of Chapter 2: The algorithm
from the literature inserts facilities one by one into the solution that way approaching the
bound in an ascending manner. However, since the expected number of facilities is usually
large it is more advantageous to approach the bound from above in a descending manner.
Finally, an extensive empirical study of 106 di®erent local access areas is presented. The
main purpose of this demonstration is to give a concrete impression of how the adapted and
developed methods can be utilized in preparation of the planning process by studying strategic
questions (e.g. CO circle enforcement, balancing between facility utilization and coverage)
and by providing information (runtime) which is useful to set up an appropriate working
environment for the future users. Additionally, the two variants of the k-median algorithm |
the ascending and the descending method | can be compared
Public service user terminus study compendium of terminus equipment
General descriptions and specifications are given for equipments which facilitate satellite and terrestrial communications delivery by acting as interfaces between a human, mechanical, or electrical information generator (or source) and the communication system. Manufactures and suppliers are given as well as the purchase, service, or lease costs of various products listed under the following cateories: voice/telephony/facsimile equipment; data/graphics terminals; full motion and processes video equipment; and multiple access equipment
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