Asgeir Tomasgard - Academia.edu (original) (raw)

Uploads

Papers by Asgeir Tomasgard

30, 2021

The Research Centre on Zero Emission Neighbourhoods (ZEN) in Smart Cities The ZEN Research Centre... more The Research Centre on Zero Emission Neighbourhoods (ZEN) in Smart Cities The ZEN Research Centre develops solutions for future buildings and neighbourhoods with no greenhouse gas emissions and thereby contributes to a low carbon society. Researchers, municipalities, industry and governmental organizations work together in the ZEN Research Centre in order to plan, develop and run neighbourhoods with zero greenhouse gas emissions. The ZEN Centre has nine pilot projects spread over all of Norway that encompass an area of more than 1 million m 2 and more than 30 000 inhabitants in total.

The service provision problem described in this paper comes from an application of distributed pr... more The service provision problem described in this paper comes from an application of distributed processing in telecommunications networks. The objective is to max imize a service provider's profit from offering computational based services to cus tomers. The service provider has limited capacity of some resources and therefore must choose from a set of software applications those he would like to offer. This can be done in a dynamic manner taking into consideration that demand for the differ ent services is uncertain. This problem is examined in the framework of stochastic integer programming. Approximations and complexity are examined for the case when demand is described by a discrete probability distribution and one resource limits the number of software applications that may be installed. For the determin istic counterpart a fully polynomial approximation scheme is known [2]. We show that introduction of stochasticity makes the problem strongly NP-hard, implying that the ...

European Journal of Operational Research, 2015

2001 IEEE Porto Power Tech Proceedings (Cat. No.01EX502)

ABSTRACT Bender's decomposition is often used to solve t wo-stage stochastic programming ... more ABSTRACT Bender's decomposition is often used to solve t wo-stage stochastic programming problems. The problem is transformed into a master problem and many subprob-lems with similar structure. For a two-stage problem with integer variables in the branch and bound may be used to resolve the integral requirements. This involves solving many relaxations of the problem. Using Bender's decomposition to solve these relaxations means there are many, many subproblems to solve with similar structure. This paper considers such problems where the subproblems have a network or transportation problem structure. Ways of exploiting the structure of the subprob-lems and the combination of branch and bound with Bender's decomposition are discussed.

The purpose of this paper is to formally describe new optimization models for distributed telecom... more The purpose of this paper is to formally describe new optimization models for distributed telecommunication networks. Modern distributed networks put more focus on the processing of information and less on the actual transportation of data than we are traditionally used to in telecommunications. This paper introduces new approaches for modelling decision support at operational, tactical and strategic levels. This is

University of Norway …, 1997

Networks, 1998

In this paper we consider a new type of mixed integer programming problem: TransportationNetwork ... more In this paper we consider a new type of mixed integer programming problem: TransportationNetwork with Supply Eating Arcs. This problem arises from an application inintelligent [telecommunications] networks, IN. It contains within its definition many classicalmixed integer programming problems. The problem is defined as a transportationnetwork with an additional condition. For an arc to have positive flow, the node capacityof its

Naval Research Logistics, 2003

Annals of Operations Research, 1998

The purpose of this paper is to formally describe new optimization models for telecommunicationne... more The purpose of this paper is to formally describe new optimization models for telecommunicationnetworks with distributed processing. Modern distributed networks put morefocus on the processing of information and less on the actual transportation of data than weare traditionally used to in telecommunications. This paper introduces new approaches formodelling decision support at operational, tactical and strategic levels. One of the mainadvantages

Interfaces, 2009

The network for transport of natural gas on the Norwegian Continental Shelf, with 7,800 km of sub... more The network for transport of natural gas on the Norwegian Continental Shelf, with 7,800 km of subsea pipelines, is the world's largest offshore pipeline network. The gas flowing through this network represents approximately 15 percent of European consumption, and the system has a capacity of 120 billion standard cubic meters (bcm) a year. In a network of interconnected pipelines, system effects are prevalent, and the network must be analyzed as a whole to determine the optimal operation. SINTEF has developed a decision support tool, GassOpt, which is based on a mixed-integer program, to optimize the network configuration and routing for the main Norwegian shipper of natural gas, StatoilHydro, and the independent network operator, Gassco. GassOpt allows users to graphically model their network and run optimizations to find the best solutions quickly. StatoilHydro and Gassco use it to evaluate the current network and possible network extensions. Both companies use operations resea...

The Energy Journal, 2009

In this paper we present a modeling framework for analyzing natural gas markets, taking into acco... more In this paper we present a modeling framework for analyzing natural gas markets, taking into account the specific technological issues of gas transportation. We model the optimal dispatch of supply and demand in natural gas networks, with different objective functions, i.e., maximization of flow, and different economic surpluses. The models take into account the physical structure of the transportation networks, and examine the implications it has for economic analysis. More specifically, pressure constraints create system effects, and thus, changes in one part of the system may require significant changes elsewhere. The proposed network flow model for natural gas takes into account pressure drops and system effects when representing network flows. Pressure drops and pipeline flows are modeled by the Weymouth equation. A linearization of the Weymouth equation makes economic analyses computationally feasible even for large networks. However, in this paper, the importance of combining economics with a model for pressure drops and system effects is illustrated by small numerical examples.

Energy, 2013

Natural gas flows in pipelines as a consequence of the pressure difference at the inlet and outle... more Natural gas flows in pipelines as a consequence of the pressure difference at the inlet and outlet. Adjusting these pressures makes it possible to inject natural gas at one rate and withdraw at a different rate, hence using the pipeline as storage as well as transport. We study the value of using the so

Computational Management Science, 2013

Infrastructure-planning models are challenging because of their combination of different time sca... more Infrastructure-planning models are challenging because of their combination of different time scales: while planning and building the infrastructure involves strategic decisions with time horizons of many years, one needs an operational time scale to get a proper picture of the infrastructure's performance and profitability. In addition, both the strategic and operational levels are typically subject to significant uncertainty, which has to be taken into account. This combination of uncertainties on two different time scales creates problems for the traditional multistage stochasticprogramming formulation of the problem due to the exponential growth in model size. In this paper, we present an alternative formulation of the problem that combines the two time scales, using what we call a multi-horizon approach, and illustrate it on a stylized optimization model. We show that the new approach drastically reduces the model size compared to the traditional formulation and present two real-life applications from energy planning.

Discrete Applied Mathematics, Jun 1, 2003

DOI to the publisher's website. • The final author version and the galley proof are versions of t... more DOI to the publisher's website. • The final author version and the galley proof are versions of the publication after peer review. • The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal. If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the "Taverne" license above, please follow below link for the End User Agreement:

The purpose of this paper is to formally describe new optimization models for telecommunication n... more The purpose of this paper is to formally describe new optimization models for telecommunication networks with distributed processing. Modern distributed networks put more focus on the processing of information and less on the actual transportation of data than we are traditionally used to in telecommunications. This paper introduces new approaches for modelling decision support at operational, tactical and strategic levels. One of the main advantages of the technological framework we are working within is its inherent exibility, which enables us to dynamically plan and consider uncertainty when decisions are made. When we present the models, emphasis is placed on the modelling discussions around the shift of focus towards processing, the new technological aspects, and how to utilize exibility to cope with uncertainty.

Reliability Engineering & System Safety, 2010

Assurance of supply is a crucial objective for producers and consumers of oil and gas. A basic re... more Assurance of supply is a crucial objective for producers and consumers of oil and gas. A basic requirement to meet this objective is that producers and transmitters have sufficient economic incentives and capabilities to assure a desired degree of supply. The topic of this paper is to evaluate these incentives from a broad perspective. We examine economic trade-offs inherent in a delay of production, including reputational issues, as well as contract incentives for gas sellers, drilling companies, and oil service companies.