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  • 127951.
    Ögren, Petter
    et al.
    Swedish Defense Research Agency.
    Fiorelli, Eddie
    Princeton University.
    Leonard, Naomi
    Princeton University.
    Cooperative Control of Mobile Sensor Networks: Adaptive Gradient Climbing in a Distributed Environment2004Inngår i: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 49, nr 8, s. 1292-1302Artikkel i tidsskrift (Fagfellevurdert)
  • 127952.
    Ögren, Petter
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), Datorseende och robotik, CVAP.
    Leonard, N
    Obstacle Avoidance in Formation,2003Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper, we present an approach to obstacle avoidance for a group of unmanned vehicles moving in formation. The goal of the group is to move through a partially unknown environment with obstacles and reach a destination while maintaining the formation. We address this problem for a class of dynamic unicycle robots. Using Input-to-State Stability we combine a general class of formation-keeping control schemes with a new dynamic window approach to obstacle avoidance in order to guarantee safety and stability of the formation as well as convergence to the goal position. An important part of the proposed approach can be seen as a formation extension of the configuration space obstacle concept. We illustrate the method with a challenging example.

  • 127953.
    Ögren, Petter
    et al.
    Mech. & Aerosp. Eng. Dept., Princeton Univ., NJ, USA.
    Leonard, Naomi Ehrich
    Mech. & Aerosp. Eng. Dept., Princeton Univ., NJ, USA.
    A Convergent Dynamic Window Approach to Obstacle Avoidance2005Inngår i: IEEE Transactions on robotics, ISSN 1552-3098, E-ISSN 1941-0468, Vol. 21, nr 2, s. 188-195Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The dynamic window approach (DWA) is a well-known navigation scheme developed by Fox et al. and extended by Brock and Khatib. It is safe by construction, and has been shown to perform very efficiently in experimental setups. However, one can construct examples where the proposed scheme fails to attain the goal configuration. What has been lacking is a theoretical treatment of the algorithm's convergence properties. Here we present such a treatment by merging the ideas of the DWA with the convergent, but less performance-oriented, scheme suggested by Rimon and Koditschek. Viewing the DWA as a model predictive control (MPC) method and using the control Lyapunov function (CLF) framework of Rimon and Koditschek, we draw inspiration from an MPC/CLF framework put forth by Primbs to propose a version of the DWA that is tractable and convergent.

  • 127954.
    Ögren, Petter
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), Datorseende och robotik, CVAP.
    Leonard, N.E.
    A Probably Convergent Dynamic Window Approach to Obstaclen Avoidance2002Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The dynamic window approach is a well known navigation scheme developed in Fox et al. (1997) and extended in Brock and Khatib (1999). It is safe by construction and has been shown to perform very e#ciently in experimental setups. However, one can construct examples where the proposed scheme fails to attain the goal configuration. What has been lacking is a theoretical treatment of the algorithm's convergence properties. Here we present such a treatment.

  • 127955.
    Ögren, Petter
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), Datorseende och robotik, CVAP.
    Leonard, N.E.
    A tractable convergent dynamic window approach to obstacle avoidance2002Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The dynamic window approach is a well known navigation scheme developed by Fox et. al. [1] and extended by Brock and Khatib [2]. It is safe by construction and has been shown to perform very efficiently in experimental setups. However, one can construct examples where the proposed scheme fails to attain the goal configuration. What has been lacking is a theoretical treatment of the algorithm's convergence properties. A first step towards such a treatment was presented in [4]. Here we continue that work with a computationally tractable algorithm resulting from a careful discretization of the optimal control problem of the previous paper and a way to construct a continuous Navigation Function. Inspired by the similarities between the Dynamic Window Approach and the Control Lyapunov Function and Receding Horizon Control synthesis put forth by Primbs et. al. [3] we propose a version of the Dynamic Window Approach that is tractable and provably convergent.

  • 127956.
    Ögren, Petter
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), Datorseende och robotik, CVAP.
    Martin, C.F.
    Optimal Vaccination Strategies for the Control of Epidemics in Highly Mobile Populations2000Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Our goal is to calculate optimal vaccination patterns for a rapidly spreading disease in an urbanized highly mobile population. The goal being to determine if vaccination can effect a disease for which there is low immunity in the population. Different types of structured SIR models are investigated. We construct a model appropriate for a traveling urbanized population and introduce a control in terms of a vaccination program. Linear constraints, a quadratic cost on the control and a linear cost on the number of infected are imposed. In this setting we calculate optimal vaccination patterns using the maximum principle of Pontryagin

  • 127957.
    Ögren, Petter
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), Datorseende och robotik, CVAP.
    Martin, C.F
    Vaccination Strategies for Epidemics in Highly Mobile Populations2002Inngår i: Applied Mathematics and Computation, ISSN 0096-3003, E-ISSN 1873-5649, Vol. 127, nr 2-3, s. 261-276Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Our goal is to calculate optimal vaccination patterns for a rapidly spreading disease in an urbanized highly mobile population. The goal being to determine if vaccination can effect a disease for which there is low immunity in the population. Different types of structured SIR models are investigated. We construct a model appropriate for a traveling urbanized population and introduce a control in terms of a vaccination program. Linear constraints, a quadratic cost on the control and a linear cost on the number of infected are imposed. In this setting we calculate optimal vaccination patterns using the maximum principle of Pontryagin. The numerics are performed using Matlab.

  • 127958.
    Ögren, Petter
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), Datorseende och robotik, CVAP.
    Petersson, L
    Egerstedt, M
    Hu, X
    Reactive mobile manipulation using dynamic trajectory tracking: design and implementation2000Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A solution to the trajectory tracking problem for mobile manipulators is proposed and implemented on a real robotic system. Given a trajectory for the gripper to follow, a tracking algorithm for the manipulator is designed, and at the same time the base motions are generated in such a way that the base is coordinated with the gripper while reactively avoiding obstacles. Furthermore, it is shown that the method allows arbitrary upper and lower bounds on the gripper-base distance to be set, and this can be achieved without introducing deadlocks into the system

  • 127959.
    Ögren, Petter
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), Datorseende och robotik, CVAP.
    Robinson, John W.C.
    Swedish Defence Research Agency (FOI), Department of Aeronautics .
    A Model Based Approach to Modular Multi-Objective Robot Control2011Inngår i: Journal of Intelligent and Robotic Systems, ISSN 0921-0296, E-ISSN 1573-0409, Vol. 63, nr 2, s. 257-282Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Two broad classes of robot controllers are the modular, and the model based approaches. The modular approaches include the Reactive or Behavior Based designs. They do not rely on mathematical system models, but are easy to design, modify and extend. In the model based approaches, a model is used to design a single controller with verifiable system properties. The resulting designs are however often hard to extend, without jeopardizing the previously proven properties. This paper describes an attempt to narrow the gap between the flexibility of the modular approaches, and the predictability of the model based approaches, by proposing a modular design that does the combination, or arbitration, of the different modules in a model based way. By taking the (model based) time derivatives of scalar, Lyapunov-like, objective functions into account, the arbitration module can keep track of the time evolution of the objectives. This enables it to handle objective tradeoffs in a predictable way by finding controls that preserve an important objective that is currently met, while striving to satisfy another, less important one that is not yet achieved. To illustrate the approach a UAV control problem from the literature is solved, resulting in comparable, or better, performance.

  • 127960.
    Ögren, Petter
    et al.
    Swedish Defence Research Agency (FOI), Department of Aeronautics and Systems Technology,.
    Robinson, John W.C.
    Swedish Defence Research Agency (FOI), Department of Aeronautics .
    Receding Horizon Control of UAVs using Gradual Dense-Sparse Discretizations2010Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper we propose a way of increasing the eciency of some direct Receding Horizon Control (RHC) schemes. The basic idea is to adapt the allocation of compu- tational resources to how the iterative plans are used. By using Gradual Dense-Sparse discretizations (GDS), we make sure that the plans are detailed where they need to be, i.e., in the very near future, and less detailed further ahead. The gradual transition in discretization density re ects increased uncertainty and reduced need for detail near the end of the planning horizon. The proposed extension is natural, since the standard RHC approach already contains a computational asymmetry in terms of the coarse cost-to-go computations and the more detailed short horizon plans. Using GDS discretizations, we bring this asymmetry one step further, and let the short horizon plans themselves be detailed in the near term and more coarse in the long term. The rationale for dierent levels of detail is as follows. 1) Near future plans need to be implemented soon, while far future plans can be rened or revised later. 2) More accurate sensor information is available about the system and its surroundings in the near future, and detailed planning is only rational in low uncertainty situations. 3) It has been shown that reducing the node density in the later parts of xed horizon optimal control problems gives a very small reduction in the solution quality of the rst part of the trajectory. The reduced level of detail in the later parts of a plan can increase the eciency of the RHC in two ways. If the discretization is made sparse by removing nodes, fewer computations are necessary, and if the discretization is made sparse by spreading the last nodes over a longer time-horizon, the performance will be improved.

  • 127961.
    Ögren, Petter
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), Datorseende och robotik, CVAP.
    Smith, Christian
    KTH, Skolan för datavetenskap och kommunikation (CSC), Datorseende och robotik, CVAP.
    Karayiannidis, Yiannis
    KTH, Skolan för datavetenskap och kommunikation (CSC), Datorseende och robotik, CVAP.
    Kragic, Danica
    KTH, Skolan för datavetenskap och kommunikation (CSC), Datorseende och robotik, CVAP.
    A Multi Objective Control Approach to Online Dual Arm Manipulation2012Inngår i: Robot Control, International Federation of Automatic Control , 2012, s. 747-752Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper, we propose a new way to exploit the redundancy of dual arm mobile manipulators when performing inherently bi-manual tasks using online controllers. Bi-manual tasks are tasks that require motion of both arms in order to be carried out efficiently, such as holding and cleaning an object, or moving an object from one hand to the other. These tasks are often associated with several constraints, such as singularity- and collision avoidance, but also a high degree of redundancy, as the relative positions of the two grippers is far more important than the absolute positions, when for example handing an object from one arm to the other. By applying a modular multi objective control framework, inspired by earlier work on sub-task control, we exploit this redundancy to form a subset of the joint space that is feasible, i.e. not violating any of the constraints. Earlier approacher added the additional tasks in terms of equality constraints, thereby reducing the dimension of the feasible subset until it was a single point. Here however, we add the additional tasks in terms of inequalities, removing parts of the feasible set rather than collapsing its dimensionality. Thus, we are able to handle an arbitrary number of constraints, instead of a number corresponding to the dimension of the feasible set (degree of redundancy). Finally, inside the feasible set we choose controls stay in the set, while simultaneously minimizing some given objective. The proposed approach is illustrated by several simulation examples.

  • 127962.
    Ögren, Petter
    et al.
    Swedish Defence Res. Agency, Stockholm.
    Svenmarck, Peter
    Swedish Defence Res. Agency, Stockholm.
    A New Control Mode for Teleoperated Differential Drive UGVs2007Inngår i: PROCEEDINGS OF THE 46TH IEEE CONFERENCE ON DECISION AND CONTROL, VOLS 1-14, 2007, s. 446-471Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper proposes a control mode that enables the users of teleoperated non-holonomic differential drive unmanned ground vehicles (UGVs) to interact with the unmanned vehicles in a new way. By introducing an intermediate control layer, a user interface that is very similar to so-called first person shooter (FPS) computer games, e.g. Doom and Half Life, can be created. The advantages of such interfaces is that they are intuitive, and that literally millions of potential future UGV-operators already have spent hundreds of hours training with them. The control mode gives the user direct control of the position and orientation of the on-board camera, while the actual orientation of the vehicle is abstracted away using feedback linearization. Thus, the idea is similar to using inverse kinematics to directly control the position and orientation of a robot arm gripper. The paper first describes the predominant direct vehicle control model, as well as the FPS interfaces. It is then shown how the proper choice of intermediate control layer can make the two equivalent

  • 127963.
    Ögren, Petter
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), Datorseende och robotik, CVAP. KTH, Skolan för datavetenskap och kommunikation (CSC), Centra, Centrum för Autonoma System, CAS.
    Svenmarck, Peter
    FOI.
    Lif, Patric
    FOI.
    Norberg, Martin
    FOI.
    Söderbäck, Nils Emil
    Swedish Defence Research Agency (FOI).
    Design and implementation of a new teleoperation control mode for differential drive UGVs2014Inngår i: Autonomous Robots, ISSN 0929-5593, E-ISSN 1573-7527, Vol. 37, nr 1, s. 71-79Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, we propose and implement a new control mode for teleoperated unmanned ground vehicles (UGVs), that exploits the similarities between computer games and teleoperation robotics. Today, all teleoperated differential drive UGVs use a control mode called Tank Control, in which the UGV chassis and the pan tilt camera are controlled separately. This control mode was also the dominating choice when the computer game genre First Person Shooter (FPS) first appeared. However, the hugely successful FPS genre, including titles such as Doom, Half Life and Call of Duty, now uses a much more intuitive control mode, Free Look Control (FLC), in which rotation and translation of the character are decoupled, and controlled separately. The main contribution of this paper is that we replace Tank Control with FLC in a real UGV. Using feedback linearization, the orientation of the UGV chassis is abstracted away, and the orientation and translation of the camera are decoupled, enabling the operator to use FLC when controlling the UGV. This decoupling is then experimentally verified. The developments in the gaming community indicates that FLC is more intuitive than Tank Control and reduces the well known situational awareness problem. It furthermore reduces the need for operator training, since literary millions of future operators have already spent hundreds of hours using the interface.

  • 127964.
    Ögren, Petter
    et al.
    Swedish Defence Research Agency (FOI).
    Winstrand, Maja
    Swedish Defence Research Agency (FOI).
    Combining Path Planning and Target Assignment to Minimize Risk in a SEAD Mission2005Konferansepaper (Fagfellevurdert)
  • 127965.
    Ögren, Petter
    et al.
    Department of Autonomous Systems Swedish Defence Research Agency.
    Winstrand, Maja
    Minimizing Mission Risk in Fuel Constrained UAV Path Planning2008Inngår i: Journal of Guidance Control and Dynamics, ISSN 0731-5090, E-ISSN 1533-3884, Vol. 31, nr 5, s. 1497-1500Artikkel i tidsskrift (Fagfellevurdert)
  • 127966.
    Ögren, Petter
    et al.
    Swedish Defence Research Agency (FOI).
    Wirkander, Sven-Lennart
    Swedish Defence Research Agency (FOI).
    Stefansson, Anna
    Swedish Defence Research Agency (FOI).
    Pelo, Johan
    Swedish Defence Research Agency (FOI).
    Formulation and Solution of the UAV Paparazzi Problem2006Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Many UAV path planning problems dealing with multiple targets are formulated as instances of classical optimization problems such as the Traveling Salesperson Problem (TSP), Vehicle Routing Problem (VRP), and the Assignment Problem (AP). In their basic forms, all these problems minimize the length of the flight path to be flown by the UAVs. Even though this is often a reasonable choice, we argue that in instances when the targets are able to hide, or move, an objective function accounting for the target value, as well as the chance of actually finding the target is more natural. In some sense, the problem is similar to the one faced by a Paparazzi photographer, deciding where to go to get snapshots of non cooperative celebrities. Hence we formulate the so-called Paparazzi utility function, and show how it can be applied to UAV path planning problems similar to the TSP, VRP and AP

  • 127967.
    Ögren, Tomas
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Byggteknik och design.
    Ökvist, Jesper
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Byggteknik och design.
    Förvaltning av en BREEAM In-Use certifierad byggnad: Fastighetsförvaltning som verktyg för främjande av miljö och hållbar utveckling2012Independent thesis Basic level (professional degree), 10 poäng / 15 hpOppgave
    Abstract [sv]

    Denna studie har utförts med avseende på förvaltning av byggnader enligt BREEAM 

    In-Use, som används för miljöcertifiering av befintliga byggnader. Rapporten är 

    inriktad på aspekterna av att certifiera en byggnads förvaltning samt den verksamhet 

    som förs inom denna. Kopplingen mellan brukaren och förvaltaren är väsentlig för att 

    säkerställa att man uppnår de krav som BREEAM ställer. Ett hjälpmedel för att främja 

    denna kommunikation mellan dessa parter är de gröna hyresavtal från 

    fastighetsägarna, som har visat sig vara en nödvändig länk. Det har visat sig att 

    befintlig förvaltningsmetodik behöver utvidgas i dess rutiner och att kunskap om 

    BREEAM är nödvändig inom förvaltningen. BREEAM In-Use ställer krav på ett 

    engagemang och kontinuerligt arbete och kommer medföra en förändring i beteende 

    hos brukare, för att en hög nivå på certifieringen ska kunna uppnås. Förvaltning har 

    visat sig ha stor potential att verka för en minskad resursanvändning samt för att 

    säkerställa en långsiktigt hållbar brukstid.  

  • 127968.
    Öhberg, Patrik
    KTH, Tidigare Institutioner                               , Fysik.
    Studies of inhomogeneous Bose-Einstein condensates1998Doktoravhandling, med artikler (Annet vitenskapelig)
  • 127969. Öhlin, David
    et al.
    Carlson, Rolf
    KTH, Tidigare Institutioner, Tal, musik och hörsel.
    Data-driven formant synthesis2004Inngår i: Proceedings FONETIK 2004: The XVIIth Swedish Phonetics Conference / [ed] Peter Branderud, Hartmut Traunmüller, Stockholm University, 2004, s. 160-163Konferansepaper (Annet vitenskapelig)
  • 127970.
    Öhlin, Jennie
    KTH, Skolan för industriell teknik och management (ITM), Industriell ekonomi och organisation (Inst.).
    Retail Business Model Change in the Era of Digital Transformation: A case study from the perspective of a business model canvas2019Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    With an increased level of digitization in the retail sector, retail incumbents need to adapt their business model to the new digital era. E-commerce business and other digital tools have transformed the retail industry and incumbent retailers have to react to the changes in order to remain competitive on the market. While previous research has examined the nature of the digital tools in retail or the general impact of digital transformation on the sector, the thesis aims to investigate the impact of digital transformation on the business model of a retail incumbent. To investigate the impact of digital transformation on the business model of a retail incumbent, a single case study has been conducted at Company X, an incumbent retailer operating in Sweden. The Business Model Canvas has been used as a tool to identify the current business model of the company, and to propose future business models for Company X. The findings have resulted in the creation of three different Business Model Canvas scenarios with different levels of change in the business model. The scenarios all implied an increased cooperation with external partners and the implementation of new customer channels.The findings of the thesis contribute to an increased knowledge of retail business model change. While earlier research findings regarding the impact of digital transformation on the retail sector were confirmed in the case study, the thesis proposes new research concerning the impact on a retail incumbent’s business model. The study also contributes to how the Business Model Canvas may be used as a unit of analysis when investigating business model change.

  • 127971.
    Öhlin, Jennie
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion.
    RFID-användning i försörjningskedjan inom detaljhandel och industri2017Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [sv]

    RFID (Radio Frequency Identification) är en teknik där information kan lagras i en RFIDsändare (även kallad RFID-tagg), som sedan kan avläsas av en RFID-läsare som kan vara kopplad till en maskin eller en dator. RFID är alltså en modernare variant av streckkoden men där avläsningsprocessen inte kräver någon manuell inskanning och inte heller en fri visuell väg mellan avläsare och sändare. I denna rapport kommer RFID-tekniken och dess användning inom detaljhandeln och industrin att presenteras. RFID har flera användningsområden i försörjningskedjan; till exempel för att spåra material och produkter, vid automatisering av produktionslinor, för en effektivare inventering i lager och butik och som stöldskydd i butik. Trots att motiven bakom en implementering av RFID ofta är de samma för företag inom detaljhandeln och industrin så är RFID-teknikens användningsområden väldigt olika beroende på om företaget befinner sig i slutet av försörjningskedjan vid försäljningen (detaljhandeln) eller i början vid produktion (industrin). Man kan se att företag inom detaljhandeln som kontrollerar en större del av försörjningskedjan kan använda tekniken i en större utsträckning än de som endast hanterar själva försäljningen av varor. Detta eftersom RFID-taggarna kan sättas på produkterna i ett tidigare skede i försörjningskedjan och företagen behöver därför inte förlita sig på att deras leverantörer gör det åt dem. Vidare redogör denna studie även för en eventuell framtida användning av RFID inom detaljhandeln och industrin. I det nya paradigmet Internet of Things och de smarta fabrikerna i Industri 4.0 kommer RFID med all sannolikhet att spela en stor roll. Trots den kunskap och erfarenhet som idag finns kring RFID, så kvarstår ännu vissa problem och hinder med tekniken som måste lösas innan RFID kan användas i en ännu större utsträckning.

  • 127972.
    Öhlin, Simon
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Samhällsplanering och miljö, Urbana och regionala studier.
    Förklaringsmodell för cykelresor i Trondheim: Fysiska och demografiska faktorers betydelse för det geografiska resmönstret2014Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    The work examines geographical variations of bicycle use in Trondheim municipality with the aim to create an understanding of what influences the use of bicycles and explain the geographical travel pattern for cycling. The work focuses on the how physical structures generates different transports effects. Where bicycle travels in Trondheim municipality are undertaken is described by using network analysis in ArcGIS, based on aggregated data from the travel habit survey (RVU) in 2009/2010. Trondheim municipality is divided into smaller geographical units (zoner) whose characteristics are described by 19 variables, categorized into 6 groups; Distance, Land use, Topography, Bicycle Facilities, Road characteristics and Demographic factors.

    By linear regression analysis in SPSS and ArcGIS Spatial Analyst, an explanatory model is elaborated. The variables

    distance to the regional center, workplace density, percentage separate bike paths and hilly terrain explains 78 percent of where cycle journeys are undertaken. Single variable with the highest explanatory power is degree of separate bicycle paths, which highlights the importance of infrastructure investment for bicyclists.

    Based on the result, recommendations are given on improvements of the bicycle routes in Trondheim, followed by a discussion of strategies for planning cycle routes.

  • 127973. Öhlén, P.
    et al.
    Skubic, B.
    Rostami, A.
    Fiorani, Matteo
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS, Optical Network Laboratory (ON Lab).
    Monti, Paolo
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS, Optical Network Laboratory (ON Lab).
    Ghebretensaé, Z.
    Mårtensson, J.
    Wang, K.
    Wosinska, Lena
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS, Optical Network Laboratory (ON Lab).
    Data plane and control architectures for 5G transport networks2016Inngår i: Journal of Lightwave Technology, ISSN 0733-8724, E-ISSN 1558-2213, Vol. 34, nr 6, s. 1501-1508, artikkel-id 7397818Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Next generation 5G mobile system will support the vision of connecting all devices that benefit from a connection, and support a wide range of services. Consequently, 5G transport networks need to provide the required capacity, latency, and flexibility in order to integrate the different technology domains of radio, transport, and cloud. This paper outlines the main challenges, which the 5G transport networks are facing and discusses in more detail data plane, control architectures, and the tradeoff between different network abstraction models.

  • 127974.
    Öhlén, Peter
    KTH, Tidigare Institutioner                               , Elektroniksystemkonstruktion.
    Transmisison limitations of 2R reshaping repeaters and applications of high-speed wavelength conversion in optical networking2000Doktoravhandling, med artikler (Annet vitenskapelig)
  • 127975.
    Öhman, Adam
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Matematisk statistik.
    The Calibrated SSVI Method - Implied Volatility Surface Construction2019Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    In this thesis will the question of how to construct implied volatility surfaces in a robust and arbitrage free way be investigated. To be able to know if the solutions are arbitrage free was an initial investigation about arbitrage in volatility surfaces made. From this investigation where two comprehensive theorems found. These theorems came from Roper in \cite{Roper2010}. Based on these where then two applicable arbitrage tests created. These tests came to be very important tools in the remaining thesis.The most reasonable classes of models for modeling the implied volatility surface where then investigated. It was concluded that the classes that seemed to have the best potential where the stochastic volatility models and the parametric representation models. The choice between these two classes where concluded to be based on a trade-off between simplicity and quality of the result. If it where possible to make the parametric representation models improve its result the best applicable choice would be that class. For the remaining thesis was it therefore decided to investigate this class. The parametric representation model that was chosen to be investigated where the SVI parametrization family since it seemed to have the most potential outside of its already strong foundation.The SVI parametrization family is diveded into 3 parametrizations, the raw SVI parametrization, the SSVI parametrization and the eSSVI parametrization. It was concluded that the raw SVI parametrization even though it gives very good market fits, was not robust enough to be chosen. This ment that the raw SVI parametrization would in most cases generate arbitrage in its surfaces. The SSVI model was concluded to be a very strong model compared to the raw SVI, since it was able to generate completely arbitrage free solutions with good enough results. The eSSVI is an extended parametrization of the SSVI with purpose to improve its short maturity results. It was concluded to give small improvements but with the trade of making the optimization procedure harder. It was therefore concluded that the SSVI parametrization might be the better application.To try to improve the results of the SSVI parametrization was a complementary procedure developed which got named the calibrated SSVI method. This method compared to the eSSVI parametrization would not change the parametrization but instead focusing on calibrating the initial fit that the SSVI generated. This method would heavily improve the initial fit of the SSVI surface but was less robust since it generated harder cases for the interpolation and extrapolation.

  • 127976.
    Öhman, Amanda
    KTH, Skolan för industriell teknik och management (ITM).
    Towards a fossil free steel sector: Conditions for technology transfer of hydrogenbased iron and steel in Europe2019Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    In order to meet the targets of the Paris Agreement, there is a need to significantly reduce emissions from energy-intensive industries, iron and steel included. One promising technology with the potential to reduce the emissions related to iron and steelmaking to basically none is direct reduction with fossil free hydrogen, which requires large amounts of fossil free electricity. This master thesis explores the conditions for this technology in a European context with an energy perspective as the main focus. Three primary steel producing countries in Europe are chosen as focus countries; Germany, France and Italy.

    The findings of the study conclude that neither of the focus countries is an optimal sociotechnical fit for hydrogen-based direct reduction for iron and steel production at present. France is the country with the best conditions from a solely energy perspective but lacks some important factors for an enabling environment for technology transfer. Germany on the other hand have the most promising characteristics for an enabling environment but still face large challenges when it comes to power sector decarbonisation. In order to overcome the barriers and create an enabling environment it is key that energy and industry transitions are aligned, that a policy framework that supports these transitions is in place and that key actors representing all aspects of the transition cooperate; from industry to research, academia, policymakers and others.

    The findings also show that the current locations of the primary steel plants are in many cases not where the most favourable conditions for renewable power generation are and given the renewable capacity and transmission limitations of today, merely switching to a hydrogenbased process is not likely viable. A future configuration could be decentralised value chains where the different processes are located where there are optimal conditions e.g. that either hydrogen or sponge iron is produced where there are favourable power conditions and then transported to steel plants for the remaining processes in the value chain.

  • 127977.
    Öhman, Amanda
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    Lundberg, Linnea
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    Maximization of electricity generation or pelletization of the surplus bagasse in a Cuban sugar mill: A comparative analysis2016Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
  • 127978.
    Öhman, Astrid
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Arkitektur.
    Bibliotek i Liljeholmen: Library in Liljeholmen2018Independent thesis Advanced level (professional degree), 20 poäng / 30 hpOppgave
  • 127979.
    Öhman, Astrid
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Arkitektur.
    Opera i Stockholm, Danvikstull2011Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
  • 127980.
    Öhman, Axel
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Hållbar utveckling, miljövetenskap och teknik.
    Edwall, Bill
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Hållbar utveckling, miljövetenskap och teknik.
    Opportunities for the Jatuwa community biogas plant: An energy demand survey and a field site examinationMinor Field Study2018Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [sv]

    De klimatförändringar som idag orsakar allt större problem för länder i Himalayaregionen har ökat beslutsfattares medvetenhet kring konsekvenserna som de ökande temperaturerna för med sig. När människor konsumerar energi från fossila bränslekällor ökar koncentrationen av bland annat koldioxid i atmosfären vilket bidrar till den växthuseffekt som sakta värmer upp jordens klimat. Detta påverkar ekosystem och ökar risken för naturkatastrofer. Nepal är ett av länderna som ser konsekvenserna av den globala uppvärmningen från nära håll och landet satsar därför på att utveckla energisektorn genom implementeringen av fossilfria energislag. En av de mest framgångsrika satsningarna är användandet av biogasteknologi. Idag har över 350 000 småskaliga biogasanläggningar installerats över hela landet. Alternative Energy Promotion Centre (AEPC), den verkställande myndighetsorganisationen för främjande av ren och hållbar energi satsar nu på att utveckla den storskaliga biogassektorn för att öka landets inhemska och hållbara energiutvinning.

     

    Shree Krishna Gau Sewa Sadan (SKGSS) är en hinduisk stiftelse belägen i byn Jatuwa i sydöstra Nepal vars syfte är att ta hand om och betjäna kor, djur som inom hinduism är betraktade som heliga. Stiftelsen siktar nu på att bli ekonomiskt självförsörjande genom att sälja biogas och rötslam från en nyligen byggd biogasanläggning till närliggande hushåll. Gasen ska produceras från dynga insamlat från stiftelsens kor och distribueras genom ett gasnät som ännu inte är byggt. Syftet med denna studie var att utreda möjligheterna för SKGSS att framgångsrikt driva biogasanläggningen och fokuserade på två områden som var av intresse för AEPC, projektets huvudsponsor. Det första var att primärt beräkna hushållens energibehov för matlagning, deras nuvarande energikostnader för matlagning och deras inställning att byta till biogas som matlagningsbränsle för att assistera planeringen av det framtida gasnätet. Det andra var att lokalisera och identifiera potentiella förbättringsområden inom biogassystemet och baserat på detta ge förslag på huvudsakligen tekniska förbättringar som kan hjälpa SKGSS att framgångsrikt driva biogasanläggningen. Studien genomfördes med hjälp av en litteraturstudie, semi-konstruerade intervjuer, enkätundersökning av hushållen och en inspektion av biogasanläggningen.

     

    Enkätundersökningen visade att hushållens intresse att byta till biogas är stort. De flesta var dessutom villiga att betala för att anslutas till gasnätet. Den positiva inställningen till biogas härrör möjligen delvis från en ökad medvetenhet kring klimatfrågor samt energisäkerhet. Undersökningen visade även att det närliggande området inte är en trolig marknad för försäljning av rötslam. Dock är Nepal en växande marknad för organiskt och högkvalitativ gödsel så möjligheterna för en lyckad försäljning av rötslam är ändå stora. De primära beräkningarna visade att anläggningen med dess idag tillgängliga mängd organiskt material inte kan förse mer än 50 hushåll med biogas. Vid planläggningen av gasnätet måste dock beräkningar baserade på faktiska mätningar av biogassystemet göras. Denna studie rekommenderar även ett antal förbättringar av biogassystemet som skulle kunna hjälpa stiftelsens biogasanläggning att fungera bättre.

  • 127981.
    Öhman, Christian
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Byggteknik och design.
    Richnau, Robert
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Byggteknik och design.
    Värmeåtervinning från spillvatten i flerbostadshus2016Independent thesis Basic level (university diploma), 5 poäng / 7,5 hpOppgave
  • 127982.
    Öhman, Daniel
    KTH, Skolan för teknik och hälsa (STH), Hälso- och systemvetenskap, Ergonomi.
    Vi sitter tillsammans: Upplevelser av samhörighet och ledarskap i ett traditionellt kontorslandskap.2014Independent thesis Advanced level (degree of Master (One Year)), 10 poäng / 15 hpOppgave
    Abstract [en]

    The office is the working environment in which an increasing proportion of the population spends their days . One type of office are open plan offices which are characterized by several people sitting together in the same room without spatial boundaries . The general discourse of this kind of offices is that they constitute an advantageous design that allows organizational changes without the need for redevelopment . From a work perspective, this office design is both criticized and acclaimed . Problems with noise is frequently reported in research which can lead to ill health. At the same time quantitative studies shows that these office designs can both positively and negatively affect the cohesion and leadership at work. A deeper understanding of how office design affects cohesion and leadership is missing. This interview study aims to examine employees ' and managers' perceptions of how the open plan office affect the cohesion and leadership at work.

    Based on twelve personal interviews , six employees and six managers of a public administration, the interview answers were transcribed and thematised.

    Nineteen themes emerged that described how the open plan office impact on cohesion and leadership. Among these nineteen, thirteen themes were common , meaning that they occurred among both employees and managers to some extent. Six themes were explicit , meaning that they occurred only among either employees or managers. Five of the explicit themes occurred only among managers. The most frequent common theme underlying several cohesion and leadership enhancement factors were to sit together, which have a clear connection to the open plan office design.

    The open plan office was perceived to contribute to the cohesion at work in a positive way . However, there was a difference in the quality of depth between the groups in their answers. In the case of the impact on leadership , most managers and employees agree that the design contributed substantially to the manager's availability . There in was a difference between employees and managers , whether it was a positive or negative attribute . The study shows that there is a difficulty in determining where office design's influence ends and where the labor organization's impact begins.

  • 127983.
    Öhman, Elena
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Byggteknik och design.
    Fredriksson, Daniel
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Byggteknik och design.
    Effektiv internlogistik på ett byggprojekt: En beskrivning och analys av den interna logistiken på Nya Karolinska, Solna2012Independent thesis Basic level (professional degree), 10 poäng / 15 hpOppgave
    Abstract [sv]

    Byggbranschen kritiseras för att vara outvecklad och ineffektiv. De svenska byggkostnaderna har ökat med 21 % jämfört med övriga Europa där de i snitt ökade med 12 % mellan åren 2005 och 2010. Trots att aktörer inom den svenska byggsektorn är eniga om att byggkostnaderna kan sänkas råder det en viss oenighet om vilka dessa kostnadsposter det är. Det man däremot vet är att logistik är ett viktigt och omfattande men ofta underskattat ämne. Logistik innefattar de verksamheter som ser till att man får rätt mängd, av rätt produkt, av rätt kvalitet, på rätt plats och vid rätt tidpunkt. Tyvärr är kompetensen inom området bristfällig. Undersökningar visar att 30-35 % av produktionskostnaden på en byggarbetsplats är slöseri. Aktiviteter som inte tillför något värde klassificeras som slöseri. Det handlar om aktiviteter som är knutna till den interna hanteringen av material på byggarbetsplatsen som väntan, överproduktion, lager, omarbete, transporter, outnyttjad kreativitet, överarbete, rörelser samt skador och stölder. Avsikten med examensarbetet är att undersöka, beskriva, tolka och analysera logistiken på Nya Karolinska Solna samt belysa vikten av en välplanerad logistik och ge förslag på hur man kan effektivisera den. Nya Karolinska Solna är Skanskas största byggprojekt någonsin. Byggarbetsplatsen är belägen i Solna, med de tungt trafikerade vägarna E4 och E20 runtom. Transportvägar, transportanordningar, upplag för material, maskiner, yrkesarbetare, förråd, verkstäder och personalutrymmen samsas på en väldigt stor men trång yta.  För att få en uppfattning om hur den interna logistiken på Nya Karolinska Solna ser ut har intervjuer gjorts med berörda personer och kompletteras med egna observationer på byggarbetsplatsen samt digitalt tillhandahållen information från Skanska Healthcare AB. Fallstudier i form av värdeflödesanalys har genomförts på material som levererats till byggarbetsplatsen, studier över kranarnas utnyttjande under en arbetsdag samt leveransprecisionen hos leverantörerna. Resultatet från fallstudierna har sedan jämförts och analyserats och avslutningsvis har slutsatser dragits. För att projektet ska färdigställas i tid är det viktigt att produktionen fungerar smidigt och att flöden av resurser, material och yrkesarbetare inte hindras. Logistiken på Nya Karolinska Solna är välutvecklad men inte perfekt, man kan alltid förbättra och förnya. Slöseri är något som måste minimeras. Genom att sprida kunskaper om logistikens betydelse bland de berörda och se till alla samarbetar, kommer det leda till en slutprodukt av högsta kvalitet.  

  • 127984.
    Öhman, Elisabeth
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Properties of MIG/MAG brazed joints in zinc coated steel sheets.2003Independent thesis Advanced level (degree of Master (One Year)), 20 poäng / 30 hpOppgave
  • 127985.
    Öhman, Emil
    KTH, Skolan för elektroteknik och datavetenskap (EECS).
    Strategiska frågeställningar vid etablering av öppna API:er hos Skatteverket, vars funktion utgår från existerande e-tjänster2018Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [sv]

    Examensarbetet föreslår en effektivare process för att analysera olika frågeställningar vid Skatteverkets utveckling av öppna API:er. Frågeställningarna är främst olika juridiska krav men också tekniska och säkerhetsmässiga. Skatteverkets har i dag ett antal e-tjänster med potential att utveckla till öppna API:er. Skatteverket är den svenska statliga myndighet som ansvarar för folkbokföring, beskattning, fastighetstaxering med mera vilket skulle vara ett steg framåt i den moderna e-förvaltningen.

    Rapporten tar också upp bakgrundsfakta om det juridiska, om öppna data samt olika sätt att använda och tillgängliggöra API:er för allmänheten och skillnaderna mellan öppna data och API:er.

    Vi har lagar och regeringsdirektiv som öppnar upp och uppmuntrar vidareutnyttjande och tillgång till data, men vi har också lagar som skapar begränsningar vilket gör analysen för att tillgängliggöra mer information väldigt viktig. Förutom vanliga lagar gäller också registerlagar som definierar mer precist hur Skatteverket får arbeta med registerlagsskyddad information.

    Skatteverkets nuvarande e-tjänster och API:er har analyserats med tanke på vidareutveckling samt undersökning av hur medarbetare på Skatteverket ser på framtida användning av dessa API:er samt nätverksekonomin.

    Som ett exempel kan det tänkas att man med hjälp av API:er via företags affärssystem enkelt kan göra en CSR-förfrågan varje månad för att då kunna justera skatteinbetalningar och minska riskerna att de anställda fått för mycket eller för lite skatt inbetalt till Skatteverket vilket kan leda till problem. Detta sparar också tid på företagens personalavdelningar.

    Ett flödesschema har konstruerats för att ge ett effektivt stöd i analysen, om det är lämpligt att en e-tjänst tillgängliggörs via API, samt utvecklingen av API-tjänsten.

    Den komplexa kravbilden gör att det är svårt att ge ett standardsvar för om det är lämpligt för att e-tjänster tillgängliggörs via API samt att det också är viktigt att ha säkerheten i åtanke. Det är också viktigt att vara införstådd med att teknik och juridik förändras över tid vilket medför att det behövs kontinuerliga analyser för att se att de uppfyller samtliga krav.

  • 127986.
    Öhman, Eric
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Matematisk statistik.
    Analys av bostadsrättspriser medmultipel linjär regression ochprissättning i praktiken2014Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [sv]

    Syftet med denna rapport är att undersöka de faktorer som påverkar priset på bostadsrätter i Stockholms innerstad och hur mycket dessa faktorer påverkar priset med multipel linjär regression.  Resultaten från regressionsanalysen används för att skapa en modell för att prissätta bostadsrätter i Stockholms innerstad.  Denna modell jämförs med de metoder som byggnationsföretag vars verksamhet riktar sig mot försäljning av nybyggda bostadsrätter direkt till kund för att se om de metoder som används idag går att förbättra.  Arbetet resulterade i en modell som kan ge en indikation på hur mycket olika faktorer påverkar priset samt en grund för bostadsrättsvärdering i Stockholms innerstad.  De metoder som används idag visade sig inte kunna förbättras med de resultat som togs fram i denna rapport då fördelarna med dessa metoder är dess anpassningsbarhet efter ett projekts unika egenskaper samt avgränsningar till relevanta marknader.

  • 127987.
    Öhman, Henrik
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    Implementation and evaluation of a low temperature waste heat recovery power cycle using NH 3 in an Organic Rankine Cycle2012Inngår i: Energy, ISSN 0360-5442, E-ISSN 1873-6785, Vol. 48, nr 1, s. 227-232Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    With increasing cost for power generation opportunities for small scale power generation from waste heat have increased. The awareness of untapped resources such as local waste heat streams as well as the available range of technology and products to harvest such streams is increasing steadily though field data is scarce for applications below 100 °C entry temperature. ORC applications have a large number of open parameters and therefore require field data for correlation of models.This paper presents field data and analysis of an ORC power generation plant operating with NH 3. The unit operates on waste heat from a Swedish pulp mill at an available temperature of 75 to 85 °C. Performance at varying heat source conditions and capacity is reported as well as an analysis of the particular investment case.The data was generated during a 15 day period and show a thermal efficiency of 8-9% at capacities from 50 to 100%. The results indicate a flat thermal efficiency from 20 to 100% capacity.Investment case analysis is based on a purchase model while the chosen economic model is a supplier own-and-operate arrangement supplying the mill with power at a predefined cost during an extended period of time.

  • 127988.
    Öhman, Henrik
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Implementation and evaluation of low temperature waste heat recovery power cycle using NH3 in an organic rankine cycle2011Inngår i: / [ed] Zvonimir Guzovic, Zagreb: Faculty of Mechanical Engineering and Naval Architecture , 2011Konferansepaper (Fagfellevurdert)
    Abstract [en]

    With increasing cost for power generation the opportunities for small scale powergeneration from waste heat have increased. The awareness of untapped resources such aslocal waste heat streams as well as the available range of technology and products toharvest such streams is increasing steadily. For ORC power plant applications the numberof open parameters is large though the reported field data is limited, particularly for lowtemperature waste heat recovery.This paper presents field data and a performance analysis of an ORC powergeneration plant operating with NH3 as media. The ORC unit operates on waste heat froma Swedish pulp mill at an available temperature level of 75 to 85degC. Performance at lowwaste heat temperatures and during capacity variation is reported as well as an analysisof the particular investment case.The field data was generated by remote logging of control system information during a 15day period.The results show a thermal efficiency of 8 to 9% during a capacity range of 50 to 100%power generation. The results indicate a flat thermal efficiency curve from 20 to 100%power generation. The investment case is a supplier own-and-operate type of arrangement supplying thepulp mill with electric power at a predefined cost during a long period of time.

  • 127989.
    Öhman, Henrik
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Low temperature difference power systems and implications of multi-phase screw expanders in Organic Rankine Cycles2016Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    New and old data on screw expanders operating with 2-phase mixtures in the admission line has been combined to enable the first public correlation of adiabatic expansion efficiency as a function of entry vapour fraction. Although not yet perfected, these findings have enabled an entirely new approach to the design and optimisation of Organic Rankine Cycles, ORCs. By allowing a continuous variation of vapour fraction at expander entry optima for thermal efficiency, second law efficiency and cost efficiency can be found. Consequently one can also find maxima for power output in the same dimension.

    This research describes a means of adapting cycle characteristics to various heat sources by varying expander inlet conditions from pure liquid expansion, through mixed fluid and saturated gas expansion, to superheated gas. Thermodynamic analysis and comparison of the above optimisations were a challenge. As most terms of merit for power cycles have been developed for high temperature applications they are often simplified by assuming infinite heat sinks. In many cases they also require specific assumptions on e.g. pinch temperatures, saturation conditions, critical temperatures etc, making accurate systematic comparison between cycles difficult. As low temperature power cycles are more sensitive to the ‘finiteness’ of source and sink than those operating with high temperatures, a substantial need arises for an investigation on which term of merit to use.

    Along with an investigation on terms of merit, the definition of high level reversible reference also needed revision. Second law efficiency, in the form of exergy efficiency, turned out to be impractical and of little use. A numerical approach, based on a combination of first and second law, was developed. A theory and method for the above is described. Eventually low temperature power cycle test data was compiled systematically. Despite differences in fluid, cycle, temperature levels and power levels the data correlated well enough to allow for a generalised, rough correlation on which thermal efficiency to expect as a function of utilization of source and sink availability. The correlation on thermal efficiency was used to create a graphical method to pre-estimate key economic factors for low temperature site potential in a very simple manner. A major consequence from the findings of this thesis is the reduced dependency on unique choices of process fluid to match heat source characteristics. This development significantly simplifies industrial standardisation, and thereby potentially improves cost efficiency of commercial ORC power generators.

  • 127990.
    Öhman, Henrik
    Svenska Rotor Maskiner AB.
    Test Results of A Screw Type Expander/. Compressor and the Implication of Phase. Separators on the Refrigeration Process2004Inngår i: 2004 International Refrigeration and Air Conditioning Conference, West Lafayette, Indiana, USA: Purdue University Press, 2004Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Running a refrigeration cycle at saturated liquid conditions at the evaporator inlet has a few interesting advantages in comparison to the conventional 2-phase situation. Opportunities in using novelty heat exchangers, increased cycle efficiency and significantly reduced main compressor sizes occur. Using the two rotor integrated

    compressor/expander idea developed by Olofsson (1993) in a refrigeration cycle theoretically offer the possibility of pure liquid evaporator inlet conditions, the device is called Phase Separator. This paper reports results from hardware tests as well as some theoretical results. To evaluate the efficiency of a Phase Separator three terms of efficiency are suggested. The test results prove that pure liquid conditions to the evaporator are obtainable with a practical Phase Separator.

  • 127991.
    Öhman, Henrik
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Lundqvist, Per
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Comparison and analysis of performance using Low Temperature Power Cycles2013Inngår i: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 52, nr 1, s. 160-169Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Low Temperature Power Cycles have become increasingly interesting means of increasing energy efficiency of processes as well as for base load power generation from solar, and geothermal, heat. Theoretical understanding of the various processes, components and limitations is constantly increasing through extensive research. Practical utilisation of this knowledge is also increasing steadily though properly published field data is scarce. In this article a number of different solutions for power generation from low temperature heat sources have been gathered and analysed. Some of the studied units have not previously been described. A method for general evaluation of LTPC's is proposed and the outcome of the analysis is discussed as well as how to use it for practical purposes. By separating thermodynamic potential from irreversibilities the analysis indicates that the irreversibilities show limited dependency on temperature, size, thermodynamic cycle or working fluid. Instead performance of the studied units follows a relatively simple correlation with utilisation of the thermal potential. This correlation is defined and discussed. One conclusion is that the correlation allows for a possibility to express the maximum expected real power generation with knowledge of the characteristics of the heat source and heat sink only.

  • 127992.
    Öhman, Henrik
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Lundqvist, Per
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Experimental investigation of a Lysholm Turbine operating with superheated, saturated and 2-phase inlet conditions2013Inngår i: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 50, nr 1, s. 1211-1218Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Low temperature power cycles can benefit from the use of multi-phase flow expansion devices from a thermodynamic cycle efficiency point of view. Particularly power cycles such as ORC, Kalina and Trilateral Flash Cycles can be improved by multi-phase expansion. This article presents the experimental findings in a series of laboratory tests on a semihermetic Lysholm Turbine operating with R134a with superheated, saturated and wet inlet gas conditions. The test arrangements are described as well as discussion on the relevance of such test data. Finally comparison is made with findings from other investigations and recommendations for further studies are made. A correlation between peak efficiency and sensitivity to inlet vapour fraction was discovered which allows for estimations of adiabatic efficiencies with 2-phase inlet conditions even when only test data, or simulations, from single phase inlet conditions exist. The conclusions made are that Lysholm Turbines are well suited for low temperature power generation and that further understanding of the performance during 2-phase conditions is required.

  • 127993.
    Öhman, Henrik
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Lundqvist, Per
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    On high level evaluation and comparison of ORC power generators2015Inngår i: Proceedings of the 3rd International Seminar on ORC Power Systems, 2015Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A review of the thermodynamic performance of ORCs from public, as well as non-public sources hasrevealed a correlation suitable to be used as a rule of thumb for  high-level performance estimation ofORC power generators. Using the correlation, the limited amount of available test data can begeneralised leading to a high level evaluation of the commercial benefits of any potential applicationfor ORCs.Power generators using ORC-technology exist in relatively low numbers. Furthermore, fieldinstallations seldom imply comparable boundary conditions. As ORCs generally  operate at lowtemperature differences between source and sink it has been shown that their relative sensitivity tovariations in temperatures i.e. the finiteness of source- and sink, is larger than the sensitivity of powergenerators operating with large temperature differences. Therefore the establishing of practical rule ofthumb performance estimation, similar to the figure of merit, Coefficient of Performance, COP, asused in refrigeration and air conditioning industry, has previously not been successful.In order to arrange field data in a manner suitable for comparison a refinement of suitable figures ofmerit was required. The suggested, refined terms are presented and explained as well as criticallyevaluated against the most common  efficiency terms traditionally used.The current lack of a performance rule of thumb leaves room for less serious vendors and laymen tomake performance claims unrealistic to practical achievements. Scrutinizing such questionablestatements requires detail process simulations and a multitude of technical assumptions. Henceargumentation becomes ineffective. If a suitable rule of thumb can be established argumentationagainst dubious claims would become significantly more forceful.This paper suggests a new term to be used as rule of thumb and explains a  method on how to use it.

  • 127994.
    Öhman, Henrik
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Lundqvist, Per
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Screw expanders in ORC applications, review and a new perspective2015Inngår i: Proceedings of the 3rd International Seminar on ORC Power Systems, 2015Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Performance of Organic Rankine Cycles is sensitive not only to the entry  temperature ratio betweenheat source and heat sink but also to the temperature  degradation of the heat source flow, caused bythe heat transfer to the process in pre-heater, evaporator and super heater. In order to adopt the cycleto the great variety of heat sources a multitude of fluids are required. Alternatively fluid mixtures,trans-critical or supercritical fluid conditions can be used to match the process temperatures with theheat source. Screw expanders offer an alternative, new approach to the matching problem of ORC’s asthey allow for flexible multi-phase expansion. Hereby the vapour fraction at the expander entry can beused to  partially match the temperatures of the process to a particular heat source. To provide aperspective on the use of such screw expanders in ORC-systems previous experimental andcommercial experience have been reviewed and discussed.Screw expanders are versatile machines used for the production of mechanical work in power rangesfrom 3kW to 1.5MW. As the functional characteristics differ significantly  from dynamic expandersthe explanatory models used to generalise results are different. Plenty of research has resulted in wellgeneralized explanatory models for dynamic expander analysis. For screw expanders similarexplanatory models exist mainly in commercially confidential environments. A few public sourcesdisclose test data. In the few cases data has been investigated the analyses tend to rely onthermodynamic models suitable for dry gas expansion. Typically that leads to reasonable replicationof test results but seldom to models suitable for detailed understanding of the process. In applicationswith 2-phase expansion the theories used to simulate functional characteristics is entirely insufficient.The main reason for  the scarcity of work in this field is probably the empirical difficulties in obtaininggood measuring data in multi-phase conditions.This paper describes a review of multi-phase screw expander experiences and explains why a uniquetheory is required to model its characteristics. In the absence of such a unique theory a correlationbased in empirical data is presented. This allow for estimations of screw expander efficiency in multi-phase conditions. Measured efficiency with dry expansion, or such efficiency simulated, can be usedto estimate adiabatic efficiency with expansion entry vapor fractions ranging from 0 to 1 by using thiscorrelation. Hence estimating expansion efficiency during multi-phase expansion is simplified,allowing for better optimisation of the ORC-systems. This way a new perspective of screw expanderpotential in ORC system integration can be presented.

  • 127995.
    Öhman, Henrik
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Lundqvist, Per
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Theory and method for analysis of low temperature driven power cycles2012Inngår i: Applied Thermal Engineering, ISSN 1359-4311, nr 37, s. 44-50Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A new method, using a combination of traditional first law and second law analysis, is developed to facilitate characterization and comparison of power cycles using low temperature heat sources. In trying to determine the best thermodynamic cycle and working media for a given application one must take the strongly non-linear effects of matching the pinch points of a particular cycle with a particular working media into account. The new method allows unbiased comparison of arbitrarily chosen power cycles, working fluids and component characteristics. The method also allows for operating conditions with finite capacity heat source and heat sink. The usefulness of the method is illustrated by the analysis of the effects of local temperature difference distribution for three different fully reversible power cycles using three different working media.

    The driver for developing this method is to simplify comparison and communication among users and industrial professionals and thus enable a better understanding of characteristics and design criteria for low temperature heat driven power cycles.

  • 127996.
    Öhman, Henrik
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Per, Lundqvist
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Organic Rankine Cycles with variable vapour fraction expansion entry: Reduced sensitivity to choice of working fluid in modified Organic Rankine Cycles by using wet vapour expansion entry conditions2014Rapport (Annet vitenskapelig)
    Abstract [en]

    The task of reducing global carbon dioxide emissions leads to a need to reduce the average CO2-emission in power generation. A more energy efficient mix of power generation on national, or regional level, will require the re-use of waste heat and use of primary, low temperature heat for power generation purposes. Low Temperature Power Cycles, such as Organic Rankine Cycles, Trilateral Flash Cycles, Kalina Cycles offer a large degree of freedom in finding technical solutions for such power generation.

    Theoretical understanding of LTPC’s advance rapidly though practical achievements in the field show very humble improvements at a first glance. Cost of applying the new knowledge in real applications seems to be an important reason for the discrepancy. One central reason for the high cost level is the diversity of process fluids required and consequently the lack of standardization and industrialization of equipment. Uses of supercritical power cycle technology tend to cause the same dilemma. Furthermore upcoming regulations prohibiting the use of several process fluids tend to lead to remedies increasing plant cost.

    By using 2-phase, variable vapour fraction, expansion inlet conditions the need to use many different process fluids is reduced, allowing simpler and more cost efficient LTPC’s by easier matching with heat source temperature characteristics. This article explores some of the associated effects on cycle output and cost efficiency. A waste heat recovery application is investigated simulating cost efficiency, thermodynamic efficiencies and power generation while using fundamentally different working fluids, lumped component efficiencies, variable utilization of the waste heat and optimisation on expansion inlet vapour fraction.

    The conclusion made is that the sensitivity to choice of working fluid is lower than intuitively anticipated, in contrast to common consensus in science. Furthermore it is shown that exceptional component efficiencies are not required in order to achieve a performance comparable to current practise and that a good business case is possible under the assumed economic conditions.

  • 127997.
    Öhman, Henrik
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Per, Lundqvist
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Thermodynamic pre-determination of power generation potential in geothermal low-temperature applications2014Inngår i: Geothermal Energy, ISSN 2195-9706, Vol. 2, nr 1, s. 1-10, artikkel-id 4Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Background: Small capacity, low temperature, geothermal heat sources providesignificant opportunities for distributed, small scale power generation. Projectdefinitions and pre-dimensioning however require advanced thermodynamicengineering at a cost independent of project size. In order to reduce this cost, anew method has been developed to allow basic level engineers to performpre-optimisation of thermodynamic potential as well as expected performance usingavailable power plant technology at such pre-optimized conditions.Results: By reducing the complexity of second-law computations, a simpletwo-dimensional diagram is shown representing the dimensioning criteria requiredfor maximum power generation using the particular heat source and sink whileconsidering expected power plant performance, using systems and componentson the market.Methods: By sensitivity analysis the combination of thermodynamic analysis and realworld data correlations was simplified and arranged for pre-dimensioning ofbusiness cases.Conclusions: Optimal pre-dimensioning of power generation system for anygeothermal heat source, with a defined heat sink, can be determined withoutadvanced thermodynamic expertise. This reduces the cost for business case proposals,pre-dimensioning and tender specifications of small-scale power generation systemsfor low temperature heat sources. The intended implication of this work is to increasethe use of low-temperature geothermal wells for distributed power generation.

  • 127998.
    Öhman, Maj-Britt
    et al.
    Uppsala universitet.
    Sandström, Camilla
    Umeå University.
    Thunqvist, Eva-Lotta
    KTH, Skolan för teknik och hälsa (STH), Hälso- och systemvetenskap, Systemsäkerhet och organisation.
    Designing Dam Safeties: Perspectives on large scale dams within the intra-actions of technology, nature and human decision making2013Inngår i: International Commission of Large Dams, ICOLD, Seattle, 2013: International Symposium, Seattle: ICOLD , 2013Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Analyzing the intra-actions between the actors involved, this paper presents results from interviews and participatory observations with local authorities, local inhabitants, power companies representatives as well as dam operators. We argue that the Swedish model for dam safety currently is suffering from a major deficiency as the expertise and understanding of the technical constructions remain among the dam owners and that the societal authority in charge of supervising the dam owners work have no capability of achieving the same level of understanding and thus to take informed and relevant decisions. Furthermore we argue that the lack of technical understanding of dams and hydropower outside of the dam sector has become a huge threat to dam safety as state representatives and political decision makers currently allow and even encourage mining exploitation both next to high risk classified hydropower dams and even within existing hydropower reservoirs.

    We argue that the actual challenge to safeguard an increased dam safety is by bridging the gap between the multitude of different actors– engineers/operators, users, political decision makers -   in order to generate new understandings and new methodologies to deal with risk, safety and security. It is necessary to bridge the gaps between the sectors and actors involved, and that this should be done through investment in close collaboration between the dam sector and engineering research on the one hand and social sciences and humanities on the other – to ensure understandings of political decision making as well as of technical artifacts and water flows.

    The geographical focus is on two rivers – the Ume River and the Lule River in the north of Sweden. Both rivers are of major importance for national production of electricity, and the rivers are water suppliers for a large amount of inhabitants.

  • 127999.
    Öhman, Maria
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Arkitektur.
    2000 nya hus i Tallkrogen2018Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [sv]

    2000 nya hus i Tallkrogen

    Tallkrogen i söderort, Stockholm är ett egnahemsområde byggt på 30-talet. Via små förändringar i många steg har området och husens egenskaper förändrats och husen har gått från en generell utgångspunkt till en strävan mot individualitet. Genom dessa stegvisa förändringar har en långsam töjning av vad platsen tillåter utvecklat området om än dolt under en form av bevarande av egna hem rörelsen. 

    Hur kan den gradvisa utveckling som skett i Tallkrogen agera generator för expansion? Hur skulle rum, hus och översiktsplan gestalta sig i en nytolkning av området sprunget ur den utveckling som skett sedan området byggdes? 

    Genom att knyta an till Tallkrogens DNA föreslår projektet två nya hus på en tomt i Tallkrogen. Storasyster och Lillebror. En mutation som med tiden skulle kunna komma att påverka hela området och senare bli 2000 nya hus.

  • 128000.
    Öhman, Maria
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    An in situ spectro-electrochemical study of aluminium/polymer interfaces: development of ATR-FTIR and its integration with EIS for corrosion studies2006Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    In order to extend the applications of aluminium, organic coatings may be applied on sheet materials, for instance for corrosion protection or aesthetic surface finish purposes in the automotive and construction industries, or on foil materials in the flexible packaging industry.

    The most common mechanisms for deterioration and structural failure of organically coated aluminium structures are triggered by exposures to the surrounding environment. Despite the great importance to elucidate the influence of exposure parameters on a buried aluminium/polymer interface, there is still a lack of knowledge regarding the mechanisms that destabilise the structure. It is generally believed that a detailed in situ analysis of the transport of corroding species to the buried interface, or of surface processes occurring therein, is most difficult to perform at relevant climatic and real-time conditions.

    In this work, Attenuated Total Reflection Fourier Transform Infrared Spectroscopy (ATR-FTIR) in the Kretschmann-ATR configuration was successfully applied to in situ studies of the transport of water and ionic species through polymer films to the aluminium/polymer interface upon exposure to ultra pure deionised water and to a 1 M sodium thiocyanate (NaSCN) model electrolyte. Other main processes distinguished were the formation of corrosion products on the aluminium surface and swelling of the surface-near polymer network. Hence, in situ ATR-FTIR was capable to separate deterioration-related processes from each other.

    To perform more unambiguous interpretations, a spectro-electrochemical method was also developed for in situ studies of the buried aluminium/polymer interface by integrating the ATR-FTIR technique with a complementary acting technique, Electrical Impedance Spectroscopy (EIS). While transport of water and electrolyte through the polymer film to the aluminium/polymer interface and subsequent oxidation/corrosion of aluminium could be followed by ATR-FTIR, the protective properties of the polymer as well as of processes at the aluminium surface were simultaneously studied by EIS. The integrated set-up provided complementary information of the aluminium/polymer sample investigated, with ATR-FTIR being sensitive to the surface-near region and EIS being sensitive to the whole system. While oxidation/corrosion and delamination are difficult to distinguish by EIS, oxide formation could be confirmed by ATR-FTIR. Additionally, while delamination and polymer swelling may be difficult to separate with ATR-FTIR, EIS distinguished swelling of the polymer network and also identified ultimate failure as a result of delamination.

    The capability of the integrated ATR-FTIR / EIS in situ technique was explored by studying aluminium/polymer systems of varying characteristics. Differences in water and electrolyte ingress could be monitored, as well as metal corrosion, polymer swelling and delamination.

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