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  • 123551.
    Ögren, Patric
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Industrial Economics and Management (Dept.), Entrepreneurship and innovation.
    Högberg, Kristoffer
    KTH, School of Industrial Engineering and Management (ITM), Industrial Economics and Management (Dept.), Entrepreneurship and innovation.
    En ”marknadsundersökning” genom att iterera fram till ett värdeskapande koncept2013Independent thesis Advanced level (degree of Master (One Year)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    A business concept has been developed into a marketplace. The marketplace is a web and mobile application whose purpose is to create value out of resources' bookable time slots which today generally have low occupation rates at activity facilities within sports, culture and entertainment.

    The marketplace is intended to bring together a wide range of low occupation rate time slots for different activity types, with types of activities that friends typically do together an ordinary day. The idea is to build a strong brand for the marketplace with the clear message that "the marketplace provides a wide range of affordable offerings for sports and spare time activities, if you choose to adjust your schedule to fit the facilities' low occupation rate time slots". In addition, the marketplace should have functionality that makes it easier for end-users to find a time slot through the marketplace that fits everyone, by synchronizing the various options of activities and time slots preferences that people within a group of friends are interested in. The marketplace is supposed to be targeted to people with flexible schedules, especially self-employed, students and seniors. There is a good potential for a third party to run such a marketplace and specialize in creating value out of low occupation rate time slots. However, the business concept does not prevent the facilities themselves to make efforts which lead to increased occupation rates at time slots with low occupation rates. Furthermore, the facilities are rather supposed to use the marketplace as a complement to their existing booking systems. Based on the examined activity facilities, there is a good potential to increase a facility's turnover with approximately 330 000 SEK yearly.

    The business concept has been developed by doing a market research based on a technical product which initially was designed as a booking system with different product development opportunities and various potential customer segments to address. The market research was done iteratively by using the project management methodology Lean Startup combined with qualitative market research techniques from Innovation Games.

  • 123552.
    Ögren, Petter
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Formations and Obstacle Avoidance in Mobile Robot Control2003Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    This thesis consists of four independent papers concerningthe control of mobile robots in the context of obstacleavoidance and formation keeping.

    The first paper describes a new theoreticallyv erifiableapproach to obstacle avoidance. It merges the ideas of twoprevious methods, with complementaryprop erties, byusing acombined control Lyapunov function (CLF) and model predictivecontrol (MPC) framework.

    The second paper investigates the problem of moving a fixedformation of vehicles through a partiallykno wn environmentwith obstacles. Using an input to state (ISS) formulation theconcept of configuration space obstacles is generalized toleader follower formations. This generalization then makes itpossible to convert the problem into a standard single vehicleobstacle avoidance problem, such as the one considered in thefirst paper. The properties of goal convergence and safetyth uscarries over to the formation obstacle avoidance case.

    In the third paper, coordination along trajectories of anonhomogenuos set of vehicles is considered. Byusing a controlLyapunov function approach, properties such as boundedformation error and finite completion time is shown.

    Finally, the fourth paper applies a generalized version ofthe control in the third paper to translate,rotate and expanda formation. It is furthermore shown how a partial decouplingof formation keeping and formation mission can be achieved. Theapproach is then applied to a scenario of underwater vehiclesclimbing gradients in search for specific thermal/biologicalregions of interest. The sensor data fusion problem fordifferent formation configurations is investigated and anoptimal formation geometryis proposed.

    Keywords:Mobile Robots, Robot Control, ObstacleAvoidance, Multirobot System, Formation Control, NavigationFunction, Lyapunov Function, Model Predictive Control, RecedingHorizon Control, Gradient Climbing, Gradient Estimation.

  • 123553.
    Ögren, Petter
    Swedish Defence Research Agency (FOI).
    Improved predictability of reactive robot control using Control Lyapunov Functions2008In: 2008 IEEE/RSJ INTERNATIONAL CONFERENCE ON ROBOTS AND INTELLIGENT SYSTEMS, VOLS 1-3, CONFERENCE PROCEEDINGS, 2008, p. 1274-1279Conference paper (Refereed)
    Abstract [en]

    Model based robot control approaches are often designed to allow the verification of certain system properties such as safety or goal convergence. However, designing such controllers is often very time consuming, and most of the time it is not possible to add additional control objectives without jeopardizing the previously proved system properties.

  • 123554.
    Ögren, Petter
    Swedish Defence Research Agency (FOI), Sweden.
    Increasing Modularity of UAV Control Systems using Computer Game Behavior Trees2012In: AIAA Guidance, Navigation, and Control Conference 2012, 2012Conference paper (Refereed)
    Abstract [en]

    In this paper, we argue that the modularity, reusability and complexity of Unmanned Aerial Vehicle (UAV) guidance and control systems might be improved by using a Behavior Tree (BT) architecture. BTs are a particular kind of Hybrid Dynamical Systems (HDS), where the state transitions of the HDS are implicitly encoded in a tree structure, instead of explicitly stated in transition maps. In the gaming industry, BTs have gained a lot of interest, and are now replacing HDS in the control architecture of many automated in-game opponents. Below, we explore the relationship between HDS and BTs. We show that any HDS can be written as a BT and that many common UAV control constructs are quite naturally formulated as BTs. Finally, we discuss the positive implications of making the above mentioned state transitions implicit in the BTs.

  • 123555.
    Ögren, Petter
    Swedish Defence Research Agency (FOI).
    Split and Join of Vehicle Formations doing Obstacle Avoidance2004In: 2004 IEEE INTERNATIONAL CONFERENCE ON ROBOTICS AND AUTOMATION, VOLS 1- 5, PROCEEDINGS, 2004, p. 1951-1955Conference paper (Refereed)
    Abstract [en]

    In this paper, we study a scenario where a set of vehicles having different origins and/or destinations move in a common region. The goal is to have the vehicles join and leave formations in a completely decentralized manner. When a vehicle traveling along its own path finds itself moving close to another vehicle it automatically switches into follower mode. The vehicle stays in follower mode as long as the path of the other vehicle is beneficial to it. If, at some point, the leader is not moving towards the destination of the follower, the follower leaves the leader and head of on its own. We address this problem for a group of dynamic unicycle robots. Incorporating the split and join capability into a Receding Horizon Control approach to obstacle avoidance we are able to show safety as well as convergence of all vehicles to their destinations under general nonconvex obstacle assumptions. We illustrate the method with a simulation example

  • 123556.
    Ögren, Petter
    et al.
    Swedish Defence Research Agency (FOI).
    Backlund, Adam
    Swedish Defence Research Agency (FOI).
    Harryson, Tobias
    Swedish Air Force, Air Combat School .
    Kristensson, Lars
    Swedish Defence Research Agency (FOI).
    Stensson, Patrik
    Swedish Air Force, Air Combat School.
    Autonomous UCAV Strike Missions using Behavior Control Lyapunov Functions2006Conference paper (Refereed)
    Abstract [en]

    An autonomous Unmanned Combat Aerial Vehicle (UCAV) carrying out a surveillance or strike mission must be able to handle situations where the different mission objectives are in conflict and a tradeoff must be made, e.g. when the time of arrival is in conflict with the prescribed safety distance to an enemy surface to air missile (SAM) site. This paper describes a framework called Behavior Control Lyapunov Functions (BCLF), to handle such tradeoffs. The framework combines the natural idea of different control behaviors for different mission objectives, suggested in the Behavior Based robotics approach, with the mathematical transparency of Control Lyapunov Functions (CLF) from control theory. First, each behavior is represented by a scalar function with certain CLF-like properties, describing to what extent that mission objective is satisfied. The operator then edits a priority table reflecting the order of importance between different objectives, as well as different levels of satisfaction. Based on the table and the current levels of satisfaction the algorithm decides which objectives should be focused on right now, and which should currently be ignored. Finally, the current high priority objectives are transformed into recommended subsets of the available control choices, and passed to the controller. The paper is concluded with simulation examples illustrating the approach.

  • 123557.
    Ögren, Petter
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Robotics, perception and learning, RPL.
    Colledanchise, Michele
    KTH, School of Computer Science and Communication (CSC), Computer Vision and Active Perception, CVAP.
    Behavior Trees in Robotics and AI: An Introduction2018 (ed. First)Book (Refereed)
    Abstract [en]

    Behavior Trees (BTs) provide a way to structure the behavior of an artificial agent such as a robot or a non-player character in a computer game.  Traditional design methods, such as finite state machines, are known to produce brittle behaviors when complexity increases, making it very hard to add features without breaking existing functionality.  BTs were created to address this very problem, and enables the creation of systems that are both modular and reactive. Behavior Trees in Robotics and AI: An Introduction provides a broad introduction as well as an in-depth exploration of the topic, and is the first comprehensive book on the use of BTs.

  • 123558.
    Ögren, Petter
    et al.
    KTH, School of Computer Science and Communication (CSC), Computer Vision and Active Perception, CVAP.
    Egerstedt, M
    Hu, X
    A Control Lyapunov Function Approach to Multi-Agent Coordination2001Conference paper (Refereed)
    Abstract [en]

    In this paper, the multiagent coordination problem is studied. This problem is addressed for a class of robots for which control Lyapunov functions can be found. The main result is a suite of theorems about formation maintenance, task completion time, and formation velocity. It is also shown how to moderate the requirement that, for each individual robot, there exists a control Lyapunov function. An example is provided that illustrates the soundness of the method

  • 123559.
    Ögren, Petter
    et al.
    KTH, School of Computer Science and Communication (CSC), Computer Vision and Active Perception, CVAP.
    Egerstedt, M
    Hu, X
    A control Lyapunov function approach to multi-agent coordination2002In: IEEE transactions on robotics and automation, ISSN 1042-296X, Vol. 18, no 5, p. 847-851Article in journal (Refereed)
    Abstract [en]

    In this paper, the multiagent coordination problem is studied. This problem is addressed for a class of robots for which control Lyapunov functions can be found. The main result is a suite of theorems about formation maintenance, task completion time, and formation velocity. It is also shown how to moderate the requirement that, for each individual robot, there exists a control Lyapunov function. An example is provided that illustrates the soundness of the method

  • 123560.
    Ögren, Petter
    et al.
    KTH, School of Computer Science and Communication (CSC), Computer Vision and Active Perception, CVAP.
    Egerstedt, M
    Hu, X
    Reactive mobile manipulation using dynamic trajectory tracking2000Conference paper (Refereed)
    Abstract [en]

    A solution to the trajectory tracking problem for mobile manipulators is proposed, that allows for the base to be influenced by a reactive, obstacle avoidance behavior. 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. 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. The solution also ensures that the control effort, spent on slow base motions, is kept small

  • 123561.
    Ögren, Petter
    et al.
    KTH, School of Computer Science and Communication (CSC), Computer Vision and Active Perception, CVAP.
    Fiorelli, E
    Leonard, N.E.
    Formations with a Mission: Stable Coordination of Vehicle Group Maneuvers2002Conference paper (Refereed)
    Abstract [en]

    In this paper we present a stable coordination strategy for vehicle formation missions that involve group translation, rotation, expansion and contraction. The underlying coordination framework uses artificial potentials and virtual leaders. Symmetry in the framework is exploited to partially decouple the mission control problem into a formation management subproblem and a maneuver management subproblem. The designed dynamics of the virtual leaders play a key role in both subproblems: the direction of motion of the virtual leaders is designed to satisfy the mission while the speed of the virtual leaders is designed to ensure stability and convergence properties of the formation. The latter is guaranteed by regulating the virtual leader speed according to a feedback measurement of an appropriate formation error function. The coordination strategy is illustrated in the context of adaptive gradient climbing missions.

  • 123562.
    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 Environment2004In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 49, no 8, p. 1292-1302Article in journal (Refereed)
  • 123563.
    Ögren, Petter
    et al.
    KTH, School of Computer Science and Communication (CSC), Computer Vision and Active Perception, CVAP.
    Leonard, N
    Obstacle Avoidance in Formation,2003Conference paper (Refereed)
    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.

  • 123564.
    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 Avoidance2005In: IEEE Transactions on robotics, ISSN 1552-3098, E-ISSN 1941-0468, Vol. 21, no 2, p. 188-195Article in journal (Refereed)
    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.

  • 123565.
    Ögren, Petter
    et al.
    KTH, School of Computer Science and Communication (CSC), Computer Vision and Active Perception, CVAP.
    Leonard, N.E.
    A Probably Convergent Dynamic Window Approach to Obstaclen Avoidance2002Conference paper (Refereed)
    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.

  • 123566.
    Ögren, Petter
    et al.
    KTH, School of Computer Science and Communication (CSC), Computer Vision and Active Perception, CVAP.
    Leonard, N.E.
    A tractable convergent dynamic window approach to obstacle avoidance2002Conference paper (Refereed)
    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.

  • 123567.
    Ögren, Petter
    et al.
    KTH, School of Computer Science and Communication (CSC), Computer Vision and Active Perception, CVAP.
    Martin, C.F.
    Optimal Vaccination Strategies for the Control of Epidemics in Highly Mobile Populations2000Conference paper (Refereed)
    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

  • 123568.
    Ögren, Petter
    et al.
    KTH, School of Computer Science and Communication (CSC), Computer Vision and Active Perception, CVAP.
    Martin, C.F
    Vaccination Strategies for Epidemics in Highly Mobile Populations2002In: Applied Mathematics and Computation, ISSN 0096-3003, E-ISSN 1873-5649, Vol. 127, no 2-3, p. 261-276Article in journal (Refereed)
    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.

  • 123569.
    Ögren, Petter
    et al.
    KTH, School of Computer Science and Communication (CSC), Computer Vision and Active Perception, CVAP.
    Petersson, L
    Egerstedt, M
    Hu, X
    Reactive mobile manipulation using dynamic trajectory tracking: design and implementation2000Conference paper (Refereed)
    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

  • 123570.
    Ögren, Petter
    et al.
    KTH, School of Computer Science and Communication (CSC), Computer Vision and Active Perception, CVAP.
    Robinson, John W.C.
    Swedish Defence Research Agency (FOI), Department of Aeronautics .
    A Model Based Approach to Modular Multi-Objective Robot Control2011In: Journal of Intelligent and Robotic Systems, ISSN 0921-0296, E-ISSN 1573-0409, Vol. 63, no 2, p. 257-282Article in journal (Refereed)
    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.

  • 123571.
    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 Discretizations2010Conference paper (Refereed)
    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.

  • 123572.
    Ögren, Petter
    et al.
    KTH, School of Computer Science and Communication (CSC), Computer Vision and Active Perception, CVAP.
    Smith, Christian
    KTH, School of Computer Science and Communication (CSC), Computer Vision and Active Perception, CVAP.
    Karayiannidis, Yiannis
    KTH, School of Computer Science and Communication (CSC), Computer Vision and Active Perception, CVAP.
    Kragic, Danica
    KTH, School of Computer Science and Communication (CSC), Computer Vision and Active Perception, CVAP.
    A Multi Objective Control Approach to Online Dual Arm Manipulation2012In: Robot Control, International Federation of Automatic Control , 2012, p. 747-752Conference paper (Refereed)
    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.

  • 123573.
    Ögren, Petter
    et al.
    Swedish Defence Res. Agency, Stockholm.
    Svenmarck, Peter
    Swedish Defence Res. Agency, Stockholm.
    A New Control Mode for Teleoperated Differential Drive UGVs2007In: PROCEEDINGS OF THE 46TH IEEE CONFERENCE ON DECISION AND CONTROL, VOLS 1-14, 2007, p. 446-471Conference paper (Refereed)
    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

  • 123574.
    Ögren, Petter
    et al.
    KTH, School of Computer Science and Communication (CSC), Computer Vision and Active Perception, CVAP. KTH, School of Computer Science and Communication (CSC), Centres, Centre for Autonomous Systems, 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 UGVs2014In: Autonomous Robots, ISSN 0929-5593, E-ISSN 1573-7527, Vol. 37, no 1, p. 71-79Article in journal (Refereed)
    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.

  • 123575.
    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 Mission2005Conference paper (Refereed)
  • 123576.
    Ögren, Petter
    et al.
    Department of Autonomous Systems Swedish Defence Research Agency.
    Winstrand, Maja
    Minimizing Mission Risk in Fuel Constrained UAV Path Planning2008In: Journal of Guidance Control and Dynamics, ISSN 0731-5090, E-ISSN 1533-3884, Vol. 31, no 5, p. 1497-1500Article in journal (Refereed)
  • 123577.
    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 Problem2006Conference paper (Refereed)
    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

  • 123578.
    Ögren, Tomas
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Technology and Design.
    Ökvist, Jesper
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Technology and 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 credits / 15 HE creditsStudent thesis
    Abstract [en]

    This study has been conducted with emphasis on managing buildings according to 

    BREEAM In-Use, which is used as an environmental certification on existing 

    buildings. The report is oriented on the aspects of certifying the management and 

    organization carried out within the building. The connection between user and 

    manager is important to ensure that the goals within BREEAM are achieved. A tool to 

    encourage communication between these two sides is the green leases from 

    Fastighetsägarna, which has shown to be a necessary link.  It has been shown that 

    current management methods need to be extended in its routines and that 

    knowledge regarding BREEAM is necessary within the management. BREEAM In- 

    Use demands commitment and a continuous work and will result in a change of 

    behavior from the user, to achieve a high rating. Management has shown to have 

    great potential to work for less resource use and to ensure a sustainable long term 

    service life.  

  • 123579.
    Öhberg, Patrik
    KTH, Superseded Departments, Physics.
    Studies of inhomogeneous Bose-Einstein condensates1998Doctoral thesis, comprehensive summary (Other scientific)
  • 123580. Öhlin, David
    et al.
    Carlson, Rolf
    KTH, Superseded Departments, Speech, Music and Hearing.
    Data-driven formant synthesis2004In: Proceedings FONETIK 2004: The XVIIth Swedish Phonetics Conference / [ed] Peter Branderud, Hartmut Traunmüller, Stockholm University, 2004, p. 160-163Conference paper (Other academic)
  • 123581.
    Öhlin, Jennie
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    RFID-användning i försörjningskedjan inom detaljhandel och industri2017Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The use of RFID in the Supply Chain in retail and manufacturing industry. RFID (Radio Frequence Identification) is a technique where information about an object can be stored in an RFID sender (often a tag in a label) which can be read by a reader that is connected to a machine or a computer. RFID is a modern version of the bar code, where the reading of the RFID tag can be done without human interaction and without a free sight between the reader and the RFID tag. This paper will present the use of RFID in retail and manufacturing industry. RFID can be used for many different purposes in the Supply Chain, such as tracking of material and products, automation of production lines, inventory in warehouses and stores and as an EAS (electronic article surveillance) in stores. Even though the reasons behind an RFID implementation are often the same for companies in manufacturing industry and those in retail, the use of RFID can be very different depending on if the company is at the selling point (retail), or in production (manufacturing industry). Retail companies that are controlling a bigger part of the Supply Chain can use RFID more effectively than those who have to rely or put pressure on suppliers to integrate the technique in an earlier stage of the Supply Chain. Furthermore, the future use of RFID in the manufacturing industry and retail will be analysed. In the new paradigm Internet of Things and the smart factories in Industry 4.0, RFID will most likely play a big role. Even though there is there is a big knowledge and experience of RFID today, there are still some problems with RFID that needs to be solved before it can be used as widely as expected in this new paradigm.

  • 123582.
    Öhlin, Simon
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Urban and Regional Studies.
    Förklaringsmodell för cykelresor i Trondheim: Fysiska och demografiska faktorers betydelse för det geografiska resmönstret2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    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.

  • 123583. Öhlén, P.
    et al.
    Skubic, B.
    Rostami, A.
    Fiorani, Matteo
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Monti, Paolo
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Ghebretensaé, Z.
    Mårtensson, J.
    Wang, K.
    Wosinska, Lena
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Data plane and control architectures for 5G transport networks2016In: Journal of Lightwave Technology, ISSN 0733-8724, E-ISSN 1558-2213, Vol. 34, no 6, p. 1501-1508, article id 7397818Article in journal (Refereed)
    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.

  • 123584.
    Öhlén, Peter
    KTH, Superseded Departments, Electronic Systems Design.
    Transmisison limitations of 2R reshaping repeaters and applications of high-speed wavelength conversion in optical networking2000Doctoral thesis, comprehensive summary (Other scientific)
  • 123585.
    Öhman, Amanda
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Lundberg, Linnea
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    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 credits / 30 HE creditsStudent thesis
  • 123586.
    Öhman, Astrid
    KTH, School of Architecture and the Built Environment (ABE), Architecture.
    Bibliotek i Liljeholmen: Library in Liljeholmen2018Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
  • 123587.
    Öhman, Astrid
    KTH, School of Architecture and the Built Environment (ABE), Architecture.
    Opera i Stockholm, Danvikstull2011Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
  • 123588.
    Öhman, Axel
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering.
    Edwall, Bill
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering.
    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 credits / 15 HE creditsStudent thesis
    Abstract [en]

    As climate change becomes an ever-bigger issue for countries in the south-Himalayan region, policy makers become more aware of the problems associated with increasing temperatures. As countries consume more energy extracted from fossil fuels the climate becomes warmer, affecting ecosystems and increasing the risk of natural disasters. Nepal is one of the countries seeing the effects of global warming from close range and the country is now seriously aiming to develop its energy sector through the implementation of sustainable energies. One of the more successful stories of the Nepali energy sector is the implementation of biogas technology. As of today, more than 350 000 small scale biogas systems for single household use are operating all over Nepal. The Alternative Energy Promotion Centre (AEPC), the focal governmental agency for the promotion of sustainable and clean energy, is now aiming to develop the large-scale biogas sector. This would increase the amount of domestic sustainable energy as well as the country’s energy security.

     

    The Shree Krishna Gau Sewa Sadan (SKGSS) is a Hindu trust located in south-eastern Nepal with the purpose of taking in and serving cows. It now aims to become economically self-sufficient by selling biogas and slurry produced from a newly constructed large-scale biogas plant to the nearby community households. The biogas will be produced from cow dung collected on the property and distributed to the households through a gas grid that is yet to be designed and built. The purpose of study was to investigate the opportunities for the trust to successfully operate the biogas plant and was focused on two areas of interest to the AEPC, which is the key sponsor of the community biogas project. The first was to primarily calculate the energy cooking demand of the nearby households, their current cost of cooking and their attitude towards a switch to biogas usage which would assist the planning of the future gas grid. The second was to localize and identify potential areas of improvements within the biogas system and based on that offer suggestions of improvements focused on technical aspects that would help the SKGSS to successfully operate the biogas plant.The study was conducted using a literature study, semi-constructed interviews, household surveys and on-site inspections of the biogas plant.

     

    The household survey showed that the nearby households’ interest in switching to biogas is high. Most of the households also showed to be willing to pay extra money to be connected to the biogas grid. The positive attitude towards biogas partly stems from a raised awareness about climate issues as well as increased security in energy security. The survey also showed that the nearby urban and semi-urban community is not a viable market for the produced slurry. However, Nepal is a big and growing market for organic high value fertilizer so the potential of a successful sale of slurry is still high. The primary calculations show that with the feedstock available, the community biogas plant cannot suffice more than 50 households’ energy demand for cooking. When designing the gas grid, proper calculations based on actual measurements of the biogas system need to be done. This study also recommends various improvements of the biogas system that will help the SKGSS biogas plant to operate successfully.

  • 123589.
    Öhman, Christian
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Technology and Design.
    Richnau, Robert
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Technology and Design.
    Värmeåtervinning från spillvatten i flerbostadshus2016Independent thesis Basic level (university diploma), 5 credits / 7,5 HE creditsStudent thesis
  • 123590.
    Öhman, Daniel
    KTH, School of Technology and Health (STH), Health Systems Engineering, Ergonomics.
    Vi sitter tillsammans: Upplevelser av samhörighet och ledarskap i ett traditionellt kontorslandskap.2014Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis
    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.

  • 123591.
    Öhman, Elena
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Technology and Design.
    Fredriksson, Daniel
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Technology and Design.
    Effektiv internlogistik på ett byggprojekt: En beskrivning och analys av den interna logistiken på Nya Karolinska, Solna2012Independent thesis Basic level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The construction industry is criticized for being undeveloped and inefficient. The Swedish construction costs have increased by 21% compared to the rest of Europe where the rate increased by 12% between 2005 and 2010. Although the players in the Swedish construction industry agree on the fact that the construction costs can be reduced, however there is some disagreement on what those cost items really are. What we do know is that logistics is an important and widespread but often underestimated topic. Logistics includes activities that ensure that you get the right amount, the right product of the right quality, at the right place and at the right time. Unfortunately the expertise in this area is inadequate. Studies show that 30-35 % of the overall production cost on a construction site is a waste. Activities that add no value are classified as waste. It involves activities related to the internal handling of material at the construction site, for example waiting, overproduction, inventory, rework, transport, unused creativity, overwork, movements, damage and theft. The purpose of this study is to investigate, describe, interpret and analyze the logistics of Nya Karolinska Solna and highlight the importance of well-planned logistics and provide suggestions on how it could be streamlined. NKS is Skanska's largest construction project of all time. The construction site is located in Solna, and surrounded by the heavily trafficked roads E4 and E20. Transport routes, transport facilities, storage areas for materials, machinery, construction workers, supplies, workshops and staff areas share a very large but narrow surface. To get an idea of what the internal logistics of NKS looks like, interviews have been made with people involved with the project. The interviews have been supplemented with personal observations on the construction site and digital information provided by Skanska Healthcare AB. Case studies in the form of value-flow analysis have been performed on the material delivered to the construction site, as well as a study of the crane utilization in a working day and delivery reliability of suppliers. The outcome of the case studies were later compared and analyzed, and at the end conclusions were made. To ensure that the project will be completed on time it is important that the production is running smoothly and that flows of resources, materials and construction workers are not prevented. Logistics is well developed but not perfect, you can always improve and innovate. Waste is something that needs to be minimized. By spreading knowledge of the importance of logistics among the involved and ensure that everyone works together, it will lead to a final product of the highest quality. 

  • 123592.
    Öhman, Elisabeth
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Properties of MIG/MAG brazed joints in zinc coated steel sheets.2003Independent thesis Advanced level (degree of Master (One Year)), 20 credits / 30 HE creditsStudent thesis
  • 123593.
    Öhman, Emil
    KTH, School of Electrical Engineering and Computer Science (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 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The thesis propose a more efficient process for analyzing different issues at the Swedish Tax Agency's development of open APIs. The issues are primarily different legal requirements but also technical and security aspects. The Swedish Tax Agency currently has a number of e-services with the potential to develop into open APIs. Skatteverket is the Swedish government agency responsible for public records, taxation, property valuation, and this would be a step forward in modern e-government.

    The report also addresses background facts about the legal, open data, and different ways of using and making available public APIs and the differences between open data and APIs.

    We have laws and government directives that open up and encourage reuse and access to data, but we also have laws that create limitations, making the analysis to make more information available very important. In addition to ordinary laws, register laws also define more precisely how the Tax Agency is allowed to work with data protection.

    The Tax Agency's current e-services and APIs are analyzed in terms of further development and examination of how employees at the Swedish Tax Agency look at the future use of these APIs as well as the network economy.

    As an example, it can be assumed that with the help of APIs through corporate business systems could easily do a monthly CSR-request to be able to adjust tax payments and reduce the risks that employees have received too much or too little tax paid to the Tax Agency which can lead to problems. This also saves a lot of manual work for the human resources department of corporations.

    The report presents a flow chart that can be used as support to determine whether it is appropriate for an e-service to be made available through an API, and the development of the API-service.

    The complex requirements makes it difficult to provide a standard response if it is appropriate for e-services to be made available through APIs and that it is also important to keep the security in mind. It is also important to be aware that technology and laws change over time which means that a continuous analysis is required to ensure that they meet all requirements.

  • 123594.
    Öhman, Eric
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Mathematical Statistics.
    Analys av bostadsrättspriser medmultipel linjär regression ochprissättning i praktiken2014Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The purpose of this report is to examine the factors that affect the price of condominiums in downtown Stockholm and how much these factors affect the price with multiple linear regression.  The results of the regression analysis is used to create a model for pricing of condominiums in downtown Stockholm.  This model is compared to the methods that construction companies use when pricing newly built condominiums to see if the methods used today can be improved.  The work resulted in a model that gives an indication of how much various factors affect the price as well as a basis for valuation condominium in downtown Stockholm.  The methods used today were not improved by the results that were presented in this report.  The current methods have the advantage of its adaptability to a project's unique characteristics and boundaries of relevant markets.

  • 123595.
    Öhman, Henrik
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Implementation and evaluation of a low temperature waste heat recovery power cycle using NH 3 in an Organic Rankine Cycle2012In: Energy, ISSN 0360-5442, E-ISSN 1873-6785, Vol. 48, no 1, p. 227-232Article in journal (Refereed)
    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.

  • 123596.
    Öhman, Henrik
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Implementation and evaluation of low temperature waste heat recovery power cycle using NH3 in an organic rankine cycle2011In: / [ed] Zvonimir Guzovic, Zagreb: Faculty of Mechanical Engineering and Naval Architecture , 2011Conference paper (Refereed)
    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.

  • 123597.
    Öhman, Henrik
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Low temperature difference power systems and implications of multi-phase screw expanders in Organic Rankine Cycles2016Doctoral thesis, comprehensive summary (Other academic)
    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.

  • 123598.
    Öhman, Henrik
    Svenska Rotor Maskiner AB.
    Test Results of A Screw Type Expander/. Compressor and the Implication of Phase. Separators on the Refrigeration Process2004In: 2004 International Refrigeration and Air Conditioning Conference, West Lafayette, Indiana, USA: Purdue University Press, 2004Conference paper (Refereed)
    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.

  • 123599.
    Öhman, Henrik
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Lundqvist, Per
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Comparison and analysis of performance using Low Temperature Power Cycles2013In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 52, no 1, p. 160-169Article in journal (Refereed)
    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.

  • 123600.
    Öhman, Henrik
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Lundqvist, Per
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Experimental investigation of a Lysholm Turbine operating with superheated, saturated and 2-phase inlet conditions2013In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 50, no 1, p. 1211-1218Article in journal (Refereed)
    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.

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