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  • Optical water types of the Nordic Seas and adjacent areas 

    Aas, Eyvind; Højerslev, Niels Kristian; Høkedal, Jo; Sørensen, Kai (Journal article; Tidsskriftartikkel; Peer reviewed, 2013-05-20)
    A new map of Jerlov's optical water types in the Nordic Seas and adjacent waters at 139 locations, as well as a table with statistical and geographical properties of the vertical attenuation coefficient of downward irradiance at 475 nm, are presented. The data analysis is based on 715 recordings at different stations, at latitudes between 54° and 82°N, and longitudes between 31°W and 49°E, obtained ...
  • Når blir skipsfarten grønn? 

    Hoff, Bjarte; Østrem, Trond (Kronikk, 2018-04-25)
    n av utfordringene i forbindelse med dagens skipsfart er utslipp til luft, hovedsakelig karbondioksid og nitrogenoksider. Disse utslippene er knyttet til oljefyrte forbrenningsmotorer som dominerer dagens skipsflåte. Det er overveiende sannsynlig at det er en direkte sammenheng mellom global oppvarming og utslipp av klimagasser. Utslipp til luft kan også bidra til sur nedbør og svevestøv, for å nevne ...
  • Estimation of upward radiances and reflectances at the surface of the sea from above-surface measurements 

    Kleiv, Øyvind; Folkestad, Are; Høkedal, Jo; Aas, Eyvind; Sørensen, Kai (Journal article; Tidsskriftartikkel; Peer reviewed, 2015-10-02)
    During 4 field days in the years 2009–2011, 22 data sets of measurements were collected in the inner Oslofjord, Norway. The data consist of recordings of spectral nadir radiances in air and water as well as spectral downward irradiance in air. The studied wavelengths are 351, 400, 413, 443, 490, 510, 560, 620, 665, 681, 709 and 754 nm. The water-leaving radiance and the reflected radiance at the ...
  • Underactuated Waypoint Tracking of a Fixed-Wing UAV 

    Oland, Espen; Schlanbusch, Rune; Kristiansen, Raymond (Journal article; Peer reviewed, 2013)
    In this paper a new method of performing waypoint tracking is shown for underactuated fixed-wing UAVs. The position error can be mapped onto the desired axis using a desired rotation matrix, while the velocity error can be mapped to the desired axis using a desired angular velocity. With all errors defined along one axis, the tracking problem is easily solved using only one thruster. A velocity ...
  • Underactuated Control of Quadrotors with Collision Avoidance 

    Oland, Espen; Andersen, Tom Stian; Kristiansen, Raymond (Journal article; Peer reviewed, 2013)
    In this paper a saturated controller is derived that solves the translational control problem for underactuated quadrotors. The controller is applied to multiple quadrotors during a formation reconfiguration where the quadrotors move from an initial position to a desired position. The null-space-based behavioral control method is a popular method for avoiding collisions between mobile agents, and ...
  • Real-Time Particle Tracking using a Formation of UAVs 

    Oland, Espen; Kristiansen, Raymond (Journal article; Peer reviewed, 2013)
    In this paper the problem of real-time particle tracking is studied. Using sensor measurements, a formation of UAVs autonomously find the closest point with high particle density where they enter a holding pattern. After converging to the holding pattern, one UAV will remain, while the rest will go looking for other maxima. To avoid collisions between the UAVs during the mission, a controller is ...
  • Quaternion guidance and control of quadrotor 

    Andersen, Tom Stian; Kristiansen, Raymond (Peer reviewed; Conference object; Chapter, 2017-07-27)
    This paper addresses the problem of trajectory tracking for underactuated quadrotors. A quaternion based guidance law is proposed which feeds into an attitude control system based on a PD+ control law. The desired attitude from the guidance law is defined such that the attitude control system tries to align the position error along the axis of the translational actuator. Simulation results are ...
  • Path-following in three dimensions using quaternions for a fixed-wing UAV 

    Andersen, Tom Stian; Kristiansen, Raymond (Peer reviewed; Conference object; Chapter, 2017-08-08)
    This paper presents a three dimensional guidance strategy for fixed-wing UAVs using quaternions. The algorithm is based on constructing two quaternions, one which makes the UAV fly towards the path and one that makes the UAV follow the path. These two quaternions are then blended together such that the path-following objective is reached. The guidance algorithm is applied to a simple kinematic model ...
  • Attitude Determination and Control System for Satellites in Elliptical Orbits - a Complete Solution 

    Oland, Espen (Peer reviewed; Conference object; Chapter, 2017-08-08)
    This paper presents a complete solution to the problem of attitude determination and control for satellites in elliptical orbits. Specifically, it shows how to create the orbital mechanics, account for perturbing gravity torques, create a nonlinear PD+ attitude controller, map the control signal to desired thrust firings, implement magnetic field and Sun vector models, and how to implement a Madgwick ...
  • Autonomous Inspection of the International Space Station 

    Oland, Espen (Peer reviewed; Conference object; Chapter, 2017-09-18)
    This paper presents a solution to autonomous inspection of the international space station using a rigid spacecraft. Specifically, the paper presents the orbital mechanics, formation dynamics as well as rotational dynamics required to control the spacecraft relative to the space station, and then presents two PD+ controllers enabling a spacecraft to track a series of waypoints while pointing a sensor ...
  • Thyristor based short circuit current injection in isolated grids 

    Hoff, Bjarte; Sharma, Pawan; Østrem, Trond (Peer reviewed; Chapter, 2017-02-16)
    This paper proposes a thyristor based short circuit current injector for providing short circuit current in isolated and weak grids, where sufficient fault current to trigger circuit breakers may not be available. This will allow the use of conventional miniature circuit breakers, which requires high fault current for instantaneous tripping. The method has been validated through experiments.
  • Quadrotor attitude estimation using adaptive fading multiplicative EKF 

    Johansen, Tor-Aleksander; Kristiansen, Raymond (Peer reviewed; Conference object, 2017-07-03)
    This paper presents the implementation of an adaptive fading multiplicative extended Kalman filter (AFMEKF), applied to the problem of attitude estimation in the context of quadrotors. The extended Kalman filter is adapted for use with quaternions and made adaptive to account for inaccurate measurement information. Simulations have been conducted in order to validate the filter performance.
  • Smarte nett - Framtidas fleksible energisystem 

    Hoff, Bjarte (Conference object, 2016)
  • Smarte nett - Framtidas fleksible energisystem 

    Hoff, Bjarte (Konferansebidrag, 2016-03-16)
  • Smarte løsninger for integrering av fornybar energi 

    Hoff, Bjarte (Konferansebidrag, 2017)
  • Experimental study of relative permittivity of atmospheric ice 

    Bhattu, Shravan K; Mughal, Umair Najeeb; Virk, Muhammad Shakeel (Journal article; Peer reviewed, 2013-01-01)
    Atmospheric icing on onshore and offshore structures is problematic, if we don’t detect and remove it. Despite of various ice detection techniques, capacitor based ice sensing technique is interesting one, as it is based on dielectric properties of material. This technique of measuring icing event is simple and cost- effective. Based on the dielectric concept, an experi mental ...
  • Subsumption architecture applied to flight control using composite rotations 

    Oland, Espen; Andersen, Tom Stian; Kristiansen, Raymond (Peer reviewed; Tidsskriftartikkel; Journal article, 2016-03-19)
    In this paper the subsumption theory is applied to flight control through composite rotations where multiple tasks can be defined as simple rotations. The tasks can then be arranged as a hierarchy, where the primary task is always fully pursued, and conflicting lower level tasks are removed by the primary rotation. The concept is applied to a group of uavs that move through an urban terrain while ...
  • A Decoupled Approach for Flight Control 

    Oland, Espen; Kristiansen, Raymond (Journal article; Tidsskriftartikkel; Peer reviewed, 2016)
    A decoupling method for flight control is presented that greatly simplifies the controller design. By approximating the higher order derivatives of the angle of attack and sideslip, it enables a rotation controller and a speed controller to be derived independently of each other, and thus gives access to a vast number of controller solutions derived for general classes of rotational and translational ...

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