• Adaptive approximation-based estimation of downhole pressure in managed pressure drilling 

      Imsland, Lars Struen; Kaasa, Glenn-Ole (Journal article; Peer reviewed, 2012)
      Low-complexity multi-model algorithms for adaptive bottomhole pressure estimation in drilling is derived, and theoretical and practical conditions for convergence (persistency of excitation) discussed, assuming a) topside ...
    • A Framework for Fault Diagnosis in Managed Pressure Drilling Applied to Flow-Loop Data 

      Willersrud, Anders; Imsland, Lars Struen; Pavlov, Alexey; Kaasa, Glenn-Ole (Journal article; Peer reviewed, 2013)
      Data from a medium-scale horizontal flow loop test facility is used to test fault diagnosis in managed pressure drilling. The faults are downhole incidents such as formation influx, fluid loss, drillstring washout, pack-off, ...
    • Analysis of Iceberg Drift Trajectories Using the Multivariate Empirical Mode Decomposition 

      Andersson, Leif Erik; Scibilia, Francesco; Copland, Luke; Aftab, Muhammad Faisal; Imsland, Lars Struen (Journal article; Peer reviewed, 2018)
      In this study we show how to detect and extract the tidal and inertial oscillation from iceberg velocity data by using the multivariate empirical model decomposition. Due to the similar frequencies of both oscillations in ...
    • An estimation-forecast set-up for iceberg drift prediction 

      Andersson, Leif Erik; Scibilia, Francesco; Imsland, Lars Struen (Journal article; Preprint, 2016)
      Iceberg drift forecasting is challenging. Large uncertainties in iceberg geometry and in iceberg driving forces – current, wind and waves – make accurate forecasts difficult. In this work, a new estimation-forecast scheme ...
    • A study on an iceberg drift trajectory 

      Andersson, Leif Erik; Scibilia, Francesco; Imsland, Lars Struen (Chapter, 2017)
      Iceberg drift forecast is a challenging process. Large uncertainties in iceberg geometry and in the driving forces — current, wind and waves — make accurate forecasts difficult. This article illustrates from a data set ...
    • Autonomous Aerial Ice Observation for Ice Defense 

      Haugen, Joakim; Imsland, Lars Struen (Journal article; Peer reviewed, 2014)
      One of the tasks in ice defense is to gather information about the surrounding ice environment using various sensor platforms. In this manuscript we identify two monitoring tasks known in literature, namely dynamic coverage ...
    • Block factorization of step response model predictive control problems 

      Kufoalor, D. Kwame Minde; Frison, Gianluca; Imsland, Lars Struen; Johansen, Tor Arne; Jørgensen, JB (Journal article; Peer reviewed, 2017)
      By introducing a stage-wise prediction formulation that enables the use of highly efficient quadratic programming (QP) solution methods, this paper expands the computational toolbox for solving step response MPC problems. ...
    • Constrained Posterior Cramér-Rao Bound for Discrete-Time Systems 

      Andersson, Leif Erik; Brekke, Edmund Førland; Imsland, Lars Struen; Scibilia, Francesco (Journal article, 2017)
      This article presents a Cramér-Rao lower bound for the discrete-time filtering problem under linear state constraints. A simple recursive algorithm is presented that extends the computation of the Cramér-Rao lower bound ...
    • Coordinated Control of Multiple HVDC links using backstepping 

      Ersdal, Anne Mai; Imsland, Lars Struen; Uhlen, Kjetil (Journal article, 2012)
      This article regards a power system containing multiple High Voltage Direct Current (HVDC) links. The topic is to exploit the HVDC lines’ ability to control the power supplied by them to increase the stability of the system. ...
    • Design and Experimental Validation of Nonlinear Infinite-Dimensional Adaptive Observer in Automated Managed Pressure Drilling 

      Hasan, Agus Ismail; Imsland, Lars Struen; Hauge, Espen (Journal article; Peer reviewed, 2017)
      Utilizing flow rate and pressure data in and out of the fluid circulation loop provides a driller with real-time trends for early detection of well-control problems that impact the drilling efficiency. Due to limited number ...
    • Drillstring Washout Diagnosis using Friction Estimation and Statistical Change Detection 

      Willersrud, Anders; Blanke, Mogens; Imsland, Lars Struen; Pavlov, Alexey K. (Journal article; Peer reviewed, 2015)
      In oil and gas drilling, corrosion or tensile stress can give small holes in the drillstring, which can cause leakage and prevent sufficient flow of drilling fluid. If such \emph{washout} remains undetected and develops, ...
    • Early pack-off diagnosis in drilling using an adaptive observer and statistical change detection 

      Willersrud, Anders; Imsland, Lars Struen; Blanke, Mogens (Journal article, 2015)
      Pack-off is a partially or complete blocking of the circulation flow in oil and gas drilling, which can lead to costly delays. Early detection and localization of a pack-off is crucial in order to take necessary actions ...
    • Economic Stochastic Model Predictive Control Using the Unscented Kalman Filter 

      Bradford, Eric; Imsland, Lars Struen (Journal article; Peer reviewed, 2018)
      Economic model predictive control is a popular method to maximize the efficiency of a dynamic system. Often, however, uncertainties are present, which can lead to lower performance and constraint violations. In this paper, ...
    • Efficient optimization in Model Predictive Control 

      Ringset, Ruben Køste (Master thesis, 2009)
      Adjoint based gradient calculation for Nonlinear Model Predictive Control.
    • Embedded Model Predictive Control on a PLC Using a Primal-DualFirst-Order Method for a Subsea Separation Process 

      Kufoalor, Kwame Minde; Richter, S; Imsland, Lars Struen; Johansen, Tor Arne; Morari, Manfred; Eikrem, Gisle Otto (Conference object; Journal article; Peer reviewed, 2014)
      The results of a PLC implementation of embedded Model Predictive Control (MPC) for an industrial problem are presented in this paper. The embedded MPC developed is based on the linear MPC module in SEPTIC (Statoil Estimation ...
    • Expectation constrained stochastic nonlinear model predictive control of a batch bioreactor 

      Bradford, Eric Christopher; Imsland, Lars Struen (Chapter, 2017)
      Nonlinear model predictive control is a popular control approach for highly nonlinear and unsteady state processes, which however can fail due to unaccounted uncertainties. This paper proposes to apply a sample-average ...
    • Fault diagnosis of downhole drilling incidents using adaptive observers and statistical change detection 

      Willersrud, Anders; Blanke, Mogens; Imsland, Lars Struen; Pavlov, Alexey (Journal article; Peer reviewed, 2015)
      Downhole abnormal incidents during oil and gas drilling cause costly delays, and may also potentially lead to dangerous scenarios. Different incidents will cause changes to different parts of the physics of the process. ...
    • Incident detection and isolation in drilling using analytical redundancy relations 

      Willersrud, Anders; Blanke, Mogens; Imsland, Lars Struen (Journal article; Peer reviewed, 2015-08)
      Early diagnosis of incidents that could delay or endanger a drilling operation for oil or gas is essential to limit field development costs. Warnings about downhole incidents should come early enough to allow intervention ...
    • Iterative algorithms for computing the feedback Nash equilibrium point for positive systems 

      Ivanov, Ivan; Imsland, Lars Struen; Bogdanova, Boryana (Journal article; Peer reviewed, 2017)
      The paper studies N-player linear quadratic differential games on an infinite time horizon with deterministic feedback information structure. It introduces two iterative methods (the Newton method as well as its accelerated ...
    • Optimization-based motion planning for trawling 

      Haugen, Joakim; Imsland, Lars Struen (Journal article; Peer reviewed, 2018-10-03)
      This work presents an optimization-based motion planning system for trawling operations. The formulation makes use of simplistic physical descriptions of the vessel and fishing gear together with catch dynamics of sweeping ...