• On-Off and PI control of methane gas production of a pilot anaerobic digestion reactor 

      Haugen, Finn; Bakke, Rune; Lie, Bernt (Journal article; Peer reviewed, 2013)
      A proposed feedback control system for methane flow control of a real pilot anaerobic digestion reactor fed with dairy waste is designed and analyzed using the modified Hill model, which has previously been adapted to the ...
    • One-dimensional model of turbulent flow of non-Newtonian drilling mud in non-prismatic channels 

      Welahettige, Prasanna Kumara Welahetti; Lundberg, Joachim; Bjerketvedt, Dag; Lie, Bernt; Vågsæther, Knut (Peer reviewed; Journal article, 2019)
      One-dimensional model of non-Newtonian turbulent flow in a non-prismatic channel is challenging due to the difficulty of accurately accounting for flow properties in the 1-D model. In this study, we model the 1-D Saint–Venant ...
    • OpenHPL for Modelling the Trollheim Hydropower Plant 

      Vytvytskyi, Liubomyr; Lie, Bernt (Peer reviewed; Journal article, 2019)
      An increase of tightly integrated, renewable energy sources with highly varying production leads to a greater need for flexible hydropower plants to “balance” the intermittent production from these sources. From a systems ...
    • Optimal design and operation of a UASB reactor for dairy cattle manure 

      Haugen, Finn; Bakke, Rune; Lie, Bernt; Hovland, Jon; Vasdal, Knut (Journal article; Peer reviewed, 2015-02-01)
      Optimal design and operation of a planned full-scale UASB reactor at a dairy farm are determined using optimization algorithms based on steady state simulations of a dynamic AD process model combined with models of the ...
    • Optimal Operation of the Peat Drying Process in Steam Tube Dryers 

      Kulakovsky, Leonid; Rosen, Victor; Sharma, Roshan; Pfeiffer, Carlos Fernando; Lie, Bernt (Journal article; Peer reviewed, 2015-11-25)
      Ukraine is an energy-dependent country and aims to reduce the import of natural gas, heat, and power in general. This implies extracting fuel from her own natural resources; one relevant and readily available energy carrier ...
    • Oxygen Effects in Anaerobic Digestion II 

      Botheju, Deshai; Lie, Bernt; Bakke, Rune (Journal article, 2010)
      Standard models describing bio-gasification using anaerobic digestion do not include necessary processes to describe digester dynamics under the conditions of oxygen presence. Limited oxygenation in anaerobic digestion can ...
    • Parameter estimation for externally simulated thermal network models 

      Brastein, Ole Magnus; Lie, Bernt; Sharma, Roshan; Skeie, Nils-Olav (Peer reviewed; Journal article, 2019)
      Obtaining accurate dynamic models of building thermal behaviour requires a statistically solid foundation for estimating unknown parameters. This is especially important for thermal network grey-box models, since all their ...
    • Population balance modelling for fertilizer granulation process 

      Vesjolaja, Ludmila; Glemmestad, Bjørn; Lie, Bernt (Journal article; Peer reviewed, 2018)
      Few granulation plants are operated optimally. It is common to operate granulation plants below their maximum design capacity, and in many cases, periodic instabilities may also occur. From a process control and optimization ...
    • Power System Stability Using Modelica 

      Øyvang, Thomas; Winkler, Dietmar; Lie, Bernt; Hegglid, Gunne John (Journal article; Peer reviewed, 2014-12-09)
      This paper is concerned with power system modeling using the Modelica language in comparison to a traditional simulation tool. Though most common power system simulation tools are computationally efficient and reasonably ...
    • Pressure wave propagation in Managed Pressure Drilling- model comparison with real life data 

      Berg, Christian; Stakvik, Jon Åge; Lie, Bernt; Vågsæther, Knut; Kaasa, Glenn-Ole (Peer reviewed; Journal article, 2019)
      Drilling for oil and gas is a complex process, involving pumping of fluid through kilometers of pipes. Even though the drilling fluid has a high speed of sound (˜1000 m/s), the large lengths involved make pressure wave ...
    • A Real-Time Flow-Measuring Algorithm for Open Venturi Channel Non-Newtonian Flow 

      Welahettige, Prasanna Kumara Welahetti; Lie, Bernt; Vågsæther, Knut (Peer reviewed; Journal article, 2019)
      A real-time flow measuring algorithm is developed for the open Venturi channel non-Newtonian flow measurement. Using a single level sensor reading at downstream of the open Venturi channel, a drilling-well return flow rate ...
    • Relaxed Ziegler-Nichols closed loop tuning of PI controllers 

      Haugen, Finn; Lie, Bernt (Journal article; Peer reviewed, 2013)
      A modification of the PI setting of the Ziegler-Nichols closed loop tuningmethod is proposed. The modification is based on a combination of the Skogestad SIMCtuning formulas for ´´integrator plus time-delay´´ processes ...
    • Second Order KP Scheme for the Solution of flow in a Venturi Channel 

      Dissanayake, Susantha; Sharma, Roshan; Lie, Bernt (Journal article; Peer reviewed, 2018)
      In many different applications, a Venturi channel is used as a tool to compute fluid flow rates. The Saint-Venant equation is a hyperbolic type Partial Differential Equation (PDE) which can be used to model fluid flows ...
    • Simulation of Transcritical Flow in Hydraulic Structures 

      Agu, Cornelius Emeka; Lie, Bernt; Elseth, Geir (Journal article; Peer reviewed, 2015-11-25)
      In hydraulic engineering, transcritical flows are often required in some applications. One example is in a Venturi channel where the occurrence of critical depth is used to estimate flow rate in the channel. In this paper, ...
    • State estimation and model-based control of a pilot anaerobic digestion reactor 

      Haugen, Finn; Bakke, Rune; Lie, Bernt (Journal article; Peer reviewed, 2014)
      A state estimator and various model-based control systems have been designed for a real anaerobic digestion (AD) pilot reactor fed with dairy manure. The model used is a modified Hill model which is a relatively simple ...
    • State Estimation of a Thermal Model of Air-cooled Synchronous Generator 

      Pandey, Madhusudhan; Øyvang, Thomas; Lie, Bernt (Peer reviewed; Journal article, 2019)
      In this paper, we extend a previous study on a totally enclosed thermal model of a synchronous generator, with temperature state estimation using experimental data. The extension includes a new formulation of the system ...
    • Structural analysis in Julia for dynamic systems in OpenModelica 

      Vytvytskyi, Liubomyr; Lie, Bernt (Peer reviewed; Journal article, 2019)
      In control theory for dynamic systems, the information about observability and controllability of states plays a key role to evaluate the possibility to observe states from outputs, and use inputs to move states to a desired ...
    • Structural observability analysis of large scale systems using Modelica and Python 

      Perera, M. Anushka S.; Lie, Bernt; Pfeiffer, Carlos Fernando (Journal article; Peer reviewed, 2015)
      State observability of dynamic systems is a notion which determines how well the states can be inferred from input-output data. For small-scale systems, observability analysis can be done manually, while for large-scale ...
    • Study of Fluidization Regimes using OpenFOAM Computational Fluid Dynamics 

      Welahettige, Prasanna Kumara Welahetti; Lie, Bernt; Vågsæther, Knut; Moldestad, Britt Margrethe Emilie (Journal article; Peer reviewed, 2017)
      The objective of this study was using computational fluid dynamics simulation with OpenFOAM to study the fluidization properties for four types of particles classified as Geldart A, B, C and D. Fluidization regimes were ...
    • Surrogate and Hybrid Models for Control 

      Lie, Bernt (Peer reviewed; Journal article, 2019)
      With access to fast computers and efficient machine learning tools, it is of interest to use machine learning to develop surrogate models from complex physics-based models. Next, a hybrid model is a combination model where ...