Eilif Pedersen | Norwegian University of Science and Technology (original) (raw)

Papers by Eilif Pedersen

International Journal of Hydrogen Energy, May 1, 2022

SAE technical paper series, Sep 20, 2019

Marine Structures, Sep 1, 2021

In this paper we present a full-scale experimental field study of the effects of floater motion o... more In this paper we present a full-scale experimental field study of the effects of floater motion on a main bearing in a 6 MW turbine on a spar-type floating substructure. Floating wind turbines are necessary to access the full offshore wind power potential, but the characteristics of their operation leave a gap with respect to the rapidly developing empirical knowledge on operation of bottom-fixed turbines. Larger wind turbines are one of the most important contributions to reducing cost of energy, but challenge established drivetrain layouts, component size envelopes and analysis methods. We have used fibre optic strain sensor arrays to measure circumferential strain in the stationary ring in a main bearing. Strain data have been analysed in the time domain and the frequency domain and compared with data on environmental loads, floating turbine motion and turbine operation. The results show that the contribution to fluctuating strain from in-plane bending strain is two orders of magnitude larger than that from membrane strain. The fluctuating in-plane bending strain is the result of cyclic differences between blade bending moments, both in and out of the rotor plane, and is driven by wind loads and turbine rotation. The fluctuating membrane strain appears to be the result of both axial load from thrust, because of the bearing and roller geometry, and radial loads on the rotating bearing ring from total out-of-plane bending moments in the three blades. The membrane strain shows a contribution from slow-varying wind forces and floating turbine pitch motion. However, as the total fluctuating strain is dominated by the intrinsic effects of blade bending moments in these turbines, the relative effect of floater motion is very small. Mostly relevant for the intrinsic membrane strain, sum and difference frequencies appear in the measured responses as the result of nonlinear system behaviour. This is an important result with respect to turbine modelling and simulation, where global structural analyses and local drivetrain analyses are frequently decoupled.

Propulsion and Power Research, Jun 1, 2022

Journal of marine science and technology, Jun 4, 2020

Although natural gas is documented as a low-emission fuel compared to the other traditional fossi... more Although natural gas is documented as a low-emission fuel compared to the other traditional fossil fuels in internal combustion engines, recent research indicates large amounts of methane emission released by lean burn gas engines and highlights the importance of this emission on global warming. This paper aims at illustrating the main sources of unburned fuel in internal combustion engines with an emphasis on spark ignited natural gas engines. In addition, two unburned hydrocarbon modeling patterns, empirical and thermodynamic, are proposed. Moreover, a verified engine model including all components with an implemented dynamic load based on harmonic sea waves has been set up and coupled to the unburned hydrocarbon formation models. Results show that load variation may contribute to further methane slip and this increment rises sharply when the load amplitude enlarges. The maximum amount of methane slip occurs at reduced loads when the time lag of the control system of the turbocharger causes additional fresh air to flow towards the combustion chamber and brings the flame into the quenching area. As well, inspecting unburned hydrocarbon emission in diverse air-fuel ratios but with the same wave frequency and amplitude uncovers the sensitivity of lean burn gas engines to the dynamic load.

The bond graph theory provides a firm and complete strategy for making mathematical models and ar... more The bond graph theory provides a firm and complete strategy for making mathematical models and are used in this work to obtain a good relation between connectivity, causality and model fidelity in distributed systems. By distributing a system more computational power is available which makes it possible to increase the model fidelity in large systems without increasing the time to solve the total system. Also, more complex models with causality switching properties may be used for simplifying the connectivity problem between distributed models and for representing changing dynamics that also affects the model causality. Stability of distributed systems are dependent on both solver stability and dynamical stability, when neglecting the stability results based on cascaded systems with certain passivity properties. For linear distributed systems solver with fixed step size solvers a stability criterion involving the system dynamics, local solver time step and global synchronization time step can be formulated. In this work a stability criterion for linear distributed systems solved with the Euler integration method will be derived and a hybrid causality model, representing a small power plant, will be used to test the stability criterion.

With the share of high-power electronic converters, the emerging marine DC hybrid power systems h... more With the share of high-power electronic converters, the emerging marine DC hybrid power systems have been increasingly attractive for ship designers because of their higher operational flexibility. The system efficiency analysis, one of the critical factors while embracing an emerging system, requires a detailed estimation and evaluation. Conventionally, the rated efficiency for each component is the basis for the system efficiency estimation. However, the efficiency may vary with the loading conditions in any component, directly affected by the actual load and the load-sharing strategies. In this work, dynamic efficiency models are developed for the DC hybrid power system components, which are used to estimate the overall system efficiency using a realistic load power profile and a rule-based power and energy management system (PEMS). The efficiency analysis shows that the overall power efficiency increases with optimal battery usage in a hybrid power system. Moreover, three different power-sharing control strategies are compared. The modified rule-based PEMS offers the highest efficiency, while conventional diesel generator operation offers the least efficiency for the given load profile and power system configuration.

Applied Energy, Dec 1, 2020

Abstract In many vessels, the prime mover is a diesel engine, while the researchers recommended u... more Abstract In many vessels, the prime mover is a diesel engine, while the researchers recommended using natural gas as an attractive option to comply with the latest emission legislations. This study aims to analyze the dynamic response of a spark-ignition engine fueled by natural gas. Due to the complexity of power system operation in transient conditions, ship propulsion modeling is performed to assess the environmental impact of dynamic load. A co-simulation modeling in MATLAB- SIMULINK platform was developed to couple the medium-speed, four-stroke, turbocharged, spark-ignition engine to a propeller immersed in seawater. The engine’s essential elements were implemented, and the validity of the modeling was evaluated using the manufacturer’s data in both steady-state and transient conditions. The main goal was to determine the importance of the transient loads on the engine response, particularly during harsh weather conditions. Hence, simulations of various wave conditions with multiple wave amplitude, wave direction, and wavelength were conducted. Compared with the steady-state, the transient condition resulted in a deterioration of the combustion efficiency. Furthermore, the amount of unburned fuel, NOX compounds, and brake specific fuel consumption have increased.

Enhancing the marine propulsion system's performance is one of the crucial issues that has receiv... more Enhancing the marine propulsion system's performance is one of the crucial issues that has received noteworthy attention due to the current strict emission legislation. A fundamental improvement without an additional after-treatment system is employing natural gas fuel in lean-burn combustion. Lean combustion may improve the thermal efficiency in a stable condition, but a real ship works in a time-varying inflow on the propeller, and the engine must afford high-efficiency combustion against the fluctuating load. Stable combustion in a lean-burn marine gas engine is guaranteed by installing controllers on the air and the fuel pipes to regulate airfuel ratio and engine speed. The present study aimed to investigate the influence of adding an air throttle during the engine's lower loads and its effectiveness during a time-varying load. A thermodynamics model of spark ignition engine with an imposed constant and transient load is presented. The results revealed that using a throttle in the lower loads may improve the engine fuel consumption and emission formation during steady-state, but, in transient condition, it showed a negligible impact on the brake specific fuel consumption and unburned hydrocarbon emission formation.

Proceedings Of The Institution Of Mechanical Engineers, Part M: Journal Of Engineering For The Maritime Environment, Nov 20, 2019

In this paper a performance evaluation of a novel system solution combining a hybrid turbocharger... more In this paper a performance evaluation of a novel system solution combining a hybrid turbocharger and a pre-turbine selective catalytic NO x reduction system is carried out. Pre-turbine selective catalytic system are used with marine two stroke diesel engines to comply with IMO Tier III. The system solution focuses on expanding the SCR operation range which is limited by fuel sulphur content by increasing exhaust temperature at low engine loads. The extended operation range is to be achieved while minimizing any fuel consumption penalties. Increasing the operation range brings improvements to emission levels during maneuvering operations which are often carried out close to populated areas. It also provides flexibility by enabling emission reduction during slow steaming operations in which mitigating fuel consumption penalties is paramount. In addition to system evaluation in still water conditions additional evaluations have been carried out taking into consideration the effect of waves on the system performance. Investigating the effect of operating in waves bring additional insight that is relevant for predicting performance in operational conditions. Analysis of the system solution found that improvements in SCR operation range can be achieved while also improving fuel consumption. Fuel consumption is significantly improved in the high load range. Effect of realistic operation conditions where found to affect performance, however significant effect are only found for harsh sea states in the load range below the design point.

Proceedings Of The Institution Of Mechanical Engineers, Part M: Journal Of Engineering For The Maritime Environment, May 29, 2018

Stricter NOx emission limits for marine diesel engines have resulted in a market demand for engin... more Stricter NOx emission limits for marine diesel engines have resulted in a market demand for engine external NOx reduction solutions. This demand has led to the development of ammonia-based selective catalytic reduction (SCR) deNOx systems for marine applications. For SCR systems in general, mathematical modelling and numerical simulation have been essential for increasing knowledge, improving design and developing control algorithms. This has resulted in higher NOx reduction performance, reduced NH3 slip and improved transient and start-up performance. Due to the increasing complexity of diesel engine based power systems, it is often argued that system development requires a simulation-based design approach to reduce development cost and increase development speed. For this to be cost-effective, reusable and interchangeable models of appropriate complexity needs to be available. In this paper a system approach is applied to modelling of SCR deNOx monolithic reactors. Three models with different levels of fidelity are developed using the bond graph method. The three models are compared by simulating dynamic conditions to uncover differences between the models. In addition, accuracy is investigated by comparing simulation results to measurement data. The contribution in this paper can be summarized to be an exploration of monolith SCR deNOx modelling in a system simulation framework, and investigation of the effect of SCR model fidelity on a coupled system performance prediction.

International Journal of Engine Research, May 12, 2021

As the emission legislation becomes further constraining, all manufacturers started to fulfill th... more As the emission legislation becomes further constraining, all manufacturers started to fulfill the future regulations about the prime movers in the market. Lean-burn gas engines operating under marine applications are also obligated to enhance the performance with a low emission level. Lean-burn gas engines are expressed as a cleaner source of power in steady loading than diesel engines, while in transient conditions of sea state, the unsteadiness compels the engine to respond differently than in the steady-state. This response leads to higher fuel consumption and an increase in emission formation. In order to improve the stability of the engine in transient conditions, this study presents a concept implementing a hybrid configuration in the propulsion system. An engine model is developed and validated in a range of load and speed by comparing it with the available measured data. The imposed torque into the developed engine model is smoothed out by implementing the hybrid concept, and its influence on emission reduction is discussed. It is shown that with the hybrid propulsion system, the NOX reduces up to 40% because of the maximum load reduction. Moreover, eliminating the low load operation by a Power Take In during incomplete propeller immersion, the methane slip declines significantly due to combustion efficiency enhancement.

Transactions of the Institute of Measurement and Control, Nov 27, 2018

In the phase of industry digitalisation, data are collected from many sensors and signal processi... more In the phase of industry digitalisation, data are collected from many sensors and signal processing techniques play a crucial role. Data preprocessing is a fundamental step in the analysis of measurements, and a first step before applying machine learning. To reduce the influence of distortions from signals, selective digital filtering is applied to minimise or remove unwanted components. Standard software and hardware digital filtering algorithms introduce a delay, which has to be compensated for in order to avoid destroying signal associations. The delay from filtering becomes more crucial while analysis measurement from multiple sensors, therefore in this paper we provide an overview and comparison of existing digital filtering methods with application based on real-life marine examples. Additionally, design of special purpose filters is a complex process and for preprocessing data from many sources, application of digital filtering in the time domain can have a high numerical cost. For this reason we describe Discrete Fourier Transformation digital filtering as a tool for efficient sensor data preprocessing, which does not introduce a time delay and has low numerical cost. The Discrete Fourier Transformation digital filtering has a simpler implementation and does not require expert-level filter design knowledge, what is beneficial for practitioners from various disciplines. Finally, we exemplify and show the application of the methods on real signals from marine systems.

Applied Ocean Research, Nov 1, 2019

Utilization of measurements from on-board monitoring systems of marine vessels is a part of shipb... more Utilization of measurements from on-board monitoring systems of marine vessels is a part of shipbuilding industry's digitalization phase. The data collected can be used to verify and improve vessel's power system design. Deployment of data-driven statistical models can enhance the knowledge about the power requirements. In this study, we describe a data-driven statistical model that can be used to study and analyze the power requirement of a vessel, which might help to understand the key factors that influence the power and to quantify their contribution. We propose a powerful tool namely, generalized additive model (GAM), which allows us to model nonlinearities. We build the GAM to see the relationship between power consumed and the key influential factors for a power system based on real data from a platform supply vessel (PSV) in a dynamic positioning (DP) mode with diesel-electric configuration. We also describe the importance of feature extraction based on Hilbert Transform to improve the model. In addition, we fit the linear regression (LR) model as a reference model. In the last phase we verify the results of GAM, LR with simulation model from ShipX to show that the data-driven model is within the boundaries of power requirement from simulations.

The electrification of a ship power-train is growing at a fast pace to improve efficiency and red... more The electrification of a ship power-train is growing at a fast pace to improve efficiency and reduce emissions. The implementation of new technologies requires test and validation using various modeling approaches. However, many of the existing models of the ship hybrid power system are too complicated and demand high computational requirements, which make them inappropriate for the real-time applications. The realtime simulation model offers the benefits of testing different control algorithms along with hardware-in-the-loop testing. The bond graph-based dynamic modeling of a ship hybrid power system with a DC grid is presented as applicable to realtime simulation. The overall system model is established using different component models with varying fidelity, so-called mixedmodeling approach. In this approach, the components and control functions are modeled with different complexity such that it can capture the necessary system dynamics while minimizing the computational time. Results show that the modeled system is capable of simulating different operating strategies of the hybrid power system. Moreover, the mixed-modeling approach has enabled the system to simulate in nearly 2.5 times faster than the real-time.

Journal of Sound and Vibration, May 1, 2020

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Mathematical and Computer Modelling of Dynamical Systems, Oct 15, 2018

Heat exchanger networks are important systems in most thermal engineering systems and are found i... more Heat exchanger networks are important systems in most thermal engineering systems and are found in applications ranging from power plants and the process industry to domestic heating. Achieving cost-effective design of heat exchanger networks relies heavily on mathematical modelling and simulation-based design. Today, stationary design calculations are carried out for all new designs, but for some special applications, the transient response of complete networks has been researched. However, simulating large heat exchanger networks poses challenges due to computational speed and stiff initial value problems when flow equations are cast in differential algebraic form. In this article, a systems approach to heat exchanger and heat exchanger network modelling is suggested. The modelling approach aims at reducing the cost of system model development by producing modular and interchangeable models. The approach also aims at improving the capability for large and complex network simulation by suggesting an explicit formulation of the network flow problem.

Journal of physics, Jun 1, 2018

View the article online for updates and enhancements. Related content Research on comprehensive p... more View the article online for updates and enhancements. Related content Research on comprehensive performance evaluation technology of wind turbine based on Analytic Hierarchy Process Xiangsheng Huang, Mingqiu Zhong, Ying Li et al.-Numerical analysis of unsteady aerodynamics of floating offshore wind turbines M. Cormier, M. Caboni, T. Lutz et al.-Quaternion-Based Conversion Formulas for Kinematic Attitude of Floating Offshore Wind Turbines (FOWT)

Mathematical and Computer Modelling of Dynamical Systems, Jul 31, 2009

ABSTRACT Basic rotordynamic models such as for the Jeffcott [H. H. Jeffcott, Lateral vibration of... more ABSTRACT Basic rotordynamic models such as for the Jeffcott [H. H. Jeffcott, Lateral vibration of laded shafts in the neighborhood of a whirling speed–Thee ffect of want of imbalance, Philos.Mag. 37, 1919, pp. 304–314] and Stodola–Green [A. Stodola, Dampf-und Gasturbinen, Springer-Verlag, Berlin, 1924, R.Green, Gyroscopic effects of the critical speeds of flexible rotors, J Appl Mech, 15 (1948), pp. 369–376] rotors are developed in a bond graph formalism. The equations of motion for a general rotor with an imbalance are derived from Lagrange's equations to include most rotordynamic phenomena including gyroscopic effects. The implementation into the bond graph models using both multibond and scalar bonds is given and discussed. An example of bond graph models for the classical Jeffcott rotor is included and the derivation of the complete state equations from the scalar bond graph is shown in detail. A more complex bond graph-modelling example using the Stodola–Green model mounted on a stiff shaft with bearing elasticity and damping is also included. Simulation results for both the models are shown. The purpose of a bond graph implementation of such rotordynamics models is to explore the modular and foundational pieces of the bond graph in more complex rotordynamic or mechatronic models and visualize the rotordynamic phenomena from the energy flow and visual perspectives.