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  • 1.
    Andersson, Emil
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity. World Wide Wind Tech AS, Alesund, Norway.
    Goude, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Vortex filament method 3D analysis of design parameters for counter-rotating axis floating tilted turbine2023In: EERA DeepWind conference 2023 / [ed] Tande, J. O. G.; Kvamsdal, T.; Muskulus, M., Institute of Physics Publishing (IOPP), 2023, article id 012001Conference paper (Refereed)
    Abstract [en]

    The Counter-Rotating Axis Floating Tilted turbine (CRAFT) is a new design for floating off-shore wind power, which utilizes a low center of gravity and allows the tower to tilt to mitigate costs for platforming.

    In this study, 3D simulations of the CRAFT have been performed to investigate the effect from the tower's tilt angle on the aerodynamics of the turbine using a vortex filament method. Due to lack of empirical data of the CRAFT, the method has been benchmark tested against a previous project on a vertical axis wind turbine.

    Using this method, the blades' twist angle has been set to achieve good lift-to-drag ratio along the entire blade. Furthermore, the blades' chord length has been determined for optimal Tip Speed Ratio (TSR) 6 when the tower is tilted 30 degrees from vertical position.

    The CRAFT has been simulated vertically and tilted 15°, 30° and 45°, for TSRs ranging between 4 and 9. The power coefficients (CP) and normal forces have been determined, and velocity plots are presented to show how the near-wake develops.

    The results from this study serves as a basis for further development and design of the CRAFT.

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  • 2.
    Bin, Bai
    et al.
    Blekinge Institute of Technology.
    Ahmad, Allouh
    Blekinge Institute of Technology.
    Study and Analysis of the Electrical and Mechanical Parts in a Wind Turbine2016Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    A wind turbine is a complex electromechanical system. It is important to know how to control it, particularly if high performance and good efficiency are needed. Understanding the rules of nature and the behavior of a wind turbine, especially in its operation, is a subject that requires a number of types of specialized knowledge. We also need to know how to work on them, and then carry out further research and development on their functionality. In this thesis we have studied in different aspects of wind turbine. There are two types of wind turbines (Horizontal axis & Vertical axis). In our thesis we have only focused on the horizontal-axis type.

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    BTN2016Bai
  • 3.
    Brinck, Daniel
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Jeremejeff, Nicklas
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    The development of a vertical axis tidal current turbine2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Globally the amount of electricity produced each year is increasing significantly. Between 1980 and 2010 the average increase was 407 billion kWh per year. To be able to meet this increasing electricity demand, without burdening the environment in a too large extent, the research and development of renewable energy production techniques is of great importance. In the light of this we wanted to dedicate our master thesis to help SubseaTechnology Scandinavia AB with the development of a vertical axis tidal current turbine.

    The project set out to do the initial design proposal of a 2 x 4 meter H-shaped Darrieus turbine by applying the Double Multiple Streamtube model. The optimization process was performed with the aid of MATLAB for four different foils. The study included two symmetrical foils; NACA 0012 and S-1046 together with two asymmetrical foils; S-1210 and E216. The parameters studied were the number of blades, chord length, tip speed ratio, fixed pitch and the operational range. In the project, effects such as blade to wake interaction, torque fluctuations etc. were also considered.

    From the simulations the two bladed turbine fitted with the S-1046 hydrofoil showed the highest performance but was struggling with an unfavorable oscillating torque. In the light of this the three bladed turbine fitted with the S-1046 hydrofoil with a chord of 0.13 m and an optimal tip speed ratio of 3.2 was determined. From the simulations the power coefficient reached 53.47 % for this case. This configuration also showed good performance in a relatively wide range of both tip speed ratios and free stream velocities.

    The model does not include several effects causing losses and the power coefficients calculated in this model are to be used as a comparison between the different turbine configurations and not as absolute values of performance.

    The simulations showed good potential for the use of asymmetrical foils in vertical axis turbines. The performance was evaluated for the upstream half of the turbine where the E216 foil exceeded the symmetrical foils in the range of ten percentage points.

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    The development of a vertical axis tidal current turbine
  • 4.
    Carpman, Nicole
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Marine Current Resource Assessment: Measurements and Characterization2015Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The increasing interest in converting energy from renewable resources into electricity has led to an increase in research covering the field of marine current energy, mainly concerning tidal currents and in-stream tidal turbines. Tides have the advantage of being predictable decades ahead. However, the tidal resource is intermittent and experiences local variations that affect the power output from a conversion system. The variability is mainly due to four aspects: the tidal regime, the tidal cycle, bathymetry at the site and weather effects. Each potential site is unique, the velocity flow field at tidal sites is highly influenced by local bathymetry and turbulence. Hence, characterizing the resource requires careful investigations and providing high quality velocity data from measurement surveys is of great importance. In this thesis, measurements of flow velocities have been performed at three kinds of sites.

    A tidal site has been investigated for its resource potential in one of all of the numerous fjords in Norway. Measurements have been performed to map the spatial and temporal variability of the resource. Results show that currents in the order of 2 m/s are present in the center of the channel. Furthermore, the flow is highly bi-directional between ebb and flood flows. The site thus have potential for in-stream energy conversion. A model is proposed that predicts peak current speed from information on tidal range at the site. A corresponding model can be set up and implemented at other similar sites affected by tides, i.e. fjord inlets connecting the ocean to a fjord or a basin.

    A river site serves as an experimental site for a marine current energy converter that has been designed at Uppsala University and deployed in Dalälven, Söderfors. The flow rate at the site is regulated by an upstream hydrokinetic power plant nearby, making the site suitable for experiments on the performance of the vertical axis turbine in its natural environment. The turbine has been run in uniform flow and measurements have been performed to characterize the extent of the wake.

    An ocean current site was a target of investigation for its potential for providing utilizable renewable energy. A measurement campaign was conducted, mapping the flow both spatially and temporally. However, the site was shown to not be suitable for energy conversion using present technique.

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  • 5.
    Carpman, Nicole
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Uppsala University.
    Resource characterization and variability studies for marine current power2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Producing electricity from marine renewable resources is a research area that develops continuously. The field of tidal energy is on the edge to progress from the prototype stage to the commercial stage. However, tidal resource characterization, and the effect of tidal turbines on the flow, is still an ongoing research area in which this thesis aims to contribute.

    In this thesis, measurements of flow velocities have been performed at three kinds of sites. Firstly, a tidal site has been investigated for its resource potential in a fjord in Norway. Measurements have been performed with an acoustic Doppler current profiler to map the spatial and temporal characteristics of the flow. Results show that currents are in the order of 2 m/s in the center of the channel. Furthermore, the flow is highly bi-directional between ebb and flood flows. The site thus has potential for in-stream energy conversion. Secondly, a river site serves as an experimental site for a marine current energy converter that has been designed at Uppsala University and deployed in Dalälven, Söderfors. The flow rate at the site is regulated by an upstream hydro power plant, making the site suitable for experiments on the performance of the vertical axis turbine in a natural environment. The turbine was run in steady discharge flows and measurements were performed to characterize the extent of the wake. Lastly, at an ocean current site, the effect that transiting ferries may have on submerged devices was investigated. Measurements were conducted with two sonar systems to obtain an underwater view of the wake caused by a propeller and a water jet thruster respectively.

    Furthermore, the variability of the intermittent renewable sources wind, solar, wave and tidal energy was investigated for the Nordic countries. All of the sources have distinctly different variability features, which is advantageous when combining power generated from them and introducing it on the electricity grid. Tidal variability is mainly due to four aspects: the tidal regime, the tidal cycle, local bathymetry causing turbulence, asymmetries etc. and weather effects. Models of power output from the four sources was set up and combined in different energy mixes for a “highly renewable” and a “fully renewable” scenario. By separating the resulting power time series into different frequency bands (long-, mid-, mid/short-, and short-term components) it was possible to minimize the variability on different time scales. It was concluded that a wise combination of intermittent renewable sources may lower the variability on short and long time scales, but increase the variability on mid and mid/short time scales.

    The tidal power variability in Norway was then investigated separately. The predictability of tidal currents has great advantages when planning electricity availability from tidal farms. However, the continuously varying tide from maximum power output to minimum output several times per day increases the demand for backup power or storage. The phase shift between tidal sites introduces a smoothing effect on hourly basis but the tidal cycle, with spring and neap tide simultaneously in large areas, will inevitably affect the power availability.

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  • 6.
    D'Ambrosio, Marco
    et al.
    Halmstad University, School of Business and Engineering (SET). Halmstad University, School of Business and Engineering (SET), Biological and Environmental Systems (BLESS), Energiteknik.
    Medaglia, Marco
    Halmstad University, School of Business and Engineering (SET). Halmstad University, School of Business and Engineering (SET), Biological and Environmental Systems (BLESS), Energiteknik.
    Vertical Axis Wind Turbines: History, Technology and Applications2010Independent thesis Advanced level (degree of Master (Two Years)), 15 credits / 22,5 HE creditsStudent thesis
    Abstract [en]

    In  this  Master Thesis  a  review  of  different  type  of  vertical  axis  wind turbines (VAWT)  and  a preliminary investigation of a new kind of VAWT are presented.

    After an introduction about the historical background of wind power, the report deals with a more accurate analysis of the main type of VAWT, showing their characteristics and their operations. The aerodynamics of the wind turbines and a review of different type on generators that can be used to connect the wind mill to the electricity grid are reported as well.

    Several statistics are also presented, in order to explain how the importance of the wind energy has grown  up  during  the  last  decades  and  also  to  show  that  this development  of  the  market  of  wind power  creates  new  opportunity  also  for VAWT,  that  are  less  used  than  the  horizontal  axis  wind turbine (HAWT).

    In the end of 2009 a new kind of vertical axis wind turbine, a giromill 3 blades type, has been built in Falkenberg, by the Swedish company VerticalWind. The tower of this wind turbine is made by wood,  in  order  to  get  a  cheaper  and  more environment  friendly  structure,  and  a  direct  driven synchronous multipole with permanent magnents generator is located at its bottom. This 200 kW VAWT represents the intermediate step between the 12 kW prototype, built in collaboration with the Uppsala University, and the common Swedish commercial size of 2 MW, which is the goal of the company.

    A  preliminary  investigation  of  the  characteristics  of  this  VAWT  has  been done, focusing  in particular on the value of the frequency of resonance of the tower, an important value that must be never reached during the operative phase in order to avoid serious damage to all the structure, and on the power curve, used to evaluate the coefficient of power (Cp) of the turbine. The results of this investigation and  the steps  followed  to  get  them  are  reported.  Moreover  a  energy production analysis of the turbine has been done using WindPro, as well as a comparison with and older type on commercial VAWT.

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    FULLTEXT01
  • 7.
    Dyachuk, Eduard
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Aerodynamics of Vertical Axis Wind Turbines: Development of Simulation Tools and Experiments2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis combines measurements with the development of simulation tools for vertical axis wind turbines (VAWT). Numerical models of aerodynamic blade forces are developed and validated against experiments. The studies were made on VAWTs which were operated at open sites. Significant progress within the modeling of aerodynamics of VAWTs has been achieved by the development of new simulation tools and by conducting experimental studies.        

    An existing dynamic stall model was investigated and further modified for the conditions of the VAWT operation. This model was coupled with a streamtube model and assessed against blade force measurements from a VAWT with curved blades, operated by Sandia National Laboratories. The comparison has shown that the accuracy of the streamtube model has been improved compared to its previous versions. The dynamic stall model was further modified by coupling it with a free vortex model. The new model has become less dependent on empirical constants and has shown an improved accuracy.    

    Unique blade force measurements on a 12 kW VAWT were conducted. The turbine was operated north of Uppsala. Load cells were used to measure the forces on the turbine. A comprehensive analysis of the measurement accuracy has been performed and the major error sources have been identified.

    The measured aerodynamic normal force has been presented and analyzed for a wide range of operational conditions including dynamic stall, nominal operation and the region of high flow expansion. The improved vortex model has been validated against the data from the new measurements. The model agrees quite well with the experiments for the regions of nominal operation and high flow expansion. Although it does not reproduce all measurements in great detail, it is suggested that the presented vortex model can be used for preliminary estimations of blade forces due to its high computational speed and reasonable accuracy.

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  • 8.
    Eklund, Petter
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Sjolund, Jonathan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Sandra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Magnetic End LeakageFlux in a Spoke Type Rotor Permanent Magnet SynchronousGenerator2017Conference paper (Other academic)
    Abstract [en]

    The spoke type rotor can be used to obtain magnetic flux concentration in permanent magnet machines. This allows the air gap magnetic flux density to exceed the remanent flux density of the permanent magnets but gives problems with leakage fluxes in the magnetic circuit. The end leakage flux of one spoke type permanent magnet rotor design is studied through measurements and finite element simulations. The measurements are performed in the end regions of a 12 kW prototype generator for a vertical axis wind turbine. The simulations are made using three dimensional finite elements to calculate the magnetic field distribution in the end regions of the machine. Also two dimensional finite element simulations are performed and the impact of the two dimensional approximation is studied. It is found that the magnetic leakage flux in the end regions of the machine is equal to about 20 % of the flux in the permanent magnets. The overestimation of the performance by the two dimensional approximation is quantified and a curve-fitted expression for its behavior is suggested.

  • 9.
    Forslund, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Experimental Results of a Load-Controlled Vertical Axis Marine Current Energy Converter2015Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis investigates the load control of a marine current energy converter using a vertical axis turbine mounted on a permanent magnet synchronous generator. The purpose of this thesis is to show the work done in the so far relatively uncharted territory of control systems for hydro kinetic energy conversion. The work is in its early stage and is meant to serve as a guide forfuture development of the control system.

    An experimental power station has been deployed and the first results are presented.

    A comparison between three load control methods has been made; a fixedAC load, a fixed pulse width modulated DC load and a DC bus voltage control of a DC load. Experimental results show that the DC bus voltage control reduces the variation of rotational speed with a factor of 3.5. For all three cases, the tip speed ratio of the turbine can be kept close to the expected optimal tip speed ratio. However, for all three cases the average extracted power was significantly lower than the average power available in the turbine times the estimated maximum power coefficient. A maximum power point tracking system, with or without water velocity measurement, should increase the average extracted power.

    A simulation model has been validated using experimental data. The simulated system consists of the electrical system and a hydrodynamic vortex model for the turbine. Experiments of no load operation were conducted to calibrate the drag losses of the turbine. Simulations were able to predict the behaviour in a step response for a change in tip speed ratio when the turbine was operated close to optimal tip speed ratio. The start position of the turbine was varied in the simulation to view the influence on the step response from a changed turbine position relative to the direction of the water flow.

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    151209
  • 10.
    Forslund, Johan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Goude, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Thomas, Karin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Validation of a Coupled Electrical and Hydrodynamic Simulation Model For A Vertical Axis Marine Current Energy Converter2018In: Energies, E-ISSN 1996-1073, Vol. 11, no 11, article id 3067Article in journal (Refereed)
    Abstract [en]

    This paper validates a simulation model that couples an electrical model in Simulink with a hydrodynamic vortex-model by comparing with experimental data. The simulated system is a vertical axis current turbine connected to a permanent magnet synchronous generator in a direct drive configuration. Experiments of load and no load operation were conducted to calibrate the losses of the turbine, generator and electrical system. The power capture curve of the turbine has been simulated as well as the behaviour of a step response for a change in tip speed ratio. The simulated results agree well with experimental data except at low rotational speed where the accuracy of the calibration of the drag losses is reduced.

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  • 11.
    Forslund, Johan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Staffan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Thomas, Karin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Experimental Results of a DC Bus Voltage Level Control for a Load-Controlled Marine Current Energy Converter2015In: Energies, E-ISSN 1996-1073, Vol. 8, no 5, p. 4572-4586Article in journal (Refereed)
    Abstract [en]

    This paper investigates three load control methods for a  marine current energy converter using a vertical axis current  turbine (VACT) mounted on a permanent magnet synchronous generator  (PMSG). The three cases are; a fixed AC load, a fixed pulse width  modulated (PWM) DC load and DC bus voltage control of a DC  load. Experimental results show that the DC bus voltage control  reduces the variations of rotational speed by a factor of 3.5 at the cost  of slightly increased losses in the generator and transmission lines.  For all three cases, the tip speed ratio   can be kept close to  the expected    . The power coefficient is estimated to be  0.36 at    ; however, for all three cases, the average  extracted power was about  \%. A maximum power point  tracking (MPPT) system, with or without water velocity measurement,  could increase the average extracted power.

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    Energies-08-04572
  • 12.
    Forslund, Johan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Thomas, Karin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    First Experimental Results of a Grid Connected Vertical Axis Marine Current Turbine using a Multilevel Power Converter2018Conference paper (Refereed)
    Abstract [en]

    An experimental marine current power station has been deployed in Söoderfors, Sweden. It comprises a vertical axis turbine directly connected to a permanent magnet synchronous generator rated at 7.5 kW. The generator is controlled by a Back-To-Back 2L-3L Cascaded H-Bridge full scale bi-directional Power Converter located on shore. This paper presents the first test results of the power converter, including grid connection. The startup of  the turbine, power extraction and initial active power injection to the grid, at 50 % of rated power, operated as predicted by laboratory experiments and simulations. After 40 seconds of grid connection the safety system disconnect the grid converter due to high currents injected to the grid. The problem is mostly likely associated with the current controller in the dq0 frame. Further tuning of the PI regulators and the potential addition of an anti-windup could mitigate the control issue.

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  • 13.
    Forslund, Johan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Thomas, Karin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Power And Energy Needed For Starting A Vertical Axis Marine Current Turbine2017Conference paper (Refereed)
    Abstract [en]

    A marine current power station has been deployed in Söderfors, Sweden. It comprises a five bladed fixed pitch vertical axis H-rotor turbine directly connected to a permanent magnet synchronous generator. The turbine is rated for 1.3 m/s, but at lower water speeds the turbine is generally not self starting. This paper investigates the energy and power needed to at low speeds start the turbine electrically with a BrushLess DC (BLDC) motor until  he turbines gives a net positive torque to the generator. A range of startup BLDC powers have been investigated. It is shown that for three water speeds (0.98 m/s, 1.04 m/s and 1.16 m/s) the energy needed for start up is equivalent to less than 1.2 s of power production at maximum power capture of the turbine. The startup time is mostly dependent on BLDC power setting, not on water speed. A BLDC power of 1/7th of rated power of the machine is enough to start the machine within 2 seconds. The results suggest that a higher BLDC power than that will not significantly reduce the startup time nor reduce the energy needed (increase the efficiency of the startup process). The water speed has the highest impact on the time it takes to recover the energy needed for startup once the BLDC power is well above the losses in the system.

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  • 14.
    Goude, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Fluid mechanical simulations and development for vertical axis turbines2011Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The aerodynamics of vertical axis turbines is typically studied using streamtube, vortex or CFD models. This thesis focuses on the first two models, which are the computationally faster ones. The streamtube model is the fastest, allowing three-dimensional modeling of the turbine, but lacks a proper description of the flow through the turbine and does not include any time dependence in the solution. The vortex model used is two-dimensional, but gives a description of the flow around the turbine and can handle time dependence. Effects of a velocity profile and the inclusion of struts have been investigated using the streamtube model. Simulations with the velocity profile indicate that the vertical axis turbine should be quite insensitive to the profile (with respect to the power coefficient). If the applied profile is perpendicular to the rotational axis, the turbine generally performs better if the blade moves against the flow at the high velocity side of the profile. When including struts, the structural mechanics was included and the calculations shows that if turbines are designed for high flow velocities, additional struts are required, reducing the efficiency for lower flow velocities. Turbines in channels and turbine arrays were studied with the vortex model. The channel study included both the numerical parts of the simulations and the effects of channel width were investigated. On the numerical side, the most prominent result was that for wide channels, the number of revolutions until convergence is high. It was seen that smaller channels give higher power coefficients, as predicted by streamtube theory, but the increase in power coefficient with decreasing width was slower, than predicted by streamtube theory. Simulations on a turbine array were performed on five turbines in a row and in a zigzag pattern, where the mean power coefficients of the turbines in the array are higher than for a single turbine. The row configuration was also shown to obtain slightly higher power coefficients and being less sensitive to misalignments in flow direction than the zigzag pattern.

  • 15.
    Goude, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Fluid Mechanics of Vertical Axis Turbines: Simulations and Model Development2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Two computationally fast fluid mechanical models for vertical axis turbines are the streamtube and the vortex model. The streamtube model is the fastest, allowing three-dimensional modeling of the turbine, but lacks a proper time-dependent description of the flow through the turbine. The vortex model used is two-dimensional, but gives a more complete time-dependent description of the flow. Effects of a velocity profile and the inclusion of struts have been investigated with the streamtube model. Simulations with an inhomogeneous velocity profile predict that the power coefficient of a vertical axis turbine is relatively insensitive to the velocity profile. For the struts, structural mechanic loads have been computed and the calculations show that if turbines are designed for high flow velocities, additional struts are required, reducing the efficiency for lower flow velocities.Turbines in channels and turbine arrays have been studied with the vortex model. The channel study shows that smaller channels give higher power coefficients and convergence is obtained in fewer time steps. Simulations on a turbine array were performed on five turbines in a row and in a zigzag configuration, where better performance is predicted for the row configuration. The row configuration was extended to ten turbines and it has been shown that the turbine spacing needs to be increased if the misalignment in flow direction is large.A control system for the turbine with only the rotational velocity as input has been studied using the vortex model coupled with an electrical model. According to simulations, this system can obtain power coefficients close to the theoretical peak values. This control system study has been extended to a turbine farm. Individual control of each turbine has been compared to a less costly control system where all turbines are connected to a mutual DC bus through passive rectifiers. The individual control performs best for aerodynamically independent turbines, but for aerodynamically coupled turbines, the results show that a mutual DC bus can be a viable option.Finally, an implementation of the fast multipole method has been made on a graphics processing unit (GPU) and the performance gain from this platform is demonstrated.

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  • 16.
    Hall, Johannes
    et al.
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Larsson, Albin
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Weight Optimization of Vertical-Axis Wind Turbine Blades constructed in Swedish Fossil Free Steel: With respect to fatigue life time2023Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Wind turbines have been utilized for centuries to harness energy from the wind. Commercial wind turbine blades are typically made from composite materials, which are difficult to recycle, leading to blades ending up in landfills at the end of their lifecycle. Additionally, these materials contribute to microplastic pollution. In response to growing environmental concerns, there has been an increased focus on addressing such issues.

    The Swedish company SeaTwirl AB develops offshore vertical-axis wind turbines (VAWT), and this study focuses on optimizing the weight of a blade from a new 10-15 MW VAWT concept using steel as the material. Steel has long been recyclable, making it an interesting material for wind turbine blades. The specific steel used in this study is the ultra-high-strength steel "Strenx 1300" from SSAB, which is not only extremely durable but is also expected to be fossil-free by 2026, by implementation of the manufacturing technology HYBRIT.

    The study found that a single blade made from Strenx 1300, when designed and optimized for 35 years of operational use, would weigh approximately 193.4 tonnes and would require 6016.8 meters of welds with a fatigue class of FAT 125. A rough estimation of the weight of a fiberglass VAWT of the same size resulted in approximately 300 tonnes. Therefore, this study concludes that it may be feasible to construct a commercially competitive VAWT blade using environmentally friendly, fossil-free steel. This approach would make wind energy a more sustainable energy source without the problems of recyclability and microplastic pollution.

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  • 17. Hammar, Linus
    et al.
    Andersson, Sandra
    Eggertsen, Linda
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Haglund, Johan
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Gullström, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Ehnberg, Jimmy
    Molander, Sverker
    Hydrokinetic Turbine Effects on Fish Swimming Behaviour2013In: PLOS ONE, E-ISSN 1932-6203, Vol. 8, no 12, p. e84141-Article in journal (Refereed)
    Abstract [en]

    Hydrokinetic turbines, targeting the kinetic energy of fast-flowing currents, are under development with some turbines already deployed at ocean sites around the world. It remains virtually unknown as to how these technologies affect fish, and rotor collisions have been postulated as a major concern. In this study the effects of a vertical axis hydrokinetic rotor with rotational speeds up to 70 rpm were tested on the swimming patterns of naturally occurring fish in a subtropical tidal channel. Fish movements were recorded with and without the rotor in place. Results showed that no fish collided with the rotor and only a few specimens passed through rotor blades. Overall, fish reduced their movements through the area when the rotor was present. This deterrent effect on fish increased with current speed. Fish that passed the rotor avoided the near-field, about 0.3 m from the rotor for benthic reef fish. Large predatory fish were particularly cautious of the rotor and never moved closer than 1.7 m in current speeds above 0.6 ms(-1). The effects of the rotor differed among taxa and feeding guilds and it is suggested that fish boldness and body shape influenced responses. In conclusion, the tested hydrokinetic turbine rotor proved non-hazardous to fish during the investigated conditions. However, the results indicate that arrays comprising multiple turbines may restrict fish movements, particularly for large species, with possible effects on habitat connectivity if migration routes are exploited. Arrays of the investigated turbine type and comparable systems should therefore be designed with gaps of several metres width to allow large fish to pass through. In combination with further research the insights from this study can be used for guiding the design of hydrokinetic turbine arrays where needed, so preventing ecological impacts.

  • 18.
    Hedlund Peters, Benjamin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Goude, Linda
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Dynamics of a CRAFT: A simulation study on a Counter Rotating vertical Axis Floating Tilting wind turbine2023Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In this thesis the Counter Rotating vertical Axis Floating Tilting wind turbine (CRAFT) has been explored by creating a simulation model in the program Simulink. The CRAFT prototype is a new type of wind turbine under development by World Wide Wind and Uppsala University with the aim to produce a large scale floating vertical axis wind turbine (VAWT) with two cone shaped counter rotating turbines. The objective of this thesis is to study the required size of the secondary generator in the CRAFT. The generator is required in order to keep both of the turbines rotating with the same but opposite rotational speed, even when the turbines are experiencing different wind loads. Further areas that are investigated are if certain parameters have a specifically high impact on the need for the secondary generator. 

    The objective was reached by creating a model of the prototype and implementing control algorithms for both the secondary and main generator in order to control the rotational speed of the turbines. The behaviour of the CRAFT was then simulated with different wind loads and varying parameters such as the size of the main load, the size of the power output to the secondary generator and the wing length of the lower turbine.

    The simulations showed that it is possible to keep the rotational speed of the two turbines equal and opposite even during turbulent wind loads with the chosen control algorithm. The simulation also showed that if a small deviation in the turbine's rotational speed is allowed, a secondary generator of only 1 kW is needed instead of the currently used 5 kW generator. It was also shown that the elongating of the lower turbine wings had a small and positive effect on the energy output of the CRAFT.

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  • 19.
    Hikkaduwa Vithanage, Ajith
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering.
    DESIGN AND PERFORMANCE ANALYSIS OF PITCHED-PLATE VERTICAL AXIS WIND TURBINE FOR DOMESTIC POWER GENERATION2012Independent thesis Advanced level (degree of Master (Two Years)), 80 credits / 120 HE creditsStudent thesis
    Abstract [en]

    Wind energy is identified a promising energy resource in Sri Lanka. Therefore, it is important to use proper technologies for efficient energy capturing in order to minimize cost of energy. Small scale wind turbines are usually installed in constricted places (particularly in urban areas) where wind flow is turbulent and difficult to predict. Savonious type vertical axis wind turbines are important due to several reasons such as good response to turbulent winds, high initial torque, low cost, low noise, less maintenance.In this study, a modified flat plate type Savonius wind rotor was proposed to cost effectively harness wind energy in constricted places. Generally, vertical axis wind turbines (VAWT) are less efficient than horizontal axis wind turbines, one reason behind this issue is wind force difference between the 2 sides of the axis is small and due to this reason torque is small and power generation capacity is less.A prototype of the proposed VAWT was fabricated and the performance was determined by acquiring experimental data. Artificial wind blow which was generated by a huge fan was used to measure rotational speed and torque characteristics at varying wind speeds. Data were collected with 1-second sampling time and a data acquisition system was developed under this study. In the proposed design one side of the turbine blades are facing the wind direction in order to capture maximum force while other side is edging the blades to have minimum opposite torque. With this concept it is expected to maximize the torque of the axis and generate more power. A sort of a passive pitch mechanism is therefore utilized in order to save energy and simplify the system. Turbine blades are simple flat plates and it eliminates usage of complex aero foils. Due to the simplicity of this design it would be possible to use this turbine for domestic electricity generation at affordable costs.Nowadays, net metering systems are being promoted in Sri Lanka and it would be beneficial to introduce low cost VAWT which operates at low winds as well as turbulent wind conditions. Based on typical household hourly load profile, viability of proposed vertical axis wind turbine was evaluated by considering rural and urban wind regimes in Sri Lanka. The costs of wind energy at two selected locations were determined in the context of net metering.

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    EGI-2013-036MSc-EKV947.pdf
  • 20.
    Imamura, Erik
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Vertical Axis Wind Turbines: A Mechanical Design Project and a Feasibility Study for Microgrids in Tanzania2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This thesis treats vertical axis wind turbines for off-grid applications, primarily for villages and small enterprises in rural regions of developing countries. Two separate projects are incorporated. The first one is about mechanical engineering, with the aim to develop a concept design to hold the turbine wings. A special feature is that the wings will be contractible, allowing variable swept area, to adjust to shifting wind conditions. The tower with the turbine is assembled and raised on-site with contracted wings. Maintenance, as well as decommissioning and relocation of the equipment, is also facilitated by contractible wings. After problem definition and function analysis, concepts were generated by systematic ideation methods. A large part of the project was dedicated to a study of loads and forces, using analytical methods. Cardboard prototypes, hand sketches, and CAD models were also used for development and evaluation. Finally, a four-bar linkage was presented. At the time of writing, a large-scale prototype is under construction, which will use a modified version of the suggested design.The second project could be labeled a pre-feasibility study. It was performed in Tanzania, which will be the first market. The commissioning company has previously worked in the country, so there is local know-how, and business contacts have been maintained. The research was based on interviews, observations, and an extensive literature study. Special focus was put on village level profitability. A number of parameters were mapped and some recommendations drafted. Funding options, availability of wind, social development effects, national electricity markets, and other issues were also covered to some extent. Some indications were found regarding the economic potential of rural electrification, but the issue is complex and no certain conclusions could be made. The project was found promising, but there are certain risks that should be considered.

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  • 21.
    Johnson, Martin
    Halmstad University, School of Business, Engineering and Science.
    Feasibility of product development for a wind turbine with a vertical axis: Mechanical analysis and design improvement2020Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    This thesis is intended primarily as estimating the technical feasibility of aninvention while achieving product development for a company as a project. Theproject tries to use the invention for covering the market of urban wind turbines.Because it is a safe device for the environment and has no noise, it will beinteresting to use it in residential areas even by a low power coefficient.The project covers a wide range of readers from those who are new in the windindustries with mathematics and mechanics background until professionals. Also,consultants and wind turbine companies will be interested in, such as new ideasand solutions. The project estimates location, height, mechanical principles, andthen it evaluates feasibilities. The design distributed in three phases, head, bracingstructure, and foundation.The head consists of two counter-rotating turbines, one inside to the other and in avertical position. Generally, the mechanism of turbines follows the Savoniusturbine. However, the curved profile of the blades does not follow the semicircularfunction but is of the improved type curve. The bracing structure hasenough height to provide the specified wind speed and keep it against a strongstorm and with enough safety. The foundation has a modern structure to carryforces and momentum.The whole structure match in a triangle profile to spend low components againstthe weight, costs and life cycle energy. At the same time, the used methods in thethesis are matched to academic and industrial procedures to carry out this kind ofinvention according to product development. The main parts of the thesis arefocused on the introduction of wind turbines, methods, theory, and results. Theresults consist of designs, calculations. Finally, a conclusion, critical review, andfurther activities presented.

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  • 22.
    Karlowskis, Victor
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Andersson, Jimmie
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Bygglovsbefriad vindkraft till småhuset: -Ur ett tekniskt och ekonomiskt perspektiv2012Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    In connection with the property crises in many countries, caused by the financial crises, people are now more aware of the risks involved in poor property-investments. The unusually cold winters along with extreme prices of electricity in Sweden in recent years has also contributed to increased interest in energy-efficient buildings.

    The process of developing a modern family home in Kiruna, Sweden is presented the first part of this paper. The house has been designed to withstand very high stresses from snow, low energy consumption as well as a high standard of living comfort. Aspects of the house covered here involves everything from construction, heating and ventilation to sanitation. Each of these areas is presented based on their underlying, scientific methods or theories. The purpose of this approach is to enable that the results presented here can be used as reference in other housing projects. Non-standard solutions for some of the areas are used in the development of this house. One example of this is the use of Masonite beams, which proved to be very useful in the roofs and floor structure between the two levels of the house. The beams simplify access for ventilation pipes and waste water pipes, as well as the use of thick isolation. They also enable large spans.

    The second part of this paper involves small wind turbines designed not to require permission from the authorities. The wind conditions as well as the choice of a suitable wind turbine are investigated from a scientific and economic stand point. The results concluded that a vertical axis wind turbine is the better choice considering the limitations of rotor diameter along with the lower wind speeds in Kiruna. The final choice was a vertical axis wind turbine with 4 kW rated power. The yearly production of electricity is estimated to 4000 kWh, which was not enough to generate profit.

    In the last part the possibility of using a filtration system for electricity prices in the future is investigated. This is based on the developed house’s energy performance and the wind turbine’s production. The assumptions made is that the wind turbine is equipped with a large battery and that private individuals have access to the same kind of debiting system that companies in Sweden have today. The model used in this simulation is self-made and enables variable energy consumption for the house as well as variable energy production for the wind turbine to give a truthful representation of the variations which occur naturally during a year. The results concluded that there are profits to be made in the range of 10 % of the value of the wind turbine’s yearly production.

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  • 23.
    Kleusberg, Elektra
    KTH, School of Engineering Sciences (SCI), Mechanics, Stability, Transition and Control.
    Wind-turbine wakes - Effects of yaw, shear and turbine interaction2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The actuator-line method is used together with the incompressible Navier–Stokes equations to investigate the flow development behind wind turbines. Initial investigations focus on providing a thorough validation of the implementation in the spectral-element flow solver Nek5000 against existing numerical and experimental datasets. It is shown that the current implementation gives an accurate representation of the flow field for different turbine geometries, inflow conditions, yaw misalignment, and when considering multiple turbines. This enables an in-depth study of the wake physics in these configurations.

    The yawed wind-turbine wake development is shown to depend on the tip-speed ratio, both in terms of the wake deficit and the generation of the counter-rotating vortices known to occur in yawed turbine wakes. For lower tip-speed ratios the wake deficit exhibited significant asymmetries with respect to the horizontal plane due to the advancing/retreating effect. At high tip-speed ratios this effect became negligible compared to the skewed wake effect, which affects the symmetry with respect to the vertical plane. These inhomogeneities in the averaged wake development also affect the tip-vortex breakdown, leading to different locations of the tip-vortex breakdown along the wake azimuth due to the significant azimuthal variations of the tip-vortex strength and convection velocity. An analysis of the interaction of a yawed wind-turbine wake with a sheared inflow exposed a dependency of the wake deflection and recovery on the yaw orientation, which then resulted in significant differences in the combined power output of a two-turbine setup. More detailed studies of the tip-vortex breakdown in sheared flows using single-frequency perturbations revealed that a sheared inflow changes the spatial growth rate of the tip vortices along the vertical axis, due to the varying tip-vortex convection velocity. However, by applying a scaling based on local vortex parameters, the growth rates collapse to the canonical case of an infinite row of point vortices. Finally, an idealized scenario of two in-line turbines with a steady tip-vortex development is investigated. By applying a range of controlled perturbations, modes were excited, which exhibited in-phase or out-of-phase displacement between the vortex system of the upstream and the downstream turbine for certain frequencies.

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  • 24.
    Koskela, Martin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Uman, Emil
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Need assessment of electricity in Namibia: Prerequisites for implementation of a small scale wind turbine2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Namibia is one of the most sparsely populated countries and with a total area of 825 000 km

    2. There are still many residents in the country without access to electricity and a rapid technological development the need for electricity is increasing constantly. However, the expansion of the electricity grid is slow and costly, resulting in that many cannot afford to be connected and therefore have a need at small scale production have been identified. For this reason it was chosen to investigate this need closer and examine how a small-scale vertical axis wind turbine designed by InnovEd would meet the need and identify suitable sites to promote wind turbine. Additionally an identification of possible changes in wind turbine performance and guidance and recommendation for future work were desired.

    In this study it was chosen to follow a grounded theory where the qualitative data was collected through interviews and general observations during a field trip in northern Namibia. The data were collected for two months in collaboration with the

    Creative Entrepreneurs Solutions.

    The results showed that the need for electricity in rural areas was large but that a small amount of electricity can make a big difference to primarily run the most important things. Lighting turned out to be most significant for the respondents, even if they would like to have all electrical equipment for everything. This was in line with the literature that shows that it is normally the next step after meeting the most basic needs. It showed also saw that the price of electricity was of very great importance.

    Finally, the authors recommend continuing to involve the user in the next stages of development where the first step is to test the product with the user and the pricing. This is followed by the creation of a business and production plan for this product to get a market as soon as possible.

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    Need assessment of electricity in Namibia
  • 25.
    Koskela, Martin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Uman, Emil
    Need assessment of electricity in Namibia: Prerequisites for implementation of a small scale wind turbine2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Namibia is one of the most sparsely populated countries with a total area of 825 600 km2. There are still many residents in the country without access to electricity, and with the present rapid technological development the need for electricity is increasing constantly. However, the expansion of the electricity grid is slow and costly, resulting in that many cannot afford to be connected and therefore a clear need for small scale electricity production has been identified. For this reason it was chosen to investigate this need closer and examine how a small-scale vertical axis wind turbine designed by InnovEd would meet the demand; also to identify suitable sites as well as purchase and maintenance schemes to promote wind turbines or other similar off-grid renewable energy solutions in rural Namibia. Additionally, an identification of possible variations and sensitivity of wind turbine performance and guidance and recommendation for future work were desired.

    In this study it was chosen to follow a grounded theory where the qualitative data was collected through interviews and general observations during a field trip in northern Namibia. The data were collected for two months in collaboration with the Creative Entrepreneurs Solutions.

    The results showed that the demand for electricity in rural areas was large but that a small amount of electricity can make a big difference to primarily run the most important devices. Lighting turned out to be most significant for the respondents, even if they would like to run all sorts of electrical equipment for everything if given a reliable and low-cost energy supply. This was in line with the literature that shows that it is normally the next step after meeting the most basic needs. It showed also that the price of electricity was of utmost importance for the local population.

    Finally, the authors recommend continuing to involve the users in the next stages of development where the major step would be to test the product with the users and to develop reasonable pricing and maintenance procedures. This should be followed by the creation of a local business and production plan for such products to reach a wider market as soon as possible.

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  • 26.
    Lundin, Staffan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Carpman, Nicole
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Thomas, Karin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Studying the Wake of a Marine Current Turbine Using an Acoustic Doppler Current Profiler2015Conference paper (Refereed)
    Abstract [en]

    Wake characteristics of marine current turbines are of significant importance to the development of the marine current power source. Turbine wake recovery determines spacing of turbines in arrays, and environmental impact on e.g. the seabed is heavily influenced by wake behaviour. The majority of previous studies on wakes has been performed on flow-aligned (horizontal) axis turbines and mainly carried out as scale model experiments or numerical simulations.

    This paper describes the performance of wake measurements at the Söderfors test site, where an experimental marine current power station is operated in a river. The turbine is of the cross-flow (vertical) axis type, and the measurements are performed using an Acoustic Doppler Current Profiler (ADCP) towed on the surface by a boat. Positioning data is taken from a high-accuracy Global Navigation Satellite System. The paper discusses various aspects of the methodology employed and provides examples of taken measurements.

  • 27.
    Lundin, Staffan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Forslund, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Goude, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Grabbe, Mårten
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Yuen, Katarina
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Experimental demonstration of performance of a vertical axis marine current turbine in a river2016In: Journal of Renewable and Sustainable Energy, E-ISSN 1941-7012, Vol. 8, no 6, article id 064501Article in journal (Refereed)
    Abstract [en]

    An experimental station for marine current power has been installed in a river. The station comprises a vertical axis turbine with a direct-driven permanent magnet synchronous generator. In measurements of steady-state operation in varying flow conditions, performance comparable to that of turbines designed for significantly higher flow speeds is achieved, demonstrating the viability of electricity generation in low speed (below 1.5 m/s) marine currents.

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  • 28.
    Makhalas, Kharsan Al
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Applied Signal Processing.
    Alsehlli, Faisal
    Blekinge Institute of Technology, Faculty of Engineering, Department of Applied Signal Processing.
    Wind Power2015Student thesis
    Abstract [en]

    This Bachelor thesis has been written at the Blekinge Institute of Technology. This thesis concentrates on the wind power and their components, also the large wind farm is studied. The electrical power is generated by using the power in wind to drive a wind turbine to produce mechanical power. This mechanical power can be converted into electrical power by using electrical induction generators. There are two types of the wind turbines, the horizontal axis and vertical axis wind turbine, where the horizontal axis wind turbine is mostly used and was studied in this thesis. The rotor can be placed in two directions: an upwind rotor where the blade of turbine faces to the wind, so it operates more smoothly and transmit more power. The other type is a downwind rotor which orients itself with respect for the wind direction. Moreover, the tower shadow makes the blade to flex, consequently resulting in fatigue, noise, and reduces output of the power. The modern wind turbine has been built with an odd number of blades which is important for the stability of the turbine. The rotor with an odd number of blades can be considered to be similar to a disc when calculating the dynamic properties of the machine. The main idea of this thesis is to study the wind power in general and large wind parks specifically. The Horns Rev wind park was taken as an example of a wind park in Denmark and the Gotland wind park as an example of a wind park in Sweden too. Into account, the distance between wind turbine in the wind direction cannot be too small. If the wind turbines are located to close to each other, the wind will be more and more turbulent after it passes through each single wind turbine. This would lead to that wind turbines downstream in the wind park, and it might even have to shut down due to that mechanical loading gets to high during strong conditions. This is due to the fact that when wind passes through the rotor of the wind turbine it gets very turbulent and the wind speed is decreased. The minimum length of the rotor should be approximately 5-7 rotor diameters to avoid that issue. Gotland Energy AB (GEAB) considered, that high voltage direct current light would be the only realistic way to solve the technical problems for the high amount of wind power in-feed. One result is that The stability of voltage during transient events, has become much better by using the high voltage direct current light so that the output current stability from the asynchronous generators have been improved, which reduces the stresses on the AC grid and on the mechanical construction of the windmills.

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  • 29.
    Möllerström, Erik
    Halmstad University, School of Business, Engineering and Science, The Rydberg Laboratory for Applied Sciences (RLAS).
    Wind Turbines from the Swedish Wind Energy Program and the Subsequent Commercialization Attempts – A Historical Review2019In: Energies, E-ISSN 1996-1073, Vol. 12, no 4, article id 690Article in journal (Refereed)
    Abstract [en]

    This paper summarizes wind turbines of Swedish origin, 50 kW and above. Both the large governmental-funded prototypes from the early 1980s and following attempts to build commercial turbines are covered. After the 1973 oil crisis, a development program for wind turbine technology was initiated in Sweden, culminating in the early 1980s with the 2 and 3-MW machines at Maglarp and Näsudden. However, government interest declined, and Sweden soon lost its position as one of the leading countries regarding wind turbine development. Nevertheless, several attempts to build commercial wind turbines in Sweden were made in the following decades. Most attempts have, like the earlier prototypes, used a two-bladed rotor, which has become synonymous with the Swedish wind turbine development line. The current ongoing Swedish endeavors primarily focus on the niche-concept of vertical axis wind turbines (VAWTs), which is a demonstration of how far from the broad commercial market of Sweden has moved. Thus far, none of the Swedish attempts have been commercially successful, and unlike countries like Denmark or Germany, Sweden currently has no large wind turbine producer. Suggested reasons include early government interventions focusing on two-bladed prototypes and political disinterest, with wind power grants cut in half by 1985, and the domestic industry not being favored in government policies for deploying wind power.

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  • 30.
    Möllerström, Erik
    et al.
    Halmstad University, School of Business, Engineering and Science, The Rydberg Laboratory for Applied Sciences (RLAS).
    Gipe, Paul
    Wind-works.org, Bakersfield, CA, USA.
    Beurskens, Jos
    SET Analysis, Schagen, the Netherlands.
    Ottermo, Fredric
    Halmstad University, School of Business, Engineering and Science, The Rydberg Laboratory for Applied Sciences (RLAS).
    A historical review of vertical axis wind turbines rated 100 kW and above2019In: Renewable & sustainable energy reviews, ISSN 1364-0321, E-ISSN 1879-0690, Vol. 105, p. 1-13Article in journal (Refereed)
    Abstract [en]

    This paper summarizes and introduces all vertical axis wind turbine (VAWT) projects where 100 kW or larger turbines have been installed. The basis for the review is both existing literature and personal correspondence with people once involved in the different developments. By citing the most relevant work for each project, the paper will also work as an information hub, making information on these projects more accessible.

    Since the 1970s, there have been several VAWT projects with installed turbines of significant size, either as attempts to commercialize VAWTs, or as university led research projects, or as a combination of the two. Most have involved Darrieus turbines built in North America during the 1980s. However, H-rotors, which have always been a favored concept in Europe, have seen a revival during the 2010s.

    The reason VAWTs have never fully challenged the success of the horizontal axis wind turbine (HAWT) is too broad a question to answer here. However, the reasons some VAWT projects have failed are addressed in this paper. Besides the fact that many of the prototypes had terminal failures, most of the installed medium or large-scale VAWTs have to some extent had problems with metal fatigue and durability. Additionally, a lack of long-term interest from governmental or private funders, as well as the introduction of reliable HAWTs, was a recurring theme from those involved in VAWT development, regarding the reason VAWTs so far have failed to succeed. © 2018 The Author(s)

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  • 31.
    Nilsson, Linda
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Cisneros, Anna
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Implementering av vertikala vindkraftverk på lyktstolpar2015Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Development of wind power has a high importance for the work of the EU Commission in the field of sustainable energy usage. This paper aims to investigate the possibility of implementing wind energy in new areas of application in Sweden. Horisontal axis wind turbines are dominating the wind turbine market today because of their high efficiency, but vertical axis wind turbines have been proven advantageous when implemented in urban areas. This work investigates the possibility of implementing small vertical axis wind turbines on lamp posts by highways in Sweden. This paper specifically focuses on the highway between Stockholm and Södertälje to examine the financial and physical limitations of the system to conclude how the wind turbine should be combined with complementing technique or further developed technically. The selection of models consists of the three wind power turbines Savonius, Darrieus and Giromill. A model for calculating the effect and profitability of the system is presented in the paper. The model transforms technical, surrounding and financial parameters to outcomes that reflects real scenarios. The model treats five different scenarios in this paper where the wind turbine is combined with batteries, solar panels and the possibility of selling energy surplus to the energy market. It therefore aims to create a foundation for the analysis of deciding which combination of techniques that can optimise the system. Based on the analysis of the scenarios, the system is optimised for two different purposes; to increase the amount of renewable energy production and to maximise the profitability of the project. To increase the usage of renewable energy, a system consisting of a Giromill turbine with a swept area of 2 m2 , a minimun effect coefficient of 30 % and a maximum cut in wind speed of 2,9 m/s. This system should be placed at a height of 2 m with the possibility of selling surplus energy to the energy market. It generates 900 MWh per year for the entire highway between Stockholm and Södertälje but is implemented without a yearly profit. If the purpuse is to maximise the profitability, the same Giromill turbine but with a swept area of 0,4 m2 placed at a height of 1,2 m is suggested. When combined with a solar panel, a battery and the possibility of selling surplus energy it can generate 450 MWh per year with a yearly profit of 5 %. If the costs are minimised this system can improve the profit to 10 % per year. In addition to a recommendation for the design of the system this paper also includes a suggested framework for implementing wind turbines in urban areas. It consists of the most vital guidelines the project has concluded. The factors of highest importance to investigate before implementing the system is: wind conditions at the highway, energy market conditions and costs of the system’s components, installation and maintenance

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  • 32.
    Talluri, L.
    et al.
    Department of Industrial Engineering, University of Florence, Florence, Italy.
    Nalianda, D. K.
    Propulsion Engineering Centre, School of Aerospace, Transport and Manufacturing, Cranfield University, Cranfield, Bedfordshire, United Kingdom.
    Kyprianidis, Konstantinos
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Nikolaidis, T.
    Propulsion Engineering Centre, School of Aerospace, Transport and Manufacturing, Cranfield University, Cranfield, Bedfordshire, United Kingdom.
    Pilidis, P.
    Propulsion Engineering Centre, School of Aerospace, Transport and Manufacturing, Cranfield University, Cranfield, Bedfordshire, United Kingdom.
    Techno economic and environmental assessment of wind assisted marine propulsion systems2016In: Ocean Engineering, ISSN 0029-8018, E-ISSN 1873-5258, Vol. 121, p. 301-311Article in journal (Refereed)
    Abstract [en]

    In recent years, the increase in marine fuel prices coupled with stricter regulations on pollutant emissions set by the International Maritime Organization have promoted the research in new propulsion technologies and the utilisation of cleaner fuels. This paper describes a novel methodology to enable quantifying and evaluating the environmental and economic benefits that new technologies and fuels could allow in the marine sector. The proposed techno economic and environmental analysis approach enables consistent assessment of different traditional propulsion systems (diesel engine and gas turbine) when operated in conjunction with a novel environmental friendly technology, such as a vertical axis wind turbine. The techno-economic and environmental assessment is focused on the potential reduction in fuel consumption and pollutant emissions that may be accrued while operating on typical Sea Lines Of Communication (Mediterranean, North Sea, Atlantic). The study demonstrates the benefits of the installation of two vertical axis wind turbines on the deck of a ship in conjunction with conventional power plants. The analysis indicates that the performance of the wind turbines and the corresponding benefits strongly depend on the routes and environment in which they operate (therefore favourable wind conditions) allowing fuel savings from 14% (in the gas turbine case) to 16% (in the diesel engine case). The study also indicates that possible benefits may diminish for weak wind conditions. The results reported in this paper establish the economic benefits of installing vertical axis wind turbines in conjunction with conventional technology (Diesel and Gas Turbine Power plants) when installed on a ship travelling through the Atlantic Ocean. The primary purpose of this study is to introduce a methodology to demonstrate the application, performance and economic benefits of the technology at a preliminary design phase and further form a foundation for more elaborate analysis on the subject in the future.

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