| 1. |
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| 2. |
- Boström, Cecilia, et al.
(författare)
-
Design proposal of electrical system for linear generator wave power plants
- 2009
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Ingår i: 35TH ANNUAL CONFERENCE OF IEEE INDUSTRIAL ELECTRONICS. - : IEEE. - 9781424446483 - 9781424446506 ; , s. 4180-4185
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Konferensbidrag (refereegranskat)abstract
- This paper describes an electrical system layout for a wave power plant connecting linear generators to the grid. The electrical power out from the wave energy converters must be converted before they can be connected to the grid. The conversion is carried out in marine substations that will be placed on the seabed.The paper presents experimental power data from a wave energy converter that has been in operation at the Lysekil research site since March 2006. Moreover, results and analyses from experiments and simulations from tests with the generator connected to a rectifier and filter are presented. A simulation is made to show the difference between having the generator connected to a linear load and a nonlinear load, which would be the case when the generator is connected to the grid.
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| 3. |
- Boström, Cecilia, et al.
(författare)
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Experimental results from an offshore wave energy converter
- 2008
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Ingår i: Volume 6. ; , s. 653-657
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Konferensbidrag (refereegranskat)abstract
- Anoffshore wave energy converter (WEC) was successfully launched at theSwedish west coast in the middle of March 2006. TheWEC is based on a permanent magnet linear generator locatedon the ocean floor driven by a point absorber. Ameasuring station has been installed on a nearby island whereall measurements and experiments on the WEC have been carriedout. The output voltage from the generator fluctuates both inamplitude and frequency and must therefore be converted to enablegrid connection. In order to study the voltage conversion, themeasure station was fitted with a six pulse diode rectifierand a capacitive filter during the autumn of 2006. Theobject of this paper is to present a detailed descriptionof the existing wave energy system of the Islandsberg project.Special attention will be given to the power absorption bythe generator when it is connected to a non linearload
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| 4. |
- Boström, Cecilia, et al.
(författare)
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Experimental Results From an Offshore Wave Energy Converter
- 2010
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Ingår i: Journal of Offshore Mechanics and Arctic Engineering-Transactions of The Asme. - : ASME International. - 0892-7219 .- 1528-896X. ; 132:4, s. 041103-
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Tidskriftsartikel (refereegranskat)abstract
- An offshore wave energy converter (WEC) was successfully launched at the Swedish west coast in the middle of March 2006. The WEC is based on a permanent magnet linear generator located on the sea floor driven by a point absorber. A measuring station has been installed on a nearby island where all measurements and experiments on the WEC have been carried out. The output voltage from the generator fluctuates both in amplitude and frequency and must therefore be converted to enable grid connection. In order to study the voltage conversion, the measuring station was fitted with a six pulse diode rectifier and a capacitive filter during the autumn of 2006. The object of this paper is to present a detailed description of the Lysekil research site. Special attention will be given to the power absorption by the generator when it is connected to a nonlinear load.
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| 5. |
- Boström, Cecilia, et al.
(författare)
-
Temperature measurements in a linear generator and marine substation for wave power
- 2010
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Ingår i: PROCEEDINGS OF THE ASME 29TH INTERNATIONAL CONFERENCE ON OCEAN, OFFSHORE AND ARCTIC ENGINEERING 2010, VOL 3. - 9780791849118 ; , s. 545-552
-
Konferensbidrag (refereegranskat)abstract
- This paper analyzes temperature measurements acquired in offshore operation of a wave energy converter array. The three directly driven wave energy converters have linear generators and are connected to a marine substation placed on the seabed. The highly irregular individual linear generator voltages are rectified and added on a common DC-link and inverted to 50 Hz to facilitate future grid-connection. The electrical power is transmitted to shore and converted to heat in a measuring station. First results of temperature measurements on substation components and on the stator of one of the linear generators are presented from operation in linear and in non-linear damping. Results indicate that there might be some convective heat transport in the substation vessel. If high power levels are extracted from the waves, this has to be considered when placing components in the substation vessel to avoid heating from neighbouring components. The results also indicate that the temperature increase in the linear generator stator is very small. Failure due to excessive heating of the stator winding PVC cable insulation is unlikely to occur even in very energetic sea states. Should this conclusion be incorrect, the thermal conductivity between the stator and the hull of the WEC could be enhanced. Another suggested alteration would be to lower the resistive losses by reducing the linear generator current density.
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| 6. |
- Boström, Cecilia, et al.
(författare)
-
Temperature measurements in a linear generator and marine substation for wave power
- 2012
-
Ingår i: Journal of Offshore Mechanics and Arctic Engineering-Transactions of The Asme. - : ASME International. - 0892-7219 .- 1528-896X. ; 134:2, s. 021901-
-
Tidskriftsartikel (refereegranskat)abstract
- This paper analyzes temperature measurements acquired in the offshore operation of a wave energy converter array. The three directly driven wave energy converters have linear generators and are connected to a marine substation placed on the seabed. The highly irregular individual linear generator voltages are rectified and added on a common dc-link and inverted to 50 Hz to facilitate future grid-connection. The electrical power is transmitted to shore and converted to heat in a measuring station. The first results of temperature measurements on substation components and on the stator of one of the linear generators are presented based on operation in linear and in nonlinear damping. The results indicate that there might be some convective heat transfer in the substation vessel. If high power levels are extracted from the waves, this has to be considered when placing components in the substation vessel in order to avoid heating from neighboring components. The results also indicate that the temperature increase in the linear generator stator is very small. Failure due to excessive heating of the stator winding polyvinyl chloride cable insulation is unlikely to occur even in very energetic sea states. Should this conclusion be incorrect, the thermal conductivity between the stator and the hull of the wave energy converter could be enhanced. Another suggested alteration is to lower the resistive losses by reducing the linear generator current density.
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| 7. |
- Chen, WenChuang, et al.
(författare)
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Numerical modelling of a point-absorbing wave energy converter in irregular and extreme waves
- 2017
-
Ingår i: Applied Ocean Research. - : Elsevier BV. - 0141-1187 .- 1879-1549. ; 63, s. 90-105
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Tidskriftsartikel (refereegranskat)abstract
- Based on the Navier-Stokes (RANS) equations, a three-dimensional (3-D) mathematical model for the hydrodynamics and structural dynamics of a floating point-absorbing wave energy converter (WEC) with a stroke control system in irregular and extreme waves is presented. The model is validated by a comparison of the numerical results with the wave tank experiment results of other researchers. The validated model is then utilized to examine the effect of wave height on structure displacements and connection rope tension. In the examined cases, the differences in WEC’s performance exhibited by an inviscid fluid and a viscous fluid can be neglected. Our results also reveal that the differences in behavior predicted by boundary element method (BEM) and the RANS-based method can be significant and vary considerably, depending on wave height.
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| 8. |
- Dolguntseva, Irina, 1981-, et al.
(författare)
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Risk based estimation of failure in a steel wire used for the wave energy converter connection line
- 2014
-
Konferensbidrag (refereegranskat)abstract
- The wave energy converter being developed at Uppsala University is of a point absorber type utilizing heaving motion of waves with a direct driven linear generator power take off. The point absorber, a buoy, is placed on the sea surface and is connected to the translator by a connection line. The connection line service life is of large importance for the lifetime of the entire device. Steel wire used as the connection line should be chosen to withstand loadings with different amplitude and frequency. In the present study, the risk of failure in the connection line is estimated.
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| 9. |
- Ekergård, Boel, et al.
(författare)
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Axial Force Damper in a Linear Wave Energy Converter
- 2013
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Ingår i: Development and Applications of Oceanic Engineering (DAOE). - 2325-3762. ; 2:2, s. 33-38
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents a study on the axial force damper in a wave energy converter. The converter itself consists of a linear generator placed on the ocean floor connected to a buoy at the ocean surface. As the development of the complete system goes forward, the economical perspective becomes more and more important. In order to ensure an economically viable alternative to the electric energy conversion, the costs associated with the use of materials have to be reduced while the survivability of the wave power unit has to be prolonged. The study presented in this paper increases the knowledge on axial forces and illustrates the damping system required to prevent the failure of the hull which houses the generator. The results are aimed to be utilized in the future design of wave energy converters and influence the choice of materials, the total costs and prolong the survivability of the wave energy converters in harsh wave climates.
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| 10. |
- Ekweoba, Chisom Miriam, 1992-
(författare)
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Hydro-mechanical optimization of a wave energy converter
- 2022
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wave energy conversion technology has gained popularity due to its potential to be-come one of the most preferred energy sources. Its high energy density and low car-bon footprint have inspired the development of many wave energy converter (WEC) technologies, few of which have made their way to commercialisation, and many are progressing.The Floating Power Plant (FPP) device is a combined floating wind and wave converter. The company, Floating Power Plant, was established in 2004 and has developed and patented a floating device that consists of a semi-submersible that serves as a foundation for a single wind turbine and hosts four wave energy converters (WECs). Each WEC consists of a partially submerged wave absorber whose pitching motion generates energy from incoming waves. The wave absorbers are connected to an oil hydraulic power take-off system located in a dry “engine room” above the free water surface, where the mechanical energy in the absorber is converted to electricity. When undergoing pitching movements, there are interactions between individual wave absorbers and the surrounding platform. This thesis focuses on developing methods to improve the FPP WEC’s hydrodynamic interactions.The first part of this thesis optimises the wave absorber (WA) ballast. An ana-lytical model is developed to enable systematic selection of WA ballast combination with significantly less computational effort when compared with the more conven-tional means, such as using CAD software. The study suggests an algorithm with which the absorbed power and resonance frequency can be improved and adjusted by manipulating the ballasts’ mass, the position of its centre of gravity, placement and inclination of the WA. The proposed method is generic and can be applied to other WEC concepts or submerged bodies in general. The results show the feasibility of designing the absorber ballast to offer passive control for increased wave absorption. It demonstrates the effect of ballast on the WA inclination, resonance frequency and response amplitude operator (RAO).The second part focuses on the optimisation of the FPP platform geometry. The genetic algorithm optimisation technique is implemented to maximise the annual en-ergy produced by the relative pitch motion of the WA to the floating platform. The optimised variables are characteristic lengths of the floating platform, most of which are part of the immediate surrounding walls of the absorber. The objective function is a function of the WA’s annual energy production (AEP) and RAO. Results show the feasibility of improving the hydrodynamic interaction between the floating platform and its integrated wave absorbers for a given wave climate by using a heuristic search technique. The number of iterations to convergence tends towards increased values when considering more optimised variables. It is also observed that the computational time appears to be independent of the number of variables but is significantly impacted by the computational power of the machine used.
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| 11. |
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| 12. |
- Gravråkmo, Halvar, et al.
(författare)
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Measurements of Extreme Forces on a Wave Energy Converter of Point Absorber Type and Estimation of Added Mass of Cylindrical Buoy
- 2014
-
Ingår i: 33Rd International Conference On Ocean, Offshore And Arctic Engineering, 2014, Vol 9B. - : ASME Press. - 9780791845547
-
Konferensbidrag (refereegranskat)abstract
- A wave energy converter (WEC) of point absorber type is tested at the west coast of Sweden. The buoy is a vertical cylinder. The linear generator on the seabed has limited stroke length. Large waves cause the generator to reach its maximum stroke length. As this happen, a spring in the generator is compressed, causing the buoy to instantly come to rest. During this process the force between the buoy and the generator is measured. Also the acceleration of the buoy is measured. This process and the extreme forces on the generator hull is described and the study shows that the magnitude of this force is greatly influenced by the added mass of the buoy and thus the buoy geometry. The ratio between the extreme forces on the hull and the forces during normal operation will affect the dimensioning and economy of the WEC. Force acting between generator and buoy were measured during various events as the WEC was operating. Added mass was estimated from the measurements
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| 13. |
- Gravråkmo, Halvar, et al.
(författare)
-
Power Production by Linear Wave Energy Converters of Point Absorber Type with Vertical Cylindrical Buoys during Various Sea States
-
Tidskriftsartikel (refereegranskat)abstract
- Two wave energy converters (WEC) were deployed near the city of Lysekil as part of Uppsala University's wave energy project. The converters were electrically identical and mechanically very similar. The converters were installed on the seabed at 25 m depth at the same site and believed to be exposed to very similar wave conditions. They utilized permanent magnets oscillating vertically due to surface buoys actuating the generators. The buoys were vertical cylinders excitated by ocean waves, with different diameters but with equal volume. The power production from the converters and the sea states were measured and comparison of power production between the two converters during various sea states was conducted. Also wind and tidal oscillations were considered and were found to influence the power production directly or indirectly, as did also significant wave height and energy period. The only difference between the two converters were the buoys, as the generators and electric loads were equal. During a 4 day period of various wave climates, the WEC with the buoy with 78 % larger water plane area than the WEC with the more narrow buoy with a water plane area of 7.07 m2 was found to produce 11 % more power.
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| 14. |
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| 15. |
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| 16. |
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| 17. |
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| 18. |
- Lejerskog, Erik, 1977-, et al.
(författare)
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Study of the operation characteristics of a point absorbing direct driven permanent magnet linear generator deployed in the Baltic Sea
- 2016
-
Ingår i: IET Renewable Power Generation. - : Institution of Engineering and Technology (IET). - 1752-1416 .- 1752-1424. ; 10:8, s. 1204-1210
-
Tidskriftsartikel (refereegranskat)abstract
- To experimentally study how a wave energy converter (WEC) behaves when parameters such as weight on the translator and buoy volume are changing is of significant importance when trying to optimise the WEC system. This study presents results from a WEC deployed at the Baltic Sea near the island of Åland. Compared with earlier experiments, the weight on the translator has been significantly increased to suit the buoy volume. Experimental results show that the power output between the upward and the downward motions are comparable up to the maximum speed for the downward motion of the translator. To study the speed of the translator in downward direction a model has been derived. The model has also been used to study the impact of having a changing active area. Moreover, finite element (FE) simulations done on the generator have been compared with experimental data and show a good agreement, but at high speeds of the translator the FE simulations start to deviate from the experiments.
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| 19. |
- Lindskoug, Patrik, et al.
(författare)
-
Electronic Contract Law
- 2015
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Ingår i: Introduction to EU Internet Law. - 9788792598387 ; , s. 265-283
-
Bokkapitel (refereegranskat)
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| 20. |
- Lindskoug, Patrik, et al.
(författare)
-
Electronic Contract Law
- 2018. - 2
-
Ingår i: Introduction to EU Internet Law. - 9788742000168 ; , s. 309-326
-
Bokkapitel (refereegranskat)
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| 21. |
- Lindskoug, Patrik, et al.
(författare)
-
Electronic Contract Law
- 2023. - 3
-
Ingår i: Introduction to EU Internet Law. - 9788742000687
-
Bokkapitel (refereegranskat)
|
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| 22. |
- Lindskoug, Patrik, et al.
(författare)
-
Jurisdiction and Applicable Law
- 2015. - 1
-
Ingår i: Introduction to EU Internet Law. - 9788792598387 ; , s. 309-348
-
Bokkapitel (refereegranskat)
|
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| 23. |
- Lindskoug, Patrik, et al.
(författare)
-
Jurisdiction and Applicable Law
- 2018. - 2
-
Ingår i: Introduction to EU Internet Law. - 9788742000168 ; , s. 355-395
-
Bokkapitel (refereegranskat)
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| 24. |
- Lindskoug, Patrik, et al.
(författare)
-
Jurisdiction and Applicable Law
- 2023. - 3
-
Ingår i: Introduction to EU Internet Law. - 9788742000687
-
Bokkapitel (refereegranskat)
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| 25. |
- Parwal, Arvind, et al.
(författare)
-
Wave Energy Research at Uppsala University and The Lysekil Research Site, Sweden : A Status Update
- 2015
-
Konferensbidrag (refereegranskat)abstract
- This paper provides a summarized status update ofthe Lysekil wave power project. The Lysekil project is coordinatedby the Div. of Electricity, Uppsala University since 2002, with theobjective to develop full-scale wave power converters (WEC). Theconcept is based on a linear synchronous generator (anchored tothe seabed) driven by a heaving point absorber. This WEC has nogearbox or other mechanical or hydraulic conversion systems,resulting in a simpler and robust power plant. Since 2006, 12 suchWECs have been build and tested at the research site located atthe west coast of Sweden. The last update includes a new andextended project permit, deployment of a new marine substation,tests of several concepts of heaving buoys, grid connection,improved measuring station, improved modelling of wave powerfarms, implementation of remote operated vehicles forunderwater cable connection, and comprehensive environmentalmonitoring studies.
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| 26. |
- Salar, Dana, 1985-, et al.
(författare)
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Low-RPM torque converter (LRTC) with Integrated direct shaft flywheel
- 2023
-
Ingår i: International Marine Energy Journal. - 2631-5548. ; 6:1, s. 1-10
-
Tidskriftsartikel (refereegranskat)abstract
- The low-RPM Torque Converter (LRTC) is a rotating generator concept for use on the seabed with the driving force from sea waves motion on the sea surface. This concept is built up of two identical generators connected opposite each other via a spring drum with a built-in ball bearing clutch. The drum is connected to a buoy on the sea surface via a wire, the wire is rolled around the spring drum. With sea waves, the buoy moves either upwards or downwards and pulls the wire upwards or downwards. This movement causes the generators to spin.This article presents an upgrade of the LRTC generator concept and upgraded measurement system, both hardware and software.A flywheel system of the thin-disc type has been designed for direct connection to the generator's rotor shaft and an electronic measuring system has also been developed for more accurate measurements and minor disturbances.More detailed tests have been performed both for the purpose of comparing the systems and to explore the performance of the generator concept in more detail.Three different experiments have been done in this article. The first two experiments were performed to investigate the performance of the flywheel and to see the performance of the LRTC system with and without flywheel.The third experiment investigated the optimization of the flywheel mass by increasing the mass of the flywheel with the addition of more thin discs.All movements are simulated with a six-joint industrial robot. Several sinusoidal types of wave motions have been simulated with different time periods and also several real wave climate motions (data taken from fields) have been simulated with the robot. The experiments show that the addition of the flywheel in the LRTC system provides advantages in increasing both peak power, average output power and also softens the output power oscillation.
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| 27. |
- Savin, Andrej, et al.
(författare)
-
Azimuth-inclination angles and snatch load on a tight mooring system
- 2012
-
Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018 .- 1873-5258. ; 40, s. 40-49
-
Tidskriftsartikel (refereegranskat)abstract
- A concept for wave energy conversion is being developed at the Swedish Center for Renewable Electric A Energy Conversion at the Angstrom Laboratory at Uppsala University, Sweden. This paper presents the results of offshore measurements where strain gauge sensors instrumented on the capsule of the WEC and a force transducer measuring line force from the floating buoy were used. A method for measurement and evaluation of the lateral force on the guiding system was developed. The experimental data allow us to define the inclination and azimuth angle between the generator and the floating buoy. The inclination angle is one of the key parameters for the design and the construction of the outer structure. It can be assumed that the inclination angle between the linear generator and the buoy with the stretched connection line did not exceed 8 at a sea state of 1.32 m waves. Snatch load between the buoy and the generator occur. This was obtained by a sudden jump of the inclination angle between the generator and the floating buoy. Moreover, the inclination and azimuth angle allow reproduction of the position of the floating buoy on the water surface.
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| 28. |
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| 29. |
- Savin, Andrej, et al.
(författare)
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Estimation of Stress in the Inner Framework Structure of a Single Heaving Buoy Wave Energy Converter
- 2012
-
Ingår i: IEEE Journal of Oceanic Engineering. - : Institute of Electrical and Electronics Engineers (IEEE). - 0364-9059 .- 1558-1691. ; 37:2, s. 309-317
-
Tidskriftsartikel (refereegranskat)abstract
- This paper details a method for strain measurements in the inner framework structure of the single heaving buoy Wave Energy Converter (WEC). This type of the WEC consists of a linear direct drive generator placed on the sea floor and connected to the floating buoy through the connection line.The study focuses on estimation of stress in the inner framework structure of the WEC using strain measurements in material. Stress in ocean structures is as important as maximum stress.The offshore experiment was made at the Lysekil research site a few kilometers from the Swedish west coast.Stresses had the maximum value when the translator hit an end stop. Interesting observations were made: compressive stress occurred in the framework crossbar at a sea state of 1.32 m waves, but both compressive and tensile stress occurred at a sea state of 3.2 m waves.A computational procedure employs good results. Error estimation is calculated and represented. This work is a step that may influence future design of wave energy devices in terms of material aspect, survivability in a hard wave climate and cost-effective renewable energies.
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| 30. |
- Savin, Andrej
(författare)
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Experimental Measurement of Lateral Force in a Submerged Single Heaving Buoy Wave Energy Converter
- 2012
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The search for new solutions for the generation of energy is becoming more and more important for our future. Big arguments and disagreements on e.g. the questions of gas transport or the dependence on energy supplied by other countries raise demands on the development of new forms of alternative energy resources. Wave power is one of the main sources of renewable energy due to the high power density stored in ocean waves. Nevertheless, the dynamic forces of waves are so large that serious questions popped up on how to design a system which could work even in an unfavourable wave climate or could at least retain working capabilities after big storms without significant damages. This thesis studies the reliability of the mechanical parts of a linear direct driven permanent magnet generator. The results of offshore experiment where strain gauge sensors instrumented on the capsule and the inner framework structure are presented. Stress estimation analyses using strain gauges are carried out. A method for measuring forces and moments in the mechanical structure of the WEC is developed. Evaluation of the lateral force acting on the outer structure is a key factor for the design and construction of the WEC. A method for the measurement of the lateral force acting on the capsule has been developed. A study of the inclination angle between the Wave Energy Converter and the floating buoy has been carried out. The aim of this work is to contribute to the development of wave energy conversion system, and especially to the estimation of structural loads which are important for the survivability of the system under hard sea states. This work is a step that may influence future design of wave energy devices in terms of material aspect, survivability in a hard wave climate and cost-effective renewable energies.
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| 31. |
- Savin, Andrej, et al.
(författare)
-
Full-Scale Measurement of Reaction Force Caused by Level Ice Interaction on a Buoy Connected to a Wave Energy Converter
- 2019
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Ingår i: Journal of cold regions engineering. - : ASCE-AMER SOC CIVIL ENGINEERS. - 0887-381X .- 1943-5495. ; 33:2
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Tidskriftsartikel (refereegranskat)abstract
- Wave energy is an attractive source of renewable energy. In regions with a cold climate, for example, in the Baltic Sea, a good understanding of ice loads is vital for developing a reliable and cost-effective buoy for a wave energy converter (WEC). The first full-scale attempt was made to measure the vertical reaction force on a floating buoy connected to the WEC under the ice level interaction process. The force equation for a buoy connected to the WEC during the ice level interaction process is presented. It provides essential information on forces from the floating level of ice, which is very important for the design and construction of a buoy in regions with a cold climate.
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| 32. |
- Savin, Andrej, et al.
(författare)
-
Low-RPM Torque Converter (LRTC)
- 2021
-
Ingår i: Energies. - : MDPI. - 1996-1073. ; 14:16
-
Tidskriftsartikel (refereegranskat)abstract
- The concept concerned in this paper is based on energy conversion of the ocean waves via rotational generators. The objective of this research is to develop a new type of slow-motion converter. The LRTC device consists of a drum that is connected via wire to a floating buoy. The drum is connected to rotary generators. The generators are heavily braked when the direction of movement changes (up/down); this is because the generators have been charged the maximum load in order to obtain maximum output power. For upcoming improvement, the generators should have some power storage as flywheel. In the future experiments, the torque converter can even be tuned to rotate in resonance with the incoming waves, strongly increasing power absorption. Constant force springs are applied for this purpose. The focus of this project is, therefore, a new generation of wave power device for utility-scale energy conversion offering a cost of energy that can compete with established energy resources.
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| 33. |
- Savin, Andrej, et al.
(författare)
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Statistical analysis of power output from a single heaving buoy WEC for different sea states
- 2018
-
Ingår i: Marine Systems & Ocean Technology. - : Springer. - 1679-396X .- 2199-4749. ; 2-4, s. 103-110
-
Tidskriftsartikel (refereegranskat)abstract
- Output power fluctuations from a wave energy converter (WEC) utilizing the principle of an oscillating body are unavoidable due to the reciprocating movement of the translator inside the generator. Moreover, the wave energy flux largely varies with time and propagates with the wave group velocity. Making use of the oscillating output power is a challenge for many wave energy conversion concepts. Therefore, estimation of the output power from a WEC solely by the mean power does not fully reflect the process of energy conversion, especially, by a direct drive linear generator. In the present paper, the output power from the WEC with a linear generator power take-off (PTO) is considered as a stochastic process, and the WEC performance is evaluated from the statistical point of view and related to the linear generator’s (LG) stroke length. Statistics as mean, standard deviation, relative standard deviation, maximum, and mode are found for different sea states. All statistics have shown an expected overall tendency with a rising significant wave height of incoming waves. As the significant wave height increases, statistics of the power output such as mean, standard deviation, maximum, and quantile are increasing, and the mode is decreasing beside the mode for the sea state C. It has been noted that for a significant wave height equal to the LG’s stroke length, the mode is greater than the same values for sea states of other significant wave heights. The results are based on a full-scale offshore experiment and may be used for the design of energy conversion systems based on a linear generator PTO.
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| 34. |
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| 35. |
- Strömstedt, Erland, 1972-, et al.
(författare)
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Time Series-, Time-Frequency- and Spectral Analyses of Sensor Measurements in an Offshore Wave Energy Converter Based on Linear Generator Technology
-
Ingår i: Energy and Power Engineering. - 1949-243X.
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The second wave energy converter (WEC) prototype launched at the Lysekil research site on the Swedish west coast in March 2009 contained a number of sensor systems for measuring the mechanical performance of the WEC and mechanical subsystems within the WEC. Measurements were carried out during the first experimental period starting from May 15th and ending on September 23rd. One of the measurement systems was a set-up of 7 laser triangulation sensors for measuring relative displacement of the piston rod mechanical lead-through transmission in the direct drive. Investigation into the measurements in the time domain with close-ups, in the frequency domain with Fast Fourier transform (FFT) and with time-frequency analysis with short time Fourier transform (STFT) is carried out to map the spectral content in the measurements. End stop impact is clearly visible in the time-frequency analysis. The FFT magnitude spectra are investigated for identifying the cogging bandwidth among other vibrations. Two measurement periods separated by 2.5 month are presented to be able to draw conclusion on what happens with time. Comparisons and correlations are made between different sensors measuring simultaneously, especially for the laser triangulation sensor measurements. Noise levels are investigated. Filtering is discussed for further refinement of the laser triangulation sensor signals in order to separate noise from actual physical displacement and vibration. Measurements are presented from the relative displacement of the piston rod mechanical lead-through, from magnetic flux in the air gap, mechanical strain in the WEC structure, translator position and piston rod axial displacement and active AC power. Generator cogging, fluctuations in the damping force and in the Lorenz forces in the stator are distinguished and varies depending on translator speed. Vibrations from cogging seem to be present in the early measurement period while not so prominent in the late measurement period in August. Vibrations frequencies due to wear is possible from comparing with the noise at generator standstill and the vibration sources in the generator. It is concluded that a moving average is sufficient filter in the time domain for further analysis of the relative displacement of the piston rod mechanical lead-through transmission.
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| 36. |
- Strömstedt, Erland, et al.
(författare)
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Time Series-, Time-Frequency- and Spectral Analyses of Sensor Measurements in an Offshore Wave Energy Converter Based on Linear Generator Technology
- 2013
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Ingår i: Energy and Power Engineering. - : Scientific Research Publishing, Inc.. - 1949-243X .- 1947-3818. ; Vol.5:No.1, s. 70-91
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Tidskriftsartikel (refereegranskat)abstract
- Inside the second experimental wave energy converter (WEC) launched at the Lysekil research site on the Swedish west coast in March 2009 a number of sensor systems were installed for measuring the mechanical performance of the WEC and its mechanical subsystems. One of the measurement systems was a set-up of 7 laser triangulation sensors for measuring relative displacement of the piston rod mechanical lead-through transmission in the direct drive. Two measurement periods, separated by 2.5 month, are presented in this paper. One measurement is made two weeks after launch and another 3 months after launch. Comparisons and correlations are made between different sensors measuring simultaneously. Noise levels are investigated. Filtering is discussed for further refinement of the laser triangulation sensor signals in order to separate noise from actual physical displacement and vibration. Measurements are presented from the relative displacement of the piston rod mechanical lead-through, from magnetic flux in the air gap, mechanical strain in the WEC structure, translator position and piston rod axial displacement and active AC power. Investigation into the measurements in the time domain with close-ups, in the frequency domain with Fast Fourier transform (FFT) and with time-frequency analysis with short time Fourier transform (STFT) is carried out to map the spectral content in the measurements. End stop impact is clearly visible in the time-frequency analysis. The FFT magnitude spectra are investigated for identifying the cogging bandwidth among other vibrations. Generator cogging, fluctuations in the damping force and in the Lorenz forces in the stator are distinguished and varies depending on translator speed. Vibrations from cogging seem to be present in the early measurement period while not so prominent in the late measurement period. Vibration frequencies due to wear are recognized by comparing with the noise at generator standstill and the vibration sources in the generator. It is concluded that a moving average is a sufficient filter in the time domain for further analysis of the relative displacement of the piston rod mechanical lead-through transmission.
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- Temiz, Irina, 1981-, et al.
(författare)
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Wave absorber ballast optimization based on the analytical model for a pitching wave energy converter
- 2021
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Ingår i: Ocean Engineering. - : Elsevier. - 0029-8018 .- 1873-5258. ; 240
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Tidskriftsartikel (refereegranskat)abstract
- The present paper considers pitching wave energy converters (WECs) integrated in a floating platform, e.g., floating foundation for a wind turbine. Each WEC consists of a partially submerged wave absorber that rotates about the hinge located above the still water level under the influence of waves. Each wave absorber contains separated ballast tanks that are used to ensure the desired initial tilting angle of the absorber with respect to the floating foundation (called the rest angle). The same rest angle can be achieved by filling different ballast compartments that impacts the inertia moment about the hinge, response amplitude operator (RAO), resonance frequency of the absorber, and the power absorption performance. The exhaustive search for a suitable ballast configuration can quickly become a computationally expensive task depending on the number of ballast tanks. In this paper, the ballast optimization algorithm based on an analytical model is developed. The algorithm is applied to investigate the impact of the ballasts on the rest angle, RAO and resonance frequency of the wave absorber. It provides a base for ballast design and location for improved power absorption performance. The proposed algorithm can be adapted to the ballast optimization of other pitching WECs.
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