| 1. |
- Chatzigiannakou, Maria Angeliki, et al.
(författare)
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Offshore deployments of wave energy converters by Uppsala University, Sweden
- 2019
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Ingår i: Marine Systems and Ocean Technology. - : Springer Science and Business Media LLC. - 1679-396X .- 2199-4749. ; 14:2-3, s. 67-74
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Tidskriftsartikel (refereegranskat)abstract
- Ocean can provide an inexhaustible amount of energy. Many marine energy converters have been developed but most of them have not surpassed the experimental phase due to the high costs in installation, operation, and maintenance. Since 2002 Uppsala University has developed and deployed several units of wave energy converters of various designs. The Uppsala University wave energy converter concept consists of a linear generator directly connected to a point absorber buoy that is mounted on a concrete gravity foundation. Uppsala University deployments have been carried out using different deployment vessels and methods. Three main methods were utilized for these deployments that are discussed in terms of cost, manpower, and time efficiency. Depending on the desired outcome—multiple- or single-device deployment, low budget, etc.—one of the proposed methods can be used for the optimal outcome.
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| 2. |
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| 3. |
- Frost, Anna E., et al.
(författare)
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Partial Stator Overlap in a Linear Generator for Wave Power : An Experimental Study
- 2017
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Ingår i: Journal of Marine Science and Engineering. - : MDPI AG. - 2077-1312. ; 5:4
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a study on how the power absorption and damping in a linear generator for wave energy conversion are affected by partial overlap between stator and translator. The theoretical study shows that the electrical power as well as the damping coefficient change quadratically with partial stator overlap, if inductance, friction and iron losses are assumed independent of partial stator overlap or can be neglected. Results from onshore experiments on a linear generator for wave energy conversion cannot reject the quadratic relationship. Measurements were done on the inductance of the linear generator and no dependence on partial stator overlap could be found. Simulations of the wave energy converter's operation in high waves show that entirely neglecting partial stator overlap will overestimate the energy yield and underestimate the peak forces in the line between the buoy and the generator. The difference between assuming a linear relationship instead of a quadratic relationship is visible but small in the energy yield in the simulation. Since the theoretical deduction suggests a quadratic relationship, this is advisable to use during modeling. However, a linear assumption could be seen as an acceptable simplification when modeling since other relationships can be computationally costly.
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| 4. |
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| 5. |
- Parwal, Arvind, et al.
(författare)
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Wave Energy Research at Uppsala University and The Lysekil Research Site, Sweden : A Status Update
- 2015
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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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| 6. |
- Ulvgård, Liselotte, 1988-, et al.
(författare)
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Line Force and Damping at Full and Partial Stator Overlap in a Linear Generator for Wave Power
- 2016
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Ingår i: Journal of Marine Science and Engineering. - : MDPI AG. - 2077-1312. ; 4:4
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Tidskriftsartikel (refereegranskat)abstract
- A full scale linear generator for wave power has been experimentally evaluated bymeasuring the line force and translator position throughout the full translator stroke. The measuredline force, in relation to translator speed, generator damping and stator overlap, has been studied bycomparing the line force and the damping coefficient, γ, for multiple load cases along the translatorstroke length. The study also compares the generator ’s behavior during upward and downwardmotion, studies oscillations and determines the no load losses at two different speeds. The generatordamping factor, γ, was determined for five different load cases during both upward and downwardmotion. The γ value was found to be constant for full stator overlap and to decrease linearly witha decreasing overlap, as the translator moved towards the endstops. The decline varied with theexternal load case, as previously suggested but not shown. In addition, during partial stator overlap,a higher γ value was noted as the translator was leaving the stator, compared to when it was enteringthe stator. Finally, new insights were gained regarding how translator weight and generator dampingwill affect the translator downward motion during offshore operation. This is important for powerproduction and for avoiding damaging forces acting on the wave energy converter during operation.
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| 7. |
- Ulvgård, Liselotte, et al.
(författare)
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Measurement System for Evaluating Wanted and Unwanted Forces on a Point Absorbing Wave Energy Converter during Offshore Operation
- 2015
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Ingår i: Proceedings of the 25th International Ocean and Polar Engineering Conference.
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Konferensbidrag (refereegranskat)abstract
- A force measurement system has been developed and installed in awave energy converter at Uppsala University. The force in theconnection line as well as the vertical and horizontal strain in thegenerator hull is measured. With these measurements the forces actingon the generator during offshore operation can be monitored andanalyzed. This paper presented the principle, implementation and testresults of the measurement system. A brief discussion of error sourcesand possible improvements is also given.
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| 8. |
- Ulvgård, Liselotte, et al.
(författare)
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Offshore Measurement System for WavePower : Using Current Loop Feedback
- 2016
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Ingår i: Electronics. - : MDPI AG. - 2079-9292. ; 5:4
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents the design and testing of a measurement system for wave powergenerators. The work is part of a project to build a robust and cheap measurement system for offshoremonitoring of wave power farms. Due to the harsh offshore environment, low accessibility andhigh cost for installation and maintenance, it is of key importance to minimize power consumption,complexity and cost of each measurement unit. For the first prototype, the objective was to measurevoltage, current and translator position inside the linear wave power generator. For this, twoprinted circuit boards (PCBs) were developed, using a two wire current loop transmitter setup.They were tested separately and in a three phase setup inside a wave power generator duringonshore tests. To ensure stability, speed and accuracy in the signal transfer, the PCBs were tested forlinearity, frequency response and step response. In addition, power consumption was measured,for operational time evaluation. Results show good agreement between expected and measuredperformance, with an input range of ±1560 V and ±420 A for alternating current measurements anda bandwidth of 10 kHz and 7 kHz, for voltage and current measurements, respectively. The powerconsumption was measured to 0.5 W for each measurement unit, at 24 V feed.
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| 9. |
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| 10. |
- Ulvgård, Liselotte
(författare)
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Wave Energy Converters : An experimental approach to onshore testing, deployments and offshore monitoring
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The wave energy converter (WEC) concept developed at Uppsala University consists of a point absorbing buoy, directly connected to a permanent magnet linear generator. Since 2006, over a dozen full scale WECs have been deployed at the Lysekil Research Site, on the west coast of Sweden. Beyond the development of the WEC concept itself, the full scale approach enables, and requires, experimental and multidisciplinary research within several peripheral areas, such as instrumentation, offshore operations, and wave power infrastructure.This thesis addresses technical challenges of testing, deploying and monitoring full scale WECs. It is divided accordingly into three topics: offshore measurement systems, onshore WEC testing and deployments. Each topic presents new or improved technical solutions to enable offshore wave power research.For the offshore measurement systems, a new portable data acquisition unit was developed, together with a new sensor system to be installed inside the WEC. The developed system offers a cheap and flexible option for short term offshore measurement ventures, when or where site infrastructure is not available. The system has been developed and tested during both onshore and offshore experiments, with promising results.On the topic of onshore WEC testing, the thesis presents an experimental approach for assessing the power take-off (PTO) damping of the WEC. In previous experimental studies, it has been measured via the generated electrical power, which neglects both mechanical losses and iron losses. Consequently, the full PTO force acting on the WEC has been underestimated. The thesis presents experimentally attained trends for the speed dependence of the PTO damping at different resistive loads, as measured from both generated electric power and from measurements of the buoy line force. A study was also performed on how the generator damping is affected by partial stator overlap, which varies with the translator position. In order to assess how the characterized damping behavior will affect the WEC operation at sea, two simulation case studies were performed.Finally, the thesis presents a new WEC deployment method, which has been developed through several deployment trials. By using only a tugboat, a WEC unit is transported and deployed, together with its buoy, in less than half a day. The procedure has proven to be faster, cheaper and safer than the previously used methods.
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