| 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. |
- Ekman, Philip, 1972
(författare)
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Numerical Study of a Method to Reduce Rescue Boat Motions during Launching from a Ship in Waves
- 2005
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Ingår i: Marine Systems and Ocean Technology. - 1679-396X .- 2199-4749. ; 1:2, s. 91-97
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Tidskriftsartikel (refereegranskat)abstract
- An attempt to improve the launching of evacuation equipment such as rescue boats or lifeboats from a ship with no forward speed in beam seas is numerically investigated in the present paper. Previous studies have shown that the vertical distance between the launch point and the mean water level is an important parameter in the launch process. Therefore, in the present paper an arm follows the evacuation equipment a certain distance to reduce the swing motion, which corresponds to continuously lower the launching point. This situation is simulated using a numerical model that includes the wave climate, the ship motions and the dynamics of the evacuation equipment. In order to keep the weight and dimensions of the arm within reasonable values it is important to have information of the moment at the launching point. Consequently, this moment is continuously calculated. The influences of the length of the arm, the launch position, the initial wire length and the wavelength are investigated by varying these parameters. The results clearly show that the risk when launching rescue boats or lifeboats can be drastically reduced when using this method.
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| 3. |
- Lundbäck, Olov, 1971
(författare)
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An investigation of hydrodynamic forcing on a semi-planing monohull in following and stern quartering seas
- 2006
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Ingår i: Marine Systems and Ocean Technology. - 1679-396X .- 2199-4749. ; 2:1-2, s. 27-32
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Tidskriftsartikel (refereegranskat)abstract
- Navigating a ship in following and stern quartering seas is well known to seafarers for the possible troublesome situations that may arise. The issue has also been addressed by many researchers during the last 50 years. In 1964 Du Cane and Goodrich presented one of the first systematic studies on ships in following seas together with a compilation of accounts on real occurrences of dangerous situations for ships in following and stern quartering seas. Later research has confirmed the possibility for occurrence of several types of allegedly capricious behaviour for a ship travelling at a course within one third of the compass card, i.e. between −60° and 60° relative to the waves. The research included in the references is covering many different types of ships from fishing boats to fast naval vessels and merchant ships. Despite the 51 years of research in the tradition pointed out by Du Cane and Goodrich’s work, there is still a lack of effective methodology within many of the areas connected to following and stern quartering seas. The present paper is mainly focusing on manoeuvring in following seas. Nevertheless, results included in the current paper, among others, show that ship motion in the horizontal plane has a major impact on the magnitude and timing of wave excitation in all degrees of freedom. Therefore the presented results are of importance for most of the seakeeping and safety issues related to navigation in following and stern quartering seas. The most significant results presented in the current paper come from semi-captive tests with a semi-planing ship model At these tests the surge force, sway force, roll moment and yaw moment were measured, while the ship model was free to heave and pitch. The test data are compared to computational data obtained by a strongly simplified hydrodynamic modelling. This comparison shows very encouraging results. The paper does also address criteria for safe manoeuvring in following and stern quartering seas, methodologies for full-scale tests and experiments with a free-running scale model.
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| 4. |
- 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
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Ingår i: Marine Systems & Ocean Technology. - : Springer. - 1679-396X .- 2199-4749. ; 2-4, s. 103-110
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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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