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Engström, Jens
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Publications (10 of 44) Show all publications
Göteman, M., McNatt, C., Giassi, M., Engström, J. & Isberg, J. (2018). Arrays of Point-Absorbing Wave Energy Converters in Short-Crested Irregular Waves. Energies, 11, Article ID 964.
Open this publication in new window or tab >>Arrays of Point-Absorbing Wave Energy Converters in Short-Crested Irregular Waves
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2018 (English)In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 11, article id 964Article in journal (Refereed) Published
Abstract [en]

For most wave energy technology concepts, large-scale electricity production and cost-efficiency require that the devices are installed together in parks. The hydrodynamical interactions between the devices will affect the total performance of the park, and the optimization of the park layout and other park design parameters is a topic of active research. Most studies have considered wave energy parks in long-crested, unidirectional waves. However, real ocean waves can be short-crested, with waves propagating simultaneously in several directions, and some studies have indicated that the wave energy park performance might change in short-crested waves. Here, theory for short-crested waves is integrated in an analytical multiple scattering method, and used to evaluate wave energy park performance in irregular, short-crested waves with different number of wave directions and directional spreading parameters. The results show that the energy absorption is comparable to the situation in long-crested waves, but that the power fluctuations are significantly lower.

National Category
Energy Systems Marine Engineering
Identifiers
urn:nbn:se:uu:diva-349295 (URN)10.3390/en11040964 (DOI)
Available from: 2018-04-25 Created: 2018-04-25 Last updated: 2018-05-03Bibliographically approved
Remouit, F., Chatzigiannakou, M.-A., Bender, A., Temiz, I., Sundberg, J. & Engström, J. (2018). Deployment and Maintenance of Wave Energy Converters at the Lysekil Research Site: A Comparative Study on the Use of Divers and Remotely-Operated Vehicles. Journal of Marine Science and Engineering, 6(2), Article ID 39.
Open this publication in new window or tab >>Deployment and Maintenance of Wave Energy Converters at the Lysekil Research Site: A Comparative Study on the Use of Divers and Remotely-Operated Vehicles
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2018 (English)In: Journal of Marine Science and Engineering, E-ISSN 2077-1312, Vol. 6, no 2, article id 39Article in journal (Refereed) Published
Abstract [en]

Ocean renewable technologies have been rapidly developing over the past years. However, current high installation, operation, maintenance, and decommissioning costs are hindering these offshore technologies to reach a commercialization stage. In this paper we focus on the use of divers and remotely-operated vehicles during the installation and monitoring phase of wave energy converters. Methods and results are based on the wave energy converter system developed by Uppsala University, and our experience in offshore deployments obtained during the past eleven years. The complexity of underwater operations, carried out by either divers or remotely-operated vehicles, is emphasized. Three methods for the deployment of wave energy converters are economically and technically analyzed and compared: one using divers alone, a fully-automated approach using remotely-operated vehicles, and an intermediate approach, involving both divers and underwater vehicles. The monitoring of wave energy converters by robots is also studied, both in terms of costs and technical challenges. The results show that choosing an autonomous deployment method is more advantageous than a diver-assisted method in terms of operational time, but that numerous factors prevent the wide application of robotized operations. Technical solutions are presented to enable the use of remotely-operated vehicles instead of divers in ocean renewable technology operations. Economically, it is more efficient to use divers than autonomous vehicles for the deployment of six or fewer wave energy converters. From seven devices, remotely-operated vehicles become advantageous.

National Category
Marine Engineering
Identifiers
urn:nbn:se:uu:diva-348816 (URN)10.3390/jmse6020039 (DOI)
Available from: 2018-04-17 Created: 2018-04-17 Last updated: 2018-04-18Bibliographically approved
Giassi, M., Göteman, M., Thomas, S., Engström, J., Eriksson, M. & Isberg, J. (2017). Multi-parameter optimization of hybrid arrays of point absorber Wave Energy Converters. In: Proceedings of the 12th European Wave and Tidal Energy Conference: . Paper presented at 12th European Wave and Tidal Energy Conference (EWTEC), Cork, Ireland, August 27-31, 2017..
Open this publication in new window or tab >>Multi-parameter optimization of hybrid arrays of point absorber Wave Energy Converters
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2017 (English)In: Proceedings of the 12th European Wave and Tidal Energy Conference, 2017Conference paper, Published paper (Refereed)
Series
European Wave and Tidal Energy Conference Series, ISSN 2309-1983
National Category
Marine Engineering Energy Engineering
Identifiers
urn:nbn:se:uu:diva-329393 (URN)
Conference
12th European Wave and Tidal Energy Conference (EWTEC), Cork, Ireland, August 27-31, 2017.
Available from: 2017-09-14 Created: 2017-09-14 Last updated: 2018-01-08Bibliographically approved
Sjökvist, L., Wu, J., Ransley, E., Engström, J., Eriksson, M. & Göteman, M. (2017). Numerical models for the motion and forces of point-absorbing wave energy converters in extreme waves. Ocean Engineering, 145, 1-14
Open this publication in new window or tab >>Numerical models for the motion and forces of point-absorbing wave energy converters in extreme waves
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2017 (English)In: Ocean Engineering, ISSN 0029-8018, E-ISSN 1873-5258, Vol. 145, p. 1-14Article in journal (Refereed) Published
Abstract [en]

Reliable simulation tools are necessary to study the performance and survivability of wave energy devices, since experiments are both expensive and difficult to implement. In particular, survivability in nonlinear, high waves is one of the largest challenges for wave energy, and since the wave loads and dynamics are largely model dependent, each device must be studied separately with validated tools. In this paper, two numerical methods based on fully nonlinear computational fluid dynamics (CFD) are presented and compared with a simpler linear method. All three methods are compared and validated against experimental data for a point-absorbing wave energy converter in nonlinear, high waves. The wave energy converter consists of a floating buoy attached to a linear generator situated on the seabed. The line forces and motion of the buoy are studied, and computational cost and accuracy are compared and discussed. Whereas the simpler linear method is very fast, its accuracy is not sufficient in high and extreme waves, where instead the computationally costly CFD methods are required. The OpenFOAM model showed the highest accuracy, but also a higher computational cost than the ANSYS Fluent model.

National Category
Marine Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-328485 (URN)10.1016/j.oceaneng.2017.08.061 (DOI)000414886600001 ()
Funder
Natural‐Disaster ScienceSwedish Research Council, 2015-04657
Available from: 2017-08-24 Created: 2017-08-24 Last updated: 2018-02-22Bibliographically approved
Remouit, F., Ruiz-Minguela, P. & Engström, J. (2017). Review of Electrical Connectors for Underwater Applications. IEEE Journal of Oceanic Engineering
Open this publication in new window or tab >>Review of Electrical Connectors for Underwater Applications
2017 (English)In: IEEE Journal of Oceanic Engineering, ISSN 0364-9059, E-ISSN 1558-1691Article in journal (Refereed) Accepted
Abstract [en]

The history of underwater electrical connectors is relativelynew: In 1858, the first transatlantic communication cable was created. Sincethen, the need for subsea electrical connectors has been growing very fastin the offshore industry. Today numerous companies offer a large choiceof underwater connectors and assemblies, and it can be intricate to distinguish the different technologies employed for each of them. However theuse, deployment, maintenance, and lifetime of any subsea equipment, froma simple sonar to a wave energy converter, relies on its connectors. Hencethe design of an underwater electrical connector is to be carefully lookedat, and especially for tailor-made applications that have more specific requirements. To produce a good connector, it is necessary to account for thermal, electrical, and mechanical properties, as well as to determine thebest materials that should be used for the application. Finally, connector issues go hand in hand with the deployment and operation of any electrical equipment, and it is of interest to review the different techniques for cable connection, as well as the challenges related to cable layout. Those challenges can be of different nature, but they should all be taken into account for any subsea connection.

Keyword
Cable, connector, electrical, review, subsea, underwater
National Category
Engineering and Technology Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-334294 (URN)10.1109/JOE.2017.2745598 (DOI)
Available from: 2017-11-22 Created: 2017-11-22 Last updated: 2017-11-27
Wang, L., Göteman, M., Engström, J., Eriksson, M. & Isberg, J. (2016). Constrained Optimal Control of Single and Arrays of Point-Absorbing Wave Energy Converters. In: : . Paper presented at Marine Energy Technology Symposium.
Open this publication in new window or tab >>Constrained Optimal Control of Single and Arrays of Point-Absorbing Wave Energy Converters
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2016 (English)Conference paper, Published paper (Refereed)
National Category
Ocean and River Engineering
Identifiers
urn:nbn:se:uu:diva-297190 (URN)
Conference
Marine Energy Technology Symposium
Available from: 2016-06-21 Created: 2016-06-21 Last updated: 2017-04-26Bibliographically approved
Wang, L., Engström, J., Leijon, M. & Isberg, J. (2016). Coordinated Control of Wave Energy Converters Subject to Motion Constraints. Energies, 9(6), Article ID 475.
Open this publication in new window or tab >>Coordinated Control of Wave Energy Converters Subject to Motion Constraints
2016 (English)In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 9, no 6, article id 475Article in journal (Refereed) Published
Abstract [en]

In this paper, a generic coordinated control method for wave energy converters is proposed, and the constraints on motion amplitudes and the hydrodynamic interaction between converters are considered. The objective of the control problem is to maximize the energy converted from ocean waves, and this is achieved by coordinating the power take-off (PTO) damping of each wave energy converter in the frequency domain in each sea state. In a case study, a wave energy farm consisting of four converters based on the concept developed by Uppsala University is studied. In the solution, motion constraints, including constraints on the amplitudes of displacement and velocity, are included. Twelve months of sea states, based on measured wave data at the Lysekil test site on the Swedish west coast, are used in the simulation to evaluate the performance of the wave energy farm using the new method. Results from the new coordinated control method and traditional control method are compared, indicating that the coordinated control of wave energy converters is an effective way to improve the energy production of wave energy farm in harmonic waves.

Place, publisher, year, edition, pages
MDPI: , 2016
Keyword
wave energy farm; coordinated control; optimal damping; motion constraints; frequency domain
National Category
Ocean and River Engineering
Identifiers
urn:nbn:se:uu:diva-297187 (URN)10.3390/en9060475 (DOI)000378854400088 ()
Funder
Swedish Energy AgencyStandUpSwedish National Infrastructure for Computing (SNIC)
Available from: 2016-06-21 Created: 2016-06-21 Last updated: 2017-11-28Bibliographically approved
Wang, L., Engström, J., Leijon, M. & Isberg, J. (2016). Performance of arrays of direct-driven wave energy converters under optimal power take-off damping. AIP Advances, 6, Article ID 085313.
Open this publication in new window or tab >>Performance of arrays of direct-driven wave energy converters under optimal power take-off damping
2016 (English)In: AIP Advances, ISSN 2158-3226, E-ISSN 2158-3226, Vol. 6, article id 085313Article in journal (Refereed) Published
Abstract [en]

It is well known that the total power converted by a wave energy farm is influenced by the hydrodynamic interactions between wave energy converters, especially when they are close to each other. Therefore, to improve the performance of a wave energy farm, the hydrodynamic interaction between converters must be considered, which can be influenced by the power take-off damping of individual converters. In this paper, the performance of arrays of wave energy converters under optimal hydrodynamic interaction and power take-off damping is investigated. This is achieved by coordinating the power take-off damping of individual converters, resulting in optimal hydrodynamic interaction as well as higher production of time-averaged power converted by the farm. Physical constraints on motion amplitudes are considered in the solution, which is required for the practical implementation of wave energy converters. Results indicate that the natural frequency of a wave energy converter under optimal damping will not vary with sea states, but the production performance of a wave energy farm can be improved significantly while satisfying the motion constraints.

National Category
Water Engineering
Identifiers
urn:nbn:se:uu:diva-301092 (URN)10.1063/1.4961498 (DOI)000383909100078 ()
Projects
Performance and Survivability of Wave power Farm
Funder
Swedish Energy Agency, 40421-1
Available from: 2016-08-17 Created: 2016-08-17 Last updated: 2017-11-28Bibliographically approved
Li, W., Isberg, J., Waters, R., Engström, J., Svensson, O. & Leijon, M. (2016). Statistical Analysis of Wave Climate Data Using Mixed Distributions and Extreme Wave Prediction. Energies, 9(6), Article ID 396.
Open this publication in new window or tab >>Statistical Analysis of Wave Climate Data Using Mixed Distributions and Extreme Wave Prediction
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2016 (English)In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 9, no 6, article id 396Article in journal (Refereed) Published
Abstract [en]

The investigation of various aspects of the wave climate at a wave energy test site is essential for the development of reliable and efficient wave energy conversion technology. This paper presents studies of the wave climate based on nine years of wave observations from the 2005-2013 period measured with a wave measurement buoy at the Lysekil wave energy test site located off the west coast of Sweden. A detailed analysis of the wave statistics is investigated to reveal the characteristics of the wave climate at this specific test site. The long-term extreme waves are estimated from applying the Peak over Threshold (POT) method on the measured wave data. The significant wave height and the maximum wave height at the test site for different return periods are also compared. In this study, a new approach using a mixed-distribution model is proposed to describe the long-term behavior of the significant wave height and it shows an impressive goodness of fit to wave data from the test site. The mixed-distribution model is also applied to measured wave data from four other sites and it provides an illustration of the general applicability of the proposed model. The methodologies used in this paper can be applied to general wave climate analysis of wave energy test sites to estimate extreme waves for the survivability assessment of wave energy converters and characterize the long wave climate to forecast the wave energy resource of the test sites and the energy production of the wave energy converters.

Keyword
wave climate, wave energy converter, ocean wave modelling, mixed-distribution model, extreme wave
National Category
Ocean and River Engineering
Identifiers
urn:nbn:se:uu:diva-300069 (URN)10.3390/en9060396 (DOI)000378854400009 ()
Funder
StandUpSwedish Energy Agency
Available from: 2016-08-02 Created: 2016-08-02 Last updated: 2017-11-28Bibliographically approved
Wang, L., Engström, J., Göteman, M. & Isberg, J. (2015). Constrained optimal control of a point absorber wave energy converter with linear generator. Journal of Renewable and Sustainable Energy, 7, Article ID 043127.
Open this publication in new window or tab >>Constrained optimal control of a point absorber wave energy converter with linear generator
2015 (English)In: Journal of Renewable and Sustainable Energy, ISSN 1941-7012, E-ISSN 1941-7012, Vol. 7, article id 043127Article in journal (Refereed) Published
Abstract [en]

This paper investigates a method for optimal control of a point absorbing wave energy converter by considering the constraints on motions and forces in the time domain. The problem is converted to an optimization problem with the cost function being convex quadratic and the constraints being nonlinear. The influence of the constraints on the converter is studied, and the results are compared with uncontrolled cases and established theoretical bounds. Since this method is based on the knowledge of the future sea state or the excitation force, the influence of the prediction horizon is indicated. The resulting performance of the wave energy converter under different regular waves shows that this method leads to a substantial increase in conversion efficiency.

Keyword
wave energy
National Category
Environmental Engineering
Research subject
Engineering Science
Identifiers
urn:nbn:se:uu:diva-263980 (URN)10.1063/1.4928677 (DOI)000360655500046 ()
Funder
Swedish Energy Agency
Available from: 2015-10-05 Created: 2015-10-05 Last updated: 2017-12-01Bibliographically approved
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