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Publications (10 of 89) 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(4), 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, no 4, 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)000434703400275 ()
Funder
Swedish Research Council, 2015-04657Swedish Energy Agency, 40421-1
Available from: 2018-04-25 Created: 2018-04-25 Last updated: 2018-09-19Bibliographically approved
Thomas, S., Giassi, M., Göteman, M., Hann, M., Ransley, E., Isberg, J. & Engström, J. (2018). Performance of a Direct-Driven Wave Energy Point Absorber with High Inertia Rotatory Power Take-off. Energies, 11(9), Article ID 2332.
Open this publication in new window or tab >>Performance of a Direct-Driven Wave Energy Point Absorber with High Inertia Rotatory Power Take-off
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2018 (English)In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 11, no 9, article id 2332Article in journal (Refereed) Published
Abstract [en]

An alternating rotatory generator using an eddy current break is developed as a physicalscale model of a direct-driven floating point absorber power take-off (PTO) for wave tank tests. It isshown that this design is a simple and cost-effective way to get an accurate linear damping PTO. Thedevice shows some beneficial characteristics, making it an interesting option for full scale devices:For similar weights the inertia can be significantly higher than for linear generators, allowing it tooperate with natural frequencies close to typical wave frequencies. The influence of the higher inertiaon the power absorption is tested using both a numerical simulation and physical wave tank tests.With the increased inertia the PTO is able to absorb more than double the energy of a comparabledirect-driven linear generator in some sea states. Moreover, the alternating rotatory generator allowsthe absorption characteristic to be tuned by changing the inertia and the generator damping.

Keywords
wave energy; power take-off; direct-driven; wave tank test; physical scale model; natural frequency tuning; floating point absorber
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Electronics; Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-359690 (URN)10.3390/en11092332 (DOI)
Funder
Swedish Energy Agency, 40421-1Swedish Research Council, 2015-04657
Available from: 2018-09-04 Created: 2018-09-04 Last updated: 2018-10-24Bibliographically approved
Wang, L., Isberg, J. & Tedeschi, E. (2018). Review of control strategies for wave energy conversion systems and their validation: the wave-to-wire approach. Renewable & sustainable energy reviews, 81, 366-379
Open this publication in new window or tab >>Review of control strategies for wave energy conversion systems and their validation: the wave-to-wire approach
2018 (English)In: Renewable & sustainable energy reviews, ISSN 1364-0321, E-ISSN 1879-0690, Vol. 81, p. 366-379Article, review/survey (Refereed) Published
Abstract [en]

Ocean waves are a promising source of renewable energy. In this paper, we briefly introduce the characteristics of ocean wave energy and summarize the principles of harvesting ocean energy by wave energy converters. We also review the prototypes or commercial devices deployed in real sea between 2005 and July 2016.

In addition, we present the concept of a wave-to-wire model as a framework to systematically review and compare control strategies for wave energy conversion systems, with a focus on the numerical and experimental validation.

Place, publisher, year, edition, pages
Netherlands: Elsevier, 2018
Keywords
Wave energy converter, Ocean wave energy conversion, Wave-to-wire model, Control strategies, Power take-off, Hydrodynamic control
National Category
Energy Engineering
Identifiers
urn:nbn:se:uu:diva-320904 (URN)10.1016/j.rser.2017.06.074 (DOI)000417070500028 ()
Funder
Swedish Research Council, 40421-1
Available from: 2017-04-26 Created: 2017-04-26 Last updated: 2018-03-12Bibliographically 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: 2018-10-24Bibliographically approved
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
Keywords
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
Suntornwipat, N., Majdi, S., Gabrysch, M. & Isberg, J. (2016). Investigation of transferred-electron oscillations in diamond. Applied Physics Letters, 108(21), Article ID 212104.
Open this publication in new window or tab >>Investigation of transferred-electron oscillations in diamond
2016 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 108, no 21, article id 212104Article in journal (Refereed) Published
Abstract [en]

The recent discovery of Negative Differential Mobility (NDM) in intrinsic single-crystalline diamond enables the development of devices for high frequency applications. The Transferred-Electron Oscillator (TEO) is one example of such devices that uses the benefit of NDM to generate continuous oscillations. This paper presents theoretical investigations of a diamond TEO in the temperature range of 110 to 140K where NDM has been observed. Our simulations map out the parameter space in which transferred-electron oscillations are expected to occur for a specific device geometry. The results are promising and indicate that it is possible to fabricate diamond based TEO devices.

National Category
Condensed Matter Physics Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-298901 (URN)10.1063/1.4952766 (DOI)000377024400026 ()
Funder
Swedish Research Council, 621-2012-5819The Royal Swedish Academy of SciencesÅForsk (Ångpanneföreningen's Foundation for Research and Development), 15-288
Note

Correction in: Applied Physics Letters 108(23) article number 239901 DOI: 10.1063/1.4953887

Available from: 2016-07-12 Created: 2016-07-12 Last updated: 2018-04-15Bibliographically approved
Majdi, S., Gabrysch, M., Kumar Kovi, K., Suntornwipat, N., Friel, I. & Isberg, J. (2016). Low temperature conduction-band transport in diamond. Applied Physics Letters, 109(16), Article ID 162106.
Open this publication in new window or tab >>Low temperature conduction-band transport in diamond
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2016 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 109, no 16, article id 162106Article in journal (Refereed) Published
Abstract [en]

By performing Time-of-Flight measurements on high-purity single-crystalline chemical vapor deposited diamond, we are able to extract the electron drift velocity of valley-polarized electrons in the low-injection regime. The aim of this study is to improve the understanding of the mechanisms involved in the conduction-band transport of valley-polarized electrons. The measurements were carried out within the temperature range of 10-80 K, and the experimental results are systematically compared with Monte Carlo charge transport simulations. We observe a rapid enhancement of the electron mobility with decreasing temperature, which reveals that inelastic effects in electron-phonon scattering become important below similar to 40 K. In addition, we obtain the momentum relaxation rate for electrons with different valley polarizations.

National Category
Condensed Matter Physics Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-310010 (URN)10.1063/1.4964720 (DOI)000386933200020 ()
Funder
Swedish Research Council, 621-2014-6026ÅForsk (Ångpanneföreningen's Foundation for Research and Development), 15-288Carl Tryggers foundation , 14:151 15:225Swedish National Infrastructure for Computing (SNIC), SNIC2014-3-65
Available from: 2016-12-12 Created: 2016-12-09 Last updated: 2018-04-15Bibliographically approved
Suntornwipat, N., Gabrysch, M., Majdi, S., Twitchen, D. J. & Isberg, J. (2016). Magnetotransport study of valley-polarized electrons in synthetic diamond. Physical Review B, 94(3), Article ID 035408.
Open this publication in new window or tab >>Magnetotransport study of valley-polarized electrons in synthetic diamond
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2016 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, no 3, article id 035408Article in journal (Refereed) Published
Abstract [en]

We demonstrate that the highly stable valley-polarized electron states in ultrapure single-crystalline diamond allow for investigation of charge transport, magnetoresistivity, and determination of the dominant scattering mechanism. The Hall effect gives rise to nonisotropic contributions in the mobility tensor that were measured at a temperature of 70 K in a time-of-flight setup with an added magnetic field. The observations of the magnetotransport of valley-polarized electrons in diamond are compared with both Monte Carlo simulations and an analytical model based on the Boltzmann transport equation. We establish that acoustic phonon scattering is the dominant electron scattering mechanism at 70 K for each of the valley polarizations in the investigated samples.

National Category
Condensed Matter Physics Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-300466 (URN)10.1103/PhysRevB.94.035408 (DOI)000379717700005 ()
Funder
Swedish Research Council, 621-2014-6026ÅForsk (Ångpanneföreningen's Foundation for Research and Development), 15-288Swedish National Infrastructure for Computing (SNIC), SNIC2014-3-65
Available from: 2016-08-09 Created: 2016-08-09 Last updated: 2018-04-15Bibliographically 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
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-2197-5352

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