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Offshore Wind Structures
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Offshore Wind Structures

A special issue of Journal of Marine Science and Engineering (ISSN 2077-1312).

Deadline for manuscript submissions: closed (30 September 2018) | Viewed by 27395

Special Issue Editor

Prof. Dr. Lance Manuel

E-Mail Website
Guest Editor
Department of Civil, Architectural and Environmental Engineering, The University of Texas at Austin, Austin, TX, USA
Interests: reliability of offshore structures; offshore renewable energy; floating platforms; uncertainty quantification
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

While offshore wind energy generation is being considered in many regions of the world today, there remain several open and active areas of research that are seeking answers to critical questions, of which answers will accelerate the development of offshore wind energy. Some of the more prominent questions deal with reliability and safety. Related to this are considerations of the role of uncertainty in safety factor calibration and in design guidelines and standards. Validation of the same requires field studies and high-fidelity modeling of individual wind turbines and entire arrays, including interactions due to wake effects. Offshore wind turbines and support structures, depending on the marine environment and external conditions, need to consider cost-effective technologies, including the possibility of bottom-supported and floating concepts, the use of control, and the consideration of aerodynamics and structural dynamics. In some regions, tropical cyclones will need special consideration.

The focus of this Special Issue is to provide the state-of-the-art on the issues above, and a forum for presentation of recent efforts that aim to advance our knowledge in the exciting field of offshore wind energy.

Topics of interest for publication in this Special Issue include, but are not limited to, the following:

•  Bottom-supported and floating concepts and technology

•  Probabilistic design, safety factor calibration, certification

•  External conditions, design load cases

•  Field monitoring

•  Structural dynamics

•  Aerodynamic effects

•  Wakes and array effects

•  Wave loading and hydrodynamics

•  Tropical cyclones

•  Foundations

•  Operations and maintenance

I look forward to receiving your contributions in the form of research papers, state-of-the-art reviews, and case studies. Thank you!

 

Prof. Dr. Lance Manuel
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Journal of Marine Science and Engineering is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

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Published Papers (5 papers)

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Research

17 pages, 1635 KiB  
Article
Iterative Frequency-Domain Response of Floating Offshore Wind Turbines with Parametric Drag
by Frank Lemmer, Wei Yu and Po Wen Cheng
J. Mar. Sci. Eng. 2018, 6(4), 118; https://doi.org/10.3390/jmse6040118 - 12 Oct 2018
Cited by 31 | Viewed by 5409
Abstract
Methods for coupled aero-hydro-servo-elastic time-domain simulations of Floating Offshore Wind Turbines (FOWTs) have been successfully developed. One of the present challenges is a realistic approximation of the viscous drag of the wetted members of the floating platform. This paper presents a method for [...] Read more.
Methods for coupled aero-hydro-servo-elastic time-domain simulations of Floating Offshore Wind Turbines (FOWTs) have been successfully developed. One of the present challenges is a realistic approximation of the viscous drag of the wetted members of the floating platform. This paper presents a method for an iterative response calculation with a reduced-order frequency-domain model. It has heave plate drag coefficients, which are parameterized functions of literature data. The reduced-order model does not represent more than the most relevant effects on the FOWT system dynamics. It includes first-order and second-order wave forces, coupled with the wind turbine structural dynamics, aerodynamics and control system dynamics. So far, the viscous drag coefficients are usually defined as constants, independent of the load cases. With the computationally efficient frequency-domain model, it is possible to iterate the drag, such that it fits to the obtained amplitudes of oscillation of the different members. The results show that the drag coefficients vary significantly across operational load conditions. The viscous drag coefficients converge quickly and the method is applicable for concept-level design studies of FOWTs with load case-dependent drag. Full article
(This article belongs to the Special Issue Offshore Wind Structures)
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12 pages, 937 KiB  
Article
Onset of Motion of Sediment underneath Scour Protection around a Monopile
by Anders Wedel Nielsen and Thor Ugelvig Petersen
J. Mar. Sci. Eng. 2018, 6(3), 100; https://doi.org/10.3390/jmse6030100 - 29 Aug 2018
Cited by 10 | Viewed by 3917
Abstract
The stability of scour protections is, potentially, an important issue during the design of fixed foundations for offshore wind turbines. One of the failure mechanisms observed at placed scour protection around offshore foundations is suction of sediment through the scour protection and subsequent [...] Read more.
The stability of scour protections is, potentially, an important issue during the design of fixed foundations for offshore wind turbines. One of the failure mechanisms observed at placed scour protection around offshore foundations is suction of sediment through the scour protection and subsequent sinking of the scour protection. Incipient motion of sediment and the initiation of suction underneath scour protections around piles in the marine environment were studied under waves, current and combined waves and current conditions. The motion of a thin layer of sediment underneath the scour protection was studied through the glass bottom of the test flume, which provided a clear view of the initiation of the motion of the sediment. The results show that the mobility depends on the Keulegan–Carpenter ( K C ) number for the pile, the ratio between waves and current flow and the ratio between the thickness of the scour protection and the base sediment. The critical mobility number is smaller for the wave-dominated situation compared to current-dominated conditions, which again are smaller than for combined waves and current conditions. Consequently, larger K C -numbers cause larger critical mobility numbers than smaller K C -numbers. Design diagrams are presented for the threshold of incipient motion of sediment underneath a scour protection in waves, current and combined waves and current. Full article
(This article belongs to the Special Issue Offshore Wind Structures)
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12 pages, 1873 KiB  
Article
Model Uncertainties for Soil-Structure Interaction in Offshore Wind Turbine Monopile Foundations
by Lars Vabbersgaard Andersen, Thomas Lykke Andersen and Lance Manuel
J. Mar. Sci. Eng. 2018, 6(3), 87; https://doi.org/10.3390/jmse6030087 - 18 Jul 2018
Cited by 9 | Viewed by 4583
Abstract
Monopiles are the most common type of foundation used for bottom-fixed offshore wind turbines. This investigation concerns the influence of uncertainty related to soil–structure interaction models used to represent monopile–soil systems. The system response is studied for a severe sea state. Three wave-load [...] Read more.
Monopiles are the most common type of foundation used for bottom-fixed offshore wind turbines. This investigation concerns the influence of uncertainty related to soil–structure interaction models used to represent monopile–soil systems. The system response is studied for a severe sea state. Three wave-load cases are considered: (i) irregular waves assuming linearity; (ii) highly nonlinear waves that are merged into the irregular wave train; (iii) slamming loads that are included for the nonlinear waves. The extreme response and Fourier amplitude spectra for external moments and mudline bending moments are compared for these load cases where a simpler static pile-cap stiffness and a lumped-parameter model (LPM) are both considered. The fundamental frequency response of the system is well represented by the static pile-cap stiffness model; however, the influence of higher modes (i.e., the second and third modes with frequencies of about 1 Hz and 2 Hz, respectively) is significantly overestimated with the static model compared to the LPM. In the analyzed case, the differences in the higher modes are especially pronounced when slamming loads are not present. Full article
(This article belongs to the Special Issue Offshore Wind Structures)
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24 pages, 1936 KiB  
Article
Response-Spectrum Uncoupled Analyses for Seismic Assessment of Offshore Wind Turbines
by Giuseppe Failla, Fabio Santangelo, Gabriele Foti, Fabio Scali and Felice Arena
J. Mar. Sci. Eng. 2018, 6(3), 85; https://doi.org/10.3390/jmse6030085 - 9 Jul 2018
Cited by 14 | Viewed by 3877
Abstract
According to International Standards and Guidelines, the seismic assessment of offshore wind turbines in seismically-active areas may be performed by combining two uncoupled analyses under wind-wave and earthquake loads, respectively. Typically, the separate earthquake response is calculated by a response-spectrum approach and, for [...] Read more.
According to International Standards and Guidelines, the seismic assessment of offshore wind turbines in seismically-active areas may be performed by combining two uncoupled analyses under wind-wave and earthquake loads, respectively. Typically, the separate earthquake response is calculated by a response-spectrum approach and, for this purpose, structural models of various degrees of complexity may be used. Although response-spectrum uncoupled analyses are currently allowed as alternative to time-consuming fully-coupled simulations, for which dedicated software packages are required, to date no specific studies have been presented on whether accuracy may vary depending on key factors as structural modelling, criteria to calculate wind-wave and earthquake responses, and other relevant issues as the selected support structure, the considered environmental states and earthquake records. This paper will investigate different potential implementations of response-spectrum uncoupled analyses for offshore wind turbines, using various structural models and criteria to calculate the wind-wave and earthquake responses. The case study is a 5-MW wind turbine on two support structures in intermediate waters, under a variety of wind-wave states and real earthquake records. Numerical results show that response-spectrum uncoupled analyses may provide non-conservative results, for every structural model adopted and criteria to calculate wind-wave and earthquake responses. This is evidence that appropriate safety factors should be assumed when implementing response-spectrum uncoupled analyses allowed by International Standards and Guidelines. Full article
(This article belongs to the Special Issue Offshore Wind Structures)
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25 pages, 2494 KiB  
Article
Integrated System Design for a Large Wind Turbine Supported on a Moored Semi-Submersible Platform
by Jinsong Liu, Edwin Thomas, Lance Manuel, D. Todd Griffith, Kelley M. Ruehl and Matthew Barone
J. Mar. Sci. Eng. 2018, 6(1), 9; https://doi.org/10.3390/jmse6010009 - 12 Jan 2018
Cited by 22 | Viewed by 8335
Abstract
Over the past few decades, wind energy has emerged as an alternative to conventional power generation that is economical, environmentally friendly and, importantly, renewable. Specifically, offshore wind energy is being considered by a number of countries to harness the stronger and more consistent [...] Read more.
Over the past few decades, wind energy has emerged as an alternative to conventional power generation that is economical, environmentally friendly and, importantly, renewable. Specifically, offshore wind energy is being considered by a number of countries to harness the stronger and more consistent wind resource compared to that over land. To meet the projected “20% energy from wind by 2030” scenario that was announced in 2006, 54 GW of added wind energy capacity need to come from offshore according to a National Renewable Energy Laboratory (NREL) study. In this study, we discuss the development of a semi-submersible floating offshore platform with a catenary mooring system to support a very large 13.2-MW wind turbine with 100-m blades. An iterative design process is applied to baseline models with Froude scaling in order to achieve preliminary static stability. Structural dynamic analyses are performed to investigate the performance of the new model using a finite element method approach for the tower and a boundary integral equation (panel) method for the platform. The steady-state response of the system under uniform wind and regular waves is first studied to evaluate the performance of the integrated system. Response amplitude operators (RAOs) are computed in the time domain using white-noise wave excitation; this serves to highlight nonlinear, as well as dynamic characteristics of the system. Finally, selected design load cases (DLCs) and the stochastic dynamic response of the system are studied to assess the global performance for sea states defined by wind fields with turbulence and long-crested irregular waves. Full article
(This article belongs to the Special Issue Offshore Wind Structures)
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