Structure Design and Assessment of a Floating Foundation for Offshore Wind Turbines

Abstract This paper summarizes the assessment of the structural analysis and design of a floating foundation for offshore floating wind turbine (FWT) based on DNVGL standard and Eurocode in terms of economy and reliability. The wind loads are calculated using empirical equations. The wave loads are obtained and verified using various methods including hand calculation, AQWA and Flow-3D. It is found that the shell thickness could be reduced significantly by introducing the stiffeners (stringer or ring), which can decrease the weight of the hull and lower the cost. While DNVGL and Eurocode yield similar design solutions if using plane shell structures, Eurocode significantly underestimates the buckling resistance of stiffened cylindrical shells.

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Advanced Concept Offshore Wind Turbine Development

Journal of Advanced Computational Intelligence and Intelligent Informatics ◽

10.20965/jaciii.2014.p0728 ◽

2014 ◽

Vol 18 (5) ◽

pp. 728-735 ◽

Cited By ~ 1

Author(s):

Abdollah A. Afjeh ◽

◽

Brett Andersen ◽

Jin Woo Lee ◽

Mahdi Norouzi ◽

...

Keyword(s):

Wind Energy ◽

Wind Turbine ◽

Wind Turbines ◽

Cost Savings ◽

Offshore Wind ◽

Offshore Wind Turbine ◽

Offshore Wind Energy ◽

Offshore Wind Turbines ◽

Floating Foundation ◽

The Cost

Development of novel offshore wind turbine designs and technologies are necessary to reduce the cost of offshore wind energy since offshore wind turbines need to withstand ice and waves in addition to wind, a markedly different environment from their onshore counterparts. This paper focuses on major design challenges of offshore wind turbines and offers an advanced concept wind turbine that can significantly reduce the cost of offshore wind energy as an alternative to the current popular designs. The design consists of a two-blade, downwind rotor configuration fitted to a fixed bottom or floating foundation. Preliminary results indicate that cost savings of nearly 25% are possible compared with the conventional upwind wind turbine designs.

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Underwater Power Kites

Mechanical Engineering ◽

10.1115/1.2017-jun-2 ◽

2017 ◽

Vol 139 (06) ◽

pp. 38-43

Author(s):

David J. Olinger

Keyword(s):

Low Cost ◽

Power Grid ◽

Offshore Wind ◽

Turbine Generator ◽

Research Teams ◽

Offshore Wind Turbines ◽

Hydrokinetic Turbines ◽

Available Technology ◽

Economic Analyses ◽

The Cost

This article discusses different features of underwater kites and its advantages in the turbine industry. The underwater kite moves fastest when it slaloms through the current in this way, much like a water skier. Electricity generated by the mounted turbine generator is transmitted along the tether to a moored, floating buoy, and then onto the power grid. This concept, now known as the Tethered Undersea Kite (TUSK), was first conceived by Magnus Landberg, a researcher in Sweden, in 2007. Underwater kites look to be feasible to build using commercial available technology. According to economic analyses conducted by other research teams, TUSK systems may be able to produce electricity at about half the current cost for fixed hydrokinetic turbines, and a bit below the cost of the power produced by offshore wind turbines. Those researchers attribute the lower costs to improved power-to-weight ratios derived from replacing the inner blades and support tower of a traditional turbine with a lightweight, low-cost tether.

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Studying the Potential of a Novel Multiple-Generator Drivetrain in Wind Energy Conversion Systems

Volume 4B: Dynamics, Vibration and Control ◽

10.1115/imece2013-63017 ◽

2013 ◽

Author(s):

N. Goudarzi ◽

W. D. Zhu

Keyword(s):

Wind Turbines ◽

Offshore Wind ◽

Offshore Wind Turbines ◽

Wind Energy Conversion ◽

Advantages And Disadvantages ◽

Wind Energy Conversion Systems ◽

Energy Conversion Systems ◽

Switch Mechanism ◽

The Cost ◽

Operational Range

A novel multiple generator drivetrain (MGD), where a single large generator in a wind turbine is replaced by multiple generators with the same or different rated powers, is proposed along with an automatic switch mechanism as an alternative to an existing MGD. To better understand the advantages and disadvantages of having a MGD in onshore/offshore wind turbines, a MGD with a single or double stage gearbox and multiple generators is compared with a conventional drivetrain with a triple-stage gearbox and a large induction generator. A simple mathematical model for a MGD with an automatic switch is developed, a novel prototype of a MGD is designed and fabricated, and experiments are conducted on the prototype. It is concluded that a multiple-generator drivetrain with generators operating individually or in parallel through an automatic switch mechanism has a better potential of improving the efficiency and the reliability, expanding the operational range, and reducing the cost of offshore and onshore wind turbines than the existing MGD configuration.

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Comparison of Spar and Semisubmersible Floater Concepts of Offshore Wind Turbines Using Long-Term Analysis

Journal of Offshore Mechanics and Arctic Engineering ◽

10.1115/1.4031312 ◽

2015 ◽

Vol 137 (6) ◽

Cited By ~ 6

Author(s):

Hasan Bagbanci ◽

D. Karmakar ◽

C. Guedes Soares

Keyword(s):

Wind Turbine ◽

Wind Turbines ◽

Transfer Functions ◽

Probability Distributions ◽

Offshore Wind ◽

Short Term ◽

Offshore Wind Turbines ◽

Floating Wind Turbine ◽

Offshore Floating Wind Turbine

The long-term probability distributions of a spar-type and a semisubmersible-type offshore floating wind turbine response are calculated for surge, heave, and pitch motions along with the side-to-side, fore–aft, and yaw tower base bending moments. The transfer functions for surge, heave, and pitch motions for both spar-type and semisubmersible-type floaters are obtained using the fast code and the results are also compared with the results obtained in an experimental study. The long-term predictions of the most probable maximum values of motion amplitudes are used for design purposes, so as to guarantee the safety of the floating wind turbines against overturning in high waves and wind speed. The long-term distribution is carried out using North Atlantic wave data and the short-term floating wind turbine responses are represented using Rayleigh distributions. The transfer functions are used in the procedure to calculate the variances of the short-term responses. The results obtained for both spar-type and semisubmersible-type offshore floating wind turbine are compared, and the study will be helpful in the assessments of the long-term availability and economic performance of the spar-type and semisubmersible-type offshore floating wind turbine.

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On the Use of Scaled Model Tests for Analysis and Design of Offshore Wind Turbines

Developments in Geotechnical Engineering - Geotechnics for Natural and Engineered Sustainable Technologies ◽

10.1007/978-981-10-7721-0_6 ◽

2018 ◽

pp. 107-129 ◽

Cited By ~ 1

Author(s):

Subhamoy Bhattacharya ◽

Georgios Nikitas ◽

Saleh Jalbi

Keyword(s):

Wind Turbines ◽

Model Tests ◽

Offshore Wind ◽

Scaled Model ◽

Analysis And Design ◽

Offshore Wind Turbines

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Comparative Modal Analysis of Monopile and Jacket Supported Offshore Wind Turbines including Soil-Structure Interaction

International Journal of Structural Stability and Dynamics ◽

10.1142/s021945542042016x ◽

2020 ◽

Vol 20 (10) ◽

pp. 2042016

Author(s):

A. Abdullahi ◽

Y. Wang ◽

S. Bhattacharya

Keyword(s):

Wind Turbines ◽

Soil Structure ◽

Natural Frequencies ◽

Model Updating ◽

Offshore Wind ◽

Fe Model ◽

Analysis And Design ◽

Offshore Wind Turbines ◽

Future Design ◽

Wide Range

Offshore wind turbines (OWTs) have emerged as a reliable source of renewable energy, witnessing massive deployment across the world. While there is a wide range of support foundations for these structures, the monopile and jacket are most utilized so far; their deployment is largely informed by water depths and turbine ratings. However, the recommended water depth ranges are often violated, leading to cross-deployment of the two foundation types. This study first investigates the dynamic implication of this practice to incorporate the findings into future analysis and design of these structures. Detailed finite element (FE) models of Monopile and Jacket supported OWTs are developed in the commercial software, ANSYS. Nonlinear soil springs are used to simulate the soil-structure interactions (SSI) and the group effects of the jacket piles are considered by using the relevant modification factors. Modal analyzes of the fixed and flexible-base cases are carried out, and natural frequencies are chosen as the comparison parameters throughout the study. Second, this study constructs a few-parameters SSI model for the two FE models developed above, which aims to use fewer variables in the FE model updating process without compromising its simulation quality. Maximum lateral soil resistance and soil depths are related using polynomial equations, this replaces the standard nonlinear soil spring model. The numerical results show that for the same turbine rating and total height, jacket supported OWTs generally have higher first-order natural frequencies than the monopile supported OWTs, while the reverse is true for the second-order vibration modes, for both fixed and flexible foundations. This contributes to future design considerations of OWTs. On the other hand, with only two parameters, the proposed SSI model has achieved the same accuracy as that using the standard model with seven parameters. It has the potential to become a new SSI model, especially for the identification of soil properties through the model updating process.

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The Effect of the Second-Order Wave Loads on Drift Motion of a Semi-Submersible Floating Offshore Wind Turbine

Journal of Marine Science and Engineering ◽

10.3390/jmse8110859 ◽

2020 ◽

Vol 8 (11) ◽

pp. 859

Author(s):

Thanh-Dam Pham ◽

Hyunkyoung Shin

Keyword(s):

Wind Turbine ◽

Wind Turbines ◽

Second Order ◽

Offshore Wind ◽

Offshore Wind Turbine ◽

Wave Loads ◽

Hydrodynamic Loads ◽

Drift Motion ◽

Offshore Wind Turbines ◽

Floating Offshore Wind Turbines

Floating offshore wind turbines (FOWTs) have been installed in Europe and Japan with relatively modern technology. The installation of floating wind farms in deep water is recommended because the wind speed is stronger and more stable. The design of the FOWT must ensure it is able to withstand complex environmental conditions including wind, wave, current, and performance of the wind turbine. It needs simulation tools with fully integrated hydrodynamic-servo-elastic modeling capabilities for the floating offshore wind turbines. Most of the numerical simulation approaches consider only first-order hydrodynamic loads; however, the second-order hydrodynamic loads have an effect on a floating platform which is moored by a catenary mooring system. At the difference-frequencies of the incident wave components, the drift motion of a FOWT system is able to have large oscillation around its natural frequency. This paper presents the effects of second-order wave loads to the drift motion of a semi-submersible type. This work also aimed to validate the hydrodynamic model of Ulsan University (UOU) in-house codes through numerical simulations and model tests. The NREL FAST code was used for the fully coupled simulation, and in-house codes of UOU generates hydrodynamic coefficients as the input for the FAST code. The model test was performed in the water tank of UOU.

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Reproduction of Monopile Ringing Events in Reduced-Duration Model Tests

Volume 7B: Ocean Engineering ◽

10.1115/omae2017-61034 ◽

2017 ◽

Author(s):

Erin E. Bachynski ◽

Trygve Kristiansen

Keyword(s):

Time Windows ◽

Full Scale ◽

Offshore Wind ◽

Maximum Deviation ◽

Wave Loads ◽

Traditional Practice ◽

Hydrodynamic Loads ◽

Offshore Wind Turbines ◽

Irregular Wave ◽

Structural Responses

Monopile support structures for offshore wind turbines may experience ringing-type responses in steep wave conditions. In order to experimentally capture the statistical distribution of the hydrodynamic loads and structural responses, traditional practice is to generate many 3-hour (full scale) realizations of the relevant sea states. An experimental campaign at 1:48 scale was carried out in the Lilletanken wave tank at NTNU/MARINTEK in order to examine the possibility of using shorter time windows to recreate irregular wave ringing events. Wave elevations and hydrodynamic loads on a rigid vertical circular cylinder in 27 m water depth were measured for a variety of 3-hour, 450 s (7.5-minute), 800 s (13.3-minute), 1150 s (19.2-minute), and 1500 s (25-minute) wave realizations, where all durations are listed in full scale. Wavelet transformations and a single degree-of-freedom oscillator were used to investigate the magnitude and repeatability of the high-frequency content of the wave loads. Large variations in the repeatability were seen among events. On average, the repeatability in the ringing response was 4.2 % for 3-hour tests, while 13.3-minute tests reproduced the same events within 9.1 %. The maximum deviation was, nonetheless, much higher when only 13.3 minutes were used.

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Experimental Study on the Wave Loads on Monopile and Jacket Type Support of Offshore Wind Turbines

Volume 11A: Honoring Symposium for Professor Carlos Guedes Soares on Marine Technology and Ocean Engineering ◽

10.1115/omae2018-77715 ◽

2018 ◽

Author(s):

Jing Zhang ◽

Qin Liu ◽

Xing Hua Shi ◽

C. Guedes Soares

Keyword(s):

Experimental Study ◽

Wind Turbine ◽

Nonlinear Wave ◽

Wave Force ◽

Offshore Wind ◽

Offshore Wind Turbine ◽

Wave Forces ◽

Wave Loads ◽

Morison Equation ◽

Offshore Wind Turbines

As the offshore fixed wind turbine developed, more ones will be installed in the sea field with the depth 15–50 meters. Wave force will be one of the main forces that dominate the design of the wind turbine base, which is calculated using the Morison equation traditionally. This method can predict the wave forces for the small cylinders if the drag and inertia coefficients are obtained accurately. This paper will give a series scaled tests of monopile and jacket type base of the offshore wind turbine in tank to study the nonlinear wave loads.

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