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Foundation Systems for Offshore Wind Turbines
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Foundation Systems for Offshore Wind Turbines

A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "A3: Wind, Wave and Tidal Energy".

Deadline for manuscript submissions: closed (31 March 2022) | Viewed by 88939

Special Issue Editor

Prof. Dr. Lars Vabbersgaard Andersen

E-Mail Website
Guest Editor
Department of Engineering, Aarhus University, Navitas, Inge Lehmanns Gade 10, DK-8000 Aarhus C, Denmark
Interests: soil dynamics; soil–structure interaction; numerical methods; foundations; wind turbines
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear colleagues,

To meet the future requirements of energy production and reduce greenhouse gas emissions, further development of renewable energy sources is required. In this regard, offshore wind power has evolved to a technological level where the cost of energy is now competitive with fossil fuels. However, this requires installation of extremely large and flexible structures, often under harsh offshore conditions, to exploit the full potential of this energy source. Thus, new challenges concerning structural safety and design have arisen, including the development of foundations and support structures for use in deeper waters and sites that may be prone to strong winds, waves, earthquakes, or ice loading.

This Special Issue focuses on the development of foundations and support structures for offshore wind turbines. Contributions may concern novel concepts; physical and computational modeling techniques; production, installation, and decommissioning methods; sustainability and life cycle analysis; cost reduction; inspection and maintenance; case studies; and the development of codes and standards.

Relevant topics include geotechnical site assessment and geological models; static, cyclic, and dynamic soil–structure interactions; the design and analysis of foundations and support structures, including bottom-fixed and floating concepts; fatigue, creep, damping, and other time effects; buckling and other instability issues; structure–fluid interactions, scour and liquefaction, and structure–soil–fluid interactions; integrated analysis of loads, structures, foundations, and soil; constitutive modeling of soil and foundation materials as well as modeling of soil–structure interfaces; macro and super-element models; and multi-scale and multi-physics modelling.

Manuscripts with novel contributions to the field as well as review papers are welcome.

Prof. Dr. Lars Vabbersgaard Andersen
Guest Editor

Manuscript Submission Information

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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. Energies is an international peer-reviewed open access semimonthly 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.

Keywords

  • wind power
  • ocean engineering
  • offshore technology
  • foundations
  • geotechnical engineering
  • soil mechanics
  • structural dynamics
  • multi-physics
  • structural design
  • structural analysis
  • loads

Published Papers (21 papers)

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21 pages, 2657 KiB  
Article
Vertical Dynamic Impedance of a Viscoelastic Pile in Arbitrarily Layered Soil Based on the Fictitious Soil Pile Model
by Xiaoyan Yang, Lixing Wang, Wenbing Wu, Hao Liu, Guosheng Jiang, Kuihua Wang and Guoxiong Mei
Energies 2022, 15(6), 2087; https://0-doi-org.brum.beds.ac.uk/10.3390/en15062087 - 12 Mar 2022
Cited by 7 | Viewed by 1870
Abstract
The vertical vibration of a viscoelastic pile immersed in arbitrarily layered soil is investigated by taking the interaction among pile, pile surrounding soil (PSS) and pile end soil (PES) into account. Firstly, considering both the stratification and stress wave effect of soil, a [...] Read more.
The vertical vibration of a viscoelastic pile immersed in arbitrarily layered soil is investigated by taking the interaction among pile, pile surrounding soil (PSS) and pile end soil (PES) into account. Firstly, considering both the stratification and stress wave effect of soil, a mathematical model of the pile–soil system is established based on the fictitious soil pile (FSP) model. Then, utilizing the impedance function transfer method and Laplace transform technique, the analytical solutions of the vertical dynamic impedance of pile are derived in the frequency domain. The analytical solutions are validated by comparing them with other existing solutions. Finally, a parametric study is put forward to investigate the properties of PES on the vertical dynamic impedance of pile. The results reveal that the properties of PES have a significant effect on the vertical dynamic impedance of pile, but there is a critical influence thickness for this effect. For the cases of the PES thickness exceeding the critical influence thickness, further increase of PES thickness will not affect the dynamic behavior of the pile–soil system. Full article
(This article belongs to the Special Issue Foundation Systems for Offshore Wind Turbines)
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14 pages, 4762 KiB  
Article
Scale Tests to Estimate Penetration Force and Stress State of the Silica Sand in Windfarm Foundations
by Jorge Soriano Vicedo, Javier García Barba, Jorge Luengo Frades and Vicente Negro Valdecantos
Energies 2021, 14(18), 5904; https://0-doi-org.brum.beds.ac.uk/10.3390/en14185904 - 17 Sep 2021
Cited by 2 | Viewed by 1528
Abstract
The analysis of the soil behavior when the pile is driving into the seabed in offshore wind platforms is one of the major problems associated with this new form of clean energy generation. At present, there are no scaled studies carried out analyzing [...] Read more.
The analysis of the soil behavior when the pile is driving into the seabed in offshore wind platforms is one of the major problems associated with this new form of clean energy generation. At present, there are no scaled studies carried out analyzing the mechanical and deformational behavior of both the material of the pile supporting the engine (large steel hollow piles with a diameter of 8 m and a thickness of 15–20 cm) and the soil where the pile is driven. Usually, these elements are installed on sands with a very small grain size displaced from the limits of dry–wet beach (water limit) toward the offshore limits, which prevents them from returning to their previous location in a natural way. This paper presents results obtained from scale tests in a steel pool to analyze the behavior of the sand where the piles were installed. First, the California Bearing Ratio (CBR) test was carried out to estimate the soil behavior in similar conditions to the steel pool. The scale tests consisted of the penetration of the steel tube into the sand using a hydraulic press. The objective was to compare the results for three tubes with different diameters, three different speeds, and two kinds of ending on the extreme of the tested element. Full article
(This article belongs to the Special Issue Foundation Systems for Offshore Wind Turbines)
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27 pages, 13090 KiB  
Article
Seismic Design of Offshore Wind Turbines: Good, Bad and Unknowns
by Subhamoy Bhattacharya, Suryakanta Biswal, Muhammed Aleem, Sadra Amani, Athul Prabhakaran, Ganga Prakhya, Domenico Lombardi and Harsh K. Mistry
Energies 2021, 14(12), 3496; https://0-doi-org.brum.beds.ac.uk/10.3390/en14123496 - 12 Jun 2021
Cited by 25 | Viewed by 9868
Abstract
Large scale offshore wind farms are relatively new infrastructures and are being deployed in regions prone to earthquakes. Offshore wind farms comprise of both offshore wind turbines (OWTs) and balance of plants (BOP) facilities, such as inter-array and export cables, grid connection etc. [...] Read more.
Large scale offshore wind farms are relatively new infrastructures and are being deployed in regions prone to earthquakes. Offshore wind farms comprise of both offshore wind turbines (OWTs) and balance of plants (BOP) facilities, such as inter-array and export cables, grid connection etc. An OWT structure can be either grounded systems (rigidly anchored to the seabed) or floating systems (with tension legs or catenary cables). OWTs are dynamically-sensitive structures made of a long slender tower with a top-heavy mass, known as Nacelle, to which a heavy rotating mass (hub and blades) is attached. These structures, apart from the variable environmental wind and wave loads, may also be subjected to earthquake related hazards in seismic zones. The earthquake hazards that can affect offshore wind farm are fault displacement, seismic shaking, subsurface liquefaction, submarine landslides, tsunami effects and a combination thereof. Procedures for seismic designing OWTs are not explicitly mentioned in current codes of practice. The aim of the paper is to discuss the seismic related challenges in the analysis and design of offshore wind farms and wind turbine structures. Different types of grounded and floating systems are considered to evaluate the seismic related effects. However, emphasis is provided on Tension Leg Platform (TLP) type floating wind turbine. Future research needs are also identified. Full article
(This article belongs to the Special Issue Foundation Systems for Offshore Wind Turbines)
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15 pages, 8031 KiB  
Article
Experimental Evaluation of Dynamic Rock Scour Protection in Morphodynamic Environments for Offshore Wind Jackets
by Javier Sarmiento, Raúl Guanche, Arantza Iturrioz, Teresa Ojanguren, Alberto Ávila and César Yanes
Energies 2021, 14(12), 3379; https://0-doi-org.brum.beds.ac.uk/10.3390/en14123379 - 8 Jun 2021
Cited by 3 | Viewed by 3260
Abstract
Bottom-fixed offshore wind turbines are generally built on continental-shelf sections that are morphodynamically active due to their shallow depths and severe wave and current conditions. Such sites are commonly protected against scour to prevent the loss of structural stability. Scour protection can be [...] Read more.
Bottom-fixed offshore wind turbines are generally built on continental-shelf sections that are morphodynamically active due to their shallow depths and severe wave and current conditions. Such sites are commonly protected against scour to prevent the loss of structural stability. Scour protection can be designed using static or dynamic solutions. Designing dynamic protection requires experimental validation, especially for singular or unconventional structures. This article presents an experimental method for the laboratory analysis of scour protection for jacket foundations placed at morphodynamically active sites. The test campaign was conducted within the project East Anglia ONE (UK) as part of the asset owner studies and aimed to evaluate operation and maintenance (O&M) aspects, independent of the contractor’s original design assessments. The physical experiments explored morphodynamic changes on the sea bottom and their importance to scour protection, as well as the importance of the history of the wave loads to the deformation of the rock scour protection. This was explored by repeating different cumulative tests, including a succession of randomly ordered sea states (Return Period (RP) 1-10-20-50 years). The experimental results show that the deformation of the rock sour protection was the greatest when the most energetic sea states occurred at the beginning of the experimental test campaign. The maximum deformation was at 5D50 when the first test was also the most energetic, while it was at 3D50 when not included as the first test, yielding a 40% reduction in the scour protection deformation. Full article
(This article belongs to the Special Issue Foundation Systems for Offshore Wind Turbines)
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17 pages, 8407 KiB  
Article
A Methodology for Estimating the Position of the Engineering Bedrock for Offshore Wind Farm Seismic Demand in Taiwan
by Yu-Shu Kuo, Tzu-Ling Weng, Hui-Ting Hsu, Hsing-Wei Chang, Yun-Chen Lin, Shang-Chun Chang, Ya-Jhu Chuang, Yu-Hsiu Tseng and Yih-Ting Wong
Energies 2021, 14(9), 2474; https://0-doi-org.brum.beds.ac.uk/10.3390/en14092474 - 26 Apr 2021
Viewed by 2040
Abstract
Taiwan lies in the circum-Pacific earthquake zone. The seabed soil of offshore wind farms in Taiwan is mainly composed of loose silty sand and soft, low-plasticity clay. The seismic demand for offshore wind turbines has been given by the local code. Ground-motion analysis [...] Read more.
Taiwan lies in the circum-Pacific earthquake zone. The seabed soil of offshore wind farms in Taiwan is mainly composed of loose silty sand and soft, low-plasticity clay. The seismic demand for offshore wind turbines has been given by the local code. Ground-motion analysis is required to consider the site effects of the soil liquefaction potential evaluation and the foundation design of offshore wind turbines. However, the depth of the engineering bedrock for ground motion analysis is not presented in the local code. In this study, we develop a three-dimensional ground model of an offshore wind farm in the Changhua area, through use of collected in situ borehole and PS (P wave (compression) and S (shear) wave velocities) logging test data. The engineering bedrock is the sediment at the depth where the average shear wave velocity of soil within 30 m, Vsd30, is larger than 360 m/s. In this ground model, the shear wave velocity of each type of soil is quantified using the seismic empirical formulation developed in this study. The results indicate that the engineering bedrock lies at least 49.5–83 m beneath the seabed at the Changhua offshore wind farm. Based on these findings, it is recommended that drilling more than 100 m below the seabed be done to obtain shear wave velocity data for a ground response analysis of the seismic force assessment of offshore wind farm foundation designs. Full article
(This article belongs to the Special Issue Foundation Systems for Offshore Wind Turbines)
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13 pages, 4539 KiB  
Article
Impacts of Mooring-Lines Hysteresis on Dynamic Response of Spar Floating Wind Turbine
by Weimin Chen, Shuangxi Guo, Yilun Li and Yijun Shen
Energies 2021, 14(8), 2109; https://0-doi-org.brum.beds.ac.uk/10.3390/en14082109 - 9 Apr 2021
Cited by 5 | Viewed by 1972
Abstract
Floating wind turbines often experience larger-amplitude motions caused by wind and ocean wave loads, while mooring-lines, such as catenary and taut mooring-lines, make the structure configurations along with an analysis of the global response more complicated compared to a fixed support foundation. Moreover, [...] Read more.
Floating wind turbines often experience larger-amplitude motions caused by wind and ocean wave loads, while mooring-lines, such as catenary and taut mooring-lines, make the structure configurations along with an analysis of the global response more complicated compared to a fixed support foundation. Moreover, the restoring performance of dynamic mooring-lines exhibits a significant hysteresis behavior, and this hysteresis behavior may have profound impacts on the structural response of floating wind turbines under environmental loads. In this study, using the coupled finite element method, a dynamic simulation model is developed to study the motion responses of a spar floating wind turbine under consideration of mooring-lines hysteresis. In order to consider large-amplitude motion and nonlinear behaviors of catenary mooring-lines, a FEM (finite element method) model is developed based on a combination of 3D nonlinear beam elements and the super-element approach, and the interaction between mooring-lines and seabed is also included. Using our FEM numerical simulations, firstly, the restoring performance of mooring-lines and its hysteresis behavior are studied. Then, the motion responses, e.g., the displacements of the spar float undergoing various wave loads, are examined. The numerical results show that: the restoring stiffness of mooring-lines exhibits significant hysteresis behavior, and the restoring force is directionally dependent. Due to the hysteresis of restoring performance, for a case of regular wave conditions, little change of the spar surge in a steady-state is seen; however, for a case of extreme wave loads, the motion response gets about 14.4% smaller, compared with the quasi-static cases. Full article
(This article belongs to the Special Issue Foundation Systems for Offshore Wind Turbines)
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24 pages, 23158 KiB  
Article
Experimental Investigation of the Movement of an Offshore Floating Platform in Straight Wind, Tornadic Wind, and Downburst Conditions
by Sarah Nichol, Rupp Carriveau, Lindsay Miller, D. S-K. Ting, Djordje Romanic, Adrian Costache and Horia Hangan
Energies 2021, 14(7), 2020; https://0-doi-org.brum.beds.ac.uk/10.3390/en14072020 - 6 Apr 2021
Cited by 3 | Viewed by 2610
Abstract
There is growing interest in multi-purpose offshore floating platforms that: harvest energy from the sun, wind, water, and waves; desalinize water; host agriculture and aquaculture; and house residents. While there are some basic commonalities with well established, oil and gas platforms, lighter variants [...] Read more.
There is growing interest in multi-purpose offshore floating platforms that: harvest energy from the sun, wind, water, and waves; desalinize water; host agriculture and aquaculture; and house residents. While there are some basic commonalities with well established, oil and gas platforms, lighter variants are functionally different with little wind research coverage. Here, we investigate a floating, multi-purpose, light duty platform under 1:150 scaled straight atmospheric boundary layer wind (ABL), tornado like vortices (TLV), and downburst (DB) conditions. The experiments examined the movement of a 1:150 geometrically scaled platform with six degrees of freedom and two mooring Configurations. Four Configurations are studied, (1) Loosely moored platform, (2) Tightly moored platform, (3) Platform with ballast, and (4) Platform with ballast and weight on the deck. DB winds produced the greatest movement, followed by the TLV winds. Little movement was seen under the ABL winds. Loosely moored platforms moved more than tightly moored. Full article
(This article belongs to the Special Issue Foundation Systems for Offshore Wind Turbines)
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18 pages, 6778 KiB  
Article
A Hybrid Method to Evaluate Soil Liquefaction Potential of Seabed at Offshore Wind Farm in Taiwan
by Yu-Shu Kuo, Kai-Jun Chong, Shang-Chun Chang, Juin-Fu Chai and Hui-Ting Hsu
Energies 2021, 14(7), 1853; https://0-doi-org.brum.beds.ac.uk/10.3390/en14071853 - 26 Mar 2021
Viewed by 2190
Abstract
This paper undertakes liquefaction analysis with simplified procedures with standard penetration test (SPT) data and cone penetration test (CPT) data obtained from an offshore wind farm in the Changhua area. The soil liquefaction resistance calculated by the SPT-based simplified procedure suggested by the [...] Read more.
This paper undertakes liquefaction analysis with simplified procedures with standard penetration test (SPT) data and cone penetration test (CPT) data obtained from an offshore wind farm in the Changhua area. The soil liquefaction resistance calculated by the SPT-based simplified procedure suggested by the Japan Railway Association was in agreement with the laboratory results. The CPT is widely used in the site investigation of offshore wind farms. However, Taiwan’s registered professional engineers are still familiar with soil liquefaction analysis for offshore wind farms using SPT-based methods. Hence, a hybrid method that incorporates an SPT–CPT correlation into the New Japan Road Association (NJRA) method is proposed to evaluate the soil liquefaction potential for offshore wind farms in Taiwan. In the case studies of soil liquefaction with five groups of adjacent boreholes in Changhua’s offshore wind farms, the hybrid method shows that the soil liquefaction potential with CPT data is consistent with the results calculated with SPT-based simplified procedures. To quantify the risk of soil liquefaction, Monte Carlo simulation is used to calculate the uncertainty of CPT–qc for estimating the probability of soil liquefaction with the hybrid method. Full article
(This article belongs to the Special Issue Foundation Systems for Offshore Wind Turbines)
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16 pages, 4125 KiB  
Article
Strengthening Mechanism of Studs for Embedded-Ring Foundation of Wind Turbine Tower
by Junling Chen, Jinwei Li, Qize Li and Youquan Feng
Energies 2021, 14(3), 710; https://0-doi-org.brum.beds.ac.uk/10.3390/en14030710 - 30 Jan 2021
Cited by 6 | Viewed by 1932
Abstract
The embedded-ring wind turbine foundations were widely applied in the early development stage of wind power industries because of its properties such as easy installation and adjustment. However, different damages occurred on some embedded-ring wind turbine foundations in recent years. Based on the [...] Read more.
The embedded-ring wind turbine foundations were widely applied in the early development stage of wind power industries because of its properties such as easy installation and adjustment. However, different damages occurred on some embedded-ring wind turbine foundations in recent years. Based on the common damage phenomena of embedded-ring wind turbine foundations, the structural defects and damage mechanisms of embedded-ring wind turbine foundations are analyzed in a gradual way. Cheese head studs are proposed to be welded on the lateral wall of the steel ring to strengthen the connection between the steel ring and the foundation concrete. The foundation pier is elevated 1 m to increase the embedded depth of the steel ring. The circumferential confining pressure is applied on the lateral side of the foundation pier to lead it into a state of pressure. One simplified method is proposed to calculate the contribution of welding studs in this strengthening method. Taking an embedded-ring wind turbine foundation as an example, the numerical analyses for the original foundation and the reinforced one are carried out to compare the stress and strain distribution changes. Based on the numerical results corresponding to the peak and valley value loads, the fatigue life of the concrete and studs are evaluated according to the relevant design codes. The numerical results show that this strengthening method can coordinate the deformation of the embedded steel ring and the foundation concrete by circumferential prestressing and welding studs. The maximum principal stresses of the foundation pier and the fatigue stress range of the concrete around the bottom of the steel ring have been greatly reduced after strengthening. The gaps between the embedded steel ring and the foundation pier are also obviously decreased because of these strengthening measures. The stress concentration phenomena of the concrete around the T-shaped flange have been remarkably improved. The fatigue life can meet the requirements of relevant design codes after strengthening. Therefore, it can be concluded that the safety performance and service life of the embedded-ring foundation can be guaranteed. Full article
(This article belongs to the Special Issue Foundation Systems for Offshore Wind Turbines)
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19 pages, 6351 KiB  
Article
Effects of Relative Roughness and Particle Size on the Interface Behavior of Concrete Suction Caisson Foundation for Offshore Wind Turbines
by Wang-chun Zhang, Hao Jing and Hai-lei Kou
Energies 2020, 13(22), 5866; https://0-doi-org.brum.beds.ac.uk/10.3390/en13225866 - 10 Nov 2020
Cited by 1 | Viewed by 2027
Abstract
The interface behavior between a caisson and the surrounding soil plays an important role in the installation of suction caissons as foundations for offshore wind turbines. A series of shear tests were carried out using a modified direct shear apparatus to study the [...] Read more.
The interface behavior between a caisson and the surrounding soil plays an important role in the installation of suction caissons as foundations for offshore wind turbines. A series of shear tests were carried out using a modified direct shear apparatus to study the interface shear behavior between sand and concrete. Sand samples with three particle size ranges (0.63–1.25 mm, 1.25–2.5 mm, 2.5–5.0 mm) and concrete plates with different relative roughness were used to explore the influence of the relative roughness parameter (Rn) and mean particle size (D50) on shear behavior. The responses from the pure sand shear test are also discussed for comparison. Test results show that the higher the relative roughness (Rn), the greater the maximum shear stress (τmax) appeared. The interface shear stress was weaker than that of the pure sand test. Furthermore, the interface friction angle (φ) of sand–concrete was closely related to the relative roughness of the concrete surface. Under the same conditions, the interface friction angle (φ) increased with relative roughness due to the effect of sand particles breakage and redistribution. By contrast, the effect of the mean particle size (D50) on the interface friction angle (φ) was less significant. However, for the pure sand shear test, the friction angle (φ′) obtained from the traditional shear test apparently increased with D50, indicating that the friction angle was more affected by D50 in the pure sand test than in the interface shear test. Full article
(This article belongs to the Special Issue Foundation Systems for Offshore Wind Turbines)
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20 pages, 21169 KiB  
Article
Representative Environmental Condition for Fatigue Analysis of Offshore Jacket Substructure
by Tsung-Yueh Lin, Yi-Qing Zhao and Hsin-Haou Huang
Energies 2020, 13(20), 5494; https://0-doi-org.brum.beds.ac.uk/10.3390/en13205494 - 20 Oct 2020
Cited by 3 | Viewed by 2339
Abstract
The 20-year cumulative fatigue damage of an offshore jacket substructure was estimated under the long-term local environmental conditions in the Taiwan Strait. Because of the nonlinearity of wave load for slender members of the structure, time-domain simulations of the dynamic finite element model [...] Read more.
The 20-year cumulative fatigue damage of an offshore jacket substructure was estimated under the long-term local environmental conditions in the Taiwan Strait. Because of the nonlinearity of wave load for slender members of the structure, time-domain simulations of the dynamic finite element model were conducted for each sea state. By utilizing the Dirlik method to process the stress signals, the fatigue damages of joints were computed. Concerning the computational time, we propose a probability-based method of using a representative combination of environmental conditions in this study, which can considerably reduce the required number of evaluations prior to determining fatigue damage, thereby improving the process of preliminary design. The results show that only three sea states among 120 can represent 28% of the average damage ratio, and up to 17 sea states fully resolved the fatigue life. Full article
(This article belongs to the Special Issue Foundation Systems for Offshore Wind Turbines)
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22 pages, 49557 KiB  
Article
Assessment of Practical Methods to Predict Accumulated Rotations of Monopile-Supported Offshore Wind Turbines in Cohesionless Ground Profiles
by Saleh Jalbi, Joseph Hilton and Luke Jacques
Energies 2020, 13(15), 3915; https://0-doi-org.brum.beds.ac.uk/10.3390/en13153915 - 31 Jul 2020
Cited by 4 | Viewed by 3093
Abstract
Monopiles supporting offshore wind turbines can experience permanent non-recoverable rotations (or displacements) during their lifetime due to the cyclic nature of hydrodynamic and aerodynamic loading exerted on them. Recent studies in the literature have demonstrated that conventional cyclic p–y curves recommended in different [...] Read more.
Monopiles supporting offshore wind turbines can experience permanent non-recoverable rotations (or displacements) during their lifetime due to the cyclic nature of hydrodynamic and aerodynamic loading exerted on them. Recent studies in the literature have demonstrated that conventional cyclic p–y curves recommended in different codes of practice (API-RP-2GEO and DNVGL-RP-C212) may not capture the effects of long-term cyclic loads as they are independent of the loading profile and the number of applied cycles. Several published methodologies based on laboratory scaled model tests (on sands) exist to determine the effect of cyclic lateral loads on the long-term behaviour of piles. The tests vary in terms of the pile behaviour (rigid or flexible pile), number of applied loading cycles, and the load profile (one-way or two-way loading). The best-fit curves provided by these tests offer practical and cost-efficient methods to quantify the accumulated rotations when compared to Finite Element Method. It is therefore desirable that such methods are further developed to take into account different soil types and the complex nature of the loading. The objective of this paper is to compare the performance of the available formulations under the actions of a typical 35-h (hour) storm as per the Bundesamt für Seeschifffahrt und Hydrographie (BSH) recommendations. Using classical rain flow counting, the loading time-history is discretized into load packets where each packet has a loading profile and number of cycles, which then enables the computation of an equivalent number of cycles of the largest load packet. The results show that the loading profile plays a detrimental role in the result of the accumulated rotation. Furthermore, flexibility of the pile also has an important effect on the response of the pile where predictions obtained from formulations based on flexible piles resulted in a much lower accumulated rotation than tests based on rigid piles. Finally, the findings of this paper are expected to contribute in the design and interpretation of future experimental frameworks for Offshore Wind Turbine (OWT) monopiles in sands, which will include a more realistic loading profile, number of cycles, and relative soil to pile stiffness. Full article
(This article belongs to the Special Issue Foundation Systems for Offshore Wind Turbines)
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17 pages, 4174 KiB  
Article
Pull-Out Capacity and Failure Mechanisms of Strip Anchors in Clay
by Fernando Cañizal, Jorge Castro, Jorge Cañizal and César Sagaseta
Energies 2020, 13(15), 3853; https://0-doi-org.brum.beds.ac.uk/10.3390/en13153853 - 28 Jul 2020
Cited by 3 | Viewed by 1795
Abstract
Plate anchors are a well-established solution for supporting the efforts of floating platforms for wind and marine renewable energies. The behavior of ultrathin rigid plate anchors buried in purely cohesive soils under undrained and plane-strain conditions is analyzed. As already known, a dimensional [...] Read more.
Plate anchors are a well-established solution for supporting the efforts of floating platforms for wind and marine renewable energies. The behavior of ultrathin rigid plate anchors buried in purely cohesive soils under undrained and plane-strain conditions is analyzed. As already known, a dimensional analysis shows that the pull-out capacity of the anchor may be expressed using a weightless break-out factor (Nc0) that only depends on the ratio between the depth and the anchor width (H/B). Using finite element analyses, tabulated values of the weightless break-out factor are provided in this paper and three different failure mechanisms are identified, namely very shallow (quasi-vertical), shallow or intermediate (semi-vertical), and deep (rotational). For very shallow failure mechanisms, the studied problem is completely equivalent to the trapdoor problem because immediate breakaway at the bottom part of the anchor is considered (vented conditions). The existing analytical solutions for the very shallow (Nc0 = 1.956 H/B) and deep cases (Nc = 3π + 2) using the slip-line method are reviewed and an analytical limit is proposed for the first time for the very shallow mechanism (H/B = 1.314). For shallow (intermediate) cases, the failure mechanism is identified and the angle of the main slip lines is numerically evaluated. Full article
(This article belongs to the Special Issue Foundation Systems for Offshore Wind Turbines)
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19 pages, 5245 KiB  
Article
Factors Influencing the Prediction of Pile Driveability Using CPT-Based Approaches
by Luke J. Prendergast, Putri Gandina and Kenneth Gavin
Energies 2020, 13(12), 3128; https://0-doi-org.brum.beds.ac.uk/10.3390/en13123128 - 16 Jun 2020
Cited by 5 | Viewed by 4281
Abstract
This paper investigates the applicability of Cone Penetration Test (CPT)-based axial capacity approaches, used for estimating pile static capacity, to the prediction of pile driveability. An investigation of the influence of various operational parameters in a driveability study is conducted. A variety of [...] Read more.
This paper investigates the applicability of Cone Penetration Test (CPT)-based axial capacity approaches, used for estimating pile static capacity, to the prediction of pile driveability. An investigation of the influence of various operational parameters in a driveability study is conducted. A variety of axial capacity approaches (IC-05, UWA-05 and Fugro-05) are assessed in unmodified and modified form to appraise their ability to be used in estimating the driveability of open-ended steel piles used to support, for example, offshore jackets or bridge piers. Modifications to the CPT-based design approaches include alterations to the proposed base resistance to account for the resistance mobilized under discrete hammer impacts and the presence of residual stresses, as well as accounting for the effects of static capacity increases over time, namely ageing. Furthermore, a study on the influence of various operational parameters within a wave equation solver is conducted to ascertain the relative impact of uncertain data in this respect. The purpose of the paper is not to suggest a new design procedure for estimating pile driveability, rather to investigate the influence of the various operating parameters in a driveability analysis and how they affect the magnitude of the resulting predictions. The study will be of interest to geotechnical design of piles using CPT data. Full article
(This article belongs to the Special Issue Foundation Systems for Offshore Wind Turbines)
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20 pages, 2880 KiB  
Article
Dynamic Response of Articulated Offshore Wind Turbines under Different Water Depths
by Pei Zhang, Shugeng Yang, Yan Li, Jiayang Gu, Zhiqiang Hu, Ruoyu Zhang and Yougang Tang
Energies 2020, 13(11), 2784; https://0-doi-org.brum.beds.ac.uk/10.3390/en13112784 - 1 Jun 2020
Cited by 9 | Viewed by 2710
Abstract
Focusing on the transitional depth offshore area from 50 m to 75 m, types of articulated foundations are proposed for supporting the NREL 5 MW offshore wind turbine. To investigate the dynamic behaviors under various water depths, three articulated foundations were adopted and [...] Read more.
Focusing on the transitional depth offshore area from 50 m to 75 m, types of articulated foundations are proposed for supporting the NREL 5 MW offshore wind turbine. To investigate the dynamic behaviors under various water depths, three articulated foundations were adopted and numerical simulations were conducted in the time domain. An in-house code was chosen to simulate the dynamic response of the articulated offshore wind turbine. The aerodynamic load on rotating blades and the wind pressure load on tower are calculated based on the blade element momentum theory and the empirical formula, respectively. The hydrodynamic load is simulated by 3D potential flow theory. The motions of foundation, the aerodynamic performance of the wind turbine, and the loads on the articulated joint are documented and compared in different cases. According to the simulation, all three articulated offshore wind turbines show great dynamic performance and totally meet the requirement of power generation under the rated operational condition. Moreover, the comparison is based on time histories and spectra among these responses. The result shows that dynamic responses of the shallower one oscillate more severely compared to the other designs. Full article
(This article belongs to the Special Issue Foundation Systems for Offshore Wind Turbines)
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23 pages, 7232 KiB  
Article
An Offshore Floating Wind–Solar–Aquaculture System: Concept Design and Extreme Response in Survival Conditions
by Xiangyuan Zheng, Huadong Zheng, Yu Lei, Yi Li and Wei Li
Energies 2020, 13(3), 604; https://0-doi-org.brum.beds.ac.uk/10.3390/en13030604 - 30 Jan 2020
Cited by 49 | Viewed by 5930
Abstract
This study presents a new concept design combining multiple megawatt (MW) vertical-axis wind turbines (VAWTs) and a solar array with a floating steel fish-farming cage. This combined wind–solar–aquaculture (WSA) system is intended to utilize the ocean space and water resources more effectively and [...] Read more.
This study presents a new concept design combining multiple megawatt (MW) vertical-axis wind turbines (VAWTs) and a solar array with a floating steel fish-farming cage. This combined wind–solar–aquaculture (WSA) system is intended to utilize the ocean space and water resources more effectively and more economically, while greatly shortening the payback period of investment in offshore power generation. The details of this WSA design are described, showing that a square-shaped fishing cage serves as a floating foundation for the 7600 m2 solar array and four multi MW VAWTs. The WAMIT program based on potential-flow theory is employed to obtain the WSA’s motion response amplitude operators (RAOs) in sinusoidal waves of varying periods. The motion RAOs indicated that the proposed concept possesses better hydrodynamic seakeeping performances than its OC3Hywind spar and OC4DeepCwind semi-submersible counterparts. A potential site located in the northwest South China Sea is selected to deploy the WSA. Its feasibility is then examined in terms of the hydrodynamic motions and structural dynamic response driven by wind, waves, and current. Fully coupled time-domain simulations are carried out for 50-year survival conditions. The whole structure exhibits outstanding performance for its small motions in random wind and seas. Moreover, under these survival conditions, the top accelerations and tower base stresses of the VAWTs and mooring line tensions readily meet the design requirements. Technically, the WSA has strong competitiveness and wide prospects in the offshore industry for both power exploitation and marine aquaculture in intermediate and deep waters. Full article
(This article belongs to the Special Issue Foundation Systems for Offshore Wind Turbines)
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28 pages, 10190 KiB  
Article
Dynamic Impedance of the Wide-Shallow Bucket Foundation for Offshore Wind Turbine Using Coupled Finite–Infinite Element Method
by Jijian Lian, Qi Jiang, Xiaofeng Dong, Yue Zhao and Hao Zhao
Energies 2019, 12(22), 4370; https://0-doi-org.brum.beds.ac.uk/10.3390/en12224370 - 16 Nov 2019
Cited by 10 | Viewed by 3156
Abstract
The dynamic impedances of foundation play an important role in the dynamic behavior and structural stability of offshore wind turbines (OWT). Though the behaviors of bucket foundation, which are considered as a relatively innovative foundation type under static loading, have been extensively investigated, [...] Read more.
The dynamic impedances of foundation play an important role in the dynamic behavior and structural stability of offshore wind turbines (OWT). Though the behaviors of bucket foundation, which are considered as a relatively innovative foundation type under static loading, have been extensively investigated, the corresponding dynamic performances were neglected in previous research. This study focuses on the dynamic impedances of wide-shallow bucket foundations (WSBF) under the horizontal and rocking loads. Firstly, the numerical model was established to obtain the dynamic impedances of WSBF using the coupled finite-infinite element technique (FE-IFE). The crucial parameters affecting the dynamic responses of WSBF are investigated. It is shown that the skirt length mainly affects the rocking dynamic impedance and the diameter significantly affects the horizontal and coupling impedances, especially when the diameter is larger than 34 m. The overall dynamic responses of WSBF are profoundly affected by the relative soil thickness and the multi-layer soil stiffness. Additionally, dynamic impedances of WSBF are insensitive to the homogeneous soil stiffness. Lastly, the safety threshold curve was calculated according to the OWT, which can provide essential reference for the design of the OWT supported by large scale WSBF. Full article
(This article belongs to the Special Issue Foundation Systems for Offshore Wind Turbines)
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Review

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31 pages, 8591 KiB  
Review
Concrete Support Structures for Offshore Wind Turbines: Current Status, Challenges, and Future Trends
by Alexandre Mathern, Christoph von der Haar and Steffen Marx
Energies 2021, 14(7), 1995; https://doi.org/10.3390/en14071995 - 4 Apr 2021
Cited by 43 | Viewed by 13811
Abstract
Today’s offshore wind turbine support structures market is largely dominated by steel structures, since steel monopiles account for the vast majority of installations in the last decade and new types of multi-leg steel structures have been developed in recent years. However, as wind [...] Read more.
Today’s offshore wind turbine support structures market is largely dominated by steel structures, since steel monopiles account for the vast majority of installations in the last decade and new types of multi-leg steel structures have been developed in recent years. However, as wind turbines become bigger, and potential sites for offshore wind farms are located in ever deeper waters and ever further from the shore, the conditions for the design, transport, and installation of support structures are changing. In light of these facts, this paper identifies and categorizes the challenges and future trends related to the use of concrete for support structures of future offshore wind projects. To do so, recent advances and technologies still under development for both bottom-fixed and floating concrete support structures have been reviewed. It was found that these new developments meet the challenges associated with the use of concrete support structures, as they will allow the production costs to be lowered and transport and installation to be facilitated. New technologies for concrete support structures used at medium and great water depths are also being developed and are expected to become more common in future offshore wind installations. Therefore, the new developments identified in this paper show the likelihood of an increase in the use of concrete support structures in future offshore wind farms. These developments also indicate that the complexity of future support structures will increase due to the development of hybrid structures combining steel and concrete. These evolutions call for new knowledge and technical know-how in order to allow reliable structures to be built and risk-free offshore installation to be executed. Full article
(This article belongs to the Special Issue Foundation Systems for Offshore Wind Turbines)
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35 pages, 1061 KiB  
Review
Decoupled Modelling Approaches for Environmental Interactions with Monopile-Based Offshore Wind Support Structures
by Pim van der Male, Marco Vergassola and Karel N. van Dalen
Energies 2020, 13(19), 5195; https://0-doi-org.brum.beds.ac.uk/10.3390/en13195195 - 5 Oct 2020
Cited by 7 | Viewed by 3036
Abstract
To meet the political goals regarding renewable energy production, offshore wind keeps expanding to waters with larger depths and harsher conditions, while the turbine size continues to grow and ever-larger foundation structures are required. This development can only be successful if further cuts [...] Read more.
To meet the political goals regarding renewable energy production, offshore wind keeps expanding to waters with larger depths and harsher conditions, while the turbine size continues to grow and ever-larger foundation structures are required. This development can only be successful if further cuts in the levelized cost of energy are established. Regarding the design of the foundation structures, a particular challenge in this respect relates to the reduction of the total computational time required for the design. For both practical and commercial reasons, the decoupled modelling of offshore wind support structures finds a common application, especially during the preliminary design stage. This modelling approach aims at capturing the relevant characteristics of the different environment-structure interactions, while reducing the complexity as much as possible. This paper presents a comprehensive review of the state-of-the-art modelling approaches of environmental interactions with offshore wind support structures. In this respect, the primary focus is on the monopile foundation, as this concept is expected to remain the prominent solution in the years to come. Current challenges in the field are identified, considering as well the engineering practice and the insights obtained from code comparison studies and experimental validations. It is concluded that the decoupled analysis provides valuable modelling perspectives, in particular for the preliminary design stage. In the further development of the different modelling strategies, however, the trade-off with computational costs should always be kept in mind. Full article
(This article belongs to the Special Issue Foundation Systems for Offshore Wind Turbines)
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41 pages, 12076 KiB  
Review
Underwater Noise Emission Due to Offshore Pile Installation: A Review
by Apostolos Tsouvalas
Energies 2020, 13(12), 3037; https://0-doi-org.brum.beds.ac.uk/10.3390/en13123037 - 12 Jun 2020
Cited by 45 | Viewed by 8419
Abstract
The growing demand for renewable energy supply stimulates a drastic increase in the deployment rate of offshore wind energy. Offshore wind power generators are usually supported by large foundation piles that are driven into the seabed with hydraulic impact hammers or vibratory devices. [...] Read more.
The growing demand for renewable energy supply stimulates a drastic increase in the deployment rate of offshore wind energy. Offshore wind power generators are usually supported by large foundation piles that are driven into the seabed with hydraulic impact hammers or vibratory devices. The pile installation process, which is key to the construction of every new wind farm, is hindered by a serious by-product: the underwater noise pollution. This paper presents a comprehensive review of the state-of-the-art computational methods to predict the underwater noise emission by the installation of foundation piles offshore including the available noise mitigation strategies. Future challenges in the field are identified under the prism of the ever-increasing size of wind turbines and the emerging pile driving technologies. Full article
(This article belongs to the Special Issue Foundation Systems for Offshore Wind Turbines)
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Other

Jump to: Research, Review

11 pages, 1985 KiB  
Technical Note
Technical Definition of the TetraSpar Demonstrator Floating Wind Turbine Foundation
by Michael Borg, Morten Walkusch Jensen, Scott Urquhart, Morten Thøtt Andersen, Jonas Bjerg Thomsen and Henrik Stiesdal
Energies 2020, 13(18), 4911; https://0-doi-org.brum.beds.ac.uk/10.3390/en13184911 - 18 Sep 2020
Cited by 31 | Viewed by 6960
Abstract
With the deployment of the TetraSpar demonstrator, a significant cost-reduction is realized in the field of offshore floating wind turbines. The TetraSpar floating wind turbine foundation brings a milestone that emphasizes on a modular and fully industrialized foundation that consists of main components [...] Read more.
With the deployment of the TetraSpar demonstrator, a significant cost-reduction is realized in the field of offshore floating wind turbines. The TetraSpar floating wind turbine foundation brings a milestone that emphasizes on a modular and fully industrialized foundation that consists of main components already widely available in the current wind energy supply chain. In an effort to provide an open approach to the development of the concept, this paper aims at giving a description of the design in order to enable an educated discussion of different design philosophies and their influence on material usage and production times. The description of the different subcomponents of the system should allow any entity to build a model for comparison and/or benchmarking any of their own findings against this concept. It is the authors’ expectation that this open approach to technological discussion is paramount to obtaining continued cost-reduction in the area of floating offshore wind—for this concept and others. Full article
(This article belongs to the Special Issue Foundation Systems for Offshore Wind Turbines)
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