The Experts below are selected from a list of 291 Experts worldwide ranked by ideXlab platform
Peter Frigaard - One of the best experts on this subject based on the ideXlab platform.
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empirical design of scour protections around Monopile Foundations part 1 static approach
Coastal Engineering, 2011Co-Authors: Leen De Vos, Julien De Rouck, Peter A Troch, Peter FrigaardAbstract:Abstract Together with new opportunities, offshore wind farms raise new engineering challenges. An important aspect relates to the erosion of bottom material around the Foundation of the wind turbines, caused by the local increase of the wave and current induced flow velocities by the pile's presence. Typically, the expected scour has a considerable impact on the stability and dynamic behavior of the wind turbine and a scour protection is placed to avoid erosion of the soil close to the Foundation. Although much experience exists on the design of scour protections around bridge piers (which are placed in a current alone situation), at present, little design guidelines exist for the specific case of a scour protection around a Monopile Foundation subjected to a combined wave and current loading. This paper describes the derivation of a static design formula to calculate the required stone size for a scour protection around a Monopile Foundation in a combined wave and current climate. Due to the difficult physical processes involved in flow disturbance and displacement of bed protection material at the base of a Foundation, the formula is based on the results of an experimental model study which is described in this paper. A linear relationship was found between the critical bed shear-stress τcr and the bed shear-stress caused by current τc and waves τw, respectively. When applying the formula for a typical situation in the North Sea, a significant reduction of the required stone size is obtained, compared to existing design criteria. In part 2, following this paper ( De Vos et al., in preparation ), an optimization of the design procedure is obtained by allowing limited stone motion for top layer stones. This is obtained by adding a damage factor to the design formula, which leads to significantly smaller stone diameters and thus a more economical approach.
Leen De Vos - One of the best experts on this subject based on the ideXlab platform.
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empirical design of scour protections around Monopile Foundations part 1 static approach
Coastal Engineering, 2011Co-Authors: Leen De Vos, Julien De Rouck, Peter A Troch, Peter FrigaardAbstract:Abstract Together with new opportunities, offshore wind farms raise new engineering challenges. An important aspect relates to the erosion of bottom material around the Foundation of the wind turbines, caused by the local increase of the wave and current induced flow velocities by the pile's presence. Typically, the expected scour has a considerable impact on the stability and dynamic behavior of the wind turbine and a scour protection is placed to avoid erosion of the soil close to the Foundation. Although much experience exists on the design of scour protections around bridge piers (which are placed in a current alone situation), at present, little design guidelines exist for the specific case of a scour protection around a Monopile Foundation subjected to a combined wave and current loading. This paper describes the derivation of a static design formula to calculate the required stone size for a scour protection around a Monopile Foundation in a combined wave and current climate. Due to the difficult physical processes involved in flow disturbance and displacement of bed protection material at the base of a Foundation, the formula is based on the results of an experimental model study which is described in this paper. A linear relationship was found between the critical bed shear-stress τcr and the bed shear-stress caused by current τc and waves τw, respectively. When applying the formula for a typical situation in the North Sea, a significant reduction of the required stone size is obtained, compared to existing design criteria. In part 2, following this paper ( De Vos et al., in preparation ), an optimization of the design procedure is obtained by allowing limited stone motion for top layer stones. This is obtained by adding a damage factor to the design formula, which leads to significantly smaller stone diameters and thus a more economical approach.
Segere M.l.a. - One of the best experts on this subject based on the ideXlab platform.
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Vibration-induced settlement of a slip-joint connection for offshore wind turbines
2018Co-Authors: Segere M.l.a.Abstract:The majority of existing offshore wind turbines typically consist of a Monopile Foundation, a transition piece with a vertically positioned grouted connection, a turbine tower, and a turbine. Of the 2,653 offshore turbines that were installed by the end of 2015, 80 percent are supported by a Monopile.Despite the current overwhelming dominance of the Monopile, its future application is rather uncertain. Offshore wind turbines have continuously increased in size and have moved to deeper waters; these developments require larger and heavier support structures. It is unlikely that floating structures will be preferred to bottom-founded structures, up to a water depth of 80 m. The question thus becomes whether jackets or Monopiles will be used under such conditions? The Monopile seems to be losing in this competition, as, to meet the requirements a Monopile would have to be extremely large; thus, it may no longer fall within industry limits, both in terms of manufacturing demands and the lifting capacity of dedicated installation vessels. One may wonder whether a single Monopile would be necessary, or if a set of intelligently connected smaller length Monopiles could suffice. The key to the success of such a concept could be the so-called slip-joint connection.A slip-joint consists of two conical sections made of steel. This connection does not require any grout and, besides being a connection option for the transition piece and Monopile, allows Monopiles to be comprised of a number of lighter sections of very large diameters. By employing a slip-joint, the applicability of the Monopile could be extended to deeper waters and to turbines that have very large rotors and power capacities.Although the slip-joint connection has been successfully used for onshore wind turbines in the past, it has not yet been used offshore. One of the challenges in using the slip-joint is ensuring a proper fit of the cones despite the imperfections that result from manufacturing tolerances, deformations by pile driving, and the potential damage that may occur during the handling of the cones.In this thesis, it is proposed that a slight difference in the cone angles be used to address the aforementioned imperfections. A steeper cone angle for the transition piece when compared to that of the Monopile is proposed. These slightly different cone angles require the upper cone to deform elastically in order to slide down the lower cone during installation. To facilitate the installation process, it is proposed that vibrations be employed in order to cause the upper cone to slide down under its own weight. In order to use this new method of connecting joints, it will be necessary to investigate the manner in which vibrations influence the relative motions of the two cones that need to achieve stable contact.The objective of this thesis is to investigate the potential of the use of vibrations in the installation and dismounting of a slip-joint with slightly different cone angles. The research is conducted by means of numerical modelling and experiments
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Vibration-induced settlement of a slip-joint connection for offshore wind turbines
2018Co-Authors: Segere M.l.a.Abstract:The majority of existing offshore wind turbines typically consist of a Monopile Foundation, a transition piece with a vertically positioned grouted connection, a turbine tower, and a turbine. Of the 2,653 offshore turbines that were installed by the end of 2015, 80 percent are supported by a Monopile.Despite the current overwhelming dominance of the Monopile, its future application is rather uncertain. Offshore wind turbines have continuously increased in size and have moved to deeper waters; these developments require larger and heavier support structures. It is unlikely that floating structures will be preferred to bottom-founded structures, up to a water depth of 80 m. The question thus becomes whether jackets or Monopiles will be used under such conditions? The Monopile seems to be losing in this competition, as, to meet the requirements a Monopile would have to be extremely large; thus, it may no longer fall within industry limits, both in terms of manufacturing demands and the lifting capacity of dedicated installation vessels. One may wonder whether a single Monopile would be necessary, or if a set of intelligently connected smaller length Monopiles could suffice. The key to the success of such a concept could be the so-called slip-joint connection.A slip-joint consists of two conical sections made of steel. This connection does not require any grout and, besides being a connection option for the transition piece and Monopile, allows Monopiles to be comprised of a number of lighter sections of very large diameters. By employing a slip-joint, the applicability of the Monopile could be extended to deeper waters and to turbines that have very large rotors and power capacities.Although the slip-joint connection has been successfully used for onshore wind turbines in the past, it has not yet been used offshore. One of the challenges in using the slip-joint is ensuring a proper fit of the cones despite the imperfections that result from manufacturing tolerances, deformations by pile driving, and the potential damage that may occur during the handling of the cones.In this thesis, it is proposed that a slight difference in the cone angles be used to address the aforementioned imperfections. A steeper cone angle for the transition piece when compared to that of the Monopile is proposed. These slightly different cone angles require the upper cone to deform elastically in order to slide down the lower cone during installation. To facilitate the installation process, it is proposed that vibrations be employed in order to cause the upper cone to slide down under its own weight. In order to use this new method of connecting joints, it will be necessary to investigate the manner in which vibrations influence the relative motions of the two cones that need to achieve stable contact.The objective of this thesis is to investigate the potential of the use of vibrations in the installation and dismounting of a slip-joint with slightly different cone angles. The research is conducted by means of numerical modelling and experiments.Offshore Engineerin
Xuefei Wang - One of the best experts on this subject based on the ideXlab platform.
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parametric study of hybrid Monopile Foundation for offshore wind turbines in cohesionless soil
Ocean Engineering, 2020Co-Authors: Xuefei WangAbstract:Abstract The hybrid Monopile Foundation is an alternative for offshore wind turbines. The parametric study has been performed through a series of centrifuge tests for the optimal design of the hybrid Foundation. The wheel diameter, wheel thickness, and pile length are considered in the analysis. The lateral capacity of the hybrid Monopile Foundation increases with the wheel diameter and tends to accelerate; it increases linearly with the wheel thickness and pile length. The influence of the wheel diameter is more pronounced compared to the other parameters. The hybrid Monopile demonstrates an enhanced performance compared to the Monopile and the single-wheel. The improvement is more significant at small pile lengths. The hybrid Monopile shows its advantages in reducing the pile length. It has great potential in reducing capital costs. An analytical method is proposed by scaling the individual capacity of the pile and the wheel. A design chart for the scale factor is suggested. The calculation is applicable for determining the initial dimension of the hybrid Monopile Foundation, and the ultimate lateral capacity is assessed.
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feasibility study of Monopile friction wheel bucket hybrid Foundation for offshore wind turbine
Ocean Engineering, 2020Co-Authors: Xiangwu Zeng, Xuefei WangAbstract:Abstract In this study, a hybrid Monopile-friction wheel-bucket (MFB) Foundation for offshore wind turbines is proposed. A bucket and a friction wheel are integrated with a Monopile. The friction wheel is filled with scattered material to provide distributed surcharge loads to the subsoil. A series of geotechnical centrifuge tests was performed under monotonic load and cyclic load to investigate the bearing capacity of the MFB Foundation. Five hybrid Foundations with variable dimensions were tested in four types of sandy soil conditions. The centrifuge test results show that the ultimate bearing capacity of the hybrid MFB Foundation could be 4 times of the Monopile Foundation. Under cyclic load, the final displacement of MFB Foundation is significantly smaller than that of the Monopile Foundation. The MFB Foundation is stiffer in the reloading process but shows slightly more plastic characteristic in the unloading process. The size of the add-on friction wheel-bucket structure is positively related to the performance of the MFB Foundation. The bucket height tends to be a more effective factor. It is illustrated that the MFB Foundation tends to demonstrates more improvements in the saturated loose sand. A simplified method is proposed to predict the bearing capacity of the hybrid MFB Foundation.
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liquefaction characteristics of offshore wind turbine with hybrid Monopile Foundation via centrifuge modelling
Renewable Energy, 2020Co-Authors: Xuefei Wang, Xiangwu ZengAbstract:Abstract Some offshore wind farms are built in seismically active areas. The offshore wind turbine (OWTs) are high-rise structures and sensitive to lateral failures during the earthquake. In this study, an innovative hybrid Monopile Foundation is proposed for OWTs. A series of centrifuge shake table tests is conducted to investigate the seismic response and liquefaction characteristics of the hybrid Monopile Foundation. Mechanisms of the seismic behavior of soil, lateral displacements of the wind turbine, and structural settlements are evaluated. Centrifuge test results indicate that the liquefaction around the hybrid Monopile Foundation is weakened compared to the traditional single pile. The soil partially keeps its strength and stiffness during the shaking due to the higher confining stress. The lateral stability of the system is enhanced. OWTs with the hybrid Monopile Foundation tends to settle more during the earthquake due to the soil-structure interaction and the static bearing induced soil shearing. Two types of hybrid Monopile Foundations are constructed with different weights and materials, which are predominant influence factors for their seismic response. This study aims to investigate the seismic behavior of the hybrid Monopile Foundation for OWTs during earthquake events and provide references for practical designs.
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investigation on offshore wind turbine with an innovative hybrid Monopile Foundation an experimental based study
Renewable Energy, 2019Co-Authors: Xuefei Wang, Xiangwu ZengAbstract:The support structure for offshore wind turbines (OWTs) plays significant roles in maintaining the structural stability and reducing the initial cost. An innovative hybrid Monopile Foundation for OWTs is proposed. The concept has a wider adaptability by using established knowledge to solve for new problems. A series of centrifuge tests is performed to investigate the behavior of this hybrid Foundation system in extreme and service conditions. OWTs with the original Monopile Foundation as well as the wheel-only Foundations are tested for comparisons, and two clay profiles are considered. The test results show that the hybrid Monopile Foundation provides larger ultimate bearing capacities compared to the traditional Foundations. Two analytical methods are proposed to estimate the ultimate bearing capacity of this innovative design, and the results are calibrated by the centrifuge tests. In service conditions, the hybrid Monopile Foundation shows stronger cyclic resistances. Influence factors of the cyclic responses are summarized. An analytical solution is put forward to estimate the accumulated lateral displacement of the hybrid Monopile Foundation. A degradation factor is suggested based on the results of the centrifuge tests. The study aims to enrich the understanding of the innovative Foundation concept and to provide design references for practical applications.
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seismic response of offshore wind turbine with hybrid Monopile Foundation based on centrifuge modelling
Applied Energy, 2019Co-Authors: Xuefei Wang, Xiangwu Zeng, Xu YangAbstract:Abstract Some large capacity offshore wind turbines are constructed in seismically active areas. The occurrence of soil liquefaction during an earthquake can result in severe failures of the offshore wind turbine. The seismic response of the structure and the failure mechanism of the soil-structure interactions are necessary to investigate. In this study, the seismic response of an innovative hybrid Monopile Foundation is investigated through a series of centrifuge tests. The seismic performance of the combined system of the superstructure, Foundation, and soil are demonstrated. Five hybrid Foundation models are tested by considering the influence of the Foundation thicknesses and diameters, and a Monopile Foundation is tested for comparison. Centrifuge test results reveal that the hybrid Monopile Foundation is effective in reducing the lateral displacement during the shaking. In the saturated condition, soil keeps its strength and stiffness beneath and adjacent to the Foundation. The hybrid Foundation system tends to settle more due to the larger shear stress caused by the soil structure interactions. Influences of the wheel specifications are illustrated. The Foundations with larger thicknesses lead to smaller lateral displacements and lower tendencies of liquefaction, but the settlements are intensified. The larger diameter Foundation provides a longer drainage path for the excess pore water pressure. With a similar weight, the structure settles less during the earthquake.
David R Fuhrma - One of the best experts on this subject based on the ideXlab platform.
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experimental study of tsunami induced scour around a Monopile Foundation
Coastal Engineering, 2018Co-Authors: Jarke Eltard Larse, Lasse Kaergaard Arboll, Sarah Frigaard Kristofferse, Stefa Carstense, David R FuhrmaAbstract:Abstract This paper presents an experimental study of the tsunami-induced scour process around a Monopile Foundation, representative of those commonly used for offshore wind farms. The scour process is studied by subjecting the Monopile to a time varying current, which enables a properly down-scaled experiment from the boundary layer and scour perspective. It is shown how the scaled experiments corresponds to real life idealized tsunami cases with periods ranging from 10 to 40 min. It is then shown that the boundary layers of the model tsunami are well described by recently developed empirical relations for tsunami boundary layers. By subjecting the Monopile to several successive tsunami waves the scour process is shown to occur in a stepwise cumulative fashion, with the final equilibrium scour depth tending to the depth limited steady current limit. It is shown that the entire scour development can reasonably be predicted by a recently developed simple engineering model. Finally, the experimental results are compared to a fully coupled hydrodynamic and morphologic CFD model and a good correspondence is obtained.