The Experts below are selected from a list of 327 Experts worldwide ranked by ideXlab platform
Leen De Vos - One of the best experts on this subject based on the ideXlab platform.
-
Large-Scale Experiments to Improve Monopile Scour Protection Design Adapted to Climate Change—The PROTEUS Project
Energies, 2019Co-Authors: Carlos Arboleda Chavez, Leen De Vos, Vasiliki Stratigaki, Peter Troch, Alexander Schendel, Mario Welzel, Raul Villanueva, Torsten Schlurmann, Dogan KisacikAbstract:This study aims to improve the design of Scour Protection around offshore wind turbine monopiles, as well as future-proofing them against the impacts of climate change. A series of large-scale experiments have been performed in the context of the European HYDRALAB-PLUS PROTEUS (Protection of offshore wind turbine monopiles against Scouring) project in the Fast Flow Facility in HR Wallingford. These experiments make use of state of the art optical and acoustic measurement techniques to assess the damage of Scour Protections under the combined action of waves and currents. These novel PROTEUS tests focus on the study of the grading of the Scour Protection material as a stabilizing parameter, which has never been done under the combined action of waves and currents at a large scale. Scale effects are reduced and, thus, design risks are minimized. Moreover, the generated data will support the development of future Scour Protection designs and the validation of numerical models used by researchers worldwide. The testing program objectives are: (i) to compare the performance of single-layer wide-graded material used against Scouring with current design practices; (ii) to verify the stability of the Scour Protection designs under extreme flow conditions; (iii) to provide a benchmark dataset for Scour Protection stability at large scale; and (iv) to investigate the scale effects on Scour Protection stability.
-
large scale experiments to improve monopile Scour Protection design adapted to climate change the proteus project
Energies, 2019Co-Authors: Carlos Arboleda Chavez, Leen De Vos, Vasiliki Stratigaki, Peter Troch, Alexander Schendel, Mario Welzel, Raul Villanueva, Torsten Schlurmann, Dogan Kisacik, Francisco Taveira PintoAbstract:This study aims to improve the design of Scour Protection around offshore wind turbine monopiles, as well as future-proofing them against the impacts of climate change. A series of large-scale experiments have been performed in the context of the European HYDRALAB-PLUS PROTEUS (Protection of offshore wind turbine monopiles against Scouring) project in the Fast Flow Facility in HR Wallingford. These experiments make use of state of the art optical and acoustic measurement techniques to assess the damage of Scour Protections under the combined action of waves and currents. These novel PROTEUS tests focus on the study of the grading of the Scour Protection material as a stabilizing parameter, which has never been done under the combined action of waves and currents at a large scale. Scale effects are reduced and, thus, design risks are minimized. Moreover, the generated data will support the development of future Scour Protection designs and the validation of numerical models used by researchers worldwide. The testing program objectives are: (i) to compare the performance of single-layer wide-graded material used against Scouring with current design practices; (ii) to verify the stability of the Scour Protection designs under extreme flow conditions; (iii) to provide a benchmark dataset for Scour Protection stability at large scale; and (iv) to investigate the scale effects on Scour Protection stability.
-
Extended validation of dynamic design formula for Scour Protection around monopiles
2012Co-Authors: Leen Baelus, Leen De Vos, Peter Troch, Nicolas Loosveldt, K Van Nieuwenhuyse, Annelies BolleAbstract:To transform Europe into a highly energy-efficient, low carbon economy, wind energy is one of the commonly applied renewable energy sources, with minimal human, ecological and environmental impacts. However, in order to evolve offshore wind energy to a competitor of the primary energy resources, the cost efficiency of this technology needs to be further improved. A critical part is the Scour Protection around the monopile foundation of the wind turbine. Due to the presence of a monopile, the current field is disturbed and local Scour occurs around the foundation. A Scour Protection is applied to prevent Scour development near the construction and to guarantee the pile's stability. Instead of designing a statically stable Scour Protection, allowing no damage to the top layer, smaller rock elements can be used for the Scour Protection. The advantages are both the lower cost of the elements as well as the need for fewer filter layers. However, allowing movement of some stones without causing failure of the Scour Protection, implies that the development of damage in time needs to be investigated and the damage needs to be incorporated in the design formula of the Protection. This paper investigates the damage to the Scour Protection by physical model tests and verifies a dynamic design formula to calculate the required stone size for a Scour Protection around a monopile foundation in a combined wave and current climate.
-
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.
Peter Troch - One of the best experts on this subject based on the ideXlab platform.
-
Evaluation of Uncertainty of Damage Results in Experimental Modelling of Monopile Foundation Scour Protection
Volume 1: Offshore Technology; Offshore Geotechnics, 2019Co-Authors: Jonas Arnout, Carlos Arboleda Chavez, Vasiliki Stratigaki, Josep Molina Ruiz, Peter TrochAbstract:Abstract The waves and currents acting near a monopile foundation will potentially lead to Scour, which may affect the stability of the wind turbine. The design of Scour Protection against the seabed lowering around a wind turbine monopile foundation is an important issue for wind energy industries. Many laboratory tests have been carried out to investigate the relationship between the hydrodynamic conditions and the monopile foundation Scour Protection layer damage, and various design criteria have been proposed. However, the experimental uncertainty of the underlying test results has not been discussed in detail. In the present research, small scale wave flume experiments of a 5m diameter monopile foundation Scour Protection under waves combined with currents in shallow water are described. Two groups of repetitive experiments are completed under the same wave and current conditions. The erosion development of the Scour Protection armor layer is measured by using a laser profiler and is evaluated based on three dimensional damage numbers. Together with visualization of the damage pattern, the damage analysis discusses the erosion in different subareas and the variances of the subarea damage number. The analysis of the uncertainty of the erosion results based on two sets of repetitive tests has been carried out. Using the uncertainty analysis methodology stated in ISO GUM standard: JCGM 100-2008, the Type A uncertainty, calibration uncertainty and combined uncertainty of the experiment are evaluated separately. The Type A uncertainty gives an overall uncertainty level and it shows that higher uncertainty occurs in the regions where stronger vortices exist. The combined uncertainty is analyzed based on Scour Protection dynamic stability design formula. Analysis result shows that the uncertainty due to modelling is a major source of the total uncertainty. The study gives a preliminary result of uncertainty level in wave flume test of monopile Scour Protection and provides a reference for future experimental research.
-
Large-Scale Experiments to Improve Monopile Scour Protection Design Adapted to Climate Change—The PROTEUS Project
Energies, 2019Co-Authors: Carlos Arboleda Chavez, Leen De Vos, Vasiliki Stratigaki, Peter Troch, Alexander Schendel, Mario Welzel, Raul Villanueva, Torsten Schlurmann, Dogan KisacikAbstract:This study aims to improve the design of Scour Protection around offshore wind turbine monopiles, as well as future-proofing them against the impacts of climate change. A series of large-scale experiments have been performed in the context of the European HYDRALAB-PLUS PROTEUS (Protection of offshore wind turbine monopiles against Scouring) project in the Fast Flow Facility in HR Wallingford. These experiments make use of state of the art optical and acoustic measurement techniques to assess the damage of Scour Protections under the combined action of waves and currents. These novel PROTEUS tests focus on the study of the grading of the Scour Protection material as a stabilizing parameter, which has never been done under the combined action of waves and currents at a large scale. Scale effects are reduced and, thus, design risks are minimized. Moreover, the generated data will support the development of future Scour Protection designs and the validation of numerical models used by researchers worldwide. The testing program objectives are: (i) to compare the performance of single-layer wide-graded material used against Scouring with current design practices; (ii) to verify the stability of the Scour Protection designs under extreme flow conditions; (iii) to provide a benchmark dataset for Scour Protection stability at large scale; and (iv) to investigate the scale effects on Scour Protection stability.
-
large scale experiments to improve monopile Scour Protection design adapted to climate change the proteus project
Energies, 2019Co-Authors: Carlos Arboleda Chavez, Leen De Vos, Vasiliki Stratigaki, Peter Troch, Alexander Schendel, Mario Welzel, Raul Villanueva, Torsten Schlurmann, Dogan Kisacik, Francisco Taveira PintoAbstract:This study aims to improve the design of Scour Protection around offshore wind turbine monopiles, as well as future-proofing them against the impacts of climate change. A series of large-scale experiments have been performed in the context of the European HYDRALAB-PLUS PROTEUS (Protection of offshore wind turbine monopiles against Scouring) project in the Fast Flow Facility in HR Wallingford. These experiments make use of state of the art optical and acoustic measurement techniques to assess the damage of Scour Protections under the combined action of waves and currents. These novel PROTEUS tests focus on the study of the grading of the Scour Protection material as a stabilizing parameter, which has never been done under the combined action of waves and currents at a large scale. Scale effects are reduced and, thus, design risks are minimized. Moreover, the generated data will support the development of future Scour Protection designs and the validation of numerical models used by researchers worldwide. The testing program objectives are: (i) to compare the performance of single-layer wide-graded material used against Scouring with current design practices; (ii) to verify the stability of the Scour Protection designs under extreme flow conditions; (iii) to provide a benchmark dataset for Scour Protection stability at large scale; and (iv) to investigate the scale effects on Scour Protection stability.
-
Development and validation of a numerical model of Scour Protection around monopiles under currents
2018Co-Authors: Carlos Arboleda Chavez, Peter Troch, Vicky StratigakiAbstract:Scour around monopiles has been widely studied, however, Scour Protection—made of stones—around monopiles has not. To cover this knowledge gap, this work presents the development of a numerical model for the study of the flow within the Scour Protection around monopiles and the first results obtained with this model. The development of the model was done using fully open source tools that have been thriving in the scientific community, such as the OpenFOAM framework, for the numerical model, and the Python programming language for the parametrization of the mesh and setup of the cases. This model approaches the flow within the Scour Protection as a porous medium. The latter has successfully been used by Nielsen et al. (2013). Their and our results show a good agreement with experimental results.
-
Feasibility of a Dynamically Stable Rock Armour Layer Scour Protection for Offshore Wind Farms
Volume 3: Offshore Geotechnics, 2014Co-Authors: Philippe De Schoesitter, Andrew Brown, Annelies Bolle, P. Haerens, Leen Baelus, T. T. Ferradosa, Francisco Taveira Pinto, Sarah Audenaert, Luciana Das Neves, Peter TrochAbstract:Armour layer Scour Protections around offshore wind turbine foundations are commonly designed to provide a static Protection in storm conditions, which means no or limited movement of rock is allowed (Den Boon et al., 2004, De Vos et al., 2011). This approach often results in large stone sizes and high Scour Protection costs. Therefore, a dynamic approach can be an interesting alternative. Such a dynamic design can be achieved by decreasing the armour stone size allowing movement of the stones and increasing the armour layer thickness to prevent filter layer exposure. A physical test program was conducted to investigate the feasibility and behaviour of such a dynamically stable Scour Protection. In this model, a monopile foundation exposed to typical North Sea combinations of unidirectional currents and waves was reproduced in a wave flume. The program included a number of test series each with different water depths. In each test series, the armour layer stone size and the armour layer thickness were varied, in order to obtain a reshaping Scour Protection, without filter material exposure. Damage and failure were assessed both visually and using a 3D-laser profiler. Because previous works on damage numbers of rock armour layer Scour Protections mainly focus on static design, a new damage number was introduced and compared to the visual observation. This allowed the definition of a ‘dynamic area’ between static design and failure. Scour pit development in time and equilibrium profiling were also analyzed. The results of the tests showed that the concept of a dynamically stable Scour Protection is feasible.
Francisco Taveira Pinto - One of the best experts on this subject based on the ideXlab platform.
-
large scale experiments to improve monopile Scour Protection design adapted to climate change the proteus project
Energies, 2019Co-Authors: Carlos Arboleda Chavez, Leen De Vos, Vasiliki Stratigaki, Peter Troch, Alexander Schendel, Mario Welzel, Raul Villanueva, Torsten Schlurmann, Dogan Kisacik, Francisco Taveira PintoAbstract:This study aims to improve the design of Scour Protection around offshore wind turbine monopiles, as well as future-proofing them against the impacts of climate change. A series of large-scale experiments have been performed in the context of the European HYDRALAB-PLUS PROTEUS (Protection of offshore wind turbine monopiles against Scouring) project in the Fast Flow Facility in HR Wallingford. These experiments make use of state of the art optical and acoustic measurement techniques to assess the damage of Scour Protections under the combined action of waves and currents. These novel PROTEUS tests focus on the study of the grading of the Scour Protection material as a stabilizing parameter, which has never been done under the combined action of waves and currents at a large scale. Scale effects are reduced and, thus, design risks are minimized. Moreover, the generated data will support the development of future Scour Protection designs and the validation of numerical models used by researchers worldwide. The testing program objectives are: (i) to compare the performance of single-layer wide-graded material used against Scouring with current design practices; (ii) to verify the stability of the Scour Protection designs under extreme flow conditions; (iii) to provide a benchmark dataset for Scour Protection stability at large scale; and (iv) to investigate the scale effects on Scour Protection stability.
-
Feasibility of a Dynamically Stable Rock Armour Layer Scour Protection for Offshore Wind Farms
Volume 3: Offshore Geotechnics, 2014Co-Authors: Philippe De Schoesitter, Andrew Brown, Annelies Bolle, P. Haerens, Leen Baelus, T. T. Ferradosa, Francisco Taveira Pinto, Sarah Audenaert, Luciana Das Neves, Peter TrochAbstract:Armour layer Scour Protections around offshore wind turbine foundations are commonly designed to provide a static Protection in storm conditions, which means no or limited movement of rock is allowed (Den Boon et al., 2004, De Vos et al., 2011). This approach often results in large stone sizes and high Scour Protection costs. Therefore, a dynamic approach can be an interesting alternative. Such a dynamic design can be achieved by decreasing the armour stone size allowing movement of the stones and increasing the armour layer thickness to prevent filter layer exposure. A physical test program was conducted to investigate the feasibility and behaviour of such a dynamically stable Scour Protection. In this model, a monopile foundation exposed to typical North Sea combinations of unidirectional currents and waves was reproduced in a wave flume. The program included a number of test series each with different water depths. In each test series, the armour layer stone size and the armour layer thickness were varied, in order to obtain a reshaping Scour Protection, without filter material exposure. Damage and failure were assessed both visually and using a 3D-laser profiler. Because previous works on damage numbers of rock armour layer Scour Protections mainly focus on static design, a new damage number was introduced and compared to the visual observation. This allowed the definition of a ‘dynamic area’ between static design and failure. Scour pit development in time and equilibrium profiling were also analyzed. The results of the tests showed that the concept of a dynamically stable Scour Protection is feasible.
Carlos Arboleda Chavez - One of the best experts on this subject based on the ideXlab platform.
-
large scale experimental study of the Scour Protection damage around a monopile foundation under combined wave and current conditions
Journal of Marine Science and Engineering, 2020Co-Authors: Lee De Vos, Carlos Arboleda Chavez, Vasiliki Stratigaki, Tiago Fazeresferradosa, Paulo Rosasantos, Francisco Taveirapinto, Pete TrochAbstract:This paper presents a series of large-scale wave flume experiments on the Scour Protection damage around a monopile under combined waves and current conditions with model scales of 1:16.67 and 1:8.33. The main objective is to compare the damage data obtained from these large-scale models with existing monopile Scour Protection design approaches, which were proposed based on small scale wave flume experiments, and to study the applicability of the existing approaches. The static stability (onset of motion and bed shear stress) and the dynamic stability (three-dimensional damage numbers) of the Scour Protection are investigated. Both results show that the existing design approaches can be conservative when applied to large scale models, which highlights the need of further investigations on scale and model effects. In addition, this paper also analyses the Scour Protection damage depth. It is observed that damage depths of the Scour Protection layer under low Keulegan–Carpenter number (KC) conditions are smaller than predictions. The study provides valuable large scale experimental data for future research on the monopile Scour Protection design.
-
Evaluation of Uncertainty of Damage Results in Experimental Modelling of Monopile Foundation Scour Protection
Volume 1: Offshore Technology; Offshore Geotechnics, 2019Co-Authors: Jonas Arnout, Carlos Arboleda Chavez, Vasiliki Stratigaki, Josep Molina Ruiz, Peter TrochAbstract:Abstract The waves and currents acting near a monopile foundation will potentially lead to Scour, which may affect the stability of the wind turbine. The design of Scour Protection against the seabed lowering around a wind turbine monopile foundation is an important issue for wind energy industries. Many laboratory tests have been carried out to investigate the relationship between the hydrodynamic conditions and the monopile foundation Scour Protection layer damage, and various design criteria have been proposed. However, the experimental uncertainty of the underlying test results has not been discussed in detail. In the present research, small scale wave flume experiments of a 5m diameter monopile foundation Scour Protection under waves combined with currents in shallow water are described. Two groups of repetitive experiments are completed under the same wave and current conditions. The erosion development of the Scour Protection armor layer is measured by using a laser profiler and is evaluated based on three dimensional damage numbers. Together with visualization of the damage pattern, the damage analysis discusses the erosion in different subareas and the variances of the subarea damage number. The analysis of the uncertainty of the erosion results based on two sets of repetitive tests has been carried out. Using the uncertainty analysis methodology stated in ISO GUM standard: JCGM 100-2008, the Type A uncertainty, calibration uncertainty and combined uncertainty of the experiment are evaluated separately. The Type A uncertainty gives an overall uncertainty level and it shows that higher uncertainty occurs in the regions where stronger vortices exist. The combined uncertainty is analyzed based on Scour Protection dynamic stability design formula. Analysis result shows that the uncertainty due to modelling is a major source of the total uncertainty. The study gives a preliminary result of uncertainty level in wave flume test of monopile Scour Protection and provides a reference for future experimental research.
-
Large-Scale Experiments to Improve Monopile Scour Protection Design Adapted to Climate Change—The PROTEUS Project
Energies, 2019Co-Authors: Carlos Arboleda Chavez, Leen De Vos, Vasiliki Stratigaki, Peter Troch, Alexander Schendel, Mario Welzel, Raul Villanueva, Torsten Schlurmann, Dogan KisacikAbstract:This study aims to improve the design of Scour Protection around offshore wind turbine monopiles, as well as future-proofing them against the impacts of climate change. A series of large-scale experiments have been performed in the context of the European HYDRALAB-PLUS PROTEUS (Protection of offshore wind turbine monopiles against Scouring) project in the Fast Flow Facility in HR Wallingford. These experiments make use of state of the art optical and acoustic measurement techniques to assess the damage of Scour Protections under the combined action of waves and currents. These novel PROTEUS tests focus on the study of the grading of the Scour Protection material as a stabilizing parameter, which has never been done under the combined action of waves and currents at a large scale. Scale effects are reduced and, thus, design risks are minimized. Moreover, the generated data will support the development of future Scour Protection designs and the validation of numerical models used by researchers worldwide. The testing program objectives are: (i) to compare the performance of single-layer wide-graded material used against Scouring with current design practices; (ii) to verify the stability of the Scour Protection designs under extreme flow conditions; (iii) to provide a benchmark dataset for Scour Protection stability at large scale; and (iv) to investigate the scale effects on Scour Protection stability.
-
large scale experiments to improve monopile Scour Protection design adapted to climate change the proteus project
Energies, 2019Co-Authors: Carlos Arboleda Chavez, Leen De Vos, Vasiliki Stratigaki, Peter Troch, Alexander Schendel, Mario Welzel, Raul Villanueva, Torsten Schlurmann, Dogan Kisacik, Francisco Taveira PintoAbstract:This study aims to improve the design of Scour Protection around offshore wind turbine monopiles, as well as future-proofing them against the impacts of climate change. A series of large-scale experiments have been performed in the context of the European HYDRALAB-PLUS PROTEUS (Protection of offshore wind turbine monopiles against Scouring) project in the Fast Flow Facility in HR Wallingford. These experiments make use of state of the art optical and acoustic measurement techniques to assess the damage of Scour Protections under the combined action of waves and currents. These novel PROTEUS tests focus on the study of the grading of the Scour Protection material as a stabilizing parameter, which has never been done under the combined action of waves and currents at a large scale. Scale effects are reduced and, thus, design risks are minimized. Moreover, the generated data will support the development of future Scour Protection designs and the validation of numerical models used by researchers worldwide. The testing program objectives are: (i) to compare the performance of single-layer wide-graded material used against Scouring with current design practices; (ii) to verify the stability of the Scour Protection designs under extreme flow conditions; (iii) to provide a benchmark dataset for Scour Protection stability at large scale; and (iv) to investigate the scale effects on Scour Protection stability.
-
Development and validation of a numerical model of Scour Protection around monopiles under currents
2018Co-Authors: Carlos Arboleda Chavez, Peter Troch, Vicky StratigakiAbstract:Scour around monopiles has been widely studied, however, Scour Protection—made of stones—around monopiles has not. To cover this knowledge gap, this work presents the development of a numerical model for the study of the flow within the Scour Protection around monopiles and the first results obtained with this model. The development of the model was done using fully open source tools that have been thriving in the scientific community, such as the OpenFOAM framework, for the numerical model, and the Python programming language for the parametrization of the mesh and setup of the cases. This model approaches the flow within the Scour Protection as a porous medium. The latter has successfully been used by Nielsen et al. (2013). Their and our results show a good agreement with experimental results.
B. Mutlu Sumer - One of the best experts on this subject based on the ideXlab platform.
-
Edge Scour at Scour Protections around piles in the marine environment - Laboratory and field investigation
Coastal Engineering, 2015Co-Authors: Thor Ugelvig Petersen, B. Mutlu Sumer, Jørgen Fredsøe, Tim Raaijmakers, Jan Joost SchoutenAbstract:Abstract When building offshore wind turbines with monopile foundations, Scour Protection typically is placed to avoid Scouring of the soil close to the monopile. An important aspect is that the Scour Protection itself causes erosion, inflicted by the local increase in current and/or wave velocities and in turn increased bed shear stresses. Scour of the edge material alongside the Scour Protection may cause deformations and failure of the Scour Protection of offshore wind turbine foundations. This can reduce the stability of the stone layer and cause exposure of cables running between the monopiles where they go from buried to the transition piece on the foundation. Although much information is available on the design of Scour Protection systems around monopiles, little is known on the mechanisms causing edge Scour and the equilibrium stages of the edge Scour process in steady current, waves and combined waves and current. This paper presents an extensive experimental campaign to explain the edge Scour process in current and combined irregular waves and current, as well as tidal current. The three-dimensional flow field around the pile and Scour Protection is resolved by particle image velocimetry and bed shear stress measurements, showing a local increase in the flow velocities and bed shear stresses leading to increased sediment transport and Scour. The governing process in steady current is a pair of symmetrical counter-rotating vortices emerging in the near bed region in the wake of the pile and Scour Protection, causing a significant downstream Scour hole. It is found that the equilibrium Scour hole depth and length scales with the pile diameter and the ratio between the thickness- and the width of the Scour Protection. In the second part of the present paper, the results from the experimental campaign are compared with the edge Scour experienced in practice, outlined by a survey program of the offshore wind park Egmond Aan Zee and a published field investigation of Scroby Sands OWF by Whitehouse et al. (2011).
-
Sinking of armour layer around a vertical cylinder exposed to waves and current
Coastal Engineering, 2015Co-Authors: Anders Nielsen, Thor Ugelvig Petersen, Thomas Probst, B. Mutlu SumerAbstract:Abstract The mechanisms of the sinking of a Scour Protection adjacent to a monopile are described in this paper, together with the determination of the equilibrium sinking depth in various wave and combined wave and current conditions based on physical model tests. Sinking of the rocks may ultimately lead to failure of the Scour Protection. It may cause exposure and free-span of cables, and possibly change the natural frequency of the wind turbine in an unfavourable manner. For these reasons it is important to consider the possible effects of sinking in the Scour Protection design, and to understand the mechanisms that could lead to unacceptable sinking of the Scour Protection. The study showed that the sinking is controlled by two mechanisms: removal of sediment adjacent to the pile (destabilizing) and infilling of sediment into the Scour Protection from the surrounding seabed (stabilizing). The latter mechanism is found to be the strongest, but it might take some time to fill the pores of the Scour Protection with sediment and during the time delay considerable sinking might take place. This means that the larger the Scour Protection, the larger the sinking will be (for a given KC-number smaller than approximately 15). The magnitude of the sinking of the Scour Protection adjacent to a monopile exposed to waves, and combined waves and current, was found to be similar to the current case.
-
Sinking failure of Scour Protection at wind turbine foundation
Proceedings of the Institution of Civil Engineers - Energy, 2013Co-Authors: B. Mutlu Sumer, Anders Wedel NielsenAbstract:This paper summarises the results of an experimental study on Scour Protection around offshore wind turbine foundations, with special emphasis on the sinking failure of the Scour Protection work in Horns Rev 1 offshore wind farm (Denmark). The paper reviews previous results obtained by the author (AN), and is organised as follows. Section 2 addresses flow around a pile with a Scour Protection. Section 3 looks at the initiation of sand motion beneath Scour Protection. Section 4 discusses sediment motion beneath Scour Protection and resulting sinking. Section 5 investigates the Horns Rev 1 case. A brief account is also given of filter criteria and their application to the Horns Rev 1 case, whereby the present results and the filter criteria results are linked.
-
Flow and bed shear stresses in Scour Protections around a pile in a current
Coastal Engineering, 2013Co-Authors: Anders Nielsen, B. Mutlu Sumer, Xiaofeng Liu, Jørgen FredsøeAbstract:Abstract Transport of bed sediment inside and beneath the Scour Protection may cause deformation and sinking of the Scour Protection for pile foundations. This may reduce the stability of the mono pile and change the natural frequency of the dynamic response of an offshore wind turbine installed on it in an unfavourable manner. Using physical models and 3D computational fluid dynamic (CFD) numerical simulations, the velocity and bed shear stresses are investigated in complex Scour Protections around mono piles in steady current. In the physical model the Scour Protections consisted of an upper cover layer with uniformly distributed coarse stones and a lower filter layer with finer stones. For the numerical simulations, the Flow-3D software was used. The Scour Protection layers were simulated with different numerical approaches, namely regularly arranged spheres, porous media, or their combinations (hybrid models). Numerical simulations with one or four layers of cover stones without filter layer were first computed. Three additional simulations were then made for a Scour Protection with a cover layer and a single filter layer. Finally, a simulation of a full scale foundation and Scour Protection was made with porous media approach. Based on the physical and numerical results, a method to determine the critical stones size to prevent motion of the base sediment is established and compared to a full scale case with sinking of Scour Protection (Horns Rev I Offshore Wind Farm, Denmark). It is also found that the CFD simulations are capable of calculating the flow velocities when the Scour Protection is represented by regular arranged spheres, while the turbulence in general is underestimated. The velocity can also be calculated using porous media flow approach, but the accuracy is not as good as for spheres. The deviation is more severe for more complex Scour Protections. In general, computational models provide valuable information for the prediction and design of Scour Protections for offshore wind farms.
-
Sinking of armour layer around a cylinder exposed to a current
Proceedings of the Institution of Civil Engineers - Maritime Engineering, 2011Co-Authors: Anders Wedel Nielsen, B. Mutlu Sumer, Jørgen Fredsøe, Erik Damgaard ChristensenAbstract:The flow processes in a Scour Protection around a monopile in steady current are described in relation to transport of sediment in the Scour Protection based on physical model tests. The Scour Protection consisted of uniformly distributed coarse stones without filter layer. Transport of sediment in the Scour Protection may cause sinking of the Scour Protection. This may reduce the stability of the monopile and change for instance the natural frequency of the dynamic response of an offshore wind turbine in an unfavourable manner. The most important flow process with regard to transport of sediment and sinking of the Scour Protection is found to be the horseshoe vortex. It is found that a larger pile diameter relative to the size of the Protection stones will cause a larger sinking and that two layers of stones will decrease the sinking relative to one layer of stones with the same size.