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1
Yang, Ray-Yeng, Hsin-Hung Chen, Hwung-Hweng Hwung, Wen-Pin Jiang, and Nian-Tzu Wu. "EXPERIMENTAL STUDY ON THE LOADING AND SCOUR OF THE JACKET TYPE OFFSHORE WIND TURBINE FOUNDATION." Coastal Engineering Proceedings 1, no. 32 (January 21, 2011): 25. http://dx.doi.org/10.9753/icce.v32.structures.25.
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A 1:36 scale model tests were carried out in the Medium Wave Flume (MWF) and Near-shore Wave Basin (NSWB) at the Tainan Hydraulics Laboratory (THL) with the jacket type offshore wind turbine foundation located in the test area. The loading of typhoon wave with current on the jacket type offshore wind turbine foundation was investigated in the MWF with fixed bed experiment. Meanwhile, the scour around the jacket type offshore wind turbine foundation exposed to wave and current was conducted in the NSWB with the moveable bed experiment. Two locations (water depth 12m and 16m) of the foundations are separately simulated in this study. Based on the analysis from the former NSWB experimental results, the suitable scour protection of a four-layer work around the foundation is also proposed to the impact of scour. Finally, a four-layer scour protection is tested and found to be effective in preventing scour around jacket type foundation of offshore wind turbines at water depth 12m and 16m.
2
Schneider, James A., and Marc Senders. "Foundation Design: A Comparison of Oil and Gas Platforms with Offshore Wind Turbines." Marine Technology Society Journal 44, no. 1 (January 1, 2010): 32–51. http://dx.doi.org/10.4031/mtsj.44.1.5.
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AbstractThe offshore oil and gas (O&G) industry has over 70 years of experience developing innovative structures and foundation concepts for engineering in the marine environment. The evolution of these structures has strongly been influenced by water depth as well as soil conditions in the area of initial developments. As the offshore wind industry expands from the glacial soil deposits of the North and Baltic Seas, experience from the O&G industry can be used to aid a smooth transition to new areas. This paper presents an introduction to issues that influence how design and construction experience from the O&G industry can be used to aid foundation design for offshore wind energy converters. A history of the evolution of foundation and substructure concepts in the Gulf of Mexico and North Sea is presented, followed by a discussion of soil behavior and the influence of regional geology on these developments. Mechanisms that influence the resistance of shallow and deep foundations for fixed and floating offshore structures are outlined so that areas of empiricism within offshore design codes can be identified and properly modified for application to offshore wind turbine foundations. It is concluded that there are distinct differences between offshore O&G and offshore wind turbine foundations, and application of continued research into foundation behavior is necessary for rational, reliable, and cost-effective design.
3
Been, K., J. I. Clark, and W. R. Livingstone. "Verification and calibration studies for the new CAN/CSA-S472 foundations of offshore structures." Canadian Geotechnical Journal 30, no. 3 (June 1, 1993): 515–25. http://dx.doi.org/10.1139/t93-044.
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In June 1992, the Canadian Standards Association (CSA) published a code for the design, construction, and installation of fixed offshore structures. This code is relatively advanced in its application of limit states design to offshore structures. The part dealing with foundations is written as a performance standard. It does not specify resistance factors (or safety factors) to achieve the target reliability of the structure. Although limit states design is common practice among geotechnical engineers, the application of resistance factors is a problem. This paper describes some of the studies and conclusions reached by the Technical Committee in the development of the CSA foundations standard. As a first step, resistance factors were developed by calibration to conventional total factors of safety for the failure mechanisms considered. This approach has severe limitations. In particular, the applicability of safety factors developed for onshore practice or other offshore areas to the ice-dominated environment of Canadian offshore regions is questionable. In addition, many offshore structure designs include consideration of dynamic loading and scour or erosion problems that cannot be satisfactorily dealt with using factors of safety. An example of the problem of applying separate load and resistance factors for a bearing-capacity problem is given to show that load and resistance are not independent of each other. Because of the problems with development of resistance factors, the CSA foundations standard dictates that offshore structure designs include a risk analysis of the foundation system. A simple form of such an analysis for a caisson-retained sand structure is included in the paper. Key words : offshore structures, foundations, standard, safety, limit states design.
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Gao, Feng, Clive Mingham, and Derek Causon. "SIMULATION OF EXTREME WAVE INTERACTION WITH MONOPILE MOUNTS FOR OFFSHORE WIND TURBINES." Coastal Engineering Proceedings 1, no. 33 (October 15, 2012): 22. http://dx.doi.org/10.9753/icce.v33.structures.22.
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Extreme wave run-up and impacts on monopile foundations may cause unexpected damage to offshore wind farm facilities and platforms. To assess the forces due to wave run-up, the distribution of run-up around the pile and the maximum wave run-up height need to be known. This paper describes a numerical model AMAZON-3D study of wave run-up and wave forces on offshore wind turbine monopile foundations, including both regular and irregular waves. Numerical results of wave force for regular waves are in good agreement with experimental measurement and theoretical results, while the maximum run-up height are little higher than predicted by linear theory and some empirical formula. Some results for irregular wave simulation are also presented.
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Esteban, M., José-Santos López-Gutiérrez, and Vicente Negro. "Gravity-Based Foundations in the Offshore Wind Sector." Journal of Marine Science and Engineering 7, no. 3 (March 12, 2019): 64. http://dx.doi.org/10.3390/jmse7030064.
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In recent years, the offshore wind industry has seen an important boost that is expected to continue in the coming years. In order for the offshore wind industry to achieve adequate development, it is essential to solve some existing uncertainties, some of which relate to foundations. These foundations are important for this type of project. As foundations represent approximately 35% of the total cost of an offshore wind project, it is essential that they receive special attention. There are different types of foundations that are used in the offshore wind industry. The most common types are steel monopiles, gravity-based structures (GBS), tripods, and jackets. However, there are some other types, such as suction caissons, tripiles, etc. For high water depths, the alternative to the previously mentioned foundations is the use of floating supports. Some offshore wind installations currently in operation have GBS-type foundations (also known as GBF: Gravity-based foundation). Although this typology has not been widely used until now, there is research that has highlighted its advantages over other types of foundation for both small and large water depth sites. There are no doubts over the importance of GBS. In fact, the offshore wind industry is trying to introduce improvements so as to turn GBF into a competitive foundation alternative, suitable for the widest ranges of water depth. The present article deals with GBS foundations. The article begins with the current state of the field, including not only the concepts of GBS constructed so far, but also other concepts that are in a less mature state of development. Furthermore, we also present a classification of this type of structure based on the GBS of offshore wind facilities that are currently in operation, as well as some reflections on future GBS alternatives.
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Barari, Amin, and Lars Bo Ibsen. "VERTICAL CAPACITY OF BUCKET FOUNDATIONS IN UNDRAINED SOIL." JOURNAL OF CIVIL ENGINEERING AND MANAGEMENT 20, no. 3 (March 10, 2014): 360–71. http://dx.doi.org/10.3846/13923730.2013.801915.
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Offshore wind turbine structures are traditionally founded on gravity concrete foundations or mono-piles. Bucket foundations were developed for the offshore oil and gas industry and are now being used in wind turbine construction. The loading in this application is characterized by a vertical load due to the slender construction combined with horizontal forces inducing a large overturning moment. Field tests on bucket foundations were performed to gain insight into the vertical load response of bucket foundations in clay soils. The field tests were accompanied by finite element numerical simulations in order to provide a better understanding of the parameters influencing bucket foundation behaviour.
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Sánchez, Sergio, José-Santos López-Gutiérrez, Vicente Negro, and M. Dolores Esteban. "Foundations in Offshore Wind Farms: Evolution, Characteristics and Range of Use. Analysis of Main Dimensional Parameters in Monopile Foundations." Journal of Marine Science and Engineering 7, no. 12 (December 2, 2019): 441. http://dx.doi.org/10.3390/jmse7120441.
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Renewable energies are the future, and offshore wind is undoubtedly one of the renewable energy sources for the future. Foundations of offshore wind turbines are essential for its right development. There are several types: monopiles, gravity-based structures, jackets, tripods, floating support, etc., being the first ones that are most used up to now. This manuscript begins with a review of the offshore wind power installed around the world and the exposition of the different types of foundations in the industry. For that, a database has been created, and all the data are being processed to be exposed in clear graphic summarizing the current use of the different foundation types, considering mainly distance to the coast and water depth. Later, the paper includes an analysis of the evolution and parameters of the design of monopiles, including wind turbine and monopile characteristics. Some monomials are considered in this specific analysis and also the soil type. So, a general view of the current state of monopile foundations is achieved, based on a database with the offshore wind farms in operation.
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Zografou, Dimitra, Susan Gourvenec, and Conleth O’Loughlin. "Vertical cyclic loading response of shallow skirted foundation in soft normally consolidated clay." Canadian Geotechnical Journal 56, no. 4 (April 2019): 473–83. http://dx.doi.org/10.1139/cgj-2018-0179.
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Skirted foundations are a potential foundation solution for a range of offshore structures, including hydrocarbon and renewable energy platforms and subsea structures. Offshore foundations can be subject to cyclic loading from environmental, installation, and operational events affecting the geotechnical response. A series of centrifuge tests have been performed on a shallow skirted foundation on normally consolidated kaolin clay under a range of vertical cyclic load sequences to investigate the effect of tensile or compressive average stress, the magnitude of the applied stress, and the effect of cyclic loading of low magnitude followed by consolidation on the foundation response. Results are presented as vertical foundation displacements normalized by the foundation geometry and interpreted within the traditional shear-strain contour approach. The findings indicate that the average, rather than maximum, vertical stress defines the foundation vertical displacement response and failure mode, a threshold stress exists below which a steady state is maintained even at a high number of cycles, and geotechnical resistance increases as a result of low-level cyclic loading followed by consolidation.
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Manzano-Agugliaro, Francisco, Miguel Sánchez-Calero, Alfredo Alcayde, Carlos San-Antonio-Gómez, Alberto-Jesús Perea-Moreno, and Esther Salmeron-Manzano. "Wind Turbines Offshore Foundations and Connections to Grid." Inventions 5, no. 1 (January 28, 2020): 8. http://dx.doi.org/10.3390/inventions5010008.
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Most offshore wind farms built thus far are based on waters below 30 m deep, either using big diameter steel monopiles or a gravity base. Now, offshore windfarms are starting to be installed in deeper waters and the use of these structures—used for oil and gas like jackets and tripods—is becoming more competitive. Setting aside these calls for direct or fixed foundations, and thinking of water depths beyond 50 m, there is a completely new line of investigation focused on the usage of floating structures; TLP (tension leg platform), Spar (large deep craft cylindrical floating caisson), and semisubmersible are the most studied. We analyze these in detail at the end of this document. Nevertheless, it is foreseen that we must still wait sometime before these solutions, based on floating structures, can become truth from a commercial point of view, due to the higher cost, rather than direct or fixed foundations. In addition, it is more likely that some technical modifications in the wind turbines will have to be implemented to improve their function. Regarding wind farm connections to grid, it can be found from traditional designs such as radial, star or ring. On the other hand, for wind generator modeling, classifications can be established, modeling the wind turbine and modeling the wind farm. Finally, for the wind generator control, the main strategies are: passive stall, active stall, and pitch control; and when it is based on wind generation zone: fixed speed and variable speed. Lastly, the trend is to use strategies based on synchronous machines, as the permanent magnet synchronous generator (PMSG) and the wound rotor synchronous generator (WRSG).
10
Stahlmann, Arne, and Torsten Schlurmann. "PHYSICAL MODELING OF SCOUR AROUND TRIPOD FOUNDATION STRUCTURES FOR OFFSHORE WIND ENERGY CONVERTERS." Coastal Engineering Proceedings 1, no. 32 (January 27, 2011): 67. http://dx.doi.org/10.9753/icce.v32.sediment.67.
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As a step to further develop the share of renewable energies, the first German offshore test site alpha ventus has been installed in the North Sea in 2009 in water depths of 30 m, where experience shall be gained and made available for
future offshore wind farms. Regarding converter foundations in deep water, it is well known that in most cases scour phenomena occur around the structures. Due to the complexity of the tripod foundations, significant knowledge gaps in scour progression in general and especially in detail as well as its probable effects on the stability and durability are given. Therefore, investigations on scouring phenomena around complex foundation structures like the tripod are
carried out within the research project. The investigation method consists of a unique combination of local scour monitoring as well as physical and numerical modeling, whereas the physical modeling part was carried by means of 1:40 laboratory tests and 1:12 large-scale physical model tests in wave flumes. The results show that scours around the tripod foundation do not only occur directly around the foundation piles, but also in the near-field of the structure. Compared to first in-situ measured scours in the test site, at least a good qualitative agreement of the modeled scour depths and evolutions could be shown.
11
Meyerhof, Geoffrey G. "Development of geotechnical limit state design." Canadian Geotechnical Journal 32, no. 1 (February 1, 1995): 128–36. http://dx.doi.org/10.1139/t95-010.
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The historical development of limit state design in geotechnical engineering is reviewed. Total and partial factors of safety used for the design of land–based and offshore structures are compared. It is found that the factors of safety in different codes for the ultimate and serviceability limit states design of earthworks, earth retaining structures, and land-based and offshore foundations are very similar. Partial factors in the ultimate limit state design are linked to the variability of the loads and soil parameters, the design approximations, and construction tolerances. They influence the nominal probability of failure of the type of structure considered and the seriousness of failure, which differ for land-based and offshore structures. These probabilities are compared with human fatality risks of common experiences. The serviceability limit states are governed by structural and operational constraints and the intended service life of the land-based or offshore structure. The corresponding partial factors are generally taken as unity. Key words : codes, earth structures, foundations, human risks, limit states design, probability of failures, factors of safety.
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Stahlmann, Arne, and Torsten Schlurmann. "INVESTIGATIONS ON SCOUR DEVELOPMENT AT TRIPOD FOUNDATIONS FOR OFFSHORE WIND TURBINES: MODELING AND APPLICATION." Coastal Engineering Proceedings 1, no. 33 (October 25, 2012): 90. http://dx.doi.org/10.9753/icce.v33.sediment.90.
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Regarding offshore constructions, there is still a lack in knowledge of scour progression for complex structures like foundations for offshore wind energy converters at present, which is however necessary for its dimensioning. As an example of such complex structure types, tripod foundations are constructed in German offshore wind farms at present. In order to describe physical processes and influencing factors on scour progression from a scientific point of view, comprehensive investigations on the scouring phenomena for tripod foundations have been carried out and will be partly presented here. The overall investigation method consists of a combination of 1:40 small and 1:12 large scale physical model tests in wave flumes, numerical simulations using CFD methods and in-situ measured scour data. For the numerical modeling part, a sediment transport model formulation has been implemented into OpenFOAM software code. The results show a general variability of scour depending on the load boundary conditions and structural parameters. Scours occur both at the foundation piles and directly under the structure, which in this form could not be predicted using standard approaches, but which has to be taken into account when regarding the soil mechanical stability and the final dimensioning of the foundations.
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Davidson, Alasdair, and Jasmin Semlitsch. "‘Solid foundations’: the advantages of using Guernsey Foundations for building a family office." Trusts & Trustees 25, no. 6 (July 1, 2019): 668–72. http://dx.doi.org/10.1093/tandt/ttz052.
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Abstract Family office services are gaining ever-increasing popularity and traction across the global offshore financial centres. The key characteristics and distinctions of Guernsey’s foundation regime make it a particularly effective tool for wealthy individuals and their dedicated family offices to achieve an array of investment, succession planning, or philanthropic objectives. In this article, we explore how Guernsey foundations can cater for the desired levels of control, tailor the rights of beneficiaries, maintain confidentiality, and be used in new and innovative ways to enhance and complement wealth management structures.
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Vieira, Mário, Miguel Viana, Elsa Henriques, and Luís Reis. "Soil Interaction and Grout Behavior for the NREL Reference Monopile Offshore Wind Turbine." Journal of Marine Science and Engineering 8, no. 4 (April 24, 2020): 298. http://dx.doi.org/10.3390/jmse8040298.
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Monopiles for offshore wind are the most used foundations by farm operators due to their low production costs, when compared to other bottom-fixed or floating foundations. In this research, a monopile foundation for offshore wind power was evaluated for its soil interaction and grout behavior, and an appropriate numerical model for the structural analysis of the foundation and tower was developed. FAST 8, an aero-hydro-servo-elastic numerical code developed by NREL, was used to obtain the loads applied on the supporting structures. These loads were pre-processed before they were inputted on the finite element model, developed using the finite element software ANSYS. The considered conical grout connection, which connects the monopile to the transition piece through friction, was modeled under a changing-status nonlinearity condition. To model the soil–pile interaction, a p-y model was applied using the ANSYS APDL commands. Static, modal, and transient structural analyses were produced to study the structure suitability for its use on offshore environments. Different soil interactions were modeled, and their results were then compared within the transient and modal analysis, indicating that the angle of the grout connection strongly affects the loading conditions on the grout. Moreover, scouring affects the dynamic behavior of the overall supporting structures, thus protection against this phenomenon is suggested.
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Andersson, Mathias H., and Marcus C. Öhman. "Fish and sessile assemblages associated with wind-turbine constructions in the Baltic Sea." Marine and Freshwater Research 61, no. 6 (2010): 642. http://dx.doi.org/10.1071/mf09117.
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Offshore wind farms are being built at a high rate around the world to meet the demand for renewable energy. We studied fish and sessile communities on and around offshore wind-turbine foundations in the southern Baltic Sea, 7 years after construction, using visual census techniques to determine how fish, sessile-invertebrate and algal communities are affected by the introduction of such structures. Fish assemblages were dominated by two-spotted gobies (Gobiusculus flavescens) that were found in large shoals in close association with the vertical surface. At the seabed, close to the foundation, the black goby (Gobius niger) was recorded in large numbers. The most obvious difference in fish densities was found between wind-power foundations extending through the entire water column and the surrounding open waters. Fouling assemblages on the vertical foundation surfaces and at the seabed just below differed from those at the seabed further away by having higher coverage of blue mussel (Mytilus edulis) and less algal growth. The results from the present study suggest that the introduction of offshore wind turbines in marine waters could have a positive effect on fish numbers and the presence of sessile invertebrates.
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Aliyeva, Sevda, and Mahmud Ismayilov. "RESEARCH OF THE WAVE FACTOR INFLUENCING HYDRAULIC STRUCTURES." ETM - Equipment, Technologies, Materials 05, no. 01 (January 20, 2021): 81. http://dx.doi.org/10.36962/etm0501202081.
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It is known that a large block of deep-sea foundations consists of a truss sheathed with wood, a metal beam system, floating structures and four pyramidal metal blocks with a truss structure. The design characteristics of the foundations of oil platforms depend on the conditions under which the vertical interaction, along with the calculation of permanent and temporary loads, is accompanied by the specific gravity of drilling equipment and rigs or horizontal wind pressure, as well as the influence of horizontal wave loads on the foundation blocks. Horizontal waves and wind loads can be constant and variable in different conditions, therefore the effect of each of these loads on the device must be considered separately. To determine the wave pressure acting on the support blocks of stationary offshore installations, SN-92-60 was used under the editorship of the team of authors under the leadership of Doctor of Technical Sciences, Professor N.N.Tsunkov. Keywords: hydraulic structures, wave factor, wave pressure, wave profile, pressure diagrams, 3D model.
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Arshad, Muhammad, and Brendan C. O'Kelly. "Analysis and Design of Monopile Foundations for Offshore Wind-Turbine Structures." Marine Georesources & Geotechnology 34, no. 6 (July 28, 2015): 503–25. http://dx.doi.org/10.1080/1064119x.2015.1033070.
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Shin, Yunsup, Thomas Langford, Kyunghwan Cho, Jongheon Park, and Junyoung Ko. "Applicability of Concrete–Steel Composite Piles for Offshore Wind Foundations." Energies 14, no. 16 (August 6, 2021): 4794. http://dx.doi.org/10.3390/en14164794.
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Offshore wind-turbine support structures are largely made of steel since steel monopiles have accounted for the majority of installations in the last decade. As turbines become bigger, steel structures have led to an exponential increase in material and installation costs. From this point of view, the use of concrete for future support structures has been initiated. In this study, concrete–steel composite piles have been investigated. A pre-tensioned high strength concrete pile was placed in the lower part, mainly to support the axial load, and a steel pile in the upper part to resist the lateral load. A mechanical joint was adapted to connect the two different types of piles. Static axial, dynamic axial, and lateral load tests were performed to evaluate the load-displacement response of the composite pile, verify the integrity of the mechanical joint, and investigate its potential application to offshore wind foundations. This paper focused on the load-displacement response and the connection integrity; in particular, it investigated the lateral load-displacement response by comparing it to the results of beam-spring analysis. Based on the results from the field tests, a site-specific lateral load-displacement curve was suggested, and the connection integrity was verified.
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Alati, Natale, Giuseppe Failla, and Felice Arena. "Seismic analysis of offshore wind turbines on bottom-fixed support structures." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 373, no. 2035 (February 28, 2015): 20140086. http://dx.doi.org/10.1098/rsta.2014.0086.
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This study investigates the seismic response of a horizontal axis wind turbine on two bottom-fixed support structures for transitional water depths (30–60 m), a tripod and a jacket, both resting on pile foundations. Fully coupled, nonlinear time-domain simulations on full system models are carried out under combined wind–wave–earthquake loadings, for different load cases, considering fixed and flexible foundation models. It is shown that earthquake loading may cause a significant increase of stress resultant demands, even for moderate peak ground accelerations, and that fully coupled nonlinear time-domain simulations on full system models are essential to capture relevant information on the moment demand in the rotor blades, which cannot be predicted by analyses on simplified models allowed by existing standards. A comparison with some typical design load cases substantiates the need for an accurate seismic assessment in sites at risk from earthquakes.
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Byrne, B. W., and G. T. Houlsby. "Helical piles: an innovative foundation design option for offshore wind turbines." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 373, no. 2035 (February 28, 2015): 20140081. http://dx.doi.org/10.1098/rsta.2014.0081.
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Offshore wind turbines play a key part in the renewable energy strategy in the UK and Europe as well as in other parts of the world (for example, China). The majority of current developments, certainly in UK waters, have taken place in relatively shallow water and close to shore. This limits the scale of the engineering to relatively simple structures, such as those using monopile foundations, and these have been the most common design to date, in UK waters. However, as larger turbines are designed, or they are placed in deeper water, it will be necessary to use multi-footing structures such as tripods or jackets. For these designs, the tension on the upwind footing becomes the critical design condition. Driven pile foundations could be used, as could suction-installed foundations. However, in this paper, we present another concept—the use of helical pile foundations. These foundations are routinely applied onshore where large tension capacities are required. However, for use offshore, a significant upscaling of the technology will be needed, particularly of the equipment required for installation of the piles. A clear understanding of the relevant geotechnical engineering will be needed if this upscaling is to be successful.
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Lin, Yung-Bin, Tzu-Kang Lin, Cheng-Chun Chang, Chang-Wei Huang, Ben-Ting Chen, Jihn-Sung Lai, and Kuo-Chun Chang. "Visible Light Communication System for Offshore Wind Turbine Foundation Scour Early Warning Monitoring." Water 11, no. 7 (July 17, 2019): 1486. http://dx.doi.org/10.3390/w11071486.
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Offshore wind farms have a superior wind source to terrestrial wind farms, but they also face more severe environmental conditions such as severe storms, typhoons, and sea waves. Scour leads to the excavation of sediments around the foundations of structures, reducing the safe capacity of the structures. The phenomenon of pier scour is extremely complex because of the combined effects of the vortex system involving time-dependent flow patterns and sediment transport mechanisms. A real-time scour monitoring system can improve the safety of structures and afford cost-effective operations by preventing premature or unnecessary maintenance. This paper proposes an on-site scour monitoring system using visible light communication (VLC) modules for offshore wind turbine installations. A flume experiment revealed that the system was highly sensitive and accurate in monitoring seabed scour processes. This arrayed-VLC sensory system, proposed in this paper, has considerable potential for safety monitoring and also can contribute to improving the accuracy of empirical scour formulas for sustainable maintenance in the life cycle of offshore structures.
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Ye, Hailin, Feng Zu, Chuwei Jiang, Wenjing Bai, and Yaojiang Fan. "Experimental Investigation of the Coupling Effect of Jackup Offshore Platforms, Towers, and Seabed Foundations under Waves of Large Wave Height." Water 15, no. 1 (December 21, 2022): 24. http://dx.doi.org/10.3390/w15010024.
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A large number of jackup offshore platforms with towers are widely applied in ocean engineering. The dynamic response of the platforms to waves of large wave height is critical, as such waves may cause platform accidents, property damage, and casualties. Therefore, it is important to investigate the coupling effect of jackup offshore platform, towers and seabed foundations under waves of large wave height. In this study, the coupling effect of offshore platforms, tower structures, and seabed foundations under the impact of waves of large wave height was studied via a physical flume model test. The experimental results show that the impact of waves of large wave height on the platforms is significant when the wave is blocked by the platform surface as the water body gathers under the platform surface, causing a pile group effect that results in the onshore piles being subjected to larger pressures than the front ones. The combined action of wave impact and pile leg squeezing force leads to an increase in the pore pressure of the foundation bed near the pile leg, and the soil near the pile leg becomes soft, revealing the mechanism of instability of the offshore platform’s pile foundation under waves of large wave height. The acceleration of the longitudinal movement of the platform increases under waves of large wave height, and the vortex-induced vibration of the platform includes the vibration along the direction of the wave and perpendicular to it. A coupled vibration effect between the tower structure and the platform occurs under waves of large wave height, reducing the vibration of the platform itself. Furthermore, damping members are installed on the tower structure, greatly reducing the natural vibration period and the motion response of the tower structure. This study provides significant enlightenment for the design of offshore platforms with towers to protect against waves of large wave height.
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Basack, Sudip, and Abhik Kumar Banerjee. "Offshore Pile Foundation Subjected to Lateral Cyclic Load in Layered Soil." Advanced Materials Research 891-892 (March 2014): 24–29. http://dx.doi.org/10.4028/www.scientific.net/amr.891-892.24.
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The pile foundations supporting offshore structures are required to be designed against cyclic load, moments and torques initiated by a combined action of waves, wind, tides, currents, etc. Such a complex loading condition produces progressive degradation in the pile-soil interactive performance which is likely to introduce significant reduction in bearing capacity with increased settlement and displacements. This paper is based on a numerical model developed by the Authors to study the response of pile foundation under lateral cyclic load in layered soil. The model is validated with a field test data and thereafter, parametric studies have been carried out. A brief description of the works conducted and the major conclusions drawn are highlighted in this paper.
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Fazeres-Ferradosa, Taveira-Pinto, Rosa-Santos, and Chambel. "Probabilistic Comparison of Static and Dynamic Failure Criteria of Scour Protections." Journal of Marine Science and Engineering 7, no. 11 (November 7, 2019): 400. http://dx.doi.org/10.3390/jmse7110400.
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The present paper provides a reliability assessment of scour protections applicable to both the static and dynamic stability design. As a case study, Horns Rev 3 hindcast data is used to simulate different failure criteria for an exemplary scour protection suitable for an offshore monopile foundation. The results show that the probability of failure is influenced by several factors, namely the wave friction factor, the definition of the acceptable damage number or the formulations used to calculate the bed shear-stress. The reliability assessment also indicates that annual probabilities of failure, associated to each criterion, might be comparable with the values presented in reliability standards for marine structures. Based on the results, this paper highlights future recommendations to improve the reliability-based design and analysis of scour protections for offshore foundations.
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Ye, Hailin, Dawei Yu, Jianhong Ye, and Zhiwen Yang. "Numerical Analysis of Dynamics of Jack-Up Offshore Platform and Its Seabed Foundation under Ocean Wave." Applied Sciences 12, no. 7 (March 24, 2022): 3299. http://dx.doi.org/10.3390/app12073299.
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Jack-up offshore platform is a type of important marine structure, which is mainly used for satellite launch, oil exploitation, and other engineering tasks in the offshore area. The offshore platform is bound to be subjected to wave loading in the course of use. Whether it can withstand the wave impact is an important engineering problem. To solve this engineering problem, the self-developed fluid–structure–foundation interaction coupling model OlaFlow-ABAQUS is used to explore the dynamic response characteristics of a jack-up offshore platform and its seabed foundation under three conventional wave conditions (wave height is 3, 5, and 7 m, respectively) in a coupled way. The numerical results show that only a small amplitude of periodic sloshing occurs for the jack-up offshore platform under the three conventional wave conditions. The maximum sloshing amplitude is up to 8 cm, and there is no visible residual displacement. It is indicated that there is no plastic deformation zone in the seabed foundation near the pile legs of the jack-up platform. It can thus be concluded that the jack-up platform has excellent stability under conventional wave conditions. Under conventional wave loading, momentary liquefaction occurs in the seabed foundation around the pile legs of the platform, and the maximum liquefaction depth is about 1 m. This study indicates that the coupling model OlaFlow-ABAQUS for the fluid–structure–foundation interaction is feasible, and has some advantages to study the dynamic response and to evaluate the stability of large-scale marine structures and their seabed foundations under ocean waves.
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Andresen, Lars, Hans Petter Jostad, and Knut H. Andersen. "Finite Element Analyses Applied in Design of Foundations and Anchors for Offshore Structures." International Journal of Geomechanics 11, no. 6 (December 2011): 417–30. http://dx.doi.org/10.1061/(asce)gm.1943-5622.0000020.
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Negro, Vicente, José-Santos López-Gutiérrez, M. Dolores Esteban, and Clara Matutano. "Uncertainties in the design of support structures and foundations for offshore wind turbines." Renewable Energy 63 (March 2014): 125–32. http://dx.doi.org/10.1016/j.renene.2013.08.041.
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Nasab, Navid Majdi, Jeff Kilby, and Leila Bakhtiaryfard. "Analysis and Design of Monopile Foundations for Offshore Wind and Tidal Turbine Structures." Water 14, no. 21 (November 5, 2022): 3555. http://dx.doi.org/10.3390/w14213555.
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This paper aims to design an integrated offshore structure capable of supporting a hybrid assembly of one wind plus two tidal turbines. The monopile has been found to be a suitable foundation type as the most inexpensive solution in water depths of less than 30 m. The Cook Strait in New Zealand is an ideal location for wind and tidal renewable energy sources due to its strong winds and tidal currents. Finite element analysis was performed to determine the displacement of the structure for different types of soils using OPTUM G3. After that, a macro-element model for soil was represented, considering the monopile as a Euler–Bernoulli beam model. The results enable the finding of optimum dimensions of monopiles with allowable tilt and deflection. Based on this, the diameter, thickness, and length of the monopile can be 6, 0.083, and 60 m, respectively. The maximum load occurs in extreme wind load scenarios when wind and waves move in same direction.
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Srokosz, Piotr, Ireneusz Dyka, and Marcin Bujko. "Determination of Shear Modulus of Soil in the RC/TS Apparatus for Designing Offshore Wind Power Plant Foundations." Polish Maritime Research 25, no. 3 (September 1, 2018): 69–83. http://dx.doi.org/10.2478/pomr-2018-0098.
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Abstract The paper presents a selected aspect of the determining the initial soil shear modulus value on the research example in resonant column – torsional shear apparatus (RC / TS). There are presented the significance of the initial value of shear modulus in design of offshore wind power plant foundations and the importance of its variability in the function of cyclical shear strains of soil related to the impact of sea and atmosphere on the designed structures. Based on the conducted analyses, a new methodology for interpreting the TS test results of soil has been proposed. It allows estimating the values of the shear modulus in the full range of shear strains occurring in issues closely related to the design and construction work of offshore wind power plant foundations.
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Van Impe, William F., and Shin-Tower Wang. "The advanced p-y method for analyzing the behaviour of large-diameter monopiles supporting offshore wind turbines." E3S Web of Conferences 205 (2020): 12008. http://dx.doi.org/10.1051/e3sconf/202020512008.
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The analyses of monopile foundations have been heavily based on the p-y response curves (to represent lateral soil resistances) published by API RP 2GEO (2011) and DNV (2013), which are proven reliable and applicable for piles with smaller diameters that were normally used for jacket structures in the offshore industry. However, concerns have been raised about the validity of semi-empirical p-y criteria for large-diameter piles. Wind turbine monopiles have a significantly larger diameter and smaller length to diameter ratio than typical piles used for offshore structures. The ratio of the length to the diameter for a monopile typically is also significantly smaller than those used in the API load tests. Therefore, the response of a monopile may be more like a rigid rotation, with components of resistance mobilized at the tip and axially along the sides as it rotates. This behaviour is in contrast to long slender piles that respond to lateral loading in bending rather than rotation. The objective of this paper is to analyze the factors that may contribute to the apparent conservatism in the current design practice for large-diameter monopile foundations and to provide improved solutions on how to analyze and design the large-diameter monopiles for offshore wind turbine using the p-y method.
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Xiao, Zhong, Yan Wang, Ying Liu, Yinghui Tian, Rong Wang, Ran Tao, and Xian Wei. "Formulas for Uniaxial Capacities of Tetrapod Bucket Foundations Considering Group Effects in Undrained Clay." Applied Sciences 12, no. 11 (May 25, 2022): 5353. http://dx.doi.org/10.3390/app12115353.
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Suction bucket foundation is a novel and cheaper foundation used in marine structures, such as offshore wind turbines, breakwater and oil platforms. Compared with a single bucket foundation, tetrapod bucket foundations can bear larger loads because of the group effects. However, the vertical, horizontal and moment capacity factors of tetrapod bucket foundations have not been presented in existing specifications. A series of three-dimensional finite-element analyses were conducted to investigate the group effects on uniaxial capacities and failure mechanisms of tetrapod bucket foundations in undrained clay considering various foundation separation distance ratios, embedment depth ratios, soil-strength heterogeneity indices and load direction angles. Generalized formulas for undrained uniaxial capacities of tetrapod bucket foundations were proposed in order to establish a bridge connecting the capacities of tetrapod bucket foundations and those of the single bucket foundation, which can provide a reference for industrial designs of capacities of tetrapod bucket foundations. The results show that the vertical group effect factor of tetrapod bucket foundations is basically not affected by the foundation separation distance ratio, embedment depth ratio, soil-strength heterogeneity index and load direction angle, which can adopted 0.9 based on a conservative estimation. The normalized horizontal and moment group effect factors of tetrapod bucket foundations are both affected by the separation distance ratio, embedment depth ratio and soil-strength heterogeneity index, but the moment group effect factor is also obviously affected by the load direction angle. The value of the horizontal and moment capacity factors of tetrapod bucket foundations are about 2.3 and 13.8 times that of a single bucket foundation, respectively, when the separation distance ratio is 3.5, embedment depth ratio is 1.0 and soil-strength heterogeneity index is 10, which have both been significantly enhanced. A value of 3.5 is suggested for the separation distance ratio to attain good capacities and a relatively high global stiffness for the tetrapod bucket foundations.
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Adhikari, S., and S. Bhattacharya. "Dynamic Analysis of Wind Turbine Towers on Flexible Foundations." Shock and Vibration 19, no. 1 (2012): 37–56. http://dx.doi.org/10.1155/2012/408493.
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Offshore wind turbines are considered as an essential part to develop sustainable, alternative energy sources. The structures themselves are both slender and highly flexible, with a subsea foundation typically consisting of a single large diameter monopile. They are subject to intense wind and wave loadings, with the result that significant movement of both the exposed structure and the upper part of the monopile can occur. Although the structures are intended for design life of 25 to 30 years, very little is known about the long term behaviour of these structures. This paper characterizes the dynamic behaviour of these structures. A simplified approach has been proposed for the free vibration analysis of wind turbines taking the effect of foundation into account. The method is based on an Euler-Bernoulli beam-column with elastic end supports. The elastic end-supports are considered to model the flexible nature of the interaction of these systems with the foundation. A closed-form expression of the characteristic equation governing all the natural frequencies of the system has been derived. Theoretical developments are explained by practical numerical examples. Analytical as well as a new experimental approach has been proposed to determine the parameters for the foundation. Some design issues of wind turbine towers are discussed from the point of view of the foundation parameters.
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Kim, Hyun-Gi, Bum-Joon Kim, and Kwang-Ho Lee. "Analysis of Piled Concrete Foundation for a 3-MW Class Offshore Wind Turbine along the Southwest Coast in Korea." Journal of Marine Science and Engineering 8, no. 3 (March 20, 2020): 215. http://dx.doi.org/10.3390/jmse8030215.
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Concrete foundations have received attention as offshore wind turbine support structures because of their various advantages. However, because of the lack of information on structural analysis and the design method of complex marine environmental loads, concrete foundations cannot be applied on actual sites. Therefore, the structure behavior mechanism and concrete reinforcement design need to be evaluated based on soil-structure interactions. Herein, an efficient method for analysis of piled concrete foundations (PCFs) is presented, and the stability of PCF structures is evaluated under environmental conditions of the coast in Korea for a 3-MW wind turbine. Three analytical parameters for PCF models were defined to consider soil-structure interaction. The results of each model were compared with the displacement, stresses, and natural frequencies. Using the analysis results, a prestressing reinforcement design for concrete foundations was proposed. Quasi-static analysis showed that maximum displacement was sufficiently small and the maximum stresses did not exceed the allowable stresses. PCF showed excellent dynamic performance and structural stability. In addition, stiffness of the soil spring model influenced the natural frequency rather than the stiffness of the pile type. Detailed analysis of the connections between piles and concrete need to be studied in the future.
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Byrne, Byron W., Harvey J. Burd, Lidija Zdravković, Ross A. McAdam, David M. G. Taborda, Guy T. Houlsby, Richard J. Jardine, Christopher M. Martin, David M. Potts, and Kenneth G. Gavin. "PISA: new design methods for offshore wind turbine monopiles." Revue Française de Géotechnique, no. 158 (2019): 3. http://dx.doi.org/10.1051/geotech/2019009.
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This paper provides a summary of the PIle Soil Analysis (PISA) project, completed in the UK during the period 2013 to 2018. The research led to the development of a new, computationally efficient, one dimensional design model for laterally loaded monopile foundations, particularly for offshore wind turbine support structures. The current form of the design model is applicable to monotonic loading only, but it could form a basis for extensions to cyclic loading. This short paper describes the background to the project, outlining the key research elements completed, as well as the main impacts that have been achieved. A number of publications describing the research in further detail are highlighted.
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Silva-Campillo, Arturo, Francisco Pérez-Arribas, and Juan Carlos Suárez-Bermejo. "Health-Monitoring Systems for Marine Structures: A Review." Sensors 23, no. 4 (February 13, 2023): 2099. http://dx.doi.org/10.3390/s23042099.
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This paper presents a comprehensive review of the state-of-the-art developments in health monitoring of marine structures. Monitoring the health of marine structures plays a key role in reducing the risk of structural failure. The authors establish the different sensors with their theoretical foundations and applications in order to determine the optimal position of the sensors on board. Once the data were collected, it was necessary to use for subsequent treatment; thus, the authors identified the different methodologies related to the treatment of data collected by the sensors. The authors provide a historical review of the location of different sensors depending on the type of ship and offshore platform. Finally, this review paper states the conclusions and future trends of this technology.
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Wu, Yuan Chieh, and Che Wei Hu. "Seismic Analysis for Pile Foundations in the Liquefiable Soil Layer Using FLAC3D." Applied Mechanics and Materials 764-765 (May 2015): 1114–18. http://dx.doi.org/10.4028/www.scientific.net/amm.764-765.1114.
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Pile foundation is the practical method to enhance earthquake-resistant ability for structures located in liquefiable soil sites. Soil liquefaction impact has been occurred such as Kashiwazaki-Kariwa NPP in 2007 Chūetsu offshore earthquake because of the soft backfill soil. To understand the behavior of pile foundations in liquefied soil during earthquake attack and conform to nuclear standard, seismic analysis with soil-structure interaction considering liquefaction using the finite difference program FLAC3D is developed to renew the traditional method used in nuclear industry. The models are verified according to a series of centrifuge model test results conducted in National Central University, Taiwan, to show the accuracy of seismic response prediction, and it provides the more advanced tool to demonstrate the detail of seismic response so that the utility and authority can easily decide the disaster prevention strategy.
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Cerfontaine, B., M. J. Brown, C. Davidson, Y. U. Sharif, M. Huisman, and M. Ottolini. "Optimised screw pile design for offshore jacket foundations in medium–dense sand." Géotechnique Letters 12, no. 2 (June 1, 2022): 1–6. http://dx.doi.org/10.1680/jgele.21.00105.
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Screw piles are well-suited foundations for offshore jacket structures, as they can be installed without significant underwater noise and have a large axial capacity. However, installation requirements for such large piles must be reduced to enable their installation in the field. This study combines geometry and installation optimisation to lower force and torque installation requirements. An original pile geometry, composed of a large diameter upper section connected to a smaller diameter lower section by a transition piece, was tested in a geotechnical beam centrifuge. The advancement ratio (AR), describing the relative vertical movement per pile rotation, was varied below the threshold usually recommended. The results show that a low AR reduces the pile penetration resistance and even generates some pull-in, while the torque remains almost unaffected. The torque is mainly associated with the upper section of the pile, which has a greater diameter to resist lateral loading in service. The pile capacity in tension generally increases as AR is reduced and reaches a maximum for AR = 0·5, while the compressive capacity reduces. It was shown that a simplified method can be used to estimate pile capacity, providing that some AR-dependent reduction factors can be calculated or assumed.
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Dixen, Martin, Iris Pernille Lohmann, and Erik Damgaard Christensen. "METHOD TO PREDICT LONG TIME SPAN OF SCOUR AROUND OFFSHORE WIND TURBINE FOUNDATIONS." Coastal Engineering Proceedings 1, no. 33 (October 25, 2012): 88. http://dx.doi.org/10.9753/icce.v33.sediment.88.
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A new method to predict scour development around offshore structures has been developed. The method has been tested on a monopile. The method consists of table of scour rates, which is used to predict the scour development around the structure at different stages of the scour hole. The scour rate tables have been made based on full 3D numerical simulations of the flow and sediment transport for fixed configurations of the scour hole. When changing the governing parameters which are causing the scour development around the structure, the erosion rate or backfilling rate can be calculated from the mass balance of the sediment. This leads to the scour rates tables that are used to analyses the development of the scour hole under different current conditions. The method has been tested against experimental scour data and showed very promising results.
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Puruncajas, Bryan, Yolanda Vidal, and Christian Tutivén. "Vibration-Response-Only Structural Health Monitoring for Offshore Wind Turbine Jacket Foundations via Convolutional Neural Networks." Sensors 20, no. 12 (June 17, 2020): 3429. http://dx.doi.org/10.3390/s20123429.
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This work deals with structural health monitoring for jacket-type foundations of offshore wind turbines. In particular, a vibration-response-only methodology is proposed based on accelerometer data and deep convolutional neural networks. The main contribution of this article is twofold: (i) a signal-to-image conversion of the accelerometer data into gray scale multichannel images with as many channels as the number of sensors in the condition monitoring system, and (ii) a data augmentation strategy to diminish the test set error of the deep convolutional neural network used to classify the images. The performance of the proposed method is analyzed using real measurements from a steel jacket-type offshore wind turbine laboratory experiment undergoing different damage scenarios. The results, with a classification accuracy over 99%, demonstrate that the stated methodology is promising to be utilized for damage detection and identification in jacket-type support structures.
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George, S. R., A. K. Verma, A. N. Desai, B. R. Dalwadi, and K. K. R. Iyer. "Effect of Soil-Pile-Structure Interaction on Behaviour of Offshore Jacket Structure." Proceedings of the 12th Structural Engineering Convention, SEC 2022: Themes 1-2 1, no. 1 (December 19, 2022): 1539–45. http://dx.doi.org/10.38208/acp.v1.686.
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Offshore jacket structures are generally supported on pile foundations. Studies have evaluated the effect of soil-pile interaction on design of foundation; however, effect of soil-pile-structure interaction on behaviour of jacket structure has received little attention. Hence, present study focuses on understanding the influence of soil conditions, soil-pile interaction and foundation modeling approach on deformation characteristics and member forces of jacket structure. Linear static analysis on a typical 4-legged battered jacket structure is performed using STAAD Pro., subjected to dead/live loads and environmental loads. The water depth of 120 m and wave heights of 5 m, 10 m and 15 m are considered for this study. Morison’s equation considering Stokes 5th order wave theory is used for calculation of wave forces on jacket structure. The supports are modelled as skirted pile groups. The piles are represented by springs, with stiffness calculated using soil-pile interaction analysis. The soil conditions used in the study are varied for different compaction states of sand and different consistency states of clay and various parameters such as lateral/vertical deflection, support reactions, forces in leg, beams and bracings have been compared. It is concluded that ignoring soil-pile-structure interaction during analysis of jacket structure would underestimate the lateral/vertical deflections, support reactions, shear force and bending moment for leg, and axial forces in beam and plan bracing of the structure. No substantial impact of the interaction on other member forces is observed. Jacket structure founded on clayey soil exhibits higher deformation and member forces as compared to sand in general. The study is expected to help structural engineers in adopting an appropriate modelling approach, considering soil-pile-structure interaction, to obtain more realistic response for jacket structures.
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Nessim, Maher A., Han Ping Hong, and James G. MacGregor. "Verification of the material resistance factors in the CSA-S474 code for offshore concrete structures." Canadian Journal of Civil Engineering 20, no. 4 (August 1, 1993): 660–71. http://dx.doi.org/10.1139/l93-083.
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The Canadian Standards Association has developed a national code for the design, construction and installation of fixed offshore structures. This code was developed on the basis of probabilistic principles. It consists of five parts (CAN/CSA-S471 to S475), dealing with general loading and design requirements, foundations, steel structures, concrete structures, and sea operations. The material resistance factors cited in the part on concrete structures (S474-M1989) were verified using data typical of offshore structures for a set of representative design cases. The test cases were based on reinforced concrete ice resisting walls with configurations typical of those contemplated for offshore structures in Canada. They covered rare and frequent ice loading for safety classes I and II under flexure, combined flexure and axial force, and shear. The test cases were designed according to the CSA and DnV code provisions, and the reliabilities associated with the resulting members were calculated and assessed. The results indicate that the reliabilities achieved by designing to the CSA standard for safety class I sections are greater than those obtained by designing to DnV rules for all cases considered. Designs carried out according to CSA-S474 meet the target reliabilities implied by CSA-S471 for values of the coefficient of variation of the in situ concrete strength of up to 12% and are, in many cases, very conservative. Sensitivity analysis of safety class I members suggests that the material resistance factors can be increased. Issues that need to be addressed in order to justify an increase in the factors include the acquisition of more data on in situ concrete strength and a more comprehensive consideration of the design conditions covered by the code. The overall consistency of the reliability levels associated with the CSA code can be improved by simultaneous verification of the material factors in CSA-S474 and the load criteria and factors in CSA-S471. Key words: concrete structures, offshore structures, code verification, structural reliability, in situ concrete strength.
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Lang, Ruiqing, Run Liu, Jijian Lian, and Hongyan Ding. "Study on Load-Bearing Characteristics of a New Pile Group Foundation for an Offshore Wind Turbine." Scientific World Journal 2014 (2014): 1–11. http://dx.doi.org/10.1155/2014/394104.
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Because offshore wind turbines are high-rise structures, they transfer large horizontal loads and moments to their foundations. One of the keys to designing a foundation is determining the sensitivities and laws affecting its load-bearing capacity. In this study, this procedure was carried out for a new high-rise cap pile group foundation adapted to the loading characteristics of offshore wind turbines. The sensitivities of influential factors affecting the bearing properties were determined using an orthogonal test. Through a combination of numerical simulations and model tests, the effects of the inclination angle, length, diameter, and number of side piles on the vertical bearing capacity, horizontal bearing capacity, and bending bearing capacity were determined. The results indicate that an increase in the inclination angle of the side piles will increase the vertical bearing capacity, horizontal bearing capacity, and bending bearing capacity. An increase in the length of the side piles will increase the vertical bearing capacity and bending bearing capacity. When the length of the side piles is close to the central pile, the increase is more apparent. Finally, increasing the number of piles will increase the horizontal bearing capacity; however, the growth rate is small because of the pile group effect.
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Abdullahi, A., Y. Wang, and S. Bhattacharya. "Comparative Modal Analysis of Monopile and Jacket Supported Offshore Wind Turbines including Soil-Structure Interaction." International Journal of Structural Stability and Dynamics 20, no. 10 (September 2020): 2042016. http://dx.doi.org/10.1142/s021945542042016x.
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Offshore wind turbines (OWTs) have emerged as a reliable source of renewable energy, witnessing massive deployment across the world. While there is a wide range of support foundations for these structures, the monopile and jacket are most utilized so far; their deployment is largely informed by water depths and turbine ratings. However, the recommended water depth ranges are often violated, leading to cross-deployment of the two foundation types. This study first investigates the dynamic implication of this practice to incorporate the findings into future analysis and design of these structures. Detailed finite element (FE) models of Monopile and Jacket supported OWTs are developed in the commercial software, ANSYS. Nonlinear soil springs are used to simulate the soil-structure interactions (SSI) and the group effects of the jacket piles are considered by using the relevant modification factors. Modal analyzes of the fixed and flexible-base cases are carried out, and natural frequencies are chosen as the comparison parameters throughout the study. Second, this study constructs a few-parameters SSI model for the two FE models developed above, which aims to use fewer variables in the FE model updating process without compromising its simulation quality. Maximum lateral soil resistance and soil depths are related using polynomial equations, this replaces the standard nonlinear soil spring model. The numerical results show that for the same turbine rating and total height, jacket supported OWTs generally have higher first-order natural frequencies than the monopile supported OWTs, while the reverse is true for the second-order vibration modes, for both fixed and flexible foundations. This contributes to future design considerations of OWTs. On the other hand, with only two parameters, the proposed SSI model has achieved the same accuracy as that using the standard model with seven parameters. It has the potential to become a new SSI model, especially for the identification of soil properties through the model updating process.
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Majdi Nasab, Navid, Jeff Kilby, and Leila Bakhtiaryfard. "Integration of wind and tidal turbines using spar buoy floating foundations." AIMS Energy 10, no. 6 (2022): 1165–89. http://dx.doi.org/10.3934/energy.2022055.
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<abstract> <p>Floating platforms are complex structures used in deep water and high wind speeds. However, a methodology should be defined to have a stable offshore structure and not fail dynamically in severe environmental conditions. This paper aims to provide a method for estimating failure load or ultimate load on the anchors of floating systems in integrating wind and tidal turbines in New Zealand. Using either wind or tidal turbines in areas with harsh water currents is not cost-effective. Also, tidal energy, as a predictable source of energy, can be an alternative for wind energy when cut-in speed is not enough to generate wind power. The most expensive component after the turbine is the foundation. Using the same foundation for wind and tidal turbines may reduce the cost of electricity. Different environment scenarios as load cases have been set up to test the proposed system's performance, capacity and efficiency. Available tidal records from the national institute of Water and Atmospheric Research (NIWA) have been used to find the region suitable for offshore energy generation and to conduct simulation model runs. Based on the scenarios, Terawhiti in Cook Strait with 110 m water height was found as the optimized site. It can be seen that the proposed floating hybrid system is stable in the presence of severe environmental conditions of wind and wave loadings in Cook Strait and gives a procedure for sizing suction caisson anchors.</p> </abstract>
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Wang, Zhuo, Zhuang Li, Tao Wang, and Bo Zhang. "Study on Clamping Mechanism of Internal and External Variable Diameter Lifting Tool for Offshore Foundation Pile." Machines 9, no. 1 (January 17, 2021): 19. http://dx.doi.org/10.3390/machines9010019.
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Large marine foundation piles are an important part of offshore structural pile foundations, and their lifting operations have always been a major problem in the construction and construction of marine structures. Based on IHC’s bilateral marine foundation pile spreader, this paper proposes a structural scheme of “internal and external clamping type variable diameter marine foundation pile spreader”. It solves the problem of poor adaptability of spreaders to foundation piles of the same specification and different pipe diameters. At the same time, this article has conducted in-depth research on the two clamping methods of friction clamping and wedge tooth embedded clamping. Through experiments, it is found that under the same lateral load, the load capacity of the wedge teeth tightening is three times that of the friction clamping. Aiming at the embedding and clamping method of the wedge teeth of the spreader, first of all, the influence of the tooth profile angle of the wedge teeth on their embedding performance was studied by the plastic mechanics slip line field theory and Abaqus simulation analysis. Subsequently, the elastic mechanics theory and Abaqus simulation analysis were used to study the stress characteristics of the wedge teeth during the lifting process, and the internal stress distribution was obtained. The article aims to provide a reference for the design of spreaders in actual projects.
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George, S. R., A. K. Verma, B. R. Dalwadi, and K. K. R. Iyer. "A Parametric Study on Effect of Wave Height, Water Depth and Support Conditions on Behaviour of Offshore Jacket Structure." Proceedings of the 12th Structural Engineering Convention, SEC 2022: Themes 1-2 1, no. 1 (December 19, 2022): 1757–63. http://dx.doi.org/10.38208/acp.v1.715.
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Fixed offshore jacket structures are constructed for facilitating oil/gas exploration and production. These structures and their foundations are designed to resist large vertical and lateral loads. Various factors including water depth, wave height and support conditions would affect the response of jacket structures. However, few studies have focused on understanding the response of offshore jacket structure due to variation in these factors. In this context, the present work evaluates response of typical X-braced, square base, 4-legged battered jacket structure using STAAD Pro. under combined vertical and lateral environmental loading. The variables included are water depth (60 m, 90 m and 120 m), wave height (5 m, 10 m and 15 m) and two foundation modelling approaches (viz., fixed at pile location and with defined pile stiffness). The connection between structure leg and pile location is modelled to simulate realistic connection. Deck loads, wind forces and current velocities are considered constant for this study. The wind and wave loads have been applied in parallel, perpendicular and diagonal directions with respect to jacket structure. The wave forces are calculated by Morrison’s equation. For obtaining pile stiffness, medium dense sand layer is considered as foundation soil. The increase in water depth and wave height results in corresponding linear increase in lateral deflection and support reactions, the effect of water depth being more prominent. Moreover, lateral and vertical deflection, shear force and bending moment in the legs, the axial forces in the lower tie beams and plan bracings, and support moments are observed to increase when pile locations are modelled with appropriate vertical, lateral and rotational stiffness instead of fixed support. The effect of water depth on member forces is higher as compared to wave height. The present work deliberates on the mechanisms/reasons to explain the observed results and contributes in direction of framing decision matrix for design optimization of jacket structures.
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Sun, Zhenzhou, Shengxiao Zhao, Chunwei Bi, Qiupan Chen, Shanshan Huang, and Jiefeng Chen. "Dynamic Response Analysis of an Offshore Converter Platform with Valve Towers under Seismic Excitation." Symmetry 14, no. 8 (August 9, 2022): 1635. http://dx.doi.org/10.3390/sym14081635.
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Converter valves are the core equipment of offshore wind power structures. However, they are highly vulnerable to vibration under strong earthquakes, which will affect normal operation of the offshore wind farm. Converter station is an axisymmetric structure with obvious asymmetry in its internal configuration of the superstructure. This study aimed to analyze the dynamic response of a supported converter valve in an offshore converter station under seismic excitation. The coupling model of the supported valve tower group and the converter station were established, and the distribution law of the valve tower dynamic response and foundation settlement were investigated. The dynamic response effect of the modal truncation, valve tower stiffness, and basic size on different areas and foundations of the valve towers were studied. The findings were as follows: (i) the effect of local vibration of the valve tower should not be simplified by using equivalent mass and node condensation; (ii) the structure–equipment coupling analysis method should be used to review the structural design scheme of the offshore converter station in the intensity VII region; (iii) the vertical higher-order modes should be considered during the vibration response calculation and its participation ratio in mass should not be lower than 90%; (iv) the frequency range that minimizes the vibration response is the characteristic frequency range of horizontal vibration, while the best vibration suppression effect cannot be obtained in both the horizontal and vertical directions; and (v) the stiffness of the valve tower itself should be adjusted and different stiffness designs of the valve tower in different positions should be adopted to realize effective vibration response control.
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de Sitter, Gert, Wout Weitjens, Mahmoud El-Kafafy, and Christof Devriendt. "Monitoring Changes in the Soil and Foundation Characteristics of an Offshore Wind Turbine Using Automated Operational Modal Analysis." Key Engineering Materials 569-570 (July 2013): 652–59. http://dx.doi.org/10.4028/www.scientific.net/kem.569-570.652.
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This paper will show the first results of a long term monitoring campaign on an offshore wind turbine in the Belgian North Sea. It will focus on the vibration levels and resonant frequencies of the fundamental modes of the support structure. These parameters will be crucial to minimize O&M costs and to extend the lifetime of offshore wind turbine structures. For monopile foundations for example, scouring and reduction in foundation integrity over time are especially problematic because they reduce the fundamental structural resonance of the support structure, aligning that resonance frequency more closely to the lower frequencies. Since both the broadband wave energy and the rotating frequency of the turbine are contained in this low frequency band, the lower natural frequency can create resonant behavior increasing fatigue damage. Continuous monitoring of the effect of scour on the dynamics of the wind turbine will help to optimize the maintenance activities on the scour protection system. To allow a proper continuous monitoring during operation, reliable state-of-the-art operational modal analysis techniques should be used and these are presented in this paper. The methods are also automated, so that no human-interaction is required and the system can track the natural frequencies and damping ratios in a reliable manner.
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Ju, Shen-Haw, Chueh-Sheng Chiu, and Hsin-Hsiang Hsu. "Studying the Settlement of OWT Monopile Foundations Using a T-Z Spring with the Torsional Effect." Processes 11, no. 2 (February 6, 2023): 490. http://dx.doi.org/10.3390/pr11020490.
Full textAbstract:
The main purpose of this paper was to study the vertical settlement of offshore wind turbine (OWT) monopile support structures, where 5, 10, 15, and 20 MW OWT support structures were analyzed under power production, seismic, and tropical cyclone loads. Moreover, a t-z spring with shear and torsional degrees of freedom was developed to simulate the shear stress along the pile and soil surface under the combined effect of vertical loads and z-direction torsions. This t-z spring does not require excessive changes to the finite element program, where only a known factor is used to modify the traditional stiffness of the t-z spring. This paper, analyzing several kinds of OWT monopile foundations, indicates that the soil shear resistance may be less than the shear stress generated by the combination of vertical loads and torsions, which causes large vertical and rotational displacements resulting in the failure of monopile structures. This situation will be worse when the natural frequency of the first vertical-direction rotation is close to the integer multiples of the 3P frequency, which cannot be well-simulated using traditional t-z springs.
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Statti, Giuseppe, Ali Mehmanparast, Romali Biswal, and Cesare Mario Rizzo. "Evaluation of Cyclic Loading Effects on Residual Stress Relaxation in Offshore Wind Welded Structures." Journal of Multiscale Modelling 12, no. 02 (June 2021): 2150005. http://dx.doi.org/10.1142/s1756973721500050.
Full textAbstract:
Monopile foundations contain welding residual stresses and are widely used in industry to support offshore wind turbines (OWTs). The monopiles are subjected to hammering loads during installation and cyclic loads during operation, therefore the influence of residual stress redistribution as a result of fatigue cycles must be evaluated in these structures. The existing empirical models to predict the residual stress redistribution in the presence of cyclic loading conditions are strongly dependent on the material, welding process and loading conditions. Hence, there is a need to predict the residual stress redistribution using finite element simulations. In this study numerical analyses have been conducted to predict the initial state of residual stress in a simplified weld geometry and examine the influence of subsequent cyclic loads on the relaxation behavior in residual stress profiles. The results have shown that fatigue cycles have a severe effect on residual stress relaxation with the greatest reduction in residual stress values observed in the first cycle. Moreover, the numerical prediction results have shown that the stress amplitude plays a key role in the extent of residual stress relaxation in welded structures.