Rozprawy doktorskie: „Offshore foundation”

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Aspizua, Lucía. "OFFSHORE FOUNDATION - A CHALLENGE IN THE BALTIC SEA". Thesis, Högskolan i Halmstad, Energivetenskap, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:hh:diva-28443.

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ABSTRACT This project deals with the search of the most proper offshore foundation to install in the Baltic Sea, in order to reduce costs and environmental impact. A pre-study was performed to define the Baltic Sea conditions and the required knowledge for the following steps. Afterwards, the specifications were set and clarified, and then the concept analysis phase was started. The analysis phase included the description of each one of the current foundations, those which are considered conventional foundations and those which are innovative ones. In order to evaluate these concept foundations, selection methods were used to assess the most relevant features of these foundations which should fulfil the requirements. The concepts ranking was studied and it led to the final results. Two different outcomes were obtained; such as, innovative concepts, which obtained the first position in this report; and conventional concepts, as a second finding. The continuous contact with different experienced professionals of this sector was essential during the whole project, in order to obtain advices, experienced knowledge and feedback.

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Villalobos, Jara Felipe Alberto. "Model testing of foundations for offshore wind turbines". Thesis, University of Oxford, 2006. http://ora.ox.ac.uk/objects/uuid:438cfe69-c8d4-4630-ab0b-482da5ea2839.

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Suction caissons are a new foundation option for offshore wind turbines. This thesis is focussed on the behaviour of suction caisson foundations in sand and in clay during installation, and under subsequent vertical and combined moment-lateral loadings. The research is based on extensive experimental work carried out using model scaled caissons. The analysis of the results allowed the determination of parameters for hyperplasticity models. Model caissons were vertically loaded in loose and dense sands to study in service states and plastic behaviour. Bearing capacity increased with the length of the caisson skirt. The bearing capacity formulation showed that the angle of friction mobilised was close to the critical state value for loose sands and close to those of peak values due to dilation for dense sands. The vertical load increased, though at a lower rate than during initial penetration, after large plastic displacements occurred. A hardening law formulation including this observed behaviour is suggested. In sand the installation of caissons by suction showed a drastic reduction in the net vertical load required to penetrate the caisson into the ground compared with that required to install caissons by pushing. This occurred due to the hydraulic gradients created by the suction. The theoretical formulations of the yield surface and flow rule were calibrated from the results of moment loading tests under low constant vertical loads. The fact that caissons exhibit moment capacity under tension loads was considered in the yield surface formulation. Results from symmetric and non symmetric cyclic moment loading tests showed that Masing’s rules were obeyed. Fully drained conditions, partially drained and undrained conditions were studied. Caisson rotation velocities scaled in the laboratory to represent those in the field induced undrained response for relevant periods of wave loading, a wide range of seabed permeabilities and prototype caisson dimensions. Under undrained conditions and low constant vertical loads the moment capacity of suction caissons was very small. Under partially drained conditions the moment capacity decreased with the increase of excess pore pressure. In clay, vertical cyclic loading around a mean vertical load of zero showed that in the short term the negative excess pore pressures generated during suction installation reduced vertical displacements. The yield surface and the flow rule were determined from moment swipe and constant vertical load tests. The moment capacity was found to depend on the ratio between the preload Vo and the ultimate bearing capacity Vu. Gapping response was observed during cyclic moment loading tests, but starting at smaller normalised rotations than in the field. The hysteresis loop shape obtained during gapping cannot be reproduced by means of the Masing’s rules.

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Ngo-Tran, Cong Luan. "The analysis of offshore foundations subjected to combined loading". Thesis, University of Oxford, 1996. http://ora.ox.ac.uk/objects/uuid:96a07b7a-58f8-4a5d-9dfd-68509546368c.

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This thesis is concerned with four different types of offshore foundations, namely gravity foundations, jack-up foundations, the mudmats for piled jacket structures and caisson foundations for jacket structures. In most applications, these can be idealised as circular rigid foundations. Unlike onshore foundations, offshore foundations are subjected to large horizontal and moment loads. This research used the finite element method to examine the elastic behaviour and stability of circular footings under combined loading. Due to the circular shape of the footings and the combination of vertical, horizontal and moment loads, three dimensional finite element analysis was used. In-depth analyses of the elastic behaviour of circular footings under combined loading (V,H,M) were performed. The vertical stiffness coefficient was investigated using two dimensional axi-symmetric analyses whereas three dimensional analyses were used to examine the other coefficients. Different features of offshore foundations such as footing embedment and cone angle were taken into consideration. Based on the numerical results, a set of empirical expressions for elastic stiffness coefficient was derived. For footing stability calculations, large horizontal or moment loads can cause the footing to lose contact with the soil, or cause the footing to slide relative to the soil. In finite element analyses, this loss of contact and sliding are modelled by interface elements. A new zero-thickness iso-parametric interface element was formulated for both two and three dimensional analyses. An exact close formed solution for integration of the stress-strain relationship (for the two dimensional interface element) was found. The element is then used to explore footing stability. It was shown that by using a yield criteria which allows the interface to behave as either frictional or cohesive interface, depending upon the normal stress, numerical stability is achieved. The footing stability was examined by establishing the bearing capacity envelope. The envelopes for footings on undrained clays were established for surface flat strip footings and for surface flat circular footings. The effects of soil strength varying with depth, cone angle and embedment on the bearing capacity envelope were also investigated.

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Floridia, Daniele. "Hybrid foundations for offshore wind turbines". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2012. http://amslaurea.unibo.it/3284/.

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Nowadays offshore wind turbines represents a valid answer for energy production but with an increasing in costs mainly due to foundation technology required. Hybrid foundations composed by suction caissons over which is welded a tower supporting the nacelle and the blades allows a strong costs reduction. Here a monopod configuration is studied in a sandy soil in a 10 m water depth. Bearing capacity, sliding resistance and pull-out resistance are evaluated. In a second part the installation process occurring in four steps is analysed. considering also the effect of stress enhancement due to frictional forces opposing to penetration growing at skirt sides both inside and outside. In a three dimensional finite element model using Straus7 the soil non-linearity is considered in an approximate way through an iterative procedure using the Yokota empirical decay curves.

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Alhamalawi, Mazen. "Offshore Wind Power Foundations' Corrosion Protection Strategy : Anlysis remotely controlled corrosion protection system and comparison to traditional corrosion protection of offshore wind foundation". Thesis, Linnéuniversitetet, Sjöfartshögskolan (SJÖ), 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-103460.

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När en metall är omgärdad av en elektrolyt, så som havsvatten, kommer det att byggas upp en naturlig potential. Det sker en elektronvandring mellan materialet och havsvattnet och ju större potentialskillnad desto större sannolikhet att metallen kommer korrodera. Korrosion är en stor och viktig fråga för offshorekonstruktioner och byggnader. För att uppnå en konstruktions designade livslängd kan åtgärder vidtas med hänsyn till kapitalkostnader och drift- och underhållskostnader. Denna studie syftar till att jämföra ekonomiska för- och nackdelar hos de två korrosionsskyddssystemen Galvanic Anode Corrosion Protection (GACP) och Impressed Current Cathodic Protection (ICCP) på havsbaserade vindkraftsfundament. Det förstnämnda systemet använder offeranoder och det sistnämnda är ett katodiskt korrosionsskydd med hjälp av påtryckt ström. Studien bestod av flera steg av litteraturstudier där teori om korrosion och korrosionssystem användes för att till slut kunna jämföra valda korrosionsskyddssystem. Resultatet visar att GACP har fler fördelar och färre nackdelar än ICCP och skulle därmed vara mer ekonomiskt fördelaktig i marina miljöer. GACP ger också önskad effekt direkt vid installation och behöver inte någon strömkälla, ICCP är mer komplicerat och är inte effektivt förrän hela systemet är monterat och i drift. Dessutom behöver ICCP extra strömkälla samt kablage.
When a metal is surrounded by an electrolyte, such as seawater, a natural potential will be built up. An electron migration between the material and the seawater will happen and the greater the potential difference, the greater the probability that the metal will corrode. Corrosion is an important issue when it comes to offshore structures. In order to achieve a structure designed lifetime, measures can then be taken with regard to capital costs and operating and maintenance costs. This study aims to compare the economic advantages and disadvantages of the two, Galvanic Anode Corrosion Protection (GACP) and Impressed Current Cathodic Protection (ICCP), corrosion protection systems on offshore wind power foundations. The first mentioned system uses sacrificial anodes and the second is a cathodic corrosion protection by an applied current. The study consisted of several stages of literature studies where theory of corrosion and corrosion systems was used to finally be able to make a comparison between selected corrosion protection systems. The result shows that GACP has more advantages and fewer disadvantages than ICCP and would thus be more economical. GACP, for example, is efficient during installation and does not need an additional power source, but ICCP is more complicated and not efficient until complete assembly of the entire system and requires additional power source and cables. Right now, there is no design standard available with detailed requirements and advice has been given as for galvanic anodes systems.

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Santa, Maria Paulo Eduardo Lima de. "Behaviour of footings for offshore structures under combined loads". Thesis, University of Oxford, 1988. http://ora.ox.ac.uk/objects/uuid:50fb3d35-90b3-4685-9ace-0ec5a50014df.

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The lack of knowledge about the behaviour of footings for jack-up rigs under storm loads poses a design problem which can be tackled by model testing. The areas of prime concern are the ultimate loads on footings under combined loading, which affects the safety of the rig, and the rotational stiffness, which affects the interaction between the foundation and the structure. A programme of loading tests was performed on model footings on clay, and was divided into two stages: monotonic loading and cyclic loading. The clay samples were obtained by consolidating Speswhite kaolin slurry in cylindrical tanks 450mm in diameter. The strength and compressibility characteristics of the samples were verified by means of standard laboratory tests. The model footings were 50mm and 100mm in diameter and several shapes were tested: circular flat plate, cones of various angles and model spud-cans. Loads and displacements were monitored using appropriate instrumentation and a data logger. A series of central vertical loading tests provided data for comparison with existing bearing capacity theories. Combined loading tests were performed applying a displacement controlled horizontal load at a fixed height above the footing which was also subjected to a fixed vertical load. The main series of tests involved a parametric study of the relevant variables. Special tests allowed the assessment of the effect of embedment of the footing and the interaction of a flexible leg with the foundation. Cyclic loading tests were carried out using a load controlled system which applied a sinusoidal load simulating wave action. Effects of currents were investigated by introducing an offset to the loading cycle. The influence of amplitude and period of loading as well as the influence of vertical load were also investigated. Special tests were carried out to cover some peculiarities of real loading conditions. Fitting of a three-parameter hyperbola to the test results provided a systematic and accurate method of analysis of monotonic loading tests, leading to valuable information involving stiffness and ultimate loads. Analysis of cyclic loading tests yielded useful qualitative information regarding the progress of settlement and the variation of rotational stiffness and damping ratio with the number of cycles.

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Byrne, Byron Walter. "Investigations of suction caissons in dense sand". Thesis, University of Oxford, 2000. http://ora.ox.ac.uk/objects/uuid:64c30b2e-155c-4642-9115-5e2bf5667af5.

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Offshore structures are used in a variety of applications ranging from the traditional oil and gas extraction facilities to emerging renewable energy concepts. These structures must be secured to the seabed in an efficient and cost effective manner. A novel approach is to use shallow inverted buckets as foundations, installed by suction, in place of the more usual piles. These foundations lead to cost savings through reduction in materials and in time required for installation. It is necessary to determine how these foundations perform under typical offshore loading conditions so that design calculations may be developed. This thesis presents experimental data from a comprehensive series of investigations aimed at determining the important mechanisms to consider in the design of these shallow foundations for dense sand. Initially the long term loading behaviour (e.g. wind and current) was investigated by conducting three degree of freedom loading {V:M/2R:H} tests on a foundation embedded in dry sand. The results were interpreted through existing work-hardening plasticity theories. The analysis of the data has suggested a number of improved modelling features. Cyclic and transient tests, representing wave loading, were carried out on a foundation embedded in an oil saturated sand. The novel feature of the cyclic loading was that a 'pseudo-random' load history (based on the 'NewWave' theory) was used to represent realistic loading paths. Of particular interest was the tensile load capacity of the foundation. The results observed suggested that for tensile loading serviceability requirements rather than capacity may govern design. Under combined-load cyclic conditions the results indicated that conventional plasticity theory would not provide a sufficient description of response. A new theory, termed 'continuous hyperplasticity' was used, reproducing the results with impressive accuracy. Surprisingly, under the conditions investigated, loading rate was found to have a negligible effect on response.

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Mangal, Jan Krishna. "Partially-drained loading of shallow foundations on sand". Thesis, University of Oxford, 1999. http://ora.ox.ac.uk/objects/uuid:205bf0bc-b801-4648-a556-8dba0d113cba.

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Wave loading on offshore structures founded on sand can result in partially drained response of the foundation soil. The characteristics of the rate of loading, the permeability of the soil, and the size of the foundation affect the degree of partial drainage. Partial drainage refers to situations where pore pressures develop in the soil, and the response of the soil is neither fully drained nor undrained. This thesis is concerned with the effects of loading rate, and consequent drainage, on the behaviour of a flat footing that is founded on the surface of a saturated sand base. The results of physical tests performed in the laboratory on a model-sized footing are reported. The footing was founded on oil-saturated fine sand and was subjected to combined loading. The effect of the vertical, horizontal, and rotational displacements are reported. The response of the footing is analysed in the context of existing drained foundation models that are based on work hardening plasticity theory. The rate dependency of the vertical load:deformation behaviour and the combined yield surfaces are described.

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Nguyen-Sy, Lam. "The theoretical modelling of circular shallow foundation for offshore wind turbines". Thesis, University of Oxford, 2005. http://ora.ox.ac.uk/objects/uuid:fa4000fb-8de6-4093-b528-3e60d774dea0.

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Currently, much research is being directed at alternative energy sources to supply power for modern life of today and the future. One of the most promising sources is wind energy which can provide electrical power using wind turbines. The increase in the use of this type of energy requires greater consideration of design, installation and especially the cost of offshore wind turbines. This thesis will discuss the modelling of a novel type of shallow foundation for wind turbines under combined loads. The footing considered in this research is a circular caisson, which can be installed by the suction technique. The combined loads applied to this footing will be in three-dimensional space, with six degrees of freedom of external forces due to environmental conditions. At the same time, during the process of building up the model for a caisson, the theoretical analyses for shallow circular flat footing and spudcans also are established with the same principle. The responses of the soil will be considered in both elastic and plastic stages of behaviour, by using the framework of continuous plasticity based on thermodynamic principles. During this investigation, it is necessary to compare the numerical results with available experimental data to estimate suitable values of factors required to model each type of soil. There are five main goals of development of the model. Firstly, a new expression for plasticity theory which includes an experimentally determined single yield function is used to model the effects of combined cyclic loading of a circular footing on the behaviour of both sand and clay. This formulation based on thermodynamics allows the derivation of plastic solutions which automatically obey the laws of thermodynamics without any further assumptions. A result of this advantage is that non-associate plasticity, which is known to be a proper approximation for geotechnical material behaviour, is obtained logically and naturally. A FORTRAN source code called ISIS has been written as a tool for numerical analysis. Secondly, since there are some characteristics of the geometric shape and installation method which are quite different from that of spudcans and circular flat footing, another objective of this study is to adapt the current model which has been developed in ISIS for spudcans to the specific needs of caissons. The third goal of this research is the simulation of continuous loading history and a smooth transition in the stress-strain relationship from elastic to plastic behaviour. The model is developed from a single-yield-surface model to a continuous plasticity model (with an infinite number of yield surfaces) and then is discretized to a multiple-yield-surface model which can be implemented by numerical calculation to be able to capture with reasonable precision the hysteretic response of a foundation under cyclic loading. This can not be described by a conventional single-yield-surface model. Fourthly, as a method to simplify the numerical difficulties arising from the calculation process, a rate-dependent solution will be introduced. This modification is implemented by changing the dissipation function derived from the second law of thermodynamics. Finally, in order to control the model to capture the real behaviour, many parameters are proposed. A parametric study will be implemented to show the effects of these parameters on the solution.

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Wilberts, Frauke. "MEASUREMENT DRIVEN FATIGUE ASSESSMENT OF OFFSHORE WIND TURBINE FOUNDATIONS". Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-337960.

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The installed capacity of offshore wind turbines in Europe is increasing with the monopile being the most common type of foundation. During its lifetime an offshore wind turbine is exposed to high dynamic loads which eventually can result in the fatigue of the substructure. This thesis will show how the linear damage accumulation approach based on the Miner’s rule can be used to estimate the damage induced on the substructure of an offshore wind turbine using measurements from strain gauges. Furthermore, the most important environmental influences will be illustrated and the different stress concentration factors and the size effect introduced in the industry guideline DNVGL-RP-C203 will be analysed towards their effect on the calculated lifetime.

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Hernando, Cabrero Álvaro. "Expansion of Existing Gravity-Based Offshore Wind Turbine Foundations". Thesis, KTH, Betongbyggnad, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-289105.

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Wind energy is one of the most promising sources of renewable energy worldwide. Its utilization has substantially increased for the last decades, both onshore and offshore. Offshore wind energy will have a lot to offer within the following decades, thus their foundations need to be prepared. Some of the current wind farms and wind turbines are now reaching their lifespan and, the turbines’ market is developing itself so rapidly that current turbines are getting behind the times with tremendous ease. It is here where the scope of this Master Thesis comes: what shall we do? Should we dismantle wind farms when they reach their lifespan, or should we maybe try to give them a further use? Accommodating for a new a larger wind turbine will need to account for new and higher climate actions and loads, namely winds, waves, ocean currents, the water level variation and the always difficult to predict ice actions. What is aimed in this Master Thesis is to set the basis for a procedure to dimension and define feasible solutions for the offshore wind turbines Gravity-Based Foundations to be expanded, avoiding the necessity of replacing them completely, with the environmental and economic benefits this would have. As this could turn to be an unmanageable problem to be solved, a Case Study where details can be set is performed at the Lillgrund Wind Farm site, in the south-west coast of Sweden, in the Öresund that separates Copenhagen and Malmö. A thorough description of the climatic actions and surrounding aspects is performed, while always dealing with uncertainties. With all that information, an analytical stability analysis is performed to account for three failure modes, namely: sliding, tilting andground failure. Additionally, a numerical FE-model is carried out in ANSYS in the aim of assessing the stresses and deformations that this kind of structure will suffer. Four alternatives are evaluated, and their behaviour is assessed based on the new external design actions. Analytical results show stability difficulties in two of the geometries inspected, while assure it in the other two. The FE-analyses show high concentrations of stresses on the GBS shaft, while model affordable deformations under the load combinations inspected. These results are also compared and contrasted in between them, and sensitivity analyses for the FE-models are performed in order to assure their good behaviour and development, and the trustworthiness ofthe results found. Based on these results, some conclusions are drawn from the developed processes. The main finding is the width and weight dependence of the solution, as well as the shape and dimensions. Future research needs such as scouring effects are finally accounted for necessary inspection to be made as continuation of the work here presented.

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Mondrago, Quevedo Monica. "Probabilistic modelling of geotechnical conditions for offshore wind turbine support structures". Thesis, Cranfield University, 2014. http://dspace.lib.cranfield.ac.uk/handle/1826/9205.

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The geotechnical conditions of the soil can fluctuate greatly across the wind farm. This is an issue since geotechnical modelling is the base of the structural design of an offshore wind farm, and the efficient installation of the wind turbines depends on its accuracy. This paper deals with the characterization of the seabed, predicting the soil properties over the total affected area by a wind farm, with the challenge to reduce the required data samples in the site investigation under the number of installed wind turbines, to reduce its cost. It is compared the prediction outcome from two different interpolation methods, kriging and radial basis function, assessing their accuracy by the Mean-Squared Error and the Goodness-of-Prediction Estimate, as well as with a visual examination of their mapping; obtaining higher accuracy for radial basis function and reducing to half the required sample points, from the initial value of installed wind turbines. In a second stage it is studied the soil effect over the foundation, analyzing the results from a FEA, where different geometries of the structure are compared submitted to different load cases to check its limit states. Those results show that the foundation cost can increase four times due to the soil conditions, taking into account only the steel volume, and demonstrating how important is the soil characterization in the foundation design, as it gives the chance to relocate those wind turbines that require more expensive foundations.

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Richardson, Mark Damian. "Dynamically installed anchors for floating offshore structures". University of Western Australia. School of Civil and Resource Engineering, 2008. http://theses.library.uwa.edu.au/adt-WU2008.0230.

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The gradual depletion of shallow water hydrocarbon deposits has forced the offshore oil and gas industry to develop reserves in deeper waters. Dynamically installed anchors have been proposed as a cost-effective anchoring solution for floating offshore structures in deep water environments. The rocket or torpedo shaped anchor is released from a designated drop height above the seafloor and allowed to penetrate the seabed via the kinetic energy gained during free-fall and the anchors self weight. Dynamic anchors can be deployed in any water depth and the relatively simple fabrication and installation procedures provide a significant cost saving over conventional deepwater anchoring systems. Despite use in a number of offshore applications, information regarding the geotechnical performance of dynamically installed anchors is scarce. Consequently, this research has focused on establishing an extensive test database through the modelling of the dynamic anchor installation process in the geotechnical centrifuge. The tests were aimed at assessing the embedment depth and subsequent dynamic anchor holding capacity under various loading conditions. Analytical design tools, verified against the experimental database, were developed for the prediction of the embedment depth and holding capacity.

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Evans, Keith Martin. "A model study of the end bearing capacity of piles in layered calcareous soils". Thesis, University of Oxford, 1987. http://ora.ox.ac.uk/objects/uuid:574ae32d-bb91-4be7-aae6-d456f4c40b70.

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The results of a series of over 120 model tests to study the end bearing capacity of piles in layered calcareous soils are described. The tests were carried out on samples enclosed in a cylindrical testing chamber, 450 mm diameter and 450 mm high, which allowed independent control of horizontal and vertical stress in the range 25 kPa to 500 kPa. The samples consisted of a loose, uncemented calcareous sand consisting predominantly of foraminifera and mollusc micro-organisms (D50 = 0.2 mm, calcium carbonate content 92%). Into this was built a layer of the same material artificially cemented by a gypsum plaster. The layer had similar properties to naturally cemented deposits, and layers with unconfirmed crushing strengths in the range 500 kPa to 4000 kPa have been prepared. All samples were tested dry. Closed end model piles of 16mm diameter were jacked at 0.1mm/s into the sample, and continuous profiles of end bearing capacity obtained during penetration. A parametric study has been carried out to examine the effects on the bearing capacity of stress level, K0, cemented layer thickness (0.5 pile diameters to 5.0 pile diameters) and layer strength. In addition, tests have been conducted with different pile geometry, multiple cemented layers, and using dynamic installation techniques. The study has identified ranges of parameters for which brittle failure of the cemented layer occurs (low stress levels and high layer strengths) and ranges where the failure is ductile (high stresses and low layer strengths). Characteristic patterns have been observed of the variation of end bearing with position as a layer is penetrated. Examination of the samples after testing has revealed details of failure mechanisms. Simple procedures are proposed for modelling the bearing capacity of such layered systems, and some implications of the results for design methods are discussed.

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Köhler, Philipp. "FACTORS INFLUENCING THE MAINTENANCE OF OFFSHORE WIND TURBINE FOUNDATIONS: A SURVEY BASED ON EXPERT OPINION". Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-413334.

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The wind industry is growing rapidly and especially in Europe, offshore wind power has become a serious business with approximately 22 GW installed in 2019. However, for the industry to become even more competitive, costs must be reduced. Especially the Operation and Maintenance (O&M) costs present a challenge to developers and operators. In order to achieve cost savings during the operational phase, the factors influencing the maintenance operations should be identified. This Thesis focuses on the factors influencing the offshore wind turbine foundation maintenance operations. The aim of the Thesis is to identify these factors and their attributes, as well as rank them according to their importance. First, a literature review was conducted to establish the theoretical background for this study. In order to do so, maintenance strategies, offshore wind turbine foundations and the scope of foundation maintenance were described in detail. After that, the factors influencing the maintenance for offshore wind turbine foundations were collected from literature, personal experience, and input from industry experts. Following that, a two-step study with seven industry experts was conducted to validate these factors and their attributes as a first step before then ranking all the attributes by their importance. The experts were asked to rank each attribute by assigning a number from 1-5 where: very high influence (5), high influence (4), medium influence (3), low influence (2) and no influence (1). Since the maintenance differs for the subsea and the above water part of the foundation, the participants had to rank each attribute twice, once for the subsea part and once for the part above water. After the results were analyzed, it can be concluded that the Quality Health Safety Environment (QHSE) was ranked as the most important, followed by technology and standards & guidelines. The environment factor was ranked as the least important before the geographical location and cost factors.

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Tedesco, Giacomo. ""Offshore tower or platform foundations: numerical analysis of a laterally loaded single pile or pile group in soft clay and analysis of actions on a jacket structure"". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amslaurea.unibo.it/6802/.

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Laterally loaded piles are a typical situation for a large number of cases in which deep foundations are used. Dissertation herein reported, is a focus upon the numerical simulation of laterally loaded piles. In the first chapter the best model settings are largely discussed, so a clear idea about the effects of interface adoption, model dimension, refinement cluster and mesh coarseness is reached. At a second stage, there are three distinct parametric analyses, in which the model response sensibility is studied for variation of interface reduction factor, Eps50 and tensile cut-off. In addition, the adoption of an advanced soil model is analysed (NGI-ADP). This was done in order to use the complex behaviour (different undrained shear strengths are involved) that governs the resisting process of clay under short time static loads. Once set a definitive model, a series of analyses has been carried out with the objective of defining the resistance-deflection (P-y) curves for Plaxis3D (2013) data. Major results of a large number of comparisons made with curves from API (America Petroleum Institute) recommendation are that the empirical curves have almost the same ultimate resistance but a bigger initial stiffness. In the second part of the thesis a simplified structural preliminary design of a jacket structure has been carried out to evaluate the environmental forces that act on it and on its piles foundation. Finally, pile lateral response is studied using the empirical curves.

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Forni, Fabio. "Investigating the axial response of pile foundations for offshore wind turbines". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2017.

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I crescenti problemi legati ai cambiamenti climatici rendono l'impiego delle energie rinnovabili sempre più interessante. In questa ottica, in Germania si sta pianificando di aumentare la produzione di energia pulita attraverso lo sfruttamento dell’energia eolica. Nuovi impianti di turbine eoliche sono previsti nel Mare del Nord in acque medio profonde (25-45m) dove la parte immersa della struttura della turbina eolica (chiamata sottostruttura) è spesso costituita da una struttura jacket (traliccio) o tripod (a treppiedi). Questo tipo di sottostrutture trasmettono principalmente carichi assiali alle fondazioni (in genere fondazioni su palo), e il carico a trazione è la forza che maggiormente ne influenza il dimensionamento. Molte compagnie energetiche tedesche sono interessate a migliorare l’efficienza e i costi dei loro impianti eolici e, per questo, incaricano università ed istituti di ricerca (come il Fraunhofer IWES) per indagarne gli aspetti, come ad esempio il comportamento delle fondazioni offshore. All’autore di questa tesi è stata data l’opportunità di studiare e lavorare al Fraunhofer IWES e perciò questa tesi tratterà del compramento di pali caricati assialmente e staticamente pensati per sottostrutture jacket o tripod per turbine eoliche. Nello studio effettuato per questa tesi, i dati seprimentali, ottenuti da una campagna sperimentale condotta (in larga scala 1:10 1:5) su pali infissi in terreno sabbioso, sono confrontati attraverso l’impiego delle load-transfer curves (funzioni che descrivono il comportamento d’interfaccia palosuolo) usando sia un’approccio classico (fornito dal metodo di calcolo API Main Text) sia approcci più recenti (dati dai metodi di calcolo CPT). Uno script Matlab creato appositamente dall’autore di questa tesi riesce ad implementare 11 diversi tipi di load-transfer curves. Il lavoro di tesi si conclude con un esempio pratico in grado di fornire un’idea di come questo script può essere usato nella progettazione.

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Dallyn, Paul A. "Advances in foundation design and assessment for strategic renewable energy". Thesis, Loughborough University, 2017. https://dspace.lboro.ac.uk/2134/24100.

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In order to meet EU legislation on emissions, significant effort is being invested into the development of cost-effective renewable power generation technologies. The two leading technologies are solar and wind power because of their potential for the lowest levelised cost of energy and for showing a growth in installed capacity and technological development. Various research findings have suggested that significant cost savings in the capital expenditure of renewable energy projects can be made through the optimisation of their support foundations, the understanding of which has formed the main goal of the research.

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Li, Xinyao. "CENTRIFUGE MODELLING AND NUMERICAL SIMULATION OF NOVEL HYBRID FOUNDATIONS FOR OFFSHORE WIND TURBINES". Case Western Reserve University School of Graduate Studies / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=case1594728306295576.

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Conti, Claudio. "Small-scale physical modelling of piled foundations for offshore wind turbines application". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019.

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Nowadays, finding alternative energy sources is becoming more and more important. Europe is particularly focusing on wind energy and in offshore wind energy especially. An issue concerning offshore wind energy which is gaining more and more attention is the noise emissions due to impact driven pile foundation. The noise caused by the installation process has been judged as “potentially dangerous for marine fauna” from the German Authorities. This research thesis is part of a project which examines a viable alternative installation method for the displacement of pile foundations for offshore wind energy called pile jacking. This technology should be developed to be cost-efficient, flexibly scalable and to produce considerably reduced vibration and air pollution emissions during its placement in the sea bed. Jacked piles technology would eliminate almost any noise deriving from the hammer impact. As most offshore piled foundations have been installed by impact driving technology, the question arises as to how piles with different the stiffness and the capacity , can otherwise be installed. In order to delineate the significant variables affecting the load-bearing capacity and especially the ultimate uplift capacity of a pile in saturated sand, a small-scale test campaign in scale 1:30 has been performed at the Test Center for Support Structures in Hanover. The campaign was supervised by the Department for Support Structures of Fraunhofer IWES. A testing schedule comprising of 15 small-scale geotechnical physical experiments was conducted on open-ended piles to an embedded length of 75 cm using two method of pile installation: static jacking and impact driving. The aim of this thesis is to obtain preliminary experimental data and set out the main features of this technology. The results obtained by this study reveal that static jacking installation lead to higher resistances and is overall beneficial to the mechanical load bearing behavior of pile foundations.

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Isorna, Rocio. "Etude de l’interaction sol-structure et de la fondation d’une éolienne offshore soumise à des chargements statiques/cycliques". Thesis, Ecole centrale de Nantes, 2017. http://www.theses.fr/2017ECDN0002/document.

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Les structures offshores sont conçues pour résister à des chargements environnementaux sévères. Des études expérimentales et numériques de la fondation d’une éolienne offshore soumise à des chargements statiques monotones/cycliques sont présentées dans ce manuscrit. Des pieux isolés (diamètre de 1,8 m et 40 m de longueur) et une structure en treillis fondée sur 4 pieux ont été testés à 100×g en centrifuge dans un massif de sable de Fontainebleau dense. Le comportement du pieu isolé a été identifié à travers des essais de chargement axial monotone. Différentes méthodes de mise en place de pieu ont été adoptées (installation à 1×g et à 100×g) et leur influence sur la capacité portante a été mesurée. Le diagramme de stabilité du pieu a été construit à partir des résultats des essais cycliques, des essais CPT ont été réalisés et l’influence des contraintes initiales a été étudiée. Des résultats expérimentaux de la fondation jacket soumise à des chargements latéraux cycliques sont enfin présentés. La méthode des éléments finis et un macro-élément pour des pieux ont été utilisés pour reproduire numériquement les résultats expérimentaux. Les lois de comportement adoptées sont basées sur la théorie d’hypo-plasticité et les contraintes initiales dans le sol sont issues de la méthode ICP-05. Les résultats numériques sont confrontés aux résultats expérimentaux et aux résultats analytiques obtenus à partir de la norme API
Offshore structures are designed to resist to severe environmental loads. This manuscript presents experimental and numerical studies on offshore wind turbine pile foundations submitted to static monotonic/cyclic loads. Isolated piles (diameter of 1.8 m and embedded length of 40m) and a four-legged truss structure installed in dense Fontainebleau sand have been tested at 100×g in a geotechnical centrifuge. The behavior of the isolated piles has been characterized under monotonic axial load. The piles have been jacketed at 1×g and 100×g and the influence of the setup method on the bearing capacity has been measured. The stability diagram of a pile has been constructed using cyclic tests, CPT experiments have been performed and the influence of the initial stresses has been studied. Finally, experimental results of the jacket foundation submitted to lateral cyclic loadings are presented. The finite element method and a macro-element for piles have been used to numerically reproduce the experimental results. Constitutive laws are based on the hypoplasticity theory and the initial stresses in the soil have been calculated using the IC-05 method. The numerical results are compared with the experimental and the analytical results from the API standards

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22

Donnini, Lorenzo. "Numerical modelling of axially loaded piled foundations with physical tests validation". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2022.

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L'oggetto della tesi è la modellazione numerica di pali di fondazione per turbine eoliche in ambiente offshore. Il metodo di modellazione comprende l'interpretazione di prove CPT per l'estrapolazione dei parametri geotecnici del terreno, la creazione di un modello dell'interazione tra struttura e terreno tramite il software agli elementi finiti Abaqus, la sua verifica, l'ottimizzazione dell'estensione del modello del terreno e della mesh e la simulazione numerica del comportamento di pali caricati assialmente in compressione. Grazie al confronto con i risultati di test su modelli fisici, eseguiti nel laboratorio dell'istituto Fraunhofer IWES di Hannover, di tre pali aventi la stessa geometria ma installati in punti con diverse condizioni di compattazione della sabbia, è stata possibile la messa a punto di una strategia di simulazione più accurata possibile e la sua validazione. A conclusione del lavoro è stato eseguito un esempio di design di una fondazione jacket per una turbina eolica offshore.

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23

Song, Zhenhe. "Pullout behaviour of suction embedded plate anchors in clay". Curtin University of Technology, Dept. of Civil Engineering, 2008. http://espace.library.curtin.edu.au:80/R/?func=dbin-jump-full&object_id=18648.

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In recent years oil and gas mining has moved into increasingly deeper water in search of undeveloped fields. As water depths approach and exceed 3000 m conventional offshore foundation systems become inefficient and ineffective in stabilising platforms and floating production storage units. The trend of supporting structure design in deep water has been to install catenary and taut leg mooring systems. Consequently, many types of anchoring systems are being developed and used in order to withstand large mooring forces. The SEPLA (Suction Embedded Plate Anchor) is ideal for use in this situation. This project has employed advanced numerical techniques and centrifuge testing to study pullout behaviour of plate anchor foundations in different soil profiles and suction caisson installation effect with the aim of generating a robust framework for design. The behaviour of strip and circular plate anchors during vertical pullout in uniform and normally consolidated clays has been studied by means of small strain and large deformation finite element analyses. Both fully bonded (attached), and ‘vented’ (no suction on rear face), anchors have been considered. The current numerical results were compared with existing laboratory test data, finite element results and analytical solutions. This study showed that the ultimate pullout capacity factors (Nc) for deep embedment were 11.6 and 11.7 for smooth and rough strip anchors and 13.1 and 13.7 for smooth and rough circular anchors respectively. When the anchor base was vented, the soil stayed attached to the anchor base for deep embedment, and the pullout capacity was therefore the same as for the attached anchor. The separation depth ratio, Hs/B or Hs/D was found to increase linearly with the normalised strength ratio, su/γ'B or su/γ'D.
Numerical simulation has been conducted to assess the bearing capacity for inclined pullout plate anchors. This bearing capacity analysis was performed by embedding the anchors in clay with different initial inclinations and different embedment ratios. Both the attached anchor base and vented base were evaluated. The results showed that the bearing capacities of the inclined plate anchors were associated with the inclination angles and base conditions. The separation depth of the plate anchors can be assessed by a simple equation from vertically pulled out plate anchors. Large deformation finite element analyses of plate anchor keying in clay has been performed. The effects of anchor thickness, anchor padeye eccentricity, anchor-soil interface roughness, soil shear strength, anchor submerged weight and soil disturbance have been studied with anchors in uniform or normally consolidated clays. The numerical results were compared with transparent soil test and existing centrifuge test data. The study showed that the RITSS method works well in simulating the anchor keying process. Anchor padeye eccentricity played an important role in anchor keying. A normalised anchor geometry ratio was used to estimate the loss in embedment during plate anchor’s keying. Both finite element analysis and centrifuge tests have been conducted to study the suction caisson installation effect. In finite element analysis, the soil disturbed zone varied from 3 times the caisson wall thickness to a full area inside a caisson.
Centrifuge tests of suction embedded plate anchors were conducted in normally consolidated kaolin clay and transparent uniform soil. It can be concluded that the reduction in anchor capacity due to soil disturbance after suction caisson installation depends on re-consolidation time and soil sensitivity. The soil disturbance also reduced the loss of embedment during the anchor keying process.

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Kopp, Duncan Rath. "Foundations for an offshore wind turbine". Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/60766.

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Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2010.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 75-76).
Worldwide energy demand is growing rapidly, and there is great interest in reducing the current reliance on fossil fuels for uses such as power generation, transportation, and manufacturing. Renewable energy sources, such as solar and wind, are abundant but have very low power densities. The US is in the process of approving its first offshore wind farm, located in Nantucket Sound. Geotechnical factors will play a large role in the development of offshore wind projects due to the high cost contribution from foundations, and the high loads associated with storm conditions. Offshore wind turbine foundations provide unique design challenges. First, various foundation alternatives exist, so it is important that an appropriate cost-effective foundation type be selected. Second, the loads and soil conditions will vary for each location. Therefore, it is important to ensure the foundation can adequately support vertical and horizontal loads. Finally, each turbine manufacturer has unique deflection and rotation criteria. Therefore, the foundation should perform within those tolerances, even under worst-case loading. This thesis considers the performance of a monopile foundation under typical vertical and horizontal storm loading conditions. Capacity, deflection, and rotation of a proposed monopile foundation are calculated by various methods to simulate the design procedure. The results show that very stiff foundations are required to keep pile head movements within design tolerances.
by Duncan Rath Kopp.
M.Eng.

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El-Gharbawy, Sherif Lotfy. "The pullout capacity of suction caisson foundations /". Digital version accessible at:, 1998. http://wwwlib.umi.com/cr/utexas/main.

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Taiebat, Hossein Ali. "THREE DIMENSIONAL LIQUEFACTION ANALYSIS OF OFFSHORE FOUNDATIONS". University of Sydney. Civil Engineering, 1999. http://hdl.handle.net/2123/499.

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This thesis presents numerical techniques which have been developed to analyse three dimensional problems in offshore engineering. In particular, the three dimensional liquefaction analysis of offshore foundations on granular soils is the main subject of the thesis. The subject matter is broadly divided into four sections: 1)Development of an efficient method for the three dimensional elasto?plastic finite element analysis of consolidating soil through the use of a discrete Fourier representation of field quantities. 2)Validation of the three dimensional method through analyses of shallow offshore foundations subjected to three dimensional loading and investigation of the yield locus for foundations on purely cohesive soils. 3)Formulation of governing equations suitable for three dimensional liquefaction analyses of offshore foundations founded on granular soil, presentation of a method for liquefaction analyses, and application of the method in modified elastic liquefaction analyses of offshore foundations. 4)Application of a conventional elasto?plastic soil model in the liquefaction analyses of offshore foundations using the three dimensional finite element method. The finite element method developed in this thesis provides a rigorous and efficient numerical tool for the analysis of geotechnical problems subjected to three dimensional loading. The efficiency of the numerical tool makes it possible to tackle some of the problems in geotechnical engineering which would otherwise need enormous computing time and thus would be impractical. The accuracy of the numerical scheme is demonstrated by solving the bearing capacity problem of shallow foundations subjected to three dimensional loading. The generalized governing equations and the numerical method for liquefaction analyses presented in this thesis provide a solid base for the analysis of offshore foundations subjected to cyclic wave loading where they are founded on potentially liquefiable soil. The practicability of the numerical scheme is also demonstrated by a modified elastic liquefaction analysis of offshore foundations. The liquefaction phenomenon is redefined in the context of the conventional Mohr?Coulomb model, so that a relatively simple and practical model for elasto?plastic liquefaction analysis is presented. The three dimensional finite element method together with the numerical scheme for liquefaction analysis and the elasto?plastic soil model provide a suitable practical engineering tool for exploring the responses of offshore foundations subjected to cyclic wave loading.

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Shi, Qun. "Centrifugal modelling of surface footings subject to combined loadings". Thesis, University of Cambridge, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.257515.

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Al-Baghdadi, Therar. "Screw piles as offshore foundations : numerical and physical modelling". Thesis, University of Dundee, 2018. https://discovery.dundee.ac.uk/en/studentTheses/336c5661-e871-416d-9d69-4bb4f421bda7.

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In reviewing the recent development of the geotechnical engineering aspects of the offshore wind farm industry, it was found that there is an urgent need for more reliable and cost-effective foundation solutions. In this thesis, screw piles (helical piles) have been proposed as a potential innovative alternative foundation for offshore wind turbines in deeper water. This type of pile has been used widely as foundation and anchor for onshore projects due to their ability to provide high compressive and tensile resistance as well as reduced noise/vibration during installation. In order to adopt the screw pile technique as an offshore foundation, the geometry of the piles would need to be scaled up so they can provide the high capacities required for this application. Such change in size and geometry will lead to uncertainties in predicting the required installation torque and the capacity in different soil types and stress histories. For example, without the ability to accurately predict installation torque, it is difficult to design screw piles for offshore use or develop appropriate installation plant with the required torque capabilities in different soils. In this thesis, non-linear Finite Element Method (2D & 3D) was used to investigate the screw pile behaviour under lateral, vertical and combined loading. The FEM was also used to investigate the optimum spacing of the helical plates and the geometry effects on the screw pile behaviour to meet requirements of the loading conditions experienced for offshore application. In addition, 29 successful centrifuge tests were carried out using a newly developed servo-actuator so that the screw pile models could be installed and tested inflight in one operation at 50g acceleration. The centrifuge tests of screw pile models and CPTs were carried out in sand at three different relative densities (loose, medium and dense). The installation force (Fv) and torque (T) were correlated to the cone resistance (qc) to establish a CPT-based design method to predict the required installation force and torque for the straight-shafted pile and the modified screw pile geometries. A modified theoretical model was used to predict the installation torque of straight-shafted pile and screw pile in sand with different relative densities based on pile geometry characteristics and soil properties. Furthermore, the ultimate compressive capacities (Qc) of straight-shafted piles and screw pile in sand with different relative densities were determined from centrifuge tests and used to develop appropriate design parameters including earth pressure coefficient (k) and bearing capacity factors (Nq) for pushed and rotated piles.

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Dunne, Helen P. "Finite element limit analysis of offshore foundations on clay". Thesis, University of Oxford, 2017. http://ora.ox.ac.uk/objects/uuid:ba9c9beb-e055-4f46-a9f9-b2d10bd292b7.

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Capacity analysis is a common preliminary step in the design of offshore foundations. Inaccuracies in traditional capacity analysis methods, and the advancement of numerical modelling capabilities, have increasingly led designers to optimise foundations using more complex methods. In this thesis, the ultimate limit state capacity of a range of foundation types is investigated using finite element limit analysis. Novel three-dimensional finite element limit analysis software is benchmarked against analytical solutions and conventional displacement finite element analysis. It is then used to find lower and upper bounds of foundation capacity, with adaptive mesh refinement used to reduce the bound gap over successive iterations of the solution. Rigid foundations subjected to short term loading on clay soil are analysed. The undrained soil is modelled as a rigid--plastic von Mises material, and attention is given to modelling any normal and/or shear stress limits at the foundation/soil interface. Shallow foundations, suction anchor foundations, and hybrid mudmat/pile foundations are considered. Realistic six degree-of-freedom load combinations are applied and results are reported in the form of normalised design charts, and tables, that are suitable for use in preliminary design. Relationships between loading combinations and failure mechanisms are also explored. A number of case studies based on authentic foundation designs are analysed. The results suggest that finite element limit analysis could provide an attractive alternative to displacement finite element analysis for preliminary foundation design calculations.

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Tavouktsoglou, N. S. "Scour and scour protection around offshore gravity based foundations". Thesis, University College London (University of London), 2018. http://discovery.ucl.ac.uk/10044922/.

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The prediction of seabed scour around offshore gravity based foundations with complex geometries is currently a significant barrier to optimising and providing cost effective foundation designs. A significant aspect that has the potential to reduce the uncertainty and costs related to the design of these foundations is the understanding of the effect the structural geometry of the foundation has on scour. This thesis focuses on an experimental investigation of the scour and scour protection around complex structure geometries. The first part of this research considers scour under clear water conditions. During this study different foundation geometries were subjected to a range of different hydrodynamic forcings which enabled a better understanding of the scour process for these foundations. The second part of the research encompasses the design and execution of a series of experiments which investigated stability of the scour protection around such structures. The structures were tested against different combinations of wave and current conditions to determine the bed shear stress required to initiate sediment motion around each structure. This research has led to a number of novel results. The experimental investigation on scour around complex geometries showed that the scour depth around cylindrical structures (with both uniform and complex cross-sections) is linked to the depth averaged pressure gradient. Following a dimensional analysis, the controlling parameters were found to be the depth averaged Euler number, pile Reynolds number, Froude number, sediment mobility number and the non-dimensional flow depth. Based on this finding a new scour prediction equation was developed which shows good agreement with experimental and prototype scour measurements. The scour protection tests indicated that under wave dominated conditions the amplification of the bed shear stress around these structures does not exceed the value of 2. In the case of current dominated flow conditions the amplification of the bed shear stress is a function of the structure type and the Keulegan–Carpenter number. The results of these experiments were used to develop a “Shields type” diagram that can guide designers to select the appropriate rock armour size that will be stable for a certain set of flow conditions. The study also revealed that the long term persistence of flow conditions that just lead to incipient motion of the scour protection material can eventually lead to complete failure of the scour protection. The study provides a set of new design techniques that can allow designers to predict the scour depth around cylindrical and complex foundation geometries and also select the appropriate stone size for their scour protection system. Together, these techniques may allow for the reduction of costs associated with the scour protection of offshore and coastal structures.

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Tapper, Laith. "Bearing capacity of perforated offshore foundations under combined loading". Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:4beb1f5c-24d9-4359-a973-95dda05e550d.

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This thesis presents experimental work and numerical analysis that has been undertaken to assess the bearing capacity of perforated offshore foundations. Perforated foundations may be used to support subsea infrastructure, including as mudmats into which a number of perforations have been made, or as grillages which consist of a series of structurally connected strip footings. Larger gravity base foundations, such as for offshore wind turbines or oil and gas platforms, may adopt a single central perforation. The advantages of using perforated foundations can include reduced material requirements and easier offshore handling as a result of smaller weight and lower hydrodynamic forces during deployment. Limited guidance currently exists for assessing the bearing capacity of these foundation types. Bearing capacity of perforated foundations has been examined in this thesis under conditions of combined vertical, horizontal and moment loading which is typical in offshore settings. Undrained soil conditions have been considered, except for the case of grillages in which drained conditions are often most relevant. Experimental work has included centrifuge testing of ring and square annular foundations on clay, and 1g testing of grillage foundations on sand. Finite element modelling has also been undertaken to assess perforated foundation capacity. A Tresca material subroutine (UMAT) and an adaptive meshing scheme have been developed to improve the accuracy of the finite element analysis carried out. The results showed that perforated foundations can be an efficient foundation solution for accommodating combined loading. As a ratio of their vertical load capacity, perforated foundations may be able to withstand higher moment and horizontal loads compared with unperforated foundations. The experimental and numerical results have been used to develop design expressions that could be employed by practitioners to estimate the vertical and combined load bearing capacity of these foundation types.

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Kirkwood, Peter Brian. "Cyclic lateral loading of monopile foundations in sand". Thesis, University of Cambridge, 2016. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.709540.

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Chaudhry, Anjum Rashid. "Static pile-soil-pile interaction in offshore pile groups". Thesis, University of Oxford, 1994. http://ora.ox.ac.uk/objects/uuid:7b4c8d56-184f-4c8d-98c9-2d9c69a1ef55.

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This thesis is a theoretical study, using both finite element and boundary element methods, of the behaviour of single-piles and pile groups under vertical and lateral loading. It offers an improved understanding of the soil-structure interaction that occurs in pile groups, particularly closely spaced piles subjected to lateral loads. The potential of a two- dimensional idealisation of what is a three-dimensional problem is demonstrated by achieving real insight into the complex nature of pile-soil and pile-soil-pile interaction in pile groups. A new load transfer mechanism is presented for a rigid, axially loaded vertical pile. From this an improvement is then derived to the analytical solution for pile head settlement given by Randolph and Wroth (1978). The improved mechanism has the further merit that it can be applied also to solutions for flexible piles and pile groups. The improved analytical solution is further adapted in the development of two correcting layers specifically for vertically loaded piles to model infinite boundaries in the finite element model. The correcting layers help in establishing superiority of the finite element method over the boundary element method. To model pile-soil interaction, a purely cohesive interface element is developed and then validated by performing various two-dimensional test problems, including stability analysis of flat surface footings. Footing-soil interface tension is successfully modelled in this way - an outcome that entails a significant modification to the Hansen (1970) bearing capacity solution. Stability analysis is also carried out of conical footings using a three-dimensional finite element model: the results help to explain the applicability of the existing bearing capacity theories to conical footings. The ultimate lateral soil reaction is determined and various pile loading stages are investigated through parametric studies. Study of the stage immediately following pile installation (i.e. the consolidation stage) highlights the need to develop an effective stress analysis for laterally loaded piles. Pile-soil interaction is studied using the cohesive interface element presented earlier, which proves to be quite successful in smoothing out the stress discontinuities around the pile. A new material model for frictional soils is presented, and validated by using it to model an extension test: it captures well post-peak behaviour and takes care of the effects of dilation on the response of laterally loaded piles. Finally, mechanisms of interaction in closely spaced pile groups are studied. Simple analytical expressions are derived which quantify the effects of interaction. A new method of analysis is presented for single-piles and pile groups which offers a considerable degree of reliability without having to do either impossibly expensive full scale field tests or prohibitively expensive full three-dimensional analysis using the currently available computers.

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Martin, Christopher Michael. "Physical and numerical modelling of offshore foundations under combined loads". Thesis, University of Oxford, 1994. http://ora.ox.ac.uk/objects/uuid:b582fb74-7a1b-4be9-884d-0daa9fda7c7b.

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In addition to vertical loads, the foundations of offshore structures are subjected to horizontal loads and overturning moments as a result of environmental (wind and wave) loading. The behaviour of circular footings on cohesive soil under conditions of combined vertical, horizontal and moment (V, H, M) loading is the primary concern of this thesis. A programme of physical model tests, involving combined loading of circular footings on reconstituted Speswhite kaolin, is reported. The shape of footing used is typical of the "spudcan" foundations of independent leg jack-up drilling platforms. Previous experience with combined loading of footings on sand has revealed that the observed load:displacement behaviour is best understood, and theoretically modelled, in terms of work hardening plasticity theory. The present tests on clay confirm this, and the results are interpreted to give empirical expressions for (i) the combined load yield surface in V:H:M space, and (ii) a suitable flow rule to allow prediction of the corresponding footing displacements (z, h, θ) during yielding. Extension to a complete plasticity model is achieved using theoretical stiffness factors to define elastic behaviour, and theoretical lower bound bearing capacity factors (derived specifically for this work) to define the size of the yield surface as a function of vertical penetration. The predictive capabilities of the numerical model are evaluated by retrospective simulation of various footing tests. Finally some plane frame structural analyses of a representative jack-up unit are described; some of these analyses incorporate the plasticity-based numerical model of spudcan footing behaviour under combined loads.

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35

Cotter, Oliver. "Installation of suction caisson foundations for offshore renewable energy structures". Thesis, University of Oxford, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.534163.

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Yang, Xu Yang. "Performance and Bearing Behavior of Foundations for Offshore Wind Turbines". Case Western Reserve University School of Graduate Studies / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=case1525707653847882.

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37

Gelotte, Lovisa, i Nilsson Alexandra Lundevall. "Optimal Placement of FloatingTwo-Turbine Foundations in Offshore Wind Farms". Thesis, KTH, Energiteknik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-209833.

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This project is conducted in cooperation with Hexicon AB, which is a Swedish design and engineering company developing floating two-turbine platforms for offshore wind power.The study aims to investigate the optimal placement of Hexicon AB’s platforms in an offshore wind farm with respect to the Annual Energy Production (AEP). Wind farm layout optimization is a complex problem and it has been approached by the development of calculation and optimization programs in Matlab. The analytical Jensen wake model has been utilized for calculation of AEP and important inputs to the program have been turbine parameters and site specific conditions. The optimization strategy used is a multi-stage algorithm where the gradient-based local search algorithm Fmincon has been used in combination with a version of the heuristic genetic algorithm. The developed programs have been tested and evaluated through a case study. Included in the case study is also a brief financial evaluation regarding how different scenarios in electricity export price and costs for cabling could affect the feasibility of the optimized layouts. Concluded from the project is that the developed programs can be used to investigate the optimal placement of floating two-turbine platforms with respect to AEP. In the case study it was found that the optimized layout obtained a wind farm efficiency of around 4% more than for the conventional staggered layout that was tested. What is also emphasized is that the feasibility of the optimized layouts obtained from the program is quite sensitive toward changes in future electricity export price and costs for cabling and installation. Hence, it is important to perform a careful financial analysis in order to draw conclusions regarding what layout is the better option for a specific situation.
Dagens utbyggnad av vindkraft sker i allt större utsträckning genom etablering av vindkraftparker. De främsta fördelarna med att placera vindkraftverken i parker är att de höga fasta kostnaderna fördelas på flera kraftverk samt att man kan beställa ett flertal enheter samtidigt och därigenom minska kostnaden per installerad Megawatt (MW). För att ytterligare kunna öka vinsten på investeringen är det viktigt att undersöka optimal inbördes placering av vindkraftverken för att erhålla en så hög energiproduktion som möjligt. Det finns många studier gjorda inom området och ett flertal programvaror utvecklade. Dock finns det endast ett fåtal studier som har inriktat sig specifikt på flytande vindkraftverk. Detta arbete är utfört i samarbete med Hexicon AB, vilket är ett Stockholmsbaserat ingenjörsföretag som utvecklar en patenterad teknik för plattformar avsedda för flytande vindkraft. Det unika med Hexicon ABs patenterade teknik är att två vindkraftverk är placerade på en gemensam plattform. Denna teknik gör det möjligt för plattformen att anpassa sig till vindriktningen vilket ger en ökning av kraftverkens energiutbyte. Då det inte finns några utvecklade optimeringsmetoder för flytande plattformar som kan anpassa sig efter vindriktning är syftet för denna studie att undersöka den optimala inbördes placeringen av Hexicon ABs plattformar i en vindkraftpark. Eftersom vindkraftsoptimering är ett komplicerat problem som bland annat är icke-linjärt och icke-konvext så finns det ingen exakt lösning tillgänglig för problemet. Komplexiteten gör även många förenklingar och antaganden nödvändiga för att kunna bearbeta problemet. I detta projekt har sambandet mellan årlig elproduktion och inbördes placering av plattformarna undersökts genom att ett kalkylerings- och optimeringsprogram utvecklats i programvaran Matlab. För att kunna undersöka den optimala inbördes placeringen av vindkraftverken är det viktigt att förstå hur vindkraftverken påverkas av att placeras tillsammans i en park. För att göra detta så behövs en modell för att beskriva den så kallade vaken som uppstår bakom respektive vindkraftverk. Detta gjordes genom att använda den analytiska Jensen vakmodellen, vilket är den vanligaste modellen att använda för optimeringssyften. Beräkningen av elproduktion gjordes baserat på given information angående turbinparametrar samt specifika förhållanden på platsen för vindparken. För det utvecklade optimeringsprogrammet användes en tvåstegsalgoritm där den gradientbaserade algoritmen Fmincon utgjorde den centrala delen. Fmincon är en effektiv algoritm för lokal optimering som finns tillgänglig i Matlab. För att generera bra startgissningar till den lokala optimeringen användes en version av en heuristisk genetisk algoritm som komplement till Fmincon. Denna algoritm bygger på samma princip som processen för naturligt urval i evolutionssammanhang där de bäst lämpade individerna för vidare sina egenskaper till nästa generation. För att ytterligare förbättra algoritmen kompletterades den även med ett moment av slumpmässighet. För att testa och utvärdera de utvecklade programmen genomfördes en fallstudie. I denna studie optimerades 50 stycken olika heuristiska startgissningar. De 20 bäst presterande konfigurationerna valdes ut för vidare analys där de blev utvärderade med avseende på olika scenarion för elpris samt kostnad för elektrisk infrastruktur. Detta för att undersöka hur den optima placeringen eventuellt skulle kunna påverkas av osäkerheter i dessa faktorer. Den genomförda fallstudien indikerade att de utvecklade programmen kan användas för att undersöka den inbördes optimala placeringen av vindkraftverk med avseende på elproduktion. Den ekonomiska utvärderingen indikerade även att den optimala placeringen var känslig för olika scenarion där elpris och kostnader för infrastruktur varierades och att detta kunde påverka lönsamheten för investeringen. Det ska därför betonas att det anses vara viktigt att utföra en mer noggrann ekonomisk utvärdering av de optimerade konfigurationerna för att undersöka vilken positionering som är mest lämplig för en viss situation.

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Chow, Fiona Ching-Man. "Investigations into the behaviour of displacement piles for offshore foundations". Thesis, Imperial College London, 1997. http://hdl.handle.net/10044/1/7894.

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Engebretsen, Espen André. "Wave Conditions for Offshore Wind Turbine Foundations in Intermediate Water Depths". Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for marin teknikk, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-18587.

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In this thesis, the effects on regular waves when propagating from deep to shallow water have been investigated, assuming linear wave theory. The effects of shoaling, refraction, reflection and diffraction have been studied. The process and types of breaking waves has also been reviewed.Linear wave theory, second and higher order Stokes theory, Stream function theory, Solitary wave theory and Cnoidal theory have been reviewed. The relative validity of the different wave theories was also assessed.The effects on the wave spectrum as a sea state travels from deep to shallow water, described by the energy balance equation, has also been addressed. The effects addressed were wind, nonlinear wave-wave interactions, white-capping, bottom friction and surf-breaking. Two computer models for numerically solving the energy balance equation was mentioned, being SWAN and STWAVE where SWAN was chosen for use in the analyses.The NORA10 hindcast was believed not to properly take the change in water depth into account at the Dogger Bank Zone. At a point north of the location of interest, the water depth was of such a magnitude (81m) that the NORA10 hindcast was believed to yield credible data for the significant wave height and spectral peak period. A long term estimate of the 50 year significant wave height was performed from the NORA10 data at the point north of the Dogger Bank Zone, by the environmental contour method. This resulted in an estimated 50 year significant wave height of 11.74m and spectral peak period of 15.68s.The SWAN model was used on a test case from Svangstu (2011) to get familiar with the program, and investigate how the different physical effects influence the solution. With the knowledge acquired from the test case, the Dogger Bank case was analyzed in SWAN, to obtain the 50 year sea state parameters at the location of interest. The 50 year sea state north of the Dogger Bank Zone, the Dogger Bank bathymetry, as well as a constant wind of 23.3 m/s was used as input. The 50 year sea state at the location of interest was found to be characterized by a significant wave height of 7.34m and a spectral peak period of 15.56s. SWAN was found to result in a significant wave height of some 15-27% lower than what was found in NORA10.By performing a short term analysis on the 50-year sea state at the location of interest, the 50-year design wave height was found to be 12.5m, assuming the individual wave heights to be modeled by the Gluhovski distribution. The 90% confidence interval of the design wave period was found to be 9.6s <T< 16.3s. This was estimated from studying the ratio between the period of the three largest waves in a time series, and the spectral peak period of the sea state in 95 time series from Svangstu (2011) By evaluating only the limiting values of the period range, the longest and shortest design wave was found to be 80% and 97.4% of the breaking wave height respectively, assuming linear theory.The wind turbine structure geometry was simplified to be modeled by a cylinder with a diameter of 6m. By computing the kinematics from the Stream Function theory, the maximum base shear and overturning moment using Morison’s equation was found to be 3.67MN and 65.93MN respectively. The effects of the rate of change of added mass momentum was also assessed.From a simplified and conservative approach, the impact loads from a breaking wave was estimated. This resulted in a base shear and overturning moment of such a magnitude that en extensive analysis is recommended on this topic in the future.

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40

Baco, Gerond. "Uplift Behaviour of Screw Piles for Offshore Deepwater Wind Turbine Foundations". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2017.

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The two main types of foundations used so far for offshore wind energy applications are the conventional solution, the so-called mono-piles and the less conventional suction caissons. In the case of the monopiles cyclic loading is identified as the main issue to be considered, and for suction caissons, a quite large number of design issues are present, but prevalent on the others, is the tension capacity. The idea to extend screw piles to offshore applications is becoming nowadays actual. This type of foundation has a quite large onshore application but not offshore so far. They have excellent promise for the wind turbines in deep water because of the very good combination of compression and tension capacity. The attention in this work is focussed on the tension capacity, this is done through a parametric analysis where the parameters are the pile and flanges diameter, the number of piles, the spacing between piles and the pitch of the helix. The commercial finite element analysis software Abaqus CAE combined with the Python scripting is used for the solution of tension capacity of this problem.

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Senders, Marc. "Suction caissons in sand as tripod foundations for offshore wind turbines". University of Western Australia. School of Civil and Resource Engineering, 2009. http://theses.library.uwa.edu.au/adt-WU2009.0163.

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[Truncated abstract] The demand for offshore wind turbines is increasing in densely populated areas, such as Europe. These constructions are typically founded on a gravity foundation or a large 'mono pile'. Gravity foundations can only be used at locations where strong soils exist and water depths are limited. Costs associated with a 'mono pile' type foundation contribute to a very large percentage of the total investment costs. This research, therefore, focuses upon a different foundation for offshore wind turbines, namely suction caissons beneath a tripod. This foundation can be used in all kinds of soil types and is cheaper than the 'mono pile' foundation, both in the amount of steel used and installation costs. Cheaper foundations can contribute to a more competitive price for offshore wind energy in comparison with other energy resources. To date, there have been relatively few studies to investigate the behaviour of this type of foundation during the installation process and during operational and ultimate loading for seabed conditions comprising dense sand. Two types of investigations were performed during this research to determine the behaviour of suction caissons beneath a tripod. Firstly, an existing computer program was extended to predict the typical loading conditions for a tripod foundation. Secondly, centrifuge tests on small scale suction caissons were performed to investigate the behaviour during the installation and loading phases. The computer program developed helped to quantify the likely ranges of environmental loading on an offshore wind turbine. For a typical 3 MW wind turbine of 90 m height, the vertical load is low at around 7 MN. During storm conditions the horizontal hydrodynamic load can be in the order of 4 MN. During normal working conditions the horizontal aerodynamic loads can reach 0.4 MN, but can increase to 1.2 MN when the pitch system malfunctions and gusts reach 30 m/s. This aerodynamic load will result in a very large contribution to the overturning moment, due to the high action point of this load. When the wind turbine is placed on top of a tripod, these large moments are counteracted by a push-pull system. ... The development of differential pressure was found to depend on the soil permeability, the extraction speed and a consolidation effect. During cyclic loading no obvious signs of a decrease in resistance were observed. During very fast cyclic loading differential pressures developed, which could increase the drained frictional resistance by approximately 40%. All centrifuge tests results were used to develop methods to predict or back calculate the installation process of suction caissons in sand and layered soil, and the behaviour during tensile and cyclic loading. These methods all use the cone resistance as the main input parameter and predict the force (or required suction) as a function of time, for a given rate of pumping or uplift displacement, in addition to the variation of suction with penetration (or force with uplift displacement). These new methods provide a useful tool in designing a reliable foundation for offshore wind turbines consisting of a tripod arrangement of suction caissons embedded in dense sand.

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Lau, Ben Hong. "Cyclic behaviour of monopile foundations for offshore wind turbines in clay". Thesis, University of Cambridge, 2015. https://www.repository.cam.ac.uk/handle/1810/248766.

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Investment into offshore wind farms has been growing to address the growing threat of climate change. The majority of offshore wind turbines (both current and planned) are founded on monopiles, large circular steel pipe piles ranging from 4.0 m – 7.5 m in diameter. Based on available borehole records, most planned wind turbines in the UK will be founded in overconsolidated clay deposits. Monopile design is done via usage of the well established p-y curves. However, there are issues with the usage of the p-y curves. Firstly, the curves may be unsuitable to model the monopile’s behaviour as it is expected to behave similarly to a rigid pile rather than flexibly. Secondly, the curves may not accurately estimate the initial pile-soil stiffness. Thirdly, the curves are not comprehensive enough to account for the accumulated strain and stiffness changes resulting from cyclic loading. Considering these issues, research was carried out to improve the current design of monopiles in clay by carrying out displacement controlled monotonic and load controlled cyclic load tests in a centrifuge. Results from monotonic tests suggest that the DNV (2014) design methodology to construct p-y curves in clay based on Matlock’s (1970) soft clay criterion significantly underestimate stiffness. Findings suggested that the experimental p-y curves could be characterised through modification of the criterion. Modification of the criterion produced estimates that matched the 3.83 m monopile experimental curves. Pile toe shear force was observed to contribute little to ultimate lateral resistance and stiffness. Despite the marginal contribution, an effort was made to characterise the pile toe shear force. Estimates of the modified criterion on the 7.62 m monopile did not match the observations, indicating that further research should be carried out to improve the modified criterion. The cyclic tests displayed two distinct regimes; the stiffening regime and the softening regime. Results suggests that cyclic loads of different characteristics influence the locked in stress conditions of the soil which in turn influence the excess pore pressure behaviour, hence dictating whether the stiffening or softening regime takes place. Suggestions were made regarding the conditions that dictated whether the stiffening or softening regime would take place. In the stiffening regime, the stiffening rate decreased with increasing strain while as the accumulated rotation rate increased with vertical load for the same cyclic load magnitude. The softening regime was determined to be extremely detrimental as the high rates of softening and accumulated rotations could cause failure of the system in the short-term. Recommendations were made to estimate the cyclic stiffness and accumulated rotations resulting from both stiffening and softening regime.

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43

Cassidy, Mark Jason. "Non-linear analysis of jack-up structures subjected to random waves". Thesis, University of Oxford, 1999. http://ora.ox.ac.uk/objects/uuid:02b96107-638b-4200-9fd7-fa49635594e3.

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There is a steadily increasing demand for the use of jack-up units in deeper water and harsher environments. Confidence in their use in these environments requires jack-up analysis techniques to reflect accurately the physical processes occurring. This thesis is concerned with the models appropriate for the dynamic assessment of jack-ups, an important issue in long-term reliability considerations. The motivation is to achieve a balanced approach in considering the non-linearities in the structure, foundations and wave loading. A work hardening plasticity model is outlined for the combined vertical, moment and horizontal loading of spudcan footings on dense sand. Empirical expressions for the yield surface in combined load space and a flow rule for prediction of footing displacements during yield are given. Theoretical lower bound bearing capacity factors for conical footings in sand have been derived and are used in a strain-hardening law to define the variation in size of the yield surface with the plastic component of vertical penetration. The complete incremental numerical model has been implemented into a plane frame analysis program named JAKUP. The spectral content of wave loading is considered using NewWave theory, and the importance of random wave histories shown by constraining the deterministic NewWave into a completely random surface elevation. Using this technique, a method for determining short-term extreme response statistics for a sea-state is demonstrated. A numerical experiment on an example jack-up and central North Sea location is shown to emphasise the difference in long-term extreme response according to various footing assumptions. The role of sea-state severity in the variation of short-term extreme response statistics is also highlighted. Finally, probabilistic methods are used to develop further understanding of the response behaviour of jack-ups. A sensitivity study of influential variables (with probabilistic formulations as opposed to deterministic values) has been conducted using the response surface methodology.

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Thompson, Richard Saint George. "Development of non-linear numerical models appropriate for the analysis of jack-up units". Thesis, University of Oxford, 1996. http://ora.ox.ac.uk/objects/uuid:5804719a-8643-49c3-a9f3-105f35dce9ca.

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Jack-up units have considerable economic significance because they are used to carry out a large proportion of the world's oil and gas exploration in water depths less than 90.0m. Due to the increase in use of jack-ups in harsher environments, analysis techniques assuming quasi-static and linear structural behaviour have had to be reassessed. This thesis is concerned with non-linear dynamic analysis methods appropriate for a jack-up assessment. Jack-up modelling requires realistic representation of the structure, the foundations and the environmental loading, together with the implementation of appropriate dynamic analysis algorithms. Techniques for each of these aspects of jack-up analysis are reviewed and the implementation of several of the methods in an advanced plane frame analysis program called JAKUP is described. Geometric non-linearity in the structure and work hardening plasticity at the foundations are accounted for in the program. Test cases are presented to verify the implementation of the methods and then some illustrative plane frame quasi-static and dynamic analyses are described. These simple models highlight the importance of accounting for dynamic motions in a jack-up analysis. For the quasi-static analyses, the assumption of pinned footing behaviour is seen to always result in the most conservative displacement and moment predictions. However, the analyses show that this is not always the case when dynamic amplification is accounted for.

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45

Collins, Carl. "Development and application of a computational model for scour around offshore wind turbine foundations". Thesis, University of Hull, 2017. http://hydra.hull.ac.uk/resources/hull:16530.

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There is a constant requirement to understand scour especially regarding its prevention, due to the potential impact and disastrous consequences. The installation of offshore wind turbines is haunted by scour mitigation and at the start of the offshore wind turbine boom in the early 2000’s this was achieved using overzealous amounts of rock armour. However, as investment and cost efficiency has increased, protection methods have been refined, but, there remains significant room for improvement. Research into offshore sediment dynamics has benefited greatly by computational advancements providing a greater understanding of processes and the driving mechanisms; leading to protection method improvements and reductions in environmental impact. The premise of this study is to push this knowledge further, by developing and validating a novel scour model within CFD software that can be used to simulate and analyse offshore scour; specifically, the scour around complex, new offshore wind turbine foundation geometries.

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46

Jardine, Richard. "Investigations of pile-soil behaviour, with special reference to the foundations of offshore structures". Thesis, Imperial College London, 1985. http://hdl.handle.net/10044/1/8519.

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47

Jin, Zhuang. "Numerical investigation of caisson foundations in sand under combined monotonic loadings for offshore wind turbines". Thesis, Ecole centrale de Nantes, 2019. http://www.theses.fr/2019ECDN0002/document.

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Cette thèse de doctorat porte sur la réponse des fondations caisson dans du sable pour les éoliennes en mer soumises à des chargements monotones et cycliques combinés. Le processus de défaillance et l’enveloppe de rupture (diagramme de capacité portante) d’une fondation en caisson dans du sable soumise à des chargements monotones combinés sont premièrement étudiés à l’aide du modèle constitutif de Mohr-Coulomb. La méthode Lagrangian-Smoothed Particle Hydrodynamics Combinée (CLSPH) est adoptée pour prendre en compte les grandes déformations et les limites de l'approche sont mises en évidence. Une loi constitutive basée sur la notion de l’état critique pour le sable récemment mis au point (SIMSAND) est ensuite introduite et utilisée avec la méthode CLSPH. Des tests d’effondrement du sol dans un canal rectangulaire et d’une colonne granulaire en prenant en compte différentes géométries sont simulés afin de valider l’approche en termes de morphologie de dépôt final, des profils d’écoulement et de zones non perturbées. La méthode CLSPH et le modèle SIMSAND sont ensuite utilisés pour étudier le diagramme de capacité portante des fondations caisson dans du sable. Différents paramètres ayant une incidence sur la forme et la taille de l'enveloppe de rupture sont pris en compte, tels que la densité et la rigidité du sol, la résistance au frottement, la rupture des grains, la géométrie et les dimensions de la fondation. Une formule analytique est introduite pour décrire la surface de rupture 3D capable à reproduire les résultats numériques. Sur la base de la formule analytique proposée, un macro-élément pour des fondations caisson dans du sable soumises à des chargements monotones et cycliques est finalement développé dans le cadre de l'hypoplasticité. L’outil numérique proposé est validé avec des résultats expérimentaux
This PhD thesis deals with the response of caisson foundations in sand for offshore wind turbines submitted to combined monotonic and cyclic loadings. First, the failure process and failure envelope (or bearing capacity diagram) of a caisson foundation in sand under combined monotonic loadings is investigated using the conventional Mohr-Coulomb constitutive model. A Combined Lagrangian-Smoothed Particle Hydrodynamics(CLSPH) method is adopted to consider large deformations and the limitations of the approach are highlighted. A recently developed critical state model for sand (SIMSAND) is then introduced and combined with the CLSPH method. Rectangular channel soil collapse tests and granular column collapse tests considering different aspect ratios are simulated to validate the approach in terms of final deposit morphologies, flow profiles and undisturbed areas.The CLSPH method and the SIMSAND model are then used to investigate the bearing capacity diagram of the caisson foundation in sand. Different parameters affecting the shape and size of the failure envelope are considered, as soil density and stiffness, friction strength, grain breakage, geometry and aspect ratio of the foundation. An analytical formula is introduced to describe the 3D failure surface reproducing the numerical results. Based on the proposed analytical formula, a macro-element for the caisson foundation in sand submitted to monotonic and cyclic loadings is finally developed within the framework of hypoplasticity. Validation is provided through comparison with experimental results

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48

WANG, XUEFEI. "CENTRIFUGE MODELLING OF SEISMIC AND LATERAL BEHAVIORS OF SUCTION BUCKET FOUNDATIONS FOR OFFSHORE WIND TURBINES". Case Western Reserve University School of Graduate Studies / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=case1480604602709635.

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Tran, Manh Ngoc. "Installation of Suction Caissons in Dense Sand and the Influence of Silt and Cemented Layers". University of Sydney, 2006. http://hdl.handle.net/2123/4064.

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Doctor of Philosophy
Suction caissons have been used in the offshore industry in the last two decades as both temporary mooring anchorages and permanent foundation systems. Although there have been more than 500 suction caissons installed in various locations around the world,understanding of this concept is still limited. This thesis investigates the installation aspect of suction caissons, focusing on the installation in dense sand and layered soils, where sand is inter-bedded by silt and weakly cemented layers. The research was mainly experimental, at both normal gravity and elevated acceleration levels in a geotechnical centrifuge, with some numerical simulations to complement the experimental observations. This study firstly explored the suction caisson installation response in the laboratory at 1g. The influence and effect of different design parameters, which include caisson size and wall thickness, and operational parameters including pumping rate and the use of surcharge were investigated in dense silica sand. The sand heave inside the caisson formed during these installations was also recorded and compared between tests. The 1g study also investigated the possibility of installing suction caissons in layered sand-silt soil, where caissons were installed by both slow and rapid pumping. The heave formation in this case is also discussed. The mechanism of heave formation in dense sand and deformation of the silt layer was further investigated using a half-caisson model and the particle image velocimetry (PIV) technique. The installation response at prototype soil stress conditions was then investigated in a geotechnical centrifuge. The effects of caisson size, wall thickness, as well as surcharge were investigated in various types of sand, including silica sand, calcareous sand dredged from the North Rankin site in the North West Shelf (Australia), and mixed soil where silica sand was mixed with different contents of silica flour. Comparison with the 1g results was also made. The general trend for the suction pressure during installation in homogenous sand was identified. The installation in layered soil was also investigated in the centrifuge. The installation tests were performed in various sand-silt profiles, where the silt layers were on the surface and embedded within the sand. Comparison with the results in homogenous sand was made to explore the influence of the silt layer. Installations in calcareous sand with cemented layers were also conducted. The penetration mechanism through the cemented layer is discussed, and also compared with the penetration mechanism through the silt layer. Finite element modelling was performed to simulate key installation behaviour. In particular, it was applied to simulate the sand deformation observed in the PIV tests. The likely loosening range of the internal sand plug during suction installation in silica sand was estimated. By investigating the development of hydraulic gradient along the inner wall, the principle underlying the suction response for different combinations of selfweight and wall thickness was identified. FE modelling was also performed to explore the influence of the hydraulic blockage by the silt layer. This study found that the caissons could penetrate into all soils by suction installation. Among the key findings are the observations that the suction pressure increases with depth following a distinct pressure slope, corresponding to a critical hydraulic condition along the inner wall; and the installation was possible in both layered sand-silt and uncemented-cemented soils if sufficient pumping was available. While the caisson could penetrate the weakly cemented layers well with no notable adverse effects, problems were observed in the installation in layered sand-silt soil. These include piping failure in slow pumping rate installation at 1g, and the formation of extremely unstable soil heave during installation.

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Jung, Jonatan Garrido. "Estudo do jateamento em solos argilosos e sua aplicação à engenharia de fundações offshore". reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2012. http://hdl.handle.net/10183/62042.

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A maior parte do petróleo explorado no Brasil encontra-se em jazidas marítimas onde a lâmina d’água pode superar os 1000 metros. As descobertas recentes de novos campos de petróleo offshore têm motivado pesquisas nesta área para enfrentar os desafios tecnológicos envolvidos nos processos de exploração do óleo. Para a extração deste material, são comumente empregadas plataformas flutuantes que utilizam um sistema de ancoragem no leito oceânico para sua operação. O presente trabalho estuda uma nova técnica de instalação de âncoras para plataformas marítimas de petróleo, que serve de alternativa e/ou adaptação a técnicas já utilizadas, e que consiste na aplicação de jatos de água para remoção do solo permitindo que a âncora penetre no subleito oceânico. No desenvolvimento do trabalho foi analisado o comportamento de duas argilas (A e B), nas quais o jateamento vertical de água é utilizado para introduzir tubos metálicos na massa argilosa. Os ensaios de jateamento foram realizados em laboratório, utilizando tanques retangulares de dimensões reduzidas com paredes em acrílico, preenchidos com solo. A geometria da cavidade formada pela injeção em cada amostra argilosa foi observada através das paredes dos tanques. A influência da técnica de instalação na adesão solo-estaca foi avaliada através de provas de carga à tração, realizadas no próprio tubo usado no jateamento em cada ensaio, cujos resultados foram comparados com provas de carga em tubos instalados sem o emprego do jateamento. Nos testes com jatos são identificados dois mecanismos de erosão, característicos de argilas com alto índice de vazios: a erosão em massa e a superficial. A máxima profundidade da zona erodida não coincidiu com o eixo do tubo na quase totalidade dos ensaios. A penetração do jato no subleito do solo argiloso reduz com o aumento da profundidade do jato, e também com a resistência da argila. O diâmetro da cavidade na saída do jato sofreu redução com o aumento da profundidade. A geometria da cava erodida em cada argila mostrou ser função da velocidade e do diâmetro do jato, sendo determinadas equações empíricas para estimar suas dimensões. Após a instalação dos tubos empregando a técnica do jateamento, a redução média da adesão solo-estaca na argila A foi de 42% e na argila B foi de 41% em relação à adesão inicial. As análises dos resultados em função da velocidade do jato e da vazão indicaram pequena influência destes parâmetros na variação da adesão do solo ao tubo.
Most of all petroleum produced in Brazil is encountered in marine deposits where the water depth may exceed 1000 meters. Recent discoveries of new offshore oil fields have motivated studies in this area designed to develop new techniques applied to oil exploration. For the extraction of oil deposits floating platforms are commonly used, supported by anchorage systems on the seabed. This work examines a new technique for installing anchors for offshore oil platforms, that can work as alternatives or complement to existing techniques, and consists of applying water jets to remove the soil allowing the anchor to penetrate into the seabed. In this study, the behavior of two clays (A and B) was analyzed during vertical jets used to induce the penetration of metal tubes into the clay. The tests were performed in laboratory using small rectangular tanks with acrylic walls, filled with soil. The geometry of the cavity formed by water injection was observed through the walls of the tanks. The influence of the installation technique in the adhesion mobilized between the clay and the pile shaft was evaluated by tensile load tests, performed in the same tubes used in jetting tests, whose results were compared with load tests on tubes introduced without the jetting technique. In tests with jets two distinct erosion mechanisms have been identified which are considered characteristic of clays with a high void ratio: mass and surface erosion. The maximum depth of eroded area did not coincide with the jet centerline in almost all tests. The jet penetration in the clay bed reduces with increasing depth of the jet, and also with the resistance of the clay. The diameter of the hole at the jet outlet decreased with increasing depth. The geometry of the eroded hole in each clay was shown to be a function of jet velocity and diameter, and empirical equations were developed to estimate these dimensions. After installation of the tubes using the jet technique, the average reduction in the adhesion between the clay and the pile shaft was 42% in clay A and 41% in clay B. Analysis of the results as a function of jet velocity and flow rate indicated small influence of these parameters on the variation of soil-tube adhesion.

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