Tesi sul tema "Offshore Structure"
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1
Robinson, Michael E. "Statistics for offshore extremes". Thesis, Lancaster University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.387465.
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2
Nwankwo, Cosmas Chidozie. "Smart offshore structure for reliability prediction process". Thesis, Cranfield University, 2013. http://dspace.lib.cranfield.ac.uk/handle/1826/9335.
Testo completoAbstract (sommario):
A review of the developments within the field of structural reliability theory shows that
some gaps still exist in the reliability prediction process and hence there is an urgent
desire for improvements such that the estimated structural reliability will be capable of
expressing a physical property of the given structure. The current reliability prediction
process involves the continuous estimation and use of reliability index as a way of
estimating the safety of any given structure. The reliability index β depends on the
Probability Density Function (PDF) distribution for the wave force and the corresponding
PDF of resistance from respective structural members of the given structure. The PDF
for the applied wave force will depend on the PDF of water depth, wave angular velocity
and wave direction hence the reliability index as currently practiced is a statistical way
of managing uncertainties based on a general probabilistic model.
This research on Smart Offshore Structure for Reliability Prediction has proposed the
design of a measurement based reliability prediction process as a way of closing the
gap on structural reliability prediction process. Structural deflection and damping are
some of the measurable properties of an offshore structure and this study aims at
suggesting the use of these measurable properties for improvements in structural
reliability prediction process. A design case study has shown that a typical offshore
structure can deflect to a range of only a few fractions of a millimetre. This implies that if
we have a way of monitoring this level of deflection, we could use the results from such
measurement for the detection of a structural member failure. This advocated concept is
based on the hypothesis that if the original dynamic characteristics of a structure is
known, that measurement based modified dynamic properties can be used to determine
the onset of failure or failure propagation of the given structure.
This technology could reveal the location and magnitude of internal cracks or corrosion
effects on any given structure which currently is outside the current probability based
approach. A simple economic analysis shows that the recommended process shows a
positive net present value and that some $74mln is the Value of Information for any life
extension technology that could reveal the possibility of extending the life of a given
10,000bopd production platform from 2025 to 2028.
3
Medori, René. "Déterminants et structure du secteur parapétrolier offshore". Paris 9, 1986. https://portail.bu.dauphine.fr/fileviewer/index.php?doc=1986PA090010.
Testo completoAbstract (sommario):
Le document comporte deux parties principales : la première partie décrit les déterminants techniques tels que le marché pétrolier, la filière technologique, la fiscalité pétrolière, et le marché parapétrolier ; la seconde partie décrit les déterminants stratégiques des acteurs (états, compagnies pétrolières, firmes parapétrolières)The document includes two main parts: the first one describes the technological factors; the second one analyses the actors strategies
4
Medori, René. "Déterminants et structure du secteur parapétrolier offshore". Grenoble 2 : ANRT, 1986. http://catalogue.bnf.fr/ark:/12148/cb37599551h.
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5
Abdolmaleki, Kourosh. "Modelling of wave impact on offshore structures". University of Western Australia. School of Mechanical Engineering, 2007. http://theses.library.uwa.edu.au/adt-WU2008.0055.
Testo completoAbstract (sommario):
[Truncated abstract] The hydrodynamics of wave impact on offshore structures is not well understood. Wave impacts often involve large deformations of water free-surface. Therefore, a wave impact problem is usually combined with a free-surface problem. The complexity is expanded when the body exposed to a wave impact is allowed to move. The nonlinear interactions between a moving body and fluid is a complicated process that has been a dilemma in the engineering design of offshore and coastal structures for a long time. This thesis used experimental and numerical means to develop further understanding of the wave impact problems as well as to create a numerical tool suitable for simulation of such problems. The study included the consideration of moving boundaries in order to include the coupled interactions of the body and fluid. The thesis is organized into two experimental and numerical parts. There is a lack of benchmarking experimental data for studying fluid-structure interactions with moving boundaries. In the experimental part of this research, novel experiments were, therefore, designed and performed that were useful for validation of the numerical developments. By considering a dynamical system with only one degree of freedom, the complexity of the experiments performed was minimal. The setup included a plate that was attached to the bottom of a flume via a hinge and tethered by two springs from the top one at each side. The experiments modelled fluid-structure interactions in three subsets. The first subset studied a highly nonlinear decay test, which resembled a harsh wave impact (or slam) incident. The second subset included waves overtopping on the vertically restrained plate. In the third subset, the plate was free to oscillate and was excited by the same waves. The wave overtopping the plate resembled the physics of the green water on fixed and moving structures. An analytical solution based on linear potential theory was provided for comparison with experimental results. ... In simulation of the nonlinear decay test, the SPH results captured the frequency variation in plate oscillations, which indicated that the radiation forces (added mass and damping forces) were calculated satisfactorily. In simulation of the nonlinear waves, the waves progressed in the flume similar to the physical experiments and the total energy of the system was conserved with an error of 0.025% of the total initial energy. The wave-plate interactions were successfully modelled by SPH. The simulations included wave run-up and shipping of water for fixed and oscillating plate cases. The effects of the plate oscillations on the flow regime are also discussed in detail. The combination of experimental and numerical investigation provided further understanding of wave impact problems. The novel design of the experiments extended the study to moving boundaries in small scale. The use of SPH eliminated the difficulties of dealing with free-surface problems so that the focus of study could be placed on the impact forces on fixed and moving bodies.
6
Johannessen, Markus. "Concept Study and Design ofFloating Offshore Wind TurbineSupport Structure". Thesis, KTH, Marina system, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-243092.
Testo completoAbstract (sommario):
There is a need for renewable energy sources that can replace the non-renewable energy sourcesthat we use today. This is on the agenda as one of the United Nations sustainable developmentgoals. Embracing new technologies is addressed as one of the ways of achieving aordable,reliable, sustainable and modern energy for all. Oshore wind power has great potential as anenergy source, and development of the oating solutions is of special importance.In this report, key design parameters of oating oshore wind turbines are identied based ona literature study on research projects as well as on-going test turbines and wind farms. Thekey design parameters should be used for determining the type of technology suitable for aproject, as well as for guidance in the design phase.Based on the key design parameters, a conceptual design of a semisubmersible substructurehas been made for the DTU 10 MW reference wind turbine for a site outside the island ofBarra, west of Scotland. The substructure is a three column semisubmersible connected witha closed shape pontoon and no bracing. The wind turbine is placed on top of one of the threecolumns to reduce number of columns and utilize more of the structure.Variation of the column diameter and distance between the columns has been studied to ndsuitable main dimensions. Mass estimations has been made and the required amount of ballasthas been calculated for a set of combinations to select a conguration for further analysis.Hydrostatic and hydrodynamic analysis has been performed on the design to understand itscharacteristics in the ocean environment. Intact stability is considered in the hydrostatic analysis,and the hydrodynamic analysis includes a study of the motions, loads and accelerationsof the structure.
7
Dimelow, David J. "Non-linear dynamics of an offshore mooring tower". Thesis, University of Aberdeen, 1997. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU092912.
Testo completoAbstract (sommario):
Offshore mooring towers are one of a number of single-point mooring (SPM) systems which provide a berthing point for tankers, enabling the transfer of crude oil to or from the moored vessel. The periodic slackening of the mooring hawser between the vessel and the tower gives rise to a discontinuously non-linear restoring function. Hence, the wave-induced motions of the tower can be highly complex, with the possibility of large amplitude, and potentially hazardous motions. A large amount of work has been carried out in studying single-point mooring systems. However, much of this work has focused on mooring forces and tanker motions. Few studies have looked in-depth at the motions of the mooring structure itself. In this thesis, mooring tower motions have been studied in detail using three techniques: numerical analysis, approximate analytical methods, and experimental modelling. Each of these approaches to the problem has demonstrated that large amplitude and hence potentially hazardous motions can occur. Numerical predictions of motion showed very good comparison with measured responses, particularly for synchronous motions. However, for more complex motions, such as subharmonic resonances, the agreement between measured and predicted results was seen to deteriorate. Approximate analytical methods did not perform so well. Useful results were obtained for the simplified single-degree-of-freedom symmetric model only, highlighting the need for a more sophisticated method. This research has been successful in providing insight into the complex non-linear motions of an offshore mooring tower. The fundamental mechanisms and features of the system have been presented. The methodology used in this study has been applied to the specific case of an offshore mooring tower. However, the general approach to investigating the non-linear motions of the structure is widely applicable in the field of offshore engineering.
8
Fu, Y.-N. "The hydroelastic analysis of jack-up structures in waves". Thesis, Brunel University, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.375483.
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9
Wolfram, Julian. "An integrated approach to fatigue cracking, reliability and inspection of offshore structures". Thesis, University of Strathclyde, 1985. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=21473.
Testo completoAbstract (sommario):
This thesis describes an integrated approach to fatigue cracking, reliability and inspection of offshore structures. The basis of the approach is statistical in nature and draws on recent experimental data and field measurements. It is intended as a working tool for those engaged in design, structural appraisal and sub-sea inspection of steel jacket structures. A review of current practice has been made and the requirements of an integrated approach are established. An approach is proposed comprising a series of compatible models dealing with fatigue cracking, the reliability of cracked joints and the inspection of welds for fatigue cracks. The primary linking parameter is the distribution of fatigue crack size which is considered as a time dependent variable. An integral part of the approach is a new statistically-based fatigue crack growth model. This is developed and the parameters involved in the model estimated from an analysis of experiment and oceanographic data. For any fatigue calculation the model allows the corresponding fatigue crack growth distribution to be estimated for any time during, or beyond, the nominal fatigue life. A number of example calculations are included; and using one of these a Bayesian procedure for revising fatigue lives in the light of inspection results is demonstrated. The effect of fatigue cracking upon the various modes of tubular joint failure is considered using linear statistical models. Example calculations are performed for a typical joint. An inspection strategy is proposed based on the concept of minimising life costs, including risk costs arising from the consequences of possible structural failure. This allows alternative inspection plans to be evaluated and compared, and a typical example calculation is included. The approach is discussed in the context of possible alternative approaches and areas for further related research are identified.
10
Nash, T. "The experimental behaviour of double skinned composite and reinforced concrete shells subjected to external hydrostatic pressure". Thesis, University of Manchester, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383249.
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11
Shi, Yongjiu. "Dynamic behaviour of guyed tower platforms". Thesis, Heriot-Watt University, 1989. http://hdl.handle.net/10399/958.
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12
Konstantopoulos, G. P. "A unified treatment of semisubmersible stability". Thesis, University of Strathclyde, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.382306.
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13
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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14
Haswell, Jane V. "A fracture mechanics methodology for the assessment of fatigue cracks in tubular joints : (based on the finite element method)". Thesis, Teesside University, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.290767.
Testo completoAbstract (sommario):
Fixed jacket offshore structures. which react environmental wave loading. are generally constructed using tubular steel members. When subject to load. severe surface and through-thickness stress gradients occur due to local bending of the tubular wall. The cyclic nature of the environmental wave loading results in high stress concentration at the joints. which can lead to fatigue cracking. British Gas currently operates twelve fixed offshore structures. two of which. the Rough A-Complex structures. are now ageing and showing signs of fatigue cracking. The objective of the work described in this thesis is the development of a fracture mechanics-based methodology for the assessment of fatigue cracking in these structures. The fracture mechanics approach uses the stress intensity factor (SIl) to characterise crack-tip conditions. and provides a means of analysing the behaviour of cracks. The SIF is defined in terms of the crack site stress distribution and the change in structural compliance with crack size. Difficulties in the application of fracture mechanics lie in the derivation of accurate solutions for the SIF. The tubular joints of offshore jacket structures present particular difficulties due to their complex loading and geometry. The current work starts with a review and assessment of tubular joint fracture mechanics models. followed by a numerical study of cracked tubular joints using shell finite element (FE) models incorporating line spring crack representation. Based on the results of this study. a general fracture mechanics model for the prediction of SIF solutions for tubular joints. is derived and assessed. The general fracture mechanics model is incorporated into a crack growth model. which is best implemented using sophisticated commercial software. Crack growth and fatigue life predictions obtained are validated against full scale tubular joint fatigue data. Finally. a complete methodology for the assessment of fatigue cracks in any tubular joint is proposed, and applied to the assessment of fatigue cracking in the Rough A-Complex structures.
15
Zeinoddini, Mostafa. "Dynamic behaviour of offshore structure members subjected to ship collision". Thesis, University of Surrey, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.298154.
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16
Kerner, Laura. "Interaction sol-structure sous sollicitations cycliques dynamiques : Application aux éoliennes offshore fondées sur monopieu". Thesis, Paris Est, 2017. http://www.theses.fr/2017PESC1118/document.
Testo completoAbstract (sommario):
Ce travail de thèse s’articule autour de la problématique de l’évolution de la première fréquence propre d’une éolienne en mer au cours de sa durée d’exploitation. Ce type de structure élancée est soumis à des chargements cycliques et dynamiques tels que le vent, les vagues, les courants marins, la rotation des pales. Ces chargements ont des fréquences de sollicitation proches de la première fréquence propre de l’éolienne, celle-ci s’inscrivant dans un intervalle restreint entre la fréquence du rotor et celle des pales. Afin d’éviter tout phénomène de résonance, il convient d’évaluer précisément à la fois la première fréquence propre de l’éolienne juste après son installation ainsi que son évolution au cours de son exploitation. Ces deux problématiques ont été considérées dans cette étude.Dans ce contexte, un travail expérimental a été réalisé autour de deux modèles physiques 1g d’éolienne en mer fondée sur monopieu et installée dans un massif de sable de Fontainebleau. En se basant sur une modélisation de la fondation à l’aide d’un ensemble de ressorts, latéral et de torsion, une série d’essais a été réalisée afin d’évaluer à la fois la raideur de ces ressorts, mais aussi la fréquence propre du modèle physique considéré. Cette méthode a été comparée à des méthodes existantes et a aussi permis le développement de méthodes originales. Réaliser les essais sur deux modèles à échelle différente (1/60 et 1/120) a permis d’adapter les résultats obtenus aux cas d’une éolienne à échelle 1. Enfin, dans le cadre de l’étude de l’évolution de la structure au cours de son exploitation, des essais de sollicitations cycliques ont été réalisés. Une étude paramétrique se concentrant sur l’influence de la fréquence de la sollicitation et de la force globale appliquée a été proposée. Les résultats obtenus permettent d’analyser le comportement des modèles réduits, soumis à un maximum d’un million de cycles, en se concentrant sur l’évolution du déplacement, de la rotation et de la fréquence propre de ces structures. Ces résultats sont comparés aux limites imposées pour l’état limite de service d’une éolienne grandeur réelleThis PhD thesis deals with the main issue which is the evolution of the first natural frequency of an offshore wind turbine. These slender structures are submitted to cyclic and dynamic loads such as wind, waves, currents, and the blade rotations. The frequencies related to these loads are close to the first natural frequency of the turbine, which lay in a narrow interval between the frequencies of the rotor and the blades. In order to avoid any resonance phenomenon, one needs a precise evaluation of not only the natural frequency of the wind turbine after its installation but also its evolution during the operation of the turbine. These two issues are considered in this work.In this context, an experimental work was developed considering two 1g physical models of an offshore wind turbine with a monopile foundation installed in Fontainebleau sand. Based on the modelling of the foundation as a set of lateral and rotational springs, an experimental program was developed in order to evaluate the stiffness of these springs and the natural frequency of the scaled models. This method was first compared to the existing methods and has allowed to develop some original methods to evaluate the natural frequency of the considered scaled model. The tests, conducted on two physical models with different scales (1/60 and 1/120), also allowed us to adapt the obtained results to a real offshore wind turbine. As a part of the study of the turbine’s evolution during its operation, cyclic load tests were conducted. A parametric study is proposed with a focus on the influence of the load’s frequency and its amplitude. The obtained results allowed us to analyze the behavior of the scaled models submitted up to one million cycles considering, mainly, the evolution of the displacement, the rotation, and the natural frequency of the structures. These results were then compared to the limits imposed by the serviceability limit state of a real offshore wind turbine
17
Wu, Xiong-Jian. "Motion and wave load analyses of large offshore structures and special vessels in waves". Thesis, Brunel University, 1990. http://bura.brunel.ac.uk/handle/2438/7865.
Testo completoAbstract (sommario):
Predictions of the environmental loading and induced motional and structural responses are among the most important aspects in the overall design process of offshore structures and ships. In this thesis, attention is focused on the wave loads and excited bodily motion responses of large offshore structures and special vessels. With the aim of improving the existing theoretical methods to provide techniques of theoretical effectiveness, computational efficiency, and engineering practicality in marine and offshore applications, the thesis concentrates upon describing fundamental and essential aspects in the physical phenomenon associated with wave-structure interactions and deriving new methods and techniques to analyse offshore structures and unconventional ships of practical interest. The total wave force arising from such a wave-structural interaction is assumed to be a simple superposition of the potential and the viscous flow force components. The linear potential forces are solved by the Green function integral equation whilst the viscous forces are estimated based on the Morison's damping formula. Forms of the Green function integral equation and the associated Green function are given systematically for various practical cases. The relevant two-dimensional versions are then derived by a transformation procedure. Techniques are developed to solve the integral equation numerically including the interior integral formulation and, in particular, to tackle the mathematical difficulties at irregular frequencies. In applying the integral equations to solve problems with various offshore structures and special vessels, some modified, improved or simplified methods are proposed. At first, simplified method is derived for predictions of the surge, sway and yaw motions of elongated bodies of full sectional geometry or structures with shallow draft. Then, a new shallow draft theory is described for both three- and two-dimensional cases with inclusion of the finite draft effect. Furthermore, a three-dimensional strip method is formulated where the end effects of the body are fully taken into account. Finally, an approximation to the horizontal mean drift forces of multi-column offshore structures are presented. Some new findings are also discussed including the multiple resonances occurring in the motions of multi-hulled marine structures due to the wave-body interaction, the mutual cancellation effect of the diffraction and the radiation forces arising from a full shaped slender body, and so on. Further to those verification studies for individual methods developed, more comprehensive example investigations are given related to two industrial applications. One is a derrick barge semi-submersible with zero forward speed; and the other, a SWATH ship with considerable speed. By correlation of all the proposed approaches with available analytical, numerical and experimental data, the thesis tries to demonstrate a principle that as long as principal physical aspects in the wave-structure interaction problem are properly treated, an appropriately modified or simplified method works, performs well and, sometimes, even better.
18
Foster, Kathryn J. "Design modelling to minimise the risk for offshore platforms". Thesis, Loughborough University, 1999. https://dspace.lboro.ac.uk/2134/7363.
Testo completoAbstract (sommario):
Safety cases must be produced by offshore operators to assess the risks posed to the personnel by potential accidents. On an offshore platform two of the major hazards are fires and explosions resulting from an accidental hydrocarbon release. The overpressures generated during an explosion can threaten the integrity of the platform structure. It is therefore important to be able to estimate the overpressures generated, should an explosion occur, and to predict the frequency of such an event. A methodology has been developed to predict the frequency of explosions of different magnitudes occurring in a module on an offshore platform. This methodology combines established risk assessment techniques, such as event tree analysis and fault tree analysis, with fluid flow modelling. Assumptions have been made in the methodology to simplify the calculation procedure. These assumptions relate to the conditions under which the leak occurs, the build up of gas in air concentration and the probability calculations. Frequency predictions are required to be as accurate as possible to enable the acceptability of the risk to be determined and reduced to a level which is as low as reasonably practicable. Hence each of the assumptions within the methodology has been addressed, to determine a more complete prediction tool. Once an accurate frequency for the explosion occurring has been determined, the risk to personnel must be minimised to an acceptable yet practical level. On existing designs it is impractical to alter the layout of the platform. However the nature of the safety systems may be changed. These safety features include isolation, blowdown, mitigation and detection systems. An optimisation study presents three schemes to identify the optimum configuration of the safety systems, in terms of the overpressures generated, as a means of reducing the risk to the platform.
19
Pinna, Rodney. "Buckling of suction caissons during installation". University of Western Australia. School of Civil Engineering, 2003. http://theses.library.uwa.edu.au/adt-WU2004.0008.
Testo completoAbstract (sommario):
Suction caissons are a foundation system for offshore structures which offer a number of advantages over traditional piled foundations. In particular, due to the method of installation used, they are well suited for deep-water applications. The suction caisson consists of an open ended cylindrical shell, which is installed below the seabed in a sequence which consists of two loading phases. The caisson is first installed part way under self weight, with the installation being completed by lowering the pressure within the cylinder and thus allowing the ambient water pressure to force the caisson into the ground. This thesis examines a number of structural issues which result from the form of the caisson — essentially a thin walled cylinder — and the interaction of the caisson with the surrounding soil during installation. To do this, variational analysis and nonlinear finite element analysis are employed to examine the buckling and collapse behaviour of these cylinders. In particular, two issues are considered; the influence of the open end, and the interaction between the cylinder and soil on the buckling and collapse loads. First, the behaviour of open ended cylinders is considered, where the boundary condition at the open end is allowed to vary continuously from completely free to pinned, by the use of a variable lateral spring. This lateral spring restraint may be considered to represent the intermediate restraint provided by a ring stiffener which is not fully effective. The effect of various combinations of boundary conditions is accounted for by the use of a multiplier on the lower bound to the buckling load of a cylinder with classical supports. The variable spring at the open end may also be considered to be an initial, simple representation of the effect of soil restraint on the buckling load. More complex representations of the soil restraint are also considered. A nondimensional factor is proposed to account for the influence of this spring on the buckling load. One combination of boundary conditions, where the upper end of the caisson is pinned, and the lower end free (referred to as a PF boundary condition), is found to have buckling and collapse behaviour which is unusual for cylindrical shells. Buckling loads for such shells are much lower than would be found for cylinders with more typical boundary conditions, and of similar dimensions. More unusually however, PF cylinders are shown to have positive postbuckling strength. The behaviour is found to be a result of the large flexibility which results from the low restraint provided by the PF boundary conditions. This is shown by continuously decreasing the flexibility of the cylinder, by increasing the axial restraint at the pinned end. It is shown that this results in a large increase in buckling load, and a return to more usual levels of imperfection sensitivity. In particular, with an intermediate level of axial restraint, buckling loads and imperfection sensitivity are intermediate between those of PF shells with no, and with full, axial restraint. Overall however, collapse loads for PF cylinders with no additional restraint are well below those of cylinders with stiffer boundary conditions, for equal geometries. Eigenvalue buckling of cylinders fully and partially embedded in an elastic material are examined, and two analytical solutions are proposed. One of these is an extension of a method previously proposed by Seide (1962), for core filled cylinders, to pin ended cylinders which have support from both a core and a surrounding material. The second method represents the elastic support as a two parameter foundation. While more approximate than the first method, this method allows for the examination of a wider range of boundary conditions, and of partial embedment. It is found that the buckling load of the shell/soil system decreases as the embedment ratio decreases. Collapse of fully and partially embedded cylinders is also examined, using nonlinear finite element analysis. The influence of plasticity in the soil is also considered. For cylinders with small imperfections, it is found that the collapse load shows a large increase over that of the same cylinder with no soil support. However, as the size of initial geometric imperfections increases, it is found that the collapse load rapidly approaches that of the unsupported cylinder. In particular, in weak soils the gain in strength over the unsupported shell may be minimal. The exception to this is again PF cylinders. As these have relatively low collapse loads, even very weak soils are able to offer an increase in collapse load over the unsupported case. Finally, a summary of these results is provided in the form of guidance for design of such structures.
20
Rasekhafshar, Samsam. "Global Fatigue Assessment of a Decommissioned Jacket Platform for a Sustainable Reuse as an Offshore Wind Turbine". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021.
Cerca il testo completoAbstract (sommario):
When the offshore oil and gas supplies exhaust, offshore platforms must be decommissioned and removed. The present thesis highlights the importance of evaluating the possibility of reuse of decommissioned offshore jacket platforms for offshore wind energy. In order to shift to the new structure, the topside must be removed from the substructure and a wind turbine can be installed in its place.
The feasibility of this project was investigated using a finite element analysis software called Sesam. To study fatigue life in offshore structures, an exhaustive review of the background and state of the art was done.
A finite element model was created by the means of Sesam and two different fatigue analysis approaches were applied and compared. In the end, an analysis methodology is suggested for the structural fatigue analysis of offshore wind turbine structures based on international standards, addressing the industry’s need to account for the combined effect of wind and hydrodynamic loads in these type of structures.
21
Chung, Yi-tak Teresa. "Quaternary stratigraphy of an offshore borehole from northern Lantau, Hong Kong". Click to view the E-thesis via HKUTO, 2009. http://sunzi.lib.hku.hk/hkuto/record/B42904730.
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22
Wang, Zhiguo. "Ice forces on a multifaceted conical structure". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq25779.pdf.
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23
Chu, N. "Wave force calculation with consideration of viscous effects". Thesis, University of Strathclyde, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.382261.
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24
Parsa, Arash. "Finite element modelling of stress concentrations in a reinforced concrete offshore structure". Thesis, University of Southampton, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.292406.
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25
Hughes, Brian R. "In-line forces on a slender structure subjected to combined waves and currents". Thesis, University of British Columbia, 1988. http://hdl.handle.net/2429/28387.
Testo completoAbstract (sommario):
The present investigation considers the hydrodynamic forces acting on a slender structure
subjected to a combined wave and current flow regime. The experimental aspect of the study measured the in-line peak-to-peak forces on a vertical cylinder mounted in a wave-current flume. Although there were some inconsistencies in the data, the general trend indicated a substantial increase in the force with a positive underlying current and a less pronounced increase for a negative current.
A numerical analysis of the problem evaluated Morison's equation using the current-invariant force transfer coefficients and flow kinematics obtained through Stokes Fifth Order Wave Theory. The results of this analysis revealed a trend qualitatively similar to that found experimentally. The important distinction between the results obtained through the experimental investigation and those obtained numerically was the consistent
over-prediction observed in the numerical analysis.Applied Science, Faculty of
Civil Engineering, Department of
Graduate
26
Fevåg, Live Salvesen. "Influence of marine growth on support structure design for offshore wind turbines". Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for bygg, anlegg og transport, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-18682.
Testo completoAbstract (sommario):
This Master's thesis addresses the effects of marine growth on the design of a lattice tower substructure for an offshore wind turbine. Marine growth is the unwanted colonization of marine structures by marine organisms. The current standards prescribe a thickness of 100 mm whereas in the literature, layers up to 200 mm thick have been reported for structures in the North Sea.Marine growth leads to increased wave loading on the structure. This is caused by the increased effective member diameter, as well as increased drag coefficient due to increased surface roughness. Marine growth also represents an additional non-structural mass, reducing the structural natural frequencies. Marine growth may increase flow instability and vortex shedding, but this has not been evaluated in this report. The effects of marine growth have been evaluated for the NOWITECH 10 MW reference turbine.Alteration of the natural frequencies caused dynamic amplification when structural natural frequencies approached the nP-values of the rotor. The effect was most prominent for the local-modes natural frequencies, the modes including out-of-plane deformation of the bracing.The relative importance of the increased hydrodynamic load and additional non-structural mass was investigated. It was concluded that both effects must be included in the model to describe the dynamic behaviour.The fatigue lifetime of the K-braces was more sensitive to marine growth thickness than that of the X-braces. The X-brace fatigue lifetime gave the design lifetime for this particular design and marine growth lead to significant reductions in the fatigue lifetime. Marine growth would increase the lifetime in certain points. Thus, it is necessary to check the design also without marine growth.
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Wuillaume, Pierre-Yves. "Simulation numérique des opérations d’installation pour les fermes d’éoliennes offshore". Thesis, Ecole centrale de Nantes, 2019. http://www.theses.fr/2019ECDN0003/document.
Testo completoAbstract (sommario):
L’éolien offshore est l’énergie marine la plus avancée et utilisée dans le monde. Afin d’accroître l’énergie extraite du vent, les dimensions des éoliennes deviennent plus importantes et les parcs éoliens sont installées de plus en plus loin des côtes, où les mers sont plus agitées et les vents plus forts. De fait, les opérations marines sont plus complexes et plus chères et les fenêtres météo sont écourtées et se raréfient. Dans le cadre de cette thèse, un logiciel de simulation numérique des opérations marines est développé, en particulier pour des applications de descentes et de remontées de colis lourds. L’Algorithme aux Corps Rigides Composites, implémenté dans le logiciel InWave, est utilisé pour modéliser le système multicorps. Un modèle de câble et de treuil est développé, suivant la théorie multicorps utilisée, et comparé à la théorie câble classique dite « lumped mass ». Les efforts hydrodynamiques ainsi que les interactions hydrodynamiques sont modélisés par une théorie potentiel instationnaire satisfaisant l’hypothèse de faible perturbation, dite « weak-scatterer ». L’approche « weak-scatterer » du logiciel WS_CN est étendue aux simulations multi-flotteurs et validée par comparaison avec des données expérimentales. InWave et WS_CN sont couplés afin de résoudre l’interaction houle-structure pour des systèmes multicorps articulés en mer. Un couplage fort est adopté pour sa robustesse. L’équation de couplage est établie et validée via des comparaisons avec WS_CN. Le logiciel ainsi crée se nomme InWaveS_CN et utilise un code d’intégration en Python. Une nouvelle stratégie de maillage, basée sur un algorithme de découpe de maillages et une méthode par avance de front, est développée dans WS_CN. Enfin, des essais en bassin d’une opération de redressement ont été menés à l’ECN. La comparaison entre les simulations numériques et les données expérimentales offre une première et prometteuse validation d’InWaveS_CNOffshore wind represents the most advanced and used marine energy in the world. To increase the wind power extraction, turbines grow in size and wind farms are installed further offshore in presence of rough seas and strong winds. Marine operations become more challenging and expensive, weather windows are shorter and less frequent. This PhD work focuses on the development of a numerical tool to simulate marine operations with consistency, in particular lowering and lifting operations. The Composite-Rigid-Body Algorithm, implemented in the numerical tool InWave, is used to model multibody systems. A cable model and a winch model are developed following this multibody approach and compared to the classical low-order lumped mass theory. Hydrodynamic loads and hydrodynamic interactions are simulated using an unsteady potential flow theory based on the weakscatterer hypothesis, implemented in the numerical tool WS_CN. This approach is extended to multibody simulations and validated with comparisons to experimental data. InWave and WS_CN are coupled to solve wavestructure interaction for articulated multibody systems with large relative motions in waves. A tight coupling is selected for its robustness. The coupling equation is derived and validated from comparisons with WS_CN. This leads to the creation of a new numerical tool, InWaveS_CN, using Python as glue code language. A new mesh strategy, based on the coupling between a panel cutting method and an advance front method, is developed in WS_CN. Experiments of an upending operation were conducted at Ecole Centrale de Nantes. The comparison between the numerical simulations and the experimental data leads to a first and promising validation of InWaveS_CN
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Azarhoushang, Azin. "Dynamic response of fixed offshore platforms to environmental loads". Thesis, Curtin University, 2010. http://hdl.handle.net/20.500.11937/135.
Testo completoAbstract (sommario):
In this thesis a simplified method for dynamic response of jacket type offshore structures to extreme environmental load is investigated using existing experience and the procedures available within the industry. Fixed Jacket type offshore platforms may, under extreme wave loading conditions, exhibit significant nonlinear behavior. This must be accounted for in the design of such platforms, in order to ensure satisfactory structural safety. The complicated and nonlinear dynamic platform behavior implies that a wide number of significant uncertainties are introduced to the design process through the included mathematical models, analysis methods and the practical use of these methods. The major sources of nonlinear behavior are the wave loading, the damping mechanisms and the soil structure interaction. The inclusion of nonlinear dynamic platform behavior in the design process implies that nonlinear stochastic dynamic response based on time domain simulation methods must be applied. Time domain stochastic dynamic response analysis is an analysis method which will be a central element of the procedure. However, it seems not to be clear so far how this method should be integrated in a practical design procedure. Initially an overview of the different sources of nonlinear platform behavior is clarified with the underlying mechanism. Furthermore, it is outlined how those nonlinear effects may be accounted for with a special focus on estimation of extreme response and dynamic amplification factors. The discussion and outlines are illustrated by an example of fixed offshore platform. Finally the practical use of the method in the design of fixed jacket type offshore platforms is recommended.
29
Hamadi, Hasan. "Structural analysis of an offshore steel monotubular platform ‘morena-1’ and fatigue assesment of leg-boat landing connection joint". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021.
Cerca il testo completoAbstract (sommario):
Structural analysis of ‘MORENA-1’ platform.
As a start for the work,a 3D model wa performed. Firstly, materials and sections were defined, and then assigned to the elements, then a check of dead load case was done to be sure that no design errors are involved. After the check of the design, soil properties for the foundation pile were defined also. For the soil property, two values of undrained shear strength of soil were given in the original project at z=0 at sea bottom and z=-50m, then lateral p-y curves were studied at 30 levels of 1 m space in between. After p-y curves were defined, non-linear springs that acts either on compression or on tension were also defined in SAP2000 and assigned at each node level.
When the model was ready, loads and weights were defined.
After load patterns were defined and assigned, load cases were defined also for each single load pattern. Where all load cases were imposed as NON-LINEAR STATIC load cases, to function properly in the NON-LINEAR STATIC ANALYSES.
Load combinations were also defined according to UNI-EN-ISO-19902-2009 code.
Finally, a NON-LINEAR ANALYSES was performed.
The selection of NON-LINEAR ANALYSIS was based on that a monotubular platform is subjected to large deformations due to extreme conditions.
As a second requirement, Fatigue of the boat landing joint under waves cyclic loading was to be evaluated.
For Fatigue assessment, FEM model according DNVGL-RP-0005 was performed in SEMICENTER FEMAP WITH NASTRAN. Then, internal actions resulted from the structural analysis for each wave were inserted in FEMAP respectively, actions were applied at the same exact positions as picked from SAP2000.
When all load cases were ready, a FEA analysis was performed for each case, and hot spots were tracked and listed.
After the evaluation of hot spot stress, cumulative damage and fatigue life of the joint were calculated.
30
Valentine, Vincent Francis. "Measuring efficiency of container ports : an analysis by organisational and ownership structure". Thesis, University of Plymouth, 2002. http://hdl.handle.net/10026.1/1146.
Testo completoAbstract (sommario):
Fundamental to any business is the concept of performance. This can be compared by using the competition as a benchmark for achievement or by comparing performance with previously defined goals and objectives. Stakeholders constantly demand to know whether their investmerit in a company is obtaining an adequate return and whilst there are established accounting techniques to calculate return on investment or capital employed, calculating efficiency can be rather a grey area in some industries. Ports are no exception and it is only by comparison that performance can be evaluated. Ports are, however, a complex business with many different sources of inputs and outputs which make direct comparison among apparently homogeneous ports seem difficult. The subject is further complicated by the various types of port ownership and organisational structures that exist throughout the world. This thesis seeks to determine whether there is a particular type of ownership and organisational structure that leads to a more efficient port. This aim is achieved by examining the efficiency of differently owned container ports, comparing privately owned ports against those remaining in the public sector, and those that have elements of both public and private ownership patterns. In addition, the organisational structure of those ports examined is analysed and classified with the results placed into a singular conceptual model for a clear comparison. The conceptual model can be then applied to any type of business enabling the performance of ownership and organisational structures to be compared with ease. The results of this thesis show that there is a strong relationship between the relative efficiency of ports examined and organisational structure and a weaker relationship between port ownership patterns. These results should assist governments, port administrators and port owners in determining the different ways they can structure their ports.
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Liu, Yuanchuan. "A CFD study of fluid-structure interaction problems for floating offshore wind turbines". Thesis, University of Strathclyde, 2018. http://digitool.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=30597.
Testo completoAbstract (sommario):
As one of the fastest growing renewable energy sources, wind energy is playing an increasingly important part in addressing the climate change and energy crisis issues the world is currently facing. The abundance of wind resource in offshore areas makes them a popular choice for turbine installation. In the past few years, several floating wind projects have emerged where wind turbines are installed far offshore in deepwater sites on moored platforms. Compared to land-based or offshore fixed-bottom wind turbines, an FOWT is a fully coupled system where the wind turbine with flexible blades and the floating platform with its mooring system interact with each other in wind and waves, which makes old design tools inadequate. This work aims to develop a fully coupled high-fidelity aero-hydro-mooring-elastic analysis tool, and to better understand the sophisticated fluid-structure interactions for FOWTs. The numerical tool developed in this work takes advantage of the open source CFD toolbox OpenFOAM to accurately solve wind turbine aerodynamics and floating platform hydrodynamics, and utilises the open source MBD code MBDyn for structural dynamics within a multibody framework while modelling flexible bodies based on a nonlinear beam theory. Coupling of these two solvers is achieved by establishing an interface library to exchange data with the help of the TCP/IP protocol. Additionally, to tackle the complex mesh movement in FOWT simulations, a mesh motion solver is developed in OpenFOAM by combining the sliding mesh technique and the dynamic mesh morphing method. A mooring system analysis module comprising a quasi-static method and a lumped-mass based dynamic approach is also implemented to simulate mooring lines in an FOWT system. A series of test cases is firstly studied to validate the various features of the tool, including basic fluid flow solving, modelling of wind turbine aerodynamics, hydrodynamic analysis of a floating structure with its mooring system, dynamic analysis of a riser or mooring line and coupled analysis of flow induced vibration of a flexible beam. The developed tool is then applied to analyse FSI problems of FOWTs under three different scenarios. Firstly, a coupled aero-hydro-mooring analysis is carried out for the OC4 semisubmersible FOWT under regular waves and uniform wind speed. Blade flexibility is ignored, and mooring lines are solved using the quasi-static method. Interactions between the moored platform and the wind turbine are investigated, focusing on of platform motion on the aerodynamic performance of the wind turbine and the impacts of wind turbine aerodynamics on the responses of the floating platform and its mooring system. Subsequently, an aeroelastic analysis is conducted for the NREL 5-MW offshore wind turbine with flexible blades under uniform wind speed. Effects of blade flexibility on wind turbine aerodynamics and structural responses are studied using the developed CFD-MBD tool. The floating platform supporting the turbine is not directly modelled for simplicity and the influence of platform motion responses on the turbine are analysed via imposing a prescribed surge motion to the turbine base. Fully coupled aero-hydro-mooring-elastic analysis is lastly carried out for the OC4 semi-submersible FOWT under a combined wind/wave condition to demonstrate the capabilities of the developed CFD-MBD tool. Responses of the floating system are investigated in terms of platform hydrodynamics, mooring system dynamics, wind turbine aerodynamics and blade structural dynamics. Interactions between the FOWT and fluid flow are analysed by visualising results obtained via the CFD approach.
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Liu, Biheng. "Reduced order models for the analysis of offshore lattice structures". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2022.
Cerca il testo completoAbstract (sommario):
The lattice is a common frame applied in offshore structures benefiting from their economic construction and easily accessible, for example, the jacket platform of the offshore wind turbine. In order to accelerate the design process of a model, this thesis proposed a method to reduce the order of the offshore lattice structure models. The full order model is constructed based on the FEM. Applying the MDOF mass discrete concept lumps the structure mass on each story center. Meanwhile, apply the DSM to determine the displacement and the forces implied on the mass center for accomplishing the unitary displacement of each DOF of the mass center node. Finally, a reduced order model for the lattice structure will be obtained. That model composed of the stiffness matrix of the mass center node has the same fundamental flexural frequency as the original model. The model can be expressed by symbolic relationship as well as possible to package as a function for further quotation. All computation processes of this thesis were executed on the Python platform.
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鍾頤德 e Yi-tak Teresa Chung. "Quaternary stratigraphy of an offshore borehole from northern Lantau, Hong Kong". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2009. http://hub.hku.hk/bib/B42904730.
Testo completo
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Nematbakhsh, Ali. "A Nonlinear Computational Model of Floating Wind Turbines". Digital WPI, 2013. https://digitalcommons.wpi.edu/etd-dissertations/170.
Testo completoAbstract (sommario):
The dynamic motion of floating wind turbines is studied using numerical simulations. Floating wind turbines in the deep ocean avoid many of the concerns with land-based wind turbines while allowing access to strong stable winds. The full three-dimensional Navier-Stokes equations are solved on a regular structured grid, using a level set method for the free surface and an immersed boundary method for the turbine platform. The tethers, the tower, the nacelle and the rotor weight are included using reduced order dynamic models, resulting in an efficient numerical approach which can handle nearly all the nonlinear wave forces on the platform, while imposing no limitation on the platform motion. Wind is modeled as a constant thrust force and rotor gyroscopic effects are accounted for. Other aerodynamic loadings and aero-elastic effects are not considered. Several tests, including comparison with other numerical, experimental and grid study tests, have been done to validate and verify the numerical approach. Also for further validation, a 100:1 scale model Tension Leg Platform (TLP) floating wind turbine has been simulated and the results are compared with water flume experiments conducted by our research group. The model has been extended to full scale systems and the response of the tension leg and spar buoy floating wind turbines has been studied. The tension leg platform response to different amplitude waves is examined and for large waves a nonlinear trend is seen. The nonlinearity limits the motion and shows that the linear assumption will lead to over prediction of the TLP response. Studying the flow field behind the TLP for moderate amplitude waves shows vortices during the transient response of the platform but not at the steady state, probably due to the small Keulegan-Carpenter number. The effects of changing the platform shape are considered and finally the nonlinear response of the platform to a large amplitude wave leading to slacking of the tethers is simulated. For the spar buoy floating wind turbine, the response to regular periodic waves is studied first. Then, the model is extended to irregular waves to study the interaction of the buoy with more realistic sea state. The results are presented for a harsh condition, in which waves over 17 m are generated, and linear models might not be accurate enough. The results are studied in both time and frequency domain without relying on any experimental data or linear assumption. Finally a design study has been conducted on the spar buoy platform to study the effects of tethers position, tethers stiffness, and platform aspect ratio, on the response of the floating wind turbine. It is shown that higher aspect ratio platforms generally lead to lower mean pitch and surge responses, but it may also lead to nonlinear trend in standard deviation in pitch and heave, and that the tether attachment points design near the platform center of gravity generally leads to a more stable platform in comparison with attachment points near the tank top or bottom of the platform.
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Yin, Y. "Turbulence model and immersed boundary method development in TELEMAC-3D for offshore structure modelling". Thesis, University of Liverpool, 2017. http://livrepository.liverpool.ac.uk/3006448/.
Testo completoAbstract (sommario):
In recent years, increased evidences suggest that offshore structures such as wind farms, tidal turbine farms, piles of bridge and breakwater have great impact on the hydrodynamics and hence may have a strong influence on the sediment transport at a site. The open-source hydrodynamic suite of software TELEMAC has been used for the study of such environmental influence around Unite Kingdom. However, the use of the 3-D version of the software, TELEMAC-3D is restricted by how structures are accounted for in the meshes, as water columns have the same number of layers all over the domain. Moreover, a large scale farm has a large impact on turbulence mixing in the coastal regional scale, and this is not properly understood. The PhD project focuses on 3-D hydrodynamics and development of an 3-D unstructured capability using an immersed boundary method to account for obstacles in the flow. Two large eddy simulation models (the 2eddy LES model and the Wall-adapted Large Eddy model) have been incorporated into TELEMAC-3D to get a more realistic and effective representation of the turbulence mixing and to account for the unsteadiness of the flow past the structures. The simulations have been performed using High Performance Computing to enable large scale applications using TELEMAC-3D and fine spatial and temporal resolutions in 3-D. The implementations carried out in the code are fully parallel. The numerical models have been validated for two laboratory scale cases, including the flow around a circular cylinder and the flow over a submerged structure. Then a far-field simulation at the southern North Sea has been carried out, where the hydrodynamics and morphological impacts of the London Array offshore wind turbine farm have been investigated. The numerical results of turbulence model implementation indicate that both turbulence models have good performance in the representation of the flow past a cylinder in laboratory scale. However in the large scale application, only the 2eddy LES model is successfully applied because the WALE model relies on a very fine mesh in the vertical direction. The implementation of IBM suggested that when dealing with an obstacle going from the bottom though the surface of the water, the immersed boundary method offers good accuracy in the prediction of surrounding flow structures. For the submerged obstacles, they can be simulated by TELEMAC-3D by implementing the Immersed Boundary method. Although the accuracy is limited currently, qualitative analysis can still be performed.
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Espinoza, Canales Elisabeth. "Structure and tectonics of the offshore region close to Kayak Island from geophysical information". ScholarWorks@UNO, 2004. http://louisdl.louislibraries.org/u?/NOD,139.
Testo completoAbstract (sommario):
Thesis (M.S.)--University of New Orleans, 2004.Title from electronic submission form. "A thesis ... in partial fulfillment of the requirements for the degree of Master of Science in the Department of Geology and Geophysics."--Thesis t.p. Vita. Includes bibliographical references.
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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.
Testo completoAbstract (sommario):
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 APIOffshore 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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Grice, James Robert. "Prediction of extreme wave-structure interactions for multi-columned structures in deep water". Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:dd7320c1-7121-4ea7-827f-527af9405e9a.
Testo completoAbstract (sommario):
With a continuing and rising demand for hydrocarbons, the energy companies are installing infrastructure ever further offshore, where such infrastructure is often exposed to extreme waves. This thesis explores some aspects of wave-structure interaction, particularly the maximum water surface elevation increase in severe storms due to these local interactions. The effects on wave-structure interactions of column cross-sectional shape are investigated using linear and second-order wave diffraction theory. For multi-column structures, the excitation of locally resonant wave modes (near-trapping) is studied for several column cross-sectional shapes, and a simple method for estimating the surface elevation mode shape is given. The structure of the quadratic transfer functions for second-order sum wave elevation is investigated and an approximation assuming these QTFs are flat perpendicular to the leading diagonal is shown to be adequate for the first few lowest frequency modes. NewWave-type focused wave groups can be used as a more realistic model of extreme ocean waves. A Net Amplification Factor based on the NewWave model is given as an efficient tool for finding the incident frequencies most likely to cause a violent wave-structure interaction and where these violent responses are likely to occur. Statistics are collected from Monte Carlo type simulations of random waves to verify the use of the Net Amplification Factor. Going beyond linear calculations, surface elevation statistics are collected to second-order and a `designer' wave is found to model the most extreme surface elevation responses. A `designer' wave can be identified at required levels of return period to help to understand the relative size of harmonic components in extreme waves. The methods developed with a fixed body are then applied to an identical hull which is freely floating, and the responses between the fixed and moving cases are compared. The vertical heave motion of a semi-submersible in-phase with the incident wave crests is shown to lead to a much lower probability of water-deck impact for the same hull shape restrained vertically. The signal processing methods developed are also applied to a single column to allow comparison with experimental results. Individual harmonic components of the hydrodynamic force are identified up to at least the fifth harmonic. Stokes scaling is shown to hold even for the most violent interactions. It is also shown that the higher harmonic components of the hydrodynamic force can be reconstructed from just the fundamental force time history, and a transfer function in the form of a single phase and an amplitude for each harmonic. The force is also reconstructed well to second-order from the surface elevation time history using diffraction transfer functions. Finally, possible causes of damage to a platform high above mean water level in the North Sea are investigated.
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Crozier, Aina. "Design and Dynamic Modeling of the Support Structure for a 10 MW Offshore Wind Turbine". Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for energi- og prosessteknikk, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-13645.
Testo completoAbstract (sommario):
This thesis presents two designs of tension-leg-platforms (TLP) support structures for the 10 MW reference wind turbine being developed by the Norwegian Research Centre for Offshore Wind Technology (NOWITECH). The designs result from iterative design processes which account for important design considerations such as performance requirements, natural frequencies and main cost drivers, and differ in their capability of providing stability to the wind turbine. TLP Towed is stable during towing and operation, whereas TLP Transported only provides stability when installed and is dependent on alternative transportation methods. The design processes are validated by investigating the influence from the various requirements and the sensitivity to wind turbine properties. The two resulting designs are compared and discussed in terms of cost competitive advantage. Fully coupled time-domain aero-hydro-servo-elastic models are established in FAST by using hydrodynamic computations from WAMIT, and the models are verified by comparisons to previous time-domain results and frequency-domain calculations. The natural frequencies of the FOWTs are obtained by model linearizations, and a discussion regarding overlap with wind turbine operational frequencies and wave excitation frequencies leads to modifications to the preliminary designs. A number of simulations with different wind and wave conditions are run and the TLP designs are compared based on displacements, upwind and downwind tether tensions, the nacelle's velocity and acceleration and extreme events. Resonant behavior, damping and instabilities are also discussed and suggestions for improvements to the designs are presented. The results presented in this thesis serve as guidance in the process of developing optimized TLP designs for an offshore wind turbine.
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Tolofari, Sonny R. "Open registry shipping : an econometric study of the cost structure of open registry shipping and its impact on freight rates". Thesis, Loughborough University, 1986. https://dspace.lboro.ac.uk/2134/10504.
Testo completoAbstract (sommario):
Whilst the issue of open registry shipping has constituted one of the greatest controversies in the shipping industry over the last thirty years, no detailed quantitative work has been carried out on the issue. In this thesis transcendental logarithmic cost functions are estimated for the production functions of open registry bulk ships and those operating under traditional maritime nations. In this way an appropriately unrestricted cost function for the flag dichotomy is estimated and the parameters of the cost functions provide the basis for determining the structure of the production technology of tankers and bulk carriers under the two· flag groupings. Evidence of scale economies and the extent to which they have been exploited by each flag group is provided along with factor substitution patterns, own-price and crossprice factor demand elasticities. It is found that the costs of bulk carriers operating under open registries are lower for all vessel sizes than for those operating under traditional registries. For tankers/open tegistry costs are found to be higher for product tanker services and lower otherwise. The translog estimates reveal that the manning cost element is the greatest contributor to the cost differential between the two groups. Open registry operations are also found to be subject to greater factor substitution flexibility. Statistical analysis of tanker and bulk carrier time charter freight rates over a ten-year period provides empirical evidence for the hypothesis that lower open registry costs are passed on to consumers of shipping services by way of lower freight rates. For this reason, a methodology for measuring this benefit is suggested. It is concluded that whilst this study provides evidence of the possible cost to international trade of phasing out open registries, such cost of itself does not provide an argument for retaining the system. The social and economic rationality of retaining the system will be determined by a wider cose-benefit analysis to which this study has contributed.
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Salles, Rafael. "Experimental analysis of fluid-structure interaction phenomena on a vertical flexible cylinder: modal coeficients and parametric resonance". Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/3/3152/tde-25082016-085120/.
Testo completoAbstract (sommario):
Oil and gas exploitation in deep waters has become more than just a profit business to be a daily necessity, since the world energy matrix is based on fossil components. Risers are offshore structures that are intimately linked with oil and gas exploitation and those are subjected to a great variety of effects in field, e.g., marine currents, Vortex Induced Vibration (VIV), heave motion caused by gravitational waves, non-linear contact with the sea floor, and many others. Riser dynamics is essentially non-linear and experimental tests in real scale are almost impossible due to a great variety of control parameters acting concomitantly. Small-scale models are a better experimental approach. Nevertheless, there are many structural and hydrodynamical parameters to be evaluated. Considering only vertical risers in the present work, Galerkin\'s modal decomposition is used in order to reduce the dynamics of a vertical flexible cylinder to a few linear modes in which the majority of energy and information are contained. From the modal analysis, added mass and structural parameters damping of a vertical flexible cylinder using data obtained from free-decay tests performed both in water and in air are evaluated. Finally, a modal Mathieu-Hill oscillator with non-linear damping is constructed and, based on aStrutt diagram, modal stability under parametric resonance is discussed.Exploração de óleo e gás em bacias de águas profundas tem-se tornado mais do que apenas uma economia lucrativa, para ser uma necessidade diária, já que a matriz energética mundial está baseada em componentes fósseis. Risers são estruturas offshore ligadas intimamente com a exploração de óleo e gás e essas estão sujeitas a uma grande variedade de efeitos na operação, e.g., correntes marítimas, Vibrações Induzidas por Vórtices (VIV), movimento de heave causado por ondas gravitacionais, contato não-linear com o solo marinho, entre outros. Dinâmica de risers é essencialmente não-linear e testes experimentais em escala real são praticamente impossíveis devido a uma enorme variedade de parâmetros de controle agindo concomitantemente. Modelos em escala reduzida são uma abordagem experimental mais conveniente. Não obstante, há muitos parâmetros estruturais e hidrodinâmicos a serem determinados. Considerando apenas risers verticais no trabalho presente, a decomposição modal de Galerkin é usada a fim de reduzir a dinâmica de um cilindro fléxivel vertical a alguns modos lineares em que a maior parte da energia e informação estão contidos. A partir da análise modal, parâmetros de massa adicional e amortecimento estrutural de um cilindro flexível vertical são obtidos usando testes de decaimento livre conduzidos na água e no ar. Finalmente, um oscilador modal de Mathieu-Hill com amortecimento não-linear é proposto e, baseado em um diagrama de Strutt, a estabilidade modal sob excitação de ressonânica paramétrica é discutida.
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Laya, Enrique J. "Système de surveillance pour la détection du dommage de fatigue cumulée dans les structures offshore en acier". Châtenay-Malabry, Ecole centrale de Paris, 1987. http://www.theses.fr/1987ECAP0048.
Testo completoAbstract (sommario):
Pour vérifier le comportement des liaisons tubulaires soudées, étude d'un système de mesure en temps réel des déformations sur la section nominale des tubes arrivant aux noeuds ; technologiquement le système est conçu à partir des matériels existants.
43
Wells, Eric M. "An Assessment of Surface Ice Sheet Loads and Their Effects on an Offshore Wind Turbine Structure". University of Toledo / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1345214125.
Testo completo
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Al-Younis, Mohamad Jawad K. Essa. "Effect of Soil-Structure Interaction on the Behavior of Offshore Piles Embedded in Nonlinear Porous Media". Diss., The University of Arizona, 2013. http://hdl.handle.net/10150/283608.
Testo completoAbstract (sommario):
Pile foundations that support offshore structures are required to resist not only static loading, but also dynamic loading from waves, wind and earthquakes. The purpose of this study is to gain a better understanding of the behavior of offshore piles under cyclic or dynamic loading using the finite element approach. To achieve this goal, an appropriate constitutive model is required to simulate the behavior of soils and interfaces. The DSC constitutive model is developed for saturated interfaces to study the behavior under severe shear deformation at the soil-pile interface. Monotonic and cyclic simple shear experiments are conducted on Ottawa sand-steel interfaces under drained and undrained conditions using the Cyclic-Multi-Degree-of-Freedom shear device with porewater pressure measurement (CYMDOF-P). The effect of various parameters such as normal stress, surface roughness of steel, type of loading, and the amplitude and frequency of the applied displacement in two-way cyclic loading are investigated. The data from the simple shear tests on saturated interfaces are used to calculate the parameters in the DSC model. The resulting parameters are then used to verify the DSC model by back predicting tests from which parameters are determined and independent tests that are not used in parameters determination. The model predictions, in general, were found to provide a highly satisfactory correlation with the observations. In the context of DSC, the concept of critical disturbance is developed to identify initiation of liquefaction in saturated Ottawa sand-steel interfaces. This method is based on using microstructural changes in material as an indication of liquefaction identification. The finite element method, along with DSC constitutive model, is used to investigate the response of offshore piles to dynamic loading. These include cyclic loading of axially loaded instrumented pile in clay and full-scale laterally loaded pile in sand. The DSC model is used to model the nonlinear behavior of saturated soils and interfaces. A nonlinear dynamic finite element program DSC-DYN2D based on the DSC modeling approach and the theory of nonlinear porous media is used for this purpose. Results from numerical solutions are compared with field measurements. Strong agreement between numerical predictions and field measurements are an indication of the ability to solve challenging soil-structure interaction problems.Based on the results of this research, it can be stated that the finite element-DSC model simulation allows realistic prediction of complex dynamic offshore pile-soil interaction problems, and is capable of characterizing behavior of saturated soils and interfaces involving liquefaction.
45
Fortaleza, Eugênio. "Active control applied to offshore structures : positioning and attenuation of vortex induced vibrations". Paris, ENMP, 2009. https://pastel.archives-ouvertes.fr/pastel-00006011.
Testo completoAbstract (sommario):
L'exploration pétrolière en eaux profondes crée des nouveaux défis technologiques. Certains de ces problèmes sont liés à des très longues structures servant à relier la plate-forme à la tête de puits. L'augmentation de la profondeur implique des structures plus longues et, par conséquent, plus souple. Deux problèmes liés à ce type de structure sont étudiés dans ce rapport : le positionnement de la structure pour sa connexion à la tête de puits (opération de rentrée), et les vibrations induites par vortex. La première partie de ce rapport est consacrée au contrôle de l'opération de rentrée. Deux stratégies différentes de planification du mouvement sont proposées. La première est basée sur un modèle obtenu par approche modale. L'autre stratégie approxime le comportement de la structure par l'équation d'un câble de Bernoulli avec amortissement. Les solutions approximées de cette EDP sont directement utilisées dans la conception du contrôleur. Deux types de contrôle en boucle fermée sont proposées: un système de suivi de trajectoire en utilisant une fonction de Lyapunov, et un autre qui utilise l'inverse du système. La deuxième partie de ce rapport est consacrée à l'étude des vibrations induites par vortex (VIV) et à leur contrôle. Elle présente une première stratégie de contrôle afin de réduire les VIV. Cette stratégie est basée sur une analyse modale des équations du système. La loi de commande génère un déplacement en opposition de phase par rapport au VIV, l'atténuation résultant d'un effet d'antirésonance. Les résultats de simulation sont confirmés par des expériences réalisées sur une maquette en modèle réduitThe petroleum exploration in deep water induces many challenges. Some of these problems are due to the extremely long structure that links the platform to the wellhead (risers). The depth increase makes the structure more slender, and consequently much more flexible, and its dynamical behavior may be described by an infinite dimensional system. Two associated problems are studied in this report: the positioning of the bottom structure, to connect it to the wellhead (reentry operation), and the vortex induced vibrations of these slender structures. The first part of this thesis is dedicated to the control of the reentry operation. Two different strategies of motion planning are proposed. The first one is based on a finite dimensional model obtained by a modal approach. The other one considers that the behavior of the structure is close to the behavior of the Bernoulli's historical cable equation, completed with a damping factor. The proposed approximate solutions of this PDE are directly used in the control design. Two different closed loop controls are proposed: one using a Lyapunov function, and another tracking system that uses the system inversion to calculate the tracking feedback. The second part is dedicated to the study of the structure's undergoing vortex induced vibrations (VIV) and to their control. It presents a first control strategy to reduce the VIV. This control strategy is based on a modal analysis of the system equations. The control system generates a displacement in phase opposition to the VIV, attenuating the VIV because of an anti-resonance effect. The simulation results are confirmed by experiments done on a reduced scale setup
46
Heidari, Shayan. "Economic Modelling of Floating Offshore Wind Power : Calculation of Levelized Cost of Energy". Thesis, Mälardalens högskola, Industriell ekonomi och organisation, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:mdh:diva-36130.
Testo completoAbstract (sommario):
Floating offshore wind power is a relatively new technology that enables wind turbines to float above the sea level, tied by anchors at the seabed. The purpose of this work is to develop an economic model for the technology in order to calculate the total cost of a planned wind farm. Cost data are retrieved from reports and academic journals available online. Based on these data, a model in Microsoft Excel is developed which calculates the Levelized cost of energy (LCOE) for floating wind power plants as a function of several input values. As an addition to this model, financing offshore projects are described using literature study and by doing interviews with three major companies, currently investing in offshore wind. As a result, the model allows the user to calculate Capital expenditures, Operating expenditures and LCOE for projects at any given size and at any given site. The current LCOE for a large floating offshore wind farm is indicated to be in the range of 138-147 £/MWh. The outline from interviews was that today there is no shortage of capital for funding wind projects. However, in order to attract capital, the governmental regulatory of that market has to be suitable since it has a crucial impact on price risks of a project.
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Randi, Nicolò. "Analysis of floating photovoltaic systems and their future role in the green economy". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021.
Cerca il testo completoAbstract (sommario):
Floating PV systems technologies have been analysed to identify the best solution. By analysing the costs of the structures and the respective LCOE. Identified the solution with the lowest value, we studied in detail project. The lower LCOE was for the OS-75 platform and is €35/MWh. The costs of connecting the energy to the land have been ignored. The project represents an investment opportunity for renewable energy companies. Taking into account the distance from the LCOE for floating PV and Ground Mounted, the LCOE of both solutions is close. On the OS-75 platform, the horizontal modules decrease the costs of the structure and the wind load. Efficient for low latitudes, a good alternative to ground installations that would not address the ground to traditional uses. The main problem concerns the anchoring and flotation system. the costs of the anchoring system were low when compared to the total cost for artificial basins of low depth. The low weight of the OS-75 structure minimizes the load and the number of floats. In OS systems aren't possible to use standard modules. Is a big limitation considering also the low power/surface ratio (186 Wp/m2). The problem could be tied to an insufficient level of maturity of the company. Concerns centre on water contamination due to the contact of the structure. Also concerns the duration of the plant, being in a difficult environment. The large-scale construction of floating PV plants started only in 2016, not possible to analyse in detail the 2 areas previously considered. A study by BayWa r.e. reported low levels of contamination of water in contact for 4 years. Remain long-term and decommissioning issues. Another issue is the horizontal positioning of the modules, which reduces the efficiency of OS platforms, especially at high latitudes. Among the solutions analysed, low LCOE was calculated for the Scotra and BayWa r.e. The difference with Ground Mounted Plants is not substantial, under the considered assumptions.
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Cardoso, OnÃzimo Carlos Viana. "Partitioned analysis of Offshore wind turbines using the Lagrange Localized Methods". Universidade Federal do CearÃ, 2014. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=13241.
Testo completoAbstract (sommario):
FundaÃÃo Cearense de Apoio ao Desenvolvimento Cientifico e TecnolÃgicoAmong the new-found data about the availability of fossil fuels, which affirms that oil and natural gas sources will be almost depleted in the next century and the coal in the following two centuries. There is a global pursuit about new ways to produce energy. Another important fact that ratify this quest, lies at rise of the environment imbalance arouse from the burn of fossil fuels which, through the greenhouse effect, leads, for instance, to melting glaciers and increasing the temperature in the earth. The wind power, already used to move ships since antiquity is a relevant alternative way to produce energy, since it dispose of, at least, two great advantages, namely, it is endless and produce low negative consequences to environment. A place is considered to be good to receive the wind power engines called wind turbines, which convert the wind kinetic energy in electricity, if it is a ground plane with little amount of barriers. The sea, especially the regions far from the coast, satisfy the two latter requirement, and, furthermore, it is a place in which there are less obstructions about the noise pollution from the offshore wind turbines and there is not concern about deceases arouse in people who leave near of wind farms. In order to install the wind turbines in those spots away from the seashore, is required that its towers must be attached at the sea floor or must be develop a system that allow the turbine to float. Therefore the objective of the present work is to develop a structural modelling of the Monopile, TLP (Tension Leg Platform) and Spar type wind turbines subject using Finite Element Methods with the coupling method accomplished by Localized Lagrange Multipliers, jointly with the software SolidWorks and Autocad (drawing creation), ANSYS (mesh development) and Matlab (solver). The obtained results are relevant since such models are those which are most commonly used in offshore wind power plants. Lastly, due to the use of the latter coupling method, there is not the requisition to develop the study using meshes that agree each other. On the contrary, the analysis can be performed with non match meshes adjusting them with the Zero Moment Rule described in this present study.
Diante dos mais recentes dados com respeito a quantidade de combustÃveis fÃsseis ainda disponÃveis na natureza, os quais atestam que nÃo hà mais nem um sÃculo sequer para que o petrÃleo e o gÃs natural sejam praticamente extintos e que as reservas de carvÃo mineral suprirÃo somente mais 2 sÃculos de consumo, levando em conta o gasto atual. A preocupaÃÃo quanto a novas formas de extraÃÃo de energia se tornam necessÃrias e urgentes. Outro importante fator que ratifica o imediatismo de se buscar diferentes fontes de energia em detrimento de combustÃvel fÃssil, à o fato de que as emissÃes intrÃnsecas à sua queima estÃo gerando desequilÃbrio no clima global pela intensificaÃÃo do efeito estufa, apontado como um dos principais contribuidores do derretimento de geleiras e aquecimento da temperatura da terra. A energia eÃlica, jà utilizada desde a antiguidade para auxÃlio de locomoÃÃo de embarcaÃÃes e em moinhos de vento, se mostra uma alternativa de extrema relevÃncia, jà que, ela nÃo à portadora dos dois problemas crÃticos citados anteriormente. A saber, ela à infindÃvel e tem baixa consequÃncia negativa ao meio ambiente. Quanto aos locais que oferecem maior rendimento e produÃÃo para instalaÃÃo dos aerogeradores, responsÃveis pela conversÃo da energia cinÃtica do vento em energia elÃtrica, sÃo os que dispÃem de terreno mais plano e ausente de barreiras que impeÃam a continuidade do fluxo de vento. O mar, sobretudo as regiÃes mais distantes da costa, satisfazem Ãs duas necessidades citadas anteriormente, e, ainda se tratam de um local no qual nÃo hà a preocupaÃÃo quanto a poluiÃÃo sonora gerada pelos aerogeradores e nem com distÃrbios e doenÃas que possam ser desencadeadas em pessoas que residam pertos de grandes parques Ãolicos. A utilizaÃÃo de aerogeradores no mar (offshore) distantes da costa, e por conseguinte, em grandes profundidades, requer torres de sustentaÃÃo fixadas ao solo ou um sistema que proporcione que a turbina flutue. Diante do exposto, o trabalho em questÃo tem por objetivo realizar a modelagem estrutural do aerogerador flutuante (Spar), do portador de torre de tripà e do modelo monopile, sujeitos a carregamentos decorrentes de situaÃÃes normais e extremas, utilizando os mÃtodos dos Elementos Finitos juntamente com o MÃtodo de Acoplamento por Multiplicadores de Lagrange Localizados, atrelados aos softwares SolidWorks e Autocad (criaÃÃo do desenho), ANSYS (malha) e Matlab (solver). E, em decorrÃncia do fato da utilizaÃÃo do mÃtodo de acoplamento, nÃo hà necessidade de que as malhas dos subdomÃnios envolvidos sejam coincidentes. Pelo contrÃrio, pode-se utilizar malhas nÃo encaixantes para discretizar o sistema e, nas regiÃes onde hà contato entre malhas que nÃo coicidem, aplica-se a Regra do Momento Zero, descrita no presente trabalho. Nesse tipo de abordagem, pode haver uma separaÃÃo dos cÃdigos computacionais utilizados para o fluido e para a estrutura, os quais sÃo inicialmente tratados como entidades individuais e sà apÃs terem sido discretizados à que a informaÃÃo sobre suas malhas à recebida pela parte do cÃdigo responsÃvel por realizar o acoplamento dos subdomÃnios. Problemas de malhas que nÃo se encaixam podem surgir por diversos motivos, dentre eles, o fato de um subdomÃnio requerer uma malha mais refinada do que outros para que dele resultem resultados acurados. Pesquisadores de diferentes Ãreas podem gerar malhas separadas de distintos subdomÃnios e desejarem unÃ-los pelo mÃtodo abordado nesse trabalho em uma simulaÃÃo, ou a conformidade das malhas pode requerer muito tempo dispendido devido ao grande esforÃo computacional para a geraÃÃo de malhas conformes. Por fim, a aplicaÃÃo do mÃtodo produz resultados de grande relevÃncia, visto que, os modelos a que dizem respeito sÃo os mais comumente utilizados em projetos de aproveitamento de energia eÃlica offshore.
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Aidibi, Ali. "Stress Concentration Factor and Fatigue Life Evaluation in offshore tubular KT-Joints". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020.
Cerca il testo completoAbstract (sommario):
In the last few decades, offshore field has grown fast especially after the notable development of technologies, explorations of oil and gas in deep water and the high concern of offshore companies in renewable energy mainly Wind Energy. Fatigue damage was noticed as one of the main problems causing failure of offshore structures. The purpose of this research is to focus on the evaluation of Stress Concentration Factor and its influence on Fatigue Life for 2 tubular KT-Joints in offshore Jacket structure using different calculation methods. The work is done by using analytical calculations, mainly Efthymiou’s formulations, and numerical solutions, FEM analysis, using ABAQUS software. As for the analytical formulations, the calculations were done according to the geometrical parameters of each method using excel sheets. As for the numerical model, 2 different types of tubular KT-Joints are present where for each model 5 shell element type, 3 solid element type and 3 solid-with-weld element type models were built on ABAQUS. Meshing was assigned according to International Institute of Welding (IIW) recommendations, 5 types of mesh element, to evaluate the Hot-spot stresses. 23 different types of unitary loading conditions were assigned, 9 axial, 7 in-plane bending moment and 7 out-plane bending moment loads. The extraction of Hot-spot stresses and the evaluation of the Stress Concentration Factor were done using PYTHON scripting and MATLAB. Then, the fatigue damage evaluation for a critical KT tubular joint based on Simplified Fatigue Damage Rule and Local Approaches (Strain Damage Parameter and Stress Damage Parameter) methods were calculated according to the maximum Stress Concentration Factor conducted from DNV and FEA methods. In conclusion, this research helped us to compare different results of Stress Concentration Factor and Fatigue Life using different methods and provided us with a general overview about what to study next in the future.
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Cantoni, Lorenzo. "Load Control Aerodynamics in Offshore Wind Turbines". Thesis, KTH, Kraft- och värmeteknologi, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-291417.
Testo completoAbstract (sommario):
Due to the increase of rotor size in horizontal axis wind turbine (HAWT) during the past 25 years in order to achieve higher power output, all wind turbine components and blades in particular, have to withstand higher structural loads. This upscalingproblem could be solved by applying technologies capable of reducing aerodynamic loads the rotor has to withstand, either with passive or active control solutions. These control devices and techniques can reduce the fatigue load upon the blades up to 40% and therefore less maintenance is needed, resulting in an important money savings for the wind farm manager. This project consists in a study of load control techniques for offshore wind turbines from an aerodynamic and aeroelastic point ofview, with the aim to assess a cost effective, robust and reliable solution which could operate maintenance free in quite hostile environments. The first part of this study involves 2D and 3D aerodynamic and aeroelastic simulations to validate the computational model with experimental data and to analyze the interaction between the fluid and the structure. The second part of this study is an assessment of the unsteady aerodynamic loads produced by a wind gust over the blades and to verify how a trailing edge flap would influence the aerodynamic control parameters for the selected wind turbine blade.På grund av ökningen av rotorstorleken hos horisontella vindturbiner (HAWT) under de senaste 25 åren, en design som har uppstod för att uppnå högre effekt, måste alla vindkraftkomponenter och blad stå emot högre strukturella belastningar. Detta uppskalningsproblem kan lösas genom att använda metoder som kan minska aerodynamiska belastningar som rotorn måste tåla, antingen med passiva eller aktiva styrlösningar. Dessa kontrollanordningar och tekniker kan minska utmattningsbelastningen på bladen med upp till 40 % och därför behövs mindre underhåll, vilket resulterar i viktiga besparingar för vindkraftsägaren. Detta projekt består av en studie av lastkontrolltekniker för havsbaserade vindkraftverk ur en aerodynamisk och aeroelastisk synvinkel, i syfte att bedöma en kostnadseffektiv, robust och pålitlig lösning som kan fungera underhållsfri i tuffa miljöer. Den första delen av denna studie involverar 2D- och 3D-aerodynamiska och aeroelastiska simuleringar för att validera beräkningsmodellen med experimentella data och för att analysera interaktionen mellan fluiden och strukturen. Den andra delen av denna studie är en bedömning av de ojämna aerodynamiska belastningarna som produceras av ett vindkast över bladen och för att verifiera hur en bakkantklaff skulle påverka de aerodynamiska styrparametrarna för det valda vindturbinbladet.