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Journal articles on the topic 'Offshore structure stability'
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1
Pfoertner, Saskia, Hocine Oumeraci, Matthias Kudella, and Andreas Kortenhaus. "WAVE LOADS AND STABILITY OF NEW FOUNDATION STRUCTURE FOR OFFSHORE WIND TURBINES MADE OF OCEAN BRICK SYSTEM (OBS)." Coastal Engineering Proceedings 1, no. 32 (January 30, 2011): 66. http://dx.doi.org/10.9753/icce.v32.structures.66.
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The Ocean Brick System (OBS) is a modular system consisting of hollow concrete precast blocs (10m x 10m x 10m) piled up like cubes and interconnected to create a stiff, light and strong structure which can be used for artificial islands, artificial reefs, elevation of vulnerable low lands, deep water ports, breakwaters and foundation of offshore wind turbines. The paper focuses on the experimental results on the wave loading and the stability of the OBS used as
a foundation of the support structure of offshore wind turbines. Diagrams for the prediction of total horizontal forces, vertical forces and overturning moments induced by irregular waves on the OB-structure are derived and verified through additional stability tests and stability analysis.
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Esmailzadeh, Ebrahim, and Avesta Goodarzi. "Stability analysis of a CALM floating offshore structure." International Journal of Non-Linear Mechanics 36, no. 6 (September 2001): 917–26. http://dx.doi.org/10.1016/s0020-7462(00)00055-x.
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Van den Abeele, F., and J. Vande Voorde. "Stability of offshore structures in shallow water depth." International Journal Sustainable Construction & Design 2, no. 2 (November 6, 2011): 320–33. http://dx.doi.org/10.21825/scad.v2i2.20529.
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The worldwide demand for energy, and in particular fossil fuels, keeps pushing the boundaries of offshoreengineering. Oil and gas majors are conducting their exploration and production activities in remotelocations and water depths exceeding 3000 meters. Such challenging conditions call for enhancedengineering techniques to cope with the risks of collapse, fatigue and pressure containment.On the other hand, offshore structures in shallow water depth (up to 100 meter) require a different anddedicated approach. Such structures are less prone to unstable collapse, but are often subjected to higherflow velocities, induced by both tides and waves. In this paper, numerical tools and utilities to study thestability of offshore structures in shallow water depth are reviewed, and three case studies are provided.First, the Coupled Eulerian Lagrangian (CEL) approach is demonstrated to combine the effects of fluid flowon the structural response of offshore structures. This approach is used to predict fluid flow aroundsubmersible platforms and jack-up rigs.Then, a Computational Fluid Dynamics (CFD) analysis is performed to calculate the turbulent Von Karmanstreet in the wake of subsea structures. At higher Reynolds numbers, this turbulent flow can give rise tovortex shedding and hence cyclic loading. Fluid structure interaction is applied to investigate the dynamicsof submarine risers, and evaluate the susceptibility of vortex induced vibrations.As a third case study, a hydrodynamic analysis is conducted to assess the combined effects of steadycurrent and oscillatory wave-induced flow on submerged structures. At the end of this paper, such ananalysis is performed to calculate drag, lift and inertia forces on partially buried subsea pipelines.
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Subcommittee on Wave-Seabed-Structu. "Stability of Foundation of Coastal and Offshore Structure Under Waves." Doboku Gakkai Ronbunshu, no. 539 (1996): 1–13. http://dx.doi.org/10.2208/jscej.1996.539_1.
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Sun, Min Young, Ki Yeol Lee, and Byung Young Moon. "A Study on the Structural Analysis of Jacket Substructure Related to Offshore Wind Power Environment." Advanced Materials Research 1125 (October 2015): 387–91. http://dx.doi.org/10.4028/www.scientific.net/amr.1125.387.
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The currently applied structure and fatigue assessment of support structure for offshore wind energy converter was based on common design rules. The accurate evaluation for environments of sea floor as to installation of support structure, loads of generator, dynamic loads in operation, and offshore environmental loads might be an essential requirement to acquire a safety design for the substructure. This study aims at dedicating to offshore-relevant technology fields by suggesting design methods of structures and estimating their safety in relation to the structural analysis of the substructure requiring high safety to various environment conditions. Especially, with respect to 5MW Offshore Wind Power System, this study will provide information about major wind directions and duration in combination with the developing wave climate at the test field. In this study in the dynamic analysis for 5MW offshore wind power substructure which is considered to be proper in Korea, it is expected that reliability of domestic technology is confirmed with respect to its structural stability.
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Dong, Ji Wu, Zhi Jun Li, Li Min Zhang, Guang Wei Li, and Hong Wei Han. "Experimental Study of Sea Ice Forces on a Structure and its Stability." Advanced Materials Research 243-249 (May 2011): 4750–53. http://dx.doi.org/10.4028/www.scientific.net/amr.243-249.4750.
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A structure was designed to reduce the large forces exerted by level ice on offshore structures in shallow icy waters, by breaking the large ice floes into small pieces from flexing-induced failure. A series of model tests was conducted to simulate ice loads on the structure. A concrete model of it was adopted to verify the stability of the structure under the action of ice floes, which had five different thicknesses. The results show that ice forces on the structure are low and that the stability of the structure under different sea bed is good.
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Kim, Hyun-Gi, and Bum-Joon Kim. "Design Optimization of Conical Concrete Support Structure for Offshore Wind Turbine." Energies 13, no. 18 (September 17, 2020): 4876. http://dx.doi.org/10.3390/en13184876.
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Various types of support structures for offshore wind turbine have been developed, and concrete structures have attracted attention due to many advantages. Although many studies have been conducted on the design of the existing steel structures, information and research on the design of concrete support structures are insufficient. Therefore, in this paper, a structural analysis model of conical concrete support structure (CCSS) is established and design optimization is presented. A detailed performance evaluation and the design of prestressed concrete were performed under the marine conditions of Phase 1 test site of southwest offshore wind project in Korea. The fluid–soil–structure interaction (FSI) was applied using the added mass method and soil spring model to represent the effects of water and soil. With the result of quasi-static analysis, a post-tensioning design was implemented by applying prestressing steel, and CCSS showed sufficient rigidity. From the natural frequency analysis, CCSS has a dynamic structural stability, and, in response spectrum and time-history analyses, the CCSS was safe enough under the earthquake loads. The methods and conclusions of this study can provide a theoretical reference for the structural analysis and design of concrete support structures for offshore wind turbines.
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Ju, G. T., and S. Kyriakides. "Thermal Buckling of Offshore Pipelines." Journal of Offshore Mechanics and Arctic Engineering 110, no. 4 (November 1, 1988): 355–64. http://dx.doi.org/10.1115/1.3257073.
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The vertical buckling of offshore pipelines caused by thermal loads is analyzed by modeling the pipeline as a long heavy beam resting on a rigid foundation. The axial restraint provided to the line by the surrounding soil is modeled as Coulomb friction. The study is concerned with the effect of localized, small initial geometric imperfections on the response and stability of the structure. In the presence of initial imperfections, the response is characterized by the temperature rise required to cause initial uplift and by a limit temperature rise beyond which the structure becomes unstable. Both of these critical values are shown to be sensitive to the form and magnitude of the imperfections as well as by the pipe material inelastic characteristics.
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Gao, Rui, Ling Qiang Yang, and Yan Wang. "Analysis of Gravity Foundation for Offshore Structure under Cyclic Loads." Applied Mechanics and Materials 580-583 (July 2014): 2177–80. http://dx.doi.org/10.4028/www.scientific.net/amm.580-583.2177.
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Cyclic characteristic of offshore environmental load may cause the accumulation of foundation settlement and excess pore pressure in the subsoil. This may lead to conditions that jeopardize the structural stability and operability of the wind turbine. This paper discusses the analysis steps of the responses of non-cohesive subsoil under cyclic loads for a gravity base foundation system.
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Dymarski, Paweł, Czesław Dymarski, and Ewelina Ciba. "Stability Analysis of the Floating Offshore Wind Turbine Support Structure of Cell Spar Type during its Installation." Polish Maritime Research 26, no. 4 (December 1, 2019): 109–16. http://dx.doi.org/10.2478/pomr-2019-0072.
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Abstract The article presents the results of selected works related to the wider subject of the research conducted at the Faculty of Ocean Engineering and Ship Technology of the Gdansk University of Technology, which concerns design and technology of construction, towing, and settlement on the seabed, or anchoring, of supporting structures for offshore wind farms. As a result of this research, several designs of this type of objects were developed, including two stationary types: gravitational and Jack-up, which are placed on the seabed, and two floating types: TLP and SPAR, anchored with tendons and anchors in the form of nailed or suction piles. Below presented is the stability analysis of the new floating CELL SPAR type support structure for offshore wind turbines during its installation in waters with a depth of over 65 m.
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Sarhan, Osamah, and Mahdy Raslan. "Offshore petroleum rigs/platforms: An overview of analysis, design, construction and installation." International Journal of Advanced Engineering, Sciences and Applications 2, no. 1 (January 31, 2021): 7–12. http://dx.doi.org/10.47346/ijaesa.v2i1.58.
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Jacket platforms are one of the most important and regularly used types of offshore structures for oil and gas extraction that have a big impact on the economy of the countries. In this paper, all aspects including design, analysis, construction and installing of the jacket type offshore structure, are summarized and classified. This type of structure is one of the specified platforms for shallow water, and for long term service, it also has the ability to carry large deck loads. This paper aims to present general guidance about the planning, design and construction of offshore jacket (template) platforms. Jacket platforms are fixed type platforms which are attached to the seabed using piles which provide stability against the wind, wave and current loads. Also, this type of offshore platform has a high initial and maintenance cost because of its exposure to corrosion, and cannot be reused after the end of its service period. Jacket platforms are most suitable for shallow water having no better alternative while it has the cost disadvantage for deep water.
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Li, Bin. "Study on Stability Analysis of Steel Cylinder Retaining Structure." MATEC Web of Conferences 232 (2018): 04014. http://dx.doi.org/10.1051/matecconf/201823204014.
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The steel cylinder structure is generally used as a wharf revetment structure. It is necessary to evaluate the safety and stability of the steel cylinder structure as the retaining structure for offshore foundation excavation. In this paper, a large finite element software PLAXIS is used to simulate the safety factor and the structural displacement of the steel cylinder structure in the wave load and the excavation of the foundation. The calculation results show that the overall stability of the steel cylinder is 1.7 when the most unfavorable condition of excavating from the foundation to the bottom of the steel cylinder. The lateral displacement is 572mm, which meets the safety requirements of the structure. The steel cylinder structure can play a role as the water retaining structure of the cofferdam and the support structure of foundation when it was put into the non-permeable layer.
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Yang, Seungho, Jinwoog Cho, Hyunjoe Kim, and Booki Kim. "Study on the Mooring Stability of Floating Dock with Ultra Large Offshore Structure." Journal of the Society of Naval Architects of Korea 52, no. 6 (December 20, 2015): 509–19. http://dx.doi.org/10.3744/snak.2015.52.6.509.
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Altaee, Ameir, and Bengt H. Fellenius. "Modeling the performance of the Molikpaq." Canadian Geotechnical Journal 31, no. 5 (October 1, 1994): 649–60. http://dx.doi.org/10.1139/t94-077.
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A nonlinear, two-dimensional (plane-strain), monotonic and cyclic undrained finite element analysis is carried out to investigate the stability of the Molikpaq offshore structure at the Amauligak I-65 site in the Canadian Beaufort Sea. The stress–strain–strength response of the hydraulically placed sand is modeled using bounding-surface elastoplastic constitutive relations. The behavior of the sand in the field as well as in the laboratory is simulated by the constitutive relations using a single set of nine parameters. The Molikpaq structure was analyzed for up to 100 cycles of lateral cyclic ice loading in the interval 3–5 MN/m. The pore-water pressures computed at three different locations agree well with piezometer measurements made in the actual structure. The results of the study demonstrate the importance of analyzing the stability of the structure for cyclic loading rather than relying on conclusions derived from static analysis. Key words : analysis, cyclic loading, Molikpaq, sand fill retention, offshore structure.
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Lu, Zhonghua, Xuebin Chi, and Lansun Chen. "Optimal harvesting and stability for fishing models with stage structure in inshore-offshore areas." Applied Mathematics-A Journal of Chinese Universities 18, no. 2 (June 2003): 151–60. http://dx.doi.org/10.1007/s11766-003-0019-0.
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Zhang, Puyang, Disheng Liang, Hongyan Ding, Conghuan Le, and Xing Zhao. "Floating State of a One-Step Integrated Transportation Vessel with Two Composite Bucket Foundations and Offshore Wind Turbines." Journal of Marine Science and Engineering 7, no. 8 (August 9, 2019): 263. http://dx.doi.org/10.3390/jmse7080263.
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Offshore wind power is an important of source renewable energy. As a new technology, the one-step integrated transportation and installation technology of offshore wind power has broader application prospects. In order to ensure stability during the towing process, it is necessary to study the behavior of the wind turbine transportation structure. The numerical model of the specialized transportation vessel was set up by MOSES software. An analysis in the frequency domain and time domain was conducted considering the effects of draft, speed, and wave height on the towing stability of the wind turbine transportation vessel. The results show that the one-step integrated transportation method can ensure stability of the wind turbine during the towing process. Reducing draft, increasing speed, and increasing wave height will reduce the towing stability of the wind turbine. In the practical towing process, the combination of various adverse situations will be avoided.
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Mohan, Poonam, and A. P. Shashikala. "Stability Assessment of Drill Ship Using Probabilistic Damage Stability Analysis." Transactions on Maritime Science 8, no. 2 (October 21, 2019): 180–97. http://dx.doi.org/10.7225/toms.v08.n02.003.
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Drill ship is a ship-shaped structure with a drilling unit at its center and with oil compartments, which is moored and kept in position using anchors. These ships should be capable of working in deep sea for a long time, hence affected by harsh ocean environment. Drill units are said to have greater heave motion, and the height of the derrick influences the vessel’s stability. MARPOL Oil Outflow Analysis is performed for damaged crude oil carriers or tankers and Mobile offshore drilling units (MODU) in damaged condition. In the present study, probabilistic analysis is performed on drill ship to understand its stability behavior under damaged condition. Stability assessments are carried out by considering single and multiple damage locations. Oil outflow analysis is carried out for different damage cases of oil tank. Probabilistic damage assessment is done for load cases up to 50% flooding, to obtain stability charts. These charts will be useful to understand variations in stability parameters under damaged conditions.
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Mori, N., Y. Ishikawa, A. Hirayama, K. Tamaoki, and H. Kobayashi. "Softening of the Clayey Seabed Foundation due to Earthquakes." Journal of Offshore Mechanics and Arctic Engineering 110, no. 1 (February 1, 1988): 17–23. http://dx.doi.org/10.1115/1.3257116.
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Offshore structures are subjected to repeated loads from earthquakes and waves which may cause softening of the clayey seabed foundation. Carrying out a series of model tests on a shaking table, the following results are obtained. Settlement and inclination of a model of the base-part of the structure occur when the excess pore water pressure beneath the model rises to about 5 percent of the initial confining pressure. The earthquake response analysis even taking the nonlinearity of the soil into account cannot predict the results of the model test when the pore water pressure does generate and accumulate. Model tests show that the values of the pore water pressure are about twice as large as those predicted by calculation. From these results, rough evaluation of earthquake stability of the clayey seabed under offshore structures are obtained.
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Wang, Hai Ying, Xiao Ming Chen, Cheng Bi Zhao, You Hong Tang, and Wei Lin. "Conceptual Design and Hydrodynamic Performance of a Floating Offshore Wind Turbine Cell-Spar-Buoy Support Structure." Applied Mechanics and Materials 472 (January 2014): 291–95. http://dx.doi.org/10.4028/www.scientific.net/amm.472.291.
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On the way to further exploit offshore wind energy, conventional fixed-bottom technology has been limited by the water depth. After the worlds first full scale floating wind turbine being installed in the North Sea in 2009, the floating support structure for offshore wind turbines is most likely becoming not only a technically feasible but also an economically viable solution, especially for regions of water depth over 50 meters. However, less attentions have been paid on floating support strucure, which is a very important part. Derived from commercialized offshore oil and gas platform of cell spar, a conceptual design of a cell-spar-buoy support structure for NREL 5 MW offshore wind turbine is proposed. In this system, structural type of cells is absorbed for cost reduction while damping configurations are used to optimize the stability of wind turbine. For further hydrodynamic performance estimations, numerical simulations have been performed to compute the response amplitude operators (RAOs) and the wave response motions, which are the key factors of the preliminary design. Meanwhile, the motion performance of the platform with mooring system in operating conditions and mooring line tensions under the 50 years return period storm survival condition in the South China Sea was calculated in time domain. The results showing excellent motion performance of cell-spar-buoy.
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Feng, Hua-Nv, Bao-Lin Zhang, Qing Li, and Gong-You Tang. "Delayed Fuzzy Output Feedback H∞ Control for Offshore Structures." Journal of Marine Science and Engineering 8, no. 6 (June 12, 2020): 434. http://dx.doi.org/10.3390/jmse8060434.
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Vibration damping of jacket platforms is among the significant issues in marine science and engineering, and the design of active vibration control schemes is very important to ensure the stability and safety of the jacket platforms against external loadings. This paper provides three fuzzy output feedback H ∞ controllers of the jacket platforms for irregular wave forces. By considering time-varying masses of jacket platforms, a Takagi-Sugeno (T-S) fuzzy dynamic model of the structure is established. Then fuzzy output feedback H ∞ control schemes are developed via using output signals of the platform with current and/or are delayed. Several existence conditions of fuzzy output feedback H ∞ controllers are derived. Simulation results demonstrate that the fuzzy output feedback H ∞ control strategies are remarkable to suppress the vibration of structure. Moreover, by choosing proper delayed output information of the system, the presented delayed fuzzy output feedback H ∞ control schemes outperform the conventional fuzzy output feedback H ∞ control approach.
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Stahlmann, Arne, and Torsten Schlurmann. "INVESTIGATIONS ON SCOUR DEVELOPMENT AT TRIPOD FOUNDATIONS FOR OFFSHORE WIND TURBINES: MODELING AND APPLICATION." Coastal Engineering Proceedings 1, no. 33 (October 25, 2012): 90. http://dx.doi.org/10.9753/icce.v33.sediment.90.
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Regarding offshore constructions, there is still a lack in knowledge of scour progression for complex structures like foundations for offshore wind energy converters at present, which is however necessary for its dimensioning. As an example of such complex structure types, tripod foundations are constructed in German offshore wind farms at present. In order to describe physical processes and influencing factors on scour progression from a scientific point of view, comprehensive investigations on the scouring phenomena for tripod foundations have been carried out and will be partly presented here. The overall investigation method consists of a combination of 1:40 small and 1:12 large scale physical model tests in wave flumes, numerical simulations using CFD methods and in-situ measured scour data. For the numerical modeling part, a sediment transport model formulation has been implemented into OpenFOAM software code. The results show a general variability of scour depending on the load boundary conditions and structural parameters. Scours occur both at the foundation piles and directly under the structure, which in this form could not be predicted using standard approaches, but which has to be taken into account when regarding the soil mechanical stability and the final dimensioning of the foundations.
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Kim, Hyun-Gi, Bum-Joon Kim, and Kwang-Ho Lee. "Analysis of Piled Concrete Foundation for a 3-MW Class Offshore Wind Turbine along the Southwest Coast in Korea." Journal of Marine Science and Engineering 8, no. 3 (March 20, 2020): 215. http://dx.doi.org/10.3390/jmse8030215.
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Concrete foundations have received attention as offshore wind turbine support structures because of their various advantages. However, because of the lack of information on structural analysis and the design method of complex marine environmental loads, concrete foundations cannot be applied on actual sites. Therefore, the structure behavior mechanism and concrete reinforcement design need to be evaluated based on soil-structure interactions. Herein, an efficient method for analysis of piled concrete foundations (PCFs) is presented, and the stability of PCF structures is evaluated under environmental conditions of the coast in Korea for a 3-MW wind turbine. Three analytical parameters for PCF models were defined to consider soil-structure interaction. The results of each model were compared with the displacement, stresses, and natural frequencies. Using the analysis results, a prestressing reinforcement design for concrete foundations was proposed. Quasi-static analysis showed that maximum displacement was sufficiently small and the maximum stresses did not exceed the allowable stresses. PCF showed excellent dynamic performance and structural stability. In addition, stiffness of the soil spring model influenced the natural frequency rather than the stiffness of the pile type. Detailed analysis of the connections between piles and concrete need to be studied in the future.
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Zhang, Jinfeng, Qianzi, Tang, and Qinghe Zhang. "STUDY ON DYNAMIC RESPONSE OF SEABED UNDER WAVES BASED ON DEM-PFV COUPLING METHOD." Coastal Engineering Proceedings, no. 36v (December 28, 2020): 26. http://dx.doi.org/10.9753/icce.v36v.sediment.26.
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The stability of nearshore/offshore structures will be affected by wave loads. The deformation, softening and liquefaction of the seabed under the action of cyclic wave will result in loss of the self-bearing capacity, which endangers the safety of the structure. In this study, based on the open-sourced discretization method software Yade, the numerical model is established by coupling discrete element method (DEM) and porescale finite volume method (PFV). The dynamic response of porous seabed under wave is analyzed.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/0SnuNQti0gI
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Ghigo, Alberto, Lorenzo Cottura, Riccardo Caradonna, Giovanni Bracco, and Giuliana Mattiazzo. "Platform Optimization and Cost Analysis in a Floating Offshore Wind Farm." Journal of Marine Science and Engineering 8, no. 11 (October 23, 2020): 835. http://dx.doi.org/10.3390/jmse8110835.
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Floating offshore wind represents a new frontier of renewable energies. The absence of a fixed structure allows exploiting wind potential in deep seas, like the Atlantic Ocean and Mediterranean Sea, characterized by high availability and wind potential. However, a floating offshore wind system, which includes an offshore turbine, floating platform, moorings, anchors, and electrical system, requires very high capital investments: one of the most relevant cost items is the floating substructure. This work focuses on the choice of a floating platform that minimizes the global weight, in order to reduce the material cost, but ensuring buoyancy and static stability. Subsequently, the optimized platform is used to define a wind farm located near the island of Pantelleria, Italy in order to meet the island’s electricity needs. A sensitivity analysis to estimate the Levelized Cost Of Energy is presented, analyzing the parameters that influence it most, like Capacity Factor, Weighted Average Capital Cost (WACC) and number of wind turbines.
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C. Subramanian, Susheelkumar, Michaela Dye, and Sangram Redkar. "Dynamic Analysis of Suction Stabilized Floating Platforms." Journal of Marine Science and Engineering 8, no. 8 (August 6, 2020): 587. http://dx.doi.org/10.3390/jmse8080587.
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The occurrence of parametric resonance due to the time varying behavior of ocean waves could lead to catastrophic damages to offshore structures. A stable structure that could withstand the wave perturbations is quintessential to operate in such a harsh environment. In this work, the authors detail the relevance of a Suction Stabilized Float (SSF) or a Suction Stabilized Floating platform towards such an application. A generic design of a symmetrically shaped float structure along with its inherent stabilization behavior is discussed. Furthermore, the authors extend their prior research on this topic towards modelling the dynamics of SSF and perform stability analysis. The authors demonstrate the dynamical characteristics of SSF analytically using Floquet theory and Normal Forms technique, in this work. Additionally, the simulation results are verified and validated with the numerical methods.
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Holland, Steven M., and Andrew Zaffos. "Niche conservatism along an onshore-offshore gradient." Paleobiology 37, no. 2 (2011): 270–86. http://dx.doi.org/10.1666/10032.1.
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Niche conservatism is increasingly recognized in diverse modern ecological settings, and it influences many aspects of modern ecosystems, including speciation mechanisms, community structure, and response to climate change. Here, we investigate the stability of niches with benthic marine invertebrates along a Late Ordovician onshore-offshore gradient on the Cincinnati Arch in the eastern United States. Using a Gaussian niche model characterized by peak abundance, preferred environment, and environmental tolerance, with these parameters estimated through weighted averaging and logistic regression, we find evidence of strong niche conservatism in peak abundance and preferred environment, particularly for abundant taxa. This conservatism is maintained in successive depositional sequences and through the nearly 9–10 Myr study interval. Environmental tolerance shows no evidence of conservatism, although numerical simulations suggest that the error rates in estimates of this parameter are so high that they could overwhelm evidence of conservatism. These numerical simulations also indicate that both weighted averaging and logistic regression produce useful estimates of peak abundance and preferred environment, with slightly better results for weighted averaging. This evidence for niche conservatism suggests that long-term shifts of higher taxa of marine invertebrates into deeper water are primarily the result of differential rates of origination and extinction. These results also add to the evidence of long periods of relatively stable ecosystems despite regional environmental perturbations, and they constrain the causes of peaked patterns in occupancy.
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Dai, Jian, Kok Keng Ang, Jingzhe Jin, Chien Ming Wang, Øyvind Hellan, and Arnstein Watn. "Large Floating Structure with Free-Floating, Self-Stabilizing Tanks for Hydrocarbon Storage." Energies 12, no. 18 (September 10, 2019): 3487. http://dx.doi.org/10.3390/en12183487.
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Hydrocarbon is a major source of energy for sustainable development. Storage of hydrocarbon products, however, requires a significant amount of land space to land-scarce countries like Singapore. This paper presents an alternative way of storing hydrocarbon in Singapore coastal waters through the innovative design of a floating hydrocarbon storage facility. The design comprises free-floating and self-stabilizing tanks enclosed by barges that form a floating hydrocarbon storage facility. The tanks are made of prestressed concrete and they are designed to be self-stabilized when floating in the sea water. Owing to the lack of available design guidelines, design requirements on the stability and motion criteria for floating storage tanks are developed based on a review of existing codes of practice and design specifications for both onshore tanks and offshore vessels. A comprehensive study on the hydrostatic performance of various proposed floating tank design concepts with different storage capacities is carried out. This paper aims to give design recommendations on the tank’s storage capacity and dimensional aspect ratios that fulfill the recommended stability requirements and motion criteria.
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Ishii, Hidenori, Tomoya Shibayama, and Jacob Stolles. "PHYSICAL AND NUMERICAL MODELLING OF THE FLOW STRUCTURE BEHIND STRUCTURE IN TSUNAMI-LIKE FLOW." Coastal Engineering Proceedings, no. 36 (December 30, 2018): 17. http://dx.doi.org/10.9753/icce.v36.currents.17.
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Coastal structures are expected to play a role as evacuation buildings. Numerous studies have been examined tsunami-induced wave force acting on an inland building (Shigihara et al., 2009; Arimitsu et al., 2014). In addition, coastal structures have the potential to obstruct inundating tsunami waves, protecting structure further from the coastline. Hydraulic experiments and numerical calculations on shielding effect are being carried out. Alternatively, the vortices from these structures can result in significant scour downstream, influencing downstream structure stability. In the 2011 Tohoku Region Pacific Offshore Earthquake, many cases were reported that the structure was scrubbed and the structure fallen down. Skakiyama et al. (2007) and Sakakiyma et al. (2008) pointed out that the standing vortex generated around the structure winds sand and causes scouring. Therefore, understanding the vortices generated around the structure is also important in predicting the scouring phenomenon. As such, the flow properties around coastal structures must be considered and acknowledged within the design process. However, there are a few studies focusing on the flow fields behind structure.Arnason et al. (2009) measured velocity fields of dam-break flow around/in the wake of a vertical column. Wei et al. (2015) reproduced the experiment performed using SPH. However, in the experiment, vortexes are not considered and the influence of the existence of structures on the surroundings has not been sufficiently considered. Therefore, in this study, the flow fields of a tsunami-like wave around structures were examined through hydraulic experiments. This experiment was performed to clarify the local vortex structure behind structures by measuring the plane flow velocity field. Also, the effect of obstructing protecting the land side structure is assessed by measuring the wave force behind structures. Furthermore, a three-dimensional model (OpenFOAM) was used to further analyze the flow, focusing on water-level and wave forces behind the structure.
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Thompson, G. R., and L. G. Long. "Hibernia geotechnical investigation and site characterization." Canadian Geotechnical Journal 26, no. 4 (November 1, 1989): 653–78. http://dx.doi.org/10.1139/t89-078.
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A detailed offshore site investigation was conducted in the Hibernia field in 1983 to provide engineering data for the preliminary design of a gravity base structure (GBS) for use as an oil production platform. Reliable information regarding the strength and variability of near-surface soils was needed to verify that the foundation would be capable of resisting large environmental design loads, including those induced by iceberg impacts and storm waves. This paper presents an overview of the geotechnical equipment and methods that were successfully used to complete the investigation, major results of the field and laboratory program, and an interpretation of soil strength parameters needed for analysis of GBS stability under the design loads. Results are presented that confirm that the preshear density and effective confining pressure, or "state," of underlying sand elements are major factors that must be considered when establishing design parameters for GBS structures. It is demonstrated that consideration of state changes resulting from GBS installation is important in the analysis of granular soil resistance under both drained and undrained loading conditions. Failure to account for this effect could lead to an unconservative design. Key words: Hibernia, offshore site investigation, CPT, sand strength, state parameter.
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Ibrahim, R. A., N. G. Chalhoub, and Jeffery Falzarano. "Interaction of Ships and Ocean Structures With Ice Loads and Stochastic Ocean Waves." Applied Mechanics Reviews 60, no. 5 (September 1, 2007): 246–89. http://dx.doi.org/10.1115/1.2777172.
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The influence of floating ice on the dynamic behavior of ships and offshore structures depends on many factors such as ice thickness and its relative speed with respect to the floating structure. The ice resistance to ship motion forms an essential problem in ship design and navigation. Furthermore, local or global ice loads acting on ocean systems are random and nonsmooth when impact interaction takes place. Impact loads on the bow of a ship navigating in solid ice may be modeled by a Poisson law. The measured stress amplitudes on the ship frame at the bow follow an exponential distribution. The nonhomogeneity and difference in ice microstructure, as well as the influence of salt and temperature, result in a great uncertainty in the ice strength. Therefore, the current review article aims at assessing the ice related problems encountered by offshore structures as well as by ships during their navigation. It also discusses the impacts of local and global ice loads on floating structures and reviews their existing probabilistic models. Moreover, this article covers the dynamic interaction of ice with flexible and rigid structures, and ships. In view of ice loads on marine systems, new design regulations have been introduced by international organizations that are involved in the design and building of ships as well as offshore structures. The ship stochastic stability and the first-passage roll stabilization problem associated with random ocean waves will also be described in an attempt to stimulate future research work dealing with ice impact loads. Moreover, due to the lack of research activities addressing the control problem of ships operating in icy waters, the current article will briefly discuss passive and active control schemes developed for controlling the ship roll motion. There are 529 references cited in this review article.
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Stahlmann, Arne, and Torsten Schlurmann. "PHYSICAL MODELING OF SCOUR AROUND TRIPOD FOUNDATION STRUCTURES FOR OFFSHORE WIND ENERGY CONVERTERS." Coastal Engineering Proceedings 1, no. 32 (January 27, 2011): 67. http://dx.doi.org/10.9753/icce.v32.sediment.67.
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As a step to further develop the share of renewable energies, the first German offshore test site alpha ventus has been installed in the North Sea in 2009 in water depths of 30 m, where experience shall be gained and made available for
future offshore wind farms. Regarding converter foundations in deep water, it is well known that in most cases scour phenomena occur around the structures. Due to the complexity of the tripod foundations, significant knowledge gaps in scour progression in general and especially in detail as well as its probable effects on the stability and durability are given. Therefore, investigations on scouring phenomena around complex foundation structures like the tripod are
carried out within the research project. The investigation method consists of a unique combination of local scour monitoring as well as physical and numerical modeling, whereas the physical modeling part was carried by means of 1:40 laboratory tests and 1:12 large-scale physical model tests in wave flumes. The results show that scours around the tripod foundation do not only occur directly around the foundation piles, but also in the near-field of the structure. Compared to first in-situ measured scours in the test site, at least a good qualitative agreement of the modeled scour depths and evolutions could be shown.
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KURAMOTO, Ryoh, Takashi WATANABE, Takeshi YOSHIOKA, and Toshiyasu MIYOSHI. "ANALYTICAL STUDY ON STABILITY EVALUATION OF OFFSHORE WIND-POWER GENERATION FOUNDATION WITH GRAVITY-TYPE SUPPORT STRUCTURE UNDER SEISMIC LOAD." Journal of Japan Society of Civil Engineers, Ser. A1 (Structural Engineering & Earthquake Engineering (SE/EE)) 77, no. 4 (2021): I_544—I_556. http://dx.doi.org/10.2208/jscejseee.77.4_i_544.
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Ding, Hongyan, Xing Zhao, Conghuan Le, Puyang Zhang, and Qiaoling Min. "Towing Motion Characteristics of Composite Bucket Foundation for Offshore Wind Turbines." Energies 12, no. 19 (October 2, 2019): 3767. http://dx.doi.org/10.3390/en12193767.
Full textAbstract:
Composite bucket foundation (CBF) is an environmentally friendly form of offshore wind power foundation. By virtue of the air-floating subdivision structure in the bucket, the foundation has a self-floating characteristic and can allow for long-distance air-floating towing and transport. In this study, first, a numerical analysis was performed on the towing motion characteristics of CBF, and the formula for foundation stability was deduced; then, we probed into the variation rules of the natural period of the foundation with draft and analyzed the response amplitude operator (RAO) responses, added mass coefficients, radiation damping coefficients, and exciting forces (moments) of the composite bucket foundation under different drafts and different wave directions. Finally, we clarified the basic hydrodynamic characteristics of the composite bucket foundation in the frequency domain and adopted multiple random wave models to investigate the effects of different wave heights, periods, and spectral peak factors on the towing motion characteristics of composite bucket foundation.
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Zhang, Qingling, Hong Niu, Lichun Zhao, and Fenglan Bai. "The Analysis and Control for Singular Ecological-Economic Model with Harvesting and Migration." Journal of Applied Mathematics 2012 (2012): 1–17. http://dx.doi.org/10.1155/2012/973869.
Full textAbstract:
To keep the resources renewable, a singular ecological-economic model is proposed for the populations with harvesting and migration. The local stability and the dynamic behavior of the model are studied. Singular induced bifurcation appears when economic interest is zero, which is different from the ordinary differential models. In order to apply variable structure control to eliminate these complex behaviors, the singular model is transformed into a single-input and single-output model with parameter varying within definite intervals. And then, a variable structure controller is designed to make the model stable. Finally, an inshore-offshore fishery model is given to illustrate the proposed method, and some numerical simulations are shown to demonstrate the control results.
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Zhang, Shihai, Zhuo Li, Yanshuang Wang, and Zimiao Zhang. "Design on the Inner Wall Crawling and Inspecting Robot for Offshore Platform Leg." Recent Patents on Mechanical Engineering 13, no. 2 (May 31, 2020): 109–17. http://dx.doi.org/10.2174/2212797613666200117121403.
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Background: The legs are important base mechanism and have a key effect on the stability and security of movable offshore platform. In the application field, the work of defects detection is operated in a manual way for offshore platform leg. The main disadvantages of manual inspection can be summarized as follows: high detection cost and risk, low detection coverage and efficiency, etc. Objective: To develop a robot with an inspecting system that can crawl on the inner wall surface of the offshore platform leg, and inspect the surface defects through the inspecting system. Methods: Based on our patented technologies and the application requirements, the telescopic mechanisms, constituted by motor-screw-nut mechanism, are applied to design the body and legs mechanism of the robot. The vacuum sucker groups are applied to design the adsorption mechanism of the robot. The PLC is applied to design the measurement and movement control system. The laser ranging sensors are applied to realize the function of obstacle detection, robot location and pose analysis. The camera and its driving system are applied to design the image acquisition system. The wireless bridge is applied to design the message remote transmission system. Results: Based on the structure characteristic and the defect inspecting requirement of offshore platform leg, the wall crawling robot and its inspecting system are designed in this study. Conclusion: A series of experiments show that the robot and its inspecting system meet the demand of field applications.
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Zheng, Xiang, and Yu Lei. "Stochastic Response Analysis for a Floating Offshore Wind Turbine Integrated with a Steel Fish Farming Cage." Applied Sciences 8, no. 8 (July 26, 2018): 1229. http://dx.doi.org/10.3390/app8081229.
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A state-of-the-art concept integrating a deepwater floating offshore wind turbine with a steel fish-farming cage (FOWT-SFFC) is presented in this paper. The configurations of this floating structure are given in detail, showing that the multi-megawatt wind turbine sitting on the cage foundation possesses excellent hydrostatic stability. The motion response amplitude operators (RAOs) calculated by the potential-flow program WAMIT demonstrate that the hydrodynamic performance of FOWT-SFFC is much better than OC3Hywind spar and OC4DeepCwind semisubmersible wind turbines. The aero-hydro-servo-elastic modeling and time-domain simulations are carried out by FAST to investigate the dynamic response of FOWT-SFFC for several environmental conditions. The short-term extreme stochastic response reveals that the dynamic behavior of FOWT-SFFC outperforms its counterparts. From the seakeeping and structural dynamic views, it is a very competitive and promising candidate in offshore industry for both power exploitation and aquaculture in deep waters.
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Abdul Malik, Asmawi, Mohd Zamani Ahmad, Azura Ahmad Radzi, Ahmad Faizal Ahmad Fuad, and Nur Hanani Ahmad Azlan. "Appraisal of Mega Float - Floating Offshore Remote Terminal (FORT) on Catenary Mooring for Deep Water." Applied Mechanics and Materials 815 (November 2015): 421–26. http://dx.doi.org/10.4028/www.scientific.net/amm.815.421.
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With the development of offshore fishing and deep sea exploitation intensifies, floating offshore remote terminal (FORT) which having many advantages can better adapt to the complicated environment of deep sea in numerous offshore platform. Due to the hull likely to to resonance phenomenon, FORT has more intense motion compared to other hull form types. Therefore, the main challenge of FORT in the deep sea operation is to design effective mooring system. This paper introduced the dynamic response by utilizing the computational effort associated with time-domain simulation of single anchor leg mooring (SALM). The influenced or the effect of significant wave height (SWH) over the structure is discussed. It is shown that a comparison of different SWH value in terms of their stability properties is sufficient and adequate; relative merit is assessed through comparison of full systems that have been designed to minimum cost, and to common performance specifications. It is found that single point or catenary systems, can outperform both static and dynamic solutions at the preliminary stage. Moreover, the results indicated that the position ability and mooring strength of SALM system whose intermediate material is studless chain of catenary mooring system on the premise that satisfies API specification at the same time.
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Kasprzak, R. A., and W. S. Perret. "USE OF OIL AND GAS PLATFORMS AS HABITAT IN LOUISIANA'S ARTIFICIAL REEF PROGRAM." APPEA Journal 36, no. 1 (1996): 681. http://dx.doi.org/10.1071/aj95048.
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Louisiana's offshore oil and gas industry began in 1947 when the first well was drilled out of sight of land south of Terrebonne Parish. Today over 3,700 offshore oil and gas platforms have been installed, supplying 25 per cent of the United States' production of natural gas and 12.5 per cent of its oil. In addition to meeting the world's energy needs, these structures also form one of the world's most extensive defacto artificial reef systems. However, federal regulations require that these structures be removed within 1 year after the lease is terminated. Disposal of obsolete offshore oil and gas structures is not only a net financial liability for private industry but can be a public loss of productive marine habitat. In 1986 the Louisiana Fishing Enhancement Act was signed into law, in response to the National Fishing Enhancement Act, creating the Louisiana Artificial Reef Program. This program was designed to take advantage of fishing habitat opportunities offered by these obsolete platforms. Since the program's inception 22 reef sites, utilising the components (jackets and decks) of 58 obsolete platforms, have been created off Louisiana's coast. The use of obsolete oil and gas platforms in Louisiana has proved to be highly successful. Their large numbers, design, longevity, and stability have provided a number of advantages over the use of traditional artificial reef materials. The participating companies also save money by converting the structure into a reef rather than abandoning it onshore; these companies are required to donate a portion of the savings to the state to run the artificial reef program. One disadvantage, however, is that the large size of these platforms restricts the distance to shore where they can be sited. To achieve the minimum clearance of 16 m over a submerged structure, as required by the Coast Guard regulations, the platforms must be placed in waters deeper than 30 m. Waters of this depth are found between 22 km and 115 km from shore on Louisiana's gently sloping continental shelf, making them almost inaccessible to many anglers. Funds generated by the program, however, can be used to develop reefs closer to shore if alternative low profile materials are used. Due to high maintenance costs of both the structure and aids to navigation, the increased liability exposure and the undetermined cost of removing the structure once it becomes a hazard to public safety and navigation, leaving the structures standing in place has thus far proved not to be a viable option in Louisiana.
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An, C., C. W. Gu, H. Qin, T. T. Li, and M. L. Duan. "An Analysis of Carcass Layer Erosion in Un-Bonded Flexible Offshore Pipework." International Journal of Maritime Engineering 163, A1 (April 7, 2021): 63–77. http://dx.doi.org/10.5750/ijme.v163ia1.6.
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In this paper, a simplified model for erosion in un-bonded flexible pipes caused by the sand entrained in the produced fluid is established. Flow field analysis is performed based on the governing equations of the continuous fluid and the discrete particles. A two-way coupled Eulerian-Lagrangian approach is employed to solve the gas-solid flow in the pipe bend. To eliminate the influence of the length of the straight pipe section on the stability of the flow field in the pipe, the flow field distribution under different lengths is analyzed to determine the optimal straight pipe length. Six commonly used erosion models are adopted to predict the erosion rate. After comparing the prediction results with experimental data, the most accurate Oka model is selected to calculate the effect of the fluid and structure parameters on erosion. Effects of particle parameters and pipe structural parameters on the erosion rate of curved flexible pipes are numerically fitted, and the quantitative description is given.
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Borg, M., and M. Collu. "A comparison between the dynamics of horizontal and vertical axis offshore floating wind turbines." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 373, no. 2035 (February 28, 2015): 20140076. http://dx.doi.org/10.1098/rsta.2014.0076.
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The need to further exploit offshore wind resources in deeper waters has led to a re-emerging interest in vertical axis wind turbines (VAWTs) for floating foundation applications. However, there has been little effort to systematically compare VAWTs to the more conventional horizontal axis wind turbine (HAWT). This article initiates this comparison based on prime principles, focusing on the turbine aerodynamic forces and their impact on the floating wind turbine static and dynamic responses. VAWTs generate substantially different aerodynamic forces on the support structure, in particular, a potentially lower inclining moment and a substantially higher torque than HAWTs. Considering the static stability requirements, the advantages of a lower inclining moment, a lower wind turbine mass and a lower centre of gravity are illustrated, all of which are exploitable to have a less costly support structure. Floating VAWTs experience increased motion in the frequency range surrounding the turbine [number of blades]×[rotational speed] frequency. For very large VAWTs with slower rotational speeds, this frequency range may significantly overlap with the range of wave excitation forces. Quantitative considerations are undertaken comparing the reference NREL 5 MW HAWT with the NOVA 5 MW VAWT.
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Ramasamy, Ramesh. "Investigation and Analysis of the Catastrophic Failure of an Offshore Water Injector Well." MATEC Web of Conferences 203 (2018): 01002. http://dx.doi.org/10.1051/matecconf/201820301002.
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The catastrophic failure of an offshore water injector well is presented in this paper. The failure mode was determined from the final collapsed state of the conductor pipe which resulted in the surface Xmas tree and wellhead to drop vertically down onto the platform deck. Various inspections and assessments are carried out to determine the integrity of the well structure and compared against the original drilling records. Stability evaluations of the casing is also carried out to account for the loss of annular cement which resulted in loss of centralisation. The analyses conclude that various sequence of events have contributed towards the failure of this well. The lack of intermediate inspections and monitoring have resulted in uninhibited corrosion and pitting on the conductor pipe. Some considerations on the necessity of an effective inspections strategy and rationalisations of a robust integrity screening are also drawn.
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Fan, Jinchang, Canjun Yang, Yanhu Chen, Hansong Wang, Zhengming Huang, Zhicheng Shou, Ping Jiang, and Qianxiao Wei. "An underwater robot with self-adaption mechanism for cleaning steel pipes with variable diameters." Industrial Robot: An International Journal 45, no. 2 (March 19, 2018): 193–205. http://dx.doi.org/10.1108/ir-09-2017-0168.
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Purpose This paper aims to present an underwater climbing robot for wiping off marine life from steel pipes (e.g. jackets of oil platforms). The self-adaption mechanism that consists of a passive roll joint and combined magnet adhesion units provides the robot with better mobility and stability. Design/methodology/approach Adhesion requirements are achieved by analyses of falling and slipping. The movement status on pipes is analyzed to design the passive roll joint. The optimized structure parameters of the combined magnet adhesion unit are achieved by simulations. An approximation method is established to simplify the simulations conditions, and the simulations are conducted in two steps to save time effectively. Findings The self-adaption mechanism has expected performance that the robot can travel on pipes in different directions with high mobility. Meanwhile, the robot can clean continuous region of underwater pipes’ surface of offshore platforms. Practical implications The proposed underwater robot is needed by offshore oil platforms as their jackets require to be cleaned periodically. Compared with traditional maintenance by divers, it is more efficient, economic and safety. Originality/value Due to the specific self-adaption mechanism, the robot has good mobility and stability in any directions on pipes with different diameters. The good performance of striping attachments from pipes makes the underwater robot be a novel solution to clean steel pipes.
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Wu, Jinming, and Zhonghua Ni. "On the Design of an Integrated System for Wave Energy Conversion Purpose with the Reaction Mass on Board." Sustainability 12, no. 7 (April 3, 2020): 2865. http://dx.doi.org/10.3390/su12072865.
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In this paper, we investigate the design of an integrated system consisting of two non-rigidly connected bodies: A floating buoy and an emerged offshore structure. When waves excite the buoy to oscillate, the relative motion between the two bodies are converted to useful energy through a spring damper system, resulting in wave energy being absorbed. The parameter to design includes the mass and underwater shape of the buoy. The spring stiffness of the power take-off (PTO) system is constrained to be non-negative with the concerns of complexity in implementation and system stability. Results suggest that a larger mass of the buoy is advantageous due to smaller optimal spring stiffness and damping coefficient of the PTO system, more absorbed wave power, and less motion amplitude of the two bodies. A favorable underwater shape of the buoy is characterized by large diameter to draft ratio, with the section profile preferring a circle or square rather than an equilateral triangle. Investigations on the designed buoy in irregular waves show that the integrated system presents its peak power absorption within the common range of energy period, and the motion amplitude of the offshore structure is larger than the wave amplitude in a certain range of sea states.
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Sweeney, J. K., J. M. Chagnon, and S. L. Gray. "A case study of sea breeze blocking regulated by sea surface temperature along the English south coast." Atmospheric Chemistry and Physics 14, no. 9 (May 6, 2014): 4409–18. http://dx.doi.org/10.5194/acp-14-4409-2014.
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Abstract. The sensitivity of sea breeze structure to sea surface temperature (SST) and coastal orography is investigated in convection-permitting Met Office Unified Model simulations of a case study along the south coast of England. Changes in SST of 1 K are shown to significantly modify the structure of the sea breeze immediately offshore. On the day of the case study, the sea breeze was partially blocked by coastal orography, particularly within Lyme Bay. The extent to which the flow is blocked depends strongly on the static stability of the marine boundary layer. In experiments with colder SST, the marine boundary layer is more stable, and the degree of blocking is more pronounced. Although a colder SST would also imply a larger land–sea temperature contrast and hence a stronger onshore wind – an effect which alone would discourage blocking – the increased static stability exerts a dominant control over whether blocking takes place. The implications of prescribing fixed SST from climatology in numerical weather prediction model forecasts of the sea breeze are discussed.
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Lian, Jijian, Pengwen Wang, Conghuan Le, Xiaofeng Dong, Xu Yang, Qi Jiang, Yilin Yang, and Junni Jiang. "Reliability Analysis on One-Step Overall Transportation of Composite Bucket Foundation for Offshore Wind Turbine." Energies 13, no. 1 (December 19, 2019): 23. http://dx.doi.org/10.3390/en13010023.
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Composite bucket foundations, which have been successfully transported, installed, and operated at the Qidong, Xiangshui, and Dafeng offshore wind farms in China, are economically advantageous due to the relatively simple transportation and installation process. The innovative one-step transportation and installation technology of foundation-tower-nacelle is the key phase in saving costs. In this paper, a “foundation lift ship” overall transport mode is proposed and introduced for the first time. Prototype data measurement, preliminary numerical simulation, and theoretical calculations were conducted to investigate whether the foundation-ship integrity, tower hoop stability, and various indexes of the nacelle met the requirements under the influences of various environmental factors. The multi-system coupling motion mechanism and analysis method of this new structure and transportation mode were expounded. Through the prototype observation data of the one-step overall transportation, the ship-foundation system reliability of the structure in the case of large wind and wave was confirmed. Furthermore, it was found that in the one-step overall transportation, the importance of factors to nacelle acceleration decreased in the order of wave height, current speed, and wind speed by the time and frequency domain analysis and data statistics.
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Aboutalebi, Payam, Fares M’zoughi, Izaskun Garrido, and Aitor J. Garrido. "Performance Analysis on the Use of Oscillating Water Column in Barge-Based Floating Offshore Wind Turbines." Mathematics 9, no. 5 (February 25, 2021): 475. http://dx.doi.org/10.3390/math9050475.
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Undesired motions in Floating Offshore Wind Turbines (FOWT) lead to reduction of system efficiency, the system’s lifespan, wind and wave energy mitigation and increment of stress on the system and maintenance costs. In this article, a new barge platform structure for a FOWT has been proposed with the objective of reducing these undesired platform motions. The newly proposed barge structure aims to reduce the tower displacements and platform’s oscillations, particularly in rotational movements. This is achieved by installing Oscillating Water Columns (OWC) within the barge to oppose the oscillatory motion of the waves. Response Amplitude Operator (RAO) is used to predict the motions of the system exposed to different wave frequencies. From the RAOs analysis, the system’s performance has been evaluated for representative regular wave periods. Simulations using numerical tools show the positive impact of the added OWCs on the system’s stability. The results prove that the proposed platform presents better performance by decreasing the oscillations for the given range of wave frequencies, compared to the traditional barge platform.
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Zhang, Puyang, Yunlong Xu, Conghuan Le, Hongyan Ding, and Yaohua Guo. "Structural Optimization Method for the Transition Section in Composite Bucket Foundations of Offshore Wind Turbines." Energies 11, no. 11 (November 21, 2018): 3230. http://dx.doi.org/10.3390/en11113230.
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A two-step structural optimization method was proposed to select the transition section of a composite bucket foundation (CBF). In the first step, based on the variable density method, a solid isotropic microstructures with penalization (SIMP) interpolation model was established under specific load conditions and boundary conditions. The solution of force transmission path and the topology of the transition section in six forms (e.g., linear, arc-shaped, linear thin-walled, and arc-shaped thin-walled) were optimized. Afterwards, finite element software ABAQUS was used to verify this model. Results show that the utilization rate of the arc-shaped thin-walled structure was the largest, and its basic transmission force was more straightforward together with smaller cross-section size at the same height and smaller influence on spoiler flow. In the second step, the detailed optimization of CBF was carried out using mathematical programming. Under the premise of minimum total construction cost, the body shape parameters of each part were set as design variables satisfying the corresponding strength, stiffness, and stability conditions; meanwhile, the minimum total structure weight was set as the objective function. MATLAB was used to solve the sequence quadratic programming (SQP) algorithm and hybrid genetic algorithm, and the optimal body parameters were obtained.
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Olunloyo, Vincent O. S., and Charles A. Osheku. "On Vibration and Noise Dissipation in Ship and FPSO Structures with Smart Systems." ISRN Mechanical Engineering 2012 (August 7, 2012): 1–19. http://dx.doi.org/10.5402/2012/127238.
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Ships and floating structure production systems are widely deployed for deep and ultradeep waters operation. Active vibration reduction and noise control in such structures can significantly improve their hydrodynamic performance and stability during navigation, exploration, and exploitation activities. One way to minimise or reduce the transmission of vibration in these moving offshore structures is to exploit the mechanism of interfacial slip in press fit joints or layered structural laminates in their internal hull configurations to dissipate vibration energy. In this paper, slip damping with heterogeneous sandwich composite viscoelastic beam-plate smart systems as a model for dissipation of vibration and active noise control mechanism in ship and floating structures is investigated. For this problem, a boundary value partial differential equation is formulated for the case of linear and nonlinear hydrodynamic wave loadings. In particular, the effect of pressure distribution variation at the interface of the layered smart system on the energy dissipation, logarithmic damping decrement, and spatial transfer function is analyzed and presented for design application and selection of appropriate stabilizers.
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Fonseca, Adriana C., Roberto Villaça, and Bastiaan Knoppers. "Reef Flat Community Structure of Atol das Rocas, Northeast Brazil and Southwest Atlantic." Journal of Marine Biology 2012 (2012): 1–10. http://dx.doi.org/10.1155/2012/179128.
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This study was conducted during 1999 to 2002 and addresses the community structure and some ecological aspects of the benthic reef flat assemblages of Atol das Rocas, located offshore the NE brazilian coast. It corresponds to the sole atoll of the SW Atlantic, which characterized by a shallow topography and is almost completely built by coralline algae. The turf forming red macroalgaeDigenea simplexand the crustose corallineHydrolithon pachydermumwere the dominant species of the reef flat. The crustose green macroalgaeDictyosphaeria ocellataand the turf forming red macroalgaeGelidiella acerosawere the subdominant species. Biomass values ofD. simplexwere about twice higher than the other species, pointing out to its relevance in the community structure of this reef zone. Biodiversity indices indicated a high equitability within the few species observed and a relative temporal stability of the community structure. Some local spatial variations were found in the community structure of the reef flat zone, enabling the definition of three subhabitats. The patterns of distribution and abundance of the benthic organisms seem to be related to the environmental conditions of the reef flat, such as low water turbulence, lengthy periods of aerial exposure, and low herbivore pressure.
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Kong, Fankai, Hengxu Liu, Binghan Wang, Huaqiu Ding, Zhen Jiang, Hailong Chen, Hongli Pan, and Weiming Su. "Wind-Load Response and Evacuation Efficiency Analysis of Marine Evacuation Inflatable Slide." Applied Sciences 10, no. 1 (December 18, 2019): 21. http://dx.doi.org/10.3390/app10010021.
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Flexible inflatable membrane structure has the characteristics of light weight, large span, and small stiffness, and it is very sensitive to wind load. Aiming at the dynamic response of marine evacuation inflatable slides under complex and changeable wind loads at sea, the response law of the inflatable slide under different wind directions, wind speeds, and internal pressure conditions is studied by using fluid–solid coupling theory. The most dangerous conditions of evacuation system installation and the ideal internal pressure of the inflatable slide meeting the stability requirements are deduced. The LS-DYNA module is used to simulate the inflation process of the slide. The evacuation sliding is rationally simplified. By changing the inflatable internal pressure of the slide, the variation law of displacement, deformation, and sliding speed of the slide is obtained, and the optimal inflation internal pressure satisfying the evacuation efficiency requirement is obtained. The results show that the inflow wind direction angle of 30° is the most dangerous condition for slideway installation, and the internal pressure of 4000 Pa is the ideal internal pressure to meet the double standards of stability and evacuation efficiency. The numerical results obtained are valuable for analyzing wind resistance of offshore inflatable membrane structures and their practical design and application in evacuation systems.