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Magray, Adil Ahmad, Amanpreet Tangri, Zehra Khan, and Naiyara Khan. "Foundation engineering for offshore gravity structures." IOP Conference Series: Earth and Environmental Science 889, no. 1 (2021): 012053. http://dx.doi.org/10.1088/1755-1315/889/1/012053.
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Abstract Gravity based structures are in play from early times. Numerous structures are being installed around the globe. These structures had shown a rigid face towards the harsh conditions/situation in the offshore environment. The key factors for sustainability are geotechnical design and the sub soil survey. These structures are used for collection, transport and also for temporary storage of crude gas and oil. These structures serve as a bridge between the much need fuel and the modern world. The installation of GBS involves major wings of modern engineering i.e. Mechanical, Structural, architecture and Geotechnical engineering because these structures are a great challenge as considering the harsh and hard off shore conditions. These structures are having a much importance apart from its features i.e. from the point of economy, as the oil prices are touching the heights, it influences construction of GBS. Now a days most of the multinational companies are focusing towards the construction of offshore GBS, as well as paying much attention on research work off these structures because to make huge profit. In this paper an effort has been made to understand the different aspects which are related to GBS i.e. pre-construction operations, soil investigation, construction, installment and some of the safety aspects as considering it one of the most focused topics now and in future.
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Wilms, Mayumi, Arne Stahlmann, and Torsten Schlurmann. "INVESTIGATIONS ON SCOUR DEVELOPMENT AROUND A GRAVITY FOUNDATION FOR OFFSHORE WIND TURBINES." Coastal Engineering Proceedings 1, no. 33 (2012): 35. http://dx.doi.org/10.9753/icce.v33.structures.35.
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Due to insufficient insights about the scour development around the STRABAG gravity foundation, the Franzius-Institute conducted small- and large-scale physical model tests in wave flumes on a scale of 1:50 and 1:17 in order to investigate the wave-induced scouring phenomena around the foundation and to design a scour protection system. The tests on scour development without a scour protection system show that the main areas which are vulnerable to scour are the contact areas of the foundation. Furthermore, the experiments show that a scour protection system is necessary for the given and investigated wave boundary conditions; the performance of the selected protection system using geotextile sand containers is verified. Additional numerical simulations indicate an amplification of the resulting flow around the foundation under combined loads (waves and current), but without significant change of the flow pattern
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Ghasempour, Roghayeh, V. S. Özgür Kirca, and B. Mutlu Sumer. "SCOUR AROUND AND SINKING OF SUBSEA STRUCTURES EXPOSED TO CURRENT AND WAVES." Coastal Engineering Proceedings, no. 38 (May 29, 2025): 127. https://doi.org/10.9753/icce.v38.structures.127.
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Many different subsea structures are used in the offshore industry, particularly for floating offshore wind farms, such as gravity anchors, tensioners, clump weights, and chains. Exposure of a subsea structure to currents and/or waves leads to changes in flow around the structure, forming flow contraction at the sides of the structure and secondary flow patterns such as horseshoe vortices, lee-wake vortices, and counter-rotating vortices (Sumer and Fredsøe, 2002). Often placed on erodible beds under current and/or wave action, scouring around these structures are experienced. The present paper presents the early results of an experimental study aiming to investigate the aforementioned scour and sinking processes around cuboid blocks (cubes, rectangular prisms and horizontal cylinders) under the action of waves, currents, and waves combined with currents.
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Wu, Tien H., Oddvar Kjekstad, In-Mo Lee, and Suzanne Lacasse. "Reliability analysis of foundation stability for gravity platforms in the North Sea." Canadian Geotechnical Journal 26, no. 3 (1989): 359–68. http://dx.doi.org/10.1139/t89-050.
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The uncertainties encountered in the evaluation of foundation stability for four offshore gravity structures in the North Sea are reviewed. The uncertainties include those about the load, the material type, the material strength, and the analytical method. The means and coefficients of variations of these are used as inputs to compute the mean and coefficient of variation of the safety factor and the reliability index. The latter are used to assess the effect of various options in site exploration and strength measurement on foundation reliability. Key words: foundation, gravity platforms, offshore structures, probability, reliability, shear strength, site investigation, stability.
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Ahmad, Omar. "An overview of design, construction and installation of gravity offshore platforms." International Journal of Advanced Engineering, Sciences and Applications 3, no. 1 (2022): 27–32. http://dx.doi.org/10.47346/ijaesa.v3i1.81.
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The offshore structures are used worldwide in different ways and for different purposes in a variety of weather conditions and water depths. The main aim of these structures is to explore and extract the gas and oil and it should works safely for approximately 25 years or more against some conditions. These structures plays a vital role on developing the economic level of the country and it is essential to be accurate in all of their planning, designing, manufacturing, transporting, and installing processes. There are many types these platforms which differ according to their function and the needed water depth. Gravity platform or condeep platform is one of these platforms which is fixed offshore platform, made by concrete. The purpose of this paper is to give some information overview about advantages, disadvantages, materials used, design, construction, transportation and installation of gravity platforms.
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Ombati, Dennis, John Githiri, Maurice K'Orowe, and Erick Nyakundi. "Delineation of Subsurface Structures Using Gravity Data of the Shallow Offshore, Lamu Basin, Kenya." International Journal of Geophysics 2022 (January 27, 2022): 1–12. http://dx.doi.org/10.1155/2022/3024977.
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Lamu Basin is located in South Eastern Kenya and covers about 170 000 km2 both onshore and offshore. Kenya’s Lamu Basin is hitherto underexplored even though there have been notable oil and gas discoveries along the margin of East Africa. This study focuses on the shallow section of the Lamu offshore bounded by 39°E to 43°E by 2°S to 6°S, whereby, unfortunately, some of the wildcat wells turned out to be dry although expensive. Gravity interpretation techniques such as spectral analysis and first horizontal derivative were applied to the reduced gravity data to delineate and model structures to minimize the high investment risks. The gravity data used in this study were sourced from the International Gravity Bureau (BGI) and National Oil Corporation of Kenya (NOCK) digital data courtesy of companies like Woodside Energy, Anadarko Kenya Limited, and Total Exploration and Production companies. The obtained reduced gravity data were gridded to produce the gravity anomaly grids (Free air, Bouguer, and Isostacy), which were consequently drawn into maps. From spectral analysis, depths to shallow sources and deep sources were estimated. These depths were used to set regional and residual separation filters using the Gaussian filter. The first horizontal derivative (FHD) applied to the regional Isostatic gravity anomaly map yielded features that were inferred as intrasediment fractures/faults trending in NW-SE and NE-SW directions. The features like the ridges, troughs, and faults mainly trending in the NW-SE direction are discernable from the regional anomaly map. The developed models show the basement highs and lows with a possibility of anticlinal and synclinal structures and thick sedimentary successions likely to represent good hydrocarbon source kitchens.
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Adakole Okpe, Samuel, and Joseph Ejelikwu Edeh. "Analysis, design and construction of gravity offshore structure; state-of-the-art." International Journal of Advanced Engineering, Sciences and Applications 3, no. 1 (2022): 12–17. http://dx.doi.org/10.47346/ijaesa.v3i1.74.
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Abstract: Offshore platforms are divided into many types which are mainly categorized according to waterdepth in the installation location. However, the design differs for each type to accomplish the target of the operation. But for some case of sea waterdepths and an aggressive environment such as the North Sea, steel ones are not suitable, so the heaviest type called gravity platform having enormous mass is used. This type of platform has its special requirements and procedures for construction and needs special types of construction materials in order to resist the climate factors applied due to the aggressive environment. The paper carefully illustrates how the principal Environmental loads (wind and wave), current forces, loads from ice and loads from earth-quake for (earth-quake prone zones) are deployed to archive the design and construction of offshore concrete gravity platforms. Two design methods (Analysis and Design of Shell structures) and the Tangent Modulus Methods of design of Offshore Concrete Gravity platforms are discussed
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Lv, Yi, Feng Yan Yang, Ming Wang Yang, Chen Gong, Jin Hua Liu, and Feng Jian Li. "Technical Study on Four-Crane Joint Lifting of Large-Sized Structures." Advanced Materials Research 945-949 (June 2014): 335–38. http://dx.doi.org/10.4028/www.scientific.net/amr.945-949.335.
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In recent years, due to rapid development of offshore engineering construction, offshore structure size and weight becomes larger and larger. In the process of offshore structures fabrication, the size and weight of the sub-structure is also becoming bigger, lifting method using single or two sets of cranes cannot meet the capacity requirement of the lifting operation, joint operation using four cranes is required in such cases. To solve this problem, this paper analyze the riskfactors(the uncertainty of the hook load, the inaccuracy of the center-of-gravity, limited working condition ) in the process of joint liftingusingfour crane.The paper also discusses the whole lifting process and simulates the process by usinganalysissoftware SACS, and the calculation result matches actual work very well.
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Esteban, M., José-Santos López-Gutiérrez, and Vicente Negro. "Gravity-Based Foundations in the Offshore Wind Sector." Journal of Marine Science and Engineering 7, no. 3 (2019): 64. http://dx.doi.org/10.3390/jmse7030064.
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In recent years, the offshore wind industry has seen an important boost that is expected to continue in the coming years. In order for the offshore wind industry to achieve adequate development, it is essential to solve some existing uncertainties, some of which relate to foundations. These foundations are important for this type of project. As foundations represent approximately 35% of the total cost of an offshore wind project, it is essential that they receive special attention. There are different types of foundations that are used in the offshore wind industry. The most common types are steel monopiles, gravity-based structures (GBS), tripods, and jackets. However, there are some other types, such as suction caissons, tripiles, etc. For high water depths, the alternative to the previously mentioned foundations is the use of floating supports. Some offshore wind installations currently in operation have GBS-type foundations (also known as GBF: Gravity-based foundation). Although this typology has not been widely used until now, there is research that has highlighted its advantages over other types of foundation for both small and large water depth sites. There are no doubts over the importance of GBS. In fact, the offshore wind industry is trying to introduce improvements so as to turn GBF into a competitive foundation alternative, suitable for the widest ranges of water depth. The present article deals with GBS foundations. The article begins with the current state of the field, including not only the concepts of GBS constructed so far, but also other concepts that are in a less mature state of development. Furthermore, we also present a classification of this type of structure based on the GBS of offshore wind facilities that are currently in operation, as well as some reflections on future GBS alternatives.
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Ali, Mohammed Y., Anthony B. Watts, and Asam Farid. "Gravity anomalies of the United Arab Emirates: Implications for basement structures and infra-Cambrian salt distribution." GeoArabia 19, no. 1 (2014): 143–58. http://dx.doi.org/10.2113/geoarabia1901143.
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ABSTRACT Gravity measurements onshore and offshore of the United Arab Emirates (UAE) have been used to construct a new Bouguer gravity anomaly map of the region. The gravity data, which has been gridded at 2,700 m × 2,700 m interval, has been used to constrain the tectonic elements, major lineation trends and structures of the Neoproterozoic basement of the Arabian Plate and the distribution of infra-Cambrian salt basins. Advanced transformation techniques (including first vertical derivative, total horizontal derivative, tilt derivative and Euler deconvolution) were applied to identify gravity source edges as an aid to structural interpretation and geological modelling of the study area. Three major structural provinces (fold-and-thrust belt, foreland and salt tectonic provinces) were identified based on the residual Bouguer gravity anomaly field. The eastern fold-and-thrust belt province is associated with short-wavelength positive gravity anomalies, which are attributed to the allochthonous series of the Semail Ophiolite and its related thrust sheets. The central foreland basin province is characterised by NNW-oriented negative gravity anomalies associated with deepening of the basement and thickening of Aruma and Pabdeh sediments in the foredeep basins and flexure of the top and base of the crust by the load of the Semail Ophiolite. The western salt tectonic province displays well-defined local gravity lows superimposed on a regional gravity high, which probably reflects the swelling of infra-Cambrian salt above a shallowing of the basement and thinning of the foredeep sediments. In addition, gravity modelling constrained by seismic and well data indicates the presence of substantial infra-Cambrian salt bodies in all basins of the UAE both onshore and offshore including the southern area of the Rub’ Al-Khali Basin. An extensive array of previously unmapped N-S, NW- and SW-trending lineaments affecting the basement and possibly overlying sediments are mapped in the UAE. The N-S Arabian trending lineament represents the effect of a major structure, along which many important oilfields are located (e.g. Bu Hasa). The SW trend has regular spacing and is dominant in the southern and central part of Abu Dhabi, east of the Falaha syncline. The NW-SE lineament is the most striking and includes two well-defined trends that cross Abu Dhabi Emirate, which in this paper are named as the Abu Dhabi Lineaments. These lineaments are associated with a linear gravity high extending from the southwestern border with Oman to the offshore close to Zakum oilfield. They are probably related to the Najd Fault System.
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Vázquez, K., R. R. Rodríguez, and M. D. Esteban. "Inventory proposal for gravity-based support structures in offshore wind farms." Ocean Engineering 266 (December 2022): 113098. http://dx.doi.org/10.1016/j.oceaneng.2022.113098.
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Ma, Guoqing, Zhexin Jiang, Rui Cao, et al. "The Joint Inversion of Seismic Ambient Noise and Gravity Data in an Ellipsoidal Coordinate System: A Case Study of Gold Deposits in the Jiaodong Peninsula." Minerals 15, no. 5 (2025): 488. https://doi.org/10.3390/min15050488.
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The three-dimensional inversion of geophysical data is an effective method for analyzing underground structures. The seismic method is widely used due to its high resolution. However, the uneven distribution of seismic stations, especially in offshore areas, increases the uncertainty of inversion results. Gravity data are easy to obtain and offer high lateral resolution. For the influence of the Earth’s curvature in large-scale inversion, we first developed the joint inversion method of seismic ambient noise and gravity data in the ellipsoidal coordinate system, achieving the acquisition of large-scale and high-precision underground density and velocity structures. Experiments were conducted to address the uneven distribution of seismic stations, which proved the accuracy of the method. The proposed method was applied to the Jiaodong Peninsula (China) to obtain the transcrustal property distribution, further revealing that gold deposits are formed by the upwelling and condensation of hydrothermal materials, which causes the destruction of the North China Craton caused by the subduction of the Western Pacific Plate. Furthermore, we inverted the high-precision gravity anomaly of Sanshan Island, obtaining the structural distribution and predicting the distribution of offshore gold deposits.
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Jamaludin, Siti Nur Fathiyah, Manuel Pubellier, and Benjamin Sautter. "Shallow vs. Deep Subsurface Structures of Central Luconia Province, Offshore Malaysia Reveal by Aeromagnetic, Airborne Gravity and Seismic Data." Applied Sciences 11, no. 11 (2021): 5095. http://dx.doi.org/10.3390/app11115095.
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Across the Luconia continental shelf, the nature and structures of the crust are lacking geological understanding and precise characterization. Newly acquired, aeromagnetic, and airborne gravity data were used to assess deep and shallow sub-surface signals within the Central Luconia Province, off the coast of Sarawak, offshore Malaysia. Regional aeromagnetic anomalies appear to primarily reflect deep crustal features while depth (Z) tensors of airborne gravity anomalies evidence shallow subsurface structures. Strike directions of the interpreted structural trend on aeromagnetic and airborne gravity anomalies maps are measured and plotted into rose diagrams to distinguish the structural orientations for all datasets. Signature patterns extracted from the depth profiles were correlated with parallel seismic lines and nearest exploration wells and coincide well with the top of carbonate for Cycle IV/V and structures seen within the Cycle I and II sediments. The orientation of faults/lineaments at shallower depth is dominated by a NW-SE orientation, similar with the faults extracted from two recently published structural maps. Deeper subsurface sections yielded E-W to NWW-SEE dominant directions which were never presented in the published literature. The E-W oriented anomalies are postulated to represent the remnants of the accretion between the Luconia crustal block and southern boundary of the Palawan block. The NW-SE trend follows the same direction as prominent faults in the region. The insight into shallow and deep subsurface structures in Central Luconia Province imaged through airborne gravity and aeromagnetic data should provide guidelines and complementary information for regional structural studies for this area, particularly in combination with detailed seismic interpretation. Further evaluation on the response of Air-FTG® gravity and aeromagnetic could lead to the zonation of potential basement highs and hydrocarbon prospects in this area.
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Gallardo‐Delgado, Luis A., Marco Antonio Pérez‐Flores, and Enrique Gómez‐Treviño. "A versatile algorithm for joint 3D inversion of gravity and magnetic data." GEOPHYSICS 68, no. 3 (2003): 949–59. http://dx.doi.org/10.1190/1.1581067.
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We describe the implementation of a versatile method for interpreting gravity and magnetic data in terms of 3D structures. The algorithm combines a number of features that have proven useful in other algorithms. To accommodate structures of arbitrary geometry, we define the subsurface using a large number of prisms, with the depths to the tops and bottoms as unknowns to be determined by optimization. Included in the optimization process are the three components of the magnetization vector and the density contrast, which is assumed to be a continuous function with depth. We use polynomial variations of the density contrast to simulate the natural increase of rock density with depth in deep sedimentary basins. The algorithm minimizes the quadratic norm of residuals combined with a regularization term. This term controls the roughness of the upper and lower topographies defined by the prisms. This results in simple shapes by penalizing the norms of the first and second horizontal derivatives of the prism depths and bottoms. Finally, with the use of quadratic programming, it is a simple matter to include a priori information about the model in the form of equality or inequality constraints. The method is first tested using a hypothetical model, and then it is used to estimate the geometry of the Ensenada basin by means of joint inversion of land and offshore gravity and land, offshore, and airborne magnetic data. The inversion helps constrain the structure of the basin and helps extend the interpretation of known surface faults to the offshore.
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Moraes, Roberto A. V., and R. O. Hansen. "Constrained inversion of gravity fields for complex 3-D structures." GEOPHYSICS 66, no. 2 (2001): 501–10. http://dx.doi.org/10.1190/1.1444940.
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As part of a research program to develop gravity interpretation tools that can be merged with seismic techniques, a full 3-D complex structural inversion scheme for (possibly multibody) polyhedral models has been developed. The forward modeling algorithm was adopted from previous work. Because the inverse problem is generally very ill posed, several methods of regularizing the inversion were investigated and a combination of the most useful was adopted. The combination includes (i) a structured matrix formulation for the system equations, (ii) an analytical expression for the Jacobian calculation, (iii) first‐derivative damping, (iv) a choice of damping parameter based on a variation of the trust region method, (v) a weighted scheme for parameter correction, and (vi) complete freezing of degrees of freedom found not to influence the gravity field significantly. This combination yields a robust inversion which was successfully demonstrated on data over the Galveston Island salt dome, offshore Texas. Variations of the technique should be applicable to magnetic data, which would make the method useful for mining problems and petroleum exploration settings involving volcanic structures.
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Bodard, J. M., J. G. Creer, and M. W. Asten. "Next Generation High Resolution Airborne Gravity Reconnaissance in Oil Field Exploration." Energy Exploration & Exploitation 11, no. 3-4 (1993): 198–234. http://dx.doi.org/10.1177/0144598793011003-402.
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Simple modelling studies of gravity fields using elementary structural forms, oilfield-type structures and geological reconnaissance situations, show that gravity gradiometry technology offers significant petroleum exploration potential. In geological environments of interest, gravity gradients are primarily due to density displacement along (near) vertical boundaries. Gradient images therefore reveal the edges and corners of intrusions, faults, fault intersections, and other such structures often associated with hydrocarbon migration pathways and traps, and/or significant basinal trends. Recent technological advances may make gravity gradiometry an airborne reconnaissance tool capable of providing sensitivity and resolution superior to the best gravimetry available today. This capacity, and the array of gradient components that may be measured, will embellish aspects of the gravity field important to developing regional geologic interpretations. While the potential advantage of gravity gradiometry is greater lateral resolution and sensitivity from a moving platform, the disadvantage is the high sensitivity to topographic and shallow buried irregularities unrelated to the deeper geological structures of interest. A further difficulty is the complex gravity field representations produced for density structures of certain geometries. Buried features that have near surface expressions will be easiest to map. However, full use of gravity gradient technology will require application-focused data processing techniques and new interpretation skills. When the technology becomes commercially available it could find application in preseismic reconnaissance, structural (and possibly stratigraphic) mapping, acreage management and assessment, and in the evolution and mapping of controls on oilfield distribution. The technology could help develop exploration in remote and inaccessible areas, and provide a new look at well-explored regions. An immediate practical implementation appears to be in offshore exploration applications, possibly linked to deepwater exploitation strategies.
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Woo, Donghan, and Mitsuru Kitamura. "Numerical Prediction of Welding Distortion Considering Gravity Force on General Ship Grillage Structure by Elastic Finite Element Method Using Inherent Strain." Journal of Marine Science and Engineering 8, no. 6 (2020): 454. http://dx.doi.org/10.3390/jmse8060454.
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The accurate numerical prediction of welding deformation is important to improve the structural safety of ships and offshore structures in heavy industries. The precise reflection of the real working condition in the numerical prediction is an essential factor to improve its result. In the present study, the effect of the gravity force on numerical prediction of the optimal welding sequence of a general ship grillage structure was validated with the introduction of a new boundary condition in which the structure is placed over rails. Additionally, the direction of the gravity force of welded structures could be changed at the final assembly process according to the production plan. The effect of the gravitational orientation on the final welding displacements was also investigated herein. The elastic finite element method using the inherent strain, interface element, and multipoint constraint function was introduced to analyze the welding deformation. This study validated the influence of the gravity force on the numerical prediction of welding displacements in a general ship grillage structure.
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Barari, Amin, and Lars Bo Ibsen. "VERTICAL CAPACITY OF BUCKET FOUNDATIONS IN UNDRAINED SOIL." JOURNAL OF CIVIL ENGINEERING AND MANAGEMENT 20, no. 3 (2014): 360–71. http://dx.doi.org/10.3846/13923730.2013.801915.
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Offshore wind turbine structures are traditionally founded on gravity concrete foundations or mono-piles. Bucket foundations were developed for the offshore oil and gas industry and are now being used in wind turbine construction. The loading in this application is characterized by a vertical load due to the slender construction combined with horizontal forces inducing a large overturning moment. Field tests on bucket foundations were performed to gain insight into the vertical load response of bucket foundations in clay soils. The field tests were accompanied by finite element numerical simulations in order to provide a better understanding of the parameters influencing bucket foundation behaviour.
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Frederking, R. M. W., and G. W. Timco. "Quantitative Analysis of Ice Sheet Failure Against an Inclined Plane." Journal of Energy Resources Technology 107, no. 3 (1985): 381–87. http://dx.doi.org/10.1115/1.3231205.
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The main force components on inclined offshore structures in the Arctic include the flexural and crushing behavior of the ice sheet, rotation and translation of broken ice, gravity and buoyancy in lifting and moving ice, and friction between ice and structure. Tests were carried out to isolate these components and analytical expressions were derived for them. Measured and predicted components compare favorably, the analytical model overpredicting by about 20 percent.
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Esteban, M. D., B. Couñago, J. S. López-Gutiérrez, V. Negro, and F. Vellisco. "Gravity based support structures for offshore wind turbine generators: Review of the installation process." Ocean Engineering 110 (December 2015): 281–91. http://dx.doi.org/10.1016/j.oceaneng.2015.10.033.
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Wang, Zhaoling. "New Hamiltonian equations of high accuracy for ocean waves with applications in determining wave forces on offshore structures." Multidiscipline Modeling in Materials and Structures 13, no. 3 (2017): 489–500. http://dx.doi.org/10.1108/mmms-06-2017-0057.
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Purpose The purpose of this paper is to propose a new approach to further obtain reduced Hamiltonian equations for certain nonlinear cases of finite amplitude. Design/methodology/approach Chebyshev polynomials are introduced to best approximate the primitive exact wave equations. Findings New results are derived for certain nonlinear cases of finite amplitude. Furthermore, ranges of applicability are determined in conjunction with the error analyses for various cases. In particular, the new structure can give a new highly accurate formula for determining the wave forces of the offshore structures. Originality/value New reduced Hamiltonian equations for nonlinear surface gravity waves have been derived for certain cases of finite amplitude for the first time. And the new structure can give a new highly accurate formula for determining the wave forces of offshore structures. These results extend the usual results for weakly nonlinear surface waves to nonlinear surface waves over certain finite ranges.
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Durling, P., K. Howells, and P. Harvey. "The near-surface geology of St. Georges Bay, Nova Scotia: implications for the Hollow Fault." Canadian Journal of Earth Sciences 32, no. 5 (1995): 603–13. http://dx.doi.org/10.1139/e95-051.
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A formline contour map, which depicts the near-surface, structural configuation of the strata underlying St. Georges Bay, northeastern Nova Scotia, was made from bedding attitude data compiled in the coastal areas; apparent dips measured from single-channel seismic reflection data; and true strikes and dips calculated at survey track intersections. The geology interpreted from the formline map is characterized by northeast-striking faults and fold axes. The folds in the bay comprise broad, open synclines and narrow, tightly folded or faulted anticlines. Gravity and deep seismic reflection data suggest that the faulted anticlines are intruded by salt. Correlations from offshore to onshore suggest that the structures mapped offshore in the bay extend onshore. The onshore extensions of the faulted anticlines are mapped as faults, and their antiformal nature is subdued. They are locally associated onshore with Carboniferous Windsor Group outcrop. The offshore extension of the Hollow Fault, which is interpreted as a major northeast-striking, Carboniferous strike-slip fault, was mapped as a 1500–2500 m wide deformation zone, using deep seismic reflection data. Gravity lows coincident with the deformation zone are interpreted as being caused by salt intrusions. The trend of the Hollow Fault Zone suggests that this fault complex (and its associated strike-slip movement) continues on land near Mabou, Cape Breton Island. However, it does not appear to continue offshore along the northwest coast of Cape Breton Island, as previously suggested.
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Sánchez, Sergio, José-Santos López-Gutiérrez, Vicente Negro, and M. Dolores Esteban. "Foundations in Offshore Wind Farms: Evolution, Characteristics and Range of Use. Analysis of Main Dimensional Parameters in Monopile Foundations." Journal of Marine Science and Engineering 7, no. 12 (2019): 441. http://dx.doi.org/10.3390/jmse7120441.
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Renewable energies are the future, and offshore wind is undoubtedly one of the renewable energy sources for the future. Foundations of offshore wind turbines are essential for its right development. There are several types: monopiles, gravity-based structures, jackets, tripods, floating support, etc., being the first ones that are most used up to now. This manuscript begins with a review of the offshore wind power installed around the world and the exposition of the different types of foundations in the industry. For that, a database has been created, and all the data are being processed to be exposed in clear graphic summarizing the current use of the different foundation types, considering mainly distance to the coast and water depth. Later, the paper includes an analysis of the evolution and parameters of the design of monopiles, including wind turbine and monopile characteristics. Some monomials are considered in this specific analysis and also the soil type. So, a general view of the current state of monopile foundations is achieved, based on a database with the offshore wind farms in operation.
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Næss, Jacqueline, Svein Inge Giske, and Lars Bjerkeli. "Concrete gravity-based structures used for offshore LNG storage and regasification in the Adriatic Sea." Structural Concrete 11, no. 2 (2010): 73–81. http://dx.doi.org/10.1680/stco.2010.11.2.73.
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Jia, Junbo. "The effect of gravity on the dynamic characteristics and fatigue life assessment of offshore structures." Journal of Constructional Steel Research 118 (March 2016): 1–21. http://dx.doi.org/10.1016/j.jcsr.2015.09.013.
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Neelamani, S., K. Al-Salem, and K. Rakha. "Extreme Gravity Waves In The Arabian Gulf." Journal of Engineering Research [TJER] 6, no. 1 (2009): 21. http://dx.doi.org/10.24200/tjer.vol6iss1pp21-36.
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The extreme significant wave heights and the corresponding mean wave periods were predicted for return periods of 12, 25, 50, 100 and 200 years for 38 different locations in the territorial and offshore locations of countries surrounding the Arabian Gulf. The input wave data for the study is hindcast waves obtained using a WAM model for a total period of 12 years, (1993 to 2004). The peak over threshold method (with 1.0 m as threshold value), is used for selecting the data for the extreme wave analysis. In general, a Weibull distribution is found to fit the data well compared to the Gumbel distribution for all these locations. From the joint probability of wave height and wave period, a simple polynomial relationship (Tmean = C3 (Hs)C4) is used to obtain the relationship between the significant wave height and mean wave period for all the 38 locations. The value of C3 is found to vary from 3.8 to 4.8 and the value of C4 is found to vary from 0.19 to 0.32. The mean wave period was found to be more sensitive to change in locations within the Gulf and it is less sensitive to change in return periods from 12 years to 200 years. The significant wave heights for 100 year return period varied from 3.0 to 4.5 for water depths of 9 to 16 m, whereas in the offshore sites (depths from 30 to 60 m) it varied from 5.0 to 7.0 m. A large number of coastal projects are in progress in the Arabian Gulf and many new projects are being planned in this region for the future. The results of the present study will be highly useful for optimal design of the ocean structures for these projects.
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Hassan, Soha, Mohamed Sultan, Mohamed Sobh, et al. "Crustal Structure of the Nile Delta: Interpretation of Seismic-Constrained Satellite-Based Gravity Data." Remote Sensing 13, no. 10 (2021): 1934. http://dx.doi.org/10.3390/rs13101934.
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Interpretations of the tectonic setting of the Nile Delta of Egypt and its offshore extension are challenged by the thick sedimentary cover that conceals the underlying structures and by the paucity of deep seismic data and boreholes. A crustal thickness model, constrained by available seismic and geological data, was constructed for the Nile Delta by inversion of satellite gravity data (GOCO06s), and a two-dimensional (2D) forward density model was generated along the Delta’s entire length. Modelling results reveal the following: (1) the Nile Delta is formed of two distinctive crustal units: the Southern Delta Block (SDB) and the Northern Delta Basin (NDB) separated by a hinge zone, a feature widely reported from passive margin settings; (2) the SDB is characterized by an east–west-trending low-gravity (~−40 mGal) anomaly indicative of continental crust characteristics (depth to Moho (DTM): 36–38 km); (3) the NDB and its offshore extension are characterized by high gravity anomalies (hinge zone: ~10 mGal; Delta shore line: >40 mGal; south Herodotus Basin: ~140 mGal) that are here attributed to crustal thinning and stretching and decrease in DTM, which is ~35 km at the hinge zone, 30–32 km at the shoreline, and 22–20 km south of the Herodotus Basin; and (4) an apparent continuation of the east-northeast–west-southwest transitional crust of the Nile Delta towards the north-northeast–south-southwest-trending Levant margin in the east. These observations together with the reported extensional tectonics along the hinge zone, NDB and its offshore, the low to moderate seismic activity, and the absence of volcanic eruptions in the Nile Delta are all consistent with the NDB being a non-volcanic passive margin transition zone between the North African continental crust (SDB) and the Mediterranean oceanic crust (Herodotus Basin), with the NDB representing a westward extension of the Levant margin extensional transition zone.
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Manzano-Agugliaro, Francisco, Miguel Sánchez-Calero, Alfredo Alcayde, Carlos San-Antonio-Gómez, Alberto-Jesús Perea-Moreno, and Esther Salmeron-Manzano. "Wind Turbines Offshore Foundations and Connections to Grid." Inventions 5, no. 1 (2020): 8. http://dx.doi.org/10.3390/inventions5010008.
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Most offshore wind farms built thus far are based on waters below 30 m deep, either using big diameter steel monopiles or a gravity base. Now, offshore windfarms are starting to be installed in deeper waters and the use of these structures—used for oil and gas like jackets and tripods—is becoming more competitive. Setting aside these calls for direct or fixed foundations, and thinking of water depths beyond 50 m, there is a completely new line of investigation focused on the usage of floating structures; TLP (tension leg platform), Spar (large deep craft cylindrical floating caisson), and semisubmersible are the most studied. We analyze these in detail at the end of this document. Nevertheless, it is foreseen that we must still wait sometime before these solutions, based on floating structures, can become truth from a commercial point of view, due to the higher cost, rather than direct or fixed foundations. In addition, it is more likely that some technical modifications in the wind turbines will have to be implemented to improve their function. Regarding wind farm connections to grid, it can be found from traditional designs such as radial, star or ring. On the other hand, for wind generator modeling, classifications can be established, modeling the wind turbine and modeling the wind farm. Finally, for the wind generator control, the main strategies are: passive stall, active stall, and pitch control; and when it is based on wind generation zone: fixed speed and variable speed. Lastly, the trend is to use strategies based on synchronous machines, as the permanent magnet synchronous generator (PMSG) and the wound rotor synchronous generator (WRSG).
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Luengo Frades, Jorge, Vicente Negro, Javier García Barba, et al. "Preliminary Design for Wave Run-Up in Offshore Wind Farms: Comparison between Theoretical Models and Physical Model Tests." Energies 12, no. 3 (2019): 492. http://dx.doi.org/10.3390/en12030492.
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Estimation of wave run-up has been of increasing concern for offshore wind structures and a critical aspect for designers. The highly nonlinear phenomenon makes the study difficult. That is the reason for the very few design rules and experimental data available to estimate it. Actual wave run-up is greater than commonly predicted. The goal of this research is to benchmark the theoretical formulations with the results of the physical model tests performed by Deltares in the field of crest elevation, run-up, forces and pressures. The laboratory reproduced in a wave tank (75 m length; 8.7 m width; 1 m depth; and a 1:60 scale, with Froude similarity) an offshore power converter platform located at intermediate water depths (25–43.80 m) in the Southern North Sea, designed by the Norwegian company Aibel. The purpose of this research is to offer a preliminary design guide for wave run–up using theoretical expressions both for cylinders and gravity based structures (GBS), leaning on the cited laboratory tests to validate the results obtained by such theoretical models.
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Cornett, Andrew, and Scott Baker. "ON THE IMPORTANCE OF CONSIDERING MULTIPLE SEASTATE REALIZATIONS WHEN ESTIMATING DESIGN LOADS IN MULTI-DIRECTIONAL SHALLOW-WATER WAVES." Coastal Engineering Proceedings, no. 36v (December 28, 2020): 46. http://dx.doi.org/10.9753/icce.v36v.management.46.
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The objectives of this work are to close some of the knowledge gaps facing designers tasked with designing new offshore structures or upgrading older structures located in shallow waters and exposed to energetic multi-directional waves generated by passing hurricanes or cyclones. This will be accomplished by first investigating and characterizing the natural variability of the maximum wave heights and crest elevations found in multiple 2-hour long realizations of several short-crested shallow-water near-breaking seastates. Following this, the variability and repeatability of peak pressures and peak loads exerted on a 1/35 scale model of a gravity-based offshore structure are explored. The analysis focuses on establishing extreme value distributions for each realization, quantifying their variability, and exploring how the variability is diminished when results from multiple seastate realizations and repeated tests are combined. The importance of considering multiple realizations of a design wave condition when estimating peak values for use in design is investigated and highlighted.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/16bCsMd0OMc
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Aliyeva, Sevda, and Mahmud Ismayilov. "RESEARCH OF THE WAVE FACTOR INFLUENCING HYDRAULIC STRUCTURES." ETM - Equipment, Technologies, Materials 05, no. 01 (2021): 81. http://dx.doi.org/10.36962/etm0501202081.
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It is known that a large block of deep-sea foundations consists of a truss sheathed with wood, a metal beam system, floating structures and four pyramidal metal blocks with a truss structure. The design characteristics of the foundations of oil platforms depend on the conditions under which the vertical interaction, along with the calculation of permanent and temporary loads, is accompanied by the specific gravity of drilling equipment and rigs or horizontal wind pressure, as well as the influence of horizontal wave loads on the foundation blocks. Horizontal waves and wind loads can be constant and variable in different conditions, therefore the effect of each of these loads on the device must be considered separately. To determine the wave pressure acting on the support blocks of stationary offshore installations, SN-92-60 was used under the editorship of the team of authors under the leadership of Doctor of Technical Sciences, Professor N.N.Tsunkov. Keywords: hydraulic structures, wave factor, wave pressure, wave profile, pressure diagrams, 3D model.
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Wang, Zhen-Ming, Kyong-Ho Chang, Shazia Muzaffer, and Mikihito Hirohata. "Fatigue Life and Crack Initiation in Monopile Foundation by Fatigue FE Analysis." Processes 11, no. 5 (2023): 1317. http://dx.doi.org/10.3390/pr11051317.
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The construction of new renewable energy infrastructures and the development of new ocean resources continues to proceed apace. In this regard, the increasing size and capacity of offshore wind turbines demands that the size of their accompanying supporting marine structures likewise increase. The types of marine structures utilized for these offshore applications include gravity base, monopile, jacket, and tripod structures. Of these four types, monopile structures are widely used, given that they are comparatively easy to construct and more economical than other structures. However, constant exposure to harsh cyclic environmental loads can cause material deterioration or the initiation of fatigue cracks, which can then lead to catastrophic failures. In this paper, a 3D fatigue finite element analysis was performed to predict both the fatigue life and the crack initiation of a welded monopile substructure. The whole analysis was undertaken in three steps. First, a 3D non-steady heat conduction analysis was used to calculate the thermal history. Second, a thermal load was induced, as an input in 3D elastoplastic analysis, in order to determine welding residual stresses and welding deformation. Finally, the plastic strain and residual stress were used as inputs in a 3D fatigue FE analysis in order to calculate fatigue crack initiation and fatigue life. The 3D fatigue finite element analysis was based on continuum damage mechanics (CDM) and elastoplastic constitutive equations. The results obtained from the 3D fatigue finite element analysis were compared with hot spot stresses and Det Norske Veritas (DNV-GL) standards.
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De Ritis, Riccardo, Luca Cocchi, Salvatore Passaro, Thomas Campagne, and Gianluca Gabriellini. "Bouguer Anomaly Re-Reduction and Interpretative Remarks of the Phlegraean Fields Caldera Structures (Southern Italy)." Remote Sensing 15, no. 1 (2022): 209. http://dx.doi.org/10.3390/rs15010209.
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Phlegraean Fields is a large, active caldera located in the densely populated westernmost sector of Naples’s Bay (Southern Italy). Several Bouguer anomaly surveys are available for this area with different resolution and accuracy; gravity data derive from the integration of stations placed below and above the sea level as the caldera develops both onshore and offshore. The comparison of these maps with the Digital Elevation Model shows a still remaining Terrain Effect hiding the shallower and deep caldera structure’s signal. This effect has an impact on the modelling of the gravity source’s depth and geometry. In this research, we apply a geologically constrained terrain correction method to the higher resolution Free Air dataset available for the study area to enhance the complete Bouguer reduction. The correlation analysis between the residual and the topography allows us to assess the quality of the outcomes. The results represent an improvement in the anomalies’ isolation and clearly show a continuous circular-like clustering of maxima related to the geometry of the caldera rim. The minima are associated with volcano-tectonic depression filled with pyroclastic and sediment. Furthermore, features alignments overlap the fault systems, along which the volcanic activity occurred.
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Bea, R. G. "Evaluation of Uncertainties in Loadings on Offshore Structures due to Extreme Environmental Conditions." Journal of Offshore Mechanics and Arctic Engineering 115, no. 4 (1993): 237–45. http://dx.doi.org/10.1115/1.2920118.
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This paper summarizes results from a Canadian Standards Association (CSA) sponsored study of the uncertainties associated with extreme (1000 to 10,000-yr return periods) environmental loadings acting on offshore structures (Bea, 1991). The evaluations of the loadings addressed loading effects that resulted from dynamic and nonlinear interactions of the structures. Loading uncertainties were organized and characterized in two categories: 1) inherent randomness (aleatory uncertainty), and 2) analytical variability (epistemic uncertainty). The study addressed the global ultimate limit state performance of three structures designed according to the provisions of the draft CSA guidelines (1989a, 1989b) for offshore structures: 1) a concrete Gravity Base Structure (GBS) located off the East coast of Canada (Hibernia), 2) a steel pile template located on the Scotian Shelf off Sable Island, and 3) a caisson retained island located in the Mackenzie Delta area of the Beaufort Sea (Amuligak). The results of this study indicate that, based on presently available information and data, it is often not possible to develop unambiguous characterizations of uncertainties. The different technical communities that background environmental conditions and forces (storms, earthquakes, ice) recognize and integrate these uncertainties into loading characterizations in different ways. In many cases, major sources of uncertainty are not included in probabilistic characterizations. Because of the needs for design code information sensitivity and consistency in demonstrating compliance with target reliability goals, there is a need for well-organized and definitive evaluations of uncertainties in extreme environmental loadings and load effects (Bitner-Gregersen et al., 1993).
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Peng, Xi, Yuanyuan Zhou, Li Wang, and Zhaoqian Liu. "Folding of Oceanic Crust Along the Davie Fracture Zone, Offshore Tanzania." Journal of Marine Science and Engineering 13, no. 6 (2025): 1179. https://doi.org/10.3390/jmse13061179.
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The Davie Fracture Zone (Davie FZ)—among the longest offshore transform systems in East Africa—mediated Madagascar’s southward displacement following Gondwana’s Early Jurassic breakup. This giant structure has a distinct topography and gravity field signals. However, it is buried by thick sediments in its northern segment offshore Tanzania, hindering understanding of the internal structures and their origin. In this study, we applied 2-D multichannel seismic to analyze the structural characteristics and evolution of the Davie FZ. The Davie FZ is located in the oceanic domain, which is bordered by the landwards-dipping overthrust fault at the continent–ocean boundary. Volcano sediments atop the basement with undulating Moho reflection below depict a typical oceanic domain. Distinct compressive deformation characterized by the crustal undulation of around 40 km wavelength forms folded oceanic crust, and Late Jurassic sediments onlap onto the crest of the folded basement. The Davie FZ is localized in a corridor with the thickened oceanic crust and is presented by positive flower structures with faulted uplifted basement and deepened Moho. The Davie FZ evolved from a proto-transform fault located in Gondwana before the spreading of the West Somali Basin. During the Late Jurassic, a kinematic change shifted the spreading direction from NW–SE to N–S, resulting in a strike-slip of the Davie FZ and contemporaneous transpressional deformation offshore Tanzania. The Davie FZ is an excellent case to understand the tectonic-magmatic process forming this transform margin.
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Crouse, C. B., and Jeff McGuire. "Energy Dissipation in Soil-Structure Interaction." Earthquake Spectra 17, no. 2 (2001): 235–59. http://dx.doi.org/10.1193/1.1586174.
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Energy dissipation as a means of reducing the seismic response of structures has become a popular topic among researchers and structural engineers who have developed and implemented devices, such as friction dampers, fluid dampers, and isolators, in the design or retrofit of structures. However, a natural source of energy dissipation is the interaction between a structure, its foundation, and the supporting soil medium. To account for this frequency-dependent energy dissipation in dynamic analysis based on modal superposition, relatively simple and practical systems-identification methods are presented to estimate the composite modal damping ratios for the significant modes of vibration. SSI experiments and analysis of simple theoretical models using this method have yielded relatively large modal damping ratios in certain situations for structures such as short to mid-rise buildings, short-span bridges, flat bottom fuel storage tanks, offshore concrete gravity platforms, nuclear power plant containments, and nuclear waste processing plants.
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Vu, Dinh Toan, Jérôme Verdun, José Cali, et al. "High-Resolution Gravity Measurements on Board an Autonomous Underwater Vehicle: Data Reduction and Accuracy Assessment." Remote Sensing 16, no. 3 (2024): 461. http://dx.doi.org/10.3390/rs16030461.
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Gravity on Earth is of great interest in geodesy, geophysics, and natural resource exploration. Ship-based gravimeters are a widely used instrument for the collection of surface gravity field data in marine regions. However, due to the considerable distance from the sea surface to the seafloor, the spatial resolution of surface gravity data collected from ships is often insufficient to image the detail of seafloor geological structures and to explore offshore natural minerals. Therefore, the development of a mobile underwater gravimetry system is necessary. The GraviMob gravimeter, developed for a moving underwater platform by Geo-Ocean (UMR 6538 CNRS-Ifremer-UBO-UBS), GeF (UR4630, Cnam) and MAPPEM Geophysics, has been tested over the last few years. In this study, we report on the high-resolution gravity measurements from the GraviMob system mounted on an Autonomous Underwater Vehicle, which can measure at depths of up to several kilometres. The dedicated GraviMob underwater gravity measurements were conducted in the Mediterranean Sea in March 2016, with a total of 26 underwater measurement profiles. All these measurement profiles were processed and validated. In a first step, the GraviMob gravity measurements were corrected for temperature based on a linear relationship between temperature and gravity differences. Through repeated profiles, we acquired GraviMob gravity measurements with an estimated error varying from 0.8 to 2.6 mGal with standard deviation after applying the proposed temperature correction. In a second step, the shipborne gravity data were downward continued to the measurement depth to validate the GraviMob measurements. Comparisons between the corrected GraviMob gravity anomalies and downward continued surface shipborne gravity data revealed a standard deviation varying from 0.8 to 3.2 mGal and a mean bias value varying from −0.6 to 0.6 mGal. These results highlight the great potential of the GraviMob system in measuring underwater gravity.
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Fichler, Christine, Egil Rundhovde, Stale Johansen, and Bjorn Saether. "Barents Sea tectonic structures visualized by ERS1 satellite gravity data with indications of an offshore Baikalian trend." First Break 15, no. 11 (1997): 355–63. http://dx.doi.org/10.1046/j.1365-2397.1997.00678.x.
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Telmat, Hamid, Jean-Claude Mareschal, and Clément Gariépy. "The gravity field over the Ungava Bay region from satellite altimetry and new land-based data: implications for the geology of the area." Canadian Journal of Earth Sciences 36, no. 1 (1999): 75–89. http://dx.doi.org/10.1139/e98-085.
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Gravity data were obtained along two transects on the southern coast of Ungava Bay, which provide continuous gravity coverage between Leaf Bay and George River. The transects and the derived gravity profiles extend from the Superior craton to the Rae Province across the New Quebec Orogen (NQO). Interpretation of the transect along the southwestern coast of Ungava Bay suggests crustal thickening beneath the NQO and crustal thinning beneath the Kuujjuaq Terrane, east of the NQO. Two alternative interpretations are proposed for the transect along the southeastern coast of the bay. The first model shows crustal thickening beneath the George River Shear Zone (GRSZ) and two shallow bodies correlated with the northern extensions of the GRSZ and the De Pas batholith. The second model shows constant crustal thickness and bodies more deeply rooted than in the first model. The gravity models are consistent with the easterly dipping reflections imaged along a Lithoprobe seismic line crossing Ungava Bay and suggest westward thrusting of the Rae Province over the NQO. Because no gravity data have been collected in Ungava Bay, satellite altimetry data have been used as a means to fill the gap in data collected at sea. The satellite-derived gravity data and standard Bouguer gravity data were combined in a composite map for the Ungava Bay region. The new land-based gravity measurements were used to verify and calibrate the satellite data and to ensure that offshore gravity anomalies merge with those determined by the land surveys in a reasonable fashion. Three parallel east-west gravity profiles were extracted: across Ungava Bay (59.9°N), on the southern shore of the bay (58.5°N), and onshore ~200 km south of Ungava Bay (57.1°N). The gravity signature of some major structures, such as the GRSZ, can be identified on each profile.
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AlHamaydeh, Mohammad, Samer Barakat, and Omar Nasif. "Optimization of Support Structures for Offshore Wind Turbines Using Genetic Algorithm with Domain-Trimming." Mathematical Problems in Engineering 2017 (2017): 1–14. http://dx.doi.org/10.1155/2017/5978375.
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The powerful genetic algorithm optimization technique is augmented with an innovative “domain-trimming” modification. The resulting adaptive, high-performance technique is called Genetic Algorithm with Domain-Trimming (GADT). As a proof of concept, the GADT is applied to a widely used benchmark problem. The 10-dimensional truss optimization benchmark problem has well documented global and local minima. The GADT is shown to outperform several published solutions. Subsequently, the GADT is deployed onto three-dimensional structural design optimization for offshore wind turbine supporting structures. The design problem involves complex least-weight topology as well as member size optimizations. The GADT is applied to two popular design alternatives: tripod and quadropod jackets. The two versions of the optimization problem are nonlinearly constrained where the objective function is the material weight of the supporting truss. The considered design variables are the truss members end node coordinates, as well as the cross-sectional areas of the truss members, whereas the constraints are the maximum stresses in members and the maximum displacements of the nodes. These constraints are managed via dynamically modified, nonstationary penalty functions. The structures are subject to gravity, wind, wave, and earthquake loading conditions. The results show that the GADT method is superior in finding best discovered optimal solutions.
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Won, Deokhee, Jihye Seo, Osoon Kwon, Hae-Young Park, and Hyoun Kang. "The Construction Conditions of a Pre-Piling Template for Foundations of Offshore Structures." Journal of Marine Science and Engineering 12, no. 1 (2024): 174. http://dx.doi.org/10.3390/jmse12010174.
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The foundations of offshore wind power can be classified as floating, tripod, jacket, monopile, or gravity-based, depending on the support type. In the case of tripod- and jacket-type supports, the structures require precise construction. There are two main methods for installing substructures: post- and pre-piling. The post-piling method involves moving the completed substructure to the site and fixing it to the seabed by inserting a pile into the leg pile and driving it, allowing it to be constructed without special off-shore equipment; however, the construction period is long. Contrarily, the precision of foundation installation can be improved by installing a pre-piling template, which is special equipment that serves as a basic structure, on the seabed in advance, and subsequently inserting substructures. This study presents a new type of underwater pre-piling template and method for achieving optimal construction environment conditions. Construction precision was analyzed based on the wave condition, current speed, winch speed, wave direction, and current direction while the under-water template was anchored to the seabed. It was found that the wave conditions, winch speed, and vessel type had a significant influence. The results obtained considering the Douglas sea scale show that precise construction could only be achieved within Grade 2 for general barge ships, while jack-up barge ships could be used even at Grade 3 or higher. The higher the winch speed, the more stable construction becomes possible, and jack-up barges show greater constructability than general barges.
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Plasman, Matthieu, Christel Tiberi, Cecilia Cadio, Anita Thea Saraswati, Gwendoline Pajot-Métivier, and Michel Diament. "From space to lithosphere: inversion of the GOCE gravity gradients. Supply to the Earth’s interior study." Geophysical Journal International 223, no. 1 (2020): 398–419. http://dx.doi.org/10.1093/gji/ggaa318.
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SUMMARY The emergence of high resolution satellite measurements of the gravitational field (GOCE mission) offers promising perspectives for the study of the Earth’s interior. These new data call for the development of innovant analysis and interpretation methods. Here we combine a forward prism computation with a Bayesian resolution approach to invert for these gravity gradient data configuration. We apply and test our new method on satellite data configuration, that is 225 km height with a global and homogeneous geographic distribution. We first quantify the resolution of our method according to both data and parametrization characteristics. It appears that for reasonable density contrast values (0.1 g cm−3) crustal structures have to be wider than ∼28 km to be detectable in the GOCE signal. Deeper bodies are distinguishable for greater size (35 km size at 50 km depth, ∼80 km at 300 km depth). We invert the six tensor components, among which five are independent. By carefully testing each of them and their different combinations, we enlighten a trade off between the recovery of data and the sensitivity to inversion parameters. We particularly discussed this characteristic in terms of geometry of the synthetic model tested (structures orientation, 3-D geometry, etc.). In terms of RMS value, each component is always better explained if inverted solely, but the result is strongly affected by the inversion parametrization (smoothing, variances, etc.). On the contrary, the simultaneous inversion of several components displays a significant improvement for the global tensor recovery, more dependent on data than on density variance or on smoothness control. Comparing gravity and gradient inversions, we highlight the superiority of the GG data to better reproduce the structures especially in terms of vertical location. We successfully test our method on a realistic case of a complex subduction case for both gradient and gravity data. While the imaging of small crustal structures requires terrestrial gravity data set, the longest wavelength of the slab is well recovered with both data sets. The precision and homogeneous coverage of GOCE data however, counterbalance the heterogeneous and often quite non-existence coverage of terrestrial gravity data. This is particularly true in large areas which requires a coherent assemblage of heterogeneous data sets, or in high relief, vegetally covered and offshore zones.
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DIMITRIU, RADU G. "Main results of marine gravity and magnetic researches carried out at the National Research & Development Institute for Marine Geology and Geoecology." Geo-Eco-Marina 25 (2019) (December 31, 2019): 31–54. https://doi.org/10.5281/zenodo.3607420.
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Since the resume in 2005 of the systematic geophysical and geo-ecological investigation of the Romanian offshore, over 13,400 km of gravity lines and over 48,000 km of magnetic lines have been acquired on the entire surface of the Romanian maritime space and over most of the Bulgarian one.Based on this data numerous maps of the gravity and magnetic anomalies, at scales ranging from regional to the highest detail, have been compiled. If prior to 1990, marine gravity and magnetic researches were exclusively used for the study of the Romanian continental shelf deep geological structure and for the assessment of its hydrocarbon potential, the latter researches has expanded the range of topics addressed: deciphering of also near surface structures, marine site characterization, geo-archaeology, environmental geophysics, detection of submerged objects, maritime space security. Mainly during the last years, an increasing involvement of marine magnetometry in projects dedicated to the study of the submarine cultural heritage and to enhancement of maritime space safety is noticed. The present results and findings due to marine magnetometry go far beyond all initial expectations.
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Nomikou, Paraskevi, Pavlos Krassakis, Stavroula Kazana, Dimitrios Papanikolaou, and Nikolaos Koukouzas. "The Volcanic Relief within the Kos-Nisyros-Tilos Tectonic Graben at the Eastern Edge of the Aegean Volcanic Arc, Greece and Geohazard Implications." Geosciences 11, no. 6 (2021): 231. http://dx.doi.org/10.3390/geosciences11060231.
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The active Kos-Nisyros-Tilos volcanic field is located in the eastern sector of the Aegean Volcanic Arc resulting from the subduction of the African plate beneath the Aegean plate. The volcanic activity is developed since Middle Pleistocene and it occurs within a tectonic graben with several volcanic outcrops both onshore and offshore. Data obtained from previous offshore geophysical surveys and ROV exploration, combined with geospatial techniques have been used to construct synthetic maps of the broader submarine area. The volcanic relief is analyzed from the base of the volcanic structures offshore to their summits onshore reaching 1373 m of height and their volumes have been computed with 24.26 km3 for Nisyros Island and a total volume of 54.42 km3 for the entire volcanic area. The volcanic structures are distinguished in: (1) volcanic cones at the islands of Nisyros (older strato-volcano), Pergousa, Yali and Strongyli, (2) volcanic domes at the islands of Pachia, East Kondeliousa and Nisyros (younger Prophitis Ilias domes), (3) submarine volcanic calderas (Avyssos and Kefalos). Submarine volcanic debris avalanches have been also described south of Nisyros and undulating features at the eastern Kefalos bay. Submarine canyons and channels are developed along the Kos southern margin contrary to the Tilos margin. Ground truth campaigns with submarine vessels and ROVs have verified the previous analysis in several submarine volcanic sites. The geohazards of the area comprise: (1) seismic hazard, both due to the activation of major marginal faults and minor intra-volcanic faults, (2) volcanic hazard, related to the recent volcanic structures and long term iconic eruptions related to the deep submarine calderas, (3) tsunami hazard, related to the seismic hazard as well as to the numerous unstable submarine slopes with potential of gravity sliding.
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Escobar, Adrián, José Santos López-Gutiérrez, María Dolores Esteban, and Vicente Negro. "A Modified Method for Assessing Hydrodynamic Loads in the Design of Gravity-Based Structures for Offshore Wind Energy." Journal of Coastal Research 85 (May 2018): 931–35. http://dx.doi.org/10.2112/si85-187.1.
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Dewoolkar, Mandar M., Jeaan Hwang, and Hon-Yim Ko. "Physical and finite element modeling of lateral stability of offshore skirted gravity structures subjected to iceberg impact load." Ocean Engineering 35, no. 16 (2008): 1615–26. http://dx.doi.org/10.1016/j.oceaneng.2008.08.005.
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Carpenter, Chris. "Study Investigates Using Borehole Gravity To Improve Reservoir Monitoring." Journal of Petroleum Technology 73, no. 03 (2021): 49–50. http://dx.doi.org/10.2118/0321-0049-jpt.
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This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 30626, “Brazil Presalt, Santos Basin: Feasibility Study for the Application of Borehole Gravity To Improve Reservoir Monitoring,” by Zhijun Du, Adrian Topham, SPE, and Jeremy C. Lofts, SPE, Silicon Microgravity, et al., prepared for the 2020 Offshore Technology Conference, originally scheduled to be held in Houston, 4-7 May. The paper has not been peer reviewed. Copyright 2020 Offshore Technology Conference. Reproduced by permission. The complete paper uses a feasibility study to present the potential application of a three-axis gravimeter borehole measurement in the Libra presalt reservoir in the Santos Basin offshore Brazil. The authors’ findings suggest that an annual survey with a limited well stock could be effective in monitoring this type of reservoir and that a wireline-deployed three-axis gravity tool is likely to provide significant additional surveillance to constrain a reservoir production strategy through better appreciation of the direction of water movement. Introduction The giant Brazilian presalt reservoirs are in ultradeep water (greater than 2000 m) and buried at a depth surpassing 5000 m. In order to conduct reservoir monitoring and achieve successful reservoir management, borehole-based geophysical technologies are preferred because the measurements can be made closer to the reservoir mass. The development of a borehole gravimeter suit-able for use in deep reservoirs, however, poses significant technical challenges, and breakthroughs have been limited by the sensor form factor (size) and measurement stabilization. By use of microelectromechanical-system (MEMS) vibrating-beam technology, the authors introduce a borehole gravimeter that enables the recording of gravitational acceleration at very high sensitivity. The new resonant MEMS gravitational sensor is designed to sense mass in the subsurface such that time-lapse wireline-based surveys can be conducted to build a picture of fluid movements at relatively large distances from a wellbore, thereby enabling time-lapse or 4D gravity monitoring. The innovation of the three-axis gravimeter also allows the acquisition of directional information about the spatial movement of fluid, even when acquired from only a single borehole. The principles of measuring gravity in the borehole environment are provided in the complete paper. Libra Field. The field is one of the largest presalt oil discoveries in the Santos Basin. It was discovered in May 2010 with recoverable resources of approximately 9 billion bbl of oil. The first appraisal well was completed and tested in February 2015. At the time of writing, nine appraisal wells have been drilled. A high-density 3D seismic program was acquired over the Santos and Campos basins, and advanced seismic processing technology has also been applied. Reservoir Simulation. The geophysics for reservoir characterization and simulation of these carbonate reservoirs is still in its early stages, and little published knowledge about their properties exists. Nonetheless, since their discovery, 2D and 3D seismic technologies have been applied intensively for imaging the region structures and delineating the reservoirs.
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Gregersen, Ulrik, Torben Bidstrup, Jørgen A. Bojesen-Koefoed, Flemming G. Christiansen, Finn Dalhoff, and Martin Sønderholm. "Petroleum systems and structures offshore central West Greenland: implications for hydrocarbon prospectivity." Geological Survey of Denmark and Greenland (GEUS) Bulletin 13 (October 12, 2007): 25–28. http://dx.doi.org/10.34194/geusb.v13.4968.
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A detailed geophysical mapping project has been carried out by the Geological Survey of Denmark and Greenland (GEUS) in the offshore region south-west and west of Disko and Nuussuaq, central West Greenland as part of the preparations for the Disko West Licensing Round in 2006 (Fig. 1). The main purpose of the study was to evaluate the prospectivity of this almost 100 000 km2 large region, and to increase knowledge of basin evolution and the structural development. Results of the work, including a new structural elements map of the region and highlights of particular interest for hydrocarbon exploration of this area, are summarised below. Evidence of live petroleum systems has been recognised in the onshore areas since the beginning of the 1990s when seeps of five different oil types were demonstrated (BojesenKoefoed et al. 1999). Oil seeps suggesting widely distributed marine source rocks of Mesozoic age are particularly promising for the exploration potential (Bojesen-Koefoed et al. 2004, 2007). Furthermore, possible DHIs (Direct Hydro carbon Indicators) such as gas-clouds, pock marks, bright spots and flat events have been interpreted in the offshore region (Skaarup et al. 2000; Gregersen & Bidstrup in press). The evaluation of the region (Fig. 1) is based on all public and proprietary seismic data together with public domainmag- netic and gravity data. The seismic data (a total of c. 28 000 line km) are tied to the two existing offshore exploration wells in the region (Hellefisk-1 and Ikermiut-1). The study also incorporates information on sediments and volcanic rocks from onshore Disko and Nuussuaq (Fig. 2). Ten seismic horizons ranging from ‘mid-Cretaceous’ to ‘Base Quaternary’ (Fig. 2) have been interpreted regionally. Large correlation distances to wells, varying data quality and a thick cover of basalt in the north-eastern part of the region, add uncertainty in the regional interpretation, especially for the deeper horizons such as the ‘mid-Cretaceous’ equivalent to Santonian sandstone interval drilled in Qulleq-1 far south. Based on the seismic interpretation (Fig. 3) structural elements maps, horizon-depth maps and isopach maps have been produced; these maps, together with general stratigraphic knowledge on potential reservoirs, seals and source rocks (Fig. 2), provide important information for discussions of critical play elements including kitchens and structures.The existence of many large structures combined with the evidence of live petroleum systems has spurred the recent major interest for hydrocarbon exploration in the region.
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Titus, P. G. "WEST TUNA I BREAM B: APPLICATION OF CONCRETE TECHNOLOGY OFFSHORE AUSTRALIA." APPEA Journal 37, no. 1 (1997): 546. http://dx.doi.org/10.1071/aj96033.
Full textAbstract:
Esso/BHPP's West Tuna and Bream B Platforms are the first completed concrete-based platforms in Australia and are Exxon's first designed, built and operated concrete gravity structures (CGSs). Both platforms were towed to location, complete with commissioned topsides facilities, in fourth quarter 1996 and successfully installed in 61 m of water. They will add in excess of 45,000 BOPD (7200 kl/d) of oil production to Bass Strait volumes. West Tuna, with 48 well slots, will be Esso/BHPP's largest and most complex Bass Strait production facility, whereas Bream B will be an 18-slot, unstaffed minimum facility satellite platform with a 720-tonne topsides. By comparison, West Tuna's topsides weigh 7,300 tonnes.Esso/BHPP chose the CGS concept for the two developments following extensive conceptual studies with selected North Sea designers. Because of rising derrick barge day rates in the early 1990s (required for steel pile jacket installations), coupled with the availability of a suitable casting basin near Sydney, the CGS concept was judged economically attractive, with savings estimated at 10 per cent of the total facilities capital expenditure relative to its steel pile jacket alternative.The project saw a number of firsts, including the use of the world's largest land-based crawler cranes to lift and set the completed production modules over 75 m in the air onto the completed CGS structures. CGS fabrication productivity problems were experienced during the early phase of construction reflecting the complex nature of the construction, however implementation of a number of project management initiatives resulted in achievement of world-class productivity by completion of the works.
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Dalhoff, Finn, Lotte M. Larsen, Jon R. Ineson, et al. "Continental crust in the Davis Strait: new evidence from seabed sampling." Geological Survey of Denmark and Greenland (GEUS) Bulletin 10 (November 29, 2006): 33–36. http://dx.doi.org/10.34194/geusb.v10.4901.
Full textAbstract:
Although the structural framework of the subsurface offshore West Greenland has been well documented based on comprehensive seismic analysis (cf. Dalhoff et al. 2003), the stratigraphy of the region is less well known. The oldest documented sedimentary rocks drilled offshore West Greenland are Santonian sandstones reached at TD in the 6354/4-1 well (Fig. 1) although reworked palynomorphs of Carboniferous, Triassic and Jurassic (Kimmeridgian) age have been reported from a number of wells in the region. In order to obtain better constraints on the pre-Upper Cretaceous stratigraphy, a preliminary screening was undertaken to identify inversion structures and erosional canyons where such deeper stratigraphic levels crop out at the seabed (Nielsen et al. 2001). Sea-floor sampling at selected sites between 62° and 67°N (Fig. 1) was undertaken during the summers of 2003 and 2004. Other objectives of these cruises were to seek direct evidence of active petroleum systems, to establish further constraints on tectonic and stratigraphic models, and to obtain a better understanding of the Neogene and Pleistocene history of the region (Dalhoff et al. 2005). The most promising seabed features identified by Nielsen etal.(2001) were investigated in more detail using a wide range of techniques in order to optimise sampling positions. In 2003, these techniques included echo sounder, side-scan sonar, singlechannel seismic and video inspection before sampling either by dredge, gravity corer, or by video-controlled grab. In 2004, comprehensive data acquisition with a deep-water sparker system was undertaken before sampling by dredge or gravity corer, supplemented by grab samples at selected stations.