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_ Crew transfer vessels (CTVs) play important roles in the operation and maintenance of facilities under offshore wind conditions. When engineers are needed to transfer to offshore wind facilities for various maintenance operations on site, in most cases, the captain of the CTV pushes the vessel bow against the offshore wind tower using propulsion to ensure easy and safe transfer. In such operations, differential motion from the normal wave-induced dynamics can occur because of discontinuous static/dynamic friction at fenders. The unexpectedly complex dynamics occurring in the transfer can have a severe impact on availability. Given these motivations, both model experiments and numerical calculations were conducted to investigate the complex dynamics. This study clarifies the effect of the friction coefficient at fenders and the bollard pushing force on the stick/slip phenomenon.
- Europe (0.46)
- North America > Canada (0.28)
- Data Science & Engineering Analytics > Information Management and Systems (1.00)
- Well Drilling > Drilling Operations (0.68)
- Facilities Design, Construction and Operation > Offshore Facilities and Subsea Systems > Platform design (0.34)
- Facilities Design, Construction and Operation > Facilities and Construction Project Management > Offshore projects planning and execution (0.34)
The p-y method according to the offshore guidelines is usually applied for the design of laterally loaded piles. However, a number of modified p-y approaches for piles in noncohesive soils were proposed in the recent years to account for the effect of the pile diameter. These approaches were developed for piles in homogeneous soil but are used in current engineering practice for piles in layered sand as well. Concerning this matter, this paper presents a comparative evaluation of the existing p-y approaches for piles in layered sand by means of three-dimensional numerical simulations. Two large-diameter piles in widely varied layered sand representing a monopile and a pile of a lattice structure for the foundation of an offshore wind energy converter are considered. It is demonstrated that the effect of the layering is limited; that is, the deviations of the analytical results from the numerical results are predominantly associated with the deviations obtained for homogeneous sand. An occasionally used overlay procedure to adapt the p-y curves depending on the adjacent soil layers is shown to have not only a small impact on the analytical results but also some major deficiencies with regard to a reliable consideration of the layering.
- Europe > Germany (0.95)
- North America > United States > Texas (0.28)
Evaluation of Dolphin Swimming Speed and Thrust Based on CFD
Wang, Xianzhou (Huazhong University of Science and Technology) | Wei, Peng (Huazhong University of Science and Technology) | Yuan, Ye (Huazhong University of Science and Technology) | Zhang, Zhiguo (Huazhong University of Science and Technology) | Feng, Dakui (Huazhong University of Science and Technology)
For many years, the maximum swimming speeds of dolphins have been reported almost entirely through observations. The objective of this paper is to estimate the swimming speed of dolphins using a theoretical analysis and numerical method. The FLUENT software solver and User Defined Function (UDF) dynamic mesh method were used to simulate the dolphin kicking during its swimming. Three peak-to-peak tail motion amplitudes and frequencies were chosen to study. The simulation results of the resistance of dolphin were compared with experimental results. The thrusts generated by dolphin fluke motion were compared with available data from the references. In conclusion, the dolphin can reach a very high speed because of its large thrust generated by its fluke motion and high propulsive efficiency. Introduction For a long time, dolphins have been considered good swimmers with extremely high thrust efficiency and minimum resistance. Swimming encompasses the transfer of kinetic energy and momentum from the animal's propulsive movements to the water. High speeds allow increased foraging and active pursuit but require large energy expenditures because thrust power is directly related to the cube of velocity. Low swimming speeds have been observed for cetaceans while foraging and migrating (Lang, 1975; Webb, 1975; Fish, 1998). A dolphin swimming at a constant speed balances forces and moments acting on it by the principle of momentum conservation. The total thrust produced by the action of the caudal flukes balances the total resistance (i.e., drag) that the animal's body encounters moving forward (Fish and Rohr, 1999). It is uncertain whether special properties of the dolphin's skin itself contribute to the drag reduction or whether it is simply due to the maintaining of an attached turbulent boundary layer (Fish, 1993). In the wild, dolphins swim over a wide range of speeds. The highest swimming speeds recorded were those of captive dolphins, ranging from 8.0 to 8.2 m/s and typically lasting for a few seconds (Rohr et al., 1998). Estimations of thrust based on the motion of the flukes can be used to assess independently the drag due to body form and swimming motions (Triantafyllou et al., 1993). Many studies of dolphin swimming have used the rigid model; this model assumes that the thrust generated by a swimming dolphin is equal to the estimation of drag from a gliding dolphin. Measurements of hydrodynamic force generated by swimming dolphins have been made using bubble digital particle image velocimetry (DPIV), where the movement of the bubbles was tracked with a high-speed video camera. Dolphins swam at speeds of 0.7 to 3.4 m/s within the bubble sheet oriented along the midsagittal plane of the animal (Fish et al., 2014).
- Asia (0.68)
- North America > United States (0.47)
- Health & Medicine (0.68)
- Energy > Oil & Gas > Upstream (0.46)
- North America > United States > Colorado > Ridgway Field (0.89)
- Europe > United Kingdom > North Sea > Southern North Sea > Southern Gas Basin > Sole Pit Basin > Block 43/27 > Johnston Field (0.89)
Abstract A comparison of fatigue and extreme loads from simulations with full-scale measurements collected over a period of ten months in the offshore test field, Alpha Ventus, is presented in this paper. There are two goals of this study:to check if the measured range of fatigue and extreme loads can be captured correctly by simulations when the variations of relevant environmental parameters are taken into account; and to investigate if measured extreme loads can be reproduced by simulations when ten-minute averages of the environmental parameters are used. The results show a good overall match of loads when the variation of environmental parameters is considered but an insufficient match when the events of maximum load occurrence are compared. Introduction The site-specific design of offshore wind turbines requires the use of simplified assumptions of the environment in order to limit the number and detail of simulations to be performed. Additionally, a set of physical assumptions is implied in the various aero-servo-hydro-elastic models used for the simulation of the loads of offshore wind turbines. These include models for the wind and wave environment and models for the load transfer from the environment to the turbine and between system components. The use of simplified environmental assumptions is generally justified by the use of conservative estimates for environmental parameters (Türk and Emeis, 2010). The verification and validation of the models used to describe offshore wind turbines involve code-to-code comparisons (Jonkman and Musial, 2010; Popko et al., 2012) and comparisons to scaled experimental data (Müller et al., 2014). To complete the design process and learn from it, a thorough validation of physical models at full scale and subsequent environmental assumptions are necessary in order to identify shortcomings and highlight the potential for less conservative designs and/or additional simplifications within the process of site-specific project certification.
- Europe > Germany (0.94)
- North America > United States (0.88)
- Europe > United Kingdom > North Sea (0.34)
- Europe > Norway > North Sea (0.34)
- Research Report > Experimental Study (0.67)
- Research Report > New Finding (0.48)
- Health, Safety, Environment & Sustainability > Environment (1.00)
- Facilities Design, Construction and Operation > Offshore Facilities and Subsea Systems > Platform design (1.00)
- Facilities Design, Construction and Operation > Facilities and Construction Project Management > Offshore projects planning and execution (1.00)
- Health, Safety, Environment & Sustainability > Sustainability/Social Responsibility > Sustainable development (0.68)
Onshore Pipeline High-Grade Steel for Challenge Utilization
Ferino, Jan (Centro Sviluppo Materiali SpA) | Fonzo, Andrea (Centro Sviluppo Materiali SpA) | Di Biagio, Massimo (Centro Sviluppo Materiali SpA) | Demofonti, Giuseppe (Centro Sviluppo Materiali SpA) | Spinelli, Carlo Maria (Eni SpA) | Karamanos, Spyros A. (University of Thessaly)
High-pressure pipeline transportation is one of the key technologies to connect remote gas fields and deliver gas at competitive prices to consumer markets. Arctic regions will become more attractive in the near future as large gas resources are located there. Long onshore pipeline systems, characterized by high-strength steels (above API 5L grade X80, i.e., exceeding 555 MPa yield strength) operated at high internal gas pressure (more than 10–12 MPa) in many cases appear to be the most convenient transportation option. This paper highlights the latest follow-up from a long-lasting R&D program launched by Eni, together with industrial/technical partners, on the exploitation of commercially available options with high-grade steels for onshore applications even in harsh environments. The results obtained in this R&D program can be useful even for applications in Arctic onshore or offshore scenarios. Introduction Natural gas has the chance to be one of the most important and strategic fuel sources in the years to come, even if the growth of the renewable source will play a fundamental role in the “next green power energy,” being the “greenest” among fossil fuels. Natural gas represents a continuous and reliable energy source on an economically viable base and a long-term span. Energy industries have analyzed several potential routes for gas exportation from giant midcontinental fields to final “end-user markets” via either pipeline or liquefied natural gas (LNG) ships. To be economically viable, these analyses include constructability and environmental impact evaluations, route optimization, proper material selection, and optimum hydraulic diameter and wall thickness selection, as well as sizing of intermediate gas-compression stations. High-pressure pipeline transportation is one of the key technologies to connect remote gas fields and to deliver gas at competitive prices to consumer markets. Several independent technical and economical evaluations have shown how natural gas pipeline transportation systems based on:traditional construction techniques, low-alloy high-strength C-steel (above API 5L grade X80), operating gas pressure higher than 10 MPa, and pipeline length of more than 1,000 km are the only solutions to exploit “stranded gas fields.” This solution allows pipeline projects to meet all the requirements and compete on the “gas to market” for distances greater than 1,000 km, even for large-volume transportation. The main economic advantage of high-pressure gas transportation consists of reduced capital expenditure (CAPEX), saving in construction costs, and operational expenditure (OPEX), as a result of a reduced number of intermediate compression stations. This paper highlights the latest follow-up from a long-lasting R&D program launched by Eni, together with industrial/technical partners, on the exploitation of commercially available options with high-grade steels for onshore application even in harsh environments. The idea was to fill existing gaps in several fields dealing with pipeline integrity, based on an advanced design approach mixed together with “in field” practical requirements.
- North America > United States (1.00)
- Europe (1.00)
- Geology > Geological Subdiscipline > Geomechanics (0.46)
- Geology > Structural Geology (0.46)
- Energy > Oil & Gas > Midstream (1.00)
- Government > Regional Government > North America Government > United States Government (0.68)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Piping design and simulation (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Offshore pipelines (1.00)
- Facilities Design, Construction and Operation > Natural Gas Conversion and Storage > Liquified natural gas (LNG) (1.00)
Previous researchers developed the vibrating table for producing mechanical vibrations into the weld pool during the welding process. The designed vibrating table produces the required frequency with suitable amplitude and acceleration in terms of voltages. This helps in producing a uniform and fine grain structure in the welded joints, which results in an improvement of the bending strength of the welded joints. This paper presents the implementation of the Generalized Regression Neural Network (GRNN) to establish a relation between vibration parameters such as the input voltage to the vibromotor, the time of vibration, and the bending strength of the vibratory welded joints. In order to validate the feasibility of the developed prediction tool, a comparison is made with the experimental results. Introduction In manufacturing industries, welding is widely used for joining metals. The welding joints prepared by the arc welding process generally offer good strength and hardness properties. Metal arc welding is the most flexible fusion welding and one of the most widely used welding processes. Mechanical vibrations into the weld specimen during the welding process improve the welded joint properties significantly. The enhancement of the welded joint properties can be altered by the variation of the vibration parameters. Vibrations applied during welding generally reduce the residual deformation and stress and improve the mechanical properties of the weldments (Lu et al., 2006; Xu et al., 2006; Lakshminarayanan and Balasubramanian, 2010). An enhancement of the mechanical properties and the quality of the fusion metal through the use of vibration during welding was considered recently and was found to improve the bending property of the welding line, tensile strength, and morphology (Hussein et al., 2011; Munsi et al., 2001; Tewari and Shanker, 1993; Weglowska and Pietras, 2012). The Generalized Regression Neural Network (GRNN) is a type of supervised network and has been widely accepted for its excellent ability to train rapidly on sparse data sets. The GRNN usually performs better and faster in the approximation of continuous functions. Tseng (2006) implemented the GRNN to create approximate models to establish a relation between the spot welding parameters, welded joint strength, and power required to prepare the welded joint. Kathersan et al. (2012) addressed the modelling of the welding parameters in the arc welding process by using a set of experimental data, utilizing regression analysis, and employing optimization via the particle swarm optimization algorithm. Though there is literature that describes the phenomenon of improving the welded joint strength properties, the relation between the vibration parameters and welded joint properties has not been established. Hence, the present work is aimed at building a relation between the vibration parameters and welded joint properties from the experimental data through the use of the Generalized Regression Neural Network.
- Research Report > New Finding (0.48)
- Research Report > Experimental Study (0.34)
For the design of monopile foundations, the soil resistance is usually modeled by the subgrade reaction method. The commonly used p-y approach described in the offshore guidelines is generally assumed to be sufficiently accurate for slender piles with diameters D ≤ 2 m. However, several investigations indicate that the pile deflections of large-diameter monopiles are underestimated for extreme loads but overestimated for small operational loads. A three-dimensional finite element (FE) model is presented to evaluate the currently used p-y approach for piles in sand under static loading conditions in dependence on the pile dimensions and the soil's relative density. In addition, modified p-y formulations to account for the effect of the pile diameter are compared to the FE results. Introduction Monopiles are currently the preferred support structure for offshore wind energy converters (OWECs) in water depths of less than 30 meters. The cost-effective and relatively simple manufacturing and installation process is a great advantage in comparison to lattice structures like jackets or tripods. A monopile foundation (see Fig. 1) consists of a single steel pipe pile driven into the seabed. These large-diameter monopiles have to withstand large and discontinuous horizontal forces H and bending moments M caused by wind and wave actions. Large water depths and sizable wind turbines necessitate large pile dimensions. Pile diameters more than D = 6 m have already been realized, and diameters up to D = 8 m are currently planned. The relative pile length, i.e., the ratio of embedded pile length L to diameter D, lies usually at approximately L/D =5. In the design of the wind turbine, the ultimate limit state (ULS) and the serviceability limit state (SLS) design proofs have to be fulfilled. In the ULS proof, a sufficient soil resistance has to be guaranteed to ensure the structural safety of the wind turbine. Thereby, effects of cyclic loading have to be considered; i.e., degradation in soil resistance has to be accounted for. For the SLS proof, the deflections and rotations under the characteristic extreme load cases (hereinafter referred to as “extreme loads”) have to stay below certain serviceability limits. In that, the accumulation of deflection due to cyclic loading also has to be considered (cf. Achmus et al., 2008). Besides these geotechnical design proofs, the stiffness of the monopile foundation system under operational loads has to be determined. Considering this stiffness in a dynamic analysis of the whole OWEC structure, it has to be ensured that the eigenfrequencies of the wind turbine have a sufficient distance to the main excitation frequencies of the dynamic loading. In that, neither an overestimation nor an underestimation of foundation stiffness is generally conservative. An incorrect estimation of foundation stiffness results in an increase of uncertainties and leads to additional but unnecessary costs. Moreover, in the worst case it could have a negative influence on the structural lifetime of the structure (Kallehave et al., 2012).
- North America > United States (1.00)
- Europe > Germany (0.94)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers (1.00)
- Health, Safety, Environment & Sustainability > Environment (0.93)
- Facilities Design, Construction and Operation > Offshore Facilities and Subsea Systems (0.93)
- Reservoir Description and Dynamics > Reservoir Characterization (0.69)
In the offshore wind energy sector, there are many different conceptual wind turbine structures, from traditional mono-pile structures to floating platforms. The management of Reliability, Availability, Maintainability, and Safety (RAMS) issues is essential as early as possible at the beginning of the turbine conceptual design phase. This paper presents guidelines to compare different offshore wind energy assets and their critical components from a system availability and safety point of view. Classification and evaluation criteria for different Reliability, Availability, Maintainability, Safety, and Inspectability (RAMS + I) factors are outlined and discussed. INTRODUCTION Offshore wind turbines are complex machinery systems consisting of many multi-technology subsystems. Beginning with the underwater substructures, there are many different conceptual structures, depending on the water depth, from traditional mono-piles to new floating platforms. Current offshore turbines in shallow waters are mostly developed from onshore designs. According to EWEA's medium and long-term scenarios, offshore wind turbine concepts will be changed from onshore-based constructions to turbine types designed specifically for an offshore environment. The main driver for offshore wind turbine development is efficiency, rather than generator size (EWEA, 2009a). The development based on land-based designs is not optimal for offshore wind turbines because of some fundamental differences in the offshore operating environment and infrastructure. Sites are far from harbours and support bases, construction costs are much higher, and operations are highly dependent on weather conditions, wave height and wind speed. Corrosive seawater exposure, wave loading added to extreme wind and fatigue load combinations, and other external conditions requiring special attention (e.g., ice and hurricanes) require different technological solutions for offshore structures and solutions. Because of these differences, future trends may move toward significant divergences between offshore and land-based designs (Musial and Ram, 2010). Wind turbines in cold climates such as Northern Europe are exposed to conditions outside the design limits of standard wind turbines. According to Baring-Gould et al. (2010), specific issues in the Nordic context, such as accessibility, temperature, ice, snow, energy potential, technology, economic risk, public safety, infrastructure and occupational safety, will require special solutions. Many of the technologies for offshore wind development have already been proven in the oil and gas industry, such as structural designs, foundations, remote monitoring, data integration, and so on. Many of the same issues that govern oil and gas platforms will also influence the design of wind platforms, but the importance of each variable will be weighted differently. Because platforms in the oil and gas industry are much larger and have unique applications, applying this experience to offshore wind will require technological innovations and new methods for manufacturing, logistics and maintenance that will be critical in lowering costs and expanding the offshore wind farms to potential new areas (Musial and Ram, 2010). There are high reliability requirements and increasing cost reduction demands in the offshore wind energy sector. The management of reliability, availability, maintainability and safety issues (RAMS) becomes essential as early as the system requirement specification phase at the beginning of the turbine conceptual design phase. Some initial attempts have been made in a collaborative project in NORCOWE to develop and extend the RAMS concept for specific Nordic conditions, by emphasising inspectability performance to develop the RAMS +I concept (Tiusanen et al., 2011 a). RAMS +I (Reliability, Availability, Maintainability, Safety, and Inspectability) objectives, benefits and costs can and should be considered from different perspectives: the wind energy company building and operating the wind farm, turbine and substructure providers, nacelle component providers, maintenance companies and electric grid companies. In these issues, as is common in system engineering, sub-optimisation is no good in the long run. RAMS + I issues related to single wind turbines and their critical components should be considered in relation to the objectives and site-specific requirements of the whole wind farm. In this paper, we present guidelines to compare different offshore wind turbine concepts and their critical components from a system availability and safety point of view. Classification and evaluation criteria for different RAMS + I factors are outlined and discussed. RAMS + I factor classification and qualitative assessment makes it possible to develop comparable risk profiles for different concepts or combinations of components. The multi-factor risk profiling presented in this paper is based on the known multi-criteria decision analysis (MCDA
- North America > United States (1.00)
- Europe (1.00)
- Health, Safety, Environment & Sustainability > Sustainability/Social Responsibility > Sustainable development (1.00)
- Health, Safety, Environment & Sustainability > Environment (1.00)
- Facilities Design, Construction and Operation > Offshore Facilities and Subsea Systems > Platform design (1.00)
- Facilities Design, Construction and Operation > Facilities and Construction Project Management > Offshore projects planning and execution (1.00)
Evaluation of Dynamic Group-Pile Effect In Dry Sand By Centrifuge Model Tests
Yoo, Min-Taek (Department of Civil & Environmental Engineering, Seoul National University) | Cha, Se-Hwan (Department of Civil & Environmental Engineering, Seoul National University) | Kim, Myoung-Mo (Department of Civil & Environmental Engineering, Seoul National University) | Choi, Jung-In (Department of Civil & Environmental Engineering, University of California) | Han, Jin-Tae (Korea Institute of Construction Technology)
It is well known that the average load for a pile in a closely spaced group is substantially less than that for a single isolated pile at the same deflection. Thus, the p-multiplier has been used to determine p-y curves for groups of piles. The p-multiplier under seismic loading is yet to be determined. In this study, a series of centrifuge shaking-table tests for a 3_3 group pile was performed for various pile spacings, ranging from 3 to 7 times the pile diameter. Test results confirm that the p-multiplier increases with increasing pile spacing. The p-multiplier of the piles in rows 1 and 3 within a group is smaller than that of the center pile in row 2. Thus, under seismic loading conditions, the group pile effect in rows 1 and 3 piles is greater than that in row 2 piles. In addition, the behavior of piles in the same row is different according to the location of each pile within group piles. INTRODUCTION In the seismic design of a pile foundation, pseudo-static analysis is widely used to convert dynamic loads to equivalent static loads. The p-y curve method, which considers the relationship between the relative displacement of a pile against soil and the nonlinear soil resistance, is most frequently used to model the lateral behavior of a pile foundation for pseudo-static analysis. To consider the group pile effect during the design of a laterally loaded group pile, the p-y curve of a pile group is determined by applying the p-multiplier to the p-y curve of a single pile. The p-multiplier recommended by AASHTO (2000), which is identical to that recommended by the Canadian Geotechnical Society (1992), is possibly the most widely used in practice (Rollins et al., 2006).
Bearing Capacity of Surface Footing On Soft Clay Underlying Stiff Nonhomogeneous Desiccated Crust
Park, Hyunku (Department of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology) | Lee, Seung Rae (Department of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology) | Jee, Sung Hyun (Institute of Technology & Quality Development, Hyundai E&C)
The aim of this paper is to provide a reasonable approach for the evaluation of the bearing capacity of a shallow footing on a very soft clay overlaid by a stiff non-homogeneous crust layer, based on both numerical analyses and a reappraisal of field load tests reported in the literature. Finite element analyses were carried out for the above problems with varying shape and magnitude of a non-homogeneous shear strength distribution in the crust and crust thickness to a footing width (or diameter) ratio H/B (or H/2R). In addition, recently reported in-situ plate load tests conducted in a reclaimed area of dredged marine clay were reappraised so as to characterize the bearing behavior of the deposit, and to assess the shear strength mobilization in the crust related to the bearing capacity estimation. INTRODUCTION The evaluation of the bearing capacity of a shallow footing on an undrained clay deposit is an important problem in foundation engineering, and a number of analytical, numerical and empirical methods has been proposed for various cases of single-layered (Terzaghi, 1943; Meyerhof, 1964; Vesic, 1973) and multi-layered clay deposits (Button, 1953; Brown and Meyerhof, 1969; Chen, 1975; Merifield et al., 1999). The latter mainly depends on the failure mechanism, which in turn depends on the geometry of the footing and characteristics of the soil, such as the ground's layered condition, the shear strength of each soil layer, the relative magnitude of shear strengths for the soil layers, etc. However, most of the existing equations and design charts for the estimation of bearing capacity have dealt with a homogeneous or layered clay whose shear strength is constant in each layer, despite the fact that most natural soil deposits exhibit varying shear strength distributions, even within a given layer.
- North America > United States (0.28)
- Asia (0.28)