Crapps, Justin M. (ExxonMobil Upstream Research Company) | Yue, Xin (ExxonMobil Upstream Research Company) | Berlin, Ronald A. (ExxonMobil Upstream Research Company) | Suarez, Heider A. (ExxonMobil Production Company) | Pribytkov, Petr A. (Exxon Neftegas Limited) | Vyvial, Brent A. (Stress Engineering Services) | Proegler, Jared S. (CRC Evans Pipeline International)
Integrity management of strain-based pipelines includes measures such as corrosion prevention, external damage prevention, ground movement monitoring, and geohazards mitigation. Despite preventive efforts, a pipeline may still become corroded or damaged. The damage may reduce the pipeline’s strain capacity and a repair method to restore the pipeline’s capacity will be required. This paper presents the qualification of the Type B split sleeve, a sealing repair methodology, for strain-based pipelines. The subjects addressed include selecting the Type B split sleeve as a repair candidate, finite element modeling of the repair, sleeve welding with in-service flow conditions, and full-scale proof testing of three repaired pipes.
Production and delivery of hydrocarbons in remote locations often require transportation of the hydrocarbons across challenging terrain. This may expose a pipeline to geohazards including faults, landslides, permafrost, earthquakes, and ice gouging. Pipelines are traditionally designed for pressure containment (a circumferential load), whereas most geohazards affect a pipeline by imposing loading in the longitudinal or axial direction. In extreme cases, the longitudinal loading can cause significant degrees of plastic deformation. Traditional pipeline design does not consider extreme longitudinal loading and the design methodology must be modified to ensure that the pipe is able to withstand all loading conditions.
Investigation of turbulence dynamics is very important for the understanding of dispersion and transport of pollutants in the marine environment. Specifically, at the surface boundary layer, dispersion phenomena are governed by the interaction of different forces (i.e., currents, waves, and winds) and are characterized by a wide range of temporal and spatial scales (Gallerano et al., 2016). Estimates of turbulence parameters able to describe the interaction of these different forces are required for an accurate prediction of pollutant pathways and concentrations. At present, turbulent dispersion simulations are mainly carried out by using Lagrangian particle models, alternatively based on a Wiener process or a Langevin scheme, which require as input data such turbulence parameters as diffusivity, velocity variance, and Lagrangian time scale (Monti and Leuzzi, 2010; De Dominicis et al., 2012). Besides, a new efficient approach is represented by kinematic chaotic models (Lacorata et al., 2014; Lacorata and Vulpiani, 2017).
Fourtakas, Georgios (University of Manchester) | Stansby, Peter K. (University of Manchester) | Rogers, Benedict D. (University of Manchester) | Lind, Steven J. (University of Manchester) | Yan, Shiqiang (City University of London) | Ma, Qingwei (City University of London)
This paper presents a two-dimensional, one-way coupling methodology between the quasi-arbitrary Lagrange–Euler finite element method (QALE-FEM) nonlinear potential flow solver and the incompressible smoothed particle hydrodynamics (ISPH) Navier-Stokes equations solver. Nonlinear potential flow solvers such as the QALE-FEM are highly efficient solvers for propagating waves in large domains; however, when extreme nonlinearity takes place, such as fragmentation, breaking waves, and violent interaction with marine structures, the methodology becomes incapable of dealing with these flow features. The particle method ISPH is known to be accurate for such highly nonlinear fragmentized flows and provides near-noise-free pressures. ISPH is thus ideal for near-field flows involving overturning, splashing, and slamming. Herein, we propose a one-way coupling methodology between QALE-FEM and ISPH where the methods are used for the far-field and inner/local regimes, respectively. To validate the one-way coupling algorithm, two sinusoidal waves have been used with satisfactory results. The intention is to extend this approach to the strong coupling of the potential flow solver with ISPH using a two-phase (air–water) solver. The aim is to reliably predict extreme wave forces and slamming on offshore structures such as decks and platforms for marine renewable energy and the oil and gas industry.
Wang, Rui (Chinese Academy of Sciences, Beijing) | Wang, Yu (Chinese Academy of Sciences, Beijing) | Wang, Shuo (Chinese Academy of Sciences, Beijing) | Tang, Chong (Chinese Academy of Sciences, Beijing) | Tan, Min (Chinese Academy of Sciences, Beijing)
This paper addresses the problem of three-dimensional (3-D) waypoint tracking for a biomimetic underwater vehicle (BUV) propelled by undulatory fins: RobCutt-II. Based on the specific mechanical design and control system configuration, the RobCutt-II can perform diversified locomotion patterns, especially submerging or surfacing vertically in the water. For practical underwater operating procedures, a selective switching control for 3-D waypoint tracking is proposed. This control scheme contains a depth controller, a waypoint tracking controller, and a selector. When tracking a series of given 3-D waypoints, the RobCutt-II can switch between two closed-loop locomotion patterns, i.e., the depth control pattern and the waypoint tracking pattern. Simulations and a comparative experimental study demonstrate the feasibility and effectiveness of the proposed switching control scheme.
Chen, Ling (University of Chinese Academy of Sciences, Beijing) | Zhou, Jifu (Chinese Academy of Sciences, Beijing) | Wang, Xu (Chinese Academy of Sciences, Beijing) | Wang, Zhan (Chinese Academy of Sciences, Beijing)
A new type of bottom-fixed structure, the so-called high-rise pile cap foundation, has been proposed and used to support offshore wind turbines in the Donghai Bridge Wind Farm, China. Engineers are unaware of the wave load mechanisms for this new structure. Using the Navier–Stokes equations and volume of fluid technique, a fully nonlinear numerical wave tank is established to investigate free surface wave loads and moments for the new structure. The interaction between the cap and piles are discussed in detail. In the case of fully nonlinear waves, the maximum horizontal wave load on all the piles with the cap can increase by 30% compared with those without the cap, and the maximum horizontal wave load on a single pile is nearly doubled. The horizontal wave load on the cap with the piles can increase by about 15%, while the vertical wave load decreases slightly. The conventional Morison formula and diffraction theory generally underestimate the wave loads on the piles and the cap as well.
This paper presents the application of a risk- and reliability-based inspection planning framework for the InnWind 20 MW reference wind turbine jacket substructure. A detailed fracture mechanics-based fatigue crack growth model is developed and used as a basis to derive optimal inspection plans for the jacket substructure. Inspection plans for different inspection techniques are proposed, and recommendations on how to optimize inspection intervals are discussed.
Upscaling current wind turbines to very large wind turbines is considered as one of the important ways to decrease the levelized cost of energy (LCoE) of wind energy. Steel jacket structures are one possible type of support structure for very large offshore wind turbines and have been considered in the EU InnWind project, INNWIND.EU (http://www.innwind.eu). Reliability with respect to fatigue failure is generally driving the design of offshore wind turbine jacket structures and is being considered in this paper in combination with applications of reliability-based inspection planning.
The pore water pressure in a seabed plays an important role in the stability of the seabed, and it is generally used to estimate seabed liquefaction induced by oceanic loads. When the principle of effective stress is applied, it can easily be derived that the increase of pore water pressure in the seabed means a decrease of effective normal stress and a higher likelihood of liquefaction. In fact, wave influences the load boundary conditions and pore water pressure boundary conditions simultaneously. On the basis of the liquefaction criterion of pore water pressure, two cases are studied: (1) the case where a different seabed is subjected to the same oceanic load and (2) the case where the same seabed is subjected to different oceanic loads. The relationship between pore water pressure in the seabed, the uplift force induced by the wave, and the possibility of liquefaction is established. The results show that the pore water pressure in the seabed under the wave trough (p < 0) should be used to estimate the likelihood of liquefaction rather than the positive pore water pressure under the wave crest (p >0). In the first case, the uplift force and possibility of liquefaction in the seabed decrease when |p| increases. However, in the second case, the uplift force and possibility of liquefaction in the seabed increase with |p|. In addition, these results are used to estimate the possibility of seabed liquefaction in examples, and the evaluation based on pore pressure is compared with that based on vertical effective stress. This conclusion will be applied for a comparison of the possibility of liquefaction due to pore water pressure between diverse cases.
In this study, undrained capacity of suction piles subjected to moment loading is examined using three-dimensional finite element analysis. The model was initially validated against well-established results in literature. The model was then used to investigate the effect of moment loading on vertical and torsional capacity by performing a sensitivity analysis by varying soil heterogeneity and suction pile geometry. The parametric study was carried out for suction piles with length to diameter ratios (L/D) varying from 1 to 7 embedded in soils with constant and linearly varying shear strength. The failure envelopes presented provide a better understanding and a simpler and quicker design method that can be readily used for the design of suction piles.
This article discusses the cyclic material behavior—in the form of stress–life, strain–life, and cyclic stress–strain curves— of different nodular cast iron materials derived from specimens taken from cast blocks and a main frame of a wind energy turbine. Results are shown for both static and cyclic strain-controlled tests performed at room temperature under constant and variable amplitude loading for alternating loading, respectively. The load-time histories used for the tests under variable amplitude loading are taken from a wind turbine hub and main frame. A negative overload was introduced to check the influence of overloads on the fatigue strength of the materials, provoking positive mean stresses in the specimen and thus a shorter lifetime.
In this paper, the authors present a finite element analysis (FEA)-based methodology for estimating the residual strength of degraded mooring chains. The paper presents work investigating FEA modeling parameter sensitivities and selection of appropriate parameters for FEA modeling. In addition, validation against break testing of full-scale chains is presented.
A typical offshore (e.g., floating production storage and offloading (FPSO)) mooring system may contain multiple components: chain stopper, fairlead or bending shoe, chain segments, wire rope, polyester rope, sockets, thimbles, anchors, and connectors or jewelry of various types. Because of its robust nature, chain is usually used at locations along the mooring line that are prone to the highest damage, such as at the top under high tension and in the touchdown or “thrash zone.” Two types of chain may be considered for mooring systems: studded and studless. Studded chains have a stud, or brace, placed between the bars in the midsection of the chain to prevent flexure and aid in fatigue endurance. Studless chains do not contain a bracing stud.