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Today, drill bits and mud motor issues can account for more than half of the reasons for pulling out of hole before total depth (TD) on directional drilling wells. The complete paper presents a methodology designed for optimally matching drill bits, mud motors, and bottomhole-assembly (BHA) components for reduced failure risks and improved drilling performance. Work Flow The overall work flow includes detailed modeling of each sophisticated component and an algorithm to combine them efficiently at the system level without losing their specific nature. The drill-bit model is created in 4D—3D space modeling plus the transient behavior with time. The detailed cutting structure model may include specifying the number of cutters and how to place them in a 3D cutter space.
Shi, Yu-min (Key Laboratory for Mechanics in Fluid Solid Coupling Systems, Institute of Mechanics, Chinese Academy of Sciences / School of Engineering Science, University of Chinese Academy of Sciences) | Gao, Fu-ping (Key Laboratory for Mechanics in Fluid Solid Coupling Systems, Institute of Mechanics, Chinese Academy of Sciences / School of Engineering Science, University of Chinese Academy of Sciences) | Liu, Jian-tao (Geophysical Services Division, China Oilfield Services Limited) | Zhu, You-sheng (Geophysical Services Division, China Oilfield Services Limited)
For the High-Pressure High-Temperature (HPHT) pipelines susceptible to global buckling, a reasonable risk assessment is particularly significant for their safe operation and structural integrity. The complex physical and mechanical characteristics of deep-sea sediments could bring great uncertainty to the pipe-soil interaction and the corresponding lateral buckling predictions. In this study, the physical and mechanical characteristics of undisturbed sediment samples recovered from certain deep-water locations of South China Sea are analyzed statistically, which exhibit inherent natural variability. Such statistical variability can be well quantified with the Coefficient of Variation (COV). Results indicate that the COV of mechanical properties is generally more pronounced than that of physical properties. The probability distributions of most soil parameters generally follow normal distributions by statistical hypothesis testing. Reliability analysis for the pipeline lateral buckling is then performed on the basis of analytical models by Hobbs (1984) etc. The pipe-soil friction coefficient is described by a random variable with an appropriate type of probability distribution to reflect the randomness of pipe-soil interaction. Monte Carlo simulations indicate that the probability for pipeline lateral buckling could be up to 50% compared to the deterministic method. Moreover, the COV values of the critical safe temperature, the corresponding buckle length and buckle amplitude are closely related to, but smaller than that of the basic random variable. In comparison with deterministic analyses, the present analyses may provide a beneficial insight into the lateral buckling of HPHT pipelines by considering the statistical characteristics of deep-sea sediments.
As offshore developments extend into deeper waters, the relatively high internal pressure and temperature becomes a dominant factor for the safety of deep-water exposed pipelines. Due to the seabed resistance against the pipeline thermal expansion, axial compressive force generates and accumulates along pipeline length (see Shi et al., 2019). Once the axial force reaches or exceeds the critical buckling force, the pipeline would experience lateral global buckling. Although lateral buckling is not a structural failure mode, the resulting excessive compressive force and bending moment may lead to structural failure. Hence, in the lateral buckling design procedure for exposed pipelines, first decision task is to check the susceptibility to experience buckling (DNV GL-RP-F110, 2018). If a pipeline is not susceptible to global buckling, only the axial walking check needs to be considered. Otherwise, the limit state check for the uncontrolled post-buckling would be further performed (DNV GL-ST-F101, 2017).
This study presents a dual-functional system, which is a submerged fluid-filled semi-circular piezoelectric membrane for breakwater and wave energy converter. The mixed Eulerian-Lagrangian method is used to simulate the fully nonlinear waves, deformation of the membrane and variation of voltage on the load . The simulation found that the variation frequency of the strain in the piezoelectric membrane is 2 times of the wave. There exists an optimum resistance of the load that can give the maximum electrical output power. The maximum electrical output power of the piezoelectric membrane occurs as the transmission coefficient of the wave approaches its minimum value.
The utilization of wave energy has been studied by many scholars for several decades. Most of studies focused on the wave energy converter (WEC) with higher wave energy extraction efficiency. This study presents a submerged fluid-filled piezoelectric membrane WEC , which is called SFPMWEC in the following section. Compared with traditional WECs, the wave energy extraction efficiency of SFPMWEC is lower. However, the construction cost of SFPMWEC is much lower than traditional WECs. Other advantages of SFPMWEC are easier maintenance and deployment, non-intrusion and cost sharing with breakwaters. As breakwaters, a submerged fluid-filled flexible membrane has been studied by some scholars. Ohyama et al (1989) had done experiments to study transmission and reflection waves over a submerged bottom-mounted fluid-filled membrane . Phadke and Cheung (1999,2001) studied the response of fluid-filled membrane in linear gravity waves by boundary element method (BEM) coupled with finite element method (FEM). The geometric nonlinearity due to the larger deformation of the membrane is considered in the work of Phadke and Cheung (2003). Das (2009) assumed small amplitude of surface waves and membrane deflection and used the threedimensional, coupled boundary element and finite element model to study the response of a bottom mounted fluid-filled membrane in a wave flume. Liu and Huang (2019) used the mixed EulerianLagrangian method to simulate the fully nonlinear interaction of waves and the submerged fluid-filled flexible membrane. These studies show that the submerged fluid-filled flexible membrane breakwater can reduce the transmission waves greatly at resonance of the membrane system. The resonance of the membrane system means that the maximum response of the membrane occurs as the natural frequency of the membrane system equal to the frequency of the incident wave. Therefore, it is possible to use a submerged fluid-filled piezoelectric membrane as both breakwater and WEC.
The Spar-type FOWT, which is a kind of the stable offshore wind generator, has been widely adopted and investigated in recent years. As a permanent mooring structure, it faces the issue on mooring line fracture. In the present work, the simulations are conducted in time domain to investigate its transient response in scenarios with fractured mooring lines. Towards this end, our in-house code SFND, which is a coupled aero-hydro-elastic numerical model is adopted to perform the simulations. The methodology includes a blade-element-momentum model for aerodynamics, a nonlinear model for hydrodynamics, a nonlinear restoring model of SPAR buoy, and a fully nonlinear dynamic algorithm for intact and fractured mooring lines. The simulations are conducted under both stochastic and freak wave scenarios. The motions of platform, the tensions in the mooring lines and the power generation performance are documented in different cases. According to the results, the large drift motion is observed and the transient response is discussed.
During the recent decades, the wind energy has attracted more and more attention because of its advantages and features, such as no pollution, no carbon emission, and so on. However, with the issues on the land limitation and the noise, the installation of the onshore wind turbines nearly reaches the bottleneck. Therefore, the wind turbines are designed to be supported by the offshore foundations, in order to catch the offshore wind energy, which is less turbulence and more strength than the onshore one. Generally, the fixed foundations, including pile, gravity, jacket, etc., are widely adopted. Nevertheless, according to previous research, the costs and difficulties of the installation and maintenance increase exponentially when the water depth exceeds 50m (Leimeister et.al, 2020). To overcome this situation, the floating offshore wind turbines (FOWTs) are proposed.
The conceptual designs of the floating foundation are basically based on the experiences from the oil and gas industry (Hsu, 2017). Hereby, the different types of the floating foundations can be majorly divided into three types, which contains the Spar type, the Semi-submersible type and the Tension Leg Platform (TLP) type. Among these innovative designs, the Spar buoy shows both well hydrodynamic performance and robustness according to numerical simulations and wave basin tests (Yang et.al, 2020, Salehyar et.al, 2017, Li et.al, 2018a, Duan et.al, 2016). Even more, the first floating wind farm, Hywind Scotland, also adopted five Spar-type FOWT and successfully generate power more than two years.
The objective of this study is to design and optimize the layout of the offshore wind farms to maximize the power at a specific location. The energy production of the downstream wind turbines decreases because of the reduced wind speed and increased level of turbulence caused by the wakes formed by the upstream wind turbines. Therefore, the overall power efficiency is lowered due to the wake interference among wind turbines. This paper focuses on using the application of a Gaussian-based wake model and different optimization algorithms like the differential evolution particle swarm optimization (DPSO). The Gaussian wake model uses an exponential function to evaluate the velocity deficit, in contrast to the Jensen wake model that assumes a uniform velocity profile inside the wake. The layout optimization framework has been created for the energy production in order to provide reference for specific conditions and constraints at the Gulf of Maine and other typical projects in the future.
With the growing requirement of energy and environmental protection, the sustainable energy like wind energy has been significantly concerned in recent years. In this case, the investigations about wind farm optimization have been concerned by lots of researchers. In wind farms, one of the most critical power reduction is caused by the wake and turbulence from the blades of previous turbines. Generally, this phenomenon would drop the power production and mechanical performance of turbines. The layout optimization of wind farms according to the wake has been an essential concern for both onshore and offshore wind energy applications.
Figure 1 indicates the annual average offshore wind speeds (m/s) in the United States. From this diagram, the Gulf of Maine have one of the greatest wind energy potential on the east coast. The Gulf of Maine locates very close to the cities such as Portland and Boston with magnificent electricity requirement. So, it is considerably valuable to investigate how to develop wind power in the Gulf of Maine.
He, Zechen (The State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology ) | Ning, Dezhi (The State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology ) | Gou, Ying (The State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology )
An optimization model of buoy dimension of wave energy converter is established by using differential evolution algorithm. The linear potential flow method is used in hydrodynamic calculation. Taking the vertical oscillating cylindrical buoy as the research object, the radius and draft of the buoy are optimized under each specified volume. Through the comparison of different volume optimization results, it is found that there is an optimal buoy volume for a specific wave condition. With the increase of the volume, the optimal draft tends to a fixed value, and the optimal radius tends to be an asymptote. In addition, the influence of different damping of power take-off systems on the optimization results is also studied.
Wave energy is a kind of renewable and clean energy. The development and utilization of wave energy is attracting the attention of many scholars and research institutions around the world, which may make a significant contribution to the world' power consumption. For the commercial feasibility of wave energy, it is very important to improve the production efficiency of wave energy device and reduce its construction, installation and operation costs. Obviously, the volume of the Wave Energy Converter (WEC) is a key factor affecting both the efficiency and the cost. De Andres et al. (2015) discussed that small equipment is usually more economical due to reduced material costs and deployment. Göteman et al. (2014) and Göteman (2017) showed that the total power production can be improved if the wave energy array consists of devices of different dimensions that are similar to the WECs that have been developed at Uppsala University since 2006 (Leijon et al.,2009). Most previous optimal studies focus on the buoy dimensions instead of the buoy volume. For example, Giassi and Göteman (2017) optimized the parameters of the single wave energy converter by parameter sweep optimization of the variables and genetic algorithm, in which the radius, draft and damping of the Power Take Off (PTO) systems are optimized simultaneously in discrete parameter space. Because there are many combinations of radius and draft under a certain volume even for a truncated cylinder buoy, it' difficult to get the relationship between the volume and the efficiency directly. That means the designer couldn't balance the cost and the efficiency with the optimal dimensions.
Gu, Yifeng (School of Mechanical Engineering, The University of Adelaide.) | Ding, Boyin (School of Mechanical Engineering, The University of Adelaide.) | Sergiienko, Nataliia Y. (School of Mechanical Engineering, The University of Adelaide.)
This paper proposes a novel power maximising control strategy for wave energy conversion applications and investigates its performance against linear spring-damper control on a fully submerged heaving point absorber wave energy converter (WEC) under both regular and irregular wave conditions. Inspired by the Phi method, the developed WEC control strategy presents an analytical solution which involves a quadratic damping term accounting for the nonlinear viscous drag in the WEC hydrodynamics. Therefore, its optimal control parameters can be analytically determined without optimisation and/or linearisation, which, however, usually accompanies conventional linear control strategies such as linear spring-damper control. Simulation results show that the proposed analytical control solution can absorb almost the same power as the optimised linear spring-damper control does in both regular and irregular wave conditions.
Due to the shortage of fossil fuel and the environmental impact caused by excessive carbon emission, renewable energy has become an emerging research field nowadays. There are various categories of renewable resources such as sunlight, wind, rain, tides, waves, and geothermal heat, among which the wave energy has great potential because of its consistency, high energy density and predictability. A wave energy converter (WEC) is a type of devices which can convert the ocean wave energy into useful electricity.
Although wave energy has several superior characteristics as mentioned above, compared with other renewable energy such as solar and wind, the main challenge in commercialising WEC technologies remains in reducing their costs by taking manufacturing, installation, and maintenance into consideration. The role of WEC control accounts for not only maximizing the WEC's power absorption efficiency but also ensuring its safety operation in harsh sea environment. Therefore, indepth understanding on WEC control can help to increase the efficiency of power absorption, lower the maintenance costs, and thus guarantee competitive energy costs.
According to linear wave theory, which assumes inviscid, irrotational and incompressible fluid (Falnes and Perlin, 2003), complex conjugate control (sometimes called impedance matching control) can achieve the maximum power absorption of a WEC but requires complex linearisation, optimisation and prediction procedures in its design due to the presence of nonlinear WEC hydrodynamics. Furthermore, in practice, the wave energy conversion process is accompanied with a resonant motion and, thus, the influence of nonlinear effects in the hydrodynamics such as the viscous drag may become significant violating the linear optimal control principles. In this case, conventional linear control strategies may no longer provide optimal solutions for the WEC power absorption leading to the emerging need of nonlinear control methods. However, the concept of WEC nonlinear control and its power absorption performance against traditional linear optimal control still requires in-depth study.
Liao, Zhenkun (College of Engineering, Ocean University of China) | Dong, Sheng (College of Engineering, Ocean University of China) | Wang, Zhifeng (College of Engineering, Ocean University of China) | Tao, Shanshan (College of Engineering, Ocean University of China)
In this paper, based on the current data since 1996 to 2015 obtained by the FVCOM ocean model, the design surface current speed of three selected sites in the Barents Sea is studied. Four types of probability distributions are applied to fit omnidirectional or directional annual extreme current speed, then corresponding return values are estimated. The results show that the return values of omnidirectional current speed are generally larger than those of directional, but there are exceptions, which should be taken into account when estimating and using the design parameters of ocean current speed.
In recent years, the ice cover of Arctic sea is declining. Bader et al. (2011) reviewed the research on the sea ice of Northern Hemisphere, and they concluded that the sea ice in the Arctic Ocean has decreased significantly in all seasons, with the fastest decline in summer, and probably will even be completely ice-free by the summer of 2040. Ross and Fissel (2018) reviewed recent findings of sea-ice research, they concluded that Arctic sea ice has changed a lot in the past 30 years, and its coverage has been greatly reduced especially in the summer and early fall, people are expected to have more Arctic commercial transportation and offshore oil and gas exploration in this century.
The Barents Sea is a marginal sea of the Arctic Ocean, with the Norwegian Seas to the west and the Kara Sea to the east. The Barents Sea has a maximum depth of 600m, and in its southeast near the Svalbard Archipelago, there is a wide continental shelf with a depth of less than 100m (ISO, 2010). This sea area is rich in oil and gas resources (U.S. Geological Survey, 2008). Herbaut et al. (2015) found that, the average area of sea ice in the Barents Sea has decreased rapidly since 2005, Specifically from 670 000 km2 in 2005 to 400,000 km2 in 2012. Duan et al (2018) found that the sea ice in the Barents Sea is experiencing a decreasing process with oscillations in some periods due to unsteady and extreme synoptic process.
In this study, a collision risk model was developed, based on gas model theory and Pedersen's collision and grounding mechanics. Busan north port was chosen as the area of assessment and, was divided into equal cells. Geometrical collision risk, both ship-ship and ship-structure, within each cell was analyzed following a probabilistic quantification. Moreover, bathymetry data of the port waters were analyzed to assess grounding risks. Results were plotted on Google EarthTM to identify the highest risk point and region within the area of assessment to aid safe maneuvering of vessels.
With the recent trends and advancements in maritime world, emergence of new ships is inescapable and consequently, maritime traffic density has continued to expand. Increased number of ships, as well as bigger ships in narrow passages attribute to higher volumes of traffic in already congested waterways and particularly, in port areas. This, in turn, makes ship maneuvering more difficult and complicated. Moreover, higher maritime traffic can increase the risk of collision accidents with unfavorable consequences. Although some major technological advancements such as ECDIS (Electronic Chart Display and Information System), ARPA (Automatic Radar Plotting Aids), GNSS (Global Navigation Satellite System) and GMDSS (Global Maritime Distress & Safety System) are successfully integrated with navigation, port and harbor areas are still more susceptible to collision accidents. Thus, evaluating the risk of collision has become an integral part in maneuvering supporting systems to improve safety in navigation by decreasing the risk of collision.
Collision risk in navigation is often misread due to the rarity of disastrous, individual accidents. Ylitalo (2010) discovered that the probability of an accident in a particular area would not be zero, although there is less or no records of previous incidents. Even though the probability of a direct ship-ship collision is very small, a minor incident can have unfavorable consequences, which can lead to loss of property as well as life at sea. Therefore, all risks in navigation have to be taken seriously. Identifying the risk areas, therefore, is vital to minimize and to avoid accidents. Once the risk areas are clearly identified, measures such as emergency planning can be taken for safe maneuvering of ships.
Tang, Pin (Shandong Provincial Key Laboratory of Ocean Engineering, Ocean University of China) | Meng, Xun (Shandong Provincial Key Laboratory of Ocean Engineering, Ocean University of China) | LI, Dejiang (Ocean University of China, CIMC Raffles Engineering Co., ltd)
The nonlinear dynamic responses of a payload hanging from an offshore large crane vessel are investigated numerically. A three dimensional fully nonlinear time domain multi-body model of crane and vessel based on pulley and cable drive is built to perform the analysis. The dynamic responses of payload under the hull motions of roll, pitch, heave and coupling motions of heave and roll, heave and pitch are investigated. The motion of the payload is proved to exhibit various nonlinear phenomena (for example, sub-harmonic motion, period doubling behavior) due to certain periodic chord motion presence of crane vessels. Conclusion drawn from this study could be used for payload pendulation forecast and devising techniques to control or damp the enormous motions.
Floating cranes are applied for a variety of tasks in offshore areas including transportation, assembling of costly structures and salvage operations. Efficient and safe operations of crane vessels at offshore are thus becoming increasingly important due to the increase in activities in deep water and particularly with a demand for higher lift capacity. Practical problems arise due to the difficulties in positioning accurately when the payload is handling with crane vessel operations. Even small disturbances in the state of the system could produce shaking of lifting weight and may entail the danger of collisions, which not only reduces the efficiency of the crane, but also threatens the safety of the staff, so the characteristic of the motion of the hull needs to be checked in advance in order to avoid potential risk by chaotic coupling effect.
Aiming at these issues, interdisciplinary research based on multi-body mechanics and virtual simulation technology has been carried out gradually by the scholars at home and abroad. Thomas Erling Schellin et al. (1991) developed a mathematical model, which treated hull and crane as one rigid body and considered elastic stretch of the hoisting rope assembly to predict the response of a shear-leg crane vessel in waves. Nonlinear large-angle swing of the suspended load coupled with surge, sway, heave, roll, pitch and yaw motions of the hull. Results showed the payload pendulation had little effect on motion of the hull. J. A. Witz (1995) used time domain numerical solution of the equations of motion to investigate the parametric excitation of loads suspended from crane vessels in random seas. Results showed large swinging motions would be generated when the dominant period of the incident waves was approximately equal to the natural period of the load or approximately equal to one half times the natural period. POSIADALA et al. (1996) established spherical pendulum model of the payload system, where the influence of vibrations in the hoist system on the crane and the load was considered. The highly nonlinear equations obtained had been numerically integrated using a fourth order Runge-Kutta algorithm. Large swinging motions were generated when the frequency of excitation applied on the base of crane was equal to the natural frequency of the payload system. C.CHIN (2001) presented the frequency content of the motion of crane vessel might contain significant energy near the natural frequency and/or twice the natural frequency of the free-swinging load. This situation could initiate an external and/or a parametric resonance. Moumen Idres et al. (2003) developed a nonlinear crane-vessel dynamic model that the vessel equations of motion were integrated simultaneously with the crane cargo equations. Simulations showed that large-amplitude response occurred at wave periods near the natural period of the hook load. Z. N. MASOUD et al. (2004) presented conditions that the frequencies of roll and pitch motions of the vessel were equal to the natural frequency of the payload pendulation and the frequency of heave motion was equal to twice the natural frequency of the payload pendulation were the worst-case excitation. B.W. Nam et al. (2017) applied both experiments and numerical calculations to investigate coupled motion responses of a floating crane vessel and a lifted subsea manifold during deep-water installation operations. For short wave periods, the efficiency of the passive heave compensator was maximized in reducing dynamic tension of hoisting wire. Y.J. Ha et al. (2018) investigated the mating operations of a topside module onto a FLNG by using a floating crane in waves. The lifted topside module showed two peak responses in sway and roll motions due to the interaction effect with the crane vessel. The higher peak happened at the roll resonant period of the floating crane vessel, while the other peak was caused by the pendulum resonance of the lifted topside module.