bluuebunny/crossref_metadata_2025_split huggingface dataset:
Leakages Through Radial Cracks in Cement Sheaths: Effect of Geometry, Viscosity and Aperture
Authors: Skorpa Ragnhild , Vrålstad Torbjørn 
Published: December 2020

Abstract
Annular cement sheath is considered to be one of the most important barrier elements in the well, both during production and after well abandonment. It is however well-known that mechanical damage to the cement sheath might result in leakage pathways, such as microannuli and radial cracks, and thus loss of zonal isolation. In this paper we have studied the effect of geometry, aperture and viscosity on the resulting pressure driven flow through real radial cracks in cement sheaths using Computational Fluid Dynamics (CFD) simulations.
Real radial cracks were created by downscaled laboratory pressure cycling experiments and the resulting geometries were mapped by X-ray Computed Tomography (CT). This gave a unique 3D volume of the degraded cement sheaths which provides detailed information about the morphology, such as the irregular apertures and roughness, as well as locations of the radial cracks.
In this study, we have used five experimentally created geometries, varying from barely connected to fully connected and almost uniform cracks. Additionally, theoretical uniform models with homogeneous aperture and a smooth surface were created for comparison. The simulations were performed by importing the experimentally created leak paths into a CFD simulation software, making it possible to determine the actual flowrate as a function of pressure drop. Methane gas, water and oil was used as model fluids.
The simulation results show that fluid flow through real cracks in cement sheath is complex with torturous paths, especially around bottlenecks and narrow sections. Additionally, the results show that flow of both methane gas- and water are not linear and hence does not follow Darcy’s law. This illustrates that simple models are not able to fully describe fluid flow through such complex geometries.
Structural Reliability Analysis Method for Assessing the Fatigue Capacity of Subsea Wellhead Connectors
Authors: Hørte Torfinn , Reinås Lorents , Wormsen Anders , Aardal Andreas , Gustafsson Per 
Published: December 2020

Abstract
Subsea Wellheads are the male part of an 18 3/4” bore connector used for connecting subsea components such as drilling BOP, XT or Workover systems equipped with a female counterpart — a wellhead connector. Subsea wellheads have an external locking profile for engaging a preloaded wellhead connector with matching internal profile. As such connection is made subsea, a metal-to-metal sealing is obtained, and a structural conduit is formed. The details of the subsea wellhead profile are specified by the wellhead user and the standardized H4 hub has a widespread use.
In terms of well integrity, the wellhead connector is a barrier element during both well construction (drilling) activities and life of field (production). Due to the nature of subsea drilling operations, a wellhead connector will be subjected to external loads. Fatigue and plastic collapse due to overload are therefore two potential failure modes. These two failure modes are due to the cyclic nature of the loads and the potential for accidental and extreme single loads respectively. The safe load the wellhead connector can sustain without failure can be established by deterministic structural capacity methods.
This paper outlines how a generic and probabilistic engineering method; Structural Reliability Analysis, can be applied to a subsea wellhead connector to estimate the probability of fatigue failure (PoF). As the wellhead connector is a mechanism consisting of a plurality of parts the load effect from cyclic external loads is influenced by uncertainty in friction, geometry and pre-load. Further, there is a inter dependence between these parameters that complicates the problem. In addition to these uncertainties, uncertainties in the fatigue loading itself (from rig and riser) is also accounted for.
This paper presents results from applications of Structural Reliability Analysis (SRA) to a wellhead connector and provides experiences and learnings from this case work.
Numerical Investigation on Wave Transmission by a Submerged Reef Using MIKE 3 WAVE FM
Authors: Raju Rahul Dev , Arockiasamy Madasamy , Sundaravadivelu Ranganathan , Selvaraj Sherlin Prem Nishold 
Published: December 2020

Abstract
Wave transmission of a 1:10 gradient slope submerged reef is studied using MIKE 3 WAVE FM software. The study focuses on the effect of wave steepness and relative submergence depth over the reef on the wave transmission for three water levels. The results from the numerical analysis are compared with published literature on wave transmission of submerged structures. The results from the numerical analysis using MIKE 3 WAVE FM software show that the wave steepness and relative submergence depth over the reef have strong dependence on the wave transmission of submerged reef. The wave transmission coefficient shows a decreasing trend with increasing wave steepness.
Calculation of Environmental Load for a Large FPSO Undocking
Authors: Yuchun Du , Zhimei Chen , Hankun Yang , Bo Zhou , Chunhui Li 
Published: December 2020

Abstract
Ship undocking is an essential process in the construction of large ship. Nowadays, the traditional empirical method is usually used to calculate the environmental load during large ship undocking of large ship and to determine the power and number of assistant tugboats in the world shipbuilding industry. Firstly, the OCIMF with traditional empirical formula mathematical model for solving the environmental load problem is established in this paper. According to the location of the dry dock and the meteorological and hydrological conditions while undocking, the environmental load of a large FPSO with different wind, wave, and current combination from 0°to 90°are is calculated by using the OCIMF with traditional empirical formula method, and then the influence of the wind, wave and current load on large FPSO are is analyzed. Secondly, the environmental load is calculated by using numerical simulation calculation method based on the same environment conditions. Through comparing the analysis results between the two calculation methods, the reliability of using the OCIMF method is testified reliable to large barge-type FPSO, and the maximum environmental load is determined. Lastly, as a result the undocking plan and the power and number of assistant tugboats are finally determined. The actual undocking project shows that the OCIMF with traditional empirical formula method is reliable for calculating the environmental load of a large barge-type FPSO.
Surface Waves Under the Sea Ice in the Western Arctic During 2019 R/V Mirai Cruise
Authors: Kodaira Tsubasa , Waseda Takuji , Nose Takehiko , Inoue Jun , Sato Kazutoshi , Voermans Joey , Babanin Alexander 
Published: December 2020

Abstract
Surface ocean waves are one of the potential processes that influence on the Arctic sea-ice extent. A better understanding of the generation, propagation, and attenuation of ocean waves under the sea ice is necessary to discuss the future Arctic climate change. We deployed two drifting wave buoys in the marginal ice zone in the western Arctic. Since the surface wave observation in the marginal ice zone is rare, the obtained data are useful for validation of the numerical modeling of the surface waves under the sea ice. The first buoy was deployed in the pancake-ice covered area and the second one in the open ocean. The distance between the two buoys at the deployment was about 40km, and the second buoy was deployed approximately 5 hours after the first deployment. The comparison of the wave bulk statistic measured by the two buoys shows the wave transformation under the sea ice. In general, the significant wave height decreases, and the mean wave periods increase by the presence of the sea ice.
Dynamic Response of a Wave Energy Converter With Resonant U-Tank
Authors: Afonja Adetoso Justus , Brizzolara Stefano 
Published: December 2020

Abstract
This paper describes the concept design and preliminary dynamic analysis of a pitching wave energy converter (WEC) device, based on a pitching resonant floater, a pitch resonance tuning tank system and Wells turbines in regular head waves. The device has a bow/stern symmetry, which gives an advantage of the U-tank been strongly coupled with the floater in the pitch degree of freedom and both chambers will have their separate pneumatic turbines. The integrated dynamic model coupling the U-tank system as given with the motion of the floating body in regular waves and the power take off (PTO) device is physically and mathematically defined. This coupling effectively creates a multi-body dynamic system and thus alters the motion response amplitude operator of the device in waves creating multiple resonance peaks. The integrated dynamic model is solved in time domain to account for non-linearities. Excitation, radiation and diffraction forces are calculated in frequency domain from a 3D boundary element method (BEM) and corrected by Cummins equation (convolution integral) for memory effects to be used in the time domain solution. The time dependent motion of the free surface creates a pressure difference inside the chamber with respect to the atmosphere which is used by the PTO turbine. The dynamic model of the integrated system is used to predict the maximum extracted power for a given incident wave power. A systematic study, considering a change in PTO damping is performed to search for the maximum extracted power in any given regular wave condition.
Reinforcement Learning From Pixels: Waterflooding Optimization
Authors: Miftakhov Ruslan , Efremov Igor , Al-Qasim Abdulaziz S. 
Published: December 2020

Abstract
The application of Artificial Intelligence (AI) methods in the petroleum industry gain traction in recent years. In this paper, Deep Reinforcement Learning (RL) is used to maximize the Net Present Value (NPV) of waterflooding by changing the water injection rate. This research is the first step towards showing that the use of pixel information for reinforcement learning provides many advantages, such as a fundamental understanding of reservoir physics by controlling changes in pressure and saturation without directly accounting for the reservoir petrophysical properties and wells.
The optimization routine based on RL by pixel data is tested on the 2D model, which is a vertical section of the SPE 10 model. It has been shown that RL can optimize waterflooding in a 2D compressible reservoir with the 2-phase flow (oil-water). The proposed optimization method is an iterative process. In the first few thousands of updates, NPV remains in the baseline since it takes more time to converge from raw pixel data than to use classical well production/injection rate information.
RL optimization resulted in improving the NPV by 15 percent, where the optimum scenario shows less watercut values and more stable production in contrast to baseline optimization. Additionally, we evaluated the impact of selecting the different action set for optimization and examined two cases where water injection well can change injection pressure with a step of 200 psi and 600 psi. The results show that in the second case, RL optimization is exploiting the limitation of the reservoir simulation engine and tries to imitate a cycled injection regime, which results in a 7% higher NPV than the first case.
Sensitivity Study About Ultimate Strength and Postbuckling Behavior of Stiffened Box Deck Girder Under Compression
Authors: Zhou Chunqi , Song Dan 
Published: December 2020

Abstract
The proper determination of this paper is to study the ultimate strength and postbuckling behavior for complicated stiffened deck girders of offshore platforms. Normally, offshore platforms are designed with reinforcing stiffeners on box deck girder.
The box deck of column stabilized platform will be simulated with FEM software ABAQUS. Linear eigenvalue analysis is firstly applied to introduce the initial imperfection into the structure. Then the non-linear postbuckling analysis for the box deck girder will illustrate ultimate strength and the failure mode under axial load after collapse. The ways how the stiffeners, eigenmode and imperfections influence the ultimate capacity will also be analyzed.
Comparing variable elements affecting the structural strength, the work shows the offshore box deck girder section from the engineering project in this paper is quite robust to the axial compression. For this kind of robust design, such as the box deck girder, the eigenmode selection and amplitude of imperfection will exert slight effects on the ultimate strength, but the severe imperfections will accelerate the local buckling. Stiffeners design will exert dramatic influence on the ultimate strength and postbuckling behaviors. And the work to find the optimum balance among structural strength variable load and allowable imperfections seems to be very promising in engineering. The conclusions provide a more clear insight into the further optimization of the offshore square structure design.
Challenges due to Welds Fabricated at a Close Proximity on Offshore Structures, Pipelines, and Piping: State of the Art
Authors: Bhardwaj Sachin , Ratnayake R. M. Chandima 
Published: December 2020

Abstract
In offshore structures, pipelines and piping, there are various configurations where welds are often in close proximity to each other. TKY joints in offshore structures, welds of nozzles, tees, elbows and circumferential welds of piping in compact layouts are a few examples. Depending on their application, different codes (ASME B31.3, ISO 19902, etc.) either recommend different criteria or provide no explanation for deciding a minimum distance between proximity welds. The guidance provided in these codes is inadequate for a field inspector to make an informed decision on site. Some international standards specify a minimum distance between welds, based upon some factor regarding the diameter or thickness of the parts under welding or they give no explanation, which creates an ambiguity among contractors and inspectors on site. The overlapping of two adjacent heat affected zones (HAZ) can have a deleterious effect on the material properties of the metals, eventually leading to catastrophic failures in the life cycle of high-risk components like offshore structures, process piping, etc. The different thermal cycles of adjacent welds with varying cooling times can drastically change the microstructure/mechanical properties of the metals, where locked in residual stress can amplify the effect towards failure. Since the aforementioned codes are deficient in providing technical justification regarding noncompliance of maintaining proximity distances, an approach for understanding close proximity effects on structural integrity is needed. This manuscript presents a brief assessment of international standards for specifying the minimum distance between close proximity welds for structural and pressure vessels’ codes. Challenges like residual stresses’ impact on fatigue strength, fatigue crack growth and fitness for service for fracture assessment are discussed briefly for proximity welds. Finally, building on the literature review, a framework for future research is presented.
Numerical Modeling of Wave Damping Induced by Emerged Moving Vegetation
Authors: Gupta Aditya , Behera Manasa R. , Heidarpour Amin 
Published: December 2020

Abstract
The unprecedented risk of global warming has put the coastal population at greater risk from coastal hazards due to an increase in sea level and other storm-related activities. Coastal vegetations are one of the soft solutions that can be implemented for wave mitigation. This study aims to investigate the wave damping effect of a regular wave by emergent moving coastal vegetation. Smoothed Particle Hydrodynamics (SPH), a particle-based method is used for generating fluid particles and Differential Variational Inequality (DVI) is coupled with SPH to deal with the dynamics of moving vegetation. The 3-D numerical model is simulated using an open-source tool DualSPHysics 4.4. The model is tested for regular wave height (H) of 0.08 m, wave period (T) of 2 seconds in a water depth (d) of 0.40 and 0.45 m for two relative vegetation height (h/d) of 1.25 and 1.11 respectively. The results are validated with the experimental study for the rigid vegetation and then the model is extended for moving vegetation. The results indicate that the wave damping is overestimated in the case of rigid vegetation. Further, the application of this study can be extended for studying the tsunami hazard mitigation in the presence of coastal forest.
Fretting Fatigue Design of Subsea Connectors: A Generalised Approach to Testing
Authors: Andresen H. , Hills D. A. , Wormsen Anders , Macdonald K. A. 
Published: December 2020

Abstract
In this paper fretting fatigue is addressed as a potential design consideration for wellhead connectors. The study of near-edge relative motion for frictional contacts under constant normal load is described using analytical, numerical and asymptotic methods. Based on published fretting fatigue experimental data an argument is drawn for a generalised fretting fatigue test design. We do this by reducing the parameters responsible for crack nucleation to the smallest number possible and thereby revealing the fretting fatigue strength as a material property independent of geometrical features. Easy to apply recipes are described and thoughts on a potential apparatus are shared with the reader. Commercial potential lies in the wide-ranging applicability of experimental results across many prototypes and loadings once an appropriate amount of fretting fatigue data has been generated for the material in question.
On the Correlation Between Floating Wind Turbine Accelerations, Rotor and Tower Loads
Authors: Choisnet Thomas , Percher Yohan , Adam Raphaël , Favré Mathieu , Harries Robert 
Published: December 2020

Abstract
Research in floating wind turbine resulted in the publication of a number of studies comparing wind turbine loads on a variety of floaters and fixed foundations. Some of them concluded that the blade and drivetrain loads would only be marginally increased -if increased at all — when a turbine would be installed on a floater [1] [2] and [3]. This paper proposes to evaluate how rotor and tower loads are correlated to nacelle acceleration, wind and wave conditions. It can somehow be considered as an extension to a barge-type floater and onsite measurements, of published work applied to fixed offshore wind turbines [4] and a spar-type floating wind turbine [5].
The body of data used for this exercise includes results from full-scale prototype measurements and simulations for a variety of turbine ratings. It can be concluded that in power production cases, blade and main shaft loads are only weakly correlated to nacelle low frequency accelerations and hence wave conditions, hence aerodynamic loads are still the main driver for rotor and tower top loads. In rotor-idling conditions, the situation is mainly dependent on the wind speed range, but aerodynamics are the largest contributor of blade and main shaft loads in severe wind conditions. These results can help understand where design uncertainties lie in floating wind turbine loads.
On Normalized Fatigue Crack Growth Modeling
Authors: Glavind Sebastian T. , Brüske Henning , Faber Michael H. 
Published: December 2020

Abstract
Modeling of fatigue crack growth plays a key role in risk informed inspection and maintenance planning for fatigue sensitive structural details. Probabilistic models must be available for observable fatigue performances such as crack length and depth, as a function of time. To this end, probabilistic fracture mechanical models are generally formulated and calibrated to provide the same probabilistic characteristics of the fatigue life as the relevant SN fatigue life model. Despite this calibration, it is recognized that the rather complex fracture mechanical models suffer from the fact that several of their parameters are assessed experimentally on an individual basis. Thus, the probabilistic models derived for these parameters in general omit possible mutual dependencies, and this in turn is likely to increase the uncertainty associated with modeled fatigue lives. Motivated by the possibility to reduce the uncertainty associated with complex multi-parameter probabilistic fracture mechanical models, a so-called normalized fatigue crack growth model was suggested by Tychsen (2017). In this model, the main uncertainty associated with the fatigue crack growth is captured in only one parameter. In the present contribution, we address this new approach for the modeling of fatigue crack growth from the perspective of how to best estimate its parameters based on experimental evidence. To this end, parametric Bayesian hierarchical models are formulated taking basis in modern big data analysis techniques. The proposed probabilistic modeling scheme is presented and discussed through an example considering fatigue crack growth of welds in K-joints. Finally, it is shown how the developed probabilistic crack growth model may be applied as basis for risk-based inspection and maintenance planning.
A Suggested Shaping Exponent in Wheeler Approach Under Overload Condition for High Manganese Steel
Authors: Park Jeong-Yeol , Kim Myung-Hyun 
Published: December 2020

Abstract
Recently, International Maritime Organization (IMO) reinforced the regulations for nitrogen oxide (NOx) and sulfur oxides (SOx) toward the reduced emission. To avoid serious environmental issues, the need for liquefied natural gas (LNG) fuel tanks arose for new constructed vessels. LNG fuel tanks are typically fabricated with low temperature materials that exhibit excellent fatigue performance at cryogenic temperature. In manufacturing of LNG fuel tanks, high manganese steel is known to be cost effective compared to other low temperature materials such as 9 wt.% nickel alloy steel, SUS304L and INVAR alloy. Therefore, extensive efforts are carried out to investigate the fatigue performance of high manganese steel. However, such investigations are yet limited to the constant amplitude load case only.
In order to reflect loading or unloading condition of LNG vessels in terms of fatigue performance, this study investigates the fatigue crack growth characteristics of high manganese steel under overload condition. The main parameters considered are the overload ratio (OLR) and the mean stress. We employ the Wheeler approach for the estimation of fatigue crack growth characteristics. In general, the Wheeler approach consists of crack length, plastic zone size and shaping exponent. Among three parameters in Wheeler approach, we assess the relationship between OLR and shaping exponent and suggest a modified equation for the shaping exponent considering the mean stress effect. In order to predict the effect of overload, the estimated fatigue life based on the Wheeler approach with the modified equation was compared to that with a constant amplitude load.