bluuebunny/crossref_metadata_2025_split huggingface dataset:
Local Ice Loads on the Sakhalin-II Project Structures: Probability Analysis and Comparison by Existing Design Codes
Authors: Sabodash Olga A. 
Published: October 2016

In the study the probabilistic modeling of local ice loads and pressures on wide structure has been carried out. Probabilistic analysis has traditionally been focused on distribution of their maximum values. The “Molikpaq” (PA-A) ice-class platform for “Sakhalin-II” project is considered as an example. The input parameters were modelled by Monte-Carlo method taking into account of full-scale data in the Piltun-Astokhskoe field during 1989÷2002 ice seasons. A comparative analysis of local ice loads and pressures on wide structure has been made on the basis of the Russian and international design codes, standards and recommendations. The obtained local pressure values were compared with public available data collected on the “Molikpaq” (PA-A) platform.
Some preliminary results and discussions are presented. Recommendations on the local ice loads and pressures for engineering design of structures on the Sakhalin offshore have been done.
Seamless Linepipe Response Under Small and Full Scale Reeling Simulation
Authors: Marines-Garcia Israel , Aldana-Díaz Jorge A. , Darcis Philippe P. , Quintanilla Hector M. 
Published: October 2016

Offshore pipelines projects, installed by reel-laying operations, are gaining momentum due to the increasing worldwide capacity of Reel Lay Vessels. It is well known that reel-laying installation causes repeated plastic straining (cyclic deformation) and, as a consequence, cyclic strain and ageing test is usually required for qualifying line pipe materials for such installation method. This qualification is typically named reeling simulation.
Reeling simulations can be made via full or small scale. In practice, full scale qualification lead time and full scale reeling simulation machines availability could be a constraint, thus, small scale reeling simulation is usually the best alternative. However, the similitude of small scale versus full scale simulations could be questioned. On this basis, an extensive study was carried-out considering tensile, toughness and sour testing, in order to evaluate the material response after reeling simulation, in order to clarify if the line pipe material will behave similarly regardless the straining method (small scale or full scale).
Different small scale samples configuration for straining were tested, depending on the posterior mechanical or sour test, and two different full scale reeling simulation machines were used for plain pipes straining.
Five seamless plain pipes, X65 line pipe were used for this study, with 3 (three) different outer diameters of 10.75″, 11.67″ & 16″ (273 mm, 296 mm & 406 mm). The current paper will present the main mechanical results of these materials after strain and ageing condition, comparing full and small scale straining methods.
Experimental Investigation of Friction and Hydraulics in Circular and Non-Circular Wellbores With Oil Based Drilling Fluids
Authors: Taghipour Ali , Lund Bjørnar , Ytrehus Jan David 
Published: October 2016

Borehole hydraulics, hole cleaning and mechanical friction are important factors for well planning and drilling operations. Many studies aim to exploit and optimize the effect of different operational parameters. The effect of wellbore geometry on hole cleaning and mechanical friction has so far not received much attention. This paper presents results from experimental laboratory tests where hydraulics, hole cleaning and mechanical friction have been investigated for circular and non-circular wellbore geometries with a relevant oil-based field drilling fluid (OBM). The non-circular wellbore geometry was made by adding spiral grooves to the wellbore walls in order to investigate the effects on cuttings transport and mechanical friction. The study contributes to describe the function and ability of deliberately induced non-circular geometry in wellbores as means to achieve a more efficient drilling and well construction. Improving hole cleaning will improve drilling efficiency in general, and will in particular enable longer reach for ERD wells. Reduced mechanical friction may improve the drilling process and many operations during the completion phase.
The laboratory experiments were performed in an advanced flow loop setup reproducing field-relevant flow conditions. The flow loop consists of a 10 m long 4″ inner diameter borehole made of concrete. A free whirling rotational string with 2″ diameter provides a realistic down hole annular geometry. A field-relevant oil based drilling fluid (OBM) was circulated through the test section at different flow rates. To represent the effect of rate of penetration, synthetic drilling cuttings (quartz sand particles) were injected at different rates through the annulus in the horizontal test section. The test results show that borehole hydraulics and cutting transport properties are significantly improved in the non-circular wellbore relative to the circular wellbore. The effect of the mechanical friction is more complex, yet significantly different for the two geometries.
Effect of Near Wall Turbulence on the Particle Removal From Bed Deposits in Horizontal Wells
Authors: Bizhani Majid , Kuru Ergun , Ghaemi Sina 
Published: October 2016

Although solids entrainment and deposition mechanisms have been studied extensively over the years, our understanding of fluids-particle interactions near bed interface is still limited. Progress toward such understanding has been relatively slow because of the difficulties inherent simultaneous measurement of local solids transport and adjacent near-bed fluid flow. With the introduction of non-intrusive measurement techniques such as Particle Image Velocimetry (PIV), it is now possible to determine the instantaneous velocity field and observe particle deposition/resuspension simultaneously under non-uniform flow conditions.
An experimental program was conducted to investigate different aspects of turbulent flow of water over the cuttings bed deposited in horizontal annuli. A large-scale horizontal flow loop consisting of 9 m long high quality optic glass pipes (95 mm ID of outer pipe and 38 mm OD of inner pipe) equipped with state of the art PIV system has been used for the experiments. Turbulent flow over cuttings bed experiments were conducted at superficial Reynolds numbers of 9300 and 10800. Natural irregular shaped quartz sands with 3 different mean sieve sizes of 260, 350 and 600 micron were used as solid particles.
The proposed work was accomplished through several tasks: i-) conduct experiments to measure the instantaneous local velocity profile during turbulent flow in the horizontal concentric annuli and examine the effect of stationary cutting bed on the local velocity profile, Reynolds stress and turbulence intensity; ii-) investigate the impact of particle size on the near-wall turbulent activities.
Results have indicated that existence of a cuttings bed on the lower side of the wellbore dramatically alters the near wall velocity profile comparing to the case with no cuttings bed. Presence of cuttings bed causes the maximum velocity to shift toward the inner pipe.
Presence of stationary cutting bed causes a reduction in Reynolds stress, axial and radial turbulence intensity, which in turn, would adversely affect the hole cleaning. Larger cuttings slightly enhanced turbulent stress and radial intensities. However, the increase in these entities as a result of increasing cutting size was far less than the decrease in them as a consequence of presence of stationary cutting bed. Axial turbulence intensity was the same in the core flow away from the cuttings bed for flow with and without a cuttings bed. However, the peak of axial intensities is shown to be less for flow near the cuttings bed.
An Investigation Into the Limitations of the Panel Method and the Gap Effect for a Fixed and a Floating Structure Subject to Waves
Authors: Peña Blanca , McDougall Aaron 
Published: October 2016

The wave-induced motions of vessels moored next to a fixed object and open to the sea impact the operability of many offshore operations, and should be assessed in order to avoid accidents and catastrophes. When analysing vessels moored by a fixed object (e.g. quay-side or platform), time domain simulations have shown numeric instabilities resulting in unreliable outcomes. The origin of the numerical instability might lie in the hydrodynamic added mass and wave radiation damping. This is typically calculated using potential flow methods and influenced by the existence of standing waves in the gap between the two bodies. For certain frequencies, these give negative values, potentially causing instabilities in non-linear (coupled) time domain simulations. In these cases, the vessel can behave unexpectedly, generating energy rather than dissipating it. As such, certain simulations have been disregarded as they are unlikely to accurately represent real-life scenarios.
This paper investigates and compares added mass and damping using two different tools and studies the gap effect when conducting diffraction analysis using 3D panel methods. The work covers a literature study into potential theory, multibody analysis, Computational Fluid Dynamics (CFD) and lid techniques.
This is followed by a study conducted using both panel method and CFD analyses. The results from both approaches have been compared, showing interesting information and the necessity of researching more into the problem addressed in this paper.
How to Deal With Basin Modes When Generating Irregular Waves on Shallow Water
Authors: van Essen Sanne , Pauw Willemijn , van den Berg Joris 
Published: October 2016

Modeling shallow-water waves in a basin with a finite length and width introduces challenges related to low-frequency (LF) waves, especially for testing of moored vessels with long natural periods. Waves in this frequency range are also present in reality, as for instance bound set-down waves and unbound free waves formed by the geometry bathymetry. In model basins, additional unwanted LF wave components will be formed as a side-product of the wave generation and due to the basin geometry though. Standing waves over the basin length and width (basin modes) can generally be identified, which are difficult to dampen using beaches. This is the case for every wave basin, as they all have finite dimensions.
Moored structures generally have natural frequencies in the LF range, which may be excited by basin modes with similar frequencies. It is therefore important to understand the natural modes of a basin before tests with moored structures in shallow water are done. The energy of these basin modes increases and their natural frequency decreases with decreasing water depth (waves travel slower in shallow water). Generally, it can be said that the issues with basin modes are present on very shallow water (typically ∼15–30 m water depth full-scale for structures with a length around 200 m at a scale around 1 to 40). The smaller the basin for the same water depth, the higher the basin mode frequencies and the higher the likelihood of resonance problems. The energy and frequencies of the basin modes and their relevance for specific tests depend on the effective length and width of the basin, the water depth, wave conditions and the (mooring stiffness of) the structure under consideration. The influence of these variables is evaluated in the current study. Tests were done in MARIN’s Offshore Basin (OB), but most of the results are also expected to be applicable to other basins. The observed basin mode frequencies during these tests were compared to the theoretical values, and an overview of the unwanted LF wave content as a function of water depth, wave height and period is presented. The energy and shape of individual basin modes is also discussed. Considering these results, a practical approach for future basin projects on shallow water is described.
Hydrodynamic Behavior of an Ultra-Deep Water Decoupled Buoy Supporting Risers
Authors: Claro Cláudia , Cruz Ivan , Karunakaran Daniel , Hepener Gustavo , Ji Chunqun , Ding Yun , Wu Chunfa , Scharnke Jule , de Wilde Jaap , Franciss Ricardo 
Published: October 2016

Hybrid risers systems used in recent offshore oil & gas projects to decouple large platform motions from main body of the risers can only support a single riser or a small number of risers. In the Sapinhoa Lula NE FPSO project, the challenge was how to design a riser system comprised of over forty risers and umbilical for each of the two FPSOs in 2,200 meter of deep water. The solution is large submerged Buoys with a unique hull form, each of them capable of supporting twenty plus risers and umbilical. The system is called Buoy Supported Riser system, or BSR system.
Comprehensive analyses have been performed during the design of the BSR system. In-depth study of the BRS’ hydrodynamic behavior has been performed to ensure that it meets all design requirements for a 30 year operation life and can be installed safely. Model tests including VIM tests have been conducted to verify hydrodynamic coefficients for the in-place and installation conditions.
The main objective of this paper is to present the hydrodynamic analysis methodology for the design of BSR system.
A Review of VIV Responses of Steel Lazy Wave Riser
Authors: Felisita Airindy , Gudmestad Ove T. , Karunakaran Daniel , Martinsen Lars Olav 
Published: October 2016

The Steel Lazy Wave Riser (SLWR) configuration is considered as one of the favorable solutions for deepwater applications. This is due to the SLWR’s capability to effectively absorb the dynamic motions from the vessel and the relatively lower cost that it offers. However, the application of SLWRs has its own challenges when it comes to fatigue due to Vortex-Induced Vibrations (VIV). The buoyancy section and the touchdown area may be critical to VIV due to curvature and current exposure onto the area. Furthermore, there is only limited previous research on VIV responses of a SLWR configuration.
This paper presents a parametric study of VIV responses of various SLWR systems. The study location is the deeper area of the Norwegian Continental Shelf. The main parametric variations are water depth, the length of the buoyancy section, the dimension of the buoyancy modules and the hydrocarbon content. These variations result in different lazy wave configurations, which give different trends of VIV responses. The analysis works are performed using the computer programs Riflex and VIVANA.
The observation results show that, for the type of current used in this study, riser configurations at the same water depth tend to have the same level of fatigue life. In addition, risers in shallower water have a lower fatigue life compared to risers in deeper water due to the current profiles used in this study and the higher system stiffness of the risers at shallower water.
The results also show that the buoyant section has only little to modest influence on the VIV-fatigue life. The influence will only become apparent when the buoyancy section creates a sufficiently high arch shape in the lazy wave configuration.
The riser’s selfweight mainly affects the riser’s fatigue life at the upper catenary part of the riser. Although the upper catenary part of the riser generally has sufficient VIV-fatigue lifetime, a riser with lighter content has a lower fatigue life at this part compared to a riser with heavier content.
Reliability Assessment of Marine Drilling Risers With Correlated Random Variables
Authors: Sengupta Piyali , Low Ying Min , Zhang Xiaodong , Adaikalaraj Peter Francis Bernad , Koh Chan Ghee 
Published: October 2016

Marine drilling risers are integral parts of the deep water offshore oil and gas industry. They are required to be designed for safe operations during their service lives with appropriate degree of reliability. With limited experience present in ultra-deep water, drilling risers are subjected to a range of uncertainties arising from untested environmental conditions. However, the current industry practice is limited to deterministic design of drilling risers which cannot account for uncertainties present in real life scenario. Under uncertain environmental conditions, deterministic methods may lead to undesired consequences, i.e. over conservative or unsafe design and misguided estimates of operability and down time of ultra-deep water drilling risers affecting the total life cycle cost. Thus, structural reliability analysis is particularly useful for prediction of the probabilities of downtime and disconnection of drilling risers incorporating the environmental uncertainties. In addition, structural reliability analysis can be used to reduce the total life cycle cost of ultra-deep water drilling risers.
In reliability analysis, many studies use uncorrelated random variables to represent uncertainties for simplification. Nevertheless, uncertainties in environmental conditions may be strongly correlated (for example wind and wave loads). If the correlation is not accounted for, it may lead to erroneous probability estimates. Thus, a joint environmental model is proposed in this paper using the conditional modeling approach where a joint density function is defined in terms of a marginal distribution and a series of conditional density functions. The joint density functions of environmental conditions are constructed in the current study using the recorded metocean data for Gulf of Mexico available from National Oceanic and Atmospheric Administration (NOAA) website. Then a computational model of connected ultra-deep water drilling riser system is constructed in ORCAFLEX to conduct time domain dynamic analysis. Thereafter, the correlated random variables in combination with the drilling riser computational model are utilized for conducting Monte Carlo Simulation (MCS) to evaluate the probabilities of downtime and disconnection. MCS is a widely accepted and robust approach and generally used as a benchmark to verify the accuracy of other reliability methods. But, in presence of large number of random variables representing environmental uncertainties, MCS is computationally demanding especially for the large number of simulations required to estimate small failure probabilities associated with extreme values. To this end, probability density functions of drilling riser responses are evaluated using Shifted Generalized Lognormal Distribution (SGLD) and Generalized Extreme-Value (GEV) Distribution both of which show similar accuracy (compared to MCS results) at a fraction of computing time (around 1/500 times).
Effect of Nano-Silicon Dioxide (SiO2) on Polymer/Salt Treated Bentonite Drilling Fluid Systems
Authors: Belayneh Mesfin , Aadnøy Bernt S. 
Published: October 2016

Recently the application of nanomaterial is attracting the oil and gas industry. The preliminary nanomaterials research results show an improving performance of cement, drilling fluid and Enhanced Oil Recovery.
In this paper, the effect of nano Silicon dioxide (SiO2) on polymer (HV-CMC, Xanthan gum, LV-CMC) and salt (KCl, NaCl) treated bentonite drilling fluid systems has been studied at room temperature.
The results show that the performance of nano SiO2 in bentonite mud system depends on its concentration and the types of salt and polymer systems used. In the considered fluid systems, it is also observed that the addition of about 0.06% SiO2 influences rheology, and filtrate loss of the drilling fluid systems. The viscoelasticity of the selected best system further studied and their hole -cleaning and hydraulics performances are simulated. The overall result shows that the formulated optimum concentration of nano-system shows good performances and rheological behavior.
ISUM: Its Birth, Growth and Future
Authors: Rashed Sherif 
Published: October 2016

ISUM (The Idealized Structural Unit Method) was born in 1972 to efficiently and accurately analyze the behavior of large size structures up to and beyond their ultimate strength. In this method a structure is divided into large elements, basically its structural units (members). Geometric and material non-linear behavior inside the element is formulated and expressed at a limited number of nodal points at the element boundaries. In this way a large structure can be modeled using a coarse mesh while still being able to consider the nonlinear behavior until the collapse of the structure.
Several ISUM elements have been formulated and used to analyze the non-linear behavior of large ship structures. In further developments, more elements with more accurate formulations have been developed and more types of structures have been analyzed using this method. The same ISUM concept has been applied to the analysis of welding deformation of large welded structures and to failure analysis of structural and mechanical components subjected to impact loads.
In this paper, the basic ISUM concept is outlined, and several elements are presented. Examples of applications to ships and marine structures are presented demonstrating the effectiveness of the method. Recent developments are also reviewed and future potential is explored.
Efficient Collapse Analysis of Ductile Components Subjected to Impact Loads
Authors: Yasuda Akihiro , Rashed Sherif 
Published: October 2016

In collapse analysis of mechanical or structural components made of ductile materials and subjected to impact loads, it is necessary to consider material tearing (cracking and crack propagation). Traditional methods that focus on material behavior at crack tip require very fine FE meshes and are not suitable for impact analysis where explicit integration codes, for very good reasons, are used. On the other hand, in methods which utilize surface separation such as the interface element approach or node break approach, crack propagation route needs to be known beforehand.
In this paper, the development of an efficient 3-D Finite element for such collapse analysis is reported. This element utilizes the ISUM concept and may be used in relatively coarse meshes at crack tips. Stress-strain relationship takes account of element size and strain rate effects. Crack propagation through the element (tearing of the element) is based on the sum of the strain energy and surface creation energy, and takes account of the effects of element size and strain rate on the tearing energy. Comparison of test and analysis results of a conical impactor dropped on a circular steel plate is utilized to confirm the validity of the element.