bluuebunny/crossref_metadata_2025_split huggingface dataset:
Pushover Load Factors for Fixed Steel Platforms Sensitive to Topside Load and Wave-in-Deck Load
Authors: Fraser Ramsay , Manzocchi Mark , Gibson Richard 
Published: October 2015

The objective of this paper is to present recent work in the development of a method for the strength assessment of offshore jacket structures subject to storm loading that is consistent across all global offshore regions.
Recent developments in the application of response based metocean analysis together with the establishment of a standardized structural reliability model has resulted in an assessment method that can be applied in a consistent manner to all fixed jacket structures in all global regions. Applying this method in the “assessment” stage of the SIM process, as published by API and ISO, would aid global standardization of both the assessment methods and the performance criteria.
The assessment methods have evolved over the last 3 years and have been subject to application and testing on several projects involving the assessment of existing offshore jacket structures. They have proven to be capable of discriminating between the differing extreme environments and differing evacuation and unmanning procedures that occur in different regions while being compatible with existing approaches to structural integrity. The paper will describe the standardized structural reliability model and provide examples of load factors for pushover and pushdown analysis for fixed steel offshore platforms that have a storm load capacity that is sensitivity to topside load and wave-in-deck load.
Analysis and Probabilistic Modeling of the Unstationary Ice Loads Stochastic Process, Based on Experiments With Models of Offshore Structures
Authors: Zvyagin Petr , Sazonov Kirill 
Published: October 2015

Experiments with models of platforms and offshore structures with vertical and inclined panels, which were conducted at Krylov Research Center (St. Petersburg), demonstrated that sometimes ice loads time series registered in these experiments cannot be considered as stationary. At the same time until nowadays methods and algorithms of probabilistic modeling were mainly based on the assumption of ice loads time series stationarity. That is because the analysis and modeling for stationary stochastic process is easier than for those unstationary.
In the paper the method for determining the presence of unstationarity in ice loads time series, based on statistical analysis, is described. This method employs sample mean normality. Fuzzy C-means algorithm is used to cluster autocorrelation vectors, which are built for different fragments of time series. In the paper ice loads time series, got in experiments in ice tank with offshore structure columns and basement models, are investigated on their unstationarity. The algorithm of unstationary ice loads time series simulation is offered.
Qualified Assessment for Lifetime Extension of Flexible Risers
Authors: Leira Bernt J. , Løtveit Svein Are , Berge Stig , Fergestad Dag , Langhelle Nina 
Published: October 2015

There have been many challenges with respect to long term operation of flexible pipes, in many cases with the need to replace or repair them before the end of the initial design life. The number of identified failure mechanisms and observed failure events is also increasing.
In the present paper, some typical issues that arise during the process of integrity assessment and qualification for lifetime extension are outlined. More detailed considerations are illustrated in relation to a particular case study. This involves elaboration of the different steps which are required in order to be able to extend the lifetime of a flexible riser for the case of corrosive annulus environments. The particular case of an outer sheath damage is applied for the purpose of illustration.
Sediment Attractors: Seabed Shear Stress Shadows Around Subsea Pipelines Cause Net Sediment Accretion
Authors: Zhao Fuyu , Griffiths Terry , Shen Wenwen , Draper Scott , An Hongwei , Leggoe Jeremy , Carneiro Daniel 
Published: October 2015

This paper presents interpretation of the results of 2D CFD modelling using ANSYS Fluent, which has been undertaken for a parametric range of over 200 cases, including over 60 different seabed geometries, pipe diameters and seabed roughnesses as well as a range of steady current, wave and combined wave / current cases. Through analysis of the results including evaluation of seabed shear stress amplification factors compared to far-field ambient values, integration across the seabed of seabed shear stresses and bedload transport potential, the conditions under which sedimentation can be expected are predicted.
The results have relevance to improving our understanding of sedimentation (backfilling) around subsea pipelines under live bed conditions, since the presence of shear-stress deficits or shadows leads to enhanced accretion of sediment in the region of a pipeline, even where there is localised amplification of shear stress right next to the pipe. The results are expected to enable better approaches design of subsea pipeline stability on erodible seabeds, or on impermeable rocky beds where veneers of mobile sediment are present.
A Computational Fluid Dynamics Approach to Predict Pressure Drop and Flow Behavior in the Near Wellbore Region of a Frac-Packed Gas Well
Authors: Molina Oscar , Tyagi Mayank 
Published: October 2015

Well completion plays a key role in reservoir production as it serves as a pathway that connects the hydrocarbon bearing rock with the wellbore, allowing formation fluids (e.g. oil, gas, water) to flow into the well and then up to production facilities on the surface. Frac-packing completion (F&P) is a well stimulation technique that vastly increases the fluid transport capability of the near wellbore region in comparison with the original formation capacity by filling fractures and perforation tunnels with high-permeability proppant, thus enabling higher production rates for the same pressure drop. Hence, it is of interest for the production engineer to have an accurate description of the actual and predicted production performance in terms of pressure drop and flowrate after the F&P completion process is done. However, in developing a mathematical model of this scenario two critical challenges should be faced: (a) as fluid flows at high flowrates it begins to deviate from linear behavior, i.e. Darcy’s law is no longer valid, (b) compressible fluid flow behavior in the near wellbore region cannot be intuitively predicted due to the geometrical complexity introduced by the well completion (e.g. perforation tunnels and fractures). Additionally, this kind of mathematical model must take into account the existence of three different domains: reservoir (porous, low permeability), completion region (porous, high permeability), and free flow region.
In view of these complications, this study presents a computational approach to model and characterize the near wellbore region with F&P completion using computational fluid dynamics (CFD) modeling, combining a non-linear (non-Darcy or Forchheimer) real gas flow in porous media with a turbulence model for the free flow region. This study is classified into three parts: 1) verification case, 2) Darcy vs. non-Darcy flow, and 3) erosion analysis. All simulation cases are assumed to be isothermal, steady state gas flow. Streamlines are implemented to identify the possible kinds of flow regimes, or patterns, in the near wellbore region and it is shown that gas flow pattern can be high unpredictable. Turbulence production and erosional velocity limit are also analyzed. Finally, mathematical correlations for well completion performance of this particular case study are derived using data curve fitting.
In conclusion, the CFD approach has proven to be a powerful yet flexible computational tool that can help the production and/or reservoir engineer to predict flow behavior as well as production performance for a gas producing well with F&P completion, while providing an insightful graphical description of pressure and velocity distribution in the near wellbore region.
Experimental Investigation of Water Entry Impact on Hydrophobic Surfaces
Authors: Guzel Bulent , Korkmaz Fatih C. 
Published: October 2015

The results of an experimental investigation on hull bottom slamming of three different geometries, sphere, cylinder and wedge, with hydrophobic surfaces are presented. In water entry of blunt bodies, different fluid dynamics phenomena like jet formation, cavity formation, water splashing, flow separation on solid surfaces and air entrapment between solid and liquid surface have been studied for decades. Our study is aimed at understanding and modeling the dynamics of slamming under an extended range of parameters including hydrophobic surfaces.
In this study, drop tests have been set up for hull bottom slamming by dropping a body from various heights toward water surface. From digital images captured using a high speed camera, flow separation and water splashing at different velocities are observed and spreading diameters and entrance characteristics are measured during the impact process. At the same time, we measure the pressure distribution on the surface of the bodies during impact via strain gages.
Effect of Nano and Micro Sized Particle Additives on the Mechanical Strength of Cement Plug
Authors: Belayneh Mesfin , Aadnøy Bernt S. 
Published: October 2015

Cements in oil wells are exposed to high temperatures, a high pressures and a degrading environment. These affect the mechanical strength of the cement over time. Cement is often part of well integrity problems, sometimes creating leak paths to surface, but also allowing sour reservoir gases to corrode casings.
Poor cement bond quality and casing corrosion are two fundamental problems with oil well cements. This paper presents the effect of vegetable fiber, nano- and micro particle additives on cement slurry. The mechanical strength of the cement plugs were analyzed through sonic measurement and uniaxial compressive test. The internal structure of the cement plugs were analyzed through Scanning Electron Microscope (SEM).
The test results show an improved internal structure, higher load carrying capacity, longer deformation and higher modulus of resilience.
Designing Drilling Fluids to Combat Circulation Losses for Arctic Environments
Authors: Belayneh Mesfin , Aadnøy Bernt S. 
Published: October 2015

Drilling fluid plays a key role in an efficient drilling operation to minimize problems such as wellbore collapse, circulation losses and stuck pipe. Well instability problems are costly as they increase the non-productive time and the overall budget (1) (2). Well instability problems controlled by designing appropriate mud density and fluid properties that controls the well. The fracture sealing ability of a drilling fluid is one very important of the drilling mud.
This paper presents design of water-based drilling fluids and results from laboratory experiments to quantify the loss circulation performance of drilling fluids.
Because it is preferable to use oil-based muds in some well sections, the paper will also include a recent study on how to minimize losses when using oil based muds. Here uses of micro/nanoparticles have shown to reduce filtrate losses and to build barriers that are more efficient during circulation loss events.
All the tests presented are at low temperature, which is suitable for Artic environments.
Experimental Investigation of Settling Velocity of Natural Sands in Power-Law Fluid Using Particle Image Shadowgraph
Authors: Shahi Shivam , Kuru Ergun 
Published: October 2015

In this study a new experimental technique, particle image shadowgraph (PIS), is used to investigate the settling velocity of natural sand particles in Power-law fluids. The particle settling velocity measurements are conducted within the Reynolds number of range of 0.01 to 17.00. Natural sands with mean sieve diameters in the range, 0.35 mm – 1.4 mm, are used. Six different equivalent diameter definitions are used to characterize size of the natural sand particles. Using the size and shape measurements in conjunction with PIS, correlations between the mean sieve diameter and equivalent diameters are obtained.
Empirical correlations for predicting the settling velocity of sand particles in Power-law fluids are developed. Multiple linear regression analyses are performed with each fluid data and empirical coefficients for the models are also reported as functions of n and K. The models presented in the study give an average error of less than 20%. In addition, the multiple linear regression tools are applied to enhance the efficiency of the correlations by 3–5%. One of the major contributions of this study is that one can use any associated diameter to predict the settling velocity, which leads to greater flexibility.
Experimental Observation on a Controllable Underwater Towed Vehicle With Vertical Airfoil Main Body
Authors: Wu Jiaming , Chen Jian , Xu Ying , Jin Xiaodong , Lu Lihua , Chen Yuqing 
Published: October 2015

An alternative type of controllable underwater towed vehicle is proposed. The vehicle is composed of horizontal fixed main wing, adjustable wing flap, and a vertical airfoil main body above which two torpedo-shaped buoyant cylinders are symmetrically fixed. The adjustable wing flap serves as an actuator for deflection of the horizontal fixed main wing to produce enough downward lifting force to the towed vehicle running at a required water depth. Principal function of the torpedo-shaped buoyant cylinders is to create a righting moment or a favorite roll damping for attitude stability of the vehicle during towing operation. Meanwhile two ducted propellers are installed at the sterns of the buoyant cylinders to provide an induced turning moment for the vertical airfoil main body, which in turn produce a driving force for the vehicle in lateral motion.
Results of our laboratory experiments indicate that flexible attitude and trajectory manipulations to the vehicle in multiple degrees of freedom can be achieved with the structural style and control mechanisms of the proposed vehicle. The manipulations to the vehicle with the proposed control mechanisms are accomplished by a joint operation of controlling the rotational speeds and directions of the ducted propellers and/or adjusting the deflection of the wing flap. By means of the proposed structural style and control manner, difficulty in designing control system of the vehicle can be reduced greatly, and stronger self stability of the vehicle during its survey towing can be guaranteed.
A Study on Resistance Performance for Various Trim Conditions and Bulb Shapes on a Container Ship Under Slow Steaming
Authors: Park Hyun-Suk , Seo Dae-Won , Han Ki-Min , Kim Dae-Heon , Ha Tae-Bum 
Published: October 2015

Hull form had been unavoidably optimized for a single speed condition, normally a contract speed at design draft in the past many years due to various reasons such as limited design period, less advanced data processing capacity of a computer and so on. For this reason, for maximizing present ship’s operating efficiency, additional analysis relevant to resistance performance for slow steaming condition is newly required since the original hull form for this study also was developed about 10 years ago.
In this paper, the resistance performances corresponding to various trim conditions are investigated not only for ship’s original contract speed (Fn: 0.255) but for slow speed (Fn: 0.163∼0.183) by slow steaming.
Through this study, it can be accomplished to identify the optimum trim condition meeting the objectives of ship operator. Further to the trim optimization, bulbous bow shape renovation was carried out for off design condition (Fn:0.173) and both of CFD results, one is from an original bulbous bow shape, the other is from a reformed bulbous bow shape by us, are compared each other to identify the concrete reason for the improvement of resistance performance.
Commercial CFD code of the STAR-CCM+ was utilized to evaluate the ship’s resistance performance on a 6,800 TEU container ship. To validate of the effectiveness of Starccm+, the experimental result of the subject hull form is referred and compared with the result from STAR-CCM+.
Form factor prediction method by CFD that is based on extracting form pressure resistance component from difference of two different computational domains is presented. In this study, it is investigated to compare the form factor calculated by CFD with the model test result. This approach allows hull form designer to calculate a form factor corresponding ship’s trim variation by CFD in order to separate total resistance into wave making resistance and viscous resistance for more accurate effective power prediction.
Application of Energy Saving Fins on Rudders
Authors: Falkenhorst Arne , Krüger Stefan , Steinbach Christoph Michael 
Published: October 2015

Due to rising fuel oil prices in the last decade as well as rising design speeds, it has become common practice to build rudders with twisted leading edges to minimize resistance and cavitation risk. The next step in this development is the application of fins on to the rudder. The aim is to generate a distinct amount of thrust through the fins by retrieving rotational kinetic energy from the propeller slipstream. This paper presents a fast method to design and calculate rudder fins in the propeller slipstream, which has been implemented in the ship design environment E4.
Because of his working principle, the propeller induces velocities to its slipstream. In the usual setup, the rudder is placed behind the propeller to generate higher steering forces caused by the higher inflow speed in the slipstream. In this arrangement, propeller and rudder together are forming a rotor–stator system. The gains of the stator can be maximized by adding fins to the rudder. The main challenge of a fin design is the maximization and prediction of the regained thrust from the propeller slipstream. In order to do this, a steady, three dimensional, direct panel method is used to calculate the flow around the rudder and fin bodies, from which later the pressures and forces are evaluated. A lifting line method is used to predict the inflow velocities caused by the vortex dominated propeller slipstream on each panel. A special focus is on the treatment of the vortex wake, as crossing wake elements can lead to numerical instabilities and a wrong wake alignment produces bad thrust predictions.
For the purpose of rudder design steady computation should be preferred over fully unsteady computation, since only time average integral values are of interest and the degrees of freedom are reduced to the relevant ones. For example, it is not necessary to know the fluctuation of the angle of attack for the basic design of the profile respective the leading edge of the foil, only the mean value is needed.
In the industrial practice, rudder fins are not often used because the calculation is difficult. Until now it is more expensive to design and build the fins than the savings earned by the ship owner. This phenomenon will change in the next years due to better calculations and rising fuel oil prices.
Optimized Hybrid Composite Flexible Pipe for Ultra-Deepwater Applications
Authors: Jha Vineet , Finch David , Dodds Neville , Latto James 
Published: October 2015

Different hybrid composite pipe solutions have been proposed and evaluated for use in ultra-deepwater applications. This includes composite and hybrid composite/metallic pipe designs made from both a thermoplastic and thermosetting matrix. Each of these designs target a proportion of the future deep sea market and will require a leveraging of present logistics and infrastructure or new developments for deployment. These design concepts primarily focus on deepwater (hence, a higher collapse load) in combination with higher pressure and/or sour service requirements. A section of this hybrid composite pipe design targets the larger diameter high through-put (low or high pressure) FLNG market.
GE Oil & Gas has proposed hybrid metallic/composite pipelines which use composite layers for both hoop and tensile loads. This paper discusses and compares several different design concepts i.e. bonded composite pressure armor, composite tensile armor and both. Although the use of composite pipe will reduce the overall weight, consideration should be given to the buoyancy versus drag requirements of each composite pipe design. Further, consideration needs to be given to manufacturing, reeling, transportation and installation for each of these different design concepts. Acceptability of these individual designs by the end customer requires detailed FMECA, qualification and testing. This paper therefore compares detailed advantages of each composite pipe design for ultra-deepwater applications, presents the latest developments and compares future applications.
Considerations have been given to development of continuous quality control procedures for the manufacture of these composite pipelines and working prototypes. In addition, the latest results are discussed. The possibilities of defects correction and repair mechanism are also explored. This paper aims to show an appreciation of various composite pipe design concepts and addresses key concerns from both a manufacturing and customer acceptability point of view.
Ship Resistance Validation Using Artificial Ice
Authors: van der Werff Solange , Brouwer Joris , Hagesteijn Gerco 
Published: October 2015

In 2013, the first model tests with artificial ice were performed in MARIN’s Concept Basin. A ‘fishbone’ type of channel was made out of rigid polypropylene (PP) particles, surrounded by large rigid PP plates, creating a testing case that is similar to pre-sawn ice conditions in refrigerated model test facilities. A subsequent testing campaign is done in 2014, where the friction between hull and artificial ice particles is further investigated.
Besides measurements of the resistance of the model ship, video images above and under water are used in this study. Results are compared with formulations such as Lindqvist. The knowledge gained with this study is used to improve MARIN’s hydrodynamic multi-body tool aNySIM for simulation studies with ice particles represented by rigid, unbreakable bodies.