bluuebunny/crossref_metadata_2025_split huggingface dataset:
Simulation of Normal Differentiable Stochastic Process of Ice Loads
Authors: Zvyagin Petr 
Published: October 2017

Ice loads time series should be treated in the other way than separate independent ice loads observations. The stochastic process approach can provide information about such important characteristic as mean length of signal’s outcome beyond some critical level and expected number of such outcomes.
The paper considers global ice loads registered in an ice tank experiment with a cylindrical indenter of 100 mm width. The autocorrelation function is fitted in a manner that the observed load process is differentiable. The study conducted in the paper demonstrates that characteristics, such as the number outcomes beyond some critical level and the time spent off this level, are governed in the same way as parameters of a stationary differentiable normal process.
Normal stationary model of ice loads process allows its simulation, if autocorrelation function is given. In the paper, such simulation is performed.
Application of Confidence Regions to Ice Ridge Keel Data Statistical Assessment
Authors: Zvyagin Petr , Heinonen Jaakko 
Published: October 2017

Sets of measurements of underwater ridge parts usually contain a limited amount of data. Outcomes need to be made while relying on small sample sizes. In this event, the chance of making inaccurate estimations increases.
This paper proposes to use stochastic confidence regions in the estimation of the unknown parameters of keel depths. A model for a random variable with a lognormal distribution for keel depths is assumed. Regions for the mean and standard deviation of keel depths are obtained from Mood’s and minimum-area confidence regions for parameters of the normally distributed random variable. Conservative safety probability of non-exceeding the critical keel depth in one random interaction of the ridge with structure is estimated.
An algorithm for statistically assessment of ice ridge keel data by means of confidence region building is here offered. The assessment of a set of ridge keel depths for the Gulf of Bothnia (Baltic Sea) is performed.
Analysis of Offshore Wind Turbine Foundations With Soil Damping Models
Authors: Hemmati Arash , Khorasanchi Mahdi , Barltrop Nigel 
Published: October 2017

Soil damping is usually modeled as a contribution to global proportional or Rayleigh damping in industry and academia. However, this soil damping model does not represent the physical behavior. In this paper, soil damping for offshore wind turbine foundation is modeled by means of dashpots with damping parameters associated with the soil stiffness. The case study used in this paper is a 5MW NREL wind turbine resting on a jacket foundation as the effect of soil damping in this type of foundation is more significant due to its structural nature and number of piles. A number of dashpots for each pile are used with six degrees of freedom to represent soil damping.
First, free decay vibrations are assesed for different soil damping levels. Next, the aerodynamic loading is applied at the interface level and the integrated analysis is performed in dynamic mode for stochastic loading. Displacements at top of the foundation, base shear and base moment forces for a number of design load cases are evaluated to assess the effect of quantifying soil damping with dashpots. Also, fatigue damages of different hotspots are assessed and compared with the damages from models with no soil damping. It can be concluded that soil damping modeled by dashpots may provide some additional damping and it is more realistic. It leads to load reductions especially mudline moment, with the maximum of 20% for the peak values. Therefore, this type of soil damping modeling can be used to optimize the design of offshore wind turbine especially for the critical hotspots near the mudline.
Design Parameters for Increased Operability of Offshore Crane Vessels
Authors: Gutsch Martin , Sprenger Florian , Steen Sverre 
Published: October 2017

Marine subsea operations are performed by highly specialized ships, referred to as Inspection, Maintenance, and Repair (IMR) and Offshore Construction Vessels (OCV). Although the ships and their on-board equipment are designed to operate in harsh environmental conditions, the current practice often is to terminate operations when a rigid and conservative weather limitation is reached, often specified in terms of the significant wave height as the exclusive criterion. Such general limitations do not account for vessel specific motion behavior. Since the offshore industry is aiming for all-year-round safe subsea operations, there is a strong interest amongst ship designers, owners and operators to establish vessel and task specific criteria. The project Vessel Performance within the Norwegian Centre for Research-based Innovation on Marine Operations (SFI MOVE), is developing response-based procedures, that are leading to case-specific operational ranges. This approach enables the full exploitation of vessel performance capabilities for safe and efficient offshore operations. Two methods with different complexity levels are proposed. Firstly, on the higher level, detailed operability analysis for a fleet and sea area of interest are performed by means of numerical tools.
This level can be used to obtain detailed results for existing ships, but the procedure can also be applied as guidance in the design stage. Secondly, on the lower level, generic diagrams can be used to estimate and compare the operational performance of different vessels based on fact sheet parameters. This is especially relevant for decision making processes where a detailed study cannot be performed.
A Constitutive Model for Soft Mud Considering the Initial State of Effective Stress
Authors: Xu Chunyang , Chen Yongping , Yu Lili 
Published: October 2017

Consolidation is one of the most important processes that are needed to be accounted for in the model of cohesive sediment transport. Previous studies have shown that the consolidation paths for soil elements are not unique at low effective stress (here low effective stress means the effective stress is smaller than a threshold effective stress, which is short as TES and denoted as σb) In this study, a new theoretical constitutive equation for the effective stress of soft mud is derived to describe the non-unique consolidation paths at low effective stress.
Firstly, based on the concept of fractal dimension, the mud flocs are treated as self-similar fractal entities and the relationship between mud floc size and sediment volume fraction is established. Due to the fact that the fractal dimension decreases as the floc size increases, the variation of fractal dimension is accounted for. Based on the self-similar model, the theoretical constitutive equation for the effective stress of soft mud is derived.
The constitutive equation is validated using two data sets obtained from consolidation tests in a settling column for soft clay. At low effective stress, the model results curves follow the data trends and the non-uniqueness of consolidation paths are captured. The model results are also compared with existing numerical results and better agreement is presented especially when η is less than 0.5.
Numerical Study on Vortex-Induced Motions of Semi-Submersibles With Various Types of Columns
Authors: Liu Mingyue , Xiao Longfei , Kou Yufeng , Lu Haining 
Published: October 2017

Vortex-induced motions (VIM) of offshore floaters occur when the frequency of the vortex shedding is close to the natural frequency in the transverse direction of the unit subjected to the current, and this can severely affect the fatigue life of mooring lines and risers. Literatures in recent years have shown an increasing interest in the VIM behavior of semi-submersibles (SS), the geometry of which implies a more complex VIM phenomenon. In the case of multi-column semi-submersibles, the vortices shed around each column. Thus the shape of the columns, circular or square, and the wake interference different for each current heading, characterize the VIM of the unit.
Based on verification by the VIM towing tests for a semi-submersible with four rounded square columns, VIM simulations were conducted using CFD method in the model scale for four semi-submersibles with different column designs: a SS model with four rounded square columns (SRC-SS), a SS model with four circular columns (CC-SS), a SS model with two tandem rounded square columns and two tandem circular columns (SRCT-CCT-SS), and a SS model with two staggered rounded square columns and two staggered circular columns (SRCS-CCS-SS). The current headings ranged from 0° to 180° and reduced velocities of 4 up to 14 were considered.
Different semi-submersibles present different VIM performances owing to the influence of the column design. The most significant transverse motions of the CC-SS model occur at the 0° current heading with the largest nominal transverse amplitudes around 74% of the column diameter. On the other hand, the maximum amplitudes in the transverse direction of the SRC-SS model, approximately 63% of the column width, are observed at the 45° current heading. Additionally, the VIM responses could be mitigated when the semi-submersible consists of combined circular-section and square-section columns.
Asphaltenes: What Do We Know So Far
Authors: Al-Qasim Abdulaziz S. , Alasker Mohammed 
Published: October 2017

Serious operational problems caused by asphaltene deposition during oil production have driven the ongoing effort to understand this phenomenon. Many studies have focused on related asphaltene precipitation flocculation and deposition in oil reservoirs and flow assurance in the wellbores. Experimental techniques and theoretical models have been developed trying to understand and predict asphaltene behavior. Nevertheless, some ambiguities still remain with regard to the characterization of asphaltene in crude oil and its stability during the primary, secondary, and tertiary recovery stages within the near-wellbore regions.
The paper will review asphaltene in crude oil systems: asphaltene properties and their impact on oil production, including the effects of pressure, temperature, and composition. Asphaltene content is an important factor in determining the properties of a crude oil. Three main methods are used to measure the asphaltene content in laboratory: the first method called SARA, which separates dead oil into saturates, aromatics, resins, and asphaltenes depending on their solubility and polarity. The second is aliphatic hydrocarbon titration using dead oil; in this method the asphaltene precipitation point is detected by the asphaltene precipitation detection unit (APDU). The third method is the depressurization of a live oil bottomhole sample, this method depends on monitoring the flocculation point due to light transmittance caused by the infrared laser [3].
Solubility and density parameters trends are proportional to the pressure depletion until the pressure reaches the bubble point. Below the bubble point pressure (Pb), the solubility and density are inversely proportional to the pressure. The solubility increases linearly with temperature until the reservoir temperature, after that, it decreases linearly as the temperature increases. These advanced measurements facilitate an understanding of petroleum heavy constituents. Anew research field called “Petroleomics” has started receiving more attention; it is based on integrating the different knowledge of chemical composition of petroleum to develop correlation studies and improve the prediction of asphaltene phase behavior.
A Novel Model for Catenary Drilling and Drill String Induced Stresses
Authors: Teodoriu Catalin , Asgharzadeh Arash 
Published: October 2017

Petroleum engineers are aware of the advantages of directional and horizontal wells. In case of intermediate deep wells, the preference is the customary solution, in which a well is drilled vertically to the kick off point, and then moved directionally to the reservoir level. Nowadays, due to the advent of extended reach drilling, this approach does not satisfy the meant goal anymore. In extended reach drilling, the concern lies on the drill pipe’s strength. Because of the great depth of the borehole, the torque and tension below the drill floor increase and could reach the drill pipe’s strength. Therefore, in order to extend the wellbore reach, it is necessary to minimize the torque and drag. Several authors have mentioned that catenary profile may help reduce torque and drag.
The purpose of the paper is to analyze the mechanics of the drill string, and to understand the stress distribution along the drill string and the geometry of the well configurations while bringing the borehole from a vertical to a horizontal position. . This will be achieved by means of an analytical comparison between the catenary profiles and the conventional well configurations.
A novel catenary profile which improves the previous models is also presented in this paper. The modified catenary has a larger curvature of the drill string; particularly in the upper parts of the borehole the bending stresses are small. The modified catenary profile, which resembles a free hanging cable, can be a novel method in directional drilling of deep and extended reach wells. Thus, the build rate in the modified catenary is being continuously increased until it reaches the desired position. It is different from conventional methods used especially in horizontal drilling to connect the vertical and the horizontal section, where the build rate is kept constant.
The focus of this paper lies on the study of catenary’s geometry as a complex well path and the induced stress. Different approaches are used and compared.
Experimental Study of the Necessary Pressure to Start-Up the Flow of a Gelled Waxy Crude Oil
Authors: Van Der Geest Charlie , Bizotto Guersoni Vanessa C. , Antônio Simões Salomão Junior Luiz , Bannwart Antonio C. 
Published: October 2017

The current study concerns a recurrent problem in the oil industry when dealing with waxy crude oils in offshore fields. When a waxy crude stays static in the seabed for any reason, it cools down below the wax appearance temperature (WAT). Hence, crystals of wax appear in the fluid. These wax crystals form a crystalline structure. The strength of a crystalline structure rises with time. What also rises with time is the minimum pressure necessary to restart the flow.
When designing subsea structures, engineers assume that flow restart will occur when the pressure is sufficient to overcome a threshold stress. This threshold stress is related to what the literature calls apparent yield stress. Considerable evidence suggests, however, that a simplified momentum equation considering only this rheological parameter and the necessary pressure will provide an overestimated value. What this study aims to accomplish is a better understanding of the phenomenon involved in this process.
To do so, we build an experimental apparatus that allows us to represent the condition of the temperature close to bottom of the sea, and a pressurization system that allows us to precisely control the inlet pressure. The apparatus is composed of a one-inch pipeline that is submerged in a water bath (5°C) and a nitrogen system with controlled valves to pressurize the inlet of the pipeline.
Much discussion in the literature concerns the restart of a flow of gelled waxy crude. Many studies have suggested that the most important phenomena involved are the following aspects of the oil: its rheological behaviour, its compressibility, and its shrinkage. The current study contributes to the literature by demonstrating that the behaviour of a gelled waxy crude oil having a high percentage of wax that builds up a strong crystalline structure is impacted by rheological behaviour, time, and aging time.
To be able to provide the industry a reliable prediction of the gelled waxy restart pressure, it is necessary for engineers to carry out a great deal of experimentation and improvement in the models. In this paper, we compare the experimental data with the prediction of a model consisting of a weakly compressible fluid with an elasto-viscoplastic thixotropic behaviour. The comparison advances our knowledge in the phenomena involved in restart of gelled crudes and, in fact, shows the model capable of approaching the results expected by the industry.
Feasibility Study of Selected Riser Concepts in Deep Water and Harsh Environment
Authors: Gemilang Gilang Muhammad , Karunakaran Daniel 
Published: October 2017

One of the well-known riser systems, the Steel Catenary Riser (SCR), has been an attractive choice for the riser system in deep water. However, the main challenge of the SCR is large motions from the host platforms due to the harsh environment. The large motion of host platforms may induce excessive buckling and fatigue at the touchdown point. By screening the downward velocities at the hang-off point in the time history graph, the time at which the critical responses (i.e. buckling utilization, bending moment and compression) peak is identified. This study investigates the feasibility of the SCR configuration in terms of the capability to cope with the vessel motion.
Several types of the SCR configurations are proposed in this study. The selected configurations of SCR in this study are conventional SCR, Weight Distributed SCR (WDSCR), and Steel Lazy Wave Riser (SLWR). The feasibility of the three riser configurations was analyzed in terms of strength and fatigue performance to understand the limitation of one over the other. The “lazy wave” configuration efficiently absorbs the vessel heave motions. Thereby the SLWR configuration is proven to be the most robust configuration to cope with large motion of the host platform. This study proves that although the SCR feasibility is limited due to vessel heave motion, innovative solutions can be established to extend its feasibility in order to cope with the vessel heave motion in harsh environment.
A Quantification of Mixing Energy During the Whole Cementing Cycle
Authors: Saleh Fatemeh , Ichim Adonis , Mbainayel Daniel , Teodoriu Catalin 
Published: October 2017

Various authors have pointed out the importance of cement mixing process and its effect on cement properties. From all cement properties, two are extremely important: the mechanical cement strength (unconfined compressive strength or UCS) and the rheology. The first is critically impacting the well integrity whereas the latter is affecting the pumping ability and displacement in the well, which will also have effects on the well integrity.
A previously performed literature survey has pointed out that mixing energy alone may not be sufficient to describe the cement slurry changes, and inferred that shear rate can also impact the final cement properties, such as thickening time or cement strength. Starting from the existing investigations, our goal is to quantify the source of maximum energy input during a conventional cement job and estimate its effect on final cement properties.
This paper is showing theoretical and experimental investigations on selected API cements with respect to their properties as a function of mixing energy. The first part of the paper is focusing on the estimation of mixing energy in different section of the cement pathway to the annulus. The second part will show some experimental results and the new way ahead, based on our findings.
Effect of Fluid Properties on the Performance of Gas-Lift Valves
Authors: AlTarabulsi Khadhr , Coutinho Renato , Waltrich Paulo J. 
Published: October 2017

This study presents an experimental and numerical investigation on the effect of fluid properties on the performance curves for Gas-Lift Valves (GLV). Nitrogen and natural gas are used as the working fluids at pressure up to 66.2 and 45.5 bar respectively (960 and 660 psig). The performance of GLVs can be obtained theoretically or experimentally. However, it has been proved in the literature that the theoretical performance curves for such valves may not work appropriately for a wide range of fluids, pressure and temperature conditions.
The objective of this study is to investigate experimentally and numerically the applicability of using air instead of natural gas and how it would impact the performance of GLVs. The experimental results have been obtained using a high-pressure gas-lift testing facility located at the Louisiana State University. The GLV evaluated in the experiments is an orifice valve with 12.7 mm (32/64 in.) opening diameter. The experimental data results is compared with results obtained using a commercial simulator using a mechanistic model, and the Thornhill-Craver empirical model, which is often used to predict the gas flow through an orifice.
The results showed a significant difference between using natural gas and nitrogen as a working with respect to flow rate mainly due to the large difference in the specific gravity. Moreover, both theoretical and mechanistic models over predicted flow rates for both gases probably due to the inaccurate estimation of the specific discharge Cd of the GLV, as this value is not constant and changes with the valve and fluid types.
Post-Reeled Behaviour of Pipelines With Global Buckling Mitigation by the Residual Curvature Method
Authors: Gallegillo Martin , Qi Xinhai , Ofoha Godman , Bhide Rohit , Messias Nicolas , Helland Torgeir 
Published: October 2017

In recent years the residual curvature method (RCM) has been used to provide buckle initiators to control and mitigate the global buckling of pipelines. Through the appropriate planning of these controlled buckles, an acceptable design of the pipeline in-place behaviour is achieved. Implementation of the residual curvature (RC) profile in the context of reel-lay installation is obtained by the modification of the vessel’s straightener settings on the sections of pipe where buckle initiators are required. This leads to a local and controlled increase of the pipeline RC.
The published literature on in-place assessment for a limited number of recent projects has considered that a local increase in curvature is achieved by subjecting the pipeline to pure bending until the target residual plastic strain is reached. This method simplifies the actual reel-lay process where the pipeline is subjected to successive bending cycles before the RC is achieved after the pipeline leaves the installation vessel. Consequently, the approach does not capture the whole complexity of the reeling process.
This paper assesses the effect of the approach used to induce pipe local curvature on the results of the in-place analysis, where the behaviour of the pipeline with RC buckle initiators is examined. From this, it draws conclusions on the complexity required to adequately represent the effect of the RCM on the in-service behaviour and the design life of pipelines.
Subsea Production Layout: Design and Cost
Authors: Hong Cheng , Wang Yuxi , Yang Jiankun , Berbert Yuri M. , Lourenço Marcelo I. , Estefen Segen F. 
Published: October 2017

The development of a subsea field implies a complex design procedure with very high costs involved. The combination of low oil price, harsh environment, very deep waters and high drilling costs has emphasized the need for new ideas to reduce both CAPEX and OPEX.
The paper considers different subsea layout scenarios of a typical deep water field. Each scenario is optimized considering pipeline length, equipment cost and flow assurance. The software QUE$TOR is then applied to estimate the cost of each optimized scenario. Two of them are selected for further studies, FPSO connected to six slots subsea manifolds, and subsea separator connected to eight slots cluster manifolds with tie-back to an existing platform. The latter representing a hybrid solution based on the subsea-to-shore concept. Cost and technical feasibility are considered in order to evaluate the two scenarios.