bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Study for a Catamaran Gripper-Monopile Mechanism of a Novel Offshore Wind Turbine Assembly Installation Procedure
Authors: Hatledal Lars Ivar , Zhang Houxiang , Halse Karl Henning , Hildre Hans Petter
Published: October 2017

Current methods for installation of offshore wind turbines are all sensitive to the weather conditions and the present cost level of offshore wind power is more than twice the cost of land-based units, increasing with water depth. This paper presents numerical simulations of a novel experimental gripper design to reduce the environmental effects applied to a catamaran type of vessel during wind turbine installation. In SFI MOVE project in NTNU Aalesund, our team proposed a novel wind turbine installation process. A new catamaran vessel will carry pre-assembled wind turbines to the installation location. Two new designed grippers on the deck will make a lifting operation to install the wind turbine onto the turbine foundation. Three prismatic grippers with several rolling contact points at the end are attached in an arc at the catamaran’s aft, designed to grasp the turbine foundation in order to make a connection between the two in the horizontal plane. This paper will only emphasize the contact responses between the turbine foundation and the three grippers during the wind turbine installation process. Numerical simulations are carried out using the virtual prototyping framework Vicosim which is developed by NTNU Aalesund. The simulation results show validation of a key part of the proposed new wind turbine installation idea.
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.
Second-Order Slowly Varying and Mean Value of Pitch Motion of the Sandglass-Type Floating Body With Dynamic Positioning System
Authors: Wang Linlin , Wang Wenhua , Du Yazhen , Huang Yi
Published: October 2017

This paper takes the presented concept of sandglass-type floating body as the research object. The shape of new sandglass-type floating body has extended oblique characteristic, which may result in special performance and the problem of pitch (or roll) motion. From the experimental tests, it can be found that its pitch natural frequency is small and the second order slowly varying pitch motion in irregular wave is significant, which may cause an unintentional interaction between the pitch and surge motions. Additionally, the floating body with small-waterplane-area and low metacentric height may have obvious mean pitch angle with wind moment under harsh sea condition. To solve the above two problems, numerical simulations have been conducted with two sea conditions. Lastly, based on the existing technique, the problems are solved and the positioning accuracy can be satisfied well for the harsher sea condition.
Statistical Characteristics of Ocean Currents: Measurements From Fixed and Moving Platforms
Authors: Bakhoday Paskyabi Mostafa
Published: October 2017

In this paper, we study statistics of ocean currents using data collected from a subsurface autonomous moored (moving) vehicle and from a nearby oceanographic mooring. Among different sensors mounted on the moored subsurface buoy, we only use an upward-looking Nortek Aquadopp (AQD) and an Acoustic Doppler Velocimeter (ADV) to measure the near surface currents (for the upper ∼8-m below the surface) and surface gravity waves from moving sensors. Using a simplified stochastic model, a theoretical representation is derived for the Probability Density Function (PDF) of ocean currents, i.e. one-parameter Rayleigh distribution. Extension of this solution to two-parameter Weibull distribution is then utilized to determine the analytical representations for the higher-order statistical moments (i.e. skewness, and kurtosis) of currents throughout the water column. The current observations from moving ADV and AQD systems near the sea surface confirm previous speculation that two-parameter Weibull distribution can reasonably provide a well approximation to the probability distribution of the upper ocean currents. The non-Weibull structures in the results can, however, be attributed to different sources of uncertainty in measurements near the sea surface such as wave-induced platform instability and effects of various scales of motions interacting in the upper ocean boundary layer. Using data from oceanographic mooring-based upward-looking Acoustic Doppler Current Profiler (ADCP) and single-point AQDs, the statistics of currents from these quasi-fixed profiling systems at depths below 8-m are observed to have relatively smaller departures from the theoretical Weibull predictions than those estimated from moving sensors.
A Novel Drillstring Dynamics Experimental Setup to Be Integrated Into Hardware in the Loop Capable Drilling Simulators
Authors: Marquez Antonio , Teodoriu Catalin
Published: October 2017

One of the limiting factors for maximizing drilling performance is drillstring vibration/dynamics. With the development of in-bit, at bit or near bit vibration monitoring sensors, it has been reported that while drilling with PDC bits in hard formations, stick-slip is mostly observed before other types of vibration. Commonly, stick slip is a mathematical problem that can be resolved using various technics (like analytical, numerical, etc.). To compliment this theoretical effort, experimental measurements are required to verify mathematical models under controlled conditions and assess their range of applicability. This is why a large number of laboratory setups around the world exist. A comprehensive literature research has shown that most of the known experimental setups are smaller than 10 m length and focused mainly on vertical wells. Building a setup that reproduces real hydrocarbon wells, including the drill string inertia and the delayed response between bit and surface, as well as the complex friction transfer process taking place between the wellbore and the drillstring, is not feasible. Thus, downscaling the typical drillstring parameters is necessary for the study of vibrations and vibration suppression at laboratory conditions. Vibration suppression modeling and validation require a particular, dedicated laboratory setup. The design of such an installation will be presented in the following paper. The newly proposed experimental setup will exceed all existing stick-slip or lateral vibration experimental setups on the market by size, while adding new features like axial movement (mimicking ROP or heave compensation) and curved sections. This new facility will be the first to integrate the hardware in the loop capabilities and can be connected with any drilling simulator that supports such an option. This design will account not only for torsional vibrations, but will also allow the string to move axially while RPM, WOB and flow rates may be directly linked to a drilling simulator. Because of its design, to resemble medium to small radius of curvature, the stick slip process can be captured and highlighted for a wide range of directional well situations. Once the range in operating conditions was defined, the equipment and mechanical components for the facility were selected and designed. The new facility will significantly improve our ability to reproduce the physics of drill string vibrations and will lead to better optimization of downhole vibration suppression. The incorporated link to drilling simulators can improve the development of the next generation of vibration suppressing models and hardware.
Experimental Study on the Interaction Effect of Sulfate Ions and Chloride Ions on Reinforcement Corrosion in Marine Environment
Authors: Huang Yi , Xu Yunze , Wang Xiaona , Song Shide , Yang Lujia
Published: October 2017

Reinforced concrete is one of the most widely used construction materials for marine structures. Due to the abundance of the aggressive ions such as chloride ions and sulfate ions in the seawater, the reinforcement exposed to the marine and costal environment are exposed to a high corrosion risk. Localized corrosion will occur once the passive film on the rebar is damaged. In this work, the corrosion behavior of the steel in the simulated pore solution containing with both sulfate ions and chloride ions are studied by using cyclic potentialdynamic polarization methods and the corrosion morphologies observed using scanning electron microscope (SEM). The test results show that the initial rebar corrosion is caused by the absorption of the chloride ions in the passive film. The sulfate ions nearly had no effect on the corrosion of the rebar in pore solution and it can further mitigate the pitting corrosion in chloride containing pore solution.
An Element-Based Finite Volume Technique Using IMPES and Fully Implicit Approaches for 3D Oil-Water Flows With Hybrid Grids
Authors: Pacheco Taisa B. , Silva António F. Carvalho da , Maliska Clovis R.
Published: October 2017

The finite volume techniques for solving fluid flow problems can be broadly classified in cell center and cell vertex methodologies. The conventional finite volume techniques belong to the former class, since the elements coming from the grid generator are used as control volumes for performing the balances of the physical quantities, like mass, momentum and energy. The majority of the available methods in the literature uses this type of approach for solving multiphase flows of oil, water and gas in porous media. In petroleum reservoir simulation it is common for the conventional finite volume method to be linked to corner-point grids. This paper presents an Element-based Finite Volume Method (EbFVM), whereby the control volumes are constructed using parts of the elements, generating polygonal meshes in which mass, momentum and energy conservation are enforced. Polygonal meshes considerably reduce the number of unknowns of the linear system when compared with conventional finite volume methods. Three-dimensional hybrid grids are employed for the solution of oil-water flows in a porous media resembling a petroleum reservoir using the IMPES, sequential and fully implicit approaches. The analytical solution of the 1D Buckley-Leverett problem is used for evaluation purposes, and numerical solutions for 2D and 3D problems using unstructured grids are carried out to demonstrate the generality of the method and for comparing the robustness, convergence rate and CPU time of the IMPES and Fully Implicit solutions. Memory usage and convergence rate are also presented for the solution of 3D problems using tetrahedral grids in a cell-center and cell-vertex methodologies.
Visualization of Oil Droplets Within ESP Impellers
Authors: Perissinotto Rodolfo Marcilli , Monte Verde William , Biazussi Jorge Luiz , Castro Marcelo Souza de , Bannwart Antonio Carlos
Published: October 2017

The objective of this research is to investigate the path of oil drops within an Electrical Submersible Pump (ESP) impeller, to evaluate its size and velocity as function of water flow rate and the ESP rotation speed. An experimental study was conducted at University of Campinas - Brazil with an ESP prototype designed to allow flow visualization within the impeller through a transparent shell. A high-speed camera with lighting set captures images of the oil droplets at a rate of 1000 frames per second. The set of data was performed at three rotational speeds — 600 rpm, 900 rpm and 1200 rpm — for three water flow rates — 80%, 100% and 120% of the best efficiency point (BEP). The results reveal that the oil drops become smaller when the rotational speed increases. The same behavior is noticed when the water flow rate increases. Generally, the oil droplets have spherical and elliptical shapes that change as function of their position inside the impeller channel. Furthermore, the drops have random trajectories, but a pattern can be detected in three cases: droplets near the pressure blade, droplets near the suction blade and droplets that move from the suction blade to the pressure blade. The average velocity of the oil droplets that move near the suction blade is significantly higher than the average velocity of the droplets that move near the pressure blade. Velocity changes as function of the impeller radius suggest different accelerations that may be caused by drag forces and pressure forces. The size of the oil drops has no significant influence on their velocities.
Experience From Introduction of the Design Code NS 9415 to the Aquaculture Industry in Norway and Expanding the Scope to Cover Also Operations
Authors: Berstad Are Johan , Fludal Heimstad Line
Published: October 2017

This paper presents the current state of regulations, guidelines and the engineering in the Norwegian aquaculture industry. The statistics of fish escapes is evaluated and the need for further developments of the regulations, in planned revisions, of the Norwegian standard, are laid. Simplified case studies are shown to present the main forces acting on fish farms.
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.
Time Dependent Carcass-Liner Interface Load Model
Authors: Skeie Geir , Wold Roger , Sødahl Nils
Published: October 2017

Flexible risers in operation may experience large forces between the carcass and the polymer liner. Especially, cool-down of a pressurized riser results in thermal shrinkage of the liner layer and will transfer tensile loading of the carcass at the end fixation. Two aspects are then important to explore; the structural load capacity of the carcass structure and the balancing load effects acting on the carcass and liner. The current paper addresses the latter: the carcass load model. This has been presented in a previous publication in form of closed form expression for the long term quasi-static axial loading [1]. The model is extended to include the time dependent evolution of the carcass-liner interface force taking account of the time dependent material behavior in the liner and the time variation of the driving forces acting on the carcass and liner. The extension expresses the axial force as a convolution integral. In all but for the simplest cases the integral needs to be evaluated through appropriate quadrature rules. The closed form solution represents a reduced, efficient and robust scheme for evaluating the critical load level of a newly discovered failure mode. Further, the model enables identification of the critical parameters driving this failure mode.
Hydrodynamic Coefficients for Suction Anchors During Installation Operations
Authors: Solaas Frøydis , Sandvik Peter Christian
Published: October 2017

Increasing demands on economy in the offshore industry and extension to North Atlantic all-year operations bring along a requirement for more accurate numerical simulations of marine installation operations. These simulations will assess the necessary vessel and crane capacity and determine the limiting sea state for the installation. An essential input to such analysis is hydrodynamic coefficients for the structures to be installed. Together with the vessel capacity, the limiting sea-state will, in many cases be dependent on the coefficients used in the simulations. A realistic estimate of the coefficients for the structure in question will therefore have directly influence on the cost of the operation. Coefficients for hydrodynamic added mass and damping for simple geometries are given in standard textbooks and in the “Recommended practice for modelling and analysis of marine operations”, DNVGL-RP-H103. For more complex structures and structure parts on the other hand, there is a lack of published data. MARINTEK and NTNU have through the last decades performed model testing of different structural details as well as complete subsea structures. During the research program MOVE, started in 2015 by NTNU, MARINTEK and SINTEF, a considerable amount of model test data is collected and compared to obtain general trends and connections suitable for engineering estimates of coefficients to be used in numerical simulations. Suction anchors are widely used for permanent mooring of floating production and storage vessels, and also for foundation of subsea structures. In several cases use of suction anchors have replaced piling for foundation of offshore wind turbines and jacket platforms. The anchors can be exposed to high hydrodynamic forces during the installation. This paper presents hydrodynamic coefficients in heave for suction anchors with different degree of perforation of the top plate and different height/diameter relations. The results range from anchors with no perforation to around 18% perforation.
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.
A Transient Inflow Performance Relationship (IPR) for the Early and Late Life of Gas Wells: The Dynamic Gas IPR
Authors: de Sousa Pedro Cavalcanti , Posenato Artur G. , Waltrich Paulo J.
Published: October 2017

This paper presents an alternative form of IPR, called in this study “Gas Dynamic IPR” (GDIPR), and compares it with the performance of conventional Inflow Performance Relationships (IPR) for gas reservoirs. The main objective of the GDIPR is to provide a simple but robust IPR solution for gas wells under transient conditions for the early and late life of gas reservoirs. Conventional IPR models are often not able to capture transient effects for the late life of gas reservoirs. The GDIPR solution, on the other hand, can be used for the cases of buildup and drawdown tests (early life), and for the modeling of transient liquid loading phenomena in gas wells (late life). The GDIPR is compared to conventional IPR models in two case studies. The comparison analysis show that the conventional IPR models do not provide reliable results, while the GDIPR is in agreement with the solution from discretized reservoir models. The GDIPR technique is computationally less expensive than discretized reservoir models, and is able to capture both the transient well behavior and the steady-state solution, for early and late life of gas reservoirs.
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.
Two-Dimensional Unsteady Viscous Flows
Authors: Shu Jian-Jun
Published: October 2017

A number of new closed-form fundamental solutions for the two-dimensional generalized unsteady Oseen and Stokes flows associated with arbitrary time-dependent translational and rotational motions have been developed. As an example of application, the hydrodynamic force acting on a circular cylinder translating in an unsteady flow field at low Reynolds numbers is calculated using the new generalized fundamental solutions.
Coupled Analysis of Offloading System in West Africa Sea
Authors: Youwei Kang , Lei Li , Bing Wang , Yanfei Deng , Yunhe Zhai
Published: October 2017

West Africa Sea, which is located in the tropical area, has special environmental conditions. Relatively mild sea state and long period swell as the main component of waves lead to significant high energy in low frequency region. Frequently there will be a special sea condition which contains long period swell and local storm wave. Research in this paper mainly focuses on motion and force characteristics of offloading system (contains offloading line, CALM buoy and its mooring system) under the special West Africa environmental conditions. Radiation/diffraction theory is adopted to calculate potential force acting on CALM buoy. The viscous drag force is considered by special disk-type Morison elements which are arranged according to certain rules. Physical model tests of truncated offloading system are carried out to verify the numerical model. The motion and force characters of offloading system under West Africa swell and wind sea are studied in both numerical method and model tests method. CALM buoy motion characteristics in specific environmental condition is analyzed. Relationships between CALM buoy motions and flexible structure (mooring line or offloading lines) tension forces are also researched.
An Investigation of Pressure and Production Data Using Decline and Type Curve Analysis
Authors: Rahman Arifur , Happy Fatema Akter , Hira Mahbub Alam , Hossain M. Enamul
Published: October 2017

Decline curve analysis is one of the most widely used production data analysis technique for forecasting whilst type curve analysis is a graphical representation technique for history matching and forecasting. The combination of both methods can estimate the reserves and the well/reservoir parameters simultaneously. The purpose of this study is to construct the new production decline curves to analyze the pressure and production data. These curves are constructed by combining decline curve and a type curve analysis technique that can estimate the existing reserves and determine the other well/reservoir parameters for gas wells. The accuracy of these parameter estimations depends on the quality and type of the pressure and production data available. This study illustrates the conventional decline curve that can be used to analyze the gas well performance data with type curves based on pseudo time function. On the other hand, log-log plots are used as a diagnostic tool to identify the appropriate reservoir model and analogous data trend. Pressure derivative and type curves are used to construct a radial model of the reservoir. In addition, Blasingame and Fetkovich type curves analysis are also presented in a convenient way. The decline curve analysis shows steady state production for a long time, then a decline is observed which indicates a boundary dominated flow. The Blasingame type curve matching points is going downward, which indicate the influence of another nearby well. The reservoir parameters that are obtained by using the decline curve and type curves analysis show a similar trend and close match for different approaches. These observations closely match results of different analysis. This analysis improves the likelihood of the results being satisfactory and reliable, though it changes with time until the end of the production period. This analysis technique can be extended to other type of well/reservoir system, including horizontal wells and fractured reservoirs.
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.
Design and Performance Investigation of the Energy Recovering Rudder Bulb-Turbine Device
Authors: Wang Chunhui , Hu Ankang , Han Fenglei
Published: October 2017

This study presents the performance investigation of a rudder bulb-turbine device (RBTD), which is designed to recover the rotational energy into torque to drive a generator inside the rudder. The blade of turbine is designed first by using lifting line theory, which is modified by lifting surface theory. The induced velocities between the forward propeller and turbine are obtained through the surface panel method (SPM). Hydrodynamic performance for the system is predicted by using SPM. An iterative calculation method is used until the hydrodynamic performance of the system converges. Through the design of turbine behind propeller of a large container ship, the influence of rotational speed of turbine on hydrodynamic performance of propeller-turbine system is observed. Then the size of rudder bulb is determined by calculating the influence of rudder bulb geometry on the hydrodynamic performance of the propeller-rudder system. Based on CFD technology, the hydrodynamic performance of the propeller-rudder system without/with RBTD is also simulated, and velocity distribution is observed. The results show that RBTD is successfully designed and as a ship energy saving device is feasible.
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.
Research on Monitoring Point Layout of Health Monitoring System of the Icebreaker
Authors: Wang Youzhen , Feng Guoqing , Li Pengfei
Published: October 2017

As one kind of special ship, polar Ice-breaking ships are used to break the ice for other ships or for researchers going deeper to the polar region. The safety of Ice-breaking ships should be emphasized not only because of it special shape but also because of its unique load case and complex marine environment. Structure Health Monitoring (SHM) should be installed in them owing to reasons mentioned above, even if there are rules that had been used while designing the ships. How to choose appropriate monitoring points is one of the most important things in this whole project. For providing more rational approach to selecting measure points in Structure Health Monitoring by FEM analysis, two methods were proposed and compared in order to determine a better one which can reduce the workload. One of these two methods is design wave approach which can show ultimate strength but just in the case of hogging, sagging and other typical cases, which ignore a large number of cases the ship may meet. The other one is composed of 240 structural responses from 20 kinds of frequencies in 12 directions (Data of spectral analysis), and weighted mean value based on ocean wave spectrum would be seen as an assessment of the damage caused by natural environment. For huge data in the finite element analysis, there must be a set of feasible algorithms to automatically process the results to get monitoring points. After that the monitoring point can be and stress measured by fiber-optic sensor at that point will be monitored in real time.
Identification of Potentially Unmanageable Ice Features
Authors: Shafrova Svetlana , Matskevitch Dmitri , Holub Curtis , Kokkinis Ted
Published: October 2017

Satellite remote sensing technology plays an important role in ice monitoring and characterization in support of ice management operations for Arctic floating drilling that previously have been described by industry to include three stages: (1) far-field reconnaissance for potentially unmanageable ice features (2) mid-field verification of ice breakability and (3) near-field ice floe size reduction.

The paper discusses the application of satellite remote sensing methods for identification of Potentially Unmanageable Ice Features (PUIF) as well as challenges associated with satellite data interpretation and feature tracking. Examples of PUIF identification using both publicly and commercially available satellite imagery and other remote sensing data collected during the Oden Arctic Technology Research Cruise 2015 (OATRC 2015) are presented and the challenges with the PUIF detection and monitoring are discussed.

In addition, airborne remote sensing systems for PUIF identification, both existing (such as Electromagnetic Induction (EMI)) and under development (such as dual frequency radar, multi-band synthetic aperture radar), are discussed and their capabilities contrasted and compared to satellite-based methods. Furthermore, potential ways of optimally combining airborne and satellite remote sensing are proposed.
Key Design Parameters to Identify Natural Frequency of Tripod Substructures for Offshore Wind Turbine
Authors: Zhang Jian-hua , Guan Cheng-yu , Lin Jia-yue , Sun Ke
Published: October 2017

Natural frequencies of the tripod are generally taken as the primary indicators of dynamic response, and pile soil interaction (PSI) will affect the natural frequency. To simulate PSI behaviour, P-Y method and simplified method are compared in a case study of tripod of 3 MW OWT in China to define the applicable clamped length in simplified method, the results demonstrate that 6 times of anchor pile diameter is suitable for simulating frequency of the tripod in the specific location. The effects of geometries and material properties of tripod on natural frequency are investigated using random finite element method considering uncertainties in the design variables and materials. It highlights a reasonable engineering judgment and understanding for structural design of tripod foundation and develops a more effective approach to regulate the design once the structures cannot meet the requirement in preliminary design.
Nonlinear Dynamic Analysis of Deepwater Risers With the Irregular Seabed
Authors: Sun Liping , Zhang Yulin , Ma Gang , Wang Hongwei
Published: October 2017

The stress of a steel catenary riser (SCR) at touch-down zone (TDZ) is substantially affected by its interaction with the seabed. Based on the slender rod theory, the paper adopts a realistic nonlinear load-deflection (P-y) curve to simulate soil deformation and resistance force. This seabed model can better reflect the change of soil stiffness along the vertical direction. According to the P-y curve, the equivalent stiffness at different points are obtained by an iterative method. In order to add the soil resistance force to the equation of motion, the seabed force is multiplied by the shape function a(s) and integrated from 0 to L of an element length. This paper use Gauss integral method to get the seabed force. In fact, the element may be not entirely in contact with the seabed. Therefore, the first step is to get the contact point between element and soil, and then to determine the real integral range. Meanwhile, existing riser-soil models mostly take the support of the seabed as a horizontal plane. However, many SCRs are unavoidable to be laid on the irregular seabed. It makes the strength characteristics of riser flow-line more complicated. This paper has studied the effect of irregular seabed on riser stress. The results indicate that there is a stress peak value at the irregular seabed. This value is almost equal to the value at TDP.
Influence of Large Drawdowns in Oil Reservoirs on Fluid Temperature and Fluid Properties
Authors: Islam R. , Hasan A. R. , Kabir C. Shah
Published: October 2017

The usual assumption of isothermal flow may be unsuitable in low-conductivity formations where large drawdowns occur. The increase in oil temperature associated with Joule-Thompson (J-T) heating triggers the consequent changes in oil viscosity and density. This paper presents an analytical 1D radial-flow model for estimating the transient flowing-fluid temperature in a single-phase oil reservoir. The model allows oil density, viscosity, and the J-T coefficient to vary with pressure and temperature. A rigorous thermodynamic expression based on fluid PVT behavior underpins the proposed model.

A detailed sensitivity analysis has shown the effect of oil production rate on reservoir heating and consequent changes in fluid properties. Specifically, we observed that fluid temperature increase above the original formation temperature occurs with a decrease in formation permeability, an increase in oil viscosity, and a decrease in overall heat-transfer coefficient. Of course, J-T heating increases with increasing flow rate.

Changes in reservoir temperature occur within about 100 ft. from the wellbore. Overall, the lessons learned from this study illuminates the need for reevaluating tubular design, flow-assurance issues related to dissolved solids, and assessment of well productivity index arising from J-T heating.
Metocean Design Criteria Considerations in South China Sea by Adopting Multivariate Extreme Value Theory
Authors: Li Ping , Zhu Qi , Zhou Chunqi , Li Linbin , Li Hongtao
Published: October 2017

The proper determination of metocean design criteria is critical for offshore structures. We study in this paper the univariate and multivariate compound extreme value theories and their applications to metocean data. Firstly, we adopt Compound Extreme Value Distribution (CEVD) method to derive the marginal distributions of wind speeds and significant wave heights respectively. Modelling uncertainties are considered with different distribution models. Secondly, the basic theory of Bivariate Compound Extreme Value Distribution (BCEVD), especially Poisson Bivariate Gumbel Logistic Distribution (PBGLD) is reviewed and utilized to analyze the joint probability distribution of significant wave heights and the concomitant wind speeds. Thirdly, Extreme Water Level (EWL) which is defined as the combination of wave crest, surge height and tidal elevation, is analyzed. We treat astronomical tide as a deterministic phenomenon and estimate the joint probability distribution of crest heights and storm surges. Case studies are given for picked position points in Northern South China Sea with 40 years hindcasted data. The results of this paper could give some knowledge for the determination and refinement of metocean design parameters.