bluuebunny/crossref_metadata_2025 huggingface dataset:
The Wave Energy Converter Control Competition: Overview
Authors: Ringwood John , Ferri Francesco , Tom Nathan , Ruehl Kelley , Faedo Nicols , Bacelli Giorgio , Yu Yi-Hsiang , Coe Ryan G.
Published: November 2019

Over the past two years, a wave energy converter control systems competition (WECCCOMP) has been in progress, with the objective of comparing different wave energy converter (WEC) control paradigms on a standard benchmark problem. The target system is a point absorber, corresponding to a single float with an absolute reference, of the WaveStar WEC prototype. The system was modelled in WEC-Sim, with the hydrodynamic parameters validated against tank test data. Competitors were asked to design and implement a WEC control system for this model, with performance evaluated across six sea states. The evaluation criteria included a weighted combination of average converted power, peak/average power, and the degree to which the system physical constraints were exploited or temporarily exceeded.

This paper provides an overview of the competition, which includes a comparative evaluation of the entries and their performance on the simulation model. It is intended that this paper will act as an anchor presentation in a special session on WECCCOMP at OMAE 2019, with other papers in the special session contributed by the competitors, describing in detail the control algorithms and the results achieved over the various sea states.
Low-Cycle-Fatigue Crack Closure Effect of Ship Cracked Plate Considering the Accumulative Plastic Damage
Authors: Song Yuelin , Yang Ping , Peng Ziya , Jiang Wei , Hu Kang
Published: November 2019

In this paper, the relationship between crack closure level and the crack length is studied with experiment and numerical simulation under different low cycle fatigue (LCF) loads. The evolution mechanism of crack closure behavior is explored through the variations of the accumulative plastic strain and compressive stress near the crack-tip. The compressive residual stress is separated into two parts for comparative analysis, namely: the stress field ahead of the crack tip and the stress field of the wake region. The magnitude of the compressive stress field is obtained by the integration along the crack propagation direction of the normal stress. The results show that there is an excellent correlation between LCF crack closure level and the magnitude of the compressive stress in the plastic wake, which provides a new way to further study the complex mechanism of crack closure under LCF loads.
CFD-Based Study of a Tidal Current Turbine in a Horizontal Axis Under Regular Waves
Authors: Liu Jing , Xiao Longfei , Jing Fengmei
Published: November 2019

The horizontal-axis tidal current turbine is often installed in near-surface to use the high flow velocity of tidal current, and many designers have found the effect of wave on the hydrodynamic performance of tidal current turbine. The present study focuses on the hydrodynamic analysis of a tidal current turbine in a horizontal axis under the condition of regular waves, based on CFD method. The experimental data are used to verify the feasibility of the method. A non-dimensional parameter k is defined as the ratio of tip submergence to wave amplitude. It is shown that the numerical method is good to predict the hydrodynamic performance of horizontal axis turbine. By comparing the power coefficient and axial load coefficient in different tip submergence and wave amplitude, the effects of tip submergence and wave amplitude on the hydrodynamic performance of tidal current turbine are analyzed.
Coastal Engineering Analysis, Field Measurements, Numerical Modeling and Design for the Optimized Extension of the Beach in Ras Al-Ardh Area, Salmiya, Kuwait
Authors: Neelamani S. , Shuhaibar Bassam N. , Al-Salem Khaled , Al-Osairi Yousef , Karam Qusaie E. , Al-Houti Dana , Al-Anjari Noor
Published: November 2019

Maintaining and retaining a quality sandy beach is a primary requirement for attracting people and tourists in any coastal country. Tourism Enterprises Company (TEC) in Kuwait owns 230 m long sandy beach in Ras Al-Ardh Sea Club, Salmiya, Kuwait. The beach has been eroding because of strong hydrodynamics forces from waves and currents. TEC wants to develop a stable sandy beach of 30 m wide. Kuwait Institute for Scientific Research (KISR), Kuwait is assigned to carry out the required scientific studies. In order to make sure a stable quality beach will exist, KISR has carried out the needed studies, which involves the field measurements such as bbathymetry survey, current and tidal variations, physical characteristics of beach soil, beach and sea bed profile, establishing the design parameters such as waves, currents, tide and wind. Hydrodynamic model study using DELFT3D model for the present and for the proposed extended groin conditions with beach nourishment were carried out. Also numerical modeling using GENESIS model to understand the future shore line changes due to the proposed development was carried out. Design of Groins to estimate the weight of armor units and weight of inner layers were carried out. The particle size and quantity of sand needed for reclamation of 30 m wide beach was estimated. Based on the study, it is recommended that the sandy soil to be used for 30 m wide beach nourishment should have D50 greater than 0.42 mm (say 0.5 mm) and D10 greater than 0.25 mm. The borrow pit much be selected by keeping this soil characters in mind. It is recommended to use a submerged offshore breakwater in order to retain the beach sand in place and for reducing the maintenance nourishment. Otherwise, large quantity of the capital nourished beach sand will escape into the deeper water due to strong current coupled with waves and steep seabed slopes. Environmental Impact Study was carried out as per Kuwait Environment Public Authority requirements to bring out the impacts due to beach filling and the construction submerged offshore barrier and extension of east groin for a distance of 30 m. TEC will implement the recommendations for developing the beach in Ras Al-Ardh sea club and will be useful to attract more people to use this beach.
Unsteady Numerical Simulation of the Behavior of a Ship Moving in Head Sea
Authors: Lungu Adrian
Published: November 2019

The paper follows a previous work of the author that dealt with ship resistance and self-propulsion numerical investigations, proposing a series of numerical simulations performed to assess the seakeeping performances of the KCS model which moves in regular head waves. Various simulations of the free-surface flow around the hull equipped with rudder moving either in calm water or in heading waves are proposed. For the calm water case, in which a series of six Fr numbers is considered, verification and validation based on the grid convergence tests are performed. Then, a series of five different simulations for various incoming wave characteristics are presented and discussed in every detail. Comparisons with the experimental data [1], [2] are provided aimed at validating the numerical approaches in terms of the total resistance coefficients as well as the heave and pitch motions characteristics. Several remarks will conclude the findings of the present work.
Parametric Resonance Analysis of a Submerged Floating Pipeline Considering Uncertainties
Authors: Yang Hezhen , Xiao Fei
Published: November 2019

The submerged floating pipeline is floating at a certain ocean depth with tethers anchored to the seabed. This novel concept of pipeline can be a promising solution for challenging seabed conditions. Because the pipeline is floating at the mid-deep water and does not interact directly with the seabed, there is no need to do any seabed intervention work and wave forces on the pipeline can also be ignored. But the dynamic response of this type of pipeline under strong currents poses several challenges for design of floating pipeline. This work investigates the parametric resonance of submerged floating pipeline between two floating structures. The parametric resonance can lead to the huge motions and fatigue damage of the pipeline. Thus, it is essential to investigate the parametric resonance of the submerged floating pipeline system under combined parametric and vortex excitations considering uncertainties. Hill’s equation of dynamic responses of the pipeline are derived and hill stability diagrams are used to analyses the corresponding motion stability. The effect of the significant uncertain factors on the probability of the parametric stability is investigated using the metamodel method. According to analyses, some effective measures are given to the designers to avoid the parametric instability for the submerged floating pipeline design.
Improved Design of Next Generation Hull-Platform “noah-FPSO Hull”
Authors: Tanaka Shigeru , Sogawa Yasuhiro
Published: November 2019

The achievement of low cost and fast-track construction for new-build FPSO hulls are challenging problems. In order to solve these problems, the authors developed and reported unique modular design and multi-yard construction concept, “noah-FPSO Hull” [1][2][3]. Since then, the authors continued to improve its design and expanded its flexibility for harsh environment and customer’s requests. As a result, new standardized fore/aft modules and cargo tank module have been developed to expand the flexibility.

This paper presents the design of the newly developed modules and the feasibility for harsh environment.
Improvement of Wave Loads Estimation From Spatial Pressure Distribution on Ship Hull
Authors: Waskito Kurniawan T. , Kashiwagi Masashi
Published: November 2019

In modern shipbuilding industry, merchant ships tend to increase in size. Accurate prediction of the vertical bending moment in large-maplitude waves has become important for structural design. For establishment of an accurate estimation method, more detailed local hydrodynamic quantities such as the spatial pressure distribution on the whole ship hull surface should be checked. For that purpose, the experiment has been conducted by means of Fiber Bragg Grating (FBG) sensing technology. Using the measured local pressure distribution by only sticking the FBG pressure sensors onto the hull surface, we can evaluate the wave loads; which may lead to establishment of a new evaluation method for the wave loads without using a segmented model. We confirm favorable agreement of the pressure distribution between measurement and computation by Rankine Panel Method (RPM). Furthermore, the vertical bending moment computed at some transverse sections shows favorable agreement between measured and computed results.
Correlation Between Steel Microstructural Characteristics and the Initiation and Arrest Toughness Determined From Small-Scale Mechanical Testing
Authors: Taylor Jessica , Moore Philippa , Mehmanparast Ali , Kulka Rob
Published: November 2019

Modern high Charpy toughness steels can nonetheless show low crack arrest toughness[1]. In this paper, the relationship between initiation and arrest toughness is investigated in five different carbon steels, including S355 structural steels, X65 pipeline steel, and high strength reactor pressure vessel, RPV, steels. The results from small-scale mechanical tests, including instrumented Charpy, drop weight Pellini, fracture toughness, and tensile testing (including STRA in the through-thickness direction) were used to determine the behaviour of the different steels in terms of initiation fracture toughness and crack arrest toughness parameters. There was no correlation between the upper shelf initiation toughness and the arrest toughness when the results from the five steels were collated. The mechanical test results were then correlated to the steels’ microstructural characteristics, including parent metal microstructure, average grain size and grain aspect ratio to identify the relative roles of microstructure and texture in the fracture initiation and arrest performance of carbon steels.
Software Simulation and Experimental Study on Wax Deposition Pattern of Deep Condensate Gas
Authors: Wang Jie , Zhou Fujian , Yao Erdong , Fan Fan , Yuan Lishan , Xue Yanpeng
Published: November 2019

The Bozi block of Tarim Oilfield is a typical tight sand condensate gas reservoir with serious wax plugging issue. It is necessary to study the phase behavior and the wax deposition pattern of well fluids in Bozi gas reservoir, which provides the phase enveloping diagram of the condensate gas and can help to control the paraffin deposition. In this study, the PVT tester and self-designed microscopic solid deposition tester are used to get the phase enveloping curve of the condensate gas, which is combined with software simulation results and production data of Bozi 104 well to analyze wax deposition from formation to wellbore, wellbore to ground and surface pipeline. The main conclusions and suggestions are as follows: with different temperature and pressure, condensate gas produces different phase regions such as gas phase, gas-liquid phase, gas-solid phase, gas-liquid-solid phase, etc. Above the dew point pressure, the WAT is less impacted from pressure while the WAT gradually decreases due to the dissolution effect below the dew point pressure. The experimental results are used to revise the software simulation results and then to obtain the phases of different temperature and pressure regions. The state envelope is used to predict the liquid separation and wax production situation at different production stages; the liquid condensation and waxing area of the Bozi 104 well lies in the surface pipeline behind the nozzle, where appropriate wax prevention measures are needed.
Estimation of Expected Loss by Storm Surges Along Tokyo Bay Coast
Authors: Hisamatsu Rikito , Kim Sooyoul , Tabeta Shigeru
Published: November 2019

In Japan, the fundamental disaster management plan was modified after a heavy rainfall event in 2015. According to the updated plan, the transfer of flood disaster risk to non-life insurance is promoted by the Japanese government. Thus, the importance of flood risk modeling for the insurance industry has increased.

Winds are expected to become even stronger, resulting in higher storm surges, when the central pressure of the typhoon is intensified. Furthermore, it is possible for an insurance system to experience peak risk when such damage occurs simultaneously. Hence, refining the assessment method of storm surge risk is very important.

An insurance company to which storm surge risk is transferred needs to assess not only the infrequent risks, for managing the risk of the company, but also the expected value of the estimated loss, for evaluating the insurance premium. However, only a few studies have assessed storm surges by stochastic approaches.

In this study, storm surge losses along the coast of Tokyo Bay are predicted using the output of a stochastic typhoon model for 10,000 years. Storm surge losses due to 600 typhoons potentially causing storm surge damage for 10,000 years are calculated. Exceedance probability curves (EP curves) of estimated storm surge loss for each asset are created. Expected loss and the loss of representative return periods are evaluated based on these EP curves. We successfully determined the expected loss with a small calculation load.
Evaluation of a Practical Approach for Numerical Propulsion Tests
Authors: Giannoulis Andreas , Halse Karl H.
Published: November 2019

Prediction of resistance and propulsion characteristics for a ship is among the most important steps in a ship design process. Traditionally, model tests are used for these predictions and the results are extrapolated to the full-scale ship. Model test techniques can provide reasonably accurate results, but the cost and time they require — and the unavoidable scaling issues — have lead Naval Architects to look for other alternatives.

With the increasing computer power and the increasing experience with numerical simulation of fluid flow, Computational Fluid Dynamics (CFD) have become an appealing alternative to model tests. Numerical computations will always be a trade-off between computational efforts and numerical accuracy. Typically, increased accuracy requirements will cause the mesh to be very fine, and hence the computational time will increase.

At a Workshop on numerical simulation of full-scale ships in Southampton in November 2016, a practical approach for predicting the propulsion characteristics of a full-scale ship was introduced by participants from Becker Marine Systems. The pragmatic CFD approach reduced the computational efforts without scarifying the level of accuracy! In the present work, the alternative practical CFD approach is evaluated in a model scale case to study its benefits and possible short-comings compared to conventional CFD simulations of the self-propulsion case.
Force Measurements and Stationarity Analysis on the Flow Around a Single Square Column With Rounded Edges
Authors: Gambarine Dennis , Koop Arjen , Assi Gustavo , Rampazzo Fabiano , Gonçalves Rodolfo T.
Published: November 2019

Studies about the flow around single column are the preliminary way to understand the behaviour of multi-column systems, e.g. semi-submersible platforms and floating offshore wind turbines. The presence of a rounded edge in a square column can include advantages in the constructive phases, on the other hand, can include difficulty in understanding the hydrodynamic behaviour. With this aim this paper presents a 2dof force measurement for a fixed single square column with and without rounded edges. The columns tested have the aspect ratio (H/L) equal to 1.5 representing the typical column height for multi-column platforms. The aim is to investigate the forces between a single square column with rounded edges and sharp edges in different flow incidence. For both edges a total of seven different current incidence angles were performed; 0, 7.5, 15, 22.5, 30, 37.5 and 45. Reynolds number used for the experiment is equal to 40,000. Additional tests were performed to evaluate a quantitative analysis of the uncertainties due to the repeatability and time length of the experiments. This procedure is necessary for the VV studies of CFD codes, and due to this, the database can be utilized for benchmarking.
Full Scale Thermal Testing of a New Flowline Intervention System
Authors: Harchambois Stéphanie , Le Toux Vincent , Guindeuil Geoffrey , Vivet Romain , Pasquet François-Xavier , Tosi Guillaume , Palermo Thierry , T'Joen Christophe , Herrera Gilbert
Published: November 2019

The Electrically Trace Heated Blanket (ETH-Blanket) is a new offshore intervention/remediation system currently in development by TechnipFMC for the efficient remediation of plugs due to hydrates or wax in subsea production and injection flowlines. The ETH-Blanket consists of a network of heating cables placed underneath an insulation layer which is laid onto the seabed above the plugged flowline. By applying electrical power to the cables, heat is generated by Joule effect which warms up the flowline content until hydrate dissociation or wax plug remediation through softening or complete melting.

As part of a Joint Industry Project (JIP) between TechnipFMC, Shell and Total, full-scale thermal testing of an ETH-Blanket prototype was carried out in Artelia facilities (in Grenoble, France). This testing was performed to verify the capability of the ETH-Blanket system to increase the temperature of the fluid inside a pipe sample above a target temperature (hydrate dissociation temperature or wax disappearance temperature) for various conditions. The impact of lateral misalignment of the ETH-blanket on the pipe and of the pipe burial depth were studied. Moreover, the tests were carried out on two pipe samples, with different designs and insulation properties. In parallel, CFD models of the test set-up were built to replicate the thermal behaviour of the ETH-Blanket. The combination of these models with the measured heating efficiency of the prototype allowed characterising the performances of the system in real subsea conditions.

This paper presents the description of the full scale thermal testing conditions. Results of the different tests are detailed and the impact of the different parameters on the ETH-Blanket thermal performances are assessed, focusing on natural convection effects, thermal losses and the overall data gathering process.
Wave-Powered AUV Recharging: A Feasibility Study
Authors: Driscol Blake P. , Gish Andrew , Coe Ryan G.
Published: November 2019

The aim of this study is to determine whether multiple U.S. Navy autonomous underwater vehicles (AUVs) could be supported using a small, heaving wave energy converter (WEC). The U.S. Navy operates numerous AUVs that need to be charged periodically onshore or onboard a support ship. Ocean waves provide a vast source of energy that can be converted into electricity using a wave energy converter and stored using a conventional battery. The Navy would benefit from the development of a wave energy converter that could store electrical power and autonomously charge its AUVs offshore. A feasibility analysis is required to ensure that the WEC could support the energy needs of multiple AUVs, remain covert, and offer a strategic military advantage. This paper investigates the Navy’s power demands for AUVs and decides whether or not these demands could be met utilizing various measures of WEC efficiency. Wave data from a potential geographic region is analyzed to determine optimal locations for the converter in order to meet the Navy’s power demands and mission set.
Study on Residual Strength of Egg-Shaped Pressure Shell With Local Damage
Authors: Yuan Siming , Gao He
Published: November 2019

The eggshell is a multifocal, rotary thin-walled structure that satisfies the positive Gaussian curve. The eggshell meets the dome principle and requires no additional rib support to achieve sufficient strength and stability with minimal material. Some scholars have applied this bionic prototype to the pressure-resistant shell, which proves that it has good comprehensive performance. However, there is less in-depth discussion of the buckling characteristics of this new pressure-resistant shell yet. In this paper, the dangerous situation of collision, reefing and other accidents during the use of deep submersibles is considered, the residual strength of the shell with partial damage is studied, which is of practical engineering significance. Firstly, the ABUQUS finite element software is used to calculate the buckling of the egg-shaped pressure shell with local deformation, and the influence of local deformation on the buckling mode and ultimate bearing capacity of the pressure shell is analyzed. Secondly, by designing the pressure-resistant shells with different concave amplitudes and recessed positions, the influence of the pressure-resistant shell on the stability of the pressure-resistant shell is analyzed. Finally, according to the calculation results, the sensitivity law of different concave positions to the concave amplitude is summarized, and the beneficial engineering opinions are given.
Three-Dimensional Numerical Simulations of Severe Gas-Liquid Slugging Flows in S-Shaped Riser
Authors: Moon Youn-Wook , Srinil Narakorn , Park Jong-Chun
Published: November 2019

S-shaped riser may be used for connecting a subsea well and floating platform for the multiphase oil-gas flow transportation. A buoyancy module is installed in the longitudinal direction of the riser section enabling a hog and sag bend arrangement. This design offers a solution to decouple motion from the boundaries and lower the riser stresses. There is an increasing tendency to implement S-shaped risers for offshore platforms operating in deep waters or harsh environments. However, a generic S shape may cause a terrain-induced, severe slugging under certain practical operational/geometrical conditions and flow rates. This phenomenon leads to unstable and intermittent slug flows creating fluctuations of pressure, fluid fraction and velocity components. In this paper, the flow pattern characteristics and formation process of a severe slugging in an S-shaped rigid riser transporting the liquid-gas flows are studied using 3-D computational fluid dynamics simulations based on a finite volume method. Numerical results are validated by comparing with experimental results in the literature. Severe slugging behaviors are presented and discussed.
Component-Based Modeling and Simulation of Nonlinear Drill-String Dynamics
Authors: Tengesdal Njål , Holden Christian , Pedersen Eilif
Published: November 2019

In this paper, we present a dynamic model for a generic drill-string. The model is developed with the intention for component-based simulation with coupling to external subsystems. The performance of the drill-string is vital in terms of efficient wellbore excavation for increased hydrocarbon extraction. Drill-string vibrations limit the performance of rotary drilling; the phenomenon is well-known and still a subject of interest in academia and in industry. In this work, we have developed a nonlinear flexible drill-string model based on Lagrangian dynamics, to simulate the performance during vibrations. The model incorporates dynamics governed by lateral bending, longitudinal motion and torsional deformation. The elastic property of the string is modeled with mode shape functions representing the elastic deformation, with a finite set of modal coordinates. By developing a bond graph model from the equations of motion, we can ensure correct causality of the model towards interacting subsystems. The model is analyzed through extensive simulations in case studies, comparing the qualitative behavior of the model with state-of-the art models. The flexible drill-string model presented in this paper will aid in developing simulation case studies and parameter identification for offshore drilling operations.
Improved Pipelay Equipment Settings Methodology for Rigid Pipes
Authors: Marmonier Geoffrey , Harrop Andrew , Lacan Ludovic
Published: November 2019

Rigid pipelay vessels use two types of equipment to hold the pipe under tension while it is being deployed on the seabed: tensioners and hang-off clamps (HOC). Tensioners are used to maintain tension while paying out the pipe behind the vessel, while the HOC holds the pipe statically during welding operations. For both pieces of equipment, the tension is held through frictional pads in contact with the pipe.

With the necessity to reach greater water depths leading to an overall increase of pipeline weights and stiffness (and therefore top tension), the installation of rigid pipelines has become more challenging. In other cases, such as pipe-in-pipe (PiP), carrier pipe wall thicknesses are often optimised as much as possible while lower grade materials are selected to reduce costs, making it more difficult to provide pipelay equipment settings that can satisfy both grip and pipe local integrity requirements. Simple hand calculations and basic equipment modelling are not sufficient to provide safe equipment settings and optimised allowable sea states. The new DNVGL-ST-N001 [1] (Marine Operations and Marine Warranty) also increases scrutiny on pipelay equipment and pipe interaction, making it imperative to develop more in-depth methodologies for settings calculation.

This paper gives an overview of a robust methodology for pipelay equipment settings and demonstrates through practical examples how it improves safety while optimising operations, therefore enabling more efficient pipelay operations and reducing waiting on weather.
Architectures and Algorithms for a Smart Drilling Robot
Authors: Geekiyanage Suranga C. H. , Løken Erik A. , Sui Dan , Wiktorski Tomasz
Published: November 2019

Robotic drilling is likely to become a key feature of the next generations of drilling rigs and novel drilling technical solutions. We have been developing a drilling robot on a laboratory scale to run different drilling scenarios and achieve high-level performances with less or even no human intervention. In this paper, we introduce its mechanical systems, perception capabilities, data management, decision-making algorithms, and digital architecture. Results illustrate its autonomous operations, incident management capabilities, learning outcomes, improvement potential, and challenges. Lab testing and evaluation is an essential part of implementing, promoting and accelerating robotic applications of drilling automation. Our drilling robot is a useful, safe and cost-effective solution for testing, integrating and improving hardware, software, data, and digital/robotic products in a laboratory scale, before expensive full-scale testing and integration.
Feature Selection for Kick Detection With Machine Learning Using Laboratory Data
Authors: Geekiyanage Suranga C. H. , Ambrus Adrian , Sui Dan
Published: November 2019

Conventional kick detection methods mainly include monitoring pit gains, surface flow data (flow in and flow out), surface and down-hole pressure variations, and outputs from physics-based models. Kick detection times depend on a driller’s individual ability to interpret these drilling measurements, symptoms and model predictions. Furthermore, testing a novel data-driven solution in a full-scale operation may induce non-productive time, safety risks and crew fatigue adding to false alarms that inevitably occur during testing. Therefore, the development of better, faster and less human intervention-dependent kick detection on a laboratory scale system is a valuable step before full-scale testing.

We have generated a dataset containing seven typical drilling measurements and a sequence of gas kicks from experiments conducted in the laboratory scale. First, we employ data analysis tools following data pre-processing steps, data scaling, outlier detection, and natural feature selection. Next, we consider additional “engineered features” and apply different feature combinations to logistic regression with an ensemble method (boosting) for developing kick detection algorithms.

In our data analysis, ‘Delta flow’ (difference between flow in and flow out of the well) and ‘Rate of change of delta flow’ designed features, combined with logistic regression and boosting, give promising results in detecting kicks. Finally, we propose an intelligent algorithm and alarm architecture for a complete kick alarm system, which draws from both data analysis and machine learning models developed in this work.
Water Wave Scattering by Two Circular-Arc-Shaped Thin Plates With Non-Uniform Permeability
Authors: Gayen R. , Gupta Sourav
Published: November 2019

The interaction of small amplitude water waves with a pair of circular-arc-shaped thin porous plates is studied under the assumption of linear theory. The plates are submerged at different depths in deep water and the permeability of the plates varies along the circumference of the plates. Applying Green’s integral theorem to the fundamental potential function and the scattered potential function and using the condition on the porous plates, the problem is reduced to that of solving a set of coupled integral equations for the potential difference functions across the plates. Two kernels of these integral equations are hypersingular and the other two kernels are regular. An expansion-cum-collocation method involving Chebyshev polynomials is employed to obtain the approximate solution of the integral equations. The numerical estimates for the reflection and the transmission coefficients are computed utilizing the approximate solution of the aforesaid integral equations. The numerical results for the reflection and the transmission coefficients are depicted graphically for several values of various parameters. Known results for dual symmetric circular-arc-shaped porous plates are recovered as special case.
Design of Buried Pipelines in Soft Clay: A Case Study
Authors: Gallegillo Martin , Cerulli Michele , Haghighi Ali , Kennedy Justin
Published: November 2019

High pressure high temperature offshore pipelines are generally buried for protection. For buried pipelines, upheaval buckling can be triggered in the presence of vertical imperfections when the pipeline compressive state is increased. One of the main uncertainties in the design calculation is the soil resistance to upward and downward movement and the displacement at which the peak resistance is mobilised. For clays the soil response will usually be undrained, certainly for most loading events, however it may also be necessary to consider the drained response (particularly if there is any long term applied uplift). In addition, local flow-round failure mechanism may occur, generally for deeply buried pipelines. If local failure dominates the design, it may not be possible to bury the pipeline. This could have significant cost implications.

An experimental programme was carried out to determine the uplift resistance of buried pipelines in soft clay soils. The results of scale model testing and computational analysis (finite element limit analysis) showed that the local behaviour was not applicable. The implications of these results are illustrated in a case study upheaval buckling (UHB) analysis. The overall result was a significant saving on rockdump quantities. The implications for the case study are presented in this paper alongside a description of other backfill requirements and practical considerations for a UHB design.
Numerical Investigation of Ductile Crack Growth Behavior at Different Locations of Weld Joint for X80 Pipeline Steel
Authors: Qiang Bin , Wang Xin
Published: November 2019

The finite element method (FEM) based on the Gurson–Tvergaard–Needleman (GTN) model was used to investigate the ductile crack growth behavior at different weld joint locations in X80 pipeline steel. The X80 weld joints are inhomogeneous and can be divided into five different zones. By fitting the results of uniaxial tension and single-edge notched bending tests, the GTN model parameters were determined using FEM in consideration of the inhomogeneity of the weld joint. The calibrated GTN model was then used to analyze the fracture toughness in single-edge notched tension tests. The results show that the different weld joint zones produce different mechanical properties and crack growth resistance curves. To accurately assess the integrity of X80 weld joints, the calibrated GTN model is a reasonable method for obtaining fracture toughness data and resistance curves for different joint locations under different loading conditions.
Vessel Interface Considerations for Ultra Deepwater Intervention Risers
Authors: Vaidya Rohit , Sonawane Mahesh , Toleman Benjamin , Whiteley Elaine , Rourke Jonathan
Published: November 2019

For ultra-deepwater subsea wells, a riser system is required to conduct completion, intervention/workover and end of life activities. For ultra-deepwater riser systems with high temperature and pressure requirements, the intervention riser system often requires vessel interface optimization to achieve acceptable design response. The upper riser can be configured in several different ways, each with its own benefit from a safety, risk and performance perspective. This paper compares the riser response for various vessel interfaces for ultra-deepwater applications.

As discussed above, intervention riser structural response is sensitive to the riser configuration at the vessel interface. For a typical intervention riser, due to ultra-deepwater and high tension requirements, the functional tension load may utilize up to 40% of yield strength thus decreasing the capacity available to accommodate bending and pressure loads. Vessel operators have options to modify the system configuration to improve the strength and fatigue response of the riser. The different vessel interface options include the tension lift frame (TLF) to vessel interface, the top tension application method and the use or otherwise of a surface tree dolly. Upper riser assembly (URA) loads may be optimized by use of rotary wear bushings, a cased wear joint assembly or flexjoints as a part of the stack-up.

The various riser-vessel interface options are evaluated and compared in this paper. This paper highlights the riser design challenges for ultra-deepwater applications.
Design and Construction of a 1/15th Scale Wave Tank Model of the Azura Commercial Wave Energy Converter
Authors: Ling Bradley A. , Lettenmaier Terry , Fowler Matthew , Cameron Matthew , Viselli Anthony M.
Published: November 2019

The design of a 1/15th geometrically scaled wave tank model of the Azura™ commercial-scale wave energy device is presented. The objectives of the wave tank tests, conducted at the University of Maine Harlod Alfond Wind/Wave Ocean Engineering Lab (W2), included verification of the Azura’s energy capture in irregular waves, evaluation of performance in survival wave conditions, and testing of two advanced control algorithms. Due to the difficulty in properly Froude Scaling a hydraulic system, the model used a direct-drive rotary motor/generator power takeoff (PTO), with the dynamics of the hydraulic PTO included via a hardware-in-the-loop simulation. This PTO implementation led to additional design requirements being imposed on the model drivetrain. In addition to the model PTO design, the instrumentation design, structural design, and test plans are presented. The resulting model and PTO achieved a high level of controllability, and accurately emulated the dynamics of the hydraulic PTO of the full-scale Azura prototype.
Progress on the Development of a Holistic Coupled Model of Dynamics for Offshore Wind Farms: Phase II — Study on a Data-Driven Based Reduced-Order Model for a Single Wind Turbine
Authors: Lin Z. , Stetco A. , Carmona-Sanchez J. , Cevasco D. , Collu M. , Nenadic G. , Marjanovic O. , Barnes M.
Published: November 2019

At present, over 1500 offshore wind turbines (OWTs) are operating in the UK with a capacity of 5.4GW. Until now, the research has mainly focused on how to minimise the CAPEX, but Operation and Maintenance (O&M) can represent up to 39% of the lifetime costs of an offshore wind farm, mainly due to the assets’ high cost and the harsh environment in which they operate. Focusing on O&M, the HOME Offshore research project (www.homeoffshore.org) aims to derive an advanced interpretation of the fault mechanisms through holistic multiphysics modelling of the wind farm.

With the present work, an advanced model of dynamics for a single wind turbine is developed, able to identify the couplings between aero-hydro-servo-elastic (AHSE) dynamics and drive train dynamics. The wind turbine mechanical components, modelled using an AHSE dynamic model, are coupled with a detailed representation of a variable-speed direct-drive 5MW permanent magnet synchronous generator (PMSG) and its fully rated voltage source converters (VSCs). Using the developed model for the wind turbine, several case studies are carried out for above and below rated operating conditions. Firstly, the response time histories of wind turbine degrees of freedom (DOFs) are modelled using a full-order coupled analysis. Subsequently, regression analysis is applied in order to correlate DOFs and generated rotor torque (target degree of freedom for the failure mode in analysis), quantifying the level of inherent coupling effects. Finally, the reduced-order multiphysics models for a single offshore wind turbine are derived based on the strength of the correlation coefficients. The accuracy of the proposed reduced-order models is discussed, comparing it against the full-order coupled model in terms of statistical data and spectrum. In terms of statistical results, all the reduced-order models have a good agreement with the full-order results. In terms of spectrum, all the reduced-order models have a good agreement with the full-order results if the frequencies of interest are below 0.75Hz.
Potentials of Nano-Designed Plugs: Implications for Short and Long Term Well Integrity
Authors: Kimanzi Raymos , Patel Harshkumar , Khalifeh Mahmoud , Salehi Saeed , Teodoriu Catalin
Published: November 2019

Cement plugs are designed to protect the integrity of oil and gas wells by mitigating movement of formation fluids and leaks. A failure of the cement sheath can result in the loss of zonal isolation, which can lead to sustained casing pressure.

In this study, nanosynthetic graphite with designed expansive properties has been introduced to fresh cement slurry. The expansive properties of nanosynthetic graphite were achieved by controlling the preparation conditions. The material was made from synthetic graphite and has a surface area ranging from 325–375 m2/gram. Several tests including compressive strength, rheology, and thickening time were performed. An addition of 1% nanosynthetic graphite with appropriate reactivity was sufficient to maintain expansion in the cement system, leading to an early compressive strength development. It has excellent thermal and electrical conductivity and can be used to design a cement system with short and long-term integrity. Rheology and thickening time tests confirmed its pumpability. Controlling the concentration of the additive is a promising method that can be used to mitigate gas migration in gas bearing and shallow gas formations.
Effect of Wind Turbulence on Extreme Load Analysis of an Offshore Wind Turbine
Authors: Chen Xiaolu , Jiang Zhiyu , Li Qinyuan , Li Ye
Published: November 2019

Evaluation of dynamic responses under extreme environmental conditions is important for the structural design of offshore wind turbines. Previously, a modified environmental contour method has been proposed to estimate extreme responses. In the method, the joint distribution of environmental variables near the cut-out wind speed is used to derive the critical environmental conditions for a specified return period, and the turbulence intensity (TI) of wind is assumed to be a deterministic value. To address more realistic wind conditions, this paper considers the turbulence intensity as a stochastic variable and investigates the impact on the modified environmental contour. Aerodynamic simulations are run over a range of mean wind speeds at the hub height from 9–25 m/s and turbulence levels between 9%–15%. Dynamic responses of a monopile offshore wind turbine under extreme conditions were studied, and the importance of considering the uncertainties associated with wind turbulence is highlighted. A case of evaluating the extreme response for 50-year environmental contour is given as an example of including TI as an extra variant in environmental contour method. The result is compared with traditional method in which TI is set as a constant of 15%. It shows that taking TI into consideration based on probabilistic method produces a lower extreme response prediction.
Research on Fatigue Life Assessment of Fiber Glass Reinforced Flexible Pipe
Authors: Bai Yong , Zhao Jiannan , Sun Xinyu , Zhang Xiaojie , Wang Zhao
Published: November 2019

Fiber glass reinforced flexible pipe (FGRFP) is a kind of submarine pipe widely used in oil and gas transportation and exploration. This paper mainly studies the theoretical and numerical simulation methods for calculating the fatigue life of the FGRFP. Firstly, the tension time-histories and bending moment time-histories of the FGRFP are obtained by using global analysis. The tension and bending moment frequency distribution histograms are obtained by using rain flow method. Then, the finite element software ABAQUS is used to build the model of the FGRFP, and the corresponding tension and bending moment are applied on the finite element model. Then, the stress time histories curve of the FGRFP is obtained. By comparing the results of numerical simulation, the main factors affecting the fatigue life of the FGRFP are studied. Finally, according to rain flow method, S-N curve and numerical simulation results, the fatigue life and single damage rate of FGRFP are obtained.
An Empirical Formula for Predicting Elastic Ultimate Buckling Strength of Flat-Bar Stiffened Panels With Initial Imperfections
Authors: Mei Hongyuan , Wang Deyu
Published: November 2019

Elastic ultimate buckling strength is an important strength design criteria to estimate the safety margin of stiffened panels subjected to axial compressive load. Based on a series of Nonlinear finite elements analysis, an empirical formula is proposed to elastic ultimate buckling strength of stiffened panels with flat-bar stiffener in this study. The elastic ultimate buckling strength is defined as that in the loading process, a certain average compressive stress of stiffened panels when the Vonmises stress of structures firstly reach the yield stress. The range of geometrical sizes for numerical samples is discussed in order to ensure the applicability of presented empirical formula. The extent of models and initial imperfection, namely initial geometrical deformation are also taken into account. Ultimately, it is shown that there are a good agreement between the results of Non-linear finite element method and the proposed empirical formula.
The Experimental Investigation of Completion Fluid Working As a Good Thermal Insulation in the Deepwater Production Well
Authors: Feng Ming , Guo Boyun
Published: November 2019

For wells, risers and pipelines in offshore, the mechanical loads as well as the thermal insulation requirements normally increase with water depth. Hence, the traditional thermal insulation foam technology used in shallow waters and the associated design and test methodology may not be adequate to deep-water projects. This research focuses on investigation of a new material for insulation of deepwater wells and pipelines.

In the research, many samples of insulation fluids are tested to find out attractive alternative to current fluids for deep water production. The paper highlights the development of these new thermal insulation fluid and its application in the lab. Compared to the current existing insulation fluids, these new insulation fluids provide high viscosity.
Numerical Estimation of Multiple Positions of Seepage of Dissolved Matter From Seafloor
Authors: Kanao Shunsuke , Sato Toru
Published: November 2019

To mitigate global warming, it is necessary to emit less CO2 into the atmosphere and the Carbon dioxide Capture and Storage (CCS) attracts attention these days as one of the solutions against the problem. Off Tomakomai coast, Japan, a CCS project has been demonstrated since 2016. However, there may be a risk of CO2 leakage and consequent seepage from the seafloor, even if the probability of such an event is almost nil. In this research, we assumed that CO2 seeps from multiple points on the seafloor and aimed at estimating the seepage locations, time and fluxes, by using CO2 concentration data observed by several sensors set on the seafloor. We adopted the adjoint marginal sensitivity method, which is a probabilistic time-backward method: an adjoint location probability is released by each sensor and spreads in the time-backward direction. The adjoint location probabilities are used to estimate the seepage fluxes. We also combined the least squares method with the adjoint marginal sensitivity method to estimate the seepage fluxes. We considered that CO2 seeps from 2 points in 2-dimensional horizontal domains as test calculations with changing seepage flux ratios, such as 1:1, 1:0.1 or 1:0.01.