bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Lateral Pipe-Soil Interaction on Controlled Lateral Buckling Using Pre-Deformed Pipeline
Authors: Chee Jayden , Walker Alastair , White David
Published: September 2018

A novel approach to eliminate the onset of global buckling in pipelines is investigated in the paper. The method is based on pre-deforming a pipeline continuously with a specific wavelength and amplitude prior to installation on the seabed. The response of the pipeline to applied high temperature and pressure was studied in conjunction with variations in the lateral pipe-soil interaction (PSI) — both as uniform friction along the pipe and also with locally varying friction.

Pipe and seabed parameters representing a typical wet-insulated infield flow line on soft clay are used. The pre-deformed pipeline has a higher buckle initiation temperature compared to a straight pipeline due to the reduced effective axial force build-up resulting from the low axial stiffness generated by the pre-deformed lobes along the pipeline.

The results from this paper show that the strains in the pre-deformed pipeline are not significantly affected by the local variability of lateral PSI but rather by the global mean PSI. At a typical lateral soil resistance, i.e. a friction coefficient of 0.5, lateral buckling occurs at a very high temperature level that is not common in the subsea operation. At a very low friction, i.e. 0.1, lateral buckling occurs at a lower operating temperature but the strain is insignificant. The longitudinal strain of the pipeline is not highly sensitive to the lateral PSI, which is a quite different response to an initially straight pipeline. Therefore, this method could prove to be a valuable tool for the subsea industry as it enables the pipeline to be installed and operated safely at very high temperatures without the need for lateral buckling design and installation of expensive structures as buckle initiators.

Even if the pre-deformed pipeline buckles at a very high temperature, during cycles of heat-up and cool-down the buckle shape ‘shakes down’ by geometric rearrangement to minimize the energy, and in doing so creates a series of ‘short pipelines’ in which the longitudinal strain is self-controlled.

The system is therefore shown to be very robust in the conditions investigated and not affected by one of the biggest unknowns in seabed pipeline engineering, which is the local variability in lateral PSI.
Numerical and Experimental Studies of Collapsing Cavitation Bubbles for Ballast Water Treatment
Authors: Kang Chang-Wei , Tandiono Tandiono , Lu Xin , Turangan Cary K. , Osman Hafiiz , Lim Fannon , Lucas Margaret , Tan Matthew
Published: September 2018

In this paper, we report both experimental and computational studies of hydrodynamic cavitation generated by accelerating liquid through a series of constrictions. The detailed process of cavitation generation is visualized using a high-speed photography. The cavitation is initiated when a gas bubble moves towards the constrictions. The gas bubble initially accelerates, expands and then splits into smaller bubbles when it moves along the constriction. As these bubbles migrate into a large liquid compartment, they collapse violently to form a bubble cloud, owing to a sudden jump in liquid pressure in the compartment. The experimental observation is further confirmed using computational fluid dynamics (CFD) simulations. We also present experimental evidence showing a significant reduction in gram-negative Escherichia coli concentration after it passes through the constrictions.
Dominant Factors Influencing Ductile Fracture on Cutting Surface During Cold Forming
Authors: Takahashi Kazunari , Yamatoki Shuichi , Namegawa Tetsuya , Kinoshita Masahiko , Fujioka Masaaki
Published: September 2018

Cracks caused by cold bending during shipyard construction were found to be longer in mild steel than in high tensile steel. Because mild steel has better elongation, the cause of such cracking was difficult to ascertain. Bending tests of large number of steel pieces to confirm the effects of multiple parameters, nonlinear finite-element analysis to check strain distribution, and fractography to determine the nature of the fracture indicated that ductile fracture initiated where the strain value was highest, as is generally expected. In the bending tests, the fractures were reproducibly longer in alloys with better ductility. One of the reasons for this phenomenon was that the surface was more hardened by plasma-arc cutting in mild steel because of its high carbon content according to hardness tests on the cutting surfaces. We therefore proposed a new equation to estimate crack length, taking into account three factors: strain, elongation and surface hardness. We showed that the relationship between crack length and the values by the equation explains the results of the bending tests. Additionally, we suggested the possibility that inclusions within an alloy affect the crack length. Cold forming is a general procedure used in shipyards. If inspections fail to find a crack, it may propagate to fatal damage after delivery. This study is therefore useful in preventing the initiation of cracks.
Multiphase Flow in a Subsea Hilly Terrain
Authors: Odan Mohamed , Ben Rajeb Faraj , Zhang Yan , Imtiaz Syed , Aborig Amer , Aziz Rahman Mohammed
Published: September 2018

Multiphase flow is an important the phenomenon existing widely in nature, daily life, as well as petroleum and chemical engineering industry. It is especially important to understand the flow behavior of multiphase flow in a subsea hilly terrain and offshore pipelines. Accurate flow regime identification in multiphase flow is critical since multiphase flow affects the measurement accuracy of phase fraction, flow rate and other phase parameters.

The main objective of this research work is to obtain a better understanding of the multiphase flow characteristics in a long pipeline. In this study, the results of an experimental research on multiphase flow that investigates fluid characteristics in a pipe has been presented. The experimental unit consists of pipes that are made up of clear PVC, which is capable of producing several different flow regimes (Stratified, bubble, slug, and annular-mist flow) of gas-liquid flows. The entire length of the flow loop is 20.574 m. The experimental unit includes sensors such as pressure transducers, thermocouples and flowmeters that enable to measure the pressure ranges from 20–300KPa, temperature ranges from 0 to 20 °C and volume flow ranges from 12–45 liter/min at numerous locations respectively. In this experimental work, bubble, and slug flow regimes have been selected in the multiphase flow pattern to be examined on the multiphase flow assurance. The results of this research will provide valuable new experimental data on multiphase flow characteristics for designated flow regimes that can improve flow assurance in subsea conditions by including the temperature and Pressure effects.
Undrained Uniaxial Capacities of Suction Bucket Foundations in Rows
Authors: Xiao Zhong , Lu Yumin , Liu Ying
Published: September 2018

Suction bucket foundations in rows, sunk by self-weight and passive suction, can be used as footings of breakwater, trestle bridge, offshore cofferdam and other structures, and they have a fine application prospect on soft soil for their advantages of good bearing capacities, simple construction, low investment, being reusable and so forth. A large number of finite-element models for suction bucket foundations in undrained soft clay were established to investigate uniaxial capacities of suction bucket foundations, and the effects of foundations spacing ratio, embedment ratio and soil shear strength were studied. The results show that foundations spacing ratio has certain effect on the uniaxial capacities of a suction bucket foundation but is less influential than other factors; embedment ratio and soil shear strengths have more influence on the uniaxial bearing capacities and failure mechanisms of bucket foundation. Based on these results, simplified formulae are proposed to predict uniaxial capacities of suction bucket foundations in rows for designers to use directly.
Ice Propulsion Performance Calculation As per Alternative System of Propeller-Hull Interaction Coefficients
Authors: Kanevskii G. I. , Klubnichkin A. M. , Sazonov K. Ye.
Published: September 2018

Propulsion performance of icebreakers cannot be calculated as per the classic system of propeller-hull interaction coefficients due to high negative values of wake fractions. To overcome this difficulty, this paper applies an alternative system of propeller-hull interaction coefficients. This system consists of thrust deduction fraction, coefficient of hull effect upon thrust and coefficient of hull effect upon torque.

The method suggested in this paper was used to analysis the data of ice trials for Vladivostok and Novorossiysk icebreakers. The input data in this analysis are speed in the ice field and required power. The sought values are propeller rotations per minute (RPM) and ice resistance. Propeller RPM values are compared versus the results of full-scale ice trials. Ice resistance values are compared versus the predictions based on the model test data obtained in ice basin of Krylov State Research Centre (KSRC).

It is shown that at low speeds in the ice field (0.5–5.0 knots), calculated propeller RPMs have good correlation with the full-scale measurement data.

This paper also gives propulsion performance calculation for Vladivostok icebreaker in 1.5-m thick ice field.
Experimental Study on Vortex-Induced Vibration of Floating Circular Cylinders With Low Aspect Ratio and Different Free-End Corner Shapes
Authors: Gonçalves Rodolfo T. , Sakata Keigo , Gambarine Dennis M. , Cicolin Murilo M. , Hirabayashi Shinichiro , Assi Gustavo R. S.
Published: September 2018

Experiments regarding vortex-induced vibration (VIV) on floating circular cylinders with low aspect ratio, L/D = 0.5, and different free-end conditions were carried out in a recirculation water channel. The floating circular cylinders were elastically supported by a set of linear springs to provide low structural damping on the system. Four different free-end corner shape conditions were tested, namely r/R = 0.0, 0.25, 0.5 and 1.0; where r/R is the relation between chamfer rounding radius, r, and the radius of cylinder, R. These different free-end conditions were selected to promote changes in the structures shedding around the free end of the cylinder. The aims were to understand the free-end effects on the VIV of floating circular cylinders with very low aspect ratio. The range of Reynolds number covered 2,800 < Re < 55,400. All the results presented here complement the work presented previously for a floating circular cylinder with L/D = 2.0 by Gambarine et al. (2016) [6] - Experimental study of the influence of the free end effects on vortex-induced vibration of floating cylinder with low aspect of ratio, OMAE2016-54623. The present results showed that the amplitudes in both directions were the highest for the semi-sphere case, r/R = 1.0. The amplitudes were almost the same for the other radius values, 0.0 < r/R ≤ 0.5; in which the maximum amplitudes decreased with increasing the corner radius. A critical value, L/Dcrit = 0.5, in which only the free-end structures affect the VIV behavior of the cylinder piercing the free-surface could be stated. The conclusion was that the cylinder free-end affects the VIV behavior for cylinders with very low-aspect ratio.
Statistical Energy Storage Sizing for Point Absorber Wave Energy Converters (WECs): A Device for Operation off the U.S. East Coast
Authors: Zhou Xiang , Jafari Mehdi , Abdelkhalik Ossama , Korde Umesh A. , Gauchia Lucia
Published: September 2018

This paper addresses the sizing problem of an energy storage system (ESS) while considering statistical tolerance for a two-body wave energy converter (WEC), which is designed to support ocean sensing applications with sustained power for long-term functioning. The power is extracted by assuming ideal power take-off (PTO) based upon historical ocean data record (significant wave height and period of wave swell) from Martha’s Vineyard Coastal Observatory. A gamma distribution is applied to generate the extracted power distribution of each sample in the time-series using Bayesian methodology. The means and standard deviation of the extracted power distributions compose the statistical annual power time-series. Finally, the required capacities for the ESS sizing are estimated and discussed while considering both ground truth values and statistical values.
Open Access Atlas of Global Spectral Wave Conditions Based on Partitioning
Authors: Portilla-Yandún Jesús
Published: September 2018

An open access atlas of wave spectral characteristics at global scale is presented (GLOSWAC). This atlas is based on a recently developed technique for deriving spectral statistics, following the concept of partitioning. This development has been possible due to the parallel release of the wave spectra variable from the ERA-Interim archive of the European Centre for Medium-Range Weather Forecast (ECMWF). Although wave spectra are commonly available nowadays for wave analysis and forecasting, standard integral wave parameters are still in dominant use, both in practical and scientific applications. Although integrated parameters can give a good account of the wave spectral distribution in unimodal cases, they are subject to serious shortcomings when the sea state is bimodal or multi-modal. This issue can be easily tackled with the use of partitioning approaches. Spectral partitioning allows identifying the different wave components with different meteorological origin present in the spectrum. These components can be represented by their integrated parameters, which are much more meaningful than the averaged ones for the whole spectrum. Apart from the increased consistency, this method allows to summarize spectral information, offering the possibility to develop wave spectral statistics. Based on a statistical descriptor, the Probability Distribution of Spectral Partitions (PDS), which is the main outcome from GLOSWAC, the local long-term wave systems can be identified and characterized. In addition, several other spectral parameters are computed and distributed in a web format. For illustration, an arbitrary reference location is used here to guide the interpretation and the use of the information derived.
Numerical Simulation of a Pre-Swirl Stator Collision With Sea Ice Incorporating Various Material Model Based on Experimental Study
Authors: Ahn Jae-Woo , Choi Joong-Hyo , Park Sung-Gun , Han Sung-Kon
Published: September 2018

The objective of this paper is to develop a realistic numerical model for ice–pre swirl stator (PSS) structure interaction problem under collision circumstance. PSS structure has been installed in front of a propeller of oil carrier or container vessel operating non-arctic region in order to increase efficiency of propulsion system, which was designed by Daewoo Shipbuilding and Marine Engineering (DSME). Recently, according to increase of port traffic in arctic region, it is being anticipated that market of PSS installed vessel operating in arctic region will be extended to pursue raised ship’s efficiency but in strength point of view, quantified assessment for dynamic interaction between PSS and sea ice is not specified in any design codes or classification rules. This standpoint will be led to an increased demand for the safe structural design of arctic vessel’s PSS structure subject to collision with sea ice.

In this study, DSME’s PSS structure design will be introduced and five types of numerical model to represent ice crushing behavior which were well-known though previous study will be investigated. The parameters of each material model of ice will be defined and more realistic numerical model for ice will be proposed through comparison study with experimental results. After that, the results of numerical simulations for a collision between PSS and sea ice with five numerical models using LS-DYNA software will be represented. In here, dynamic responses of PSS and failure behaviors of each ice model at each load case will be thoroughly evaluated. Collision loading scenarios and ice dimension were properly assumed based on polar class rule for propeller-sea ice interaction. Consequently, simplified analytic method and proper numerical model for ice corresponding to PSS-sea ice collision simulation will be proposed and discussed, respectively.
Hydrogen Induced Stress Cracking of Superduplex Steels: Effect of Operation Temperature
Authors: Haldorsen Lars M. , Nyhus Bård , Rørvik Gisle
Published: September 2018

Duplex stainless steel has been used on subsea facilities since the mid 80-ties. The experiences with these materials have been relative good and only a few failures have been reported. However, BP and Shell experience some serious cracking of duplex steel in the mid 90-ties and in beginning of the century. The root cause of these failures was identified to be Hydrogen Induced Stress Cracking, HISC, where the hydrogen source was the cathodic protection system of the subsea facility. These and other similar failures resulted establishment of Joint Industry Projects, JIPs with financial and technical contribution from leading oil companies, contractors, material suppliers and research institutions as TWI, SINTEF and DNVGL. The objective of the JIPs was to establish practical usage limits for duplex stainless steels. The JIPs resulted in a recommended practice “DNV-RP-F112 - Design of duplex stainless subsea equipment exposed to cathodic protection.”

This document minimized the failure rate of duplex steel components used subsea. However, since duplex steels components have been used on subsea facilities long before the guidelines and recommendations were issued, there are lot of components presently in use that may be overloaded compared to guidelines and recommendations. As a part of life time extension of one of Statoil’s long time producing fields, a HISC re-calculation of spools connecting SPSs to infield pipelines showed that many of the spools were exposed to stresses above the recommended stresses given in DNV-RP-F112. Since these recommendations were primarily based on testing at ambient seabed temperature (4°C), Statoil, together with SINTEF, started in 2016 a project where the aim was to evaluate the resistance against HISC as an effect of the operation temperature.

The results of this project show that the critical net section stress/AYS (HISC resistance) increases with increasing temperature. Based on this, the before mentioned spools can be considered safe even though the spools are exposed to stresses above the recommendations in DNV-RP-F112.

Further, the investigations show that the guidelines and recommendations given in DNV-RP-F112 may be conservative for temperatures above 4°C. It is therefore recommended to perform more testing to confirm and incorporate the findings from the present investigation in future revision of DNV-RP-F112.
Experimental Investigation of Negative Damping Effects for a TLP Type Offshore Wind Turbine
Authors: Aoki Masaaki , Srinivasamurthy Sharath , Iijima Kazuhiro , Hara Naoyuki , Ikoma Tomoki , Nihei Yasunori
Published: September 2018

Wind power generation has been paid much attention over the years as a countermeasure against global warming. Especially in recent years, researches and developments have also been made on Floating Offshore Wind Turbine (FOWT) in relatively deep offshore. Unlike Bottom-mounted Offshore Wind Turbine (BOWT), the motion characteristics of FOWT is complicated owing to coupled response of wind turbine and floating platform motions since the FOWT system is not fixed to the seabed. Due to these complexities, negative damping is one of the major problems reported for SPAR type FOWT moored by catenary chains. Negative Damping, in which the natural periodic motion is excited by blade pitch control employed for keeping the power generation constant, has to be addressed.

In this paper, we discuss the negative damping of TLP type FOWT with a series of dedicated experiments. We manufactured a 1/100th-scale model TLP type FOWT model with a primary control system of the blade pitch angle for a geometrically scaled model of the 5MW wind turbine based on the NREL. At first, we formulated the mechanism for occurrence of Negative Damping and derived the conditions under which unstable fluctuations of the floating platform occurs using the motion equation. After that, we conducted scale model tank tests in wind alone and confirmed the phenomenon wherein the fluctuation of the floating platform does not converge. Finally, how dangerous such coupled motion of wind turbine and floating platform would be for real-scale FOWT is discussed.
Modeling, Simulation and Validation of the Fluid Temperature of a Physical Drilling Simulator for Experimental Planning
Authors: Höhn Patrick , Aragall Roger , Koppe Michael , Oppelt Joachim
Published: September 2018

Drilling equipment tests during field operations are always affected by uncertainties and variations regarding the local conditions in the borehole. In order to provide a more controlled testing environment for research, a hardware simulator was established at the Drilling Simulator Celle, Clausthal University of Technology. The simulator replicates the last 25 meters of a horizontal borehole and permits the drilling of a five-meter long rock sample. The setup includes a flow loop with two pumps for borehole cleaning and cuttings transport during the drilling process. During operation, temperature of the fluid increases due to pressure losses in the loop.

This paper introduces a basic model to determine the maximum allowable continuous operation time of the hardware setup. Further improvements can be achieved by doing sensitivity analyses of the parameters affecting the system behavior, e.g. ambient temperatures or mass flow rate. Measurements from the hardware setup are used for validation of the model and show consistent results.
Estimation of Technical Wave Energy Potential in Exclusive Economic Zone of India
Authors: Nagababu Garlapati , Patel Ravi , Moideenkunju Seemanth , Bhasuru Abhinaya Srinivas , Kachhwaha Surendra Singh , Surisetty V. V. Arun Kumar , Aich Bhowmick Suchandra
Published: September 2018

Identification of the best location for wave farm installation, wave resource assessment needs to be carried out. In the present work, wave resource assessment along the Indian EEZ was carried out using the 17-year (2000 to 2016) output simulation of the third generation wave model WAVEWATCH-III (WWIII). Spatial distribution of significant wave height, mean wave energy period and annual mean of wave power is plotted. Further, the monthly and seasonal variation has been carried out to assess the effect on temporal variability at a specific location. The results show the annual mean wave power is in the range of 1–12 kW/m across the Indian EEZ. Further, it was observed that wave power along the western coast of India is more energetic than the eastern coast of India, with annual average wave power of 8–12 kW/m and 2–6 kW/m respectively. However, coastlines of Gujarat and Maharashtra experience the maximum seasonal and monthly variability across Indian EEZ, which is 2 and 3.5 respectively. By using different wave energy converters (WEC), the capacity factor and technical wave energy potential over the study area are estimated. Oceantec WEC shows maximum capacity factor (0.35) among the all selected wave energy converters. The results reveal that the electric wave power generation is 3 times more in the western coastal region as compared to the eastern coast of India.
Study of Piezomagnetic Behaviors Surrounding X80 Steel Subjected to Cyclic Stress
Authors: Bao Sheng , Bai Shuzhuang , Gu Yibin
Published: September 2018

This research aims to explore the evolutions of the piezomagnetic field (B field) of X80 steel under cyclic tensile stress at different piezomagnetic field measurement distances. The X80 sample was subjected to cyclic preloading with a large stress amplitude. Subsequently, a series of cyclic tensile experiments were conducted to measure the piezomagnetic fields in the vicinity of the X80 sample at pre-determined distances by a fluxgate magnetometer. It was found that the magnetic parameters of X80 steel have quantitative relationship with the piezomagnetic field measurement distance. The B field-stress curves with different maximum stresses share a same evolution trajectory during the loading process when the starting point of the loading processes stays unchanged. The unloading curves have different traces with the tendency towards the starting points. Additionally, the relationship between Tail reversals and piezomagnetic field measurement distance was also discussed in this paper. Based on the piezomagnetic signals, the stresses of the pipelines can be detected and safety problems can be also prevented.
Shadowing Effect Analyzing for Propeller-Ice Milling Condition With Peridynamics
Authors: Xiong Wei Peng , Chao Wang
Published: September 2018

During the research of propeller-ice contact process, we found that shadowing effect has great influence on the ice loads of propeller blade. Therefore, more study in the shadowing effect would be helpful to solve the complicated propeller-ice contact problem. A numerical simulation model is established based on the coupling of peridynamics and panel method in this paper, and ice force for the whole blade and for blade back and blade face separately are obtained through the calculation of the simulation model. The influence law to ice loads of shadowing effect would be revealed clearly by comparing the loads of blade face with the loads of blade back .On this basis, more research is carried out on the mechanism of shadowing effect. In addition, a new calculation formula for shadowing coefficient is put forward in this paper. The results show that the influence of shadowing effect on propeller loads is well predicted by the calculation result of shadowing coefficient formula.
Numerical Analysis of Wave and Current Interaction With Moored Floating Bodies Using Overset Method
Authors: Di Paolo Benedetto , Lara Javier L. , Barajas Gabriel , Paci Agnese , Losada Iñigo J.
Published: September 2018

Numerical modelling of floating bodies is still being a very challenging issue, especially for large body displacements. Despite of the good performance of potential flow models in predicting floating body dynamics, there are still physical processes which are not well reproduced with that approximation. Their strong assumptions yield a lack of accuracy when high non-linear effects become predominant. In addition, the presence of restrictions to motion induced by mooring elements also introduces additional non-linear features which are sometimes out of the framework of the use of potential flow models. The use of CFD approach overcomes potential model limitations especially for non-linear effects. When CFD models are applied to solve waves and current interaction with floating bodies, several issues arise such as the numerical treatment of the floating element, mooring implementation and also the computational cost. Although several approaches are available in literature regarding the numerical implementation of floating bodies, the use of the Overset mesh appears as the more suitable one for large body displacement. Although accurate results have been obtained with re-meshing or even morphing techniques, large mesh deformation can yield into non-acceptable skewness and aspect ratio for the cells, consequently inducing numerical instabilities. In this work, we will present a numerical analysis of wave and current interaction with floating bodies. The objective of the work is to present a set of numerical implementations performed in OpenFOAM environment with the use of the Overset mesh method to study moored floating body dynamics due to the combined action of waves and current.

The implementations, included in IHFOAM (www.ihfoam.ihcantabria.com) are a new set of boundary conditions to generate waves and current without the use of relaxation zones. The main consequence is that the computational cost can be reduced due to the use of smaller domains. In addition, the implementation of mooring will be also presented in order to extend the use of the model to realistic conditions. Numerical model predictions compared with laboratory data of wave interaction with moored floating bodies have been performed showing a high degree of agreement. Comparison of floating body displacement and mooring tension will be presented. The combined effect of waves and current, traveling in the same and in opposite directions than waves, and their interaction with floating bodies and mooring will be also studied. Results will show the applicability of current method to model floating bodies.
Investigations Into Uncertainties in Fatigue Damage During Transport Phase for Topside Structures
Authors: Zhu Suji , Haaheim Helene Høgseth , Lefranc Marc
Published: September 2018

Up to now, the uncertainties in the fatigue utilization during operation (long-term, typical 20 to 30 years) phase have been widely investigated for various oil and gas installations while limited attentions have been paid to the fatigue damage during the transport phase. In normal, the fatigue damage during the transport phase is assumed to contribute limited proportions (for example, less than 5%) of the total fatigue damage for the whole life since the transport duration is at most several months. However, as the size of oil and gas installations increases, the fatigue damage during the transport phase may increase noticeably considering the inertia forces in moderate or severe sea states. During the transport, the weather encountered may deviate significantly from the long-term statistical values. It becomes crucial to determine the uncertainties in the calculated fatigue damage during the transportation phase. Nowadays, the uncertainties are mainly accounted for using Design Fatigue Factor (DFF) while the value of DFF may be different in different standards. In this paper, the fatigue damage for a topside module during the transport phase is studied. Three different vessels are to be used for comparison purpose. The uncertainties due to the sea states encountered are focused. Simplified approach is adopted to investigate the factors influencing fatigue damage. In addition, the calculated fatigue damage is also compared with the fatigue damage based on simplified fatigue analysis.
Bubble Breakup and Coalescence Modelling for Subsea Gas Releases Using Computational Fluid Dynamics
Authors: Wu Kejia , Green Johnathan , Sivandran Subajan
Published: September 2018

Bubble breakup and coalescence is a phenomenon which occurs within a developing subsea gas plume. A Computational Fluid Dynamics (CFD) model incorporating bubble breakup and coalescence was developed to describe the behaviour of a subsea gas release and the subsequent rising gas plume. The model was assessed for its suitability in capturing the characteristic behaviour of a rising gas plume by comparing the CFD results with experimental data obtained from underwater gas release experiments.

The study shows bubble breakup and coalescence plays a key role in determining the shape and the behaviour of a subsea gas release. Without the bubble breakup and coalescence included in the CFD model a narrower plume width and higher rising velocity is observed when compared to the experimental data. With bubble breakup and coalescence included the results obtained from the CFD model more accurately match the experimental data. Breakup and coalescence is a mechanism which redistributes the energy within the core of the gas plume towards the edge of the plume. This has a significant impact on the plume characteristics and is vital to be included in the CFD model to describe the behaviour of the released gas.

The study was carried out using air as the released gas. This was done to compare with the available experimental data where air was used as the source. However the CFD model developed is applicable for hydrocarbon subsea gas releases.
Slug Flow-Induced Oscillation in Subsea Catenary Riser Experiencing VIV
Authors: Safrendyo S. , Srinil Narakorn
Published: September 2018

Slug flow appearance in a multiphase-carrying riser with a long tie-back distance and deeper water is inevitable, depending on the operational and environmental conditions. Several state-of-the-art technologies in mitigating the effects of internal slug flows might not be completely effective or cost-efficient. In addition to the slug excitation, the external current flows can also affect the riser structural behavior and integrity by the presence of vortex-induced vibration (VIV). This study aims to investigate and understand the behavior of slug-conveying catenary riser under uniform and random slug excitations, in combination with VIV. The steady-state slugs are considered and modelled by a series of liquid and gas phases flowing at certain rates inside the riser pipe. Each slug unit consists of a slug liquid (oil, water or their mixture) and gas pocket. In the uniform slug flow cases, all slug units have their equal slug liquid lengths. Time-domain simulations are conducted for different slug units of 20D, 30D, 40D and 50D, where D is the pipe internal diameter, and for different internal flow rates. The non-uniform slug flow case is considered by randomly generating the time-varying slug liquid and unit lengths. Multi-frequency oscillations of the catenary riser are observed, triggered by the transient slug excitations rendering the fundamental vibration mode which is sustained over the ensuing steady-state slugging period. The random slug-induced vibration (SIV) entails larger response amplitudes which are critical from the fatigue life viewpoint, especially when VIV is also accounted for. For riser SIV analysis, only in-plane response is observed; nevertheless, the interaction of riser SIV and VIV generates both in-plane and out-of-plane responses with larger 3-D dynamic responses, deformations and stresses. Such combined SIV and VIV should be specially considered during the riser analysis and design by also taking into consideration the travelling random-like or intermittent slug flows.
Experimental and Numerical Study of Vortex Induced Vibrations on a Spool Model
Authors: Gross David , Roux Yann , Rousse Benjamin , Pétrié François , Assier Ludovic , Minguez Matthieu
Published: September 2018

The problem of Vortex-Induced Vibrations (VIV) on spool and jumper geometries is known to present several drawbacks when approached with conventional engineering tools used in the study of VIV on risers. Current recommended practices can lead to over-conservatism that the industry needs to quantify and minimize within notably cost reduction objectives.

Within this purpose, the paper will present a brief critical review of the Industry standards and more particularly focus on both experimental and Computational Fluid Dynamic (CFD) approaches. Both qualitative and quantitative comparisons between basin tests and CFD results for a 2D ‘M-shape’ spool model will be detailed. The results presented here are part of a larger experimental and numerical campaign which considered a number of current velocities, heading and geometry configurations. The vibratory response of the model will be investigated for one of the current velocities and compared with the results obtained through recommended practices (e.g. Shear7 and DNV guidelines).

The strategy used by the software K-FSI to solve the fluid-structure interaction (FSI) problem is a partitioned coupling solver between fluid solver (FINE™/Marine) and structural solvers (ARA).

FINE™/Marine solves the Reynolds-Averaged Navier-Stokes Equations in a conservative way via the finite volume method and can work on structured or unstructured meshes with arbitrary polyhedrons, while ARA is a nonlinear finite element solver with a large displacement formulation.

The experiments were conducted in the BGO FIRST facility located in La Seyne sur Mer, France. Particular attention was paid towards the model design, fabrication, instrumentation and characterization, to ensure an excellent agreement between the structural numerical model and the actual physical model. This included the use of a material with low structural damping, the performance of stiffness and decay tests in air and in still water, plus the rationalization of the instrumentation to be able to capture the response with the minimum flow perturbation or interaction due to instrumentation.
Adaptive Methods for Reliability Analysis of Marine Structures
Authors: Teixeira A. P. , Guedes Soares C.
Published: September 2018

This paper reviews methods and strategies that have been developed recently for reliability analysis of complex and realistic structural systems using advanced non-linear Finite Element methods. The focus is on adaptive response surface techniques able to provide high quality local approximations in the region of the random variable space that contributes most to the probability of failure. In particular, polynomial regression models, artificial neural networks, Kriging models (or Gaussian process models) with adaptive capabilities, and their applications to the reliability analysis of ship structures and subsea pipelines are reviewed. The paper also addresses the role of the structural reliability methods to assess the safety levels of damaged ships and to code calibration, particularly to derive the target safety levels of the ship hull girder. The review presented in the paper is mainly focused on the contribution of the authors to the developments in this subject area.
Floating Moored Oscillating Water Column With Meshless SPH Method
Authors: Crespo Alejandro J. C. , Hall Matthew , Domínguez José M. , Altomare Corrado , Wu Minghao , Verbrugghe Tim , Stratigaki Vasiliki , Troch Peter , Gómez-Gesteira Moncho
Published: September 2018

The meshless method called Smoothed Particle Hydrodynamics (SPH) is here proposed to simulate floating Oscillating Water Column (OWC) Wave Energy Converters (WECs). The SPH-based DualSPHysics code is coupled with MoorDyn, an open-source dynamic mooring line model. The coupled model is first validated using laboratory tests of a floating solid box moored to the wave flume bottom using four mooring lines interacting with regular waves. The numerical free-surface elevation at different locations, the motions of the floating solid box (heave, surge and pitch) and the tensions in the mooring lines are compared with the experimental data. Secondly, the coupled model is employed to simulate a floating OWC WEC moored to the sea bottom, while numerical results are also validated using data from physical modelling. The numerical results are promising to simulate floating OWC WECs. However, some discrepancies are noticed since the simulations presented in this work only consider a single-phase (water) so the full OWC WEC behaviour is only partially reproduced. Nevertheless, considering the aforementioned limitations, DualSPHysics can be used at this stage as complementary tool to physical modelling for a preliminary design of floating wave energy converters.
Numerical Simulation of Wave Transformation Over Deep-Sea Platform Reef Using SPH Method
Authors: Zhang Xiang , Ren Bing , Wang Yongxue , Wen Hongjie
Published: September 2018

A non-reflective SPH (Smoothed Particle Hydrodynamics) wave flume is developed to study wave transformation over the deep-sea platform reef with a steep reef-face. The left and right boundaries of the flume are modeled using the periodic boundary conditions and a water circulation technology, and a momentum source wave maker is applied to generate the required wave. Wave transformation over the reef-flat is analyzed and compared with the experimental data. The results show that the present SPH model can effectively overcome the non-physical rise of the mean water level in the lagoon and over the reef-flat, which can be observed in the long time simulation with the traditional vertical two-dimensional numerical model. Furthermore, the present model can accurately reproduce the wave breaking process and give a good agreement with the experimental data in terms of the spatial distribution of wave height and wave setup on the reef flat.
Scale Effect Studies on Hydrodynamic Performance for DTMB 5415 Using CFD
Authors: Zhang Heng , Zhang Hang , Chen Xuanshu , Liu Hao , Wang Xianzhou
Published: September 2018

Making CFD with the capability of predicting ship scale design performance, rather than relying on scale model tests will help reduce design costs and provide a greater opportunity to develop more energy efficient ship designs. The key objective of this paper is to perform a fully nonlinear unsteady RANS simulation to predict the ship motions and resistance of a full scale DTMB 5415 ship model. The analyses are performed at design speeds, at a certain Fr number, using in-house computational fluid dynamics (CFD) to solve RANS equation coupled with six degrees of freedom (6DOF) solid body motion equations. RANS equations are solved by finite difference method and PISO arithmetic. Computations have been made using structured grid with overset technology. Simulation results shown that the total resistance coefficient in calm water at service speed is predicted by 2.36% error compared to the related towing tank results. The ship resistance for different scale demonstrated that the current in-house CFD model could predict the resistance in a reasonable range of the EFD data. The comparison of flow field for wave pattern for different scale model were analyzed and discussed.
A Preliminary Study on Site Selection for Tidal Current Power Plants in Seto Inland Sea
Authors: Kikukawa Koki , Tabeta Shigeru
Published: September 2018

Tidal current power generation is one of marine renewable energies whose merit is stable and predictable power generation. In the present study, a potential map of tidal current energy in Seto Inland Sea is developed on GIS from the datasets of hydraulic model experiments. Fisheries value maps are also developed from the database of fish catch for typical species in the target area. The developed maps are integrated through GIS, to investigate suitable locations for tidal current power plants in Seto Inland Sea. From the combined map considering both the economic value of tidal current power generation and the fishery, it is found that the areas with positive total value significantly decrease as damage rate on fishery becomes larger, though the areas with high energy potential of tidal current have larger total economic values even when the damage rate increases. On the other hand, some areas where the fishery value is small will become candidate site when the damage rate on fishery gets larger.
Analysis of Local Vibration and Strength of Water Jet Propulsion Unit of High Speed Ship
Authors: Zhang Xin , Ren Huilong , Feng Guoqing , Liu Yifu , Wu Zhaonian
Published: September 2018

In recent years, water jet propulsion unit has been widely used in the field of high speed ship. Compared with traditional propeller, water jet propulsion unit has excellent maneuverability with high speed, and lateral force generated by water jet propulsion unit can reduce the radius of turning. High speed ship with water jet propulsion has higher efficiency, lower noise. However, water jet propulsion unit needs to be opened in stern transom plate, and it causes the water jet force when ship is operating, all of these will affect the local strength of stern. It remains to be researched whether the vibration generated by water jet excitation force has a significant influence. These problems are designers worried about. To solve these problems, this paper builds the finite element model of stern contains water jet propulsion unit, considering hull deck load, broadside load, bottom load, bulkhead load and water jet load, checking the local strength of stern. Analysis of vibration problem, considering the influence of added mass of entrained water, dividing stern into deck, bottom, water jet propulsion unit, stern transom plate and other local structure, calculating natural frequencies of plate, panel and grillage of each local structures. Comparing the results with shaft frequency and blade frequency, checking the reserve frequency, judging whether water jet propulsion unit on vibration problem meets standards, providing reference for the following hull design.
Research in Ballast Water Exchange for a Jack-Up Drilling Unit
Authors: Chunhui Li , Xuehui Zhang , Jianwei Xiao , Bo Zhou , Lei Cheng , Nan Zhao
Published: September 2018

A new IMO Ballast Water Management Convention was adopted and came into force in 8th Sep. 2017. The IBWMC (International Ballast Water Convention) covered four major vessel types: Single/Double Hull Tanker, Bulk Carrier and Containership. Research in BWM (Ballast Water Management) of Jack-up Platform is rare.

The Jack up was built prior to the date which Convention comes into force and was delivered after date, so BWM of the Jack up is focused on Ballast Water Exchange Plan, which should be approved by Flag State or by CLASS (if authorized by Flag State). In this paper, a sequential method is hosen to exchange ballast water, and calculation is carried out to ensure that the stability is maintained in whole process.
Float-Over Installation Analysis of Semisubmersible Production Platform Topside
Authors: Gang Chen , Huan Zhang , Yuhan Wang , Chao Wang , Wei Zhang , Yan Yin
Published: September 2018

Compared with split lifting by floating crane, the float-over is less time-consuming and has larger lifting capacity, especially suitable for large and medium sized offshore platforms. Float-over installation process of a deepwater semisubmersible platform topside is analyzed in this paper. And the multi-floating coupling calculation is carried out in the typical loading conditions of mating process between topside and column top structure. The motion response of leg mating unit in position of barge is received. The calculation results show that the float movement condition meets float-over installation requirements of topside. The analysis can provide a reference for the project of the float-over installation in the future.
Storm Surge Estimation Along Tokyo Bay Based on a Simple Stochastic Approach
Authors: Hisamatsu Rikito , Kim Sooyoul , Tabeta Shigeru
Published: September 2018

In recent years, refinement of stochastic storm surge estimation is essential for risk management in insurance industries because the Japanese government promotes flood risk transfer to insurance companies. Insurance systems may reach peak risk when storm surge damage occurs; however, there are only a few studies on the stochastic analysis of storm surges. This paper presents the stochastic evaluation of storm surges in Tokyo Bay. First, storm surges are assessed using two methods of an empirical formula and a numerical model. Then, the return period of storm surges is stochastically evaluated. It is found that an empirical formula underestimates the surge level in comparison to the numerical model. Based on the results of numerical model, the return period of a storm surge is proposed in Tokyo Bay.