bluuebunny/crossref_metadata_2025 huggingface dataset:
Artificial Intelligence Machine Learning in Marine Hydrodynamics
Authors: Sclavounos Paul D. , Ma Yu
Published: September 2018

Artificial Intelligence (AI) Support Vector Machine (SVM) learning algorithms have enjoyed rapid growth in recent years with applications in a wide range of disciplines often with impressive results. The present paper introduces this machine learning technology to the field of marine hydrodynamics for the study of complex potential and viscous flow problems. Examples considered include the forecasting of the seastate elevations and vessel responses using their past time records as “explanatory variables” or “features” and the development of a nonlinear model for the roll restoring, added moment of inertia and viscous damping using the vessel response kinematics from free decay tests as “features”. A key innovation of AI-SVM kernel algorithms is that the nonlinear dependence of the dependent variable on the “features” is embedded into the SVM kernel and its selection plays a key role in the performance of the algorithms. The kernel selection is discussed and its relation to the physics of the marine hydrodynamic flows considered in the present paper is addressed.
Bending Capacity of Corroded Pipeline Subjected to Internal Pressure and Axial Loadings
Authors: Gao Jie , Peng Zengli , Li Xin , Zhou Jing , Zhou Wenxing
Published: September 2018

Offshore pipelines operating in a harsh environment are usually subjected to combinations of bending moment and axial loadings in addition to internal pressure. Due to the corrosive media transported in the pipelines and corrosive substances within seawater and soil outside the pipelines, local corrosion defects will generate on the pipeline’s inner and outer walls, reducing its ultimate bearing capacity.

This paper presents a series of full-scale failure tests and nonlinear finite element analysis (FEA) to study the bending capacity and failure mode of corroded pipelines with outside locally-thinned-areas (LTAs) subjected to combinations of internal pressure, axial compressive force and bending moment. The LTAs are loaded in compression to simulate corrosion. Material tests of API 5L X56 seamless pipe steel were conducted and the stress-strain relationship was obtained. FEA results of the moment versus curvature relation, bending capacity and local buckling behavior of each specimen model matched the experimental results very well, validating the accuracy of this simulation. Additional FEA is then performed to investigate the effect of corrosion geometric parameters, such as corrosion depth, corrosion width, and corrosion length, on the ultimate moment. Among them, the width is of the greatest impact, followed by is the depth, the length impact can be ignored.
Shutdowns Management: Changing Things Up by Only Applying Best Practices
Authors: Alonso Jose-Luis , Neal Bernie , Jolly Simon , Auld Steven , Adesanya Adetola
Published: September 2018

Production efficiency is a key factor for oil & gas companies to have a good performance in a low oil prices environment, and planned shutdowns are events that impact crucially in this factor.

This technical paper objective is to explain how, starting from a point of high planned losses due to shutdowns bad performance (13%), the application during only one year of best practices compiled from oil & gas and other business experience is able to change things up to achieve an impressive outcome (3%).

Long term planning, meticulous preparation and efficient execution are achieved when best practices are applied with accountability, rigor and common sense.

Maintenance and Integrity shutdown plans compliance is also improved as they are considered inside a big picture that allows us to schedule them in the more efficient way to assure our HSE standards, and helped by some new technologies as the so called NII (Non-Intrusive Inspections).

Standards, procedures, deliverables, communication channels, materials control, organigrams… are the specific tools to be used and refed to implement the lessons we learn at the end of each shutdown.

Sharing regularly our experience with other operators is also a source of best practices and cross-pollination.

Maintaining this quality standard along the time and improving to the extent possible will drive us to excellence in the middle term. As our teams become more and more involved on this new method, they start to feel more comfortable and propose improvements, being more and more committed as they see good results arriving.
Investigation of Hydrodynamic Behaviour of Wind Turbine GBS During Offshore Installation and Engineering Design Outcomes
Authors: Ducasse Marie-Laure , Soulat Damiano , Vertallier Florent
Published: September 2018

Gravity Based Structure (GBS) is one of the main structural foundation concept planned to be used to accommodate offshore wind turbines in shallow water depth areas. Large scale deployment of such massive foundations raises technical issues regarding transport and installation of the GBS. This paper aims at presenting major outcomes of hydrodynamic analyses carried out to assess dynamic behaviour of the GBS during offshore installation. This study focuses on the last critical step of the installation process when the foundation is almost completely ballasted and close to the seabed grading layer. CFD analyses are conducted with OpenFOAM to estimate viscous damping of the GBS and to investigate the impact of seabed proximity and bedding layer porosity on hydrodynamic parameters. Based on damping coefficients derived from CFD, motion analyses are performed with Diodore™ to assess dynamic behaviour of the GBS in irregular waves. Results are benchmarked against responses obtained from different damping parameters and computation methods. This study allows providing some recommendations regarding hydrodynamics design methodology for this type of GBS installation analysis.
The Evaluation Method of the Hydrodynamic Frictional Resistance for the Painted Rough Surface
Authors: Katsui Tokihiro , Tanaka Hisao
Published: September 2018

The present study shows a method to evaluate the performance of the paints to reduce the additional frictional resistance in full scale ship Reynolds number. Simultaneous non-linear ordinary differential equations are developed to calculate the hydrodynamic frictional resistance of flat plate based on the momentum equation and Coles’ wall wake law which is the similarity law of the velocity distribution in the turbulent boundary layer. Roughness influence of painted surface is taken into account by adding the roughness function to Coles’ wall wake law. The expression of the roughness function should be determined based on the experimental results of the additional frictional resistance for various kinds of paints. The obtained roughness function depends on the roughness Reynolds number, and it also depends on both the roughness wave height and wave length fraction to its height which are obtained FFT analysis for measured paint surface profiles. The calculated local frictional stress coefficients on the painted surfaces well agreed with the measured ones. The total frictional resistance coefficients of painted surface in the actual ship scale Reynolds number can be evaluated considering influence of surface roughness.
Finite Element Simulation of an Embedded Anchor Chain
Authors: Sun Chao , Feng Xiaowei , Gourvenec Susan , Neubecker Steven R. , Randolph Mark F.
Published: September 2018

The embedded portion of a mooring line plays an important role for efficient and economic design of an overall mooring system. This paper presents a methodology for numerical simulation of the behaviour of an embedded anchor chain as it cuts through the soil, focusing on the tensioning of a catenary mooring. The Coupled Eulerian–Lagrangian (CEL) approach within ABAQUS is used to capture the interaction between the embedded chain (Lagrangian structure) and the soil (Eulerian material). The anchor chain is simulated by a series of rigid cylindrical segments connected together by LINK connectors.

Before analysing the global behaviour of an embedded chain, a calibration exercise is undertaken where a straight multi-link portion of the chain is displaced normally and axially in soil. The resulting normal and frictional resistances (per unit length) are compared with those adopted in general practice, in order to calibrate the relationship between the diameter of the cylindrical segments and the bar diameter of the chain. After that, the tensioning process of an anchor chain is simulated, starting from an initial configuration with a 9 m length embedded vertically (attached to a fixed padeye), with the remaining length lying on the seabed. Horizontal tensioning of the chain causes it to cut through the soil until it forms an inverse catenary with an angle of just under 35 degrees to the horizontal at the padeye (and zero degrees at the mudline).

The loading curve, and also the inverse catenary profile of the chain for different angles at the padeye, are shown to agree well with the Neubecker-Randolph closed-form analytical solution. However, the ratio of the tensions at the padeye and the mudline from the CEL results differs significantly from the analytical solution. Insights from the CEL results indicate that this is because the frictional soil resistance is not fully mobilised, particularly for the portion of the chain in the stronger soil at depth, near the padeye, where the axial displacements are small. This result has significant implications for the geotechnical design of anchoring systems that involve a (nominally) fixed padeye. The simulation methodology also has considerable potential for exploring the creation of an open trench adjacent to a fixed anchor due to monotonic and cyclic perturbations of the anchor chain.
Control of Floating Offshore Wind Turbines: Reduced-Order Modeling and Real-Time Implementation for Wind Tunnel Tests
Authors: Fontanella Alessandro , Bayati Ilmas , Belloli Marco
Published: September 2018

The present work deals with the implementation of a variable-speed variable-pitch control strategy on a wind turbine scale model for hybrid/HIL wind tunnel tests on floating offshore wind turbines. The effects that scaling issues, due to low-Reynolds aerodynamics and rotor structural properties, have in combination with the HIL technique developed by the authors are studied through a dedicated reduced-order linear coupled model. The model is used to tune the original pitch controller gains so to be able to reproduce the system response of the full-scale floating wind turbine during HIL tests.
Boom Overtopping Assessment Based on a Coupled Hydrodynamic - CFD Analysis
Authors: Limburg Hans , Sainte-Rose Bruno , Verjut Jean-Sébastien
Published: September 2018

Plastic pollution in the marine environment is an increasing problem with severe impacts on ecosystems and economies around the globe. The Ocean Cleanup (TOC) Foundation develops a floating barrier able to intercept, concentrate and extract plastic from the marine environment.

TOC has conducted several experiments and numerical studies to determine the capture efficiency of its system. One of the phenomena leading to its decrease is wave overtopping or under-flowing when the system cannot properly follow the waves, this issue is amplified by the use of a stiffer barrier than the original deep-water moored concept. When such events occur, plastic debris won’t be captured by the system and will escape into the open ocean. Such an event will therefore be decreasing the capture efficiency.

To model and quantify plastic loss due to wave overtopping and under-flowing, the ideal approach would be to use a nonlinear 3D CFD method including hydro-elasticity of the barrier structure. Given the size of the problem and the number of conditions that need to be simulated to characterize the design space of the system, the use of such a method is computationally very expensive and therefore unrealistic. Therefore, the objective of this work is to propose an alternative method.

This paper presents a method of quantifying plastic loss by coupling a hydrodynamic solver to a 2D CFD solver. A hydrodynamic model is set up to predict the dynamics of the boom. A 2D CFD model with imposed motion is used to analyze the local effects of wave overtopping. From there, wave overtopping events along the barrier system are analyzed and quantified using the results found in the 2D CFD study.
A Fundamental Study on Collision of a Tsunami Drifting Objects Against Structures Using MPS Method and FEM
Authors: Masuda Koichi , Ikoma Tomoki , Murata Daichi , Eto Hiroaki , Matsuoka Akihiro , Aida Yasuhiro , Ikegami Masaharu
Published: September 2018

The large-scale tsunami generated by the Great East Japan Earthquake on March 11, 2011 caused a great deal of damage. In addition to tsunami hydrodynamic forces, loads generated by drifting objects such as ships and cars can cause destruction in coastal areas. As such, impact forces due to collisions of drifting objects are an important consideration in the design and planning of structures in coastal areas.

Depending on the size of the drifting object, it is difficult to evaluate the effect of the impact force at the time of collision through tank experiments. Therefore, it is necessary to develop a numerical simulation method that can reasonably evaluate such effects. Such a method must consider the nonlinear interactions among drifting objects, a fluid, and fixed structures.

In the present study, we used the moving particle semi-implicit (MPS) and finite element methods to calculate the effect of collisions between drifting objects and structures, and then verified the results experimentally. The MPS method was applied to calculate the loads and pressures due to the collisions. These results were then used to simulate the deformation of the structure using the finite element method. A tank experiment was then conducted in order to confirm the accuracy of the numerical calculations. The deformation of a rod-shaped steel structure was measured following collision with a floating acrylic plate. The experimental results confirmed the accuracy of the numerical calculations.
Study on the Influence of Ice-Water Coupling on Numerical Calculation of Ice Load
Authors: Li Hui , Yang Zheng , Feng Yan , Wang Yu-Bo , Wang Si-Yu
Published: September 2018

The interaction between sea ice and sea water is a complicated fluid-solid coupling dynamic process during the operation of polar ships. Using the finite element numerical simulation software LS-DYNA to simulate the continuous ice breaking of icebreaker, the ice load numerical calculation method considering the ice water coupling is presented. The effect of ice water coupling on ice load is studied. Based on the ice pool test data and the calculated results of this paper, the accuracy and rationality of the algorithm are verified. On this basis, the multiple factors affecting the coupling between sea ice and sea water are further studied, including the thickness of sea ice and the collision velocity of ship and ice which are affected by the environment of different polar sea areas. By simulating the numerical results obtained from the collision ice breaking of the targeted ship, the influence of various factors on the coupling effect between sea ice and sea water is summarized, and the local strength of the hull head structure is checked and evaluated. Furthermore, the impact-type icebreaking ability of the hull is put forward, which has certain guiding significance for the development of ship ice collision numerical simulation.
Drifting Rogue Packets
Authors: Chabchoub Amin , Hoffmann Norbert , Akhmediev Nail , Waseda Takuji
Published: September 2018

Modulation instability (MI) is one possible mechanism to explain the formation of extreme waves in uni-directional and narrow-banded seas. It can be triggered, when side-bands around the main frequency are excited and subsequently follow an exponential growth. In physical domain this dynamics translates to periodic pulsations of wave groups that can reach heights up to three times the initial amplitude of the wave train. It is well-known that these periodic wave groups propagate with approximately half the waves phase speed in deep-water. We report an experimental study on modulationally unstable wave groups that propagate with a velocity that is higher than the group velocity since the modulation frequency is complex. It is shown that when this additional velocity to the wave groups is small a good agreement with exact nonlinear Schrödinger (NLS) models, that describe the nonlinear stage of MI, is reached. Otherwise a significant deviation is observed that could be compensated when increasing accuracy of the water wave modeling beyond NLS.
Ocean Wave Non-Linearity and Wind Input in Directional Seas: Energy Input During Wave-Group Focussing
Authors: Adcock Thomas A. A. , Taylor Paul H.
Published: September 2018

There has been speculation that energy input (wind) can play an important role in the formation of rogue waves in the open ocean. Here we examine the role energy input can play by adding energy to the modified non-linear Schrödinger equation. We consider NewWave type wave-groups with spectra which are realistic for wind waves. We examine the case where energy input is added to the group as the wave-group focuses. We consider whether this energy input can cause significant non-linear effects to the subsequent spatial and spectral evolution. For the parameters considered here we find this to have only a small influence.
A Numerical Study on the Ultimate Strength of Damaged Tubular Bracing Members Under Axial Compression
Authors: Zhu Ling , Kong Jieling , Liu Qingyang , Yang Han , Wang Bin
Published: September 2018

The tubular bracing members of offshore structures may sustain collision damages from the supply ships, which lead to the deterioration of the load carrying capacity of tubular bracing members. This paper presents a numerical simulation of the ultimate strength of damaged tubular bracing members under axial compression with the nonlinear finite element code ABAQUS, based on previous experimental investigations. Parametric studies are conducted to investigate the load capacity of damaged tubular bracing members, by considering the effects of diameter (D), wall thickness (H), pipe length (L) and the damage positions on the ultimate strength of tubular members. It is found that lateral damage can cause great reduction of the axial load capacity of tubular members. In addition, an approximate equation to predict the ultimate strength of tubular members based on the given damage depth is proposed.
Performance of Embedded Mooring Lines During Keying and Diving of Gravity Installed Anchors
Authors: Zhao Yanbing , Liu Haixiao
Published: September 2018

Gravity installed anchors (GIAs) are the most recent generation of anchoring solution to moor floating facilities for deepwater oil and gas developments. After the installation of GIAs, the anchors are connected with the floating facility via the mooring lines, which interact with the anchors at the shackle and influence the keying and diving performance of GIAs. In the present work, a three-dimensional large deformation finite element (LDFE) model is established using the coupled Eulerian–Lagrangian method to investigate the performance of embedded mooring lines during keying and diving of GIAs. To verify the efficiency of the LDFE model, comparisons with the plasticity models are performed. Then, a parametric study is undertaken to quantify the relationship between the drag force Ta and drag angle θah at the shackle and the drag force T0 and drag angle θ0 at the mudline, in terms of the frictional coefficient, drag angle at the mudline and soil strain rate and strain softening. It is demonstrated that the drag angle at the mudline has the most significant effect on the performance of embedded mooring lines and hence the keying and diving of GIAs.
Coupled Dynamics of a Vertical Axis Wind Turbine (VAWT) With Active Blade Pitch Control on a Semi-Submersible Floater
Authors: Vlasveld Ebert , Huijs Fons , Savenije Feike , Paillard Benoît
Published: September 2018

A vertical axis wind turbine (VAWT) typically has a low position of the center of gravity and a large allowable tilt angle, which could allow for a relatively small floating support structure. Normally however, the drawback of large loads on the VAWT rotor during parked survival conditions limits the extent to which the floater size can be reduced. If active blade pitch control is applied to the VAWT, this drawback can be mitigated and the benefits can be fully utilized.

The coupled dynamics of a 6 MW VAWT with active blade pitch control supported by a GustoMSC Tri-Floater semi-submersible floater have been simulated using coupled aero-hydro-servo-elastic software. The applied blade pitch control during power production results in a steady-state thrust curve which is more comparable to a HAWT, with the maximum thrust occurring at rated wind velocity.

During power production, floater motions occur predominantly at low frequencies. These low frequency motions are caused by variations in the wind velocity and consequently the rotor thrust and torque. For the parked survival condition, it is illustrated that active blade pitch control can be used to effectively reduce dynamic load variations on the rotor and minimize floater motions and mooring line tensions.
Large Scale Earthquake Analysis of Integrated Subsea Facilities
Authors: Hesar Majid
Published: September 2018

Subsea facilities located in earthquake-prone regions of the world can be subjected to severe excitation and have to be designed in a two-tier manner against both ELE and ALE level earthquakes. The return period of these earthquake levels can be 100–300 years and greater than 1000 years, respectively. These facilities may typically consist of rigid pipelines, sliding PLET structures on skirted or hybrid mudmat foundations, connected via rigid spools or jumpers to manifolds on suction pile foundations, with flexible flowlines hanging off goosenecks.

In recent practice Subsea 7 have developed a novel methodology for modelling and simulating the seismic response of such complex clusters in which the so called “system effects” are intractable and dominate the response of certain critical components. Chief amongst the latter are rigid spools and jumpers that span large distances between PLEM, PLET and X-Tree structures without touching the seabed.

In the nonlinear implicit direct integration dynamic FE analyses in Abaqus each of the cluster models in a project is subjected to time history accelerations of seven representative earthquakes, as per ISO 19901-2 requirements. Hysteretic damping characteristics of soil-structure interfaces are modelled with special kinematically hardening elements, calibrated to the site-specific seabed geotechnical properties. Specially developed post processing scripts are used to automatically extract the vital information from the large amount of data produced and perform the unity checks of various components to their respective codes of practice.
Experimental Study of Water Cutoff Performance of Steel Pipe Sheet Piles With Interlocked Joint
Authors: Hong Youngho , Lim Daesung , Seo Doowon , Jeon Jaeku , Chae Kwangseok , Lee Jongsub
Published: September 2018

For the most proper solution of annual increase of solid and other waste treatment in the limited landfill site, the global leading countries develop and keep expanding operation of the offshore waste landfill sites. In this report, we examined the most proper mix ratio of the water cut-off materials for the prevention and enforcement of the performance of the existing cut-off wall inter-connection parts of the offshore waste landfill site, which might be deteriorated by the external force inherent in the sea area. For acquiring the most proper mixed ratios in back-up water cut-off materials, we examined and evaluated the physical characteristics of the applied back-up water cut-off materials — on-site marine clay materials, which might be possible to be acquired near to site, admixtures and bentonite. Also, we applied those back-up water cut-off materials into the new concept applied to the vertical cut-off wall connection parts and investigated variation of the water cut-off performances throughout the changes of the permeability coefficient before and after deformation of the inter-connection joints of the vertical cut-off walls. For the investigation of the permeability performances, we carried out half sized mock-up tests in the laboratory and checked the variation of permeability coefficients referred to the changes in the applying location of back-up water cut-off materials and finally reach to application of back-up water cut-off materials as a proper solution of water cut-off performances in the inter-connection parts of the vertical cut-off wall at offshore waste landfill site.
Fatigue Strength Assessment of a Structure Considering Corrosion Wastage and Corrosion Fatigue
Authors: Yamamoto Norio , Sugimoto Tomohiro , Ishibashi Kinya
Published: September 2018

It is known that the fatigue strength decreases in corrosive environment and many experiments were carried out to comprehend the decrease in fatigue strength in corrosive environment. In order to comprehend the actual state, a cycle speed of fatigue test loads should correspond to a wave frequency. Therefore, an experiment in the long life region is practically difficult, then the corrosion fatigue data available for the life assessment of the structure is quite limited.

In this study, the fatigue strength of the welded joints in long life service was evaluated according to the calculations of corrosion fatigue crack propagation subjected to the random loadings which followed an exponential distribution. In the crack propagation calculations, the progress of corrosion wastage from the plate surface and the resultant stress increase were considered simultaneously. In the high stress and the short life region, the decrease in fatigue strength due to the accelerated crack propagation in corrosive environment was dominant because the progress of corrosion wastage was little. On the other hand, in the low stress and the long life region, the decrease in fatigue strength became dull as longer the fatigue life because the corrosion fatigue crack propagation was suppressed by the corrosion wastage, but after that the fatigue strength showed the precipitous decrease due to the increase in stress resulted by the progress of corrosion wastage.
A Fundamental Study on the Damage of Wash Up to the Quay of the Moored Vessel in Tsunamis Using the MPS Method Considered the Fender Influences
Authors: Masuda Mitsuhiro , Minami Kiyokazu , Masuda Koichi
Published: September 2018

In the case of vessels are moored at the quay, the drift and the wash up to the quay due to the broke of mooring lines is occurred by the tsunamis. In the previous study, the authors are examined to the applicability of the proposed tsunami protection measures as the install more mooring lines (IMML) and the floating tsunami protection wharf (FTPW). However, the Fender influences were not considered in previous authors studies. In this study, the fender influences are considered on the numerical simulation. The three-dimensional MPS (Moving Particle Semi-implicit) method is used as numerical simulation method. The linear compressing spring model is used as the fender model. The fender influences were investigated against the influences of tsunami protection measures using IMML and the damage status of vessel.
Sensitivity and Cost Analysis of Mooring Solutions for Large Renewable Energy Structures
Authors: Thomsen Jonas Bjerg , Andersen Morten Thøtt
Published: September 2018

Mooring of offshore structures is a well-known concept in the naval and offshore Oil & Gas sectors, but has been proven to cause complications and be infeasible in the newer wave and wind energy sectors when applying the traditional solutions and experience. Early-stage wave energy concepts are often planned for deployment in shallow to intermediate water depths, where the traditional catenary systems are insufficient, and have experienced several failures due to large line loads. As a result, considerable amount of line and anchor material is often required and causes undesirably high mooring cost. A need for applying more novel systems and materials is present in order to increase durability and decrease the cost. This study focusses on three different mooring systems, which have been considered in earlier studies and makes direct comparison between the lifetime cost using existing cost databases and design procedures stated in design standards from certification companies. All systems are primarily composed of synthetic lines, and are designed using validated numerical models together with a surrogate based optimization routine. Furthermore, the study investigates the sensitivity on line tensions from varying environmental loads in order to quantify the sensibility and the importance of pre-assessment of the conditions at the expected deployment site.
Integrity Assessment and Control of Offshore Topside Piping: An Expert System Based Approach
Authors: Ratnayake R. M. Chandima
Published: September 2018

Downtime has a significant influence on the productive capability of offshore topside operating systems. Integrity assessment and control (IA&C) disciplines face major challenges in implementing a plant integrity control strategy, due to the lack of a methodology for incorporating fuzziness present in the data. To date, the employed IA&C practices face challenges in maintaining uniform quality from one integrity control program to another, due to the variability present in the technical IA&C process, especially among the different integrity assessment experts. Hence, it is vital to use expert systems-based approaches to sustain IA&C activities at an anticipated level and maintain the performance of operating assets at a target level. This manuscript provides a methodology and an illustrative case for how to perform IA&C activities for offshore topside piping. The illustrative case is demonstrated using a fuzzy inference system (FIS). Technical condition (TC) and relative degradation (RD) are selected as the inputs to the FIS for assessing the likelihood of failure (LoF). Expert system-based calculations, and how to use such results for IA&C, are demonstrated. The practical significance of the suggested approach is also discussed.
Hydraulic Analytical Model of the BOP Control System to Estimate Related Response Times
Authors: Quispe José Luis Párraga , Estefen Segen F. , Jorge Nilo de Moura , Souza Marcelo Igor Lourenço
Published: September 2018

During activities of ultra-deepwater exploration using drilling vessels an emergency disconnection between Lower Marine Riser Package (LMRP) and Blowout Preventer (BOP) stack could occur due to extreme environmental conditions. The disconnection is not instantaneous; it takes time due to the discharge of pressurized liquid from the system of hydraulic accumulators and the entire process is known as emergency disconnect sequence — EDS. Therefore, estimate the response time of the BOP control system is important to avoid damages that compromise the drillship safe operation. In this study, the BOP control system uses a hydraulic system constituted of accumulator bottles, a pressure regulator, rams, valves, and connectors. This system is considered to estimate the response time of cutting and sealing the BOP. The response time is estimated by applying the theory of fluid mechanics and Bernoulli equation to calculate the system equilibrium pressure. The accumulators are sized according to API 16 D and considered to have adiabatic behavior. Nitrogen is simulated as real gas. The validation of the proposed model is performed by comparison with a surface test for cutting of drill pipe with blind shear ram. The model is applied to a case study for ultra-deepwater in Campos Basin Brazil.
Study About Maintenance and Management on an Artificial Beach in Okinawa-Honto
Authors: Tajima Yoshiyuki , Kuroyanagi Akio , Sugahara Ryo
Published: September 2018

At the main island of Okinawa, land preparation developed to the sea side and many seacoasts were lost. The development of the artificial beach had progressed for suppling the lost coasts, and many artificial beaches were developed after “Emerald beach” was developed as the first artificial beach in Japan, 1975. In the suburbs, artificial beaches of beachpark type had developed in the place developed by reclaimed, and it is used by people. In this study, We verify the condition of the beach maintenance, the beach shape, the installation facility, the utility form and the management method for artificial beaches in the main island of Okinawa, and arrange the way of the seacoast use in the main island of Japan.
Conceptual Design of an Autonomous Underwater Vehicle Powered by a Direct Methanol Fuel Cell to Enlarge Endurance
Authors: Villalba-Herreros Antonio , Leo Teresa J. , Abad Ricardo
Published: September 2018

Autonomous underwater vehicles (AUVs) are versatile machines capable of more and more complex missions including the offshore industry. The ability to carry out some missions relies on the endurance the vehicle is provided with. In this sense, fuel cells are found to be very adequate devices to enlarge AUVs endurance because of the high energy density and specific energy they can achieve, but the application of fuel cell technology to AUVs faces specific challenges that need to be overcome. The present work describes the conceptual design process of a typical AUV powered by a direct methanol fuel cell. Methanol is a high available fuel and its handling system is simple. The obtained results indicate that the manufacturing of such a vehicle is possible within several constrains, being the carbon dioxide treatment system the most critical component of the energy plant. The projected vehicle is compared to current vehicles on the market showing the improved endurance.
Free Span Design Development: Experience With the New Revision of DNVGL-RP-F105
Authors: Vedeld Knut , Sollund Håvar , Fyrileiv Olav
Published: September 2018

Free spans constitute a threat to the integrity of offshore pipelines. Ocean currents and wave induced flow near the seabed can cause excitation of vortex induced vibrations (VIV), exposing the pipeline to cyclic loading which may result in fatigue failure. In extreme environmental events, waves and currents may cause significant bending moments due to VIV or direct wave loading, which may cause unacceptably high combined loading potentially resulting in pipeline failure. Safe and reliable free span design is therefore a key aspect of pipeline design in general.

When free spans are located in close proximity to each other, modal response may cause span interaction, effectively coupling potential VIV or direct wave action response of two or more spans. Such spans configurations are called multi-spans. Treatment, and particularly identification of multi-span configurations has long been a challenge in the pipeline industry.

In 2017, a new revision of the DNV GL recommended practice for free span pipeline design DNVGL-RP-F105 was issued. Among other subjects, the new revision provides significantly improved guidance on identification and classification of multi-span free spanning pipelines. The new guidance facilitates the option of automating identification, modal analysis and ultimately fatigue analysis of multi-span configurations.

This paper demonstrates background for and benefits with01 the new revision of DNVGL-RP-F105 in systematic and automated treatment of multi-span identification, fatigue and extreme loading assessments based on recent experience from a selection of pipeline design and operations management case studies.
Preliminary Analytical Formulation of Ice-Floater Interactions Including the Effect of Wave Load
Authors: Ahmed Aziz , Al Maruf M. Abdullah , Dev Arun Kr. , Hannan Mohammed Abdul
Published: September 2018

Diminishing ice presence in the Arctic provides the potential for extended operable period for oil and gas exploration in the Arctic. Floaters are a flexible solution for such scenario whereas they can fully take advantage of the extended drilling season as well as operate in other harsh environment regions during the off-season. Such floaters can disconnect and reconnect to avoid large ice features such as icebergs and multi-year ice ridges. However, they still need to encounter relatively large level ice. Accompanying icebreakers will ideally assist in breaking the level ice into manageable pieces. The interaction of such level ice floes with floater has a significant influence on the dynamic ice load on the floater and resulting mooring load. There is significant uncertainty in the simulation of level ice-floater interaction numerically. Most of the current research focuses on the influence of ice breaking and subsequent flow of the broken ice around the floater. However, the hydrodynamic load due to the incoming level ice will also affect the response of the floater, which is usually not simulated. A recent study simulated the multibody hydrodynamics of level ice and floater Such multibody hydrodynamic analysis is computationally expensive, and complexity in the modelling is a hindrance to its implementation in the design phase. The present study, therefore, employs a conservative estimation to include the effect of wave load on the floater in addition to the ice load. Parametric studies are performed to estimate this effect by varying the incoming wave amplitude and wave period, ice sheet thickness, ice drift velocity, floater’s hull angle, mooring stiffness and the distance of large ice-sheet from the floater. Significant impacts of waves on the floater in terms of total force are observed which clearly reflects the importance of this study. The effect of mooring stiffness on total load is also investigated at the end of this study which can be considered as a foundation for further research on optimizing the mooring stiffness for such kind of arctic floater.
Riser Concept Selection for FPSO in Deepwater Norwegian Sea: A Case Study
Authors: Keprate Arvind , Ratnayake R. M. Chandima
Published: September 2018

Selecting a riser concept for FPSOs stationed in deep water has posed challenges, due to the high hydrostatic pressure and large vessel payload. One of the major factors governing the riser concept selection for deepwater FPSOs is the geographical location and weather conditions prevalent in the region. For example, the free hanging flexible riser has been mostly used in the moderate environments of offshore Brazil, while concepts like the SCR and Hybrid Riser Tower (HRT) are dominant in the calm weather conditions of the West of Africa (WoA). Selecting a riser concept for an FPSO stationed in harsh weather conditions like those of the Northern Norwegian Sea is a daunting task. This is due to the large vessel offsets and dynamics, which are directly transferred along the riser’s length to its base, thereby causing considerable fatigue damage to the riser. The main aim of this paper is to recommend a suitable riser concept, which may be hooked to an internal turret moored FPSO stationed in water of 1500m depth and in the harsh environmental conditions of the Northern Norwegian Sea. The recommendations are based on the literature review and the case study performed in the manuscript. On the basis of the literature review, a lazy wave configuration of flexible riser and Steel Lazy Wave Riser (SLWR) has been considered as a viable riser concept. Thereafter, a case study is performed to compare the two riser concepts, on the basis of vessel payload, fabrication cost and installation cost.
On the Possibility to Compute Slowly-Varying Drift in a CFD Solver
Authors: Monroy Charles , Housseine Charaf Ouled , Malenica Sime
Published: September 2018

Slowly-varying drift is a phenomenon very familiar to offshore industry, but usually not so much relevant or discussed in naval industry. The classical theoretical background consists in considering a bichromatic wave composed of two regular wave trains of pulsations ω1 and ω2 evolving in the same direction and without any forward speed. The force which varies at low frequency (ω2 – ω1) is known as the slowly-varying drift force and is important in case of moored vessels because it may excite them at their natural periods. The equivalent application in the naval industry is related to maneuvering and added resistance in waves. However, as already indicated, up to the authors’ knowledge, there has not been much work on these issues in the past.

State-of-the-art potential flow tools predict well this slowly-varying drift at zero forward speed. However, with an additional forward speed or a strong current, traditional linear potential codes are outside the scope of their underlying hypothesis and cannot predict accurately the low frequency force. With the constant rise of CPU power and accuracy of CFD solvers, this problem may now be addressed in CFD. The results of foamStar, in-house OpenFOAM solver, will be shown with and without additional forward speed.
Numerical and Experimental Studies on Ship Motions Induced by Passing Ship
Authors: Pedro Francisco G. , Santos João A. , Pinheiro Liliana V. , Fortes Conceição J. , Hinostroza Miguel
Published: September 2018

To investigate the ability of numerical models to simulate the behavior of moored ships subjected by ship-wake waves, use is made of scale model tests where a ship model sails with constant speed along a straight path at a constant distance from an otherwise motionless ship.

The tests were carried out at one of the wave tanks of the Portuguese Civil Engineering Laboratory (LNEC). The moving ship is a self-propelled scale model of the “Aurora” chemical ship whereas the otherwise motionless ship is a scale model of the “Esso Osaka” tanker. The free-surface elevation was measured with a set of resistive wave gauges and ADVs. The tanker’s movements, induced by the wake waves, were measured along the six degrees of freedom with a gyroscope deployed inside the ship.

The numerical model WAMIT provides, in the frequency domain, the quantities required to estimate the hydrodynamic forces associated to the interaction of a free-floating ship with waves. The BAS model uses those hydrodynamic forces to study in the time domain the ship interaction with any sea-waves acting on it. Wind and current actions can also be accounted for.

The results of these numerical models are compared to the measurements made in the several repeats of one of those scale-model tests, in terms of the response amplitude to several wave components. These comparisons enabled the evaluation and validation of the numerical models parameters’ calibration process.
Fully Coupled Time Domain Simulation Model Used for Planning and Offshore Decision Support During Riser Replacement Operations
Authors: Chrolenko Michael , Gundersen Gerhard , Eikanger Tom Eirik , Tveraaen Boje
Published: September 2018

This paper presents a dynamic analysis model where installation vessel in coupled with the riser system using the SIMA software. The model is used to assess risk and weather limitations for riser replacements performed with SIMOPRO (Simultaneous Marine Operation and Production). The SIMA model has been used in several complex riser replacement operations in the North Sea during 2017, and proven to be a vital support tool for decision making offshore. The analysis supported critical operational decisions that resulted in reduced weather downtime and enabled the marine operations to be completed in a safe and efficient manner, while the platforms were kept in production. In the planning phase the analysis model was used to test specific DP settings to minimize vessel footprint, optimize procedure steps and provide accurate limits to an Activity Specific Operating Guideline (ASOG). The model was further used to verify vessel and riser response subjected to various “emergency situations”, such as wire break and partial or full vessel black-out. The results were used to establish detailed contingency procedures. During the offshore operations, analyses were performed at regular intervals at the vessel with measured and forecasted weather data, to monitor vessel response and predict vessel drift-off trajectories in case of a vessel black-out scenario. The information provided by the DP recorder was fed back into the fully coupled analysis model where the Kongsberg Maritime DP settings were updated to reflect actual vessel system behaviour. The analysis model also provided vessel drift-off predictions in good agreement with real drift-off test results. With the optimized fully coupled analysis model it was then possible to perform simulations of the planned installation steps based on forecasted weather data.
Coupled Dynamics Modelling of a Floating Wind Farm With Shared Mooring Lines
Authors: Hall Matthew , Connolly Patrick
Published: September 2018

This work presents a coupling of numerical models to allow simulation of a farm of floating wind turbines in which some mooring lines are shared between platforms. This shared mooring approach has potential to reduce mooring costs for floating offshore wind farms, but introduces additional complexity in system behaviour and design considerations for which new simulation capabilities are needed. Multiple instances of the FAST floating wind turbine simulator are coupled modularly to the MoorDyn mooring system simulator to achieve a coupled simulation of a full shared-mooring floating wind farm. The model is demonstrated on a square-shaped four-turbine shared mooring farm configuration in the presence of irregular waves and turbulent winds. Results show reasonable behaviour of the platform motions, with surge displacements under wind and wave loading that reflect the complex restoring properties of the shared mooring arrangement. Varying phase relationships in the platforms’ motions arising from their spatial offsets in the sea state show that the shared mooring lines will see different excitation at either end. Fluctuations in the mooring line tensions bear out this fact, and also show the importance of line dynamics in these shared mooring arrangements. In particular, the shared mooring lines show a greater tendency for resonance due to the absence of seabed contact.
Performance Characteristics of Vertical-Axis Off-Shore Savonius Wind and Savonius Hydrokinetic Turbines
Authors: Talukdar Parag K. , Kulkarni Vinayak , Saha Ujjwal K.
Published: September 2018

The rise in energy demand, climate change and depletion of fossil fuel, encourages the researchers to find a solution to the scarcity of clean energy. Therefore, the extraction of energy from renewable energy sources has become a topic of interest in the past few decades across the globe. Thus, harvesting the offshore wind and hydro energy and converting it to electrical power using various electromechanical devices has been a challenge. In this context, the vertical-axis Savonius wind and Savonius hydrokinetic turbines appear to be promising concept for energy conversion because of their good self-starting capability and simplicity in design. The present study attempts to characterize the performances of a Savonius wind turbine (SWT) and a Savonius hydrokinetic turbine (SHT) under identical input flow conditions. In order to characterize their performances, the SWT is tested in a low-speed wind tunnel with closed test section whereas the SHT is tested in an open channel flume. In each case, the torque and power coefficients are estimated at different mechanical loading conditions. It is observed that the SWT and SHT demonstrate peak power coefficients of 0.25 and 0.28 respectively for the same input power. However, the SWT is found to operate over a slightly wider range of tip-speed ratios than the SHT before the onset of stall. Finally, the computational study using ANSYS 14.5 has been carried out to evaluate the flow physics of the turbine at various azimuthal positions.