bluuebunny/crossref_metadata_2025 huggingface dataset:
Assessment of LNG Pump Tower Loads
Authors: Thome Michael , Neugebauer Jens , el Moctar Ould
Published: November 2019

The assessment of design loads acting on Liquefied Natural Gas (LNG) pump tower are widely based on Morison equation. However, the Morison equation lacks consideration of transverse flow, impact loads and the interaction between fluid and structure. Studies dealing with a direct simulation of LNG pump tower loads by means of Computational Fluid Dynamics (CFD), which can cover the aforementioned effects, are currently not available.

A comparative numerical study on LNG pump tower loads is presented in this paper focusing on the following two questions: Are impact loads relevant for the structural design of LNG pump towers? In which way does the fluid-structure interaction influence the loads?

Numerical simulations of the multiphase problem were conducted using field methods. Firstly, Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations, extended by the Volume of Fluid (VoF) approach were used to simulate the flow inside a three-dimensional LNG tank in model scale without tower structure. The results were used to validate the numerical model against model tests. Motion periods and amplitudes were systematically varied. Velocities and accelerations along the positions of the main structural members of the pump tower were extracted and used as input data for load approximations with the Morison equation.

Morison equation, URANS and Delayed Detached Eddy Simulation (DDES) computed tower loads were compared. Time histories as well as statistically processed data were used. Global loads acting on the full (with tower structure) and simplified structure (no tower structure, but using Morison equation) are in the same order of magnitude. However, their time evolution is different, especially at peaks, which is considered significant for the structural design.
Thermal and Mechanical Coupled Analysis of Marine Composite Cryogenic Pipeline
Authors: Hu Haitao , Yan Jun , Zhou Baoshun , Yang Zhixun , Yang Liang , Fan Jiakun
Published: November 2019

Marine composite cryogenic pipeline is one of the key equipment for offshore gas explorations, which is mainly used in the transmission of liquefied natural gas. Due to the harsh marine environment and extreme temperature of transmission medium, the marine composite cryogenic pipeline needs to bear both the tensile and bending loads caused by marine environments and the ultra-low temperature load caused by transmission medium. Due to the extremely low temperature of liquefied natural gas, about −163 °C, the structure and the composed material of cryogenic pipelines will be faced greatly challenges. Previous studies have considered mechanical properties or temperature loading separately. In this research, the structural performance of the marine composite cryogenic pipeline under the combined action of mechanical loads and thermo-load is studied with numerical methods. The framework of the coupled mechanical and thermo-analysis for the structure of composite cryogenic pipeline is established. The numerical results show that the temperature distribution has great impacts on the structural responses of the cryogenic pipeline. The coupled mechanical and thermo analysis of the cryogenic pipeline is proved to be necessary. The established method and framework provide a reference for the engineering design and application of the marine composite cryogenic pipeline.
Numerical Simulation of Trim Optimization on Resistance Performance Based on CFD Method
Authors: Duan Wenyang , Zhang Hongsen , Huang Limin , Liu Jianyu , Shao Wenbo , Cao Guanzhou , Shi Zhang
Published: November 2019

In response to the gradually stringent carbon emission requirements of the International Maritime Organization (IMO), the energy-saving methods of the shipping industry have received increasing attention. Today how to reduce fuel consumptions so as to lower carbon emissions to improve the economic and environmental benefits of ships has become a hot topic. As one of the most easily implemented energy-saving methods, trim optimization has caught more and more researchers’ eyes.

In this paper, a commercial CFD software STAR-CCM+ was adopted to analyze the influence of trim on the resistance performance of VLCC ship mainly with fixed model method under various typical conditions of the design draft and the ballast draft respectively. The grid convergence was studied at the design draft and the typical numerical simulations were verified by the experimental results before carrying out various numerical simulations of trim optimization. Seven different kinds of trim conditions, which correspond to the changing process of the full scale ship from trimming by stern 4m to bow 4m, were simulated with 3 different speeds of design draft and ballast draft. The changes of total resistance, frictional resistance and residual resistance were analyzed to explore the effect of trims on the ship’s resistance. The variation of ship’s wetted surface area and waterplane area under different trim angles were studied. It was found that under the condition of low Froude number, both the simulation of free trim and sink method and the fixed model method can achieve good accuracy with the method of fixed model reducing the simulation time obviously. Both conditions of the design draft and ballast draft had a certain reduction effect of total resistance for trimming by bow properly, of which the change of frictional resistance is dominant in the decrease of total resistance at design draft while the change of residual resistance is the main cause at ballast draft. The optimum trims were found and the optimal total resistance reduction effects were evaluated. The optimal total resistance reduction effect increased with speed whether at the design or the ballast draft and the reduction effects were more obvious at ballast draft. Meanwhile, it was found that the changes of wetted surface area and the waterplane area with different trims were close to the variation tendency of the frictional resistance.
Study of the Influence of Controlled Axial Oscillations of pVARD on Generating Downhole Dynamic WOB and Improving Coring and Drilling Performance in Shale
Authors: Abugharara Abdelsalam N. , Molgaard John , Hurich Charles A. , Butt Stephen D.
Published: November 2019

This work concentrates on the investigation of enhancing drilling performance through increasing drilling rate of penetration (ROP) by using a passive vibration assisted rotary drilling (pVARD) tool. It also involves analysis of how ROP was significantly increased when drilling using pVARD compared to drilling using conventional system “rigid” using coring and drilling in shale rocks. The apparatus used was a fully instrument laboratory scale rig and the bits were dual-cutter polycrystalline diamond compact (PDC) bit for drilling and diamond impregnated coring bit for coring. The flow rate was constant of (7 litter / min) using clean water at atmospheric pressure. In addition, for accuracy data recording, a data acquisition system (DAQ-Sys) using a LabVIEW software was utilized to record data at 1000HZ sampling rate. The output drilling parameters involved in the analysis included operational rpm, torque (TRQ), and ROP. All the output-drilling parameters were analyzed with relation to downhole dynamic weight on bit (DDWOB). The result of this work explained how pVARD can increase the DDWOB and improve ROP. The result also demonstrated generating a balanced and concentric increase in DDWOB and minimizing the wide-range fluctuation of DDWOB generated in rigid drilling, particularly at high DDWOB.
A Field Study on the Marine Environmental Impact of the Drilling Fluid’s Discharge
Authors: Jiang Meirong , He Xiaohan
Published: November 2019

In view of the inadequate research for the far-field effect of the drilling fluid’s discharge, a field study has been carried out to investigate the discharge impacts of a water-based fluid on the marine environment. According to an offshore oilfield exploitation project in Bohai Sea, the waste drilling fluid is discharged from pipes pointed vertically downward into the ocean. A relative large tracking range at distances up to 2,000 meters from the discharge point is determined in the light of the results from the previous study and the environment impact assessment report. The concentration of the suspended solids in different time, distances and depths are tracked and monitored by the field measurement. The suspended solids concentration and their distribution characteristics are analyzed from the different stations during the discharge and recovery phase and the contrast stations. From this field monitoring of the drilling fluid’s discharge, the average concentrations for the surface, middle and bottom layers are evenly distributed along the water depth. The maximum concentration of suspended solids monitored in the discharge and recovery period are smaller than that in the contrast station. Meanwhile, the average monitoring concentrations of suspended solids in the surface, middle and bottom layers during the discharge and recovery period are also all lower than the corresponding ones from the contrast station. Within the range of this monitoring, the discharged drilling fluid has been rapidly diluted and spread, and there is no phenomenon for the suspended solids concentration in excess of the primary standard. Therefore the monitoring results in the discharge and recovery period can be attributed to the natural fluctuation of the background value. In another word, the influence range of the drilling fluid’s discharge is no more than 200 meters under the current condition. This study can provide some practical reference for the environmental evaluation of the drilling fluid’s discharge in the offshore petroleum engineering.
Experimental and Numerical Study of Horizontal Wave Impact Loads for a Semi-Submersible Drilling Unit
Authors: Kim Joo-Sung , Yoo Seon Oh , Kim Hyun Joe , Lee Jong Hun , Han So Lyoung , Lee Dong Yeon
Published: November 2019

A semi-submersible drilling unit model was tested to estimate horizontal wave impact loads on vertical side of deckbox following the procedure recommended by DNVGL OTG-14. The present model test data show that there is clear difference in the relationships between upwell and horizontal wave impact pressure between near column/pontoon and around centerline. Near column and pontoon, not only is the maximum pressure much lower but the pressure increases more smoothly to its maximum value, compared to those of centerline.

CFD simulations with focusing breaking waves have been made to examine the effect of wave-body interaction on horizontal wave impact on deck-box. The present CFD simulation results clearly show that the flows in front of column are strongly accelerated in vertical direction by blocking effect of column and pontoon, eventually producing strong run-up jets. The run-up jets in the present study are so strong that the direct impact of the incoming breaker on the wall does not occur, which leads to much smaller peak pressures, compared to those of centerline.
Effects of Platform Mounting Orientations on the Long-Term Performance of a Semisubmersible Wind Turbine
Authors: Zhou Shengtao , Li Chao , Xiao Yiqing , Lemmer Frank , Yu Wei , Cheng Po Wen
Published: November 2019

Due to the non-fully-symmetrical configuration, the platform laying angle of semi-submersible floating offshore wind turbines relative to wind/wave load directions has a noticeable influence on the dynamics characteristics of the whole structure, which indicates that the platform mounting orientation should be carefully considered before installation at sea. The directionality effects of short-term wind/wave loads had been discussed in previous studies, which are, however, insufficient to make a full understanding of the directionality impacts. In our study, based on a 25-year met-ocean database, long-term analysis is carried out by means of an efficient frequency-domain model with eight degrees of freedom. The nonlinear quantities such as aerodynamic loads, aerodynamic damping and mooring stiffness are derived from the time-domain simulation tool FAST, serving as a preprocessing database for the frequency-domain model. A case study is carried out by comparing the long-term responses of a Y-shape semi-submersible floating wind turbine in four mounting orientations. Significant differences can be seen. The platform mounted in the most unfavorable orientation tends to suffer from larger peak nacelle acceleration, which would increase the loads and cause higher tower base fatigue damage. These findings highlight the importance of platform mounting orientations and can serve as a basis for the installation of semi-submersible floating wind turbines.
The Influence of Non-Prescriptive Legislation in the Evolution of Offshore Well Integrity Practices: An Exploratory Review
Authors: Morais Carlos H. B. , Abreu Danilo T. M. P. , Santos Joaquim , Maturana Marcos C. , Colombo Danilo , Martins Marcelo R.
Published: November 2019

Among the stochastic tools and risk analysis techniques, ALARP (As Low As Reasonably Practicable) concept has proved to be the most influential guidance regarding the development of regulations and standards of the offshore industry in terms of risk assessment and consequently of equipment integrity. The reasons for that can be traced back to early seventies, when the British Health and Safety Executive (HSE) released its seminal document “The Health and Safety at Work etc. Act 1974”. The 1974 Act was the first regulation to adopt a non-prescriptive approach as a basis to configure the ruling legislation of industrial activities. Since then, risk analysis methods have encountered a vast field of opportunities in the wide range of options proportionated by such framework. In this sense, the Safety Case and the NORSOK standards play a significant role in the non-prescriptive approach application in the offshore industry. The present work discusses the influence of these two frameworks in the definition of the current Brazilian offshore legislation, especially in terms of the design, tests, and monitoring of the so called Solidary Well Barriers throughout the well life cycle. The United States legislation, largely reviewed after the Macondo accident, will be used to counterpoint the prescriptive and non-prescriptive approaches.
Numerical Study on the Temporal Discretization Schemes in Two-Phase Wave Simulation
Authors: Kim Young Jun , Bouscasse Benjamin , Seng Sopheak , Le Touze David
Published: November 2019

The generation and propagation of waves in a viscous flow solver are indispensable part of naval computational fluid dynamic (CFD) applications. This paper presents numerical simulations of two-dimensional wave propagation in the framework of two-phase finite volume method (FVM) with different temporal discretization schemes. Implicit Euler, Crank-Nicolson (CN) and second-order backward temporal discretization schemes are compared by using viscous flow solver based on the open source library OpenFOAM. The combinations of each temporal discretization scheme and explicit limiter are used for the formulation of the Volume Of Fluid (VOF) field convection equation. A new formulation using the second-order backward temporal discretization scheme with explicit limiter are investigated. Two-dimensional periodic domains are considered to compare different time-stepping methods. Also, five different refinement levels of meshes are used to study the convergence properties of each method. The non-linear wave is generated with stream function wave theory using ‘foamStar’, which is a specialized OpenFOAM library package developed by Bureau Veritas in collaboration with École Centrale de Nantes.
Development of a Panel Cutting Method Coupled With an Unsteady Potential Flow Model Based on the Weak-Scatterer Approximation
Authors: Wuillaume Pierre-Yves , Ferrant Pierre , Babarit Aurélien , Lynch Mattias
Published: November 2019

This paper presents a new mesh strategy for unsteady potential flow based solvers. It is based on the coupling between a panel cutting method used for the body mesh and an advance front method to generate the free surface mesh. The goal is to deal with complex geometries for time-domain simulations for marine operations. Firstly, the new mesh generation process is presented in details. Then, two validation tests are presented, using an academic geometry (vertical surface-piercing cylinder) and a complex geometry (FPSO).
A Fracture Mechanics-Based Feasibility Study of Damped Steel Catenary Risers for Pre-Salt Field Developments
Authors: Garmbis Alexandre G. , Zumpano Petrônio , Aguiar Ludimar L. , Brito Raphael M. , Rade Domingos A.
Published: November 2019

In order to enhance competitiveness of rigid risers for the Brazilian pre-salt, great effort has been devoted to study the feasibility of Steel Catenary Risers (SCR) directly connected to Floating Production Storage and Offloading (FPSO) units, where cost savings are expected from the reduction of pipe buoyance modules and overall piping length. A recent paper presented the technical feasibility of Damped SCR, which is a new SCR concept. In that study, some non-field-proven fatigue performance improvements were required, such as girth welds for mechanically lined pipe (MLP) with increased fatigue strength and/or upset end pipes. During the development of this technology, a fracture mechanics approach became essential for the assessment of fatigue and fracture limit state in order to guarantee that the risks associated with fabrication and inspection are within acceptable safety levels. This paper presents the main issues related to fabrication and inspection activities with a particular focus on the smallest critical flaw size. A semi-deterministic Engineering Critical Assessment (ECA) was performed as part of the conceptual design. The uncertainties about input data are discussed and a simplified procedure is proposed. Results are compared with relevant non-destructive testing reliability statistics. This study indicates that the benefits obtained from the use of materials with superior fatigue resistance are limited to the non-destructive testing reliability at some degree. As the proposed methodology deals with uncertainty in input data, a roadmap for the development of a full probabilistic risk assessment of fabrication and inspection feasibility at early design stages is devised.
Controlling Factors of Carcass Fatigue in Unbonded Flexible Pipes
Authors: Fernando Upul S. , Roberts Andrew P. , Davidson Michelle
Published: November 2019

Carcass, the innermost layer of a flexible pipe structure is designed to prevent the collapse of the pressure sheath due to external pressure. Weakness, damage or failure of the carcass layer can result in collapse with associated loss of production and potentially serious risk to pipe integrity and hydrocarbon leakage to the environment. Avoiding carcass failure in service is therefore an essential consideration during the design of unbonded flexible pipes.

Carcass failure is rare in service. This paper highlights the three possible failure modes and presents further analysis on the fatigue failure mode, relevant to dynamic service. Two key features of carcass manufacture are identified as causes for dynamic stress; locking of the carcass profile due to extended pitch and polymer ingress within the carcass cavity.

Guidelines for the design of carcass profiles, setting safe pitch limits and appropriate barrier profile controls to mitigate carcass fatigue failure in dynamic service are presented.
Computational Methods for Moving and Deforming Objects in Extreme Waves
Authors: Veldman Arthur E. P. , Seubers Henk , Hosseini Matin , Chang Xing , Wellens Peter R. , van der Plas Peter , Helder Joop
Published: November 2019

Wave forces can form a serious threat to offshore platforms and ships. The damage produced by these forces of nature jeopardizes their operability as well as the well-being of their crews. Similar remarks apply to coastal defense systems. To develop the knowledge needed to safely design these constructions, in close cooperation with MARIN and the offshore industry the numerical simulation method ComFLOW is being developed. So far, its development was focussed on predicting wave loads (green water, slamming) on fixed structures, and for those applications the method is already being used successfully by the offshore industry. Often, the investigated object (ship, floating platform) is dynamically moving under the influence of these wave forces, and its hydrodynamic loading depends upon the position of the object with respect to the oncoming waves. Predicting the position (and deformation) of the body is an integral part of the (scientific and engineering) problem. The paper will give an overview of the algorithmic developments necessary to describe the above-mentioned physical phenomena. In particular attention will be paid to fluid-solid body and fluid-structure interaction and non-reflecting outflow boundary conditions. Several illustrations including validation, will demonstrate the prediction capabilities of the simulation method.
Fatigue Performance and Crack Growth Assessments of Riser Welds in Mild Sour Environment
Authors: Ghosh Rupak , Aune Robert P. , Popelar Carl F.
Published: November 2019

Fatigue design of deepwater riser system in a sour environment is a challenging task in a project cycle. More often, the challenge is in identifying an appropriate project specific fatigue curve using accurate environmental representation, and establishing a crack growth curve to confirm the acceptance criteria of the welds. Conventional practice in industry is to use a knock down factor (KDF) to capture the effect of corrosion fatigue, rather than taking an effort in executing detailed test/qualification program. A KDF approach can turn out to be very unreliable, specifically, for mild sour environment where significant test data are not available. As a result, there can be several impacts, including delivery of an under-designed system with potential operational risks.

This paper presents comprehensive findings from a sour service qualification program executed in a project cycle. The sour environment is mild, and is slightly above NACE limit (0.1psi ppH2S, pH ∼ 6). The program included a detailed scope of work consisting of in-air and in-environment fatigue test as well as limited scope in understanding fatigue crack growth rate in the same environment. The material used is API 5L X65 seamless pipe with mechanized GMAW girth weld. The results show the unpredictable side of corrosion fatigue, especially in this kind of mild sour environment, which is not well understood.
Wave Effects on the Turning Ability of an Ultra Large Container Ship in Shallow Water
Authors: Tello Ruiz Manases , Mansuy Marc , Donatini Luca , Villagomez Jose , Delefortrie Guillaume , Lataire Evert , Vantorre Marc
Published: November 2019

The influence of waves on ship behaviour can lead to hazardous scenarios which put at risk the ship, the crew and the surroundings. For this reason, investigating the effect of waves on manoeuvring is of relevant interest. Waves may impair the overall manoeuvring performance of ships hence increasing risks such as collisions, which are of critical importance when considering dense traffic around harbour entrances and in unsheltered access channels. These are conditions met by Ultra Large Container Ships (ULCS) when approaching a port, e.g. in the North Sea access channels to the main sea ports of Belgium. Note that due to the large draft of ULCS and the limited water depth, shallow water effects will also influenced the ship. Thus, in such scenarios the combined effects of shallow water and waves on the ship’s manoeuvring need to be studied.

The present work investigates the effect of waves on the turning ability of an ULCS in shallow water. Simulations are carried out using the two time scale approach. The restricted water depth corresponds to 50% Under Keel Clearance (UKC). To gain a better insight on the forces acting on the ship, the propulsion, and the rudder behaviour in waves experimental studies were conducted. These tests were carried out in the Towing Tank for Manoeuvres in Confined Water at Flanders Hydraulics Research (in co-operation with Ghent University) with a scale model of an ULCS. Different wave lengths, wave amplitudes, ships speeds, propeller rates, and rudder angles were tested. The turning ability characteristics obtained from simulations in waves and calm water are presented, and discussed.
Metocean Criteria for the Fatigue Analysis of Subsea Pipelines
Authors: Gibson Richard , Christou Marios
Published: November 2019

This paper is concerned with a methodology for defining metocean criteria for the analysis of subsea pipelines. The approach that has been developed incorporates the statistical dependence between wave and current loading. The method achieves this through a combination of the application of the conditional extreme value model of Heffernan and Tawn (2004) and clustering algorithms. This is particularly important in regions where the currents are largely wind driven as there can be a strong correlation between the two. The results can be used to assess fatigue damage from vortex-induced-vibrations and wave loading. The same model can be used to derive deterministic design events. The method is applied to a pipeline in the Caspian Sea. The results are compared to models that assume either independence or a perfect correlation between waves and currents. It is shown that simpler models that do not accurately model the dependence between the waves and the currents can provide estimates of fatigue damage that are an order of magnitude too high or too low.
Computational Simulation of the Drilling Vessel Motion and its Effects on the Riser/BOP Connection
Authors: Castello Xavier , Párraga Quispe José Luis , Estefen Segen F. , de Souza Marcelo Igor Lourenço , de Moura Jorge Nilo
Published: November 2019

During subsea offshore drilling operations, the floating vessel is connected to the wellhead through a series of equipment assemblies. The riser is exposed to dynamic loads from currents, waves, and drilling platform motions. Therefore, a dynamic analysis of the riser system is required to obtain forces and moments in the wellhead. It is even more important in dynamic positioning (DP) operations, where the knowledge of boundary conditions for a safe emergency disconnection is highly relevant. The objective of this paper is to calculate the effects of changing the light and older BOP (typically with 4 rams) for newer and heavier BOPs (after Macondo accident, with 6 rams) on the Emergency Disconnect Sequence (EDS) time and on wellhead equipment strength. A typical scenario of drilling is proposed, in which the marine riser system considers the drilling string, the lower flex-joint, the marine riser, the kill and choke lines and the tensioners. Tensioners are used to top tension the marine riser and to compensate relative heave motion between the riser and the floating vessel. Riser systems were designed using the API RP 16Q and simulated using Orcaflex software. Vessel dynamic motions were calculated according to the response amplitude operator (RAO) data from a typical offshore drilling semi-submersible. The vessel motion is superimposed by a drift-off motion, which consists of a horizontal displacement along time in the direction of the propagating waves. It is employed to simulate the condition of vessel position loss due to thruster and or control system failure. Results indicate that the use of heavier BOPs reduces significantly the available time for initiating the EDS. Results are worse if older generation of wellhead equipment is used, where a smaller drift-off is necessary to safely disconnect the riser before potential equipment and environmental damage occurs.
The State-of-the-Art in Structural Integrity Management: A Review and Proposed Data-Driven Approach
Authors: Heo YeongAe
Published: November 2019

Probabilistic risk-based approaches have been used for cost-effective structural design and maintenance guidelines. The effectiveness of these provisions, however, has yet to be adequately validated. Also, current risk management approaches are hardly adaptable to changes in operational and environmental conditions as well as structural properties over the service life of structures. As the need and demand of real-time monitoring systems have increased dramatically for high-value and high-risk facilities such as offshore structures particularly, it is important to discuss directions for future research to advance the risk-based management approaches by utilizing the invaluable “big-scale” field data obtained from sensor network systems. Therefore, knowledge gaps in the current state-of-the-art structural risk management approaches are discussed in this paper. Subsequently, a novel risk management framework is presented in this paper integrating physics-based data into a data-driven decision model. The proposed decision framework will improve system adaptability to future performance requirements due to changing operational and environmental conditions and will be applicable to any structural systems instrumented by sophisticated SHM systems such as complex naval and marine systems.
Additives to Enhance Cement Sheath Durability
Authors: Tabatabaei Maryam , Dahi Taleghani Arash , Alem Nasim
Published: November 2019

The primary goal of the oil and gas well cementing is zonal isolation. During the production life of a well, the cement experiences various severe conditions affecting its permeability. These conditions include cracking, debonding, and shear failure which can be worsened by pressure fluctuations during hydraulic fracturing operations. Any of these conditions by forming micro-cracks within the cement or micro-annuli at the casing/cement or cement/rock interfaces create cement permeabilities far beyond the intrinsic permeability of the intact cement sheath. Recently, some studies have been devoted to improving the overall mechanical behavior of the cement by adding carbon nanotubes and carbon nano-fibers. Although these nano-additives offer considerably high strength and modulus, the high costs of these materials persuade us to find alternatives at relatively low costs, such as, graphite nanoplatelets (GNPs). Our preliminary laboratory studies show the effectiveness of GNPs in the enhancement of durability characteristics of the prepared nanocomposite cement paste by improving its compressive strength, ductility and toughness resistance. Considering the importance of dispersion of nanoadditives within the cementitious matrix, we physically or chemically manipulate the surface properties of GNPs to prevent the agglomeration of nanoparticles.
Trend of Utilization of Ocean Space According to Structural Form of Oceanic Architectures
Authors: Sugahara Ryo , Kuroyanagi Akio
Published: November 2019

The aims of this research are to understand the construction history, subsequent refurbishment, and use of existing oceanic architectures and to clarify the establishment cause, location, and facility use of oceanic architectures, from which the current state of the oceanic buildings and propose new ways of using maritime areas in the future may be recognized.

First, a wide variety of facilities of oceanic architectures have been built all over Japan in line with economic growth since 1960. However, in the 2000s as public interest in oceanic architectures become sluggish, many facilities have been forced to close. After these circumstances, the use of marine areas has been recognized again in recent years, and the interest in oceanic architectures has been reintroduced.

For the survey method, existing examples using aerial photographs are confirmed and the operation status of the facilities are clarified. Based on this, we selected ten study subjects. We carried out on-site survey at the target facilities and conducted interview survey to local governments, facility owners, and other concerned parties. In addition, relevant design books and materials are collected, and facility outline, construction history, usage trends, and the surrounding locations are studied.

As a result, it was confirmed that oceanic architectures are closely related to the surrounding seas. In addition, it was confirmed that oceanic architectures have a certain base as regional entities, and increasing the usefulness of facilities can be achieved by acquiring new added values through continuous use of the maritime area.
Effect of Non-Gaussian Distribution of Fully-Nonlinear Waves on Offshore Platform Motion Responses
Authors: Baquet Aldric , Lim Ho-Joon , Kim Jang Whan
Published: November 2019

In this paper, we focus on the effect of the non-Gaussian distribution in the fully-nonlinear wave on offshore platform response. The motion responses of two kinds of floating platforms are investigated numerically using a conventional time domain program. The input wave is generated using two methods. In the first method, linear wave components with randomly distributed wave phases are used as input in the time domain software as it is usually done in the global performance analysis during offshore projects. In the second method, the wave components come from a nonlinear irregular wave simulation using a potential numerical wave tank (PNWT). For both cases, twenty realizations of 3-hour duration are performed and the ocean wave is described by a JONSWAP spectrum. Then the response spectra, the probability distributions and the extreme responses of the platform motions and air gaps are compared.
Predictions of Tensile Strain Capacity for Strain-Based Pipelines With a Circumferential and Internal Surface Flaw
Authors: Jang Youn-Young , Kang Ju-Yeon , Huh Nam-Su , Kim Ik-Joong , Kim Cheol-Man , Kim Young-Pyo
Published: November 2019

Strain-based design assessment (SBDA) has been known for suitable assessment concept for pipelines subjected to displacement-controlled load and high plastic deformation rather than conventional stress-based design assessment. Tensile strain capacity (TSC) has been used for one of important factors to indicate limit state in strain-based design, so that it is main concern to predict accurate TSC to ensure the structural safety and integrity of pipelines. For the pipeline containing a flaw, especially a girth weld flaw, TSC based on fracture mechanics can be determined. Crack-tip opening displacement (CTOD) has been widely used for typical elastic-plastic fracture parameter, representing crack-driving force and crack-resistance curve, which are required to assess unstable crack propagation. The one of the main principles of crack assessment is that the definitions of crack-driving force and crack resistance curve should be coincident. However, there exist two kinds of the definitions of CTOD, which are based on 90° and original crack-tip concept, and these have been not unified in practical regions until now. Moreover, it is reported that the deviations of crack-resistance curve can occur in the same specimen and experiment, caused by the different definitions of CTOD. Therefore, CTOD solutions based on each of different definitions of CTOD should be highly required since inaccurate TSC would be assessed when using not the identical definition of that.

In the present study, CTOD solutions of pipelines with a circumferential and internal surface flaw are suggested by using two kinds of definitions of CTOD based on 90° and original crack-tip concept. For this purpose, FE analyses were systematically carried out considering various pipe geometries and material properties. And single-edge notched tension (SENT) specimen was used for representing resistance curve of API X70/X65 material. Moreover, the effect of the choice of each CTOD definitions on TSC was investigated through crack-driving force diagram (CDFD) assessment.
Effect of Coal Loading Conditions on Structural Characteristics of LFTS
Authors: Eto Hiroaki , Iizuka Koji , Nishigochi Ryo , Ikoma Tomoki , Aida Yasuhiro , Masuda Koichi
Published: November 2019

Indonesia is a main country supplying coal in the Asia-Pacific region, it is important to ensure a stable coal supply to Japan. Because the topography of the seabed near East Kalimantan Island, Indonesia’s main coal production area, is shallow, it is difficult for bulk carriers to reach the coast. Therefore, Large-Scale Floating Coal Transshipment Station (LFTS) was proposed, which will be used as a relay base between coal-barging barges from land and bulk carriers offshore. Installing an LFTS offshore from East Kalimantan is expected to improve coal transport productivity. LFTS can store coal equivalent to five times the capacity of one bulk carrier (total 500,000T), and can accommodate 2 bulk carriers at the same time during offloading. The scale of LFTS is 590m × 160m. The LFTS has a flat spread and the elastic behavior becomes the dominant Structure. The upper part of the LFTS is different rigidity partly because the partition wall to be loaded by dividing the coal into each quality is provided. Loaded coal not only changes the draft of the LFTS but also greatly deforms the LFTS and is expected to cause local stress concentration on the structural members. Therefore, this paper investigates wave response characteristics and stress characteristics with the coal loading of the LFTS, and then evaluation of structural strength by limit state design method.

In this study, linear potential theory and the finite element method (FEM) were used to analyze the static hydroelastic motion under various coal loading condition and wave response of LFTS. And, to grasp the local stress concentration occurring inside the LFTS by using the response results, a detailed model modeling a complicated internal structure was prepared. Zooming analysis which is a method of giving the deformation result by the whole model of LFTS as forced displacement to the local detailed model was carried out. As a result, depending on the coal loading condition and wave conditions, it became clear that LFTS will be in a tough situation.
Dynamic Positioning Observer Design Using Exogenous Kalman Filter
Authors: An Song , Chen Dengshuo , Bai Yong
Published: November 2019

Observer of a dynamic positioning (DP) system utilizes DP’s measurement data, to predict vessel’s velocities, positions, and unknown environmental forces on the vessel, as well as to handle model uncertainties and errors. Stability and optimality of a DP observer is important for overall DP performance. Nonlinear observer (NLO) designs usually take global asymptotic or exponential stability as the primary goal, and discard the noise. On the other hand, linearized Kalman filter (KF) algorithm, e.g. the extended Kalman filter (EKF), is optimal in minimizing the covariance of observer states by taking both measurement and process noise into account. The applied exogenous Kalman filter (XKF) algorithm in this paper, is a two-stage cascade of NLO and linearized KF, which uses the first-stage NLO estimated states as exogenous inputs for the second-stage linearized KF. XKF approach is proved to have both the stability property inherited from NLO and optimality from linearized KF. Stability and optimality of XKF based observer is studied through DP station-keeping numerical simulations.
Asset Integrity Control: Prioritization of Offshore Topside Flange Openings During Preventive Maintenance Shutdowns
Authors: Ratnayake R. M. Chandima
Published: November 2019

Top side flange inspection on offshore production and process facilities (P&PFs) has been a challenging task, due to complex geometries, produced crude oil and gas quality changes over the production well’s maturity, as well as the stringent regulatory requirements that need to be followed to assure the anticipated integrity of the operating assets. The complex geometries hinder the use of non-destructive testing (NDT) testing approaches and necessitate shutting down the system or subsystem in order to disassemble the flange to perform close visual inspection (CVI). Using risk-based asset integrity (AI) assessment and control (RBAIA&C) approaches, it is possible to classify the flanges into different classes, according to probability of failure (PoF). The PoF is estimated by considering the last inspection date, past inspection data, findings from similar locations/systems in the same offshore facility, etc. Together with consequence of potential failures (CoF), it is possible to estimate the risk of a potential failure due to the loss of integrity of a selected flange. Although several flanges are qualified to be disassembled, based on RBAIA&C activities, it is not possible to take all of them off during a certain preventive maintenance (PM) shutdown. Currently, ad hoc approaches have been used to further prioritize the flanges that have been recommended for inspection during a PM shutdown, based on RBAIA&C activities. The aforementioned jeopardizes the integrity of flanges and subsequently the overall system, possibly leading to catastrophic accidents. This manuscript demonstrates a methodology for the systematic further prioritization of flanges that need routine CVI. The flange inspection related system analytics have been incorporated with the analytic hierarchy process (AHP) to make logical further prioritization with sufficient transparency. The approach has been demonstrated with an illustrative case study that has been chosen from an offshore P&PF. A sensitivity analysis has also been performed and is presented to demonstrate how to carry out trade-off evaluations between different factors in the flange prioritization in a PM shutdown.
Analysis of Subsea Umbilical Mechanical Behavior Under Simultaneous Bending, Tension and Torsion
Authors: Saneian Mohsen , Gao Yifan , Bai Yong , Liu Ting
Published: November 2019

One of the major failure modes of an umbilical is found to occur under simultaneous bending, tension and torsion. Umbilical cables are compatible in bending but have a rigid response to tension and torsion, hence validation the axisymmetric performance of it, is a significant matter. This paper has applied theoretical models to analyze umbilical cables mechanical behavior under combined loading. Lanteigne (1985) theoretical model, which its feature is a large-diameter central pipe umbilical cross section with homogeneous materials that a number of wires helically wrapped around it, is developed in this article. The equilibrium equations are presented and showed the helical elements effects on bending, tension and torsion of the umbilical cable.
A Conjoint Analysis of the Stability and Time-Domain Analysis on Floating Platform During Mooring Line Breaking
Authors: Feng Jiaguo , Yu Yi , Qu Yan , Xie Wenhui , Wu Min , Zhao Jingrui
Published: November 2019

The stability of platform is important to ensure the platforms are safe, especially during the mooring line breaking process in typhoon condition. The paper presents a stability analysis method for floating platforms of the mooring line breaking process based on the time-domain analysis. The time-domain simulation during the mooring line breaking is provided. The time of the mooring line break, the max tilt angle of platform and the amended equivalent overturning moment are calculated for the stability analysis. The results show that the platform would have a serious tilt when the mooring line breaks, this increases the overturning moments and may cause the platform not meets the stability requirements during this process. It is necessary to pay attention to the stability problem during the mooring line breaking process in typhoon condition. And properly locating the down-flooding points is recommended to avoide the stability problem.
Multiobjective Reliability-Based Design of Ship Structures Subjected to Fatigue Damage and Compressive Collapse
Authors: Garbatov Yordan , Huang Ying Cai
Published: November 2019

This work deals with reliability-based design and optimization of ship structures subjected to stochastic loads and accounting for the local fatigue damage and ultimate global strength. The reliability multi-objective structural optimization is performed in minimizing the structural component net-section area, lateral deflection and fatigue damage. The probability of compressive collapse and fatigue damage of the ship hull is used to define the minimum risk of structural collapse and best design solution. The Pareto frontier solutions calculated by the Non-Dominated Sorting Genetic Algorithm (NSGA-II) is employed in defining the feasible solutions of the design variables. The first order reliability method is employed to estimate the beta reliability index based on the topology of the structural component as a part of the Pareto frontier solutions. Comparing with the original design solution, the optimized section area decreased by 9%.
Synergistic Flow Induced Oscillation of Multiple Cylinders in Harvesting Marine Hydrokinetic Energy
Authors: Hai Sun , Bernitsas Michael M. , Zhiyun Chen
Published: November 2019

Flow Induced Oscillations (FIO) of cylinders in tandem can be enhanced by proper spacing to increase hydrokinetic energy harnessing. In a farm of multiple cylinders in tandem, the issue of the effect of interference on harnessing efficiency arises. Over the course of three years of development in the Marine Renewable Laboratory of the University of Michigan, systematic experiments on an isolated cylinder, and two and three cylinders in tandem have revealed that synergistic FIO can actually enhance oscillations of cylinders in close proximity. Two cylinders in tandem can harness 2.5–13.5 times the hydrokinetic power of one isolated cylinder. Three cylinders in tandem can harness 3.4–26.4 times the hydrokinetic power of one isolated cylinder.
Quantification of the Effects of Filtercake on Wellbore Strengthening: Filtercake Rupture Resistance and Fracture Sealing Time
Authors: Yang Mingzheng , Chen Yuanhang , Growcock Frederick B.
Published: November 2019

Wellbore strengthening (WBS) has proven to be an effective method for expanding the pressure windows of drilling operations. Recent research on WBS disclosed the critical role of filtercake in sealing microfractures during the initial stages of fracture initiation and propagation. In this study, a new parameter — “filtercake rupture resistance” — is proposed to simplify the quantitation of the filtercake’s potential to withstand pressure over a small fracture. A modified permeability plugging apparatus (PPA) was used to experimentally simulate the processes of filtercake rupture over a fracture on the wellbore wall and fracture sealing. The effects of filtercake thickness (permeability), filtercake yield strength in shear, and concentration of bentonite and a fine fibrous LCM on filtercake rupture resistance were investigated, along with the effects of these parameters on the effectiveness of filtercake in reducing fracture sealing time. Pressure spikes and fluctuations were observed when applying differential pressure across the filtercakes after formation of the cake. Filtercake of lower permeability and higher shear yield strength produce greater filtercake rupture resistance and shorter fracture sealing time. These results can be used to guide drilling fluids design for improved control of fluid loss.