bluuebunny/crossref_metadata_2025 huggingface dataset:
Application of 7%Ni-TMCP Steel Plate to Large Scale LNG Storage Tank
Authors: Onishi Kazushi , Kawabata Tomoya , Kamo Takahiro , Tanino Yuichi , Yamashita Maki , Iida Atsushi , Kusagawa Masaki , Nishigami Hiroshi , Sakato Naokazu , Mitsumoto Masahiko , Hirai Syuichi , Hirose Hitoshi , Hagihara Yukito
Published: August 2013

Increase of natural gas demand has led the increase of constructions of Liquefied Natural Gas (LNG) storage tanks worldwide. The inner tank material for above ground LNG storage tanks has mostly been made of 9% nickel steel plate over the last 50 years as it has excellent mechanical properties under the cryogenic temperature of −160deg.C. During this period, the LNG storage tanks made of 9%Ni steel plate have safely been operated. Meanwhile, technologies of steel making, welding, design, construction and inspection of 9%Ni steel plate have been improved significantly and enable us to achieve enlarging volumetric capacity of the tank to 2–3 times.

It is known that nickel is an expensive and valuable rare metal and recent tendency of increase in nickel price has influenced the price of 9%Ni steel plate. In such a circumstance lowering the Ni content would save cost and this has led to an extensive research and development resulting in the 7%Ni-TMCP steel plate. This 7%Ni-TMCP steel plate developed is characterized by adjustment of chemical compositions and application of suitable Thermo-Mechanical Controlled Process (TMCP).

In order to evaluate fitness of the 7%Ni-TMCP steel plate and its weld for LNG storage tanks, a series of testing was conducted. Several different kinds of plate thicknesses from 6 to 50 mm were chosen to run large scale fracture toughness tests such as duplex ESSO tests, cruciform wide plate tests as well as small scale tests. As a result it was demonstrated that the 7%Ni-TMCP steel plate had a quite excellent resistance to brittle fracture of the inner tank steel and its welds exposed to the cryogenic temperature of LNG.

Furthermore, other various issues such as extent of applicable heat input, repair weld, difference of physical constants and so on were investigated and found acceptable.

In Japan Ministry of Economy, Trade and Industry (METI) approved to apply this steel to new LNG storage tanks of Osaka Gas. After that Osaka Gas decided to construct a new full containment LNG storage tank applying 7%Ni-TMCP steel in Senboku terminal 1. The capacity is 230,000m3, which is larger than present largest scale of 180,000m3 in Japan. The construction is planned to start in September 2012 and be completed by November 2015.
Nonlinear Dynamic Analysis of Jack-Up Platforms Exposed to Extreme Random Waves
Authors: Mirzadehniasar Jalal , Kimiaei Mehrdad , Cassidy Mark J.
Published: August 2013

Deterministic waves with uniquely specified parameters remains widely used in the analysis of offshore platforms, even though the random nature of the sea-state is one of the main uncertainties in loading. The response of dynamically sensitive and highly redundant structures is significantly changed when random wave loading is considered. Therefore, to more confidently simulate wave loads, all of the randomness of water surface should be taken into account.

Load history also plays an important role in the nonlinear dynamic response of structures. Accordingly, an appropriate way to consider these effects is dynamic analysis of offshore platforms using random time-domain generation of the sea surface over a long period of time. However, in general, this method is very complex and time consuming. Constrained NewWave theory is an alternative method that can effectively simulate many hours of random time domain simulation for wave loading but in a more computationally efficient manner. It takes a NewWave — a deterministic wave of predetermined height that accounts for the spectral composition of the sea — and constrains it within a random background.

In this paper, both the singular NewWave and multiple constrained NewWaves are employed to simulate random sea-states in order to investigate the nonlinear dynamic response and collapse mechanisms of a jack-up platform subjected to extreme waves. Different assumptions of the behavior of the jack-up spudcan-soil interaction are considered.
Post-Ultimate Strength Behavior of Very Large Floating Structure Subjected to Extreme Wave Loads
Authors: Iijima Kazuhiro , Fujikubo Masahiko
Published: August 2013

In this paper, post-ultimate strength behavior of VLFS to extreme wave-induced loads is investigated. A mathematical model to describe the post-ultimate strength behavior of VLFS is developed taking the hydroelasticity into account. The whole VLFS is modeled by two beams on an elastic foundation connected via a nonliner rotational spring assuming that VLFS collapses amidship under severe bending moment. The model is solved numerically by using FEM. It is shown that the extent of collapse of VLFS is smaller than that of ship structures for given amplitude of vertical bending moment on condition that the structures have the same cross section and the same moment-displacement relationship. A simple formula to represent the extent of collapse of VLFS is derived. Its efficacy is shown.
A Numerical Study of a Focused Wave Packet Near the Surf Zone
Authors: Pakozdi Csaba , Kendon Timothy E. , Stansberg Carl-Trygve
Published: August 2013

In this paper the numerical modeling of breaking waves propagating on a gently sloping bottom in shallow water is investigated. As more and more countries look to install offshore wind farms in their coastal waters, the breaking wave impact force on wind turbine foundations has been an area of increased research. For meaningful comparisons between measurement and simulation, the numerical reconstruction of the model test breaking wave event must be fairly exact. The combination of numerical reconstruction of model tests using computational fluid dynamics has proved a valuable tool to provide insight into the physics of the breaking wave phenomenon in deep water ([1]). To refine the technique of numerically reconstructing the breaking wave in shallow water, comparisons to a series of model tests with breaking wave events near the surf zone are made. The sloping bottom is modeled with a ramp with a gradient of 2.8 degrees in a wave tank. This paper describes the numerical reproduction of a focused wave packet, for studying its shoaling and breaking. The commercial CFD tool Star-CCM+ has been used to reproduce a measured focused wave packet train in a numerical wave tank. Its RANSE physical model with VOF technique is applied for this investigation. The numerical wave generation is based on the technique presented in [1], where the measured angle of the wave makers flap and the measured free surface elevation at the flap has been used to define a transient inlet condition for the simulation. In this paper, the numerically simulated wave elevation around the breaking point is compared with the measured time series. Promising results are obtained. The numerical model reproduces, at the same location and time, the breaking events as it was observed during the model test. One conclusion from this particular case is that the time step is critical; it should be very small during the breaking events which may result in a very long simulation time. Further work is suggested to meet this challenge, as well as for more refined studies to improve the complete numerical wave tank model.
An Investigation About the Trajectory Control During the Subsea Equipment Installation Using Cable
Authors: Fortaleza Eugenio , Albuquerque Daniel , Yamamoto Marcio
Published: August 2013

Nowadays, several seafloor equipments have been developed and deployed in order to enhance the production of petroleum and natural gas from reservoirs in deep and ultra-deep waters. Thus the installation and maintenance of such seafloor equipments shall be an issue.

The most important seafloor equipment during the production phase is the “Wet Christmas-Tree” (X-tree), which is a set of valves that controls the pressure at well bottom. This equipment is installed by a Mobile Offshore Drilling Unit (MODU) after the drilling and completion are finished. Recently, beside the X-mas, a variety of subsea pumps, usually called as Subsea Booster System, have been deployed in the development of new reservoirs in deep-water. At the beginning, such subsea pumps and even other seafloor equipments had been installed by a MODU. But the high-cost of the MODUs is one of the main concerns about the installation and maintenance of the subsea equipments. One alternative to reduce the installation cost is to use cable system installed on a service boat instead the completion riser of a MODU.

This paper presents an initial investigation for the installation of a seafloor equipment using cable. The dynamic model will be featured; the dynamic analysis will be carried out using an in house developed simulation program in time-domain. Discussion about the trajectory and control of the equipment to be installed is also included.
New Conceptual Style of Ultra Large Floating System
Authors: Liu Jianhui , Zhong Wenjun , Zeng Hengyi , Shen Keli
Published: August 2013

In the process of exploitation of oil and gas in deeper water and ultra deep water, the problem of how to guarantee the effective support for work boats is inevitable. This is especially vital for the oilfields in harsh environment several hundreds of nautical miles away from the terrestrial supply center. In order to solve logistic support problem, an ultra large floating system concept arising from the intermediate base was put forward with functions of material reserves, refuge harbor for work boats, and landing pad for helicopters. The ring ultra large floating system with outer diameter of 400 m comprises eight modules and each module has four columns with heavy draft. The wave chamber composed of horizontal perforated double-layer breakwaters is positioned close to the water plane to reduce the reflection and dynamic pressures on the vertical hull. The applicable water depth can exceed 2000 m. This paper describes a physical test for the purpose of evaluating the various functions of ULFS concept.
Wax Deposition in Laminar and Turbulent Flow in Pipelines
Authors: Veiga H. B. , Souza L. B. , Minchola L. R. , Palomino L. F. , Nieckele A. O. , Azevedo L. F. A.
Published: August 2013

Accurate prediction of wax deposition rates and deposited wax spatial distribution is invaluable information for the design of subsea lines. Unfortunately wax deposition mechanisms are still not fully understood. The present paper is part of an ongoing research program developed with the objective of identifying the relative importance of the different wax deposition mechanisms proposed in the literature. To this end, laboratory experiments conducted at controlled conditions were performed in a geometry formed by a rectangular channel having two glass walls and two heat exchanging walls. A laboratory solution of wax and solvent was pumped through the channel while the heat exchanging walls were cooled. The wax deposit formed was optically measured by a traversing microscope imaging the deposit through the glass walls. This setup allowed the determination of both, the temporal and spatial evolution of the wax deposit. Laminar and turbulent flow conditions were investigated. Numerical simulation of the equations governing conservation of mass, momentum, energy and concentration were solved for the channel configuration employing the known thermophysical properties of the solution used in the tests. A comparison of measured and predicted results yielded good agreement for the steady state distribution of the deposited wax for laminar flow conditions. The transient behavior of the deposit was, however, under predicted by the calculations. Turbulent flow predictions were obtained using Reynolds-averaged models. The simulations were able to predict the correct trends of thinner deposits when compared to laminar deposition.
Lateral Buckling Analysis and ECA for Pipeline With Complex Temperature Profile
Authors: Yang Zhengmao , Mageshwaran Yadhavaraj , Kittur Vijay , Lim Gerry , Chia Hong Kiat
Published: August 2013

Lateral buckling analysis of a 32 inch export pipeline operating under high temperature and high pressure in sour service environment was evaluated in this paper. In addition Engineering Critical Assessment (ECA) as per DNV-OS-F101 Appendix A was performed to derive flaw acceptance criteria for pipeline girth weld fabrication during installation.

Due to the sour operating environment, low fracture toughness and increased fatigue crack growth rate during operation is expected. Consequently stringent tolerable flaw sizes are obtained for the pipeline sections subject to large strain arising from lateral buckling. In order to improve the reliability of the design and constructability of the pipeline, sleepers will be used to introduce vertical imperfections and initiate buckles at selected locations. In undertaking this it can be illustrated that all the potential lateral buckles are predetermined and pipeline sections with large strains are identified. The stringent tolerable flaw criteria from ECA are applied only on the identified high strain sections.

In this paper the design of sleepers and the influence of these additional sleepers on the lateral buckling behavior are investigated.
Evaluation of Pipeline Impact Damage
Authors: Alsos Hagbart S. , Igland Ragnar T. , Søreide Tore H.
Published: August 2013

The safety of pipelines and subsea structures are key elements in subsea field developments. As part of the safety engineering, protection from dropped objects and third party impact actions is required. This article addresses this aspect. The combined response from global deflection and denting of pipelines subjected to impacts is investigated. Analysis and testing methods applied in pipeline design are presented. Focus is placed on the overall interaction between the impacting object, the deformed pipeline and energy dissipation by soil.

Typically, pipeline damage from design codes provides conservative cross sectional damage estimates. This is confirmed from both simplified and detailed FE analyses, as well as impact experiments performed by REINERTSEN AS.

One of the main objectives promoted by the authors is the importance of impact velocity and mass during impact, and not only the kinetic energy of the impact. The kinetic energy from a dropped object is unlikely to be fully dissipated as cross sectional deformation of the pipeline. Global deformations will be triggered, which implies that the dissipated energy going into local denting is reduced to a fractional value. This paper discusses the impact mechanics and seeks to estimate the fractional value by using simplified element analysis.
Effects of Directionality of the Waves in the Mooring Systems Design
Authors: Rezende Flávia C. , Brun Cédric
Published: August 2013

In the analysis of the mooring system, one of the most important steps concerns the computation of the low-frequency wave loads that will excite the system at its resonance periods. Therefore, over the last decades much work has been devoted to this topic, especially for unidirectional waves although some publications can be found which deal with the computation of second-order loads in multi-directional waves. The common practice in the design of mooring systems is to ignore the interaction between waves coming from different directions even if we know that the unidirectional sea is an idealized situation that does not exist in practice. In Rezende & Chen (OMAE 2010), new method for computation of the low-frequency loading has been presented which is more efficient than the method based on the computations of the complete QTF in multi-directional waves, even though this method is still much more time consuming than the usual approximations in unidirectional seas. In this paper, the effects of the directionality of the waves are evaluated for typical mooring systems in deep water and in shallow water. The contribution of the directional interaction terms in the loads will be assessed in order to conclude on its importance to the mooring design.
Mechanical Integrity Modeling of Forge Welded Pipes for Offshore Applications
Authors: Marimuthu Ganesan S. , Moe Per Thomas , Liu Junyan , Salberg Bjarne
Published: August 2013

In this paper, we discuss how through-process multi-scale models can be designed and combined with properly constructed experiments in order to assess the mechanical integrity of forge welded connectors. Shielded Active Gas Forge Welding (SAG-FW) is a fully automatic solid state method for joining steel pipes and other metallic articles. After heating, welding occurs almost instantaneously when the mating surfaces of the metallic parts are brought into intimate contact at high temperature and co-deformed. The result is a metallic bond with properties similar to those of the base material. If mating surfaces have been properly prepared and are essentially free from oxides the forge weld line is completely indistinguishable even when studied under a microscope. However, improper surface finish, oxides and contaminants may contribute to reducing weld quality. The paper consists of analytical and experimental parts. First, approaches for modeling forge welding and weld integrity are assessed. Second, a Gurson-type model is studied in great detail as it appears to be the simplest and most promising concept in relation to quantitative modeling and testing of mechanical integrity of forge welds. Third, miniature notched specimens for determining parameters of a modified Gurson-model are proposed and evaluated in relation to small scale forge welding. The small scale forge welding method has been established in order to simulate full scale welding of for example line pipe and casing, but mechanical testing of small samples constitute a significant challenge. Fourth, a set of experiments is performed to further assess the concept, to the extent possible determine material parameters of the Gurson-model and to evaluate the effect of process parameter settings on the weld quality. Results from tests of welds with and without oxides are subsequently compared with results from tests of base material specimens. All tests have been performed for an API 5L X65 alloy. The results demonstrate that both capacity and ductility of the forge welds are similar to those of base material. Finally, Gurson-model parameters are assessed, and a comparison with physical observations is made. Further development of the small scale tests is needed. More extensive test programs should be performed and a comparison with full scale welding should be carried out. However, the experiments demonstrated that the proposed notched specimen designs complements conventional fracture mechanical tests (CT, SENT, SENB) or field tests proposed by various standards (Charpy, Izod, bend tests).
Small Scale Sour Fatigue Testing With Dense Phase Gases
Authors: Yu Weiwei , Vargas Pedro M. , Crowder Ben , Mishael Sam , Thodla Ramgopal
Published: August 2013

One way generally accepted by industry to evaluate the effect of sour environment on fatigue performance of girth welds is by small scale testing in sour brines. These tests are commonly done at room temperature and pressure and therefore can only contain a maximum of 14.7psia of H2S in a gaseous phase. In comparison, very little has been published about fatigue performance in sour environments where negligible amounts or no water is present. Such condition can be found for pipelines serving in a “dry” sour environment (H2S and other gases in dense phase) with high H2S concentration.

This paper documents both small scale fatigue crack growth rate (FCGR) tests and S-N fatigue tests in a dense phase sour environment with ultra-low water content and high H2S concentration under high pressure. Fatigue life reduction factors were calculated from FCGR approach (with the name crack growth acceleration factor, CGAF) and S-N approach (with the name knockdown factor), respectively.

Industry understanding today is that water is necessary for accelerating fatigue crack growth. Quite opposite to the expected effect of water content on crack growth, even ultra-low water content (<450ppm) resulted in high crack growth rates. Crack growth rates were comparable among tests with various water contents, all ultra low. Through limited testing, no temperature dependency on crack growth rate was identified. It is postulated that hydrogen dissociation due to high pressure and high concentration may be the cause for high crack growth rates on the absence of water.

Small scale S-N tests on smooth specimens reveal that fatigue performance in ultra-low-water sour environments is the same as in air. We find that the dry gas environment dose not attack the metal surface preserving the fatigue performance.
New Installation Method for Subsea Pipelines in South China Sea
Authors: Chen Chi , Zhang Kai , Yang Tianxiao , Xiong Ouyang , Tang Qiang , Cheng Yongming
Published: August 2013

The subsea pipelines between two platforms located in South China Sea were required to be replaced. In between the two platforms is a Floating Production Storage and Offloading (FPSO) unit including the mooring system, anchors and Pipeline End Termination (PLET). The new pipelines need to run below the FPSO and the mooring lines. This paper discusses a new installation method for the subsea pipelines in South China Sea.

There are technical challenges to install the new 18-km pipelines in Panyu oil field. On the one hand, it needs to ensure a 500-m radius safety zone from the FPSO. The pipeline laying vessel shall not work within the safety zone due to possible interference with anchor lines. On the other hand, the new pipelines have to run below the FPSO and the mooring lines in order to avoid potential interference with existing cable and riser system.

This paper considers the existing pipeline installation methods and generates a new method to install the pipelines in South China Sea. A concept of ‘dummy pipe’ is introduced to simulate the installation operation. The paper presents a series of installation sequences including assisting the pipeline laying and pulling, accurately positioning the pipelines, and protecting the existing facility. Figures are used to illustrate the installation deployment. Messenger lines were installed to run below the FPSO. The installation process was monitored. The new pipelines were installed in the field successfully. In addition, this paper further presents some recommendation for future installation practice.
Thrust Enhancement From Radial Velocity in Squid Inspired Thrusters
Authors: Krieg Michael , Mohseni Kamran
Published: August 2013

Squid and jellyfish generate propulsive forces by successively taking in and expelling high momentum jets of water. This method of propulsion offers several advantages to underwater vehicles/robots. The driving mechanism can be placed internal to the vehicle, reducing the drag associated with an abundance of external thrusters and control surfaces. The thrusters can generate accurate predictable forcing in the low thrust range, while still generating thrust nearly instantaneously over the entire force range. Vortex ring formation dynamics play an important role in creating thrust. It is observed that squid and jellyfish eject fluid jets which are not exactly parallel, and have a contracting velocity in the radial direction. A prototype thruster was developed which generates both parallel and converging propulsive jets. The total impulse of the jet is determined from DPIV techniques to determine the effect a non-zero radial velocity had on thrust production. The radial velocity was observed to increase the total impulse of the jet by 70% for low stroke ratio jets, and 75% for large stroke ratio jets.
Fatigue Estimation in Deepwater Risers Based on Wavelets and Second Order Blind Identification
Authors: Huang Chaojun , Nagarajaiah Satish , Varadarajan Nadathur
Published: August 2013

The safety of deepwater risers is essential for sustainable operation of offshore platforms. The structural health monitoring (SHM) system for deepwater risers is important to detect damage and perform repairs before failure occurs. Two main sources of damage are fatigue and corrosion. Failure of the riser would not only be an economical and environmental disaster, but also have far reaching consequences affecting communities. Combining global and local monitoring can greatly increase the accuracy of damage detection and fatigue estimation. Local inspection using robotic Magnetic Flux leakage (MFL) sensors is efficient and provides high resolution estimate of wall thickness changes due to corrosion or damage, while proposed vibration-based system identification can estimate global damage locations and fatigue life.

A new SHM system for deepwater risers was recently developed to monitor damage to the risers with both global and local monitoring methods proposed in this paper. The global monitoring is achieved by wavelet transform (WT) and second order blind identification (SOBI) method, from which, the likely location of fatigue damage is estimated. Once the location of the damage is identified by the proposed Wavelets/SOBI global identification method, local monitoring is performed using a robotic crawler with MFL sensors to further estimate the extent of the damage. Local monitoring with MFL sensors is verified by experimental results. Wavelets/SOBI global identification method is verified using Gulfstream test data.

Possible applications for the proposed SHM systems are for deepwater risers and deepwater platforms. A robotic MFL crawler can be used for in-line inspection for various pipelines. The proposed damage detection method and fatigue estimation can be adapted to other offshore structures, both fixed and floating. The proposed global method can also be used to analyze Tensioned Leg Platforms (TLP). To demonstrate the applicability of the proposed Wavelets/SOBI method to risers and floating platforms, verification using Gulfstream riser field data and TLP model data is presented in the paper.
Dynamic Analysis of a Floating Offshore Wind Turbine Under Extreme Environmental Conditions
Authors: Utsunomiya Tomoaki , Yoshida Shigeo , Ookubo Hiroshi , Sato Iku , Ishida Shigesuke
Published: August 2013

This paper is concerned with the development of a Floating Offshore Wind Turbine (FOWT) utilizing spar-type floating foundation. In order to design such a structure, it is essential to evaluate the dynamic response under extreme environmental conditions. In this study, therefore, a dynamic analysis tool has been developed. The dynamic analysis tool consists of a multi-body dynamics solver (MSC.Adams), aerodynamic force evaluation library (NREL/AeroDyn), hydrodynamic force evaluation library (In-house program named SparDyn), and mooring force evaluation library (In-house program named Moorsys). In this paper, some details of the developed dynamic analysis tool are given. In order to validate the program, comparison with the experimental results, where the wind, current and wave are applied simultaneously, has been made. The comparison shows that satisfactory agreements between the simulation and the experimental results are obtained. However, when VIM (Vortex Induced Motion) occurs, the current loads and cross flow responses (sway and roll) are underestimated by the simulation since the simulation code does not account for the effect of VIM.
Validation of CFD Predictions of the Hull Resistance and the Wave System of a Catamaran
Authors: Alho Alexandre T. P.
Published: August 2013

In response to the need for better designs in less time and at low costs, computational fluid dynamics (CFD) is becoming an integral part of the vessel’s design process. Recent studies have shown that CFD techniques can be used with relative success for the problem of ship resistance prediction. This paper reports on the simulation of the flow around a typical catamaran hull by means of CFD computations. The numerical model used in the simulations was developed in full scale with the experimental model in order to eliminate any source of scale effects. The paper presents a discussion on grid configuration and an analysis of the performance of the numerical model in describing the characteristics of the in-between hulls flow. The results obtained were validated against experimental data.
An Experimental Study of Wave Loads on Deck in Irregular Waves
Authors: Kota Ravikiran S. , Moan Torgeir
Published: August 2013

Global loads on deck-structures due to air-gap loss in irregular seas are discussed. Estimation of such loads is important in structural integrity verification of fixed and floating platforms. The current study presents results from wave-tank experiments in which global forces and wetted lengths arising from wave impact on a rigid deck-box from several pseudo-random realizations of long-crested waves of moderate steepness are recorded. Short-term statistics and distributions of these quantities are estimated and compared against estimates from semi-analytical results previously reported by the authors for von Karman-type impact events in Gaussian waves. The scope of work presented here does not address wave loads on decks in extreme seas where the waves are steep and predominantly non-Gaussian.
Flow Induced Fluttering and Autorotation of a Hinged Vertical Flat Plate
Authors: Fernandes Antonio Carlos , Sefat Sina Mirzaei
Published: August 2013

This paper addresses the investigations on fluttering and autorotation motions which may occur in the interaction of uniform current and freely rotating plate about a fixed vertical axis. The autorotation is a name given to the case that the plate turns continuously about the vertical axis and the fluttering motion is the periodic or chaotic oscillations of the plate around the vertical axis. According to the dimensional analysis the motion in flow induced rotation motion is governed essentially by dimensionless moment of inertia, Reynolds number and initial conditions. Certain combinations define the stability boundaries between fluttering and autorotation. Hence, a bifurcation diagram was prepared by the experiments to classify different states observed the small fluttering, fluttering and autorotation based on different Reynolds number and dimensionless moment of inertia.
An Exploratory Study on Optimum Layout of the Cluster Manifold
Authors: Wang Yingying , Duan Menglan , Wang Deguo , Yuan Xu , Tian Kai
Published: August 2013

There are four typical layout types for the subsea production system. These include single well tie back, the daisy chain, the template manifold and the cluster manifold. In the early development phase, an appropriate layout type needs to be selected. The layout design of the subsea production system is based on the data of oil and gas fields. Due to many advantages, such as less initial investment, being installed in advance, flexibility for development schedule and so on, the cluster manifold is becoming more popular and has been applied extensively in the layout of deepwater subsea production systems. In this layout type, the number and locations of cluster manifolds, and the connection types between subsea production facilities have a direct effect on the safety, flexibility and cost of the target deepwater oil and gas fields. Hence, how to design the optimal layout of the cluster manifold is of key importance. This paper will focus on the cluster manifold layout by the math means programmed using C++. For any given subsea well and the floating production system, the basic layout of the cluster manifold with the lowest cost can be obtained based on the assumptions, including the number, locations and cost of the jumpers, PLETS and flowlines. This mathematical method can reduce subjective bias from the engineers and provide a more scientific reference for obtaining the optimal cluster manifold layout.
Well Control Research and Development
Authors: Ribeiro Paulo R. , Santos Otto L. A.
Published: August 2013

Well control has been an inexhaustible source of research/development/innovation for the past four decades due to its impact in oil and gas exploration and production. Such an importance is based on three pillars: i) human safety, ii) environmental protection, and iii) economic issues.

Macondo incident has proved that continuing development of the subject is an issue to be tackled by oil companies to preserve and also rebuild their image to society. One of the most important aspects of well control is the development of kick simulators capable of handling increasing complexity of well geometry (diameters and trajectory), drilling fluids (synthetic drilling fluid), well location (land and offshore) and wellbore conditions (increasing pressure and temperature severity with depth). Such simulators have the following missions: i) to help the drilling engineer to make decisions during well control procedures and kick situations, ii) to provide personnel training and certification and iii) to guarantee a better understanding and interpretation of field observations.

The main objectives of the present work are three-fold: i) to present an overview of the evolution of kick modeling and simulation over the years, ii) to focus on the R&D efforts of the joint work of academia and industry to build a well control model to handle deep and ultra-deepwater drilling challenges and iii) to present a software based on that model to assist drilling engineers during well control operations.

Experimental data has been based on PVT measurements of gas and synthetic drilling fluid mixtures under HPHT conditions. Phase behavior modeling has proved to be a very important issue to be taken into account in the two-phase flow model that represents the kick circulation process.

The current work presents the results of the interaction of experimental lab work and numerical modeling to develop a kick simulator to handle complex drilling scenarios to assist drilling personnel in well control operations.
3D Fracture Simulations of SENT Specimens Including Welding Residual Stresses
Authors: Kane Alexandre , Ås Sigmund , Østby Erling
Published: August 2013

In pipe-laying and reeling operations, high levels of plastic deformation may occur in the pipe wall. The effect of plastic deformation should be investigated and quantified in order to qualify a steel material for a given pipe-laying process. This paper presents a numerical modeling approach for realistic simulation of ductile fracture, including results from FE welding simulations. A 3D model of a SENT specimen is adopted, where crack propagation is modelled using a Gurson model. An elastic-plastic hardening model is used to capture the global deformation of the specimen. Results compare well with experiments. This work is part of an effort to develop an experimental and numerical framework where the influence of welding (HAZ properties, residual stresses and hardening) in fracture assessment. Preliminary results show that there is no influence of residual stresses on fracture strength of an X65 ductile steel.
Effects of Porosity on the Creep Behavior of Hydrate-Bearing Sediments
Authors: Wang Rui , Liu Weiguo , Li Yanghui , Yu Feng , Nie Xiongfei , Song Yongchen
Published: August 2013

In this paper, a triaxial apparatus system was set up. The creep behavior of hydrate-bearing sediments was measured by loading different shear stress on various porosity sediments. The creep curves were attempted to simulate. The experimental results indicated that, the internal cementation of the sediments was changed with the change of porosity. The viscoplastic structural was also changed with the change of porosity. High porosity sediments have a high viscosity and hardness. Moreover, the high porosity sediments have larger initial strain than the low porosity sediments.
Lifecycle Fatigue Load Spectrum Estimation for Mooring Lines of a Floating Marine Energy Converter
Authors: Thies Philipp R. , Johanning Lars , Smith George H.
Published: August 2013

One of the key engineering challenges for the installation of floating marine energy converters is the fatigue of the load-bearing components. In particular the moorings which warrant the station-keeping of such devices are subject to highly cyclic, non-linear load conditions, mainly induced by the incident waves.

To ensure the integrity of the mooring system the lifecycle fatigue spectrum must be predicted in order to compare the expected fatigue damage against the design limits. The fatigue design of components is commonly assessed through numerical modelling of representative load cases. However, for new applications such as floating marine energy converters numerical models are often scantily validated.

This paper describes an experimental approach, where load measurements from tank tests are used to estimate the lifecycle fatigue load spectrum for a potential deployment site. The described procedure employs the commonly used Rainflow cycle analysis in conjunction with the Palmgren-Miner rule to estimate the accumulated damage for individual sea states, typical operational years and different design lives.

This allows the fatigue assessment of mooring lines at a relatively early design stage, where both information from initial tank tests and the wave climate of potential field sites are available and can be used to optimise the mooring design regarding its lifecycle fatigue conditions.
A Model for Long-Term Distribution of Wave Induced Loads in Steep and Breaking Shallow Water Waves
Authors: Hansen Hans Fabricius , Lohmann Iris Pernille , Sørensen Jacob Tornfeldt , Schlütter Flemming
Published: August 2013

A new approach to determine the design wave load on bottom-fixed structures in shallow water breaking waves is presented here. The method takes into account the effects that wave breaking has on both the wave height distribution and the wave induced loads on the structure. The loads on offshore wind turbine foundations in irregular seas with a significant amount of wave breaking are modeled in a physical wave tank. The loads are related to wave characteristics as steepness and Ursell number, and a non-linear transfer function between wave height/period and wave load is established.

Characteristic historical load events are now established by combining the transfer function with a record of the wave climate at the site. The latter is taken from a hindcast database, but could also come from site measurements. The long-term distribution of the load is estimated by adopting traditional extreme value analysis techniques to the historical characteristic loads.
Investigation on the Use of Different Approaches to Mooring Analysis and Appropriate Safety Factors
Authors: Vasudevan Sojan , Westlake Paul
Published: August 2013

This paper presents the results of the analyses of a twelve line catenary mooring system using a quasi-static method in the frequency domain, and uncoupled and coupled dynamic methods in the time domain. The latter is found to produce significantly higher tensions. The reasons for these differences are investigated.

The minimum line tension safety factors required by design codes do not distinguish between uncoupled and coupled dynamic analyses and some codes use the same factors even for quasi-static analyses. Consequently, the present mooring system passes the acceptance criteria based on quasistatic frequency domain and uncoupled dynamic time domain analyses but does not meet the same criteria when a coupled dynamic time domain analysis is employed.

It is understood that because the coupled time domain analysis determines the vessel motions using all forces the accuracy of mooring line tension estimation will be improved over other methods. Hence the application of less conservative safety factors is proposed.
A Statistical Time Dependent Degradation Curve Analysis for Marine Structures
Authors: Witte Carlos C. , Ribeiro Duperron M.
Published: August 2013

Structural integrity assessments are important for the protection of the environment, offshore crew and company status. Marine structures, through the lifetime, must be maintained by a reliable management system of inspections, repairs and coatings protections. Planned thickness measurements are necessary to update the structure conditions and certify the operation in the marine environment. By these inspections is possible to calculate corrosion rates using statistical regression methods and time dependent corrosion curves. Corrosion rates analysis may well alert structure integrity problems and predict future corrosion tendencies. This study shows the application of field information by using a time dependent corrosion model. This method can be found on asset structure integrity management system [1], which is dominant in the offshore Brazilian industry.
Riser Dynamic Analysis Using WKB-Based Dynamic Stiffness Method
Authors: Cheng Yongming , Vandiver J. Kim
Published: August 2013

Risers are fluid conduits from subsea equipment to surface floating production platforms. The integrity of a riser system plays a very important role in deepwater developments. Riser dynamic analysis is an important part to the system design. This paper investigates riser dynamic analysis using the WKB-Based dynamic stiffness method.

This paper first presents a theoretical formulation of the dynamic stiffness method. It then combines the dynamic stiffness method with the WKB theory, which assumes that the coefficients in the differential equation of motion are slowly varying. The WKB-based dynamic stiffness method is derived and a frequency dependent shape function is expressed implicitly. The Wittrick and Williams (W-W) algorithm is further extended to solve eigen value problem for a general non-uniform marine riser.

Examples of non-uniform riser are analyzed and the results show the efficiency of this method. In addition, a pipe-in-pipe riser system is analyzed for natural frequencies and mode shapes using the WKB-based dynamic stiffness method with the W-W algorithm. The characteristic of the mode shapes is described for such a riser system.
Stiffness Modeling, Testing, and Global Analysis for Polyester Mooring
Authors: Kwan C. T. , Devlin Paul , Tan Pao-Lin , Huang Ken
Published: August 2013

This paper summarizes one of the studies conducted by the ABS Joint Industry Project (JIP), “Polyester Rope Stiffness Modeling, Testing, and Analysis”. The objective of this study was to collect and investigate results of past studies, test procedures and data, code requirements, and fiber rope mooring analysis methods dealing with polyester rope stiffness. Based on the results of the study, conservative and practical stiffness models, test data analysis, and mooring analysis method were developed. The results from this study have been incorporated in the 2011 ABS Guidance Notes on The Application of Fiber Rope for Offshore Mooring [13]. Major conclusions of this study are as follows:

1. The 2-slope static-dynamic model is the best approximation for the complex fiber rope elongation behavior. It is based on rigorous research and allows efficient mooring analysis using typical commercial software.

2. Stiffness testing should be conducted to generate stiffness equations and design charts instead of design stiffness values. The design stiffness values can be obtained from these equations and design charts. A practical procedure for test data analysis is recommended.

3. Mooring analysis can be efficiently conducted in frequency or time domain with commercial mooring analysis software based on the recommended stiffness model.
Effect of Polyester Mooring Stiffness on SCR Design for FPSO Application
Authors: Chang Gwo-Ang , Tan Pao-Lin , Huang Ken , Kwan Tom
Published: August 2013

Polyester rope is a visco-elastic material and its stiffness is affected by mean tension, tension amplitude, loading period, and loading history. Qualitatively it may be felt that rope stiffness significantly affects vessel offset, which in turn affects riser performance and cost. However, a systematic investigation of the impact of rope stiffness on riser stress and fatigue life has not been published for a wide variety of design conditions. This paper describes such a study, and provides specific guidance to designers for the prudent selection of a rope stiffness model and values to achieve safe and cost effective riser design. This study investigated the effect of polyester rope stiffness on steel catenary riser (SCR) design for an FPSO sited in a variety of water depths considering environmental conditions representative of West Africa. Static/dynamic stiffness models for polyester rope in the recently issued ABS Guidance Notes on the Application of Fiber Rope for Offshore Mooring [1] were used in a global analysis to provide motion responses for the riser analysis. Time domain riser analysis was performed to obtain maximum riser stress and fatigue damage under various conditions. Based on the results of the investigation of riser and mooring analysis, guidance on the impact of rope stiffness to the riser design has been developed.
Extracting Energy From the Hydrodynamic Instability of a Yawing Flat Plate
Authors: Fernandes Antonio Carlos , Armandei Mohammadmehdi
Published: August 2013

The extraction of energy from currents is still an issue. Both design point and off-design behavior should be addressed conveniently. In the present study, a new concept based on the flow-induced instability of an elastic structure is introduced by which the energy can be extracted from the water current. The energy extractor device is named “Fernandes-Armandei”, which consists of a simple flat plate attached to a torsion spring and located vertically in the water current. The flat plate has only 1 DOF that is yawing about its axis, which is in its mid chord length. A concurrent-schedule research (Armandei and Fernandes, 2012) demonstrates that one such motion becomes dynamically unstable, as the velocity exceeds a special threshold. The motivation of doing this research was the robustness of the oscillations created due to the flow-induced instability. Two different cases (a) and (b) are studied, case (a) with larger natural frequency and case (b) with larger mass moment and added moment of inertia. A damper is also applied in the device as a transmission system which converts oscillation to rotation. The rotary motion is utilized to lift a weight up to a prescribed height, to assess the energy extraction behavior of each case. The results show that case (b) can lift heavier weights than case (a). However, the maximum efficiency of case (a) (9.18%) is about three times more than the maximum efficiency of case (b) (3.26%).
A Study on the Use of Reduced Order Models for Unsteady Fluid Dynamic Analysis of Flexible Structures
Authors: Ebrahimnejad L. , Yadollahi Farsani H. , Valentine D. T. , Janoyan K. D. , Marzocca P.
Published: August 2013

Reduced order models (ROMs) are computationally efficient techniques, which have been widely used for predicting unsteady aerodynamic response of airfoils and wings. However, they have not been applied extensively to perform unsteady fluid dynamic analysis of flexible structures in civil engineering. This paper discusses the application of reduced order computational fluid dynamics (CFD) model based on the eigensystem realization algorithm (ERA) in the aerodynamic analysis of flexible structures with arbitrary shaped cross sections. As an example of a civil structure we examine the GBB long-span bridge for which there are published experimental data. The aerodynamic impulse responses of the GBB Bridge are used to construct the ROM, and then the aerodynamic forces due to arbitrary inputs are evaluated and compared to those of the model coupled with an advanced CFD code. Results demonstrate reasonable prediction power and high computational efficiency of the technique that can serve for preliminary design, optimization and control purposes. The methodology described in this paper has wide application in many offshore engineering problems where flexible structures interact with unsteady fluid mechanical phenomena.