bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulation System for Dynamic Analysis of the Ship Structures
Authors: Feng Guoqing , Feng Guan , Ren Huilong , Luan Jian , Zhao Xueqian
Published: January 2011

A vibration and fatigue simulation system[1]–[3] based on the dynamic analysis in time domain of the ship structures when subjected to a certain sea state is presented. The development of the system is based on VC++ and OpenGL. The system covers the simulation of 3D waves, ship hull, free vibration and forced vibration of the ship, as well as the fatigue damage prediction of the ship structures. Irregular waves are simulated by linear superposition of a series of regular cosine waves for a certain sea state. On the basis of this expression of the irregular waves, the wave loads can also be obtained in a similar way. The stress history of the ship structures may be acquired by a dynamic response analysis. The free vibration of the ship hull can give the natural frequencies and the relevant vibration modes. The forced vibration can show the time variant displacement, velocity and acceleration caused by the exciting force of the propeller, main engine and wave slamming. The fatigue prediction is performed by means of rain flow counting and Miner rule[16]. The numerical example shows the system is applicable in the vibration response and fatigue perdition of the ship structures and the visual interface is user-friendly.
The Effect of Cyclic Loading Frequency on Corrosion-Fatigue Crack Growth in High-Strength Riser Materials
Authors: Hudak Stephen J. , Feiger James H. , Patton Jason A.
Published: January 2011

Corrosion-fatigue is a significant design consideration in deepwater floating production systems. Mechanical loading is accentuated due to the compliant nature of these structures, and sour service conditions can also occur either due to the nature of the crude production or due to seawater flooding of the reservoir to enhance production yield. New high-strength riser steels have recently been developed to meet the demands of deepwater development. The objective of this study was to characterize the corrosion-fatigue resistance of these materials in terms of crack growth rates as a function of applied stress intensity factor range (ΔK), as well as cyclic loading frequency. Experiments were performed on five different steels with yield strengths ranging from 848 to 1080 MPa. Two environments were considered: seawater with cathodic protection to simulate the environment outside of the riser, and a sour brine environment with low oxygen (< 10 ppb) to simulate the environment inside the riser. Not all steels were tested in the sour brine environment since not all were designed to operate in sour service. For both environments, higher strength steels were found to exhibit higher growth rates and lower saturation frequencies. Fatigue crack growth rates as a function of ΔK were also measured, and exhibited two different frequency responses. At high ΔK, the classical frequency response occurred: decreased frequency gave increased crack growth rates. At low ΔK, an inverse frequency effect was observed: deceased frequency gave decreased crack growth rates, as well as increased corrosion-fatigue crack growth thresholds. These differences are believed to be caused by different underlying processes controlling crack growth — specifically, material-environment reaction kinetics at high ΔK, and crack closure due to corrosion-product wedging at low ΔK. The practical significance of these results is discussed, including selection of frequencies for corrosion-fatigue crack growth testing, and applicability of results to structural integrity assessments.
Dynamic Analysis of Floating Bodies Considering Multi-Body Interaction Effects
Authors: Kim Young-Bok , Kim Moo-Hyun , Kim Yong Yook , Kim Young-Hun
Published: January 2011

Recently, there are several problems in space, infra-structure, and facility in the contiguity of existing harbors due to the trend of enlarged container vessels. In this regard, the Mobile Harbor has been proposed conceptually as an effective solution for those problems. This concept is a kind of transfer loader of the containers from the large container ship to the harbor on land, which is a floating barge of a catamaran type. The catamaran-type vessel is well known for its advantage in maneuverability, resistance, and the effectiveness for working on board. For the safe and effective operation of the two floating bodies, a container ship and the mobile harbor in the near sea apart from the quay, robot arms, novel crane systems, and pneumatic fenders are specially devised with additional mooring facility or DP (dynamic positioning) system. The concept is to be verified through comparison and simulation studies under various environmental conditions. It is shown that the proposed concept is in general feasible but there are several areas for further investigation and improvement.
Effect of Foundation Modeling on Extreme Response of Offshore Jack-up Unit
Authors: Jafari Azadeh , Asgarian Behrouz , Daghigh Mohammad
Published: January 2011

The demand for operation of mobile jack-up drilling rigs in offshore industry is increasing. Extreme response of jack-up platforms in sea environment requires improving the understanding of their nonlinear behavior. A sample jack-up platform located in Persian Gulf is modeled using three dimensional capabilities of USFOS considering both geometric and material nonlinearity. USFOS is a numerical tool for ultimate strength and progressive collapse analysis at frame structures such as jack-up platforms. Results of the analysis for the sample jack-up subjected to storm load pattern are compared for three different foundation modeling cases (pinned, fixed and spudcan modeling of foundation). Static pushover analysis is performed to determined jack-up behavior assuming different cases for fixity of foundation. It is observed that modeling of exact foundation by a simplified pinned model underestimates ultimate lateral strength of jack-up. A fixed based modeling overestimates lateral ultimate strength of the platform.
Numerical Analysis of a Floating Body With Two-Dimensional Moonpool Including Piston Mode
Authors: Heo Jaekyung , Park Jong-Chun , Kim Moo-Hyun , Koo Weon-Cheol
Published: January 2011

In this paper, the potential and viscous flows are simulated numerically around a 2-D floating body with a moonpool (or a small gap) with particular emphasis on the piston mode. The floating body with moonpool is forced to heave in time domain. Linear potential code is known to give overestimated free-surface heights inside the moonpool. Therefore, a free-surface lid in the gap or similar treatments are widely employed to suppress the exaggerated phenomenon by potential theory. On the other hand, Navier-Stokes equation solvers based on a FVM can be used to take account of viscosity. Wave height and phase shift inside and outside the moon-pool are computed and compared with experimental results by Faltinsen et al. (2007) over various heaving frequencies. Pressure and vorticity fields are investigated to better understand the mechanism of the sway force induced by the heave motion. Furthermore, a nonlinear potential code is utilized to compare with the viscous flow. The viscosity effects are investigated in more detail by solving Euler equations. It is found that the viscous flow simulations agree very well with the experimental results without any numerical treatment.
Flow Around a Pipeline Near a Smooth Bed in Steady Current
Authors: Wang Xikun , Hao Zhiyong , Tan Soon Keat
Published: January 2011

The flow around submarine pipelines is represented by a circular cylinder near a horizontal plane wall. The combined effects of Reynolds number (Re = 4000, 6400 and 9200) and gap ratio (S/D = 0.125–2, where S is the gap height between the cylinder bottom and the wall surface, and D is cylinder diameter) on the flow are investigated experimentally using Particle Image Velocimetry (PIV). Detailed velocity vector maps, contours of vorticity, root-mean-square (rms) velocities and Reynolds shear stress are provided. Results show that both the ensemble-averaged and the instantaneous flow fields are primarily dependent on S/D, yet the effects of Re are also obvious over the Re-range considered. Shear layers surrounding the recirculation region behind the cylinder are discussed in terms of the flow physics and vortex formation lengths of large-scale Karman vortices. It is found that the critical gap ratio is about 0.3, higher than which the wake flow is characterized by the alternate Karman-like vortex shedding from the two sides of the cylinder, whereas below which there is no mutual coupling between the two shear layers. Flow structures depending upon the gap ratio and Reynolds number are interpreted with quantitative representations.
On the Crashworthiness of Steel-Plated Structures in an Arctic Environment: An Experimental and Numerical Study
Authors: Paik Jeom Kee , Kim Bong Ju , Park Sung Kuk , Kim Do Kyun , Park Chang Hee , Park Dong Hee , Jang Bong Suk
Published: January 2011

The aim of this study is to investigate the crashworthiness characteristics of steel-plated structures subject to low temperatures that are equivalent to the Arctic environment. Structural crashworthiness with regard to crushing and fracture is a key element in the strength performance assessment of ship collisions in the Arctic, which provides the primary motivation for the study. This article is a sequel to the authors’ previous paper [1]. In contrast to the previous paper, which dealt with test structures made of American Society for Testing and Materials (ASTM) A500-type carbon steel with the wall slenderness coefficient (b/t) of 37.5, the present paper considers grade A steel with the wall slenderness coefficient (b/t) of 25. Crushing tests are undertaken on square tubes subject to a quasi-static crushing load at both room and low temperatures. The effect of low temperatures on the material properties is examined on the basis of tensile coupon test results. The crushing behavior of the square tubes in this test is compared with LS-DYNA computations. It is found that low temperatures have a significant effect on the crashworthiness of steel-plated structures in terms of mean crushing loads and brittle fracture. The use of grade A steel for ships and offshore structures in an Arctic environment is not relevant. The modeling techniques for the structural crashworthiness analysis presented in this paper are found to be pertinent by comparison with experimental results and nonlinear finite element method computations. It is suggested that the collision-accidental limit state design of ships intended to operate in the Arctic region be carried out by taking the effect of low temperatures into account.
Experimental Study on Influences of Wave Height on Liquefaction Depth of Silty Soil Bed
Authors: Yu Yueqian , Xu Guohui , Wang Xin , Liu Huixin , Zhao Qingpeng
Published: January 2011

Storm waves tend to cause seabed liquefaction by exerting strong cyclic loads on the seabed of the Yellow River Delta. In order to study influences of different wave heights on liquefaction depth of the soil bed, silty soil taken from the Yellow River Delta is used to prepare a soil bed for flume experiments and local parts of superficial soil layer were disturbed by hand. The weakened soil tended to liquefy and slide under wave actions and the liquefaction depth increased with the increasing of wave height. Based on the experimental results, an empirical relationship was proposed between liquefaction depth of silty soil bed and wave height under experimental conditions.
Comparative Study of Output-Based Modal Identification Methods Using Measured Signals From an Offshore Platform
Authors: Wang S. Q. , Zhang Y. T. , Feng Y. X.
Published: January 2011

Research on vibration based damage identification using changes of modal parameters has been expanding rapidly over the last decades. And modal parameter identification methods are essentially important since these parameters directly affect the damage detection results. Many modal identification methods have been proposed and further verified based on numerical and laboratory data. However, few papers are reported on comparative investigation of several output-only modal identification methods, especially based on measured signals from offshore platform in service. The main objective of the present paper is to investigate the effectiveness and applicability of several output-only modal identification methods, including Ibrahim Time Domain(ITD), Eigensystem Realization Algorithm(ERA), Auto-Regressive Moving Average method(ARMA) and Stochastic Subspace Identification(SSI) methods. First the four modal identification methods are briefly reviewed. Field measurements are conducted and vibration signals are recorded for modal identification. The effectiveness is compared for the four identification methods. Useful results could be obtained.
A Coupled-Mode Model for the Transformation of Wave Systems Over Inhomogeneous Sea/Coastal Environment
Authors: Belibassakis K. A. , Gerosthathis Th. P. , Athanassoulis G. A.
Published: January 2011

The transformation of the directional wave spectrum over an inhomogeneous sea/coastal environment is considered. Inhomogeneities include intermediate-water depth, strongly varying 3D bottom topography and ambient currents. The consistent coupled-mode model, developed by Athanassoulis and Belibassakis (1999), extended to three dimensions by Belibassakis et al. (2001) and applied to the transformation of wave systems over 3D bottom topography (Gerostathis et al 2008) is exploited for the calculation of the transfer function, connecting the incident wave with the wave conditions at each point in the field. This model is fully dispersive and takes into account reflection, refraction, and diffraction phenomena. In the present work, the coupled mode system is enhanced to account also for the effects of steady currents (Belibassakis et al, 2008), as well as, the effect of wave energy dissipation due to bottom friction and wave breaking. Numerical results obtained by the present model are compared with other models (as, e.g., Li et al 1993, Yoon et al 2004) and experimental measurements (Vincent and Briggs 1989), demonstrating the usefulness and practical applicability of the present method.
Analysis on Microstructure and Deformation Mechanics of X100 Linepipe Steel
Authors: Li Yang , Li Meng , Qi Lihua , Ji Lingkang , Huo Chunyong , Feng Yaorong
Published: January 2011

In present paper, mechanical tests have been conducted on WT20.6mm×OD1016mm diameter Grade 690 linepipe. Microstructure is studied by means of OM, SEM, EBSD and TEM analysis. It is founded that the morphology of X100 steel consists mainly of fine acicular ferrite with little lath-shaped homogeneously distributed polygonal ferrite and very fine M/A constituent distributed on grain boundary, and the proportion of acicular ferrite reaches 64%. It is measured that effective grain size of steel material is 2.07μm for grains with an orientation as 15°. Contrast analysis for Kikuchi Pattern shows that the proportion of small-angle boundary is 45%, which provides X100 linepipe steel with a good performance of higher strength and toughness for large quantity of dislocation and substructure. High-density tangled and blocked dislocation in acicular ferrite lath is also observed in TEM morphology of X100 linepipe steel. Deformation mechanics will be discovered by micro-analysis on specimens deformed with different strain level as 0%, 5% and 8%. With the increment of deformation level, it is observed that substructure in effective grain and the proportion of small-angle grain boundary increases greatly, and the orientation of grain is also changed evidently. To study the deformation process of linepipe steel, an in situ tensile test is also conducted with SEM observation. It is also discovered that crack is initiated at the place of stress concentration, which is mainly close to the interface, and propagates along the length of M/A chip.
Research and Development of Offshore Platforms for SMS Mining: Part 1—An Integrated Design Tool of Offshore Platforms
Authors: Chujo Toshiki , Ishida Shigesuke , Yukawa Kazuhiro , Namba Yasuhiro , Nakajima Yasuharu , Kato Shunji
Published: January 2011

The exclusive economic zone (EEZ) of Japan has a very large area because Japan consists of many islands. As the worldwide supply and demand of natural resources and food are being tight, the technology for the effective use of the EEZ will become the key for the future development of Japan. From this background, the Ministry of Land, Infrastructure, Transport and Tourism of Japan (MLIT) started an R&D project of floating offshore platform technologies in 2007. In this project an integrated design support tool, called “Harmonic Design Tool”, has been developed for evaluating economical and safety aspects of the offshore platforms. At the first stage, the tool makes the basic planning based on many kinds of relating datasets. In the second and third stages, safety assessment and economic evaluation are carried out by datasets and numerical simulation programs. In this paper the outlines of the total tool, each stage, some technical components and a trial estimate for seafloor massive sulphides (SMS) mining platform are presented.
From Subsurface to Riser: An Integrated Approach to Subsea Surveillance
Authors: Machin Jon
Published: January 2011

The high reliability performance of a subsea surveillance system, from subsurface to riser, is of the utmost importance for maximizing production availability. In designing such a surveillance system, there are a multitude of considerations that need to be addressed. These have traditionally focused on safe and cost effective production control system availability. However, they are now being extended to also address enablers for secondary recovery, production optimization, and increased recovery activities. This paper addresses the idea that latest-generation surveillance systems must operate seamlessly from the subsurface to the seabed and in turn from seabed to riser. In doing so they must integrate a number of key enabling technologies over different physical layers and predefined technical interfaces. They must also serve to integrate these technologies over the project management interfaces which arise from the selection of the different proprietary technologies, and the commercial and contractual barriers which can result.
Modeling Traveling Waves Using Mode Superposition
Authors: Jaiswal Vivek , Sheshadri Aditi , Vandiver J. Kim
Published: January 2011

Analysis of the data from two Vortex-Induced Vibration (VIV) experiments conducted in the Gulf Stream on a 500-foot-long, 1.43 inches diameter, flexible, tension dominated riser model revealed that the response is predominantly characterized by the presence of traveling waves. It was also observed that the location of the VIV excitation region (power-in) affects the characteristics of the response. The conventional method of modeling the excitation force as a standing wave was found inadequate to predict the location of the peak measured response accurately, especially in the cases where the excitation region is close to a boundary (the ends of the riser model). A modified excitation force model consisting of a combination of standing and traveling wave excitation regions is demonstrated to predict the location of the peak response more accurately. This work presents the idea of modifying the VIV excitation model to include traveling wave characteristics and using mode superposition method for computing the response to this modified force. Examples of the implementation of this method are shown for the two distinct cases of the location of the power-in region — the power-in region adjacent to the boundary and the power-in region away from the boundary. Depending on the location of the power-in region, different proportions of standing and traveling wave excitations are used to yield predicted responses that match the measured response characteristics.
The Development of the Torpedo-Piezocone
Authors: de Campos Porto Elisabeth , de Medeiros Junior Cipriano Jose´ , Henriques Junior Paulo Roberto Dionysio , Foppa Diego , Ferreira Antoˆnio Carlos Pimentel , Costa Rachel Guerreiro Basi´lio , Fernandes Jane Vieira Volota¯o , Danziger Fernando Artur Brasil , Jannuzzi Graziella Maria Faquim , de Mello Guimara¯es Gustavo Vaz , da Silva Junior Silvio Pinheiro , de Lima Alves Antoˆnio Marcos
Published: January 2011

The paper describes the development of a soil investigation equipment, consisted of a piezocone installed at the tip of a torpedo-pile. The new equipment, named torpedo-piezocone, is able to measure cone resistance (qc), sleeve friction (fs), pore-pressure at the cone face (u1) and cone shoulder (u2) as well as cone temperature during free-fall and some time after final stop. Velocity, as well as displacement (depth) are obtained from accelerometer data, as in the case of the torpedo-pile. The various steps to develop the equipment are presented, from the requirements of the transducers until the calibration procedures in the laboratory. The first tests performed onshore are also presented. In general, very good results have been obtained.
A Numerical Study on Oil Leakage and Damaged Stability of Oil Carrier
Authors: Cheng Liang-Yee , Gomes Diogo Vieira , Nishimoto Kazuo
Published: January 2011

The objective of the present paper is to carry out a study on coupled transient process of the oil leakage and the damaged stability of a crude oil carrier. For this purpose, numerical simulations based on MPS (Moving particle Semi-Implicit) method are carried out considering a two dimensional small scaled model and the oil-water multiphase flow with free surface. The results are compared with that obtained by the stability analysis software SSTAB, which provides the final list angle in case of the damage, and show good agreement.
Fatigue Analysis Technique of Deepwater Steel Catenary Risers
Authors: Cao Jing
Published: January 2011

With the advances in deepwater offshore industries, Steel Catenary Riser (SCR) offers advantages over others and has been widely deployed worldwide including Gulf of Mexico (GoM), West of Africa (WoA), and Offshore Brazil. SCR concept has been applied to all types of deepwater floaters. Among analyses and design criteria, fatigue is still the number one governing design criterion of the deepwater SCR regardless the floater types (SPAR, TLP, SEMI, and FPSO). Typical SCR fatigue analyses include first order and second order floater motion induced fatigue; vortex induced vibration (VIV), deep draft floater vortex induced motion (VIM) fatigue, floater vertical motion induced VIV, slugging fatigue, start-up and shut-down, installation, and other kinds of dynamic loading imposed to the SCR. This paper presents the state-of-art fatigue analysis requirement and technique of different kinds of fatigue analysis for deepwater SCRs. Detailed discussion is given to different kinds of fatigue damage of SCRs. Focus of fatigue analysis of each type of deepwater floater is pointed out. Detailed discussion is also given to the selection of SN curves, stress concentration factors, influence of sweet and sour service, and post-processing of fatigue sensitive welds. Several examples of SCR fatigue analysis are given to demonstrate the analysis techniques and practices.
On SIF and SCF of Circumferential Welds on Steel Tubular Piles Under Bending Moments
Authors: Li Yi , Wang Duo-Yin , Zhou Shi-Liang
Published: January 2011

Circumferential welds, also called splice welds, on steel piles installed in marine and offshore structures are potential fatigue hot spots, given harsh and cyclic loadings. This paper is devoted to linear elastic fracture mechanics (LEFM)-based fatigue assessment for pile splice welds under bending moments. Specifically, this paper studies two important factors for the LEFM analysis of surface crack at the circumferential welds, stress intensity factor (SIF) and stress concentration factor (SCF). So far, LEFM-based fatigue assessment has not been widely conducted for steel tubular piles. Particularly, the two factors have not been properly developed with regard to typical features of marine steel piles, i.e., small aspect ratio of crack shape, thin-walled condition, misalignments at splice, thickness transition, complicated loading effects including bending moments, etc. The determination of SIF heavily relies on a geometry function for the growth of a fatigue crack. Based on a literature review, this paper has identified a database of geometry functions that may be suitable in practice for the circumferential welds on tubular piles with a thickness ratio around 10 under bending moments. SCF is used to accommodate stress concentration effects due to assorted geometric misalignments at a pile splice, including diameter difference (or concentricity), center eccentricity, thickness difference, and out of roundness. Currently, SCFs for tubular connections are produced for axial forces. In this paper, a practical approximation to the SCF under bending moments is mathematically formulated on the basis of a flat-plate configuration. This paper presents practical information for LEFM-based fatigue assessment of steel piles installed in marine and offshore works.
Numerical Simulation of Pipeline Undergoing Cyclic Lateral Motion in Clay
Authors: Tho K. K. , Leung C. F. , Chow Y. K. , Palmer A. C. , Hu H. J. E.
Published: January 2011

In a deepwater oil and gas development, a pipeline is often laid directly on the seabed rather than being buried in a trench. In addition to the cost benefit of not having to perform expensive underwater trenching, a pipeline laid in such a manner with planned geometric imperfection accommodate the axial elongation arising from thermal expansion and contraction cycles. Under such a scheme, the change in length of the pipeline during a thermal expansion and contraction cycle manifests itself as a lateral deflection of the pipeline on the seabed and the process relieves additional axial stress that would otherwise be induced. In order to employ this scheme successfully, comprehensive understanding of both the evolution of lateral soil resistance as well as the tendency of pipeline to self-embed into the seabed is required. As an alternative to experimental investigation, numerical analysis can be performed to simulate the response of the system under a cyclic lateral displacement of the pipe. In order to circumvent the deficiencies of a Lagrangian-based finite element approach in analyzing such problems, an Eulerian based finite element technique is employed in this study.
Mid-Water Flowline Integrity Monitoring Strategy
Authors: Lim Tze King , Natarajan Shreenaath , An Pei
Published: January 2011

Mid-water flowlines are a more efficient way of product transfer between floating facilities in deepwater, with flow assurance benefits compared to traditional risers and seabed flowlines. However, the design process for mid-water flowlines is complex as these flowlines are subjected to both environment and vessel loading. During the operational phase, changes in vessel offsets, fluid composition or uncertainties in environmental data and vessel motion characteristics may lead to increased loads and escalated risk of failure. Various mid-water flowline configurations have been considered and the design issues such as strength and fatigue are discussed for each configuration. This paper also outlines an integrity monitoring strategy for mid-water flowlines to track system performance and manage the risk. A case study of such a monitoring system deployed on a mid-water flowline is also presented. This paper also discusses the methodology through which certain Key Performance Indicators (KPIs) are obtained to effectively manage the inspection intervals, and enable pre-cognition to trigger repair or remedial measures. The benefits of using a combined approach of monitoring and inspection to ensure integrity, improve operational efficiency, and develop cost-effective inspection regimes for mid-water flowlines are also presented.
Analysis of Hydrogen Sulfide Impact From Sour Gas Well Blowout in Offshore Platform
Authors: Zhu Yuan , Chen Guo-ming , Deng Hai-fa
Published: January 2011

Several sour gas leakage accidents have occurred in the offshore platform during the past decades, such as the Kab 121 platform in 2007, which caused serious consequences mainly resulting from the lethal toxicity of hydrogen sulfide (H2S). Under the threat of H2S, it is a challenge to exploit resource in the sour gas filed. Especially during the drilling operation, an abrupt blowout or kick could bring huge amount of H2S, envelop the platform and disperse in the cabins. The present paper is aimed at introducing our analysis of H2S dispersion both in the outer deck and inner mud treatment cabin so as to fully assess the potential poisoning during well blowout. The method we chosen was computational fluid dynamics according to the spatial environment characteristics of the offshore platform. First, we drew a comparison between accident consequences deriving from the wellhead configurations of an opened bell nipple and a sealed rotary blowout preventer (BOP) in the outer deck under various wind directions and speeds. The instantaneous concentrations and hazard zone distributions show that the second configuration is much better from the view of accident control. And the accident severity is much lower when the wind blows from the larboard, not from the prow for both configurations. As a result, the potential hazard zone would not envelop the entire platform with suitable platform position and arrangements of the mud return ditch, accommodation, helicopter deck et al. Then, the simulations of H2S dispersion in the mud treatment cabin were conducted in case of the closed outlet doors, opened outlet doors and sealed cabin with air ventilator working. An immediately dangerous to life level may come up in a short break with the door closed. In such a dangerous situation, H2S can only be made to disperse to other areas through the opened door or effectively ventilated away by means of a ventilator. It is a good practice to isolate the cabins with the potential H2S leakage and install ventilator. And a simple model was proposed to calculate the working time for the ventilator.
The Effect of Base Metal and Core Rod Carbon Content on Underwater Wet Weld Porosity
Authors: Andrade Luciano G. D. , Pessoa Ezequiel C. P. , Bracarense Alexandre Q. , Dias Weslley C. , Ribeiro Leandro F. , Liu Stephen
Published: January 2011

Porosity is a common defect observed in underwater wet welding. Several research programs have been developed to understand how pores form in order to mitigate the problem. No superficial pores and a limited number of internal pores (based on size) are important requirements to classify underwater wet welds according to the American Welding Society – AWS D3.6M standard. The main objective of this work is to study the effect of base metal and core rod carbon content on weld metal porosity. A pressure chamber with 20 atmospheres capacity was used to simulate depth with fresh water. To perform the welds, a gravity feeding system able to open an electric arc and deposit the weld automatically was used. Beads-on-plate were made using Direct Current Electrode Negative (DCEN) configuration on two base metals with different carbon contents (C2 – 0.1 wt. pct. and C7 – 0.7 wt. pct.) at 50 meters water depth. Commercial E6013 grade electrodes were used to deposit the welds. These electrodes were produced with core rods with two different carbon content (E2 – 0.002 wt. pct. and E6 – 0.6 wt. pct.) and painted with varnish for waterproofing. Samples were removed from the beginning, middle and end of the BOP welds and prepared following metallographic techniques including macroetching and image analysis for weld porosity. A data acquisition system was used to record current, voltage and welding time at 1.0 kHz rate. The porosity measurements indicated an increase of about 85% and 70% when E6 electrodes were used instead of E2 electrode on C2 and C7 steel plates, respectively. Simultaneously, the increase in porosity was followed by an increase in short circuiting events, an increase in weld bead penetration and a decrease in welding voltage. These observations seem to confirm, a direct effect of carbon content of the core rod on weld metal porosity and that porosity is associated with the CO reaction that can occur during metal transfer in that molten droplets carry gas bubbles to the welding pool. On the other hand, the increase of carbon content in the base metal was seen to decrease the porosity in the weld metal. This result can be related with the decrease in penetration observed when changing C2 to C7 plates. The smaller participation of carbon from the base metal in the weld pool reactions should then reduce the CO formation and, consequently, the amount of pores in the weld.
Multi-Scale Modeling of Wind-Wave Interaction in the Presence of Offshore Structures for Renewable Energy Applications
Authors: Liu Yi , Yang Di , Guo Xin , Shen Lian
Published: January 2011

We develop a multi-scale modeling capability for the simulation of wind and wave coupling dynamics, with a focus on providing environmental input for wind and wave loads on offshore structures. For the large-scale wind–wave environment, large-eddy simulation for the wind turbulence and high-order spectral simulation for the nonlinear ocean waves are dynamically coupled. For the local-scale air and water flows past the structure, we use a hybrid interface capturing and immersed boundary method. Coupled level-set/volume-of-fluid/ghost-fluid method is used to capture the wave surface. Immersed boundary method is used to represent the structure. The large-scale wind–wave simulation provides inflow boundary conditions for the local-scale air–water–structure simulation. Our simulation captures the dynamic evolution of ocean nonlinear wavefield under the wind action. The wind field is found to be strongly coupled with the surface waves and the wind load on a surface-piercing object is largely wave-phase dependent.
An Innovative Synthetic Mooring Solution for an Octagonal FPSO in Shallow Waters
Authors: Fan Mo , Li Da , Liu Tuanjie , Ran Alex , Ye Wei
Published: January 2011

An octagonal FPSO has been proposed for marginal oil and gas development in shallow waters. A shuttle tanker will be deployed near the FPSO during offloading operations. This new concept simplifies the design and manufacturing processes, yet maintains full production, storage, and offloading functions of a conventional ship-shaped FPSO. However, design of the mooring system for this floating unit imposes technical challenges due to: 1) high environmental loads expected on this unit, 2) large dynamic offsets of the unit in shallow waters, and 3) inadequate performance of catenary mooring systems in shallow waters. Thus, development of a viable station keeping solution becomes a key issue to the new concept FPSO design. In this paper, an innovative mooring system is designed to meet the challenges. The FPSO mooring system consists of pile anchors, bridle chains, anchorage buoys, and polyester ropes. Nine mooring lines are grouped into three bundles which evenly spread around the FPSO. The shuttle tanker is attached to the FPSO with a nylon rope hawser at the bow and secured to pre-installed anchorage buoys at the stern with two other nylon ropes. Analyses have been performed for the FPSO mooring system. It is concluded that the proposed mooring system is fully functional and effective.
Ultra Heavy Wall Linepipe X65: Ratcheting in Severe Cyclic Straining
Authors: Di Vito Luigi , Ferino Jan , Mannucci Gianluca , Lucci Antonio , Vitali Luigino , Marchesani Furio , Armengol Mariano , Novelli Paolo , Tintori Federico , Darcis Philippe , Izquierdo Alfonso , Quintanilla He´ctor
Published: January 2011

Tenaris and Centro Sviluppo Materiali (CSM) launched a Joint Industrial Project aimed at developing heavy wall line pipes. The suitability for very severe applications, involving high service pressures and temperatures, the latter causing large strain fluctuations, in presence of an aggressive sour environment, is analyzed both theoretically and experimentally, including small and full pipe models. The full project program aims at developing a new generation heavy wall product, supported by: a comprehensive laboratory analysis of the material response under severe mechanical loading in aggressive environment; and full scale testing program, including both pipe and girth weld. Both investigations are mainly addressed to basic understanding of impact on design criteria from interaction between severe loading and aggressive environment. Two papers have been already presented on this project, [2] and [3]. The present paper deals with the study, carried out in cooperation with Saipem Energy Services, aimed at setting up a tool for the prediction of ratcheting extent for the pipeline in pressure subjected to axial cyclic, even plastic, straining. In such conditions, ratcheting may develop in the circumferential direction, as a consequence of both material cyclic performance and bi-axial plastic flow. So, detailed characterization of material is required, as well as calibration of plastic performance parameters, particularly in relation to relevant modeling. The final objective of the study is to establish a threshold for the plastic strain development at peak load, beyond which circumferential ratcheting may develop. A numerical model was set up, on-purpose developed and implemented on commercial software, where reverse yielding is modeled by kinematic hardening referring to Von-Mises yield criterion. Use of relevant parameters describing/approximating the actual material response has been made, based on laboratory Multi Plastic Straining Cycling (MPSC) of pipe full thickness samples. Full scale testing of pressurized X65, 10 3/4″ OD × 46 mm WT linepipe has been performed including plastic axial and cyclic straining. A huge measurement campaign allowed to establish the relevant parameters that characterize the response from numerical modeling, facilitating the validation of the set up by comparing the actual ratcheting exhibited by the heavy wall pipe with predictions obtained by the model. Limits of current tools for numerical modeling are also shown, with some degree of dependence on applied straining sequence. Possible paths of numerical modeling improvement are then envisaged.
Numerical and Experimental Study of a Flexible Pipe Under Torsion
Authors: Merino He´ctor E. M. , de Sousa Jose´ Renato M. , Magluta Carlos , Roitman Ney
Published: January 2011

The torsional behavior of a 4″ flexible pipe is here studied. The pipe was subjected to clockwise and anticlockwise torsion and also to torsion combined with tension. For pure torsion, two different boundary conditions were considered: ends free to elongate and prevented from elongating. When tensional and torsional loads are imposed to the pipe, only analyses with ends prevented from elongating are carried out. In all cases, the response of the pipe is predicted with a three-dimensional nonlinear finite element (FE) model and with a classical analytical model. Experimental tests performed at COPPE/UFRJ are also employed to validate the theoretical estimations. The obtained results point out that the pipe is torque balanced for clockwise torsion, but it is not balanced for anti-clockwise torsion. Moreover, analytical models for axissymetric analyses assume that the layers of a flexible pipe are subjected to the same twist and elongation, but the FE results state that this hypothesis holds only for anti-clockwise torsion. Therefore, some differences were found between the FE and analytical models mainly when clockwise torsion is considered. Finally, due to its ability to deal with friction and adhesion between layers, the FE estimations agreed quite well with the experimental measures.
Design and Qualification of Fatigue Resistant Heavy Wall Threaded and Coupled Premium Connectors for Drilling and Production Riser Applications in Deepwater HPHT Dry Tree Systems
Authors: Sches Ce´line , Shilling Roy
Published: January 2011

In the late 2006, as a part of its GoM HPHT technology program, BP initiated with V&M the design and qualification of a 15k dual barrier dry tree production riser system capable of being installed in water depths up to 10,000 ft. This was driven by the fact that X-80 riser systems became so heavy that they were not considered workable, whereas switching to higher strength steel and T&C connector designs made the systems much lighter and became enabling technologies for dry trees. Developments concern an 11 3/4″ OD with 1.1″ wall thickness C-110 sour service resistant material as the inner riser rated to 15k, a 16″ OD with 1″ wall thickness Q-125 material as the outer riser rated to 10k, and a 21″ OD with 1″ wall thickness Q-125 material as the drilling riser rated to 10k. The specification called for all three connections to be designed with an external environmental metal to metal seal, and superior fatigue performance. Based on existing know-how on fatigue resistant T&C connectors, the development work started with the 11 3/4″ inner riser, with a need to accommodate existing design rules for such a heavy pipe. A comprehensive evaluation program was built, with a total of 39 samples including 5 design variations, and full scale tests combining Make & Break, sealability, fatigue, and thermal cycles. The qualification was completed with a connector achieving over 25 M&B and a stress factor less than 1.5 compared to DNV-B1 curve, that is a stress factor matching DNV-C. With success on the 11 3/4″ and some lessons learned along the way, focus was then shifted to the 16″ outer riser. Key issues were identified here concerning the surface treatment quality of the metal to metal seals when combining large sliding distance and high contact pressure. The 21″ drilling riser development is on-going. As we near full product qualification, we focus on final optimizations to ensure easy field running. This paper will prove the robustness of the design process elaborated to develop heavy wall riser T&C premium connectors, leading to outstanding fatigue performance and fatigue compliant internal and external environmental metal to metal seals. Such results prove the applicability of T&C for dry tree HPHT systems, and further establish the potential of T&C to be used for SCR and Flowline applications.
The Bayesian Networks Applied to a Steering Gear System Fault Diagnostics
Authors: Martins Marcelo R. , da Silva Daniel F. , Maruyama Fabio M. , Loriggio Fabio F. , Pedro Marcelo F. , Varela Marcelo
Published: January 2011

In this paper it is presented a brief description of a method that consists in using Bayesian Belief Network (BBN) created by converting Fault Trees (FT) to determine the most probable causes of a failure in a system given some evidence through observation. In addition, it is presented an example based on the steering gear system of a containership focusing on the cases in which the vessel is operating in restricted waters or performing the procedure for mooring/unmooring. The steering gear system was chosen due to its importance to restricted water navigation and to the mooring operation. The system must be completely available for these situations; otherwise, the ship security and the crew safety are implicated.
An Efficient Field Assessment of Offshore Pipeline Damage
Authors: Wang James , Eltaher Ayman , Jafri Syed
Published: January 2011

An offshore pipeline may experience overstress due to improper installation, an accident or other unplanned incidents. An assessment of potential damage in the pipeline is important, since it allows operators to determine whether the pipeline can operate under planned conditions, reduced conditions or must be repaired, which may have significant technical and financial consequences. However, such an assessment can be challenging because of the many unknown parameters in the field and pressing project schedule. Therefore, planning and conducting an efficient assessment study becomes particularly important under such circumstances. This paper describes an analysis methodology that addresses the following aspects of the pipeline damage assessment: relevant criteria, reconstructing and modeling the sequence of events, and required numerical simulations. Criteria that determine acceptability of the affected pipeline could be the original design criteria or less stringent fit-for-service criteria that, nevertheless, call for additional material information and more detailed analyses. The sequence of events and characteristics of the relevant loads are often not readily clear, and reconstruction of the events may constitute a significant part of the assessment study. The attempt to determine the level of pipe damage/overstress usually starts with simple approximations but oftentimes eventually requires sophisticated numerical simulations. A modeling approach that comprises gradual levels of details and necessary levels of accuracy and efficiency is presented and discussed in this paper.
Numerical Simulation of Cavities Flow
Authors: Hu Jing , Zhang Zhiguo , Feng Dakui
Published: January 2011

Flow across the cavity represents a simple geometry complex flow phenomena for many industry field. This paper presents a series of simulation results of both laminar and turbulent flows over cavities. Several important results and conclusions are reported. The mathematical model corresponds to the incompressible, Reynolds-averaged, Navier-Stokes equations plus a turbulence model, and the numerical simulation is performed using the SIMPLE algorithm.
Investigation on Suppression of Vortex-Induced Vibration Using Helical Strakes
Authors: Zhou Tongming , Razali S. F. Mohd. , Cheng Liang
Published: January 2011

While the effect of helical strakes on suppression of Vortex-Induced Vibrations (VIV) has been studied extensively, the mechanism of VIV mitigation using helical strakes is less well documented in the literature. In the present study, experiments were conducted in a wind tunnel at four velocities, i.e. 1.92, 3.83, 5.74 and 7.65 m/s. Strakes with a dimension of 10d in pitch and 0.12d in height were fitted onto a rigid cylinder of diameter d = 80mm, and subjected to a transverse air flow. Hotwire techniques were used to measure the instantaneous velocity fluctuations at various locations to explore the mechanism for VIV mitigation by using helical strakes. It was found that the helical strakes reduce VIV by about 98%. Unlike the bare cylinder which experiences lock-in over the reduced velocity of 5 ∼ 9, the straked cylinder does not show any lock-in region. In exploring the mechanism of VIV reduction by helical strakes, it was found that vortices shed from the straked cylinder are weakened significantly. The dominant frequency of the vortex structures along the spanwise direction of the bare cylinder was very stable. This is not the case for the straked cylinder wake, which differs by about 36% of the averaged peak frequency over the length of 3.125d along the cylinder axial direction, indicating that the vortex shed from the latter is out-of-phase and mismatching. This is supported by the phase shift between the velocity signals measured at two locations separated in the spanwise direction. The cross-correlation coefficients in the bare cylinder wake were much larger than that obtained in the straked cylinder wake, indicating that the correlation length of the former is much larger than that of the latter.
Calculation of Typhoon-Induced Sudden Siltation Using Effective Wind Energy in Yangtze Estuary
Authors: Kong Lingshuang , Wan Yuanyang , Gu Fengfeng , Qi Dingman , Wang Wei
Published: January 2011

The concept of effective wind energy is used in this study. The correlation among effective wind energy, wind and siltation of channel is derived. A formula is developed for calculation of channel siltation using effective wind energy. The formula is applied to calculate typhoon-induced sudden siltation in Yangtae estuary and good agreement with field measurements is obtained.