bluuebunny/crossref_metadata_2025 huggingface dataset:
Finite Element Analysis of Strain Concentration in Field Joint of Concrete Coated Pipelines
Authors: Nourpanah Nikzad , Taheri Farid
Published: February 2010

Realistic and accurate modeling of the strains developed in concrete coated pipelines is an important objective to offshore pipeline industry. This is because of the acceptance of the strain-based design methods and also the increasing demand on pipelines to operate under harsher environments/loading conditions. The problem has several sources of nonlinearity, namely: material plasticity, concrete cracking and crushing and concrete slippage on the steel pipe. In this paper, a framework and procedure for finite element (FE) modeling of concrete coated pipelines is presented and verified against test results available in literature. The mechanics of strain concentration at the Field Joint (FJ), where the coating has an abrupt discontinuity is described and studied via the verified FE model. These aspects are all described and modeled appropriately using the general purpose FE software ABAQUS, resulting in a realistic and accurate FE model which predicts the strain and stress distribution in the steel, concrete coating and the anticorrosion layer. Output results, presented in the form of variation of moment versus strain, longitudinal distribution of the axial strains, the maximum FJ strains, strain concentration factor as a function of global strain and relative slippage of concrete coating are reported and verified with comparison to test data. Good agreements, both in trend and also quantities are observed, thereby verifying the integrity of the framework suited for the further development, which would include a parametric study with the aim of developing practical design equations. Discussion on the circumferential distribution of shear stresses in the anticorrosion layer is also presented. FE results show a constant shear stress distributed nearly all along the circumference, in concert with the test results.
The Influence of Slope on the Stability of Pipelines Subjected to Horizontal and Vertical Loading on Clay Seabeds
Authors: Morrow Damian R. , Bransby Fraser
Published: February 2010

Stability under horizontal (H) and vertical (V) loading is an important design consideration for seabed lain subsea pipelines. From initial installation, extending through their design life, these pipelines are subjected to a combination of H and V loading due to various external and internal driving mechanisms. These mechanisms include self weight loading, forces applied during installation, temperature and pressure driven expansion and in some cases significant hydrodynamic loading. All these aspects need to be considered in design, requiring an understanding of the interaction between the pipeline and the seabed it rests upon, i.e. pipe-soil interaction. In the past, emphasis has been placed on empirical methods of considering pipe-soil interaction. Typically model testing has been used to consider vertical and subsequent horizontal load response. Recently, progress has been made away from purely empirical methods to include the derivation of theoretical upper bound solutions for combined H-V loading and the use of numerical analysis to calculate H-V stability envelopes. This and previous work relating to the H-V stability of pipelines has largely been confined to the case of a flat seabed with no consideration of the influence of seabed slopes. This paper presents a suite of finite difference analysis undertaken to investigate the influence of a seabed slope on pipeline H-V stability envelopes. Initially modeling considers a slope on weightless soil with subsequent modeling considering the additional influence of soil weight. Analysis comprised a series of displacement controlled excursion through H-V load space, defining stability envelopes for a range of conditions. For a weightless soil the pipeline stability envelope was seen to rotate through H-V load space reducing vertical resistance to penetration and producing significant asymmetry in the horizontal load response. In addition to this rotation consideration of soil weight introduced a change in the geometry of the stability envelope. The results presented in this paper suggest that the influence of seabed slope on pipe soil interaction and the stability envelope in H-V load space is significant and worthy of consideration in design.
Analysis of Postbucking Drillstring Vibrations in Rotary Drilling of Extended-Reach Wells
Authors: Tikhonov Vadim S. , Safronov Alexander I.
Published: February 2010

One of the most serious concerns of extended-reach drilling is the dynamic behavior of the drillstring and cleaning of well. Good cleaning requires an increased angular speed. However, at higher rotary speeds, the drill string sections lying on the borehole horizontal sections tend to buckle, first, in the form of “snake”, sliding up and down the borehole bottom wall, and then in the form of whirling as the angular velocity increases. This paper presents the 3D nonlinear dynamic model of drillstring in a wellbore of 3D profile. The model suggests the possible contact/lift-off of drill pipes with/from the wellbore wall. The interaction of lateral, torsion and axial vibrations is taken into account. The relation between the normal component of contact force and the deformation of the wellbore wall is taken as quadratic-elastic. The friction force is described based on a hysteretic dynamic model. The friction force model also takes into account the transition from a sliding to a whirling. The equations of the drillstring dynamics are solved numerically using the method of lines. The DYNTUB computer program is developed to analyze the drillstring time-varying processes under different loading. The program is used to study the effects of the angular velocity, compression load, torque, friction factor, well profile, and availability of connectors on the drillstring dynamic behavior.
Modelling the Installation of Stiffened Caissons in Overconsolidated Clay
Authors: Westgate Z. J. , Tapper L. , Lehane B. M. , Gaudin C.
Published: February 2010

Design of suction caissons for installation in overconsolidated clay presents several geotechnical engineering challenges. These include (i) predicting the installation resistance and required ‘suction’ pressure, (ii) ensuring adequate skirt length to account for vertical plug heave, and (iii) accommodating the structural engineering stiffening requirements and their effects on the penetration resistance and plug heave. A suite of centrifuge tests in overconsolidated kaolin clay was carried out to investigate the effects of stiffener geometry on penetration resistance during direct jacking and suction installation. Three caisson geometries were compared: caissons with (i) no stiffeners, (ii) horizontal stiffeners only and (iii) both vertical and horizontal stiffeners. Results show negligible differences in penetration resistance between jacked and suction installation for each caisson type. The magnitude of soil heave within the caisson is seen to be highly dependent on the level of applied suction as well as on the volume of the stiffeners. Observations during and following testing indicated that minimal flow-round of the overconsolidated clay occurred for skirts with horizontal stiffeners. These included (i) linear penetration resistance profiles following penetration of the lowest horizontal stiffener, (ii) a wedge of clay observed only below the lowest horizontal stiffener following extraction, and (iii) unsupported plug heave heights following penetration. A comparison of measured data with back-calculated resistance factors suggests that current design methods adequately predict the measured penetration resistance assuming zero flow-round conditions, implying additional end bearing of the upper horizontal stiffener during penetration was negligible.
Quantitative Environmental Assessment for Deep-Sea Mining: Status and Approaches
Authors: Yamazaki Tetsuo
Published: February 2010

Deep-sea mining has been a subject of interest for several groups and countries for over four decades, due to its potential for the economic recovery of large reserves of minerals that would provide an alternative resource of strategic metals for industrial development. A deep-sea mining operation will offer a variety of challenges, owing to deep-sea mineral occurrences, extreme physical and chemical conditions and unknown environmental settings. Owing to growing concern for the environmental impact of deep-sea mining, multi-disciplinary environmental studies have been progressive in many countries. The historic approaches in the world are summarized. The important role of quantified environmental assessment for deep-sea mining is introduced. Some efforts necessary for keeping benthic habitat safe and sustainable in the coming commercial mining phases are discussed.
Validation of a 3-Dimensional Finite Element Analysis Model of Deep Water Steel Tube Umbilical in Combined Tension and Cyclic Bending
Authors: Le Corre Vincent , Probyn Ian
Published: February 2010

This paper focuses upon validation of the 3-D FEA model for cyclic bending under tension load case. An important aspect of accurately modelling the behaviour is the complex stick, partial slip and full slip behaviour of the internal components. Particular attention is paid to the resisting moment resulting from internal friction, known as the friction moment. The effect of increasing tension on the friction moment is studied. The kinematics of sliding are compared to analytical models developed for helically wound structures, such as flexible pipes, and show a very good correlation that confirms the accuracy of the model. Also, the mean axial strain of the steel tubes due to the friction induced by this sliding is highlighted. The hysteretic curves of the axial strain in steel tubes subjected to cyclic bending under tension are derived and validated against full scale experimental data.
Experimental Validation of an Absorbing Wavemaker Controller
Authors: Carneiro Mario L. , de Mello Pedro C. , Tannuri Eduardo A. , Simos Alexandre N.
Published: February 2010

A new Active Absorption Basin (AAB) is under development, and will be used for the calibration of simulation models developed in the Numerical Offshore Tank of University of Sa˜o Paulo (TPN-USP). The AAB will be equipped with 148 independent flap-type wave makers arranged around its 14×14m rectangular section. Due to the small dimensions of the tank, it is necessary to use active absorption, in order to avoid the contamination of the wave field by the reflected waves, allowing the emulation of the infinite multi-directional ocean behavior. The wave maker actuation feedback control is based on the measurement of surface elevation at each flap, as proposed by [1]. The generation-absorption algorithm disregards the evanescent wave modes that are present in the sensor measurements. In the present paper, the absorption algorithm was tested in a 2D wave flume. A wave probe array installed in the middle of the flume was used to check the quality of the absorption algorithm. With this experiment, several implementation problems could then be identified and solved. High-frequency oscillations and drift of the flaps were observed using the original algorithm. Novel terms were then introduced, in order to reduce the overall gain of the controller, include the effect of the evanescent wave and eliminate the drift of position. The modified version of the algorithm was then used in an extensive calibration procedure for regular waves, in order to improve the absorption efficiency. Reflection coefficients smaller than 11% were obtained for waves up to 1,5Hz, proving the efficiency of the method.
Numerical Non-Reflecting Irregular Wave Flume Based on VOF Method
Authors: Ren Bing , Li Xuelin , Han Peng , Wang Yongxue
Published: February 2010

A numerical irregular wave flume is developed using VOF method in conjunction with Reynolds equations. An active absorbing wave-maker based on linear wave theory is set on the left boundary of the wave flume to absorb the re-reflected waves. A sponge layer is set on the open boundary to absorb the outgoing waves. The numerical results of regular and irregular waves using the active absorbing-generating boundary are compared to the numerical results using the ordinary generating boundary to verify the performance of the active absorbing-generator boundary. The linear damping coefficient is used in the sponge layer. The damping characteristics of the sponger layer implemented in the wave flume are discussed. The computed wave spectra are compared with the target spectra.
Numerical Study of Green Water on a Freely Moving Object
Authors: Liang Xiufeng , Yang Jianmin , Yang Chi , Ferrant Pierre
Published: February 2010

Green water effect is a highly nonlinear free surface problem. It can cause severe damage on floating marine structures. Therefore, it is of great importance to be able to predict the green water occurrence on the freely-moving floating marine structures and the associated dynamic loads acting on them. In the proposed paper, a solution scheme for solving the green water problem in the numerical wave tank with commercial CFD software FLUENT will be presented. This solution scheme consists of the decompositions of the computational domain, and an automatic updating method for the motion of the moving object. The numerical wave tank is set up by using a plunge-type wave-maker to generate waves and by adding source terms in the dissipation zone to eliminate the reflected waves. The computational domain is divided into dynamic zones, stationary zones, dense rigid zone that is useful in capturing the green water details, and the fine mesh zone near the free surface. The mesh in the vicinity of the moving object (dense rigid zone) is refined to better model the green water problem. The motion response of the object is obtained based upon the solution of the general equations of rigid body motion (6-DOF) and the hydrodynamic forces acting on the object. In order to compare with the existing experimental data, a 2D object is used in the numerical study. The motion of the object is restrained from surge, which means only heave and pitch motions are allowed. The details of the green water occurrences including water running up onto the deck, water propagating on the deck, water impacting the vertical wall, water running up along the vertical wall, wave breaking and water spray have been modeled successfully. The quantitative analysis on the impact load on deck and the upper structure has also been carried out. The comparison of the numerical results and experimental measurements shows that the current numerical solution scheme is robust and reliable in modeling green water problem.
Modeling the Random Environment of Offshore Structures
Authors: Ellermann Katrin
Published: February 2010

When analyzing the dynamical behavior of offshore structures, several aspects of the random nature of environmental forces are of interest: The time series of the wave surface or wind forces could serve directly as an input to a nonlinear set of equations of motion. The spectral properties have to have certain characteristics corresponding to a given location and certain environmental conditions. Many environmental forces are inherently random in nature and various models for the numerical description have been presented in literature. Some of these approaches are essentially based on the work of Rice [1] who described two techniques: the Deterministic Spectral Amplitude and the Nondeterministic Spectral Amplitude. While they were initially intended to characterize electrical signals, they are widely used to model ocean waves as Gaussian stationary processes. Both techniques are superposition or summation models. Later, numerical methods have been developed based on filtering techniques which use white noise to generate a signal with the required spectral characteristics in time domain. These methods include autoregressive (AR) and moving average (MA) filters as well as a combination of both. The quality of wave models is restricted by the availability of data of the seaway they are supposed to describe. Even though the amount of wave data from various sensors has increased significantly since the development of the Pierson-Moskowitz spectrum, some nonlinear and transient effects in the wave motion are still hard to capture in suitable models. This talk addresses different techniques for the description of stochastic environmental forces and the effect of these descriptions on the analysis of dynamical systems. Examples illustrate the various mathematical methods.
Calculation of Arrival Intensity of Ridges Accounting for the Relative Angle Between Ridge Direction and Ice Drift Direction
Authors: Trumars Jenny , Lo̸set Sveinung
Published: February 2010

The purpose of the study is to investigate the effect of the relative angle between ice ridges and sea ice drift directions on the arrival rate of ridges. The arrival rate is of importance both for estimating the load conditions at a site and for possible ice management connected to the operation. If the number of encounters increases, the probability of encounter of an extreme ice feature and load increases. A Monte Carlo simulation has been made to calculate the ridge arrival intensity for input formulated as distributions. In probabilistic calculations of design loads today the average arrival intensity is used and the ridge directions are assumed to be uniformly distributed. The implications of accounting for the varying arrival intensity due to the distribution of the relative direction of ridges to velocity on the design load are discussed.
Pipeline Design Methodology With Respect to Internal Corrosion
Authors: Brækstad Lars Lo̸berg , Hval Morten , Halvorsen Vidar Henrik , Holden Ole Magnus
Published: February 2010

The present paper originating from the Ormen Lange project, presents a methodology on how to treat the local wall thickness reduction due to internal corrosion with respect to different design criteria for production flowlines and spools. The methodology presented was implemented in pipeline design for the deepwater part of the project where water depth ranged from 250 m to 875 m. The combination of long design life and mildly corrosive well fluid requires a rather high corrosion allowance. With up to 10 mm general corrosion allowance accumulated over the 50 years design life of the pipelines, together with deep water, free spans, global buckling and possibilities for hydrate/ice formation inside the pipe, it would result in a much too conservative design if the full corrosion allowance is used for all aspects of pipeline design. In order to achieve a more realistic estimate of the effect of internal corrosion and a more optimal pipeline design, the internal corrosion was treated in different ways depending on where the corrosion is expected, and what design criteria is considered. By carrying out 2D and 3D finite element analyses of the pipe cross section with the predicted local corrosion distribution, where also the combined loading effects are included, it can be shown that for local buckling and propagating buckling during operation, a significant reduction in the average corrosion depth can be considered in design calculation. Therefore an equivalent corrosion depth, where the corrosion is distributed evenly for the different sections of the route can be estimated. This value can be used directly in the design calculations and allows optimisation of nominal wall thickness, on-bottom stability calculations, free span lengths, global buckling and cost driving factors such as pre- and post-lay seabed intervention and installation methodology.
Time Domain VIV Analysis of a Free Standing Hybrid Riser
Authors: Liu Nicole , Cheng Yongming , de Wilde Jaap , Burke Roger , Lambrakos Kostas F.
Published: February 2010

A free standing hybrid riser (FSHR) is a proven solution for deepwater floating production systems. In this system, a submerged buoyancy can supports and tensions a vertical riser. The riser top is connected to a floating production system through a flexible jumper. The FSHR has been used in West Africa and Brazil and will be put into application in the Gulf of Mexico. Experimental and analytical efforts are continuing to better understand the vortex-induced vibration (VIV) response of this riser system. This paper presents a comparison of experimental and numerical results of the VIV response of a FSHR. The analysis is performed with a time domain VIV code ABAVIV, which uses the finite element software package ABAQUS to calculate the response from the VIV forcing. Unlike frequency domain VIV codes, ABAVIV captures structural nonlinearities and the transient nature of the VIV phenomenon. Comparisons between numerical and experimental results for buoyancy can VIV response and loading at the bottom of the riser are presented and show generally good agreement. The relative contributions of buoyancy can and riser VIV to the overall system response are investigated. The paper will also include calculated VIV response from frequency domain methods.
Pipeline Bundle: A Smart Solution for Infield Transportation—Part 1: Overview and Engineering Design
Authors: Song R. , Kang Z. , Qin Yuanlong , Li Chunrun
Published: February 2010

Pipeline bundle system consisting of carrier pipe, sleeve pipe and internal flowlines offers innovative solution for the infield transportation of oil and gas. Due to its features, pipeline bundle offers a couple of advantages over conventional pipeline in particular for cases where multi-flowlines and high thermal performance are of great interests. The main benefits and advantages of such system include excellent thermal performance to prevent wax formation and hydrates, multiple bundled flowlines, mechanical and corrosion protection, potential reuse, etc. With the developments of offshore oil and gas industries, more and more hydrocarbon resources are being explored and discovered from shallow to deep water. Pipeline bundle system can be a smart solution for certain applications, which can be safe and cost effective solution. The objective of this paper is to overview pipeline bundle technology, outline detailed engineering design issue and procedure. Focus is given to its potential application in offshore for infield transportation. Engineering design principles and procedures for pipeline bundle system has been highlighted. A companion paper addressed the details of the construction and installation of pipeline bundle system. An example is given at the end of this paper to demonstrate the pipeline bundle system concept and its application.
Experimental and Theoretical Study of Three-Dimensional Effects on Vertical Wave-in-Deck Forces
Authors: Baarholm Rolf
Published: February 2010

In order to validate theory for computing wave-in-deck loads of offshore platforms, a small scale model test campaign of wave impact on an idealized platform deck is performed at Towing Tank no. II at MARINTEK. The main objectives of the tests were to assess three-dimensional effects and to better understand the effect transverse and longitudinal structural members have on the fluid flow. The emphasis in the present paper is to demonstrate the three-dimensional effects. Model tests of the same structure were performed for both two-dimensional and three-dimensional flow conditions. The model test results show that three-dimensional effects significantly reduce the wave-in-deck loads. In particular, for the water exit phase, the vertical force is almost halved due to three-dimensional effects. Two different two-dimensional methods are used to study water impact on the deck: one method is based on a generalization of Wagner’s impact theory while the latter is a simple von Karman approach. Moreover, a three-dimensional correction is introduced. Comparisons show that the Wagner based method yields good results for the water entry phase, but it overestimates the water exit force and underestimates the duration of the wave-in-deck event. The von Karman type approach underestimates the water entry force.
Statistical Investigation of the Nonlinear Behavior of Structures Operating Offshore
Authors: Reimers Juergen , Ellermann Katrin
Published: February 2010

Due to the increasing amount of ship and offshore operations taking place in the ocean environment, the amount of reports concerning damage, loss of cargo or even loss of human lives increases, too. The reasons for these incidents have been a subject of intensive research for many years. Recently, the aim of some research concentrated on extreme wave phenomena such as ‘rogue waves’ or ‘the three sisters’. These phenomena are a severe danger, but they do not play a decisive role for most of the incidents happening at sea. More often, the reason for endangerment of structures in the environment is a fluid-structure-interaction that leads to unstable dynamical system behaviour. Including nonlinear effects in the calculations, through statistical investigation of structures in waves, it can be shown that critical behaviour of ships and structures can occur without the absolute necessity of heavy sea conditions or the occurrence of dangerous sea phenomena. The reason that many of these incidents do not lead to severe accidents lies in the experience of the master and his crew and their ability to change system parameters in a way that prevents the catastrophe. The aim of this paper is to show the current state of development of a program that uses a Monte-Carlo-Simulation technique based on a common panel-method for the creation of added masses and added damping with hydrodynamic coupling to predict the behaviour of the structure in several wave conditions.
An Experimental Investigation of Wave Impacts on the Deck of a Gravity Based Structure
Authors: Roos Jannicke , Swan Chris , Haver Sverre , Gudmestad Ove T.
Published: February 2010

The occurrence of wave impacts is a critical feature in the design and re-assessment of many offshore structures. With evidence of increasing storm severity, and with subsidence an important characteristic of some mature fields, the quantification of impact loads arising on both the columns and the underside of these structures remains a difficult but important issue. In contributing to this debate, this paper presents the results of a physical model study of a gravity based structure. This comprises an arrangement of storage caissons located on the sea bed, with four large diameter surface-piercing columns supporting the topside structure at a significant height above mean sea level. The purpose of the study was to provide new physical insights into the nature of the wave-structure and the local wave-wave interactions. This has been achieved by employing a large number of traditional wave gauges within the vicinity of the model structure and by complementing this data with two new measuring techniques in order to quantify the behaviour of the water surface in close proximity to the columns. These observations provide a clear understanding of how a large volume structure modifies the incident waves and why wave-structure and subsequent wave-wave interactions lead to a higher probability of wave impacts on the overlying deck. In particular, considerable attention was paid to the nature of the wave run-up on the front face of the columns. The results show that far from being a highly localised effect, involving a thin sheet of water, the run-up associated with a steep wave can involve significant volumes of water, traveling at very high velocities, leading to the occurrence of large impact pressures acting over substantial areas. Estimates of the run-up velocity are coupled with slamming coefficients to provide load predictions which are comparable to the measured wave-in-deck loads. Perhaps surprisingly, it is also shown that the highest and steepest waves do not always cause the largest impacts.
Non-Linear Wave Loads Acting on Obliquely Slowly Advancing Platform
Authors: Nihei Yasunori , Sugimoto Sota , Tsubogo Takashi , Bao Weiguang , Kinoshita Takeshi
Published: February 2010

It is necessary to evaluate wave drift force for ships advancing obliquely. There are some approaches, for instance the strip method, solving the Navier-Stokes equation directly in the fluid domain (CFD), potential theory and so on. In the present study, the non-linear wave loads acting on the ship with constant oblique forward speed is considered based on the potential theory. Consistent perturbation expansion based on two parameters, i.e. the incident wave slope and the ratio of the forward speed compared to the phase velocity of the waves, is performed on a moving frame (body-fixed) coordinate system to simplify the problem. So obtained boundary value problems for each order of potentials is solved by means of the hybrid method. The fluid domain is divided into two regions by an artificial circular cylinder surrounding the body. The potential in the inner region is expressed by an integral over the boundary surface with a Rankin source as its Green function while it is expressed in the eigen function expansion for the outer region. Consequently, the boundary value problems can be solved efficiently. In the present paper, the authors will discuss the effects of the obliquely advancing on the wave drift force in a diffraction wave field up to the order proportional to the advancing speed. An ellipsoid model is used in the calculation and the wave drift force is evaluated for various Froude number.
Real-Time Current and Wave Monitoring Using Acoustic and Iridium Satellite Links
Authors: Shih H. H. , Sprenke James , Trombley David , Cassidy John , Mero Tom
Published: February 2010

The U.S. National Ocean Service (NOS) of NOAA maintains and operates a Physical Oceanography Real Time System (PORTS®) in the Nation’s major ports, harbors and bays. The traditional method of obtaining real-time data from bottom mounted instruments is via underwater cable link. However, this is vulnerable to damage and costly to install and maintain. This paper describes an approach utilizing acoustic and Iridium satellite links to report in real-time wave and current data. The system consists of an ocean bottom instrumentation platform and a U.S. Coast Guard Aid-to-Navigation buoy for data relay. The bottom platform contains a Nortek 1 MHz Acoustic Wave and Current profiler (AWAC) with an integrated Nortek Internal Processor (NIP), a LinkQuest omni-directional UWM2000H underwater acoustic transmitting modem, an ORE acoustic release-based recovery component, and a Teledyne-Benthos UAT-376/EL acoustic transponder. The surface buoy supports an omni-directional UWM2000H receiving modem, an Iridium antenna, and an electronic box containing an Iridium modem, a controller, battery packs, and temperature and voltage sensors. The AWAC measures current profiles along the vertical water column at 30-minute intervals and surface waves at hourly intervals. The NIP processes a set of user selected wave and current parameters and sends these data to the controller on the surface buoy through acoustic modems. The data are then transmitted via Iridium satellite to remote offices in real-time. Sample measurement results and reference data from a near-by Datawell’s Waverider directional wave buoy are presented. The Waverider is operated by the U.S. Army Corps of Engineers (USACE) and Scripps Institution of Oceanography (SIO). Several unique system design features and interesting wave phenomenon observed at the measurement site are discussed. The goal of this project is to demonstrate the performance of AWAC, NIP, shallow water acoustic modems, and Iridium satellite in real-time data telemetry.
Study on the Residual Strength Assessment Method on Corroded Subsea Pipeline Based on Reference Stress Method
Authors: Li Hui , Pan Xiaobing , Ren Huilong , Feng Guoqing
Published: February 2010

In this paper, the reference stress method is adopted in the residual strength assessment of corroded subsea pipeline. Through the monitoring of the von Mises stress σlocal in the minimum cross section, the relationship between the stress response and input pressure is found. Then, based on this relationship, a simple and effective method to assess the residual strength of corroded subsea pipeline is proposed. Through the comparison with experimental results, the accuracy and reliability of this method is confirmed.
Thermo-Mechanical Design of Canapu PIP System
Authors: Solano Rafael Familiar , de Azevedo Fa´bio Braga , Carr Malcolm , Tindall Leanne , Dolinski Anderson , Valer Carlos Eduardo Ingar
Published: February 2010

This paper discusses the thermo-mechanical design of the pipe-in-pipe (PIP) flowline installed in the Canapu field, located in Espi´rito Santo State, offshore Brazil. The pipeline is approximately 20km in length and connects the gas producing well 4-ESS-138 positioned in a depth of 1608m to Cidade de Vito´ria FPSO, located in Golfinho field. The Canapu PIP will operate under high pressure and temperature (HP/HT) conditions and is laid on the seabed. Due to the operational conditions, the thermo-mechanical design evaluated the susceptibility of the pipeline to the phenomenon of lateral buckling and pipeline walking in addition to free spanning and on-bottom stability. The lateral buckling behavior of the PIP is the major challenge for the design. It can be a safe and effective way to accommodate the thermal expansion of a hot pipeline, however high stress and strains can be developed in the buckles and a conventional stress based approach is not suited to design a pipeline that buckles laterally. The conventional stress limits are therefore relaxed and replaced by a strain limit. For this the methodology and recommendations of the SAFEBUCK JIP were adopted. The thermo-mechanical analysis selected a buckle initiation strategy based on distributed buoyancy. The strategy combines three distributed buoyancy triggers along the route together with the beneficial effect of the bathymetric out-of-straightness. The analysis shows that this initiation strategy is robust and highly reliable. From the start, this project represented a great challenge for Petrobras; it is the first PIP in Petrobras; has a low value specified for OHTC; and the pipeline is susceptible to lateral buckling. Besides all that, since the Canapu project was included among the priorities of Petrobras Plangas, it was executed as a fast track project.
Numerical Study on the Interaction of In-Line and Cross-Flow VIV
Authors: Tang Shizhen , Huang Weiping
Published: February 2010

The fatigue damage induced by in-line vibration and cross-flow vibration was addressed in this paper using a statistical methodology and also the amplitude ratio. Traditionally, engineers have concentrated on cross-flow vibrations, assuming that in-line oscillations are less important. In-line amplitudes are generally lower, but the high-frequency nature of these oscillations can result in significant fatigue damage. The ratio between amplitude of in-line oscillation and cross-flow vibration in four different current velocity was studied, and also be analyzed by statistical method. For the fatigue analysis, the ratio between damage of in-line and cross-flow was obtained, the maximum ratio curve and the mean ratio curve were presented. The conclusions presented the fatigue damage caused by in-line vibration couldn’t be neglected, especially in low velocity.
Positioning of Sea/River Routes as Effective Means of Access for Disaster Relief in Waterfront Metropolitan City
Authors: Koga Takahiro , Kondo Takeo , Yamamoto Kazukiyo , Egami Kazuya , Hashikawa Takashi , Orimo Ryousuke
Published: February 2010

The Central Disaster Management Council of the Japanese Cabinet Office estimates that a class-M7 earthquake will occur in Metropolitan Tokyo or the Tokai area within the next 30 years. In 1995, Japan suffered devastating damage from the Great Hanshin-Awaji Earthquake and has since been devoted to disaster management. Since there has been no report anywhere in the world on a sea-based relief system, our research will lead to a review of ocean spaces in terms of their value in waterfront metropolitan cities. In this research, we have explored the feasibility of a relief system utilizing Entertainment and Party Boat (EPB) which can cover areas from the sea to rivers, and we investigated navigable routes of rivers to suggest effective utilization of ocean spaces and river areas in the event of disaster. As a result, we determined the rescue potential drawing upon EPB. A river survey was also conducted to classify navigable routes by boat size.
Casing Point Selection for Drilling Operations at Shallow Depths
Authors: Paknejad Amir Saman , Schubert Jerome J. , Amani Mahmood
Published: February 2010

In shallow sediments, unlike deep sediments with elastic behavior, the failure mechanism of the casing shoe is strongly affected by the plasticity of the rock. Hence, the common practice in casing design which is based on using the pore pressure and fracture pressure gradients plots is not applicable in shallow sediments. Moreover, because of the plastic behavior of the sediments, the interpretation of Leak-Off Tests (LOT) in Shallow Marine Sediments (SMS) could be inconclusive. Therefore, because of uncertainties in prediction of formation fracture and pore gradients, the conductor and surface casing setting depths have always been subject to debate. Also, incorrect interpretation of LOT would lead to costly problems that might jeopardize well progress such as; well control issues, unnecessary squeeze jobs, premature setting of casing, and lost circulation problems. Two of the most important factors in any design are safety and cost. Since safety is one of the most important concerns during drilling an offshore well, planning a design based on the well control aspects would be an appropriate approach to come up with a safe and better design. A well control simulator was used to plan for well control situations. In this paper, the results were generalized for different design scenarios and a simple design method is presented. Also, a new method, supported by field data from LOT in SMS, is presented to accurately analyze casing shoe leak-off pressure in the SMS. A safe design based on the optimum lengths of conductor and surface casing would enable the operator to handle possible formation kicks. Extension of this method to well design in general suggests the potential for safer drilling operations and cost optimization.
Friction Factor Estimation for Turbulent Flows in Corrugated Pipes With Rough Walls
Authors: Pisarenco Maxim , van der Linden Bas , Tijsseling Arris , Ory Emmanuel , Dam Jacques
Published: February 2010

The motivation of the investigation is critical pressure loss in cryogenic flexible hoses used for LNG transport in offshore installations. Our main goal is to estimate the friction factor for the turbulent flow in this type of pipes. For this purpose, two-equation turbulence models (k–ε and k–ω) are used in the computations. First, fully developed turbulent flow in a conventional pipe is considered. Simulations are performed to validate the chosen models, boundary conditions and computational grids. Then a new boundary condition is implemented based on the “combined” law of the wall. It enables us to model the effects of roughness (and maintain the right flow behavior for moderate Reynolds numbers). The implemented boundary condition is validated by comparison with experimental data. Next, turbulent flow in periodically corrugated (flexible) pipes is considered. New flow phenomena (such as flow separation) caused by the corrugation are pointed out and the essence of periodically fully developed flow is explained. The friction factor for different values of relative roughness of the fabric is estimated by performing a set of simulations. Finally, the main conclusion is presented: the friction factor in a flexible corrugated pipe is mostly determined by the shape and size of the steel spiral, and not by the type of the fabric which is wrapped around the spiral.
Discrete and Analytic Model Predictive Control for Path Following of Underactuated Ships
Authors: Wang Xiaofei , Zou Zaojian , Li Tieshan , Luo Weilin
Published: February 2010

The control problem of underactuated surface ships and underwater vehicles has attracted more and more attentions during the last years. Path following control aims at forcing the vehicles to converge and follow a desired path. Path following control of underactuated surface ships or underwater vehicles is an important issue to study nonlinear systems control, and it is also important in the practical implementation such as the guidance and control of marine vehicles. This paper proposes two nonlinear model predictive control algorithms to force an underactuated ship to follow a predefined path. One algorithm is based on state space model, the other is based on analytic model predictive control. In the first algorithm, the state space GPC (Generalized Predictive Control) method is used to design the path-following controller of underactuated ships. The nonlinear path following system of underactuated ships is discretized and re-arranged into state space model. Then states are augmented to get the new state space model with control increment as input. Thus the problem is becoming a typical state space GPC problem. Some characters of GPC such as cost function, receding optimization, prediction horizon and control horizon occur in the design procedure of path-following controller. The control law is derived in the form of control increment. In the second algorithm, an analytic model predictive control algorithm is used to study the path following problem of underactuated ships. In this path-following algorithm, the output-redefinition combined heading angle and cross-track error is introduced. As a result, the original single-input multiple-output (SIMO) system is transformed into an equivalent single-input single-output (SISO) system. For the transformed system, we use the analytic model predictive control method to get path-following control law in the analytical form. The analytic model predictive controller can be regarded as special feedback linearization method optimized by predictive control method. It provides a systematic method to compute control parameters rather than by try-and-error method which is often used in the exact feedback linearization control. Relative to GPC, the analytic model predictive control method provides an analytic optimal solution and decreases the computational burden, and the stability of closed-loop system is guaranteed. The path-following system of underactuated ships is guaranteed to follow and stabilize onto the desired path. Numerical simulations demonstrate the validity of the proposed control laws.
Partial Strake Coverage Vortex-Induced Vibration Benchmarking Using SHEAR7v4.5
Authors: Marcollo Hayden , Vandiver J. Kim
Published: February 2010

A VIV benchmarking study was undertaken using SHEAR7v4.5 against NDP high mode VIV response laboratory data. The purpose of which was to derive an improved set of modeling parameters for partial strake coverage cases whilst not comprising previous accuracy of shear flow bare riser response predictions. Fifty percent (50%) partial strake coverage experimental data was utilized from both uniform and shear flow conditions while bare data was also included in the activity for reference purposes. The results showed that such an activity can derive an improved set of modeling parameters that significantly improve the ability to match experimental results and also highlight where future improvement efforts can be targeted.
Experimental Study of a Radial Turbine Using Floating Nozzle for Wave Energy Conversion
Authors: Konno Toshio , Nagata Yoshihiro , Takao Manabu , Setoguchi Toshiaki
Published: February 2010

The objective of this study is to propose a new radial flow turbine for wave energy conversion and to clarify its performance by model testing under steady flow condition. The proposed radial turbine has a rotor blade row for unidirectional airflow and two guide vane rows. The guide vane rows are named ‘floating nozzle’ in the study. The guide vane rows slide in an axial direction and work as nozzle in the turbine alternately for bi-directional airflow, so as to rectify bidirectional airflow and to make uni-directional airflow. The radial flow turbine with a diameter of 500mm has been manufactured and investigated experimentally under steady flow condition generated by a wind tunnel using a piston/cylinder system with a diameter of 1.4m. As a result, it has been found in the study that the peak efficiency of the proposed radial turbine is approximately 57% and the rotational speed of this turbine is considerably lower that that of Wells turbine. Further, the effect of nozzle setting angle on the turbine performance was investigated and clarified in the study.
Transient Mechanistic Model for Slug Damper/Gas-Liquid Cylindrical Cyclone (GLCC©) Compact Separator System
Authors: Pereyra E. , Gomez L. , Mohan R. , Shoham O. , Kouba G.
Published: February 2010

A dynamic model and a simulator have been developed for the Gas-Liquid Cylindrical Cyclone/Slug Damper (GLCC©-SD) system, for the prediction of its flow behavior under transient slugging flow conditions. Separate dynamic models and simulators are developed for the GLCC© and the SD units, which are integrated together with a slug generator model/simulator into an overall model/simulator for the GLCC©-SD system. Two numerical schemes are utilized for the developed integrated simulator, namely, fixed time step and variable time step schemes. Simulation examples are presented for the GLCC©, SD and integrated GLCC©-SD system, for the prediction of their performance under transient flow conditions. The GLCC©-SD simulation results demonstrate clearly the advantage of this system in dampening and smoothing the liquid flow rate under slug flow conditions, providing fairly constant flow rate at the GLCC© outlet liquid leg. The developed GLCC©-SD simulator can be extended to other separators, such as the gravity vessel separators and liquid hydrocyclones.
Indium oxide thin film transistors fabricated by low-energetic ion bombardment technique at room temperature
Authors: Chu A. K. , Hong T. I. , Tien W. C.
Published: February 2010

The authors report on InOx transparent thin-film transistor (TTFT) fabricated by low-energetic ion bombardment technique at room temperature. The InOx TTFTs were prepared using a coplanar bottom gate configuration with indium tin oxide (ITO), SiNx, and InOx thin films as the electrode, gate dielectric, and channel, respectively. The quality of the films could be significantly improved by eliminating bombardment of energetic particles created in the discharge processes using a prolonged target-to-substrate distance. The target-to-substrate distance for depositing SiNx was 15cm, and 18cm for depositing ITO and InOx. The leakage current density of the 180nm thick SiNx films under 1.0MV∕cm field strength was less than 1nA∕cm2. The C-V measurement of the Al∕InOx∕p-Si∕Al capacitor structure showed that no hysteresis voltage was observed from the high-resistivity InOx films. This indicated that the electrical defects of the 150nm thick InOx channels could be reduced using the long-throw deposition technique. In addition, the InOx TTFTs were engineered to operate in the enhancement mode with improved carrier mobility by adjusting the oxygen partial pressure during growth. The proposed InOx TTFTs with a 20μm channel length presented a saturation mobility of 3.8cm2V−1s−1, a threshold voltage of 1.7V, an on/off ratio of 2.3×106, and a subthreshold slope of 1.5V/decade.
A New Role for RPTPσ in Spinal Cord Injury: Signaling Chondroitin Sulfate Proteoglycan Inhibition
Authors: Duan Yuntao , Giger Roman J.
Published: February 2010

RPTPσ mediates the inhibitory effects of chondroitin sulfate proteoglycans on axonal growth.