bluuebunny/crossref_metadata_2025 huggingface dataset:
On the Probability Distribution of Mooring Line Tensions in a Directional Environment
Authors: Mathisen Jan , Okkenhaug Siril , Larsen Kjell
Published: November 2011

A joint probabilistic model of the metocean environment is assembled, taking account of wind, wave and current and their respective heading angles. Mooring line tensions are computed in the time domain, for a large set of short-term stationary conditions, intended to span the domain of metocean conditions that contribute significantly to the probabilities of high tensions. Weibull probability distributions are fitted to local tension maxima extracted from each time series. Long time series of 30 hours duration are used to reduce statistical uncertainty. Short-term, Gumbel extreme value distributions of line tension are derived from the maxima distributions. A response surface is fitted to the distribution parameters for line tension, to allow interpolation between the metocean conditions that have been explicitly analysed. A second order reliability method is applied to integrate the short-term tension distributions over the probability of the metocean conditions and obtain the annual extreme value distribution of line tension. Results are given for the most heavily loaded mooring line in two mooring systems: a mobile drilling unit and a production platform. The effects of different assumptions concerning the distribution of wave heading angles in simplified analysis for mooring line design are quantified by comparison with the detailed calculations.
Influence of the Guide Vanes Solidity on the Performance of a Radial Impulse Turbine With Pitch-Controlled Guide Vanes
Authors: Pereiras Bruno , Takao Manabu , Garcia Fernando , Castro Francisco
Published: November 2011

One of the most developed technologies in ocean energy is the OWC concept. In this kind of device there is a turbine which plays an essential role, it is one of the factors which determine the efficiency of the system because of its own efficiency and its coupling with the chamber. One of the main characteristics in a turbine for OWC purposes, especially impulse turbines, is to use Guide vanes to optimize the energy extraction. However, they also are the largest source of losses. Improving the Guide vanes performance could reduce the pressure drop and, thus, the efficiency increases and the damping becomes smaller. In this paper the solidity of the guide vanes is analyzed to determine the optimum one. The study has been conducted on a radial impulse turbine with pitch-controlled guide vanes to minimize the incidence losses and, therefore, analyze the effect of the solidity. Experimental tests were carried out to validate a numerical model created in FLUENT®. The numerical model has been used to analyze the same turbine design but with different solidities of the guide vanes. The results have been conclusive: there is an optimal solidity for the guide vanes, which maximize the turbine efficiency by means of improving the guide vanes performance. Moreover, it has been seen that the optimum solidity is different for the inner and outer guide vanes.
A Numerical Investigation on 2D and 3D Sloshing Effects
Authors: Celis C. Miguel A. , Wanderley Juan B. V. , Neves Marcelo A. S.
Published: November 2011

In this paper, we study the effect of sloshing in a compartment of a naval artifact. The sloshing is of great importance in the dynamics of ships and offshore platforms, it is one of the factors that may cause the capsizing. This happens when the ship is under undesirable conditions, such as progressive flooding or fault conditions. The goal is to represent numerically the effect of sloshing. The numerical code is validated through comparisons with numerical and experimental data obtained in the literature. The numerical model is based on the finite difference method, where the Euler equations are solved using the upwind scheme and TVD (Total Variation Diminishing) Roe (1984) and Sweby (1984). The computer code for 2D represents the effect of sloshing in a closed vessel. To adequately represent the reservoir of the naval artifact, we used a structured computational mesh, where the fluid is forced to move by the excitation applied to the tank, this type of excitation is harmonic in sway. For the 3D computer code, a sloped free surface elevation is used as initial condition. Another attempt to realize the versatility of the computer code was the fall of a sphere of water on the free surface of the tank.
Steel Catenary Riser Response Identification Based on Field Measurements
Authors: Constantinides Yiannis , Tran Lee , Enuganti Prahlad , Campbell Mike
Published: November 2011

The existing riser design and analysis methodologies rely on empirically derived parameters to conservatively represent the complex dynamic behavior. With exploration moving to deeper water and the increasing need of existing asset support, there is a strong need to evaluate and refine these methodologies. This is especially true for Steel Catenary Risers (SCR) as they are the most widely used riser type and due to their complex soil-pipe interaction at the touchdown point. Given the small amount of small scale experiments that have been performed in the past, there is a strong industry need for large scale field measurements. This paper presents valuable field data collected from a deepwater SCR under storm conditions. The presented data includes riser accelerations and strains compared against vessel motions. The measured SCR response is also analyzed and qualitatively compared against the current understanding of SCR response that constitutes the industry analysis methodologies.
Integral Buckle Arrestors for Deepwater Rigid Pipelines Installed by Reeling Method
Authors: Sriskandarajah T. , Rao Venu , Manouchehri Soheil
Published: November 2011

Prevention and arresting buckle propagation under high external hydrostatic pressure is a necessity for the deepwater rigid pipelines during installation and operation. The local compromise in geometric integrity will propagate at a high velocity, flattening the pipeline until it encounters a physical barrier that arrests the buckle. Traditionally, external clamp-on type buckle arrestors are considered by the pipeline designers for rigid pipelines that are installed by reeling method. Integral Buckle Arrestors (IBAs) could provide a more reliable method of arresting the propagating buckle during installation and subsequent design life. However, design and installation of integral buckle arrestors for rigid reeled pipeline installation would be a challenge. IBA is fabricated from a thick walled pipe section with the same inner / outer diameter as that of pipeline and wall thickness transition to match the thickness of the pipe towards the ends. For the reeled pipelines, additional cost economies will be achieved by the use of IBAs which allow continuous installation by reel lay vessel without interruptions. This paper gives background information, design and installation considerations and practical issues in the fabrication of IBAs. Recent Subsea7 experiences in design and installation of IBAs will be also addressed in this paper. This paper does not cover the aspects to be taken into consideration, if the buckle arrestor is also serving dual purpose as a J-lay support collar.
Evaluation of the Operational Behaviour of a Deepwater Oil Export Pipeline Designed on the Basis of Controlled Lateral Buckling
Authors: Sriskandarajah T. , Bedrossian Arek , Roberts Graeme , Tanscheit Peter , Solano Rafael F. , Hansen Alexandre , Antunes Bruno R.
Published: November 2011

An account is given of the methods used to evaluate the operating structural performance of a reel laid deepwater oil HP/HT pipeline which had been designed based on the controlled lateral buckling principle. The objective was to develop a finite element (FE) model of the line based on its operating status and to use the model to confirm its present and future structural integrity. The line is surface laid on a fairly undulating soft clay seabed at its deep end and sand at the shallower end. It incorporates three different man-made buckle triggering mechanisms of buoyancy modules, dual sleepers and locally increased lateral curvature along its entire length. The steps involved in the inclusion of the in-situ operating condition of the pipeline, provided through various surveys made of the as-built and operating line and historical records of operating temperatures and pressures and flow rates made at inlet and outlet of the line, into the FE model, is discussed. Several key considerations essential for the successful development and validation of such an operation-based FE model, and for completion of the evaluation task, are highlighted in the paper. Also, a specific challenge encountered as a result of changes in regulatory guidelines on engineering critical assessments, from initial design to current evaluation stage, is discussed. The evaluation has demonstrated that it is feasible to carry out in-situ assessments of laterally buckling subsea lines, and that such assessments can provide not only reliable information regarding current and future structural integrity of the lines, but also invaluable confirmation of initial design data and rationale. This comparison between initial design and the actual operating behavior of the line is not included in this paper but will be described in detail in a future separate paper.
Extreme Load-Response Mechanisms of a Tension Leg Platform due to Larger Wave Crests: Some Results of the ‘CresT’ JIP
Authors: Hennig Janou , Scharnke Jule , Buchner Bas , van den Berg Joris
Published: November 2011

For the design of ships and offshore structures the largest crest height which can be expected in their lifetime is of key importance. This was confirmed by several incidences e.g. in hurricanes in the Gulf of Mexico during the recent years. This is why MARIN started up the CresT JIP with a number of partners. The CresT JIP is now completed and some results of the extreme wave load and response mechanisms observed during model tests with a TLP will be presented in this paper. First an overview is given of the loading and response process during the most extreme event observed. As a next step the loading and response is related to the time and spatial characteristics of the waves, as it is not per definition the highest local crest or wave height that results in the most extreme dynamic response. Furthermore, the effect of different TLP design variations and short-crestedness will be discussed.
Consistent Endurance Fatigue Knockdown Factors for Sour Service From Industry-Wide Database
Authors: Yu Weiwei , Vargas Pedro M. , Bowman Jonathan
Published: November 2011

The embrittlement of steel in the presence of water and hydrogen sulfide is a well known phenomenon. For the resulting degradation in fatigue performance, the industry today applies a knock-down factor onto in-air S-N endurance curve that relates the sour-service life to the in-air performance. Several published results are available, and most of these, although rigorous in test approach, report knock-down factors that include unspecified levels of conservatism, consistent with that particular author’s engineering intuition. (For example, typically a lower bound S-N curve in sour-service testing is related to a mean S-N curve in-air). This paper summarizes all of the published small scale sour service testing results, and applies a consistent knock-down factor calculation. Analyses of the data show that sour degradation is highly correlated to H2S concentration and solution pH value. In practice frequency scanning test is highly recommended since sour fatigue test results are highly dependent on loading frequency. Although the database is small, some trends are discernable. In particular, observations indicate that sour service exposure may act as an equalizer, removing the initiation life associated with the time for initial micro-defects at the weld toes to become macro-cracks and leaving only aggravated propagation due to sour service. In this paper, we use initiation life (for welds) to describe the life for the micro-defects (∼0.1mm height) to become macro-cracks (∼1.0 mm height), and a postulation is made that associates the fatigue performance of girth welds (F2, E, D, etc.) with the size and magnitude presence of these micro-defects. The metal surface attack of the sour environment is postulated to provide pitting-like initiation sites for the macro-crack for fatigue propagation. As a base we can use the F2 level performance as the performance due to presence of macro-cracks, and any margin for the D and E level fatigue performances then is associated with more benign initial micro-defects. Once we remove the differences in initiation life; all of the sour performance converges on a single lower performance curve. In this scenario, the knockdown factor is more consistently computed from a standard performance S-N curve rather than the same girth weld’s in-air performance since the in-air data may include significant initiation life. Furthermore, if project sour condition is less severe than NACE TM0177, Solution B with pH = 3.5 and H2S partial pressure = 70mbar, a knock down factor of 45 indexed to BS7608 E design curve is supported from the current database. This provides a design recommendation which can be used for preliminary design in sour environments.
Application of Regional Frequency Analysis for Identification of Homogeneous Regions of Design Wave Conditions Offshore Portugal
Authors: Lucas Cla´udia , Muraleedharan G. , Guedes Soares C.
Published: November 2011

Regional frequency analysis (RFA) based on L-moments is applied to the HIPOCAS hindcast data using daily maximum significant wave heights offshore Portugal to identify the homogeneous regions and to suggest the appropriate regional frequency distribution and extreme quantiles. Several statistics are computed at the various grid points in the area of study to classify the wave conditions of the regions. The daily maximum significant wave heights of the rough winter month January are used for this case study. The results of the study have shown that there are 3 homogeneous regions in the offshore region under investigation (35°–45°N, −9.5°–−11°W) comprising from 15 equally spaced grid points referring to an area of 0.25°×0.25°. It is interesting to observe that the algorithm is able to identify neighboring grid points as members of different regions. The maximum discrepancy between the at-sites’ extreme quantiles and their respective regional quantiles is 0.82 m for a return period of 100 years.
An Efficient Time-Frequency Domain Solution Procedure for the Analysis of Offshore System
Authors: Correˆa F. N. , Jacob B. P.
Published: November 2011

This work presents a formulation review of a hybrid time-frequency domain Green approach method (HTF-GA) for the solution of offshore systems. A step-by-step time domain solution procedure is established, based on the convolution between the Green functions of the problem and the vector of external loads. The Green functions are implicitly calculated in the frequency-domain. The accuracy is significantly improved when compared with traditional direct integration methods, or with other methods based on the Green approach. This method is able to deal with non-linear behaviour and implicity consider the frequency dependence of added mass and potential damping, encountered in offshore systems problems.
Effects of Shaping on Viscous Damping and Motion of Heaving Cylinders
Authors: Yeung Ronald W. , Jiang Yichen
Published: November 2011

Fluid viscosity is known to influence hydrodynamic forces on a floating body in motion, particularly when the motion amplitude is large and the body is of a bluff shape. While these hydrodynamic force or force coefficients have been predicted traditionally by inviscid-fluid theory, much recent advances had taken place in the inclusion of viscous effects. Sophisticated RANS (Reynolds-Averaged Navier Stokes) software are increasingly popular. However, they are often too elaborate for a systematic study of various parameters, geometry or frequency, where many runs with extensive data grid generation are needed. The Free-Surface Random-Vortex Method (FSRVM), developed at UC Berkeley in the early 2000, offers a middle-ground alternative, by which the viscous-fluid motion can be modeled and yet allowing vorticity generation be either turned on or turned off. The heavily validated FSRVM methodology is applied in this paper to examine how the draft-to-beam ratio and the shaping details of two-dimensional cylinders can alter the added inertia and viscous damping properties. A collection of four shapes is studied, varying from rectangles with sharp bilge corners to a reversed-curvature wedge shape. For these shapes, basic hydro-dynamic properties are examined, with the effects of viscosity considered. With the use of these hydrodynamic coefficients, the motion response of the cylinders in waves are also investigated. The origin of viscous damping is clarified. It is a pleasure and honor for the authors to contribute to the Jo Pinkster Symposium, held in his honor in OMAE-2011.
Collaborated and Constrained Neural-EKF Algorithm for the Vessel Traffic Monitoring and Information System
Authors: Perera Lokukaluge P. , Oliveira Paulo , Guedes Soares C.
Published: November 2011

Maneuvering vessel detection and tracking in cooperation with vessel state estimation and navigational trajectory prediction are important tasks for the Vessel Traffic Monitoring and Information Systems (VTMIS) to improve maritime safety and security in ocean navigation. In this study, collaborated and constrained Neural-EKF algorithm is proposed for the above purpose. The proposed methodology consists of two main units: an Artificial Neural Network based Vessel Detection and Tracking Unit and an Extended Kalman Filter based State Estimation and Trajectory Prediction Unit. Finally, the proposed algorithm, is implemented on the MATLAB software platform, and successfully illustrate the results attainable in respect to vessel detection and tracking, vessel state estimation and navigational trajectory prediction in ocean navigation is also presented in this study.
Dynamic Parameter Estimation of a Nonlinear Vessel Steering Model for Ocean Navigation
Authors: Perera Lokukaluge P. , Oliveira Paulo , Guedes Soares C.
Published: November 2011

In this paper the stochastic parameters describing the nonlinear ocean vessel steering model are identified, resorting to an Extended Kalman Filter. The proposed method is applied to a second order modified Nomoto model for the vessel navigation that is derived from first physics principles. The results obtained resorting to a realistic numerical simulator for the nonlinear vessel steering model considered are illustrated in this study.
Reliability and (Re)Assessment of Fixed Steel Structures
Authors: Efthymiou Mike , van de Graaf Jan Willem
Published: November 2011

This paper reviews the structural integrity and reliability of fixed steel offshore structures with a focus on improved models and incorporation of these models in design standards. Technical achievements in four key areas are reviewed which, when combined, resulted in a step improvement in the calculation of structural reliability. The first area is the extreme environmental loading on an offshore platform; the second area is the joint occurrence of waves, winds and currents, i.e. accounting for the fact that these do not, in general, peak at the same time and do not act in the same direction. The third area is the estimation of the ultimate strength of a fixed steel platform, accounting for component strength, including the buckling and post-buckling behaviour and the uncertainty in system strength. The fourth and final area is the integration of the above models to estimate the probability of failure. The historical performance of platforms and the improvements in successive editions of API RP 2A are reviewed; reliability targets appropriate for different exposure levels and corresponding performance standards are developed, aimed at harmonizing design practices worldwide. A differentiation is recommended between permanently manned L-1 installations and manned-evacuated L-1 installations in the Gulf of Mexico; this is because the consequences of failure are considerably different.
An Approach for the Optimum Design of TLP Type Offshore Wind Turbines
Authors: Nihei Yasunori , Matsuura Midori , Fujioka Hiroyuki , Suzuki Hideyuki
Published: November 2011

In this paper, we will show a new approach to design a Tension Leg Platform (TLP) type offshore wind turbine. Generally, TLPs are used in deepwater oil and gas development fields due to their favorable motion characteristics. In this field, they have high set up costs. An upper structure of 5MW wind turbine, however, is only 450tons at its total weight, which is much lighter than that of oil and gas platforms. Therefore the displacement and water plane area of the platform might be smaller. As a result, wave forces could decrease and it could lead initial tensions to be lower. This idea that leads to low set up costs will be discussed and also principal particulars of two types of TLP prototypes will be proposed in the present work. A tank test using 1/100 scale models was conducted under combined wind and wave conditions in this work. We measured not only motion characteristics, tensions on tendons, but also rotation speed of the turbine blades. Important phenomena in terms of a gyro effect, snapping and so on could be observed, and will be introduced in this paper.
Systematic Study of the Hydrodynamic Forces on a Sailing Yacht Hull Using Parametric Design and CFD
Authors: Huetz Lionel , Alessandrini Bertrand
Published: November 2011

In order to predict the velocity and attitude of a sailing yacht travelling in a given wind speed and wind angle, the hydrodynamic problem and the aerodynamic problem need most of the time to be decoupled. Two matrices are built to characterize the hydrodynamic and the aerodynamic behavior separately. Then a Velocity Prediction Program (VPP) interpolates the matrices and finds the equilibrium between the forces acting on the hull and appendages on one side, and the forces acting on the sails on the other side. This gives the velocity and attitude of the yacht depending on the wind speed and wind angle. Two main approaches are currently used to build the hydrodynamic matrix. The first method is to build a reduced or a virtual model with the proper hull shape and test it in a towing tank or a Computational Fluid Dynamics (CFD) program. This approach can lead to a very precise estimation of the matrix for a given hull shape, but it is time consuming and gives no indication on other possible hull shapes. The second method is to build and test various hull shapes and use this database to build analytical formulas describing the evolution of the hydrodynamic forces depending on the speed and attitude, but also on the hull shape, via several “shape parameters”. During the early stage of design, numerous hulls are to be evaluated, and it is very valuable to understand the influence of the design parameters on hydrodynamic efficiency of the hull. Therefore, the second method should be much more efficient at this stage of the design process. The most used regressions have been provided by J.A. Keuning et al., based on the Delft Systematic Yacht Hull Series, [1], [2]. This work began in 1971; the sailing yacht hull shapes have changed a lot since then. The aim of the present work is to enhance these regressions, by using new shapes in the database and by adding new “shape parameters” to describe the hulls. A powerful loop driven by the commercial software ModeFrontier has been developed in order to build a database by means of CFD. Systematic morphing of the hull shapes, parallel computing, automatic meshing and automatic post-treatment will provide a large database in a relatively short time. The aim of the ongoing work is to improve the accuracy and sensitivity of the prediction of yacht hull performance during the early stages of the design process. The study will focus on flat water, steady predictions. The following results concern exclusively bare hulls, the interaction between the hull and its appendages will be treated separately.
Practical Methods for Assessing the Reliability of Mooring Systems
Authors: Morandi Alberto , Shi Xiaobing
Published: November 2011

Floating drilling and production systems are subject to increasing levels of scrutiny by governments and the general public. This paper discusses practical methods for the reliability analysis and risk management of the moorings systems of such drilling and production systems.
The Development of the Compact Size INS for Underwater Vehicle
Authors: Ishibashi Shojiro , Watanabe Yoshitaka
Published: November 2011

Generally, Autonomous underwater vehicles (AUVs) are equipped with an inertial navigation system (INS) in order to understand its own absolute position in real time. Recently, the strap-down INS, which has accelerometers and optical gyros, is the mainstream. The position accuracy of it depends strongly on its size. So, in order to get more accurate position, the size of the INS becomes large. In fact, the large-size INS is needed to improve the position accuracy. It is difficult for small AUVs to be equipped with the large-size INS because they may not have enough payloads to install it. As the result, they are often equipped with an INS which is compact and less-accurate. Japan Agency for Marine-Earth Science and Technology (JAMSTEC) has worked to develop the high performance and compact size INS and we developed its prototype. Now the utility including to the position accuracy of the prototype has been verified using a real AUV. In the next step, we try to develop a new INS which is more compact and high performance than the prototype.
Comparison of Numerical Results With Experiments on the Ultimate Strength of Long Stiffened Panels
Authors: Xu Mingcai , Guedes Soares C.
Published: November 2011

The behavior of long stiffened panels are simulated numerically and compared with test results of axial compression until collapse, to investigate the influence of the stiffener’s geometry. The material and geometric nonlinearities are considered in the simulation. The initial geometric imperfections, which affect the collapse behavior of stiffened panels, are also analyzed. The initial imperfections are assumed to have the shape of the linear buckling mode. Four types of stiffeners are made of mild or high tensile steel for bar stiffeners and mild steel for ‘L’ and ‘U’ stiffeners. To produce adequate boundary conditions at the loaded edges, three bays stiffened panels were used in the tests and in the numerical analysis.
First-Principles Finite Element Modeling of Coiled Tubing in Directional Wellbores
Authors: Hill Lance T. , Datye Deepak V.
Published: November 2011

Coiled tubing is utilized in a variety of oil well operations. For applications such as drilling, completions, and remediation, coiled tubing offers the benefits of reduced costs, increased insertion speed, and reduced environmental impact. Coiled tubing possesses a limitation, however, in that it can buckle in service causing damage to the tube and disruption of operations. There have been numerous papers published during the last 50 years on helical buckling. Numerous fast running engineering codes have been developed to determine the onset of sinusoidal buckling, helical buckling, and lock-up of drill pipe in a wellbore, with particular emphasis on coiled tubing. We provide a methodology for evaluating the complete nonlinear mechanical behavior of coiled tubing insertion from a first-principles finite element modeling perspective. Using this approach the buckling, post-buckling, and lock-up behavior of the drill pipe can be studied. Additionally, post lock-up methods such as vibration loading and downhole lubrication can also be evaluated.
Development of Heavy Wall High-Strength UOE Linepipe by Means of Microstructural Control in Base Metal and Seam Weld
Authors: Ishigami Atsushi , Murakami Yoshiaki , Hayakawa Naoya , Tanizawa Akihiko
Published: November 2011

The growing demand of the transport of gas and oil under severe conditions, such as in deepwater and onshore in cold climates, requires heavy wall thickness line pipes with both high strength and excellent toughness at low temperature in order to reduce the cost of gas transportation and constructions. In particular, when developing and efficiently manufacturing high strength line pipes with heavy wall thickness, achieving excellent heat affected zone (HAZ) toughness of seam weld is one of the key subjects. In general, steel plate for heavy wall thickness line pipes relatively contains large amount of alloy elements to secure required mechanical properties, whereas addition of alloy elements cause deterioration of HAZ toughness of seam weld. This paper deals with the method of improving HAZ toughness in UOE pipe seam weld. Relationship between microstructure and toughness of simulated HAZ was investigated, and volume fraction of martensite-austenite constituent was reduced by optimization of chemical composition of steel plates. Moreover, low heat input double submerged arc welding (DSAW) process with using welding wires with smaller diameter was newly developed to enhance HAZ toughness. With this new DSAW process, decrease of HAZ width and reduction of austenite grain size were also achieved. Based on the above knowledge, the manufacturing condition was optimized and heavy wall thickness X70 UOE pipe with excellent toughness was successfully developed.
The Effect of Third-Order Nonlinearities on the Statistical Distributions of Wave Heights, Crests and Troughs in Bimodal Crossing Seas
Authors: Petrova Petya G. , Tayfun M. Aziz , Guedes Soares C.
Published: November 2011

This paper investigates the effect of third-order nonlinearities on the statistical distributions of wave heights, crests and troughs of waves mechanically generated in a deep-water basin, simulating two crossing systems characterized by bimodal spectra. Observed statistics exhibit various effects of third-order nonlinearities in a manner dependent on both the distance from the wave-maker and the angle between the mean directions of the component wave systems. In order to isolate and demonstrate the effects of third-order nonlinearities by themselves, vertically asymmetric distortions induced by second-order bound waves are removed from the observed time series. It appears then that the distributions of wave crests, troughs and heights extracted from the non-skewed series clearly deviate from the Rayleigh distribution, suggesting that waves are characterized by nonlinear corrections of higher order than the typical of second-order waves. Nonetheless, some models developed for weakly nonlinear second-order waves can still be used in describing wave heights, crests and troughs in mixed seas, provided that relevant distribution parameters are modified so as to reflect the effects of third-order corrections and some basic characteristics of mixed seas.
Experimental Investigation of the First and Second Order Wave Exciting Forces on a Restrained Body in Long Crested Irregular Waves
Authors: Pessoa Joa˜o , Fonseca Nuno , Rajendran Suresh , Guedes Soares C.
Published: November 2011

The paper presents an experimental investigation of the first order and second order wave exciting forces acting on a body of simple geometry subjected to long crested irregular waves. The body is axis-symmetric about the vertical axis, like a vertical cylinder with a rounded bottom, and it is restrained from moving. Second order spectral analysis is applied to obtain the linear spectra, coherence spectra and cross bi-spectra of both the incident wave elevation and of the horizontal and vertical wave exciting forces. Then the linear and quadratic transfer functions (QTF) of the exciting forces are obtained. The QTF obtained from the analysis of irregular wave measurements are compared with results from experiments in bi-chromatic waves and with numerical predictions from a second order potential flow code.
Fatigue Damage Repair and Life Extension of a Floating Production Unit: The VFB Platform Revisited
Authors: Haagensen P. J. , Larsen J. E. , Va˚rdal O. T.
Published: November 2011

The Veslefrikk B platform was built in 1985 as a drilling exploration unit but was converted to a production platform in 1989. After only two years in service fatigue cracks were discovered and several repairs were made. However, extensive fatigue cracking continued and a retrofitting program was planned. In addition, increased payload was necessitated by more topside equipment required for a tie-in to the Huldra field which was scheduled to start production in 2001. In 1999 the platform was temporarily decommissioned and dry-docked for a comprehensive repair and upgrading program, this was completed in approximately two months. The life extension program was described in the OMAE 2000 conference paper 2954. However, after only one more year of service new cracks were found and subsequent fatigue damage necessitated new repairs. It is noteworthy that cracking this time occurred only in areas of the structure that were left untreated in the 1999 retrofitting program due to assumed low levels of stress in those areas. The paper describes the original repair and strengthening program, and the types of subsequent fatigue damage that required new repairs. Most of the cracks occurred in the hull skin plates and caused water leakage. The objective of the recent life extension program is to ensure safe operation of the platform for a period of another 20 years.
Development of a Novel 1:7 Scale Wave Energy Converter
Authors: Rhinefrank Ken , Schacher Al , Prudell Joe , Hammagren Erik , Zhang Zhe , Stillinger Chad , Brekken Ted , von Jouanne Annette , Yim Solomon
Published: November 2011

This paper presents a novel 1:7 scale point absorber wave energy converter (WEC), developed by Columbia Power Technologies (COLUMBIA POWER). Four hydrodynamic modeling tools were employed in the scaled development and the optimization process of the WEC, including WAMIT, Garrad Hassan’s GH WaveFarmer, OrcaFlex and ANSYS AQWA. The numerical analysis development is discussed, and the performance and mooring estimates at 1:7 scale and full scale are evaluated and optimized. The paper includes the development of the 1:7 scale physical model and the associated WEC field testing in Puget Sound, WA.
Analysis of Oil Spill Risk in DP Shuttle Tanker Direct Offloading Operations
Authors: Chen Haibo , Moan Torgeir , Lerstad Arve , Breivik Ka˚re
Published: November 2011

DP shuttle tankers performing offloading directly from fixed or geostationary floating offshore installations is addressed in this paper. It is important to ensure that disconnection of offloading hose can be achieved in time given shuttle tanker DP failure and position loss. The accident scenario is the hose fail-to-disconnect while shuttle tanker has an excessive position excursion. The consequence can be oil spill combined with the damage the offloading system. The spill amount can be as much as the crude oil volume in the hose, or over 1000 m3 if isolation and shutdown of oil export pump on the installation are not achieved timely. Various barriers to prevent oil spill have been developed over the past 30 years’ history of shuttle tanker offshore loading. However, the direct offloading is a new operational context to the traditional offloading. A quantitative frequency model for oil spill initiated by DP shuttle tanker position loss in direct offloading is presented in this paper. Case study results show that in the base case where only traditional barriers are used, the frequency for large oil spill up to 1000 m3 or more may reach 2.48E−03 per year, given 20 hours offloading cargo transfer time and 52 times offloadings per year. This frequency is not negligible, and risk reduction measures are viewed necessary. Novel safety barriers, i.e. Automatic Shutdown and Release (ASDR), as well as the HPR (Hydroacoustic Position Reference) and BLS (Bow Loading System) weak link mode, are analyzed as sensitivity cases. Results show that the frequency of large oil spill can then be reduced to 3.81E−05 per year, i.e. 1.5% of the base case value, and this is well within 1.0E−04 per year level. Recommendations to minimize oil spill risk during DP shuttle tanker direct offloading operations are proposed in this paper.
Integrity Assessment, Repair and Verification of Fitness for Service of a Damaged Offshore Platform Radio Tower
Authors: Nezamian Abe , Nicolson Robert J.
Published: November 2011

The maintenance of structural integrity is a significant consideration in the safety management of offshore installations. This paper presents an integrated approach for fitness-for-service evaluation of a deteriorating offshore radio tower structure. The approach is intended to assist engineers in assessing the overall fitness and survivability of aged offshore structures. A 43 m tall radio tower on an oil and gas platform located offshore Australia was reported with areas of heavy and medium corrosion of structural members. Severe corrosion in one leg of the radio tower had caused an obvious hole (extensive damage) through the leg at approximately 36m above the main deck and raised structural integrity concerns with the tower. The platform had been shut down due to concerns of a possible collapse of the tower. An assessment/repair program was developed to assure the short term integrity of the tower with minimal repair works. The integrity of the critically damaged leg had been temporarily restored using a clamped sleeve repair to allow progress with the inspection / thickness measurement of the corroded areas of the tower. As part of the fitness-for-service assessment, the minimum thickness acceptance criteria for the suspected corroded structural members were developed to enable initial assessment of the measured remaining wall thicknesses of the corroded member. Fitness for service integrity assessment requirements were developed to assess the locations that did not meet the minimum thickness criteria. The integrity requirements were adopted based on the average measured wall thickness, sensitivity structural analyses for reduced wind speeds for shorter life spans, and stability/survival assessment of the tower. An inspection program was carried out for the suspected locations and any additional locations identified during the inspection process. The inspection measurements were assessed against the fitness-for-service criteria. Where the measurements indicated that members did not meet the acceptance criteria temporary repairs were specified. Consequently, the tower fitness-for-service was found sustainable for up to 12 months until a more permanent repair or replacement of the tower could be completed, thus enabling the platform to resume normal operations.
Modelling Wave Energy Resources in the Irish West Coast
Authors: Bento A. Rute , Martinho Paulo , Campos Ricardo , Guedes Soares C.
Published: November 2011

In order to assess the potential wave energy extraction, a study is made to validate a model that can be used to characterize Ireland’s wave climate in a more extensive study. The target area is the Irish West Coast, known for having the highest average wave power in Europe. The wave conditions in the coastal area were characterized by coupling the wave models SWAN and WAVEWATCH III. Validation tests are carried out with buoy data so that the model’s performance can be evaluated. The wave parameters considered for the comparisons in the time domain are significant wave height and mean period, and the spatial distribution of wave energy is examined in a case study. Theoretical values of wave power are obtained for sites close to the coast and in particular for the two tests sites of Galway and Belmullet.
API 579 Level 3 Assessment of Dents Using High-Resolution ILI Data
Authors: Jandu Chas , Taylor Mike , Narikotte Suji
Published: November 2011

In-line Inspection (ILI) surveys are periodically performed to determine the condition of the pipeline. Typical ILI surveys involve Magnetic Flux Leakage primarily to determine metal loss and simple single channel Calliper surveys to determine any signs of geometry imperfections. Additional surveys such as high-resolution multi-channel Calliper deformation tools are occasionally used to accurately record imperfections to enable a more accurate assessment of the integrity of the pipeline containing the imperfection. Such tools have had limited employment, and therefore little experience exists of using the data obtainable for the detailed assessment of defects. This paper presents a study of such a case. As part of an In-line Inspection (ILI) of an offshore pipeline, a high-resolution deformation survey recorded numerous dent anomalies which had potentially resulted from a single dragged anchor incident before the pipeline was trenched. This data set was correlated to Magnetic Flux Leakage inspection data to confirm external mechanical damage. Pipeline sections having anomalies that were either found close to girth welds, or had associated corrosion defects were automatically selected for repair. The remaining anomalies were assessed in order to determine their acceptability for the maximum allowable operating pressure using the approaches detailed in API-579. Due to the sharp nature of some of the dents, elastic-plastic finite element analyses (FEA) were performed using denting profiles generated from the calliper data of the ILI run. API-579 level 3 assessments were then carried out using the FEA results. This paper details the high-resolution deformation tool findings and the approach used in order to assess the fitness-for-purpose of the pipe with the recorded anomalies.
Lipotoxicity Causes Multisystem Organ Failure and Exacerbates Acute Pancreatitis in Obesity
Authors: Navina Sarah , Acharya Chathur , DeLany James P. , Orlichenko Lidiya S. , Baty Catherine J. , Shiva Sruti S. , Durgampudi Chandra , Karlsson Jenny M. , Lee Kenneth , Bae Kyongtae T. , Furlan Alessandro , Behari Jaideep , Liu Shiguang , McHale Teresa , Nichols Larry , Papachristou Georgios Ioannis , Yadav Dhiraj , Singh Vijay P.
Published: November 2011

Unsaturated fatty acids cause lipotoxicity and mediate acute adverse outcomes in obese individuals with pancreatitis.
Molecular Mechanism for a Gateway Drug: Epigenetic Changes Initiated by Nicotine Prime Gene Expression by Cocaine
Authors: Levine Amir , Huang YanYou , Drisaldi Bettina , Griffin Edmund A. , Pollak Daniela D. , Xu Shiqin , Yin Deqi , Schaffran Christine , Kandel Denise B. , Kandel Eric R.
Published: November 2011

The finding that nicotine enhances the brain’s response to cocaine may explain how smoking acts as a gateway drug for this addictive stimulant.
Molecular Dissection of an Outbreak of Carbapenem-Resistant Enterobacteriaceae Reveals Intergenus KPC Carbapenemase Transmission through a Promiscuous Plasmid
Authors: Mathers Amy J. , Cox Heather L. , Kitchel Brandon , Bonatti Hugo , Brassinga Ann Karen C. , Carroll Joanne , Scheld W. Michael , Hazen Kevin C. , Sifri Costi D.
Published: November 2011

Carbapenem-resistant
Enterobacteriaceae
(CRE) have emerged as major causes of health care-associated infections worldwide. This diverse collection of organisms with various resistance mechanisms is associated with increased lengths of hospitalization, costs of care, morbidity, and mortality. The global spread of CRE has largely been attributed to dissemination of a dominant strain of
Klebsiella pneumoniae
producing a serine β-lactamase, termed
K. pneumoniae
carbapenemase (KPC). Here we report an outbreak of KPC-producing CRE infections in which the degree of horizontal transmission between strains and species of a promiscuous plasmid is unprecedented. Sixteen isolates, comprising 11 unique strains, 6 species, and 4 genera of bacteria, were obtained from 14 patients over the first 8 months of the outbreak. Of the 11 unique strains, 9 harbored the same highly promiscuous plasmid carrying the KPC gene
bla
KPC
. The remaining strains harbored distinct
bla
KPC
plasmids, one of which was carried in a strain of
Klebsiella oxytoca
coisolated from the index patient and the other generated from transposition of the
bla
KPC
element Tn
4401
. All isolates could be genetically traced to the index patient. Molecular epidemiological investigation of the outbreak was aided by the adaptation of nested arbitrary PCR (ARB-PCR) for rapid plasmid identification. This detailed molecular genetic analysis, combined with traditional epidemiological investigation, provides insights into the highly fluid dynamics of drug resistance transmission during the outbreak.

IMPORTANCE
The ease of horizontal transmission of carbapenemase resistance plasmids across strains, species, and genera of bacteria observed in this study has several important public health and epidemiological implications. First, it has the potential to promote dissemination of carbapenem resistance to new populations of
Enterobacteriaceae
, including organisms of low virulence, leading to the establishment of reservoirs of carbapenem resistance genes in patients and/or the environment and of high virulence, raising the specter of untreatable community-associated infections. Second, recognition of plasmid-mediated outbreaks, such as those described here, is problematic because analysis of resistance plasmids from clinical isolates is laborious and technically challenging. Adaptation of nested arbitrary PCR (ARB-PCR) to investigate the plasmid outbreak facilitated our investigation, and the method may be broadly applicable to other outbreaks due to other conserved mobile genetic elements. Whether infection control measures that focus on preventing transmission of drug-resistant clones are effective in controlling dissemination of these elements is unknown.
Child malnutrition and recurrent flooding in rural eastern India: a community-based survey
Authors: Rodriguez-Llanes Jose Manuel , Ranjan-Dash Shisir , Degomme Olivier , Mukhopadhyay Alok , Guha-Sapir Debarati
Published: November 2011

Objectives

This study aims to improve the understanding of the relationship between exposure to floods and malnutrition in children aged 6–59 months in rural India. Research has focused exclusively on Bangladeshi children, and few controlled epidemiological studies are available.

Method

A community-based cross-sectional study of child nutritional status was carried out in 14 flooded and 18 non-flooded villages of Jagatsinghpur district (Orissa) within one month of the September 2008 floods, and similarly affected by flooding in August 2006. Face-to-face interviews were conducted in 757 households in the flooded villages and 816 in the non-flooded communities. Data used in this study were from those households with children aged 6–59 months. In total, 191 and 161 children were measured, respectively. The association between various malnutrition indicators and the exposure to floods was assessed by univariate and multivariate logistic regression.

Results

Adjusted analyses revealed that children in flooded households were more likely stunted compared with those in non-flooded ones (adjusted prevalence ratio 1.60; 95% CI 1.05 to 2.44). The prevalence of underweight was also higher in children living in the flooded communities (adjusted prevalence ratio 1.86; 95% CI 1.04 to 3.30). Further analyses found that the 26–36-month flooded cohort, thus those children younger than 1 year during the precedent flood in August 2006, attained the largest difference in levels of stunting compared with the unexposed group of the same age.

Conclusion

Exposure to floods is associated with long-term malnutrition in these rural communities of Orissa, India. Children exposed to floods during their first year of life presented higher levels of chronic malnutrition. Long-term malnutrition prevention programmes after floods should be implemented in flood-prone areas.