bluuebunny/crossref_metadata_2025 huggingface dataset:
Dimensional Study for Brazilian FPSO
Authors: Cueva Daniel , Donato Marcos , Torres Fernando , Campos Felipe , Ferrari Jose A. , Nishimoto Kazuo
Published: November 2008

After the boom of converted floating, production, storage and offloading systems, based on the old VLCC design, many engineering institutes started thinking about optimum dimension for new units. However, these new FPSOs designs carried out worldwide concerns about good seakeeping behavior when considering general weather conditions, in order to apply their project to different locations around the globe. Analyzing the Brazilian specific conditions, it was verified that, considering waves, current and wind characteristics, the dimension proportions found in the projected units were not the best options, mostly because of the swell waves influence. Thus, in a cooperative project between University of Sao Paulo and PETROBRAS, the best dimensions for a specific case were studied, based on real premises from Campos Basin. During the study, the roll motion, which usually creates operational limits during hard environmental conditions, was focused. It was possible not only to evaluate the best breath and draught relations, but also the inclusion of a structured skirt in the ship bilge. The influence of different shapes in the ship’s bow and stern were also evaluated, showing interesting results regarding the forces applied on the vessel. All the analyses were conducted considering numerical analysis, and the final dimensions were applied to a scaled model, which allowed to verify the real behavior of the projected unit in a test basin. As a conclusion, it was possible to define an optimized hull for the PETROBRAS premises, giving them a real design to be used in future explorations.
7000m Operable Deep-Sea ROV System, “KAIKO7000”
Authors: Nakajoh Hidehiko , Murashima Takashi , Yoshida Hiroshi
Published: November 2008

On May 29, 2003, the KAIKO’s secondary cable snapped, and the KAIKO’s vehicle has been missing. JAMSTEC (Japan Agency for Marine-Earth Science and Technology) has lost a method to survey more than 6,500m deep areas where submersible “Shinkai6500” cannot reach. JAMSTEC decided to remodel the vehicle of UROV7K system instead of the lost vehicle in order to continue the scientific activities. This system is called “KAIKO7000” system. After the accident, safety measures of the KAIKO system must be reconsidered in order to improve the safety measures of the KAIKO7000 system. The KAIKO7000 system was finished remodeling in March 2004, and the sea trials have been started in April 2004. Then, we succeeded in the maximum operation depth test, which was reached at a depth of 7031 m. This paper describes on the development of the KAIKO7000 system.
FEA of Out-of-Plane Fatigue Mechanism of Chain Links
Authors: Vargas Pedro , Jean Philippe
Published: November 2008

Several mooring chains of an off-loading buoy failed after only 8 months of service. These chains were designed according to conventional fatigue assessment using API RP 2SK T-N curves to a fatigue life of 20 years with a factor of safety equal to 3 on life. Of particular interest is that the mooring chain failure underwent significant mooring chain motions that caused interlink rotations. Although traditionally neglected, these interlink rotations, when combined with significant chain tensions can cause bending stresses in the chain links. In this paper we identify a mechanism, here identified as Out-of-Plane Bending (OPB) that explains the extensive fatigue damage causing the mooring chains of the off-loading buoy to fail. A previous paper [4] presented experimental results of applying inter-link rotation to a pre-tensioned chain. Various pretension levels were used, with instrumentation to extract link angles and chain link stresses. In this paper, the physics of the OPB mechanism is examined through finite element models of the 124mm chain link tests. The various modes of interlink rotation are examined. The proof loading procedure that the chain undergoes at manufacture is identified as a likely cause for creating a tightly mated surface that is conducive to activating the OPB mechanism. To comply with Single Buoy Moorings (SBM) requirements addressing publication of internal research, many of the graphs included in this paper have had the stress values removed from the y-axis. However, with SBM’s management approval, some numerical references to stress amplitudes remain in the text. Overall, this limitation does not detract from the study, trends are evident and relevant comparisons can be made.
CFD Investigation of the Effect of Current Turbulence on the Hydrodynamic Forces on a Cylinder
Authors: Ahn Hyung Taek , Kallinderis Yannis
Published: November 2008

Practical cases of flow-structure interactions involve ocean currents with turbulence. Ocean turbulence effects on offshore structures are of high interest due to the lack of information about its role regarding the hydrodynamic forces and fatigue load on structures. Current turbulence profiles are employed for various Reynolds numbers that are based on an isotropic geophysical turbulence model. These turbulence profiles are specified as the inflow condition for the numerical simulations over a circular cylinder. The present work consists of three parts: (i) determination of appropriate mesh and time step resolution to accommodate the turbulence, (ii) investigation of the effect of current profile turbulence on the amplitude and frequencies of the hydrodynamic forces acting on a cylinder, and (iii) study of the sensitivity of the hydrodynamic load exerted on the cylinder for a range of Reynolds numbers with a turbulent inflow profile. Spalart-Allmaras one-equation turbulence model is used for high Reynolds number simulations.
Static Stress Redesign of Plates by Large Admissible Perturbations
Authors: Kristanto Bhineka M. , Bernitsas Michael M.
Published: November 2008

The LargE Admissible Perturbation (LEAP) methodology is developed further to solve static stress redesign problems for shell elements. The static stress general perturbation equation, which expresses the unknown stresses of the objective structure in terms of the baseline structure stresses, is derived first. This equation depends on the redesign variables for each element or group of elements; namely the plate thickness. LEAP enables the designer to redesign a structure to achieve specifications on modal properties, static displacements, forced response amplitudes, and static stresses. LEAP is implemented in code RESTRUCT which post-processes the FEA results of the baseline structure. Changes on the order of 100% in the above performance particulars and in redesign variables can be achieved without repetitive FEA’s. Several numerical applications on a simple plate and an offshore tower are used to verify the LEAP algorithm for stress redesign.
A Comparison of Experiment and FSRVM Modelling of Larger Than Normal Bilge Keels
Authors: Braddock R. A. , Timms R. J. , Thiagarajan K. P.
Published: November 2008

This paper details an experimental study on bilge keels of up to 20% of half beam of a FPSO with rectangular geometry. Both free decay and forced oscillation tests were conducted on a range of bilge keel widths at different amplitudes and frequencies. The results show that, for a given amplitude of roll motion, the damping coefficient increases with increasing bilge keel size up to a certain point and then declines. Numerical simulations using the free surface random vortex method were performed on rectangular cross-sections with bilge keels which show good agreement with the experimental results. Simulations of the effect of even larger keels indicates that the same trend for damping coefficient as a function of keel size is found. An examination of the simulation results suggests a likely explanation for this behaviour.
Numerical Simulation of Tidal Current in the Coastal Region With an Artificial Seabed Mound for Upwelling
Authors: Tabeta Shigeru , Kinoshita Tsuguki , Shimizu Yuta
Published: November 2008

The technology of generating an artificial upwelling by constructing a seabed mound to increase the primary production is being examined off Ikitsuki Island, Nagasaki, Japan. A numerical simulation model is being developed in order to evaluate the effects and environmental influence of the artificial seabed mound. At the first stage of the modeling, tidal current is calculated for the coastal region including the artificial upwelling area. Since most of the boundaries of the computational domain are open to the ocean, it is necessary to give incoming tidal wave all over them, which is not easy because of complicate topography. A newly developed inverse method using the observation data at tidal stations along the coastline was applied to determine the boundary conditions of tide. The calculated tide by the method agreed fairly well with the observation data. Currents near the seabed mound was also investigated, whose result is indicated that internal wave induced by the mound makes the mixing larger.
Heavy Marine Transport Analysis Procedure: Spar Transport Case Studies
Authors: Lehtonen Eero , Mikkola Timo P. J. , Ajosma¨ki Antti , Kukkanen Timo
Published: November 2008

The analysis procedure for heavy marine transports is based on spectral approaches and on the use of 3D hydrodynamic and structural models. The analyses are aimed at designing the transport supports and at guaranteeing the structural safety during the voyage. The analyses are typically conducted concurrently with the design of the spar structures. Brief description is given of the analysis procedure. Its application is illustrated with examples from recently completed projects. Main effort in most projects is in local strength and fatigue issues caused by localized support loads between the spar and ship hulls. The spar transports have had relatively large overhanging sections, which are subject to wave slamming and impact loads under rough seas.
Simulation of a Coupled System of Long Wave-Short Waves With a Slight Detuning in Group Velocities
Authors: Poon C. K. , Lai D. W. C. , Chow K. W.
Published: November 2008

The resonances among long and short waves have been studied intensively. The focus of this paper is on flow configurations with two short wave groups with slight detuning in group velocities. This detuning effect will introduce a much richer set of dynamics as the mismatch in group velocities will have profound effects on the motion of pulses. Exact solitary waves are calculated for the coupled set of nonlinear evolution equations by the Hirota bilinear transform. The Hopscotch method is applied to solve the set of equations numerically. Physically, the goal is to study the effects of mismatch in group velocities and the initial phase difference of arbitrary solitary pulses between wave guides. The outcome will depend on the strength of the group velocity differences, initial amplitudes and phase differences.
Joint Probabilistic Description for Combined Seas
Authors: Bitner-Gregersen Elzbieta M.
Published: November 2008

An extension of joint omnidirectional probabilistic model including combined seas and possibility of environmental parameters approaching from different direction is presented. The following parameters are considered: mean wind speed, wind direction, significant wave height (sea and swell), spectral peak period (sea and swell), wind sea direction, swell direction, current speed and current direction. Two approaches for wind sea and swell modelling are proposed. The joint description is developed for three locations at the Norwegian Continental Shelf and for the West Shetland. Uncertainties related to it are discussed. The model is meant to be applied in reliability analysis of offshore structures, in particularly FPSO units, for which a proper account of directional effects and combined seas is important.
Improved Strake Design for Vortex Induced Motions of Spar Platforms
Authors: Irani Mehernosh , Finn Lyle
Published: November 2008

An extensive model test program was conducted to explore the effectiveness of alternate strake designs to reduce Truss Spar VIV response. Different strake configurations were tested to minimize VIV response. The paper presents results of the model tests. The model test set-up is described, important parameters that are modeled (including hull and truss geometry, strake configuration, mass and mooring properties) and considerations of instrumentation and test methodology are discussed. The paper also describes the analysis of the test results and shows the effectiveness of new strake design. The present results are compared with VIV response of existing Truss Spars with conventional strake design.
Permanent Magnetized Generator for Marine Current Power Conversion: Proposed Experimental Setup
Authors: Segergren Erik , Nilsson Karin , Leijon Mats
Published: November 2008

In order to verify the theoretical work considering very low speed permanent magnetized generators for marine current power conversion, an experimental setup is under construction. Earlier 2-dimensional Finite Element Method (FEM) simulations have been performed and in this paper focus is on the practical considerations regarding the rotor construction of the generator as well as the total system configuration with motor, frequency transformer and generator. A rotor configuration with milled grooves for magnet fixation along with a power feedback option with a resistive load is chosen for the first experimental setup.
Hydrodynamic Coefficients From In-Line VIV Experiments
Authors: Aronsen Kristoffer H. , Larsen Carl Martin , Mo̸rk Kim
Published: November 2008

For subsea pipelines installed in areas with uneven seabed free spans may occur and fatigue failure due to vortex induced vibrations (VIV) is one of the main concerns related to these spans. In order to install pipelines in such areas the safety against fatigue failure from in-line (IL) and cross-flow (CF) VIV must be documented. Although maximum oscillation amplitudes in the IL direction are considerably smaller than the maximum amplitudes in the CF direction, the IL fatigue damage normally prevails and may limit the allowable span length. The reason for this is that the IL vibrations initiate at a lower current velocity (i.e., reduced velocity) than the CF vibrations and would hence be excited for a longer period of time. Prediction tools for VIV may be split into parametric Response Models such as described in DNV-RP-F105 and methods based on empirical coefficients such as SHEAR7 and VIVANA. Methods based on force coefficient have until recently been limited to CF VIV due to lack of hydrodynamic coefficients for IL response. This paper presents results from forced IL oscillation experiments of a smooth, rigid cylinder in uniform flow. The results are presented as dynamic in-line coefficients for the pure IL regime, i.e. reduced velocity between 1 and 4, at Reynolds number 24.000. The results are compared with IL results from free oscillation experiments found in the literature.
Modelling of Competition for Space and Food Among Mussels Under a Coastal Floating Platform
Authors: Kitazawa Daisuke , Ruardij Piet
Published: November 2008

A competition model among mussels (Mytilus galloprovincialis) was developed to predict the environmental impacts of mussels under a coastal floating platform, which is called Mega-Float. The model describes the dynamics of mussels as controlled by competition for space and food availability. The model consists of a physiological growth submodel based on the Dynamic Energy Budget (DEB) model and a competition submodel for space and food. First, the parameter values in the physiological submodel are calibrated by using observations on growth of mussels (Mytilus galloprovincialis) cultivated in the north-west coast of Spain. Then the competition submodel for space and food among mussels is described as a function of the mussel density, and is calibrated by using observations on time variation in the population number of the mussels on the cultivation ropes. The population number of mussels starts with 5,000 individuals per meter and some mussels are shoved to the inner layer of the mussel bank as mussels grow. This undoubtedly leads to food shortage and starvation for them due to their unfavorable position. As a result, some mussels are starved to death and about half of the remaining mussels are inactive in the inner layer of the mussel bank. The competition model can predict well the decrease in the population number of mussels at the cultivation ropes. Finally, the competition model is combined with three-dimensional marine ecosystem model and numerical simulation is conducted to predict the growth of the mussel bank on the under-surface of an imaginary Mega-Float, which is anchored in the head of Tokyo Bay. It was revealed that about two-thirds of mussels are inactive in the inner layer of the mussel bank and do not contribute to food ingestion rate of the mussel bank.
Estimating the Voyage Duration of Transoceanic LNG Transports
Authors: Ma Wei , Cooper Cortis
Published: November 2008

A study was made to estimate the transit time of time-critical cargo (LNG) from Western Australia to the Far East (e.g. Japan) or the southern U.S. west coast. Unexpected delays during transit can result in stiff financial penalties imposed by LNG buyers. Conversely, quicker than expected voyages will underutilize expensive tankers. Since there was no prior experience along the two routes using the proposed new-build vessels, the SafeTrans computer simulation program was used to calculate the voyage duration. SafeTrans is a comprehensive routing simulator that accounts for weather routing, ship dynamics, and weather forecast errors. Basic voyage duration statistics are presented and indicate important differences between a) outgoing and returning voyages, b) the two routes, and c) weather-routed and non-weather-routed scenarios. These differences are examined and reveal that voyage duration estimate is significantly impacted by weather routing, and a comprehensive ship motion model and weather database. Finally, our results demonstrate an application of SafeTrans that goes beyond the original purposes of the program, and suggests it might well be useful for estimating the voyage duration for other types of time-critical cargo.
Effects of a Thermal Coating Process on X100 UOE Line Pipe
Authors: Timms Chris , DeGeer Duane , McLamb Martin
Published: November 2008

The increased demand for high strength linepipe for onshore and offshore pipeline systems has been well documented over the past few years. The economic benefits have been demonstrated, and solutions have been developed to address the technical issues facing high strength linepipe use. However, there are still a few unanswered questions, one of which is addressed in this paper: what is the effect of thermal treatment during the pipeline coating process on the material behaviour of high strength linepipe? This paper presents the results of a thermal coupon study investigating the effects of low temperature heat treatment on the tensile and compressive stress strain curves of samples taken from X100 linepipe. Thirty axial test coupons and thirty circumferential test coupons were machined from a 52 inch diameter, 21 mm wall thickness UOE X100 linepipe. Some of the coupons were maintained in the as-received condition (no heat treatment) while others were heat-treated in a manner that simulates a coating plant induction heat treatment process. All coupons were subsequently tested in tension or compression, either at room temperature or at −18°C. This study has provided a number of interesting results. In regards to material strength, the heat treatment increased the tensile and compressive yield strengths in the longitudinal and circumferential coupons. Axial tensile, axial compressive and circumferential tensile yield strength increases ranged from 5 to 10%. Circumferential compressive yield strength increases ranged from 14 to 24%. A Y/T ratio increase of approximately 7% was observed for all heat-treated tensile coupons. The coupon tests conducted at −18°C were only slightly different than their room temperature counterparts; with an average yield strength increase of 4% in all directions and orientations and a slight reduction in Y/T ratio.
Flexible Riser Resistance Against Combined Axial Compression, Bending, and Torsion in Ultra-Deep Water Depths
Authors: Brack Marcelo , Troina Le´a M. B. , Sousa Jose´ Renato M. de
Published: November 2008

The experience in the Brazilian offshore production systems is to adopt the traditional riser solution composed of unbonded flexible pipes at a free-hanging catenary configuration. In deep waters, the tendency has been to use different pipe length sections (normally two), each of them designed to resist typical loadings. At the bottom, pipe structure is dimensioned against external pressure, axial compression, bending and torsion, for example. The theoretical prediction of riser responses under the crescent combined loading conditions is a key issue at the TDP region. The potential failure modes are buckling of the armour tendons and also rupture of the high resistance tapes. Much effort has been done in order to have available, from the market, larger envelopes of certified methodologies and qualified products, applicable to the Brazilian ultra-deep scenarios. Since 2002, an extensive R&D Program has been conducted (i) to improve current design evaluation tools & criteria and (ii) to establish representative test procedures and scope, for prototype qualification against the potential failure modes associated with combined axial compression, bending and torsion, at the TDP regions of bottom riser sections in ultra-deep water depths. This paper describes the main steps of the R&D Program, as below: I. Improvement of computational tools to better represent the behavior of the tendons, II. Consolidation of a new strategy for structural analysis, under more realistic conditions, III. Issue of a more adequate set of pipe technical specifications, and IV. Review of both theoretical and experimental results obtained from Feasibility Technical Studies and offshore field tests, respectively. Some examples and results are showed to illustrate, step by step, the whole process covered by the cited Program. Finally, the authors document their main conclusions for further discussion.
Constructability of Offshore Platforms
Authors: Saad Pascinthe , Salama Mamdouh M.
Published: November 2008

As part of the effort to achieve an economical development of offshore fields, focus is directed towards reducing construction cost while ensuring that the quality of construction details is maintained. This construction quality is particularly important for deepwater developments because of the increased demand for higher structural integrity to minimize in-service inspection, maintenance, and repairs. High structural integrity requires that particular attention is given to improved welding details. Achieving high integrity, while maintaining adequate control on cost, requires a thorough evaluation of the constructability factors that have major influence on a project CAPEX. These factors include project organization, contracting plans, materials and welding specifications, fabrication schemes and erection and load-out procedures. While significant benefits may be achieved through knowledge base transfer and lessons learned, these factors are typically design specific and can vary on a project by project basis. I this paper, constructability parameters will be discussed along with yard selection criteria and impact of design requirements on construction cost.
Covered Electrodes Temperature Variation During Wet Welding and Its Influence on Weld Metal Porosity
Authors: Pessoa Ezequiel C. P. , Bracarense Alexandre Q. , Liu Stephen , Guerrero Faustino Peres , Zica Eduardo M.
Published: November 2008

The objective of this work was to evaluate the porosity variation along weld bead and its relation with weld metal mechanical properties and electrode heating during underwater wet welding. Three commercial covered electrodes were used to make bead-on-plate welds. V-groove welds were also made using two electrodes at 50 and 100 meters depth in three different steels. Electrode temperature and weld metal porosity measurements and mechanical tests were performed. The results of temperature measurements indicated that electrode temperature increases during underwater wet welding. Simultaneously, porosity reduces along the BOP and V-groove weld beads. Mechanical tests showed that the mechanical properties are better at the end of welds. Additionally, the load supported by side bend tests samples extracted from 50 meter welds were higher than that measured for the 100 meter welds. Tensile test results also showed similar trend. Charpy test did not reveal any relation between the absorbed energy and porosity reduction along weld bead. However presented the same trend of bend and tensile tests at 50 and 100 m depth.
Ice Loads on a Model Podded Propeller Blade in Milling Conditions
Authors: Wang Jungyong , Akinturk Ayhan , Jones Stephen J. , Bose Neil
Published: November 2008

Propeller-ice interaction experiments were conducted in the ice tank at the National Research Council of Canada’s Institute for Ocean Technology. A podded propeller was used in “Puller” mode and loads on an instrumented blade were measured. During the propeller-ice interaction, hydrodynamic loads and ice milling loads were acting on the propeller blade. This paper focuses on the ice milling loads both in water and in air. The ice milling loads, however, cannot be separated from the hydrodynamic loads perfectly. Even if the blade is milling the ice within an ice block, it is still experiencing hydrodynamic loads designated as inseparable hydrodynamic loads. The non-dimensional ice milling loads including inseparable hydrodynamic loads on the blade are presented against advance ratio with varied depths of cut. The results help to reduce the gap of knowledge for interaction between ice and propeller and give information about significant variables acting on the propeller blade during interaction.
Development of a CFD Simulation Method for Extreme Wave and Structure Interactions
Authors: Yang Chi , Lo¨hner Rainald , Yim Solomon C.
Published: November 2008

A robust Volume of Fluid (VOF) technique is presented together with an incompressible Euler/Navier Stokes solver operating on adaptive, unstructured grids to simulate the interactions of extreme waves and three-dimensional structures. The incompressible Euler/Navier Stokes equations are solved using projection schemes and a finite element method. The classic dam-break problem has been used to validate the computer code developed based on the method described above. The numerical simulations of a three dimensional dam-break wave interacting with a single cylinder and a cylinder array have been carried out. Computational results have demonstrated that the present CFD method is capable of simulating the interactions of extreme waves and three-dimensional structures, which are of great importance for the comprehension of many natural phenomena in marine, coastal and marine engineering.
Coating Life Prediction for Water Ballast Tank
Authors: Melchers R. E. , Jiang X. L. , Lu K. J.
Published: November 2008

Corrosion is the key factor responsible for the degradation of ship structures and in no place is this truer than water ballast tanks. Coating protection system is a continual research interest for classification societies and coating industries. Up to now, most coating performance analyses are qualitative not quantitative. Coating life prediction is almost always based on experience and various assumptions, due to unavailability of practical data support systems. This paper describes a preliminary impartial investigation of coating life carried out with interviewees from the Australian Defence Science and Technology Organization (DSTO), shipyards, coating supplier and an independent expert. Plate surface, edges and welds in ballast tank were considered and the influences of dry film thickness (DFT) and surface preparation (SP) are addressed. The investigation gives some insight into the life of practical coating systems for water ballast tanks. Coating life is proposed to be representable by a normal distribution when corrosion breakdown is below 10% of plate thickness, which is of practical implication.
Fatigue Safety Factors for Flexible Risers Based on Case Specific Reliability Analysis
Authors: Leira Bernt J. , Igland Ragnar T. , Baarholm Gro S. , Farnes Knut A. , Percy Dick
Published: November 2008

In the present paper, fatigue safety factors for flexible risers are assessed. A procedure for reliability analysis of wave-induced fatigue is first described. The procedure is based on performing a number of parametric studies with respect to variables that influence the fatigue lifetime. The results of these parametric studies are subsequently combined with models describing the statistical scatter of the same parameters. By application of this procedure, the safety factors which are required in order to reach specific target reliability levels can be computed. Such safety factors are computed for three specific flexible riser configurations. Different SN -curves which correspond to different corrosive environments are considered. The percentwise contribution from each parameter to the total statistical variation of the limit state function is also quantified.
Simulation Program for Berthing and Mooring of Two Vessels in Consideration of Exact Hydrodynamic Interactions
Authors: Sakakibara Shigeki , Wakabayashi Masashi , Shimada Kiyoshi , Yamaguchi Hiroshi
Published: November 2008

A numerical simulation system has been developed for safety evaluation of berthing and side-by-side transfer offshore operations between two vessels. Water-tank experiment has been conducted on behaviors of connected two vessels in waves, providing accuracy of the system. Also behavior of two vessels during ship-to-ship transfer offshore operation of crude oil has been simulated by the present system to demonstrate usefulness of the system.
A Review of Occupational Safety and Health Management Principles With Reference to the Needs of the Shipbuilding and Offshore Construction Industries: A Client Point of View
Authors: da Silva Barboza Tania , Soares Medeiros Edmilson
Published: November 2008

Accidents related to production, processing, storage and transportation of oil and its by-products have been studied extensively because of their social and environmental impacts. However, researchers have largely ignored accidents related to the construction of oil facilities, perhaps because such accidents involve a small group of people and result in smaller-scale environmental impacts. In this paper we discuss the major potential risks in every phase of an offshore unit construction. We identified the limitations of traditional safety management systems in coping with the critical problems related to safety issues. Many companies are using integrated management systems as the major tools to control risk. Such systems cover health, safety and environmental issues (HSE). PETROBRAS, the largest Brazilian oil company and one of the leading oil companies in the world, has adopted the HSE system. The system focuses on employee participation in implementation of the HSE system. We highlight leader commitment as one of the keys to good results. In many cases, management commitment is low, implying a need to convince them of the importance of health and safety performance to the future prosperity of their company. Contractual directives are baselines to build good relationships during the project. Another relevant point is to demand a management system like OHSAS 18001 from contractors. Awareness of health risks is generally below that of safety risks and emphasis should be placed on increasing understanding of the causes.
Nonstationary Stochastic Modelling of Multivariate Long-Term Wind and Wave Data
Authors: Stefanakos Christos N. , Belibassakis Konstandinos A.
Published: November 2008

In the present work, a nonstationary stochastic model, which is suitable for the analysis and simulation of multivariate time series of wind and wave data, is being presented and validated. This model belongs to the class of periodically correlated stochastic processes with yearly periodic mean value and standard deviation (periodically correlated or cyclostationary stochastic process). First, the time series is appropriately transformed to become Gaussian using the Box-Cox transformation. Then, the series is decomposed, using an appropriate seasonal standardization procedure, to a periodic (deterministic) mean value and a (stochastic) residual time series multiplied by a periodic (deterministic) standard deviation. The periodic components are estimated using appropriate time series of monthly data. The residual stochastic part, which is proved to be stationary, is modelled as a VARMA process. This way the initial process can be given the structure of a multivariate periodically correlated process. The present methodology permits a reliable reproduction of available information about wind and wave conditions, which is required for a number of applications.
Yaw Drift Moment of a Floating Structure in Waves
Authors: Spanos Dimitris , Papanikolaou Apostolos
Published: November 2008

The wave induced yaw drift moment on floating structures is of particular interest when the lateral yaw motion of the structure should be controlled by moorings and/or active dynamic positioning systems. In the present paper, the estimation of the yaw drift moment in the modeled natural wave environment is conducted by application of a nonlinear time domain numerical method accounting for the motion of arbitrarily shaped floating bodies in waves. The computational method is based on linear potential theory and includes the non-linear hydrostatic terms in an exact way, whereas the higher-order wave-induced effects are partly approximated. Despite the approximate modeling of the second order hydrodynamic forces, the method proved to satisfactorily approach the dominant part of the exerted hydrodynamic forces enabling the calculation of drift forces and of other drift effects in irregular waves. Hence, the subject yaw drift moment in the modeled natural wave environment is derived, resulting to a basic reference for the design of similar type floating structures.
Low Cycle Fatigue of T-Tubular Joints With In-Plane Bending Loading
Authors: Waalen Jo̸rn , Berge Stig
Published: November 2008

Tubular T-joints were fatigue tested with in-plane bending loading. Six models were tested, three models with R-ratio of 0 and three with R = −1. Hot spot stress was measured for the brace and for the chord using the ECSC linear extrapolation procedure. Fatigue loading was applied in load control, to obtain through thickness cracking at a number of cycles in the range 3 000–64 000 cycles. The data were analysed and compared with the current fatigue design criteria for tubular joints.
Prediction of Pipeline Roll During S-Laying
Authors: Li Yousun
Published: November 2008

During S-laying a pipeline on the seafloor, the pipe is subjected to plastic strains over the stinger of the laying boat. The residue curvature may result in pipe axial rotation, which causes concerns about the orientation of the valves or connections. This paper presents two approaches to predict the pipe roll. The first approach idealizes the pipeline as a pre-bent helix by the residue curvature stretched on the solid floor. The second approach is a 3-D model, simulating the process of the pipe roll during the laying procedure in a quasi-static manner. The pipe loading path and deformation history are fully considered. Other factors, such as soil conditions, can be included. Empirical graphs for the pipeline axial roll versus a normalized residue curvature is established, by which the roll can be preliminarily estimated and the sensitivity of the roll to various parameters is explicitly expressed.
Non-Linear Wave Forces Acting on a Body of Arbitrary Shape Slowly Oscillating in Waves
Authors: Nihei Yasunori , Kinoshita Takeshi , Bao Weiguang
Published: November 2008

In the present study, non-linear wave loads such as the wave drift force, wave drift damping and wave drift added mass, acting on a moored body is evaluated based on the potential theory. The body is oscillating at a low frequency under the non-linear excitation of waves. The problem of interaction between the low-frequency oscillation of the body and ambient wave fields is considered. A moving coordinate frame following the low frequency motion is adopted. Two small parameters, which measure the wave slope and the frequency of slow oscillations (compared with the wave frequency) respectively, are used in the perturbation analysis. So obtained boundary value problems for each order of potentials are solved by means of the hybrid method. The fluid domain is divided into two regions by an virtual circular cylinder surrounding the body. Different approaches, i.e. boundary element method and eigen-function expansion, are applied to these two regions. Calculated nonlinear wave loads are compared to the semi-analytical results to validate the present method.
Bending Capacity of Girth-Welded Pipes
Authors: Torselletti Enrico , Vitali Luigino , Bruschi Roberto
Published: November 2008

In the last ten years, several studies were completed with the aim to define a design format for the local buckling of pipes subjected to differential pressure, axial load and bending moment. Experimental tests were carried out and simplified analytical solutions were developed in order to predict the pipe bending moment capacity and the associated level of deformation. Standard finite element (FE) structural codes, such as ABAQUS, ADINA, ANSYS, etc., were and are used as a “numerical testing laboratory”, where the model is suitably calibrated to few experimental tests. The outcomes of these research efforts were implemented in the design equations enclosed in international design rules, as DNV OS-F101. The local buckling design formats, included in these rules, give the limit bending moment and associated longitudinal strain as a function of the relevant parameters. The effect of the girth weld is introduced with a reduction factor only for what regards the strain at limit bending moment. This paper addresses the effects of the presence of the girth weld on both limit bending moment and corresponding compressive longitudinal strain. A 3-dimensional (3D) FE model developed in ABAQUS has been developed to perform a parametric analysis. The FE model results are shown to compare reasonably well with full scale experiments performed for on-shore pipelines. The limit bending moment is reduced by the weld misalignment and this reduction is also dependent on both internal pressure load and linepipe material mechanical strength. The FE results are compared with the limit bending moment calculated with DNV OS-F101.
Dynamic Behavior of Moored Ship Motions Induced by Initial Attack of Large Scaled Tsunami
Authors: Sakakibara Shigeki , Kubo Masayoshi , Kobayashi Eiichi , Koshimura Shunichi
Published: November 2008

In this paper, we propose a numerical simulation procedure of moored ship motions due to initial attack of large scaled tsunamis and investigate the effects on the motions and mooring loads. The effect of methodology on selection of tsunami wave components and of the drag forces are then considered by using the numerical simulation method, applying to several case studies for LNG-carrier. Large ship motions and excessive mooring loads beyond the safe working loads are induced by the resonant tsunami wave components in the sway and surge motions, and drag forces.
Numerical Wave Tanks Based on Finite Element and Boundary Element Modelling
Authors: Eatock Taylor R. , Wu G. X. , Bai W. , Hu Z. Z.
Published: November 2008

This work forms part of an investigation into the non-linear interaction between steep transient waves and flared structures, using a coupled finite element and boundary element model. The use of a coupled approach is based on consideration of the relative strengths and weaknesses of the finite element (FE) and boundary element (BE) methods when implemented separately (e.g. efficiency of computation versus complexity of adaptive mesh generation). An FE model can be used to advantage away from the body, where the domain is regular, and a BE discretisation near the body where the moving mesh is complex. The paper describes aspects of the FE and BE models which have been developed for this analysis, each based on the use of quadratic isoparametric elements implemented in a mixed Eulerian-Lagrangian formulation. Initially the two approaches have been developed side by side, in order to ensure the use of robust components in the coupled formulation. Results from these methods are obtained for a series of test cases, including the interaction of an impulse wave with a circular cylinder in a circular tank, and non-linear diffraction by a cylinder in a long tank.
Fatigue Life Analysis of Polyurethane Bending Stiffeners
Authors: Demanze Fre´de´ric , Hanonge Didier , Chalumeau Alain , Leclerc Olivier
Published: November 2008

Following some experiences of bending stiffeners fatigue failures during full scale tests performed at Flexi France on flexible pipe and stiffener assemblies, Technip decided to launch in 1999 a major research program on fatigue life analysis of bending stiffeners made of Polyurethane material. This fatigue life assessment is now systematically performed by Technip for all new design of flexible riser bending stiffeners. This totally innovative method comprises a number of features as follows: Firstly fatigue behaviour of polyurethane material is described. The theoretical background, based on effective strain intensity factor, is detailed, together with experimental results on laboratory notched samples, solicited under strain control for various strain ratios, to obtain fatigue data. These fatigue data are well fitted by a power law defining the total number of cycles at break as a function of the effective strain intensity factor. The notion of fatigue threshold, below which no propagation is observed, is also demonstrated. Secondly the design used by Technip for its bending stiffeners, and most of all the critical areas regarding fatigue for these massive polyurethane structures are presented. Thirdly the methodology for fatigue life assessment of bending stiffeners in the critical areas defined above is discussed. Calibration of the strain calculation principle is presented versus finite element analysis. Based on all fatigue test results, the size of the equivalent notch to be considered at design stage, in the same critical areas, is discussed. Finally, a comprehensive calibration of the methodology according to full and middle scale test results is presented. The present paper is therefore a step forward in the knowledge of fatigue behaviour of massive polyurethane bending stiffener structures, which are critical items for flexible risers integrity, and widely used in the offshore industry. The confidence in bending stiffeners reliability is greatly enhanced by the introduction of this innovative methodology developed by Technip.
IceMS: A Software for Ice Management
Authors: So¨derkvist Johan , Jansson Tomas
Published: November 2008

A combined system consisting of a forecast model to predict ice drift and a viewer tool for ice management, IceMS were developed for providing ice information during the Arctic Coring EXpedition (ACEX). The main task during the multi international expedition ACEX was to retrieve sediment cores from the Lomonosov Ridge in the central Arctic Ocean. Large ice floes or thick ice that drifts towards the drill ship threaten the operation by forcing the drill ship from its position. The gathered ice information was imported into IceMS and presented to the ice management team. Risk analysis for continued drilling operation was made, and instructions of where the Icebreakers Oden and Sovjetski Soyuz should break ice in the drilling area were carried out. The software IceMS contains tools to update the ice conditions, history lines of ships and buoys, and includes the possibility to import track lines showing the ice drift forecasts. The key concept is the combined visualization of map data and up to date imagery from satellite, airplane photos and ice charts, together with results from an ice drift forecast model. It is possible to move the images in IceMS map according to the observed ice drift recorded by the buoys placed on drifting ice floes. An overlay to mark and edit polygons, e.g. representing areas with certain ice classification, can be shown on top of the images. The edit overlay can be exported to file, which enables sharing of judgments and forecasts to other units. The model to predict ice drift is a state of the art ice drift model that is developed for describing rapid changes such as circular motion with a period of about twelve hours called inertial motion. The ice drift forecast was based on weather forecast and measured ocean currents near the drill site. The combined system of IceMS and the forecast model is being further developed for supporting ice management teams on offshore platforms and other constructions in ice infested areas. Results from Ice Management will be presented, showing examples of how IceMS presented ice information and validation of the ice drift model during the Arctic Coring EXpedition (ACEX). New tools in IceMS will also be presented.
Fracture Control — Offshore Pipelines: Probabilistic Fracture Assessment of Surface Cracked Ductile Pipelines Using Analytical Equations
Authors: Sandvik Andreas , O̸stby Erling , Naess Arvid , Sigurdsson Gudfinnur , Thaulow Christian
Published: November 2008

Since modern pipelines usually display ductile fracture behaviour, fracture assessments accounting for ductile tearing should be used. In this work we use a simplified strain-based fracture mechanics equation in the probabilistic fracture assessments. Furthermore, we use the traditional tangency criterion between the crack driving force and the crack growth resistance, in calculation of the onset of critical ductile tearing. Additionally, two types of external load on the line-pipe are considered, namely strains due to external bending moments and internal pressure. We establish the probability of fracture for line-pipes with relevant diameter to thickness ratios, and thicknesses, for J-laid or S-laid offshore pipelines. The distinction between system effects, in which all defects are likely to be subject to the same loading, and cases where only a small part of the pipeline will experience high loading, is also discussed.
Fracture Control — Offshore Pipelines: New Strain-Based Fracture Mechanics Equations Including the Effects of Biaxial Loading, Mismatch, and Misalignment
Authors: O̸stby Erling
Published: November 2008

In this paper a framework for a strain-based fracture mechanics crack driving force methodology for pipes with surface cracks, are presented. The model addresses the effects of crack depth, crack length, pipe diameter, wall thickness and yield to tensile ratio. Based on FE simulations, an equation to calculate the applied crack driving force, either through CTOD or J, has been derived. The equation is intended for use in cases where global plastic deformation occurs. A general approach to introduce the effects of biaxial loading, yield stress mismatch, and misalignment on the driving force, through definition of an effective wall thickness and an effective crack ligament height, is outlined. Models to quantify the effects of the different parameters are also derived. Finally, results are presented from comparison between 2D and 3D FE simulations and the predictions made by the proposed driving force equations.