bluuebunny/crossref_metadata_2025 huggingface dataset:
Computational Systems for Offshore Pipeline Launching Simulations
Authors: Masetti Isai´as Q. , Sparano Joa˜o Vicente , Jacob Breno Pinheiro , Albrecht Carl Horst , Barros Claudio R. Mansur
Published: January 2009

Computational systems have been developed to help the BGL-1 crew to perform safe mooring procedures. They calculate the deformed catenary configuration of all mooring lines, and simulate the pipeline launching operation itself, regarding the subsea interferences and the local environmental conditions. An onboard real case validation test was carried out and a comparison between the two systems was evaluated, with good agreement between the results of several mooring line parameters.
The Effect of PWHT on the Material Properties and Micro Structure in Inconel 625 and Inconel 725 Buttered Joints
Authors: Olden Vigdis , Kvaale Per Egil , Simensen Per Arne , Aaldstedt Synno̸ve , Solberg Jan Ketil
Published: January 2009

This report describes investigations performed on as welded and post weld heat treated samples of AISI 8630 steel, buttered with Inconel 625 and Inconel 725. The investigations have focused on the properties and microstructure in the partial mixed zone between the buttering and the steel before and after post weld heat treatment. The samples were heat treated for 4 1/2 hours at 640°C, 665° and 690°C and investigated with respect to mechanical properties and microstructure near the fusion line. A range of testing and analyses were performed including notch impact toughness testing, identification of fracture initiation and propagation in impact specimens, hydrogen measurements, examination of the micro structure in steel and Inconel using light microscope, hardness testing and electron micro-probe analysis of the alloying elements across the fusion line. Additional investigations in TEM on samples from an actual joint, post weld heat treated at 665°C were also performed. The results show that post weld heat treatment at 665°C and 690°C reduced the impact toughness in coarse grained heat affected zone, caused by decarburisation, ferrite formation and grain growth. The partially mixed zone (5–10μm) of the Inconel buttering, gained partly extremely high hardness caused by carbon enrichment, reaustenitization and formation of virgin martensite. As welded samples gave more favorable properties and microstructure than the post weld heat treated ones.
Design of Crack Removal Profiles Based on Shape Development of Surface Defects
Authors: Rodri´guez-Sa´nchez J. Efrai´n , Dover William D. , Brennan Feargal P.
Published: January 2009

A crack removal has the purpose to stop crack propagation and prevent future crack reinitiation, thus fatigue life of the component is extended. A profile design for the removal of fatigue cracks that grow under bending loading is presented. The design is based on the preferred shape development of surface defects under bending loading. Preferred shape development of surface defects was experimentally identified and validated with observations previously reported by other authors. The design of a crack removal profile consists on determining a notch geometry and its dimensions to cut out a crack. The crack removal profile presented here induces crack reinitiation, if it would occur, on the surface plate at the notch ends rather than in the bottom of the notch, so original plate thickness is reinstalled for propagation and inspection is easier. This repair procedure is recommended for the removal of fatigue cracks in tubular joints of offshore jackets steel structures.
Designing, Making, and Testing Syntactic Foam of Precisely Controlled Hydrostatic Strength
Authors: Wang Wen-Tsuen , Watkins Lou
Published: January 2009

This paper describes a recently developed syntactic foam material designed to collapse under precisely defined conditions of temperature and pressure to protect ultra-deep high pressure offshore oil and gas wells. Each grade of syntactic foam is engineered to have a specific set of characteristics, tailored for the region of the well it occupies. In the startup phase, the materials remain intact, with no significant volume change. As pressure and temperature in the well rise during operations, the materials begin to compress and relieve pressure in the narrow, confined space of the annulus. Finally, when conditions reach preset limits, the syntactic foam undergoes a sudden and dramatic collapse, preventing excessive overpressure, and protecting the steel casing. An important advantage of this material is that it is passive, requiring no controls or active intervention. It responds automatically to protect the well casing from overpressures and temperature spikes. The properties of the material can be adjusted to suit a wide range of conditions inside a given well, or from one well to another.
Static Stress Redesign of Structures by Large Admissible Perturbations
Authors: Bernitsas Michael M. , Kristanto Bhineka M.
Published: January 2009

The LargE Admissible Perturbation (LEAP) methodology is developed further to solve static stress redesign problems. The static stress general perturbation equation, which expresses the unknown nodal stresses of the objective structure in terms of the baseline structure stresses, is derived first. This equation depends the on the redesign variables for each element or group of elements; namely, the cross-sectional area and moment of inertia, and the distance between the neutral axis and the outer fiber of the cross section. This equation preserves the shape of the cross-section in the redesign process. 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 FE analyses. Several numerical applications on a simple cantilever beam and an offshore tower are used to verify the LEAP algorithm for stress redesign.
Progress of COSMOS (CO2 Sending Method for Ocean Storage) and OACE (Ocean Abyssal Carbon Experiment)
Authors: Aya Izuo , Namie Sadahiro , Yamane Kenji , Kojima Ryuji , Nakajima Yasuharu , Shirota Hideyuki , Brewer Peter G. , Peltzer Edward T. , Haugan Peter M. , Johannessen Truls , Kvamme Bjorn , Bellerby Richard G. J.
Published: January 2009

The storage of liquid CO2 at an ocean floor, one of promising measures to mitigate the global warming, requires 3500 m depth for the gravitationally stable storage, a breakthrough technology and a reasonable cost to realize, although it has large advantages such as the sequestration term longer than 2000 years. However CO2 can be sent to the ocean floor by shallow release, if we can use the nature that the cold CO2 to be shipped by a CO2 carrier is much denser than the ambient seawater even at shallow depths. The National Maritime Research Institute (NMRI) conducted several joint field CO2 release experiments with the Monterey Bay Aquarium Research Institute (MBARI, USA) since 1999 under the auspices of the NEDO, and proposed the improved COSMOS, CO2 Sending Method for Ocean Storage, in which CO2 is released into 200 m depth as slurry masses (mixture of dry ice and cold liquid CO2). Since 2002, under the NEDO Grant, the NMRI started a new international joint research, OACE, Ocean Abyssal Carbon Experiment with the MBARI and the University of Bergen (UoB, Norway), in order to accumulate the basic data on the long-term stability of stored CO2 and its environmental effects around storage site.
The Diffraction of Multidirectional Random Waves by Trapezoidal Submarine Pits
Authors: Lee Hong Sik , Williams A. Neil , Kim Sung Duk
Published: January 2009

A numerical model is presented to predict the interaction of multidirectional random surface waves with one or more trapezoidal submarine pits. In the present formulation, each pit may have a different side slope, while the four side slopes at the interior edge of any given pit are assumed equal. The water depth in the fluid region exterior to the pits is taken to be uniform, and the solution method for a random wave system involves the superposition of linear-wave diffraction solutions based on a two-dimensional boundary integral equation approach. The incident wave conditions are specified using a discrete form of the Mitsuyasu directional spectrum. The results of the present numerical model have been compared with those of previous theoretical studies for regular and random wave diffraction by single or multiple rectangular pits. Reasonable agreement was obtained in all cases. Based on these comparisons it is concluded that the present numerical model is an accurate and efficient tool to predict the wave field around multiple submarine pits of trapezoidal section in many practical situations.
Buckle Propagation and Its Arrest: Buckle Arrestor Design Versus Numerical Analyses and Experiments
Authors: Torselletti Enrico , Bruschi Roberto , Marchesani Furio , Vitali Luigino
Published: January 2009

Buckle propagation under external pressure is a potential hazard during offshore pipeline laying in deep waters. It is normal design practice to install thicker pipe sections which, in case of buckle initiation and consequent propagation, can stop it so avoiding the lost of long pipe sections as well as threats to the installation equipment and dedicated personnel. There is still a series of questions the designer needs to answer when a new trunkline for very deep water applications is conceived: • What are the implications of the actual production technology (U-ing, O-ing and Expansion or Compression e.g. UO, UOE and UOC) on the propagation and arrest capacity of the line pipe, • How formulations for buckle arrestors design can be linked to a safety objective as required in modern submarine pipeline applications. The answers influence any decision on thickness, length, material and spacing of buckle arrestors. This paper gives an overview of buckle propagation and arrest phenomena and proposes a new design equation, applicable for both short and long buckle arrestors, based on available literature information and independent numerical analyses. Partial safety factors are recommended, based on a calibration process performed using structural reliability methods. Calibration aimed at fulfilling the safety objectives defined in DNV Offshore Standards OS-F101 and OS-F201.
Possibilistic Analysis of Structural Systems Subjected to Blast Loads
Authors: Kanegaonkar Hari B.
Published: January 2009

The accidental release of the hydrocarbons and the possibility of resulting explosion have to be taken into account while designing the topside systems of the offshore structures. Determination of design explosion loads for the topside structures is a complex task since it involves several sources of uncertainty. Dimensioning of blast loads is important in achieving the desired safety level against the structural failure and related consequences. The design loads must incorporate uncertainties due to variability in the ignition point location, the type of ignition source, the volume of the gas released and the characteristics of the gas cloud etc. These uncertainties which are not statistical in nature may not be categorised as random or probabilistic but are cognitive and fuzzy in nature. The probabilistic framework for structural analysis subjected to blast loads could be quite cumbersome due to high number of uncertain variables and complex interdependency. The uncertainty in the load and corresponding uncertainty in the structural response can either be predicted from variations in the uncertain load parameters — a sensitivity evaluation or through a compact “possibilistic analysis”. The blast loads are usually defined as a triangular pulse through peak pressure, rise time and the blast pulse duration as the parameters. In the present investigation, the parameters in the triangular blast load description are assumed fuzzy. The peak pressure, rise time and blast pulse duration are defined using triangular fuzzy numbers. The possibilistic dynamic response of simple structural system — beam — used in the blast wall is obtained using single-degree of freedom approximation. It is shown that the possibilistic response provides rational decision making tool to arrive at desired safety level.
Thermal Stresses and Crack Propagation in PVDF Pressure Barriers Submitted to High Temperature Variations
Authors: Demanze Fre´de´ric
Published: January 2009

During the use of flexible pipes, important thermal variations can occur leading to thermal stresses. As a result two aspects were identified, in the past, due to thermal stress cycling [1,2] : – pull out of the pressure barrier, – crack growth of the pressure sheath. Pull out of the PVDF pressure sheath has been stopped by the design of new end connections [3]. Nevertheless, in order to get more knowledge of thermal stresses, Technip-Coflexip has developed a theoretical approach which is able to calculate whatever the plasticizer content, the initial temperature, the final temperature and the temperature variation, the thermal stresses for flexible pipes using PVDF materials. Comparisons between theoretical predictions and full scales test results show very good accordance and allow confirming that the Technip-Coflexip designs of end-connections are suitable for the offshore industry. Crack growth through the pressure sheath has been experienced only during accelerated testing at SINTEF and has not so far been seen in risers in operations. Crack growth through PVDF pressure sheath can be fully predicted by a model developed by Technip-Coflexip. The two major conclusions of the work performed are: – failure experienced at SINTEF are only linked to rough hand-machining and very severe test conditions, – failure can not occur in normal operation due to the fact that thermal stresses generated, linked with a good surface machining, are below the threshold of crack propagation.
Application of Genetic Algorithms to the Synthesis of Riser Configurations
Authors: Vieira Luciano T. , de Lima Beatriz de S. L. P. , Evsukoff Alexandre G. , Jacob Breno P.
Published: January 2009

The purpose of this work is to describe the application of Genetic Algorithms in the search of the best configuration of catenary riser systems in deep waters. Particularly, an optimization methodology based on genetic algorithms is implemented on a computer program, in order to seek an optimum geometric configuration for a steel catenary riser in a lazy-wave configuration. This problem is characterized by a very large space of possible solutions; the use of traditional methods is an exhaustive work, since there is a large number of variables and parameters that define this type of system. Genetic algorithms are more robust than the more commonly used optimization techniques. They use random choice as a tool to guide a search toward regions of the search space with likely improvements. Some differences such as the coding of the parameter set, the search from a population of points, the use of objective functions and randomized operators are factors that contribute to the robustness of a genetic algorithm and result in advantages over traditional techniques. The implemented methodology has as baseline one or more criteria established by the experience of the offshore engineer. The implementation of an intelligent methodology oriented specifically to the optimization and synthesis of riser configurations will not only facilitate the work of manipulating a huge mass of data, but also assure the best alternative between all the possible ones, searching in a much larger space of possible solutions than classical methods.
Composite Riser and Export Line Systems for Deep Offshore Applications
Authors: Odru Pierre , Poirette Yann , Stassen Yves , Saint Marcoux Jean Franc¸ois , Abergel Laurent
Published: January 2009

Composite materials offer an interesting alternative to classical steel solutions in the deep offshore risers and export lines systems. They are able to bring lightness both with high mechanical and compliance resistance, and important developments have been made by the industry to qualify them for offshore use. Most applications planned up to now have been however for TLPs, SPARs or Drilling Risers, where saving weight has direct influence on the design of the floating supports and corresponding equipment. However new riser system concepts have appeared, such as catenary risers, hybrid towers, or “Lazy W” export lines, used for instance on the Girassol field. The objectives of the present study are, starting from operational hypothesis, to design and verify feasibility of steel and composite risers for these types of applications in the very deep offshore (down to 2500m), including laying conditions. Composite and steel solutions are then compared and the advantages induced by the composite version can be evaluated. An acceptable cost of the composite version can then be deduced. Main conclusions are that both steel and composite versions are technically feasible in the mild conditions of the Gulf of Guinea or of Brazil. Steel is however close to its limit and may not work in more severe conditions. The cost advantages of the composite version are found essentially during the laying phase, and may justify the use of such an application. An important issue will be however the industrial availability of long length composite joints.
Sensitivity of Fatigue Assessment to the Use of Different Reference S-N Curves
Authors: Wang Xiaozhi , Cheng Zhan
Published: January 2009

The S-N curve based fatigue assessment approach is the most widely used one in both ship and offshore industry, in contrast with a fracture mechanics approach. The S-N approach, implemented by either simplified or spectral method, has to apply S-N curves to calculate fatigue strength. The S-N curve, which represents the number of cycles (N) of a constant amplitude stress range (S) that will cause a fatigue failure, is normally developed based on experimental data. Which S-N curve should be applied to a particular detail depends very much on the geometry of the detail, welding information as well as loading condition. There are various S-N curves published by different institutions, e.g., S-N curves published by UK HSE, IIW, AWS etc. The newly developed ABS “Guidance on Fatigue Assessment of Offshore Structures”, [1], proposes the ABS S-N curves, in which two categories of joints, tubular and non-tubular, are included, and both size and environment effects are taken into account. However, the application in Gulf of Mexico is also influenced by API recommendations. In API RP 2A, AWS S-N curves are referred, which in US practice is accepted for fixed (buoyant and non-buoyant) platform deck structures. The objective of this paper is to address the difference between different S-N curves and to present the detailed results of fatigue assessment by using different S-N curves for non-tubular joints. Conclusions made based on the study provide more background on the S-N curve application in fatigue assessment.
Numerical Simulation of Vortex Shedding From a Circular Cylinder in the Presence of a Free Surface
Authors: Nagaya S. , Baddour R. E.
Published: January 2009

CFD simulations of crossflows around a 2-D circular cylinder and the resulting vortex shedding from the cylinder are conducted in the present study. The capability of the CFD solver for vortex shedding simulation from a circular cylinder is validated in terms of the induced drag and lifting forces and associated Strouhal numbers computations. The validations are done for uniform horizontal fluid flows at various Reynolds numbers in the range 103 to 5×105. Crossflows around the circular cylinder beneath a free surface are also simulated in order to investigate the characteristics of the interaction between vortex shedding and a free surface at Reynolds number 5×105. The influence of the presence of the free surface on the vortex shedding due to the cylinder is discussed.
Reliability of Tubular Joints of Marine Jacket Platforms
Authors: Castro-Tello Francisco , Campos Dante , Garci´a-Pe´rez Jaime , Palma-Herna´ndez Eduardo
Published: January 2009

This paper presents a group of methods for studying the structural reliability of tubular joints of marine jacket platforms, and shows also the way of using this information on the estimation of the global structural reliability. For the analysis of the joints, the following four failure modes are considered: yielding, punching, buckling and fatigue. In the process each failure mode is analyzed separately, since mechanical interactions between the different failure modes are not taken into account. In order to consider the combinations of the different failure modes, the correlation coefficients among them are taken into account. The main contribution in this paper is to provide procedures and adequate models for the analysis of the tubular joints, whose local handling is decisive on the correct estimation of its global performance and reliability.
Expanding Missions for Small Unmanned Undersea Vehicles (UUVs)
Authors: Fletcher Barbara , Wernli Robert L.
Published: January 2009

Small unmanned undersea vehicles (UUVs), those less than 150 pounds, have many advantages for field operations over the larger models. The increase in number and capabilities of these vehicles is opening doors for an ever expanding number of applications. Current and anticipated mission areas will be discussed, including hydrographic survey, mine countermeasure survey / classify / map, target reacquisition and identification, chemical detection and plume mapping, and harbor security. New trends in applicable technologies will be described and recommendations made for the further development and use of small UUVs.
Integration of Field Investigation to Evaluate the Degradation of the Bearing Capacity of Platform Foundations Due to the Gas Presence
Authors: Cruz Roque Diego , Nu´n˜ez Farfa´n Jaime , Barrera Nabor Pro´coro , Koh Cambranis Wilbert
Published: January 2009

Natural Gas emanations at the Campeche Sound in the Gulf of Mexico have caused in some cases the failure of soils under existent platforms. The gas pockets that were detected in shallow geophysical surveys prior to the platform installations have migrated invading the area of some platforms. The presence of these shallow gas pockets and sudden gas emanations (blow out) is a cause of concern regarding the safety of the existent and planned platforms. An investigation was carried out in order to assess the effect of the gas emanations and the presence of the shallow gas on the safety of the platforms. The investigation included a desk study with the purpose of integrating all relevant information from the reservoir and up to the sea bed with the participation of all the disciplines involved. On these bases, a field investigation was planned, to confirm the results of the desk study. This investigation included the application of several new techniques in the exploration field. The field investigation included geophysical, geotechnical and geochemical exploration, as well as the installation of a monitoring system to better understand the complex gas effects on the structures foundation. A 3D high resolution seismic survey was used to investigate the origin and dimensions of the shallow gas pockets. Te evaluation of the effects of shallow gas and hydrocarbon deposits on the existing and proposed structures in the Cantarell field was achieved through an integrated analysis of the geophysical data, in situ measurement of pore pressure, in situ and laboratory geotechnical analysis of gas in soil boring profiles, special static and cyclic laboratory testing on hydrocarbon saturated soils, and special cyclic testing on gas-saturated granular soils. The study shows that the current levels of pressure in the hydrocarbon pockets are not expected to affect the existent structures safety; however, as it has happened in the past, it is possible that pressure could build up and cause a sudden gas expulsion affecting existing platforms. Taking this in consideration a monitoring system was installed in order to measure the pressurization of the foundation zone strata that could result in weakening of the soil response affecting the structure stability.
Effect of Nickel on Toughness of Underwater Wet Welds
Authors: Perez Faustino , Liu Stephen , Smith Charles , Rodriguez Efrain
Published: January 2009

Underwater wet welding has been used as an option for the repair of offshore platforms. Rutile-grade electrodes are typically used to carry out the underwater repairs because of their good arc stability, bead appearance, and bead morphology. However, the main problems to overcome are porosity and reduction of toughness and strength as the water depth increases. During wet welding, the welding arc decomposes water into hydrogen and oxygen, which results in the formation of oxides and pores in the weld metal. The loss of alloying elements in the oxidation process and the fast cooling rate due to the quenching effect of water surrounding the weld are responsible for the deterioration in mechanical properties. This paper presents evidence of toughness improvements on wet welds made with experimental rutile-grade electrodes. Experimental electrodes with nickel added to the flux covering (0, 1.2, 2.3, and 3.0 wt. pct.) were extruded. A commercial rutile electrode was used for comparison. Bead-on-plate and multipass V-groove wet welds were made at 1 ft. water depth in fresh water. Charpy impact test specimens were machined from the V-groove welds and tested at four temperatures. The toughness measured at −50°C of wet welds with 3.0 wt pct. nickel was improved by a factor of four over the wet welds without nickel content. Smaller improvements were obtained with 2.3 wt. pct. nickel at −50°C. At higher temperatures, the toughness did not increase with nickel additions. All-weld-metal reduced-size tensile specimens made from the wet welds deposited with the commercial and experimental electrodes presented similar yield and tensile strength. The tensile specimen with 3.0 wt. pct. nickel presented lower ductility.
Alternative Design Philosophies for Achieving Target Safety Levels in Fixed Offshore Structures
Authors: Cole Geoff , Ernestine Annalisa , Rooney John
Published: January 2009

This paper explores two alternative design philosophies for achieving target safety levels in fixed offshore structures. The first uses a Working Stress Design format, and examines the relationship between the return period of the metocean design criteria and the configured structural reliability. The second uses a Load and Resistance Factor Design format, and considers suitable environmental partial load factors required to achieve acceptable safety levels. An example case study of two unmanned structures demonstrates the importance of local environment and structural configuration in determining reliability. The results indicate that for certain combinations of structural configuration and environment, previously recommended design approaches appear inadequate. This study proposes more appropriate design criteria for two specific configurations on the North West Shelf of Australia.
Modal Experimental Study on Added Mass of Elastic Plate Supported by Free Floating Condition
Authors: Maruyoshi Koichi , Saijo Osamu , Eto Hiroaki
Published: January 2009

The floating structure of pontoon type is expected to be used for an artificial base. Assuming that its floating structure is constructed of plate structural system, we have studied on added mass yielded from elastic behavior of the plate. It is considered naturally that added mass is dependent on mode shape of vibration, for the analysis of the added mass, special knowledge of fluid dynamics is required. Therefore, a proposal of simple calculation method is significant. This paper aims to propose the simple equation for calculation of added mass. In order to develop it, we carried out modal experiment by floating elastic plate model. The distribution characteristic of added mass was grasped through that experiment. By applying those characteristics, the simple equation for calculation of added mass became successful in the proposal. The validity of the obtained simple equation was examined by comparison with present experimental results and other results.
Offshore Platform Repaired by Wet Welding Weathers Huricane Lili
Authors: DeFranco Samuel J. , Reynolds Thomas J. , Buescher Frank J. , O’Connor Patrick
Published: January 2009

The Eugene Island 273 B structure is a four-pile production and drilling platform installed in 184 feet of water in the Gulf of Mexico. The platform was installed in 1970. During the 2000 underwater structural inspection program, delamination damage to two main structural brace members was discovered through the use of flooded member detection. This paper describes the process of engineering, Project Management, Hazard Identification, planning and execution to complete repairs to the damaged members using wet welding techniques.
An Inverse Numerical Technique to Estimate the Undrained Shear Strength of Marine Clays in Deep Waters
Authors: Ramos Ju´nior Adeildo S. , Vieira Luciana C. L. M. , Amaral Cla´udio S. , Ramos Viviane C. L.
Published: January 2009

The study of alternative techniques to characterize the geomechanical properties of marine clays in deep waters has been the objective of numerous studies. Such research is warranted because of the difficulty in the use of traditional inspection methods under those environmental conditions. This paper presents an inverse numerical technique to evaluate the undrained soil shear strength of the marine soil. This technique is based on the response measurement during penetration in the marine soil by a gravity released pile. By inverse here we mean that the algorithm developed uses the experimental data to fit the parameters of the differential equation of motion of the pile during the penetration, using the least square method. In this procedure the parameters are associated to the undrained shear strength of the marine clay and to the drag coefficient of the pile. Examples are shown to illustrate the feasibility of the method when compared to other conventional tests.
Wave Diffraction of Steep Stokes Waves by Bottom-Mounted Vertical Cylinders
Authors: Kim J. W. , Kyoung J. H. , Ertekin R. C. , Bai K. J.
Published: January 2009

The diffraction of highly nonlinear Stokes waves by vertical cylinders of circular cross section is numerically simulated in the time domain. A finite-element method, based on Hamilton’s principle, is used to discretize the fluid domain. The Stokes waves, input at the numerical wave maker, are obtained numerically from the two-dimensional steady solution of the finite-element method. A new matching scheme is developed to match the two-dimensional wave at the far field and the three-dimensional diffracted wave in the near field. The method developed here can easily be extended to the diffraction of irregular, nonlinear waves. Numerical examples are presented for the diffraction of Stokes waves with various steepnesses by a circular cylinder. The wave elevation and run-up on the cylinder are calculated and compared with the available theoretical results.
Assessment of Corrosion Risks to Aging Ships Using an Experience Database
Authors: Wang Ge , Spencer John , Sun Haihong
Published: January 2009

Damages to ships due to corrosion are very likely, and the likelihood increases with the aging of ships. Risk and reliability approaches are more and more frequently applied in design and maintenance planning. These advanced approaches require reliable data reflecting the structural condition of ships in service. Such data is scarce. This paper presents a database of corrosion wastage. It is based on over 110,00 thickness measurements recently collected from 140 trading tankers. This database is larger than most other corrosion databases in the public domain. Corrosion wastage exhibits a high level of variability. In addition to thickness measurements of individual structural members, this database also has information on hull girder’s geometrical properties and strength of ships in service. Corrosion wastage has an influence on the hull girder strength. Statistical interpretations of the database are used to represent corrosion wastage in oil tankers. The severity of corrosion is ranked by three levels: slight, moderate and severe levels corresponding respectively to 50, 75 and 95% cumulative probability on the database. The risks of corrosion wastage to aging ships’ structural integrity are assessed using the observations of the corrosion wastage database. The investigated risks are loss of local member’s strength, loss of global hull girder strength, and shortened inspection intervals. The experience database can be used in many aspects, such as design requirements for corrosion additions and wastage allowance for plate renewal, establishment of limits to hull girder strength of FPSOs, time variant reliability approach and risk based inspection schemes.
On the Constraint-Based Failure Assessment of Surface Cracks in T-Plate Welded Joints
Authors: Wang X. , Bell R. , Lambert S. B.
Published: January 2009

The loss of crack tip constraint leads to enhanced resistance to both cleavage and ductile tearing. However, conventional failure assessment schemes (CEGB-R6, BS-7910) use lower bound toughness obtained from highly constrained test specimens. Cracks in many real engineering structures are not highly constrained, which makes failure predictions using conventional failure assessment schemes based on lower bound fracture toughness values overly pessimistic. Excessive pessimism in the structural assessment can lead to unwarranted repair or decommissioning of structures, and thus cause unneeded cost and inconvenience. Recent developments on constraint-based fracture mechanics have enabled the practical assessment of defective components including the constraint effect. For example, the recent revision of R6 and the newly developed structural integrity assessment procedures for European industry (SINTAP) have suggested a framework for failure assessments including the constraint effect. In this paper, the constraint-based failure assessment of surface cracked T-plate welded joints under tension load is presented. Different issues including the constraint-based failure assessment diagrams, the treatment of combining primary and the secondary loads, and the calculation of stress intensity factors, limit loads and constraint parameters for surface cracked T-plate joints are discussed. It is demonstrated that when the lower constraint effect is properly accounted for, the maximum allowable tensile stress level increases substantially.
Field Implementation of RBI for Jacket Structures
Authors: Faber Michael H. , Straub Daniel , So̸rensen John D. , Tychsen Jesper
Published: January 2009

The present paper first gives a brief outline of the simplified and generic approach to reliability and risk based inspection planning and thereafter sets focus on a recent application of the methodology for planning of in-service NDT inspections of the fixed offshore steel jacket structures in the DUC concession area in the Danish part of the North-Sea. The platforms are operated by Maersk Oil and Gas on behalf of DUC partners A.P. Mo̸ller, Shell and Texaco. The study includes a sensitivity analysis performed for the identification of relevant generic parameters such as the bending to membrane stress ratio, the design fatigue life and the material thickness. Based on the results of the sensitivity analysis a significant number of inspection plans were computed for fixed generic parameters (pre-defined generic plans) and a data-base named iPlan was developed from which inspection plans may be obtained by interpolation between the pre-defined generic plans. The iPlan data-base facilitates the straightforward production of large numbers of inspection plans for structural details subject to fatigue deterioration. In the paper the application of the generic inspection plan database iPlan is finally illustrated on an example.
Case Study on the Universal Town Planning for Water Front Redevelopment in Okinawa Prefecture
Authors: Yamamoto Kazukiyo , Kamise Satoshi , Kagami Masaaki
Published: January 2009

In Japan, recently, the word ‘Universal Design’ is getting to settle down in the field of town planning and producing subsistence goods owing to the prospects of coming super-aged society. This study tried to generalize Universal Design concept in the planning of fishing port redevelopment Chatan town in Okinawa Prefecture, Japan. In traditional town planning process of Japan, it was led by administrative organizations with limited public involvement. But in this study, we would like to introduce the idea of Public Involvement, especially participation of land users and investors on town and fishing port redevelopment planning procedure from the very early step of plan to the final decision of land zoning, nearly for the first working example in Japan. And as for the construction plan of project, Universal Design concept is also accepted as main motto based on angle of the most economically but considering natural environment and human need and high technical assistance. For example, regarding the planning of roads and facilities, accessibility of aged and handicapped people was considered as important factor. In this paper, it was shown of the results of facility planning, project establishment and resident involvement on the town planning under the concept of Universal Design.
A Numerical Study on Change in the Marine Environment of Tokyo Bay in the Latest 70 Years
Authors: Kitazawa Daisuke , Fujino Masataka , Tabeta Shigeru
Published: January 2009

A numerical study by means of a marine ecosystem model is conducted to examine the causes of change in the marine environment of Tokyo Bay in the latest 70 years. First, the marine ecosystem model is validated by comparing the predicted water quality such as water temperature, dissolved oxygen (DO), chemical oxygen demand (COD), total phosphorus (T-P) and total nitrogen (T-N) for the year of 1994 with the field data, which has been observed at 48 spots in Tokyo Bay. In addition, topography of Tokyo Bay and the discharge of chemical matters from the rivers are estimated for each year of 1935, 1979, and 1994, and the marine environment in the summer of each year is reproduced by numerical simulation. From comparing the results, it is revealed that the marine environment varies corresponding mainly to change in the discharge of chemical matters, and that the impact of reclamation is about 30% of the impact of change in the discharge of chemical matters.
Effects of Two-Peak Spectra on Wave Crest Statistics
Authors: Bitner-Gregersen Elzbieta M. , Hagen O̸istein
Published: January 2009

Effects of two-peak spectra on the second order wave statistics is investigated by second order time domain simulations. Particular attention is given to the wave crest statistics. The two-peak Torsethaugen frequency spectrum (1996) currently used by the Norwegian industry is adopted. Both 2D and 3D seas are considered, and for 3D different directional spreading functions for wind sea and swell are applied. The results for the Torsethaugen frequency spectrum are compared with prediction given by the JONSWAP spectrum and the 2nd order Forristall (2000) crest model.
Seismic Retrofit of Coastal Dikes
Authors: Adalier Korhan , Pamuk Ahmet , Zimmie Thomas F.
Published: January 2009

Soil liquefaction and associated ground failures have caused much damage to coastal and waterfront structures in the past major earthquakes. The prevalence of liquefaction in the coastal environment necessitates the development of appropriate remediation countermeasures. This paper presents an experimental study involving centrifuge physical modeling to assess the earthquake performance of countermeasure retrofit techniques for a liquefiable marine foundation under an existing coastal dike-embankment. Currently, such testing results offer a valuable alternative to studying actual full-scale dynamic response, since such data is virtually non-existent for retrofitted dikes. The response of a cohesive dike supported on a loose saturated sand layer is analyzed under dynamic base excitation conditions. In a series of four separate heavily instrumented model tests, this embankment foundation system was studied first without, and then with, the following three foundation liquefaction countermeasure-retrofit techniques: crushed gravel (drain) walls, cemented soil walls, and sheet-pile enclosure. The underlying mechanism and effectiveness of each countermeasure is discussed, based on the recorded dynamic response. All of the implemented countermeasures were found to significantly reduce embankment deformations. In some cases, cracking and lateral spreading of the dikes were practically eliminated.
A Robust Structural Stress Method for Fatigue Analysis of Ship Structures
Authors: Dong P.
Published: January 2009

Recent rapid advances in developing mesh-insensitive structural stress methods are summarized in this paper. The new structural stress methods have been demonstrated to be effective in reliably calculating structural stresses that can be correlated with fatigue behavior from simple weld details to complex structures. As a result, a master S-N curve approach has been developed and validated by a large amount weld S-N data in the literature. The applications of the present structural stress methods in a number of joint types in offshore/marine structures will be illustrated in this paper. The implications on future applications in drastically simplifying fatigue design and evaluation for offshore/marine structures will also be discussed, particularly for using very coarse finite element mesh designs in ship structures.
Sea State Duration and Probability of Occurrence of a Freak Crest
Authors: Bitner-Gregersen Elzbieta
Published: January 2009

For design purpose extreme wave crests can be determined by direct extrapolation or by estimating an extreme sea state condition. In the latter procedure it is common to estimate a n-year Hs level as a fractile of a marginal long-term distribution of significant wave height, combined with adequately chosen characteristics values for the other sea-state parameters. In this approach a sea state duration needs to be assumed when extremes are calculated. In the present study sensitivity of extreme crest characteristics to an assumed sea state duration is investigated for wave records which include a freak event. The wave time series recorded at the Draupner platform, January 1, 1995, and the data registered at Ekofisk, October 25, 1998, are used in the analysis. Predictions of several models are compared with the prediction given by the 2nd order Forristall crest distribution. Implications of the results for the current design practice are discussed.
A New Analytical Expression to Estimate the Bending Stiffness of Flexible Risers
Authors: Ramos Roberto , Pesce Celso P. , Martins Clo´vis A.
Published: January 2009

Flexible risers are complex structures used in offshore oil exploitation activities. Such structures are composed of several concentric polymeric and steel armour layers which withstand static and dynamic loads applied by the floating production vessel and by the ocean environment. Determining the equivalent flexural stiffness of such structures is an important task for the global structural analysis, since it provides a probable value that can be used in this analysis to predict the load distribution along the line (that is important in critical regions such as the TDP and the top). Besides that, estimates for the flexural stiffness are also important for predicting instabilities in the line (loop formation). However, the complexity imposed mainly by geometry and contact conditions renders a finite element analysis of these structures practically unfeasible, even considering that all the materials obey a linear elastic behaviour. So, in order to achieve this task, analytical methods have been proved to be, till now, a better choice. The aim of this work is to present the basis of a new analytical equation to estimate the flexural structural behaviour of flexible risers. Emphasis is given on the geometrical analysis of armour layers.
Corrosion Fatigue Testing of Flexible Riser Armour: Procedures for Testing and Assessment of Design Criteria
Authors: Berge Stig , Bendiksen Erik , Gudme Jonas , Clements Richard
Published: January 2009

Fatigue design of armour wires in flexible risers is reviewed, with particular emphasis on effects of corrosive environments in pipe annulus. Test procedures for corrosion fatigue testing of armour wire and assessment of fatigue design criteria are described.
Study on the Coastal Eco-Tourism and C.V.M. in the Seto Island Sea
Authors: Iwaki Masanori , Arai Yoichi , Kimoto Masaharu
Published: January 2009

As Japan is surrounded by the ocean, it has always been one of the key strategies in the nation’s industrial policy making to take advantage of the ocean. The nation’s industrial structure has changed, however, and the emphasis has shifted from the heavy industries to the service industries. How to revitalize the activities related to the ocean and the coastal towns has become an extremely important task. In response to this need, a new development concept has attracted much attention, in which vitalization of a given local area is achieved through utilization of its own resources. Eco-tourism offers a new and sustainable tourism development, incorporating the philosophy of harmony with the indigenous nature and unique culture. The keyword of Sustainable Development is particularly important not only in the revitalization of local industries but also in the preservation of global resources. In this paper, Eco-tourism is considered to be a new tourism industry that gives vitality to local communities. To gain basic data, residents’ views on the local environmental factors are represented in concrete terms through Contingent Valuation Method (C.V.M.). The suburban town area of the Higashi-Geiyo Islands has been selected as the subject of the survey.
Risk Based Inspection of Jackets Submitted to Through-Wall Cracks
Authors: Schoefs Franck , Rguig Mustapha
Published: January 2009

The actual challenge for the requalification of existing offshore structures through a rational process of reassessment leads to state the importance of Risk Based Inspection methodology. This paper points out the inspection results modelling and their contribution to decision aid tools. The study of the impact of through cracks on structural integrity of jacket platforms is still a challenge. The detection of large cracks is first addressed. In order to minimize inspections and maintenance costs, all the available data from inspection results, such as probability of detection and probability of false alarm, must be addressed, as well as the probability of crack presence. This can be achieved by the use of the decision theory. These capabilities of Non Destructive Testing give a first input for the risk study. A cost function is suggested to introduce this modelling into a risk analysis and is devoted to help rank the NDT tools. The case of large through-wall cracks is specifically addressed.
Vibration of Plate Structures Solved by DQEM Using EDQ
Authors: Chen Chang-New
Published: January 2009

The vibration of plate structures is solved by DQEM using EDQ. In the DQEM discretization, EDQ is used to define the discrete element model. Discrete eigenvalue equations defined at interior discrete points in all elements, transition conditions defined on the inter-element boundary of two adjacent elements and boundary conditions at the structural boundary form the overall discrete eigenvalue equation system. Numerical results obtained by the developed numerical algorithms are presented. They demonstrate the developed numerical solution procedure. This vibration analysis model can be used to solve wide range of offshore engineering structures.