bluuebunny/crossref_metadata_2025 huggingface dataset:
Unified Model for Gas-Liquid Pipe Flow Via Slug Dynamics: Part 1 — Model Development
Authors: Zhang Hong-Quan , Wang Qian , Sarica Cem , Brill James P.
Published: January 2009

A unified hydrodynamic model is developed for predictions of flow pattern transitions, pressure gradient, liquid holdup and slug characteristics in gas-liquid pipe flow at different inclination angles from −90 to 90 deg. The model is based on the dynamics of slug flow, which shares transition boundaries with all the other flow patterns. By use of the entire film zone as the control volume, the momentum exchange between the slug body and the film zone is introduced into the momentum equations for slug flow. The equations of slug flow are used not only to calculate the slug characteristics, but also to predict transitions from slug flow to other flow patterns. Significant effort has been made to eliminate discontinuities among the closure relationships through careful selection and generalization. The flow pattern classification is also simplified according to the hydrodynamic characteristics of two-phase flow.
Prediction of Slug Length Distribution Along a Hilly Terrain Pipeline Using Slug Tracking Model
Authors: Al-Safran Eissa M. , Taitel Yehuda , Brill James P.
Published: January 2009

Accurate prediction of slug length distribution and the maximum slug length in a hilly terrain pipeline is crucial for designing downstream separation facilities. A hilly terrain pipeline consists of interconnected uphill and downhill pipe sections, where slugs can dissipate in the downhill sections and grow in the uphill sections. Furthermore, new slugs can be generated at the dips (bottom elbows) and dissipate at the top elbows. Although existing steady-state models are capable of predicting the average slug length for pressure drop calculations and pipeline design, they are incapable of predicting detailed flow characteristics such as the maximum slug length expected at the exit of a hilly terrain pipeline. A transient slug tracking model based on a quasi-equilibrium formulation was developed to track the front and back of each individual slug, from which individual slug lengths are calculated. The model was verified with large-scale two-phase flow hilly terrain experimental data acquired at the Tulsa University Fluid Flow Projects (TUFFP). The results show a fairly accurate match between the model predictions and experimental data.
Mechanical Fault Diagnosis Using Numerical Hilbert Analysis
Authors: Yang Baozhong , Suh C. Steve
Published: January 2009

Dynamic instability induced by the initiation and development of mechanical faults in a rotary element is known to have a large negative impact on the reliability and operation safety of an entire system. This type of nonlinear system response is generally perturbed by shock impulses of extremely short time scale and amplitude. Thus difficulty presents itself in identifying and isolating features indicative of the presence and progression of faults possibly leading to mechanical deterioration. The perturbed and deteriorated states of a bearing-shaft system subjected to the actions of various types of commonly seen mechanical faults are investigated using the Numerical Hilbert Transform. The presented approach characterizes and realizes temporal events of both short and long time scales as instantaneous frequencies in the joint time-frequency domain. Examples are given to demonstrate the feasibility of applying the approach to the characterization of various deteriorating bearing states and the identification of parameters associated with several failure modes.
Nonlinear Model for Dynamic Behavior of Drill-String
Authors: Melakhessou Hayat , Berlioz Alain , Ferraris Guy
Published: January 2009

This article is devoted to the study of the contact between the drill-string and the well during drilling operations. The study focuses on the Bottom-Hole-Assembly (BHA), which is submitted to compression. The work is motivated by the need to understand the complex behavior of such a system, in order to improve control their constructive and destructive potentials. The contact, which is supposed to be localized on the drill-collar or stabilizers, is prejudicial and involves a premature abrasive wear of the drill-string, reduction of the rate of penetration of the tool into the rock (ROP) and reduction of the mean time between failure (MTBF). The proposed mathematical model is expressed in terms of four independent degrees of freedom. They include the effects of bending and torsion; the whirling motion of the drill-string as well as the phenomena of friction between the drill-string and the well. The tangential effect is modeled by using Coulomb’s law of friction. The nonlinear equations of the movement are derived using Lagrange equations and are solved numerically to obtain the response. Specific attention is paid to the study of friction and a consistent contact model which is capable of taking into account the rolling of the drill-string, both with and without slip, is included in the model. This paper also presents a parametric study on the influence of the initial position of the string and the friction coefficient of the contact on the dynamic behavior of the structure. An experimental set-up, equipped with two optolineic devices, is used to validate the model.
An Independent-Flow-Field Model for a SDOF Nonlinear Structural System: Part II — Analysis of Complex Responses
Authors: Lin Huan , Yim Solomon C. S.
Published: January 2009

Complex responses observed in an experimental, nonlinear, moored structural system subjected to nearly periodic wave excitations are examined and compared with the simulations of a newly proposed independent-flow-field (IFF) model in this paper. Variations in wave heights are approximated by additive random perturbations to the dominant periodic component. Simulations show good agreement with the experimental results in both time and frequency domains. Noise effects on the experimental results including bridging and transition phenomena are investigated and interpreted by comparing with the simulations of its deterministic counterpart. Possible causes of a chaotic-like experimental result as previously observed are also inferred.
On Controlled Oscillating Bodies With Submerged Reaction Mass
Authors: Korde Umesh A.
Published: January 2009

This paper discusses coupled oscillating bodies used in wave energy absorption in deeper waters. In particular, systems using submerged reaction masses are considered using a frequency domain approach based on regular wave excitation. Approximate optimal reactive and resistive loads, and the corresponding capture width ratios are computed for a system of two vertically oscillating coupled axisymmetric bodies with an actuator operating between them. Results obtained over a range of frequencies indicate the advantages of dynamic coupling between oscillation modes. Such results could be used in adjustable “tuning” of 2-degree-of-freedom devices to different wave spectra for efficient energy absorption.
Model Experiments of a Tension Leg Platform
Authors: Karatas¸ Hasan , Mastanzade Nijat , Kiymaz Gu¨ven
Published: January 2009

The present paper presents the results of an experimental program on tension leg platforms. The geometric form of the test model structure is a conical shell surface. The model structure was tested in a hydraulics laboratory. The dynamic behavior depends on the buoyancy of the main structure and tension in the legs. Dynamic characteristic values for the TLP model test were compared against the theoretical values according to the Frude law. The difference between the model test values and theoretical values was found to be 7.5% and therefore is considered to be satisfactory.
Multi-Modal VIV Excitations: Measurements and Predictions
Authors: Le Cunff C. , Gue´rin P. , Molin B.
Published: January 2009

An elongated structure in a current will experience vibrations due to vortex shedding (VIV). In the offshore industry, the main concern is to quantify the fatigue damage due to VIV. For in-situ applications, the current will vary as a function of depth, the structure can be made of sections with different diameters, all these parameters will modify the shedding frequency, leading to multi-modal excitations. In order to better understand and quantify the response of such a structure, experiments were carried out in the BGO-First facilities in la Seyne sur Mer. This tank is equipped with a current generation system that permits to produce uniform currents all throughout the tank section, 16 m wide and 3 m deep. The model consisted in an inclined cable under tension, about 24 m long, in a vertical plane perpendicular to the current, with about half of its length in the water. Its submerged part was fitted with flexible sheaths of different diameters, inducing vortex shedding at varying frequencies along the cable and a multi-modal response. Seven different geometries were tested, at varying top tension and current velocities. The cable motion was measured in twenty locations of its aerial part, through an optical tracking system. Displacements were of the order of 10mm with a measurement accuracy of 0.1mm. In the present paper, one configuration with two sheath diameters is studied in details. Crossflow and in-line results on RMS displacements and frequencies are reported. Comparisons with two numerical methods are also performed. The first method is a simple modal approach restricted to crossflow vibrations. The modal lift forces are evaluated and the response of the structure is obtained in the frequency domain. The second technique is based on the resolution of the Navier-Stokes equations in two-dimensional slices perpendicular to the structure. The Navier-Stokes solver is coupled with a finite-element model used to discretize the structure. Good agreement between numerical and experimental results is obtained for the displacements and dominant frequencies.
Engineering an Autonomous Underwater Vehicle for Under Ice Operations
Authors: Stevenson P. , Millard N. W. , McPhail S. D. , Riggs J. , White D. , Pebody M. , Perrett J. R. , Webb A. T.
Published: January 2009

The autonomous underwater vehicle (AUV) Autosub II is presently engaged on a three-year science programme to carry out surveys under Arctic and Antarctic floating ice shelves and sea ice. This under ice mode of operation necessitates a review of how the vehicle control and navigation operate to account for ice cover, inaccessibility during the mission and get home strategies in the event of sub system failure. The paper reports on lessons learnt during an Antarctic campaign in 2001, subsequent development work and proving trials in waters off the UK.
Analysis of the Dynamic Behaviour of Flexible Risers Considering Hysteretic Damping
Authors: de Siqueira Marcos Q. , de Sousa Jose´ Renato M. , Mourelle Ma´rcio M.
Published: January 2009

This paper proposes a three-dimensional beam element that can predict the dynamic response of flexible risers considering their bending hysteretic behaviour. The finite element implementation relies on a previously presented co-rotated beam finite element and an analytical formulation for determining the bending moment vs. curvature relationship for flexible risers. A comparison between the dynamic response predicted with the proposed finite element and the one obtained with the traditional approach was performed.
Subsea and Platform Options for Satellite Field Developments
Authors: Ronalds Beverley F. , Heng Elvin I. H.
Published: January 2009

As offshore infrastructure matures, satellite field developments are becoming increasingly common. The essential components of a satellite production facility are the well(s), by which reservoir fluids flow to the seabed or surface, and a means of export of the produced fluids. In addition, various auxiliary facilities may be required. These may include: drilling and workover equipment; processing, control and metering systems; and power and utilities to support these operations and ensure their safe performance. These supporting functions may be shared between the host, the satellite and mobile vessels in many ways. Various satellite production arrangements are compared in detail in the paper, utilising a database of North Sea subsea and surface satellites. With satellite developments being employed in ever-deeper waters and over longer step-out distances, prudent selection between subsea or surface options is vital to achieving favourable field economics.
Interactions of Gravity Waves Generated by a Moving Source With the Shelf: Laboratory Experiment
Authors: Afanasyev Yakov , Korabel Vasily
Published: January 2009

Rapidly moving storm crossing the shelf from shallow water to deep water can generate tsunami-like waves which can cause local flooding and damage to docks when the waves hit the coast. We report on laboratory experiments to examine the reflection of waves generated by a moving disturbance from the shelf. Experiments are performed in a two-layer fluid consisting of a layer of oil based ferrofluid lying on top of a layer of water with step bottom. The disturbance is generated by a permanent magnet moving above the surface of ferrofluid. Digital images of the flow are analyzed to obtain the evolution of the wave field. The experimental flows demonstrate two distinct regimes, namely subcritical when the speed of the magnet is less than the phase speed of the wave, and supercritical when the speed of the magnet is greater than the phase speed of the wave. In subcritical regime the disturbance is localized and its size is determined by the spatial extent of the forcing. In supercritical regime the waves form two beams extending at “Mach angle” with respect to the direction of motion. Oblique wave incident on the shelf can experience total reflection if the angle between the wave front and the shelf is greater than a critical value.
Extreme Non-Linear Wave Forces on a Monopile in Shallow Water
Authors: Trumars Jenny M. V. , Jonsson Johan O. , Bergdahl Lars
Published: January 2009

A phase averaging wave model (SWAN) is used to transform offshore sea states to the near to shore site of an offshore wind energy converter. The supporting structure of the wind turbine consists of a cylindrical monopile, and the wave forces and resulting base moments on it are calculated by Morison’s equation integrating from the bottom to the instantaneous free surface. For that purpose the wave-motion in the time domain at the monopile is realized by a second-order random wave model.
3D FEM Parametric Modeling Applied to Optimization of Ship Hull Girder
Authors: Hougaz Augusto Borella , Dias Carlos Alberto Nunes
Published: January 2009

By describing the whole ship structure in its primary, secondary and tertiary components and by incorporating FEM structural analysis to a ship-like structure optimization, it was observed a significant capability of reducing the weight of ship structure, in an amount impossible to be reached by an usual design process, since, by nonlinear programming in a fast computer, the “best design” can be “selected” among thousands of different and feasible ones.
Structural Behavior of Flexible Pipe Carcass During Launching
Authors: Martins Clo´vis A. , Pesce Celso P. , Aranha Jose´ A. P.
Published: January 2009

The interlocked carcass of a flexible pipe, besides being designed to withstand hydrostatic and squeezing loads applied by the tensioned armor layers, must resist to localized loads applied by caterpillars during the launching operation. Load distribution is dependent on the number of tensioners and on their geometry, as well as on the properties of external plastic layers and cross section design. Being the winding pitch of an interlocked carcass small enough and considering that the plastic layers extrusion process provides some confinement to this structure, one may consider, at least as a first approach, an equivalent pipe to model the structural behavior for radial loads. Any alternative approach, as a finite element model, would depend on a difficult assessment of parameters, as those related to the internal contact problem. Recovering classical results from the theory of elasticity, the structural behavior is formulated, for a general radial load distribution. The instability problem is also addressed. Despite the simplicity of such a model, results agree quite well with experiments conducted under controlled conditions. Applied to a typical carcass, the model predicts a safe behavior regarding instability and recovers elastic deformation as a function of a general dimensionless load parameter.
Fatigue Life Extension of Structural Details of a Floating Production Unit by Weld Improvement Methods
Authors: Haagensen P. J. , Fredborg Andreas
Published: January 2009

Fatigue life improvement methods are typically used for life extension of welded joints in connection with repair of damaged or aging structures. Additionally, several design codes allow the use of such methods for increasing the fatigue strength in cases where too short predicted fatigue lives are found during a late stage of the design or fabrication process. This paper describes the use of hammer peening and needle peening to increase the fatigue strength of two types of structural details in Troll C, a new floating production unit fabricated in Korean during 1998–1999. The improvement work was carried out shortly before shipping the platform to Norway where the deck and production equipment was installed. The need for upgrading became apparent at a late stage during construction following refined finite element analyses that were carried out after all major structural changes had been implemented. Close cooperation was maintained with the classification society, and the new guidelines for peening techniques that resulted from the project are now included as a informative procedure in the NORSOK Fabrication Standard M-101.
Cost-Benefit Model for Risk-Based Design of a Typical Marine Platform in Mexico
Authors: de Leon David , Ang Alfredo H.-S.
Published: January 2009

A reliability-based cost-benefit model for the risk management of oil platforms in the formulation of optimal decisions based on life-cycle consideration is proposed. The model is based on structural risk assessments and the integration of social issues and economics into the management decision process. Structural risks result from the platform’s exposure to the random environmental loading associated with the offshore site where it is located. Several alternative designs of a typical platform are proposed and assessed from the cost-effectiveness viewpoint. This assessment is performed through the generation of cost/benefit relationships that are used, later on, to select the optimal design.
Risk Analysis: Heavy Lifts — Norne FPSO Gas Export Project
Authors: Rettedal Wenche K. , Mong Henning , Hausberg Gunnar
Published: January 2009

In 2000 The Norne FPSO was upgraded with an export riser and necessary process equipment for gas export. Due to high risks during installation of the new units onto the FPSO, it was decided to carry out a risk analysis of the most critical lifts. This paper concentrates on the risk analysis carried out for the lifting of one particular module, the TEG unit. The static clearance between the FPSO and the lifting vessel Regalia during the lift was very small and studies of vessel motions showed that a vessel collision could occur based on a normal vessel motion and DP inaccuracies. In particular the lift was very sensitive to the heading control of the FPSO and 1 degree heading change reduced the clearance between the vessels by 2 m. The purpose of this paper is to show that risk analyses have shown to be a very useful tool to identify where efforts in terms of economic resources and manpower should be directed to control and reduce risk prior to critical marine operation.
On the Performance of the MPI Algorithm for the Retrieval of Significant Wave Height From ERS Synthetic Aperture Radar
Authors: Violante-Carvalho Nelson , Robinson Ian S.
Published: January 2009

Spaceborne Synthetic Aperture Radar (SAR) is to date the only source of two dimensional directional wave spectra with continuous and global coverage when operated in the so-called SAR Wave Mode (SWM). Since the launch in 1991 of the first European Remote Sensing Satellite ERS-1 and more recently with ENVISAT millions of SWM imagettes containing detailed spectral information are now available in quasi-real time. This huge amount of directional wave data has opened up many exciting possibilities for the improvement of our knowledge of the dynamics of ocean waves. However the retrieval of wave spectra from SAR images is not a trivial exercise due to the nonlinearities involved in the mapping mechanism. The Max-Planck Institut (MPI) scheme was the first ever proposed and most widely used algorithm to retrieve directional wave spectra from SAR images. In this work significant wave height retrieved from SAR images using the MPI scheme are compared against one year of directional buoy measurements obtained in deep water and against WAM spectra. Our results show that for periods shorter than 12 seconds the WAM model performs better than the MPI method, even considering the fact that the model is used as first guess to the MPI scheme. However, for periods longer than 12 seconds (the part of the spectrum directly observed by SAR) the MPI method performs better than WAM. This is in contrast with the results obtained by Voorrips et al. (2001), who found that the performance of the WAM model is superior even when only the low wavenumber part of the spectrum is considered.
Reduction of Wave Pressures on Vertical Seawall/Caissons Due to an Offshore Breakwater
Authors: MuniReddy Muthukuru G. , Neelamani Subramanian
Published: January 2009

Estimation of wave pressures on vertical impermeable caissons and seawall is needed to determine the dimensions and appropriate material selection of the structure. Reduction of extreme wave loadings (pressures) by constructing an offshore breakwater on seaward side of these structures is investigated. A series of physical model tests were carried out in a wave flume to examine the performance of the defense structure (offshore breakwater) in reducing the wave pressures on the seawall/caisson. Quasi-static nature of the wave pressures was observed due to piling-up of fluid mass behind the breakwater. The influence of the pool length on reduction of pressures on seawall/caisson is also investigated for regular waves.
Behaviour of Marine Clay Under Wave Type of Cyclic Loading
Authors: Narasimha Rao S. , Moses G. Gerald
Published: January 2009

This paper presents the results of two series of cyclic triaxial shear tests carried out under both uniform and Varied cyclic shear loading and these bring out the influence of load cycles on strain and undrained strength of a cemented marine clay from East coast of India. The undrained shear strength and deformation behaviour of Indian coastal marine clay have been established through a detailed shear testing carried out. In order to estimate the effect brought in by varied cyclic loading, it becomes necessary to conduct reference standard tests under uniform cyclic loading at various cyclic stress ratios (CSR) on identical soil specimens and these stress levels are chosen in such a way that there is no failure taking place during testing. In field situations, storm wave loading is considered to be irregular cyclic loading in which there is a continuous variation in the load level from one cycle to the other. The results obtained from tests under uniform cyclic loading are compared with the results obtained from tests under varied cyclic loading.
Research on Applicability of New Materials to Marine Structures in Tropical Climates: Specimens Exposed for 2 Years
Authors: Tomosawa Fuminori , Tsujikawa Shigeo , Ono Tadashi , Nakatsuji Teruyuki , Yonemaru Keisuke , Kugai Yasuo , Kitano Akihiko , Miura Hideo
Published: January 2009

New structural materials that are light and durable are anticipated to reduce the running and maintenance costs of structures exposed to harsh marine environments, such as offshore oil production facilities, thereby reducing their life-cycle cost. This study aims to investigate the applicability of new materials to marine structures, focusing on their durability. To this end, a 5-year exposure test has been conducted from 1999 on 3 types of specimens (for corrosion observation, tension testing, and joint strength testing) made of 21 selected materials (6 nonferrous metals, 8 steels, 4 composite materials, and 3 rope materials). The specimens are exposed at 3 sites: Okinotori-shima and Miyako-jima, corrosive environments with high temperature and humidity, and a thermo-hygrostatic room in a laboratory. In 2003, the fourth year of the ongoing exposure testing, the results of the observation and experiments of specimens recovered in 2002 after exposure for 3 years are subjected to analysis. The authors have already reported the detailed plan of the exposure test, initial performance of the specimens, and results of investigation on specimens exposed for 1 year. This paper reports on the results of appearance observation of specimens at Okinotori-shima and Miyako-jima carried out mostly in 2001, as well as the findings from observation and experiments on specimens exposed for 2 years at Miyako-jima. The state of corrosion at each site was grasped during the appearance observation. Observation and tension tests on jointed and unjointed specimens at Miyako-jima also revealed the state of corrosion of each material during the 2nd year of exposure.
Application of β-Unzipping Method in Offshore System Reliability Analysis Under Changing Load Pattern
Authors: Daghigh M. , Makouie S. Helal
Published: January 2009

This paper is concerned with the reliability assessment of a fixed platform operating in intermediate water depth under extreme environmental conditions. The structure is modelled by two-dimensional frame structure and subjected to quasi-static loads. Extreme wave loads acting on the platform in the unidirectioal mode are estimated together with their probabilistic characteristics. Fully plastic capacities of the members are also treated as random variables. The structure is modelled as a plane truss by using beam-column models and the plastic collapse of the structure is evaluated by using a linearized plasticity condition of the section under effect of axial force to generate the safety margins. For compressional elements, the strength reduction is assumed proportional to the yield stress and for the tension members, it is assumed that the material has a perfect elastic-plastic behavior. Both hydrodynamic drag / inertia forces and slamming loads have been considered in strength and reliabilitry analysis. Using a matrix method, probabilistically dominant collapse modes are selected by applying the β-unzipping method. The system reliability is evaluated by using wave fragility analysis (changing load pattern) and the results have been compared with the fixed load pattern.
Development of Structural Steel With Superior Resistance Against Fatigue Crack Growth
Authors: Konda Noboru , Arimochi Kazushige , Hirota Kazuhiro , Watanabe Eiichi , Tada Masuo , Kitada Hiroshige , Fukui Tsutomu , Yamamoto Motomichi , Kho Yunbo , Yajima Hiroshi
Published: January 2009

The fatigue crack problems that broke out at the end of the twentieth century were fatigue crack properties in hull structures. This motivated research on a lot of technologies against fatigue fracture. It was clarified that the detection of fatigue crack initiation in complex welded structures like hulls is quite difficult, and that the crack length at recognition is mostly long compared to mechanical parts. From these research results, not only stress reduction at critical areas by improvement in design but also newly developed materials with excellent resistance to fatigue crack growth has been desirable for structural integrity. The newly developed structural steel, in which fatigue crack growth resistance is controlled by microstructures, will be introduced in this report. Various fatigue properties of the base steel plates in air and in synthetic sea water are compared. And the fatigue life extension effects by FCA is observed in fatigue tests of welded joints and welded structural models.
Numerical Study on Forced Turbulence in Stratification
Authors: Sato Toru , Sato Kei
Published: January 2009

A method for computational reconstruction of fluctuating flows in the small-scale ocean was proposed based on single-point measurement in the real sea. Full-3D LES on the spatial scale of O(100m) was conducted for this purpose. Small-wavenumber components of fluctuation are forced in the whole computational domain and large-wavenumber components evolve freely in the computation. The reconstruction of spatial information from the time-sequential data obtained at a single measurement point is theoretically impossible with no assumptions. We assumed spherically even distribution of energy for large eddies. The numerical results were compared with the measurement in the time domain and their validity is discussed.
Hydraulic Model Test and Numerical Simulation of Density Current
Authors: Sato Toru , Koike Kazunori , Yoshikawa Takuro , Tsuchiya Yoshihiro
Published: January 2009

The behaviours of density current were visualised in a simple cylindrical tank and a hydraulic model shaped as Ariake Bay, set in a rotating tank. In both, water was stratified by dissolving salt in the lower layer. In the cylindrical tank, the spread of density current was well parameterised by newly proposed dimensionless numbers. When the Rossby number decreases, we observed that the current was divided into two parts. This may be interpreted as baroclinic instability. In Japan, recently, there is a big discussion on the effect of Isahaya Dyke on the marine ecosystems in Ariake-Bay. We conducted a hydraulic model test and saw the flow difference between the cases with and without the dyke. Also measured was the effect of artificial density current. We found a suitable location for the apparatus for having nutrient-rich water stay at the seaweed cultivation field before it is diffused very much. In addition, we conducted numerical simulations of the above case.
Prediction on Aging of Reconstitutive Clayey Marine Soils Using Fuzzy-Logic
Authors: Moreno Jorge Sa´nchez , Prates de Lima Edison Castro , Ellwanger Gilberto Bruno
Published: January 2009

This paper presents an application of the fuzzy logic theory for the prediction of the soil strength depth variation due to aging effects. The results of experimental tests with reconstituted clayey soils of the Bay of Campeche in Mexico were used for the fuzzy rule-based system training. The Evolutionary Strategy (ES) was employed as an optimization method for the learning of the Mamdani-type fuzzy rule base. Fuzzy logic provides an easy and transparent method for incorporating common-sense type reasoning. The fuzzy logic model is based on a decision (inference) process that can be better described on a linguistic level using rules with soft facts. In this manner the clay soil strength through the time could be fuzzily predicted as a function of the mean effective normal stress, the time of consolidation and the water content. Illustrative examples showed that the result of prediction seems to be acceptable in engineering practice.
Comparison of the Dynamic Properties and Undrained Shear Strengths of Offshore Calcareous Sand and Artificially Cemented Sand
Authors: Valle Celestino , Camacho Beatriz I. , Stokoe Kenneth H. , Rauch Alan F.
Published: January 2009

Calcareous sand specimens were obtained from Campeche Bay in the southern Gulf of Mexico. The dynamic properties of these specimens were measured in resonant column and torsional shear (RCTS) tests, while the undrained shear strength was measured in unconsolidated-undrained (UU) triaxial compression tests. For weakly cemented, natural materials like this, it is difficult to obtain reliable properties from laboratory tests because sampling and handling of the soil specimens damages the particle cementation to an unknown degree. Artificially cemented specimens can be studied to better understand this problem. In this work, the strength and dynamic properties of artificially cemented sand were also measured using RCTS and UU tests. The artificially cemented specimens were formed by mixing uniform sand with a sodium silicate solution. The degree of cementation was varied by using different sodium silicate concentrations. This approach could be used to reproduce cemented test specimens in the laboratory with similar mechanical properties as cemented offshore soils. The results from this limited study show that the small-strain dynamic properties measured in the laboratory, and their variation with confining pressure, clearly identifies disturbance in the calcareous soils.
Wave Action on Double-Cylinder Structure With Perforated Outer Wall
Authors: Li Yucheng , Sun Lu , Teng Bin
Published: January 2009

Based on an eigenfunction expansion of velocity potential and a linear model between the pressure difference between two sides of a perforated wall and the fluid velocity inside it, a semi-analytic linear solution has been acquired for wave interaction with a combined cylinder with an solid interior column surrounded by a coaxial exterior column with perforated wall at a section in azimuthal direction. Numerical experiments have been carried out to examine the influences on the wave force and wave run-up on the combined cylinders with perforated wall by the porous coefficient, the size of the perforated section, and the ratio between the radii of the interior and the exterior columns. This paper also presents the comparison between the numerical experiments results and the physical experiments results. It is acceptable of the comparison of these two results. The combined cylinder may reduce both the wave run-up and the wave loads on it through combination of certain parameters.
A Combined Riser Mooring System for Deepwater Applications
Authors: Hogg Brendan , Harte Annette , Grealish Frank
Published: January 2009

For deepwater developments, riser and mooring system requirements become a significant factor in the cost of the overall field development. Therefore, methods for reducing the riser and mooring design requirements and minimizing the cost of these systems become increasingly important. This paper presents the design methodology for a combined riser mooring (CRM) system and demonstrates the feasibility of the system for a test case application in a deepwater development offshore West of Africa. The CRM system offers significant benefits over the independent riser and mooring systems, namely: reduced riser dynamics, reduced vessel offsets, a smaller seafloor footprint and system installation prior to the arrival of the FPSO.
Comparing Measured and Calculated Forces of a Manifold Deployment in 940 Meters Water Depth
Authors: Roveri Francisco Edward , Sudati Sagrilo Lui´s Volnei , Prates de Lima Edison Castro , Cicilia Federico Barranco
Published: January 2009

In August 2001 the MRL-5 production manifold was installed by PETROBRAS in 940 meters water depth at the Marlim field offshore Brazil. The semi-submersible Amethyst, using an 18-5/8” marine riser, deployed it into the location. During the manifold deploying, several in-site measurements of the hook forces (force at the drill line dead end) and the semi-submersible accelerations were done. Both time series for the vertical accelerations and forces were obtained for two positions of the manifold along the water column. The main objective of this paper is to compare the results from the column riser system numerical analysis with the riser axial forces measurements obtained by the monitoring system.
Recover of the RG-2 Gas Pipeline of Roncador Field
Authors: Lima Henri F. , Pinto Fla´vio J. C. P.
Published: January 2009

This paper gives an overview of Petrobras’ experience on the salvage operation of RG-2 gas pipeline of Roncador Field, as part of Petrobras effort to recover the Roncador production after P-36 accident. The RG-2 gas pipeline, a 10in ND rigid steel pipe, 38 km longer, that has used to export gas production of P-36 to Roncador PLAEM-1, was connected to the floating unit through a steel catenary riser. After P-36 sunk on March 2001, a set of analyses and surveillance on RG-2 was performed and concluded that only 2 km near P-36’s connection was lost and addressed the pipeline reuse is feasible. These facts were very important to Petrobras because allows a fast and effective solution to the gas production exportation of FPSO Brasil, the unit that will replace P-36 production at the first phase. At that moment, the RG-2 was connected on P-36 wreckage on the seafloor at 1300m of water depth, not flooded and filled with gas at very low pressure. Under this scenery, it was developed a procedure to flood RG-2 with seawater, in order to remove the gas and to equalize the internal pressure and the external one, however at the same time it should avoid hydrate formation. The flooding operation was crucial because it allows futures operation in a safety way. The procedure consisted basically of to “break” the pipeline, with no special tools and no special vessel than RSV and AHST, to keep the method effective in cost and time. The operation was performed on August 2001 with good results. The RG-2 was flooded smoothly and quickly, without evidence of hydrate formation. The gas inside pipe was removed entirely. Also, the operation was performed as forecasted showing consistency between simulation results and observations in site.
Selection of Variables for Structural Redesign by Large Admissible Perturbations
Authors: Koo Bonhyung , Bernitsas Michael M.
Published: January 2009

Redesign or inverse design is the process of generating a new optimal design which satisfies performance specifications starting from a baseline design with undesirable performance. The LargE Admissible Perturbation (LEAP) methodology makes it possible to redesign a structure for large changes in performance objectives and redesign variables without trial and error or repetitive finite element analyses. The next level of challenge in redesign automation is to identify a priori the structural elements and their properties that have the biggest impact and use only those in redesign. Based on LEAP, guidelines are developed in this paper for identifying effective selection of redesign variables for improved accuracy and reduced CPU time. These guidelines enable the designer to define the elements to be redesigned, to partition those elements among redesign groups, and to specify redesign variables in each group. In the numerical applications, an offshore tower is used to verify the developed guidelines. Three models of this tower with 160, 320, and 480 elements are used.
New Guidance on the Design of Offshore Structures to Resist the Explosion Hazard
Authors: Walker Steve , Bleach Rod , Carney S. , Fairlie Greg , Louca L. A.
Published: January 2009

In 1992 Interim Guidance Notes were issued in the UK to provide guidance for the design of offshore topsides for fires and explosions. This Guidance was one consequence of the Piper Alpha Tragedy in the North Sea. Since 1992 a great deal of further research and technology has been developed in order to improve understanding of the characteristics of fires and explosions and the response of the structures and equipment to these events. In order to collate this new information in a readily useable format, the United Kingdom Offshore Operators Association (UKOOA) and the Health and Safety Executive (HSE) commissioned the MSL Consortium to update the existing Interim Guidance Notes and produce Part 1 of the new Guidance. The MSL Consortium consisted of the organisations represented by the authors with contributions from WS Atkins (Houston) and Beth Morgan Safety Solutions. The project manager was Minaz Lalani of MSL. The new Guidance is being developed in three parts. The first two parts deal with the philosophy for the avoidance and mitigation of explosions and fires respectively, which together establish the background for Part 3 which will provide detailed guidance on design practices for fire and explosion engineering. This paper describes the first document. Specific issues which are discussed include installation risk screening, nominal explosion loads, inherently safer design, hazard management, and the derivation of Design Explosion loads. This paper also describes the recommended method for explosion response assessment given in the Guidance.
Non-Dimensional Parameters Governing the Onset of Wake-Induced Marine Riser Collision
Authors: Huang Shan , Wu Wusheng
Published: January 2009

Wake-induced riser oscillation can lead to riser clashing. Furthermore, the onset of the wake-induced riser oscillation, which is typified by its large amplitude and low frequency, is attributed to the loss of stability of the downstream riser in the wake once the current exceeds a critical value. The loss of stability is mathematically characterised by a stationary bifurcation. Based upon our previous work, further results are presented in the paper on the non-dimensional parameters which govern the critical current speed. These non-dimensional parameters, once computed, can then be used by riser designers to assess potential riser clashing and/or ascertain the minimum riser spacing and top tension required in order to avoid riser clashing.
The Soft Yoke Mooring and Offloading System for LNG Offloading Applications
Authors: Naciri Mamoun , Que´au Jean-Pierre
Published: January 2009

The ever-rising need for energy and environmental issues have propelled LNG as one of the most promising source of clean energy for the near future. LNG differs greatly from oil when it comes to loading and offloading in at least two respects. Firstly, owing to its temperature at atmospheric pressure (−162°C), Liquefied Natural Gas does not lend itself to offloading via the well-known floating hoses routinely used for oil. Instead, specially designed articulated steel structures are used in all jetty terminals around the world. Secondly, the very nature of long-term contracts negotiated with utility companies requires regular, uninterrupted LNG supply to their network. This requires extremely high availability figures for import/export terminals or floating, moored LNG producing facilities. A new concept based on the well-known soft yoke principle has been developed whereby the yoke structure has the dual function of mooring the LNG carrier to a fixed import terminal or to the stern of a permanently moored Floating LNG (FLNG) FPSO and of supporting the rigid pipe fluid transfer system. Whilst all soft yoke systems built to date permanently moor an oil FPSO to a fixed jacket structure, the new SYMO® system is designed as a temporary mooring for a fleet of dedicated LNG carriers. This paper addresses new engineering challenges associated with the SYMO® system.
Field Observations and Modelling of the Self-Burial of a North West Shelf Pipeline
Authors: Pinna Rodney , Weatherald Andrew , Grulich John , Ronalds Beverley F.
Published: January 2009

The Goodwyn Interfield Pipeline was laid on the Australian North West Shelf, connecting the Goodwyn and North Rankin platforms, in 1993. It is operated by Woodside Energy Limited, and is used to transport hydrocarbon fluid from the Goodwyn and Echo/Yodel fields to the North Rankin A platform, which is connect to onshore processing facilities by the 140 km North Rankin trunkline. This pipeline was expected to self-bury along the majority of its length. After nine years however, some sections of the pipeline have experienced significant self-burial, however, other sections remain exposed. The first part of this paper details the results collected from annual surveys of the pipeline, while the second part looks at modelling the self-burial process. The effect of internal waves is found to be a key driver in the self-burial process.
Experimental Investigation on the Dynamic Response of an Internal Turret Moored FPSO System Under Sea Waves
Authors: Kannah T. Rajesh , Natarajan R.
Published: January 2009

An experimental investigation on the dynamic behaviour of a typical internal turret moored FPSO system with a turret located at midships position is reported. A 1:100 scale model of 140000t DWT turret moored FPSO system was tested under regular waves for three operating conditions i.e. 40%DWT, 70%DWT and 100%DWT in a 2m wide wave flume at a water depth of 1m for the wave frequencies from 0.55Hz to 1.25Hz in steps of 0.04Hz. The motions were measured by rotary type potentiometers and specially ring type load cells were used to measure the mooring forces. The model tests results are analysed and presented with discussions in this paper.
Local Buckling Behavior of X100 Linepipes
Authors: Suzuki Nobuhisa , Muraoka Ryuji , Glover Alan , Zhou Joe , Toyoda Masao
Published: January 2009

Local buckling behavior of API 5L X100 grade linepipes subjected to axial compression and/or bending moment is discussed in this paper based on results obtained by finite element analyses. Yield-to-tensile strength (Y/T) ratio and design factor were taken into account in the finite element analyses in order to discuss their effects on the local buckling behavior. The local bucking behavior of such lower strength linepipes as X60 and X80 grade linepipes is also discussed for comparison. Two-dimensional solid elements and four-node shell elements were used for the finite element modeling of the linepipes subjected to axial compression and bending moment, respectively. The study has improved the understanding of local buckling behavior of the X100 grade linepipes and observed the following trends. When a linepipe is subjected to axial compression, the critical axial stress decreases with increasing design factor and Y/T ratio. However, the nominal critical strain increases with increasing design factor and decreasing Y/T ratio. When a linepipe is subjected to bending moment, the critical bending moment decreases with increasing design factor and Y/T ratio. Similarly, the nominal critical strain increases with increasing design factor. However, the nominal critical strain increases with decreasing Y/T ratio when the design factor is less than and equal to 0.6 and decreases with decreasing Y/T ratio when the design factor is equal to 0.8.
Seakeeping Analysis of a Turret-Moored FPSO by Using Artificial Neural Networks
Authors: Mazaheri S. , Mesbahi E. , Downie M. J. , Incecik A.
Published: January 2009

Floating offshore structures, particularly floating oil production, storage and offloading systems (FPSOs) are still in great demand, both in small and large reservoirs, for deployment in deep water. The prediction of such vessels’ responses to her environmental loading over her lifetime is now often undertaken using response-based design methodology, although the approach is still in its early stages of development. Determining the vessel’s responses to hydrodynamic loads induced by long term sea environments is essential for implementing this approach effectively. However, it is often not practical to perform a complete simulation for every 3-hour period of environmental data being considered. Therefore, an Artificial Neural Networks (ANN) modelling technique has been developed for the prediction of FPSO’s responses to arbitrary wind, wave and current loads that alleviates this problem. Comparison of results obtained from a conventional mathematical model with those of the ANN-based technique for the case of a 200,000 tdw tanker demonstrates that the approach can successfully predict the vessel’s responses due to arbitrary loads.