bluuebunny/crossref_metadata_2025 huggingface dataset:
Vertical and Horizontal Migration of Gas Through the Marine Sediments of the Gulf of Mexico
Authors: Nava Castro Rau´l , Koh Cambranis Wilbert E. , Baerenwald Paul
Published: November 2011

Since petroleum exploitation began activity in the Gulf of Mexico, geophysical studies have been carried out to detect geological hazards and features, which can affect the design or installation of platforms or pipelines. In some of the studies it was noted that shallow gas accumulations increase their size and number through time. This paper presents a comparison of three geophysical studies which were carried out in 1978 [1], 1997 [2] and 2002 [3]. The comparison is complemented with results obtained from geotechnical studies performed in 2002 [4–7] to evaluate the influence of the gas on the properties of the foundation zone soils. In the 1997 geophysical study, there were more detected gas accumulations than in 1978. The existing gas accumulations (originally detected in 1978) also increased in size over the nineteen-year period. The same phenomenon was also identified in the geophysical study of 2002, when the results were compared with the study performed in 1997, it appeared that the shallow gas accumulations increased both their size and number considerably over a period of only five years. The only explanation found for this phenomenon was that gas migrates vertically from the reservoir along a major geological fault that crosses the entire area, forming a chimney. Once the gas reached the shallow strata, the gas spread laterally, saturating the area around the geological fault with gas. Sand Strata A, B, C and D (identified in the geotechnical investigation) were the primary gas-charged strata, that is, the gas migrates laterally within these strata until encountering soils that can not confine the pressure developed by the gas accumulation [8] or until the gas finds a route to escape upwards. As a consequence, a sudden or gradual emanation occurs, altering the initial characteristics of the foundation zone soils and/or possibly damaging marine structures, resulting in economic loss.
Wake of a Vibrating Cylinder at Re = 105
Authors: Blevins R. D. , Saint-Marcoux Jean-Franc¸ois
Published: November 2011

Measurements have been made of the wake of a circular cylinder at Reynolds number of 105 for a stationary cylinder and a cylinder vibrating +/− 1.25 diameters under natural vortex induced vibration. Wake velocity profiles were taken at 2, 4, 6, 12, 24 and 50 diameters downstream. The stationary cylinder profile reproduces the well known wake deficit law. The vibrating cylinder near wake is wider, deeper and flatter than that of the stationary cylinder. Flow visualization reveals the vortex dynamics in the wake. Correlation is shown with theory.
Aided Inertial Measurement System Applied to Torpedo Pile Trajectory Reconstruction
Authors: Lavieri Rodrigo Sauri , Tannuri Eduardo Aoun , Fujarra Andre´ L. C. , Correˆa Diego Cascelli
Published: November 2011

Torpedo pile has become one of the most popular foundation systems in Brazil’s offshore oil exploitation, mostly, due to its low installation cost. Additionally, torpedo piles have shown good fixation capability even when applied in mooring configuration such as taut leg with relatively close angles to the vertical. This fixation capability is closely dependent to the depth of penetration and the final attitude of the pile. In order to determine these parameters, MEMS-based Inertial Measurement Units have been used. Units of this kind are known for high noise density and, alone, are not adequate to any kind of navigation. Concerning these limitations, other sources of data are added to the inertial measurements, in order to improve the system state estimation. This data fusion is carried out by the Kalman Filtering and is also called Aided Inertial Measurement Units. This paper presents the Kalman Filter implementation and the results obtained from the fusion of the pressure gage signal, alternative pitch and roll measurements and the inertial measurements applied to the torpedo pile deployment.
Numerical Studies on Hydrodynamics of a Floating Oscillating Water Column
Authors: Sheng Wanan , Lewis Anthony , Alcorn Raymond
Published: November 2011

The oscillating water column (OWC) is one of the more successful wave energy converters so far due to its mechanical and structural simplicity; there are no components for power take-off in seawater. Though there are some successful practical developments in bottom-fixed OWCs, floating OWCs are still in different stages of development. A specific oscillating water column, the OE Buoy (i.e. backward-bent duct device, ‘B2D2’), developed by OceanEnergy (Ireland), has recently attracted much attention. A 1:2.5 scale device has finished a sea-trial in Galway Bay (Ireland) for a period over two years during which period the device has gone through a severe storm. Thus its survivability has been confirmed to some extent. In this research, numerical simulations to the floating wave energy device are performed using a boundary element method code WAMIT. To consider the motions of the internal water in the column for energy extraction, a “numerical lid” is placed on the free surface in the column. In WAMIT, the motions of the “numerical lid” can be calculated by introducing relevant generalized modes to the conventional 6-DOF motions of the floating structure. For wave energy extraction, the “piston effect” of the internal water must be considered. To include the effect of the mooring system to the motions of floating structure, the mooring forces have been linearised, and their equivalent spring coefficients have been input to WAMIT for analysis of the moored floating structure. For the numerical simulation, the first case is to tune the damping coefficients based on wave tank results since in WAMIT, only hydrodynamic damping is included in calculation. In reality, larger damping may be needed to limit the large responses in heave of floating structure and the motion of the internal water surface. The tuned damping coefficients are then applied to the modified OWCs of different duct length, in which it is hoping that the corresponding responses of the internal free surface structure are used to assess the performance of the floating OWC. The aim of the research is to explore the relation between the OWC size and its performance so that it may provide a reference for optimizing the design of a floating OWC in the future.
Predicting Roll Added Mass and Damping of a Ship Hull Section Using CFD
Authors: Jaouen Frederick , Koop Arjen , Vaz Guilherme
Published: November 2011

In this paper, the flow around a forced rolling body is analyzed with MARIN in-house CFD code ReFRESCO. The objective is to assess if the code can correctly predict the added mass and damping coefficients of a rolling vessel. After a description of code and numerical methods, the results for the flow computed around a 2D rolling hull section are presented. Sharp and rounded bilges are investigated for three roll amplitudes and three roll periods. The influence of grid and time discretisation and iterative errors are analyzed. The CFD results with Re-FRESCO are compared to experiments and to results obtained with the commercial CFD package CFX. The results shown here indicate that ReFRESCO is capable of accurately predicting the added mass and damping coefficients. However, it is also shown that fine grids and time-steps are required to obtain a grid and time-step converged solution.
KP4: Ageing and Life Extension Inspection Programme for Offshore Installations
Authors: Stacey A.
Published: November 2011

The HSE’s Offshore Division has embarked on a three-year inspection programme on ageing and life extension, also known as ‘KP4’. This paper describes the aims, objectives, scope of KP4, the approach being adopted to KP4 and an overview of ageing and life extension issues for offshore installations.
Hydroelastic Response of Square VLFS With Line Hinge Connector System
Authors: Wang Chien Ming , Gao Rui Ping , Koh Chan Ghee
Published: November 2011

This paper investigates the hydroelastic response of pontoon-type, very large floating structures (VLFS) with a line hinge connector system under wave action. In the hydroelastic analysis, the water is assumed to be an ideal fluid and its motion is irrotational so that a velocity potential exists. The VLFS is modeled as an isotropic plate according to the Mindlin plate theory. In order to decouple the fluid-structure interaction problem, the modal expansion method is adopted for the hydroelastic analysis which is carried out in the frequency domain. The boundary element method is used to solve the Laplace equation for the velocity potential, whereas the finite element method is employed for solving the equations of motion of the floating plate. One, two, three and four line hinge connectors along two directions for a square-shaped VLFS are considered. The effects of the wavelength and heading angle on the hydroelastic response and the stress-resultants of the VLFS are investigated.
Testing of Inflatable Structures of Rapidly Deployable Port Infrastructures
Authors: Bloxom Andrew L. , Yim Solomon C. , Medellin Abel J. , Vince Chris S.
Published: November 2011

An experimental investigation of the fluid-structure interaction of a water filled inflatable membrane structure in the near shore environment was performed in the Coastal Marine Engineering Laboratory at the United States Naval Academy. The structure of interest was a 10′ × 2′ × 0.75′ (304.8 × 60.9 × 22.8cm) tubular bag developed at the Center for Innovation in Ship Design (CISD) at the Naval Surface Warfare Center (NSWC), Carderock Division as a proof of concept for the design of a rapidly deployable inflatable structure causeway to be used either as a ship to shore connector or a breakwater. The experiments were performed over a range of test conditions including three incident wave angles, three water depths, and a number of wave heights corresponding to various sea states. Results confirmed that the bag is stable and well grounded for most operational sea conditions. Large amplitude and low frequency waves can induce significant motions of the structure, but the static and dynamic frictional coefficients between the structure and the surface in contact play a critical role in these motions. For conditions where the structure was at an angle of 45° to the incident waves, highly nonlinear wave conditions are produced which created wave over-topping and oscillatory motions of the structure.
Geometrical Parametric Study and Development of Design Formulae for the SCF Distribution Along the Weld Toe in Multi-Planar CHS DKT-Connections of Offshore Structures
Authors: Lotfollahi-Yaghin Mohammad Ali , Ahmadi Hamid , Shahverdi Sajad
Published: November 2011

In the present paper, effects of geometrical parameters on the SCF distribution along the weld toe of multi-planar tubular DKT-joints under the axial loads are investigated. In order to study the multi-planar effect, SCF distribution in multi-planar joints is compared with the distribution in a uni-planar joint having the same geometrical properties. Based on the multi-planar DKT-joint FE models which are verified against experimental results and the predictions of Lloyd’s Register (LR) equations, a complete set of SCF database is constructed. The FE models cover a wide range of geometrical parameters. Through nonlinear regression analysis, a new set of SCF parametric equations is established for the accurate and reliable fatigue design of multi-planar DKT-joints under axial loads. An assessment study of these equations is conducted against the experimental data and the acceptance criteria recommended by the UK DoE.
Concept Design for Offshore DOW Platform as Infra-Structure of Isolated Island
Authors: Ouchi Kazuyuki , Jitsuhara Sadayuki , Watanabe Takayuki
Published: November 2011

DOW (Deep Ocean Water: The sea water below 200m depth) which has three major characteristics, Low Temperature, Rich Nutrient and Very Clean, is expected as a future renewable resources in the ocean. Toward the era of environment and low carbon, utilizing the ocean renewable resource is absolutely important because the land base resources are now peaking out. In order to making use of DOW effectively and economically, multi-purpose utilizing of DOW is recommended because it has many aspects of characteristics and advantages. First, Electric Power generation by OTEC (Ocean Thermal Energy Conversion) is carried out using the difference of water temperature between the cold DOW (5°C) and the warm surface water (25°C). Second, a fresh water generation by a desalination of the sea water is carried out using residual difference of temperature after OTEC operation. Third, the DOW after discharging cold temperature in the heat exchanger of fresh water generator is scattered into a photosynthetic surface layer in the sea and its nutrient enhances primary production of the sea and eventually make a rich fishing ground. Forth, Lithium and some other rare metal are absorbed from DOW by putting special filters in the continuous large quantity flow of DOW. In this paper, the multi-purpose DOW platform which generates the electric power, the fresh water, the fishes and the Lithium from only DOW and surface water is proposed as a supplier of infra-structure for an isolated island. Technical and economical feasibility study is carried out and the result is that the enough sized multi-purpose DOW platform is very feasible for the forthcoming environment era.
A Novel Design of Mobile Offshore Drilling Unit for Arctic Conditions
Authors: Bereznitski Alexei
Published: November 2011

Exploration of Arctic offshore for oil and gas sets extremely high requirements for Mobile Offshore Drilling Units (MODU). Arctic offshore is one of the harshest environments on the planet. Low temperatures, high winds and ice infested waters represent great challenge. Drilling units, which are optimized for severe ice loads, are vulnerable to waves when water clears from the ice. MODU’s specifically designed for open water and extreme waves have poor ice resistant performance. A Novel Design of column stabilized Mobile Offshore Drilling Unit named JBF Arctic is presented in the paper. The major feature of the unit is the combination of exceptional seakeeping characteristics and excellent ice resistance. This is achieved by utilization of a dual draft concept. In open water the unit has a draft which is typical for column stabilized units. In ice the unit is submerged to a deeper draft where a cone shaped heavily reinforced upper structure receives the ice loads. This paper deals with results of extensive research including seakeeping calculations, model testing in a seakeeping tank, studies on ice loads, model testing in an ice tank, and analysis of the mooring system.
Development of a Full Scale Two Dimensional Pipeline Uplift Test Apparatus for Upheaval Buckling (UHB) Model Testing on the Tangguh LNG Project
Authors: Marcollo Hayden , Griffiths Terry , Johnson Richard , Abbs Tony
Published: November 2011

This paper summarises the development of a full scale test apparatus used to facilitate Upheaval Buckling (UHB) testing for the Tangguh LNG Project. Model testing was performed to investigate the statistical variance of the planar uplift resistance provided by a specified variety of layered cover materials to a 24″ full scale circular cross section pipe. To effectively model uplift resistance in a two dimensional manner, a model with a discrete length and known end effects was required. To quantify end effects created by using a discrete length of pipe, a mitigation technique was developed to isolate the measurement uplift resistance from any out of plane loads on the pipe. Additionally, the effect of uplift speed was investigated during the testing program to ensure that the tests were quasi-static in nature.
Advanced Weathervaning in Ice
Authors: Hidding William , Bonnaffoux Guillaume , Naciri Mamoun
Published: November 2011

The reported presence of one third of remaining fossil reserves in the Arctic has sparked a lot of interest from energy companies. This has raised the necessity of developing specific engineering tools to design safely and accurately arctic-compliant offshore structures. The mooring system design of a turret-moored vessel in ice-infested waters is a clear example of such a key engineering tool. In the arctic region, a turret-moored vessel shall be designed to face many ice features: level ice, ice ridges or even icebergs. Regarding specifically level ice, a turret-moored vessel will tend to align her heading (to weather vane) with the ice sheet drift direction in order to decrease the mooring loads applied by this ice sheet. For a vessel already embedded in an ice sheet, a rapid change in the ice drift direction will suddenly increase the ice loads before the weathervaning occurs. This sudden increase in mooring loads may be a governing event for the turret-mooring system and should therefore be understood and simulated properly to ensure a safe design. The paper presents ADWICE (Advanced Weathervaning in ICE), an engineering tool dedicated to the calculation of the weathervaning of ship-shaped vessels in level ice. In ADWICE, the ice load formulation relies on the Croasdale model. Ice loads are calculated and applied to the vessel quasi-statically at each time step. The software also updates the hull waterline contour at each time step in order to calculate precisely the locations of contact between the hull and the ice sheet. Model tests of a turret-moored vessel have been performed in an ice basin. Validation of the simulated response is performed by comparison with model tests results in terms of weathervaning time, maximum mooring loads, and vessel motions.
ISO Offshore Structures Standards
Authors: Smedley Philip , O’Connor Pat , Snell Richard
Published: November 2011

The ISO 19900 series of Standards address the design, construction, transportation, installation, integrity management and assessment of offshore structures. Offshore structural types covered by ISO include: bottom-founded ‘fixed’ steel structures; fixed concrete structures; floating structures such as monohull FPSOs, semi-submersibles and spar platforms; arctic structures; and site-specific assessment of jack-up platforms. All the fundamental ISO Offshore Structural Standards have now been published representing a major achievement for the Oil and Gas Industry and representative National Standards Organizations. A summary of the background to achieving this milestone is presented in this paper. In parallel, other Codes and Standards bodies such as API, CEN, CSA, Norsok and the Classification Societies are looking to harmonize some, or all, of their Offshore Structures Standards in-line with ISO, wherever this is desirable and practical. API, in particular, have been pro-active in reviewing and revising their Offshore Recommended Practices (RPs) to maximize consistency with ISO, including revising the scope and content of a number of existing API RPs, adopting ISO language, and embracing technical content. Given API’s long heritage of Offshore Standards it is not surprising that this remains very much a mutual effort between ISO and API with much in ISO Standards building on existing API design practice. Now published, those involved in developing and maintaining the ISO 19900 series of Standards have to deal with both new and existing challenges, including encouraging wider awareness and adoption of these Standards, enhancing the harmonization effort, ensuring technical advances are captured in timely revisions to these Standards, and most pressing to ensure that the next generation of offshore engineers are encouraged to participate in the long-term development of the Standards that they will be using and questioning. This paper is one of a series of papers at this OMAE Conference that outline the technical content and future strategy of the ISO Offshore Structures Standards.
Effect of Initial Imperfections on the Strength of Restrained Plates
Authors: Gordo Jose´ Manuel
Published: November 2011

Most common studies on the strength of plates under compressive longitudinal loading are related to plates having unrestrained edges which lead to a zero net load in the transverse direction. In ships, the framing system and the continuity of the plating in the transverse direction tend to induce rather different boundary conditions on the ‘unloaded’ edges, which results in a completely different state of stresses when the external loads are applied. This is due to the surge of a significant level of induced membrane stresses in the direction perpendicular to loading. In this work, the behavior of long restrained plates under compressive axial loading is analyzed and compared with the one of plates having other boundary conditions. The finite element method is applied for the nonlinear analysis of the plates using a commercial package. 56 cases are considered corresponding to different levels of plate slenderness which ranges between 0.35 and 3.46 covering the practical range of structural plates used in the shipbuilding industry. Various shapes of initial imperfections are considered in order to establish the minimum level of resistance. Also the influence of the magnitude of the distortions associated to each mode is discussed. The study conducted to the establishment of the minimum compressive strength of restrained plates and it defines the expected range of strength’s variation due to the magnitude level of distortions. The biaxial axial state of stresses resulting from these boundary conditions is characterized and its dependence from the plate’s slenderness is quantified for the most common type of the hull plating.
Top Tension Riser Fatigue Monitoring System
Authors: Frazer G. Ross , Reagan Daniel , Ruf Wolfgang , Cheng Jun
Published: November 2011

ATP Oil and Gas Corporation (ATP) is utilizing the MinDOC 3 vessel design for their Mirage, Morgus and Telemark fields. The modeling techniques utilized during the design and verification stages of the project suggest that the production top tension risers (TTR) may be affected by a phenomenon known as Wake Induced Oscillation (WIO). The current modeling techniques are insufficient at predicting the expected amplitude the TTRs will experience due to the WIO and what effect the occurrence will have on the overall fatigue performance of the TTR’s. To acquire a thorough understanding of the effects of WIO, ATP has prudently undertaken an extensive assurance initiative with the purpose of assessing and maintaining structural integrity of their TTRs. As part of ATP’s Integrity Management (IM) program, ATP is monitoring localized strain as well as the motion response of the riser at discrete locations. The paper presents, in detail, ATP’s real-time TTR monitoring system deployed on the ATP MinDOC 3 vessel for their Telemark field. Specific topics to be covered are the monitoring system configuration drivers such as; monitoring objectives, instrumentation requirements, specification, and installation. The paper will cover the number and location of monitoring devices and justification for selection. The data acquired will provide state-of-the-art full-scale riser response information especially during significant events such as hurricanes and loop currents. The goals of the project are: 1. To gain a more in depth understanding of WIO with respect to large diameter hull columns and smaller diameter production TTR’s; 2. Bolster the understanding of the fundamental hydrodynamic behaviour of TTRs and, specifically, vessel-motion induced response of TTRs, and VIV of the TTRs with varying levels of strake fouling. 3. To accurately assess the role of WIO in fatigue damage to the TTR(s).
Dynamic Modeling of Underway Ship-to-Ship Operations
Authors: Souza Carlos Eduardo Silva de , Morishita Helio Mitio
Published: November 2011

A dynamic model for underway ship-to-ship operations with surge velocity is developed. It is admitted that one ship develops power ahead, towing the other vessel together. Models for all relevant loads involved in such operation are present, like environment, mooring, fenders and hydrodynamic interaction loads. The equations of motion take fluid memory effects and wave interaction into account. The model was implemented and simulations were carried out, focusing in the transfer phase of a STS operation. The results are used to analyze mooring lines loads, which is a useful tool for mooring schemes design.
Sensitivity of Plastic Response of Defective Pipeline Girth Welds to the Stress-Strain Behavior of Base and Weld Metal
Authors: Hertele´ Stijn , De Waele Wim , Denys Rudi , Verstraete Matthias
Published: November 2011

One of the key parameters influencing the acceptability of a pipeline girth weld defect subjected to remote plastic deformation is the strength mismatch between weld and base metal. However, no single definition exists for weld strength mismatch, as it can be defined either on the basis of yield stress, ultimate tensile stress or any intermediate flow stress. To investigate the relevance of such definitions, the authors have performed a series of analyses of curved wide plate tests, using a validated parametric finite element model. The results indicate that, whereas yield stress overmatch determines crack driving force for small plastic strains, ultimate tensile stress overmatch is the more important parameter for advanced plastic strains and determines the eventual failure mode. Further, the strain capacity and exact crack driving force curve are additionally determined by uniform elongation and crack growth resistance.
Tidal Energy in Nova Scotia, Canada: The Fundy Ocean Research Center for Energy (FORCE) Perspective
Authors: Keefe Douglas J. , Kozak Joseph
Published: November 2011

Ocean energy developments are appearing around the world including Scotland, Ireland, Wales, England, Australia, New Zealand, Japan, Korea, Norway, France Portugal, Spain, India, the United States, Canada and others. North America’s first tidal energy demonstration facility is in the Minas Passage of the Bay of Fundy, near Parrsboro, Nova Scotia, Canada. The Fundy Ocean Research Center for Energy (FORCE) is a non-profit institute that owns and operates the facility that offers developers, regulators, scientists and academics the opportunity to study the performance and interaction of instream tidal energy converters (usually referred to as TISECs but called “turbines” in this paper.) with one of the world’s most aggressive tidal regimes. FORCE provides a shared observation facility, submarine cables, grid connection, and environmental monitoring at its pre-approved test site. The site is well suited to testing, with water depths up to 45 meters at low tide, a sediment -free bedrock sea floor, straight flowing currents, and water speeds up to 5 meters per second (approximately 10 knots). FORCE will install 10.896km of double armored, 34.5kV submarine cable — one for each of its four berths. Electricity from the berths will be conditioned at FORCE’s own substation and delivered to the Provincial power grid by a 10 km overhead transmission line. There are four berth holders at present: Alstom Hydro Canada using Clean Current Power Systems Technology (Canada); Minas Basin Pulp and Power Co. Ltd. with technology partner Marine Current Turbines (UK); Nova Scotia Power Inc. with technology partner OpenHydro (Ireland) and Atlantis Resources Corporation, in partnership with Lockheed Martin and Irving Shipbuilding. In November 2009, NSPI with technology partner OpenHydro deployed the first commercial scale turbine at the FORCE site. The 1MW rated turbine was secured by a 400-tonne subsea gravity base fabricated in Nova Scotia. The intent of this paper is to provide an overview of FORCE to the international marine energy community during OMAE 2011 taking place in Rotterdam, Netherlands.
On Dynamic Compression of Risers: An Analytical Expression for the Speed of Compression Waves
Authors: Amarante Rodrigo Mota , Pinto Marcos Mendes de Oliveira , Fujarra Andre Luis Condino
Published: November 2011

Several aspects of risers’ dynamics still demand extensive researches as to improve the understanding about physical phenomena involved, so check the adequacy among analytical and numerical results in offshore applications. Dynamic compression of risers is one of these subjects, which has extreme practical relevance in the sense of both design and structural analysis. In this work a riser is anchored at its top end and the other one remains resting on the seabed. Consider that the riser has quasi-vertical configuration. Thus, the angle between the tangent line at the top end and the vertical is small, and its tension on the vicinity of the touchdown point (TDP) is also small. The riser is statically subject to its own submerged weight and on it can act a horizontal ocean current. Furthermore, it supposed a harmonic motion imposed at the top in the tangent direction to the line, caused by local waves on the floating unit. Since the dynamic tension τ(s) changes cyclically in time and the tension T(s) in the TDP is small, it is possible that in this region, the first exceeds the second one in part of cycle’s wave. In these situations occurs a phenomenon known as dynamic compression, widely discussed in Aranha; Pinto and Silva (2001), Aranha; Pinto (2001), Ramos; Pesce (2003) and Fujarra; Simos (2006). During the dynamic compression occurs riser buckling-like. In a strict sense, the behavior of a riser is similar to a cable, although its bending stiffness is not null. Hence, risers have some resistance to buckling-like and can support a certain level of compression. The maximum loading of compression that can be measured in a riser segment is known as critical load (Pcr). Aranha; Pinto and Silva (2001) proposed a simple analytical formulation for the critical load. The aim of the present paper is to propose a simple analytical equation for the speed of compression waves that propagate from the TDP to the riser’s top end. This formulation depends on physical characteristics of the riser and the levels of tension to which it is submitted. As a result, it is possible to compare the theoretical results obtained with numerical simulations and physical experiments. The outcomes provide more understanding to the phenomenon of dynamic compression of risers.
3D Scour of Submarine Pipeline at Touchdown Point: An Experimental Investigation
Authors: Dwivedi Ambuj , Low Ying Min , Chiew Yee-Meng , Wu Yushi
Published: November 2011

This research presents the preliminary results obtained from the experimental study of 3D scour of submarine pipelines at its touchdown point. The results obtained from this study will increase our understanding on the mechanism of scour propagation at the touch down point of pipelines. Experiments were carried out inside a laboratory flume with piezoelectric miniature pressure sensors to measure pressure gradient across the pipe. Experiments were performed under unidirectional steady current with uniform sediments as bed. The scour pattern under initial embedment depth of pipeline is obtained. Preliminary result showed the importance of span-wise (longitudinal) scour in causing failure of the submarine pipelines.
Wave Run-Up Simulations With a Moving Large Volume Semi-Submersible Platform
Authors: Watai Rafael de Andrade , Matsumoto Fabio Tadao , Sparano Joa˜o Vicente , Simos Alexandre Nicolaos , Ferreira Marcos Donato A. S.
Published: November 2011

Since July 2008, the Numerical Offshore Tank (TPN) of the University of Sa˜o Paulo and Petrobras have been working on a research project intended to improve knowledge and modeling of advanced hydrodynamics topics, such as the wave run-up phenomenon. Among other activities, wave basin tests were performed with small-scale model of a large volume semi-submersible designed to operate in Campos Basin. These tests evidenced significant run-up effects on its squared-section columns for the steepest waves in several design conditions. In order to evaluate the difficulties involved in modeling the wave run-up phenomenon, simplified tests were also carried out with the model fixed and moored in regular waves with varying steepness. Previous studies using a 2nd order BEM model and a VOF CFD code to predict free-surface elevations below the deck under regular waves were presented in Matsumoto et al. (2010). The studies illustrated considerable differences between the wave elevation results in fixed and moored model setup; however, by that time, the analysis of the moored model by a VOF CFD code was not yet complete. This paper, therefore, presents wave run-up estimations with a moving large volume semi-submersible platform performed with the CFD code ComFLOW, which solves the Navier-Stokes equations employing a local height function to the free surface displacement. The phenomenon is investigated by simulating the flow around the semi-submersible model under the influence of high steepness regular waves on a non-uniform grid. Platform motions, derived from a first order BEM code, are imposed and synchronized with the incoming wave. Aiming at avoiding numerical wave reflections, a damping zone is also applied and positioned downstream the platform model. Predicted results are compared to experimental data, measured by seven vertical wave probes located in different positions below the model deck. Although considerably time-consuming, it will be shown that simulations present very good agreement with the experimental results.
A Comparison of Radial Wellbay and Traditional Truss Spar Designs
Authors: Murray John , Muehlner Edmund , Choi Guibog
Published: November 2011

The Spar continues to be a popular drilling and production platform design for ultra-deep water. In recent years, developers have introduced a number of design variations such as the Arctic Spar, closed centerwell Spar, and long Spar. As the industry moves production into ultra-deep water, the escalation in drilling costs, particularly for deeper more complicated wells, prompts the need to look for new deepwater floater designs, including Spars. This paper introduces some new features to the Truss Spar, including a radial wellbay layout and an adjustable buoyancy centerwell device. This new Radial Wellbay Spar design is investigated and compared to the traditional Truss Spar for the same topside and riser weights and subjected to the same environments. The base case assumes a drilling and production platform with the performance comparison made in terms of hull weights and dimensions and hull motions for post-Katrina Gulf of Mexico conditions. In general, the Radial Wellbay Spar offers a smaller hull with fewer mooring lines for the same payload while maintaining the Spar’s low motion performance.
Statistical Characterization of Slacking and Snap Loading During Offshore Lifting and Lowering in a Wave Environment
Authors: Thurston Kevin W. , Swanson Richard C. , Kopp Frans
Published: November 2011

During offshore lifting operations, appropriate characterization of the dynamic forces is critical to ensuring that the proper lifting equipment has been selected and designed. When a load is supported by a wire rope, or any member that will not support compression, there is a possibility of the rope becoming slack during the lift. The resulting shock load when the rope becomes taut again can produce significant impact loads in the lifting equipment, which is a situation preferably avoided. Thus, of particular importance is the reasonably accurate estimate of the probability of occurrence of sudden loading events. During offshore lifting operations, this situation can occur under the following circumstances: 1) During a transfer of a weighted load between two vessels in an offshore wave environment. 2) Lowering a load through the water surface, particularly in a wave environment. 3) Lowering a load through the water column with significant motions of the support at the surface. This paper deals with the first two situations. First, a model to predict the probability of slacking the rope while lowering a load through the water surface in a wave environment will be presented. Secondly, some commentary will be made about the possible magnitude of the shock loads that can occur during vessel to vessel transfers and lowering through the water surface. Finally, a brief comparison will be made between these models and others that have been proposed within the industry, some of which have been incorporated in design standards and guidelines.
Experimental Study on Wet Tow and Upending of a Truss Spar
Authors: Liu Lin , Xiao Longfei , Hu Zhiqiang , Yang Lijun
Published: November 2011

In recent years, with the development of the deepwater oil and gas exploitation, the Spar platform has received more and more attention. A lot of research work has been done on the Spar platform, but experimental study on the process of wet tow and upending of Truss Spar is seldom conducted. Recently, a wet tow and upending model test of a Truss Spar was carried out in the State Key Laboratory of Ocean Engineering in Shanghai Jiao Tong University. The hydrodynamic characteristics and the global loads on the key points of the Truss Spar during the period of wet tow and upending are focused on. In the wet tow tests, the tow resistance, 6DOF motions, global loads and the relative wave elevations are measured and analyzed. During the upending simulation, the measuring parameters consist of the motions and the global moment at the connection points between the hard tank and the truss. The test program and test results are presented and discussed in this paper offering the value references for the wet tow and upending operation in reality of the Truss Spar.
Flat Buoy Concept for Free Standing Riser Application: An Improvement of the In-Place Hydrodynamic Behaviour
Authors: Vivet Romain , Minguez Matthieu , Berhault Christian , Jacquin Erwan , Petrie Franc¸ois , Flamand Olivier
Published: November 2011

The study focuses on the in-place hydrodynamic behavior and Flow Induced Response of a novel design of Free Standing Riser (FSR) system tensioned by a ‘Flat-Buoy’. The paper presents results review of both Experimental and Numerical approaches initiated in the framework of a comprehensive Research & Development program. Experimental and numerical study conclusions converge on the excellent hydrodynamic Stability of such FSR system. First, wind tunnel campaign, based on Reynolds similitude, has focused on the flow features over the fixed Flat Buoy. No Vortex Shedding has been clearly highlighted. Moreover, results have pointed out a more pronounced dependence of the hydrodynamic coefficients to the flow incidence than to the Reynolds number. Secondly, basin model tests, based on Reduced Velocity similitude, have highlighted the stability of such scaled FSR system concluding to maximum Cross-Flow and In-Line amplitude such as A/D<0.35 (A represents the amplitude and D the Buoy diameter). In parallel, hydrodynamic stability has been investigated Benchmarking Computational Fluid Dynamic (CFD) methods. Preliminary validation steps have pointed out ability of such CFD approaches to globally predict both Wind Tunnel and Basin Test results. Finally, extending CFD and Fluid Structure Interaction (FSI) modeling to full-scale configuration, stability of the FSR tensioned by a Flat-Buoy has been proved.
Development of New IMO Type B Tank Based on the Results of Cryogenic Material Property Tests
Authors: Kim Kwang Seok , Park Chang Youl , Kang Joong Kyoo
Published: November 2011

As the LNG industry is rapidly growing, the demand of FLNG (Floating LNG) is also increasing. Since the medium to long-term forecasts predict a shortage of LNG supply, the introduction of offshore LNG production can be seen in the near future. In recent, DSME has developed the new IMO type B tank (ACTIB: Aluminum Cargo Tank Independent type B) considering the cryogenic material properties. This paper describes engineering works done during the ACTIB development. A lot of engineering works were carried out from the basic scantling of the tank to characteristic works for IMO type B tank such as thermal stress, crack propagation & fracture analysis and leak & drip tray design concept. As a result of study, DSME received AIP from DNV and could unveil the ACTIB to the market.
An Experimental Study on Behaviors of IMO Type B CCS Materials at Room and Cryogenic Temperatures
Authors: Yoo Chang-Hyuk , Kim Kyung-Su , Choung Joonmo , Kim Sung-Hoon , You Won-Hyo
Published: November 2011

IMO (international maritime organization) type B CCS (cargo containment system) is considered for LNG (liquefied natural gas) FPSOs. For the three materials of SUS304, Al 5083-O alloy and 9% Ni steel regarded as possible candidates for IMO type B CCS, extensive tensile, fatigue, fatigue crack growth rate and CTOD (crack tip opening displacement) tests were carried out at room, intermediate low (−100°C) and cryogenic (−163°C) temperatures and described in this paper. All materials show a tendency for initial yield and tensile strengths to increase with decrease in the temperature, while change in elastic moduli is not as remarkable. The largest and smallest increase ratios of the initial yield strengths due to temperature reduction are seen in SUS304 and Al 5083-O alloy, respectively. In fatigue tests, fatigue strengths increase due to the temperature decrease for three materials. The highest increase of fatigue strength due to the temperature decrease is observed in Al 5083-O alloy, while 9% Ni steel shows lowest increase. In fatigue crack growth rate test, SUS304 and Al 5083-O alloy show reduction in crack propagation rate, due to the reduction in temperature, while any visible improvement of da/dN is not witnessed in case of 9% Ni steel. In CTOD test, CTODs tend to decrease in case of SUS304 and CTODs for Al 5083-O alloy increase with reduction in temperature.
Introducing Wave Regeneration by Wind in a Mild-Slope Wave Propagation Model MILDwave to Investigate the Wake Effects in the Lee of a Farm of Wave Energy Converters
Authors: Stratigaki Vasiliki , Troch Peter , Baelus Leen , Keppens Yannick
Published: November 2011

The increasing energy demand, the need to reduce greenhouse gas emissions and the shrinking reserves of fossil fuels have all enhanced the interest in sustainable and renewable energy sources, including wave energy. Many concepts for wave power conversion have been invented. In order to extract a considerable amount of wave power, single Wave Energy Converters (abbreviated as WECs) will have to be arranged in arrays or ‘farms’ using a particular geometrical layout, comprising large numbers of devices. As a result of the interaction between the WECs within a farm, the overall power absorption is affected. In general, the incident waves are partly reflected, transmitted and absorbed by a single WEC. Also, the wave height behind a large farm of WECs is reduced and this reduction may influence neighbouring farms, other users in the sea or even the coastline (wake effects of a WEC farm). The numerical wave propagation model MILDwave has been recently used to study wake effects and energy absorption of farms of WECs, though without taking into account wave regeneration by wind in the lee of the WEC-farm which can be significant in large distances downwave the WECs. In this paper, the implementation of wave growth due to wind in the hyperbolic mild-slope equations of the wave propagation model, MILDwave is described. Several formulations for the energy input from wind found in literature are considered and implemented. The performance of these formulations in MILDwave is investigated and validated. The modified model MILDwave is then applied for the investigation of the influence of the wind on the wakes in the lee of a farm of wave energy converters.
Evaluation of Premature Failure of Links in the Docking System of a FPSO
Authors: Largura Junior Luiz Carlos , Piana Luciano Andre´ , Craidy Pedro da Silva
Published: November 2011

Oil production in offshore areas has increased in recent years, especially with deeper water creating new challenges to be overcome. In this scenario, the mooring systems of floating units need to withstand higher operating loads. The mooring system is designed to keep the FPSO (Floating Production Storage and Offloading) properly positioned. Being fundamental to the integrity of risers and the platform itself, the failure can cause the overloading of other lines and generate the collapse of the whole mooring system in an extreme environmental situation, so the design and material selection are essential to the success of the venture. This work presents the investigation of the premature failure in some lines of the mooring system for an FPSO, in this case links in class R3. There were flaws in the weld between the link and the stud, with the subsequent complete failure of link. Some analyses were performed to understand the problem, including chemical composition, microstructural evaluation, hardness, corrosion potential, numerical analysis and fatigue tests. Finally, we concluded that the use of materials from different links to the stud generated a localized corrosion leading to increased local tensions and the failure by fatigue.
On Roll Hydrodynamics of FPSO’s Fitted With Bilge Keels and Riser Balcony
Authors: van ’t Veer R. , Fathi F. , Kherian J. G.
Published: November 2011

The topic of this paper is the roll motion prediction of ship-shaped FPSO’s, designed for continuous operation at site location. The maximum roll amplitude is a critical operability parameter which is difficult to predict accurately due to the nonlinear roll damping associated with the appendages. This paper contributes to the understanding of roll damping physics through model test results, CFD simulations and potential flow predictions. The model tests discussed concern two different Floating Production, Storage and Offloading (FPSO) units, designed by SBM as spread-moored units for operation offshore Brazil. The relevant roll damping appendages are the bilge keels on both sides and the submerged riser balcony on one side of the vessel. In particular the riser balcony complicates the motion prediction and was a main reason for the model tests and CFD investigation. The results presented focus on roll motion prediction in the frequency domain.