bluuebunny/crossref_metadata_2025 huggingface dataset:
An Investigation Into the Behaviour of Composite Repaired Pipelines Under Combined Internal Pressure and Bending
Authors: Shouman Ahmed , Taheri Farid
Published: February 2010

The repair of corroded pipelines with fiber reinforced composite materials has gained wide acceptance in the oil and gas transportation industry over recent times. It has been integrated into the ASME B31.4 and B31.8 pipeline codes, along with CSA Z662. A considerable amount of experimental research has been conducted on fiber reinforced composite repaired pipelines with external corrosion defects subject to hydrostatic internal pressure. However, the effects of the internal pressure, thermal loads and geotechnical loads create combined loading conditions on the buried pipeline that need to be considered. This paper aims to address the effectiveness of fiber reinforced composite repair systems on externally corroded pipelines under combined internal pressure and bending. For that, finite element analysis is conducted to examine the effects of various loading conditions on the effectiveness of the fiber reinforced composite repair system. Typical conventional commercially available fiber reinforced composite wrap systems are used for this purpose. Three loading conditions are considered on both conventionally repaired and unrepaired pipes subject to internal pressure, pure bending and combined internal pressure and bending. Results show that up to the stage of yielding of the steel in the defect region, the steel elastic stiffness counteracts most of the stress that is induced by the in-service loading conditions. Once the pipe is loaded beyond the yielding point of its material at the defect region, the composite starts to take effect, thus carrying a significant portion of the applied stresses. Essentially, by comparing the burst pressures of repaired pipes against unrepaired pipes, it is shown that the fiber reinforced composite system restores the minimum specified strength of the pipe to its value before the defects were applied. The results presented in the paper are believed to reveal the response of the wraps subject to realistic combined loading conditions that to our knowledge are nonexistent in open literature.
Flexural Gravity Wave Scattering Due to Variations in Bottom Topography
Authors: Karmakar D. , Bhattacharjee J. , Sahoo T.
Published: February 2010

Oblique flexural gravity wave scattering due to abrupt change in bottom topography is investigated under the assumption of linearized theory of water waves. The problem is studied first for single step in case of finite water depth whose solution is obtained based on the expansion formulae for flexural gravity wavemaker problem and corresponding orthogonal mode-coupling relation. The results for the multiple step topography are obtained from the result of single step using the method of wide-spacing approximation. Energy relation for oblique flexural gravity wave scattering due to change in bottom topography is used to check the accuracy of the computation. Using shallow water approximation the wave scattering due to multiple step topography is derived considering the continuity of mass and energy flux. In this case also the result for single step topography is obtained and then using the wide-spacing approximation the result for multiple steps are derived. Numerical results for reflection and transmission coefficients and deflection of ice sheet are obtained to analyze the effect of multiple step topography on the propagation of flexural gravity waves.
Reference Load for a Conventional 138K CBM LNG Carrier in a Comparative Approach
Authors: Ryu Min Cheol , Jung Jun Hyung , Jeon Soo Sung , Hwang Yoon Sik , Han Sung Kon , Kim Yong Soo , Cho Tae Ik , Kwon Sun Hong
Published: February 2010

Still limited to knowledge about the actual phenomena so far, the comparative method has been used to assess the design load and the strength of cargo containment system for target ship designs. In the comparative approach, the sloshing load and strength of a conventional sized LNG carrier are compared with the load and strength for target LNG vessels. A 138,000 m3 LNG carrier with 4 cargo tanks is used as a reference vessel in the comparative approach according to the market practice. Recently, a Joint Development Project (JDP) on the formal assessment of the reference design sloshing load has been undertaken with four major Classification Societies using the sloshing test facility (21). During the JDP period, a “common” test procedure to make a reference load was developed. After a detailed investigation of the test data obtained using the developed procedure, the reference load was derived. The reference load will be used for the safety assessment of the NO96 containment system for DSME’s future LNG carriers or LNG related offshore floating vessels. This paper describes the test procedure and some investigated results.
Spudcan Penetration in Loose Sand Over Uniform Clay
Authors: Yu Long , Hu Yuxia , Liu Jun
Published: February 2010

Punch through failures of spudcan foundations of mobile jack-up rigs have been reported every year. The potential of punch through failure of spudcan foundations on loose sand over uniform clay soils was studied numerically in the present paper. Large deformation finite element analyses were carried out to simulate the load-penetration responses of a 14m diameter spudcan during continuous penetration into this sand over clay soil. The numerical results were compared with existing centrifuge data. The critical penetration depths were derived from the load-penetration responses. The soil flow mechanisms, the shape of sand plug and the distribution of plastic points were also reported.
WindFloat: A Floating Foundation for Offshore Wind Turbines—Part I: Design Basis and Qualification Process
Authors: Roddier Dominique , Cermelli Christian , Weinstein Alla
Published: February 2010

This paper and the corresponding hydrodynamic and structural study paper (also in these proceedings) summarize the feasibility study conducted for the WindFloat technology. The WindFloat is a 3-legged floating foundation for very large offshore wind turbines. It is designed to accommodate a wind turbine, 5 MW or larger, on one of the columns of the hull with minimal modifications to the tower, nacelle and turbine. Technologies for floating foundations for offshore wind turbines are evolving. It is agreed by most experts that the offshore wind industry will see a significant increase in activity in the near future. Fixed offshore turbines are limited in water depth to approximately 30∼50m. Market transition to deeper waters is inevitable, provided suitable technologies can be developed. Despite the increase in complexity, a floating foundation offers distinct advantages: • Flexibility in site location. • Access to superior wind resources further offshore. • Ability to locate in coastal regions with limited shallow continental shelf. • Ability to locate further offshore to eliminate visual impacts. • An integrated structure, without a need to redesign the mast foundation connection for every project. • Simplified offshore installation procedures. Anchors are significantly cheaper to install than fixed foundations and large diameter towers. This paper focuses on the design basis for wind turbine floating foundations, and explores the requirements that must be addressed by design teams in this new field. It shows that the design of the hull for a large wind turbine must draw on the synergies with oil and gas offshore platform technology, while accounting for the different design requirements and functionality of the wind turbine.
Experimental Study on Hydrodynamic Behavior of Jacket Spar Platform
Authors: Sajini U. S. , Sundaravadivelu R. , Anantha Subramanian V.
Published: February 2010

This paper presents the experimental study on the hydrodynamic behavior of a jacket spar platform designed for 10 MLD (million liters per day) desalination plant in the water depth of 375 m with the pay load of 50×103 kN. The surge, heave and pitch natural periods from free decay tests are presented and validated with the numerical results obtained using NAOS (Non-linear Analysis of Offshore Structures) developed in IIT Madras. The jacket spar is modeled using sixty beam elements and each mooring lines by ten beam elements with axial prestress to model the pretension. The beam elements with axial prestress do not take any compressive load. The surge, heave and pitch response and mooring line tension of the jacket spar platform for three wave height range of 2.6m to 8.75m in the wave period range of 7.82s to 19.00s are presented. The maximum surge of 0.5% of water depth, the maximum heave RAO of 0.1 and maximum pitch of 1.54° are within the operational limits. The maximum tension in mooring line is only 10% of breaking strength.
The Dynamic Response of a Moored Vessel in Shallow Water Using Boussinesq Equations
Authors: Park Byeong W. , Yuck Rae H. , Cho Seok K. , Choi Hang S.
Published: February 2010

In this study, firstly nonlinear waves in shallow water were simulated by using the Boussinesq equations. The simulated waves represented well the wave deformations such as shoaling and refraction as well as non-linear wave interactions among wave components as they approach coastal region from far field. The velocity components of the simulated waves at an arbitrary location in the fluid domain can be computed most effectively by introducing the so-called utility velocity. By taking the deformed wave field into account, the motion response of a moored floating barge was analyzed. The wave excitation and radiation force were estimated by the Constant Panel Method (CPM) based on linear potential theory. In order to estimate the wave excitation force including shallow water effects, the wave height and the wave velocity components obtained from the Boussinesq simulation were used. This approach used to estimate the wave excitation force including shallow water effects is herein referred to as Hybrid Boussinesq-CPM. An example calculation was made for the Pinkster barge, which is supposed to be located in a specific bottom topography and moored by the Tower Yoke Mooring System. The results were compared with those obtained for the equivalent constant water depth condition. The comparison showed that the motion responses obtained by the Hybrid model were larger than those for the even bottom case. In particular, the horizontal surge motion was significantly enlarged because of two facts: the wave deformation due to the bottom topography and the low frequency waves caused by nonlinear wave-wave interactions. The enlarged horizontal surge motion is important for mooring design in shallow water.
An Experimental Study of the Interaction Between Pipe Structure and Internal Flow
Authors: Yamamoto Marcio , Murai Motohiko , Maeda Katsuya , Uto Shotaro
Published: February 2010

Nowadays pipes are widely deployed in the offshore environment especially in the petroleum industry where rigid and flexible pipes are used for well drilling and hydrocarbon production. Whereas during drilling, a mixture of drilling mud, rock cuttings and sometimes gas flows through the drilling riser, during production mono or multiphase (comprising oil, water and gas) flow takes place within the system. However up till now, most of the studies on offshore pipelines and risers have been focused on the pipe structure and its interaction with hydrodynamic forces and offshore platforms. In particular for numerical computation studies and reduced scale model experiments, the pipe is usually modeled as a tensioned beam and sometimes only the internal pressure is taken into account with other effects due to its internal flow being neglected. This paper deals with the interaction between the pipe structure and its internal flow. In order to verify the internal flow effects, an experimental analysis was carried out not using a reduced scale model. In particular, mono-phase fluid flows into the pipe and a parametric analysis using the flow rate was carried out. Discussion about the experimental results and numerical applications is also included.
Field Trial and Numerical Back-Analysis of Suction Caisson Extraction in Hong Kong
Authors: Lorenti Leon S. D. , Shum Dora Y. N. , Lehane Barry M.
Published: February 2010

An in-situ push-out test was carried out on a 3.4m diameter, 12m high trial suction caisson to determine the ultimate uplift capacity and, in particular, the shaft friction that could be generated along the walls of the caisson. The test was performed in the south-eastern waters of Hong Kong in ground conditions comprising soft clay with alluvial sand at the caisson tip. Numerical back-analysis of test reveal that considerable suction was generated at the caisson base due to a combination of the relatively high rate of loading adopted in the test and the silty nature of the alluvium. Inferred friction values generated on the outside wall of the caisson are found to be in line with existing data reported in the literature.
Far-Field Effects of Large Tsunamis Produced by the Makran Subduction Zone
Authors: Heidarzadeh Mohammad
Published: February 2010

The 2004 Indian Ocean tsunami which exported death and destruction to far distant shores, once more emphasized the tsunami hazards associated with transoceanic tsunamis. Historical records of tsunamis in the Makran subduction zone (MSZ) reveal that Makran tsunamis are capable of producing large waves in the far-field. The Makran tsunami of 1945 produced by an Mw8.1 earthquake was reported to cause far-field effects in the Indian Ocean and reached a height of about 30 cm in the Seychelles, at the distance of about 3500 km from the MSZ. Here, we assess historical observations of this event and perform numerical modeling of this tsunami with emphasis on its far-field effects. Our numerical modeling successfully reproduces most feathers of the historical observations including its far-field effects. Southward propagation of Makran large tsunamis is investigated and their possible effects on Maldives and Seychelles islands are discussed. This study will help to better understand tsunami hazard associated with the MSZ, especially its far-field hazard.
Real Time Estimation of Ship Motions in Short Crested Seas
Authors: Naaijen P. , van Dijk R. R. T. , Huijsmans R. H. M. , El-Mouhandiz A. A.
Published: February 2010

The presented research is part of the development of an onboard wave and motion estimation system that aims to predict wave elevation and vessel motions some 60–120 s ahead, using wave elevation measurements by means of X-band radar. In order to validate the prediction model, scale experiments have been carried out in short crested waves for 3 different sea states with varying directional spreading, during which wave elevation and vessel motions were measured. To compare predicted and measured wave elevation, three wave probes were used at different distances from a large set of wave probes that was used as input to the model. At one of the prediction locations, also tests were performed to measure vessel motions. This setup allowed validation of a method that was used for initializing the linear wave prediction and ship motion prediction model. Various observations and conclusions are presented concerning optimal combinations of prediction model parameters, probe set-up and sea state.
Systematic Investigation of Loads and Motions of a Bulk Carrier in Extreme Seas
Authors: Clauss Gu¨nther F. , Kauffeldt Andre´ , Klein Marco
Published: February 2010

During their lifetime ships often operate in severe weather and rough sea states. To ensure survival, a precise knowledge of global and local loads is an inevitable integral part for a safe design. One of the key parameters for ship design is the vertical bending moment. Not only vertical forces but also longitudinal forces can contribute to this bending moment. As the overall effect of longitudinal forces is still not fully understood, all structural loads are investigated in detail, especially in extreme seas. Within the project “Handling Waves”, funded by the European Union, three segmented ships, equipped with force transducers, are investigated systematically at several cruising speeds and in various deterministic wave sequences to identify structural loads, i.e. the vertical bending moment as well as the superimposing longitudinal forces. Within this paper a detailed overview of the results for the bulk carrier is given and both, frequency- and time-domain results are presented. With Response Amplitude Operators (RAOs), delivered by frequency-domain analysis, the profound data for the standard assessment of structures, concerning seakeeping behaviour, operational limitations and fatigue are obtained. In addition, time domain analyses in rogue waves such as the so called “New Year Wave” provide essential data for extreme motions and structural loads. Former investigations on a FPSO revealed that, due to the location of the neutral axis, the longitudinal forces are significant and generate a counteracting moment compared to the vertical bending moment [1]. The new results show to what extent the above mentioned conclusions are applicable for various hull designs.
Nonlinear Effects on Interfacial Wave Growth Into Slug Flow
Authors: Campbell Bryce K. , Hendrickson Kelli , Liu Yuming , Roberts Randy
Published: February 2010

The objective of this study is to understand the effects of non-linearity on the interfacial stability of a two fluid stratified flow through a horizontal channel. An efficient perturbation expansion based high-order spectral method is developed, for the simulation of the generation and nonlinear evolution of interfacial waves. The method is capable of accounting for the nonlinear interactions of a large number of wave components in a broadband spectrum, and obtains an exponential convergence of the solution with grid refinement and interaction order. The method is applied to investigate the role that nonlinear effects have on the initial development of Kelvin-Helmholtz (KH) instabilities and nonlinear wave-wave interactions with the purpose of gaining insight into the physical mechanisms which cause slug flow. It will also be demonstrated that nonlinearity can introduce unstable inter-facial wave growth in regions predicted to be stable by linear analysis. In addition, it is shown that energy transfer from short (KH unstable) waves to long (KH stable) waves due to nonlinear resonant wave-wave interactions is an effective mechanism for the development of slug flow.
Free-Surface Viscous Flow Computations: Validation of URANS Code FreSCo
Authors: Vaz Guilherme , Jaouen Frederick , Hoekstra Martin
Published: February 2010

In this paper, the free-surface modelling in MARIN’s URANS code FreSCo is analysed and tested. FreSCo is a finite-volume code using a two-phase Volume-Of-Fluid approach to handle free-surfaces. After a description of code and method, attention is paid to wave generation and propagation. More specifically, the objective of this study is to assess if the code can model correctly travelling waves of 2nd order Stokes type and what it requires to do so with a quality needed for engineering purposes. Analysis of the effect of numerical schemes and of discretisation errors (via grid-refinement studies) is reported. Dispersion and diffusion errors are quantified by comparison with analytical solutions. Furthermore, two typical benchmark free-surface problems, viz. a 3D Dam-breaking flow and the Duncan foil test case, are used to illustrate the current capabilities of FreSCo. The results are validated against experiments and numerical data available in the literature. The results here shown indicate that FreSCo comes up to expectation, but also that issues such as compressive convection schemes and non-reflective boundary conditions require further research.
Optimum Power Capture of a New Wave Energy Converter in Irregular Waves
Authors: Aggidis George A. , Rahmati Mohammad T. , Chaplin Robert V. , McCabe Andrew P. , Bhinder Majid A. , Mingham Clive G. , Causon Derek M.
Published: February 2010

This paper presents the optimum power capture of a new point-absorber wave energy converter, in irregular waves. A stepwise control system for the wave energy converter (WEC) is developed. The control system is used to efficiently extract power from irregular waves where amplitudes vary from wave to wave. The Bretschneider spectrum is used in the experiment and the device is ‘tuned’ to the peak period of the sea state. It is shown that this WEC has a reasonable capture width in irregular waves. However, the optimum mean power depends on the wave spectrum, the shape of the collector body, its freeboard and the device pivot depth.
Recent Developments in Drilling Riser Disconnect and Recoil Analysis for Deepwater Applications
Authors: Lang Donogh W. , Real James , Lane Michael
Published: February 2010

With exploration and development of hydrocarbon resources moving into ever deeper waters, there is significantly increased demand for drilling vessels capable of drilling in water depths of up to 10,000 ft and beyond. One of the main challenges associated with drilling in these water depths is control of the recoil behavior of the drilling riser after an emergency disconnect. This is required from time to time in the event of loss of the vessel’s station-keeping capability, either in extreme weather or through a failure of the dynamic positioning system. In these scenarios, the riser must be quickly disconnected below the Lower Marine Riser Package (LMRP) to avoid damage to the riser or well structure. Once disconnected, the LMRP should lift sufficiently clear of the Blow-Out Preventer (BOP) to avoid subsequent contact between the LMRP and the BOP, while at the same time the upward movement of the riser must be arrested in time to prevent collapse of the telescopic joint (which could cause impact loads on the drillfloor) or compression in the tensioning lines. These conflicting requirements become more severe in deepwater, where the ratio between the wet weight and inertia of the riser is reduced. This highlights the requirement for an accurate recoil analysis capability in order to determine the optimum riser stack-up and operability limits for deepwater operations. This paper describes the development of a disconnect and recoil analysis software tool that for the first time has been integrated with a 3D finite element (FE) structural model of the drilling riser system. The tool incorporates a detailed model of the riser tensioning system, including the ability to model the behavior of each tensioning cylinder independently and the ability to model the behavior of the anti-recoil control system. The tool also incorporates an advanced fluid flow model, implemented by means of a finite volume numerical model, that models the flow of drilling mud out of the riser immediately after disconnect. The details of the tensioner system and fluid flow models are discussed, along with the approach taken to integrate these into the existing FE structural analysis code. A number of case studies are presented to illustrate the application of the tool to deepwater riser recoil analysis and to examine the effect of key parameters (including vessel offset) on the recoil behavior of the riser system.
Challenges in Hydrate Plug Prevention in Pipelines Seen Over the Lifetime of a Field
Authors: Hadsbjerg Casper , Krejbjerg Kristian
Published: February 2010

When the oil and gas industry explores subsea resources in remote areas and at high water depths, it is important to have advanced simulation tools available in order to assess the risks associated with these expensive projects. A major issue is whether hydrates will form when the hydrocarbons are transported to shore in subsea pipelines, since the formation of a hydrate plug might shut down a pipeline for an extended period of time, leading to severe losses. The industry practices a conservative approach to hydrate plug prevention, which is the addition of inhibitors to ensure that hydrates cannot form under pipeline pressure and temperature conditions. The addition of inhibitors to subsea pipelines is environmentally unfriendly and also a very costly procedure. Recent efforts has therefore focused on developing models for the hydrate formation rate (hydrate kinetics models), which can help determine how fast hydrates might form a plug in a pipeline, and whether the amount of inhibitor can be reduced without increasing the risk of hydrate plug formation. The main variables determining whether hydrate plugs form in a pipeline are: 1) the ratio of hydrocarbons to water, 2) the composition of the hydrocarbons, 3) the flowrates/flow regimes in the pipeline, 4) the amount of inhibitor in the system. Over the lifetime of a field, all 4 variables will change, and so will the challenge of hydrate plug prevention. This paper will examine the prevention of hydrate plugs in a pipeline, seen from a hydrate kinetics point of view. Different scenarios that can occur over the lifetime of a field will be investigated. Exemplified through a subsea field development, a pipeline simulator that considers hydrate formation in a pipeline is used to carry out a study to shed light on the most important issues to consider as conditions change. The information gained from this study can be used to cut down on inhibitor dosage, or possibly completely remove the need for inhibitor.
Constraint-Based Fracture Mechanics Analysis of Cylinders With Circumferential Cracks
Authors: Bach Michael , Wang Xin , Bell Robert
Published: February 2010

In this paper, the fracture behaviour of hollow cylinders with internal circumferential crack under tensile loading is examined extensively. Finite element analysis of the cracked cylinders is conducted to determine the fracture parameters including stress intensity factor, T-stress, and J-integral. Linear elastic finite element analysis is conducted to obtain K and T-stress, and elastic plastic analysis is conducted to obtain fully plastic J-integrals. A wide range of cylinder geometries are studied, with cylinder thickness ratios of ri/ro = 0.2 to 0.8 and crack depth ratio a/t = 0.2 to 0.8. These fracture parameters are then used to construct conventional and constraint-based failure assessment diagrams (FADs) to determine the maximum load carrying capacity of cracked cylinders. It is demonstrated that these tensile loaded cylinders with circumferential cracks are under low constraint conditions, and the load carrying capacity are higher when the low constraint effects are properly accounted for, using constraint-based FADs, comparing to the predictions from the conventional FADs.
Tensile, Torsional and Bending Strain at the Adhesive Rupture of an Iced Substrate
Authors: Laforte Caroline , Laforte Jean-Louis
Published: February 2010

In order to develop an effective deicing device using mechanical deformation of substrates, the adhesive and/or cohesive strains of ice at rupture were measured for three different modes of solicitation: tensile, twisting and bending. A total of 108 icing/deicing tests were conducted with aluminum and nylon samples covered with hard rime ice deposits 2, 5, and 10 mm thick strained at various strains rates in brittle regime at −10°C. Real time deformation was precisely monitored using a strain gage fixed to the A1 interface, and force by means of load cells and a torque-meter. Deicing strain was determined at the time of ice detachment, which corresponds to a visible, instant change in the slope of stress-strain curves. The mean values of deicing strains, ε %, measured in tensile, torsion and bending experiments are respectively, 0.037 ± 0.015%, 0.043 ± 0.023% and 0.004 ± 0.003% As for adhesion strength, the highest values were obtained in tension, 4 MPa ± 50%, and the lowest in bending, 0.014 MPa ± 36%. In torsion, the value was intermediary, at 1.26 MPa ± 67%. Measurements also showed that deicing stress and strain tended to increase with substrate roughness, whereas they decrease with increasing ice thicknesses. In summary, this work points out the effects of two major factors on ice adhesion strength, the solicitation mode and the ice thickness. Finally these results suggest that the first criteria for a mechanical deicing device has to satisfy to be effective is to have the capacity to generating a strain at around 0.04% ice/substrate interface.
Undrained Load Capacity of Torpedo Anchors in Cohesive Soils
Authors: de Aguiar Cristiano S. , de Sousa Jose´ Renato M. , Ellwanger Gilberto Bruno , de Campos Porto Elisabeth , de M. Ju´nior Cipriano Jose´ , Foppa Diego
Published: February 2010

This paper presents a numerical based study on the undrained load capacity of a typical torpedo anchor embedded in a purely cohesive isotropic soil using a three-dimensional nonlinear finite element (FE) model. In this model, the soil is simulated with solid elements capable of representing its nonlinear physical behavior as well as the large deformations involved. The torpedo anchor is also modeled with solid elements and its complex geometry is represented. Moreover, the anchor-soil interaction is addressed with contact finite elements that allow relative sliding with friction between the surfaces in contact. Various analyses are conducted in order to understand the response of this type of anchor when different soil undrained shear strengths, load directions as well as number and width of flukes are considered. The obtained results point to two different failure mechanisms: one that mobilizes a great amount of soil and is directly related to its lateral resistance; and a second one that mobilizes a small amount of soil and is related to the vertical resistance of the soil. Besides, the total contact area of the anchor seems to be an important parameter in the determination of its load capacity and, consequently, the increase of the undrained shear strength and the number of flukes and/or their width significantly increases the load capacity of the anchor.
Application of Flexible Risers in Shallow Water: Weight Added Wave Configuration
Authors: Tan Zhimin , Loper Cobie , Hou Yucheng , Sheldrake Terry
Published: February 2010

Unbonded flexible pipe has been a proven technology for riser solutions in offshore oil and gas production since the 1970s with over 2000 risers installed. The operating envelope for flexible riser configurations has continually expanded to meet the challenges of both shallow and deep water applications [1]. This paper presents recent innovations in technology for flexible riser solutions to enable oil and gas development in water depths as low as 20m with required system reliability as well as cost effectiveness. For shallow water applications, the traditional technology is the wave or S configuration. S configurations require a structure such as a mid-water buoyancy arch (MWA) to support the riser configuration, which increases the cost of both fabrication and installation. The wave configuration with distributed buoyancy is a more cost-effective approach in terms of installation. The disadvantage of this solution is that the riser could either float to the water surface or sink to the seabed when its content density varies or the floating production, storage and offloading vessel (FPSO) deviates from its nominal mooring position during field production. A new modified wave configuration, referred to as the Weight Added Wave (WAW) configuration (Patent pending) is presented, which enjoys the low installation cost of the wave configuration and performance reliability of the S riser configuration. The WAW configuration has been applied to two FPSO shallow water field developments and the results are presented herein to confirm the solution for real life applications.
Effect of Spatial Variation of a Wave Field on the Resulting Ripple Characteristics and Comparison to Present Ripple Predictors
Authors: Landry Blake J. , Catan˜o-Lopera Yovanni A. , Hancock Matthew J. , Mei Chiang C. , Garci´a Marcelo H.
Published: February 2010

Laboratory experiments analyzed herein focus on the validity of ripple predictors under spatially variable wave envelopes. Present-day ripple predictors commonly derived from laboratory data (for smaller wave periods of about 1 to 4 s) within which only small regions of the facilities were used to observe and measure the sand ripple geometric characteristics of the nearly progressive waves measured overhead. When extended to large sediment test sections, our results show that the predictors are still valid along the tank under wave conditions which have significant wave envelope spatial variation (e.g., standing waves), provided that ripple predictors use the wave measurements directly above the respective locations within the computations. Results indicate that even under the case of mild reflection, noticeable variation in ripple characteristics can be seen along the sediment test section; thus, compels the necessity of measuring the wave field along the entire sediment section to achieve accurate results.
Investigation on Natural Modes of Floating Structures Considering Design Strength
Authors: Kim B. W. , Sung H. G. , Hong S. Y.
Published: February 2010

In this paper, influences of design strength on natural modes of floating structures are examined by analyzing natural frequencies and mode shapes of floating bodies with nonuniform stiffness. A FSRU (Floating Storage and Regasification Unit) is considered as an example structure. Natural modes such as natural frequencies and modes shapes are calculated by the subspace iteration method which is widely used as a solver of eigenvalue problem. Various numerical models of FSRU are considered. One is a simplified model of which stiffness is uniformly distributed. The other is a model with stepped distribution of stiffness. The third model has a triangular stiffness distribution. By comparing the results of each model, the influences of nonuniform strength distribution on natural modes are investigated.
Some Aspects of Hydro-Structure Coupling for Combined Action of Seakeeping and Sloshing
Authors: Malenica Sˇime , Sireta Franc¸ois-Xavier , Bigot Fabien , Wang Chao , Chen Xiao-Bo
Published: February 2010

The techniques for hydrodynamic load transfer from combined action of waves (seakeeping) and internal liquid flow (sloshing), onto 3DFEM structural model are discussed. The problem is relevant both for a ship transporting liquids in tanks (LNG carriers, tankers...) as well as for any ship sailing in ballast conditions. Correct pressure transfer to the FEM model is essential for spectral fatigue assessment of structural details. The methods that are used in practice do not appear to be very clear and different levels of approximations based on some empirical considerations are usually employed. In this paper, a fully consistent method is proposed in the context of the linear frequency domain model.
Hydrodynamic Effects of Bilge Keels on the Hull Flow During Steady Turns
Authors: Dai Charles M. , Miller Ronald W. , Percival A. Scott
Published: February 2010

The hydrodynamic design of the bilge keels is important for the ship’s resistance and roll performance. It also affects the ship wake field at the propeller plane and can greatly influence the propulsor performances in terms of noise, efficiency and cavitation. The objective of this work is to investigate the effect of bilge keels on the hull flow during steady turns for a displacement ship with a skeg and a bow dome. An Unsteady Reynolds Averaged Navier Stokes Solver (URANS) CFDShip-Iowa, Version 4, developed at the University of Iowa is used to simulate the flow around the Naval Surface Warfare Center-Carderock Division (NSWCCD) ship model# 5617 with bilge keels at different steady turning conditions. The effect of separated flows caused by the bilge keels and the skeg during steady turns on the flow distributions at the propeller plane will greatly influence the flow at the propeller planes. It was observed that during a high speed port turn at full rudder angle, the onset flow to the port side bilge keel was mainly influenced by the flow around the bow dome and the onset flow to the starboard side bilge keel was subject to the free stream hull flow. The drift angle varies along the bilge keel span during steady turning and complex vortical flow structures were developed on the leeward side of the bilge keels due to flow separations caused by the flow over the tip of the bilge keel from the windward side to the leeward side. The vortical flow generated by the starboard bilge keel also merged with the separated flow caused by the skeg and form a streamwise vortical structure that was convected downstream into the propeller plane. The wake field at both port and starboard propeller planes were analyzed from the simulation results. It can be concluded from the analysis that the starboard side propeller plane was subject to a uniform cross flow and the port side propeller plane was subject to a cross flow that consisted of both cross flow component and a mean swirl that was caused by the streamwise vortical flow generated by the flow separation upstream. The cross flow component at the propeller planes can effectively produce side force affecting the lateral motion of the ship. It can be concluded from the simulations that the bilge keels have great influence on the wake distributions at the propeller planes and can affect the propeller performance during maneuvering in terms of hydrodynamic and structural loadings. Great care should be taken to ensure that the bilge keels be designed properly in the future not just for both seakeeping and propulsion, but also for maneuvering.
On the Dynamics and Stability of a Viscoelastic Pipe Conveying a Non-Newtonian Fluid
Authors: Olunloyo Vincent O. S. , Osheku Charles A. , Kuye Sidikat I.
Published: February 2010

Flow induced vibration of pipeline and riser systems are strongly dependent on internal fluid flow parameters as well as the mechanical properties of the conveyance vessel. The effect of variability of flow parameters especially at elevated temperatures can lead to instability, buckling and bursting of these systems. In this paper, the effect of high temperature fluid transmission on the vibration and stability of an offshore viscoelastic pipeline conveying a non-Newtonian fluid is investigated analytically. By idealising the viscoelastic pipeline resting on the sea bed as a viscoelastic beam that is resting on an elastic continuum, a non-linear boundary value partial differential equation governing the fluid-structure-soil interaction mechanics is formulated. In particular, formal linearization of the governing partial differential equation, under slight perturbation of the internal fluid velocity and other flow variables revealed their impact, on the natural frequency and stability of the system which can then be computed for design analysis and applications.
Numerical Simulation of Surface Waves Generated by a Subaerial Landslide at Lituya Bay, Alaska
Authors: Basu Debashis , Green Steve , Das Kaushik , Janetzke Ron , Stamatakos John
Published: February 2010

This paper presents preliminary results of a computational study conducted to analyze the impulse waves generated by the subaerial landslide at Lituya Bay, Alaska. The volume of fluid (VOF) method is used to track the free surface and shoreline movements. The Renormalization Group (RNG) turbulence model and Detached Eddy Simulation (DES) multiscale model were used to simulate turbulence dissipation. The subaerial landslide is simulated using a sliding mass. Results from the two-dimensional (2-D) simulations are compared with results from a scaled-down experiment. The experiment is carried out at a 1:675 scale. In the experimental setup, the subaerial rockslide impact into the Gilbert Inlet, wave generation, propagation, and runup on the headland slope are considered in a geometrically undistorted Froude similarity model. The rockslide is simulated by a granular material driven by a pneumatic acceleration mechanism so that the impact characteristics can be controlled. Simulations are performed for different values of the landslide density to estimate the influence of slide deformation on the generated tsunami characteristics. Simulated results show the complex flow patterns in terms of the velocity field, shoreline evolution, and free surface profiles. The predicted wave runup height is in close agreement with both the observed wave runup height and that obtained from the scaled-down experimental model.
Experimental Assessment of Hydrodynamic Coefficients of Disks Oscillating Near a Free Surface
Authors: Wadhwa Hemlata , Thiagarajan Krish P.
Published: February 2010

The use of different types of subsea equipment is continuously increasing in offshore field development. Installation operations such as lifting and lowering of these equipments require knowledge of the hydrodynamic coefficients of the object. An accurate prediction of these coefficients on typical subsea structures is a challenging task. The main coefficients in this context relate to added mass, damping and slamming effects. Formulations have been presented by various authors in literature for evaluating these coefficients for simple shapes. Some of them have found widespread application in the industry. The authors have considered a solid circular disk as a base case for initiating study on subsea module hydrodynamics. Experiments were conducted on an oscillating solid disk of diameter 200 mm and thickness 2 mm near the free surface. Forced oscillations were conducted at amplitudes varying from 3mm–36mm and frequencies 0.9–1.5 Hz respectively. The forces on the disk were measured using a submersible high-sensitivity load cell. The motions of the disk were restricted to axial (heave) direction, and were measured with a displacement transducer. The measured forces and displacement were analyzed using a Fast Fourier Transform algorithm to separate the added mass and damping effects. From the rate of change of added mass with depth of submergence, slamming forces were identified. The measured coefficients were compared with similar published data by Vu et al [1] and Tao & Dray [2]. The paper presents various formulations for added mass, damping and slamming obtained from literature and currently in use in the industry. These formulations are compared with measured values of the coefficients and suggestions are made on the importance of these formulations for flat subsea structures.
Numerical Investigation of 2-D Optimal Profile of Backward-Bent Duct Type Wave Energy Converter
Authors: Suzuki Masami , Kuboki Toshiari , Nagata Shuichi , Setoguchi Toshiaki
Published: February 2010

A floating type Backward-Bent Duct Buoy (BBDB) is a wave energy conversion device with an Oscillating Water Column (OWC) at the front side. The device captures the wave energy using the heaving, the pitching, the surging motion of BBDB and the heaving motion of OWC, and generates the reverse time-mean drift force reducing the mooring loads over specific frequency ranges. Investigations are carried out to find more reasonable devices than the traditional OWC type floating device. An eigenfunction expansion method is introduced for analyzing the BBDB with OWC. It is confirmed that these solutions give good agreement with several experimental results in this paper. It is shown in a design method how to make BBDB match the turbine characteristics. This feature is being able to select the optimum profile of the turbine and the BBDB individually from each characteristic before comprehensive evaluation of the BBDB and the turbine in the design. After grasping the element characteristics which are appropriate for the wave energy conversion system, the synthetic design method is built. The BBDB size and the turbine diameter are determined by considering the cost corresponding to the smallest size under the same output. In this way we can obtain the optimal profiles considering the construction cost including the turbines.
Seismic Fault Displacement of Buried Pipelines Using Continuum Finite Element Methods
Authors: Odina Lanre , Tan Roger
Published: February 2010

In deep waters, pipelines are usually installed exposed on the seabed, as burial is generally not required to ensure on-bottom stability. These exposed pipelines are nevertheless susceptible to seismic geohazards like slope instability at scarp crossings, soil liquefaction and fault movements which may result in failure events, although larger diameter pipelines are generally known to have good tolerances to ground deformation phenomena, provided the seismic magnitudes are not too onerous. Regardless of the pipeline size, these seismic geohazard issues are usually addressed during the design stage by routing the pipeline to avoid such hazardous conditions, where possible. However, extreme environmental conditions like hurricanes or tropical cyclones, which are typically experienced in the Gulf of Mexico and Asia-Pacific regions, are also factors which can cause exposed pipelines to be susceptible to large pipeline displacements and damage. Secondary stabilisation in the form of rock dump is sometimes employed to reduce the hydrodynamic loads from high turbidity currents acting on the pipeline. However, rock dumping (or burying the displaced pipeline) on a fault line could again pose a threat to its integrity following a seismic faulting event. The traditional method of assessment of a buried pipeline subjected to seismic faulting is initially carried out using analytical methods. Due to the limitations of these techniques for large deformation soil movement associated with fault displacement, non-linear finite element (FE) methods are widely used to assess the pipeline integrity. The FE analysis typically idealises the pipeline using discrete structural beam-type elements and the pipeline-soil interaction as discrete non-linear springs, based on the concept of subgrade reactions proposed by Winkler. Recent research from offshore pipeline design activities in the arctic environment for ice gouge events have however suggested that the use of the discrete Winkler element model leads to over-conservative results in comparison to the coupled continuum model. The principal reason for the conservatism is related to the poor modeling of realistic surrounding soil behaviour for large deformation events. This paper discusses the application of continuum FE methods to model the fully coupled seabed-buried pipeline interaction events subject to ground movements at active seismic faults. Using the continuum approach, a more realistic mechanical response of the pipeline is established and can be further utilised to confirm that calculated strains are within allowable limits.
Research to Realization of Submarine Hotel
Authors: Hamada Noritaka , Koto Yutaka , Eto Hiroaki , Saijo Osam
Published: February 2010

This paper summarized the investigation results on the technological subjects in order to realize marine facilities constructed at the sea bottom, where human can live or work for a long period. It is important to grasp the needed technology for realization beforehand so as to expand the human activity field. The subjects to be solved obtained by evaluating the present construction technology was considered. From the results, the necessary functions and items to be researched and developed newly on the basis of scientific grounds, are reported. This technology must make it possible to built seabed natural resource development facility, seabed research facility and submarine city, etc. It can be said such a kind of building has many options and big possibility. Nowadays, necessity of research and development for the future rises needs are rising. Our own design of submarine hotel is shown using this study, and seismic response analysis was demonstrated. In consideration of Japan is earthquake country.