bluuebunny/crossref_metadata_2025 huggingface dataset:
Green Water Loads on a Cruise Ship
Authors: Ley Jens , Oberhagemann Jan , Amian Christoph , Langer Markus , Shigunov Vladimir , Rathje Helge , Schellin Thomas E.
Published: November 2013

A linear boundary-element method and a Reynolds-averaged Navier-Stokes (RANS) equations solver were combined to predict maximum green water loads on a typical cruise ship of medium size. For structural analysis, a one-way coupling mapped the hydrodynamic pressure from the finite-volume grid onto the computational structural dynamics finite element mesh. First, linear long-term maximum ship responses were determined by a boundary element method combined with long-term statistics based on spectral methods; transfer functions of these responses were used to define response-conditioned wave trains inducing the linear long-term maximum ship response. The investigated wave sequences were correlated to a dedicated probability level for a lifecycle time of 20 years in the North Atlantic environmental wave conditions and for a ship speed of six knots.

Critical impact locations were found to include the weather deck in the foreship, the front wall of the superstructure and the overhanging bridge deck. Predicted loads were compared to experimental data obtained in conditioned wave trains and in extreme irregular sea states. Numerical and experimental results revealed significantly higher loads than design loads specified by classification society rules. Pressure peaks on the weather deck and the superstructure front wall were comparable to rule-based design pressures for breakwaters on containerships and exceeded pressure peaks on the bridge deck.
Hydrodynamic Characteristics of Floating Pipes in Random Waves
Authors: Xu Tiaojian , Dong Guohai , Zhao Yunpeng , Ma Xiaozhou , Ma Yuxiang
Published: November 2013

The hydrodynamic performance characteristics of a round floating pipe model moored to the flume floor with pre-tensioned moorings has been investigated in random waves through an experimental program. The details of the models, set-up, experimental procedure and analysis of results are presented and discussed. The drag coefficient of floating pipes in random waves are analyzed. The motion responses, as well as the variations in the forces on the seaside mooring lines, are presented. In addition, statistical analysis has been carried out to prove that the heave and surge motions, as well as the peak mooring forces, follow the Rayleigh distribution.
Experimental Study on the Characteristics of VIV and Whirl Motion of Rotating Drill Pipe
Authors: Inoue Tomoya , Rheem Chang-Kyu , Kyo Masanori , Sakaguchi Hide , Matsuo Miki Y.
Published: November 2013

During drilling operations, the scientific drilling vessel Chikyu encounters vortex-induced vibration (VIV) of the riser during riser drilling as well as that of the drill pipe during riserless drilling. The characteristics of the VIV of the drill pipe will differ from those of the riser because the drill pipe rotates during operations. Therefore, investigating the characteristics of the VIV during drill pipe rotation is important. In this paper, the results of model experiments that show the characteristics of the VIV of a rotating drill pipe and drill pipe whirl are described. The authors conducted model experiments on the VIV response of a rotating cylinder in a water tank to observe the motion of the rotating cylinder. The results confirmed that rotating affects the characteristics of the VIV. When the rotating frequency of the drill pipe was low, the VIV resonated with the rotation; as the rotating frequency increased, the frequency of the VIV decreased. In addition, a self-excited whirl motion was also observed during the experiments. This “drill pipe whirl,” which rotated in the direction opposite to the rotation of the drill pipe at a low frequency, was larger in amplitude than the VIV. The results demonstrate that rotation of the drill pipe affects the characteristics of the VIV and generates the whirl motion.
Annular Frictional Pressure Losses During Drilling: The Effect of Drillstring Rotation
Authors: Saasen Arild
Published: November 2013

Controlling the annular frictional pressure losses is important in order to drill safely with overpressure without fracturing the formation. To predict these pressure losses, however, is not straightforward. First of all, the pressure losses depend on the annulus eccentricity. Moving the drillstring to the wall generates a wider flow channel in part of the annulus reducing the frictional pressure losses significantly.

The drillstring motion itself also affects the pressure loss significantly. The drillstring rotation, even for fairly small rotation rates, creates unstable flow and sometimes turbulence in the annulus even without axial flow. Transversal motion of the drillstring creates vortices that de-stabilize the flow. Consequently, the annular frictional pressure loss is increased even though the drilling fluid becomes thinner because of added shear rate.

Naturally, the rheological properties of the drilling fluid play an important role. These rheological properties include more properties than the viscosity as measured by API procedures. It is impossible to use the same frictional pressure loss model for water based and oil based drilling fluids even if their viscosity profile is equal because of the different ways these fluids build viscosity. Water based drilling fluids are normally constructed as a polymer solution while the oil based are combinations of emulsions and dispersions. Furthermore, within both water based and oil based drilling fluids there are functional differences. These differences may be sufficiently large to require different models for two water based drilling fluids built with different types of polymers. In addition to these phenomena washouts and tool joints will create localised pressure losses. These localised pressure losses will again be coupled with the rheological properties of the drilling fluids. In the paper, all the above mentioned different phenomena and their consequences for annular pressure losses will be discussed in detail. Application of Det norske field data will be used as an example. The data cannot be used to build general models. The arguments for this model restriction are based on flow stability analysis and the consequences of using drilling fluids with different rheological properties. These different rheological properties include shear dependent viscosity, elongational viscosity and other viscoelastic properties.
Small High Frequency Powerful Vibrator and its Application to Underwater Sound Generator
Authors: Takagawa Shinichi
Published: November 2013

The author has developed a small and powerful high frequency cam-type vibrator using roller thrust bearings with uneven races. The diameter of the vibrator is nearly the same as the outer diameter of the thrust bearing, and it is very small compared with other vibrators. This vibrator can be installed at the bottom end of a drill string as a high frequency vibro-hammering gear.

Although the amplitude of the axial displacement is fixed, combination of two vibrators of this type can make the amplitude variable by superimposition. This variable superimposition can also be used as an On-Off switch of the vibration.

The underwater sound used for seismic survey is usually a short pulse with a duration of several to several tens of milliseconds. The vibrator described in this paper is capable of generating such short sound pulses owing to the variable superimposition.

Present sound generators for seismic survey are usually big and heavy and generate sound pulses with a wide frequency spectrum, centered around 100Hz. The cam-type vibrator described in this research is much smaller and lighter than present systems, making the deployment near the seafloor easy for even at great depths, which in return leads to more detailed results in stratum surveys. The emitted sound is a pure tone whose frequency can be anywhere between 100 and 1000Hz.

The author has tried to develop this type of sound generator under the support of JOGMEC (Japan Oil, Gas and Metals National Corporation).

In this paper, the principle of the vibration, the design of the sound generator and the result of the experiment shall be discussed.
Modelling Sand Foundation Behaviour Underneath Caisson Breakwaters Subject to Breaking Wave Impact
Authors: El Safti Hisham , Oumeraci Hocine
Published: November 2013

A one-way CFD-CSD coupled model system is presented to reproduce large scale experiments of a caisson breakwater, subject to wave attack. The Computational Structural Dynamics (CSD) model is developed using the finite volume method for the fully dynamic, fully coupled Biot equations. The fully coupled poro-mechanical analysis is handled in a segregated approach in which the skeleton displacement, the pore fluid pressure and the pore fluid velocity (relative to the skeleton) are decoupled at the iteration level. The pore fluid pressure-velocity coupling is resolved using the PISO (Pressure Implicit with Splitting of Operators) algorithm. Two simplifications to the porous media formulations were introduced: (1) neglecting convective acceleration of pore fluid and (2) fully neglecting acceleration of the pore fluid (the u-p approximation). A frictional contact model is implemented to model soil-structure interaction. A multi-surface plasticity model with the Drucker-Prager failure criterion is introduced to model the behavior of sand foundations under cyclic load posed by wave action on the caisson breakwater. An incompressible (constant density) multiphase Computational Fluid Dynamics (CFD) solver is developed for solving flow inside and outside porous media simultaneously using the principle of volume averaged velocity. A seepage model is implemented to model flow resistance of porous media that includes viscous, transitional, inertial and transient terms. An additional term is introduced to the fluid continuity equation to account for fluid mixture (water and air) compressibility (inverse of bulk modulus). The CFD-CSD model system is developed using the OpenFOAM® framework.
A Brazilian Northeast Coast Wave Data Comparison: Radar vs Buoy
Authors: Ribeiro Eric O. , Ruchiga Taina S. , Lima Jose A. M.
Published: November 2013

Wave buoys are well known by its accuracy in measuring sea surface elevations while wave radars were developed later. Buoy’s motions are considered direct wave measurements while microwave radars use remote sensing for tracking the sea surface. Due to sensitivity to winds, sea surface roughness, rain, etc, it is a good practice to check radar data against buoys records. Even both systems installed being 6 km apart in a deep water region offshore northeast Brazilian shelf, there were differences in wave directional spectral parameters calculated by both equipments. The wave measurements at Sergipe and Alagoas basin were in good agreement in terms of significant wave height. Hs correlation was 91% and bias was only 0.06 m. A particular behavior of radar Hs when compared to buoy Hs was overestimation in high sea states and underestimation in low ones. Tp1 correlation was 69%, bias was 0.02 s and linear regression coefficient was 0.64. The worst correlated parameter was peak direction Dp1 with 60% of correlation for E-ESE directional band. Time series matched each other and showed the typical regional wave climate with Hs 1.0–2.0 m, Tp 6–10 s and Dp1 from E-ESE. The distinction between radar and the buoy directions is related to radar susceptibility to SE trade winds during Spring and Summer seasons. However, the difference did not diverge from prevailing wave regional climate.
Environment-Induced Cracking in Weld Joints in Subsea Oil and Gas Systems: Part II
Authors: Dodge M. F. , Dong H. B. , Milititsky M. , Barnett R. P. , Gittos M. F.
Published: November 2013

In subsea oil and gas systems, low-alloy steel (LAS) forgings need to be welded to leaner steels such as X and F-65. While the LAS needs to be post-weld heat treated (PWHT) to relieve stresses and temper the HAZ microstructure in order to avoid hydrogen cracking, the same heat cycle would, in general, result in the degradation of the properties of the leaner alloy. A buttering technique is, therefore, usually used so that the buttered LAS forging can be heat treated before the closure weld is carried out. In the case of clad components, nickel alloy filler materials such as Alloy 625 are commonly used for both buttering and closure welds.

This is an issue for subsea structures protected from corrosion by cathodic polarisation (CP) using aluminium based anodes. Whilst CP has proven successful as a means of preventing corrosion of steel components within subsea structures, failures along the dissimilar metal interfaces have been observed. This is due to hydrogen evolution as a result of CP. To further our understanding on this issue, this paper focuses on the correlation between microstructures, obtained by changing material combinations and PWHT conditions, and the resistance to hydrogen assisted cracking.

Slow strain rate single edge notched bend (SENB) tests were carried out on the interfaces between AISI alloy 8630 and Alloy 625 buttering, retrieved from subsea service and tested in 3.5% NaCl solution under an applied potential of −1100mVsce.

Retrieved specimens were pre-charged with hydrogen and tested at 4°C and 80°C, approximately in-line with commissioning/shutdown and service temperatures, respectively. In addition to the retrieved specimens, a testing programme has been developed to explore the effect of PWHT time on the performance of 8630-Alloy 625 and F22-Alloy 625 interfaces. The microstructures most susceptible to hydrogen cracking in these systems have been assessed by examination of the SENB test specimens.
Finite Element Method Simulating the Pipeline Mechanical Response During Reel-Lay Installation
Authors: Dawood Ali A. , Kenny S.
Published: November 2013

Finite element modelling procedures to simulate the pipeline mechanical response during reel lay installation are calibrated from the available literature. A three-dimensional continuum model was developed to simulate the bending and straightening processes during reel lay installation and was compared with physical tests conducted within a bending rig and four-point bending test frame. A range of pipeline diameters, wall thicknesses, material grades and weld offsets are examined.
A Study on Non-Linear Response of Moored Floating Body Considering Dynamic Motion of Mooring Lines
Authors: Nonaka Keiji , Murai Motohiko , Nagamine Atsushi
Published: November 2013

Recently, the utilization of the ocean space has attracted researcher’s attention which encouraged by the development of resources in seafloor and the offshore structure such as wind turbine. Offshore structure is essential for the utilization of the ocean space. In the case that we install an offshore structure in the shallow sea area, we use simpler structure such as the TLP (Tension Leg Platform) which can reach the sea bottom. However, in recent years the demand for offshore structure in deeper sea area has increased, thus we frequently use more flexible floating type offshore structure with strand chain mooring.
Study on Grinding Technology for Seafloor Mineral Processing
Authors: Nakajima Yasuharu , Yamamoto Joji , Kanada Shigeo , Masanobu Sotaro , Takahashi Ichihiko , Okaya Katsunori , Matsuo Seiji , Fukushima Tomohiko , Fujita Toyohisa
Published: November 2013

Seafloor Massive Sulfides (SMSs), which are formed by precipitates from hydrothermal fluids vented from seafloor, have been expected as one of mineral resources to be developed. The authors have proposed the concept of seafloor mineral processing for SMS mining, where valuable minerals contained in SMS ores are separated on seafloor. To apply a ball mill to the grinding unit for seafloor mineral processing, grinding experiments were carried out using a small-scale ball mill applicable to high-pressure condition. In the experiments, wet grinding and water-filled grinding of size-classified silica sands were carried out at three rotation rates to compare the grinding performance in both cases. In both cases, the silica sands were finely ground. The measurement of particle size of samples from the experiments showed that water-filled grinding had comparable grinding performance to wet grinding while the suitable rotation rate for water-filled grinding shifted to higher than that for wet grinding. This result suggests the possibility of water-filled grinding for seafloor mineral processing. If water-filled grinding can be employed for the grinding unit, the structure of the grinding unit would be simplified in comparison with wet grinding that leads to the saving of grinding costs.
Subsea Pipelines: The Remotely Welded Retrofit Tee for Hot Tap Applications
Authors: Woodward Neil , Apeland Kjell Edvard , Berge Jan Olav , Verley Richard , Armstrong Mike
Published: November 2013

Over the last 10 years Statoil has developed subsea remote hot tap technology. The first use of the remote hot tap technology was the Tampen Link hot tap in 2008. The hot tap cutting operation itself was performed without the use of divers; however, the preparatory works including hyperbaric welding of the hot tap tee was performed with saturation divers. The world’s deepest hot tap operations on a pressurized pipeline were performed on the Ormen Lange field in the Norwegian Sea in August 2009. Two Hot Taps were conducted in a water depth of 860 meters on pre-installed tees. The development of the Pipeline Repair System Remote Hot Tap equipment is the result of targeted research and development effort and extensive qualification work over many years. The Retrofit Tee remote installation, welding and cutting equipment has now been employed as part of a production installation: the Åsgard Subsea Compression project to extend the Åsgard gas-field lifetime.

This paper describes the dry hyperbaric GMA weld procedure development and qualification performed in the laboratory, using the Corrosion Resistant Alloy consumable filler material Alloy 59, for the Remote Hot Tapping application using the Retrofit Tee. Specific attention was paid to areas of concern prior to performing the formal Weld Procedure Qualification work, particularly with regard to the effects of moisture and temperature upon the resultant weld quality. Weld procedures developed in the laboratory were successfully tested subsea in representative environments using the Remote Tee Welding Tool (RTWT) equipment in the Sognefjord, Norway, with offshore tests performed at 265 and 350msw in 2011. Further tests were performed in 2012 at 265msw and in the Retrofit Tee itself at 316msw in the Nedstrandfjord.

The hyperbaric GMA weld procedures have now been applied for the production application for the Åsgard Subsea Compression project, with the installation of a Retrofit Tee, associated valve module and gooseneck spool to enable a cost-effective modification to the existing pipeline network without interfering with ongoing production. The Retrofit Tee will be connected with a Subsea Compressor station to extend the gas-field lifetime.

This milestone represents the world’s first application of diverless dry hyperbaric GMA welding for a subsea production application.
Rankine Source Method for Ship-Ship Interaction Problems
Authors: von Graefe Alexander , Shigunov Vladimir , el Moctar Ould
Published: November 2013

A Rankine source method is extended and applied to ship-ship interaction problems. The method covers the nonlinear steady flow and linear seakeeping in the frequency domain. The nonlinear steady flow solution accounts for the nonlinear free-surface conditions, ship wave and dynamic trim and sinkage. Periodic flow due to waves is linearized with respect to the wave amplitude, taking into account interactions with the nonlinear steady flow following Hachmann approach, which considers the steady perturbation potential as constant in the body-fixed reference frame. This is advantageous for the prediction of ship motions at moderate to high Froude numbers. In this context, a new formulation of the boundary condition for the multi-body case is derived.

Two examples are considered, overtaking in calm water and replenishment at sea. For a feeder vessel overtaken by a container ship, computed forces and yaw moment are compared with model test data. As an example of replenishment operation, interaction between a frigate and a supply vessel is studied. Ship motions are computed for two relative positions and three forward speeds and compared with model test data for the largest forward speed. The Rankine source method proves as more accurate compared with a zero-speed free-surface Green function method.
Flexible Riser Response Induced by Combined Slug Flow and Wave Loads
Authors: Ortega Arturo , Rivera Ausberto , Larsen Carl M.
Published: November 2013

Flexible risers provide optimum solutions for deep water offshore fields. Reliable dynamic analysis of this kind of slender structure is crucial to ensure safety against long time fatigue failure. Beyond the effects from wave loads, the influence from transient internal slug flow on the slender structure dynamics should also be taken into account.

In this study two coupled in-house codes were used in order to identify and quantify the effects of an internal slug flow and wave loads on the flexible riser dynamics. One code carries out a global dynamic analysis of the slender structure displacements using a finite element formulation. The other program simulates the behaviour of the internal slug flow using a finite volume method. The slug flow is influenced by the dynamic shape of the riser, while the time varying forces from internal slug flow plus external waves will influence the shape. Hence, a fully coupled analysis is needed in order to solve the coupled problem. By means of the distributed simulation these two programs run synchronously and exchange information during the time integration process.

A test case using hydrodynamic forces according to the linear Airy wave theory, coupled with an internal unstable slug flow was analysed and the results show: amplification of the dynamic response due to the interaction between the two load types, effects on the effective tension caused by the internal two-phase flow, and influence on the internal slug flow caused by the wave induced response.
Probabilistic Modelling of Extreme Offshore Structural Response due to Random Wave Loading
Authors: Wang Y. , Mallahzadeh H. , Abu Husain M. K. , Mohd Zaki N. I. , Najafian G.
Published: November 2013

Offshore structures are exposed to random wave loading in the ocean environment and hence the probability distribution of the extreme values of their response to wave loading is required for their safe and economical design. This paper investigates the suitability of the Gumbel, the Generalized Extreme Value (GEV), and the Generalized Pareto (GP) distributions for modelling of extreme responses by comparing them with empirical distributions derived from extensive Monte Carlo time simulations. It will be shown that none of these distributions can model the extreme values adequately but that a mixed distribution consisting of both GEV and GP distributions seems to be capable of modelling the extreme responses with very good accuracy.
Fatigue Crack Propagation Under Biaxial Tensile Loading: Effect of the Phase Difference on Biaxial Loading
Authors: Gotoh Koji , Niwa Toshio , Anai Yosuke , Omori Tetsuya , Tanaka Yoshihisa , Murakami Koji
Published: November 2013

Fatigue crack propagation under biaxial tensile loading is highlighted in this study. Ships and offshore structures are subjected to many types of loading, e.g. wave induced forces, gravity, and inertia forces. Generally, these loadings have different axial components with different phases. However, the structural integrities of structures and vessels are evaluated according to design codes based on theoretical and experimental investigations under a uniaxial loading condition. Most of these codes are based on the S-N curves approach. An approach that does not use S-N curves has been favored by researchers, with the fracture mechanics approach preferred for evaluating the fatigue life of structures. An advanced fracture mechanics approach was developed based on the Re-tensile Plastic zone Generating (RPG) stress criterion for fatigue crack propagation. In this study, fatigue crack propagation tests under biaxial loading with four different phase conditions are performed and the effect of the phase difference under biaxial loading is evaluated. A numerical simulation method of fatigue crack propagation based on the RPG stress criterion under different biaxial loading phase conditions is presented and compared to measured data.
Inclusion of Crack Face Pressure in Reference Stress for Thick Walled Risers and Flowlines
Authors: Cerkovnik Mark , Akhtar Wasy
Published: November 2013

A methodology is developed to account for the effect of crack face pressure on the reference stress in high pressure, thick walled, flowlines and risers. Risers and flowlines in production service may be exposed to corrosive attack resulting in pitting. In such cases, cracks can initiate and fitness for service assessment, including fatigue crack growth and fracture analysis, is required. For such thick walled lines, the effect of high internal pressure on the crack face is significant and must be taken into account. Current industry standards, including API-RP-579 [1] and BS7910 [2], are silent on the effects of crack face pressure on the reference stress.

Reference stress, a quantity similar to the net section stress, can be used to predict the local plastic failure of the remaining ligament ahead of the crack tip, or the collapse of the full cross section. The reference stress is also used in the abscissa on the Failure-Assessment-Diagram (FAD) to determine the allowable stress intensity ratio for fracture assessment.

The methodology described in the paper follows from systematic detailed finite element analysis (FEA) conducted using linear material properties. The analysis is conducted over a range of pipe thickness ratios (D/t), crack depths (a/t) and crack aspect ratios (c/a). The results presented permit an accurate calculation of the effect of crack face pressure that can be implemented within the framework of existing methods of fitness for service analysis without the use of FEA. This paper presents a detailed analysis of the effect of crack face pressure on the reference stress for axial and circumferential internal flaws. The results from this study provide expressions to estimate the reference stress with crack face pressure loading, thus, allowing an improved fracture prediction for high pressure risers and flowlines.
Irregular Nonlinear Wave Simulation and Associated Loads on Offshore Wind Turbines
Authors: Marino E. , Nguyen H. , Lugni C. , Manuel L. , Borri C.
Published: November 2013

The accuracy of predicted loads on offshore wind turbines depends on the mathematical models employed to describe the combined action of the wind and waves. Using a global simulation framework that employs a domain-decomposition strategy for computational efficiency, this study investigates the effects of nonlinear waves on computed loads on the support structure (monopile) and the rotor-nacelle assembly of a bottom-supported offshore wind turbine. The fully nonlinear (FNL) numerical wave solver is invoked only on sub-domains where nonlinearities are detected; thus, only locally in space and time, a linear solution (and associated Morison hydrodynamics) is replaced by the FNL one. An efficient carefully tuned linear-nonlinear transition scheme makes it possible to run long simulations such that effects from weakly nonlinear up to fully nonlinear events, such as imminent breaking waves, can be accounted for. The unsteady nonlinear free-surface problem governing the propagation of gravity waves is formulated using potential theory and a higher-order boundary element method (HOBEM) is used to discretize Laplace’s equation. The FNL solver is employed and associated hydrodynamic loads are simulated in conjunction with aerodynamic loads on the rotor of a 5-MW wind turbine using the NREL open-source software, FAST. We assess load statistics associated with a single severe sea state. Such load statistics are needed in evaluating relevant load cases specified in offshore wind turbine design guidelines; in this context, the influence of nonlinear wave modeling and its selection over alternative linear or linearized wave modeling is compared. Ultimately, a study such as this one will seek to evaluate long-term loads using the FNL solver in computations directed towards reliability-based design of offshore wind turbines where a range of sea states will need to be evaluated.
On the Dynamic Collapse of Cylindrical Shells Under Combined Hydrostatic and Impulsive Pressure Loadings
Authors: Silva L. Loureiro , Netto T. A.
Published: November 2013

The dynamic collapse of submerged cylindrical shells subjected to lateral impulsive pressure loads caused by underwater explosions is studied via coupled experimental and numerical work. Aluminum tubes with 50.6mm outside diameter and diameter-to-thickness ratio of 32 were tested in a 5m × 5m × 1.6mdeep water tank under various explosive charges placed at different distances. Explosive charges and standoff distances were combined so as to eventually cause collapse of the specimens. Subsequently, the parent problem of the dynamic collapse of such structures under hydrostatic pressure is also investigated to determine the collapse and propagation pressures. Additional experiments were then conducted combining hydrostatic pressure and impulsive pressure loads. In these cases, hydrostatic pressure was applied quasi-statically and kept nearly constant. Subsequently, an explosive charge was detonated inside the pressure vessel. Dynamic pressure sensors were placed in various locations in the water around the tube in order to monitor the pressure wave propagation. In both sets of experiments, dynamic pressure and strain measurements were recorded using a fit-for-purpose data acquisition system with sampling rates of up to 1 mega samples/sec per channel. The characteristics of the pressure pulses and the charges necessary to collapse the pipe under different hydrostatic pressure levels were then compared. In parallel, finite element models were developed using commercially available software to simulate underwater explosion, the pressure wave propagation, its interaction with a cylindrical shell and the subsequent onset of dynamic collapse. The surrounding fluid was modeled as an acoustic medium, the shells as J2 flow theory based materials with isotropic hardening, and proper fluid-structure interaction elements accounting for relatively small displacements of the boundary between fluid and structure were used. Finally, the physical experiments were numerically reproduced with good correlation between results.
Numerical Simulation of Hydrodynamics of a Circular Disk Oscillating Near a Seabed
Authors: Garrido-Mendoza Carlos A. , Souto-Iglesias Antonio , Thiagarajan K. P.
Published: November 2013

This paper studies how the hydrodynamics coefficients of added mass and damping varies when an oscillating disk approaches a seabed. Analysis was performed by OpenFOAM code using the ‘PIMPLE’ algorithm. The simulations considered the flow as laminar and hence no turbulence model was used. Simulations were conducted for a solid disk of 200 mm diameter, 2 mm thick, oscillating at amplitudes varying from 1–48 mm and elevation ‘h’ of the disk from the seabed varying from 0.2–2 times the disk radius. The geometry and parameters used here were the same as that of Wadhwa et al. (2010) [1] and Vu et al. (2008) [2]. The forces on the disk were calculated using a Tool for post-processing force/lift/drag data with function tool available in OpenFOAM. The motions of the disk were restricted to axial (heave) direction. The calculated forces and displacement were analyzed using a Fourier projection to separate the added mass and damping effects. Numerical results were compared with the experiments conducted by Wadhwa et al. (2010) [1] with a sandy bottom.

Results show that the added mass and damping increase monotonically with the Keulegan-Carpenter number (KC) up to a critical value, beyond which the behavior becomes random. The critical KC increases linearly with increasing distance from the seabed. The hydrodynamic problem has important applications in structures such as foundation templates and subsea structures oscillating in proximity to the seabed. The computations show vortex lines of the flow, and the influence of the seabed on the flow around the structure.
Simulation of Wave-Body Interaction Using a Single-Phase Level Set Function in the SWENSE Method
Authors: Reliquet Gabriel , Drouet Aurélien , Guillerm Pierre-Emmanuel , Jacquin Erwan , Gentaz Lionel , Ferrant Pierre
Published: November 2013

The purpose of this paper is to present combination of the SWENSE (Spectral Wave Explicit Navier-Stokes Equations – [1]) method — an original method to treat fully nonlinear wave-body interactions — and a free surface RANSE (Reynolds Averaged Navier-Stokes Equations) solver using a single-phase Level Set method to capture the interface. The idea is to be able to simulate wave-body interactions under viscous flow theory with strong deformations of the interface (wave breaking in the vicinity of the body, green water on ship decks…), while keeping the advantages of the SWENSE scheme.

The SWENSE approach is based on a physical decomposition by combining incident waves described by a nonlinear spectral scheme based on potential flow theory and an adapted Navier-Stokes solver where only the diffracted part of the flow is solved, incident flow parameters seen as forcing terms.

In the single-phase Level Set method [2, 3], the air phase is neglected. Thus, only the liquid phase is solved considering a fluid with uniform properties. The location of the free surface is determined by a Level Set function initialised as the signed distance. The accuracy of simulation depends essentially on the pressure scheme used to impose free surface dynamic boundary condition.

Comparisons of numerical results with experimental and numerical data for US navy combatant DTMB 5415 in calm water and in head waves are presented.
Wrinkling Failure of Lined Pipe Under Bending
Authors: Yuan Lin , Kyriakides Stelios
Published: November 2013

Lining internally a carbon steel pipe with a thin layer of corrosion resistant material is an economical method for protecting offshore tubulars from the corrosive ingredients of hydrocarbons. In applications involving severe plastic bending, such as reeling, the liner can detach from the outer pipe and develop large amplitude buckles that compromise the flow. This paper outlines a numerical framework for establishing the extent to which lined pipe can be bent before liner collapse. The manufacturing process of lined pipes is simulated and a set of 12-inch pipes are plastically bent. The two tubes ovalize and the liner detaches from the outer pipe developing small amplitude wrinkles. The wrinkles initially grow stably but at a higher curvature yield to a diamond-shaped buckling mode that catastrophically collapses the liner. The onset of collapse is shown to be very sensitive to small geometric imperfections in the liner.
COBRA Riser Concept for Ultra Deepwater Condition
Authors: Nurwanto Tomy , Karunakaran Daniel , Franciss Ricardo
Published: November 2013

Offshore ultra deepwater field is being promising as the future of oil and gas reserves. However, the development of ultra deepwater field posed many challenges, in particular, on the selection of the riser concept. Long suspended length of riser will significantly increase the vessel payload. High external hydrostatic pressure on the riser will increase the probability of collapse failure. Large dynamic motions of the vessel and large vessel offset yields potential buckling issues at the touch-down-point (TDP). In addition, potential fatigue problems due to vessel motions and soil-riser interactions also present at TDP area. Large current speed in deepwater field might also lead to vortex induced vibration (VIV) which eventually will contribute to significant fatigue damage for particular riser sections. By looking into these challenges, it is very important to select the most appropriate riser concept for the ultra deepwater field.

Catenary Offset Buoyant Riser Assembly (COBRA) as newly developed hybrid riser concept offers a solution to overcome the challenges in ultra deepwater field. In general, COBRA consists of a catenary riser section with a long-slender sub-surface buoyancy module on top which is tethered down to sea bed via two mooring lines. The catenary section from top of the sub-surface buoy is connected to the floater by a flexible jumper. This flexible jumper can effectively absorb the floater motions, which give significant improvements for both strength and fatigue performance on the overall system. As a hybrid riser concept, this concept offers cost effective solution by avoiding all the expensive bottom assemblies that normally needed for a hybrid riser concept.

This paper focuses on COBRA riser concept specifically for Santos Basin Central Cluster region at 2200 m water depth. It is observed that there is common sudden change phenomenon on the current direction in Santos Basin area. The effect of bidirectional current is analyzed, and the comparison with unidirectional current is discussed thoroughly. The analyses are focused on the global strength design performance under extreme environmental load and global fatigue design performance of the riser due to wave induced and VIV induced.

The results clearly indicate that COBRA riser concept has a robust design and it is feasible for 2200 m water depth, in particular for Santos Basin Cluster Region area. It is also shows that COBRA riser has sufficient strength performance even for extreme bidirectional current.
A Surface Ice Module for Wind Turbine Dynamic Response Simulation Using FAST
Authors: Yu Bingbin , Karr Dale G. , Song Huimin , Sirnivas Senu
Published: November 2013

The simulation software FAST is an open source CAE package maintained by the National Renewable Energy Laboratory. A new module of FAST for assessing the dynamic response of offshore wind turbines subjected to ice forcing is presented. This paper describes the recent addition of capabilities for analyzing the response of wind turbines subjected forces resulting from ice impact on the turbine support structure. Several models are presented which involve both prescribed forcing and coupled response. For conditions in which the ice forcing is essentially decoupled from the structural response, ice forces are established from existing models for brittle and ductile ice failure modes. For conditions in which the ice failure and the structural response are coupled, such as lock-in conditions, a rate-dependent ice model is described, which is developed in conjunction with a new modularization framework for FAST.

The ice loading module includes ice mechanics models, that incorporate ice floe forcing, deformation, and failure. For lower speeds, forces slowly build until the ice strength is reached and ice fails resulting in a quasi-static condition where the frequency of the forcing is about an order of magnitude lower than the response of the structure. For intermediate speeds, the ice failure response can be coupled with the structural response resulting in response where the ice feature failure period and the response period of the structure approximately coincide. A third response regime occurs at high speeds of encounter in which brittle fracturing of the ice feature in contact with the structure occur in a more or less random pattern, which results in random vibration excitation of the structure. These three conditions are specifically addressed in the ISO standard 19906:2010 for consideration in the design of arctic offshore structures. Special consideration of lock-in vibrations is required due to the detrimental effects of such response with regard to fatigue and foundation/soil response. The use of FAST for transient, time domain simulation with the new ice module is well suited for such analyses.
Case Study of Tsunami Bore Impact on RC Wall
Authors: Robertson Ian N. , Carden Lyle P. , Chock Gary Y. K.
Published: November 2013

The Tohoku Tsunami of March 11, 2011 caused tremendous damage to many coastal buildings, bridges and port facilities. During field surveys following this event, the authors documented a number of structures that were damaged to a near-collapse condition as a result of hydrodynamic loading. Analysis of survivor videos provided information on the tsunami flow characteristics at these locations, allowing for an assessment of current hydrodynamic loading expressions under full-scale conditions.

Based on laboratory experiments performed at Oregon State University, the lead author and colleagues developed a new hydrodynamic loading expression for a broken bore striking a vertical wall [1]. This expression was applied to a case study of a large vertical reinforced concrete (RC) wall damaged by an incoming bore strike during the Tohoku Tsunami. The damaged wall is on the seaward side of a high-bay building in the Minami Gamou Sewage Treatment plant near the Sendai coastline. A non-linear finite element model of the building was subjected to the hydrodynamic pressure distribution derived from the laboratory experiments. It is shown by structural analysis of the wall that using this loading expression generates the same yielding response in the wall as observed in the field, as reflected in the deflected shape measured by LiDAR. Similar analysis using current Japan Tsunami design provisions indicates that these provisions are considerably more conservative from a structural perspective than is necessary to resist hydrodynamic loading from a tsunami bore.

This paper presents the application of hydrodynamic loading by the leading edge of a bore, determined based on laboratory experiments, to the non-linear analysis of a reinforced concrete building damaged during the Tohoku Tsunami.
West Africa Swell Spectral Shapes
Authors: Olagnon Michel , Ewans Kevin , Forristall George , Prevosto Marc
Published: November 2013

Wave spectra measured at sites off West Africa are dominated by the constant presence of one or several swell wave systems. The West Africa Swell Project (WASP JIP) was carried out to propose and assess parametric models for the shapes of the swell components. Bias, variability, and dispersion of estimates are affected by the length/stationarity compromise of the record lengths and the window-tapering used to reduce their variability. In particular, shapes with sharp angles are strongly smoothed, for instance a triangular peak would appear round and reduced by 15 to 25% with rectangular or Tuckey windowing. Models that consider each wave system individually, and an arbitrary number of those, were preferred to global ones. Partitioning of directional spectra is thus a prerequisite, and needs to be tuned taking account some prior knowledge of the swell characteristics. Triangular, log-normal, Gaussian and Glenn-Jonswap shapes were considered. Sampling variability makes it difficult to distinguish between those shapes as far as swells are concerned. The models also indicate that the width of the spectrum in frequency should be inversely proportional to the peak frequency. Directional spreading width shows a similar trend. Fits to the measurements established proportionality factors for each location.
Simulation of the Gap Resonance Between Two Rectangular Barges in Regular Waves by a Free Surface Viscous Flow Solver
Authors: Elie B. , Reliquet G. , Guillerm P.-E. , Thilleul O. , Ferrant P. , Gentaz L. , Ledoux A.
Published: November 2013

This paper compares numerical and experimental results in the study of the resonance phenomenon which appears between two side-by-side fixed barges for different sea-states.

Simulations were performed using SWENSE (Spectral Wave Explicit Navier-Stokes Equations) approach and results are compared with experimental data on two fixed barges with different headings and bilges.

Numerical results, obtained using the SWENSE approach, are able to predict both the frequency and the magnitude of the RAO functions.
New Methods and Insights in Advanced and Realistic Basin Wave Modelling
Authors: Schmittner Christian , Scharnke Jule , Pauw Willemijn , van den Berg Joris , Hennig Janou
Published: November 2013

For model tests, the correct generation of the most realistic representation of the natural wave field is of greatest importance as the environmental conditions denote the starting point for all following analyses of any behaviour of a marine structure. Thus, it has to be defined first what “reality” is, followed by a thorough analysis of the inherent limitations of basin wave fields. Furthermore, all realistic aspects of the wave field have to be modelled at sufficient accuracy involving the wave maker control, flap geometries and appropriate analysis techniques. This paper gives an overview of the most recent developments in advanced basin wave modelling including a wide range of aspects as realistic wave spreading, deterministic wave generation, focusing waves, directional wave analysis, spurious waves and shallow water wave generation.
Thermal Analysis and Strength Evaluation of Cargo Tanks in Offshore FLNGs and LNG Carriers
Authors: Wang Bo , Chen Yong , Shin Yung-Sup , Wang Xiaozhi
Published: November 2013

The objective of this study is to develop a procedure for thermal analysis and strength evaluation of cargo tank structures in offshore FLNGs and LNG carriers. In this paper, a heat transfer analysis methodology has been employed, and a computational tool has been developed for its application on hull and tank structures in both membrane-type and independent Self-supporting Prismatic type B (SPB) LNG vessels. Using this method, the temperature distribution and corresponding heat transfer coefficients (HTCs) in both the hull structure and void spaces can be estimated so the appropriate steel grade can be selected for the inner hull and the boil-off rate (BOR) can be calculated for LNG vessels. Based on these estimated temperature environmental profiles and HTCs in void spaces, the detailed temperature distribution of an independent SPB tank including the tank boundary and internal structures can be calculated using steady-state thermal FE analysis. Then, the temperature distribution obtained from thermal FE modeling is applied to the FE model as loading conditions for thermal stress FE analysis on cargo tanks. In stress FE analysis, design loads usually include temperature distribution, design vapor pressure, and internal pressure caused by cargo during vessel acceleration. For temperature distribution among design loads, there are three loading conditions which are: cooling down, partial filling level, and full filling level loading conditions in an independent tank. Finally, FE results are to be used for assessing the yielding and buckling strength of a tank structure in terms of acceptance criteria. A case study for an LNG SPB tank demonstrates strength assessment considering thermal effects. The complete procedure has been developed for thermal analysis and strength evaluation of cargo tank structures in offshore FLNGs and LNG carriers.
Mesoscale Modeling of Non-Isothermal Fluid Displacement in Capillary Tube Using Dissipative Particle Dynamics
Authors: Zaman M. S. , Satish M. G.
Published: November 2013

It is crucial to understand how one fluid is displaced by another at different temperature through a capillary, as many industrial and reservoir enhanced recovery methods fall into this category. Dissipative particle dynamics (DPD) method has been successfully applied to model mesoscale behaviors of many processes. In this paper, DPD method with energy conservation has been applied to model non-isothermal fluid displacement in capillary tube. Validation of the in-house computer code written in C# is carried out by modeling isothermal no-slip fluid flow. Simulation of non-isothermal fluid displacement using energy conserving DPD gives insight about the parameters affecting the flow.