bluuebunny/crossref_metadata_2025 huggingface dataset:
Radiation Hydrodynamics of a Surface Effect Ship
Authors: Ananthakrishnan Palaniswamy
Published: November 2013

The radiation hydrodynamics of a heaving surface effect ship (SES) is examined including the effect of air compressibility on the hydrodynamic forces and surface waves. Of particular focus of the study has been on determining the nonlinear viscous and air compressibility effects at natural frequencies corresponding to the piston and sloshing wave modes between the hulls and at the natural frequency corresponding to the heave motion of a surface effect ship with the restoring force dominated by the compressibility of the air cushion. In the present paper, the air cushion pressure is assumed to be uniform with its variation due to change of volume modeled using the adiabatic gas law pVγ = constant, where p denotes the absolute pressure of the air, V the air volume bounded by the side hulls, the free surface and the wet deck, and γ the ratio of specific heats Cp/Cv which is about 1.4 for air. The incompressible Navier-Stokes equations governing the nonlinear viscous wave-air-body interaction problem is solved in the time domain using a finite-difference method based on boundary fitted coordinates. New results presented in this paper show that air cushion compressibility affects the generation of waves and wave radiation forces significantly even at small amplitude of hull motion. As already well known, the free surface nonlinearity due to hull motion is significant for large amplitude of oscillation. At small amplitude of body oscillation, significant nonlinearity can be caused by air compressibility resulting in the generation of higher harmonic waves and forces. The results also highlight the significance of viscosity and flow separation, in conjunction with air compressibility, in the case of large amplitude hull motion with a small draft.
Offshore Launching of Jack-Up Units: An Experimental Approach
Authors: Rodríguez Claudio A. , Esperança Paulo T. T. , Moura Mário , Raigorodsky Jacques
Published: November 2013

Ships and most offshore structures are commonly launched into water from dry docks. But, sometimes due to practical and economical restrictions, launching of some offshore structures takes place at floating launching platforms, usually barges. The latter type of launching is quite “usual” for jacket rigs. To assess the success of the launch operation usually numerical simulations are enough and model tests are usually not required. However, more recently, as part of the construction project of the new Brazilian jack-up oil platforms, an innovative launching operation was required: launching a jack-up using a jacket launching barge. The marked differences between the two types of structures involve hydrodynamic and structural complexities. From the hydrodynamical point of view, due to its greater volume compared to jackets, the jack-up may be subjected to greater loads as enters in water during launching, and then suffers great motions that may affect the barge motions and these, affect back, the jack-up motions. From the structural point of view, the heavier jack-up structure may cause greater stresses on the barge deck and rocker arms that should be properly addressed in order to determine the necessity for reinforcements in the jack-up and/or the barge. To assess the feasibility of this innovative launching operation, model tests were required to measure the motions of the barge and the jack-up and to evaluate the loads on the rocker arms. The present paper describes the experimental approach developed for simulating this unique launching operation. The calibration procedures are outlined and the main results of the systematic set of tests carried out are presented. Furthermore, the influence of some launching parameters such as friction coefficient, position of the center of gravity of the jack-up and initial launching angle are discussed.
Pore Pressure Generation and Dissipation Effects on Spudcan Fixity in Normally Consolidated Clay
Authors: Yang Yu , Lee Fook Hou , Goh Siang Huat , Wu Jer-Fang , Zhang Xi Ying
Published: November 2013

Spudcan rotational fixity under combined vertical, horizontal and moment loading is often assumed to be invariant with time. In reality, the actual rotational fixity of spudcan footing is likely to change with time as excess pore pressure builds up and dissipates. This paper describes a series of centrifuge experimental tests conducted at 100-g acceleration using a small spudcan model and specimens of normally consolidated reconstituted kaolin clay. Using a servo-motor, belt-driven actuator system, loading episodes comprising one thousand cycles of combined loading were applied to model foundation. The PPTs are installed in soil specimens to measure the excess pore pressure and degree of saturation of soil. One small-rotation test is conducted just after spudcan’s penetration; while another one small-rotation is conducted when the excess pore pressure is fully dissipated after the spudcan’s penetration. The results show bending moments at four locations along the spudcan shaft, which indicates that the lattice confers a significant lateral soil resistance, and the presence of the lattice will also cause the location of maximum bending moment to be up-shifted along the leg, towards to the soil surface. The rotational fixity of the spudcan shows distinct changes over time, which is attributed to consolidation and settlement effects. Comparison of fixity of spudcan with and without lattice leg indicates that the lattice leg can lead to a large increase in lateral resistance of deeply penetrated spudcans. This lattice leg effect has been largely ignored in both academic study and industrial design.
Guidelines for CFD Simulations of Spar VIM
Authors: Lefevre Charles , Constantinides Yiannis , Kim Jang Whan , Henneke Mike , Gordon Robert , Jang Hyunchul , Wu Guangyu
Published: November 2013

Vortex-Induced Motion (VIM), which occurs as a consequence of exposure to strong current such as Loop Current eddies in the Gulf of Mexico, is one of the critical factors in the design of the mooring and riser systems for deepwater offshore structures such as Spars and multi-column Deep Draft Floaters (DDFs). The VIM response can have a significant impact on the fatigue life of mooring and riser components. In particular, Steel Catenary Risers (SCRs) suspended from the floater can be sensitive to VIM-induced fatigue at their mudline touchdown points.

Industry currently relies on scaled model testing to determine VIM for design. However, scaled model tests are limited in their ability to represent VIM for the full scale structure since they are generally not able to represent the full scale Reynolds number and also cannot fully represent waves effects, nonlinear mooring system behavior or sheared and unsteady currents. The use of Computational Fluid Dynamics (CFD) to simulate VIM can more realistically represent the full scale Reynolds number, waves effects, mooring system, and ocean currents than scaled physical model tests.

This paper describes a set of VIM CFD simulations for a Spar hard tank with appurtenances and their comparison against a high quality scaled model test. The test data showed considerable sensitivity to heading angle relative to the incident flow as well as to reduced velocity. The simulated VIM-induced sway motion was compared against the model test data for different reduced velocities (Vm) and Spar headings. Agreement between CFD and model test VIM-induced sway motion was within 9% over the full range of Vm and headings. Use of the Improved Delayed Detached Eddy Simulation (IDDES, Shur et al 2008) turbulence model gives the best agreement with the model test measurements. Guidelines are provided for meshing and time step/solver setting selection.
Investigation of the Mighty Servant 3 Accident by a Progressive Flooding Method
Authors: Dankowski Hendrik , Dilger Hendrik
Published: November 2013

The semi-submersible heavy-lift vessel Mighty Servant 3 sank off the port of Luanda, Angola in the morning of December 6th, 2006 during a ballast operation to offload the drilling platform Aleutian Key. The official investigations carried out after the accident identified an error in the control of the submerging ballast operations as the direct cause of the sinking. However, the detailed phenomenons and reasons for the sudden excessive trim development has not been investigated further. This paper intends to identify the most likely sceneario which lead to the hydrostatic stability failure during the discharge operation by computing the flooding process during the ballast operation in the time domain. A numerical progressive flooding simulation method is presented for applications like accident investigations or damage stability assessments. This method is modified to fit the special requirements of simulating the operational procedures of semi-submersible vessels in the time domain. Extensions like the inclusion of pump elements but also the multi-body interaction of the cargo and the vessel with regard to the hydrostatics is presented. The direct flooding simulation computes the flux between the compartments based on the Bernoulli equation and the current pressure heads at each intermediate step. Large and partly flooded holes are taken into account as well as optional air compression and flooding through completely filled rooms. Pressure losses due to viscous effects are taken into account by applying semi-empirical discharge coefficients to each opening. The flooding paths are modeled by directed graphs.

A detailed investigation of the Mighty Servant 3 accident and an identification of the possible failure modes leading to the sinking of the vessel is presented. This will help to better understand the phenomenons leading to critical situations during the submerging procedure of semi-submersible heavy-lift vessels and to avoid such accidents in the future. Applying time domain flooding simulations allows to predict the ship behavior during ballast operations to identify critical situations and to better schedule the different steps of such an operation in advance.
Modelling Thruster-Hull Interaction With CFD
Authors: Maciel P. , Koop A. , Vaz G.
Published: November 2013

The application of CFD for the analysis of thruster interactions effects (or degradation effects) is still a largely unexplored area. Quantifying these effects is essential to the design of dynamic positioning (DP) vessels. Presently, thruster interactions can be quantified using data available from literature, which unfortunately is often scarce, too general or not applicable to specific designs. Dedicated model tests, on the other hand, do provide detailed results but are relatively expensive and tend to become available relatively late in the design process. Alternatively, with CFD different vessel designs and thruster layouts can be investigated for thruster interaction effects in a cost-efficient manner early in the design process.

This paper presents a practical method for modelling thrusters, describing the propeller blades as an actuator disk. Numerical choices for the calculations are discussed and steady state calculations are performed. This approach is evaluated on thruster-hull interaction cases in both bollard pull and under current conditions, for a series of configurations with increasing complexity: a thruster in open water, a thruster positioned under a flat plate and a thruster under a barge.

A comparison to experimental results is presented for the flow field (against PIV experimental data) and forces on the thrusters and hull of the vessel. A modern Verification and Validation procedure is used to quantify uncertainties. The results are encouraging, both in a qualitative and quantitative sense. In this context, the modelling approach employed proves to be a robust and accurate solution, with low computational effort, and therefore appropriate to be used for much more complex real applications.
Challenges, Requirements and Advances for Distributed Fiber Optic Sensors in SURF Structures and Subsea Well Monitoring
Authors: Ravet Fabien , Rochat Etienne , Niklès Marc
Published: November 2013

During the past 10 years, the oil and gas industry has gained confidence in the capabilities and the reliability of Fiber Optic Distributed Sensing (OFDS). Real world implementation can be found in both downstream and upstream branches. For example, at one end of the industry spectrum, service companies have started to use Distributed Temperature Sensing (DTS) for in-well temperature monitoring to optimize oil recovery processes. At the other end, pipeline operators have installed pipeline integrity monitoring systems based on Distributed Temperature and Strain sensing (DITEST) to fulfill realtime monitoring of soil stability, pipeline 3D deformation and leak detection.

The use of OFDS for offshore structure integrity monitoring such as flow lines, risers and umbilicals has been qualified and field tested already whereas other applications such as performance rating of power umbilicals and enhanced flow assurance system using OFDS are being evaluated.

Currently, the offshore full scale implementation of OFDS technologies still faces challenges of its own. In particular, sensor integration into the structure to be monitored is a minimum requirement which applies to any OFDS. If fiber optic is a common mean of data transmission, subsea conditions imply the use of specific components such as Wet Mate Connectors (WMC) and Fiber Optic Rotary Joints (FORJ). These components present large insertion and return loss characteristics for which OFDS require special attention to the OFDS system to comply with such characteristics. The effect of these components is twofold. First it impacts the sensor optical budget limiting its measurement range. Second, sensor sections remain completely blind due to the high reflection levels leaving the structure without status information over distances that can be as large as several kilometers.

The present works describes how the DITEST based on Stimulated Brillouin Scattering (SBS) can overcome the limitations imposed by both WMC and FORJ components and fully comply with SURF monitoring requirements. The ability of the DITEST is justified theoretically and demonstrated experimentally through qualification trials involving hotspot detection while WMC and FORJ are part of the sensor path. Their effects are quantified through the determination of the measurement dead zone (shorter than 4m), the temperature uncertainty and the resolution. The work also reports the subsequent installation on operational structures as these trials were successful. The DITEST has been installed to continuously monitor the temperature of a 3km long power umbilical and control the heating system of subsea rigid flowlines whose length can be as large a 45km.
Predicting the Probability of Riser Collision Under Stochastic Excitation and Multiple Uncertainties
Authors: He Jian Wen , Low Ying Min
Published: November 2013

As the offshore industry moves to deeper waters, riser collision becomes a more crucial concern. Riser interference assessments need to rely on time domain simulations due to nonlinearities such as hydrodynamic interferences, but one difficulty is that riser collision is an extreme event. In a recent work, the authors proposed an efficient procedure for predicting the probability of riser collision, based on extrapolating the dynamic response characteristics, thus obviating the need to capture actual collisions during simulation. However, the prior work considers randomness only from the irregular waves. This paper extends the prior work by developing a method to account for multiple uncertainties. The random variables considered herein are current, drag coefficient, vessel motions and riser mass. The proposed method is computationally efficient; the additional simulations necessary to incorporate four random variables are only slightly more than the original simulation case. Taking a top-tensioned riser system as a case study, the likelihood of collision predicted by the proposed method is found to compare well with Monte Carlo simulation. Moreover, it is shown that the random variables can increase the probability by an order of magnitude, and all the considered variables contribute meaningfully to this increase.
Top Tensioned Riser System Design for the FHSB Dry Tree Semisubmersible Platforms
Authors: Yu Jim , Mansour Alaa M. , Yu Alan , Zuccolo Ricardo
Published: November 2013

The dry tree production and drilling Top Tensioned Riser (TTR) systems have been extensively used with Tension Leg Platforms (TLPs) and Spar floaters in deepwater applications. However, the large heave response of the conventional Semisubmersible floaters makes this type of platforms not suitable for dry tree applications largely due to the ultra-long stroke tensioner that would be required in this case.

The Free Hanging Solid Ballast (FHSB) Semi is an innovative new semisubmersible design that is suitable for dry tree applications due to its low heave response that is comparable to that offered by Spar floaters. The new design resembles the conventional Semisubmersibles with an added free-hanging solid ballast tank placed deep below the keel of the Semisubmersible hull and connected to the hull through four groups of chains. The Solid Ballast Tank (SBT) acts as a motion damper that significantly improves the heave motion response.

In this paper, the design of the dry tree TTR system for the FHSB Semi is presented. The typical GoM’s drilling and production conditions are used in designing the TTR system including the tensioning system and the interface between the SBT and the riser keel joint. The feasibility and performance of the designed TTR system are demonstrated through static and dynamic TTR analyses.
Physics-Based Approach to Wave Statistics and Probability
Authors: Babanin Alexander V.
Published: November 2013

Design criteria in ocean engineering, whether this is one in 50 years or one in 5000 years event, are hardly ever based on measurements, and rather on statistical distributions of relevant metocean properties. Of utmost interest is the tail of these distributions, that is rare events such as the highest waves with low probability. Engineers have long since realised that the superposition of linear waves with narrow-banded spectrum as depicted by the Rayleigh distribution underestimates the probability of extreme wave crests, and is not adequate for wave heights either, which is a critical shortcoming as far as the engineering design is concerned. Ongoing theoretical and experimental efforts have been under way for decades to address this issue.

Here, we will concentrate on short-term statistics, i.e. probability of crests/heights of individual waves. Typical approach is to treat all possible waves in the ocean or at a particular location as a single ensemble for which some comprehensive solution can be found. The oceanographic knowledge, however, now indicates that no single and united comprehensive solution is possible. Probability distributions in different physical circumstances should be different, and by combining them together the inevitable scatter is introduced. The scatter and the accuracy will not improve by increasing the bulk data quality and quantity, and it hides the actual distribution of extreme events. The groups have to be separated and their probability distributions treated individually.

The paper offers a review of physical conditions, from simple one-dimensional trains of free waves to realistic two-dimensional wind-forced wave fields, in order to understand where different probability distributions can be expected. If the wave trains/fields in the wave records are stable, distributions for the second-order waves should serve well. If modulational instability is active, rare extreme events not predicted by the second-order theory should become possible. This depends on wave steepness, bandwidth and directionality. Mean steepness also defines the wave breaking and therefore the upper limit for wave heights in this group of conditions. Under hurricane-like circumstances, the instability gives way to direct wind forcing, and yet another statistics is to be expected.
Design Advantages on Umbilical Systems Brought by a New High Performance SDSS Tube
Authors: Wagner Olivier , Durand Guy , Peultier Jérôme , Courbot Anne , Roques Jean-Philippe , Romazzotti Henri
Published: November 2013

Subsea umbilical systems developed for deep offshore applications become more and more demanding regarding injection capacity, number of functionalities and water depth. Some applications, such as subsea boosting, subsea separation or gas lift are even more severe, leading to tube temperature, which can exceed, in some cases 70°C.

These operating conditions and requirements are significantly impacting the performance of the main umbilical. The most common solution, to avoid such issues, is to design thicker tubes to improve the strength of the umbilical cross section. The positive effect of the wall thickness increase has to be opposed to major drawbacks, such as weight increase and fatigue performance degradation generating more issues than providing solutions.

To face these challenges, Vallourec Umbilicals, with the technical support of TOTAL SA headquarter Technology Division, has developed a new manufacturing process for seam welded stainless steel tubes (SAF 2507), with higher mechanical properties and tighter wall thickness tolerances. The benefit of this innovation is to provide for a given application (i. e. pressure, water depth and temperature) thinner tubes able to meet severe operating conditions without impacting performances of the umbilical structure.

This paper, after a description of the manufacturing process and product qualification protocol (that led to a Type Approval Certificate from Bureau Veritas in October 2012), presents the technical advantages brought by seam welded solution, compared to seamless super duplex tubes.
Theoretical Modelling of Free Falling Wedges Entering the Water Surface: Part II — Cavity Dynamics
Authors: Wang Jingbo
Published: November 2013

As the second of two companion papers, we propose theoretical models to describe the cavity dynamics for free falling wedges vertically entering the water surface at Froude numbers: 1 ≤ Fn < 9. An ideal cavity model is developed which gives the first approximation to the evolution of the cavity. Discussions are made on the characteristics of the transient cavity. It is found that, the characteristics of the transient cavity, such as the pinch-off time, pinch-off depth and wedge depth at pinch-off, scale roughly as the Froude number. The cavity seal (closure) point moves to the deeper water zone with increasing Froude number. This is opposite of the cavity seal mechanism from deep seal to surface seal for circular disks or spheres entering the water. Finally, we study the cavity dynamics at the pinch-off depth. A semi-analytical model is proposed to describe the evolution of the cavity at the pinch-off depth. By applying the semi-analytical model to any water depth, improved predictions for the characteristics of the transient cavity are obtained.
A Structural Capacity Evaluation for Corrugated Membrane Structure of LNG Cargo Containment System
Authors: Chun Min Sung , Rodda Krishna K. , Park Tae Yoon , Yoon Jong Won , Han Sang Min , Jang Ki Bok , Suh Yong Suk , Kim Sung Chan
Published: November 2013

Corrugated membrane structure is adopted as 1st barrier of membrane type LNG cargo containment system of LNG carrier to reduce thermal stress caused by cryogenic temperature of LNG. The corrugated structure, however, can lead to buckling and large deformation followed by plastic strain at a local area of the 1st barrier under sloshing load. Therefore in order to evaluate structural capacity of the corrugated membrane, structural response against various environmental loading such as hull deformation, sloshing load as well as thermal loading should be investigated. In this study, failure criteria for corrugated membrane is proposed based on rupture strain of the material considering the objective of the 1st barrier of LNG cargo containment system with respect to functionality. And the structural responses of corrugated membrane, for each environmental loading, are carefully evaluated. To evaluate structural response under sloshing load and thermal loading, a series of finite element analysis is carried out and plastic strains for each loadings condition are estimated. In addition, to investigate the effect of plastic strain developed during metal forming process for corrugated membrane on structural response, plastic strain on corrugated membrane developed by metal forming is measured through real manufacturing process. By comparing accumulated plastic strain due to thermal, sloshing load as well as material forming to material rupture strain obtained from material tensile test, structural capacity of the corrugated membrane structure of LNG cargo containment system is evaluated.
Large Eddy Simulation of Flow Past a Stationary and Controlled Oscillating Circular Cylinder at Re=5500
Authors: Kim Sunghan , Wilson Philip A. , Chen Zhi-Min
Published: November 2013

Vortex shedding from a stationary cylinder and transversely oscillating circular cylinder in a uniform flow at a Reynolds number of 5500 is numerically studied by three-dimensional Large Eddy Simulation (LES). The filtered equations are discretised using the finite volume method with an O-type structured grid and a second-order accurate method in both time and space. Firstly, the main wake parameters of a stationary cylinder are examined and compared for different grid resolutions. Secondly, a transversely oscillating cylinder with a constant amplitude in a uniform flow is investigated. The cylinder oscillation frequency ranges between 0.75 and 0.95 of the natural Kármán frequency, and the excitation amplitude is 50% of the cylinder diameter. Comparisons with the available experimental data indicate that the present study has properly predicted the flow statistics of the cylinder wake for both the fixed and oscillating cylinder case, and numerically captured the vortex switching phenomenon, which is characterized by changes in forces and wake mode of shedding observed in the previous experiments at high values of Reynolds number.
Minimum Energy DP Heading Control: Critical Analysis and Comparison of Different Strategies
Authors: Miyazaki Michel R. , Tannuri Eduardo A. , de Oliveira Allan C.
Published: November 2013

DP offshore operations require that the vessel reference point is controlled in relation to a fixed reference frame. In some cases, the heading is allowed to change, searching for an adequate angle in which the environmental conditions induce small loads in the hull and minimum DP power is required to keep the position. This DP mode is usually referred as “weathervane control”.

There is no exact method to determinate the minimum energy heading of a vessel in real-time with only the sensors available in a DP system. Therefore, some control strategies were developed in order to control the vessel heading, and estimate the optimal value.

This paper addresses the analysis of the final equilibrium heading of several published weathervane control strategies for two different DP vessels: a typical DP tanker and an asymmetrical DP crane-barge. A static procedure is used to calculate the final heading and the DP power and thrust demand for each controller.

Several environmental combinations of wind, current, local sea-waves and swell are considered, with a systematic variation of the intensities and the direction of the environmental agents.

For non-aligned environmental agents, differences in the final heading are verified for the zero yaw and zero sway strategies. These headings are also compared to the exact minimum power heading, obtained by an optimization procedure considering the DP thrust allocation.
Deepwater Current Profile Data Sources for Riser Engineering Offshore West Africa
Authors: Jeans Gus , Harrington-Missin Liam , Calverley Mark , Maisondieu Christophe , Frelin Cyril , Quiniou Valerie
Published: November 2013

Reliable quantification of current profiles is required for safe and cost effective offshore exploration and field development. The current regime offshore West Africa is often considered benign, compared to some regions of oil and gas activity, but still presents challenges to reliable quantification. A key challenge to all offshore developments is acquisition of appropriate data. The primary source of data for riser design is site specific full water column measurement. Such in-situ data are generally expensive and time consuming to collect, so there is an increasing tendency for numerical model current data to be considered. Model data are often relatively quick and inexpensive to obtain, with the added benefit of a much longer duration, potentially allowing inter-annual variability and extreme events to be captured. However, the accuracy and reliability of numerical model data remains questionable, or unproven, in many deepwater development regions. This paper explores the suitability of such models to represent a deepwater site offshore West Africa, in relation to the key oceanographic processes revealed within the in-situ data.
Navigation in the Russian Arctic: Sea Ice Caused Difficulties and Accidents
Authors: Marchenko Nataliya
Published: November 2013

The 5 Russian Arctic Seas have common features, but differ significantly from each other in the sea ice regime and navigation specifics. Navigation in the Arctic is a big challenge, especially during the winter season. However, it is necessary, due to limited natural resources elsewhere on Earth that may be easier for exploitation. Therefore sea ice is an important issue for future development. We foresee that the Arctic may become ice free in summer as a result of global warming and even light yachts will be able to pass through the Eastern Passage. There have been several such examples in the last years. But sea ice is an inherent feature of Arctic Seas in winter, it is permanently immanent for the Central Arctic Basin. That is why it is important to get appropriate knowledge about sea ice properties and operations in ice conditions.

Four seas, the Kara, Laptev, East Siberian, and Chukchi have been examined in the book “Russian Arctic Seas. Navigation Condition and Accidents”, Marchenko, 2012 [1]. The book is devoted to the eastern sector of the Arctic, with a description of the seas and accidents caused by heavy ice conditions. The traditional physical-geographical characteristics, information about the navigation conditions and the main sea routes and reports on accidents that occurred in the 20th century have reviewed. An additional investigation has been performed for more recent accidents and for the Barents Sea.

Considerable attention has been paid to problems associated with sea ice caused by the present development of the Arctic. Sea ice can significantly affect shipping, drilling, and the construction and operation of platforms and handling terminals.

Sea ice is present in the main part of the east Arctic Sea most of the year. The Barents Sea, which is strongly influenced and warmed by the North Atlantic Current, has a natural environment that is dramatically different from those of the other Arctic seas. The main difficulties with the Barents Sea are produced by icing and storms and in the north icebergs. The ice jet is the most dangerous phenomenon in the main straits along the Northern Sea Route and in Chukchi Seas.

The accidents in the Arctic Sea have been classified, described and connected with weather and ice conditions. Behaviour of the crew is taken into consideration. The following types of the ice-induced accidents are distinguished: forced drift, forced overwintering, shipwreck, and serious damage to the hull in which the crew, sometimes with the help of other crews, could still save the ship. The main reasons for shipwrecks and damages are hits of ice floes (often in rather calm ice conditions), ice nipping (compression) and drift.

Such investigation is important for safety in the Arctic.
Analysis and Design of Small Scale Pipe Forge Welding Process
Authors: Liu Junyan , Marimuthu Ganesan S. , Moe Per Thomas
Published: November 2013

Shielded Active Gas Forge Welding is a high speed welding method for joining inter alia steel pipeline and casing. The process consists of a heating step, in which the bevels of the sections to be joined are heated locally to temperatures exceeding 1000 °C, and a subsequent forging step in which joining takes place by the application of a high axial force. In order to make possible cost-effective welding qualification and research a small scale forge welding machine has been developed. Down-scaling of the forge welding process should be carefully assessed in order to establish the limits of the process. In this paper two aspects of the forge welding process have been studied in detail by the use of finite element modeling and experiments: a) coupled thermal and electromagnetic modeling of heating and b) coupled thermo-mechanical modeling of forging. Special attention is given to the study of the limits of buckling of the pipe wall during forging. A high thermal gradient in the axial direction in the pipe wall facilitates local plastic deformation during forging and proper fusion of welds. For elongated temperature fields buckling is more likely to occur since the effective stiffness of the wall section is reduced. The limits of buckling depend on the wall thickness and diameter of section to be joined. While the forge welding process works very well for virtually all types of full scale pipeline and casing sections, buckling has been observed when joining very thin-walled small scale pipes. For welding of stainless steel small scale pipes local heating proves challenging. These challenges may be overcome by innovative welding machine design, and by carefully assessing welding process limitations. Certain physical limitations must still be considered.
Instantaneous Probability of Uncontrolled External Leakage During the Production Phase of a Subsea Well
Authors: Alves Andre L. R. , Netto Theodoro A.
Published: November 2013

This work develops a methodology for evaluating the uncontrolled external leakage probability of a subsea well during the production phase. Based on a barrier diagram, an algorithm for possible leak paths identification is proposed, considering different operation modes: gas lift operation, free flowing or well closed at the subsea Xmas Tree.

Considering the equivalency between these paths and the minimum cut sets from a fault tree modeling, the uncontrolled external leakage probability is calculated using the upper bound approximation. The effect of common cause failures is considered for the failure mode fail-to-close-valve.

The instantaneous availability function of each component is modeled to represent the maintenance strategy applied. Non repairable, repairable and periodically tested items are used. For the latter, a nomenclature to distinguish two subtypes is introduced: the PT-R and PT-NR models, respectively Periodically Tested Repairable, and Periodically Tested Non Repairable.

Probability distributions parameters are roughly estimated in order to make a case study. The failure rate functions determined are used as input for the proposed model, regarding the following failure modes: fail-to-close, external-leakage, and internal-leakage at the closed position. The objective of this section is to adjust a Weibull distribution, eliminate the usual assumption of constant failure rate and account for eventual wear-out effects.

Finally, instantaneous probability results and sensitivity analysis are demonstrated for a base case study. Parameters like time between tests, inspections, and component reliability are varied in order to identify the impact on the uncontrolled external leakage probability. Therefore, the main objective is to propose a model that could support decision making on the well integrity management system during the production phase of a subsea well. To make this possible, reliable input data should be further considered.
A Numerical Model for Environmental Impact on Marine Organisms for Seafloor Resources Development
Authors: Yamamoto Joji , Nakajima Yasuharu , Oka Hideyuki , Masanobu Sotaro
Published: November 2013

The exclusive economic zone (EEZ) of Japan has a very wide area due to a lot of islands in the Japanese Archipelago. Recently, the development of power generation facilities, food production facilities, and the natural resources in the Japanese EEZ are planned. As the worldwide supply and demand of mineral resources are being tight, the technology for effective exploitation and the use of mineral resources in the EEZ will become a key for sustainable development in the Japanese industry. Prior to development of marine mineral resources, it is necessary to evaluate its environmental impact on the water column and seafloor of ocean. However, the environmental evaluation method for open ocean has not been established yet. Then, we are developing the environmental impact prediction model for the seafloor mineral resources development in deep sea area with the consideration of benthic organisms. This model can estimate the impacts of excavating seafloor and sedimentation of particles on marine organisms using an ecosystem model. In addition, the influence of an increase in dissolved oxygen on bacteria caused by the discharging of oxygen-rich waste water at seafloor, is considered in this model. The ecosystem in this model includes benthic organisms, zooplankton, bacteria, particulate organic matter and dissolved oxygen as the components. This paper introduces the calculation case using the prototype model.
Static Analysis of New Type Composite Mono-Piles for Offshore Wind Farm
Authors: Zhang Jian-hua , Gao Dian-wei , Liu Xin-sheng , Sun Ke
Published: November 2013

The wind energy converters have extreme requirements to lateral deformation and rotation for support structures. Mono-pile, as a popular foundation structure for offshore wind energy towers, must be with sufficient large diameter and deep embedded length to limit the deformation and rotation within the tolerance under cyclic loads. Larger power offshore wind turbine (OWT), bigger pile diameter should be needed. However, large outer diameter pile will lead to difficult construction and high cost. In this study, a new conception of composite mono-pile is presented to decrease the outer diameter of pile. To investigate the structural behavior of composite mono-pile, the finite elements software ABAQUS is employed to analyze and compare with general mono-pile for 1.5 MW OWT under static loads. The numerical results demonstrate that stiffness of composite mono-pile can be improved effectively. Therefore, in same environment condition, composite mono-pipe diameter will be smaller than typical mono-pile, correspondingly, construction difficult and cost will be decreased. In addition, mechanical characteristics of composite mono-pile are analyzed and rational diameter and thickness selection of inserted pile are advised. The research results can provide the reference for practical engineering.
Combined Random Swell and Transient Long Waves: Dissipation Characteristics
Authors: Kaihatu James M.
Published: November 2013

The dissipation characteristics of combined short swell and transient long waves are investigated. A methodology for deducing the instantaneous dissipation from each breaking wave is employed to determine the overall dissipation and the ensuing dissipation rate in each set of experiments. It is determined that the bulk characteristics of dissipation of the combined short-long wave signals are different than those seen in each individual signal, but that the frequency dependencies of dissipation rates seen in the combined short-long wave signals are quite similar to those of the swell waves in isolation.
Experimental Investigation of Dynamic Response of Tension Leg Platform With Perforated Members
Authors: Srinath Vishruth , Chandrasekaran Srinivasan
Published: November 2013

Perforated cylindrical structures are extensively used in near-shore breakwaters to reduce wave-structure interaction and scouring; however use of perforated members on floating offshore structures is not widespread. Current study investigates the influence of perforated members on the dynamic response of Tension Leg Platforms (TLP) through model testing. Detailed experimental investigations are carried out on the scale model of TLP with and without porous outer cover, under unidirectional regular waves. Based on studies conducted, it is shown that fluid-structure interaction is reduced in the presence of outer perforated covers; as a result, surge and pitch responses decrease.
Long-Range Rescue Capability for Operations in the Barents Sea
Authors: Jacobsen Sigurd R. , Gudmestad Ove T.
Published: November 2013

The purpose of this paper is to examine the feasibility of providing long-range search and rescue for personnel in the Barents Sea. This may be due to a helicopter ditching or accident while en route to or from an offshore petroleum installation in the Barents Sea or a maritime accident. The paper will propose a combination of a SAR helicopter and multipurpose emergency response vessels. The paper will illustrate improved search and rescue capacity both for personnel involved in the petroleum industry and others i.e., fisheries, maritime transport and tourism.

The basis for this paper is petroleum exploration activity in the far North Eastern area of the Norwegian sector of the Barents Sea. The area is currently being evaluated in a process that most probably will lead to opening the area for oil and gas exploration. There is currently little or no infrastructure in the area beyond the coast. The paper considers a method to provide SAR coverage over a distance of 260 nautical miles with a minimum rescue capacity of 21 persons within two hours.

Issues related to survival in cold water, immersion survival suits and performance requirements for search and rescue resources will be considered in order to provide an optimum combination and enhanced probability of survival if an incident should occur.

Operational considerations involving departure criteria for helicopter transport should be developed in order to ensure that persons travelling on a helicopter to remote locations in the Barents Sea have a reasonable prospect of surviving a helicopter ditching and subsequently being rescued.

Multipurpose Emergency Response Vessels, ERVs, equipped with dual Fast Recovery Daughter Craft, FRDC, capable of operating in an Arctic climate deployed at the remote location and en route together with an onshore based search and rescue, SAR, helicopter may provide a rescue capacity for 21 persons within 120 minutes.

As vessels of the type proposed in this paper may be of a benefit to all stakeholders performing activities in the Barents Sea, joint venture financing by the authorities, petroleum, maritime, fishing and tourism industries could be considered.
Further Development and Benchmarking of a Novel Pipe-Soil Interaction Model for Subsea Pipeline Design
Authors: Griffiths Terry , Shen Wenwen
Published: November 2013

For well over a decade it has been widely recognised that our existing models and tools for subsea pipeline stability design fail to account for the fact that seabed soils tend to become mobile well before the onset of pipeline instability. Despite ample evidence obtained from both laboratory and field observations that sediment mobility has a key role to play in understanding pipeline/soil interaction, no models have been presented previously which account for the tripartite interaction between the fluid and the pipe, the fluid and the soil, and the pipe and the soil.

This paper presents further development of a novel non-cohesive pipe-soil interaction algorithm which has been developed to enable modelling of pipe-soil-fluid interaction and offer a more realistic representation of the evolution of soil profiles around the pipeline compared to existing hysteresis friction spring approaches. The paper describes the methods applied to discretisation of the soil profile and interpolation between timesteps to conserve soil volume. The approach used to deform the seabed profile to account for pipe movement and predict pipeline / soil reaction forces enable the model to be benchmarked against the Verley model [12].

The model has been specifically developed to minimise computational cost compared to computationally intensive CEL continuum soil FEA approaches [6,14], but still enable the profile of the soil around the pipe to be established. This model has application to modelling of sediment transport and scour [4]. It may also offer advantages in the modelling of globally buckling pipelines where differing levels of embedment and support at buckle shoulders versus the apex of the buckle are not well handled by existing approaches. The model may also assist where existing, generally applied approaches are also not well developed to capture coupling of behaviour in axial and lateral resistances.
Preliminary Economic Examination of Seafloor Massive Mining Venture Under Japan’s Conditions
Authors: Yamazaki Tetsuo , Nakamoto Yusuke , Nakatani Naoki , Arai Rei
Published: November 2013

In Papua New Guinea (PNG), a seafloor massive sulfide (SMS) mining venture has been proposed to start in 2013 and the expected high profitability was presented. However, the geophysical and social conditions are quite different from Japan’s ones. The technologies and model used for the PNG mining are difficult to apply under Japan’s conditions. The economy of SMS mining has no reality in Japan, because the tailing waste disposal is very expensive. Based on a preliminary economic evaluation of seafloor massive sulfide mining venture under Japan’s conditions, some modifications in the mining system and material flow are proposed for the improvement of the economy.
3D SPH Numerical Investigation for the Sloshing Impact in LNG Tank
Authors: Bai Zhigang , Zhao Jun , Zhang Wei , Wang Weiling
Published: November 2013

Sloshing in liquid natural gas (LNG) tankers includes extremely large deformations of the free surface. To better understand such deformations, a three-dimensional Smoothed Particle Hydrodynamics (SPH) method is developed to analyze the dynamic responses of liquid sloshing in LNG tank. The numerical model solves the Euler equation in the SPH style, the Monaghan-type artificial viscosity has been used in the current SPH model, sloshing wall boundaries were treated by improved coupling boundary pressure treatment. The numerical model is first validated against experimental data for two-dimensional and three-dimensional liquid sloshing in a LNG tank, it shows a fair agreement of overall fluid motions and hydrodynamic pressures. The fields of 3D sloshing pressure and velocity are compared for one period. Finally, the model is used to study 3D liquid sloshing in a tank with vertical baffles. The effect of the baffle on pressure and velocity is investigated and discussed. It shows that the SPH method is a natural numerical technique for coupled fluid-structure problems with large free-surface deformations.