bluuebunny/crossref_metadata_2025 huggingface dataset:
Jackup Designed for Optimum Operational Time in Ice Conditions
Authors: Gudmestad Ove T.
Published: August 2013

There is at present a large interest in exploration for hydrocarbons in the Arctic. In shallow waters, up to, say, 70m, jackups are utilized outside the ice season, while there is a wish to extend the season when the jackups can be on site. We will report on an attempt to extend the operational season to earlier installation and later decommissioning than possible with present jackup designs for ice conditions.

The installation of the jackup can take place after the ice cover has cleared sufficiently for the jackup to be maneuvered to site. It should be noted that remaining drifting ice ridges may represent a hazard as the drift of these into the jackup legs can damage the legs. The situation is particularly vulnerable when waves or strong currents cause the remaining of the ridges to impact with the jackup legs.

During the operational season the jackup will operate in conventional mode. This phase should NOT been forgotten in the design as the wave and current load on the jackup might be higher than the ice pressure.

Towards the end of the drilling season and prior to ice aggregation, the operator of a conventional jackup rig will become very cautious of the requirement to move the jackup out of the ice cover in due time before the sea freezes up and the jackup could get stuck in the ice cover. It should be noted that a jackup frozen into the ice cover and susceptible to loads from drifting ice sheet and ice ridges might collapse. Should the situation occur that the jackup be frozen into the ice cover, it would be necessary to call for costly ice breaker assistance to free the jackup.

A jackup that could stay in the ice for a longer period in the fall season would extend the drilling season considerably. In the case such design be considered, the strength of the foundation should be checked to avoid loads that will exceed the foundation capacity of the mud mats. We will in this paper in particular discuss how we can deal with the problem of the requirement for an extended drilling season.

The paper covers some of the main issues that are governing for the design of a jackup for arctic conditions. We will in particular cover the issue of leaving the offshore location safely as late as possible when ice has started to form. In this situation traditional jackups have problems and could need the very costly assistance of icebreakers. Other important issues that are not covered are the behavior of the jacket in ice. It should, however, be noted that the jackup is designed to leave the location prior to the ice situation becoming unmanageable.
Validation of HVS Semisubmersible VIM Performance by Model Test and CFD
Authors: Xu Qi , Kim Jang , Bhaumik Tirtharaj , O’Sullivan Jim , Ermon James
Published: August 2013

The present paper describes the validation of the HVS (Heave and VIM Suppressed) semisubmersible’s VIM response by model test and Computational Fluid Dynamics (CFD). The HVS semisubmersible is designed to achieve significantly improved motion characteristics for supporting steel catenary risers in hurricane and Loop Current environment of the Gulf of Mexico. In the development of the HVS design, a simplified and efficient CFD analysis in which the rotational motions are ignored was first used as a high-level screening tool. A towing tank model test was then performed to validate the VIM performance of the HVS design. Both the model test and CFD analysis demonstrated that the HVS design has superior VIM response compared to an equivalent conventional semisubmersible design.
Fundamental Analysis for the SWING Motion of Single Moored FPSO in South China Sea
Authors: Ma Yu , Hu Zhiqiang , Qu Yan
Published: August 2013

FPSO moored by STP mooring system plays a dominate role in oil and gas production in South China Sea. To study its hydrodynamic characters, a joint industry project on full scale measurement for Fenjin FPSO, headed by Shanghai Jiao Tong University and sponsored by CNOOC, was initiated in October 2007 and lasted for 25 months. During the project, a special phenomenon, named as SWING, was noticed. When a SWING happened, the FPSO’s heading angle would change greatly within a relatively short period, beyond the normal range of the weather-vane effect. Due to the large low-frequency motion, the tension forces of mooring system would increase greatly. Also, it may lead to positioning failure during the tandem offloading operation. So, the SWING motion is a great threat to the safety of FPSOs. A preliminary prediction for its cause as well as a fundamental analysis of its hydrodynamic mechanism is completed in this paper.

According to the statistical results of the SWING based on the Fenjin’s motion data during the full scale measurement as well as the corresponding wind wave and current data in the same period, a plausible prediction for its cause is provided. It is pointed out that the change of direction and velocity of the current within a short time might be the cause of SWING.

The research for the mechanism of the SWING is carried out through both the methods of analytical analysis and the model test. A hydrodynamic model is built to simulate the low-frequency motions of FPSO in time domain. And an in-house MATLAB program is written on the basis of the hydrodynamic model, to do the calculation. Analysis results are compared with the full-scale measured data, to prove the cause prediction.

Furthermore, on purpose of validating the program, a model test was conducted in Deepwater Offshore Basin in Shanghai Jiao Tong University. Several different current velocities were chosen in the test. The program results show a good agreement with both the data of full scale measurement and the model test results, which indicates that the hydrodynamic model and the code are both credible.
LNG Market Outlook: LNG Value Chain for Yamal Offshore Regarding to Recent Developments in Ice-Class Tankers Design and LNG Offloading System
Authors: Bulakh Maria
Published: August 2013

Arctic LNG is getting to be increasingly feasible and seems to become a prospective transporting method for natural gas in the near future. Recent evaluation of geological information has suggested that 25% of the world’s remaining natural resources lie below thick ice in the Arctic offshore. Russian Arctic offshore has according to estimates 31% of the world’s known and currently unexploited reserves of natural gas. Longer-term prospects are therefore promising. A six-fold increase in LNG trade from now until 2030 is expected [1]. Over this longer term it seems likely that exploitation of the giant natural gas fields of the Western Arctic regions of Russia will enhance the development of Arctic LNG shipping.

Increasing energy demand is driving greater interest in the exploration and production of natural gas in the Arctic Region. This creates a challenge for shipping gas in such extreme conditions. In this paper, we mainly investigate the overall LNG market. And explore available alternative transportation options.

Over the last five years there has been significant research and development done in the areas of LNG ships and ice-class tankers. In this paper the most promising ship design and power concepts of Arctic LNG ships/tankers are going to be reviewed. We will discuss in detail recent developments and trends in LNG ship and ice-strengthening tanker design such as:

• The first large double-acting ice-class tanker (DAT) design

• Double acting pusher puller barge (DAPPB) design

Also, offloading systems for LNG carriers are going to be touched upon in this paper. Analysis of the mentioned above concepts will be carried out with Russian Arctic Offshore Yamal region as an example. Potential solution for the issue of Arctic-class tankers’ limitation to navigate in thick ice areas is ship-to-ship LNG transfer, which is also presented in this paper. Arctic tanker could transport its cargo of LNG to the edge of the ice sheet and transfer the load to another, faster vessel, or perhaps offload at a dedicated storage site. The possible offloading concept from shore to offshore in the harsh ice condition of this region and further loading to tankers seems to be very feasible issue to observe. Comparison between two offloading system like STS (ship-to-ship) and Tandem in the Arctic condition will be given.
A Re-Examination of the Hydrodynamic Forces Acting on Partially-Buried Submarine Pipelines
Authors: An Hongwei , Luo Chengcai , Cheng Liang , White David
Published: August 2013

The hydrodynamic forces exerted on a pipeline partially buried in a permeable seabed subjected to combined random oscillatory flow are investigated experimentally. The tests were carried out in a re-circulating flume that can generate steady currents, oscillatory flow and combined flow, known as the O-tube. The performance of the testing facility was validated against published experimental data under regular oscillatory flow conditions. Four tests with different embedment depths, under random oscillatory flow conditions were then carried out. The flow velocity, hydrodynamic pressure around the model pipe and pore pressure in the soil were monitored. The hydrodynamic forces were calculated through pressure integration around the model pipe. The hydrodynamic force reduction due to embedment was compared with the model given in the most widely-used pipeline stability design guideline, DNV-RPF109. A horizontal load reduction of 55% was found for the fully buried pipe, which was lower than the 70% reduction suggested by DNV-RP-F109. The variation of the vertical hydrodynamic load with embedment ratio (embedment depth to pipe diameter) was also found to be different from the model suggested by DNV-RP-F109. It was found the fully buried pipe experienced a large vertical force, even higher than that of the fully exposed pipe, under low KC number conditions.
Experimental Evaluation of VIM on MPSO in Combined Environmental Conditions for Waves and Current
Authors: Saito Masakatsu , Masanobu Sotaro , Taniguchi Tomoki , Otsubo Kazuhisa , Asanuma Takayuki , Maeda Katsuya
Published: August 2013

MPSO, mono-column hull type FPSO, is attracting the interest as a floating production system which has high performance for motion and large tank capacity in recent years.

The authors had performed a mooring system safety evaluation of a MPSO named ‘MONOBR’ which was assumed to be installed at the Gulf of Mexico in the international collaborative research and development project between PETROBRAS and JOGMEC.

There exists a strong current called the Loop current in the Gulf of Mexico. It is known that cylindrical floaters like SPARs or MPSOs sway with the long period and large amplitude in the transverse direction of the current. The motion is called Vortex Induced Motion (VIM), and is caused by vortex shedding from the sidewall of the floater. VIM is one of the important issues in the safety evaluation of mooring system of MPSO.

Generally, the combined environmental conditions in which wind, waves and current exist are concerned for the safety evaluation of mooring systems. Therefore, it needs to estimate VIM in waves and current. The authors had performed the VIM measurement tests in order to investigate the estimation method of VIM in waves and current. The results of the VIM measurement test in waves and current and the results of the mooring safety evaluation method using the estimation method of VIM in waves and current are described in this paper.
Distributed Wake-Body Resonance of a Long Flexible Cylinder in Shear Flow
Authors: Bourguet Rémi , Triantafyllou Michael S. , Tognarelli Michael , Beynet Pierre
Published: August 2013

The fluid-structure interaction mechanisms involved in the development of narrowband and broadband vortex-induced vibrations of long flexible structures placed in non-uniform currents are investigated by means of direct numerical simulation. We consider a tensioned beam of aspect ratio 200, free to move in both the in-line and cross-flow directions, and immersed in a sheared flow at Reynolds number 330. Both narrowband and broadband multi-frequency vibrations may develop, depending on the velocity profile of the sheared oncoming current.

Narrowband vibrations occur when lock-in, i.e. the synchronization between vortex shedding and structure oscillations, is limited to a single location along the span, within the high current velocity region; thus, well-defined lock-in versus non-lock-in regions are noted along the span. In contrast, we show that broadband responses, where both high and low structural wavelengths are excited, are characterized by several isolated regions of lock-in, distributed along the length. The phenomenon of distributed lock-in impacts the synchronization of the in-line and cross-flow vibrations, and the properties of the fluid-structure energy transfer, as function of time and space.
A Penalty-Based Body-Pipeline Contact Element for Simulation of Pull-Over Events
Authors: Longva Vegard , Sævik Svein
Published: August 2013

This paper deals with determination of trawl gear pull-over loads on subsea pipelines by use of finite element analysis. A new contact element that handles interaction between a general 3-dimensional rigid body and a pipeline modeled by beam elements is proposed. The contact element is based on a frictionless penalty formulation, which in contrast to previous work by the authors, employs a continuous normal vector description at the contact interface.

A comparison study with existing model test results was carried out to verify the performance of the contact element. The model test setup was reconstructed by a full-scale finite element model containing a trawl board, a flat frictionless seabed surface and a short pipe section. In this study several span heights were examined for both fixed and flexible support conditions. Consistent behavior with the model test was demonstrated for span heights of 3 m and 6 m with fixed support conditions.

The proposed contact element performed satisfactorily in terms of computing time, and due to the continuous surface normal vector a good numerical robustness was also provided. The contact element is believed to be especially useful for pipeline pull-over scenarios outside the scope of present design codes. This can include analysis of free-spanning pipelines with high flexibility, simultaneous interference of two trawl boards and establishment of design pull-over loads caused by novel trawl gears. To expand the application area it is recommended in future work to verify, and possibly improve the contact element, for handling of subsea template pull-overs and oblique trawl gear crossings of pipelines.
Customized CFD for VIV: Advantages and Applications
Authors: Heynes Oliver
Published: August 2013

A new concept is introduced in the field of Computational Fluid Dynamics modeling of vortex-induced-vibrations: a CFD code written specifically for modeling riser VIV. The concept of the “single-purpose” CFD code has numerous advantages over the conventional method of running a simulation within “general-purpose” CFD software. By virtue of choosing the most efficient numerical techniques for the type of flow encountered, accurate solutions can be obtained two orders of magnitude quicker than the equivalent simulation using general-purpose CFD software. This is demonstrated through several examples, where accurate run times are obtained within a few seconds of simulation time.
A Damping Tugger System for Offshore Heavy Lifts
Authors: Meskers Geert , van Dijk Radboud
Published: August 2013

HMC’s new Deep Water Construction Vessel, Aegir has reeling capabilities using an exchangeable reel concept. The reel logistics is performed by transport vessel or barges while the vessel utilizes its 4000mT main crane to take on board new full reels and unload the empty reels at the offshore location. To ensure sufficient workability for this critical lift operation, a damping tugger system is developed to control the swinging motion of the suspended load which is often a governing criterion for the offshore lift operation. The patented system not only dampens the swinging motion of the suspended reel, but also has a large damping effect on the vessel roll. The roll motion is almost critically damped resulting in very calm motions of the vessel during the reel lift, to enable a controlled and safe operation. The paper describes the critical aspects of the reel exchange operation and how this is extensively analyzed both in frequency and time domain simulations to finally come to the system with damping tuggers to significantly improve the operability. The concept has been verified with model test and the simulation models are validated.
Conceptual Design of a Floating Support Structure and Mooring System for a Vertical Axis Wind Turbine
Authors: Berthelsen Petter Andreas , Fylling Ivar , Vita Luca , Paulsen Uwe S.
Published: August 2013

This paper deals with the conceptual design of a floating support structure and mooring system for a 5MW vertical axis offshore wind turbine. The work is carried out as part of the DeepWind project, where the main objective is to investigate the feasibility of a floating vertical axis offshore wind turbine. The DeepWind concept consists of a Darrieus rotor mounted on a spar buoy support structure. The conceptual design is carried out in an iterative process, involving the different subcomponents. The present work is part of the first design iteration and the objective is to find a feasible floating support structure and mooring system for the DeepWind concept.

The conceptual design is formulated as an optimization problem: Starting with an initial configuration, the optimization procedure tries to find a cheaper solution while satisfying a set of design requirements. This approach utilizes available response analysis programs for mooring system forces and vessel motions, and combines this with a gradient search method for solution of nonlinear optimization problems with arbitrary constraints. Two different mooring system configurations are considered: Chain systems with 3 and 6 lines, respectively.
Study on Seafloor Mineral Processing for Mining of Seafloor Massive Sulfides
Authors: Nakajima Yasuharu , Yamamoto Joji , Kanada Shigeo , Masanobu Sotaro , Takahashi Ichihiko , Sadaki Jun , Abe Ryosuke , Okaya Katsunori , Matsuo Seiji , Fujita Toyohisa
Published: August 2013

Seafloor Massive Sulfides (SMSs), which were formed by deposition of precipitates from hydrothermal fluids vented from seafloor, has been expected as one of unconventional mineral resources on deep seafloors in the oceans. The authors have proposed the concept of seafloor mineral processing for SMS mining, where valuable minerals contained in SMS ores are separated on seafloor while gangue minerals are disposed on seafloor in appropriate ways. To confirm the applicability of column flotation, which is one of conventional mineral processing methods, to seafloor mineral processing, the authors carried out experiments simulating column flotation under the pressure conditions corresponding to the water depths down to 1000m in maximum using ore samples containing copper, iron, zinc and lead. In the experiments, formation of fine bubbles suitable to flotation and overflow of froth layer were observed at high pressures. The contents of copper and zinc in the concentrates recovered in the experiments at 1MPa were higher than those in the feed ores while the contents of silicon and calcium in the concentrates were lower than those in the feed ores. These results suggest that column flotation would be applicable to seafloor mineral processing.
Offshore Software Challenges for New Builds and Existing Assets
Authors: Walters Paul , Selvam Naveen , Staiger John , Das Bibek
Published: August 2013

Complex integrated control systems are involved in nearly every aspect of offshore drilling, safety, environmental protection and other aspects of vessel operation. Safety, reliability and productivity are expected from high specification control systems such as those found on offshore supply vessels, drilling and production platforms. The ability of a control system to perform as expected is dependent on the underlying software which should be conceptualized, engineered, programmed and verified to provide the required stability and performance. Undetected errors in the software can cause hesitation and doubt for the operator upon execution of subsequent actions, in normal and/or emergency situations. The operator, who should be focused on normal operations, now has to deal with the added complexities and confusion brought about by unexpected software behavior.

Traditionally, commissioning and sea trials are periods when there is increased effort to update the functionality of the control systems. Statistics indicate that updates done during traditional commissioning introduces a larger number of unintentional software defects than if the functionality issues were thoroughly vetted during the software development process. During the asset’s operational life, vendor software updates on existing systems should be coordinated to maintain or improve safety and productivity.

Software development should be managed to uncover issues early in the development process, where effective solutions can be discussed to resolve issues and manage risk using a number of risk mitigation methods. The software development should follow a process wherein participation is garnered from stakeholders and the operational philosophy is documented in a Functional Description or Concept of Operation document. These documents facilitate safety as well as environmental and project risk mitigation.

The challenge of the software development process is compounded by the fact that many different suppliers have diverse requirements and inherent limitations which necessitate the development of effective and specific solutions. Verification of software involves utilizing a number of test cases and exercising the software to uncover defects in the code. Testing the integration involves conducting test to verify proper communication and timeliness of the commands and data transfer between the different connected equipment in the integrated control system. Following an internationally recognized process for software development leads to reduced errors in the software, a more predictable control system and thereby, a safer and more productive asset. The methodology summarized in this paper has been created to assist developers, owners and users in software risk mitigation and is built upon industry best practices.
Electromagnetic, Mechanical and Manufacturing Properties for Cable Wound Direct-Drive PM Linear Generators for Offshore Environments
Authors: Hultman Erik , Ekergård Boel , Leijon Mats
Published: August 2013

Renewable energy conversion in offshore environments, such as wave, wind and tidal energy, can potentially give a considerable contribution to the global electric energy demand. These harsh environments require robust generators with minimal need for maintenance at competitive costs. To reduce the generator cost, the electromagnetic design must be done with manufacturing in mind. An optimal design provides high electric efficiency, long device life-time, little need for maintenance and low manufacturing costs.

Modern simulation tools can be used to optimize the electromagnetic design of a generator for a specific task and operation mode. Hereby both electromagnetic losses and material stresses can be reduced. Industrial robots might provide new possibilities to automate generator-specific manufacturing tasks.

A generator design with a cable wound stator, surface mounted permanent magnets on the translator and direct-drive linear technology is investigated in this article. This concept has a simpler and more robust mechanical design, while both the electromagnetic losses and the need for maintenance are reduced. By reducing the number of generator assembly steps, manufacturing might also be facilitated. Further work is however needed in developing automated assembly methods and comparing them to conventional generator manufacturing.
Model DP System for Ice-Tank Research
Authors: Dal Santo Xavier , Jochmann Peter
Published: August 2013

Arctic areas raise a continuously increasing interest for exploration and research expeditions that must be performed in more and more extreme conditions. Fierce competition and constraints in polar environment require technologic improvements that are progressively enabled by research activities. Amongst them HSVA and SIREHNA participate to the European DYPIC project (www.dypic.eu) that aims at improving ship design and dynamic positioning systems in ice-covered waters. Feasibility studies are being performed with free running ship models controlled by a dynamic positioning system installed in the ice tank facility. Main issues to be tackled are induced by the model scale that raises constraints in thruster fabrication, model equipment and real-time control. In parallel algorithms and guidance strategies have to be adapted to the characteristics of ice withstand forces that present a high variability in amplitude with respect of time. In conclusion trials demonstrate the feasibility of free running model tests in ice conditions where a high level of control performance is expected. The results obtained by model tests will be scaled real life, giving way to optimized ship design techniques, control means and guidance algorithms.
Study of a Floating Foundation for Wind Turbines
Authors: Gueydon Sébastien , Weller Sam
Published: August 2013

Offshore wind farms are currently located predominantly in shallow water as it is possible to cost effectively install bottom fixed offshore turbines. Where shallow water sites are not available, floating offshore turbines could be a better solution than bottom fixed turbines.

Currently three main concepts are promoted for the design of a floating wind turbine: a ballast stabilized floater (i.e. spar), a buoyancy stabilized floater (i.e. barge or semi-submersible) or a mooring stabilized floater (tension leg platform). In April 2011 the DeepCWind consortium visited MARIN to carry out model tests in the offshore wave basin with these three types of floating wind turbine platform.

This paper reports a numerical study of a wind turbine supported by a semi-submersible floater. The response of the floating system to wind and wave conditions is compared to physical measurements at 1:50 model scale. The outcome of these comparisons is discussed in the conclusions of this paper.
Development of Fixed Hydrodynamic Lifting Surfaces to Stabilise Anchoring Structures in Energetic Tidal Flows
Authors: Harding Samuel F. , Bryden Ian G.
Published: August 2013

This paper presents the research currently being carried out on the potential contribution of hydrofoils to generate additional down-force on seabed fastenings in energetic tidal flows.

Firstly, the dynamic lift of a hydrofoil subjected to vertical velocity perturbations was analyzed numerically, showing the reduced response to the fluctuation when unsteady aerodynamic theories are introduced. Secondly, an experimental set-up was developed for the deterministic generation of two-dimension velocity perturbations in a recirculating water flume. This will allow the combined effect of vertical and longitudinal velocity fluctuations on the lift force to be measured.
X-Ray Diffraction Study of Microstructural Changes During Fatigue Damage in Steel Pipelines
Authors: Pinheiro Bianca , Lesage Jacky , Pasqualino Ilson , Benseddiq Noureddine , Bemporad Edoardo
Published: August 2013

Steel pipes used for oil and gas exploitation undergo the action of cyclic loads that can cause their failure by fatigue. A consistent evaluation of the fatigue behavior should take into account the micromechanisms of fatigue damage initiation, which precede macroscopic cracking and macrocrack propagation. In this work, microstructural changes in terms of variations in microdeformations and residual stresses (macrostresses) are evaluated by X-ray diffraction in real time during alternating bending fatigue tests performed on samples taken from an API 5L X60 grade steel pipe. Three stages of microstructural changes are detected. It is found that their amplitudes and durations are proportional to the level of alternating stress applied. Changes in density and distribution of dislocations are observed by transmission electron microscopy combined with the technique of focused ion beam. To understand the role of the initial dislocation structure, fatigue tests on annealed samples are performed under the same test conditions. Again, three stages of changes are observed, but with an increase in microdeformations during the first stage instead of a decrease as found for as-machined samples, suggesting the influence of the initial state of the dislocation network. The results obtained are very encouraging for the consideration of microstructural evolutions in the development of an indicator of fatigue damage initiation in steel pipes.
The Effect of the Spectral Distribution of Wave Energy on the Performance of a Bottom Hinged Flap Type Wave Energy Converter
Authors: Clabby D. , Henry A. , Folley M. , Whittaker T.
Published: August 2013

The power output from a wave energy converter is typically predicted using experimental and/or numerical modelling techniques. In order to yield meaningful results the relevant characteristics of the device, together with those of the wave climate must be modelled with sufficient accuracy.

The wave climate is commonly described using a scatter table of sea states defined according to parameters related to wave height and period. These sea states are traditionally modelled with the spectral distribution of energy defined according to some empirical formulation. Since the response of most wave energy converters vary at different frequencies of excitation, their performance in a particular sea state may be expected to depend on the choice of spectral shape employed rather than simply the spectral parameters. Estimates of energy production may therefore be affected if the spectral distribution of wave energy at the deployment site is not well modelled. Furthermore, validation of the model may be affected by differences between the observed full scale spectral energy distribution and the spectrum used to model it.

This paper investigates the sensitivity of the performance of a bottom hinged flap type wave energy converter to the spectral energy distribution of the incident waves. This is investigated experimentally using a 1:20 scale model of Aquamarine Power’s Oyster wave energy converter, a bottom hinged flap type device situated at the European Marine Energy Centre (EMEC) in approximately 13m water depth. The performance of the model is tested in sea states defined according to the same wave height and period parameters but adhering to different spectral energy distributions.

The results of these tests show that power capture is reduced with increasing spectral bandwidth. This result is explored with consideration of the spectral response of the device in irregular wave conditions. The implications of this result are discussed in the context of validation of the model against particular prototype data sets and estimation of annual energy production.
The Evolution of Lazy-S Flexible Riser Configuration Design for Harsh Environments
Authors: Anderson Keith , O’Connor Mark
Published: August 2013

Flexible riser configurations in harsh environments require riser buoyancy in order to decouple vessel induced motions from the seabed interface. This is achieved through either wave (distributed buoyancy) or S (subsea buoy) solutions.

In the UK sector of the North Sea circa 30% of all floating production system field developments utilise subsea buoys in Lazy-S configurations. The majority of these fields have been in service for many years and designed prior to the widespread adoption of current industry standards, the analytical rigour available today, and better characterisation of the metocean environment. In many cases original system design has also been for 50yr return period conditions, compared to the specified 100yr return period events required in todays codes and standards, e.g. ISO 13628-2 [1].

Therefore, when replacement riser or life extension work is performed on existing structures or new developments are being designed there can be significant challenges in confirming the applicability of traditional system configuration designs.

The principal challenges with these configurations is minimising sag bend compressions driven by differential buoy vs. vessel motions and maintaining the riser or umbilical minimum curvature and compression criteria at the seabed touch down. The latter point is a particular problem for umbilicals routed via Lazy-S configurations owing to their relatively low weight and stiffness, and constraining MBR criteria.

This paper considers the applicability of Lazy-S configurations as a solution to modern harsh environment field developments and the evolution in Lazy-S system design to address the design challenges with particular emphasis on the TDP response.
Comparison of Different Equivalent Design Waves With Spectral Analysis
Authors: de Hauteclocque Guillaume , Derbanne Quentin , El-Gharbaoui Amine
Published: August 2013

Design waves are widely used to assess stress in vessels. Compared to a full spectral analysis, this method reduces the number of required structural calculations and is expected to provide similar results. Moreover in a rule context, it allows loading a structural model with a simplified hydrodynamic loading, via explicit formulae for extreme hydrodynamic loads and associated load combination factors (LCF).

In a broad sense, an equivalent design wave (EDW) is a wave on which a selected response is equal to a target value (generally the spectral extreme response). If general practice is to define the EDW as a regular wave, it is possible to define it more realistically; there are also different ways to define heading and period of the EDW which can lead to significantly different results. In this paper the EDW are not restricted to regular waves: response conditioned waves (RCW) and directional response conditioned waves (DRCW) are also investigated. Those waves include more physics and are shown to overcome some of the inconsistencies of the regular wave (Load Combination Factor above 1 for instance).

The different methods are then applied to an FSRU; hydro-structure calculations are carried out, the resulting stress is calculated in more than 2000 relevant elements. The way to select a few design waves among a lot of individual loads from the hydro-dynamic calculation (motion, acceleration, internal loads, pressure) is discussed and finally, the stress computed by the different design waves is compared to the direct spectral calculation.
On Pipeline Lateral Buckling: Lessons Learned and Current Design Challenges
Authors: Maschner Emil A. , Abdalla Basel
Published: August 2013

The subject of lateral buckling design in recent years has by necessity become increasingly more involved as pipeline projects have moved into more difficult environments where there is a need for optimized economic solutions with assured through-life reliability.

The authors have had direct design responsibility and specialist involvement with a large number of projects covering a diverse range of environments, single or PIP systems, variable product characteristics and operating conditions, external applied loading type, and geographical installation limitations. These include shallow and deep water, large thin walled and small thick walled diameter pipes, flat to undulating hard to soft seabed, variable cohesive and non-cohesive surficial soil types and various other project considerations which have impacted on the chosen design solution.

The purpose of this paper will be to highlight aspects of global buckling design associated with reliable in place systems and conversely those aspects associated with integrity risks to the as-laid operational pipelines. A review of past project challenges along with a commentary as to the state of the art at the time gives an opportunity to evaluate risks and challenges being faced on current projects. Particularly, as it seeks to develop ever more cost effective designs with proven robustness but optimized safety margins for the installation and operation of HT/HP pipelines in marginal fields.
A Simple Criterion to Predict Fracture of Offshore Steel Structures in Extremely-Low Cycle Fatigue Region
Authors: Siriwardane S. A. Sudath C. , Ratnayake R. M. Chandima
Published: August 2013

This paper presents a simple criterion to predict the fracture of offshore steel structures due to the interaction effect of ductile fracture and fatigue, which is termed as extremely-low cycle fatigue (ELCF) fracture. The criterion has been obtained from further simplification of available cyclic void growth model (CVGM). The main advantage behind this simplified criterion (i.e. simple criterion) is that it can be easily utilized with commonly available elasto-plastic finite element (FE) packages than the previous CVGM criterion. Initially the simplified ELCF fracture criterion is clearly presented. And the associated ELCF fracture prediction methodology is also indicated. The simplified criterion is then employed to determine ELCF fracture of some structural models. Hence verification of the simplified criterion is confirmed by comparing the results with previous criterion-based estimations. Then the simplified criterion is applied to predict the ELCF fracture of a reduced beam section specimen. Finally, study tends to conclude that the simplified criterion provides reasonable accurate prediction to ELCF fracture of offshore steel structures where magnitude of triaxiality remains relatively constant.
Computational Investigation of Irregular Wave Cancelation Using a Cycloidal Wave Energy Converter
Authors: Fagley Casey P. , Seidel Jürgen J. , Siegel Stefan G.
Published: August 2013

The ability of a Cycloidal Wave Energy Converter (CycWEC) to cancel irregular deep ocean waves is investigated in a time integrated, inviscid potential flow simulation. A CycWEC consists of one or more hydrofoils attached eccentrically to a shaft that is aligned parallel to the incoming waves. The entire device is fully submerged in operation. A Bretschneider spectrum with 40 discrete components is used to model an irregular wave environment in the simulations. A sensor placed up-wave of the CycWEC measures the incoming wave height and provides a signal for the wave state estimator, a non-causal Hilbert transformation, to estimate the instantaneous frequency, phase and amplitude of the irregular wave pattern. A linear control scheme which proportionally controls hydrofoil pitch and compensates for phase delays is adopted. Efficiency for the design Bretschneider spectrum shows more than 99% efficiency, while non-optimum, off design operating conditions still maintain more than 85% efficiency. These results are in agreement with concurrent experimental results obtained at a 1:300 scale.
Experimental Investigation on Element Immersing Process of Immersed Tube Tunnel of Hong Kong-Zhuhai-Macao Bridge
Authors: Peng Sheng , Wu Weiguo , Chen Keqiang , Xiong Aokui , Xia Ziyu
Published: August 2013

Hong Kong-Zhu hai-Macao Bridge, connecting world famous tri-cities in China, will consists of three different construction elements: a man made peninsula, a world’s longest and widest immersed tunnel and a cross-sea bridge. The key point of this megastructure is the construction of the immersed tube tunnel construction. The accuracy of tunnel element positioning directly determines the quality of tunnel construction. In order to study the behavior of elements during its lowering to the sea bed, the scaled model test has carried out in the Key Laboratory of High-speed Ship Engineering of Ministry of Education, Wuhan, China. Experiment was carried out to investigate the motion responses of the tunnel element in the immersion under wave and current actions and the tensions acting on the controlling cables of its immersing system. A concise description of the model wave-current test is carried out, and the variation of motion responses of the tunnel element and cable tensions against wave, current and immersing depth were obtained, which could be a guidance to the construction of the immersed tunnel of Hong Kong-Zhu hai-Macao Bridge.
Dynamics of Heavy Deck Lift-Off From Transportation Barge
Authors: Kanotra Rahul , Aboumalwa Mohamed , Joe-Joe Chellakat , Nair Sajith , Koottungal Vijoy
Published: August 2013

The size of present day offshore topsides are growing rapidly, with large capacity, complex modules being transported and lifted offshore. This increase in size results in offshore lift weights which are near crane capacity of HLVs (heavy lift vessels). The offshore installation operation involves lift-off of heavy modules from a transportation barge moored perpendicular to the stern of the HLV. Previous experiences with lift analyses indicate that most significant hook load occurs while the module is being lifted off the transportation barge. This can be attributed to the fact that the crane vessel, topside and the transportation barge are all dynamically coupled together and during the “lift-off” condition the module experiences upward and downward impulsive forces from the transportation barge, which in turn increase the apparent weight of the module and hence the hook loads. This paper studies the dynamics of heavy deck lift-off from the transportation barge, when the sea fastening from the module has been removed and all three bodies (transportation barge, HLV and Module) are mechanically coupled through slings, lashings and fenders. The effect of various crane line pretensions, wave, current and wind has been investigated and the resulting DAFs (dynamic amplification factors) of the hook loads have been compared. The effect of wind and current on the lift operation has also been investigated. The “lift in air” case has been studied and compared with the “lift off” case. Multi Operational Structural Engineering Simulator (MOSES) has been used to carry out 3D time domain analysis of lift off and lift in air cases. McDermott’s HLV, 300 class transport barge and a topside weight of 1,500MT have been analyzed for the study.
Challenges About Testing, Welding and NDT of CRA Pipelines in Brazilian Pre-Salt
Authors: Zumpano Petrônio , Zanon Genaro , Garmbis Alexandre Galiani , Alkmin Luciano Braga , Richter Manfred Ronald , Oazen Eduardo Valente , Chaves Paulo Nunez , Hippert Eduardo
Published: August 2013

Some new pre-salt fields at Santos Basin in Brazil are located in water depths as deep as 2200m and about 300 km away from the coast. There is variable level of contaminants in the produced fluid, mainly CO2 that affects the material selection of the infield flowlines and risers. Based on these constraints, Petrobras has selected UNS N06625 clad or lined steel linepipes to develop the first fields in Pre-Salt area and also the module 3 of Roncador a post-salt field in Campos Basin. Several challenges have arisen during design, construction and installation of these facilities related to pipeline welding procedures, NDT inspection and Engineering Critical Assessment (ECA). Firstly weld overmatching condition may not be fully achieved due to differences in mechanical properties between UNS 06625 and API X65, and concern increases when reel-lay installation method is chosen. Another welding issue is the maximum interpass temperature of nickel alloys (DNV and PETROBRAS standards limit that to 100°C) and this impacts pipeline installation productivity. Thirdly, back purging characteristics and number of passes protected with purging gases affects the possibility of root oxidation. Also, the inspection of the weld overlay in the pipe end of lined linepipes is other point of great concern. As defect sizing is mandatory for ECA, lined pipes have been designed with a weld overlay length which allows the inspection of the final girth weld by AUT. However, AUT solutions are normally more efficient in rolled or extruded materials than in weld overlaid ones. Additionally, the ECA methodology for both girth welds and weld overlay has complexities that are not usually addressed in a regular ECA for carbon steel pipelines (e.g. internal misalignment of girth welds in risers has stringent requirements because of its effects on fatigue performance and, consequently, the ECA girth weld criteria). Also CRA clad/lined pipelines and risers qualification program may include additional testing when compared with usual carbon steel welding qualification process (namely pitting and intergranular corrosion, full scale fatigue, spooling trials of lined linepipes, segment testing for ECA, and others). Finally, the contribution of clad/lined layer in pipeline design strength is also discussed. This work presents challenges PETROBRAS has faced at design and construction phases of on-going Guaré and Lula-NE pre-salt fields and Roncador field projects, as well as the solutions proposed by the project team in order to overcome the issues raised during project execution.
Underwater Stress Relief and Fatigue Improvement by Ultrasonic Peening
Authors: Kleiman Jacob , Kudryavtsev Yuri , Lugovskoy Alexander
Published: August 2013

A new ultrasonic peening instrument was developed for underwater treatment of welds and welded structures. The Ultrasonic Peening (UP) established itself as a promising process for fatigue life improvement of welded elements and structures. The beneficial effect of UP is obtained through relieving of harmful tensile residual stresses and introducing of compressive residual stresses into surface layers of materials, and through decreasing of stress concentration in weld toe zones and enhancement of mechanical properties of the surface layers of the materials.

In the design of the underwater UP instrument specially selected anti-corrosion materials are used. The underwater UP instrument can be used for treatment of welds at depths up to 30 meters or, if required, with certain modifications, even deeper. Acoustic pump principle is used in the originally developed system for water cooling of the transducer. The developed UP system allows for improvement treatments at four different power levels and is using replaceable working heads that come in various configurations with variable numbers of pins, depending on the application.
Offshore Platform Fluid Structure Interaction Simulation
Authors: Marzban Ali , Lakshmiraju Murthy , Richardson Nigel , Henneke Mike , Wu Guangyu , Vargas Pedro M. , Oakley Owen
Published: August 2013

In this study a one-way coupled fluid-structure interaction (FSI) between ocean waves and a simplified offshore platform deck structure was modeled. The FSI model consists of a Volume of Fluid (VOF) based hydrodynamics model, a structural model and an interface to synchronize data between these two.

A Computational Fluid Dynamics (CFD) analysis was used to capture the breaking wave and impact behavior of the fluid on the structure using commercially available software STAR-CCM+. A 3D Finite Element (FE) model of the platform deck developed in ABAQUS was used to determine the deflection of the structure due to hydrodynamic loads. Nonlinear material behavior was used for all structural parts in the FE model. Transient dynamic structural analysis and CFD analysis were coupled by transferring the CFD-predicted pressure distribution to the structural part in each time step using the co-simulation capabilities of STAR-CCM+ and ABAQUS. The one-way FSI model was applied to investigate the possible physical causes of observed wave damage of an offshore platform deck during a hurricane. It was demonstrated that with proper physical conditions/configurations, the FSI model could reproduce a structural deformation comparable to field measurement and provide valuable insight for forensic analysis.