bluuebunny/crossref_metadata_2025_split huggingface dataset:
Simplified Approaches to Modeling of Lateral Wire Buckling in the Tensile Armour of Flexible Pipes
Authors: Østergaard Niels H. , Lyckegaard Anders , Andreasen Jens H. 
Published: August 2013

In the present paper, simplifications of methods developed for modeling of lateral wire buckling in the tensile armour layers of flexible pipes are proposed. Lateral wire buckling may occur during pipe laying in ultra-deep waters. In this scenario a flexible pipe is subjected to repeated bending and axial compression due to hydrostatic pressure on the end cap of an empty pipe. If the outer sheath is breached, these loads may cause wire slippage towards states in which the load carrying ability is reduced and wire buckling in the circumferential pipe direction occurs. This leads to characteristic deformation patterns, which may compromise the structural integrity of the entire pipe structure. On the other hand, these loads may cause overstressing of the wires, if the outer sheath is intact.
Simplifications of established models for calculation of the load carrying ability are in the present context proposed in a manner, by which the effect of adjacent pipe layers on the postbuckled response can be estimated. The simplifications enables significant reduction of the computational time, which is necessary to calculate the load carrying ability of a given pipe structure.
Forced Motion Experiments With Measured Motions From Flexible Beam Tests Under Uniform and Sheared Flows
Authors: Yin Decao , Larsen Carl M. 
Published: August 2013

Hydrodynamic forces on a cylinder under realistic combinations of in-line (IL) and cross-flow (CF) vortex induced vibrations (VIV) have been investigated.
Signals of strain gauges and accelerometers from the Norwegian Deepwater Programme (NDP) tests with a long, slender beam were used to identify cross section orbits. 19 cross sections almost evenly distributed along the pipe were selected, and their motions were applied in controlled motion experiments with a rigid cylinder. Dimensionless parameters like Reynolds number and non-dimensional frequency were identical for the two sets of experiments.
Comparison between hydrodynamic coefficients found from forced motion tests with observed motion time histories and periodic approximations are presented. Force histories are also investigated in detail.
Orbit types for combined IL and CF VIV are categorized based on relative amplitude and phase, and it is shown that IL motions exhibit chaotic character more easily than CF. Amplitude modulation is observed frequently.
Cases where cross section motions are close to periodic have similar hydrodynamic forces as for periodic motion, implying that periodic forced motion tests are relevant to get valid force information. Many cases have amplitude modulated IL motions, while CF motions are quasi-steady. In such cases, IL amplitude modulation can cause abrupt change of IL forces and also 3rd order CF forces, which can accumulate large fatigue damage. When both IL and CF motions are chaotic, the force-motion relationship is impossible to describe by constant coefficients.
Analysis of the Creep Behaviour of the Polymer Barrier Layer in Unbonded Flexible Pipes Under Different Fluid Temperatures
Authors: Shen Yijun , Zhao Jian , Tan Zhimin , Sheldrake Terry 
Published: August 2013

This paper discusses the influence of different fluid temperatures on the creep behaviour of the polymer barrier inside unbonded flexible pipes. The creep behaviour of the polymer material is generally time-dependent and associated with larger, nonlinear deformation. Excessive creep deformation may lead to structural failure, due to the over-reduction of the barrier layer thickness, and is therefore an important design consideration in ensuring the structural integrity of this layer.
Creep behaviour in polymer material is complex, as it is governed by a number of variables, such as the stress/strain state, temperature, and pressure for example. This paper deals with the influence of different fluid temperatures on the creep behaviour of the polymer barrier layer under pipe design pressures, particularly in high temperature fluid transportation pipelines for deep or ultra-deep sea applications.
The analysis model was established using commercial finite element software ANSYS, where an implicit time hardening creep model, based on the Maxwell viscoelastic model, was selected to represent the creep behaviour of the polymer materials. The coefficients of the implemented polymer material gap span creep model are calibrated to represent the worst case of the small-scale sample gap span creep tests performed in-house.
A comparison is made between the simulation results of the calibrated gap span creep model and the corresponding small-scale creep test measurements. The experimental test results and the finite element modelling results show good correlation. This demonstrates that the creep model predictions are conservative for the polymer material of the barrier layer inside an unbonded flexible pipe.
Residual Stress Management in Welding: Residual Stress Measurement and Improvement Treatments
Authors: Kleiman Jacob , Kudryavtsev Yuri 
Published: August 2013

Residual stress (RS) can significantly affect engineering properties of materials and structural components, notably fatigue life, distortion, dimensional stability, corrosion resistance etc. Residual stresses play an exceptionally significant role in fatigue of welded elements. The influence of residual stresses on the multi-cycle fatigue life of butt and fillet welds can be compared with the effects of stress concentration. Even more significant are the effects of residual stresses on the fatigue life of welded elements in the case of relieving harmful tensile residual stresses and introducing beneficial compressive residual stresses in the weld toe zones.
Residual stress management is a concept that addresses major aspects of residual stresses in welds and welded structures. According to the concept three major stages, i.e. RS determination, RS analysis and RS redistribution are considered and evaluated, either experimentally or theoretically to achieve the optimum performance of welded structures.
All three stages as well as a number of new engineering tools such as ultrasonic computerized complex for residual stress measurement, UltraMARS, software for analysis of the effect of residual stresses on the fatigue life of welded elements and new technology and, based on it, compact system for beneficial redistribution of residual stresses by ultrasonic peening, UltraPeen will be discussed. Examples of industrial applications of the developed engineering tools for residual stress analysis and fatigue life improvement of welded elements and structures will be given.
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.
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.
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.
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.
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.