bluuebunny/crossref_metadata_2025_split huggingface dataset:
Determining Fitness for Service of SCRs and Flowlines With Probabilistic Tools
Authors: Cerkovnik Mark , Saldana David , Yang Tracy 
Published: November 2013

Inspection of deepwater risers for flaws or pits using ILI tools can be challenging. Some lines are designed as “non-piggable”, and it is not unusual for an inspection to be incomplete because of physical constraints. As with any measurement, there will be a degree of error. While deterministic conclusions cannot be reached based on such incomplete data sets, probabilistic methods can be used effectively to make judgments about fitness for service.
Commonly, different sections along a riser or flowline experience different fatigue spectra and extreme loads. Applying the loads from the sections with the highest loading to all flaws/pits can be too conservative. It is useful to employ statistical methods to assess the probability that a large defect occurs in a region with critical loads. These methods are especially useful when ILI data are incomplete or when estimates of damage must be made based on lines in similar corrosion environments.
Properties and parameters other than inspection findings have an element of uncertainty. Fracture toughness, yield stress, and fatigue crack growth rates will be known in terms of mean and standard deviation. Soil properties may be known in terms of upper and lower bound. Likewise, there will be a range of uncertainty about service history and chemical environment. In such cases where fitness for service is based on the interaction of multiple random variables, Monte Carlo methods are appropriate for determining if the probability of failure is sufficiently low to tolerate. In the case of deepwater risers and flowlines where failure could result in loss of containment of hydrocarbons, permissible failure rates are on the order of 1E−5 to 1E−6 per year.
This paper examines a riser and a flowline case study. For each case, a fitness for service analysis is conducted using a Monte Carlo simulation to evaluate the probability of failure based on incomplete ILI data and statistical characterization of other pertinent parameters. The results are compared against the conclusions of deterministic analysis.
Risk and Reliability Centered Maintenance for Maritime Operations in the Arctic: Experience From Fishing
Authors: McGuinness Edgar , Dypvik Tora Gjermstad , Utne Ingrid Bouwer , Holmen Ingunn Marie 
Published: November 2013

The Arctic is a vast area with many future economic possibilities for the oil and gas, shipping and the fishing industries. The climate is harsh, the environment vulnerable, but the potential profits from future expansion in the area are huge. The on-going public debate on the Arctic includes discussions both for and against industrial development in these areas, however the reality is that as resources become scarcer in other parts of the world, Arctic expansion will become inevitable. Therefore adequate preplanning of the activities, understanding of the operational environment and development of barriers against undesired events becomes infinitely more important for sustainable, reliable and safe operation in the future.
The fishing fleet has been operating in the Arctic region for decades and while the safety for the fishers is questionable, it is a matter of resources that drove and will continue to drive this expansion. The IMO’s Polar Code for shipping is now under construction and the fishing fleet will have to comply with this and other regulations for future operations in the Arctic.
This paper focuses on the maintenance and safety management regimes and requirements of the fishing fleet currently operating in the Arctic. With long distances to service and help, and a short operating season, a reliable system is a mandatory requirement for the economic stability of these operations. Mutual benefits may be gained if operational experiences from fishing can be utilized by the oil and gas industry and ship transport when moving their operations into the arctic areas, whereas the fishing fleet can improve their safety performance through closer alignment with those standardized procedures applied in other industries.
Drilling Riser Design and Analysis for Deepwater Applications
Authors: Cheng Yongming , Qi Tao 
Published: November 2013

A riser is a fluid conduit from subsea equipment to surface floating production systems such as spars, TLPs, and semi-submersibles. It is a key component in a drilling and producing system. Drilling risers include the applications in marine drilling (low pressure) and tie-back drilling (high pressure). This paper discusses drilling riser design and analysis for a deepwater application.
This paper first discusses the configuration of marine drilling and tie-back drilling risers. It then presents the drilling riser design procedure and analysis methodology. The riser design and analysis cover the riser tensioner setting, marine operation window, strength and fatigue, etc. A marine drilling riser example is used in the paper to demonstrate the design and analysis for a deepwater application. This paper shows the dynamic strength analysis results for the riser. It then identifies governing locations for the riser design. A tie-back drilling riser example is also provided to illustrate its global dynamic performance. This paper finally discusses the design and analysis challenges of a drilling riser for a deepwater application.
Investigations Into Motion Characteristics of a Multi-Column Type FOWT in Waves and Winds
Authors: Murai Motohiko , Takei Miki , Saeki Hotsuma , Nihei Yasunori , Iijima Kazuhiro , Ikoma Tomoki 
Published: November 2013

Many researches about various type of FOWT have been already carried out by many researchers including the authors of this paper. As a result, we know that each type has own advantages and own disadvantages. On the other hand, in general, because the floating type is different for each project, it has not compared its performance among those projects in the same condition. Therefore, the authors have examined the performance of the various types of FOWT under the same experimental conditions.
In this paper, the performance of the FOWT focusing on Semi-submersible type of multi-column type in particular is reported. First, we examined as design requirements the shape of a column with footing, the distance between the columns and the number and the arrangement of the multi-column. Within it, we investigated the combination of the variables for good performance in waves and winds. We manufactured a 1/100 experiment model which is based on the design requirements and carried out the experiment in waves and winds. Then we discuss the effectiveness of the model using the experimental results and the numerical results.
Non Linearity of Extreme Vertical Bending Moment: Discussion on the Existing Rule Formulation
Authors: Derbanne Quentin , de Hauteclocque Guillaume , Mienahou Therard 
Published: November 2013

The current rule formulation for Vertical Bending Moment is a common formula for all the IACS members. This formula introduces an asymmetry between hogging and sagging bending moment, with a non linear coefficient only depending on the block coefficient. This non linear coefficient is equal to 1.0 for hogging moment (no non linear effect) and is comprised between 1.0 and 1.26 for sagging moment (a maximum of 26% increase for low Cb ships).
Non linear bending moment can be evaluated by non linear seakeeping computations taking into account Froude-Krylov and hydrostatic pressure correction. Extreme bending moment corresponding to a 25 years return period requires very long simulations on a large number of sea states. However some techniques have been developed to shorten the duration of the simulation by defining an equivalent design sea state. It is hence possible to compute in a reasonable time the non linear hogging and sagging moment corresponding to a 25 years return period, and to compare with the rule formulation.
Non linear hogging and sagging coefficients have been computed for a large database of ships, including 19 tankers, 29 bulk carriers, and 9 container-ships, in full load or ballast condition. Results are highly dependent on the ship shape, and are ranging from 0.5 to 1.1 for the hogging moment and from 1.0 to 2.0 for the sagging moment. The difference with the actual rule formulation is shown, and some new formulations are proposed based on ships main particulars, in order to have a better fit with the computation results.
Maximizing Drilling Riser Installation Operability for TLP Top Tensioned Risers
Authors: Campbell Mike , Kaculi Jim , Koska Ryan , Mills Darren 
Published: November 2013

Top tensioned risers (TTRs) are a key component in Dry Tree Tension Leg Platform (TLP) systems. TTRs are used for both production and drilling operations.
The operability of the drilling riser system can be a key factor in the project economics. In addition to the in-place operability, maximizing the weather windows for running and retrieval of the drilling riser system minimizes down time and increases operational flexibility.
This paper presents the approach taken to determine drilling riser installation envelopes. It discusses the solutions evaluated for increasing drilling riser installation envelopes and documents the associated equipment selection and specification.
A CFD Simulation of Near Wall Turbulent Flow in Concentric Annulus
Authors: Rahman Aziz , Rodriguez Corredor Fabio Ernesto , Bizhani Majid , Kuru Ergun 
Published: November 2013

A CFD simulation study was conducted to analyse the near wall turbulence characteristics of water flow through concentric annulus. The continuity and momentum equations were solved by using a commercial CFD package (CFX 14) with the Shear-Stress-Transport (SST) model option. The simulation results were compared to the experimental data obtained by using high resolution Particle Image Velocimetry (PIV) analyses of water flow in a horizontal concentric annulus. A fully developed turbulent flow of water through a horizontal flow loop (ID = 9.5 cm) with concentric annular geometry (inner to outer pipe radius ratio = 0.4) was used for comparison purpose. Reynolds number ranged from 17,500 to 68,500.
Annular velocity profile obtained from simulation study showed good agreement with the experimental data. Near wall velocity profile obtained from CFD simulation followed the universal wall law (u+ = y+) up to y+ = 11. CFD analyses using the SST model resulted a good number of velocity data up to y+ = 11, which is normally a very difficult task to achieve experimentally.
The CFD analyses using SST model is computationally inexpensive and therefore, can be conveniently used for investigating the near wall turbulent characteristics of flow in concentric annulus.
Design, Modelling and Analysis of a Combined Semi-Submersible Floating Wind Turbine and Wave Energy Point-Absorber
Authors: Touzón González Imanol , Ricci Pierpaolo , Sánchez Lara Miren Josune , Pérez Morán Germán , Boscolo Papo Francesco 
Published: November 2013

Floating platforms for offshore wind tend to be very expensive and different solutions have been proposed to increase their cost-effectiveness. One of them involves the combination of offshore wind generation with other forms of ocean renewable energy, as is the subject of the FP7 project Marina Platform. In particular, wave energy from the sea has been investigated since the ’70s and although a few technologies have already reached a pre-commercial stage, their actual economic feasibility can still be questioned so that the possibility of sharing cables, moorings and even the structure with offshore wind turbine is very interesting also from the point of view of wave energy developers.
This paper presents the design, modeling and analysis of a combined concept composed of a semi-submersible platform hosting a single 5 MW wind turbine and a heaving point-absorber consisting of a floating cylinder placed at the geometric center of the platform.
A preliminary design of the concept is carried out by a frequency-domain analysis focused on the definition of the most suitable geometry with the objective of a limited dynamic response of the platform and satisfactory wave power absorption at the same time. It is shown how the requirement of maintaining reduced amplitude on the platform motions imposes the adoption of relatively slender cylinders as point-absorbers.
After a conventional catenary mooring arrangement is assumed and its basic line parameters determined by applying a quasi-static approach, a global coupled time-domain model is built based on the Cummins equation and the use of panel codes (e.g. WAMIT, AQWA) for the computation of the hydrodynamic coefficients. Moorings are modeled as individual catenary lines whereas the dynamics of the wind turbine are modeled by introducing thrust and power curves as function of the motions of the platform, after previous determination with the Blade Element Momentum theory.
The analysis is carried out over a set of operational sea states for different locations around Europe. Through the analysis of power performance, platform and point-absorber motions and mooring tensions, it is shown how the introduction of a Wave Energy Converter (WEC) can occasionally have a positive effect on the whole response of the platform though the significance of its energy contribution is relatively small and additional synergies have to be sought to justify its adoption.
Numerical Simulation of an Oscillating Cylinder at High Reynolds Number
Authors: Mandelli Simone , Muggiasca Sara , Malavasi Stefano 
Published: November 2013

In this work a numerical investigation of the main flow field characteristics around a free oscillating rigid circular cylinder immersed in a turbulent flow is proposed (Re ≈ 5 · 104). The cylinder is characterized by high value of mass ratio and mass damping (m* = 145; ξ = 0.6 ÷ 1.14 · 10−3; m*ξ = 0.1 ÷ 0.25). The numerical results are compared with experimental data obtained in the wind tunnel under very similar fluid dynamic conditions. There are few works in literature that consider both numerical and experimental results under these conditions. This is probably due to the experimental facilities limitations and the computational difficulties correlated to modeling the flow at high Reynolds number. A numerical URANS model was developed through a CFD commercial code using a k–ω SST turbulence model in a 3D domain with the aim of matching the experimental results in the last years in the Politecnico di Milano Wind Tunnel on a suspended oscillating cylinder.
The numerical setup is characterized by the use of the DFBI-Morphing (Dynamic Fluid Body Interaction) model that allows reproducing the body motion in response to fluid forces treating the cylinder as a mass-damping-spring system by introducing spring and damping forces acting on it.
A preliminary check of this numerical setup was provided by a benchmark case involving a simple case of fixed cylinder at the same Reynolds number, where the movements of the cylinder were disabled. The numerical results of this case have been compared with experimental and numerical results reported in literature in terms of Drag and Lift coefficients and Strouhal number at high Reynolds numbers (Re ≈ 5 · 104). After that benchmark, the full setup has been checked by considering specific fluid dynamic conditions out of the lock in region in which the oscillations of the cylinder are negligible.
Finally two points of the cylinder steady state response curve in the lock in region were investigated. The numerical model gave good results in terms of amplitude response of the cylinder and aerodynamic forces in agreement with experimental results.
The analysis of the numerical reconstruction of the flow field evolution are therefore considered to have more information on the vortex shedding mode especially in the transition region between 2S and 2P mode.
Effect of Forming on Behavior of UOE Pipe Material
Authors: Serebrinsky Santiago , Arroyo Fábio , Valdez Martín , Silva Ronaldo 
Published: November 2013

The worldwide share of oil&gas produced from offshore sources is constantly increasing. Accordingly, deep and ultra-deep water projects go to ever increasing depths. Large diameter pipes for this type of projects are often manufactured by the UOE process. After the cold work associated with UOE forming, mechanical properties of pipe material are different from those of the original plate. In particular, the circumferential compression behavior is markedly affected by the Baushcinger effect which develops after the last expansion step, and this is a key property for the resistance to collapse under external pressurization. Standard formulas for the assessment of the collapse pressure pc variedly account for this effect. For instance, DNV OS-F101 penalizes the SMYS of the pipe with a fabrication factor αfab that reduces the pc rating of UOE pipes.
Understanding the effect of deformation history on final material properties becomes desirable for a proper identification of processing strategies. A testing program was developed aimed at evaluating the effect of UOE forming on final transverse compression behavior, as it is relevant for collapse resistance. Work softening (i.e., the Bauschinger effect) and hardening were quantified under a variety of deformation operations.
Second-Order Random Wave Kinematics and Resulting Loads on a Bottom-Fixed Slender Monopile
Authors: Stansberg Carl Trygve , Amundsen Andreas , Fouques Sebastien , Økland Ole David 
Published: November 2013

The importance of including second-order nonlinear random wave kinematics in the numerical prediction of drag-induced shear forces and moments, at various levels on a bottom-fixed slender monopile in 40m water depth, is investigated. A vertical circular cylinder of diameter 0.5m is considered, representing typical dimensions of members in jacket type foundations of offshore wind turbines. The focus is here on the wave loads only, and wind and a propeller are therefore not included in this study. In particular, the main focus is on the effects from second-order random wave kinematics on the structural quasi-static time-varying loads due to drag forces in heavy storm wave conditions. Comparisons are made to the traditional use of Airy waves with various ways of stretching.
An in-house numerical FEM code developed for structural analysis, NIRWANA, is used for this study. Thus one purpose of the present work is also to verify the implementation of the second-order random waves in the code.
The results show significant effects, especially in the wave zone. Extreme crests are around 15%–20% increased, free-surface extreme particle velocities increase by around 30%–40%, while the velocities at levels below MWL are, on the other hand, somewhat reduced. The resulting peak shear forces, and in particular the moments, are thereby increased by typically 50%–100% in the upper parts of the column. At the base the peak shear forces are comparable to the traditional methods, while moments are still somewhat higher. Another effect is the generation of more high-frequency load contributions, which may be important to address further with respect to natural frequencies of such towers.
Numerical Modeling of Wake Effect on Aquaculture Nets
Authors: Endresen Per Christian , Føre Martin , Fredheim Arne , Kristiansen David , Enerhaug Birger 
Published: November 2013

Accurate modeling of drag forces on net cages due to water current is important when designing floating fish farm systems. These drag forces give a major contribution to the total environmental forces on a fish farm, especially mooring line forces. When subjected to current, the net cage will deform. High current velocities can result in large deformations and lead to collapse of the net cage. For circular fish farms with a flexible floating collar, large deformations may induce contact between the weighting system and the net, resulting in abrasion that can cause tearing of the net material and consequently failure that will lead to fish escape.
The motivation for this paper is to obtain a better understanding and more accurate model for drag forces and corresponding deformations of circular net cages due to water current. Calculation of drag forces on a net cage is complicated due to the porous nature of the net, geometry and flexibility of the system. Adding to the complexity is the wake effect, or reduced velocity, behind each individual twine which will have a significant effect on the forces and deformations of the net cage. This wake effect will result in reduced inflow velocity on parts of the net being downstream.
A method for estimating wake effects acting within an aquaculture net structure was developed and implemented in a numerical code taking net deformation into account. Numerical simulations of a cylindrical net cage were compared with experimental results. Comparison between simulations with and without wake effect revealed a reduction in total drag up to 22% when wake effect was applied. Although the model consistently overestimated drag forces on the net cage (average deviation of 25%), simulation results compared well with measurement data, particularly for low current velocities where deviations were as low as 7%. This indicates a consistent wake effect and drag model that produces conservative estimates of drag forces on net cages.
On Safety and Reliability for Platforms That are Unmanned During Severe Storms
Authors: Hagen Øistein , Solland Gunnar 
Published: November 2013

The paper addresses safety and reliability issues for platforms where an unmanning strategy is premised.
The standard NORSOK N-006 recommends how to deal with the specific aspects that engineers meet when assessing existing structures, including life extension. A possible mitigating measure for structures that do not meet today’s structural requirements for environmental loads is to unman the platform during storms. The basis for the unmanning criteria in this standard is that the safety for personnel on a platform that needs to be unmanned during storms is consistent with the safety for personnel on platforms that satisfy structural requirements for manned platforms.
The prevailing metocean conditions at a North Sea location is modeled by a storm statistics approach. The capacity waves according to the codes checks are calculated for a jacket structure and the limiting metocean conditions that comply with the acceptance criterion are established. The expected frequency of unmanning events is determined, and the issue of forecast uncertainty discussed.
The annual maximum wave height distribution for the location is compared with the corresponding distribution that applies when the platform is manned, i.e. for metocean conditions that do not trigger unmanning. The probability of failure for important limit states is calculated on condition that no unmanning is required, and for a platform that satisfies the requirements for manned platforms. The most likely realizations of sea state variables and extreme wave cycle are determined for the different cases.
Parts of the structure may be loaded into the non-linear range and consequently the load-carrying resistance of the structure against future load cycles may be reduced. In such cases it is required to carry out a check of the cyclic capacity of the structure. The statistics for the second highest wave during storm conditions is investigated for unmanning scenarios and for a platform that satisfies the requirements for manned platforms.
It is normally acknowledged that the structural failure probability associated with normal statistical variations is considerably less than the failures that are due to gross errors. The difference in risk due to gross errors between platforms that are operated as unmanned during storms compared to the gross error risk level for manned platforms is discussed.