bluuebunny/crossref_metadata_2025_split huggingface dataset:
Calibration of Partial Safety Factors for Suction Caissons in Connection to Catenary and Taut-Leg Mooring Systems
Authors: Silva-González Francisco L. , Heredia-Zavoni Ernesto , Valle-Molina Celestino , Sánchez-Moreno Jorge , Gilbert Robert B. 
Published: August 2013

A risk and reliability based calibration of partial safety factors for the ultimate limit state of suction caissons subjected to inclined tension loads from floating production systems is presented. The formulation is for the case of normally consolidated clay deposits with undrained loading conditions.
The load capacity analysis is carried out using the plastic limit model proposed by Aubeny et al. [1–3]. A procedure to calibrate the plastic limit model based on finite element numerical results is described. Line tensions from two mooring systems of an FPSO designed for two sites in deep water at the Bay of Campeche, Gulf of Mexico, are used.
A procedure to characterize probabilistically the load capacity of the caisson at mudline is presented. The physical lower limit of the load capacity and soil-chain interaction are taking into account. The mean and dynamic tensions of mooring lines are modeled through response surfaces in terms of uncertain metocean variables describing extreme sea-states. Reliability analyses are performed using FORM and considering both mooring line tensions and load capacity of the soil-caisson system at the mudline, rather than at the padeye. Partial safety factors for the design of caissons in connection to catenary and taut-leg mooring systems are calibrated separately. This is considered to be most appropriate taking into account their differences in terms of relative contributions of the mean and dynamic tension components, failure mechanisms controlling the loading capacity, and lower bound capacity. Calibration of safety factors is performed for a target reliability index equal to 4.2.
Nonlinear Structural Consequence Analysis of Blast Wall Structures Under Hydrocarbon Explosive Loads
Authors: Sohn Jung Min , Kim Byoung Hoon , Paik Jeom Kee , Schleyer Graham 
Published: August 2013

Many accidents that occur on offshore structures, especially explosions, are extremely hazardous. Violent explosions can have serious consequences for health, safety, and the marine environment. The topsides of offshore platforms are the most likely areas to be exposed to hazards such as hydrocarbon explosions. Therefore, profiled barriers are being increasingly used as blast walls in offshore topsides modules to provide a safety barrier for personnel and critical equipment.
The aim of this study is to develop a practical procedure for the nonlinear structural response analysis of corrugated blast walls under explosion. Within the framework of quantified risk assessment and management of offshore installations, more refined computations are required to assess the consequences or hazardous action effects of explosions.
In addition, appropriate guidance will be presented on the use of the finite element numerical tool for the above purpose. The structural response has been computed using commercial nonlinear finite element analysis (NLFEA) code and the results compared with the single degree of freedom (SDOF) method. The relationships between blast pressure and the impulse of corrugated blast walls are developed. This study’s insights into modeling techniques and procedures will be applicable to the explosion risk assessment of offshore structures.
Pipeline Stabilisation Using Pre-Trenching and Sand Backfill
Authors: Chamizo David J. , Campbell Dean R. , Erbirch Carl T. , Jas Eric P. , Cheng Liang 
Published: August 2013

Stabilizing large diameter natural gas pipelines on the seabed against extreme hydrodynamic loading conditions has proven to be challenging in the northwest of Australia. Tropical storms, which affect the area annually between November and April, can generate wave heights exceeding 30 m and on-bottom steady-state currents of 2 m/s or more. Consequently, in shallow water depths, typically less than 40–60 m, subsea pipelines can experience very high hydrodynamic loads, potentially causing significant lateral movement. If the seabed is rugged, or at locations where the pipeline approaches a point of fixity, this can lead to the pipeline suffering mechanical damage, which is undesirable.
In many places on the Northwest Shelf of Australia, there is a layer of minimum 3 m deep marine sediments. The sediments predominantly comprise of relatively stable, fine to medium sized carbonate silts and sands, sometimes with some clay content. Traditionally, in Australia and other parts of the world, post-trenching techniques such as ploughing and jetting have been applied in such areas. These techniques can successfully lower the pipeline into the seabed. However, in many situations on the Northwest Shelf of Australia, post-trenching has had limited success. This has in part been due to the unpredictable levels of cementation of the carbonate sand, which has often resulted in an insufficient trench depth, with the need to implement costly and time consuming remedial works to ensure pipeline stability.
The uncertainties in the success of post-trenching tools lead to the development of the pre-trenching and sand backfill method, which was first applied in Australia in 2003 on a 42-inch diameter natural gas trunkline. This technique has several advantages compared to post-trenching and other conventional pipeline stabilization methods such as rubble mound pipeline covers or gravity anchors.
This paper presents an overview of the pre-trenching and sand backfill method, its design principles, benefits, and risks and opportunities.
Rock Berm Design for Pipeline Stability
Authors: Chamizo David J. , Campbell Dean R. , Jas Eric P. , Ryan Jay R. 
Published: August 2013

Stabilizing large diameter natural gas pipelines on the seabed against extreme hydrodynamic loading conditions has proven to be challenging in the northwest of Australia. Tropical storms, which affect the area annually between November and April, can generate wave heights exceeding 30 m and storm steady state currents of 2 m/s or more. Consequently, in shallow water depths, typically less than 40–60 m, subsea pipelines can be subjected to very high hydrodynamic loads, potentially causing significant lateral movement. To mitigate the risk of the pipeline suffering mechanical damage due to excessive lateral movement, quarried and graded rock is often dumped over the pipeline as a secondary stabilization solution.
In order to satisfy functional requirements, the rock berm must comprise of a sufficiently large rock grading size and berm volume to withstand the design hydrodynamic loading such that the pipeline cannot break out of the berm. The design of rock berms for pipeline secondary stabilization has traditionally followed a deterministic approach that uses empirical equations for preliminary rock sizing, followed by small-scale physical modeling for design verification and optimization. Whilst the traditional approach can be effective in producing a robust rock berm design, opportunities for further optimization are inhibited by a lack of available data and an imperfect understanding of the failure mechanisms.
This paper presents an overview of an improved approach for rock berm design optimization. A general overview of rock berms, the design principles, benefits and risks are also presented.
Comparison of Design Wave Approach and Short Term Approach With Increased Wave Height in the Evaluation of Whipping Induced Bending Moment
Authors: Derbanne Quentin , Bigot Fabien , de Hauteclocque Guillaume 
Published: August 2013

The evaluation of extreme bending moment corresponding to a 25 years return period requires very long simulations on a large number of sea states. This long term analysis is easy to do with a linear model of the ship response, but is impractical when using a time consuming model including non linear and slamming loads. In that case some simplified methods need to be applied. These methods are often based on Equivalent Design Waves (EDW) which are calibrated on the extreme linear value.
The general practice is to define the EDW as a regular wave. A very simple method is to compute the non linear bending moment applying the pressure correction on the hull without recomputing the ship motions. A better method is to recompute in time domain the non linear ship response on this Design Wave. It is even possible to define a more realistic Design Wave, taking into account the frequency and directional content of the sea states used in the long term analysis: those waves are called Response Conditioned Wave and Directional Response Conditioned Waves.
The different methods are applied to an Ultra Large Container Ship (ULCS). Hydro-structure calculations are carried out on a severe design sea state, taking into account Froude-Krylov pressure correction, slamming forces and whipping response. Results of a very long computation are compared to the results of the Design Wave approaches.
Another method is proposed to compute very rare events. It is based on an artificial increase of the significant wave height of the sea state, and the assumption of the independence of the non linear effects to the significant wave height. Using this method it is possible, with a simulation of only a few hours, to predict a very rare short term event, corresponding to a very long return period. The results are compared to the Design Wave results and appear to be much more precise.
Techniques for Predicting Tensile Armour Buckling and Fatigue in Deep Water Flexible Pipes
Authors: Sævik Svein , Thorsen Mats J. 
Published: August 2013

Free hanging deep water flexible risers are associated with high static top tension. In addition comes significant dynamic tension due to the tangential drag forces mobilised along the riser due to floater motions and wave loads. At the upper end fitting where conditions of direct metallic contact between tensile armours might occur, this may result in the fretting fatigue failure mode. This mechanism may be additionally triggered by the increase in longitudinal stress resulting from local bending at the end fitting fixation.
At the touch down point, the pipe cross-section is exposed to high external pressures resulting in true wall compression possibly initiating local buckling modes in the tensile armour wires. The buckling process may be initiated by cyclic bending effects leading to a gradual reduction of each tendon’s capacity resulting in excessive transverse displacements and cross-section failure.
The present paper presents a finite element formulation and analytical models addressing both of the above topics. A case study is further carried out to document the performance of the FE model and to investigate effects related to the transverse bending stress at the end fitting and under which conditions one single armour tendon will fail in different buckling modes.
A Nonlinear Numerical Algorithm for Time-Domain Hydrodynamic Simulations of Vessel Motions in the Presence of Waves
Authors: Pasquetti Eduardo , Coelho Luiz Cristóvão G. , Neves Marcelo A. S. , Oliveira Mauro C. , Esperança Paulo T. T. , Rodríguez Claudio A. , Celis Miguel Angel , Polo Julio Cesar F. 
Published: August 2013

Linear approaches have been traditionally employed to simulate the dynamic behavior of floating vessels and its interaction with regular or irregular waves. Some difficulties arise when large waves and vessel motions occur. Under these circumstances, the linear assumptions to compute the restoring and wave forces, which are computed on the mean position of body and water surface, are not capable of accurately representing the physics of the interactions between waves and vessels.
Hydrostatic analysis of generic hull forms has already been implemented with a geometrical face representation of the hull and also internal ballast and oil tanks [1]. With the goal of improving the modeling the non-linear computation of hydrostatic in waves (at the instantaneous free surface) is implemented, thus using a generic geometric modeling of the hull to perform hydrodynamic simulations of vessel motions in the presence of waves. Additionally, for the computation of the instantaneous non-linear Froude-Krylov force (6 DOF time-domain model) the contribution of each geometrical face to the global Froude-Krylov force is calculated at the exact relative position of the vessel and the incident waves. After computing the relative position of each face, possibly being cut at the free surface, the pressure at the wetted face centers determines the contribution to the integral calculation.
The paper presents the main aspects of the proposed methodology and highlights its capabilities and differences with respect to the linear approach. Complementarily, comparisons with model experiments are discussed.
Grid Impact of a Wave Farm on its Local Network: Analysis of Voltage and Flicker Levels
Authors: Blavette Anne , O’Sullivan Dara L. , Alcorn Ray , Lewis Anthony W. , Egan Michael G. 
Published: August 2013

Most oscillating wave energy converters without significant amounts of energy storage capacity generate significant electrical power fluctuations in the range of seconds. Because of these fluctuations, a wave farm may have a negative impact on the power quality of the local grid to which it is connected. Hence, the impact of these devices on both distribution and transmission networks needs to be well understood, before large scale wave farms can be allowed to connect to the grid.
This paper details a case study on the impact of a wave farm on the distribution grid around the national wave test site of Ireland. The electrical power output of the oscillating water column (OWC) wave energy converters was derived from experimental time series produced in the context of the FP7 project “CORES”. The results presented in this paper consider voltage fluctuation levels and flicker levels for a typical time series. Simulations were performed using DIgSILENT simulation tool “PowerFactory”.
Three-Dimensional Pushover Analysis of a Jack-Up Platform
Authors: Cheng Ning , Kimiaei Mehrdad , Cassidy Mark J. 
Published: August 2013

Jack-ups, as the name indicates, are self-elevating units consisting of a floatable hull and, usually, three truss work or circular legs. As a mobile structure, jack-ups are mainly utilized for oil and gas exploration and maintenance purposes in shallow to medium water (up to 120 meters), though they have recently seen application in the construction of offshore wind energy infrastructure.
The use of the finite element method for structural analyses of jack-ups is a common practice. However, most jack-up models remain elastic with the yielding of structural members or even the soil around the spudcan not accounted for. This paper describes the development of a comprehensive and integrated elasto-plastic jack-up model in ABAQUS [1]. This model is representative of a modern jack-up structure, and it can capture geometrical nonlinearities and plastic behaviour of the structural and soil materials.
In this study, the discretisation of the structural elements, the choice of elements, the elasto-plastic behaviour of the material, and the mesh generation are described. Numerical results of a series of static pushover analyses for this sophisticated model under extreme loads are presented. The sensitivity of the results to the structural configurations is discussed. For instance, the choice of sectional properties of the chord member and the assumption of the behaviour of the spudcan (jack-up foundation)-soil interaction are shown to be critical to the prediction of the ultimate strength of the platform and the progressive failure mechanism.
In conclusion, generic issues associated with static pushover analyses of jack-ups are discussed and possible numerical solutions are proposed.
Collision Consequence Assessment of ROPAX Vessels Operating in the Baltic Sea
Authors: Tabri Kristjan , Ehlers Sören , Kõrgesaar Mihkel , Ståhlberg Kaarle , Heinvee Martin 
Published: August 2013

A Ship collision accident represents a daily threat for vessels operating in dense traffic zones. The collision consequences may include loss of life or severe injuries if passengers are on board. The latter would be the case for ROPAX vessels, which are fairly dominant in the Baltic Sea connecting various member states. Furthermore, their routes tend to be in cross-traffic with the cargo vessels travelling through the full extent of the Baltic Sea. Therefore, it is of utmost importance to be able to assess the collision consequences for ROPAX vessels operating in the Baltic Sea with sufficient accuracy. This will result in an overview of possible damage scenarios for the actual traffic situation at a given location. As an example location the dense cross traffic between Helsinki and Tallinn will be analyzed and discussed.
The analysis procedure combines three steps: (1) determination of possible accidental scenarios based on traffic statistics; (2) assessment of the structural resistance of the colliding ship and (3) the evaluation of selected accidental scenarios using a time-efficient semi-analytical approach. The level of structural resistance of the chosen ships is assessed in a quasi-static manner using finite element method. This information is the basis for the calibration of a semi-analytical collision simulation model used to simulate large number of the accidental scenarios typical to the selected location. The presented results will be limited to the initial choice between vessels and dimensions, respectively masses, but the procedure can easily be extended to cover a vast amount of colliding vessels. However, the actual collision risk can be obtained using the presented results if the traffic along the vessels route is known.
Analyses of Different FE Models for HP/HT-Pipeline Walking With Sliding End Structures
Authors: Castelo Adriano , Galgoul Nelson Szilard 
Published: August 2013

Non-buried subsea pipelines subjected to high internal pressures and high operational temperatures (HP/HT) might experience significant axial expansion. If this movement is restrained by an end structure, considerably high loads can be imposed to the system. Sliding foundations have been used to minimize this effect, allowing free end displacements.
Regarding the aforementioned loads, the thermo-mechanical behavior of HP/HT pipelines interacts with the end restraints in a complex manner. Axial displacements can accumulate over the operational cycles, in a phenomenon known as “pipeline walking”. If the sliding foundation design does not account for these accumulated displacements, axial loads (not considered in the pipeline design) might be imposed. As a result, the overall thermo-mechanical behavior in terms of lateral buckling and walking can change significantly.
Two recently published papers present the results of different analysis methodologies for the same structure. The corresponding analyses were performed using two different tools: (1) a non-linear three-dimensional finite element model considering pipe-soil interaction with full 3D seabed bathymetry and (2) a simplified one-dimensional model published in OMAE 2011.
In both cases, the limited sliding range was imposed to the model ends. Both calculation tools show similar overall results of pipeline global behavior, but the results of the end reaction after a few operational cycles are somewhat different.
Stimulated by these recently published papers, which present the results of different performed finite element analyses; this paper was developed to investigate the same problem, but now starting off with a third software, and rerunning the two previous analyses in the same software and adding an intermediate modeling level.
Optimisation of Heat Pressure Welding of Steel Wire in Flexible Riser Manufacture, Applying Taguchi Design-of-Experiment Approaches
Authors: Rafferty John G. 
Published: August 2013

The safety, quality and overall integrity of flexible risers has a high dependence on the robustness of joining processes used in their manufacture. One such process used in this industry is the heat–pressure welding process, used in the joining of high tensile steel wires.
The optimisation of such welding processes now demands that a statistically–valid and systematic approach be taken. The application of Taguchi methodology to the welding of high tensile steel wires described in this paper is a relatively new departure for Wellstream Flexibles. This paper describes the approaches taken to optimise the heat pressure welding of new steel grades in this demanding application, and the subsequent confirmation of the optimised parameters in real–world environments.
Quality response factors are defined and analysed for welds in a range of carbon steel wire materials, leading to the subsequent optimisation of target quality for the manufacture of flexible riser pipe.
A Discussion of Practical Aspects of Reeled Flowline Installation
Authors: Manouchehri Soheil 
Published: August 2013

Reeling is a fast, reliable and cost effective method for installing subsea flowline systems up to 20 inch in diameter. The individual flowline joints are lined up and welded together onshore to make long stalks of pipe before being spooled onto the large reels of reel lay vessels. On arrival in the field offshore, it is spooled off, straightened and laid on the seabed up to 10 times faster than conventional S-lay or J-lay methods. The ability to carry out the fabrication and welding onshore, off-line from the vessel critical path, allows very high quality welding and coating to be achieved.
Over the last few years, it is evident that the engineering fundamentals, mechanics and cost effectiveness of the reeling process are now well understood within different quarters of the offshore industry as many major pipelaying Contractors own, or are planning to own, a reel lay vessel. What is apparently missing, however, is the implications and practical aspects of the reeling process when it comes to implementation during project execution.
This paper reviews the engineering fundamentals of the reeling process first and then discusses the practical aspects and applications of reeling mechanics from spoolbase fabrication to spooling-on process up to the offshore campaign and spooling-off process and subsea installation.
Lateral Stability of Umbilical in Intermittent Rock-Berms
Authors: Hoff Ronny , Asklund Per Olav 
Published: August 2013

The most common ways to ensure stability of umbilicals are post-lay trenching and rock-dumping. For a number of reasons, exposed sections of the umbilical on seabed may sometimes be part of the design, e.g. as a temporary condition prior to finalizing intervention measures. Light umbilicals in shallow waters may be subject to hydrodynamic forces resulting in continuing dynamic motions of the exposed sections. If the sea state is sufficiently severe, the umbilical may experience a break-out effect and gradually displace out of the rock-berm over time. Such a gradual degradation of effective rock-berm length will increase the projected drag area of the umbilical. This will in turn render the system susceptible for continued break-out at less severe sea states. The potential consequences of rock-berm failure are damage to the umbilical as well as other assets in close proximity.
This paper presents an approach to evaluate the required length of rock-berm to avoid initiation of the break-out effect. A dynamic FE model is established, using time series of water particle velocities for load calculations. The time series correspond to full 3 hr sea states of irregular waves for a range of significant wave heights. Non-linear lateral resistance curves are applied for the sections of umbilical within a rock-berm, including the hysteretic effect of displacement. The ambition of this paper is to facilitate evaluation of intervention measures for the benefit of the industry, providing a design methodology in accordance with the DNV rules system.