bluuebunny/crossref_metadata_2025_split huggingface dataset:
Carcass Tear Out Load Model for Multi-Layer Pressure Sheath Risers
Authors: Kristensen Claus Egebjerg , Muren Jan , Skeie Geir , Skjerve Håvard , Sødahl Nils 
Published: September 2014

Recent failures of multi-layer pressure sheath risers have shown that the carcass may fail in the top termination due to excessive axial loads. This is a new failure mode for flexible risers, recently presented by the authors in more general terms. The present paper explains details of the established load model and the validation against mid-scale tests, risers failed during operation, and operating risers close to failure by this new mode. The key driver in the model is the temperature contraction of pressure sheath layers. Also influenced by changes in polymer properties over the operational history, temperature and time is explained. Other contributing factors in the load model are gravity-component and bore pressure.
The prediction model for the carcass loads are developed during Statoils investigation in 2011–12. The model is regarded representative for 20% of the most exposed risers. Several of the input parameters are uncertain and a Monte Carlo simulation approach is selected to study the variability and predict the probability of failure, given that radial contact pressure is sufficiently low.
The approach adopted in the model may be applicable to other risers where polymers and steel components act together, and in such circumstances act as a guide for alternative model developments.
Non-Linear Dynamics of Parametric Roll of Container Ship in Irregular Seas
Authors: Somayajula Abhilash S. , Falzarano Jeffrey M. 
Published: September 2014

Parametric motion is the phenomenon where a structure is excited into large amplitude motion even when there is no direct excitation. A well-known example of this type of motion is the parametric roll of ships in head or following seas. Parametric roll of container ships in head seas is relatively a new problem which has gained much importance after the catastrophic incidence of APL China in 1998. Many studies have investigated this phenomenon in the case of a ship being excited in regular waves. However, ships do not encounter regular waves in the actual ocean. So, it is imperative to study the importance of parametric roll in irregular seas.
In this paper the analysis of roll equation of motion is performed by nonlinear modeling. The problem of parametric roll is approached as a non-linear dynamics problem with due consideration to nonlinear time varying hydrostatics as well as the nonlinear damping. A nonlinear damping model is used to approximate the actual viscous damping in the system. The variation of the roll righting arm with time has been modeled using a Volterra series representation which includes the hydrostatic non-linearity.
Various realizations of the roll motion have been simulated and analyzed to study the ergodic behavior of the phenomenon. The paper also discusses future ideas of how to analyze parametric roll in irregular seaways.
Study of Bending Capacity of an HPHT CRA-Lined Seamless Pipeline
Authors: Gil Cyprian , Tørnes Knut , Damsleth Per 
Published: September 2014

A study has been performed to better understand ultimate bending moment and strain capacities of pipelines in relation to criteria defined in the design codes. An 18″ HPHT flowline was designed to undergo global buckling on uneven seabed and to resist trawl gear interference. The high temperature (155 degC) and pressure (300 bar) posed considerable design challenges for material selection and design criteria. A CRA-lined X60 CMn pipeline was selected for the project. The pipeline was of seamless manufacture for which the stress/strain characteristics are subject to the effect of Lüders bands. The DNV-OS-F101 code covers a wide range of D/t but does not specifically address Lüder’s material behaviour which could significantly reduce the bending moment capacity of pipe.
The global buckling and trawl pull-over FE analysis results indicated the pipe was highly utilized, requiring excessive amounts of seabed intervention at great cost to meet the DNV LCC criteria. Detailed FE simulation of limit states for local buckling and strain localization of a 3D solid element pipe model was performed, with both Roundhouse and Lüders material properties, to investigate pipe capacity in relation to that stipulated by the design codes. The pipe moment capacity was established by obtaining the moment curvature relationship by bending the local pipe section subject to internal pressure until the maximum resistance was reached. Imperfections were introduced to initiate local buckling at the desired location. To determine strain concentration factors and strain localization, the effects of thickness changes and weld misalignment were also studied.
The DNV OS-F101 LCC moment criterion formulation computes a decreasing moment capacity for increasing internal pressure. It has been suggested in the literature that this is correct for higher D/t but the criterion may be conservative for pipes with lower D/t. The combination of Lüders material with low D/t is not specifically addressed by any design code. Clarification of these aspects will provide a better understanding of the risk of failure for highly utilized seamless pipelines and allow for modified design criteria that will reduce seabed intervention costs.
The results of the study showed that a higher bending moment criterion and associated strain criterion could be adopted for the design that allows for the higher initial strain caused by Lüder’s plateau. The ultimate bending moment capacity of low D/t pipe with Lüder’s material was found to be similar to that of Roundhouse material due to work hardening. In addition, it was demonstrated that the potential strength of the CRA liner could enhance the moment capacity of the seamless pipe.
Detecting Stationary Intervals for Random Waves Using Time Series Clustering
Authors: Euán Carolina , Ortega Joaquín , Alvarez-Esteban Pedro C. 
Published: September 2014

The problem of detecting changes in the state of the sea is very important for the analysis and determination of wave climate in a given location. Wave measurements are frequently statistically analyzed as a time series, and segmentation algorithms developed in this context are used to determine change-points. However, most methods found in the literature consider the case of instantaneous changes in the time series, which is not usually the case for sea waves, where changes take a certain time interval to occur.
We propose a new segmentation method that allows for the presence of transition intervals between successive stationary periods, and is based on the analysis of distances of normalized spectra to detect clusters in the time series. The series is divided into 30-minutes intervals and the spectral density is estimated for each one. The normalized spectra are compared using the Total Variation distance and a hierarchical clustering method is applied to the distance matrix. The information obtained from the clustering algorithm is used to classify the intervals as belonging to a stationary or a transition period We present simulation studies to validate the method and examples of applications to real data.
Numerical Calculation of Residual Stress Corrected J-Integral Using ABAQUS
Authors: Zhu Xian-Kui 
Published: September 2014

Residual stresses exist in welded structures due to thermal stresses. Without temperature change, large plastic deformation can result in “cold” residual stresses in a wrinkle or dent in a metallic pipe. For a crack in residual stress field, residual stresses might have strong effect on fracture parameter, the J-integral. In order to ensure its path-independence, different correction methods have been developed in consideration of residual stress effect. Recently, the finite element commercial software ABAQUS adopted one of the correction methods, and is able to calculate the residual stress corrected J-integral.
A brief review is first given to the J-integral definition, the conditions of path-independence or path-dependence, and the modifications to consider the residual stress effect. A modified single edge-notched bend (SENB) specimen is then used, and a numerical procedure is developed for ABAQUS to evaluate the path-independence of the residual stress corrected J-integral. Detailed elastic-plastic finite element analyses are performed for the SENB specimen in three-point bending. The residual stress field, crack-tip stress field, and J-integral with and without consideration of residual stresses are discussed.
Modeling the Dynamic Lateral Buckling Response of Subsea Pipelines Using Rate-Dependent Seabed Friction
Authors: Westgate Zack , Chee Kin Yin , Walker Alastair 
Published: September 2014

As subsea pipeline installation methods become increasingly sophisticated through use of increased vessel power and advanced stability and positioning controls, pipelines are likely to exhibit lower levels of horizontal out-of-straightness on the seabed than currently considered to occur during the lay process. This has resulted in an increased tendency for the problematic phenomenon of snap-buckling to occur as part of the controlled lateral buckling design.
A key parameter affecting the pipeline response during lateral buckling is the friction between the pipeline and the seabed, which is strongly influenced by the rate of pipe displacement. Under stable buckle formation, the relatively slow rate of pipe displacement is more predictable and leads to acceptable strains in the pipeline. During the formation of less stable snap-through buckles, the rate of pipe displacement can mobilize a wide range in friction factors that can cause high strains in the pipeline. Quasi-static methods cannot model the dynamic transition between a high friction (drained) response and a low friction (undrained) response. To circumvent this problem in design, a fully dynamic finite element approach is required which captures the rate-dependent frictional response.
This paper presents the results of a series of FE analyses that illustrate how the changing seabed friction affects the lateral buckling response of typical subsea pipelines. A contractile seabed is modeled, chosen to capture the general case where high values of slow drained friction are followed by low values of fast undrained friction, leading to changes in the buckle shapes compared to those obtained from static buckle modeling. The results are used to examine the conditions under which dynamic buckle analysis should be used and the effects of dynamic pipeline response on the levels of strain and deformation induced in buckles.
Motion of a Large Disconnectable Buoy Within FPSO Turret Moon-Pool
Authors: Bian Sean , Leverette Steve 
Published: September 2014

The disconnectable buoy turret mooring (BTM) for an FPSO has been a proven technology for areas where hurricane and seasonal cyclones are predominant, or are subject to ice features which need to be avoided. With the requirements of large buoy payload from deep water moorings and heavy risers, the disconnectable buoy size can be substantial. Recent projects are considering buoy net displacements well above 5000Te. The increased buoy size imposes large inertia loads on the supporting structure and mechanical connectors when connected, and possibly more so on the structural integrity and winching system during disconnect and reconnect operations. In order to provide structure design loads as well as to estimate safe operational windows and procedures, it is desirable to understand the physical properties of 2-body motions when the buoy and ship are close enough to have significant interactions.
This paper focuses on the hydrodynamic and structural (Winch, Mooring/riser, Fender/bumper etc.) interactions with the buoy operating in close proximity to the turret. Since the readily available offshore engineering tools have limitations to deal with close body hydro-interaction, particularly with the presence of moon-pool resonances, rational approximations are derived for hydrodynamic forces during pull-in and disconnection of the buoy. To analyze fully coupled motions and loads in combined environmental conditions, a typical diffraction/convolution based numerical tool (AQWA) is extended by a custom defined external force function. This analysis allows simulating the real time motions during disconnect, reconnect, or at suspended elevations. Various findings from dedicated model tests and analyses are presented and discussed with implications for configuring and operating the disconnectable buoy system.
Pipe Soil Interaction During Cyclic Buckling: The Importance of Site-Specific Seabed Properties
Authors: Borges Rodriguez A. , Draper S. , Boylan N. P. , Begaj L. , Bransby M. F. 
Published: September 2014

Knowledge of how an unburied pipeline interacts with the seabed during operational buckling is critical both to check the fatigue life of a pipeline in the buckling zone and to make accurate predictions of the pipeline end-expansions and walking. This paper explains how site-specific seabed conditions affect pipe-soil interaction (PSI) for buckling pipelines during their operational life.
The paper first demonstrates that for many soil conditions, cyclic PSI models that only consider the ‘berm push’ resistance fail to capture all the key elements of the pipeline-seabed interaction during cyclic buckling. An additional mechanism associated with the changing pipeline trajectory which develops after many pipeline lateral movements (‘sweeps’) is identified. For some soil and pipeline conditions this second mechanism provides the main component of the seabed resistance after many operational cycles. Appropriate analysis methodologies are discussed which allow the ‘berm-push’ and trajectory mechanisms to be considered in light of soil conditions and pipeline input conditions.
Secondly, published design approaches to assess cyclic PSI during buckling have typically assumed that the seabed around pipelines is not mobile (i.e. unscourable). However, in some situations, the combination of pipeline geometry, seabed properties and metocean conditions may lead to seabed scour around the pipeline and surrounding soil berms. This may therefore affect how the lateral soil resistance develops during the operational lifetime of a pipeline and should be considered in design. The paper discusses this issue, presenting results from CFD scour analyses of a particular berm geometry for different metocean conditions. The implications of berm scour on pipe-soil interaction for this geometry is explained.
Norwegian Work on Search and Rescue in Barents Sea
Authors: Dyrkoren Erik , Berg Tor Einar 
Published: September 2014

Increased shipping and offshore activities in the Barents Sea need improved emergency response capability in Norway and Russia. In both countries there are several projects and initiatives that aim towards mitigating the consequences from small accidents and larger catastrophes, some coordinated across borders, others not.
In this paper we aim towards giving an overview of the current and near future state of emergency response in the Barents Sea. First we describe the emergency response preparedness that is fully operational today. Then we give a brief description of operations and activities we see today and in the foreseen future, and discuss types of challenges and risks associated with them in this particular environment. Using this as a background, we look on Norway’s ambitions for future search and rescue preparedness in the Norwegian Arctic waters and the ways emerging technologies can improve emergency response operations.
Finally we give some recommendations on what needs to be done by Norway, Russia and the industrial operators in order to achieve an improved level of emergency response preparedness.
Implementing Nonlinear Buoyancy and Excitation Forces in the WEC-Sim Wave Energy Converter Modeling Tool
Authors: Lawson Michael , Yu Yi-Hsiang , Nelessen Adam , Ruehl Kelley , Michelen Carlos 
Published: September 2014

Wave energy converters (WECs) are commonly designed and analyzed using numerical models that combine multibody dynamics with hydrodynamic models based on the Cummins equation and linearized hydrodynamic coefficients. These modeling methods are attractive design tools because they are computationally inexpensive and do not require the use of high-performance computing resources necessitated by high-fidelity methods, such as Navier-Stokes computational fluid dynamics. Modeling hydrodynamics using linear coefficients assumes that the device undergoes small motions and that the wetted surface area of the devices is approximately constant. WEC devices, however, are typically designed to undergo large motions to maximize power extraction, calling into question the validity of assuming that linear hydrodynamic models accurately capture the relevant fluid-structure interactions.
In this paper, we study how calculating buoyancy and Froude-Krylov forces from the instantaneous position of a WEC device changes WEC simulation results compared to simulations that use linear hydrodynamic coefficients. First, we describe the WEC-Sim tool used to perform simulations and how the ability to model instantaneous forces was incorporated into WEC-Sim. We then use a simplified one-body WEC device to validate the model and to demonstrate how accounting for these instantaneously calculated forces affects the accuracy of simulation results, such as device motions, hydrodynamic forces, and power generation.
Other aspects of WEC-Sim code development and verification are presented in a companion paper [1] that is also being presented at OMAE2014.
Insights in the Application of Structural Reliability Analysis (SRA) for Challenging Pipeline Lateral Buckling Design
Authors: Gerginov Elena , Rathbone Andrew , Sullivan Chris , Griffiths Terry 
Published: September 2014

Lateral buckling of pipelines is influenced by, and sensitive to, a complex combination of factors associated with considerable uncertainty. Key elements such as pipe to soil friction, vertical and horizontal imperfections can vary significantly not only along sections of the same pipeline, but at the same location over time. These factors carry a probabilistic likelihood of occurrence that results in a probabilistic distribution of buckle formation forces and locations, as well as post buckle loads, as described by Rathbone et. al. (2008).
To effectively capture all possible combinations of inputs and results, and thus gain a full understanding of potential buckle behaviour and interaction, would require many individual finite element analyses to be undertaken, which is not viable. The paper describes new insights into challenging pipeline lateral buckling design gained through use of a highly adaptable Structural Reliability Analysis (SRA) method. It discusses the difficulties in defining pipeline and seabed complexities while still retaining adequate detail to fully describe the pipeline system.
A range of realistic lateral buckling design scenarios will be discussed, illustrating how to reduce existing limitations in probabilistic design through the use of the SRA method. The method is flexible enough to enable varying levels of detail to be modelled, from simple idealised checks of buckling susceptibility, which are commonly performed during the early phases of design, to the more complex analysis of pipeline failure, performed during detailed design. The paper will demonstrate the ability for the method to capture complex real life scenarios such as the effect of a bi-modal distribution in observed pipeline embedment, as well as the influence of covariance between frictions, on the probability of buckling and resulting strains.
Numerical Evaluation of the Straight-Line Stability of a VLCC-Tanker Using Computational Fluid Dynamics
Authors: Lamas Francisco , Fernandes Antonio Carlos 
Published: September 2014

The main objective of the present work is to propose a methodology to evaluate the Directional Stability index of a displacement ship using Computational Fluid Dynamics to evaluate its linear hydrodynamic derivatives.
The first step is the review of the ship’s equations of motion, followed by the formulation of the straight-line stability problem, which depends basically on the evaluation of the ship’s linear hydrodynamic derivatives. After this, the experimental methods that are normally used to evaluate these characteristics during ship design are presented, since they will be simulated in a numerical environment.
Having reviewed the common experimental methods applied to determine the straight-line stability of a ship, the numerical code used to evaluate it in this work is presented, in order to show how the physical constitution of the experimental apparatus is adapted to a computational environment. Together with this will be presented the KVLCC2 model used or the computations, together with the numerical mesh where the computations were carried out. With this, it becomes possible to show the numerical results obtained in this work.
The last part of this paper consists in comparing the numerical results obtained in the step before with the Clarke statistical correlations in order to assess or not the accuracy of the methodology proposed.
Probabilistic Red Limit Study for Mobile Offshore Drilling Units
Authors: Gjerde Tony , Chen Haibo 
Published: September 2014

More and more mobile offshore drilling units (MODUs) are equipped with dynamic positioning (DP) system to maintain vessel position during drilling and well operations. A failure in the DP system might in worst case lead to position loss in terms of drive-off or drift-off. In a position loss scenario, the operator needs to activate the emergency disconnect sequence (EDS) of the marine riser at the time when the vessel reaches a site specific critical distance, denoted the red limit. The red limit distance takes into account the time it takes for the EDS sequence to complete, in addition to the vessel position loss speed and the physical excursion limit for the marine riser, BOP and wellhead system.
The red limit is a site-specific parameter, which is dependent on many factors. This paper presents an alternative probabilistic methodology to determine the red limit based on probabilistic modeling of position loss scenarios, using a case study of DP class 3 drilling vessels at specific well sites and environmental conditions.