bluuebunny/crossref_metadata_2025_split huggingface dataset:
Reliability Assessment Approach for DCV Aegir Pipeline Installation Analyses
Authors: Karjadi Erwan , Smienk Henk 
Published: September 2014

Heerema Marine Contractors (HMC) is entering a new era of pipe laying with the new Deepwater Construction Vessel (DCV) Aegir. This vessel is designed to be able to reel/J-lay pipelines for a wide range of pipe dimension and water depth combinations.
To define the limit of installation workability windows, the pipeline installation analyses (reeling or J-lay method) during the project engineering preparation phase are normally performed based on the consideration that a combination of several “worst case” scenarios will occur at the same time during the installation event. The worst case scenarios are assumed in terms of pipe resistance (geometry/property), positioning of the vessel/equipment, environmental loads, etc. This method of calculations can be considered as the most practical and safe approach.
However, as an accumulation of conservative assumptions is inherently being made within this approach, it can lead to a situation that the pipeline cannot be installed or lead to insufficient workability window for pipeline installation operation. Another shortcoming of this worst case scenario approach is that we are not able to quantify the probability of failure for a certain pipeline installation scenario. The reliability analyses and assessment for pipeline construction/installation as described in the DNV-OS-F101 code [1] can be used as an alternative. The assessment can lead to some relaxations of the pipeline installation workability in a safe manner whilst accepting some level of the risks.
The purpose of this paper is to present the development of reliability assessment approach for pipeline installation analyses for the DCV Aegir. One of the important steps of the development is the setup of a pipeline database based on the as-built pipeline data from HMC’s past projects. The database can be used to estimate the typical distributions of the pipe dimension and properties as input for the reliability analyses.
Three examples are given in this paper, two are related to the reeling pipeline analysis with standard pipe ends and counterbored pipe ends (First Order Reliability Method FORM and Monte Carlo approach) and another example is related to J-lay pipeline installation analysis. The results of the assessments are correlated with the DNV guideline for the acceptance of nominal target probability of failures against the safety classes.
Full-Scale Measurements of Wave and Current Loads on Splitter Fairings
Authors: Spencer Don , Liapis Stergios , Constantinides Yiannis , Islam Mohammed , Edwards Zachary 
Published: September 2014

This paper presents measurements of the mechanical loads that splitter fairings on vertical and inclined risers will experience while in the wave zone or due to current drag. A 21″ pipe was utilized for the measurements, which corresponds to prototype size for a production riser and a 1:2.5 scaled model for a 54″ drilling riser. The program had three objectives, (a) to determine the nature of wave and current loading on a riser segment that was fitted with a fairing to provide sufficient internal strength and stiffening; (b) to determine the wave and current loading on the fairing connection system to assist in designing reliable latching systems, and (c) to investigate if the measured loading on the fairings from forced oscillation experiments can be used to simulate loading resulting from wave motion.
Of primary interest was the effect of wave loading on the fairings in prototype or near prototype conditions. One significant impediment to conducting such experiments in a model wave basin was the very limited ability of the basin to generate full scale wave in terms of period or height. However the horizontal component of the oscillatory wave velocity can be simulated by oscillating the fairings at prototype wave periods and amplitudes to obtain the same relative flow condition. One of the fundamental questions that remained prior to the research was whether the novel forced oscillation technique could actually replicate the real world wave induced loads and some experiments were directed at confirming this.
While exploratory in nature, these forced oscillation experiments demonstrated that the test apparatus and methodology were able to replicate the corresponding measurements from the wave experiments, thus providing reliable data to assist in predicting hydrodynamic loading on fairings due to current, forced oscillatory motion, and waves. The basin carriage was successfully used to force the fairings in a prescribed oscillatory motion. The analysis of the measurements of the forced oscillation experiments showed that the inertial force correlated well and was linearly proportional to acceleration while the viscous force was a linear function of velocity. It was demonstrated that the forced oscillation experiments could provide reasonably good estimates of the global loading resulting from wave action. This implies that the experimental technique of replacing wave motion with forced oscillation can be used for design. As a result, prototype or near prototype scale models of fairings can be tested in wave conditions well beyond the capability of model basins. While the global loads due to waves could be predicted from the forced experiments it appeared the latching load were about 70% higher while in waves relative to those recorded during the forced oscillation experiments. This discrepancy could be attributed to free surface effects.
A Structural Strain Method for Fatigue Evaluation of Welded Components
Authors: Dong Pingsha , Pei Xianjun , Xing Shizhu 
Published: September 2014

In this paper, a new structural strain method is presented to extend the early structural stress based master S-N curve method to low cycle fatigue regime in which plastic deformation can be significant while an elastic core is still present. The method is formulated by taking advantage of elastically calculated mesh-insensitive structural stresses based on nodal forces available from finite element solutions. The structural strain definition is consistent with classical plate and shell theory in which a linear through-thickness deformation field is assumed a priori in both elastic and elastic-plastic regimes. With considerations of both yield and equilibrium conditions, the resulting structural strains are analytically solved if assuming elastic and perfectly plastic material behavior. The formulation can be readily extended to strain-hardening materials for which structural strains can be numerically calculated with ease. The method is shown effective in correlating low-cycle fatigue test data of various sources documented in the literature into a single narrow scatter band which is remarkable consistent with the scatter band of the existing master S-N curve adopted ASME B&PV Code since 2007.
With this new method, some of the inconsistencies of the pseudo-elastic structural stress procedure in 2007 ASME Div 2 Code can now be eliminated, such as its use of Neuber’s rule in approximating structural strain beyond yield. More importantly, both low cycle and high cycle fatigue behaviors can now be treated in a unified manner. The earlier mesh-insensitive structural stress based master S-N curve method can now be viewed as an application of the structural strain method in high cycle regime, in which structural strains are linearly related to traction-based structural stresses according to Hook’s law. In low-cycle regime, the structural strain method characterizes fatigue damage directly in terms of structural strains that satisfy linear through-thickness deformation gradient assumption, material nonlinear behavior, and equilibrium conditions. The use of a pseudo-elastic structural stress definition is not fundamental, but merely a means to put low-cycle and high-cycle fatigue test data in a conventional stress-based S-N data representation which is typically preferred in engineering practice, than a strain-based representation.
Collapse Analysis of Offshore Platforms Using Constrained New Waves
Authors: Kimiaei Mehrdad , Edgarth Daud W. 
Published: September 2014

Traditionally regular deterministic wave theories are employed to estimate wave loads on offshore platforms but they cannot capture random nature of the sea states. Randomly generated sea surfaces will lead to most accurate results for structural responses due to waves but they are usually based on long duration simulations and hence need excessive computational efforts. Constrained NewWaves (CNWs), with significantly shorter computational time, have recently been used successfully for estimating of structural response of offshore platforms due to waves. For extreme waves, as long as there is no indication of major structural nonlinearity in the system, they have shown reasonably accurate results as an alternative for long duration randomly generated sea surfaces.
This paper is concerned with using CNWs in collapse analysis of offshore platforms under extreme waves where large geometrical and material nonlinearities are expected. It shows how the plastic level of the response, total duration of the loading, the loading pattern and dynamic characteristics of the platform can influence the extreme response and collapse rates of the offshore platforms.
Pipe-Soil Interactions for a Pipeline With Strakes on a Furrowed Seabed
Authors: Brunner Mark , Bai Qiang 
Published: September 2014

Although significant pipe-soil interaction information is now available in the industry for shallowly-embedded, cylindrical pipelines on a flat seabed, there is little information available for subsea pipelines with vortex-induced vibration (VIV) suppression strakes on a furrowed seabed.
A heavily furrowed seabed may have multiple free spans that are subjected to seabed currents and potential VIV. To suppress VIV at the free spans, strakes are often applied to the pipeline over the entire length of the furrowed area. At the tops of the furrows, the pipeline will penetrate further into a soft clay seabed due to the weight of adjacent free spans. Significantly different pipe-soil interactions are possible in these areas, especially with the presence of VIV suppression strakes. Accounting for these differences is essential when assessing thermal expansion issues, such as global lateral buckling and pipeline walking.
This paper presents the findings for a test case of a pipeline with strakes on a furrowed seabed and provides suggestions for a user subroutine to be used for a pipeline system with beam elements in a finite-element analysis. The CEL method is first used to assess the impact of straked-pipeline penetration into a flat, soft-clay seabed, then to assess lateral and axial pipe resistances at different penetration depths. This information is used to develop a user subroutine for beam elements to further assess the pipeline on a furrowed seabed, in which the effects of vertical pipeline load and penetration on the lateral soil resistance are included.
The test case also considers a typical analysis for a pipeline subjected to elevated temperature and pressure cycles.
InWave: A New Flexible Design Tool Dedicated to Wave Energy Converters
Authors: Combourieu Adrien , Philippe Maxime , Rongère François , Babarit Aurélien 
Published: September 2014

This article presents the novel methodology used in the software InWave to address the problem of wave energy converters (WEC) modelling. The originality compared to other recently developed tools lies in a fast semi-recursive multibody dynamic solver which integrates a flexible hydrodynamic solver.
The multibody solver works in time domain and is fully nonlinear. It solves the dynamic of systems formed of a fixed or free base articulated with any number of bodies that can be floating or not, with branchy structure ([1]).
The integrated hydrodynamic solver is a linear potential flow solver based on boundary elements method. It uses the generalized degrees of freedom approach ([11]). Combined with a relative coordinate parameterization, it allows for a minimization of the number of hydrodynamic boundary value problems that have to be solved, thus allowing a reduction of computational time both for BEM computations and time domain simulations. Time domain reconstruction is performed to link hydrodynamic loads with the multibody dynamic solver. Interaction between bodies through radiation is thus taken into account.
InWave is a complete WEC modelling tool including incident wave generation, multibody dynamic solver, hydrodynamic solver, power take-off and mooring models, post-processing and visualization.
A successful comparison with the linear potential flow solver Aquaplus ([5]) on a basic cylinder test case is carried out.
Finally, a complex test case on a Langlee-like device is presented, comparing InWave results with those from the NumWec project ([2]). A good agreement between both models is found, which increases the confidence in InWave algorithms and implementation.
The Effect of the Computational Grid Size on the Prediction of a Flammable Cloud Dispersion
Authors: Miralles Schleder Adriana , Martins Marcelo Ramos , Pastor Ferrer Elsa , Planas Cuchi Eulàlia 
Published: September 2014

The consequence analysis is used to define the extent and nature of effects caused by undesired events being of great help when quantifying the damage caused by such events. For the case of leaking of flammable and/or toxic materials, effects are analyzed for explosions, fires and toxicity. Specific models are used to analyze the spills or jets of gas or liquids, gas dispersions, explosions and fires. The central step in the analysis of consequences in such cases is to determine the concentration of the vapor cloud of hazardous substances released into the atmosphere, in space and time. With the computational advances, CFD tools are being used to simulate short and medium scale gas dispersion events, especially in scenarios where there is a complex geometry. However, the accuracy of the simulation strongly depends on diverse simulation parameters, being of particular importance the grid resolution. This study investigates the effects of the computational grid size on the prediction of a cloud dispersion considering both the accuracy and the computational cost.
Experimental data is compared with the predicted values obtained by means of CFD simulation, exploring and discussing the influence of the grid size on cloud concentration the predicted values.
This study contributes to optimize CFD simulation settings concerning grid definition when applied to analyses of consequences in environments with complex geometry.
Top Tensioned Riser Interface With Dry-Tree Semisubmersible
Authors: Xiang Sherry , Cao Peimin , Otten Jeff , Jiang Lei , Bian Sean 
Published: September 2014

Dry Tree Semisubmersibles (DTS), with the capability of supporting surface wellheads and allowing drilling and completion through direct vertical access risers, have attracted intense interest from the oil and gas industry. A wet tree deep draft semisubmersible has been carefully reconfigured considering the balance between the overall floater configuration and the tensioner stroke for a harsh environment application. A large amount of simulation efforts have been performed for the optimization of the integrated hull/deck/mooring/riser system. Recently, a basin model test was also successfully completed and further demonstrated its technical feasibility.
The paper presents the overall design of a Top-Tensioned Riser (TTR) system for a DTS application focusing on the complexity of the DTS-TTR interface including ram style tensioning system, riser conductor and riser top assembly design with keel joint, etc. Due to the heavy weight of the TTR system in the ultra-deep water application, the riser top sections are subject to high reaction loads with the DTS in severe environments. The riser system faces the challenge to have a feasible and economic top assembly design. In this paper, an engineered riser conductor pipe is introduced to interface the riser top assembly with hull. The riser conductor pipe, which spans from deck to keel, is integrated with riser top assembly and the tensioner system design. The riser conductor protects the riser in the splash zone and prevents the high reaction loads directly transferring from hull to riser, thus reducing the riser keel joint and tension joint size. The feasibility and performance of the TTR system are demonstrated through the static and dynamic analyses. Pipe-in-pipe (PIP) contact model is employed in the simulation to ensure the dynamic interaction loads between riser and riser conductor are captured. The TTR overall system design consideration for the DTS application is discussed.
Current Developments in the Validation of Numerical Methods for Predicting the Responses of an Ocean Thermal Energy Conversion (OTEC) System Cold Water Pipe
Authors: Halkyard John , Sheikh Rizwan , Marinho Thiago , Shi Shan , Ascari Matthew 
Published: September 2014

Ocean Thermal Energy Conversion (OTEC) was a subject of intense research in the late 1970s and early 1980s in response to a historical jump in oil prices from the 1973 oil embargo. The principal author for this paper first met Prof. Paulling as a participant in a National Research Council (NRC) Panel to review OTEC Technology around 1982. Prof. Pauling had authored a frequency domain program to analyze the coupled response of a platform and OTEC pipe. The author was involved in model tests to validate the program. The United States (U.S.) Department of Energy (DoE) and National Oceanic and Atmospheric Administration (NOAA) had sponsored this work, along with the development of other numerical methods. Shortly after the NRC completed its review, oil prices fell and interest in renewable energy, including OTEC, evaporated. Fast forward to the 2000s, the price of oil skyrocketed again, and OTEC research saw a rebirth. Lockheed Martin and others have been working on new OTEC designs over the course of the last several years. As was the case thirty-five years ago, the cold water pipe remains a key technical challenge.
A commercial scale OTEC plant requires a pipe diameter of about 10-meter (m) and a length of 1,000m to pump about half the average discharge of the Colorado River from the deep ocean to the surface and through heat exchangers. Because of the large effective mass of the CWP and entrained water, the dynamic response of the OTEC CWP and the platform can only be considered as a coupled system. This conclusion is not new, but is worth repeating and doubly important to consider when the supporting platform is a semi-submersible as opposed to a large water plane ship shaped vessel.
A new generation of software is available to analyze the cold water pipe-platform responses, including the important effect of the fluid flow inside the pipe and the local effects at the connection of the pipe to the platform. The DoE and Lockheed Martin recently sponsored a 1:50 scale wave basin model test of a commercial OTEC platform with an elastically scaled model of a 10m pipe. The purpose of the test was to validate the use of current software for the large CWP diameters in the designs of a pilot or commercial systems in the near future. This paper will briefly review past work on the OTEC cold-water pipe and present the current state of the art in numerical modeling and the results of the model tests recently completed. It will include recommendations for further experimental and numerical work to be prepared for the future design of OTEC systems.
South Stream Deepwater Pipeline System: A Case for Waiving the Hydrotest
Authors: Timmermans Jeroen , Meijer Arjen , Ethembabaoglu Sakir 
Published: September 2014

The traditional scope of pre-commissioning for a pipeline system includes filling the pipeline with liquid (typically water) and pressure testing to confirm the integrity and leak-tightness of the system. This methodology is described in almost all design codes, and typically represents an important criterion for the acceptance of the completed system by the owner / operator.
As the industry takes on offshore pipeline systems in deeper and deeper water, the relevance of this traditional approach has come into question. Specifically, it is not clear that the benefit of hydrotesting a deepwater pipeline system outweighs the costs, risks and potential environmental impact. For this reason DNV introduced the possibility of ‘waiving’ (= omitting) the hydrotest in OS-F101, its offshore standard for submarine pipeline design. In order to waive the system hydrotest, OS-F101 demands that specific, additional conditions be satisfied to ensure that the overall level of safety is maintained.
To date, only two smaller pipeline projects have received such a hydrotest waiver. The South Stream Offshore Pipeline project, which is presently approaching its implementation phase, will be the third. South Stream comprises four 32-inch diameter pipelines each with a length of approximately 930 km and traversing water depths up to 2,200m. The South Stream project is re-defining the state-of-the-art in offshore pipelines. Due to the extreme water depth, harsh seabed and large internal volume of the South Stream lines, traditional hydrostatic testing would not be the most environmentally friendly and risk averse solution to ensure pipeline integrity and safety.
This paper will present the main requirements and associated solutions for the South Stream pipelines in order to obtain a DNV OS-F101 hydrotest waiver, including:
• Review of the benefits and challenges for deepwater pipeline hydrotest
• Discussion of the DNV OS-F101 waiver requirements
• Implementation of the waiver requirements on South Stream
Investigation of Back Pressure Effects on Transient Gas Flow Through Porous Media via Laboratory Experiments and Numerical Simulation
Authors: Liu Xiaolei , Limpasurat Akkharachai , Falcone Gioia , Teodoriu Catalin 
Published: September 2014

When developing a transient numerical reservoir simulator, it is important to consider the back pressure effects that waves propagating from one end of the porous medium will have on the temporal distribution of pore fluid pressure within the medium itself. Such waves can be triggered by changing boundary conditions at the interface between reservoir and wellbore. An example is given by the transient reservoir response following pressure fluctuations at the wellbore boundary for gas wells suffering from liquid loading.
Laboratory experiments were performed using a modified Hassler cell to mimic the effect of varying downhole pressure on gas flow in the near-wellbore region of a reservoir. Gauges were attached along a sandstone core to monitor the pressure profile. The results of the experiments are shown in this paper.
A numerical code for modelling transient flow in the near-wellbore region was run to mimic the experiments. The comparisons of simulations and laboratory test results are presented here, for the initial and final steady-state flowing conditions, and where the inlet pressure was maintained constant while initiating a transient pressure build up at the core outlet.
The concept of the U-shaped pressure profile along the near-wellbore region of a reservoir under transient flow conditions, originally proposed by Zhang et al. [1], was experimentally and numerically reproduced for single-phase gas flow. This is due to a combination of inertia and compressibility effects, leading to the reservoir response not being instantaneous. The results suggest that, in two phase gas-liquid conditions, liquid re-injection could occur during liquid loading in gas wells. From the experimental results, the U-shaped curves were more obvious and of longer duration in the case of greater outlet pressure. The transition from the initial to the final steady state condition occurred rapidly in all the cases shown here, with the U-shaped pressure profile appearing only over a relatively short time (at the small scale and low pressures tested in this study).