bluuebunny/crossref_metadata_2025_split huggingface dataset:
Probabilistic Modeling of Extreme Value Distributions of Ice Loads on “Molikpaq” Platform for Sakhalin-II Project
Authors: Bekker Alexander T. , Sabodash Olga A. , Kovalenko Roman G. 
Published: November 2013

Characteristics of the drifting ice cover and the scenarios of the ice loads on offshore structures are the major parameters defining durability and reliability of the ice-resistant platforms on the Sakhalin offshore.
The study is devoted to the problems of probabilistic and numerical modeling of the process of interaction between the ice cover and the ice-resistant concrete structures on the Sakhalin offshore zone. Geometry of the “Molikpaq” (PA-A) platform for Sakhalin-II Project is used as an example. The input statistical data were received on the basis of full-scale observations of the ice conditions in the Piltun-Astokhskoe deposit area during 1989–2002.
The distribution of probability exceedance of ice loads for various ice scenarios on the “Molikpaq” (PA-A) platform was received. A probabilistic estimation of extreme values of ice loads was carried out, taking into account return period of ice conditions.
Friction, Contact Pressure and Non-Linear Behavior of Steel Tubes in Subsea Umbilicals
Authors: Parsinejad Farzan , Kassner Chris , Kurtz Mark , Ye Naiquan 
Published: November 2013

Steel tube umbilical risers in deep water applications are subject to significant variable environmental loads during operation. These tubes are designed to carry high pressure fluids, up to 15,000 psi. The stresses accumulated in the walls consist of contribution from movement of the floating platform on which the umbilical is connected, axial tension due to the weight of umbilical and ancillaries, and internal pressure due to end cap effect.
The helically wound steel tubes in umbilicals are un-bonded and can slip against adjacent layers. Therefore the stresses in these tubes experience a hysterical feature when the slip changes directions. It is known that in addition to bending stress, friction stress range has a major contribution in fatigue damage. If there is full slip, the friction stress range will be a constant value regardless of the load variation. However in many cycles the full slip is not reached and the stress range is proportional to load variation.
This paper focuses on evaluating the impact of friction and contact pressure on helical steel tubes. The initial gaps between steel tubes and adjacent layers, friction coefficients and the contact stiffness are the main factors that affect such investigation. A novel methodology by using UFLEX2D (a MARINTEK product) has been applied for modeling complex umbilical cross sections and for the study of these parameters.
Two cross sections for the same subsea application but with different designs have been investigated in the study. It has been shown how fatigue damage can be significantly impacted by different cross sectional design.
For this study, non-linear moment/curvature relationship has been included in the analyses. Based on the findings of this study, more realistic results can be achieved by including the non-linear behavior in global analysis for fatigue damage calculations instead of using nominal bending stiffness supplied by umbilical manufacturer.
Failure of Rubble Mound Beneath Caisson due to Earthquake-Induced Tsunami
Authors: Zen Kouki , Kasama Kiyonobu , Kasugai Yasuo , Dong Simeng 
Published: November 2013

The 2011 off the Pacific Coast of Tohoku Earthquake on the 11th of March, 2011 had induced a gigantic Tsunami and caused the catastrophic damage in the northeast coast area of Japan. Lots of breakwaters have been seriously damaged in this disaster, including the world deepest breakwaters, Kamaishi Harbor Mouth Breakwaters. According to a wave height recorder, a large hydraulic head difference between the seaside and harbor side of breakwaters was observed for long duration of several minutes or more. Such a hydraulic head difference as observed generates the seepage flow in the rubble mound underneath the caisson. The seepage flow is considered one of the influential factors causing the instability of caisson type composite breakwaters.
In order to find out the instability mechanism of caisson type composite breakwaters against tsunami, 1) the pop-out phenomena of armored blocks on the mound, 2) the possibility of shear failure of rubble mound and 3) the reduction of bearing capacity of rubble mound due to seepage flow are investigated. Both theoretical analysis and laboratory experiment are represented in this paper.
The safety factors for the pop-out failure and shear failure of rubble mound were theoretically derived. A scale of 1/100 model experiment was performed in laboratory. Loading tests were carried out to investigate the reduction of bearing capacity under the existence of seepage flow. From the results of laboratory experiment and theoretical analysis, it was confirmed that the pop-out phenomenon happens and the bearing capacity of rubble mound can considerably decrease due to the tsunami-induced seepage flow. It is concluded that the effect of seepage flow in the rubble mound should be taken into account when making a design of the caisson type composite breakwater against tsunami.
Real-Time Finite Element Analysis of a Remotely Operated Pipeline Repair System
Authors: Steinke Dean M. , Nicoll Ryan S. , Roy André R. 
Published: November 2013

Remotely operated vehicle (ROV) pilots are frequently trained to operate in increasingly complex subsea environments using ROV simulators. These computer simulators de-risk important subsea operations by increasing ROV pilots’ skill levels in performing tasks under challenging environmental and operational constraints. ROV pilot-training simulation scenarios typically involve a variety of subsea equipment, such as trees, flow lines, pipeline end terminations (PLETs), etc. However, many critical ROV tasks, such as pipeline repair or riser installation, involve flexible structures. The following paper investigates a method for accurately simulating pipelines and flexibles within an ROV pilot-training simulator. The goal of the technology development is to enable engineers and marine operators to assess the risks associated with certain tasks, such as pipeline repair or flexible hook-up, in real-time using ROV simulation technology. In particular, the challenge that this paper will address is how to determine the stresses in a subsea pipeline using a lumped mass finite-element cable model within a multi-body simulation framework.
Repair of subsea pipelines is a complex multi-step process typically carried out by ROVs. During pipeline repair, a pipeline repair system (PRS) is lowered to the seabed. The PRS must lift the pipeline off the seabed and the damaged section of pipeline must then be cut and removed, and a new section of pipeline put in place. During the lifting, cutting and installation phases it is important that the pipeline is not overstressed and the equipment used in the repair operation is not overloaded. In addition, there are a wide array of operational variables, procedures and decisions that must be evaluated. Towards this end, an ROV simulation facility capable of assessing stresses and operations in real-time was constructed using the finite element simulation software package ProteusDS in conjunction with GRI Simulations Inc.’s VROV simulator. The system was designed to evaluate the impact of different combinations of operating parameters and is intended to be useful for system design and analysis. The system would be of immense utility in rapid response to a real-world incident where the system may be called into action. The following paper reviews the simulation framework, the models employed, the results of model verification, and discusses the challenges of the project.
Lateral Buckling Behaviour of Snake-Lay Pipeline With Vertical Support at Crown
Authors: Raveendra Reddy N. 
Published: November 2013

Most hydrocarbon pipelines installed recently in the Middle East operate at relatively high pressures and temperatures: maximum inlet operating temperatures >90°C and pressures >135 barg. These pipelines are susceptible to Euler buckling from high axial compressive force induced in the pipeline by the temperature and pressure. Any uncontrolled lateral buckling is a potential hazard for a pipeline’s structural integrity, especially when all compressive force is released at one point and excessive feed-in occurs.
Possible mitigation measures include lateral restraint by rock dumping or trenching, or midline spools. Another possibility is to induce the pipeline to buckle in a controlled manner, perhaps at several locations, rather than allowing it to suffer an uncontrolled, large buckle at one location only. This is known as buckle initiation. “Snake-lay” and “Vertical Imperfection” are two methods that have been implemented successfully to initiate controlled buckling. “Buoyancy” is another method, but is yet to be implemented.
Snake-lay is a relatively reliable solution but, depending on pipe-soil interaction, sometimes requires a very short radius to initiate the buckle. Installing large diameter pipelines with short radii may invite other problems such as pipeline instability during laying, or may require additional counteracting measures to maintain the specified lay radius. The lay radius can be increased with additional sleepers at the crown of the snake-lay, with a well-defined low friction factor between the pipeline and the support.
This paper discusses the behavior of snake-lay pipeline with and without vertical sleeper supports at the crown of the pipeline, and demonstrates what effects supporting the pipeline at the crown will have on the buckling mechanism and the pipeline integrity.
Optimal Shear Key Interval for Offshore Shallow Foundations
Authors: Feng Xiaowei , Gourvenec Susan 
Published: November 2013

Embedment of offshore shallow foundations is typically achieved by ‘skirts’, i.e. thin vertical plates that protrude from the underside of a foundation top plate and penetrate the seabed confining a soil plug. Skirted shallow foundations are often idealized as a solid, rigid element for geotechnical analysis of the foundation, on the assumption that sufficient skirts, or ‘shear keys’ will be provided to ensure that the deformable soil plug displaces as a rigid body. Should too few shear keys be provided, failure mechanisms involving deformation within the soil plug may occur, leading to a reduction in load-carrying capacity.
There is currently no formal guidance regarding the optimal spacing of shear keys to ensure rigid body displacement of the soil plug. The absence of guidance may lead to unconservative designs if the number of shear keys is under estimated to save on fabrication or to conservative designs if additional shear keys are provided to minimize the risk associated with the uncertainty. Either case is undesirable and clear benefit is to be gained from a better understanding of shear key spacing.
This paper presents guidance on the minimum number of shear keys required to achieve optimal capacity of square and rectangular skirted foundations (i.e. equivalent to that of a solid rigid foundation) under undrained generalized six degree-of-freedom loading in soft soils with linearly increasing shear strength with depth.
Design and Testing of Scale Model Wind Turbines for Use in Wind/Wave Basin Model Tests of Floating Offshore Wind Turbines
Authors: Fowler Matthew J. , Kimball Richard W. , Thomas Dale A. , Goupee Andrew J. 
Published: November 2013

Model basin testing is a standard practice in the design process for offshore floating structures and has recently been applied to floating offshore wind turbines. 1/50th scale model tests performed by the DeepCwind Consortium at Maritime Research Institute Netherlands (MARIN) in 2011 on various platform types were able to capture the global dynamic behavior of commercial scale model floating wind turbine systems; however, due to the severe mismatch in Reynolds number between full scale and model scale, the strictly Froude-scaled, geometrically similar wind turbine underperformed greatly. This required significant modification of test wind speeds to match key wind turbine aerodynamic loads, such as thrust. To execute more representative floating wind turbine model tests, it is desirable to have a model wind turbine that more closely matches the performance of the full scale design.
This work compares the wind tunnel performance, under Reynolds numbers corresponding to model test Froude-scale conditions, of an alternative wind turbine designed to emulate the performance of the National Renewable Energy Laboratory (NREL) 5 MW turbine. Along with the test data, the design methodology for creating this wind turbine is presented including the blade element momentum theory design of the performance-matched turbine using the open-source tools WT_Perf and XFoil. In addition, a strictly Froude-scale NREL 5 MW wind turbine design is also tested to provide a basis of comparison for the improved designs. While the improved, performance-matched turbine was designed to more closely match the NREL 5 MW design in performance under low model test Reynolds numbers, it did not maintain geometric similitude in the blade chord and thickness orientations. Other key Froude scaling parameters, such as blade lengths and rotor operational speed, were maintained for the improved designs. The results of this work support the development of protocols for properly designing scale model wind turbines that emulate the full scale design for Froude-scale wind/wave basin tests of floating offshore wind turbines.
Comparison of Applicable Codes and Standards for Design of End Bulkheads of Pipe-in-Pipe Systems
Authors: Manouchehri Soheil , Potter Jason 
Published: November 2013

Pipe-In-Pipe (PIP) systems are increasingly used where the primary objective is to prevent wax deposition and/or hydrate formation and to achieve a low Overall Heat Transfer Coefficient (OHTC) value. PIP systems are also increasingly considered as an additional protective layer against loss of containment (e.g. in Arctic pipelines) or to withstand the interaction of a third party (e.g. trawl gear impact) in lieu of costly pipeline burial.
At the end of each PIP section, either at a midline connection or end point tie-in, bulkheads are used as a way of transition from a double wall (PIP) system to a single wall (hub in the subsea structure) system. End bulkheads are designed using detailed Finite Element Analysis (FEA) in accordance with more stringent Pressure Vessel Codes (PVC) and manufactured by forging followed by heat treatment and detailed machining to the required dimensions. As the design of end bulkheads does not fall under the Pipeline Codes, a distinction (so called “code break”) may be required on where the governing code changes from the PVC to a Pipeline Code.
This paper firstly discusses the application and validity of internationally known PVCs (ASME BPVC Section VIII Division 2 [1], BS EN 13445 [2], PD 5500 [3]) that can be used in the design of end bulkheads. This is then shown in practice by using an example of a typical end bulkhead, designed to various PVCs. Finally, results are compared and conclusions and recommendations are made.
Riser and J-Tube VIV Analysis Using CFD and FSI for Platform Retrofit Application
Authors: Rubinstein David , Campbell Andrew , Pinna Rodney 
Published: November 2013

INTECSEA has been supporting a client in designing, modelling and assessing a proposal to add additional riser capacity to an existing platform through spare drill slots in the jacket structure. Traditional empirical analysis indicated that the spans between the guides would be subject to Vortex Induced Vibration (VIV), prompting the use of VIV suppression strakes. Analysis was performed to quantify the effectiveness of strakes and to optimise where they are required to minimize jacket loads and operational maintenance and inspection requirements. The current models for VIV have been developed for pipelines and long dynamic risers. Traditional rigid risers installed into a traditional jacket are not well covered.
Computational Fluid Dynamics (CFD) modelling was undertaken using ANSYS CFX on bare riser sections, along with strakes of various characteristic parameters based on vendor specifications. A range of current conditions were modelled to stimulate the onset of VIV. Validation of the performance against shedding frequency and mesh independence was performed. This work demonstrated the performance of the strakes in reducing cross flow force amplitude as well as the fluctuating component of the in-line force. The frequency of the force response was also shown to be more random and act on a longer timescale than the bare riser. The increase in drag forces was also found to be of the order reported by the vendors contacted as part of this project.
Fluid Structure Interaction (FSI) simulations were performed for the full riser length to better capture the interdependence of the vortex shedding and the motion of the riser by two-way coupling of the CFD and an FEA model built within ANSYS. Simulations also examined the splash zone where only part of the span was submerged. Larger simulations were performed to quantify the effect of damping due to the adjacent spans which have lateral constraints at the guides within the drill slots. This has been a challenging modelling activity as the CFD model is very large and required High Performance Computing (HPC) to run the model in parallel.
The work has shown that the application of strakes is an effective method of addressing VIV phenomena within this application. The FSI simulations have examined the dynamic damping along the full riser length. Further modelling work can be performed to better understand the conservativeness of these mitigation strategies saving operators significant cost and time in installation and operating costs.
Adapting a Linear Potential Theory Solver for the Outer Hull to Account for Fluid Dynamics in Tanks
Authors: Ludvigsen Arild , Pan Zhi Yuan , Gou Peng , Vada Torgeir 
Published: November 2013

The linear boundary value problem for the wave dynamics inside a tank is very similar to the solution for the outer hull. Because of this, the boundary value solver for the outer hull can be re-used for the tank. The oscillating hydrostatic pressure in the tank may also be calculated in the same way as for the outer hull. Thereby, the hydrostatic coefficients from the tank can also be obtained from the outer solution.
This makes it, in principle, easy to adapt outer solution computer code to also account for the inner solutions for all the tanks. The procedure is discussed by Newman (2005). We have used it in a different way, isolating the tank solution into more flexible independent sub-runs. This approach provides part-results for the tanks, like added mass and restoring from the tanks. It also has numerical benefits, with the possibility to reuse the calculations for tanks of equal geometrical shape. We have also extended the procedure to account for full tanks without waves and restoring effects.
The linear tank fluid dynamics is programmed into a quite general hydrodynamic frequency domain solver, with the possibility of automatic transferring of local loads to structural (FEM) analysis.
Results for local loads are presented. A simpler method of quasi-static loading in tanks is discussed, with comparison to the present method. Effects on global motions and local pressure coming from the tank dynamics contributions are pointed out, such as the shifted resonance of the vessel and the added mass which differs from rigid masses of the tanks.
Strength and Deformation Capacity of Corroded Pipes: The Joint Industry Project
Authors: Levold Erik , Restelli Andrea , Marchionni Lorenzo , Molinari Caterina , Vitali Luigino 
Published: November 2013

Considering the future development for offshore pipelines, moving towards difficult operating condition and deep/ultra-deep water applications, there is the need to understand the failure mechanisms and better quantify the strength and deformation capacity of corroded pipelines considering the relevant failure modes (collapse, local buckling under internal and external pressure, fracture / plastic collapse etc.).
A Joint Industry Project sponsored by ENI E&P and Statoil has been launched with the objective to quantify and assess the strength and deformation capacity of corroded pipes in presence of internal overpressure and axial/bending loading. In this paper:
• The State-of-the-Art on strength and deformation capacity of corroded pipes is presented;
• The full-scale laboratory tests on corroded pipes under bending moment dominated load conditions, performed at C-FER facilities, are shown together with the calibrated ABAQUS FE Model;
• The results of the ABAQUS FEM parametric study are presented.
Comprehensive Downtime Analysis of DP-Assisted Offloading Operation of Spread Moored Platforms in Brazilian Waters
Authors: Corrêa Diego C. , de Oliveira Allan C. , Tannuri Eduardo A. , Sphaier Sergio H. 
Published: November 2013

Oil offloading from Spread Mooring System (SMS) FPSO is usually done by means of a dynamically positioned shuttle tanker (DPST) in tandem configuration. The ST receives the oil pumped by the FPSO from a bow or stern offloading station, and the operation may take up to 3 days. In order to minimize the risks associated with the operation, the shuttle tanker (ST) should be kept within a safety zone with respect to the FPSO, which is usually given as a minimum distance between the two ships and an aperture angle from the FPSO centerline. In order to guarantee the tanker position during the whole operation, the operation must be performed with tankers provided with DP (dynamic positioning) systems. Since SMS FPSOs may be not aligned to the environmental forces, keeping the shuttle tanker in position may be a hard task for the DP system, depending on the environmental conditions. There are non-rare situations in which the ST must be disconnected and the operation interrupted.
The present paper applies a methodology based on static calculation of DP capacity for evaluating the downtime of such offloading operation. The three generations of DP tankers applied in Brazilian waters are considered. Santos and Campos Basin long-term (8-year) environmental conditions (current, wind, local-sea and swell) are used in the downtime calculation. The main objective is to provide a quantitative tool to analyze important parameters of the operation, in order to support some redefinitions in the operational procedure adopted by Petrobras. The main parameters are: the angle of the safe green-zone defined from the FPSO centerline, the installed DP power, the necessity of bow and stern offloading stations in the FPSO, among others.
The results indicated that due to the large variation of wave-wind conditions along the year, both offloading stations are indeed necessary, since the ST can avoid the conditions in which it is pushed towards the FPSO. The results also indicated that incrementing the angle that defines the green-zone substantially decreases the offloading downtime. However, such decision also depends on a comprehensive risk analysis, since in that case the ST may be kept in a perpendicular position related to the FPSO. The risk analysis is beyond the scope of the present work. The DP power specified for the ST generations 2 and 3 are shown to be quite adequate, since it is demonstrated that increasing this power will not lead to a substantial reduction in the downtime.