bluuebunny/crossref_metadata_2025_split huggingface dataset:
Comparison Between Numerical Prediction and Model Tests Measurements on the Centerwell Tank of a Radial Wellbay Spar
Authors: Muehlner Edmund , Murray John , Banumurthy Surya , Lakhotia Chandan 
Published: August 2013

The radial wellbay (RAW) Spar is, for the most part, based on conventional Truss Spar technology. The primary difference between the RAW Spar and the conventional Truss Spar is the wellbay arrangement.
An integral structural component of the RAW Spar is the ABCD (Adjustable Buoyancy Centerwell Device) located in the lower portion of the centerwell. The ABCD is connected to the interior of the hard tank using a number of shear plates. The ABCD captures the buoyancy in the open centerwell and contributes to the total buoyancy of the hard tank. As an option, the ABCD can be used for in-hull storage. On the RAW drilling Spar, the ABCD can be used to support the setback and pipe racking system.
Design applications using the ABCD raise an additional requirement in the design of the hard tank, specifically, an accurate estimate of the load in the structure that connects the ABCD to the hard tank. Contributions to this load come from the inertia effect of the Spar motions, hydrostatic responses affected by ballast conditions in the device, and hydrodynamic forces affected by pressure in the riser slot gap. Connection loads are required to design the structure connecting the ABCD to the interior walls of the hard tank.
An ABAQUS™ based time domain semi-empirical model was developed to predict the local and global loads on the ABCD. A series of 1:50 scale model tests on the RAW Spar were carried out at the OTRC basin in College Station, Texas. The model’s ABCD, mounted on a dynamometer system inside the hard tank, was used to measure the six-degree-of-freedom forces between the hard tank and the ABCD. The paper focuses on a comparison of the predicted and measured loads.
Experimental and Numerical Study of a Multi-Layer Flexible Pipe Depressurization
Authors: Lambert Anaïs , Felix-Henry Antoine , Gilbert Philippe , Gainville Martin 
Published: August 2013

Unbonded flexible pipelines used for offshore fields developments usually rely upon a stainless steel carcass as innermost layer for collapse resistance and a polymeric pressure sheath for internal leakproofness. For some dynamic flexible risers, this pressure sheath is a multi-layer construction made of 2 or 3 layers. In this multi-layer configuration, during operation, the fluid transported in the bore of the pipe can penetrate the annular space between the pressure sheath layers by means of flow paths through the end-fitting. Then, when the pipe bore is depressurized, the pressure of the fluid trapped between the sacrificial sheath and the pressure sheath does not decrease as fast as in the bore. This is due to the small annular flow path between the sheaths. Depressurization of the pipe bore should thus be performed at a limited and controlled rate to avoid an excessive differential pressure between the pipe bore and the annulus that could potentially cause the collapse of the carcass. The allowable depressurization rate is a key parameter the field operators need to know to avoid such an issue.
A model was developed and implemented in a numerical software to calculate the evolution of the differential pressure during the depressurization. It is based on a one dimension gas/liquid transient transport model. More specifically, it is composed of the mass and momentum conservation laws. The thermodynamics properties of the fluid are computed with a simple model. In addition, the dynamic behavior of the annulus is coupled with the conservation equations and the pressure of both the bore and the external environment. A Finite Volume Method is chosen to both discretize and keep the conservative properties of the model on a discrete level.
In addition, a large test campaign was carried out on a full scale pipe to validate the model. A test consists in a pressure increase followed by a depressurization. The pressures in the bore and in the annulus were permanently recorded using a specific device which enables to know in real time the differential pressure between the pipe bore and the annulus. Various conditions were tested by varying the fluid viscosity, the initial bore pressure and the depressurization rate.
After explaining the physics of the depressurization for this specific flexible pipe construction, this paper will present the numerical model developed to calculate the maximum differential pressure and the test campaign performed to validate this model.
Wellhead Fatigue Analysis Method: Benefits of a Structural Reliability Analysis Approach
Authors: Hørte Torfinn , Reinås Lorents , Mathisen Jan 
Published: August 2013

Structural Reliability Analysis (SRA) methods have been applied to marine and offshore structures for decades. SRA has proven useful in life extension exercises and inspection planning of existing offshore structures. It is also a useful tool in code development, where the reliability level provided by the code is calibrated to a target failure probability obtained by SRA. This applies both to extreme load situations and also to a structural system under the influence of a time dependent degradation process such as fatigue.
The current analysis methods suggested for service life estimation of subsea wells are deterministic, and these analyses are associated with high sensitivity to variations in input parameters. Thus sensitivity screening is often recommended for certain input parameters, and the worst case is then typically used as a basis for the analysis. The associated level of conservatism embedded in results from a deterministic analysis is not quantified, and it is therefore difficult to know and to justify if unnecessary conservatism can be removed from the calculations.
By applying SRA to a wellhead fatigue analysis, the input parameters are accounted for with their associated uncertainty given by probability distributions. Analysis results can be generated by use of Monte-Carlo simulations or FORM/SORM (first/second order reliability methods), accounting for the full scatter of system relations and input variations. The level of conservatism can then be quantified and evaluated versus an acceptable probability of failure.
This article presents results from a SRA of a fictitious but still realistic well model, including the main assumptions that were made, and discusses how SRA can be applied to a wellhead fatigue analysis. Global load analyses and local stress calculations were carried out prior to the SRA, and a response surface technique was used to interpolate on these results. This analysis has been limited to two hotspots located in each of the two main load bearing members of the wellhead system.
The SRA provides a probability of failure estimate that may be used to give better decision support in the event of life extension of existing subsea wells. In addition, a relative uncertainty ranking of input variables provides insight into the problem and knowledge about where risk reducing efforts should be made to reduce the uncertainty.
It should be noted that most attention has been given to the method development, and that more comprehensive analysis work and assessment of specific input is needed in a real case.
Large Eddy Simulations of Three-Dimensional Flow Around a Pipeline in a Uniform Current
Authors: Prsic Mia , Ong Muk Chen , Pettersen Bjørnar , Myrhaug Dag 
Published: August 2013

Three-dimensional (3D) modeling of the flow around a circular cylinder in a steady, uniform current subjected to low and intermediate Reynolds numbers (Re) is considered. Large eddy simulations (LES) are used to simulate the flow due to their ability to study fine structures in the turbulent wake of the cylinder. The turbulence is resolved by the Smagorinsky model. The open-source code OpenFOAM is used in the simulations. Influences of various numerical parameters, such as the grid resolution close to the cylinder, domain width and spanwise resolution are investigated through mean values of the drag and the lift coefficients, the Strouhal number, as well as through the details of the flow field in the near wake of the cylinder.
The main purpose of the present paper is to study the numerical influences on the 3D LES simulations of the flow around the cylinder in the free stream at Re = 13100. However, first the flow around a cylinder in the free stream at Re = 3900 is investigated. The latter case has previously been thoroughly investigated, both with LES and direct numerical simulations (DNS); hence these results will be used for verification of the OpenFoam solver.
At Re = 13100 the drag and lift coefficients and the Strouhal number are calculated for the comparable Re. Details of the flow in the intermediate wake of the cylinder are also investigated. So far, this has been investigated experimentally and by two-dimensional (2D) numerical simulations. Previous studies were conducted for moderate Re in the range 103–105.
Modelling Details of Fenders in Float-Over Installation Experiments
Authors: Cole Jason C. , Islam Mohammed , Garvin Matthew , Herrington Paul 
Published: August 2013

Fenders are a key element of float-over topsides installations protecting the vessel and jacket legs by absorbing impact energy. Fender capacity is defined in accordance with expected vessel motions, vessel hull strength, and anticipated impact energy. Translating those dependencies from full-scale float-over scenarios to model-scale experiments provides added challenges when devising experimental approaches.
This paper describes the design and development of model-scale fenders and their application in float-over topsides installation experiments. Current model fenders use multi-stage cantilevered leaf springs to develop the required non-linear stiffness curve which is calculated from full-scale fender data. Spring material and geometry, relative position, and loading location are key variables used to match the target fender stiffness as changes in these parameters directly affect the force-deflection characteristics of the model-scale fenders.
The force-deflection characteristics (stiffness) of the model-scale fenders were checked before, during, and after wave experiments, using both isolated bench tests and in situ verifications. Multiple iterations of stiffness checks were completed during the stiffness curve matching process prior to the experimentation. The achieved load-deflection characteristics of the fender units were within 2% of the target stiffness curve. The damping characteristics of the fenders were not specifically modeled, but were measured for each of the stiffness stages. The model fenders have successfully been used in multiple float-over experimental campaigns.
Effects of Low Temperature on ASTM A131: An Experimental and Numerical Study
Authors: Park Dae Kyeom , Kim Do Kyun , Kim Bong Ju , Seo Jung Kwan , Paik Jeom Kee 
Published: August 2013

The aim of this study was to investigate the effects of low temperatures on the material properties and crashworthiness of ASTM A131-type carbon steel. A series of tensile coupon tests and crushing tests on square tubes were performed in a liquid nitrogen cooled chamber to examine their material behavior and crashing behavior at a series of low temperatures under quasistatic conditions. The temperature conditions cover a cryogenic condition, the typical Arctic temperatures and room temperature.
In the previous study, ASTM A500-type carbon steel is considered [13] and in present study the different grades of ASTM A131-type carbon steel for ships and offshore structures are considered, including Grades A, B and D of mild steel and Grades AH and DH of high tensile steel.
The results of the tensile coupon tests showed an increase in the strength and in non-uniform fracture strain behavior in different grades and temperatures. Unstable crushing behavior and fractures were observed in the crushing tests. LS-DYNA nonlinear finite element method analyses were performed using reliable nonlinear finite element method modeling techniques to assess the structural crashworthiness of the materials at low temperatures.
Numerical Study of Hydrodynamic Forces on a Submarine Piggyback Pipeline Under Wave Action
Authors: Cheng Xiaofei , Wang Yongxue , Ren Bing , Wang Guoyu 
Published: August 2013

In the paper, a 2D numerical model is established to simulate the hydrodynamic forces on a submarine piggyback pipeline under regular wave action. The two-dimensional Reynolds-averaged Navier-Stokes equations with a κ-ω turbulence model closure are solved by using a three-step Taylor-Galerkin finite element method (FEM). A Computational Lagrangian-Eulerian Advection Remap Volume of Fluid (CLEAR-VOF) method is employed to simulate free surface problems, which is inherently compatible with unstructured meshes and finite element method.
The numerical results of in-line force and lift (transverse) force on the piggyback pipeline for e/D = G/D = 0.25 and KC = 25.1 are compared with physical model test results, which are conducted in a marine environmental flume in the State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, China. It is indicated that the numerical results coincide with the experimental results and that the numerical model can be used to predict the hydrodynamic forces on the piggyback pipeline under wave action. Based on the numerical model, the surface pressure distribution and the motion of vortices around the piggyback pipeline for e/D = G/D = 0.25, KC = 25.1 are investigated, and a characteristic vortex pattern around the piggyback pipeline denoted “anti-phase-synchronized” pattern is recognized.
Gas Explosion Analysis for FLNG Plant Layout Design
Authors: Otsubo Kazuhisa , Masanobu Sotaro , Yaguchi Yuta , Asanuma Takayuki , Maeda Katsuya , Taniguchi Tomoki 
Published: August 2013

Recently, the natural gas is expected to be an environmentally friendlier energy and alternative to the nuclear energy. In the social situation, many oil and gas and engineering companies had studied FEEDs (Front End of Engineering Designs) of FLNG (LNG-FPSO) expected to be a new production system for offshore natural gas development in the near future. The FLNG system is no proven technology and there is no FLNG operation, which can make it difficult to design FLNG. Furthermore, it is noted that FLNG designers can’t get enough information for the design.
Gas explosion is the technical problems for the topside facilities of FLNG. The objective of this paper is to study the gas explosion for the FLNG design.
Application of Breather Solutions for the Investigation of Wave/Structure Interaction in High Steep Waves
Authors: Clauss Günther F. , Klein Marco , Dudek Matthias , Onorato Miguel 
Published: August 2013

During the design process of floating structures, different specifications have to be aligned such as the range of application, the warranty of economical efficiency as well as the reliability and are an inevitable integral part of the evaluation process during the design stage. The validation of the performance by means of model tests in terms of sea state behavior and the associated local and global structural loads are an important milestone within this process. Therefore it is necessary to determine an adequate test procedure which covers all essential areas of interest. Thereby one field of interest are limiting criteria of the design such as maximum local and global loads as well as maximum accelerations due to the impact of extraordinarily high waves, at which the floating structure has to survive. Different alternatives are available to conduct model tests in high, steep waves — transient wave packages, regular waves, irregular waves with random phases or more sophisticated deterministic tailored irregular wave sequences such as reproductions from numerical simulations and real-world measurements.
This paper introduces a new approach for the systematic investigation of wave/structure interaction in high, steep waves. Exact solutions of the nonlinear Schrodinger equation — the so called breather solutions — are implemented for the generation of extraordinarily high waves. Three types of breather solutions are investigated in the seakeeping basin and to cover the full range of interest, each solution has been used to generate freak waves at certain frequencies.
To evaluate the applicability of breather solutions for model tests two types of ships — a LNG Carrier and a Chemical Tanker — are investigated in the seakeeping basin. The ships are segmented and connected with strain gauges to detect the vertical wave bending moment. Furthermore, green water probes are installed on deck to evaluate the local impact on the bow of the freak waves. The obtained results are compared to investigations in regular waves with certain frequency and steepness as well as in real-world freak wave reproductions.
Effect of High-Frequency Response on TLP Tendon Fatigue
Authors: Muehlner Edmund , Banumurthy Surya , Murray John 
Published: August 2013

High-frequency vibrations of Tension Leg Platforms (TLPs), commonly known as ringing and springing, have challenged TLP designers since the first full-scale TLP was installed in the North Sea in 1984. Although current design codes recognize the significance of the ringing and springing response for tendon design, no widely accepted modeling approach for their calculation has yet emerged.
This paper presents a nonlinear time-domain model of a TLP that exhibits the ringing and springing response of the vessel. The analysis model uses large displacement theory for the vessel and tendons and a semi-empirical wave model based on a modified linear wave theory. Predictions of vessel motions and tendon loads made with the analysis model were compared to model tests and were found in good agreement with the measurements.
The analysis model was also was used to investigate the fatigue damage in the tendons caused by the vessel’s high-frequency response. Tendon stress time histories were computed for nine different unidirectional sea-states. These sea-states represent a condensed wave scatter diagram for the Gulf of Mexico (GoM). The tendon fatigue was calculated from the stress histories by rainflow counting. Fatigue contributions from different frequency ranges were identified by Fourier analysis.
The analysis showed that high-frequency response was present in all sea-states even though ringing occurred only in sea-states with significant wave heights above 10 ft. Tendon fatigue damage contribution from high-frequency loads were found to be significant in every sea-state. For all sea-states combined 73% of the up-wave tendon fatigue damage was due to high-frequency response. For the down-wave and the cross-wave tendons, the high-frequency contributions were 57% and 34%, respectively.
This paper demonstrates the importance of considering high-frequency response for the fatigue design of TLP tendons. Another finding of the study is that the analysis model using a modified linear wave theory can describe the ringing and springing behavior of a TLP provided other significant nonlinearities of the system are considered.
On-Bottom Stability Analysis for a Pipeline on a Mobile Seabed
Authors: McMaster Scott Y. , O’Brien Dermot , Scholtz David E. , Ryan Jay R. 
Published: August 2013

This paper describes the work performed to assess the stability of an existing pipeline off the North Western coast of Western Australia. Originally, the pipeline was post-trenched (for stability), by ploughing. The plough formed an open v-shaped trench below the pipeline. Several years after the pipeline was installed, a severe cyclone caused significant changes to the seabed along the pipeline. The v-shaped ploughed trench is generally no longer visible with the trench backfilled in places and the pipeline exposed in others. In addition to this, the embedment profile either side of the pipeline was often found to be assymetrical, with higher embedment on one side of the pipeline relative to the other.
Current on-bottom stability guidelines and recommended practices do not account for the effects of assymetrical embedment and seabed mobility (Ref. 5). These two factors are believed to contribute significantly to the overall stability of the pipeline. Consequently, it was decided to use physical model testing to obtain a better understanding of hydrodynamic loading and changes in embedment over the duration of a design storm. The physical model testing was performed for various pipeline embedment profiles. The results of these 2D physical model tests were then applied to the 3D FEA on-bottom stability software, CORUS 3D.
This paper provides a detailed description of the physical model testing program performed as part of the pipeline stability assessment. The method used to combine the results of the physical model testing and apply them to the 3D FEA on-bottom stability software is also presented.
State of Art in Life Extension of Existing Offshore Structures
Authors: Nezamian Abe , Nicolson Robert J. , Iosif Dorel 
Published: August 2013

A large number of the old oil and gas facilities have reached or exceeded their initial design life. With a continued requirement to produce oil or gas, either from the original fields or as a base for neighbouring subsea completions, many of these respective offshore installations are likely to remain operational for a period of time in the foreseeable future. The ageing offshore infrastructure presents a constant and growing challenge. Ageing is characterised by deterioration, change in operational conditions or accidental damages which, in the severe operational environment offshore, can be significant with serious consequences for installation integrity if not managed adequately and efficiently.
In order to ensure technical and operational integrity of these ageing facilities, the fitness for service of these offshore structures should be maintained. The maintenance of structural integrity is a significant consideration in the safety management and life extension of offshore installations. Detailed integrity assessments are needed to demonstrate that there is sufficient technical, operational and organisational integrity to continue safe operation throughout a life extension. Information on history, characteristic data, condition data and inspection results are required to assess the current state and to predict the future state of the facility and the possible life extension.
This paper presents state of art practices in life extension of existing offshore structures and an overview of various aspects of ageing related to offshore facilities, represented risk to the integrity of a facility and the required procedures and re assessment criteria for deciding on life extension.
This paper also provides an overall view in the structural requirements, justifications and calibrations of the original design for the life extension to maintain the safety level by means of a maintenance and inspection programs balancing the ageing mechanisms and improving the reliability of assessment results.