bluuebunny/crossref_metadata_2025 huggingface dataset:
Steel Steep Wave Riser as an Alternative Configuration for FPSO’s Compliant Risers
Authors: Pereira Paulo S. D. , Mourelle Marcio M. , de Aguiar Ludimar L.
Published: October 2015

The work was focused in the chase for alternative configurations that could resist to the high FPSO motions in the Brasil’s Pre-Salt harsh wave environment, and that could also be less compliant laterally when compared to the SLWR solution.

A case study was taken where an infield 8 inch SLWR configuration has been taken for comparisons.

After adjusting the SSWR (Steel Steep Wave Riser) main characteristics such as top angle, buoyant section length, buoyancy modules geometry and spacing, feasible configurations have been obtained. For a configuration to be considered as feasible, a set of verifications have been carried out including extreme events, wave fatigue, vortex induced vibration and installation. The verification was performed considering several riser top connection positions and azimuths along the FPSO riser support balcony.

The interference with neighboring risers has been also taken as an important issue, but was taken solely for comparison with the SLWR configurations.

The installation phase has been focused including the stages of bottom connection, normal pipe lay and the connection at the FPSO. The main problems associated to the installation phase of the steep wave configuration were identified and addressed in the discussion presented.

As the SSWR configuration has a fixed point at the sea bottom, two different solutions for this connection have been studied, and the final choice is described. The main differences between SSWRs and SLWRs, and the possible advantages of the SSWR configuration are discussed and a direct comparison is presented.
Free Dry and Wet Vibration of 2-Way Tapered Hollow Marine Rudder With Non-Classical Pivot: Theoretical Study
Authors: Jindal Rahul , Datta Nabanita
Published: October 2015

A theoretical analysis of free dry and wet vibration of a trapezoidal, 2-way tapered, marine spade rudder, is presented. The rudder is considered as a hollow Kirchhoff’s plate, with the chord section as a NACA profile. The chord length and the thickness taper from the top to the bottom, over the vertical span. The rudder is pivoted at the top, with the pivot behind the leading edge. The pivot is modeled as a combination of a translational and a rotational spring, in order to include the rigid body modes of the rudder vibration. The span-wise and chord-wise non-uniform beam vibration is first analyzed by the Rayleigh-Ritz method, in order to establish the non-uniform beam mode shapes. The span-wise beam is a linearly tapered vertical cantilever, with non-classical edge at the top and free at the bottom. The chord-wise section is a 2-span beam with the ends free, and four continuity conditions at the pivot. The non-uniform mode shapes, in either direction, are a weighted summation of the uniform beam mode shapes, which also satisfy the boundary/continuity conditions. They now act as admissible spatial functions to the plate vibration, which is analyzed by the Galerkin’s method. Eigenvalue analysis generates the plate natural frequencies. A weighted superposition, of the product of the beam mode shapes, in either direction, generates the plate mode shapes. Alternately, uniform beam mode shapes are used as admissible functions into the Galerkin’s method for the plate natural frequencies and mode shapes. The natural frequencies are generated for various positions of the rudder stock along the chord length. The pivot conditions (in both translational and rotational rigid body degree of freedom) influence the prominence of the rigid body mode shapes. The natural frequencies are analyzed for various pivot fixities, taper ratios, and aspect ratios of the plate. This is followed by the wet vibration analysis of the rudder. First, 2D strip theory is used to generate the added mass of each chord section. Constant strength source distribution technique is used to generate the added mass in sway and yaw of a 2D aerofoil. Each flexural and torsional mode is associated with its own added mass. Various empirical corrections are done to account for the 3D flow. Finally, 3D panel method is used to generate the modal added masses, and hence the wet natural frequencies. The added mass coefficient is generated for various aerofoil fineness ratios, pivot fixities, taper ratios, and aspect ratios of the plate.
Stochastic Model Construction of Correlated Nonlinear Wave Fields
Authors: Poirion Fabrice , Benoit Michel
Published: October 2015

The aim of this work is to present a method for constructing simulations of correlated trajectories of sea surface vertical displacement at different locations. It can also be used in order to construct a stochastic model for a single wave with given physical characteristics.
Helical Wire Behavior of Unbonded Flexible Pipes Under Bending
Authors: Lu Yutian , Yan Huibin , Bai Yong , Cheng Peng
Published: October 2015

The bending behavior of unbonded flexible pipe is governed by the response of the helical wires in the tensile armor to bending. The behavior of the helical wire, especially the axial strain, is influenced by the slip mechanism as a result of an increasing curvature under bending. In the present paper, two limit curves are considered with a certain curvature. A 3-D finite element model using ABAQUS is developed to simulate the practical behavior of the helical wires under bending. By comparing the FEA and theoretical results, a basic conclusion about the real slip path of the helical wire between two limit curves is introduced. A hysteretic bending moment-curvature relationship induced by the slip mechanism is obtained from the finite element model as well.
Theoretical and Practical Considerations of Helical Cable Elements Subject to End Effects at Cable Bending
Authors: Komperød Magnus , Konradsen Bjørn , Slora Roger
Published: October 2015

Most cable elements of subsea cables and umbilicals are helical. If helical cable elements are restrained from sliding freely when the cable is bent, large axial strains and stresses will arise in the elements. This paper focuses on the case where the helical cable elements are fixed to end terminations, or to the beneath cable layer, at two points along the cable’s length. The elements can slide freely between these two points. Mathematical expressions are derived to calculate the strains that arise in the helical cable elements when bending the cable segment. The mathematical results have intuitive, practical interpretations that are thoroughly explained. It is shown that the maximum strains and stresses arise when the length of the cable segment is an integer number of pitch lengths plus one half pitch length.
Steady State Motion Analysis of an Offshore Wind Turbine Transition Piece During Installation Based on Outcrossing of the Motion Limit State
Authors: Guachamin-Acero Wilson , Moan Torgeir , Gao Zhen
Published: October 2015

Installation of OffshoreWind Turbine structural components need to be executed in sea states for which their dynamic responses are expected to remain within a safe domain or perform a limited number of outcrossings from the safe boundary beyond which the responses may lead to unsafe working conditions, large impact loads or even structural failure. A critical installation activity limiting the installation of a Transition Piece TP is often the motion monitoring phase of the mating points until its landing on the foundation. The operational limit is normally given by the horizontal displacement and the safe domain could conveniently be defined by a circle of radius r in the horizontal plane. This paper presents an existing general accurate method and its solution to estimate the outcrossing rate of dynamic responses for a circular safe boundary in short crested seas which is applicable for the motion monitoring phase of offshore wind turbine components prior to mating. The required input is calculated from spectral analysis in the frequency domain and the solution is derived for Gaussian processes. It is found that both 1st and 2nd order responses have to be included and that the Gaussian assumption for the slow drift motions is not valid so that its real PDF is required. Also wave spreading has large influence in the outcrossing rate and should realistically be applied. The suggested approach is in agreement with real offshore practice, and is efficient when compared with time domain simulations. Then, the outcrossing rate method could help on Marine Operations decision making during critical installation activities.
Optimum Distance Between Two Advancing Ships Arranged Side by Side
Authors: Yuan Zhi-Ming , Incecik Atilla , Day Sandy
Published: October 2015

The hydrodynamic interaction between two advancing ships is very important. Because of the hydrodynamic interactions, even relatively small waves can induce large motions of the smaller ship due to the proximity of the larger ship. The aim of this paper is to develop a method to optimize the spacing between two advancing ships, in order to minimize the hydrodynamic interactions. The optimization method is based on the far-field wave patterns produced by a translating and oscillating source point. For values of the parameter τ > 0.25 (τ = ωeu/g) there is a fan-shaped quiescent region in front of the vessel. As τ increases, the range of the fan-shaped quiescent region will be expanded. It can be supposed that if the two ships are located in each other’s fan-shaped quiescent region, the hydrodynamic interactions can be minimized. This assumption was validated through the numerical simulation, which was based on a 3-D Rankine source panel method. We calculated and compared the wave exciting forces and wave patterns of two Wigley hulls advancing in waves side by side. The numerical results were consistent with our theoretical assumption.
An Extension of the BWH Instability Criterion: Numerical Study
Authors: Storheim Martin , Alsos Hagbart , Hopperstad Odd Sture , Amdahl Jørgen
Published: October 2015

The BWH criterion for simulating instability prior to necking in sheet metal has been extended with a post-necking damage model, in which the effect of the local neck inside a large element is accounted for with low mesh dependency. The model is incorporated in the explicit FE code LS-DYNA. The material model can be calibrated from a single uniaxial tensile test, and gives good prediction of rupture for a range of stress triaxialities.

This paper investigates the robustness of the criterion through numerical simulations of different experiments, from forming limit tests to large impact experiments on stiffened panel structures. A full-scale collision is simulated with two different mesh-sizes to investigate the robustness of the fracture prediction.

The validation cases are simulated with good accuracy considering the coarse meshes involved. Based on the validation, the post-necking extension of the BWH criterion can readily be used for structural design of offshore structures in order to assess the technical safety level of the structure against collisions in all phases of the design process. The method has a good ratio of accuracy vs. computational cost, and is less prone to user-errors as the calibration is simple and the mesh-scaling is automated.
A Study for Riser Response From Global Dynamic Analysis With Irregular Wave (Continued)
Authors: Zhang Yanqiu , Hou Yucheng , Yuan Jiabei , Tan Zhimin
Published: October 2015

The results of a study on the statistic properties of the stochastic processes of both irregular wave and riser response were presented in the paper OMAE2014-23196. Following on from that work, the present paper is devoted to the statistic properties of the mean-crossing maxima of the stochastic process of riser response and the statistic properties of the largest maxima, resulting from a number of 3-hour simulations with different wave seeds. The objective of the study is to find a more efficient method for evaluating the most probable maximum (MPM) value of riser response, i.e. using as few as possible simulations to find a reliable expectation to the MPM.

Global dynamic analysis with irregular wave is widely used in riser system design, though it is very time-consuming compared with regular wave. This is because irregular wave can more realistically model the sea state in the field of the riser system compared with regular wave. However time consuming irregular wave analysis may be there remains a perplexing issue, which is the randomness in the analysis results induced by wave seed; i.e. the extreme value of riser response resulting from a 3-hour simulation varies with the wave seed which is arbitrarily selected for the simulation. If a number of 3-hour simulations are performed, then a statistic method is used to evaluate the MPM value, two questions must be answered. First, how many simulations should be run, and second, what statistic method should be used?

Based on the study to the statistic properties of the maxima of riser response and the largest maxima, answers to the above questions are proposed. For universal applicability the study was conducted reflecting four risers which had different configurations and water depths.
Study on Weight Control Methods of Single Point Mooring System of FPSO in Deepwater
Authors: Hongtao Yuan , Ji Zeng , Gang Chen , Jian Mo , Nan Zhao
Published: October 2015

This paper applies 3D potential theory and non-linear time domain coupled analysis method to analyze motion response of FPSO and dynamic response of mooring line of single mooring system. In addition, respectively to calculate mooring line tension of tension type and composite mooring line type and added buoy in mooring line. There the paper analyze different mooring lines to affect on the weight of single point mooring system of deepwater FPSO. Which expects to provide a theoretical basis for single point mooring system design and weight control.
Estimation of High Energy Collision Response for Jacket Structures
Authors: Notaro Gabriele , Johansen Atle , Selås Stine Myhre , Nybø Terje
Published: October 2015

This paper presents a procedure for evaluating the collision response of fixed offshore structures exposed to high energy collisions with Offshore Service Vessels (OSV) or other floating units. A combination of traditional non-linear frame analyses for screening purposes and more detailed non-linear FE analyses using an explicit code is proposed. In the detailed integrated FE analyses, both the fixed offshore structure and the impacting vessel are explicitly modeled as deformable bodies. The progressive changes in contact and the resistance of both deforming objects are fully accounted for, enabling for more accurate results compared to methods where the resistances of the two objects are assessed separately.

Results from case studies are shown. The calculated resistances for the striking objects are compared to the load-indentation curves presented in DNV-RP-C204 [1] and NORSOK N-004 [2].
Evaluation of Wearing Pipe for Subsea Mining With Large Particles in Slurry Transportation
Authors: Takano Satoru , Ono Masao , Masanobu Sotaro
Published: October 2015

For a fundamental understanding of pipe wear under hydraulic transportation of deep-sea mining, a small scale test is conducted because there are many restrictions in conducting a full scale test. The small scale test apparatus are set up using the pipes of about 80mm in diameter and the rocks of which maximum particle diameters are about 20mm are used. In the test, the pipe materials and the pipe inclination are changed to evaluate the differential of the amount of pipe material loss. Furthermore, the amount of the pipe material loss in full scale is estimated based on the small scale test results.
Very Low Concentration Sand Transport in Multiphase Horizontal Pipelines: An Experimental Study and Modeling Guidelines
Authors: Najmi Kamyar , McLaury Brenton S. , Shirazi Siamack A. , Cremaschi Selen
Published: October 2015

Very low concentration sand transport in multiphase horizontal pipes is experimentally investigated in this study. Sand concentration is chosen to be low enough to ignore the effect of particle-particle interaction. This is done to obtain the liquid and gas threshold flow rates which are required to move particles at low concentration (0.002 volume percent) of particles in multiphase pipelines. Along with obtaining the threshold flow rates, the effects of sand concentration, sand size, pipe size and liquid viscosity are also experimentally investigated. Critical velocity is defined to make sure all grains of sand continuously move in the pipe. The experimental data were obtained for a wide range of operating conditions in both intermittent and stratified flow regimes. A comparison of the obtained experimental data in this study with similar studies in the literature reveals the effect of some physical parameters affecting sad transport in multiphase flow pipelines. This study also gives some general guidelines for a more accurate model to predict minimum flow rates to move sand in multiphase flows.
Design Requirement of a Renewable Energy Plus Compressed Air Energy Storage and Regeneration System
Authors: Finnigan Tim , Roddier Dominique
Published: October 2015

There are potential offshore applications where renewable energy and more distributed power sources could supplement or replace costly equipment upgrades for additional power supply, or costly fuel operating costs. Renewable energy technologies can also be employed in lieu of expensive power umbilicals to provide power to subsea pumps for long distance tiebacks in deepwater. For example, power umbilicals alone required to provide 69kV to subsea pumps in deepwater could be upwards of $300MM for 100 mile long distance tie-backs. A renewable energy source, with storage, integrated into that system could significantly reduce both the CAPEX and OPEX costs.

In 2013, Chevron performed an in-depth evaluation of a Renewable Energy plus Compressed Air Energy Storage and Regeneration system for a 2.6MW application. For the purpose of that study, a floating wind turbine in 365m water depth off the coast of Oregon was evaluated as the energy source as the base case. The system was found to be feasible with initial CAPEX costs replaced within 12 years of operations as compared to installation of a diesel power generation system and the requisite fuel required to run the equipment.

This paper provides a description of the OCAES system, and discusses potential applications in support of the offshore oil and gas industry.
Exploring Potential of Towing Pipeline in Emergency Scenarios
Authors: Puthiyaparambath Vinod , Kumar Praveen , John Manoj , Stanley Alexander
Published: October 2015

Subsea pipelines-deemed as the safest and most efficient means for transporting hydrocarbons, their integrity and long term maintenance are among the highest priorities for the oil and gas industry. These assets have a design life and are susceptible to damage from various factors during its operation. Operators should have in place a comprehensive Emergency Pipeline Repair System (EPRS). The EPRS should entail rigorous measures to minimize loss of production, the potential consequences of catastrophes and adverse effects on environment in case of an unforeseen event such as pipeline rupture or spill. The system should ensure swift response to restore the mechanical integrity of a damaged section whilst maintaining high HSE standards and minimizing the production shutdown-time duration. Accidental damages call for remedial response actions on an emergency basis. Considering short lengths of pipeline to be replaced, tow technique can offer an effective alternative to the time consuming and expensive conventional pipe-lay barge operations.

An installation method constituting the tow technique is proposed as a part of EPRS to replace damaged section of an operational pipeline. The paper discusses the applicable scenarios, the installation criteria and operational constraints involved in entire set of activities based on the study undertaken. The scenario analyzed involves launching a pre-fabricated pipe string offshore, towing and lay down at repair location. The pipe string is launched from an onshore facility by means of a lead tug, facilitated by rollers placed at designed intervals. The onerous task of pulling the pipe strings through long stretches of shallow water depths emphasizes the need of neutrally buoyant or slight positively buoyant pipe strings. Placing roller supports for the entire stretch is likely to pose several practical and economic constraints. The pipe string is towed to the intended offshore repair location with the assistance of a trailing tug. The pipe strings are laid down at the intended location in a controlled manner by means of winches and sequential release of buoys.

Numerical models of the system for towing and laydown operations are developed and related investigations are undertaken to evaluate the installation parameters, supplementary buoyancy requirements and to assess the criticality at various stages of installation. Further, the limiting weather criteria to carry out the operation are established based on the wave and current imposed hydrodynamic loadings on the strings and several governing parameters. The paper also briefs merits and limitations of the method.
A Study of Possible Solutions for Cost Efficient Subsea Well Abandonment
Authors: Moeinikia Fatemeh , Fjelde Kjell Kåre , Sørbø Jostein , Saasen Arild , Vrålstad Torbjørn
Published: October 2015

There is a large number of subsea production wells offshore Norway approaching the end of their lifetime. Considering high spread rate of semisubmersible rigs, abandonment operations of these wells will be quite expensive. Moreover, Plug and abandonment (P&A) can easily contribute with 25% of the total costs of drilling for exploration wells offshore Norway. Hence it is of great importance to seek approaches and solutions to reduce the P&A cost. This paper reviews some possible new ways and also alternative technologies as the solutions to cut down the P&A expenses. Some of these technologies are now being used offshore Norway.

In the first section of this paper, challenges of performing P&A operations offshore Norway together with the main cost drivers are discussed. It is then briefly argued how to consider issues such as barriers setting depth, cementing depth and logging in the design and well construction phases to ease or avoid future P&A challenges. For hydrocarbon exploitation in the Barents Sea and Arctic regions it is important to take into account the P&A phase in the early stage of planning and development.

Light well intervention vessels as alternatives to semisubmersible rigs are recognized of being the largest contributor to cost saving. It will then be discussed to what extent vessel technologies can cut down the expenses for subsea abandonment. New ways of performing P&A can be another contributor to cost saving. It is shown how research and testing can assure the operators of new ways for performing P&A. Retrieval of production tubing is a challenging suboperation such that it imposes significant cost to subsea well abandonment. There have been performed studies on how P&A could be performed with tubing left in hole and it is of interest to pursue this further. We will investigate how the abandonment operations can be simplified and be more cost efficient if the production tubing can be left inside the well where the basic assumptions for being able to do it is accounted for.

In addition, some complexities in abandonment operations can cause additional cost. An example of such complexities can be the need to establish two permanent barriers for potential permeable zones in overburden. It will be demonstrated how much can be saved with respect to cost if the regulations allow to ease some parts of abandonment operations.

In this study, a probabilistic approach as a systematic tool to produce unbiased results is applied to quantify cost savings of new alternatives compared to the traditional ones.
Thermal Insulation With Latent Energy Storage for Flow Assurance in Subsea Pipelines
Authors: Parsazadeh Mohammad , Duan Xili
Published: October 2015

Flow assurance is critical in offshore oil and gas production. Thermal insulation is an effective way to reduce heat loss from subsea pipelines and avoid the formation of hydrates or wax deposits that could block the flowlines. This paper presents heat transfer analysis from a subsea flowline with different insulation materials, particularly with nano-enhanced phase change materials (NPCMs) that allow thermal energy storage in the pipeline system. The phase change materials (PCMs) can effectively regulate fluid temperature during production fluctuations or increase the cool-down time during production shutdown. This paper considers a pipe in pipe configuration with different insulation methods; the cool-down times are calculated and compared. The results show that thermal insulation can greatly delay the fluid cool-down process. A significant improvement of cool-down time can be achieved with PCM energy storage under a good conventional insulation layer. Moreover, with nanoparticles in a PCM, the latent energy storage is enhanced thus it takes even longer time for the internal fluid to reach its hydrate formation temperature.
Development and Testing of a Post-Installable Deepwater Monitoring System Using Fiber-Optic Sensors
Authors: Seaman Calvin H. , Brower David V. , Le Suy Q. , Tang Henry H.
Published: October 2015

This paper addresses the design and development of a fiber-optic monitoring system that can be deployed on existing deep water risers and flow lines; and provides a summary of test article fabrication and the subsequent laboratory testing performed at the National Aeronautics and Space Administration-Johnson Space Center (NASA-JSC).

A major challenge of a post-installed instrumentation system is to ensure adequate coupling between the instruments and the riser or flow line of interest. This work investigates the sensor coupling for pipelines that are suspended in a water column (from topside platform to seabed) using a fiber-optic sensor clamp and subsea bonding adhesive. The study involved the design, fabrication, and test of several prototype clamps that contained fiber-optic sensors. A mold was produced by NASA using 3-D printing methods that allowed the casting of polyurethane clamp test articles to accommodate 4-inch and 8-inch diameter pipes. The prototype clamps were installed with a subsea adhesive in a “wet” environment and then tested in the NASA Structures Test Laboratory (STL). The tension, compression, and bending test data showed that the prototype sensor clamps achieved good structural coupling, and could provide high quality strain measurement for active monitoring.
Mooring Chain Fatigue Assessment Methodology and Software of Williams Gulfstar 1 Spar Platform Using Comparison Between Field Measured Data and the Design Basis Information
Authors: Park Young-Chan (Y. C.) , Antony Arun , Moideen Hisham , Jamnongpipatkul Arada , Hwang Jinsang , Song Duckyong , Gim Hwanseok
Published: October 2015

In 2014 Williams Companies delivered a Spar-based FPS to be used by the Hess Corporation for developing their “Tubular Bells” field as well as for future tiebacks for other developments. Tubular Bells is located in the Mississippi Canyon region of the Gulf of Mexico.

The Spar hull is the ‘Classic hull form’, 584 ft (178 m) long, 85 ft (26 m) in diameter with 60 ft (18 m) hull freeboard. The mooring system consists of 9 mooring lines in 3 groups composed of a chain-polyester-chain configuration.

This paper describes the tools and methodology Williams plans to use for assessing the fatigue damage of the mooring chain over the operating life of the platform. The basic plan is to collect field-measured data for parameters that impact mooring fatigue damage, such as: environmental conditions, Spar motions (particularly Vortex Induced Motions data) and mooring line tensions, then process that data with specialized software so it can be effectively compared to the applicable data that was used in the design of the mooring system for fatigue.

A key element in the plan to compare the field data with the design data is new computer software developed specifically to process the field measured data and generate the field measured, fatigue design parameters on a regular basis and in a form that is readily comparable to the design data. Additionally, a graphic user interface in this software will provide a clear visualization of the Spar motions that is linked with the associated environmental conditions for the same time periods.
Numerical Solution of 2-D Water Entry Problems Based on a CIP Method and a Parallel Computing Algorithm
Authors: Wen Peng , Qiu Wei
Published: October 2015

A constrained interpolation profile (CIP) method has been developed to solve 2-D water entry problems. This paper presents the further development of the numerical method using staggered grids and a parallel computing algorithm. In this work, the multi-phase slamming problems, governed by the Navier-Stokes (N-S) equations, are solved by a CIP-based finite difference method. The interfaces between different phases (solid, water and air) are captured using density functions. A parallel computing algorithm based on the Message Passing Interface (MPI) method and the domain decomposition scheme was implemented to speed up the computations. The effect of decomposition scheme on the solution and the speed-up were studied.

Validation studies were carried out for the water entry of various 2-D wedges and a ship section. The predicted slamming force, pressure distribution and free surface elevation are compared with experimental results and other numerical results.
Comparison of Cyclic P-Y Methods for Offshore Wind Turbine Monopiles Subjected to Extreme Storm Loading
Authors: Carswell Wystan , Fontana Casey , Arwade Sanjay R. , DeGroot Don J. , Myers Andrew T.
Published: October 2015

Approximately 75% of installed offshore wind turbines (OWTs) are supported by monopiles, a foundation whose design is dominated by lateral loading. Monopiles are typically designed using the p-y method which models soil-pile resistance using decoupled, nonlinear elastic Winkler springs. Because cyclic soil behavior is difficult to predict, the cyclic p-y method accounts for cyclic soil-pile interaction using a quasistatic analysis with cyclic p-y curves representing lower-bound soil resistance. This paper compares the Matlock (1970) and Dunnavant & O’Neill (1989) p-y curve methods, and the p-y degradation models from Rajashree & Sundaravadivelu (1996) and Dunnavant & O’Neill (1989) for a 6 m diameter monopile in stiff clay subjected to storm loading. Because the Matlock (1970) cyclic p-y curves are independent of the number of load cycles, the static p-y curves were used in conjunction with the Rajashree & Sundaravadivelu (1996) p-y degradation method in order to take number of cycles into account. All of the p-y methods were developed for small diameter piles, therefore it should be noted that the extrapolation of these methods for large diameter OWT monopiles may not be physically accurate; however, the Matlock (1970) curves are still the curves predominantly recommended in OWT design guidelines. The National Renewable Energy Laboratory wind turbine analysis program FAST was used to produce mudline design loads representative of extreme storm loading. These design loads were used as the load input to cyclic p-y analysis. Deformed pile shapes as a result of the design load are compared for each of the cyclic p-y methods as well as pile head displacement and rotation and degradation of soil-pile resistance with increasing number of cycles.
Measurement of Residual Stress Shakedown in Pressure/Tensile Armour Wires of Flexible Pipes by Neutron Diffraction
Authors: Fernando Upul S. , Davidson Michelle , Simpson Christopher , Pirling Thilo , Yan Kun , Callaghan Mark D. , Roy Matthew , Francis John A. , Withers Philip J.
Published: October 2015

The manufacture of unbonded flexible pipes (flowlines and risers) involves wrapping steel wires to create pressure and tensile armour layers. The forming of armour wires from vendor supply conditions to a helix shape on the pipe involves significant plastic straining and the wires that are wrapped onto the pipe are not unloaded. Therefore the armour wires in flexible pipes are expected to contain significant residual stress (RS) as a result of the plastic straining and loading during manufacture and placement. This may lead to detrimental effects on the strength, durability and the service integrity of the pipe. It is postulated that the unfavorable RS introduced during pipe manufacture reduces due to stress shakedown during the factory acceptance test (FAT) where the pipe is subjected to a high internal pressure.

This paper describes the first attempts to measure RS in the armour wires in unbonded flexible pipes. The key development is the use of a neutron diffraction method which allows the measurement of RS in-situ on the manufactured pipe through the whole wire sections. Pipe samples were prepared exposing the relevant metal layer and the measurements were performed on pipe samples taken before and after performing the pressurized FAT. The effect of the FAT on the shakedown of residual stress in pressure armour wires is discussed. As shown by the measurements, the elastic strains and stresses in the pressure armour wires are much larger in the hoop direction of the pipe (i.e. along the length of the wire) than radial or axial to the pipe. In pre-FAT pipe the hoop stresses are essentially tensile on the extrados and compressive on the intrados. The results have shown that the FAT reduces the hoop strains and stresses to approximately 1/3 of their as manufactured level.
Effects of Buoyancy Modules Geometry on Hydro-Elastic and Hydrodynamic Performance of a Steep Wave Riser in Steady Current
Authors: Calvert Samuel J. , Balash Cheslav , Chai Shuhong , Izarn Cecile , Morand Henri
Published: October 2015

Analysis of the hydrodynamic properties and response of flexible risers in various configurations is paramount to understanding their operative performance. Buoyancy modules play an integral role in providing compliance to flexible riser systems in wave configuration. This study utilised both model testing and numerical simulations to quantify the impact of discretised and smeared buoyancy module sections on the performance of a flexible riser in shallow water steep wave configuration under steady current loading. Model testing was facilitated in the Australian Maritime College’s Circulating Water Channel by a 1:15 scale 8″ flexible riser constructed from silicon hose and foam. Variances in the model’s buoyancy module section and system offset were tested at different flow velocities to estimate the effect on in-line drag and top tension, and the change in curvature radius experienced by the riser. The tested systems were also modelled in dynamic analysis software for comparative purposes, where industry recommended practices were employed to specify drag coefficients. Numerical simulations exhibited an appreciably higher in-line drag compared to model testing results at higher flow velocities. Comparison of curvature radius results demonstrated close agreement at lower flow velocities, with numerical simulations exhibiting increased deformations due to the higher in-line drag estimated at higher flow velocities. This discrepancy might be partially attributed to an overestimation of drag coefficients defined within industry recommended practices. The findings from this study have shown the significance of utilising scale model testing to quantify the hydrodynamic responses of a flexible riser, and facilitate a basis for further work which might provide additional insight into the discrepancies between analytical modelling and scale model tests.
Load Uncertainties Effects on the Fatigue Life Evaluation by the Common Structural Rules
Authors: Liao Po-Kai , Quéméner Yann , Lee Chi-Fang , Chen Kuan-Chen
Published: October 2015

This study evaluated the fatigue life of various hot spots located amidship a handy size oil tanker and a capesize bulk carrier. Specifically, the fatigue was evaluated accordingly to the harmonized common structural rules for bulk carriers and oil tankers recently released by the international association of classification societies. This study examined the stillwater and wave loads uncertainties effect on the fatigue life assessment. Hydro-structure coupling analyses were thus carried out enabling direct hydrodynamic load computations and accurate structural response assessment by finite element analyses. The comparison between direct and rules assessment allowed to identify the load uncertainties effect on the fatigue evaluation. As a result, the fatigue life evaluated by both approaches was significantly different, as expected with regard to the stillwater and dominant wave loads deviations. In addition, the study showed that the influence of the subjected loads was underestimated by the rules, leading to overestimated hot spot stress.
Effect of Micro-Bubbling on Settling Behavior of Fine Particles for Deep-Sea Mining
Authors: Yamazaki Tetsuo , Nakatani Naoki , Arai Rei , Yamamoto Yuta
Published: October 2015

A preliminary tank experiment for clarifying the effect of micro-bubbles on settling behavior of fine particles was conducted. The behavior of the particles was continuously photographed by a still camera and the images were analyzed by the gray scale intensity. From the results the authors found a suspension effect of micro-bubbles for the settling of fine particles. The effect should be studied in detail for preventing some serious environmental impacts during deep-sea mining.
On Prediction for Structural Performance of Ship Side Structures in Head-On Collision Scenario
Authors: Sun Bin , Hu Zhiqiang , Wang Jin
Published: October 2015

The crashworthiness of ship side structures should be taken into consideration during the structural design phase. When a ship is struck by a head-on collision, the main participants of the side structures include outer plating, longitudinal girders, transverse frames and the stiffeners attached on them. This paper is centered on establishing an integrated deformation mechanism program by identifying the theoretical deformation modes of the side structures, including the plating and stiffeners. The primary failure models of plating structures are the crushing, stretching and tearing modes, and a new crushing model of side plating structures subject to an ellipsoid-shaped indenter is proposed. As for the stiffeners on outer plating, the smeared thickness method is often used, but the role of the stiffeners cannot be traced clearly during the deformation process and the structural performance predictive accuracy may not be guaranteed. Therefore, a theoretical model of stiffeners is established in this paper, on purpose of providing deep insight of the deformation mechanism with reasonable accuracy. The expressions of resistance force of the side structures are also derived based on a study of the progressive deformation process of numerical simulation results and the plastic analytical methods.

The accuracy of the analytical method is verified by numerical simulations using code LS_DYNA. The proposed analytical method can be used for quick assessment of the performances of ship side structures during ship collision.
Research on the Crashworthiness of FLNG Side Structures in the Side-by-Side Offloading Operation With LNGC
Authors: Zhang Dongwei , Hu Zhiqiang , Chen Gang
Published: October 2015

On purpose of evaluating the crashworthiness of FLNG side structures in case of the collision accident during the side-by-side offloading operation, a unique research is conducted in this paper with numerical simulation method. According to the model test completed in Deepwater Offshore Basin in Shanghai Jiao Tong University, there does exist a high probability of collision between FLNG and LNGC in the side-by-side offloading operation. To perform numerical simulations, finite element models were built. For the FLNG model, the side structures contain the detailed LNG cargo containment system. According to the parameters obtained from the model test, two typical collision scenarios are defined. Then the collision scenarios are simulated by the LS_DYNA code. A special limit collision state is proposed based on the structural response of LNG CCS. With respect to the numerical results, great attention is paid to the structural response of CCS to evaluate the safety of FLNG side structures. Furthermore, some insights useful for the basic design of FLNG are put forward.
Simulation of Dynamic Tracking System for Rescue at Sea
Authors: Shi Qian , Fu Shixiao , Deng Ning , Xu Jinsong
Published: October 2015

In this paper, a time domain simulation is established to investigate the feasibility of a PID controller for rescue at sea. In the problem, the endangered ship loses its power and moves freely under environmental forces. The control target for Dynamic Tracking (DT) is to maintain a certain distance between the endangered and rescue ships. The time domain simulation includes multi-body hydrodynamics and Guidance Navigation Control (GNC) system. The multi-body hydrodynamics is modeled with the ship-ship interaction considered. The first and second order wave loads, added mass and damping in frequency domain is calculated using potential theory. Current and wind loads are estimated by empirical formulas summarized from experimental data. As for the design of the GNC system, PID control strategy is applied for the controller and the Kalman Filter for the observer. The time domain simulation in this research is performed in MATLAB.
Nonlinear Interactions in Crossing Sea States
Authors: Brennan Joseph , Dias Frédéric
Published: October 2015

Presented here is a study on the nonlinear effects contributing to extreme events in wave fields characterised by the presence of two distinct spectral peaks, otherwise known as crossing sea states. Simulations based within the framework of the nonlinear Schrödinger equation have shown that the coupling of two wave groups impinging at various angles strongly influences the growth rate of the Benjamin Feir instability, with various angles enhancing the instability and the characteristics of the rogue event itself. This investigation is based on the more general framework of the Euler equations, employing a Higher Order Spectral Method (HOSM) to numerically solve these equations and obtain the time evolution of the crossing sea state.
Investigation of Hydrodynamic Loads and Flow Patterns Near an Escort Tug in Oblique Flows
Authors: Jahra Fatima , Islam Mohammed , Thanyamanta Worakanok , Molyneux David
Published: October 2015

The present research investigates the hydrodynamic forces and moments and the flow pattern near the hull of an escort tug at steady oblique flow conditions. An escort tug is modelled and numerical simulations have been carried out using a commercial RANS solver. In the simulations, the viscous flow field is calculated by the finite volume method, adapting the k-ε turbulence model. Free surface is modeled using the Volume of Fluid (VOF) approach for calm water condition. The hull is assumed fixed in space with an even keel. Grid dependency studies are conducted to obtain insight into the reliability and accuracy of the results. Flow velocities around the escort tug as well as integral variables are computed at different Froude numbers and compared to the corresponding measurement data available in the public domain. The measurements was completed using a Planar Motion Mechanism (PMM) apparatus to measure the resistance, side force and yaw moment of the tug hull. Additionally, the velocity distributions on the upstream and downstream sides of the tug were measured by Particle Image Velocimetry (PIV).

The measurements and simulations have been completed at one draft, and at 15°, 30° and 45° inflow conditions. A reasonable agreement has been obtained between the predicted axial and lateral forces and the corresponding measurements. The flow pattern and the velocity distribution at different drift angle are comparable with the measurements. The variation of the pattern of flow separation at the suction side of the hull at different yaw angle is also analyzed and presented.
Fatigue Evaluation Procedures for Multi-Axial Stress State in Welded Joints
Authors: Hong Jeong K. , Forte Thomas P.
Published: October 2015

The Battelle structural stress method (BSSM) for fatigue life evaluation is examined for multi-axial stress states that develop due to uniaxial loading in welded structures. The resultant multi-axial stress state due to simple uniaxial loading is easily observed in common joint types such as a plate with a welded tube or a plate with an angled attachment. In these joint types, under simple loading, the stress distribution at the location of failure along the weld line shows significant in-plane shear stress (parallel to the weld line) as well as normal stress (normal to weld line). Although the fatigue data, as exemplified by the inverse slope of the S-N curve for the subject joints under uniaxial loading, are observed to be similar to that for normal-loading-mode dominant (Mode I) failures in welded joints, when only the normal structural stress is considered for these joints the predictions of both the fatigue failure location and the fatigue life using the master S-N curve approach are inaccurate because the in-plane shear stress plays a significant role in the development of the crack.

The slope of fatigue data exhibited in S-N curves taken from weld fatigue data for resultant multi-axial stress state generated by uniaxial loading is different from multi-axial fatigue loading conditions for tubular joints as discussed in the recent work [OMAE2014-23459].

In this article, the fatigue behavior of welded joints with multi-axial stress states is evaluated using an effective equivalent structural stress range parameter that is formulated as a von Mises form of the combined normal and in-plane shear equivalent structural stress ranges. When the effective equivalent structural stress range parameter is employed, the fatigue failure location can be predicted correctly. It is also found that the cycles-to-failure data from the subject joint types are comparable with the master S-N curve for Mode I loading dominant behavior (inverse slope of 3.125). Therefore, the master S-N curve that was developed for Mode I failures can be equally applicable for fatigue life prediction for these joints by replacing the equivalent structural stress range with effective equivalent structural stress range on the ordinate axis.
Spectra Evolution of Single Wave Packets in Finite Water Depth
Authors: Ma Yuxiang , Ma Xiaozhou , Dong Guohai
Published: October 2015

A series of physical experiments were conducted to investigate the spectra evolution of single wave packets. Chirped-typed wave groups were selected in this study. Nine wave packets varying initial amplitudes and wave components were generated in the wave flume. Hence both non-breaking and breaking wave groups can be performed. It is found that the evolution process is far more than the linear superposition, and that it experiences significant nonlinear process. The modulational instability is found in the evolution of wave groups. For non-breaking groups, it is found that the most non-breaking energy dissipation occurs in the vicinity of the spectral peak (f/fp = 0.9–1.1). The non-breaking dissipation energy for spectral peak depends on depend on BFI (Benjamin-Feir Index). For breaking cases, the energy level of the above-peak frequency region (f/fp = 1.1–2.0) first increase slightly, and decrease during breaking occurring, but the overall change is limited. However, the below-peak frequency region (f/fp = 0.5–0.9) gains with the expense energy of the peak and above-peak frequency regions and the growth depends on the initial spectra width.